High Levels Of Catalytic Activity Research Articles

Erbium doped samarium oxide nanoballs functionalized cluster surface as a robust electrocatalyst for efficient water oxidation

The oxygen evolution reaction (OER) is a crucial energy-storing and energy-changing half-process in water splitting. It is critical to expand the availability of renewable energy reservoirs, and effective electrodes must be robust and possess a high level of catalytic activity. However, it is difficult to eliminate overpotential and improve the performance of OER. In this study, Erbium (Er)-doped samarium oxide (Sm2O3) was synthesized by a facile co-precipitation technique. Using X-ray diffraction analysis, it was determined that a Sm2O3 cubic structure was formed when sharp peaks were observed. Using Fourier-transform infrared (FTIR spectroscopy) and scanning electron spectroscopy (SEM) pictures, the existence of Sm2O3 crystals was detected and surface geometry was observed. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) confirm the successful Er doping in Sm2O3. The OER activities of pure Sm2O3 and Sm2O3 coupled with Er were determined using electrochemical. In comparison to pure Sm2O3, a high amount of Er-doped Sm2O3 possessed a low overpotential (365 mV for the OER) and a small Tafel slope (47 mV/dec). Consequently, OER became extremely active, metal oxide's structure and catalytic capabilities were altered by inclusion of rare earth metals. Erbium is an essential component when doped in Sm2O3 that improves the performance of OER. Among all 2% Er doped Sm2O3 is an excellent material for energy conversion.

Using energy to go downhill-a genoprotective role for ATPase activity in DNA topoisomerase II.

Type II topoisomerases effect topological changes in DNA by cutting a single duplex, passing a second duplex through the break, and resealing the broken strand in an ATP-coupled reaction cycle. Curiously, most type II topoisomerases (topos II, IVand VI) catalyze DNA transformations that are energetically favorable, such as the removal of superhelical strain; why ATP is required for such reactions is unknown. Here, using human topoisomerase IIβ (hTOP2β) as a model, we show that the ATPase domains of the enzyme are not required for DNA strand passage, but that their loss elevates the enzyme's propensity for DNA damage. The unstructured C-terminal domains (CTDs) of hTOP2β strongly potentiate strand passage activity in ATPase-less enzymes, as do cleavage-prone mutations that confer hypersensitivity to the chemotherapeutic agent etoposide. The presence of either the CTD or the mutations lead ATPase-less enzymes to promote even greater levels of DNA cleavage in vitro, as well as in vivo. By contrast, aberrant cleavage phenotypes of these topo II variants is significantly repressed when the ATPase domains are present. Our findings are consistent with the proposal that type II topoisomerases acquired ATPase function to maintain high levels of catalytic activity while minimizing inappropriate DNA damage.

Highly porous interconnected MoP decorated graphene oxide as remarkably efficient electrocatalyst

Hydrogen (H2) production through water splitting has less viable applications due to the unfavourable kinetics of the reaction. Electrocatalysts with a robust structure, high levels of catalytic activity, and a high degree of stability are in high demand but challenging. This paper reports the synthesis of highly porous interconnected molybdenum phosphide (MoP) assembled with graphene oxide (GO) to form MoP/RGO hybrid electrocatalysts in a novel phosphorization process at a reasonably low temperature under an argon (Ar) atmosphere by a mixing and heat-treating method for the hydrogen evolution reaction (HER). Bifunctional MoP anchored on reduced graphene oxide (MoP/RGO) porous structures exhibited extra permeability for ion and electrolyte transport. An efficient MoP/RGO-based electrocatalyst exhibited brilliant electrocatalytic performance, having HER overpotential of 96 mV at a current density of 10 mA/cm2 with a low Tafel slope of 64 mV/dec in an alkaline solution. The effectiveness of an optimised electrocatalyst indicates significant HER activity for all intermediate chemical reactions. A highly efficient electrocatalyst also exhibited long-term stability with a minor potential decrease over 24 h. RGO shows great potential as a material possessing remarkable strength in the context of high temperature phosphorization. It effectively hinders particle agglomeration, enhances catalyst conductivity, and ultimately betters both the performance and durability of an electrocatalyst in HER applications.

