Self-assembly of Lipid A-phosphates: Supramolecular Liquid Crystals - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 273

appearing as macro ion shielding. Furthermore, for lipid A-diphosphate assemblies in
the presence of Na + , K + , and Ca 2+ , and Mg 2+ , condensation of counterions at the par-
ticle surface might occur for large surface charge densities but without a change in the
particle number density, n. For sufficiently large particle number densities, the lipid
A-mono and diphosphate initiated crystallization in distinct cubic lattices (Faunce and
Paradies, 2007, 2009, 2011; Faunce et al. 2003b, 2007). Crystallization occurred with
a n increased in effective particle charge, Z eff and in effective temperature T* = k B × T/V
( d ) at low ionic strength. Note : The elasticity charges were significantly lower than
the conductivity charges, indicating the presence of macroion shielding.
A decrease in crystal stability was observed at pH 5.5 with the occurrence signifi-
cant deviations in large bare charges. This was seen for lipid A-diphosphate complexes
with ERI-1 (Aschauer et al., 1990) and other nontoxic lipid A-analogues (Christ et
al., 2003), when examining the charge from conductivity measurements. The system
first freeze and then re-melted through modifying the charge by adding OH - , or after
complex formations with the following: single chained N -cationic lipids (Paradies and
Habben, 1993; Thies et al., 1996) and double chained N -cationic surfactants (Alonso
et al., 2009; Thies et al., 1996), nontoxic lipid A-phosphates or CAM peptides (de-
fensins). High packing density and volume fractions of f = 0.3-0.5 were essential in
generating short-range order. It was not possible to achieve this condition for lipid
A-phosphate dispersions because the nearest neighbors were generally located at a
distance of one molecular diameter. Dispersions of particles exhibiting long-range re-
pulsive interactions also undergo a less apparent order-disorder transition, providing
the ionic strength is very low. If the repulsion between the particles is large and low
polydispersity is achieved, the transition from liquid-like to ordered solid-like behavior
occurs over a very narrow volume-fraction regime f. Consequently, it was possible
for interactions to take place between colloidal lipid A-phosphate particles as well
as assemblies comprised of for example lipid A-diphosphate and non-toxic lipid A-
phosphate analogues. These may have different chain lengths, numbers of chains and
disaccharides. The tuning of these systems was made possible by modifying either
the particle surfaces or the properties of the matrix in which they were suspended. As
long as at pH of between 5.5 and 7.0 and temperatures of between 5 and 25°C were
maintained vari o us lipid A- ph ospha te crystalline cubic and trigonal assemblies formed
for example Im 3 m, Fdm, R 3 m, Pm 3 m, and Ia 3 d, and R32 .
BiomiNeraliZatioN iN the PreseNCe oF liPid a-PhosPhates
With the presence of lipid A-diphosphate, in vitro crystallization of various forms of
CaCO 3 took place for example calcite, vaterite or aragonite. This demonstrated that
lipid A-diphosphate induced and stabilized the metastable vaterite phase above a vol-
ume fraction f = 7.8 × 10 -4 , at low ionic strength, a pH 5.8 and at ambient tempera-
ture. The morphology of the vaterite phase did not change with an increase in volume
fraction. The calcite phase formed at significantly lower volume fraction value, f =
5.8 × 10 -4 , at pH 8.5, and in the presence of 1 mM Ca 2+ . An elemental analysis of the
supersaturated bicarbonate solution showed that the Mg 2+ concentration was too low
with respect to the Ca 2+ concentration to allow the nucleation of significant amounts
of aragonite. In the light of the considerable influence of Ca 2+ and Mg 2+ ions on the