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  • 1
    Electronic Resource
    Electronic Resource
    Chiral Polysiloxane-Fixed Metal 1,3-Diketonates (Chirasil-Metals) as Catalytic Lewis Acids for a Hetero Diels-Alder Reaction -Inversion of Enantioselectivity Upon Catalyst -Polymer Binding (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 879-885 
    Details
    ISSN: 0009-2940
    Keywords: Asymmetric catalysis ; Cycloadditions ; Lewis acids ; Polymers ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dimethylpolysiloxane chain is covalently bound to the monomeric Lewis acid catalyst (1R)-(+)-oxovanadium(1V) bis[3- heptafluorobutanoylcamphorate] [(+)-5a] at the C-10 position of the camphor moiety yielding the novel chiral polymeric (1S)-( +)-oxovanadium(1V) bis[3-heptafluorobutanoylcamphorate] -dimethylpolysiloxane [( +)-6a][1]. The Lewis acid promoted hetero Diels-Alder reaction of trans-l-methoxy-3-(trimethylsilyloxy)- 1,3-butadiene (1) and benzaldehyde (2) is studied in the presence of the enantiomerically pure monomeric (5a, 5b) and polymeric (6a, 6b) catalysts. The monomeric and polymeric catalysts of identical chirality[1] invoke opposite enantioselectivities toward the formation of 2-phenyl- 2,3-dihydro-4H-pyrone (4). This remarkable result is corroborated by numerous control experiments. Thus, it is demonstrated that the environment of the active site of the catalyst is changed when the complex is fixed to a polymeric chain. In contrast to 5 and 6, the monomeric 12 and polymeric 13 europium(III) tris[3-heptafluorobutanoylcamphorates] of identical chirality invoke the same enantioselectivity toward the formation of 4. The concept of polymer attachment is utilized to recover the catalyst from the reaction mixture by precipitation and to recycle it for subsequent catalytic runs.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300711
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  • 2
    Electronic Resource
    Electronic Resource
    Enantiomerization of Environmentally Significant Overcrowded Polychlorinated Biphenyls (PCBs) (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 350-353 
    Details
    ISSN: 0899-0042
    Keywords: xenobiotics ; pollutants ; non-planar aromatics ; chirality ; atropisomerism ; ab initio calculations ; electron correlation ; density functional theory ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational barriers of overcrowded PCBs are predicted by ab initio methods including electron correlation, thus settling the controversy between theory and experiment. For 2,2′,3,3′,4,6′-hexachlorobiphenyl (PCB 132), an enantiomerization barrier of 185 kJ/mol is calculated by B3LYP/6-31G*, in excellent agreement with the experimental data. Chirality 9:350-353, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of the rotational barriers of atropisomeric polychlorinated biphenyls (PCBs) by a novel stopped-flow multidimensional gas chromatographic technique (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 316-320 
    Details
    ISSN: 0899-0042
    Keywords: atropisomeric polychlorinated biphenyls (PCBs) ; Chirasil-Dex ; rotational barrier ; stopped-flow multidimensional gas chromatographic technique ; on-line enantiomerization kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational barriers ΔG
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Peak coalescence phenomena in enantioselective chromatography (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 140-146 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective chromatography ; chiral selectands ; chiral selectors ; peak coalescence ; enantiomer separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Six scenarios of peak coalescence are distinguished in enantioselective chromatography. Where appropriate, they are verified by an experiment. Chirality 10:140-146, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.22
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  • 5
    Electronic Resource
    Electronic Resource
    Racemization, enantiomerization, diastereomerization, and epimerization: Their meaning and pharmacological significance (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 396-400 
    Details
    ISSN: 0899-0042
    Keywords: configurational lability ; enantiomers ; diastereomers ; epimers ; macroscopic processes ; microscopic processes ; pharmacological time scale ; pharmaceutical time scale ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational lability of enantiomers can be characterized by different terms, each defining a specific process. Racemization relates to the macroscopic and statistical process of the irreversible transformation of one of the enantiomers into the racemic mixture. Enantiomerization refers to the microscopic and molecule process of the reversible conversion of one enantiomer into the other. Methods allowing the experimental determination of rate constants of racemization (krac) and enantiomerization (kenant) are discussed, and it is shown that kenant = 1/2 krac. Neglect of this fact is a source of some confusion in the literature. When two or more elements of chirality are present in a molecule and one of them is configurationally labile, epimerization occurs, a particular case of diastereomerization. These processes of interconversion between diastereomers are kinetically more complicated than racemization and enantiomerization since the rate constants of the forward and reverse reactions are always different (kdiast/A-to-B ≠ kdiast/B-to-A), however small the difference. An important aspect of the configurational lability of stereoisomeric drugs is the time scale of the phenomenon. When interconversion occurs to a significant extent during the residence time of a drug in the body, a pharmacological time scale is implied. In contrast, the pharmaceutical time scale refers to slower rates of interconversion that affect the configurational purity of a drug during its shelf-life. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070603
