180,064 research outputs found
Characterization of an alternatively spliced G(M2) activator protein, G(M2A) protein - An activator protein which stimulates the enzymatic hydrolysis of N-acetylneuraminic acid, but not N-acetylgalactosamine, from G(M2)
No full textG(M2) activator protein is a protein cofactor which stimulates the enzymatic hydrolysis of both GalNAc and NeuAc from G(M2). We have previously isolated two cDNA clones, G(M2) activator cDNA and G(M2A) cDNA, for human G(M2) activator protein (Nagarajan, S., Chen, H.-C., Li, S.-C., Li, Y.-T., and Lockyer, J. M. (1992) Biochem. J. 282, 807-813). G(M2A) mRNA is an RNA alternative splicing product that contains exons 1, 2, 3, and intron 3 of the genomic DNA sequence of G(M2) activator protein (Klima, H., Tanaka, A., Schnabel, D., Nakano, T., Schroder, M., Suzuki, K., and Sandhoff, K. (1991) FEES Left. 289, 260-264). G(M2A) cDNA encodes a protein (G(M2A) protein) containing 1-109 of the 160 amino acids of human G(M2) activator protein, plus a tripeptide (VST) encoded by intron 3 at the COOH terminus. Thus, G(M2A) protein can be regarded as a form (truncated version) of G(M2) activator protein. We have expressed G(M2A) cDNA in Escherichia coli using pT7-7 as the vector. The recombinant G(M2A) protein was purified to an electrophoretically homogeneous form and was found to stimulate the hydrolysis of NeuAc from G(M2) by clostridial sialidase, but not the hydrolysis of GalNAc from G(M2) by beta-hexosaminidase A. Like G(M2) activator protein, G(M2A) protein also specifically recognized the terminal G(M2) epitope in GalNAc-GD1a and stimulated the hydrolysis of only the external NeuAc from this ganglioside by clostridial sialidase. These results enabled us to discern the enzymatic hydrolyses of GalNAc and NeuAc from the G(M2) epitope and established that the NeuAc recognition domain of G(M2) activator protein is located within amino acids 1-109. The presence of G(M2A) mRNA in human tissues and the selective stimulation of NeuAc hydrolysis by G(M2A) protein indicate that this activator protein may be involved in the catabolism of G(M2) through the asialo-G(M2) pathway
TiF<sub>3</sub> catalyzed MgH<sub>2</sub> as a Li/Na ion battery anode
No full textMgH2 has been considered as a potential anode material for Li ion batteries due to its low cost and high theoretical capacity. However, it suffers from low electronic conductivity and slow kinetics for hydrogen sorption at room temperature that results in poor reversibility, cycling stability and rate capability for Li ion storage. This work presents a MgH2–TiF3@CNT based Li ion battery anode manufactured via a conventional slurry based method. Working with a liquid electrolyte at room temperature, it achieves a high capacity retention of 543 mAh g−1 in 70 cycles at 0.2 C and an improved rate capability, thanks to the improved hydrogen sorption kinetics with the presence of catalytic TiF3. Meanwhile, the first realization of Na ion uptake in MgH2 has been evidenced in experiments.Accepted Author ManuscriptChemE/Materials for Energy Conversion and Storag
A new structure of Nd1+?Fe4B4 phase in NdFeB magnet
No full textA new structure for Nd1+eFe4B4 phase has been observed, which has the same structure as Gd1+eFe4B4. The compound has Pccn structure with a = 0.71 nm and c = 2.74 nm, and its composition was found to be Nd2Fe7B7
SPECIFIC RECOGNITION OF N-ACETYLNEURAMINIC ACID IN THE G(M2) EPITOPE BY HUMAN G(M2) ACTIVATOR PROTEIN
No full textG(M2) Activator is a low molecular weight protein cofactor that stimulates the enzymatic conversion of G(M2) into G(M3) by human beta-hexosaminidase A and also the conversion of G(M2) into G(A2) by clostridial sialidase (Wu, Y.-Y., Lockyer, J. M., Sugiyama, E., Pavlova, N. V., Li, Y.-T., and Li, S.