Stereoselective interactions and photo-electron transfers between mononucleotides or DNA and the stereoisomers of a HAT-bridged dinuclear Ru-II complex (HAT=1,4,5,8,9,12-hexaazatriphenylene)

The dinuclear complex [{Ru(phen)(2)}(2)(mu -HAT)](4+) (phen = 1,10-phenanth roline, HAT = 1,4,5,8,9,12-hexaazatriphenylene), can exist in three differe nt stereoisomeric forms: the meso (AA) and rac diastereoisomers, the latter of which has two enantiomeric forms, namely AA and AA. Each of the stereoi somers was studied in the presence of the mononucleotides guanosine 5 ' -mo nophosphate (GMP) and adenosine 5 ' -monophosphate (AMP), and deoxyguanosin e (dG) at pH = 7 and 9. Absorption studies revealed the formation of ion pa irs or aggregates between the complexes and the mononucleotides (GMP and AM P) and dG, The equilibrium constants for the formation of these species wer e higher for the meso form than for the AA and AA enantiomers. Laser flash photolysis indicated the existence of a stereoselective photo-induced elect ron-transfer between the guanine of GMP and the stereoisomers. Luminescence data with the purine mononucleotides also indicated the existence of an eq uilibrium between the free excited complex and a luminescent ion pair or an emitting aggregate between the complex and the mononucleotide. The lumines cence of these species depended on the pH and on the identity of the stereo isomer. The investigated spectroscopic behaviour of the complex stereoisome rs in the presence of denatured CT-DNA was also isomer-dependent, in agreem ent with the conclusions drawn from the data with the mononucleotides, The results of this work clearly indicate stereoselectivity of the interaction with the purine mononucleotides and denatured CT-DNA in the ground and exci ted state of the complex, in favour of the meso form in both cases.