How Do Phenolic Compounds React toward Superoxide Ion? A Simple Electrochemical Method for Evaluating Antioxidant Capacity

The reactivities of different phenols and polyphenols versus superoxide ion (O-2(center dot-)) were investigated as an easy-to-handle electrochemical method for evaluating antioxidant capacities. In view of this application, the O-2/O-2(center dot-) couple and associated reactions between O-2(center dot-) and polyphenols (or phenols) were examined in an aprotic solvent [dimethylformamide (DMF)] by cyclic voltammetry. Comparisons based on simple criteria (reversibility of the O-2 reduction in the presence of the phenolic compound, electron stoichiometry, or apparent kinetic constants) allow discriminations between the possible mechanistic pathways (acid-base or radical reaction type). The results highlight that the proton-transfer and radical-transfer pathways are both present for monophenols and polyphenols, with the relative contributions of the two pathways depending on the phenol structure. In agreement with the literature, polyphenols containing an o-diphenol ring (as in flavonoids) were found to present the highest reactivities.