Multilamellar dispersions

The membranes used in EPR measurements are usually multilamellar dispersions of lipids (mul-tilamellar liposomes) containing an investigated carotenoid and 0.5-1.0mol% of an appropriate lipid spin label (Figure 10.1). The total amount of lipids usually is 5-10 pmol per sample. 

Fig. 14, Representative proton-decoupled 31P NMR spectra of multilamellar dispersions of (3 1) DOPE/16 in excess water at either 25.4 °C or 48.2 °C. The spectra on the left (a) are from an unpolymerized sample, and the spectra on the right (b) are for a sample where lipid 16 has been 33% photopolymerized.

The multilamellar dispersions or vesicles were formed in the conventional manner (4). Drying down the lipid and suspending it in the desired aqueous solution (0.1M NaCl, 0.01M tris, pH 7.5) yielded, on gentle agitation, vesicles of the appropriate size for microelectrophoresis... 

The molecular mechanism of local anesthesia, the location of the local anesthetic dibucaine in model membranes, and the interaction of dibucaine with a Na+-channel inactivation gate peptide have been studied in detail by 2H- and 1H-NMR spectroscopy [24]. Model membranes consisted of PC, PS, and PE. Dibucaine was deuterated at H9 and H3 of the butoxy group and at the 3-position of the quinoline ring. 2H-NMR spectra of the multilamellar dispersions of the lipid mixtures were obtained. In addition, spectra of deuterated palmitic acids incorporated into mixtures containing cholesterol were obtained and the order parameter, SCD, for each carbon... 

Fig. 2 Hydrogenation of multilamellar dispersions (o) and single bilayer vesicles ( ) of soya lecithin in the presence of the sulfonated derivative of Wilkinson s catalyst [22],...

The reactivity of water-soluble palladium catalyst, Pd(QS)2 (palladium di(sodirmi) alizarine monosulfonate) has been examined in multilamellar dispersions of unsaturated phospholipids [4]. With substrates of dioleoylphosphatidylcholine there is a transient appearance of trans co9 but no cis double bonds were observed when the trans 9 derivative of phosphatidylcholine was used as substrate. 

Figure 4.4. In this phase diagram we find the Lp-, Pp-, Lp and phases that have already been described, plus a few new ones, namely Iv, Lo and L p. W (denoted c in the figure) is the pure DPPC crystalline or subgel phase, that is only observed in annealed (i.e. kept at 4 °C for several days) aqueous multilamellar dispersions of DPPC. A thermotropic transition, the subtransition , converts the Lc- into the Lp- phase at ca. 18 °C. Lo and Lop are two different hquid ordered (Lo) regions, respectively called liquid-crystalUne-like liquid ordered (Loo) and gel-like liquid ordered (Lop). The latter two phases differ in the orientational order of the hydrocarbon chains, and in the relative position of the cholesterol molecule in the host PC bUayer.

The membranes used in this work (13) were a multilamellar dispersion of several PC. Liposomes were prepared according to the protocol described by Kusumi and others (18). 50 J,L glass capillaries were used for the ESR oximetry measurements. The capillary was placed inside the ESR Dewar insert and equilibrated with a flow of nitrogen for temperature control. CTPO is water soluble and was used at a concentration of 0.14 mM in the oxygen consumption study. Spin label of 6-PC(SA LA) at 0.5 mol% was used as a depth probe in the membranes for the phase transition temperature study. 

Multilamellar dispersions of homogeneous phosphatidylcholines exhibit two reversible phase transitions. The major chain-melting transition is a sharp symmetrical first-order endothermic transition in the DSC thermogram. For a series of saturated phospholipids, the enthalpy of the main transition is a linear function of the transition temperature (Fig. 10) [94], and the extrapolation to zero enthalpy suggests that saturated phosphatidylcholines with hydrocarbon chains shorter than 12 carbon atoms cannot form stable bilayers. 

Polymerization studies were performed on multilamellar dispersions prepared at low concentration, 2 mg/ml. The dispersions were gel filtered on Sephadex G 50-150 column, so that any of the short chain lipid component that might be present in micelle form would be separated from the mixed lipid vesicles. The vesicle preparations from the 1 1, 1 2 and 2 1 DC 8,9 PC mixtures were used in the polymerization study. The UV irradiated samples showed no evidence of participation by the acetylenic lipid in the polymerization reaction, as indicated by measuring the phosphorus content after separation of monomer by TLC. Diacetylenes polymerize when they are aligned, - and in bilayer systems this situation arises only below the lipid phase transition temperature. Thus, temperature may be expected to play an important role in polymerization. Indeed, after UV irradiation at room temperature brown or yellow dispersions resulted which contained a substantial fraction of unreacted monomer. However, polymerization of the mixtures for 1 minute at -5 C resulted in extensive polymerization (more than 90% elimination of monomer). Figure 4 shows that visible spectra of both the samples at 1 minute irradiation contained two major peaks at 532 and 494 nm. In contrast, pure DC 8,9 PC dispersion, prepared and irradiated under identical conditions, showed no clear signature of a polymer spectrum (defined peak around 500 nm) and very little monomer participation. Schoen and Yager, on the other hand, have demonstrated that the diacetylene lipid in tubular morphology shows a defined spectrum, but that the participation of monomers in polymerization process is low. ... 

