New insights into the interaction between dissolved organic matter and different types of antibiotics, oxytetracycline and sulfadiazine: Multi-spectroscopic methods and density functional theory calculations

Dissolved organic matter (DOM) is composed of numerous fluorescent components. It is an indispensable parameter to affect the environmental fate of antibiotics in various ways. To assess the migration of antibiotics in environment com-partments, it is crucial to understand the binding mechanism between DOM and antibiotics. How a particular compo-nent in DOM interacts with coexistence antibiotics is not still fully understood. Therefore, in the present study, interactions of two antibiotics oxytetracycline (OTC) and sulfadiazine (SD) with humic acid (HA) and L-tryptophan (L-Trp) which were representative DOM components, were investigated by multispectral techniques and density func-tional theory (DFT) calculations. The fluorescence quenching mechanism was static quenching. In the binding process, the quenching ability of OTC was stronger than that of SD in HA, which was the same as in L-Trp. DFT calculations were applied to confirm a stronger interaction between OTC and HA or L-Trp than SD. Meanwhile, analyzing the bind-ing sequence by two-dimensional correlation spectroscopy (2D-COS), a humic-like substance bound antibiotics was earlier than a protein-like substance. In HA system, the combination of two antibiotics had a synergistic effect on HA quenching. In L-Trp system, the quenching relationship between the two antibiotics and L-Trp was antagonistic. The FTIR spectra showed that hydroxyl and amide were involved in the binding process of individual DOM compo-nents with OTC and SD. The work will help to further understand the behavior of coexistence antibiotics in the envi-ronment.

Automated summary

Dissolved organic matter (DOM) plays a crucial role in the environmental behavior of antibiotics. This study investigated the interactions between two antibiotics and representative DOM components using multispectral techniques and DFT calculations. The results showed strong binding interactions between certain DOM components and coexistence antibiotics, providing important insights into the behavior of antibiotics in the environment.