Aggregates globular

In the case of amphiphilic molecules, characterized by the coexistence of spatially separated apolar (alkyl chains) and polar moieties, both parts cooperate to drive the intermolecular aggregation. This simple but pivotal peculiarity makes amphiphilic molecules soluble in both polar and apolar solvents and able to realize, in suitable conditions, an impressive variety of molecular aggregates characterized by spatially separated apolar and polar domains, local order at short times and fluidity at long times, and differences in size, shape (linear or branched chains, cyclic or globular aggregates, extended fractal-like molecular networks), and lifetime. 

The structure of these globular aggregates is characterized by a micellar core formed by the hydrophilic heads of the surfactant molecules and a surrounding hydrophobic layer constituted by their opportunely arranged alkyl chains whereas their dynamics are characterized by conformational motions of heads and alkyl chains, frequent exchange of surfactant monomers between bulk solvent and micelle, and structural collapse of the aggregate leading to its dissolution, and vice versa [2-7]. 

Certain azacrown-appended cholesterol derivatives can form unique vesicular or lamellar structures in the absence and the presence of metal salts in aqueous solution.187-190 These superstructures created from the azacrown-appended cholesterol derivatives are useful as a template for the transcription into the silica structure. Azacrown-appended cholesterol gelator creates the novel multilayered spherical structure in acetic acid, whereas this gelator results in the fluffy globular aggregates in the presence of Pd(N03)2.191... 

Figure 7. Electron microscope photographs of PVC globular aggregates. Each photograph is 1.25 p wide...

Fig. 5 Synthesis of PVME particles by irradiation of phase-separated solutions. Above the phase transition temperature Tc, the polymer chains collapse to globular aggregates. The collapsed structures are fixed by electron beam irradiation to yield temperature-sensitive microgel particles...

Since the suggestion of Hartley in the 30 s that surfactants can self-assemble to form globular aggregates - micelles - in which the hydrophobic chains are essentially molten, it has been clear that in order for surfactant molecules to pack into aggregates, the molecular dimensions must be compatible. For... 

In order to sustain life, a bioartificial liver device should contain at least 10-30% of the normal liver mass (i.e., 150-450 g of cells in the case of an adult). In a bioartificial liver device, the animal or human liver cells can conceivably be cultured and used in several forms, including (i) independent single-cell suspensions (ii) spheroid (i.e., globular) aggregates of cells of 100-150 pm diameter (iii) cylindroid, rod-like aggregates of cells of 100-150 pm diameter (iv) encapsulated cells and (v) cells attached to solid surfaces, such as microcarriers, flat surfaces, and the inside or outside of hollow fibers. In order to facilitate mass transfer, a direct contact between the cells and the blood seems preferable. Among the various types of bioartificial liver device tested to date, four distinct groups can be identified [19] ... 

Chen L, Wei Y, Wang X, He R (2009) D-Ribosylated Tau forms globular aggregates with high cytotoxicity. CeU Mol Life Sd 66 2559-2571... 

A reversed I2 structure of globular aggregates packed in a cubic array also has been reported recently for some surfactants [46-49], despite previous doubts about their existence. Here it appears that the micelles are spherical, but of two different sizes (Fig. 8). For reversed micelles the alkyl chain packing constraints no longer limit the micelle diameter, hence the coexistence of two spherical micelles of different sizes is more plausible than with the Ij phases. The Fd3m phase is well established now [48, 49], but again, there appear to be several other distinct symmetries possible in the I2 region [48]. It is likely that the confusion in this area will be resolved in the next few years as the surfactant structures necessary for both I] and I2 phases are now clear, hence we can obtain the phases with many more surfactant types. 

Reviews of globular aggregates can be found in Statistical Thermodynamics of Micelles and Microemulsions, eds. S. Chen and R. Ra-jagopalan (Springer-Verlag, New York, 1990). 

The micromorphology of the ordered phases depends upon the conditions of crystallization and may be characteristic of that of flat dendrite crystals, lamellae, fibrillar and globular aggregates, and rhombohedric single crystals. The thickening of these crystals may be the result of either superimposition of lamellae or spiral growth originating from screw dislocations [281]. 

Soap molecules form globular aggregates in water called micelles, with their polar hydrophilic heads facing the water and their nonpolar lipophilic tails In the center. 

Besides naturally occurring phospholipids also synthetic surfactants were demonstrated to form globular aggregates. In general, double chain amphiphiles are better suited for vesicle formation than single chain ones. 

Many Al-acyl-aminoacids contain substituents with enhanced polarity, such as sulfonates, quaternary ammonium groups, and zwitterionic moieties, that endow them with interesting physicochemical properties, such as the ability to form vesicles [26] or globular aggregates [27]. In a similar way (see Scheme... 

Another interesting type of surfactant are double-chain amphiphiles. As an example of this surfactant-type hexadecyloctyldimethylammoniumbromide (CieCgDMABr) has been investigated. Here just above the cmc globular aggregates are formed whereas above a second transition concentration relatively short (150 A) rod-like micelles are formed [108]. 

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