A COMPARATIVE-STUDY ON THE TIO2 MEDIATED PHOTOOXIDATION OF URACIL, THYMINE AND 6-METHYLURACIL

The semiconductor TiO2 assisted photo-oxidation of uracil, thymine and 6-methyluracil has been carried out in aqueous suspension with an exc itation wavelength of 365 nm. The rate and quantum yield (empty set) o f this heterogeneous photoprocess were measured based on the disappear ance of the pyrimidine bases spectrophotometrically (265 nm) and hence the quantum yield (empty set) has been evaluated as a function of con centration of the substrate (pyrimidine bases), weight of TiO2 and pH. The reaction rates are found to conform to the Langmuir-Hinshelwood i sotherm and the k and K values thus determined are reported. The influ ence of pH on the empty set values reveals a varying proportion of con tribution of h(vb)(+) and (OH)-O-. on the reactivity of the substrate biomolecules, and the effect of [Ag+](0) on empty set points to a decr eased h(+)-e(-) recombination with a concomitant increase in h(+) capt ure by the substrate biomolecules, leading to an enhancement of the re action rate. A mechanism consistent with the observed data is proposed . (C) 1997 Elsevier Science S.A.