- C. (1994) J. Biol. Chem. 269, 16276-16283). Among the five known activator proteins for the enzymatic hydrolysis of glycosphingolipids, only G(M2) activator is effective in stimulating the hydrolysis of G(M2). However, the mechanism of action of G(M2) activator is still not well understood, Using a unique disialosylganglioside, GalNAc-G(D1a), as the substrate, we were able to show that in the presence of G(M2) activator, GalNAc-G(D1a) was specifically converted into GalNAc-G(M1a) by clostridial sialidase, while in the presence of saposin B, a nonspecific activator protein, GalNAc-G(D1a) was converted into both GalNAc-G(M1a) and GalNAc-G(M1b). individual products generated from GalNAc-G(D1a) by clostridial sialidase were identified by thin layer chromatography, negative secondary ion mass spectrometry, and immunostaining with a monoclonal IgM that recognizes the G(M2) epitope. Our results clearly show that G(M2) activator recognizes the G(M2) epitope in GalNAc-G(D1a). Thus, G(M2) activator may interact with the trisaccharide structure of the G(M2) epitope and render the GalNAc and NeuAc residues accessible to beta-hexosaminidase A and sialidase, respectively
Effects of vinyl ethylene carbonate additive on elevated-temperature performance of cathode material in lithium ion batteries
No full textThe addition of 2% vinyl ethylene carbonate (VEC) into LiPF6/EC + DMC electrolyte can significantly improve the cyclic performance of a LiNio.8Co0.2O2/Li cell at elevated temperatures such as 50 °C. In situ electrochemical mass spectrometry (EMS) was used to investigate the gas evolution spectroscopy in the cell during a charge/discharge process with and without VEC additive. Fourier transform infrared (FTIR), ultraviolet-visible (UV-vis), and liquid nuclear magnetic resonance (NMR) spectroscopies were also carried out to investigate the reactions between various electrolyte components and VEC without the electrochemical reaction. We propose the possible polymerized products based on the spectroscopy and the acting mechanism of the VEC additives. © 2008 American Chemical Society
Studies on storage characteristics of Li Ni0.4 Co0.2 Mn0.4 O2 as cathode materials in lithium-ion batteries
No full textLi Ni0.4 Co0.2 Mn0.4 O2 prepared by mixed-hydroxide method has shown excellent electrochemical performance and storage stability as a cathode material in lithium-ion batteries. The changes of the crystal structure, oxygen species on the surface, and oxidation state of transition metals of the samples under various storing conditions were examined by X-ray diffraction, iodometric titration, X-ray photoelectron spectroscopy, and the depth-profile experiments. It was found that the surface reaction between samples and C O2 H2 O was so negligible that it could not affect the electrochemical performance of the material. But if storing the material in Ar-filled glove box, the oxygen might release from the surface, and, consequently, Mn and Co ions could decrease their oxidation state, take part in the electrode reaction, and then dissolve into electrolyte during the cycling process. The regular ion arrangement on the surface of the materials might be destroyed. Thus cyclic performance of the samples stored in Ar is poorer than that for samples stored in other conditions. © 2007 The Electrochemical Society
A Study of the Thermodynamics and Kinetics of LiₓFePO₄ as a Cathode Material for Li Batteries
Full text linkOlivine-type LiFePO4 has been recognized as one of the most promising cathode materials for rechargeable Li batteries. Its advantages include high capacity, high stability, nontoxicity, and low cost. Our methods for synthesizing nanocrystalline LixFePO4 with the olivine structure are described. Solid-state reactions and precipitation reactions were both successful, and ball milling was especially effective at reducing crystallite sizes. Diffractometry and microscopy were used to characterize these materials, and results of impurity phases, excess Fe3+, and internal stresses are reported for the different types of synthesis.
Applications of lithium-ion batteries, including automotive applications, require fast kinetics and high conductivity of ions and electrons. Unfortunately, LixFePO4 has the electronic structure of an insulator, an entirely unsatisfactory situation if it is to be used as a battery electrode. Electrical conductivity in LixFePO4 occurs by the motion of small polarons, which are valence electrons at Fe atoms plus their distorted local environments. Electrical conductivity of LixFePO4 is interpreted in terms of small polaron hopping. There are other factors of importance in these measurements, such as impurities or defects that block the one-dimensional conduction channels of the olivine structure of LixFePO4.
