Visible light-promoted interactions between riboflavin and 3-hydroxypyridine in aqueous solution

Visible light-promoted interactions between the natural pigment Riboflavin (Rf) and 3hydroxypyridine (3-OHP) have been studied in air equilibrated aqueous solution, as a model system for the natural photodegradation of some aquatic contaminants. Results from static and dynamic fluorescence, laser flash photolysis, and polarography of oxygen consumption support the existence of competitive oxidation processes that involve singlet molecular oxygen and/or superoxide anion, with their relative importance depending on the 3-OHP concentration. Both the excited singlet and triplet states of Rf are quenched by 3-OHP, with respective rate constants of 5.9×109 M-1 s-1¯¯close to the diffusion rate constant¯¯and 8.9× 108 M-1 s-1. The final result of the interactions is the photooxidation of 3-OHP and the partial photostabilization of Rf.