Solvation Thermodynamics of a Series of Homologous α-Amino Acids in Non-aqueous Binary Mixtures of Protic Ethylene Glycol and Dipolar Aprotic Acetonitrile

Standard transfer Gibbs energies $ \left( {\Updelta G_{t}^{0} (i)} \right) $ ( Δ G t 0 ( i ) ) and entropies $ \left( {\Updelta S_{t}^{0} (i)} \right) $ ( Δ S t 0 ( i ) ) of transfer of the homologous α-amino acids: glycine, dl-alanine, dl-α-amino butyric acid and dl-nor-valine (nor-val) from protic ethylene glycol (EG) to proton/cation-phobic dipolar aprotic acetonitrile (ACN) mixed solvents with 0, 20, 40, 60, 80 and 100 wt% ACN compositions have been determined at 25 °C. For this purpose solubilities of the α-amino acids were measured by “formol titrimetry” at 15, 20, 25, 30 and 35 °C. The chemical components of these Gibbs energies $ \left( {\Updelta G_{t,\rm{ch}}^{0} (i)} \right) $ ( Δ G t , ch 0 ( i ) ) and entropies $ \left( {{\rm T}\Updelta S_{t,\rm{ch}}^{0} (i)} \right) $ ( T Δ S t , ch 0 ( i ) ) of the homologous α-amino acids have been computed by subtracting the cavity effects and dipole–dipole interaction effects. The chemical contributions of transfer energetics of these homologous α-amino acids are determined by different types of interactions. The decreased acidity, basicity, H-bonding capacity, solvophilic solvation and solvophobic solvation and increased dispersion and soft–soft interaction of ethylene glycol and acetonitrile mixtures, as compared to EG, are the guiding factors. The characteristics of the solvation thermodynamics of α-amino acids in protic EG and proton/cation-philic dipolar aprotic DMF mixed solvent systems studied earlier are also discussed here for comparison.     

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.     

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.     

Micellization of Alkyltriphenylphosphonium Bromides in Ethylene Glycol and Diethylene Glycol + Water Mixtures: Thermodynamic and Kinetic Investigation

The thermodynamics of micellization and other micellar properties of alkyl- (C₁₀-, C₁₂-, C₁₄- and C₁₆-) triphenylphosphonium bromides in water + ethylene glycol (EG) (0 to 30% v/v) mixtures over a temperature range of 298 to 318 K and cetyltriphenylphosphonium bromide in water + diethylene glycol (DEG) mixtures (0 to 30% v/v) at 298 K have been studied conductometrically. In all cases, an increase in the percentage of co-solvent results in an increase in the cmc values. On the basis of these results, the thermodynamic parameters, the Gibbs energy (ΔG _m^o), enthalpy (ΔH _m^o) and entropy (ΔS _m^o) of micellization have been evaluated. In addition to the conductivity measurements, kinetic experiments have also been done to determine the dependence of observed rate constant for the nucleophilic substitution reaction of p-nitrophenyl acetate and benzohydroxamate ions in the presence of the surfactant cetyltriphenylphosphonium bromide with a varying concentration of EG and DEG ranging from 0 to 50% v/v at pH=7.9 and 300 K. All of the reactions followed pseudo-first-order kinetics. An increase in the surfactant concentration results in an increase in the reaction rate and for a given surfactant concentration, the rate constant decreases as the concentration of co-solvent in the mixture increases. The kinetic micellar effects have been explained by using the pseudophase model. The thermodynamic and structural changes originating from the presence of solvents control the micellar kinetic effects.     

The Effect of the Molecular Size and Shape on the Volume Behavior of Binary Liquid Mixtures. Branched and Cyclic Alkanes in Heptane at 298.15 K

