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An Acyl-NHC Osmium Cooperative System: Coordination of Small Molecules and Heterolytic B–H and O–H Bond Activation

Experimental Section


All reactions were carried out with rigorous exclusion of air using Schlenk-tube techniques or in an argon-filled Unilab glovebox (O2 levels below ppm). Glassware was previously pretreated with 5% Me3SiCl in dichloromethane solution, to silylate the glass surface. Acetone, methanol, tetrahydrofuran, and 2-propanol were dried and distilled under argon. Other solvents were obtained oxygen- and water-free from an MBraun solvent purification apparatus; additionally, pentane was treated with P2O5. Alcohols were dried by standard procedures and distilled under argon prior to use. Pinacolborane (HBpin; 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and all other reagents were purchased from commercial sources and used without further purification. NMR spectra were recorded on a Varian Gemini , a Bruker ARX MHz, a Bruker Avance MHz, or a Bruker Avance MHz instrument. Chemical shifts (expressed in parts per million) are referenced to residual solvent peaks (1H, 1H{31P}, 13C{1H}) or external standard (31P{1H} to 85% H3PO4 and 11B to BF3·OEt2). Coupling constants J and N (N = J(PH) + J(P′H) for 1H and N = J(PC) + J(P′C) for 13C{1H}) are given in hertz. Attenuated total reflection infrared spectra (ATR-IR) of solid samples were run on a PerkinElmer Spectrum FT-IR spectrometer. C, H, and N analyses were carried out in a PerkinElmer CHNS/O analyzer. High-resolution electrospray mass spectra (HRMS) were acquired using a MicroTOF-Q hybrid quadrupole time-of-flight spectrometer (Bruker Daltonics, Bremen, Germany). OsH6(PiPr3)2 and 1-(2-methoxyoxoethyl)methylimidazolium chloride were prepared according to the published methods. (13, 24)

Preparation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(PiPr3)2 (3)

OsH6(PiPr3)2 ( g, mmol) was dissolved in a 1/1 THF/toluene mixture (10 mL) and treated with 1-(2-methoxyoxoethyl)methylimidazolium chloride ( g, mmol). The mixture was stirred under reflux for 3 h before the volatiles were removed under vacuum. Subsequent addition of methanol (2 mL) to the resulting residue, at approximately −70 °C, led to the formation of a reddish brown solid, which was washed with further portions of diethyl ether (2 × 3 mL) and dried in vacuo. Yield: g (74%). Orange crystals suitable for X-ray diffraction analysis were obtained from a concentrated solution of 1 in acetone. Anal. Calcd for C24H49ClN2OOsP2: C, ; H, ; N, Found: C, ; H, ; N, HRMS (electrospray, m/z): calcd for C24H49N2OOsP2 [M – Cl]+ , found IR (cm–1): ν(C═O) (s). 1H NMR ( MHz, (CD3)2CO, K): δ and (both d, JH–H = , 1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), (dvt, N = , JH–H = , 18 H, PCH(CH3)3). 31P{1H} NMR ( MHz, (CD3)2CO, K): δ (s). 13C{1H}-APT NMR plus HMBC and HSQC ( MHz, C6D6, K): δ (s, C═O), (t, JC–P = , NCN), and (both s,CHimidazole), (s, NCH2), (s, NCH3), (vt, N = , PCH), and (both s, PCH(CH3)3).

Reaction of 3 with CO: Formation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(CO)(PiPr3)2 (4)

A solution of 3 ( g, mmol) in toluene (5 mL) was stirred under a CO atmosphere (1 atm) at room temperature for 5 min. The resulting colorless solution was reduced to dryness. Addition of diethyl ether (3 mL) to the residue obtained led to the formation of a white solid, which was washed with additional portions of diethyl ether (2 × 3 mL) and dried in vacuo. Yield: g (40%). Colorless crystals suitable for X-ray diffraction analysis were obtained from a concentrated solution of 4 in acetone. Anal. Calcd for C25H49ClN2O2OsP2: C, ; H, ; N, Found: C, ; H, ; N, HRMS (electrospray, m/z): calcd for C25H49N2O2OsP2 [M – Cl]+ , found IR (cm–1): ν(C≡O) (s), ν(C═O) (m). 1H NMR ( MHz, CD2Cl2, K): δ and (both d, JH–H = , 1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), (dvt, N = , JH–H = , 18 H, PCH(CH3)3). 31P{1H} NMR ( MHz, CD2Cl2, K): δ (s). 13C{1H}-APT NMR plus HSQC and HMBC ( MHz, CD2Cl2, K): δ (t, JC–P = , C═O), (t, JC–P = , C≡O), (s, NCN), and (both s, CHimidazole), (s, NCH2), (s, NCH3), (vt, N ═ , PCH), and (both s, PCH(CH3)3).

Reaction of 3 with O2: Formation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(η2-O2)(PiPr3)2 (5)

A solution of 3 ( g, mmol) in toluene (5 mL) was stirred under an O2 atmosphere (1 atm) at −20 °C for 15 min. After removal of volatiles, diethyl ether (3 × 3 mL) was added to extract the product. The diethyl solution was concentrated to ca. 4 mL and placed in the freezer (−30 °C). Red crystals corresponding to 5, suitable for X-ray diffraction analysis, were grown. IR (cm–1): ν(C═O) (s), ν(O–O) (s). 1H NMR ( MHz, CD2Cl2, K): δ and (both d, JH–H = , 1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), (dvt, N = , JH–H = , 18 H, PCH(CH3)3). 31P{1H} NMR ( MHz, CD2Cl2, K): δ − (s). 13C{1H} NMR plus HSQC and HMBC ( MHz, CD2Cl2, K): δ (br, C═O), (s, NCN), and (both s, CHimidazole), (s, NCH2), (s, NCH3), (br, PCH), and (both s, PCH(CH3)3).

Reaction of 3 with H2: Formation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(η2-H2)(PiPr3)2 (6)

A J. Young NMR tube was charged with a solution of 3 ( g, mmol) in C6D6 ( mL). Argon was replaced by H2 (1 atm), causing the red solution to turn pale yellow. The immediate and quantitative evolution of 3 to 6 was observed by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy. 1H NMR ( MHz, C6D6, K): δ and (both d, JH–H = , 1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), − (t, JH–P = , 2 H, OsH). 31P{1H} NMR ( MHz, C6D6, K): δ (s). 13C{1H}-APT NMR plus HSQC and HMBC ( MHz, C6D6, K): δ (t, JC–P = , C═O), (t, JC–P = , NCN), and (both s, CHimidazole), (s, NCH2), (s, NCH3), (vt, N = , PCH), and (both s, PCH(CH3)3). T1(min) (ms, OsH, MHz, toluene-d8, K): 8 ± 1 (− ppm).

Determination of the JH–D Value for Complex 6 (6′)

A J. Young NMR tube was charged with a solution of 3 ( g, mmol) in toluene-d8 ( mL). Argon was replaced by HD (1 atm), which was generated in situ by reaction of NaH with D2O. An immediate color change from red to pale yellow was observed in the solution. The 1H and 1H{31P} NMR spectra, in a MHz apparatus at K, of this solution exhibit a triplet with JH–D = Hz in the hydride region.

Reaction of 3 with Pinacolborane: Formation of OsHCl{κ2-C,C-[CN(CH3)CHCHNCH2C(OBPin)]}(PiPr3)2 (7)

In a NMR tube, a reddish brown suspension of 3 ( g, mmol) in CD2Cl2 ( mL) was treated at room temperature with pinacolborane ( μL, mmol). Immediately the initial suspension disappeared and an intense pink solution was observed. The quantitative formation of a new species corresponding to 7 was confirmed by 1H, 31P{1H}, 11B, and 13C{1H} NMR spectroscopy. 1H NMR ( MHz, CD2Cl2, K): δ and (both d, JH–H = , 1 H each, CHimidazole), (s, 3 H, NCH3), (m, 6 H, PCH), (t, JH–P = , 2 H, NCH2), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), (s, 12 H, CH3-BPin), (dvt, N = , JH–H = , 18 H, PCH(CH3)3), − (t, JH–P = , 1 H, OsH). 31P{1H} NMR ( MHz, CD2Cl2, K): δ (s). 11B NMR ( MHz, CD2Cl2, K): δ (br). 13C{1H}-APT NMR plus HSQC and HMBC ( MHz, C6D6, K): δ (t, JC–P = , Os═C(OBpin)), (t, JC–P = , NCN), and (both s, CHimidazole), (s, C-Bpin), (s, NCH2), (s, NCH3), (vt, N = , PCH), (s, CH3-BPin), and (both s, PCH(CH3)3

Alcoholysis Reactions of Pinacolborane Catalyzed by OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(PiPr3)2 (3)

In a typical procedure, the alcohol (except for PhOH, which was dissolved in μL of toluene) ( mmol) was added via syringe to a solution of the catalyst ( × 10–2 mmol) and HBPin ( mmol) in toluene (5 mL) placed in a 25 mL flask attached to a gas buret and immersed in a 30 °C bath (eq S1 and Figure S2 in the Supporting Information), and the mixture was vigorously shaken ( rpm) during the run. The reaction was monitored by measuring the volume of the evolved hydrogen with time until hydrogen evolution stopped. Representative gas vs time plots are given in the Supporting Information. The solution was then passed through a silica gel column. Removal of the volatiles gave the boryl ether. The products were analyzed by 1H, 13C{1H}, and 11B NMR spectroscopy.

Spectroscopic Data of the Products of the Alcoholysis

MeOBpin

1H NMR ( MHz, C6D6, K): δ (s, 12 H, CH3-BPin), (s, 3 H, −OCH3). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH3), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

EtOBPin

1H NMR ( MHz, C6D6, K): δ (q, JH–H = , 2 H, −OCH2CH3), (t, JH–H = , 3 H, −OCH2CH3), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH2CH3), (s, CH3-BPin), (s, −OCH2CH3). 11B NMR ( MHz, C6D6, K): (s).

nBuOBPin

1H NMR ( MHz, C6D6, K): δ (t, JH–H = , 2 H, −OCH2(CH2)2CH3), and (both m, 2 H each, −OCH2(CH2)2CH3), (s, 12 H, CH3-BPin), (t, JH–H = , 3 H, −OCH2(CH2)2CH3). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH2(CH2)2CH3), and (both s, −OCH2(CH2)2CH3), (s, CH3-BPin), (s, −OCH2(CH2)2CH3). 11B NMR ( MHz, C6D6, K): (s).

noctylOBPin

1H NMR ( MHz, C6D6, K): δ (t, JH–H = , 2 H, −OCH2(CH2)7CH3), (m, 2 H, −OCH2(CH2)7CH3), – (m, 10 H, CH2), (s, 12 H, CH3-BPin), (t, JH–H = , 3 H, −OCH2(CH2)7CH3). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH2(CH2)7CH3), , , , , and (all s, −OCH2(CH2)7CH3), (s, CH3-BPin), (s, −OCH2(CH2)7CH3). 11B NMR ( MHz, C6D6, K): (s).

PhCH2OBPin

1H NMR ( MHz, C6D6, K): δ – (m, 5 H, CH-Ph), (s, 2 H, −OCH2Ph), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, Cipso-Ph), , , and (all s, CH-Ph), (s, C-Bpin), (s, −OCH2Ph), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

iPrOBPin

1H NMR ( MHz, C6D6, K): δ (m, 1 H, CH-iPr), (d, JH–H = , 6 H, CH3-iPr), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, CH-iPr), (s, CH3-BPin), (s, CH3-iPr). 11B NMR ( MHz, C6D6, K): (s).

tBuOBPin

1H NMR ( MHz, C6D6, K): δ (s, 9 H, CH3-tBu), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, C-tBu, (s, CH3-tBu), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

PhOBPin

1H NMR ( MHz, C6D6, K): δ – (m, 5 H, CH-Ph), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, Cipso-Ph), , , and (all s, CH-Ph), (s, C-Bpin), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

Hydrolysis Reactions of Pinacolborane Catalyzed by OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(PiPr3)2 (3)

The hydrolysis reactions were carried out by the same procedure as the alcoholysis but using water instead of alcohols (eq S2 in the Supporting Information). Since the product obtained is an alcohol (HOBPin), a second addition of HBPin was injected in order to obtain (Bpin)2O.

Spectroscopic Data of the Products of the Hydrolysis

HOBPin

1H NMR ( MHz, C6D6, K): δ (br, 1 H, −OH), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

Bpin)2O

1H NMR ( MHz, C6D6, K): δ (s, 24 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-BPin), (s, CH3-BPin)). 11B NMR ( MHz, C6D6, K): (s).

Structural Analysis of Complexes 36

X-ray data were collected for the complexes on a Bruker Smart APEX CCD diffractometer equipped with a normal focus, kW sealed tube source (Mo radiation, λ = Å) operating at 50 kV and 40 mA (5) or 30 mA (3, 4, and 6) . Data were collected over the complete sphere. Each frame exposure time was 10 s (3, 4, and 6) or 40 s (5) covering ° in ω. Data were corrected for absorption by using a multiscan method applied with the SADABS program. (25) The structures were solved by Patterson or direct methods and refined by full-matrix least squares on F2 with SHELXL97, (26) including isotropic and subsequently anisotropic displacement parameters. The hydrogen atoms (except hydrides) were observed in the least-squares Fourier maps or calculated and refined freely or refined using a restricted riding model. Hydrogens bonded to metal atoms were observed in the last cycles of refinement but refined too close to metals; therefore, a restricted refinement model was used for all of them (d(Os–H) = (1) Å).

Complex 6 was first solved and refined in the monoclinic Cc space group. However, a pseudomerohedric twin that simulated orthorhombic (β approximately 90°) and racemic twin laws was observed. Once the refinement was finished, the ADDSYM option in Platon (27) suggested the orthorhombic Cmcm as the correct space group. (28) With this symmetry, the osmium is site in the 2-fold axis along (1/2, y, 3/4). As a result, the chlorine, carbene, and dihydrogen ligands are disordered by symmetry. To complete the anisotropic refinement, restraints were used in some distances (DFIX command) and thermal parameters (SIMU and DELU commands) in the disordered groups.

Crystal data for 3:

C24H49ClN2OOsP2·2C3H6O, Mw , orange, irregular block ( × × mm), orthorhombic, space group Pnma, a = (7) Å, b = (9) Å, c = (4) Å, V = (3) Å3, Z = 4, Z′ = , Dcalc = g cm–3, F() = , T = (2) K, μ = mm–1, measured reflections (2θ = 3–58°, ω scans °), unique reflections (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 = , data/restraints/parameters /0/; GOF = , largest peak and hole (close to osmium atom) and − e/Å3.

Crystal data for 4:

C25H49ClN2O2OsP·2C3H6O, Mw , colorless, irregular block ( × × mm), orthorhombic, space group Pbcm, a = (4) Å, b = (8) Å, c = (10) Å, V = (3) Å3, Z = 4, Z′ = , Dcalc = g cm–3, F() = , T = (2) K, μ = mm–1, measured reflections (2θ = 3–58°, ω scans °), unique (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 = , data/restraints/parameters /0/, GOF = , largest peak and hole (close to osmium atoms) and − e/Å3.

Crystal data for 5:

C24H49ClN2O3OsP2, Mw , red, irregular block ( × × mm), orthorhombic, space group Pbca, a = (6) Å, b = (6) Å, c = (7) Å, V = (3) Å3, Z = 8, Z′ = 1, Dcalc = g cm–3, F() = , T = (2) K, μ = mm–1, measured reflections (2θ = 3–51°, ω scans °), unique (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 = , data/restraints/parameters /6/, GOF = , largest peak and hole (close to osmium atoms) and − e/Å3.

Crystal data for 6:

C24H51ClN2O1OsP2·2C3H6O, Mw , orange, irregular block ( × × mm), orthorhombic, space group Cmcm, a = (6) Å, b = (8) Å, c = (12) Å, V = (3) Å3, Z = 4, Z′ = , Dcalc = g cm–3, F() = , T = (2) K, μ = mm–1, measured reflections (2θ = 3–58°, ω scans °), unique (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 = , data/restraints/parameters //, GOF = , largest peak and hole and − e/Å3.

Supporting Information


Figures and CIF files giving positional displacement parameters, crystalllographic data, and bond lengths and angles of compounds 36, IR spectrum of complex 5, NMR spectra of complexes 5, 6, 6′, and 7, and plots of hydrogen evolution versus time for the alcoholysis and hydrolysis of pinacolborane catalyzed by complex 3. The Supporting Information is available free of charge on the ACS Publications website at DOI: /mauitopia.usmet.5b

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Author Information


    • Miguel A. Esteruelas - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain;  Email: [email&#;protected]

    • Miguel Yus - Departamento de Quı́mica Orgánica, Facultad de Ciencias-Instituto de Sı́ntesis Orgánica (ISO), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Alicante, Apdo. 99, Alicante, Spain;  Email: [email&#;protected]

    • Tamara Bolaño - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain

    • M. Pilar Gay - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain

    • Enrique Oñate - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain

    • Isidro M. Pastor - Departamento de Quı́mica Orgánica, Facultad de Ciencias-Instituto de Sı́ntesis Orgánica (ISO), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Alicante, Apdo. 99, Alicante, Spain

  • The authors declare no competing financial interest.

Acknowledgment


Financial support from the MINECO of Spain (Projects CTQP and CTQREDC), the Diputación General de Aragón (E), and the European Social Fund (FSE) and FEDER. M.P.G. thanks the Spanish MINECO for her FPI fellowship. T.B. thanks the Spanish MINECO for funding through the Juan de la Cierva program.

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    Gunanathan, Chidambaram; Milstein, David

    Accounts of Chemical Research (), 44 (8), CODEN: ACHRE4; ISSN (American Chemical Society)

    A review. In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on "cooperating" ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation. We have discovered a new mode of metal-ligand cooperation, involving aromatization-dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidn. state, and so far the activation of H-H, C-H (sp2 and sp3), O-H, and N-H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H2 and light-induced liberation of O2, using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique "long-range" metal-ligand cooperation in the activation of H2 and in reaction with ammonia. In this Account, we begin by providing an overview of the metal-ligand cooperation based on aromatization-dearomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal-ligand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcs. to ketones, (2) acceptorless dehydrogenative coupling of alcs. to esters, (3) acylation of secondary alcs. by esters with dihydrogen liberation, (4) direct coupling of alcs. and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H2 liberation, (6) selective synthesis of imines from alcs. and amines, (6) facile catalytic hydrogenolysis of esters to alcs., (7) hydrogenolysis of amides to alcs. and amines, (8) hydrogenation of ketones to secondary alcs. under mild hydrogen pressures, (9) direct conversion of alcs. to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcs. and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being mol. hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes.

    >> More from SciFinder &#;

    mauitopia.us?origin=ACS&resolution=options&coi=1%3ACAS%3A%3ADC%BC3MXosFyktbc%D&md5=74d99cec4dbd2f8dbc51dc16cc
  6. 6
    Nelson, D. J.; Nolan, S. mauitopia.us Soc. Rev, 42, – DOI: /c3csc
    [Crossref], [PubMed], [CAS], Google Scholar
    6

    Quantifying and understanding the electronic properties of N-heterocyclic carbenes

    Nelson, David J.; Nolan, Steven P.

    Chemical Society Reviews (), 42 (16), CODEN: CSRVBR; ISSN (Royal Society of Chemistry)

    A review. The use of N-heterocyclic carbenes (NHCs) in chem. has developed rapidly over the past twenty years. These interesting compds. are predominantly employed in organometallic chem. as ligands for various metal centers, and as organocatalysts able to mediate an exciting range of reactions. However, the sheer no. of NHCs known in the literature can make the appropriate choice of NHC for a given application difficult. A no. of metrics were explored that allow the electronic properties of NHCs to be quantified and compared. In this review, these various metrics and what they can teach about the electronic properties of NHCs are discussed. Data for approx. three hundred NHCs are presented, obtained from a detailed survey of the literature.

    >> More from SciFinder &#;

    mauitopia.us?origin=ACS&resolution=options&coi=1%3ACAS%3A%3ADC%BC3sXhtFeqtrnJ&md5=db28f52bca1def03
  7. 7
    (a) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. mauitopia.us Chem., Int. Ed, 46, – DOI: /anie
    [Crossref], [CAS], Google Scholar
    7a

    Palladium complexes of N-heterocyclic carbenes as catalysts for cross-coupling reactions - a synthetic chemist's perspective

    Kantchev, Eric Assen B.; O'Brien, Christopher J.; Organ, Michael G.

    Angewandte Chemie, International Edition (), 46 (16), CODEN: ACIEF5; ISSN (Wiley-VCH Verlag GmbH & Co. KGaA)

    A review. Palladium-catalyzed C-C and C-N bond-forming reactions are among the most versatile and powerful synthetic methods. For the last 15 years, N-heterocyclic carbenes (NHCs) have enjoyed increasing popularity as ligands in Pd-mediated cross-coupling and related transformations because of their superior performance compared to the more traditional tertiary phosphanes. The strong σ-electron-donating ability of NHCs renders oxidative insertion even in challenging substrates facile, while their steric bulk and particular topol. is responsible for fast reductive elimination. The strong Pd-NHC bond contribute to the high stability of the active species, even at low ligand/Pd ratios and high temps. With a no. of com. available, stable user-friendly, and powerful NHC-Pd precatalysts, the goal of a universal cross-coupling catalyst is within reach. This review discusses the basics of Pd-NHC chem. to understand the peculiarities of these catalysts and then gives a crit. discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions.

    >> More from SciFinder &#;

    mauitopia.us?origin=ACS&resolution=options&coi=1%3ACAS%3A%3ADC%BD2sXksleitb4%D&md5=bf0dbb89dfbb0ff
    (b) Dı́ez-González, S.; Marion, N.; Nolan, S. mauitopia.us Rev, , – DOI: /crm
  8. 8
    Kühl, mauitopia.us Soc. Rev, 36, – DOI: /BH
    (b) John, A.; Ghosh, mauitopia.us Trans, 39, – DOI: /ca
  9. 9

    For some representative examples, see:

    (a) McGuinness, D. S.; Cavell, K. mauitopia.usmetallics, 19, – DOI: /omc
    (b) Peñafiel, I.; Pastor, I. M.; Yus, M.; Esteruelas, M. A.; Oliván, M.; Oñate, mauitopia.us J. Org. Chem, – DOI: /ejoc
Источник: mauitopia.us

EF Commander Crack Full Version

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Installation Guide

 Preparing Installation Sources

As explained in Chapter 2, Downloading Red Hat Enterprise Linux, two basic types of media are available for Red Hat Enterprise Linux: a minimal boot image and a full installation image (also known as a binary DVD). If you downloaded the binary DVD and created a boot DVD-ROM or USB drive from it, you can proceed with the installation immediately, as this image contains everything you need to install the system.

However, if you use the minimal boot image, you must also configure an additional source of the installation. This is because the minimal boot image only contains the installation program itself and tools needed to boot your system and start the installation; it does not include the software packages to be installed on your system.

The full installation DVD ISO image can be used as the source for the installation. If your system will require additional software not provided by Red Hat, you should configure additional repositories and install these packages after the installation is finished. For information about configuring additional Yum repositories on an installed system, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The installation source can be any of the following:

  • : You can burn the binary DVD ISO image onto a DVD and configure the installation program to install packages from this disk.

  • : You can place the binary DVD ISO image on a hard drive and install packages from it.

  • : You can copy the binary DVD ISO image or the installation tree (extracted contents of the binary DVD ISO image) to a network location accessible from the installation system and perform the installation over the network using the following protocols:

    • : The binary DVD ISO image is placed into a Network File System (NFS) share.

    • , or : The installation tree is placed on a network location accessible over , , or .

When booting the installation from minimal boot media, you must always configure an additional installation source. When booting the installation from the full binary DVD, it is also possible to configure another installation source, but it is not necessary - the binary DVD ISO image itself contains all packages you need to install the system, and the installation program will automatically configure the binary DVD as the source.

You can specify an installation source in any of the following ways:

  • In the installation program's graphical interface: After the graphical installation begins and you select your preferred language, the Installation Summary screen will appear. Navigate to the Installation Source screen and select the source you want to configure. For details, see:

  • Using a boot option: You can specify custom boot options to configure the installation program before it starts. One of these options allows you to specify the installation source to be used. See the option in Section , “Configuring the Installation System at the Boot Menu” for details.

  • Using a Kickstart file: You can use the command in a Kickstart file and specify an installation source. See Section , “Kickstart Commands and Options” for details on the Kickstart command, and Chapter 27, Kickstart Installations for information about Kickstart installations in general.

 Installation Source on a Hard Drive

Hard drive installations use an ISO image of the binary installation DVD. To use a hard drive as the installation source, transfer the binary DVD ISO image to the drive and connect it to the installation system. Then, boot the Anaconda installation program.

You can use any type of hard drive accessible to the installation program, including USB flash drives. The binary ISO image can be in any directory of the hard drive, and it can have any name; however, if the ISO image is not in the top-level directory of the drive, or if there is more than one image in the top-level directory of the drive, you will be required to specify the image to be used. This can be done using a boot option, an entry in a Kickstart file, or manually in the Installation Source screen during a graphical installation.

A limitation of using a hard drive as the installation source is that the binary DVD ISO image on the hard drive must be on a partition with a file system which Anaconda can mount. These file systems are , , , , and (). Note that on Microsoft Windows systems, the default file system used when formatting hard drives is , and the file system is also available; however, neither of these file systems can be mounted during the installation. If you are creating a hard drive or a USB drive to be used as an installation source on Microsoft Windows, make sure to format the drive as .

The file system does not support files larger than 4 GiB. Some Red Hat Enterprise Linux 7 installation media can be larger than that, which means you cannot copy them to a drive with this file system.

When using a hard drive or a USB flash drive as an installation source, make sure it is connected to the system when the installation begins. The installation program is not able to detect media inserted after the installation begins.

 Installation Source on a Network

Placing the installation source on a network has the advantage of allowing you to install multiple systems from a single source, without having to connect and disconnect any physical media. Network-based installations can be especially useful when used together with a TFTP server, which allows you to boot the installation program from the network as well. This approach completely eliminates the need for creating physical media, allowing easy deployment of Red Hat Enterprise Linux on multiple systems at the same time. For further information about setting up a TFTP server, see Chapter 24, Preparing for a Network Installation.

 Installation Source on an NFS Server

The installation method uses an ISO image of the Red Hat Enterprise Linux binary DVD placed in a server's exported directory, which the installation system must be able to read. To perform an NFS-based installation, you will need another running system which will act as the NFS host.

For more information about NFS servers, see the Red Hat Enterprise Linux 7 Storage Administration Guide.

