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  • Organic Chemistry  (4)
  • Capillary electrophoresis  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Chiral discrimination by ligand-exchange chromatography: A comparison between phenylalaninamide-based stationary and mobile phasesThis work is dedicated to the memory of Professor Emanuel Gil-Av. (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 452-461 
    Details
    ISSN: 0899-0042
    Keywords: enantiomers ; HPLC ; DNS-animo acids ; fluorescence quenching ; ligand-exchange mechanism ; adsorption ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copper(II) complexes of two new diastereomeric ligands, N2-(R)- and N2-(S)-2′-hydroxypropyl-(S)-phenylalaninamide [(R, S)-1 and (S, S)-1], have been used as additives to the eluent in high-performance liquid chromatography (HPLC) reversed phase for the chiral separation of DNS-amino acids. The aim was that of comparing the separation process obtained by the chiral eluent with that obtained by an analogous bonded stationary phase containing (S)-phenylalaninamide, previously studied [CSP-(S)-Phe-NH2]. The affinity of the ternary complexes for the C18 column was determined by adsorption experiments in HPLC. It was shown that the two systems (chiral eluent, chiral stationary phase) work according to different mechanisms. Ternary complex formation in solution was studied by fluorescence spectroscopy. It was shown that chiral separation with the Cu(II) complexes added to the eluent was determined by the relative affinities of the ternary complexes for the column-stationary phase rather than by their stabilities in solution. With CSP-(S)-Phe-NH2 the separation is accounted for by the relative stabilities of the ternary complexes, which depends mainly on the “allowed” geometry of the complex and on the steric repulsion of the amino acid side chain with the spacer. © 1996 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chiral separation of unmodified α-hydroxy acids by ligand exchange HPLC using chiral copper(II) complexes of (S)-phenylalaninamide as additives to the eluent (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 331-336 
    Details
    ISSN: 0899-0042
    Keywords: α-hydroxy acids ; ligand exchange mechanism ; chiral mobile phases ; amino acid amides ; fluorescence ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) complexes of (S)-phenylalaninamide have been successfully used for the direct enantiomeric separation of unmodified (R,S)-α-hydroxy acids in reversed phase high-performance liquid chromatography (RP-HPLC). The effect of various parameters (pH, eluent polarity, selector concentration) on enantioselectivity is discussed. Evidence is provided that a mechanism of ligand exchange is actually occurring during the chromatographic separation. The method is very convenient and easy to use, and the chiral selector is commercially available and can be recovered at the end of the analysis. A conventional achiral RP-ODS-2 column is used and no pretreatment of the samples is required. This method allows the accurate determination of the enantiomeric excess of α-hydroxy acids in synthetic and biological samples. © 1995 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070504
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  • 3
    Electronic Resource
    Electronic Resource
    Copper(II) complexes of N2-alkyl-(S)-amino acid amides as chiral selectors for dynamically coated chiral stationary phases in RP-HPLC (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 189-196 
    Details
    ISSN: 0899-0042
    Keywords: chiral ligand exchange chromatography ; chiral coating ; chiral discrimination ; chiral copper(II) complexes ; amino acids ; amino acid esters ; amino acid amides ; hydroxy acids ; dipeptides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) complexes of N2-octyl-(S)-phenylalaninamide (Noc-Phe-NH2), N2-dodecyl-(S)-phenylalaninamide (Ndo-Phe-NH2), and N2-octyl-(S)-norleucinamide (Noc-NLeu-NH2), dynamically adsorbed on a reversed-phase C18 column, were able to perform the direct enantiomeric separation of unmodified amino acids, amino acid amides and esters, hydroxy acids, and dipeptides by elution with aqueous or mixed aqueous-organic solutions containing copper(II) sulphate or acetate. The role played by several parameters in the separation procedure was examined with the copper(II) complex of Noc-Phe-NH2 [concentration of the copper(II) ion in the eluent, pH and eluent polarity, amount of adsorbed selector]. The separation was shown to occur entirely on the stationary phase. The mechanism of chiral discrimination is discussed in terms of the chromatographic parameters and of the structure of the copper(II) complexes in solution and in the solid state. The chiral stationary phase maintained its separation ability for about 3 months. However, the column could be easily restored by recovering the selector with methanol and repeating the loading procedure. © 1996 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Histamine-modified β-cyclodextrins for the enantiomeric separation of dansyl-amino acids in capillary electrophoresis (1997)
    Weinheim : Wiley-Blackwell
    Electrophoresis 18 (1997), S. 905-911 
    Details
    ISSN: 0173-0835
    Keywords: Enantiomeric separation ; Charged β-cyclodextrins ; Dansyl-amino acids ; Capillary electrophoresis ; Histamine-modified β-cyclodextrins ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Two novel monosubstituted β-cyclodextrins (CD) bearing the histamine moiety linked to the upper CD rim, either through the amino group or the imidazole nitrogen 1N, CD-hm and CD-mh, were successfully used as chiral selectors in capillary electrophoresis for the enantiomeric discrimination of dansyl (Dns)-amino acids. Good results were obtained by using low concentrations of the selectors (1-3 mM). The effect of pH on the chiral discrimination was studied in order to modulate the number and the position of the positive charges. By increasing the pH from 5 to 7.5, chiral discrimination decreased along with the deprotonation of the imidazolyl moiety. Inversion of the migration order was observed with the two CDs, depending on the relative position of the charged moieties on the upper rim. Ion pair interaction coupled to inclusion complexation seems to account for the discrimination process. The effects of the temperature, CD concentration and capillary length on chiral resolution were also examined.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150180609
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  • 5
    Electronic Resource
    Electronic Resource
    Chiral Diaminodiamide Copper(II) Complexes for the Enantioselective Recognition of Amino Acids: Synthesis of the Ligands and Formation Constants (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1916-1922 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (S,S)-N,N′ -Bis(aminoacyl)ethane- and (S,S)-N,N′ -bis(aminoacyl)propanediamines (AA-NN-2 and AA-NN-3, respectively, AA = alanine, phenylalanine, valine) were synthesized as the dihydrochlorides, and their complexes with Cu(II) studied potentiometrically. Since these ligands in the presence of Cu(II) are able to perform chiral resolution of D,L-dansylamino acids in HPLC (reversed phase), in a certain pH range (6.5-8.5), it is important to know the equilibria existing between ligands and copper in aqueous solution. For AA-NN-2, four species, CuLH3+, CuL2+, Cu2L2H-22+, and CuLH-2, were detected, whereas for AA-NN-3, only CuLH3+, CuL2+, and CuLH-2 were found. The aim is to find out which complexes may be involved in the recognition process.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690818
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