Synthesis, characterization, DFT calculations and molecular docking studies of metal (II) complexes

Abstract

Two novel ligands, 2-methyl-6-[(5-methyl benzothiazol-2-ylimino)-methyl]-2-methoxycyclohexa-1,5-dienol (HL1) and 2-methyl-6-[(5-floro-benzothiazol-2-ylimino)-methyl]-2-methoxycyclohexa-1,5-dienol (HL2) were synthesized from the condensation reaction of 2-hydroxy-3-methoxybenzaldehyde with 2-amino-6-methylbenzothiazole and 2-amino-6-florobenzothiazole respectively. Mononuclear Cu(II), Ni(II) and Co(II) complexes of the ligands were synthesized and characterized using elemental analysis, magnetic susceptibility, thermogravimetric, conductance, infrared and UV-visible spectroscopic measurements. The 1H NMR, 13C NMR, Dept-90 NMR spectroscopy of the ligands was also recorded to establish the formation of the Schiff bases. The analytical data of the complexes showed that the metal to ligand ratio was 1:1 for Cu(II), Ni(II) and Co(II) complexes of HL1 and Cu(II) complexes of HL2, while Ni(II) and Co(II) complexes of HL2 was 1:2. The infrared spectral data showed that the chelation behaviour of the ligands towards transition metal ions was through phenolic oxygen and azomethine nitrogen atoms. Molar conductivity revealed the non-electrolytic nature of all chelates in DMSO solution. The geometry of the complexes was deduced from thermal, magnetic susceptibility and UV-visible spectroscopic results and was further confirmed with DFT calculations. The compounds were subjected to in-vitro antibacterial screening using agar well diffusion method on some clinically isolated Gram positive and Gram negative bacteria strains. The compounds showed varied antibacterial activities. Molecular docking studies were carried out to study the molecular interaction between the compounds and different enzymes of the bacterial strains. The antioxidant potentials of the compounds were studied using ferrous ion chelating assay and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. However, the complexes had better antioxidant potentials compared to the ligands.