Electron transfer to aliphatic amino acids in neutral potassium collisions

Electron transfer in potassium collisions with alanine (C3H7NO2) and valine (C3H11NO2) is investigated at 15 and 100 eV. The fragmentation patterns obtained in the unimolecular decomposition through time-of-flight (TOF) mass spectrometry are compared for both amino acids as a function of the collision energy. In the case of alanine, the most prominent feature in the collision regime is the relative decrease of the dehydrogenated parent anion signal with respect to the hydrogen anion as the collision energy increases. For low collision energies this can be rationalised in terms of autodetachment inhibition, whereas at higher collision energies the negative molecular ion can be formed with an excess of internal energy which might even result in fragmentation. Regarding valine, such behaviour was not observed which has been interpreted as a result of side chain effect contributing to an increase of the internal degrees of freedom in comparison to alanine. (C) 2014 Elsevier B.V. All rights reserved.