Synthesis, Spectroscopic Inspection, Antibacterial, Molecular Docking, and DFT Analysis of Metal Chelates Incorporating Coumarin-Isatin Schiff Base with Proline as a Mixed Ligand

In this work, the Schiff base ligand (COM-IST) was synthesized from the condensation of 6-aminocoumarin and isatin. The new Co(II), Ni(II), Cu(II), and Zn(II) complexes were synthesized from the Schiff base (COM-IST) with the proline (Pro) amino acid as a mixed ligand. The structure of the Schiff base was confirmed by FTIR, ¹H-, and ¹³C-NMR spectroscopy and CHN analysis. Its complexes were confirmed through FTIR, UV-vis spectroscopy, CHN analysis, magnetic susceptibility, XRD, and molar conductivity measurements. The spectral results indicate that the ligands exhibit bidentate behavior in all four complexes, and octahedral geometries are observed in each metal complex. The antibacterial activity of the prepared compounds was tested against various types of Gram-positive and negative bacteria. Molecular docking investigations proved that the ligand had intriguing interactions with the active sites of the receptors (DNA gyrase) for both bacterial strains. Frontier molecular orbitals (FMOs), various quantum chemical descriptors (QCDs), and molecular electrostatic potential (MEP) surfaces were computed using density functional theory (DFT) for the ligand and complex at the B3LYP functional with the 6-31G(++)d,p basis set for the ligand and the LANL2DZ basis set for the complexes.