Synthesis, structural elucidation and DNA binding profile of Zn(II) bis-benzimidazole complexes

Abstract

Complexes of zinc (II) (L1ZnBr2, L2ZnBr2) were prepared in good yields using bis-benzimidazole ligands with olefinic bridges and different substituents on the nitrogen atoms in the benzimidazole cores (L1=H, L2=Bz). The crystal structure of L2 was determined, showing that both benzimidazole rings and the carbon atoms of the olefinic bridge are coplanar with a slight deviation and that the benzyl substituent is perpendicular to this plane. Also, the crystal structure of L1ZnBr2 was determined showing that in coordinated L1, benzimidazole rings are out the plane with respect to the olefinic bridge, allowing their coordination through the nitrogen atoms to get a strain-free seven-membered ring, achieving a distorted tetrahedral geometry. Both crystal structures of L2 and L1ZnBr2 exhibit π-π stacking interactions that hold their supramolecular arrangement. All ligands and complexes were fully characterized. Additionally, through DNA binding studies using absorption spectral titrations it was possible to determine a slight hypochromism and bathochromism when ligands and complexes interact with calf thymus DNA in neat DMSO and 3% DMSO/Tris-HCl buffer, the spectral changes being consistent with partial intercalation. The intrinsic binding constant Kb of ligands and complexes are reported for each medium.