The following procedure is only meant as a basic outline of the process. The precise steps you must take to set up an NFS server will vary based on the system's architecture, operating system, package manager, service manager, and other factors. On Red Hat Enterprise Linux 7 systems, the procedure can be followed exactly as documented. For procedures describing the installation source creation process on earlier releases of Red Hat Enterprise Linux, see the appropriate Installation Guide for that release.

Procedure  Preparing for Installation Using NFS

  1. Install the nfs-utils package by running the following command as :

  2. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to a suitable directory on the NFS server. For example, you can create directory for this purpose and save the ISO image here.

  3. Open the file using a text editor and add a line with the following syntax:

    /exported_directory/clients

    Replace /exported_directory/ with the full path to the directory holding the ISO image. Instead of clients, use the host name or IP address of the computer which is to be installed from this NFS server, the subnetwork from which all computers are to have access the ISO image, or the asterisk sign () if you want to allow any computer with network access to the NFS server to use the ISO image. See the man page for detailed information about the format of this field.

    The following is a basic configuration which makes the directory available as read-only to all clients:

    /rhel7-install *
  4. Save the file after finishing the configuration and exit the text editor.

  5. Start the service:

    If the service was already running before you changed the file, enter the following command instead, in order for the running NFS server to reload its configuration:

After completing the procedure above, the ISO image is accessible over and ready to be used as an installation source.

When configuring the installation source before or during the installation, use as the protocol, the server's host name or IP address, the colon sign (), and the directory holding the ISO image. For example, if the server's host name is and you have saved the ISO image in , specify as the installation source.

 Installation Source on an HTTP, HTTPS or FTP Server

This installation method allows for a network-based installation using an installation tree, which is a directory containing extracted contents of the binary DVD ISO image and a valid file. The installation source is accessed over , , or .

For more information about HTTP and FTP servers, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The following procedure is only meant as a basic outline of the process. The precise steps you must take to set up an FTP server will vary based on the system's architecture, operating system, package manager, service manager, and other factors. On Red Hat Enterprise Linux 7 systems, the procedure can be followed exactly as documented. For procedures describing the installation source creation process on earlier releases of Red Hat Enterprise Linux, see the appropriate Installation Guide for that release.

Procedure  Preparing Installation Using HTTP or HTTPS

  1. Install the httpd package by running the following command as :

    An server needs additional configuration. For detailed information, see section Setting Up an SSL Server in the Red Hat Enterprise Linux 7 System Administrator's Guide. However, is not necessary in most cases, because no sensitive data is sent between the installation source and the installer, and is sufficient.

    If your Apache web server configuration enables SSL security, make sure to only enable the protocol, and disable and . This is due to the POODLE SSL vulnerability (CVE). See mauitopia.us for details.

    If you decide to use and the server is using a self-signed certificate, you must boot the installer with the option.

  2. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to the HTTP(S) server.

  3. Mount the binary DVD ISO image, using the command, to a suitable directory:

    Replace /image_directory/mauitopia.us with the path to the binary DVD ISO image, and /mount_point/ with the path to the directory in which you want the content of the ISO image to appear. For example, you can create directory for this purpose and use that as the parameter of the command.

  4. Copy the files from the mounted image to the HTTP server root.

    This command creates the directory with the content of the image.

  5. Start the service:

After completing the procedure above, the installation tree is accessible and ready to be used as the installation source.

When configuring the installation source before or during the installation, use or as the protocol, the server's host name or IP address, and the directory in which you have stored the files from the ISO image, relative to the HTTP server root. For example, if you are using , the server's host name is , and you have copied the files from the image to , specify as the installation source.

Procedure  Preparing for Installation Using FTP

  1. Install the vsftpd package by running the following command as :

  2. Optionally, open the configuration file in a text editor, and edit any options you want to change. For available options, see the man page. The rest of this procedure assumes that default options are used; notably, to follow the rest of the procedure, anonymous users of the FTP server must be permitted to download files.

    If you configured SSL/TLS security in your file, make sure to only enable the protocol, and disable and . This is due to the POODLE SSL vulnerability (CVE). See mauitopia.us for details.

  3. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to the FTP server.

  4. Mount the binary DVD ISO image, using the command, to a suitable directory:

    Replace /image_directory/mauitopia.us with the path to the binary DVD ISO image, and /mount_point with the path to the directory in which you want the content of the ISO image to appear. For example, you can create directory for this purpose and use that as the parameter of the command.

  5. Copy the files from the mounted image to the FTP server root:

    This command creates the directory with the content of the image.

  6. Start the service:

    If the service was already running before you changed the file, restart it to ensure the edited file is loaded. To restart, execute the following command:

After completing the procedure above, the installation tree is accessible and ready to be used as the installation source.

When configuring the installation source before or during the installation, use as the protocol, the server's host name or IP address, and the directory in which you have stored the files from the ISO image, relative to the FTP server root. For example, if the server's host name is and you have copied the files from the image to , specify as the installation source.

Источник: mauitopia.us

Allosteric Regulation of Bk Channel Gating by Ca2+ and Mg2+ through a Nonselective, Low Affinity Divalent Cation Site

RESULTS

Millimolar Concentrations of Mg2+ and Ca2+ Produce Similar Shifts in the Voltage of Half Activation (V).

Fig. 1 shows currents from an excised inside-out patch expressing mSlo1 ± subunits. On the left, currents were activated with ¼M, 2 mM, 10 mM, and 50 mM Ca2+. On the right, currents were activated with ¼M Ca2+ with 2, 10, and 50 mM Mg2+. Qualitatively, it can be seen that the effect produced by increases in [Ca2+] above ¼M appear to be mimicked by comparable increases in [Mg2+].

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Figure 1

Similar enhancement of Slo1 current activation by high concentrations of either Ca2+ and Mg2+. Each family of traces shows currents from the same inside-out patch from a Xenopus oocyte, expressing mSlo1 ± subunits. Currents were activated by the voltage protocol shown on the top left with the indicated divalent cation concentrations applied to the cytosolic face of the patch. On the left, traces were obtained with ¼M Ca2+, 2 mM Ca2+, 10 mM Ca2+ and 50 mM Ca2+ from top to bottom. On the right, each family of traces was obtained with ¼M Ca2+ but with added 2, 10, and 50 mM Mg2+ from top to bottom. Tail currents were recorded at &#x; mV. For solutions containing 10 and 50 mM divalent, the potential before the activation steps (&#x; to + mV) was &#x; mV, and &#x; in other cases. Note the strong slowing of deactivation with either Ca2+ and Mg2+, the similar activation of current with additions of mM Ca2+ or Mg2+, and the strong block of current at positive activation potential at higher divalent concentrations.

Fig. 2 A shows corresponding conductance-voltage relationships (G-Vs) determined from measurements of tail current for the four Ca2+ concentrations illustrated in Fig. 1, whereas Fig. 2 B shows the effects of additions of Mg2+ to current activated by ¼M Ca2+. In Fig. 2 C, G-V curves resulting from ¼M Ca2+, 10 mM Ca2+ and ¼M Ca2+ plus 10 mM Mg2+ are directly compared. It can be seen that once current is activated by ¼M Ca2+, additions of either Ca2+ or Mg2+ are relatively comparable in their ability to shift G-V curves.

High concentrations of Ca2+ also block Slo1 currents. This block is indicated by the voltage-dependent reduction of current at the most positive activation voltages in the presence of 10 and 50 mM Ca2+ (Fig. 1). Mg2+ also produces a similar voltage-dependent reduction of peak current. This reduction in peak macroscopic conductance is almost entirely mediated by fast channel block (Vergara and Latorre ; Ferguson ), which can be seen in the reduction of single-channel current amplitude with high [Ca2+] (data not shown for Ca2+ [unpublished data], but see results in Fig. 3 with Mg2+ below).

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Figure 3

Millimolar Mg2+ and Ca2+ produce similar shifts to more negative potentials in the relationship between open probability and voltage. In A, traces show currents from an inside-out patch containing two BK channels. Patches were held at &#x;40 mV with repeated voltage steps to either +60 mV (A1 and A3), or &#x;60 mV (A2 and A4). On the left (A1 and A2), channels were activated with ¼M Ca2+, whereas on the right (A3 and A4) channels were activated with ¼M Ca2+ plus 10 mM Mg2+. In each panel, the ensemble average expressed in units of probability of being open (Po) is plotted at the bottom. At +60 mV, the addition of Mg2+ has little effect on Po, but reduces the single-channel current amplitude. At &#x;60 mV, Mg2+ produces a substantial increase in Po, with only a mild reduction in the single-channel amplitude. In B, Po estimates obtained from the ensemble averages are plotted as a function of command potential for the patch shown in A. Solid lines are fits of . At ¼M Ca2+, fitted values with 90% confidence limits were gmax = ± , V = &#x; ± mV, and k = ± mV; for ¼M Ca2+ plus 10 mM Mg2+, gmax = ± , V = &#x; ± mV, and k = ± mV. In C, Po versus voltage is plotted for a different patch showing that activation by 10 mM Ca2+ is similar to that produced by 10 mM Ca2+ plus 10 mM Mg2+. Fitted values were as follows: for ¼M Ca2+, gmax = ± , V = &#x; ± mV, and k = ± mV; for ¼M Ca2+ plus 10 mM Mg2+, gmax = ± , V = &#x; ± mV, and k = ± mV; for 10 mM Ca2+, gmax = ± , V = &#x; ± mV, and k = 25 ± mV; and for 10 mM Ca2+ plus 10 mM Mg2+, gmax = ± , V = &#x; ± mV, and k = ± mV.

For a set of patches, the relationship between conductance and activation voltage was determined over Ca2+ concentrations from 1 ¼M to mM (Fig. 2 D). Similarly, in parallel experiments, the effect of Mg2+ from 1 mM to mM on currents activated by ¼M Ca2+ was determined (Fig. 2 E). G-V curves were fit with a single Boltzmann () and the relationship between V and pCa for a large number of patches is plotted in Fig. 2 F. There are two key features. As [Ca2+] is raised to ¼M, the rate of change in the voltage of half activation appears to slow similar to previous observations (Wei et al. ; Cox et al. b; Cui et al. ). However, at 10 mM Ca2+, activation is shifted dramatically to more negative potentials by an additional 40&#x;50 mV.

Activation of Slo1 by Ca2+ Is Potentiated by Internal Mg2+

The additional leftward shift of activation caused by mM concentrations of Ca2+ coupled with the inflection observed in the V versus pCa plot raise the possibility that Ca2+ is shifting activation of Slo1 channels through a process distinct from the Ca2+-dependent activation steps that occur at lower [Ca2+]. The fact that, in the presence of ¼M Ca2+, millimolar Mg2+ and Ca2+ are similarly effective at shifting the V also supports the idea that effects of mM divalents may involve a different site and mechanism than the gating effects produced by micromolar Ca2+.

It has been shown previously that, in the presence of micromolar Ca2+, millimolar concentrations of internal Mg2+ can potentiate activation of BK channels recorded from rat skeletal muscle transverse tubule membranes (Golowasch et al. ; Oberhauser et al. ). Because Mg2+ produces minimal channel activation in the absence of Ca2+, it has been proposed that Mg2+ is a positive allosteric modulator of BK channel activity. ¼M nickel in the presence of 1 ¼M Ca2+ is also able to shift the V of this channel by 44 mV negative to that measured with 1 ¼M Ca2+ alone (Oberhauser et al. ). Like Mg2+, Ni2+ alone is relatively ineffective at activating BK channels. This suggests that some divalent cations may influence BK gating at a secondary allosteric site. The leftward shift of V measured for Slo1 with 10 mM Ca2+, then, could be caused by an association of Ca2+ itself with this relatively nonselective site. The experiments presented below address this hypothesis.

Mg2+-induced Shifts in the Single-channel Probability of Being Open Are Similar to Shifts in Macroscopic Currents

Fig. 3 shows that a leftward shift of activation by 10 mM Mg2+ is also evident at the single-channel level. For these experiments, inside-out patches containing one or two channels were stepped repeatedly to particular test potentials. Fig. 3 A shows sample records from a patch containing two channels in which activation is compared at both +60 and &#x;60 mV in the presence of either ¼M Ca2+ or ¼M Ca2+ + 10 mM Mg2+. For a given condition, the probability of channels being open (Po) was measured for each sweep and an average Po was generated for a set of sweeps. Fig. 3 B summarizes the average Po determined over a range of voltages from the experiment in Fig. 3 A. Superimposed solid lines are fitted single Boltzmann relations. The plot shows that 10 mM Mg2+ is able to shift activation, as measured by Po, leftward by 50 mV. This is similar to the magnitude of the shift measured for macroscopic currents. Both with and without Mg2+, the saturating Po is similar and approaches 90%.

Fig. 3 C plots Po estimates as a function of test potential for an experiment similar to that of Fig. 3 A in which channels were activated by either ¼M Ca2+, ¼M Ca2+ plus 10 mM MgCl2, 10 mM Ca2+ or 10 mM Ca2+ plus 10 mM Mg2+. The Po-V relationships for the latter three solutions are all quite similar. This indicates that, in the presence of ¼M Ca2+, addition of Mg2+ is about as effective as an increase in Ca2+ at producing leftward shifts in the activation curves. In contrast, the further addition of 10 mM Mg2+ to 10 mM Ca2+ is ineffective at producing an additional shift. The V estimates measured at the single-channel level in the presence and absence of 10 mM Mg2+ are similar to those measured for macroscopic currents.

The Magnitude of the Shift in V Produced by Mg2+ Is Not Ca2+-dependent

We next examined the ability of Mg2+ to shift G-V curves at lower [Ca2+]. Fig. 4 A gives an example of the effect of 10 mM Mg2+ on Slo1 currents activated in the absence of Ca2+. G-V curves (Fig. 4 B) were generated for a set of patches with 0-¼M Ca2+ solutions, 0 Ca2+/10 mM Mg2+, and 0 Ca2+/50 mM Mg2+. When 10 mM Mg2+ is added to 0-Ca2+ solutions, conductance begins to be activated 50 mV negative to that observed absence of Mg2+, a shift similar to that observed when 10 mM Mg2+ is added to a solution with ¼M Ca2+. It might be argued that this shift results from the addition of contaminant Ca2+ in the Mg2+ solution. However, as described in the materials and methods, in the solutions with 0 ¼M Ca2+/10 mM Mg2+/5 mM EGTA, the free [Ca2+] is unlikely to exceed even 10 nM, a concentration that does not activate BK current. Furthermore, the effects of the addition of Mg2+ on current activation time course appear inconsistent with the expected effects of an addition of Ca2+. Although the effects of Ca2+ on activation time course are complex at activation potentials above the voltage of half activation of current, 10 mM Mg2+ produces little effect on the current activation time course (Fig. 9 E), whereas small increases in [Ca2+] typically increase current activation rates. Thus, the effect of Mg2+ appears to differ from what would be expected from the addition of Ca2+. This slowing in activation rate also suggests that the mechanism of Mg2+ action is clearly distinct from the changes in gating that occur with lower concentrations of Ca2+.

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Figure 4

Mg2+ also shifts current activation in lower Ca2+ or 0 Ca2+. In A, currents on the left were activated by the indicated protocol with a solution containing trace Ca2+ with 10 mM EGTA. On the right, currents were activated from the same patch with a solution containing 0 Ca2+, 5 mM EGTA but with 10 mM Mg2+. In 0 Ca2+, time constants of activation (Äa) were , , ms for +, +, and + mV, respectively. With 10 mM Mg2+, Äa was , , and ms at +, +, and + mV, respectively. In B, the normalized conductance is plotted as a function of command potential for 0 Ca2+ (eight patches), 10 mM Mg2+ (eight patches) and 50 mM Mg2+ (seven patches). Conductance values were normalized in each patch to the maximum value obtained with 50 mM Mg2+. Fits of (solid lines) yielded values for V of ± mV (k = mV) for 0 ¼M Ca2+, ± mV (k = mV) for 10 mM Mg2+, and ± mV (k = mV) for 50 mM Mg2+. In C, currents activated at + mV were normalized to peak steady-state amplitude of a single exponential fit to the rising phase of currents activated either with 0 Ca2+ or with 0 Ca2+ + 10 mM Mg2+. The time constant of activation with 0 Ca2+ was ms, whereas with 10 mM Mg2+ was ms. The slowing of activation with Mg2+ was consistently observed at all activation voltages and argues that the additional activation by Mg2+ is not the result of an increase in trace Ca2+. In D, currents were activated by a voltage step to +80 mV with either 4 or 10 ¼M Ca2+ without or with the addition of 10 mM Mg2+. Unbuffered divalent cation solutions were prepared as described in the materials and methods. Note the increased current amplitude and slower activation of current in the presence of Mg2+. In E, G-V curves were constructed from measurement of tail currents from a set of 4 patches studied as in D. Error bars represent the SEM of four patches. The V for each curve is ± mV (10 ¼M Ca2+), ± (10 ¼M Ca2+ + 10 mM Mg2+), ± mV (4 ¼M Ca2+), and ± mV (4 ¼M Ca2+ plus 10 mM Mg2+). Buffered Ca2+ solutions prepared at the same time and tested on the same patches yielded V values of ± mV for 10 ¼M Ca2+ and ± mV for 4 ¼M Ca2+. In F, ensemble averaged currents were generated from channels activated with the indicated solutions for a voltage-step to +40 mV from a patch containing two channels. The addition of Mg2+ increases the open probability towards maximal values but slows down the time constant of current activation. With 10 ¼M Ca2+, the activation time constant was ± ms, whereas with 10 ¼M Ca2+ plus 10 mM Mg2+ the time constant was ± ms.

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Figure 9

Millimolar concentrations of either Ca2+ or Mg2+ are similar in their effects on current activation rates. In A, the time constant of activation (Äa) is plotted as a function of command potential for Ca2+ concentrations of 1 ¼M (&#x;), 4 ¼M (Ë), 10 ¼M (&#x;), 30 ¼M (Ä), 60 ¼M (´), ¼M (µ), and ¼M (ª). Error bars in A and B are SEM for patches. In B, Äa is plotted as a function of command potential for Ca2+ concentrations of ¼M (&#x;), 1 mM (Ë), 2 mM (&#x;), 5 mM (Ä), 10 mM (ª), 20 mM (¡), 50 mM (´), and mM (µ). In C, Äa is plotted as a function of command potential for solutions containing ¼M with added Mg2+ of 0 mM (&#x;), 1 mM (Ë), 2 mM (&#x;), 5 mM (Ä), 10 mM (ª), 20 mM (¡), 50 mM (´), and mM (µ). Each point shows the mean and SEM of patches. In D, the mean rate of current activation for Slo1 currents is plotted as a function of Ca2+ for command potentials of +20 (&#x;), +60 (Ë), + (&#x;), and + (Ä) mV. Error bars are SEM. Solid lines are fits of . At +20 mV, kmax was , Kd = ± ¼M, and n = ± At +60 mV, kmax was , Kd = ± ¼M, and n = ± ; at + mV, kmax = , Kd = ± 59 ¼M, and n = ± ; at + mV, kmax = , Kd = 59 ± 25 ¼M, and n = ± Note the anomalous slowing of current activation rate at 1 ¼M Ca2+ relative to 0 ¼M at + mV. This point was not included in the fit. In E, current activation rate is plotted as a function of total divalent in the solution at + mV for solutions with no added Mg2+ (&#x;) and solutions with Mg2+ added to ¼M Ca2+ (Ë), showing that Mg2+ has little effect on the limiting rate of current activation, although additional depolarization will produce an increase in current activation rate. Note the inhibition of activation rate at the highest [Mg2+]. Current activation with 0 Ca2+ and various [Mg2+] is also plotted (¡), showing the relative lack of effect of Mg2+ in comparison to Ca2+.

The ability of Mg2+ to shift activation was also examined with solutions containing either 4 or 10 ¼M free Ca2+. (Fig. 4, D&#x;F). The shift resulting from 10 mM Mg2+ in this set of four patches was 25 mV, less than observed either at 0 or ¼M Ca2+. An even smaller shift was produced by 10 mM Mg2+ with 10 ¼M Ca2+ in the experiments of Shi and Cui b. Given that 10 mM Mg2+ appears to produce similar shifts in V at both 0 Ca2+ and more elevated Ca2+, the smaller effect at intermediate [Ca2+] seems at first glance unusual. Shi and Cui interpreted this smaller shift as the result of an inhibitory effect of Mg2+ on the Ca2+ binding site (see Shi and Cui b, in this issue). Perhaps consistent with this possibility, when Mg2+ was added to solutions with either 4 or 10 ¼M Ca2+, there was a slowing in the current activation time course (Fig. 4D and Fig. F). Such a slowing might result simply from inhibition by Mg2+ of Ca2+ binding.

The slowing of the activation time course might also be explained by the possibility that Mg2+ was shifting channel activation from a condition of very low open probability to approximately half-maximal open probability. For example, in the simple case of a two-state system,

where Ä(V) = 1/(±(V) + ²(V)), the slowest Ä(V) is achieved when ±(V) = ²(V). For the effect of Mg2+ on Slo1 currents shown in Fig. 4 D, this possibility seemed unlikely since at 10 ¼M [Ca2+] and +80 mV, currents should be at least half maximally activated. To verify this directly, the ability of Mg2+ to enhance current activation at a given potential was examined in one or two channel patches in which it was possible to directly define the effect of Mg2+ on single-channel open probability. Such an experiment shown in Fig. 4 F confirms that the slowing of the activation time course even occurs as the open probability goes from about half maximal to near maximal. If Mg2+ produced a shift in V by simply shifting the effective activation voltage by 30&#x;50 mV, an increase in activation rate would have been expected. This is clearly not observed. This leaves us with the possibility that the slowing of activation time course reflects inhibition by Mg2+ of Ca2+ binding, when [Mg2+] sufficiently exceeds [Ca2+].

A Low Affinity, Relatively Nonselective Divalent Cation Binding Site May Account for the Effects of Mg2+ and Ca2+

Fig. 5 A summarizes the ability of Mg2+ to shift V for currents activated by ¼M Ca2+ for two separate sets of patches. For both sets of patches, the shift in V at mM Mg2+ is less than at 50 mM Mg2+. The reduction in shift with mM Mg2+ is the result expected, if Mg2+ inhibits the ability of ¼M Ca2+ to shift gating. Because of this possible inhibitory action of Mg2+, it is more difficult to ascertain whether the shift in V produced by Mg2+ exhibits saturation. However, because of the saturation in the shift of V observed over the range of 20&#x; mM Ca2+, it seems likely that the effects of Mg2+ also exhibit a similar saturation. However, it should be noted that both in our experiments and the experiments of Shi and Chi (b) additions of Mg2+ over the range of 10&#x; mM to 0-Ca2+ solutions do not result in full saturation of the shift in V.

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Figure 5

The ability of mM concentrations of Ca2+ and Mg2+ to shift G-V curves is similar. In A, the V for activation is plotted as a function of Mg2+ for G-V curves obtained in two separate sets of patches each activated by ¼M Ca2+ plus the indicated Mg2+. The predictions for the shift in V as a function of Mg2+ based on two sets of fitted values for Fig. 1 (Table , columns A [&#x;] and D [ª]) are also displayed. In B, the ability of Mg2+ to shift V at different Ca2+ is displayed. Triangles show V values from macroscopic currents without (´) or with (µ) 10 mM Mg2+. Circles ([&#x;] no Mg2+; [Ë]: + 10 mM Mg2+) are means and SD for V determined from Po measurements from four patches with either one or two channels as in Fig. 3. Diamonds ([&#x;] no Mg2+;[Ä] +10 mM Mg2+) are values obtained with unbuffered Ca2+ solutions. Predictions from the fitted values for Fig. 1 (Table , column D) are also shown for Ca2+ alone (ª) and with 10 mM Mg2+ (¡). In C, the change in V (&#x;V) produced by 10 mM Mg2+ at different [Ca2+] is displayed for macroscopic current measurements (Ë) and single-channel estimates (ª). Estimates of predicted &#x;V based on a fit of Fig. 1 to G-V curves with or without Mg2+ are also shown for two cases: first, Mg2+ inhibition of the high affinity site is allowed (&#x;; Table , column D) and no inhibition by Mg2+ occurs (&#x;; Table II; column F). In D, values of V obtained as a function of Ca2+ (¡) are replotted along with estimates of the V corrected at Ca2+ of 1 mM and above by the additional shift produced by Mg2+ shown in A obtained with ¼M Ca2+. These values (Ë) provide an indication of the ability of the higher affinity, Ca2+ selective site to shift activation of BK channels, in the absence of the low affinity effect, assuming that the high and low affinity effects are independent and additive. Predicted values for V based on a fit of Fig. 1 are also shown for the case of both low and high affinity Ca2+ binding sites (ª; Table II; column D), and also for Ca2+ action alone in the absence of a high affinity site (&#x;). The latter values were also corrected for the approximately &#x;mV shift that ¼M Ca2+ should produce by acting at the low affinity sites (&#x;). The discrepancy between the Mg2+ corrected data and the prediction from Fig. 1 arises from the fact that the Mg2+ correction was obtained with solutions with ¼M Ca2+ such that the effect of ¼M Ca2+ on the low affinity site is not taken into account.

Another interesting aspect of the action of Mg2+ is the magnitude of the shift in V produced by 10 mM Mg2+ at various [Ca2+] up through 10 mM (Fig. 5 B). The results in Fig. 5 B include data from a variety of experimental conditions (Solaro et al. ), including estimates of single-channel open probability from one and two channel patches and macroscopic current estimates. Over the range of 30 ¼M&#x;1 mM Ca2+, 10 mM Mg2+ seems to produce a rather constant shift of about &#x;40 to &#x;60 mV. Similarly, the shift at 0 Ca2+ is also about &#x;50 mV. However, when 10 mM Mg2+ is added to mM Ca2+ solutions, the resulting shift is substantially reduced. This latter effect is consistent with the idea that Mg2+ and Ca2+ are competing for a saturable, low affinity binding site. The magnitude of the shift caused by 10 mM Mg2+ over all Ca2+ is summarized in Fig. 5 C. Fig. 5 (B and C) also includes data obtained with unbuffered 4- and ¼M Ca2+ solutions in which the shifts produced by 10 mM Mg2+ were only about &#x;25 mV, similar to the results of Shi and Cui b. In general, the ability of Mg2+ to shift gating over all [Ca2+] qualitatively supports the idea that, even under conditions where the higher affinity site is only partially occupied by Ca2+, Mg2+ still produced substantial shifts in gating and does so without substituting for Ca2+ at the higher affinity sites.

Because of the possibility that the effect described here may reflect an important regulatory role of free cytosolic Mg2+, we also examined the ability of Mg2+ to shift activation, when Mg is added as MgATP. When Mg2+ is added as 2 mM Mg-ATP, solutions with nominal ¼M Ca2+ are much less effective at activating current. ATP will bind both Mg2+ and Ca2+. Based on published stability constants (Martell and Smith, ), the solution used here ( ¼M added Ca2+, 2 mM added MgATP) is calculated to have 33 ¼M free Ca2+ and ¼M free Mg2+. The V observed for the solution containing 2 mM added MgATP (&#x; ± mV) is similar to that which would be expected for a ¼M Ca2+ solution (about +8 mV) with an additional negative shift of 10 mV resulting from ¼M Mg2+. Thus, the experiment is consistent with the idea that the shift produced by high Mg2+ depends on the free Mg2+ concentration, and that ATP reduces both free Ca2+ and free Mg2+.

