Potential Dominates Structural Recombination of Single Atom Mn Sites for Promoting Oxygen Reduction Reaction.

Single atom sites (SAS) often undergo structural recombination in oxygen reduction reaction (ORR), while the effect of valence state and reconstruction on active centers needs to be investigated thoroughly. Herein, the Mn-SAS catalyst with uniform and precise Mn-N4 configuration is rationally designed. We utilize operando synchrotron radiation to track the dynamic evolution of active centers during ORR. Under the applied potential, the structural evolution of Mn-N4 into Mn-N3 C and further into Mn-N2 C2 configurations is clarified. Simultaneously, the valence states of Mn are increased from +3.0 to +3.8 and then decreased to +3.2. When the potential is removed, the catalyst returned to its initial Mn+3.0 -N4 configuration. Such successive evolutions optimize the electronic and geometric structures of active centers as evidenced by theory calculations. The evolved Mn+3.8 -N3 C and Mn+3.2 -N2 C2 configurations respectively adjust the O2 adsorption and reduce the energy barrier of rate-determining step. Thus, it can achieve an onset potential of 0.99 V, superior stability over 10,000 cycles, and a high turnover frequency of 1.59 s-1 at 0.85 VRHE. Our present work provides new insights into the construction of well-defined SAS catalysts by regulating the valence states and configurations of active centers.

Effects of Scutellaria strigillosa Hemsl. extract on HepG2 cell proliferation and apoptosis through binding to aspartate ß-hydroxylase.

This study aims to examine the impacts of Scutellaria strigillosa Hemsl. (SSH) on the proliferation, apoptosis of human hepatoma cell HepG2 and screen the bioactive components. We found that SSH extract inhibited HepG2 proliferation, arrested cell division prior to S phase. Additionally, SSH extract exposure induced apoptosis, and increased the proportions of late apoptotic cells. Specifically, we focus on the inhibitory effect of SSH extract on aspartate ß-hydroxylase, a key therapeutic target of hepatocellular carcinoma closely related with the proliferation and apoptosis of HepG2. We found SSH extract with notable inhibitory activity against aspartate ß-hydroxylase, elucidated the main bioactive constituents by HPLC-Q-TOF/MS and Molecular docking analysis. In conclusion, these results provided the antiproliferative and proapoptotic effects of SSH on HepG2 cell, elucidated the main bioactive constituents based on aspartate ß-hydroxylase inhibition. These data revealed the potential value of SSH and its bioactive components for the prevention and treatment of liver cancer for the first time.

Reconstruction of Highly Dense Cu-N4 Active Sites in Electrocatalytic Oxygen Reduction Characterized by Operando Synchrotron Radiation.

The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt-substituted electrocatalyst for oxygen reduction reaction (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu-N4 SAS with a metal loading of 5.61 wt% supported on 3D N-doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H2 /O2 AEMFC, it could reach an open-circuit voltage of 0.90 V and a peak power density of 324 mW cm-2 . Operando synchrotron radiation analyses identify the reconstruction from initial Cu-N4 to Cu-N4 /Cu-nanoclusters (NC) and the subsequent Cu-N3 /Cu-NC under working conditions, which gradually regulate the d-band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity.

Atomically Dispersed Fe-N3 C Sites Induce Asymmetric Electron Structures to Afford Superior Oxygen Reduction Activity.

Introducing heteroatoms into atomically dispersed Fe-N4 sites with symmetric electron distribution can adjust the imperfect oxygenated adsorption-activation and promote oxygen reduction reaction (ORR) activity. However, the relevant design synthesis and deeply understanding the electrocatalytic mechanism of such an asymmetric structure by introducing Fe-C coordination remains challenging. Herein, the structural stability of Fe-Nx Cy (x = 0 ≈ 4, y = 4-x) is first theoretically predicted and indicates that the energy of Fe-N4 in the two most stable structures is greater than that of Fe-N3 C. Subsequently, Fe-N4 and Fe-N3 C configurations are controlled synthesized by adjusting pyrolytic temperature. The Fe-N3 C-based electrocatalyst displays a boosted ORR activity with a half-wave potential of 0.91 V and superior long-term stability, outperforming Fe-N4 , Pt/C, and state-of-the-art noble metal-free electrocatalysts. Density functional theory calculations unveil that Fe-N3 C is much more favorable for electron delocalization than Fe-N4 . Furthermore, the residual Zn atom derived from ZIF-8 would give its d-orbit electron to the Fe atom, so the synergy between Fe-N3 C and Zn-N4 makes an enhanced ORR activity.

