Influence of microstructural variations on morphology and separation properties of polybutadiene-based polyurethanes

Polybutadiene-based polyurethanes with different cis/trans/1, 2-vinyl microstructure contents are synthesized. The phase morphology and physical properties of the polymers are investigated using spectroscopic analysis (FTIR and Raman), differential scanning calorimetry (DSC), X-ray scattering (WAXD and SAXS) and atomic force microscopy (AFM). In addition, their gas transport properties are determined for different gases at 4 bar and 25 °C. Thermodynamic incompatibility and steric hindrance of pendant groups are the dominant factors affecting the morphology and properties of the PUs. FTIR spectra, DSC, and SAXS analysis reveal a higher extent of phase mixing in high vinyl-content PUs. Moreover, the SAXS analysis and AFM phase images indicate smaller microdomains by increasing the vinyl content. Smaller permeable soft domains as well as the lower phase separation of the PUs with higher vinyl content create more tortuous pathways for gas molecules and deteriorate the gas permeability of the membranes

Graphene oxide-fullerene nanocomposite laminates for efficient hydrogen purification

Graphene oxide (GO) with its unique two-dimensional structure offers an emerging platform for designing advanced gas separation membranes that allow for highly selective transport of hydrogen molecules. Nevertheless, further tuning of the interlayer spacing of GO laminates and its effect on membrane separation efficiency remains to be explored. Here, positively charged fullerene C₆₀ derivatives are electrostatically bonded to the surface of GO sheets in order to manipulate the interlayer spacing between GO nanolaminates. The as-prepared GO-C₆₀ membranes have a high H₂ permeance of 3370 GPU (gas permeance units) and an H₂/CO₂ selectivity of 59. The gas separation selectivity is almost twice that of flat GO membranes because of the role of fullerene

Enhanced selectivity in mixed matrix membranes for CO2 capture through efficient dispersion of amine-functionalized MOF nanoparticles

Mixed matrix membranes (MMMs) for gas separation applications have enhanced selectivity when compared with the pure polymer matrix, but are commonly reported with low intrinsic permeability, which has major cost implications for implementation of membrane technologies in large-scale carbon capture projects. High-permeability polymers rarely generate sufficient selectivity for energy-efficient CO2 capture. Here we report substantial selectivity enhancements within high-permeability polymers as a result of the efficient dispersion of amine-functionalized, nanosized metal–organic framework (MOF) additives. The enhancement effects under optimal mixing conditions occur with minimal loss in overall permeability. Nanosizing of the MOF enhances its dispersion within the polymer matrix to minimize non-selective microvoid formation around the particles. Amination of such MOFs increases their interaction with thepolymer matrix, resulting in a measured rigidification and enhanced selectivity of the overall composite. The optimal MOF MMM performance was verified in three different polymer systems, and also over pressure and temperature ranges suitable for carbon capture

Ultrapermeable Thin Film ZIF-8/Polyamide Membrane for H-2/CO2 Separation at High Temperature without Using Sweep Gas

The use of thin film composites containing metal-organic frameworks (MOFs) as filler is of widespread interest for nanofiltration issues, since their thin selective layer allows a high permeation flow. The application of this kind of membranes for gas separation should provide a better permeance in comparison with other polymeric membranes and a reduction in the amount of MOF required for their fabrication. Here, the preparation of 50-100 nm thick polyamide flat membranes containing zeolitic imidazolate framework-8 (ZIF-8) nanoparticles is shown via interfacial polymerization, containing a lower amount of MOF (0.013 g m(-2) membrane) as compared to other membranes used for gas separation. The membranes are applied for H-2/CO2 separation at high temperatures and pressures, showing a stable performance at 180 degrees C for at least seven days. Outstanding separation values are 328 GPU of H-2 and a H-2/CO2 selectivity of 18.1 at 180 degrees C and 6 bar feed without transmembrane pressure. These membranes, also measurable without sweep gas, are highly suitable for industrial application

Genetic dissection of early endosomal recycling highlights a TORC1-independent role for Rag GTPases

Endocytosed cell surface membrane proteins rely on recycling pathways for their return to the plasma membrane. Although endosome-to-plasma membrane recycling is critical for many cellular processes, much of the required machinery is unknown. We discovered that yeast has a recycling route from endosomes to the cell surface that functions efficiently after inactivation of the sec7-1 allele of Sec7, which controls transit through the Golgi. A genetic screen based on an engineered synthetic reporter that exclusively follows this pathway revealed that recycling was subject to metabolic control through the Rag GTPases Gtr1 and Gtr2, which work downstream of the exchange factor Vam6. Gtr1 and Gtr2 control the recycling pathway independently of TORC1 regulation through the Gtr1 interactor Ltv1. We further show that the early-endosome recycling route and its control though the Vam6 > Gtr1/Gtr2 > Ltv1 pathway plays a physiological role in regulating the abundance of amino acid transporters at the cell surface

