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  • Articles: DFG German National Licenses  (1,471)
  • 1995-1999  (1,471)
  • 1996  (1,471)
  • Engineering General  (686)
  • Organic Chemistry  (539)
  • Industrial Chemistry and Chemical Engineering  (246)
  • Nuclear reactions
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  • Articles: DFG German National Licenses  (1,471)
Material
Years
  • 1995-1999  (1,471)
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 6-10 
    ISSN: 0899-0042
    Keywords: enantiopure levodropropizine ; synthesis ; (R)-glycidol ; enantiomeric separation ; chiral HPLC ; enantiomeric enrichment ; binary melting point phase diagram ; crystal structure determination ; intermolecular hydrogen-bonding interactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure levodropropizine can be synthesized in high yield by the direct nucleophilic addition of 1-phenylpiperazine to (R)-glycidol followed by recrystallization in absolute ethanol. A chiral HPLC method has been developed for the determination of its optical purity. The enantiomeric enrichment behavior of this compound in the recrystallization process is discussed according to its binary melting point phase diagram. Single crystal x-ray structural analysis shows the intermolecular hydrogen-bonding interactions between the hydroxyl and piperazinyl groups within the crystal lattice of levodropropizine. © 1996 Wiley-Liss, Inc.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 24-29 
    ISSN: 0899-0042
    Keywords: CHO cells ; HeLa cells ; lipid peroxidation ; catalase ; D-amino acids ; L-amino acids ; toxicity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While the L-configuration of amino acids predominates in all known living systems, D-enantiomers of amino acids have been detected with highly sensitive chromatographic techniques in human physiological fluids. In the present study, the survival of Chinese hamster ovary cells (CHO) and HeLa cells was inhibited by exposure to high concentrations of some D- or L-amino acids. Inhibition of colony formation, though, was not necessarily observed to be chiral-dependent. Some L-amino acids (LAAS) were found to be toxic while other D-amino acids (DAAS) were innocuous in both cultures. This is contradictory to the previous observations that DAAS were generally considered to be harmful. Frequently it was implied, although not experimentally proven, that the LAAS were not toxic. One of the metabolites produced by oxidative deamination of D- or LAAS is hydrogen peroxide (H2O2), a reactive oxygen species (ROS) that is decomposed by catalase. Increased intracellular H2O2 can result in peroxidation of lipids. We measured catalase activity and the lipid peroxide levels (LPO) after incubating cells in either D- or LAAS. The amino acids (AAS) that were found to inhibit colony formation were found to be associated with higher levels of catalase activity and LPO. Therefore, we hypothesize that enhanced ROS generation may be, in part, responsible for the observed toxicity of some amino acids. © 1996 Wiley-Liss, Inc.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 35-38 
    ISSN: 0899-0042
    Keywords: ion channels ; receptors ; state-dependent interactions ; stereoselectivity ; local anesthetics ; 1,4-dihydropyridines ; Ca2+ channels ; Na+ channels ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion channels are pharmocologic receptors and as such exhibit stereoselective interactions with drugs. Ion channels are conformationally mobile transmembrane proteins existing in a number of open and closed states. Drug interactions with these different states may differ quantitatively and qualitatively. Stereoselectivity may not be a constant factor and may change according to channel state as determined by stimulus mode or experimental conditions. Selected examples are cited for Na+ and Ca2+ channels. © 1996 Wiley-Liss, Inc.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 39-48 
    ISSN: 0899-0042
    Keywords: α-pinene ; β-pinene ; camphene ; limonene ; borneol ; isoborneol ; succinite ; geochemistry ; stereochemistry ; pine resins ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among the more prevalent chiral monoterpenoid compounds in conifers are α-pinene, β-pinene, and smaller amounts of camphene and limonene. The most prevalent chiral monoterpenoid compounds in fossilized resin (referred to as amber in this paper) appear to be borneol, isoborneol, and camphene. Most of these compounds have easily measured enantiomeric excesses. The borneol and isoborneol in some amber samples have pronounced enantiomeric excesses despite the fact that they are tens of millions of years old. The enantiomeric ratios of the monoterpenoids in different ambers vary tremendously and often are distinct. However, in any single amber sample, the stereochemistry (absolute configuration) of the excess monoterpenoid enantiomers appears to be identical. The camphene in amber may be a secondary reaction product formed over time, possibly from the dehydration of borneol. Although a compound's original stereochemistry can be preserved, it also may diminish with the number and type of chemical transformations over geological time. The monoterpene enantiomeric ratios in modern conifer resins vary tremendously. Future stereochemical studies are outlined that could provide the data necessary for more exact geochemical interpretations and possibly for obtaining pertinent paleobiological information. © 1996 Wiley-Liss, Inc.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 77-83 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Excellent separations were achieved using a coated column to suppress electroosmotic flow and employing a countercurrent process between chiral selector and racemic solute. Using the macrocyclic antibiotic vancomycin as a chiral selector in capillary electrophoresis the resolution of nonsteroidal antiinflammatories and dansyl amino acids was achieved. Improvement in sensitivity due to the elimination of background absorbance and increased efficiency due to the removal of wall adsorption effects are both achieved using this technique. © 1996 Wiley-Liss. Inc.
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  • 6
    ISSN: 0899-0042
    Keywords: chiral purity ; pharmaceutical ; achiral ; cyclodextrin ; SBE cyclodextrin ; purity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the past several years, capillary electrophoresis (CE) has generated considerable interest from pharmaceutical companies for control of both the chiral and achiral purity of bulk drugs and drug products. This paper evaluates the use of CE as: (1) a technique complementary to HPLC for the determination of peak homogeneity of a drug, (2) for determination of chiral purity, and (3) for determination of achiral purity. It would be greatly advantageous if CE could be used to determine both the chiral and achiral purity in a single assay. This investigation compares the results obtained for the separation of the enantiomers of duloxetine using several neutral cyclodextrins to those obtained using anionic cyclodextrins (sulfobutyl ether derivatives) as chiral selectors added to the separation buffer. In addition, it reports chiral separations obtained by using neutral cyclodextrins in a sulfonic acid-coated capillary column, which give a negatively charged capillary surface and electro-osmotic flow even in low pH buffers. The possible mechanism of separation is discussed. © 1996 Wiley-Liss, Inc.
    Additional Material: 15 Ill.
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  • 7
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Investigations into the parameters affecting the enantiomeric separation of an intermediate in the synthesis of a drug targeted for cardiac arrhythmia is presented. The separation was achieved under subcritical fluid chromatography using CO2 modified with methanol and co-modifiers isopropyl amine and methylene chloride. The stationary phase was a cellulose based stationary phase manufactured under the trade name Chiracel OB. The results showed the addition of methylene chloride had a noticeable effect on resolution while the separation factor, α, remained constant. The co-modifier, isopropyl amine, did not considerably influence the resolution, or separation factor. Temperature studies were performed in order to establish the thermodynamic parameters of the interaction between the enantiomers and the stationary phase. Plots of In k′ vs. 1/T proved to be curved, while plots of In α vs. 1/T were linear. © 1996 Wiley-Liss, Inc.
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  • 8
    ISSN: 0899-0042
    Keywords: chiral ligand exchange chromatography ; chiral coating ; chiral discrimination ; chiral copper(II) complexes ; amino acids ; amino acid esters ; amino acid amides ; hydroxy acids ; dipeptides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) complexes of N2-octyl-(S)-phenylalaninamide (Noc-Phe-NH2), N2-dodecyl-(S)-phenylalaninamide (Ndo-Phe-NH2), and N2-octyl-(S)-norleucinamide (Noc-NLeu-NH2), dynamically adsorbed on a reversed-phase C18 column, were able to perform the direct enantiomeric separation of unmodified amino acids, amino acid amides and esters, hydroxy acids, and dipeptides by elution with aqueous or mixed aqueous-organic solutions containing copper(II) sulphate or acetate. The role played by several parameters in the separation procedure was examined with the copper(II) complex of Noc-Phe-NH2 [concentration of the copper(II) ion in the eluent, pH and eluent polarity, amount of adsorbed selector]. The separation was shown to occur entirely on the stationary phase. The mechanism of chiral discrimination is discussed in terms of the chromatographic parameters and of the structure of the copper(II) complexes in solution and in the solid state. The chiral stationary phase maintained its separation ability for about 3 months. However, the column could be easily restored by recovering the selector with methanol and repeating the loading procedure. © 1996 Wiley-Liss, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 234-243 
    ISSN: 0899-0042
    Keywords: enantiomeric ; non-racemic mixtures ; binaphtol ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that chromatography with achiral phases of non-racemic mixture of binaphthol can furnish fractions which differ in enantiomeric excess. The first fraction contains one pure enantiomer i.e., has an enantiomeric excess (ee %) close to 100% and the following fractions have an ee % close to 0% (racemic mixture). As a consequence, such chromatography may be used to enrich a non-racemic mixture of binaphthol in one enantiomer. In this paper a model is proposed allowing us to calculate with good accuracy the experimental elution curves. This simple model is capable of using only a few chromatographic experiments to predict the enantiomeric enrichment of a non-racemic mixture and to calculate precisely the retention time of each fraction. © 1996 Wiley-Liss, Inc.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 249-257 
    ISSN: 0899-0042
    Keywords: chiral SubFC resolution ; analysis time ; column efficiency ; library of chiral columns ; selectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model is presented that predicts a defined relationship between chiral SubFC resolution and analysis time. This model is based upon ideal chromatographic behavior and requires column efficiency and selectivity to be independent of mobile phase modifier level and flow rate. The validity of these assumptions was found to be imperfect but acceptable for two model compounds on two commonly used chiral columns.A major implication of the model is that the maximum resolution obtainable with a particular column and mobile phase modifier may be predicted from one injection. The retention time required to obtain a desired resolution is also calculable. This information enables the practitioner to discern quickly the futility of method development efforts. Insufficient maximum resolution predicted from the first injection would require an increase in selectivity to achieve a useful separation. Selectivity may then be altered by temperature, modifier, or stationary phase. The increased column efficiency of SubFC at typical flow rates rescues separations that fail by HPLC, thus shrinking the practitioner's required library of chiral columns. This work demonstrates that SubFC also allows the practitioner to skim through that library very quickly. © 1996 Wiley-Liss, Inc.
