Volume and compressibility effects in the formation of metal-EDTA complexes

We used precise measurements of ultrasonic velocity and density to study the complexation of ethylendiaminetetraacetic acid (EDTA) with Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ at 25‡C and pH 12. From these measurements we obtained the changes in the molar concentration increment of the ultrasonic velocity δA, the apparent molar adiabatic compressibility δK_sΦ, and the apparent molar volume δV_Φ of complex formation. The hydration contributions δ(AV_h) to the volume effect of binding range from 39.6 to 46.6 cm³-mol^-1 while the hydration contribution to the adiabatic compressibility change in the binding, δ(δK_h), ranges from 103.9X 10^-4 to 131.1 X 10^-4 cm³-mol^-1-bar^-1. These data are interpreted in terms of dehydration of interacting molecules,i.e., transfer of water molecules from the hydration shells of cations and EDTA into the bulk water. The ratio δ(δV_h)/ δ(δV_h) is in the range 0.35 to 0.38 bar, indicating a dominant contribution from the dehydration of charged atomic groups in the volume and the compressibility effects of complex formation.     

Solvation of magnesium chloride and sulfate in aqueous solutions at 278.15–323.15 K

Isoentropy compressibilities of aqueous magnesium chloride and sulfate were determined based on precision measurements of ultrasound velocity, density, and isobaric heat capacity at low to high concentrations at 278.15–323.15 K. The hydration numbers h and the molar parameters of volume and compressibility were calculated based on thermodynamically correct equations for hydration complexes (V _h , β _h V _h ), water in the hydration shell (V _1h , β_1h V _1h ), and the void containing a stoichiometric mixture of ions (V _2h , β_2h V _2h ). The h and β _h V _h values were found to be independent of temperature; the molar compressibility of the hydration sphere (β_1h V _1h ) and the stoichiometric mixture of ions without a hydration shell (β_2h V _2h ) were independent of the concentration under the stated conditions. The effect of the electrostatic field of ions on the temperature dependence of the molar volume of water in the hydration sphere was more significant than the effect of pressure on the temperature dependence of the molar volume of bulk water. This is attributed to changes in the dielectric constant of water in the vicinity of the electrolyte ions.     

Adiabatic compressibility and structural features of non-electrolyte aqueous solutions

Structural characteristics of the hydration complexes of non-electrolytes such as the hydration numbers h, molar adiabatic compressibility of hydration complexes β _h V _h , the molar volume of water in the hydration sphere V _1h , the solute molar volume without hydration environments V _2h and others are determined using the data on the ultrasonic velocity, the density and heat capacity of aqueous solutions of urea, urotropine, acetonitrile, and a number of amides of N-acetyl amino acids. A theoretical model of solvation is also applied. A comparison of the environments of hydrated urotropine molecules with those of urea and acetonitrile molecules in an aqueous medium shows a considerable hydrophobic interaction of urotropine with a solvent.     

Solvation of the Electrolytic Components of Seawater

A new modification of the adiabatic compressibility method of investigating solvation in solutions is presented and applied to the analysis of the following structurally-related characteristics of hydrated complexes of seawater electrolytes (NaCl, KCl, MgCl₂, CaCl₂, Na₂SO₄, MgSO₄) at different concentrations (0.1 to 5.0 mol⋅kg⁻¹) and temperatures (278.15 to 308.15 K): solvation numbers (h) and their dependences on concentration, volumes of stoichiometric mixtures of ions without their hydration shells (V _2h ), compressibilities (β _1h ) and molar volumes of water in their solvation shells (V _1h ), their dependences on concentration and temperature, etc.     

Quantitative estimation of the discontinuous function of the solvent in aqueous electrolyte solutions

The adiabatic compression method is used to determine quantitative solvation parameters such as hydration numbers h, the molar adiabatic compressibility of hydrated complexes β _h V _h , the volume V _1h and compressibility β_1h of water in ion hydration shells, and several other properties in the temperature range 278.15–323.15 K. Hydration numbers are used to determine the verified activity coefficient of the solvent, γ _R . The concentration dependence of the coefficient is shown to be a discontinuous function, with the discontinuity point corresponding to the complete solvation boundary.     

