Stereoselective interactions and photo-electron transfers between mononucleotides or DNA and the stereoisomers of a HAT-bridged Dinuclear RuII Complex (HAT 5 1,4,5,8,9,12-hexaazatriphenylene)

Abstract

The dinuclear complex [{Ru(phen)2}2(μ-HAT)]4+ (phen = 1,10-phenanthroline, HAT = 1,4,5,8,9,12-hexaazatriphenylene), can exist in three different stereoisomeric forms: the meso (ΔΛ) and rac diastereoisomers, the latter of which has two enantiomeric forms, namely ΔΔ and ΛΛ. Each of the stereoisomers was studied in the presence of the mononucleotides guanosine 59-monophosphate (GMP) and adenosine 59-monophosphate (AMP), and deoxyguanosine (dG) at pH = 7 and 9. Absorption studies revealed the formation of ion pairs or aggregates between the complexes and the mononucleotides (GMP and AMP) and dG. The equilibrium constants for the formation of these species were higher for the meso form than for the ΔΔ and ΛΛ enantiomers. Laser flash photolysis indicated the existence of a stereoselective photo-induced electron-transfer between the guanine of GMP and the stereoisomers. Luminescence data with the purine mononucleotides also indicated the existence of an equilibrium between the free excited complex and a luminescent ion pair or an emitting aggregate between the complex and the mononucleotide. The luminescence of these species depended on the pH and on the identity of the stereoisomer. The investigated spectroscopic behaviour of the complex stereoisomers in the presence of denatured CT-DNA was also isomer-dependent, in agreement 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 excited state of the complex, in favour of the meso form in both cases.