Electrochemical oxidation of the synthetic anthocyanin analogue 4-methyl-7,8-dihydroxyflavylium salt

The oxidation of the synthetic flavylium 4-methyl-7,8-dihydroxyflavylium (analysed for the first time using electrochemical tools) was studied and compared with kuromanin, an anthocyanin present in raspberry Rubus idaeus, using cyclic and square voltammetry. Most studies were done at pH 1 where the dominant species is the flavylium cation. This pH also corresponds to the highly acidic environment of the stomach. For kuromanin, the electrochemical signal is due to the oxidation of the catechol 3′,4′-dihydroxyl groups on ring B and corresponds to a two-electron two-proton reversible reaction coupled to an irreversible homogeneous chemical reaction. A similar behaviour was found for the synthetic flavylium. However, the electrochemical signal can only be due to the oxidation of the o-dihydroxy groups in ring A since no such groups are present on ring B. The oxidation occurs at a potential more favourable than that of the natural compound. This fact may be relevant as to a possible antioxidant role of the synthetic analogues.