THE SYNERGY OF THE ANTIRADICAL ACTION OF NATURAL PHENOLS IN MIXTURES WITH MONO- AND OLIGOSACCHARIDES

Abstract

It has been established that in an acidic medium with pH = 2, the rate of deactivation of the 2,2'-diphenyl-1-picrylhydrazyl radical in the reaction with natural phenolic compounds significantly increases in the presence of mono- and oligosaccharides compared to the additive action of the mixture. The maximum antiradical synergistic effect (65% and more) was shown by the binary compositions caffeic acid–maltotriose and dihydroquercetin–maltotriose in the ratio of 80:20% and 70:30%, respectively. Mixtures of saccharides with protocatechuic and pyrocatechuic acids turned out to be less active. For all groups of phenols, the synergistic activity increases with the transition from mono- to di- and trisaccharides. An increase in the medium pH from 2 to 9 actually leads to a complete leveling of antiradical synergism (up to 10%) in all studied phenol-saccharide mixtures, as well as to the appearance of antagonism effects at a high carbohydrate content in the composition. Using NMR spectroscopy, it has been established that the mechanism of synergism consists in the formation of a phenol–saccharide donor-type hydrogen complex between the reactants, which interacts with the radical more effectively than the corresponding monomers. An increase in sugar percentage in the mixture, as well as an increase in the medium pH, leads to the growth of the content of H-complexes of the acceptor-type when phenol acts as a proton acceptor, thus the reducing properties of the complexes and the synergistic effect of the compositions in the reaction with hydrazyl radical will decrease. As a structural parameter associated with the synergistic effect of the composition, the ionization potential of the phenolic component of the mixture, calculated by the DFT method, was used. The established linear relationship between the maximum synergistic effect of the phenol-saccharide mixture and the ionization potential of phenols can later be used to form semi-empirical models for predicting the effectiveness of the antiradical action of natural phenol-carbohydrate synergistic compositions. A comprehensive study of phenol-saccharide mixtures will expand the range of natural synergistic systems with expressed antiradical activity for practical use in pharmacy, perfumery, and the food industry.