Liquid crystal glycolipids - Carbohydrate Chemistry: Chemical and Biological Approaches - page 327

Fig. 16 Structure of the hexagonal disordered columnar phase of the archael lipid mimics
with the liquid-like aliphatic chains located on the exteriors of the columns.
Fig. 17 The liquid-crystalline properties of four naturally occurring cerebrosides.
the materials. Where the two chains are only slightly different in length,
þ / 2carbonatoms,e.g., for the palmitoyl derivative, higher clearing
points were realized, whereas typically if the chains have considerably
different lengths (asymmetrical) then the melting points were much lower,
e.g., the stearoyl derivative. Differential scanning calorimetry of the ma-
terials showed complex melting from the solid state to the liquid crystal
state, with many solid - solid transitions occurring. In addition to ex-
hibiting thermotropic liquid crystal phases, the materials were also found
to exhibit lyotropic inverted hexagonal phases upon the addition of water.
As with the naturally occurring cerebrosides, the synthetic D , L -dihydro
analogues were also found to exhibit columnar mesophases. The melting
and isotropization points are shown in Table 2 for the C 15 ,C 17 and C 23
homologues of the galacto-and gluco-cerebrosides respectively.
The synthetic materials have melting points that are much lower than
those for the naturally occurring materials, which means that the liquid
crystal phases are exhibited over wider temperature ranges. However,
there was almost no change in the isotropization temperature with re-
spect to change in the sugar unit (i.e. galactose versus glucose), thereby