Solvent interaction, nature strength

Association and mobilities are related in a complex way to the bulk properties of the solvent and solute. These properties include the charge density and distribution on the ions and the Lewis base properties, the strength and nature of the solvent molecule dipole, the hydrogen-bonding capability, and the intermolecular structure of the solvent. Some correlations can be made on the basis of mobility and association trends in series such as the halides and alkali metals within a single solvent others can be drawn between solvents for a given ion. It appears that conductance measurements provide a clear measure of the sum of ion-solvent interactions, but that other techniques must be used in conjunction with conductance if assessments of individual contributions from specific factors are to be made. 

The objective of this paper is to illustrate the efficacy of inferring the interdroplet forces in a concentrated protein stabilized oil-in-water emulsion from the knowledge of the equilibrium profile of continuous phase liquid holdup (or, dispersed phase faction) when the emulsion is subjected to a centrifugal force field. This is accomplished by demonstrating the sensitivity of continuous phase liquid holdup profile for concentrated oil-in-water emulsions of different interdroplet forces. A Mef discussion of the structure of concentrated oil-in-water emulsion is presented in the next section. A model for centrifugal stability of concentrated emulsion is presented in the subsequent section. This is followed by the simulation of continuous phase liquid holdup profiles for concentrated oil-in-water emulsions for different centrifugal accelerations, protein concentrations, droplet sizes, pH, ionic strengths and the nature of protein-solvent interactions. 

A might also be viewed as a perturbative parameter in cases where it appears naturally as a gauge of the strength of solute-solvent interactions. In either case. 

Solvent interactions with solute molecules are predominately electrostatic in nature and may be classified as dipolar or hydrogen-bonding. The position of the fluorescence band maximum in one solvent, relative to that in another, depends on the relative separations between ground and excited state in either solvent and, therefore, the relative strengths of ground- and excited-state solvent stabilization. 

One of the most powerful features of HPLC stems from the fact that the eluent is not merely a transport medium, it rather contributes significantly to the mechanism of separation. Retention as well as selectivity arise from the combined action of mobile and stationary phase on the solutes. Because of its distinct physicochemical characteristics, a given solvent interacts in a specific manner with the solutes. Its capacity to donate or accept protons or to induce a dipole moment defines the nature of its interaction with the solutes in solution. Slight differences in these interactions complemented by stationary-phase action are often enough to provide the desired selectivity in HPLC. Solvent classification based on their elution strength or polarity represents a classic area of investigation into the fundamentals of retention mechanisms in HPLC (2S-27), and the chapter is not yet closed on its development and refinement (28-30). Here we will present a practical and comprehensive way to exploit the effect that the nature of the solvent has on retention and selectivity in reversed phase HPLC. 

The Macinnes, Debye-HUckel, and pH conventions describe the ionic activity as a function only of ionic strength. It is, however, not reasonable to expect the chloride ion, for example, always to have the same activity coefficient at a fixed temperature and ionic strength, regardless of the nature of the counter cation. Bjerrum (58) showed in 1920 that the behavior of electrolytes, including the minima observed in plots of In y+ vs. I, provides evidence for ion-solvent interactions. Hydration of the ions must be considered, and "single-parameter conventions are inadequate from the standpoint of solution theory. 

In the case of nonstructured solvents, the interaction of solvent molecules in the bulk solution is rather weak and plays only a limited role in host/guest binding. However, the extent of solvation, that is, the amount of solvating molecules, the thickness of solvation shell, and the strength of the host-solvent and guest-solvent interactions, critically varies depending on the nature of the solvent employed, as exemplified below for CDCI3 versus CeDe. 

Solvent molecules are involved in acid-base equilibria as acceptors or donors of protons, so that the acidic or basic strength of a substance varies with the nature of the solvent. The lower alcohols resemble water, in that they can form the ions ROHa" and RO , but their dissociation is less than for water (pA cHsOH =16.7, pATcjHsOH =19.1, cf. pATw = 14.0). Consequently, substances dissolved in alcohols are weaker acids and bases than in water. Other factors influencing acidic and basic strengths in solutions include the dielectric constant and solute-solvent interactions which, in mixed solvents, can lead to the further complication of selective ordering of solvent molecules around ionic species. 

---