Interaction of triorganotin(IV) moiety with quinolone antibacterial drug ciprofloxacin: Synthesis, spectroscopic investigation, electronic structure calculation, and biological evaluation

Abstract

New triorganotin(IV) derivatives of ciprofloxacin (HL) with general formula R₃Sn(L) (where R = Me (1)/Cy (2) and L is the monoanion of ciprofloxacin) have been synthesized and structurally characterized on the basis of elemental analysis, IR, Raman, multinuclear (¹H-, ¹³C- and ¹¹⁹Sn-) NMR, ESI-MS, UV-Visible, and emission spectroscopy. A distorted trigonal bipyramidal geometry around tin has been tentatively proposed for these triorganotin(IV) derivatives in which the ligand may act as monoanionic bidentate coordinating through the O_carboxylate and O_pyridone. The proposed structure has been validated by density functional theory (DFT)-based electronic structure calculations at B3LYP/6-31G(d,p)/Def2-SVP(Sn) level of theory. The atomic charges have been calculated at the selected atoms, and the reactive sites have been assigned on the surface of the molecules through molecular electrostatic potential map. The frontier molecular orbitals and selected conceptual-DFT-based global reactivity descriptors have been calculated to obtain an insight into the structure and reactivity behavior of the complexes. A comparative analysis of the experimental vibrational frequencies and simulated harmonic frequencies indicates good correlation between them. The complexes were screened for their in vitro antibacterial activity against two Gram-positive and five Gram-negative bacterial strains. The results revealed that both the complexes exhibited promising antibacterial activity against the chosen strains (MIC: 0.062-0.125 μg/mL).