Some aspects of electron-transfer reaction of ascorbate with quinones

A single-electron oxidation of ascorbate by a series of low-potential quino nes was investigated. It was determined that bimolecular rate constants cor relate with the single-electron reduction potential (E-7(1)) of quinones. T he results were interpreted in the framework of the "outer-sphere" electron -transfer theory given by Marcus. The consistency of Marcus model for these reactions was verified by comparison of the experimentally determined data with the predicted ones. Energetic considerations suggest that the single- electron transfer between ascorbate and quinone proceeds with a concomitant transfer of proton rather than via an electron transfer and a subsequent t ransfer of proton. This position to some extent was supported by the fact t hat over pH range, where no protonation/depratonation of reagents occurs, t he coefficient of proportionality (Delta log{k(exp)}Delta pH) for most acti ve quinones in the ascorbate oxidation reaction was close to 0.5.