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New data on the valine molecule (C5H11NO2) fragmentation under the low-energy electron-impact are presented. These data are related to the formation of ionized products due to the ionizing radiation influence on the above amino acid molecule. A series of the fragments produced are identified by applying an extensive DFT-theory approach. The results obtained allowed the principal pathways of the valine molecule fragmentation to be found. The absolute appearance energies of some fragments are both measured experimentally and calculated theoretically. The experimental and theoretical data are compared and analysed. [ABSTRACT FROM AUTHOR]

The present study describes the fragmentation of the amino acid L-threonine (C4H9NO3) with and without the inclusion of water influence. The fragmentation of the L-threonine molecule was theoretically studied using the Becke’s three-parameter hybrid functional method by applying the non-local correlation provided by Lee, Yang and Parr (B3LYP) with the correlation consistent triple zeta basis (cc-pVTZ). The polarizable continuum model (PCM) was used to evaluate the influence of water. Fragments were selected based on data from mass spectrometry experiments. The chemical compositions of fragments were identified, and the appearance energy was calculated. Based on the obtained results, we can conclude that water affects the appearance energy, the fragment structure and the fragment formation processes.

The fragmentation of the alanine (C3H7NO2) molecule due to the low-energy electron impact was studied both experimentally and theoretically using the mass spectroscopic technique combined with the density functional theoretical approach. The main emphasis was given to the mechanisms of initial molecule fragment production. Special attention was paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of initial molecule rearrangement were also analysed. [ABSTRACT FROM AUTHOR]