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101.
Shamsipur M Dastjerdi LS Haghgoo S Armspach D Matt D Aboul-Enein HY 《Analytica chimica acta》2007,601(1):130-138
19F NMR spectroscopy was applied to the quantitative determination of fluoxetine enantiomers using different chiral recognition agents in pharmaceutical formulations. Several parameters affecting the enantioresolution including the type and concentration of chiral selector, concentration of fluoxetine and temperature were studied. The chiral selectors investigated are the cyclic oligosaccharides α-, β- and γ-cyclodextrin and a diamino derivative of methylated α-cyclodextrin (DAM-α-CD), linear polysaccharides (maltodextrin with dextrose equivalents of 4.0-7.0, 13.0-17.0 and 16.5-19.5) and the macrocyclic antibiotic vancomycin. Among the chiral selectors used, DAM-α-CD turned out to give the best resolution of the 19F NMR signals of (R)- and (S)-fluoxetine. The calibration curve was linear for (R)- and (S)-fluoxetine over the range 0.10-1.35 mg mL−1, the detection limits (S/N = 3) being 5.9 and 7.5 μg mL−1 for the pure solutions of (R)- and (S)-fluoxetine, respectively. The recovery studies performed on pharmaceutical samples ranged from about 90 to 110% with relative standard deviations of <8%. The results showed that the proposed method is rapid, precise and accurate. Applying statistical Student's t-test revealed insignificant difference between the real and measured contents at the 95% confidence level. 相似文献
102.
Poorters L Armspach D Matt D Toupet L Choua S Turek P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(34):9448-9461
The C2-symmetrical diphosphane TRANSDIP was obtained in high yield by treating 6A,6B,6D,6E-tetramesylated, permethylated alpha-cyclodextrin with PPhLi2 in excess. The double cascade cyclisation thus produced is regioselective as phosphinidene capping involves only adjacent glucose units. It is also stereospecific, as both lone pairs on the phosphorus atoms are orientated towards the cyclodextrin axis. The restricted flexibility of the phosphorus atoms, which are part of nine-membered heterocyclic rings, is responsible for JP,C spin-spin couplings with the eight-bond distant CH2OMe carbon atoms of glucose units C and F. The treatment of TRANSDIP with Group 10 metal dihalides quantitatively gave square-planar chelate complexes, in which a M--X bond points towards the centre of the cavitand. The favourable P...P separation and the directional control of the lone pairs on the phosphorus atoms rule out the possibility of forming binuclear complexes or higher oligomers. Further, in all the complexes, the phosphorus atoms are in a trans arrangement. TRANSDIP may therefore be regarded as an authentic trans-spanning diphosphane. In the complex [NiBr2TRANSDIP], the cavity provides effective protection of the encapsulated M--X bond towards nucleophilic attack by MeLi. The same complex, upon activation with methylaluminoxane, efficiently dimerises ethene and propene. 相似文献
103.
Ying‐Hung So Donald L. Schmidt Matt T. Bishop Daniel R. Miller Patrick B. Smith Michael J. Radler Mindy Magyar Britton L. Kaliszewski 《Journal of polymer science. Part A, Polymer chemistry》2000,38(8):1283-1290
Upon photolysis or heating, aryl cyclic sulfonium (ACS) zwitterions polymerize by ring‐opening and loss of charge to yield nonionic polymers. These water‐soluble monomers potentially are useful for photolithography because they can be cast from and developed in water. The ACS zwitterion from bisphenol A, 1,1′‐[isopropylidenebis(6‐hydroxy‐3,1‐phenylene)] bis (tetrahydrothiophenium hydroxide) bis(inner salt) (1) is a negative‐tone, photosensitive material that after photolysis yields a crosslinked film. Unexposed regions are removed by water. The cured film has a low dielectric constant, high volume resistivity, a high degree of planarization, low residual stress, thermogravimetric stability, acceptable fracture toughness, and high hardness. These are desirable properties for a dielectric material used in microelectronic applications. However, a shortcoming of the material is its low Tg, at about 140 °C. A second ACS zwitterion, 1,1′‐[fluorenylidenebis(6‐hydroxy‐3,1‐phenylene)] bis(tetrahydrothiophenium hydroxide) bis(inner salt) (2) was prepared that yields a crosslinked polymer with a higher Tg of about 190 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1283–1290, 2000 相似文献
104.
