Photosensitized isomerization of resveratrol: Evaluation of energy and electron transfer pathways.

Resveratrol (3,5,4′-trihydroxystilbene, RSV) is a natural stilbene synthetized as trans -isomer in plants exposed to oxidative stress. In order to understand the mechanism involved during photosensitized degradation of trans -resveratrol, steady-state and time-resolved experiments were performed and compared with quantum-chemical calculations using density functional theory (DFT). Pterin (Ptr), a well-known photosensitizer, under UV-A radiation induces the oxidation of several biomolecules mainly through electron-transfer mechanisms. On the one hand, it was observed that trans -RSV participates in an energy-transfer pathway with Ptr triplet excited state (3Ptr*) forming 3 trans -RSV*, which dissipates the energy by isomerization to cis -RSV. On the other hand, RSV neutral radical (trans -RSV(-H)•) was detected in laser flash photolysis experiments, evidencing an electron-transfer mechanism. The electron-transfer from 3Ptr* to trans -RSV is a barely feasible reaction, however, more favorable is the formation of trans -RSV(-H)• in a reaction between trans -RSV and Ptr radical cation (Ptr•+), which is produced during irradiation. The combination of experimental and theoretical approaches evidences the capability of trans -RSV to undergo energy-transfer (feasible by DFT calculations) and/or one-electron transfer pathways with 3Ptr*. These findings reveal the mechanisms involved in the interaction of trans -RSV and pterin excited states and provide information on the antioxidant action of resveratrol during photosensitized oxidation of biomolecules. [Display omitted] • Resveratrol is a natural polyphenol synthesized against oxidative stress in plants. • Pterin excited states with the ability to oxidize biomolecules are deactivated by resveratrol. • Energy transfer from trans -resveratrol to pterin triplet excited state is feasible. • Resveratrol acts as electron donor to pterin triplet excited state. [ABSTRACT FROM AUTHOR]