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Digitale Medien

Kinetics and Mechanism of the Outer-Sphere Oxidation of Horse-Heart Cytochrome c by an Anionic Chromium(v) Complex - Kinetic Evidence for Precursor Formation and a Late Electron-Transfer Transition State (1999)

Körner, Manuela ; van Eldik, Rudi

Weinheim : Wiley-Blackwell

Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1805-1812

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ISSN: 1434-1948

Schlagwort(e): Cytochrome c ; Chromium(v) ; Saturation kinetics ; Separation of K and kET ; Volume profile ; Kinetics ; Chemistry ; General Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The irreversible outer-sphere electron-transfer reaction between trans-bis(2-ethyl-2-hydroxybutanoato(2-))oxochromate(v) and cytochrome cII was investigated as a function of pH, concentration, temperature and pressure. The plot of the observed pseudo-first order rate constant as a function of the CrV concentration shows a clear trend towards saturation at higher CrV concentrations, from which the precursor formation constant and the electron-transfer rate constant could be separated (K = 37 ± 5 M-1 and kET = 1510 ± 180 s-1 at pH 4.8 and 279 K). In the low CrV concentration range the second-order electron-transfer rate contants were measured as a function of temperature (ΔH# = 20.9 ± 0.6 kJ mol-1; ΔS# = -79.9 ± 2.1 J K-1 mol-1; ΔG# (279 K) = 43.2 kJ mol-1). High-pressure experiments were performed at two different pH values. The kinetic (stopped-flow) and thermodynamic (electrochemical) measurements as a function of pressure enabled the construction of a volume profile for the system at 279 K. The activation volumes for the redox process are -9.2 ± 0.2 (pH 5.0) and -11.1 ± 0.8 cm3 mol-1 (pH 4.7), and the overall reaction volumes were estimated to be -7 ± 2 (pH 5.0) and -10 ± 2 cm3 mol-1 (pH 4.7) . The transition state of the redox reaction lies to a large extent on the product side and can be described as “late”. The results are discussed in comparison to earlier measurements using cobalt and ruthenium complexes as reaction partners for cytochrome c.

Zusätzliches Material: 7 Ill.

Materialart: Digitale Medien

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Digitale Medien

Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes - The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap (1999)

Poth, Tilo ; Paulus, Helmut ; Elias, Horst ; [weitere]

Weinheim : Wiley-Blackwell

Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 643-650

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ISSN: 1434-1948

Schlagwort(e): Cobalt(III) complexes ; Tetrapodal pentadentate ligand ; Hydrolysis ; Kinetics ; Mechanism ; Chemistry ; General Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Multi-wavelength stopped-flow spectrophotometry was used to study the kinetics of base hydrolysis of the octahedral cobalt(III) complex CoLCl2+ (2), in which the tetrapodal pentadentate ligand L has an NN4 donor set and forms a square-pyramidal coordination cap [L = 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine, 1]. The kinetic investigation, carried out at different temperatures, pressures and ionic strengths I, led to second-order kinetics, rate = kOH [2][OH-], with kOH = 0.139 ± 0.001 M-1s-1 (I = 0.1 M) and kOH = 0.0570 ± 0.0004 M-1s-1 (I = 1.0 M) at 298 K. The temperature and pressure dependence of kOH resulted in ΔH

Zusätzliches Material: 5 Ill.

Materialart: Digitale Medien

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