Interaction of [Ru(bpy)2(dppz)]2+ with human telomeric DNA: Preferential binding to G-quadruplexes over i-motif

Inspired by the enormous importance attributed to the structure and function of human telomeric DNA, we focus our attention on the interaction of [Ru(bpy)2(dppz)]2+ with the guanine-rich single-strand oligomer 5′-AGGGTTAGGGTTAGGGTTAGGG-3′ (22AG) and the complementary cytosine-rich strand (22CT). In Na+ buffer, 22AG may adopt an antiparallel basket quadruplex, whereas, it favours a mixed parallel/antiparallel structure in K+ buffer. 22CT may self-associate at acidic pH into an i-motif. In this paper, the interaction between [Ru(bpy)2(dppz)]2+ and each unusual DNA was evaluated. It was interesting that [Ru(bpy)2(dppz)]2+ could promote the human telomeric repeat 22AG to fold into intramolecular antiparallel G-quadruplex without any other cations. What's more, [Ru(bpy)2(dppz)]2+ was found to have a strong preference for binding to G-quadruplexes that were induced through either Na+ or K+, while weak binding to i-motif was observed. The results also indicated that [Ru(bpy)2(dppz)]2+ could serve as a prominent molecular “light switch” for both G-quadruplexes, revealing a potential application of the title complex in luminescent signaling of G-quadruplex DNA.