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21.
The use of salting-out effect for the off-line preconcentration of charged analytes in capillary electrophoresis is demonstrated for the first time. Using benzalkonium chloride (BAK) as model compound, a mixture of cationic surfactants consisting of even-numbered alkylbenzyl quaternary ammonium homologues (C8-C18), the addition of appropriate amounts of sodium chloride and acetonitrile in the sample solution (2 mL sample volume) was found to be capable of providing ca. 40-fold enhancement in detection sensitivity. In addition to affording a preconcentrating effect due to the extraction of BAK in the smaller volume water-miscible organic solvent phase (acetonitrile), the organic solvent also serves to improve the peak area and shape of the longer chain surfactants. Optimal experimental conditions, such as volume of acetonitrile and concentration of sodium chloride, for the preconcentration of BAK with good preconcentration factors and reproducibility were investigated. The usefulness of the present method was demonstrated for the improved determination of BAK present in commercially available industrial and pharmaceutical products. 相似文献
22.
Toshio Nishi Hideyuki Nukaga So Fujinami Ken Nakajima 《高分子科学》2007,(1):35-41
Atomic force microscopy (AFM) has the advantage of obtaining mechanical properties as well as topographic information at the same time. By analyzing force-distance curves measured over two-dimensional area using Hertzian contact mechanics, Young's modulus mapping was obtained with nanometer-scale resolution. Furthermore, the sample deformation by the force exerted was also estimated from the force-distance curve analyses. We could thus reconstruct a real topographic image by incorporating apparent topographic image with deformation image. We applied this method to carbon black reinforced natural rubber to obtain Young's modulus distribution image together with reconstructed real topographic image. Then we were able to recognize three regions; rubber matrix, carbon black (or bound rubber) and intermediate regions. Though the existence of these regions had been investigated by pulsed nuclear magnetic resonance, this paper would be the first to report on the quantitative evaluation of the interfacial region in real space. 相似文献
23.
Chang-Eun Yeom Young Jong Kim So Young Lee Yong Je Shin B. Moon Kim 《Tetrahedron》2005,61(52):12227-12237
Fast and chemoselective desilylation of silyl-protected alcohols was achieved using a catalytic amount of 1-chloroethyl chloroformate in methanol. With a minimal amount of 1-chloroethyl chloroformate as the source for anhydrous HCl, extremely efficient cleavage of silyl ethers of primary and secondary alcohols was accomplished, and chemoselective deprotection of one silyl ether in the presence of another silyl or other acid-labile group was possible through controlling the amount of the chloroformate and reaction time. 相似文献
24.
Peter Gajdoš Soňa Pavlíková Filip Bureš Alžbeta Krutošíková 《Central European Journal of Chemistry》2005,3(2):311-325
The synthesis and reactions of methyl 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole-5-carboxylate (1a) are described. Upon reaction with methyl iodide, benzyl chloride, or acetic anhydride, this compound gave N-substituted products 1b-d. By hydrolysis of compounds 1a-c, the corresponding acids 2a-c were formed, or by reaction with hydrazine-hydrate, the corresponding carbohydrazides 3a-c were formed. By heating 2-[3-(trifluoromethyl)phenly]-4H-furo[3,2-b]pyrrole-5-carboxylic acid (2a) in acetic anhydride, 4-acetyl-2-[3-(trifluoromethyl)phenyl]furo[3,2-b]pyrrole (4) was formed. By hydrolysis of 4, 2-[3-(trifluoromethyl)phenyl]-4H-furo[3,2-b]pyrrole (5a) was formed, and reactions with methyl iodide or benzyl chloride gave N-substituted products 5b-c. The reaction of 4 with dimethyl butynedioate gave substituted benzo[b]furan 6. Compound 3a reacted with triethyl orthoesters giving 7a-c, which afforded with phosphorus (V) sulphide the corresponding thiones 8a-c. The thiones 8a-c reacted with hydrazine hydrate to form hydrazine derivatives 9a-c. The reaction of triethyl orthoformiate with compounds 9a-c led to furo[2′,3′: 4,5]pyrrolo[1,2-d][1,2,4]triazolo[3,4-f][1,2,4]triazines 10a-c. Hydrazones 11a-c were formed from 3a-c and 5-[3-(trifluoromethyl)phenyl]furan-2-carboxaldehyde. The effect of microwave irradiation on some condensation reactions
was compared with “classical” conditions. The results showed that microwave irradiation shortens the reaction time while affording
comparable yields. 相似文献
25.
