DNA-binding studies and antioxidant activities of two-, three- and four-coordinate silver(I) complexes containing bis(2-benzimidazolyl)aniline derivatives

Three ligands bis(benzimidazol-2-ylmethyl)aniline (bba), bis(N-methylbenzimidazol-2-ylmethyl)aniline (Mebba), and bis(N-ethylbenzimidazol-2-ylmethyl)aniline (Etbba) have been prepared. Reaction of these shape-specific designed ligands with Ag(pic) (pic = picrate) afforded three novel complexes, namely, [Ag-2(bba)(2)](pic)(2)center dot 2DMF 1, [Ag(Mebba)(2)](pic)center dot Et2O 2 and [Ag(Etbba)(pic)] 3. The ligands and Ag(I) complexes were characterized by elemental analysis, UV-vis, IR, NMR and X-ray crystallography. 1 is a dinuclear metallacycle with 2-fold rotational symmetry in which two syn-conformational bba ligands are connected by two linearly coordinated Ag(I) atoms. 2 consists of a centrosymmetric uninuclear pore canal structure assembled from a Ag(I) ion and two Mebba ligands, resulting in a distorted tetrahedron geometry. The structure of 3 consists of a ligand of Etbba, one picrate anion, and one Ag(I) atom, and the coordination geometry around Ag(I) is best described as Y-shaped. In order to explore the relationship between the structure and biological properties, the DNA-binding properties have been investigated by electronic absorption, fluorescence, and viscosity measurements. The experimental results suggest that Ag(I) complexes bind to DNA in an intercalation mode, and their binding affinity for DNA follows the order 2 > 1 > 3. Moreover, antioxidant activities of the title complexes have been investigated. The result demonstrates that the three Ag(I) complexes have a strong potential to be applied as scavengers to eliminate hydroxyl and superoxide radicals in vitro.