A Study on Hydration of Urea and Urotropin by Density and Speed of Sound Measurements in Aqueous Solutions

Experimental data on the speed of propagation of ultrasound waves, density, and isobaric heat capacity in aqueous solutions of urea and urotropin have been considered. The findings have been used for calculating the molar isentropic compressibilities of solutions of the investigated substances over the temperature range 278.15 to 308.15 K. Invoking a theoretical solvation model based on the isentropic compressibility, which takes into account compressibilities of the hydrated complexes, their structural characteristics have been determined in aqueous solutions of nonelectrolytes: hydration numbers h, molar isentropic compressibility of hydrated complexes ?? _h V _h , molar volumes of water in a hydration shell V _1h , molar volumes of the solute without its hydration environment V _2h , and many other properties. The possibility of hydrophobic solvation has been shown for urotropin solutions and hydrophilic solvation for urea solutions.     

Structural state of solvent in electrolyte solutions

Isoentropic compressibilities were determined for aqueous solutions of five electrolytes ranging from dilute to almost saturated solutions at 278.15–308.15 K based on precision measurements of ultrasound velocity. Using correct relations we have found hydration numbers (h) and molar parameters of volume and compressibility of hydrated complexes (V _h , β_h V _h ), water in the hydration shell (V _1h , β 1_h V _1h ), and void containing a stoichiometric mixture of ions (V _2h , β _2h V _2h ). In the temperature range under study, the hydration numbers h and the parameters β_h V _h are independent of temperature; molar compressibilities of hydration sphere (β _1h V1_h) are independent of concentration. Since β_h V _h is independent of temperature at a constant concentration of electrolyte, Y _K,S ^e also becomes independent of temperature. It is shown that the chemical potentials of bound and unbound water are equal and that γ_R = F(h) is an example of a discontinuous function that defines the abrupt change in the solvent at the complete solvation limit in solution.     

Hydrolysis of cis- and trans-Diammineplatinum(II) Complexes: Hydration, Equilibrium, and Kinetics Properties

We have used a combination of ultrasound and density techniques to measure the hydration parameters, apparent molar volume, and apparent molar adiabatic compressibility, of the antitumor drug cis-dichlorodiammineplatinum(II), cis-[Pt(NH₃)₂Cl₂], and its inactive isomer trans-dichlorodiammineplatinum(II), trans-[Pt(NH₃)₂Cl₂], in 10 mM NaNO₃, pH 5.6 at 37°C. The data have been interpreted in terms of the overall hydration of each isomer, the actual hydration contribution to the adiabatic compressibility, K _h, ranges from –56.4 × 10^–4 to –20.3 × 10^–4 cm³-mol^–1-bar^–1, and the volume contribution, V _h, ranges from –16.3 to –6.4 cm³-mol^–1. The negative signs of these hydration contributions indicate that the volume and compressibility of the water immobilized by the platinum complexes is smaller than the volume and compressibility of bulk water. The V _h and K _h parameters for all platinum complexes investigated are linearly dependent on the relative amount of hydrolyzed chlorides. The values of each parameter become more negative with increasing hydrolysis, and show that the degree of hydration increases. The similar dependence of the amount of hydrolyzed chloride ligands reveals similar hydration properties for these two complexes. Thus, the symmetry of the complexes, which is of crucial importance for anticancer activity, has no influence on their hydration properties. Under our experimental conditions, the equilibrium constants for the hydrolysis of cis-[Pt(NH₃)₂Cl₂] are K ₁ = 2.52 mM and K ₂ = 0.04 mM. The equilibrium constant for the first step of hydrolysis of trans-[Pt(NH₃)₂Cl₂] is 0.03 mM, while the second chloride ligand cannot be substituted by water, even in the irreversible reaction with AgNO₃. Furthermore, continuous measurements of the ultrasonic velocity during hydrolysis permits the accurate evaluation of the pseudo-first-order rate constant k ₁ for the hydrolysis of the first chloride ligand of cis-[Pt(NH₃)₂Cl₂], which is 16±1×10^–5 s^–1.     

