Institute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, Zeromskiego 112, 90-924 Lodz, Poland.
Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany.
Int J Mol Sci. 2019 Nov 26;20(23):5955. doi: 10.3390/ijms20235955.
Hexachlorocyclohexane (HCH) isomers constitute a group of persistent organic pollutants. Their mass production and treatment have led to a global environmental problem that continues to this day. The characterization of modes of degradation of HCH by isotope fractionation is a current challenge. Multi isotope fractionation analysis provides a concept to characterize the nature of enzymatic and chemical transformation reactions. The understanding of the kinetic isotope effects (KIE) on bond cleavage reaction contributes to analyses of the mechanism of chemical and enzymatic reactions. Herein, carbon, chlorine, and hydrogen kinetic isotope effects are measured and predicted for the dehydrochlorination reaction of γ-HCH promoted by the hydroxyl ion in aqueous solution. Quantum mechanical (QM) microsolvation with an implicit solvation model and path integral formalism in combination with free-energy perturbation and umbrella sampling (PI-FEP/UM) and quantum mechanical/molecular mechanical QM/MM potentials for including solvent effects as well as calculating isotope effects are used and analyzed with respect to their performance in reproducing measured values. Reaction characterization is discussed based on the magnitudes of obtained isotope effects. The comparative analysis between the chemical dehydrochlorination of γ-HCH in aqueous media and catalyzed reaction by dehydrochlorinase, LinA is presented and discussed. Based on the values of isotope effects, these two processes seem to occur via the same net mechanism.
六氯环己烷 (HCH) 异构体构成了一组持久性有机污染物。它们的大规模生产和处理导致了一个全球性的环境问题，至今仍在继续。通过同位素分馏来描述 HCH 的降解模式是当前的一个挑战。多同位素分馏分析为表征酶促和化学转化反应的性质提供了一个概念。对键断裂反应的动力学同位素效应 (KIE) 的理解有助于分析化学和酶反应的机制。在此，通过量子力学 (QM) 微溶剂化，采用隐式溶剂模型和路径积分形式理论，结合自由能微扰和伞状采样 (PI-FEP/UM) 以及量子力学/分子力学 QM/MM 势，用于包含溶剂效应并计算同位素效应，并分析其在重现测量值方面的性能。根据获得的同位素效应的大小讨论了反应的特征。介绍并讨论了γ-HCH 在水介质中的化学脱氯化氢反应和脱氯化氢酶 LinA 催化反应之间的比较分析。根据同位素效应的值，这两个过程似乎通过相同的净机制发生。
