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991.
Jin‐Chul Kim Dae Ho Kim Min Chul Kwon Hae Gon Chung Seung‐Jun Lee Jong‐Duk Kim 《Journal of Dispersion Science and Technology》2013,34(2):165-169
Microspheres were prepared using N‐methylolurea‐dodecylamine conjugate (MU‐DOA), an emulsifiable and self‐condensaible oil. MU was prepared by reacting urea and formaldehyde at 70°C in alkali conditions and then conjugating it to DOA by a condensation reaction. The MU‐DOA conjugate was emulsified in distilled water without an emulsifier, and then the oil droplets were hardened to obtain microspheres by a self‐condensation reaction among methylols of the conjugate. The reactions of each step, e.g., the preparation of MU, the conjugation of MU and DOA, and the self‐condensation of emulsified oil, were confirmed by Fourier transform infrared (FTIR) spectra. On scanning electron microscopy (SEM), the microspheres formed by the self‐condensation of the emulsified MU‐DOA were shown as spherical and less than 30 µm in diameter. The phase transition temperatures of DOA, MU‐DOA, and MU‐DOA microspheres were 30.3°C, 21.1°C, and 20.1°C, respectively. The lower transition temperature of MU‐DOA is probably due to the bulky MU, which could reduce the intermolecular interaction of MU‐DOA. Zeta potentials of the microspheres decreased from positive to negative value as pH increased from 3.5 to 10.5. The deprotonation of the amines of MU‐DOA would be responsible for that result. 相似文献
992.
Abstract Films of poly(dipropargylsilane derivatives) were easily prepared by solvent casting. The resulting red-black films were relatively flexible and ductile. By doping with electron acceptors, the electrical conductivity increased up to the order of 10?1-100 S/cm. The activation energy for the conduction of doped film was 4 kcal/mol. The change in Raman, IR, and UV-visible spectra by doping suggests electron transfer from the poly(dipropargylsilane derivatives) to the dopant, leading to the formation of polaron. It also was observed that doping with I2 drastically destroys the crystallinity of the polymer. 相似文献
993.
Yun-Hi Kim Soon-Ki Kwon Jin-Kuk Lee Kyeong-Ku Jeong Sam-Kwon Choi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1761-1772
Abstract Poly(2,2-dipropargyl-1,3-propylene benzaldehyde acetal) (PDPBA), a cyclopolymer containing a bulky acetal functional group, was prepared with transition metal catalysts. MoCl5 was found to be the most effective catalyst, and any cocatalyst effect was hardly observed. Polymerization was quantitatively carried out under mild conditions (30°C, M0 = 0.125) with MoCl5-based catalysts. The structure and physical properties of the resulting polymer were investigated. The spectral data indicated that the polymer contains alternating double and single bonds along the polymer backbone and a cyclic recurring unit with spiro acetal group. The polymer was completely soluble in common organic solvents. The M n value of the polymer was in the 70,000 to 80,000 range relative to polystyrene standards by GPC. In addition, the polymer possessed good thermal and oxidative stability. The electrical conductivity of the undoped polymer was 10?12 S/cm. 相似文献
994.
