Synthesis, characterization, and DNA binding of complexes [Pt(bpy)(pip)](2+) and [Pt(bpy)(hpip)] (2+)

Two new platinum(II) complexes, [Pt(bpy)(pip)](NO3)2 (1) and [Pt(bpy)(hpip)](NO3)2·2H2O (2) (bpy is 2,2'-bypyridine; pip is 2-phenylimidazo[4,5-f][1,10]phenanthroline; hpip is 2-(2-hydroxyphenyl) imidazo[4,5-f][1,10]phenanthroline), have been synthesized and fully characterized by CHN analysis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, (1)H-NMR spectroscopy, IR spectroscopy (attenuated total reflection), and UV-vis spectroscopy. The DNA-binding behaviors of both complexes have been studied by spectroscopic methods and viscosity measurements, and their ability to inhibit DNA transcription was measured. The results indicate that both complexes show some degree of binding to DNA in an intercalative mode, resulting in intrinsic binding constants of (2.88 ± 0.4) × 10(4) and (5.38 ± 0.8) × 10(4) for 1 and 2, respectively. The comparatively observed difference in the DNA-binding affinities of the two complexes can be reasonably explained by the presence of intramolecular hydrogen bonding between the ortho phenolic group and the nitrogen atom of the imidazole ring. The extended coplanarity of the hpip ligand due to intramolecular hydrogen bonding may lead to an enhancement of the DNA-binding affinity of the hpip complex. In addition, the complexes can promote photocleavage of pUC19 DNA on irradiation as revealed by the spectroscopic and viscometric measurements, with 2 promoting cleavage of pUC19 DNA at lower concentration. Moreover, increasing concentrations of both complexes inhibited DNA transcription, and as expected 2 was shown to be a better antitumor agent than 1.