Riboflavin and rose bengal sensitised photooxidation of sulfathiazole and succinylsulfathiazole - Kinetic study and microbiological implications

In the presence of the synthetic xanthenic dye rose bengal or the pigment r iboflavin, the bacteriostatics sulfathiazole (STZ) and succinylsulfathiazol e (SCSTZ) suffer visible-light promoted degradation in dilute aqueous and a queous-ethanolic solutions. The events occur to a different extent, dependi ng on the chemical structures of the thiazoles and pH of the medium. The ph oto-oxidation process is accompanied by a partial loss of the antibacterial activity of the thiazoles. The extent of photodegradation occurs quickly u nder alkaline conditions and is less aggressive in the physiological pH reg ion, although not negligible in kinetic terms. Photo-oxidation quantum effi ciencies, evaluated through singlet molecular oxygen [O-2((1)Delta(g))] pho sphorescence detection, spectrophotometric and polarographic methods, range from 0.002 to 0.31 as the upper limit in alkaline media. With rose bengal as a sensitiser in aqueous medium, photooxidation essentially proceeds via singlet molecular oxygen. The results indicate the occurrence of several ph otoprocesses that involve a series of competitive reactions, including sing let molecular oxygen photo-oxidation, when the vitamin riboflavin was emplo yed as a sensitiser, in a 1:1 water: ethanol medium. Their relative importa nce depends on the concentration of the thiazoles and riboflavin. The bacte riostatics efficiently quench both the excited singlet and triplet states o f the pigment. The final result of the interactions is the phototransformat ion of the thiazoles and the partial photostabilization of riboflavin. The O-2((1)Delta(g))-mediated photo-oxidation of STZ produces a decrease in its bacteriostatic properties. (C) 2000 Elsevier Science Ltd. All rights reser ved.