Electrochemical behaviour of hypocrellin A in acetonitrile and aqueous micellar media

Abstract

The electrochemical behaviour of hypocrellin A (HAH₂) has been studied in acetonitrile and in aqueous micellar media. In acetonitrile (CH₃CN) the two successive one-electron transfers are reversible on the cyclic voltammetry time scale and allow different reduced forms of HAH₂ to be produced by exhaustive electrolysis. In addition, the one-electron reduction of HAH₂ has been studied by UV-visible and EPR spectroscopy, showing that the one-electron transfer is associated with a protonation phenomenon leading to the formation of HAH₂^•− and HAH₃^•. In an aqueous micellar medium the first reduction step behaves similarly to that in an organic medium and has allowed us to establish the influence of the pH value on E_1/2 and to determine the two pK_a values of HAH₂ , while pK_a values of the one-electron reduced forms of HAH₂ have been evaluated.