Salting-in phenomenon

The aromatic ring of alkylphenols imparts an acidic character to the hydroxyl group the piC of unhindered alkylphenols is 10—11 (2). Alkylphenols unsubstituted in the ortho position dissolve in aqueous caustic. As the carbon number of the alkyl chain increases, the solubihty of the alkah phenolate salt in water decreases, but aqueous caustic extractions of alkylphenols from an organic solution can be accomphshed at elevated temperatures. Bulky ortho substituents reduce the solubihty of the alkah phenolate in water. The term cryptophenol has been used to describe this phenomenon. A 35% solution of potassium hydroxide in methanol (Qaisen s alkah) dissolves such hindered phenols (3). 

Watei has an unusually high (374°C) ctitical tempeiatuie owing to its polarity. At supercritical conditions water can dissolve gases such as O2 and nonpolar organic compounds as well as salts. This phenomenon is of interest for oxidation of toxic wastewater (see Waste treatments, hazardous waste). Many of the other more commonly used supercritical fluids are Hsted in Table 1, which is useful as an initial screening for a potential supercritical solvent. The ultimate choice for a specific appHcation, however, is likely to depend on additional factors such as safety, flammabiUty, phase behavior, solubiUty, and expense. 

An important difference between Protein-Pak columns and other size exclusion columns is the silica backbone of the Protein-Pak columns. Because the silica structure is unaffected by the solvent, these columns do not swell or shrink as a function of the solvent. This is a general advantage compared to other size exclusion columns. However, silica-based columns can only be used up to pH 8, which limits their applicability. Also, surface silanols are accessible for interaction with the analytes, but this phenomenon has been minimized by proper derivatization techniques. Generally, a small amount of salt in the mobile phase eliminates interaction with silanols. 

It is remarkable that more than a century after the discovery of tetrazoliums, they continue to have wide applications. In particular, the reductive ring opening reaction leading to formazans continues to receive a lot of attention. In 1993, there were 316 citations to tetrazolium salts in Chemical Abstracts, 23 of which were to their reduction. Yet, the same reaction that makes them a unique class of reduction indicator leuco dyes, may be a part of a broader phenomenon. 

The solubility of any solid can be either increased or decreased by the addition of an electrolyte to the solvent, a phenomenon known as the salt effect. Salting-out describes the situation in which the solubility of the solid is decreased by the salt effect, whereas salting-in is the term used when the solubility is increased. Salting-out takes place when the added electrolyte sufficiently modifies the water structure so that the amount of water available for solute dissolution is effectively reduced, and it is a procedure convenient for the isolation of highly soluble substances. 

Figure 8,12 Salting-out phenomenon for aqueous CO2. Activity coefficient of neutral species increases with increasing salinity, determining decreased solubility of aqueous CO2 in water, T and P conditions being equal. Reprinted from Garrels and Christ (1965), with kind permission from Jones and Bartlett Publishers Inc., copyright 1990.

In 1824, while studying the flora of a salt marsh, he noticed a deposit of sodium sulfate which had crystallized out in a pan containing mother liquor from common salt. In an attempt to find a use for these waste liquors he performed a number of experiments, and noticed that when certain reagents were added, the mother liquor became brown. His investigation of this phenomenon, made when he was only twenty-three years old led to the remarkable discovery which P.-L. Dulong described in the following letter to Berzelius written on July 1, 1826 ... 

A seemingly minor technical problem, the ability of triphenylmethyl to pick up virtually any solvent as solvent of crystallization, occupied Gomberg for some time and led him into consideration of then fashionable structures involving tetravalent oxygen, which were later abandoned. Another sidetrack, more serious in view of the absence of a useful theory, was caused by experiments based on the known fact that triphenylchloromethane showed salt-like conductivity in solution in liquid SO2 It was thus definitively established that there are carbonium salts in the true sense of the definition applied to salts. When triphenylmethyl was dissolved in liquid SO2, it was found that it too conducted the electric current quite well. " How should one explain this strange phenomenon, a hydrocarbon behaving like an electrolyte ... 

Could this salt activation phenomenon be a result of relaxed diffusional limitations in a concentrated salt/enzyme formulation as compared to the salt-free preparation To answer this question, Bedell et al. [99] measured the initial rates of subtilisin Carlsberg-catalyzed transesterification of APEE with n-PrOH in hexane (Scheme 3.4) with two different enzyme preparations (Figure 3.8) (a) 98% (w/w)... 

Sodium iodate dissolves copiously in warm dil. sulphuric acid without decomposition but it is decomposed by hydrochloric acid. The presence of potassium iodide causes potassium iodate to dissolve more readily than in pure water and although A. Ditte says that a double salt is not obtained from the soln., yet the phenomenon is probably due to the formation of a complex salt in soln. J, N. Bronsted measured the solubility of potassium iodate in aq. soln. of potassium hydroxide. Potassium iodate does not dissolve in alcohol. According to H. L. Wheeler, 100 grms. of water at 23° dissolve 21 grms. of rubidium iodate, and 26 grms. of caesium iodate at 24°. The specific gravity of a sat. aq. soln. of lithium iodate 52 at 18° is 1 568 thesp. gr. of soln. of potassium iodate calculated by G. T. Gerlach. from P. Kremers data, are ... 

