Influence of light and Fe(III) ions on tetracycline degradation

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2019-06, Vol.216, p.273-282
• Main Authors: Smyk, Bogdan, Piotrowicz-Cieślak, Agnieszka I., Grajek, Hanna, Rydzyński, Dariusz, Margas, Małgorzata, Wasilewski, Janusz
• Format: Article
• Language: English
• Subjects: Fluorescence; Gauss decomposition; Iron; Spectroscopy; Tetracycline
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2019.03.031

Tetracycline (TC) is an antibiotic produced on the largest scale in the world and used for the treatment of both humans and animals. Its removal from the circulation chain between the natural environment and animals is still a serious problem. Fe(III) ions can be used to break this chain. Fe(III) ions appear in water in spite of irradiation of Fe(III)-Cit complex and oxidation by oxygen present in water. Fe(III)-Cit was a reservoir of Fe(III) ions from which they were continuously released. Therefore, in this paper we studied an interaction between tetracycline (TC) and Fe(III) ions under fluorescent light at 20 °C and 30 °C in the water environment. This interaction leads to TC + Fe(III) coordinating complex formation. Changes caused by this process were monitored within 1860 min by measuring absorption and fluorescence spectra. The absorption spectra showed a charge-transfer stacking band(s) of oxidized and non-oxidized form of TC above 400 nm; in turn the fluorescence spectra revealed decay of initial bands and formation of the new ones. The initial, main fluorescence band at 16,660 cm−1 associated with the intramolecular proton transfer has gradually disappeared after Fe(III) ions binding to oxygen atoms in the BCD system rings of a TC molecule. Gaussian decomposition of all fluorescence spectra allowed extracting new bands, their evolution in time and calculating the rate of the first reaction step. Temperature rise of 10 °C caused more than a ten-fold increase in the first-order reaction rate. [Display omitted] •Fe(III) and tetracycline (TC) form a molecular complex in BCD ring system of TC.•The resulting complex of TC and Fe (III) does not fluoresce.•Charge-transfer complex of oxidized and unoxidized form of TC is formed.•New fluorescence bands are formed during 2 days of light irradiation.•To analyze the data, Gaussian decomposition of fluorescence spectra was applied.