Conformationally controllable amphiphiles as tunable supramolecular hosts and catalysts

Abstract

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 βaminocholic 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 α and the β 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 photoresponsiveness 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 solventtunable supramolecular catalyst.