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

Reactions between horseradish peroxidase (HRP) compound I and II and some natural phenolic antioxidants were studied at pH 7. The bimolecular rate constants for these reactions were determined using a sequential mixing stopped-flow spectrometer. The rate constants for the reactions of compound I were found to be two orders of magnitude higher than those for compound II. The phenols under study showed a significant difference in their one-electron reduction potential values. As the rate constants also changed systematically with their one-electron potentials, the Marcus theory of electron transfer was applied to the above determined rate constants and the thermodynamic driving force (ΔG°), from which the reorganization energy (λ) for the electron transfer from phenols to both compound I and II was estimated.