Henryk Piekarski

Effect of non-electrolyte properties on the enthalpic interaction coefficients for NaCl/Nal–non-electrolyte pairs in water. Dissolution enthalpies of NaCl and Nal in aqueous solutions of butan-2-one and 1,2-dimethoxyethane at 25 °C

Dissolution enthalpies of NaCl and Nal in aqueous solutions of butan-2-one and 1,2-dimethoxyethane have been measured and appropriate enthalpic pair interaction coefficients, hxy(electrolyte–non-electrolyte) in water have been determined. These results along with the other data concerning the NaCl–non-electrolyte and Nal–non-electrolyte pairs taken from our earlier reports and from the literature, were analysed with respect to the effect of the non-electrolyte properties on variations of the hxy values in water. The hxy coefficients for both NaCl–nonelectrolyte and Nal–non-electrolyte systems are linearly correlated with the heat capacity of the non-electrolyte interaction with solvent water.The group contributions illustrating the interactions between the electrolyte (NaCl or Nal) and CH2, OH, O, CO, ‘Pep’ and ‘iPep’ groups in the non-electrolyte molecules were calculated and discussed from the viewpoint of a competition between the solute–solute and solute–solvent interactions.The analysed enthalpic pair interaction coefficients are well correlated through the multiparameter equation of the Abraham–Kamlet–Taft type.

Enthalpies of solution of glycine in aqueous solutions of 1,2-diols and glycerol at 25°C

Dissolution enthalpies of glycine in mixtures of water with 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,3-propanediol and glycerol have been measured at 25°C. The enthalpic pair interaction coefficients of the glycine zwitterion with the polyalcohol molecule have been determined by using the standard solution enthalpies of glycine in water and in aqueous solutions of the polyalcohols. The values of the resultant enthalpic interaction coefficients are interpreted assuming a criterion in the form of the effect of hydrophobic alkyl radicals on the interactions between the hydroxyl groups of polyalcohols and the zwitterion of glycine.

Hydration effect on urea-non-electrolyte enthalpic pair interaction coefficients. Dissolution enthalpies of urea in aqueous solution of alkoxyethanols at 298.15 K

Abstract The dissolution enthalpies of urea in aqueous solutions of 2-methoxyethanol and 2-butoxyethanol have been measured and the relevant enthalpic pair interaction coefficients hxy(urea-non-electrolyte) in water have been determined. These results, in conjunction with the data concerning urea-non-electrolyte pairs taken from our earlier reports and from the literature, were analysed with respect to the effect of non-electrolyte hydration on variations of the hxy values in water. The coefficients for urea-non-electrolyte systems are linearly correlated with the heat capacity of interaction of the non-electrolyte with solvent water.

Interaction between PAMAM-NH2 G4 dendrimer and 5-fluorouracil in aqueous solution

The formation equilibrium of poly(amidoamine) dendrimer (PAMAM-NH₂ G4) complex with an oncologic drug such as 5-fluorouracil (5-FU) in water at room temperature was examined. Using the results of the drug solubility in dendrimer solutions and the method of equilibrium dialysis, the maximal number of drug molecules in the dendrimer-drug complex and its equilibrium constant were evaluated. Solubility results show that PAMAM-NH₂ G4 dendrimer can transfer tens 5-fluorouracil molecules in aqueous solution. The number of active sites in a dendrimer macromolecule being capable of combining the drug, determined by the separation method, amounts to n=30 ± 4. The calculated equilibrium constant of the 5-FU-active site bonding is equal to K=(400 ± 120).

Studies on homogeneous interactions between zwitterions of severall-α-amino acids in water at a temperature of 298.15 K

Abstract Enthalpies of solution and dilution of L-α-aminobutyric acid, L-α-isoleucine, L-α-phenylalanine, L-proline and L-α-methionine in water at a temperature of 298.15 K have been measured. The values of dilution enthalpy were used to determine enthalpic homogeneous interaction coefficients which characterize the interactions between zwitterions of the examined L-α-amino acids in water. The effect of side substituents in a molecule of L-α-amino acids on the direct homogeneous interactions in water and the effect of these substituents on the surrounding water molecules have been discussed. Quantum chemical semiempirical calculations of the structure of L-a-aminobutyric acid and several of its hydrates were carried out.

