bluuebunny/crossref_metadata_2025 huggingface dataset:
ERMs colocalize transiently with L1 during neocortical axon outgrowth
Authors: Mintz C. David , Dickson Tracey C. , Gripp Mark L. , Salton Stephen R.J. , Benson Deanna L.
Published: July 2003

L1 is a member of the Ig superfamily of cell adhesion molecules (CAMs) that functions in many aspects of neuronal development including axonal outgrowth and neuronal migration. These functions require coordination between L1 and the actin cytoskeleton. Because CAMs and the cytoskeleton do not bind directly, membrane–cytoskeletal linkers (MCLs) such as ankyrin are thought to be crucial to their interactions, but data from a knockout mouse suggest that ankyrin is not necessary for the earliest events attributed to L1 function. Recent findings in hippocampal cell culture show that members of the ERM family of proteins (ezrin, radixin, and moesin) can also serve as MCLs between L1 and actin in neurons. Here, we demonstrate that ERM proteins are expressed in extending neuronal processes in the intermediate zone of the developing cortex, a region that is densely packed with migrating neurons and growing axons. ERMs and L1 are codistributed extensively over a transient time course that coincides with rapid axon growth and cortical expansion. This codistribution is strong at embryonic day 17 and 19 but diminishes by postnatal day 0, at which time ankyrin‐L1 codistribution increases dramatically. These findings suggest that in the developing neocortex, ERMs are the predominant MCL for L1 during migration and axon extension, neither of which requires ankyrin function. Furthermore, these data suggest that there is a developmentally regulated switch in MCL function in the developing brain. J. Comp. Neurol. 464:438–448, 2003. © 2003 Wiley‐Liss, Inc.
Rearrangement of synaptic connections with inhibitory neurons in developing mouse visual cortex
Authors: Yamashita Akiko , Valkova Katia , Gonchar Yuri , Burkhalter Andreas
Published: July 2003

Cortical inhibition is determined in part by the organization of synaptic inputs to γ‐aminobutyric acidergic (GABAergic) neurons. In adult rat visual cortex, feedforward (FF) and feedback (FB) connections that link lower with higher areas provide ∼10% of inputs to parvalbumin (PV)‐expressing GABAergic neurons and ∼90% to non‐GABAergic cells (Gonchar and Burkhalter [1999] J. Comp. Neurol. 406:346–360). Although the proportions of these targets are similar in both pathways, FF synapses prefer larger PV dendrites than FB synapses, which may result in stronger inhibition in the FF than in the FB pathway (Gonchar and Burkhalter [1999] J. Comp. Neurol. 406:346–360). To determine when during postnatal (P) development FF and FB inputs to PV and non‐PV neurons acquire mature proportions, and whether the pathway‐specific distributions of FF and FB inputs to PV dendrites develop from a similar pattern, we studied FF and FB connections between area 17 and the higher order lateromedial area (LM) in visual cortex of P15–42 mice. We found that the innervation ratio of PV and non‐PV neurons is mature at P15. Furthermore, the size distributions of PV dendrites contacted by FF and FB synapses were similar at P15 but changed during the third to sixth postnatal weeks so that, by P36–42, FF inputs preferred thick dendrites and FB synapses favored thin PV dendrites. These results suggest that distinct FF and FB circuits develop after eye opening by rearranging the distribution of excitatory synaptic inputs on the dendritic tree of PV neurons. The purpose of this transformation may be to adjust differentially the strengths of inhibition in FF and FB circuits. J. Comp. Neurol. 464:426–437, 2003. © 2003 Wiley‐Liss, Inc.
Regenerating crayfish motor axons assimilate glial cells and sprout in cultured explants
Authors: Pearce Joanne , Lnenicka Gregory A. , Govind C.K.
Published: July 2003

Phasic and tonic motor nerves originating from crayfish abdominal ganglia, in 2–3‐day‐old cultured explants, display at their transected distal ends growth zones from which axonal sprouts arise. The subcellular morphology of this regenerative response was examined with thin serial‐section electron microscopy and reveals two major remodeling features. First, the external sprouts that exit the nerve are a very small part of a much more massive sprouting response by individual axons comprising several orders of internal sprouts confined to the nerve. Both internal and external sprouts have a simple construction: a cytoskeleton of microtubules and populations of mitochondria, clear synaptic vesicles, membranous sacs, and extrasynaptic active zone dense bars, features reminiscent of motor nerve terminals. Close intermingling of the sprouts of several axons give rise to a neuropil‐like arbor within the nerve. Thus, extensive sprouting is an intrinsic response of crayfish motor axons to transection. Second, an equally dramatic remodeling feature is the appearance of nuclei, which resemble those of adjacent glial cells, within the motor axons. These nuclei often appear where the adjoining membranes of the axon and glial cell are disrupted and where free‐standing lengths of the double membrane are present. These images signify a breakdown of the dividing membranes and assimilation of the glial cell by the axon, the nucleus being the most visible sign of such assimilation. Thus, crayfish motor axons respond to transection by assimilating glial cells that may provide regulatory and trophic support for the sprouting response. J. Comp. Neurol. 464:449–462, 2003. © 2003 Wiley‐Liss, Inc.
Synaptic and morphologic properties in vitro of premotor rat nucleus tractus solitarius neurons labeled transneuronally from the stomach
Authors: Glatzer Nicholas R. , Hasney Christian P. , Bhaskaran Muthu D. , Smith Bret N.
Published: July 2003

