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91.
The behavior of methane hydrate was investigated after it was pressurized with helium or nitrogen gas in a test system by monitoring the gas compositions. The results obtained indicate that even when the partial pressure of methane gas in such a system is lower than the equilibrium pressure at a certain temperature, the dissociation rate of methane hydrate is greatly depressed by pressurization with helium or nitrogen gas. This phenomenon is only observed when the total pressure of methane and helium (or nitrogen) gas in the system is greater than the equilibrium pressure required to stabilize methane hydrate with just methane gas. The following model has been proposed to explain the observed phenomenon: (1) Gas bubbles develop at the hydrate surface during hydrate dissociation, and there is a pressure balance between the methane gas inside the gas bubbles and the external pressurizing gas (methane and helium or nitrogen), as transmitted through the water film; as a result the methane gas in the gas bubbles stabilizes the hydrate surface covered with bubbles when the total gas pressure is greater than the equilibrium pressure of the methane hydrate at that temperature; this situation persists until the gas in the bubbles becomes sufficiently dilute in methane or until the surface becomes bubble-free. (2) In case of direct contact of methane hydrate with water, the water surrounding the hydrate is supersaturated with methane released upon hydrate dissociation; consequently, methane hydrate is stabilized when the hydrostatic pressure is above the equilibrium pressure of methane hydrate at a certain temperature, again until the dissolved gas at the surface becomes sufficiently dilute in methane. In essence, the phenomenon is due to the presence of a nonequilibrium state where there is a chemical potential gradient from the solid hydrate particles to the bulk solution that exists as long as solid hydrate remains. 相似文献
92.
Glass Formation of a Coordination Polymer Crystal for Enhanced Proton Conductivity and Material Flexibility 下载免费PDF全文
Dr. Wenqian Chen Dr. Satoshi Horike Dr. Daiki Umeyama Naoki Ogiwara Tomoya Itakura Dr. Cédric Tassel Yoshihiro Goto Prof. Hiroshi Kageyama Prof. Susumu Kitagawa 《Angewandte Chemie (International ed. in English)》2016,55(17):5195-5200
The glassy state of a two‐dimensional (2D) Cd2+ coordination polymer crystal was prepared by a solvent‐free mechanical milling process. The glassy state retains the 2D structure of the crystalline material, albeit with significant distortion, as characterized by synchrotron X‐ray analyses and solid‐state multinuclear NMR spectroscopy. It transforms to its original crystal structure upon heating. Thus, reversible crystal‐to‐glass transformation is possible using our new processes. The glass state displays superior properties compared to the crystalline state; specifically, it shows anhydrous proton conductivity and a dielectric constant two orders of magnitude greater than the crystalline material. It also shows material flexibility and transparency. 相似文献
93.
Hiroshi Masai Dr. Jun Terao Dr. Tetsuaki Fujihara Dr. Yasushi Tsuji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6624-6630
We describe a new concept for rotaxane synthesis through intramolecular slippage using π‐conjugated molecules as rigid axles linked with organic soluble and flexible permethylated α‐cyclodextrins (PM α‐CDs) as macrocycles. Through hydrophilic–hydrophobic interactions and flipping of PM α‐CDs, successful quantitative conversion into rotaxanes was achieved without covalent bond formation. The rotaxanes had high activation barrier for their de‐threading, so that they were kinetically isolated and derivatized even under conditions unfavorable for maintaining the rotaxane structures. 1H NMR spectroscopy experiments clearly revealed that the restricted motion of the linked macrocycle with the rigid axle made it possible to control the kinetic stability by adjusting the length of the rigid axle in the precursor structure rather than the steric bulkiness of the stopper unit. 相似文献
94.
Prof. Dr. Katsuhiro Isozaki Tomoya Yokoi Ryota Yoshida Dr. Kazuki Ogata Dr. Daisuke Hashizume Dr. Nobuhiro Yasuda Prof. Dr. Koichiro Sadakane Prof. Dr. Hikaru Takaya Prof. Dr. Masaharu Nakamura 《化学:亚洲杂志》2016,11(7):1076-1091
Two (ONO pincer)ruthenium‐complex‐bound norvalines, Boc?[Ru(pydc)(terpy)]Nva?OMe ( 1 ; Boc=tert‐butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc?[Ru(pydc)(tBu‐terpy)]Nva?OMe ( 5 ), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single‐crystal X‐ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high‐temperature conditions enabled us to perform selective transformations of the N‐Boc and C?OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru‐bound norvaline, n‐C11H23CO?l ‐[Ru(pydc)(terpy)]Nva?NH‐n‐C11H23 (l ‐ 4 ) was found to have excellent self‐assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru‐bound norvaline l ‐ 1 exhibited a higher catalytic activity for the oxidation of alcohols by H2O2 than parent complex [Ru(pydc)(terpy)] ( 11 a ). 相似文献
95.