The solubility of sodium chloride in aq. acetone at 20° falls to 27"18 with 10 c.c. of acetone per 100 c.c. of solvent to 0 25 with 90 c.c. of acetone per 100 c.c. of solvent at 0°, 100 grms. of acetone dissolve 4"6 grms. of lithium chloride, and at 58°, 214 grms., so that the solubility is diminished by a rise of temp. The solubility of potassium in aq. soln. of acetone increases from almost zero with 100 per cent, acetone at 20° to 8"46 with 50 per cent, acetone and to 21 "38 with 20 per cent, acetone. At 30°, 100 grms. of a soln. with 696 per cent, acetone carries 23 42 per cent, potassium chloride and the remainder is water 8"06 per cent, of this salt is present in a soln. with 45 98 per cent, acetone and 0-13 per cent, of this salt in a soln. with 89"88 per cent, of acetone. At 40°, a soln. with 15"75 per cent, acetone carries 21 "28 per cent, of potassium chloride and with 79"34 per cent, of acetone there is 0"58 per cent, of potassium chloride. At 40°, therefore, for cone, of acetone between 20 and 80 per cent., the sat. soln. separates into two layers the upper layer has 55 2 per cent, water, 31 "82 acetone, and 12"99 KC1, when the lower layer has 28"14 per cent, water, 69 42 acetone, and 2"44 KC1. Similarly, when the upper layer has water, acetone, and potassium chloride in the respective ratio 46 49, 45"34, and 8 17 the lower layer has 38 68, 56"17, and 5 25. The separation into two layers with sat. soln. of potassium chloride containing 26 per cent, acetone, occurs at 46"5° and the temp, of separation with other proportions of acetone is indicated in Fig. 22. C. E. Linebarger (1892) and J. E. Snell (1898) 34 found the phenomenon also occurs with the chlorides of lithium, ammonium, sodium, rubidium, calcium, strontium, cobalt, and many other radicles also with bromides, sulphates, cyanides, and numerous other salts with aq. acetone,... 

The specific optical rotation of many sugars and sugar derivatives is altered by the presence of metal salts, the alteration being the greater, the greater the concentration of the salt. This phenomenon, which is now generally attributed to the formation of adducts, will be considered later in more detail. 

Salt concentration. The addition of a small amount of neutral salt usually increases the solubility of a protein, and changes the interaction between the molecules as well as changing some amino-acid charges. The overall effect is to increase the solubility. This phenomenon is known as salting in. However, at high concentrations of salts the solvating interactions between protein and water are reduced, and the protein may be precipitated from solution—a process termed salting out. 

Because of reports of severe hyperthyroidism after the introduction of iodized salt in two severely iodine-deficient African counties (Zimbabwe and the Democratic Republic of the Congo), a multicenter study has been conducted in seven countries in the region to evaluate whether the occurrence of iodine-induced hyperthyroidism after the introduction of iodized salt was a generalized phenomenon or corresponded to specific local circumstances in the two affected countries (46). Iodine deficiency had been successfully eliminated in all of the areas investigated and the prevalence of goiter had fallen markedly. However, it was clear that some areas were now exposed to iodine excess as a result of poor monitoring of the quality of iodized salt and of the iodine intake of the population. In these areas, iodine-induced hyperthyroidism occurred only when iodized salt had been recently introduced. 

Figure 21.1 has been drawn to suggest that F+ > r. This inequality is generally true for nucleic acids in low to moderate salt, a phenomenon sometimes called the polyelectrolyte effect (Draper, 2008 Record and Richey, 1988). Any RNA conformational change that increases the density of phosphate charges will also increase T+ at the expense of T (Record et al., 1998). Flowever, T + may be similar to T at high salt concentrations for instance, T+ = 0.46 and T = —0.54 ions/nucleotide for DNA in 0.98 MNaBr (Strauss et al., 1967). 

As a logical consequence of evaporation there is concentration of buffer salts in the dryer zones, and this increases the intensity of the electrical field which in turn aggravates the phenomenon. This stresses the great importance of an equilibration period of several hours, with current applied, before considering the hydrodynamic flow on the curtain as being stabilized. 

Predictably, cold temperature will slow the progression of a cadaver through the sigmoidal decomposition curve. In theory, decomposition should still proceed at 0 °C because of the concentration of salts in a cadaver. However, Micozzi (1997) observed a lack of putrefaction at temperatures below 4 °C. This phenomenon is believed to be the result of the simultaneous suppression of decomposer activity and promotion of desiccation (Janaway 1996). Interestingly, the freezing and thawing of a cadaver tends to promote aerobic decomposition rather than the anaerobic breakdown typically associated with putrefaction (Micozzi 1986). The reason for this is unknown. 

It has been pointed out previously that silylation of ylides leads to stabilized products and that this is only one example of the very general phenomenon of carbanion stabilization through silicon (34, 61, 72). This effect was also found for arsenic ylides (34, 73), and is the basis for the preparation of other compounds of this series. The influence of silicon is by no means solely an electronic effect. In many cases, where alkylsilyl substituents are introduced, a steric effect may well dominate, which may reduce lattice energies for salts in transylidation reactions, preventing intermolecular contacts in decomposition processes, and rendering the formation of salt adducts unfavorable. This steric effect is reduced to a minimum, but not eliminated, if simple SiH3 groups are employed (61). Even then, however, a pronounced silicon effect is found, which must be based on electronic influences (49, 60, 61). 

Neutral salts have a pronounced effect on the solubility of proteins, especially if they are globular. At low concentration, salts increase the solubility of many proteins in a phenomenon known as salting-in. This solubilization is a function of the solvent ionic strength, which depends on the concentration and on the electrical charge of the cations and anions that constitute the salt. These effects are caused by changes in the ionization of dissociating groups of the protein. 

For Nal a peculiar phenomenon is observed. After the polyelectrolyte precipitates at a certain concentration of added Nal ( salting out ) it dissolves again upon further increase of the salt concentration ( salting in ). For the polyvinylpyridinium system this phenomenon is only observed for added salt containing iodide, whereas long ago the salting in was also observed for anionic polyelectrolytes [21, 22]. 

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