Copper(II) complexes derived from halogen-substituted Schiff base ligands : synthesis, crystal structures, antibacterial activity, and molecular docking studies

Abstract

In the face of escalating bacterial resistance to conventional antibiotics, the quest for novel antimicrobial strategies is urgenter than ever. Metal complexes, particularly those with biological activity, stand out as a promising alternative due to their unique mechanisms of action and potential for fewer side effects in comparison to standard organic antibiotics. This investigation focuses on the synthesis and characterization of six Cu(II) complexes, each formulated from halogen-substituted bidentate Schiff base ligands. Employing a suite of analytical methods, Fourier transform infrared, UV–vis, elemental analysis, and single-crystal X-ray diffraction, the structures of the complexes were fully established. All of the complexes were assigned to have square planar geometry, with the ligand acting as a bidentate and coordinate to the Cu(II) ion via nitrogen and oxygen atoms. The antibacterial efficacy of these complexes was rigorously tested against both Gram-positive bacteria Staphylococcus aureus and Streptococcus pyogenes and Gram-negative bacteria Escherichia coli and Klebsiella pneumoniae, utilizing the broth microdilution technique. The results revealed a spectrum of activity, with minimum inhibitory concentrations (MICs) spanning from less than 15.63 to 125 μg/mL. Notably, Complex 2 demonstrated remarkable potency against S. aureus and S. pyogenes, registering an MIC of less than 15.63 μg/mL. To elucidate the underlying mechanism of action, molecular docking studies were performed targeting the topoisomerase IV receptor. The docking outcomes corroborated the empirical data, underscoring the strong affinity of the complexes for the bacterial targets.