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  • 1
    Digitale Medien
    Digitale Medien
    Enantiomeric recognition of aralkyl ammonium salts by chiral pyridino-18-crown-6 ligands: Use of circular dichroism spectroscopy (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 545-549 
    Details
    ISSN: 0899-0042
    Schlagwort(e): circular dichroism (CD) ; chiral crown ethers ; enantiomeric recognition ; heterochiral complexing ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: CD studies were performed on the enantiomeric recognition of chiral aralkyl ammonium salts 1-3 by chiral pyridino-18-crown-6 ligands 4 and 6. Heterochiral complexing was found to result in larger spectral effects in both the 1Lb and 1La band regions of the chiral crown ethers. Based on the results reported herein, CD spectroscopy can be an efficient tool for discriminating between enantiomeric chiral aralkyl ammonium salts and determining the stoichiometry and relative stability of their complexes with chiral pyridino-18-crown-6 ligands. Chirality 9:545-549, 1997. © 1997 Wiley-Liss, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Structure and conformation of pyridino- and diesterpyridino-18-crown-6 complexes with primary ammonium salts in solution and crystalline states (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 656-662 
    Details
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Structures in CD3OD—CDCl3 mixtures of pyridino-18-crown-6 and diesterpyridino-18-crown-6 complexes with primary ammonium cations containing an α-phenyl group were found to be significantly different. The π-π overlap between the α-phenyl group of the ammonium cation and the pyridine ring of the ligand occurs in the pyridino-18-crown-6 complexes but not in the diesterpyridino-18-crown-6 complexes. The solution structure of a diesterpyridino-18-crown-6 complex with an α-phenyl-containing primary ammonium cation was also found to differ markedly from the corresponding crystal structure in that π-π overlap occurs in the crystal structure, but not in the solution structure.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/poc.610051007
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  • 3
    Digitale Medien
    Digitale Medien
    Chromatographic evaluation of chiral (1R-trans)-N, N′ -1,2-cyclohexylenebisbenzamide-oligodimethylsiloxane copolymeric stationary phases for capillary supercritical fluid chromatography (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 4 (1992), S. 155-162 
    Details
    ISSN: 1040-7685
    Schlagwort(e): chiral stationary phase ; copolymeric stationary phase ; supercritical fluid chromatogrphy ; open tubular columns ; enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel approach to the design of chiral stationary phases (CSPs) is illustrated by the synthesis and evaluation of selective and efficient copolymeric CSPs with alternating chiral (1R-trans)-N, N′-1,2-cyclohexylenebisbenzamide and achiral (oligodimethylsiloxane) blocks. These materials are shown to resolve a variety of chiral diols. Evaluation of the performance of one of these phases in GC and SFC suggests that SFC can produce higher resolution because of its lower operating temperature which facilitates solute-stationary phase interactions. The influence of different chiral (position of substitution) and achiral (chain length) blocks of the copolymer on solute retention, efficiency, chiral selectivity, and resolution were studied, as well as the reproducibility of the column preparation method.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220040207
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  • 4
    Digitale Medien
    Digitale Medien
    4-(Methylsulfonyl)phenyl-containing polysiloxane stationary phase for capillary column gas chromatography (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 3 (1991), S. 349-353 
    Details
    ISSN: 1040-7685
    Schlagwort(e): gas chromatography ; open tubular columns ; sulfonyl-containing polysiloxane ; polar stationary phase ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new polar polysiloxane stationary phase for capillary column gas chromatography containing 4-(methylsulfonyl)phenyl substitution was synthesized and compared to a cyanophenylpolysiloxane, OV-225. The sulfonylphenylpolysiloxane phase was useful and stable over a wide temperature range from 70°C to 320°C, and it exhibited similar overall polarity to OV-225. However, because of the specific chemical properties of the 4-(methylsulfonyl)phenyl group, this phase demonstrated unique selectivities for certain classes of compounds including basic nitrogen heterocycles and polychlorinated biphenyls.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220030409
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  • 5
    Digitale Medien
    Digitale Medien
    Charged surface coatings for capillary electrophoresis (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 199-205 
    Details
    ISSN: 1040-7685
    Schlagwort(e): capillary electrophoresis ; charged surface coating ; cryptand coating ; sulfonic acid coating ; quaternary amine coating ; protein separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Fused-silica capillaries with specially designed charged surface coatings were developed for the control of electroosmotic flow and for the separation of peptides and proteins in capillary electrophoresis. Cryptand moieties were immobilized onto the capillary surface through a crosslinking reaction of a cryptand-containing polymer and copolymerization of a cryptand-containing monomer. The resultant coatings provided switchable electroosmotic flow from low to high pH due to the complexing ability of the cryptand moieties with the metal ions from the buffer solution. A positively charged quaternary amine surface-coated column was found to be very effective in reversing the electroosmotic flow compared to an untreated fused silica capillary, and to be suitable for separation of proteins whose pI values are greater than the buffer pH. Also, a negatively charged sulfonic acid surface-coated column could be used to stabilize the electroosmotic flow from pH 3 to 9, and the magnitude of the electroosmotic flow could be controlled by varying the concentration of sulfonic acid groups in the coating solution. This negatively charged surface coating gave excellent reproducibility for the separation of a tryptic digest of β-casein.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220050304
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  • 6
    Digitale Medien
    Digitale Medien
    New nitrophenyl- and nitromethoxyphenyl-substituted methylpolysiloxane stationary phases for capillary column gas chromatography (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 1 (1989), S. 309-319 