Breaking the N-limitation with N-enriched porous submicron carbon spheres anchored Fe single-atom catalyst for superior oxygen reduction reaction and Zn-air batteries

Nitrogen-doped carbon supported metal single-atom catalysts (M-N-C SACs), especially Fe-N-C SACs appear as very promising catalysts for oxygen reduction reaction (ORR). However, precisely modulating of the Fe-Nx configuration and geometric microenvironment in Fe-N-C SACs to achieve the highest level of catalytic activity remains grand challenges. Herein, we describe a N-rich heterocycle regulated supramolecular coordination self-assembly strategy to fabricate Fe single atoms anchored on N-enriched porous submicron carbon spheres (FeSA/N-PSCS), with ultra-high N-dopant content (14.81 at.%) for facilitating the formation of atomically dispersed Fe-N4. Density functional theory calculations validate that N-doping at the periphery of the Fe-N4 active sites optimizes the adsorption of oxygen-containing intermediates and significantly reduces the ORR overpotential. Benefitting from the localized N-enriched atomic configuration, highly microporous, and regular submicron-spherical structure, FeSA/N-PSCS exhibit enhanced ORR performance. More importantly, FeSA/N-PSCS catalyzed Zn-air battery (ZAB) outperforms Pt/C+RuO2-based ZAB in the aspects of maximum power density, specific capacity and cycling stability.

Improvement of catalytic activity of aluminum complexes for the ring-opening polymerization of ε-caprolactone: aluminum thioamidate and thioureidate systems.

In this study, a series of Al complexes bearing amidates, thioamidates, ureidates, and thioureidates were synthesized and their catalytic activity for ε-caprolactone (CL) polymerization was evaluated. SPr-Al exhibited a higher catalytic activity than OPr-Al (3.2 times as high for CL polymerization; [CL] : [SPr-Al] : [BnOH] = 100 : 0.5 : 2; [SPr-Al] = 10 mM, conv. = 93% after 14 min at 25 °C), and USCl-Al exhibited a higher catalytic activity than UCl-Al (4.6 times as high for CL polymerization; [CL] : [USCl-Al] : [BnOH] = 100 : 0.5 : 2; [USCl-Al] = 10 mM, conv. = 90% after 15 min at 25 °C). Regardless of whether aluminum amidates or ureidates were present, thioligands improved the polymerization rate of aluminum catalysts. Density functional theory calculations revealed that the eight-membered ring [SPr-AlOMe2]2 decomposed into the four-membered ring SPr-AlOMe2. However, [OPr-AlOMe2]2 did not decompose because of its strong bridging Al-O bond. The overall activation energy required for CL polymerization was lower when using [SPr-AlOMe2]2 (18.1 kcal mol-1) as a catalyst than when using [OPr-AlOMe2]2 (23.9 kcal mol-1). This is because the TS2a transition state of SPr-AlOMe2 had a more open coordination geometry with a small N-Al-S angle (72.91°) than did TS3c of [OPr-AlOMe2]2, the crowded highest-energy transition state of [OPr-AlOMe2]2 with a larger N-Al-O angle (99.63°).

Tuning Enzyme Thermostability via Computationally Guided Covalent Stapling and Structural Basis of Enhanced Stabilization.

Enhancing the thermostability of enzymes without impacting their catalytic function represents an important yet challenging goal in protein engineering and biocatalysis. We recently introduced a novel method for enzyme thermostabilization that relies on the computationally guided installation of genetically encoded thioether “staples” into a protein via cysteine alkylation with the noncanonical amino acid O-2-bromoethyl tyrosine (O2beY). Here, we demonstrate the functionality of an expanded set of electrophilic amino acids featuring chloroacetamido, acrylamido, and vinylsulfonamido side-chain groups for protein stapling using this strategy. Using a myoglobin-based cyclopropanase as a model enzyme, our studies show that covalent stapling with p-chloroacetamido-phenylalanine (pCaaF) provides higher stapling efficiency and enhanced stability (thermodynamic and kinetic) compared to the other stapled variants and the parent protein. Interestingly, molecular simulations of conformational flexibility of the cross-links show that the pCaaF staple allows fewer energetically feasible conformers than the other staples, and this property may be a broader indicator of stability enhancement. Using this strategy, pCaaF-stapled variants with significantly enhanced stability against thermal denaturation (ΔTm′ = +27 °C) and temperature-induced heme loss (ΔT50 = +30 °C) were obtained while maintaining high levels of catalytic activity and stereoselectivity. Crystallographic analyses of singly and doubly stapled variants provide key insights into the structural basis for stabilization, which includes both direct interactions of the staples with protein residues and indirect interactions through adjacent residues involved in heme binding. This work expands the toolbox of protein stapling strategies available for protein stabilization.

