Binding studies of asymmetric pentacoordinate copper(II) complexes containing phenanthroline and ethane-1,2-diamine ligands with calf-thymus DNA

New chiral complexes of the composition [MLL'], where HL = 1,2-bis(1H-benzimidazol-2-yl)ethane-1,2-diol = H(2)bimedol, M = Co-II, Ni-II, Cu-II, and L' = 1,10-phenanthroline (phen) or ethane-1,2-diamine (en), were synthesized and characterized. The ligand L exhibited a coordination mode involving the O-atom of only one OH group, the other one being directed away from the metal center. The complexes [Cu(Hbimedol)(en)]Cl (1), [Cu(Hbimedol)(phen)]Cl (2), [Co(Hbimedol)(phen)]Cl (3), [Ni(Hbimedol)(en)]Cl (4), and [Ni(Hbimedol)(phen)]Cl (5) were ionic in nature and stable at room temperature. The donor sets involved in coordination with the metal ions were the O-atom of one OH group and two N-atoms of the two benzimidazole moieties, besides the two N-atoms of phen or en (Fig. 1.). The proposed five-coordinate geometry of 1-5 was established by analysis of spectroscopic data; the ball-and-stick models supported the proposed structures of 1-5 since they showed apparently no strain on any bond and angle. The interaction of complexes 1 and 2 with calf-thymus DNA were carried out by UV/VIS titration, circular dichroism, electrochemical methods, and viscometry. The intrinsic binding constant K-b of 1 and 2 was determined as 1.57 (.) 10 and 1.51 (.) 10' m(-1), respectively, suggesting that both complexes bind strongly to calf-thymus DNA.