期刊
ENVIRONMENTAL POLLUTION
卷 214, 期 -, 页码 831-839出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.envpol.2016.04.084
关键词
Oxytetracycline; Cu2+; Chelation; Direct photolysis; TD-DFT
资金
- National Key Basic Research Program of China [2014CB441105]
- Outstanding Youth Fund of Natural Science Foundation of Jiangsu, China [BK20150050]
- National Natural Science Foundation of China [21507036, 21377138, 41271327]
The extensive usage of OTC and Cu2+ in livestock and poultry industry caused high residues in natural environment. Co-contamination of OTC and Cu2+ was a considerable environmental problem in surface waters. In this study, Cu2+ mediated direct photolysis of OTC was studied. Cu2+ chelating with OTC was found to greatly inhibit OTC photodegradation. To reveal the chelation mechanism of OTC-Cu complexes, multiple methods including UV-Vis absorption spectra, Infrared (IR) spectra, mass spectroscopy, and density functional theoretical (DFT) modeling were performed. Four OTC-Cu complexes were proposed. Cu2+ preferably bond to O-11-O-12 site with the binding constants logK = 8.19 and 7.86 for CuHL+ and CuL +/-, respectively. The second chelating site was suggested to be O2-O3 with the binding constants of logK = 4.41 and 4.62 for Cu2HL3+ and Cu2L(2+), respectively. The suppressed quantum yield of OTC by Cu2+ chelation was accused for their intra-/inter-molecular electron transfer, by which the energy in activated states was distributed. The occurrence of electron transfer between BCD ring and A ring also from BCD ring to Cu was evidenced by the TD-DFT result only for the OTC-Cu complexes. Besides, the cyclic voltammetry measurement also suggested one OTC-Cu(II)/OTC-Cu(I) redox couple. These results suggested that the persistence of OTC in environmental surface waters will probably be underestimated for neglecting the chelating effect of Cu2+. The photolysis quantum yield of OTC-Cu complexes, as well as the specific molar absorption constants, the equilibrium binding constants of Cu2+ with OTC could contribute to more accurate kinetic models of OTC. (C) 2016 Elsevier Ltd. All rights reserved.
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