One-electron oxidation of molecules with aromatic and thioether functions: Cl2•-/Br2•- and •OH induced oxidation of penicillins studied by pulse radiolysis

Advanced oxidation processes are about to be implemented for the elimination of the residual antibacterial activity of wastewater matrices that has a stimulating effect on the evolution of antibiotic resistance. These techniques apply (OH)-O-center dot which by scavenging Cl-/Br- yields Cl-2(center dot-)/Br-2(center dot-) in case of brackish or saline waters. The one-electron oxidation mechanism is peculiar in case of penicillins since a competition occurs between the aromatic and thioether moieties for the free radical attack. This competition determines the efficiency of antibacterial inactivation due to the vicinity of the sulfur to the beta-lactam pharmacophore. In order to unravel the (OH)-O-center dot and Cl-2(center dot-)/Br-2(center dot-) induced oxidation mechanism, pulse radiolysis techniques were applied. As a result, reactive intermediates typical of sulfur oxidation were observed. Interestingly, a higher sulfur radical cation concentration was obtained by applying Cl-2(center dot-)/Br-2(center dot-) compared to (OH)-O-center dot, on account of a unique stabilized intermediate that formed during the (OH)-O-center dot induced oxidation. The reported mechanism anticipates that scavenging of (OH)-O-center dot by Cl-/Br- can even have a positive effect on advanced oxidation of organic sulfides. (C) 2016 Elsevier B.V. All rights reserved.