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991.
AurelioG. Cskÿ Rocío Medel M.Carmen Murcia Joaquín Plumet 《Helvetica chimica acta》2005,88(6):1387-1396
A new method for the synthesis of spiro‐β‐lactams tethered to tetrahydrofuran rings is described. The procedure is based on Ru‐catalyzed metathesis sequences with oxanorbornene precursors easily obtained by the Staudinger [2+2] cycloaddition of related imines. 相似文献
992.
Kótai László Horváth Tibor Szentmihályi Klára Keszler Ágnes 《Transition Metal Chemistry》2000,25(3):293-294
We have investigated the effect of temperature on the postulated quasi-intramolecular acid-base reactions in aqueous solutions of Cu(NH3)4(MnO4)2 and Ag(NH3)2ClO4. Pure ammonium permanganate and perchlorate were obtained above 5 C and at room temperature, respectively, due to quasi-intramolecular acid-base reactions. 相似文献
993.
Fernando A Iñón 《Analytica chimica acta》2003,477(1):59-71
A mathematical model for fitting the experimental ICM (integrated conductimetric method) curves developed by the authors in a previous work, is presented for the first time in this study. The proposed model fits the experimental curves with great precision and allows to predict physical dispersion for single-line flow injection system. The correlation of the model’s parameters with typical reactionless FIA peak parameters is also assessed. The IDQ coefficient—a novel dispersion estimator previously reported by the authors—can also be predicted when operational FIA variables are changed. Experimental and modelled profiles are compared as a function of the system’s variables, showing an excellent agreement. 相似文献
994.
995.
Determination of sulfametoxazole, sulfadiazine and associated compounds in pharmaceutical preparations by capillary zone electrophoresis 总被引:3,自引:0,他引:3
Berzas Nevado JJ Castañeda Peñalvo G Guzmán Bernardo FJ 《Journal of chromatography. A》2001,918(1):205-210
A capillary zone electrophoresis method is presented to separate sulfadiazine, sulfamethoxazole, trimethoprim, bromhexine and guaiacol by using a fused-silica capillary (60.2 cm x 75 microm I.D.). The separation was carried out at 30 kV and 25 degrees C in a 15 mM phosphate buffer adjusted to pH 6.2 as electrolyte. Under these conditions, the run time was 6 min and the limits of quantification were about 1 mg/l for every component. The method was applied to pharmaceutical preparations and the results provided recoveries close to 100%. 相似文献
996.
Pospísil M Kalendová A Capková P Simoník J Valásková M 《Journal of colloid and interface science》2004,277(1):154-161
Na(+)-montmorillonite type Wyoming, cloisite Na(+) from Southern Clay Products, Inc., was intercalated (i) with octadecylammonium cations and subsequently intercalated with octadecylamine molecules, (ii) with dodecylamine molecules, and (iii) with octylamine molecules to determine the applicability of these intercalates for nanocomposite materials on the base of polymer/clay. The structures were determined on the basis of a combination of results from X-ray diffraction and molecular simulations. The calculated values of basal spacings are in good agreement with experimental basal spacings when experimental samples were prepared. The interlayer space of intercalated montmorillonite shows a monolayer or bilayer arrangement of alkyl chains in dependence on the concentration of the intercalation solution. The values of the total sublimation energy, interaction energy, and exfoliation energy were calculated for all investigated samples. Low values of exfoliation energies lead to better exfoliation of intercalated silicate layers and this material appears suitable for use as a precursor for polymer/clay nanocomposites. The values of exfoliation energy for the investigated samples show that montmorillonite intercalated with dodecylamine or octadecylamine molecules is suitable for exfoliation of silicate layers. 相似文献
997.
J. J. Ramírez-García M. Jiménez-Reyes M. Solache-Ríos E. Fernández-Ramírez H. López-González A. Rojas-Hernández 《Journal of Radioanalytical and Nuclear Chemistry》2003,255(2):299-303
The solubility of europium at 0.02M, 0.1M and 0.7M NaClO4 ionic strength solutions was determined by a radiometric method and pEus-pCH diagrams were obtained. Hydrolysis constants were also determined at the same ionic strengths by pH titration and the values found were log *1 = -7.68±0.11, -8.07±0.10 and -8.20±0.11. The log K
sp values were -23.5±0.2, -22.7±0.2 and -21.9±0.2 for 0.02M, 0.1M and 0.7M NaClO4 ionic strengths, respectively, at 303 K under CO2-free conditions and the extrapolated value at zero ionic strength was log K
sp
0 = -24.15. The working pCH ranges for the calculation of the hydrolysis constants were selected from the pEus-pCH diagrams in the region where precipitation of europium oxide or hydroxide was less than 20%. Europium removal from aqueous solutions with zeolites was explored. 相似文献
998.
Anna Painelli Francesca Terenziani Zoltán G. Soos 《Theoretical chemistry accounts》2007,117(5-6):915-931
We discuss electron-transfer processes that govern the physics of several materials or systems of interest for advanced applications.
The discussion touches upon several topics, ranging from solvatochromism to solvent-induced symmetry breaking, from excitonic
to cooperative effects in molecular crystals, from phase transitions to vibrational contributions to the dielectric constant
in organic materials, from spectroscopy to molecular transport. In all these diverse systems electron transfer (ET) plays
a major role and is discussed with reference to simple models for delocalized charges. 相似文献
999.
Aranka Pilbáth Ilona Felhősi Gyula Tolnai Erika Kálmán 《Journal of Solid State Electrochemistry》2006,10(9):721-729
Due to the toxic and carcinogenic properties of hexavalent chromium ion, the corrosion protection with chromating technique needs replacement. Several environmentally friendly alternative metal pretreatments have already been proposed. One of these methods is the application of self-assembling molecules to form mono- or multilayers on the metal surfaces. These layers can prevent metal dissolution due to their dense and stable structure. The objective of our studies was to protect zinc surface against corrosion, with a thin phosphonate layer. Aqueous solutions of diphosphonic acid with different alkyl chain lengths were applied with different treatment times. The layer formation, stability, and corrosion protection of these films were monitored by electrochemical impedance spectroscopy and the effect of 1,5-diphosphono-pentane (DPP) on zinc was studied by polarization curves. The wetting properties were determined by static contact angle measurement. 1,5-Diphosphono-pentane forms a thin layer, with a pronounced protective ability in neutral aqueous solutions. The application of self-assembling molecules can be a promising method to replace the chromating technique on zinc surface. 相似文献
1000.
Ascorbic acid (AA) is determined by amperometric detection based on the photochemical reduction of Methylene Blue (MB(+)) in 0.1 M phthalate buffer at pH 3.8. In this medium, MB(+) using flow-injection analysis. The carrier stream is 1 mM MB(+) is reduced quasi-reversibly at a glassy carbon electrode at -0.34 V vs. Ag/AgCl, while AA is oxidized irreversibly at about 0.3 V. The reactor is irradiated with a 500 W halogen lamp to facilitate the development of the photochemical reaction. A laboratory-built wall-jet electrode system was used. The Leucomethylene Blue formed in the reaction is detected at +0.050 V. At 2.2 ml min(-1) and using a sample loop of 43 mul, the method allows the determination of AA in the range 5.0-90.0 mug ml(-1), with a relative standard deviation of 1.3-4.8%, a detection limit of 1.9 mug ml(-1) and a sampling frequency of 45-50 h(-1). 相似文献