[Ru(bpy)2dppz-idzo]2+: a colorimetric molecular "light switch" and powerful stabilizer for G-quadruplex DNA.

A new ruthenium complex, Ru(bpy)2dppz-idzo (bpy = 2,2'-bipyridine, dppz-idzo = dipyrido-[3,2-a:2',3'-c] phenazine-imidazolone), was synthesized and characterized. The luminescent titrations showed that the Ru-complex exhibited an outstanding "light switch" effect with an emission enhancement factor of about 300 in the presence of G-quadruplex DNA in a K(+) solution. This remarkable "light switch" behavior can even be observed by the naked eye under irradiation with UV light. To get an insight into the "light switch" mechanism, quantum-chemical calculations were performed based on the DFT/TDDFT/PCM method at the B3LYP/6-31G* level. Furthermore, the CD titrations and thermal melting experiments indicated that Ru(bpy)2dppz-idzo could not only induce the formation of an antiparallel G-quadruplex structure in the absence of monocations, but also has the ability to stabilize the G-quadruplex architecture, implying potential applications in anticancer therapeutics. Both the "light switch" effect and the structure stabilization ability of Ru(bpy)2dppz-idzo were found to be superior to the well-known DNA molecular "light switch" Ru(bpy)2dppz. Finally, a "sandwich-like" binding model was proposed on the basis of molecular docking simulations.