Evaluation and comparison of antioxidant abilities of five bioactive molecules with C–H and O–H bonds in thermodynamics and kinetics

Abstract

In this work, the antioxidant abilities of NADH coenzyme analogue BNAH, F420 reduction prototype analogue F420H, vitamin C analogue iAscH⁻, caffeic acid, and (+)-catechin in acetonitrile in chemical reactions were studied and discussed. Three physical parameters of the antioxidant XH, homolytic bond dissociation free energy ΔG^°(XH), self-exchange HAT reaction activation free energy ΔG^≠_XH/X, and thermo-kinetic parameter ΔG^≠°(XH), were used to evaluate the antioxidant ability of XH in thermodynamics, kinetics, and thermo-kinetics. By comparing ΔG^°(XH), ΔG^≠_XH/X and ΔG^≠°(XH) of these five bioactive antioxidants to release hydrogen atoms, it is easy to find that iAscH⁻ is the best hydrogen atom donor both thermodynamically and kinetically among these antioxidants. Caffeic acid is the worst hydrogen atom donor thermodynamically, and F420H is the worst hydrogen atom donor kinetically. In addition, the thermodynamic hydride donating abilities of BNAH, F420H, and iAscH⁻ were also discussed, and the order of thermodynamic hydride donating abilities was BNAH > F420H > iAscH⁻. Four HAT reactions BNAH/DPPH^˙, (+)-catechin/DPPH^˙, F420H/DPPH^˙, and caffeic acid/DPPH^˙ in acetonitrile at 298 K were studied by the stopped-flow method. The actual order of H-donating abilities of these four antioxidants in the HAT reactions is consistent with the order predicted by thermo-kinetic parameters. It is feasible to predict accurately the antioxidant abilities of antioxidants using thermo-kinetic parameters.