Some Physicochemical Properties of Aqueous Solutions of Isomeric Butanediols

Abstract Density, viscosity, electric permittivity and refractive indices for mixtures of water with four isomeric butanediols were measured over the whole composition range at 298.15K. From these data the excess molar volumes, apparent and partial molar volumes of butanediols and water, the excess electric permittivity and Kirkwoods correlation factor for investigated mixtures were calulated. Analysis of the results obtained showed that although the investigated butanediols exhibit their individual features in the mixtures with water, there is a substantial similarity in the behaviour of butane-1, 2-diol and butane-2,3-diol. The analogous similarity, but to a lower extent, is also observed in the case of the other pair of butanediols. i.e. butane-1,3-diol and butane-1,4-diol which have their apolar fragments shielded by the hydroxyl groups.

Heat of solution of 15-crown-5 ether in the mixtures of water with DMSO, DMF, DMA and HMPA at 298.15K

Abstract Enthalpies of solution of 15-crown-5 ether in dimethylsulfoxide-water, N,N-dimethylformamide-water, N,N-dimethylacetamide-water, and hexamethylphosphoramide-water systems have been measured at 298.15K. The plot of enthalpy of solution of 15C5 in these mixtures exhibits maximum at xw ≈ 0.5 for DMSO and DMA, xw ≈ 0.4 for DMF, xw ≈ 0.7 for HMPA, respectively. The results were discussed on the basis of the “cage model” of hydrophobic hydration.

Thermochemical properties of electrolyte solutions in 2-alkoxyethanol–water mixtures

Dissolution enthalpies for NaCl in mixtures of water with 2-methoxyethanol, 2-ethoxyethanol and 2-butoxyethanol at 298.15 K and for Nal in mixtures of water with 2-butoxyethanol at 298.15 K and 308.15 K have been measured. The standard solution enthalpies ΔsH° of the salts go through a maximum within the range of high water content. The position and the height of the maximum depend both on the nature of the salt and the size of the 2-alkoxyethanol molecule. It was conclued that 2-alkoxyethanols in water are hydrophobically hydrated and that their hydration shell is weaker than that of alkanols. The mixtures of water with 2-alkoxyethanols, when used as solvents for the electrolytes, exhibit some similarities in thermochemical properties both to water–alkanol mixtures and to mixtures of water with some aprotic solvents.

Thermochemical properties of NaI solutions in water―2-methoxyethanol and water―2-ethoxyethanol mixtures. The temperature dependence of enthalpic pair interaction coefficients in water solution

Abstract Enthalpies of solution of NaI in mixtures of water with 2-methoxyethanol and 2-ethoxyethanol (known as cellosolves) at 298.15, 308.15 and 318.15 K were measured. The enthalpies of solution in all investigated systems pass through a maximum in the water-rich region. This extremum is lower and flatter than that observed in water-unsubstituted alkanol mixtures. The enthalpic pair interaction coefficients h xy [(Na + +I − )-cellosolve] were calculated and compared with appropriate data for (Na + +I − )-alkanol pairs. The group additivity concept was used for the analysis of h xy coefficients calculated at 308.15 K, and the influence of the temperature change on the group contributions was discussed.

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents. Part III. Hydrophobic hydration and preferential solvation of crown ethers in water-amide mixtures at 298.15 K

Enthalpies of solution of 15-crown-5 (15C5) and benzo-15-crown-5 ether (B15C5) in the mixture of water with formamide (F) and N-methylformamide (NMF) have been measured at 298.15 K. The values of standard enthalpies of solution of 15C5 are negative and those of B15C5 are positive in the mixtures. The results of calorimetric measurements of dissolution enthalpies of 15C5 and B15C5 in the mixture of water and organic solvents at 298.15 K are discussed with regard to the intermolecular interactions that occur in the solution. Considering the properties and molecular structure of the examined crown ethers, particular attention is given to the hydrophobic hydration and preferential solvation of solute in the mixed solvents. The preferential solvation in the examined systems was analysed using the Covington model developed by Balk and Somsen. The relative importance of the solvation mechanism appeared to depend on co-solvent properties.