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31.
A scale-up of analytical capillary zone electrophoresis (CZE) to preparative free-flow electrophoresis (FFE) is described. FFE allows fractionations based on charge densities in larger amounts than in CZE, enabling further off-line analysis of the fractions. Model compounds (carboxylic acids and polystyrene sulfonates) showed a similar behavior in FFE as in CZE. Diffusion and electrodynamic distortion effects are more pronounced in FFE than in CZE. A soil fulvic acid was analyzed by CZE and fractionated by FFE. A comparison of the FFE fractions with CZE measurements of the same sample using the effective mobility scale showed good agreement of the two methods. 相似文献
32.
Construction of Insulin 18‐mer Nanoassemblies Driven by Coordination to Iron(II) and Zinc(II) Ions at Distinct Sites 下载免费PDF全文
Dr. Henrik K. Munch Jesper Nygaard Dr. Niels Johan Christensen Dr. Christian Engelbrekt Mads Østergaard Dr. Trine Porsgaard Dr. Thomas Hoeg‐Jensen Prof. Dr. Jingdong Zhang Prof. Dr. Lise Arleth Prof. Dr. Peter W. Thulstrup Prof. Dr. Knud J. Jensen 《Angewandte Chemie (International ed. in English)》2016,55(7):2378-2381
Controlled self‐assembly (SA) of proteins offers the possibility to tune their properties or to create new materials. Herein, we present the synthesis of a modified human insulin (HI) with two distinct metal‐ion binding sites, one native, the other abiotic, enabling hierarchical SA through coordination with two different metal ions. Selective attachment of an abiotic 2,2′‐bipyridine (bipy) ligand to HI, yielding HI–bipy, enabled ZnII‐binding hexamers to SA into trimers of hexamers, [[HI–bipy]6]3, driven by octahedral coordination to a FeII ion. The structures were studied in solution by small‐angle X‐ray scattering and on surfaces with AFM. The abiotic metal ligand had a higher affinity for FeII than ZnII ions, enabling control of the hexamer formation with ZnII and the formation of trimers of hexamers with FeII ions. This precise control of protein SA to give oligomers of oligomers provides nanoscale structures with potential applications in nanomedicine. 相似文献
33.
Numerical approximation of the boundary control for the wave equation with mixed finite elements in a square 总被引:1,自引:0,他引:1
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Wagner HP Pepich BV Pohl C Later D Joyce R Srinivasan K Thomas D Woodruff A Deborba B Munch DJ 《Journal of chromatography. A》2006,1118(1):85-93
Since 1997 there has been increasing interest in the development of analytical methods for the analysis of perchlorate. The US Environmental Protection Agency (EPA) Method 314.0, which was used during the first Unregulated Contaminant Monitoring Regulation (UCMR) cycle, supports a method reporting limit (MRL) of 4.0 microg/L. The non-selective nature of conductivity detection, combined with very high ionic strength matrices, can create conditions that make the determination of perchlorate difficult. The objective of this work was to develop an automated, suppressed conductivity method with improved sensitivity for use in the second UCMR cycle. The new method, EPA Method 314.1, uses a 35 mm x 4 mm cryptand concentrator column in the sample loop position to concentrate perchlorate from a 2 mL sample volume, which is subsequently rinsed with 10 mM NaOH to remove interfering anions. The cryptand concentrator column is combined with a primary AS16 analytical column and a confirmation AS20 analytical column. Unique characteristics of the cryptand column allow perchlorate to be desorbed from the cryptand trap and refocused on the head of the guard column for subsequent separation and analysis. EPA Method 314.1 has a perchlorate lowest concentration minimum reporting level (LCMRL) of 0.13 microg/L in both drinking water and laboratory synthetic sample matrices (LSSM) containing up to 1,000 microg/L each of chloride, bicarbonate and sulfate. 相似文献
37.
Alkyl and aryl amines are converted smoothly to the corresponding isothiocyanates via the dithiocarbamates in good to excellent yields using di-tert-butyl dicarbonate (Boc2O) and 1-3 mol % of DMAP or DABCO as catalyst. As most of the byproducts are volatile, the work-up involves simple evaporation of the reaction mixture. 相似文献
38.
Sauveur J. Candau Rachid Skouri Franois Schosseler Jean-Pierre Munch 《Macromolecular Symposia》1994,83(1):183-192
We report results of static light scattering for partially charged gels at different swelling degrees and different ionization degrees. We measured both the ensemble-average and the rms fluctuations of the scattered intensity by scanning through various positions in the gel. It is shown that the dynamic concentration fluctuations are, to the first order, the same as in semi-dilute solutions at the same concentration. The excess of scattering of the gel with respect to the solutions arises mainly from frozen-in scattering domains with spatial extent less than ∼ 300 Å. 相似文献
39.
Herbert P. Wagner Barry V. Pepich Daniel P. Hautman David J. Munch 《Journal of chromatography. A》1999,850(1-2):119-129
In July 1997, the US Environmental Protection Agency (EPA) began sampling and analyzing drinking water matrices from US municipalities serving populations greater than 100 000 for low-level bromate (>0.20 μg/l) in support of the Information Collection Rule (ICR) using the selective anion concentration (SAC) method. In September 1997, EPA published Method 300.1 which lowered the Method 300.0 bromate method detection limit (MDL) from 20.0 to 1.4 μg/l. This paper describes the research conducted at the EPA’s Technical Support Center laboratory investigating a single post-column reagent, o-dianisidine (ODA), which has been successfully coupled to EPA Method 300.1 to extend the MDL for bromate. Initial studies indicate that this method offers a MDL which approaches the EPA’s SAC method with the added benefit of increased specificity, shortened analysis time and reduced sample preparation. The method provides excellent ruggedness and acceptable precision and accuracy with a bromate MDL in reagent water of 0.1 μg/l, and a method reporting limit of 0.50 μg/l. 相似文献
40.
Salt‐containing membranes based on polymethacrylates having poly(ethylene carbonate‐co‐ethylene oxide) side chains, as well as their blends with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), have been studied. Self‐supportive ion conductive membranes were prepared by casting films of methacrylate functional poly(ethylene carbonate‐co‐ethylene oxide) macromonomers containing lithium bis(trifluorosulfonyl)imide (LiTFSI) salt, followed by irradiation with UV‐light to polymerize the methacrylate units in situ. Homogenous electrolyte membranes based on the polymerized macromonomers showed a conductivity of 6.3 × 10?6 S cm?1 at 20 °C. The preparation of polymer blends, by the addition of PVDF‐HFP to the electrolytes, was found to greatly improve the mechanical properties. However, the addition led to an increase of the glass transition temperature (Tg) of the ion conductive phase by ~5 °C. The conductivity of the blend membranes was thus lower in relation to the corresponding homogeneous polymer electrolytes, and 2.5 × 10?6 S cm?1 was recorded for a membrane containing 10 wt % PVDF‐HFP at 20 °C. Increasing the salt concentration in the blend membranes was found to increase the Tg of the ion conductive component and decrease the propensity for the crystallization of the PVDF‐HFP component. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 79–90, 2007 相似文献