Revealing the catalytic kinetics and dynamics of individual Pt atoms at the single-molecule level.

SignificanceHere, with single-molecule fluorescence microscopy, we study the catalytic behavior of individual Pt atoms at single-turnover resolution, and then reveal the unique catalytic properties of Pt single-atom catalyst and the difference in catalytic properties between individual Pt atoms and Pt nanoparticles. Further density functional theory calculation indicates that unique catalytic properties of Pt single-atom catalyst could be attributed intrinsically to the unique surface properties of Pt1-based active sites.

In Situ Insertion of Silicon Nanowires into Hollow Porous Co/NC Polyhedra Enabling Large-Current-Density Hydrogen Evolution Electrocatalysis.

N-doped carbon (NC)-encapsulated transition metal (TM) nanocomposites are considered as alternatives to Pt-based hydrogen evolution reaction (HER) electrocatalysts; however, their poor electron transfer and mass diffusion capability at high current densities hinder their practical application. Herein, an oriented coupling strategy for the in situ grafting of ultrafine Co nanoparticle-embedded hollow porous C polyhedra onto Si nanowires (Co/NC-HP@Si-NWs) is proposed to address this concern. Experimental investigations reveal that the intimate coupling between the Si-NW and Co/NC nanocage forms a multithreaded conductive network, lowering the energy barrier for internal electron transfer. When functionalized as an HER electrocatalyst in 0.5 m H2 SO4 , Co/NC-HP@Si-NWs deliver overpotentials as low as 57 and 440 mV at 10 and 500 mA cm-2 , respectively, which are much better than those of the pristine Co/NC-HP. Moreover, Co/NC-HP@Si-NWs show an outstanding cycle durability of 24 h at 10 and 500 mA cm-2 . The findings of this study are expected to inspire revolutionary work on the development of Si-mediated TM-based electrocatalysts for the HER.

Amorphous hollow manganese silicate nanosphere oxidase mimic for ultrasensitive and high-reliable colorimetric detection of biothiols.

Metal-based nanozymes with exceptional physicochemical property and intrinsic enzymatic properties have been widely used in industrial, medical, and diagnostic fields. However, low substrate affinity results in unsatisfying catalytic kinetic and instability in complicated conditions, which significantly decreases their sensitivity and reliability. Herein, an amorphous hollow manganese silicate nanosphere (defined as AHMS) has been successfully synthesized via a facile one-step hydrothermal method and utilized in the archetype for colorimetric detection of biothiols with high sensitivity and high reliability. The experimental data demonstrates that ultrafast affinity of the substrate contributes to enhanced sensitivity with outstanding catalytic kinetic features (Km = 27.1 µM) and low limit of detection (LODGSH = 20 nM). The designed sensor demonstrates a reliable applicability for analysis of biological liquids (fetal calf serum and Staphylococcus aureus) and design of visual logic gates. Therefore, AHMS provides a promising strategy for ultrasensitive and high-reliable biosensing.

Kinetics Driven by Hollow Nanoreactors: An Opportunity for Controllable Catalysis.

As a novel class of catalytic materials, hollow nanoreactors offer new opportunities for improving catalytic performance owing to their higher controllability on molecular kinetic behavior. Nevertheless, to achieve controllable catalysis with specific purposes, the catalytic mechanism occurring inside hollow nanoreactors remains to be further understood. In this context, this Review presents a focused discussion about the basic concept of hollow nanoreactors, the underlying theory for hollow nanoreactor-driven kinetics, and the intrinsic correlation between key structural parameters of hollow nanoreactors and molecular kinetic behaviors. We aim to provide in-depth insights into understanding kinetics occurred within typical hollow nanoreactors. The perspectives proposed in this paper may contribute to the development of the fundamental theoretical framework of hollow nanoreactor-driven catalysis.

Plasmon-Driven Modulation of Reaction Pathways of Individual Pt-Modified Au Nanorods.

Understanding the underlying kinetic mechanism of plasmon-enhanced catalysis is important for designing optimized bimetal nanostructures. Here, we characterize product formation rate at both the single-particle and ensemble level. The single-particle measurement allows us to reveal the underlying catalytic kinetic mechanisms of a bimetal nanostructure. Combining this with ensemble observations of two different catalytic behaviors of this catalyst with and without illumination shows that energetic charge carriers induce a transition from a competitive reactant adsorption type to a noncompetitive adsorption type, which leads to the suppression of catalytic rate decay at high reactant concentration. Theoretical modeling as well as analysis of hole acceptability of scavengers on Pt and Au surfaces indicates that the Pt light absorptivity is enhanced near Au and the energetic charges may form directly from the Pt part of the Au-Pt nanostructure. The presented study deepens our understanding of plasmon-enhanced catalysis by bimetal nanostructures.

