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  • Chemistry  (44)
  • Biological data  (11)
  • General Chemistry  (11)
  • Polymer and Materials Science  (10)
  • H55
  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 18 (1989), S. 301-307 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectra of many rifamycins cannot be obtained by electron ionization (EI) owing to their thermal decomposition. When a laser beam is used to vaporize the sample through an optic fibre inserted in a hollow probe which reaches the sample cup, decomposition is minimized and the EI spectra show abundant molecular ions and fragments of structurally high diagnostic value. These ionic species are easily observed owing to the lack of chemical noise often present in soft ionization methods, such as direct liquid chemical ionization and fast atom bombardment.
    Additional Material: 2 Ill.
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  • 2
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The influence of fluorine substitution on the fragmentation processes of some substituted isoxazoles has been studied by comparing the electron-impact-induced mass spectrometric behaviour of some 5-monofluoromethyl-3,4-disubstituted isoxazoles with that of the corresponding 5-methyl analogs. Some interesting and unusual cleavages have been detected and a rationale has been developed for them on the basis of metastable ion studies and accurate mass measurements. Evidence has been found of the influence of fluorine in the stabilization of molecular and fragment ions.
    Additional Material: 4 Ill.
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  • 3
    ISSN: 0959-8103
    Keywords: anthracene ; fluorescence ; naphthalene ; non-radiative singlet energy transfer ; polyesters ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Steady state fluorescence has been used to study the efficiency of nonradiative single energy transfer for naphthalene → naphthalene and naphthalene → anthracene for polyesters and their bichromophoric model compounds. Polyesters containing only naphthalene groups were derived from 2,6-naphthalene dicarboxylic acid as the rigid unit, and two series of glycols, HO—(CH2)m—OH and HO—(CH2CH2O)n;—OH, where m=2-6 and n=1-4, as flexible spacers. Bichromophoric model compounds were derived from 2-naphthoic acid and the same glycols. In order to study the transfer for naphthalene → anthracene, a first attempt was made by studying bichromophoric model compounds D—(CH2)m—A, where D and A denote 2-naphthoate (donor) and 9-anthranoate (acceptor) groups, respectively. The fluorescence anisotropy measurements in a solid matrix of glassy poly(methyl methacrylate), for the compounds containing only naphthalene groups, and the simple excitation and emission spectra, for the compounds containing naphthalene and antharacene groups, clearly demonstrate the presence of non-radiative singlet-singlet energy transfer, the efficiency of which depends mainly on n (or n). A theoretical treatment using the rotational isomeric state model of the conformatin of these molecules has also been performed. The combination of the experiments and the theoretical analysis establishes that the Förster radii are 1.2 and 1.4 nm for the naphthalene → naphthalene transfer in the bichromophoric model compounds and polyesters, respectively, and 1.6 ± 0.2 nm for the naphthalene → anthracene transfer in the model compounds studied.
    Additional Material: 16 Ill.
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  • 4
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The behaviour of three fluorinated acyclic nucleoside analogs has been examined under different ionization conditions, i.e. by electron ionization, fast-atom bombardment and positive-ion chemical ionization using methane, isobutane and ammonia as reactant gases. The protonated molecules have been studied by collisional spectroscopy. In general, protonation takes place on the functional groups exhibiting a proton affinity higher than that of the reactant species but some discrepancies are present. They have been explained by the presence of quasi S—H—F structures implicating proton bridging between sulphur and fluorine atoms.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 376-380 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The electron ionization mass spectrometry of some β-hydroxy alkyl aryl sulphoxides halogenated in the γ-position is described and the mechanism of the common fragmentation patterns are discussed with the aid of linked scans at constant B/E, mass-analysed ion kinetic energy spectra and labelling experiments. The influence of the presence of halogens is also discussed.
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 72-77 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Electron ionization and fast-atom bombardment mass spectrometry are shown to provide a valid analytical tool for the structural characterization of the title compounds. In fact, diagnostic fragmentation pathways were observed depending on the presence of different substituents (benzyloxy, p-tolylthio, p-tolylsulphinyl) as swell as of different bases. Regioisomeric compounds could be differentiated by kinetic energy release measurements.
    Additional Material: 1 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 591-595 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Characterization of stereoisomeric 3,4-dideoxy-3-fluoro-hexoses has been carried out using fast-atom bombard-ment. Diagnostic fragments were observed in the daughter-ion spectra of the [M-H]- and [M+H]+ ionic species. Notable differences were also observed in the relataivae abundances of ionic species corresponding to [M-H]-, [M-H-HF]- and [C11H11O2]- ions.
    Additional Material: 4 Tab.
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  • 8
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectrometric behaviour of four homochiral 3-deoxy-3-fluoro muscarins has been studied by means of fast atom bombardment. Neither naturally occurring nor collisionally induced decompositions were effective for the structural characterization of the different diastereoisomers. In contrast such results have been easily obtained by angle-resolved mass spectrometry, i.e. by the study of the variation of absolute abundance of collisionally induced decomposition products versus scattering angle.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1741-1748 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The migration of compounds from polymer-based packaging may impart undesirable odors to foods. We, therefore, undertook a study of the volatile compounds produced during the heating of polyethylene (PE) in the presence of excess O2 at temperatures of 150-350°C and for heating times of 5-15 min. Eightyfour volatile compounds in the range of C5 - C23 were identified by gas chromatography mass spectrometry. The major products were aliphatic hydrocarbons, aldehydes, ketones, and olefins. Changes in temperature and heating times affected the amount and type of compounds produced, with hexanal being found in the largest amount and 300°C resulting in the greatest quantity of volatile compounds. At 350°C, greater amounts and numbers of low-boiling and fewer high-boiling compounds were formed. Only small amounts of volatiles were produced at 150°C. Many of the compounds identified have been reported to have odor and/or toxicological significance. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 375-384 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Glass fibers have been treated with γ-aminopropyl-triethoxysilane (APES) through different silanizating procedures, which include APES aqueous solutions and APES vapor adsorption. Transmission Fourier transform IR (FTIR) measurements have been performed on the silanized samples to characterize the silanization reaction. Dansyl-sulfonamide conjugates have then been formed by reaction of dansyl chloride in dimethylformamide solution with the amine functionality's immobilized on the glass fiber surface. Steady-state and time-resolved fluorescence measurements have been performed on dansylated samples. A dependence of the fluorescence intensity and the wavelength of the maximum emission on the silanization procedure has been observed. Good fits of the fluorescence decays of dansyl labels are found when biexponential functions are used for deconvolution, whereas the decay of dansylamides in fluid solution is single exponential. A two-state model for the solid solvent relaxation seems to apply for this samples. Several surface structural changes produced by the different silanization methods have been proposed. FTIR results support the conclusions drawn from fluorescence measurements. © 1996 John Wiley & Sons, Inc.
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