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.

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