Solvents organic cosolvents

An also frequently occurring problem may be the low solubility of test compounds in aqueous solvents. Organic cosolvents, such as DMSO or ethanol can be used however, due to limited cell viability, final concentrations above 1 % have to be avoided. 

TSK-GEL SW columns allow use of elution buffers comprised completely of water-soluble organic solvents, whereas the TSK-GEL PW packings limit organic cosolvent use to a maximum of 50%. 

In the following text, examples of solvent effects on enzyme selectivity, referred either to systems based (i) on water-miscible organic cosolvents added to aqueous buffers or (ii) on organic media with low water activity, are discussed. 

Influence of Organic Cosolvents. Rao et al. (49) have recently presented a solvophobic model for estimating the sorption of a hydrophobic solute from a mixed solvent. This model is based on the work of Yalkowsky et al. (27), who developed an empirical relationship between the solubility in a mixed solvent system, Sm, and that in pure water given by... 

The densities and volumetric specific heats of some alkali halides and tetraalkylammonium bromides were undertaken in mixed aqueous solutions at 25°C using a flow digital densimeter and a flow microcalorimeter. The organic cosolvents used were urea, p-dioxane, piperadine, morpholine, acetone, dime thy Isulf oxide, tert-butanol, and to a lesser extent acetamide, tetrahydropyran, and piperazine. The electrolyte concentration was kept at 0.1 m in all cases, while the cosolvent concentration was varied when possible up to 40 wt %. From the corresponding data in pure water, the volumes and heat capacities of transfer of the electrolytes from water to the mixed solvents were determined. The converse transfer functions of the nonelectrolyte (cosolvent) at 0.4m from water to the aqueous NaCl solutions were also determined. These transfer functions can be interpreted in terms of pair and higher order interactions between the electrolytes and the cosolvent. 

Explain in words how organic cosolvents affect the activity coefficients in water-solvent mixtures Which organic solvents are most effective Is it true that the effect of an organic cosolvent is linearly related to its volume fraction in the solvent-water mixture Below which volume fraction can the effect of an organic cosolvent be neglected ... 

To evaluate the effects of salts or organic cosolvents on air-water (or more correctly, air-aqueous phase or air-organic solvent/water mixture) partitioning, we may simply apply the approaches discussed in Section 5.4 (Eqs. 5-27 and 5-29). Thus, knowing how salt affects a compound s aqueous solubility, while having no effect on its saturation vapor pressure, we deduce that the impact of salt on Ki3V/ may be expressed by ... 

We can now evaluate how a given organic cosolvent will affect the various parameters in Eq. 9-32. In Section 5.4 we discussed the dependence of the activity coefficient of a compound in a solvent-water mixture on the fraction of the cosolvent. We have seen that, depending on solute and cosolvent considered, this dependence may be quite complex (Figs. 5.6 and 5.7 Table 5.8). In the following discussion, we confine ourselves to rather small cosolvent concentrations (i.e.,/v < 0.2 to 0.3) for which we may assume a log-linear relationship (Eq. 5-32). We may then express the activity coefficient, Yu, of compound i in the solvent-water mixture as ... 

The solvation of metal ions in mixtures of solvating solvents, for example aqueous alcohols or aqueous dimethyl sulfoxide, provides examples of a special case of ternary complexes and, in preferential solvation, an indication of the relative affinities of the metal ion for water and for the organic cosolvent in question. The preferential hydration of Co2+ in aqueous methanol is shown by... 

The simplest and most generally useful synthetic method for metal diketonates is from the diketone and a metal such as a halide, hydroxide, oxide, sulfate, carbonate, carboxylate, etc. in a variety of solvents such as water, alcohol, carbon tetrachloride or neat diketone. Since many / -diketones are poorly soluble in water, use of an organic solvent or cosolvent may be helpful. Optionally, a base such as sodium carbonate, triethylamine or urea may be added. Addition of a base early in the reaction converts the diketone to its conjugate base, which usually has greater solubility in aqueous media.159 In some cases, metal halide complexes of the diketone form as intermediates, e.g. SnCl4(MeCOCH2COMe), which has been formulated as... 

There is a large body of experimental work on ternary systems of the type salt + water + organic cosolvent. In many cases the binary water + organic solvent subsystems show reentrant phase transitions, which means that there is more than one critical point. Well-known examples are closed miscibility loops that possess both a LCST and a UCST. Addition of salts may lead to an expansion or shrinking of these loops, or may even generate a loop in a completely miscible binary mixture. By judicious choice of the salt concentration, one can then achieve very special critical states, where two or even more critical points coincide [90, 160,161]. This leads to very peculiar critical behavior—for example, a doubling of the critical exponent y. We shall not discuss these aspects here in detail, but refer to a comprehensive review of reentrant phase transitions [90], We note, however, that for reentrant phase transitions one has to redefine the reduced temperature T, because near a given critical point the system s behavior is also affected by the existence of the second critical point. An improper treatment of these issues will obscure results on criticality. 

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