Sans Investigation of the Pressure- and Temperature-Dependent Structure of the Bile Salt/Lecithin System

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Abstract
We used small angle neutron scattering to investigate the pressure and temperature dependent particle structure in mixed colloids of egg yolk phosphatidylcholine with the bile salt, glycocholate in D2O. The concentrations and compositions of the mixtures, at ambient temperature and pressure, corresponded to the mixed vesicle region of the isotropic (I) phase. Upon increasing the hydrostatic pressure at ambient temperature, interesting morphological changes were observed. At a pressure of 6.9 MPa, the system is best described by a coexistence of the mixed, spherical single bilayer vesicle, stacked lamellar and stacked ribbon phases. At higher pressures, the system transformed to a stacked ribbon phase. Analysis of scattering data as a function of temperature, at ambient pressure, revealed that a vesicle phase remained stable with the average spherical radius decreasing as the temperature was increased from 15 to 40°C.