Structures and Interaction with DNA of Ternary Palladium(II) Complexes: [Pd(Gly)(X)] (Gly=Glycine; X=2,2′-Bipyridine, 1,10-Phenanthroline and 2,2′-Bi-pyridylamine)

The structures of the ternary palladium(II) complexes of the formulations [Pd(Gly)(bpy)]+Cl−·4H2O (Gly=glycine; bpy=2,2′-bipyridine) (1), [Pd(Gly)(phen)]+Cl−·4H2O (2) (phen=1,10-phenanthroline) and {[Pd(Gly)(bpa)]+Cl−}2·6H2O (3) (bpa=2,2′-bipyridylamine) were determined. All complexes are positively charged and neutralized by the chloride anion located nearby the complexes. The central Pd(II) atoms of the complexes 1, 2 and 3 have a similar distorted square planar coordination geometry, in which each Pd(II) atom is coordinated to two N atoms of the bidentate heterocyclic ligand, and N and O atoms of the bidentate glycine ligand. The interaction of the complexes with calf thymus (CT) DNA was also studied using the fluorescence method. All complexes showed the inhibition of ethidium bromide binding to CT DNA, and the DNA-binding strengths were reflected as the relative order 2>1>3. The remarkable reduction of UV absorption intensity of 2 caused in the presence of DNA suggests the presence of π–π stacking interaction between the heterocyclic ring of the phen ligand and nucleobases. The intercalative DNA-binding of 2 is suggested by UV and CD measurements. DNA cleavage studies indicated that the cleavage of the plasmid supercoiled pBR322 DNA in the presence of H2O2 and ascorbic acid could be enhanced by the complexes.