Spectroscopic, structural and antibacterial evaluation of some lomefloxacin metal complexes

A new metal complexes of the second-generation quinolone antimicrobial agent lomefloxacin hydrochloride (LFX) with Ti(IV), V(IV), Pd(II) and Ce(IV) have been prepared and characterized by physicochemical, spectroscopic and thermal analyses techniques. In all complexes lomefloxacin reacts as a bidentate deprotonated ligand bound to the metal through the pyridone oxygen and a carboxylate oxygen. The central metal ion in each complex is six-coordinate and a slightly distorted octahedral geometry is proposed. The decomposition mechanisms proposed for lomefloxacin hydrochloride and their metal complexes were discussed. The activation energies, E*, enthalpies, ?H*, entropies, ?S* and Gibbs free energies, ?G*, of the thermal decomposition reactions have been derived from thermogravimetric (TG) and differential thermogravimetric (DTG) curves, using Coats-Redfern (CR) and Horowitz-Metzeger (HM) methods. The lowest energy model structure of Ti(IV), V(IV), Pd(II) and Ce(IV) complexes were detected by using the density functional theory (DFT) at the B3LYP/CEP-31G level of theory. The antimicrobial activity of the free lomefloxacin hydrochloride, metal salts and their metal complexes have been tested against some Gram-positive and Gram-negative microorganisms.