Article pubs.acs.org/jced
Thermochemical Characteristics of the Dissolution of D‑Valine in Aqueous Solutions of Some Amides at T = 298.15 K Valeriy I. Smirnov* and Valentin G. Badelin Laboratory of Thermodynamics of Non-electrolytes Solutions and Biologically Active Substances, G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences, 1 Akademicheskaya Street, 153045, Ivanovo, Russia ABSTRACT: Enthalpies of the dissolution of D-valine in the mixtures of water with formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) with the mole fraction (x2) of amides ranging up to 0.3 have been measured at T = 298.15 K. The standard enthalpies of the dissolution (ΔsolH°) and the transfer enthalpies (ΔtrH°) of Dvaline have been calculated. On the basis of McMillan−Mayer’s theory, the enthalpic coefficients of pairwise interaction (hxy) have been calculated. The enthalpic coefficients (hxy) of the solute−amide pairwise interaction in the water proved to be positive and increasing in the series: FA < MFA < DMF. It is associated with the increasing of the hydrophobic properties of amides and the energy of intermolecular interactions between components of water+organic mixtures in the same sequence.
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INTRODUCTION In recent years, considerable interest in the determination of various thermodynamic characteristics of amino acid dissolution in aqueous organic mixtures is observed.1−11 A large number of the thermochemical data already is available for discussion. These data testify that hydrophobic effects play the significant role in both the hydration process and solute−solute intermolecular interactions. The hydrophobic influences of alkyl side-chains of α-amino acids on the thermochemical characteristics of their dissolution has been clearly detected in apolar solvents11,12 or in DMF.13 The energy of the processes of α-amino acids dissolution depends on the nature and concentration of the cosolvent.2,5,8 In our work5 it was shown that the structure of alcohols exerts a strong influence on the intermolecular interactions of alcohol with the enantiomers of valine in aqueous solution. The aims of this investigation are (a) to study intermolecular interactions between D-valine molecules and amide molecules in aqueous solutions, as a function of the amides concentration; (b) to extend the database of the experimental values of dissolution enthalpies of D-valine in aqueous solutions of organic solvents. As the organic cosolvents, polar aprotic solvents were selected, namely, formamide (FA), N,N-methylformamide (MFA), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA). The aqueous mixtures of amides are widely used in industry, biochemistry, and pharmacology as well as to study intermolecular interactions between molecules of biologically active substances, since they contain a functional group (−CONH), which is a fragment of protein systems.1,12−20 The experiment was carried out at T = 298.15 K and mole fraction of amides: x2 = 0−0.3. The experimental data on the enthalpies of dissolution were used to calculate the standard values of dissolution enthalpies and transfer enthalpies, of Dvaline and enthalpic coefficients of the pairwise interactions, hxy, of D-valine with the molecules of amides. The results were © 2016 American Chemical Society
analyzed from the point of view of the influence of amide concentration and structure of amide on the thermochemical characteristics of dissolution and solvation of D-valine. These experimental data are originally presented by the authors.
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EXPERIMENTAL SECTION Materials. D-Valine was dried up in a vacuum box at T = 333 K within 48 h, stored over P2O5 in a desiccator and used without further purification. Molality (m) of D-valine in a mixed solvent varied in the range from (0.5 to 1.5)·10−2 mol·kg−1. Amides were used without further purification, their concentration varying from 0 to 0.3 mole fractions. The data characterizing the solvents and D-valine under study are presented in Table 1. H2O has been purified by double distillation followed by degassing (electrical conductivity p ≈ 1 × 10−6 S·cm−1). Mixtures and samples of D-valine have been weighed using balances VLR-200 (“Gosmetr”, Sankt-Peterburg, Russia), the accuracy of measurements being 5·10−5 g. Calorimetric Measurement. Calorimetric measurements of the enthalpies of D-valine dissolution have been carried out in a calorimeter with an isothermal shell at T = (298.15 ± 0.01) K and P = (100.5 ± 0.7) kPa. Calorimeter calibration data and calculation of measurement errors are presented in Supporting Information to the article.21 A scheme of the experimental setup and the scenario of the experimental procedure have been described in ref 22. Reliability of the resulting values of dissolution of some amino acids and peptides in water is confirmed by their comparison with similar results derived by other authors. For example, our values of ΔsolH° (glycine) = (14.25 ± 0.06) kJ·mol−1,23 ΔsolH°(glycylglycylglycine) = (17.62 Received: December 25, 2015 Accepted: April 26, 2016 Published: May 3, 2016 1864
