Nucleation control and crystallization of l-glutamic acid polymorphs by swift cooling process and their characterization

Abstract

The region of preferred crystal nucleation of the two known polymorphs of l-glutamic acid (C5H9NO4), the metastable α and stable β, from pure aqueous solution has been recognized by following a swift cooling crystallization process in the temperature range 1–40°C. Aqueous solution prepared for a selected saturation was taken to 80°C and cooled down to various temperatures in the range 1–40°C in steps of every 1°C abruptly with constant stirring. The observed nucleation and grown micro-crystallites in the solution were examined under optical microscope and their morphologies and polymorphic forms were evaluated. Results obtained from this investigation at all the 40 experimental temperatures elucidated a clear distinction of the preferred nucleation regions of α, β and combinations of α and β in the solution in the above mentioned temperature range and the results are repeatable. Form of crystallization was confirmed by Powder X-ray Diffraction (PXRD). Further the grown polymorphs were characterized by Differential Scanning Calorimetry (DSC), optical transmittance and Second Harmonic Generation (SHG) studies.