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 11-17 
    ISSN: 0899-0042
    Keywords: thalidomide enantiomers ; mobile phase additive ; stereoselective analysis ; high-performance liquid chromatography ; chiral separation ; β-cyclodextrin ; inclusion complex ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: R- and S-Thalidomide were resolved by reversed-phase HPLC on a C-18 column with β-cyclodextrin in the mobile phase. As the concentration of β-cyclodextrin was increased stepwise from 0 to 20 mM, enantiomeric resolution increased and retention times decreased significantly. The influence of different organic modifiers in the mobile phase were evaluated, and ethanol, among others, proved to be effective. Equilibrium constants for the formation of β-cyclodextrin inclusion complexes of R- and S-thalidomide in EtOH-buffer (5:95) were calculated to be 64 and 76 M-1, respectively. © 1996 Wiley-Liss, Inc.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 58-66 
    ISSN: 0899-0042
    Keywords: molecular mechanics ; HPLC ; chiral separation ; methylphenobarbitone ; hexobarbitone ; ibuprofen ; mandelic acid ; ephedrine ; pseudoephedrine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-Cyclodextrin and its derivatives have been utilised to effect chiral separation in HPLC and CZE, both as stationary phases and mobile phase additives. The basis of the method is assumed to depend upon the formation of inclusion complexes of differing stabilities between enantiomeric analytes and the cyclodextrin, resulting in a differential dynamic distribution between chromatographic phases. In this study, force field calculations have been employed to model the inclusion complexes of enantiomeric brompheniramine, ephedrine, pseudoephedrine, ibuprofen, mandelic acid, methylphenobarbitone, and hexobarbitone with β-cyclodextrin. The resulting values for Δ(ΔH), the difference in enthalpy of complex formation between enantiomeric pairs has been compared with literature chromatographic data to explain the ability of the systems to achieve enantiomeric separations. © 1996 Wiley-Liss, Inc.
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  • 15
    ISSN: 0899-0042
    Keywords: optical resolution ; conglomerate ; preferential crystallization ; optically active 2-amino-3-chloropropanoic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The racemic structures of (RS)-2-amino-3-chloropropanoic acid [(RS)-ACP] and (RS)-2-amino-3-chloropropanoic acid hydrochloride [(RS-ACP·HCl] were examined to obtain (R)- and (S)-ACP via optical resolution by preferential crystallization. The melting point, infrared spectrum, solubility, and ternary solubility diagram suggested that (RS)-ACP·HCl exists as a conglomerate and that (RS)-ACP forms a racemic compound. Optical resolution by preferential crystallization of (RS)-ACP·HCl was successfully achieved to yield (R)- and (S)-ACP·HCl. Optically pure (R)- and (S)-ACP were obtained from the purified (R)-and (S)-ACP·HCl, respectively. © 1996 Wiley-Liss, Inc.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 207-213 
    ISSN: 0899-0042
    Keywords: CS-670 ; anti-inflammatory drug ; stereoselective metabolism GC-MS ; diastereomer HPLC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CS-670, a novel nonsteroidal anti-inflammatory drug, is a racemic prodrug. Plasma concentrations and urinary excretion of CS-670 and its metabolites were determined in experimental subjects after oral administration at a single 120 mg dose. CS-670 and four metabolites, the saturated ketone (M-A), unsaturated-alcohol (M-B), cis-alcohol (M-C), and trans-alcohol (M-D), were quantitated by GC-MS. The major metabolites in human plasma were M-B, M-C, and M-D and their terminal half-lives (t½) were 0.9, 2.6, and 1.2 h, respectively. The total recovery in the urine was 26% of the dose, but unchanged CS-670 accounted for less than 2% over a 48 h period. In addition, the absolute configurations of the metabolites were examined by HPLC after derivatization with chiral reagents. It was found that the configuration of the propionic acid moiety of the metabolites, M-B, M-C, and M-D, in human plasma, was rapidly inverted from (-)-(R) to the (+)-(S) configuration in stereoselective biotransformation. Furthermore, the configurations of the 1′- and 2′-carbons of M-C and M-D, were found to be (1′R,2′S) and (1′R,2′S), respectively. These results show that CS-670 is readily biotransformed by chiral inversion of the 2-arylpropionic acid moiety and stereoselective reduction of the α, β-unsaturated ketone moiety in humans. © 1996 Wiley-Liss, Inc.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 356-356 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
    ISSN: 0899-0042
    Keywords: NSAIDs ; esterification ; resolution ; Candida antarctica lipase ; Mucor miehei lipase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The resolution of rac-suprofen (1) catalysed by lipase in organic solvents was investigated. Direct esterification of rac-1 with methanol in dichorometane catalysed by Novozym® 435 furnished the pharmacologically active (+)-(S)-suprofen as unreacted product with excellent enantiomeric excess. The same procedure in toluene using Mucor miehei lipase adsorbed in Celite as catalyst afforded (-)-(R)-suprofen with good optical purity. © 1996 Wiley-Liss, Inc.
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  • 19
    ISSN: 0899-0042
    Keywords: enantioseparation ; HPLC ; cyclodextrin ; phenylcarbamate ; chiral stationary phase ; optical resolution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New dichloro-, dimethyl-, and chloromethylphenylcarbamate derivatives of cyclodextrins (CDs) were prepared and their enantiomeric recognition abilities were evaluated as chiral stationary phases (CSPs) in normal phase high-performance liquid chromatography (HPLC). The effects of the type of cyclodextrins, the nature and position of the substituents on the phenyl ring, binding mode and spacer on the chiral recognition were studied in detail. No marked change of chiral recognition abilities was established by reversing the binding side of CDs (i.e., by the narrower [primary] opening of the cone-shaped CD to silica gel with the wider [secondary] opening sides). This result indirectly proves the previously drawn conclusion about the minor role of inclusion phenomena in chiral recognition in this case. Nevertheless, chiral recognition of these CSPs toward some compounds critically depends on the type of CDs used. All CD derivatives described in this study show rather low enantiomeric resolving abilities compared with corresponding polysaccharide (cellulose and amylose) derivatives, although very high enantioselectivity of separation was observed for a few compounds, such as racemic flavanone and cyclopropanedicarboxilic acid dianilide. © 1996 Wiley-Liss, Inc.
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  • 20
    ISSN: 0899-0042
    Keywords: rac-propranolol ; enantiomers ; drug intoxication ; cardiovascular function ; respiratory function ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The contribution of the individual enantiomers ([+]-[R]- and [-]-[S]-propranolol) to rac-propranolol intoxication was studied in anaesthetized, spontaneously breathing (SB) rats and artificially ventilated (AV) rats and rabbits. In the SB rat, propranolol (30 mg.kg-1.h-1 i.v.) decreased heart rate and mean arterial blood pressure and caused hypoventilation, serious hypoxaemia, respiratory acidosis, and death by respiratory arrest. Survival time (ST) in the (+)-(R)-propranolol group (ST 91 ± 5 min) was significantly longer than in the rac-propranolol group (ST 68 ± 6 min). In AV rats and rabbits toxic doses of rac-, (-)-(S)- and (+)-(R)-propranolol, 30 mg.kg-1.h-1 and 15 mg.kg-1.h-1 i.v., respectively, induced comparable effects on haemodynamic variables as in the SB rat. Artificial ventilation lengthened ST by a factor of three to four in rats. In the AV rat, ST's were not significantly different between the rac-, (-)-(S)- and (+)-(R)-propranolol groups. In the rabbit, as in the SB rat, ST in the (+)-(R)-propranolol group was significantly longer than ST's in the rac- and (-)-(S)-propranolol groups. The acute respiratory acidosis in SB rats and the prolonged ST in AV rats suggest that respiratory failure is the primary and cardiovascular failure the secondary cause of death in propranolol intoxication. The potentiation of the toxic effect of the enantiomers observed after dosing the racemate instead of the pure enantiomers could not be explained by a stereoselective difference in plasma propanolol concentration. © 1996 Wiley-Liss, Inc.
