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Trapping Crystal Nucleation of Cholesterol Monohydrate: Relevance to Pathological Crystallization

Inna Solomonov ^*, Markus J. Weygand , Kristian Kjaer , Hanna Rapaport  and Leslie Leiserowitz ^*

^* Department of Materials and Interfaces, The Weizmann Institute of Science, 76100 Rehovot, Israel; Materials Research Department, Risø National Research Laboratory, 4000 Roskilde, Denmark; and Department of Biotechnology Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel

Correspondence: Address reprint requests to Leslie Leiserowitz, E-mail: leslie.leiserowitz{at}weizmann.ac.il.

Crystalline nucleation of cholesterol at the air-water interface has been studied via grazing incidence x-ray diffraction using synchrotron radiation. The various stages of cholesterol molecular assembly from monolayer to three bilayers incorporating interleaving hydrogen-bonded water layers in a monoclinic cholesterol·H₂O phase, has been monitored and their structures characterized to near atomic resolution. Crystallographic evidence is presented that this multilayer phase is similar to that of a reported metastable cholesterol phase of undetermined structure obtained from bile before transformation to the triclinic phase of cholesterol·H₂O, the thermodynamically stable macroscopic form. According to grazing incidence x-ray diffraction measurements and crystallographic data, a transformation from the monoclinic film structure to a multilayer of the stable monohydrate phase involves, at least initially, an intralayer cholesterol rearrangement in a single-crystal-to-single-crystal transition. The preferred nucleation of the monoclinic phase of cholesterol·H₂O followed by transformation to the stable monohydrate phase may be associated with an energetically more stable cholesterol bilayer arrangement of the former and a more favorable hydrogen-bonding arrangement of the latter. The relevance of this nucleation process of cholesterol monohydrate to pathological crystallization of cholesterol from cell biomembranes is discussed.