Microencapsulation is an effective technology to reduce the environmental losses of pesticides during their use. This paper reports the complexation mechanism of chlorophenoxy herbicide MCPA with nativeβ-cyclodextrin (CD) and its methyl and hydroxypropyl derivatives by a molecular dynamics/quantum mechanics/continuum solvent model (MD/QM/CSM) approach developed recently. The results reveal that the solvation effect plays a dominant role in determining the relative stabilities of the three CD/MPCA inclusion complexes. However,the results in vacuum environment are opposite to those in solvent media. The calculated relative binding affinities of the three systems in aqueous solution decrease in the order:DM-β-CD>HP-β-CD>β-CD,which agrees with the experimental results,with a correlation coefficientR=0.99. This demonstrates that the MD/QM/CSM method is able to determine the relative stability of host-guest systems with different host molecule.%利用β-环糊精(β-CD)及其衍生物控制二甲四氯农药分子的释放是目前研究的热点.本文使用一种最近发展的分子动力学/量子力学/连续介质溶剂模型(MD/QM/CSM)方法计算β-CD及其甲基、羟丙基衍生物对二甲四氯(MPCA)农药分子的包合机理.揭示了溶剂效应在决定对这3种CD相对包合能力时发挥了主导作用,而真空包合自由能顺序与溶剂中的正好相反.算得的3个体系包合能力强弱排序为:DM-β-CD>HP-β-CD>β-CD,与实验测量结果一致,且线性相关度达到R=0.99.结果表明:MD/QM/CSM方法对于计算不同主体的超分子复合物体系的相对稳定性是可靠的.
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