“…Photodynamic oxidation of nucleic acids and their components in the presence of various dyes has been extensively studied (Berg et al, 1978a;Berg, 1978b;Kittler et al, 1980;Girotti, 1983;Cadet et ul., 1983). It has been shown that guanine is the most readily disrupted residue (Sussenbach and Berends, 1964;Waskell et al, 1966;Rosenthal, 1971;Houba-Herin et ul., 1983) and that several mechanisms seem to be involved in the process, the major mechanisms being either a singlet-oxygen Type I1 mechanism, or a Type I process involving the formation of a complex between the triplet state of sensitizer and substrate, followed by an oxidation of the latter by ground-state triplet oxygen (Gollnick, 1968).…”