William B. Tucker Aaron M. McCoy Samantha M. Fix Melissa F. Stagg Matt M. Murphy Sandro Mecozzi 《Journal of polymer science. Part A, Polymer chemistry》2014,52(23):3324-3336
Linear, dibranched, and miktoarm amphiphiles containing both hydrophobic and fluorophilic moieties were synthesized and characterized in an attempt to elucidate the relationship between semifluorinated amphiphile structure and aggregate behavior in aqueous solution. For the linear and dibranched amphiphiles, there was an exponential decrease in critical aggregation concentration (CMC) and a logarithmic increase in core microviscosity with increasing length of the fluorocarbon segments; while the miktoarm architecture produced no notable trend in microviscosity or CMC. Furthermore, the linear and dibranched surfactants showed enhanced kinetic stability, dissociating more slowly in the presence of human serum than did either the dibranched or miktoarm amphiphiles. Finally, encapsulation studies with the hydrophobic drug paclitaxel (PTX) showed that the ability to solubilize and retain PTX increased with the presence and with the increasing size of the fluorocarbon moiety for both the linear and dibranched amphiphiles, while no such trend was observed for the miktoarm amphiphiles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3324–3336 相似文献
105.
Jason A. Kautz Donald F. Mullica J. Matt Farmer 《Journal of chemical crystallography》1999,29(6):729-733
The structural analysis of [(n-C4H9)4N]3[Y(NCS)6] (I) using single-crystal diffraction data and full-matrix least squares refinement has been carried out. The hexaisothiocyanate complex crystallizes in the centrosymmetric triclinic space group P
(No. 2) with unit cell constants of a = 12.431(1), b = 12.866(1), c = 22.750(2) Å, = 90.78(1), = 92.05(1), = 96.67(1)°, and Z = 2. The molecular unit consists of three separate cationic tetra-n-butylammonium groups and an independent hexakisisothiocyanatoyttrate anionic group in which the six thiocyanate ligands are octahedrally coordinated through the N atom to the Y central ion. Selected bond distances and angles are presented as well as the synthesis and peripheral studies of (I). 相似文献
106.
The application of theoretical methods based on density-functional theory is known to provide atomic and cell parameters in very good agreement with experimental values. Recently, construction of the exact Hartree-Fock exchange gradients with respect to atomic positions and cell parameters within the Gamma-point approximation has been introduced. In this article, the formalism is extended to the evaluation of analytical Gamma-point density-functional atomic and cell gradients. The infinite Coulomb summation is solved with an effective periodic summation of multipole tensors. While the evaluation of Coulomb and exchange-correlation gradients with respect to atomic positions are similar to those in the gas phase limit, the gradients with respect to cell parameters needs to be treated with some care. The derivative of the periodic multipole interaction tensor needs to be carefully handled in both direct and reciprocal space and the exchange-correlation energy derivative leads to a surface term that has its origin in derivatives of the integration limits that depend on the cell. As an illustration, the analytical gradients have been used in conjunction with the QUICCA algorithm to optimize one-dimensional and three-dimensional periodic systems at the density-functional theory and hybrid Hartree-Fock/density-functional theory levels. We also report the full relaxation of forsterite supercells at the B3LYP level of theory. 相似文献
107.
Frost RL Weier ML Clissold ME Williams PA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(14):3313-3319
Infrared spectroscopy has proven most useful for the study of anions in the interlayer of natural hydrotalcites. A suite of naturally occurring hydrotalcites including carrboydite, hydrohonessite, reevesite, motukoreaite and takovite were analysed. Variation in the hydroxyl stretching region was observed and the band profile is a continuum of states resulting from the OH stretching of the hydroxyl and water units. Infrared spectroscopy identifies some isomorphic substitution of sulphate for carbonate through an anion exchange mechanism for the minerals carrboydite and hydrohonessite. The infrared spectra of the CO3 and SO4 stretching region of takovite is complex because of band overlap. For this mineral some sulphate has replaced the carbonate in the structure. In the spectra of takovites, a band is observed at 1346 cm(-1) and is attributed to the carbonate anion hydrogen bonded to water in the interlayer. Infrared spectroscopy has proven most useful for the study of the interlayer structure of these natural hydrotalcites. 相似文献
108.
