Decrease In Catalytic Efficiency Research Articles

A Ru-Based Complex for Sustainable One-Pot Tandem Aerobic Oxidation-Knoevenagel Condensation Reactions.

Our novel binuclear complex-anchored Ru(III) catalyst, designed and assembled by sonicating 2,2'-(4,6-dihydroxy-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid), Ru(DMSO)4Cl2 and 4-methylpyridine, demonstrates remarkable efficiency and selectivity. It promotes one-pot reactions, including active methylenes and benzyl alcohols in water, via a tandem aerobic oxidation/Knoevenagel condensation process, yielding benzylidene malononitrile in excellent yields. The catalyst's ability to oxidize benzyl alcohols to aldehydes, which then undergo Knoevenagel condensation with active methylenes, makes it a multifunctional catalyst. Notably, the catalyst can be successfully retrieved and recycled for five successive rounds with no significant decrease in catalytic efficiency. The ICP study showed that no catalyst leaching was observed, indicating that the designed catalyst is indeed heterogeneous. The Ru catalyst outperformed other documented catalysts in terms of lower dose, shorter duration, decreased working temperature, and the absence of dangerous additives. This demonstrates the catalyst's robustness and sustainability, making it a promising candidate for future organic conversions and industrial uses.

Enhanced dye degradation using MIL-53(Fe)-Modified kraft lignin as a heterogeneous Fenton catalyst

MIL-53(Fe), a metal–organic framework (MOF), is capable of degrading harmful organic contaminants, but it has relatively low Fenton catalytic efficiency. To enhance the degradation performance of MIL-53(Fe), we synthesized MIL-53(Fe)-MKL by incorporating modified kraft lignin (MKL) into pristine MIL-53(Fe). The as-prepared composite demonstrated Fenton activity, degrading 97 % of methylene blue (MB) within 50 min. Compared to pristine MIL-53(Fe) (which achieved 62.4 % MB degradation), the MIL-53(Fe)-MKL composite showed a 34.6 % improvement in MB degradation under identical reaction conditions. The incorporated MKL promotes Fe2+ regeneration from Fe3+ in the Fenton process, activating H2O2 to produce OH radicals, which were identified through scavenging experiments and chemical dosimetry with ESR analysis. The MIL-53(Fe)-MKL composite was reused for at least five cycles without a significant decrease in catalytic efficiency. This reported catalyst takes advantage of both MKL and MIL-53(Fe) to enhance catalytic activity, providing a basis for developing innovative catalysts for organic pollutant degradation.

Pd Nanoparticle Supported on N‐Doped Carbon Derived from Sodium Alginate/Melamine Blends as Efficient Heterogeneous Catalyst for Heck Reactions

AbstractN‐doped porous carbon shows great potential in the field of heterogenous supports due to its high porosity, large surface area, rich active sites, and strong chelation with catalytic active metals species. Herein, we successfully prepared a novel N‐doped porous carbon derived from sodium alginate/melamine blends (SAMNC) with different mass ratio through a simple carbonization and activation process. Hierarchical porous structure of the derived N‐doped carbon has been confirmed with the SEM, TEM, and N2 adsorption characterization. After Na2PdCl4 solution impregnation and further reduction process, Pd0 nanoparticles have been uniformly immobilized on the SAMNC support to produce novel Pd@SAMNC catalyst. The optimal Pd@SAMNC‐0.6 possesses a high N content (5.13%), Pd content (5.90%), large BET specific surface area of 1884.5 m2·g−1. Positron annihilation lifetime spectroscopy (PALS) investigation of the porous carbon materials provided the sub‐nano level microporous information proofs of Pd@SAMNC‐0.6 had the capability to provide more active sites for reactions than commercial Pd supported on activated carbon (Pd@AC). Pd@SAMNC‐0.6 catalyst showed superior catalytic efficiency in Heck coupling reaction between aromatic halides and alkenes and can be recycled for 17 runs without significant decrease in catalytic efficiency.

Cu(I)-Glutathione Assembly Supported on ZIF-8 as Robust and Efficient Catalyst for Mild CO2 Conversions.