Enhanced Redox Electrocatalysis in High-Entropy Perovskite Fluorides by Tailoring d-p Hybridization.

High-entropy catalysts featuring exceptional properties are, in no doubt, playing an increasingly significant role in aprotic lithium-oxygen batteries. Despite extensive effort devoted to tracing the origin of their unparalleled performance, the relationships between multiple active sites and reaction intermediates are still obscure. Here, enlightened by theoretical screening, we tailor a high-entropy perovskite fluoride (KCoMnNiMgZnF3-HEC) with various active sites to overcome the limitations of conventional catalysts in redox process. The entropy effect modulates the d-band center and d orbital occupancy of active centers, which optimizes the d-p hybridization between catalytic sites and key intermediates, enabling a moderate adsorption of LiO2 and thus reinforcing the reaction kinetics. As a result, the Li-O2 battery with KCoMnNiMgZnF3-HEC catalyst delivers a minimal discharge/charge polarization and long-term cycle stability, preceding majority of traditional catalysts reported. These encouraging results provide inspiring insights into the electron manipulation and d orbital structure optimization for advanced electrocatalyst.

Surface Ligand Modification on Ultrathin Ni(OH)2 Nanosheets Enabling Enhanced Alkaline Ethanol Oxidation Kinetics.

The ethanol oxidation reaction (EOR) is an economical pathway in many electrochemical systems for clean energy, such as ethanol fuel cells and the anodic reaction in hydrogen generation. Noble metals, such as platinum, are benchmark catalysts for EOR owing to their superb electrochemical capability. To improve sustainability and product selectivity, nickel (Ni)-based electrocatalysts are considered promising alternatives to noble-metal EOR. Although Ni-based electrocatalysts are relieved from intermediate poisoning, their performances are largely limited by their relatively high onset potential. Therefore, the EOR usually competes with the oxygen evolution reaction (OER) at working potentials, resulting in a low EOR efficiency. Here, we demonstrate a strategy to modify the surface ligands on ultrathin Ni(OH)2 nanosheets, which substantially improved their catalytic properties for the alkaline EOR. Chemisorbed octadecylamine ligands could create an alcoholophilic layer at the nanosheet surface to promote alcohol diffusion and adsorption, resulting in outstanding EOR activity and selectivity over the OER at higher potential. These non-noble-metal-based 2D electrocatalysts and surface ligand engineering showcase a promising strategy for achieving high-efficiency electrocatalysis of EOR in many practical electrochemical processes.

Catalytic Kinetics Regulation for Enhanced Electrochemical Nitrogen Oxidation by Ru-Nanoclusters-Coupled Mn3 O4 Catalysts Decorated with Atomically Dispersed Ru Atoms.

Electrochemical N2 oxidation reaction (NOR), using water and N2 in the atmosphere, represents a sustainable approach for nitric production to replace the conventional industrial synthesis with high energy consumption and greenhouse gas emission. Meanwhile, owing to chemical inertness of N2 and sluggish kinetics for 10-electron transfer, emerging electrocatalysts remain largely underexplored. Herein, Ru-nanoclusters-coupled Mn3 O4 catalysts decorated with atomically dispersed Ru atoms (Ru-Mn3 O4 ) are designed and explored as an advanced electrocatalyst for ambient N2 oxidation, with an excellent Faraday efficiency (28.87%) and a remarkable NO3 - yield (35.34 µg h-1 mg-1 cat. ), respectively. Experiments and density functional theory calculations reveal that the outstanding activity is ascribed to the coexistence of Ru clusters and single-atom Ru. The synergistic effect between the Ru clusters and Mn3 O4 can effectively activate the chemically inert N2 , lowering the kinetic barrier for the vital breakage of N≡N. The intensive *OH supply and enhanced conductivity are used to regulate the catalytic kinetics for optimized performance. This work provides brand-new ideas for the rational design of electrocatalysts in complicated electrocatalytic reactions with multiple dynamics-different steps.

