Master Thesis defense by Karis Zecchi – Niels Bohr Institutet - Københavns Universitet

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Master Thesis defense by Karis Zecchi

Electro-mechanical properties of lipid membranes at their phase transition

Lipid membranes in physiological conditions sustain significant transmembrane voltages. The effect of such voltages on the thermodynamical properties of the system, however, is not fully understood. Furthermore, couplings between the electrical and mechanical properties of lipid bilayers have been observed and well documented in literature. Both these properties are known to undergo significant changes in the lipid melting. In this thesis, the effect of the lipid phase transition on the electro-mechanical properties of the system is analysed theoretically, with a special focus on the coupling between the membrane curvature and the electric polarization,phenomenon known as flexoelectricity. The effect of flexoelectricity on the melting properties of the membrane is also analysed.

Curved membranes are here shown to display transmembrane potentials that depend on the geometry of the system. This offset potential can induce asymmetry in the electrical properties of the membranes. This asymmetry has been investigated in the experimental part of the thesis through experiments on membrane patches formed using a new instrument. It is also proposed how electrical measurement on lipid patches can be interpreted in the light of the theoretical predictions, and how further experiments can be performed to test the predictions.

Finally, a simple experimental method to measure the temperature dependence of the relative permittivity of lipid membranes is here proposed. It can, in principle, give important information, that together with the theoretical considerations made in the first part of the thesis, could allow for a better understanding of the dielectric properties of lipid membranes at the phase transition.

Supervisor: Thomas Heimburg