Anomalous Protein Aggregation on Nanotubular Titanium Dioxide

Forstater, Jacob

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March 19, 2019

Creator

Forstater, Jacob
- Affiliation: College of Arts and Sciences, Department of Physics and Astronomy

Abstract

Immobilized enzymes are widely used as catalysts in industrial chemical production, diagnostic devices, and biosensors. Immobilization improves an enzyme's stability and creates an insoluble enzyme-based material that is easier to manipulate and recover. This is typically achieved by either covalently immobilizing enzymes to the surface of an inorganic carrier or by confining them within an inorganic scaffold. Both of these strategies are problematic -- surface adsorption limits immobilization to a monolayer, while confinement prevents access to the enzymatically active site. The desired approach would be to assemble enzymes, without chemical modification, into solid enzyme-based materials with an accessible microstructure. In this dissertation, I detail the discovery and development of an inorganic nanomaterial, titania nanotubes, that can initiate and template the non-covalent, self-assembly of enzymes into stable, micron-sized, enzyme-based superstructures which retain their native enzymatic activity. On the basis of quantitative adsorption measurements, dynamic light scattering, and microcalorimetry, I demonstrate that this process occurs in two stages -- at low enzyme concentrations, enzyme multilayers form around the nanotube; above a critical enzyme concentration the enzyme-coated nanomaterial and any additional free enzyme self-assemble into micron-sized ellipsoidal structures. The resulting enzyme-based material has enhanced enzymatic activity and contains more than 99.9% enzyme by weight. Using solid-state nuclear magnetic resonance (NMR), x-ray diffraction (XRD), and thermogravimetric analysis (TGA), I investigate the interfacial properties of the nanotube and similar materials and I show that this phenomenon is uniquely associated with the active anatase-(001) like surface of titania nanotubes, which contain a high density of stable, coordinatively undersaturated Ti sites on its surface. These findings present a nanotechnology-enabled mechanism for creating stable protein-based materials and present a new route for creating such materials without covalent modification. In this dissertation I detail the assembly of these structures, the role of the nanomaterial's surface chemistry, and the design rules suggested by these findings for creating other nanomaterial templates for biomolecule assembly.

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