Neurons in the rat nucleus tractus solitarius (NTS) possess morphologic characteristics that have been correlated with the type of synaptic information they receive. These features have been described for viscerosensory neurons but not for premotor NTS neurons. The morphologic and synaptic features of neurons in the rat caudal NTS were assessed using whole‐cell patch‐clamp recordings and biocytin labeling in brainstem slices. Gastric‐related premotor NTS neurons were identified for recording after inoculation of the stomach wall with a transneuronal retrograde viral label that reports enhanced green fluorescent protein. Three morphologic groups of NTS neurons were identified based on quantitative aspects of soma area and proximal dendritic arborization, measures that were consistent across slice recordings. The most common type of cell (group I) had relatively small somata and one to three sparsely branching dendrites, whereas the other groups had larger somata and more than three dendrites, which branched predominantly close to (group II) or distant from (group III) the soma. Voltage‐clamp recordings revealed spontaneous excitatory and inhibitory postsynaptic currents in all neurons, regardless of morphology. Gastric‐related premotor NTS neurons composed two of the three morphologic types (i.e., groups I and II). Compared with unlabeled neurons, these cells were less likely to receive constant‐latency synaptic input from the tractus solitarius. These results refute the hypothesis that general patterns of synaptic input to NTS neurons depend on morphology. Gastric premotor neurons comprise a subset of NTS morphologic types, the organization of the viscerosensory input to which has yet to be defined. J. Comp. Neurol. 464:525–539, 2003. © 2003 Wiley‐Liss, Inc.
Effects of lipid oxidation on fish lipids — amylopectin interactions
Authors: Bienkiewicz Grzegorz , Kołakowska Anna
Published: July 2003

The results of studies on fish lipid oxidation effects on lipid‐amylopectin starch interactions are presented. Particular attention is paid to fish lipid availability (extractability from the system) and fatty acid contributions to individual lipid groups after mixing‐provoked interaction and after a 30‐day storage at —18 °C. The study involved model systems containing fish lipids at different levels of oxidation, lipids containing an antioxidant (BHA), and gelatinised amylopectin starch in a 10% aqueous solution. The lipid to starch ratio was 1:1. The test systems were subjected to selective extraction. The extracts were assayed for lipid content, peroxide value, anisidine value, fluorescence, and fatty acid composition.

Compared to fresh fish lipids, those lipids, which were oxidised to a higher extent were shown to be more amenable to complexing with amylopectin, but they were also more readily released during frozen storage. On the other hand, addition of BHA stabilised the lipid‐amylopectin starch interaction during storage at —18 °C.

In the entire systems tested, polyunsaturated fatty acids, eicosapentaenoic and docosahexaenoic acids in particular, proved to be most susceptible to binding, up to 90% of the latter being complexed.
Antioxidant activity of evening primrose phenolics in sunflower and rapeseed oils
Authors: Schmidt Štefan , Niklová Ivana , Pokorný Jan , Farkaš Pavel , Sekretár Stanislav
Published: July 2003

Crude ethanol/ethyl acetate extracts of industrial evening primrose (Oenothera biennis L.) seed meal were separated into six fractions using the Sephadex LH‐20 column chromatography and 96% aqueous ethanol as a mobile phase. Their antioxidant activities were tested in sunflower and rapeseed oils by using an Oxidograph apparatus at a temperature of 110 °C. Only the fractions III and IV displayed a pronounced antioxidant activity while the other fractions were either inactive or even pro‐oxidative. The active fractions contained phenolic acids and their esters; gallic acid, methyl and ethyl gallates, protocatechuic acid and its methyl ester were identified by GC/MS. Catechin was present, too, but exhibited only moderate antioxidant activity in sunflower oil.
Enantioseparation of warfarin and its metabolites by capillary zone electrophoresis
Authors: Zhou Qingyu , Yau Wai‐Ping , Chan Eli
Published: July 2003

A capillary zone electrophoresis (CZE) method with direct ultraviolet (UV)‐absorbance detection is presented for the simultaneous enantiomeric separation of warfarin and its main metabolites, including warfarin alcohols, 4’‐, 6‐, and 7‐hydroxywarfarin, using highly sulfated β‐cyclodextrin (HS‐β‐CD) as the chiral selector. This chiral separation method was optimized in terms of the electrophoretic parameters, which included the concentration of HS‐β‐CD used, the type and composition of organic modifier added to the background electrolyte (BGE) buffer, and the BGE buffer pH. Chiral separation of warfarin and its major metabolites was achieved with high resolution, selectivity, efficiency, repeatability, and reproducibility. This optimized chiral analysis of warfarin along with its metabolites was completed within a satisfactory electrophoresis time of 20 min.
Chiral electromigration methods in food analysis
Authors: Simó Carolina , Barbas Coral , Cifuentes Alejandro
Published: July 2003

This review article addresses the different chiral capillary electrophoretic methods that are being used for the study and characterization of foods and food compounds (e.g., amino acids, organic acids, sugars, pesticides). An updated overview, including works published till December 2002, on the principal applications of enantioselective procedures together with their main advantages and drawbacks in food analysis is provided. Some anticipated applications of chiral electromigration methods in food characterization are also discussed.
Quantitation of talinolol and other β‐blockers by capillary electrophoresis for in vitro drug absorption studies
Authors: Awadallah Bilal , Schmidt Peter C. , Holzgrabe Ulrike , Wahl Martin A.
Published: July 2003

A capillary zone electrophoresis method is described for the enantioseparation of talinolol using heptakis(2,3‐diacetyl‐6‐sulfo)‐β‐cyclodextrin (HDAS‐β‐CD) as a chiral selector. After liquid‐liquid extraction of talinolol from physiological solution, electrokinetic injection was employed to improve the sensitivity. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A baseline separation of the talinolol enantiomers was achieved in less than 10 min using 100 mM phosphate solution as background electrolyte and pH 3.5, at the presence of 3.0 mM HDAS‐β‐CD and at 20°C. In addition, this analytical condition proved to be useful for the enantioseparation of a number of other β‐blocking agents such as alprenolol, atenolol, bisoprolol, celiprolol, metipranolol, oxprenolol, and sotalol. For determing talinolol, the method could be validated in terms of precision, accuracy and linearity, and was found to be suitable in determination of talinolol enantiomers in highly diluted samples obtained from in vitro experiments.
Comparison of charged cyclodextrin derivatives for the chiral separation of atropisomeric polychlorinated biphenyls by capillary electrophoresis
Authors: García‐Ruiz Carmen , Crego Antonio L. , Marina M. Luisa
Published: July 2003

