Formation of anion fragments from gas-phase glycine by low energy (0–15 eV) electron impact

Abstract

Dissociative electron attachment to pentaerythritol tetranitrate: Significant fragmentation near 0 eV Absolute partial cross sections for electron-impact ionization of CH4 from threshold to 1000 eV We have measured the formation of anion fragments in gas phase glycine (H 2 NCH 2 COOH) via dissociative electron attachment ͑DEA͒ reactions in the 0-15 eV electron energy range, using a monochromatic electron beam and mass spectrometric detection of the negative ions. By far the most intense product observed is the closed shell glycine anion (H 2 NCH 2 COO) Ϫ which appears from a low-energy resonance with a peak located at 1.4 eV and a cross section in the range 10 Ϫ16 cm 2 . The corresponding precursor ion can be characterized by electron attachment into the empty * orbital of the ϪCOOH group as recently assigned from electron transmission experiments and ab initio self-consistent field calculations ͓Aflatooni, Hitt, Gallup, and Burrow, J. Chem. Phys. 115, 6489 ͑2001͔͒. This precursor state is also observed to decompose ͑with much lower intensity͒ yielding a negative ion fragment with 58 amu, which is attributed to anions of the stoichiometric composition H 2 C 2 O 2Ϫ or H 4 C 2 NO Ϫ . A further prominent DEA peak is observed at 6 eV, which is likely associated with a core excited resonance, and leads to formation of at least six different negative ion fragment species with the following mass numbers: 16 amu (O Ϫ /NH 2 Ϫ ), 17 amu (OH Ϫ ), 26 amu (CN Ϫ ), 28 amu (H 2 CN Ϫ ), 45 amu (HCO 2 Ϫ ), 56 amu (H 2 C 2 NO Ϫ ).

Total dissociative electron attachment cross sections of selected amino acids

“…The common feature in the DEA cross sections we observe between 1.18 and 1.27 eV has been seen previously in mass analyzed data in glycine, [17][18][19] alanine, 20 proline, 21 and tryptophan. 22 A similar feature appears in HCOOH.…”

“…Finally, we note that estimates of the total DEA cross sections at the 1.2 eV feature have been given elsewhere for glycine 18,19 ͑5 ϫ 10 −16 and ϳ10 −16 cm 2 ͒ and for alanine ͑1.5ϫ 10 −16 cm 2 ͒. 20 The reasons for these substantial overestimates have been discussed previously.…”

Theory of dissociative electron attachment: Biomolecules and clusters

“…This shift is called sometimes the "solvation energy." Because of some uncertainties in this quantity, we present results of two calculations: one with 07001-p. 7 EPJ Web of Conferences 6 cluster for the geometry of Ref. [40] for two solvation energies, 0 and −0.2434 eV.…”

“…From gas phase experiments, it was found that all the nucleobases [1][2][3][4], organic acids [5] and also amino acids [6][7][8] exhibit a hydrogen loss due to low-energy electrons. In biological environment, the anion (M−H) − can initiate further reactions leading to the cell damage.…”

“…Interaction of low-energy electrons with DNA nucleobases (thymine, adenine, cytosine, and guanine), organic acids, and amino acids is of great significance for the description of the molecular mechanisms in radiation damage [1][2][3][4][5][6][7][8]. When high-energy radiation interacts with a biological medium, it produces free radicals and low-energy electrons.…”