Lipopolysaccharides
(LPSs) based on lipid A produced by bacteria
are of interest due to their bioactivity in stimulating immune responses,
as are simpler synthetic components or analogues. Here, the self-assembly
in water of two monodisperse lipid A derivatives based on simplified
bacterial LPS structures is examined and compared to that of a nativeEscherichia coliLPS using small-angle X-ray scattering
and cryogenic transmission electron microscopy. The critical aggregation
concentration is obtained from fluorescence probe experiments, and
conformation is probed using circular dichroism spectroscopy. TheE. coliLPS is found to form wormlike micelles, whereas
the synthetic analogues bearing six lipid chains and with four or
two saccharide head groups (Kdo2-lipid A and monophosphoryl
lipid A) self-assemble into nanosheets or vesicles, respectively.
These observations are rationalized by considering the surfactant
packing parameter.