Dr. Janna Maranas
Department of Chemical Engineering
The Pennsylvania State University
University Park, PA

Thursday, December 1, 2005
3:00 pm (CT)
3269 Beckman Institute

Abstract

The behavior of cells and their membranes under anhydriobiotic conditions is of considerable scientific and technological importance. In nature, survival under such conditions is often accompanied by the presence of the disaccharide trehalose. As such there is currently a considerable effort to understand the mechanisms of trehalose as a preservation agent and incorporate this effect in engineered systems. This seminar presents results from quasi-elastic neutron scattering [QENS] experiments on dehydrated model membranes, both alone and freeze-dried with trehalose. A number of unique features are available in QENS: deuterium labeling makes it possible to follow the motion of trehalose, lipid head, and lipid tail protons separately, spatial resolution of dynamics over length scales bracketing the inter-lipid distance is possible, and accessible time scales [picoseconds to nanoseconds] overlap with those of molecular simulation, such that simulation can provide more detailed information to guide interpretation of experimental data. These features are utilized to probe the nature of the melting transition and associated dynamics. We observe significantly different contributions of tail and head groups to the melting transition in dry liposomes. When trehalose is added, mobility of trehalose and lipids heads are coupled, suggesting considerable hydrogen bonding. We propose that the dynamics along the lipid tails are heterogeneous, and that this feature leads to the participation of different portions of tail protons in the main melting transition with and without trehalose.