bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of chiral zwitterionic surfactants for enantiomeric resolutions by capillary electrophoresis
Authors: Hadley Mark R. , Harrison Mark W. , Hutt Andrew J. 
Published: July 2003

AbstractThe enantiomeric resolution of 1,1’‐binaphthyl‐2,2’‐diamine and Tröger’s base was investigated using the commercially available zwitterionic surfactants 3‐[(3‐cholamidopropyl)dimethylammonio]‐1‐propanesulphonate (CHAPS) and 3‐[(3‐cholamidopropyl)dimethylammonio]‐2‐hydroxy‐1‐propanesulphonate (CHAPSO). Resolution of the weakly basic chiral probes was achieved using varying concentrations of surfactant, above their critical micellar concentrations, in a phosphate buffer (pH 2.5; 100 mM) to ensure ionisation of the analytes. Both CHAPS and CHAPSO were employed in the absence of additional coselectors or surfactants as sole micellar‐forming agents. The addition of organic modifiers, methanol and acetonitrile (ACN), to the background electrolyte (BGE) was found to have a detrimental effect on enantioselectivity presumably by alteration of the phase polarity.
Study on thioridazine 5‐sulfoxide epimerization and degradation by capillary electrophoresis
Authors: Masetto de Gaitani Cristiane , Souto Martinez Alexandre , Sueli Bonato Pierina 
Published: July 2003

AbstractWe present a method for the stereoselective analysis of thioridazine 5‐sulfoxide (THD 5‐SO) in human plasma based on liquid‐liquid extraction with diethyl ether and chiral resolution of the stereoisomers by capillary electrophoresis using hydroxypropyl‐β‐cyclodextrin and sulfated β‐cyclodextrin as chiral selectors. The method showed recovery rates of 85.5% for both THD 5‐SO (slow‐eluting, SE) enantiomers. The coefficients of variation observed in the precision studies, as well as the accuracy values, were below 10%. After validation, the method was used to study the stability and configurational changes of this THD metabolite. Our results showed that both enantiomers of THD 5‐SO (SE) were stable under conditions of variation of temperatures (38°C, 4°C and −20°C), pH (5.0, 7.0 and 8.5) and ionic strengths (0.2, 0.5 and 1.0 mol/L). The influence of light on the stability of the THD 5‐SO (SE) stereoisomers was also studied using standard solutions prepared in methanol and an inversion in configuration was observed under UV light (254 and 366 nm).
Infinite enantiomeric resolution of basic compounds using highly sulfated cyclodextrin as chiral selector in capillary electrophoresis
Authors: Rudaz Serge , Calleri Enrica , Geiser Laurent , Cherkaoui Samir , Prat Josiane , Veuthey Jean‐Luc 
Published: July 2003

AbstractFour chiral basic analytes, namely methadone, fluoxetine, venlafaxine, and tramadol, were selected as model compounds for investigating their stereoselective separation with highly sulfated γ‐cyclodextrin (HS γ‐CD) by capillary electrophoresis (CE)‐UV and CE‐mass spectrometry (MS). At high concentration of chiral selector, the preferentially bonded enantiomer migrated faster in the anodic mode to the detector and high resolutions were obtained for all analytes. In the cathodic mode, at lower highly sulphated cyclodextrin (HS‐CD) concentration, basic compounds could be detected, with the weakly bonded enantiomer migrating first (enantiomeric migration order inversion). It was also then possible, at intermediate HS‐CD concentration, that only one enantiomer migrated to the detector as cation while the other enantiomer complexed with the CD was negatively charged and presented an opposite mobility. The latter never reached the detector achieving a perfect enantiomeric selectivity. Infinite chiral resolutions were thus achieved by CE‐UV as well as by CE‐electrospray ionisation (ESI)‐MS where concentrations of HS‐CD were adapted according to the negative contribution of the nebulization gas pressure of the interface.
Chiral resolution of diastereomeric di‐ and tripeptides on a teicoplanin aglycone phase by capillary electrochromatography
Authors: Schmid Martin G. , Grobuschek Nina , Pessenhofer Verena , Klostius Andrea , Gübitz Gerald 
Published: July 2003

