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  • 1
    Electronic Resource
    Electronic Resource
    Anion effects on equilibria and kinetics of the disorder-order transition of κ-carrageenan (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 139-155 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of a number of tetramethylammonium salts on the equilibria and kinetics of the disorder to order transition in the polysaccharide κ-carrageenan have been investigated. Data from the temperature dependence of optical rotation show that anion stabilization of the ordered form follows the lyotropic series I- 〉 Br- 〉 NO-3 〉 Cl- 〉 F-. Stopped-flow polarimetry was used to study the kinetics of conformational ordering following a rapid increase in salt concentration. The transition to the new equilibrium position was shown to be biphasic for all of the tetramethylammonium salts studied. The rate equation for the fast phase and the temperature dependence of the observed forward rate constant accord with a cooperative dimerization process. Activation parameters for helix nucleation, ΔH* and ΔS*, vary with both salt concentration and (at constant ionic strength) the anion type, increasing through the lyotropic series from I- to F-. The slow phase shows second-order kinetics, and is interpreted as further stabilization of the ordered form either through limited aggregation or annealing. The rate constant for the slow phase also follows the lyotropic series. Thus we have shown that both the growth and nucleation processes are anion dependent.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270111
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  • 2
    Electronic Resource
    Electronic Resource
    Quantification of trace levels of β-cyclodextrin and substitution patterns in hydroxypropyl-β-cyclodextrin using high-performance liquid chromatography with polarimetric detection (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 220-223 
    Details
    ISSN: 0899-0042
    Keywords: hydroxypropyl-β-cyclodextrin ; cyclodextrin ; polarimetric detection ; optical rotation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A high-performance liquid chromatographic (HPLC) method has been developed for separation and determination of components in hydroxypropyl-β-cyclodextrin (HP-β-CD). The method involves separation on an amino-bonded HPLC column using water-acetonitrile as a mobile phase with a polarimetric HPLC detector for quantification. It provides good selectivity and sensitivity and can also be used to compare different sources of HP-β-CD and to measure batch to batch variation. The similarity of the values of molar optical rotation for β-cyclodextrin (β-CD) and HP-β-CD suggests that a polarimetric HPLC detector may be used with a straightforward area normalization method, to quantify the proportion of β-CD in any HP-β-CD sample. Trace amounts of β-CD in HP-β-CD have been measured to a precision of 0.01%. © 1993 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050405
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective separations using capillary electrophoresis (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 25-40 
    Details
    ISSN: 0899-0042
    Keywords: Review ; capillary electrophoresis ; enantiomeric resolution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preconditions are outlined for enantioselective separations in capillary electrophoresis (CE) with chiral selectors as additives to the background electrolyte. Free solution capillary electrophoresis conditions are characterised by a single solution phase. Chiral separations are reviewed by selector type (chiral ligand exchange, cyclodextrins, crown ethers, glycoproteins) with the extensive studies on cyclodextrins grouped into sections on amino acids, pharmaceuticals, and speciality chemicals, optimisation, biological fluids, and quantitative aspects. In micellar electrokinetic capillary chromatography, enantioselective discrimination occurs by partition in a two-phase system, with a chiral micellar phase as selector. Optimum separation conditions can be readily predicted for a given selector-selectand combination, and absolute values of binding constants determined by CE. Advantages of CE in comparison with HPLC using a chiral stationary phase include robust, rapid assays and the use of small volumes of aqueous solutions; disadvantages include less favourable detection limits. © 1994 Wiley-Liss, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530060107
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  • 4
    Electronic Resource
    Electronic Resource
    Preparation of milligrams of pure enantiomers using analytical-scale high-performance liquid chromatography (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 290-294 
    Details
    ISSN: 0899-0042
    Keywords: preparative chromatography ; chiral separation ; polarimetric detection ; dual detection technique ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pure enantiomers of an agrochemical process intermediate, (RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-pentan-3-one (1), have been prepared on the milligram scale under overload chromatographic conditions on an analytical chiral column (250 × 4.6 mm i.d.). The effects of variation of temperature and mobile phase composition on retention factor, separation factor, and peak resolution have been investigated. Effects of flow rate, enantiomer ratio, sample concentration, and column load on productivity are also studied. Seven milligrams of the less retained (+)-enantiomer and 5 mg of the (-)-enantiomer were obtained from a single injection of 21 mg of (RS)-1. © 1994 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530060412
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  • 5
    Electronic Resource
    Electronic Resource
    Polarimetric detection in high-performance liquid chromatography (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 1 (1989), S. 251-264 
    Details
    ISSN: 0899-0042
    Keywords: optical activity ; optical rotation ; chiroptical detection ; enantiomeric purity ; chiral separation ; enantioselective reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiroptical detection for HPLC is particularly useful as a selective detection method for chiral molecules, and in enantiomeric purity determination with partial chiral separation or without chiral separation. The recent development of laser-based polarimeters with microdegree sensitivity has increased the applicability of optical rotation detection in HPLC. The detection limit of these instruments is submicrogram on-column for many chiral compounds in analytical HPLC. A variety of applications of the selective detection of optically active molecules are reviewed. The use of polarimetric detection with partial chiral separation is considered, both as an aid to method development and for enantiomeric purity determination. Finally applications to enantiomeric purity determination without chiral separation are reviewed, with the dual use of nonchirally selective and chiroptical detectors to determine the total amount and optical purity of the analyte. Determinations of chiral purity for samples of high enantiomeric excess are described, which with laser-based instrumentation may give accuracies of better than ± 1% with sample loadings of 50 μg on an achiral column. Applications to the study of enantioselective reactions are also considered, with determination of enantiomeric excess in near-racemates to better than ± 0.1%.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530010403
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  • 6
    Electronic Resource
    Electronic Resource
    Quantitative applications and validation of the resolution of enantiomers by capillary electrophoresis (1994)
    Weinheim : Wiley-Blackwell
    Electrophoresis 15 (1994), S. 824-827 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The separation and quantitation of enantiomers is an important application of capillary electrophoresis. This paper reviews the performance and validation of capillary electrophoretic methods for this application. Limits of detection of 〈 0.1% are shown for determinations of minor enantiomer levels. Application areas include enantiomeric purity testing of pharmaceuticals and herbicides, reaction rate monitoring, stability testing, and clinical analysis. It is concluded that the number of quantitative application areas will undoubtedly expand as capillary electrophoresis becomes more widely established as an alternative and complement to high-performance liquid chromatography.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.11501501116
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  • 7
    Electronic Resource
    Electronic Resource
    Enantiomeric separation of salbutamol and related impurities using capillary electrophoresis (1994)
    Weinheim : Wiley-Blackwell
    Electrophoresis 15 (1994), S. 808-817 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The enantiomeric resolution of salbutamol and its chiral and achiral related impurites is investigated using capillary electrophoresis. The effects of nine varieties of cyclodextrin, cyclodextrin concentration and organic modifier concentration were studied in an attempt to resolve all possible analytes in a complex mixture of salbutamol-related solutes. Eleven components including three enantiomeric pairs were baseline resolved using 112 mM dimethyl-β-cyclodextrin at pH 2.5 in a citric acid/phosphate buffer. Both methanol and iso-propyl alcohol at up to 20% were found to have a deleterious effect on the separation. Binding constants and mobility values for the free and complexed forms for each solute were determined. The results are interpreted by considering the physical properties of the molecules under the conditions employed and a rationale proposed for the underlying basis for chiral and achiral selectivity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.11501501114
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