Synthesis and Characterization of Co(II), Cu(II), and Ni(II) Complexes of 2,2′‐Bipyridine‐4,4′‐Dicarboxamide Ligands: Antibacterial Evaluation Against Resistant Bacteria and Enzyme Inhibition

Two new 2,2′-bipyridine-4,4′-dicarboxamide ligands and their Co(II), Cu(II), and Ni(II) complexes are synthesized and characterized. The L2-Co complex shows strong antibacterial activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The L2-Ni complex displays the most potent enzyme inhibition with IC50 values of 1.35 μM (lipase), 4.33 μM (AChE), and 6.42 μM (BChE).

In this study, two new 2,2′-bipyridine-4,4′-dicarboxamide ligands, namely N4,N4′-bis(pyridin-2-ylmethyl)-[2,2′-bipyridine]-4,4′-dicarboxamide (L1) and N4,N4′-bis(piperidin-2-ylmethyl)-[2,2′-bipyridine]-4,4′-dicarboxamide (L2), and their Co(II), Cu(II), and Ni(II) complexes are synthesized and characterized. Elemental analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass techniques confirmed the structures of the synthesized compounds. The L1 structure is also determined by single-crystal X-ray diffraction. Antibacterial activities of ligands and metal complexes against resistant strains are investigated. The L2-Co complex demonstrates promising antibacterial qualities against these resistant strains, which is noteworthy. Additionally, enzyme inhibition studies are conducted to assess their potential therapeutic applications. The results show that the L2-Ni complex had the strongest inhibitory effect with IC₅₀ values of 1.35 μM for lipase enzyme, 4.33 μM for acetylcholinesterase enzyme, and 6.42 μM for butyrylcholinesterase.

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