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  • 1
    Electronic Resource
    Electronic Resource
    Available phosphorus in lake sediments in The Netherlands (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 491-500 
    Details
    ISSN: 1573-5117
    Keywords: phosphate ; sediment ; bioassay ; algae ; phosphate fractionation ; NTA extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The amount of phosphorus available to algae in the sediments of four lakes in the western part of the Netherlands has been assessed by means of chemical extraction and bioassay techniques. In addition to direct chemical sediment analyses, extractions were carried out with an NTA column method and a stepwise NH4 Cl-NaOH-HCI shaking method, the latter supposedly separating the weakly bound, the Fe- and Al-bound and the Ca-bound phosphates in the sediments. Bioassays, with sediment as the sole source of P, were made with Scenedesmus quadricauda in modified Skulberg's 28 medium to determine the amount of phosphates available to algae. The average total P concentration of the sediments varied from 0.8 to 3.6 mg P g−1 dry wt and correlated well with the net external P loading of the lakes. Uptake of P by algae in the bioassays varied from 0.4 to 36% — while NTA extracted 36–69% of the total P. The ratio NH4Cl extracted/ NaOH extracted/ HCI extracted phosphates is different from lake to lake, although in all lakes the highest extractions (27–62% of total P) are found in the NaOH fraction. However, in the peaty sediments of these lakes, the NaOH step extracted not only the Fe- and Al-bound phosphates but, also, large amounts of humus compounds. Hence, this fraction also contains non-available organic P. The results are related to soil type and chemical characteristics of the sediments, and compared with data from other authors. A positive correlation was found between phosphate available to algae and NTA- and NaOH-extractable P, but the correlation with total phosphorus was higher. Moreover, algal-extractable P proved to be positively correlated with total iron and clay content and negatively with the amount of organic matter. It is concluded that the sediments in the investigated lakes show great variability and that the chemical extraction techniques cannot replace the bioassays to assess the amount of phosphorus available to algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000047
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  • 2
    Electronic Resource
    Electronic Resource
    Available phosphorus in lake sediments in The Netherlands (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 491-500 
    Details
    ISSN: 1573-5117
    Keywords: phosphate ; sediment ; bioassay ; algae ; phosphate fractionation ; NTA extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The amount of phosphorus available to algae in the sediments of four lakes in the western part of the Netherlands has been assessed by means of chemical extraction and bioassay techniques. In addition to direct chemical sediment analyses, extractions were carried out with an NTA column method and a stepwise NH4 Cl-NaOH-HCI shaking method, the latter supposedly separating the weakly bound, the Fe- and Al-bound and the Ca-bound phosphates in the sediments. Bioassays, with sediment as the sole source of P, were made withScenedesmus quadricauda in modified Skulberg's 28 medium to determine the amount of phosphates available to algae. The average total P concentration of the sediments varied from 0.8 to 3.6 mg P g−1 dry wt and correlated well with the net external P loading of the lakes. Uptake of P by algae in the bioassays varied from 0.4 to 36% — while NTA extracted 36–69% of the total P. The ratio NH4Cl extracted/ NaOH extracted/ HCI extracted phosphates is different from lake to lake, although in all lakes the highest extractions (27–62% of total P) are found in the NaOH fraction. However, in the peaty sediments of these lakes, the NaOH step extracted not only the Fe- and Al-bound phosphates but, also, large amounts of humus compounds. Hence, this fraction also contains non-available organic P. The results are related to soil type and chemical characteristics of the sediments, and compared with data from other authors. A positive correlation was found between phosphate available to algae and NTA- and NaOH-extractable P, but the correlation with total phosphorus was higher. Moreover, algal-extractable P proved to be positively correlated with total iron and clay content and negatively with the amount of organic matter. It is concluded that the sediments in the investigated lakes show great variability and that the chemical extraction techniques cannot replace the bioassays to assess the amount of phosphorus available to algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02391963
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  • 3
    Electronic Resource
    Electronic Resource
    Available phosphorus in lake sediments in The Netherlands (1982)
    Springer
    Hydrobiologia 91-92 (1982), S. 491-500 
    Details
    ISSN: 1573-5117
    Keywords: phosphate ; sediment ; bioassay ; algae ; phosphate fractionation ; NTA extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The amount of phosphorus available to algae in the sediments of four lakes in the western part of the Netherlands has been assessed by means of chemical extraction and bioassay techniques. In addition to direct chemical sediment analyses, extractions were carried out with an NTA column method and a stepwise NH4 Cl-NaOH-HCI shaking method, the latter supposedly separating the weakly bound, the Fe- and Al-bound and the Ca-bound phosphates in the sediments. Bioassays, with sediment as the sole source of P, were made withScenedesmus quadricauda in modified Skulberg's 28 medium to determine the amount of phosphates available to algae. The average total P concentration of the sediments varied from 0.8 to 3.6 mg P g−1 dry wt and correlated well with the net external P loading of the lakes. Uptake of P by algae in the bioassays varied from 0.4 to 36% — while NTA extracted 36–69% of the total P. The ratio NH4Cl extracted/ NaOH extracted/ HCI extracted phosphates is different from lake to