Multilamellar structure

Formation from Template Surfaces Recently, a new method for the preparation of LUV was reported by Lasic et al. (1988). The method is based on a simple procedure which leads to the formation of homogeneous populations of LUV with a diameter of around L vim. Upon addition of solvent to a dry phospholipid film deposited on a template surface, vesicles are formed instantly without any chemical or physical treatment. The formation of multilamellar structures is prevented by inducing a surface charge on the bilayers. The size of the vesicles is controlled by the topography of the template surface on which the phospholipid film was deposited (Lasic, 1988). 

Above a critical concentration certain amphiphiles may aggregate into membranous micelles, which are globular structures with a nonpolar interior and with a polar surface that interfaces the aqueous environment. At still higher concentrations micelles may fuse into multilamellar structures composed of bilayers. [138]... 

At low concentrations, a hollow vesicle results with usually just one double layer and, as the concentration is increased, the number of double layers can increase in a transition from unilamellar vesicles to multilamellar structures. Since the hydro-plilic head groups are exposed on the inside as well as the outside of the vesicular structure this provides an opportunity to entrap hydrophilic guest drug molecules both inside the center of the vesicle and, if multilamellar, between the phospholipid bilayers as well. On the other hand, hydrophobic molecules can become incorporated in the hydrophobic regions of the bilayers where the hydrophobic tails overlap. 

The effect of AB diblock size relative to the homopolymers on the compati-bilization of A/B homopolymer blends was examined using numerical self-consistent field theory (in two dimensions) by Israels et al. (1995). They found that the interfacial tension between homopolymers can only be reduced to zero if the blocks in the diblock are longer than the corresponding homopolymer. Short diblocks were observed to form multilamellar structures in the blend, whereas a microemulsion was formed when relatively long copolymers were added to the homopolymer mixture. These observations were compared to experiments on blends of PS/PMMA and symmetric PS-PMMA diblocks reported in the same paper. AFM was used to measure the contact angle of dewetted PS droplets on PMMA, and the reduction in the interfacial tension caused by addition of PS-PMMA diblocks was thereby determined. The experiments revealed that the interfacial tension was reduced to a very small value by addition of long diblocks, due to emulsification of the homopolymer by the diblock, in agreement with the theoretical expectation (Israels et al. 1995). 

Using the new procedure, attempts were made to quantitate the cerebrosides located on the surface of myelin. Myelin is composed of multilamellar bilayers of membrane of approximately 70% lipid and 30% protein (16). About 20% of the total lipid consists of cerebroside and sulfatide. Because of the lipophilic nature of the ceramide moiety and the hydrophilic nature of galactose, it has been postulated that the galactose moiety of myelin cerebrosides is facing the surface while the ceramide moiety is buried within the bilayer. Even considering the multilamellar structure of myelin, at least several percent of the cerebrosides should be present on the myelin surface. The method described in this manuscript should allow us to determine surface cerebrosides to as little as 0.5% of the total cerebrosides. 

Multilamellar structure the DNA strand is intercalated in multilamellar liposome membrane. 

The structural dependence of phospholipid solutions on water content is called lysotropic polymorphism. At a water content of up to 30% dipalmitoylphosphatidyl-choline (DPPC) forms lamellar phases consisting of superimposed bilayers. Increasing the water content results in heterogeneous dispersions formed by multilamellar structures, the so-called liposomes (see also Section 1.3.1). 

A systematic study on the structural polymorphism of lipid A and LPS Re with synchrotron radiation small-angle X-ray scattering showed, that at lower water content (<70 w%) and higher concentration of divalent cations such as Mg2+ ([lipid A] [ Mg2+] < 3 1 molar ratio), only multilamellar structures are formed (Brandenburg et al., 1990, 1992). In contrast, at high water content and... 

In further investigations on other rough mutant LPS Rd through Ra (Seydel et al., 1993) from enterobacterial strains, non-lamellar aggregate structures were also found under near physiological conditions. No multilamellar structures were found, except at low water content and high divalent cation concentrations. 

