Guanine Can Direct Binding Specificity of Ru–dipyridophenazine (dppz) Complexes to DNA through Steric Effects

Abstract

X-ray crystal structures of three Λ-[Ru(L)2dppz]2+ complexes (dppz=dipyridophenazine; L=1,10-phenanthroline (phen), 2,2′-bipyridine (bpy)) bound to d((5BrC)GGC/GCCG) showed the compounds intercalated at a 5′-CG-3′ step. The compounds bind through canted intercalation, with the binding angle determined by the guanine NH2 group, in contrast to symmetrical intercalation previously observed at 5′-TA-3′ sites. This result suggests that canted intercalation is preferred at 5′-CG-3′ sites even though the site itself is symmetrical, and we hypothesise that symmetrical intercalation in a 5′-CG-3′ step could give rise to a longer luminescence lifetime than canted intercalation.