Department of Environmental Engineering, Peking University, The Key Laboratory of Water and Sediment Sciences, Ministry of Education , Beijing 100871, China.
Center for Quantitative Biology, Peking University , Beijing 100871, China.
Environ Sci Technol. 2018 Feb 20;52(4):2162-2169. doi: 10.1021/acs.est.7b03871. Epub 2018 Feb 5.
The recently developed three-step ternary halogenation model interprets the incorporation of chlorine, bromine, and iodine ions into natural organic matter (NOM) and formation of iodine-, bromine-, and chlorine-containing trihalomethanes (THMs) based on the competition of iodine, bromine, and chlorine species at each node of the halogenation sequence. This competition is accounted for using the dimensionless ratios (denoted as γ) of kinetic rates of reactions of the initial attack sites or halogenated intermediates with chlorine, bromine, and iodine ions. However, correlations between the model predictions made and mechanistic aspects of the incorporation of halogen species need to be ascertained in more detail. In this study, quantum chemistry calculations were first used to probe the formation mechanism of 10 species of Cl-/Br-/I- THMs. The HOMO energy (E) of each mono-, bi-, or trihalomethanes were calculated by B3LYP method in Gaussian 09 software. Linear correlations were found to exist between the logarithms of experimentally determined kinetic preference coefficients γ reported in prior research and, on the other hand, differences of E values between brominated/iodinated and chlorinated halomethanes. One notable exception from this trend was that observed for the incorporation of iodine into mono- and di-iodinated intermediates. These observations confirm the three-step halogen incorporation sequence and the factor γ in the statistical model. The combined use of quantum chemistry calculations and the ternary sequential halogenation model provides a new insight into the microscopic nature of NOM-halogen interactions and the trends seen in the behavior of γ factors incorporated in the THM speciation models.
新开发的三步三元卤化模型基于卤化序列每个节点处碘、溴和氯物种的竞争，解释了氯、溴和碘离子掺入天然有机物 (NOM) 以及形成碘、溴和氯三卤甲烷 (THM) 的过程。这种竞争是通过初始攻击位点或卤化中间体与氯、溴和碘离子反应的动力学速率的无量纲比（表示为γ）来计算的。然而，需要更详细地确定模型预测与卤化物物种掺入的机制方面之间的相关性。在这项研究中，首先使用量子化学计算来探究 10 种 Cl-/Br-/I-THM 的形成机制。在 Gaussian 09 软件中使用 B3LYP 方法计算了每种一卤、二卤或三卤甲烷的最高占据分子轨道能量 (E)。研究发现，实验测定的动力学优先系数 γ的对数与先前研究中报道的γ值之间存在线性相关性，另一方面，溴化/碘化和氯化卤代甲烷之间的 E 值差异也存在线性相关性。这种趋势的一个显著例外是碘掺入一碘和二碘化中间体的情况。这些观察结果证实了三步卤化掺入序列和统计模型中的γ因子。量子化学计算和三元顺序卤化模型的结合使用为 NOM-卤化物相互作用的微观性质以及在 THM 形态模型中包含的γ因子的行为趋势提供了新的见解。
