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排序方式: 共有114条查询结果,搜索用时 11 毫秒
1.
E. Hatta H. Hosoi H. Akiyama T. Ishii K. Mukasa 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):347-349
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface
by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes
itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is
caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure.
The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There
are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions.
Received: 8 July 1997 / Accepted: 4 November 1997 相似文献
2.
Temperature dependence of ion and water transport in perfluorinated ionomer membranes for fuel cells
To clarify the mechanisms of transport of ions and water molecules in perfluorosulfonated ionomer membranes for fuel cells, the temperature dependence of their transport behaviors was investigated in detail. Two types of Flemion membranes having different equivalent weight values (EW) were utilized along with Nafion 117 as the perfluorinated ionomer membranes, and H-, Li-, and Na-form samples were prepared for each membrane by immersion in 0.03 M HCl, LiCl, and NaCl aqueous solutions, respectively. The ionic conductivity, water self-diffusion coefficient (D(H)(2)(O)), and DSC were measured in the fully hydrated state as a function of temperature. The ionic conductivity of the membranes was reflected by the cation transport through the intermediary of water. Clearly, H(+) transports by the Grotthuss (hopping) mechanism, and Li(+) and Na(+) transport by the vehicle mechanism. The differences of the ion transport mechanisms were observed in the activation energies through the Arrhenius plots. The D(H)(2)(O) in the membranes exhibited a tendency similar to the ionic conductivity for the cation species and the EW value. However, no remarkable difference of D(H)(2)(O) between H- and the other cation-form membranes was observed as compared with the ionic conductivity. It indicates that water in each membrane diffuses almost in a similar way; however, H(+) transports by the Grotthuss mechanism so that conductivity of H(+) is much higher than that of the other cations. Moreover, the D(H)(2)(O) and DSC curves showed that a part of water in the membranes freezes around -20 degrees C, but the nonfreezing water remains and diffuses below that temperature. This fact suggests that completely free water (bulk water) does not exist in the membranes, and water weakly interacting with the cation species and the sulfonic acid groups in secondary and higher hydration shells freezes around -20 degrees C, while strongly binding water in primary hydration shells does not freeze. The ratio of freezing and nonfreezing water was estimated from the DSC curves. The D(H)(2)(O) in the membranes was found to be influenced by the ratio of freezing and nonfreezing water. DFT calculation of the interaction (solvation) energy between the cation species and water molecules suggested that the water content and the ratio of freezing and nonfreezing water depend strongly on the cation species penetrated into the membrane. 相似文献
3.
A glucose electrode was composed of a dissolved oxygen electrode and an immobilized glucose oxidase membrane prepared by plasma polymerization of propargyl alcohol as a monomer. Fairly good precision of the electrode response to sample solutions was obtained by measurements using the steady-state method or the reaction rate method. Activity of the glucose oxidase immobilized within the membrane and mounted on the electrode lasted for 50 consecutive measurements over 5 days, and, if the membrane was stored in a buffer solution of pH 7.0 at a temperature of 0°C, the activity was preserved for more than 2 months. Such immobilization of the glucose oxidase with the plasma polymer effectively suppressed interference from Cu2+ions, which would seriously interrupt oxidation of the glucose in homogeneous solutions, in the sample solutions. 相似文献
4.
Tsuzuki S Tokuda H Hayamizu K Watanabe M 《The journal of physical chemistry. B》2005,109(34):16474-16481
The intermolecular interaction energies of nine ion pairs of room temperature ionic liquids were studied by MP2/6-311G level ab initio calculations. The magnitude of the interaction energies of 1-ethyl-3-methylimidazolium (emim) complexes follows the trend CF(3)CO(2)(-) > BF(4)(-) > CF(3)SO(3)(-) > (CF(3)SO(2))(2)N(-) approximately PF(6)(-) (-89.8, -85.2, -82.6, -78.8, and -78.4 kcal/mol, respectively). The interaction energies of BF(4)(-) complexes with emim, ethylpyridinium (epy), N-ethyl-N,N,N-trimethylammonium ((C(2)H(5))(CH(3))(3)N), and N-ethyl-N-methylpyrrolidinium (empro) are not very different (-85.2, -82.8, -84.6, and -84.4 kcal/mol, respectively), while the size of the orientation dependence of the interaction energies follows the trend emim > epy approximately (C(2)H(5))(CH(3))(3)N > empro. Comparison with the experimental ionic conductivities shows that the magnitude and directionality of the interaction energy of the ion pairs play a crucial role in determining the ionic dissociation/association dynamics in the ionic liquids. The electrostatic interaction is the major source of attraction between ions. The induction contribution is small but not negligible. The hydrogen bonding with the C(2)-H of imidazolium is not essential for the attraction in the ion pair. The interaction energy of the BF(4)(-) complex with 1-ethyl-2,3-dimethylimidazolium (em2im) (-81.8 kcal/mol) is only 4% smaller than that of the emim complex. 相似文献
5.
