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31.
The time evolution of the density fluctuation of molecules is investigated by dynamic light scattering in six neat fluids in supercritical states. This study is the first to compare the dynamics of density inhomogeneity between hydrogen- and non-hydrogen-bonded fluids. Supercritical methanol and ethanol are used as hydrogen-bonded fluids, whereas four non-hydrogen-bonded fluids were used: CHF(3), C(2)H(4), CO(2), and Xe. We measure the time correlation function of the density fluctuation of each fluid at the same reduced temperatures and densities and investigate the relationship between the dynamic and static density inhomogeneities of those supercritical fluids. In all cases, the profile of the time correlation function of the density fluctuation is characterized by a single-exponential function, whose decay is responsible for the dynamics characterized by hydrodynamic conditions. We obtain correlation times from the time correlation function and discuss dynamic and static inhomogeneity using the Kawasaki theory and the Landau-Placzek theory. While the correlation times in the six fluids show noncoincidence, those values agree well with each other except for the supercritical alcohols when scaled to a dimensionless parameter. Although the principle of corresponding state is observed in the non-hydrogen-bonded fluids, both the supercritical methanol and ethanol deviate from that principle. This deviation is attributed to the presence of hydrogen bonding among alcohol molecules at high temperature and low density. The average cluster size of each fluid is estimated under the same thermodynamic conditions, and it is shown that the clusters of supercritical alcohols are on average 1.5-1.7 times larger than those of the four non-hydrogen-bonded fluids. Moreover, the thermal diffusivity of each neat fluid is obtained over wide ranges of density and temperature. 相似文献
32.
Yasushi Mizobe Reiko Ono Yasuzo Uchida Masanobu Hidai Meguru Tezuka Suehiro Moue Atsuhiko Tsuchiya 《Journal of organometallic chemistry》1980,204(3):377-385
Diazoalkane complexes of type [MF(NNCRR′)(dpe)2][BF4] (M = Mo or W; dpe = Ph2PCH2CH2PPh2), which are easily derived from bis(dinitrogen) complexes [M(N2)2(dpe)2], undergo consecutive one- and two-electron oxidations and reductions under voltammetric conditions at a platinum electrode. The ESR spectra of the species generated by the controlled potential electrolysis show that primary oxidation occurred on the metal atom (M = Mo) and reduction on the two nitrogen atoms in the diazoalkane ligands (M = Mo or W). 相似文献
33.
Masahiko Ishikawa Ken-ichi Okamoto Jinsai Hidaka Hisahiko Einaga 《Helvetica chimica acta》1985,68(7):2015-2021
Substitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine)-glycinatocobalt(III) complex has been studied in the presence of photo-excited tris(2,2′-bipyridine)ruthenium(II) complex in alkaline aqueous solution (buffered around pH 12) containing 1.0M chloride ion at 25°C. VIS absorption and CD spectra were used for the racemate and the optically active isomers of the Co(III) complexes, respectively. The reaction was catalyzed by the excited Ru(II) complex to give tris(ethylenediamine)cobalt(III) complex. Mechanism of the ligand-substitution reaction and role of the excited Ru(II) complex were discussed. 相似文献
34.
Doi H Sakai T Iguchi M Yamada K Tomioka K 《Journal of the American Chemical Society》2003,125(10):2886-2887
The external chiral ligand-controlled asymmetric conjugate addition reaction of lithium amides with alpha,beta-unsaturated esters provided beta-amino esters in high yields and high enantioselectivities. 相似文献
35.
36.
Dipping versus spraying: exploring the deposition conditions for speeding up layer-by-layer assembly
Izquierdo A Ono SS Voegel JC Schaaf P Decher G 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7558-7567
Polyelectrolyte film fabrication by successive spraying of polycation and polyanion solutions is described and compared to classic dipping. The poly(styrenesulfonate)/poly(allylamine) system is examined in detail. The influence of various parameters such as spraying time, polyelectrolyte concentration, and effect of film drying during multilayer construction is investigated. It is found that film deposition by spraying is easily controlled and very reliable. The thickness of the multilayers grows linearly with the number of deposition cycles similarly to what is observed when dipping substrates or when polyelectrolyte solutions flow over a surface. The assembly of films is very fast and leads to films with small surface roughness as estimated by atomic force microscopy and X-ray reflectometry. Spray deposition allows achieving regular multilayer growth even under conditions for which dipping fails to produce homogeneous films (e.g., extremely short contact times). Moreover, because drainage constantly removes a certain quantity of the excess material arriving at the surface, one can even skip the rinsing step and, thus, speed up even further the whole buildup process. 相似文献
37.
Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption. 相似文献
38.
Yoshizawa M Ono K Kumazawa K Kato T Fujita M 《Journal of the American Chemical Society》2005,127(31):10800-10801
Two molecules of planar MII(acac)2 complexes (M = Pt, Pd, and, Cu; acac = acetylacetonato) are efficiently stacked within an organic-pillared coordination cage, exhibiting characteristic spectroscopies (for M = Pt and Pd) and electron spin-spin coupling (for M = Cu) attributable to metal-metal interaction. 相似文献
39.
Takao K Yasui H Yamamoto S Sasaki D Kawasaki S Watanabe G Tadano K 《The Journal of organic chemistry》2004,69(25):8789-8795
The total syntheses of (+)-mycoepoxydiene and (-)-1893A have been completed. The present synthetic strategy features the use of one-pot ring-opening/cross metathesis (ROM/CM) followed by a ring-closing metathesis (RCM) reaction, allowing for the concise construction of the 9-oxabicyclo[4.2.1]nona-2,4-diene framework from a 7-oxabicyclo[2.2.1]hept-2-ene derivative and 1,3-butadiene. The sequential metathesis product was converted into (+)-mycoepoxydiene through the oxidative rearrangement of a furfuryl alcohol to a pyranone, thereby establishing its absolute stereochemistry. From the common intermediate, a structurally related natural product (-)-1893A was also synthesized via the vinylogous aldol reaction. 相似文献
40.
The crystal habit of fcc metal particles formed on an amorphous carbon film electrode in solution at different electrode
potentials is discussed. The fcc metal particles have different crystallographic habits depending on applied electrode potential;
that is, icosahedral and/or decahedral particles are formed at lower potentials, and fcc single-crystalline or polycrystalline
particles at higher potentials. It was found that decahedra and icosahedra of Cu-Au alloy particles are formed in the potential
region of underpotential deposition (UPD) of Cu at which only fcc Au single-crystalline particles and Au polycrystalline particles
appear. This is attributed to the charge transfer from the UPD Cu ions to the Au overlayer of Cu-Au alloy particles. The formation
of decahedral and icosahedral Cu-Au alloy particles depends on the composition of the Cu-Au alloy. On the basis of these results
it was deduced that the contraction of the surface lattice of the growing particles is responsible for the formation of icosahedral
and decahedral particles.
Received: 25 February 1997 / Accepted: 21 April 1997 相似文献