Excited-state controlled peroxide formation of DNA

Reactions with water and 2 + 2-cycloadditions of individual bases are the primary steps held responsible for the deformation of DNA at short wavelengths. From the observed data however the influence of atmospheric oxygen on the light-induced reaction of DNA is evident. A plausible explanation for these effects is the formation of reactive oxygen species during the UV irradiation of DNA. In the present work the deformation of DNA by different oxygen species like singlet oxygen (1O2), superoxideanion (O2), hydroxyradical (OH.), and ozone (O3) is excluded with the help of chemical-trapping experiments. The photoinduced transformation proceeds via excited states of DNA, which react with oxygen to afford peroxide.