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

Abstract

Chelation Direct photolysis TD-DFT a b s t r a c tThe extensive usage of OTC and Cu 2þ in livestock and poultry industry caused high residues in natural environment. Co-contamination of OTC and Cu 2þ was a considerable environmental problem in surface waters. In this study, Cu 2þ mediated direct photolysis of OTC was studied. Cu 2þ chelating with OTC was found to greatly inhibit OTC photodegradation. To reveal the chelation mechanism of OTC-Cu complexes, multiple methods including UVeVis absorption spectra, Infrared (IR) spectra, mass spectroscopy, and density functional theoretical (DFT) modeling were performed. Four OTC-Cu complexes were proposed. Cu 2þ preferably bond to O 11 eO 12 site with the binding constants logK ¼ 8.19 and 7.86 for CuHLþ and CuL±, respectively. The second chelating site was suggested to be O2eO3 with the binding constants of logK ¼ 4.41 and 4.62 for Cu2HL3þ and Cu2L2þ, respectively. The suppressed quantum yield of OTC by Cu2þ 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 Cu2þ. The photolysis quantum yield of OTC-Cu complexes, as well as the specific molar absorption constants, the equilibrium binding constants of Cu2þ with OTC could contribute to more accurate kinetic models of OTC.

Adsorption of tetracycline on Fe (hydr)oxides: effects of pH and metal cation (Cu 2+ , Zn 2+ and Al 3+ ) addition in various molar ratios

“…The formation of Cu–TC complexes at a slightly acidic pH, e.g. pH 5, could be evidenced by a red-shift for the absorption peak of TC from 357 to 365 nm (electronic supplementary material, figure S2) [ 32 ]. However, the Cu–TC complexation was restricted under more acidic conditions.…”

Yeast-TiO<sub>2</sub> Biotemplate for Oxytetracycline Solar Photodecomposition

“…"Without effective antibiotics, we will lose our ability to treat simple infections like pneumonia." The results presented in the WHO report confirm the need for urgent action to reduce antibiotic discharge in the environment, to promote the enforcement of prescription policies, and to reduce unnecessary antibiotic use, not only in humans but also in veterinary medicine [9] [10]. Also, the reliable data on antibiotic use in livestock are essential to help countries raise awareness of the appropriate use of antimicrobials, and the need for policy and regulatory changes to improve their use and control, as well as veterinary use.…”

Direct and Indirect Recycling Strategies of Expired Oxytetracycline for the Anode Material in Lithium Ion Batteries

“…In the case of expired oxytetracycline, the signal peaks were sharp and ample. In detail, one peak at 3,479 cm −1 could be ascribed to the stretching vibration of O-H bond, while three peaks at 1,395, 1,315, and 678 cm −1 could be assigned to the bending vibration of O-H bond (Jin et al, 2016;Hou et al, 2018a). One peak at 3,372 cm −1 resulted from the stretching vibration of N-H bond, and two peaks at 1,245 and 781 cm −1 were due to the bending vibration of N-H bond (Jin et al, 2016;Hou et al, 2018a).…”

“…In detail, one peak at 3,479 cm −1 could be ascribed to the stretching vibration of O-H bond, while three peaks at 1,395, 1,315, and 678 cm −1 could be assigned to the bending vibration of O-H bond (Jin et al, 2016;Hou et al, 2018a). One peak at 3,372 cm −1 resulted from the stretching vibration of N-H bond, and two peaks at 1,245 and 781 cm −1 were due to the bending vibration of N-H bond (Jin et al, 2016;Hou et al, 2018a). Three peaks at 1,650, 1,622, and 1,590 cm −1 were attributed to the stretching vibrations of C=O bonds on the amide and the rings (Aristilde et al, 2010;Mahamallik et al, 2015).…”