Antiradical potential of phenolic compounds fingerprints of propolis extracts: DFT approach

Phenolic compounds are the major chemical constituents of propolis extracts (PE) and are characterized by possessing antiradical activity. In this work the structure-antiradical properties relationship of flavonoids (chrysin, galangin, pinocembrin and pinostrobin) and phenolic acid (caffeic acid phenethyl ester) commonly found in PE was investigated trough M05-2X functional in conjunction with the 6-31G(d,p) and 6-31+G(d,p) basis sets, considering the structural properties, and free-radical inhibition mechanism: H-atom transfer (HAT), the stepwise electron-transfer-proton-transfer (SPLET) and the sequential proton loss electron transfer (SET-PT). To complement the ability of phenolic compounds to act as antiradical the chemical indexes and Fukui indexes were analyzed. Thermodynamically, the HAT mechanism contributes much in the antiradical activity of reactive group (O-H and C-H) of phenolic compounds. All compounds present a greater tendency to give electrons than to attract them. We found different reactive sites for nucleophilic, electrophilic and radical attack in molecules, which could mark differences in their antiradical activity. (C) 2015 Elsevier B.V. All rights reserved.