Engineered Self-Assemblies from Synthetic Tripodal Ligands for the Formation Soft Materials with Desirable Properties

Abstract

This thesis, entitled “Engineered Self-Assemblies from Synthetic Tripodal Ligands for the Formation of Soft Materials with Desirable Properties” describes the synthesis and characterisation of various novel benzene-1,3,5-tricarboxamide (BTA) derivatives adorned with 2,2’;6’,2”-terpyridine (tpy) and their self-assembly into supramolecular materials. The thesis is divided into eight chapters, which are summarised below. Chapter 1 introduces concepts and literature relevant to the work described herein. The tripodal platform BTA will be discussed, with a focus on how the self-assembly of the system can be tuned by structural modifications and the introduction of metal-ions. The formation of coordination-polymers using tpy will be described, with particular attention paid to the generation of functional supramolecular materials. A photophysical background will be provided for the lanthanide ions, as well as examples of their use in luminescent materials. A review will then summarise the progress made to date in the development of printing supramolecular gels based on low-molecular-weight gelators (LMWGs). Finally, relevant research from the Gunnlaugsson group will be discussed, particularly surrounding the BTA- tris(tpy) motif, which provides a foundation for the research explored herein. Chapter 2 introduces the molecular structures of the novel compounds which formed a basis for this thesis, the principles behind their design, and the aim of their research. Their synthesis will be described, and their characterisation will be provided in detail. Chapter 3 will discuss the self-assembly of three structurally similar LMWGs based on 4-functionalised tpy, with structures akin to unnatural peptides with different N-protecting groups, which further acted as ‘single arm’ analogues to the BTA described in Chapter 4. Their gelation properties were compared and the differences were correlated to their self-assembly properties, which were investigated by various approaches. The microstructures of the gels were attempted to be optimised for printing by exposing the gels to post-gelation treatments, and attempts were made to print the gels in an extrusion-printer. The interactions of the ligands with metal-ions was assessed and compared to previously developed BTA-tris(tpy) systems. Chapter 4 discusses the self-assembly of a novel tripodal BTA gelator fitted with a spacer aimed to induce strong interactions between monomers for improved supramolecular polymerisation. The gelation properties of the native gel will be discussed, and the effect of introducing metal ions on the properties of the material will be assessed. The photophysical and rheological properties of the native gel and the metallogels will be compared, where both types of gels were shown to be extrudable. Finally, a C2-symmetric analogue was designed and its capability to form supramolecular polymers was contrasted to the tripodal compound. Chapter 5 describes the generation of luminescent RNA aggregates with Eu(III)- complexes, where some of the LMWGs described in previous chapters were used as ligands. A tripodal ligand and a ‘single arm’ analogue formed Eu(III)-complexes which exhibited luminescence enhancements and aggregation upon the introduction of RNA. The luminescence enhancement was quantified, and comparisons between the ligands were made in order to discern the effect a tripodal design may have had on the self-assembly of these aggregates. Investigations were made into determining the binding site of the complexes to RNA, and finally they were employed as rudimentary fluorescence imaging agents o f a simple peptide- RNA based system. Chapter 6 presented the formation of self-assembled materials, most commonly microspheres, based on various cysteine derivatives of the BTA-tris(tpy) motif. The derivatives were based on trityl-protected and free cysteines, with and without a flexible hydrophilic spacer, in order to assess the effect each component had on the size distribution of the microspheres. The self-assembly of four derivatives was investigated in various aqueous solvent compositions, and all but one derivative were found to create solid microspheres. Chapter 7 presents the conclusions to this research work and Chapter 8 details the experimental procedures employed throughout the thesis. A list of the literature references will then be provided, followed by the supplementary data in the Appendix.