Structural characterization, spectroscopic studies, and molecular docking studies on metal complexes of new hexadentate cyclic peptide ligand

Abstract

New cyclic peptide ligand (L), 4,7,17,20‐tetrabenzyl‐2,5,8,16,19,22‐hexaoxo‐3,6,9,15,18,21‐hexaaza‐1(1,3)‐benzenacyclodocosaphane‐10‐carboxylic acid (BOABCA), was prepared using the recommended method. The ligand (L) and its complexes have been proven by using elemental analyses, molar conductivity, and magnetic moment measurements. The structural properties of the title compounds were explored using spectroscopy (1H NMR, ultraviolet [UV]–visible, and Fourier transform infrared [FT‐IR]) and mass spectrometry. The thermal decomposition of the ligand and its complexes are measured by thermal analysis (thermogravimetry [TG] and derivative thermogravimetry [DTG]) technique. The ligand (L) acts as neutral hexadentate with NNOOOO coordination sites and coordinating to the metal ions via the two nitrogen and four oxygen atoms. Bond lengths, bond angles, and quantum chemical characteristics have been established for the ligand and its complexes. The scanning electron microscope (SEM) analysis confirmed the presence of Fe(III) and Ni(II) complexes in nanostructure. The structural formula for the examined cyclic peptide ligand was optimized using Gaussian09 program. The energy gaps and other relevant theoretical parameters were computed applying the DFT/B3LYP technique. Antibacterial properties of the BOABCA ligand (L) and its transition metal complexes have been evaluated. In vitro biological properties for BOABCA ligand (L) and its transition metal complexes were carried out against Gram(+) bacteria (Bacillis subtilis and Staphylococcus aureus) and Gram(−) bacteria (Escherichia coli and Pseudomonas aeruginosa) employing agar diffusion method. The results showed that title compounds are biologically active than the parent BOABCA ligand. Molecular docking has shown favorable interaction between the title compounds and crystal structure of 3t88‐E. coli, 3ty7‐S. aureus, 5h67‐B. subtilis, and 5i39‐P. aeruginosa receptors.