Synthesis, spectroscopic, thermal analyses, biological activity and molecular docking studies on mixed ligand complexes derived from Schiff base ligands and 2,6‐pyridine dicarboxylic acid

Abstract

Two novel Schiff base ligands (La and Lb) were prepared from the condensation of quinoline 2‐aldehyde with 2‐aminopyridine (ligand La) and from the condensation of oxamide with furfural (ligand Lb). Mixed ligand complexes of the type M+2La/b Lc were prepared, where (La and Lb) the primary ligands and Lc was 2,6‐pyridinedicarboxylic acid as secondary ligand. Metal ions used were Fe(II), Co(II), Ni(II) and Zn(II) for mixed ligands La Lc and Fe(II), Co(II), Ni(II), Cu(II), Hg(II) and Zn(II) for LbLc mixed ligands. La and Lb Schiff base ligands were both characterized using elemental analyses, molar conductance, IR, 1H and 13C NMR. Mass spectra for Lb, [Zn(La)LcCl]Cl and [Cu(Lb)LcCl]Cl were also studied. ESR spectrum of the [Cu(Lb) LcCl]Cl complex was also recorded The metal complexes were synthesized and characterized using elemental analyses, spectroscopic (IR, 1H NMR, UV‐visible, diffused reflectance), molar conductance, magnetic moment and thermal studies. The IR and 1H NMR spectral data revealed that 2,6‐pyridinedicarboxalic acid ligand coordinated to the metal ions via pyridyl N and carboxylate O without proton displacement. In addition, the IR data showed that La and Lb ligands behaved as neutral bidentate ligands with N2 donation sites (quinoline N and azomethine N for La and two azomethine N for Lb). Based on spectroscopic studies, an octahedral geometry was proposed for the complexes. The thermal stability and degradation of the metal complexes were investigated by thermogravimetric analysis. The binding modes and affinities of La, Lb and Zn(II) complexes towards receptors of crystal structure of E. coli (PDB ID: 3 t88) and mutant oxidoreductase of breast cancer (PDB ID: 3 hb5) receptors were also studied.The antimicrobial activity against two species of Gram positive, Gram negative bacteria and fungi were tested for the Schiff base ligands, 2,6‐pyridinedicarboxylic acid and the mixed ligand complexes and revealed that the synthesized mixed ligand complexes exhibited higher antimicrobial activity than their free Schiff base ligands.