Salting-in agent

Salting-in or salting-out of analytes as a consequence of the addition of the IM that leads to decreased or increased surface tension, respectively, of the eluent. IPC ions are usually salting-in agents because they lower the surface tension of the eluent [40] it was recently demonstrated that these salting effects may be revised based on the ion-pair concept. 

In this pioneering work [la], Breslow studied the kinetics of the cycloaddition between cyclopentadiene and methyl vinyl ketone (Eq. (1) and Table 1). The implication of the hydrophobic effect in Diels-Alder reactions was extensively supported by the effect of cyclodextrins [26] and additives, such as lithium chloride (salting-out agent) or guanidinium chloride (salting-in agent), which respectively increases or decreases the rate of the reaction [27]. 

It has been found that in the Diels-Alder reaction (Scheme 7), the rate increased 2.5 times if the reaction was carried out in a 4.86 M aqueous solution of LiCl. In this case LiCl is a prohydrophobic ( salting out ) agent. However, the rate decreased considerably if the reaction was carried out in presence of 2.0 M aqueous solution of guanidinum perchlorate. In this case, guanidinium perchlorate is an antihydrophobic ( salting-in ) agent. 

While a direct binding of salting-in agent to swollen collagen could quantitatively be determined (13), the final proof of the binding mechanism should be based ori Che corresponding demonstration of salt - polymer adducts in the molten state, in the absence of water. The occurrence of specific interactions in binary system is demonstrated in the present investigation in the case of LiCl and lactams such as e-caprolactam and pyrrolidone. 

Additives such as GnCl decrease the hydrophobic effect, so they increase the solubility of hydrocarbons in water. They are commonly called "salting in" agents to indicate this. By contrast, ordinary salts such as NaCl decrease hydrocarbon solubility in water, and are "salting out" agents. We have studied both the reasons for this behavior and the general use of these effects to detect hydrophobic contributions to rates and equilibria. Recently we have initiated a program to put the effects on a more quantitative basis. 

We have also compared this with the effect of such salting in agents on the binding of a hydrophobic molecule into cyclodextrin. In the molecule 12 that we call BANS, a t-butylphenyl group can bind into P-cyclodextrin, and this binding leads to an increase in the fluorescense intensity of the BANS. We find that binding of BANS into the cyclodextrin is decreased when 6M GnCl is added to the water, and by the same 4-fold by which the solubility of t-butylbenzyl alcohol was increased ... 

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