The diagnostic value of them/z 102 peak in the positive-ion fast-atom bombardment mass spectra of peptides

Autor: W. Heerma, W. D. van Dongen, Johan Haverkamp, C. G. de Koster
Rok vydání: 1995
Předmět:
Zdroj: Rapid Communications in Mass Spectrometry. 9:845-850
ISSN: 1097-0231
0951-4198
DOI: 10.1002/rcm.1290090925
Popis: The mass spectrometric characteristics of a number of different m/z 102 ions, which might occur in the fast-atom bombardment mass spectra of peptides, appeared to be sufficiently different for an unequivocal structural assignment and they have successfully been applied in the structural analysis of an unknown. Special attention has been paid to the structure of m/z 102 ions from threonine-containing compounds. Attempts to generate m/z 102 product ions from peptides containing threonine at the N-terminus were not successful. From experiments with 18O-labelled threonine it was concluded that the side-chain hydroxyl group is exclusively involved in the water loss from protonated threonine. Based on ab initio calculations of feasible m/z 102 production structures, N-protonated dehydroamino-2-butyric acid from protonated threonine and peptides containing threonine at the C-terminus seems to be the most likely product-ion structure. Although relative stability calculations revealed that the threonine B1-type ion has the lowest heat of formation, it could also be concluded that a B1-type ion from threonine should be considered as an electrostatically bound ion/molecule complex, which will immediately dissociate into a threonine immonium ion (A1) and a carbon monoxide molecule. The energy requirement for this fragmentation reaction (B1→A1 + CO) is less than 7 kJ/mol without an energy barrier, which makes B1-type ions of threonine unlikely to exist in the gas phase.
Databáze: OpenAIRE
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