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  • 1
    ISSN: 0009-2940
    Schlagwort(e): Enantiomerization ; Dynamic complexation gas chromatography ; Homofuran ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: By computer simulation of experimental interconversion profiles, obtained by complexation gas chromatography, rate constants of enantiomerization have been determined for homofuran between 95 and 130°C. Since enantiomerization proceeds at similar rates in the mobile and stationary phase, the rate constants obtained by an Arrhenius plot are in excellent agreement with values determined independently by polarimetry between 60 and 90°C. We thus demonstrate that dynamic chromatography can be an easy means for the rapid determination of enantiomerization (or isomerization) barriers of ca. 70-120 kJ mol-1 requiring only minute amounts of racemic sample.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 289-298 
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective GC ; Polysiloxane-anchored cyclodextrin stationary phase ; Chirasil-Dex-TFA ; Immobilized 2,6-di-O-alkyl-3-O-acyl-cyclodextrin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Heptakis(2,6-di-O-methyl-3-O-trifluoroacetyl)-†-cyclodextrin has been chemically bonded to a polydimethylsiloxane via an octamethylene spacer and subsequently immobilized on to the surface of fused silica capillaries, the first time a cyclodextrin derivative with mixed substituents has been immobilized in this way. The enantioselectivity of the new chiral stationary phase has been investigated as a function of the cyclodextrin content. It was found to be higher than that reported for heptakis (2,6-di-O-methyl-3-O-trifluoroacetyl)-†-cyclodextrin or hepta-kis(2,6-di-O-methyl-3-O-acetyl)-†-cyclodextrin dissolved in polysiloxane (e.g. OV-1701). The degree of immobilization was over 90 %. The temperature stability is, however, inferior to that of Chirasil-Dex (a permethylated cyclodextrin): the maximum operating temperature is approximately 200 °C.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 215-223 
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective capillary (open-tubular) SFC ; Polysiloxane-anchored cyclodextrin stationary phase ; Immobilized Chirasil-Dex ; Separation of cyclodextrin derivatives by SFC ; Non-steroidal anti-inflammatory drugs (NSAIDs) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Immobilized polysiloxane-anchored permethyl-β-cyclodextrin (Chirasil-Dex) with a cyclodextrin content of approximately 30 % by weight, previously employed as a versatile chiral stationary phase for the separation of enantiomers by GC, has been used for the separation of enantiomers by capillary supercritical fluid chromatography (SFC). A considerable number of racemates could be resolved, e.g. aromatic alcohols, amino alcohols (TFA derivatives), and underivatized acids. Many pharmaceutical compounds were among those analyzed, including several NSAIDs (e.g. ibuprofen and ketoprofen), a steroidal drug (nor-gestrel), a barbiturate (hexobarbital), and others.Among the racemates resolved were many which cannot be analyzed by GC owing to low volatility or decomposition at elevated temperatures. For two racemates, analysis temperature and mobile phase density were systematically varied to give constant analysis times or capacity factors k. Low temperatures (ca 60 °C) yielded the best separation in term of separation factor, α, or resolution, Rs, even though higher densities had to be used. In comparison with GC, capillary SFC was able to furnish higher separation factors and similar resolution. The applicability of capillary SFC for the analysis of mixtures of cyclodextrin derivatives, e.g. those used in the synthesis of Chirasil-Dex, was, furthermore, demonstrated.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective capillary gas chromatography ; Enantiomer separation of volatiles ; Cyclodextrin derivatives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: High-resolution capillary gas chromatographic separation of enantiomers, belonging to different classes of compounds on cyclodextrin derivatives is described. The solutions of heptakis (2,3,6-O-trimethyl)-β-cyclodextrin (Phase I), heptakis (2,6-O-dimethyl-3-O-trifluoro-acetyl)-β-cyclodextrin (Phase II) and heptakis (2,6-O-dimethyl-3-O-heptafluorobutyryl)-β-cyclodextrin (Phase III) in the moderately polar polysiioxane OV-1701 were coated onto deactivated fused silica capillaries furnishing columns of high efficiency. The three phases show different enantioselectivities for various racemic mixtures.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective gas chromatography ; Polysiloxane-anchored cyclodextrin stationary phases ; Chirasil-Dex ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 4 (1992), S. 23-28 
    ISSN: 1040-7685
    Schlagwort(e): enantioselectivity ; immobilized permethyl-β-cyclodextrin ; capillary supercritical fluid chromatography ; gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Immobilized permethyl-β-cyclodextrin was used for enantiomer separation by capillary supercritical fluid chromatography and gas chromatography. The influences of pressure and temperature on chiral separation factors, α, and capacity factors, k, have been studied for four representative racemic solutes. The enantioselectivities in supercritical fluid chromatography and gas chromatography are compared. Solvation effects by supercritical carbon dioxide are discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 11-22 
    ISSN: 1040-7685
    Schlagwort(e): enantioselective gas chromatography ; immobilized permethyl-β-cyclodextrin ; Chirasil-Dex ; permethylated β-cyclodextrin dissolved in OV-1701 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Polysiloxane-anchored permethylated β-cyclodextrin (Chirasil-Dex) was used for enantiomeric separation by GC. Four types of Chirasil-Dex, containing up to 36% permethylated β-cyclodextrin by weight, were synthesized and compared with 10% permethylated β-cyclodextrin dissolved in OV-1701. The influence of the cyclodextrin weight percentage on the chiral separation factor α and on polarity, as expressed by the Kovats indices, was studied. The chiral separation factors α did not increase significantly above a threshold of ˜30% permethylated β-cyclodextrin by weight. The plots of α vs. weight percentage depend on the complexation strength of the chiral solutes, as do the Kovats indices; for weakly complexing solutes, changes in the cyclodextrin concentration result in larger changes in α, but in less pronounced changes in the Kovats indices, as compared to strongly complexing solutes. Column performances were investigated for immobilized and nonimmobilized stationary phases. As expected, immobilization properties were found to depend on the content of Si-H groups in the polysiloxane backbone. Immobilized columns exhibited a much better long-term stability of all chromatographic variables investigated.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 15 (1992), S. 723-729 
    ISSN: 0935-6304
    Schlagwort(e): Enantioselective GC ; Polysiloxane-anchored cyclodextrin stationary phase ; Chirasil-Dex ; Cyclodextrin derivatives dissolved in OV-1701 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: GLC on polysiloxane-anchored permethylated β-cyclodextrin (Chirasil-Dex) has been used to separate the enantiomers of 106 racemates of different classes of compounds ranging from alkanes to highly polar compounds such as underivatized diols and free acids. Chromatographic data are listed and compared with those obtained by GLC on permethylated β-cyclodextrin dissolved in OV-1701.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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