SDS micelles

Figure Bl.16.18. TREPR spectra observed after laser excitation of tetraphenylhydrazine in an SDS micelle at room temperature. Reprinted from [61].

Table 5.2. Analysis using the pseudophase model partition coefficients for 5.2 over CTAB or SDS micelles and water and second-order rate constants for the Diels-Alder reaction of 5.If and 5.1g with 5.2 in CTAB and SDS micelles at 25 C.

Calculations usirig this value afford a partition coefficient for 5.2 of 96 and a micellar second-order rate constant of 0.21 M" s" . This partition coefficient is higher than the corresponding values for SDS micelles and CTAB micelles given in Table 5.2. This trend is in agreement with literature data, that indicate that Cu(DS)2 micelles are able to solubilize 1.5 times as much benzene as SDS micelles . Most likely this enhanced solubilisation is a result of the higher counterion binding of Cu(DS)2... 

Retardation of back ET was also observed with phenanthrene solubilized in the SDS micelle (kb = 6.8 x 107 M-1 s-1) (see Fig. 13) [75]. However, as can be seen from Fig. 13, the transient yield of SPV- for the micellar system is extremely low, presumably because only a small fraction of SPV- can escape from the geminate ion pair. This finding implies that SPV preferably resides inside the micelle and that the electron transfer mainly takes place in the micelle, not across the charged surface. 

Human amylin, or islet amyloid polypeptide (hlAPP), is a 37-residue peptide hormone which forms both intracellular and extracellular (EC) amyloid deposits in the pancreas of most type II diabetic subjects. The core of the structure in the SDS micelle is an ot-helix that runs from about residues 5-28. Although the basic structural unit in the fibrils in... 

Pervushin KV, Orekhov V, Popov AI, Musina L, Arseniev AS (1994) Three-dimensional structure of (l-71)bacterioopsin solubilized in methanol/chloroform and SDS micelles determined by 15N-1H heteronuclear NMR spectroscopy. Eur J Biochem 219 571-583... 

It has also been observed that the ionic strength of the solution or the presence of SDS micelles will affect the rate of dissociation of iron-siderophore complexes (22,181). 

The reverse micelles stabilized by SDS retard the autoxidation of ethylbenzene [27]. It was proved that the SDS micelles catalyze hydroperoxide decomposition without the formation of free radicals. The introduction of cyclohexanol and cyclohexanone in the system decreases the rate of hydroperoxide decay (ethylbenzene, 363 K, [SDS] = 10 3mol L [cyclohexanol] =0.03 mol L-1, and [cyclohexanone] = 0.01 mol L 1 [27]). Such an effect proves that the decay of MePhCHOOH proceeds in the layer of polar molecules surrounding the micelle. The addition of alcohol or ketone lowers the hydroperoxide concentration in such a layer and, therefore, retards hydroperoxide decomposition. The surfactant AOT apparently creates such a layer around water moleculesthat is very thick and creates difficulties for the penetration of hydroperoxide molecules close to polar water. The phenomenology of micellar catalysis is close to that of heterogeneous catalysis and inhibition (see Chapters 10 and 20). 

With increasing temperature the CMC passes through a minimum (Fig. 15). The initial small decrease at low temperatures is due to a positive enthalpy of the micelle formation whereas the stronger increase of CMC towards higher temperatures is caused by a thermal perturbation of the emulsifier molecules in the micelles. The smaller influence of the temperature on the CMC in case of EUP indicates that these micelles are thermally more stable than SDS-micelles. 

Fig. 17.14. Separation principle in MECC. A compound (neutral or charged) is partitioned between the micellar and aqueous phase. A fully solubilized neutral compound migrates with the velocity of the micelles. A neutral compound with no affinity for the micelles migrates with the velocity of the EOF. A neutral compound with an affinity for both the micellar and the aqueous phase migrates with an intermediate velocity. (A) Schematic overview of the partitioning of compound (N the EOF moves toward the cathode and the typical SDS micelles toward the anode. (B) Diagram of the zone distribution within the capillary. (C) Reconstructed typical electropherogram.

Sukenik and Bergman, 1976). This material gives 2-octanol with 100% inversion of configuration in non-micellar and CTAB-micellar systems, but in the presence of the SDS micelle the reaction is strongly inhibited and there is a significant change (56% inversion) in stereochemistry. 

Figure 5.3 displays a comparison of one-dimensional spectra of a neuropeptide in the presence of either DPC or SDS micelles at various pH values. Note that the signal at approx. 8.6 ppm due to HE1 of His vanishes in SDS at a much higher pH compared to DPC. In general, spectra in SDS still yield reasonable quality at neutral pH in contrast to those recorded in DPC. 

In the SDS solutions containing 0.1-0.4 M NaCl, the turbidity increase is mainly due to micellar solubilization. The solubilization rate (di/dt) of the solutions seems to be in this order 0.1M> 0.2M> 0.3M> 0.4M NaCl. The final solubilization of the solutions is also in the same order. The size of the pure SDS micelles in solutions containing NaCl has been shown to increase with the NaCl concentration (Table II). Our instrument is not sensitive enough to distinguish the size between these small micelles at different NaCl concentrations. In the solubilization of oleic acid in 0.5% SDS solutions, the maximum seems to occur when the NaCl concentration is around 0.1 M. 

The structure and properties of water soluble dendrimers, such as 46, is, in itself, a very promising area of research due to their similarity with natural micellar systems. As can be seen from the two-dimensional representation of 46 the structure contains a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups (Fig. 12). However these dendritic micelles differ from traditional micelles in that they are static, covalently bound structures instead of dynamic associations of individual molecules. A number of studies have exploited this unique feature of dendritic micelles in the design of novel recyclable solubilization and extraction systems that may find great application in the recovery of organic materials from aqueous solutions [84,86-88]. These studies have also shown that dendritic micelles can solubilize hydrophobic molecules in aqueous solution to the same, if not greater, extent than traditional SDS micelles. The advantages of these dendritic micelles are that they do not suffer from a critical micelle concentration and therefore display solvation ability at nanomolar... 

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