Exploiting the ‘Complex’ Relationship between Cucurbituril, Peptides and Gold Nanoparticles for the Development of Biomaterials Suitable for Delivery
This thesis explores aspects of cucurbit[n]uril (CB[n]) chemistry that can be utilised and exploited in the formation of materials suitable for therapeutic peptide delivery and diagnostics. Biomedical applications of CB[n] span simple therapeutic complexation leading to increased solubility and circulation times as well as their incorporation into more complex designs.
CB exhibits the strongest binding affinities of the CB[n] family as well as the highest water solubility, making it of high biomedical interest. Therefore, it is the homologue that is investigated throughout this thesis.
Chapter 1 introduces the CB[n] family, taking the reader from synthetic functionalisation, an overview of CB[n] utility in biomedical applications such as peptide delivery and analyte detection, ending with a brief description of techniques used to characterise CB[n] complexes.
In Chapter 2, isothermal titration calorimetry methodology is developed for the characterisation of ultra-tight CB-guest binary complexes enabling accurate determination of complexes with affinities up to 10¹⁷ M⁻¹. This methodology is then used to assess the binding strength between CB and immunogenic peptide, SIINFEKL, modified with a variety of binding motifs in Chapter 3. In vitro investigations into the effect of binding strength on the bio-activity of SIINFEKL peptides complexed with CB is assessed. The ideal binding motif is dependent on the mechanism of therapeutic action.
Functionalisation of CB[n] opens up avenues for its use in more complex architectures. Chapter 4 explores the functionalisation of CB with short thiolated poly(ethylene) glycol (PEG) chains (CBSH) and reports the facile route towards isolation of allyloxy CB species with a definitive number of functional groups.
Following these successful results, methodology was applies to CB resulting in an allyloxy CB species, yet to be reported in the literature. These preliminary results are reported in the Appendix.
The thiol terminal of CBSH synthesised in Chapter 4 is subsequently used in Chapter 5 to tether CB to the surface of gold nanoparticles (AuNPs) creating a delivery system whose surface chemistry can be readily modified with therapeutic and targeting agents. Preliminary in vitro investigations into the delivery of a pro-apoptotic peptide, (KLAKLAK)₂, are presented as well as a perspective as to where the use of such AuNP-CB structures could be utilised in biomedicine.
Chapter 6 investigates an additional CB bioapplication: the self-assembly of AuNP aggregates stabilised with thiolated PEG molecules. Aggregates are shown to disassemble in the presence of common biomolecules found in intracellular and extracellular fluid with timescales that can be tuned depending on the molecular weight of the selected PEG chains. Such aggregates were also shown to be suitable SERS substrates demonstrating a new class of materials that could be developed for in vivo SERS measurements and diagnostics.
Chapter 7 ends the thesis with a brief overview as to what has been achieved as well as preliminary results regarding the functionalisation of CB, providing a foundation that could be developed in future works.
Overall, this thesis focuses on the utilisation of CB in a variety of applications and highlights important design principles that must be considered when employing this unique macrocycle in biomedical applications.