Bromouracil-Substituted ssDNA Fragments

In the presence of GSH, 5 -d(T4AT7) and 5 -d(T4A) are formed [reactions (20) and (21)]. In the presence of 02, the primary radical is trapped by 02. In a subsequent step, the C(4 ) peroxyl radical is reduced to the corresponding hydroperoxide (the source of the reduction equivalent is as yet unknown potentially 02 generated in side reactions), and treatment with NH3 increases the yield of the glycolate which is also formed upon the bimolecular decay of the peroxyl radial [reactions (23)-(25)]. 

The photolysis of 5BrUra-substituted DNA has been widely used as tool to study certain aspects of DNA free-radical chemistry. The basic reactions that occur on the nucleobase to nucleotide level are discussed in Chapter 10.7. Some of the primary reactions seem to be different on going from the nucleotide level to dsDNA (Chap. 12.6). Experiments with ssODNs are quite limited. 

In ssODNs containing 5BrUra, the stand break yield observed right after photolysis in aerated solution is 1/6 of that after piperidine treatment (Doddridge et 

A higher level of strand breakage is observed in the absence of 02) and a markedly different pattern of 3 -termini damage is observed. It has been suggested that in the presence of 02 Ura-5-peroxyl radicals may play a role (for its complex chemistry see Chap. 10.7), but details are not yet understood. 

Aravindakumar CT, Schuchmann MN, Rao BSM, von Sonntag J, von Sonntag C (2003) The reactions of cytidine and 2 -deoxycytidine with SO4-revisited. Pulse radiolysis and product studies.Org Biomol Chem 1 401-408 

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