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111.
The mechanism of the ion permeation is investigated for an anion-doped carbon nanotube, as a model of the K+ channel, by analyzing the free energy surface and the dynamics of the ion permeation through the model channel. It is found that the main rate-determining step is how an ion enters the channel. The entrance of the ion is mostly blocked by a water molecule located at this entrance. Only about 10% of K+ ions which reach the mouth of the channel can really enter the channel. The rejection rate sensitively depends on the location of this water molecule, which is easily controlled by the charge of the carbon nanotube; for example, the maximum permeation is obtained when the anion charge is at a certain value, -5.4e in the present model. At this charge, the facile translocation of the ion inside the channel is also induced due to the number of fluctuations of the ions inside the channel. Therefore, the so-called "Newton's balls", a toy model, combined with a simple ion diffusion model for explaining the fast ion permeation should be modified. The present analysis thus suggests that there exists an optimum combination of the length and the charge of the carbon nanotube for the most efficient ion permeation. 相似文献
112.
We propose a new oxidation rate equation for silicon supposing only a diffusion of oxidizing species but not including any rate-limiting step by interfacial reaction. It is supposed that diffusivity is suppressed in a strained oxide region near SiO(2)/Si the interface. The expression of a parabolic constant in the new equation is the same as that of the Deal-Grove model, while a linear constant makes a clear distinction with that of the model. The estimated thickness using the new expression is close to 1 nm, which compares well with the thickness of the structural transition layers. 相似文献
113.
A formal synthesis of the telomerase inhibitory marine pyrrolocarbazole alkaloid dictyodendrin B is described. The key features are consecutive palladium-catalyzed cross-coupling reactions and intramolecular reductive coupling reaction to construct the pyrrolo[2,3-c]carbazole framework. 相似文献
114.
Iwao Sugimoto Masumi Okamoto Kazuhiko Takahashi 《Polymer Degradation and Stability》2010,95(6):929-934
Carbonaceous films with microcolumnar layer have been prepared by radio-frequency sputtering of polysaccharides pectin. The repeated sputtering has developed the densely packed seamless microcolumns, which are separated by the narrow grooves. The residual film stress has formed the honeycomb-patterned ridges. X-ray photoelectron spectroscopy and energy dispersion spectroscopy revealed the inclusion of nitrogen in the film constituents. The film surface is hydrophilic mainly due to the polar functional groups, such as the carboxyl and amino groups. Nitrogen adsorption measurement revealed that the specific surface area of the film was no less than 109 m2/g. Impedance analysis of the film-coated quartz crystal resonator clarified that the film had the higher adsorption capacities to the polar and cohesive vapors, such as ethyl alcohol. The adsorption of organic vapors has not induced the viscoelastic changes in the film. 相似文献
115.
116.
[reaction: see text] New monodentate phosphite ligands have been developed from axially chiral biphenols, which show excellent enantioselectivity in the Rh(I)-catalyzed hydrogenation of dimethyl itaconate. The new chiral ligand system is suitable to create libraries and possesses fine-tuning capability. 相似文献
117.
Iwao?KatayamaEmail author Yoshihiro?Suzuki Yoshiaki?Yamamoto Toshio?Oishi 《Monatshefte für Chemie / Chemical Monthly》2005,136(11):1955-1961
Summary. The EMF of galvanic cells with stabilized zirconia solid electrolyte was measured to determine the activity of indium in solid
Ni–In alloys in the temperature range of 970–1170 K and composition range of 5–55 mol% In. Activity of indium increases sharply
in the ζ phase and Ni13In9 phase. The activity values are compared with literature data. 相似文献
118.
Dehydrotripeptides, X-CH(Ri)-ΔPhe-CH(Rk)COOMe (: X = tBOC-NH,CBZ-NH, CF3CONH and N3), were employed for the asymmetric hydrogenation catalyzed by chiral rhodium complexes and it was found that tBOC- brought about by far the best results. Stereoselective dideuteration of a tBOC- was successfully performed. 相似文献
119.