Charged cyclodextrin (CD) derivatives were used as chiral selectors in electrokinetic chromatography (EKC) for the chiral separation of highly hydrophobic neutral racemates such as atropisomeric polychlorinated biphenyls (PCBs). β‐CD‐phosphated, β‐CD sulfated, succinylated‐γ‐CD (Succ‐γ‐CD) and succinylated‐β‐CD (Succ‐β‐CD) were used as anionic CDs. As cationic CD, 6‐monodeoxy‐6‐monoamino‐β‐CD (β‐CD‐NH2) was tested for the first time in order to separate PCBs. From the different CD derivatives employed, the best separations were obtained with the cationic CD derivative. Thus, the use of β‐CD‐NH2 in phosphate buffer at pH 2.0 containing urea allowed the chiral recognition of eleven PCBs (45, 84, 88, 91, 95, 131, 136, 144, 149, 176, and 197). In this case, the addition of 2 M urea to the buffer solution was crucial to achieve the chiral separation of PCBs. The addition of acetonitrile to 10 mM phosphate buffer (pH 2.0) with 30 mM β‐CD‐NH2 and 2 M urea improved considerably the chiral resolution obtained for PCBs 91, 95, 136, 144, 149, and 197 although an increase in the analysis time was also observed. All the results obtained were compared with those previously obtained with the dual CD system carboxymethyl‐γ‐CD/β‐CD.
Influence of peak measurement parameters on the quality of chiral electrophoretic separations
Authors: Perrin Catherine , Fabre Huguette , Massart D. Luc , Vander Heyden Yvan
Published: July 2003

The effect of nine peak measurement/analysis parameters on chiral capillary electrophoresis (CE), followed by UV detection, was studied. The parameters pertained UV‐detection (detection wavelength, reference wavelength, and wavelength bandwidths), signal processing (data acquisition rate, type and amount of filtering) and peak detection (detection threshold and peak width). The influence of these factors on the chiral separation of dimethindene enantiomers was studied at two different concentrations (i.e., at high and low signal‐to‐noise (S/N) ratio) by the means of experimental designs. The electropherogram characteristics considered were the resolution between the two enantiomers, the peak areas, and the S/N ratio. A D‐optimal design was first used as screening design to identify the most critical parameters. Afterwards, a modelling of the different responses as a function of these critical parameters was performed based on the results of a face‐centered central composite design. The results showed that the signal‐processing parameters should be carefully selected when developing a CE separation since very important variations in the separation, the S/N ratio and the peak area of the substances can occur by setting these parameters at different levels. The detection wavelength should also be carefully chosen for optimal peak area measurement. The role of these parameters becomes more important with decreasing concentration of the analytes (i.e., low S/N ratio). This study showed that the peak measurement/analysis parameters should be optimized as the chemical and physical parameters of a method. They also should always be well specified in order to allow a good transfer of a method from one instrument to another.
Chiral characterization of deprenyl‐N‐oxide and other deprenyl metabolites by capillary electrophoresis using a dual cyclodextrin system in rat urine
Authors: Tábi Tamás , Magyar Kálmán , Szökő Éva
Published: July 2003

A chiral capillary electrophoresis method has been developed for the simultaneous separation of the enantiomers of deprenyl and eight of its metabolites, among them the recently described metabolite deprenyl‐N‐oxide. Although heptakis‐(2,6‐di‐O‐methyl)‐β‐cyclodextrin (DIMEB) was suitable for the enantioresolution of deprenyl and its dealkylated derivatives, the enantiomers of deprenyl‐N‐oxide were just partly resolved. Carboxymethyl‐β‐cyclodextrin (CMBCD) in as low as 2 mM concentration was capable of the enantiomer separation of all the nine examined compounds, however co‐migration of 1R,2S‐(−)‐norephedrine and 1R,2R‐(−)‐pseudoephedrine, as well as 1S,2R‐(+)‐ephedrine and R‐(−)‐amphetamine was observed. This problem could be overcome by the use of a dual cyclodextrin system containing 4 mM DIMEB in addition to 2 mM CMBCD; simultaneous separation of all the compounds could be achieved. The optimized method was used for the analysis of rat urine samples after 10 days of treatment of animals with either R‐(−)‐ or S‐(+)‐deprenyl. The stereospecific biotransformation of both deprenyl enantiomers was confirmed, and the stereoselectivity of N‐oxide formation was demonstrated.
Separation of basic drug enantiomers by capillary electrophoresis using chicken α1‐acid glycoprotein: Insight into chiral recognition mechanism
Authors: Matsunaga Hisami , Sadakane Yutaka , Haginaka Jun
Published: July 2003

