Formation Mechanism of Iodinated Aromatic Disinfection Byproducts: Acid Catalysis with H₂OI⁺

Abstract

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 −1 ) and hydroxylated Tyr-Gly (OH-Tyr-Gly) (46.0 kcal mol −1 ) 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 H 2 OI + 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 H 2 OI + is the key step to initiate the iodination process. When H 2 OI + serves as an acid catalyst and an iodinating agent, with HOI or H 2 O acting as a proton acceptor, the energy barrier of I-DBP formation was significantly lower (10.8−13.1 kcal mol −1 ). Therefore, even with its low concentration, H 2 OI + 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.

Enrichment of Geogenic Organoiodine Compounds in Alluvial-Lacustrine Aquifers: Molecular Constraints by Organic Matter

“…The proportions of polycyclic aromatics and phenolic iodinated DOM products exceeded 50%, indicating that aromatic structures were favorable for the binding of OM to iodine. ,, Moreover, the number of phenolic iodinated DOM products was significantly higher than that of polycyclic aromatic iodinated DOM products (Figure S8). Although the above organic compounds contain aromatic structures, phenolic compounds contain more ring-activating functionalities and are more conducive to electrophilic substitution of iodine compared to polycyclic aromatics with condensed aromatic structures. ,, Besides these two organic compounds, the remaining iodinated DOM products were highly unsaturated compounds (accounting for 49.7%). Highly unsaturated compounds are the most dominant component of DOM in groundwater, accounting for approximately 50% of all organic compounds.…”

“…Although the above organic compounds contain aromatic structures, phenolic compounds contain more ring-activating functionalities and are more conducive to electrophilic substitution of iodine compared to polycyclic aromatics with condensed aromatic structures. 11,42,43 Besides these two organic compounds, the remaining iodinated DOM products were highly unsaturated compounds (accounting for 49.7%). Highly unsaturated compounds are the most dominant component of DOM in groundwater, accounting for approximately 50% of all organic compounds.…”

Water Analysis: Emerging Contaminants and Current Issues

“…In a study of formation mechanisms, Gao et al investigated formation of iodinated aromatic DBPs from H 2 OI + . Because it is the most abundant reactive iodine species in chloraminated water, HOI is typically assumed to be the active oxidant in high iodide waters.…”

“…In a study of formation mechanisms, Gao et al investigated formation of iodinated aromatic DBPs from H 2 OI + . 103 Because it is the most abundant reactive iodine species in chloraminated water, HOI is typically assumed to be the active oxidant in high iodide waters. However, as shown through computational modeling of thermodynamic results, new research found that H 2 OI + was key to the initiation of iodination in the formation of an iodinated peptide DBP (iodo-tyrosine-glycine).…”

Predicting THM Formation and Revealing Its Contributors in Drinking Water Treatment Using Machine Learning

“…The primary goal of disinfection is to inactivate pathogenic microorganisms (e.g., viruses, protozoa, algae, etc.) and help to control the spread of waterborne diseases (e.g., cholera, typhoid). − Nevertheless, the major downside of chemical disinfection (e.g., chlorination and chloramination) is that disinfectants (e.g., chlorine and chloramines) react with natural organic matter (NOM) to form disinfection byproducts (DBPs) of health concerns. ,,− Trihalomethanes (THMs) and haloacetic acid (HAAs), two common classes of DBPs, are currently regulated by the United States Environmental Protection Agency (USEPA) at maximum contaminant limits (MCLs) of 80 and 60 μg/L, respectively. , The generation of emerging DBPs (e.g., iodinated THMs, N -nitrosodimethylamine [NDMA]) is also alarming because these emerging DBPs are often more toxic than the DBPs regulated by USEPA. − Currently, NDMA is regulated in many regions. , For example, the California Department of Public Health established a notification levels of 10 ng/L, Canada set a national guideline value of 40 ng/L, and Australia adopted a target value of 100 ng/L for this contaminant in drinking water . Epidemiological studies revealed that DBPs in drinking water can be associated with several health issues including cancer, miscarriage, and birth defects. ,− As water cycles have multiple interconnected components (e.g., stormwater, sewage, and drinking water), DBPs can be introduced into a water cycle in a variety of ways.…”