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  • Analytical Chemistry and Spectroscopy  (3)
  • Uranium isotopes  (2)
  • 1
    ISSN: 0016-7835
    Keywords: Key words Manganese nodules ; Thorium dating ; Uranium isotopes ; Peru basin ; TIMS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Thorium- and uranium isotopes were measured in a diagenetic manganese nodule from the Peru basin applying alpha- and thermal ionization mass spectrometry (TIMS). Alpha-counting of 62 samples was carried out with a depth resolution of 0.4 mm to gain a high-resolution 230Thexcess profile. In addition, 17 samples were measured with TIMS to obtain precise isotope concentrations and isotope ratios. We got values of 0.06–0.59 ppb (230Th), 0.43-1.40 ppm (232Th), 0.09–0.49 ppb (234U) and 1.66–8.24 ppm (238U). The uranium activity ratio in the uppermost samples (1–6 mm) and in two further sections in the nodule at 12.5±1.0 mm and 27.3–33.5 mm comes close to the present ocean water value of 1.144±0.004. In two other sections of the nodule, this ratio is significantly higher, probably reflecting incorporation of diagenetic uranium. The upper 25 mm section of the Mn nodule shows a relatively smooth exponential decrease in the 230Thexcess concentration (TIMS). The slope of the best fit yields a growth rate of 110 mm/Ma up to 24.5 mm depth. The section from 25 to 30.3 mm depth shows constant 230Thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule. From 33 to 50 mm depth, the growth rate is approximately 60 mm/Ma. Two layers in the nodule with distinct laminations (11–15 and 28–33 mm depth) probably formed during the transition from isotopic stage 8 to 7 and in stage 5e, respectively. The Mn/Fe ratio shows higher values during interglacials 5 and 7, and lower ones during glacials 4 and 6. A comparison of our data with data from adjacent sediment cores suggests (a) a variable supply of hydrothermal Mn to sediments and Mn nodules of the Peru basin or (b) suboxic conditions at the water sediment interface during periods with lower Mn/Fe ratios.
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  • 2
    ISSN: 0749-1581
    Keywords: Thyrsiferol ; Thyrsiferyl acetate ; NOE ; Spectral assignments ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The assignment of all reasonances in the 13C and 1H NMR spectra of thyrsiferyl acetate has been made through the application of 2D NMR experiments, together with the use of difference NOE spectroscopy.
    Additional Material: 3 Ill.
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  • 3
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The 13C NMR spectra of some polysaccharides and their methyl derivatives have been analysed. The numbers and positions of the assigned 13C NMR signals give some information about the structure of the monomer unit and the positions of the glycosidic linkage but no information about the anomeric configuration. In this case the 1J(C-1, H) coupling constants make it possible to identify the anomeric configuration, because the mean differences of the J values for the α- and β-anomers are 12 Hz (at least 5 Hz) with the higher values for the α-anomers.
    Notes: Die 13C-NMR-Spektren einer Reihe von Polysacchariden und ihrer Methylderivate wurden aufgenommen, zugeordnet und für die methylierten Polysaccharide außerdem die Kopplungskonstanten 1J(CH) bestimmt. An Beispielen wird gezeigt, daß die Zahl der 13C-Signale und deren Lage im Spektrum Aussagen über den Aufbau der Polysaccharide, sowie über die Verknüpfungsstellen der glykosidischen Bindung gestatten. Während aus den Signallagen die anomere Konfiguration nicht eindeutig zu ermitteln ist, gelingt dies bei den methylierten Polysacchariden mit Hilfe der Kopplungskonstanten 1J(C-1, H); diese weisen Unterschiede von durchschnittlich 12 Hz (aber mindestens 5 Hz) zwischen den α- und β-Anomeren auf, wobei die gröβeren Werte den α-Anomeren entsprechen.
    Additional Material: 3 Tab.
