Complex formation equilibria of aluminum(III), gadolinium(III), and yttrium(III) ions with the fluoroquinolone antibacterials moxifloxacin, ofloxacin, fleroxacin, lomefloxacin, levofloxacin, and ciprofloxacin were studied in aqueous solution by potentiometric and spectroscopic methods.
The identity and stability of metal–fluoroquinolone complexes were determined by analyzing potentiometric titration curves (310 K, μ = 0.15 M NaCl, pH range = 2–11, C
M = 1 : 1
to 3 : 1, C
M = 1.0 mM) with the aid of Hyperquad2006 program. The main species formed in the system may be formulated as MpHqLr (p = 1, q = −2 to 2, r = 1–3, L = fluoroquinolone
anion, logarithm of overall stability constant, log β
p,q,r = in the range ca. −10 to 45). The stability of complexes is mostly influenced by metal ion properties (ionization potential, ionic radius) indicating partial ionic character of the coordination
bond. The complexes were also characterized by spectroscopic measurements: spectrofluorimetry, 1H-NMR, and ESI-MS. Fluorimetric data were evaluated with the aid of HypSpec2014 and indicated the formation of MLr (r = 1–3) complexes with cumulative conditional
stability constants significantly lower than the thermodynamic ones. NMR and MS data corroborate potentiometrically determined speciation. Calculated plasma mobilizing capacity of the ligands generally follows the order levofloxacin > moxifloxacin > ciprofloxacin
at concentration levels of the ligands higher or equal to ca. 10−4 M.
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Document Type: Research Article
Faculty of Science, University of Kragujevac, Kragujevac, Serbia
Laboratory for Radioisotopes, Institute of Nuclear Science “VINČA”, Belgrade, Serbia
CBRN Training Center of the Serbian Armed Forces, Kruševac, Serbia
Faculty of Pharmacy, Analytical Chemistry Department, University of Belgrade, Belgrade, Serbia
December 17, 2015