Combined experimental and theoretical studies on the diorganotin(IV) complexes of sparfloxacin: Synthesis, spectroscopic and DFT studies, and biological activity

Abstract

New diorganotin(IV) derivatives of sparfloxacin having general formula R2SnCl(L), (where L = monoanion of sparfloxacin (HL) and R = n-Bu (1)/Ph (2)) have been synthesized and structurally characterized by elemental analysis, IR, NMR (1H, 13C, 119Sn), HMQC, ESI-MS, UV–Vis and emission spectroscopy. These investigations suggest that, in these 1:1 monomeric derivatives the sparfloxacin ligand acts as monoanionic bidentate coordinating through the Ocarboxylate and Opyridone, and the polyhedron around tin is intermediate between pseudotetrahedral and cis-trigonal bipyramidal. The proposed structures have been validated by density functional theory (DFT) based electronic structure calculations at B3LYP/6-31G(d,p)/Def2-SVP(Sn) level of theory through the calculation of the atomic charges at the selected atoms, molecular electrostatic potential (MEP) map to assign sites on the surface of the molecules, the selected conceptual-DFT based global reactivity descriptors to obtain an insight into the structure and reactivity behaviour, and the frontier molecular orbital analysis to analyze the nature of frontier orbitals. A comparative analysis of the experimental vibrational frequencies and simulated harmonic frequencies indicates good correlation between them. The simulated UV–Vis spectrum was obtained with time dependent-DFT method in gas phase and in the solvent field with IEFPCM model. The simulated 1H and 13C NMR spectra were obtained by gauge-independent atomic orbital (GIAO) method and the results were in good agreement to the experimental results. The complexes were screened for their in vitro antibacterial activity against two Gram-positive and five Gram-negative bacterial strains. Both the complexes exhibited promising antibacterial activity against all the chosen strains (MIC: 0.062–0.125 μg ml−1).