Keywords and Phrases
"From a practical perspective, host-guest complexes are vehicles for understanding and using supramolecular interactions for purposeful function in sensors, molecular machines and switches, while from a fundamental perspective they may lead to novel supramolecular protection schemes in basic organic reactions. This dissertation examines the interactions of cucurbiturils as barrel-shaped hosts, exhibiting a hydrophobic cavity, with substituted benzoylpyrydinium, phenypyrylium, and diazaanthraquinonediium cations as guests. In water, N-methyl-4-(p-substituted benzoyl)pyridinium cations exist in equilibrium with their hydrated forms (gem-diols), whose concentrations depend on the para substituent. In the presence of cucurbit7uril (CB), the benzoyl group shows a preference for the CB cavity, and the ketone to gem-diol equilibrium is shifted toward the keto form, meaning that the stabilization through hydrophobic interactions of the benzoyl group in the CB cavity exceeds the hydrogen bonding stabilization of the gem-diols in the aqueous environment. In an aprotic polar solvent such as dimethylsulfoxide, 4-benzoylpyridinium cations undergo heterogeneous electron transfer simultaneously from both their free state as well as their complexes with CB. In the same line of work, N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication in water not only exists in equilibrium with its gem-diol but also forms aggregates which cause line-broadening in ¹H NMR. At low pH (<1), the aggregates break up and the equilibrium is shifted exclusively toward the quinone form. In the presence of CB, the quinone form undergoes inclusion with CB by slow exchange in both water and aqueous acid. Both free and CB-intercalated quinone forms are observed by ¹H NMR. To gain more insight on the intercalation of monocationic guests in the cucurbituril cavity not only as a function of their hydrophobic properties but also in terms of their shape, size and the size of the cavity, 4-phenylpyrylium cation (Pylm) was chosen as a guest and both CB and CB as hosts. The size and shape of the guest was modified by 2,6-substitution (Me, iPr, Ph, t-Bu). In water, 2,6-disubsituted-Pylm form dimers, but they enter as such only in CB. All guests insert their 4-phenyl groups in either cavity, except (iPr-Pylm)₂@CB where iPr-groups are inserted. Stereochemistry is interpreted by an interplay of size and hydrophobicity of pyrylium substituents, solvation effects, and size and flexibility of the hosts"--Abstract, page iv.
Winiarz, Jeffrey G.
Ph. D. in Chemistry
Missouri University of Science and Technology. Department of Chemistry
Missouri Research Board
National Science Foundation (U.S.)
Missouri University of Science and Technology
Journal article titles appearing in thesis/dissertation
- Control of the ketone to gem-diol equilibrium by host-guest interactions
- Simultaneous electron transfer from free and intercalated 4-benzoylpyridinium cations in cucurbituril
- Control of quinone to gem-diol equilibrium by interactions with cucurbituril
- Factors at play in the orientation of pyrylium guests in cucurbituril hosts
xvii, 137 pages
© 2010 Arumugam Thangavel, All rights reserved.
Dissertation - Open Access
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Electronic OCLC #
Link to Catalog Record
Thangavel, Arumugam, "The stereochemistry of selected supramolecular complexes of cucurbiturils and the effect of homogeneous equilibria and electron transfer of the guest" (2010). Doctoral Dissertations. 2097.