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  • 1
    Digitale Medien
    Digitale Medien
    Stability constants and thermodynamic data for complexes of 12-crown-4 with alkali metal and alkaline-earth cations in methanol solutions (1987)
    Springer
    Journal of solution chemistry 16 (1987), S. 181-190 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Crown ethers ; cryptands ; calorimetry ; potentiometry ; conductometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The formation of 1:1- and 2:1-complexes of the crown ether 12C4 with mono- and bivalent cations was studied in methanol solutions by calorimetric, potentiometric and conductometric titrations. It is shown that not all donor atoms of the ligand 12C4 take part in complex formation. The accuracy of the three experimental methods are checked by comparing the results for the complexation of alkali ions with crown ether 18C6.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00646985
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  • 2
    Digitale Medien
    Digitale Medien
    The influence of acetonitrile on complex formation of crown ethers containing different donor atoms (1988)
    Springer
    Journal of solution chemistry 17 (1988), S. 277-286 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Acetonitrile ; crown ethers ; glymes ; alkali metal ions ; calorimetric titrations ; potentiometric titrations ; complex formation ; ligand solvation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The complexation reactions of crown ethers with monovalent cations and Ba2+ were studied in acetonitrile solutions by means of calorimetric and potentiometric titration. The reaction enthalpies measured clearly demonstrate the influence of the interactions between 18-crown-6 and the acetonitrile solvent molecules. Changing the donor atoms or other substituents on the ligand molecule can exert a strong influence on the interactions with the solvent. Thus, all the reaction enthalpies measured for the reaction of 15-crown-5 with different cations are higher compared with 18-crown-6. On comparison with results in methanol, an approximate estimation is made of the influence of solvent molecules on the reaction enthalpies measured in acetonitrile. Due to the strong interaction between silver ion and acetonitrile, complex formation is only observed with crown ethers containing additional nitrogen or sulphur donor atoms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00646180
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  • 3
    Digitale Medien
    Digitale Medien
    Influence of ligand structure and solvent effects on complexation of neutral guests by several crown ethers (1994)
    Springer
    Journal of solution chemistry 23 (1994), S. 53-61 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Crown ethers ; benzocrown ethers ; non-charged complexes ; host-guest complexes ; calorimetric titration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The formation of complexes between crown ethers and acetonitrile, chloroform, and nitromethane were investigated in carbon tetrachloride at 25°C. A significant influence of the ring size on the selectivity of the host is evident. The host 18-crown-6 forms complexes for which the reaction enthalpy and entropy are quite high. Host molecules with benzene side groups form complexes of lower reaction enthalpy and entropy and therefore the complexes formed are less stable than that of the analogous crown ethers without aromatic groups. Solvent effects on the stability constant K, the reaction enthalpy ΔH, and the reaction entropy ΔS were studied for the complexation of malonitrile by 18-crown-6. The reaction enthalpy and entropy values change in accordance with the dielectric constant of the solvent used, but no overall effect on complex stability with change in solvent dielectric constant was observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00972607
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  • 4
    Digitale Medien
    Digitale Medien
    Liquid membrane transport of supramolecular complexes of some amines and amino acids with macrocyclic ligands (1995)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 23 (1995), S. 167-174 
    Details
    ISSN: 1573-1111
    Schlagwort(e): Amines ; amino acids ; liquid membrane ; macrocyclic ligands ; active transport
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The transport of some amines in protonated form was studied (viz. methylamine, dimethylamine, diethylamine andn-propylamine) and α-amino acids (l-leucine,l-methionine,l-isoleucine,l-phenylalanine,l-valine,l-α-alanine andl-cysteine). The following macrocyclic ligands were used as carriers throughout the experiments: 15-crown-5 (15C5), 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), diazacrown ether [2.2] (1,7,10,16-tetraoxa-4,13-diazacyclooctadecane) and cryptand [2.2.2] (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo [8.8.8] hexacosane). The active transport, assisted by pH gradient, of amino acids and amines in protonated form as ion pairs in the presence of picrate anion was performed. The experiments suggested the influence of the ligand size, the donor atom type, and the substituents on the transport phenomena.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00709574
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  • 5
    Digitale Medien
    Digitale Medien
    The complexation of alkali metal ions by crown ethers, aza crown ethers, and cryptands in propylene carbonate (1989)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 7 (1989), S. 581-588 
    Details
    ISSN: 1573-1111
    Schlagwort(e): Crown ethers ; cryptands ; solvent influence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The reactions between alkali metal ions and crown ethers, aza crown ethers, and cryptands in propylene carbonate were studied by potentiometric and calorimetric titrations. The most stable complexes formed by macrocyclic and macrobicyclic ligands are when the ligand and cation dimensions are comparable. On comparing the complex stabilities of crown ethers and aza crown ethers of the same size, crown ethers were, on the whole, found to form the most stable complexes, with the exception of the lithium cation. Enthalpic factors are responsible. Substitution of the amino group protons of the aza crown ethers by benzyl groups leads to a high increase in values of the reaction enthalpy. This effect is partly compensated by entropic contributions. The bulky benzyl groups reduce the ligand solvent interactions and induce a ligand conformation with the lone pair of electrons from the nitrogen donor atoms which are more or less directed inside the cavity. The thermodynamic data for the transfer from methanol to propylene carbonate indicate that the ligands containing nitrogen show specific interactions with methanol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01084708
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  • 6
    Digitale Medien
    Digitale Medien
    The Complexation of Amino Acids by Crown Ethers and Cryptands in Methanol (1998)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 30 (1998), S. 21-28 
    Details
    ISSN: 1573-1111
    Schlagwort(e): Amino acids ; crown ethers ; cryptands ; complexes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007941023186
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