Spectral, band gap and DFT studies of novel cobalt (II) complexes of N(4)-cyclohexylthiosemicarbazones: Molecular docking with DNA and SARS-CoV-2 Mpro

Abstract

The synthesis and characterization of four novel cobalt complexes CoL12 (1), [Co(HL2)L2]Cl (2), CoL22 (3) and [Co(HL2)L2]Br (4) of thiosemicarbazones HL1 and HL2, (where HL1 is 2-benzoylpyridine-N(4)-cyclohexylthiosemicarbazone and HL2 is quinoline-2-carbaldehyde-N(4)-cyclohexylthiosemicarbazone) are reported. The new ligand HL2 was characterized physicochemically and the structure was confirmed by single crystal X-ray diffraction technique. The relevant intermolecular interactions of HL2 were quantified using Hirshfeld surface analysis. The coordination of the Schiff bases to the metal ions were assigned with the help of physicochemical methods, which indicate octahedral geometry for all the complexes. The deprotonated ligands coordinate via pyridinyl nitrogen, azomethine nitrogen and thiolate sulfur atoms in all the complexes. However, the NNS coordination of the neutral thione ligand is also present in the complexes 2 and 4. Furthermore, geometrical optimization and theoretical calculations of the compounds were achieved by density functional theory quantum chemical computational methods. The direct bandgaps of the complexes were calculated experimentally using the Kubelka-Munk model, which shows a range of 1.62–2.09 eV and corroborates with the theoretical studies. In silico molecular docking studies of all the compounds were performed with B-DNA dodecamer and are all indicative of groove mode of binding. All the compounds exhibit strong putative binding potentials toward duplex DNA. Interestingly, the putative binding efficiency of the complexes 1 and 3 with SARS-CoV-2 main protease is also found very higher compared to the repurposed drugs that are specifically active at 6Y2F.