Semi‐Rationally Designed Short Peptides Self‐Assemble and Bind Hemin to Promote Cyclopropanation

The self‐assembly of short peptides gives rise to versatile nanoassemblies capable of promoting efficient catalysis. We have semi‐rationally designed a series of seven‐residue peptides that form hemin‐binding catalytic amyloids to facilitate enantioselective cyclopropanation with efficiencies that rival those of engineered hemin proteins. These results demonstrate that: 1) Catalytic amyloids can bind complex metallocofactors to promote practically important multisubstrate transformations. 2) Even essentially flat surfaces of amyloid assemblies can impart a substantial degree of enantioselectivity without the need for extensive optimization. 3) The ease of peptide preparation allows for straightforward incorporation of unnatural amino acids and the preparation of peptides made from d ‐amino acids with complete reversal of enantioselectivity.     

Semi-Rationally Designed Short Peptides Self-Assemble and Bind Hemin to Promote Cyclopropanation

The self-assembly of short peptides gives rise to versatile nanoassemblies capable of promoting efficient catalysis. We have semi-rationally designed a series of seven-residue peptides that form hemin-binding catalytic amyloids to facilitate enantioselective cyclopropanation with efficiencies that rival those of engineered hemin proteins. These results demonstrate that: 1) Catalytic amyloids can bind complex metallocofactors to promote practically important multisubstrate transformations. 2) Even essentially flat surfaces of amyloid assemblies can impart a substantial degree of enantioselectivity without the need for extensive optimization. 3) The ease of peptide preparation allows for straightforward incorporation of unnatural amino acids and the preparation of peptides made from d -amino acids with complete reversal of enantioselectivity.     

Coupling Titanium and Chromium Catalysis in a Reaction Network for the Reprogramming of [BH4]− as Electron Transfer and Hydrogen Atom Transfer Reagent for Radical Chemistry

We describe a unique catalytic system with an efficient coupling of Ti- and Cr-catalysis in a reaction network that allows the use of [BH₄]⁻ as stoichiometric hydrogen atom and electron donor in catalytic radical chemistry. The key feature is a relay hydrogen atom transfer from [BH₄]⁻ to Cr generating the active catalysts under mild conditions. This enables epoxide reductions, regiodivergent epoxide opening and radical cyclizations that are not possible with cooperative catalysis with radicals or by epoxide reductions via Meinwald rearrangement and ensuing carbonyl reduction. No typical S_N2-type reactivity of [BH₄]⁻ salts is observed.     

MOF Encapsulated AuPt Bimetallic Nanoparticles for Improved Plasmonic-induced Photothermal Catalysis of CO2 Hydrogenation

Exploring new catalytic strategies for achieving efficient CO₂ hydrogenation under mild conditions is of great significance for environmental remediation. Herein, a composite photocatalyst Zr-based MOF encapsulated plasmonic AuPt alloy nanoparticles (AuPt@UiO-66-NH₂) was successfully constructed for the efficient photothermal catalysis of CO₂ hydrogenation. Under light irradiation at 150 °C, AuPt@UiO-66-NH₂ achieved a CO production rate of 1451 μmol g_metal⁻¹ h⁻¹ with 91 % selectivity, which far exceeded those obtained by Au@Pt@UiO-66-NH₂ with Pt shell on Au (599 μmol g_metal⁻¹ h⁻¹) and Au@UiO-66-NH₂ (218 μmol g_metal⁻¹ h⁻¹). The outstanding performances of AuPt@UiO-66-NH₂ were attributed to the synergetic effect originating from the plasmonic metal Au, doped active metal Pt, and encapsulation structure of UiO-66-NH₂ shell. This work provides a new way for photothermal catalysis of CO₂ and a reference for the design of high-performance plasmonic catalysts.     

Photochemical In Situ Exfoliation of Metal–Organic Frameworks for Enhanced Visible-Light-Driven CO2 Reduction

Two novel two-dimensional metal–organic frameworks (2D MOFs), 2D-M₂TCPE (M=Co or Ni, TCPE=1,1,2,2-tetra(4-carboxylphenyl)ethylene), which are composed of staggered (4,4)-grid layers based on paddlewheel-shaped dimers, serve as heterogeneous photocatalysts for efficient reduction of CO₂ to CO. During the visible-light-driven catalysis, these structures undergo in situ exfoliation to form nanosheets, which exhibit excellent stability and improved catalytic activity. The exfoliated 2D-M₂TCPE nanosheets display a high CO evolution rate of 4174 μmol g⁻¹ h⁻¹ and high selectivity of 97.3 % for M=Co and Ni, and thus are superior to most reported MOFs. The performance differences and photocatalytic mechanisms have been studied with theoretical calculations and photoelectric experiments. This study provides new insight for the controllable synthesis of effective crystalline photocatalysts based on structural and morphological coregulation.     

Heat-Treated Aerogel as a Catalyst for the Oxygen Reduction Reaction

Aerogels are fascinating materials that can be used for a wide range of applications, one of which is electrocatalysis of the important oxygen reduction reaction. In their inorganic form, aerogels can have ultrahigh catalytic site density, high surface area, and tunable physical properties and chemical structures—important features in heterogeneous catalysis. Herein, we report on the synthesis and electrocatalytic properties of an iron–porphyrin aerogel. 5,10,15,20-(Tetra-4-aminophenyl)porphyrin (H₂TAPP) and Fe^II were used as building blocks of the aerogel, which was later heat-treated at 600 °C to enhance electronic conductivity and catalytic activity, while preserving its macrostructure. The resulting material has a very high concentration of atomically dispersed catalytic sites (9.7×10²⁰ sites g⁻¹) capable of catalyzing the oxygen reduction reaction in alkaline solution (E_onset=0.92 V vs. RHE, TOF=0.25 e⁻ site⁻¹ s⁻¹ at 0.80 V vs. RHE).     

