Volumetric Properties of Amino Acids in Aqueous N-methylacetamide Solutions at 298.15 K

The apparent molar volumes (V _φ ) of glycine, L-alanine and L-serine in aqueous 0 to 4 mol⋅kg⁻¹ N-methylacetamide (NMA) solutions have been obtained by density measurement at 298.15 K. The standard partial molar volumes (V_f⁰)V_{\phi}^{0}) and standard partial molar volumes of transfer (D_trV_f⁰)\Delta_{\mathrm{tr}}V_{\phi}^{0}) have been determined for these amino acids. It has been show that hydrophilic-hydrophilic interactions between the charged groups of the amino acids and the –CONH– group of NMA predominate for glycine and L-serine, but for L-alanine the interactions between its side group (–CH₃) and NMA predominate. The –CH₃ group of L-alanine has much more influence on the value of D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0} than that of the –OH group of L-serine. The results have been interpreted in terms of a co-sphere overlap model.     

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.     

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.     

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.     

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 and Surface Properties of Short Chain Alcohols in Aqueous Solution–Air Systems at 293?K

From measurements of the surface tension, density, viscosity and light scattering of aqueous solutions of methanol, ethanol and propanol at 293?K, their activity in the surface monolayer, surface excess concentration, and apparent and partial molar volume were determined. The surface excess concentration of alcohols at the water?Cair interface was determined from the Gibbs equation by using both the alcohol's activity and their molar fraction in the bulk phase and recalculated by using the Guggenheim?CAdam equation. The values of the surface excess concentration determined from the Gibbs equation were also applied to determine the standard Gibbs energy of alcohol adsorption at the water?Cair interface from Langmuir??s equation and compared to those determined from that of Aronson and Rosen.     

Enthalpies of Solution of L–L- and D–D- Isomers of Valine in Aqueous Alkanols at 298.15 K

The enthalpies of solution of L- and D-valines in water-ethanol, water-n-propanol, and water-i-propanol mixtures were measured calorimetrically at 298.15 K at alcohol mole fractions, x ₂, ranging up to 0.4. Enthalpies of transfer, Δ_tr H°, from water to aqueous alkanol were calculated for each of the system studied. The enthalpic coefficients, h _xy , of the solute-cosolvent pair-wise interaction in water proved to be positive and increasing in the series: ethanol, n-propanol, and i-propanol. It was shown that both the nature of the amino acid L–L- and D–D-isomerization and dimensions of linear or branched cosolvent molecules define the energetics of interaction between valine and alkanol molecules.     

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.     

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 Study of Aqueous Solutions of Polyethylene Glycol as a Function of the Polymer Molar Mass in the Temperature Range 283.15 to 313.15 K and 0.1 MPa

Density measurements were made for binary aqueous solutions of polyethylene glycol at seven temperatures: 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. Polyethylene glycol samples with nominal average molar masses of 3000 g⋅mol⁻¹ (PEG 3000), 6000 g⋅mol⁻¹ (PEG 6000), 10000 g⋅mol⁻¹ (PEG 10000) and 20000 g⋅mol⁻¹ (PEG 20000) were used. These results were used to determine the specific volumes of solutions with solute-to-solvent mass ratios (mass of the solute/mass of the solvent) in the range 0.0546 to 1.4932 for PEG 3000, from 0.0553 to 1.4986 for PEG 6000, from 0.0552 to 1.2241 for PEG 10000, and from 0.0530 to 1.2264 for PEG 20000. The differences between the specific volume of a solution and the specific volume of the pure solvent, at a given temperature, were represented by a virial-type equation in terms of solute concentration. The first-order coefficient of the expansion is the partial specific volume of the solute at infinite dilution. The higher-order coefficients are related to the contribution of pairs, triplets, and higher-order solute aggregates, according to the Constant-Pressure Solution Theory. The functional dependence of the virial coefficients upon temperature is discussed in terms of solute-solute and solute-solvent interactions. The effect of the PEG molar mass on the partial specific volume of solute at infinite dilution, as well as the contributions of pairs of solute molecules to the solution volume, are also investigated. The apparent specific volume, apparent specific expansibility, apparent specific expansibility at infinite dilution and virial coefficients of the apparent specific expansibility are also presented.     

