The effect of Cu2+ chelation on the direct photolysis of oxytetracycline: A study assisted by spectroscopy analysis and DFT calculation. (July 2016)

• Record Type: Journal Article
• Authors: Jin, Xin; Qiu, Shanshan; Wu, Ke; Jia, Mingyun; Wang, Fang; Gu, Chenggang; Zhang, Aiqian; Jiang, Xin
• Is Part Of: Environmental pollution. Volume 214(2016)
• Page Start: 831
• Page End: 839
• Publication Date: 2016-07
• Subjects: Oxytetracycline -- Cu2+ -- Chelation -- Direct photolysis -- TD-DFT; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2016.04.084
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: The extensive usage of OTC and Cu 2+ in livestock and poultry industry caused high residues in natural environment. Co-contamination of OTC and Cu 2+ was a considerable environmental problem in surface waters. In this study, Cu 2+ mediated direct photolysis of OTC was studied. Cu 2+ 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. Cu 2+ preferably bond to O11 O12 site with the binding constants logK = 8.19 and 7.86 for CuHL+ and CuL±, respectively. The second chelating site was suggested to be O2O3 with the binding constants of logK = 4.41 and 4.62 for Cu2HL3+ and Cu2L2+, 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. Graphical abstract: Highlights: Four OTC-Cu 2+ complexes were proposed and the association constants was calculated. The molar absorption constants of OTC-Cu complexes were derived. Photolysis quantum yields of OTC and OTC-Cu complexes in neutral pH were calculated. Cu 2+ chelation typically inhibited the direct photolysis rate of OTC. The inter/intra-molecular electron transfer was responsible for the inhibition effect. Abstract : Cu 2+ strongly chelated with OTC in water and caused significant inhibition to OTC photolysis due to energy distributing through intra-/intermolecular electron transfer.