Physical properties of cholesteryl esters having 20 carbons or more.
By polarizing microscopy and differential scanning calorimetry we observed that the relative stability of the smectic and cholesteric mesophases of cholesteryl esters of acyl chain length of 20 carbons or more depends on the length of the acyl chain and its degree of unsaturation. Significantly, the addition of a single double bond to the acyl chain of a fully saturated cholesteryl ester which exhibits no mesophases (e.g., cholesteryl behenate (C22:0) and cholesteryl lignocerate (C24:0) yields an ester which displays an unusually stable smectic mesophase, bot no cholesteric mesophase. In fact, increasing unsaturation was found to have a destabilizing effect on the cholesteric phase. Similarly, a decrease in thermal stability of the cholesteric mesophase was observed with increasing thermal stability of the smectic mesophase increased in the same series. X-ray scattering data are presented on the smectic mesophase of cholesteryl erucate (C22:1) and cholesteryl nervonate (C24:1). Significant differences in molecular packing of these two monounsaturated omega = 9 cholesteryl esters in the crystalline state are demonstrated by preliminary X-ray scattering experiments.
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