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.     

On the stability of extremely diluted aqueous solutions at high ionic strength

An extensive study has been carried out on extremely diluted aqueous solutions (EDS). These solutions revealed a really intriguing physico-chemical behaviour, characterized by multiple independent variables. Because of their behaviour, EDS can be described as far-from-equilibrium systems, capable of self-organization as a consequence of little perturbations. In this paper we investigate the stability of the calorimetric behaviour of EDS with a high ionic force, due to the presence of the sodium chloride electrolyte. We measured the excess heats of mixing of EDS with basic solutions, both with and without a high concentration of NaCl, and compared the results. In particular, we explored these concentrations: 0.5 and 1Mmol kg⁻¹). The analysis of the experimental results shows that the calorimetric response of the EDS is stable when they are in a concentrated solution of NaCl. That is of great relevance for the eventual pharmacological action of these solutions, since it involves the interaction with fluids of complex chemical composition and high concentration.     

Hydrohysteretic Phenomena of “Extremely Diluted Solutions” Induced by Mechanical Treatments: A Calorimetric and Conductometric Study at 25 <Superscript>∘</Superscript>C

The purpose of this study was to obtain information about the influence of successive dilutions and succussions (violent shaking) on the structure of water. “Extremely diluted solutions” (EDS) are solutions obtained through the iteration of two processes: 1:100 dilution and succussion. Those two processes are repeated until extreme dilutions are reached, so that the chemical composition of the end solution is identical to that of the solvent. We measured the heats of mixing and the electrical conductivity of basic solutions of such EDS, and compared these results with the analogous heats of mixing and electrical conductivity of the untreated solvent. The measurements were carried out as a function of the age of the samples. We found some relevant exothermic excess heat of mixing, and higher electrical conductivity than those of the untreated solvent, also in function of time. The measurements show a good linear correlation between the two independent physico-chemical quantities, implying a single cause for this behavior of the extremely diluted solutions. The slopes of the linear correlation depend on the age of the EDS. Such a phenomenon could result from a variation of the shape of molecular aggregates that characterize the two different supramolecular structures of the water of different ages. This behavior could provide important support for understanding the nature of the phenomena described herein. A really intriguing phenomenon is the evolution of some physico-chemical properties with time. This hints at a “trigger” effect on the formation of molecular aggregates that result from the succussion procedure. We show that successive dilutions and succussions can permanently alter the physico-chemical properties of the aqueous solvent, the extent of which depends on the age of the samples.     

New Physico-chemical Properties of Water Induced by Mechanical Treatments. A calorimetric study at 25°C

An extensive thermodynamic study has been carried out on aqueous solutions, obtained through the iteration of two processes: a dilution 1:100 in mass and a succussion. The iteration is repeated until extreme dilutions are reached (less than 1⋅10^–5 mol kg^–1 ) to the point that we may call the resulting solution an 'extremely diluted solution'. We conducted a calorimetric study, at 25°C, of the interaction of those solutions with acids or bases. Namely, we measured the heats of mixing of acid or basic solutions with bidistilled water and compared them with the analogous heats of mixing obtained using the 'extremely diluted solutions'. Despite the extreme dilution of the latter solutions, we found a relevant exothermic excess heat of mixing, excess with respects to the corresponding heat of mixing with the untreated solvent. Such an excess has been found in about the totality of measurements, and of a magnitude being well beyond one that could arise any issue of sensibility of the instrumental apparatus. Here we thus show that successive dilutions and succussions can permanently alter the physico-chemical properties of the solvent water. The nature of the phenomena here described still remains unexplained, nevertheless some significant experimental results were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.

