Binding and stabilization effect of arene ruthenium(Ⅱ) polypyridyl complexes toward the triple-helical RNA poly(U)•poly(A)⁎poly(U)

Abstract

To determine the binding properties of η6‑arene Ru(Ⅱ) complexes with the RNA triplex poly(U)•poly(A)⁎poly(U), two arene Ru(Ⅱ) complexes, [(ŋ6-C6H6)Ru(m-npip)Cl]+ (Ru1) and [(ŋ6-C6H6)Ru(m-fpip)Cl]+ (Ru2), have been synthesized and characterized in this study. The binding of Ru1 and Ru2 with the triplex RNA poly(U)•poly(A)⁎poly(U) have been investigated by viscosity measurement and various spectroscopic methods. Results demonstrate that the RNA-binding behaviors of Ru1 and Ru2 are intercalation mode. From the analyses of electronic absorption spectra and fluorescence spectra, we observed that the binding affinity for Ru2 is remarkably stronger than that for Ru1. Furthermore, thermal denaturation studies reflect that Ru1 and Ru2 selectively stabilize the RNA triplex, among them, Ru1 can stabilize the Hoogsteen base-paired strand poly(U) (the third strand), while it is little effect on the Watson-Crick base-paired duplex poly(U)•poly(A) (the template duplex). Contrary to Ru1, Ru2 can stabilize both the template duplex and the third-strand, and Ru2 is more effective for stabilization of the third-strand. To our knowledge, this work is the first example of arene metal complexes interacting with triple-helical nucleic acids. The obtained results suggest that subtle differences of substituent on the intercalation ligand may be the important factor affecting on the binding properties of the both arene Ru(Ⅱ) complexes with the RNA triplex, when Ru1 and Ru2 contain the same ancillary ligands.