Issue 9, 2024

Identifying initial transformation products during chlorination of the indole moiety and unveiling their formation mechanisms

Abstract

To identify toxicity drivers within poorly characterized high-molar-weight disinfection by-products (DBPs), relatively stable high-yield initial transformation products generated from aromatic amino acids and peptides and humic substances have drawn much attention. In this study, initial transformation products in chlorination of the indole moiety in tryptophan (Trp) are proposed and their formation mechanisms were investigated using a quantum chemical computational method. The results indicate that 3-Cl-Trp+ is initially formed after the Cl+ of HOCl attacks the indole moiety, and nucleophilic addition with nucleophilic agents (H2O and OCl) is thermodynamically preferred over deprotonation to generate 2-X-3-Cl-indoline moiety (X = OH and OCl), which is in contrast to indole. Over 25 types of initial transformation products are proposed from the 2-X-3-Cl-indoline moiety and two ring opening pathways were found at N1–C2 and C2–C3 bonds. Significantly, most structures of initial transformation products proposed based on experimental detection m/z values were confirmed using quantum chemical calculations and some new products are proposed in this work. The results are helpful to expand our understanding of the intrinsic reactivity of aromatic ring towards chlorination by hypochlorous acid.

Graphical abstract: Identifying initial transformation products during chlorination of the indole moiety and unveiling their formation mechanisms

Supplementary files

Article information

Article type
Paper
Submitted
08 4月 2024
Accepted
28 7月 2024
First published
01 8月 2024

Environ. Sci.: Processes Impacts, 2024,26, 1629-1640

Identifying initial transformation products during chlorination of the indole moiety and unveiling their formation mechanisms

M. Huan, Y. D. Liu and R. Zhong, Environ. Sci.: Processes Impacts, 2024, 26, 1629 DOI: 10.1039/D4EM00196F

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