Pyridine-2,4-dicarboxylate as an organic chelating ligand towards cobalt(II) for designing a novel complex: X-ray studies, DFT analysis, and evaluation of catechol oxidase mimic activity and anticancer property towards A549 cell line

Enzyme mimic modeling aimed to explore the diverse molecular mechanisms that enzymes could employ, providing insights into their functional versatility. The Co(II) complex, [NH₂(CH₃)₂]₂[Co(H₂PDC)₂(H₂O)₂] (ZS-1), was synthesized solvothermally and fully characterized using SCXRD, FTIR, EPR and PXRD. It is evaluated as an enzyme mimic of catechol oxidase (CO) using 2,4-pyridinedicarboxylic acid (H₂PDC). X-ray diffraction studies reveal an octahedral geometry around the Co(II) ion, and the resulting complex exhibits a polymeric structure stabilized by CH and OH H-bonding interactions leading to 1D or 2D propagating networks due to non-covalent interactions. While the DFT analysis provides solid corroboration of structural parameters, the UV–Vis absorption spectra were examined using TD-DFT calculations. These calculations indicated that the observed spectral bands are primarily due to ILCT transitions. The biomimetic catalytic activity for catechol oxidase enzyme was thoroughly examined including reaction kinetics. ZS-1 complex speeds up the reaction between catechol and oxygen, creating o-quinone as the desired product. In methanol, the K_cat value is determined to be 108.2 h⁻¹ which is comparatively higher than other cobalt-based complexes. Further, the CV investigations provide strong support for the order of enzyme activity. Further, the anticancer efficacy of ZS-1 complex against lung cancer A549 cells was assessed using the MTS assay. This colorimetric assay quantifies cell viability by measuring the absorbance of a product generated by metabolically active cells.