1H and 19F NMR study of the processes of dissociation of complexes Tm3+ and Ho3+ with ciprofloxacin

Abstract

The thermodynamics and kinetics of the dissociation processes of the Tm3+ and complexes with ciprofloxacin were studied by 1H and 19F NMR (at different temperatures). This is one of the few studies on the dynamics of lanthanide complexes on 19F nuclei.The Gibbs free energy of activation of the dissociation processes (ΔG≠298) was found to be 60±3 and 58±3 kJ/mol for the Tm3+ and Ho3+ complexes, respectively. The calculated dissociation constant Kdis for the Ho3+ complex with ciprofloxacin turned out to be 0.02 mol/L (which is consistent with the corresponding Kdis values ​​for the Al3+ and Fe3+ complexes, which were determined earlier). Complexes of lanthanides with ciprofloxacin are kinetically and thermodynamically unstable, and are in solution in a partially dissociated state {in the "physiological" temperature range (35–42 ° C)}.