The shift caused by increasing [Mg2+] from 1 to 10 mM is 45&#x;50 mV, whereas the shift caused by increases in [Ca2+] from 1 to 10 mM is also 50 mV. Thus, high concentrations of Ca2+ and Mg2+ may be acting at the same site(s) on the channel protein to modulate BK channel gating, independent of the action of Ca2+ at the higher affinity, Ca2+-specific sites. This implies that there are at least two types of Ca2+ binding sites that are important for channel function. First, there are high affinity, relatively Ca2+-specific sites that, along with depolarization, produce channel opening. Second, there are low affinity sites that can bind either Ca2+ or Mg2+ to potentiate activation of channels, no matter whether channels are activated in the presence or absence of Ca2+.

If we assume that high concentrations of Ca2+ and Mg2+ bind to the same or similar sites and are able to promote activation of Slo1 currents in a similar fashion, then the results in Fig. 5 A can be used to subtract the effect of Ca2+ at the putative low affinity site from the V-pCa relationship shown in Fig. 2 E. This manipulation would then reveal the effect of Ca2+ acting only at the putative high affinity sites. This makes the assumption that the effects of high and low affinity sites on V are independent, an issue which is addressed below. The consequences of this assumption are presented in Fig. 5 D. The open squares are V values resulting from the action of [Ca2+] reproduced from Fig. 2 E. The additional shift in V resulting from higher [Ca2+] were then assumed to be equivalent to the additional shift in V resulting from high [Mg2+]. Therefore, the closed squares were obtained by subtracting the magnitude of the shift of V caused by a given [Mg2+] in the presence of ¼M Ca2+ (Fig. 5 A) from the V measured in the presence of the identical [Ca2+], but without Mg2+. For example, the V measured at 2 mM Ca2+ was shifted positive by the amount of shift caused by 2 mM Mg2+. Thus, assuming Ca2+ and Mg2+ act equivalently at the same (or similar) binding site(s), the closed squares reflect the action of Ca2+ at the higher affinity sites alone. Once a correction is made for the effect of Ca2+ on low affinity binding sites, it is evident that for [Ca2+] greater than ¼M, the corrected V's are no longer shifted negative by additional Ca2+, even though activation remains voltage-dependent. This is consistent with the idea that high affinity, Ca2+-dependent steps leading to activation are separate from voltage-dependent steps (Wei et al. ; Cox et al. a; Horrigan and Aldrich ; Horrigan et al. ). Another way of thinking about this is that the relationship between V and Ca2+ in the presence of 10 mM Mg2+ is essentially constant from ¼M to mM (Fig. 5 B). Thus, the channel is essentially unaffected by changes in [Ca2+] over two orders of magnitude, although gating continues to be controlled by voltage.

Concentrations of Ca2+ and Mg2+ of 1 mM and above Have Minor Effects on Current Activation Rates at Potentials from +40 mV and More Positive

The above results argue that, at Ca2+ or Mg2+ concentrations of 1 mM and above, leftward shifts in the open probability of BK channels result primarily from the action of divalent cations at a relatively nonselective site distinct from higher affinity sites that specifically mediate Ca2+-dependent gating of the channel. If [Ca2+] or [Mg2+] at &#x;1 mM potentiates activation by acting at a site distinct from the Ca2+ binding site that regulates activation at lower [Ca2+], effects of higher [Ca2+] or [Mg2+] concentrations on channel gating kinetics might be distinct from those of more modest [Ca2+]. The activation and deactivation behavior of Slo1 currents at [Ca2+] up to 1 mM has previously been examined in some detail (Cox et al. a; Cui et al. ). Here, we have examined the effects of [Ca2+] at up to 10 mM, and also examine current activation and deactivation in the presence of Mg2+.

The rate of Slo1 current activation was examined in inside-out patches as a function of both [Ca2+] and voltage with sampling rates and command steps of sufficient duration to allow determination of activation time course. Over a wide range of [Ca2+] and voltage, the activation time course was approximately exponential in nature (Fig. 6), although some initial delay in activation was observed. Representative currents activated at either +40 or +80 mV with [Ca2+] of 1&#x; ¼M are shown in Fig. 6 (A and B). In Fig. 6C and Fig. D, the currents were normalized to their maximal steady-state amplitude and each fit to a single exponential. To facilitate comparison of changes in activation rate, the normalized current activation time course for currents activated over approximately two orders of magnitude of [Ca2+] is plotted on a logarithmic time base in Fig. 6E and Fig. F. At both +40 and +80 mV, fold changes in concentration produce an approximately three to fivefold change in activation rate over this range of [Ca2+]. In Fig. 7A and Fig. B, currents activated by ¼M, 1 mM, and 10 mM Ca2+ are plotted for both +40 and +80 mV. The normalized currents are plotted on both a linear scale (Fig. 7C and Fig. D) and logarithmic time base (Fig. 7E and Fig. F) showing that the increase in [Ca2+] from ¼M to 10 mM results in only a small additional increase in activation rate, compared with the large changes seen in Fig. 6.

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Figure 6

The current activation rate increases substantially as Ca2+ is raised from 1 ¼M to ¼M. In A, currents were activated by a voltage step to +40 mV with Ca2+ concentrations of 0, 1, 4, 10, 30, 60, and ¼M as indicated. In B, currents were activated in the same patch by a voltage-step to +80 mV with the same Ca2+ concentrations. In C, currents activated by the step to +40 mV were normalized to their maximal amplitude and fit with single exponentials. The activation time constants (Äa) were , , , , and ms, for 4, 10, 30, 60, and ¼M, respectively. In D, the normalized current activation time course for the voltage-steps to +80 mV are shown. Äa's were , , , , , and , for 1, 4, 10, 30, 60, and ¼M Ca2+, respectively. In E and F, the same normalized traces shown in C and D are plotted on a logarithmic time base to show the shift in activation time course with Ca2+. An increase in Ca2+ from 1 to 10 ¼M produces a similar three to fourfold change in activation rate as the increase from 10 to ¼M. At +40 mV, the trace in response to 4 ¼M Ca2+ is plotted since at 1 ¼M there is almost no detectable current activation.

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Figure 7

Increases of Ca2+ from ¼M to 10 mM produce smaller increases in current activation time rate. In A and B, currents were activated by ¼M, 1 mM, and 10 mM Ca2+ at either +40 mV (panel A) or +80 mV (panel B). In C and D, each trace in A and B was normalized to the maximal current amplitude to compare the activation time course. Points show every fourth digitized current value. Solid lines are the best fit of a single exponential function to the activation time course. At +40 mV, the activation time constant (Äa) was , , and ms for ¼M, 1 mM, and 10 mM Ca2+, respectively. At +80 mV, Äa was , , and ms for ¼M, 1 mM, and 10 mM Ca2+, respectively. In E and F, the normalized current activation time course is plotted on a logarithmic time base to allow better comparison of the relatively small concentration dependence of the activation rate for this fold change in concentration compared with that shown in Fig. 6.

The effect of mM Mg2+ on Äa was examined as above. The effects of 1 and 10 mM Mg2+ on currents activated with ¼M Ca2+ are displayed in Fig. 8 (A and B). At 10 mM Mg2+, there is a substantial shift in the G-V curve and substantial open channel block, but the activation course is similar to that in the absence of Mg2+. Comparison of the activation time course of the normalized currents either on a linear (Fig. 8C and Fig. D) or logarithmic (Fig. 8E and Fig. F) time base further emphasizes the lack of effect of Mg2+ on Äa in the presence of ¼M Ca2+. Thus, at potentials where additional depolarization would enhance current activation rate, concentrations of Ca2+ and Mg2+ above 1 mM have little effect on current activation rates. Thus, the lack of effect of Mg2+ on Äa indicates that, whatever the mechanism of action of Mg2+ (and mM Ca2+), it does not affect the voltage-dependent rate limiting activation steps.

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Figure 8

Addition of Mg2+ concentrations which markedly shift G-V curves does not increase the limiting rate of Slo1 current activation. In A and B, traces were elicited in each panel with ¼M Ca2+ alone, and with ¼M Ca2+ with either 1 mM or 10 mM Mg2+. Traces on the left were activated by a voltage step to +40 mV and, on the right, to +80 mV. In C and D, the normalized current activation time course is plotted on a linear time base (every fourth digitized value is plotted), while, in E and F, the same traces are shown on a logarithmic time base. Solid lines are fits of a single exponential function to the activation time course. At +40 mV, Äa was , , and ms for ¼M Ca2+, ¼M Ca2+ + 1 mM Mg2+, and ¼M Ca2+ + 10 mM Mg2+, respectively. At +80 mV, Äa was , , and ms for each solution. Raising Mg2+ up to 10 mM results in little effect on the time course of current activated in the presence of ¼M Ca2+.

The dependence of Äa on voltage is plotted for 0&#x; ¼M Ca2+ in Fig. 9 A and for ¼M&#x; mM Ca2+ in Fig. 9 B. Again at Ca2+ above ¼M, the change in Äa is much smaller than at lower [Ca2+]. Furthermore, at each [Ca2+], the dependence of Äa on voltage is similar. There appears to be an anomalous aspect of the effect of Ca2+ on activation in comparing the results at 0 and 1 ¼M Ca2+. Specifically, there is a slowing of activation at potentials of + mV and more positive as [Ca2+] is elevated to 1 ¼M, whereas activation is again faster at 4 ¼M. We have not examined other concentrations over the range of 0 to 4 ¼M. This result is consistently observed in different sets of patches both in our own experiments and those of others (Cui, J., personal communication). For comparison to the effects of Ca2+, the effect of 1 to mM Mg2+ on current activation elicited with ¼M Ca2+ is shown in Fig. 9 C. Over the range of &#x;60 through + mV, Mg2+ is essentially without effect on current activation rates, with only some slowing of activation at 50 and mM Mg2+.

Time constants were converted to activation rates and the mean rate of activation is plotted as a function of [Ca2+]i from 1 ¼M to 50 mM in Fig. 9 D for potentials of +20, +60, +, and + mV. The rate of activation at a given voltage increases markedly with increases in [Ca2+] up to 1 mM before exhibiting saturation over millimolar concentrations that still produce additional shifts in GV curves. The dependence of activation rate on [Ca2+] (ignoring the rate at 0 Ca2+) was fit with the following function:

equation M2

2

where k(Ca) is the rate of activation at a given [Ca2+], kmin is the minimal activation rate, kmax is the limiting rate at saturating [Ca2+], KD is the concentration of half-maximal Ca2+ effect, and n is a Hill coefficient. The limiting activation rate increases with depolarization at and above 1 ¼M [Ca2+], while the apparent Kd is also shifted to lower concentrations with depolarization. The Hill coefficient shows little variation with voltage.

The saturation in Slo1 current activation rate is consistent with the idea that a key Ca2+-dependent step no longer influences current activation rates at [Ca2+] above 1 mM. However, despite the fact that additional elevations in [Ca2+] do not increase the activation rate, additional depolarization can result in faster current activation. Thus, the saturation in the Ca2+ dependence of activation rate is unrelated to any limit on the channel activation process itself. Rather, the limiting activation rate at saturating [Ca2+]i does vary with voltage, consistent with the idea that solely voltage-dependent transitions determine the limiting rate of activation at [Ca2+] of 1 mM and above.

The effect of Mg2+ on current activation is summarized in Fig. 9 E. When currents were activated with ¼M Ca2+, additions of [Mg2+] from 1 through mM resulted in no additional increase in current activation rate. In fact, at [Mg2+] above 10 mM, a slowing in the activation rate was observed, consistent with the idea that Mg2+ may inhibit Ca2+ binding at the low affinity activation site (Shi and Cui b). We also examined the effect of Mg2+ on activation of current with 0 Ca2+/5 mM EGTA. It was shown earlier that Mg2+ slows current activation with 10 ¼M Ca2+ (Fig. 5), an effect probably resulting from an inhibitory effect of Mg2+ on the high affinity Ca2+ binding site. However, with 0 Ca2+, there was essentially no effect of 10 mM Mg2+ on activation time constant at potentials positive to + mV, whereas at more negative potentials and less than maximal open probabilities, activation and deactivation were slowed, both effects probably resulting from the effects of Mg2+ on transitions involved in deactivation described below. Thus, Mg2+ does not appear to directly influence rate limiting, voltage-dependent activation steps in the absence of Ca2+. However, it should be noted that, with 0 Ca2+ and [Mg2+] above 10 mM, we also observed an increase in current activation rate (Fig. 9 E) that cannot be easily accounted for by the mechanisms presented below.

Deactivation Is Slowed by Either Increases in Ca2+ or Mg2+

Deactivation tails resulting from closure of Slo1 channels after repolarization were examined over a range of potentials with [Ca2+] from 0 ¼M to mM. Deactivation, under most conditions, could be described by a single exponential. The deactivation time constant (Äd) is plotted as a function of voltage in Fig. 10 A over Ca2+ concentrations spanning six orders of magnitude. Similarly, Äd is plotted as a function of voltage in Fig. 10 B for solutions containing ¼M Ca2+ with or without either 1, 10, or mM Mg2+. The dependence of Äd on Ca2+ and Mg2+ appears similar but differs from the dependence of Äa on Ca2+ and Mg2+. Namely, increases in [Ca2+] above ¼M continue to result in additional slowing of current deactivation, implying that there may be Ca2+-dependent effects at higher [Ca2+] that influence rates of exit from open states or closed states near open states, but which have no affect on the limiting rates of channel activation. Similarly, although Mg2+ is without effect in substituting for Ca2+-dependent activation steps, Mg2+ does slow deactivation in a fashion qualitatively similar to the effect of mM Ca2+. For both Mg2+ and Ca2+, the slowing of deactivation is substantial over the range of 1&#x;10 mM of either cation, concentrations at which activation rates are unaffected. However, above 10 mM of either cation, there is an indication that the effect on deactivation exhibits saturation, which is consistent with the saturation in the shift of G-V curves at high divalent cation concentrations. The change in Äd as a function of [Mg2+] is plotted in Fig. 10 C and compared with the effect of a similar total concentration of divalent with Ca2+ alone. Millimolar concentrations of Mg2+ and Ca2+ appear similar in their effects on deactivation.

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Figure 10

Millimolar concentrations of Mg2+ and Ca2+ have similar effects on current deactivation. In A, the deactivation time constants are plotted as a function of command potential for [Ca2+] spanning over six orders of magnitude, 1 ¼M&#x; mM. Points and error bars are means and SEM of 5&#x;15 patches. In B, the deactivation time constants are plotted as a function of command potential for tail currents obtained with ¼M Ca2+ and ¼M Ca2+ plus 1, 10, and mM added Mg2+. Points show means and SEM for 4&#x;8 patches. In C, the deactivation time constant measured at &#x; mV is plotted as a function of total [divalent] for solutions with only Ca2+ (&#x;) and for solutions with ¼M Ca2+ with added Mg2+ (Ë). The slowing of deactivation with either elevated Ca2+ or Mg2+ exhibits saturation, although at somewhat different concentrations.

To summarize the similarities and differences in the effects of Ca2+ and Mg2+ on kinetic aspects of Slo1 currents, effects of various [Ca2+] and [Mg2+] were compared in the same sets of patches. At any given [Ca2+] and [Mg2+], the relaxation time constant (deactivation and activation) exhibits an approximately bell-shaped dependence on voltage. In Fig. 11 A, 10 ¼M Ca2+ is shown to shift both activation and deactivation times constants to a somewhat similar extent compared with 0 Ca2+, whereas with ¼M Ca2+, the effects on Äd begin to diminish while effects on activation remain pronounced. In Fig. 11 B, 4 ¼M Ca2+ produces a leftward shift qualitatively similar to that with 10 ¼M, although smaller. 1 ¼M Ca2+ results in the unusual slowing of activation described above, producing a slowing of the principle time constant at all voltages. In Fig. 11C and Fig. D, Fig. 10 and 50 mM Ca2+ are compared with 10 and 50 mM Mg2+. 10 and 50 mM Ca2+ produce a similar leftward shift in the relaxation time constant. In contrast, with 10 mM Mg2+, there is no apparent effect on current activation, but deactivation is slowed. 50 mM Mg2+ produces some slight additional slowing in deactivation, but also results in some increase in current activation rate. In Fig. 11 E, 10 and 50 mM Ca2+ are shown to produce a substantial additional slowing of deactivation relative to ¼M Ca2+, with only weaker effects on current activation at positive potentials. The effects of 10 and 50 mM Mg2+ when added to ¼M Ca2+ are quite similar (Fig. 11 F), producing a substantial slowing of current deactivation, with little effect on current activation, except for a clear slowing of activation at 50 mM. Thus, these kinetic effects remain generally consistent with the effects of Ca2+ and Mg2+ on GV curves. There is a higher affinity effect of Ca2+ that influences both current activation rates and deactivation rates. There is little evidence that Mg2+ acts at this site except for a slowing of activation, when [Mg2+] is perhaps at least three orders of magnitude greater than [Ca2+]. In contrast, both Mg2+ and Ca2+ share an ability to slow deactivation at mM concentrations, while having minimal effects on limiting rates of current activation at these concentrations.

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Figure 11

Comparison of effects of Ca2+ and Mg2+ on primary time constant of Slo1 current relaxations. In A, activation and deactivation time constants obtained at 0, 10, and ¼M Ca2+ are plotted as a function of potential. In B, the shift in relaxation time constant with 1 and 4 ¼M are compared with 0 ¼M Ca2+. Note the unusual slowing of activation with 1 ¼M Ca2+. In C, the effects of 10 and 50 mM Ca2+ are compared with 0 Ca2+, whereas, in D, the effects of 10 and 50 mM Mg2+ are compared with 0 Ca2+. In E, the effects of 10 and 50 mM Ca2+ are compared with ¼M Ca2+, whereas, in F, the effects of 10 and 50 mM Mg2+ plus ¼M Ca2+ are compared with ¼M Ca2+.

Mg2+ Increases the Hill Coefficient for Activation of Slo1 Current by Ca2+ by Shifting the Relationship between Hill Coefficient and Membrane Potential

One interesting aspect of the effect of Mg2+ reported in earlier studies was that Mg2+ increases the Hill coefficient for activation by Ca2+ of BK channels in bilayers (Golowasch et al. ) and that other divalent cations act similarly (Oberhauser et al. ). For gating by Ca2+, the Hill coefficient is generally used as an indicator of the minimal number of Ca2+ ions that are required for channel activation. Where this has been examined for Slo1 current, the Hill coefficient is typically around two with some tendency to increase with depolarization (Cui et al. ; Bian et al. ). Here, we addressed this issue in two ways. First, we examined the behavior of the Hill coefficient over a wider range of [Ca2+] than previously studied to assess how the proposed two binding sites might impact on Hill plots. Second, we determined whether effects of Mg2+ on the Hill coefficient would be reproduced here. To address the first issue, normalized conductance values from Fig. 2 C were replotted to display the relationship between conductance and [Ca2+] over a range of voltages (Fig. 12 A). Curves obtained at each command potential were fit with a Hill equation G/Gmax = B + A/[1 + (Kd/[Ca])n, where n is the Hill coefficient and Kd is the apparent Ca2+ dissociation constant. B is a term included to account for the Ca2+-independent activation of current at the most positive activation potentials. At some voltages, this function did not describe the shape of the relationship between conductance and [Ca2+ x

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Iperius is a complete backup utility for Windows that can be used by both home users and Company servers (without any time/license limitation). Iperius also has different paid editions available, which allow for making advanced backup types, such as Drive imaging, VSS (open file backup), backup of databases (SQL Server, MySQL, MariaDB, PostgreSQL, Oracle), backup to Cloud (Google Drive, Amazon S3, OneDrive, Dropbox), FTP Backup (upload and download), VMware ESXi backup (virtual machines), backup to Tape (LTO, DAT, etc.), backup to NAS and Synchronization. Iperius Backup is both stable and reliable software, which can be installed by home/business users and as a Windows service monitored through a Web Console.

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EF Commander is a complex and multi-featured file manager that a wide range of users, from beginners to professionals, will find easy to use. It is the result of many requests received by the author. The first version was written in , under the OS/2 operating system using Presentation Manager, as a personal replacement for the old DOS program Norton Commander™. In it was ported to the 32 bit Microsoft Windows™ operating system.

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TapinRadio keeps it simple with this efficient, lightweight radio software, ideal for anyone wanting to listen to streaming-radio without a lot of fuss. TpinRadio Supports most of the internet radio formats – mp3, wma, ogg, aac. TapinRadio Pro is simple, fairly reliable and works most of the time. Plenty of stations to choose from and continuously updated. Supports most of the internet radio formats – mp3, wma, ogg, aac. Quick search. Graphic Equalizer. Scheduled recordings. Record what you are listening to – as separate tracks or continuously. Automatic checking for software and station listing (only if configured in settings). Show your favorites in groups. Alarm feature. Sleep timer to shutdown TapinRadio or even your computer!

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GlassWire is a network monitoring tool that displays and alerts you about the network traffic originating from your computer. This allows you to quickly see what applications are communicating over the network and the Internet, how much bandwidth they are using, and what hosts they are connecting to. Use GlassWire’s simple to use interface to view all your past and present network activity on a graph. Click the graph to see what applications initiated the incoming or outgoing bandwidth and instantly see what hosts the applications were communicating with. Hosts are automatically resolved and also include their country of origin. Click the Apps and Traffic options to break down network activity by applications and traffic types.

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Advanced Installer is a powerful and easy to use Windows Installer authoring tool, enabling developers to create reliable MSI packages that meet the latest Microsoft Windows logo certification guidelines. Extremely easy to use, powerful, fast and lightweight. Advanced Installer simplifies the process of building Windows Installer packages by providing a very easy to use, high level interface to the underlying technology. The program implements all Windows Installer rules and follows all the advised best practices. With this simple, intuitive interface, building a Windows Installer package will take just a few minutes. Start the program, add a few files, change the name, hit the Build button and you are done. No scripts to learn, no seminars to attend.

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Syncovery is a great application used to back up data and to synchronize PCs, servers, and notebooks. Users can choose the user interface that suits them best: Wizard Mode or Advanced Mode. The settings are stored in multiple profiles, and the software comes with support for FTP and secure FTP servers, SSH, WebDAV, Amazon S3, http, partial file updating, ZIP compression, data encryption, and a scheduler for automated backups. The scheduler can run as a service without users having to log on. On Windows XP or later, locked files can be copied using the Volume Shadow Service.

This program features the ability to freely select files and folders across the whole folder hierarchy in a tree view, and it has support for e-mail notification, profile categories, and various filters. The software also supports Unicode characters in file names, file paths as long as characters, and much more. It also includes Real Time Synchronization (folder monitoring).

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EarthTime displays the local time and date of any place in the world. It has a built-in database of thousands of cities worldwide but users can add any number of custom locations. EarthTime shows a map of the earth with daylight and night shadows and optionally a cloud layer with current satellite cloud data. Alarms can be set on the local time of any city in the world. Many options allow flexible customization.

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EarthView is a dynamic desktop wallpaper and screen saver, which displays beautiful views of the earth with daylight and night shadows. It produces colorful, high quality, high resolution images for every screen resolution – even beyond ×! The program supports map and globe views, urban areas, city lights, atmospheric effects, clouds, weather information, local time display and much more. EarthView supports different maps that show our planet earth in different ways, including seasonal changes of vegetation, snow cover and ocean ice. Many options allow total customization of all view parameters. EarthView has won countless awards for its absolutely breathtaking images. EarthView supports five different beautiful maps of the earth, starting at 10 km resolution, which means that at % zoom level, 1 pixel on your screen equals 10 kilometers on earth. If you purchase the full version, you’ll get the possibility to download even more detailed versions of some maps, which have higher resolution. This means, they have much more detail, so you can zoom in even further!

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Ashampoo Burning Studio you are well equipped for all burning tasks whether they involve movies, music or simply files. Create backups or data discs, rip music and create audio CDs or simply archive your movies to Blu-ray discs – the highly improved usability and sleek design make Ashampoo Burning Studio the ideal choice for all burning-related tasks.

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Nero is a capable media suite with tools for organising, editing, converting, playing, and of course burning your media files.

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Easy Disk Catalog Maker is an easy-to-use application that enables you to organize your DVD, CD and Blu-ray disk collections. Easy Disk Catalog Maker is a handy tool to have around when you work with rich music collections stored on your disks.

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One of the software tool’s advanced features enables you to scan inside archive files like rar, iso, gz, zip, tar, vhd or 7z.

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Sharp World Clock is a powerful desktop world clock for Windows with many bonus features. It can display the local time for multiple cities and time zones with correct daylight savings. You can decide how many clocks you would like to see at any time. The clocks are resizable without any loss of visual quality. Sharp World Clock can show analog clocks (with hands) or digital clocks – or both. You can arrange the clocks in a grid array with adjustable columns and grids or in a horizontal or vertical line, but you can also undock clocks from the main window and position them anywhere on the desktop. Accurate calculation of sunrise and sunset times and moon phase. Integrated tools: time zone converter, meeting planner, alarm center with multiple alarms (single and recurrent), calendar widget for 1, 2, 4 or 6 months, feed reader, weather report and atomic time synchronization. Chime function with hourly and quarterly signal or speak-the-time. Export / import function for settings.

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Master PDF Editor is a powerful, easy to use PDF editor that provides ability to create, review, annotate, and edit PDF documents. It includes the full support of PDF and XPS files, import/export PDF pages into JPG, TIFF, PNG, or BMP formats, converting XPS into PDF and vice versa, and bit encryption. You can insert, edit, remove, copy, add images or graphics. Export, import, remove and change page layouts. Also Master PDF Editor provides full functionality for changing PDF information, including author, title, subject, keywords, creator, and producer information.

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Cover Commander creates professional, custom-designed three-dimensional virtual boxes and mockups for your software, e-books, iPhone/iPad apps, manuals, and even screenshots. A simple picture, Cover Commander Wizard, and a few mouse clicks are all that’s necessary to get the job done. The program’s extensive light, shadow, and reflection controls allow you to render a box or a cover of just about any complexity and see the final product as it is being made in the real-time preview window. The intelligent project creation wizard does the complex work for you, thus you can concentrate on the creative part of your project.

