Acid–base effects, light emission, DNA-binding and photocleavage studies of oligo-homonuclear ruthenium(II) complexes and their computational study

Abstract

The ground- and excited-state acid ionization constants and the DNA binding properties of mono-, di- and trinuclear ruthenium(II) polypyridine complexes have been studied by electronic absorption and fluorescence emission spectroscopy. The DNA binding abilities of the complexes increase with increasing π-electron multiplicity of phenanthroline groups and the H-bonding properties of imidazole moieties increase from the mononuclear (R1) to dinuclear (R2), followed by trinuclear (R3) complexes. In addition, the increasing surface area of the complexes relatively leads to a corresponding enhancement in binding affinity. The DNA-binding constants, Kb, of the complexes were determined systematically by spectrophotometric titration. In addition to the various ionic interactions, van der Waals interaction, hydrogen bonding, DNA-binding constants Kb and hypochromism of Ru(II) polypyridine complexes inferred the existence of intercalation mode of binding. The trend in DNA-binding affinities as well as the spectral properties of this series of complexes can be reasonably explained by applying the DFT at the B3LYP/LanL2DZ/6-31G level. The results suggest that the multiplication of complex unit has important effects on the electronic structures, a trend in the DNA-binding affinities and an improvement of spectral properties of the complexes. The binding affinity of the ruthenium complexes with biological receptors namely, G-quadraplexes from human telomeres has been investigated. The binding characteristics of complexes have been compared with each other using molecular docking. Further, these complexes tend to promote cleavage of plasmid DNA under photolytic conditions.