Photosensitization and Singlet Dioxygen Reactions

Photoexcited anthraquinone-2,6-disulfonate undergoes ET with Thy and its methyl derivatives, and the EPR results (Geimer et al. 1997 Geimer and Beckert 1998,1999) have been discussed above. 

The products that are formed upon photosensitization of dCyd by menadione were already given in Table 10.16 together with those formed upon OH-attack. It has again been suggested that the precursor of these products is the dCyd radical cation formed by ET to excited menadione (Decarroz et al. 1987). 

The riboflavin triplet reacts with dGMP acid by ET (k = 6.6 x 109 dm3 mol-1 s 1), and evidence for the formation of the (deprotonated) Gua radical cation has been obtained by laser flash photolysis (Lu et al. 2000). The photosensitized reactions of dGuo by TRP is thought to follow two pathways, the formation of Z has been attributed to an ET reaction (Type I), and the reaction of singlet dioxygen [ChCAg) Type II] leads to 4-OH-8-oxo-G and 8-oxo-G (Ravanat et al. 1998). The effect of D20 and azide on the 4-OH-8-oxo-G yields shows that this 

TRP = g [meso-5,10,15,20-tetra(pyridyl) porphyrin]tetrakis[bis(bipyridine)chloride ruthenium(ll)] 

These studies have been extended to the photooxidation of d(TpG) by riboflavin and methylene blue, and again Z and its precursor Iz have been characterized (Buchko et al. 1995b). When d(TpG) is photooxidized with benzophenone or menadione, an additional product, d(TpG) , is formed [reactions (305) and (305) Delatour et al. 1999], It constitutes a tandem lesion. 

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