Mesoscopic and microstructural characterization of liposomes formed by the lipooligosaccharide from Salmonella minnesota strain 595 (Re mutant)

Large unilamellar liposomes formed by the Re LPS (from here below named LOS) from Salmonella enterica serotype minnesota strain 595 (Re mutant) have been prepared by the extrusion techniques. The physico-chemical investigation of these systems has been performed by a combined experimental strategy, which has allowed a characterization at different observation scales, from the morphological to the micro-structural level. Particularly, dynamic light scattering (DLS) measurements have revealed the formation of liposomes with a narrow dimension distribution; small-angle neutron scattering (SANS) measurements have led to an estimation of the thickness of the LOS bilayer, which is consistent with an extended conformation of the acyl chains; electron paramagnetic resonance (EPR) measurements have allowed to investigate the bilayer fluidity, as determined by LOS acyl chain conformation and packing; Pulsed-field-gradient stimulated echo nuclear magnetic resonance (PGSTE-NMR) measurements have shown that water permeability through the LOS bilayer is low. The effect of temperature has been considered. Liposome dimension does not change; however, centered at 30–35 °C, a progressive transition of the acyl chain self-organization from a gel to a liquid crystalline phase is detected. Above this temperature, the water permeability through the bilayer increases. The effect of introducing the zwitterionic phospholipid dilauroyl phosphatidylcholine (DLPC) in the liposome formulation have been also analysed. A comparative analysis of the results points out a clear relation between the microstructure of LOS molecules in the bilayer and liposome functional properties.