Solubilization temperature effect

Caution should be exercised when considering temperature effects on solubilization by micelles, since the aqueous solubility of the solute and thus its micelle/water partition coefLcient can also change in response to temperature changes. For example, it has been reported that although tt solubility of benzoic acid in a series of polyoxyethylene nonionic surfactants increases with temperature, the micelle/water partition coefLci rt, shows a minimum at 2C, presumably due to the increase in the aqueous solubility of benzoic acid (Humphreys and Rhodes, 1968). The increasr in Km with increasing temperature was attributed to an increase in micellar size, as the cloud point temperature of the surfactant is approached (Humphreys and Rhodes, 1968). 

Factors Affectinc Micellization and Solubilization Temperature and Concentration Effects on Micellization... 

In investigating temperature effects on drug solubilization in micellarsystems, changes in the micellar properties as well as those in the aqueous solubility of the solute signiLcantly affect the solubilization... 

The term inverse transition was first used in connection with the increase in order of the antibiotic stendomycin on raising the temperature (D.W. Urry and A. Ruiter, Conformation of Polypeptide Antibiotics. VI. Circular Dichroism of Stendomycin. Biochem. Biophys. Res. Commun., 38,800-806,1970). The term became specifically inverse temperature transition in relation to coacervation of elastin fragments that exhibited a phase separation with increased order on raising the temperature (B.C. Starcher, G. Saccomani, and D.W. Urry, Coacervation and Ion-Binding Studies on Aortic Elastin. Biochim. Biophys. Acta, 310, 481 86,1973, and D.W. Urry, B. Starcher, and S.M. Partridge, Coacervation of Solubilized Elastin Effects a Notable Conformational Change. Nature, 222,795-796,1%9). 

Severe paraffin and asphaltene damage may require repeated treatment or sequences of treatment and flowback. This is because dissolution of deposited solids may be inefficient or slow, requiring repeated efforts. Also, a soak time ranging from 2 to 24 hours may be required in order to slowly solubilize deposits effectively before flowing back. Typical soak periods are from 4 to 8 hours. The higher the temperature is, the less soak time will be required. Laboratory testing can be performed to determine the necessary soak time. 

Several references were made above to the term phase inversion temperature. With the exceptions of Eqs. (9.17) and (9.18), however, no specific reference was made to the effect of temperature on the HLB of a surfactant. From the discussions in Chapter 4, it is clear that temperature can play a role in determining the surface activity of a surfactant, especially nonionic amphiphiles in which hydration is the principal mechanism of solubilization. The importance of temperature effects on surfactant solution properties, especially the solubility or cloud point of nonionic surfactants, led to the evolution of the concept of using that property as a tool for predicting the activity of such materials in emulsions. Since the cloud point is defined as the temperature, or temperature range, at which a given amphiphile loses sufficient solubility in water to produce a normal surfactant solution, it was assumed that such a temperature-driven transition would also be reflected in the role of the surfactant in emulsion formation and stabilization. 

Micellar properties are affected by changes in the environment, eg, temperature, solvents, electrolytes, and solubilized components. These changes include compHcated phase changes, viscosity effects, gel formation, and Hquefication of Hquid crystals. Of the simpler changes, high concentrations of water-soluble alcohols in aqueous solution often dissolve micelles and in nonaqueous solvents addition of water frequendy causes a sharp increase in micellar size. 

Natural Ethoxylated Fats, Oils, and Waxes. Castor oil (qv) is a triglyceride high in ticinoleic esters. Ethoxylation in the presence of an alkaline catalyst to a polyoxyethylene content of 60—70 wt % yields water-soluble surfactants (Table 20). Because alkaline catalysts also effect transestenfication, ethoxylated castor oil surfactants are complex mixtures with components resulting from transesterrfication and subsequent ethoxylation at the available hydroxyl groups. The ethoxylates are pale amber Hquids of specific gravity just above 1.0 at room temperature. They are hydrophilic emulsifiers, dispersants, lubricants, and solubilizers used as textile additives and finishing agents, as well as in paper (qv) and leather (qv) manufacture. 

Microemulsions or solubilized or transparent systems are very important ia the marketing of cosmetic products to enhance consumer appeal (32,41). As a rule, large quantities of hydrophilic surfactants are required to effect solubilization. Alternatively, a combination of a solvent and a surfactant can provide a practical solution. In modem clear mouthwash preparations, for example, the flavoring oils are solubilized in part by the solvent (alcohol) and in part by the surfactants. The nature of solubilized systems is not clear. Under normal circumstances, microemulsions are stable and form spontaneously. Formation of a microemulsion requires Httle or no agitation. Microemulsions may become cloudy on beating or cooling, but clarity at intermediate temperatures is restored automatically. 

Aromatic steroids are virtually insoluble in liquid ammonia and a cosolvent must be added to solubilize them or reduction will not occur. Ether, ethylene glycol dimethyl ether, dioxane and tetrahydrofuran have been used and, of these, tetrahydrofuran is the preferred solvent. Although dioxane is often a better solvent for steroids at room temperature, it freezes at 12° and its solvent effectiveness in ammonia is diminished. Tetrahydrofuran is infinitely miscible with liquid ammonia, but the addition of lithium to a 1 1 mixture causes the separation of two liquid phases, one blue and one colorless, together with the separation of a lithium-ammonia bronze phase. Thus tetrahydrofuran and lithium depress the solubilities of each other in ammonia. A tetrahydrofuran-ammonia mixture containing much over 50 % of tetrahydrofuran does not become blue when lithium is added. In general, a 1 1 ratio of ammonia to organic solvents represents a reasonable compromise between maximum solubility of steroid and dissolution of the metal with ionization. 

Fig. 4 Effect of DNA duplex stability on the formation of DNA lesions. Samples (75 pg/ ml of calf thymus DNA) were solubilized in pure water. The different conditions were heated (the solution was heated at 100°C prior to irradiation) control (irradiations were performed at room temperature) compacted (irradiations were performed in the presence of 0.1 mM spermidine)...

Solubilization increases almost linearly with hydrogen pressure, at constant temperature and methanol charge. There is a strong effect of temperature, leading to complete solubility at 275°C in less than 30 minutes. Incorporation is best limited by using lower methanol ratios and higher hydrogen pressures. 

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