title: Photoproducts of tetracycline and oxytetracycline involving self-sensitized oxidation in aqueous solutions: effects of Ca2+ and Mg2+.
abstract: Tetracyclines constitute one of the most important antibiotic families and represent a classic example of phototoxicity. The photoproducts of tetracyclines and their parent compounds have potentially adverse effects on natural ecosystem. In this study, the self-sensitized oxidation products of tetracycline (TC) and oxytetracycline (OTC) were determined and the effects of Ca2+ and Mg2+ on self-sensitized degradation were investigated. The Ca2+ and Mg2+ in the natural water sample accounted for enhancement (pH 7.3) and inhibition (pH 9.0) of photodegradation of TC and OTC due to the formation of metal-ions complexes. The formation of Mg2+ complexes was unfavorable for the photodegradation of the tetracyclines at both pH values. In contrast, the Ca2+ complexes facilitated the attack of singlet oxygen (1O2) arising from self-sensitization at pH 7.3 and enhanced TC photodegradation. For the first time, self-sensitized oxidation products of TC and OTC were verified by quenching experiments and detected by LC/ESI-DAD-MS. The products had a nominal mass 14 Da higher than the parent drugs (designated M+14), which resulted from the 1O2 attack of the dimethylamino group on the C-4 atom of the tetracyclines. The presence of Ca2+ and Mg2+ also affected the generation of M+14 due to the formation of metal-ions complexes with TC and OTC. The findings suggest that the metal-ion complexation has significant impact on the self-sensitized oxidation processes and the photoproducts of tetracyclines.
authors.affiliation: School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China. ychen@mail.hust.edu.cn
authors.forename: Yong
authors.initials: Y
authors.lastname: Chen
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Zongping
authors.initials: Z
authors.lastname: Wang
authors.forename: Tao
authors.initials: T
authors.lastname: Tao
authors.forename: Chun
authors.initials: C
authors.lastname: Hu
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D002413:Cations, Divalent / Q000737:chemistry; D002853:Chromatography, Liquid; D008274:Magnesium / Q000737:chemistry*; D010084:Oxidation-Reduction; D010782:Photolysis; D012996:Solutions; D021241:Spectrometry, Mass, Electrospray Ionization; D013754:Tetracyclines / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D002413:Cations, Divalent; D012996:Solutions; D013754:Tetracyclines; D014874:Water Pollutants, Chemical; D014867:Water; D008274:Magnesium; D002118:Calcium