Enthalpic Pairwise Interaction Coefficients Research Articles

Thermodynamic parameters of L-carnosine dissolution and solvation in binary aqueous-organic mixtures at T = 298.15 K.

Isothermal calorimetry was used to measure the enthalpies of L-carnosine digestion in aqueous solutions of acetonitrile (AN) 1,4-dioxane (DO), acetone (AC), dimethyl sulfoxide (DMSO), ethanol EtOH), 1-propanol (1-PrOH), and 2-propanol (2-PrOH). The values of ΔsolH° obtained were combined with the standard enthalpies of L-carnosine sublimation to obtain the corresponding enthalpies of solvation ΔsolvH°. In addition, the enthalpic coefficients of pairwise interactions (hxy) of L-carnosine with organic solvent molecules and the enthalpy of transfer (ΔtrH°) from water in their mixture with the latter were calculated. It is established that the solvation of L-carnosine is weakened in a series of (H2O + EtOH) > (H2O + 1-PrOH) > (H2O + 2-PrOH). This may be due to an increase in the hydrophobicity of alcohols of the same order as well as the presence of CH3-groups within the alcohol molecule. The weakening of the solvation energy of L-carnosine by co-solvent molecules in a series of mixed solvents: (H2O + AN) < (H2O + AC) < (H2O + DO) < (H2O + DMSO) is associated both with an increase in the hydration energy of co-solvents in the same order and with their physicochemical properties. The enthalpic coefficients of water-organic solvent pairwise interactions were discovered to be linearly related to the corresponding coefficients of L-carnosine-organic solvent interactions. An increase in the polarity and acidity of an organic solvent increases the energy of pairwise interactions between L-carnosine and the organic solvent. Increasing the cohesion energy density, molar volume, and basicity of the organic solvent reduces the energy of the pairwise interactions between L-carnosine and the organic solvent.

Features of l-Tryptophan Solvation in Some Water–Organic Mixtures at T = 298.15 K

The effect of changes in the composition of some water–organic mixtures on the thermodynamic parameters of dissolution and solvation of l-tryptophan was studied by the method of calorimetry of dissolution at T = 298.15 K. To explain the experimental results, the enthalpic coefficients of pairwise interactions between l-tryptophan and organic cosolvent molecules and the energy contributions of the side chain to the energy of intermolecular interactions are calculated, and the influence of some properties of organic solvents on these interactions is estimated. All the data obtained were compared with those for l-phenylalanine to reveal the influence of the side chain structure on the energy of intermolecular interactions of aromatic amino acids with organic solvent molecules in aqueous solutions.

Thermochemical investigation of glycyl-L-alanine dissolution in aqueous solution of some acetamides and formamides at T = 298.15 K (Similarities and differences)

The paper presents data on the glycyl-L-alanine dissolution enthalpies in aqueous solutions of formamide (FA), N-methyl-formamide (MFA), N,N-dimethylformamide (DMF), acetamide (AM), N-methyl-acetamide (NMA), and N,N-dimethylacetamide (DMA) at an organic co-solvent concentration x2 = 0 ÷ 0.25 - mole fraction and T = 298.15 K, obtained by calorimetry. The standard values of dissolution enthalpies (ΔsolHo), transfer enthalpies (ΔtrHo), and enthalpic coefficients of pairwise interaction (hxy) were calculated from these data. The dependences of the enthalpic characteristics of glycyl-L-alanine dissolution on the mixture composition and the interaction energy between the mixture components have been established. A comparative analysis of the values of the enthalpic coefficients of pairwise interactions of glycyl-L-alanine, glycyl-glycine, and glycyl-L-tyrosine in similarly mixed solvents has been carried out. A quantitative assessment of the enthalpy contributions of the side-chains of glycyl-L-alanine and glycyl-L-tyrosine to the energetics of interaction with amide molecules in an aqueous solution is given.

Thermochemical investigation of L-glutamine dissolution processes in aqueous co-solvent mixtures of acetonitrile, dioxane, acetone and dimethyl sulfoxide at T = 298.15 K

This article reports on the results of calorimetric studies of the processes of L-glutamine dissolution in some aqueous-organic mixtures, namely (H2O + acetonitrile), (H2O + 1,4-dioxane), (H2O + acetone) and (H2O + dimethyl sulfoxide) at T = 298.15 K and mole fractions of an organic solvent up to x2 ~ 0.25. The standard values of solution (ΔsolH°) and transfer (ΔtrH°) enthalpies of L-glutamine from water to a mixed solvent as well as the enthalpic coefficients of pair-wise interactions (hxy) were calculated. The interrelation between enthalpic characteristics of L-glutamine dissolution (transfer) and the composition of water-organic mixtures was determined. It is found that the values of hxy are correlated with some physicochemical properties of different organic solvents. Contributions of the organic solvent properties (molar volume, cohesion energy density, polarity/polarizability, acidity, and basicity) to the energy of pair-wise interactions of L-glutamine - organic solvent were estimated quantitatively using of a modified Kamlet-Taft equation. The parameters of pair-wise interactions were additionally used to assess the contributions of the side chains of several L-amino acids to the energy of the intermolecular interactions amino acid-organic co-solvent in aqueous solutions.

