Phase equilibria in four lysophosphatidylcholine/water systems

Abstract

The phase equilibria in four lysophosphatidylcholine/water systems were investigated at different temperatures. Each of the 1 -palmitoyl-, 1-stearoyl-, 1 -0leoyl-and 1 -linoleoyl-sn-glycero-3-phosphocholines was dispersed in heavy water at different concentrations. The phase structures were determined by 2H-, 14N-and 31P-NMR, polarization microscopy and low-angle X-ray diffraction.The phase diagrams of the oleoyl and linoleoyl systems were quite similar. At room ternpcrature and with decreasing water content the isotropic micellar solution was followed by a hexagonal phase and then a cubic phase. Finally the lamellar phase appeared before the region of hydrated crystals. The same sequence of phases was observed in the stearoyl system at elevated temperatures. The palmitoyl system differed from the others: here a cubic phase followed after the micellar solution, then came a hexagonal phase and after this a lamellar phase. In general the lysophosphatidylcholines seem to behave similarly to the many soaps and detergents as they show the same sequence of isotropic micellar solution, hexagonal phase, lamellar phase with interspersed cubic phases.The presently established phase diagrams demonstrate that the major lysophosphatidylcholines which may be generated by phospholipase A2 in mammalian cell membranes, viz. 1 -palmitoyl-and l-stearoyl-glycerophosphocholines differ greatly in their packing properties. The extraordinary ability of 1-palmitoyl-glycerophosphocholine to form a cubic phase in equilibrium with a micellar solution is of particular interest with regard to the possible occurrence of cubic structures in bioinembranes during the process of fusion.Lysophosphatidylcholines are natural constituents of many biological membranes. They usually occur in small amounts but have nevertheless attracted much interest, mainly because of their membrane-perturbing properties which make them both cytolytic and fusogenic (for a review see [I]). In vivo lysophosphatidylcholines may play an important role in secretory processes involving membrane fusion such as the release of histamine [2] and neurotransmitters [3] and the gastric secretion of hydrochloric acid (Olaisson, H., Mirdh, S., and Arvidson, G., unpublished work). The presence of a calcium-dependent phospholipase Az provides the possibility for a controlled formation of lysophosphatidylcholine in these secretory membranes. In vitro lysophosphatidylcholines and their structural analogues have proved to be of particular value for gentle solubilization of easily denatured membrane proteins [4].How lysophosphatidylcholines interact with cell membranes is still not very well understood. This may in part be due to the lack of information on their physico-chemical properties. The main features of the phase diagram and the phase structures of a lysophosphatidylcholine/water system have been obtained by X-ray diffraction studies [ S ] . However, the lysophosphatidylcholine used in these experiments was CorrcJspondence to G . Arvidson, Institutionen for Medieinsk och Fysiolog...

Ordered micellar and inverse micellar lyotropic phases

“…The best-known group of lipids that, in conjunction with water, will form ordered Type I micellar phases are the saturated lysophospholipids [62][63][64][65][66]. Although relatively scarce, with fewer than one phospholipid in 20 found in a typical cell being a lysophospholipid, they have been shown to play a major role in several signalling pathways, membrane fission and many other biological processes (see, e.g., [67,68]).…”

Aqueous phase behaviour of choline carboxylate surfactants—exceptional variety and extent of cubic phases

“…28,47,51,52 However, the detailed structure of Pm3n has in the past been the object of debates. 27,28,[53][54][55][56] Eventually, NMRdiffusion measurements 53 as well as detailed X-ray 57 and freezefracture electron microscopy studies 58 support the model of Charvolin and Sadoc, who proposed a structure comprising two spherical and six disc-shaped (oblate) micelles per unit cell without any dynamic disorder.…”

Proton magic-angle spinning–NMR investigation of surfactant aqueous suspensions

“…In addition broad lines are in general incompatible with a high sensitivity. 1 H, on the other hand, is an abundant and sensitive nucleus and its chemical shift allows one to differentiate molecules in a heterogeneous mixture if lines are narrow enough. In the case of small surfactant micelles, the rotation correlation time of the aggregates associated with rapid diffusion of the amphiphiles around the micelle and the rapid exchange between monomers and micelles generally suffice to efficiently average out the dipolar interactions between neighboring protons.…”

“…A classical sequence of phase transformation of surfactants in water as the concentration of surfactant increases is the following: monomers → micelles → hexagonal H I phase → lamellar phase → reverse H II phase → inverse micellar phase [1][2][3]. Nuclear magnetic resonance (NMR) is one of the numerous techniques that provide structural information on surfactant phases.…”