Synthesis, spectroscopic characterization, in vitro cytotoxic, antimicrobial and antioxidant studies of Co(II) complexes bearing pyridine-based macrocyclic ligands with density function theory (DFT) and molecular docking investigations

The absolute necessity to fight some class of tumour is perceived as serious health concerns, and the discovery and development of effective anticancer agents are urgently needed. So, the novel ligands (N 4 MacL 1 –N 6 MacL 3 ) and bivalent cobalt complexes with tetraaza macrocyclic ligands were produced and characterised using spectroscopic methods including physico-chemical and spectral (FTIR, UV–visible, 1 H-NMR, 13 C-NMR, Mass, EPR, TGA, molar-conductance measurements and PXRD) studies. The FTIR spectrum data point to the ligands' chelation behaviour towards Cobalt metal ion through the secondary amine group's nitrogen atom. The complexes' octahedral geometry was verified by the EPR spectrum data and UV–vis spectroscopy results. Then, molar conductance measurements confirmed the non-electrolytic nature of the complexes. Density theoretical calculations of the compounds' computational aspects have been examined and found to be in strong agreement with the outcomes of the experiments. Through simultaneous thermogravimetric analysis (TGA), thermal behaviour of the compounds was examined. Kinetic and thermodynamic parameters were calculated using Coats Redfern and Ozawa Fyn-wall method. The in vitro antimicrobial effectiveness of these resulting compounds has been scrutinized against a number of bacterial strains ( E. coli, S. Marcescence, S. aureus ) and fungal strains (A. flavus, C. albicans, and F. oxysporum) by disc diffusion method and prominent results were obtained. Complex [Co(N 6 MacL 3 )Cl 2 ] has shown excellent antibacterial and antifungal activity with MIC 3.50 µM and 4.25 µM, respectively. Furthermore, the compounds have also been tested for antioxidant activity. The complexes [Co(N 6 MacL 2 )Cl 2 ] and [Co(N 6 MacL 3 )Cl 2 ] exhibited the upright activity as antioxidant. In addition, in vitro cytotoxic activity of the compounds was screened against human cervical cancer cells (HeLa), human breast cancer cells (MCF-7), IMR-32 and A549 using MTT assay. The complexes [Co(N 6 MacL 2 )Cl 2 ] and [Co(N 6 MacL 3 )Cl 2 ] showed the tremendous cytotoxic activity. For targeting molecular docking study, the drugs were tested using the receptors 5H67, 3TY7, 3DRA, 3ROW and 3T88. Graphical abstract