Effects of water-alcohol binary solvents on the thermochemical characteristics of L-tryptophane dissolution at 298.15 K

The enthalpies of L-tryptophane solution in water-methanol, water-ethanol, water-1-propanol, and water-2-propanol mixtures at alcohol concentrations of x ₂ = 0–0.4 mole fractions were measured by calorimetry. The standard enthalpies of L-tryptophane solution (Δ_sol H ^°) and transfer (Δ_tr H ^°) from water to the binary solvent were calculated. The influence of the composition of the water-alcohol mixture and the structure and properties of L-tryptophane on the enthalpy characteristics of the latter was considered. The enthalpy coefficients of pair interactions (h _xy ) of L-tryptophane with alcohol molecules were calculated. The coefficients were positive and increased in the series: methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), and 2-propanol (2-PrOH). The solution and transfer enthalpies of L-tryptophane were compared with those of aliphatic amino acids (glycine, L-threonine, DL-alanine, L-valine, and L-phenylalanine) in similar binary solvents.     

The thermochemistry of solution of L-α-alanyl-L-α-alanine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution of L-α-alanyl-L-α-alanine in water-ethanol, water-n-propanol, and water-isopropanol mixtures were measured calorimetrically at alcohol concentrations x ₂ ranging from 0 to 0.4 mole fractions. The standard enthalpy of peptide solution Δ_sol H ^o and transfer Δ_tr H ^o from water into a mixed solvent were calculated. The effect of the structure and properties of peptides and mixture composition on the enthalpy characteristics is discussed. The enthalpy coefficients of pair interactions h _xy between L-α-alanyl-L-α-alanine and alcohol molecules were calculated; these coefficients were positive and increased in the series ethanol, n-propanol, isopropanol. The analysis performed allowed the differences in the thermodynamic characteristics of solution of L-α-alanyl-L-α-alanine and DL-α-alanyl-DL-α-alanine in water-alcohol mixtures to be determined.     

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x ₂ = 0–0.3. The standard enthalpies of solution (Δ_sol H°) and transfer (Δ_tr H°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (h _xy ) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.     

The Enthalpies of Solution and Solvation of L-Serine in Aqueous Alcoholic Solutions at 298.15 K

The integral enthalpies of solution (Δ_sol H ^m ) of L-serine in water-alcohol (ethanol, n-propanol, isopropanol) mixtures were measured over the range of alcohol concentrations up to 0.32 mole fractions. The standard enthalpy of solution (Δ_sol H°), enthalpy of transfer of L-serine from water into a mixed solvent (Δ_tr H°), and enthalpy of solvation (Δ_solv H°) were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of mixtures had extrema. The calculated enthalpy coefficients of the pair interactions of L-serine with alcohol molecules were positive and increased along the series ethanol, n-propanol, isopropanol. The data obtained were interpreted in terms of different types of interactions in solutions and the influence of the nature of amino acid residues on the thermochemical solution characteristics. Original Russian Text ? I.N. Mezhevoi, V.G. Badelin, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4, pp. 789–791.     

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.     

The use of positron spectroscopy for revealing the nanosized structures in liquid mixtures. Identification of n-propanol nanoagglomerates in aqueous solutions

The potential of positron spectroscopy for identification of nanosized structures in liquid mixtures, which is a difficult problem that still remains a challenge in physical chemistry of liquids, was demonstrated. The water-n-propanol mixtures were chosen as an example. An analysis of the concentration dependences of the mean lifetime of ortho-positronium atoms in water-n-propanol binary mixtures and water-propanol mixtures containing CoCl₂ (0.4 M) and Co(ClO₄)₂ (0.6 M) suggested that the water-n-propanol mixture with ～0.1 to ～0.4 mole fractions of propanol resembled an emulsion of alcohol nanodrops suspended in water.     

Effect of organic co-solvents on the solvation enthalpies of amino acids and dipeptides in mixed aqueous solutions

Transition enthalpies (Δ_tr H ^o) of substances from water to binary solutions were calculated at 298.15 K on the basis of standard dissolution enthalpies (Δ_sol H ^o) for six amino acids and five dipeptides in the mixtures of water with organic solvents of various chemical natures. The enthalpy pair coefficients of interaction h _xy for biomolecules with organic component of mixture were estimated within the formalism of the McMillan-Mayer theory. The change in the character of the interaction of the components of solution was demonstrated in dependence on the physicochemical properties of the solvent and nature of the side radical of the dissolved bioorganic substance. Quantitative estimation of the type of interaction of the substance with the solvent was performed on the basis of correlation ratios relating the enthalpy characteristics of bioorganic substances to properties of organic cosolvents. It was shown that in the solutions under study, the effects of both the specific (mainly electron donor) and non-specific solvation of amino acids and peptides are observed.     

