Y. Abe et al., BILAYER STRUCTURE OF GLYCOLIPID CRYSTALS - THERMAL-STABILITY OF THE CRYSTAL AND STATE OF THE ALKYL CHAIN, Perkin transactions. 2, (1), 1998, pp. 177-186
The role of alkyl chains in the stabilization of a bilayer structure o
f glycolipids in the crystalline state has been studied for a series o
f methyl 6-O-acyl-beta-D-glucopyranosides and methyl 6-O-acyl-alpha-D-
galactopyranosides. Thermal properties and crystal structures of these
glycolipids with an odd number of alkyl carbon atoms in the acyl moie
ty have been investigated by thermal analysis and X-ray methods. The m
elting temperatures of methyl 6-O-acyl-beta-D-glucopyranosides, which
are lower than those of the corresponding methyl 6-O-acyl-alpha-D-gala
ctopyranosides, decrease with increasing number of alkyl carbon atoms
from one to seven, but increase for longer alkyl chains. The alpha-gal
actosides show only a monotonic decrease in melting temperature with i
ncreasing alkyl chain length. In the crystals, the molecules form a bi
layer structure with interdigitated alkyl chains, The arrangement of s
ugar moieties in the crystals differs between the beta-glucosides and
the alpha-galactosides, but they are almost the same among sugar deriv
atives with various alkyl chain lengths. The packing of the acetyl moi
ety in a crystal of methyl 6-O-alpha-D-galactoside is different from t
hat of the other alpha-galactoside derivatives with longer alkyl chain
s, The carbonyl oxygen atom causes steric hindrance with adjacent alky
l chains, and such unfavorable intermolecular contact explains the rel
atively low thermal stability of the crystal, On the other hand, the c
ontribution of the beta-glucoside to thermal stability is ascribed to
the well-ordered packing of the long alkyl chain moiety.