DFT-validated structures and conformational studies of Cd(II), Ni(II), Hg(II) and Cu(II) complexes with 3-(2-(4-aminobenzoyl)hydrazono)-N-(pyridin-2-yl)butanamide: electrochemical, biological and docking evaluations

In this work, Cd(II), Ni(II), Hg(II), and Cu(II) complexes of the hydrazono ligand 3-(2-(4-aminobenzoyl)hydrazono)-N-(pyridin-2-yl)butanamide (H 2 ABHPB) were synthesized and characterized using spectroscopic techniques and DFT calculations (DMol 3 ). The electronic parameters revealed band gap values ranging from 1.878 to 3.036 eV. Cytotoxic evaluation against the HepG2 cell line showed that the free ligand exhibited the highest activity (IC 50 = 8.63 ± 0.7 μg/ml), followed by the Hg(II) complex (IC 50 = 10.33 ± 0.9 μg/ml), whereas the Cu(II) complex displayed the lowest activity (IC 50 = 64.14 ± 3.8 μg/ml). Interestingly, no direct correlation was observed between the HOMO-LUMO gap and cytotoxicity, indicating that biological activity is influenced by combined electronic and structural factors. Electrochemical studies demonstrated that complexation significantly alters redox behavior. Molecular docking supported the experimental findings, highlighting favorable interactions for the most active compounds. These results provide new insight into the structure activity relationship of H 2 ABHPB and its metal complexes. • Synthesis of Cd(II), Ni(II), Hg(II), and Cu(II) complexes. • Structural characterization via (IR, UV–Vis, 1 H NMR, 13 C NMR, EDX, SEM, EPR, and MS). • DFT method was applied to determine the geometry optimizations, along some quantum parameters. • Studying the biological activities (antimicrobial, antioxidant, cytotoxic assay, and colorimetric DNA detection test). • Molecular Operating Environmental module (MOE) • Cyclic voltammetry studies of Hg(II) solution.