Recombinant chicken α1‐acid glycoprotein (α1‐AGP) was prepared by the Escherichia coli expression system and completely deglycosylated α1‐AGP (cd‐α1‐AGP) was obtained by treatments of native α1‐AGP with a mixture of endoglycosidase and N‐glycosidase. The average molecular masses of chicken α1‐AGP, cd‐α1‐AGP and recombinant α1‐AGP were estimated to be about 29 200, 21 700 and 20 700, respectively, by matrix‐assisted laser desorption‐time of flight‐mass spectrometry. We compared the chiral recognition ability of chicken α1‐AGP, cd‐α1‐AGP and recombinant α1‐AGP using them as chiral selectors in capillary electrophoresis. The chicken α1‐AGP showed higher resolution for eperisone, pindolol and tolperisone than cd‐α1‐AGP or recombinant α1‐AGP. Recombinant α1‐AGP still showed chiral recognition for three basic drugs tested. By addition of propranolol as a competitor in the separation solution in CE, no enantioseparations of three basic drugs were observed with chicken α1‐AGP, cd‐α1‐AGP or recombinant α1‐AGP. These results reveal that the protein domain of the chicken α1‐AGP is responsible for the chiral recognition ability, and that the chiral recognition site(s) for basic drugs exists on the protein domain.
Capillary electrochromatographic separation of enantiomers on chemically bonded type of cellulose derivative chiral stationary phases with a positively charged spacer
Authors: Chen Xiaoming , Jin Wenhai , Qin Feng , Liu Yueqi , Zou Hanfa , Guo Baochuan
Published: July 2003

Positively charged chiral stationary phases (CSPs) were prepared for capillary electrochromatography (CEC) separation of enantiomers by chemically immobilizing cellulose derivatives onto diethylenetriaminopropylated silica (DEAPS) with tolylene‐2,4‐diisocyanate (TDI) as a spacer reagent. Anodic electroosmotic mobility was observed in both nonaqueous and aqueous mobile phases due to the positively charged amines on the surface of the prepared CSPs. For comparison, the traditionally used 3‐aminopropyl silica (APS) was also adopted as the base material instead of DEAPS to prepare CSP. It was observed that the EOF on the DEAPS‐based CSP was 18%–60% higher than that on the APS‐based CSP under nonaqueous mobile phase conditions. Separation of enantiomers in CEC was performed on the positively charged CSPs with the nonaqueous mobile phases of pure ethanol or mixture of hexane‐alcohol and the aqueous phases of acetonitrile‐water or 95% ethanol. Fast separation of enantiomers was achieved on the newly prepared CSPs.
Enantioseparations of basic and bifunctional pharmaceuticals by capillary electrochromatography using polysaccharide stationary phases
Authors: Mangelings Debby , Hardies Nancy , Maftouh Mohamed , Suteu Christina , Massart D. Luc , Vander Heyden Yvan
Published: July 2003

A fast screening strategy was developed in capillary electrochromatography (CEC) for the chiral separation of basic and bifunctional compounds. The screening conditions were determined on polysaccharide chiral stationary phases using 15 pharmaceutical compounds. The content and type of organic modifier, as well as the pH of the mobile phase appeared to have the largest influence on the chiral resolution. It was seen that for acidic compounds, our approach was not suitable. A generic mobile phase for basic and bifunctional compounds was determined. The testing on 20 additional compounds showed that the proposed mobile phase performed well since enantioselectivity was observed for 86% of the investigated compounds. A comparison of CEC and reversed‐phase liquid chromatography (RPLC) results was attempted to demonstrate the potential of the used technique for chiral method development.
Chiral separation of diastereomeric flavanone‐7‐O‐glycosides in citrus by capillary electrophoresis
Authors: Gel‐Moreto Nuria , Streich René , Galensa Rudolf
Published: July 2003

The 2S‐ and 2R‐diastereomers of major flavanone‐7‐O‐glycosides found in sweet orange (Citrus sinensis), mandarine (Citrus deliciosa), grapefruit (Citrus paradisi), lemon (Citrus limon), and sour or bitter orange juice (Citrus aurantium) were separated for the first time by chiral capillary electrophoresis (CE) employing various buffers with combined chiral selectors. Native cyclodextrins (CDs), neutral and charged CD derivatives were examined as chiral additives to the background electrolyte (BGE). Separation efficiency has not proved satisfactory with one single CD as chiral selector in the buffer, a full and simultaneos separation could often be achieved only by using combined buffer with two different CDs. Chiral separation of major flavanones in sweet orange, mandarine and grapefruit juices raised more difficulties than in lemon and sour orange juices as narirutin will not readily build complexes with most CDs. Diastereomeric flavanones of mature and immature grapefruits were compared and some differences were found: naringin showed different diastereomeric ratio and 2S‐prunin appeared only in immature grapefruit. Marmalade was also examined by chiral CE. Its major flavanones corresponded to flavanone pattern of mixed sour and sweet oranges.
Quantitative chiral analysis in capillary electrophoresis from unresolved peaks using derivative electropherograms, experimental design, and artificial neural networks
Authors: Dohnal Vlastimil , Zhang Fang , Li Hua , Havel Josef
Published: July 2003

Quantitative capillary electrophoretic analysis of chiral compounds might be difficult or even impossible when baseline separation is not reached. In this work, the use of n‐th derivative of the electropherogram was studied and examined on model and experimental data. The electropherograms should be first smoothed using Savitzky‐Golay method and the quantitative analysis is then possible using either a graphical method or multivariate calibration applying a combination of experimental design (ED) and artificial neural networks (ANNs). The best results were obtained for the first derivative, higher derivatives are not suitable because of noise accumulation. The method was applied to real experimental data to quantify chiral amino acids from unresolved peaks, but it is applicable for quantitative analysis of any other chiral analytes from poorly resolved peaks. Precision of analysis from partially resolved peaks reached was about ± 3.2% relative standard deviation.
Capillary electrophoresis as a probe of enantiospecific interactions between photoactive transition metal complexes and DNA
Authors: Schaeper James P. , Nelsen Lori A. , Shupe M. Alyson , Herbert Brad J. , Kane‐Maguire Noel A. P. , Wheeler John F.
Published: July 2003

