Bimolecular versus Trimolecular Reaction Pathways for H2O2 with Hypochlorous Species and Implications for Wastewater Reclamation

Insights into the catalytic effect of atmospheric organic trace species on the hydration of Criegee intermediates

The bimolecular reactions between Criegee intermediates (CIs) and atmospheric trace species have been extensively investigated, with a particular focus on the reaction with water, while the catalytic role of atmospheric organic compounds in hydration reactions was often neglected. In this study, we employed quantum chemical calculations and Born-Oppenheimer molecular dynamics (BOMD) simulations to investigate the catalytic effects of atmospheric organic amines, organic acids, and alcohols on the hydration reactions of CIs in the gas phase and at the gas-liquid interface. The catalytic reactions were found to follow a cyclic catalytic structure and a stepwise reaction mechanism. Gas-phase studies revealed that organic acids exhibited stronger catalytic effects compared to amines and alcohols, and the catalytic efficiency of amines and alcohols was similar to those of single water molecule. In addition, the catalytic reaction barriers of organic acids and alcohols were positively correlated with their gas-phase acidity (R2 = 0.94 to 0.97). A negative correlation was observed between the catalytic reaction barrier of amines and their gas-phase basicity (R2 = 0.84 to 0.90) and proton affinity (R2 = 0.84 to 0.92). At the gas-liquid interface, organic acids promoted the formation of hydroxyethyl hydroperoxide (HEHP, CH3CH(OH)(OOH)), organic acid ions, and H3O+, whereas the catalytic hydration of CIs by organic amines resulted in the formation of CH3CH(OH)OO and amine ions. Both HEHP and CH3CH(OH)OO can be further decomposed to form OH and HO2, or participate in new particles formation as precursors. This study complements the research gap on the reaction of CIs with water, providing valuable insights into the atmospheric sources of HEHP and HOx as well as the formation of secondary organic aerosols (SOAs).

Estrogenic disruption effects and formation mechanisms of transformation products during photolysis of preservative parabens

The ubiquitous presence of emerging contaminants (ECs) in the environment and their associated adverse effects has raised concerns about their potential risks. The increased toxicity observed during the environmental transformation of ECs is often linked to the formation of their transformation products (TPs). However, comprehension of their formation mechanisms and contribution to the increased toxicity remains an unresolved challenge. To address this gap, by combining quantum chemical and molecular simulations with photochemical experiments in water, this study investigated the formation of TPs and their molecular interactions related to estrogenic effect using the photochemical degradation of benzylparaben (BZP) preservative as a representative example. A non-targeted analysis was carried out and three previously unknown TPs were identified during the transformation of BZP. Noteworthy, two of these novel TPs, namely oligomers BZP-o-phenol and BZP-m-phenol, exhibited higher estrogenic activities compared to the parent BZP. Their IC50 values of 0.26 and 0.50 μM, respectively, were found to be lower than that of the parent BZP (6.42 μM). The binding free energies (ΔGbind) of BZP-o-phenol and BZP-m-phenol (-29.71 to -23.28 kcal·mol-1) were lower than that of the parent BZP (-20.86 kcal·mol-1), confirming their stronger binding affinities toward the estrogen receptor (ER) α-ligand binding domain. Subsequent analysis unveiled that these hydrophobic residues contributed most favorably to ER binding, with van der Waals interactions playing a significant role. In-depth examination of the formation mechanisms indicated that these toxic TPs primarily originated from the successive cleavage of ester bonds (OCH2C6H5 and COO group), followed by their combination with BZP*. This study provides valuable insight into the mechanisms underlying the formation of toxic TPs and their binding interactions causing the endocrine-disrupting effects. It offers a crucial framework for elucidating the toxicological patterns of ECs with similar structures.