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  • 1
    Electronic Resource
    Electronic Resource
    NMR relaxation and ESR spin probe studies of some surfactant micelles (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 1000-1011 
    Details
    ISSN: 0749-1581
    Keywords: NMR relaxation ; Carbon-13 ; Deuterium ; ESR ; Micelles ; Surfactants ; Spin probes ; Alkyl chains ; Molecular dynamics ; ‘Two-step’ model ; ‘Three-step’ model ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multi-frequency relaxation studies combined with the ‘two-step’ and ‘three-step’ models for molecular motion have been applied to a range of anionic surfactant molecules. From the internal dynamic parameters (τf and S) conclusions have been drawn about the dependence of surfactant molecular dynamics inside micelles on molecular structure, and two unusual conformations have been identified. Slow correlation time (τs) data have also been obtained for these compounds. Three deuteriated surfactant molecules were subjected to the ‘three-step’ model and data are presented showing how the dimensions of the non-spherical micelles vary with temperature. An ESR spin probe study has been carried out on the compounds giving probe rotational correlation times at various temperatures. Information on alkyl chain packing at or near the water/micelle interface can be obtained from the derived thermodynamic parameters.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260301016
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of the Woessner and the ‘model-free’ approaches for the analysis of carbon-13 spin-lattice relaxation data for methyl groups (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 259-262 
    Details
    ISSN: 0749-1581
    Keywords: Carbon-13 relaxation times ; NOE factors ; Methyl groups ; Dicyclohexyl compounds ; Alkyl chains ; Model lubricants ; Molecular dynamics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR relaxation data obtained for methyl groups in two dicyclohexane compounds were used to compare the Woessner and ‘model-free’ approaches. It is shown that the extra flexibility offered by the latter leads to a more successful analysis of the data.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300312
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  • 3
    Electronic Resource
    Electronic Resource
    ESR spectroscopy of some dicyano-, pyrazino- and quinoxalino-1,3,2-dithiazolyl radicals (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 774-778 
    Details
    ISSN: 0749-1581
    Keywords: ESR ; 1,3,2-Dithiazol-2-yl radicals ; Pyrazine ; Quinoxaline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several symmetrical 1,3,2-dithiazol-2-yl radicals have been examined that have in common nitrogen-containing substituents at the 4- and 5-positions, namely 4,5-dicyano-1,3,2-dithiazol-2-yl, [15N2]-1,3,2-dithiazolo [4,5-b] pyrazin-2-yl and 1,3,2-dithiazoleo [4,5-b] quinoxalin-2-yl. The ESR spectrum of the 4,5-dicyano radical does not reveal any 14N splittings from the cyanide groups; however, the pyrazine and the quinoxaline derivatives do have multi-lined well resolved spectra arising from substantial hyperfine interactions with these nuclei. The interactions are sufficiently large to be observed in the powder spectra of the latter. The presence of proton hyperfine interactions shows that unpaired-electron spin density is delocalized over all the rings. It has been found that the radicals attached to pyrazine and quinoxaline can be incorporated into single crystals of naphthalene and phenazine, respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300814
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  • 4
    Electronic Resource
    Electronic Resource
    Carbon-13 NMR relaxation study of the overall and internal motions in compounds containing n-octyl chains (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 273-281 
    Details
    ISSN: 0749-1581
    Keywords: Molecular motion ; Carbon-13 relaxation ; Octyl chains ; Polydecene ; Model lubricants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C nuclear relaxation behaviour of n-alkyl chains in a variety of compounds can be described in terms of two relaxation times, one for tumbling (τc) and one for each carbon nucleus for the internal motions (τc). Relaxation data for the quaternary carbon nuclei of n-octylbenzene and n-octyl cyanide have been used to determine τc) and their activation energies [Ea(τc)]. These values have enabled τe and their associated activation energies [Ea(τe)] to be calculated for each carbon in the alkyl chains of the two compounds. In these compounds the values for C-6 appear to be invariant with τe(298) = 15 ± 2 ps and Ea(τc) = 15 ± 1 kJ mol-1. Assuming that these are universal values for all n-octyl chains, we have used them to calculate τe and Ea(τe) for other simple n-octyl compounds, thus allowing τc and E.a(τc) to be determined. It was found that Ea(τc) values correlate well with those for Ea(n/T) obtained from viscosity measurements. Di-n-octyl ether shows motional properties similar to those of the straightchain compounds.Simultaneous fitting of relaxation rate and NOE enhancement data measured over a range of radiofrequencies and temperatures permits a wealth of motional properties to be discerned when there is a suitable frequency dispersion. Both tri-n-octylamine and polydecene tumble sufficiently slowly to allow both relaxation rate and NOE data to be used to evaluate τc and τe and their activation energies without making any assumptions about C-6. The values of τc(298) and Ea(τc) obtained from C-6 for tri-n-octylamine are 314 ± 12 ps and 18.5 ± 0.4 kJ mol-1, respectively, and the corresponding values for polydecene are 576 ± 41 ps and 16.1 ± 1.3 kJ mol-1, respectively.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290314
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  • 5
    Electronic Resource
    Electronic Resource
    Multi-frequency, variable-temperature and high-pressure study of carbon-13 spin - lattice relaxation in tetraoctyltin (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 1221-1225 
    Details
    ISSN: 0749-1581
    Keywords: High pressure ; Molecular motion ; Carbon-13 relaxation ; Octyl chains ; Tetraoctyltin ; Polydecene ; Model lubricants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR spin-lattice relaxation times, T1, and nuclear Overhauser effect data were obtained for neat tetra-n-octyltin at 22.5 and 100.6 MHz over a wide temperature range. T1 values were also measured at 25.16 MHz at pressures up to 211 MPa. The ambient-pressure data were fitted to the ‘model-free’ two-correlation time spectral density with a temperature-dependent order parameter, S2. The pressure data were interpreted by assuming that internal motions of the octyl chain are independent of pressure while the overall (tumbling) motion and S2 are pressure dependent. The values of the motional parameters for tetra-n-octyltin lie in the ranges expected for compounds containing long n-alkyl chains. The results show that this approach is applicable to complex liquids such as synthetic lubricants of the polydecene type.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260291211
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