Photo‐induced Electron Transfer From Nucleotides to Ruthenium‐tris‐1,4,5,8tetraazaphenanthrene: Model for Photosensitized Dna Oxidation

Abstract

Abstract— The luminescence quenching of ruthenium‐tris‐l,4,5,8‐tetraazaphenanthrene [Ru(tap)32+] by nucleotides approaches the diffusion rate only with guanosine‐5′‐monophosphate (GMP), the most reducing nucleotide, and leads to an electron transfer with the production of the monoreduced complex and the oxidized base. The resulting deprotonated GMP(‐H)radical recombines with the monoreduced complex according to a bimolecular equimolar process. The pH dependence of the decay of the transient reduced complex, in the presence of an oxidant (oxygen or benzoquinone) indicates the formation of Ru(tap)2(tapH)2+i.e. the reduced protonated species, subsequent to the electron transfer, with a pKa of 7.6 as confirmed from pulse radiolysis experiments. As the non‐protonated reduced complex, Ru(tap)2(tap2)+ has a higher reducing power than the protonated one, oxygen is able to reoxidize only the non‐protonated species, whereas benzoquinone reoxidizes both species but with different rate constants. The flash photolysis of Ru(tap),2+ in the presence of DNA and the effect of Mg2+ ions and GMP as supplementary additives also show the existence of a photo‐induced electron transfer with the nucleic acid, which can be correlated to the photosensitized cleavage of DNA by this complex.

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)]2+ and [Ru(bpy)2(nitatp)]2+

“…8) is lower than that in air also suggests that besides the reactive oxygen species, a direct oxidative process may contribute to the cleavage. Photoinduced electron transfer from the guanine to the excited complex has been demonstrated as the primary process that initiates DNA cleavage, and guanine is the easiest nucleobase to oxidize [54]. Briefly, making the complex more oxidizing in the excited state will accelerate the electron transfer process, thus promoting the DNA cleavage.…”

Ru–TAP complexes and DNA: from photo-induced electron transfer to gene photo-silencing in living cells

“…It is well known that the coiled circular plasmid is transformed, just by one single nick, into its open circular form. It has been demonstrated that these photocleavages by the Ru-TAP complexes originate also from the PET process from a G base [23]. On the basis of these results, we should thus complete the photochemical reactions scheme shown in figure 1 by the addition of a supplementary reaction, subsequent to the PET process, i.e.…”

“…As explained above, the conditions to produce a mono-adduct of a G base of a mono-or polynucleotide to a Ru-TAP complex such as that shown in figure 2 have been fully investigated previously [23,24]. The formation of bi-adducts was first discovered with another complex, [Ru(HAT) 2 phen] 2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene) (figure 3a) [32].…”

Synthesis, DNA‐Binding and Photocleavage Studies of the Ruthenium(II) Complexes [Ru(phen)2(ppd)]2+ and [Ru(phen)(ppd)2]2+ (ppd=Pteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione, phen=1,10‐Phenanthroline)

“…8) is lower than that in air also suggests that, besides the reactive oxygen species, a direct oxidative process may contribute to the cleavage. Photoinduced electron transfer from the guanine to the excited complex has been demonstrated as the primary process, which initiates DNA cleavages [45]. Briefly, making the complex more oxidizing in the excited state will accelerate the electron-transfer process, thus will promote the DNA cleavages.…”