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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Amines ; amino acids ; liquid membrane ; macrocyclic ligands ; active transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00709574
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  • 2
    Electronic Resource
    Electronic Resource
    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
    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
    URL: http://dx.doi.org/10.1023/A:1007941023186
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: Crown ethers ; cryptands ; solvent influence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01084708
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: Acetonitrile ; crown ethers ; glymes ; alkali metal ions ; calorimetric titrations ; potentiometric titrations ; complex formation ; ligand solvation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646180
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: Crown ethers ; benzocrown ethers ; non-charged complexes ; host-guest complexes ; calorimetric titration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00972607
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  • 6
    Electronic Resource
    Electronic Resource
    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
    Keywords: Crown ethers ; cryptands ; calorimetry ; potentiometry ; conductometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646985
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  • 7
    Electronic Resource
    Electronic Resource
    Stabilitätskonstanten und thermodynamische Werte für die Bildung von 1:1- und 2:1-Komplexen von Kronenethern mit Alkali- und Erdalkali-Ionen in Methanol (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 2746-2756 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Stability Constants and Thermodynamic Values for the Formation of 1:1- and 2:1-Complexes of Crown Ethers with Alkali and Alkaline-earth Ions in MethanolThe determination of stability constants and thermodynamic values for the reaction of crown ethers with alkali-, alkaline-earth ions, and the silver ion was achieved by calorimetric titration in methanol. Through modification of the experimental conditions it is possible to measure separately the formation of 1:1- and 2:1-complexes (ratio of ligand to cation). With the exception of Ag+ and Ca2+ all ions examined form both kinds of complexes with the various 15 C 5 ligands. The complex stabilities are influenced by enthalpic and entropic contributions. 18 C 6 and DC 18 C 6, having a bigger diameter than 15 C 5, show a definite increase of the stability of 1:1-complexes. Only the Cs+ ion with the largest radius forms 2:1-complexes. A good agreement is found with values determined potentiometrically for the 1:1- and 2:1-complex formation of Na+.
    Notes: Die Komplexstabilitäten und thermodynamischen Werte für die Reaktion von Kronenethern mit Alkali-, Erdalkali-Ionen und dem Silber-Ion in Methanol wurden mittels kalorimetrischer Titrationen bestimmt. Durch Veränderung der experimentellen Bedingungen ist es möglich, sowohl die Bildung von 1:1- als auch 2:1-Komplexen (Verhältnis von Ligand zu Kation) getrennt voneinander zu messen. Mit Ausnahme von Ag+ und Ca2+ bilden alle untersuchten lonen beide Arten von Komplexen mit den verschiedenen 15 K 5-Liganden. Die Komplexstabilitäten werden von enthalpischen und entropischen Faktoren beeinflußt. 18 K 6 und DC 18 K 6, die einen größeren Durchmesser als 15 K 5 besitzen, zeigen einen deutlichen Anstieg der Stabilität der 1:1-Komplexe. 2:1-Komplexe bildet nur noch das Cs+ -Ion mit dem größten Radius. Ein Vergleich mit potentiometrisch bestimmten Daten für die 1:1- und 2:1-Komplexbildung von Na+ zeigt gute Übereinstimmung.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851180717
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  • 8
    Electronic Resource
    Electronic Resource
    Komplexierung von Blei(II) durch Azakronenether und Kryptanden in Methanol (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 3408-3412 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation of Lead(II) by Aza Crown Ethers and Cryptands in MethanolThe stability of PbII complexes with the mono- and bicyclic ligands 1 - 5 in methanol was determined by potentiometric titrations using an ion-selective lead(II) electrode. Reaction enthalpies ΔH were measured by calorimetric titrations. Substitution of the protons at the nitrogen atoms of aza crown 1b by the long decyl chains in 1d leads to a great increase in ΔH, whereas the complex stability is scarcely influenced. Benzo anellands (3, 4) reduce the ligand flexibility and cause a decrease in reaction enthalpies. The reaction entropies are nearly unchanged.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851180837
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  • 9
    Electronic Resource
    Electronic Resource
    Komplexierung von AgI durch Kronenether mit unterschiedlichen Donoratomen und strukturell variierten Kryptanden in Methanol (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 4297-4302 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Complexation of AgI by Crown Ethers with Different Donor Atoms and Structural Varied Cryptands in MethanolThe complex stability of AgI with mono- and bicyclic ligands 1-6 was measured by potentiometric titrations in methanol. The reaction enthalpies were estimated by means of calorimetric titrations. All examined monocyclic ligands not only containing oxygen as donor atoms form - with one exception - more stable complexes than crown ethers. Ligands with a cavity too small for Ag+ ions are able to complex the cation with a ratio of ligand to cation of 2:1. Reducing the cavity size of cryptands by benzo anellands (4, 5) leads to a small decrease in complex stability. Other structural changes at the bicyclic ligands do not influence the complex formation.
    Notes: Die Komplexstabilität von AgI mit mono- und bicyclischen Liganden 1-6 wurde durch potentiometrische Titrationen in Methanol gemessen. Mit Hilfe kalorimetrischer Titrationen wurden die Reaktionsenthalpien bestimmt. Alle monocyclischen Liganden, die neben Stickstoff auch Sauerstoff und Schwefel als Donoratome enthalten, bildeten - mit einer Ausnahme - stabilere Komplexe als reine Kronenether. Liganden, deren Durchmesser kleiner ist als der von Ag+, sind in der Lage Komplexe zu bilden, deren Zusammensetzung Ligand zu Kation 2:1 ist. Die Verkleinerung des Hohlraumes der Kryptanden durch Benzo-Anellanden (4,5) führt nur zu einer kleinen Abnahme der Komplexstabilität. Andere strukturelle Veränderungen an den bicyclischen Liganden beeinflussen die Komplexbildung nicht.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851181102
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  • 10
    Electronic Resource
    Electronic Resource
    Determination of complex stabilities with nearly insoluble host molecules. Part I. Spectrophotometric detection (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 479-484 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The determination of stability constants by measuring the increase in solubility of a nearly insoluble host molecule due to complex formation with a soluble guest is discussed. If the host molecule absorbs in the UV-visible region, spectrophotometric measurements are easily performed to obtain the stability constants. The solubilities of the crown ether dibenzo-18-crown-6 and of the cryptand (222BB) in aqueous solutions and the molar absorptivities of these ligands and their complexes with alkali and alkaline earth metal cations were determined. The increase in solubility of these ligands due to complex formation with cations was used to calculate the stabilities of the complexes formed. Even under the assumption that neither the molar absorptivities nor the solubilities are known, the calculated stability constants agree very well with those obtained using the measured values of the molar absorptivities and solubilities. The accuracy of the stability constants even increases with decreasing solubility of the ligands.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070903
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