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Cacheman is a utility which provides performance enhancement and memory recovery. By optimizing the Disk Cache and additional system settings it can prevent frequent swapping of the data to hard drive resulting in improved performance, system reaction time and even stability. It is designed to speed up your computer by optimizing several caches, managing RAM and fine tuning a number of system settings. Auto-Optimization makes it suitable for novice and intermediate users yet it is also powerful and versatile enough for computer experts. Backups of settings ensure that all user modifications can be reversed with a single click. Unlike other tuneup utilities, Cacheman runs as a system service, minimizing resource usage and tweaking Windows at system-level. Cacheman runs on Windows XP, Vista, 7, 8 x86 very well. However, terms for the Kd (Fig. 12 C) and Hill coefficient (Fig. 12 D) were determined for voltages from &#x; to + mV. The apparent affinity increases markedly with depolarization while appearing to reach a limiting value at the most negative activation potentials. The apparent Hill coefficient exhibits a surprisingly erratic appearance. However, consistent with other results (Cui et al. ), the Hill coefficient increases from 1 to over the range of &#x;20 to +80 mV. The error bars indicate the 90% confidence limits on the fitted parameter and indicate that the fitting function in some cases did not describe the shape of the curves very adequately. This sort of experiment suggests that two other factors are also likely to impact on estimates of Hill coefficient in various studies. First, large variation in estimates of Hill coefficient might be expected to result from the fact that, in some studies, the number of Ca2+ concentrations over which the change in conductance is determined can be rather minimal. Second, at positive potentials where activation of current occurs in the absence of Ca2+, if this activation is not taken into account, Hill coefficients will be estimated incorrectly. In sum, these results suggest that a typical Hill function may not be a mechanistically meaningful way of evaluating the Ca2+ dependence of Slo1 current activation and that the apparent Hill coefficient may exhibit some unusual dependence on voltage. Possible reasons for this behavior are addressed below.

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Figure 12

The behavior of Kd and Hill coefficient over all [Ca2+]. In A, conductances given in Fig. 2 D were replotted to show the Ca2+ dependence of conductance at a given voltage. Each point is the mean and SEM for the estimate. Solid lines are fits of the modified Hill equation given in the text. Symbols correspond to potentials of &#x; (&#x;), &#x; (Ë), &#x; (&#x;), &#x; (Ä), &#x; (ª), &#x; (¡), &#x;80 (´), &#x;60 (µ), &#x;40 (¾), &#x;20 (¿), 0 (¸), +20 (¹), +40 (Â), +60 (Ã), +80 (&#x;), + (Æ), + (closed six-pointed star), and + (open six-pointed star) mV. In B, conductance values predicted from Fig. 1 (see Fig. 14) based on values given in Table (column D) were plotted as a function of [Ca2+] and fit with the modified Hill equation (solid lines). Symbols are as in A. In C, estimated values for the Kd for apparent Ca2+ affinity (&#x;) obtained from fitting the data in Fig. 12 A are plotted as a function of command potential. The solid line with small filled circles corresponds to values for Kd predicted from Fig. 1 as shown in Fig. 12B. The line with small open circles corresponds to Kd values assuming no Mg2+ inhibition of the high affinity site. In D, the Hill coefficients determined from Fig. 12 A (&#x;) are plotted as a function of voltage. Error bars represent the 90% confidence limit on the estimate of the Hill coefficient. The dotted lines show the predictions from Fig. 1 as determined from values in Table , column D (Fig. 12 B, small closed circles) or from Table , column F (small open circles, no Mg2+ inhibition).

We next examined the effects of [Mg2+] on the behavior of Hill plots. This analysis used a different set of patches than those used in Fig. 2 and used a more limited set of Ca2+ concentrations, but typical of those used in other investigations. Hill plots obtained for this data set in the absence of Mg2+ are shown for several voltages in Fig. 13 A, whereas similar plots in the presence of 10 mM Mg2+ are shown in Fig. 13 B. As above, the Hill equation was used to make estimates of Kd and the Hill coefficient. Given the more limited number of Ca2+ concentrations used in this set of patches, the estimate of Hill coefficient in particular exhibited large confidence limits. Both with and without Mg2+, the Kd varied exponentially with command potential with a zero-voltage Kd of 25 ¼M in the absence of Mg2+ and 10 ¼M in the presence of Ca2+ (Fig. 13 C). Both with and without Mg2+, there was a trend for the Hill coefficient to became larger at more positive potentials (Fig. 13 D), which is consistent with the observations in Fig. 12 D and other work (Cui et al. ). This increase in the Hill coefficient is, in part, the simple expectation of the fact that, for each increment in Ca2+, G-V curves are shifted more at lower than at higher [Ca2+], such that over the range of ¼M&#x;1 mM Ca2+, little additional shift is observed (Wei et al. ; Cox et al. b). As a consequence, at more negative potentials, relatively large increments in [Ca2+] produce relatively small increases in conductance, resulting in a less steep Ca2+ dependence of activation. Since, as shown above, 10 mM Mg2+ produces an essentially mV leftward shift of the G-V curve obtained at each [Ca2+], this would be expected to cause an apparent increase in Hill coefficient at any command potential. Another way of viewing the results is that the relationship between Hill coefficient and command potential (Fig. 13 D) is simply shifted leftward 50 mV in the presence of Mg2+. Thus, the present results suggest that Mg2+ does cause an increase in the apparent Hill coefficient for Ca2+ at a given voltage, but that this effect reflects a shift of the relationship between Hill coefficient and voltage along the voltage axis.

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Figure 13

The apparent Hill coefficient for activation of conductance by Ca2+ is increased by Mg2+. In A, each point is the estimate of conductance activated at a given Ca2+ and voltage obtained from normalized G-V curves. Solid lines are fits of the modified Hill equation given in the text. Fitted values for apparent Kd and Hill coefficient are plotted in C and D, respectively. Values used in this figure were from a different set of patches than shown in Fig. 2 or Fig. In B, conductance estimates obtained in the presence of 10 mM Mg2+ are plotted as a function of Ca2+ for a range of voltages. At comparable voltages, the Hill coefficient for activation is higher in the presence of Mg2+. In C, the apparent Kd (in ¼M) for activation of conductance by Ca2+ either in the absence (&#x;) or presence (Ë) of 10 mM Mg2+ is plotted as a function of activation potential. The apparent Ca2+ affinity is increased at a given potential in the presence of Mg2+. The error bars are 90% confidence limits from the estimates of K obtained in A and B. Predictions from Fig. 1 (Table , column D) for solutions without Mg2+ (ª) or with Mg2+ (¡) are also shown. In D, the Hill coefficient and confidence limits for the activation of conductance by Ca2+ either in the absence (&#x;) or presence (Ë) of Mg2+ are plotted as a function of command potential, along with estimates (no Mg2+ [&#x;], +10 mM Mg2+ [Ä]) from Fig. 1 based on estimates of Mg2+ affinities from column B of Table . Both for experimental data and the theoretical predictions, there is a trend for increased Hill coefficient at more positive potentials and, at any given potential, Mg2+ increases the apparent Hill coefficient. In E, the Kd for Ca2+ effect predicted from Fig. 1 is plotted over a wider range of potentials. Both with (Ë) and without (&#x;) 10 mM Mg2+, at the most negative potentials a limit in the Kd is observed, while affinity increases dramatically with depolarization. In F, the behavior of Hill coefficient as a function of command potential predicted by Fig. 1 is displayed over a wider range of potentials. Predictions from Fig. 1 assuming Mg2+ inhibition of the high affinity site (Table , column D) are shown both without (&#x;) and with (Ë) 10 mM Mg2+. Predictions from Fig. 1 with no Mg2+ inhibition (Table , column F) are also shown without (&#x;) and with (Ä) 10 mM Mg2+.

Mg2+ Produces Shifts of G-V Curves Resulting from ± + ²1 Subunit Coexpression

The ability of Mg2+ to shift G-V curves at a given Ca2+ is somewhat reminiscent of the effect of the ²1 and ²2 auxiliary subunits of BK channels (McManus et al. ; Meera et al. ; Wallner et al. ; Xia et al. ). If Mg2+ were acting to mimic the effects of an associated ² subunit, Mg2+ might be ineffective on channels resulting from ± + ² subunit coexpression. To test this possibility, the effects of different concentrations of Mg2+ on ± + ²1 currents elicited with ¼M Ca2+ were examined. Normalized G-V curves were generated for a set of four patches. The V for current activation with ¼M Ca2+ was &#x; ± mV, whereas, for 1, 2, 10, and 20 mM Mg2+, values for V were &#x; ± mV, &#x; ± mV, &#x; ± , and &#x; ± mV, respectively. In this set of patches, the net effect of 10 mM Mg2+ is to shift the V about &#x;30 mV, which is less than observed in the absence of the ²1 subunit. However, it is clear that Mg2+ is able to exert much of its effect, irrespective of the presence or absence of the ²1 subunit.

Effects of Mg2+ Do Not Result from Changes in Ca2+ Binding Affinity

The primary effects of Mg2+ that require explanation are as follows. First, 10 mM Mg2+ appears to produce a similar shift in V at both 0 and ¼M Ca2+ with somewhat smaller shifts at 4 and 10 ¼M. Second, Mg2+ does not substitute for Ca2+ in the high affinity Ca2+-dependent steps that participate in increases in current activation rate. Third, mM Mg2+ shares with mM Ca2+ the ability to slow deactivation, an effect which does not exhibit saturation until over 10 mM divalent. Finally, Mg2+ produces a slowing of current activation with 4 and 10 ¼M Ca2+ under conditions of near maximal current activation. Can these effects be accounted for by a single mechanism of action?

To guide our thinking, we first consider the particular state model presented by Cox and Aldrich to account for the dependence of steady-state conductance on voltage and Ca2+. The steady-state predictions of their formulation are summarized in the following equation:

equation M3

3

where B = [(1 + Ca/Kc)/(1 + Ca/Ko)]4 with Kc is the Ca2+ binding equilibrium for the closed channel, Ko is the Ca2+ binding equilibrium for the open channel, L(0) is the open-to-closed equilibrium constant when no voltage sensors are active and no Ca2+ binding sites are occupied, Q, the gating charge associated with this closed to open equilibrium, Vhc, is the voltage at which a single voltage sensor is active half the time when the channel is closed, and Vho, is the voltage at which a single voltage sensor is active half the time when the channel is open, and Z is the equivalent gating charge associated with each voltage-sensor's movement. This formulation assumes that voltage-dependent transitions and Ca2+ binding transitions in each subunit are independent and that Ca2+ binding affinity is not influenced by movement of voltage sensors.

Might alteration by Mg2+ of any parameters in the above equation provide suggestions concerning how Mg2+ may produce relatively similar shifts in G-V curves at both 0 and ¼M Ca2+? To test this possibility, we empirically adjusted various parameters in to ascertain whether any would reproduce the key features of the G-V curves, i.e., the relatively constant shift at all [Ca2+] and the increase in slope at 0 Ca2+. Of all the possible parameters, only adjustment of two parameters were qualitatively able to mimic the effects of Mg2+. First, adjustment of Vho, the term for the voltage at which a single voltage sensor is half the time active when the channel is open, could produce a relatively similar shift at all Ca2+ and increase the slope at 0 Ca2+. Similarly, the magnitude of L(0) shifts the family of G-Vs in a somewhat parallel fashion along the voltage axis as shown previously (Cox and Aldrich ). Thus, in accordance with the assumptions of this model, this would argue that the effects of Mg2+ might result from an increase in the stability of the open states perhaps either by stabilizing the voltage sensors in the active configuration or by simply affecting the equilibrium between the closed and open conformations. In contrast, the effects of Mg2+ are entirely inconsistent with any model in which Mg2+ might somehow change the affinity of Ca2+, i.e., Kc or Ko.

A state Allosteric Model Describes the Effects of Mg2+

We next considered whether a particular stochastic model incorporating binding of Mg2+ might allow an explicit analytical evaluation of the effects of Mg2+. We begin with the specific state model proposed by Cox and Aldrich described above in which Ca2+ binding and voltage-sensor movement are not coupled. Based on the tetrameric nature of the channel (Shen et al. ), we postulate a Mg2+ binding site on each subunit. The result of the addition of four independent Mg2+ binding steps to the basic state model is shown for one case in Fig. 1. Basically, for each of the two tiers characteristic of the state model, there are now four additional sets of the two tiers corresponding to binding of one, two, three, or four Mg2+ cations. Each pair of tiers corresponding to a different extent of ligation by Mg2+ is designated by I-V. Any state in I is connected to the corresponding state in II by a Mg2+ binding step. Similarly, any state in II is connected to the corresponding states in either I or III by Mg2+ dissociation and association, respectively. This is indicated in Fig. 1 by the pathways connecting the lower and leftmost state in each tier to the lower and leftmost states in adjacent tiers with constants determined by K(l)o and K(l)c, the binding constants of a divalent cation to the low affinity site on either open or closed channels, respectively. This results in a total of states, which results naturally from the fact that gating is regulated by three parameters, voltage, Ca2+, and Mg2+ (or other divalent).

Analytic evaluation of a state model depends on specific assumptions about the relationship between Mg2+ binding steps and other transitions. Because the effects of Mg2+ are apparent in 0 Ca2+, we exclude from consideration the case where binding of Mg2+ is assumed to influence either Ko or Kc, the affinities of Ca2+ to open or closed channels, respectively. Here, we first consider the case (given in Fig. 1) in which we propose that binding of Mg2+ (or mM Ca2+) to open and closed channels may occur with different affinities. This low affinity binding would have no effect on voltage-sensor equilibria or Ca2+ binding affinities. The shift in V would be driven by the higher affinity with which Mg2+ binds to open states. This would be analogous to the binding of Ca2+ to its high affinity site, although independent of that effect. In essence, binding of Mg2+ would be coupled to changes in L(0) between adjacent pairs of tiers given in Fig. 1.

For solution of steady-state equations for the state model for Fig. 1, in addition to the seven parameters required to describe the state model in , the system is also defined by two additional parameters, K(l)o and K(l)c, the affinity of Mg2+ (and or Ca2+) to the low affinity divalent cation binding site when the channel is either open or closed, respectively. Fractional conductance for Fig. 1 as a function of [Ca2+], voltage, and divalent cation concentration ([D]) is given by:

equation M4

4

where

equation M5

[D] corresponds to the concentration of divalent cation acting at the low affinity sites, and other parameters are as defined above. Despite the marked increase in number of states compared with the state model, the form of the equation is similar to with only two additional free parameters. For cases in which there are two species of divalent cations that may act at the low affinity sites, but with somewhat differing affinities, this expression is obviously not sufficient.

To examine the effects of Mg2+ and high Ca2+ in terms of Fig. 1, we used four different data sets, each a set of patches obtained under a particular range of divalent cation concentrations. Set 1 entailed [Ca2+] from 0 to mM, set 2 used 0 Ca2+ with [Mg2+] from 0 to mM, set 3 used ¼M Ca2+ with [Mg2+] from 0 to mM, and set 4 used both 0 and ¼M with [Mg2+] from 0 to mM. In Fig. 14 A, it can be seen that the G-V curves from data set 1 can be quite well-described by . The displayed fit in Fig. 14 A is based on the values in Table (column A). When L(0) was left unconstrained, the value converged within the range of ,&#x;, with very large confidence limits. Varying this value did not result in any improvement in the fit, which indicates that L(0) cannot be well-defined by this procedure. Of the parameters in , those pertaining to the Ca2+ binding steps are the most well constrained, whereas the parameters relating to movement of voltage sensors do not appear to be precisely described. The large confidence limits for Vhc, Vho, and L(0) reflect the fact that these parameters tend to be correlated and relatively large changes in one parameter can be compensated for by changes in another parameter. However, for a variety of assumptions about the values of L(0), Vhc and Vho, the estimates of affinity for Ca2+ of the low affinity site was consistently near mM when the channel is closed and mM when the channel is open. The difference in affinities for the low affinity site is quite a bit smaller than that observed for the high affinity Ca2+ sites, defined by Kc and Ko. However, these values for K(l)o and K(l)c suggest that the low affinity site, should this model be correct, may contribute substantially to the position of the G-V curve over the range of Ca2+ from ¼M to 1 mM.

Table 1

Parameter Estimates from Fitting Fig. 1 to GV Curves Generated under Various Conditions

(A) &#x;Ca2+(B) &#x;Mg2+ alone(C) ¼M Ca2+ + &#x;Mg2+(D) 0, ¼M Ca2+ + &#x;Mg2+(E) 0, ¼M Ca2+ + &#x;Mg2+
K(h,mg)c = K(h,mg)oK(h,mg)c! = K(h,mg)o
UnitsData set 1Data set 2Data set 3Data set 4Data set 4
K(h,ca)c¼M ±
K(h,ca)o¼M ±
VhcmV ±
VhomV&#x; ± &#x;&#x;&#x;&#x;
ze
Q0. 86 ± e ± ± ± ±
L(0),,,,,
K(l,mg)cmM&#x; ± ± ± ±
K(l,mg)omM&#x; ± ± ± ±
K(l,ca)cmM ± &#x;
K(l,ca)omM ± &#x;
K(h,mg)cmM&#x;&#x; ± ± ±
K(h,mg)omM&#x;&#x; ± &#x; ±
SSQ/pt

Open in a separate window

An external file that holds a picture, illustration, etc.
Object name is JGPfjpg

Open in a separate window

Figure 14

The dependence of Slo1 conductance on Ca2+, Mg2+ and voltage can be described by a state allosteric model involving the independent action of Ca2+, Mg2+ and voltage-sensor movement. In A, G-V curves obtained at different [Ca2+] given in Fig. 2 D (data set 1) were fit with with the solid lines resulting from the values given in column A, Table . L(0) was constrained to In B, G-V curves obtained with 0 Ca2+ (&#x;) plus (Ë), 1 (&#x;), 2 (Ä), 5 (ª), 10 (¡), 20 (´), 50 (µ), and (5) mM Mg2+ (data set 2) were also fit with , with parameters given in Table , column B. In C, G-V curves obtained with ¼M Ca2+ with [Mg2+] from 0 to mM (data set 3; symbols are as in B, but with no ¼M points) were fit with . The solid lines correspond to the fit resulting from the values given in column C, Table . Comparison of the values in columns A, B, and C indicate that quite similar values yield a good general description of G-V curves over all [Ca2+], all [Mg2+], and all voltages, except that the multiple Mg2+ binding affinities defined by are not well-described in the fit to data set 3. In D1&#x;D3, G-V curves shown in A-C were simultaneously fit with , yielding the values given in Table (column D). Again, the general features of the shift in curves as a function of Ca2+ and Mg2+ is reasonably well-described. In E, G-V curves obtained over all [Ca2+] were fit with , which assumes that Mg2+ influences the voltage-sensor equilibrium. Fitted curves correspond to values given in Table (column A). In F, G-V curves at 0 Ca2+ were also fit with . When values obtained from fitting G-V curves at higher Ca2+ were used, it was not possible to obtain estimates for Km and E that resulted in adequate descriptions of the data. The curves with open circles were generated from values in column C, Table . L(0) was set to a value in which currents in 0 Ca2+ were well-described. However, the G-V curves at 10 and 50 mM Mg2+ could not be captured. However, when more parameters were left unconstrained, could yield a fit that captured the G-V curves in 0 Ca2+ (smaller closed circles), but these values (column D, Table ) totally failed to describe the behavior of G-V curves at higher Ca2+.

We next examined the ability of to describe the G-V curves obtained with 0 Ca2+ with varying Mg2+ (data set 2). The resulting fit is shown graphically in Fig. 14 B with values listed in Table (column B). For fitting the 0 Ca2+ plus &#x;[Mg2+] G-V curves, values for Ko and Kc were constrained to those obtained when fitting the data over all [Ca2+], since in the absence of Ca2+, these parameters are not defined. Furthermore, we constrained the value of L(0) to that used in column A. This gave an adequate fit to the data, with K(l)o of mM and K(l)c of mM. When the 0 Ca2+ plus various [Mg2+] curves from data set 4 were similarly fit, the resulting estimates of K(l)o and K(l)c were ± and ± mM, respectively. Thus, binding of Mg2+ to the low affinity site appears to be about seven to eight times weaker than binding of Ca2+.

Guided by the analysis of Shi and Cui b, we have extended to include terms for both the differential affinities of Ca2+ and Mg2+ for the low affinity site and for the inhibitory action of Mg2+ on the high affinity site. From of Shi and Cui b and our , an equation defining the fractional conductance as a function of voltage, [Ca2+], and [Mg2+], reflecting the differential affinities of both divalent cations to each binding site is obtained:

equation M6

5

where

equation M7

6

and

equation M8

7

This system is defined by four separate binding affinities for both Ca2+ and Mg2+, reflecting binding of each divalent cation to either the open or closed states (subscripts o and c) or to the low or high affinity sites (K(l), K(h)). Term, Bh, and is equivalent to that used by Shi and Cui b to describe competition between Mg2+ and Ca2+ for the higher affinity site, whereas Bl arises from the same considerations applied to the lower affinity site. The relative ability of a cation to act as an activator or inhibitor depends on the ratio of the relative affinities of a particular cation for the closed state compared with the open state. As proposed by Shi and Cui b, at the high affinity site K(h,mg)c = K(h,mg)o so that occupancy of the high affinity site by Mg2+ simply inhibits the ability of Ca2+ to activate the channel.

Therefore provides a tool to evaluate the adequacy of Fig. 1 in the presence of potentially competing species of divalent cations. Therefore, we used to fit G-V curves obtained with ¼M Ca2+ and varying [Mg2+]. Using values defined above for the high affinity Ca2+ binding, the result of fitting to the G-V curves with ¼M Ca2+ is shown in Fig. 14 C. Again, values for can be found that fit the G-V curves reasonably well (Table , column D) even when most parameters are constrained to values obtained for the Ca2+ data set. However, estimates for K(l,mg)c and K(l,mg)o differ from those in Table (column B), possibly because of the limited data set being used to define four different Mg2+ affinities. Therefore, we also fit data set 4 in which mM Mg2+ was added to either 0- or ¼M Ca2+ solutions in the same set of patches. This yielded the values in Table , column E, for the assumption that K(h,mg)c = K(h,mg)o and column F for the assumption that K(h,mg)c! = K(h,mg)o. Although the latter assumption improves the fit, these data sets are probably not robust enough to define such parameters well.

We next used to fit all G-V values in data sets 1&#x;3 or data sets 1 and 4 simultaneously. In this case, we left the binding affinities for both low and high affinity sites unconstrained during the fitting procedure. The result of a simultaneous fit of data sets 1&#x;3 is shown in Fig. 14 D with values given in Table , column B. Although individual curves are not as well-described as in Fig. 14 (A&#x;C), the general features of the dependence of the G-V curves on Mg2+ and Ca2+ are retained. Similar values were also obtained from a simultaneous fit to data sets 1 and 4 (Table , column D). Table also lists the fits to the various data sets with differing assumptions about affinity of Mg2+ to the high affinity sites, including the absence of Mg2+ binding to those sites. Although adequate fits can be obtained when it is assumed that Mg2+ does not bind to the high affinity sites, it is clear that such an assumption fails to describe the rightward shift of G-V curves that occurs at mM Mg2+ in the presence of ¼M Ca2+.

Table 2

Parameter Estimates from Simultaneous Fitting of Data Sets Generated under Different Conditions

Fitting assumption(A) K(h,mg)c! = K(h,mg)o(B) K(h,mg)c = K(h,mg)o(C) No Mg2+ high affinity binding(D) K(h,mg)c! = K(h,mg)o(E) K(h,mg)c = K(h,mg)o(F) No Mg2+ high affinity binding
UnitsData set 1&#x;3Data set 1&#x;3Data set 1&#x;3Data set 1,4Data set 1,4Data set 1,4
K(h,ca)c¼M ± ± ± ± ± ±
K(h,ca)o¼M ± ± ± ± ± ±
VhcmV
VhomV&#x;&#x;&#x;&#x;&#x;&#x;
z
Q ± ± ± ± ± ±
L(0),,,,,
K(l,mg)cmM ± ± ± ± ± ±
K(l,mg)omM ± ± ± ± ± ±
K(l,ca)cmM ± ± ± ± ± ±
K(l,ca)omM ± ± ± ± ± ±
K(h,mg)cmM ± ± &#x; ± ± &#x;
K(h,mg)omM ± &#x;&#x; ± &#x;&#x;
SSQ/ pts / pts / pts / pts / pts / pts / pts

Open in a separate window

On balance, examination of the values in Table suggest that, despite some variation, the two sets of data (data sets 1&#x;3, and data sets 1 and 4) yield quite comparable estimates for various binding affinities. The results indicate that Ca2+ affinity to the low affinity site is approximately seven- to eightfold greater than the Mg2+ affinity. The intrinsic allosteric effectiveness (Kc/Ko) of Mg2+ for the low affinity site may be somewhat greater than that of Ca2+. However, when data sets with either Ca2+ alone or Mg2+ alone are compared, the allosteric effectiveness of either Ca2+ or Mg2+ at the high affinity site appears similar. It is possible that other effects of the very high divalent cation concentrations used here may impact somewhat on the reliability of these estimates. Finally, Mg2+ appears to inhibit the high affinity site, with a Kd of 7&#x;20 mM. Thus, on balance, the particular formulation of the state model given in and provides a quite good description of the effects of high concentrations of Ca2+ or Mg2+ on the steady-state G-V curves of Slo1 currents, with the binding of Ca2+ being approximately seven- to eightfold stronger than that of Mg2+.

The values in Table exhibit some deviations in some parameters from those estimated in earlier studies (Cox and Aldrich ; Zeng et al. ). Although some variation is expected simply because of variability in the positions of G-V curves along the voltage-axes among different sets of data, the values of Z and Q seem a bit surprising. We refit the G-Vs obtained with different Ca2+ solutions using only data obtained with [Ca2+] of ¼M and lower using to determine to what extent the use of or might have impacted on the parameter estimates. These values are given in column E of Table . In this case, values for Q and Z fall much closer to those obtained by Cox and Aldrich (given in column F), which were guided by estimates from Horrigan for voltage-dependent parameters obtained from activation of Slo1 currents at 0 Ca2+ (Horrigan and Aldrich ; Horrigan et al. ). Some of the variation in estimates of Z and Q among different studies most certainly results from the simple process of averaging G-V curves, such that variation among individual G-V curves among patches will result in averaged curves with lessened voltage dependence. In addition, to evaluate the significance of the rather large value for Q and smaller value for Z obtained through the use of and , we refit the G-V curves obtained over all Ca2+ (data set 1) while constraining the values for Q and Z to those used by Cox and Aldrich This resulted in estimates of K(l,ca)o and K(l,ca)c for Ca2+ similar to those already given, although values for L(0), Vhc, and Vho were altered. On balance, the overall quality of the fits were only somewhat poorer. This analysis would suggest that values for L(0), Vhc, Vho, Q and Z are not well-constrained by this procedure, presumably because of correlations between parameters. However, values for Ca2+ and Mg2+ affinities appear to be critical for obtaining acceptable fits.

