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Porous Iron‐Nitrogen‐Carbon Electrocatalysts for Anion Exchange Membrane Fuel Cells (AEMFC)
High‐performance platinum group metal‐free (PGM‐free) electrocatalysts were prepared from porous organic polymers (POPs) precursors with highly‐porous structures and adjustable surface area. A resin phenol‐melamine‐based POP and an iron salt were used to synthesize Fe−N−C catalysts with different iron contents (0.2–1.3 wt.%). Electrochemical and spectroscopical characterization allowed us to elucidate the effect of Fe content on the material's structure, surface chemistry, and electrocatalytic activity toward the oxygen reduction reaction (ORR). The increase of iron content led to a specific surface area decrease, preserving the morphological structure, with the formation of highly‐active catalytic sites, as indicated by X‐ray photoelectron spectroscopy (XPS) analysis. The rotating ring disk electrode experiments, performed at pH=13, confirmed the high ORR activity of both 0.5 Fe (E1/2=0.84 V) and 1.3 Fe (E1/2=0.83 V) catalysts, which were assembled at the cathode of a H2‐fed anion exchange membrane fuel cells (AEMFC) equipped with a FAA‐3‐50 membrane, evidencing promising performance (0.5 Fe, maximum power density, Max PD=69 mA cm−2 and 1.3 Fe, Max PD=87 mA cm−2) with further advancement prospects. More or less: A sustainable soft templating strategy allowed preparing highly porous Fe−N−C catalysts with different Fe contents. The effect of Fe content on the material's structure and electrocatalytic activity toward the oxygen reduction reaction (ORR) was elucidated. The formation of high‐active nitrogen‐ and iron‐based functional groups endowed electrocatalysts with excellent ORR activity.
Journal Article
Brassinosteriod Insensitive 2 (BIN2) acts as a downstream effector of the Target of Rapamycin (TOR) signaling pathway to regulate photoautotrophic growth in Arabidopsis
The components of the target of rapamycin (TOR) signaling pathway have been well characterized in heterotrophic organisms from yeast to humans. However, because of rapamycin insensitivity, embryonic lethality in tor null mutants and a lack of reliable ways of detecting TOR protein kinase in higher plants, the key players upstream and downstream of TOR remain largely unknown in plants.
Using engineered rapamycin-sensitive Binding Protein 12-2 (BP12-2) plants, the present study showed that combined treatment with rapamycin and active-site TOR inhibitors (asTORis) results in synergistic inhibition of TOR activity and plant growth in Arabidopsis.
Based on this system, we revealed that TOR signaling plays a crucial role in modulating the transition from heterotrophic to photoautotrophic growth in Arabidopsis. Ribosomal protein S6 kinase 2 (S6K2) was identified as a direct downstream target of TOR, and the growth of TOR-suppressed plants could be rescued by up-regulating S6K2. Systems, genetic, and biochemical analyses revealed that Brassinosteriod Insensitive 2 (BIN2) acts as a novel downstream effector of S6K2, and the phosphorylation of BIN2 depends on TOR-S6K2 signaling in Arabidopsis.
By combining pharmacological with genetic and biochemical approaches, we determined that the TOR-S6K2-BIN2 signaling pathway plays important roles in regulating the photoautotrophic growth of Arabidopsis.
Journal Article
Histidine residues at the copper-binding site in human tyrosinase are essential for its catalytic activities
Tyrosinase is a copper-binding enzyme involved in melanin biosynthesis. However, the detailed structure of human tyrosinase has not yet been solved, along with the identification of the key sites responsible for its catalytic activity. We used site-directed mutagenesis to identify the residues critical for the copper binding of human tyrosinase. Seven histidine mutants in the two copper-binding sites were generated, and catalytic activities were characterised. The tyrosine hydroxylase activities of the CuA site mutants were approximately 50% lower than those of the wild-type tyrosinase, while the dopa oxidation activities of the mutants were not significantly different from that of wild-type tyrosinase. By contrast, mutations at CuB significantly decreased both tyrosine hydroxylation and dopa oxidation activities, confirming that the catalytic sites for these two activities are at least partially distinct. These findings provide a useful resource for further structural determination and development of tyrosinase inhibitors in the cosmetic and pharmaceutical industries.
