Jože Škerjanc

Thermodynamics of the isothermal interaction of β-lactoglobulin with guanidinium chloride and urea

A thermodynamic study of the isothermal interaction of beta-lactoglobulin with guanidinium chloride and urea has been performed. Enthalpies of interaction of the two denaturants have been obtained by calorimetric measurements, and the free energy of interaction calculated from previously determined preferential binding of denaturants. In separate dilatometric experiments the volume changes accompanying the interaction of guanidinium chloride with beta-lactoglobulin have also been determined.

Formation of ordered microstructures in polyelectrolyte/surfactant systems: linear anionic polyelectrolytes and cetylpyridinium chloride

Synchrotron X-ray scattering was used for the structural investigation of complexes between anionic polyelectrolytes and cetylpyridinium chloride (CPC). According to the Bragg peaks, different types of ordering are proposed. Cetylpyridinium chloride in conjunction with carrageenan forms bilayers connecting rigid polysaccharide chains. In the presence of poly(styrenesul-fonate), several micelles are bound to one chain. They appear rather small in size due to specific interactions with this polyion. In poly(acrylate)/CPC and poly(methacrylate) /CPC solutions, a cubic structure is indicated.

Studies of polyelectrolyte solutions containing mixtures of mono‐ and divalent counterions. II. Heat of dilution

The heats of dilution of aqueous solutions containing mixtures of polystyrenesulfonic acid and its magnesium salt have been measured at 25°C in the concentration range 0.1–0.001M. From these data the enthalpy difference between two concentrations has been obtained as a function of the equivalent fraction of the acid. The curve representing this function has a sigmoidal shape. On the basis of the cell model with cylindrical symmetry, the electrostatic contribution to the enthalpy of the polyelectrolyte solution containing a mixture of mono‐ and divalent counterions has been calculated. A reasonable agreement between theory and experiment has been found.

Contributions of the polyion and counterions to the internal and free energies of polyelectrolyte solutions

From the solution of the Poisson–Boltzmann equation for the cell model of a polyelectrolyte solution, the contributions of the polyion and counterion to the electrostatic internal and free energies, and to the heat of dilution, are calculated. Computations are made not only for polyelectrolyte solutions containing one kind of counterions species, but also for mixtures of counterions differing in charge and size. The results are presented as functions of the polymer concentration, its degree of ionization, and valencies and mole fractions of the counterions.

Thermodynamic properties of a polyelectrolyte solution containing a mixture of counterions differing in charge

From the solution of the Poisson–Boltzmann equation for the cell model of a polyelectrolyte solution with mixtures of counterions of different charge, the electrostatic internal and free energies, the degree of binding of counterions, the osmotic coefficient, and the heat of dilution are calculated. These thermodynamic properties are presented as functions of valences, and mole fractions of the counterions, and the possibility of their application for interpretation of the scarce experimental data is discussed.

Water-soluble fullerene electrolytes. Electrostatic contribution to thermodynamic functions

The Poisson–Boltzmann equation has been solved to obtain the electrostatic potential for the spherical cell model of a fullerene molecule at which charged groups are attached. The electrostatic internal and free energies, degree of binding of counterions, osmotic coefficient, and distribution of counterions around the charged fullerene shell are calculated. These properties are presented as functions of the concentration, radii of counterions, and surface charge density of the fullerene macroion. Calculated osmotic coefficients are compared with preliminary experimental data for the sodium salt of fullerenehexamalonic acid, C66(COONa)12.

Transport phenomena and ion binding in poly(styrenesulfonate) solutions containing mixtures of two counter ions differing in charge and size

By the combination of electrical conductivity and polyion constituent transport number measurements, fractions of free counter ions were calculated in salt-free polyelectrolyte solutions containing mixtures of mono- and di-valent or mono- and tri-valent counter ions. The poly(styrenesulfonate) anion was chosen as the polyion and mixtures of hydrogen and magnesium or hydrogen and lanthanum ions were taken as counter ions. All measurements were performed in aqueous solutions at 25 °C in the concentration range from ca. 0.002 to 0.1 mol l–1 for various equivalent fractions of the hydrogen ion in the counter ion mixture. The experimental results were compared with the theoretical predictions based on the analytical and numerical solution of the Poisson–Boltzmann equation for the cell model of a polyelectrolyte solution with mixtures of two counter ions differing in charge and size. A pronounced dependence of the fraction of free counter ions on the composition of the mixture has been found, a finding which is in agreement with the theory. The fraction of free monovalent counter ions is much higher than the fraction of free di- or tri-valent counter ions and decreases, whereas that for the multivalent ones increases upon increasing the corresponding equivalent fraction in the counter ion mixture.

Electrostatic contributions to thermodynamic functions of systems containing polyions and mixtures of counterions differing in charge and size

By the combination of the analytical and numerical solutions of the Poisson–Boltzmann equation for the cell model of a polyelectrolyte solution with mixtures of counterions differing in size and charge, the electrostatic internal and free energies, degree of binding of counterions, osmotic coefficient and distribution of counterions around the polyion are calculated. These properties are presented as functions of charges, radii and mole fractions of counterions, and the possibility of their application for interpretation of the scarce experimental data is discussed.

Studies of polyelectrolyte solutions containing mixtures of mono‐ and divalent counterions. III. Volume change on dilution

The volume change on dilution of aqueous solutions containing mixtures of polystyrenesulfonic acid and its magnesium salt have been determined at 25 °C by dilatometry for various equivalent fractions of the acid. Experimental values have been compared with those predicted by the cell model with cylindrical symmetry. A reasonable agreement between theory and experiment has been found.

Heats of mixing of poly(styrenesulphonic acid) and its tetramethylammonium salt with alkali-metal poly(styrenesulphonates) in dioxan + water mixtures

The heats of mixing of poly(styrenesulphonic acid) and its tetramethylammonium salt with alkali-metal poly(styrenesulphonates) have been measured at 25 °C in 25 and 50 wt% dioxan + water mixtures. The solutions to be mixed were of the same concentration (0.06 mol dm–3). The heat effects were similar to those observed in aqueous solutions, i.e. either endothermic or exothermic. The experimental results are qualitatively interpreted in terms of the solute–solvent structural properties.