DOI: 10.1021/acs.jced.5b01087 J. Chem. Eng. Data 2016, 61, 1864−1867
Journal of Chemical & Engineering Data
Article
Table 1. List of Chemicals, Their Provenance, and Purity Values chemical
formula
Ma
CAS No.b
provenance
purityc
D-valine
C5H11NO2 CH3NO C2H6NO C3H7NO C4H9NO H2O
117.15 45.04 59.07 73.09 87.12 18.02
640-68-6 75-12-7 123-39-7 68-12-2 127-19-5
Sigma-Aldrich Sigma-Aldrich Aldrich Sigma-Aldrich Sigma-Aldrich
≥ 0.998, (HPLC) ≥ 0.998 ≥ 0.990 ≥ 0.990, (anhydrous) ≥ 0.998,(anhydrous)
formamide N-methyl-formamide N,N-dimethyl-formamide N,N-dimethyl-acetamide water a
waterd content < < <
0.08) and FA (x2 > 0.10) gives to the increase of the exothermic contribution from D-valine + DMA (FA) hydrophilic−hydrophilic interactions to a total enthalpy interaction effect. The dependencies of ΔtrH°= f(x2) change their direction for the opposite one. In the case of (H2O + MFA) and (H2O + DMF) mixtures, the endothermicity of ΔtrH° value of D-valine grows monotonically in all concentration ranges studied. According to the treatment of solution properties originally proposed by McMillan−Mayer28 and specifically applied to those of aqueous solutions of nonelectrolytes by Kauzmann29 and other authors,30,31 the interparticle interaction between molecules of D-valine and amide can be analyzed using the enthalpy coefficients of pairwise interactions (hxy). These coefficients reflect the sum of the enthalpy effects of interactions between solutes in aqueous solutions. For this purpose, the ΔsolH°(m2) functions were approximated by a third-degree polynomial of the form: Δsol H ° = a0 + a1m2 + a 2m22 + a3m23
These parameters allow the information about the influence of the structure of organic solvents on the energetics of interactions of hydrated molecules of D-valine with cosolvent molecules to be obtained. The positive sign at hxy values for the aqueous solutions of all amides shows that the solutes are strongly hydrated, while the hydrophilic−hydrophilic interaction between hydrated D-valine and amide molecules becomes rather weak. The endothermicity of hxy values of Dvaline with amide molecules increases in the series: FA < MFA < DMFA < DMA. Such a sequence is due to both increasing hydrophobic properties of amides and the energy of intermolecular interactions between components of the mixtures. Linear dependence depicted in Figure 2 shows that
Figure 2. Correlation between of the enthalpy coefficients of pairwise interactions, (hxy), of D-valine and of the enthalpy coefficients of pairwise interactions, (hA+W), of H2O with FA, MFA, and DMF.
there exists an obvious interrelation between hxy of D-valine and the enthalpic coefficients of the pairwise interaction (hA+W) between the molecules of H2O and those of formamides. Earlier we received a similar result for some amino acids and peptides in mixtures of H2O + alcohols and H2O + formamides.13,19−21 Apparently, there is a similar dependence for a series of acetamides. In other words, one can argue that the intensification of the pairwise interaction between amide and H2O molecules in the mixtures results in the increase in the endothermic contribution to hxy of D-valine−amide interactions.
(2)
where m2 is the molal concentration of the amides, and ai is the coefficient calculated by the least-square method. The correlation coefficient, R, and Student criterion value, tα, were in the range from 0.991 to 0.998 and from 0.041 to 0.116, respectively. To calculate the coefficients of pairwise interactions of D-valine with amide molecules, hxy (J kg mol−2), use has been made of a quotient a1 which is related to hxy as hxy = a1/2.32 The hxy values for all the systems in question are listed in Table 3.
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CONCLUSIONS We would like to note that the energy of intermolecular interactions of D-valine with the amides molecules in aqueous solution will be determined (a) by energy of the formation of the mixed solvent (the strong intermolecular interactions in the mixtures of (H2O + FA) < (H2O + MFA) < (H2O + DMF) < (H2O + DMA) weakens the solvation of D-valine), and (b) by the structure (hydrophobycity) and the concentration of an organic cosolvent.
