engleski

Contribution of C-ring Hydrogens to Free Radical Scavenging by Equol

Epidemiological studies have shown that diets rich in soy isoflavones are beneficial to human health [1]. However, these benefits aren’t ascribed to parental molecules of ingested isoflavones but to their intestinal metabolites [2]. Among these metabolites, equol has been extensively studied because of its bioactivity [3, 4], which may help to reduce the incidence of age-related disorders [1]. In this work, free radical scavenging potency of equol was investigated by using M06-2X/6-311++G(d, p) level of theory, accompanied with the TST and Eckart tunneling corrections for the estimation of rate constants. The influence of solvents was calculated with an implicit continuum solvation model, SMD [5]. Spin unrestricted calculations were used for openshell systems. Local minima and transition states (TSs) were identified by the number of imaginary frequencies (0 and 1, respectively). Intrinsic reaction coordinate calculation was performed on both sides of the TS to confirm that it properly connects with the corresponding reactants and products. All computations were performed in gas-phase, pentyl ethanoate and water at 298.15 K. BDE related to H-atom donation was calculated as described elsewhere [6]. Performed electronic structure and kinetic calculations indicate phenolic hydrogens of equol as much more abstractable than C-ring hydrogens. Thus, the C-ring hydrogens are poor HOO• scavengers with negligible contribution to equol antioxidant potency. This is in line with the known facts related to phenolic O−H vs C−H reactivity and structural requirements needed for antioxidant activity of flavonoids, but opposite to recently published predictions.

equol ; BDE ; kinetics ; tunneling ; scavenging potency

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