Preparation of lanthanum and nickel complexes based on a newly prepared Schiff base ligand: Structural elucidation, molecular docking, and density functional theory calculations

This study describes the synthesis of new Lanthanum (La) and Nickel (Ni) complexes using a novel Schiff base ligand derived from the condensation reaction of 4-aminoantipyrine, 5-bromosalicylaldehyde, and o-phenylenediamine. The Schiff base ligand was characterized using various spectroscopic techniques, such as ¹H and ¹³C NMR spectroscopy, and UV–visible spectral studies, to confirm its structure and purity. The metal complexes were prepared by reacting the ligand with LaNO₃.6H₂O and NiCl₂.6H₂O under reflux conditions, and their structural properties were determined through ¹H and ¹³C NMR spectroscopy. Density Functional Theory (DFT) calculations were employed to investigate the geometry and electronic structure of the complexes, providing insights into their stability, frontier molecular orbitals (HOMO-LUMO), and reactivity indices. DFT analysis showed that the La complex forms the strongest bond with the ligand, indicated by its higher binding energy compared to the Ni complex. HOMO and LUMO energy gap levels indicate that the Ni complex is the most reactive compound, while the La complex exhibits lower reactivity due to its larger energy gap. Molecular docking studies were conducted to assess the biological activity of the Schiff base ligand and its complexes against the active sites of Entamoeba coli (ID: 1C14) as Gram-negative bacteria, Staphylococcus aureus (ID: 2XCT) as Gram-positive bacteria, and Xanthine oxidase (ID: 1FIQ) as an antioxidant agent protein-selected biological target, revealing strong binding interactions that suggest potential applications as antimicrobial or anticancer agents. Overall, this study demonstrates the successful synthesis and characterization of Lanthanum and Nickel complexes, supported by computational analyses, and highlights their promising biological relevance, opening up avenues for further research in medicinal chemistry and materials science.