The complexation of levofloxacin hemihydrate with divalent metal ions in aqueous medium at variable temperatures: Combined UV-Visible spectroscopic and DFT studies

Herein, we have studied the binding of levofloxacin hemihydrate (LFH) drug with different metal ions e.g., alkali earth metal ions and transition metal ions through spectrophotometry and Density Function Theory (DFT) studies. The binding constant (K-f) of LFH with alkali earth metal ions was observed to be increased with the boost of temperature while the opposite trend was observed in the case of transition metal ions. The K-f values were experienced to be reduced with the increase of size of the alkali earth metal ions. The K-f values in case of transition metal follow the order Cu2+ > Ni2+ > Co2+ > Zn2+. The Gibbs free energy (Delta G(0)) of binding values reveal that binding phenomena are spontaneous in nature. The values of enthalpy (Delta H-0) and entropy (Delta S-0) of binding suggest that hydrophobic interactions are the key forces for the binding of LFH and alkali earth metal ions while electrostatic, dipole-dipole, iondipole, and hydrogen bonding are the key forces in case of transition metal ions. The enthalpy-entropy compensation parameters were also estimated and explained in detail. From the DFT study, the bond lengths, bond angles, HOMO and LUMO orbitals energy, band gap, hardness, and the highest wavelengths of the drug/ drug-metal complexes have been calculated and explained with appropriate reasoning. (C) 2021 Elsevier B.V. All rights reserved.