Synthesis, characterization, cytotoxic and DNA binding studies of diimine Platinum(II) and Palladium(II) complexes of short hydrocarbon chain ethyldithiocarbamate ligand

Two novel Platinum(II) and Palladium(II) complexes of 2,2′-bipyridine (bpy) with ethyldithiocarbamate (Et-dtc) were synthesized. These complexes were characterized by spectroscopic methods such as ultraviolet-visible, infrared and ¹H NMR as well as conductivity measurements and chemical analysis. In these complexes, the dithiocarbamate ligand coordinates with Pt(II) or Pd(II) center as bidentate with two sulfur atoms. These water soluble complexes were tested for their in vitro anti-tumor activity against chronic myelogenous leukemia cell line, K562. They show Cc₅₀ values lower than those of cisplatin. The mode of binding of the complexes to calf thymus DNA, were investigated by circular dichroism, ultraviolet difference and fluorescence spectroscopy. These complexes can denature DNA at very low concentrations (~100 μM). Both complexes exhibit cooperative binding and presumably intercalate into DNA. Remarkably, most of the experimental results indicate that the tendency of the Pd(II) complex to interact with DNA and its anti-tumor activity against K562 is more than that of its Pt(II) analog.