Excess molar volumes V ^E for 40 mixtures of heptane with a liquid alkane and apparent molar volumes in heptane for eight solid alkanes have been obtained at 298.15 K. They include five linear, 30 branched-chain, and 13 cyclic alkanes. Almost all systems exhibit negative V ^E values. For mixtures with open chain alkanes, V ^E increases from C5 to C7 and then decreases. A similar trend is shown by mixtures with cycloalkanes. V ^E values are compared with known H ^E data for mixtures with heptane and tetrachloromethane. Signs and trends of V ^E and H ^E are correlated with the free volume and interactional terms of the Flory theory. The partial molar volumes at infinite dilution in heptane, V°, have also been obtained and discussed together with literature data on other hydrocarbons and polar compounds. The calculated contributions to V° by CH₃, CH₂, CH and C groups are compared with previously determined contributions of polar groups. The lower contributions of the latter groups are explained with the volume contraction caused by dipole-induced dipole interaction. The volume effects associated with branching and cyclization have been evaluated and compared with the corresponding effects on solvation enthalpy. The branching effect, in the order of magnitude of few cm³·mol^?1, and the larger negative values of cyclization volumes, down to ?24 cm³·mol^?1, are discussed in terms of packing and solute–solvent interactions, in analogy to polar organic solutes either in heptane and tetrachloromethane. A negative cyclization effect is also exhibited by the solvation enthalpies.     

Densities and Refractive Indices of Binary Mixtures of Olive Oil + Alkanols at 298.15 K

Densities and refractive indices of mixing of olive oil with the alkanols: methanol, ethanol, 1-propanol, 2-propanol and 1-butanol, have been measured as a function of the composition at T = 298.15 K. Excess molar volumes, $ V_{\text{m}}^{\text{E}} $ , and deviation in refractive index, Δn _D, were calculated and correlated by a Redlich–Kister type function, to derive the coefficients and estimate the standard error. For mixtures of olive oil with alkanols, $ V_{\text{m}}^{\text{E}} $ is positive, except with ethanol and methanol where a sigmoidal variation is observed. Δn _D is positive over the entire range of mole fraction. The effect of chain length of the alkanols on the excess molar volumes and deviation in refractive index of the mixtures with olive oil are discussed.     

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.     

Solubility of Ketoconazole in Polyethylene Glycol 200 + Water Mixtures at 298.2–318.2 K

The solubility of ketoconazole in binary mixtures of polyethylene glycol 200 (PEG 200) + water is reported at temperatures ranging from 298.2 to 318.2 K. The Jouyban–Acree model and its combined version including the van’t Hoff equation were used for correlating the reported data; the obtained mean relative deviations are 9.5 and 9.9 %, respectively. Also, two previously trained versions of the Jouyban–Acree model were used for predicting the reported data points in which the prediction errors were 34.6 and 31.0 %.     

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.     

Solubility and preferential solvation of phenacetin in methanol + water mixtures at 298.15 K

The mole fraction solubility of phenacetin (PNC) in methanol + water binary solvent mixtures at 298.15 K was determined along with density of the saturated solutions. All these solubility values were correlated with the Jouyban–Acree model. Preferential solvation parameters of PNC by methanol (δx_1,3) were derived from their thermodynamic solution properties using the inverse Kirkwood–Buff integrals (IKBI) method. δx_1,3 values are negative in water-rich mixtures but positive in methanol mole fraction of >0.32. It is conjecturable that in the former case the hydrophobic hydration around non-polar groups of PNC plays a relevant role in the solvation. The higher solvation by methanol in mixtures of similar cosolvent compositions and methanol-rich mixtures could be explained in terms of the higher basic behaviour of methanol.     

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XII. Effect of the Acid–Base Properties of the Mixture on the Thermodynamic Functions of Complex Formation of Benzo-15-Crown-5 with Na<Superscript>+</Superscript> in Water–Methanol Mixtures at 298.15 K

The enthalpies of solution of benzo-15-crown-5 ether in methanol–water mixtures and methanol–water–sodium iodide systems have been measured at 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and methanol within the whole range of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with the sodium cation have been determined by conductivity measurements at 298.15 K. The thermodynamic functions of the formation of these complexes have been calculated. The Gibbs energy of complex formation depends on the base–acid properties of methanol–water mixture.     

