Changes in electronic structures of flavonoids upon electrochemical oxidation and a theoretical model for the estimation of the first oxidation potential

This paper studies the electronic structures of the 14 flavonoids and their cation and radical forms involved in the first electrochemical oxidation step, associated with the oxidation peak appearing at potential Ep1. The sum of differences in Net atomic charges on atoms in skeleton of cations and neutral flavonoids (Σs(C)ΔNACCat.-Neut.) and the sum of Atomic orbital electron and spin populations on atoms in skeleton of radicals (Σs(C)AOEP and Σs(C)AOSP) revealed that electron distribution between skeleton atoms and active OH oxygen is more evenly distributed in cations and radicals of flavonoids that are more prone to oxidation. Those less susceptible to oxidation are more polarized, i.e. the skeleton becomes more positively charged. Also, Σs(C)AOSP proved to be an excellent descriptor for modelling the first oxidation potential, especially in combination with Σs(C)pzAOEP (common model for pH = 3 and 7 yielded R2 = 0.978 and S.E. = 0.43).