The Cu-glutathione (GSH) redox system, essential in biology, is designed here as a supramacromolecular assembly in which the tetrahedral 18e Cu(I) center loses a thiol ligand upon adsorption onto ZIF-8, as shown by EXAFS and DFT calculation, to generate a very robust 16e planar trigonal single-atom Cu(I) catalyst. Synergy between Cu(I) and ZIF-8, revealed by catalytic experiments and DFT calculation, affords CO2 conversion into high-value-added chemicals with a wide scope of substrates by reaction with terminal alkynes or propargyl amines in excellent yields under mild conditions and reuse at least 10 times without significant decrease in catalytic efficiency.

Cu(I)‐Glutathione Assembly Supported on ZIF‐8 as Robust and Efficient Catalyst for Mild CO2 Conversions

AbstractThe Cu‐glutathione (GSH) redox system, essential in biology, is designed here as a supramacromolecular assembly in which the tetrahedral 18e Cu(I) center loses a thiol ligand upon adsorption onto ZIF‐8, as shown by EXAFS and DFT calculation, to generate a very robust 16e planar trigonal single‐atom Cu(I) catalyst. Synergy between Cu(I) and ZIF‐8, revealed by catalytic experiments and DFT calculation, affords CO2 conversion into high‐value‐added chemicals with a wide scope of substrates by reaction with terminal alkynes or propargyl amines in excellent yields under mild conditions and reuse at least 10 times without significant decrease in catalytic efficiency.

Construction of Azo‐Linked Covalent Organic Frameworks via Monomer Exchange for Enhanced Photocatalytic Performance

AbstractThe structural uniqueness of covalent organic frameworks (COFs) has brought great potential for their applications in photocatalysis. Two novel azo‐linked COFs AZO‐B‐COF and AZO‐T‐COF were successfully constructed by the monomer exchange method. Significantly, two as‐synthesized azo COFs presented a much higher photodegradation rate of 96 % and 51 % for AZO‐T‐COF and AZO‐B‐COF, respectively, which was in sharp contrast to the almost 0 degradation rate of imine COFs. And as expected, AZO‐T‐COF could be cycled at least 5 runs without a significant decrease in catalytic efficiency. Systematical experiments and theoretical calculations showed that comparing with imine COFs, conjugated structure of azo COFs broadened the visible‐light absorption range and improved the transfer efficiency of the photocarriers. The N‐rich azo bonds acted as an electron acceptor and made the materials better planarity. This work not only enriches COFs family but also demonstrated the superiority of azo‐linked COFs.

Anthraquinone-based covalent organic framework as a recyclable direct hydrogen atom transfer photocatalyst for C-H functionalization.

Photocatalytic direct hydrogen atom transfer (d-HAT) is a synthetically important strategy to convert C-H bonds to useful C-X bonds. Herein we report the synthesis of an anthraquinone-based two-dimensional covalent organic framework, DAAQ-COF, as a recyclable d-HAT photocatalyst for C-H functionalization. Powder X-ray diffraction, N2 sorption isotherms, solid-state NMR spectra, infrared spectra, and thermogravimetric analysis characterized DAAQ-COF as a crystalline, porous COF with a stable ketoenamine linkage and strong absorption in the visible region. Under visible light irradiation, DAAQ-COF is photo-excited to cleave C(sp3)-H or C(sp2)-H bonds via HAT to generate reactive carbon radicals, which add to different radical acceptors to achieve C-N or C-C coupling reactions. DAAQ-COF is easily recovered from the reaction mixture via centrifugation or filtration and used in six consecutive reaction runs without any decrease in catalytic efficiency. The ease of catalyst separation allows sequential conversion of the C-N coupling intermediate to synthetically useful amide, ester, or thioester products. Photophysical and isotope labelling experiments support the d-HAT mechanism of DAAQ-COF-catalyzed C-H bond functionalization.

