Micelle comparison

Chiral imidazole-functionalized micelles. Comparison of rates and enantioselectivities... 

Lagueerr, A., Stoll, S., Kirton, G. and Dubin, P.L. (2003). Interactions of a polyanion with a cationic micelle comparison of Monte Carlo simulations with experiment. J. Phys. Chem. B, 107, 8056-8065. 

Students then prepare three aqueous samples - one below the critical micelle concentration (or cmc, the concentration required for micelles to form), one above cmc, and one significantly above cmc. The addition of a fluorescent probe (with a visible emission that is sensitive to the polarity of its environment) presents students with a visible cue of the formation of micelles using a handheld ultraviolet lamp. At low surfactant concentration, the luminescent probe is in a polar environment (water), while above cmc it becomes trapped within the non-polar interior of the micelle. Comparison of the color and intensity of samples below and above cmc provides evidence for the notable difference of environment in the immediate vicinity of the probe (see Figure 2 b-c). The third sample becomes quite viscous, which provides evidence for the presence of elongated worm-like micelles that become entangled at high concentration (55). 

Ninomiya, R., Matsuoka, K., Moroi, Y. Micelle formation of sodium chenodeox-ycholate and solubilization into the micelles comparison with other unconjugated bile salts. Biochim. Biophys Acta 2003, 1634(3), 116-125. 

In this section the influence of micelles of cetyltrimethylammonium bromide (CTAB), sodium dodecylsulfate (SDS) and dodecyl heptaoxyethylene ether (C12E7) on the Diels-Alder reaction of 5.1a-g with 5.2 in the absence of Lewis-add catalysts is described (see Scheme 5.1). Note that the dienophiles can be divided into nonionic (5.1a-e), anionic (5.If) and cationic (5.1g) species. A comparison of the effect of nonionic (C12E7), anionic (SDS) and cationic (CTAB) micelles on the rates of their reaction with 5.2 will assess of the importance of electrostatic interactions in micellar catalysis or inhibition. 

Table 5.2 shows that the partition coefficients of 5.2 over SDS or CTAB micelles and water are similar. Comparison of the rate constants in the micellar pseudophase calculated using the... 

In contrast to SDS, CTAB and C12E7, CufDSjz micelles catalyse the Diels-Alder reaction between 1 and 2 with enzyme-like efficiency, leading to rate enhancements up to 1.8-10 compared to the reaction in acetonitrile. This results primarily from the essentially complete complexation off to the copper ions at the micellar surface. Comparison of the partition coefficients of 2 over the water phase and the micellar pseudophase, as derived from kinetic analysis using the pseudophase model, reveals a higher affinity of 2 for Cu(DS)2 than for SDS and CTAB. The inhibitory effect resulting from spatial separation of la-g and 2 is likely to be at least less pronoimced for Cu(DS)2 than for the other surfactants. 

In contrast to statics, the relaxational kinetics of living polymers and of giant wormlike micelles is unique (and different in both cases). It is entirely determined by the processes of scission/recombination and results in a nonlinear approach to equilibrium. A comparison of simulational results and laboratory observations in this respect is still missing and would be highly desirable. 

As a result of the micellar environment, enzymes and proteins acquire novel conformational and/or dynamic properties, which has led to an interesting research perspective from both the biophysical and the biotechnological points of view [173-175], From the comparison of some properties of catalase and horseradish peroxidase solubilized in wa-ter/AOT/n-heptane microemulsions with those in an aqueous solution of AOT it was ascertained that the secondary structure of catalase significantly changes in the presence of an aqueous micellar solution of AOT, whereas in AOT/n-heptane reverse micelles it does not change. On the other hand, AOT has no effect on horseradish peroxidase in aqueous solution, whereas slight changes in the secondary structure of horseradish peroxidase in AOT/n-heptane reverse micelles occur [176],... 

Figure 21. Room-temperature optical-absorption spectra of various digestively ripened Au colloids prepared by the inverse-micelle method. For comparison, the spectrum of the as-prepared colloid is also displayed. (Reprinted with permission from Ref [49], 2002, American Chemical Society.)...

Yang and Russell [7] made comparison of lipase-catalyzed hydrolysis in three different systems organic, biphasic, and reversed micelles. They affirmed that water content is an important factor that distinctly affects every system. Their results demonstrated that activity of lipase in organic-aqueous biphasic media was lower than that obtained in reversed micelles. However, better productivities were obtained in biphasic media, which were the most suitable environment. 

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. 

LJ Naylor, V Bakatselou, JB Dressman. Comparison of the mechanism of dissolution of hydrocortisone in simple and mixed micelle systems. Pharm Res 10 865-870, 1993. 

For comparison, included in Table 14.3 are the kq values obtained in detergent micelles along with kq values obtained in homogeneous solvent benzene. As can be seen, the second-order rate constant for 02 quenching in a liposomal environment is a factor of 4 lower for (3-CAR compared to the second-order rate constant obtained in the aromatic solvent. While, there is a marked 80-130 fold difference between the kq values determined in liposomal environments compared to the kq values determined in the aromatic solvent for the XANs. 

The physicochemical data underline the striking influence of the dicyclopentadienyl unit on the properties of these silicone surfactants. In comparison to conventional products [7], the critical micelle formation concentration was lowered for up to two orders of magnitude whereas the minimum surface tension reached rose only slightly. The data collected indicate that the type of surfactant has been changed from the initial "effective" to a more "efficient" one. 

SAXS studies are sensitive mainly to the inorganic species [6,7] and offer then a complementary vision of the hybrid micelles with respect to SANS. A comparison between SAXS and SANS is given in part 3. 

Figure 5 Comparison between SAXS and SANS. The two experimental scattering curves are given in absolute units (cm1) for PI23 micelles in D20 at 40°C, at a volume fraction of 2.6 %.

This hypothesis is satisfactory for nucleophilic reactions of cyanide and bromide ion in cationic micelles (Bunton et al., 1980a Bunton and Romsted, 1982) and of the hydronium ion in anionic micelles (Bunton et al., 1979). As predicted, the overall rate constant follows the uptake of the organic substrate and becomes constant once all the substrate is fully bound. Addition of the ionic reagent also has little effect upon the overall reaction rate, again as predicted. Under these conditions of complete substrate binding the first-order rate constant is given by (8), and, where comparisons have been made for reaction in a reactive-ion micelle and in solutions... 

For a number of reactions in functional micelles and comicelles second-order rate constants are similar in micelles and in water. Except for aromatic nucleophilic substitution they are slightly smaller in the micelles than in water, and the pattern of behavior is exactly that found for reactions of organic nucleophilic anions in non-functional micelles. Some examples of these comparisons are in Table 9. 

The basicity constants in water and micelles then have the same units (M 1), and values of K and Kb are not very different for arenimidazoles and nitroindoles under a variety of conditions (Table 10). The comparisons suggest that inherent basicities are not very different in water and cationic micelles, but, as with second-order rate constants of bimolecular reactions (Section 5), there is a limited degree of specificity because K /Kb is slightly larger for the nitroindoles than for the arenimidazoles, almost certainly because of interactions between the cationic micellar head groups and the indicator anions. 

Comparison of rate constants of reactions in micelles and in non-micellar assemblies... 

Hydroxamate-, imidazole- and thiol-functionalized micelles and chymotrypsin. Rate comparisons... 

---