SMALL-ANGLE NEUTRON-SCATTERING STUDIES OF VESICLE STABILITY

Small-angle neutron scattering (SANS) was used to investigate the stru cture of mixed colloids of egg yolk phosphatidylcholine (EYPC) with th e bile salt, cholylglycine (CG), in D2O as a function of pressure (P) and temperature (T). At atmospheric pressure, the system forms an isot ropic phase of mixed, single bilayer vesicles (SLVs). Increasing the e xternal hydrostatic pressure brought about significant changes in part icle morphology. At T = 25 degrees C, application of a pressure of 3.5 MPa resulted in collapse of the SLVs. A further increase in P, up to 51.8 MPa, resulted in a transition from a phase of ordered (stacked), collapsed vesicles to one of stacked, ribbon-like particles. A similar collapse of the vesicles was observed at a higher temperature (T = 37 degrees C) with increasing P, but at this temperature, no ribbon phas e was found at the highest pressure explored.