Puerarin (PUE), as an isoflavone component, has a wide range of pharmacological activities, while its poorly aqueous solubility limits the development of solid oral dosage forms. In this study, PUE along with nicotinamide (NIC) were prepared into the coamorphous system by solvent-evaporation method and characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). In addition, its dissolution behavior and solubilization mechanism were also investigated. PUE-NIC coamorphous was a single homogeneous binary system, with a single glass transition temperature at 35.1 ℃. In comparison to crystalline PUE, during the dissolution process, coamorphous PUE-NIC not only exhibited the "liquid-liquid phase separation" (LLPS) phenomenon, but the formation of A_p type complexation (1∶1 and 1∶2) between PUE and NIC molecules was also verified, which significantly improved the solubility of PUE and prolonged the supersaturation time, and would benefit its absorption.

Cocrystal separation technology is a technology that utilizes coformers to selectively form cocrystals with target compounds and separate them from mixed systems. Our study used puerarin (PUE), daidzein (DDZ), and genistein (GEN) as model drugs, which have similar structures and are the main isoflavones in Pueraria lobata root. The separation and purification processes in the modern traditional Chinese medicine (TCM) of these three components use conventional column chromatography, recrystallization, and other technologies, which have the issues of lengthy separation cycles, high solvent consumption, and inefficient preparation. Different with existing separation technology, our team used the early-found cocrystal separation method to design a step-by-step extraction and separation experiment of GEN-PUE-DDZ ternary mixture. Caffeine and L-proline were added to the mixed system in turn, GEN-caffeine cocrystal and PUE-proline cocrystal were prepared by suspension method. The cocrystals precipitated out of the solution. The purities of the GEN-caffeine cocrystal and the PUE-proline cocrystal could achieve 93% (the purity of GEN) and 99% (the purity of PUE). Besides, the purity of DDZ could also be increased by 6.76 times. This study proposed a simple operating, low cost and wide application range separation method different from the traditional separation method and realized the separation of structurally similar chemical components in TCM, laying a foundation for the application of cocrystal technology in the separation and refining of TCM.

The solubility/dissolution, hygroscopicity and mechanical properties of drug candidates have a profound effect on oral bioavailability, processability and stability. The physicochemical properties of crystalline drug are closely related to inner crystal structure. Crystal engineering technologies, as strategies of altering the crystal structure and tailoring physicochemical properties at molecular level, possess the potential of enhancing the pharmaceutical performance of product. The current article reviewed the modification of drug solubility/dissolution, hygroscopicity and mechanical properties by crystal engineering technologies through polymorphic selection, amorphization/co-amorphization, as well as co-crystallization, which provided a reference for the applications of pharmaceutical crystallography in improving physicochemical properties and druggability.