Designed Synthesis and Catalytic Mechanisms of Non-Precious Metal Single-Atom Catalysts for Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the important half-reaction for metal-air batteries and fuel cells (FCs), which plays the decisive role for the performance of whole devices. Developing high-efficiency non-precious metal ORR catalysts is urgent and still challenging. Single-atom catalysts (SACs) are considered to be one of the promising substitutes for Pt due to their maximum atom utilization efficiency and mass activity. Despite considerable efforts in preparing various SACs, the reaction mechanism and intrinsic activity modulation during the ORR reaction are still not understood in-depth. In this review, the latest advances in the current synthetic strategies for SACs are summarized. The effect of various coordination environments including central metal atoms, coordination atoms, environmental atoms, and guest groups on the intrinsic ORR activity of SACs are discussed. The electrocatalytic mechanisms are clarified by combining density functional theory calculations with in situ advanced characterization technologies. Then, the applications of SACs in FCs and Zn-air batteries are reviewed. Finally, the prospects and challenges for further development of SACs are highlighted.

Operando Cooperated Catalytic Mechanism of Atomically Dispersed Cu-N4 and Zn-N4 for Promoting Oxygen Reduction Reaction.

Dual-metal single-atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual-metal single-atom catalyst consisted of Cu-N4 and Zn-N4 on the N-doped carbon support (Cu/Zn-NC). It exhibits high-efficiency ORR activity with an Eonset of 0.98 V and an E1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state-of-the-art Pt/C and great mass of Pt-free single atom catalysts. Operando XANES demonstrates that the Cu-N4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn-N4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d-orbital electron distribution of Cu could benefit to the stretch and cleavage of O-O on Cu active center, speeding up the process of rate determining step of OOH*.

High-Efficient, Stable Electrocatalytic Hydrogen Evolution in Acid Media by Amorphous Fex P Coating Fe2 N Supported on Reduced Graphene Oxide.

Development of efficient and durable non-Pt catalysts for hydrogen evolution reaction (HER) in acid media is highly desirable. Iron nitride has emerged as a promising catalyst for its cost-effective nature, but the corresponding acidic stability must be promoted. Herein, phosphorus-decorated Fe2 N and reduced graphene oxide (P-Fe2 N/rGO) composite are designed and synthesized. X-ray photoelectron spectroscopy and X-ray absorption fine structure (XAFS) show that a thin layer amorphous iron phosphide is coated on the surface of Fe2 N nanoparticles, which could be responsible for the well resistance of chemical corrosion in acidic media. Meanwhile, the P-decoration could tune the electronic state and coordination environment of iron atom as evidenced by XAFS, resulting in dramatically enhanced electrocatalytic activity of P-Fe2 N/rGO. Density functional theory calculations reveal that both the P-connected N atoms and the Fe atoms in P-Fe2 N/rGO catalyst are the main active sites for H* adsorption. The hydrogen-binding free energy |ΔGH* | value is close to zero for P-Fe2 N/rGO, suggesting a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, P-Fe2 N/rGO catalyst could achieve a low ηonset of 22.4 mV, a small Tafel plot of 48.7 mV dec-1 , and remarkable stability for HER in acid electrolyte.

Co-VN encapsulated in bamboo-like N-doped carbon nanotubes for ultrahigh-stability of oxygen reduction reaction.

The electrocatalytic activity of carbon-based non-precious metal composites towards oxygen reduction reaction (ORR) is far from that of the recognized Pt/C catalyst. Thus, it is necessary to exploit novel catalysts based on multicomponent carbon-based composites with both high activity and high stability. Herein, a bottom-up strategy was used for constructing bamboo-like N-doped graphitic CNTs with a few encapsulated Co and VN nanoparticles (namely, NGT-CoV) by adopting melamine as both a nitrogen source and a carbon source. During the synthesis, melamine initially coordinated with cobalt and vanadium ions and then decomposed into carbon nitride nanosheet structures. Simultaneously, cobalt ions/clusters were converted into metal nanocatalysts by the reduced gases that were generated, which further rearranged the carbon nitride nanostructures to form N-doped CNTs. The presence of vanadium species strengthened the electronic structure and increased the contents of Co and N species by enhancing the interactions among Co and N species. The optimized NGT-Co35V65-45-900 exhibited an Eonset of 0.92 V (vs. RHE), an E1/2 of 0.81 V (vs. RHE), and a Tafel slope of 66.1 mV dec-1 in the ORR. It also displayed much higher durability (a negative shift in E1/2 of only 11 mV after 10 000 cycles) and methanol tolerance than a commercial Pt/C catalyst. The excellent performance should be attributed to the high exposure level of active sites that originated from Co-N, VN and N-doped bamboo-like graphitic CNTs. Moreover, the skeleton composed of hollow graphitic ultra-long CNTs could not only provide smooth mass transport pathways but also facilitate fast electron transfer.

