Title : Synthesis, thermal, infrared spectroscopic and x-ray crystallographic characterization of gatifloxacin metal complexes and their antimicrobial properties
Abstract:
The rapid increase of antimicrobial resistance has compromised many antibiotics, highlighting the need for drug optimization. Metal complexation can improve antimicrobial agents’ properties by enhancing activity and stability. Gatifloxacin readily forms metal complexes with various ions, potentially boosting its biological efficacy. Using specific transition and alkaline-earth metals, such as Mn(II), Sr(II), Co(II), Ca(II), Ni(II), Mg(II), Ba(II), Cu(II), Zn(II), Fe(II), Pb(II), and Ag(I), gatifloxacin metal complexes were created at a 1:1 molar ratio. Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), and microscopic examination were used to analyze the complexes to ascertain their thermal characteristics and coordination behavior. Gatifloxacin's bidentate coordination via its carboxylate and keto groups was confirmed by FT-IR spectra, which showed significant changes in the carboxylate and quinolone carbonyl bands. Different thermal profiles between the complexes were shown by DSC analysis, revealing differences in crystallinity and thermal stability based on the metal ion. PXRD analysis revealed that the Mn(II) complex exhibits a mixed amorphous–crystalline phase, whereas the Ba(II) complex forms a stable orthorhombic barite-like structure. The disc diffusion method was used to assess the complexes' antibacterial activity against eleven Gram-positive and Gram-negative pathogenic bacteria. When compared to free gatifloxacin, a number of complexes, including those of Cu(II), Pb(II), Ag(I), Sr(II), and Mn(II), showed significantly increased antibacterial activity, with inhibition zones larger than 45 mm against strains like Bacillus tropicus, Salmonella typhi, and Streptococcus β-hemolyticus. Ni(II) and Fe(II) complexes, on the other hand, exhibited decreased activity. The findings show that metal coordination significantly affects gatifloxacin's structural and antibacterial characteristics. Particularly promising for future development as next-generation antibacterial agents are the Cu(II), Pb(II), and Ag(I) complexes.
