Transition metal complexes of imidazole derived Schiff bases: Antioxidant/anti-inflammatory/antimicrobial/enzyme inhibition and cytotoxicity properties

Abstract

A flexible class of Ni(II) and Zn(II) complexes were prepared with a novel Schiff base ligand containing imidazole moiety. The synthesized compounds were taken for structural characterizations such as elemental analysis, UV-Vis, FT-IR, 1H and 13C NMR, mass spectra, thermogravimetric investigation, magnetic susceptibility, and conductivity estimations. The coordination building of Ni(II) and Zn(II) complexes were found as octahedral and tetrahedral where Ni(II) and Zn(II) metal ions were composed by a nitrogen atom of the azomethine, imidazole ring, and oxygen atom of acetate derivative. All of the synthesized compounds were tried for their biochemical properties, including antioxidant, anti-inflammatory, antimicrobial activities, enzyme inhibition, and cytotoxicity. The antioxidant activity of designed compounds was screened by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) technique and all the Schiff base ligand and some of its Ni(II)/Zn(II) complexes showed close antioxidant activities against the standards (BHA, BHT, and ascorbic acid). Anti-inflammatory activity was estimated by the in-vitro human red blood cell (HRBC) membrane stabilization method, the Zn(II) complexes exhibited more activity for inflammation compared with Diclofenac, which is used as a standard drug. The in-vitro antimicrobial movement of synthesized compounds have been examined in microorganisms like Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, Streptococcus mutans, Enterobacter cloacae, Aspergillus niger and Candida albicans by agar disk diffusion method. Nystatin and Ciprofloxacin were selected as reference drugs. Enzyme inhibitions of the Schiff bases and their metal complexes were investigated using α-amylase and the best inhibition value (Ki) was observed for the Ni(II)/Zn(II) complex of 4-[(5-methyl-3H-imidazole-4-ylmethylene)-amino]-2-nitro-phenol (MINPN/MINPZ) (0.022/0.020 mM) with Acarbose as standard compound. The cytotoxic behavior of synthesized compounds was evaluated against cancer cell lines: DLA cells (Trypan blue exclusion method) and HepG2 cells (MTT assay) and determined the cell viability of the respective human cell, H9c2 via MTT assay. Encouragingly, most of the compounds are generally non-toxic, to the human cells, H9c2.