Srivastava A Metaxas AC So P Matsudaira P Ehrlich D Georghiou GE 《Electrophoresis》2005,26(6):1130-1143
A numerical model is presented for the accurate and efficient prediction of preconcentration and transport of DNA during sample introduction and injection in microcapillary electrophoresis. The model incorporates conservation laws for the different buffer ions, salt ions, and DNA sample, coupled through a Gaussian electric field to account for the field modifications that cause electromigration. The accuracy and efficiency required to capture the physics associated with such a complex transient problem are realized by the use of the finite element-flux corrected transport (FE-FCT) algorithm in two dimensions. The model has been employed for the prediction of DNA sample preconcentration and transport during electrophoresis in a double-T injector microdevice. To test its validity, the numerical results have been compared with the corresponding experimental data under similar conditions, and excellent agreement has been found. Finally, detailed results from a simulation of DNA sample preconcentration in electrophoretic microdevices are presented using as parameters the electric field strength and the other species concentrations. The effect of the Tris concentration on sample stacking is also investigated. These results demonstrate the great potential offered by the model for future optimization of such microchip devices with respect to significantly enhanced speed and resolution of sample separation. 相似文献
26.
A new experimental technique has been developed to determine the phase equilibrium diagram for the system K2SO4-K2S.The technique involves isothermal thermogravimetry of potassium sulphate during reduction to potassium sulphide at elevated temperatures in a stream of dry oxygen-free hydrogen gas. Several abrupt changes in the rate of weight loss occur in each curve and these can be related to phase changes in the phase diagram for the system.On the basis of such results the liquidus and solidus (solid solution) boundaries can be located.Simple thermal analysis is used to confirm the eutectic temperature and various liquidus temperatures.The diagram K2SO4-K2S is a simple eutectic system with the eutectic at 610 and 23 mole % K2S. The limits of solid solubility of K2S in K2SO4 and K2SO4 in K2S at the eutectic temperature are 11 % and 36 mole% respectively.The odd shape of the liquidus curves on each side of the eutectic suggests the possibility of phase changes in both K2SO4 and K2S solid solutions. No evidence for this was obtained from thermal analysis.
The authors would like to thank the National Research Council of Canada for their financial support. 相似文献
Zusammenfassung Eine neue experimentelle Technik wurde zur Bestimmung des Phasengleichgewichtsdiagramms des Systems K2SO4-K2S entwickelt.Die Technik umfasst die isotherme Gravimetrie von Kaliumsulfat wÄhrend der Reduktion zu Kaliumsulfid bei erhöhten Temperaturen in strömenden trockenen und Sauerstoff-freien Wasserstoff. Verschiedene plötzliche Änderungen der Geschwindigkeit des Gewichtsverlustes treten bei jeder Kurve auf und können mit den PhasenÄnderungen im Phasendiagramm des Systems in Zusammenhang gebracht werden.Durch diese Ergebnisse können die GrenzflÄchen der flüssigen und der Festphasenlösung festgestellt werden.Die einfache Thermoanalyse wird zur BestÄtigung der eutektischen Temperatur und verschiedener Liquidus-Temperaturen herangezogen.Das Diagramm K2SO4-K2S ist ein einfaches eutektisches System mit dem Eutektikum bei 610 und 23 Mol % K2S. Die Grenzwerte einer festen Lösung von K2S in K2SO4 und K2SO4 in K2S betragen bei der eutektischen Temperatur 11% bzw. 36 Mol %.Die aussergewöhnliche Form der Liquidus-Kurven zu beiden Seiten des Eutektikums lÄsst auf die Möglichkeit von PhasenÄnderungen in den Festlösungen von sowohl K2SO4 wie auch von K2S schliessen Hierzu ergab jedoch die Thermoanalyse keine BestÄtigung.
Résumé Une nouvelle technique expérimentale a été développée afin de déterminer le diagramme d'équilibre des phases dans le système K2SO4-K2S.La technique fait appel à la thermogravimétrie isotherme du sulfate de potassium lors de sa réduction en sulfure de potassium à températures élevées dans un courant de gaz hydrogène sec exempt d'oxygène. Plusieurs changements abrupts de vitesse de perte de poids ont lieu sur chaque courbe et ces changements peuvent Être rapportés aux changements de phases dans le diagramme de phases du système.A partir de tels résultats on peut déterminer les limites du liquidus et du solidus (solution solide).L'analyse thermique simple a été utilisée pour confirmer la température eutectique etdiverses températures du liquidus.Le diagramme K2SO4-K2S forme un système eutectique simple à 610 et 23 p.c. molaires de K2S. Les limites de la solubilité en phase solide de K2S dans K2SO4 et de K2SO4 dans K2S sont, à la température eutectique, respectivement de 11 et 36 mol %.La forme particulière des courbes du liquidus de chaque cÔté de l'eutectique fait penser à la possibilité de changements de phases dans les solutions solides tant de K2SO4 que de K2S, mais l'analyse thermique n'en a pas donné de preuve.