The Partial Molar Heat Capacities and Expansions of Inosine, 2′-Deoxyinosine and 2′-Deoxyguanosine in Aqueous Solution at 298.15 K

Solution densities over the temperature range 288.15 to 313.15 K have been measured for aqueous solutions of the nucleosides inosine, 2′-deoxyinosine, and 2′-deoxyguanosine, from which the partial molar volumes of the solutes at infinite dilution, V ₂^o, were obtained. The partial molar expansions for the nucleosides at infinite dilution and 298.15 K, E ₂^o {E ₂^o=(∂ V ₂^o/∂ T) _p }, were derived from the V ₂^o results. The V ₂^o values at 298.15 K for the two sugars D-ribose and 2-deoxyribose also have been determined. The partial molar heat capacities at infinite dilution for all the solutes, C _p,2^o, have been determined at 298.15 K. These V ₂^o,E ₂^o, and C _p,2^o results are critically compared with all of the results available from the literature, and the use of group additivity to evaluate these solution thermodynamic properties for the sparingly soluble nucleoside guanosine is explored.     

Thermodynamics of Selected Aqueous Rare-Earth Elements Containing Triflate Salts at T=(288.15, 298.15, 313.15 and 328.15) K and p=0.1 MPa

Aqueous acidified solutions of the rare-earth-element (REE) triflates (Gd(CF₃SO₃)_3(aq), Dy(CF₃SO₃)_3(aq), Nd(CF₃SO₃)_3(aq), Er(CF₃SO₃)_3(aq), Yb(CF₃SO₃)_3(aq) and Y(CF₃SO₃)_3(aq)) have been prepared by the dissolution of the corresponding REE oxides in dilute aqueous trifluoromethanesulfonic acid (triflic acid, CF₃SO₃H_(aq)). Relative densities and relative massic heat capacities have been measured for these systems over the approximate ionic strength range 0.10≤I/(mol?kg^?1)≤1.35 at T=(288.15, 298.15, 313.15 and 328.15) K and p=0.1 MPa. These measurements were completed using a Sodev O2D vibrating tube densimeter and Picker-flow microcalorimeter, respectively. Relative densities and relative massic heat capacities for aqueous solutions of triflic acid and its sodium salt have also been measured over the concentration range 0.018≤m ₂/(mol?kg^?1)≤0.23 over the same temperature range at p=0.1 MPa. Young’s rule has been used to calculate apparent molar volumes and apparent molar heat capacities of the aqueous solutions of REE triflate salts from the calculated apparent molar properties of the acidified salt solutions. These properties have been modeled using the Pitzer ion-interaction equations. The apparent molar properties of aqueous triflic acid solutions and aqueous solutions of its sodium salt have also been modeled using the same Pitzer ion-interaction equations. The apparent molar properties at infinite dilution obtained from our property modeling have been used to calculate single ion volumes and single ion heat capacities for each of the aqueous ions; Gd _(aq) ³⁺ , Dy _(aq) ³⁺ , Nd _(aq) ³⁺ , Er _(aq) ³⁺ , Yb _(aq) ³⁺ , and Y _(aq) ³⁺ . The reported single ion values have been compared with those previously reported in the literature.     

Study of the interaction between ethanol and natural amino acids containing ionic side groups in water at T = 298.15 K

The enthalpies of solution of l-α-aspartic acid, l-α-glutamic acid, l-α-arginine, l-α-lysine, and l-α-histidine have been measured in aqueous ethanol solutions at 298.15 K. From the obtained experimental results, the standard enthalpies of solution of amino acids in water–ethanol solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan–Mayer’s formalism. These values were interpreted in the terms of the ionic or no polar effect of the side chains of l-α-amino acids on their interactions with a molecule of ethanol in water.     

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 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...