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  • 1
    Electronic Resource
    Electronic Resource
    Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 31-36 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ammonia desorption chemical ionization (NH3-DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non-reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH4 - 42]+ ion is not formed direct from [M + NH4]+ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH4+. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH3CO to afford neutral species which complex with NH4+. The structures of the ions resulting from H transfer have been inferred by comparison of their mass-analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH4]+ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210270108
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of the glycosidic linkage in peracetylated disaccharides comprised of d-glucopyranose units by use ofr desorption electron-ionization mass spectrometry (1991)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 446-449 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An oxonium ion at m/z 317 is present in the desorption electron ionization and ammonia desorption chemical ionization mass spectra of peracetylated disaccharides, comprised of glucopyranose units linked (1 → 2), (1 → 3), (1 → 4) and (1 → 6), but is absent in the spectra of the (1 → 1)-linked isomer. The ion aat m/z 317, which is derived from the reducing moiety, has an O-formyl group at the position of linkage to the non-reducing moiety, and O-acetyl groups at each of the remaining positions. The iosmeric monoformyl, triacetyl oxonium ions (at m/z 317), derived from the (1 → 2)-, (1 → 3)-, (1 → 4)- and (1 → 6)-linked disaccharides, give distinctly different mass-analysed ion kinetic energy spectra, thereby enabling the linkage position to be assigned unambiguously.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290051005
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  • 3
    Electronic Resource
    Electronic Resource
    1H NMR assignment and conformational analysis of glucitol: Comparison with maltitol (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 458-464 
    Details
    ISSN: 0749-1581
    Keywords: Alditols ; Conformational analysis ; Glucitol ; Maltitol ; 1H NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H NMR spectrum of glucitol in D2O solution contains eight strongly-coupled multiplets covering a chemical shift range of about 0.21 ppm. The spectrum is severely complicated by second-order effects and was assigned by a combination of 2D NMR experiments and extensive spin simulation of the 1D spectra. The magnitudes of the spin coupling constants were analysed in terms of preferred conformations about each bond in the backbone of glucitol, and the results were compared with those found for maltitol in solution, with crystal conformations of both glucitol and maltitol and with low-energy conformations computed using the MM2CARB force field. The results show a surprising degree of agreement between computed low-energy conformations and those observed in the crystal, but little correspondence with conformations observed by NMR in solution. Although maltitol is derived from glucitol sustituted in the 4-position with the bulky α-D-glucopyranose moiety, NMR measurements indicate approximately free rotation about all bonds in the glucitol moiety of maltitol. This is in contrast to glucitol, where the proton-proton trans conformer predominates (74%) for the C—4-C—5 bond which, in turn, stabilizes the gauche-gauche conformer of the adjacent C—5-C—6 bond (53%) and destabilizes the trans conformer of the C—3-C—4 bond (3%).It is found from molecular modelling studies that steric factors alone cannot explain these results, and it is postulated that intramolecular hydrogen bonding stabilizes the local conformations in glucitol whereas disruption of the hydrogen-bond network occurs as a result of substitution of the glucitol moiety in maltitol.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280514
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  • 4
    Electronic Resource
    Electronic Resource
    1H NMR structural analysis of isomeric tetrazole-substituted spirostan steroids: Shielding effects and conformational study (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 63-72 
    Details
    ISSN: 0749-1581
    Keywords: Spirostan steroids ; Tetrazole-substituted ; 1H NMR ; Structural and conformational analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of two pairs of tetrazole-substituted spirostan steroids were characterized by the use of one- and two-dimensional 1H NMR measurements. The conformation of the seven-membered spirostan ring A of the steroid was determined by analysis of proton spin coupling constants and confirmed by 1D and 2D NOE experiments showing interactions between the methyl group and ring protons. The conformation of the tetrazole-substituted ring A was found to be the same for the four isomers, allowing them to be differentiated by the analysis of the effect of tetrazole-ring isomerization on the chemical shifts of neighbouring protons.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290113
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  • 5
    Electronic Resource
    Electronic Resource
    6Li—15N heteronuclear multiple quantum correlation (HMQC) spectroscopy: Application to the structure determination of lithium 2,2,6,6-tetramethylpiperidide mixed aggregates (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 855-859 
    Details
    ISSN: 0749-1581
    Keywords: 6Li—15N HMQC spectroscopy ; Lithium tetramethylpiperidide mixed aggregates ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A heteronuclear multiple quantum correlation (HMQC) experiment was used to correlate the 6Li and 15N chemical shifts of mixed aggregates of [6Li, 15N]lithium 2,2,6,6-tetramethylpiperidide with [6Li]LiBr, [6Li]LiCl, and [6Li]lithium cyclohexenolate. Optimization of the experiment to spin systems containing more than one weak spin is discussed. The two-dimensional correlations represent a substantial improvement in sensitivity and resolution relative to one-dimensional methods.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300911
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