Self-assembly of Lipid A-phosphates: Supramolecular Liquid Crystals - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 270

the Pm3n ( a and d ), or of sites a and d in the Fd3m (Figure 5). This could be attributed
to two different space-filling packings: (i) two dodecahedra on site a and six tetrakaid-
ecahedra on site d , forming a Pm3n lattice; (ii) or sixteen dodecahedra on site d and
eight hexadecahedra on site a , forming an Fd3m lattice. The space-filling network of
lipid A-diphosphate consisting of slightly distorted polyhedra was similar to known
basic frameworks of gas-hydrates and sodium silicon sodalites. The final geometry of
the “spheres” that is whether they were rounded or faceted in shapes, was established.
The equilibrium separation distance between the interfaces of the “spheres” suggested
that they repel each other as a result of electrostatic, steric, van der Waals forces as
well as water layer surrounding the spheres.
Figure 5. (A) Packing of Fd3m and Pm3n tetrahedrally close-packed (tcp) lipid A-diphosphate and
lipid A-monophosphate structures for two cubic crystalline phases. For both structures, aqueous
bilayer compartmentalizes the hydrophobic portion of the lipid A-phosphates into tetrahedrally
networks. This network is a combination of a pentagonal dodecahedron (blue) with 14-face
polyhedra (green) in Pm3n and with 16-face polyhedra (green) in Fd3m, (B) possible stacking of
tetrakaidecahedra along the [001] and along the [100], and [010] in cubic (Pm3n) assuming in-plane
orientation of the fatty acid chains. (C)-(E) possible polygon representations assuming polyballs of
different lipid A-phosphates as multiple components, shown as Wigner-Seitz cells as derived from
X-ray diffraction and electron microscopy. Multiplicity and Wyckoff positions, coordination number
are 2b and 12 in (C), 4f and 15 in (D), and 8i and 12 in (E).
The cubic Pm3n structure, which was seen in the lipid A-monophosphate clusters
Faunce and Paradies 2009), materialized as a result of a space-filling combination
of two polyhedra, a dodecahedra and a tetrakaidodecahedra. This is in contrast to
the tetrakaidecahedra ( Im3m) or rhombodo-decadecahedra ( Fd3m ) packings observed
for the lipid A-diphosphate assemblies (Faunce et al., 2005). The lipid A-diphosphate