Surface of micelle

FORMATION. Aqueous solutions of highly surface-active substances spontaneously tend to reduce interfacial energy of solute-solvent interactions by forming micelles. The critical micelle concentration (or, c.m.c.) is the threshold surfactant concentration, above which micelle formation (also known as micellization) is highly favorable. For sodium dodecyl sulfate, the c.m.c. is 5.6 mM at 0.01 M NaCl or about 3.1 mM at 0.03 M NaCl. The lower c.m.c. observed at higher salt concentration results from a reduction in repulsive forces among the ionic head groups on the surface of micelles made up of ionic surfactants. As would be expected for any entropy-driven process, micelle formation is less favorable as the temperature is lowered. 

In the case of mineral particles, by making them smaller and smaller, you gain a larger and larger total surface. Is this also true for the total surface of micelles and vesicles when they divide What about the total volume ... 

Molecular weight (hydrated) Molecular weight (dehydrated) Number of peptide chains Number of paticles per ml milk Surface of micelles per ml milk Mean free distance... 

Like as2-casein, /e-casein has two disulfide bonds which can form cross-links with /3-lactoglobulin. The N-terminal two-thirds of the molecule is hydrophobic and contains the two disulfide bonds. The C-termi-nal end is hydrophilic, polar, and charged. It varies in the number of attached carbohydrate moieties and has only one phosphate group. These characteristics make /c-casein ideal for the surface of casein micelles, where it is most often found. It is not susceptible to calcium ion binding, as the other caseins are, and when present on the surface of micelles, it protects the other caseins from calcium (McMahon and Brown 1984A Swaisgood 1982). 

A similar phenomenon of recognizing the strongest matrix in the process of polymerization was observed in the system where the surface of micelles SAS (in the system MA-PVPD-polyethyleneglycolmonolaurate) was used as one of the matrices 93). 

On balance, electron microscopy appears to show a distribution of K-casein throughout the micelle and, less certainly, a preferential location toward the periphery. No support is given to those experiments with immobilized reagents that appear to show that K-casein is located overwhelmingly on the external surface of micelles. 

Figure 2.4 Effect of size of interface on molecular recognition efficiency as exemplified by guanidinium-phosphate interaction (a) molecularly dispersed system (b) mesoscopic interface (surfaces of micelles and bilayers) (c) macroscopic interface (air-water interface).31 (Reprinted with permission from...

Adsorption of water is accompanied with swelling of wood. Since cellulose constitutes almost 50% of the wood substance, its fractional contribution to sorption is the highest. Swelling of wood is thus manifested by the adsorption of water by hydroxyl groups located on surface of micells and amorphous regions of cellulose, crystalline zones being impenetrable. Reduction in... 

Molecular Recognition and Chemistry in Restricted Reaction Spaces. Photophysics and Photoinduced Electron Transfer on the Surfaces of Micelles, Dendrimers and DNA [N. J. Turro, J. K. Barton, D. A. Tomalia, Acc. Chem. Res. 1991, 24, 332], Self-Assembly in Synthetic Routes to Molecular Devices. Biological Principles and Chemical Perspectives A Review [J. S. Lindsey, New J. Chem. 1991,15, 153], Amorphous molecular materials synthesis and properties of a novel starburst molecule, 4,4, 4 -tri(N-phenothiazinyl)triphenylamine [A. Higuchi, H. Inada, T. Kobata, Y. Shirota, Adv. Mat. (Weinheim, Ger.) 1991, 3(11), 549-550],... 

The best activity was observed for PCMEDDAC dissolved in n-hexane. Initial waxy crude oil behaves hke a viscoplastic fluid. Doped by PCMEDDAC, waxy oil approaches a Newtonian liquid, and the shear stress decreases considerably due to the modification of the paraffin crystals by the hydropho-bized macromolecules, hi oily environments, PCMEDDAC forms micelles consisting of a hydrophihc core (made of the betaine groups) and a hydrophobic corona (made of the dodecyl groups). The PPD mechanism of PCMEDDAC with respect to waxy crude oil suggests the adsorption of definite fractions of paraffin molecules on the surface of micelles and further retardation of agglomeration. 

