UV-Visible spectroscopic and DFT studies of the binding of ciprofloxacin hydrochloride antibiotic drug with metal ions at numerous temperatures

Ciprofloxacin hydrochloride (CPFH) is a very common antibiotic drug for the treatment of different types of bacterial infections. The activity of the drug depends on the complexation of the employed drug with different metals present in the body. In the current investigation, the complexation behavior of CPFH drug with numerous metal ions was explored by means of UV-Visible spectroscopic and density functional theory (DFT) techniques at various temperatures. The binding constants (Kf) of CPFH+metal ions complexes were determined from the Benesi-Hildebrand equation. The Kf values experience an alteration with the nature of metal ions employed and the change of temperature. The binding of CPFH with alkali earth metals decreases with the increase of metal size and increases with the increase of temperature, while the opposite effect of temperature was observed for transition metals. The Gibbs free energy of binding (ΔGo) for the complexation between CPFH and metal ions was negative in all cases, which reveals that the complexation phenomenon is spontaneous. The values of enthalpy and entropy connote the presence of both hydrophobic and electrostatic interactions. The complexation of CPFH was observed to be endothermic in the case of alkali earth metals while exothermic for transition metals. The intrinsic enthalpy gain (ΔIIo, *) values signify the higher stability of metal-drug complexes. The compensation temperature (TC) values were found to be comparable to the biological systems. DFT studies show the formulation of 1:1 complexes with transition metals as well as the square planar geometry of the complexes. HOMO and LUMO analyses reveal that the stability of CPFH-Ni complexes is higher than that of CPFH-Co/CPFH-Zn complexes.