The Donnan osmotic pressure of a solution containing charged colloidal entities is divided into electrostatic and non-electrostatic contributions. The expression adopted for the former contribution is obtained from a general thermodynamic treatment of the diffuse double layer. Expressions are derived which allow for specific binding and which also provide a definition of amounts bound electrostatically. When the approximation is made that the electrostatic binding of indifferent coions Γcoions is negligible the equations which result have the same form as those that apply to non-interacting uncharged systems and can be handled in the same way. The treatment provides a basis for a successful but somewhat arbitrary approach developed previously. In particular an expression for the activity coefficient of unbound counterions and coions is justified. The prediction (based on the application of the Poisson—Boltzmann equation to cell models) that Γcoions is negative is contradicted by work concerning the significance of single ionic chemical potentials.

Electrostatic effects in dilute solutions containing charged colloidal entities

Electrochemical properties of spherical polyelectrolytes

The enthalpy change associated with the isothermal pH-induced uncharged coil-to-helix transition ΔHh° in poly(L-ornithine) in 0.1 N KCl has been determnined calorimetrically to be −1530 ± 210 and −1270 ± 530 cal/mol at 10° and 25°C, respectively. Titration data provided information about the state of charge of the polymer in the calorimetric experiments, and optical rotatory dispersion data about its conformation. In order to compute ΔHh°, the observed calorimetric heat was corrected for the heat of breaking the sample cell, the heat of dilution of HCl, the heat of neutralization of the OH− ion, and the heat of ionization of the δ-amino group in the random coil. The latter was obtained from similar calorimetric measurements on poly(D,L-ornithine). Since it was discovered that poly(L-ornithine) undergoes chain cleavage at high pH, the calorimetric measurements were carried out under conditions where no degradation occurred. From the thermally induced uncharged helix–coil transition curve for poly(L-ornithine) at pH 11.68 in 0.1 N KCl in the 0°–40°C region, the transition temperature Ttr and the quantity (∂θh/∂T)Ttr have been obtained. From these values, together with the measured values of ΔHh°, the changes in the standard free energy ΔGh° and entropy ΔGh°, associated with the uncharged coil-to-helix transition at 10°C have been calculated to be −33 cal/mol and −5.3 cal/mol deg, respectively. The value of the Zimm–Bragg helix–coil stability constant σ has been calculated to be 1.4 × 10−2 and the value of s calculated to be 1.06 at 10°C, and between 0.60 and 0.92 at 25°C.

Calorimetric measurement of enthalpy change in the isothermal helix–coil transition of poly(L‐ornithine) in aqueous solution

For a number of weak polyelectrolytes potentiometric titration data are interpreted on the basis of the dependence of the pK on the degree of ionization σ by considering the separate contributions for a) the mean electrostatic potential field, b) interactions between neighbouring functional groups, c) the distribution of the functional groups over the macromolecule, d) specific conformational aspects and branching. For the various polyelectrolytes this procedure leads at low ionic strength to a satisfactory picture of the charging process. However, on increasing the ionic strength definite discrepancies between the two weak polybases with strong neighbour interactions, poly(ethylene-imine) and poly(vinylamine), and the other polyelectrolytes are found. The very strong dependence of pK on σ in these two cases even at high ionic strength can only be explained by concluding that the electrostatic potential at the site of reaction in these molecules is much higher than expected on the basis of additivity of the various specific effects.

Evaluation of potentiometric data of weak polyelectrolytes taking account of nearest-neighbour interaction

A fast and accurate method to compute the total solvation free energies of proteins as a function of pH is presented. The method makes use of a combination of approaches, some of which have already appeared in the literature; (i) the Poisson equation is solved with an optimized fast adaptive multigrid boundary element (FAMBE) method; (ii) the electrostatic free energies of the ionizable sites are calculated for their neutral and charged states by using a detailed model of atomic charges; (iii) a set of optimal atomic radii is used to define a precise dielectric surface interface; (iv) a multilevel adaptive tessellation of this dielectric surface interface is achieved by using multisized boundary elements; and (v) 1:1 salt effects are included. The equilibrium proton binding/release is calculated with the Tanford−Schellman integral if the proteins contain more than ∼20−25 ionizable groups; for a smaller number of ionizable groups, the ionization partition function is calculated directly. The FAMBE method i...

/pdf/fambe-ph-a-fast-and-accurate-method-to-compute-the-total-cslon77d1a.pdf

FAMBE-pH: a fast and accurate method to compute the total solvation free energies of proteins.

Electrochemical properties of permeable multichain polyamino acids

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Electrochemical properties of permeable multichain polyamino acids