High-Performance Anode-Free Li–S Batteries with an Integrated Li2S–Electrocatalyst Cathode

To develop commercially viable lithium–sulfur batteries, it is critical to stabilize lithium deposition and mitigate lithium polysulfide (LiPS) shuttling, while minimizing excess Li. Here, we present the loading of Li2S nanoparticles into a carbon host that has been decorated with Co9S8 and Co (Li2S–Co9S8/Co) through a simple carbothermal reaction. The Co9S8/Co electrocatalyst functions as nucleation sites to ensure that Li2S is distributed uniformly throughout the composite. The molecular-level mixing of Li2S and the electrocatalyst provides a high level of catalytic activity toward Li–S redox to improve Li2S utilization and mitigate LiPS shuttling, which prevents the accumulation of large amounts of inactive Li2S on the Li anode, thus ensuring efficient utilization of Li in the cell. Benefiting from this rational design, a high capacity of 969 mA h g–1 is achieved in an anode-free cell with the Li2S–Co9S8/Co cathode. This work paves the way for the development of low-cost cathodes for anode-free Li–S batteries.

High-quality and deeply excavated PtPdNi nanocubes as efficient catalysts toward oxygen reduction reaction

The oxygen reduction reaction (ORR) on the cathode of a polymer electrolyte fuel cell requires the use of a catalyst based on Pt, one of the most expensive metals on the earth. A number of strategies, including optimization of a different metal into the core, have been investigated to enhance the activity of a Pt-based catalyst and thus reduce the loading of Pt. By dedicating to compounding high catalytic activity Pt2.7Pd0.3Ni concave cubic with high index crystal face, the paper shows that concave structures can offer more active site and high level of catalytic activity and if mixed with other metal, decrease the proportion of Pt and improve its mass activity. The paper also makes an exploration into the theory and conditions behind the formation of Pt2.7Pd0.3Ni concave cubic structure, and investigates the difference it demonstrates by modifying the reactive conditions. The results of the oxygen reduction performance of the electrochemical test are as follows: the concave cube-shaped Pt-Pd-Ni catalyst has a mass activity of 1.28 A mgPt–1 at 0.9 V, its highest mass activity is 8.20 times that of commercial Pt/C, and its specific activity is 8.68 times of that commercial Pt/C. And the Pt-Pd-Ni ternary nanocage has excellent structural invariance. After the stability test, there is no obvious structural change and performance degradation in the nanostructure.

Synthesis of Polymer–Metal Composites by the Impregnation of Hypercrosslinked Polystyrene with Palladium Compounds in Supercritical Carbon Dioxide and Their Catalytic Activity in the Liquid-Phase Hydrogenation of Diphenylacetylene

Composites—palladium metal particles in a polymer matrix—are obtained by impregnation of hypercrosslinked polystyrene with palladium compounds in supercritical carbon dioxide (SC-CO2) followed by molecular hydrogen reduction. The synthesized composites exhibit a high level of catalytic activity in the liquid-phase hydrogenation of diphenylacetylene (DPA). The turnover frequency (TOF) is 15–50 min–1 and the selectivity in the formation of diphenylethylene is 60–80% at ~90% conversion of the substrate.

