Laccase-Catalyzed Oxidative Coupling Reaction of Triclosan in Aqueous Solution
2016
Sun, Kai | Huang, Qingguo | Gao, Yanzheng
Triclosan (TCS) is an antimicrobial agent that is extensively used in personal care products (PCPs), and its residue is frequently reported in aquatic environments. In this study, we investigated the reaction behavior of TCS during enzyme-catalyzed oxidative coupling reactions (ECOCRs) by laccase from Pleurotus ostreatus and determined how the presence of natural organic matter (NOM) influenced the formation of the products. Results indicated that the optimum pH for TCS transformation was 6.0 in laccase-mediated ECOCRs. At pH values below 5.0 and above 7.0, the pseudo first-order kinetic rate constants (k) of TCS transformation declined significantly. Moreover, the k values of TCS transformation increased as the laccase activity increased (0.1179–0.5757 h⁻¹). A total of four product peaks were generated, and they were more hydrophobic than TCS. High-resolution mass spectrometry (HRMS) analysis indicated that these products could be the oligomers resulting from TCS self-coupling reactions. The relative peak areas of these oligomers displayed strong linear correlations with the different initial TCS concentrations, and the saturation point of laccase (3.0 U mL⁻¹), when the binding with TCS was 40 μmol L⁻¹. In the presence of NOM (i.e., humates and fulvates), humates in particular strongly inhibited TCS transformation and lowered the extent of its self-coupling, which likely resulted from the cross-coupling between TCS and NOM. Our study improves a better understanding of the reaction behavior of TCS in the natural aquatic environment during laccase-mediated ECOCRs.
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