Predicció de les fragmentacions d’aminoàcids en espectrometria de masses

Abstract

The mass spectrometry (MS) is one of the most important instrumental techniques. In the case of electron ionization spectrometry (MS-EI), the ionized molecules undergo different fragmentations that give the characteristic peaks of the spectrum. There are two ways of predicting these signals: using generic rules or using theoretical calculations. This work focuses on the prediction of the major signals of the spectra, that is, expected fragmentations of amino acids in the cation radical state, with the help of the so-called molecular energy decomposition schemes. With this method, we can make electronic structure calculations of the neutral and radical cation species, but we do not have to consider the systematic study of all the possible unimolecular decomposition reactions that the ionized species can suffer. To make the study as complete as possible, we have tried to take into account factors that have not been covered in similar previous studies, such as expanding the number of amino acids to be studied, making a full conformational study for each amino acid in its neutral and radical cation states, and take into account both electronic and nuclear relaxation in ionized species. The results obtained were quite satisfactory since, from the minimal energy structures of the neutral and cation radical species of each amino acid, the main peak of the MS-EI spectrum was correctly predicted in 9 of the 10 cases studied