Synthesis of a novel trinuclear palladium complex: the influence of an oxime chelate ligand on biological evaluation towards double-strand DNA, BSA protein and molecular modeling studies

Abstract

A trinuclear palladium complex with an aryl oxime ligand, [Pd₃(C₁₂H₈CNO)₆], has been synthesized and structurally characterized by elemental analysis (C, H, N), IR, NMR resonance signals, and single crystal X-ray diffractometry. The crystal structure had a distorted square planar geometry. Binding interactions of the trinuclear Pd(II) complexes with calf thymus deoxyribonucleic acid (CT-DNA) and bovine serum albumin (BSA) were investigated by vivid spectroscopic techniques and molecular modeling studies. In vitro studies (UV-vis spectroscopy, competitive emission titration, circular dichroism (CD) and helix melting methods) show that the complex interacts with DNA via a groove mechanism binding mode. The intrinsic binding constants, K_b, of the complex with CT-DNA obtained from UV-vis absorption studies were 2 ± 0.02 × 10⁵ M⁻¹. Moreover, the addition of the complexes to CT-DNA (1 : 2) led to an increase in the melting temperature of DNA, up to 2.97 °C. Competitive studies with methylene blue (MB), as a fluorescence probe with trinuclear palladium, revealed that it cannot release MB molecules of the DNA-bound MB, suggesting there is no competition with MB. Furthermore, the microenvironment and secondary structure of BSA are changed in the presence of the trinuclear Pd(II) complex. Competitive binding using the site markers, Eosin and Ibuprofen, demonstrated that the complex binds to domain I (subdomain IIA) on BSA. Finally, molecular modeling studies were conducted to determine the binding sites of the DNA and BSA with the complex.