Synthesis, Characterization, and Biological Evaluation of Co(II), Cu(II), and Ni(II) Complexes With 2,2′‐Bipyridine‐5,5′‐Dicarboxamide Ligands: Antibacterial and Enzyme Inhibition Studies

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This study reports the synthesis and characterization of two novel 2,2'-bipyridine-5,5'-dicarboxamide ligands (L1 and L2) and their corresponding Co(II), Cu(II), and Ni(II) complexes. The structures of the free ligands were verified using FTIR, NMR, UV-Vis, elemental analysis, and mass spectrometry, while the metal complexes were characterized through FTIR, MALDI-TOF MS, UV-Vis, and magnetic susceptibility techniques. Single-crystal X-ray diffraction was employed to elucidate the structure of L1. Biological evaluation against resistant bacterial strains identified Co-L2 as a potent antimicrobial agent, exhibiting a quantitative Minimum inhibitory concentration (MIC) of 500 μg/mL against E. coli, P. aeruginosa, and S. aureus. Furthermore, enzyme inhibition assays revealed that Ni-L2 was the most effective inhibitor for pancreatic lipase (IC50 = 0.36 μM) and butyrylcholinesterase (IC50 = 4.53 μM). In contrast, the free L2 ligand demonstrated the strongest inhibitory potency against acetylcholinesterase (IC50 = 0.479 μM). These findings underscore the influence of 5,5'-regiochemistry on the biological efficacy of bipyridine-based systems.