(229r) Ultrasound-Assisted Acceleration of Form Transformation of Glycine

Glycine is a kind of amino acids which is widely used in many fields, e.g. medicine, food, chemical industry, etc. Normally, it takes about 2 days for the metastable αform to be transformed to the stable Υ-form. In our work, ultrasound was applied to accelerate and enhance the form transformation process. The effects of ultrasonic power, length of time and timing on the crystal form of glycine were investigated systematically.

The mass fraction of γ-glycine in the dried crystals after 40 minsâ?? growth were quantitively analyzed using XRD. The results show that the mass fraction of theγ-glycine increases from 16 % to 50 % with the increase of the ultrasonic power in range of 0 ~ 6.5 kW/L applied before nucleation, and increases from about 16 % to 33 % when the duration of the ultrasound increases from 0 min to 5 min. Moreover, the content of γ-glycine grow steadily thereafter. These results imply that the application of ultrasonic before nucleation promotes the nucleation of the stable γ-form, and then enhances the steady growth of γ-glycine. Ultrasound imposes a part of energy to the crystallization system, and help to surpass the relatively higher nucleation barrier of γ-glycine.

However, applying ultrasonic after nucleation will cause a fluctuation in the form composition of glycine during the crystallization process: the content of γ-form reaches an extreme high point after the ultrasound application being finished in ~20 min, then decrease to a lower point, and finally achieve a content close to that without ultrasound. Further, the sharp increase of the content of γ-form occurs earlier when the application timing is closer to nucleation. The fluctuation may be contributed to the unsteady γ-form nucleus formed during homogeneous nucleation under ultrasound.

Ultrasound application closely before nucleation is proved to be a useful method to enhance the production of stable γ-form of glycine.