Physico-chemical properties of aqueous extremely diluted solutions in relation to ageing

An extensive study has been carried out on aqueous ‘extremely diluted solutions’ (EDS). The employed experimental methodologies were well established physico-chemical techniques: flux calorimetry, conductometry, pH-metry, e.m.f. of suitable galvanic cell. The obtained results show that the preparation procedure significantly alters the physico-chemical behaviour of such solutions. Moreover, the analysis of the experimental data vs. the ‘arrow of time’ turned out to be astonishingly important. In fact some measured physico-chemical parameters evolve with time. Some experimentally measurable physico-chemical properties of the solvent water were largely affected by both time and the ‘life path’ of the samples. In particular, we evidenced two new experimental phenomena characterizing the EDS: the presence of a series of maximums in the measured electrical conductivity vs. the sample age; the dependence of said maximums on the volume of the EDS during its ageing. All of these new experimental results clearly suggest the presence of an extended and ‘ordered’ dynamics involving the whole of the water molecules in the liquid. A temporal evolution, featuring three maximums in the course of four years of ageing and the dependence on the ageing volumes do not fit the framework of classical thermodynamics. It therefore seems appropriate to interpret these phenomena on the basis of the thermodynamics of dissipative structures, which are far from equilibrium systems.     

New physico-chemical properties of extremely diluted aqueous solutions

The 'extremely diluted solutions', anomalous solutions prepared through the iteration of a process of dilution and succussion, have been studied with the aim of obtaining information about the influence of the preparation method on the water structure of the solutions. We measured the heats of mixing of basic solutions with such 'extremely diluted solutions', and their electrical conductivity, comparing with the analogous heats of mixing, electrical conductivity of the solvent. We found some relevant exothermic excess heats of mixing, and higher conductivity than those of the untreated solvent. The heats of mixing and electrical conductivity show a good correlation, underlining a single cause for the behaviour of the extremely diluted solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the stability of extremely diluted solutions to temperature

Conductometric and calorimetric titrations of extremely diluted solutions (EDS) were performed by adding HCl or NaOH solutions. The aim of this work was to confirm the hypothesised presence of molecular aggregates of water molecules in EDS stored for 15 months at 5 different temperatures. Conductometric and calorimetric measurements on the EDS samples revealed significant differences compared to the solvent. The experimental data can be interpreted as indicating a favourable interaction between the H₃O⁺ and OH^? ions and the dissipative structures, leading to the formation of complexes between the two ions deriving from probes and the molecular aggregates of water molecules. These results suggest that storing EDS at different temperatures does not alter the non-equilibrium changes in the supramolecular structure of water in the studied solutions.     

Dependence of enthalpic pairwise self-interactions on ionic strength: Some 2-deoxy and N-acetyl monosaccharides in aqueous NaCl solutions at T = 298.15 K

The dilution enthalpies of four derivatives of monosaccharides, namely 2-deoxy-d-glucose (2-DGlu), N-acetyl-d-glucosamine (GluNAc), 2-deoxy-d-galactose (2-DGal) and N-acetyl-d-galactosamine (GalNAc), in aqueous NaCl solutions of various molalities (b = 0–3.0 mol · kg⁻¹) have been determined respectively at T = 298.15 K by isothermal titration calorimetry (MicroCal ITC200). The corresponding values of enthalpic pairwise self-interaction coefficients (h₂) have been calculated according to the McMillan–Mayer theory. It was found that across the range studied of ionic strength (I) or molality (b = I), the h₂ coefficients are all positive, in the order h₂ (GluNAc) > h₂ (GalNAc) > h₂ (2-DGlu) > h₂ (2-DGal), and decrease gradually after increasing first up to a maximum at b ≈ 1.5 mol · kg⁻¹. The effects of ionic strength (I) on the trends of h₂ have been discussed from the point of view of complex (solute + solute) and (solute + solvent) interactions in solutions.     

A comparison of equations for fitting protonation constants of carboxylic acids in aqueous tetramethylammonium chloride at various ionic strengths

The protonation of acetic, malonic, succinic, citric, 1,2,3-propanetricarboxylic, 2-methyl-1,2,3-propanetricarboxylic, 1,2,3,4-butanetetracarboxylic, and benzenehexacarboxylic acids was studied potentiometrically, at 25°C and at various ionic strengths in aqueous tetramethylammonium chloride, in the range 0 ≤I _c ≤ 3 mol-dm^-3 (0≤I _m≤ 4.4 mol-kg^-1). Protonation constants were fitted by several equations (Debye-Hückel type, Pitzer and Bromley equations) for the dependence on ionic strength. General equations, containing some common parameters, independent of the acid considered, are reported.     

