Investigations of electron-transfer reactions and the redox mechanism of 2′-deoxyguanosine-5′-monophosphate using electrochemical techniques

Abstract

Electron-transfer reactions of 2′-deoxyguanosine-5′-monophosphate (dGMP) have been investigated in phosphate buffers of different pH at a pyrolytic graphite electrode (PGE). In cyclic voltammetry, two well-defined oxidation peaks, Ia (pH 1.9–10.6) and IIa (pH ≥ 5.8), were noticed. The peak potentials shifted towards less positive potential when pH was increased. Concentration and sweep rate studies established the adsorption of dGMP on the electrode surface. UV-vis spectral analysis at pH 2.9 and 7.1 indicated formation of a UV-absorbing intermediate, which decayed in a pseudo first-order reaction (k = ∼5.05 × 10−4 s−1). Coulometric, voltammetric and UV studies revealed the 4H+,4e− oxidation of dGMP by an EC (electrode reactions followed by chemical reactions) mechanism. The characterization of the oxidation products was achieved by converting them to their trimethylsilyl derivatives. At pH 7.1, 5-hydroxyhydantoin-5-carboxamide (9) and a N–O–C8 linked trimer (18) and, at pH 2.9, monohydrated alloxan (12), deoxyriboside urea (11), two C8O–OC8 and one C8–C8 bridged dimers of dGMP (13, 14 and 15, respectively) were formed as the major oxidation products. A tentative redox mechanism has been suggested for the electrooxidation of dGMP.