Synthesis, biological assay, chemical descriptors, and molecular docking calculations of novel copper(II) mixed-ligand complexes of n-benzoyl-dl-phenylalanine and n-heterocyclic nitrogen bases

Abstract

The emergence of drug-resistant pathogens has greatly limited the use of antibiotics in treating microbial infections. Therefore, Cu complexes have emerged as potential alternatives to ordinary antibiotics. Ternary Cu(II) complexes with N-benzoyl-dl-phenylalanine (Bzphe) and imidazole (Imi), methyl imidazole (Mimi), 2,2′-bipyridine (Bipy), and 1,10-phenanthroline (Phen) ligands were prepared and investigated for antimicrobial efficacy against two Gram-positive bacteria (Bacillus subtilis and Micrococcus luteus), one Gram-negative bacteria (Escherichia coli), and three fungal cultures (Aspergillus niger, Candida glabrata, and Saccharomyces cerevisiae). The new complexes were characterized by elemental analysis, infrared (IR) spectroscopy, electronic spectroscopy, thermogravimetry, and measurements of their molar conductivity and melting point. The formulas of the new complexes were Cu(Bzphe)2(Imi)2(OH2)2, Cu(Bzphe)2(Mimi)2(OH2)2], Cu(Bzphe)2(Bipy)(OH2)2, and Cu(Bzphe)2(Phen)(OH2)2. The obtained data revealed that the Bzphe invariably coordinates to the Cu(II) ions through carboxylic oxygen as a monobasic ligand. The addition of secondary ligands such as amines does not affect the unidentate coordination behavior of the Bzphe. The new compounds were screened for antimicrobial activity against different strains of bacteria and fungi. The results for the Bzphe ligand and its mixed-ligand Cu(II) complexes showed that the ligands exhibit low potency to inhibit the growth of both Gram-positive bacteria (B. subtilis and M. luteus) and Gram-negative bacteria (E. coli). However, the new ternary complexes greatly suppressed the growth of these pathogens according to the order CuBipyBzphe > CuPhenBzphe > CuMimiBzphe > CuImiBzphe. In addition, computational studies using density functional theory calculations and molecular docking experiments were carried out to characterize the molecular properties of the new complexes and provide insights into their role in inhibiting the growth of bacterial and fungal strains.