Synthesis, Structural Characterization, in Vitro Biological Activity, and Computational Quantum Chemical Studies of New Cobalt (II), Nickel (II), and Copper (II) Complexes Based on an Azo-Azomethine Ligand

Abstract

As previously reported, we have synthesized an azo azomethine ligand 4-((E)-(2,5 dichloro phenyl) diazenyl)−2-((E)-((4-hydroxyphenyl) imine) methyl) phenol (L). The synthesized ligand has been used to prepare copper(II), nickel(II), and cobalt(II) metal complexes and characterized using various analysis techniques. To identify complexes, methods, such as elemental analyses, electrical conductivity, IR spectroscopy, mass spectrometry, magnetic moment, vibrating sample magnetometry (VSM), ¹HNMR, UV–Vis, and thermal analysis were utilized, and a mononuclear structure was proposed for all compounds and all the complexes are non-electrolytes in nature. The chelation of the ligands to the metal ions occurs through phenolic oxygen and nitrogen atoms of the azomethine group of the ligands. According to various analytical and spectral data, a square planar structure is proposed for copper and nickel metal complexes and a quadrilateral structure is proposed for cobalt complexes. The antibacterial properties of ligands and complexes of copper(II), nickel(II), and cobalt(II) were investigated in vitro on standard bacteria as well as on bacteria isolated from clinical specimens (urine). The results revealed that the ligand and its metal complexes had a very high antibacterial activity against Staphylococcus aureus, but were ineffective against other studied bacteria. The synergistic effect of the compounds with the three antibiotics (vancomycin (V), methicillin (M), and trimethoprim (T)) was also investigated, along with the cytotoxicity of its ligand and copper complex in HFF cell line. At a concentration of 3.90 μl of these compounds, cell viability was significant. The structure of ligand and complexes was optimized by DFT calculations. Computational methods were performed for deeper understanding of the interaction between ligands and metal by EDA calculations. This result confirmed that the bonding between ligands to metal was mainly covalent. The complexes investigated are reported for the first time. The search for new antimicrobial agents against Staphylococcus aureus is an urgent medical need. Therefore, sensitive and selective diagnosis of this pathogenic bacterium is of great importance, which has been obtained in this study. The compounds synthesized from among the nine gram-negative and gram-positive bacteria are only sensitive to Staphylococcus aureus bacteria.

Keywords:

• Metal complexes
• azo-azomethine
• DFT
• antimicrobial
• synergistic effect

Acknowledgments

The authors would especially appreciate the Arak University for providing financial support of this research. We also thank the staff at Dena Pathobiology Laboratory for their contribution to biological studies.

Disclosure statement

We declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

Additional information

Funding

This work was financially supported by the Arak University.