Ni-supported catalysts on mesoporous carbon modified by Al(H2PO4)3 to obtain 1-propanol

The aim of this work was to investigate the catalytic properties of nickel over a carbon-based support modified with phosphorus for the hydrogenolysis of glycerol to obtain 1-propanol. For this, a series of nickel phosphide catalysts with different compositions were prepared employing Al(H2PO4)3 and NiCl2 supported on mesoporous carbon and characterized by N2 adsorption-desorption, acid-base properties measurements, TEM, XRD and XAFS analysis. These Ni catalysts presented different phases (NixPy, NiPOx, AlPOx), responsible of the increase in surface acidity, which depended on the Al(H2PO4)3 content. For Al(H2PO4)3 contents between 4 and 10 wt.%, an increase in surface acidity occurs that favors both the conversion and the selectivity of glycerol towards 1-propanol. These results show that the presence of the phosphates is necessary to reach high levels of catalytic activity. However, for Al(H2PO4)3 contents higher than 10 wt.%, a fall or loss of selectivity was produced due to the strong contribution of dehydration reactions on the support acid sites. The Ni/CPAl(10) catalyst, allows reaching 97 % conversion of glycerol with a selectivity of 74 % towards 1-propanol, employing an 80 wt.% glycerol aqueous solution, after 6 h of reaction.

Bidentate N‐based Ligands for Highly Reusable, Ligand‐coordinated, Supported Pt Hydrosilylation Catalysts

AbstractA significant challenge in designing supported metal‐ligand catalysts for solution‐phase reactions is the stabilization of the metal active sites against leaching into solution. Here, we examine alkene hydrosilylation reactions as model systems to improve the stability of highly dispersed Pt using a metal‐ligand coordination strategy on high surface area oxide supports. By evaluating a series of bidentate N‐based ligands, we demonstrate several design strategies to improve stability of the highly dispersed Pt2+ centers against leaching, while maintaining a high level of catalytic activity, selectivity, and recyclability for alkene hydrosilylation batch reactions under mild conditions. These involve a bi‐functional approach to ligand design, which considers interaction to the support and a well‐defined coordination environment for the metal active site. Three strategies are reported: modifying ligands for stronger interaction with oxide surfaces, mixing ligands, and pre‐depositing an “anchoring ligand” to the support before loading the metal‐ligand catalyst. Each of these is successful in enhancing Pt recyclability. Particularly, two Pt‐phenanthroline catalysts exhibit excellent reusability for multiple batch reaction cycles, due to high stability of the active Pt species. Addressing the active site leaching problem significantly enhances the utility of ligand‐coordinated supported metal catalysts as highly stable and selective catalysts for solution‐phase reactions.

Investigating the structural properties of the active conformation BTL2 of a lipase from Geobacillus thermocatenulatus in toluene using molecular dynamic simulations and engineering BTL2 via in-silico mutation.

The discovery or development of thermoalkalophilic lipases that show high levels of catalytic activity in organic solvents would have important industrial ramifications. However, this goal is yet to be achieved because organic solvents induce structural changes in lipases that suppress their catalytic abilities. A deep understanding of these structural changes to lipases in the presence of organic solvents is required before strategies can be devised to stop them from occurring. In this work, we investigated the effects of an organic reaction medium, toluene, on the structure of the Bacillus thermocatenulatus lipase BTL2 using MD simulation. The main aims were to identify the regions of the protein that are particularly sensitive to the presence of an organic solvent, and how the presence of a hydrophobic medium affects the overall stability of the enzyme. Upon analyzing how the behavior of the enzyme differed in aqueous and hydrophobic media, it was found that many significant zones of the protein suffer in the presence of an organic solvent, which increases the rigidity of the system. This was readily apparent when we investigated important noncovalent interactions (salt bridges) and probed how distances between the atoms of the catalytic triad Ser114, Asp318, and His359 change in the presence of toluene. Moreover, the high tendency for the system to destabilize in toluene was explained by the results of FoldX calculations. Calculations showed that the addition of a small amount of water to the hydrophobic reaction environment should restore the required flexibility of BTL2. The insights gained from the analysis of our simulations allowed us to propose a modification of BTL2, the G116P mutation, that should result in the structural behavior of BTL2 in organic solvent being closer to that of BTL2 in water.

