Year 2007, Month 4 (Section Full Articles, Page 739)
Amino acids in aqueous solution. Effect of molecular structure and temperature on thermodynamics of dissolution
V. P. Korolev, D. V. Batov, N. L. Smirnova, and A. V. Kustov
The enthalpies of dissolution of glycine (Gly) and Lαalanine (Ala) in water at 288.15—318.15 K were measured. The results were compared with the earlier obtained data for Lαphenylalanine (Phe) and Lαhistidine (His). The standard enthalpies of dissolution (ΔsolnH 0) and differences (ΔÑp 0) between the limiting partial molar heat capacity of the amino acids in solution and the heat capacity of the amino acids in the crystalline state (ΔÑp0 = – Ñð) were calculated in the temperature interval 273—373 K. Changes in the entropy of dissolution (ΔΔsolnS 0) and reduced Gibbs energy [Δ(ΔsolnG 0/Ò )] in the temperature interval from 273 to 373 K were determined from the known thermodynamic relationships. The ΔÑp 0 value is negative for hydrophilic glycine and positive for other amino acids. The ΔΔsolnS 0 values increase with an increase in the hydrophobicity of the amino acids. The Δ(ΔsolnG 0/Ò ) values become more negative in the order Ala, Phe, Gly, His.
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