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  • Title: Rigid versus flexible: how important is ligand "preorganization" for metal ion recognition by lower rim-functionalized calix[4]arenes?
    Author: Talanova GG, Talanov VS, Hwang HS, Park C, Surowiec K, Bartsch RA.
    Journal: Org Biomol Chem; 2004 Sep 21; 2(18):2585-92. PubMed ID: 15351822.
    Abstract:
    For an assessment of the outcomes from use of an appropriately "preorganized" calixarene-based ionophore versus its conformationally mobile prototype, solvent extraction propensities of flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] for alkali, alkaline earth metal cations, Pb2+, Ag+ and Hg2+ are compared with those for seven new rigid analogs fixed in the cone, partial cone and 1,3-alternate conformations. For each of the metal ions, the preferred calix[4]arene conformation was determined from the NMR spectra for the metal salt of the flexible ligand. Except for Ag+, flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] were found to provide greater metal ion extraction efficiency and better selectivity than the corresponding "preorganized" ionophores.
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