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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: circular dichroism (CD) ; chiral crown ethers ; enantiomeric recognition ; heterochiral complexing ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 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.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051007
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: cyanobiphenyl polysiloxanes ; gas chromatography ; stationary phases ; synthesis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nine isomeric cyanobiphenyl-substituted polysiloxanes were synthesized using a four-step procedure and tested as stationary phases in open tubular column gas chromatography.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220040610
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: stationary phases ; cyanobiphenylpolysiloxanes ; gas chromatography ; supercritical fluid chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220040611
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: stationary phase ; liquid crystal polysiloxane ; supercritical fluid chromatography ; capillary column ; steroids ; androstanes ; estrogens ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220010305
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  • 6
    Electronic Resource
    Electronic Resource
    Structural characteristics of pendant and copolymeric cyclodextrin polysiloxane stationary phases and their influence on chiral selectivity and resolution in capillary gas chromatography (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 7 (1995), S. 91-105 
    Details
    ISSN: 1040-7685
    Keywords: cyclodextrin stationary phases ; polysiloxane stationary phases ; structural characteristics ; gas chromatography ; chiral selectivity ; enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dependence of gas chromatographic properties on stationary phase structural characteristics was evaluated for three different types of cyclodextrin-bonded polysiloxanes: small-rim-tethered, large-rim-tethered, and copolymeric. Separation efficiency, chiral selectivity, and resolution were investigated as functions of stationary phase structural features such as length and chemical composition of the connecting arms, chemical composition of the substituent groups on the small rim of the cyclodextrin toroid, and the position(s) of connecting arm attachment(s) on the cyclodextrin rims. For all of the solutes and experimental conditions used in this study, the small-rim-tethered cyclodextrin phases were found to provide superior chromatographic performances compared to the other two types of cyclodextrin phases. The chiral selectivities of the investigated phases were found to depend both on chemical composition and length of the connecting arm(s). Shorter connecting arms were found to provide improved chiral selectivities. Stationary phases having a four-carbon connecting arm with an etheric oxygen linkage in the chain provided higher chiral selectivities compared to stationary phases with hydrocarbon or phenoxy group-containing connecting arm(s). The chiral selectivities of the studied phases did not change when the substituents at the C-6 positions were changed from -CH2OCH2 to -CH3. Efficiency values of up to 5,000 theoretical plates per meter were obtained using 200 μm i.d. columns. Column efficiency was found to be independent of structural features of the cyclodextrin toroid and the connecting arms.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220070202
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  • 7
    Electronic Resource
    Electronic Resource
    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
    Keywords: capillary column gas chromatography ; cyanophenyl polysiloxane ; stationary phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220010307
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  • 8
    Electronic Resource
    Electronic Resource
    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
    Keywords: gas chromatography ; open tubular columns ; sulfonyl-containing polysiloxane ; polar stationary phase ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220030409
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  • 9
    Electronic Resource
    Electronic Resource
    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
    Keywords: chiral stationary phase ; copolymeric stationary phase ; supercritical fluid chromatogrphy ; open tubular columns ; enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220040207
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  • 10
    Electronic Resource
    Electronic Resource
    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
    Keywords: capillary electrophoresis ; charged surface coating ; cryptand coating ; sulfonic acid coating ; quaternary amine coating ; protein separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220050304
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