Chemistry Reference
In-Depth Information
The aforementioned lyotropic phases are mostly equilibrium structures and
are typically observed for lipid-water binary mixtures (Fig. 6.2a). Commonly
used lipids are monoglycerides; for example, monolinolein and monoolein,
which are used in their commercial grades as Dimodan-U/J
3
(DU) and glyc-
erol monooleate (GMO),
4
respectively. Two advantages of these products
(consisting of a mixture of saturated and unsaturated lipid chains) are the
accessibility of their nonlamellar phases at or below room temperature and
their lower degradation rates under ambient conditions, in contrast to their
pure counterparts. These advantages, along with their inexpensiveness, increase
their applicability in diverse fi elds (Leser et al., 2006; Sagalowicz et al., 2006a).
The addition of extra components to this mixture, for example, hydrophobic
additive oil, generates more space for present structures but can also give rise
to new phases, such as Fd3m (Yaghmur et al., 2006b), which is absent in the
binary phase diagram. This is achieved, specifi cally, by varying either tempera-
ture (Fig. 6.2b) or water content (Fig. 6.2c) while altering the lipid-oil ratio
(
value), as shown by their ternary phase diagrams (Fig. 6.2).
Lyotropic LC phases have many applications in various biotechnological
fi elds, ranging from drug delivery to protein crystallization (Caffrey, 2003;
Clogston and Caffrey, 2005; Landau and Rosenbusch, 1996; Sennoga et al.,
2003; Shah et al., 2001). However, they face severe problems in the food and
pharmaceutical industries, where their rather high viscosity and variable
domain consistency causes diffi culties in their handling. To facilitate their
applicability in various fi elds, they can be modulated into other forms and/or
hierarchical structures. LC nanostructures are spontaneous self-assemblies
driven by van der Waals interactions, hydrogen bonding, hydrophobic effects,
and interfacial tension. However, with high external energy input it is possible
to break these assemblies into hierarchically ordered forms to give partial
equilibrium structures. These superstructures usually need to be kinetically
stabilized by an external stabilizer.
Depending on the method of preparation and amount of dispersed phase,
LC nanostructures reorganize into oil - in - water (O/W) or water - in - oil (W/O)
emulsions (Figs 6.2d and 6.2e). The oil phase (lipid or lipid
δ
oil) itself displays
a wide range of nanostructures; when dispersed in water in the form of par-
ticles, they are termed ISAsomes (Yaghmur et al., 2005). When the oil phase
forms a continuous wall-like architecture enclosing water droplets, this is
called a W/O nanostructured emulsion (Kulkarni et al., 2010b).
+
3
Dimodan U/J is a commercial product from Danisco, Brabrand, Denmark, containing more than
98 wt % monoglycerides. The major components are linoleates, forming 62% of the total mixture.
The hydrocarbon tails largely consist of C18 chains (91%), the composition of which is as follows:
C18 : 2 (61.9%), C18 : 1 (24.9%), and C18 : 0 (4.2%), where the number after the colon indicates
the number of unsaturations; additional lipids are C16 : 0 chains (7.4%) and a residual amount of
diglycerides (1.6%).
4
GMO: Glycerol monooleate (1-monooleoyl-glycerol) contains 98.1 wt % monoolein, which was
also obtained from Danisco, Braband, Denmark.
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