Journal of Lipid Research, Vol 32, 1187-1194, Copyright © 1991 by Lipid Research, Inc.
Crystal structure of cholestanyl caprylate and binary phase behavior with cholesteryl caprylate
GW Han and BM Craven
Department of Crystallography, University of Pittsburgh, PA 15260.
The crystal structure of cholestanyl n-octanoate (caprylate) (C35H62O2) is
monoclinic with space group A2 and cell dimensions a = 10.103(7), b =
7.646(7), c = 87.63(7) A, beta = 90.51(6) degrees; Z = 8 [two molecules (A,
B) in asymmetric unit], V = 6769 A3, Dc = 1.010 g cm-3. Integrated X-ray
intensities for 3798 reflections with I greater than 2 sigma (I) were
measured with a rotating anode diffractometer at room temperature. The
structure was determined using direct methods. Block diagonal least squares
refinement gave R = 0.111. Molecules A and B have almost fully extended
conformations, but differ significantly in the rotation about the ester
bond and in the C17 chains. The molecular packing in the crystal structure
of cholestanyl caprylate consists of stacked bilayers each having d002 =
43.8 A in thickness and within each bilayer, cholestanols pack with
cholestanols and caprylate chains pack with caprylate chains. The crystal
structure is very similar to that of cholesteryl myristate but is quite
different from that of cholesteryl caprylate. The phase equilibria of the
cholestanyl caprylate/cholesteryl caprylate binary system have been shown
to involve limited mutual solubility of the two components and to have a
eutectic point at 73% cholestanyl caprylate. The cholesteric mesophase is
monotropic at all compositions except for a narrow range near the eutectic
point where it is enantiotropic.
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