Analysis for partition equilibrium of amino acid derivatives in aqueous/organic biphasic systems

The overall partition coefficients of the acid and amine components of amin o acid derivatives, the substrates for proteinase-catalyzed synthesis of ol igopeptide precursors, in an aqueous/organic biphasic system were studied b oth experimentally and theoretically. In a single-component system containi ng either an acid or amine component, the overall partition coefficient was well expressed by a model using the acid dissociation constant and partiti on coefficients for the non-ionized and ionized forms of the component. The overall partition coefficient in a binary-component system containing both acid and amine components was well simulated by the model when the formati on of ion-pair complexes in the organic solvent phase was taken into consid eration in addition to the partitioning of the non-ionized and ionized form s of the components. The formation of ion-pair complexes in the organic sol vent phase was indicated by an analysis using Fourier transform infrared ra y spectroscopy (FT-IR). In addition to the partition equilibrium, the aqueo us-phase pH change after partitioning could be predicted by the model.