DNA Binding Study of a Redox Active Enantiopure Bis(arylimino)acenaphthene (BIAN) Os(II) Bipyridine Complex

This work presents the synthesis, characterization, and evaluation of DNA binding for a bis(arylimino)acenaphthene (BIAN) containing Os(II) octahedral dipyridyl complex [Os(dmbpy)₂BIAN](An)₂ [1](An)₂ (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl, BIAN = bis(arylimino)acenaphthene, An = PF₆ ^- or Cl^-). Complex 1 is characterized by X-ray crystallography and cyclic voltammetry, which reveal a series of fully reversible redox couples. The visible absorption spectrum is dominated by metal-to-ligand charge-transfer bands between 400 and 600 nm, whose assignment is supported by time dependent density functional theory computational studies with solvent corrections. For the first time, chiral discriminating chromatography is used to resolve the Δ- and Λ-enantiomers of a metal BIAN complex. UV-visible absorption and circular dichroism measurements reveal significant differences in the binding strength of the enantiomers to double-stranded natural DNA, with a greater affinity observed for Δ-1 (K_b ≈ 10⁶ M^-1), which is comparable to that observed for other group 8 polypyridyl intercalating species and is supported by the thermal denaturation temperature recorded in the presence of DNA. Linear dichroism confirms that both enantiomeric species bind through the intercalation of the BIAN component. The development of DNA-binding chiral metal complexes containing redox-active ligands described in this work offers the potential to expand the activity of therapeutic bioinorganic systems in new directions.