Catechin electrochemical oxidation mechanisms

The oxidation of flavonoids is of great interest because of their action as antioxidants with the ability to scavenge radicals by electron transfer processes. The electrochemical oxidation of the flavonoid (+)-catechin, was investigated, over a wide range of conditions, using cyclic, differential and square wave voltammetry. The oxidation mechanism proceeds in sequential steps, related with the catechol and resorcinol groups and the oxidation is pH dependent. The oxidation of the catechol 3',4'-dihydroxyl electron-donating groups occurs first, at very low positive potentials, and is a reversible reaction. The hydroxyl groups of the resorcinol moiety oxidised afterwards were shown to undergo an irreversible oxidation reaction. (+)-Catechin also adsorbs strongly on the electrode surface and the final oxidation product is not electroactive and blocks the electrode surface. (C) 2004 Elsevier B.V. All rights reserved.