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

To determine the binding properties of η 6 ‑arene Ru(Ⅱ) complexes with RNA triplexes, two arene Ru(Ⅱ) complexes [( ŋ 6 -C 6 H 6 )Ru( m -npip)Cl] + (Ru 1 ) and [( ŋ 6 -C 6 H 6 )Ru( m -fpip)Cl] + (Ru 2 ) have been synthesized and characterized in this study. The obtained results will contribute to our understanding of the binding of arene Ru(Ⅱ) complexes with RNA triplexes. • ←6 -C 6 H 6 = benzene ring, m -npip = 2-(3′‑nitro)imidazo[4,5- f ][1,10]phenanthroline. • m -fpip = 2-(3′‑fluorine)imidazo[4,5- f ][1,10]phenanthroline. • Complexes [(← 6 -C 6 H 6 )RuLCl]PF 6 (Ru 1 , L = m -npip; Ru 2 , L = m -fpip) were synthesized. • Binding properties of Ru 1 and Ru 2 with poly(U)*poly(A)•poly(U) were investigated. • This work is the first example of arene metal complexes with triple-helical nucleic acids . To determine the binding properties of η 6 ‑arene Ru(Ⅱ) complexes with the RNA triplex poly(U)•poly(A)⁎poly(U), two arene Ru(Ⅱ) complexes, [( ŋ 6 -C 6 H 6 )Ru( m -npip)Cl] + (Ru 1 ) and [( ŋ 6 -C 6 H 6 )Ru( m -fpip)Cl] + (Ru 2 ), have been synthesized and characterized in this study. The binding of Ru 1 and Ru 2 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 Ru 1 and Ru 2 are intercalation mode. From the analyses of electronic absorption spectra and fluorescence spectra, we observed that the binding affinity for Ru 2 is remarkably stronger than that for Ru 1 . Furthermore, thermal denaturation studies reflect that Ru 1 and Ru 2 selectively stabilize the RNA triplex, among them, Ru 1 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 Ru 1 , Ru 2 can stabilize both the template duplex and the third-strand, and Ru 2 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 Ru 1 and Ru 2 contain the same ancillary ligands.