lake, although in all lakes the highest extractions (27–62% of total P) are found in the NaOH fraction. However, in the peaty sediments of these lakes, the NaOH step extracted not only the Fe- and Al-bound phosphates but, also, large amounts of humus compounds. Hence, this fraction also contains non-available organic P. The results are related to soil type and chemical characteristics of the sediments, and compared with data from other authors. A positive correlation was found between phosphate available to algae and NTA- and NaOH-extractable P, but the correlation with total phosphorus was higher. Moreover, algal-extractable P proved to be positively correlated with total iron and clay content and negatively with the amount of organic matter. It is concluded that the sediments in the investigated lakes show great variability and that the chemical extraction techniques cannot replace the bioassays to assess the amount of phosphorus available to algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00940137
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  • 4
    Electronic Resource
    Electronic Resource
    Ligand-induced association of epidermal growth factor receptor to the cytoskeleton of A431 cells (1989)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 39 (1989), S. 455-465 
    Details
    ISSN: 0730-2312
    Keywords: Scatchard analysis ; dissociation kinetics ; epidermal growth factor ; binding analysis ; Triton X-100 extract ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Recently, we have obtained evidence in favor of a structural interaction between the epidermal growth factor (EGF) receptor and the Triton X-100-insoluble cytoskeleton of epidermoid carcinoma A431 cells. Here we present a further analysis of the properties of EGF receptors attached to the cytoskeleton. Steady-state EGF binding studies, analyzed according to the Scatchard method, showed that A431 cells contain two classes of EGF-binding sites: a high-affinity site with an apparent dissociation constant (KD) of 0.7 nM (7.5 × 104 sites per cell) and a low-affinity site with a KD of 8.5 nM (1.9 × 106 sites per cell). Non-equilibrium binding studies revealed the existence of two kinetically distinguishable sites: a fast-dissociating site, with a dissociation rate constant (k-1) of 1.1. × 10-3s-1 (1.0-1.3 × 106 sites per cell) and a slow-dissociating site, with a k-1 of 3.5 × 10-5s-1 (0.6-0.7 × 106 sites per cell).The cytoskeleton of A431 cells was isolated by Triton X-100 extraction. Scatchard analysis revealed that ∼5% of the original number of receptors were associated with the cytoskeleton predominantly via high-affinity sites (KD = 1.5 nM). This class of receptors is further characterized by the presence of a fast-dissociating component (k-1 = 2.0 × 10-3s-1) and a slow-dissociating component (k-1 = 9.1 × 10-5s-1). The distribution between fast and slow sites of the cytoskeleton was similar to that of intact cells (65% fast and 35% slow sites). Incubation of A431 cells for 2 h at 4°C in the presence of EGF resulted in a dramatic increase in the number of EGF receptors associated to the cytoskeleton. These newly cytoskeleton-associated receptors appeared to represent low-affinity binding sites (KD = 7 nM). Dissociation kinetics also revealed an increase of fast-dissociating sites. These results indicate that at 4°C EGF induces the binding of low-affinity, fast-dissociating sites to the cytoskeleton of A431 cells.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240390411
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison of two force fields by molecular dynamics simulations of glucose crystals: Effect of using ewald sums (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 1281-1289 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: To compare the GROMOS force field with one designed by Ha et al., molecular dynamics simulations of α-D-glucose anhydrate and monohydrate crystals were performed. Also, the long-range interactions were calculated both with a cutoff approximation and with Ewald summations. The results are compared with results obtained experimentally by neutron and X-ray diffraction. The force-field parameters had been optimized with the cutoff approximation; this apparently led to worse results when the Ewald summations were used. However, in all simulations the symmetry was roughly preserved and the mean atomic coordinates and thermal parameters, bond angles, and dihedrals without hydrogen atoms were rather well reproduced. The dihedrals with hydrogen atoms exhibited conformational transitions, which resulted in a disordered hydrogen bonding scheme. In general, the GROMOS force field performed better than the Ha force field. © John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540141104
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  • 6
    Electronic Resource
    Electronic Resource
    ToBaD: A method for the estimation of torsion barriers from crystal structure data; conformational analysis of N,N-dimethylaniline and derivatives (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 15 (1994), S. 1429-1436 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A new method for the estimation of torsion barriers and its application to conformational analysis is presented. This method, the ToBaD method (method of the torsion barrier derivative), makes use of crystal structure data. It is based on the assumption that the conformation of a compound in the crystalline phase must be very close to a (local) minimum energy conformation of this compound in the gas phase. The ToBaD method is demonstrated for the rotation of the phenyl-N bond in N,N-dimethylaniline. Two geometries of this compound are handled separately: one in which the nitrogen substituents are in a pyramidal or sp3 geometry, and the other in which the nitrogen atom and its substituents are coplanar (the sp2 geometry). It is predicted, by means of the ToBaD method, that for both geometries the conformation in which the nitrogen lone pair or p orbital is perpendicular to the aromatic ring is the lowest energy conformation. © 1994 by John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540151212
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