AbstractThe chiral separation ability of a capillary packed with teicoplanin aglycone as a chiral stationary phase was investigated. This stationary phase was used successfully for chiral resolution of both diastereomeric dipeptides and tripeptides possessing one or two chiral centers. The composition of the mobile phase was shown to be crucial for separation. The use of reversed‐phase mode was clearly superior to the polar‐organic mode. The nature of the organic modifier was found to have a marked influence on separation. After optimizing conditions, all diasteromeric dipeptides and tripeptides investigated were baseline‐resolved, however, it was not possible to find a uniform mobile phase showing optimal results for all peptides investigated.
Enantiomeric impurity profiling in ephedrine samples by enantioselective capillary electrochromatography
Authors: Bicker Wolfgang , Hebenstreit Dieter , Lämmerhofer Michael , Lindner Wolfgang 
Published: July 2003

AbstractThis study reports on the development and preliminary validation of a capillary electrochromatographic (CEC) method for the enantioselective impurity profiling of D‐ephedrine. As chiral selector a novel low‐molecular‐weight strong chiral cation exchanger, based on penicillamine sulfonic acid, immobilized on thiol‐modified silica particles (3.5 μm) was employed. Under optimized conditions, the ephedrine enantiomers were separated on this chiral stationary phase (CSP) with an enantioselectivity of 1.11, an average efficiency of 321 550 plates per meter, and a resolution value of 4.77. A preliminary method validation was carried out to demonstrate the applicability of CEC for enantiomeric excess (ee) determination. Run‐to‐run repeatabilities (n = 5) reached relative standard deviation values (RSD) of 0.18 and 0.19% for the migration times of L‐ and D‐enantiomer, respectively, 0.3% for the resolution, and about 0.9% for the peak efficiencies. An approach called self‐internal standard method was utilized to measure a standard calibration curve. Excellent linearity with a correlation coefficient of R2 = 0.9998 was found for samples with concentrations in the range between 0.03 and 5 mg·mL−1 D‐ephedrine spiked with L‐ephedrine at a constant concentration of 0.2 mg·mL−1. The high loadability of the investigated CSP and good peak sensitivity allowed us to determine less than 0.1% enantiomeric impurity with good accuracy. The limit of detection (LOD) for the L‐enantiomer in a 3 mg·mL−1 D‐ephedrine solution was found to be 0.035% (S/N = 3) and the limit of quantitation (LOQ) 0.058% (S/N = 5). For L‐ephedrine samples the strong cation‐exchange (SCX)‐type CSP with opposite configuration was utilized so that the enantiomeric impurity eluted before the main component peak yielding similar results in terms of separation and validation. Based on these results, the presented nonaqueous CEC methods are assessed as principally suitable for ee determination of ephedrine in terms of repeatability and method sensitivity.
Capillary electrophoresis to assess drug metabolism induced in vitro using single CYP450 enzymes (Supersomes™): Application to the chiral metabolism of mephenytoin and methadone
Authors: Prost Francine , Thormann Wolfgang 
Published: July 2003

AbstractCapillary electrophoresis (CE) with multiwavelength absorbance detection is demonstrated to be an effective tool for the assessment of in vitro drug metabolism studies using microsomes containing single human cytochrome P450 enzymes (CYPs) expressed in baculovirus‐infected insect cells (Supersomes™). Mephenytoin (MEPH), dextromethorphan, diclofenac, caffeine, and methadone (MET) were successfully applied as test substrates for CYP2C19, CYP2D6*1, CYP2C9*1, CYP1A2, and CYP3A4, respectively. For each system, the CE‐based assay could be shown to permit the simultaneous analysis of the parent drug and its targeted metabolite. Using a chiral micellar electrokinetic capillary chromatography assay, the aromatic hydroxylation of MEPH catalyzed by CYP2C19 could thereby be confirmed to be highly stereoselective, an aspect that is in agreement with data obtained via urinary analysis after intake of racemic MEPH by extensive metabolizer phenotypes. The MET to 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine (EDDP) conversion was investigated with a chiral zone electrophoresis assay. Incubation of racemic and nonracemic MET with CYP3A4 revealed no stereoselectivity for the transformation to EDDP, whereas no EDDP formation was observed with CYP1A2. CYP2C9 and CYP2C19 provided enhanced formation of R‐EDDP and CYP2D6 incubation resulted in the preferential conversion to S‐EDDP. Investigations using racemic MET and human liver microsomes revealed a modest stereoselectivity with an R/S EDDP ratio < 1 which is similar to the in vivo findings in urine.
Enantiomeric separation of citalopram and its metabolites by capillary electrophoresis
Authors: Mandrioli Roberto , Fanali Salvatore , Pucci Vincenzo , Raggi Maria A. 
Published: July 2003

