2,4-二氯苯氧乙酸代谢中的水解反应机理

2,4-二氯苯氧乙酸(2,4-D)是应用广泛的农用除草剂和植物生长素,在它的代谢过程中,涉及多种化学反应. 本文采用密度泛函理论B3LYP方法, 分别研究了它在代谢过程中的三条水解反应途径的机理. 研究结果表明: (I) 2,4-D水解反应有两种模式, C(1)―O键解离的氢转移和C―Cl键解离的氯被取代. (Ⅱ) C―Cl键的解离能垒明显低于C(1)―O键的解离能垒, 即水解速率较快, 反应动力学占优势. 在三条反应途径中, 途径(2)和(3)优先水解C―Cl键, 再水解C(1)―O键. 由于受反应速率的影响, 不同中间体在降解过程中的浓度有明显区别.(III) 对于水解反应,采用导体极化连续模型(CPCM)考虑溶剂化效应,可更合理地阐述水解反应机理.

Hydrolysis Reaction Mechanismof 2, 4-Dichlorophenoxy Acetic Acid Metabolism

2,4-Dichlorophenoxy acetic acid (2,4-D) is a herbicide and plant growth regulator that is widely applied inagriculture.Many chemical reactions takeplace inthemetabolismof 2,4-D. Herein, the hydrolysis reaction mechanismin 2,4-D metabolismwill be presented. In this study, a density functional theory approach, B3LYP, was employed toinvestigatethehydrolysis reaction mechanismalong three different paths. The computed results indicate that: (Ⅰ) there are two models of the hydrolysis reaction of 2,4-D. The dissociation mechanismof C(1)―O and C―Cl involve hydrogen transfer and Cl substitution, respectively. (Ⅱ) The energy barrier of C―Cl dissociation was lower and the dissociation showed advantageous dynamics. Two of the reaction paths that initiate the dissociation of C―Cl were primary reactions. The dissociation of C(1)―O was the last step in the primary reactions and had a higher energy barrier. In metabolism, the different intermediates have different concentrations, and this impacts on the reaction rate. (Ⅲ) In addition, it was necessary to consider the solvent effect to investigate the hydrolysis reaction. To characterize the solvent effect, the conductor-like polarizable continuum model (CPCM) was used to simulate the hydrolysis reaction with respect to the bond length and energy barrier.