Reaction of HO* with guanine derivatives in aqueous solution: formation of two different redox-active OH-adduct radicals and their unimolecular transformation reactions. Properties of G(-H)*.
The reaction of *OH with 2'-deoxyguanosine yields two transient species, both identified as OH adducts (G*-OH), with strongly different reactivity towards O2, or other oxidants, or to reductants. One of these, identified as the OH adduct at the C-8 position (yield 17% relative to *OH), reacts with oxygen with k=4 x 10(9)M(-1)s(-1); in the absence of oxygen it undergoes a rapid ring-opening reaction (k = 2 x 10(5) s(-1) at pH4-9), visible as an increase of absorbance at 300-310 nm. This OH adduct and its ring-opened successor are one-electron reductants towards, for example, methylviologen or [Fe(III)(CN)6]3-. The second adduct, identified as the OH adduct at the 4-position (yield of 60-70% relative to *OH), has oxidizing properties (towards N,N,N',N'-tetra-methyl-p-phenylenediamine, promethazine, or [Fe(II)(CN)6]4-). This OH adduct undergoes a slower transformation reaction (k = 6 x 10(3) s(-1) in neutral, unbuffered solution) to produce the even more strongly oxidizing (deprotonated, depending on pH) 2'-deoxyguanosine radical cation, and it practically does not react with oxygen (k< or = 10(6)M(-1)s(-1)). The (deprotonated) radical cation, in dilute aqueous solution, does not give rise to 8-oxoguanosine as a product. However, it is able to react with ribose with k< or =4 x 10(3)M(-1)S(-1).
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Max-Planck-Institut für Strahlenchemie, Mülheim, Germany.
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D004247:DNA / Q000378:metabolism; D003849:Deoxyguanosine; D006147:Guanine / Q000031:analogs & derivatives*; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012996:Solutions; D013054:Spectrophotometry, Atomic
D012996:Solutions; D017665:Hydroxyl Radical; D006147:Guanine; D004247:DNA; D003849:Deoxyguanosine