A biophysical study of the effect of ionic liquids on single proteins and amyloids, and on biomembranes and cells by means of atomic force microscopy, neutron and light spectroscopies, computational and cell biology approaches

The primary subject of my Ph.D research work was focussed on the role of a new family of organic electrolytes, known as ionic liquids (ILs), on the amyloidogenesis of proteins, which was investigated using a palette of three different experimental techniques such as atomic force microscopy (AFM), optical tweezers, and neutron scattering. In parallel, I have studied the effect of ILs on cell membranes and cell migration, which is relevant for various bionanotechnological applications with the help of molecular dynamics (MD) simulation and biological assays, respectively. As a part of the main interest of my Ph.D. work, I focused on the comprehensive chemical- physical study of the two opposite effect of small concentrations of two ILs, EAN and TMGA, on the amyloidogenesis of the model protein lysozyme. AFM used to study the amyloid fibrils’ morphology and their surface electric potential, showed the opposite effects of the two ILs: in comparison to IL-free aqueous solutions, the presence of EAN led to thicker fibrils of greater surface electric potential, whereas TMGA led to thinner fibrils of lower surface electric potential. Optical tweezers and neutron scattering have been used to unveil the mechanisms of action of the two ILs. We proved that EAN mechanically destabilizes the protein monomer via direct IL-protein interaction, which facilitates the formation of oligomer intermediates leading to thicker fibrils. On the other hand, TMGA mechanically stabilizes the protein monomer by forming an IL-rich solvation cage around the monomers, which leads to an oligomeric-free proto-fibril amyloidogenesis. The huge variety of ILs can offer a completely new and vast playground to tune protein amyloidogenesis with implications in nano-bio applications from health to material sciences. As a parallel project, MD simulation based on an empirical force field was applied to inves- tigate the effects of phosphonium cations ([P 6,6,6,6]+) and dications ([DxC10]2+) on hydrated POPC phospholipid bilayers considering their importance in cell biology. It was observed that incorporation of cations and dications into the structure of a bilayer changes its properties such as diffusion, viscosity and electrostatic pattern, with the only difference in absorption kinetics. At high ionic concentration, the bilayer acquires a long-wavelength standing undulation, corresponding to a change of phase from fluid planar to ripple. As an extension of the aforementioned interactions of ILs with cell membranes, at the cellular level, the effect of [bmim][Cl] and [dmim][Cl] ILs directly with MDA-MB-231 cells using biological assays was investigated. It was shown that subtoxic doses of ILs are able to enhance cell mobility by reducing the elasticity of the cellular lipid membrane, and that both mobility and elasticity can be tuned by IL-concentration and IL-cation chain length, which can have a huge impact in bionanomedicine and bionanotechnology.2022-10-03 JG: Author's signature removed from PD