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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 30 (1998), S. 21-28 
    ISSN: 1573-1111
    Keywords: Amino acids ; crown ethers ; cryptands ; complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Complex formation between several crown ethers and the cryptand (222) and α-amino acids in methanol was studied by calorimetric titration. The ligand structure and the donor atoms of the ligands play an important role in determining the measured values of the reaction enthalpies and entropies. However, with the exception of the diaza crown ether (22) all stability constants are of the same order of magnitude. The enthalpic and entropic contributions to the stabilities of the complexes formed compensate each other. In methanolic solution the amino acids exist in their zwitterionic form. This equilibrium can be influenced. Under acidic, neutral or basic conditions different values of the reaction enthalpies are measured for the complexation of some amino acids with 18-crown-6. These results demonstrate that the concentration of the zwitterionic form of the α-amino acids can be influenced. Thus the reaction between macrocyclic and macrobicyclic ligands and amino acids should be described by at least two different reaction schemes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0009-2940
    Keywords: Carbocycles ; Homocalixarenes ; Calixarenes, Homo- ; Large rings ; Macrocycles ; [2n]Metacyclophanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: all-Homocalixarenes: Carbocyclic Host Compounds with Intra- and Extraannular Ligand ArmsMethoxy-substituted [2n]metacyclophanes 1-10, obtained by Müller-Röscheisen cyclization, are converted into all-homocalixarenes 11-20 with free phenolic hydroxy functions. The well-soluble cyclic pentamer 11 and octamer 14 with endo-acidic host properties are investigated with regard to guest binding. They exhibit selectivity towards alkaline earth metal ions (Ba2+) in liquid/liquid extraction studies. Some of the macrocyclic oligophenols are transformed into homocalixarenes 21-25 with intra- or extraannular oxapropionate groups. The diester 22 and the tetraester 23 are converted into carbocycles 26 and 27 with two and four free oxapropionic acid groups. Complexation properties of the oligoesters in extraction studies and log K values in water are reported. X-ray structural analyses were performed of the [6]-, [8]- and [4]- homocalixarenes 9 and 21, 14 and 23; the inclusion of solvent molecules is proven.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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