Endocytosis at reduced temperature has been used to define and characterize endosome subpopulations. Thus, the temperature sensitivity of endosome subpopulations involved in transport to lysosomes and transcytosis in rat hepatocytes was analyzed applying endosome labeling in the isolated perfused rat liver with route-specific ligands in combination with temperature shift protocols. Free-flow electrophoresis (FFE) that separates membranes and organelles based on their surface charge was then applied to isolate functional endosomes. Using asialoorosomucoid (ASOR) and polymeric immunoglobulin A (pIgA) as specific ligands of the lysosomal and transcytotic route, respectively, two distinct endosome subpopulations along either pathway were separated by FFE. Upon a short (1-3 min) internalization at 37 degrees C, 125I-ASOR and fluorescein isothiocyanate (FITC)-pIgA were colocalized in common early endosomes. Following a 5-10 min chase of the ligands at 37 degrees C endosomes labeled with 125I-ASOR were separated from endosomes labeled with FITC-pIgA, indicative of two distinct late compartments along the lysosomal and transcytotic route. Internalization at 16 degrees C resulted in accumulation of both ligands in common early endosomes and, consequently, in inhibition of transport to lysosomes and transcytosis. When 125I-ASOR or 125I-pIgA were first chased into late compartments at 37 degrees C and the temperature was subsequently lowered to 16 degrees C, biliary secretion of 125I-ASOR-derived counts was arrested, while biliary output of 125I-pIgA continued. In summary, ASOR en route to lysosomes can be blocked in early as well as in late endosomes at 16 degrees C, while biliary secretion of pIgA cannot be prevented by temperature reduction once the ligand had been transferred from early to late compartments. 相似文献
Polypropene and poly(1-butene) have been synthesized under very similar experimental conditions with a series of MAO-activated C2-symmetric and C1-symmetric ansa-zirconocenes. The C1-symmetric zirconocenes bearing the bilaterally symmetric fluorenyl or bis(2-methylthieno)cyclopentadienyl ligand connected through a dimethylsilyl bridge to substituted indenyl ligands produce isotactic polybutene of similar or higher molecular mass and with noticeably higher isotacticity, compared to isotactic polypropene prepared with the same catalysts under comparable conditions. Structural and mechanistic reasons for such behavior are discussed on the basis of QM/MM calculations. 相似文献
The paper reports the results of a study carried out to evaluate the use of three 1‐alkyl‐3‐methylimidazolium‐based ionic liquids as non‐covalent coating agents for bare fused‐silica capillaries and additives of the electrolyte solutions (BGE) for CE of basic proteins in the co‐EOF separation mode. The three ionic liquids are differentiated from each other by the length of the alkyl group on the imidazolium cation, consisting of either an ethyl, butyl or octyl substituent, whereas tetrafluoroborate is the common anionic component of the ionic liquids. Coating the capillary with the ionic liquid resulted in improved peak shape and protein separation, while the EOF was maintained cathodic. This indicates that each ionic liquid is effective at masking the protein interaction sites on the inner surface of the capillary, also when its adsorption onto the capillary wall has not completely neutralized all the negative charges arising from the ionization of the silanol groups and the ionic liquid is not incorporated into the BGE employed for separation. Using the coated capillaries with BGE containing the ionic liquid employed for the coating, at concentration low enough to maintaining the EOF cathodic, both peak shape and protein separation varied to different extents, based on the particular ionic liquid used and its concentration. Fast and efficient separation of the model basic protein mixture in co‐electroosmotic CE is obtained with the 1‐butyl‐3‐methylimidazolium tetrafluoroborate coated capillary and 100 mM acetate buffer (pH 4.0) containing 4.4 mM 1‐butyl‐3‐methylimidazolium tetrafluoroborate as the BGE. 相似文献
We present a numerical investigation of a degenerate nonlinear parabolic–elliptic system, which describes the chemical aggression
of limestones under the attack of SO2, in high permeability regime. This system has been introduced in the first part of this paper. We present a finite element
scheme for our model and its numerical stability is given under suitable CFL conditions. Numerical tests are discussed as
well as some examples of the numerical behavior of the solutions. 相似文献
Water and methanol transport behavior, morphology, and solvent adsorption of filler-free Nafion membrane, Nafion–SiO2, Nafion–TiO2, and two Nafion–Zr(HPO4)2 composites were investigated using nuclear magnetic resonance methods, including spin-lattice relaxation and pulsed-field-gradient
spin-echo diffusion conducted under both variable temperature and variable hydrostatic pressure conditions and scanning electron
microscopy analysis. A comparison between water and methanol self-diffusion coefficients reveals that the water mobility is
higher than the methanol mobility in all the membranes. Additionally, the inclusion of inorganic fillers improves both the
solvent uptakes and the transport properties of the composite membranes relative to filler-free Nafion, with the exception
of one of the Nafion–Zr(HPO4)2 composite. Nafion–Zr(HPO4)2 composites were prepared by two different procedures, in situ and ex situ. Although phosphorus-31 magic-angle spinning nuclear
magnetic resonance spectra show the same structures of the particles in both kinds of membranes, the morphology, solvent absorption
properties, and solvent mobilities are very different.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur Mer, Sept. 9–15, 2007. 相似文献
Here, we present a series of exclusively heteronuclear multidimensional NMR experiments, based on 13C direct detection, which exploit the 1H polarization as a starting source to increase the signal-to-noise ratio. This contributes to make this spectroscopy more useful and usable. Examples are reported for a suitable system such as securin, an intrinsically disordered protein of 22 kDa. 相似文献
In this study, two different synthetic methods in aqueous solution are presented to tune the optical properties of CdTe and CdSe semiconductor nanoparticles. Additionally, the influence of different temperatures, pressures, precursor ratios, surface ligands, bases, and core components in the synthesis was investigated with regard to the particle sizes and optical properties. As a result, a red shift of the emission and absorption maxima with increasing reaction temperature (100 to 220°C), pressure (1 to 25 bar), and different ratios of core components of alloyed semiconductor nanoparticles could be observed without a change of the particle size. An increase in particle size from 2.5 to 5 nm was only achieved by variation of the mercaptocarboxylic acid ligands in combination with the reaction time and used base. To get a first hint on the cytotoxic effects and cell uptake of the synthesized quantum dots, in vitro tests mesenchymal stem cells (MSCs) were carried out.
Summary: The aim of this work was to study the comonomer distribution and the chemical composition distribution generated by different Ziegler-Natta (ZN) systems (different internal donors, ID, dicyclopentadienyl-dimethoxy silane, D donor, as the external donor) and to define the potentialities of different IDs to produce improved heterophasic copolymers (HECO). A methodology to quantify the amount of ethylene-propylene copolymer (EP) portion in ZN-HECO and ethylene content of the EP portion by 13C-NMR was established. By using this method, it was possible to analyze the composition of ZN-HECO obtaining results comparable to those obtained with a more complex fractionation technique. 相似文献
Monobromo-, monochloro- and monoiodopyrroles are obtained in excellent yields by using N-halosuccinimides in dimethylformamide as halogenating agents. 相似文献