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  • Analytical Chemistry and Spectroscopy  (19)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 5 (1991), S. 417-434 
    ISSN: 0886-9383
    Keywords: Factor analysis ; Power density distribution ; Chromatography ; Absorption spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Evaluation of the results of factor analysis of sets of spectroscopically detected chromatograms is carried out by examining the shapes of the abstract factors. This is done either by visual inspection or by analysis of the power density spectra produced from them. Owing to constraints imposed by the column function and the spectroscopic instrument function, the information content of the chromatograms necessarily occurs at low spatial frequencies. As a consequence, it appears as relatively broad features in the abstract chromatograms and as a peak in the low-frequency region of the corresponding power density plot. On the basis of examination of the power density distribution, a well-defined distinction is made between primary and secondary abstract factors. The major uncertainty encountered in determining the number of chemical components appears to arise from effects of contaminants in reagents.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 738-743 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: [M+H+16]+ ions were observed in the electrospray ionization mass spectra of several synthetic and maturally occurring peptides. Initial results have shown that the appearance of the modification is dependent on the field strength at the electrospray needle and the flow rate of the solution passing through the capillary. Mass spectrometric experiments on peptides showing the +16 Da modification attributed the change to the selective oxidation of either a methionyl, tryptophanyl, or tyrosyl residue present in the peptide. These results were further confirmed by tandem mass spectrometry experiments on prptides with a methionyl residue at either the N- or C-tgerminus, or within the peptide chain. This effect can occur under normal operating conditions and therefore care must be taken in the analysis of samples containing these oxidizable residues. Conversely, the selectivity of the oxidative process may be used to enhance the information obtained from the mass spectrometric analysis. For example, we show results for the analysis of a tryptic digest of the protein myoglobin where the occurrence of the [M+H+16]+ ion is used, along with the molecular weight data, to correctly identify the tryptic fragment.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 369-372 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Design considerations for an electrospray ionization source on a double-focusing magnetic sector mass spectrometer are discussed. A source with two additional pumping stages before the source housing has been constructed. High sensitivity for multiply charged ions from high molecular weight proteins up to 66 kDa is demonstrated with this source.
    Additional Material: 5 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Mass Spectrometry Reviews 9 (1990), S. 37-70 
    ISSN: 0277-7037
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 11 (1978), S. 561-564 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The 13C NMR chemical shifts of some cyclohexane derivatives containing 1,3-diaxial methyl groups are assigned. The resonance signals of the methyl carbon atoms 1 and 3 in these compounds are shifted on average by 4.5 ppm to lower field (δ-effect). The ring carbon atoms 1 and 3 also show shifts to lower field, averaging 0.7 ppm (γ-effect). In open-chain hydrocarbons, analogous shift effects are observed when the investigated compounds have the geometry of the gPgM conformer of n-pentane.
    Notes: Die 13C-NMR-Spektren einer Reihe von Cyclohexanen mit 1,3-diaxialen Methylgruppen wurden bestimmt. Die Resonanzsignale der Methyl-Kohlenstoffatome 1 und 3 sind in diesen Verbindungen um durchschnittlich 4,5 ppm nach tieferem Feld verschoben (δ-Effekt). Auch die Ringkohlenstoffatome 1 und 3 zeigen Verschiebungen um durchschnittlich 0,7 ppm nach tieferem Feld (γ-Effekt). In offenkettigen Kohlenwasser-stoffen werden analoge Verschiebungseffekte beobachtet, wenn in den betreffenden Verbindungen die Geometrie des gPgM-Konformeren des n-Pentans vorkommt.
    Additional Material: 3 Tab.
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  • 6
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 358-360 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectrometric fragmentation of the five cis-trans isomeric 1,2,4,5-tetramethylcyclohexanes is influenced by their configuration. The thermochemically stable isomers show a higher abundance of the [M—CH3]+ ions and a lower abundance of the [M—C2H5]+ ions than the strained isomers. The [M—CH3]+/[M—C2H5]+ intensity ratio correlates with the enthalpy difference ΔHisom and with the mean number of gauche arrangements ZgI of the stereoisomers.
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 7 (1975), S. 478-484 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 1H NMR chemical shifts of 18 methyl substituted cyclohexane-1,2-dicarboxylic anhydrides were determined. In compounds with asymmetric substitution vicinal coupling constants were measured. In the series of trans-anhydrides it can be deduced from the NMR data, that the 6-membered ring has a chair-like conformation. Additionally, in the series of the cis-anhydrides a twisted chair conformation is favoured for the most part.
    Notes: Die chemischen Verschiebungen der 1H-NMR-Spektren von 18 methylsubstituierten Cyclohexandicarbonsäure-(1,2)-anhydriden wurden bestimmt. Von den unsymmetrisch sub-stituierten Verbindungen wurden die vicinalen Kopplungskonstanten ermittelt. Bei den trans-Anhydriden lässtsich aus den NMR-Daten ableiten, dass der Sechsring in einer sesselähnlichen Form vorliegt. Auch bei den cis-Anhydriden sind in den meisten Fällen Konformationen mit verdrillter Sesselanordnung des Cyclohexans bevorzugt.
    Additional Material: 4 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 5 (1973), S. 119-124 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The chemical shifts of methyl protons of 51 methyl and tert-butyl substituted cyclohexanes were determined. The resonance range of axial methyls extends from δ = 0,63 to 0,98 ppm and equatorial groups from δ = 0,81 to 1,02 ppm. the chemical shifts of axial methyl groups are more greatly influenced by neighbouring groups than those of equatorial methyls. The shift effects of alkyl groups on the chemical shifts of methylprotons and ring protons were compared.
    Notes: Die chemischen Verschiebungen der Alkylprotonen von 51 methyl- und tert-butyl-substituierten Cyclohexanen wurden bestimmt. Der Resonanzbereich axialer Methyl-gruppen erstreckt sich von δ = 0,63 bis 0,98 ppm, der von äquatorialen von δ = 0,81 bis 1,02 ppm. Die chemischen Verschiebungen axialer Methylgruppen werden durch Nachbargruppen stärker beeinflusst als die der äquatorialen Methylgruppen. Die Shifteffekte von Alkylgruppen auf Methylprotonen werden mit denen auf Ringprotonen verglichen.
    Additional Material: 7 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 5 (1973), S. 179-186 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Chemical shifts and coupling constants of methyl substituted 4-cyclohexene-1,2-dicarboxylic anhydrides were determined. The NMR data demonstrate the boat conformation of the cis-anhydrides. The orientation of the cis-anhydride ring relative to the cyclohexene boat depends on the constitution and configuration of the compounds, and can be deduced from coupling constants and δ-values of the H1- and H2-protons. Methyl groups in the neighbourhood of these protons shift the resonance frequencies dependent upon molecular conformation.
    Notes: Es wurden die chemischen Verschiebungen und Kopplungskonstanten von methylsubstituierten Cyclohexen-(4)-dicarbonsäure-(1,2)-anhydriden bestimmt. Die NMR-Daten beweisen die Bootkonformation der cis-Anhydride. Die Orientierung des cis-Anhydridringes relativ zum Cyclohexenboot wird durch die Konstitution und Konfiguration der Verbindungen bestimmt und kann von den Kopplungskonstanten und den δ-Werten der H1- und H2-Protonen abgeleitet werden. Methylgruppen in Nachbarschaft zu diesen Protonen verschieben die Resonanzfrequenzen in Abhängigkeit von der konformativen Anordnung.
    Additional Material: 3 Tab.
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