Vesicle aqueous dispersions

Figures 9d,e show aqueous dispersions of vesicles. The smaller the vesicles, the less probable is an upcoming cross-fracture. Thus the question whether the vesicle is uni- or multilamellar can hardly be answered. At least for fluid vesicle dispersions it is possible to solve the problem with the help of cryotransmission electron microscopy.

Aqueous dispersions of polymerizable lipids and surfactants can be polymerized by UV irradiation (Fig. 18). In the case of diacetylenic lipids the transition from monomeric to polymeric bilayers can be observed visually and spectroscopically. This was first discussed by Hub, 9) and Chapman 20). As in monomolecular layers (3.2.2) short irradiation brings about the blue conformation of the poly(diacetylene) chain. In contrast, upon prolonged irradiation or upon heating blue vesicles above the phase transition temperature of the monomeric hydrated lipid the red form of the polymer is formed 23,120). The visible spectra of the red form in monolayers and liposomes are qualitatively identical (Fig. 19). 

Uchegbu, I.F., et al. 1996. Phase-transitions in aqueous dispersions of the hexadecyl diglycerol ether (c(16)g(2)) non-ionic surfactant, cholesterol and cholesteryl poly-24-oxyethylene ether-vesicles, tubules, discomes and micelles. STP Pharm Sci 6 33. 

Although the detailed nature of the surface of costal strips is not known, evidence from binding studies indicate that cations such as Co and Fe + are preferentially adsorbed onto these structures (9). Similar interactions have been shown with organic and colloidal materials (9). For example, phospholipid vesicles were shown to be closely attached to the surfaces of costal rods incubated in aqueous dispersions of phosphatidylcholine for 24 hr. Similar observations were made for costal rods incubated in solutions of colloidal silica. These results indicate that a range of interactions can take place on the surface of biogenic silica and such events may serve important functional roles, such as inhibition of dissolution and adhesion of components in the construction of microscopic structures. 

Figure 4,13 Aqueous dispersions of vesicles embrace one large bulk volume of water (region 1) and 8 vesicular regions with different spatial relationships to region 1 and different polarities. See text.

In the field of sensors, ion-binding block copolymers, which allow the formation of functionalized vesicles, could be of special interest. Vesicles sensitive to magnetic field were obtained from aqueous dispersion of hydrophobic iron oxide nanoparticles and block copolymers of PGA and PBD [272], Sachsenhofer and coworkers reported on the embedding of hydrophobic gold nanoparticles into PEO-PBD polymersomes [273]. Recently, polymer vesicles containing Ru(bpy )32+ units in the wall with a high potential for application in catalysis were introduced [274],... 

FIG. 12.8 Electron micrograph of a DHTDMAC aqueous dispersion. An intact vesicle is seen on the left, a cross section on the right, in which the lamellar structure is apparent (freeze fracture, magnification x2500). 

In aqueous dispersion DHTDMAC spontaneously adopts the vesicle structure. This is uncommon, as vesicle formation not only requires molecular characteristics (double fatty chain molecules, no strong repulsion) but usually also a strong... 

The yield of 02 in aqueous dispersions of small unilamellar vesicles and time-resolved IR phosphorescence show that 02 molecules diffuse through vesicle bilayers sufficiently quickly to establish equilibrium between hydrophilic and hydrophobic phases. 74... 

Aqueous dispersion of a triple-chain glutamic acid diester monoamide shows beautiful helical fibers under the light microscope, which slowly close to form tubules. Above 50°C the fibers melt and rearrange to vesicles. Twisted ribbons made of similar molecules with azobenzene in the hydrophobic core polymerize upon UV irradiation. This leads to the disappearance of an induced CD spectrum of surface adsorbed methyl orange. Alanine-derived amphiphiles with azobenzene units in the chain also form helical fibers in water. They absorb at 350 run when the number of the methylene groups in the outer chain is even and at 320 nm when odd. The chromophore in the fiber is presumably less stacked in even-numbered alkyl chain assemblies (Fig. 9.5.i). 

Li, Y.T. Armes, S.P. RAFT synthesis of sterically stabilized methacrylic nanolatexes and vesicles by aqueous dispersion polymerization. Angew. Chem. Int. Ed. 2010, 49 (24), 4042-4046. 

There are some potential applications in which the external phase is nonaqueous. Florence and co-workers (79, 80) and Albert et al. (81) described systems in which the aqueous suspension of vesicles are dispersed in the continuous oil phase. The technique was exercised both for the study of its use in drug-delivery systems and as immunological adjuvants, as well as an intrinsically interesting colloidal system. The system is an emulsion prepared from a dispersion of niosomes in water, re-emulsified in an oil using a surfactant mixture of low HUB to achieve a stable W/0 emul-... 

Most glycerolipids and sphingolipids in aqueous dispersions form closed vesicles, limited by lipids in the lamellar (bilayer) disposition. Depending on the lipid structure, different thermotropic transitions may be observed, of which the following are the most common. 

Yaghmur, A., Laggner, P., Ahngren, M. Rappolt, M. (2008). Self-assembly in monoelaidin aqueous dispersions direct vesicles to cubosomes transition. PloS one, 3(11), C31M. 

Fig. 2. Formation of vesicles by ultrasonication of aqueous dispersions of amphiphiles...

While single chain amphiphiles of structure I were mainly investigated in the crystalline state, mono- and/or multilayerscompounds of structure II and III 104-106,111-121) preferentially studied in aqueous dispersions of hi- and multi-lamellar layer aggregates (vesicles, liposomes). Amphiphiles of structure IV have only been studied in the bulk crystalline state A survey of the physicodiemical and physical studies on the individual compounds is given in Table 1. 

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