AbstractA simple and fast capillary electrophoretic method has been developed for the enantioselective separation of citalopram and its main metabolites, namely N‐desmethylcitalopram and N,N‐didesmethylcitalopram, using β‐cyclodextrin (β‐CD) sulfate as the chiral selector. For method optimisation several parameters were investigated, such as CD and buffer concentration, buffer pH, and capillary temperature. Baseline enantioseparation of the racemic compounds was achieved in less than 6 min using a fused‐silica capillary, filled with a background electrolyte consisting of a 35 mM phosphate buffer at pH 2.5 supplemented with 1% w/v β‐CD sulfate and 0.05% w/v β‐CD at 25°C and applying a voltage of −20 kV. A fast separation method for citalopram was also optimized and applied to the analysis of pharmaceutical formulations. Racemic citalopram was resolved in its enantiomers in less than 1.5 min using short‐end injection (8.5 cm, effective length) running the experiments in a background electrolyte composed of a 25 mM citrate buffer at pH 5.5 and 0.04% w/v β‐CD sulfate at a temperature of 10°C.
Enantiomeric separation of chiral peptide nucleic acid monomers by capillary electrophoresis with charged cyclodextrins
Authors: Galaverna Gianni , Sforza Stefano , Tedeschi Tullia , Corradini Roberto , Dossena Arnaldo , Marchelli Rosangela 
Published: July 2003

AbstractDirect chiral separation of chiral peptide nucleic acid (PNA) monomers has been achieved for the first time by capillary electrophoresis (CE) with charged cyclodextrins as chiral selectors added to the electrophoretic buffer. Selectively modified 6‐deoxy‐6‐N‐histamino‐β‐cyclodextrin and sulfobutyl ether‐β‐CD were successfully used as chiral selectors for the enantiomeric separation of chiral monomers based on different aminoethylamino acids bearing thymine or adenine as nucleobases. Chiral separations were obtained at low selector concentrations (1–3 mM) with good enantioselectivity and resolution factors. Separations were optimized as a function of pH in order to exploit the effect of the electrostatic interactions between the oppositely charged selector and selectand. The method has been applied to the analysis of the enantiomeric excess of chiral monomers used for the solid phase synthesis of chiral PNA oligomers. CE chiral analysis showed that a very high enantiomeric purity was generally achieved in the synthesis of all monomers, except for histidine and aspartic acid based monomers in which ca. 10% of the “wrong” enantiomer was always present.
Microchip electrophoresis for chiral separations
Authors: Belder Detlev , Ludwig Martin 
Published: July 2003

AbstractMicrochip electrophoresis (MCE) is a promising new technique for the separation of enantiomers. This recently introduced technique enables chiral separations to be performed in seconds on tiny micromachined devices. This review is intended to give a brief introduction into the principles of chiral separations with MCE with regard to methodology and instrumentation. Different approaches to realize chiral separations in microfluidic devices are described and discussed. This review gives an overview of original work done in this field with emphasis on approaches to improve detection and resolution in chiral MCE.
Enantioseparation of dihydrofurocoumarin derivatives by various separation modes of capillary electrophoresis
Authors: Egger Matthew D. , Liu Ying , Sevčík Juraj , Tesařová Eva , Rozhkov Roman , Larock Richard C. , Armstrong Daniel W. 
Published: July 2003

AbstractChiral dihydrofurocoumarin compounds are currently the focus of industrial and pharmacological research. These derivatives have been shown to possess many physiological properties that could be medically beneficial. This work proposes four different chiral separation methods using capillary electrophoresis and micellar capillary electrophoresis (MCE). Several different cyclodextrin chiral selectors were examined to evaluate their effectiveness in the enantioseparation of dihydrofurocoumarins. In addition, the effects of the chiral selector concentration, the presence of an organic modifier, run buffer pH, and in two cases, the ratio between the chiral selector and an additional charged pseudophase were investigated. Overall, the best separations for this class of chiral compounds were achieved using sulfated β‐cyclodextrins at low pH in the reversed polarity mode.
Polymeric alkenoxy amino acid surfactants: I. Highly selective class of molecular micelles for chiral separation of β‐blockers
Authors: Rizvi Syed A. A. , Shamsi Shahab A. 
Published: July 2003

