Insight into the Phase Transformation among Various Solid Forms of Baicalein

A new polymorph and three hydrates of baicalein, a widely prescribed anti-inflammatory TCM drug, were discovered through comprehensive polymorph screening experiments. The forms were fully characterized by a range of analytical techniques, including PXRD, Raman spectra, FTIR, HSM, SEM, TGA, DSC, and DVS. Single crystal structures and the transformation pathways among different polymorphs and hydrates are discussed in detail. Single-crystal-to-single-crystal transformation behavior between monohydrate and hemihydrate was revealed. Thermodynamic stability, hygroscopicity, and powder dissolution behavior were investigated. The results show that the newly discovered form gamma presents better dissolution behavior and remarkably greater apparent solubility compared with the current widely used marketed drug substance.