Preparation and characterization of baicalin-poly -vinylpyrrolidone coprecipitate

Baicalin-polyvinylpyrrolidone (PVP) coprecipitate was prepared by the solvent method of solid dispersion technology to improve the dissolution rate of baicalin. The coprecipitate was characterized using differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), infrared spectrometry (IR) and dissolution testing. Furthermore, AFM·IPC-208B high-resolution atomic force microscopy (AFM) was utilized to characterize the molecular morphology of baicalin within its carrier and the interaction between baicalin and its carrier. The results of DSC and XRD indicated that baicalin resided in PVP polymers in an amorphous or molecular phase, dissolution test results demonstrated that the dissolution rate of the coprecipitate was 21.4 times that of the active pharmaceutical ingredient (API). The results of IR indicated the possibility of the formation of intermolecular hydrogen bonds. The AFM·IPC-208B findings revealed that baicalin was dispersed in PVP polymers with a molecular size of 2 nm and either wrapped or surrounded by approximately 0.4 nm of a five-membered ring of PVP arranged along the carbon chain sequentially. An intermolecular hydrogen bond was formed between the 4-OH of the glucuronide of baicalin and the O of the carbonyl group from PVP in addition to the formation of intramolecular hydrogen bonds within baicalin.