The remarkable ability of a new dinuclear Ru-II complex Ru-2(obip)L-4 [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 Ru-2(obip)L-4 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 degrees 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)L-4 at x = 0.48 was observed. The data were consistent with a 1:1 [quadruplex]/[complex] binding mode, which was suggestive of a specific Ru-2(obip)L-4-quadruplex interaction with a single guanine tetrad.