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  • 1
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Metastable ions arising from pseudomolecular [M — H]- ions produced by fast-atom bombardment negative-ion mass spectrometry of a range of free ecdysteroids, ecdysteroid conjugates and polar metabolites were investigated by means of linked scanning at constant B/E. Free ecdysteroids displayed daughter-ion spectra which allow 20-hydroxyecdysteroids and ecdysteroids lacking C-20 hydroxylation to be readily distinguished. The ejection of acetic acid from acetylated ecdysteroids was also readily detectable. Characteristic metastable-ion decomposition of ecdysteroid acids was not observed, presumably as a result of charge localization. High-mass daughter ions were also lacking in the case of phosphate conjugates.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 477-481 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: High-performance liquid chromatography/mass spectrometry (HPLC/MS) with thermospray ionization has been applied to the analysis of free ecdysteroids (polyhydroxylated steroids that serve as arthropod moulting hormones). Of a range of analytical conditions that were tested, optimum results were obtained by the use of re versed-phase HPLC using a methanol + water mixture containing 0.1 M ammonium acetate. The positive-ion spectra of ecdysteroids showed pseudo-molecular ions, [M + H]+, and fragment ions corresponding to the sequential losses of hydroxyl groups. The [M + H - H2O]+ and [M + H - H2O]+ ions were the most abundant for all the compounds tested. Ecdysteroids bearing a C-20 hydroxyl group (e.g. 20-hydroxyecdysone) showed ions characteristic of cleavage of the side-chain from the steroid nucleus. This mode of fragmentation was much less obvious in the case of ecdysteroids lacking C-20 hydroxylation (e.g. ecdysone). Full-scan mass spectra were readily obtained from 1 μg of free ecdysteroids, while a limit of detection of 5 ng (signal-to-noise ratio 3) was attained in the selected-ion monitoring mode. The application of HPLC/MS to the study of ecdysteroids in biological materials is demonstrated by the analysis of extracts of newly laid eggs of the desert locust (Schistocerca gregaria) and pupae of the cotton leafworm (Spodoptera litoralis).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positive ion and negative ion fast atom bombardment mass spectra of several natural and synthetic enzyme inhibitors are presented. It is shown that the fast atom bombardment method is well suited to the analysis of these unusual peptides. Complete amino acid sequences can be deduced from the mass spectra in most cases. Structural features typical of the inhibitors include (a) C-terminal aldehyde groups (e.g. leupeptin), (b) urea linkages in the peptide backbone (e.g. antipain, chymostatin), (c) prevalence of arginyl or α-(2-iminohexahydropyrimidyl)glycl residues, and (d) presence of an N-(glycosylphosphoryl) group (e.g. phosphoramidon). Several examples of synthetic peptides with common protecting groups are also presented. It is concluded that positive ion and negative ion fast atom bombardment mass spectra provide complementary information, the two techniques being sensitive to entirely different structural aspects of the inhibitors.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1984), S. 101-104 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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