Synthesis and characterisation of a new DNA-binding bifunctional ruthenium(II) complex

Abstract

A new DNA-binding molecule, Ru(tap)₂POQ²⁺, in which a polypyridylruthenium(II) complex is linked to an aminochloroquinoline by a flexible chain, has been prepared and characterised (tap = 1,4,5,8-tetraazaphenanthrene and POQ corresponds to a 1,10-phenanthroline linked to an aminochloroquinoline by an aliphatic chain). This complex is regarded as bifunctional because it contains two moieties of different binding modes and photoreactivities vs. DNA. The ¹H NMR data of this compound indicate the presence of an equilibrium between two molecular species. The spectroscopic properties of Ru(tap)₂POQ²⁺ in absorption and luminescence are examined and compared with those of the corresponding ruthenium(II) complex which does not contain the aminochloroquinoline moiety: Ru(tap)₂phen²⁺. Luminescence relative quantum yields and lifetimes show that the MLCT excited-state behaviour is influenced by the presence of the linked quinoline. An intramolecular photoinduced electron transfer in one of the two species in equilibrium, is considered to be responsible for a quenching of the ruthenium(II) complex iuminescence. Preliminary results on the binding characteristics of Ru(tap)₂POQ²⁺ to DNA and [poly(d[A-T])]₂ from luminescence and thermal denaturation studies are reported. The intramolecular quenching of luminescence in Ru(tap)₂POQ²⁺ is inhibited when it interacts with nucleic acids. Consequently, the resulting emission is more substantially enhanced in the presence of the polynucleotide relative to the luminescence increase observed with the reference complex, Ru(tap)₂phen²⁺.