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  • Articles  (6)
  • Chemistry  (6)
  • Capillary isotachophoresis
  • 1995-1999  (6)
  • Physics  (6)
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  • Articles  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 644-650 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A new approach, bio-affinity characterization mass spectrometry (BACMS), aimed at providing a more rapid, sensitive and potentially more flexible alternative to techniques presently employed for the characterization of noncovalent interactions in mixtures, such as would be encountered in combinatorial chemistry, is presented. BACMS avoids some of the difficulties and potential artifacts associated with affinity chromatography since the noncovalent associations occur in solution; thus, BACMS avoids the requirement of solid support media and the development of non-interfering linker species. This paper describes the conceptual basis for the methodology and its potential use in applications which include the screening of high affinity ligands in support of new drug development. BACMS exploits new Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry technologies which, when coupled to electrospray ionization (ESI), allow the investigation of specific noncovalent complexes formed in solution. BACMS utilizes the well-known attributes of FTICR, such as the high resolution mass analysis and (MS)n (n ≥ 2) capabilities; however, it is even more directly a result of recently developed techniques involving quadrupolar excitation, such as selected-ion accumulation. These tools are demonstrated and the results illustrate the extraordinary sensitivity achievable (solution concentrations of 1 × 10-9 M without the use of separations prior to ESI). Thus, the new capabilities demonstrated here, in conjunction with ESI, will be useful for the investigation of very low relative concentration noncovalent association directly from solution, and promote a faster alternative for combinatorial mixture screening and analysis.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 312-316 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The stoichiometry of a noncovalent, hydrogen-bonded supramolecular complex, hub(M)3·RCA3, was characterized using electrospray ionization from chloroform. The intact (1:3) complex was observed in the negative-ion mode as a Cl--bound species using Ph4PCl as the source of the charge donor. Collisionally and thermally induced dissociation of the (1:3) complex resulted in the simultaneous loss of all the three RCA units, indicating a cooperative binding of RCA units in the (1:3) complex. These results suggest that the attachment of small, organic-soluble ions may be a useful technique for mass spectrometric characterization of neutral supramolecular complexes that are stable or soluble only in non-polar organic solvents.
    Additional Material: 3 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1552-1555 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An entire series of Starburst polyamidoamine (PAMAM) dendrimers consisting of generations 1 through 10 (G1-10) have been studied by positive-ion electrospray ionization mass spectrometry (ESI-MS) using an extended m/z range quadrupole mass spectrometer. Charge-state distributions were detected as high as m/z 12 000 for the generation 10 dendrimer, having a theoretical molecular weight of 1 megadalton and containing approximately 93 maximum positive charges on the molecule. Accurate molecular weight determinations of the smaller generation dendrimers (G1-3, Mr ∼ 1.4kDa to 6.9kDa) were obtained using a commercial triple quadrupole instrument. The unit resolution ESI mass spectra provide information on the number of incomplete reactions which may occur during polymer synthesis. The extent of gas-phase charging observed by ESI-MS on the entire series of macromolecules was found to exhibit a linear relationship to Mr2/3, consistent with theoretical models prediciting a spherical ion structure with maximum charging controlled by Coulombic effects.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative non-covalent binding behavior of two small molecule ligands to the tetrameric protein streptavidin was investigated by electrospray ionization mass spectrometry (ESI-MS). An extended m/z range quadrupole mass spectrometer was employed to observe the intact multimeric form of the protein and to probe the relative stabilities of the tetrameric protein- ligand complexes in the gas phase. Various protein:ligand molar ratio concentrations and incubation times were studied for the ligands biotin (Kd ≈ 10-15 M) and iminobiotin (Kd ≈ 10-7 M), in combination with the adjustment of variables in the ESI atmosphere-vacuum interface region. Positive-ion ESI-MS of a 1:7 molar ratio streptvidin-biotin sample produced peaks corresponding to the intact tetrameric complex (16+ to 14+ charge states) with four ligands binding to the active from of the protein. Only the expected specific non-covalent complexes of four ligand molecules binding to the protein tetramer were detected, consistent with known solution behavior and without the appearance of any random aggregation. However, under identical interface conditions, complete iminobiotin binding to the protein was not observed, even when higher ligand concentrations, longer complexation times and gentler interface conditions were employed. The thermally induced dissociation (TID) of the non-covalent complexes was studied by applying more severe conditions in the ESI interface region. In addition, observation of an intact streptavidin-biotinylated oligonucleotide non-covalent complex (17- to 14- tetrameric charge states) by negative-ion ESI-MS at m/z 4500-5000 is presented. The results show that the complexes observed in the mass spectrometer are representative of those that exist in solution, under the ESI conditions employed, and that the ability to observe such complexes is at least qualitatively related to stability in solution.
    Additional Material: 6 Ill.
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  • 5
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An electrospray ionization-Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometer has been used in conjunction with the technique of selected-ion accumulation (SIA) to investigate its utility for the study of the gas phase behavior of noncovalent complexes from solution. SIA is demonstrated to provide the selective accumulation of weakly bound species, providing a significant enhancement in the attainable signal-to-noise ratio and dynamic range. The frequency response of quadrupole excitation was first determined by selectively accumulating single charge states of large, highly adducted, highly charged molecules such as bovine albumin and bovine albumin dimer. Under the conditions employed, the response (selective accumulation) was found to be as narrow as 500 Hz. Additionally the SIA was found to be sufficiently gentle to allow accumulation of both specific and nonspecific weak noncovalent complexes, such as the myoglobin-heme complex observed in basic solutions and complexes of myoglobin and single amino acids, such as tryptophan. This result is probably due to the continual application of quadrupole excitation during the high pressure accumulation event, preventing any significant growth of magnetron motion, and subsequently, allowing interconversion to form only small cyclotron radii. We also demonstrate the simultaneous application of SIA with dipolar sustained off-resonance irradiation (SORI) during the ion accumulation period so as to allow selective accumulation of dissociation products. The SIA/SORI combination promises to greatly extend (MS)n capabilities by allowing the selective accumulation of any dissociation product in any step along a given dissociation pathway.
    Additional Material: 9 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 339-347 
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two types of gas-phase proton transfer reactions were examined with electrospray ionization-generated peptide and protein ions; (i) bases reacting with multiply protonated molecules and (ii) acids reacting with multiply deprotonated molecules. For reactions of type (i) with bases spanning a range of proton affinities, the proton transfer reaction rate was observed to increase with increasing proton affinity of the charge transfer reagent. Proton transfer was not observed for the low proton affinity reagents (ethyl acetate, acetonitrile and water). These studies also qualitatively measured for the first time the temperature dependences for reactions with multiply charged peptides and proteins. Negative temperature dependences were observed for the weaker bases and positive dependences for the stronger bases. A negative temperature dependence was also observed in the reaction of propionic acid with [M - nH]n- ions. Two hypotheses are proposed to explain the data. In the first, negative temperature dependences are attributed to slightly exothermic reactions, while the positive dependences may reflect contributions from a competing clustering pathway, a pathway which could be more dominant with the heavier reagents. Alternatively, the positive temperature dependences may reflect the barrier in the reaction coordinate arising from the repulsion of like-charged ions, while negative temperature dependences could reflect a cluster-mediated reaction in which charge delocalization lowers the barrier to proton transfer. In the latter cases, clustering is invoked with the lower proton affinity reagents because of the higher concentrations employed.
    Additional Material: 6 Ill.
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