Table 3

Allosteric Regulation of Voltage-sensor Equilibria Is Unlikely to Account for the Dependence of Slo1 G-V Curves on Millimolar Ca2+ or Mg2+

Units(A) Ca2+ alone: unconstrained(B) &#x;[Mg2+]; 0 Ca2+(C) &#x;[Mg2+]; 0 Ca2+
Источник: mauitopia.us

CO2 mineralization and utilization by alkaline solid wastes for potential carbon reduction

Abstract

CO2 mineralization and utilization using alkaline solid wastes has been rapidly developed over the last ten years and is considered one of the promising technologies to stabilize solid wastes while combating global warming. Despite the publication of a number of reports evaluating the performance of the processes, no study on the estimation of the global CO2 reduction potential by CO2 mineralization and utilization using alkaline solid wastes has been reported. Here, we estimate global CO2 mitigation potentials facilitated by CO2 mineralization and utilization as a result of accelerated carbonation using various types of alkaline solid wastes in different regions of the world. We find that a substantial amount of CO2 (that is,  Gt per year) could be directly fixed and indirectly avoided by CO2 mineralization and utilization, corresponding to a reduction in global anthropogenic CO2 emissions of %. In particular, China exhibits the greatest potential worldwide to implement CO2 mineralization and utilization, where it would account for a notable reduction of up to % of China’s annual total emissions. Our study reveals that CO2 mineralization and utilization using alkaline solid wastes should be regarded as one of the essential green technologies in the portfolio of strategic global CO2 mitigation.

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Data availability

The datasets generated during this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This study was supported by the Ministry of Science and Technology, Taiwan (ROC) under Grant No. MOSTI S.-Y.P. also received financial support from the National Taiwan University under Grant No. L H.K. was supported by the Korea Institute of Energy Technology Evaluation and Planning and the Ministry of Trade, Industry & Energy of the Republic of Korea under Grant No.

Author information

Affiliations

  1. Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei, Taiwan (ROC)

    Shu-Yuan Pan

  2. Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, Taiwan (ROC)

    Yi-Hung Chen

  3. Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, USA

    Liang-Shih Fan

  4. Department of Environmental Engineering, The University of Seoul, Seoul, South Korea

    Hyunook Kim

  5. State Key Laboratory of Clean Energy Utilization, College of Energy Engineering, Zhejiang University, Hangzhou, China

    Xiang Gao

  6. Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha, China

    Tung-Chai Ling

  7. Graduate Institute of Environmental Engineering, National Taiwan University, Taipei, Taiwan (ROC)

    Pen-Chi Chiang

  8. Research Institute of Tianying in Splash 2.0 full crack - Crack Key For U, China Tianying Inc., Shanghai, China

    Si-Lu Pei

  9. College of Environmental Science and Engineering, Tongji University, Shanghai, China

    Guowei Gu

Contributions

S.-Y.P. conceived and led the study. Y.-H.C., S.-L.P. and T.-C.L. provided data of alkaline waste production. L.-S.F., H.K., X.G., P.-C.C. and G.G. took part in the discussion of CO2 reduction potential. S.-Y.P. wrote the paper with input from all co-authors. All authors reviewed the manuscript.

Corresponding author

Correspondence to Shu-Yuan Pan.

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auto-bypass [ server ] }

Syntax Description

cache

Clears DREOPT cache.

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(Optional) Clears DREOPT peer statistics table.

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(Optional) Clears DREOPT statistics using peer-no for the specified peer ID.

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clear sdwan bfd transitions

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clear sdwan bfd transitions

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Cisco IOS XE Release v

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The BFD protocol detects link failures as part of the Cisco SD-WAN high availability solution and by default, it is enabled on all Cisco IOS XE SD-WAN devices. You cannot disable this protocol. The BFD protocol functionalities include path liveliness and quality measurement.

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clear sdwan control connection-history

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clear sdwan control connection-history

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Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

Cisco IOS XE SD-WAN devices establish control plane connection with Cisco SD-WAN Controllers (Cisco vManage, Cisco vSmart Controller, and Cisco vBond Orchestrator), and maintains these connections with Cisco vSmart Controller and Cisco vManage.

This command can be used to erase all the connection history information from the Cisco IOS XE SD-WAN devices.

Example

The following example erases the connection history information from a Cisco IOS XE SD-WAN device:

Related Commands

Command

Description
clear control connections Resets the DTLS connections from a local device to all Cisco IOS XE SD-WAN devices.
show sdwan control connection-history Displays control connection history.

clear sdwan control connections

To reset the DTLS connections from a Cisco IOS XE SD-WAN device to the SD-WAN controllers, use the clear sdwan control connections command in privileged EXEC mode.

clear sdwan control connections

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

ReleaseModification
Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

Cisco IOS XE SD-WAN devices establish control plane connection with Cisco SD-WAN Controllers (Cisco vManage, Cisco vSmart Controller, and Cisco vBond Orchestrator), and maintains these connections with Cisco vSmart Controller and Cisco vManage.

This command can be used to reset the DTLS connections from a Cisco IOS XE SD-WAN device to the Cisco SD-WAN Controllers.

Example

The following example shows how to reset the DTLS connections.

Related Commands

Command

Description
clear control connections-history Erases the connection history on a Cisco IOS XE SD-WAN device.
show sdwan control connections Displays information about control connections.
show sdwan control connection-history Displays information about control connections history.

clear sdwan dns app-fwd cflowd flow-all

To clear the DNS cache for all cflowd flows, use the clear sdwan dns app-fwd cflowd flow-all command in privileged EXEC mode.

clear sdwan dns app-fwd cflowd flow-all

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

ReleaseModification
Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

This command can be used to clear the DNS cache for all cflowd flows in a Cisco IOS XE SD-WAN device.

Example

The following example shows how to clear the DNS cache for all cflowd flows in a Cisco IOS XE SD-WAN progdvb professional 7.24.2 crack - Free Activators.

Related Commands

Command

Description
clear control connections-history Erases the connection history on a Cisco IOS XE SD-WAN device.
clear sdwan dns app-fwd cflowd flow-all Clears all cflowd flows.

clear sdwan dns app-fwd cflowd statistics

To clear the cflowd statistics from a Cisco IOS XE SD-WAN device, use the clear sdwan dns app-fwd cflowd statistics command in privileged EXEC mode.

clear sdwan dns app-fwd cflowd statistics

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

ReleaseModification
Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

This command can be used to clear the cflowd statistics from a Cisco IOS XE SD-WAN device.

Example

The following example shows how to clear the cflowd statistics from a Cisco IOS XE SD-WAN device.

Related Commands

Command

Description
clear sdwan dns app-fwd cflowd flow-all Clears all cflowd flows from a Cisco IOS XE SD-WAN device.

clear sdwan dns app-fwd dpi flow-all

To clear the DNS Deep Packet Inspection (DPI) flows from a Cisco IOS XE SD-WAN device, use the clear sdwan dns app-fwd dpiflow-all command in privileged exec mode.

clear sdwan dns app-fwd dpi flow-all

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged exec (#)

Command History

ReleaseModification
Cisco IOS XE Release vCommand qualified for use in Cisco vManage CLI templates.

Usage Guidelines

This command can be used to clear the DNS DPI flows from a Cisco IOS XE SD-WAN device.

Example

The following example shows how to clear the dpi flows from a Cisco IOS XE SD-WAN device.

Related Commands

Command

Description
clear sdwan dns app-fwd dpi summary Clears all DPI statistics.

clear sdwan dns app-fwd dpi summary

To clear all known dpi statistics for all related app information, use the clear sdwan dns app-fwd dpi summary command in privileged EXEC mode. This command does not have a no form.

clear sdwan dns app-fwd dpi summary

Syntax Ef commander 19.02 - Crack Key For U This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

ReleaseModification

Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

Use this command to clear out any dpi statistics for all related app information.

Example

The following example clears the dpi statistics for all related app information.

Commands

Description

clear sdwan dns app-fwd dpi flow-all

Clears all dpi flows in the entire system.

clear sdwan dns app-route statistics

To clear all app-route statistics, use the clear sdwan dns app-route statistics command in privileged EXEC mode. This command does not have a no form.

clear sdwan dns app-route statistics

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC(#)

Command History

ReleaseModification

Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

Use this command to clear all app route related statistics from the system.

Example

The following example clears all app route statistics from the router.

clear sdwan dns cache

To clear the cache of DNS entries on a Cisco IOS XE SD-WAN device, use the clear sdwan dns cache command in privileged EXEC mode.

clear sdwan dns cache

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

Источник: mauitopia.us

An Acyl-NHC Osmium Cooperative System: Coordination of Small Molecules and Heterolytic B–H and O–H Bond Activation

Experimental Section


All reactions were carried out with rigorous exclusion of air using Schlenk-tube techniques or in an argon-filled Unilab glovebox (O2 levels below ppm). Glassware was previously pretreated with 5% Me3SiCl in dichloromethane solution, to silylate the glass surface. Acetone, methanol, tetrahydrofuran, and 2-propanol were dried and distilled under argon. Other solvents were obtained oxygen- and water-free from an MBraun solvent purification apparatus; additionally, pentane was treated with P2O5. Alcohols were dried by standard procedures and distilled under argon prior to use. Pinacolborane (HBpin; 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and all other reagents were purchased from commercial sources and used without further purification. NMR spectra were recorded on a Varian Geminia Bruker ARX MHz, a Bruker Avance MHz, or a Bruker Avance MHz instrument. Chemical shifts (expressed in parts per million) are referenced to residual solvent peaks (1H, 1H{31P}, 13C{1H}) or external standard (31P{1H} to 85% H3PO4 and 11B to BF3·OEt2). Coupling constants J and N (N = J(PH) + J(P′H) for 1H and N = J(PC) + J(P′C) for 13C{1H}) are given in hertz. Attenuated total reflection infrared spectra (ATR-IR) of solid samples were run on a PerkinElmer Spectrum FT-IR spectrometer. C, H, and N analyses were carried out in a PerkinElmer CHNS/O analyzer. High-resolution electrospray mass spectra (HRMS) were acquired using a MicroTOF-Q hybrid quadrupole time-of-flight spectrometer (Bruker Daltonics, Bremen, Germany). OsH6(PiPr3)2 and 1-(2-methoxyoxoethyl)methylimidazolium chloride were prepared according to the published methods. (13, 24)

Preparation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(PiPr3)2 (3)

OsH6(PiPr3)2 ( g, mmol) was dissolved in a 1/1 THF/toluene mixture (10 mL) and treated with 1-(2-methoxyoxoethyl)methylimidazolium chloride ( g, mmol). The mixture was stirred under reflux for 3 h before the volatiles were removed under vacuum. Subsequent addition of methanol (2 mL) to the resulting residue, at approximately −70 °C, led to the formation of a reddish brown solid, which was washed with further portions of diethyl ether (2 × 3 mL) and dried in vacuo. Yield: g (74%). Orange crystals suitable for X-ray diffraction analysis were obtained from a concentrated solution of 1 in acetone. Anal. Calcd for C24H49ClN2OOsP2: C, ; H, ; N, Found: C, ; H, ; N, HRMS (electrospray, m/z): calcd for C24H49N2OOsP2 [M – Cl]+found IR (cm–1): ν(C═O) (s). 1H NMR ( MHz, (CD3)2CO, K): δ and (both d, JH–H =1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N =JH–H =18 H, PCH(CH3)3), (dvt, N =JH–H =18 H, PCH(CH3)3). 31P{1H} NMR ( MHz, (CD3)2CO, K): δ (s). 13C{1H}-APT NMR plus HMBC and HSQC ( MHz, C6D6, K): δ (s, C═O), (t, JC–P =NCN), and (both s,CHimidazole), (s, NCH2), (s, NCH3), (vt, N =PCH), and (both s, PCH(CH3)3).

Reaction of 3 with CO: Formation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(CO)(PiPr3)2 (4)

A solution of 3 ( g, mmol) in toluene (5 mL) was stirred under a CO atmosphere (1 atm) at room temperature for 5 min. The resulting colorless solution was reduced to dryness. Addition of diethyl ether (3 mL) to the residue obtained led to the formation of a white solid, which was washed with additional portions of diethyl ether (2 × 3 mL) and dried in vacuo. Yield: g (40%). Colorless crystals suitable for X-ray diffraction analysis were obtained from a concentrated solution of 4 in acetone. Anal. Calcd for C25H49ClN2O2OsP2: C, ; H, ; N, Found: C, ; H, ; N, HRMS (electrospray, m/z): calcd for C25H49N2O2OsP2 [M – Cl]+found IR (cm–1): ν(C≡O) (s), ν(C═O) (m). 1H NMR ( MHz, CD2Cl2, K): δ and (both d, JH–H =1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N =JH–H =18 H, PCH(CH3)3), (dvt, N =JH–H =18 H, PCH(CH3)3). 31P{1H} NMR ( MHz, CD2Cl2, K): δ (s). 13C{1H}-APT NMR plus HSQC and HMBC ( MHz, CD2Cl2, K): δ (t, JC–P =C═O), (t, JC–P =C≡O), (s, NCN), and (both s, CHimidazole), (s, NCH2), (s, NCH3), (vt, N ═PCH), and (both s, PCH(CH3)3).

Reaction of 3 with O2: Formation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(η2-O2)(PiPr3)2 (5)

A solution of 3 ( g, mmol) in toluene (5 mL) was stirred under an O2 atmosphere (1 atm) at −20 °C for 15 min. After removal of volatiles, diethyl ether (3 × 3 mL) was added to extract the product. The diethyl solution was concentrated to ca. 4 mL and placed in the freezer (−30 °C). Red crystals corresponding to 5, suitable for X-ray diffraction analysis, were grown. IR (cm–1): ν(C═O) (s), ν(O–O) (s). 1H NMR ( MHz, CD2Cl2, K): δ and (both d, JH–H =1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N =JH–H =18 H, PCH(CH3)3), (dvt, N =JH–H =18 H, PCH(CH3)3). 31P{1H} NMR ( MHz, CD2Cl2, K): δ − (s). 13C{1H} NMR plus HSQC and HMBC ( MHz, CD2Cl2, K): δ (br, C═O), (s, NCN), and (both s, CHimidazole), (s, NCH2), (s, NCH3), (br, PCH), and (both s, PCH(CH3)3).

Reaction of 3 with H2: Formation of OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(η2-H2)(PiPr3)2 (6)

A J. Young NMR tube was charged with a solution of 3 ( g, mmol) in C6D6 ( mL). Argon was replaced by H2 (1 atm), causing the red solution to turn pale yellow. The immediate and quantitative evolution of 3 to 6 was observed by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy. 1H NMR ( MHz, C6D6, K): δ and (both d, JH–H =1 H each, CHimidazole), (s, 3 H, NCH3), (s, 2 H, NCH2), (m, 6 H, PCH), (dvt, N =JH–H =18 H, PCH(CH3)3), (dvt, N =JH–H =18 H, PCH(CH3)3), − (t, JH–P =2 H, OsH). 31P{1H} NMR ( MHz, C6D6, K): δ (s). 13C{1H}-APT NMR plus HSQC and HMBC ( MHz, C6D6, K): δ (t, JC–P =C═O), (t, JC–P =NCN), and (both s, CHimidazole), (s, NCH2), (s, NCH3), (vt, N =PCH), and (both s, PCH(CH3)3). T1(min) (ms, OsH, MHz, toluene-d8, K): 8 ± 1 (− ppm).

Determination of the JH–D Value for Complex 6 (6′)

A J. Young NMR tube was charged with a solution of 3 ( g, mmol) in toluene-d8 ( mL). Argon was replaced by HD (1 atm), which was generated in situ by reaction of NaH with D2O. An immediate color change from red to pale yellow was observed in the solution. The 1H and 1H{31P} NMR spectra, in a MHz apparatus at K, of this solution exhibit a triplet with JH–D = Hz in the hydride region.

Ef commander 19.02 - Crack Key For U of 3 with Pinacolborane: Formation of OsHCl{κ2-C,C-[CN(CH3)CHCHNCH2C(OBPin)]}(PiPr3)2 (7)

In a NMR tube, a reddish brown suspension of 3 ( g, mmol) in CD2Cl2 ( mL) was treated at room temperature with pinacolborane ( μL, mmol). Immediately the initial suspension disappeared and an intense pink solution was observed. The quantitative formation of a new species corresponding to 7 was confirmed by 1H, 31P{1H}, 11B, and 13C{1H} NMR spectroscopy. 1H NMR ( MHz, CD2Cl2, K): δ and (both d, JH–H =1 H each, CHimidazole), (s, 3 H, NCH3), (m, 6 H, PCH), (t, JH–P =2 H, NCH2), (dvt, N =JH–H =18 H, PCH(CH3)3), (s, 12 H, CH3-BPin), (dvt, N =JH–H =18 H, PCH(CH3)3), − (t, JH–P =1 H, OsH). 31P{1H} NMR ( MHz, CD2Cl2, K): δ (s). 11B NMR ( MHz, CD2Cl2, K): δ (br). 13C{1H}-APT NMR plus HSQC and HMBC ( MHz, C6D6, K): δ (t, JC–P =Os═C(OBpin)), (t, JC–P =NCN), and (both s, CHimidazole), (s, C-Bpin), (s, NCH2), (s, NCH3), (vt, N =PCH), (s, CH3-BPin), and (both s, PCH(CH3)3

Alcoholysis Reactions of Pinacolborane Catalyzed by OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(PiPr3)2 (3)

In a typical procedure, the alcohol (except for PhOH, which was dissolved in μL of toluene) ( mmol) was added via syringe to a solution of the catalyst ( × 10–2 mmol) and HBPin ( mmol) in toluene (5 mL) placed in a 25 mL flask attached to a gas buret and immersed in a 30 °C bath (eq S1 and Figure S2 in the Supporting Information), and the mixture was vigorously shaken ( rpm) during the run. The reaction was monitored by measuring the volume of the evolved hydrogen with time until hydrogen evolution stopped. Representative gas vs time plots are given in the Supporting Information. The solution was then passed through a silica gel column. Removal of the volatiles gave the boryl ether. The products were analyzed by 1H, 13C{1H}, and 11B NMR spectroscopy.

Spectroscopic Data of the Products of the Alcoholysis

MeOBpin

1H NMR ( MHz, C6D6, K): δ (s, 12 H, CH3-BPin), (s, 3 H, −OCH3). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH3), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

EtOBPin

1H NMR ( MHz, C6D6, K): δ (q, JH–H =2 H, −OCH2CH3), (t, JH–H =3 H, −OCH2CH3), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH2CH3), (s, CH3-BPin), (s, −OCH2CH3). 11B NMR ( MHz, C6D6, K): (s).

nBuOBPin

1H NMR ( MHz, C6D6, K): δ (t, JH–H =2 H, −OCH2(CH2)2CH3), and (both m, 2 H each, −OCH2(CH2)2CH3), (s, 12 H, CH3-BPin), (t, JH–H =3 H, −OCH2(CH2)2CH3). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH2(CH2)2CH3), and (both s, −OCH2(CH2)2CH3), (s, CH3-BPin), (s, −OCH2(CH2)2CH3). 11B NMR ( MHz, C6D6, K): (s).

noctylOBPin

1H NMR ( MHz, C6D6, K): δ (t, JH–H =2 H, −OCH2(CH2)7CH3), (m, 2 H, −OCH2(CH2)7CH3), – (m, 10 H, CH2), (s, 12 H, CH3-BPin), (t, JH–H =3 H, −OCH2(CH2)7CH3). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, −OCH2(CH2)7CH3),, and (all s, −OCH2(CH2)7CH3), (s, CH3-BPin), (s, −OCH2(CH2)7CH3). 11B NMR ( MHz, C6D6, K): (s).

PhCH2OBPin

1H NMR ( MHz, C6D6, K): δ – (m, 5 H, CH-Ph), (s, 2 H, −OCH2Ph), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, Cipso-Ph), and (all s, CH-Ph), (s, C-Bpin), (s, −OCH2Ph), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

iPrOBPin

1H NMR ( MHz, C6D6, K): δ (m, 1 H, CH-iPr), (d, JH–H =6 H, CH3-iPr), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, CH-iPr), (s, CH3-BPin), (s, CH3-iPr). 11B NMR ( MHz, C6D6, K): (s).

tBuOBPin

1H NMR ( MHz, C6D6, K): δ (s, 9 H, CH3-tBu), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, C-tBu, (s, CH3-tBu), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

PhOBPin

1H NMR ( MHz, C6D6, K): δ – (m, 5 H, CH-Ph), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, Cipso-Ph), and (all s, CH-Ph), (s, C-Bpin), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

Hydrolysis Reactions of Pinacolborane Catalyzed by OsCl{κ2-C,C-[CN(CH3)CHCHNCH2C(O)]}(PiPr3)2 (3)

The hydrolysis reactions were carried out by the same procedure as the alcoholysis but using water instead of alcohols (eq S2 in the Supporting Information). Since the product obtained is an alcohol (HOBPin), a second addition of HBPin was injected in order to obtain (Bpin)2O.

Spectroscopic Data of the Products of the Hydrolysis

HOBPin

1H NMR ( MHz, C6D6, K): δ (br, 1 H, −OH), (s, 12 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-Bpin), (s, CH3-BPin). 11B NMR ( MHz, C6D6, K): (s).

Bpin)2O

1H NMR ( MHz, C6D6, K): δ (s, 24 H, CH3-BPin). 13C{1H}-APT NMR ( MHz, C6D6, K): δ (s, C-BPin), (s, CH3-BPin)). 11B NMR ( MHz, C6D6, K): (s).

Structural Analysis of Complexes 36

X-ray data were collected for the complexes on a Bruker Smart APEX CCD diffractometer equipped with a normal focus, kW sealed tube source (Mo radiation, λ = Å) operating at 50 kV and 40 mA (5) or 30 mA (3, 4, and 6). Data were collected over the complete sphere. Each frame exposure time was 10 s (3, 4, and 6) or 40 s (5) covering ° in ω. Data were corrected for absorption by using a multiscan method applied with the SADABS program. (25) The structures were solved by Patterson or direct methods and refined by full-matrix least squares on F2 with SHELXL97, (26) including isotropic and subsequently anisotropic displacement parameters. The hydrogen atoms (except hydrides) were observed in the least-squares Fourier maps or calculated and refined freely or refined using a restricted riding model. Hydrogens bonded to metal atoms were observed in the last cycles of refinement but refined too close to metals; therefore, a restricted refinement model was used for all of them (d(Os–H) = (1) Å).

Complex 6 was first solved and refined in the monoclinic Cc space group. However, a pseudomerohedric twin that simulated orthorhombic (β approximately 90°) and racemic twin laws was observed. Once the refinement was finished, the ADDSYM option in Platon (27) suggested the orthorhombic Cmcm as the correct space group. (28) With this symmetry, the osmium is site in the 2-fold axis along (1/2, y, 3/4). As a result, the chlorine, carbene, and dihydrogen ligands are disordered by symmetry. To complete the anisotropic refinement, restraints were used in some distances (DFIX command) and thermal parameters (SIMU and DELU commands) in the disordered groups.

Crystal data for 3:

C24H49ClN2OOsP2·2C3H6O, Mworange, irregular block ( × × mm), orthorhombic, space group Pnma, a = (7) Å, b = (9) Å, c = (4) Å, V = (3) Å3, Z = 4, Z′ =Dcalc = g cm–3, F() =T = (2) K, μ = mm–1, measured reflections (2θ = 3–58°, ω scans °), unique reflections (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 =data/restraints/parameters /0/; GOF =largest peak and hole (close to osmium atom) and − e/Å3.

Crystal data for 4:

C25H49ClN2O2OsP·2C3H6O, Mwcolorless, irregular block ( × × mm), orthorhombic, space group Pbcm, a = (4) Å, b = (8) Å, c = (10) Å, V = (3) Å3, Z = 4, Z′ =Dcalc = g cm–3, F() =T = (2) K, μ = mm–1, measured reflections (2θ = 3–58°, ω scans °), unique (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 =data/restraints/parameters /0/, GOF =largest peak and hole (close to osmium atoms) and − e/Å3.

Crystal data for 5:

C24H49ClN2O3OsP2, Mwred, irregular block ( × × mm), orthorhombic, space group Pbca, a = (6) Å, b = (6) Å, c = (7) Å, V = (3) Å3, Z = 8, Z′ = 1, Dcalc = g cm–3, F() =T = (2) K, μ = mm–1, measured reflections (2θ = 3–51°, ω scans °), unique (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 =data/restraints/parameters /6/, GOF =largest peak and hole (close to osmium atoms) and − e/Å3.

Crystal data for 6:

C24H51ClN2O1OsP2·2C3H6O, Mworange, irregular block ( × × mm), orthorhombic, ef commander 19.02 - Crack Key For U group Cmcm, a = (6) Å, b = (8) Å, c = (12) Å, V = (3) Å3, Z = 4, Z′ =Dcalc = g cm–3, F() =T = (2) K, μ = mm–1, measured reflections (2θ = 3–58°, ω scans °), unique (Rint = ), minimum/maximum transmission factors /, final agreement factors R1 = ( observed reflections, I > 2σ(I)) and wR2 =data/restraints/parameters //, GOF =largest peak and hole and − e/Å3.

Supporting Information


Figures and CIF files giving positional displacement parameters, crystalllographic data, and bond lengths and angles of compounds 36, IR spectrum of complex 5, NMR spectra of complexes 5, 6, 6′, and 7, and plots of hydrogen evolution versus time for the alcoholysis and hydrolysis of pinacolborane catalyzed by complex 3. The Supporting Information is available free of charge on the ACS Publications website at DOI: /mauitopia.usmet.5b

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: mauitopia.us

Author Information


    • Miguel A. Esteruelas - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain;  Email: [email&#;protected]

    • Miguel Yus - Departamento de Quı́mica Orgánica, Facultad de Ciencias-Instituto de Sı́ntesis Orgánica (ISO), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Alicante, Apdo. 99, Alicante, Spain;  Email: [email&#;protected]

    • Tamara Bolaño - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain

    • M. Pilar Gay - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain

    • Enrique Oñate - Departamento de Quı́mica Inorgánica, Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea (ISQCH), Centro de Ef commander 19.02 - Crack Key For U en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC, Zaragoza, Spain

    • Isidro M. Pastor - Departamento de Quı́mica Orgánica, Facultad de Ciencias-Instituto de Sı́ntesis Orgánica (ISO), Centro de Innovación en Quı́mica Avanzada (ORFEO-CINQA), Universidad de Alicante, Apdo. 99, Alicante, Spain

  • The authors declare no competing financial interest.

Acknowledgment


Financial support from the MINECO of Spain (Projects CTQP and CTQREDC), the Diputación General de Aragón (E), and the European Social Fund (FSE) and FEDER. M.P.G. thanks the Spanish MINECO for her FPI fellowship. T.B. thanks the Spanish MINECO for funding through the Juan de la Cierva program.

