Chemistry Reference
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Table 2 Transition temperatures (
1
C) as a function of chain length
(n) for the alkanoyl-
DL
-dihydrogluco- and galacto-cerebrosides.
n
Cryst
Col
Iso
15
94.7
184.5
17
108.1
191.1
23
95.6
193.1
n
Cryst
Col
Iso
15
95.3
185.5
17
91.3
193.2
23
102.1
193.0
demonstrating that the polar head group does not greatly affect the
mesomorphic properties. In this case it appears that the self-organization
is relatively insensitive to stereochemical structure in the head
group. This may be due to the curvature of packing being greater for the
hexagonal phase than for the lamellar, because the overall molecular
lengths are shorter in relation to the cross-sectional areas of the aliphatic
chains.
Other interesting naturally occurring materials and synthetic mimics
include the diacyl derivatives of galactosylglycerols, 16. Up to 75% of the
total lipid content of plant chloroplast membranes consist of galacto-
glycerolipids,
26
many of which are being investigated in relation to the
development of biodiesel fuels. The glucoglycerolipids, such as the a-
D
-
glucopyranosyl-diacylglycerols, shown in Table 3 for the C
12
to C
20
homologues, were investigated in detail with respect to their liquid
crystal properties. These materials were originally reported as exhibiting
smectic A* phases, however, at a later date the classification of their
mesomorphic properties was changed to columnar in keeping with the
cerebrosides described above.
In addition to pyranosides, derivatives of furanosides also form hexa-
gonal columnar phases. Furanosides tend to be associated with lipids of
the membranes of methanogenic and halophilic archaebacteria, which
are characterized by high proportions of diether-type components that
have a 2,3-diphytanyl-sn-glycerol backbone. We describe the evaluation of
the liquid-crystalline properties of some synthetic diether-type glycolipid
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