Self-assembly bilayer sheet

Random interface models for ternary systems share the feature with the Widom model and the one-order-parameter Ginzburg-Landau theory (19) that the density of amphiphiles is not allowed to fluctuate independently, but is entirely determined by the distribution of oil and water. However, in contrast to the Ginzburg-Landau approach, they concentrate on the amphiphilic sheets. Self-assembly of amphiphiles into monolayers of given optimal density is premised, and the free energy of the system is reduced to effective free energies of its internal interfaces. In the same spirit, random interface models for binary systems postulate self-assembly into bilayers and intro-... 

Figure 1. (A) Schematic illustration of a phospholipid molecule with hydrophilic head and hydrophobic tail. Cross-sectional view of (B) the micelle structure and (C) the bilayer sheet structure built through the self-assembly of the lipid molecules (A).

Self-assembly of phospholipids, such as phosphatidylcholine, a nutritional supplement, in the presence of calcium creates 50-500 nm large, continuous, solid, lipid bilayer sheets rolled into a spiral structure termed nanocochleates.f These can be made to envelope a lipid-soluble drug, such as amphotericin B, to exclude water and protect against pH, oxidation, light, enzymatic attack, hydrolysis, and extremes in temperature. The nanocochleates will convert to liposomes at a pH greater than 6.5 in a calcium deficient environment as is found in the cell (typically less than 1-2... 

Lipid bilayers form spontaneously by a self-assembly process. In other words, the structure of a bimolecular sheet is inherent in the structure of the constituent lipid molecules. The growth of lipid bilayers from phospholipids is rapid and spontaneous in water. Hydrophobic interactions are the major driving force for the formation of lipid bilayers. Recall that hydrophobic interactions also play a dominant role in the stacking of bases in nucleic... 

Nonionic block copolypeptides made of PEGylated L-lysine and L-leucine residues, PELLys- -PLLeu (Fig. lOh) have also been described [52], The copolymers adopted a rod-like conformation, due to the strong tendency of both segments to form a-helices (CD spectroscopy), and produced a variety of self-assembled structures in aqueous solution. Micrometer vesicles and sheet-like membranes could be obtained for copolymers with fractions of the hydrophobic leucine ranging from 10 to 30mol%. Conventional uncharged block copolymers of this composition would be expected to form spherical or cylindrical micelles. The assembly into bilayers was related to a secondary structure effect, as illustrated in Fig. 12. Accordingly, samples with the same composition but nonhelical chain conformation (CD),... 

Fuhrhop, J.-H., Krull, M. (1991). Self-assembling lipid membranes—from planar bilayer sheets to cloth-like aggregates of micellar fibers, Frontiers in Supramolecular Organic Chemistry and Photochemistry (Schneider, H.-J., Diirr, H., eds.), VCH, Weinheim. 

The surfaces that we consider are made of surfactants which are amphipathic molecules. They contain a hydrophilic (polar) head group and a hydrophobic (oily) hydrocarbon tail (or tails) shown schematically in Fig. 1. While the polar head "likes" water, the tails will be expelled from it (because of the hydrophobic interaction). For example, surfactants or lipids (e.g. biological surfactants with usually two tails) in water may self-assemble to form a bimolecular sheet which we call a membrane (Fig. la). A multilayer system then consists of stacks of alternating membranes and water as we show in Fig. la. If the constituent molecules are allowed to diffuse freely inside each two-dimensional bilayer (referred to as a fluid membrane), then the resulting multilayered structure is in the lamellar phase (which is in fact... 

Similarly, Lodge and coworkers have presented the formation of vesicles. However, these vesicles are not really common, since they incorporate hexagonally packed cylinders [12]. The aggregates were formed by the self-assembly of a miktoarm star terpolymer, where one of the arms is fluorinated. Interestingly, it was found that the assembly of these vesicles proceeds via the formation of metastable polygonal, faceted bilayer sheets. 

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