Freeze-fracture TEM

Figure 5.9 Transmission electron microscopy (TEM) photographs of 3 wt % fluorinated glu-cophospholipid (13) dispersion at room temperature (a) cryo TEM (b) freeze-fracture TEM. Reprinted from Ref. 50 with permission of Academic Press.

When concluding on the particle size and shape from images obtained by freeze fracture TEM, the fact that the particles are fractured randomly with respect to the localization of the fracture site within the particle and to orientation toward the fracture plane has to be taken into consideration. Most of the particle remains hidden from observation. Therefore, a sufficiently large number of particles have to be investigated to obtain a realistic impression. The determination of a particle size distribution will not be possible when the particles are of anisometric shape. 

Spicule formation takes place within the intracellular environment. The spicules, however, are much larger than individual cells. This is achieved by many cells fusing their membranes to enclose an extended space (called a syncytium) (Fig. 1.9). Spicule formation takes place inside a membrane delineated vacuole within this space [70, 71]. The size and the shape of the syncytium constantly increase and change during growth of the spicule [72, 73]. In fact, a freeze-fracture TEM study of the relation between the membrane and the growing spicule shows that the membrane is always juxtaposed to the spicule surface. There is thus no bulk solution within which the spicule forms [74], Thus spicule... 

Although freeze-fracture TEM provides direct visualization of ME structures, it is not currently in wide use probably due to the experimental difficulties associated with the technique. The points to consider when preparing conventional TEM replicas are the physical and chemical sample properties, freezing, cleaving, etching, replication, cleaning, and mounting steps of the procedure. 

Freeze-fracture TEM combined with nuclear magnetic resonance and quasielastic light scattering was used to study the microstructure of surfactant-water systems and dynamics of o/w and bicontinuous ME systems [41], The authors reported a rather abrupt transition from a discontinuous droplet (o/w) to bicontinuous (oil-and-water) microstructure occurring at low surfactant concentration, close to a three-phase region in the constructed phase diagram of pentaethylene glycol dodecyl ether, water, and octane [41],... 

Freeze-fracture reveals intravesicular details in three dimensions. Samples are frozen rapidly in liquid nitrogen and fractured to reveal internal structure. Additionally, lyotropic behavior of amphiphilic ABA triblock copolymers in water has been investigated using polarized light optical microscopy and freeze-fracture TEM [188],... 

A new polymeric amphiphile based on cationic poly(L-lysine), which was partially modified with hydrophobic palmitoyl chains and hydrophilic neutral methoxy-poly(ethylene glycol) (Fig. 7e), was introduced by Uchegbu et al. [38,39], In water in the presence of cholesterol, these copolymers assembled into vesicles with diameters ranging from 200 to 600 nm (DLS, freeze-fracture TEM), depending on the chemical composition of the copolymer and the length of the polypeptide backbone. More detailed information about the secondary structure of chains and the structure of vesicle membranes were not given. 

Nakache et al. attempted the polymerization of isodecyl acrylate (ISODAC) in anionic sodium di-2-ethylhexyl phosphate (SEHP) vesicles [9]. QLS and freeze fracture TEM were used to characterize the morphologies and no polymer phase separation was reported. Entrapment of hydrophobic moieties was possible in the polymerized vesicles, but hydrophiHc moieties could not be entrapped. Polymerized vesicles were apparently more temperature stable than unpolymerized structures and the addition of electrolytes induced polymer precipitation. 

Of all the characterization methods employed to study the morphologies of polymerized vesicles, cryo TEM is perhaps the most powerful. SEM, freeze fracture TEM, QLS, and probe diffusion studies alone cannot adequately distinguish between the polymer morphologies that have been proven to occur such as between hollow polymer shells and phase separated polymer-vesicle systems. 

Mixtures of hydrocarbon (CH) and fluorocarbon (CF) surfactants can provide important considerations for both theoretical and applied interest. Their properties have been reviewed. Similar to hydrogenated surfactant mixtures, the ones of hydrocarbon and fluorocarbon surfactants can also self-assemble into various aggregates, including mixed micelles and vesicles. However, completely different phase behavior and self-assembly of CH/CF surfactant mixtures can be observed because of the repellence between the two hydrophobic chains. Several advantaged techniques, including SANS, SAXS, F- and H-NMR, cryo-TEM, and Freeze-fracture TEM (FF-TEM) have been widely employed to characterize these systems. ... 

Figure 9.7. Freeze-fracture TEM images and corresponding ESR spectra of the lipid nanoparticles labeled with cholestane, 0.025%. Top SEN (glyceryl behenate), middle NEC (glyceryl behenate/MCT 8 2) and bottom emulsion (MCT). Reprinted from J. Control. Rel., Vol. 119, C. Braem et al., Interaction of drug molecules with carrier systems as studied by parelectric spectroscopy and electron spin resonance, 128-135, Copyright (2004), with permission from Elsevier.

The cationic fluorinated surfactant, FC-4, unlike other surfactants, forms micelles in the room temperature ionic liquid, l-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (bmimTf2N). Surface tension, freeze-fracture TEM, F NMR, H NMR, and FTIR measurements revealed that the FC-4 cation forms an ion pair with the Tf2N anion, the ion pairs undergo association to form premicellar aggregates, and the premicellar aggregates transform into micelles at the CMC. Reverse micelles are... 

Fig. 3 TEM photographs of an aqueous 3% H-Glu solution at different temperatures (a) 4°C cryo-TEM (b) 25 C freeze-fracture TEM...

Phase behavior, self-assembly, and rheology properties of 3-amino-propyltriethojq silane (APTES) and nonionic surfactant C12E04 in water were studied. The self-assembled structures were detected by means of small angle X-ray scattering (SAXS), cryo-transmission electron microscopy (ctyo-TEM), freeze-fracture TEM (FF-TEM), and H NMR measurements and the properties of self-assembled mixtures were obtained by rheology measurements. With a variation of the compn., different self-assembled structures were obtained. ... 

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