[Studies on optimizing extraction technics of flowers of Polygonum orientale by response surface methodology].

OBJECTIVE: To analyze and optimize extraction technics of Polygonum orientale flowers by response surface methodology. METHODS: With the index for the content of taxifolin in flowers of Polygonum orientale, the effect of three factors such as concentration of alcohol, extraction time and solvent-solid ratio was designed by Box-Behnken central composite. Extraction technic parameters of Polygonum orientale flowers was optimized by response surface methodology. RESULTS: The optimizing extraction conditions of Polygonum orientale flowers were as follows: ethanol concentration was 65%, extracting time was 129 min and solvent-solid ratio was 18. Under the conditions, the average yield of taxifolin in 3 validation experiments was 2.79 mg/g. CONCLUSION: Optimizing extraction technics by response surface methodology is reasonable, simple, and has good predictability.

[Simultaneous determination of four flavones in root and stem of Cudrania tricuspidata and C. cochinchinensis by HPLC-DAD].

OBJECTIVE: To establish a HPLC-DAD method for the determination of axifolin, naringenin, quercetin and kaempferol in Cudrania tricuspidata and C. cochinchinensis in order to provide a scientific reference for species identification and quality evaluation, by establishing. METHOD: The determination was performed by HPLC-DAD on an Agilent C18 column (4.6 mm x 150 mm, 5 microm) by gradient elution (0-15 min, 35%-50% A; 15-30 min, 50% - 65% A) using methanol (A) and 0.1% phosphoric acid (B) as the mobile phase. The flow rate was 1 mL x min(-1). The detection wavelength was 290 nm for taxifolin and naringenin, 365 nm for quercetin and kaempferol with column temperature at 30 degrees C. RESULT: The content of axifolin and quercetin in the root of C. tricuspidata were remarkably higher than that in the root of C. cochinchinensis, and the content in stem of C. tricuspidata was also higher than that in the stem of C. cochinchinensis, the content of axifolin and quercetin was variable in different species. The content of naringenin and kaempferol in the root of C. cochinchinensis was visibly higher than that in the root of C. tricuspidata, and the content in the stems of the two herbs was similar, the content of naringenin and kaempferol was visibly variable in different medicinal parts of the herb, but similar between the two herbs. CONCLUSION: There's some difference of the content of the four ingredients in different medicinal parts and different herbs, so clinical use should not be confused.

[Determination of taxifolin in Polygonum orientale of different storage period].

OBJECTIVE: To find out the correlation between the content of taxifolin in Polygonum orientale and the storage time. METHOD: HPLC was used to determine taxifolin. The chromatographic condition was as following: Diamonsil C18 column (4.6 mm x 200 mm, 5 microm), mobile phase acetonitrile -0.1% phosphoric acid (gradient elution), the detection wavelength 290 nm and flow rate 1.0 mL x min(-1), the column temperature 30 degrees C. RESULT: The injection volume of taxifolin was in good linearity within 0.07 and 0.35 microg, the average recovery was 99.7% with RSD 0.2%. Taxifolin content was 0.84, 1.36, 1.75, 1.99 mg x g(-1) corresponding to storage time of 10, 7, 6, 5 years, respectively. CONCLUSION: The content of taxifolin decreased with the storage time. When the storage period is more than six years, the content is lower than that required by Chinese Pharmacopoeia (2010 version). This method has a good repeatability and accuracy, it provides a scientific reference for clinical use and quality evaluation of P. orientale.

[Study on characteristic HPLC fingerprint of Polygonum orientale inflorescence].

OBJECTIVE: To establish a characteristic HPLC fingerprint of Polygonum orientale inflorescence, and to provide reference for its quality evaluation. METHODS: Taxifolin was used as reference. HPLC analysis was carried out with Diamonsil C18 column (200 mm x 4.6 mm, 5 microm) using acetonitrile -0.1% phosphoric acid(gradient elution)as mobile phase at flow rate of 1.0 mL/min. The detection wavelength was set at 280 nm and the column temperature was 30 degrees C. RESULTS: Eighteen common peaks were pointed out from the HPLC fingerprint of Polygonum orientale inflorescence from 12 different habitats. Among of them,four common peaks were identified as taxifolin, catechin, gallic acid and 3,3'-dimethyl ellagic acid-4-O-beta-D-glucoside. Analyzed by "Similarity Evaluation for Chromatographic Fingerprint of Traditional Chinese Medicine" software, the HPLC fingerprint similarities of 12 samples were more than 0.9. CONCLUSION: This method is repeatable and exclusive. It can be used for identification and quality control of Polygonum orientale inflorescence.