Comparison of the electrochemical and enzymic oxidation of 1,3,7-trimethyluric acid at solid electrodes

The electrochemical oxidation of 1,3,7-trimethyluric acid has been studied in phosphate buffers in the pH range 2.1-10.2 at solid electrodes. In cyclic voltammetry a single, well defined, pH-dependent oxidation peak was obtained at all of the three electrodes used. However, the reduction behavior of the oxidation product was different at pyrolytic graphite, glassy carbon (GCE), and platinum due to adsorption at PGE and GCE. The nature of the electrode reaction was established as EC, in which a charge transfer is followed by competitive chemical reactions. The formation of the same UV-absorbing intermediate and products and identical rate constants for the decay of the UV-absorbing intermediate indicated that the electrochemical oxidation of 1,3,7-trimethyluric acid proceeds by an identical mechanism at PGE, GCE, and Pt. The results of a peroxidase-catalyzed oxidation of 1,3,7-trimethyluric acid were compared with the electrochemical oxidation; it is concluded that both of the oxidations follow a similar pathway.