Liposome bilayers, molecular

Srivastava A and Eisenthal K B 1998 Kinetics of molecular transport across a liposome bilayer Chem. Phys. Lett. 292 345-51... 

Figure 2. An oversimplified representation of molecular motions in liposome bilayers. Individual lipids can rotate (A), undergo sequential motion (B), flip-flop (C), undergo lateral diffusion (D), or intervesicle exchange (E).

AndreollTE. On the anatomy of amphotericin B-cholesterol pores in lipid bilayer membranes. Kidney Int 1973 4 337-45. DeKruijiff B, Demel RA. Polyene antibiotic-sterol interactions in membranes of Acholeplesma laidlawii cellsand lecithin liposomes. III. Molecular structure of the polyene antibiotic-cholesterol complexes. Biochem Biophys Acta 1974 339 57-70. HoIzRW.Theeffectsofthe polyene antibiotics nystatin and amphotericin Bon thin lipid membranes. Ann N Y Acad Sell 974 235 469-79. 

Whether phase transition changes are directly responsible for the permeability changes observed in liposomes and bilayers is debatable but results obtained by DSC are indicative that polyene addition to sterol-containing liposomes, bilayers or membranes markedly alters the molecular structure of the membrane by reducing the phospholipid-sterol interaction. Such alterations may be the basis for the observed polyene-mediated permeability changes to ions and small nonelectrolytes [ 101,103-106,201 -212,216]. 

Lentz BR (1993) Use of fluorescent-probes to monitor molecular order and motions within liposome bilayers. Chem Phys Lipids 64(l-3) 99-l 16. doi 10.1016/0009-3084(93)90060-g... 

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

Experimental investigations of the model system of dye molecules adsorbed onto surfaces of polystyrene spheres have finuly established the sensitivity and surface specificity of the SHG method even for particles of micrometre size [117]. The surface sensitivity of die SHG process has been exploited for probing molecular transport across the bilayer in liposomes [118], for measurement of electrostatic potentials at the surface of small particles [119] and for imaging... 

When liposomes are prepared from a molecular mixture of lipid components it is important that all lipids be homogeneously dissolved in an organic solvent in order to obteiin bilayers with evenly distributed lipids after hydration. For example, the solubilities of phosphatidylcholine and cholesterol in chloroform are similar their solubility in benzene differs. Upon removal of benzene from the lipid solution an inhomogeneous lipid film is formed on the glass wall and... 

The most versatile method to prepare such hollow capsules is self-assembly [203-205, 214, 215]. Owing to their amphiphilic nature and molecular geometry, lipid-based amphiphiles can aggregate into spherical closed bilayer structures in water so-called liposomes. It is quite reasonable that the hollow sphere structure of liposomes makes them suitable as precursors for the preparation of more functional capsules via modification of the surfaces with polymers and ligand molecules [205, 216, 217]. Indeed, numerous studies based on liposomes in this context have been performed [205, 209, 213]. 

Molecules containing an ionic group and long alkyl chain(s) compose a molecular assembly such as a micell, a bilayer membrane, or a vesicle (liposome) (Fig. 4).19a) These assemblies bind reaction components by hydrophobic interaction, give a high... 

FIG. 1.3 Molecular cargo in a liposome. The cargo molecules are carried in different parts of the liposome depending on their chemical nature. Hydrophobic molecules are carried inside the hydrophobic part of the bilayer, whereas hydrophilic molecules reside in the interior. More complex molecules are wholly or partly embedded in the bilayer or chemically bound to the interior or exterior surface. 

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