Volumetric Properties of l-Alanine and l-Serine in Aqueous N,N-Dimethylformamide Solutions at 298.15 K

The densities of l-alanine and l-serine in aqueous solutions of N,N-dimethylformamide (DMF) have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes $ (V_{\phi } ) $ ( V ? ) , standard partial molar volumes $ (V_{\phi }^{0} ) $ ( V ? 0 ) , standard partial molar volumes of transfer $ (\Updelta_{\text{tr}} V_{\phi }^{0} ) $ ( Δ tr V ? 0 ) and hydration numbers have been determined for the amino acids. The $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 values of l-serine are positive which suggest that hydrophilic–hydrophilic interactions between l-serine and DMF are predominant. The –CH₃ group of l-alanine has much more influence on the volumetric properties and the $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 have smaller negative values. The results have been interpreted in terms of the cosphere overlap model.     

Volumetric Properties of Some Aliphatic Mono- and Dicarboxylic Acids in Water at 298.15 K

The apparent molar volumes, V _φ , of two series of homologous aliphatic carboxylic acids, H(CH₂) _n COOH [n=0–5] and (CH₂) _n (COOH)₂ [n=0–5], were determined in dilute aqueous solutions by density measurements at T=298.15 K. Densities were measured using a vibrating-tube densimeter (DMA 5000, Anton Paar, Austria) at T=298.15 K. These results were used to calculate the apparent molar volumes of each solute over the concentration range 0.0050≤m/(mol⋅kg⁻¹)≤0.3000. Values of the apparent molar volumes of undissociated acids V_f(u)⁰V_{\phi (u)}^{0} were also calculated. The variation of V_f(u)⁰V_{\phi (u)}^{0} was determined as a function of the aliphatic chain length of the studied carboxylic acids.     

Solute–Solvent Interactions of Amino Acids in Aqueous 1-Propyl-3-Methylimidazolium Bromide Ionic Liquid Solutions at 298.15 K

Densities, viscosities, and refractive indices of three amino acids (glycine, L-alanine, and L-valine) in aqueous solutions of an ionic liquid, 1-propyl-3-methylimidazolium bromide, have been measured at 298.15 K. These data have been used to calculate apparent molar volumes (V _φ ), viscosity B-coefficients, and molar refractions of these mixtures. The standard partial molar volumes (V_f⁰V_{\phi}^{0}) and standard partial molar volumes of transfer (D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0}) have been determined for these amino acid solutions from these density data. The resulting values of V_f⁰V_{\phi}^{0} and D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0} for transfer of amino acids from water to aqueous ionic liquid solutions have been interpreted in terms of solute + solvent interactions. These data also indicate that hydrophobic interactions predominate in L-alanine and L-valine solutions. Linear correlations were found for both V_f⁰V_{\phi}^{0} and the viscosity B-coefficient with the number of carbon atoms in the alkyl chain of the amino acids, and have been used to estimate the contribution of the charged end groups (NH₃⁺\mathrm{NH}_{3}^{+}, COO⁻), the CH₂ group, and other alkyl chains of the amino acids. The viscosity and molar refractivity results have been used to confirm the conclusions obtained from volumetric properties.     

Calorimetric and Volumetric Studies of the Interactions of Propionamide in Aqueous Alkan-1-ol Solutions at 298.15 K

Enthalpies of solution and apparent molar volumes have been determined for propionamide in aqueous methanol, ethanol and propanol solutions at 298.15 K using a C-80 microcalorimeter and a DMA60/602 vibrating-tube digital densimeter. The enthalpic and volumetric interaction coefficients have been calculated. Using the present results along with results from previous studies for formamide, the pair-interaction coefficients are discussed from the perspective of dipole-dipole and structural interactions. In addition, the triplet interaction coefficients are interpreted by using the solvent-separated association mechanism.     

Thermodynamic Studies of Amino Acid–Denaturant Interactions in Aqueous Solutions at 298.15 K

As proteins and other biomolecules consisting of amino acid residues require external additives for their dissolution and recrystallization, it is important to have information about how such additives interact with amino acids. Therefore we have studied the interactions of simple model amino acids with the additives urea and guanidine hydrochloride in aqueous solutions at 298.15 K, using vapor pressure osmometry. During the measurements, the concentration of urea was fixed as ∼2 mol⋅kg⁻¹ and that of guanidine hydrochloride was fixed as ∼1 mol⋅kg⁻¹ whereas the concentrations of amino acids were varied. The experimental water activity data were processed to get the individual activity coefficients of all the three components in the ternary mixture. Further, the activity coefficients were used to get the excess Gibbs energies of solutions and Gibbs energies for transfer of either amino acids from water to aqueous denaturant solutions or denaturant from water to aqueous amino acid solutions. An application of the McMillan-Mayer theory of solutions through virial expansion of transfer Gibbs energies was made to get pair and triplet interaction parameter whose sign and magnitude yielded information about amino acid–denaturant interactions, relative to their interactions with water. The pair interaction parameters have been further used to obtain salting constants and in turn the thermodynamic equilibrium constant values for the amino acid–denaturant mixing process in aqueous solutions at 298.15 K. The results have been explained in terms of hydrophobic hydration, hydrophobic interactions and amino acid–denaturant binding.     

