AGGREGATION BEHAVIOR OF LIPID-IV(A) IN AQUEOUS-SOLUTIONS AT PHYSIOLOGICAL PH .1. SIMPLE BUFFER SOLUTIONS

We have investigated the aggregation behaviour of lipid IV(A) (a bioactive precursor of lipid A and the lipid anchor of lipopolysaccharide) in aqueous solutions in the physiological pH range using dynamic light scattering, nuclear magnetic resonance, fluorescence, surface pressure, electron microscopy and force field simulation studies. The sonication of lipid IV(A) in PBS, Tris and Hepes produces vesicles which are stable in the concentration range of 10(-3)-10(-7) M, possibly even at lower concentrations. The vesicle size is not sensitive to the nature of the buffer, only to the pH and to some extent to the ionic strength. The long time stability of the small unilamellar vesicles as well as the structureless H-1-NMR spectra might be attributed to a rigid surface structure. This structure is also supported by the simulation studies. We have tentatively proposed a coexistence of micelles and/or other aggregates with the bilayered vesicles at higher lipid concentrations in order to explain some of the experimental observations.