Application of Marcus theory of electron transfer for the reactions between HRP compound I and II and 2,4-disubstituted phenols

Reactions between horseradish peroxidase (HRP) compound I and II and some n atural phenolic antioxidants were studied at pH 7. The bimolecular rate con stants for these reactions were determined using a sequential mixing stoppe d-flow spectrometer. The rate constants for the reactions of compound I wer e found to be two orders of magnitude higher than those for compound II. Th e phenols under study showed a significant difference in their one-electron reduction potential values. As the rate constants also changed systematica lly with their one-electron potentials, the Marcus theory of electron trans fer was applied to the above determined rate constants and the thermodynami c driving force (DeltaG degrees), from which the reorganization energy (lam bda) for the electron transfer from phenols to both compound I and II was e stimated. (C) 2000 Elsevier Science B.V. All rights reserved.