AbstractTwo amino acid‐based alkenoxy micelle polymers were synthesized for this study. These include polysodium N‐undecenoxy carbonyl‐L‐leucinate (poly‐L‐SUCL) and polysodium N‐undecenoxy carbonyl‐L‐isoleucinate (poly‐L‐SUCIL). The polymerization time and concentration of the synthesized micelle polymers were optimized by 1H‐nuclear magnetic resonance (NMR) and capillary electrophoresis (CE) experiments. Detailed physicochemical properties (1H NMR, critical micelle concentration (CMC), optical rotation, partial specific volume, aggregation number, and polarity) were determined, and these molecular micelles were introduced as a pseudostationary phase in micellar electrokinetic chromatography to study the molecular recognition and to develop a method for simultaneous separation of eight chiral β‐blockers. It is found that poly‐L‐SUCL gives overall better chiral resolution and wider chiral window than poly‐L‐SUCIL. After optimizing the type of micelle polymer, injection size and temperature, simultaneous separation and enantioseparation of eight β‐blockers were achieved in less than 35 min. A comparison with the amide‐type surfactants of the same polar head group and alkyl chain length showed that carbamate‐type surfactants always work better than the corresponding amide‐type surfactant.
Influence of injection gate definition on the flow‐front approximation in numerical simulations of mold‐filling processes
Authors: Modi Dhiren , Šimáček Pavel , Advani Suresh 
Published: July 2003

AbstractFlow through porous media has been used to model resin impregnation in composites manufacturing processes such as resin transfer molding. Many numerical schemes have been used to explore the efficiency and accuracy in description of the movement of the liquid front when it is introduced through injection gates into a mold containing stationary and compacted fibrous porous media. In all numerical schemes, injection gates are modelled with a single node. Mathematically, a single node definition for a finite radius injection gate imparts a singularity. In this paper, an approach to avoid this singularity by modelling the injection gate with more than one node is presented. An analytical solution relating the fill time to the injection gate radius is developed for a constant pressure injection from a spherical injection gate into an isotropic media. A new parameter ‘mesh density level’, defined as the ratio of the injection radius to the element size, is used to investigate the accuracy and the convergence of the numerical results. It is shown that the numerical results converge when the mesh density level is increased. The accuracy of the results depends on the ratio of the flow‐front radius to the injection gate radius as well as on the mesh density level. In many situations, a spherical injection gate may not represent the correct physics and model simplification may be necessary.The impact of such simplifications is also quantified. The systematic analysis presented in this paper should prove useful to the modeller in taking the decision whether to select the proper, geometric definition for the injection gate to obtain accurate results or to define the injection gate using a single node and be aware of the errors introduced due to the singularity. Copyright © 2003 John Wiley & Sons, Ltd.
Synthesis and Characterization of Photocrosslinkable Biodegradable Polymers Derived from 4‐Hydroxycinnamic Acid
Authors: Nagata Minoru , Hizakae Sigeki 
Published: July 2003

AbstractA novel series of photocrosslinkable biodegradable polymers was prepared by a high‐temperature solution polycondensation from a dichloride of 4,4′‐(adipoyldioxy)dicinnamic acid (CAC) and alkane diols of various methylene lengths (HO(CH2)nOH; n = 6–10) or poly(ethylene glycol)s (PEG) of various molecular weights $(\bar M = 200 - 8300)$. The CAC was synthesized by the condensation of adipoyl chloride and 4‐hydroxycinnamic acid. The chemical structures and properties of these polymers were characterized by elemental analysis, ultraviolet‐visible spectroscopy (UV‐VIS), Fourier transform infrared spectroscopy (FT‐IR), 1H NMR spectroscopy, differential scanning calorimertry (DSC), and thermogravimetry (TG). All polymers had a high molecular weight and good solubility in organic solvents. DSC showed that Tm values of CACn (134–180 °C) were much higher than those of CACEm (25–56 °C). The CACE200 degraded very rapidly in the buffer solutions (pH 7.2) of Ps. Cepacia or Rh. delemar lipase at 37 °C, while CACn resisted the hydrolysis by these lipases during the test period. The ultraviolet light irradiation (λ ≥ 280 nm) caused the photocrosslinking reaction by an intermolecular dimerization at ambient temperature without a photosensitizer, as examined by UV‐VIS, FT‐IR spectroscopy, and gel formation. The gels prepared from CACEm (m ≈ 1 000) were swollen in water and showed characteristic properties of a hydrogel. The irradiation time and the molecular weight of PEGs controlled the degree of swelling of these hydrogels. The CACE8 300 gel irradiated for 20 min showed the largest degree of swelling of 10.5.Weight loss of a CACE200 film as a function of time in a phosphate buffer solution containing no lipase (□), Ps. cepacia lipase (•), or Rh. delemar lipase (○) at 37 °C.magnified imageWeight loss of a CACE200 film as a function of time in a phosphate buffer solution containing no lipase (□), Ps. cepacia lipase (•), or Rh. delemar lipase (○) at 37 °C.
Interferometric Sizing of Single‐Axis Birefringent Glass Fibers
Authors: Onofri Fabrice , Lenoble Anne , Radev Stefan , Bultynck Hervé , Guering Paul‐Henri , Marsault Nicolas 
Published: July 2003

