A theoretical study of the structure-radical scavenging activity of trans-resveratrol analogues and cis-resveratrol in gas phase and water environment.

Quantum calculations based on the density functional theory (DFT) have been employed to study the relation between the structure and antioxidant activity of trans-resveratrol (TR), cis-resveratrol (CR), trans-4.4'-dihydroxystilbene (trans-4,4'-DHS), trans-3,4-dihydroxystilbene (trans-3,4-DHS), trans-3,4,4'-trihydroxystilbene (trans-3,4,4'-THS), trans-3,4,5-trihydroxystilbene (trans-3,4,5-THS) and alpha,beta-dihydro-3,4',5-trihydroxystilbene (alpha,beta-dihydro-3,4',5-THS) in the gas phase and water environment. We have shown that the antioxidant activity of trans-stereoisomers of the compounds considered is related to their phenoxy radicals showing a planar and semiquinone conformation that allows delocalization of the unpaired electron through the whole trans-stilbene skeleton. The calculations have revealed that trans-3,4-DHS, trans-3,4,4'-THS, trans-3,4,5-THS and trans-4,4'-DHS exhibit higher antioxidant activity than TR, while alpha,beta-dihydro-3,4',5-THS and CR are less efficient antioxidants than TR. We have proved that all compounds have higher ability to donate hydrogen atom in the gas phase than in the presence of water medium in which they are very sensitive to electron donation. The results obtained demonstrate that the H-transfer mechanism for scavenging of the free radicals is more preferable than the single-electron transfer in both types of environment. They are consistent with the experiments confirming the specific biological activity of the compounds considered.