# Novel amide-based macrocyclic Co(ii) complexes: correlating structural, computational, and biological properties through DFT and docking

## TL;DR

Researchers created cobalt complexes with amide-based structures that show strong antimicrobial and antioxidant properties, supported by computational and experimental studies.

## Contribution

The study introduces novel amide-based macrocyclic Co(ii) complexes with demonstrated antimicrobial, antioxidant, and selective cytotoxic properties.

## Key findings

- The Co(ii) complexes exhibit octahedral geometry confirmed by magnetic and spectral data.
- Complex [Co(N4O4MacL3)Cl2] showed highest antioxidant activity via DPPH assay.
- Molecular docking confirmed favorable interactions with biomolecular targets.

## Abstract

A series of Co(ii) complexes incorporating functionalized macrocyclic scaffolds, designated as [Co(N4O4MacL1)Cl2]–[Co(N4O4MacL3)Cl2], were synthesized using three structurally related macrocyclic ligands (N4O4MacL1–N4O4MacL3), each featuring an amide-based tetradentate donor framework. The complexes were comprehensively characterized by elemental analysis, FTIR spectroscopy, magnetic susceptibility measurements, UV-visible spectroscopy, 1H and 13C NMR spectroscopy, and powder X-ray diffraction. Spectroscopic and analytical findings confirm that the ligands act as monoanionic tetradentate donors, coordinating through nitrogen and oxygen donor sites. The magnetic and electronic spectral data support an octahedral coordination geometry around the Co(ii) center in all complexes. Thermal stability and kinetic parameters were assessed through thermogravimetric analysis, employing the Coats-Redfern and Flynn-Wall-Ozawa (FWO) models to determine activation energies and thermodynamic parameters. Moreover, density functional theory (DFT) calculations provided insights into optimized geometries, bond parameters, and frontier molecular orbital characteristics, which corroborate the experimental observations. The biological activities of the ligands and their Co(ii) complexes were evaluated through in vitro antimicrobial assays against fungal strains A. niger and C. albicans, and bacterial strains B. subtilis, S. aureus, E. coli, and S. typhi. Additionally, antioxidant activity assessed by the DPPH free-radical scavenging assay revealed that [Co(N4O4MacL3)Cl2] demonstrated the highest radical-quenching efficiency. Among the complexes studied, [Co(N4O4MacL2)Cl2] displayed the most promising antimicrobial activity with minimal cytotoxic effects. Molecular docking studies further validated the biological results, indicating favourable interactions of the complexes with relevant biomolecular targets. Overall, these findings highlight the therapeutic potential of amide-containing macrocyclic ligands and their cobalt(ii) complexes as promising candidates for antimicrobial applications, selective cytotoxic behaviour, and effective antioxidant activity.

Amide-based macrocyclic Co(ii) complexes with octahedral geometry were synthesized and characterized by spectral, thermal and DFT studies. The complexes showed enhanced antimicrobial and antioxidant activity, supported by docking results.