Single-crystal x-ray diffraction structures of covalent organic frameworks.

The crystallization problem is an outstanding challenge in the chemistry of porous covalent organic frameworks (COFs). Their structural characterization has been limited to modeling and solutions based on powder x-ray or electron diffraction data. Single crystals of COFs amenable to x-ray diffraction characterization have not been reported. Here, we developed a general procedure to grow large single crystals of three-dimensional imine-based COFs (COF-300, hydrated form of COF-300, COF-303, LZU-79, and LZU-111). The high quality of the crystals allowed collection of single-crystal x-ray diffraction data of up to 0.83-angstrom resolution, leading to unambiguous solution and precise anisotropic refinement. Characteristics such as degree of interpenetration, arrangement of water guests, the reversed imine connectivity, linker disorder, and uncommon topology were deciphered with atomic precision-aspects impossible to determine without single crystals.

Selecting and controlling API crystal form for pharmaceutical development--strategies and processes.

The success of designing, developing, manufacturing and introducing oral dosage forms of pharmaceutical products into the market relies on many steps, processes, stages and usually three phases of clinical trials. One key process is selecting an appropriate active pharmaceutical ingredient (API) crystal or amorphous form for the final dosage product: the ultimate goal of this selection process is to ensure that the manufactured product contains a stable and bioavailable active ingredient. A thorough knowledge of the solid-state chemistry of the API, the related excipients and the processes to make the product are critical in meeting this goal. Through recently published literature and the authors' experiences, this review describes the concepts and approaches that are used in the development of a truly knowledge-based crystalline API form selection process and highlights the appropriate studies which fit the Quality by Design (QbD) framework for pharmaceutical development activities. This review also discusses the potential API crystal form transformations in the API crystallization, post-crystallization and formulation stages, which are demonstrated by case study examples.

Bioavailability enhancement of a COX-2 inhibitor, BMS-347070, from a nanocrystalline dispersion prepared by spray-drying.

Spray drying drug with excipients is usually associated with the preparation of microcrystalline or amorphous drug in order to improve bioavailability. It was found that BMS-347070, when spray-dried with Pluronic F127 from acetone or methylene chloride, was dispersed as nanosized crystalline drug within the water-soluble Pluronic matrix. The reduction in drug particle/crystallite size, coupled with wetting by the Pluronic, resulted in a fast-onset formulation with bioavailability comparable to that of a solubilized and a NanoCrystal formulation. For this system, it is theorized that the polyethylene oxide segments of Pluronic crystallize and that the polypropylene oxide segments remain amorphous, providing a size-restricted domain in which the COX-2 drug crystallizes. This results in improved bioavailability while limiting the potential risk of conversion of an amorphous drug to its crystalline state.