Sodium dodecylsulfate, micelle

The order of elution when using MEKC is vitamin B3 (5.58 min), vitamin Be (6.59 min), vitamin 82 (8.81 min), and vitamin Bi (11.21 min). What conclusions can you make about the solubility of the B vitamins in the sodium dodecylsulfate micelles ... 

Hong et al. applied capillary EKC with dodecyltrimethylammonium-bromide/sodium dodecylsulfate (12.7/21.1 mM) vesicles to the separation of alkylphenones (Fig. 8A) and obtained better resolution than with sodium dodecylsulfate micelles (59). The logarithms of the retention factors for 20 neutral compounds of similar structures showed an excellent linear correlation with log Poct (R2 = 0.98). Similarly, Razak et al. (60) showed that the log capacity factors for interaction between neutral and positively charged analytes and cetyltrimethylammoniumbromide/sodium octylsulfate vesicles correlated linearly with the log Poa values. 

Aqueous micelles have diameters ranging typically from 0.5 to 5 nm, and being so small, do not scatter visible light and form transparent solutions. Figure 9.6 shows some basic parameters for aqueous micelles, relative to the well-known SDS (sodium dodecylsulfate). Micelles are thermodynamically stable, and this is a signihcant difference with respect to most large vesicle aggregates. 

Gesell, J., Zasloff, M. and Opella, S.J. (1997) Two-dimensional 1H NMR experiments show that the 23-residue magainin antibiotic peptide is an alpha-helix in dodecylphosphocholine micelles, sodium dodecylsulfate micelles, and trifluo-roethanol/water solution. J. Biomol. NMR 9, 127-135. 

Abraham, M.H., Chadha, H.S., Dixon, J.P., Rafols, C. and Treiner, C. (1995a) Hydrogen bonding. Part 40. Factors that influence the distribution of solutes between water and sodium dodecylsulfate micelles. J. Chem. Soc. Perkin Trans. 2, 887-894. 

An example of recovered distribution is shown in Figure B6.1.2. It concerns the distribution of lifetimes of 2,6-ANS solubilized in the outer core region of sodium dodecylsulfate micelles . In fact, the microheterogeneity of solubilized sites results in a distribution of lifetimes. 

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. 

Micellar catalysis of azo coupling reactions was first studied by Poindexter and McKay (1972). They investigated the reaction of a 4-nitrobenzenediazonium salt with 2-naphthol-6-sulfonic and 2-naphthol-3,6-disulfonic acid in the presence of sodium dodecylsulfate or hexadecyltrimethylammonium bromide. With both the anionic and cationic additives an inhibition (up to 15-fold) was observed. This result was to be expected on the basis of the principles of micellar catalysis, since the charges of the two reacting species are opposite. This is due to the fact that either of the reagents will, for electrostatic reasons, be excluded from the micelle. 

Subsequently, cationic rhodium catalysts are also found to be effective for the regio- and stereoselective hydrosilation of alkynes in aqueous media. Recently, Oshima et al. reported a rhodium-catalyzed hydrosilylation of alkynes in an aqueous micellar system. A combination of [RhCl(nbd)]2 and bis-(diphenylphosphi no)propanc (dppp) were shown to be effective for the ( >selective hydrosilation in the presence of sodium dodecylsulfate (SDS), an anionic surfactant, in water.86 An anionic surfactant is essential for this ( )-selective hydrosilation, possibly because anionic micelles are helpful for the formation of a cationic rhodium species via dissociation of the Rh-Cl bond. For example, Triton X-100, a neutral surfactant, gave nonstereoselective hydrosilation whereas methyltrioctylammonium chloride, a cationic surfactant, resulted in none of the hydrosilation products. It was also found that the selectivity can be switched from E to Z in the presence of sodium iodide (Eq. 4.47). 

