Spontaneous vesiculation

Hauser, H. (1987). Spontaneous vesiculation of uncharged phospholipid dispersions consisting of lecithin and lysolecithin, Chem. 

Hauser, H., and Gaines, N. (1982). Spontaneous vesiculation of phospholipids a simple and quick method of forming unilamellar vesicles, Proc. Natl. Acad. Sci. USA. 79. 1683-1687. 

It appears, therefore, that the presence of vesicles accelerates the formation of new vesicles. It is not easy to rationalize how and why. What comes to mind is a general observation from the field of surfactants, that pre-organization makes the organization of further material easier. For example, there is no spontaneous vesiculation when POPC is simply added to water, and no significant amount of... 

In the case of the matrix effect, contrary to the autopoietic experiments described earlier, there is no need of water-insoluble precursors - it is the very addition of the same surfactant to an already existing family of vesicles that brings about the multiplication of the same size distribution. All that is needed is an initial narrow distribution of vesicles, and a continuous addition of fresh surfactant. Methods to obtain narrow size distributions in the case of spontaneous vesiculation have been described (Domazou and Luisi, 2002 Stano et al., in press). In fact a prebiotic scenario may be conceived where the fresh surfactant is continuously synthesized in situ, and thanks to the matrix effect the same sizes are propagated over and over again. Of course there is no way to demonstrate that this is what really happened in prebiotic times - it is fair, however, to claim that, given the simpUcity of the process, there is a reasonable probability that a process of this sort may have occurred (Luisi et al, 2004). 

Figure 3. Freeze-fracture electron microscopy analysis of the vesicle size distribution in the case of the spontaneous vesiculation of oleic acid/oleate. (A) Vesicles formed from the hydrolysis of 25 mM oleic anhydride (overall concentration) at 30 °C, yielding 50 mM oleic acid/oleate. (B) Vesicles extruded throughout 50 nm diameter filters. (C) Vesicles formed upon hydrolyzing 20 mM oleic anhydride (same conditions as in A) in the presence of pre-added extruded vesicles B—all in 0.2 M bicine buffer pH 8.5. For details see ref. 8.

In this example of spontaneous vesiculation, a total of about 10 oleic acid-oleate molecules are involved in the formation of one vesicle. It is self-assembly and self-organization in the highest form, and unprecedented in chemistry-unless we consider crystallization. It is useful to remember that this creation of order operates under thermodynamic control ordered structures are built by a process which is... 

Abstract Possible ways of producing bilayer vesicles are reviewed from the theoretical point of view. The emphasis is on vesiculation driven by a negative bending energy of spherical vesicles, called spontaneous vesiculation. A new model is presented to explain the existence... 

In the following we consider vesiculation, in particular spontaneous vesiculation, and we concentrate on theoretical aspects. Apart from referring to existing theory (a fair review would require more time and space), we will propose a new theoretical model for onions . Simons and Cates [2], who introduced this graphic name for multilamellar vesicles, were the first to deal with onions in thermodynamic equilibrium. Unlike these authors, we will assume the bending energies of the spheres to be negative. 

In order to express the condition for spontaneous vesiculation in terms of curvature elastic moduli, we start from the usual formula for the bending energy per unit area of fluid bilayer... 

Whenever the condition of spontaneous vesiculation is satisfied, the bilayer may be expected to split up into smaller and smaller vesicles. Obviously, Eq. (1), being quadratic in the principal curvatures, does not tell us where this process stops. The fact that there is a limit can be taken into account, in a natural but approximative way, by adding to (1) a quartic term [3]. For the surface of a sphere of radius r, we may write... 

In addition, the possibility of demixing favors phase separation. The coexistence of micelles and bilayers in two separate phases has recently been explained in terms of the demixing associated with differences in mono-layers curvature [38]. A significant demixing in the same phase between small vesicles and extended bilayer, planar or sponge, could upon up new ways of controlling spontaneous vesiculation. 

Spontaneous vesiculation of sheep-erythrocyte membranes is accompanied by an enrichment of specific membrane proteins in certain regions of the lipid bilayer. ... 

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