K2SO4-K2S . , . , . ( ). . K2SO4-K2S 610 23% K2S. K2S K2SO4 K2SO4 K2S , , 11 36 . K2SO4 K2S . , .
The authors would like to thank the National Research Council of Canada for their financial support. 相似文献
27.
Chung HS Park SR Choi EK Park HJ Griffin RJ Song CW Park H 《Experimental & molecular medicine》2003,35(3):181-188
The role of sphingomyelinase (SMase) activation and mitogen activated protein kinases (MAPKs) activation in cellular apoptosis was investigated during the hyperthermic treatment of HL-60 human leukemia cells. Treating the cells for 1 h at 43(o)C caused more than 50% of cellular apoptosis within several hours. The neutral-SMase activity in the cells treated for 1 h at 42(o)C was slightly increased but decreased in the cells treated at 43(o)C or 44(o)C for the same period whereas the acid SMase activity was slightly increased after heating the cells at 42(o)C and 43(o)C and markedly increased at 44(o)C for 1 h. Treatment of cells with inhibitors of SMase activation and ceramide formation significantly reduced the heat-induced apoptosis. Three major families of mitogen-activated protein kinases (MAPKs), i.e. ERK1/2, p38 and JNK, were activated by the hyperthermic treatment of cells. Inhibition of ERK1/2 with PD98059 exerted little effect on the heat-induced apoptosis and p38 inhibition with SB203580 slightly lessened apoptosis whereas, inhibition of JNK with SP600125 markedly suppressed the heat-induced apoptosis. These results indicate that heat-shock induced the activation of SMase, particularly acid-SMase, thereby causing apoptosis and that JNK played a pivotal role in heat-induced apoptosis in HL-60 leukemia cells. 相似文献
28.
Investigation on the stress behavior of cellulose acetate and the development of highly moisture‐resistant optical films for display devices 下载免费PDF全文
Min Sang Park Seokwon Jung So Jeong Heo Seung Geol Lee 《Journal of Polymer Science.Polymer Physics》2017,55(19):1470-1479
An optical film with high optical anisotropy was prepared by the stretching of a cellulose acetate film and the consequential orienting of a retardation‐enhancing additive. The change in retardation in response to moisture absorption was explored and it was found that the degree of the retardation variation is strongly related to the stretching temperature. Stress generated by the stretching and its relaxation was systematically investigated to elucidate the effect of stretching temperature on the irreversible change in retardation upon moisture absorption. The results show that the magnitude of releasable stress plays an important role in controlling changes in optical properties. In addition, the difference in the deformation behavior between glassy and rubbery states should be taken into account in the development of a moisture‐resistant optical film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1470–1478 相似文献
29.
Expedient and Diastereodivergent Assembly of Terpenoid Decalin Subunits having Quaternary Stereocenters through Organocatalytic Robinson Annulation of Nazarov Reagent 下载免费PDF全文
Barbara Berkes Kristóf Ozsváth Laura Molnár Tamás Gáti Tamás Holczbauer György Kardos Tibor Soós 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18101-18106
We report an expedient approach to highly functionalized cis‐ and trans‐decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters. 相似文献
30.
A. S. Barabash V. Ya. Bradnova V. V. Dubinina N. P. Egorenkova S. I. Konovalov E. A. Pozharova N. G. Polukhina V. A. Smirnitskii N. I. Starkov Tan Nang So M. M. Chernyavskii T. V. Shchedrina V. I. Yumatov 《Bulletin of the Lebedev Physics Institute》2012,39(10):300-304
Ranges of monochromatic muons in nuclear photoemulsion, produced in the ?? ?? ??? ?? decay, are measured by the coordinate method to determine their energy by the range. The variance of the muon energymeasured by this method ?? ?? = (0.11±0.01) MeV, which corresponds to the accuracy of the determination of the charged particle energy by the range in nuclear emulsion ??3.1%. The developed technique will allow electron energy measurements in the 2??-decay (??3 MeV)with an accuracy of (5?C6)%. 相似文献