The reverse emulsion stabilized by sodium dodecylsulfate (SDS, R0S03 Na+) retards the autoxidation of dodecane [24] and ethylbenzene [21,26,27]. The basis for this influence lies in the catalytic decomposition of hydroperoxides via the heterolytic mechanism. The decay of hydroperoxides under the action of SDS reverse micelles produces olefins with a yield of 24% (T=413 K, 0.02mol L 1 SDS, dodecane, [ROOH]0 = 0.08 mol L 1) [27], The thermal decay gives olefins in negligible amounts. The decay of hydroperoxides apparently occurs in the ionic layer of a micelle. Probably, it proceeds via the reaction of nucleophilic substitution in the polar layer of a micelle. 

The alternative noncovalent functionalization does not rely on chemical bonds but on weaker Coulomb, van der Waals or n-n interactions to connect CNTs to surface-active molecules such as surfactants, aromatics, biomolecules (e.g. DNA), polyelectrolytes and polymers. In most cases, this approach is used to improve the dispersion properties of CNTs [116], for example via charge repulsion between micelles of sodium dodecylsulfate [65] adsorbed on the CNT surface or a large solvation shell formed by neutral molecule (e.g. polyvinylpyrrolidone) [117] around the CNTs. 

Winsor [15] classified the phase equilibria of microemulsions into four types, now called Winsor I-IV microemulsions, illustrated in Fig. 15.5. Types I and II are two-phase systems where a surfactant rich phase, the microemulsion, is in equilibrium with an excess organic or aqueous phase, respectively. Type III is a three-phase system in which a W/O or an O/W microemulsion is in equilibrium with an excess of both the aqueous and the organic phase. Finally, type IV is a single isotropic phase. In many cases, the properties of the system components require the presence of a surfactant and a cosurfactant in the organic phase in order to achieve the formation of reverse micelles one example is the mixture of sodium dodecylsulfate and pentanol. 

To obtain a true k in MEEKC, it is important to trace the migration of the pseudostationary phase accurately. Sudan III, timepidium bromide, and quine, which have generally been used as tracers for micelles in MEKC, could not be employed as tracers for microemulsions consisting of sodium dodecylsulfate salt (SDS) or cetyltrimethylammonium bromide (CTAB), n-butanol and heptane (12). An iteration method based on a linear relationship between log k and the carbon number for alkylbenzenes (13) seems to provide a reasonable value of the migration time of the microemulsions. Dodecylbenzene shows a migration time larger than the value calculated by the iteration method and those of other hydrophobic compounds, such as phenanthrene, fluoranthrene, and Sudan III (Table 1). Methanol and ethanol were used as tracers for the aqueous phase. 

The anionic surfactant, sodium dodecylsulfate, SDS, was obtained from Merck, Darmstadt, Federal Republic of Germany. It has a stated purity of 99.99% and was used without further purification. Surface tension measurements gave no minimum in the surface tension at the critical micelle concentration, indicating that the sample did not contain highly surface active impurities. 

Figure 9.6 Aqueous micelles from sodium dodecylsulfate (SDS) and their physical properties. Average radius of a micelle (7 h), 2.2 nm average aggregation number, 62 approximate relative mass of a micelle (Mr), 1.8 x 10 average half-life of a SDS molecule in the micelle, 0.1 ms CMC (25 °C, H2O), 8.1 x 10 M i.e., monomer concentration by 10 g SDS 1 (35 mM), 2.3 g 1 ...

Electron transfer can be accomplished by quenching of a micelle trapped chromophore by ions capable of ion pairing with the micelle surface. For example, excited N-methylphenothiazine in sodium dodecylsulfate (SDS) micelles can exchange electrons with Cu(II). The photogenerated Cu(I) is rapidly displaced by Cu(II) from the aqueous phase so that intramicellar recombination is averted, Fig. 5 (266). Similarly, the quantum yield for formation of the pyrene radical cation via electron transfer to Cu(II) increases with micellar complexation from 0.25 at 0.05 M SDS to 0.60 at 0.8 M SDS (267). The electron transfer quenching of triplet thionine by aniline is also accelerated in reverse micelles by this mechanism (268). 

Figure 18.16 (a) Apparent molar volume and (b) apparent molar heat capacities for aqueous sodium dodecylsulfate at T = 298.15 K and /> = 0.1 MPa, graphed as a function of 1 /m. The insets give the values at low m where a second transition occurs in the micelle. 

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