Synthesis and antibacterial evaluation of transition metal complexes derived from salicylaldehyde based Schiff base ligands supported by DFT studies and molecular docking

A series of transition metal complexes of three ligands, namely (E)-6-((2-hydroxybenzylidene)amino)hexanoic acid (L1), (E)-2-amino-5-(3-(2-hydroxybenzylidene)guanidino)pentanoic acid (L2), and 2-((2-hydroxybenzylidene)amino)butanoic acid (L3), synthesized from the condensation of salicylaldehyde with 6-aminohexanoic acid, L-arginine, and DL-2-aminobutyric acid, respectively, have been reported. The complexes generated from the ligand L1, with the formula [Cu(II)(L1)2] (1), [Mn(II)(L1)2] (2), [Co(II)(L1)2] (3), [Ni(II)(L1)] (4), [Cd(II)(L1)] (5), and [ZrO(II)(L1)] (6); complexes formed by the ligand L2, having the formula [Ni(II)(L2)] (7), [Co(II)(L2)] (8), and [Mn(II)(L2)] (9); and complexes produced from the ligand L3, with the formula [Cd(II)(L3)2] (10) and [Ni(II)(L3)2] (11) were investigated using a variety of spectroscopic techniques, including Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectrophotometry (UV-Vis), ¹H-nuclear magnetic resonance (¹H-NMR), and thermogravimetric studies. The molecular structure, reactivity, and electronic characteristics of the synthesized compounds were studied using Density Functional Theory (DFT) simulations. The binding energy at the active site of these compounds was predicted using molecular docking experiments against the target 16 S subunit of bacterial ribosomal rRNA. Bacillus cereus (Gram +ve) and Escherichia coli (Gram −ve) were used to examine the metal complexes derived from ligand L1. Complexes 1 and 5 showed comparable antibacterial activity against both bacterial strains when compared to the reference drug kanamycin.