The growing interest in metal-quinolone complexes is sustained by a large number of compounds obtained and tested for antibacterial [1], antitumoral [1,2], antifungal [1], and antiparasitic [3] properties. Having these aspects in mind, in this study, the interaction of difloxacin, a second-generation quinolone with veterinary use, with some transition metal ions was investigated.
Four metal complexes of difloxacin were synthesized in different media (weakly acidic: Cu(II) and Ru(III) complexes, weakly basic: Cu(II) complex and neutral: Pd(II) complex) and characterized with physicochemical techniques (elemental analysis, conductivity measurements, IR, UV-Vis spectroscopy) and thermal analysis (TG, DTG, DTA).
Three of the compounds present the characteristic IR absorption bands for the ν(OCO) symmetric and antisymmetric bands. The difference between the two values is around 200 units, confirming that the carboxylate moiety is bound as monodentate, while the quinolone molecule is acting as a bidentate deprotonated ligand, bounded to the metalion through the pyridone and one carboxylate oxygen [4]. This is not the case of the Cu(II) complex obtained in acidic medium, as it occurs as a salt of the tetrachlorocuprate(II) complex ion. These conclusions are confirmed by the UV-visible spectra and thermal analysis. The intermediate steps corresponding to the quinolone moiety oxidative degradation were also highlighted.
Based on these findings, we propose the chemical formulas for the four synthesized compounds, which will further be subjected to DNA, serum albumin binding, and antimicrobial testing.
Acknowledgments
This research was financially supported by “Carol Davila” University of Medicine and Pharmacy through Contract no. 23PFE/17.10.2018 funded by the Ministry of Research and Innovation within PNCDI III, Program 1—Development of the National RD system, Subprogram 1.2—Institutional Performance—RDI excellence funding projects.
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