This article references 28 other publications.

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    A review. This minireview focuses on selected examples for efficient homogeneous catalysis based on functional ligands, which were inspired by heterogeneous and metalloenzyme catalysis. The strategies discussed are already established and cooperative catalysis by the action of either multiple metal centers or metal centers and cooperating ligands has been discussed by other authors as a useful concept to improve catalyst performance. By covering parts of their own recent results and related work, the authors, here, want to emphasize some basic principles assocd. with catalyst design form a more inorg. perspective, including topics, such as polymn. or org. and inorg. substrates, and applications relevant to energy conversion and storage.

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    A review. In view of Freegate Free Activate concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh keyshot 6 free download with crack - Free Activators to catalytic design are desirable. In recent years, complexes based on "cooperating" ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation. We have discovered a new mode of metal-ligand cooperation, involving aromatization-dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidn. state, and so far the activation of H-H, C-H (sp2 and sp3), O-H, and N-H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H2 and light-induced liberation of O2, using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique "long-range" metal-ligand cooperation in the activation of H2 and in reaction with ammonia. In this Account, we begin by providing an overview of the metal-ligand cooperation based on aromatization-dearomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal-ligand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcs. to ketones, (2) acceptorless dehydrogenative coupling of alcs. to esters, (3) acylation of secondary alcs. by esters with dihydrogen liberation, (4) direct coupling of alcs. and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H2 liberation, (6) selective synthesis of imines from alcs. and amines, (6) facile catalytic ant download manager mac - Activators Patch of esters to alcs., (7) hydrogenolysis of amides to alcs. and amines, (8) hydrogenation of ketones to secondary alcs. under mild hydrogen pressures, (9) direct conversion of alcs. to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcs. and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being mol. hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes.

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    A review. The use of N-heterocyclic carbenes (NHCs) in chem. has developed rapidly over the past twenty years. These interesting compds. are predominantly employed in organometallic chem. as ligands for various metal centers, and as organocatalysts able to mediate an exciting range of reactions. However, the sheer no. of NHCs known in the literature can make the appropriate choice of NHC for a given application difficult. A no. of metrics were explored that allow the electronic properties of NHCs to be quantified and compared. In this review, these various metrics and what they can teach about the electronic properties of NHCs are discussed. Data for approx. three hundred NHCs are presented, obtained from a detailed survey of the literature.

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    A review. Palladium-catalyzed C-C and C-N bond-forming reactions are among the most versatile and powerful synthetic methods. For the last 15 years, N-heterocyclic carbenes (NHCs) have enjoyed increasing popularity as ligands in Pd-mediated cross-coupling and related transformations because of their superior performance compared to the more traditional tertiary phosphanes. The strong σ-electron-donating ability of NHCs renders oxidative insertion even in challenging substrates facile, while their steric bulk and particular topol. is responsible for fast reductive elimination. The strong Pd-NHC bond contribute to the high stability of the active species, even at low ligand/Pd ratios and high temps. With a no. of com. available, stable user-friendly, and powerful NHC-Pd precatalysts, the goal of a universal cross-coupling catalyst is within reach. This review discusses the basics of Pd-NHC chem. to understand the peculiarities of these catalysts and then gives a crit. discussion on their application in C-C and C-N cross-coupling as well as carbopalladation reactions.

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Источник: mauitopia.us

Installation Guide

 Preparing Installation Sources

As explained in Chapter 2, Downloading Red Hat Enterprise Linux, two basic types of media are available for Red Hat Enterprise Linux: a minimal boot image and a full installation image (also known as a binary DVD). If you downloaded the binary DVD and created a boot DVD-ROM or USB drive from it, you can proceed with the installation immediately, as this image contains everything you need to install the system.

However, if you use the minimal boot image, you must also configure an additional source of the installation. This is because the minimal boot image only contains the installation program itself and tools needed to boot your system and start the installation; it does not include the software packages to be installed on your system.

The full installation DVD ISO image can be used as the source for the installation. If your system will require additional software not provided by Red Hat, you should configure additional repositories and install these packages after the installation is finished. For information about configuring additional Yum repositories on an installed system, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The installation source can be any of the following:

  • : You can burn the binary DVD ISO image onto a DVD and configure the installation program to install packages from this disk.

  • : You can place the binary DVD ISO image on a hard drive and install packages from it.

  • : You can copy the binary DVD ISO image or the installation tree (extracted contents of the binary DVD ISO image) to a network location accessible from the installation system and perform the installation over the network using the following protocols:

    • : The binary DVD ISO image is placed into a Network File System (NFS) share.

    • , or : The installation tree is placed on a network location accessible over, or.

When booting the installation from minimal boot media, you must always configure an additional installation source. When booting the installation from the full binary DVD, it is also possible to configure another installation source, but it is not necessary - the binary DVD ISO image itself contains all packages you need to install the system, and the installation program will automatically configure the binary DVD as the source.

You can specify an installation source in any of the following ways:

  • In the installation program's graphical interface: After the graphical installation begins and you select your preferred language, the Installation Summary screen will appear. Navigate to the Installation Source screen and select the source you want to configure. For details, see:

  • Using a boot option: You can specify custom boot options to configure the installation program before it starts. One of these options allows you to specify the installation source to be used. See the option in Section , “Configuring the Installation System at the Boot Menu” for details.

  • Using a Kickstart file: You can use the command in a Kickstart file and specify an installation source. See Section , “Kickstart Commands and Options” for details on the Kickstart command, and Chapter 27, Kickstart Installations for information about Kickstart installations in general.

 Installation Source on a Hard Drive

Hard drive installations use an ISO image of the binary installation DVD. To use a hard drive as the installation source, transfer the binary DVD ISO image to the drive and connect it to the installation system. Then, boot the Anaconda installation program.

You can use any type of hard drive accessible to the installation program, including USB flash drives. The binary ISO image can be in any directory of the hard drive, and it can have any name; however, if the ISO image is not in the top-level directory of the drive, or if there is more than one image in the top-level directory of the drive, you will be required to specify the image to be used. This can be done using a boot option, an entry in a Kickstart file, or manually in the Installation Source screen during a graphical installation.

A limitation of using a hard drive as the installation source is that the binary DVD ISO image on the hard drive must be on a partition with a file system which Anaconda can mount. These file systems are, and (). Note that on Microsoft Windows systems, the default file system used when formatting hard drives isand the file system is also available; however, neither of these file systems can be mounted during the installation. If you are creating a hard drive or a USB drive to be used as an installation source on Microsoft Windows, make sure to format the drive as.

The file system does not support files larger than 4 GiB. Some Red Hat Enterprise Linux 7 installation media can be larger than that, which means you cannot copy them to a drive with this file system.

When using a hard drive or a USB flash drive as an installation source, make sure it is connected to the system when the installation begins. The installation program is not able to detect media inserted after the installation begins.

 Installation Source on a Network

Placing the installation source on a network has the advantage of allowing you to install multiple systems from a single source, without having to connect and disconnect any physical media. Network-based installations can be especially useful when used together with a TFTP server, which allows you to boot the installation program from the network as well. This approach completely eliminates the need for creating physical media, allowing easy deployment of Red Hat Enterprise Linux on multiple systems at the same time. For further information about setting up a TFTP server, see Chapter 24, Preparing for a Network Installation.

 Installation Source on an NFS Server

The installation method uses an ISO image of the Red Hat Enterprise Linux binary DVD placed in a server's exported directory, which the installation system must be able to read. To perform an NFS-based installation, you will need another running system which will act as the NFS host.

For more information about NFS servers, see the Red Hat Enterprise Linux 7 Storage Administration Guide.

The following procedure is only meant as a basic outline of the process. The precise steps you must take to set up an NFS server will vary based on the system's architecture, operating system, package manager, service manager, and other factors. On Red Hat Enterprise Linux 7 systems, the procedure can be followed exactly as documented. For procedures describing the installation source creation process on earlier releases of Red Hat Enterprise Linux, see the appropriate Installation Guide for that release.

Procedure  Preparing for Installation Using NFS

  1. Install the nfs-utils package by running the following command as :

  2. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to a suitable directory on the NFS server. For example, you can create directory for this purpose and save the ISO image here.

  3. Open the file using a text editor and add a line with the following syntax:

    /exported_directory/clients

    Replace /exported_directory/ with the full path to the directory holding the ISO image. Instead of clients, use the host name or IP address of the computer which is to be installed from this NFS server, the subnetwork from which ef commander 19.02 - Crack Key For U computers are to have access the ISO image, or the asterisk sign () if you want to allow any computer with network access to the NFS server to use the ISO image. See the man page for detailed information about the format of this field.

    The following is a basic configuration which makes the directory available as read-only to all clients:

    /rhel7-install *
  4. Save the file after finishing the configuration and exit the text editor.

  5. Start the service:

    If the service was already running before you changed the file, enter the following command instead, in order for the running NFS server to reload its configuration:

After completing the procedure above, the ISO image is accessible over and ready to be used as an installation source.

When configuring the installation source before or during the installation, use as the protocol, the server's host name or IP address, the colon sign (), and the directory holding the ISO image. For example, if the server's host name is and you have saved the ISO image inspecify as the installation source.

 Installation Source on an HTTP, HTTPS or FTP Server

This installation method allows for a network-based installation using an installation tree, which is a directory containing extracted contents of the binary DVD ISO image and a valid file. The installation source is accessed over, or.

For more information about HTTP and FTP servers, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The following procedure is only meant as a basic outline of the process. The precise steps you must take to set up an FTP server will vary based on the system's architecture, operating system, package manager, service manager, and other factors. On Red Hat Enterprise Linux 7 systems, the procedure can be followed exactly as documented. For procedures describing the installation source creation process on earlier releases of Red Hat Enterprise Linux, see the appropriate Installation Guide for that release.

Procedure  Preparing Installation Using HTTP or HTTPS

  1. Install the httpd package by running the following command as :

    An server needs additional configuration. For detailed information, see section Setting Up an SSL Server in the Red Hat Enterprise Linux 7 System Administrator's Guide. However, is not necessary in most cases, because no sensitive data is sent between the installation source and the installer, and is sufficient.

    If your Apache web server configuration enables SSL security, make sure to only enable the protocol, and disable and. This is due to the POODLE SSL vulnerability (CVE). See mauitopia.us for details.

    If you decide to use and the server is using a self-signed certificate, you must boot the installer with the option.

  2. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to the HTTP(S) server.

  3. Mount the binary DVD ISO image, using the command, to a suitable directory:

    Replace /image_directory/mauitopia.us with the path to the binary DVD ISO image, and /mount_point/ with the path to the directory in which you want the content of the ISO image to appear. For example, you can create directory for this purpose and use that as the parameter of the command.

  4. Copy the files from the mounted image to the HTTP server root.

    This command creates the directory with the content of the image.

  5. Start the service:

After completing the procedure above, the installation tree is accessible and ready to be used as the installation source.

When configuring the installation source before or during the installation, use or as the protocol, the server's host name or IP address, and the directory in which you have stored the files from the ISO image, relative to the HTTP server root. For example, if you are usingthe server's host name isand you have copied the files from the image tospecify as the installation source.

Procedure  Preparing for Installation Using FTP

  1. Install the vsftpd package by running the following command as :

  2. Optionally, open the configuration file in a text editor, and edit any options you want to change. For available options, see the man page. The rest of this procedure assumes that default options are used; notably, to follow the rest of the procedure, anonymous users of the FTP server must be permitted to download files.

    If you configured SSL/TLS security in your file, make sure to only enable the protocol, and disable and. This is due to the POODLE SSL vulnerability (CVE). See mauitopia.us for details.

  3. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to the FTP server.

  4. Mount the binary DVD ISO image, using the command, to a suitable directory:

    Replace /image_directory/mauitopia.us with the path to the binary DVD ISO image, and /mount_point with the path to the directory in which you want the content of the ISO image to appear. For example, you can create directory for this purpose and use that as the parameter of the command.

  5. Copy the files from the mounted image to the FTP server root:

    This command creates the directory with the content of the image.

  6. Start the service:

    If the service was already running before you changed the file, restart it to ensure the edited file is loaded. To restart, execute the following command:

After completing the procedure above, the installation tree is accessible and ready to be used as the installation source.

When configuring the installation source before or during the installation, use as the protocol, the server's host name or IP address, and the directory in which you have stored the files from the ISO image, relative to the FTP server root. For example, if the server's host name is and you have copied the files BuzzBundle 2.62.1 Crack + Serial Key 2021 - Activators Patch the image tospecify as the installation source.

Источник: mauitopia.us
very well. However, terms for the Kd (Fig. 12 C) and Hill coefficient (Fig. 12 D) were determined for voltages from &#x; to + mV. The apparent affinity increases markedly with depolarization while appearing to reach a limiting value at the most negative activation potentials. The apparent Hill coefficient exhibits a surprisingly erratic appearance. However, consistent with other results microsoft office 2016 product key - Crack Key For U et al. ), the Hill coefficient increases from 1 to over the range of &#x;20 to +80 mV. The error bars indicate the 90% confidence limits on the fitted parameter and indicate that the fitting function in some cases did not describe the shape of the curves very adequately. This sort of experiment suggests that two other factors are also likely to impact on estimates of Hill coefficient in various studies. First, large variation in estimates of Hill coefficient might be expected to result from the fact that, in some studies, the number of Ca2+ concentrations over which the change in conductance is determined can be rather minimal. Second, at positive potentials where activation of GraphPad Prism 9.1.2 Crack With Key and Free Download 2021 occurs in the absence of Ca2+, if this activation is not taken into account, Hill coefficients will be estimated incorrectly. In sum, these results suggest that registry cleaner full version with crack - Activators Patch typical Hill function may not be a mechanistically meaningful way of evaluating the Ca2+ dependence of Slo1 current activation and that the apparent Hill coefficient may exhibit some unusual dependence on voltage. Possible reasons for this behavior are addressed below.

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Figure 12

The behavior of Kd and Hill coefficient over all [Ca2+]. In A, conductances given in Fig. 2 D were replotted to show the Ca2+ dependence of conductance at a given voltage. Each point is the mean and SEM for the estimate. Solid lines are fits of the modified Hill equation given in the text. Symbols correspond to potentials of &#x; (&#x;), &#x; (Ë), &#x; (&#x;), &#x; (Ä), &#x; (ª), &#x; (¡), &#x;80 (´), &#x;60 (µ), &#x;40 (¾), &#x;20 (¿), 0 (¸), +20 (¹), +40 (Â), +60 (Ã), +80 (&#x;), + (Æ), + (closed six-pointed star), and + (open six-pointed star) mV. In B, conductance values predicted from Fig. 1 (see Fig. 14) based on values given in Table (column D) were plotted as a function of [Ca2+] and fit with the modified Hill equation (solid lines). Symbols are as in A. In C, estimated values for the Kd for apparent Ca2+ affinity (&#x;) obtained from fitting the data in Fig. 12 A are plotted as a function of command potential. The solid line with small filled circles corresponds to values for Kd predicted from Fig. 1 as shown in Fig. 12B. The line with small open circles corresponds to Kd values assuming no Mg2+ inhibition of the high affinity site. In D, the Hill coefficients determined from Fig. 12 A (&#x;) are plotted as a function of voltage. Error bars represent the 90% confidence limit on the estimate of the Hill coefficient. The dotted lines show the predictions from Fig. 1 as determined from values in Tablecolumn D (Fig. 12 B, small closed circles) or from Tablecolumn F (small open circles, no Mg2+ inhibition).

We next examined the effects of [Mg2+] on the behavior of Hill plots. This analysis used a different set of patches than those used in Fig. 2 and used a more limited set of Ca2+ concentrations, but typical of those used in other investigations. Hill plots obtained for this data set in the absence of Mg2+ are shown for several voltages in Fig. 13 A, whereas similar plots in the presence of 10 mM Mg2+ are shown in Fig. 13 B. As above, the Hill equation was used to make estimates of Kd and the Hill coefficient. Given the more limited number of Ca2+ concentrations Movavi PDF Editor Crack in this set of patches, the estimate of Hill coefficient in particular exhibited large confidence limits. Both with and without Mg2+, the Kd varied exponentially with command potential with a zero-voltage Kd of 25 ¼M in the absence of Mg2+ and 10 ¼M in the presence of Ca2+ (Fig. 13 C). Both with and without Mg2+, there was a trend for the Hill coefficient to became larger at more positive potentials (Fig. 13 D), which is consistent with the observations in Fig. 12 D and other work (Cui et al. ). This increase in the Hill coefficient is, in part, the simple expectation of the fact that, for each increment in Ca2+, G-V curves are shifted more at lower than at higher [Ca2+], such that over the range of ¼M&#x;1 mM Ca2+, little additional shift is observed (Wei et al. ; Cox et al. b). As a consequence, at more negative potentials, relatively large increments in [Ca2+] produce relatively small increases in conductance, resulting in a less steep Ca2+ dependence of activation. Since, as shown above, 10 mM Mg2+ produces an essentially mV leftward shift of the G-V curve obtained at each [Ca2+], this would be expected to cause an apparent increase in Hill coefficient at any command potential. Another way of viewing the results is that the relationship between Hill coefficient and command potential (Fig. 13 D) is simply shifted leftward 50 mV in the presence of Mg2+. Thus, the present results suggest that Mg2+ does cause an increase in the apparent Hill coefficient for Ca2+ at a given voltage, but that this effect reflects a shift of the relationship between Hill coefficient and voltage along the voltage axis.

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Figure 13

The apparent Hill coefficient for activation of conductance by Ca2+ is increased by Mg2+. In A, each point is the estimate of conductance activated at a given Ca2+ and voltage obtained from normalized G-V curves. Solid lines are fits of the modified Hill equation given in the text. Fitted values for apparent Kd and Hill coefficient are plotted in C and D, respectively. Values used in this figure were from a different set of patches than shown in Fig. 2 or Fig. In B, conductance estimates obtained in the presence of 10 mM Mg2+ are plotted as a function of Ca2+ for a range of voltages. At comparable voltages, the Hill coefficient for activation is higher in the presence of Mg2+. In C, the apparent Kd (in ¼M) for activation of conductance by Ca2+ either in the absence (&#x;) or presence (Ë) of 10 mM Mg2+ is plotted as a function of activation potential. The apparent Ca2+ affinity is increased at a given potential in the presence of Mg2+. The error bars are 90% confidence limits from the estimates of K obtained in A and B. Predictions from Fig. 1 (Tablecolumn D) for solutions without Mg2+ (ª) or with Mg2+ (¡) are also shown. In D, the Hill coefficient and confidence limits for the activation of conductance by Ca2+ either in the absence (&#x;) or presence (Ë) of Mg2+ are plotted as a function of command potential, along with estimates (no Mg2+ [&#x;], +10 mM Mg2+ [Ä]) from Fig. 1 based on estimates of Mg2+ affinities from column B of Table. Both for experimental data and the theoretical predictions, there is a trend for increased Hill coefficient at more positive potentials and, at any Loaris Trojan Remover For Windows potential, Mg2+ increases the apparent Hill coefficient. In E, the Kd for Ca2+ effect predicted from Fig. 1 is plotted over a wider range of potentials. Both with (Ë) and without (&#x;) 10 mM Mg2+, at the most negative potentials a limit in the Kd is observed, while affinity increases dramatically with depolarization. In F, the behavior of Hill coefficient as a function of command potential predicted by Fig. 1 is displayed wise disk cleaner apk - Crack Key For U a wider range of potentials. Predictions from Fig. 1 assuming Mg2+ inhibition of the high affinity site (Tablecolumn D) are shown both without (&#x;) and with (Ë) 10 mM Mg2+. Predictions from Fig. 1 with no Mg2+ inhibition (Tablecolumn F) are also shown without (&#x;) and with (Ä) 10 mM Mg2+.

Mg2+ Produces Shifts of G-V Curves Resulting from ± + ²1 Subunit Coexpression

The ability of Mg2+ to shift G-V curves at a given Ca2+ is somewhat reminiscent of the effect of the ²1 and ²2 auxiliary subunits of BK channels (McManus et al. ; Meera et al. ; Wallner et al. ; Xia et al. ). If Mg2+ were acting to mimic the effects of an associated ² subunit, Mg2+ might be ineffective on channels resulting from ± + ² subunit coexpression. To test this possibility, the effects of different concentrations of Mg2+ on ± + ²1 currents elicited with ¼M Ca2+ were examined. Normalized G-V curves were generated for a set of four patches. The V for current activation with ¼M Ca2+ was &#x; ± mV, whereas, for 1, 2, 10, and 20 mM Mg2+, values for V were &#x; ± mV, &#x; ± mV, &#x; ±and &#x; ± mV, respectively. In this set of patches, the net effect of 10 mM Mg2+ is to shift the V about &#x;30 mV, which is less than observed in the absence of the ²1 subunit. However, it is clear that Mg2+ is able to exert much of its effect, irrespective of the presence or absence of the ²1 subunit.

Effects of Mg2+ Do Not Result from Changes in Ca2+ Binding Affinity

The primary effects of Mg2+ that require explanation are as follows. First, 10 mM Mg2+ appears to produce a similar shift in V at both 0 and ¼M Ca2+ with somewhat smaller shifts at 4 and 10 ¼M. Second, Mg2+ does not substitute for Ca2+ in the high affinity Ca2+-dependent steps that participate in increases in current activation rate. Third, mM Mg2+ shares with mM Ca2+ the ability to ef commander 19.02 - Crack Key For U deactivation, an effect which does not exhibit saturation until over 10 mM divalent. Finally, Mg2+ produces a slowing of current activation with 4 and 10 ¼M Ca2+ under conditions of near maximal current activation. Can these effects be accounted for by a single mechanism of action?

To guide our thinking, we first consider the particular state model presented by Cox and Aldrich to account for the dependence of steady-state conductance on voltage and Ca2+. The steady-state predictions of their formulation are summarized in the following equation:

equation M3

3

where B = [(1 + Ca/Kc)/(1 + Ca/Ko)]4 with Kc is the Ca2+ binding equilibrium for the closed channel, Ko is the Ca2+ binding equilibrium for the open channel, L(0) is the open-to-closed equilibrium constant when no voltage sensors are active and no Ca2+ binding sites are occupied, Q, the gating charge associated with this closed to open equilibrium, Vhc, is the voltage at which a single voltage sensor is active half the time when the channel is closed, and Vho, is the voltage at which a single voltage sensor is active half the time when the channel is open, and Z is the equivalent gating charge associated with each voltage-sensor's movement. This formulation assumes that voltage-dependent transitions and Ca2+ binding transitions in each subunit are independent and that Ca2+ binding affinity is not influenced by movement of voltage sensors.

Might alteration by Mg2+ of any parameters in the above equation provide suggestions concerning how Mg2+ may produce relatively similar shifts in G-V curves at both 0 and ¼M Ca2+? To test this possibility, we empirically adjusted various parameters in to ascertain whether any would reproduce the key features of the G-V curves, i.e., the relatively constant shift at all [Ca2+] and the increase in slope at 0 Ca2+. Of all the possible parameters, only adjustment of two parameters were qualitatively able to mimic the effects of Mg2+. First, adjustment of Vho, the term for the voltage at which a single voltage sensor is half the time active when the channel is open, could produce a relatively similar shift at all Ca2+ and increase the slope at 0 Ca2+. Similarly, the magnitude of L(0) shifts the family of G-Vs in a somewhat parallel fashion along the voltage axis as shown previously (Cox and Aldrich ). Thus, in accordance with the assumptions of this model, this would argue that the effects of Mg2+ might result from an increase in the stability of the open states perhaps either by stabilizing the voltage sensors in the active configuration or by simply affecting the equilibrium between the closed and open conformations. In contrast, the effects of Mg2+ are entirely inconsistent with any model in which Mg2+ might somehow change the affinity of Ca2+, i.e., Kc or Ko.

A state Allosteric Model Describes the Effects of Mg2+

We next considered whether a particular stochastic model incorporating binding of Mg2+ might allow an explicit analytical evaluation of the effects of Mg2+. We begin with the specific state model proposed by Cox and Aldrich described above in which Ca2+ binding and voltage-sensor movement are not coupled. Based on the tetrameric nature of the channel (Shen et al. ), we postulate a Mg2+ binding site on each subunit. The result of the addition of four independent Mg2+ binding steps to the basic state model is shown for one case in Fig. 1. Basically, for each of the two tiers characteristic of the state model, there are now Loaris Trojan Remover For Windows additional sets of the two tiers corresponding to binding of one, two, magix vegas movie studio 14 suite, or four Mg2+ cations. Each pair of tiers corresponding to a different extent of ligation by Mg2+ is designated by I-V. Any state in I is connected to the corresponding state in II by a Mg2+ binding step. Similarly, any state in II is connected to the corresponding states in either I or III by Mg2+ dissociation and association, respectively. This is indicated in Fig. 1 by the pathways connecting the lower and leftmost state in each tier to the lower and leftmost states in adjacent tiers with constants driver updater with registration key by K(l)o and K(l)c, the binding constants of a divalent cation to the low affinity site on either open or closed channels, respectively. This results in a total of states, which results naturally from the fact that gating is regulated by three parameters, voltage, Ca2+, and Mg2+ (or other divalent).

Analytic evaluation of a state model depends on specific assumptions about the relationship between Mg2+ binding steps and other transitions. Because the effects of Mg2+ are apparent in 0 Ca2+, we exclude from consideration the case where binding of Mg2+ is assumed to influence either Ko or Kc, the affinities of Ca2+ to open or closed channels, respectively. Here, we first consider the case (given in Fig. 1) in which we propose that binding of Mg2+ (or mM Ca2+) to open and closed channels may occur with different affinities. This low affinity binding would have no effect on voltage-sensor equilibria or Ca2+ binding affinities. The shift in V would be driven by the higher affinity with which Mg2+ binds to open states. This would be analogous to the binding of Ca2+ to its high affinity site, although independent of that effect. In essence, binding of Mg2+ would be coupled to changes in L(0) between adjacent pairs of tiers given in Fig. 1.

For solution of steady-state equations for the state model ef commander 19.02 - Crack Key For U Fig. 1, in addition to the seven parameters required to describe the state model inthe system is also defined by two additional parameters, K(l)o and K(l)c, the affinity of Mg2+ (and or Ca2+) to the low affinity divalent cation binding site when the channel is either open or closed, respectively. Fractional conductance for Fig. 1 as a function of [Ca2+], voltage, and divalent cation concentration ([D]) is given by:

equation M4

4

where

equation M5

[D] corresponds to the concentration of divalent cation acting at the low affinity sites, and other parameters are as defined above. Despite the marked increase in number of states compared with the state model, the form of the equation is similar to with only two additional free parameters. For cases in which there are two species of divalent cations that may act at the low affinity sites, but with somewhat differing affinities, this expression is obviously not sufficient.

