Thermochemistry of antioxidant action of isoflavones and their deprotonated forms in aqueous solution: hydrogen or electron transfer?

Abstract Isoflavones possessing several weak acidic hydroxyl groups can undergo successive deprotonations in aqueous solutions. Therefore, their antioxidant properties cannot be ascribed only to the neutral forms but also corresponding phenoxide anions. It was already confirmed that isoflavones prefer formation of dianions solution. For eight and preferred (poly)deprotonated forms, thermochemistry hydrogen atom transfer electron abstraction studied terms reaction enthalpies, i.e., O—H bond dissociation enthalpies ionization potentials. Our results clearly indicate increase negative charge causes significant drop potential enthalpy. On other hand, proton affinities show opposite trend. Thus, it is unfeasible find a generally valid trend for — strongly depend on structure isoflavone, especially number/positions OH groups.