Structural Features of Ion Hydration in Sodium Nitrate and Thiosulfate

The features of formation of hydration spheres around electrolyte ions in aqueous solutions of sodium nitrate and thiosulfate in a wide concentration range (from 2 to 42 wt %) at temperatures from 278.15 to 318.15 K were determined from the isoentropy compressibility data. The structural characteristics of the solute hydration complexes were determined. The hydration numbers decrease with increasing concentration and are independent of temperature. Na2S2O3 has the highest hydration number at infinite dilution (h ⁰) and is characterized by the lowest molar isoentropy compressibility of water in the hydration spheres of the ions (S,1hV1h). Sodium thiosulfate, compared to sodium nitrate, interacts with water stronger, and its aqueous solutions show a greater degree of ordering.     

Volumetric properties of glucose in aqueous HCl solutions at temperatures from 278.15 to 318.15 K

Densities have been measured for Glucose + HCl +Water at 10-degree intervals from 278.15 to 318.15 K. The apparent molar volumes (V _Φ,G) and standard partial molar volumes (V _Φ,G ⁰ ) for Glucose in aqueous solution of 0.2, 0.4, 0.7, 1.1, 1.6, 2.1 mol·kg⁻¹ HCl have been calculated as well as volumetric interaction parameters (V _EG) for Glucose — HCl in water and standard partial molar expansion coefficients (∂V _Φ,G ⁰ / ∂T)_p. Results show that (1) the apparent molar volume for Glucose in aqueous HCl solutions increases lineally with increasing molality of Glucose and HCl; (2) V _Φ,G/0 for Glucose in aqueous HCl solutions increases lineally with increasing molality of HCl; (3) the volumetric interaction parameters for Glucose — HCl pair in water are small positive and vary slightly with temperature; (4) the relation between V _Φ,G ⁰ and temperature exists as V _Φ,G ⁰ = a ₀ + a ₁(T − 273.15 K)^2/3; (5) values of (∂V _Φ,G ⁰ / ∂T)_p are positive and increase as temperatures rise, and at given temperatures decrease slightly with increasing molalities of HCl, indicating that the hydration of glucose decreases with increasing temperature and molality of HCl. These phenomena are interpreted successfully by the structure interaction model. Translated from Acta Chimica Sinica, 2006, 64(16): 1635–1641 (in Chinese)     

Quantitative characteristics of hydration in solutions of sodium sulfate and sodium chloride at 278.15–323.15 K

The solvation parameters of aqueous solutions of sodium chloride and sodium sulfate were studied on the basis of published density and ultrasound velocity data. Correct thermodynamic relations for temperature variation from 278.15 to 323.15 were used to determine quantitative parameters of solvation, in particular, the hydration numbers h, the molar adiabatic compressibility of hydrate structures β _h V _h , the volume V _1h and compressibility β _1h of water in the hydration shells of ions, and others. h and β _h V _h do not depend on temperature in the range of parameters studied, and electrostriction compression about the ions has a more pronounced effect on the structure than mere pressure change.     

Partial Molar Volumes of Some of α-Amino Acids in Binary Aqueous Solutions of MgSO4·7H2O at 298.15 K

The apparent molar volume, V ^o _{φ, 2}, of glycine, alanine, α-amino-n-butyric acid, valine and leucine have been determined in aqueous solutions of 0.25, 0.5 and 1.0 mol⋅dm⁻³ magnesium sulfate, and the partial specific volume from density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volume, V ^o _2,m , group contribution of amino acids and partial molar volume of transfer, Δ_tr V _2,m ^o, from water to aqueous magnesium sulfate solutions. The linear correlation of V _2,m ^o for a homologous series of amino acids has been utilized to calculate the contributions of charged end groups (NH₃ ⁺, COO⁻), CH₂ - groups and other alkyl chains of amino acids to V _2,m ^o. The results for Δ_tr V _2,m ^o of amino acids from water to aqueous magnesium sulfate solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. The values of the standard partial molar volume of transfer for the amino acids with different hydrophobic contents, from water to aqueous MgSO₄ are in general positive, indicating the predominance of the interactions of zwitterionic/hydrophilic groups of amino acids with ions of the salt. The hydration number decreases with increasing concentration of salt. The number of water molecules hydrated to amino acids decreases, further strengthening the predominance of ionic/hydrophilic interactions in this system.     

