Theoretical and experimental investigation of mixed-ligand metal(II) Schiff base complexes using maleic acid as the auxiliary ligand

Abstract

This work is focused on the synthesis of several transition metal complexes [ML(MA)], where M = Copper (II), Zinc (II), Cobalt (II) and Nickel (II), MA = maleic acid and L = Schiff base generated from benzene-1,2-diamine [o-phenylenediamine] and 4-chlorobenzaldehyde. The characterization using Fourier-Transform Infrared, Nuclear Magnetic Resonance spectroscopy, Ultraviolet-Visible spectra, Mass, Electro Paramagnetic Resonance and elemental analysis confirm the square planar geometry of the complexes. The in vitro antimicrobial potential of the complexes has been tested by the broth dilution method and the antioxidant method has been done by free radical scavenging analysis. The in vitro methods reveal the outstanding biological characteristics of the copper complexes. The molecular structure of the ligand and its metal (II) complexes has been optimized using Density Functional Theory studies performed by the Gaussian-09 software and their parameters have been discussed. Natural Bond Orbital and Frontier Molecular Orbital analyses have assessed the presence of a metal-ligand bond in complexes. In addition, molecular docking studies have also been performed on antiviral activity of all the complexes using a viral protein and their interacting amino acids.