Journal of Lipid Research, Vol 35, 2069-2082, Copyright © 1994 by Lipid Research, Inc.
Crystal structure of cholesteryl butanoate at 123 K
GW Han, BM Craven and DA Langs
Department of Crystallography, University of Pittsburgh, PA 15260.
Cholesteryl butanoate has a complex crystal structure that differs from
those of the three main structure type for cholesteryl esters. It contains
four molecules (C31H52O2) unrelated by crystal symmetry. The molecules are
packed in almost planar sheets and have molecular long axes nearly
parallel. However, the molecules have different orientations about their
long axes and furthermore, in a given sheet, one of the independent
molecules is antiparallel to the other three. Viewed down the molecular
long axes, each molecule has six nearest neighbors, but the detailed
environment is different for the four independent molecules. Thus the
molecular arrangement has features that are characteristic of the
short-range order present in the cholesteric mesophase. The monotropic
transformation from the crystalline to the cholesteric phase occurs at 98
degrees C. The crystal structure has been accurately determined using
12,146 independent X-ray reflections having sin theta/lambda < 0.63 A-1.
All hydrogen atoms were located from a difference Fourier and were included
in a refinement that gave R(F2) = 0.064. The C-C bond lengths have sigma =
0.003 A and C-C-C bond angles have sigma = 0.2 degrees. Conformations for
the steroid ring system are similar but there are differences in the C17
side chains and the butanoate chains of the four independent molecules.
Analysis of atomic m.s. displacement tensors using a segmented-body model
indicates that there are internal librations involving both the C17 and
butanoate chains in all molecules.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