Jermiah Y. Shen Matt S. Chang Sheng‐Hsiung Yang Gaston J. Wu 《Journal of separation science》2012,35(19):2544-2552
The presence of triclosan and triclocarban, two endocrine‐disrupting chemicals and antimicrobial agents, and transformation products of triclocarban, 1,3‐di(phenyl)urea, 1,3‐bis(4‐chlorophenyl)urea and 1,3‐bis(3,4‐dichlorophenyl)urea, in tap water, treated household drinking water, bottled water, and river water samples were investigated using solid‐phase micro‐extraction coupled with‐HPLC‐MS/MS, a rapid, green, and sensitive method. Factors influencing the quantity of the analytes extracted onto the solid‐phase micro‐extraction fiber, such as addition of salt, sample pH, extraction time, desorption time, and sample volume, were optimized using solid‐phase micro‐extraction‐HPLC‐MS/MS. The results showed that the method gave satisfactory sensitivities and precisions for analyzing sub‐part‐per‐trillion levels of triclosan, triclocarban, and transformation products of triclocarban in samples collected locally. The recoveries of analytes ranged from 97 to 107% for deionized water samples, and 99 to 110% for river water samples, and limits of detection were in the range of 0.32–3.44 and 0.38–4.67 ng/L for deionized water and river water samples, respectively. On average, the daily consumption of triclosan and triclocarban by an adult by consuming 2 liters of different types of drinking water were estimated to be in the range of 6.13–425 ng/day as a result of the concentrations of triclosan and triclocarban measured in this study. 相似文献
109.
Previous studies describe derivatization of metal ions followed by analysis using gas chromatography, usually on packed columns. In many of these studies, stable and volatile derivatives were formed using fluorinated β‐diketonate reagents. This paper extends previous work by investigating separations of the derivatives on small‐diameter capillary gas chromatography columns and exploring on‐fiber, solid‐phase microextraction derivatization techniques for beryllium. The β‐diketonate used for these studies was 1,1,1,2,2,6,6,7,7,7‐decafluoro‐3,5‐heptanedione. Derivatization of lanthanides also required addition of a neutral donor, dibutyl sulfoxide, in addition to 1,1,1,2,2,6,6,7,7,7‐decafluoro‐3,5‐heptanedione. Unoptimized separations on a 100‐μm i.d. capillary column proved capable of rapid separations (within 15 min) of lanthanide derivatives that are adjacent to one another in the periodic table. Full‐scan mass spectra were obtained from derivatives containing 5 ng of each lanthanide. Studies also developed a simple on‐fiber solid‐phase microextraction derivatization of beryllium. Beryllium could be analyzed in the presence of other alkali earth elements (Ba(II) and Sr(II)) without interference. Extension of the general approach was demonstrated for several additional elements (i.e. Cu(II), Cr(III), and Ga(III)). 相似文献
110.
In the moduli space M \mathcal{M}
g
of genus-g Riemann surfaces, consider the locus RMO \mathcal{R}{\mathcal{M}_{\mathcal{O}}} of Riemann surfaces whose Jacobians have real multiplication by the order O \mathcal{O} in a totally real number field F of degree g. If g = 3, we compute the closure of RMO \mathcal{R}{\mathcal{M}_{\mathcal{O}}} in the Deligne–Mumford compactification of M \mathcal{M}
g
and the closure of the locus of eigenforms over RMO \mathcal{R}{\mathcal{M}_{\mathcal{O}}} in the Deligne–Mumford compactification of the moduli space of holomorphic 1-forms. For higher genera, we give strong necessary
conditions for a stable curve to be in the boundary of RMO \mathcal{R}{\mathcal{M}_{\mathcal{O}}} . Boundary strata of RMO \mathcal{R}{\mathcal{M}_{\mathcal{O}}} are parameterized by configurations of elements of the field F satisfying a strong geometry of numbers type restriction. 相似文献