Synthesis, characterization, DFT, biological activities and molecular docking analysis of Schiff base ligand and its transition metal complexes

In this study, we synthesized a tetradentate Salen type Schiff base ligand (H2L = 6,6'-(((4-chloro-1,2-phenylene)bis(azanylylidene))bis(methanylylidene)) bis(2-isopropyl-5-methyl-phenol)) containing N2O2 donor atoms and its analogous transition metal complexes, namely CoL, NiL, CuL, and ZnL. The ligand was prepared through the condensation reaction of 3-isopropyl-6-methylsalicyaldehyde and 4-chloro-1,2-phenylene diamine. Various spectroscopic methods viz. FT-IR, UV-Vis, 1H- and 13C-NMR, ESI-MS, and elemental analysis were utilized to elucidate the synthesized compounds. The free ligand coordinates with the metal ions in 1:1 molar ratio. The bactericidal investigations of the compounds were performed against S. aureus, S. pyogenes, E. coli, and P. aeruginosa. Antimalarial, anti-inflammatory and antioxidant activities were also studied. The DFT study was performed to optimize the geometry and evaluate the chemical reactivity parameters. The molecular docking investigation was performed to evaluate the binding interactions and binding energy of the synthesized compounds against cysteine protease SpeB and lactate dehydrogenase receptor proteins. This investigation established a good correlation between theoretical and practical outcomes.