Mass Spectrometric Studies of Valine Molecules by Electron Shock in the Gas Phase

Abstract

Relevance. Valine is one of the eight amino acids not synthesised by the human body, necessary for the synthesis and growth of body tissues, muscle coordination; regulation of nervous processes, nitrogen metabolism, and stabilisation of the hormonal background. Since α-amino acids contain an asymmetric carbon atom, they can exist as optical isomers (mirror antipodes) that play an essential role in protein biosynthesis. The structure of matter and the physical processes that occur in it are studied using the method of mass spectrometry and spectral analysis. This indicates the relevance of the problem that was studied in this paper. Purpose. Mass spectrometric studies of the formation of ionic products of single and dissociative ionisation of the valine molecule (C5H11NO2) with electrons according to the method of beams intersecting within the energy range of bombarding electrons 6-70 eV. To consider the mechanisms of formation of the most intense ion fragments during dissociative ionisation by electron shock. Methods. The experiment was conducted on an installation with a monopole mass spectrometer of the MX-7304A type, which belongs to the class of dynamic mass analysers with electron shock ionisation in the range of mass numbers 0-120 Da. The mass spectra of molecules were investigated at different temperatures of the source of molecules in the range of 300-600 K. Results. The obtained results are compared with the mass spectra of the D-, L-, and DL-enantiomeric forms of the valine molecule with data from the NIST and SDBS databases. The features of the processes of formation of ion fragments of valine molecules by electronic shock are analysed in detail, and the dynamics of the yield of ion fragments in the range of evaporation temperatures of the initial substance of 300-440 K is also studied. The total relative ionisation cross-section of the molecule under study was measured according to mass spectrometric method with an ionising electron energy of 5-60 eV. Based on the results of experimental studies, a threshold section of the dependence of the total relative cross-section of valine ionisation is determined and given in this paper. Conclusions. A detailed analysis of the processes of formation of fragment ions in the mass spectra allows demonstrating the influence of the structural forms of valine enantiomers on the redistribution of relative intensities of product ions