Dybala-Defratyka Agnieszka, Szatkowski Lukasz, Kaminski Rafał, Wujec Monika, Siwek Agata, Paneth Piotr
Institute of Applied Radiation Chemistry, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland.
Environ Sci Technol. 2008 Nov 1;42(21):7744-50. doi: 10.1021/es800276y.
In order to interpret the observed isotopic fractionation it is necessaryto understand its relationship with the isotope effect(s) on steps that occur during the conversion of the initial reactant to the final product. We examine this relationship from the biochemical point of view and elaborate on the consequences of the assumptions that it is based on. We illustrate the discrepancies between theoretical and experimental interpretation of kinetic isotope effects on examples of dehalogenation reactions that occur at an aromatic carbon atom. The examples include 4-chlorobenzoyl-CoA dehalogenase-catalyzed conversion of 4-chlorobenzoyl-CoA to 4-hydroxybenzoyl-CoA, dehaloperoxidase-catalyzed conversion of 2,4,6-trichlorophenol to 2,6-dichloroquinone, and spontaneous hydrolysis of atrazine at pH 12. For this latter reaction we have measured the chlorine kinetic isotope effect and estimated its value theoretically at the DFT level of theory. Results of chlorine kinetic isotope effects suggest that the studied dechlorination reactions proceed in a single step with significant weakening of the carbon-chlorine bond in the transition state.
为了解释观察到的同位素分馏现象，有必要了解其与初始反应物转化为最终产物过程中发生的步骤上的同位素效应之间的关系。我们从生化角度研究这种关系，并详细阐述其基于的假设的后果。我们以芳香碳原子上发生的脱卤反应为例，说明动力学同位素效应的理论解释与实验解释之间的差异。这些例子包括4-氯苯甲酰辅酶A脱卤酶催化4-氯苯甲酰辅酶A转化为4-羟基苯甲酰辅酶A、脱卤过氧化物酶催化2,4,6-三氯苯酚转化为2,6-二氯醌，以及阿特拉津在pH 12时的自发水解。对于后一个反应，我们测量了氯动力学同位素效应，并在密度泛函理论（DFT）水平上理论估计了其值。氯动力学同位素效应的结果表明，所研究的脱氯反应以单一步骤进行，过渡态中碳-氯键显著弱化。