Recently, we have demonstrated the capacity to separate chiral transition metal (TM) complexes of the type [M(diimine)3]n+ using CE buffers containing chiral tartrate salts. In separate work, several chromium(III)‐tris‐diimine complexes in particular have been shown to bind enantioselectively with calf‐thymus (CT) DNA, and a qualitative assessment of the relative strength and enantiospecificity of this interaction is of significant interest in the characterization of these complexes as potential DNA photocleavage agents. Here, we describe two convenient approaches to investigate such binding behavior using chiral CE. For complexes with lower DNA affinities exhibiting primarily surface binding, DNA itself is used as the chiral resolving agent in the electrophoretic buffer. In this approach, resolution of the TM complexes into their Λ and Δ isomers is achieved with the isomer eluting later exhibiting superior binding affinity toward DNA. For more strongly bound TM complexes containing ligands known to intercalate with DNA, the [Cr(diimine)3]3+ complexes are preincubated with oligonucleotide and subsequently enantiomerically resolved in a dibenzoyl‐L‐tartrate buffer system that facilitates analysis of the unbound TM species only. Differences in isomer binding affinity are distinguished by the relative peak areas of the Λ‐ and Δ‐isomers, and relative binding strengths of different complexes can be inferred from comparison of the total amount of unbound complex at equivalent DNA/TM ratios.
Rapid determination of salbutamol in pharmaceutical preparations by chiral capillary electrophoresis
Authors: Ekiert Ela , García‐Ruiz Carmen , García Maria A. , Marina Maria L.
Published: July 2003

A fast and simple method of chiral capillary electrophoresis (CE) has been applied to the analysis of salbutamol in different pharmaceutical preparations. Using of a 25 mM acetate buffer (pH 5.0), containing 13.1 mg/mL carboxymethyl‐β‐cyclodextrin (CM‐β‐CD), an applied voltage of 20 kV and a temperature of 25°C, the enantiomers of salbutamol could be separated in about 2 min. Three different pharmaceutical preparations (two syrups, one oral solution, and two kind of tablets) containing a racemate of salbutamol were injected directly in the CE system, following dilution in dimethyl sulfoxide (DMSO). Appreciable differences in the retention times were observed for salbutamol enantiomers in the different formulations studied, which were attributed to the effect of the matrix components on the electrophoretic mobility. The standard addition method was used for the calibration due to the existence of matrix interferences. Finally, the stability of the enantiomers of salbutamol in the oral solution was studied calculating the enantiomeric ratio values when the solution was injected immediately after being opened in the first case and after being opened and stored in the fridge for two months in the second case.
Capillary electrophoresis evidence for the stereoselective metabolism of itraconazole in man
Authors: Breadmore Michael C. , Thormann Wolfgang
Published: July 2003

Itraconazole (ITC) is a hydrophobic antimycotic drug with three chiral centers that is used clinically as a stereoisomeric mixture. A chiral capillary electrophoretic method for the separation of ITC stereoisomers and those of its main metabolite hydroxyitraconazole (HITC) was developed to determine the stereoselective nature of the ITC to HITC biotransformation. The method is based on the formation of inclusion complexes of the target analytes with the negatively charged sulfated β‐cyclodextrin in the presence of moderate concentrations of methanol in a low‐pH phosphate buffer. The addition of polyethylene glycol 4000 was found to be critical in obtaining baseline resolution of eight peaks, two from ITC, four from HITC, and two from R051012 (internal standard), in under 20 min. Application of the developed procedure to serum samples from patients being treated with ITC showed clearly the presence of a stereoselective component in the metabolism of this antimycotic drug. This could be shown from in vitro incubations with single enzyme Supersomes™ to be in part due to the stereoselective formation of HITC by the human CYP3A4 enzyme. For one patient, monitoring of the ITC and HITC concentrations and peak ratios over a 103 day period of treatment with ITC showed a strong dependency of the chiral ITC ratio to the concentration of ITC, while the dominant enantiomeric ratio of HITC was largely independent of the total HITC concentration.
Coated microfluidic devices for improved chiral separations in microchip electrophoresis
Authors: Ludwig Martin , Belder Detlev
Published: July 2003

Chiral separations of fluorescein isothiocyanate‐labeled amines have been performed in poly(vinyl alcohol) (PVA)‐coated microfluidic glass chips. Baseline separation of enantiomers could be realized in coated devices while they could not be resolved in uncoated chips. The electroosmotic flow (EOF) in PVA‐coated channels is suppressed over a wide pH range which leads to a considerable improved reproducibility of migration times in repetitive analysis. Due to the high resolution obtained in such devices, it was possible to reliable determine the enantiomeric purity with high accuracy. One percent of the minor enantiomer could be determined in the presence of large excess of the other enantiomer. As the EOF was suppressed, the anionic compounds were detected at the anode whereas the dominant EOF in uncoated devices resulted in an effective mobility to the cathode. Applying PVA‐coated channels considerable improved precision of migration times was found. The relative standard deviation of migration times was below 1% in PVA‐coated devices. Accordingly, excessive rinsing or etching steps in order to stabilize the EOF could be omitted while this was necessary for a reliable operation of uncoated devices.
Enantioselectivity of alcohol‐modified polymeric surfactants in micellar electrokinetic chromatography
Authors: Tarus Jepkoech , Agbaria Rezik A. , Morris Kevin , Billiot Fereshteh H. , Williams Alicia A. , Chatman Trenderlyn , Warner Isiah M.
Published: July 2003

