Salting-in effect

Poly(ethylene oxide) associates in solution with certain electrolytes (48—52). For example, high molecular weight species of poly(ethylene oxide) readily dissolve in methanol that contains 0.5 wt % KI, although the resin does not remain in methanol solution at room temperature. This salting-in effect has been attributed to ion binding, which prevents coagulation in the nonsolvent. Complexes with electrolytes, in particular lithium salts, have received widespread attention on account of the potential for using these materials in a polymeric battery. The performance of soHd electrolytes based on poly(ethylene oxide) in terms of ion transport and conductivity has been discussed (53—58). The use of complexes of poly(ethylene oxide) in analytical chemistry has also been reviewed (59). 

Reactions involving organic substances have some special features. Many of these substances are poorly soluble in aqueous solutions. Sometimes their solubilities can be raised by adding to the solution the salts of aromatic sulfonic acids with cations of the type [NHJ or alkali metal ions. These salts have a salting-in effect on poorly soluble organic substances. In many cases solutions in mixed or nonaque-ous solvents (e.g., methanol) are used. Suspensions of the organic substances in aqueous solutions are also useful for electrosynthesis. 

The salting-in effect may be used to increase the solubility of a drug substance through the formation of associated ion pairs, most commonly making use of anionic countering (hydrochloride being the most popular). Detailed reviews of pharmaceutical salts have been published, which contain extensive tables of anions and cations acceptable for pharmaceutical use [44,47]. These articles also describe useful processes for the selection of the most desirable salt... 

Since [Fe(lll)]jojaj [Fe " ], the formation of ion pairs and complexes is greatly enhancing the equilibrium solubility of ferrihydrite. This is called the salting-in effect and illustrates why mineral solubility calculations in seawater must take ion speciation into consideration. 

Vesala, A. and Lonnberg, H. Salting-in effects of alkyl-substituted pyridinium chlorides on aromatic compounds, Acta Chem. 5canrf., A34 187-192, 1980. 

The salt effect parameter ko is plotted in Figure 2, and the data for lithium chloride and lithium bromide reported in the previous paper (3) are also plotted for the purposes of comparison. It can be seen from Figure 2 that ko depends markedly on the solvent composition. The values of ko decrease and in the extremely water-rich region k0 is negative at 50° and 25°C. In other words, 2-propanol is salted in by the addition of lithium perchlorate. The salting-in effect of 2-propanol increases with reduction in temperature. 

In Table XVIII, there are several trends that can be noted in k if one proceeds through the R4NBr series. First of all, k tends to decrease as the size of the TAA cation increases and, in fact, tetra-n-butylammonium bromide shows a large salting-in effect. This trend is emphatically demonstrated by Figure 13, which shows the smoothed salt effects of the various salts studied in the ethanol-water system at x = 0.206. Secondly, it appears that there is a larger salting-out effect as the mole fraction of ethanol increases in the binary solvent mixture. 

The effects of four different salts on the solubility of hemoglobin at pH 7 can be seen in figure 6.2. All four salts produce the salting-in effect with this protein two of them, sodium sulfate and ammonium sulfate, also produce a greatly decreased solubility of the protein at high salt con-... 

A quantitative assessment of the effects of head group bulk on, S k2 and E2 reactions in cationic micelles has been made.148 The kinetics of the acid-catalysed hydrolysis of methyl acetate in the presence of cationic, anionic, and non-ionic surfactants has been reported on.149 The alkaline hydrolysis of -butyl acetate with cetyltrimethylammonium bromide has also been investigated.150 The alkaline hydrolysis of aromatic and aliphatic ethyl esters in anionic and non-ionic surfactants has been studied.151 Specific salting-in effects that lead to striking substrate selectivity were observed for the hydrolysis of /j-nitrophenyl alkanoates (185 n = 2-16) catalysed by the 4-(dialkylamino)pyridine-fimctionalized polymer (186) in aqueous Tris buffer solution at pH 8 and 30 °C. The formation of a reactive catalyst-substrate complex, (185)-(186), seems to be promoted by the presence of tris(hydroxymethyl)methylammonium ion.152... 

There are some ions which effect the water spectra like a -increase. Ions with the largest structure-breaker effect can have salt-in effects on organic molecules. This can be understood as follows the water becomes more hydrophilic because the content of orientation defects of OH groups increases. Structure breakers are mainly large mono-valent anions. 

CNS- > CIO4 > Ac- > Br > Cl > HCOO-. A similar series is found on the solubility of the bases thymine, adenine etc.212. Cl3COO >CNS >C10j >J > Br have salt-in effects, SO4 Cl- show salt-out effects181 212. Salt-in effects were observed on acetyltetraglycine ethyl ester too in the series213 SCN- >... 

The effect of salts on the biopolymers is clearly shown by the results of v. Hippel and Wong218 (Fig. 32). Salts with possibility of giving salt-in effects reduce Tm of ribonuclease. Salt-out effects giving ions like sulfate increase 7, they reduce the interactions of biopolymere bulk water. Using models, there are opinions that proteins are preferentially hydrated in the presence of SO4 , less with Cl- > Br- > CNS- > J-218. If this is true, weaker interaction with the bulk water should strengthen the stability of fixed hydrates on the polymers. 

The retardation corresponds to a salt-in effect by water becoming more hydrophilic by large anions. The same series is obtained by hindering the gel formation228,240, 241 because structure-disturbing ions increase the content of non H-bonded OH groups in water. 

The solubility of mineral salts may be enhanced with the formation of ion pairs, a salting-in effect, requiring the inclusion of ion speciation effects. Conversely, there is commonly a salting-out effect of dissolved constituents across a salinity gradient. This can be particularly important when examining more hydrophobic organic compounds (HOC), such as aromatic hydrocarbons in estuaries. 

Salting-in effect the solubility of other mineral salts may be enhanced with the formation of ion pairs,... 

Nonionic surfactants dissolve in aqueous solutions through hydrogen bonding between the water molecules and the oxyethylenic portion of the surfactant. These interactions are weak but enough in number to maintain the molecule in solution up to the cloud point temperature, at which the surfactant separates as a different phase (4). Figure 3 shows that electrolytes like calcium chloride, potassium chloride, or sodium chloride reduce the cloud point of Triton X-100. Hydrochloric acid instead promoted a salting-in effect similar to that observed for ethanol. 

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