Square-wave and cyclic voltammetry of epicatechin gallate on glassy carbon electrode

The mechanism of electrochemical oxidation of (−)-epicatechin (EC) and (−)-epicatechin gallate (ECG) on a glassy carbon electrode was investigated over a wide range of conditions, using cyclic and square-wave voltammetry. Electrochemical behavior of gallic acid has been studied as well, in order to elucidate the influence of catechol and galloyl groups on the overall electrochemical response of ECG. The first oxidation peak of both catechins, ECG and EC, originates primarily from the oxidation of the catechol 3′,4′-dihydroxyl groups. The oxidation of galloyl group in the molecule of ECG constitutes only a minor component of the response, and causes the shift of the ECG peak potential (ca. 20 mV) towards more positive values when compared with the peak potential of EC. The oxidation of the catechol group is a two electron two proton reaction. After successive scans, the oxidation products of EC and ECG adsorb at the electrode surface, forming a polymeric film that undergoes reversible oxidation at a lower potential than the catechol group.