Different temperature sensitivity of endosomes involved in transport to lysosomes and transcytosis in rat hepatocytes: analysis by free-flow electrophoresis

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.     

Comparing propene polymerization with 1-butene polymerization catalyzed by MAO-activated C2- and C1-symmetric zirconocenes: An experimental and computational study on the influence of olefin size on stereoselectivity

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.     

Co‐electroosmotic capillary electrophoresis of basic proteins with 1‐alkyl‐3‐methylimidazolium tetrafluoroborate ionic liquids as non‐covalent coating agents of the fused‐silica capillary and additives of the electrolyte solution

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.     

A mathematical model of sulphite chemical aggression of limestones with high permeability. Part II: Numerical approximation

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.     

NMR investigation of water and methanol mobility in nanocomposite fuel cell membranes

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.     

H-start for exclusively heteronuclear NMR spectroscopy: The case of intrinsically disordered proteins

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.     

Tuning optical properties of water-soluble CdTe quantum dots for biological applications

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.

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NMR Characterization of Ethylene/Propylene Copolymers and Propylene Impact Copolymers from MgCl2/TiCl4/ID+AlR3/ED Catalytic Systems

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.     

Preparation of monohalopyrroles

Monobromo-, monochloro- and monoiodopyrroles are obtained in excellent yields by using N-halosuccinimides in dimethylformamide as halogenating agents.