Heterologous Expression and Characterization of Tea (Camellia sinensis) Polyamine Oxidase Homologs and Their Involvement in Stresses.

Polyamine oxidase (PAO) is a key enzyme maintaining polyamine homeostasis, which affects plant physiological activities. Until now, the gene members and function of PAOs in tea (Camellia sinenesis) have not been fully identified. Here, through the expression in Escherichia coli and Nicotiana benthamiana, we identified six genes annotated as CsPAO in tea genome and transcriptome and determined their enzyme reaction modes and gene expression profiles in tea cultivar 'Yinghong 9'. We found that CsPAO1,2,3 could catalyze spermine, thermospermine, and norspermidine, and CsPAO2,3 could catalyze spermidine in the back-conversion mode, which indicated that the precursor of γ-aminobutyric acid might originate from the oxidation of putrescin but not spermidine. We further investigated the changes of CsPAO activity with temperature and pH and their stability. Kinetic parameters suggested that CsPAO2 was the major PAO modifying polyamine composition in tea, and it could be inactivated by ß-hydroxyethylhydrazine and aminoguanidine. Putrescine content and CsPAO2 expression were high in tea flowers. CsPAO2 responded to wound, drought, and salt stress; CsPAO1 might be the main member responding to cold stress; anoxia induced CsPAO3. We conclude that in terms of phylogenetic tree, enzyme characteristics, and expression profile, CsPAO2 might be the dominant CsPAO in the polyamine degradation pathway.

Highly efficient hydrogen production from hydrolysis of ammonia borane over nanostructured Cu@CuCoOx supported on graphene oxide.

Designing highly efficient and cheap nanocatalysts for room-temperature hydrolysis of ammonia borane (AB) is of great significance for their real application in hydrogen (H2)-based fuel cells. Here, we report a kind of noble metal (NM)-free hybrid nanocatalysts composed of heterostructured Cu@CuCoOx nanoparticles and a graphene oxide support (denoted as Cu@CuCoOx@GO) and demonstrate their high catalytic performance toward the hydrolysis of AB. By rationally controlling synthetic parameters, we find that optimum Cu0.3@Cu0.7CoOx@GO achieves a superior catalytic activity with a turnover frequency of 44.6 molH2 molM-1 min-1 in H2O and 98.2 molH2 molM-1 min-1 in 0.2 M NaOH, better than most of previously reported NM-free nanocatalysts. This catalyst also discloses a very low activation energy (Ea) of 35.4 kJ mol-1. The studies on catalytic kinetics and isotopic experiments attribute the high activity to synergistically structural and compositional advantages of Cu0.3@Cu0.7CoOx@GO, which kinetically accelerates the oxidative cleavage of OH bond in attacked H2O (the rate-determining step of the hydrolysis of AB). This study thus provides an opportunity for rational design of cheap NM-free nanocatalysts for H2 production from chemical H2-storage materials.

The catalytic kinetics of chicken transthyretin towards human Aß1-42.

The novel property of transthyretin (TTR) as a protease has been proposed to be significant. However, the study of TTR proteolysis properties has not been completely elucidated. Herein, we first report the catalytic activity of chicken TTR from plasma determined by using fluorescently labeled amyloid beta 1-42 peptide (Aß1-42), and compared it with human TTR (human TTR) from plasma and recombinant Crocodylus porosus TTR. The enzyme kinetic study revealed that the affinity for Aß1-42 of chicken TTR and C. porosus TTR (KM values were 12.72 ±â€¯0.27 µM and 16.21 ±â€¯0.02 µM, respectively) were significantly lower than human TTR (KM was 43.05 ±â€¯0.39 µM). In addition, the catalytic efficiency of chicken TTR (Kcat/KM was 310,386.87 ±â€¯13,627.12 M-1 s-1) was 4.3 and 5.5 folds higher than those of C. porosus TTR and human TTR (Kcat/KM were 72,893.80 ±â€¯355.74 M-1 s-1 and 56,519.12 ±â€¯5009.50 M-1 s-1, respectively), respectively. These results does not only indicated the relationship between structure and the proteolytic activity of TTR, but also suggested a potential development of TTR as a therapeutic anti-Aß agent.

Ternary Palladium-Boron-Phosphorus Alloy Mesoporous Nanospheres for Highly Efficient Electrocatalysis.

