Eur. Phys. J. E (2009) 30: 215-221
https://doi.org/10.1140/epje/i2009-10498-2

Regular Article

Hydrated cholesterol: Phospholipid domains probed by synchrotron radiation

¹ Department of Materials and Interfaces, The Weizmann Institute of Science, 76100, Rehovot, Israel
² Institut Laue-Langevin, 6 Rue Jules Horowitz, BP 156, 38042, Grenoble Cedex 9, France
³ CEA, IRAMIS, LIONS, CEA-Saclay, F-91191, Gif-sur-Yvette, France
⁴ CEA-INAC, 17 Avenue des Martyrs, F-38054, Grenoble Cedex 9, France
⁵ Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen, Denmark

^* e-mail: jean.daillant@cea.fr
^** e-mail: leslie.leiserowitz@weizmann.ac.il

Received: 21 January 2009
Revised: 12 May 2009
Accepted: 26 May 2009
Published online: 23 July 2009

Abstract

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 10×7.5 Å^2 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.