Synthesis, Characterisation and Acetylcholinesterase Inhibition Activity of Nickel(II) and Copper(II) Complexes of 3-Hydroxybenzaldehyde-4-nitrobenzoic Acid Hydrazone

Abstract

A new ligand namely 3-hydroxybenzaldehyde-4-nitrobenzoic acid hydrazone, its Nickel(II) and Copper(II) complexes were synthesised and characterised by spectroscopic methods: 1H NMR, Infrared (IR), UV-Vis, magnetic susceptibility measurement and % metal analysis. 1H NMR spectroscopy showed the diagnostic N-H signal at 12.10 ppm indicating the formation of the ligand. Infrared spectra showed that the ligand coordinated to the metal ion in keto form through the carbonyl oxygen (C=O) and the azomethine nitrogen (C=N). The UV-Vis spectrum of the ligand displayed two prominent bands at 47169 cm-1 and 30303 cm-1 which were ascribed to the intraligand transitions of π-π*, and n-π* respectively. These bands had hypsochromic shifts in the metal complexes indicating coordination with the metal ion. The nickel complex had a magnetic moment of 2.92 B.M, suggesting an octahedral geometry, while the copper complex had a value of 1.65 B.M. which is close to the expected value for a d9 copper(II) complex with possibility antiferromagnetic interactions. The % metal calculated had a good agreement with the observed values. The acetylcholinesterase inhibition activity of the ligand measured was 190 ± 20 μg/mL compared to the standard Eserin that had 68 ± 1.13 μg/mL. The copper(II) complex had a value of 220 ± 20 μg/mL, while the Nickel(II) complex had the least inhibitory value at 390 ± 80 μg/mL. The compounds could serve as primary target in the study of acetylcholinesterase inhibitors