Hexadecyltrimethylammonium dodecyl

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

The Diels-Alder reaction of methyl methacrylate with cyclopentadiene was studied [72] with solutions from three different regions of the pseudophase diagram for toluene, water and 2-propanol, in the absence and in the presence of surfactant [sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB)]. The composition of the three solutions (Table 6.11) corresponds to a W/O-fiE (A), a solution of small aggregates (B) and a normal ternary solution (C). The diastereoselectivity was practically constant in the absence and in the presence of surfactant a slight increase of endo adduct was observed in the C medium in the presence of surfactant. This suggests that the reaction probably occurs in the interphase and that the transition state has a similar environment in all three media. 

It is noteworthy that the indenyl complex RuCl(q5-C9H7)(PPh3)2 provides an efficient catalyst precursor for the anti-Markovnikov hydration of terminal alkynes in aqueous media and micellar solutions with either anionic (sodium dodecyl sulfate) or cationic (hexadecyltrimethylammonium bromide) surfactants [32]. This system can be applied to the hydration of propargylic alcohols to selectively produce /J-hydroxyaldehydes (Eq. 4). 

SDS sodium dodecyl sulfate HDTC1 hexadecyltrimethylammonium chloride HDTBr hexadecyltrimethylammonium bromide Brij 35 polyoxyethylene (23) lauryl ether DTAC dodecyltrimethylammonium chloride TTAC1 tetradecyltrimethylammonium chloride HDPB hexadecylpyridinium bromide KDC potassium decanoate SPFO sodium perfluorooctanoate KTC potassium tetradecanoate... 

Micellar ratalysis of azo >upling re tions is possible it has been studied recently by Poindexter and McKay and in more detail by Rufer The first mentioned authom studied the reaction of 4-nitroben nediazonium salt with 2-naphthol-6-sulfonic and 2-naphthol-3,6-disulfonic adds in the presence of sodium dodecyl-sulfate and hexadecyltrimethylammonium bromide. With the anionic as well as with the cationic additive an inhibition (up to 15-fold) was observed. This result was to be expected based on the prindples of micellar catalysis, since the charges of the two reacting spedes are opposite to one another. 

Aggregation to form micelles usually occurs over a very narrow concentration range as the total concentration is raised, and is associated with an abrupt change in the turbidity of the solution. The concentration of the surfactant that corresponds to the point at which micelles first form in the solution (critical micelle concentration, cmc) usually decreases with increase in the hydrocarbon chain length. The cmc for sodium dodecyl sulfate (SDS), a 12-carbon anionic surfactant, is 8.1 mM and the cmc for hexadecyltrimethylammonium bromide [cetyltrimethylammonium bromide (CTAB)], a 16-carbon cationic surfactant, is 0.92 mM. In general, the number of surfactant monomers per micelle, i.e., its aggregation number, can vary from less than 10 to more than 100. 

Average value obtained using 2,6-diphenyl-4-(2,4,6-triphenyl-l-pyridinio)phenoxide, 1-hexadecyl-4-[(oxocyclohexadienylidene)ethylidene]-l,4-dihydropyridine, l-hexadecyl-5-hydroxyquinoline and l-hexadecyl-6-hydroxyquinoline, average deviation <9 % calculated from [47d]. Abbreviations SDS = sodium dodecyl sulfate DBS = dodecyl benzenesulfonate CTAC = hexadecyltri-methylammonium chloride CTAB = hexadecyltrimethylammonium bromide DTAC = dodecyl-trimethylammonium chloride DTAB = dodecyltrimethylammonium bromide DHP = dihexadecyl phosphate DDDAB = didodecyldimethylammonium bromide DMPC = dimyristoylphosphati-dylcholine DPPC = dipalmitoylphosphatidylcholine POPC = l-palmitoyl-2-oleoylphosphati-dylcholine PCA = phosphatidic acid. 

Abbreviations CTAB = hexadecyltrimethylammonium bromide SHDTE = sodium hexadecyl-trioxyethylene sulfate SDS = sodium dodecyl sulfate DTAB = dodecyltrimethylammonium bromide TTAB = tetradecyltrimethylammonium bromide bpy = 2,2 -bipyridyl MV- = N,N -dimethyl-4,4 -bipyridinium Rh = octadecylrhodamine DMA = A, .V-dimethylaniline. 

SDS sodium dodecyl sulfate STS sodium tetradecyl sulfate SHS sodium hexadecyl sulfate TTAC tetradecyltrimethylammonium chloride CTAC hexadecyltrimethylammonium chloride DMPC dimyristoyl phosphatidylcholine DPPC dipalmitoyl phosphatidylcholine. Exciplex/monomer fluorescence intensity ratio, measured at the exciplex emission maximum (/ ) and at 310 nm (I). 

Tomasic, V., Stefanic, I., and Filipovic-Vincekovic, N., Adsorption, association, and precipitation in hexadecyltrimethylammonium bromide/sodium dodecyl snlfate mixtures. Colloid Polym. Sci, 277, 153-163 (1999). 

Micellar catalysis has been investigated for the aquation of the cis- and trans-[Co(en)aCla]+ ions in the presence of sodium dodecyl sulphate. This negatively charged micelle affects the reaction rate, but non-catalytically. The positively charged micellar agent hexadecyltrimethylammonium bromide has no effect. 

