Electrochemical and spectroscopic studies of the interaction of (+)-epicatechin with bovine serum albumin

The mechanism of the electrochemical oxidation of (+)-epicatechin (epiCAT) in a hydro-alcoholic medium, at a glassy carbon electrode, was studied using cyclic and square wave voltammetric techniques and at different pHs. It proceeds in a cascade mechanism related to the two resorcinol hydroxyl groups and the other three hydroxyl groups in epiCAT which present electroactivity and is pH-dependent. The oxidation of the 3 ',4 '-dihydroxyl moiety, occurs first at a very low positive potential, and it is a two-electron/two proton reversible reaction. The product obtained from the oxidation of the 3 ',4 '-dihydroxyl moiety then undergoes a chemical reaction followed by an electrochemical process to give an electroinactive product. The proposed mechanism is an ECE type mechanism. After the addition of bovine serum albumin (BSA) to epiCAT solution, the oxidation peak currents decreased with no peak potential shift and no new peaks appeared. The diffusion coefficients of both free and bound epiCAT were estimated from the cyclic voltammetry data (D-f = 2.37 x 10(-10) cm(2)s(-1) and D-b = 6.28 x 10(-11) cm(2)s(-1)). An epiCAT-BSA complex is formed with binding constant K-app = 1.8 x 10(4), calculated from UV-vis spectroscopy data.