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排序方式: 共有221条查询结果,搜索用时 15 毫秒
51.
Chang-Woo Kwon Tae-Sik Yoon Sung-Soo Yim Sang-Hyun Park Ki-Bum Kim 《Journal of nanoparticle research》2009,11(4):831-839
The effect of excess surfactants (oleic acids) in a colloidal solution on the adsorption behavior of 9.5-nm-sized, sterically
stabilized iron oxide (γ-Fe2O3) nanoparticles on hydrogen terminated Si (Si:H) substrates during a dip-coating process is examined. While the particle coverage
follows a type of Langmuir adsorption isotherm as initially increasing and subsequently saturating with increasing particle
concentration, it also critically depends on the excess surfactant concentration in the solution. For instance, it is noted
that by adding the oleic acids from 0.06 to 2.80 × 1018 ml−1 in the solution with 4.65 × 1013 ml−1 particle concentration, the coverage is gradually reduced from 0.42 to 0.25. In addition, increasing surfactant concentration
distinctly changes the morphology of a self-assembled particle layer from densely distributed smaller clusters to sparsely
connected, larger ones with enlarged space. The reduced coverage and enlarged cluster size with increasing oleic acid concentration
are explained by the reduced interaction energy between particle and substrate and the increased capillary force between particles. 相似文献
52.
Sang Jun Yim 《Tetrahedron letters》2007,48(31):5393-5395
The reaction of aromatic esters with alkynyllithiums in the presence of lithium morpholinide and BF3·OEt2 gave aromatic alkynyl ketones in good yield (78-87%). 相似文献
53.
Prof. Dr. Masakazu Nambo Yasuyo Tahara Dr. Jacky C.-H. Yim Prof. Dr. Cathleen M. Crudden 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(8):1923-1926
A new method for the synthesis of benzhydryl amines from the reaction of readily available sulfone derivatives with amines is described. The Cu-catalyzed desulfonylative amination not only provides structurally diverse benzhydryl amines in good yields, but is also applicable to iterative and intramolecular aminations. Control experiments suggested that the formation of a Cu-carbene intermediate generated from the sulfone substrate, which represents a new route for desulfonylative transformations. 相似文献
54.
Xinfang Xu Yongming Deng David N. Yim Peter Y. Zavalij Michael P. Doyle 《Chemical science》2015,6(4):2196-false
β-Lactam derivatives are produced through intermediate donor–acceptor cyclopropene intermediates in high yield, exclusive cis-diastereoselectivity, and high enantiocontrol in a chiral dirhodium carboxylate catalyzed intramolecular C–H functionalization reaction of enoldiazoacetamides. 相似文献
55.
Unusual hydrogen bonding in water-filled carbon nanotubes 总被引:2,自引:0,他引:2
Byl O Liu JC Wang Y Yim WL Johnson JK Yates JT 《Journal of the American Chemical Society》2006,128(37):12090-12097
We present the first experimental vibrational spectroscopy study providing direct evidence of a water phase inside single-walled carbon nanotubes that exhibits an unusual form of hydrogen-bonding due to confinement. Water adopts a stacked-ring structure inside nanotubes, forming intra- and inter-ring hydrogen bonds. The intra-ring hydrogen bonds are bulk-like while the inter-ring hydrogen bonds are relatively weak, having a distorted geometry that gives rise to a distinct OH stretching mode. The experimentally observed infrared mode at 3507 cm(-1) is assigned to vibrations of the inter-ring OH-groups based on detailed atomic-level modeling. The direct observation of unusual hydrogen bonding in nanotubes has potential implications for water in other highly confined systems, such as biological channels and nanoporous media. 相似文献
56.
