Bianca Sesta

Solution properties of octyl-β-D-glucoside. Part 2: Thermodynamics of micelle formation

Solution properties of octyl-β-D-glucoside have been examined in a wide temperature and concentration range, by means of freezing point depression, volumetric and calorimetric methods. Partial molal quantities and the variations consequent to micellization have been evaluated and discussed. Strong support to the hypothesis of a growth of the micellar aggregates was inferred from heat capacity findings.

Acetonitrile + nitromethane : an example of ideal solvent mixtures

Densities, viscosities, static dielectric constants and refractive indices of acetonitrile + nitromethane mixtures in the temperature range between 5 and 45°C are reported. Density and viscosity data, analyzed in terms of molar excess volumes and molar excess fluidities, show a weak interactions field between acetonitrile and nitromethane molecules. Lorentz-Lorenz molar refractivities and Kirkwood correlation factors, obtained from refractive indices and dielectric constants data, respectively, indicate that such weak interactions can be atributed to an antiparallel alignment between neighboring dipoles of unlike solvent molecules. Such specific features do not significantly perturb the local structures of the pure components so that acetonitrile + nitromethane mixtures can be considered, in a first approximation, one of the few ideal solvent mixtures for which the physical properties can be determined by applying the additivity rules to the pure components.

Solution properties of octyl β-D glucoside. Part 1: Aggregate size. shape and hydration

Aqueous solutions of octyl-β-D-glucoside have been examined in a wide concentration range. By combining information from density, viscosity and dielectric permittivity, the transition from molecular to micellar state has been evidentiated. Classical equations for the viscosity colloidal dispersions have been reexamined and applied to get information on micelle shape. A combined analysis of dielectric and viscosity findings indicates a slight and continuous dependence of micellar shape on surfactant content. The role of hydration on micellar stability is significant.

Evidence of viscoelastic effects in highly concentrated aqueous solutions of the bile salt sodium deoxycholate by ultrasonic measurements

Absorption (5–300 MHz and velocity (5–65 MHz) of ultrasound, density, and viscosity have been measured in highly concentrated aqueous solutions of sodium deoxycholate at 20 °C. Ultrasonic results show that classical viscous losses represent a large fraction of the experimental ones and that a small velocity dispersion is present. These experimental findings are interpreted on the grounds of a viscoelastic behavior of these solutions. Accordingly, the contributions from both volume and shear viscosity relaxation processes have been evaluated. For the former process a previously suggeted model of associated reactions is considered while the dynamic shear viscosity is related to the flexibility of the large micellar super aggregates.

Transport properties of lithium picrate and lithium perchlorate in isodielectric solvents and in their mixtures with the 15-Crown-5 macrocyclic ligand

Abstract Electrical conductance measurements of lithium picrate and lithium perchlorate in isodielectric solvents (i.e. acetonitrile, methanol and N,N -dimethylformamide in the concentration range 10 −4 ≤ c /mol dm −3 ≤ 10 −2 are reported. The data analysed by the Fuoss three-parameter equation have shown that, in spite of the similarity of the macroscopic dielectric constants of the solvents, the ion pair association constants of both electrolytes strongly depend on the molecular details of ions and solvent molecules. The complexation of lithium ion by the 15-crown-5 (15C5) macrocyclic ligand in the above solvents has also been investigated. The results show that the presence of 15C5 increases the ionization of the electrolytes in relation to the solvation efficiency of the solvents. Such a result is of particular interest in view of the technological applications of lithium salt solutions.

Micellization and surface activity ofn-alkyldimethylaminopropanesulfonates in aqueous solutions

Surface tension experiments were performed on severaln-alkyldimethylaminopropanesulfonate aqueous solutions at 15°, 25°, and 35°C. The critical micellar concentrations have been obtained and the surface properties calculated. The enthalpic and entropic contributions to either micellization and adsorption processes have been discussed. The observed properties have been related to the zwitterionic character of these surfactants.

Hydration properties of lyotropic mesophases in para-nonylphenol decaoxyethylene glycol-water mixtures

Abstract The regions of existence and the phase transitions from lyotropic to solution phases occurring in the binary systems p-nonylphenol decaoxyethylene glycol-water have been probed by polarized light. Dielectric and NMR techniques have been applied to study hydration processes occurring at the interfaces. The results indicate the occurrence of interactions among water and polar head groups and suggest some nonspecific arrangement of water molecules at interfaces. It was found that about 9 water molecules interact with hydrophilic sites of the amphiphile in lamellar phase and about 15 water molecules in hexagonal phase.

Ion-ion and ion-solvent interactions of lithium picrate and lithium perchlorate in pure nitromethane and in 15-crown-5 + nitromethane mixtures at 25°C

Abstract Solutions of LiPi and LiClO4 in nitromethane were studied by conductance at 25°C in the concentration range 0–10−2 mol l−1. Although the dielectric environment is the same, the conductometric behavior of these two electrolytes is quite different: LiPi is almost non-conducting whereas LiClO4 behaves like a normal electrolyte. The analysis of the conductance data gives ion pair association constants of the order of 106 for LiPi and 102 for LiClO4. The results are discussed in terms of specific ion-ion and ion-solvent interactions related to the molecular details of the anions and the solvent molecules. One-to-one complexes between 15-crown-5 and the lithium ion were observed, adding the macrocyclic ligand to the systems. A dramatic increase in the conductance of both electrolytes in the presence of 15-crown-5 was also observed. The overlap of the complexation process and the ion-pair process is discussed.

Interactions Between Tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazocyclotetradecane and Perchlorate Anion in Propylene Carbonate, Nitromethane, Acetonitrile, and Tetrahydrofuran

Electrical conductance measurements are reported for lithium perchlorate andthe anion receptor tetra(trifluoromethylsulfonyl)-1,4,8,11-tetraazocyclotetradecane(TTCD) in different aprotic solvents (propylene carbonate, nitromethane,acetonitrile, and tetrahydrofuran). The data have been analyzed by a suitablemethod based on the Lee-Wheaton theory on mixed electrolytes in order to obtainthe true thermodynamic formation constants of macrocyclic-anion complexes andthe ion pairs of both the uncomplexed (ClO4−)and complexed (TTCD-ClO4−)anions. The results show that the anion-ligand formation constants increase withdecreasing dielectric constant and that the presence of the ligand increases theionization of lithium perchlorate and enhances the transference number of lithiumion. These findings are of particular interest in view of the technologicalapplication of anion receptors in electrolyte solutions for lithium batteries.

Interactions between octyl-β-D-glucoside and α-amino acids or small peptides

The interactions between octyl-β-D-glucoside and glycine in water have been investigated by surface tension, viscosity, and density measurements. The results show that the α-amino acid causes an unexpected lowering of the critical micellar concentration of octyl-β-D-glucoside. Such a finding has been interpreted in temss of dipole-dipole interactions between the hydrophilic site of the surfactant and the peptidic cosluttes. From three to seven amino acid molecules have been estimated to be coordinated with each glucoside unity in the micellar state. The research has been extended to glycine oligopeptides and L-lysine. The latter compound has effects similar to those observed with glycine whereas diglycine and triglycine show weaker effects on the micellization process.