Acetone-water micelles

The solubility of the sodium salt of (meta-sulfonatophenyl)diphenylphos-phine, TPPMS in water is approximately 12 g/L at room temperature.5 It dissolves slightly in cold ethanol, but is soluble at elevated temperatures. It is virtually insoluble in acetone and aliphatic, aromatic, or chlorinated hydrocarbons, but is soluble at room temperature in tetrahydrofuran. The compound crystallizes with two waters of crystallizations however, the anhydrous form can also be obtained.3 Dry TPPMS is stable to air but is oxidized rapidly when wet, especially in basic aqueous solutions. It is a highly surfactant compound and forms aggregates and micelles in neutral aqueous... 

Nile Blue is used as a 0.01 to 0.1 %W/V aqueous solution and is simply added to or mixed with the substrate. The active component of the dye is actually a minor contaminant of the solution, not the blue-colored material [31]. The preparations are viewed with 450-490 nm excitation (an FTTC filter set. Figure 6). Emulsion stability is sometimes an issue in the presence of the cationic blue component of Nile Blue. In this case we use Nile Red, the pure form of this colorant. Nile Red solution is made fresh from a stock solution (0.1%W/V in acetone). This stock is added dropwise to water until a moderate blue color is seen and the solution is used immediately (it deteriorates quickly). For either colorant, the active molecule is fluorescent only when it is in a suitably hydrophobic environment. This usually means neutral lipid droplets [31] but other sites (aggregates of surfactants, the center of casein micelles, cutin plates in some seeds) are possibilities. 

FIGURE 28.1 Chemical modification of the protein with a water-insoluble reagent in the reverse micelles of Aerosol OT in octane. The protein molecule is entrapped in the reverse micelle surrounded by a cover of hydrated surfactant molecules. The water-insoluble reagent is located in the bulk organic phase and can be incorporated into the micelle surface layer coming into contact with the reactive group in the protein. After completion of the reaction the reverse micelle system is disintegrated and the protein is precipitated by cold acetone. 

A wide variety of organic solvents has been used to conduct bioconversions including nonpolar solvents such as isooctane, n-hexane, and toluene, in addition to methanol, acetone, and other water-miscible solvents. Dipolar aprotic solvents dimethylformamide (DMF) and dimethylsulfoxide (DMSO) are also compatible with many enzymes and are often used to enhance the solubility of substrates in combination with a nonpolar solvent. Tertiary alcohols such as f-butanol and t-amyl alcohol have been used for many lipase-mediated esterifications as the hindered tertiary alcohol is not typically a good substrate for most enzymes. It should be noted that the presence of small amounts of water is essential for the effective use of most biocatalysts in organic solvents. In some cases an enzyme may only require a monolayer of water molecules on its surface in order to operate. In other cases there may need to be enough water to form reverse micelles where the biocatalyst is contained within a predominantly aqueous... 

The critical micelle contraction values were obtained using the conductance method from the usual equivalent conductance vs. the square root of concentration plots. The apparatus has been described before (21). About 20 experimental points were obtained for each cmc determination. No cmc could be detected above 20 wt % of acetone and 30 wt % of n-propanol. Surfactants were studied in water - - acetone mixtures at 298.15 K in water + n-propanol mixtures at 308.15 K for comparison purposes with other systems (12) (see the Discussion section). 

Figure 2 compares the variation of a with solvent composition for related surfactants as obtained from emf (12) and conductivity data. The emf results (at 308.15 K) have made use of the Botre Equation (39), the validity of which has been questioned (40,41). However, the main characteristics of these results are that they qualitatively present the same micelle behavior, i.e. an increase of a with the addition of acetone or propanol to water. The increase is much faster with propanol using the emf method than with the conductivity method and as Miyagishi apparently could not determine an a value above mole fraction 0.02 we suspect some electrode problems in this particular case. In the water -f-acetone mixtures the two methods yield similar results. Nevertheless, we believe that the conductivity method is more reliable than the emf method. Finally, Mathews et al. (13) found no change of a with addition of organic molecules in apparent contradistinction with the present results. However, these authors used scarcely soluble additives (e.g., CCL ) and Figure 2 shows that a changes slowly with the addition of acetone or propanol. 

