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91.
Enhanced chiral separation performance has been observed for ketoprofen enantiomers in capillary electrochromatography (CEC) with an open-tubular (OT) column prepared with a specific molecule imprinted polymer (MIP) on the innerwall of 50mum ID capillary. The column was prepared by in situ thermal polymerization inside the pretreated and silanized fused silica capillary. A specific diluted monomer mixture composed of S-ketoprofen, methacrylic acid (MAA, functional monomer), ethylene glycol dimethacrylate (EDMA, cross-linker), and 4-styrenesulfonic acid (4-SSA) dissolved in 9/1 (v/v) acetonitrile/2-propanol was used to fabricate the OT-MIP layer. 4-SSA was added to form a MIP layer capable of stable and strong electro-osmotic flow (EOF) over the pH range of this study securing CEC elution of ketoprofen having partial negative charge near the optimized pH. Various parameters such as buffer pH, organic modifier composition, salt concentration, and applied potential have been optimized for CEC chiral separation of ketoprofen enantiomers. Very good separation selectivity and efficiency were observed, thus the chromatographic resolution of ketoprofen enantiomers was as high as 10.5, and the number of theoretical plates of R-ketoprofen, 156,000/m (40,000/m for S-ketoprofen), which proves that the OT-MIP-CEC type approach is a promising strategy in MIP study. 相似文献
92.
93.
Shabi Abbas Zaidi Kyoung Moon Han Sung Soon Kim Dong Guk Hwang Won Jo Cheong 《Journal of separation science》2009,32(7):996-1001
An open tubular molecule imprinted polymer (OT‐MIP) capillary column has been prepared for chiral separation of ofloxacin enantiomers in CEC. The S‐ofloxacin imprinted OT column was fabricated by thermally initiated non‐covalent polymerization procedure inside a pretreated and silanized fused silica capillary. The template molecule was incorporated with methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and 4‐styrenesulfonic acid (4‐SSA) and dissolved in a porogen mixture of ACN/2‐propanol (9:1). The separation efficiency of the 4‐SSA MIP column was found quite better than that of the MIP column without 4‐SSA. It has been demonstrated that our OT‐MIP column can separate ofloxacin enantiomers with excellent chiral separation efficiency after tuning the various chromatographic conditions. The optimized chromatographic eluent was 85:15, v/v%, ACN/60 mM sodium acetate at pH 7. The separation efficiency and selectivity of chiral separation of this study were far better than those obtained by previous methods for chiral separation of R‐ and S‐ofloxacin. 相似文献
94.
To reduce the use of organic solvent, pressurized hot water extraction (PHWE) has been shown to be a feasible option for the extraction of bioactive and marker compounds in botanicals and medicinal plants. The parameters that may affect the extraction efficiencies in PHWE include temperature, extraction time and addition of small percentage of organic solvent or surfactants. Currently, applications of PHWE for the extraction of thermally labile compounds in botanicals are still rather limited. PHWE with and without the additional of a small percentage of organic solvent such as ethanol is highly suited for the chemical standardization and quality control of medicinal plants. At the same time, it can be applied at the pilot scale as a manufacturing process for medicinal plants. Surfactant assisted PHWE was found to enhance the extraction of thermally labile and more hydrophobic species in medicinal plants at a lower temperature. The addition of small amount of surfactants in PHWE is highly suited for the determination of bioactive or marker compounds in medicinal plants. With proper optimization, PHWE was observed to have good extraction efficiency and precision when compared to other reference methods of extraction. 相似文献
95.
Kim HS Lee SY Lee H Bae JY Park SJ Cheong M Lee JS Lee CH 《The Journal of organic chemistry》2006,71(3):911-914
The isomerization reaction of 5-vinyl-2-norbornene (VNB) to 5-ethylidene-2-norbornene (ENB) has been performed using a catalytic system consisting of an alkali metal hydride and an amine. Among various amines tested, only aliphatic 1,2-diamines exhibited the activity for the isomerization. The isomerization was also affected by the alkali metal hydride employed. The activity of the alkali metal hydride increased with the increasing size of alkali metal: KH > NaH > LiH. A series of electron paramagnetic resonance (EPR) and UV-vis experiments on the active species suggest that the isomerization of VNB proceeds through a radical mechanism. 相似文献
96.
