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  • 1
    Electronic Resource
    Electronic Resource
    Copper(II) complexes of potentially terdentate N2-[(R)-2-hydroxypropyl]- and N2-[(S)-2-hydroxypropyl]-(S)-phenylalaninamide for chiral recognition: Synthesis of the Ligands and Formation Constants (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1785-1792 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper(II) complexes of the ligands N2-[(R)-2-hydroxypropyl]- and N2-[(S)-2-hydroxypropyl]-(S)-phenylalaninamide performed chiral separation of N-dansyl-protected and unmodified amino acids in HPLC (reversed phase). With the aim of investigating which species are potentially involved in the discrimination mechanism, the two ligands were synthesized and their complexation equilibria with Cu2+ studied by potentiometry and spectrophotometry in aqueous solution up to pH 11.7. The formation constants of the species observed, [CuL]2+, [CuL2]2+, [CuLH-1]+, [CuL2H-1]+, [CuL2H-2], and [CuL2H-3]-, were quite similar for both compounds and were compared to those of (S)-phenylalaninamide. Most probably, in [CuL2H-3]- the ligands behave as terdentate, with the deprotonated OH group occupying an apical position.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780712
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  • 2
    Electronic Resource
    Electronic Resource
    Stereoselective Formation of Ternary Copper(II) Complexes of (S)-amino-acid amides and (R)- or (S)-amino acids in aqueous solution (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 1623-1630 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formation constants of ternary complexes of CuII with (S)-amino-acid amides (phenylalaninamide, prolinamide, and tryptophanamide) and (R)- or (S)-amino acids (valine, phenylalanine, proline, and tryptophan) were determined potentiometrically at 25° and I = 0.1M (KC1). Significant stereoselectivity was found for the systems (S)-tryptophanamide/proline, (S)-prolinamide/tryptophan, and (S)-phenylalaninamide/proline, the diastereoisomeric complexes with ‘homochiral’ (SS) being more stable than with ‘heterochiral’ (SR) ligands. The stereoselectivity observed may be explained on the basis of repulsive interactions between the ligand side-chain residues. The present data on the stability of mixed complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination of amino acids in HPLC (reversed-phase) using CuII complexes of (S)-amino-acid amides as selectors for ligand-exchange chromatography (LEC).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770619
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  • 3
    Electronic Resource
    Electronic Resource
    Stereoselective Formation of Ternary Copper(II) Complexes of (S)-Amino-acid Amides and (R)- or (S)-Histidine and (R)- or (S)-Tyrosine in Aqueous Solution (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1818-1824 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formation constants of ternary complexes of CuII with (S)-amino-acid amides ((S)-phenylalaninamide, (S)-prolinamide, and (S)-tryptophanamide) and (R)- or (S)-histidine and (R)- or (S)-tyrosine were determined potentiometrically in aqueous solution. Significant stereoselectivity was presented by all three amides towards histidine, the diastereoisomeric complexes with ‘heterochiral’ ligands being more stable than those with ‘homochiral’ ligands (see Table 3). The stereoselectivity observed with (S)-phenylalaninamide and (S)-tryptophanamide may be explained on the basis of hydrophobic stacking interactions between 1H-imidazole and the aromatic side chain, favoured by the terdentate behaviour of histidine (see Fig.2), whereas repulsive effects seem to be prevalent with (S)-prolinamide. Only (S)-prolinamide and (S)-phenylalaninamide show appreciable stereoselectivity with tyrosine, which is bidentate, probably on account of repulsive interactions. The present results on the stability of ternary complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination performed by CuII complexes of (S)-amino-acid amides added to the mobile phase in HPLC (reversed phase).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790707
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    Paper (German National Licenses)
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