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151.
Peterca M Imam MR Ahn CH Balagurusamy VS Wilson DA Rosen BM Percec V 《Journal of the American Chemical Society》2011,133(7):2311-2328
The synthesis, structural, and retrostructural analysis of two libraries containing 16 first and second generation C(3)-symmetric self-assembling dendrimers based on dendrons connected at their apex via trisesters and trisamides of 1,3,5-benzenetricarboxylic acid is reported. A combination of X-ray diffraction and CD/UV analysis methods demonstrated that their C(3)-symmetry modulates different degrees of packing on the periphery of supramolecular structures that are responsible for the formation of chiral helical supramolecular columns and spheres self-organizable in a diversity of three-dimensional (3D) columnar, tetragonal, and cubic lattices. Two of these periodic arrays, a 3D columnar hexagonal superlattice and a 3D columnar simple orthorhombic chiral lattice with P222(1) symmetry, are unprecedented for supramolecular dendrimers. A thermal-reversible inversion of chirality was discovered in helical supramolecular columns. This inversion is induced, on heating, by the change in symmetry from a 3D columnar simple orthorhombic chiral lattice to a 3D columnar hexagonal array and, on cooling, by the change in symmetry from a 2D hexagonal to a 2D centered rectangular lattice, both exhibiting intracolumnar order. A first-order transition from coupled columns with long helical pitch, to weakly or uncorrelated columns with short helical pitch that generates a molecular rotator, was also discovered. The torsion angles of the molecular rotator are proportional to the change in temperature, and this effect is amplified in the case of the C(3)-symmetric trisamide supramolecular dendrimers forming H-bonds along their column. The structural changes reported here can be used to design complex functions based on helical supramolecular dendrimers with different degree of packing on their periphery. 相似文献
152.
Abstract The rate of sulfonation of bead copolymers of styrene cross-linked with 8 mole % divinylbenzene (mixed isomers) is remarkably sensitive to the isomeric (para/meta) composition of the mixture of divinylbenzenes. The rate is enhanced by a factor of 4 for compositions containing 20–40% para isomer. 相似文献
153.
Liu Q Hong IP Ahn MJ Yoo HS Han SB Hwang BY Lee MK 《Natural product communications》2011,6(12):1839-1841
Inhibition of adipocytes differentiation is suggested to be an important strategy for prevention and/or treatment of obesity. In our present study, Cordyceps militaris showed significant inhibitory activity on adipocyte differentiation in 3T3-L1 preadipocytes as assessed by measuring fat accumulation using Oil Red O staining. Activity-guided fractionation led to the isolation of cordycepin (1), guanosine (2) and tryptophan (3) as active compounds. All the three compounds were more effective in the prevention of early stage of adipogenesis than in lipolysis. In addition, combinational treatment of three compounds significantly increased anti-adipogenic activity. 相似文献
154.
155.
Sang-Woo Bae Kihun Ahn Yoon-Mo Koo Sung Ho Ha 《Applied biochemistry and biotechnology》2013,171(5):1289-1298
Ionic liquids (ILs) are molten salts which do not crystallize at room temperature. Tunable physicochemical properties of ILs including hydrophobicity and polarity facilitate their applications in many biological processes. In this study, a copper-based IL was employed in order to enhance the refolding efficiency of laccase from Trametes versicolor which requires copper as a cofactor. When 1-ethyl-3-methylimidazolium trichlorocuprate ([EMIM][CuCl3]) was added to refolding buffer instead of urea, the laccase refolding yield was improved more than 2.7 times compared to the conventional refolding buffer which contains urea. When the refolding of laccase was carried out at different temperatures (4, 25, and 37 °C), the highest refolding yield was obtained at 25 °C. At low temperature, two conflicting effects, i.e., suppression of the aggregate formation and decrease of folding rate, influence the protein refolding. In contrast, a copper-based IL did not enhance the refolding of lysozyme, a non-copper-containing protein. From these results, we can conclude that this copper-based IL, [EMIM][CuCl3], was exclusively effective on the refolding process of a copper-containing protein. 相似文献
156.
Zaesung No Shi Yong Ryu Seong-Kie Kim Jong Woong Ahn Bok Ju Song Keun Jae Kim 《合成通讯》2013,43(5):887-892
Thermal or base-promoted conversion of 5′-O-TBDMS-3′-O-(1H-imidazole-1-thiocarbonyl)thymidine (1) afforded 5′-O-TBDMS-2,3′-anhydro-thymidine (2), a pivotal intermediate for the transformation of the 3′-hydroxy group of 2′-deoxyribonucleosides, in high yield. 相似文献
157.
The palladium-catalyzed arylation and vinylation of 2,3-dihydrofuran with aryl and alkenyl iodonium salts afforded 2-phenyl- or 2-alkenyl-2,5-dihydrofurans at room temperature in an aqueous medium. 相似文献
158.
Marimuthu M Kandasamy K Ahn CG Sung GY Kim MG Kim S 《Analytical and bioanalytical chemistry》2011,401(5):1645-1653
Complementary metal oxide semiconductor (CMOS)-based image sensors have received increased attention owing to the possibility
of incorporating them into portable diagnostic devices. The present research examined the efficiency and sensitivity of a
CMOS image sensor for the detection of antigen–antibody interactions involving interferon gamma protein without the aid of
expensive instruments. The highest detection sensitivity of about 1 fg/ml primary antibody was achieved simply by a transmission
mechanism. When photons are prevented from hitting the sensor surface, a reduction in digital output occurs in which the number
of photons hitting the sensor surface is approximately proportional to the digital number. Nanoscale variation in substrate
thickness after protein binding can be detected with high sensitivity by the CMOS image sensor. Therefore, this technique
can be easily applied to smartphones or any clinical diagnostic devices for the detection of several biological entities,
with high impact on the development of point-of-care applications. 相似文献
159.
Moo-Jin Kim Soo-Hyun Chang Jung-Sik Choi Wha-Seung Ahn 《Reaction Kinetics and Catalysis Letters》2004,82(1):27-32
Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al2O3 catalyst exhibited much better catalytic activity than the Rh-Ni/-Al2O3 catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe3O4—Cr2O3) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
160.
A gas chromatographic–mass spectrometric method has been developed for rapid and sensitive determination of odorous compounds in water. The water sample (200 mL), at pH 6.5, was extracted with 1 mL pentane in a 250-mL separatory funnel. Fluorobenzene was added to the water sample as internal standard and the solution was mechanically shaken for 5 min and analyzed by GC–MS, with selected ion monitoring, without further concentration or purification steps. The peaks had good chromatographic properties and extraction of the compounds from water resulted in relatively high recoveries with small variations. The detection limits of the assay were 0.1 ng L–1 for 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, and geosmin, 0.5 ng L–1 for anisole, and 1.0 ng L–1 for 2,4,6-trichloroanisole and trans, trans-2,4-heptadienal. Turn-around time was one day for up to approximately 40 samples. The method is simple, convenient, and can be learned easily by relatively inexperienced personnel. It was used to analyze seven odorous compounds in water from Decheung-Lake in Korea, and raw and treated water originating from the same lake. In the summer of 2001 significant levels of anisole (up to 225 ng L–1) were observed, and geosmin and 2-methylisoborneol were detected at concentrations of up to 23.8 and 26.7 ng L–1, respectively. 2-Isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, and trans, trans-2,4-heptadienal levels during that period were not significant. The method can used for simultaneous detection of several odorous compounds in water. 相似文献