Table 3. Enthalpic Coefficients of the Pairwise Interaction (hxy, J kg mol−2) of D-Valine with Amide Molecules in Aqueous Solution and Standard Uncertainty u(hxy, J kg mol−2)
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AUTHOR INFORMATION
Corresponding Author FA
MFA
DMF
*E-mail:
[email protected] (
[email protected]). Phone: +7 4932 351859. Fax: +7 4932 336246.
DMA
amino acid
hxy
u(hxy)
hxy
u(hxy)
hxy
u(hxy)
hxy
u(hxy)
D-valine
345
25
710
25
1300
80
1490
45
Notes
The authors declare no competing financial interest. 1866
DOI: 10.1021/acs.jced.5b01087 J. Chem. Eng. Data 2016, 61, 1864−1867
Journal of Chemical & Engineering Data
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Article
(20) Smirnov, V. I.; Badelin, V. G. Enthalpies of L-threonine dissolution in some aqueous amides at 298.15 K. Thermochim. Acta 2010, 503−504, 97−99. (21) Smirnov, V. I.; Badelin, V. G. Enthalpies of L-proline dissolution in aqueous solution of N, N-dimethylformamide at 293.15−308.15 K. Thermochim. Acta 2015, 606, 41−44. (22) Badelin, V. G.; Tyunina, E.; Yu; Mezhevoi, I. N. Calorimetric Study of Dissolution of Amino Carboxylic Acids in Water at 298.15 K. Russ. J. Appl. Chem. 2007, 80, 711−715. (23) Badelin, V. G.; Smirnov, V. I.; Mezhevoi, I. N. Dependence of the hydration enthalpy of amino acids and oligopeptides from their molecular structure. Russ. J. Phys. Chem. 2002, 76, 1299−1308. (24) Badelin, V. G.; Smirnov, V. I. The dependence of the enthalpy of solution of L-methionine on the composition of water−alcohol binary solvents. Russ. J. Phys. Chem. 2010, 84, 1163−1168. (25) Palecz, B. Enthalpies of Solution and Dilution of some L-α− amino acids in water at 298.15 K. J. Therm. Anal. Calorim. 1998, 54, 257−263. (26) Piekarski, H.; Nowicka, B. Calorimetric studies of interactions of some peptides with electrolytes, urea and ethanol in water at 298.15 K. J. Therm. Anal. Calorim. 2010, 102, 31−36. (27) Palecz, B.; Piekarski, H.; Romanowski, S. Studies on homogeneous interactions between zwitterions of several L-alphaamino acids in water at a temperature of 298.15 K. J. Mol. Liq. 2000, 84, 279−288. (28) McMillan, W. G.; Mayer, J. E. The statistical thermodynamics of multicomponent systems. J. Chem. Phys. 1945, 13, 276−305. (29) Kozak, J. J.; Knight, W. S.; Kauzmann, W. Solute-solute interactions in aqueous solutions. J. Chem. Phys. 1968, 48, 675−690. (30) Krishnan, C. V.; Friedman, H. L. Studies of hydrogen bonding in aqueous alcohols: enthalpy measurements and model calculations. J. Solution Chem. 1973, 2, 119−138. (31) Desnoyers, J. E.; Perron, G.; Avedikian, L.; Morel, J. P. Enthalpies of the urea-tert-butanol-water system at 25C. J. Solution Chem. 1976, 5, 631−644. (32) Piekarski, H.; Tkaczyk, M. Effect of Non-electrolyte Properties on the Enthalpic Interaction Coefficients for NaCI/Nal-Non-electrolyte Pairs in Water. J. Chem. Soc., Faraday Trans. 1991, 87, 3661−3666.