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 22
    ISSN: 0899-0042
    Keywords: enantiomers ; HPLC ; DNS-animo acids ; fluorescence quenching ; ligand-exchange mechanism ; adsorption ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copper(II) complexes of two new diastereomeric ligands, N2-(R)- and N2-(S)-2′-hydroxypropyl-(S)-phenylalaninamide [(R, S)-1 and (S, S)-1], have been used as additives to the eluent in high-performance liquid chromatography (HPLC) reversed phase for the chiral separation of DNS-amino acids. The aim was that of comparing the separation process obtained by the chiral eluent with that obtained by an analogous bonded stationary phase containing (S)-phenylalaninamide, previously studied [CSP-(S)-Phe-NH2]. The affinity of the ternary complexes for the C18 column was determined by adsorption experiments in HPLC. It was shown that the two systems (chiral eluent, chiral stationary phase) work according to different mechanisms. Ternary complex formation in solution was studied by fluorescence spectroscopy. It was shown that chiral separation with the Cu(II) complexes added to the eluent was determined by the relative affinities of the ternary complexes for the column-stationary phase rather than by their stabilities in solution. With CSP-(S)-Phe-NH2 the separation is accounted for by the relative stabilities of the ternary complexes, which depends mainly on the “allowed” geometry of the complex and on the steric repulsion of the amino acid side chain with the spacer. © 1996 Wiley-Liss, Inc.
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  • 23
    ISSN: 0899-0042
    Keywords: rac-amlodipine ; amlodipine ; liquid chromatography ; chiral ; charged cyclodextrin ; optimisation ; central composite design ; mobile phase additive ; experimental design ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A negatively charged derivative of β-cyclodextrin, sulphobutyl ether-β-cyclodextrin (SBE-β-CD), was examined as a chiral mobile phase additive in reversed-phase high-performance liquid chromatography for the enantiomeric resolution of the calcium channel blocker rac-amlodipine. Theoretical and practical aspects are discussed for setting up a central composite design applicable to any analytical method. These include the correct location of factor points for maintaining orthogonality within the design and the augmentation of centrepoint experiments to allow a larger factor space by increasing the distance of axial star points. Optimised separation was achieved using a reverse-phase column with eluent comprising: acetonitrile (ACN) - potassium dihydrogen phosphate (pH 3.93) containing 2.66 mM SBE-bgr;-CD (26.5:73.5% v/v) at a flow rate of 1.0 ml/min. This yielded a Kaiser peak separation index, Pi = 0.96, at tR2 = 52 min with satisfactory reproducibility, relative standard deviation values: tR1, 0.39%; tR2, 0.47% (n = 5). These experimental results were in excellent agreement with those predicted by the SAS software package for a chromatographic response function model. Multiple regression analysis in four dimensions, with three response models based on Rs, Pi, and a function of Pi, produced response surfaces which revealed zones of optimum robustness and illustrated the interactions involved between the key chromatographic factors. Putative proposals for a mechanism involving the interaction of each of the positively charged enantiomers with the negatively charged cyclodextrin are also discussed. These examine the possibility of ion-pairing and inclusion phenomena to account for the excellent resolution observed. © 1996 Wiley-Liss, Inc.
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  • 24
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 503-510 
    ISSN: 0899-0042
    Keywords: enantioseparations ; carrageenans ; sulfated polysaccharides ; beta blockers ; tryptophan and derivatives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lambda-carrageenan, a linear high molecular weight sulfated polysaccharide, has been employed as a chiral selector in capillary electrophoresis for the separation of enantiomers of weakly basic pharmaceutical compounds. The racemic compounds that were enantioresolved included propranolol, pindolol, tryptophanol, laudanosine and laudanosoline. In addition, the diastereomeric pair of cinchonine and cinchonidine were also resolved. Method conditions such as buffer pH, electrolyte concentration, column temperature, and chiral selector concentration were found to be important for improvement of enantioselectivity. © 1996 Wiley-Liss, Inc.
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  • 25
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 137-142 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The equilibria and kinetics of adsorption of lysozyme and bovine serum albumin on the Fractogel-EMD tentacle-type cation exchanger and the Fractogel-TSK conventional cation exchanger have been studied experimentally by batch stirred-tank method. Adsorption equilibrium data corresponded well to the Langmuir isotherm. For both proteins, the tentacle-type exchanger exhibited a higher binding capacity than the conventional exchanger. This is attributed to the flexibility of the functional groups in the tentacle-type exchanger which enhance optimal electrostatic interactions. The dynamic data were analyzed by a simplified data model which lumped mass transfer resistances and intrinsic adsorption kinetics into a single rate constant. For both proteins, it was found that the tentacle-type exchanger showed a smaller lumped rate coefficient than the conventional exchanger. The difference in the values of the lumped rate coefficients was shown to be due to the influence of nonlinear equilibrium constants rather than due to any difference in rate of adsorption.
    Additional Material: 5 Ill.
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  • 26
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 27
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 103-112 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Comparative calculations of several methods of characterization for three multicomponent mixtures that include paraffin, naphthene, and aromatic fractions are shown. Each method requires different experimental information about the mixtures but all use the numerical Gauss-Legendre quadrature. The results show that characterization making direct use of the TPB distillation curve is the most suitable approach for characterizing complex multicomponent mixtures.
    Additional Material: 9 Ill.
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  • 28
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    Chemical Engineering & Technology - CET 19 (1996), S. 448-455 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model has been developed to simulate the operation of an absorption-driven multiple-effect evaporator. The model is based on mass and enthalpy balances and heat transfer rate equations of the various components of the system. The model has been validated by comparing model predictions to experimental results from the operation of a four effect absorption-driven falling film evaporator coupled with a two-effect regenerator which operated using solutions of sodium hydroxide as an absorptive medium. The model predictions are in satisfactory agreement with the experimental results.
    Additional Material: 10 Ill.
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  • 29
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    Chemical Engineering & Technology - CET 19 (1996), S. 467-472 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Knowledge of the compression factor is essential for the transport, storage and utilization of natural gas. The normal way to determine this property is by using an equation of state (EOS) which utilizes the gas temperature, pressure, volume, and composition. In many industrial situations, the composition of the natural gas is not available, yet it is still necessary to calculate the compression factor. In this paper, we present an EOS which uses relative density, heating value, and diluent compositions to determine the compression factor. The applicable ranges of conditions are 220 to 500 K up to 70 MPa (-60-450°F up to 10,000 psia). The calculations agree with data within 0.1% average absolute deviatation up to 10 MPa with a maximum deviation of 1.9% near pure component critical points or mixture cricondentherms. The equation also extrapolates through data up to 70 MPa within 1.9% We present comparisons to data of AGA Report No. 8 and to data in the paper.
    Additional Material: 2 Ill.
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  • 30
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Complex configurations of distillation columns have been shown to consume less energy than simple configurations. These complex configurations mainly results from two considerations: either a feed split, where the condensing vapor from the top of the high pressure column is used to heat the reboiler of the low pressure column, or the overheads from a high pressure column in a distillation train used to reboil a column under lower pressure. Industrial experience shows that very often in these configurations there is still incentive for more energy reduction simply because of inefficient control. The energy integration increases the control loop coupling the system, so that the operating strategy for the columns is no longer apparent. Therefore, the dynamic behaviour and the operational constraints of such systems become very important. The use of rigorous dynamic model of the processes is an essential instruments to pursue the goal of good and reliable process control Such models allow the engineer to realistically simulate the process with the desired control system in place and to analyze the effects of equipment sizing, hest integration, and disturbances. Variable pairing proved is used to illustrate that effective control of energy-integrated distillation columns can be achieved by proper selection of manipulated variables and pairing them correctly with control variables. Hints will also be given, when multivariable predictive control schemes should be used.
    Additional Material: 16 Ill.
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  • 31
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    Chemical Engineering & Technology - CET 19 (1996), S. 514-525 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many rectification processes are used to separate corrosive substances with high boiling points. This reports deals with a new type of structured column pacing mode of corrosion-resistant carbon fiber material. These column internals allows for low pressure drop at high throughput rated with reasonable column efficiency. Experiments in columns of 50 and 100 mm diameter have been carried out to investigated separation efficiency, pressure drop and liquid holdup of the packing even at low operation pressures. In the respective columns twp geometrical different types of packing have been tested using binary mixtures of chlorobenzene/ethylbenzene with a packing geometry similar to the Sulzer EX packing, the 100 mm diameter column was filled with elements of rougher structure and smaller specific surface. Basing on the experimental results, model equations are presented, which allow the calculation of the investigated performance characteristics.
    Additional Material: 14 Ill.
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  • 32
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    Chemical Engineering & Technology - CET 19 (1996), S. 398-404 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Affinity separations rely on the highly specific binding between a protein in solution and an immobilized ligand to achieve a high degree of protein purification. A mathematical model including convection, diffusion, and rate kinetics is formulated to analyze the design and operation of affinity membrane bioseparation. The model equations are solved by orthogonal collocation method. Danckwerts' boundary conditions are used. The results obtained from model simulation show that the breakthrough of the protein is significantly influenced by Péclet number, feed protein concentration, Ligand number, Damköhler number, membrane thickness, and flow rate. Breakthrough profiles are quantitatively discussed in terms of protein recovery efficiency, ligand utilization efficiency, thickness of unused membrane, and width of the mass transfer zone.
    Additional Material: 8 Ill.
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  • 33
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    Chemical Engineering & Technology - CET 19 (1996), S. 391-397 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In this paper the simulation of hybrid processes containing membrane units will be discussed. For this purpose a user-defined module for simulation and design of membrane processes was implemented into the simulation program AspenPlus.The advantages can be summarized as follows:-any combination of membrane processes with all other units already implemented in AspenPlus is possible, including internal recycle streams-utilization of the physical property models and data bases of AspenPlus is possible- cost and sensitivity analysis can be performed.These benefits are demonstrated in detail for a membrane vapor recovery unit for the treatment of tank farm off -gas, for a two-stage reverse osmosis plant for organic/-organic separations and for a combination of distillation and pervaporation for the separation of a dimethylcarbonate/methanol mixture.
