Hydrophobic salt effects

The ernes of ionic surfactants are usually depressed by tire addition of inert salts. Electrostatic repulsion between headgroups is screened by tire added electrolyte. This screening effectively makes tire surfactants more hydrophobic and tliis increased hydrophobicity induces micellization at lower concentrations. A linear free energy relationship expressing such a salt effect is given by ... 

Salt Effects. The definition of a capacity factor k in hydrophobic interaction chromatography is analogous to the distribution coefficient, in gel permeation chromatography ... 

Activation volumes for peroxodisulfate oxidation of [Fe(bipy)2(CN)2] and of [Fe(diimine)(CN)4] with diimine = bipy, phen, Mc2bsb, ein (HN=CHCH=NH) show a large ligand effect, 4-5 for [Fe(ein)(CN)4] to —10 cm moD for [Fe(Mc2bsb)(CN)4]. This reflects the big difference in solvation properties, from hydrophilic ein to strongly hydrophobic Mc2bsb. There is a moderately good correlation between AV and AS for peroxodisulfate oxidation of the sequence of complexes [Fe(diimine)3] , [Fe(diimine)2(CN)2], [Fe(diimine)(CN)4], and [Fe(CN)6]" (diimine = bipy or phen). Salt effects ([salt] up to 6 moldm ) on have been established for peroxodisulfate oxidation of this sequence of complexes for bipy as diimine. ... 

The salt effects of potassium bromide and a series office symmetrical tetraalkylammonium bromides on vapor-liquid equilibrium at constant pressure in various ethanol-water mixtures were determined. For these systems, the composition of the binary solvent was held constant while the dependence of the equilibrium vapor composition on salt concentration was investigated these studies were done at various fixed compositions of the mixed solvent. Good agreement with the equation of Furter and Johnson was observed for the salts exhibiting either mainly electrostrictive or mainly hydrophobic behavior however, the correlation was unsatisfactory in the case of the one salt (tetraethylammonium bromide) where these two types of solute-solvent interactions were in close competition. The transition from salting out of the ethanol to salting in, observed as the tetraalkylammonium salt series is ascended, was interpreted in terms of the solute-solvent interactions as related to physical properties of the system components, particularly solubilities and surface tensions. 

Alcohols exhibit a bifunctional nature in aqueous solution. On the one hand, there exists a hydrophobic hydrocarbon group which resists aqueous solvation on the other, there is the hydrophilic hydroxyl group which interacts intimately with the water molecules. Franks and Ives (30, 31) have reviewed experimentation and theoretical treatises on the structure of water, the structure of liquid alcohols, and the thermodynamic, spectroscopic, dielectric, and solvent properties and P-V-T relationships of alcohol-water mixtures. Sada et al. (27) reviewed, in particular, the salt effects of electrolytes in alcohol-water systems and discussed the various correlations of the salt effect applied to these systems. Inorganic salts were used almost universally in these salt effect studies. 

Ryoo et al. [6] reported an improvement of hydrothermal stability of MCM-41 via so-called salt effects their XRD results didn t show any structural losses for the materials treated in boiling water for only 12 h. Other researchers [1,7,8] also claimed that the hydrophobicity and hydrothermal stability could be improved by trimethylsilylation. However, Pan et al. [9] found that the BET surface area and pore size of the silylated MCM-48 by (CH3)3Si-Cl decreased markedly after silylation, the BET surface area of MCM-48 dropped to about 45%, and pore diameter decreased from 27 A to <16 A, thus retarding the advantages of MCM mesoporous materials possessing high BET surface area and big pore size. 

Melander, W. and Horvath, C. 1977. Salt effects on hydrophobic interactions in precipitation and chromatography of proteins An interpretation of the lyotropic series. Arch. Biochem. Biophys. 183 200-215. 

When secondary chemical equilibrium prevail, such as salt in or salt out effects involving changes in the self-association or aggregation state of the polypeptide or protein, or alternatively when additional hydrophobic interaction effects are manifested, or finally if conformational transitions are induced due to the choice of a water structuring or water-destabilizing salt species from the Hofmeister series,91-93 then divergences from this ideal behavior will be evident. 

One of the main factors influencing the activation barrier in fast electron-transfer reactions is the change in the polarization of the immediate space surrounding the activated complex in solution. The more-well-known salt effects as well as the relatively new field of micellar effects can be used as mechanistic probes in this context. Since micelles have a hydrophobic as well as a hydrophilic part, this creates two different kinds of interfaces where electron transfer can occur if one of either the oxidant or reductant is contained or associated with these molecular aggregates. A futuristic approach could be that studies of this kind may serve as models for enzymatic reactions with complex bioaggregates such as membranes. 

Holz M, Grander R, Sacco A, Meleleo A. Nuclear magnetic resonance study of self-association of small hydrophobic solutes in water salt effects and the lyotropic series. J. Chem. Soc. Faraday Trans. 1993 89 1215-1222. 

Melander W and Horvath C. Salt Effect on Hydrophobic Interactions in Pprecip-itation and Chromatography of Proteins An Interpretation of the Lyotropic Series. Arch Biochem Biophys 1977 183(1) 200-215. 

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