Volumetric Properties of Aqueous Solutions of L-Glutamic Acid and Magnesium-L-Glutamate

Densities of aqueous solutions of L-glutamic acid and magnesium-L-glutamate were determined from T=288.15 to 333.15 K at 5 K temperature intervals. The measured densities were used to evaluate the apparent molar volumes, V _2,φ (m,T), the cubic expansion coefficients, α(m,T), and the changes of isobaric heat capacities with respect to pressure, (∂ C _p /∂ p) _T,m . They were qualitatively correlated with changes in the structure of water that occur when L-glutamic acid or magnesium-L-glutamate are present.     

Volumetric Studies of 2,2,2-Cryptand in Aqueous and Aqueous KBr Solutions at 298.15 K: An Example Involving Solvent-Induced Hydrophilic and Hydrophobic Interactions

Density measurements of good precision are reported for aqueous and aqueous salt (KBr) solutions containing 2,2,2-cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) (~0.009 to ~0.24 mol·kg^?1) for the binary systems and for the ternary system with ~0.1 mol·kg^?1 2,2,2-cryptand and varying KBr concentrations (~0.06 to ~ 0.16 mol·kg^?1) at 298.15 K. The density data have been used to study the variation of apparent molar volume (\( \varphi_{V} \)) of 2,2,2-cryptand and of KBr as a function of concentration. 2,2,2-Cryptand is a diamine and hence it is hydrolyzed in aqueous solutions and needs an appropriate methodology to obtain meaningful thermodynamic properties. We have adopted a method of hydrolysis correction developed initially by Cabani et al. and later by Kaulgud et al. to analyze our volumetric data for the aqueous solutions. The method is described and we were successful in obtaining the limiting partial molar volume of the bare (free) cryptand in water at 298.15 K. Volumes of ionization as well as volumes of complexation (with KBr) are calculated. Estimations of the apparent molar volume of 2,2,2-cryptand in CCl₄ are also reported. There is a loss in volume for the cryptand on transferring it from CCl₄ to water. The volume changes due to ionization for the cryptand in water are calculated to be –20.5 and –0.6 cm³·mol^?1 for the mono- and di-protonation equilibria respectively, while the volume of complexation for K⁺ is +24.5 cm³·mol^?1. The results are discussed in terms of conformation, protonation equilibria and selective encapsulation of K⁺ ions in cryptand cavities. The solution volume properties seem to depend upon water–solute interaction as well on the solute–solute association because of hydrophobic interactions caused by lowering of the charge density on formation of cryptand-K⁺ species in solution.     

The Enthalpies of Solution of L-cysteine, L-serine and L-asparagine in Aqueous Solutions of Some Alcohols at 298.15 K

Heats of solution, Δ_sol H _m , of L-cysteine, L-serine and L-asparagine amino acids have been measured at different concentrations of aqueous ethanol, propanol and 2-propanol at 298.15 K using solvation calorimetry. These data are compared with the results reported earlier for L-alanine in ethanol. The enthalpic coefficients, h _xy , of the solute-organic cosolvent pair interaction in water have been obtained from the McMillan-Mayer approach and the data have been interpreted in terms of various interactions and changes in solvent structure.     

Volumetric Properties of Aqueous Solutions of Acetamide in the 274.15–333.15 K Range of Temperatures

Russian Journal of Physical Chemistry A - The densities of aqueous solutions of acetamide up to a mole fraction of x2 = 0.3875 are measured over a wide range of temperatures (274.15–333.15) K...     

Transfer Volumes of Small Peptides from Water to Aqueous Xylitol Solutions at 298.15 K

Densities have been measured by an oscillating-tube densimeter for aqueous solutions of glycylglycine and glycylglycylglycine in aqueous xylitol solutions with xylitol mass fractions ranging from 0 to 0.15 at 298.15 K. Apparent molar volumes and limiting partial molar volumes have been used to calculate the corresponding transfer volumes from water to different concentrations of xylitol + water mixtures. The results are interpreted in terms of the cosphere overlap model.     