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  • 4
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: H-NMR investigations using a high resolution 220 MHz spectrometer were performed on methyl, acetyl and benzoyl derivatives of mannan from ivory nuts and Tubera salep, and on the corresponding d-mannopyranose derivatives. With the exception of the C(1) configuration the structure of these polysaccharides may be determined by comparing the coupling constants and chemical shifts of the substituted polysaccharides with those of the corresponding monosaccharide derivatives. The particularly broad signals in the spectra of low as well as high molecular weight acetyl and benzoyl mannans and furthermore, the differences between the chemical shifts of protons in 1,2,3,4,6-penta-O-acetyl-d-mannopyranose and those of the benzoylated mannans, are discussed in terms of relatively small flexibility of the polymer chains or chain segments in solution. In addition studies to determine the type of glycosidic bonds in polysaccharides from a comparison of the δH(1)-values of various polyglycan derivatives are reported.
    Notes: Die PR-Spektren einiger Methyl-, Acetyl- und Benzoylderivate von Mannan aus Steinnuß und Tubera salep sowie der d-Mannopyranose wurden analysiert. Durch einen Vergleich der Kopplungskonstanten und der Signallagen von entsprechend substituierten Polymeren und Monomeren wird, mit Ausnahme der Konfiguration an C(1), die Struktur dieser Polysaccharide bestimmt. Es wird auf charakteristische Unterschiede der Resonanzlagen von H(1) in Polysacchariden mit α-bzw. β-glycosidischen Bindungen hingewiesen. Dieser Befund eröffnet die Möglichkeit, auch in solchen Fällen eine Entscheidung über die Art der glycosidischen Bindung zu treffen, in denen, wie im Falle der Mannoside mit äquatorialständigem H(2), der Wert der Kopplungskonstante J12 keine Aussage erlaubt.Die auffallend große Breite der Signale in den Spektren der nieder- und hochmolekularen Acetyl- und Benzoylmannane wird auf eine geringe Beweglichkeit der Kette oder einzelner Kettensegmente bei Mannanderivaten in Lösung zurückgeführt.
    Additional Material: 3 Tab.
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  • 5
    ISSN: 1437-3262
    Keywords: Manganese nodules ; Thorium dating ; Uranium isotopes ; Peru basin ; TIMS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Thorium- and uranium isotopes were measured in a diagenetic manganese nodule from the Peru basin applying alpha- and thermal ionization mass spectrometry (TIMS). Alpha-counting of 62 samples was carried out with a depth resolution of 0.4 mm to gain a high-resolution230Thexcess profile. In addition, 17 samples were measured with TIMS to obtain precise isotope concentrations and isotope ratios. We got values of 0.06–0.59 ppb (230Th), 0.43–1.40 ppm (232Th), 0.09–0.49 ppb (234U) and 1.66–8.24 ppm (238U). The uranium activity ratio in the uppermost samples (1–6 mm) and in two further sections in the nodule at 12.5±1.0 mm and 27.3–33.5 mm comes close to the present ocean water value of 1.144±0.004. In two other sections of the nodule, this ratio is significantly higher, probably reflecting incorporation of diagenetic uranium. The upper 25 mm section of the Mn nodule shows a relatively smooth exponential decrease in the230Thexcess concentration (TIMS). The slope of the best fit yields a growth rate of 110 mm/Ma up to 24.5 mm depth. The section from 25 to 30.3 mm depth shows constant230Thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule. From 33 to 50 mm depth, the growth rate is approximately 60 mm/Ma. Two layers in the nodule with distinct laminations (11–15 and 28–33 mm depth) probably formed during the transition from isotopic stage 8 to 7 and in stage 5e, respectively. The Mn/Fe ratio shows higher values during interglacials 5 and 7, and lower ones during glacials 4 and 6. A comparison of our data with data from adjacent sediment cores suggests (a) a variable supply of hydrothermal Mn to sediments and Mn nodules of the Peru basin or (b) suboxic conditions at the water sediment interface during periods with lower Mn/Fe ratios.
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