Photo-induced electron transfer from nucleotides to ruthenium-tris-1,4,5,8-tetraazaphenanthrene: model for photosensitized DNA oxidation.
The luminescence quenching of ruthenium-tris-1,4,5,8-tetraazaphenanthrene [Ru(tap)3(2+)] 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(tap-.)+, 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)3(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.
Lecomte
J P
JP
Université Libre de Bruxelles, Chimie Organique CP 165, Belgium.
Kirsch-De Mesmaeker
A
A
Kelly
J M
JM
Tossi
A B
AB
Görner
H
H
D004247:DNA / Q000737:chemistry / Q000528:radiation effects*; D004579:Electron Transport; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry / Q000528:radiation effects*; D010084:Oxidation-Reduction; D010616:Phenanthrenes / Q000737:chemistry / Q000528:radiation effects*; D010782:Photolysis; D011838:Radiation-Sensitizing Agents / Q000737:chemistry / Q000528:radiation effects
D009942:Organometallic Compounds; D010616:Phenanthrenes; D011838:Radiation-Sensitizing Agents; C076699:ruthenium-tris-1,4,5,8-tetraazaphenanthrene; D004247:DNA