A proton and deuterium nuclear magnetic reasonance study of orientational order in aqueous dispersions of lipopolysaccharide and lipopolysaccharide/dipalmitoylphosphatidylcholine mixtures

Abstract

Magnetic resonance measurements of orientational order have been carried out in aqueous dispersions of lipopolysaccharide derived from Escherichia coli K-12 cells and the phospholipid dipalmitoylphosphatidylcholine. Proton magnetic resonance experiments demonstrated that the orientational order of pure lipopolysaccharide dispersions at 6°C was one-third of that predicted for completely rigid lipopolysaccharide molecules. The orientational order decreased by a factor of 2 as the temperature was increased to 40°C. The lipopolysaccharide orientational order was not affected significantly by the presence of phospholipid in the dispersion. Deuteron magnetic resonance experiments indicated that the dispersions of phospholipid and lipopolysaccharide are homogeneously mixed and that the presence of lipopolysaccharide decreased the phospholipid average hydrocarbon chain order in the gel phase and increased it in the liquid-crystalline phase. In the temperature range between 26 and 40°C, there was a coexistence of gel and liquid-crystalline phospholipid.