The aromatic amino acid behaviour in aqueous amide solutions |
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Authors: | A V Kustov |
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Institution: | (1) United Physico-Chemical Center of Solutions of Institute of Solution Chemistry and Ivanovo State University of Chemistry and Technology, Russian Academy of Sciences, 1 Academicheskaya str., 153045 Ivanovo, Russia |
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Abstract: | The enthalpies of solution of L-phenylalanine in the mixtures of water with the protein denaturant urea have been measured
in the temperature range of 288.15–318.15 K. Using the results of the present research and literature data of free energies,
the standard thermodynamic functions of the solute transfer from water to aqueous urea solutions have been estimated in a
wide temperature range. The enthalpic, heat capacity, entropic and free energy parameters of the solute-urea pair and triplet
interactions have been computed. The amino acid — amide pair interaction was found to be attractive in the temperature range
studied due to the favourable enthalpic term. The triplet interaction being slightly repulsive reveals the enthalpic origin
also. The examination of the Savage and Wood additivity-of-groups approach does indicate the inapplicability of this scheme
to enthalpies and entropies of interaction. It has been found for the first time that the heat capacity of interaction changes
its sign at 303 K, i.e. the temperature dependence of enthalpic and entropic parameters passes through the pronounced extrema
near the temperature of the minimum of the heat capacity of pure water. |
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Keywords: | amino acids denaturant aqueous solutions enthalpy of solution L-phenylalanine-urea interaction |
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