A survey of photoproducts of an irradiated oligodeoxynucleotide by monochromatic photons with the energy ranged from 6.5 to 22.5 eV

We have irradiated 2'-deoxyadenylyl-(3'-5')-2'-deoxyadenosine (dephospho(dA)2) in solid state with a newly developed synchrotron irradiation system over 6.5 to 22.5 eV photon energy range (190 to 55 nm in wavelength). Densitometric analysis of thin-layer chromatogram of photoproducts indicated that adenine and deoxyadenosine monophosphate were commonly produced above 7.3 eV (170 nm) in approximately equal amount. Deoxyribose was not detected by the fluorescence method with scratched materials from the chromatogram at any location except deoxyadenosine monophosphate and parent oligonucleotide positions. The photoproducts above mentioned were not observed at 6.5 eV (190 nm) even after very high radiation fluence. The energy dependence of this degradation indicates that the shorter the wavelength in use the smaller the fluence it requires. Careful examination of irradiated oligonucleotide on the chromatograms shows that the major portion of deoxyadenosine monophosphate so produced was the 5'phospho derivative. This site-selective degradation, independent of photon energy, seemed to be a remarkable characteristic of vacuum-UV induced effects above 7 eV. It is hypothesised that the deoxypentose moiety was first destroyed in one of the nucleoside residues due to the strong absorption in the sugar-phosphate group, liberating adenine on the one hand and leaving 5'-deoxyadenosine monophosphate. (author)