The enthalpy of solution of DL-α-alanyl-DL-α-valine depending on the composition of water-alcohol binary solvents at 298.15 K

The integral enthalpies of solution of DL-α-alanyl-DL-α-valine in water-ethanol, water-n-propanol, and water-isopropanol mixtures at alcohol concentrations x ₂ = 0–0.4 mole fractions were measured calorimetrically. The enthalpies of solution of the peptide Δ_sol H° and transfer from water to a mixed solvent Δ_tr H° were calculated. The effect of the structure and properties of the peptide and mixture composition on the enthalpy characteristics of the peptide are discussed. The enthalpy coefficients of pair interactions h _xy of DL-α-alanyl-DL-α-valine with alcohol molecules were calculated. It was found that they were positive and increased in the series ethanol, n-propanol, isopropanol. An analysis of the results allows the general features of changes in the thermodynamic parameters of solution of peptides of the DL-α-alanine series with different amino acid residues in water-alcohol mixtures to be established.     

Thermal properties of tetraalkylammonium bromides in several solvents

The enthalpies of solution of tetraethyl- and tetra-n-hexylammonium bromides have been measured in mixtures of formamide with ethylene glycol at 298.15 and 313.15 K in the whole mole fraction range by the calorimetric method. The standard enthalpies of solution in binary mixtures have been calculated with Redlich–Rosenfeld–Meyer type equation. The enthalpy and heat capacity parameters of pair interaction of organic electrolytes with EG in FA and with FA in EG have been computed and discussed. The enthalpy interaction parameters of single ions with EG in FA medium have been evaluated and compared with those for ion–water and ion–MeOH interaction in FA. The standard heat capacities of solution have been evaluated. The excess enthalpies of solution, Δ_sol H ^E, of Et₄NBr, Bu₄NBr, and Hex₄NBr have been determined. The Δ_sol H ^E values are positive for Et₄NBr and negative for Bu₄NBr and Hex₄NBr and become more negative from Bu₄NBr to Hex₄NBr.     

The enthalpies of formation of Sm1 + xBa2 ? xCu3Oy substitution solid solutions

The enthalpies of reactions of Sm_{1 + x} Ba_{2 − x} Cu₃O _y substitution solid solutions (x = 0, 0.1, 0.2, 0.3, 0.7, and 0.8) with 1.07 N HCl were measured at 298.15 K in a hermetic isothermic-shell swinging calorimeter. The results and the literature data were used to calculate the standard enthalpies of their formation from simple substances and binary oxides (Δ_f H _298.15^o and Δ_ox H _298.15^o). The dependence of the enthalpy of formation on the degree of samarium substitution for barium was obtained.     

Thermochemistry of Aniline Solution in Isomeric Butyl Alcohols and Their Aqueous Solutions

The enthalpies of solution (_s H ⁰) of aniline in isomeric butyl alcohols and their aqueous solutions at 25°C were determined. The dissolution of aniline becomes more endothermic with increasing content of alcohol in aqueous solution. The enthalpy coefficients of pair interaction alcohol-aniline in aqueous solution were calculated. This interaction is enhanced in the order tert-butanol-sec-butanol-iso-butanol-n-butanol. The correlations of these characteristics with physicochemical properties of solvents were revealed.     

Enthalpy characteristics of solution of L-cysteine and L-asparagine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-cysteine and L-asparagine in mixtures of water with ethanol, n-propanol, and isopropanol at a mole fraction of alcohol of up to 0.32 were determined by calorimetry of solution. The standard enthalpies of solution (Δ_sol H ⁰) of L-serine and of its transfer (Δ_tr H ⁰) from water to a mixed solvent were calculated. The dependences of Δ_sol H ⁰ and Δ_tr H ⁰ on the composition of water-alcohol mixtures pass through a maximum. The calculated enthalpy coefficients of pair interaction of amino acids with alcohol molecules are positive and increase in the order ethanol, n-propanol, isopropanol. The data obtained were interpreted from the viewpoint of various types of interaction in solution and effect of the amino acid residue on the thermochemical characteristics of solution.     

Solvation of Aniline in Mixtures of Water with N,N-Dimethylformamide and Acetonitrile

Thermal effects of aniline solution in water-N,N-dimethylformamide (DMF) and water-acetonitrile mixtures were measured at 25°C. In almost the whole range of compositions of the mixed solvents, the thermal effects are more positive in aqueous acetonitrile than in aqueous DMF. Particular attention was given to binary solvents with a very low content of the organic cosolvent. In the mixture with the mole fraction of DMF of 10^{- 3}, the enthalpy of aniline solution is higher than in water by 5%, and in the mixture with the mole fraction of acetonitrile of 4 × 10^{- 4}, even by 15%. Features of specific solvation of aniline and an aliphatic amine (n-BuNH₂) in the water-DMF mixture were discussed taking into account the acid-base properties of the mixtures. The coefficients of pair interactions aniline-organic solvent in water and aniline-water in the organic solvent were calculated using the McMillan-Mayer theory. These coefficients correlate with the enthalpies of hydration of aprotic solvent molecules.     

