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Issue 13, 1997
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Molecular engineering. Part 2.1 Influence of side-chainsubstituents in lariat-type upper-rim calix[4]crowns on their bindingproperties and the reversal of these

Abstract

Cone-structured upper-rim 1,3-calix[4]crowns have been synthesized from the distal dibromo diol 6 which is itself regioselectively synthesized from p-bromocalix[4]arene hexyl ether by transmetallation, quenching with B(OMe)3 and oxidation. The dibromo substituents in these calix[4]crowns have been transformed into hydrophobic or hydrophilic groups to give lariat-type hosts. Picrate extraction experiments show that alkylammonium ions bind more strongly than alkali-metal cations to hosts having hydrophobic side-arms such as bromo or p-methoxyphenyl, which means that the hydrophobic binding of the calix[4]arene unit and the hydrophilic binding of the crown unit synergistically increase the affinity of the calix[4]crowns for alkylammonium ions. 1H NMR spectra also support the conformational change of the calix[4]crowns from pinched-cone to cone upon complexation. With amide or ester side-arms the affinity tendency is reversed. It is presumed that the hydrophilic side-arms have a high affinity for the charged part of the guest, which leads to a collapse of the hydrophobic cavity.

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Article type: Paper
DOI: 10.1039/A700165G
J. Chem. Soc., Perkin Trans. 1, 1997, 1997-2004

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    Molecular engineering. Part 2.1 Influence of side-chain substituents in lariat-type upper-rim calix[4]crowns on their binding properties and the reversal of these

    H. Ihm, H. Kim and K. Paek, J. Chem. Soc., Perkin Trans. 1, 1997, 1997
    DOI: 10.1039/A700165G

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