Binding propterties of two Ru(II) polypyridyl complexes containing dppz units and fluorine groups with poly(U)·poly(A) ∗ poly(U) triplex.

In this work, two Ru(II)-dppz (dppz = dipyrido[3,2-a:2',3'-c]phenazine) complexes containing fluorine substituents, [Ru(bpy)2 (7-F-dppz)]2+ (Ru1, bpy = 2,2'-bipyridine, 7-F-dppz = 7-fluorodipyrido[3,2-a:2',3'-c]phenazine) and [Ru(phen)2 (7-F-dppz)]2+ (Ru2, phen = 1,10-phenanthroline), have been synthesized and characterized. Binding properties of Ru1 and Ru2 with the RNA poly(U)·poly(A) ∗ poly(U) triplex have been studied by spectroscopic methods and viscosity measurements. The obtained results indicate that the binding differences of the two complexes with the triplex may be attributed to the ancillary ligand effects, implying that the better planarity and greater hydrophobicity of ancillary ligands are advantageous to the π-π stacking interaction between Ru2 and the triplex, thus Ru2 stabilizes the triplex strongly than Ru1. Denaturation of the triplex shows that both Ru1 and Ru2 can not only highly stabilize the template duplex of the triplex, but also significantly stabilize the third strand. Compared with the triplex stabilizing effects for the reported Ru(II)-dppz complexes, thermal melting experiments suggest that the fluorine substituent on the ligand dppz can probably decrease electrostatic repulsion between the three strands of the triplex, thereby Ru1 and Ru2 significantly increase the triplex stabilization. Results obtained from this work further confirm that the substituent electron effect of dppz-based ligands and the planarity and hydrophobicity of ancillary ligands play an important role in the triplex stabilizing effects by Ru(II)-dppz complexes.