Journal Article
Insight into the Mechanism of Dual-metal Atoms on N, S-codoped Graphene toward Oxygen Evolution Reactions: High Performance Inspired by Dual Active Sites
The development of highly efficient and cost-effective catalysts to drive the oxygen evolution reaction (OER) is of significant importance for sustainable energy and energy conversion. However, the acceleration of the sluggish kinetics of the OER relies primarily on the use of noble metals at present. In this work, we proposed a series of single/dual metal atoms loaded on N, S-doped graphene and investigated the OER mechanism with dual metal and nonmetal active sites at the atomic level using density functional theory (DFT). The theoretical results reveal that dual active sites, including the doping of N, S and dual transition metals in catalysts (M
1
M
2
N
8
S-gra, M
1
= Co, Ni, Fe, M
2
= Co, Ni, Fe, Cu), can reduce the overpotential and thereby synergistically promote the catalytic efficiency in the OER process. Notably, CoCo and FeFe based dual atoms catalysts exhibit the lowest theoretical overpotential and the promising OER catalytic activity. The superior catalytic activity arises from the modulated charge transfer between the catalysts and the adsorbed intermediates, appropriate adsorption energies for adsorption and desorption and resulted reduced overpotential, and can be attributed to the dual active sites with the incorporation of S and the second metal atoms. Our study provides theoretical insights into the dual active site mechanisms for the OER at the atomic level, offering a new perspective for designing high performance OER catalysts.
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Journal Article
Enhancement in catalytic activity of Aspergillus niger XynB by selective site-directed mutagenesis of active site amino acids
XynB from Aspergillus niger ATCC1015 (AnXynB) is a mesophilic glycoside hydrolase (GH) family 11 xylanase which holds great potentials in a wide variety of industrial applications. In the present study, the catalytic activity and stability of AnXynB were improved by a combination of computational and experimental approaches. Virtual mutation and molecular dynamics simulations indicated that the introduction of Glu and Asn altered the interaction network at the − 3 subsite. Interestingly, the double mutant S41N/T43E displayed 72% increase in catalytic activity when compared to the wild type (WT). In addition, it also showed a better thermostability than the WT enzyme. Kinetic determination of the T43E and S41N/T43E mutants suggested that the higher xylanase activity is probably due to the increasing binding affinity of enzyme and substrate. Consequently, the enzyme activity and thermostability of AnXynB was both increased by selective site-directed mutagenesis at the − 3 subsite of its active site architecture which provides a good example for a successfully engineered enzyme for potential industrial application. Moreover, the molecular evolution approach adopted in this study led to the design of a library of sequences that captures a meaningful functional diversity in a limited number of protein variants.
Journal Article
Alkali Induction Strategy for Artificial Photosynthesis of Hydrogen by TiO2 Heterophase Homojunctions
The robust separation and utilization of photogenerated electrons‐holes (e−‐h+) are key in accelerating redox reactions. Unlike traditional heterojunction photocatalysts, homojunction features different energy bandgaps with interchangeable compositions that can significantly trigger charge carrier dynamics, but their precise construction remains an ongoing challenge owing to quick lattice‐level modulations. Herein, TiO2‐based homojunction (HTM‐OH) holding dissimilar yet discernible crystalline phases (anatase and rutile) are rationally constructed by a straightforward alkali‐induced strategy which enables controllable lattice‐transition/orientation. The resulting HTM‐OH exhibits speedy separation and well‐guided flow of e−‐h+ over redox sites with extended carrier lifetime, leading to high‐rate hydrogen generation (HER, 34.35 mmol g−1 h−1) under simulated sunlight. Moreover, a self‐made thin film of HTM‐OH indicates a notable scale‐up potential under real‐time sunlight. This work furnishes a new non‐complex homojunction strategy for speeding charge carrier kinetics, credibly extendable to a diverse range of catalysts and applications. A straightforward alkali‐induced strategy is implemented to rationally construct controllable lattice‐transition/orientation in TiO2‐based homojunction (HTM‐OH). The resulting HTM‐OH exhibits speedy separation and well‐guided flow of e−‐h+ over redox sites with extended carrier lifetime, leading to high‐rate hydrogen generation (HER, 34.35 mmol g−1 h−1) under simulated sunlight and a notable scale‐up potential under real‐time sunlight.