Assessment of Joule heating and its effects on electroosmotic flow and electrophoretic transport of solutes in microfluidic channels 总被引:4,自引:0,他引:4
Joule heating is inevitable when an electric field is applied across a conducting medium. It would impose limitations on the performance of electrokinetic microfluidic devices. This article presents a 3-D mathematical model for Joule heating and its effects on the EOF and electrophoretic transport of solutes in microfluidic channels. The governing equations were numerically solved using the finite-volume method. Experiments were carried out to investigate the Joule heating associated phenomena and to verify the numerical models. A rhodamine B-based thermometry technique was employed to measure the solution temperature distributions in microfluidic channels. The microparticle image velocimetry technique was used to measure the velocity profiles of EOF under the influence of Joule heating. The numerical solutions were compared with experimental results, and reasonable agreement was found. It is found that with the presence of Joule heating, the EOF velocity deviates from its normal "plug-like" profile. The numerical simulations show that Joule heating not only accelerates the sample transport but also distorts the shape of the sample band. 相似文献
97.
Tiegang Liu A. W. Chowdhury & Boo Cheong Khoo 《advances in applied mathematics and mechanics.》2011,3(5):611-632
In this work, the modified ghost fluid method is developed to deal with
2D compressible fluid interacting with elastic solid in an Euler-Lagrange
coupled system. In applying the modified Ghost Fluid Method to treat the
fluid-elastic solid coupling, the Navier equations for elastic solid are
cast into a system similar to the Euler equations but in Lagrangian coordinates.
Furthermore, to take into account the influence of material deformation and
nonlinear wave interaction at the interface, an Euler-Lagrange Riemann problem
is constructed and solved approximately along the normal direction of the
interface to predict the interfacial status and then define the ghost fluid
and ghost solid states. Numerical tests are presented to verify the resultant
method. 相似文献
98.
Vaisagh Viswanathan Chong Eu Lee Michael Harold Lees Siew Ann Cheong Peter M. A. Sloot 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(2):1-11
Crowd simulation is rapidly becoming a standard tool for evacuation planning and evaluation. However, the many crowd models in the literature are structurally different, and few have been rigorously calibrated against real-world egress data, especially in emergency situations. In this paper we describe a procedure to quantitatively compare different crowd models or between models and real-world data. We simulated three models: (1) the lattice gas model, (2) the social force model, and (3) the RVO2 model, and obtained the distributions of six observables: (1) evacuation time, (2) zoned evacuation time, (3) passage density, (4) total distance traveled, (5) inconvenience, and (6) flow rate. We then used the DISTATIS procedure to compute the compromise matrix of statistical distances between the three models. Projecting the three models onto the first two principal components of the compromise matrix, we find the lattice gas and RVO2 models are similar in terms of the evacuation time, passage density, and flow rates, whereas the social force and RVO2 models are similar in terms of the total distance traveled. Most importantly, we find that the zoned evacuation times of the three models to be very different from each other. Thus we propose to use this variable, if it can be measured, as the key test between different models, and also between models and the real world. Finally, we compared the model flow rates against the flow rate of an emergency evacuation during the May 2008 Sichuan earthquake, and found the social force model agrees best with this real data. 相似文献
99.
Pierce MD Johnston RC Mahapatra S Yang H Carter RG Ha-Yeon Cheong P 《Journal of the American Chemical Society》2012,134(33):13624-13631
Computational study of the mechanisms and stereoselectivities of a dual amino-catalyzed synthesis of cyclohexenones containing all-carbon γ-quaternary and ?-tertiary stereocenters is reported. Extensive conformational search with density functional theory optimizations, the high-accuracy SCS-MP2/cc-pV∞Z energies, and PCM solvation corrections were used to characterize all intermediates and transition states. Six mechanisms were considered, all consistent with available experiments. The reaction proceeds via sequential Michael and Mannich conjugate additions whereby the primary amine activates the aldehyde and the catalyst activates the pentenone. We have discovered a rare duumvirate stereocontrol: the Michael reaction sets the enantioselectivity, but both the Michael and the Mannich reactions control the diastereoselectivity. 相似文献
100.
Yang JJ Choi YJ Oh YS Hogan A Horibe Y Kim K Min BI Cheong SW 《Physical review letters》2012,108(11):116402
Using transmission electron microscopy, the anomalies in resistivity and magnetic susceptibility at ~262 K in IrTe2 are found to accompany the superlattice peaks with q[over q=(1/5,0,-1/5). The wave vector is consistent with our theoretical calculation for the Fermi surface nesting vector, indicating that the ~262 K transition is of the charge-orbital density wave (DW) type. We also discovered that both Pd intercalation and substitution induce bulk superconductivity with T(c) up to ~3 K, which competes with DW in a quantum critical pointlike manner. 相似文献