A novel method of modifying sodium undecanoyl‐L‐leucinate (SUL) micelles employed in chiral separation of analytes in micellar electrokinetic chromatography (MEKC) to enhance selectivity toward specific analytes is discussed. The current study aimed at modifying the SUL micelles by introducing different alcohols into the mono‐SUL micelles. The micellar solutions were then polymerized in the presence of alcohols followed by postpolymerization extraction of the alcohols to yield alcohol‐free polymeric surfactants (poly‐L‐SUL). The effects of hexanol (C6OH) and undecylenyl alcohol (C11OH) on micellar properties of this surfactant were investigated by use of surface tensiometry, fluorescence spectroscopy, pulsed field gradient‐nuclear magnetic resonance (PFG‐NMR), and MEKC. The surface tension and PFG‐NMR studies indicated an increase in the critical micelle concentration (cmc) and micellar size upon increasing the alcohol concentration. Fluorescence measurements suggested that alcohols induce closely packed micellar structures. Coumarinic and benzoin derivatives, as well as (±)‐1, 1'‐binaphthyl‐2,2'‐dihydrogen phosphate (BNP) were used as test analytes for MEKC experiments. Examination of MEKC data showed remarkable resolutions and capacity factors of coumarinic derivatives obtained with modified poly‐L‐SUL as compared to the unmodified poly‐L‐SUL. Evaluation of fluorescence, PFG‐NMR, and MEKC data suggest a strong correlation between the polarity and hydrodynamic radii of alcohol‐modified micelles and the resolution of the test analytes.
Synthesis, analytical characterization and initial capillary electrophoretic use in acidic background electrolytes of a new, single‐isomer chiral resolving agent: Hexakis(2,3‐di‐O‐acetyl‐6‐O‐sulfo)‐ α‐cyclodextrin
Authors: Li Shulan , Vigh Gyula
Published: July 2003

The sodium salt of hexakis(2,3‐di‐O‐acetyl‐6‐O‐sulfo)‐α‐CD (HxDAS), the first member of the family of single‐isomer, fully sulfated α‐CDs, has been synthesized and used for the initial capillary electrophoretic separation of the enantiomers of nonionic, weak acid, weak base, and ampholytic analytes. HxDAS complexes less strongly with many of the analytes tested than the analogous β‐ and γ‐cyclodextrin derivatives, namely, heptakis(2,3‐di‐O‐acetyl‐6‐O‐sulfo)‐β‐cyclodextrin (HDAS) and octakis(2,3‐di‐O‐acetyl‐6‐O‐sulfo)‐γ‐cyclodextrin (ODAS). Nevertheless, it facilitated the separation of the enantiomers of a large number of weak electrolyte and nonelectrolyte analytes in acidic aqueous background electrolytes. For all analytes, the effective mobilities and separation selectivities as a function of the background electrolyte concentration of HxDAS followed the trends that were found for HDAS and ODAS.
Mechanistic study of the enantiomeric recognition of a basic compound with negatively charged single‐isomer γ‐cyclodextrin derivatives using capillary electrophoresis, nuclear magnetic resonance spectroscopy, and infrared spectroscopy
Authors: Zhou Lili , Thompson Richard , Reamer Robert A. , Lin Zhihao , French Mike , Ellison Dean , Wyvratt Jean
Published: July 2003

The possible mechanisms for the chiral recognition of 2‐(R)‐N‐[1‐(6‐aminopyridin‐2‐ylmethyl)piperidin‐4‐yl]‐2‐[(1R)‐3,3‐difluorocyclopentyl]‐2‐hydroxy‐2‐phenylacetamide (RR‐M3), and its enantiomer (SS‐M3) with octakis(2,3‐di‐O‐acetyl‐6‐sulfo)‐γ‐cyclodextrin (ODAS‐γ‐CD) and octakis(6‐sulfo)‐γ‐cycöpdextrom enantiomer; (OS‐γ‐CD), were investigated using capillary electrophoresis (CE), proton (1H), fluorine (19F) and carbon (13C) nuclear magnetic resonance spectroscopy (NMR), and infrared (IR) spectroscopy. Clear evidence for the formation of diastereomeric complexes between the enantiomers and the two CDs was observed. NMR spectra suggest that the phenyl and difluorocyclopentyl rings are involved in the complexation. The phenyl ring on the guest molecule is deeply penetrated into the cavity of OS‐γ‐CD, but it is not included into the cavity of ODAS‐γ‐CD. The continuous variation plots built based on the 1H NMR and IR spectra indicate a 1:1 complex stoichiometric ratio of the M3 enantiomers for both CDs. The affinity of the enantiomers for the two CDs is opposite.
Assessment of the stereoselective metabolism of methaqualone in man by capillary electrophoresis
Authors: Prost Francine , Thormann Wolfgang
Published: July 2003

Methaqualone (MQ) and its hydroxylated metabolites are quinazoline derivatives that exhibit atropisomerism. As a continuation of our previous work with these compounds (Electrophoresis 2001, 22, 3270–3280), chiral capillary zone electrophoresis with hydroxypropyl‐β‐cyclodextrin as buffer additive and multiwavelength absorbance detection is shown to be an effective tool to provide insight into the stereoselectivity of the MQ metabolism. The five major monohydroxy MQ metabolites formed during biotransformation do not show enantiomerization at temperatures up to 85°C. Enzymatic and acidic hydrolysis of urines that were collected after concomitant administration of 250 mg of MQ and 25 mg diphenhydramine (DH) chloride are both shown to provide stereoselective metabolic patterns with 4’‐hydroxymethaqualone, the major urinary metabolite, being excreted almost exclusively as a single enantiomer. A stereoselectivity in the formation of 2’‐hydroxymethaqualone and 2‐hydroxymethaqualone was also observed in vitro using human liver microsomes and preparations containing the cytochrome P450 enzyme (CYP) CYP3A4 only. The presence of DH during incubation with human liver microsomes did not reveal a difference in the metabolic pattern obtained. Furthermore, CYP2D6 and CYP2C19 do not significantly contribute to the metabolism of MQ. This was independently observed in vitro and via analysis of urines of individuals that are either efficient metabolizer phenotypes or poor metabolizer phenotypes for the two polymorphic enzymes. Although interindividual differences in the monitored metabolic patterns were noted, no marked difference could be related to a CYP2D6 or CYP2C19 polymorphism.
pH‐dependent cyclodextrin capillary electrophoresis resolution of atropisomers
Authors: Zerbinati Orfeo , Trotta Francesco
Published: July 2003

