A SANS Study of High Pressure Phase Transitions in Model Biomembranes

Abstract

The phase behaviour and thermotropic and barotropic phase transitions of different model biomembranes (DPPC, DMPC, DEPC and POPC*)), which consist of different hydrocarbon chain length and degree of unsaturation, have been investigated by small‐angle neutron scattering (SANS) as a function of temperature and pressure up to about 65°C and 3 kbar, respectively. A pressure induced structural phase transition from a liquid‐crystalline to a gel state is observed for the whole temperature range studied. The pressure of this transition increases with increasing temperature with a slope dTm/dP of about 21°C/kbar, which is common for all the different lipids investigated. The SANS experiments indicate that the effect of the two trans double bonds in DEPC and the cis double bond in the sn‐2 hydrocarbon chain of POPC enhances the conformational disorder in the hydrocarbon chains not only in the liquid‐crystalline, but also in the gel state. For DEPC and POPC the prefered structural conformation in the gel state is probably not tilted as it is in the gel state of the saturated phospholipids DMPC and DPPC. Only for DPPC multilamellar vesicles, an additional gel phase at higher pressures has been observed, which can be ascribed to an interdigitation of the hydrocarbon chains of opposing chains in the lipid bilayer system.

A Small-Angle Neutron Scattering Investigation of the TDMAO Micelle System at High Hydrostatic Pressure

“…The number of experiments using hydrostatic pressure on surfactant/water binary systems or membranes is still limited (Nishikido, Kobayashi & Tanaka, 1982;Wong & Mantsch, 1983;Winter & Pilgrim, 1989). On the other hand, pressure, along with temperature, is one of the important parameters which determine the properties of matter and is a tool for obtaining information about phase transitions and chemical equilibria.…”

Hydration Forces Between Lipid Bilayers: A Theoretical Overview and a Look on Methods Exploring Dehydration

“…The dependence of the transition pressure, P tr , on the temperature is given by the equation of Clapeyron-Clausius (Eq. 4.38), which is also valid for main phase transitions of phospholipids (Winter and Pilgrim 1989): …”

“…Furthermore, it is important to realise that˛is nearly a constant (' 0.2 K/MPa (Winter and Pilgrim 1989;Pfeiffer et al 2003c)) for about all phospholipids, because it is mainly determined by the ratio of the volume and entropy change per CH 2 -segment in the hydrocarbon chain, in this way it is also not a function of hydration itself because it is even invariant concerning the use of other solvents (Pfeiffer et al 2003d). This finally enables an estimation of hydration pressure in phospholipids when the dehydration-induced temperature shift of the main phase transition is known, i.e.…”

“…Therefore, this section will present a small overview on principal configurations to adjust hydrostatic pressure, chemical potential and/or water concentration (Fig. 4.6), see also Configuration I -Iso-compositional: This is the standard configuration to investigate high-pressure effects on closed lipid dispersions (Winter and Pilgrim 1989) which are situated in a sealed vessel preventing a change of the global solvent concentration. Changes in the hydration state of the lipid by hydrostatic pressure means amplification or weakening of solvent-solute interactions probably leading to a change of hydration numbers.…”

Pressure-induced phase transitions of lipid bilayers observed by fluorescent probes Prodan and Laurdan

“…Such studies have concentrated on a few members of phosphatidylcholines containing two identical linear saturated fatty acyl chains and the thermotropic phase behavior of some phosphatidylcholines (especially dipalmitoylphosphatidylcholine, DPPC) has been relatively well understood. The succeeding high-pressure studies on the DPPC bilayer membrane have been performed with various physical techniques including electron spin resonance [10], dilatometry [11,12], calorimetry [13,14], X-ray diffraction [15], dynamic light scattering [16], Raman spectroscopy [17,18], FT-IR [19], neutron diffraction [20,21], light transmittance [22,23] and NMR [24 -26]. These measurements have revealed that the temperature of main transition from the gel phase to the liquid crystalline phase is elevated linearly by applying pressure.…”