EPR study of phenolic radical stabilization by grafting on SiO2

A hybrid [SiO2-GA] material has been synthesized by grafting Gallic acid (3,4,5-trihydroxybenzoic acid, GA) on SiO2 via formation of amide bonds between amine groups on aminopropyl-silica and the carboxyl group of GA. The spatial fixation of GA prevents polymerization effects. EPR spectroscopy shows that GA radicals on [SiO2-GA] show remarkable stability, comparable to that previously observed only for radicals in biological matrices on in soil organic matter. EPR reveals a bundle-like organization of the GA molecules on [SiO2-GA] material. The relation of these factors to the enhanced radical stability is discussed.