    Additional Material: 8 Ill.
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  • 34
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    Particle and Particle Systems Characterization 13 (1996), S. 254-259 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When properly measured and interpreted angle of repose (AOR) can be a useful method of characterising a powder. Unfortunately, a multitude of definitions and measuring equipment is used. A review of the inherent problems is presented in the first part of this paper.The second part of the paper describes the improvements made to a measuring device developed originally for measuring the angle of repose of soda ash, so that a wider range of powders can be tested. In the improved design, the tendency of cohesive and semi-cohesive powders to block the device's funnel has been eliminated.A total of 73 powders consisting of four different materials, and covering Groups A, A/C and C of Geldart's classification, have been tested using the new equipment. The results show that AOR increases systematically with decrease in mean particle size. Combination of AOR measured in the new device with aerated bulk density provides a quick, sensitive and effective method for characterising a wide range of powders.
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  • 35
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 13 (1996) 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 36
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    Particle and Particle Systems Characterization 13 (1996), S. 322-326 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: During the spherical agglomeration process, a suspended solid is agglomerated by adding a binding liquid. First, mircoagglomerates or flocs are produced, which are compacted in the course of the process. Agglomerate size was evaluated by laser diffraction spectrometry, image analysis was used to determine the size and some adequately defined shape parameters calculated by Fourier analysis of the particle contour.The shape analysis confirms the visual observations; the compaction of the flocs is expressed by the corresponding change of the shape parameters. The influence of several process parameters on changes in agglomerate shape can be described quantitatively and help to gain an insight into agglomeration mechanisms. The particle size distributions determined by image analysis and laser diffraction spectrometry hardly differ for fairly spherical flocs or agglomerates. Concerning the size distribution of the irregular flocs, laser diffraction spectrometry measures larger particles than image analysis.
    Additional Material: 10 Ill.
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  • 37
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    Particle and Particle Systems Characterization 13 (1996) 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 38
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    Particle and Particle Systems Characterization 13 (1996), S. 339-339 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 39
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    Particle and Particle Systems Characterization 13 (1996), S. 333-338 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes the use of a capacitance tomography system for imaging gas bubbles in a fluidized bed in the vicinity of an air distributor plate. The results show how the solid concentration distribution varies as a function of time for three different flow regimes: bubbling, slugging and the transition to turbulent. Bubble shape, Length and coalesence can be observed. A method of spatial correlation to elucidate the bubble formation process is described.
    Additional Material: 11 Ill.
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  • 40
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    Particle and Particle Systems Characterization 13 (1996), S. 327-332 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes the evaluation of the transfer function for the TSI-short differential mobility analyzer (DMA) in the nanometer particle size rang. The TSI-short DMA is identical with the TSI-long DMA (Model 3071) but has shortened inner and outer electrodes and the insulator material Teflon was replaced by black Delin. The DMA transfer function was determined by operating two identical DMAs in series. The DMA was investigated at a sheath to aerosol flow rate ratio of between 10 and 1. Usually for particles above 50 nm the parameters of the assumed triangular transfer function, i.e. height and half-width, approach the ideal values, which depend only on the flow ratio. For particle size below 50 nm the height decreases from 0.9 at 50 nm to 0.18 at 5 nm. The half-width increase from the ideal value 0.1 to about 0.17. The observed changes of the transfer function are due to diffusional effects resulting in losses mainly in the inlet and outlet and also broadening of the aerosol stream inside the DMA. The determined transfer functions were also compared with transfer functions calculated using a theoretical model. The agreement proved to be satisfactory. The half-widths and the transmission efficiencies of the conventional TSI-DMA (Model 3071), TSI-short with Teflon and also black Delin insulator as a function of particle size are compared to demonstrate the improvements in performance.
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  • 41
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    Particle and Particle Systems Characterization 13 (1996), S. 342-342 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 42
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    Particle and Particle Systems Characterization 13 (1996), S. 343-349 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Response of a phase Doppler system to irregularly shaped particles is examined and shown to deviate qualitatively as well as quantitatively from the spherical particles. Nevertheless, the measured phase distributions based on an ensemble of particles exhibit a high degree of order and simplicity. The experimental data and the stochastic modeling of the process have shown that the phase Doppler technique can be used successfully for in-situ sizing and velocimetry of irregular particles. In the case of irregular crystalline particles, mean size and standard deviation can be deduced without requiring any assumptions regarding the functional form of the size distribution. As opposed to other optical techniques, phase Doppler can be used, in principle, near the backscattering location, so that a single optical window would be employed for transmission of laser light and collection of the scattered signals. Furthermore, size measurements can be velocity-resolved, i.e. a size distribution can be associated with each bin of the velocity histogram.
    Additional Material: 7 Ill.
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  • 43
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    Particle and Particle Systems Characterization 13 (1996), S. 354-361 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A series of industrial powders, most of them organic, were characterized in terms of volumetric mean size, size distribution, density, particle shape, water rentention characteristics (under a series of controlled ambient relative humidities) and loosely packed and densely packed voidages (giving the compressibility). The behaviour of the powders in powder handling apparatus (a precision powder filler) was also determined. The minimum and maximum bulk densities of the powders were related to the properties of the individual particles by means of a semi-empirical equation. The filling capacity of the powder handling apparatus was found to be related to the maximum bulk density of the powder while the filling accuracy turned out to be related to the compressibility of the powder. Knowing these interrelations made it possible to predict the powder behaviour in the handling apparatus directly on basis of the particle properties.
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  • 44
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    Particle and Particle Systems Characterization 13 (1996), S. 350-353 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fiber optic dynamic light scattering (FODLS) was used to study the kinetics of aging processes in emulsions of n-alkanes stabilized by a surfactant. The method is particularly useful for this purpose because it permits measurements in concentrated emulsions. Complications that may occur in traditional DLS due to the extreme dilution, such as solubilization of the particles in the medium, can be easily avoided in this way. The experimental results show that the main aging process is Ostwald ripening. The results are in agreement with theoretical predictions based on the Lifshitz-Slyozov-Wagner (LSW) theory as far as it concerns the relation between the molecular solubility of the n-alkanes (in the aqueous phase) and the Ostwald ripening rate. This illustrates that the main rate-determining factor is the molecular diffusion of the alkane molecules through the continuous (aqueous) phase. The Ostwald ripening rate is affected by the concentration of surfactant but in all situations is higher than expected from LSW theory.
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  • 45
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    Particle and Particle Systems Characterization 13 (1996), S. 362-367 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Designing modern devices for bulk solids storage and handling requires an increasingly complex understanding of the handled bulk solids' mechanical behaviour. Models able to describe the behaviour of bulk solids can neither be formulated nor their parameters determined from common shear tests, since these do not contain sufficient information especially about the materials' stiffness characteristics. The paper describes the response envelope as a measure of the deformation resistance and its experimental determination from biaxial tests. It is shown that for fine limestone powder the stiffness in compression is only about 1/70 of the stiffness in expansion. The shape of the response envelope depends only on the ratio between the principal stresses at the stress state considered, whereas the size of the response envelope also depends on the stress magnitude.
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  • 46
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    Particle and Particle Systems Characterization 13 (1996), S. 368-373 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials - glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) - were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.
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  • 47
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    Particle and Particle Systems Characterization 13 (1996), S. 381-382 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 48
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    Particle and Particle Systems Characterization 13 (1996), S. 379-380 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 49
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    Particle and Particle Systems Characterization 13 (1996) 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 50
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    Particle and Particle Systems Characterization 13 (1996), S. 2-2 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 51
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    Particle and Particle Systems Characterization 13 (1996), S. 3-9 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel technique to determine the size of particles suspended in a stirred vessel is investigated. The method uses microphotography to obtain a still image of the particles in situ. The equivalent circular diameter of the particles is obtained from the photographs using digital image analysis. The particles used for the test were certified particle size standards of a very small tolerance in diameter deviation. The size comparison was determined as a percent error between the measured particle diameter (equivalent circular diameter) and the diameter established by the particle manufacturer. To determine the limiting ranges of particle size and concentrations, spherical particles in a size range of approximately 1 to 10.0 μm (microns) in diameter were employed in the test. Concentrations varied from 0.00005% to 0.1% (mass basis). For each particle size, an aqueous solution of the particles was prepared at the desired concentration and placed in a stirred vessel. Photographs of the solutions were made at 25.5x, 40x, 60x and 80x magnification. For all sizes of particles, the entire range of concentration was examined.The results indicate a minimum size resolution of approximately 3μm, in a corresponding concentration range of 0.0001% to 0.05%. Similar limits on concentration were found for the larger diameter particles, although a true upper limit for the largest particle sizes was not established. The functional concentration range appears to shift towards higher mass concentrations with increasing particle size. For 2.92 μm diameter particles, the error in size measurement was found to be below 10% for a concentration range of 0.0005% to 0.05%. Additionally, a relationship between turbidity and the error was seen at low particle concentration levels where decreasing levels of turbidity generated increasing levels of error.