Five noncommercial and four commercially available cyclodextrin (CD) derivatives were tested as chiral auxiliaries for the capillary electrophoretic (CE) resolution of racemic 1,1’‐bi‐(2‐naphthol) (BN), 1,1’‐binaphthyl‐2,2’‐diyl hydrogenphosphate (BNHP), and 1,1’‐binaphthyl‐2,2’‐diamine (BNA) at pH 4.0, 6.5, and 8.6. The noncommercial CDs were ethyloxycarbonyl‐γ‐CD (ethylcarbonate‐γ‐CD), dimethylamino ethyloxycarbonyl‐β‐CD, a mercaptosuccinic acid derivative of β‐CD, a maleic acid derivative of β‐CD and heptakis(6‐deoxy‐6‐amino)‐β‐CD derivative with one amino group on the C‐6 carbon of each glucose unit. Except for the latter, the remaining derivatives were synthesized for this work. Also commercially available methyl‐β‐CD, hydroxypropyl‐β‐CD and the native β‐ and γ‐CDs were examined. Among the nine CDs tested, the maleic acid derivative of β‐CD gave the most interesting performances, since it resolved the atropisomers of BNA and BNHP in the same electrophoretic run at pH 4.0. It resolved the BNA racemate also at pH 6.5. Both the negatively charged CD tested were found to resolve anionic BNHP enantiomers, while positively charged CDs did not with cationic BNA. Several of the CDs investigated in this work were found to resolve the BNHP racemate, although at nonoptimal concentration. None of the experimented CDs was found to resolve the electrically neutral BN atropisomers pair at the three pHs considered, while some among these nine, experimented in a previous work, did so at higher pH.
A three‐dimensional contact algorithm for sliding surfaces
Authors: Dawes A. S.
Published: July 2003

This paper describes a model for sliding contact between materials. This has been embodied in a contact algorithm which has been incorporated into a three‐dimensional, time‐dependent, staggered mesh, finite element Lagrangian code. We first present an overview of the code and then describe the model underpinning the contact algorithm. The stages of the algorithm are then described and finally, results are presented for a number of different problems. Copyright © 2003 John Wiley & Sons, Ltd.
Modified method of characteristics for solving population balance equations
Authors: Pilon Laurent , Viskanta Raymond
Published: July 2003

This paper presents a new numerical method for solving the population balance equation using the modified method of characteristics. Aggregation and break‐up are neglected but the density function variations in the three‐dimensional space and its dependence on the external fields are accounted for. The method is an interpretation of the Lagrangian approach. Based on a pre‐specified grid, it follows the particles backward in time as opposed to forward in the case of traditional method of characteristics. Unlike the direct marching method, the inverse marching method uses a fixed grid thus, making it compatible with other numerical schemes (e.g. finite‐volume, finite elements) that may be used to solve other coupled equations such as the mass, momentum, and energy conservation equations. The numerical solutions are compared with the exact analytical solutions for simple one‐dimensional flow cases. Very good agreement between the numerical and the theoretical solutions has been obtained confirming the validity of the numerical procedure and the associated computer program. Copyright © 2003 John Wiley & Sons, Ltd.
Discontinuous Galerkin spectral element lattice Boltzmann method on triangular element
Authors: Shi Xing , Lin Jianzhong , Yu Zhaosheng
Published: July 2003

Discontinuous Galerkin spectral element method is used to solve the lattice Boltzmann equation (LBE) in the discrete velocity space. The triangular elements are adopted because of their flexibility to deal with complex geometries. The flow past a circular cylinder is simulated by the proposed scheme. The results are consistent with those obtained from the previous numerical methods and experiments. Copyright © 2003 John Wiley & Sons, Ltd.
Cyclodextrins in Polymer Synthesis: Enzymatic Polymerization of a 2,6‐Dimethyl‐β‐Cyclodextrin/2,4‐Dihydroxyphenyl‐4′‐Hydroxybenzylketone Host‐Guest Complex Catalyzed by Horseradish Peroxidase (HRP)
Authors: Mejias Lorenzo , Schollmeyer Dieter , Sepulveda‐Boza Silvia , Ritter Helmut
Published: July 2003

This paper reports the enzymatic polymerization of the inclusion complex 2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone/2,6‐dimethyl‐β‐cyclodextrin by horseradish peroxidase (HRP) in aqueous media. The structure of the complex was determined by means of NOESY‐NMR and crystallographic analysis (indicating an orthorhombic structure). The enzymatic polymerization of the uncomplexed 2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone yields oligomers with molecular weights up to $\overline M _{\rm w} = 4 \times 10^3$ in organic‐aqueous media, but because of its poor solubility in aqueous systems, no polymerization is observed if water is used as solvent. An increase of the availability of the ketone in solution is achieved by complexing it with random‐methylated β‐cyclodextrin in water. We found that the use of methylated β‐cyclodextrin in equimolar concentration to the monomer increases the polymerization yield and the average molecular weight. The polymers formed were analyzed by GPC and ATR‐FTIR techniques.

Representation from X‐ray diffraction analysis of the 2,6‐dimethyl‐β‐cyclodextrin/2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone host‐guest complex (3).

