Micellar oxidative transformation of ciprofloxacin: a kinetic investigation

Abstract

Environmental contextPollution of the aquatic environment by drugs results not only during their manufacture, but also from the excretion of drug residues and the discharge of expired drugs by households and hospitals. The transformation of ciprofloxacin, one of the leading antibiotic drugs, in the presence of surfactants has been investigated. The results provide a better understanding of how ciprofloxacin degrades in aquatic environments by considering the effect of omnipresent surfactants. AbstractThe kinetics of the oxidative transformation, i.e. oxidative degradation, of ciprofloxacin (CIP) by chloramine-T (CAT) in cationic and anionic micelle media during the water chlorination process was studied spectrophotometrically at 275nm and 298K. The influence of added salts (1–10×10–4moldm–3) and solvent polarity of the medium on the reaction was studied. The orders with respect to substrate CIP and oxidant CAT were found to be first order in each. The variation of acid concentrations showed opposite effects in cationic and anionic micellar aggregates. Liquid chromatography–electrospray ionisation mass spectrometry was used to identify degradation products of CIP, which confirmed the full dealkylation of the piperazine ring in CIP as the major product. The piperazine moiety of CIP is the principal active site for the CAT during oxidation. Activation parameters for the CIP degradation in cationic and anionic micelles were evaluated by studying the reaction at different temperatures, which lent further support to the proposed degradation mechanism for CIP. The rate constants were evaluated to confirm the micellar effect from incorporating sodium dodecyl sulfate and cetyltrimethylammonium bromide in the reaction mixture and the intrinsic reactivity constants were determined in the aqueous as well as in the micellar pseudo-phases as 4.85 and 0.0083.