ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Some Aspects of Electron-Transfer Reaction of Ascorbate with Quinones

Ž. Anusevičius, A. Ramanavičius, and J. Šarlauskas

Institute of Biochemistry of Lithuanian Academy of Sciences, 2600 Vilnius, Lithuania

Abstract: A single-electron oxidation of ascorbate by a series of low-potential quinones was investigated. It was determined that bimolecular rate constants correlate with the single-electron reduction potential (E₇¹) of quinones. The 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 transfer of proton. This position to some extent was supported by the fact that over pH range, where no protonation/depratonation of reagents occurs, the coefficient of proportionality (∆ log{k_exp}∆ pH) for most active quinones in the ascorbate oxidation reaction was close to 0.5.

Full paper in Portable Document Format: 525a643.pdf

Chemical Papers 52 (5) 643–649 (1998)