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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

Year Degree Awarded

2019

Month Degree Awarded

February

First Advisor

Prof. Sankaran Thayumanavan

Subject Categories

Materials Chemistry | Organic Chemistry | Polymer Chemistry

Abstract

Developing an understanding of how molecules, materials and complex systems contribute to biological functions is important since the interpretation of such mechanisms paves the way to further the development of materials that replicate natural functions or impart the observed properties to synthetic materials. The self-assembly of stimuli-responsive scaffolds based on micelles, liposomes, hydrogels and thin films has been of considerable interest. These systems need to be endowed with certain design features which influence the self-assembly and the responsiveness of the scaffold when subjected to external stimuli which could be physical, chemical or biological in nature. This kind of insight is still lacking in our understanding of how these systems respond to various stimuli. In this thesis, our objective is to establish structure-property relationships between the influence of structural design and the target material properties. Of interest to us are pH, temperature (chemical) and enzyme/proteins (biological) as stimuli and we have performed experiments to validate the responsive features of these systems.

The design principles for oligomeric peptides to exhibit a unique temperature-dependent size transition were elucidated and it was found that incorporation of aromatic hydrophobic groups diminishes the thermo-sensitivity of the peptide nanoassemblies. Since these molecules are designed to incorporate FDA (Food and Drug Administration) approved components and the assembly is biodegradable, this system has interesting applications in the food industry and in cryptic catalysis.

Parameters that dictate the morphology of calcium cross-linked alginate gels and the release of an artificial sweetener, aspartame from these hydrogels were studied. We have validated the effect of cross link densities and sizes on the release kinetics of the microgel spheres and bulk hydrogels. The release data was fitted to kinetic models available from literature to elucidate the pathway constraints which were further, found to dictate the release pathway. Lastly, structure-property relationships were developed using libraries of oligomeric amphiphiles to make possible rational design of triggers for amplification via liquid crystal (LC) response. To this end, we synthesized a wide range of amphiphilic oligomers that responded to a protein, carbonic anhydrase (CA II). The mechanism of binding-induced anchoring transition at the LC/aqueous interface was corroborated using addition of inhibitor by modulating the strength of binding. The design rules established here provide insight into the rational design of oligomers with triggers that can couple specific molecular events to LCs to achieve highly amplified responses. This paves way to develop principles based on LCs that permit incorporation of feedback for massive amplification that can be leveraged for targeting, sensing and triggering.

Available for download on Saturday, February 01, 2020

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