Nucleobases, Nucleosides and Nucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 231

Table 10.12 . γ -Radiolysis of N 2 O-saturated aqueous solutions of 1,3Me 2 Ura. Products and
their G values (unit: 10 −7 mol J −1 ; Al-Sheikhly and von Sonntag 1983)

Product pH 3 pH 6.5 pH 10.4

5,6-Dihydro-5-hydroxy-1,3-dimethyluracil 0.4 0.8 0.6

5,6-Dihydro-6-hydroxy-1,3-dimethyluracil <0.1 0.2 <0.1

1,3-Dimethylisobarbituric acid 0.15 0.1 ≤ 0.1

5,6-Dihydro-5,6-dihydroxy-1,3-dimethyluracil 1.6 0.9 0.85

Dimers (of 6-yl radicals, in monomer units) 1.8 3.5 3.3

Dimers (involving H-adduct radicals) <0.1 0.2 <0.1

1,3Me 2 Ura consumption 4.0 5.9 5.3

In competition, the C(6)-yl and C(5)-yl radicals may disproportionate, possibly
via an adduct [reactions (80) and (81)]. This yields the hydrate via an enol [reac-
tion (83)]. The other product is the glycol [reaction (82)]. In the original paper
(Al-Sheikhly and von Sonntag 1983), it has been proposed that it may be formed
in an ET reaction. Due the considerable rearrangement energies involved in ET
reactions as compared to radical recombination reactions, it is now considered
that this ET reaction might occur via an addition/elimination process [reactions
(80) and (81)] such as has also been found for other systems.