Kinetics and mechanism of the pressure-induced lamellar order/disorder transition in phosphatidylethanolamine: a time-resolved x-ray diffraction study

Abstract

By using synchrotron radiation, a movie was made of the X-ray scattering pattern from a biological liquid crystal undergoing a phase transition induced by a pressure jump. The system studied includes the fully hydrated phospholipid dihexadecylphosphatidylethanolamine in the lamellar gel (L beta') phase at a temperature of 68 degrees C and a pressure of 9.7 MPa (1400 psig). Following the rapid release of pressure to atmospheric the L beta' phase transforms slowly into the lamellar liquid crystal (L alpha) phase. The pressure perturbation is applied with the intention of producing a sudden phase disequilibrium followed by monitoring the system as it relaxes to its new equilibrium condition. Remarkably, the proportion of sample in the L alpha phase grows linearly with time, taking 37 s to totally consume the L beta' phase. The time dependencies of radius, peak intensity, and width of the powder diffraction ring of the low-angle (001) lamellar reflections were obtained from the movie by image processing. The concept of an "effective pressure" is introduced to account for the temperature variations that accompany the phase transition and to establish that the observed large transit time is indeed intrinsic to the sample and not due to heat exchange with the environment. The reverse transformation, L alpha to L beta', induced by a sudden jump from atmospheric pressure to 9.7 MPa, is complete in less than 13 s. These measurements represent a new approach for studying the kinetics of lipid phase transitions and for gaining insights into the mechanism of the lamellar order/disorder transition.

Manipulating Mesophase Behavior of Hydrated DHPE: An X-ray Diffraction Study of Temperature and Pressure Effects

“…The data in Figure 3 are in general agreement with related measurements on this system. 2 However, there are quantitative differences. The endothermic and volume-increasing transition .…”

“…2,5,6,[30][31][32][33] The L R /H II transition was not investigated in any detail in this study. However, the L R /H II transition temperature did increase at elevated pressures (Figure 2), which implies that a volume increase (see eq 6) is associated with this phase change that is known to be endothermic.…”

High‐pressure freezing causes structural alterations in phospholipid model membranes

“…For DMPC, DPPC and DSPC bilayers temperature shifts of 15–30 °C kbar −1 have been reported ( Trudell et al ., 1974 ; Liu & Kay, 1977; Mountcastle et al ., 1978 ; Chong et al ., 1983 ). Characteristic transition times of the gel‐to‐fluid transition as measured with real‐time X‐ray‐scattering after sudden depressurization are in the range of several seconds ( Mencke & Caffrey, 1991; Caffrey et al ., 1991 ). The reverse transition (fluid‐to‐gel) measured after sudden pressurization (pressure‐jump) occurred at a rate more than 2.5 times faster.…”

Nanocharacterization of Lyotropic Liquid Crystalline Systems

“…Around the same time, the temperature -composition phase diagram of monoglycerides in water was published by Lutton (1965) . Since then, a great diversity of amphiphile systems have been studied using SAXS, including simple and complex natural/synthetic surfactants, phospholipids, glycolipids, synthetic and natural carbohydrate surfactants, dispersed LLCs (see later), and many more (B ä verback et al, 2009 ;Briggs et al, 1996 ;Mencke and Caffrey, 1991 ). Figure 4.5 is a schematic diagram of a SAXS experiment.…”