Structural Basis for Antioxidant Activity of trans-Resveratrol: Ab Initio Calculations and Crystal and Molecular Structure

From the experimental crystal structure and ab initio calculations on resveratrol and its derivatives, structural features of mechanistic importance are described. The molecular structure reveals the relative coplanarity of the trans-stilbene skeleton, and the molecular packing in the solid state shows an extensive hydrogen bond network that elucidates the flip-flop motion of the three hydroxyl groups that alternately form and break H bonds with each of the neighboring phenolic oxygens. The dynamic behavior provoked by the alternation of hydrogen bond formation and breaking can result in the ready mobility of up to three hydrogen atoms per resveratrol molecule that can be transferred to reactive oxidants that are rich in electron density. In addition, theoretical studies confirm the planarity of resveratrol as well as for half of the molecule of a condensation dimeric derivative of resveratrol, trans-σ-viniferin. Furthermore, these studies show the p-4'-OH group to be more acidic compared to the other two m-OH groups. These features correlate with the biological activity of resveratrol as an antioxidant and support earlier studies showing H-atom transfer to be the dominant mechanism by which phenolic antioxidants intercept free radicals. Keywords: Resveratrol; crystal structure; ab initio calculations; flip-flop hydrogen bonding; structural features; antioxidant activity