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891.
Temperature effect on photochemical reactions of ortho-alkylphenacyl benzoates, one of the recently developed photoremovable protecting groups (PPG), giving indanones (IN) and benzocyclobutenols (CB) was examined. As temperature was lowered, CB was formed preferentially over IN and the amount of IN increased as temperature was elevated. Arrhenius plot of ln(IN/CB) versus 1/T gave a straight line from which EaIN–EaCB and AIN/ACB were obtained. The least sterically hindered 2-methylphenacyl benzoate (1) gave the highest EaIN–EaCB and AIN/ACB among the ortho-alkylphenacyl benzoates tested in this research including 2,4,6-trimethylphenacyl benzoate (2) and 2,4,6-triisopropylphenacyl benzoate (3). 相似文献
892.
Seung Yeop Lee Min Hoon Baik Hye-Ryun Cho Euo Chang Jung Jong Tae Jeong Jong Won Choi Young Boo Lee Yong Jae Lee 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(3):1311-1319
Sulfate-reducing bacteria and their by-products, such as iron sulfides, are widely distributed in groundwater and sediments, and can affect subsurface aqueous chemistry. Here we show the catalytic reduction of hexavalent uranium by FeS particles, which were largely generated by the activities of Desulfovibrio desulfuricans and D. vulgaris in anaerobic condition. Characterization of FeS particles by X-ray diffraction and high-resolution transmission electron microscopy revealed the presence of mackinawite having thin and flexible platy sheets with 0.5-nm lamellar spacing. This biogenic phase mediated abiotic reduction of U(VI) to U(IV) which was confirmed by UV–Vis absorption spectroscopy. The U conversion occurred through surface catalysis that involved adsorption of aqueous U(VI)–carbonate complexes (predominantly UO2(CO3) 3 4? ) onto the mackinawite, but the transformed uranium was then released and remained in suspended form in the solution phase. This surface catalysis and subsequent U(IV) remobilization has not been reported as a pathway to occur under sulfate-reducing conditions. Our results suggest that the iron sulfide solid, which is characteristic of conductive property, is very sensitive and variable depending on the electron supplying and transferring environment, negatively affecting the surface uranium to be strongly stabilized and fixed on the FeS surface. 相似文献
893.
Song Hee Jung Hyang Yul Kim Myoung‐Hoon Lee John Moon Rhee Seung Hee Lee Corresponding author 《Liquid crystals》2013,40(2):267-275
Transmittance characteristics were studied as a function of cell gap for a homogeneously aligned liquid crystal (LC) cell driven by a fringe‐electric field—named fringe‐field switching (FFS) mode. The light efficiency of a conventional LC cell using in‐plane switching and twisted nematic modes, where the LC director is determined by competition between elastic energy and electrical energy, does not depend on cell gap as long as the cell retardation value remains the same; i.e. only dielectric torque contributes to the deformation of the LC director. However, the transmittance of the FFS mode is dependent on the cell gap such that it decreases as the cell gap decreases, although the cell retardation value remains the same. This unusual behaviour (unlike that of conventional LC cells) arises because in the device the elastic and dielectric torques have the role of determining the LC director, such that the driving voltage giving rise to maximum transmittance becomes strongly dependent on the electrode position when the cell gap is as small as 2?µm. In addition, the LCs at the centre of the pixel and common electrodes are not sufficiently twisted because of a competition between the two elastic forces, which tries to twist the LCs in plane and hold them in their initial state by surface anchoring. 相似文献
894.
Yong Beom Jo Sung Hoon Park Jong-Ki Jeon Chang Hyun Ko Changkook Ryu Young-Kwon Park 《Applied biochemistry and biotechnology》2013,170(6):1426-1436
Calcined waste starfish was used as a base catalyst for the production of biodiesel from soybean oil for the first time. A batch reactor was used for the transesterification reaction. The thermal characteristics and crystal structures of the waste starfish were investigated by thermo-gravimetric analysis and X-ray diffraction. The biodiesel yield was determined by measuring the content of fatty acid methyl esters (FAME). The calcination temperature appeared to be a very important parameter affecting the catalytic activity. The starfish-derived catalyst calcined at 750 °C or higher exhibited high activity for the transesterification reaction. The FAME content increased with increasing catalyst dose and methanol-over-oil ratio. 相似文献
895.
