Mechanistic insight into the DPPH radical-scavenging activity of hydroxystilbene derivatives

Resveratrol is a naturally occurring hydroxystilbene derived from grapes and possesses multiple biological activities. Resveratrol and many hydroxystilbene derivatives exhibit antioxidant potential and can scavenge various free radicals, such as DPPH radical. In the present paper, with the aim to elucidate the mechanism underlying how DPPH radical is scavenged by hydroxystilbene derivatives, quantum chemical calculations were performed to estimate the theoretical parameters, including homolytic O–H bond dissociation enthalpies (BDEs) and adiabatic ionization potentials (IPs), of hydroxystilbene derivatives in ethanol. After examining the possible DPPH radical-scavenging reactions by hydroxystilbene derivatives, it was found that H-atom transfer is feasible on thermodynamic grounds, while the stepwise electron-transfer/proton-transfer process is unfavorable thermodynamically. Thus, it can be inferred that the H-atom transfer is more likely than the stepwise electron-transfer/proton-transfer process to be responsible for the hydroxystilbene derivatives’ DPPH radical-scavenging activity in ethanol.