Abstract— The absorption and emission properties of the photochemically produced dipyrimidine adducts are analyzed at 300 and 77K. Those adducts which have a saturated C(5)—C(6) bond in the pyrimidin-2,4-dione (Pyr) ring and a pyrimidin-2-one (Pyo) ring behave spectroscopically as a substituted Pyo. However, those consisting of one Pyr and one Pyo moiety can be considered as bichromophoric molecules and their spectral properties can be understood in terms of the relative torsional angle between the two rings. The adduct with the most bulky substituents ortho to the torsional bond bears the largest torsional angle and exhibits relatively independent absorption and emission phenomenon. At the other extreme, those adducts with no substituents at this position exist as almost planar molecules and exhibit considerable overlap of absorption bands as well as room temperature fluorescence which, in certain cases, is characteristic of intramolecular exciplex interaction. Using inter-ring torsional angles of ortho-substituted biphenyl molecules as a basis for comparative calculation, quantitative estimates of the torsional angles in dipyrimidine adducts at 300K have been made. 相似文献
6.
Shintaro Wakamatsu Yuka Takahashi Dr. Hidetsugu Tabata Dr. Tetsuta Oshitari Norihiko Tani Prof. Dr. Isao Azumaya Dr. Yukiteru Katsumoto Dr. Takeyuki Tanaka Dr. Shinzo Hosoi Prof. Dr. Hideaki Natsugari Prof. Dr. Hideyo Takahashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(22):7056-7063
The stereochemistry around the N‐benzoylated indole moiety of indometacin was studied by restricting the rotation about the N? C7′ and/or C7′? C1′ bond. In the 2′,6′‐disubstituted ones, an atropisomeric property was found and the atropoisomers were separated and isolated as stable forms. Their biological abilities to inhibit cyclooxygenase‐1 (COX‐1) and cyclooxygenase‐2 (COX‐2) were examined. Only the aR‐isomer showed specific inhibition of COX‐1, and COX‐2 was not inhibited by either atropisomer. Conformational analysis in NMR studies and X‐ray crystallography, and CD spectra in combination with calculations were utilized to elucidate the bioactive conformations. 相似文献
7.
Self‐Replication and Amplification of Enantiomeric Excess of Chiral Multifunctionalized Large Molecules by Asymmetric Autocatalysis
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Prof. Dr. Tsuneomi Kawasaki Mai Nakaoda Yutaro Takahashi Yusuke Kanto Nanako Kuruhara Kenji Hosoi Prof. Dr. Itaru Sato Arimasa Matsumoto Prof. Dr. Kenso Soai 《Angewandte Chemie (International ed. in English)》2014,53(42):11199-11202
Self‐replication of large chiral molecular architectures is one of the great challenges and interests in synthetic, systems, and prebiotic chemistry. Described herein is a new chemical system in which large chiral multifunctionalized molecules possess asymmetric autocatalytic self‐replicating and self‐improving abilities, that is, improvement of their enantioenrichment in addition to the diastereomeric ratio. The large chiral multifunctionalized molecules catalyze the production of themselves with the same structure, including the chirality of newly formed asymmetric carbon atoms, in the reaction of the corresponding achiral aldehydes and reagent. The chirality of the large multifunctionalized molecules controlled the enantioselectivity of the reaction in a highly selective manner to construct multiple asymmetric stereogenic centers in a single reaction. 相似文献
8.
We report the spontaneous emergence of a doubly periodic train of sedimented knolls in a dense suspension. These solidified knolls rise out of, and coexist alongside, a sea of freely flowing liquid in a slowly rotating horizontal bottle. We apply a variable viscosity model that permits simultaneous analysis of fluidlike and solidlike behaviors that are ubiquitous in a variety of sedimenting flows. The model generates qualitative agreement with experiments, and produces new insights into mechanisms by which sedimented structures form. 相似文献
9.
10.
William S. Price Kikuko Hayamizu Yoji Arata 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,126(2):256-265
In this paper, the recently developed “Water-PRESS” method of water suppression [W. S. Price and Y. Arata (1996),J. Magn. Reson. B112,190] in which homospoil pulses are used to manipulate the effects of radiation damping on the water resonance and thereby selectively alter the effective relaxation times of the water resonance with respect to the solute (e.g., biological macromolecules) resonances is further developed and applied. In the present work, methods for optimization in terms of degree of water suppression and in temporal terms (important for the application of Water-PRESS to multidimensional experiments) are considered so that recycle delays of less than 2.3 s (including the acquisition time) are possible. Also, a simple modification which allows the observation of solute resonances with relaxation times similar to that of the water resonance is presented. Finally, the inclusion into more complicated pulse sequences is also discussed. Experimental examples using aqueous samples of lysozyme and immunoglobulin are given. Compared to most other NMR water suppression techniques, this method is extremely simple to implement and optimize and does not require accurately calibrated RF pulses or perfect lineshape. 相似文献