Lipid films mixed

Lipids are mixed with the nanoparticles in an apolar solvent. The mixed film obtained is hydrated. Thereafter, the nanoparticle-containing micelles and empty micelles are separated by centrifugation. 

Entrapment of plasmid DNA and/or protein into liposomes entails the preparation of a lipid film from which multilamellar vesicles and, eventually, small unilamellar vesicles (SUVs) are produced. SUVs are then mixed with the plasmid DNA and/or protein destined for entrapment and dehydrated. The dry cake is subsequently broken up and rehydrated to generate multilamellar dehydration-rehydration vesicles (DRV) containing the plasmid DNA and/or protein. On centrifugation, liposome-entrapped vaccines are separated from nonentrapped materials. When required, the DRV are reduced in size by microfluidization in the presence or absence of nonentrapped materials or by employing an alternative method (7) of DRV production, which utilizes sucrose (see below). 

The different behavior of 7 and 8 is probably due to the charged head group in 7. Phase separation to form enriched domains of this lipid in mixed monolayers would be inhibited by electrostatic repulsion. Interestingly, mono-layer films of 7 mixed with the biologically important molecule cholesterol did exhibit phase separation at all compositions provided the temperature was maintained below the Tm of 7. Presumably the significantly different shapes of the two molecules promotes the phase separation and overcomes the electrostatic barrier. 

Due to the topochemical restrictions of diacetylene polymerization, diacetylenic lipids are solely polymerizable in the solid—analogous phase. During the polyreaction an area contraction occurs leading to a denser packing of the alkyl chains. In addition to surface pressure/area isotherms the polymerization behavior of diacetylenic lipids containing mixed films give information about the miscibility of the components forming the monolayer ... 

Influence of the Acidic Lipid. Unlike DPL films, mixed films containing 10 and 50% DPPA showed a prompt response to the introduction... 

All lipids are mixed well and dried down on a rotary evaporator. The temperature of drying should be above the highest transition temperature of the individual lipid components. At this stage, lipids should dry onto wall of the vessel as a completely clear glassy film. 

Lipids are mixed together and solvent is removed using freeze-drying. Then an aqueous solution is introduced and the hpid cake around the vessel wall is reconstituted. This method works best for manufacture of neutral liposomes, as the hydro-phobic lipids readily dissolve in solvents such as chloroform and are deposited dry on the wall of the rotavapor vessel. Then the material to be encapsulated is dissolved in an aqueous solution and the dry film on the vessel wall is hydrated with this solution. The exact steps involved in the preparation of hydrogenated soy phosphatidylcholine (PHSPC)- and cholesterol-containing vesicles at a molar ratio of 60 to 40% are as listed here ... 

The dependence of the ttv values on the composition of the vapor and condensed states for DML-CHOL, DOL-CHOL, and DOL-DML mixtures is shown in Figure 6. The upper curve is the surface vapor pressure as a function of the mole fraction of the liquid-expanded film the lower curve is for the dependence of irv on the composition of the gaseous phase. Ideal mixing behavior is given by the linear dotted line which joins the 7ry° points for each of the pure compounds. In all cases there was complete miscibility of the components as represented by the continuous function of 7rv with x. In the cholesterol mixtures positive deviations from Raoult s law are observed for the mixture of lecithins, ideal mixing is observed. These results confirm those obtained with lipid mixtures—i.e., cholesterol mixed with liquid-expanded lipid films forms rion-ideal mixtures with positive deviations for mixtures of lipids which are in the same monolayer state, as in the case of the liquid-expanded DOL-DML mixtures, ideal mixing results (8). 

Figure 7. Average area per molecule in mixed lipid films as a function of composition. Data obtained from Figures 3-5 along F-F, i.e., at the low area portion of the transition region in the 7r-A isotherm.

The picture is fairly clear for the sharply altered behavior of 5-NS, 5-NS (Me), and the rest of the series in view of the ready stabilza-tion of the bent conformation, it is less clear for the differences between other positions of the oxazolidine ring on the chain. In particular, a detailed evaluation of changes in the role that a bent conformation might play for 12-NS and 16-NS requires further study of mixed lipid films. While it seems likely that under typical membrane conditions a bent conformation will play only a minor role, present indications are that it is not negligible and will vary with the shift from the 12 to the 16 position (24). 

The preparation methods of these vesicles are various. In some cases, the liposomal suspension is firstly prepared and then amphiphilic CyDs are inserted inside the phospholipid-bilayer, for example by sonication [93]. Another method mixes phospholipid (+/— cholesterol) and amphiphilic CyD solutions, to form hposomes by conventional methods [92, 94]. Lastly, vesicles consisting of bilayers of purely amphiphilic CyDs as raw material can be prepared applying a technique used to prepare hposomes, i.e. hydration of lipidic film followed by sonication [99-101]. 

On the other hand, the incorporation of Cyt c in the monolayer of Chi a produces a blue shift of the entire spectrum. The Soret band is displaced from 439 to 436 nm and the red band from 680 to 673 nm. In addition, the red band is 3 nm narrower than that of pure Chi a monolayer. These spectroscopic characteristics of Cyt c-Chl a mono-layers are comparable to those of mixed films of Chi a-MGDG in a molar ratio of 1 100. Therefore, it is assumed that in mixed Chi a-protein films, Chi a is diluted by Cyt c as it is in mixed Chi a-lipid films. However, the fluorescence lifetime of Cyt c-Chl a films is shorter than 0.2 ns and has the characteristics of a concentrated Chi a system. This apparent contradiction can be lifted out by taking into consideration energy transfer occurring... 

Caracciolo, G., Piotto, S., Bombelli, C., Canriniti, R., Mancini, G. Segregation and phase transition in mixed lipid films. Langmuir 21(20), 9137-9142 (2005)... 

Mixing fatty acids with fatty bases can dissolve films as the resulting complexes become water-soluble however, in some cases the mixed Langmuir film is stabilized [128]. The application of an electric field to a mixed lipid monolayer can drive phase separation [129]. 

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