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of the rotational barriers of atropisomeric polychlorinated biphenyls (PCBs) by a novel stopped-flow multidimensional gas chromatographic techniqueThis article was orginally published in Chirality, Volume 10, Number 4, pages 316-320. As it is suited to the theme of this issue, this article appears again here. All citations to this article should use the original volume, issue, and page range. (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 425-429 
    Details
    ISSN: 0899-0042
    Keywords: atropisomeric polychlorinated biphenyls (PCBs) ; Chirasil-Dex ; rotational barrier ; stopped-flow multidimensional gas chromatographic technique ; on-line enantiomerization kinetics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rotational barriers ΔG† (T) of the four atropisomeric polychlorinated biphenyls (PCBs) 2,2′,3,5′,6-pentachlorobiphenyl (PCB 95), 2,2′3,3′,4,6′-hexachlorobiphenyl (PCB 132), 2,2′,3,3′,6,6′-hexachlorobiphenyl (PCB 136), and 2,2′,3,4′,5′,6-hexachlorobiphenyl (PCB 149) were determined via on-line enantiomerization kinetics by a new stopped-flow multidimensional gas chromatographic technique (stopped-flow MDGC) employing Chirasil-Dex as chiral stationary phase for enantiomer separation. The calculated rotational barriers ΔG† (T) of the trichloro-ortho-substituted atropisomers are 184 ± 2 kJ/mol for PCB 95, 189 ± 4 kJ/mol for PCB 132, and 184 ± 1 kJ/mol for PCB 149 at 300°C. The rotational barrier ΔG† (T) of tetrachloro-ortho-substituted PCB 136 is at least (or higher than) 210 kJ/mol at 320°C. Chirality 10:425-429, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    In memoriam - Emanuel Gil-Av (1996)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 19 (1996), S. 462-462 
    Details
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240190808
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  • 8
    Electronic Resource
    Electronic Resource
    Enantiomer separation of DNP-amino acids by capillary electrophoresis using chiral buffer additives (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 7 (1995), S. 17-22 
    Details
    ISSN: 1040-7685
    Keywords: enantiomer separation ; capillary electrophoresis ; chiral buffer additives ; proteins ; cyclodextrins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct enantiomeric analysis of six DNP-amino acids by capillary electrophoresis is reported. This study describes a comparison of several chiral buffer additives. Both the natural proteins BSA, AGP, ovomucoid and casein, and the cyclic oligosaccharides α-, β-, and γ-cyclodextrin were used as chiral selectors. For the first time, casein from goat milk was successfully applied for chiral discrimination. The influence of the modifier n-propanol on chiral discrimination is demonstrated with BSA as a buffer additive.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220070103
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  • 9
    Electronic Resource
    Electronic Resource
    Quantification and determination of enantiomeric ratios of chiral PCB 95, PCB 132, and PCB 149 in shark liver samples (C. coelolepis) from the Atlantic Ocean (1996)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 19 (1996), S. 392-396 
    Details
    ISSN: 0935-6304
    Keywords: Multidimensional gas chromatography (MDGC) ; Chiral polychlorinated biphenyls (PCBs) ; Enantiomeric ratio ; Shark ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral 2,2′,3,5′,6-pentachlorobiphenyl (PCB 95), 2,2′,3,3′,4,6′-hexachlorobiphnyl (PCB 132) and 2,2′,3,4′,5′,6-hexachlorobiphenyl (PCB 149) were quantified in Atlantic Ocean shark liver samples (C. coelolepis) by gas chromatography-mass spectrometry (GC-MS) and their enantiomeric ratios were studied by multidimensional gas chromatography (MDGC) with an achiral-chiral column combination and detected by ECD and MS/SIM. The concentration range of the chiral PCBs was from 2 to 6 ng/g (fresh weight), which represents 2-6 % of the total PCB mean concentration. The investigations revealed a small enantiomeric bias of PCB 132 in most of the samples studied (ER = 0.75-0.89, ee = 6-14%), while PCB 95 and PCB 149 were present in racemic or almost racemic form.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240190706
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  • 10
    Electronic Resource
    Electronic Resource
    Die absoluten Konfigurationen der Inhalationsanästhetica Isofluran und Desfluran (1996)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 108 (1996), S. 1814-1816 
    Details
    ISSN: 0044-8249
    Keywords: Inhalationsanästhetica ; Konfigurationsbestimmung ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19961081524
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