Hydrostatic pressure effects on a hydrated lipid inverse micellar Fd3m cubic phase

Abstract

Graphical contents entry. The effect of hydrostatic pressure on an inverse micelllar Fd3m cubic phase is studied by small-angle 20 synchrotron diffraction.Over a range of hydration, unsaturated diacylglycerol / phosphatidylcholine mixtures adopt an inverse micellar cubic phase, of crystallographic space group Fd3m. In this study hydrated DOPC: 25 DOG mixtures with a molar ratio close to 1:2 were examined as a function of hydrostatic pressure, using synchrotron x-ray diffraction. The small-angle diffraction pattern at atmospheric pressure was used to calculate 2-D sections through the electron density map. Pressure initially has very little effect on the structure of the Fd3m cubic phase, in contrast to its effect on hydrated inverse bicontinuous cubic phases. At close to 2 kbar, a sharp transition occurs from the Fd3m phase to a 30 pair of coexisting phases, an inverse hexagonal H II phase plus an (ordered) lamellar phase. Upon increasing the pressure to 3 kbar, a further sharp transition occurs from the H II phase to a (fluid) lamellar phase, in coexistence with the ordered lamellar phase. These transitions are fully reversible, but show hysteresis. Remarkably, the lattice parameter of the Fd3m phase is practically independent of pressure. These results show that these two lipids are miscible at low pressure, 35 adopting a single lyotropic phase (Fd3m); they then become immiscible above a critical pressure, phase separating into DOPC-rich and DOG-rich phases.

Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains

“…These branched inverse micellar phases are now part of the standard phase diagram of lipid self-assembly. 10,61,89,90 In this article, we analyse hypothetical polycontinuous geometries as candidate structures for lipid self-assembly under the following assumptions: the self-assembled system consists of three or four identical network-like aqueous domains, termed K, centred on periodic intertwined (or interthreaded) networks. The aqueous domains are bound by surfaces, S, of a constant mean curvature (CMC) with the same topology and symmetry as the underlying network; h 0 denotes the value of the mean curvature.…”

Effects of High Pressure on Internally Self-Assembled Lipid Nanoparticles: A Synchrotron Small-Angle X-ray Scattering (SAXS) Study

“…4). The above observed phase sequence is same as conventional phase transition (L2-cubic Fd3m-H2) in excess water based on average mean curvatures of phases 30 . No phase transitions were seen in case of the L2 phase inside lipid particles (these dispersions are also known in literature as emulsified microemulsions, EMEs), but its characteristic nearest neighbour distance did increase when the sample was compressed (see Table 1).…”

“…It should be noted that most of the earlier studies in literature were focused on the effect of pressure on equilibrium non-lamellar liquid crystalline, bulk phases. These studies involved, the effects of hydrostatic [30][31][32][33] and hydrodynamic [34][35][36][37] pressure on pure lipids and their mixtures under dry (solvent-free lipid), limited hydration, or excess water conditions. Most of these reports were focused on understanding isothermal pressure-induced structural alterations and dynamic phase transitions of the lipid crystalline and liquid crystalline phases [30][31][38][39][40][41][42] .…”

“…These studies involved, the effects of hydrostatic [30][31][32][33] and hydrodynamic [34][35][36][37] pressure on pure lipids and their mixtures under dry (solvent-free lipid), limited hydration, or excess water conditions. Most of these reports were focused on understanding isothermal pressure-induced structural alterations and dynamic phase transitions of the lipid crystalline and liquid crystalline phases [30][31][38][39][40][41][42] . In advantage to temperature, pressure equilibrates homogenously and rapidly with the speed of sound within the sample and therefore it has triggered great interest in coupling rapid pressure induction experiments with synchrotron X-ray sources to capture the membrane dynamics and monitor in real time kinetics of phase transitions within microseconds 36 .…”

A lyotropic inverse ribbon phase in a branched-chain polyoxyethylene surfactant: pressure effects

“…However, one might expect a transition from the Fd3m phase to 5 the inverse hexagonal H II phase, rather than the inverse ribbon Rb II phase, to be observed. Indeed, recently 23 we have shown that application of pressure to a hydrated binary lipid mixture of dioleoyl-phosphatidylcholine (DOPC) and dioleoyl-glycerol (DOG) in the Fd3m cubic phase, induces a sharp transition at a 10 critical pressure (close to 2000 bar) to a phase separated mixture of an H II phase and ordered lamellar phase; such a pressure induced phase separation is not possible in the single surfactant system studied in the present work. Here, the preferred stability of the inverse ribbon phase, with non-uniform interfacial 15 curvature, suggests that the polyoxyethylene surfactant may preferentially adopt different conformations in the differentlycurved regions of the inverse ribbons; further research is needed to confirm this hypothesis.…”