Manganese peroxidase mediated oxidation of sulfamethoxazole: Integrating the computational analysis to reveal the reaction kinetics, mechanistic insights, and oxidation pathway

In this study, manganese peroxidase (MnP) was applied to induce the in vitro oxidation of sulfamethoxazole (SMX). The results indicated that 87.04% of the SMX was transformed and followed first-order kinetics (k obs   =   0.438 h −1 ) within 6 h when 40 U L −1 of MnP was added. The reaction kinetics were investigated under different conditions, including pH, MnP activity, and H 2 O 2 concentration. The active species Mn 3+ was responsible for the oxidation of SMX, and the Mn 3+ production rate was monitored to reveal the interaction among MnP, Mn 3+ , and SMX. By integrating the characterizations analysis of the MnP/H 2 O 2 system with the density functional theory (DFT) calculations, the proton-coupled electron transfer (PCET) process dominated the catalytic circle of MnP and the transformation of Mn 3+ . Additionally, possible oxidation pathways of SMX were proposed based on single-electron transfer mechanism, which primarily included the S–N bond cleavage, the C–S bond cleavage, and one electron loss without bond breakage. It was then transformed to hydrolysis, N–H oxidation, self-coupling, and carboxylic acid coupling products. This study provides insights into the atomic-level mechanism of MnP and the transformation pathways of sulfamethoxazole, which lays a significant foundation for the potential of MnP in wastewater treatment applications.