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Supramolecular Polymers and Supramolecular Velcro Based on the Strong Host-Guest Interaction between CB[7] and Ferrocene

Supramolecular Polymers and Supramolecular Velcro Based on the Strong Host-Guest Interaction between CB[7] and Ferrocene
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This thesis describes the synthesis, characterization of monofunctionalized cucurbit[7]uril (CB[7]) derivatives and their applications towards formation of supramolecular polymers and supramolecular velcro based on the strong host-guest interactions between CB[7] and ferrocene derivatives (Fc) in aqueous environment. The extraordinarily high binding affinity (K ~ 1015 M-1), exhibited by CB[7]/Fc pair is on par with avidin-biotin complex, which is one of the tightest binding biomolecular systems. By taking advantage of the high binding affinity in water, where most non-covalent complementary binding systems show poor binding affinity, formation of supramolecular polymers with mechanical robustness and supramolecular velcro for strong underwater adhesion in aqueous environment were achieved. Furthermore, degradability of the supramolecular polymer and reversibility of the supramolecular velcro were demonstrated by careful control of the binding affinity through addition of competitor guest molecules or applying electro-chemical stimuli. Chapter 2 describes the synthesis and characterization of monofunctionalized-CB[7] derivatives, a hitherto challenging task. To begin with, monohydroxy-CB[7] was synthesized through controlled oxidation and characterized by various NMR tools, MALDI-TOF and X-ray crystallography. Subsequently, monoallyloxy- and monopropargyloxy-CB[7] were successfully synthesized, which served as substrates for other functional derivatives through straightforward click reactions such as photo-initiated thiol-ene click reaction and alkyne-azide Huisgen cycloaddition reaction, respectively. Furthermore, molecular recognition properties of the newly synthesized monofunctionalized CB[7] derivatives were investigated. Chapter 3 presents the novel strategy for constructing mechanically robust supramolecular polymers in aqueous media by taking advantage of strong host-guest interactions between CB[7]/Fc pair. A dimeric CB[7] (diCB[7]) host and dimeric Fc guest (diFc) were newly designed and synthesized. By mixing them in water under varying and appropriate concentrations, a supramolecular polymer was readily obtained, which was characterized by various spectral and microscopic techniques and analytical tools. Significantly, the supramolecular polymer exhibited an excellent mechanical strength (storage modulus G’ ~ 106 Pa) in water, which is unprecedented. Furthermore, degradation of the robust supramolecular polymers was achieved by adding a competitive guest molecule (BFc), which has higher binding affinity than Fc, akin to enzyme degradation of biological polymers present in nature. Our results present a facile route to the formation of robust supramolecular polymers under aqueous environment, with promising application towards green chemistry, and as a model system to study biological systems. Chapter4 describes an orthogonal strategy for achieving strong and reversible underwater adhesion based on a synthetic ultrahigh-affinity host-guest binding pair of CB[7] and aminomethylferrocene (Fc). Our strategy involved functionalizing two separate silicon surfaces: a “loop” surface functionalized with CB[7] hosts and a “hook” surface with Fc guests. The CB[7] “loops” and Fc “hooks” form a supramolecular “velcro” which adheres in water without need of any curing agents. It exhibits excellent holding power and lap shear adhesion strength (~ 1.1 MPa) which can be tuned by controlling the density of Fc molecules. Remarkably, not only mechanical reversibility but also chemical switchability at the macroscopic level was demonstrated.
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