To examine the effects of Mg2+ and high Ca2+ in terms of Fig. 1, we used four different data sets, each a set of patches obtained under a particular range of divalent cation concentrations. Set 1 entailed [Ca2+] from 0 to mM, set 2 used 0 Ca2+ with [Mg2+] from 0 to mM, set 3 used ¼M Ca2+ with [Mg2+] from 0 to mM, and set 4 used both 0 and ¼M with [Mg2+] from 0 to mM. In Fig. 14 A, it can be seen that the G-V curves from data set 1 can be quite well-described by. The displayed fit in Fig. 14 A is based on the values in Table (column A). When L(0) was left unconstrained, the value converged within the range of ,&#x;, with very large confidence limits. Varying this value did not result in any improvement in the fit, which indicates that L(0) cannot be well-defined by this procedure. Of the parameters inthose pertaining to the Ca2+ binding steps are the most well constrained, whereas the parameters relating to movement of voltage sensors do not appear to be precisely described. The large confidence limits for Vhc, Vho, and L(0) reflect the fact that these parameters tend to be correlated and relatively large changes in one parameter can be compensated for by changes in another parameter. However, for a variety of assumptions about the values of L(0), Vhc and Vho, the estimates of affinity for Ca2+ of the low affinity site was consistently near mM when the channel is closed and mM when the channel is open. The difference in affinities for the low affinity site is quite a bit smaller than that observed for the high affinity Ca2+ sites, defined by Kc and Ko. However, these values for K(l)o and K(l)c suggest that the low affinity site, should this model be correct, may contribute substantially to the position of the G-V curve over the range of Ca2+ from ¼M to 1 mM.

Table 1

Parameter Estimates from Fitting Fig. 1 to GV Curves Generated under Various Conditions

(A) &#x;Ca2+(B) &#x;Mg2+ alone(C) ¼M Ca2+ + &#x;Mg2+(D) 0, ¼M Ca2+ + &#x;Mg2+(E) 0, ¼M Ca2+ + &#x;Mg2+
K(h,mg)c = K(h,mg)oK(h,mg)c! = K(h,mg)o
UnitsData set 1Data set 2Data set 3Data set 4Data set 4
K(h,ca)c¼M ±
K(h,ca)o¼M ±
VhcmV ±
VhomV&#x; ± &#x;&#x;&#x;&#x;
ze
Q0. 86 ± e ± ± ± ±
L(0),,,,,
K(l,mg)cmM&#x; ± ± ± ±
K(l,mg)omM&#x; ± ± ± ±
K(l,ca)cmM ± &#x;
K(l,ca)omM ± &#x;
K(h,mg)cmM&#x;&#x; ± ± ±
K(h,mg)omM&#x;&#x; ± &#x; ±
SSQ/pt

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Figure 14

The dependence of Slo1 conductance on Ca2+, Mg2+ and voltage can be described by a state allosteric model involving the independent action of Ca2+, Mg2+ and voltage-sensor movement. In A, G-V curves obtained at different [Ca2+] given in Fig. 2 D (data set 1) were fit with with the solid lines resulting from the values given in column A, Table. L(0) was constrained to In B, G-V curves obtained with 0 Ca2+ (&#x;) plus (Ë), 1 (&#x;), 2 (Ä), 5 (ª), 10 (¡), 20 (´), 50 (µ), and (5) mM Mg2+ (data set 2) were also fit withwith parameters given in Tablecolumn B. In C, G-V curves obtained with ¼M Ca2+ with [Mg2+] from 0 to mM (data set 3; symbols are as in B, but with no ¼M points) were fit with. The solid lines correspond to the fit resulting from the values given in column C, Table. Comparison of the values in columns A, B, and C indicate that quite similar values yield a good general description of G-V curves over all [Ca2+], all [Mg2+], and all voltages, except that the multiple Mg2+ binding affinities defined by are not well-described in the fit to data set 3. In D1&#x;D3, G-V curves shown in A-C were simultaneously fit withyielding the values given in Table (column D). Again, the general features of the shift in curves as a function of Ca2+ and Mg2+ is reasonably well-described. In E, G-V curves obtained over all [Ca2+] were fit withwhich assumes that Mg2+ influences the voltage-sensor equilibrium. Fitted curves correspond to values given in Table (column A). In F, G-V curves at 0 Ca2+ were also fit with. When values obtained from fitting G-V curves at higher Ca2+ were used, it was not possible to obtain estimates for Km and E that resulted in adequate descriptions of the data. The curves with open circles were generated from values in column C, Table. L(0) was set to a value in which currents in 0 Ca2+ were well-described. However, the G-V curves at 10 and 50 mM Mg2+ could not be captured. Ef commander 19.02 - Crack Key For U, when more parameters were left unconstrained, could yield a fit that captured the G-V curves in 0 Ca2+ (smaller closed circles), but these values (column D, Table ) totally failed to describe the behavior of G-V curves at higher Ca2+.

We next examined the ability of to describe the G-V curves obtained with 0 Ca2+ with varying Mg2+ (data set 2). The resulting fit is shown graphically in Fig. 14 B with values listed in Table (column B). For fitting the 0 Ca2+ plus &#x;[Mg2+] G-V curves, values for Ko and Kc were constrained to those obtained when fitting the data over all [Ca2+], since in the absence of Ca2+, these parameters are not defined. Furthermore, we constrained the value of L(0) to that used in column A. This gave an adequate fit to the data, with K(l)o of mM and K(l)c of mM. When the 0 Ca2+ plus various [Mg2+] curves from data set 4 were similarly fit, the resulting estimates of K(l)o and K(l)c were ± and ± mM, respectively. Thus, binding of Mg2+ to the low affinity site appears to be about seven to eight times weaker than binding of Ca2+.

Guided by the analysis of Shi and Cui b, we have extended to include terms for both the differential affinities of Ca2+ and Mg2+ for the low affinity site and for the inhibitory action of Mg2+ on the high affinity site. From of Shi and Cui b and ouran equation defining the fractional conductance as a function of voltage, [Ca2+], and [Mg2+], reflecting the differential affinities of both divalent cations to each binding site is obtained:

equation M6

5

where

equation M7

6

and

equation M8

7

This system is defined by four separate binding affinities for both Ca2+ and Mg2+, reflecting binding of each divalent cation to either the open or closed states (subscripts o and c) or to the low or high affinity sites (K(l), K(h)). Term, Bh, and is equivalent to that used by Shi and Cui b to describe competition between Mg2+ and Ca2+ for the higher affinity site, whereas Bl arises from the same considerations applied to the lower affinity site. The relative ability of a cation to act as an activator or inhibitor depends on the ratio of the relative affinities of a particular cation for the closed state compared with the open state. As proposed by Shi and Cui b, at the high affinity site K(h,mg)c = K(h,mg)o so that occupancy of the high affinity site by Mg2+ simply inhibits the ability of Ca2+ to activate the channel.

Therefore provides a tool to evaluate the adequacy of Fig. 1 in the presence of potentially competing species of divalent cations. Therefore, we used to fit G-V curves obtained with ¼M Ca2+ and varying [Mg2+]. Using values defined above for the high affinity Ca2+ binding, the result of fitting to the G-V curves with ¼M Ca2+ is shown in Fig. 14 C. Again, values for can be found tally erp 9 gst crack download full version free - Crack Key For U fit the G-V curves reasonably well (Tablecolumn D) even when most parameters are constrained to values obtained for the Ca2+ data set. However, estimates for K(l,mg)c and K(l,mg)o differ from those in Table (column B), possibly because of the limited data set being used to define four different Mg2+ affinities. Therefore, we also fit data set 4 in which mM Mg2+ was added to either 0- or ¼M Ca2+ solutions in the same set of patches. This yielded the values in Tablecolumn E, for the assumption that K(h,mg)c = K(h,mg)o and column F for the assumption that K(h,mg)c! = K(h,mg)o. Although the latter assumption improves the fit, these data sets are probably not robust enough to define such parameters well.

We next used to fit all G-V values in data sets 1&#x;3 or data sets 1 and 4 simultaneously. In this case, we left the binding affinities for both low and high affinity sites unconstrained during the fitting procedure. The result of a simultaneous fit of data sets 1&#x;3 is shown in Fig. 14 D with values given in Tablecolumn B. Although individual curves are not as well-described as in Fig. 14 (A&#x;C), the general features of the dependence of the G-V curves on Mg2+ and Ca2+ are retained. Similar values were also obtained from a simultaneous fit to data sets 1 and 4 (Tablecolumn D). Table also lists the fits to the various data sets with differing assumptions about affinity of Mg2+ to the high affinity sites, including the absence of Mg2+ binding to those sites. Although adequate fits can be obtained when it is assumed that Mg2+ does not bind to the high affinity sites, it is clear that such an assumption fails to describe the rightward shift of G-V curves that occurs at mM Mg2+ in the presence of ¼M Ca2+.

Table 2

Parameter Estimates from Simultaneous Fitting of Data Sets Generated under Different Conditions

Fitting assumption(A) K(h,mg)c! = K(h,mg)o(B) K(h,mg)c = K(h,mg)o(C) No Mg2+ high affinity binding(D) K(h,mg)c! = K(h,mg)o(E) K(h,mg)c = K(h,mg)o(F) No Mg2+ high affinity binding
UnitsData set 1&#x;3Data set 1&#x;3Data set 1&#x;3Data set 1,4Data set 1,4Data set 1,4
K(h,ca)c¼M ± ± ± ± ± ±
K(h,ca)o¼M ± ± ± ± ± ±
VhcmV
VhomV&#x;&#x;&#x;&#x;&#x;&#x;
z
Q ± ± ± ± ± ±
L(0),,,,,
K(l,mg)cmM ± ± ± ± ± ±
K(l,mg)omM ± ± ± ± ± ±
K(l,ca)cmM ± ± ± ± ± ±
K(l,ca)omM ± ± ± ± ± movavi video editor full version ±
K(h,mg)cmM ± ± &#x; ± ± &#x;
K(h,mg)omM ± &#x;&#x; ± &#x;&#x;
SSQ/ pts / pts / pts / pts / pts / pts / pts

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On balance, examination of the values in Table suggest that, despite some variation, the two sets of data (data sets 1&#x;3, and data sets 1 and 4) yield quite comparable estimates for various binding affinities. The results indicate that Ca2+ affinity to the low affinity site is approximately seven- to eightfold greater than the Mg2+ affinity. The intrinsic allosteric effectiveness (Kc/Ko) of Mg2+ for the low affinity site may be somewhat greater than that of Ca2+. However, when data sets with either Ca2+ alone or Mg2+ alone are compared, the allosteric effectiveness of either Ca2+ or Mg2+ at the high affinity site appears similar. It is possible that other effects of the very high divalent cation concentrations used here may impact somewhat on the reliability of these estimates. Finally, Mg2+ appears to inhibit the high affinity site, with a Kd of 7&#x;20 mM. Thus, on balance, the particular formulation of the state model given in and provides a quite good description of the effects of high concentrations of Ca2+ or Mg2+ on the steady-state G-V curves of Slo1 currents, with the binding of Ca2+ being approximately seven- to eightfold stronger than that of Mg2+.

The values in Table exhibit some deviations in some parameters from those estimated in earlier studies (Cox and Aldrich ; Zeng et al. ). Although some variation is expected simply because of variability in the positions of G-V curves along the voltage-axes among different sets of data, the values of Z and Q seem a bit surprising. We refit the G-Vs obtained with different Ca2+ solutions using only data obtained with [Ca2+] of ¼M and lower using to determine to what extent the use of or might have impacted on the parameter estimates. These values are given in column E of Table. In this case, values for Q and Z fall much closer to those obtained by Cox and Aldrich (given in column F), which were guided by estimates from Horrigan for voltage-dependent parameters obtained from activation of Slo1 currents at 0 Ca2+ (Horrigan and Aldrich ; Horrigan et al. ). Some of the variation in estimates of Z and Q among different studies most certainly results from the simple process of averaging G-V curves, such that variation among individual G-V curves among patches will result in averaged curves with lessened voltage dependence. In addition, to evaluate the significance of the rather large value for Q and smaller value for Z obtained through the use of andwe refit the G-V curves obtained over all Ca2+ (data set 1) while constraining the values for Q and Z to those used by Cox and Aldrich This resulted in estimates of K(l,ca)o and K(l,ca)c for Ca2+ similar to those already given, although values for L(0), Vhc, and Vho were altered. On balance, the overall quality of the fits were only somewhat poorer. This analysis would suggest that values for L(0), Vhc, Vho, Q and Z are not well-constrained by this procedure, presumably because of correlations between parameters. However, values for Ca2+ and Mg2+ affinities appear to be critical for obtaining acceptable fits.

Table 3

Allosteric Regulation of Voltage-sensor Equilibria Is Unlikely to Account for the Dependence of Slo1 G-V Curves on Millimolar Ca2+ or Mg2+

Units(A) Ca2+ alone: unconstrained(B) &#x;[Mg2+]; 0 Ca2+(C) &#x;[Mg2+]; 0 Ca2+
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very well. However, terms for the Kd (Fig. 12 C) and Hill coefficient (Fig. 12 D) were determined for voltages from &#x; to + mV. The apparent affinity increases markedly with depolarization while appearing to reach a limiting value at the most negative activation potentials. The apparent Hill coefficient exhibits a surprisingly erratic appearance. However, consistent with other results (Cui et al. ), the Hill coefficient increases from 1 to over the range of &#x;20 to +80 mV. The error bars indicate the 90% confidence limits on the fitted parameter and indicate that the fitting function in some cases did not describe the shape of the curves very adequately. This sort of experiment suggests that two other factors are also likely to impact on estimates of Hill coefficient in various studies. First, large variation in estimates of Hill coefficient might be expected to result from the fact that, in some studies, the number of Ca2+ concentrations over which the change in conductance is determined can be rather minimal. Second, at positive potentials where activation of current occurs in the absence of Ca2+, if this activation is not taken into account, Hill coefficients will be estimated incorrectly. In sum, these results suggest that a typical Hill function may not be a mechanistically meaningful way of evaluating the Ca2+ dependence of Slo1 current activation and that the apparent Hill coefficient may exhibit some unusual dependence on voltage. Possible reasons for this behavior are addressed below.

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Figure 12

The behavior of Kd and Hill coefficient over all [Ca2+]. In A, conductances given in Fig. 2 D were replotted to show the Ca2+ dependence of conductance at a given voltage. Each point is the mean and SEM for the estimate. Solid lines are fits of the modified Hill equation given in the text. Symbols correspond to potentials of &#x; (&#x;), &#x; (Ë), &#x; (&#x;), &#x; (Ä), &#x; (ª), &#x; (¡), &#x;80 (´), &#x;60 (µ), &#x;40 (¾), &#x;20 (¿), 0 (¸), +20 (¹), +40 (Â), +60 (Ã), +80 (&#x;), + (Æ), + (closed six-pointed star), and + (open six-pointed star) mV. In B, conductance values predicted from Fig. 1 (see Fig. 14) based on values given in Table (column D) were plotted as a function of [Ca2+] and fit with the modified Hill equation (solid lines). Symbols are as in A. In C, estimated values for the Kd for apparent Ca2+ affinity (&#x;) obtained from fitting the data in Fig. 12 A are plotted as a function of command potential. The solid line with small filled circles corresponds to values for Kd predicted from Fig. 1 as shown in Fig. 12B. The line with small open circles corresponds to Kd values assuming no Mg2+ inhibition of the high affinity site. In D, the Hill coefficients determined from Fig. 12 A (&#x;) are plotted as a function of voltage. Error bars represent the 90% confidence limit on the estimate of the Hill coefficient. The dotted lines show the predictions from Fig. 1 as determined from values in Table , column D (Fig. 12 B, small closed circles) or from Table , column F (small open circles, no Mg2+ inhibition).

We next examined the effects of [Mg2+] on the behavior of Hill plots. This analysis used a different set of patches than those used in Fig. 2 and used a more limited set of Ca2+ concentrations, but typical of those used in other investigations. Hill plots obtained for this data set in the absence of Mg2+ are shown for several voltages in Fig. 13 A, whereas similar plots in the presence of 10 mM Mg2+ are shown in Fig. 13 B. As above, the Hill equation was used to make estimates of Kd and the Hill coefficient. Given the more limited number of Ca2+ concentrations used in this set of patches, the estimate of Hill coefficient in particular exhibited large confidence limits. Both with and without Mg2+, the Kd varied exponentially with command potential with a zero-voltage Kd of 25 ¼M in the absence of Mg2+ and 10 ¼M in the presence of Ca2+ (Fig. 13 C). Both with and without Mg2+, there was a trend for the Hill coefficient to became larger at more positive potentials (Fig. 13 D), which is consistent with the observations in Fig. 12 D and other work (Cui et al. ). This increase in the Hill coefficient is, in part, the simple expectation of the fact that, for each increment in Ca2+, G-V curves are shifted more at lower than at higher [Ca2+], such that over the range of ¼M&#x;1 mM Ca2+, little additional shift is observed (Wei et al. ; Cox et al. b). As a consequence, at more negative potentials, relatively large increments in [Ca2+] produce relatively small increases in conductance, resulting in a less steep Ca2+ dependence of activation. Since, as shown above, 10 mM Mg2+ produces an essentially mV leftward shift of the G-V curve obtained at each [Ca2+], this would be expected to cause an apparent increase in Hill coefficient at any command potential. Another way of viewing the results is that the relationship between Hill coefficient and command potential (Fig. 13 D) is simply shifted leftward 50 mV in the presence of Mg2+. Thus, the present results suggest that Mg2+ does cause an increase in the apparent Hill coefficient for Ca2+ at a given voltage, but that this effect reflects a shift of the relationship between Hill coefficient and voltage along the voltage axis.

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Figure 13

The apparent Hill coefficient for activation of conductance by Ca2+ is increased by Mg2+. In A, each point is the estimate of conductance activated at a given Ca2+ and voltage obtained from normalized G-V curves. Solid lines are fits of the modified Hill equation given in the text. Fitted values for apparent Kd and Hill coefficient are plotted in C and D, respectively. Values used in this figure were from a different set of patches than shown in Fig. 2 or Fig. In B, conductance estimates obtained in the presence of 10 mM Mg2+ are plotted as a function of Ca2+ for a range of voltages. At comparable voltages, the Hill coefficient for activation is higher in the presence of Mg2+. In C, the apparent Kd (in ¼M) for activation of conductance by Ca2+ either in the absence (&#x;) or presence (Ë) of 10 mM Mg2+ is plotted as a function of activation potential. The apparent Ca2+ affinity is increased at a given potential in the presence of Mg2+. The error bars are 90% confidence limits from the estimates of K obtained in A and B. Predictions from Fig. 1 (Table , column D) for solutions without Mg2+ (ª) or with Mg2+ (¡) are also shown. In D, the Hill coefficient and confidence limits for the activation of conductance by Ca2+ either in the absence (&#x;) or presence (Ë) of Mg2+ are plotted as a function of command potential, along with estimates (no Mg2+ [&#x;], +10 mM Mg2+ [Ä]) from Fig. 1 based on estimates of Mg2+ affinities from column B of Table . Both for experimental data and the theoretical predictions, there is a trend for increased Hill coefficient at more positive potentials and, at any given potential, Mg2+ increases the apparent Hill coefficient. In E, the Kd for Ca2+ effect predicted from Fig. 1 is plotted over a wider range of potentials. Both with (Ë) and without (&#x;) 10 mM Mg2+, at the most negative potentials a limit in the Kd is observed, while affinity increases dramatically with depolarization. In F, the behavior of Hill coefficient as a function of command potential predicted by Fig. 1 is displayed over a wider range of potentials. Predictions from Fig. 1 assuming Mg2+ inhibition of the high affinity site (Table , column D) are shown both without (&#x;) and with (Ë) 10 mM Mg2+. Predictions from Fig. 1 with no Mg2+ inhibition (Table , column F) are also shown without (&#x;) and with (Ä) 10 mM Mg2+.

Mg2+ Produces Shifts of G-V Curves Resulting from ± + ²1 Subunit Coexpression

The ability of Mg2+ to shift G-V curves at a given Ca2+ is somewhat reminiscent of the effect of the ²1 and ²2 auxiliary subunits of BK channels (McManus et al. ; Meera et al. ; Wallner et al. ; Xia et al. ). If Mg2+ were acting to mimic the effects of an associated ² subunit, Mg2+ might be ineffective on channels resulting from ± + ² subunit coexpression. To test this possibility, the effects of different concentrations of Mg2+ on ± + ²1 currents elicited with ¼M Ca2+ were examined. Normalized G-V curves were generated for a set of four patches. The V for current activation with ¼M Ca2+ was &#x; ± mV, whereas, for 1, 2, 10, and 20 mM Mg2+, values for V were &#x; ± mV, &#x; ± mV, &#x; ± , and &#x; ± mV, respectively. In this set of patches, the net effect of 10 mM Mg2+ is to shift the V about &#x;30 mV, which is less than observed in the absence of the ²1 subunit. However, it is clear that Mg2+ is able to exert much of its effect, irrespective of the presence or absence of the ²1 subunit.

Effects of Mg2+ Do Not Result from Changes in Ca2+ Binding Affinity

The primary effects of Mg2+ that require explanation are as follows. First, 10 mM Mg2+ appears to produce a similar shift in V at both 0 and ¼M Ca2+ with somewhat smaller shifts at 4 and 10 ¼M. Second, Mg2+ does not substitute for Ca2+ in the high affinity Ca2+-dependent steps that participate in increases in current activation rate. Third, mM Mg2+ shares with mM Ca2+ the ability to slow deactivation, an effect which does not exhibit saturation until over 10 mM divalent. Finally, Mg2+ produces a slowing of current activation with 4 and 10 ¼M Ca2+ under conditions of near maximal current activation. Can these effects be accounted for by a single mechanism of action?

To guide our thinking, we first consider the particular state model presented by Cox and Aldrich to account for the dependence of steady-state conductance on voltage and Ca2+. The steady-state predictions of their formulation are summarized in the following equation:

equation M3

3

where B = [(1 + Ca/Kc)/(1 + Ca/Ko)]4 with Kc is the Ca2+ binding equilibrium for the closed channel, Ko is the Ca2+ binding equilibrium for the open channel, L(0) is the open-to-closed equilibrium constant when no voltage sensors are active and no Ca2+ binding sites are occupied, Q, the gating charge associated with this closed to open equilibrium, Vhc, is the voltage at which a single voltage sensor is active half the time when the channel is closed, and Vho, is the voltage at which a single voltage sensor is active half the time when the channel is open, and Z is the equivalent gating charge associated with each voltage-sensor's movement. This formulation assumes that voltage-dependent transitions and Ca2+ binding transitions in each subunit are independent and that Ca2+ binding affinity is not influenced by movement of voltage sensors.

Might alteration by Mg2+ of any parameters in the above equation provide suggestions concerning how Mg2+ may produce relatively similar shifts in G-V curves at both 0 and ¼M Ca2+? To test this possibility, we empirically adjusted various parameters in to ascertain whether any would reproduce the key features of the G-V curves, i.e., the relatively constant shift at all [Ca2+] and the increase in slope at 0 Ca2+. Of all the possible parameters, only adjustment of two parameters were qualitatively able to mimic the effects of Mg2+. First, adjustment of Vho, the term for the voltage at which a single voltage sensor is half the time active when the channel is open, could produce a relatively similar shift at all Ca2+ and increase the slope at 0 Ca2+. Similarly, the magnitude of L(0) shifts the family of G-Vs in a somewhat parallel fashion along the voltage axis as shown previously (Cox and Aldrich ). Thus, in accordance with the assumptions of this model, this would argue that the effects of Mg2+ might result from an increase in the stability of the open states perhaps either by stabilizing the voltage sensors in the active configuration or by simply affecting the equilibrium between the closed and open conformations. In contrast, the effects of Mg2+ are entirely inconsistent with any model in which Mg2+ might somehow change the affinity of Ca2+, i.e., Kc or Ko.

A state Allosteric Model Describes the Effects of Mg2+

We next considered whether a particular stochastic model incorporating binding of Mg2+ might allow an explicit analytical evaluation of the effects of Mg2+. We begin with the specific state model proposed by Cox and Aldrich described above in which Ca2+ binding and voltage-sensor movement are not coupled. Based on the tetrameric nature of the channel (Shen et al. ), we postulate a Mg2+ binding site on each subunit. The result of the addition of four independent Mg2+ binding steps to the basic state model is shown for one case in Fig. 1. Basically, for each of the two tiers characteristic of the state model, there are now four additional sets of the two tiers corresponding to binding of one, two, three, or four Mg2+ cations. Each pair of tiers corresponding to a different extent of ligation by Mg2+ is designated by I-V. Any state in I is connected to the corresponding state in II by a Mg2+ binding step. Similarly, any state in II is connected to the corresponding states in either I or III by Mg2+ dissociation and association, respectively. This is indicated in Fig. 1 by the pathways connecting the lower and leftmost state in each tier to the lower and leftmost states in adjacent tiers with constants determined by K(l)o and K(l)c, the binding constants of a divalent cation to the low affinity site on either open or closed channels, respectively. This results in a total of states, which results naturally from the fact that gating is regulated by three parameters, voltage, Ca2+, and Mg2+ (or other divalent).

Analytic evaluation of a state model depends on specific assumptions about the relationship between Mg2+ binding steps and other transitions. Because the effects of Mg2+ are apparent in 0 Ca2+, we exclude from consideration the case where binding of Mg2+ is assumed to influence either Ko or Kc, the affinities of Ca2+ to open or closed channels, respectively. Here, we first consider the case (given in Fig. 1) in which we propose that binding of Mg2+ (or mM Ca2+) to open and closed channels may occur with different affinities. This low affinity binding would have no effect on voltage-sensor equilibria or Ca2+ binding affinities. The shift in V would be driven by the higher affinity with which Mg2+ binds to open states. This would be analogous to the binding of Ca2+ to its high affinity site, although independent of that effect. In essence, binding of Mg2+ would be coupled to changes in L(0) between adjacent pairs of tiers given in Fig. 1.

For solution of steady-state equations for the state model for Fig. 1, in addition to the seven parameters required to describe the state model in , the system is also defined by two additional parameters, K(l)o and K(l)c, the affinity of Mg2+ (and or Ca2+) to the low affinity divalent cation binding site when the channel is either open or closed, respectively. Fractional conductance for Fig. 1 as a function of [Ca2+], voltage, and divalent cation concentration ([D]) is given by:

equation M4

4

where

equation M5

[D] corresponds to the concentration of divalent cation acting at the low affinity sites, and other parameters are as defined above. Despite the marked increase in number of states compared with the state model, the form of the equation is similar to with only two additional free parameters. For cases in which there are two species of divalent cations that may act at the low affinity sites, but with somewhat differing affinities, this expression is obviously not sufficient.

