Nucleobases, Nucleosides and Nucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 249

10.4
Radical Anions and their Protonated Forms

The radical anions may be formed by reacting the nucleobases with e aq − which
may be either generated radiolytically or in a two-step reaction, e.g., in the la-
ser f flash photolysis of anthraquinonedisulfonate in the presence of pyrimidines
(yielding the pyrimidine radical cation and an anthraquinonedisulfonate radi-
cal anion) and subsequent photoionization of the anthraquinonedisulfonate
radical anion (Lü et al. 2001). The latter approach, combined with Fourier trans-
form EPR spectroscopy, yielded detailed information as to the conformation of
the radical anions of Ura and Thy in aqueous solution (for a discussion see Close
2002; Naumov and Beckert 2002). Similarly valuable EPR information has been
obtained from

-irradiated single crystals (cf. Box and Budzinski 1975; Box et al.
1975; Sagstuen et al. 1998).

γ

Pyrimidines. The pyrimidines react with e aq − at practically diffusion-controlled
rates (Table 10.6). The ensuing reactions of the radical anions of Ura and Thy are
very well understood, while with that of Cyt some open questions still remain.
Thy and Ura behave like typical carbonyl compounds, and the first inter-
mediate is a radical anion [reaction (163), in the case of Thy/Thd] which is in
equilibrium with its O -protonated conjugate acid [equlibrium (164)].