LASER FLASH AND STEADY‐STATE PHOTOLYSIS OF BENOXAPROFEN IN AQUEOUS SOLUTION*

Abstract

Abstract— On laser flash photolysis of aqueous solutions of benoxaprofen (BP), the BP triplet state is produced with a quantum yield of 0.19. One other unidentified species is also formed probably in a yield less than 0.02. Identical observations were made in alcoholic solution. The effect of potential hydrogen donors, isopropanol and histidine, on the kinetic reactivity of the BP triplet state, showed that for isopropanol the rate constant is slow (< 8 × 103 dm3 mol‐1 s‐1) if it occurs at all, whilst no reactivity with histidine could be seen. In oxygen uptake experiments, it was deduced that singlet oxygen is produced via the BP triplet state with a quantum yield of 0.18. There was no evidence for superoxide anion radical production. In other steady‐state photolysis experiments using high performance liquid chromatography, the quantum yield for loss of BP was determined to be 0.20, while the quantum yield for the only observed product, decarboxylated benoxaprofen, was estimated as 0.18. The involvement of the two major processes, i.e. singlet oxygen formation and BP decarboxylation, in BP phototoxicity is discussed.