Phospholipids e.g. form spontaneously multilamellar concentric bilayer vesicles73 > if they are suspended e.g. by a mixer in an excess of aqueous solution. In the multilamellar vesicles lipid bilayers are separated by layers of the aqueous medium 74-78) which are involved in stabilizing the liposomes. By sonification they are dispersed to unilamellar liposomes with an outer diameter of 250-300 A and an internal one of 150-200 A. Therefore the aqueous phase within the liposome is separated by a bimolecular lipid layer with a thickness of 50 A. Liposomes are used as models for biological membranes and as drug carriers. 

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

As indicated by Puig et al. (35). surfactant retention and attendant pressure buildup in the rock can be greatly reduced if the surfactant dispersion is converted into the liquid crystalline state. Unilameller vesicles are preferred in the field work rather than the multilamellar... 

The multilamellar bilayer structures that form spontaneously on adding water to solid- or liquid-phase phospholipids can be dispersed to form vesicular structures called liposomes. These are often employed in studies of bilayer properties and may be combined with membrane proteins to reconstitute functional membrane systems. A valuable technique for studying the properties of proteins inserted into bilayers employs a single bilayer lamella, also termed a black lipid membrane, formed across a small aperture in a thin partition between two aqueous compartments. Because pristine lipid bilayers have very low ion conductivities, the modifications of ion-conducting... 

Figures 9d,e show aqueous dispersions of vesicles. The smaller the vesicles, the less probable is an upcoming cross-fracture. Thus the question whether the vesicle is uni- or multilamellar can hardly be answered. At least for fluid vesicle dispersions it is possible to solve the problem with the help of cryotransmission electron microscopy.

Sustained release from disperse systems such as emulsions and suspensions can be achieved by the adsorption of appropriate mesogenic molecules at the interface. The drug substance, which forms the inner phase or is included in the dispersed phase, cannot pass the liquid ciystals at the interface easily and thus diffuses slowly into the continuous phase and from there into the organism via the site of application. This sustained drug release is especially pronounced in the case of multilamellar liquid crystals at the interface. 

Closed, spherical, single-bilayer, 300- to 600-A-diameter surfactant and/or phospholipid aggregates dispersed in aqueous solutions. Ultrasonic dispersal of multilamellar vesicles (MLVs) or employing procedures such as French Press filtration result in SUV formation. 

In preliminaty experiments, problems occured during the fusion of giant liposomes with cells. The induced dipole of cells is much larger than that of vesicles leading primarily to cell-cell contacts and thus to cell-cell fusion. By using vesicles filled with electrolyte or multilamellar vesicle dispersions this problem could be overcome. 

Materials and Methods. PS was purified from bovine brain in this laboratory as previously described (45). Dispersions of multilamellar vesicles and sonicated unilamellar vesicles were prepared as described earlier (15, 45) in a standard buffer containing 100mm NaCl, 7mm L-histi-dine N-tris-(hydroxymethyl) methyl 2-amino ethane-sulfonic acid (TES), and approximately 0.1mm EDTA, adjusted to pH 7.4. CF containing vesicles were prepared by hydration and sonication in a solution of 100mm CF, 0.1mm EDTA, and 1/10 (v/v) of the standard buffer, adjusted to pH 7.4, separated by passage through a Sephadex G-75 (1.0 X 20 cm) column equilibrated with the standard (0.1M NaCl) buffer and stored on ice. 

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). 

Even if membranous vesicles were commonplace on the early Earth and had sufficient permeability to permit nutrient transport to occur, these structures would be virtually impermeable to larger polymeric molecules that were necessarily incorporated into molecular systems on the pathway to cellular life. The encapsulation of macromolecules in lipid vesicles has been demonstrated by hydration-dehydration cycles that simulate an evaporating lagoon [53] or by freeze-thaw cycles [54]. Molecules as large as DNA can be captured by such processes. For instance, when a dispersion of DNA and fatty acid vesicles is dried, the vesicles fuse to form a multilamellar sandwich structure with... 

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