Mixed solvent-water systems

B. Effect of Mixed Solvent-Water Systems on Grafting... 

Another type of ternary electrolyte system consists of two solvents and one salt, such as methanol-water-NaBr. Vapor-liquid equilibrium of such mixed solvent electrolyte systems has never been studied with a thermodynamic model that takes into account the presence of salts explicitly. However, it should be recognized that the interaction parameters of solvent-salt binary systems are functions of the mixed solvent dielectric constant since the ion-molecular electrostatic interaction energies, gma and gmc, depend on the reciprocal of the dielectric constant of the solvent (Robinson and Stokes, (13)). Pure component parameters, such as gmm and gca, are not functions of dielectric constant. Results of data correlation on vapor-liquid equilibrium of methanol-water-NaBr and methanol-water-LiCl at 298.15°K are shown in Tables 9 and 10. 

To obtain the higher complexes such as Ag(SeCN)4 it was often necessary to introduce non-aqueous solvents. For example, in aqueous solution the most abundant high complex was found to be Ag(SeCN)2- however, on addition of acetone, the complex Ag(SeCN)4 became prevalent. A similar effect was observed in methanol. Formation constants in mixed methanol-water systems have been determined and in 74% MeOH log j83 and logjEJ4 were 14.60 and 15.13 respectively.149... 

The cell where X- is Br" has been investigated in anhydrous ethanol but not in mixed ethanol-water systems. This study involves the cell using water, 30%, 60%, 90%, and 99% ethanol-water, and anhydrous ethanol at 25°, 35°, and 45°C, and similar compositions and temperatures for the water-tert-butanol system and anhydrous terf-butanol. This cell had not been studied previously in this latter solvent system. 

The calculations have been carried out for those systems for which the solubility calculations have been performed. The dilute region of sodium chloride (c < 0.3) was selected to ensure that the condition F /x = s = constant is satisfied. The partial molar volume was estimated using literature data [67-69]. According to the latter data, depends weakly on C3 and this dependence is linear in the dilute range [68,69]. For sodium chloride and potassium chloride, decreases by at most 1 cm /mol when Cj is changed from 0 to 2mol/l. In our calculations, the above decrease was taken 1 cm /mol. On this basis the composition dependence of was evaluated in the composition range 0 < C3 < 0.3. The partial molar volumes Vi and V3 of water and sodium chloride in the binary mixture water (1) + sodium chloride (3) were obtained from data available in the literature [70,71], and the composition dependence of the isothermal compressibility of the mixed solvent (water (1) + sodium chloride (3)) was taken from reference [71]. 

A similar expression can be written for multiple solvents. Our primary interest is on systems containing a protein (2) in a mixed solvent water (1)—cosolvent (3). An inorganic salt or a small organic molecule is considered as a cosolvent. 

As an example, let us consider mixed solvent water-formie aeid. Both components of the system are subject to autoprotolysis ... 

In the mixed solvents water - non-aque-ous solvent, in spite of its donor and polar properties, water is a preferred solvating agent. This generalization has some exceptions (solvation in systems Ag - HjO -acetonitrile, Cr - HjO - DMSO, F - HjO-eth-ylene glycol). ... 

Table 9.14. Complexation process characteristics for system Cd Mhiourea in mixed solvent water-methanol at 298.15K...

DBC complexes with metal salts in the water-benzene system are the products of the interfacial reaction [119]. The measured work of adsorption (15.9 kJ/mol) can be taken as a sum of the free energy of complex formation and work of adsorption of DBC at the water-benzene interface. The dissolution of complexes in bulk phases was neglected. The interfacial constants of complex formation (Table 3) calculated from the work of adsorption are close to the constants determined in the mixed solvent - water-tetrahydrofuran [114]. The only exceptions are the complexes of DBC with Ba " and La salts. Apparently this is due to stronger Coulomb repulsion of ions in DBC-salt complexes at the interface as compared to the bulk phases. (At the interface, the anions... 

The activity of the hydrogen ion is affected by the properties of the solvent in which it is measured. Scales of pH only apply to the medium, ie, the solvent or mixed solvents, eg, water—alcohol, for which the scales are developed. The comparison of the pH values of a buffer in aqueous solution to one in a nonaqueous solvent has neither direct quantitative nor thermodynamic significance. Consequently, operational pH scales must be developed for the individual solvent systems. In certain cases, correlation to the aqueous pH scale can be made, but in others, pH values are used only as relative indicators of the hydrogen-ion activity. 

