Preparation and characterization of 5-fluorouracil drug cocrystal and its dynamic monitoring of cocrystallization process via SERS spectroscopy

Cocrystal is a new class of pharmaceutical crystal form, which could improve the physical and chemical properties of drug substance without affecting the internal structure of drug substance. Therefore, the cocrystals show a great deal of potential in the development and research of drugs. 5-Fluorouracil (5-FU) is one of the most widely used anti-pyrimidine drugs. However, its solubility is poor and its oral bioavailability is low. In this work, the cocrystal of 5-FU with nicotinamide was prepared by the solvent evaporation method. The cocrystal structure was confirmed by infrared spectroscopy (IR), X-ray diffraction (XRD) and Raman spectroscopy. The X-ray diffraction and infrared spectroscopy presented that there were significantly different peaks between the raw drug and the cocrystal. Raman spectral results also indicated the differences of such cocrystal compared with the raw drug. In addition, TiN-Ag composite SERS substrate was used to study the formation of 5-FU cocrystal drugs and the formation process was dynamically monitored, and the interaction between molecules during the cocrystal reaction was deeply understood. The cocrystal reaction process was tracked, it can be found that the peak intensity of the raw drug and cocrystal changes with the reaction, indicating that the TiN-Ag composite substrate can monitor the cocrystal transformation process.