Structural Investigation into the Threading Intercalation of a Chiral Dinuclear Ruthenium(II) Polypyridyl Complex through a B‑DNA Oligonucleotide

Herein
we report the separation of the three stereoisomers of the
DNA light-switch compound [{Ru­(bpy)2}2(tpphz)]4+ (tpphz = tetrapyrido­[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]­phenazine)
by column chromatography and the characterization of each stereoisomer
by X-ray crystallography. The interaction of these compounds with
a DNA octanucleotide d­(GCATATCG).d­(CGATATGC) has been studied using
NMR techniques. Selective deuteration of the bipyridyl rings was needed
to provide sufficient spectral resolution to characterize structures.
NMR-derived structures for these complexes show a threading intercalation
binding mode with slow and chirality-dependent rates. This represents
the first solution structure of an intercalated bis-ruthenium ligand.
Intriguingly, we find that the binding site selectivity is dependent
on the nature of the stereoisomer employed, with Λ RuII centers showing a better intercalation fit.