Myelinic figures

Cyclic carbohydrates with two alkyl chains (e.g. 1,2-dialkyl (or 1,2-diacyl) glycerol 8 a (sug=Glcp, Galp) present structural similarities with glycerophospho-lipids. They form complex mesophases such as bicontinuous cubic phases, inverted hexagonal phases or myelin figures [58-61]. Other dialkyl derivatives... 

Fig. 4 Sponge (L3) phase growing as myelinic figures dissolve for a drop of CulEOja injected into water at 40 °C...

Fig. 10 Granule of Zeolite 4A/pure CnfEOls in water at 30 °C. Myelinic figures form, and no disintegration occurs...

Pure Surfactants with Low Solubility Myelinic Figures... 

Lamellar phases of phospholipids often exhibit myehnic figures when contacted with water. Electron micrographs [24,26] showed that each tubular myehnic figure in the egg-yolk phosphatidylcholine/water system consisted of a water core surrounded by many concentric bilayers. More recently Raman spectroscopy techniques have confirmed the concentric bilayer arrangement [1,18]. Myelinic figures are not equilibrium structures, however, and eventually break up to form vesicles or other lamellar structures. Indeed, adding water to a vessel whose inner walls are coated with a thin layer of a lamellar phase of low water content is a well-known way of forming vesicles. 

Fig. 14 A Schematic diagram of motion of latex particles toward the base of myelinic figures, confirming that their growth is due to swelling, not to diffusion as in (B)...

As the base of the myehns is fixed at the initial surface of contact, according to the experimental observations, the volumetric flow rate of aqueous solution entering the lamellar phase must equal the rate of increase in volume of the myelinic figures ... 

There may be limitations in applying the above model to other systems. For instance, the initial surfactant often exists as a lamellar phase as for phospholipids, so that there are no interfaces between various liquid crystalline phases whose velocities can be measured and used to determine effective dif-fusivities as in the AOT analysis above. As a result, the base of the myelinic figures must approach the base of the vertical cell as the volume of the lamellar phase shrinks, and the assumption made above that the composition of the myelins is independent of time may not be valid. 

Cell swelling Loss of microvilli Membrane blebs ER swelling Myelin figures... 

Our present treatment clearly does not apply to these structures, though some of the observation on mesomorphic phases have a bearing on bilayer vesicles. One of these concerns the observation that phospholipids do not always readily form into vesicles, but rather into multilamellar bilayers or myelin figures. Sonication is often, but not always, necessary to break up and transform these bilayers into vesicles. But once formed, these vesicles are homogeneous and stable, and unaffected by the length of time and intensity of sonication. It seems that as soon as bulk phospholipid... 

In extended bilayer lipid membranes ( Myelin figures ), made of single... 

Figure 5.1 The swelling of lecithin crystallites in water produces myelin figures composed of many hydrated molecular bilayers. The process depicted in the four pictures (kindly provided by Prof. I. Sakurai) takes a few hours.

These fibres are solid-like and should not be confused with the fluid myelin figures and their helical precursors obtained upon the swelling of lecithin crystals (see Figure 5.1). The fluid structures flow and change their shape and width constantly, whereas the solid types simply widen after addition of more material. Once a crystalline fibre is formed it adds material to the highly curved edges, much less to the more planar bilayer surfaces (Figure 5.7). 

An extended experiment was performed for the 2.0 gm/dl-salinity Pm system to determine the effect on relative interface velocities of the formation of myelinic figures and the C phase. With reference to Figure. 18, the formation of a uniform layer of C phase at t1 = 12 hr1 (6 days) corresponds to a decrease in relative velocity of the brine-microemulsion interface. The layer of C phase grew uniformly after its initial formation. In Figure 18, all positions are plotted relative to the same reference position. The offset of the liquid crystal interface at t = 0 indicates brine formation due to initial mixing. 

The aqueous solution at the highest salinity studied was entirely C in structure. No myelinic figures formed during the contacting experiment. The interface between C and brine remained smooth throughout. From Table IV, one can see that the interface motion was very much slower than that for lamellar aqueous structures. No contacting experiments were performed with solutions that were initially C+L because of problems with phase separation. 

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