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).
✍ Scribed by Luis P. Candeias; Steen Steenken
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 189 KB
- Volume
- 6
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
The reaction of . OH with 2'deoxyguanosine yields two transient species, both identified as OH adducts (G . -OH), with strongly different reactivity towards O 2 , 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 Â 10 9 m À1 s À1 ; in the absence of oxygen it undergoes a rapid ring-opening reaction (k 2 Â 10 5 s À1 at pH 4 ± 9), visible as an increase of absorbance at 300 ± 310 nm. This OH ad-duct and its ring-opened successor are one-electron reductants towards, for example, methylviologen or [Fe III (CN) 6 ] 3À . 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'-tetramethyl-p-phenylenediamine, promethazine, or [Fe II (CN) 6 ] 4À ). This OH adduct undergoes a slower transformation reaction (k 6 Â 10 3 s À1 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 10 6 m À1 s À1 ). 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 4 Â 10 3 m À1 s À1 .