PRESSURE EFFECTS ON LAMELLAR AND INVERSE CURVED PHASES OF FULLY HYDRATED DIALKYL PHOSPHATIDYLETHANOLAMINES AND BETA-D-XYLOPYRANOSYL-SN-GLYCEROLS

We report on the effects of hydrostatic pressure and temperature on th e phase and structural behavior of the complete range of the known, ex cess water, inverse lyotropic mesophases. This range of interfacial to pologies is exhibited by homologous series of saturated C-12, C-14, an d C-16 dialkyl phosphatidylethanolamines (PE) and saturated C-12 and C -16 dialkyl xylopyranosylglycerols (xylolipids) in the p-T region 0-2. 5 kbar and 30-130 degrees C. The PEs cover the mesophases with gentle interfacial curvature while the xylolipids cover the more curved mesop hases. We demonstrate that temperature and pressure have noncongruent effects on the structural and the phase behavior. Quantitatively, meso phase lattice parameters and phase boundaries show small but observabl e differences in their functional dependence on pressure and temperatu re. Qualitatively, increasing pressure stabilizes inverse bicontinuous cubic phases in C-14 PE At atmospheric pressure only the C-12 PE cont ains such phases. Conversely we find that increasing pressure destabil izes the inverse micellar cubic phase observed in the C-16 xylolipid. In general a trend is seen for a stronger pressure effect in eliminati ng phases with larger packing costs, which we infer is due to differen ces in the effects of pressure and temperature on the monolayer's spon taneous mean curvature and its bending rigidity.