sorry, we can't preview this file

...but you can still download cg034051u_si_001.cif

cg034051u_si_001.cif (7.57 kB)

Crystallization of a Desired Metastable Polymorph by Pseudoseeding, Crystal Structure Solution from Its Powder X-ray Diffraction Data, and Confirmation of Polymorphic Transition

Download (7.57 kB)
posted on 10.07.2003 by Hidenori Miura, Takaniro Ushio, Keiko Nagai, Daisuke Fujimoto, Zsolt Lepp, Hiroki Takahashi, Rui Tamura
Described are the successful, selective crystallization and characterization of one (δ-form) of the metastable polymorphs of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl]dimethylsulfonium p-toluenesulfonate (1a), which is assumed to exist as a transient key-intermediate crystalline phase relevant to the mechanism of Preferential Enrichment, an unusual enantiomeric resolution phenomenon observed upon crystallization of a certain kind of racemates from solvents. By pseudoseeding the supersaturated solution with the δ-form seed crystals of an anlogous compound, the desired δ-form crystals of (±)-1a could be obtained as a monophasic powder sample. This selective crystallization can be interpreted in terms of the interplay between an inhibition of the nucleation or crystal growth process of the undesired stable α-polymorphic form and a heterogeneous nucleation of the desired metastable δ-form through epitaxy. The physicochemical properties of the δ-form crystal such as melting point and solubility have been compared with those of the stable α-form one to evaluate the relative stability of the metastable δ-form. It has also been confirmed that polymorphic transition of the metastable δ-form crystal to the stable α-form one occurs in contact with a solvent. On the basis of the δ-form crystal structure solved from its powder X-ray diffraction data measured with a laboratory X-ray source by means of the direct-space approach employing the Monte Carlo method and the subsequent Rietveld refinement, the origin of the metastability of the δ-form crystal has been discussed.