Polymorphism in Cholesteryl Esters: Cholesteryl Palmitate

Abstract

The thermal transitions in cholesteryl palmitate have been evaluated and compared to previously reported data. A sample synthesized from carefully purified cholesterol and palmitic acid using p-toluene sulfonic acid compared directly with previously reported data. A sample of recrystallized ester from a commercial source showed a slightly depressed solid to mesophase transition temperature. However, the mesophase proved t o be smectic, commonly reported as monotropic with respect to the solid phase. Both smectic to cholesteric and cholesteric to isotropic liquid transitions were very sharp, indicating a very pure material. It is postulated that a specific impurity, an antioxidant, is responsible for this previously unreported effect. This effect of related compound interaction has been reported for nematic mesophase forming compounds. Thin layer chromatography, microscopy, depolarized light intensity analysis, differential scanning calorimetry and NMR spectroscopy data are discussed.