Comparison of electrochemical and enzymic oxidation of 7,9-dimethyluric acid

276-282The oxidation of 7,9-dimethyluric acid has been studied in aqueous phosphate buffers in the pH range 2.3-10.0 at a variety of solid electrodes. The conjugate base is found as the electroactive species which on 2e, H+ oxidation gives an unstable diimine. The attack of water molecule on the diimine in a follow up chemical reaction gives a UV-absorbing intermediate which decomposes-in a pseudo-first order reaction to give alloxan and 1,3-dimethylurea at pH 3.0 and 1,3-dimethylallantoin and 1,3-dimethyl-5-hydroxyhydantoin-5-carboxamide at pH 7.2. The electrochemical behaviour of dimethyluric acid at PGE, GCE and Pt electrodes is the same. A comparison of electrochemical behavior with unsubstituted uric acid indicates that methyl groups at positions 7 and 9 shift the Eptowards less positive potential. However, the overall course of electrode reaction remains unchanged. The peroxidase catalysed oxidation of 7,9-dimethyluric acid also exhibites the same spectral and kinetic behaviour and hence it is concluded that electrochemical and enzymic oxidation proceed by an identical EC mechanism