CO2 Reforming of Methane over Ni/MgO Catalysts Promoted with Zr and La Oxides

AbstractAn investigation on carbon dioxide reforming of methane (DRM) to synthesis gas (H2 and CO) was carried out with several synthesized Ni‐based catalysts. Mixed oxide supports (MgO‐ZrO2 and MgO‐La2O3), were prepared using co‐precipitation method with K2CO3 as the precipitant. The findings indicated a high level of catalytic activity and stability of synthesized Ni‐based catalysts for DRM. Different techniques, namely, XRD, XPS, H2‐TPR, BET, TEM, FESEM, and TGA, were employed to perform the characterization of synthesized catalysts. It was found that with the addition of promoter Zr, the catalyst Ni/Mg0.85Zr0.15O showed a high level of activity (CH4; 86%, and CO2; 98%) and better stability. The significant anti‐coking activity of the reduced catalyst with low Ni metal was evaluated. Furthermore, this research study also examined the performance of the catalyst activity and stability. The results obtained from the temperature program reduction (H2‐TPR) revealed that the presence of ZrO2 with MgO support can enhance Ni reducibility in comparison to La2O3, which is an important indicator of high activity and stability of the Ni catalysts for DRM. It was also found that the presence of La2O3 did not show any effects on the stability of the catalyst.

An OPAA enzyme mutant with increased catalytic efficiency on the nerve agents sarin, soman, and GP.

The wild-type OPAA enzyme has relatively high levels of catalytic activity against several organophosphate G-type nerve agents. A series of mutants containing replacement amino acids at the OPAA Y212, V342, and I215 sites showed several fold enhanced catalytic efficiency on sarin, soman, and GP. One mutant, Y212F/V342L, showed enhanced stereospecificity on sarin and that enzyme along with a phosphotriesterase mutant, GWT, which had the opposite stereospecificity, were used to generate enriched preparations of each sarin enantiomer. Inhibition of acetylcholinesterase by the respective enantioenriched sarin solutions subsequently provided identification of the sarin enantiomers as separated by normal phase enantioselective liquid chromatography coupled with atmospheric pressure chemical ionization-mass spectrometry.

A Binaphthyl-Based Scaffold for a Chiral Dirhodium(II) Biscarboxylate Ligand with α-Quaternary Carbon Centers

A chiral dirhodium(II) paddlewheel complex has been synthesized from biscarboxylate ligands derived from BINOL, and the resulting complex has been used in enantioselective carbene/alkyne cascade reactions. The ligand design was guided by requirements of α,α-dimethyl substituted carboxylates and bidentate ligands to ensure high levels of catalytic activity. Previously disclosed chiral complexes lack these features, resulting in low product yields. The design successfully replicated or exceeded the yields of the unusually effective achiral catalyst for the cascade reaction, Rh2(esp)2, which often shows unique reactivity. Promising enantioselectivity was observed for aldehyde-derived hydrazone substrates (29–96% ee), showing that the new scaffold has significant potential.

Engineered Surface-Immobilized Enzyme that Retains High Levels of Catalytic Activity in Air

In the absence of aqueous buffer, most enzymes retain little or no activity; however, "water-free" enzymes would have many diverse applications. Here, we describe the chemically precise immobilization of an enzyme on an engineered surface designed to support catalytic activity in air at ambient humidity. Covalent immobilization of haloalkane dehalogenase on a surface support displaying poly(sorbitol methacrylate) chains resulted in ∼40-fold increase in activity over lyophilized enzyme powders for the gas-phase dehalogenation of 1-bromopropane. The activity of the immobilized enzyme in air approaches 25% of the activity obtained in buffer for the immobilized enzyme. Poly(sorbitol methacrylate) appears to enhance activity by replacing protein-water interactions, thereby preserving the protein structure.

EstDZ3: A New Esterolytic Enzyme Exhibiting Remarkable Thermostability.

