Title

Molecular recognition properties of cucurbituril receptors

Date of Award

2007

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

This dissertation is concerned with the molecular recognition properties of cucurbituril hosts in three different aspects: synthesis of a novel poly(pseudo)rotaxane based on CB[7] host, design of a novel CB[8]-based fluorescent sensor for indole and indole derivatives, and the comparative guest properties of two bipyridinium guests towards CB[7] and CB[8]. Additionally, the author also utilized the CB[7] host to stabilize cyanine dyes and enhance their optical properties. These projects span topics from materials science to biological chemistry and highlight the versatility of this synthetic host. These studies were performed using a broad range of analytical techniques including 1H-NMR, PGSE-NMR spectroscopy, MALDI-TOF mass spectroscopy, UV-Vis spectroscopy, fluorescent spectroscopy, cyclic voltammetry, and X-ray diffraction.Chapter one is a brief introduction to the cucurbituril family and coves the life span of this synthetic host from early discovery, recent progress and future outlook. The author highlights the extraordinary binding affinity and selectivity of the CB[n] hosts towards organic compounds and their important role in the construction of supramolecular structures.Chapter two describes the complexation of the CB[7] host towards p-xylylene sulfonium salts which are commonly used as monomers to obtain poly(phenylenevinylene)(PPV). A side-chain poly(pseudo)rotaxane was synthesized with CB[7] docking on the sulfonium branches of the cationic polyelectrolyte. The CB[7] host was found to have a catalytic effect on the thermal conversion from the precursor polymer to conjugated PPV. Additionally, CB[7] forms an insulating sheath around the PPV chain and efficiently protect the luminescence of the polymer from being quenched by DNT vapor.Chapter three describes the application of DPT2+ CB[8] binary complex as a fluorescent detector for indole and indole derivatives. CB[8] facilitates the charge transfer interactions between a fluorescent dication DPT2+ and indole which lead to sensitive detection of indole and its biologically important derivatives. Additionally, the author provides the methodology to determine the equilibrium constant for a ternary complex using carefully tailored fluorescent measurements.Chapter four is a comparative study of the binding of two structurally related cationic guests, paraquat and diquat, towards CB[7] and CB[8]. The author describes the pronounced sensitivity of cucurbituril hosts to guest features such as charge, charge distribution and shape. In comparison, CB[7] appears to be more sensitive to the charge distribution of the cationic guest than CB[8].Chapter five is an expansion from chapter four in which the author selectively investigated the binding affinity of five structurally similar cyanine dyes towards CB[7]. The binding motif of CB[7] varies with the length of the polymethine chain in the cyanine structure. CB[7] forms both 1:1 and 2:1 complexes with cyanine dyes containing 3 or more methine units. Complexation by CB[7] significantly enhances the brightness and stability of cyanine dyes in aqueous solution. Additionally, the author also finds that CB[7] can modulate the formation of the J-aggregates in aqueous solution.

Keywords

Chemistry, Analytical; Chemistry, Physical; Chemistry, Polymer

Link to Full Text

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