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  • General Chemistry  (3)
  • 15N NMR  (1)
  • Agroforestry  (1)
  • Androgen  (1)
  • Springer  (3)
  • Wiley-Blackwell  (3)
  • American Chemical Society
  • American Society of Hematology
  • Springer Nature
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  • 2020-2022
  • 2000-2004
  • 1995-1999  (4)
  • 1960-1964  (2)
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  • 1996  (3)
  • 1964  (1)
  • 1961  (1)
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  • Springer  (3)
  • Wiley-Blackwell  (3)
  • American Chemical Society
  • American Society of Hematology
  • Springer Nature
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  • 2020-2022
  • 2000-2004
  • 1995-1999  (4)
  • 1960-1964  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Tree fallows: A comparison between five tropical tree species (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 50-56 
    Details
    ISSN: 1432-0789
    Keywords: Agroforestry ; 15N ; Nitrogen fixation ; Phenolics ; 13C ; Tree fallows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The natural abundance of 15N and 13C, conventional soil analyses, and biomass production by maize were used to study the influence of five tropical tree species on soils and their fertility. The experiment was conducted in Morogoro, Tanzania, to compare Cassia (Senna) siamea, Eucalyptus camaldulensis, E. tereticornis (all non-N2-fixing), Leucaena leucocephala, Prosopis chilensis (both N2-fixing), and a grass fallow. Maize biomass production, which was correlated with N uptake (P=0.001), was higher on soils from plots with 5-year-old Leucaena and Prosopis spp. compared to the grass fallow, while other tree species had less favourable effects on maize growth. The per cent N was higher in soil and δ15N of soil total N was lower under Prosopis sp. compared to soil under other tree species, which suggests an input from N2 fixation by Prosopis sp. A transfer of fixed N to maize or to understorey grass species was, however, not indicated by the 15N natural abundance. Prosopis sp. contributed more C to the soil than the other four tree species; the difference in δ13C between soils from Prosopis sp. plots and from grass fallow plots showed that the tree contributed 11% to the total C of the soil over a period of 8 years. The leaves of the N2-fixing species had a low ratio of lignin+phenols to N, and maize growth was negatively correlated with this parameter. The Eucalyptus spp. had leaves with a high lignin+phenols to N ratio, contributed very little C to the soil, and lowered the soil pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335818
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  • 2
    Electronic Resource
    Electronic Resource
    Anisotropic rotational diffusion of perdeuterated HIV protease from 15N NMR relaxation measurements at two magnetic fields (1996)
    Springer
    Journal of biomolecular NMR 8 (1996), S. 273-284 
    Details
    ISSN: 1573-5001
    Keywords: 15N NMR ; Rotational diffusion ; Chemical shift anisotropy ; Dynamics ; Magnetic field dependence ; Deuteration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary 15N NMR relaxation times in perdeuterated HIV-1 protease, complexed with the sub-nanomolar inhibitor DMP323, have been measured at 600 and 360 MHz 1H frequency. The relative magnitudes of the principal components of the inertia tensor, calculated from the X-ray coordinates of the protein-drug complex, are 1.0:0.85:0.44. The relation between the T1/T2 ratios observed for the individual backbone amides and their N-H orientation within the 3D structure of the protease dimer yields a rotational diffusion tensor oriented nearly collinear to the inertia tensor. The relative magnitudes of its principal components (1.00:1.11:1.42) are also in good agreement with hydrodynamic modeling results. The orientation and magnitude of the diffusion tensors derived from relaxation data obtained at 360 and 600 MHz are nearly identical. The anisotropic nature of the rotational diffusion has little influence on the order parameters derived from the 15N T1 and T2 relaxation times; however, if anisotropy is ignored, this can result in erroneous identification of either exchange broadening or internal motions on a nanosecond time scale. The average ratio of the T1 values measured at 360 and 600 MHz is 0.50±0.015, which is slightly larger than the value of 0.466 expected for an isotropic rigid rotor with τc = 10.7 ns. The average ratio of the T2 values measured at 360 and 600 MHz is 1.14±0.04, which is also slightly larger than the expected ratio of 1.11. This magnetic field dependence of the T1 and T2 relaxation times suggests that the spectral density contribution from fast internal motions is not negligible, and that the chemical shift anisotropy of peptide backbone amides, on average, is larger than the 160 ppm value commonly used in 15N relaxation studies of proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00410326
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  • 3
    Electronic Resource
    Electronic Resource
    Heat-induced testicular apoptosis occurs independently of hormonal depletion (1998)
