The dinuclear ruthenium(II) complex [{Ru(Phen)2}2(HAT)]4+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene), a new photoreagent for nucleobases and photoprobe for denatured DNA

Abstract

The photophysical and photochemical properties of a dinuclear ruthenium(II) complex, [{Ru(Phen)2}2(HAT)]4+ (Phen = 1,10-phenanthroline, HAT = 1,4,5,8,9,12-hexaazatriphenylene), have been examined in the presence of mononucleotides and different polynucleotides. Characteristic new features, not observed with monometallic ruthenium(II) complexes, appear with this dimeric compound. First it forms strong ion pairs with the mononucleotides, adenosine- and guanosine-5′-monophosphate, detected from the absorption and emission characteristics under steady state and time-resolved conditions. Secondly, under steady state illumination, very weak luminescence enhancements are induced by the addition of double stranded calf thymus DNA (CT-DNA) whereas important increases of emission occur by the addition of denatured CT-DNA. The dinuclear species may thus be regarded as an excellent photoprobe for denatured DNA. On the other hand, the same photoreactivity with the nucleobases as that of the monometallic TAP (1,4,5,8-tetraazaphenanthrene) and HAT complexes has been retained by the dinuclear species, i.e. (i) a photoelectron transfer from guanosine monophosphate to the excited complex correlated with the formation of a photoproduct and (ii) a photoelectron transfer with DNA; in that case, however, this process is not systematically correlated with the formation of photoproduct in contrast to the monometallic species.