Synthesis, structure, DNA-binding properties and antioxidant activity of silver(i) complexes containing V-shaped bis-benzimidazole ligands†
Abstract
A V-shaped ligand bis(2-benzimidazol-2-ylmethyl)benzylamine L1 with its two derivatives bis(N-methylbenzimidazol-2-ylmethyl)benzylamine L2 and bis(N-benzylbenzimidazol-2-ylmethyl)benzylamine L3 have been prepared. Reaction of these shape-specific designed ligands with Ag(pic) (pic = picrate) afforded three novel complexes, namely, [Ag2L12](pic)21, [Ag2L22](pic)2ยท2DMF 2 and [AgL3(pic)] 3. The ligands and complexes were characterized on the basis of elemental analysis, UV-Vis, IR, NMR spectroscopy and X-ray crystallography. Complex 1 is a dinuclear metallacycle with a 2-fold rotational symmetry in which two syn-conformational L1 ligands are connected by two linearly coordinated Ag(I) atoms. Due to the strong interaction between two adjacent Ag(I) atoms, the coordination mode of the central Ag(I) atom can be described as T-shaped. Complex 2 consists of a centrosymmetric dinuclear pore canal structure assembled from two nearly linearly coordinated Ag(I) atoms and two L2 ligands. The structure of complex 3 adopts a four-coordinate environment for AgN2O2, with the counterion participating in an eight-shaped geometry. In order to explore the relationship between the structure and biological properties, the DNA-binding properties have been investigated by viscosity measurements, electronic absorption, and fluorescence. The results suggest that the ligands and complexes bind to DNA in an intercalation mode, and their binding affinities for DNA are also different. Moreover, the three Ag(I) complexes also exhibited potential antioxidant properties in vitro studies.