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  • 1
    ISSN: 1573-4943
    Keywords: Accurate mass ; MALDI-TOF ; delayed extraction ; mass spectrometry ; peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is now an essential tool in biopolymer analysis. Sensitivity and mass range are unsurpassed, but mass measurement accuracy and resolution have been limited. With delayed extraction and a reflecting analyzer, mass measurements using MALDI-TOF can be made with an accuracy of a few parts per million (ppm). It is possible to distinguish Lys from Gln in peptides, and to determine the elemental composition of smaller molecules (mass 100–500). In database searching strategies, a smaller mass window, resulting from an increase in mass accuracy, greatly decreases the number of possible candidates. Mass measurement accuracy with errors less than 5 ppm is demonstrated on a mixture of 12 peptides ranging in mass from ca. 900 to 3700 Da. Mass measurements on 13 peaks in an unseparated tryptic digest of myoglobin gave results with an overall average error less than 3.5 ppm, with a maximum error of 7 ppm.
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  • 2
    ISSN: 1573-4943
    Keywords: Cytochrome b5 ; molecular weight determination ; amino acid sequence ; tandem mass spectrometry ; mass spectrometry of peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The sequence and blocking group of the amino-terminal 15 amino acids of rabbit trypsin-solubilized cytochrome b5 were determined by liquid secondary ion mass spectrometry (LSIMS) and tandem mass spectrometry (MS/MS). The molecular weights of peptides generated from aStaphylococcus aureus V8 protease digest of this protein were determined by LSIMS analysis and the two peptides containing the blocked amino-terminus were sequenced by tandem mass spectrometry to yield the sequence; N-acetyl-Ala-Ala-Glu-Ser-Asp-Lys-Asp-Val-Lys-Tyr-Tyr-Thr-Leu-Glu-Glu. Comparison of this sequence with a recently reported cDNA sequence (Dariushet al., 1988) indicates that Gln at position 3 is selectively deamidated, although no other discrepancies were found. Intact rabbit and bovine trypsin-solubilized cytochrome b5 were also analyzed by LSIMS on a high-field mass spectrometer equipped with a diode array detector. Mass measurement of the unresolved protonated molecular ion peak tops gave average molecular weights of 9462.2±2 and 9502.3±2 for bovine and rabbit trypsin-solubilized cytochrome b5, respectively. In both cases, these molecular weights correspond to a cytochrome b5 fragment consisting of amino acids Asp(7)-Arg(88). The average molecular weight for the rabbit amino-terminal-blocked form of trypsin-solubilized cytochrome b5 was found to be 10,144.5±2, which was consistent with the molecular weight predicted for the extended N-acetylated form (residues 1–88) of Mr 10,146.1.
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  • 3
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 4
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative rates of the McLafferty rearrangement in n-butyl acetate and several related molecules have been examined over the time range 10-11 to 10-5 s by means of a field ionization mass spectrometric technique. It was found that the introduction of a substituent group of low ionization potential (phenyl, dimethylamino) at sites remote from the ester oxygens reduces the rate of the McLafferty rearrangement and that the rate becomes lower as the substituent is moved further away from the ester group. The results suggest that for the cases examined the charge on the molecular ion may be localized on the functional group of lowest ionization potential.
    Additional Material: 6 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1976), S. 409-414 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative rates of competing metastable decompositions of fourteen isomeric C7H14 monoolefins were measured and compared. In every case except one the most important metastable reaction was loss of either CH3 or C2H4, but the rates of these and the other reactions observed varied over a wide range. It was concluded that the molecular ions of these compounds probably do not isomerize to a common structure prior to metastable decay. It was found that a terminal double bond strongly enhances metastable loss of C2H4 and that the additional presence of a 2-methyl substituent favours this reaction still more. Several possible mechanisms for this transition are discussed, but none was found to explain the observed results satisfactorily.
    Additional Material: 2 Tab.
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  • 8
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unimolecular decompositions of 2-methyl-1-hexene and several labelled analogues were studied following 70 eV electron impact (normal and metastable spectra) and field ionization (field ionization kinetic measurements). Molecules labelled with 13C in the 1-position and the methyl position were found to behave essentially identically. This is attributed to rapid transfer of a hydrogen atom mainly from C-5 to C-1 (γ-hydrogen shift). Loss of ethene, propene or propenyl do not involve loss of the methyl carbon or C-1. All three reactions are better than 90% specific in this respect under all conditions studied. At shorter times, C3H6 loss is the dominant reaction, while at longer times C2H6 loss accounts for 〉90% of the ion current. It is proposed that at least two distinct pathways for C2H4 loss operate in linear 1-alkenes, one of which (loss of carbons 1 and 2) is blocked by a 2-methyl substituent. The [C6H11]+· and [C5H10]+· ions formed from 13C labelled 2-methyl-1-hexenes fragment in an essentially statistical fashion.
    Additional Material: 1 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 7 (1973), S. 887-898 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: H/D randomization is not observed within the octan-2-one-1,1,1,3,3-d5 molecular ion at times less than 7 × 10-10 sec following field ionization. Partial H/D randomization is observbed at 10-6 to 10-5 sec. It is deduced that the curves of microscopic rate constant k against internal excitation energy E for the reactions effecting randomization and for the McLafferty rearrangement intersect. The field ionization kinetics (FIK) for the McLafferty rearrangement in octan-2-one-1,1,1,3,3-d5 are investigated over a time range extending from 10-11 to 10-6 sec. The maximum microscopic rate constant k for the reaction is estimated as 5 × 1010 sec-1. It is suggested that FIK measurements with a double focusing mass spectrometer be made by sweeping the blade potential rather than by the alternative technique of sweeping the electric sector analyzer potential. The ‘normnal’ FI mass spectra of octan-2 one and octan-2-one and octan-2-one-1,1,1,3,3-d5 are presented and discussed. It is proposed that the m/e 56 species in the ‘normal’ FI mass spectrum of octan-2-one represents a doubly charged ion formed by loss of oxygen in a surface process.
    Additional Material: 5 Ill.
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  • 10
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A combination of mass spectrometric techniques (electrospray mass spectrometry, liquid secondary-ion mass spectrometry (LSIMS), tandem mass spectrometry) has been used for variant hemoglobin detection and characterization. Electrospray mass spectrometry allowed analysis of mixtures of intact globins giving the molecuar weights (accuracy 1-2 Da), and information about relative amounts of globins present, simultaneously. Abnormal hemoglobins detected in this way and by other means (screening, clinical symptoms) were fractionated by C-4 reverse phase high-performance liquid chromatography (HPLC), and the separated globin chains (or the mixture of whole precipitated globin) were digested with trypsin. The tryptic peptides were separated by C-18 reverse phase HPLC and analysed by LSIMS to narrow down the mutation site to a single peptide. In some instances, the molecular weight of a variant peptide was sufficient to determine the mutation uniquely. When molecular weight information alone was insufficient to identify the mutation and its site, the peptide was sequenced by tandem mass spectrometry on a 4-sector instrument. In cases where more than one possible mutation site was present in the peptide and the mutation resulted in a change of only 1 Da in the peptide mass, the resolution and mass measurement accuracy of the 4-sector machine were esential in determining the correct sequence. The practical application of the methodologies presented is illustrated by the identification and analysis of Hb G-San Jose, Hb Willamette and Hb D-Iran.
    Additional Material: 5 Ill.
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