CTAB precipitation

Endo-exo ratios of the micelle-catalysed reactions have been determined by adding 0.25 mmol of 5.1c and 0.5 mmol of 5.2 to a solution of 5 mmol of surfactant and 0.005 mmol of EDTA in 50 ml of water in carefully sealed 50 ml flasks. The solutions were stirred for 7 days at 26 C and subsequently freeze-dried. The SDS and CTAB containing reaction mixtures were stirred with 100 ml of ether. Filtration and evaporation of the ether afforded the crude product mixtures. Extraction of the Diels-Alder adducts from the freeze-dried reaction mixture containing C12E7 was performed by stirring with 50 ml of pentane. Cooling the solution to -18 C resulted in precipitation of the surfactant. Filtration and evaporation of the solvent afforded the adduct mixture. Endo-exo ratios... 

The liquids to be studied in this experiment are water, hexane, n-octanol and aqueous solutions of CTAB. It is recommended that they be measured in the order written, where the most critical with respect to contamination is first. The water used should be the best available, such as double distilled, and should be stored in a sealed flask before use. Pure samples of the other liquids should also be used as well as top-quality water to make up the CTAB solutions. The CTAB solutions should be measured at concentrations of 0.01, 0.1, 0.3, 0.6, 1 and 10 mM at a temperature above 21°C. CTAB has a Krafft temperature around 20°C - below this temperature the surfactant will precipitate from aqueous solution at the higher concentrations (see later). 

Mesoporous silica spheres were synthesized under the catalyst of ammonia in the mixed water-DMF solvent. In typical synthesis, 0.8 g (2.2 mmol) CTAB was heated slightly to allow it dissolved in the mixed solvent of 19.0 g (1.06 mol) water and 19.0 g (0.26 mol) DMF. After cooling to room temperature, 1.0 g (15 mmol) ammonia and 2.08 g (10 mmol) TEOS were added to the mixture with an electromagnetic stirrer and the stirring rate was kept about 480 rpm. After stirring for 16 to 25 h, the white solid product was Filtered on a Buchner funnel and allowed to dry in air at room temperature. The dried precipitate was immersed into highly diluted aqueous ammonia (pH 10) and kept at 100 °C for 2 days, the product was washed with distilled water and dried at room temperature in air. Then the product was calcined at 550 °C for 4h to remove the templates. 

Preparation A TEOS (Fluka) and PTES (Fluka) in a 4 1 molar ratio are mixed with an acidic solution of CTAB (CTAB/Si = 0.12 HC /H20/Si = 9.2/130/1), and stirred for several hours. The precipitate is then filtered, rinsed with distilled water and dried at 100°C. 

Synthesis of the corresponding non-mediated metal sulfides was accomplished using the above described procedures, but excluding the CTAB and ethanol components. The non-mediated precipitates rapidly settled from solution and thus were not believed to be nanocrystalline particle size distributions were not established as part of this study. 

The metallic Cu clusters on Mo02 (denoted Cu/Mo-CTAB) were completely inactive for CO PROX at 90 °C (Table 2.2). Metallic Cu clusters on ZnO (Cu/Zn-CTAB) and Si02 (Cu/Si-CTAB) were active for the methanol dehydrogenation but they were inactive for the PROX reaction. Similarly prepared Cu/Zr-CTAB, Cu/Fe-CTAB and Cu/Al-CTAB catalysts were also inactive for the PROX reaction. In contrast, the new Cu/Ce-CTAB catalyst exhibited tremendous activity with the feed C0/02/H2/He = 1 1 50 48 (mol.%) (Table 2.2), whereas the activities of conventional impregnated Cu/Ce02 and Cu/Ce203 catalysts and co-precipitated Cu-Ce catalysts were much lower. 

Baxendale, Evans and coworkers reported in 1946 that the polymerization of methyl methacrylate (MMA) in aqueous solution was characterized by homogeneous solution kinetics, i.e. where mutual termination of free radicals occurred, in spite of the fact that the polymer precipitated as a separate phase. Increases in the rates of polymerization upon the addition of the surfactant cetyl trimethyl ammonium bromide (CTAB) were attributed to the retardation of the rate of coagulation of particles, which was manifested in a reduction in the effective rate constant for mutual termination,... 

In a typical reaction, initial concentrations of NIPAM, styrene, CTAB, KPS, and TMEDA are 0.16 M, 5.24 mM, 17.3 mM, 0.34 mM, 0.67 mM, respectively. The styrene content (3.9 mol %) of the resultant segmented PNIPAM-seg-St copolymer can be determined by pyrolysis gas chromatography. The average degree of polymerization between two styrene segments can be over a wide range, mainly depending on the initial NIPAM/styrene ratio. The resultant copolymer can be purified and fractionated by a number of successive dissolution-and- precipitation cycles in a mixture of extremely dried... 

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. 

H. citelli, H. diminuta and H. microstoma, one of which is mitochondrial DNA (mtDNA) (394). The mtDNA of H. diminuta has been isolated (118) and has been shown to be a typical circular molecule. The characteristics of H. diminuta DNA are shown in Table 6.11. In contrast, E. multilocularis and E. granulosus produced two distinct DNA bands after fractionation in caesium chloride, but there was no evidence that the DNA from either band represented mtDNA (493). There is presumably so little mtDNA in comparison to nuclear DNA in these organisms that it is completely masked in preparations of total DNA by this method. That this is the case has been shown by a recent study (976), where a different procedure, based on the selective precipitation of nucleic acids by cetyltrimethylammonium bromide (CTAB), was employed to extract mtDNA from isolated mitochondria. Some 300 g and 50 g, respectively, of Taenia spp. and Echinococcus sp. tissue yielded approximately only 1 ng mtDNA. 

To isolate genomic DNA from E. coli, the cells are treated with lysozyme and then lysed by SDS in the presence of proteinase K. Proteinase K, which is active even in SDS solution, degrades proteins including nudeases. Cell debris, polysaccharides and unhydrolysed protein are removed by precipitation at room temperature with cetyltrimethylammonium bromide (CTAB). DNA is isolated from the supernatant by precipitation with alcohol. RNA can be removed from DNA preparations by incubation with DNase-free RNase. Further purification can be effected by a phenol/ chloroform/isoamyl alcohol (25 24 1) extraction, and/or by CsCl gradient centrifugation (see Sect. 4.3.4.2 ) to remove the remaining protein and RNA. 

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