AbstractThis paper deals with the on‐line sizing of small diameter glass fibers (i.e. d<30 μm) produced for textiles and reinforcement applications. Two models based on the Lorenz‐Mie Theory are introduced to predict the basic light scattering properties and the response of a phase Doppler interferometer (PDI) to the sizing of infinite glass fibers. Among other parameters, these models take into account particular effects such as the fiber's single‐axis birefringence and the fiber's refractive index dependence on its cooling rate (i.e. diameter). Both effects have a weak influence on the mean response of the PDI but a strong influence on the resonance structures of its phase‐diameter relationship. Two optical set‐ups were selected from a numerical optimization procedure and tested experimentally. Experimental results are presented demonstrating the validity of the models and the ability of the developed PDI set‐ups to study some features of the fiber drawing‐process: fluctuations of the fiber diameter when the nozzle is submitted to a convective perturbation and, when the fiber take‐up velocity is modulated, the detection of hollow fibers.
Quantitative Measurement of Planar Droplet Sauter Mean Diameter in Sprays using Planar Droplet Sizing
Authors: Domann Roland , Hardalupas Yannis 
Published: July 2003

AbstractThe purpose of this investigation is to assess and improve the accuracy of Sauter Mean Diameter measurements in dense sprays using a Planar Droplet Sizing (PDS) technique, based on the intensity ratio of scattered and fluorescence light. A novel data processing method of the PDS technique is suggested, which was derived from a theoretical light scattering investigation, and reduced possible sizing errors larger than 30% to below 10%. The novel approach for droplet sizing was applied to measure in a spray generated by a pressure swirl atomiser in a liquid‐fuelled burner operated with water at isothermal conditions, in order to avoid the effect of liquid evaporation on the accuracy of PDS technique. The Sauter Mean diameter results from the PDS technique were compared to Phase Doppler Anemometer (PDA) sizing measurements. Good agreement was obtained between the two techniques in dense regions of the spray. Discrepancies remained in dilute spray regions due to systematic statistical uncertainties of the PDS technique and the dynamic range of the intensity of the CCD cameras, which did not allow detection of large single droplets in the dilute spray region.
Bubble Velocity and Size Measurement with a Four‐Point Optical Fiber Probe
Authors: Guet Sébastien , Fortunati Robbert V. , Mudde Robert F. , Ooms Gijs 
Published: July 2003

AbstractThe possibility to measure the velocity and size of individual bubbles in a high‐void fraction bubbly flow is investigated by using a four‐point optical fiber probe. The air bubbles have an initial spherical equivalent diameter ranging from 4 to 10 mm and the void fraction is up to 0.3. Firstly, single bubble experiments show that intrusiveness effects, i.e. bubble deformations due to the probe, are negligible provided that the bubble approaches the probe at the axis of the central fiber. A selection criterion is utilized for multiple bubble experiments. A good compromise can be found between the required accuracy, the duration of the measurements and the number of validated bubbles required for reliable statistical averaging. In an air‐water high‐void fraction vertical bubbly pipe flow, the void fraction obtained with the instrument is found to be in good agreement with both local single‐fiber probe measurements, and with the volume average void fraction obtained from pressure gradient measurements. The area average volumetric gas flow rate, based on the bubble velocity and void fraction as measured with the four‐point probe, agree with the measured gas flow rate. Also, the liquid velocity is measured by means of a laser‐Doppler anemometer, to investigate the slip velocity. The results show that reliable and interesting measurements can be obtained by using a four‐point optical fiber probe in high void fraction flows.