There is increasing interest in copolymer systems, which, due to their chemical heterogeneity, may require very complex eluent systems in order to dissolve the sample and ensure that the separation ensues hy a pure size exclusion mechanism. In these examples, the PLgel is also compatible with eluent systems containing mixed solvents of different polarity (including water as a cosolvent up to 10% hy volume) and in organic solvents modified with acids or bases (e.g., acetic or formic acid, triethanolamine) as it is stable in the pH range of 1-14. 

Unlike earlier sulfonated styrene/divinylbenzene copolymers, these sulfonated gels can he run in virtually any solvent from water and buffers to pure organics as well as most any mixed solvent systems desired. In aqueous systems they absorb water and in organic solvents they stay swollen by imbibing organic solvents. 

The solubility of latex in water can be improved by replacing the solvent used in the system. Initially, the water is removed and than a hydrophobic organic solvent is replaced by a hydrophilic solvent, which has a boiling point above 100 C. This last solvent can be ethylene glycol, diethyl ether of diethylene glycol, monoethyl ether of ethylene glycol, or polyethylene glycols. This treatment results in a pastelike composition that can be easily mixed with water and used as a final product. 

As already indicated, ion exchange resins are osmotic systems which swell owing to solvent being drawn into the resin. Where mixed solvent systems are used the possibility of preferential osmosis occurs and it has been shown that strongly acid cation and strongly basic anion resin phases tend to be predominantly aqueous with the ambient solution predominantly organic. This effect (preferential water sorption by the resin) increases as the dielectric constant of the organic solvent decreases. 

Purification of the activation products (PMs). The methylamine activation product dissolved in methanol is purified by chromatography, first on a column of silica gel using a mixed solvent of chloroform/ethanol, followed by reversed-phase HPLC on a column of divinylbenzene resin (such as Jordi Reversed-Phase and Hamilton PRP-1) using various solvent systems suitable for the target substance (for example, acetonitrile/water containing 0.15% acetic acid). 

Mixed solvent systems containing water are included below even in case water is only a minor constiment, molten salts are listed after liquid solvent-based systems. 

Investigations of the solubilization of water and aqueous NaCl solutions in mixed reverse micellar systems formed with AOT and nonionic surfactants in hydrocarbons emphasized the presence of a maximum solubilization capacity of water, occurring at a certain concentration of NaCl, which is significantly influenced by the solvent used [132],... 

An IL solvent system is applicable to not only lipase but also other enzymes, though examples are still limited for hpase-catalyzed reaction in a pure IL solvent. But several types of enzymatic reaction or microhe-mediated reaction have been reported in a mixed solvent of IL with water. Howarth reported Baker s yeast reduction of a ketone in a mixed solvent of [hmim] [PFg] with water (10 1) (Fig. 16). Enhanced enantioselectivity was obtained compared to the reaction in a buffer solution, while the chemical yield dropped. 

Okrasa and co-workers reported an interesting combination reaction of glucose oxidase and peroxidase in a mixed solvent of [bmimJpFg] with water (Fig. 18). Asymmetric oxidation of sulfide was accomplished successfully in the reaction system. ... 

Modem oil spill-dispersant formulations are concentrated blends of surface-active agents (surfactants) in a solvent carrier system. Surfactants are effective for lowering the interfacial tension of the oil slick and promoting and stabilizing oil-in-water dispersions. The solvent system has two key functions (1) to reduce the viscosity of the surfactant blend to allow efficient dispersant application and (2) to promote mixing and diffusion of the surfactant blend into the oil film [601]. 

A similar technique, the so-called spontaneous emulsification solvent diffusion method, is derived from the solvent injection method to prepare liposomes [161]. Kawashima et al. [162] used a mixed-solvent system of methylene chloride and acetone to prepare PLGA nanoparticles. The addition of the water-miscible solvent acetone results in nanoparticles in the submicrometer range this is not possible with only the water-immiscible organic solvent. The addition of acetone decreases the interfacial tension between the organic and the aqueous phase and, in addition, results in the perturbation of the droplet interface because of the rapid diffusion of acetone into the aqueous phase. 

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