To examine the effects of Mg2+ and high Ca2+ in terms of Fig. 1, we used four different data sets, each a set of patches obtained under a particular range of divalent cation concentrations. Set 1 entailed [Ca2+] from 0 to mM, set 2 used 0 Ca2+ with [Mg2+] from 0 to mM, set 3 used ¼M Ca2+ with [Mg2+] from 0 to mM, and set 4 used both 0 and ¼M with [Mg2+] from 0 to mM. In Fig. 14 A, it can be seen that the G-V curves from data set 1 can be quite well-described by . The displayed fit in Fig. 14 A is based on the values in Table (column A). When L(0) was left unconstrained, the value converged within the range of ,&#x;, with very large confidence limits. Varying this value did not result in any improvement in the fit, which indicates that L(0) cannot be well-defined by this procedure. Of the parameters in , those pertaining to the Ca2+ binding steps are the most well constrained, whereas the parameters relating to movement of voltage sensors do not appear to be precisely described. The large confidence limits for Vhc, Vho, and L(0) reflect the fact that these parameters tend to be correlated and relatively large changes in one parameter can be compensated for by changes in another parameter. However, for a variety of assumptions about the values of L(0), Vhc and Vho, the estimates of affinity for Ca2+ of the low affinity site was consistently near mM when the channel is closed and mM when the channel is open. The difference in affinities for the low affinity site is quite a bit smaller than that observed for the high affinity Ca2+ sites, defined by Kc and Ko. However, these values for K(l)o and K(l)c suggest that the low affinity site, should this model be correct, may contribute substantially to the position of the G-V curve over the range of Ca2+ from ¼M to 1 mM.

Table 1

Parameter Estimates from Fitting Fig. 1 to GV Curves Generated under Various Conditions

(A) &#x;Ca2+(B) &#x;Mg2+ alone(C) ¼M Ca2+ + &#x;Mg2+(D) 0, ¼M Ca2+ + &#x;Mg2+(E) 0, ¼M Ca2+ + &#x;Mg2+
K(h,mg)c = K(h,mg)oK(h,mg)c! = K(h,mg)o
UnitsData set 1Data set 2Data set 3Data set 4Data set 4
K(h,ca)c¼M ±
K(h,ca)o¼M ±
VhcmV ±
VhomV&#x; ± &#x;&#x;&#x;&#x;
ze
Q0. 86 ± e ± ± ± ±
L(0),,,,,
K(l,mg)cmM&#x; ± ± ± ±
K(l,mg)omM&#x; ± ± ± ±
K(l,ca)cmM ± &#x;
K(l,ca)omM ± &#x;
K(h,mg)cmM&#x;&#x; ± ± ±
K(h,mg)omM&#x;&#x; ± &#x; ±
SSQ/pt

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Figure 14

The dependence of Slo1 conductance on Ca2+, Mg2+ and voltage can be described by a state allosteric model involving the independent action of Ca2+, Mg2+ and voltage-sensor movement. In A, G-V curves obtained at different [Ca2+] given in Fig. 2 D (data set 1) were fit with with the solid lines resulting from the values given in column A, Table . L(0) was constrained to In B, G-V curves obtained with 0 Ca2+ (&#x;) plus (Ë), 1 (&#x;), 2 (Ä), 5 (ª), 10 (¡), 20 (´), 50 (µ), and (5) mM Mg2+ (data set 2) were also fit with , with parameters given in Table , column B. In C, G-V curves obtained with ¼M Ca2+ with [Mg2+] from 0 to mM (data set 3; symbols are as in B, but with no ¼M points) were fit with . The solid lines correspond to the fit resulting from the values given in column C, Table . Comparison of the values in columns A, B, and C indicate that quite similar values yield a good general description of G-V curves over all [Ca2+], all [Mg2+], and all voltages, except that the multiple Mg2+ binding affinities defined by are not well-described in the fit to data set 3. In D1&#x;D3, G-V curves shown in A-C were simultaneously fit with , yielding the values given in Table (column D). Again, the general features of the shift in curves as a function of Ca2+ and Mg2+ is reasonably well-described. In E, G-V curves obtained over all [Ca2+] were fit with , which assumes that Mg2+ influences the voltage-sensor equilibrium. Fitted curves correspond to values given in Table (column A). In F, G-V curves at 0 Ca2+ were also fit with . When values obtained from fitting G-V curves at higher Ca2+ were used, it was not possible to obtain estimates for Km and E that resulted in adequate descriptions of the data. The curves with open circles were generated from values in column C, Table . L(0) was set to a value in which currents in 0 Ca2+ were well-described. However, the G-V curves at 10 and 50 mM Mg2+ could not be captured. However, when more parameters were left unconstrained, could yield a fit that captured the G-V curves in 0 Ca2+ (smaller closed circles), but these values (column D, Table ) totally failed to describe the behavior of G-V curves at higher Ca2+.

We next examined the ability of to describe the G-V curves obtained with 0 Ca2+ with varying Mg2+ (data set 2). The resulting fit is shown graphically in Fig. 14 B with values listed in Table (column B). For fitting the 0 Ca2+ plus &#x;[Mg2+] G-V curves, values for Ko and Kc were constrained to those obtained when fitting the data over all [Ca2+], since in the absence of Ca2+, these parameters are not defined. Furthermore, we constrained the value of L(0) to that used in column A. This gave an adequate fit to the data, with K(l)o of mM and K(l)c of mM. When the 0 Ca2+ plus various [Mg2+] curves from data set 4 were similarly fit, the resulting estimates of K(l)o and K(l)c were ± and ± mM, respectively. Thus, binding of Mg2+ to the low affinity site appears to be about seven to eight times weaker than binding of Ca2+.

Guided by the analysis of Shi and Cui b, we have extended to include terms for both the differential affinities of Ca2+ and Mg2+ for the low affinity site and for the inhibitory action of Mg2+ on the high affinity site. From of Shi and Cui b and our , an equation defining the fractional conductance as a function of voltage, [Ca2+], and [Mg2+], reflecting the differential affinities of both divalent cations to each binding site is obtained:

equation M6

5

where

equation M7

6

and

equation M8

7

This system is defined by four separate binding affinities for both Ca2+ and Mg2+, reflecting binding of each divalent cation to either the open or closed states (subscripts o and c) or to the low or high affinity sites (K(l), K(h)). Term, Bh, and is equivalent to that used by Shi and Cui b to describe competition between Mg2+ and Ca2+ for the higher affinity site, whereas Bl arises from the same considerations applied to the lower affinity site. The relative ability of a cation to act as an activator or inhibitor depends on the ratio of the relative affinities of a particular cation for the closed state compared with the open state. As proposed by Shi and Cui b, at the high affinity site K(h,mg)c = K(h,mg)o so that occupancy of the high affinity site by Mg2+ simply inhibits the ability of Ca2+ to activate the channel.

Therefore provides a tool to evaluate the adequacy of Fig. 1 in the presence of potentially competing species of divalent cations. Therefore, we used to fit G-V curves obtained with ¼M Ca2+ and varying [Mg2+]. Using values defined above for the high affinity Ca2+ binding, the result of fitting to the G-V curves with ¼M Ca2+ is shown in Fig. 14 C. Again, values for can be found that fit the G-V curves reasonably well (Table , column D) even when most parameters are constrained to values obtained for the Ca2+ data set. However, estimates for K(l,mg)c and K(l,mg)o differ from those in Table (column B), possibly because of the limited data set being used to define four different Mg2+ affinities. Therefore, we also fit data set 4 in which mM Mg2+ was added to either 0- or ¼M Ca2+ solutions in the same set of patches. This yielded the values in Table , column E, for the assumption that K(h,mg)c = K(h,mg)o and column F for the assumption that K(h,mg)c! = K(h,mg)o. Although the latter assumption improves the fit, these data sets are probably not robust enough to define such parameters well.

We next used to fit all G-V values in data sets 1&#x;3 or data sets 1 and 4 simultaneously. In this case, we left the binding affinities for both low and high affinity sites unconstrained during the fitting procedure. The result of a simultaneous fit of data sets 1&#x;3 is shown in Fig. 14 D with values given in Table , column B. Although individual curves are not as well-described as in Fig. 14 (A&#x;C), the general features of the dependence of the G-V curves on Mg2+ and Ca2+ are retained. Similar values were also obtained from a simultaneous fit to data sets 1 and 4 (Table , column D). Table also lists the fits to the various data sets with differing assumptions about affinity of Mg2+ to the high affinity sites, including the absence of Mg2+ binding to those sites. Although adequate fits can be obtained when it is assumed that Mg2+ does not bind to the high affinity sites, it is clear that such an assumption fails to describe the rightward shift of G-V curves that occurs at mM Mg2+ in the presence of ¼M Ca2+.

Table 2

Parameter Estimates from Simultaneous Fitting of Data Sets Generated under Different Conditions

Fitting assumption(A) K(h,mg)c! = K(h,mg)o(B) K(h,mg)c = K(h,mg)o(C) No Mg2+ high affinity binding(D) K(h,mg)c! = K(h,mg)o(E) K(h,mg)c = K(h,mg)o(F) No Mg2+ high affinity binding
UnitsData set 1&#x;3Data set 1&#x;3Data set 1&#x;3Data set 1,4Data set 1,4Data set 1,4
K(h,ca)c¼M ± ± ± ± ± ±
K(h,ca)o¼M ± ± ± ± ± ±
VhcmV
VhomV&#x;&#x;&#x;&#x;&#x;&#x;
z
Q ± ± ± ± ± ±
L(0),,,,,
K(l,mg)cmM ± ± ± ± ± ±
K(l,mg)omM ± ± ± ± ± ±
K(l,ca)cmM ± ± ± ± ± ±
K(l,ca)omM ± ± ± ± ± ±
K(h,mg)cmM ± ± &#x; ± ± &#x;
K(h,mg)omM ± &#x;&#x; ± &#x;&#x;
SSQ/ pts / pts / pts / pts / pts / pts / pts

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On balance, examination of the values in Table suggest that, despite some variation, the two sets of data (data sets 1&#x;3, and data sets 1 and 4) yield quite comparable estimates for various binding affinities. The results indicate that Ca2+ affinity to the low affinity site is approximately seven- to eightfold greater than the Mg2+ affinity. The intrinsic allosteric effectiveness (Kc/Ko) of Mg2+ for the low affinity site may be somewhat greater than that of Ca2+. However, when data sets with either Ca2+ alone or Mg2+ alone are compared, the allosteric effectiveness of either Ca2+ or Mg2+ at the high affinity site appears similar. It is possible that other effects of the very high divalent cation concentrations used here may impact somewhat on the reliability of these estimates. Finally, Mg2+ appears to inhibit the high affinity site, with a Kd of 7&#x;20 mM. Thus, on balance, the particular formulation of the state model given in and provides a quite good description of the effects of high concentrations of Ca2+ or Mg2+ on the steady-state G-V curves of Slo1 currents, with the binding of Ca2+ being approximately seven- to eightfold stronger than that of Mg2+.

The values in Table exhibit some deviations in some parameters from those estimated in earlier studies (Cox and Aldrich ; Zeng et al. ). Although some variation is expected simply because of variability in the positions of G-V curves along the voltage-axes among different sets of data, the values of Z and Q seem a bit surprising. We refit the G-Vs obtained with different Ca2+ solutions using only data obtained with [Ca2+] of ¼M and lower using to determine to what extent the use of or might have impacted on the parameter estimates. These values are given in column E of Table . In this case, values for Q and Z fall much closer to those obtained by Cox and Aldrich (given in column F), which were guided by estimates from Horrigan for voltage-dependent parameters obtained from activation of Slo1 currents at 0 Ca2+ (Horrigan and Aldrich ; Horrigan et al. ). Some of the variation in estimates of Z and Q among different studies most certainly results from the simple process of averaging G-V curves, such that variation among individual G-V curves among patches will result in averaged curves with lessened voltage dependence. In addition, to evaluate the significance of the rather large value for Q and smaller value for Z obtained through the use of and , we refit the G-V curves obtained over all Ca2+ (data set 1) while constraining the values for Q and Z to those used by Cox and Aldrich This resulted in estimates of K(l,ca)o and K(l,ca)c for Ca2+ similar to those already given, although values for L(0), Vhc, and Vho were altered. On balance, the overall quality of the fits were only somewhat poorer. This analysis would suggest that values for L(0), Vhc, Vho, Q and Z are not well-constrained by this procedure, presumably because of correlations between parameters. However, values for Ca2+ and Mg2+ affinities appear to be critical for obtaining acceptable fits.

Table 3

Allosteric Regulation of Voltage-sensor Equilibria Is Unlikely to Account for the Dependence of Slo1 G-V Curves on Millimolar Ca2+ or Mg2+

Units(A) Ca2+ alone: unconstrained(B) &#x;[Mg2+]; 0 Ca2+(C) &#x;[Mg2+]; 0 Ca2+
Источник: mauitopia.us

CO2 mineralization and utilization by alkaline solid wastes for potential carbon reduction

Abstract

CO2 mineralization and utilization using alkaline solid wastes has been rapidly developed over the last ten years and is considered one of the promising technologies to stabilize solid wastes while combating global warming. Despite the publication of a number of reports evaluating the performance of the processes, no study on the estimation of the global CO2 reduction potential by CO2 mineralization and utilization using alkaline solid wastes has been reported. Here, we estimate global CO2 mitigation potentials facilitated by CO2 mineralization and utilization as a result of accelerated carbonation using various types of alkaline solid wastes in different regions of the world. We find that a substantial amount of CO2 (that is,  Gt per year) could be directly fixed and indirectly avoided by CO2 mineralization and utilization, corresponding to a reduction in global anthropogenic CO2 emissions of %. In particular, China exhibits the greatest potential worldwide to implement CO2 mineralization and utilization, where it would account for a notable reduction of up to % of China’s annual total emissions. Our study reveals that CO2 mineralization and utilization using alkaline solid wastes should be regarded as one of the essential green technologies in the portfolio of strategic global CO2 mitigation.

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The datasets generated during this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This study was supported by the Ministry of Science and Technology, Taiwan (ROC) under Grant No. MOSTI S.-Y.P. also received financial support from the National Taiwan University under Grant No. L H.K. was supported by the Korea Institute of Energy Technology Evaluation and Planning and the Ministry of Trade, Industry & Energy of the Republic of Korea under Grant No.

Author information

Affiliations

  1. Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei, Taiwan (ROC)

    Shu-Yuan Pan

  2. Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, Taiwan (ROC)

    Yi-Hung Chen

  3. Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, USA

    Liang-Shih Fan

  4. Department of Environmental Engineering, The University of Seoul, Seoul, South Korea

    Hyunook Kim

  5. State Key Laboratory of Clean Energy Utilization, College of Energy Engineering, Zhejiang University, Hangzhou, China

    Xiang Gao

  6. Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, Changsha, China

    Tung-Chai Ling

  7. Graduate Institute of Environmental Engineering, National Taiwan University, Taipei, Taiwan (ROC)

    Pen-Chi Chiang

  8. Research Institute of Tianying in Shanghai, China Tianying Inc., Shanghai, China

    Si-Lu Pei

  9. College of Environmental Science and Engineering, Tongji University, Shanghai, China

    Guowei Gu

Contributions

S.-Y.P. conceived and led the study. Y.-H.C., S.-L.P. and T.-C.L. provided data of alkaline waste production. L.-S.F., H.K., X.G., P.-C.C. and G.G. took part in the discussion of CO2 reduction potential. S.-Y.P. wrote the paper with input from all co-authors. All authors reviewed the manuscript.

Corresponding author

Correspondence to Shu-Yuan Pan.

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Competing interests

The authors declare no competing interests.

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Cisco IOS XE SD-WAN Qualified Command Reference

clear sdwan app-fwd cflowd flow-all

To clear the cflowd flows in all VPNs, use the clear sdwan app-fwd cflowd flow-all command in privileged exec mode.

clear sdwan app-fwd cflowd flow-all

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged exec (#)

Command History

ReleaseModification
Cisco IOS XE Release vCommand qualified for use in Cisco vManage CLI templates.

Usage Guidelines

This command can be used to clear all the cflowd flows from all VPNs in a Cisco IOS XE SD-WAN device.

Example

The following example shows how to clear the cflowd flows from all VPNs from a Cisco IOS XE SD-WAN device.

Related Commands

Command

Description
clear sdwan app-fwd cflowd statistics Clears all cflowd statistics from a Cisco IOS XE SD-WAN device.

clear sdwan app-fwd cflowd statistics

To clear the cflowd packet statistics, use the clear sdwan app-fwd cflowd statistics command in privileged EXEC mode.

clear sdwan app-fwd cflowd statistics

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

ReleaseModification
Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

This command can be used to clear the cflowd packet statistics from a Cisco IOS XE SD-WAN device.

Example

The following example shows how to clear the cflowd packet statistics from a Cisco IOS XE SD-WAN device.

Related Commands

Command

Description
clear sdwan app-fwd cflowd flow-all Clears all cflowd flows from a Cisco IOS XE SD-WAN device.

clear sdwan app-route statistics

To clear the app-route statistics from a Cisco IOS XE SD-WAN device, use the clear sdwan app-route statistics command in privileged EXEC mode.

clear sdwan app-route statistics

Syntax Description

This command has no keywords or arguments.

Command Default

None

Command Modes

Privileged EXEC (#)

Command History

ReleaseModification
Cisco IOS XE Release v

Command qualified for use in Cisco vManage CLI templates.

Usage Guidelines

This command can be used to clear the application aware routing statistics from a Cisco IOS XE SD-WAN device.

Example

The following example shows how to clear the app-route statistics from a Cisco IOS XE SD-WAN device.

clear sdwan appqoe dreopt

To clear DRE cache and restart DRE service, use the clear sdwan appqoe dreopt cache command in privileged EXEC mode.

clear sdwan appqoe dreopt { cache

Installation Guide

 Preparing Installation Sources

As explained in Chapter 2, Downloading Red Hat Enterprise Linux, two basic types of media are available for Red Hat Enterprise Linux: a minimal boot image and a full installation image (also known as a binary DVD). If you downloaded the binary DVD and created a boot DVD-ROM or USB drive from it, you can proceed with the installation immediately, as this image contains everything you need to install the system.

However, if you use the minimal boot image, you must also configure an additional source of the installation. This is because the minimal boot image only contains the installation program itself and tools needed to boot your system and start the installation; it does not include the software packages to be installed on your system.

The full installation DVD ISO image can be used as the source for the installation. If your system will require additional software not provided by Red Hat, you should configure additional repositories and install these packages after the installation is finished. For information about configuring additional Yum repositories on an installed system, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The installation source can be any of the following:

  • : You can burn the binary DVD ISO image onto a DVD and configure the installation program to install packages from this disk.

  • : You can place the binary DVD ISO image on a hard drive and install packages from it.

  • : You can copy the binary DVD ISO image or the installation tree (extracted contents of the binary DVD ISO image) to a network location accessible from the installation system and perform the installation over the network using the following protocols:

    • : The binary DVD ISO image is placed into a Network File System (NFS) share.

    • , or : The installation tree is placed on a network location accessible over , , or .

When booting the installation from minimal boot media, you must always configure an additional installation source. When booting the installation from the full binary DVD, it is also possible to configure another installation source, but it is not necessary - the binary DVD ISO image itself contains all packages you need to install the system, and the installation program will automatically configure the binary DVD as the source.

You can specify an installation source in any of the following ways:

  • In the installation program's graphical interface: After the graphical installation begins and you select your preferred language, the Installation Summary screen will appear. Navigate to the Installation Source screen and select the source you want to configure. For details, see:

  • Using a boot option: You can specify custom boot options to configure the installation program before it starts. One of these options allows you to specify the installation source to be used. See the option in Section , “Configuring the Installation System at the Boot Menu” for details.

  • Using a Kickstart file: You can use the command in a Kickstart file and specify an installation source. See Section , “Kickstart Commands and Options” for details on the Kickstart command, and Chapter 27, Kickstart Installations for information about Kickstart installations in general.

 Installation Source on a Hard Drive

Hard drive installations use an ISO image of the binary installation DVD. To use a hard drive as the installation source, transfer the binary DVD ISO image to the drive and connect it to the installation system. Then, boot the Anaconda installation program.

You can use any type of hard drive accessible to the installation program, including USB flash drives. The binary ISO image can be in any directory of the hard drive, and it can have any name; however, if the ISO image is not in the top-level directory of the drive, or if there is more than one image in the top-level directory of the drive, you will be required to specify the image to be used. This can be done using a boot option, an entry in a Kickstart file, or manually in the Installation Source screen during a graphical installation.

A limitation of using a hard drive as the installation source is that the binary DVD ISO image on the hard drive must be on a partition with a file system which Anaconda can mount. These file systems are , , , , and (). Note that on Microsoft Windows systems, the default file system used when formatting hard drives is , and the file system is also available; however, neither of these file systems can be mounted during the installation. If you are creating a hard drive or a USB drive to be used as an installation source on Microsoft Windows, make sure to format the drive as .

The file system does not support files larger than 4 GiB. Some Red Hat Enterprise Linux 7 installation media can be larger than that, which means you cannot copy them to a drive with this file system.

When using a hard drive or a USB flash drive as an installation source, make sure it is connected to the system when the installation begins. The installation program is not able to detect media inserted after the installation begins.

 Installation Source on a Network

Placing the installation source on a network has the advantage of allowing you to install multiple systems from a single source, without having to connect and disconnect any physical media. Network-based installations can be especially useful when used together with a TFTP server, which allows you to boot the installation program from the network as well. This approach completely eliminates the need for creating physical media, allowing easy deployment of Red Hat Enterprise Linux on multiple systems at the same time. For further information about setting up a TFTP server, see Chapter 24, Preparing for a Network Installation.

 Installation Source on an NFS Server

The installation method uses an ISO image of the Red Hat Enterprise Linux binary DVD placed in a server's exported directory, which the installation system must be able to read. To perform an NFS-based installation, you will need another running system which will act as the NFS host.

For more information about NFS servers, see the Red Hat Enterprise Linux 7 Storage Administration Guide.

The following procedure is only meant as a basic outline of the process. The precise steps you must take to set up an NFS server will vary based on the system's architecture, operating system, package manager, service manager, and other factors. On Red Hat Enterprise Linux 7 systems, the procedure can be followed exactly as documented. For procedures describing the installation source creation process on earlier releases of Red Hat Enterprise Linux, see the appropriate Installation Guide for that release.

Procedure  Preparing for Installation Using NFS

  1. Install the nfs-utils package by running the following command as :

  2. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to a suitable directory on the NFS server. For example, you can create directory for this purpose and save the ISO image here.

  3. Open the file using a text editor and add a line with the following syntax:

    /exported_directory/clients

    Replace /exported_directory/ with the full path to the directory holding the ISO image. Instead of clients, use the host name or IP address of the computer which is to be installed from this NFS server, the subnetwork from which all computers are to have access the ISO image, or the asterisk sign () if you want to allow any computer with network access to the NFS server to use the ISO image. See the man page for detailed information about the format of this field.

    The following is a basic configuration which makes the directory available as read-only to all clients:

    /rhel7-install *
  4. Save the file after finishing the configuration and exit the text editor.

  5. Start the service:

    If the service was already running before you changed the file, enter the following command instead, in order for the running NFS server to reload its configuration:

After completing the procedure above, the ISO image is accessible over and ready to be used as an installation source.

When configuring the installation source before or during the installation, use as the protocol, the server's host name or IP address, the colon sign (), and the directory holding the ISO image. For example, if the server's host name is and you have saved the ISO image in , specify as the installation source.

 Installation Source on an HTTP, HTTPS or FTP Server

This installation method allows for a network-based installation using an installation tree, which is a directory containing extracted contents of the binary DVD ISO image and a valid file. The installation source is accessed over , , or .

For more information about HTTP and FTP servers, see the Red Hat Enterprise Linux 7 System Administrator's Guide.

The following procedure is only meant as a basic outline of the process. The precise steps you must take to set up an FTP server will vary based on the system's architecture, operating system, package manager, service manager, and other factors. On Red Hat Enterprise Linux 7 systems, the procedure can be followed exactly as documented. For procedures describing the installation source creation process on earlier releases of Red Hat Enterprise Linux, see the appropriate Installation Guide for that release.

Procedure  Preparing Installation Using HTTP or HTTPS

  1. Install the httpd package by running the following command as :

    An server needs additional configuration. For detailed information, see section Setting Up an SSL Server in the Red Hat Enterprise Linux 7 System Administrator's Guide. However, is not necessary in most cases, because no sensitive data is sent between the installation source and the installer, and is sufficient.

    If your Apache web server configuration enables SSL security, make sure to only enable the protocol, and disable and . This is due to the POODLE SSL vulnerability (CVE). See mauitopia.us for details.

    If you decide to use and the server is using a self-signed certificate, you must boot the installer with the option.

  2. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to the HTTP(S) server.

  3. Mount the binary DVD ISO image, using the command, to a suitable directory:

    Replace /image_directory/mauitopia.us with the path to the binary DVD ISO image, and /mount_point/ with the path to the directory in which you want the content of the ISO image to appear. For example, you can create directory for this purpose and use that as the parameter of the command.

  4. Copy the files from the mounted image to the HTTP server root.

    This command creates the directory with the content of the image.

  5. Start the service:

After completing the procedure above, the installation tree is accessible and ready to be used as the installation source.

When configuring the installation source before or during the installation, use or as the protocol, the server's host name or IP address, and the directory in which you have stored the files from the ISO image, relative to the HTTP server root. For example, if you are using , the server's host name is , and you have copied the files from the image to , specify as the installation source.

Procedure  Preparing for Installation Using FTP

  1. Install the vsftpd package by running the following command as :

  2. Optionally, open the configuration file in a text editor, and edit any options you want to change. For available options, see the man page. The rest of this procedure assumes that default options are used; notably, to follow the rest of the procedure, anonymous users of the FTP server must be permitted to download files.

    If you configured SSL/TLS security in your file, make sure to only enable the protocol, and disable and . This is due to the POODLE SSL vulnerability (CVE). See mauitopia.us for details.

  3. Copy the full Red Hat Enterprise Linux 7 binary DVD ISO image to the FTP server.

  4. Mount the binary DVD ISO image, using the command, to a suitable directory:

    Replace /image_directory/mauitopia.us with the path to the binary DVD ISO image, and /mount_point with the path to the directory in which you want the content of the ISO image to appear. For example, you can create directory for this purpose and use that as the parameter of the command.

  5. Copy the files from the mounted image to the FTP server root:

    This command creates the directory with the content of the image.

  6. Start the service:

    If the service was already running before you changed the file, restart it to ensure the edited file is loaded. To restart, execute the following command:

After completing the procedure above, the installation tree is accessible and ready to be used as the installation source.

When configuring the installation source before or during the installation, use as the protocol, the server's host name or IP address, and the directory in which you have stored the files from the ISO image, relative to the FTP server root. For example, if the server's host name is and you have copied the files from the image to , specify as the installation source.

Источник: mauitopia.us

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