Promoting the formation and stabilization of G-quadruplex by dinuclear Ru^II complex Ru₂(obip)L₄

The remarkable ability of a new dinuclear Ru^II complex Ru ₂(obip)L₄ [obip = 2-(2-pyridyl)imidazo[4,5-f][1,10]- phenanthroline; L = 2,2′-bipyridine] to promote the formation and stabilization of the human telomeric repeat AG3(T2AG3)3 quadruplex was reported. The experimental results indicated that Ru₂(obip)L₄ could induce the formation of an antiparallel G-quadruplex structure in the absence of metal cations. It could induce positive T_m shifts of +9.4 and +5.8°C in Na⁺ and K⁺ buffers, respectively, in which an increase in the melting temperature of the quadruplex indicated a stabilizing effect. Binding stoichiometry with the quadruplex was investigated through a luminescence-based Job plot. The major inflection point for Ru ₂(obip)L₄ at x = 0.48 was observed. The data were consistent with a 1:1 [quadruplex]/[complex] binding mode, which was suggestive of a specific Ru₂(obip)L₄-quadruplex interaction with a single guanine tetrad.