Ojima I Vu AT Lee SY McCullagh JV Moralee AC Fujiwara M Hoang TH 《Journal of the American Chemical Society》2002,124(31):9164-9174
The reaction of a 1,6-enyne with a hydrosilane catalyzed by Rh(acac)(CO)(2), Rh(4)(CO)(12), or Rh(2)Co(2)(CO)(12) under ambient CO atmosphere or N(2) gives 2-methyl-1-silylmethylidene-2-cyclopentane or its heteroatom congener in excellent yield through silylcarbocycization (SiCaC) process. The same reaction, but in the presence of a phosphite such as P(OEt)(3) and P(OPh)(3) under 20 atm of CO, affords the corresponding 2-formylmethyl-1-silylmethylidene-2-cyclopentane or its heteroatom congener with excellent selectivity through carbonylative silylcarbocycization (CO-SiCaC) process. The SiCaC reaction has also been applied to a 1,6-enyne bearing a cyclohexenyl group as the alkene moiety and a 1,7-enyne system. The functionalized five- and six-membered ring systems obtained by these novel cyclization reactions serve as useful and versatile intermediates for the syntheses of natural and unnatural heterocyclic and carbocyclic compounds. Possible mechanisms for the SiCaC and CO-SiCaC reactions as well as unique features of these processes are discussed. 相似文献
120.
Summary A rapid sensitive method for the determination of microgram amounts of sulphur is described. Sulphur (free or combined) in organic substances is oxidised completely in an oxygen atmosphere over a platinum gauze catalyst after a preliminary incomplete combustion in air. The oxides of sulphur are collected on silver gauze at 550°. The oxygen is purged from the apparatus with a stream of nitrogen and then the silver sulphate is heated in a stream of hydrogen to yield hydrogen sulphide which is collected in an alkaline zinc acetate solution and subsequently determined spectrophotometrically by the methylene blue method.The recovery of sulphur in the range 5–40g was 100±5%. The method takes less than 25 minutes for a single determination and is reliable for the determination of as little as1
g of sulphur in all types of organic compounds. Solid, liquid, or gaseous samples may be used.
Zusammenfassung Eine schnelle, empfindliche Methode zur Bestimmung von Mikrogrammmengen Schwefel wurde beschrieben. Freier oder gebundener Schwefel in organischem Material wird nach unvollständiger Verbrennung in Luft in Sauerstoffatmosphäre über einem Platindrahtnetz vollständig oxydiert. Die Schwefeloxide werden auf Silberdrahtnetz bei 550° gebunden. Der Sauerstoff wird mit Stickstoff aus der Apparatur gespült und dann das Silbersulfat im Wasserstoffstrom zu Schwefelwasserstoff reduziert, der in alkalischem Zinkacetat aufgefangen und dann nach der Methylenblaumethode spektrophotometrisch bestimmt wird.In der Größenordnung zwischen 5 und 10g wird der Schwefel zu 100±5% erfaßt. Eine Einzelbestimmung dauert weniger als 25 Minuten. Für alle Arten organischer Verbindungen, ob fest, flüssig oder gasförmig, eignet sich das Verfahren für die Bestimmung von 1g Schwefel und darüber.
Résumé On décrit une méthode rapide et sensible pour le dosage de quantités de soufre de l'ordre du microgramme. Le soufre (libre ou combiné) dans les substances organiques est oxydé complètement en atmosphère d'oxygène sur une toile de platine, catalyseur, après une combustion préliminaire incomplète dans l'air. Les oxydes du soufre sont rassemblés sur une toile d'argent à 550°. On purge l'appareil de l'oxygène par un courant d'azote puis le sulfate d'argent est chauffé dans un courant d'hydrogène en donnant de l'hydrogène sulfuré qui est rassemblé dans une solution alcaline d'acétate de zinc et dosé ensuite par spectrophotométrie par la méthode au bleu de méthylène.La récupération du soufre entre 5 et 40g atteint 100±5%. La méthode demande moins de 25 minutes pour un dosage individuel et reste valable pour les teneurs descendant jusqu'à 1g de soufre dans les composés organiques de toutes natures. On peut utiliser des échantillons solides, liquides ou gazeux.相似文献