Liquid crystal glycolipids - Carbohydrate Chemistry: Chemical and Biological Approaches - page 317

Fig. 5 Shapes of glycolipids expected to form lamellar phases.
Fig. 6 Lamellar phases are formed by materials where the molecules have cylindrical
shapes.
length, the number of hydroxyl groups in the head group and the type of
linkage between the head group and the aliphatic chain. 9,10 These ma-
terials in their thermotropic phases were found to exhibit smectic A/A*
phases, the * representing compounds that possess stereogenic centres.
The smectic A phase is relatively easy to identify using thermal, polarized-
light transmission microscopy (POM) from its characteristic focal-conic
defect texture as shown in Fig. 7. The focal-conic domains are charac-
terised by hyperbolic and elliptical lines of optical discontinuity, 11 as
labelled in the figure. These defects are diagnostic for the presence of a
lamellar phase, and the clarity of the fan-like regions also indicates that
the phase is smectic A in type (other smectic phases exhibit patches on
the domains).
In studies aiming at understanding the relationships between the
structure of the carbohydrate amphiphiles and their liquid crystalline
properties, structural variations can concern the number of hydroxyl
groups, the position of the hydrophobic chain on the sugar backbone, the