Electrochemical and Antioxidant Properties of (+)-Catechin, Quercetin and Rutin

The electrochemical properties of three structurally different flavonoids ((+)-catechin, quercetin and rutin) on a glassy carbon electrode were studied at different pH by cyclic, differential pulse and square-wave voltammetry. It was determined that in all investigated compounds oxidation of catechol 3',4'-dihydroxy group on the B-ring (the first oxidation peak) occurs. This process is reversible, pH dependent and includes the transfer of 2e and 2H. The products of electrochemical oxidation of all investigated flavonoids (especially of quercetin) strongly adsorb on the electrode surface. In terms of quantification, the absorbance value, proportional to the remaining ABTS+• concentration, is measured after a fixed reaction time. Results are expressed as Trolox equivalents (TEAC value), that is, as the concentration of Trolox solution (mmol dm) with an antioxidant capacity equivalent to that found for 1.0 mmol dm of the substance under investigation. It was found that the TEAC values depend on the concentration of the investigated compounds. The activity sequence of the investigated, structurally different, flavonoids follows the sequence: quercetin > (+)-catechin > rutin.