The dispersion stability of carbonyl iron (CI)-based magnetorheological (MR) fluid was improved by coating soft magnetic CI particles with an environmentally benign biopolymer of xanthan gum to reduce the density gap between the medium oil and dispersed particles. The sedimentation test of the MR fluid showed that the xanthan gum/CI composite particles improved the sedimentation drawback of the pristine CI-based MR fluid. The rheological properties of the MR fluid were also examined using a rotational rheometer to observe the typical MR characteristics, such as yield stress and shear viscosity. 相似文献
896.
Ji-Young Bae Bon-Kyung Koo Han-Bong Ryu Jung-A Song Minh Tan Nguyen Thu Trang Thi Vu Young-Jin Son Hyang Kyu Lee Han Choe 《Applied biochemistry and biotechnology》2013,169(5):1633-1647
Extracellular superoxide dismutase (EC-SOD) is the only enzyme that removes superoxide radical in the extracellular space. The reduction of EC-SOD is linked to many diseases, suggesting that the protein may have therapeutic value. EC-SOD is reported to be insoluble and to make inclusion bodies when overexpressed in the cytoplasm of Escherichia coli. The refolding process has the advantage of high yield, but has the disadvantage of frequent aggregation or misfolding during purification. For the first time, this study shows that fusion with maltose-binding protein (MBP), N-utilization substance protein A, and protein disulfide isomerase enabled the soluble overexpression of EC-SOD in the cytoplasm of E. coli. MBP-tagged human EC-SOD (hEC-SOD) was purified by MBP affinity and anion exchange chromatography, and its identity was confirmed by MALDI-TOF MS analysis. The purified protein showed good enzyme activity in vitro; however, there was a difference in metal binding. When copper and zinc were incorporated into hEC-SOD before MBP tag cleavage, the enzymatic activity was higher than when the metal ions were bound to the purified protein after MBP tag cleavage. Therefore, the enzymatic activity of hEC-SOD is associated with metal incorporation and protein folding via disulfide bond. 相似文献
897.
Satoshi Ogawa Mieko Kikuchi Yasushi Kawai Ryu Sato 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):433-434
Abstract Novel stable benzodithiolium salts have been synthesized and characterized by X-ray crystallographic analysis, which have been readily converted to the first isolable dithiolyl radicals by one-electron reduction. 相似文献
898.
899.
Seok-Hee Park Young-Woo Choi Chang-Soo Kim Seung Bin Park 《Journal of Solid State Electrochemistry》2013,17(4):1247-1254
The development of alkaline membrane fuel cells (AMFCs) will enable the use of non-platinum catalysts and hydrocarbon-based electrolyte membranes. Such catalysts are intrinsically stable and have activities similar to that of platinum in an alkaline environment. A pore-filling membrane has been made from a porous, high-density polyethylene substrate to fabricate durable, AMFC membrane electrode assemblies (MEAs). Because of the low binding ability of the hydrocarbon ionomer in the preparation of AMFC MEAs, polymer binders were added to the catalyst slurries to form a firmly bound interface. A content of 20 wt% polyethylene (PE) binder, the same material as the porous substrate in the pore-filling membrane, exhibits the best attachment of the non-platinum catalyst particles to the pore-filling, hydrocarbon anion-exchange membranes. The addition of a PE binder improves adhesion at the MEA interface and diminished contact resistance. The improved durability of the MEA is confirmed by continuous, constant-voltage operation. Adhesion between the cathode catalyst layer and the pore-filling membrane is also investigated after mild hot-pressing to test the use of decal method in the fabrication of AMFCs. The catalyst layer with the PE binder was completely transferred to the pore-filling membrane at 50 °C and 30 bar?cm?2, but not for the PTFE binder. 相似文献
900.
Redox ions are deposited on a polyelectrolyte‐coated gold electrode by an electric field to fabricate an ion‐selective thin film electrode. The Fe(CN)${{{4- \hfill \atop 6\hfill}}}$ ions are deposited on a few monolayer‐coated polyelectrolyte gold electrode by a slow periodic potential cycle. The deposition process and electrode properties are quantitatively and simultaneously monitored by cyclic voltammetry and a novel technique, using a Scanning Electrometer for Electrical Double‐layers (SEED). No redox properties are obtained without the electric‐field‐deposition. Owing to the redox mediation and net charge due to the redox ion, the electrode is ion‐selective. We demonstrate the principle to detect 1 µM of dopamine in a mixture with 1 mM of ascorbic acid. 相似文献