We studied the polaron hopping directly, which allows us to understand the intrinsic electrical conductivity, and how it depends on microstructure and composition of LixFePO4. The experimental technique was Mossbauer spectrometry, which has been used for many years as a means for determining the fractions of Fe2+ and Fe3+ in a material. Usually the spectral signatures of Fe2+ and Fe3+ are distinct. When valence electrons hop between Fe2+ and Fe3+ at a frequency of 108 Hz or higher, however, the valence changes during the timescale of the Mossbauer measurement and the spectrum is blurred. By measuring Mossbauer spectra at elevated temperatures, we can determine the fractions of Fe atoms participating in polaron hopping, and determine the activation energy of the process. From this we estimate intrinsic electrical conductivities of 10-7S/cm at room temperature for nanocrystalline Li0.5FePO4, for example. We find a comparable conductivity for LixFePO4 prepared as a solid solution, but the conductivity of conventional LixFePO4 is much lower.
There has been much discussion about how surface area might thermodynamically stabilize the solid solution phase of nanocrystalline LixFePO4. In a series of X-ray diffraction measurements, some at elevated temperatures, we found the solid solution phase of LixFePO4 to be especially robust at room temperature when the material was prepared in nanocrystalline form. Moreover, the consistent phase transition temperature around 200°C was observed, as evidence for the unchanged equilibrium phase diagram by crystallite size. This is consistent with our evaluation on the boundaries of the two-phase mixture of triphylite and heterosite during Li insertion and extraction. Profiles of entropy and enthalpy changes were evaluated by open-circuit voltage measurements. The boundaries were found at x=0.05 and 0.95 in the LixFePO4 with crystal size of 70 nm, similar to the reported values on bulk-LixFePO4. These are important in practice, because electrochemical lithiation and delithiation at room temperature should remain as a two-phase transformation, even if a solid solution of lithium is present in the initial electrode material.</p
The effects of TiO2 coating on the electrochemical performance of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material for lithium-ion battery
No full textTiO2-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials have been synthesized and investigated as cathode materials for lithium-ion batteries at both 25 °C and elevated temperature (55 °C). The structure and morphology of the coated samples were characterized and compared. The XRD results indicate that lattice parameters of the materials did not change distinctly after surface coating. The SEM images demonstrate that the surface of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 samples were covered with nano-sized TiO2 particles. Differential scanning calorimetry (DSC) analysis results show that thermal stability of the materials was improved. It is also shown that the irreversible capacity loss of the materials was obviously reduced and their capacity retention behaviour was improved after surface modification. © 2008 Elsevier B.V. All rights reserved
Thermal insulation performance of bamboo- and wood-based shear walls in light-frame buildings
No full textLight-frame buildings commonly employ shear wall realized by framing and sheathing panels made of wood materials. Recently, much research has focused on the use of engineered bamboo composites to substitute wood in light-frame buildings. The aim of this study is to investigate the thermal insulation performances of bamboo- and wood-based shear walls in light-frame buildings. First, an archetype wall with characteristics similar to those commonly employed in wood shear walls was defined. Starting from the archetype wall, four specific configurations representing one classical full wood-based configuration, one hybrid bamboo-wood-based configuration and two full bamboo-based configurations with different studs thickness were identified to be tested. The thermal conductivity of the materials composing the wall was measured using a hot plate apparatus varying the temperature in the range of 10–50°C. The anisotropy of the thermal conductivity was analyzed for the wood and bamboo materials. The four specific configurations of the archetype wall were tested in a guarded hot box apparatus in order to determine the thermal resistance and transmittance. The experimental results were compared with the estimates obtained using the ISO 6946 procedure and a Finite Element (FE) model of the wall, both adopting the thermal conductivity previously measured. A good agreement between the experiments and the models was found with the better results obtained with the FE model. Finally, the so-validated FE model was used to optimize the archetype wall with only bamboo-based materials to the Chinese thermal regions, showing the possibility of real application in the practice. All the results indicate that the thermal insulation performances of engineered bamboo composites are slightly lower compared with wood ones, both at the material and the shear wall levels. This indicates that there is the possibility of using bamboo-based shear walls in light-frame buildings ensuring thermal insulation performances similar to classical wood-based one
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