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Characterization of Solid-Supported Dipalmitoylphosphatidylcholine Membranes Containing Cholesterol
The
incorporation of cholesterol into dipalmitoylphosphatidylcholine
(DPPC) membranes, even in small amounts, has been shown to significantly
alter the properties of the membrane. In this work, force–distance
interaction profiles of DPPC membranes containing 8 mol % cholesterol
obtained using the surface force apparatus are analyzed in the context
of high-resolution structural characterization by atomic force microscopy
and neutron reflectometry. The adhesion between the mixed membranes
was greater than that for pure DPPC and was variableî—¸depending
on the number of defects in the outer membrane leaflets. These defects
were only detectable by atomic force microscopy and had an average
size of 230 ± 30 nm and 1–5% surface density in the outer
leaflet. The adhesion between the membranes monotonically increased
as the thickness of the membrane decreasedî—¸in direct correlation
with the number of defects present (exposed hydrophobic groups) in
the membrane contact region. Because of the low diffusion rate of
gel-phase membranes, the interaction force profiles were stable and
no membrane restructuring was observed