Ni(II) complexes with 2,2-dipyridylamine and salicylaldehydes: Synthesis, crystal structure and interaction with calf-thymus DNA and albumins.

The synthesis of four cationic mixed-ligand Ni(II) complexes with 2,2'-dipyridylamine (dpamH) and substituted salicylaldehydes (X-saloH) was undertaken in an effort to discover new biologically active compounds. The complexes with the general formula [Ni(dpamH)(X-salo)]Cl, 3-6, namely [Ni(dpamH)(5-Cl-salo)]Cl, 3, [Ni(dpamH)(5-Br-salo)]Cl, 4, [Ni(dpamH)(5-CH-salo)]Cl, 5, and [Ni(dpamH)(3-OCH-salo)]Cl·CHOH, 6, were characterized by elemental analyses, FT-IR and UV-vis spectroscopy, magnetic and conductivity measurements. In addition, two analogous nickel-salicylaldehydato complexes in the absence of dpamH were prepared and characterized as [Ni(5-Cl-salo)(CHOH)], 1 and [Ni(5-Br-salo)(CHOH)], 2. The structures of complexes 1-6 were determined by X-ray crystallography revealing octahedral coordination of nickel (II) and monomeric nature of the compounds. Spectroscopic (UV-vis), electrochemical (cyclic voltammetry) and physicochemical (viscosity measurements) techniques were employed in order to study the binding mode and strength of the complexes to calf-thymus (CT) DNA, while competitive studies with ethidium bromide (EB), performed by fluorescence spectroscopy, revealed the ability of the complexes to displace the DNA-bound EB. The complexes bind to DNA probably via intercalation exhibiting high DNA-binding constants. For the cationic complexes 3-6, the coexistence of an electrostatic interaction with CT DNA may be also suggested. The interaction of the complexes with serum albumins was studied by fluorescence emission spectroscopy and the determined binding constants exhibit relative high values.