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The diagnostic value of the m/z 102 peak in the positive‐ion fast‐atom bombardment mass spectra of peptides
Author(s) -
van Dongen W. D.,
Heerma W.,
Haverkamp J.,
de Koster C. G.
Publication year - 1995
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1290090925
Subject(s) - chemistry , threonine , protonation , ion , mass spectrum , fragmentation (computing) , molecule , mass spectrometry , crystallography , analytical chemistry (journal) , stereochemistry , organic chemistry , serine , chromatography , computer science , enzyme , operating system
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 18 O‐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 B 1 ‐type ion has the lowest heat of formation, it could also be concluded that a B 1 ‐type ion from threonine should be considered as an electrostatically bound ion/molecule complex, which will immediately dissociate into a threonine immonium ion (A 1 ) and a carbon monoxide molecule. The energy requirement for this fragmentation reaction (B 1 →A 1 + CO) is less than 7 kJ/mol without an energy barrier, which makes B 1 ‐type ions of threonine unlikely to exist in the gas phase.