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
✍ Scribed by Manuela Körner; Rudi van Eldik
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 360 KB
- Volume
- 1999
- Category
- Article
- ISSN
- 1434-1948
No coin nor oath required. For personal study only.
✦ Synopsis
Keywords: Cytochrome c / Chromium(v) / Saturation kinetics / Separation of K and k ET / Volume profile / Kinetics
The irreversible outer-sphere electron-transfer reaction High-pressure experiments were performed at two different pH values. The kinetic (stopped-flow) and thermodynamic between trans-bis(2-ethyl-2-hydroxybutanoato(2-))oxochromate(v) and cytochrome c II was investigated as a function of (electrochemical) measurements as a function of pressure enabled the construction of a volume profile for the system pH, concentration, temperature and pressure. The plot of the observed pseudo-first order rate constant as a function of the at 279 K. The activation volumes for the redox process are -9.2 ± 0.2 (pH 5.0) and -11.1 ± 0.8 cm 3 mol -1 (pH 4.7), and the Cr V concentration shows a clear trend towards saturation at higher Cr V concentrations, from which the precursor overall reaction volumes were estimated to be -7 ± 2 (pH 5.0) and -10 ± 2 cm 3 mol -1 (pH 4.7) . The transition state of the formation constant and the electron-transfer rate constant could be separated (K = 37 ± 5 M -1 and k ET = 1510 ± 180 s -1 at redox reaction lies to a large extent on the product side and can be described as "late". The results are discussed in pH 4.8 and 279 K). In the low Cr V concentration range the second-order electron-transfer rate contants were measured comparison to earlier measurements using cobalt and ruthenium complexes as reaction partners for cytochrome c. as a function of temperature (∆H = 20.9 ± 0.6 kJ mol -1 ; ∆S = -79.9 ± 2.1 J K -1 mol -1 ; ∆G (279 K) = 43.2 kJ mol -1 ).
represent K•k ET . If K[Red] >> 1, then the observed rate [a] Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, well as a series of chelated Co(II/III) diimine com-Egerlandstraße 1, D-91058 Erlangen, Germany
plexes. [12Ϫ14] In these systems precursor formation was so