Hydrolysis of methyltin(IV) trichloride in aqueous NaCl and NaNO3 solutions at different ionic strengths and temperatures

The hydrolysis of methyltin(IV) trichloride (CH₃SnCl₃) has been studied in aqueous NaCl and NaNO₃ solutions (0 < I/mol dm⁻³ ≤ 1), at different temperatures (15 ≤ T/°C ≤ 45) by­potentiometric measurements (H⁺‐glass electrode). By considering the generic hydrolytic <?tw=97.2%>reaction pCH₃Sn³⁺ + qH₂O = (CH₃Sn)_p(OH)_q^3p−q<?tw>­+ qH⁺ (logβ_pq), we have the formation of five species and logβ₁₂ = −3.36, logβ₁₃ = −8.99, logβ₁₄ = −20.27 and logβ₂₅ = −7.61. The first hydrolysis step is measurable only at very low pH values and was not determined: a rough estimate of the hydrolysis constant is logβ₁₁ = −1.5 (± 0.5). The dependence on ionic strength of logβ_pq is quite different in NaNO₃ and NaCl solutions, and the formation at low pH values of the species CH₃Sn(OH)Cl⁺ has been found with logβ = −1.40. Hydrolysis constants strongly depend on temperature and from the relationships logβ_pq = f(T), ΔH ° values have been calculated. Speciation problems of CH₃Sn³⁺ in aqueous solution are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermodynamic parameters for the protonation of carboxylic acids in aqueous tetraethylammonium iodide solutions

The protonation constants of 21 carboxylic acids (formic, acetic, propionic, benzoic, phenoxyacetic, salicylic, oxalic, malonic, succinic, itaconic, malic, tartaric, oxydiacetic, thiodiacetic, thiodipropionic, phthalic, maleic, citric, 1,2,3-tricarboxylic, 1,2,4-tricarboxylic and 1,2,4,5-tetracarboxylic), have been determined potentiometrically, by pH-metric measurements, at several temperatures and ionic strengths, 5T55°C, 0<11 mol-dm^–3, using tetraethylammonium iodide as background salt. General equations for the dependence on ionic strength of thermodynamic parameters have been found. The statistical significance of results and the possibility of using a simple model for the thermodynamics of carboxylic acids protonation, is discussed.     

氨基酸季铵离子液体水溶液的密度和黏度

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The conductivity of dilute aqueous solutions of magnesium chloride at 25°C

There is a disagreement in the literature regarding the best value of _o[1/2MgCl₂]. For this reason, the conductivity of dilute aqueous MgCl₂ solutions have been determined at 25°C. The new experimental data and those available in the literature have been analyzed with two theoretical treatments of electrolytic conductivity. On the basis of that analysis, the values 129.72±0.05 and 53.40±0.05 S-cm²-mol^–1 for _o[1/2MgCl₂] and _o[1/2Mg²⁺], respectively, are recommended.     

Observation of a combined dilution and salting effect in buffers under conditions of high dilution and high ionic strength

The pH value of buffer solutions is crucially dependent on the relative concentrations of all species in solution. The addition of water or neutral salt can have a significant effect on the pH of a buffer solution. This study examines the magnitude of the "dilution effect" and the "salt effect" for several commonly used inorganic and biological buffers. Novel data are obtained for the change in pH observed upon dilution or addition of neutral salt to these buffers which add to, complement and extend existing literature values. The validity of considering the dilution and salt effects as a combined ionic strength effect is also considered as well as the ability of the pH measuring device to perform valid measurements in these extreme conditions.     

Conductance of aqueous NaCl solutions at pressures up to 2000 atm

Electrical conductance measurements are reported for aqueous NaCl solutions at 25°C as a function of concentration up to 0.02M and pressures up to 2000 atm. The data were analyzed with the Fuoss-Hsia-Fernandez-Prini (FHFP) equation. The standard error of fit, , varies from 0.04 at 1 atm to 0.10 at 2000 atm. The increase of with pressure arises from increasing non-randomness in the distribution of errors about the FHFP equation suggesting that modifications in the theory are necessary. The pressure dependence of _O for NaCl and KCl is nearly identical.Contribution of the Scripps Institution of Oceanography, New Series     

Viscosity of aqueous calcium chloride solutions at high temperatures and high pressures

Viscosity of six (0.10, 0.33, 0.65, 0.97, 1.40, and 2.00) mol kg⁻¹ binary aqueous CaCl₂ solutions has been measured with a capillary-flow technique. Measurements were made at pressures up to 60 MPa. The range of temperature was from 293 to 575 K. The total uncertainty of viscosity, pressure, temperature, and composition measurements was estimated to be less than 1.6%, 0.05%, 15 mK, and 0.014%, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous CaCl₂ solutions was studied. The measured values of viscosity of CaCl₂(aq) were compared with data, predictions, and correlations reported in the literature. The temperature and pressure coefficients of viscosity of CaCl₂(aq) were studied as a function of concentration and temperature. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for the relative viscosity (η/η₀) to accurate calculate the values of viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity B-coefficients were compared with the values calculated from the ionic B-coefficient data. The physical meaning parameters V and E in the absolute rate theory of viscosity and hydrodynamic molar volume (effective rigid molar volume of salt) V_k were calculated using present experimental viscosity data. TTG model has been used to compare predicted values of the viscosity of CaCl₂(aq) solutions with experimental values at high pressures.     

