Mechanistic study on the radical scavenging activity of viniferins

Abstract

As an important chemical component of grapes, viniferins are essential dimers of natural product resveratrol with good antioxidant activity. In this study, we have examined the antioxidant activity of two viniferin molecules (δ-viniferin and ε-viniferin) with ·OH/·OOH radicals. Density functional theory (DFT) calculations at the M062X/6–311++G(d,p)-SMD//M062X/6–311G(d,p) level of theory in the gas phase, water, and benzene used to examine two crucial radical scavenging pathways: hydrogen atom transfer (HAT) and the radical adduct formation (RAF). Then, the radical scavenging activities of the two molecules are compared kinetically and thermodynamically. The Gibbs free energy of activation (ΔG≠) and rate constant (kTST) are calculated using the conventional transition state theory (TST), and the results reveal that HAT and RAF processes compete in different solvents. Furthermore, molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) of both the compounds are computed to elucidate their antioxidant activity. The results show that the RAF site appears at the >C7C8< double bond position of δ- and ε-viniferins, and the most favorable HAT positions of δ-viniferin and ε-viniferin are 12′-OH and 12-OH, respectively; in addition, ε-viniferin is a more potent radical scavenging agent than δ-viniferin. These findings provide useful insights on the antioxidant activity of viniferins and different radical scavenging mechanisms of antioxidants, which can be beneficial for improving the practical utilization of resveratrol dimer and other analogs.