Han-Mo Yang Baek-Kyung Kim Ju-Young Kim Yoo-Wook Kwon Sooryeonhwa Jin Joo-Eun Lee Hyun-Jai Cho Hae-Young Lee Hyun-Jae Kang Byung-Hee Oh Young-Bae Park Hyo-Soo Kim 《Experimental & molecular medicine》2013,45(11):e65
Vascular smooth muscle cells (VSMCs) undergo phenotypic changes in response to vascular injury such as angioplasty. Protein kinase G (PKG) has an important role in the process of VSMC phenotype switching. In this study, we examined whether rosiglitazone, a peroxisome proliferator-activated receptor (PPAR)-γ agonist, could modulate VSMC phenotype through the PKG pathway to reduce neointimal hyperplasia after angioplasty. In vitro experiments showed that rosiglitazone inhibited the phenotype change of VSMCs from a contractile to a synthetic form. The platelet-derived growth factor (PDGF)-induced reduction of PKG level was reversed by rosiglitazone treatment, resulting in increased PKG activity. This increased activity of PKG resulted in phosphorylation of vasodilator-stimulated phosphoprotein at serine 239, leading to inhibited proliferation of VSMCs. Interestingly, rosiglitazone did not change the level of nitric oxide (NO) or cyclic guanosine monophosphate (cGMP), which are upstream of PKG, suggesting that rosiglitazone influences PKG itself. Chromatin immunoprecipitation assays for the PKG promoter showed that the activation of PKG by rosiglitazone was mediated by the increased binding of Sp1 on the promoter region of PKG. In vivo experiments showed that rosiglitazone significantly inhibited neointimal formation after balloon injury. Immunohistochemistry staining for calponin and thrombospondin showed that this effect of rosiglitazone was mediated by modulating VSMC phenotype. Our findings demonstrate that rosiglitazone is a potent modulator of VSMC phenotype, which is regulated by PKG. This activation of PKG by rosiglitazone results in reduced neointimal hyperplasia after angioplasty. These results provide important mechanistic insight into the cardiovascular-protective effect of PPARγ. 相似文献
995.
Electrochemical carbon dioxide and bicarbonate reduction on copper in weakly alkaline media 总被引:1,自引:0,他引:1
R. Kortlever K. H. Tan Y. Kwon M. T. M. Koper 《Journal of Solid State Electrochemistry》2013,17(7):1843-1849
The electrochemical reduction of CO2 on copper is an intensively studied reaction. However, there has not been much attention for CO2 reduction on copper in alkaline electrolytes, because this creates a carbonate buffer in which CO2 is converted in HCO3 ? and the pH of the electrolyte decreases. Here, we show that electrolytes with phosphate buffers, which start off in the alkaline region and, after saturation with CO2, end up in the neutral region, behave differently compared to CO2 reduction in phosphate buffers which starts off in the neutral region. In initially alkaline buffers, a reduction peak is observed, which is not seen in neutral buffer solutions. In contrast with earlier literature reports, we show that this peak is not due to the formation of a CO adlayer on the electrode surface but due to the production of formate via direct bicarbonate reduction. The intensity of the reduction peak is influenced by electrode morphology and the identity of the cations and anions in solution. It is found that a copper nanoparticle-covered electrode gives a rise in intensity in comparison with mechanically polished and electropolished electrodes. The peak is observed in the SO4 2?-, ClO4 ?-, and Cl?- containing electrolytes, but the formate-forming peak is not seen with Br? and I?. 相似文献
996.
Joon Yub Kwon Seo Bong Chang Yong Oh Jang Mohamed Dawod Doo Soo Chung 《Journal of separation science》2013,36(12):1973-1979
Electrokinetic supercharging is one of the most powerful sample‐stacking methods that combines field amplified sample injection and transient ITP. In counter‐flow electrokinetic supercharging, a constant counter pressure is applied during sample injection in order to counterbalance the movement of the injected sample zone. As a result, there will be a pronounced increase in the amount of sample injected and the portion of the capillary available for electrophoresis. In this report, counter‐flow electrokinetic supercharging optimization factors such as the electric field application in the constant voltage and constant current modes, the magnitude of counter pressure, and the terminating electrolyte concentrations were investigated. The enrichments obtained with a 30 min injection of 10 nM catecholamines in 5 mM terminating electrolyte solution in the constant voltage mode applying a counter pressure of 1.3 psi were 41000‐fold for dopamine, 50 000‐fold for norepinephrine, and 32 000‐fold for epinephrine, yielding detection limits of 1.3, 1.4, and 1.2 nM, respectively, with absorbance detection at 200 nm. 相似文献
997.
