Abstract
The electrochemical oxidation of 3,9-dimethyl uric acid in aqueous solution has been studied between pH 3.3 and 8.8 at graphite electrodes. A single 2 e − I H + oxidation voltammetric peak is observed corresponding to the formation of a very unstable cationic diimine intermediate. This reacts very rapidly with water to give an imino-alcohol intermediate. The latter intermediate may be observed as a U.V.-absorbing species (λ max = 290 nm between pH 3.3–8.8) and by means of its voltammetric reduction peak noted on cyclic voltammetry of 3,9-dimethyl uric acid. The location of the absorption spectrum of this imino-alcohol has been used to deduce its probable structure and the structures of imino-alcohol intermediates formed on oxidation of other uric acid derivatives. Hydration of the imino-alcohol gives the 4,5-diol of 3,9-dimethyl uric acid which decomposes to the final reaction products. The observed first-order rate constant for the latter reaction between pH 3.3 and 8.8 is 0.20 ± 0.05 s −1. Oxidation of 3,9-dimethyl uric acid in the presence of peroxidase and H 2O 2 gives rise to an intermediate which has identical spectral and electrochemical properties and very similar kinetic properties to the imino-alcohol intermediate generated electrochemically. Accordingly, it appears that the electrochemical and peroxidase-catalyzed oxidations of 3,9-dimethyl uric acid proceed via identical reaction mechanisms.
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