Imaging of Oxygen Diffusion in Individual Platinum/Ce2Zr2Ox Catalyst Particles During Oxygen Storage and Release 下载免费PDF全文
Dr. Hirosuke Matsui Dr. Nozomu Ishiguro Kaori Enomoto Dr. Oki Sekizawa Prof. Dr. Tomoya Uruga Prof. Dr. Mizuki Tada 《Angewandte Chemie (International ed. in English)》2016,55(39):12022-12025
The spatial distribution of Ce3+ and Ce4+ in each particle of Ce2Zr2Ox in a three‐way conversion catalyst system was successfully imaged during an oxygen storage/release cycle by scanning X‐ray absorption fine structure (XAFS) using hard X‐ray nanobeams. For the first time, nano‐XAFS imaging visualized and identified the modes of non‐uniform oxygen diffusion from the interface of Pt catalyst and Ce2Zr2Ox support and the active parts in individual catalyst particles. 相似文献
96.
Matrix isolation infrared spectroscopy has been applied to study an ozone-water complex of atmospheric interest. The complex was identified in the spectral region of three normal modes of ozone and water. Ab initio calculation at MP4(SDQ), QCISD, and CCSD(T) levels indicates the existence of only one stable conformer, which accords with the present experimental result. This conformer belongs to the Cs symmetry group where two molecular planes of ozone and water are perpendicular to the Cs symmetry plane. The binding energy was calculated to be 1.89 kcal/mol at the CCSD(T)/6-311++G(3df,3pd)//CCSD(T)/6-311++G(d,p) level of theory. The formation constant and atmospheric abundance of the ozone-water complex are estimated using the thermodynamic and spectroscopic data obtained. 相似文献
97.
Haruko Ikeuchi Kaoru Naganuma Marie Ichikawa Hiromichi Ozawa Tomoya Ino Makoto Sato Hiroko Yonezawa Sonomi Mukaida Akihiro Yamamoto Takeshi Hashimoto 《Journal of solution chemistry》2007,36(10):1243-1259
The diffusion coefficients of several tris(β-diketonato) ruthenium complexes in acetonitrile solutions containing a supporting electrolyte were determined by chronoamperometry.
The diffusion coefficients of the charged complexes, which were produced by electrochemical oxidation or reduction, were also
determined by double potential step chronoamperometry. Two kinds of radii of the complexes were evaluated. One was the Van
der Waals radius and the other was the geometric distance from the center of the complex to the outer surface of the farthest
atom. The latter quantity was determined from X-ray diffractometric data. The diffusion coefficients of the neutral complexes
were discussed on the basis of the Stokes-Einstein equation. Those of charged complexes could not be explained by the theoretical
equation presented by Hubbard and Onsager. 相似文献
98.
Prof. Dr. Kosei Ueno Prof. Dr. Tomoya Oshikiri Prof. Dr. Hiroaki Misawa 《Chemphyschem》2016,17(2):194-194
The front cover artwork is provided by the group of Prof. Hiroaki Misawa (Hokkaido University, Japan, and National Chiao Tung University, Taiwan). The image shows a plasmon‐induced water‐splitting system, which can collect hydrogen and oxygen separately and employs a semiconductor substrate. Read the full text of the Review at 10.1002/cphc.201500761 相似文献
99.
Yuki Kanazawa Prof. Hayato Tsuji Prof. Masahiro Ehara Prof. Ryoichi Fukuda Dr. Deborah L. Casher Prof. Kohei Tamao Prof. Hiroshi Nakatsuji Prof. Josef Michl 《Chemphyschem》2016,17(19):3010-3022
The photophysical properties of oligosilanes show unique conformational dependence due to σ‐electron delocalization. The excited states of the SAS, AAS, and AEA conformations of peralkylated n‐hexasilanes, in which the SiSiSiSi dihedral angles are controlled into a syn (S), anti (A), or eclipsed (E) conformation, were investigated by using UV absorption, magnetic circular dichroism (MCD), and linear dichroism spectroscopy. Simultaneous Gaussian fitting of all three spectra identified a minimal set of transitions and the wavenumbers, oscillator strengths, and MCD B terms in all three compounds. The results compare well with those obtained by using the symmetry‐adapted‐cluster configuration interaction method and almost as well with those obtained by time‐dependent density functional theory with the PBE0 functional. The conformational dependence of the transition energies and other properties of free‐chain permethylated n‐hexasilane, n‐Si6Me14, was also examined as a function of dihedral angles, and the striking effects found were attributed to avoided crossings between configurations of σσ* and σπ* character. 相似文献
100.
[reaction: see text] On treatment of 5-siloxyhexa-1,2,5-trienes with a catalytic amount of W(CO)(6) under photoirradiation, formal Cope rearrangement proceeded to give 2-siloxyhex-1-en-5-ynes in good yield. The electrophilic activation of the allenyl moiety by W(CO)(5) triggers the intramolecular attack of the silyl enol ether in a 6-endo manner to produce a cyclohexenyl tungsten species. Carbon-carbon bond cleavage occurs by electron donation from the anionic W(CO)(5) into the silyloxonium moiety to afford the products with regeneration of the W(CO)(5)(L). 相似文献