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  • 1995-1999  (2)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 845-850 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: 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.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The protonated and sodium cationized pseudomolecular ions of a series of reducing and non-reducing oligosaccharides possessing aldopentopyranosyl, 6-deoxyaldohexopyranosyl, ketohexofuranosyl, 4-O-methyl glucuronopyranosyl methyl ester and N-acetyl 2-deoxyglucopyranosylamine units were studied using collision-induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H]+ ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na]+ ions by two-bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 → 2 and 1 → 4 linkages. The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H]+ and [M + Na]+ ions is discussed. An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H]+ ions and oxonium ions from several oligosaccharides containing monosaccharide residues with different masses.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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