Riboflavin as a Visible-Light-Sensitiser in the Aerobic Photodegradation of Ophthalmic and Sympathomimetic Drugs
This chapter compiles and discusses results published by our group related to the study of the kinetic and mechanistic behavior and, in some cases, the distribution of photoproducts in the Riboflavin (Rf)-promoted photooxygenation of two families of drugs of pharmaceutical relevance, namely sympathomimetic and ophthalmic drugs. The drugs only absorb ultraviolet light, nevertheless, in the presence of Rf, visible-light irradiation under aerobic conditions produce a series of kinetically competitive processes which mainly depend on the relative concentrations of Rf and the drugs, and on the redox properties of the drugs. The overall picture comprises photochemical mechanisms that initiate with the quenching of Rf singlet and triplet excited states, and include the participation of the oxidative species singlet molecular oxygen and superoxide radical anion, which produce the photodegradation of both Rf and the drugs in different extents depending on the characteristics of the drug involved. On the contrast, in particular cases the drugs behave as excellent non-sacrificial (physical) deactivatiors of the oxidative species protecting Rf toward photodestruction.