Roberto Sartorio

Diffusion properties of cyclodextrins in aqueous solution at 25°C

Diffusion, density, and viscosity data are collected for the systems α-cyclodextrin and β-cyclodextrin in water. Frictional coefficients were computed with the help of literature activity data and a qualitative discussion of their concentration dependence was attempted.

Hydrophobic interactions of alkanols. A calorimetric study in water at 298.15 K

Enthalpies of dilution in water of binary aqueous solutions of n-diols of increasing alkyl chain length are performed using a flow microcalorimeter. The pairwise enthalpic coefficients of these hydrophobic solutes depend mainly on the mutual positions of the —OH groups in the molecule. A rationalization of the excess enthalpies of positional isomers is attempted.

Volumetric properties of aqueous solutions of alcohols and diols at 25 °C

Partial molar volumes at infinite dilution, text-decoration:overlineV0x, and pairwise contributions to the volume, vxx, are computed from density measurements of aqueous solutions of some polyhydroxylated compounds. A modified group-additivity approach is proposed to evaluate with precision the text-decoration:overlineV0x values of positional isomeric compounds, when the text-decoration:overlineV0x values of the first members of a few homologous series are known. The vxx values are correlated to the corresponding text-decoration:overlineV0x values, confirming a previous hypothesis (C. Cascella, G. Castronuovo, V. Elia, R. Sartorio and S. Wurzburger, J. Chem. Soc., Faraday Trans., 1990, 86, 85) of a preferential ‘side-on’ orientation in non-bonding interactions for this type of compound.

Volumetric properties of aqueous solutions of polyols between 0.5 and 25 °C

The volumetric properties of aqueous solutions containing non-electrolytes have been determined by density measurements in the temperature range 0.5–25 °C. Linear polyols CH2OH(CHOH)nCH2OH with n= 2–4 (n= 4 has three diasteroisomers), myo-inositol and t-butylurea have been studied. text-decoration:overlineV°x and the coefficients of the virial expansion of the excess property (Vxx, Vxxx…) have been evaluated and interpreted in terms of solute–solute and solute–solvent interactions with the aid of the enthalpy and free-energy data where known. The theory of group contributions has been used to interpret the Vxx values of those linear polyols not exhibiting solute–solute interactions at 25 °C. The results confirm the relation between the signs of the enthalpic and volumetric contributions also found for other kinds of non-electrolyte.

Mutual diffusion in aqueous solution of poly(ethyleneglycol) samples. Some comments on the effect of chain length and polydispersity

Mutual diffusion in aqueous solution of polydisperse poly(ethyleneglycol) samples (PEG) was analysed through Gouy interferometry with special attention to the molecular weight and concentration effects. For PEG samples with molecular weight higher than 1000 g mol-1 the diffusive trend on concentration is justified in thermodynamic terms. The diffusion properties of polydisperse samples and pure oligomers are compared. We emphasise that the refractive index gradient at the diffusion boundary in polydisperse PEG significantly deviates from a Gaussian distribution expected where the PEG monodisperse. The combination of mutual diffusion with literature intradiffusion and activity data allows testing of the Darken equation for each PEG sample. Because of the polydispersity the analysis of the velocity cross correlation coefficients (VCCs) or the distinct diffusion coefficients becomes critical.

Network formation in polyethyleneglycol solutions. An intradiffusion study

Intradiffusion coefficients of binary mixtures, water–polyethyleneglycol (PEG) (molecular weight 200, 400, 2000, 3400, 10000 Da), were measured by pulsed gradient spin echo (PGSE)-NMR to determine the mass and concentration effects. The properties of polydisperse samples are compared with those of oligomers, and the effect of polydispersity is discussed. The PEG diffusion coefficients approach a constant value at high concentration, indicating the formation of a dynamic network between water and PEG molecules. The stochiometry of this network is evaluated and compared with the result of a model derived from an extension of gelation theory. It was found that at infinite dilution limiting self and mutual diffusion coefficients are not equal: this has been interpreted as an effect of polydispersity.

Mutual diffusion in aqueous solution of ethylene glycol oligomers at 25 °C

Mutual diffusion coefficients have been measured, at 25 °C, for binary systems of some ethylene glycol oligomers in aqueous solution over the whole mole fraction range. The results have been combined with activity and intradiffusion data to calculate the velocity cross-correlation coefficients (VCCs). An attempt has been made to explain the results in terms of molecular interactions.

Analysis of velocity cross-correlation and preferential solvation for the system N-methylpyrrolidone–water at 20 °C

Viscosity, density, diffusion and self-diffusion data have been collected on the system N-methylpyrrolidone–water at 20 °C over the entire composition range. From density and vapour pressure data, affinities, Gαβ(α,β= 1, 2), were computed and compared with the velocity cross-correlation coefficients, fαβ. Good agreement was found between the interpretation of dynamic, fαβ, and thermodynamic, Gαβ, data. Both data are in favour of preferential solute–solvent interactions leading to short-lived hydration aggregates.

Kirkwood–Buff integrals for polymer–solvent mixtures. Preferential solvation and volumetric analysis in aqueous PEG solutions

The effect of the molecular size of components on preferential solvation analysis has been investigated by studying aqueous solutions of the poly(ethylene glycol) (PEG) homologous chemical series. Precise density data are analyzed for some PEG–water systems, for polymers of molecular weight up to 3400 at 25 °C, at the highest practicable concentrations. The combination of density, activity, and compressibility data allows the evaluation of Kirkwood–Buff integrals for these systems. Data were discussed in terms of preferential solvation, showing that co-operativity takes part to some extent in the PEG–PEG interaction, depending on PEG concentration and molecular weight. The size mismatch between solvent and solute requires a proper reference state, the Matteoli–Shulgin–Ruckenstein state, which takes into account the excluded volume effect. This correction must be applied when considering macromolecular systems, otherwise physically meaningless analyses are developed. Density data at high concentration have been analyzed in order to evaluate progressive aggregation up to network formation, recently proposed for PEG–water systems. The study provides a new picture of aqueous PEG solutions useful for the interpretation of protein precipitation induced by this uncharged polymer. Comparisons with a preferential solvation analysis of the PEG oligomers and with a recent velocity-correlation analysis of PEG polymers have been also made. This paper provides a new picture of PEG–water media, useful to interpret the colloidal stability in the presence of PEG.

Ionic surfactant–polymer interaction in aqueous solution

The interactions in aqueous solution between poly(vinylpyrrolidone) (PVP) and sodium nonanoate (C8COONa), sodium octylsulfonate (C8SNa), lithium perfluorononanoate (C8FCOOLi), respectively, were investigated. In all the studied systems, the presence of PVP induces a lowering of the aggregation number of the surfactant as evidenced by fluorescence quenching measurements. However, no direct surfactant–polymer interaction has been found for the systems C8COONa–PVP and C8SNa–PVP. Strong hydrophobic interaction in the system C8FCOOLi–PVP has been shown by the fluorescent behavior of pyrene used as a probe. The presence of the fluorinated surfactant induces an increment of ∼14% of the polymer gyration radius, as shown by viscosimetry. Calorimetry confirms the experimental results obtained through fluorescence and shows that the adsorption of C8FCOOLi on PVP is an endothermic process.