Experimental studies of electron-transfer reactions occurring on the surface of micelles confirm the exponential character of the kinetics results from some of these studies are summarized in Table 4. The values of the surface diffusion coefficients estimated from Eq. 12 using the measured rate constants are close to values determined by using NMR relaxation and fluorescence measurements [44]. 

Conflicting hypotheses were also put forward with respect to the mechanism of interfacial activation. Desnuelle et al. (1960) were the first to suggest that a conformational change in the enzyme could be responsible for the enhancement of activity at the oil-water interface. There were also other hypotheses. For example. Wells (1974) suggested that the apparent activation of lipases is due to the orientation of the scissile ester bond on the surface of micelles Brockerhoff (1968), on the other hand, pointed to the possibility of differences in solvation of the ester bond in solution versus a lipid phase, whereas Brockman et al. (1973) postulated that a steep substrate concentration gradient at the interface may provide an explanation. 

Water is not an especially nucleophilic solvent, but water effectively solvates anionic leaving groups so that in water considerable ionization in the transition state should occur (72). The surfaces of micelles are water-rich (34, 35) and values of k+/k for hydrolyses of alkyl halides and arenesulfonates suggest that nucleophilic participation is dominant in reactions at methyl... 

The model of Slattery and Evard (171) explains many of the properties of micelles, including the events associated with clotting by rennin action. For example, it explains the crenated surface of micelles observed on electron micrographs (179), the subunit structure of casein micelles (180), the porous nature of micelles (177, 178) allowing syneresis by continued action of rennin on interior subunits, and the more or less random distribution of the caseins in the micelle (170,177, 178,183). 

Several different phospholipases can be distinguished on the basis of the site at which they hydrolyze phosphohpids (Figure 21.2). Phospholipase A2 is widely distributed in nature it is also being actively studied by biochemists interested in its structure and mode of action, which involves hydrolysis of phospholipids at the surface of micelles (Section 2.1). Phospholipase D occurs in spider venom and is responsible for the tissue damage that accompanies spider bites. Snake venoms also contain phospholipases the concentration of phospholipases is particularly high in venoms with comparatively low concentrations of the toxins (usually small peptides) that are characteristic of some kinds of venom. The lipid products of hydrolysis lyse red blood cells, preventing clot formation. Snakebite victims bleed to death in this situation. 

However, joining of K-casein to any of other caseins via its hydrophobic region leads to the termination of micelle growth because /c-casein just owns 1 hydrophobic segment and does not interact with CCP nanoclusters due to the lack of phosphoseiyl residues [2, 40]. This model is basically different in comparison with previous models in term of internal structure of micelles however, the cement role of CCP and location of K-casein on the surface of micelle are identical. 

In our opinion these examples demonstrate the value of our way of looking at the problem. Emphasis must finally be laid on one thing. In spite of the fact that we consider the phenomena in soap solutions throughout as equilibrium phenomena, we use terms as micelle , coacervate, and so on, which on account of their colloid chemical past call forth ideas of strictly determined boundary surfaces (Freundlich s Kapillarchemie). We wish however to retain these terms without crediting the boundary surface of micelle-equilibrium liquid with a separate significance. We thus look upon a micelle in a soap solution as a formation which is in equilibrium with the rest of the solution but which through its large dimensions and its structure has properties which the soap molecule as such does not possess. It is only with this restriction that we wish to continue to speak of micelles, coacervates, etc. 

Recent results on silicate MCM-41 have revealed that the liquid crystalline phase is not present in the synthesis mixture during the formation of MCM-41 [9,10]. More likely randomly oriented rod-like micelles interact with silicate species to yield two or three monolayers of silica encapsulating the external surface of micelles. Subsequently, these composite species spontaneously assemble into the long-range ordered structure characteristic of MCM-41. 

Theoretical works describe some models of mutual diffusion of reactants within the micelles and over the surface of micelles [56-62]. The general conclusion was that, but for a very short initial period of time, the mutual diffusion of the reactants obeys a single-exponential law. 

P. Mukerjee and A. Ray, Charge-transfer interactions and the polarity at the surface of micelles of long-chain pyridinium iodides, 1966, J. Phys. Chem. 70, 2144—2149. 

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