Understanding Molecular Control in Supramolecular Systems

Abstract

Gels can be found in all aspects of life. They are used not only in cosmetics, hand soaps, and food, but also have presence in complex biological systems such as the vitreous humor in the eye and thrombi. The gels in natural systems are often dynamic materials, constructed from the self-assembly of reversible, non-covalent chemical bonds.

Self-assembled hydrogels have emerged as exciting materials with excellent potential to mimic the complexity of natural systems. This thesis contributes to advancing a rationale understanding of controlling self-assembled hydrogel properties. This is achieved conceptually through two approaches, i) understanding how molecular structure relates to hydrogel properties and ii) understanding the kinetics of gelation and their effects on hydrogel properties.

Structure-property studies resulted in the rational design of a novel class of supramolecular gelators based on an unsymmetrical perylene-3,4,9,10-tetracarboxylic monoimide dibutyl ester. Related compounds based on these derivatives were shown to have excellent potential as bio-organic field-effect transistors, due to the packing arrangement of the perylenes. Crystal analysis of structurally similar perylene-3,4,9,10-tetraethyl esters gave insights into the packing arrangements of the perylenes and showed previously unreported halogen bonding to a non-core substituted perylene, which affected the photophysical properties.

In addition, the relationship between gelator structure and biocompatibility of the hydrogels was investigated. A comparative study on the three-dimensional cell culture of neuroblastoma tumour spheroids highlighted the importance of aromatic capping group choice. As an extension of this work, these gelators were modified with cell adhesive epitopes to improve their biocompatibility. Serendipitously, one of these gelators showed an unconventional gelation trigger, which formed hydrogels upon heating. This system was studied to further develop a rationale design of this unconventional gelation trigger for translation to other self-assembled hydrogels.

Ultimately, to mimic the complexity of natural systems requires hydrogels with spatiotemporal control. This was achieved through the rational design of a redox-responsive hydrogel. The assembly and disassembly of the hydrogel was kinetically controlled, which allowed for chemically programmed temporal control of the hydrogel lifetimes.