Electron transfer reaction between cytochrome c and trisoxalatocobalt(III)

Abstract

The irreversible outer-sphere electron transfer reaction between the oxidant [Co(ox)₃]³⁻ and the redox protein horse heart cytochrome c^II according to the reaction,

[Co^III(ox)₃]³⁻ + cytochrome c^II6+ → [Co^II(ox)₃]⁴⁻ + cytochrome c^III7+

was studied as a function of pH, concentration, temperature and pressure using UV–Vis and stopped-flow techniques. The concentration dependence of the observed rate constant showed a saturation of the rate constant at high concentrations of [Co(ox)₃]³⁻, indicative of effective precursor formation between the reactants. The temperature (6–35 °C) and pressure (up to 1300 atm) dependencies at low and high complex concentrations were carried out and activation parameters (ΔH^‡, ΔS^‡, ΔV^‡) were determined. The results are discussed in reference to earlier studies performed in our laboratories and elsewhere, and the importance of efficient precursor formation in such reactions is highlighted.