Salting-out agents

The sensitivity of analyses may be inereased by variation of parameters what provides the rise of the eompleteness of gaseous extraetion - t°, v, for hydrophilie organie substanees - the presenee of salting-out agents. It has been determined that the most effeetive extraetion of aliphatie aleohols is a eharaeteristie feature for high eoneentration alkaline solutions. 

The method of extraction of Ru(III) from thiocyanate solutions by water soluble extractants in the presence of ammonium sulfate as salting out agent followed by photometric determination of it in extract has been elaborated. 

Sometimes mixed solvents may be used to improve the above properties. Salting-out agents may also improve extractability. 

Rideout and Breslow first reported [2a] the kinetic data for the accelerating effect of water, for the Diels Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile and the cycloaddition of anthracene-9-carbinol with N-ethylmaleimide, giving impetus to research in this area (Table 6.1). The reaction in water is 28 to 740 times faster than in the apolar hydrocarbon isooctane. By adding lithium chloride (salting-out agent) the reaction rate increases 2.5 times further, while the presence of guanidinium chloride decreases it. The authors suggested that this exceptional effect of water is the result of a combination of two factors the polarity of the medium and the... 

Mokili, B., Poitrenaud, C. 1995. Modeling of nitric acid and water from aqueous solutions containing a salting-out agent by tri-butylphosphate. Solvent Extr. Ion Exch. 13 (4) 731-754. 

PAGS-8 and PAGS-12 are also water insoluble. The tendency toward side-chain crystallization and the hydrophobic backbone of the polymer contributes to their poor water solubility. Gloud points could be measured in 3% aqueous solutions of PM MS-8 in the presence of various salts (Figure 1). Gonsistent with data reported for nonionic surfactants and polymers with oxyethylene moieties, the cloud points are sensitive to the type of salts added, especially that of the anion. Fluorides and sulfates are effective salting-out agents, whereas thiocyanates raise the cloud points. 

One should distinguish between the effects on aqueous protein solubility of two different types of cosolvents organic cosolvent and salts. Experiment has shown that the addition of an organic cosolvent reduces the aqueous protein solubility [36,37]. Therefore, the organic cosolvents are, in general, salting-out agents. However, there are exceptions for instance, urea increases the aqueous solubihty of ribonuclease Sa [44]. 

The present analysis shows that the same classification can be made with respect to the effect of a small amount of a cosolvent on the protein solubility in an aqueous solvent (see Eqs. (11) and (12)). Namely, the cosolvents of the first Timasheff s group (e. g. urea) increase the protein solubility compared to the solubility in water when a small amount is added to water. Compounds of the second group (e. g. salts) decrease the solubility and they are well-known salting-out agents [14]. Substances of the third group (we have no example) do not essentially change the solubility compared to the solubility in pure water. 

The effect of the addition of a cosolvent on the aqueous protein solubility was examined both experimentally and theoretically. Experiments have shown that the addition of organic substances reduces the aqueous protein solubihty [5,6,8]. Therefore, the organic substances constitute salting-out agents. Arakawa and Timasheff [5] explained this salting-out effect as a result of (i) the decrease of the dielectric constant because the dielectric constants of organic substances are smaller than that of water, and (ii) the redistribution of water... 

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