Uncovering the role of sorbitol in Renilla luciferase kinetics: Insights from spectroscopic and molecular dynamics studies

Renilla luciferase catalyzes the oxidation of coelenterazine to coelenteramide, resulting in the emission of a photon of light. This study investigated the impact of sorbitol on the structural and kinetic properties of Renilla luciferase using circular dichroism, fluorescence spectroscopy, and molecular dynamics simulations. Our investigation, carried out using circular dichroism and fluorescence analyses, as well as a thermal stability assay, has revealed that sorbitol induces conformational changes in the enzyme but does not improve its thermal stability. Moreover, through kinetic studies, it has been demonstrated that at a concentration of 0.4 M, sorbitol enhances the catalytic efficiency of Renilla luciferase. However, at higher concentrations, sorbitol results in a decrease in catalytic efficiency. Additionally, molecular dynamics simulations have shown that sorbitol increases the presence of hydrophobic pockets on the enzyme's surface. These simulations have also provided evidence that at a concentration of 0.4 M, sorbitol facilitates substrate access to the active site of the enzyme. Nevertheless, at higher concentrations, sorbitol obstructs substrate trafficking, most likely due to its impact on the gateway to the active site. This study may provide insights into the kinetic changes observed in enzymes with buried active sites, such as those with α/β hydrolase fold.

Palladium(II)-immobilized Triptycene based Hypercrosslinked Polymers: An Efficient, Green, and Reusable Heterogenous Catalyst for Suzuki-Miyaura Cross-coupling Reaction.

The Suzuki-Miyaura cross-coupling (SMCC) involves the coupling of organohalides and organoboron molecules in the presence of Pd(II)-based catalysts. Often SMCC reactions employ homogenous catalysts. However, such homogenous SMCC reactions are associated with certain limitations which has motivated design of effective and sustainable Pd(II)-based heterogeneous catalytic systems. Herein, we report a systematic development of a Pd(II)-immobilized and triptycene based ionic hyper crosslinked polymer (Pd@TP-iHCP) and explored its application as a heterogeneous catalyst for SMCC reaction. Pd@TP-iHCP has ample N-heterocyclic carbene (NHC) pendants that anchor Pd(II) centres on the polymeric matrix. Pd@TP-iHCP was characterized satisfactorily using FT-IR, 13 C CP-MAS NMR, BET surface area analysis, SEM, EDX and HRTEM. The performance of Pd@TP-iHCP as a heterogeneous catalyst for SMCC reactions was explored using various combinations of aryl boronic acids and aryl halides. Experimental results show that Pd@TP-iHCP is associated with a moderately high surface area. It is an efficient catalyst for SMCC (in aqueous media) with a modest loading of 0.8 mol % Pd(II)-catalyst since high yields of the expected products were obtained in shorter time intervals. Pd@TP-iHCP also features excellent stability and catalyst recyclability since it could be re-used for several cycles without any significant decrease in catalytic efficiency.

A novel POM/LDH/GO nanocomposite as highly efficient heterogeneous catalyst in green epoxidation of alkenes with hydrogen peroxide

In the present work, various transition metal substituted Keggin-type polyoxometalates/Ni-Al layered double hydroxide/graphene oxide (PWM/Ni-Al LDH/GO; M = Fe, Ni, Cu, Mn, Co, Cr, Zn) nanocomposites have been synthesized and utilized as catalysts in the epoxidation of alkenes. Results confirmed that in the epoxidation of alkenes, PWFe/Ni-Al LDH/GO nanocomposite could perform its role as the best catalyst. The selected nanocomposite evaluated as a heterogeneous catalyst in the green oxidation of various alkenes into the corresponding epoxides while aqueous hydrogen peroxide was used as an environmentally benign oxidant. The results of recovery and reusability experiments on PWFe/Ni-Al LDH/GO nanocomposite revealed that even after five times it could be easily reused without any considerable decrease in catalytic efficiency.

Recyclable bispyridine functionalized polyacrylonitrile fibers as ligand of Cu(II) for A3 coupling reaction

Developing an effective and economical technology to achieve the recovery of catalysts in the process of organometallic synthesis has attracted significant attention. Herein, a novel functional fiber catalyst with bispyridine structure was successfully constructed by modifying the commercial polyacrylonitrile fiber. Modified bidentate ligand fiber-based can be used to efficiently complexe Cu(II). The functional fibers were fully characterized by FTIR, ICP, XPS, XRD, SEM, and TGA. To verify the catalytic activity of PANbis(Py)-Cu(II)F, A3 coupling reaction was applied in this work. The results showed that only 0.1 mol% catalyst dosage was needed and the maximum isolated yield was up to 99%. Recycle experiments showed that PANbis(Py)-Cu(II)F has fine recycling performance, and there is no decrease in catalytic efficiency during the first six cycles. Consequently, as a recyclable functional fiber catalyst based on commercial polyacrylonitrile fiber, it provided a new insight for green synthesis and industrial production.

