Direct Capturing and Regulating Key Intermediates for High-Efficiency Oxygen Evolution Reactions.

Developing efficient oxygen evolution reaction (OER) electrocatalysts can greatly advance the commercialization of proton exchange membrane (PEM) water electrolysis. However, the unclear and disputed reaction mechanism and structure-activity relationship of OER pose significant obstacles. Herein, the active site and intermediate for OER on AuIr nanoalloys are simultaneously identified and correlated with the activity, through the integration of in situ shell-isolated nanoparticle-enhanced Raman spectroscopy and X-ray absorption spectroscopy. The AuIr nanoalloys display excellent OER performance with an overpotential of only 246 mV to achieve 10 mA cm-2 and long-term stability under strong acidic conditions. Direct spectroscopic evidence demonstrates that * OO adsorbed on IrOx sites is the key intermediate for OER, and it is generated through the O-O coupling of adsorbed oxygen species directly from water, providing clear support for the adsorbate evolution mechanism. Moreover, the Raman information of the * OO intermediate can serve as a universal "in situ descriptor" that can be obtained both experimentally and theoretically to accelerate the catalyst design. It unveils that weakening the interactions of * OO on the catalysts and facilitating its desorption would boost the OER performance. This work deepens the mechanistic understandings on OER and provides insightful guidance for the design of more efficient OER catalysts.

In Situ Raman Observation of Oxygen Activation and Reaction at Platinum-Ceria Interfaces during CO Oxidation.

Understanding the fundamental insights of oxygen activation and reaction at metal-oxide interfaces is of significant importance yet remains a major challenge due to the difficulty in in situ characterization of active oxygen species. Herein, the activation and reaction of molecular oxygen during CO oxidation at platinum-ceria interfaces has been in situ explored using surface-enhanced Raman spectroscopy (SERS) via a borrowing strategy, and different active oxygen species and their evolution during CO oxidation at platinum-ceria interfaces have been directly observed. In situ Raman spectroscopic evidence with isotopic exchange experiments demonstrate that oxygen is efficiently dissociated to chemisorbed O on Pt and lattice Ce-O species simultaneously at interfacial Ce3+ defect sites under CO oxidation, leading to a much higher activity at platinum-ceria interfaces compared to that at Pt alone. Further in situ time-resolved SERS studies and density functional theory simulations reveal a more efficient molecular pathway through the reaction between adsorbed CO and chemisorbed Pt-O species transferred from the interfaces. This work deepens the fundamental understandings on oxygen activation and CO oxidation at metal-oxide interfaces and offers a sensitive technique for the in situ characterization of oxygen species under working conditions.

Understanding the Roles of Electrogenerated Co3+ and Co4+ in Selectivity-Tuned 5-Hydroxymethylfurfural Oxidation.

The Co-based electrocatalyst is among the most promising candidates for electrochemical oxidation of 5-hydroxymethylfurfural (HMF). However, the intrinsic active sites and detailed mechanism of this catalyst remains unclear. We combine experimental evidence and a theoretical study to show that electrogenerated Co3+ and Co4+ species act as chemical oxidants but with distinct roles in selective HMF oxidation. It is found that Co3+ is only capable of oxidizing formyl group to produce carboxylate while Co4+ is required for the initial oxidation of hydroxyl group with significantly faster kinetics. As a result, the product distribution shows explicit dependence on the Co oxidation states and selective production of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 2,5-furandicarboxylic acid (FDCA) are achieved by tuning the applied potential. This work offers essential mechanistic insight on Co-catalyzed organic oxidation reactions and might guide the design of more efficient electrocatalysts.

[The effects and mechanism of caloric restriction on energy metabolism].

Caloric restriction (CR) is explored to limit the caloric intake without malnutrition. CR can affect the levels of various metabolites in organism, such as lipids, free fatty acids, ketones, bile acids and amino acids, etc, and is thought being able to extend the lifespan, postpone and reduce the incidence of age-related disorders (e.g., type 2 diabetes, cancer and cardiovascular diseases). These effects are mainly attributed to the role of CR in energy metabolism. The mechanism of CR on energy metabolism is closely related to biological clock, hormonal production, gastrointestinal flora and inflammation. Here we briefly review the effects and mechanism of CR on energy metabolism.

