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91.
92.
The binding of palladium to high-molecular-mass compounds in palladium-treated lettuce is investigated as an example for a biological matrix. The total palladium concentration in lettuce leaves is 10.3 ng/g wet weight. After homogenization, high-molecular-mass compounds (> 10 kDa) are isolated by ultrafiltration. For separation of these palladium species a combination of preparative gel permeation chromatography (GPC) and preparative isotachophoresis (ITP) is used. Palladium is determined in separated fractions by using a highly sensitive total reflection X-ray fluorescence (TXRF) method after preconcentration. After GPC separation, four main fractions of palladium species are collected, each containing palladium in ng quantities (3-10 ng). Two of these fractions are further separated by ITP, yielding at least three main peaks per GPC fraction, each containing palladium in the range of 0.3-3 ng. These palladium containing peaks are characterized by high-performance size exclusion chromatography (HPSEC) and capillary isotachophoresis (cITP) in parallel. HPSEC enables the estimation of the molecular mass of six main palladium peaks, covering a molecular mass range of 69-200 kDa. It is also shown that the estimation of molecular mass after separation is more reliable than the respective estimation directly in the first GPC run. However, cITP reveals that each of the separated peaks is still a mixture of at least five different compounds. 相似文献
93.
Jürgen Haase 《Annalen der Physik》1987,499(7):507-513
Composite Pulses in Nuclear Magnetic Resonance For the compensation of spatial inhomogeneity of the radiofrequency field and a resonance offset in NMR experiments, composite pulses are used instead of the conventional single pulses. In the present work the effect of a resonance offset on composite pulses is treated quantitatively. It will be shown also experimentally that the various constructions for \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{\pi }{2} $\end{document} composite pulses (contrary to π composite pulses) lead to only two different degrees of compensation depending on the choice of the phase of the pulses or the sign of the resonance offset. 相似文献
94.
The lattice model for equilibrium polymerization in a solvent proposed by Wheeler and Pfeuty is solved exactly on a Bethe lattice (core of a Caylay tree) with general coordination numberq. Earlier mean-field results are reobtained in the limitq, but the phase diagrams show deviations from them for finiteq. Whenq=2, our results turn into the solution of the one-dimensional problem. Although the model is solved directly, without the use of the correspondence between the equilibrium polymerization model and the diluten0 model, we verified that the latter model may also be solved on the Bethe lattice, its solution being identical to the direct solution in all parameter space. As observed in earlier studies of the puren0 vector model, the free energy is not always convex. We obtain the region of negative susceptibility for our solution and compare this result with mean field and renormalization group (-expansion) calculations. 相似文献
95.
96.
Let R be a complete analytic k-algebra of dimension one, where k is a field of characteristic 0. For a Noetherian normalization
, the cotangent functors Ti(R/A, R) are of finite length. It is shown that if R is smoothable, then for all j, where denotes the complementary module. This result is used to give estimates for the length of the torsion of the module of differentials R/k. 相似文献
97.
Knudsen B Andersen ES Damgaard C Kjems J Gorodkin J 《Computational Biology and Chemistry》2004,28(3):219-226
Predicting RNA secondary structure using evolutionary history can be carried out by using an alignment of related RNA sequences with conserved structure. Accurately determining evolutionary substitution rates for base pairs and single stranded nucleotides is a concern for methods based on this type of approach. Determining these rates can be hard to do reliably without a large and accurate initial alignment, which ideally also has structural annotation. Hence, one must often apply rates extracted from other RNA families with trusted alignments and structures. Here, we investigate this problem by applying rates derived from tRNA and rRNA to the prediction of the much more rapidly evolving 5'-region of HIV-1. We find that the HIV-1 prediction is in agreement with experimental data, even though the relative evolutionary rate between A and G is significantly increased, both in stem and loop regions. In addition we obtained an alignment of the 5' HIV-1 region that is more consistent with the structure than that currently in the database. We added randomized noise to the original values of the rates to investigate the stability of predictions to rate matrix deviations. We find that changes within a fairly large range still produce reliable predictions and conclude that using rates from a limited set of RNA sequences is valid over a broader range of sequences. 相似文献
98.
Summary A reversed-phase high-performance liquid chromatographic (RP-HPLC) method with UV detection (270 nm) for the determination of nitrite as its pentafluorobenzyl derivative with and without ion-pair extraction is described. Ion-pair extraction of nitrite from aqueous solutions was performed by using a 1 mol/l solution of the liquid ion exchanger methyltrioctylammonium chloride in toluene. The residue of the ion-pair extraction or an aliquot of an aqueous nitrite solution or of a biological fluid (100 l) were treated with 400 l of acetone and 10 l of pentafluorobenzyl bromide. Nitrite was converted into its pentafluorobenzyl derivative by heating at 50°C for 90 min. After evaporation of acetone the aqueous phases were diluted with 100 to 400 l of methanol, and up to 100 l were injected into the RP-HPLC system. The method allows accurate analysis of nitrite in the presence of nitrate directly in aqueous solutions and biological fluids in concentrations down to 2.0 mg/l. The method is also applicable to the determination of nitrate following its reduction to nitrite by cadmium. 相似文献
99.
H.-D. Bauer Reinhold Rennekamp Jürgen Thomas 《Analytical and bioanalytical chemistry》1998,361(6-7):515-521
Concerning the conventional TEM-imaging as well as the analytical procedures the capabilities are pointed out: electron diffraction,
energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). The possibilities of investigation
of both nanocrystalline materials and multilayers are discussed, accompanied by examples of current investigations: At alloys,
produced by intense milling, at single nanocrystals the imaging by diffraction contrast was successful, the analysis has failed
because of the sample thickness. By means of energy spectroscopic imaging multilayers from Fe-SiB/NbCu and Fe/Cr as well as
Al2O3/TiN have been characterized.
Received: 15 July 1997 / Revised: 16 February 1998 / Accepted: 21 February 1998 相似文献
100.
Clemens C. Freyhardt Michael Wiebcke Jürgen Felsche Günter Engelhardt 《Journal of inclusion phenomena and macrocyclic chemistry》1994,18(2):161-175
Single-crystal X-ray structure analyses of N(nPr)4[B5O6(OH)4][B(OH)3]2,1, and N(nBu)4 [B5O6(OH)4][B(OH)3]2,2, reveal that these materials are novel clathrates, the isotypic host structures of which are three-dimensional assemblies of hydrogen-bonded [B5O6(OH)4]– ionsand B(OH)3 molecules. The assembly of only the pentaborate anions is a distorted (i.e., along [102] elongated) fourconnected diamond-related network. The N(nPr)
4
+
and N(nBu)
4
+
ions are trapped within the complex three-dimensional channel systems of the host frameworks. Both1 and2 crystallize monoclinically with space groupP21/c andZ=4. The cell constants are:1:a=13.592(5),b=12.082(2),c=17.355(6) Å, =106.60(2)° (298K);2:a=13.874(3),b=12.585(1),c=17.588(4) Å, =107.04(1)° (238 K). The results obtained by both11B and13C MAS NMR spectroscopy are discussed. Thermogravimetric studies under a flowing inert-gas atmosphere suggest that water, stemming from polycondensation of the hydrous borate species, is released from the clathrates at ca. 443 K (1) and 398 K (2) before the decomposition of the organic cations starts at ca. 603 K (1) and 603 K (2).Author for correspondence.
Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82172 (82 pages). 相似文献