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  • 1
    Electronic Resource
    Electronic Resource
    Simultaneous detection of ions and neutrals produced by matrix-assisted laser desorption (1993)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 569-575 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Ionic and neutral products of matrix-assisted laser desorption were simultaneously detected in a time-of-flight mass spectrometer. The neutrals were photoionized with coherent vacuum ultraviolet radiation. Mass spectra were obtained for primary and secondary alkyl amines in various absorbing matrices. Based upon relative signal intensities of directly formed analyte ions and photoionized analyte neutrals, the ratio of neutrals-to-ions ejected was found to be of the order of 10000 or greater with desorption irradiances near the threshold for ion formation. The ratio decreased with increasing irradiance of the desorption laser beam. This dependence is consistent with a collisional mechanism tor analyte-ion formation during the desorption event that is initiated by photoionization of the matrix. Matrices which gave large signal intensities of directly formed analyte ions also gave large signal intensities of photoionized analyte neutrals. Conversely, matrices which gave small signal intensities of directly formed arelyte ions also gave small signal intensities of photoionized analyte neutrals. These results suggest that the efficiency of analyte vaporization by matrix-assisted laser desorption is an intrinsic property of the matrix-analyte pair, independent of the ion-formation process.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290070702
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  • 2
    Electronic Resource
    Electronic Resource
    Laser microprobe fourier transform mass spectrometry. Preliminary results for feasibility and evaluation (1988)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 2 (1988), S. 146-150 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The feasibility is reported of coupling a laser microprobe sampling system with a Fourier transform mass spectrometer (FTMS) for surface characterization. Analysis of an integrated circuit chip demonstrates capabilities for focusing the laser on a selected spot on a sample surface. Analysis of a model glass sample for which high resolution is required to separate metal ions from metal oxide ions emphasizes the advantages of coupling such a sampling system to an FTMS instrument.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290020708
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  • 3
    Electronic Resource
    Electronic Resource
    tert-Butyl 7-cycloheptatrienylperacetate: The proton NMR spectrum and conformational analysis (1975)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 7 (1975), S. 94-96 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton magnetic resonance spectrum of tert-butyl 7-cycloheptatrienylperacetate has been analyzed with the aid of the lanthanide shift reagents, Eu(fod)3 Yb(fod)3. Observation of the lanthanide-induced shifts showed, in conjunction with variable temperature studies establishing the conformational purity of the cycloheptatrienyl ring, that the peracetate substituent has a definite equatorial preference.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270070210
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  • 4
    Electronic Resource
    Electronic Resource
    Structure elucidation with lanthanide-induced shifts. 4For Part 3, see Ref. 1. - Bound shifts vs relative shifts (1978)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 11 (1978), S. 323-328 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of lanthanide shift reagents (LSR's) to obtain additional structural information from nuclear magnetic resonance studies has gained widespread acceptance. However, there has not been general agreement with regard to the most appropriate methodology for analysis of the shifted NMR spectra. We present arguments that only the bound shifts (Δ1) corresponding to the LS complex should be used for correlation of lanthanide-induced shifts with molecular structure by means of the pseudocontact equation. Several examples are discussed of compounds for which the relative induced shifts are dependent on the concentration of LSR. For such cases it is not possible for both Δ1 and Δ2 (the bound shift corresponding to the LS2 complex) to correlate successfully with the correct structure. Alternative methods of obtaining bound shifts are critically evaluated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270110702
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  • 5
    Electronic Resource
    Electronic Resource
    Structure elucidation with lanthanide induced shifts. 6For Part 5 see Ref. 1. - solvent effects on bound shifts and association constants (1980)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 14 (1980), S. 32-37 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The NMR spectra of acetone, adamantanone and 1-adamantanecarbonitrile have been studied in the presence of Eu(fod)3 in various solvents. A substantial solvent dependence is found for the association constants between shift reagent and substrate. The magnitude of the association constants is correlated with solvent polarity, and a tenfold decrease in K1 is observed upon changing from carbon tetrachloride to the more polar dichloromethane. Only a very small solvent dependence is observed for the bound shifts. The relative bound shifts (and therefore the structures of the LS complexes) are found to be solvent independent. The small solvent dependence of the absolute magnitude of the bound shifts for the LS complexes is suggested to result from experimental errors.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270140107
