Biophysics of lipids.

Lipid layers structure, stability and phase behavior.

Bolalipids: We are studying the structural, mechanical and phase behavior of layers formed by mixtures of linear and bolalipids. The aim of this work is to understand and the fundamental level how molecules that have two head-groups anchored by a flexible hydrophobic backbone changes the properties of the lipid layers as compared to the linear counterparts. Namely, what is the fraction of bolalipids that are found across the layer as compared to forming a U shape? What are the elastic properties of the layers? What is the thermodynamic stability of bola and linear lipids? The understanding of these properties will be used (in collaboration with our experimental collaborators, Profs. D. Thompson and C. Hrycina) in the building of integral membrane protein based sensors.

Spontaneous liposome formation and stability in mitures of lipids with pegolated lipids: The goal in this project is to understand the conditions necessary for the formation and stability of spherical liposomes formed by mixtures of lipids with lipids conjugated with PEG (poly ethylene glycol). The idea is to find the optimal conditions for stabilization of the aggregates to be used as drug carriers and their destabilization upon arrival to target cells. From the fundamental point of view it is a fascinating problem in which the understanding of the coupling between curvature and composition is governed by the nature of the polymers in the lipid head-groups and the mixing of the lipid chains.

Lipid-Poloxamer mixtures: Inspired by the experimental work of Prof. Ka-Yee Lee at the University of Chicago we have been studying the interactions between lipid molecules and block copolymers. We have found that the addition of hydrophobic-hydrophilic block copolymers to a dilute lipid monolayer results in the clustering of the lipid that tend to be organized in well-ordered domains. The results from the lipid-polymer mixtures have implications for the formation of ordered domains of nanoparticles in two dimensions. We are currently studying the structure of the polymer molecules within a lipid bilayer with the aim to understand the role that poloxamers play in sealing cell membranes.

Lipid phase behavior: In collaboration with Dr. R. Elliot and Prof. M. Schick we are studying the phase behavior of mixtures of saturated and unsaturated lipids as well as ternary mixtures of saturated-unsaturated-cholesterol. We predict liquid-liquid coexistence due to differences in lipid and cholesterol packing that may be related to the presence of rafts in biological membranes. We are continuing these studies and plan to study the formation of domains within a membrane.