摘要:
Triclosan is an antimicrobial agent that is extensively used in various consumer care products. It entered the aquatic environment, mainly through municipal and industrial effluents, which acted by hindering one of the highly conserved enzymes of bacterial fatty-acid biosynthesis. It was noted that laccase could catalyze one-electron oxidation of phenolic pollutants into radical intermediates, and subsequently coupled to each other via the covalent binding. In this study, the transformation of triclosan in aqueoussolution was investigated by laccase-mediated enzyme-catalyzed oxidative coupling reactions (E-COCRs) in the absence and presence of 1-hydroxybenzotriazole (HBT, a redox mediator). The transformation products of triclosan were identified using high-resolution mass spectrometry (HRMS), and the transformation mechanism of triclosan was also proposed. Results indicated that laccase fromPleurotus ostreatus was effective in removing triclosan, and the presence of HBT significantly improved triclosan removal. The reactions followed the apparent pseudo first-order kinetics during 0~4h incubation (R2≥0.9465), the rate constant (k) values were respectively 0.43 and 0.95/h in the absence and presence of HBT, and the removal half-life (T1/2) values were 1.60 and 0.73h, respectively. The oligomerization (dimers, trimers and tetramers) of triclosan was identified as the dominant reaction pathway by laccase without HBT present, whereas the ether cleavage led to triclosan decomposition (2,4-dichlorophenol and 3-chlorophenol) in the presence of HBT was the predominant pathway. These findings presented in this study provide a novel insight into the fate and transformation of triclosan by laccase-mediated E-COCRs in aquatic environment in the absence and presence of HBT.%探讨了氧化还原介质(HBT)对漆酶调控水体中三氯生转化的影响,并利用高分辨质谱鉴定了其转化产物,综合地阐明了漆酶催化氧化水溶液中三氯生转化的作用机理.结果表明,平菇Pleurotus ostreatus分泌的胞外漆酶能够有效地去除水溶液中的三氯生,添加HBT显著地促进了漆酶对三氯生的去除效率.反应前期(0~4h),三氯生的转化符合表观假一级动力学方程(R2≥0.9465);在缺乏或存在HBT条件下,三氯生的转化速率常数(k)分别为0.43和0.95/h,半衰期(T1/2)分别为1.60和0.73h.缺乏HBT的反应体系中,漆酶催化氧化三氯生转化的主要机制是通过自由基介导的耦合反应形成低聚物,如二聚体、三聚体和四聚体等;而存在HBT的反应系统中,三氯生转化的主要途径是通过醚键断裂生成2,4-二氯苯酚和3-氯苯酚.该研究结果有利于评估氧化还原介质对漆酶催化氧化抗菌剂在环境中转化过程的影响及机理.