Photochemical and photophysical properties, and photodegradation mechanism, of the non-steroid anti-inflammatory drug Flurbiprofen

The photodegradation mechanism of the widely used non-steroidal anti-inflammatory drug 2-(4-phenyl-3-fluorophenyl) propanoic acid, Flurbiprofen, and its photochemical and photophysical properties have been investigated by means of computational quantum chemistry at the DFT-B3LYP/6-31G(d,p) level. Comparison of computed and experimental singlet and triplet–triplet absorption spectra point to that most experiments, using a range of different solvents, are conducted on the neutral, protonated form of Flurbiprofen. The deprotonated acid, which should dominate at physiological pH, shows no sign of decarboxylation from the lowest singlet excited states, whereas from its first excited triplet state this should readily occur by passing over an energy barrier of <0.5 kcal/mol. Further reactions in the proposed photodegradation mechanism, after decarboxylation, as well as the probability for reactive oxygen species formation are discussed in detail. The generation of the corresponding peroxyl radical from the decarboxylated radical and molecular oxygen is strictly exergonic and occurs without barrier under aerobic conditions. The thus formed peroxyl radical will in turn be capable of initiating propagating lipid peroxidation processes.