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  • 52
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    Particle and Particle Systems Characterization 13 (1996), S. 27-33 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new phase Doppler anemometry (PDA) signal processing method based on a Hilbert transform algorithm is introduced and analysed. By generating a 90° phase-shifted burst signal in the time domain, the envelope of the Doppler burst can be determined. In addition, this envelope is approximated by a Gaussian exponential function. The difference of the maxima of these Gaussian approximations for two related PDA bursts gives an estimate of the time difference between these time shifted signals. With the introduction of this estimation method, the restriction to the [0,360°] interval resulting from conventional signal analysis may be avoided in many cases. To investigate the dependence on SNR, burst position, burst frequency and sampling rate, results of computer simulations are presented. The feasibility of the method is demonstrated briefly by experimental results. Phase differences of more than 2000° arising from the measurement of monodisperse droplets by a conventional PDA setup could be determined.
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  • 53
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    Particle and Particle Systems Characterization 13 (1996), S. 54-54 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 54
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    Particle and Particle Systems Characterization 13 (1996), S. 41-46 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, particles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate into large particles or are deposited on the walls. Particles larger than 4nm and molecular clusters penetrate through a wire-screen type diffusion battery, but particles in the size range between 2 and 4nm are collected. Among the organic compounds tested (aromatics, alcohols, ketones and others), only aromatic compounds appear to yield unstable clusters which grow into detectable particles (〉2nm) through Brownian coagulation. The other compounds either do not undergo the gas-to-particle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle formation.
    Additional Material: 10 Ill.
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  • 55
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    Particle and Particle Systems Characterization 13 (1996) 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 56
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    Particle and Particle Systems Characterization 13 (1996), S. 58-58 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 57
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    Particle and Particle Systems Characterization 13 (1996), S. 68-78 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper reviews the principle of the phase-Doppler particle sizer by means of examples of the effects of varying the various experimental parameters. The examples are computed by means of a comprehensive numerical model of a complete phase-Doppler system including many practical aspects such as aperture size, polarization filters and detector properties. First the phase-Doppler principle is explained as a logical development of an interferometric measurement of the phase of the light scattered from a particle. Then the standard phase-Doppler analyzer (PDA) is decribed followed by some newer or less known variations of the principle intended to measure, e.g., in the backscatter direction, to size very small particles or to determine the refractive index of a particle. Finally, the trajectory problem in PDA measurements is briefly discussed.
    Additional Material: 30 Ill.
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  • 58
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    Chirality 8 (1996), S. 122-125 
    ISSN: 0899-0042
    Keywords: aminophosphonic acids ; asymmetric synthesis ; chiral HPLC ; ligand-exchange chromatography ; enantiomeric analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An aqueous solution of the (+)-monoethyl ester of N-(l′-hydroxymethyl-)propyl-α-aminobenzylphosphonic acid has been proposed as a suitable chiral eluent for enantiomeric analysis of amino acids by ligand-exchange chromatography. Asymmetric synthesis of the chiral selector using (-)-(R)-2-aminobutan-1-ol as a starting reactant is described. The dependence of the parameters of separation of valine enantiomers on concentration of the complexing ion, pH, and temperature has been investigated. It is shown that the order in which enantiomers are eluted from a column depends on the concentration of the complexing ion and pH. © 1996 Wiley-Liss, Inc.
    Additional Material: 4 Tab.
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  • 59
    ISSN: 0899-0042
    Keywords: Cellulose tris-(3,5-dimethylphenyl carbamate) ; resolution ; tetramisole ; propanolol ; microporous APS-silica ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity of a series of chiral analytes was examined on tris-(3,5-dimethylphenyl carbamate) coated onto microporous APS-silica. The effects of the nature of the carbohydrate, the weight ratio of carbamate/support and the type of alcohol present in the mobile phase were investigated. Among the chiral analytes examined, propanolol showed an extremely good resolution. The resolution of tetramisole was optimized and the method developed was shown to be suitable for analysis of the drug in commercial tablets and in a suspension. © 1996 Wiley-Liss, Inc.
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  • 60
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    Chirality 8 (1996), S. 352-352 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 61
    ISSN: 0899-0042
    Keywords: 13C NMR ; chiral recognition difference ; elution order ; cellulose tris(4-methylbenzoate) ; 1-phenylethanol ; 1-indanol ; 1,2,3,4-tetrahydro-1-naphthol ; glutethimide ; Tröger's base ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To elucidate chiral recognition difference between pairs of enantiomers which interacted with a cellulosic stationary phase of chiral discrimination high performance liquid chromatography (HPLC), 13C NMR spectroscopy was applied for enantiomers of 1-phenylethanol, 1-indanol, 1,2,3,4,-tetrahydro-1-naphthol, glutethimide, and Tröger's base. Their 13C nuclear spin-spin relaxation times (T2Cs) and spectra were obtained in deuterated HPLC solvents in the presence of column packing material made of cellulose tris(4-methylbenzoate) coated on silica gel. The first-eluted enantiomers on the HPLC showed longer T2Cs and stronger signal intensities of 13C NMR spectra than the second-eluted enantiomers. These results indicated that the chiral recognition difference of enantiomers was observed by their T2Cs and intensities of 13C NMR spectra. The T2C difference was found to reflect the retention order of enantiomers on the chiral HPLC column. © 1996 Wiley-Liss, Inc.
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  • 62
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    Chirality 8 (1996), S. 1-1 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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  • 63
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    Chirality 8 (1996), S. 3-5 
    ISSN: 0899-0042
    Keywords: stereospecific decarboxylation ; asymmetric synthesis ; inhalational anesthetic ; halothane ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new synthesis of non-racemic halothane (1-bromo-1-chloro-2,2,2-trifluoroethane) is reported. The stereospecificity of the key reaction, decarboxylation of a salt of optically enriched 1-bromo-1-chloro-2,2,2-trifluoropropionic acid to give halothane, is shown to be highly dependent on the nature of the cation. When the cation is trialkylammonium, a high level of stereospecificity is observed. © 1996 Wiley-Liss, Inc.
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  • 64
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    Chirality 8 (1996), S. 18-23 
    ISSN: 0899-0042
    Keywords: racemate ; enantiomer ; bioavailability ; pharmacokinetic ; ibutilide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ibutilide fumarate, a new drug for the treatment of cardiac arrhythmias, contains a stereogenic center bearing a secondary alcohol group. Several single dose and multiple dose studies of racemic ibutilide or its enantiomers were performed by the oral and intravenous routes in dogs. A chiral assay was used to examine racemization and the individual enantiomer pharmacokinetics. Following low oral or intravenous doses (approximately 0.3 mg/kg), the pharmacokinetics of the enantiomers were nearly identical, with no substantial chiral conversion. Both enantiomers exhibited high clearance rates, large volumes of distribution, and low oral bioavailability. As the dose increased, pharmacokinetic differences between the enantiomers were observed. The greatest differences (3-fold) were seen after oral administration at 4 mg/kg, indicating that first-pass metabolism of ibutilide was highly enantioselective at high doses. The clearances of the enantiomers differed by up to 34% at 5 mg/kg followed intravenous administration of the racemate. At high doses, other non-linear pharmacokinetic behavior was also apparent. The intravenous clearance of ibutilide declined from 5.3 L/h/kg at 0.3 mg/kg to 3.7 L/h/kg at a dose of 5 mg/kg. The absolute oral bioavailability of the racemate increased from 2% at 0.3 mg/kg to as much as 84% at 5 mg/kg. © 1996 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 65
    ISSN: 0899-0042
    Keywords: gas chromatography ; modified β-cyclodextrin column ; chiral separation ; assay ; mexiletine ; hydroxylated metabolites ; urine ; conjugation/deconjugation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomers of mexiletine and four of its hydroxylated metabolites were directly separated by capillary gas chromatography using a heptakis(6-O-tert-butyl-dimethylsilyl-2,3-di-O-methyl)-β-cyclodextrin column. The method was applied to the analysis of urine samples from cancer patients who were treated with racemic mexiletine as part of a study of the use of mexiletine in the relief of neuropathic pain. Samples analyzed before and after deconjugation of the urine with β-glucuronidase/arylsulfatase showed a high stereoselectivity in the formation and conjugation of these compounds. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 66
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    Chirality 8 (1996), S. 49-57 
    ISSN: 0899-0042
    Keywords: racemization ; fermented beverages ; beer ; D-amino acids ; D-leucine ; D-phenylalanine ; D-proline ; cyclodextrin columns ; column switching ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Even though amino acids are important trace components in the brewing of beers, they have not been extensively evaluated in these beverages. Studies involving the enantiomeric composition of these amino acids are even less prevalent. A brief summary of the brewing process for malt beverages is given. The total concentration and enantiomeric composition of three amino acids (leucine, phenylalanine, and proline) were determined in 25 different beers. Proline tended to have the highest average absolute concentration and the lowest percentage of the D-enantiomer in most samples. In some cases the relative amounts of D-phenylalanine and D-leucine exceeded 10% of the individual amino acids. The enantiomeric composition of the amino acids in different beer samples did not vary as extensively as the absolute concentrations. The reason for the concentration differences between proline and the other amino acids is discussed. A knowledge of amino acid concentrations and enantiomeric compositions appears to be useful in characterizing specific beers and brewing processes. © 1996 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 67
    ISSN: 0899-0042
    Keywords: spectral analysis ; spectral contrast ; HPLC ; MECC ; peak homogeneity ; peak tracking ; method development ; photodiode array detection ; isomers ; enantiomers ; diastereomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of mathematically enhanced ultraviolet/visible (UV/VIS) absorbance spectral analysis and spectral contrast software techniques in high performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (MECC) as an aid for the determination of peak homogeneity, identification, and tracking during method development was investigated. Various structurally similar pharmaceutical compounds, and compounds present as either cis/trans isomers, diastereomers, or enantiomers were used as test compounds to probe the limits of this technique. Two tricyclic antidepressants, nortriptyline and imipramine, were employed to study the effects of HPLC mobile phase composition and pH on the ability to identify and track peaks during method development. It was found that method changes altered the spectral matches used for identification, but not enough to cause incorrect peak identification. It was also shown using HPLC that the cis/trans isomers of doxepin and the diastereomers ephedrine and pseudoephedrine could be distinguished.The mathematically enhanced spectral analysis and spectral contrast software techniques were also employed with MECC. Peaks tracking during method development as pH and the concentration of surfactant changes is shown for a separation of various penicillin type antibiotics. It was shown that during chiral MECC (CMECC) analyses ephedrine/pseudoephedrine diastereomers as well as ephedrine enantiomers could be distinguished. The determination of enantiomers is possible in CMECC since enantiomers are eluted as diastereomeric complexes, as opposed to HPLC where they are eluted in their native state. © 1996 Wiley-Liss, Inc.
