Surface electrochemical oxidation and polymerization mechanism of epicatechin

Electrochemical process of epicatechin, one of the flavonoids antioxidants, was studied here by cyclic voltammetry and semiempirical molecular orbital computation (MOPAC). Electrochemical oxidation of epicatechin showed a multistep mechanism with two anodic peaks being recognized at about +0.14 V and +0.52 V (vs. Ag/AgCl). The first peak is strong concentration dependent, showing an adsorptive feature between 1 × 10−8 M and 2 × 10−7 M, a diffusion controlled feature between 2 × 10−7 M and 1 × 10−5 M, and a surface polymerization feature between 1 × 10−5 M and 1 × 10−3 M. Computation showed that the first electron was released at 4′-hydroxyl group in B-ring. No charge delocalization occurs between A- and B-rings. Higher pH medium favors oxidation. The oxidation rate is faster in strong acidic or basic medium and slower in a weak acidic medium. This research may help to explain the complexity of antioxidant activity of flavonoids and as a complement method to characterize the role of flavonoids antioxidants in treating oxidative stress diseases.