Hydrated cholesterol: phospholipid domains probed by synchrotron radiation.
X-ray scattering experiments on mixed films of cholesterol and phospholipids at air-water and Si solid-water interfaces were undertaken to glean information on pathological crystallization of cholesterol bilayers. Grazing-incidence X-ray diffraction patterns at the air-water interface of various cholesterol:dipalmitoyl-phosphatidylcholine (Ch:DPPC) monolayer mixtures compressed beyond monolayer collapse yielded the established 10 x 7.5 Å² Ch bilayer motif, for Ch:DPPC molar ratios higher than 2.5:1. Attempts to obtain a diffraction signal from various Ch:phospholipid film mixtures at the Si solid-water interface, indicative of the presence of the Ch bilayer motif, were unsuccessful. Only after removal of sufficient water from the cell was a weak diffraction signal obtained suggestive of a cholesterol film two bilayers thick. Off-specular X-ray reflectivity measurements made on a 1.75:1 mixture of Ch and bovine cardiac phosphatidylcholine (BCPC) deposited as a bilayer on a Si wafer and placed in a cell filled with water yielded positive results. The derived electron density profile showed the presence of a bilayer mixture consistent with a phase separation of cholesterol and BCPC, and possible formation of a crystalline cholesterol bilayer within the hydrated mixed bilayer, but not a proof thereof.
Solomonov
I
I
Department of Materials and Interfaces, The Weizmann Institute of Science, Rehovot 76100, Israel.
Daillant
J
J
Fragneto
G
G
Kjaer
K
K
Micha
J S
JS
Rieutord
F
F
Leiserowitz
L
L
D000818:Animals; D002417:Cattle; D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry; D021962:Membrane Microdomains / Q000737:chemistry*; D009206:Myocardium / Q000378:metabolism; D033363:Neutron Diffraction / Q000379:methods*; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D017356:Synchrotrons; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction / Q000379:methods*
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010743:Phospholipids; D014867:Water; D002784:Cholesterol