Reactivity of Decagalloylglucose in Complexation and Radical Oxidation Processes

Abstract

NMR, FTIR, and differential UV spectroscopy were used to confirm the formation of intermolecular hydrogen-bonded complexes in binary systems of decagalloylglucose (tannic acid) with phenolcarboxylic acids and their derivatives in benzene at 298 ± 2 K. Job’s plots were used to determine a 1 : 2 stoichiometry for the decagalloylglucose–phenolic acid complex. Stability constants obtained by the Benesi–Hildebrand method showed that the equilibrium is shifted toward the formation of associates. Complexation forms the basis of the antiradical synergistic effect of binary tannin–phenolic systems in reactions with the 2,2′-diphenyl-1-picrylhydrazyl radical. Density functional theory calculations showed that the ionization energies of complexes involving methoxylated and hydroxylated acids are lower than those of the corresponding individual components, indicating enhanced reducing and antiradical properties of the complexes compared with the free compounds.