Sensitized photomodification of DNA by binary systems of oligonucleotide conjugates. IV. Photoinduced electron transfer

The photomodification of single-stranded DNA sensitized to visible light (4 50-580 nm) by a binary system of oligonucleotide conjugates complementary t o adjacent DNA sequences was studied. One oligonucleotide carries a residue of the photoreagent p-azidotetrafluorobenzaldehyde hydrazone at its 3'-ter minal phosphate, and the other has a residue of the sensitizer, perylene or 1,2-benzanthracene, at the 5'-terminal phosphate. The rate of photomodific ation senzitized by the perylene derivative is 300000-fold higher than the rate of photomodification in the absence of the sensitizer. Since the excit ation energy of perylene is lower than the energy necessary for the initiat ion of azide photodecomposition, it is likely that the sensitization in the complementary complex occurs by electron transfer from the azido group of the photoreagent to the excited sensitizer. The sensitization by the 1,2-be nzanthracene oligonucleotide derivative occurs by means of singlet-singlet energy transfer, which enables this sensitizer to act as a unconsumable cat alyst each molecule of which is able to initiate the photomodification of m ore than 20 DNA molecules. By both mechanisms, the photomodification occurs with high specificity on the G(11) residue of the target DNA. The degree o f sensitized photomodification reaches 72%.