Radiolysis of DNA in the Solid State

Sensitization of anoxic cells is also brought about by non-toxic concentrations of transition metal ions ( some 10-4 mol dm-3) such as Cu(I). A dose-modifying factor of 1.5 (at 6.6 x 10-5 mol dm-3 Cu(I)) has been observed for mammalian cells (Hesslewood et al. 1978), but no sensitizing effects were observed for oxygenated cells. Under anoxic conditions, reduction of Cu(II) to Cu(I) occurs within the cells without an added reductant (see also Cramp 1967). It would be premature to come up with detailled mechanistic concepts, but some aspects of the actions of transition-metal ions have been discussed in Chapter 2.5. 

Hydration of the DNA has also a strong influence on the radical yield at 77K (Wang et al. 1993). The G values increase by over fourfold upon addition of the primary hydration layer, that is about 20 water molecules per nucleotide. Upon further water addition, the excess water freezes into an apparently independent bulk ice phase which steals about five water molecules from the hydration layer and thus reduces the DNA radical yield. It has been concluded that efficient hole 

Upon y-irradiation of dry DNA unaltered bases are set free with a G value of about 0.2 x 10 7 mol J 1 for Ade, Cyt and Thy, and 0.12 x 10 7 mol J-1 for Gua in the absence of O2, and 0.4 x 10-7 mol J 1 (Ade, Cyt and Thy) and 0.25 x 10-7 mol J 1 (Gua) in its presence (Swarts et al. 1992). Hydration of the DNA lowers these values somewhat. The precursor of these unaltered bases are sugar radicals, i.e. largely sugar radical cations. These are strong oxidants, and since G is the best electron donor among the nucleobases, it is likely that the G-hound sugar radical cation may effectively be reduced by the neighboring G (Sect. 12.10). This must 

As SSBs are concerned, data are available on single crystals of dsODNs of different composition (Debije et al. 2001 Razskazovskiy et al. 2003a, 2003b). There is little base sequence specificity and preference of 5 -cleavage vs 3 -cleavage. Although there is a certain span for G(SSB) among the various systems studied ((-0.4-1.4) x 10-7 mol J-1), these data clearly point to the importance of SSB formation by the direct effect. 

In the presence of electron scavengers such as iodoacetamide, electron-gain centers are transformed into alkyl-type radicals which preferentially abstract a 

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