Synergistic Effect of Binary Compositions of Pentadigalloyl Glucose with Plant Phenols in the Reaction with Hydrazyl Radical

It has been established that the maximum synergistic effect (more than 100%) is characteristic of the binary mixtures of pentadigalloyl glucose mixed with protocatechuic and vanillic acids in a ratio of 90 : 10 vol % in the reaction with the 2,2'-diphenyl-1-picrylhydrazyl radical in benzene. With an increase in the polarity of the solvent (dimethyl sulfoxide), an increase in the maximum synergistic effect by 15–20% on the average is observed. Using the methods of quantum chemical calculations and difference UV spectroscopy, it is shown that the resulting effect of the compositions of pentadigalloyl glucose with monomeric phenols depends on the following two mechanisms of synergistic action: the first mechanism is related to the formation of the intermolecular H-complex between reagents, which exhibits higher antiradical activity than that of the initial compounds; the second one is associated with the reduction of oxidized forms of the weaker antioxidant (monomeric phenol) by the stronger antioxidant (pentadigalloyl glucose). The mixture of pentadigalloyl glucose with methoxylated forms of plant phenols is a promising synergistic composition with high antiradical activity.