Micelle charging mechanism

Figure 16 Schematic illustration of micelle charging mechanism, a) Preferential ion adsorption b) weak-elcctrolytc-likc ionization c) collision between micelles.

Fig. 7. A plausible mechanism of tuning the activity of reduced glucose oxidase by micelle charge toward solubilized re-alkylferricenium cations.

When micelles (charged aggregate of molecules or particles) are formed with other species in the processing fluid, or when we deal with slurries, electrophoresis may become significant. Diffusion is an important transport mechanism, but it is a very slow process, so it is estimated to only have a minor influence on contaminant transport during electrochemical remediation. 

Figure 17 The clcctric-ficld-induced charging mechanism in inverse micelle systems.

In a word, the conductivity of inverse micelle systems is essentially controlled by ionic transportation under an electric field, and the ions are the charged inverse micelles. The electric-field-induced charging mechanism may well describe how inverse micelles are charged and well explain the observed experimental phenomena to date. Since the charged micelles arc major components, the dielectric property of the inverse micelle systems may simply controlled by the electrode polarization process, which will be described in next section. 

The importance of the material exchange process can hardly be overemphasized since it is the mechanism whereby the equUibrium miceUar size and polydispersity are reached and maintained, the reversed micelles of ionic surfactants become charged, polar and amphiphilic solubilizates are transported, and hydrophilic reactants can come in... 

Figure 7.22b shows that hydrophilic molecules, those with log Kj < 1, are much more permeable in octanol than in olive oil. The same may be said in comparison to 2% DOPC and dodecane. Octanol appears to enhance the permeability of hydrophilic molecules, compared to that of DOPC, dodecane, and olive oil. This is dramatically evident in Fig. 7.7, and is confirmed in Figs. 7.8c and 7.22b. The mechanism is not precisely known, but it is reasonable to suspect a shuttle service may be provided by the water clusters in octanol-based PAMPA (perhaps like an inverted micelle equivalent of endocytosis). Thus, it appears that charged molecules can be substantially permeable in the octanol PAMPA. However, do charged molecules permeate phospholipid bilayers to any appreciable extent We will return to this question later, and will cite evidence at least for a partial answer. 

In the discussions of micellar effects thus far there has been essentially no discussion of the possible effect of micellar charge upon reactivity in the micellar pseudophase. This is an interesting point because in most of the original discussions of micellar rate effects it was assumed that rate constants in micelles were affected by the presence of polar or ionic head groups. It is impracticable to seek an answer to this question for spontaneous reactions of anionic substrates because they bind weakly if at all to anionic micelles (p. 245). The problem can be examined for spontaneous unimolecular and water-catalysed reactions of non-ionic substrates in cationic and anionic micelles, and there appears to be a significant relation between reaction mechanism and the effect of micellar charge upon the rate of the spontaneous hydrolysis of micellar-bound substrates. 

Micellar catalytic methods were used to operate a choice between these two mechanisms. When an ion-radical has a charge opposite to that of the micelle surface, it is trapped by the micelle (Okamoto et al. 2001). In the presence of a surface-active compound, the aromatic substrate is nitrated in the very depth of a micelle, and the reaction rate depends on the local concentration of the nitrating agent on phase boundaries between the micelle and solution. A positively charged... 

For the anode process at comparable conditions, the yield of l,2-dimethoxy-2-nitrobenzene depends distinctly on the electrical natnre of a micelle. Namely, the yields are equal to 30, 40, and 70% for the positively, negatively, and nentrally charged micelles, respectively. The observed micellar effect corroborates the mechanism that inclndes 1,4-dimethoxybenzene cation-radical and nitrogen dioxide radical as reacting species. 

The effect of the local non-neutral environment (4) should be considered together with the detailed reaction mechanism of the hydrolysis reaction and together with the charge development in the activation process in particular. The electrostatically non-neutral environment offered by ionic micelles is generally thought to be the reason for the observation that rate-retarding effects exerted by anionic surfactants on this type of hydrolysis reaction are typically stronger than those by other surfactants. 

Counterion Binding. The fractional counterion binding on charged mixed micelles is of fundamental interest because it gives an indication of surface charge density which is related to the mechanism of mixing nonidealities in ionic/nonionic micelles. It is also a necessary... 

The best known CE buffer ingredient is sodium dodecyl sulfate (SDS) proposed by Terabe [10,11]. SDS forms micelles and the separation of neutral analytes is achieved by their partitioning between the buffer and the SDS micelles, that is, by their hydrophobicity. This is the basis of MEKC and the mobility of analytes correlates linearly well with logP values, where P is the octanol/water partition ratio. Many other buffer ingredients have been proposed. Most of them implement hydrophobic interactions between the analytes and the buffer ingredients but also ciral selectors have been used as well as various affinity probes. Interest in the ILs used as buffer additives in capillary electromigration methods is due to the fact that they could provide an alternative separation mechanism to two currently implemented mechanisms in CE which are based either on the charge to mass ratio or on the hydrophobicity of the analytes. 

Figure 11.16 Relationship between sorbed and dissolved amphi-phile concentrations (upper isotherm plot). These different parts of the isotherm reflect changes in the solid surface as sorption proceeds, possibly explainable by the following in portion (I) with low dissolved concentrations, sorption occurs via ion exchange and related mechanisms. At some point, sufficient near-surface concentration enhancement occurs that micelles form there (Ha) and rapid coagulation between oppositely charged micelles and the surface follows (lib). When the surface becomes fLilly coated with such micelles, additional sorption is stopped (III). In portion III, the solid surface charge is converted from one sign to the other, implying sorbates must become physically associated with the particle surface, as opposed to simply being present in the diffuse double layer or the vicinal water layer.

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