Thermodynamics of amino acids in aqueous electrolyte solutions

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" Thermodynamics of amino acids in aqueous electrolyte solutions "
M. K. Khoshkbarchi J. H. Vera

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113176
Doc. No	:	TLpq304404067
Main Entry	:	J. H. Vera
	:	M. K. Khoshkbarchi
Title & Author	:	Thermodynamics of amino acids in aqueous electrolyte solutions\ M. K. KhoshkbarchiJ. H. Vera
College	:	McGill University (Canada)
Date	:	1997
student score	:	1997
Degree	:	Ph.D.
Page No	:	199
Abstract	:	A novel method has been developed for the measurement of the activity coefficients of an amino acid and the mean ionic activity coefficients of an electrolyte in water-electrolyte-amino acid systems. The method uses an electrochemical cell with two ion selective electrodes and a reference electrode. Activity coefficient data, at 298.15 K, for eight water-electrolyte-amino acid systems were measured. The cell consisted of a cation and an anion ion selective electrode, and the potential of each was measured versus a double junction reference electrode. The amino acids studied were glycine, DL-alanine, DL-valine and DL-serine and the electrolytes studied were NaCl and KCl. For the same systems, the solubilities at 298.15 K of the amino acids were measured at various electrolyte concentrations. The results show that the activity coefficients and the solubility of the amino acid in aqueous electrolyte solutions are strongly affected by the concentrations of both the electrolyte and the amino acid, the chemical structure of the amino acid and the nature of the cation of the electrolyte. The activity coefficients of amino acids in aqueous electrolyte solutions were modelled using a two-parameter excess Gibbs free energy model based on the contribution of a long range interaction term represented by the Bromley or the K-V model and a short range interaction term represented by the NRTL or the Wilson model. A model based on the perturbation of a hard sphere reference system, coupled with a mean spherical approximation model, was also developed to correlate the activity coefficient of the amino acid and the mean ionic activity coefficient of the electrolyte in water-electrolyte-amino acid systems. The model can also predict the activity coefficients of amino acids in aqueous electrolyte solutions, without adjusting any parameter, at low electrolyte concentrations and slightly deviates from the experimental data at higher electrolyte concentrations. A model was developed to correlate the solubilities of amino acids in aqueous and aqueous electrolyte solutions. The activity coefficients of amino acids in both aqueous and aqueous electrolyte solutions were represented by the perturbed mean spherical approximation model. It was shown that upon availability of independently evaluated experimental data for usd\Delta\ husd and usd\Delta\ gusd, the water-amino acid solubility model can accurately predict the solubility of amino acids in aqueous solutions without any adjustable parameter.
Subject	:	Amino acids
	:	Applied sciences
	:	Aqueous electrolyte solutions
	:	Chemical engineering
	:	Thermodynamics