(754e) Crystallization of Non-Needlelike ?-Glyine From Water Solutions Via Droplet Evaporation

Glycine is among the most well studied organic molecular systems with regards to its nucleated crystalline polymorphs and resulting growth morphologies.  Because of this existing work, it has become a common case study for crystallization science and technology such as those performed with laser induced (Zaccaro, et. al. 2001) or templated (Kang, et. al. 2000) nucleation as well as morphology prediction (Snyder and Doherty, 2009) and additive behavior (Lovette, et. al, 2008).  Additionally, it serves as a basis for understanding the molecular foundation of crystallization phenomena though studies ranging from atomic force microscopy and solution based studies to molecular simulation (Chen and Trout, 2010).  Despite this body of study, the basic drivers towards nucleating the various polymorphs readily attainable at atmospheric pressure (e.g. the stable γ form, the commonly found α form, or the metastable β form) are not fully understood (Chen and Trout, 2010).   Recently, monodisperse droplet evaporation has been shown to be an effective tool at forming metastable polymorphs and unique particle morphologies for another small organic molecular system, succinic acid (Carver and Snyder, 2012).  In that case the polymorphism and morphology was strikingly different in comparison with those readily obtained through more traditional solution crystallizations.

In this talk, we will highlight our work on forming crystalline glycine particles through the evaporation of monodisperse droplets produced using a vibrating orifice aerosol generator (VOAG).  The metastable β polymorph of glycine is often obtained from water-alcohol solvent mixtures or other more complex solutions.  In this work, the β polymorph is formed as expected from water-ethanol mixtures.  However, we also show for the first time that the β polymorph can be obtained from pure liquid water solutions at ambient temperature and pressure.  Thus, this work provides evidence that solvent is not the only dominant factor in determining glycine polymorph formation, which had long been the proposed determining factor.  Rather, through droplet evaporation we demonstrate that supersaturation likely plays a dominant role under some conditions in glycine polymorph determination.  The β polymorph of glycine also usually forms a long needlelike habit; however, we show that our crystalline particles are nearly spherical with some ridging features.  Thus, this method changes the aspect ratio from more than 10:1 to 1:1.  Such a habit modification is usually a daunting task from a perspective of modifying the chemistry; however, in this case only the process of crystal formation needed to be changed to have a dramatic impact (e.g. not just shortening the needles) with a single pure solvent.  Finally, we will discuss the broader potential for the use of monodisperse droplet evaporation as a tool for future crystallization studies with regards to crystal nucleation, polymorphism, growth morphologies and amorphous particle formation. 

References

Zaccaro, J., Matic, J., Myerson, A. S., Garetz, B. A.. Cryst. Growth. Des. 2001, 1, 5-8.

Kang, J. F., Zaccaro, J., Ulman A., Myerson, A. S. Langmuir. 2000, 16, 3791-3796.

Snyder R. C., Doherty M. F., Proc. Royal. Soc. A.  2009, 465, 1145-1171.

Lovette, M. A., Browning, A. R., Griffin, D. W, Sizemore, J. P., Snyder, R. C. Doherty M. F., Ind. Eng. Chem. Res.  2008, 47, 9812-9833.

Chen, J., Trout, B. L ., J. Phys. Chem. B, 2010, 114, 13764-13772.

Carver, K. M., Snyder, R. C. Ind. Eng. Chem. Res. 2012, 51, 15720-15728.