     

Broadband dielectric spectroscopic, calorimetric, and FTIR-ATR investigations of D-arabinose aqueous solutions

The dielectric relaxation behavior of D-arabinose aqueous solutions at different water concentrations is examined by broadband dielectric spectroscopy in the frequency range of 10(-2) -10(7) Hz and in the temperature range of 120-300 K. Differential scanning calorimetry is also performed to find the glass transition temperatures (T(g)). In addition, the same solutions are analyzed by Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflectance (ATR) method at the same temperature interval and in the frequency range of 3800-2800 cm(-1). The temperature dependence of the relaxation times is examined for the different weight fractions (x(w)) of water along with the temperature dependence of dielectric strength. Two relaxation processes are observed in the aqueous solutions for all concentrations of water. The slower process, the so-called primary relaxation process (process-I), is responsible for the T(g) whereas the faster one (designated as process-II) is due to the reorientational motion of the water molecules. As for other hydrophilic water solutions, dielectric data for process-II indicate the existence of a critical water concentration above which water mobility is less restricted. Accordingly, FTIR-ATR measurements on aqueous solutions show an increment in the intensity (area) of the O-H stretching sub-band close to 3200 cm(-1) as the water concentration increases.     

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.     

Electric conductivity of concentrated aqueous solutions of propionic acid, sodium propionate and their mixtures

Specific electric conductivity (EC) of concentrated aqueous solutions of propionic acid (PA), sodium propionate (SP), and water/PA/SP mixtures is measured in the temperature range of 15–90°C. Specific EC passes a maximum at the increase in the electrolyte concentration in the mixtures of water/PA, water/SP, and water/PA/SP containing a similar PA concentration. The maximum EC value of the aqueous PA solution at the given temperature is used as the generalizing term. It is shown that the values of reduced EC (ratio of EC and its maximum value at the given temperature) fall on a single curve in the whole studied range of temperatures and concentrations of the water/PA mixture. The EC activation energy is calculated for all the studied solutions. It is found that the EC activation energy of these solutions decreases at the temperature increase and grows at the increase of the concentration of electrolyte.     

Temperature effect on the volume properties of a bisurea aqueous solutions

The densities of aqueous solutions of bisurea (2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione) were measured using a vibrating-tube densimeter at 288.15, 298.15, 308.15, and 318.15 K in the concentration range up to ∼3·10⁻³ moles of solute (1000 g of H₂O)⁻¹ with the error at most ±5· 10⁻⁶ g cm⁻³ (reproducibility up to 2·10⁻⁶ g cm⁻³). The limiting partial molar volume and expansibility of bisurea in water were calculated. The bicyclic molecules under study form in aqueous solution H-bonded hydrate complexes with rather high structure-packing density. These complexes are more subjected to the destroying effect of temperature than the corresponding urea complexes. The hydration of bisurea weakens with the temperature increase. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1929–1932, October, 2007.     

Models having the thermodynamic properties of aqueous solutions of tetraalkylammonium halides

The hypernetted-chain integral-equation-approximation method is used to calculate the ion-ion pair correlation functions and the thermodynamic properties of models of the kind previously studied,⁽¹⁾ which are based on an ion-ion pair potential having four terms: the usual Coulomb term, a core repulsion term, a term to represent a well-known dielectric repulsion effect, and a Gurney term to represent the effect of the overlap of the structure-modified regions, solvation shells or cospheres, when the ions come close together. The coefficientA _ij of the last term for each pairi,j of ionic species is the only parameter that is adjusted to fit the solution data. It is determined by fitting excess-free-energy (osmotic-coefficient) data. It is scaled to represent the molar free-energy change of water displaced from the cospheres when they overlap. The corresponding entropy changeS _ij and volume changeV _ij are determined by fitting, respectively, excessenthalpy and excess-volume data. Problems of finding a uniquely best set of parameters are discussed together with many examples of variations of the model, most of which require further investigation. A consistent set of these parameters, which represents much of what is known about the thermodynamic excess functions of these solutions at concentrations up to about 0.5M, is interpreted as far as possible in terms of the data for thermodynamic solvation functions for the same systems.This study was aided by a grant from the Office of Saline Water, U.S. Department of Interior.     

Enthalpy of dilution and heat capacity of aqueous solutions of tetrabutylammonium butyrate as a function of temperature

Enthalpies of dilution of tetrabutylammonium butyrate are reported as a function of temperature between 10° and 50°C. Heat capacities of aqueous solutions of tetrabutylammonium butyrate were measured in order to obtain values of _cp at 15°, 25°, and 35°C. These data were combined with the enthalpy of dilution data to obtain _cp as a function of molality and temperature. The apparent molal heat content _L decreased with increasing temperature in concentrated solutions but increased with increasing temperatures in dilute solutions (below0.7 m). Over the temperature range studied _cp shows a maximum as a function of molality at approximately 0.5m. The decrease in _cp with increasing concentration of hydrophobic solute is consistent with the view that the hydrophobic hydration cages, formed under the influence of the tetrabutylammonium and butyrate ions, are saturated at about 0.5m, and that at higher molalities increased overlap of the hydration cages occurs.     

