Bile acids: Electrochemical oxidation on bare electrodes after acid-induced dehydration

Bile acids and sterols in general have long been considered practically inactive for direct redox processes. Herein, a novel way of electrochemical oxidation of primary bile acids is reported, involving an initial acid-induced dehydration step, as confirmed by capillary electrophoresis–mass spectrometry, thereby extending the electrochemical activity of the steroid core. Oxidation potentials were found to be ca + 1.2 V vs. Ag/AgNO₃ in acetonitrile on boron doped diamond, glassy carbon, and platinum electrodes in a mixed acetonitrile–aqueous medium employing perchloric acid as a chemical reagent, and as a supporting electrolyte for the voltammetric measurements. The chemical step proved to be effective only for primary bile acids, possessing an axial 7α-hydroxyl group, which is a prerequisite for providing a well-developed voltammetric signal. Preliminary results show that other steroids, e.g., cholesterol, can also be oxidized by employing a similar approach.