Cetyltrimethylammonium bromide CTAB

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. 

Another standard industry method for surface area is based on the adsorption of cetyltrimethylammonium bromide (CTAB) from aqueous solution. This is ASTM method D3765-85 (2). This method measures the specific surface area of carbon black exclusive of the internal area contained in micropores that are too small to admit the large CTAB molecules. Eor mbber-grade nonporous blacks the CTAB method gives excellent agreement with nitrogen surface areas. 

The new way of quantitative determination of the ascorbic acid (AC) by means of ion-pair thin layer chromatography (TLC) in organo-aqueous mobile phases containing cetyltrimethylammonium bromide (CTAB) has been alaborated. 

The cycloadditions of cyclopentadiene 1 and its spiro-derivatives 109 and 110 with quinones 52, 111 and 112 (Scheme 4.20), carried out in water at 30 °C in the presence of 0.5% mol. of cetyltrimethylammonium bromide (CTAB), gave the endo adduct in about 3 h with good yield [72b]. With respect to the thermal Diels-Alder reaction, the great reaction rate enhancement in micellar medium (Scheme 4.20) can be ascribed to the increased concentration of the reactants in the micellar pseudophase where they are also more ordered. 

Table 2.7 lists techniques used to characterise carbon-blacks. Analysis of CB in rubber vulcanisates requires recovery of CB by digestion of the matrix followed by filtration, or by nonoxidative pyrolysis. Dispersion of CB within rubber products is usually assessed by the Cabot dispersion test, or by means of TEM. Kruse [46] has reviewed rubber microscopy, including the determination of the microstructure of CB in rubber compounds and vulcanisates and their qualitative and quantitative determination. Analysis of free CB features measurements of (i) particulate and aggregate size (SEM, TEM, XRD, AFM, STM) (ii) total surface area according to the BET method (ISO 4652), iodine adsorption (ISO 1304) or cetyltrimethylammonium bromide (CTAB) adsorption (ASTM D 3765) and (iii) external surface area, according to the dibutylphthalate (DBP) test (ASTM D 2414). TGA is an excellent technique for the quantification of CB in rubbers. However, it is very limited in being able to distinguish the different types of... 

Using cetyltrimethylammonium bromide (CTAB) as a surfactant, Krafft et al. have developed an efficient stoichiometric inter- and... 

The reductive coupling of allyl halides to 1,5-hexadiene at glassy C electrodes was catalyzed by tris(2, 2,-bipyridyl)cobalt(II) and tris(4,4 -dimethyl-2, 2/-bipyridyl)cobalt(II) in aqueous solutions of 0.1 M sodium dodecylsulfate (SDS) or 0.1 M cetyltrimethylammonium bromide (CTAB).48 An organocobalt(I) intermediate was observed by its separate voltammetric reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene... 

It is seen from Table 11.1 that surfactant cetyltrimethylammonium bromide (CTAB, RN MexBr ) exerts a positive catalytic effect on ethylbenzene autoxidation. The kinetic study of this phenomenon [21,27] showed that the acceleration was caused by the additional reaction of hydroperoxide with the bromide ion of CTAB to form free radicals [30],... 

See also Cetyltrimethylammonium bromide (CTAB) surface area antimicrobial used in cosmetics, 7 847 cosmetic surfactant, 7 834t Cetus, 11 12 Cetyl alcohol, 22 756 properties of commercial, 2 llt Cetyl bromide, physical properties of, 4 350t... 

Figure 4.23 Synthesis space diagram for a ternary system composed of tetraethylorthosilicate (TEOS), cetyltrimethylammonium bromide (CTAB), and sodium hydroxide (H, hexagonal phase [MCM-41] C, cubic phase [MCM-48] L, lamellar phase [MCM-50] H20/Si02 = 100, reaction temperature 100°C, reaction time 10 days). (Reprinted from Science, Vol. 267, A. Firouzi, D. Kumar, L.M. Bull, T. Besier, R Sieger, Q. Huo, S.A. Walker, J.A. Zasadzinski, C. Glinka, J. Nicol, D.l. Margolese, G.D. Stucky, B.F. Chmelka, Cooperative Organization of Inorganic-Surfactant and Biomimetic Assemblies, pp. 1138-1143. Copyright 1995. With permission of AAAS.)...

Other commonly used surfactants are cetyltrimethylammonium bromide (CTAB), Brij, Tween, Triton X and Siloxane polyether copolymer (PSPEO) [53]. 

Fig. 5.6 Example of electrostatic hybridization of cetyltrimethylammonium bromide (CTAB) capped Pt nanocubes with PSS-wrapped CNTs. Reprinted with permission from [81] (2008), Wiley.

The cleavage of /7-nitrophenyl alkanoates (222 n = 1-8) at high pH is modestly catalysed by micelles formed from cetyltrimethylammonium bromide (CTAB) in aqueous solution. Rate constants exhibit saturation behaviour with respect to [CTAB], consistent with substrate binding in the micelles. The strength of substrate binding and transition state binding to the micelles increases monotonically with the acyl chain length, and with exactly the same sensitivity. As a result, the extent of acceleration... 

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. 

If proteins are in contact with some detergents as sodium do-decylsulfate (SDS) or cetyltrimethylammonium bromide (CTAB) they become denaturated, e.g., their secondary, tertiary, and quaternary structures are destroyed. They get a rod-like shape and the amount of bound detergent is proportionate to the molar mass of the proteins These protein-detergent complexes have negative charges at slightly alkaline pH if SDS is used and their size (hydrodynamic radius) is approximately proportional to their molar... 

Check the proper connection by wires In SDS electrophoresis the migration is (mostly black wire) -I- (mostly red wire), when cetyltrimethylammonium bromide (CTAB) is used instead of SDS the direction is -I- ... 

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