Journal of Solution Chemistry

The emf of the cell $${\text{Pt, H}}_{\text{2}} ({\text{g, 1 atm}})|{\text{HCI(}}m_{\text{A}} {\text{),GdCl}}_{\text{3}} (m_B )|{\text{AgCl, Ag}}$$ without a liquid junction was used to investigate the HCl + GdCl3 + H2O mixedelectrolyte system. The emf of the cell was measured for HCl + GdCl3 + H2Osolutions at ionic strengths of 0.025, 0.05, 0.1, 0.5, 1.0, 1.5, and 2.0 mol-kg−1and at eleven temperatures ranging from 5 to 55°C at 5°C intervals. The meanactivity coefficients for HCl in the mixtures were determined using the Nernstequation. About 793 experimental emf data points were treated by the Harnedequations. Results show that hydrochloric acid follows Harned's rule at all ionicstrengths, but the quadratic term is needed for I = 1.5 mol-kg−1. Theion-interaction treatment of Pitzer was used to evaluate the results. The binary andternary mixing parameters at 25°C were found to be ΘH,Gd = 0.07 ± 0.03 andΨH,Gd,Cl = 0.14 ± 0.03. These values were determined using literature values ofβ(0), β(1), and C ψ for GdCl3 at 25°C and estimates of the effect of temperaturefrom 5 to 55°C using enthalpy and heat capacity data.

It is known that the electromotive force (emf) of cells with transference is dependent on an integral involving electrical transport numbers, t i , and chemical potentials. However, the origin of this integral, the conditions under which it is valid, its properties and utility are not well understood. This article aims to clarify such aspects. A general emf equation is derived in a manner in which the integral arises from the entropy production due to diffusion. Five important properties of the equation are recognized: (1) invariance with respect to the reference frame for t i measurements, (2) redundancy of single-ion activities, (3) lack of a potential function for the integral when the number of independent t i is greater than 1, (4) irrelevance of any metric on the junction 3-D space, and (5) invariance with respect to the free-diffusion time. As an application, the emf equation is tested for calibration of cells with dissimilar electrodes and junctions between the saturated potassium chloride solution and hydrogen chloride solutions in a range of concentration. It is found that (1) the standard emf can be estimated with a precision of about 0.1 mV for accurate enough data sets, and (2) the free-diffusion model is more appropriate for the flowing junctions than the continuous mixture model, although the difference between the two models is slight. In similar systems with less concentrated potassium chloride solutions, the free-diffusion mass density profiles are found to bear a sign of convective instability, because of which previously reported steady emfs for such cells may pertain to a changed solution composition in one of the two half-cells.

The Savage and Wood group additivity method has been applied to enthalpic pair interaction coefficients of more than 30 solutes dissolved in N,N-dimethylformamide. The results are not satisfactory. Better results are obtained by using a method which accounts for the differences in the numbers of molecular groups between solute and solvent molecules. With this excess group additivity method reasonable correlations are obtained even for solutes as large as dipeptide amides.

The interactions between myriocin (ISP-1) and human serum albumin (HSA) were studied by fluorescence spectroscopy, synchronous fluorescence spectroscopy, three-dimensional fluorescence spectroscopy and molecular docking approach. The intrinsic fluorescence of HSA was quenched through a combination of static and dynamic quenching. The binding constants and the number of binding sites were evaluated according to the Stern–Volmer equation. ISP-1 could not bind efficiently to HSA at higher temperatures. The electrostatic force, hydrogen bonding and hydrophobic force were dominant for the binding ISP-1 and HSA. The site I was the primary binding site for the binding ISP-1 and HSA. What’s more, the conformational and microenvironmental changes of HSA during the binding process were studied by synchronous fluorescence spectroscopy and three-dimensional fluorescence spectroscopy. Lys-195, Arg-218, Arg-222 and Val-293 were the important amino acid residues involved in the binding process.

The complex formation equilibria involving trans-diamminepalladium(II) chloride (PdII), 1,6-hexanediamine (HDA), and DNA constituents were investigated. The formation constant of all possible mononuclear and binuclear complexes were determined at 25 °C and 0.1 mol⋅L−1 NaNO3. The speciation diagrams of the binuclear complex of PdII–HDA–DNA reveal that these complexes predominate in the physiological pH range and the reaction of the binuclear complex PdII–HDA–PdII with DNA constituents is quite feasible.

The densities of glycyl-glycine (diglycine) and glycyl-l-leucine, in water and in aqueous sodium acetate, potassium acetate, magnesium acetate and calcium acetate solutions, were measured at 298.15 K. The apparent molar volumes, V 1, and the partial molar volumes, $$ \bar{V}_{1} $$ , of diglycine and glycyl-l-leucine have been calculated. The solvation number, n S, of diglycine was also calculated. The limiting apparent molar volumes of the studied peptides were also analyzed in terms of the Setschenow relationship. The effect of the acetate salt solutions on the volumetric properties of the studied peptides was also discussed in terms of the Setschenow coefficients, k 1. The results indicate that the limiting apparent molar volume in aqueous acetate solutions is higher than that in water and the values increase with the concentration of the co-solutes (NaA, KA, MgA and CaA). The results indicate that the peptide interactions are stronger with MgA/CaA than NaA/KA. Also the data suggest that the peptide interactions are stronger with NaA than KA and with MgA than CaA. Further, the limiting apparent molar volume values increase from diglycine to glycyl-l-leucine. It was also noted that the solvation numbers for the diglycine in aqueous acetate salt solutions are less than in water and decrease as the concentration of acetate salt increases.

Static dielectric constant values of the binary mixtures of N-methylformamide with formamide, N,N-dimethylformamide and N,N-dimethylacetamide have been measured in the whole composition range at 303 K. The Kirkwood correlation factor values of the amide–amide mixtures were determined from the measured values of the static dielectric constant and high-frequency limit dielectric constant. The evaluated values of the excess dielectric constant and deviation in the Kirkwood correlation factor infer that deviations of their mixture values occur from the mole-fraction mixture law. Results confirm that there are strong hydrogen-bond interactions between unlike molecules of amide–amide mixtures and that 1:1 complexes are formed.

Specific heats at constant pressure for the mixed system K/Na/Cl/SO4 in H2O have been obtained from heat content measurements by means of a drop calorimeter between 60 and 220°C over the salt concentration range 0.5–5m, with ionic strengths up to 7.5. Measurements have also been made on aqueous K2SO4 solutions in the same temperature range between 0.3 and 1.6m. The heat capacities of the quaternary system were represented using the semiempirical Pitzer equations neglecting the mixed interaction terms as a first approximation. A comparison of experimental with calculated data shows that the ability of this method to describe the system is satisfactory even at rather high concentrations, but only for solutions of low sulphate ion content.