    Springer
    Apoptosis 3 (1998), S. 281-288 
    Details
    ISSN: 1573-675X
    Keywords: Androgen ; apoptosis ; heat stress ; hormone ; temperature ; testis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Previous studies have demonstrated that testicular germ cell apoptosis can be induced both by heat stress and by withdrawal of androgens and gonadotrophins. To investigate whether heat-induced germ cell apoptosis occurs independently of the altered levels of hormones that occur with heat exposure, mouse testicular apoptosis was studied using an in vitro system with controlled levels of testosterone, FSH and LH. It was observed that cells underwent apoptosis sooner in the absence of hormones at the same temperature. Apoptosis also occurred earlier at abdominal temperature compared to scrotal temperature with the same hormonal levels. No somatic tissues studied underwent apoptosis at 37°C under the same culture conditions. These results suggest that heat stress may independently activate an apoptotic pathway in the testis, and that hormone deprivation may induce apoptosis via a separate mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009665309915
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  • 4
    Electronic Resource
    Electronic Resource
    The silaguanidinium cation and the search for a stable silylium cation in condensed phases (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 869-876 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; silaguanidinium cations ; silylium cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantium mechanical calculations at the MP2/6-31 G(d) level are reported for the silaguanidinium cation Si(NH2)3+ (1) and derivatives thereof. The equilibrium structure 1a has D3 symmetry with planar amino groups rotated out of the SiN3 plane by 19.60. The Si-N bond length of 1 a (1.658 Å) is intermediate between a single and a double bond. Isodesmic reactions show that the stabilization of the silylium cation 1 a by the amino groups (63.5 kcal mol-1) is about 40% of the resonance stabilization of the guanidinium cation (159.3 kcal mol-1), but 1 a is clearly better stabilized than alkyl-substituted silylium cations. The electronic stabilization of 1 a by the amino groups is also made obvious by the calculated complexation energy with one molecule of water. The calculated stabilization through complexation of water at HF/6- 31 G(d) is markedly lower for Si(NH2)3-(H2O)+ (6) (28.8 kcal mol-1) than for SiMe3(H2O)+ (40.6 kcal mol-1). The tris(dimethylamino) silylium cation Si(N-Me2)3+ (8) is even more stable than 1 a. The complexation energy of Si(NMe2)3-(H2O)+ (10) is only 17.3 kcal mol-1. IGLO calculations of the 29Si N M R chemical shifts predict that 1 a and 8 should not show the same extremely low shielding that is calculated for alkyl-sub-stituted silylium ions. The calculated 29Si resonances for 8 are in reasonable agreement with the experimental N M R spectrum of (Me2N)3 SiB(C6F5)4. AM 1 calculations predict that the substituted tripyrrolidino silylium cation 12 would be an even better candidate for a stable tricoordinate silylium cation in condensed phases. One of the pyrrolidine rings of 12 has tert-butyl groups in the 2 and 5 positions, which serve as a steric fence around the silicon atom.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020717
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  • 5
    Electronic Resource
    Electronic Resource
    Neue Anwendungsgebiete der Dünnschicht-Chromatographie (1961)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 73 (1961), S. 646-654 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zur analytischen und mikropräparativen Schnelltrennung von Stoffgemischen dient in steigendem Maße die Chromatographie in dünnen, feinkörnigen Schichten. Auf aktiven Schichten läßt sich ähnlich wie bei adsorptionschromatographischen Säulentrennungen arbeiten und auf inaktiven Schichten sind verteilungschromatographische Schnelltrennungen möglich. Einfache Handhabung und Schnelligkeit machen die Dünnschicht-Chromatographie in vielen Laboratorien zu einem unentbehrlichen Hilfsmittel.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19610731904
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  • 6
    Electronic Resource
    Electronic Resource
    Gradient and Low-Temperature Thin-Layer Chromatography (1964)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 784-791 
    Details
    ISSN: 0570-0833
    Keywords: Thin layer chromatography ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and the use of gradient layers for thin-layer chromatography are described. On a gradient layer there are three flow surfaces, all differing in their separation behavior. It is therefore possible to determine, for example, the basicity and/or activity which gives the optimum separation for a mixture of substances. Gradient thin-layer chromatography was also carried out at low temperatures, after the effect of temperature on the separation of various mixtures had been studied.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.196407841
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