Results 1 - 10 of 4943
Results 1 - 10 of 4943. Search took: 0.027 seconds
|Sort by: date | relevance|
[en] The crystal structure of the protein product of the C. acetobutylicum ATCC 824 gene CA-C0359 is structurally similar to YteR, an unsaturated rhamnogalacturonyl hydrolase from B. subtilis strain 168. Substrate modeling and electrostatic studies of the active site of the structure of CA-C0359 suggests that the protein can now be considered to be part of CAZy glycoside hydrolase family 105. Clostridium acetobutylicum ATCC 824 gene CA-C0359 encodes a putative unsaturated rhamnogalacturonyl hydrolase (URH) with distant amino-acid sequence homology to YteR of Bacillus subtilis strain 168. YteR, like other URHs, has core structural homology to unsaturated glucuronyl hydrolases, but hydrolyzes the unsaturated disaccharide derivative of rhamnogalacturonan I. The crystal structure of the recombinant CA-C0359 protein was solved to 1.6 Å resolution by molecular replacement using the phase information of the previously reported structure of YteR (PDB entry (http://scripts.iucr.org/cgi-bin/cr.cgi?rm)) from Bacillus subtilis strain 168. The YteR-like protein is a six-α-hairpin barrel with two β-sheet strands and a small helix overlaying the end of the hairpins next to the active site. The protein has low primary protein sequence identity to YteR but is structurally similar. The two tertiary structures align with a root-mean-square deviation of 1.4 Å and contain a highly conserved active pocket. There is a conserved aspartic acid residue in both structures, which has been shown to be important for hydration of the C=C bond during the release of unsaturated galacturonic acid by YteR. A surface electrostatic potential comparison of CA-C0359 and proteins from CAZy families GH88 and GH105 reveals the make-up of the active site to be a combination of the unsaturated rhamnogalacturonyl hydrolase and the unsaturated glucuronyl hydrolase from Bacillus subtilis strain 168. Structural and electrostatic comparisons suggests that the protein may have a slightly different substrate specificity from that of YteR
[en] Body composition is a useful means for athletes' body composition assessment, relying on reference population data. This study aims at comparing body composition multifrequency impedance data of athletes and healthy adult populations. Differences were found in tissular, hydration and metabolic indices. They were significant, in the expected direction, but quite weak and additional data from reference technologies would set if specific equations are needed. The current ones are nevertheless suitable for reliable follow-up studies.
[en] The electroactive behavior of an ionic polymer–metal composite (IPMC) actuator was modeled and the optimum design parameters for actuation were also studied. An actuation model characterizing the mechanical response of the IPMC under a given electrical field was proposed considering the electro-chemical parameters. To find the optimum conditions maximizing the tip deflection and blocking force, a multivariable constrained optimization equation was proposed in which the saturation level of hydration, applied voltage and the thickness of IPMC were used as decision variables. IPMC samples with variable thickness were manufactured based on a Nafion membrane and the effect of decision variables on the tip deflection, blocking force and response time of the IPMC was studied. The proposed model and the simulation of optimization were validated by experiment
[en] The structure of the trivalent lanthanide and actinide aquo ions has been investigated recently through radiochemical methods based on transport properties. The volume Vt of the aquo ions was deduced. The variation of Vt vs. the crystallographic radius shows a discontinuity corresponding to a change in the hydration number. New evaluations of the volume of the water molecules in the vicinity of the cation are obtained in this work using electrostriction theory. More accurate values of the dynamic hydration number are calculated for all the members of the series. 30 refs
[en] Preliminary glass compositions for immobilizing Hanford low-activity waste (LAW) by the in-container vitrification (ICV) process were fabricated at crucible- and engineering-scale and tested at Pacific Northwest National Laboratory. This testing showed that glasses with LAW loading of 20 mass% can readily be made and meet all product constraints by a far margin. It was found that the response constraint of the vapor hydration test (VHT) of less than 50 g/(m2d) alteration rate was the most restrictive constraint placed on LAW glasses. Glasses with over 22 mass% Na2O can be made to meet this constraint along with all other product quality and processability constraints imposed by this process. The results of crucible melts with simulants were scaled-up to engineering scale and also tested with actual (radioactive) LAW. All the results suggest that the baseline glass can be successfully processed by the ICV technology and can meet all the constraints related to product quality