REFERENCES
(1) Hu, X.-G.; Liu, J.-M.; Guo, Z.; Liang, H.-Y.; Jia, Z.-P.; Cheng, W.N.; Guo, A.-D.; Zhang, H.-J. Enthalpic discrimination of homochiral pairwise interactions: Enantiomers of proline and hydroxy-proline in (dimethyl formamide (DMF) + H2O) and (dimethyl sulfoxide (DMSO) + H2O) mixtures at 298.15 K. J. Chem. Thermodyn. 2013, 63, 142−147. (2) Yu, Q.; Ma, X.; Xu, L. Solubility, dissolution enthalpy and entropy of l-glutamine in mixed solvents of ethanol + water and acetone + water. Thermochim. Acta 2013, 558, 6−9. (3) Wang, X.; Guo, Y.; Zheng, Q.; Lin, R. Transfer enthalpies of amino acids and glycine peptides from water to aqueous solutions of trimethylamine N-oxide at 298.15 K. Thermochim. Acta 2014, 587, 48−51. (4) Aslan, N.; Erden, P. E.; Dogan, A.; Canel, E.; Kılic, E. Protonation constants of some alanyl dipeptides in mixed aqueous organic solvents. J. Solution Chem. 2016, 45, 299−312. (5) Smirnov, V. I.; Badelin, V. G. Enthalpies of solution of L−L- and D−D- isomers of valine in aqueous alkanols at 298.15 K. J. Solution Chem. 2008, 37, 1419−1424. (6) Ren, X.; Ni, Y.; Lin, R. Enthalpies of dilution of glycine, l-serine and l-valine in mixtures of water and N, N-dimethylformamide at 298.15 K. Thermochim. Acta 2000, 348, 19−24. (7) Barone, G.; Castronuovo, G.; Del Vecchio, F.; Elia, V. Chiral recognition between enantiomeric α-aminoacids. A calorimetric study at 25°C. J. Solution Chem. 1989, 18, 1105−1116. (8) Yu, L.; Hu, H.; Lin, R.; Zhang, H.; Xu, G. Enthalpies of Dilution and Enthalpies of Mixing of r-Amino Acids + Pyridine and r-Amino Acids + Methylpyridine in Aqueous Solutions at 298.15 K. J. Chem. Eng. Data 2003, 48, 990−994. (9) Castronuovo, G.; Elia, V.; Postiglione, C.; Velleca, F. Interactions of aminoacids in concentrated aqueous solutions of urea or ethanol. Implications for the mechanism of protein denaturation. Thermochim. Acta 1999, 339, 11−19. (10) Gal, J. F.; Stone, M.; Lebrilla, C. B. Chiral recognition of nonnatural α-amino acids. Int. J. Mass Spectrom. 2003, 222, 259−267. (11) Castronuovo, G.; Elia, V.; Velleca, F. On the role of the functional group in determining the strength of hydrophobic interactions in aqueous solutions of α-amino acid derivatives. J. Solution Chem. 1996, 25, 971−983. (12) Sijpkes, A. H.; Somsen, G.; Blankenborg, S. G. J. Enthalpies of interaction of some N-acetyl amino acid amides dissolved in Nmethylformamide at 298.15 K. J. Chem. Soc., Faraday Trans. 1990, 86, 3737−3742. (13) Sijpkes, A. H.; Somsen, G. Enthalpic interaction coefficients of some dipeptides dissolved in N, N-dimethylformamide. J. Chem. Soc., Faraday Trans. 1 1989, 85, 2563−2573. (14) Zhou, L.; Liu, C.; Ma, L.; Lin, R. Enthalpies of transfer of amino acids from water to aqueous solutions of N-methylformamide and N,N-dimethylformamide at T = 298.15K. Thermochim. Acta 2008, 468, 116−118. (15) Józw ́ iak, M.; Józw ́ iak, A. Enthalpy of solution of hexaglyme in mixtures of water with N, N-dimethylformamide at 298.15 K. J. Mol. Liq. 2014, 199, 224−226. (16) Liu, C.; Zhou, Li.; Lin, R. Interactions of some amino acids with aqueous N, N-dimethylacetamide solutions at 298.15 and 308.15 K: A volumetric approach. J. Solution Chem. 2007, 36, 923−937. (17) Zhou, Li.; Liu, C. Enthalpies of transfer of amino acids from water to aqueous solutions of N-methylacetamide and N,Ndimethylacetamide at T = 298.15 K. Thermochim. Acta 2009, 482, 72−74. (18) Yu, L.; Zhu, Y.; Zhang, H.; Pang, H.; Geng, F. Enthalpic interactions between some amino acids and cyclohexanone in aqueous solutions at 298.15K. Thermochim. Acta 2006, 448, 154−156. (19) Badelin, V. G.; Smirnov, V. I. Enthalpies of solution of Lphenylalanine in aqueous solution of amides at 298.15 K. Thermochim. Acta 2013, 551, 145−148. 1867
DOI: 10.1021/acs.jced.5b01087 J. Chem. Eng. Data 2016, 61, 1864−1867