The effect of the side chain structures on the energy of intermolecular interactions of α-amino acids with some formamides in aqueous solutions at T = 298.15 K

To evaluate the effect of amino acid side chains on the thermodynamics of their interaction with the formamides molecules in aqueous solutions, we expanded the range of amino acids by studying in the present investigation the thermodynamics of the dissolution of glutamine in mixed solvents {water + (formamide, N‑methylformamide and N,N‑dimethylformamide)} at T = 298.15 K and organic solvent mole fractions up to x2 ~ 0.3. The standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of l-glutamine from water to a mixed solvent as well as the enthalpy coefficients of pairwise interactions (hxy) were calculated. The interrelation between enthalpic characteristics of l-glutamine dissolution (transfer) and the composition of water-organic mixtures was determined. Using the enthalpic coefficients of pairwise interactions of l-glutamine and five more amino acids (glycine, dl-α-alanine, l-valine, l-methionine, and l-threonine), the enthalpic contributions of the side chains of these amino acids to their interparticle interactions with the molecules of formamides were calculated.

Influence of the composition of aqueous-alcohol solvents on enthalpic characteristics of l-glutamine dissolution at T = 298.15

The enthalpies of the solution of l‑glutamine in aqueous solution of ethanol (EtOH), 1‑propanol (1-PrOH) and 2‑propanol (2-PrOH) with alcohol content up to 0.25mol fractions, have been determined calorimetrically at T=298.15K. The standard enthalpies of the solution (ΔsolH∘) and transfer (ΔtrH∘) of l‑glutamine from water to aqueous alcohol have been calculated. The enthalpic coefficients of pairwise interactions (hxy) between l‑glutamine and alcohol molecules have been computed by the McMillan–Mayer formalism. It has been found that these coefficients become increasingly positive in EtOH, 1-PrOH, and 2-PrOH sequence. A linear relationship between the enthalpic coefficients of pairwise interactions of l‑glutamine-alcohol and those of alcohol-H2O is also established. A comparative analysis of the thermochemical characteristics of L‑glutamine dissolution and some amino acids in the mixtures studied has been made.

Enthalpy parameters of molecular interactions of dl-α-alanyl-dl-α-alanine with polyhydric alcohols in the aqueous solution

Integral enthalpies of dissolution Δsol H m of DL-α-alanyl-DL-α-alanine in aqueous solutions of glycerol, ethylene glycol, 1,2-propylene glycol, and 1,3-propylene glycol at the concentration of the organic component up to 0.33 molar fraction have been determined by calorimetry. Standard enthalpies of dissolution (Δsol Н 0) and the transfer (Δtr Н 0) of the dipeptide from water to aqueous solutions of the polyhydric alcohols have been calculated. The calculated enthalpic coefficients of pairwise interactions of DL-α-alanyl-DL-α-alanine with polyhydric alcohols are positive. The influence of the position of hydroxy groups in the polyhydric alcohol molecule on the enthalpic parameter of the interaction with the dipeptide has been revealed. The effect of various types of the interaction in the solution and structural features of biological molecules and the cosolvent on the enthalpic parameters of the dissolution has been analyzed.

Solvent and pH Dependences of Mixing Enthalpies of N-Glycylglycine with Protocatechuic Acid

Protocatechuic acid (PA) is a natural phenolic compound which has been proven to have chemopreventive property against chemically induced carcinogenesis. The mixing enthalpies of PA with N-glycylglycine in sodium phosphate and potassium phosphate buffer solutions with different pH values have been investigated by mixing-flow isothermal microcalorimetry at T = 298.15 K. The heterotactic enthalpic interaction coefficients (hxy) in the pH range of phosphate buffer solution from 3.0 to 8.0 have been calculated according to the McMillan–Mayer theory. Trends of the enthalpic pairwise interaction coefficients (hxy) with increasing pH in both phosphate buffer solutions were obtained. The solvent and pH dependence of the hxy were discussed in terms of molecular interactions between solvated solute molecules.

