The relationship between the first oxidation potential and changes in electronic structures upon the electrochemical oxidation of flavonoids: Approach to O-glycosyl, galloyl and methoxy substituents

In continuation of our investigation of the dependence of the first electrochemical oxidation potential, Ep1, on the electronic structures of flavonoids, the potentials of nine additional flavonoids (hesperetin, daidzein, kaempferol, acacetin, naringin, neohesperidin, hesperidin, quercitrin, and gossypin) were assessed using square-wave voltammetry on a glassy-carbon electrode in aqueous buffer solutions with a pH of 3 and 7. Our standard model for the estimation of the Ep1, based on the sum of atomic orbital spin populations over the carbon atoms in the skeleton of the radical molecule, Σ s(C) AOSPRad, yielded S.E. = 0.063 and S.E.cv = 0.072 on this enlarged set of 29 flavonoids. We also introduced a new complementary model that yielded similar statistics, S.E. = 0.055 and S.E.cv = 0.059. This model was based on the differences in the net atomic charges between cations and neutral flavonoids also summed over the carbon atoms in their skeleton ( Σ s(C) ΔNACCat-Neut). Such an excellent agreement between Σ s(C) ΔNACCat-Neut and Ep1 may be proof that the electrochemical oxidation of all 29 flavonoids starts with ionization, i.e. abstraction of an electron, at both of the pHs indicated.