RESUMO
The electronic structure and geometric configuration of catalysts play a crucial role to design novel perovskite-type catalysts for oxygen reduction reaction (ORR). Nowadays, many studies are more concerned with the influence of electronic structure and ignore the geometric effect, which plays a nonnegligible role in enhancing catalytic performances. Herein, this work regulates the MnO6 octahedral tilting degree of LaMnO3 by modulating the concentration of Y3+, excluding the electronic effect from the valence state of manganese. Plotting the MnO6 octahedral tilting degree as a function of concentration of Y3+ produces a volcano-shaped plot. The octahedral tilting can reduce the Mn-O covalency, generating more highly active Mn3+ and oxygen vacancies during ORR process. The specific activity has a positive correlation with octahedral tilting degree. Meanwhile, the octahedral tilting stabilizes Mn-O interactions during ORR process and promote stability. Based on experimental results and DFT calculations, octahedral tilting alters the rate-determining step (RDS) and decrease the energy barrier. Subsequent extended experiment confirms that octahedral tilting is the key factor to affect the catalytic performances.
RESUMO
A series of indirubin derivatives hydrochloride were obtained using a convenient and mild method from indirubin. The newly synthesized compounds and their derivatives were characterized by 1 H NMR, 13 C NMR, and MS. Furthermore, we tested their IDO1 enzyme inhibitory activity and anti-proliferative activities in K562 tumor cells. The experimental results revealed that some of the compounds showed potential anti-enzyme and anti-tumor activity. Among of them, compound 4b exhibited certain inhibitory activity on IDO1 (IC50 : 29.52 µmol/L), and compound 4a displayed activity similar to indirubin in K562 tumor cells (IC50 : 24.96 µmol/L). This type of indirubin derivative is expected to have the potential to act as an immunologically active anti-tumor drug, indicating that further research will be worthwhile.