    Details
    ISSN: 1040-7685
    Schlagwort(e): capillary column gas chromatography ; nitrophenyl polysiloxanes ; stationary phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Nitrophenyl-, nitrophenylethyl-, dinitrophenylethyl-, and methoxynitrophen- ylethyl-substituted polysiloxanes (25-50% substitution) have been synthesized and evaluated as stationary phases in capillary column gas chromatography. Phases with 25% substitution and with ethylene spacers between the phenyl substituents and the polysiloxane backbone were found to provide high efficiencies, moderate thermal stabilities, and useful selectivities. Without flexible hydrocarbon spacers, the station- ary phases exhibited poor efficiencies. The 50% substituted phases generally provided narrower operational temperature ranges and lower efficiencies, and they were more difficult to immobilize by free radical crosslinking. Several methods of immobilization were evaluated, and a dynamic procedure with dicumylperoxide (DCP) was found to produce the best results for these nitrophenyl-containing phases. The enhancements in polarity resulting from the resonances of the nitrophenyl substituent groups pro- vided unique selectivities for specific applications involving aromatic compounds. The dinitrophenyl-containing phases showed, in addition, selectivity based on charge transfer complex formation.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220010610
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  • 7
    Digitale Medien
    Digitale Medien
    Separation of steroid isomers using a liquid crystalline polysiloxane stationary phase in capillary supercritical fluid chromatography (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 1 (1989), S. 131-135 
    Details
    ISSN: 1040-7685
    Schlagwort(e): stationary phase ; liquid crystal polysiloxane ; supercritical fluid chromatography ; capillary column ; steroids ; androstanes ; estrogens ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A liquid crystalline biphenylcarboxylate ester polysiloxane stationary phase was used to study the effect of solute structure on retention for the separation of isomeric steroids in capillary supercritical fluid chromatography. It was determined that theretention mechanism is related to solute molecular shape rather than to properties such as volatility or polarity. The elution order of isomeric androstanes and estrogens could be correlated with the planarity of molecules: more-planar molecules were retained longer on the column. The resolution of steroid isomers was improved significantly using the liquid crystalline stationary phase when compared with results obtained using other stationary phases.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220010305
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  • 8
    Digitale Medien
    Digitale Medien
    Syntheses of isomeric cyanobiphenyl-substituted polysiloxanes for stationary phases in gas chromatography (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 4 (1992), S. 521-527 
    Details
    ISSN: 1040-7685
    Schlagwort(e): cyanobiphenyl polysiloxanes ; gas chromatography ; stationary phases ; synthesis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Nine isomeric cyanobiphenyl-substituted polysiloxanes were synthesized using a four-step procedure and tested as stationary phases in open tubular column gas chromatography.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220040610
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  • 9
    Digitale Medien
    Digitale Medien
    New cyanophenyl-containing polysiloxane stationary phases for capillary column gas chromatography (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 1 (1989), S. 142-149 
    Details
    ISSN: 1040-7685
    Schlagwort(e): capillary column gas chromatography ; cyanophenyl polysiloxane ; stationary phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New p-cyanophenylethylpolysiloxane and p-cyanophenylpolysiloxane stationary phases exhibiting high efficiency, cross-Iinkability, and thermal stability up to 300°C are reported in this paper. These stationary phases possess a unique blend of polar and polarizable character that has resulted in excellent selectivities for compounds having delocalized nelectrons. Another advantage of the p-cyanophenyl phases is their demonstrated relatively low elution temperatures for polar materials compared with the typical cyanopropyl polysiloxane phases.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220010307
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  • 10
    Digitale Medien
    Digitale Medien
    Novel cyanobiphenylpolysiloxane stationary phases for gas and supercritical fluid chromatography (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 4 (1992), S. 529-540 
    Details
    ISSN: 1040-7685
    Schlagwort(e): stationary phases ; cyanobiphenylpolysiloxanes ; gas chromatography ; supercritical fluid chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Nine different 25% cyanobiphenyl-substituted polysiloxane (CBP) stationary phases were evaluated for use in gas and supercritical fluid chromatography. They were easily coated and cross-linked on fused silica capillaries to produce highly efficient columns. For a 200 μm i.d. column, an efficiency of as high as 5,100 plates m-1 was obtained. For most of the new phases, the upper temperature limit was 300°C. A comparative study of the chromatographic behaviors of the cyanobiphenyl and commercial reference phases was made. Some of the cyanobiphenyl stationary phases showed polarities higher than those for carbowax 20M or 50% cyanopropyl. All six positional isomers of dodecylxylene and the five isomers of four-ring polycyclic aromatic hydrocarbons were baseline resolved on GC capillary columns with certain of the cyanobiphenyl phases, demonstrating higher selectivity over SE-54 or Carbowax 20M phases. In SFC, a cyanobiphenyl column provided better separation of a standard coal tar sample than columns with biphenyl or cyanopropyl phases. The retention behavior of fatty acid methyl esters and a mixture of polar solutes was investigated on the cyanobiphenyl and references phases. With respect to certain solute pairs, the selectivities of the new stationary phases were found to increase with temperature. The new cyanobiphenyl phases were found to be useful for GC and SFC separations of various classes of complex mixtures including essential oils, explosives, and polycyclic aromatic hydrocarbons.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mcs.1220040611
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