By means of a vacuum time-lag method, gas transport properties of apolyimide based on 2, 2- bis (3, 4- decarboxyphenyl ) hexafluoropropane dianhydride (6FDA )and meta- phenylenediamine (mPDA ) have been measured as a function of upstream pres-sure and temperature. The results show that no gas-induced plasticization occurs for thispolyimide in the upstream pressure range from 1 atm to 20atm. The temperature depen-dence of P and D can be described by the Arrhenius equations. The activation energiesof permeation and diffusion were obtained for the gas/polymer pair studied and correlatedwith the size of penetrant gas. 相似文献
A new family of eight poly(urethane-amide-imide) (PUAI) block copolymers with the same hard block and different soft blocks were synthesized in two steps from a dianhydride monomer containing amide functions (4,4′-methylene-bis(trimellitic anhydride-N-phenylamide)) and α,ω-dihydroxy telechelic oligomers which varied in both chemical structure (polyethers: PEG, PTMG, PPG; polyester: PCL) and molar weight (MW ≅ 600 or 1000 g/mol). The PUAI were obtained in high yields (ranging from 81 to 98 wt%) and with reduced viscosities which varied from 0.36 to 0.84 dL/g (for C = 1 mg/mL in DMF at 25 °C). Their characterization by FTIR and 1H NMR fully confirmed their chemical structure. Their solubility was typically limited to a few wt/vol% even in strong apolar diprotic solvents like DMF and NMP. This particular feature showed the very strong physical cross-linking of their very stiff hard block and enabled to cast membranes capable of withstanding exposure to many common organic solvents. Systematic permeability experiments showed that the PUAI membranes could be used to separate the azeotropic mixture EtOH (20 wt%)/ETBE very easily, with interesting prospects for the purification of ETBE (a fuel octane enhancer used instead of lead derivatives in the European Community). An analysis in terms of structure-property relationships pointed out that the soft block molar weight and polarity were two key parameters for the optimization of selective permeability. The best compromise was obtained with the soft block PEG1000. The corresponding polymer led to performances so far outstanding for polyamideimides with a very high flux of more than 1.1 kg/h m2 for a normalized thickness of 5 μm at 50 °C and a selectivity α = 22.7 in the high range for this kind of separation. 相似文献
Membrane foaming is a new method of foaming. To enlarge the knowledge about the influencing factors and to know how to vary the structure of the resulting foam, different factors were evaluated. A whey protein solution with 10% protein was foamed as a model solution by means of a tubular cross-flow filtration membrane. The pore size of the membrane was varied. The smaller the pore size, the smaller the bubbles produced. As a result, the foam firmness increases and less drainage was observed when smaller pore sizes were applied.
An important factor is that the added amount of gas must be stabilised as completely as possible in the foam. In order to achieve this, both the process and the product parameters were varied. Raising the foaming temperature increased the quantity of stabilised gas. The whey proteins then diffuse faster to the bubble surfaces and stabilise these by unfolding and networking reactions to prevent the coalescence of the bubbles.
