Low-energy (5-25 eV) electron damage to homo-oligonucleotides

Radiation-induced damage to homo-oligonucleotides is investigated by electr on-stimulated desorption of neutral fragments from chemisorbed organic film s. Six and 12 mers of cytidine phosphate (poly dCs) and thymidine phosphate (poly dTs) are chemisorbed from various solutions onto a crystalline gold substrate by a thief modification at the 3' end and are irradiated under ul tra-high vacuum conditions with 5-25 eV electrons, The mass selected neutra l desorption yields consist mainly of fragments of the DNA bases, i.e. CN a nd OCN (and/or H2NCN for poly dCs) from both poly dCs and poly dTs, indicat ing that the electrons interact specifically via fragmentation of the aroma tic ring of either of the bases. Other heavier fragments are also detected such as H3CC-CO from poly dTs, The yields generally possess a threshold nea r 5 eV and a broad maximum around 12-13 eV incident electron energy, Dissoc iative electron attachment as well as electronically excited neutral or cat ion states are believed to be responsible for the various desorption yields , The latter yields are consistently larger for oligos chemisorbed from wat er and acetone solutions, compared to methanol solution, The invariance of the fragment yield intensities with oligo length suggests that the molecule s are likely to adsorb almost parallel to the surface. (C) 1999 by Radiatio n Research Society.