Hongyuan Wei

Preparation, crystal structure and solution-mediated phase transformation of a novel solid-state form of CL-20

Herein, the 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) acetonitrile solvate, a novel solid-state form of CL-20, was first discovered and characterized by various analytical techniques. The results of single-crystal X-ray diffraction (SCXRD) indicate that it is a channel-type solvate. Intermolecular interactions inside the crystal were investigated to elucidate the assembly behaviors with the assistance of the Hirshfeld surface analysis. The solvation profile and solubility data were determined to identify the thermodynamic stability of the acetonitrile solvate and form e. The solution-mediated phase transformation (SMPT) from the acetonitrile solvate to form e in acetonitrile–chloroform mixed solvents was online monitored by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and in situ Raman spectroscopy. The results reveal that the nucleation and growth of the form e is the rate-determining step. Moreover, the Johnson–Mehl–Avrami (JMA) model was employed to obtain deeper insights into the transformation kinetics. Furthermore, the effects of solvent composition, solid loading, and agitation rate were examined. This study provides an alternative approach for obtaining the desired form e crystals and lays a foundation for the optimization of the crystallization process in the future.

Effects of inorganic additives on polymorphs of glycine in microdroplets

Salt-dependent polymorphic control of glycine was investigated by using the microdroplet technique in this work. Sodium chloride (NaCl) was chosen as the additive to probe the influence of inorganic ions on the polymorphic nucleation of glycine. The thermodynamics and nucleation kinetics of glycine polymorphs in microdroplets were systematically analyzed based on the microdroplet technique. The crystal structures of the polymorphs were confirmed by powder X-ray diffraction (PXRD). The results illustrate that the critical concentration of NaCl required to induce the pure γ-form in the microdroplets is lower than that in the conventional method, which means that the microdroplet technique is more sensitive for the control of polymorph nucleation. The polymorphic nucleation selectivity of glycine was then discussed in view of classical nucleation theory. The results demonstrate that NaCl reduces the nucleation energy barrier of the γ-form of glycine, and for the same form of glycine, crystallization by the conventional method has a higher interfacial tension than in microdroplets.