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)*

Chemistry. 2000 Feb 4;6(3):475-84. doi: 10.1002/(sici)1521-3765(20000204)6:3<475::aid-chem475>3.0.co;2-e.

Abstract

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).

MeSH terms

  • DNA / metabolism
  • Deoxyguanosine
  • Guanine / analogs & derivatives*
  • Hydrogen-Ion Concentration
  • Hydroxyl Radical*
  • Models, Chemical*
  • Oxidation-Reduction
  • Solutions
  • Spectrophotometry, Atomic

Substances

  • Solutions
  • Hydroxyl Radical
  • Guanine
  • DNA
  • Deoxyguanosine