Direct UV photodegradation of nalidixic acid in aqueous solutions: A mechanistic study

• Published in: Chemosphere (Oxford) Vol. 334; p. 138952
• Main Authors: Tyutereva, Yuliya E., Snytnikova, Olga A., Fedunov, Roman G., Yanshole, Vadim V., Plyusnin, Victor F., Xu, Jing, Pozdnyakov, Ivan P.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-09-2023
• Subjects: DFT calculations; Kinetics; Nalidixic Acid; Photodegradation; Photolysis; Quantum yield; quinolone Antibiotics; Sunlight; UV photolysis; Water - chemistry; Water Pollutants, Chemical - analysis; UV photolysis; Photodegradation; quinolone Antibiotics; Quantum yield; Nalidixic acid; DFT calculations
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2023.138952

Mechanism of direct UV photolysis of nalidixic acid (NA), a model quinolone antibiotic, was revealed using a combination of steady-state photolysis coupled with high resolution LC-MS and DFT quantum-chemical calculations. Both quantum yields of photodegradation and detailed identification of final products were performed for the first time for two main forms of NA: neutral and anionic. The quantum yield of NA photodegradation is 0.024 and 0.0032 for the neutral and anionic forms in the presence of dissolved oxygen and 0.016/0.0032 in deoxygenated solutions, respectively. The main process is photoionization with the formation of a cation radical, which undergoes transformation into three different neutral radicals and further into final photoproducts. It is shown that the triplet state does not play a role in the photolysis of this compound. The main products of photolysis are the products of the loss of carboxyl, methyl and ethyl groups in the NA molecule, as well as the dehydrogenation of the ethyl group. The results obtained may be important for understanding the fate of pyridine herbicides in the processes of disinfection by UV and in natural waters under the action of sunlight.
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•Mechanism of photolysis of anionic and neutral forms of nalidixic acid (NA) was revealed.•Three main short-lived radical was proposed based on DFT calculations.•The quantum yield of photodegradation of anionic and neutral forms (308 nm) is 2.4 and 0.32%.•Detailed identification of main final products were performed.