FIG. 5 Thermograms of hexadecyltrimethylammonium decyl sulfate (CTADeS), hexa-decyltrimethylammonium dodecyl sulfate (CTADDS), and hexadecyltrimethylammonium tetradecyl sulfate (CTATDS) obtained by differential scanning calorimetry during heating (full line) and cooling (dashed hne) scans. 

The forward reaction of Equation 3.4 is diffusion controlled and consequently its rate will vary inversely with the viscosity of the medium. The ratio /e/f m is commonly used as a measure of the ease of excimer formation, and /m being the excimer and monomer emission, respectively. Excimer formation in micellar systems requires at least two probe molecules per micelle for the reaction of Equation 3.4 to occur within the micelles. The ratio /e//m is thus dependent on the distribution of probe molecules among the micelles which is assumed to follow a Poisson distribution. At the commonly used probe/surfactant molar ratio of 0.01, Zachariasse [13] calculates from Poisson statistics that 27% of sodium dodecyl sulphate (NaDS) micelles are more than singly occupied. There is difficulty in the interpretation of the fluorescence data since excimer emission occurs alongside the partly quenched monomer fluorescence in doubly or higher occupied micelles, whereas singly occupied micelles show only unquenched monomer fluorescence. This situation leads to uncertainty in the calculated microviscosity and may explain the anomalous value of 150 cP proposed by Pownall and Smith [11] for the micro viscosity of the micellar core of hexadecyltrimethylammonium bromide. 

The Cotton effect of the probe when incorporated in micelles of both hexadecyltrimethylammonium bromide and sodium dodecyl sulphate more closely resembles that of water than heptane, suggesting an aqueous environment for the solubilized probe. 

FIGURE 3.1 Some examples of common surfactant molecules, from top anionic surfactant SDS (sodium dodecyl sulfate, also commonly known as sodium lauryl sulfate) cationic surfactants CTAB (hexadecyltrimethylammonium bromide), DDAB (didecyidimethylammonium bromide) commercial nonionic detergent Triton X-100 and zwitterionic lipid DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine). 

Surfactants are those molecules that comprise both hydrophilic and hydrophobic groups simultaneously. The hydrophilic groups can be either ionic (e.g., -SOj, -SO3, -COOH, and -N(CHsIj) or nonionic (e.g., -0-(CH2-CH2-0) -H). As to the hydrophobic groups, the most widely used ones are the alkyl chains (-C H2 +i) and arakyl chains (-C H2 +i-C6H4-). Representative surfactants include anionic sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), sodium bis(2-ethylhexyl) sulfosuccinate, sodium stearate, cationic hexadecyltrimethylammonium bromide, and nonionic i-octophenol polyethoxylate with an average of 40 monomeric units of ethylene oxide per molecule. Such amphoteric species tend to diffuse toward the interface between the oily and aqueous phases and reside therein. 

Figure 6.6. Changes in the MTR with pressure for typical ionic surfactants (a) sodium decyl sulfate, (b) sodium dodecyl sulfate, (c) sodium tetradecyl sulfate, (d) sodium hexadecyl sulfate, (e) hexadecyltrimethylammonium bromide. (Reproduced with permission of the American Chemical Society.)...

In its deprotonated form, cinnamic acid already presents some prerequisites of surfactants and is easily incorporated in reversed micelles, as demonstrated bySawaki and co-workers " " and others.Then-results support the view that increased local concentration and alignment can be achieved at micellar interfaces. Substantially higher conversion of cinnamate to its photodimers is observed upon irradiation of reversed micelles formed by laurylammonium or hexadecyltrimethylammonium cinnamate in carbon tetrachloride. The photoproducts are mainly the P- and 5-truxinates, consistent with the requirements imposed by the assembly for the formation of contact ion pairs. Unfortunately, these are also the main products observed by Reiser upon irradiation of ethyl cinnamate (albeit in different proportions). Interestingly, however, the observed dimer distribution varies as a function of added water that is proposed to He near the ion pair interface. Similar results were also obtained for indene-2-carboxylate and using sodium dodecyl sulfate microemulsions in water. " The photodimerization of coumarin in micelles has been investigated by Ramamurthy and co-workers. ... 

Tamura and Aida reported the unique influence of shape and volume of inner micellar space on product distribution. They irradiated ACN in aqueous sodium octyl sulfate, decyl sulfate, dodecyl sulfate, and hexadecyltrimethylammonium bromide under pressures up to 150 MPa. Pressure enhanced the dimerization reaction in all micellar systems due to the formation of a van der Waals dimer in the ground state. Plots of the consumed ACN vs. concentration of micelles exhibited a minimum under constant concentration (9.7 mmol kg" ) of ACN. Thus, the number of micelles in the solution increases with increase of surfactant concentration and, as a result, the number of ACN molecules solubilized per micelle decreases. This leads to a decrease of probabihty of collision between ACN molecules that undergo bimolecular reaction. Viscosity measurements indicate that spherical micelles start to aggregate and form rod-shaped micelles with larger volumes at ca. 9 wt% of micelle, which exactly coincides with the minimum concentration of micelles. At concentrations of micelles higher than the minimum, the number of ACN molecules included in a micelle increases due to aggregation of spherical micelles into rod-shaped micelles, leading to enhanced dimerization of ACN. 

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