Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangzhou Key Laboratory Environmental Catalysis and Pollution Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China.
Division of Analytical and Environmental Toxicology, Department of Laboratory Medicine and Pathology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2G3, Canada.
Environ Sci Technol. 2022 Feb 1;56(3):1791-1800. doi: 10.1021/acs.est.1c05484. Epub 2022 Jan 21.
Iodinated aromatic disinfection byproducts (I-DBPs) are a group of nonregulated but highly toxic DBPs. The formation of I-DBPs is attributed mainly to HOI because it is the most abundant reactive iodine species in chloraminated water. In this study, we used computational modeling of thermodynamics to examine the mechanism of iodination of aromatic contaminants, e.g., dipeptides and phenols. Computational prediction of the energy barriers of the formation of iodinated tyrosylglycine (I-Tyr-Gly) (66.9 kcal mol) and hydroxylated Tyr-Gly (OH-Tyr-Gly) (46.0 kcal mol) via iodination with HOI favors the formation of OH-Tyr-Gly over I-Tyr-Gly. Unexpectedly, mass spectrometry experiments detected I-Tyr-Gly but not OH-Tyr-Gly, suggesting that I-Tyr-Gly formation cannot be attributed to HOI alone. To clarify this result, we examined the thermodynamic role of the most reactive iodine species HOI in the formation of aromatic I-DBPs under chloramination. Computational modeling of thermodynamic results shows that the formation of a loosely bonded complex of aromatic compounds with HOI is the key step to initiate the iodination process. When HOI serves as an acid catalyst and an iodinating agent, with HOI or HO acting as a proton acceptor, the energy barrier of I-DBP formation was significantly lower (10.8-13.1 kcal mol). Therefore, even with its low concentration, HOI can be involved in the formation of I-DBPs. These results provide insight into the mechanisms of aromatic I-DBP formation and important information for guiding research toward controlling I-DBPs in drinking water.
含碘的芳香族消毒副产物（I-DBPs）是一组未经监管但毒性很高的 DBPs。I-DBPs 的形成主要归因于 HOI，因为它是氯胺水中含量最丰富的反应性碘物种。在这项研究中，我们使用热力学计算建模来研究芳香族污染物（如二肽和酚类）碘化的机制。通过 HOI 碘化形成碘化酪氨酸甘氨酸（I-Tyr-Gly）（66.9 kcal mol）和羟基化 Tyr-Gly（OH-Tyr-Gly）（46.0 kcal mol）的形成能垒的计算预测有利于 OH-Tyr-Gly 的形成而不是 I-Tyr-Gly。出乎意料的是，质谱实验检测到了 I-Tyr-Gly，但没有检测到 OH-Tyr-Gly，这表明 I-Tyr-Gly 的形成不能仅仅归因于 HOI。为了澄清这一结果，我们研究了在氯胺化条件下，最具反应性的碘物种 HOI 在芳香族 I-DBPs 形成中的热力学作用。热力学结果的计算建模表明，芳香族化合物与 HOI 形成松散结合的络合物是引发碘化过程的关键步骤。当 HOI 作为酸催化剂和碘化剂，HOI 或 HO 作为质子受体时，I-DBP 形成的能垒显著降低（10.8-13.1 kcal mol）。因此，即使其浓度很低，HOI 也可以参与 I-DBPs 的形成。这些结果为芳香族 I-DBP 形成的机制提供了深入了解，并为指导饮用水中 I-DBPs 控制的研究提供了重要信息。
