Vesicle forms, polymerized

In order to determine whether these surfactant vesicles were of polymerized vesicle forms, a 25% V/V ethanol (standard grade) was added to the three year old sample solution. Alcohols are known (34) to destroy surfactant vesicles derived from natural phospholipids, however, synthetically prepared polymerized vesicles are stable in as much as 25% (V/V) alcohol addition. Photomicrographs shown in Figures 7c and 7d indicate that these vesicles partially retain their stability (being mesomorphic) and therefore are suspected to be polymerized surfactants. Whether surfactant molecules of these vesicles are single or multipla bonds in tail, or in head groups remains to be seen. 

Poly(A) synthesis also occurred in the second system, but the product remained within the vesicles. Walde also determined the increase of the vesicle concentration, which corresponds to that expected for an autocatalytic process. In this experiment, the enzyme PNPase is first captured by the vesicle envelope, and in the second step, ADP and oleic anhydride are added the anhydride is hydrolysed to the acid. ADP passes through the vesicle double layer and is polymerized in the interior of the vesicle by PNPase to give poly(A). Hydrolysis of the anhydride causes a constant additional delivery of vesicle-forming material, so that the amount of vesicle present increases during the poly(A) synthesis. These experiments demonstrated a model for a minimal cell. Autocatalytically synthesised giant vesicles could be prepared under similar conditions and observed under a microscope (Wik et al., 1995). 

Several workers have introduced polymerizable groups into twin-tailed amphiphiles and formed vesicles by sonication. They then link the amphi-philes by initiating polymerization, either chemically or photochemically. The polymerized vesicles which are so generated show little tendency to fuse, and are much more stable than the vesicles formed by sonication or vaporization. They therefore have considerable potential for compartmentalizing reagents, although as with normal vesicles there is always the... 

The need for increased stabilities and for controllable permeabilities and morphologies led to the development of polymerized surfactant vesicles [55, 158-161]. Vesicle-forming surfactants haw been functionalized by vinyl, methacrylate, diacetylene, isocyano, and styrene groups in their hydrocarbon chains or headgroups. Accordingly, SUVs could be polymerized in their bilayers or across their headgroups. In the latter case, either the outer or both the outer and inner surfaces could be polymerized separately (Fig. 38). Photopolymerization links both surfaces selective polymerization of the external SUV surface is accomplished by the addition of a water-soluble initiator (potassium persulfate, for example) to the vesicle solution. 

Phospholipid vesicles form spontaneously when distilled water is swirled with dried phospholipids. This method of preparation results in a highly polydisperse array of multicompartment vesicles of various shapes. Extrusion through polymeric membranes decreases both the size and polydispersity of the vesicles. Ultrasonic agitation is the most widely used method for converting the lipid dispersion into single-compartment vesicles of small size. 

Isocyanides bearing ammonium side-chains 51 and 52 have been polymerized in the presence of nickel catalysts [72, 73]. The amphiphilic isocyanide 51 forms vesicles on dispersion in water. The isocyano groups located in the vesicle bilayers were polymerized by nickel capronate to form polymerized vesicles. The isocyanide 51 was also used in the preparation of polymerized vesicles containing metalloporphyrin components within the bilayer membrane [74]. The redox behavior of this membrane-bound cytochrome P-450 mimic has been investigated in detail. In addition to those bearing cationic side chains, isocyanides 53 and 54 bearing zwitterionic side chains were successfully used [75]. 

In other reports, solvents immiscible with water were used to form polymeric vesicles. Feijen and coworkers reported on vesicle formation for diblock copolymers of PEO and polyesters or poly(carbonates) with both water-miscible and immiscible solvents [155], In some cases it is very difficult to remove the organic solvent and experiments with vesicles formed in water-immiscible solvents are limited to some extent. 

Electron micrograph of clathrin cages, like those that surround clathrin-coated transport vesicles, formed by the in vitro polymerization of clathrin heavy and light chains. [John Heuser,... 

Fig. 2a, b. Templating vesicles a vesicle-forming polymerizable surfactants are fixed into place by polymerization (synergistic approach) b a hydrophobic monomer swells the interior of a vesicle bUayer and is subsequently polymerized to form a hoUow polymer shell (tran-scriptive approach)... 

Metallization of Polymerized Vesicles Formed from Mixtures of Zwitterlonic and Negatively Charged Phospholipids... 

Polymerized vesicles formed from mixtures of 1,2-bisCtricosa-10,12-diynoyl)-4n-gIycero-3-phosphohydroxyethanol or... 

The general approach used to attain such structures has been the synthesis of conventional vesicle-forming amphiphilic materials containing polymerizable functionalities in the molecule, vesicle formation, and subsequent polymerization, preferably by some nonintrusive means such as irradiation. In principle, the polymerizable functionality can be located at the end of the hydrophobic tail, centrally within the tail, or in association with the ionic or polar head group (Fig. 15.14). The choice of a preferred structure will probably be determined by the final needs of the system and the synthetic availability of the desired materials. 

The first approach in using vesicle membranes in nanoparticle synthesis was to polymerize vesicles formed from 9 1 and 1 1 mixtures of 1 and 2 in the presence of Pd(NH3)4Cl2. Palladium ions bound to negatively charged phospholipids in bilayer membranes had been previously demonstrated to serve as catalytic sites for electroless metallization (47). Light scattering revealed that bimodal populations of vesicles were formed both from the 9 1 (31 + 15 nm and 114 + 40 nm) and 1 1 (38 + 13 nm and 109 + 41 nm) mixtures. Exposure of the vesicles to UV radiation (254 nm) resulted in the reaction of 33 % + 6% of the lipid monomer when 10 % of 2 was present and 50% + 4% for vesicles containing 50% 2. The differences in the amount of reaction of monomer are probably due to both ion and pH effects. Non-cross linked polymerized vesicle membranes consist of many individual... 

If the diacetylene moiety is introduced into phospholipids or similar double-layered membrane and/or micelle/vesicle-forming molecular structures, these special forms of orgemisation may be polymerized as well providing a solid-like arrcungement of the reactive groups is attained. Vesicles and micelles of polydiacetylenes have been prepared in a great variety following this principle (12,16). 

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