Unexpected structure of enaminone Pd(II) complex in comparison with Cu(II) complex: Synthesis, characterization, DNA binding and antitumor activity

Novel Pd(II) and Cu(II) complexes have been synthesized by the reaction of Na2PdCl4 and CuCl2·2H2O with fluorinated enaminone ligand leading to the formation of complexes having the formulae [Pd(enm)Cl2] and [Cu2(diCO)4]; where enm and diCO are enaminone and deprotonated dicarbonyl containing ligands, respectively. The structures and geometry of the two metal chelates have been elucidated by applying alternative spectral and analytical tools including elemental analysis, FT-IR spectra, 1H NMR spectra and UV–Vis spectra. The molecular structure of the Cu(II) complex has been determined by single crystal X-ray diffraction; the complex crystalizes in monoclinic P21/c space group. Square pyramidal geometry has been confirmed for Cu(II) complex where Pd(II) complex has the expected square planar geometry. The mechanism of the in-situ conversion of the enaminone to dicarbonyl ligand with CuCl2·2H2O was illustrated. The type of interaction between the two complexes and salmon sperm DNA (SS-DNA) has been studied applying absorption spectra and viscosity measurements. The binding constant values (kb) was calculated to be (1.17 ± 0.6) × 104 and (3.62 ± 0.4) × 104 M−1 for Pd(enm)Cl2 and Cu2(diCO)4, respectively, which confirmed the interaction of the two complexes with DNA via intercalative mode of interaction. Intercalative binding mode between the studied compounds and DNA was further confirmed by the results of viscosity measurements. The anticancer activity of the two metal complexes has been evaluated against breast cancer cell line (MCF-7) and the liver cancer cell line (HepG-2) in comparison with the well-known anticancer drug cis-DDP. Surprisingly, we found that Cu2(diCO)4 complex has activity (IC50 = 3.26 μg/mL) against a human liver cancer cell line (HepG2) exceeding the efficiency of the reference drug cis-DDP (IC50 = 3.67 μg/mL). © 2020 Elsevier B.V.