Synthesis and Application of Double Cavity Cucurbit[n]urils
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Molecular containers are a unique set of compounds that are able to recognize and associate with other molecules. It is these molecular recognition properties that has resulted in a large number of research groups studying such phenomena. The cucurbit[n]uril (CB[n]) family of macrocyclic hosts are well known for their high binding affinities and selectivity towards guests, particularly ammonium compounds, in water. Synthesizing new types of CB[n] hosts will lead to new and exciting applications for these exceptional molecular receptors. Chapter 1 introduces the concept and importance of noncovalent interactions. A review of cucurbit[n]uril chemistry, including the nor-seco-cucurbit[n]urils and glycoluril hexamer, is covered. The potential applications of the double cavity host, bis-nor-seco-cucurbituril (bis-ns-CB), and of the mono-functionalized CB derivatives recently synthesized are discussed. The wide range of applications incorporating CB as a host for ternary complexes is also reviewed. Chapter 2 describes the synthesis of a new double cavity host (II-1) derived from bis-ns-CB. Host II-1 is synthesized by the double bridging reaction of bis-ns-CB with II-2 under acidic conditions. Host II-1 binds a variety of aliphatic and aromatic ammonium ions (II-3-II-17) in water as the corresponding ternary complexes. Conducting the bridging reaction in the presence of guest II-4 delivers rotaxane II-1*II-42 by a clipping process, the first published rotaxane of a cucurbituril prepared via a clipping mechanism. Chapter 3 describes the synthesis and potential application of two new double cavity hosts (III-1 and III-2) synthesized through condensation of two equivalents of glycoluril hexamer (III-3) with one equivalent of tetra-aldehydes III-4 and III-5, respectively. Host III-1 has been shown to bind four different PEG derivatives (III-16300, III-161000, III-163350, III-1610000) in D2O, and the degree of polymerization was measured by diffusion ordered spectroscopy (DOSY). The highly symmetrical and rigid host III-2 binds to synthesized guests III-20 - III-23 to form discrete complexes and supramolecular ladders.