Short communicationEnthalpies of solution of L-phenylalanine in aqueous solution of amides at 298.15 K
Introduction
As the continuation of previous thermochemical researches of the processes of aliphatic amino acids dissolving in water solutions of organic solvents [1], [2], [3], [4], [5], [6], [7], in this article we represent the investigation of the processes of dissolution of aromatic amino acid – L-phenylalanine in aqueous solutions of FA, MFA, DMF and DMA at 298.15 K and an amide mole fraction x2 = 0–0.4. The experimental data on the enthalpies of solution, , have been used for calculation of the standard values of dissolution enthalpies , and transfer , of L-phenylalanine from water to binary solvent, and also enthalpic coefficients of pairwise interactions, hxy, L-phenylalanine with molecules of amides. For the quantitative assessment of the energy contributions, caused by polarity, polarizability, basicity and acidity of cosolvent in the coefficients of pairwise interactions L-phenylalanine–amide we used Kamlet–Taft correlation equation.
Section snippets
Experimental
L-Phenylalanine (Aldrich Chemical Co., Ltd., the content of the basic component >99%) was dried up in a vacuum box at 333 K within 48 h, was stored over P2O5 in space, in a desiccator and was used without further purification. Molality (m) L-phenylalanine in mixed solvent varied in a range from 5 × 10−3 to 1.5 × 10−2 mol kg−1. FA (CAS-No. 75-12-7 purum, ≥98.0%, Fluka, ρ = 1.12916 g cm−1, 25nD = 1.4465), MFA (CAS-No. 123-39-7, 99%, Aldrich, ρ = 0.99894 g cm−1, 25nD = 1.4302), DMF (CAS-No. 68-12-2, anhydrous, 99.8%,
Results
Standard values of enthalpies of dissolution, L-phenylalanine and standard deviations of these values in mixtures water + amide are presented in Table 1. Enthalpies of transfer of L-phenylalanine, from water in water solutions of amides are calculated from standard values of enthalpies of dissolution in water and in amide water solution by Eq. (1).where is the enthalpy of L-phenylalanine solution in each aqueous solutions of amides.
Discussion
The analysis of Table 1 data and Fig. 1 has shown that the process of interaction L-phenylalanine with molecules of amides depends both on their structure, and on the composition of binary solvent. On increasing of concentration of amides to x2 ∼ 0.18, increases the endothermicity of the process of L-phenylalanine dissolution in (H2O + MFA), (H2O + DMF) and (H2O + DMA) mixtures. In (H2O + FA) mixture the endothermicity of L-phenylalanine dissolution decreases slightly. In the range of concentration 0.18 < x
Acknowledgement
The financial support of this work by the Russian Foundation for Basic Researches is gratefully acknowledged (Grant No. 11-03-00013a).
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