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  • 68
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    Chirality 8 (1996), S. 126-130 
    ISSN: 0899-0042
    Keywords: cyclodextrin ; chiral ; propranolol ; chromatography ; stationary phase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A β-cyclodextrin bonded stationary phase was employed for the enantioresolution of propranolol and several analogues in conjunction with various polar organic mobile phases. The effects of structural alterations in the non-polar regions of the analytes were found to exert profound changes upon chiral resolution and capacity values, indicating that features which cannot hydrogen-bond with the cyclodextrin molecule still play an important role in this chiral recognition process. This was linked to a repulsive steric effect facilitating the necessary conditions for chiral resolution. The degree of ionization of the analytes and the type and concentration of organic modifier used were also seen to influence the analytes1 enantio-selectivity and capacity values. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 69
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    Chirality 8 (1996), S. 147-152 
    ISSN: 0899-0042
    Keywords: amylose ; (S)-α-methylbenzyl carbamate ; chiral sulfoxides ; microporous silica ; polysaccharide phases ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric resolution of chiral sulfoxides was investigated on amylose (S)-α-methylbenzyl carbamate phase coated on aminopropylated 7 μm silica with 500Å diameter pores. This was shown to be very successful in the separation of alkyl/aryl, aryl/aryl, and non-aromatic sulfoxides. The effect of pore size using naked silica was also investigated, demonstrating that the pore size does not affect the resolution. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 70
    ISSN: 0899-0042
    Keywords: propranolol enantiomers ; fluorinated analogs ; chiralcel OD and chiralcel OD-R columns ; chiral recognition mechanism(s) ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric separation of several racemic aryloxyaminopropan-2-ol derivatives related to propranolol on normal and reversed phase of cellulose tris (3,5-dimethylphenylcarbamate) chiral stationary phases known as Chiralcel OD and Chiralcel OD-R were studied. It was observed that the chiral separation depends on the substitution pattern of the aryl group, i.e., 1-naphthyl, 2-naphthyl, and phenyl group and polarity on the basic nitrogen in the side chain. In both normal and reversed phase modes the (+)-R-enantiomer eluted first in all of the analogs resolved. It can be concluded that: (1) substituents on the side chain did affect the interaction of the enantiomers with the polar carbamate moiety in the CSP; and (2) the dipole-dipole stacking between the π-donor 3,5-dimethylphenyl carbamate group pending from the glucose rings of the CSP and π-acceptor aryl group of the analyte is crucial for the efficient chiral discrimination. The chiral recognition mechanism(s) between these analogs and the chiral stationary phases are proposed. © 1996 Wiley-Liss, Inc.
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  • 71
    ISSN: 0899-0042
    Keywords: arylpropionic acid ; ketoprofen ; enantiomer ; stereoselectivity ; Coenzyme A thioester ; hybrid triacylglycerols ; inversion ; adipose tissue ; hepatocytes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantiomeric bioinversion of ketoprofen (KP) enantiomers and their incorporation into triacylglycerols were investigated in the rat (1) in vitro, using liver homogenates, subcellular fractions, and hepatocytes, and (2) in vivo, in different tissue samples after oral administration of the radiolabelled compounds. In liver homogenates or subcellular fractions, the enantiomer (S)-ketoprofen (S-KP) was recovered unchanged, whereas (R)-ketoprofen (R-KP) was partially converted into its Coenzyme A (CoA) thioester and inverted to S-KP. Both processes occurred mainly in the mitochondrial fraction. This supports the mechanism of inversion via stereoselective formation of CoA thioesters of R-KP, already described for other non-steroidal anti-inflammatory drugs. Incorporation into triacylglycerols was detected after incubation with intact hepatocytes in the presence of added glycerol. The process was stereoselective for R-KP vs. S-KP (covalently bound radioactivity 26,742 ± 4,665 dpm/106 cells vs. 6,644 ± 3,179 dpm/106 cells, respectively). However, no incorporation was found in liver samples after oral administration of either R-KP or S-KP. On the contrary, in adipose tissue samples a significant and stereoselective formation of hybrid triacylglycerols was observed: 11,076 ± 2,790 dpm.g-1 for R-KP vs. 660 ± 268 dpm.g-1 for S-KP. The incorporated R/S ratio, higher in adipose tissue (R/S = 17) than in hepatocytes (R/S = 4), indicates that fat may be the main tissue store for the xenobiotic R-KP in rats. © 1996 Wiley-Liss, Inc.
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  • 72
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    Chirality 8 (1996), S. 84-87 
    ISSN: 0899-0042
    Keywords: capillary electrophoresis ; aminophosphonic acid ; enantiomers ; osteoporosis ; cyclodextrin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic aminophosphonic acids were completely resolved into their enantiomers by capillary electrophoresis using β-cyclodextrin as a chiral selector in a borate electrolyte. The reproducibility of sample injection, solute migration time, and detection limits of the solute were studied. The calibration curve obtained from peak areas was linear over the concentration range of 10 to 300 μg/mL. © 1996 Wiley-Liss, Inc.
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  • 73
    ISSN: 0899-0042
    Keywords: teicoplanin ; glycopeptide antibiotics ; capillary electrophoresis ; enantioselectivity ; separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Teicoplanin is the third in a series of macrocyclic glycopeptide antibiotics that has been evaluated as a chiral selector in capillary electrophoresis (CE). It was used to resolve over 100 anionic racemates at low selector concentrations. Like the other related glycopeptide antibiotics, its enantioselectivity tends to be opposite to that of the ansa-type antibiotics which prefers cationic compounds, particularly amines. Factors that affect teicoplanin-based enantioseparations include the selector concentration, pH, and the concentration of the organic modifier. The temperature and the nature and strength of the buffer are also known-to affect the stability of the chiral selector as well as the enantioseparation. Teicoplanin exhibited some features that were not noted with the other glycopeptide antibiotics. For example, it aggregates (forms micelles) in aqueous solutions and this influences its enantioselectivity. Unlike the other studied glycopeptides, teicoplanin precipitates in alcohol-water mixtures. It also binds less to the capillary wall than vancomycin as evidenced by the faster electroosmotic flow velocity. The micellization of teicoplanin is pH dependent so that the effect of pH on enantiorecognition is more complex for teicoplanin than for other chiral selectors. Also it is shown that the simple model proposed to explain the role of organic modifiers in cyclodextrin-based CE enantioseparations may not apply to these and other systems. © 1996 Wiley-Liss, Inc.
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  • 74
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    Chirality 8 (1996), S. 131-135 
    ISSN: 0899-0042
    Keywords: polysaccharides ; optical resolution ; phase loading ; racemic compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution of a range of racemic compounds was investigated using bis(aryl carbamate) derivatives of chitin coated onto microporous organosilane-modified silica. The influence on chiral discrimination of factors such as the carbamate/support weight ratio, the nature of polysaccharide, and the influence of the aryl group substituents was investigated. The bis(3,5-dimethylphenyl carbamate) derivative of a noncommerical chitin gave the best results. © 1996 Wiley-Liss, Inc.
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  • 75
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    Chirality 8 (1996), S. 136-142 
    ISSN: 0899-0042
    Keywords: enantioseparations ; high-performance liquid chromatography ; mobile phase modifier and additive ; cellulose-based CSP ; chiral acidic and basic drugs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eight randomly selected pharmaceuticals, which included ibuprofen, ketoprofen, albuterol, acebutolol, propafenone, betaxolol, methylphenidate, and homatropine, were directly separated on a cellulose tris(4-methylbenzoate) chiral stationary phase (CSP) without derivatization via normal phase mode HPLC. Enantioresolution was achieved by the optimization of the type and the ratio of mobile phase modifiers and additives. The modifiers included alcohols; the mobile phase additives were trifluoroacetic acid (TFA) and triethylamine (TEA). It was found that methanol and ethanol were superior to isopropanol as mobile phase modifiers for enhancing chiral separation of some of the chiral drugs. The results also demonstrated that TFA has a dominant effect on chiral separations for both acidic and basic chiral drugs, although for some basic drug such as homatropine, TEA was more beneficial at improving enantioseparation. The separation of acebutolol enantiomers was achieved for the first time by adding both TFA and TEA to the mobile phase. The purpose of this paper is to demonstrate that the applicability of cellulose based CSPs can be expanded by controlling the mobile phase compositions through the addition of trace amounts of achiral additives and the selection of the appropriate alcoholic modifier. © 1996 Wiley-Liss, Inc.