A puzzle of life: crafting ribosomal subunits

The biogenesis of eukaryotic ribosomes is a complicated process during which the transcription, modification, folding, and processing of the rRNA is coupled with the ordered assembly of ∼80 ribosomal proteins (r-proteins). Ribosome synthesis is catalyzed and coordinated by more than 200 biogenesis factors as the preribosomal subunits acquire maturity on their path from the nucleolus to the cytoplasm. Several biogenesis factors also interconnect the progression of ribosome assembly with quality control of important domains, ensuring that only functional subunits engage in translation. With the recent visualization of several assembly intermediates by cryoelectron microscopy (cryo-EM), a structural view of ribosome assembly begins to emerge. In this review we integrate these first structural insights into an updated overview of the consecutive ribosome assembly steps

Etude de la spéciation du Tc et de ses homologues Mn et Re sous irradiations y et He2+ en milieu carbonate hautement concentré

This project is one part of the fundamental study and deals with theoxidation/reduction reactions and speciation of technetium and its homologous manganese and rhenium in highly concentrated carbonate solutions under γ and He²⁺ irradiation. Firstly the electrochemistry experiment is carried out for the reduction of Mn(VII) in order to obtain the best experimental conditions. As the experiments are performed under irradiation, the carbonate radicals,which are produced by radiolysis, play an important role in the reactions. The formation and decay kinetics of the carbonate radicals in concentrated carbonate solutions were studied by electron picosecond pulse radiolysis. The reduction of Mn(VII) and the oxidation of Mn(II) experiments in carbonate solution ([CO₃²⁻] = 5 mol.l⁻¹) are carried out under γ and He²⁺ irradiation. By the obtained data from the produced H₂, UV-Vis spectra and the final structure determination, the mechanisms of the reaction are discussed. Re(III)is oxidized easily in concentrated carbonate solution under irradiation (γ and He²⁺) but Re(VII) cannot be reduced unless addition of formate in order to prevent carbonate radical formation. Also Tc(VII) cannot be reduced in concentrated carbonate solutions under irradiation (γ and He²⁺) without formate addition. The oxidation state of the final product of reduction of Tc(VII) was determined by XANES spectroscopy and is +IV. Moreover, the final structure of the product was determined by EXAFS spectroscopy. The mechanisms of reaction, decay and formation radiolytic yield of Tc and also the effect of concentration of carbonate on final product of reduction ofTc(VII) under irradiation are discussed.Ce projet s’inscrit dans le cadre d’une étude fondamentale liée à l'oxydation et la réduction de ces éléments sous irradiation γ et He²⁺. ⁺. Tout d'abord la technique d’électrochimie a été utilisée pour la réduction du Mn (VII) afin d'obtenir les meilleures conditions expérimentales. Car les expériences étant réalisées sous irradiation ainsi les radicaux carbonate qui sont produits par radiolyse jouent un rôle important dans les réactions. La cinétique de formation et la décroissance des radicaux carbonate dans les solutions de carbonate concentrées ont été étudiés par radiolyse pulsée β pico-seconde. Après la réduction du Mn (VII) et l'oxydation du Mn (II) dans une solution de carbonate ([CO₃²⁻] = 5 mol.l⁻¹) sont réalisées sous irradiation γ et He²⁺. Par des données obtenues pour H₂ produit, les spectres UV-Vis et structure finale, les mécanismes de la réaction sont discutés. Re (III) est oxydé facilement dans une solution de carbonate concentré sous irradiation (γ et He²⁺) mais Re (VII) ne peut être réduite à moins que l'addition de formiate afin d'empêcher la formation de radicaux carbonate. De la même façon, Tc (VII) ne peut être réduit dans les solutions concentrées de carbonate sous irradiation (γ et He²⁺) sans ajout de formiate. L'état d'oxydation du produit final de la réduction de Tc(VII) a été déterminée par spectroscopie XANES et est de + IV. En outre, la structure finale du produit final a été déterminée par spectroscopie EXAFS. Le mécanisme de la réaction, le rendement radiolytique de décroissance et la formation du Tc et l’effet de concentration du carbonate sur la produit final de la réduction du Tc(VII) sous irradiation sont discutés

Etude de la spéciation du Tc et de ses homologues Mn et Re sous irradiation γ et α en milieu carbonate hautement concentré

National audienc