Micelles globular

A colloid suspension of casein micelles, globular proteins, and lipoprotein particles... 

Since the PS reference sample is almost monodisperse, a cumulant analysis of that material would yield a very small Q, say Q < 0.03. That is, all the correction terms are negligible and Eqs. (17) collapse to Eqs. (12). But cumulant analysis is a useful way to handle practical samples such as pigments, inks, microemulsions, swollen micelles, globular proteins, and spherical virus particles, where there is a size distribution but one that is not very broad (say Q < 0.3). This analysis should be made for the milk data using a non-linem teast-squares fitting of Eq. (17a), neglecting /1.3 and all higher order terms. Report the F, D, and R values as well as the second cumulant /t2 aiid the polydispersity index Q. 

Possible candidates for aggregates can now be examined. For surfactant-water systems these have been restricted in the past to spherical micelles, non-spherical micelles (globular, cylindrical), vesicles, liposomes, bilayers, and for oil-water-surfactant systems spherical drops, normal or inverted (water in oil) or (oil in water). 

Figure C2.3.16. Adsorbed micelle stmctures (a) bilayer admicelle (b) spheroidal, globular adsorbed micelle.

The logarithm of the micellar molecular weight (M) and consequently the aggregation number of sodium dodecyl sulfate at 25°C in aqueous sodium chloride solutions is linearly related to the logarithm of the CMC plus the concentration of salt (Cs), both expressed in molar units, through two equations [116]. Below 0.45 M NaCl micelles are spherical or globular, and Eq. (18) applies ... 

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]. 

In our earlier efforts to synthesize dendritic amphiphiles, we described a triden-dron (43) which was prepared by a two-step (alkylation-amidation or triester-tris) reaction sequence applied to l,3,5-tris(bromomethyl)benzene [117]. TEM and light scattering experiments suggested that 43 aggregated by stacking of its hydrophilic exterior into a spherical array of ca. 20 nm (diameter) reminiscent of globular micelles. 

C. J. Hawker, K. L. Wooley, and J. M. J. Frechet, Unimolecular micelles and globular amphiphiles Dendritic macromolecules as novel recyclable solubilization agents, J. Chem. Soc. Perkin Trans. 1, 12 (1993) 1287-1297. 

Fig. 1 Schematic representation of a globular micelle O, hydrophilic head group VvV, hydrocarbon tail...

The peptide chain in globular proteins is folded into fairly compact conformations. Water-soluble enzymes are typical globular proteins which have most of the hydrophobic amino acid residues located in the interior and the hydrophilic residues located mainly at the surface in contact with solvent water. The average radii are 20-40 A (Boyer, 1970). It is clear that there are common morphological features between surfactant micelles and enzyme molecules. This fact has prompted many chemists to use micelles as enzyme models. However, it must be emphasized that micelles exist in dynamic equilibria with monomeric surfactant and their hydrophobic core is quite fluid, whereas enzyme molecules have precisely fixed three-dimensional structures. 

As discussed in the preceding sections, fluid, globular micelles are formed from monoalkyl surfactants, whereas the liquid-crystalline bilayer structure is formed from a variety of dialkyl amphiphiles and from single-chain amphiphiles with rigid hydrophobic segments. It may then be asked what structure is expected from amphiphiles with three alkyl chains. 

Charged polysoaps (polymer micelles) combine within a molecule structural characteristics of the conventional micelles and polyelectrolytes, and supposedly adopt globular conformations in aqueous media with the hydrophobic region inside and charged groups outside as in water-soluble proteins. Thus,... 

Explosive research activity is going on in micellar photochemistry. This is related to the development of artificial photosynthetic systems, and the anisotropic nature of globular micelles and bilayer membranes is used for conservation of excitation energy. The subject has been recently reviewed (Kalyanasundaram, 1978). 

Above a critical concentration certain amphiphiles may aggregate into membranous micelles, which are globular structures with a nonpolar interior and with a polar surface that interfaces the aqueous environment. At still higher concentrations micelles may fuse into multilamellar structures composed of bilayers. [138]... 

By fitting the conductivity data to the above equations, one usually finds a theoretical limit of 0.29. At this volume fraction, charge transfer laetween w/o globular micelles submitted to attractive interactions take place. Moreover, as we will see later, such systems contain easily deformable and flexible interfaces. 

One of the possible alternative to micelles are spherical dendrimers of diameter generally ranging between 5 and 10 nm. These are highly structured three-dimensional globular macromolecules composed of branched polymers covalently bonded to a central core [214]. Therefore, dendrimers are topologically similar to micelles, with the difference that the strnctnre of micelles is dynamic whereas that of dendrimers is static. Thus, unlike micelles, dendrimers are stable nnder a variety of experimental conditions. In addition, dendrimers have a defined nnmber of fnnctional end gronps that can be functionalized to prodnce psendostationary phases with different properties. Other psendostationary phases employed to address the limitations associated with the micellar phases mentioned above and to modnlate selectivity include water-soluble linear polymers, polymeric surfactants, and gemini snrfactant polymers. 

Enzymes and micelles resemble each other with respect to both structure (e.g., globular proteins and spherical aggregates) and catalytic activity. Probably the most common form of enzyme catalysis follows the mechanism known in biochemistry as Michaelis-Menton kinetics. In this the rate of the reaction increases with increasing substrate concentration, eventually leveling off. According to this mechanism, enzyme E and substrate A first react reversibly to form a complex EA, which then dissociates to form product P and regenerate the enzyme ... 

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