Chun‐Ho Wong Lai‐Sheung Choi Sui‐Lung Yim Dr. Kwun‐Ngai Lau Prof. Dr. Hak‐Fun Chow Sin‐Kam Hui Prof. Dr. Kong‐Hung Sze 《化学:亚洲杂志》2010,5(10):2249-2257
Two series of aliphatic hydrocarbon‐based G1–G3 dendritic 2‐ureido‐4‐pyrimidinones (UPy) ( S‐Gn )2 and ( L‐Gn )2, differing from one another by the distance between the branching juncture to the urea end, were prepared and characterized. These hydrocarbon dendrons were also appended to a p‐aminonitrobenzene solvatochromic chromophore in order to probe their microenvironment polarity. While positive solvatochromism was observed which indicated the chromophore was solvent accessible, there was no significant difference between the microenvironment polarities on going from the G1 to the G3 dendrons. The self‐assembling behavior and tautomeric preference of the dendritic UPy derviatives were examined by 1H NMR spectroscopy. The dimerization constants (Kdim*) of the DDAA tautomers were unchanged at 107 M ?1 in CDCl3 at both 25 and 50 °C, which were comparable to those of UPy compounds bearing other nonpolar substitutents. Furthermore, the lower limits on the K′dim* of the DADA tautomeric forms of the ( S‐Gn )2 and ( L‐Gn )2 series were determined to be 106 and 105 M ?1 in CDCl3, respectively. It was found that a closer proximity of the dendron branching juncture to the UPy unit could lead to a destabilization effect on the dimeric states. Hence, the ( L‐Gn )2 dimers are more stable than those of ( S‐Gn )2 in the DDAA form, but the latter are more stable than the former in the tautomeric DADA state. This study showed that both the highly nonpolar microenvironment and the proximity of the dendritic branching juncture to the UPy motif could alter the strength and profile of the hydrogen bond‐mediated self‐assembling process. 相似文献
57.
Ultrasound accelerates the formation of alpha-benzoylbenzyl cyanide and benzoic acid in the reaction of benzyl cyanide with potassium superoxide in the presence of 18-crown-6. Similarly, 4-methylbenzyl cyanide, 4-methoxybenzyl cyanide and 4-chlorobenzyl cyanide gave the corresponding alpha-(4-methylbenzoyl)-4-methylbenzyl cyanide, alpha-(4-methoxybenzoyl)-4-methoxybenzyl cyanide and alpha-(4-chlorobenzoyl)-4-chlorobenzyl cyanide in 25-43% isolated yields under the same reaction conditions. Benzoic, p-toluic, 4-methoxybenzoic and 4-chlorobenzoic acids were also formed in these reactions. No reaction was observed when the mixture was simply stirred. Reflux instead of sonication gave lower yields of the products. However, alpha-alkylbenzyl cyanide produced a high yield of the phenylalkyl ketones when stirred. Interestingly, the corresponding benzoic acid was not formed in these reactions. Possible mechanisms for the formation of alpha-benzoylbenzyl cyanide from benzyl cyanide and phenylalkyl ketones from alpha-alkylbenzyl cyanide are also proposed. 相似文献
58.
59.
Various characteristics of dewetting of thin polystyrene (PS) films absorbed on highly cross-linked epoxy-coated and silicon oxide covered substrates are studied as a function of PS film thickness (20h(c1) whereas the spinodal dewetting (SD) occurs through the growth of surface undulations for hh(c2) while the SD mechanism is observed for h相似文献
60.
Jeongbin Yim Sujeong Kim Gunter Walcher Wolfgang Pfleiderer 《Helvetica chimica acta》1993,76(5):1970-1979
The nonenzymatic synthesis of aurodrosopterin ( 5 ) from 6-acetyl-2-amino-3, 7, 8, 9-tetrahydro-4H-pyrimido-[4,5-b][1,4]diazepin-4-one ( 3 ) and 7,8-dihydrolumazine ( 4 ) at pH 3 (HCl) was performed. The identity of the synthesized compound with the natural eye pigment isolated from drosophila heads was confirmed by thin-layer chromatography on cellulose and by comparisons of the 1H-NMR and UV/VIS spectra. The nonenzymatic synthesis of a neodrosopterin-like red pigment from 3 and 2,4-diamino-7,8-dihydropteridine was also carried out, but its identity could not be established. This pigment, called aminodrosopterin, has an absorption peak at 489 nm, which is very close to that of neodrosopterin. 相似文献