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  • 1
    Electronic Resource
    Electronic Resource
    New 2-methylenepropylene-bridged cryptands with high sodium ion selectivity: A thermodynamic study of complexation (1995)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 23 (1995), S. 223-231 
    Details
    ISSN: 1573-1111
    Keywords: Cryptand ; alkali metal ion selectivities ; equilibrium constant ; enthalpy change ; entropy change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermodynamic quantities for the interactions of mono- and tri(2-methylenepropylene)-bridged cryptands, cryptand [3.3.1], cryptand [2.2.2], and 18-crown-6-with Na+, K+, Rb+, and Cs+ have been determined by calorimetric titration in an 80:20 (v/v) methanol: water solution at 25°C. Incorporation of the 2-methylenepropylene (−CH2C(=CH2)CH2−) bridge(s) into cryptand [2.2.2] results in a large change in the ligand-cation binding properties. Tri(2-methylenepropylene)-bridged cryptand [2.2.2] (2) shows high selectivity factors for Na+ over K+ and other alkali cations, while 2-methylenepropylene-bridged cryptand [2.2.2.] (1) selects K+ over Na+, as does cryptand [2.2.2]. The K+/Na+ selectivity is reversed with increasing number of 2-methylenepropylene bridges. This observation indicates that increasing the number of 2-methylenepropylene bridges on cryptand [2.2.2] favors complexation of a small cation over a large one. The logK values for the formation of 1 and 2 complexes (except 1-Cs+ and 2-Na+) decrease as compared with those for the corresponding [2.2.2] complexes. Formation of six-membered chelate ring(s) by the propyleneoxy unit(s) of 1 and 2 with a cation stabilizes the cryptate complexes of the small Na+ and destabilizes the complexes of large alkali metal cations. Thermodynamic data indicate that the stabilities of the cryptate complexes studied are dominated mostly by the enthalpy change. In most cases, both stabilization of Na+ complexes and destabilization of the complexes of large alkali metal cations by six-membered chelate ring(s) also result from an enthalpic effect. Cryptand [3.3.1] shows a selectivity for K+ over Cs+, despite its two long CH2(CH2OCH2)3CH2 bridges. The [3.1] macroring portion of [3.3.1]may be too small to effectively bind the Cs+, resulting in the low stability of the Cs+ complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00709580
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  • 2
    Electronic Resource
    Electronic Resource
    Complexation of Metal Ions with Azacrown Ethers Bearing an 8-Hydroxyquinoline Side Arm (1997)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 29 (1997), S. 259-268 
    Details
    ISSN: 1573-1111
    Keywords: Crown ether ; metal ion selectivity ; equilibrium constant ; enthalpy change ; entropy change ; 8-hydroxyquinoline side arm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermodynamic quantities (log, K, ΔH, and TΔS) for theinteractions of six azacrown ethers each bearing an 8-hydroxyquinoline (CHQ)side arm (1-6) with Na+, K+, Ba2+, and Cu2+ were determined by calorimetrictitration in methanol solution at 25°C. The results indicate that theseligands form stable complexes with the cations studied. Ligands 1 and 3 thathave CHQ attached through position 7 (next to the OH group) show highselectivity for Cu2+ (log K values of 8.12 and 9.44, respectively) over Na+,K+, and Ba2+ by more than four orders of magnitude. On the other hand,ligands 2 and 4 that have CHQ attached through position 2 (next to thequinoline nitrogen group) form more stable complexes with Na+, K+, and Ba2+,but less stable complexes with Cu2+, than ligands 1 and 3. All ligandsinteract more strongly with K+ than with Na+. The K+/Na+ selectivity forligands 4 and 5 is about 1.5 log K units. All complexation reactions displaynegative enthalpy changes. In most cases the entropy changes are alsonegative, indicating that formation of the complexes is enthalpy driven. 1HNMR spectral experiments demonstrate coordination of the cations by alldonor atoms of the ligands including those of the CHQ arm. In all cases, theOH signal is observed in the 1H NMR spectra, suggesting that thecomplexation with the cations does not involve deprotonation of the CHQgroups in the ligands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007959629553
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