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  • 1
    Electronic Resource
    Electronic Resource
    Energy-resolved collisional activation of dimethyl phosphonate and dimethyl phosphite ions in a quadrupole ion trap and a triple quadrupole mass spectrometer (1988)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 23 (1988), S. 6-9 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Collision-activated dissociation spectra of dimethyl phosphonate and dimethyl phosphite ions were measured as a function of the amplitude of a supplementary AC voltage applied across the end-caps of an ion-trap mass spectrometer. These spectra yield breakdown graphs which bear a close resemblance to those obtained by varying collision energy in a triple-quadrupole mass spectrometer operating under multiple-collision conditions. Variation in the time of excitation at the resonance frequency provides an alternative route to breakdown graphs. The results demonstrate that energy deposition occurs via multiple activating collisions in the ion trap. Maximum energy deposition observed is somewhat smaller under normal operating conditions in the ion trap than in the triple-quadrupole mass spectrometer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210230103
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of functional group interactions on the dissociation reactions of protonated amino alcohols (1993)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 28 (1993), S. 665-671 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dissociation reactions of protonated amino alcohols were examined in a quadrupole ion trap mass spectrometer. Multi-stage collision-induced dissociation techniques were used to characterize the ions and their fragments and to assist in the determination of the dissociation mechanisms. In addition, semi-empirical calculations were used to rationalize the results on the basis of the thermodynamics of the reactions in question. The reaction of special interest was the double elimination of water and ammonia. For this high-energy process, it is shown that the initial deamination step is the thermodynamically favored one in most cases. The enthalpies of formation for the various precursor and product ions and also those for some of the reaction intermediates were estimated using molecular modelling and semi-empirical calculation methods. The values obtained indicated that the minimum endothermicity of the sequential deamination-dehydration reaction ranges from 209 to 460 kJ mol-1 for the compounds studied here. Moreover, protonation at the amine site was found to be energetically favored by 38-192 kJ mol-1 over protonation at the hydroxyl site.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210280603
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  • 3
    Electronic Resource
    Electronic Resource
    Ion-molecule reactions and dissociation of glycols in a quadrupole ion trap mass spectrometer: Evidence of intramolecular interactions (1993)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 28 (1993), S. 737-744 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyethylene glycols react with CH3OCH2+ ions from dimethyl ether to form [M + 13]+ products. The [M + 13]+ ions are stabilized by intramolecular interactions involving the internal ether oxygen atoms and the terminal methylene group. Collisionally activated dissociation (CAD), including MSn and deuterium labeling experiments show that fragmentation reactions involving intramolecular cyclization are predominant. Scrambling of hydrogen and deuterium atoms in the ion-molecule reaction products is not indicated. The CAD spectra of the [M + 13]+ ions provide unambiguous assignment of the glycol size.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210280703
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  • 4
    Electronic Resource
    Electronic Resource
    Application of site-selective ion-molecule reactions to the analysis of the cinchona alkaloids (1993)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 28 (1993), S. 1608-1615 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Functional group interactions within biologically relevant molecules are among the most influential yet least understood factors in determining their reactive behaviors. Reactions of dimethyl ether ions, which have previously been shown to be site-selective, with four cinchona alkaloids, cinchonine, cinchonidine, quinine and quinidine, have been examined. These reactions are each shown to produce qualitatively similar spectra for the stereoisomeric pairs cinchonidine-cinchonine and quinidine-quinine, but small variations in the relative abundances of the products indicate that some stereoselectivity can be observed. The site selectivity of each of the reagents was investigated by observing the reactions occurring with model subunits of the alkaloids.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210281237
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  • 5
    Electronic Resource
    Electronic Resource
    Selective ion-molecule reactions of ether reagent ions with nucleoside antibiotics in a quadrupole ion trap (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 625-631 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The analysis of a targeted group of nucleoside antibiotics has been accomplished through the use of selective ion-molecule reactions and collision-activated dissociation (CAD) techniques in a quadrupole ion trap. A series of homologous ether reagent ions generated from dimethyl ether, di-n-butyl ether and 2-methoxyethanol were used as chemical ionization reagents. Because chemical ionization with dimethyl ether and di-n-butyl ether reagent ions did not provide selectivity and signal enhancement for the analysis of these biopharmaceuticals, a chemical ionization reagent with special hydrogen-bonding capabilities was used. The reagent ion that showed the greatest promise is a product of 2-methoxyethanol, CH3OCH2CH2OCH2 +. This highly reactive species, which reacts selectively with nitrogen-containing compounds, can undergo both nucleophilic attack and anchoring via hydrogen bond formation between the methoxy oxygen and an acidic hydrogen of the nucleoside substrate. The reaction of the CH3OCH2CH2OCH2+ ion with each of the nucleoside antibiotics resulted in formation of [M + 13]+ and [M + 89]+ products. The CAD spectra indicated that the adducts are covalently bound species and that the nucleotide moiety dominates both the reactive and dissociative behavior of the nucleoside antibiotics.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300414
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  • 6
    Electronic Resource
    Electronic Resource
    Structurally-selective gas-phase ion-molecule reactions of dibenzo-16-crown-5 compounds (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 572-580 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Steric and substituent effects can play large roles in influencing the outcomes of organic reactions. In this work, the use of ion-molecule reactions of dibenzo-16-crown-5 compounds (lariat ethers) by tandem mass spectrometry to probe the influence of the pendant groups on the selectivity of their gas-phase reactions was evaluated. Lariat ethers are macrocyclic ethers with pendant substituents that have been developed as new types of hosts for molecular recognition. Dimethyl ether (DME) was the reactant chosen because of its well characterized reactivity with various organic substrates possessing different functional groups. Only those dibenzo-16-crown-5 compounds with no or at most one substituent at the center carbon of the three-carbon bridge form the diagnostic [M + 13]+ product ion through a methylene substitution process. Dibenzo-16-crown-5 compounds with geminal substituents on the center carbon of the three-carbon bridge form the [M + 45]+ ion, but not the characteristic [M + 13]+ ion. Causative factors may be steric blocking of the reaction pathway by the geminal groups or a requirement for the presence of at least one hydrogen on the center carbon of the three-center bridge for formation of the [M + 13]+ ion. CAD, deuterium labelling, molecular orbital calculations and comparisons with model compounds provide additional information about the reaction pathways.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300408
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