Approach to elucidate the reaction mechanism of natural antioxidants using electrochemical methods

The oxidation reaction mechanisms of chlorogenic acid and caffeic acid, were studied by various electrochemical studies. Cyclic voltammetry (CV) and its digital simulation analysis, flow coulometry, and analysis of electrolytic oxidation products by HPLC-UV, ECD, MS detection were performed. These measurements clarified the mechanism of dimer formation associated with oxidation and the resulting increase in reducing power of the polyphenols. The reaction between DPPH radical and several antioxidants were monitored by CV. Antioxidants were classified into three groups with different reaction mechanisms depending on the substitution position of the OH group. The linear correlation between the DPPH radical scavenging activity and the number of electrons involved in the oxidation, n value, was proved. Thus, it was revealed that the subsequent chemical reaction following the oxidation is a key reaction that influences the antioxidant activity. Through the development of the electron conductor separating oil water (ECSOW) system and digital simulation analysis of CV, it was clarified that the electron transfer at the oil-water interface between Fe(CN)6 and ferrocene is proceeding by the ion transfer mechanism. A novel analytical method called liquid-liquid optical waveguide spectroscopy was developed, and fast electron transfer between ascorbic acid and DPPH radical at the miscible liquid/liquid interface was observed by the method.