Thermal Properties of Systems Containing Cholesteryl Esters and Triglycerides.

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Abstract
Binary and ternary systems of the 3 cholesteryl esters, linoleate, oleate and stearate and the 2 triglycerides, triolein and tristearin were studied in order to determine the phase transitions and the conditions for the cholesteric and smectic mesophases. Phase transitions were determined using differential thermal analysis, melting point determination and polarizing microscopy. Of the cholesteryl esters the linoleate-oleate system showed complete miscibility in both the liquid and solid phases. The linoleate-stearate and oleate-stearate systems are of the eutectic type with limited solid solubility. The mesophases are monotropic as to the crystalline state and exist over the entire composition interval in all cholesteryl ester systems studied. The triglycerides studied showed no mesophase transitions. In mixed systems with cholesteryl esters even low concentrations of the triglycerides removed the cholesteric transition typical for cholesteryl ester systems. At higher concentration of triolein the smectic mesophase was also removed. In systems with tristearin and cholesteryl esters an apparently smectic mesophase with mosaic texture was found. In ternary systems the property of the low melting lipids to depress the melting points of the high melting ones was additive. Cholesteryl esters and triglycerides belong to the major components of atherosclerotic deposits and serum lipoproteins and the phase conditions of these lipids serve directly to explain the state of the oil phase in atherosclerotic deposits and of the lipid core of serum lipoproteins.

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