Thermophysical and thermoacoustical properties of benzaldehyde mixtures with ethylbenzene at 303.15, 308.15, and 313.15 K and a pressure of 0.1 MPa

Ultrasound velocity (u), density (ρ) and viscosity (η) measurements of benzaldehyde + ethylbenzene mixtures have been carried out at 303.15, 308.15, and 313.15 K. These values have been used to calculate the excess molar volume (V ^E), deviation in viscosity (δη), and deviation in isentropic compressibility (δβ_s), deviations in ultrasound velocity (δu), excess free volume (δV _f), excess intermolecular free length (δL _f) and excess Gibbs free energy of activation of viscous flow (δG ^E). McAllister’s three body interaction model is used for correlating kinematic viscosity of binary mixtures. The excess values were correlated using the Redlich-Kister polynomial equation to obtain their coefficients and standard deviations. The thermophysical properties under the study were fit to the Jouyban-Acree model. The observed variation of these parameters helps in understanding the nature of interactions in these mixtures. Further, theoretical values of the ultrasound speed were evaluated using theories and empirical relations.     

Apparent molar volume and apparent molar adiabatic compressibility of 2-hydroxy-5-methyl acetophenone in <Emphasis Type="Italic">N,N</Emphasis>-dimethylformamide at different temperatures

The speed of sound and density of 2-hydroxy-5-methyl acetophenone in dimethylformamide have been measured over the range of temperatures 25–40 °C. From the experimentally determined data, values of apparent molar volume (V _ϕ), adiabatic compressibility (β_s), apparent molar adiabatic compressibility (K _s,ϕ) and their limiting values have been computed. Values at infinite dilution provide information regarding solute–solvent interaction. The density and velocity increases with increase in concentration and decreases with increase in temperature. These results have been analyzed in terms of molecular interactions between acetophenone and dimethylformamide.     

Effect of free solvent on the solvation of electrolytes and nonelectrolytes

An approach is developed for analyzing hydration of sodium and magnesium sulfate electrolytes over a wide range of concentrations up to 1.8 mol/L at temperatures from 278.15 to 318.15 K. The model of free water (water that does not enter hydrate complexes) is used to analyze the hydration numbers, mean compressibility of water in the hydration sphere, its temperature dependence, and several other solvation parameters that are determined with difficulty. A comparative analysis of the behavior of the β_h V _h = f(h) function is carried out for zwitterions and electrolytes. This function has an identical slope for amino acids, halides, and nitrates; that is, the adiabatic compressibility of water in the hydrate complex of an electrolyte or nonelectrolyte (β_1h V1h) is independent of the solution concentration over a wide range of compositions. This suggests that the clathrate solvation mechanism operates both for a stoichiometric ion mixture and for zwitterions. Aqueous solutions of sodium sulfate and magnesium sulfate behave quite differently: they appreciably deviate from the solutions of the specified systems.     

Interactions of Some Amino Acids with Aqueous N,N-Dimethylacetamide Solutions at 298.15 and 308.15 K: A Volumetric Approach

The apparent molar volumes, V _φ , of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg⁻¹ N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume, V _φ ^o, and standard partial molar volumes of transfer, Δ_tr V _φ ^o, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions between its side group (—CH₃) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model.     

Apparent Molar Volume and Isentropic Compressibility for the Binary Systems {Methyltrioctylammonium Bis(trifluoromethylsulfonyl)imide + Methyl Acetate or Methanol} and (Methanol + Methyl Acetate) at <Emphasis Type="Italic">T</Emphasis>=298.15, 303.15, 308.15 and 313.15 K and Atmospheric Pressure

The densities and speeds of sound for binary mixtures containing the solute ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]⁺[Tf₂N]⁻), solute/solvent methanol, and solvent methyl acetate have been measured at 298.15, 303.15, 308.15 and 313.15 K at atmospheric pressure. The binary mixtures studied are ([MOA]⁺[Tf₂N]⁻ + methyl acetate or methanol), and (methanol + methyl acetate). The apparent molar volume, V _φ and the apparent molar isentropic compressibility, k _φ , have been evaluated from the experimental density and speed of sound data, respectively. The parameters of a Redlich–Mayer type equation were fitted to the apparent molar volume and apparent molar isentropic compressibility data. The apparent molar volume and apparent molar isentropic compressibility at infinite dilution, V_f⁰V_{\phi}^{0} and k_f⁰k_{\phi}^{0}, respectively, of the binary solutions have also been calculated at each temperature. The infinite dilution apparent molar volume indicates that intermolecular interactions for (IL + methyl acetate) mixtures are stronger than for (IL + methanol) mixtures at all temperatures except at 298.15 K, and that V_f⁰V_{\phi}^{0} for the (IL + methyl acetate or methanol) binary systems increases with an increase in temperature. For the (methanol + methyl acetate) system the intermolecular interaction are weaker and V_f⁰V_{\phi}^{0} also increases with an increase in temperature. Values of the infinite dilution apparent molar expansibility, E_f⁰E_{\phi}^{0}, indicate that the interaction between (IL + methyl acetate) is greater than for (IL + methanol) and (methanol + methyl acetate).     

