COLL 534 |
| We have investigated the adsorption of binary phospholipid mixtures to silica using neutron reflection. Small sonicated unilamellar vesicles (SUV) composed of DOPC and d62-DPPC were incubated at 50°C in contact with a silica-surface using a method commonly employed to form supported model membranes. An asymmetric bilayer arrangement was discovered in all the cases studied, with a clear preferential adsorption of DPPC to the side of the silica surface. The total bilayer composition differed by as much as 35 mol% from that of the SUVs, but the composition of the distal monolayer was approximately the same. To our knowledge, this is the first direct determination of the structure and lipid composition of a mixed supported bilayer. The bilayer compositions indicate that equilibrium between the vesicles and the surface bilayer must be at least partially established during adsorption above the lipid phase transition temperature. The current models of vesicle fusion to surfaces do not consider the rupture and spreading of vesicles to be an equilibrium process. We discuss possible mechanisms for establishing the lipid asymmetry and their implications for the properties of supported bilayers as model membranes. |
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Chemistry at Membrane Interfaces
2:00 PM-5:20 PM, Wednesday, 13 September 2006 Sir Francis Drake -- Carmel Room, Oral
Division of Colloid & Surface Chemistry |