| Summary: | This thesis aims at understanding the interaction between insulin and interfaces with a multi-disciplinary approach. We investigate three facets of the interaction. In the first part (chapter 4), we study the interaction of insulin with the air/water interface, for different oligomeric compositions of the solution phase. With the help of Sum Frequency Spectroscopy and calculations of the second order nonlinear susceptibility, we can show that insulin monomers segregate to the hydrophobic air/water interface. Since the insulin monomer is the key species to denature and refold to fibrils, our finding explains for the first time why agitation of insulin solutions and the accompanying increase in air/water interface area accelerates fibril formation. In the second part (chapter 5), we investigate the interaction of insulin monomers at low pH with model hydrophilic and hydrophobic solid surfaces. We use a combination of spectroscopic methods, like ATR FT-IR, XPS, SFG and QCM-D to characterise the silicon functionalised solid surface, to quantify the amount of adsorbed protein and to determine its secondary structure. We show that, contrary to physiological conditions, where insulin monomers are known to change secondary structure upon adsorption, an acidic environment leads to near-native adsorbed insulin, which is stable for at least a day. We further show that heat is needed to restructure the adsorbed insulin monolayer and that this restructured monolayer appears to provide the template for further growth. In the final part (Chapter 6), we apply a comparatively simple experimental method, Reflection Anisotropy Spectroscopy for the first time to the formation of amyloid fibrils at interfaces. In a comparison with FT-IR spectroscopy of our model solid surfaces, we show that a drastic change in the peptide backbone arrangement occurs at a hydrophobic surface, when FT-IR merely detects a thick layer with partial beta-sheet structure. We believe this structural change is the beginning of insulin fibril formation and we use the new tool to explore further changes in the adsorbed layer as it ages over several months.
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