Emulsion-Directed Synthesis of Poly-Porphyrin Nanoparticles as Heterogeneous Photocatalysts for PET-RAFT Polymerization.

Heterogeneous photocatalysts have attracted extensive attention in photo-induced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization due to their remarkable advantages such as easy preparation, tunable photoelectric properties, and recyclability. In this study, zinc (II) 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (ZnTAPP)-based poly-porphyrin nanoparticles (PTAPP-Zn) are constructed by an emulsion-directed approach. It is investigated as a heterogeneous photocatalyst for PET-RAFT polymerization of various methacrylate monomers under visible light exposure, and the reactions show refined polymerization control with high monomer conversions. Furthermore, it is demonstrated that the PTAPP-Zn nanoparticles with the larger pore size enhance photocatalytic activity in PET-RAFT polymerization. In addition, the capabilities of oxygen tolerance and temporal control are demonstrated and PTAPP-Zn particles can be easily recycled and reused without an obvious decrease in catalytic efficiency.

Effect of Long-Term and Short-Term Droughts on the Hydrolytic Enzymes in Haplic Luvisol

The transformation of organic matter in the soil is largely determined by hydrolytic enzymes. Under the conditions of climate change, understanding the mechanisms of microbial response is of particular importance for predicting the carbon cycle. Until now, the effect of drought duration and frequency on soil hydrolytic enzymes has been little studied. A multifactorial field manipulation experiment was carried out, simulating in the presence of plants and without them: two short-term droughts, a long-term drought, and an optimal level of soil moisture. The maximum reaction rate Vmax, Michaelis constant Km, and catalytic efficiency Ka of five groups of enzymes involved in the carbon cycle (cellobiase, glucosidase, xylanase), phosphorus (phosphatase), and nitrogen (chitinase) were determined. In phosphatases, glucosidases, and xylanases, Vmax decreased during short-term drought. During prolonged drought, the Vmax value of phosphatases, cellobiohydrolases, and xylanases decreased and increased in chitinases, while remaining unchanged in glucosidases. Both long-term and short-term droughts led to an increase in Km and a decrease in catalytic efficiency (Ka) for almost all enzymes. Short-term droughts were not a “weakened version” of a long-term drought, but had their own specifics – a decrease in Km in glucosidases, which led to an increase in Ka. Long-term drought was characterized by an increase in Vmax of chitinases and spatial variability of Vmax of phosphatases and glucosidases. The influence of the presence of plants was secondary and affected only during short droughts. The reversibility of the effect of drought on Vmax, Km, Ka decreased in the series first short-term drought second short-term drought long-term drought due to an increase in the total duration of the stress impact.

Two non-active site residues W165 and L166 prominently influence the beta-lactam hydrolytic ability of OXA-23 beta-lactamase.

Dissemination of class D OXA-type carbapenemases is one of the significant causes of beta-lactam resistance in Gram-negative bacteria. The amino acid residues present near the active site are involved in hydrolytic mechanism of class D carbapenemases, though it is not identified in OXA-23. Here, with the help of site-directed mutagenesis, we aimed to explicate the importance of the residues W165, L166 and V167 of the possible omega loop and residue D222 in the short β5-β6 loop on the activity of OXA-23. All the residues were substituted with alanine. The resultant proteins were assayed for the changes in activity in E. coli cells and purified for in vitro activity, and stability assessment. E. coli cells harboring OXA-23_W165A and OXA-23_L166A, individually, exhibited a significant decrease in resistance towards beta-lactam antibiotics as compared to OXA-23. Further, purified OXA-23_W165A and OXA-23_L166A imparted about >4-fold decrease in catalytic efficiency and displayed reduced thermal stability as compared to OXA-23. Bocillin-FL binding assay revealed that W165A substitution results in improper N-carboxylation of K82, leading to deacylation deficient OXA-23. Therefore, we infer that the residue W165 maintains the integrity of N-carboxylated lysine (K82) of OXA-23 and the residue L166 might be responsible for properly orientating the antibiotic molecules.

