UV₂₅₄-induced peptide bond cleavage: A critical pathway for N-DBP precursor formation from N-chloro-peptides

Peptides are abundant in source waters and susceptible to transformation into nitrogenous disinfection by-products (N-DBPs) during the drinking water treatment. This study systematically investigates the degradation kinetics of nine N‑chloro-peptides (NCl-peptides) and their associated DBPs formation mechanisms under UV₂₅₄ irradiation. UV₂₅₄ irradiation accelerated the degradation rates of nine NCl-peptides by 8.6 to 806.6-fold compared to dark controls. Notably, NCl-peptides exhibited lower photodegradation rates than their corresponding NCl-amino acid monomers, demonstrating that peptide bond-induced stabilization and intramolecular shielding synergistically enhanced their photolytic resistance. UV₂₅₄ irradiation markedly increased the formation potentials of N-DBPs from these NCl-peptides. Weak alkaline conditions could suppress N-DBPs yields. Structural characterization via LC-QTOF/MS revealed a critical pathway for N-DBPs precursors formation, which initiated by cleavage of peptide C-N bonds, through which amide groups underwent conversion to imine moieties. These findings fundamentally clarified the pivotal role of peptide bonds in N-DBPs formation during UV-involved water treatment processes, establishing a scientific basis for targeted precursor removal or pH modulation strategies to mitigate N-DBPs risks.