It is clear from this relation that AGt° is negative (see Table V) if there is no mixed-micelle formation (RT In Xf = 0), A In cmc must be positive the cmc must increase with the addition of organic solvent (as in the case of acetone). If there is some participation of the organic solvent in the micelle formation (as the case of n-propanol), then RT In Xf would be negative, the variation of A In cmc depends on the relative magnitude of AGt° and RT In Xf. From Figure 3 it can be concluded that RT In X/ > AG ° below Z2 — 0.03, but that RT In X/ < aG ° above this propanol composition. The case of SDS in water +... 

Table V. Aggregation Numbers of Ionic Micelles in Water + Acetone Mixtures at 298.15 K°...

Several methods for effective solubilization of drugs into polymer micelles have been developed (Fig. 2). The dialysis method (Fig. 2A) is most widely used for many polymeric micelle systems. The first step involves the dissolution of both polymer and drug in a water-miscible organic solvent such as acetonitrile, acetone, dimethylformamide, or ethanol. Then, the polymer-drug solution is dialyzed against water. As the organic... 

The use of modifiers occasionally improves the extraction process. Water as extractant can be modified with organic solvents such as methanol, acetone or acetonitrile in low proportions (< 5%) in order to decrease its dielectric constant — and hence its polarity — without the need for a drastic temperature increase [37]. Also, an acid or base can be used to alter the pH in those cases where it significantly influences the extraetion yield [29,46]. On the other hand, surfactants facilitate the extraction of non-polar compounds by formation of micelles [47]. Modifiers are less frequently used with extractants other than water. One example is the addition of sodium acetate to methanol to extract organotins (OTs) the additive increases the efficiency in two ways, namely (a) acetate ion by complexing OTs and (b) sodium ion through cation exchange of OTs sorbed to the clay fraction of sediments [21]. 

Antibodies can be utifized under a variety of non-physiological conditions and are excellently suited for preparative applications due to their intrinsic stability. We have found that antibodies catalyzing the retro-Diels-Alder reaction of 63 function equally well between pH 4 and pH 11. Aldolase antibody 72D4 operates in the presence of 10% acetone. Janda et al. have used an immobilized esterase antibody with up to 40% dimethylsulfoxide [110]. Esterase catalytic antibodies have been used in reverse micelles and in lipid-coated form to transform lipophilic substrates [111]. Catalytic antibodies can also be used in a biphasic alkane/water system [112]. The lipophilic substrate remains in the alkane phase where it does not undergo any reaction, which suppresses any uncatalyzed reaction. In case that the reaction product is still lipophilic and returns to the alkane phase, product inhibition is also suppressed under these conditions. 

The CAD in the surfactant micelle was prepared by spreading 1 mL of 1 mmol/L dye solution (prepared in acetone) to each 50 mL Pyrex glass tube and air-dried so that the dye was evenly coated onto the tube wall. Various amounts of stock surfactant solution and additives (if any) were added to each tube and diluted by distilled and deionized water to a predetermined concentration with a final volume of 25 mL. Samples were then mixed with the solution, sealed with a Teflon-lined screw cap, and shaken in a mechanical rotary shaker at 20°C for 24 hrs. Different initial pH levels were adjusted by sulphuric acid or sodium hydroxide so that the consequence of initial pH to the overall reaction rates can be realised. 

The importance of the hydrophobic effect in the self-association of amphiphilic solutes means that any factor which disrupts three-dimensional solvent structure also disrupts normal micelles. For example, addition of relatively large amounts of such organic solvents as ethanol or acetone to water makes the micelles smaller, and eventually they disappear and the surfactant behaves as a simple solute. On the other hand apolar solutes can enter the micelle and stabilize it and so lower the cmc, and added electrolytes also lower the cmc [15]. 

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