Journal of The American Society for Mass Spectrometry

, Volume 24, Issue 11, pp 1787–1797

NCO, a Key Fragment Upon Dissociative Electron Attachment and Electron Transfer to Pyrimidine Bases: Site Selectivity for a Slow Decay Process

  • Filipe Ferreira da Silva
  • Carolina Matias
  • Diogo Almeida
  • Gustavo García
  • Oddur Ingólfsson
  • Helga Dögg Flosadóttir
  • Benedikt Ómarsson
  • Sylwia Ptasinska
  • Benjamin Puschnigg
  • Paul Scheier
  • Paulo Limão-Vieira
  • Stephan Denifl
Research Article

Abstract

We report gas phase studies on NCO fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition. Utilizing partially methylated thymine, we demonstrate that the remarkable site selectivity of the initial hydrogen loss as a function of the electron energy is preserved in the prompt as well as the metastable NCO formation in DEA. Site selectivity in the NCO yield is also pronounced after deprotonation in MALDI, though distinctly different from that observed in DEA. This is discussed in terms of the different electronic states subjected to metastable decay in these experiments. In potassium collisions with 1- and 3-methylthymine and 1- and 3-methyluracil, the dominant fragment is the NCO ion and the branching ratios as a function of the collision energy show evidence of extraordinary site-selectivity in the reactions yielding its formation.

Graphical abstract

Key words

NCO anion Electron transfer Negative ion formation Metastable decay DEA Collision dynamics Matrix assisted laser desorption/ionization (MALDI) 

Supplementary material

13361_2013_715_MOESM1_ESM.pdf (3.2 mb)
ESM 1(PDF 3.22 MB)

Copyright information

© American Society for Mass Spectrometry 2013

Authors and Affiliations

  • Filipe Ferreira da Silva
    • 1
  • Carolina Matias
    • 1
    • 2
  • Diogo Almeida
    • 1
  • Gustavo García
    • 3
  • Oddur Ingólfsson
    • 4
  • Helga Dögg Flosadóttir
    • 4
  • Benedikt Ómarsson
    • 4
  • Sylwia Ptasinska
    • 5
  • Benjamin Puschnigg
    • 2
  • Paul Scheier
    • 2
  • Paulo Limão-Vieira
    • 1
  • Stephan Denifl
    • 2
  1. 1.Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e TecnologiaUniversidade Nova de LisboaCaparicaPortugal
  2. 2.Institut für Ionenphysik und Angewandte Physik and Center for Biomolecular Sciences InnsbruckLeopold-Franzens Universität InnsbruckInnsbruckAustria
  3. 3.Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas (CSIC)MadridSpain
  4. 4.Department of Chemistry and Science InstituteUniversity of IcelandReykjavikIceland
  5. 5.Department of Physics and Radiation LaboratoryUniversity of Notre DameNotre DameUSA

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