Another use of the DNA-lipid complex was reported by Wong and coworkers [33]. The DNA molecule structural features can be imprinted into CdS nanostructures by using self-assembled DNA-membrane templates. The initial application of the DNA-lipid multilamellar structure was the use as gene carriers in gene therapy, and many reports [34-39] were published (Fig. 6b). To prepare the DNA templates, anionic DNA was reacted with a mixture of... 

If multilamellar structures are formed, water is present in the core of the hposome, and also entrapped between the bilayers. Depending on the physico-chemical nature of the dmg, it can either ... 

Unilamellar vesicles are usually formed from lipid dispersions with sonication. Thus the suspension is metastablc, and vesicles aggregate to form a multilamellar structure. The decay time of sonicated phosphatidylcholine vesicles, as measured by DLS, showed a bimodal distribution 50. The hydrodynamic radius estimated from the smaller decay time was consistent with the values obtained by other experimental techniques such as ultracentrifugation. 

The SANS data demonstrated that as a result of lipoplex formation, the SUVs were converted to multilamellar lipid-DNA complexes. This transition occurred via three stages. The first step, occurring on a millisecond timescale, was inaccessible to SANS as the smallest time slice used was 1 sec. This step was, however, observable by stopped-flow turbidity and fluorescence experiments. The next step, occurring on a timescale of seconds, which was observable by SANS, was found to correspond to the formation of an (unstable) intermediate with a locally cylindrical structure. The final step, occurring over minutes, involved the conversion of the unstable cylindrical intermediates to a multilamellar structure. As fluorescence measurements can only give information about the conformational changes of DNA, SANS measurements are necessary to probe the structure of the different intermediates that occur during the formation of the DNA-lipid complexes. No other technique lends itself to such studies. 

The situation for diblock copolymers has been examined in detail by Washiyama et al. in the PS-PVP system [33]. As shown in Fig. 33, they found that for symmetric copolymers of 510-540, the fracture toughness passed through a maximum at 2 = 0.2 chains/nm2 corresponding to a nominal areal density of chains a little higher than what is contained in a pure block copolymer lamella of thickness L. At higher values of 2, TEM observations showed that a multilamellar structure formed at the interface, as illustrated in Fig. 34 for the 510-540 copolymer. The fracture toughness of such an interface dropped sharply to stabilize then at a plateau value. The areal density at which Cjc reached this plateau value corresponded closely to what would be expected for the thickness of 3/21. The... 

Recently, the formation of multilamellar structures by the self-assembly technique was also reported [39,40] After the formation of the first monolayer, suitable processing of the end groups of the molecule (e.g., the... 

Fig. 9. Freeze-fracture micrographs of the sarcolemma after ischemia and reperfusion showing severe >68 6gation of intramembranous particles (a) and the extrusion of multilamellar structures (b and c). A schematic representation of this lipid extrusion and IMP aggregation as a result of lateral phase segregation in the cytoplasmic leaflet is shown in d.

Specifically, phospholipids may form multilamellar structures around the oil-water interface, and presumably these layers will have different spacing depending on the... 

Amphiphiles with two chains per charged head group, such as didodecyldi-methylammonium cation, dicetylphosphate anion, and the lecithin of biomembranes tend to form bilayers, not micelles, in which the chains are presumably more ordered than those in simple micelles. Such layers can exist as flat sheets, as in multilamellar structures (21) or as the curved surface of a spherical micelle (22). N.m.r. evidence... 

Liposomes are multilamellar structures that consist of several bilayers of lipids (several pm) (see Chapter 12). They are produced by simply shaking an aqueous solution of phospholipids, e.g. egg lecithin. When sonicated, these multilayer structures produce unilamellar structures (size range 25-50 nm) that are referred to as liposomes. Figure 13.27 gives a schematic picture of liposomes and vesicles. 

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