In order to understand the phase behavior of the approximately 1-micron-diameter droplets which occur in the cytoplasm of
cholesterol-enriched cells, differential scanning calorimetry has been utilized to elucidate the factors controlling the rate of crystallization of
cholesteryl esters. The kinetics of the thermotropic transitions between liquid, liquid-crystal, and crystal states which occur in mixtures of
cholesteryl oleate and
cholesteryl palmitate present in monodisperse,
phospholipid-stabilized,
emulsion droplets have been determined and are compared to the characteristics of these transitions in bulk mixtures.
Cholesteryl palmitate is observed to crystallize in undercooled
phospholipid-stabilized dispersions of
cholesteryl palmitate/
cholesteryl oleate (50/50 w/w) at temperatures up to 50 degrees C lower than it does in bulk mixtures of the same
cholesteryl ester composition. It is postulated that this difference between crystallization temperatures is due primarily to the presence of impurities present in bulk mixtures which act as catalysts that promote crystallization. It is suggested that
phospholipid-stabilized dispersions of
cholesteryl palmitate/
cholesteryl oleate are more appropriate models than bulk mixtures of these
cholesteryl esters for studying the kinetic and thermodynamic basis of the phase behavior in
cholesteryl ester rich inclusions characteristic of foam cells and
atherosclerotic plaque. The thermotropic phase behavior of these dispersions can be satisfactorily analyzed by using the equations of homogeneous nucleation theory. The interfacial tension between the crystal nucleus and the surrounding fluid
cholesteryl ester is about 10 erg/cm2.(ABSTRACT TRUNCATED AT 250 WORDS)