Enthalpies of solution of L-phenylalanine in aqueous solution of amides at 298.15 K

doi:10.1016/j.tca.2012.11.004

Thermochimica Acta

Volume 551, 10 January 2013, Pages 145-148

https://doi.org/10.1016/j.tca.2012.11.004 Get rights and content

Abstract

The enthalpies of solution $Δ_{sol} H^{m}$ have been determined for L-phenylalanine in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA). The measurements have been made at 298.15 K and mole fraction of amide x₂ = (0–0.4) on the precise isothermic calorimeter. The results obtained have been used to calculate the standard enthalpies of solution ( $Δ_{sol} H °$ ) and transfer ( $Δ_{tr} H °$ ) of L-phenylalanine from water into mixtures as well as the enthalpy coefficients of pairwise interaction (h_xy) of the solute with amide in aqueous media. The interrelation between enthalpy characteristics of dissolution (transfer) of L-phenylalanine and the composition of (water + amide) binary mixtures has been established. Contributions of the amides properties (molar volume, dipolarity/polarizability, acidity and basicity) to the energy of pairwise interactions have been estimated quantitatively by means of a modified Kamlet–Taft equation.

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, $Δ_{sol} H^{m}$ , have been used for calculation of the standard values of dissolution enthalpies $Δ_{sol} H °$ , and transfer $Δ_{tr} H °$ , of L-phenylalanine from water to binary solvent, and also enthalpic coefficients of pairwise interactions, h_xy, 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, ²⁵n_D = 1.4465), MFA (CAS-No. 123-39-7, 99%, Aldrich, ρ = 0.99894 g cm⁻¹, ²⁵n_D = 1.4302), DMF (CAS-No. 68-12-2, anhydrous, 99.8%,

Results

Standard values of enthalpies of dissolution, $Δ_{sol} H °$ L-phenylalanine and standard deviations of these values in mixtures water + amide are presented in Table 1. Enthalpies of transfer of L-phenylalanine, $Δ_{tr} H °$ 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). $Δ_{tr} H ° = Δ_{sol} H ° (w + y) - Δ_{sol} H ° (w),$ where $Δ_{sol} H ° (w + y)$ is the enthalpy of L-phenylalanine solution in each aqueous solutions of amides. $Δ_{sol} H °$

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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Short communicationEnthalpies of solution of L-phenylalanine in aqueous solution of amides at 298.15 K

Abstract

Introduction

Section snippets

Experimental

Results

Discussion

Acknowledgement

Thermochim. Acta

Thermochim. Acta

J. Chem. Thermodyn.

Thermochim. Acta

Solvation of glycine and its oligomers in a water–acetonitrile binary solvent at 298.15 K

Russ. J. Phys. Chem.

The enthalpies of solution and solvation of glycine in mixed water–formamide solvents at 298.15 K

Russ. J. Phys. Chem.

The enthalpies of solution of dl-α-alanine in water–organic solvent mixtures at 298.15 K

Russ. J. Phys. Chem.

Enthalpies of solution of l–l- and d–d-isomers of valine in aqueous alkanols at 298.15 K

J. Solut. Chem.

The dependence of the enthalpy of solution of L-methionine on the composition of water–alcohol binary solvents

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The Chemist's Companion: A Handbook of Practical Data

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Thermochim. Acta

Short communication
Enthalpies of solution of L-phenylalanine in aqueous solution of amides at 298.15 K