Synthesis of Au@TiO2 core-shell nanoparticles with tunable structures for plasmon-enhanced photocatalysis.

Plasmonic metal-semiconductor nanocomposites, especially those with core-shell nanostructures, have received extensive attention as they can efficiently expand light absorption and accelerate electron-hole separation thus improving the photocatalytic efficiency. However, controlled synthesis and structure manipulation of plasmonic metal-semiconductor nanocomposites still remain a significant challenge. Herein, a simple and universal method has been developed for the preparation of plasmonic Au@TiO2 core-shell nanoparticles. Using such a method, uniform TiO2 shells are successfully coated on Au nanoparticles with various morphologies including nanorods, nanocubes, and nanospheres, and the thickness and crystallinity of the TiO2 shell can be simply tuned by adjusting the pH value and thermal treatment, respectively. Furthermore, the influence of the morphology of the Au core and the thickness and crystallinity of the TiO2 shell on the photocatalytic performance of Au@TiO2 towards the photodegradation of methylene blue is systematically explored. It is found that Au@TiO2 NPs with nanorod morphology and crystalline TiO2 shells display the best performance, which is 5 times higher than that of bare Au nanoparticles. This work provides a facile strategy for the fabrication of plasmonic core-shell nanostructures that show excellent performance in plasmon-enhanced photocatalysis.

Gastric mammalian target of rapamycin signaling, hormone production and energy metabolism.

The obesity epidemic imposes a significant health burden on human beings. Current understanding of the mechanisms underlying the development of obesity is incomplete and contemporary treatment is often ineffective. Gastrointestinal hormones are important regulators of food intake and energy metabolism. Previous studies indicate that the mammalian target of rapamycin signaling pathway in the gastric mucosa is crucially involved in fuel sensing in the gastrointestinal tract and plays a critical role in the coordination of nutrient availability and ingestive behavior via the production of gastric hormones. As an important component of the brain-gut axis regulating food intake and energy homeostasis, energy sensing in the gastrointestinal tract may provide a novel insight into our understanding of the precise coordination between the organism and cellular energy state.

[Assay of endogenous hydrogen sulfide from erythrocytes].

OBJECTIVE: To construct a detection method of endogenous hydrogen sulfide (H2S) from erythrocytes. METHODS: Prepared rat erythrocyte (10(6) cell) was added in 4 mL 2-amino-2-methyl-1,3-propanediol(225 mmol/L, pH=9.55) and ultrasonically lysed for 3 times. The erythrocyte lysis was transferred into a 25 mL Erlenmeyer flask and beta-mercaptopyruvate was added for final concentration of 2 mmol/L. Cryovial test tubes (2 mL) were used as the centre wells each contained 0.5 mL of 1% zinc acetate as trapping solution and a filter paper of 2.0x2.5 cm2 to increase the air/liquid contacting surface. The flasks containing reaction mixture and centre wells were flushed with N2 before being sealed with a double layer of Parafilm. Reaction was initiated by transferring the flasks from ice to a 37 degrees C shaking water bath. After incubation at 37 degrees C for 60 min, 0.5 mL of 50% trichloroacetic acid was added into the reaction mixture to stop the reaction. The flasks were sealed again and incubated at 37 degrees C for another 60 min to ensure a complete trapping of the H2S released from the mixture. Released H2S is absorbed by zinc acetate and generation zinc sulfide. The zinc sulfide formed is dissolved in a hydrochloric acid solution of amino-dimethylaniline (N,N-dimethyl-p-phenylenediamine), and methylene blue is formed within 10 min at room temperature in the presence of ferric chloride. The blue color of methylene blue is measured at 670 or 650 nm on spectrophotometer. RESULTS: We first demonstrated the key enzymes of endogenous H2S generation-3-mercaptopyruvate sulfurtransferase (MPST) gene expression by RT-PCR. Endogenous H2S production from rat erythrocytes was 22.76+/-1.53 micromol/min/10(8) cells, about 4-folds as compared with to the liver and kidney tissues. However, the endogenous H2S production from erythrocyte by L-cysteine pathway was little detected. CONCLUSION: Endogenous H2S released from erythrocytes depended mainly on MPST pathway. Our method is effective to detect the erythrocytic endogenous H2S.