Amphiphile self-assembly, protein conformations and activity in protic ionic liquids and molecular solvents

Enzymes have been used in many industrial biological applications. Native conformation in enzymes is required in order for catalytic reactions to take place. However, due to their marginal stability, they are prone to denature and aggregation, thus resulting in enzyme inactivation. In bioprocess applications, enzyme inactivation would result in a decrease in reaction yield and efficiency. In other cases, proteins that are prone to denature and have short lifespan will not be suitable for long-term storage. In human body, protein misfolding and aggregation might result in neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases. Thus the mechanisms that govern protein conformation in solutions need to be better understood in order to maintain protein native conformation and enhance activity, if possible. There are many solvent features that influence how proteins fold into specific conformation, such as pH, temperature, ion concentration, ion kosmotropicity and viscosity. However, investigating individual features is a challenge due to the interconnected correlations between solvent features. For instance, modifying salt concentration would directly change its iconicity. Moreover, proteins themselves have specific properties that make them unique, e.g. isoelectric point, binding sites, net surface charge and the presence of disulfide bonds. Studying two different proteins in the same solvent solutions may give different outcomes due to the different interactions that occur. This thesis investigates the role of solvents, specifically the solvophobic effect and its governing factors in non-aqueous solvents. These solvents include molecular solvents and protic ionic liquids. The physiochemical properties of a number of non-aqueous solvents, such as viscosity, chemical moieties and liquid mesostructure, are considered based on their ability to support amphiphile self-assembly. The use of the Gordon parameter value as a tool to predict the capability of non-aqueous solvents as self-assembly media is justified herein. Initially the role of solvophobicity in the self-assembly of amphiphiles in non-aqueous solvents was studied. With the knowledge gained from studies of amphiphile self-assembly, the solvophobic effect in protein folding was then investigated using lysozyme. Structure-property-activity relationship was established by exploring solvent-solvent and solvent-protein interactions in various solvent compositions, and protein conformation correlated with functionality. A systematic study of a range of non-aqueous solvents with various properties was used to assess solvent-solvent interactions and how they relate to amphiphile self-assembly and protein folding. Further understanding of the solvophobic effect for non-aqueous solvents was developed to aid in amphiphile self-assembly and protein stabilization in non-aqueous solvents to suit different applications.