Dependence of the enthalpies of alanyl-alanine dissolution on the composition of mixed water + acetone and water + DMSO solvents at 298.15 K

The enthalpies of dissolution of two dipeptides, DL-α-alanyl-β-alanine and β-alanyl-β-alanine, in mixed solvents H2O + acetone (AC) and H2O + dimethyl sulfoxide (DMSO) are measured via calorimetry at an organic component concentration of x 2 = 0–0.25 mole fraction at 298.15 K. The standard enthalpies of dissolution (Δsol H po) and the transfer (Δtr H po) of dipeptides from water to the mixed solvent and the enthalpic coefficients of pairwise interactions (h xy ) with AC and DMSO molecules are calculated from these data. The effect the composition of aqueous organic mixtures has on the enthalpy characteristics of the dissolution of DL-α-alanyl-β-alanine and β-alanyl-β-alanine is considered. A comparative analysis of h xy values is performed for alanine dipeptides in the investigated mixed solvents.

Temperature Dependences and Enthalpic Discrimination of Homochiral Pairwise Interactions of Six α-Amino Acid Enantiomers in Pure Water

Dilution enthalpies of six α-amino acid enantiomers (l-alanine vs d-alanine, l-serine vs d-serine, and l-proline vs d-proline) in pure water were determined at T = (288.15 to 323.15) K by isothermal titration calorimetry (ITC). Homochiral enthalpic pairwise interaction coefficients (hxx) at each temperature were evaluated according to the McMillan–Mayer theory. The hxx values of α-alanine and α-proline enantiomers are all positive (hLL > hDD > 0), while those of α-serine enantiomers are all negative (hLL < hDD < 0). In both cases, the hxx values increase uniformly and gradually with elevating temperatures. A slight but significant enthalpic discrimination effect is found in the homochiral pairwise interactions of these α-amino acid enantiomers. The positive growth of hxx values indicates that increasing temperature promotes the predominance of hydrophobic interactions in the binary aqueous solutions studied.

Energetics of pairwise interaction between glycidol enantiomers in (dimethylformamide + water) mixtures rich in water at T = 298.15 K

Successive dilution enthalpies (ΔH(mN-1→mN)) of glycidol enantiomers (R-(+)-glycidol, S-(−)-glycidol) and the racemate (R/S-(±)-glycidol) in (dimethylformamide (DMF)+water) mixtures rich in water (mass fractions of DMF, wDMF=0 to 0.25) have been determined respectively by isothermal titration calorimetry (ITC) at T=298.15 K. The corresponding homotactic enthalpic pairwise interaction coefficients (hXX) of each compound have been evaluated from the framework of McMillan–Mayer theory. Across the studied composition range of (DMF+water) mixtures the hXX values of these compounds are all positive, and decrease gradually with the mass fraction of DMF by the order hRR>hRS≈hMM>hSS>0 (M represents the racemate R/S-(±)-glycidol, and hRS is the estimated value for the heterochiral pair R–S). The positive values of hXX indicate that pairwise interactions of these compounds are endothermic and unfavourable from the point of view of enthalpy. The interaction of S–S pair is considered to be slightly stronger than M–M, R–S and R–R pairs since the former absorbs less heat than the latter in pairwise interactions. The addition of cosolvent (DMF) is in favour of pairwise interactions of these compounds in the mixtures rich in water.

Studies of interparticle interactions among some l-α-amino acids and 1,2 (1,3)-propanediols in aqueous solution at 298.15 K

Mixing enthalpies of aqueous glycine, l-α-alanine, l-α-valine, l-α-serine. l-α-threonine and l-α-proline solutions and aqueous 1,2-propanediol and 1,3-propanediol solutions and their dilution enthalpies have been measured with a Thermometric-2277 Thermal Activity Monitor at 298.15K. Experimental data were treated according to the McMillan–Mayer theory and the heterogeneous enthalpic pairwise interaction coefficients (hxy) of the natural amino acids and propanediol molecules in aqueous solution were obtained. Combining the hxy coefficients of amino acids with glycol and glycerol in aqueous solution reported by our previous works, the effects of number and position of OH groups in polyalcohols on the interactions between them and amino acids are discussed in the terms of solute–solute interactions.

