Investigation of protonation and decomposition of tyrosine by ion mobility spectrometry and DFT calculations

The present study was designed to investigate the ionization and decomposition of tyrosine amino acid via an ion mobility spectrometer equipped with a corona discharge ionization source in the positive ion mode. Several peaks were observed in the ion mobility spectra of tyrosine with adjusting injection port and cell temperature at 250 and 200 degrees C, respectively. The experimental results were confirmed with density functional theory calculations. The topical proton affinities of the six lowest energy conformers of tyrosine were calculated for the protonation of several sites in each conformer. One of the peaks was assigned to the protonated tyrosine and other peaks were attributed to the fragment ions. The ion mobility spectra of eventual fragments as well as the mass-to-mobility correlation equation were utilized in order to identify of product fragments. The topical proton affinity and bond dissociation energies were calculated as additional hints to the identification of possible fragments. It was revealed that the combination of the theoretical and experimental tools results in a reliable identification of product ions in a corona discharge ionization source. (C) 2018 Elsevier B.V. All rights reserved.