Conformal ionic mixtures aqueous solutions

Equation (87) and analogous equations for AG , AHm, and for surface tensions apply to molten salt mixtures in which the interaction potential can be classed as conformal. These relations may also be used to test whether the ionic interaction potential in aqueous solutions may be considered as conformal. Thus, as will be shown in one simple example, the limits of usefulness of some interionic interaction potentials may be tested in ranges of concentration of salts in water too high to obtain absolute values for the partition functions. A similar test may be made for associations in salt vapors such as... 

An example of the studies of Tanford and co-workers is given in Fig. 4. The addition of a number of nonaqueous solvents to an aqueous solution of jS-lactoglobulin at pH 3.0, ionic strength 0.02, results in a gradual increase in — 60 the parameters — [m ] d and — Oo in Eq. (13), however, first show an increase and then a decrease as the solvent mixture is enriched in the nonaqueous component. The maximum values of — and — Oo occur at a solvent composition at which only a small change in bo is found. These results suggest that at least two successive conformational changes are produced on the addition of the nonaqueous solvent to the aqueous... 

Agonists - The existence of two receptor populations for histamine raises the interesting question of whether the chemical mechanism of histamine interaction differs between the two receptor types. Some indications of the chemical properties which may differentiate receptor action come from studies of histamine chemistry and from structure-activity considerations of congeners. Histamine in aqueous solution is a mixture of equilibrating species, viz. ionic forms, tautomers and conformers nmr studies confirm earlier pK work indicating a N -H N -H (structures 1 and 2) tautomer ratio of approximately 4 1 for histamine monocation, and a comparable ratio for histamine base. The latter result contrasts with crystal structure data and molecular orbital predictions, and may indicate an influence of solvent on tautomer stability. Recent studies of properties pertinent to consideration of ligand-receptor interactions are conformation (MO calculations and infra-red comparison of solid state and chloroform solutions of histamine base ), electronic charge distribution, metal complexation, and phospholipid inter-... 

Table 6.2 shows values of the standard molar enthalpy and entropy for the transfer of ions from water into equimolar aqueous mixtures with cosolvents at 25°C, A, /f or A j5 "(I, W 0.5W-i-0.5S), taken from the compilation by Hefter et al. [13]. Further values for the solvents shown there are available at 0.1 mole fraction steps over the entire composition range. The ionic data were selected from data on electrolytes hsted in these references on the basis of their conformation to the TATB or TPTB assumptions (Section 4.3.1). Data are available in this reference also for many other aqueous solvents (n- and i-PrOH, f-BuOH, glycerol, tetrahydrofuran, 1,4-dioxane, acetone, A,A-dimethylacetamide, and sulfolane) for at least a part (the water-rich part) of the composition range, as well as for some other ions that were not measured atX3=0.5 in the solvents shown in Table 6.2 or that could not be traced to the TATB or TPTB assumptions. This table also includes data for these functions for the transfer of ions into aqueous urea, which, though urea is not a solvenf it behaves in aqueous solutions as if it were a liquid amide. 

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