Enthalpic discrimination of homochiral pairwise interactions: Enantiomers of proline and hydroxyproline in (dimethyl formamide (DMF) + H2O) and (dimethylsulfoxide (DMSO) + H2O) mixtures at 298.15 K

Dilution enthalpies of two pairs of α-amino acid enantiomers, namely l-proline vsd-proline, and l-hydroxyproline vsd-hydroxyproline, in water-rich regions of dimethyl formamide (DMF)+H2O and dimethylsulfoxide (DMSO)+H2O mixtures (mass fractions of cosolvents wCOS=0 to 0.30) have been determined respectively at 298.15K by isothermal titration calorimetry (ITC). The successive values of dilution enthalpy obtained in a single run of ITC determination were used to calculate homochiral enthalpic pairwise interaction coefficients (hxx) at the corresponding composition of mixed solvents according to the McMillan–Mayer’ statistical thermodynamic approach. The sign and magnitude of hxx were interpreted in terms of solute–solute interactions mediated by solvent and cosolvent molecules, and preferential configurations of homochiral pairwise interactions (l–l or d–d pairs) in aqueous solutions. The variations of hxx with wCOS were considered to be dependent greatly on the competition equilibrium between hydrophobic and hydrophilic interactions, as well as the structural alteration of water caused by the two highly polar aprotic cosolvents (DMF and DMSO). Especially, it was found that when one of the two kinds of interactions (hydrophobic or hydrophilic interactions) preponderates over the other in solutions, enthalpic effect of homochiral pairwise interactions is always remarkable, and is characterized by a large absolute value of hxx, positive or negative, which corresponds respectively to the prevailing interactions of hydrophobicity or hydrophilicity. Interestingly, it was also found that the hxx values of l-enantiomers are generally larger than those of d-enantiomers across the whole studied composition range of mixed solvents, i.e. |hLL|>|hDD|, which is defined as enthalpic discrimination effect and attributed to the influence of preferential configuration on homochiral pairwise interactions in aqueous solutions.

Enthalpies of Dilution of Penicillamines in N,N-Dimethylformamide + Water Mixtures at 298.15 K

Dilution enthalpies of two penicillamine enantiomers, namely, d-penicillamine, l-penicillamine, and their racemate d,l-penicillamine, in N,N-dimethylformamide (DMF) + water mixtures of various compositions have been determined at 298.15 K respectively, using an isothermal titration calorimeter (MicroCal ITC200). According to the McMillan–Mayer theory, homochiral enthalpic pairwise interaction coefficients (hXX) of the three penicillamines in DMF + water mixtures of different mass fractions (wDMF = 0 to 0.3) have been calculated regressively. It is found that hXX coefficients of each enantiomer and their racemate change increasingly with wDMF to the maxima at wDMF = 0.20 and then decrease relatively rapidly, which follows the order hLL > hDD ≈ hRR > 0 (R represents the racemate mixture of penicillamine). The results are discussed from the point of view of competitive equilibrium between hydrophobic and hydrophilic interactions in solutions.

Homotactic enthalpic pairwise interactions of four deoxynucleosides (dU, dC, dG, dT) in dimethylformamide (DMF) + water mixtures at 298.15 K

The dilution enthalpies of four 2′-deoxynucleosides, namely 2′-deoxyuridine (dU), 2′-deoxycytidine (dC), 2′-deoxyguanosine (dG) and 2′-deoxythymidine (dT), in dimethylformamide (DMF)+water mixtures have been determined at 298.15K respectively, using an isothermal titration calorimeter (ITC200 MicroCal). On the basis of the McMillan–Mayer theory, the homotactic enthalpic pairwise interaction coefficients (hXX) of the four 2′-deoxynucleosides in DMF+water mixtures of various mass fractions (wDMF=0–0.30) have been calculated. It was found that the values of hXX of the four 2′-deoxynucleosides are all large negative and increase gradually across the whole studied composition range of the mixed solvent, though the variation degrees of them are somewhat different. The results are discussed from the point of view of solute–solute and solute–solvent interactions in solutions.

Enthalpic discrimination of position isomerism: Pairwise interaction of piperidinecarboxylic acid isomers in DMSO + H2O mixtures at 298.15 K

Dilution enthalpies of three piperidinecarboxylic acid isomers, namely 2-piperidinecarboxylic acid, 3-piperidinecarboxylic acid and 4-piperidinecarboxylic acid in dimethylsulfoxide (DMSO)+H2O mixtures (mass fractions of DMSO w=0–0.3) have been determined respectively using an isothermal titration calorimeter (ITC200, MicroCal) at 298.15K. According to the McMillan–Mayer theory, the corresponding homogeneous enthalpic pairwise interaction coefficients (hXX) of the three isomers have been calculated at each composition of mixed solvents. It is found that position isomerization effect of the three piperidinecarboxylic acid isomers can be discriminated completely by enthalpic effects from pairwise interactions between solute molecules. The results were interpreted from the point of view of solute–solute and solute–solvent interactions in these ternary aqueous systems, as well as competition equilibrium between hydrophobic–hydrophobic, hydrophobic–hydrophilic and hydrophilic–hydrophilic interactions.

