Hydrogen Evolution Facilitates Reduction of DNA Guanine Residues at the Hanging Mercury Drop Electrode: Evidence for a Chemical Mechanism

Guanine (G), as well as G residues in nucleosides, nucleotides and nucleic acids, undergo chemically reversible (but electrochemically irreversible) reduction/oxidation processes at the mercury‐based electrodes. It has been established that G is reduced to 7,8‐dihydroguanine at highly negative potentials. The reduction product is oxidized back to G around −0.25 V, giving rise to anodic peak G. Previous studies suggested involvement of a chemical mechanism involving electrochemically generated hydrogen radicals in the G reduction process. In this work we studied effects of cisplatin and pH on the G reduction process. We have found that catalytic hydrogen evolution accompanying electrochemical reduction of cisplatin markedly facilitates reduction of G. Minimum negative potential required for G reduction were shifted to less negative values and correlated with the onset of catalytic currents of cisplatin. Analogous shifts of the potential of G reduction were observed upon lowering pH of the background electrolyte (i.e., increasing the availability of protons to generate hydrogen radicals). Ammonium ions markedly increased efficiency of G reduction, which may be explained by generation of active hydrogen via formation and subsequent decomposition of ammonium amalgam. Our results strongly suggest that chemical mechanism(s) involving hydrogen radicals, electrochemically and/or electrocatalytically generated at the HMDE, contribute to the guanine → 7,8‐dihydroguanine conversion.