The solid-liquid equilibrium of precursors and products of the enzymatic synthesis of ampicillin (AMP) [6-aminopencillanic acid (6-APA) and D(À)phenylglycine (PG)] was investigated at different temperatures (283-298 K) and pHs (5.5-7.5). Solubility data were obtained using an analytical methodology. Equilibrium dissociation constants were experimentally measured at several temperatures for AMP, 6-APA, PG, and D(À)phenylglycine methyl ester. A model based on the simplified perturbed hard sphere theory proposed by Khoshkbarchi and Vera (Ind Eng Chem Res. 1996;35:4319-4327) was fitted against solubility data. The model could describe the water solubility behavior for AMP and PG as function of pH and temperature, but a bias was observed when fitting the model to the solubility of 6-APA. V

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