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171.
A molecular basket with four cholate units assembled on a cone-shaped calix[4]arene assumed reversed micelle-like conformation in 5% methanol/carbon tetrachloride. The inwardly facing hydroxyl groups on the cholates concentrated the polar solvent from the mostly nonpolar mixture. Methanolysis of alkyl halides benefited from the concentrated pocket of methanol if the substrate was capable of entering the basket. Substrates that were too large or too hydrophobic to fit within the basket showed no rate acceleration. 相似文献
172.
Jeong GT Lee KM Yang HS Park SH Park JH Sunwoo C Ryu HW Kim D Lee WT Kim HS Cha WS Park DH 《Applied biochemistry and biotechnology》2007,137(1-12):935-946
Hydrogels are materials with the ability to swell in water through the retention of significant fractions of water within their structures. Owing to their relatively high degree of biocompatibility, hydrogels have been utilized in a host of biomedical applications. In an attempt to determine the optimum conditions for hydrogel synthesis by the free-radical polymerization of sorbitan methacrylate (SMA), the hydrogel used in this study was well polymerized under the following conditions: 50% (w/v) SMA as monomer, 1% (w/w) alpha, alpha'-azo-bis(isobutyro-nitrile) as thermal initiator, and 1% (w/w) ethylene glycol dimethacrylate as cross-liking agent. Under these conditions, the moisture content of the polymerized SMA hydrogel was higher than in the other conditions. Moreover, the moisture content of the poly(SMA) hydrogel was also found to be higher than that of the poly(methyl methacrylate [MMA]) hydrogel. When the Fourier transform-infrared spectrum of poly(SMA) hydrogel was compared with that of poly(MMA) hydrogel, we noted a band at 1735-1730/cm, which did not appear in the Fourier transform-infrared spectrum of poly(MMA). The surface of the poly(SMA) hydrogel was visualized through scanning electron microscopy, and was uniform and clear in appearance. 相似文献
173.
Synthesis of aligned single-walled nanotubes using catalysts defined by nanosphere lithography 总被引:1,自引:0,他引:1
Ryu K Badmaev A Gomez L Ishikawa F Lei B Zhou C 《Journal of the American Chemical Society》2007,129(33):10104-10105
174.
Lee BH Ryu MK Choi SY Lee KH Im S Sung MM 《Journal of the American Chemical Society》2007,129(51):16034-16041
We report a new layer-by-layer growth method of self-assembled organic multilayer thin films based on gas-phase reactions. In the present molecular layer deposition (MLD) process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and titanium hydroxide. The MLD method is a self- limiting layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good thermal and mechanical stability, and various unique electrical properties. The MLD method, combined with ALD, was applied to the preparation of organic-inorganic hybrid nanolaminate films in the ALD chamber. The organic-inorganic hybrid superlattices were then used as active mediums for two-terminal electrical bistable devices. The advantages of the MLD method with ALD include accurate control of film thickness, large-scale uniformity, highly conformal layering, sharp interfaces, and a vast library of possible materials. The MLD method with ALD is an ideal fabrication technique for various organic-inorganic hybrid superlattices. 相似文献
175.
Kim EK Kwon KB Han MJ Song MY Lee JH Lv N Ka SO Yeom SR Kwon YD Ryu DG Kim KS Park JW Park R Park BH 《Experimental & molecular medicine》2007,39(2):149-159
We demonstrated previously that Coptidis rhizoma extract (CRE) prevented S-nitroso-N-acetylpenicillamine-induced apoptotic cell death via the inhibition of mitochondrial membrane potential disruption and cytochrome c release in RINm5F (RIN) rat insulinoma cells. In this study, the preventive effects of CRE against cytokine-induced beta-cell death was assessed. Cytokines generated by immune cells infiltrating pancreatic islets are crucial mediators of beta-cell destruction in insulin-dependent diabetes mellitus. The treatment of RIN cells with IL-1beta and IFN-gamma resulted in a reduction of cell viability. CRE completely protected IL-1beta and IFN-gamma-mediated cell death in a concentration-dependent manner. Incubation with CRE induced a significant suppression of IL-1beta and IFN-gamma-induced nitric oxide (NO) production, a finding which correlated well with reduced levels of the iNOS mRNA and protein. The molecular mechanism by which CRE inhibited iNOS gene expression appeared to involve the inhibition of NF-kappaB activation. The IL-1beta and IFN-gamma-stimulated RIN cells showed increases in NF-kappaB binding activity and p65 subunit levels in nucleus, and IkappaB alpha degradation in cytosol compared to unstimulated cells. Furthermore, the protective effects of CRE were verified via the observation of reduced NO generation and iNOS expression, and normal insulin-secretion responses to glucose in IL-1beta and IFN-gamma-treated islets. 相似文献
176.
