Synthesis, structural characterization, and dual DNA/HSA binding of novel Palladium(II) violurate complex with selective p53/Caspase-3-mediated anticancer activity

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Abstract A novel palladium(II) complex with the violurate ligand, [Pd(H₂L)₂], was synthesized and characterized. Molar conductivity (15.55 Ω -1 cm² mol -1 ) confirmed its non-electrolytic nature, and ESI-MS showed a molecular ion peak at m/z 417.57 matching [C₈H₄N₆O₈Pd]⁺. PXRD structural analysis revealed a triclinic crystal system (space group P-1) with τ₄ = 0.04, confirming square-planar geometry around Pd(II), with Pd–O bond lengths ranging from 2.065 to 2.178 Å. Thermal analysis showed three decomposition stages (41.00%, 15.00%, and 18.50% mass losses) with palladium metal as the final residue. The complex exhibited DNA binding constants of K b = 1.694 × 10⁴ M -1 (UV-Vis) and 2.870 × 10 7 M -1 (fluorescence) with ΔG = -24.12 and − 42.94 kJ mol -1 , respectively, indicating groove binding mode as confirmed by viscosity measurements. HSA binding constants were K b = 2.784 × 10 5 M -1 (UV-Vis) and 6.546 × 10 9 M -1 (fluorescence). Cytotoxicity assays against MDA-MB-231, HCT-116, and HepG-2 cell lines gave IC₅₀ values of 29.42, 38.11, and 24.68 µM, respectively, with selectivity indices (1.99, 1.78, and 1.29) higher than cisplatin. The complex induced late apoptosis (8.46-fold increase) via p53/caspase-3 upregulation (4.46-fold and 3.96-fold, respectively). DFT calculations showed reduced HOMO-LUMO gap (5.406 eV vs. 6.517 eV for free ligand), correlating with enhanced bioactivity. These findings present [Pd(H₂L)₂] complex as a promising dual-targeting anticancer candidate. Unlike conventional Pd(II) complexes that target DNA via intercalation or N/S coordination, our complex employs an unusual O₄ coordination sphere from violurate ligands, demonstrating a non-intercalative groove-binding mode and a p53/caspase-3 mediated apoptosis with enhanced selectivity index.

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