Electron Ionization of Serine and Threonine: a Discussion about Peak Intensities

Document Type: Regular Article

Authors

1 Chemistry Department, University of Zanjan, Zanjan 45371-38791, Iran

2 Chemistry Department, University of Zanjan, Zanjan , Iran

Abstract

The present study describes the fragmentation under electron ionization (EI) of gas phase serine and threonine amino acids. Ab initio methods were performed to calculate the fragmentation paths and interpret the mass spectra. The six lowest energy conformers of L-serine, L-threonine and L-allo-threonine were obtained with B3LYP, G3MP2 and MP2 methods. The adiabatic and vertical ionization energies of the most stable conformers are reported. The structures of fragment ions and neutral species formed by direct bond cleavages as well as rearrangement reactions were obtained. Appearance energies (AE) were calculated for the formation of particular fragment ions at 200 °C. The order of peak intensities were compared with the theoretical calculated AEs, and a complementary explanation was provided about the relative abundance of fragmentation products.

Graphical Abstract

Electron Ionization of Serine and Threonine: a Discussion about Peak Intensities

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