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Two ruthenium(II) polypyridyl complexes containing 1,8-naphthalimide group as DNA binders, photonucleases, and inhibitors of topoisomerases I and IIα are evaluated. The binding properties of [Ru(phen) 2 (pnip)] 2 + { 1 ; phen = 1,10-phenanthroline; pnip = 12-[ N -( p -phenyl)-1,8-napthalimide]- imidazo[4′,5′- f ] [1,10]phenanthroline} and [Ru(bpy) 2 (pnip)] 2 + ( 2 ; bpy = 2,2′-bipyridine) with calf thymus DNA increases with increasing the bulkiness and hydrophobic character of ancillary ligands, although the two complexes possess high affinities for DNA via intercalation. Moreover, photoirradiation (λ = 365 nm) of the two complexes are found to induce strand cleavage of closed circular pBR322 plasmid DNA via singlet oxygen mechanism, while complex 1 displays more effective photocleavage activity than complex 2 under the same conditions. Topoisomerase inhibition and DNA strand passage assay reflect that complexes 1 and 2 are efficient dual poisons of topoisomerases I and IIα. [ABSTRACT FROM AUTHOR]

Stable RNA triplexes play key roles in many biological processes, while triplexes are thermodynamically less stable than the corresponding duplexes due to the Hoogsteen base pairing. To understand the factors affecting the stabilization of RNA triplexes by octahedral ruthenium(II) complexes, the binding of [Ru(bpy) 2 (ppn)] 2 + ( 1 , bpy = 2,2′-bipyridine, ppn = 2,4-diaminopyrimido[5,6-b]dipyrido[2,3-f:2′,3′-h]quinoxaline) and [Ru(phen) 2 (ppn)] 2 + ( 2 , phen = 1,10-phenanthroline) to poly(U)·poly(A)*poly(U) (· denotes the Watson-Crick base pairing and * denotes the Hoogsteen base pairing) has been investigated. The main results obtained here suggest that complexes 1 and 2 can serve as molecular “light switches” and stabilizers for poly(U)·poly(A)*poly(U), while the effectiveness of complex 2 are more marked, suggesting that the hydrophobicity of ancillary ligands has a significant effect on the two Ru(II) complexes binding to poly(U)·poly(A)*poly(U). This study further advances our knowledge on the binding of RNA triplexes with metal complexes, particularly with octahedral ruthenium polypyridyl complexes. [ABSTRACT FROM AUTHOR]

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]