Temperature and pressure dependence of the free volume in the perfluorinated polymer glass CYTOP: A positron lifetime and pressure‐volume‐temperature study

The microstructure of the free volume was studied for an amorphous perfluorinated polymer (T_g = 378 K). To this aim we employed pressure–volume–temperature experiments (PVT) and positron annihilation lifetime spectroscopy (PALS). Using the Simha‐Somcynsky equation of state the hole free volume fraction h and the specific free and occupied volumes, V_f = hV and V_occ = (1 ? h)V, were determined. Their expansivities and compressibilities were calculated from fits of the Tait equation to the volume data. It was found that in the glass V_occ has a particular high compressibility, while the compressibility of V_f is rather low, although h (300 K) = 0.108 is large. In the rubbery state the free volume dominates the total compressibility. From the PALS spectra the hole size distribution, its mean, 〈v_h〉, and mean dispersion, σ_h, were calculated. From a comparison of 〈v_h〉 with V_f a constant hole density of N_h′ = 0.25 × 10²¹ g^?1 was estimated. The volume of the smallest representative freely fluctuating subsystem, 〈V_SV〉 ∝ 1/σ_h², is unusually small. This was explained by an inherent topologic disorder of this polymer. 〈v_h〉 and σ_h show an exponential‐like decrease with increasing pressure P at 298 K. The hole density, calculated from N_h′ = V_f/〈v_h〉, seems to show an increase with P which is unexpected. This was explained by the compression of holes in the glass in two, rather than three, dimensions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2519–2534, 2007     

The influence of the molar ratio [H<Subscript>2</Subscript>O]/[Ti(OR)<Subscript>4</Subscript>] on the kinetics of the titanium-oxo-alkoxy clusters nucleation

The influence of the molar ratio h = [H₂O]/[Ti(OR)₄] (R = Pr ⁱ ) on the kinetics of the titanium-oxo-alkoxy clusters (TOAC) nucleation was studied. Clusters were formed by the titanium tetraisopropoxide Ti(OPr ⁱ )₄ chemical reaction with H₂O in n-propanol solution, with the fixed concentration of Ti(OPr ⁱ )₄ (c = 0.04 M), molar ratio h ∈ {11, 14, 17, 20} and temperature T ∈ {298, 308, 318} K. It was determined that the isothermal rate of clusters nucleation is a power law function of the molar ratio h. The kinetic parameter β value changes complexly as h and T change. The value of apparent activation energy of the nucleation process (E _a) decreases with the increase of value h. It was found that nucleation is a reaction with complex kinetics whose elementary stages are hydrolysis Ti(OR)₄ to Ti(OR)₃OH and formation of titanium-oxo-alkoxy clusters [Ti _{n + β}O_β](OR)_{4n + 2β} through the alcoxolation reaction.     

Evidence of solvation of aqueous electrolytes in a range from diluted to concentrated solutions

Parameters of solvation of strong electrolytes in aqueous solutions have been investigated based on literature data on their densities, thermal capacities, and rates of ultrasound propagation. By using appropriate thermodynamic equations, such quantitative parameters of solvation as hydration number (h), molar adiabatic compressibility of the hydrated forms (β _h V _h ), volume (V _1h ), and compressibility (β_1h ) of water in the hydrated shells of ions have been determined in the temperature interval from 278.15 to 323.15 K. It has been demonstrated that the h and β _h V _h values are temperature-independent within the studied interval and that electrostrictive compression near ions has a stronger effect on their structure than a simple change in pressure.