IDENTIFICATION OF AMINO-ACIDS EXHIBITING THE ION-EXCHANGE ISOTHERMAL SUPERSATURATION EFFECT

This paper reports the results obtained by theoretical and experimenta l study of the phenomenon called ion-exchange isothermal supersaturati on (IXISS). This effect is observed, e.g., by passing a monosodium sal t of amino acids (AA) through the bed of a sulfonate cation exchanger in the H-form. Frontal separation of Na+ and AA anions (AA(-)) in this case is accompanied by conversion of AA(-) into AA zwitterions (AA(+/ -)) due to interaction of AA(-) with H+ released from the resin phase. Formation of the pure AA zone proceeds simultaneously with the concen tration of AA up to and beyond the level exceeding its solubility at a given temperature. Moreover, this supersaturated solution remains sta ble within the column interstitial space for a period of 6-10 h. The m echanism of stabilization of AA supersaturated solutions in the inters titial space of the ion-exchange column has been shown to be attribute d to the chainlike amine-carboxylate interaction of AA molecules. The validity of the mechanism proposed is confirmed by the results obtaine d by studying sorption isotherms of beta-alanine and gamma-aminobutyri c acid on sulfonate (KU-2 x 8) and carboxylic (KB-4P2) resins in the H -forms. A number of physicochemical parameters of AA solutions such as enthalpies of crystallization, activity coefficients, and some others have been shown to be applicable for identification of AA exhibiting the IXISS effect. This identification can also be based on the structu ral features of AA molecules.