基于同位素标记的唑菌酯水解和光解动态及其降解产物质谱分析研究

为深入探究唑菌酯在水中的降解特性,研究了不同温度和pH值下唑菌酯的水解动态和不同光照下的光解动态,并以13 C-唑菌酯为对照,采用质谱分析研究唑菌酯的水解和光解产物及途径。结果表明,唑菌酯的水解和光解均符合一级动力学方程。在酸性至弱碱性(pH 8.0)水溶液中,唑菌酯较难水解;在碱性水溶液(pH 10.0~13.0)中,唑菌酯的水解速率随温度升高而加快。水解反应为碱基催化反应,唑菌酯的水解速率常数对数值与pH值成线性正相关,且温度越高,反应速率常数越大。在室内模拟太阳光、30℃下,唑菌酯易光解,光解反应速率随着光强和紫外强度增加而增加;在室外自然光、13~19℃下,唑菌酯难光解。由质谱分析结果推测,唑菌酯水解过程可能是未标记C原子上的酯键断裂脱去1个烷基后加氢,形成(E)-2-2-3-(4-氯苯基)-1-甲基-1H-吡唑-5-氧基]甲基]苯基]-3-甲氧基丙烯酸(C 21 H 19 ClN 2O 4),光解过程可能是未标记C原子上的羰基加氢、脱水后成环形成3-(4-氯苯基)-5-2-(4-甲氧基呋喃-3-基)苯基]甲氧基]-1-甲基-1H-吡唑(C 22 H 19 ClN 2O 3)。本研究对唑菌酯在水环境中的安全评价具有重要的参考价值。

Hydrolysis and Photolysis of Pyraoxystrobin Based on Isotope Labeling and Mass Spectrometric Analysis of Its Degradation Products

Pyraoxystrobin is a methoxyacrylic fungicide with low toxicity, high efficiency and broad spectrum. It has good control effect on rice blast, rice sheath blight, cucumber downy mildew and cucumber powdery mildew. In order to explore the degradation characteristics of pyraoxystrobin in water, the hydrolysis dynamics of pyraoxystrobin at different temperatures, pH values and the photolysis dynamics under different illumination were studied, the hydrolysis and photolysis products and pathways of pyraoxystrobin were studied by mass spectrometry with ¹³C-pyraoxystrobin as control. The test results showed that the Pyraoxystrobin was difficult to hydrolyze in acidic and alkalescent aqueous solution (pH 8.0). In alkaline aqueous solution (pH 10.0-13.0), the hydrolysis dynamics of pyraoxystrobin was affected by temperature. With the increase of temperature and pH values, the degradation rate was accelerated. The hydrolysis rate constants were linearly positively correlated with the pH values. Hydrolysis reaction was base-catalyzed reaction, and the higher temperatures, was the higher rate constants of base catalytic reaction were. Under indoor simulated sunlight and 30 ℃, pyraoxystrobin was easy to photolysis, and the photolysis reaction rate was increased with light intensity and ultraviolet intensity. Pyraoxystrobin was difficult to photolyze under the outdoor natural light at 13-19 ℃. It was speculated that the ester bond was broken on the unlabeled atom C and an alkyl group (CH3) was removed in the hydrolysis process of pyraoxystrobin. The product might be (E)-2-［2-［［3-(4-chlorophenyl)-1-methyl-1H-pyrazol-5-oxy］methyl］phenyl］-3-methoxyacrylic acid（C₂₁H₁₉ClN₂O₄）. The photolysis products was presumed to be 3-(4-chlorophenyl)-5-((2-(4-methoxyfuran-3-yl) benzyl) oxy)-1-methyl-1H-pyrazole after carbonyl hydrogenation on unlabeled atom C, dehydration and ring formation. The hydrolysis and photolysis products of zolexin ester and ¹³C-pyraoxystrobin ester were analyzed by mass spectrometry. It was speculated that the hydrolysis process of zolexin ester may be the breaking of ester bond on unmarked C atom and the dehydration of an alkyl group to form C₂₁H₁₉ClN₂O₄. The photolysis process may be carbonyl hydrogenation and dehydration on unmarked C atom. After cyclization, 3-(4-chlorophenyl)-5-［［2-(4-methoxyfuran-3-phenyl］ methoxy］-1-methyl-1H-pyrazole (C₂₂H₁₉ClN₂O₃) was formed. In this study, ¹³C-labelled pyraoxystrobin was used as internal standard, the degradation dynamics of zoxomycin in water were researched at different pH values and temperatures, and the photolysis of zoxomycin in water were researched under different light conditions. The hydrolysis and photolysis products and pathways of zoxomycin were analyzed and speculated in order to provide data for rational drug use, water source protection, ecological balance maintenance and food safety.