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  • 6
    Electronic Resource
    Electronic Resource
    Structure elucidation with lanthanide induced shifts. 7For Part 6 see Ref. 1. - development of a reliable method for structure evaluation and the application to organic nitriles (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 57-67 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A useful and reliable procedure has been developed for the evaluation of the structures of organic nitriles using lanthanide shift reagents. The procedure is based on a statistical comparison of the experimental lanthanide induced shifts (LIS) with values which are predicted with the pseudocontact equation for a proposed structure. The experimental LIS are obtained by nonlinear regression analysis of the chemical shifts observed in the presence of varying amounts of the shift reagent, Eu(fod)3. The precise geometry for a proposed structure is obtained from molecular mechanics calculations. The LIS are then predicted with the pseudocontact equation using k=976.6 and a europium-nitrogen bond length of 2.50 Å. (Detailed arguments are presented in support of these values.) The carbon-nitrogen-europium array is approximately linear, although small distortions from linearity are both expected and observed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270150113
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  • 7
    Electronic Resource
    Electronic Resource
    o-Nitrobenzylidene compounds. I - Competitive ortho interactions in the mass spectra of n-o-nitrobenzylidene-o-substituted anilines (1976)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1976), S. 609-622 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intense [M - 17]+ ion, which is a characteristic feature of the mass spectra of N-o-nitrobenzylideneaniline and its simple derivatives, may be substantially reduced in intensity when the aniline-derived ring is also ortho substituted: the intensity is lowest when this ortho substituent has a nucleophilic character and can itself interact with the CH=N group. The ortho substituents examined are Br, CH3, OH, NH2, SH, SC6H4CH3(p), CO2CH3 and CO2C2H5.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210110607
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  • 8
    Electronic Resource
    Electronic Resource
    Letters to the editor (1982)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 17 (1982), S. 643-645 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210171211
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  • 9
    Electronic Resource
    Electronic Resource
    Structural identification of alkene isomers by photodissociation-photoionization mass spectrometry (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 27 (1992), S. 949-954 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photodissociation-photoionization, mass spectrometry (PDPI/MS) is used to probe the neutral dissociation chemistry of branched alkenes and dienes. Molecules are photodissociated with an ultraviolet laser and the resulting neutral fragments are subsequently photoionized with coherent vacuum ultraviolet radiation. The neutral fragmen tation observed is useful for characterizing compounds which isomerize prior to ionic fragmentation. Unimolecular photodissociation of dienes and branched alkenes is dominated by cleavage of the β C—C bond. In a few cases, α-cleavage is also observed. When two isomers produce isomass primary products, secondary fragmentation can be used to distinguish the structures. The primary and secondary product distributions are predictable and usually occur without iomerization. As a result, PDPI/MS can be used to determine the sites of branching and unsaturation in small (C5-C8) aliphatic compounds.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210270904
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  • 10
    Electronic Resource
    Electronic Resource
    Sequence-specific fragmentation of benzyloxycarbonyl dipeptides by resonance-enhanced multiphoton ionization (1989)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 24 (1989), S. 176-182 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of fragment ion formation in resonance-enhanced multiphoton ionization (REMPI) of benzyloxycarbonyl (CBZ)-derivitized dipeptides is presented. At 266 nm, the entire multiphoton process can be thought of as a two-part scheme where ionization occurs by resonant two-photon ionization followed by photodissociation of the created ions. When the energy of two photons exceeds the molecular ionization energy by a significant amount, REMPI has the advantage of producing both parent ions and low appearance energy fragments in large amounts. For CBZ dipeptides, resonant two-photon ionization at 266 nm produces parent ions as well as A type sequence ions with high abundance. On the other hand, a three-photon process (resonant two-photon ionization followed by parent ion photodissociation) forms sequence-related ions which also involve complex fragmentations of the CBZ chromophore. These results are compared to mass spectra obtained by other ionization/dissociation methods and to REMPI mass spectra of related compounds. Factors related to molecular structure elucidation based upon REMPI mass spectra are discussed. Enhanced isomer distinction is demonstrated for CBZ-leu-ala-OCH3 and CBZ-ile-ala-OCH3 based upon REMPI fragmentation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210240307
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