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排序方式: 共有103条查询结果,搜索用时 31 毫秒
1.
Noncatalytic reaction pathways and rates of dimethyl ether (DME) in supercritical water are determined in a tube reactor made of quartz according to liquid- and gas-phase 1H and 13C NMR observations. The reaction is studied at two concentrations (0.1 and 0.5 M) in supercritical water at 400 degrees C and over a water-density range of 0.1-0.6 g/cm3. The supercritical water reaction is compared with the neat one (in the absence of solvent) at 0.1 M and 400 degrees C. DME is found to decompose through (i) the proton-transferred fragmentation to methane and formaldehyde and (ii) the hydrolysis to methanol. Formaldehyde from reaction (i) is consecutively subjected to four types of redox reactions. Two of them proceed even without solvent: (iii) the unimolecular proton-transferred decarbonylation forming hydrogen and carbon monoxide and (iv) the bimolecular self-disproportionation generating methanol and carbon monoxide. When the solvent water is present, two additional paths are open: (v) the bimolecular self-disproportionation of formaldehyde with reactant water, producing methanol and formic acid, and (vi) the bimolecular cross-disproportionation between formaldehyde and formic acid, yielding methanol and carbonic acid. Methanol is produced through the three types of disproportionations (iv)-(vi) as well as the hydrolysis (ii). The presence of solvent water decelerates the proton-transferred fragmentation of DME; the rate constant is reduced by 40% at 0.5 g/cm3. This is caused by the suppression of low-frequency concerted motion corresponding to the reaction coordinate for the simultaneous C-O bond scission and proton transfer from one methyl carbon to the other. In contrast to the proton-transferred fragmentation, the hydrolysis of DME is markedly accelerated by increasing the water density. The latter becomes more important than the former in supercritical water at densities greater than 0.5 g/cm3. 相似文献
2.
Mesoporous Silica Particles as Topologically Crosslinking Fillers for Poly(N‐isopropylacrylamide) Hydrogels
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Prof. Nobuyoshi Miyamoto Kotaro Shimasaki Kosuke Yamamoto Morio Shintate Yuichiro Kamachi Dr. Bishnu Prasad Bastakoti Dr. Norihiro Suzuki Dr. Ryuhei Motokawa Prof. Yusuke Yamauchi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):14955-14958
Here it is demonstrated that mesoporous silicas (MPSs) can be used as effective “topological crosslinkers” for poly(N‐isopropylacrylamide) (PNIPA) hydrogels to improve the mechanical property. Three‐dimensional bicontinuous mesporous silica is found to effectively reinforce the PNIPA hydrogels, as compared to nonporous silica and two‐dimensional hexagonally ordered mesoporous silica. 相似文献
3.
Ganesh Shenoy Jessica Ettedgui Chandrasekhar Mushti Jennifer Hong Kelly Lane Burchelle Blackman Hak-Sung Jung Yasuharu Takagi Yeonee Seol Martin Brechbiel Rolf E. Swenson Keir C. Neuman 《Molecules (Basel, Switzerland)》2022,27(3)
Carboxylic acid is a commonly utilized functional group for covalent surface conjugation of carbon nanoparticles that is typically generated by acid oxidation. However, acid oxidation generates additional oxygen containing groups, including epoxides, ketones, aldehydes, lactones, and alcohols. We present a method to specifically enrich the carboxylic acid content on fluorescent nanodiamond (FND) surfaces. Lithium aluminum hydride is used to reduce oxygen containing surface groups to alcohols. The alcohols are then converted to carboxylic acids through a rhodium (II) acetate catalyzed carbene insertion reaction with tert–butyl diazoacetate and subsequent ester cleavage with trifluoroacetic acid. This carboxylic acid enrichment process significantly enhanced nanodiamond homogeneity and improved the efficiency of functionalizing the FND surface. Biotin functionalized fluorescent nanodiamonds were demonstrated to be robust and stable single-molecule fluorescence and optical trapping probes. 相似文献
4.
Morita H Kawaguchi H Yoshimura T Tsukurimichi E Shimasaki C Horn E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(21):3976-3983
5-(N-p)-Toluenesulfonyl)iminothianthrenes, whose sulfur atoms are oxidized to a sulfoxide or sulfone at the 10-position, were hydrolysed readily in high yield to N-unsubstituted-sulfilimines by using concentrated H2SO4. During hydrolysis, 10-monoxy-5-N-unsubstituted-sulfilimines were obtained as a separable mixture of the cis and trans isomers. The stereochemical interconversion of these compounds was studied under both hydrolytic and thermal conditions and their structures were elucidated by using X-ray crystallography. 相似文献
5.
Osamu Sugino Ikutaro Hamada Minoru Otani Yoshitada Morikawa Tamio Ikeshoji Yasuharu Okamoto 《Surface science》2007,601(22):5237-5240
First-principles molecular dynamics simulations have been carried out for water in contact with Pt(1 1 1) surface. To apply negative bias potential to the water/Pt interface, excess electrons were added to our slab model using the recently developed computational scheme called “effective screening medium (ESM)”. Water molecules located away from the surface reoriented themselves to screen the electric field, but they responded differently near the surface. Water molecules nearest to the surface, forming a distinct layered structure with the hydrogen atom directed to the surface, increased the density with increasing field. On these bases, we discuss microscopic aspects of the electric double layer. 相似文献
6.
Yasuharu Yoshimi Kosuke Kobayashi Keisuke Nishikawa Kousuke Maeda Tatsuya Itou Minoru Hatanaka 《Tetrahedron letters》2010,51(17):2332-6179
Radical addition to a glyoxylic oxime ether was accomplished under mild conditions using an alkyl radical generated from a free carboxylic acid via photochemical decarboxylation. The photoreaction provided an efficient route to α-substituted α-aminoesters from carboxylic acids and oxime ether. 相似文献
7.
Hitoshi Shimasaki Makoto Tsutsumi 《International Journal of Infrared and Millimeter Waves》1989,10(9):1131-1138
Conclusions We have analyzed coupling properties of the coupled microstrip lines whose substrate contain electron-hole plasma by means of the spectral domain method. Scattering parameters in each ports have been evaluated numerically as a function of plasma density.Experiments were carried out using high resistivity silicon and LEDs. The agreement of the theoretical and experimental results was satisfactory. The plasma density observed in the experiments is one-third as large as the theoretically estimated value. 相似文献
8.
The boundary contraction method is generalized in such a way that it is applicable to the Neumann and mixed boundary value problems over regions of irregular shape. Various variants of mixed boundary value problems can be solved numerically in a unified way with mesh points fewer than those required of ADI and SOR. The method is not iterative and therefore does not require the positive definiteness of eigenvalues which is the necessary condition of the stability of ADI and SOR. The method is also applicable to exterior problems. Thus the applicability of the contraction method to problems of practical importance is substantially improved. 相似文献
9.
A statistical theory is proposed for the calculation of the total capture cross section of a neutrino by a nucleus. Close references are made to the statistical theory of β-decay and electron capture developed by Yamada and his collaborators. As a test of the theory, we calculate the total cross section for the capture of a solar neutrino by a 37Cl nucleus. 相似文献
10.
Sakai K Koyata Y Shimada N Shibata K Hanamaki Y Itakura S Yagi T Hirano Y 《Optics letters》2008,33(5):431-433
We developed a new master-oscillator power-amplifier scheme consisting of a tapered semiconductor amplifier and a fiber-grating-stabilized laser diode for efficient green-light generation in a planar MgO:PPLN waveguide, and demonstrated cw green-light generation of 346 mW. 相似文献