177.
Iranzo O Thulstrup PW Ryu SB Hemmingsen L Pecoraro VL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(33):9178-9190
The use of de novo designed peptides is a powerful strategy to elucidate Hg(II)-protein interactions and to gain insight into the chemistry of Hg(II) in biological systems. Cysteine derivatives of the designed alpha-helical peptides of the TRI family [Ac-G-(L(a)K(b)A(c)L(d)E(e)E(f)K(g))(4)-G-NH(2)] bind Hg(II) at high pH values and at peptide/Hg(II) ratios of 3:1 with an unusual trigonal thiolate coordination mode. The resulting Hg(II) complexes are good water-soluble models for Hg(II) binding to the protein MerR. We have carried out a parallel study using (199)Hg NMR and (199m)Hg perturbed angular correlation (PAC) spectroscopy to characterize the distinct species that are generated under different pH conditions and peptide TRI L9C/Hg(II) ratios. These studies prove for the first time the formation of [Hg{(TRI L9C)(2)-(TRI L9C-H)}], a dithiolate-Hg(II) complex in the hydrophobic interior of the three-stranded coiled coil (TRI L9C)(3). (199)Hg NMR and (199m)Hg PAC data demonstrate that this dithiolate-Hg(II) complex is different from the dithiolate [Hg(TRI L9C)(2)], and that the presence of third alpha-helix, containing a protonated cysteine, breaks the symmetry of the coordination environment present in the complex [Hg(TRI L9C)(2)]. As the pH is raised, the deprotonation of this third cysteine generates the trigonal thiolate-Hg(II) complex Hg(TRI L9C)(3)(-) on a timescale that is slower than the NMR timescale (0.01-10 ms). The formation of the species [Hg{(TRI L9C)(2)(TRI L9C-H)}] is the result of a compromise between the high affinity of Hg(II) to form dithiolate complexes and the preference of the peptide to form a three-stranded coiled coil. 相似文献
178.
In this study, a facultative bacterium that converts fumarate to succinate at a high yield was isolated. The yield of biocon
version was enhanced about 1.2 times by addition of glucose into culture medium at an initial concentration of 6 g/L. When
the initial cell density was high (2 g/L), the succinate produced at pH 7.0 for initial fumarate concentrations of 30, 50,
80, and 100 g/L were 29.3, 40.9, 63.6, and 82.5 g/L, respectively, showing an increase with the initial fumarate concentration.
The high yield of 96.8%/mole of fumarate in just 4 h was obtained at the initial fumarate concentration of 30 g/L. Comparing
these values to those obtained with low cell culture (0.2 g/L), we found that the amount of succinate produced was similar,
but the production rate in the high cell culture was about three times higher than was the case in the low cell culture. This
strain converted fumarate to succinate at a rate of 3.5 g/L·h under the sparge of CO2. 相似文献
179.
Sung-Sik You Hyeong-Won Ryu Young Cho Dae-Young Kim Thong-Sung Ko 《Reaction Kinetics and Catalysis Letters》1999,66(1):121-126
The nonenzymatic hydrolysis of RNA by polyvinylpyrrolidone (PVP) has been investigated. A bell-shaped kinetics was observed
when the first order rate constant of the reaction was ploted as a function of PVP concentration, which means the kinetic
feature of PVP as a degradative receptor distinct from those of degradative enzymes (e.g., ribonuclease). 相似文献
180.
Four different Ni/YSZ cermets were prepared by combining two sets of NiO and YSZ powders of different size. The microstructural
change evolved during the course of electrode adhesion and cell operation was monitored using scanning electron microscopy
(SEM) and energy dispersive spectroscopy (EDS). The anodic activity was compared by analyzing the ∝ impedance spectra of four
Ni/YSZ cermet (H2) / YSZ half cells at 1000 °C. Among the cermets, the one that prepared from the smaller NiO and larger YSZ powder showed
the best anodic performances on aspects of the initial activity and long-term stability. This favorable performance is partly
responsible to the presence of larger YSZ particles which provide a supporting matrix to suppress the microstructural change
against Ni sintering and concomitant volume shrinkage, and partly to an easy formation of Ni channel for electronic conduction.
Anodic performances of the other cermets were also discussed based on their microstructure. 相似文献