Abstract：
This study investigated degradation behaviors of a nonsteroidal anti-inflammatory drug Nabumetone (NMT) and its major metabolite 6-methoxy-2-naphthylacetic acid (MNA) in the coupling process of ultraviolet and monochloramine (UV/NH2Cl). The second-order rate constants of the contaminants reacting with reactive radicals (HO•, Cl•, Cl2•⁻, and CO3•⁻) were determined by laser flash photolysis experiments. HO• and Cl• contributed predominantly with 52.3% and 21.7% for NMT degradation and 60.8% and 22.3% for MNA degradation. The presence of chlorides retarded the degradation of NMT, while promoted the destruction of MNA, which was ascribed to the photosensitization effects of MNA under UV irradiation. Density functional theory (DFT) calculations revealed that radical adduct formation (RAF) was dominant pathway for both HO• and Cl• reacting with the contaminants, and hydrogen atom transfer (HAT) preferred to occur on side chains of NMT and MNA. NMT reacted with NO2• through single electron transfer (SET) with the second-order rate constant calculated to be 5.35 × 107 (mol/L)-1 sec-1, and the contribution of NO2• was predicted to be 13.0% of the total rate constant of NMT in pure water, which indicated that NO2• played a non-negligible role in the degradation of NMT. The acute toxicity and developmental toxicity of NMT were enhanced after UV/NH2Cl treatment, while those of MNA were alleviated. The transformation products of both NMT and MNA exhibited higher mutagenicity than their parent compounds. This study provides a deep understanding of the mechanism of radical degradation of NMT and MNA in the treatment of UV/NH2Cl.
摘要：
本研究研究了非甾体抗炎药萘丁美酮（NMT）及其主要代谢产物6-甲氧基-2-萘乙酸（MNA）在紫外线和一氯胺（UV/NH2Cl）偶联过程中的降解行为。污染物与反应性自由基反应的二阶速率常数(HO•，Cl•,Cl2•,并通过激光闪光光解实验确定了CO3•)。HO•和Cl•对NMT降解的贡献主要为52.3％和21.7％，对MNA降解的贡献为60.8％和22.3％。氯化物的存在延缓了NMT的降解,在推动破坏MNA的同时，这归因于MNA在紫外线照射下的光敏作用。密度泛函理论（DFT）计算表明，自由基加合物的形成（RAF）是HO•和Cl•与污染物反应的主要途径。和氢原子转移(HAT)优选发生在NMT和MNA的侧链上。NMT通过单电子转移（SET）与NO2•反应，二阶速率常数为5.35×107（mol/L）-1sec-1，预计NO2•的贡献为13.0％。纯水中NMT的总速率常数，这表明NO2·在NMT的降解中起着不可忽视的作用。UV/NH2Cl处理后NMT的急性毒性和发育毒性增强,而MNA则有所缓解。NMT和MNA的转化产物均表现出比其母体化合物更高的致突变性。本研究对UV/NH2Cl处理中NMT和MNA的自由基降解机理有了深入的了解。
