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

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2016-07, Vol.326, p.50-59
• Main Authors: Szabó, László, Tóth, Tünde, Takács, Erzsébet, Wojnárovits, László
• Format: Article
• Language: English
• Subjects: Hydroxyl radical; Kinetics; Radical reaction; Sulfur oxidation; Time-resolved spectroscopy
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2016.04.025

[Display omitted] •OH/Cl2−/Br2− targets predominantly the sulfur atom.•Intermediates of the one-electron oxidation of the thioether function are observed.•Higher >S(+) concentration is obtained applying Cl2−/Br2− compared to OH.•The higher concentration is due to a stabilized OH-adduct at the sulfur. 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 which by scavenging Cl−/Br− yields Cl2−/Br2− 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 β-lactam pharmacophore. In order to unravel the OH and Cl2−/Br2− 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 Cl2−/Br2− compared to OH, on account of a unique stabilized intermediate that formed during the OH induced oxidation. The reported mechanism anticipates that scavenging of OH by Cl−/Br− can even have a positive effect on advanced oxidation of organic sulfides.