Abstract
Factors affecting the solid state miscibility of saturated chain cholesteryl esters were determined from electron diffraction and differential scanning calorimetric measurements on a homologous series which included two types of crystal packing. Electron diffraction patterns from solution- and epitaxially crystallized microcrystals gave measured unit cell constants consistent with the bilayer crystal form for myristate, pentadecanoate, palmitate, and stearate esters. Cholesteryl undecanoate crystallized as the monolayer I structure and cholesteryl laurate was polymorphic, packing in either monolayer I or bilayer forms. No evidence was found for the monolayer II form of the laurate claimed in earlier work. It is clear that solid solution formation follows general rules formulated earlier by Kitaigorodskii for molecular crystals. A symmetry criterion must be satisfied first of all, i.e., two compounds that solidify in greatly different crystal structures will not form continuous solid solutions (e.g., cholesteryl undecanoate/cholesteryl myristate). Within a given crystal structure type, solid solution is permitted when the molecular volumes are similar. (For example, cholesteryl myristate forms an ideal solid solution with cholesteryl pentadecanoate, a nonideal solution with cholesteryl palmitate, and a eutectic of solid solutions with cholesteryl stearate.) For the polymorphic cholesteryl laurate, solid solutions of either the monolayer I structure (e.g., with cholesteryl undecanoate) or bilayer structure (e.g., with cholesteryl myristate) are permitted.
Highlights
Ahtract Factors affecting the solid state miscibility of saturated chain cholesteryl esters were determined from electron diffraction and differential scanning calorimetric measurements on a homologous series which included two types of crystal packing
It is clear that lipid deposition can be described in physical chemical terms, i.e., the progression of a lesion is characterized by the three-component phase diagram of cholesterol-cholesteryl ester-phospholipid in excess water [6, 7]
Since mostly cholesteryl ester deposition is important for the progression of the lesion, it is clear that the physical state of the lesion is dependent upon the chemical type of esters incorporated, since the phase behavior of these materials is largely determined by the fatty acid chain moiety [8]
Summary
Included with purity and thermal data are the crystal forms for various members of the homologous series determined by X-ray diffraction in other laboratories compared to the results of electron diffraction determination (see below)
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