Functional characterization of the p.(Gln195His) or Tainan and novel p.(Ser184Cys) or Toluca glucose-6-phosphate dehydrogenase (G6PD) gene natural variants identified through Mexican newborn screening for glucose-6-phosphate dehydrogenase deficiency

BackgroundNewborn screening for glucose-6-phosphate dehydrogenase deficiency (G6PDd) was implemented in Mexico beginning in 2017. In a Mexican population, genotyping analysis of G6PD as a second-tier method identified a previously unreported missense variant, p.(Ser184Cys), which we propose to call “Toluca”, and the extremely rare p.(Gln195His) or “Tainan” variant, which was previously described in the Taiwanese population as a Class II allele through in silico evaluations. Here, we sought to perform in vitro biochemical characterizations of the Toluca and Tainan G6PD natural variants and describe their associated phenotypes. MethodsThe “Toluca” and “Tainan” variants were identified in three unrelated G6PDd newborn males, two of whom lacked evidence of acute hemolytic anemia (AHA) or neonatal hyperbilirubinemia (NHB). We constructed wild-type (WT), Tainan, and Toluca G6PD recombinant enzymes and performed in vitro assessments. ResultsBoth variants had diminished G6PD expression, decreased affinities for glucose-6-phosphate and NADP+ substrates, significant decreases in catalytic efficiency (∼97 % with respect to WT-G6PD), and diminished thermostabilities that were partially rescued by NADP+. In silico protein modeling predicted that the variants would have destabilizing effects on the protein tertiary structure, potentially reducing the enzyme half-lives and/or catalytic efficiencies. ConclusionOur data suggest that G6PD “Tainan” and “Toluca” are potential Class II natural variants, which agrees with the absence of chronic nonspherocytic hemolytic anemia (CNSHA) in our patients. It remains to be determined whether these variants represent high-risk genetic factors for developing CNSHA, AHA, and/or NHB.

HIV-1 protease with 10 lopinavir and darunavir resistance mutations exhibits altered inhibition, structural rearrangements and extreme dynamics

Antiretroviral drug resistance is a therapeutic obstacle for people with HIV. HIV protease inhibitors darunavir and lopinavir are recommended for resistant infections. We characterized a protease mutant (PR10x) derived from a highly resistant clinical isolate including 10 mutations associated with resistance to lopinavir and darunavir. Compared to the wild-type protease, PR10x exhibits ∼3-fold decrease in catalytic efficiency and Ki values of 2–3 orders of magnitude worse for darunavir, lopinavir, and potent investigational inhibitor GRL-519. Crystal structures of the mutant were solved in a ligand-free form and in complex with GRL-519. The structures show altered interactions in the active site, flap-core interface, hydrophobic core, hinge region, and 80s loop compared to the corresponding wild-type protease structures. The ligand-free crystal structure exhibits a highly curled flap conformation which may amplify drug resistance. Molecular dynamics simulations performed for 1 μs on ligand-free dimers showed extremely large fluctuations in the flaps for PR10x compared to equivalent simulations on PR with a single L76V mutation or wild-type protease. This analysis offers insight about the synergistic effects of mutations in highly resistant variants.

Enzyme sensor for simultaneous determination of cholesterol, triglyceride and HDL cholesterol in serum.

A three-electrode lipid biosensor that simultaneously measures the total cholesterol (CHO), triglyceride (TG), and HDL cholesterol (HDL-C) in standard serum has been developed. The lipid biosensor is designed for clinical use where production cost, low sample requirement, portability, stability, and speed are high priorities. The device design filters out blood cells and lipoproteins from the serum, where the target molecules are catalyzed by enzymes encapsulated in carboxymethyl cellulose (CMC) to produce electron mediators, potassium ferrocyanide. These electron mediators were subsequently detected by amperometric determination. The sensor exhibit high selectivity towards the targets and can measure the target lipids in 4min with 10 µL of serum. Lastly, the device can be stored up to 18months with a minimal decrease in catalytic efficiency.