The dilution enthalpies of l-prolinol in N,N-dimethylformamide aqueous solutions at T = 298.15 K

Values of the enthalpy of dilution were measured for l-prolinol in pure water and N,N-dimethylformamide (DMF) aqueous solutions with various mass fractions of DMF at T=298.15K using a flow-mixing microcalorimeter. A pseudo phase equilibrium model was proposed to simplify the complex aggregation equilibrium and interpret the abnormality in the dilution enthalpy, which together with the McMillan–Mayer approach was used to fit the experimental data to obtain the enthalpic pairwise interaction coefficients and the molar aggregation enthalpies of l-prolinol in DMF aqueous solutions. The results are discussed in terms of the hydrophobic interaction and the interactions between the solvated solutes.

The Mixing Enthalpy Interaction Coefficients of N,N′-Hexamethylenebisacetamide with l-Alanine and l-Serine in Aqueous Glucose Solutions at 298.15 K

The mixing enthalpies of N,N′-hexamethylenebisacetamide (HMBA) with l-alanine and l-serine in aqueous glucose solutions have been determined by using mixing-flow isothermal microcalorimetry along with their dilution enthalpies at the temperature of 298.15 K. These results can be used to obtain the heterotactic enthalpic interaction coefficients (h xy , h xxy , and h xyy ) in the range of the glucose molality, (0 to 1.5) mol⋅kg−1, according to the McMillan–Mayer theory. Combining our previous research results for glycine (see Liu et al. in J. Chem. Eng. Data 55, 5258–5263, 2010), we find that the heterotactic enthalpic pairwise interaction coefficients h xy between HMBA and the investigated amino acids in aqueous glucose solutions are all positive and reach maximum values at about 0.3 mol⋅kg−1 glucose. In addition, the order for the value of h xy of the three amino acids in pure water and aqueous solution of the same glucose molality is h xy (l-alanine)>h xy (l-serine)>h xy (glycine). All variations of the heterotactic enthalpic pairwise interaction coefficients with the molalities of glucose in the quaternary systems are discussed in terms of solute–solute and solute–solvent interactions.

Pairwise interaction enthalpies of enantiomers of β-amino alcohols in DMSO + H2O mixtures at 298.15 K

The dilution enthalpies of enantiomers of six β-amino alcohols, namely (R)-(-)-2-amino-1-propanol versus (S)-(+)-2-amino-1-propanol, (R)-(-)-2-amino-1-butanol versus (S)-(+)-2-amino-1-butanol, and (R)-(-)-2-amino-1-pentanol versus (S)-(+)-2-amino-1-pentanol in dimethylsulfoxide (DMSO) + H(2)O mixtures (mass fractions of DMSO w = 0 to 0.3) have been determined respectively using an isothermal titration calorimeter (MicroCal ITC200, Northampton, MA, USA) at 298.15 K. According to the McMillan-Mayer theory, the corresponding homochiral enthalpic pairwise interaction coefficients (h(XX)) of the six amino alcohols have been calculated. It is found that across the whole studied composition range of mixed solvent, values of h(XX) for S-enantiomer are almost universally higher than those of R-enantiomer for each amino alcohol and that the variations of h(XX) depend largely on the composition of mixed solvent. The results were interpreted from the point of view of solute-solute interaction mediated by cosolvent DMSO, as well as competition equilibrium between hydrophobic-hydrophobic, hydrophilic-hydrophilic, and hydrophobic-hydrophilic interactions.

Effect of sodium chloride concentration on the interaction of N-(N-glycylglycyl)glycine with xylitol and D-mannitol in aqueous solutions

Abstract Enthalpies of mixing of N -( N -glycylglycyl)glycine with xylitol and D-mannitol and their respective enthalpies of dilution in aqueous sodium chloride solutions have been determined at 298.15 K using flow microcalorimetry. The experimental results obtained have been analyzed to give the heterotactic enthalpic interaction coefficients ( h xy , h xxy , h xyy ) of the solutes in terms of the McMillan–Mayer model. It has been found that the heterotactic enthalpic pairwise interaction coefficients h xy between N -( N -glycylglycyl)glycine and xylitol or D-mannitol in aqueous sodium chloride solutions are negative and become less negative with the increase of the concentration of sodium chloride. The h xy values for the interaction between N -( N -glycylglycyl) glycine and D-mannitol are less than that between N -( N -glycylglycyl) glycine and xylitol. The results are discussed in terms of solute–solute and solute–solvent interactions.