Vital metal complexes of levofloxacin as potential medical agents: Synthesis and their spectroscopic, thermal, computational, and anticancer studies

Abstract

Metals chelation to biologically active molecules can be used as a medical model of enhancement of their antimicrobial activity. This paper is devoted to synthesis, physicochemical characterization, computational and antimicrobial studies of some complexes of vital metal ions including Ca(II), Fe(III), Pd(II), and Au(III) with levofloxacin (LFX) ligand. Structures of such complexes were elucidated with the help of elemental analyses and spectral measurements (IR, Raman, 1H NMR, 13C NMR and electronic). The accumulated data confirmed that formation of LFX complexes had two coordination pathways as bidentate ligands. One of those proceeded via deprotonation of the carboxylic group followed by bounding to Ca(II) or Fe(III) ion via the carbonyl group and carboxylate oxygen atoms. Alternatively, LFX acted as a neutral ligand bound to Pd(II) or Au(III) ion via nitrogen atoms of the piperazine ring. Molar conductance measurements of the 1: 1 complexes in DMSO had non-electrolyte nature with the exception of Au(III) complex. Formulae assigned to the complexes were [Ca(LFX−)(Cl)(H2O)] (I), [Fe(LFX−)(Cl)2(H2O)2]·6H2O (II), [Pd(LFX)(Cl)2)] (III), and [Au(LFX)(Cl)2]·Cl (IV). The nano-scale nature of Pd(II) and Au(III) complexes has been elucidated on the basis of X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The antimicrobial tests of the complexes I–IV demonstrated some activity against several kinds of bacteria and fungi. Cytotoxic activity of the complex IV was tested against the human colon carcinoma (HCT-116) and human hepatocellular carcinoma (HepG-2) tumor cell lines.