Effect of ancillary ligands on the interaction of ruthenium(II) complexes with the triplex RNA poly(U)·poly(A)*poly(U).

Two new Ru(II) complexes with 1,8-naphthalimide group, [Ru(phen) 2 (pnip)] 2 + (Ru 1 ; phen = 1,10-phenanthroline, pnip = 2-[ N -( p -phenyl)-1,8-napthalimide]imidazo[4',5'- f ][1,10]phenanthroline) and [Ru(bpy) 2 (pnip)] 2 + (Ru 2 ; bpy = 2,2′-bipyridine), have been synthesized and characterized. The interactions of Ru 1 and Ru 2 with the triplex RNA poly(U)•poly(A)*poly(U) (where • denotes the Watson–Crick base pairing and * denotes the Hoogsteen base pairing) were studied by various biophysical. Electronic spectra established that the binding affinity for Ru 1 was greater than that for Ru 2 . Fluorescence and viscosity studies gave convincing evidence for a true intercalative binding of both complexes with the RNA triplex. UV melting studies confirmed that the two complexes could stabilize the triplex, whereas the effects of the two complexes on the stability of the Hoogsteen base-paired strand ploy(U) and the Watson–Crick base-paired duplex poly(U)•poly(A) of the triplex were different. In the case of Ru 1 , the increase of the thermal stability of the Hoogsteen base-paired strand was stronger than that of the Watson–Crick base-paired duplex. However, an opposite effect was observed in the case of Ru 2 . Circular dichroic studies suggested that the RNA triplex undergoes a conformational transition in the presence of Ru 1 , whereas the helicity of the RNA triplex still remains A-type in the presence of Ru 2 . The main results obtained here further advance our knowledge on the interaction of RNA triple-stranded structures with metal complexes, particularly ruthenium(II) complexes. [ABSTRACT FROM AUTHOR]