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Representation from X‐ray diffraction analysis of the 2,6‐dimethyl‐β‐cyclodextrin/2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone host‐guest complex (3).
Synthesis of Strong Electrolyte Temperature‐Sensitive Hydrogels by Radiation Polymerization and Application in Protein Separation
Authors: Yang Hua , Song Weiqiang , Zhuang Yinfeng , Deng Xianmo
Published: July 2003

Strong electrolyte temperature‐sensitive hydrogels were synthesized by radiation polymerization using N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methylpropanesulfonate. The influence of irradiation dose and mole ratio of the monomers was examined by swelling measurements in aqueous solution and organic solvents. The hydrogels without any pollution were applied in concentrating protein.

Effect of irradiation dose on swelling ratios of P(NIPA‐co‐NaAMPS) hydrogels.

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Effect of irradiation dose on swelling ratios of P(NIPA‐co‐NaAMPS) hydrogels.
Role of Water Activity on the Synthesis of Vinyl Thymidine Catalyzed by Protease from Bacillus Subtilis
Authors: Fan Hong , Kitagawa Masaru , Raku Takao , Tokiwa Yutaka
Published: July 2003

The transesterification activity of Bioprase, a protease from Bacillus subtilis, in dimethylformamide (DMF) is found to depend strongly on water addition. For the transesterification between thymidine and divinyl adipate by Bioprase in DMF with water (5–40%), the conversion rate of thymidine to the ester is much higher than the rate in DMF without the addition of water. For example, the transesterification reaction of 0.25 M thymidine with 1 M divinyl adipate in DMF in the presence of 10% water was catalyzed by Bioprase (50 mg · ml−1) at 30 °C for only 10–20 minutes to give 5′‐O‐vinyladipoyl thymidine (conversion ca. 90%), but the reaction did not proceed without the addition of water. Furthermore, the water effect is useful for the transesterification of thymidine with divinyl sebacate, which has a longer alkyl chain than divinyl adipate. This investigation showed that DMF adsorbs on the enzyme surface instead of essential water in the reaction of DMF without addition of water. On the other hand, in the reaction of DMF/water cosolvents, essential water bound to enzyme was not removed by DMF, and a higher transesterification activity occurs thereafter.

Effect of water on the transesterification of thymidine catalyzed by Bioprase in DMF.

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Effect of water on the transesterification of thymidine catalyzed by Bioprase in DMF.
Enzymatic Synthesis and Polymerization of Cyclic Trimethylene Carbonate Monomer with/without Methyl Substituent
Authors: Tasaki Hiroaki , Toshima Kazunobu , Matsumura Shuichi
Published: July 2003

The direct enzymatic synthesis of a cyclic trimethylene carbonate (1,3‐dioxane‐2‐one) monomer with/without a methyl substituent was carried out using dimethyl or diethyl carbonate and 1,3‐diol with the objective of producing aliphatic poly(trimethylene carbonate), a typical biodegradable synthetic plastic. The lipase‐catalyzed condensation of dimethyl or diethyl carbonate with aliphatic 1,3‐diols using immobilized Candida antarctica lipase (lipase CA) in an organic solvent at 70 °C afforded the corresponding methyl‐substituted and unsubstituted cyclic trimethylene carbonates. The cyclic trimethylene carbonates obtained by the reaction of dimethyl or diethyl carbonates with 1,3‐propanediol and 2‐methyl‐1,3‐propanediol were polymerized by lipase to produce the corresponding polycarbonates.

Total TMC yield as a function of the reaction time.

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Total TMC yield as a function of the reaction time.
Applications of Defocusing DPIV to Bubbly Flow Measurement
Authors: Jeon David , Pereira Francisco , Gharib Morteza
Published: July 2003

Defocusing digital particle image velocimetry (DDPIV) was used to investigate a bubbly flow in the wake of a hydrofoil. DDPIV is a three component volumetric velocimetry technique that operates at full video rate. Complex, three‐dimensional, and time‐dependent flows can be measured. To measure the bubble sizes, an extension to DDPIV was made to infer bubble sizes from their intensities. Both bubble size distributions and bubble velocity fields were simultaneously measured. Results indicate that DDPIV can reliably measure bubble sizes in the range of 100 microns, as well as resolving their aggregate motion.
Planar Droplet Sizing for the Characterization of Droplet Clusters in an Industrial Gun‐Type Burner
Authors: Zimmer Laurent , Ikeda Yuji
Published: July 2003

An important problem in spray combustion deals with the existence of dense regions of droplets, called clusters. To understand their formation mechanism, the droplet dynamics and fuel concentration profile are investigated by means of planar laser techniques in an industrial gun‐type burner. The simultaneous measurement of elastic Mie scattering and Laser Induced Fluorescence (LIF) allows the instantaneous measurement of the Sauter Mean Diameter (SMD), after proper calibration. Using two different CCDs to get the two signals requires a detailed calibration of the CCD response before getting absolute diameters. Pixels are binned 6 by 6 to obtain the final SMD map, this is a compromise between spatial accuracy and noise. Velocity field is measured on both sets of images using standard Particle Image Velocimetry (PIV) algorithms. The comparison of cross‐correlation technique with PDA results shows that the velocity measured on the LIF images are close to the velocity based on D30, whereas the Mie scattering results are similar to D20. On Mie scattering images, regions of high interfacial area forming clusters can be detected. A special tracking scheme is used to characterize their dynamics in terms of velocity and diameters by ensuring that the same volume of fluid is tracked. It is shown that the clusters have a velocity similar to the velocity of droplets with the same diameter as the mean SMD of the cluster. It is also shown that an increase of pressure tends to trigger the appearance of such a group of droplets, due to a smaller diameter of the droplets caused by the increase of pressure discharge. Uncertainties for the different techniques used are discussed.