Solute concentrations, hexadecyltrimethylammonium bromide

Treiner, C., Chattopadhyay, A.K., Bury, R. Heat and solution of various alcohols in aqueous micellar solutions of hexadecyltrimethylammonium bromide as a function surfactant concentration the preferential solvation phenomenon. J. Colloid... 

A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na, and acesulfame-K), preservatives (sodium dehydroacetate, SA, salicyclic acid, BA, succinic acid, methyl-para-hydroxybenzoic acid, ethyl-para-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 ml aqueous tr-hydroxyisobutyric acid solution (pH 4.5) (2.2 3.4 or 2.4 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a Clg column with a flow rate of 1.0 ml/min and detection at 233 nm were used. This method was found to be very reproducible detection limits ranged from 0.15 to 3.00 p,g. The retention factor (k) of each additive could be affected by the concentrations of hexadecyltrimethylammonium bromide and a-hydroxyisobu-tyric acid and the pH and ratio of mobile phase. The presence of additives in dried roast beef and sugared fruit was determined. The method is suitable for routine analysis of additives in food samples (81). 

The viscosity starts to increase above the CMC and it is well established that the viscosity of a colloidal solution can give information on size and shape of the particles. From studies of the viscosity as a function of micellar concentration, the intrinsic viscosity may be obtained by extrapolation. The intrinsic viscosity depends on a shape factor, and the micelle specific volume and viscosity studies are therefore used to determine micelle shape and hydration. In many cases, these factors appear to be quite constant over a wide concentration range above the CMC. In other cases, such as hexadecyltrimethylammonium bromide (Fig. 2.9), dramatic increases in viscosity are observed at higher concentrations35). Studies of surfactants with low... 

Aqueous solution of SWNTs was suspended with different types of surfactants a) anionic (SDS) (CH3(CH2)ii(S04) Na+), b) cationic (hexadecyltrimethylammonium bromide (CTAB) (CH3(CH2)i5N+(CH3)3Br) and c) and non-ionic (Tween-80) H(Et-0)n0(C4H602CH0HCH20 CO(Ci8H23). Surfactants SDS and CTAB were purchased from Serva , Tween-80 from Shuchard (Germany). 0.05 mg/mL nanotube dispersion with surfactant was mixed and then the suspension was sonicated for 40 minutes. A concentration of surfactants in water solution was 1%. Water was prepared by distillation and then passed through Multi-Q system. The deionized water has resistance 18 MO. 

DNA from those sources rich in polysaccharides can be purified by the addition of CTAB (hexadecyltrimethylammonium bromide) before chloroform isoamyl alcohol extraction [6], After adjusting NaCl concentration to 0.7 M with 5 M NaCl in a DNA solution solution (ca. 0.05 mg/mL in TE), CTAB solution (10% CTAB in 0.7 M NaCl) is added so that the final concentration of CTAB is about 1%. The samples are incubated at 65°C for 10 minutes. It is important to keep the salt at a concentration of greater than 0.5 M so that the DNA does not precipitate as a CTAB-DNA complex. After the addition of an equal volume of chloroform-isoamyl alcohol (24 1 by volume) and gentle but complete mixing, the phases are separated by centrifugation for 10 minutes at 2000 x g. The interphase will appear as a white precipitate of CTAB-polysaccharides/protein complex. The aqueous phase containing DNA is transferred with a wide-bore pipette to a tube, and the CTAB chloroform-isoamyl alcohol extraction can be repeated until no cellular material is visible at the interphase. The DNA from the aqueous phase is precipitated with ethanol as described earlier, and any residual CTAB is washed with 70% ethanol washes. 

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. 

The conductance of the bromide counterion associated with the emulsifier micelles is 4.212x10% divided by the conductance readout (8). The concentration of hexadecyltrimethylammonium bromide in the micelles at a 1 3 molar ratio is (53.1-41.0)/4.212xl03 or 2.87x10"%. The total concentration of hexadecyltrimethylannnaniun bromide in the system is (0.15/364.6) (1000/25) or 1.65x10"%. The solute and micellar hexadecyltrimethylammonium bromide concentrations are subtracted from the total concentration to give the concentration in the crystalline rodlike particles. Table III gives these concentrations for the hexadecyltrimethylammonium bromide-cetyl alcohol ratios of 1 6 to 1 0.33. 

The actual solute and micellar concentrations of hexadecyltrimethylammonium bromide should be lower than the calculated values because the rodlike particles and micellar aggregates are assumed to be non-conducting. The negative value calculated for the concentration in rodlike particles for the 1 0.33 hexadecyltrimethylammonium bromide-cetyl alcohol molar ratio is essentially zero. Figure 2 shows that the benzene conductometric titration curve for the 1 0.33 hexadecyltrimethylammonium bromide-cetyl alcohol ratio is very close to that for the same concentration of hexa-decyltrimethylammonium bromide without cetyl alcohol (Figure 1). 

Figure 14.6. Phase diagrams of lyotropic mixtures (temperature versus amphiphile concentration), (a) Hexadecyltrimethylammonium bromide (CTAB)/water, after [50]. L isotropic micellar solution hexagonal phase V bicontinuous cubic phase L lamellar phase C several heterophasic regions containing crystalline components Nc nematic phase of rod-like micelles, (b) Cesium pentadecafluorooctanoate (CsPFO)/water, after [8].

Figure 6.42 Diagrams showing temperatures and surfactant concentration (Cs) at which (a) tartrazine and (b) amaranth-alkyltrimethylammonium bromide solutions separate into two or more phases. Dye concentration 15 mmol 1" hexadecyltrimethylammonium bromide system A tetradecyltrimethylammonium bromide cetrimide O dodecyltri-methylammonium bromide. From Barry and Gray [277] with permission.

Figure 6.43 Effect of surfactant concentration (Cs, mmol 1" ) and alkyl chain length on the specific viscosity ( ) of aqueous amaranth solutions, (a) surfactant above and (b) surfactant below the CMC and 1.5mmol/l dye, dodecyltrimethylammonium bromide , tetradecyltrimethylammonium bromide and, hexadecyltrimethylammonium bromide. Dotted regions represent coacervated systems. From [266] with permission.

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. 

Chloride is bound by the sols formed upon the extensive hydrolysis of Al(III) salt solutions. Binding to liquid crystal systems is also studied and chloride and bromide bind to the micelles formed by hexadecyltrimethylammonium salts. The relaxation rate changes when the micelles change from spheres to rods and there is a marked difference between the behavior of the two ions. Many enzymes bind chloride and this may affect their activity. Thus horse liver alcohol dehydrogenase is stabilized by low concentrations of Cl which binds to two sites, neither of which is Zn. Phosphate ligands compete for the binding sites. Interaction between Zn ",... 

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