Modified solvent structure

Both these effects are of great importance for ion-solvent interactions in solution. In particular, their existence implies that ions do modify solvent structure. This, in turn, implies that there must be consequent modification of solute-solute interactions in particular, and also of solvent-solvent interactions though these are of relatively less importance. 

A question is whether or not the hydration force should be considered as a solvation force. It was reported [24] that the forces between bilayers in a variety of non-aqueous solvents were very similar to those measured in water, while other data do not appear to support the modified solvent-structure origin of hydration forces [23]. 

These ligands were used in protic and biphasic media by modifying their structure using hydroxyalkyl groups [28,29]. The solubihty of the corresponding Ru(II) complexes was significantly increased in protic solvents. Hence, by performing the reaction in mixtures of toluene and water or al-... 

Miscible organic solutes modify the solvent properties of the solution to decrease the interfacial tension and give rise to an enhanced solubility of organic chemicals in a phenomenon often called cosolvency . According to theory, a miscible organic chemical such as a short chain alcohol will have the effect of modifying the structure of the water in which it is dissolved. On the macroscopic scale, this will manifest itself as a decrease in the surface tension of the solution [238,246]. 

Schure, M.R., Molecular dynamics of liquid chromatography chain and solvent structure visuahzation, in Pesek, J.J., Leigh, l.E. (Eds.), Chemically Modified Surfaces. The Royal Society of Chemistry, Cambridge, 1994, p. 181. 

The concepts and techniques discussed by Cirkel and Okada are relevant with a view toward modifying the structure of solution cast Nafion membranes by manipulating counterion type, solvent, temperature, and other variables. 

This article deals with the polymer-metal complexes (Schemes 1 —5), because they have the following merits in comparison with other polymeric metal complexes, (i) Metal ion and ligand site can be chosen for study without restrictions, (ii) It is not difficult to control the molecular weight of a polymer complex and to modify the structure of a polymer ligand, (iii) The polymer complex is soluble in both aqueous and nonaqueous solvent, (iv) It is possible to change the ratio of the organic polymer part to the inorganic metal complex part. This explains why the polymer often affects the behavior of the metal complex. 

Harris and Hsu modified the structure of the rigid-rod poly(pyro-mellitimides) so they would display solubility in common organic solvents [59]. The approach involved the synthesis of 3,6-diphenylpyromellitic dianhydride and its polymerization with various pendent 4,4 -biphenylene diamines. The polymers, represented by structure XIV, were prepared in refluxing m-cresol... 

The second approach that has been rather popular with mixed aqueous solvents is to assume that the mixture is more or less structured than that of pure water. There is much evidence to show that the particular hydrogen-bonded structure of water influences many of the properties of electrolytes in water (15). If nonelectrolytes can modify the structure of water (15), they can have an indirect effect on the properties of electrolytes. This explanation has been particularly successful in the case of U + W mixtures (1,2). Such a simple approach is not as successful with hydrophobic cosolvents. For example, AHe°(W — W + TBA) are positive for both alkali halides (16) and tetraalkylammonium bro-... 

The apparent acid strength of boric acid is increased both by strong electrolytes that modify the structure and activity of the solvent water and by reagents that form complexes with B(OH) 4 and/or polyborate anions. More than one mechanism may be operative when salts of metal ions are involved. In the presence of excess calcium chloride the strength of boric acid becomes comparable to that of carboxylic acids, and such solutions may be titrated using strong base to a sharp phenolphthalein endpoint. Normally titrations of boric acid are carried out following addition of mannitol or sorbitol, which form stable chelate complexes with B(OH) 4 in a manner typical of polyhydroxy compounds. Equilibria of the type ... 

Choice of the Lignin Modification Reaction. The phenolysis reaction was selected as a means of modifying the structure and reactivity of the ammonium lignin sulfonate for three main practical reasons. First, because this lignin derivative is soluble in (and will ultimately be used in conjunction with) liquid phenol itself second, because unreacted phenol, unlike other reaction solvents, would not have to be removed from the phenolated product after reaction and before conversion to the adhesive resin and third, because lignins and carbohydrates are known to react with phenols under acidic conditions (6,7). 

The absorption spectrum of the solvated electron depends not only on the nature of the solvent but also on parameters that modify the structure and properties of the solvent, such as pressure and temperature. The optical absorption band shifts to higher energies (shorter wavelengths) with increasing pressure up to 2000 bar the shift is larger in primary alcohols than in water and it correlates with the increase in liquid density rather than with the rise in dielectric constant. A rise in the temperature induces a red shift of the solvated electron absorption spectrum. Thus, the absorption maximum in water is located around 692 nm at 274 K and 810 nm at 380... 

Non-ideality also corresponds to all solvent-solvent interactions which are over and above those considered to be present in the ideal solution, i.e. any modified solvent-solvent interactions resulting from the presence of the solute (cation and anion) at concentrations greater than infinite dilution. However, this is a relatively minor effect and of less importance than contributions to non-ideahty which are discussed above. For instance, the cation or anion, or both, could disturb the solvent structure present in the pure solvent, and this in mrn would lead to modified solvent-solvent interactions which would then be considered as non-ideal. This modification would become increasingly greater as the solute concentration increases, giving rise to increasing non-ideality. 

Meanwhile, it is constmctive to look again at the physical basis of the simple Debye-Hiickel model and its mathematical development to see where both could be modified, and to consider whether this would be mathematically possible. What has been written in Chapter 1 on ions and solvent structure shows that the Debye-Huckel model is painfiiUy naive and cannot even approach physical reality. A brief reassessment of the features 1-7 of the simple Debye-Hiickel model is given below, along with indications as to how these problems have been tackled. 

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