Crystallization transformation of amorphous extracts of traditional Chinese medicine and its effect on dissolution behavior — Taking total flavonoids from Pueraria lobata as an example / 中国药科大学学报

@#In order to guarantee the quality of traditional Chinese medicines (TCMs), the crystallization transformation of complex extracts of TCMs and the influence of solid form on their physicochemical properties were studied.The extract of total flavonoids from Pueraria lobata was taken as a model.Crystallization transformation happened when lofting under different conditions, and the intrinsic dissolution tests were carried out.It was found that humidity was the key factor to induce crystallization of total flavonoids from Pueraria lobata.The greater the wettability was, the more the crystallization was.The dissolution rate of total flavonoids from Pueraria lobata with the most crystallization amount significantly decreased by 96.51% compared to the sample without crystallization.After further simulating the preparation process of total flavonoids from Pueraria lobata, it was found that the wet granulation process with introduced water would also lead to crystallization and reduced dissolution rate.As for all crystallization samples, there was an inversely proportional relationship between the dissolution rates and the amount of crystallization.The risk of crystallization existed both in the storage and preparation process of TCM extracts.Crystallization would significantly affect the dissolution rate, and thus the quality of TCM products.In this study, the crystallization transformation of amorphous complex TCM extracts was discovered, and the effect of the crystallization transformation on its dissolution behavior was systematically studied, which provides a new research idea for assuring the quality of TCM products and promoting the improvement of TCM preparation level.

In Situ TEM Study of the Amorphous-to-Crystalline Transition during Dielectric Breakdown in TiO2 Film.

Dielectric breakdown of oxides is a main limiting factor for improvement of the performance of electronic devices. Present understanding suggests that defects produced by intense voltage accumulate in the oxide to form a percolation path connecting the two electrodes and trigger the dielectric breakdown. However, reports on directly visualizing the process at nanoscale are very limited. Here, we apply in situ transmission electron microscopy to characterize the structural and compositional changes of amorphous TiO2 under extreme electric field (∼100 kV/mm) in a Si/TiO2/W system. Upon applying voltage pulses, the amorphous TiO2 gradually transformed into crystalline substoichiometric rutile TiO2-x and the Magnéli phase Ti3O5. The transitions started from the anode/oxide interface under both field polarities. Preferred growth orientation of rutile TiO2-x with respect to the Si substrate was observed when Si was the anode, while oxidation and melting of the W probe occurred when W was the anode. We associate the TiO2 crystallization process with the electrochemical reduction of TiO2, polarity-dependent oxygen migration, and Joule heating. The experimental results are supported by our phase-field modeling. These findings provide direct details of the defect formation process during dielectric breakdown in amorphous oxides and will help the design of electronic devices with higher efficiency and reliability.

YbCl3 electrode in alkaline aqueous electrolyte with high pseudocapacitance.

Inorganic pseudocapacitors often select synthetic solid materials as electrode materials, which show low utilization of pseudocapacitive metal cations. We reported the crystallization transformation of YbCl3 pseudocapacitor electrodes in alkaline electrolytes, which can show high cation utilization ratio. The electrochemical reactive YbOOH colloids were crystallized through the chemical coprecipitation and Faradaic redox reactions. The effect of crystallization kinetics on electrochemical performances of YbCl3 pseudocapacitor was studied. YbCl3 pseudocapacitor can show ultrahigh specific capacitance of 2210 F/g, where the commercial YbCl3 salts were used directly as pseudocapacitor electrodes in an aqueous electrolyte neglecting the complex synthesis procedures. The present strategy provides a novel route to crystallize electrochemical active compounds with unusual reactivity toward Faradaic redox reaction. The development of ion-based pseudocapacitors can advance the understating of the redox mechanism of active cations.