Abstract
The thermotropic phase behavior of cholesterol monohydrate in water was investigated by differential scanning calorimetry, polarizing light microscopy, and x-ray diffraction. In contrast to anhydrous cholesterol which undergoes a polymorphic crystalline transition at 39 degrees C and a crystalline to liquid transition at 151 degrees C, the closed system of cholesterol monohydrate and water exhibited three reversible endothermic transitions at 86, 123, and 157 degrees C. At 86 degrees C, cholesterol monohydrate loses its water of hydration, forming the high temperature polymorph of anhydrous cholesterol. At least 24 hours were required for re-hydration of cholesterol and the rate of hydration was dependent on the polymorphic crystalline form of anhydrous cholesterol. At 123 degrees C, anhydrous crystalline cholesterol in the presence of excess water undergoes a sharp transition to a birefringent liquid crystalline phase of smectic texture. The x-ray diffraction pattern obtained from this phase contained two sharp low-angle reflections at 37.4 and 18.7 A and a diffuse wide-angle reflection centered at 5.7 A, indicating a layered smectic type of liquid crystalline structure with each layer being two cholesterol molecules thick. The liquid crystalline phase is stable over the temperature range of 123 to 157 degrees C before melting to a liquid dispersed in water. The observation of a smectic liquid crystalline phase for hydrated cholesterol correlates with its high surface activity and helps to explain its ability to exist in high concentrations in biological membranes.
Highlights
The thermotropic phase behavior of cholesterol monohydrate in water was investigated by differential scanningcalorimetry,polarizing light microscopy,and x-ray diffraction
I n this report we describe the phase behavior of cholesterol monohydrate in water as a function of temperature
25 mg of wet cholesterol monohydrate crystals were placed on a microbalance pan and periodically weighed
Summary
The thermotropic phase behavior of cholesterol monohydrate in water was investigated by differential scanningcalorimetry,polarizing light microscopy,and x-ray diffraction. The observation of a smectic liquid crystalline phase for hydrated cholesterol correlates with its high surface activity and helps to explain its ability to exist in high concentrations in biological membranes.--Loomis, C. When the cholesterol concentration exceeds the solubility limit in lipid bilayers or micelles, deposition of crystalline cholesterol monohydrate is observed [1, 3, 7]. This process of saturation and deposition of crystalline cholesterol is known to occur in certain pathological states in man, most notably, gallstone disease [4] and atherosclerosis [13, 14]. Sonicated systems of synthetic homogeneous chain lecithins have been shown to contain u p to 3 moles of cholesterol per 1 mole of phospholipid (lo), a n d liposomes prepared from certain organic solvents contain nearly
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