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

Stereoselective Interactions and Photo-Electron Transfers between Mononucleotides or DNA and the Stereoisomers of a HAT-Bridged Dinuclear RuII Complex (HAT = 1,4,5,8,9,12-hexaazatriphenylene)

“…Consequently, the plateau value I 0 /I is Ͼ 1, when the equilibrium is displaced to the right. As explained previously, a higher k et can be attributed [10] to an increased driving force of the electron transfer process due to partial deprotonation of the guanine at pH ϭ 9 (the base form of the guanine has a higher reducing power).…”

“…[10] However, since each stereoisomer exhibited a different absorption and luminescence behaviour in the presence of GMP at pH ϭ 7, laser flash photolysis experiments were carried out again in the present work with each stereoisomer separately. In each case, the differential transient absorption recorded 1 µs after the laser pulse, in the presence of 70 m GMP, indicated the existence of a long-lived mono-reduced complex (even with the meso compound).…”

“…[10] The intensity of the transient absorption ( Figure 5) was too weak to perform a kinetic analysis. However, the differential transient absorption was slightly higher for the ΛΛ enantiomer than for the ∆∆ form, and the signal of the latter was somewhat higher than that of the ∆Λ (meso) form.…”

“…No NaCl was added in order to induce a higher binding of the complex to the DNA. In this part of the work, as explained in the introduction, only the effect of denatured CT-DNA was examined because normal double-stranded DNA had no effect, [10] even when the experiment was performed with each stereoisomer.…”

“…[10] These experiments with GMP had been performed with the nonseparated stereoisomers present after synthesis of the dinuclear complex. As the stereoisomeric mixture could be the cause of the complicated behaviour, in this work, we have carefully examined the effects of GMP and the other mononucleotides on the photophysical behaviour of each stereoisomer (viz.…”