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  • 76
    ISSN: 0899-0042
    Keywords: amino acids ; chiral rhodium complexes ; aminophosphine-phosphinite ; D- and L-enantiomers ; NMR spectra ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted N-Cbz and N-Boc protected arylamino acrylic acids and esters have been prepared and used in asymmetric hydrogenations catalyzed by PROPRAPHOSRh. Stereoselectivities 〉 90% ee could be achieved, the rate of which is dependent on the position of the substituent in the aromatic ring. The N-Boc derivatives provide advantages compared with the N-Cbz analogues. The amino acid derivatives were fully characterized by 19F, 13C, and 1H NMR spectroscopy. © 1996 Wiley-Liss, Inc.
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  • 77
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    Chirality 8 (1996), S. 397-401 
    ISSN: 0899-0042
    Keywords: chiral derivatization ; capillary GC ; capillary SFC ; diastereoisomeric esters ; optical resolution ; (S)-Trolox methyl ether ; primary alcohols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (S)-Trolox methyl ether is known as a powerful chiral reagent for the e.e. determination of chiral alcohols by separation of the corresponding diastereoisomeric esters on achiral GC and SFC columns. In order to further improve his methodology, five possible candidates resultings from variation of structural elements of parent reagent have been tested for derivatization with selected alcohols and subsequent analysis of the diastereoisomeric pairs of esters. The results of this optimization procedure showing the ways to new potent reagents are discussed. © 1996 Wiley-Liss, Inc.
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  • 78
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    Chirality 8 (1996), S. 258-263 
    ISSN: 0899-0042
    Keywords: stereoselectivity ; radioactivity ; distribution ; hepatocytes ; metabolism ; protein binding ; analbuminemic rats ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselective pharmacokinetics of two enantiomers of [14C]-labeled KE-298 [2-acetylthiomethyl-4-(4-methylphenyl)-4-oxobutanonic acid] were investigated in rats. The blood levels of radioactivity after the oral administration of (+)-(S)-[14C]KE-298 were higher than that for (-)-(R)-[14C]KE-298; the AUC of the former was approximately twice that of the latter. No significant stereoselectivity was observed in absorption rate. The tissue/plasma level ratios at 30 min after oral administration of (-)-(R)-[14C]KE-298 in the liver and kidney, the major metabolic and/or excretory organs, were 2 to 3 times higher than those for (+)-(S)-[14C]KE-298. Neither was evidence of stereoselectivity found in the excretion of radioactivity. During incubation with isolated rat hepatocytes in vitro, the metabolic rates of KE-298 enantiomers were not significantly different. Plasma protein binding 30 min after the oral administration of (+)-(S)-[14C]KE-298 and (-)-(R)-[14C]KE-298 was 99.3% and 97.0%, respectively. Comparing the unbound fraction, (-)-(R)-[14C]KE-298 was approximately 4 times higher than (+)-(S)-[14C]KE-298. In order to make clear the relationship between stereoselective pharmacokinetics and protein binding for [14C]KE-298, the comparative pharmacokinetics of (+)-(S)-[14C]KE-298 and (-)-(R)-[14CC]KE-298 were investigated in analbuminemic rats. In these animals, no evidence of stereoselectivity was found for either blood level-time profiles or plasma protein binding. These results revealed that the stereoselective pharmacokinetics of KE-298 in rats might be due to enantiomeric differences in binding to plasma albumin. © 1996 Wiley-Liss, Inc.
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  • 79
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    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 80
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 316-324 
    ISSN: 0899-0042
    Keywords: sulfated cyclodextrin ; catecholamine ; chiral ; CZE ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The utility of negatively charged sulfated cyclodextrins (SCD) as chiral additives (CA) in capillary electrophoresis (CE) was studied in the chiral resolution of several compounds of pharmaceutical interest, including catecholamines such as norepinephrine, epinephrine, DOPA and their precursors, phenylalanine, and tyrosine. Experiments were conducted using 10 mM sodium phosphate monobasic solution and 2% SCD adjusted to pH 3.2 with phosphoric acid. Chiral recognition mechanisms were explored using structurally related analytes including basic, acidic, and neutral compounds as well as 3,5-dinitrobenzoyl phenylglycine, phenylalanine, and homophenylalanine. The advantage of the reversed electrophoretic polarity mode for the enantioresolution of these compounds is also discussed. © 1996 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 81
    ISSN: 0899-0042
    Keywords: chiral discrimination ; β-Cyclodextrin ; complexation ; enantiodiscrimination ; computational chemistry ; molecular modeling ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiodifferentiation of methyl mandelate by β-Cyclodextrin in the liquid phase is explored in detail. Temperature dependent studies using a β-cyclodextrin chiral stationary phase provided differential binding enthalpies and entropies. NMR studies revealed where around the host molecule the guest tends to reside. Molecular dynamics simulations correctly predict the retention order and provide an atomistic account of how chiral discrimination takes place. It is found that short range dispersion forces rather than long range coulombic forces are responsible for both complexation and for enantiodiscrimination. The intermolecular hydrogen bonds are not discriminating and the idea that a tight fit of included species within a cyclodextrin cavity be a requirement for chiral discrimination is questioned. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 82
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 83
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 84
    ISSN: 0899-0042
    Keywords: aminotetralin ; catechol group ; homochiral derivatization ; (+)-(R)-1-phenylethyl isocyanate ; enantiomers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new chiral derivatization procedure for the HPLC resolution of chiral catecholamines and structurally related compounds is described. The homochiral reagent, (+)-(R)-1-phenylethyl isocyanate (RPEIC), was added to separate and quantitate the enantiomers of rac-5,6-dihydroxy-2-methyl-aminotetralin, the main metabolite of rac-5,6-diisobutyryl-2-methyl-aminotetralin, a potent dopamine agonist, by reversed-phase HLPC analysis. To avoid catecholamine degradation in the basic reaction medium and to obtain the selective and quantitative derivatization of the amino group of the compound, the reversible complex formation between diphenylborinic acid (DPBA) and the catechol group, in alkaline medium, was performed before homochiral isocyanate addition. The RPEIC derivatization was completed in 30 min and then the DPBA complex was dissociated by adding dilute acid. The structure of intermediates and urea derivatives was confirmed by mass spectrometry. The use of an electrochemical detector, operating in redox mode, allowed HPLC quantitation of enantiomers at the nanogram level in plasma and urine. The derivatization procedure is also suitable for other catecholamine-related compounds. © 1996 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
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  • 85
    ISSN: 0899-0042
    Keywords: diarylcarbinol ; arylarylmethanol ; chiral stationary phase ; enantioseparation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fast and efficient baseline separation of asymmetrically substituted diarylmethanols and 1,1-diarylethanols was achieved on an endcapped, amide-linked N-3,5-dinitrobenzoylated, (R, R)-1,2-diphenyl-1,2-ethanediamine-derived chiral stationary phase (CSP). Optimal enantioselectivities on this CSP were obtained using 1% 2-propanol in n-heptane as the mobile phase. Enantiorecognition was found to be governed by π-basicity and the substitution pattern of the aromatic substituents. © 1996 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 86
    ISSN: 0899-0042
    Keywords: hydrolysis ; carboxylesterase ; bioconversion ; plasma concentration ; pharmacokinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The in vitro and in vivo stereoselective hydrolysis characteristics of the mutual prodrug FP-PPA, which is a conjugate of flurbiprofen (FP) with the histamine H2-antagonist PPA, to reduce gastrointestinal lesions induced by FP were investigated and compared with those of FP methyl ester (rac-FP-Me) and FP ethyleneglycol ester (rac-FP-EG). The rac-FP derivatives were hydrolyzed preferentially to the (+)-S-isomer in plasma and to the (-)-R-isomer in liver and small intestinal mucosa. Interestingly, in the gastric mucosa, the stereoselectivity of hydrolysis of (-)-R-FP-PPA was opposite from that of rac-FP-Me and rac-FP-EG, which suggested that the stereoselective hydrolysis of FP-PPA was helpful in reducing gastric damage induced by (+)-S-FP. However, hydrolysis of all rac-FP derivatives was found to be catalyzed by carboxylesterases in the gastric mucosa. The stereoselective disposition of FP enantiomers early after intravenous administration of rac-FP-PPA could be explained by the stereoselective formation of (-)-R-FP from rac-FP-PPA in the liver. (-)-R-FP-PPA was completely hydrolyzed to form (-)-R-FP in vivo, while 78% of (+)-S-FP-PPA was hydrolyzed to (+)-S-FP, with a corresponding decrease in the area under the curve. Twenty-five percent of (+)-S-FP-PPA might be eliminated as the intact prodrug or its metabolites other than FP. The most important bioconversion of FP-PPA occurred in plasma, and additional hydrolysis of the R-enantiomer in liver resulted in the stereoselectivity observed following both i.v. and p.o. administration. © 1996 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 87
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 525-530 
    ISSN: 0899-0042
    Keywords: temazepam ; 3-O-methyltemazepam ; 3-O-ethyltemazepam ; stereoselectivity ; nucleophilic substitution ; racemization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric 3-O-methyltemazepam and 3-Oethyltemazepam were highly stereoselectively substituted by the 3-methoxy group of methanol in acidic anhydrous methanol and by the 3-ethoxy group of ethanol in acidic anhydrous ethanol, respectively. The stereoselectivity of the homonucleophilic substitution reactions was determined by circular dichroism spectropolarimetry and gas chromatography-mass spectrometry. In anhydrous solutions containing 0.5 M D2SO4 at 50°C, for example, the stereoselectivity was ∼63:1 for enantiomeric 3-O-methyltemazepam in CD3OD and ∼94:1 for enantiomeric 3-O-ethyltemazepam in C2D5OD. The high stereoselectivity at C3 position was primarily due to the presence of a methyl group at N1 position. © 1996 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
    Additional Material: 5 Ill.