A Porphyrinic Donor-Acceptor Conjugated Porous Polymer as Highly Efficient Photocatalyst for PET-RAFT Polymerization.

Heterogeneous catalysts offer a highly desirable platform for exploring environmental-benign transformation systems, yet, they typically suffer from significant loss of catalytic efficiency compared with their homogeneous counterparts. Here, the facile synthesis of a porphyrinic conjugated porous polymer incorporated with imidazolium bromide moieties by taking advantage of the Debus-Radziszewski reaction is reported. Owing to the unique donor-acceptor structure, this heterogeneous and metal-free photocatalyst exhibits much improved catalytic activity compared with its small molecular analogs in photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, producing polymers with narrow distribution (Đ = 1.06-1.18) and high degree of chain-end fidelity. Moreover, the heterogeneous catalyst can be easily separated at the end of polymerization by centrifugation and recycled for five independent PET-RAFT polymerizations without obvious decreases in catalytic efficiency.

Efficient and recyclable bimetallic Co–Cu catalysts for selective hydrogenation of halogenated nitroarenes

Silica supported N-doped carbon layers encapsulating Co–Cu nanoparticles (Co1Cux@CN/SiO2) were prepared by a one-step impregnation of Co(NO3)2·6H2O, Cu(NO3)2·3H2O, urea and glucose, following in situ carbothermal reduction. Effects of Cu contents on the catalytic performance of the Co1Cux@CN/SiO2 catalysts were investigated for selective hydrogenation of p-chloronitrobenzene to p-chloroaniline. The Co1Cu0.30@CN/SiO2 with Cu/Co molar ratio of 0.30:1 presented much higher activity and stability than the monometallic Co@CN/SiO2 catalyst. The addition of Cu into Co1Cux@CN/SiO2 catalysts had favorable effects on the formation of highly active Co–N sites and N-doped carbon layer. The role of the N-doped carbon layer was to protect the Co from oxidation by air, and the Co1Cu0.30@CN/SiO2 could be reused for at least 12 cycles without decrease in catalytic efficiency. Mechanistic and in situ infrared studies revealed that the interaction effect between the Co and Cu atoms made the surface of Co highly electron rich, which decreased adsorption of halogen groups and resulting in the enhanced selectivity during chemoselective hydrogenation of halogenated nitroarenes for a wide scope of substrates.

A122S, A205V, D376E, W574L and S653N substitutions in acetolactate synthase (ALS) from Amaranthus palmeri show different functional impacts on herbicide resistance.

Amaranthus palmeri S. Watson, a problematic weed infesting summer crops in Argentina, has developed multiple herbicide resistance. Resistance to acetolactate synthase (ALS)-inhibiting herbicides is particularly common, with high-level resistance mostly caused by different mutations in the ALS enzyme. Six versions of the enzyme were identified from a resistant A. palmeri population, carrying substitutions D376E, A205V, A122S, A282D, W574L and S653N. This work aims to provide a comparative analysis of these mutants and the wild-type (WT) enzyme to fully understand the herbicide resistance. Thus, all the versions of the ALS gene from A. palmeri were heterologously expressed and purified to evaluate their kinetics and inhibitory response against imazethapyr, diclosulam, chlorimuron-ethyl, flucarbazone-sodium and bispyribac-sodium. A decrease in catalytic efficiency was detected in the A205V, A122S-A282D, W574L and S653N ApALS enzymes, whereas only A205V and W574L substitutions also produced a decrease in the substrate affinity. In vitro ALS inhibition assays confirmed cross-resistance to almost all the herbicides tested, with the exception of A282D ApALS, which was as susceptible as WT ApALS. Moreover, the results confirmed that the novel substitution A122S provides cross-resistance to at least one herbicide within each of the five families of ALS inhibitors, and this property could be explained by a lower number of hydrophobic interactions between the herbicides and the mutant enzyme. This is the first report to compare various mutations in vitro from A. palmeri ALS. Our data contribute to understanding the impacts of herbicide resistance in this species. © 2021 Society of Chemical Industry.