Taxifolin tubes: crystal engineering and characteristics.

Taxifolin, also known as dihydroquercetin, is the major flavonoid in larch wood. It is well known as an antioxidant and a bioactive substance. Taxifolin as an active pharmaceutical ingredient is produced industrially in crystalline form during the processing of larch wood. Some information is available on nano- and microstructured particles of taxifolin. This paper reports on the generation of a new form of taxifolin as microtubes. These self-assembled tubes were obtained from raw taxifolin by crystal engineering with urea at ambient temperature and pressure. The parameters of temperature, pH value, molar ratio of taxifolin and urea, and time duration were optimized for yield enhancement of the microtubes. The water solubility and melting point of the new form of taxifolin were established. The microtubes were characterized by X-ray diffraction, X-ray powder diffraction, microscopy, mass spectrometry, ¹H NMR spectroscopy, UV spectroscopy and Fourier transform infrared spectroscopy methods. The experimental results demonstrate that the microtubes and raw taxifolin both exist in crystalline form with the same structure of the crystal unit. However, they are characterized by different morphological and physicochemical properties. Computer simulation was performed to explain the mechanism of the self-assembly process.