Alloying palladium (Pd) catalysts with various metalloid and nonmetal elements can improve their catalytic performance in different chemical reactions. However, current nanosynthesis methods can only generate Pd alloys containing one metalloid or nonmetal, which limits the types of element combinations that may be used to improve Pd-based nanocatalysts. Herein, we report a simple soft-templating synthetic strategy to co-alloy Pd with the metalloid boron (B) and the nonmetal phosphorus (P) to generate ternary PdBP mesoporous nanospheres (MSs) with three-dimensional dendritic frameworks. We use a one-step aqueous synthesis method where dimethylamine borane and sodium hypophosphite serve as the B and P sources, respectively, as well as the co-reducing agents to drive the nucleation and growth of ternary PdBP alloy on a sacrificial dioctadecyldimethylammonium chloride template. The concentration of metalloid to nonmetal and the diameters of dendritic MSs can be tailored. The synthetic protocol is also extended to other multicomponent PdMBP alloy MSs to generate different types of dendritic mesoporous frameworks. Boron and phosphorus are known to accelerate the kinetics of the electrochemical oxygen reduction reaction (ORR) and alcohol oxidation reactions (AORs), because their alloys promote the decomposition of oxygen-containing intermediates on Pd surfaces. The dendritic mesoporous morphology of the ternary PdBP MSs also accelerates electron/mass transfer and exposes numerous active sites, enabling better performance in the ORR and AORs. Extending the surfactant-templating synthetic route to multiple types of elements will enable the generation of libraries of multicomponent metal-metalloid-nonmetal alloy nanostructures with functions that are suitable for various targeted applications.

Real-Time Label-Free Kinetics Monitoring of Trypsin-Catalyzed Ester Hydrolysis by a Nanopore Sensor.

Trypsin is an important proteolytic enzyme in the digestive system and its activity is a major indicator for evaluating diseases such as chronic pancreatitis. Here, we present a novel label-free method to detect trypsin kinetics using a nanopore technique. A mutant α-hemolysin (M113R)7 protein nanopore equipped with a polyamine decorated ß-cyclodextrin (am7ß-CD) was employed as a sensing platform for the real-time monitoring of the process of trypsin enzymatic cleavage of a substrate Nα-benzoyl-l-arginine ethyl ester (BAEE) at the single molecule level. Significantly, this sensor can exclusively respond to the current modulation caused by the product and prevent interference from the substrate, thus improving detection sensitivity, and it provides a new scheme to detect enzyme activity for cleaving small molecules.

The excellent performance of nest-like oxygen-deficient Cu1.5Mn1.5O4 applied in activated carbon air-cathode microbial fuel cell.

This study investigated the performance of nano spinel nest-like oxygen-deficient Cu1.5Mn1.5O4 doping activated carbon (AC) as air cathode in microbial fuel cell (MFC). The Cu1.5Mn1.5O4 was synthesized via hydrothermal method and subsequent annealed. The maximum power density (MPD) of MFC with oxygen-deficient Cu1.5Mn1.5O4 modified cathode was 1928±18mWm-2, which was 1.53 times higher than the bare cathode. The electrochemical studies showed that Cu1.5Mn1.5O4 doping AC exhibited higher kinetic activity and lower resistance. The mechanism of oxygen reduction for the catalyst was a four electron pathway. The oxygen deficient of Cu1.5Mn1.5O4 played an important role in catalytic activity. So Cu1.5Mn1.5O4 would be an excellent promising catalyst for ORR in MFC.

The addition of ortho-hexagon nano spinel Co3O4 to improve the performance of activated carbon air cathode microbial fuel cell.

Commercial Co3O4 and ortho-hexagon spinel nano-Co3O4 (OHSNC) were doped in the AC at a different percentage (5%, 10% and 15%) to enhance the performance of microbial fuel cell (MFC). The maximum power density of MFC with 10% OHSNC doped cathode was 1500±14 mW m(-2), which was 97.36% and 41.24% higher than that with the bare AC air cathode and commercial Co3O4 respectively. The electrocatalytic behavior for their better performance was discussed in detail with the help of various structural and electrochemical techniques. The OHSNC was characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results showed that the improved performance owed to the enhancement of both kinetics activity and the number of electron transfer in the ORR, and the internal resistance was largely reduced. Therefore, OHSNC was proved to be an excellent cathodic catalyst in AC air cathode MFC.