[en] At this study the effect of Cr2O3 nanoparticles (up to 3wt.%) on the physical and mechanical properties of MgO–CaO refractory composition with emphasis on the hydration resistance improvement have been investigated. Specimens pressed at 90MPa then were sintered at 1650°C for 5h in an electric furnace. Properties such as bulk density, apparent porosity, cold crushing strength and hydration resistance were examined. The crystalline phases and microstructure characteristics of sintered specimens were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS), respectively. Results shown that add of the 1.5wt.% Cr2O3 nanoparticles have the best results i.e. increased the bulk density (3.41g/cm3), cold crushing strength (848kg/cm2), hydration resistance (1.5%) and decreased apparent porosity (5.58%), respectively. The mechanism of specimens hydration resistance improvement are: (i) decreasing the amount of free CaO and MgO with converted to high hydration resistance phases such as CaCr2O4 and MgCr2O4 phases, (ii) promotion of the densification as well as (iii) modification of the microstructure. (Author)
[en] Problems on similarity of actinoids with elements of other groups of the Periodic System are considered. Analogy between actinoids and transition elements is shown to be observed for the change in stability of high and low states of oxidation with the growth of the atomic number of an element, as well as magnetic properties of metals. Actinoids and lanthanoids are the analogs of alkali and alkali-earth elements in the low state of oxidation; they begin to show resemblance to d-elements in the tetravalent state. Bivalent actinoid and lanthanoid ions with an electron at the d-level are of special interest. Being analogous to bivalent elements, they form cluster compunds of the different type
[en] In order to study the dependence of water solubility and hydration behavior of nanoparticles on their surface polarity, we designed polar nanoparticles with varying surface polarity by assigning atomic partial charge to the surface of C60. The water solubility of the nanoparticle is enhanced by several orders of magnitude after the introduction of surface polarity. Nevertheless, when the atomic partial charge grows beyond a certain value (qM), the solubility continuously decreases to the level of nonpolar nanoparticle. It should be noted that such qM is comparable with atomic partial charge of a variety of functional groups. The hydration behaviors of nanoparticles were then studied to investigate the non-monotonic dependence of solubility on the surface polarity. The interaction between the polar nanoparticle and the hydration water is stronger than the nonpolar counterpart, which should facilitate the dissolution of the nanoparticles. On the other hand, the surface polarity also reduces the interaction of hydration water with the other water molecules and enhances the interaction between the nanoparticles which may hinder their dispersion. Besides, the introduction of surface polarity disturbs and even rearranges the hydration structure of nonpolar nanoparticle. Interestingly, the polar nanoparticle with less ordered hydration structure tends to have higher water solubility.
[en] Clathrate hydrates are non-stoichiometric compounds that form when water and certain low molecular weight hydrocarbons coexist at high pressures and low temperatures. The majority of the earth hydrocarbons are in the hydrate phase and are primarily located along the ocean bottoms and to a lesser degree in the permafrost regions. In addition, hydrate formation is induced in undersea gas transmission lines and causes costly pipeline plugs and requires expensive inhibition measures to be taken. Therefore, both a stick and a carrot motivate hydrate research. They are a costly and dangerous nuisance to the oil and gas industry and represent a tremendous, untapped energy resource of the future. The formation mechanism of clathrate hydrate formation has always been shrouded in mystery, and an ongoing debate has ensued as to whether their formation is a bulk or surface phenomenon. Molecular dynamics simulation and fractal modeling suggest that this may be an irrelevant issue and that two independent factors contribute to the symmetrical ordered structure of clathrate hydrates: hydrophobic hydration of hydrocarbon molecules in water and formation of linked cavities as these small clusters aggregate. (Author)
[en] The shift in the polarographic halfwave potential caused by changes in the concentration of a non-complexing supporting electrolyte was investigated. The depolarizer systems studied were the cadmium(II) and zinc(II) amine complex ions, and cadmium(II), zinc(II) and thallium(I) aquo ions. These systems exhibited half-wave potential shifts that were dependent on 5 factors affected by the ionic strength of the solution: the activity and diffusion coefficients of the depolarizer ions, the activity of the complexing agent and/or water and the liquid junction potential. An equation was derived relating these factors to the half-wave potential shift and evaluated for the change in the activity co-efficient of the depolarizer over the ionic strength range 4-10. As expected, the observed potential shift showed a strong correlation with the charge and primary hydration numbers of the aquo ions. (author). 24 refs.; 3 figs.; 2 tabs