The product parameter viscosity was found to influence the foaming result in such a way that up to a viscosity of 40 mPa s the incorporated gas bubbles are stabilised by the higher viscosity. At viscosities higher than 40 mPa s it is difficult to incorporate in the bubbles, and the foam structure becomes coarser due to increased coalescence at the pores of the membrane. The foam stability is enhanced with higher viscosities. 相似文献
Corona virus disease 2019 (COVID-19) endemic has havoc on the world; the causative virus of the pandemic is SARS CoV-2. Pharmaceutical companies and academic institutes are in continuous efforts to identify anti-viral therapy or vaccines, but the most significant challenge faced is the highly evolving genome of SARS CoV-2, which is imparting evolutionary selective benefits to the virus. To understand the viral mutations, we have retrieved nine hundred and thirty-four samples from different states of India via the GISAID database and analyzed the frequency of all types of point mutation in all structural, non-structural proteins, and accessory factors of SARS CoV-2. Spike glycol protein, nsp3, nsp6, nsp12, N and NS3 were the most evolving proteins. High frequency point mutations were Q496P (nsp2), A380V (nsp4), A994D (nsp3), L37F (nsp6), P323L & A97V (nsp12), Q57H (ns3), D614G (S), P13L (N), R203K (N), G204R (N) and S194L (N). 相似文献
Imide-siloxane block copolymer/silica hybrid membranes with covalent bonds were prepared via sol–gel reaction. The structural informations of these hybrid membranes were obtained by using Fourier transform-infrared spectrometry (FT-IR), 29Si nuclear magnetic resonance (29Si NMR), XPS and thermogravimetric analysis (TGA). The gas separation properties of the hybrid membranes were also investigated in terms of organosiloxane (PDMS) or silica content at various temperatures. In the hybrids, the addition of PDMS phase increased the permeabilities of gases such as He, CO2, O2, and N2, indicating that the gas transport occurred mainly through rubbery organic matrix. Meanwhile, the PDMS phase contributed the decreased gas selectivities to nitrogen but the reduction in selectivities was very small in comparison with other siloxane containing polymeric membranes. This might be due to the restriction of chain mobility by the existence of inorganic component such as silica network in the hybrids. Additionally, the increase of silica content in these hybrid membranes considerably retarded the falling-off of gas selectivity at elevated temperature. The increase of silica content in hybrid membranes resulted in well-formed silica networks and hence these inorganic components restricted the plasticization of organic matrix by the thermal segmental motion of organic components, leading to preventing the large decrease of the gas selectivity. 相似文献
A nonradioactive method was employed to detect different cell membrane antigens on human polymorphonuclear granulocytes, monocytes and platelets. We compared the reactivity of one monoclonal antibody, N1III10, assumed to be FcγRII-specific by functional assays, with other well-characterized monoclonal antibodies and human sera. Intact cells were incubated with biotin N-hydroxysulfosuccinimide ester which preferentially reacts with lysine residues in polypeptides. Biotin-labeled cells were lysed and the antigen was isolated from the cell lysate by immunoprecipitation with the antibody bound to Protein A-Sepharose. The precipitates were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred onto nitrocellulose membrane, and visualized by a streptavidin-alkaline phosphatase system with a suitable substrate. Using this biotin-labeling system we could show that N1III10 detects a 40 kDa antigen on monocytes and platelets, comparable to that expected of FcγRII monoclonal antibodies. 相似文献
Interferons are potent biologically active proteins synthesized and secreted by somatic cells of all mammalian species. Dye-affinity adsorption is increasingly used for protein separation. Hollow fibers have several advantages as adsorbents in comparison to conventional bead supports because they are not compressible and they eliminate internal diffusion limitations. The aim of this study was to explore in detail the performance of polyamide hollow fibers to which Cibacron Blue F3GA was attached for adsorption of recombinant interferon-α (rHuIFN-α). The hollow fiber was characterized by scanning electron microscopy. These dye-carrying hollow fibers (35.8 μmol/g) were used in the rHuIFN-α adsorption-elution studies. The effects of initial concentration of rHuIFN-α, medium pH, ionic strength and temperature on the adsorption efficiency of dye-attached hollow fibers were studied in a batch system. The non-specific adsorption of rHuIFN-α on the hollow fibers was 1.2 mg/g. Cibacron Blue F3GA attachment significantly increased the rHuIFN-α adsorption up to 99.8 mg/g. Significant amount of the adsorbed rHuIFN-α (up to 94.8%) was eluted in 1 h in the elution medium containing 1.0 M NaCl. In order to determine the effects of adsorption conditions on possible conformational changes of rHuIFN-α structure, fluorescence spectrophotometry was employed. We resulted that dye-affinity hollow fibers can be applied for rHuIFN-α adsorption without causing any significant conformational changes. Repeated adsorption/elution processes showed that these dye-attached hollow fibers are suitable for rHuIFN-α adsorption. 相似文献