Thermodynamics of NaCl in Aqueous Ethylene Glycol, Acetonitrile, and 1,4-Dioxane Mixtures from Emf Measurements at 25°C

The electromotive force of the amalgam cell {Na_xHg_1-xNaCl(m)AgClAg} has been measured at 25°C as a function of the mole fraction x of Na in amalgams and of the molality m of NaCl in (ethylene glycol + water), (acetonitrile + water), and (1,4-dioxane + water) mixed solvents, containing up to 0.8 mass fraction of the organic component, with relative permittivities 27. The relevant standard molal electromotive forces have been determined, together with the mean molal activity coefficient _± of NaCl as a function of its molality. In the case of (ethylene glycol + water) mixtures, a linear dependence of on the mass fraction of ethylene glycol is observed, which is quite unusual, The Debye-Hückel equation is applicable successfully over the whole range of molalities explored, which extends to the vicinity of the solubility limit of NaCl in each solvent. The dependence of the standard emf on the logarithm of the volume fraction of water in the aqueous-organic solvent mixtures have been analyzed in terms of Feakins and French's theory, leading to a primary hydration number 7.2 for NaCl, in good agreement with previous results employing different methods.     

Abraham Model Correlations for Triethylene Glycol Solvent Derived from Infinite Dilution Activity Coefficient,Partition Coefficient and Solubility Data Measured at 298.15 K

A gas chromatographic headspace analysis method was used to experimentally determine gas-to-liquid partition coefficients and infinite dilution activity coefficients for 29 liquid organic solutes dissolved in triethylene glycol at 298.15 K. Solubilities were also determined at 298.15 K for 23 crystalline nonelectrolyte organic compounds in triethylene glycol based on spectroscopic absorbance measurements. The experimental results of the headspace chromatographic and spectroscopic solubility measurements were converted to gas-to-triethylene glycol and water-to-triethylene glycol partition coefficients, and molar solubility ratios using standard thermodynamic relationships. Expressions were derived for solute transfer into triethylene glycol by combining our measured experimental values with published literature data. Mathematical correlations based on the Abraham model describe the observed partition coefficient and solubility data to within 0.16 log₁₀ units (or less).     

Effect of the Charge and the Nature of Both Cations and Anions on the Solubility of Zwitterionic Amino Acids,Measurements and Modeling

The effect of the charge and the nature of both the cations and the anions of some electrolytic salts: sodium fluoride (NaF), potassium fluoride (KF), sodium bromide (NaBr), potassium bromide (KBr), sodium iodide (NaI), potassium iodide (KI), sodium sulfate (Na₂SO₄), potassium sulfate (K₂SO₄), calcium chloride (CaCl₂), and barium chloride (BaCl₂), on the solubility of zwitterionic amino acids (glycine, DL-alanine, DL-valine, and DL-serine) in aqueous solutions at 298.15 K are studied and discussed. A salting-in effect is observed for all amino acids under investigation with all electrolytes used in the present study, except for DL-alanine and DL-valine in aqueous solutions containing sodium fluoride where a salting-out effect was observed. The orders of the effect of the nature and the charge of both the anions and the cations are: F^- < Cl^- < Br^- < I^- < NO₃^- < SO₄^2-\mathrm{F}^{-}<{}\mathrm{Cl}^{-}<{}\mathrm{Br}^{-}<{}\mathrm{I}^{-}<\mathrm{NO}_{3}^{-}<{}\mathrm{SO}_{4}^{2-} with both sodium and potassium cations; Na⁺<K⁺<Ca²⁺<Ba²⁺ with chloride anion.     

Equilibrium Phase Behavior of Ethylene Glycol/Glycerin＋RbNO3/CsNO3＋H2O at 288.15 and 298.15 K

The solubilities, densities and refractive indices for the four ternary systems ethylene glycol/glycerin＋ RbNOJCsNO3＋H20 were measured with mass fractions of ethylene glycol or glycerin in a range of 0 to 1.0 at 288.15 and 298.15 K. In all the cases, the presence of either ethylene glycol or glycerin significantly reduces the solubilities of the rubidium nitrate and cesium nitrate in aqueous solution, but the refractive indices increase with the increase of mass fraction of either ethylene glycol or glycerin. The density, refractive index and solubility of the saturated ternary systems were correlated with each other via polynomial equations. In addition, the refractive indices and densities of unsaturated solutions were also determined for the four ternary systems with different salt concentrations, which were correlated with the salt concentration and proportion of ethylene glycol or glycerin in the solution.