Determination of the crystallization thermodynamics and kinetics of l-tryptophan in alcohols–water system

Aimed at exploring new solvents for the crystallization of l-tryptophan, the solubility and metastable zone of l-tryptophan in binary solvents of methanol–water, ethanol–water and 1-propanol–water were measured using a laser method. It is demonstrated that the dielectric constant of the solvent significantly affects the solubility of l-tryptophan. Furthermore, results indicate that 1-propanol–water is a better solvent system from which regular and perfect crystals can be obtained. The induction time of l-tryptophan was measured to analyze the nucleation and growth mechanism. It is found that homogeneous nucleation is inclined to occur at high supersaturation while heterogeneous nucleation would be dominant at low supersaturation. The growth mechanism of l-tryptophan follows the continuous mode.

► The solubility, metastable zone and induction time of l-tryptophan were measured.
► The dielectric constant of the solvent plays an important role in the solubility.
► 1-propanol–water is a better solvent system to crystallize l-tryptophan.
► The growth mechanism of l-tryptophan follows the continuous mode.