Joong-Ho Kwon Jae-Jun Ahn Kashif Akram Ik-Jae Son Sang-O Lee 《Analytical and bioanalytical chemistry》2013,405(12):4225-4234
Two kinds (20 each) of gamma-irradiated (0, 5, and 10 kGy) tea samples, blended powders and packed in sachets (tea bags), were investigated using photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance spectroscopy (ESR) to identify their irradiation status. PSL-based rapid screening was possible for all the control samples except for one packed and two powdered samples. The irradiated samples presented a good dose-dependent PSL count except two powdered samples with very low PSL sensitivity. TL analysis provided the most reliable results, in which all the irradiated samples were identified using a well-defined high-intensity TL glow curve in a temperature range of 150–250 °C. The TL results were also confirmed by determining the TL ratio (TL1/TL2), which was <0.1 in all the non-irradiated samples and >0.1 in the irradiated ones. ESR spectroscopy was effective for only 3 packed and 6 powdered samples showing the radiation-induced cellulosic and sugar radical signals, respectively. Figure
TL-based detection of irradiated teas 相似文献
998.
Dr. Amit Kumar Dr. Nitee Kumari Dr. Sateesh Dubbu Dr. Sumit Kumar Taewan Kwon Dr. Jung Hun Koo Jongwon Lim Inki Kim Prof. Yoon-Kyoung Cho Prof. Junsuk Rho Prof. In Su Lee 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(24):9547-9556
Interest and challenges remain in designing and synthesizing catalysts with nature-like complexity at few-nm scale to harness unprecedented functionalities by using sustainable solar light. We introduce “nanocatalosomes”—a bio-inspired bilayer-vesicular design of nanoreactor with metallic bilayer shell-in-shell structure, having numerous controllable confined cavities within few-nm interlayer space, customizable with different noble metals. The intershell-confined plasmonically coupled hot-nanospaces within the few-nm cavities play a pivotal role in harnessing catalytic effects for various organic transformations, as demonstrated by “acceptorless dehydrogenation”, “Suzuki–Miyaura cross-coupling” and “alkynyl annulation” affording clean conversions and turnover frequencies (TOFs) at least one order of magnitude higher than state-of-the-art Au-nanorod-based plasmonic catalysts. This work paves the way towards next-generation nanoreactors for chemical transformations with solar energy. 相似文献
999.
Nguyen Thi Minh Hien Joo Hee Chung Xiang‐Bai Chen Woo Jun Kwon Chul Sung Kim In‐Sang Yang 《Journal of Raman spectroscopy : JRS》2015,46(11):1161-1165
LiFe1 − xMnxPO4 olivines are promising material for improved performance of Li‐ion batteries. Spin–phonon coupling of LiFe1 − xMnxPO4 (x = 0, 0.3, 0.5) olivines is studied through temperature‐dependent Raman spectroscopy. Among the observed phonon modes, the external mode at ~263 cm−1 is directly correlated with the motions of magnetic Fe2+/Mn2+ ions. This mode displays anomalous temperature‐dependent behavior near the Néel temperature, indicating a coupling of this mode with spin ordering. As Mn doping increases, the anomalous behavior becomes clearly weaker, indicating the spin–phonon coupling quickly decreases. Our analyses show that the quick decrease of spin–phonon coupling is due to decrease of the strength of spin–phonon coupling, but not change of spin‐ordering feature with Mn doping. Importantly, we suggest that the low electrochemical activity of LiMnPO4 is correlated with the weak spin–phonon coupling strength, but not with the weak ferromagnetic ground state. Our work would play an important role as a guide in improving the performances of future Li‐ion batteries. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
1000.
Four kinds of poly(4-methacryloyloxychalcone) (PCEMA) photo-alignment materials were synthesized. The effect of the cinnamoyl group on liquid crystal (LC) aligning capabilities and electro-optical characteristics of photo-aligned twisted nematic (TN) liquid crystal displays (LCDs) was investigated by photo-dimerization. Uniform NLC alignment by linearly polarized UV exposure at normal incidence on the PCEMA surfaces having a high density of cinnamoyl groups was observed. Also, excellent voltage-transmittance (V-T) curves for the photo-aligned TN-LCDs on the PCEMA surfaces was achieved. We find that the V-T and response time characteristics can be improved by increasing the density of cinnamoyl groups. 相似文献