Conformationally controllable amphiphiles as tunable supramolecular hosts and catalysts

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2006-01-01
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Ryu, Eui-Hyun
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The objective of this project is to use solvophobic interactions to guide conformational changes of molecular containers constructed with cholic acid as a building block. This dissertation describes (1) conformationally controllable amphiphilic molecules with solvent-responsiveness and/or photo-responsiveness, and their applications as supramolecular hosts and catalysts, (2) inclusion compounds of beta-aminocholic acid with high guest/host (=4/1) ratio, and (3) an efficient synthetic method to make multivalent water-soluble calixarenes with click chemistry;Amphiphilic "molecular baskets" with multiple facially amphiphilic cholates could aggregate intramolecularly to form a micelle-like conformer in polar solvents and a reversed-micelle-like one in nonpolar solvents. The stability of the reversed micelle-like conformers were influenced by the preorganization of the scaffold, the difference in solvophobicity between the alpha and the beta faces of the cholate, and the spacers between the cholates and the scaffold. Microphase-separation of solvents was found to occur within the baskets. The environmentally responsive baskets could act as a novel supramolecular host to bind hydrophilic guests in nonpolar solvent mixtures and hydrophobic guests in polar solvents. Solvent-responsiveness could be easily coupled with photo-responsiveness by the introduction of azobenzene-spacers. A porphyrin could be used as the scaffold as well. Binding studies of the basket with the Zn-porphyrin scaffold indicated that the conformational change could be utilized to tune the substrate-selectivity of the metalloporphyrin. The basket with a Fe-porphyrin scaffold could act as a solvent-tunable supramolecular catalyst;Bile acids such as cholic acid are well known to include a wide variety of organic compounds in their crystal lattices. 3beta-Amino cholic acid was found to include with a high guest/host (=4/1) ratio into the solid state, because of the charge-assisted hydrogen bonds between the amino and the carboxyl group;Despite broad interest in water-soluble calixarenes as multivalent ligands, their synthesis represents a challenge because many reactions to introduce water-soluble groups have poor functional-group tolerance. Via the high-yielding [3+2] cycloaddition between an azide and an alkyne (i.e., a click reaction), water-soluble calixarenes carrying cationic, anionic, and nonionic groups were synthesized. Cationic and anionic calixarenes were fully soluble in water and their aggregation was investigated by 1H NMR spectroscopy.

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