Evaluation of biomolecular interaction, catecholase activity and in vitro cytotoxic activity of mononuclear and dinuclear cobalt(II) complexes

Mononuclear and dinuclear cobalt(II) complexes C1 and C2 were synthesized, characterized and examined for their potential biological studies. The structural validation of C1 and C2 was ascertained by various analytical and spectral methods which corroborated well with single-crystal X−ray diffraction studies. DFT/TD−DFT investigations of C1 and C2 were performed to understand their electronic and structural properties. In vitro DNA/BSA interactions of synthesized complexes were conducted using a range of biophysical techniques including UV−vis, fluorescence, circular dichroism (CD), cyclic voltammetry (CV) and electron paramagnetic resonance (EPR). The binding strength of complexes C1 and C2 with DNA were calculated to be 8.06(±0.84) × 10⁴ and 8.63(±1.03) × 10⁵ M⁻¹, and with BSA, were found to be 2.8(±0.31) × 10⁴ and 6.7(±0.54) × 10⁴ M⁻¹, respectively. The catechol oxidase activity of complexes C1 and C2 were assessed employing 3,5−di−tert−butylcatechol (3,5−DTBC) as a substrate, and its subsequent conversion to 3,5−di−tert−butylquinone (3,5−DTBQ) product was validated. We also validated the antioxidant potential of C1 and C2 via a DPPH assay. Furthermore, the cytotoxic activity of C1 and C2 was measured against A549 (lung), MCF−7 and MDA−MB−231 (breast), MIA−Pa−Ca−2 (pancreas) and Hep−G2 (liver), employing ADR (adriamycin) as a standard. The results specified that the complexes C1 and C2 demonstrated cytotoxicity against A549 cell lines with relatively low GI₅₀ values (8−10 µg mL^‒1).