Lipids mixture

Fig. 1.9 S urface pressure ( r)-area (A) isotherms obtained for a lipid mixture (DPPC POPG PA, 68 22 9 (by weight)), alone and with 10% (w/w) of either SP-C peptide or SP-C peptoid added. Results indicate that the addition of the SP-C mimics engenders biomimetic surface activity, as indicated by lift-off at a higher molecular area and the introduction of a plateau...

The system reported by Avdeef and co-workers [25-28,556-560] is an extension of the Roche approach, with several novel features described, including a way to assess membrane retention [25-28,556,557] and a way to quantify the effects of iso-pH [558] and gradient pH [559] conditions applied to ionizable molecules. A highly pure synthetic phospholipid, dioleoylphosphatidylcholine (DOPC), was initially used to coat the filters (2% wt/vol DOPC in dodecane). Other lipid mixtures were subsequently developed, and are described in detail in this chapter. 

The analytical techniques proposed in the literature generally give reliable information on lipids present in the paint layer. However, the presence of lipid mixtures and of particular environmental conservation conditions may affect the lipid pattern to such an extent that their identification may be very difficult and sometimes erroneous. Thus, a multianalytical approach is recommended which integrates chromatographic data with techniques such as mapping based on Fourier transform infrared spectroscopy or SIM on cross-sections, in order to better understand the distribution of lipids in the various paint layers. 

Mixtures of phospholipids in aqueous solution will spontaneously associate to form liposomal structures. To prepare liposomes having morphologies useful for bioconjugate or delivery techniques, it is necessary to control this assemblage to create vesicles of the proper size and shape. Many methods are available to accomplish this goal, however all of them have at least several steps in common (1) dissolving the lipid mixture in organic solvent, (2) dispersion in an aqueous phase, and (3) fractionation to isolate the correct liposomal population. 

An example of a lipid mixture preparation based on mass would be to dissolve 100 mg of PC, 40 mg of cholesterol, and 10 mg of PG in 5 ml of chloroform/methanol solution. When using activated PE components, inclusion of 10 mg of the PE derivative to this recipe will result in a stable liposome preparation. 

Solvent-mediated dispersion techniques used to create liposomes first involve dissolving the lipid mixture in an organic solvent to create a homogeneous solution, and then introducing this solution into an aqueous phase. The solvent may or may not be soluble in the aqueous phase to effect this process. There also may be components dissolved in the aqueous phase to be encapsulated in the developing liposomes. 

Add the protein or peptide to be conjugated to the liposome suspension. The protein may be dissolved first in PBS, pH 7.2, and an aliquot added to the reaction lipid mixture. The amount of protein to be added can vary considerably, depending on the abundance of the protein and the desired final density required. Reacting from 1 mg protein per ml liposome suspension up to about 20 mg protein/ml can be done. 

Lambert O, Lev D, Ranck J-L, Leblanc G, Rigaud J-L. A new gel-like phase in dodecyl maltoside-lipid mixtures implications in solubilization and reconstitution studies. Biophys J1998 74 918-930. 

As very accurate input data are needed for a successful MD run on lipid systems, it is not surprising that most of the simulations done are for a very limited number of systems for which these are available. Phosphatidylcholine (PC) bilayers have been and still are popular [31,33-41], but, nowadays, other types of lipid bilayers are under investigation as well [42-46]. MD studies on lipid mixtures, as well as a lipid bilayer including some protein-like object, give all kinds of additional problems that we will touch upon below. 

M. W. De Jager, G. S. Gooris, I. P. Dolbnya, W. Bras, M. Ponec, and J. A. Bouwstra. The phase behaviour of skin lipid mixtures based on synthetic ceramides. Chem. Phys. Lipids 124 123-134 (2003). 

Weldon et al.5 used Raman in the surface-enhanced mode (SERS) to monitor bacterial (P. acnes) hydrolysis of triglycerides in lipid mixtures that model sebaceous gland secretions. While technically not a process monitor, it paves the way for methods to monitor specific moieties in very complicated matrices. 

Oriented membrane samples were prepared by depositing peptide-lipid mixtures (co-solubilized in CHCls/MeOH 2 1, v/v) on glass slides (0.08x 7.5 x 18 mm, Paul Marienfeld KG, Mergentheim, Germany). Drops of 20-30 xL... 

FUmix/lipid mixture shell air Animal studies [21]... 

Phase behavior of lipid mixtures is a much more difficult problem, due to nonideal mixing of lipid components. Ideal mixing implies like and unlike lipids have the same intermolecular interactions, while nonideal mixing results from differential interactions between lipid types. If the difference is too great, the two components will phase separate. While phase separation and lateral domain formation have been observed in many experiments, we lack a molecular-level physical description of the interactions between specific lipids that cause the macroscopic behavior. The chemical potential of a lipid determines phase separation, as phase coexistence implies the chemical potential of each type of lipid is equal in all phases of the system [3,4],... 

Veatch, S.L., Soubias, O., Keller, S.L., Gawrisch, K. Critical fluctuations in domain-forming lipid mixtures. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 17650-5. 

This review emphasizes an intriguing and potentially useful aspect of the polymerization of lipid assemblies, i.e. polymerization and domain formation within an ensemble of molecules that is usually composed of more than one amphiphile. General aspects of domain formation in binary lipid mixtures and the polymerization of lipid bilayers are discussed in Sects. 1.1 and 1.2, respectively. More detailed reviews of these topics are available as noted. The mutual interactions of lipid domains and lipid polymerization are described in the subsequent sections. Given the proper circumstances the polymerization of lipid monolayers or bilayers can lock in the phase separation of lipids, i.e. pre-existing lipid domains within the ensemble as described in Sect. 2. Section 3 reviews the evidence for the polymerization-initiated phase separation of polymeric domains from the unpolymerized lipids. 

The most complete insights into the behavior of mixtures of nonpolymeriz-able lipids have come from the phase diagrams of these systems. These data have provided important reference points for the polymerizable lipid systems described next, even though few phase diagrams have been reported for polymerizable lipid mixtures. In spite of this deficiency the polymerization studies have... 

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