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Solution and structural properties of colloidal charged lipid A (diphosphate) dispersions

By CA Faunce, HH Paradies and P Quitschau

Abstract

It has been possible to prepare electrostatically stabilized aqueous dispersions of lipid A (diphosphate) particles of low polydispersity at low ionic strength (1-10 mM NaCl) over a range of volume fractions of 1.5 × 10<sup>-4</sup> &#60; &#60; 5.75 × 10<sup>-4</sup> (25 C). These suspensions have been characterized by transmission electron microscopy, light scattering, osmotic pressure measurements, and small-angle X-ray scattering experiments at 25 C. All four measurements yielded independent values for particle sizes, weighted-average molecular weights, number-average molecular weights, and particle surface charge. The mean values obtained are = 37.59 &#177; 0.75 nm, = 24.89 &#177; 0.88 nm, = (10.55 &#177; 0.78) × 106 g/mol, = (9.81 &#177; 0.90) × 106 g/mol, and the effective surface charge Z* = (756 &#177; 85). Very good experimental agreement is found for the directly measured osmotic pressure values and those determined from light scattering and small-angle X-ray scattering measurements as a function of volume fraction, , by applying liquid-state theory models. Using the particle parameters for the lipid A (diphosphate) system as determined, the scattering functions and the osmotic pressures can be compared as a function of volume fraction with no adjustable parameters. The ordering of lipid A in solution revealed a body-centered cubic (bcc) type lattice (a = 36.14 nm) at volume fractions of 3.75 × 10<sup>-4</sup> &#60; &#60; 4.15 × 10<sup>-4</sup>, whereas at volume fractions of 4.15 × 10<sup>-4</sup> &#60; &#60; 5.75 × 10<sup>-4</sup> in the presence of 1.0 mM NaCl a face-centered cubic (fcc) lattice type (a = 57.25 nm) was observed. Small-angle X-ray scattering experiments also indicate the presence of long-ranged order at 1.0 mM or at 10.0 mM NaCl for lipid A dispersions of 3.75 × 10<sup>-4</sup> &#60; &#60; 5.75 × 10<sup>-4</sup>

Topics: QD, QC, other
Publisher: ACS Publications
Year: 2003
OAI identifier: oai:usir.salford.ac.uk:398
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