Supramolecular Nanostructures Based On Calixarenes
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This dissertation describes a systematic approach towards the design, synthesis, characterization, and application of calixarene-based supramolecular nanostructures. Chapter 1 briefly overviews the field of supramolecular chemistry and highlights its horizons. Chapter 2 introduces a modular strategy towards synthesis of nanoscale receptor macromolecules--calix-peptide conjugates. This strategy combines the unique host-guest capabilities of calixarene chemistry with synthetically flexible peptide synthesis. A series of calixarene amino acids was prepared and further utilized to synthesize calixarene dipeptides. Through this approach, calixarene amino acids are now available to be incorporated into peptide networks and nanostructured biologically relevant materials. Chapter 3 demonstrates supramolecular applications of calixarene-peptide conjugates. These calixarene amino acids serve as building blocks for the construction of a novel type of calixarene peptide dendrimers. Calixarene amino acids, peptides, and peptide dendrimers containing tetra-ester functions at their lower rims can extract sodium cations from aqueous solutions. Calixarene-peptide conjugates, possessing urea moieties at the upper rim, were demonstrated to reversibly form self-assembling capsules and supramolecular polymers in apolar solvents. Chapter 4 shows how CO2 gas can be used to construct novel types of supramolecular polymers. These polymers employ both hydrogen bonding and dynamic, thermally reversible carbamate bonds. Addition of a competitive solvent, such as DMSO, breaks hydrogen bonding in the assembled structures but does not influence the carbamate linkers. On the other hand, thermal release of CO2 was easily accomplished but the hydrogen bonded capsules remained intact. Chapter 5 demonstrates functions of supramolecular, calix-peptide based polymers. A switchable, supramolecular polymer is introduced, which is held together through hydrogen bonding and reversibly precipitates-redissolves upon changing the pH. Precipitating, it entraps and stores guest molecules within the self-assembling capsules, incorporated within the polymeric chain. CO2 was used to build switchable, supramolecular polymeric materials, which has fluorescent properties. Formation of a cross-linked, porous supramolecular polymer leads to instant entrapment of organic guest species. These can be stored and then released upon changing solvent polarity, temperature, pH, and concentration.