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1.
Derivatization of a variety of peptides by a method known to enhance anhydride formation is demonstrated by mass spectrometry to yield ions that have elemental composition and fragmentation properties identical to [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation. The [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation and the solution-phase [b(n-1) + OH + H]+ ion structural analogs formed by derivatization chemistry show two different forms of dissociation using multiple-collision CAD in a quadrupole ion trap and unimolecular decomposition in a TOF-TOF; one group yields identical product ions as a truncated form of the peptide with a free C-terminal carboxylic acid and fragments at the same activation energy; the other group fragments differently from the truncated peptide, being more resistant to fragmentation than the truncated peptide and yielding primarily the [b(n-2) + OH + H]+ product ion. Nonergodic electron capture dissociation MS/MS suggests that any structural differences between the specific-fragmenting [b(n-1) + OH + H]+ ions and the truncated peptide is at the C-terminus of the peptide. The specific-fragmentation can be readily observed by MS(n) experiments to occur in an iterative fashion, suggesting that the C-terminal structure of the original [b(n-1) + OH + H]+ ion is maintained after subsequent rearrangement and fragmentation events in peptides which fragment specifically. A mechanism for the formation of specific-fragmenting and nonspecific-fragmenting [b(n-1) + OH + H]+ ions is proposed. 相似文献
2.
Ronald L. Cerny Kenneth B. Tomer Michael L. Gross 《Journal of mass spectrometry : JMS》1986,21(10):655-660
Combining desorption ionization with tandem mass spectrometry overcomes the disadvantage of limited fragmentation accompanying desorption and permits mixtures of closely related substances to be investigated directly. These features of the combination are illustrated by completing the structure-proof of a minor component of an ornithine-containing lipid mixture isolated from Thiobacillus thiooxidans. The minor component is a homolog of the major constituent and differs from the principal component owing to the presence of a double bond in lieu of a cyclopropyl ring in one of the constituent fatty acids. Another feature of the combined method is the potentially complementary nature of collision-activated dissociation spectra of protonated and cationized biomolecules. This is illustrated by the differences in the collision-activated dissociations of the [M + Na]+ of sucrose, desorbed by field desorption, and [M + H]+, desorbed by fast atom bombardment. A third illustration is the application of field desorption and tandem mass spectrometry to an organometallic compound. The combined approach allows the ligands to be identified and the relative ligand binding energies to be approximated. 相似文献
3.
The mass spectra of a group of m- and p-substituted acetanilides were measured to determine the effect of the substituents, if any, on the rate of C2H2O expulsion (rearrangement) vs. the rate of [CH3CO]+ formation (simple cleavage). Our results agree with observations of others in that substituents which raise the ionization potential of the aromatic ring appear to localize, on the average, less charge density on this locus, and conversely. The atomic composition of the substituent, however, irrespective of its position, seems to determine the relative rates of the competing reaction. Although in several cases Zm/Zp values were close to unity, rearrangement of isomeric molecular ions to a common species is shown not to occur. 相似文献
4.
Mixtures of peptides have been analyzed by capillary zone electrophoresis in conjunction with mass spectrometry (MS) using an on-line coaxial continuous-flow fast atom bombardment interface. MS and MS-MS spectra have been acquired in electrophoretic real time from femtomole levels of the peptides, while maintaining separation efficiencies in excess of 100,000 theoretical plates. 相似文献
5.
Kenneth B. Tomer 《Journal of mass spectrometry : JMS》1974,9(7):686-689
Ion cyclotron resonance spectrometry and deuterium labeling have been used to determine that nondecomposing \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_{\rm 3} {\rm)}_{\rm 2} \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2}$\end{document} ions do not isomerize to \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} {\rm CH = }\mathop {\rm N}\limits^{\rm + } {\rm HCH}_{\rm 3}$\end{document}. 相似文献
6.
C. E. Parker J. R. Perkins K. B. Tomer Y. Shida K. O’Hara M. Kono 《Journal of the American Society for Mass Spectrometry》1992,3(5):563-574
Nanoscale separation techniques, nanoscale packed capillary columns (75 μm id), and capillary zone electrophoresis (CZE), on-line with electrospray mass spectrometry (ESI/MS), were applied to the separation of a series of ten macrolide antibiotics. Both techniques use sub-microliter-per-minute flow rates through the analytical column and therefore require an electrospray probe that incorporates coaxial sheath flow. Positive ion electrospray mass spectra of these compounds yielded mainly protonated molecules. Fragmentation to yield structurally significant fragment ions was achieved by collision-induced dissociation (CID) at increased skimmer voltages. Separations were achieved using both techniques, with CZE/ESI/MS showing improved peak shapes and detection limits combined with faster analysis times. Nanoscale packed capillary columns provided better chromatographic resolution and was less susceptible to peak broadening caused by overloading of the analytes. 相似文献
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9.
Chakrabarty Sankalpita Offen-Polak Inbal Burshtein Tomer Y. Farber Eliyahu M. Kornblum Lior Eisenberg David 《Journal of Solid State Electrochemistry》2021,25(1):159-171
Journal of Solid State Electrochemistry - The urea oxidation reaction (UOR) is an important challenge in electrocatalysis, in the context of electrolyzers, fuel cells, medical sensing, and... 相似文献
10.
Paul Hemmes Onkar S. Tomer Arthur T. Poulos William Macanka 《Journal of Molecular Liquids》1984,28(1):33-47
A spectroscopic method for studying quadrupole formation is described, and experimental results are presented for lithium thiocyanate in a tetrahydrofuran/hexane solvent system. From molar absorptivity equations and an equation by Fuoss and Kraus, a direct relationship is derived between the quadrupole formation constant, KQ, and the dielectric constant of the medium. Experimental results are consistent with the equation and allow an estimate of the distance between lithium and thiocyanate in the ion pair. 相似文献