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  • 88
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 89
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 263-271 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Catalyst surface characterizations have been carried out to investigate the role of dispersion on catalyst activity and to probe the occurrence of oscillations in coking levels with cycle number generally observed during multiple deactivation and regeneration schemes. The titrations were done, cycle by cycle, at 430°C after oxidation and at the same temperature (430°C) after reduction at 500°C. Results show the usually observed trend - that the dispersions after oxidation are higher than those after reduction. The average decline in dispersion from oxidation to reduction was calculated to be 39.25%. It was observed that the cycles with high toxic coke removal were characterised by high deactivation times. The deactivation times were still high even for cycles subsequent to those with low dispersion. At high dispersions the catalyst had short deactivation times, that is the small crystallites deactivate faster than large ones. The nature of reducebale coke and the efficiency of its removal is a much more determinant factor of catalyst activity than the level of metal disperision. Thus prolonged toxic coke reduction at the high temperature of 500°C, though resulting in an apparent lowering of dispersion, does not affect the quality of the catalyst. The dispersion before reduction could be retained on oxidation. Hence reduction at 500°C did not introduce sintering.
    Additional Material: 8 Ill.
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  • 90
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 291-298 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Reasons are given why the axial dispersion in a gas flowing through a packed bed may be influenced by the elasticity - or compressibility - of the fluid. To support this hypothesis, experiments have been done in a packed column at pressures from 0.13 to 2.0 MPa. The elasticity E of a gas is proportional to the pressure P and the compressibility to 1/P. The axial dispersion coefficients as determined were found to be a function of the pressure in the packed bed in the turbulent flow region of 3 〈 Rep 〈 150 if the Bodenstein number is plotted as a function of the particle Reynolds number. This is shown to be an artifact. The pressure influence is eliminated, if Bom, ax is plotted versus the ratio of the kinetic forces over the elastic forces ϱu2/E. Regrettably, Bom, ax seems to be independent of ϱu2/E. For the moment we only can conclude that Bom, ax in the turbulent region is a unique function of the velocity of the gas which flows through the packed bed. Although the fact that a constant Bo value is obtained when plotted against ϱu2/E, the experimental results are so intriguing we wanted to make them public already now. The experimental work proceeds.
    Additional Material: 15 Ill.
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  • 91
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 89-95 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The dynamic behavior of a Pt-Rh/CeO2-Al2O3 three-way catalyst (TWC) under pulsed flow operation conditions (intermittent mode), such as occur in a newly developed hybrid drive system, has been studied experimentally in a laboratory apparatus with simulated exhaust gas. The parallel hybrid system is based on the combination of an Otto-cycle engine with an electric motor and a flywheel providing a short-term energy storage. This configuration permits intermittent charging of the flywheel by the combustion engine which runs only during about 10% of the driving time. Each exhaust gas pulse (duration typically ca. 3 s) is proceeded by an air pulse, which results from the filling of the engine cylinders with air at start up and shut off. Experimental studies indicated that the air pulses have a negative impact on the performance of the catalytic converter, reducing the inherent benefits resulting from the intermittent operation mode of the combustion engine.Forced asymmetric λ-cycling during exhaust pulse was found to be most beneficial for improving catalyst performance. A simple reduced kinetic model derived from a Langmuir-Hinshelwood model for CO oxidation, which was extended by introducing CO and O2 equivalents to mimic the complex exhaust gas, was used to describe the dynamic behavior of the TWC. The model proved to be useful for finding the optimal λ-cycling conditions. Experiments with the real Otto-cycle engine exhaust proved that the reduced kinetic model is suitable for use in a closed loop λ-control.
    Additional Material: 8 Ill.
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  • 92
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 117-126 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When appropriate membrane was used for the assistance of chemical and biochemical equilibrium reactions, it is possible to enhance the yield and the purity of the reaction product by selectively adding educts or selectively removing products and to a lower the energy input and the reaction time compared to conventional process.In this paper a review on membrane reactors with special emphasis on membrane-assistance of esterification reactions and a continuous tube membrane reactor for the pervaporation-assistance of the esterification are presented. The heterogeneously catalyzed esterification of ethanol and acetic acid to ethyl acetate and water was investigated as a typical chemical equilibrium reaction.The selective and simultaneous water separation from the reaction mixture of the esterification with polyvinyl alcohol pervaporation membranes is considered to be an interesting process alternative to the conventional distillation process. Compared to the distillation process, for the pervaporation-assisted process a decrease of the energy input of over 75% and of the investment and operating coasts of over 50% each was calculated.
    Additional Material: 15 Ill.
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  • 93
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The paper briefly reviews the historical development of exergoeconomics, the existing methodologies, and their application. Particular emphasis is placed on the optimization of the design of new energy-conversion systems.
    Additional Material: 1 Ill.
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  • 94
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A critical comparison of the strength and weakness of two optimization strategies for thermochemical process is made, i.e. pinch analysis and exergy analysis. Although both methods have a unique root, i.e. the minimization of the exergy losses, pinch analysis has evolved to become an instrument of direct and optimal design of a heat exchanger network while exergy analysis as such does not give an indication about process optimization. In combination with an adequate simulation code of a process, however, it can help to find the optimum process structure.
    Additional Material: 5 Ill.
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  • 95
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 215-221 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The growth of a thin liquid film surrounded by gas pocket(s), undergoing absorption with a zero-order chemical reaction, has been simulated by an apt mathematical model in order to study the influence of various parameters involved. The solution has been obtained semi analytically using Goodman's integral method and solving the resulting differential equation by a fourth-order Runge-Kutta numerical integration algorithm. The computations reveal the strong dependence of film growth on reaction rate, diffusivity, and molar volume whereas the effect of gas-pocket volume and initial film thickness are moderate.
    Additional Material: 7 Ill.
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  • 96
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The optimal layout of a chemical plant is determined by both economic and environmental aspects. The mathematical approach to this problem is given by representing the process through a superstructure, including any foreseeable process topology. It is described by integer variables, whereas real variables arise from the unit models and the thermodynamic calculations. By including process constraints and an objective function, a Mixed Integer Nonlinear Programming (MINLP) optimization problem is postulated. In this paper MINLP algorithms are combined with a technique for the exergy analysis of chemical processes for the preliminary screening of process alternatives. The exergy analysis as a screening technique is advantageous due to a significantly smaller amount of required data and computing time, compared with true optimization, including cost estimation at an earlier stage of process synthesis and analysis. Thus, a broader solution space can be examined. The subsequent cost analysis has then only to be focused on a reduced set of parameters.
    Additional Material: 5 Ill.
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  • 97
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 28-33 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Existing design codes propose different methods for the analysis for the junction region of conical and toriconical shells (limit analysis, shake down analysis, Kellog design approach, area replacement method) submitted to internal pressure load. However, now it is possible to develop generally valid an very precise guidelines based on linear and nonlinear Finite Elements-Analyses. A clear difference is made between design with respect to fatigue strength and design according to load carrying capacity criteria. A. Major advantage of the Finite-Elements-Method(FEM) is the opportunity of its adaptation to given design criteria such as a strain limit or a plastification limit. It shown how design curves can be directly derived from the FE-analysis with respect to fatigue strength (stress concentration factors) and load carrying capacity (design factors for the calculation of a required wall thickness). The materials behavior in the plastic region is considered with an without strain hardening. Large deformation effects as geometric nonlinearities can be involved in the analysis. The method can easily be applied for the analysis of other pressure vessel components.
    Additional Material: 7 Ill.
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  • 98
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 34-38 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We developed the oxidation reaction of Cu(I) ion in aqueous hydrochloric solution by oxygen in a gas-lift capillary bubble column. The method of gas-liquid absorption with chemical reaction was used. Test data confirmed that the rate constant of the reaction is strongly affected by solution compositions, and that chloride ions induce an inhibition effect. The kinetical orders found are equal to 1 and 2 for oxygen and Cu(I) respectively. The influence of temperature on reaction rate constant showed the existence of a maximum value between 303 and 313K. The effect of gas-liquid of gas-liquid system on the liquid-side mass transfer coefficient kL was also investigated.
    Additional Material: 6 Ill.
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  • 99
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 308-314 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A random packing hydrodynamic simulator is designed specially to carry out experiments under reduced pressures with a counter-current flow air/water system. The simulator results (air/water system) compared to those obtained in a real packed distillation column (benzylchloride/ ethylbenzene system) show a good agreement between hydrodynamic parameters like pressure drop, flooding flow rate, and total liquid hold-up. Empirical relationships derived from the simulator experimental results are proposed allowing the calculation of the pressure drop in a packed distillation column, operating in the pressure range between 10 kPa and atmospheric pressure. The influence of reduced pressure on the HETP in the distillation column and interfacial area in the simulator was also investigated.
    Additional Material: 12 Ill.
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