Pulse radiolytic investigation of the hypoxanthine-xanthine-uric acid system: evidence for transient species

The oxidation in aqueous solutions of hypoxanthine into xanthine and xanthine into uric acid by OH radicals has been investigated using pulse radiolysis and fast kinetic absorption spectrophotometry. After hypoxanthine irradiations the spectrum of transient R1 has been characterized. This radical is formed with a rate constant k/sub (Hyx+OH) = 6.5 x 109 M-1 sec-1 and disappears by disproportionation leading to xanthine and hypoxanthine with a rate constant 2K/sub (R1+ r1/ = 1.3 x 108 M-1 sec-1. After xanthine irradiations a radical intermediate R2 is formed with a rate constant k/sub(X+ OH)/= 5.2 x 108 M-1 sec-1 and disappears through a second-order reaction 2K/sub (R2+ R2)/ = 2.0 x 108 M-1 sec-1. Finally, after aeration only uric acid and xanthine are measured