Nucleobases, Nucleosides and Nucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 297

The dimer can be split by e aq − and by other reducing radicals such as CO 2 • − or
• C(CH 3 ) 2 OH, albeit with a much lower efficiency. The resulting Thy radical an-
ion is also capable of transferring an electron to the Thy dimer, and this leads to
a short chain reaction.
The C (5) )-linked dihydrothymine dimers are also readily split by e aq −

[reaction (309)] forming H 2 Thy but also Thy in appreciable yields (Ito et al.
2000).

− C (5 ′

Reaction with • OH also leads to the splitting of the dimer ( 30% efficiency), and

there is evidence that one-electron oxidants such as SO 4 • − may also induce the
splitting of the dimer (Heelis et al. 1992). The • NO 3 -radical-induced splitting of
the tetramethyl-substituted Ura cyclobutane dimer has been investigated in ace-
tonitrile (Krüger and Wille 2001). The • NO 3 radical has been generated photo-
lytically from a Ce(VI) salt (Chap. 5.2). Under theses conditions, the 5-5

∼

-linked
intermediate is also trapped, possibly by a deprotonation or a Ce(IV)-mediated
oxidation that competes with

′

β -fragmentation [reactions (310)−(313)].

-linked dihydrothymine dimer by SO 4 • − , N 3 • or
photoexcited anthraquinone-2-sulfonate also affords Thy together with H 2 Thy
(Ito et al. 1999).
The reaction of CO 2 • − with Tg affords Thy, H 2 Thy and 6OHH 2 Thy (Nishi-
moto et al. 1985). The yield of the former two products is noticeably enhanced

One-electron oxidation of the 5,5 ′