Lipolytic enzymes that retain high levels of catalytic activity when exposed to a variety of denaturing conditions are of high importance for a number of biotechnological applications. In this study, we aimed to identify new lipolytic enzymes, which are highly resistant to prolonged exposure to elevated temperatures. To achieve this, we searched for genes encoding for such proteins in the genomes of a microbial consortium residing in a hot spring located in China. After performing functional genomic screening on a bacterium of the genus Dictyoglomus, which was isolated from this hot spring following in situ enrichment, we identified a new esterolytic enzyme, termed EstDZ3. Detailed biochemical characterization of the recombinant enzyme, revealed that it constitutes a slightly alkalophilic and highly active esterase against esters of fatty acids with short to medium chain lengths. Importantly, EstDZ3 exhibits remarkable thermostability, as it retains high levels of catalytic activity after exposure to temperatures as high as 95°C for several hours. Furthermore, it exhibits very good stability against exposure to high concentrations of a variety of organic solvents. Interestingly, EstDZ3 was found to have very little similarity to previously characterized esterolytic enzymes. Computational modeling of the three-dimensional structure of this new enzyme predicted that it exhibits a typical α/β hydrolase fold that seems to include a “subdomain insertion”, which is similar to the one present in its closest homolog of known function and structure, the cinnamoyl esterase Lj0536 from Lactobacillus johnsonii. As it was found in the case of Lj0536, this structural feature is expected to be an important determinant of the catalytic properties of EstDZ3. The high levels of esterolytic activity of EstDZ3, combined with its remarkable thermostability and good stability against a range of organic solvents and other denaturing agents, render this new enzyme a candidate biocatalyst for high-temperature biotechnological applications.

Polyoxometalate/chitosan–electrochemically reduced graphene oxide as effective mediating systems for electrocatalytic reduction of persulfate

Heteropolymolybdate H4SiMo12O40 (SiMo12) and chitosan–electrochemically reduced graphene oxide (CS-ERGO) multilayer composite films have been processed on Indium tin oxide electrode (ITO) through electrochemical growth method. The use of CS favored the adsorption of negatively charged SiMo12 anions and thus facilitated the growth of the multilayered films. The presence of ERGO enhanced the area of conductive surface, which is beneficial for the increase of the coverage value of SiMo12 on the electrode. By combining these two materials, the loading of SiMo12 was significantly increased. Thus, the CS-ERGO/SiMo12 multilayer films provide more catalytically active centers, which results in a high level of catalytic activity towards the reduction of S2O82−. Results of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry indicated the successful fabrication of CS-ERGO/SiMo12 multilayer film modified electrode. Application of the proposed electrode in electrochemical sensing was further demonstrated by electrocatalytic reduction of persulfate. Amperometry showed that the proposed sensor exhibited a linear detection range for S2O82− from 0.67 to 30.62μM with excellent sensitivity of 0.0448μAμM−1 and a low detection limit of 0.05μM, which outperformed most previously reported electrochemical sensors. In addition, good anti-interference and stability was also demonstrated. These features make the new SiMo12 modified electrode an ideal substrate for S2O82− detection.

Preparation and characterization of HypoGel-supported Pd nanocatalysts for Suzuki reaction under mild conditions

A new heterogeneous catalyst composed of Pd nanoparticles immobilized within a HypoGel resin has been prepared in the absence of any ligands using an extensive cross-linking method. This newly developed nanocatalyst was characterized by N2 adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy and inductively coupled plasma-mass spectrometer (ICP-MS) techniques. TEM and XRD results revealed that the Pd nanoparticles were well dispersed with diameters in the range of 4–12 nm, and an average size of about 8 nm. The cross-linked Pd catalyst demonstrated excellent catalytic activity towards the synthesis of a series of biaryl compounds by the reaction of various aryl halides (e.g., bromides andiodides) with phenylboronic acid in the presence of tetrabutylammonium bromide. ICP-MS analysis indicated that there was only 0.25% weight loss of Pd (0.55 ± 0.02 ppm) from the supported catalyst after the first cycle reaction. Furthermore, the catalyst showed excellent reusability (up to five uses) with consistently high levels of catalytic activity following its recovery by filtration.

An ionic liquid catalyzed reusable protocol for one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-one under mild conditions

This article describes an efficient protocol for the syntheses of 2,3-dihydroquinazolinones. The synthetic utility of this methodology has been demonstrated with 30 different substrates. The reaction showed good functional group tolerance and high levels of catalytic activity.