Self-Assembled Structures in Applications

Bilayer structures provide a protective barrier around biological cells and inter-cellnlar entities. For that reason they form the matrix of biological membranes. Preparation of vesicles or liposomes in the presence of desired gnest molecules leads to a fraction of these molecnles entrapped inside the vesicles. The vesicles may be separated (e.g., by size-exclusion chromatography) from their snrroundings. 

Finally, the use of vesicles in DNA-transfection is mentioned. Complexes of negatively charged DNA fragments with cationic vesicles appear, in one way or another, capable of passing cell membranes. DNA transfection is used in gene therapy to block or to initiate synthesis of desired (poly)peptides. 

Microemulsions are widely used in cosmetics, cleansing products, foodstuffs, pharmaceuticals, and other products where ultrafine dispersion of one phase in another is desired. Other applications are tertiary oil recovery and polymer synthesis in a so-called emulsion polymerization process. 

In particular, in pharmaceuticals, agrochemicals, foodstuffs, and in biocatalysis functional components are preferably finely dispersed in an oily or an aqueous environment. Microemulsions are eminently suitable to serve that purpose, provided that the droplets are sufficiently large to solvate the functional molecules. By way of example, the relation between the radius of a water in oil microemulsion droplet and the number of water molecules it contains is given in Table 11.3. It shows that the droplet should have a size of at least a few nanometers to be able to dissolve (hydrate) polar compounds in its interior. 

TABLE 11.3 Number of Water Molecules in a Microemulsion Droplet as a Function of the Droplet Radius  

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