Calculation of activities and solubilities of alkali metal perchlorates at high ionic strengths in multicomponent aqueous systems

The equations of Nývlt, of Bromley, and of Pitzer for the representation of activity coefficients of electrolytes in multicomponent ionic systems have been used to fit solubility data for some alkali metal perchlorates and ammonium perchlorate in mixture with other electrolytes at ionic strengths varying from 0.08 mol-kg^–1 to as high as 24 mol-kg^–1. Only the Pitzer equations can be used rellably to fit the solubility data over the whole range of ionic strengths encountered for ternary systems but there are certain limitations and certain assumptions which have to be made concerning the Pitzer ionic interaction parameters. A method is also proposed for the calculation of the Pitzer single electrolyte parameters, ⁰,¹ andC , for the less soluble perchlorates from fitting their solubility data over a wide range of high ionic strengths.     

Effects of pH and ionic strength on the stability of nanobubbles in aqueous solutions of alpha-cyclodextrin

Formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules is a spontaneous process. Using a combination of laser light scattering (LLS) and zeta-potential measurements, we investigated the effects of salt concentration and pH on their stability in alpha-cyclodextrin (alpha-CD) aqueous solutions. Our results reveal that the nanobubbles are unstable in solution with a higher ionic strength, just like colloidal particles in an aqueous dispersion, but become more stable in alkaline solutions. The zeta-potential measurement shows that the nanobubbles are negatively charged with an electric double layer, presumably due to adsorption of negative OH- ions at the gas/water interface. It is this double layer that plays a critical dual role in the formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules, namely, it not only provides a repulsive force to prevent interbubble aggregation and coalescence but also reduces the surface tension at the gas/water interface to decrease the internal pressure inside each bubble.     

On the properties of surfactant aqueous solutions

Summary From studies of aqueous solutions of dodecylammoniumnitrate an association mechanism has been proposed involving multiequilibrium. In the concentration range considered we can differentiate between two aspects: ranges of marked qualitative and quantitative changes and formation of differently structured surfactant species.

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Zusammenfassung Aus der Untersuchung wäßriger Lösungen von Dodecylammoniumnitrat würde ein Assoziationsmechanismus abgeleitet, welcher ein Multiequilibrium beinhaltet. Im untersuchten Konzentrationsbereich können zwei Bereiche unterschieden werden: Bereiche mit ausgeprägten qualitativen und quantitativen Änderungen und Bereiche mit der Bildung von verschieden strukturierten oberflächenaktiven Spezies.

     

Variations of activity coefficients in concentrated electrolyte solutions at constant lonic strength

Measurements of different types on various (trace) electrolytes in HClO₄–Na(Li)ClO₄ solutions at several (constant) values of the ionic strength have been used to determine the variation of their activity coefficients with changing amount of perchloric acid in the solution. These variations (with respect to the hydrogen ion) differ considerably among different cations and anions. The results for the alkali metal ions and the anions are interpreted in the light of the recent work of Pitzer on short-range ionic interactions. The results for the cations with outerd-electrons and the alkaline earth metal ions are interpreted in terms of ion-solvent interactions. It is concluded that the use of HClO₄–NaClO₄ solutions of high ionic strength (rather than the use of HClO₄–LiClO₄ solutions) is advisable in studies where the variation in activity coefficients must be accounted for. Finally, it is shown that the usual interpretation of the influence of the salt medium in studies of complex equilibria and reaction kinetics is sometimes questionable.     

Near-infrared spectra of water and aqueous electrolyte solutions at high pressures

The near-infrared spectra (9500 to 11000 cm^–1) of pure water and aqueous solutions of alkali halides, MgCl₂, NaClO₄, and R₄NBr were measured at temperatures between 10 and 55°C and pressures up to 500 MPa. From the analysis of the absorption spectra the following conclusions are drawn. (1) The ice I-like open structure is destroyed and the packed structure is formed as the pressure is increased. (2) The open structure of water is destroyed by the addition of alkali halides and MgCl₂ and water molecules are restricted around the ions by ion-dipole interactions. This results in a loosening of the O–H bond. (3) The perchlorate ion destroys the open structure of water and the ion-dipole interaction with water is insignificant. (4) The Bu₄N⁺ ion forms water structure around the ion similar to that of the clathrate open structure.     

Enhanced stability of the model mini‐protein in amino acid ionic liquids and their aqueous solutions

Using molecular dynamics simulations, the structure of model mini‐protein was thoroughly characterized in the imidazolium‐based amino acid ionic liquids and their aqueous solutions. Complete substitution of water by organic cations and anions further results in hindered conformational flexibility of the mini‐protein. This observation suggests that amino acid‐based ionic liquids are able to defend proteins from thermally induced denaturation. We show by means of radial distributions that the mini‐protein is efficiently solvated by both solvents due to a good mutual miscibility. Amino acid‐based anions prevail in the first coordination sphere of positively charged sites of the mini‐protein whereas water molecules prevail in the first coordination sphere of negatively charged sites of the mini‐protein. © 2015 Wiley Periodicals, Inc.