Structural aspects of aqueous tetraalkylammonium salt solutions

Various thermodynamic and spectroscopic investigations on aqueous tetraalkylammonium salt solutions are reviewed from a structural viewpoint. At present, it is not yet clear what kind of water structure is formed around the alkyl groups of the large cations. However, the importance of cosphere overlap and ion-ion interaction (cation-anion, cation-cation, cation-anion-cation, etc.) in determining the solution properties are emerging more clearly. In this regard, model calculations based on the approach of Friedman and his coworkers are expected to be of considerable value.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

The conductivity of concentrated aqueous mixtures of NaCl and MgCl2 at 25°C

As part of a cooperative study of the thermodynamic and transport properties of aqueous mixtures of NaCl and MgCl₂ at 25°C, we report values of the molar conductivities of the mixed electrolyte in the concentration range 0.5 to 3.6 molar. It was found that the conductivities in the mixtures differ from those calculated assuming additivity of the conductivities of the component binary solutions by 4.65 S-cm²-mol^–1 at constant total molarity and 0.50 S-cm²-mol^–1 at total ionic strength.     

Enthalpies of interaction of glycine with some amides in aqueous solutions at 298.15 K

The dissolution enthalpies of glycine in aqueous solutions of acetamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylformamide, N,N-diethylformamide and N,N-diethylacetamide were measured at 298.15 K. The enthalpic pair interaction coefficients of glycine zwitterion-amide molecules were determined by using standard solution enthalpies of glycine in water and aqueous solutions of amides. The additivity of groups concept of Savage and Wood was used to estimate the contribution of each of the functional groups of the studied amides.     

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.     

High-frequency dielectric and conductometric properties of poly-l-lysine aqueous solutions at the crossover between semidilute and entangled regime

The dielectric and conductometric properties of poly-l-lysine aqueous solutions have been investigated in the frequency range from 1 MHz to 1.8 GHz, where micro-Brownian dynamics and internal motion of side-chain polar groups result in a well-defined relaxation process, intermediate between that caused by counterion polarization (characteristic of the polyelectrolyte nature of the polyion investigated) and that associated with the orientational polarization of the aqueous phase. The polymer concentration has been varied in a wide interval in order to investigate the influence of different chain conformations on the dielectric parameters as a consequence of the different concentration regimes occurring in these systems. With the help of polymer scaling theories, scaling relations for the dielectric strength and the relaxation time are presented, predicting, as the polymer concentration is increased, a transition from semidilute-unentangled to semidilute-entangled regimes. We compare these predictions with the experimental findings over the whole concentration range investigated, with a qualitative agreement. Deviations from the scaling behavior related to a crossover regime between unentangled and entangled regions are briefly discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3123–3130, 1999     

Sonoluminescence of aqueous solutions of sulfuric acid and sulfur dioxide

Sonoluminescence (SL) of aqueous solutions of sulfuric acid and sulfur dioxide enhances with an increase in their concentration and reaches a maximum at 16 and 0.05 mol L^–1, respectively. The further increase in the concentration of these substances decreases the SL intensity. The SL spectra of the solutions have a broad maximum at 450 nm. Excited SO₂ molecules formed in sulfuric acid due to sonolysis are luminescence emitters. The proposed mechanism of bright SL in these systems is based on the energy transfer from the electron-excited sonolysis products to the SO₂ molecules in cavitation bubbles.     

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     

Nuclear magnetic resonance relaxation of methane protons in aqueous solutions

Proton nuclear magnetic resonance longitudinal relaxation rates are reported at 100MHz for CH₄ and CHD₃ in deuterium oxide solutions. The results demonstrate that methane reorients with a correlation time on the order of 0.1 psec, considerably faster than molecule correlation times in aqueous solutions.