School of Chemistry - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemInteractions between inverse bicontinuous cubic phase materials and encapsulated biomolecules( 2016)The inverse bicontinuous lipidic cubic phase provides a robust, thermodynamically stable membrane mimetic, with the ability to encapsulate a wide range of biomolecules, including amino acids, peptides and proteins. The unique structural architecture and desirable properties of cubic phase lipids have led to their use in wide range of applications, including as a crystallization matrix for membrane proteins, as well as a hosting environment for therapeutic compounds, enabling the design of drug delivery materials. Within the cubic phase-biomolecule system, a complex structural relationship exists between the chemical structure of the lipid, the overall mesostructure of the system, and the structure and properties of encapsulated compounds. At present this relationship is poorly defined, slowing the further development and implementation of these materials. To investigate the structural relationship between lipidic bicontinuous cubic phase bilayers and encapsulated biomolecules, a number of different cubic phase-biomolecule systems have been examined. The encapsulated biomolecules range in complexity from free amino acids to large integral membrane proteins, and give this work relevance to a number of different end use applications, including the delivery and release of small molecule drugs and peptides, as well as the in meso crystallization of integral membrane proteins. We have examined the effects of encapsulating L-histidine and L-phenylalanine within a range of different cubic phase lipids on the mesostructure of the cubic phase. Subsequently, the translational diffusion of these compounds was measured using PFG-NMR, and a linear relationship was discovered with the diameter of the nanoscale water channels. It was demonstrated that a simple mathematical model can be used to predict in vitro release rates of small molecules based solely upon NMR determined in meso diffusion coefficients. Encapsulation of the transmembrane, anti-microbial peptide gramicidin A’ in the lipidic bicontinuous cubic phase revealed a number of interesting structural changes, both in the bilayer and the peptide itself. These changes were found to be strongly correlated with bilayer parameters such as lateral pressure profile and hydrophobic mismatch, providing further insight into the structural considerations of the system. Studies of peptide encapsulation were expanded to include a broader range of antimicrobial peptide structures, including melittin and alamethicin, which along with gramicidin A’ were encapsulated within a number of different cubic phase nanoparticle formulations. Thorough characterization and analysis of each system revealed that as in the bulk phase, the structural changes in cubosome systems were dependent on factors such as hydrophobic mismatch and lateral pressure of the bilayer, as well as peptide structure and charge. The host lipid identity was also found to significantly modulate peptide uptake. In later work, we examine the encapsulation of the integral membrane protein intimin in the lipidic cubic phase, in a study which elucidates the mesophase properties which lead to successful protein crystallization. The structural parameters of the mesophase were tracked throughout the crystallization process, providing insight into the mesoscale changes occurring during crystal nucleation. Cubic phase bilayers comprised of a range of lipids were also characterized and a strong correlation was found between properties such as protein and lipid diffusion, and successful crystallization. This body of work constitutes a significant contribution to our understanding of the interactions between encapsulated biomolecules and the cubic phase bilayer. The structural trends and considerations highlighted have implications for the further implementation of these materials, including in the rational design and formulation of drug delivery materials and in meso crystallization experiments. Information of a fundamental interest is provided through broader observations regarding the interaction of biomolecules with lipid membranes.