Synthesis, Characterization, And Antimicrobial Evaluation Of Metal Complexes Derived From A Novel Benzimidazole-Pyrazole-Quinoline Hybrid Ligand

Abstract

A novel nitrogen-containing hybrid ligand, 5-((3-((1H-benzo[d]imidazol-1-yl)methyl)-5-(4-fluorophenyl)-1H-pyrazol-1-yl)methyl)-8-hydroxyquinoline (BIFPHQ), was synthesized by reacting 1-((5-(4-fluorophenyl)-1H-pyrazol-3-yl)methyl)-1H-benzo[d]imidazole (BIFP) with 5-chloromethyl-8-hydroxyquinoline. This ligand was further complexed with divalent metal ions including Cu(II), Ni(II), Co(II), Zn(II), and Mn(II). The structural elucidation of the ligand and its metal complexes was accomplished through elemental analysis, FT-IR, NMR (¹H and ¹³C), and mass spectroscopy. The analytical data confirmed a 1:2 (metal:ligand) stoichiometry for all complexes. Magnetic susceptibility measurements and electronic spectral studies suggested an octahedral geometry for the synthesized metal chelates. The thermal stability of the compounds was assessed by thermogravimetric analysis (TGA).

The ligand and its metal complexes were evaluated for their antimicrobial activity against a panel of Gram-positive and Gram-negative bacteria, as well as fungal strains, by determining the Minimum Inhibitory Concentration (MIC). The biological screening revealed that the metal complexes exhibited significantly enhanced antimicrobial potency compared to the free ligand. Notably, the copper(II) complex demonstrated the most promising activity, outperforming the standard drugs Amoxicillin and Nystatin in several cases. This study underscores the potential of metal complexation to enhance the biological efficacy of organic ligands and positions the BIFPHQ-Cu(II) complex as a particularly attractive candidate for further development.