Electrooxidation of flavonoids at platinum electrode studied by cyclic voltammetry

Flavonoids are natural vegetable dyes synthesized from phenylalanine. They are responsible for colour of blooming plant portions. Moreover, they are very important for human health due to their activity as free radical acceptors. Cyclic and differential pulse voltammetry was used in the determination of kinetic parameters of flavonoids electrooxidation. Electrochemical measurements of the oxidation of organic compounds can be helpful in understanding how these compounds are metabolised by living organisms. Flavonoids electrochemical oxidation is an irreversible reaction at a platinum electrode. In the case of morin hydrate, rutin, dihydroxyflavone, trihydroxyflavone, hesperidin, quercetin, the first step of the electrooxidation includes an exchange of two electrons during the oxidation of hydroxyl groups in the ring B. Hydroxyl groups in the rings A and C are probably oxidised in subsequent steps. The heterogeneous rate constants (kbh) determined for the flavonoids electrooxidation are as follows: morin – 3.59 × 10−4, rutin – 4.42 × 10−4, dihydroxyflavone – 4.54 × 10−4, trihydroxyflavone – 4.19 × 10−4, hesperidin – 4.50 × 10−4 and quercetin – 4.63 × 10−4 cm s−1. Their anodic transition coefficient ranged from 0.63 to 0.48 (n = 2). Xanthone and flavone were oxidised easiest and quickest among other substrates at the platinum electrode with the heterogeneous rate constants (kbh) of 7.08 × 10−4 and 6.46 × 10−4 cm s−1, respectively.