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Urea Solution (urea + solution)
Selected AbstractsProperties and Bioapplications of Blended Cellulose and Corn Protein FilmsMACROMOLECULAR BIOSCIENCE, Issue 9 2009Quanling Yang Abstract A series of blend films have been prepared from cellulose and corn protein in a NaOH/urea solution by a simple, low cost, and ,green' pathway. Their structure and properties are characterized by amino acid analysis, X-ray diffraction, scanning electron microscopy, thermogravimetry, and tensile testing. The results reveal that a certain miscibility exists between cellulose and corn protein and their thermal stability and mechanical properties are improved significantly, compared with the protein materials, when the protein content is less than 18 wt.-%. The protein, which contains tyrosine and histidine, could remain in the blend films after being washed for ten days, which indicates the strong hydrogen bonding between the hydroxy groups of cellulose and the hydroxyphenyl of tyrosine and imidazolyl of histidine in the protein. Furthermore, they exhibit good biocompatibility capable of supporting cell adhesion and proliferation. [source] Novel nanoporous membranes from regenerated bacterial celluloseJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Muenduen Phisalaphong Abstract Bacterial cellulose (BC) in an NaOH/urea aqueous solution was used as a substrate material for thefabrication of a novel regenerated cellulose membrane. The dissolution of BC involved swelling BC in a 4 wt % NaOH/3 wt % urea solution followed by a freeze,thaw process. The BC solution was cast onto a Teflon plate, coagulated in a 5 wt % CaCl2 aqueous solution, and then treated with a 1 wt % HCl solution. Supercritical carbon dioxide drying was then applied to the formation of a nanoporous structure. The physical properties and morphology of the regenerated bacterial cellulose (RBC) films were characterized. The tensile strength, elongation at break, and water absorption of the RBC membranes were 4.32 MPa, 35.20%, and 49.67%, respectively. The average pore size of the RBC membrane was 1.26 nm with a 17.57 m2/g surface area. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Temperature and urea induced denaturation of the TRP-cage mini protein TC5b: A simulation study consistent with experimental observationsPROTEIN SCIENCE, Issue 10 2009Z. Gattin Abstract The effects of temperature and urea denaturation (6M urea) on the dominant structures of the 20-residue Trp-cage mini-protein TC5b are investigated by molecular dynamics simulations of the protein at different temperatures in aqueous and in 6M urea solution using explicit solvent degrees of freedom and the GROMOS force-field parameter set 45A3. In aqueous solution at 278 K, TC5b is stable throughout the 20 ns of MD simulation and the trajectory structures largely agree with the NMR-NOE atom,atom distance data available. Raising the temperature to 360 K and to 400 K, the protein denatures within 22 ns and 3 ns, showing that the denaturation temperature is well below 360 K using the GROMOS force field. This is 40,90 K lower than the denaturation temperatures observed in simulations using other much used protein force fields. As the experimental denaturation temperature is about 315 K, the GROMOS force field appears not to overstabilize TC5b, as other force fields and the use of continuum solvation models seem to do. This feature may directly stem from the GROMOS force-field parameter calibration protocol, which primarily involves reproduction of condensed phase thermodynamic quantities such as energies, densities, and solvation free energies of small compounds representative for protein fragments. By adding 6M urea to the solution, the onset of denaturation is observed in the simulation, but is too slow to observe a particular side-chain side-chain contact (Trp6-Ile4) that was experimentally observed to be characteristic for the denatured state. Interestingly, using temperature denaturation, the process is accelerated and the experimental data are reproduced. [source] On-line measurements of ,15N in biological fluids by a modified continuous-flow elemental analyzer with an isotope-ratio mass spectrometerRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2008Xu Wang A modified continuous-flow elemental analyzer coupled to an isotope-ratio mass spectrometer (modified EA-IRMS) was tested for on-line ,15N measurement on urea solution and biological fluids (e.g. urine). The elemental analyzer configuration was adapted by adding a U-shaped cold trap and an X-pattern four-way valve for on-line trapping/venting of water from the liquid samples. Results indicate that the ,15N ratios show little variation (standard deviation (SD),=,0.05,) with a sample size above the equivalent N yield of 0.2,mg urea (0.092,mg N) when the mass spectrometer conditions were carefully optimized. By contrast, a significant logarithmic decrease in ,15N with sample size was observed but this can be offset by applying a linearity correction or blank correction when the sample size is between equivalent N yields of 0.05 and 0.2,mg urea. The blank corrected ,15N ratios give an overall precision of ,0.16, whereas the average precision for ,15N corrected using combined linearity and shift correction is 0.05,. The relatively large variation in blank corrected ,15N values may be attributed to the variability of the blank ,15N in the sequence. Therefore, the blank correction should be carefully performed in routine measurements. As a result, the linearity range of a modified EA-IRMS can be extended to a minimum sample size of 0.023,mg N. In addition, the reproducibility of the new system is good, as indicated by the precision (<0.2,) for a set of standards and unknowns. The data show that fluids containing nitrogen can be successfully analyzed in the modified EA-IRMS. Copyright © 2008 John Wiley & Sons, Ltd. [source] In-situ catalytic synthesis of ammonia from urea in a semi-batch reactor for safe utilization in thermal power plantASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010J. N. Sahu Abstract Urea as the source of ammonia for the flue gas conditioning/NOx reduction system in thermal power plant has the obvious advantages that no ammonia shipping, handling and storage is required. The process of this invention minimizes the risks and hazards associated with the transport, storage and use of anhydrous and aqueous ammonia, as ammonia is a highly volatile noxious material. But no such rapid urea conversion process is available as per requirement of high conversion in shorter time, so here we study the catalytic hydrolysis of urea for fast conversion in a semi-batch reactor. The catalysts used in this study are: TiO2, fly ash, mixture of Ni and Fe and Al2O3. Number of experiments was carried out in a semi-batch reactor at different catalyst doses, temperatures and concentration of urea solution from 10 to 30% by weight and equilibrium study has been made. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] "Setting paint" analogy for the hydrophobic self-association of tropoelastin into elastin-like hydrogelBIOPOLYMERS, Issue 5 2009Christoph Naumann Abstract Alkaline tropoelastin solutions (pH 11) were optically clear at low temperatures, but a firm gel formed when the temperature was raised to 37°C. Reversion to a clear solution took place if the temperature was lowered to below 20°C within less than 2 h, but not if 37°C was maintained for several hours. The precipitated elastin-like hydrogel thus formed did not visually redissolve at low temperatures. Tropoelastin hydrogel was stable to subsequent washings with alkaline solution at 37°C, but at 4°C some hydrogel redissolved showing that association is at least partly reversible. Washing the hydrogel with neutral 8M urea solution at 4°C dissolved less than 10% of tropoelastin in 24 h. We characterized this phenomenon by combining temperature-controlled light microscopy analysis, 1H NMR spectroscopy (temperature, diffusion, and relaxation time studies), and UV-absorption-based concentration measurements. The self-association of tropoelastin at pH 11 is due to hydrophobic interactions in an emulsion-like system in which the spherules coalesce in a manner like a water-based latex paint that forms a durable hydrophobic sheet as water and the organic solvent evaporate. In the present case, the sedimentation and entanglement of the tropoelastin porous sheets means that reverse dissolution is a kinetically slow process. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 321,330, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] High Recovery Refolding of rhG-CSF from Escherichia coli, Using Urea Gradient Size Exclusion ChromatographyBIOTECHNOLOGY PROGRESS, Issue 1 2008Chaozhan Wang Protein folding liquid chromatography (PFLC) is a powerful tool for simultaneous refolding and purification of recombinant proteins in inclusion bodies. Urea gradient size exclusion chromatography (SEC) is a recently developed protein refolding method based on the SEC refolding principle. In the presented work, recombinant human granulocyte colony-stimulating factor (rhG-CSF) expressed in Escheriachia coli ( E. coli) in the form of inclusion bodies was refolded with high yields by this method. Denatured/reduced rhG-CSF in 8.0 mol·L -1 urea was directly injected into a Superdex 75 column, and with the running of the linear urea concentration program, urea concentration in the mobile phase and around the denatured rhG-CSF molecules was decreased linearly, and the denatured rhG-CSF was gradually refolded into its native state. Aggregates were greatly suppressed and rhG-CSF was also partially purified during the refolding process. Effects of the length and the final urea concentration of the urea gradient on the refolding yield of rhG-CSF by using urea gradient SEC were investigated respectively. Compared with dilution refolding and normal SEC with a fixed urea concentration in the mobile phase, urea gradient SEC was more efficient for rhG-CSF refolding&‐;in terms of specific bioactivity and mass recovery, the denatured rhG-CSF could be refolded at a larger loading volume, and the aggregates could be suppressed more efficiently. When 500 ,L of solubilized and denatured rhG-CSF in 8.0 mol·L -1 urea solution with a total protein concentration of 2.3 mg·mL -1 was loaded onto the SEC column, rhG-CSF with a specific bioactivity of 1.0 × 108 IU·mg -1 was obtained, and the mass recovery was 46.1%. [source] Studies on the Refolding of Egg White Lysozyme Denatured by Urea Using "Phase Diagram" Method of FluorescenceCHINESE JOURNAL OF CHEMISTRY, Issue 12 2007Liu-Jiao BIAN Abstract The refolding of reduced and non-reducing egg white lysozymes in a urea solution was studied by a "phase diagram" method of fluorescence. The result showed that in the refolding of the reduced egg white lysozyme, an intermediate state of an egg white lysozyme exists at the urea concentrations in a final renaturation solution being about 4.5 mol/L, their refolding follows a three-state model; while in the refolding of the non-reducing egg white lysozyme, two intermediate states exist at the urea concentrations being separately 4.0 and 2.5 mol/L, and their refolding follows a four-state model. Through the comparison between the unfolding and refolding of an egg white lysozyme in the urea solution, it was found that both of the refolding of reduced and non-reducing egg white lysozyme molecules was irreversible to their unfolding in the urea solution. Finally, a suggested refolding was separately presented for the reduced and non-reducing egg white lysozymes in the urea solution. [source] Solid Contact Micropipette Ion Selective Electrode for Potentiometric SECMELECTROANALYSIS, Issue 10 2007Gergely Gyetvai Abstract New solid contact ammonium micropipette electrodes (ISE), well applicable in scanning electrochemical microscopy are reported. The solid contact was made of a PEDOT nanowire coated carbon fiber, lowered down close to the orifice, and dipped inside the cocktail being in the pipette tip. This configuration provided low electrical resistance and good potential stability. Submicron tip size, usual in case of micropipette ISE-s easily can be fabricated in this way. The applicability of the electrode in SECM has been proved in SG/TC mode imaging urease enzyme active spots in urea solutions. [source] | |||||||||||||