Self-assembly of Lipid A-phosphates: Supramolecular Liquid Crystals - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 271

structures may be reconciled as credible structures of compressed emulsions (De
Geyer at al., 2000). Thus, it may be argued that favorable space filling packings will
be achieved when satisfactory geometrical conditions were fulfilled (Plateaus's law).
For the lipid A-phosphates this resulted from minimizing the surface area between
the aqueous films and so achieving a high homogeneous curvature. However, in the
case of the lipid A-monophosphate, rhombodo-decadecahedra ( Fd3m ) packing seems
to be suppressed a result of instability in the mean curvature between the tetrahedral
and the octahedral nodes. Tetrakaidodecahedra packing shows only tetrahedral nodes.
However, the tetrahedral angle (109.47°) can only be restored between all of the edges
if the hexagonal faces of the truncated octahedron change and generate change and
generate planer surfaces with no mean curvature and form Kelvin's minimal polyhedra
(Weaire and Phelan, 1994).
Furthermore in case of the lipid A-monophosphate, the flat-faced lipid A mono-
phosphate cluster observed in position “ c ” implies space-filling combinations with
at least two different polyhedra. This was shown by Rivier and Aste (1996) for tcp
ensembles, as well as in a study of lipid A-diphosphate (Faunce et al., 2003a). The
structure reported by Rivier and Aste (1996), face and edge angles was close to the
ideal values of 120° and 109.47°. In the Pm 3 n and Fd3m cellular networks there were
two examples of 24 tcp structures. One structure with A15 tc p packing was comprised
of two dodecahedra and eight tetradecahedra showing a Pm 3 n symmetry. The other
structure with C15 tcp packing consisted of 16 dodecahedra and eight hexakaideca-
hedra with a space group Fd3m . However, a similar spatial arrangement may be as-
sumed for lipid A-monophosphate clusters and other comparable assemblies (Faunce
and Paradies, 2009), producing two types of cells with different volumes by reduction
in the total surface area (Ziherl and Kamien, 2001). In the case of lipid A-monophos-
phate this would cause an ideal structure to coarsen, by either particle diffusion, where
small nanocrystals form larger nanocrystals or by growth of the larger nanocrystals
at the expense of the smaller ones (Ostwald ripening). However, unlike the reported
foam systems, the lipid A-monophosphate system revealed both the A15 and the C15
structures to be stable and which and possessed polyhedral cells each of different vol-
umes. These cells corresponded to an A15 structure, displaying space-filling packing
and polyhedra with very little distortion.
Glass Phases
Glass phase were found recently, which could play a crucial role in the preparation
of pharmaceuticals, adjutants and vaccine formulation (Reichelt et al., 2008). The
glassy phase occurred in almost all of the humoral-biochemical, cellular activities,
and studies; nevertheless, the phase went unnoticed because the solutions were buff-
ered. Furthermore, a loss of ergodicity was observed with either an increase in volume
fraction or ionic strength and by the addition of HCl at 20°C. All of these factors hindered
particle motion as a result of cluster formation with the neighboring lipid A-diphosphate
particles (attractive glass). It was also possible, that at a temperature ~40°C and at a
high-volume fraction f @ 5.8 × 10-4, the system experienced a re-entrant liquid-glass
transition.