Photosensitized Oxidation of Oxopurines by Rose Bengal

Article abstract of DOI:10.1111/j.1751-1097.1998.tb02501.x

Photosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7-trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive ¹O₂ quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, E_T[30], AN, DN, π*, ∈), the initial formation of an exciplex between ¹O₂ and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3-methyl-5-(methylamine)-1,5-dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.