Department of Physics


Department of Physics Apple - Gravity

Phone (701) 231-8974, fax (701) 231-7088


Seminar Abstract

April 21, 2005

"Lipid Corralling and Poloxamer Squeeze-out in Membranes"

Professor Ka Yee C. Lee
Dept. of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute
University of Chicago


Victims of electrical trauma suffer extensive loss of structural integrity of cell membranes. Stable structural defects -- "pores" in the range of 0.1 mm -- have been demonstrated in electroporated cell membranes. Poloxamer 188, a triblock copolymer of the form poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) is known to help seal electroporated cell membranes, arresting the leakage of intracellular materials of the damaged cell. Using a monolayer to mimic the outer leaflet of the cell membrane, we have examined the interaction between the poloxamer and dipalmitoylphosphatidylcholine or dipalmitoylphosphatidylglycerol monolayers. With synchrotron x-ray reflectivity and grazing-incidence x-ray diffraction, both the out-of-plane and in-plane structures of mixed phopholipid-poloxamer 188 monolayers were investigated at the air-water interface. P188 selectively inserts into low lipid-density regions of the membrane and "corrals" lipid molecules to pack tightly, leading to unexpected Bragg peaks at low nominal lipid density and inducing the film to separate into P188-rich and -poor phases. At tighter lipid packing, the once inserted P188 is squeezed out, providing a route for the poloxamer to gracefully exit when the membrane integrity is restored.