Journal Article
The contribution of specific subsites to catalytic activities in active site architecture of a GH11 xylanase
BackgroundXylanase with high specific activity plays a crucial role in hemicellulose biodegradation and has important industrial application. The amino acids located in the active site determine the enzyme biological characterization. In this study, structure bioinformatics analysis and alanine screening experiments were performed to explore the roles of amino acids at each subsite of the GH11 xylanase active site.ResultsThere are highly conserved amino acids at − 2 to + 1 subsites, and the network of the interactions is concentrated near the catalytic sites (E86, E178). However, the amino acids at relatively distal subsites, especially at the + 2 and + 3 subsites, are few but diverse. Alanine substitution of amino acids in the active site architecture exerted different impacts on catalytic efficiency. Interestingly, mutants Y180A at the + 2 subsite and Y96A at the + 3 subsite had reduced enzymatic activities by almost 95%, which indicate that these two aromatic residues are necessary for the catalysis of substrates in addition to the highly conserved residues at the − 2 and + 1 subsites. Moreover, in these two subsites, aromatic amino acids with different side-chain properties also affected enzyme activity. The mutants Y180W and Y96W showed 6.2% and 12.8% increase in specific activities by comparison with wild-type enzyme at 50 °C, respectively.ConclusionWe elucidated the interaction between amino acids and substrates in the active site, which will aid understanding of the protein-ligand interaction in enzyme engineering.Key points• Xylanase of GH11 family is a good industrial candidate.• The roles of residues at each subsite of GH11 xylanase active site are explored.• The two aromatic residues at the + 2 and + 3 subsites are necessary for the catalysis.• Y180W and Y96W increased the enzymatic activity by 6.2% and 12.8% at low temperature.
Journal Article
Hydrogen Rich Syngas Production over Ni Catalysts on Mg‐Stabilized Zirconia through Partial Oxidation of Methane: The Role of Magnesium as Stabilizer for Support & Active Sites
Catalytic conversion of methane in the presence of O2 into hydrogen‐rich syngas is known as partial oxidation of methane (POM). Achieving good H2 yield with H2/CO ≈ 3 by using a low amount of Ni‐based active sites at a low reaction temperature (600 °C) through POM remains challenging. Herein, magnesia‐stabilized zirconia (MSZ) is prepared by the coprecipitation method by varying the amount of Mg from 8 to 14 mol%. Ni supported over MSZ catalysts are investigated for POM reaction and characterized by diffraction techniques, spectroscopic techniques, surface area‐porosity, temperature‐programed reduction‐oxidation, and thermogravimetry. The incorporation of magnesium stabilizes both the support and the active sites. Under the oxidizing environment, the strong interaction of NiO surmounts over moderate interaction. Upon incorporation of 14 mol% Mg into ZrO2 (14MSZ), the catalyst attains stable support and the largest surface area, where most of the active sites are formed by “NiO under strong interaction”. The catalyst surface is also enriched by Ni, Mg, and lattice oxygen. 5 wt% Ni dispersed over 14MSZ acquires the highest H2 yield (37%) and H2/CO ≈ 3 at 600 °C and 85% H2 yield with ≈ 2 H2/CO at 750 °C. Over 5Ni/14MSZ catalyst, the high reaction temperature restricts the indirect pathway of POM by limiting the CO2 yield and ensures high hydrogen yield through the direct pathways of POM. The role of 8–14 mol% MgO along with 92–86 mol% ZrO2 as support for Ni‐catalyst is investigated toward partial oxidation of methane (POM). Upon raising the proportion of MgO from 8 to 14 mol%, the physico‐chemical properties are modified and catalyst activities toward POM are increased at 600° accordingly. Upon increasing temperature from 600 to 700 °C further, the H2 yield is increased, whereas the CO2 yield and H2/CO ratio are decreased proportionally.
Journal Article
Effect of the reignition characteristics on long-flame coal by oxidization and water immersion
After a coal seam is mined, the coal remaining in the goaf is prone to flooding and spontaneous combustion accidents. To explore the reignition (secondary oxidation) characteristics of long-flame coal after oxidation and water immersion, the experimental methods of thermogravimetric analysis and infrared spectroscopy were used to analyze coal samples of oxidation first and then water immersion (FO) and samples of water immersion first and then oxidization (FI) at different pre-oxidation temperatures. The results showed that the content of main oxygen-containing functional groups (hydroxyl, carbonyl, and carboxyl groups) of the FO120 (oxidation 120 °C first and then water immersion) coal sample increased, and the FI 90 (water immersion first and then oxidization 90 °C) coal sample decreased. Pre-oxidation at 120 °C will slow down the decrease in the extent of low-temperature secondary oxidation TG, as the pre-oxidation temperature increases, the total heat release of the FO coal samples first increase and then decrease, and the heat released is high at 120 °C. The FI coal samples transfer active sites during the water immersion process, and the high pre-oxidation temperature leads to the rapid increase of the speed of the primary active site, which leads to the transformation between the secondary active site and the oxygen-containing group, resulting in the cleavage of the oxygen-containing group and increasing the heat production. Water immersion pre-oxidation performed under different conditions has the dual effects of promoting and inhibiting spontaneous coal combustion. This result provides a theoretical basis for preventing spontaneous combustion in coal-mined areas in shallow coal seams after soaking in water.
Journal Article