Reaction enthalpies of OH bonds splitting-off in flavonoids: The role of non-polar and polar solvent

- Antioxidant action thermodynamics is studied for 10 flavonoids in water and benzene.
- IEF-PCM B3LYP/6-311++G∗∗ approach is used for reaction enthalpies calculations.
- In the two solvents, preferred OH group and reaction mechanism are identified.
- Solvent can modify the effect of various structural features of flavonoids.

Flavonoids play important role in the scavenging of free radicals in biological systems. As the phenolic chain-breaking antioxidants they can act via three distinct mechanisms, namely hydrogen atom transfer (HAT), Single Electron Transfer-Proton Transfer (SET-PT) and Sequential Proton-Loss Electron-Transfer (SPLET). Therefore, it is inevitable to study the corresponding reaction enthalpies in solution-phase. For 10 naturally occurring flavonoids: apigenin, luteolin, fisetin, kaempferol, quercetin, epicatechin, taxifolin, tricetin, tricin and cyanidin, OH bond dissociation enthalpies, ionization potentials, proton dissociation enthalpies, proton affinities and electron transfer enthalpies were investigated using IEF-PCM B3LYP/6-311++G∗∗ method in benzene and water in order to: (i) identify the thermodynamically preferred mechanism and OH group in the two solvents and (ii) describe the solvent effect on the homolytic and heterolytic cleavage of OH groups in studied flavonoids.