Volumetric Properties of the Nucleoside Thymidine in Aqueous Solution at T = 298.15 K and p = (10 to 100) MPa

Sound speeds have been measured for aqueous solutions of the nucleoside thymidine at T = 298.15 K and at the pressures p = (10, 20, 40, 60, 80, and 100) MPa. The partial molar volumes at infinite dilution, $ V_{2}^{\text{o}} $ , the partial molar isentropic compressions at infinite dilution, $ K_{S,2}^{\text{o}} $ , and the partial molar isothermal compressions at infinite dilution, $ K_{T,2}^{\text{o}} $ $ \{ K_{T,2}^{\text{o}} = - (\partial V_{2}^{\text{o}} /\partial p)_{T} \} $ , have been derived from the sound speeds at elevated pressures using methods described in our previous work. The $ V_{2}^{\text{o}} $ and $ K_{T,2}^{\text{o}} $ results were rationalized in terms of the likely interactions between thymidine and the aqueous solvent. The $ V_{2}^{\text{o}} $ results were also compared with those calculated using the revised Helgeson–Kirkham–Flowers (HKF) equation of state.     

Volumetric Properties of Dilute Solutions of Water in Acetone between 288.15 and 318.15 K

Densities of dilute solutions of water in acetone, with solute mole fractions ranging up to 0.03, have been measured with an error of 8 ×10⁻⁶ g⋅cm⁻³, at 288.15, 298.15, 308.15 and 318.15 K, using a precision vibrating-tube densimeter. The partial molar volumes of the solute water (down to infinite dilution) and solvent acetone, as well as the excess molar volumes of the specified mixtures, have been calculated. The effects of the solute concentration and temperature on the volume packing changes, caused by solvation of water in acetone, have been considered.     

Enthalpies of Dilution of N,N′-hexamethylenebisacetamide in Pure Water and Aqueous Solutions of Alkali Halide at 298.15 K

Enthalpies of dilution of N,N′-hexamethylenebisacetamide in water and aqueous alkali halide solutions at the concentration of 0.150 mol⋅kg⁻¹ (approximately the concentration of physiological saline) have been determined by isothermal titration microcalorimetry at 298.15 K. The enthalpic interaction coefficients in the solutions have been calculated according to the excess enthalpy concept based on the calorimetric data. The values of enthalpic pair-wise interaction coefficients (h ₂) of the solute in aqueous solutions of different salts were discussed in terms of the different alkali salt ions and weak interactions of the diluted component with coexistent species as well as the change in solvent structure caused by ions.     

Densities and Partial Molar Volumes of Some Amino Acids and Diglycine in Aqueous n-Propanol Solutions at 25°C

Apparent molar volumes, V , of glycine, DL--alanine, DL--amino-n-butyric acid, L-valine, L-leucine, and diglycine in water and in 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 m _B [molality of n-propanol in water (mol-kg^–1)] aqueous solutions of n-propanol have been obtained from densities of their solutions at 25 °C measured by using a precise vibrating-tube digital densimeter. The calculated partial molar volumes of amino acids and diglycine at infinite dilution, V _2,m ^o , have been used to obtain the corresponding transfer volumes, _tr V _2,m ^o , from water to different n-propanol–water mixtures. _tr V _2,m ^o values are positive for glycine, DL-- alanine, and diglycine (except at lower concentration 1.0 m _B ), negative for L-valine, and both positive and negative for the remaining amino acids over the concentration range studied. The side-chain contributions and hydration numbers have been calculated from V _2,m ^o data. Interaction coefficients have also been obtained from the McMillan–Mayer approach and the data have been interpreted in terms of various interactions.     

Volumetric Properties of Aqueous Solutions of Tetramethyl-<Emphasis Type="Italic">bis</Emphasis>-urea between 278.15 and 338.15 K at Atmospheric Pressure

Densities of aqueous solutions of tetramethyl-bis-urea (TMbU) with solute mole fractions ranging up to 7.0×10⁻² have been measured with an uncertainty of 1.5×10⁻⁵ g⋅cm⁻³, at 278.15, 298.15, 318.15, and 338.15 K using a vibrating-tube densimeter. The partial molar volumes and expansibilities of TMbU (down to the infinite dilution) and water have been computed. The effects of solute concentration and temperature on the volume packing changes, caused by dissolution (and hydration) of TMbU in an aqueous medium, have been considered.     

Partial Molar Volumes of Glycine and dl-Alanine in Aqueous Ammonium Sulfate Solutions at 278.15, 288.15, 298.15 and 308.15 K

In this work, the partial molar volumes of glycine and dl-alanine in aqueous solutions of ammonium sulfate at 0.0, 0.1, 0.3, 0.7, and 1.0 mol·kg^?1 are determined between 278.15 and 308.15 K. Transfer volumes were obtained, which are larger for glycine than dl-alanine. On the contrary, the hydration numbers are higher for dl-alanine than glycine, and dehydration of the amino acids is observed with increasing temperature or salt molality. The data suggest that interactions between ion and charged/hydrophilic groups are predominant and, by applying the methodology proposed by Friedman and Krishnan, it was concluded that they are mainly pairwise. A group-contribution scheme has been successfully applied to the pairwise volumetric interaction coefficient. Finally, the dehydration effect on glycine, alanine and serine in the presence of different electrolytes has been rationalized in terms of the charge density and a parameter accounting for the cation’s hydration.