Cholesterol monohydrate nucleation in ultrathin films on water |
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| Authors: | Rapaport H Kuzmenko I Lafont S Kjaer K Howes P B Als-Nielsen J Lahav M Leiserowitz L |
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| Affiliation: | Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel. |
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| Abstract: | The growth of a cholesterol crystalline phase, three molecular layers thick at the air-water interface, was monitored by grazing incidence x-ray diffraction and x-ray reflectivity. Upon compression, a cholesterol film transforms from a monolayer of trigonal symmetry and low crystallinity to a trilayer, composed of a highly crystalline bilayer in a rectangular lattice and a disordered top cholesterol layer. This system undergoes a phase transition into a crystalline trilayer incorporating ordered water between the hydroxyl groups of the top and middle sterol layers in an arrangement akin to the triclinic 3-D crystal structure of cholesterol x H(2)O. By comparison, the cholesterol derivative stigmasterol transforms, upon compression, directly into a crystalline trilayer in the rectangular lattice. These results may contribute to an understanding of the onset of cholesterol crystallization in pathological lipid deposits. |
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