PHOTODEGRADATION OF SODIUM RIFAMICYN SV

The intense colouring antibiotic Sodium Rifamicyn SV (Rfc) is decompos ed by direct and sensitized photoirradiation, through a complex mechan ism. This influences the microbiological activity of Rfc. It reacts fr om its electronic excited stares upon light absorption and by a single t molecular oxygen- and superoxide ion-mediated mechanism upon sensiti zed photoirradiation, employing Rose Bengal as a dye sensitizer. The r ate constant for the reaction with singlet molecular oxygen was determ ined as 1.2x10(8) and 5.1x10(8) M(-1)s(-1) at pH 6 and 12, respectivel y, by means of comparative methods. Both art increase in the decomposi tion rate as the solvent polarity, decreases and a clear dependence of the decomposition kinetics on the pH of the medium can be observed. T he latter factor suggests that the hydroquinonic structure of Rfc is t he molecular moiety responsible for the photorreaction. The decrease i n the antimicrobial power parallels the progress of the photodegradati on. This indicates the lack of antibiotic activity by the reaction pro ducts. (C) 1998 Elsevier Science.