The thermochemical characteristics of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-ethanol, water-n-propanol, and water-isopropanol mixtures were measured calorimetrically at alcohol concentrations x ₂ = 0?0.4 mole fractions. The standard enthalpies of solution (Δ_sol H°) of the peptides and their transfer (Δ_tr H°) from water into the mixed solvents were calculated. The influence of the structure and properties of the solutes and mixture composition on the enthalpy characteristics were considered. The Δ_sol H° = f(x ₂) and Δ_tr H° = f(x ₂) dependences were found to have extrema. The enthalpy coefficients of pair interactions (h _xy ) between the peptide and alcohol molecules were calculated. The coefficients were positive and increased in the series ethanol, n-propanol, isopropanol.     

Synthesis and characterization of the rare-earth complexes with salicylic acid

Seven rare-earth complexes with salicylic acid RE(HSal)₃·nH₂O (HSal = C₇H₅O₃; RE = La-Sm, n = 2; RE = Eu, Gd, n = 1) were synthesized and characterized by elemental analysis, the IR spectrum, and cyclic voltammetry. The constant-volume combustion energies of complexes, Δ_c U, were determined by a precise rotating-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, Δ_c H _m ^o , and standard molar enthalpies of formation, Δ_f H _m ^o , were calculated.     

Thermodynamic characteristics of the acid dissociation of dopamine hydrochloride in water-ethanol solutions

Enthalpies of the interaction of protonated dopamine with a hydroxide ion in water-ethanol mixtures in the concentration range of 0–0.8 EtOH mole fractions are measured calorimetrically. The neutralization process of dopamine hydrochloride is shown to occur endothermally in solvents with an ethanol concentration of ≥0.5 mole fractions. Standard thermodynamic characteristics (Δ_r H ^○, Δ_r G ^○, and Δ_r S ^○) of the first-step acid dissociation of dopamine hydrochloride in solutions are calculated with regard to the autoprotolysis enthalpy of binary solvents. It is found that dissociation enthalpies vary within 9.1–64.8 kJ/mol, depending on the water-ethanol solvent composition.     

The Solubility and Solvation of Salts in Mixed Nonaqueous Solvents. 2. Potassium Halides in Mixed Protic Solvents

The solubilities of potassium fluoride, chloride, and bromide in ethanol, formamide, and N-methylformamide and in binary mixtures of these solvents were determined at 25°C. The standard molar Gibbs energies of solution, Δ_soln G ^o, in the neat solvents were related to their hydrogen bonding abilities. The values of Δ_soln G ^o in the mixtures were fitted with expressions of the quasilattice quasichemical theory, and the preferential solvation of the ions was thereby established.     

Microhydration of protonated nucleic acid bases and protonated nucleosides in the gas phase

Thermochemical data, ΔH _n ^o , ΔS _n ^o , and ΔG _n ^o , for the hydration of protonated nucleic acid bases and protonated nucleosides have been experimentally studied by equilibrium measurements using an electrospray high-pressure mass spectrometer equipped with a pulsed ion-beam reaction chamber. For protonated nucleobases the hydration enthalpies were found to be similar for all studied systems and varied between 12.4–13.1 kcal/mol for the first and 11.2–11.5 kcal/mol for the second water molecule. While for protonated nucleosides the water binding enthalpies (11.7–13.3 kcal/mol) are very close to those for protonated nucleobases, the entropy values are “more negative.” The structural and energetic aspects of hydrated ions are discussed in conjunction with the available theoretical data.     

Excess thermodynamic parameters of binary mixtures of methanol,ethanol, 1-propanol,and 2-butanol + chloroform at (288.15–323.15 K) and comparison with the Flory theory

In this work we used the experimental result for calculating the thermal expansion coefficients α, and their excess values α ^E , and isothermal coefficient of pressure excess molar enthalpy and comparison the obtain results with Flory theory of liquid mixtures for the binary mixtures {methanol, ethanol, 1-propanol and 2-butanol-chloroform} at 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K. The excess thermal expansion coefficients α ^E and the isothermal coefficient of pressure excess molar enthalpy ((∂H _m^E/∂P) _T,x for binary mixtures of {methanol and ethanol + chloroform} are S-shaped and for binary mixtures of {1-propanol and 2-butanol + chloroform} are positive over the mole fraction. The isothermal coefficient of pressure excess molar enthalpy (∂H _m^E/∂P) _T,x , are negative over the mole fraction range for binary mixture of {1-propanol and 2-butanol + chloroform}. The calculated values by using the Flory theory of liquid mixtures show a good agreement between the theory and experimental.