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  • 1
    Electronic Resource
    Electronic Resource
    Comparison of numerical simulation of solute transport with observed experimental data in a silt loam subsoil (2000)
    Springer
    Environmental geology 39 (2000), S. 977-989 
    Details
    ISSN: 1432-0495
    Keywords: Key words Solute ; Ion transport ; Modeling ; Soil column ; Adsorption ; Dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Solute transport experiments were conducted on loamy soils of north-eastern Iowa, USA, and the results were compared with a numerical solution of a classical advection-dispersion transport model developed in this study. Flow experiments in the laboratory on undisturbed soil columns showed a flow rate of water much higher than was estimated from the soil properties and grain-size analysis data, suggesting preferential flow regime in the soil. In contrast, the relative concentration peaks of Cl– and Br– in the effluent were only approximately 70% of those predicted by the classical advection-dispersion equation (ADE). In addition, the experimental breakthrough curves (BTCs) showed greater tailings of these ions than the model solution. These observations suggest a loss of solute mass during transport from the dynamic flowing regions to a stagnant, immobile water phase in the soil matrix. Experiments in small disturbed soil columns showed that movement of Cl– and Br– is in good agreement with predictions of the classical ADE when the tracers are applied as a continuous source. However, in the case of a pulse source, the BTCs of Cl– and Br– matched the model only in the ascending part of the curves. Such variation indicates greater retardation of these ions than that of simulation, probably caused by the decrease in soil permeability due to cation exchange reactions in the soil involving monovalent and divalent cation pairs such as K+–Ca2+ and K+–Mg2+. In addition, retardation occurred as a result of the continuous saturation of soil columns which seemed to have caused an expansion of clay minerals, thus resulting in decreased soil permeability. In both the continuous and the pulse-source experiments, K+ was not detected in the effluent samples, which seemed to have been lost in exchange reactions and adsorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002549900067
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  • 2
    Electronic Resource
    Electronic Resource
    Aggregation of apolar peptides in organic solvents. Concentration dependence of 1H-nmr parameters for peptide NH groups in 310 helical decapeptide fragment of suzukacillin (1982)
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 1427-1433 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Peptide NH chemical shifts and their temperature dependences have been monitored as a function of concentration for the decapeptide, Boc-Aib-Pro-Val-Aib-Val-Ala-Aib-Ala-Aib-Aib-OMe in CDCl3 (0.001-0.06M) and (CD3)2SO (0.001-0.03M). The chemical shifts and temperature coefficients for all nine NH groups show no significant concentration dependence in (CD3)2SO. Seven NH groups yield low values of temperature coefficients over the entire range, while one yields an intermediate value. In CDCl3, the Aib(1) NH group shows a large concentration dependence of both chemical shift and temperature coefficient, in contrast to the other eight NH groups. The data suggest that in (CD3)2SO, the peptide adopts a 310 helical conformation and is monomeric over the entire concentration range. In CDCl3, the 310 helical peptide associates at a concentration of 0.01M, with the Aib(1) NH involved in an intermolecular hydrogen bond. Association does not disrupt the intramolecular hydrogen-bonding pattern in the decapeptide.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360210711
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  • 3
    Electronic Resource
    Electronic Resource
    Crystal structure of Boc-Ala-Aib-Ala-Aib-Aib-methyl ester, a pentapeptide fragment of the channel-forming ionophore suzukacillin (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 1499-1505 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: t-Buthyoxycarbonyl-L-alanyl-α-aminiosobutyryl-L-alanyl-α-aminoisobutyryl-α-aminoisobutyric acid methyl ester (t-Boc-L-Ala-Aib-L-Ala-Aib-Aib-OMe), C24H43N5O8, an end-protected pentapeptide with a sequence corresponding to the 6th through the 10th residues in suzukacillin, crystallizes in the orthorhombic space group P212121 with a = 11.671, b = 14.534, c = 17.906 Å and z = 4. The molecule exists as a right-handed 310-helix with a pitch of 6.026 Å. The helix is stabilized by three 4 → 1 hydrogen bonds with the NH groups of Ala(3), Aib(4), and Aib(5) hydrogen bonding to the carbonyl oxygens of t-Boc, Ala(1), and Aib(2), respectively. The helical molecules arrange themselves in a head-to-tail fashion along the a direction in such a way that the NH groups of Ala(1) and Aib(2) hydrogen bond to the carbonyl oxygens of Aib(4) and Aib(5), respectively, of a translationally related molecule. The helical columns thus formed close-pack nearly hexagonally to form the crystal.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360220606
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  • 4
    Electronic Resource
    Electronic Resource
    Studies of uranium - cerium admixture solutions by EDXRF spectroscopy (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 24 (1995), S. 298-306 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Uranium and cerium were studied in nitric acid solutions after presentation to an energy-dispersive x-ray fluorescence (EDXRF) spectrometer on filter-paper fixed on Scotch tape. Ce Lα and U Lα peaks were used as analyte lines after excitation with a tungsten tube target at low potential (20 kV). These non-conventional excitation conditions were considered to be suitable for low contents of cerium strongly but high contents of uranium weakly in a nuclear fuel. Lower net integrated line intensities observed in an actinide as compared with a lanthanide are discussed along with the scattered, Auger and Coster-Kronig intensities responsible for the production of back-ground before calibrations with known concentrations. Difficulties in establishing an explicit relationship between these with change in matrix composition are discussed. The known concentrations of the mixed solutions when compared with the results from various computer programs using regression analysis showed that the algorithm developed by Plesch and Thiele for Siemens is better than the others. An accuracy of 〈2% was achieved. The importance of certified, standard or simulated reference materials is realized for quality analysis of occasional samples.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300240605
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