Effects of the ancillary ligands of polypyridyl ruthenium(ii) complexes on the DNA-binding behaviors

Abstract

A new polypyridyl ligand PMIP {PMIP = 2-(4-methylphenyl)imidazo[4,5-f]1,10-phenanthroline}, and its Ru(II) complexes, [Ru(bpy)₂PMIP]²⁺1 (bpy = 2,2′-bipyridine), [Ru(phen)₂PMIP]²⁺2 (phen = 1,10-phenanthroline) and [Ru(dmp)₂PMIP]²⁺3 (dmp = 2,9-dimethyl-1,10-phenanthroline), have been synthesized and characterized. The binding of the three complexes to calf thymus DNA (CT DNA) has been investigated with spectrophotometic methods, viscosity measurements, as well as equilibrium dialysis and circular dichroism spectroscopy. Complexes 1 and 2 can bind to CT DNA through intercalation. Complex 3 binds to CT DNA via partial intercalative mode. All the three complexes can enantioselectively interact with CT DNA in a way. Complex 3 is a much better candidate as an enantioselective binder to CT DNA than complex 1 and complex 2. The Δ enantiomer of complex 1 is slightly predominant for binding to CT DNA to the Λ enantiomer. The experimental results suggest that the ancillary ligands of polypyridyl Ru(II) complexes have significant effects on the spectral properties and the DNA-binding behaviors of the complexes. On the basis of the experiments, the theoretical calculations applying the density functional theory (DFT) on the level of B3LYP/LanL2DZ basis set for these three complexes have been used to further discuss the trend in the binding strength or binding constants (K_b) of the complexes to DNA, as well as predict roughly some of their spectral properties.