Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 12, Issue 10, Pages 2772-2777Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200500968
Keywords
calixarenes; crown compounds; host-guest systems; NMR spectroscopy; supramolecular chemistry
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Diffusion-ordered H-1 NMR spectroscopy techniques have been used to determine the binding strength of p-sulfonatocalix[4]arene (SO3[4]) towards a number of charged crown ether species in aqueous conditions. For several (doubly) charged (di)azacrown ethers, all were bound by SO3[4] either well or very well with binding constants between 5.1 x 10(2) - 9.9 x 10(5) m(-1). These results correlate with, and thus explain the phenomenon of rapid capture of azacrown ethers in molecular capsules based on p-sulfonatocalix[4]arene and lanthanide metals. Similarly, the formation of Russian doll superanions in the solution phase is also elucidated. These superanions have been shown to selectively crystallise particular polynuclear aquated metal ions from mixtures in the aqueous phase. Neutral [18]crown-6 is not bound by p-sulfonatocalix[4]arene and displays a binding constant of 0 m(-1). When sodium [18]crown-6 is examined in a similar fashion, binding by SO3[4] is observed in solution with K-a similar to 3.1 x 10(3) m(-1).
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