Amino Acid Uptake by Ion Exchangers

Factors Influencing the Ion-Exchange Affinity of Amino Acids 

Whereas the ion-exchange affinity of various mineral ions to ion exchangers is reasonably well understood, the ion-exchange affinity of various amino acid ions is not because of their more complex nature. 

With such representation of the chemical potential of electroneutral components the equilibrium distribution of difiusible components such as NX, MX, and H2O between a crosslinked, polyelectrolyte gel phase and an external solution phase can be represented by equating the chemical potential of each difiusible component in the two phases as follows  

In these equations the bar is used to identify each component s association with the gel phase. By choosing the standard state to be the same in both phases (p° = and P° = P°) and by equating P - P to the swelling pressure, n, the following convenient relationships are obtained  

Up until this point components have been treated as if they are accessible in an isolated state in order to satisfy Gibbsian thermodynamics. However, when the three components of the two-phase system under scrutiny reach their equilibrium distribution the total concentration of M and N greatly exceeds the concentration of X in the gel phase. The extra electric charge and the resultant electrical force on the ions affect their equilibrium distribution and have to be taken into account. In correcting for this aspect thermodynamic rigor is necessarily lost in the process which consists of redefining equilibrium as that condition in which the electrochemical potential, E, of the separate ionic species are equal in both phases  

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B. Mechanism of Amino Acid Uptake by Ion Exchanger at Low Solution Concentrations... 

In Chapter 8, Zuyi Tao, in order to provide a better understanding of the ion-exchange behavior of amino acids, has compiled their particular acid-base properties, their solubility in water, their partial molal volumes, and their molal activity coefficients in water at 25 C. This information has been used in Gibbs-Donnan-based equations to facilitate a better understanding of the mechanism of amino acid uptake by ion exchangers at low and high solution concentration levels. Measurement of distribution coefficients and separation factors are also described. The eventual resolution of thermodynamic ion-exchange functions (AG, AH, and AS) is provided for the reader. 

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