Effect of C-C Bond Type on the Radical Scavenging Activity of Hydroxy Stilbenes: Theoretical Insights in the Gas and Liquid Phase.

Density functional theory/Becke's three-parameter hybrid functional combined with the Lee-Yang-Parr correlation functional (DFT/B3LYP) was used to examine the radical scavenging potential of resveratrol, piceatannol, and their dehydro/dihydro counterparts. For this reason, the values of molecular descriptors predicting the hydrogen atom transfer (HAT) and the single electron transfer preceding (SET-PT) or following a proton transfer (SPLET) were computed in the gas and liquid (benzene, water) phases. The double bond, resulting in molecular planarity, was predicted to favor the single hydrogen or electron transfer. The triple bond, resulting in a linear backbone, was predicted to decrease the ease of these transfers, whereas the saturation, resulting in loss of planarity, was expected to decrease the activity even more. The impact of saturation was predicted to be detrimental for resveratrol. However, for piceatannol, an enhancement of activity was proposed only under stepwise HAT because allylic hydrogen atoms could be prone for abstraction after the formation of quinone. The predictions (gas, liquid phase) were in agreement with experimental evidence for resveratrol and its derivatives. The lipophilicity, which may affect antioxidant activity in real systems, increased according to partition coefficient (log P) values as follows: dihydrostilbene > stilbene > dehydrostilbene. On the basis of dipole moment values, no clear trend was observed.