Activating Bi p-orbitals in Dispersed Clusters of Amorphous BiOx for Electrocatalytic Nitrogen Reduction

Catalytic strategies based on main group metals are significantly less advanced than those of transition metal catalysis, leaving untapped areas of potentially fruitful research. We here demonstrate an effective approach for the modulation of Bi 6p energy levels during the construction of atomically dispersed clusters of amorphous BiO_x. Bi oxidation state is proposed to strongly affects the nitrogen fixation activity, with the half-occupied p_z orbitals of the Bi²⁺ ions being highly efficient toward electron injection into the inert N₂ molecule. With sufficient catalytic sites to adsorb and activate N₂, the bonding between N₂ and catalyst is able to be in situ identified. The catalyst shows an outstanding Faraday efficiency (≈30 %) and high yield (≈113 μg h⁻¹ mg⁻¹_cat) in NH₃ production, outperforming most of the existing catalysts in aqueous solution. These results lay the basis for developing the potential of p-block elements for catalysis of multi-electron reactions.     

Insight into How Telomeric G‐Quadruplexes Enhance the Peroxidase Activity of Cellular Hemin

The toxic oxidative damage of G‐quadruplexes (G4), linked to neurodegenerative diseases, may arise from their ability to bind and oxidatively activate cellular hemin. However, there have been no precise studies on how telomeric G4 enhances the low intrinsic peroxidase activity of hemin. Herein, a label‐free and nanopore‐based strategy was developed to explore the enhancement mechanism of peroxidase activity of hemin induced by telomeric G4 (d(TTAGGG)_n). The nanopore‐based strategy demonstrated that there were simultaneously two different binding modes of telomere G4 to hemin. At the single‐molecule level, it was found that the hybrid structural telomeric G4 directly binds to hemin (the affinity constant (K_a)≈10⁶ m ^?1) to form a tight complex, and some of them underwent a topological change to a parallel structure with an enhancement of K_a to approximately 10⁷ m ^?1. Through detailed analysis of the topology and peroxidase activity and molecular modeling investigations, the parallel telomere G4/hemin DNAzyme structure was proven to be preferable for high peroxidase activity. Upon strong π–π stacking, the parallel structural telomere G4 supplied a key axial ligand to the hemin iron, which accelerated the intermediate compound formation with H₂O₂ in the catalytic cycle. Our studies developed a label‐free and single‐molecule strategy to fundamentally understand the catalytic activity and mechanism of telomeric DNAzyme, which provides some support for utilizing the toxic, oxidative‐damage property in cellular oxidative disease and anticancer therapeutics.     

Peroxidase activity-structure relationship of the intermolecular four-stranded G-quadruplex-hemin complexes and their application in Hg ion detection

The peroxidase activities of the complexes of hemin and intermolecular four-stranded G-quadruplexes formed by short-stranded X_nG_mX_p sequences (X = A, T or C), especially T_nG_mT_p sequences, were compared. The results, combining with those of circular dichroism (CD) spectra and acid-base transition study for DNA-hemin complexes, provide some important information about DNAzymes based on G-quadruplex-hemin complexes, such as the formation of a G-quadruplex structure is an important factor for determining whether a DNA sequence can enhance the catalytic activity of hemin; both intramolecular parallel G-quadruplexes and intermolecular four-stranded parallel G-quadruplexes can enhance the catalytic activity of hemin; the addition of T nucleotides to the 5′-end of a G-tract confers corresponding G-quadruplex greatly enhanced catalytic activity, whereas the addition of T nucleotides to the 3′-end of the G-tract has little effect; the high catalytic activity of hemin in the presence of some short-stranded G-rich sequences may be a result of the reduction of the acidity of the bound hemin cofactor. These studies provide more information for the DNA-hemin peroxidase model system, may help to elucidate the structure-function relationship of peroxidase enzymes and to develop novel, highly efficient peroxidase-liking DNAzymes. As a sequence of such an investigation, a new Hg²⁺ detection method was developed.     

Lattice Distortion and H-passivation in Pure Carbon Electrocatalysts for Efficient and Stable Two-electron Oxygen Reduction to H2O2

The exploration of inexpensive and efficient catalysts for oxygen reduction reaction (ORR) is crucial for chemical and energy industries. Carbon materials have been proved promising with different catalysts enabling 2 and 4e⁻ ORR. Nevertheless, their ORR activity and selectivity is still complex and under debate in many cases. Many structures of these active carbon materials are also chemically unstable for practical implementations. Unlike the well-discussed structures, this work presents a strategy to promote efficient and stable 2e⁻ ORR of carbon materials through the synergistic effect of lattice distortion and H-passivation (on the distorted structure). We show how these structures can be formed on carbon cloth, and how the reproducible chemical adsorption can be realized on these structures for efficient and stable H₂O₂ production. The work here gives not only new understandings on the 2e⁻ ORR catalysis, but also the robust catalyst which can be directly used in industry.     

A Phage Display-Identified Short Peptide Capable of Hydrolyzing Calcium Pyrophosphate Crystals—The Etiological Factor of Chondrocalcinosis

Chondrocalcinosis is a metabolic disease caused by the presence of calcium pyrophosphate dihydrate crystals in the synovial fluid. The goal of our endeavor was to find out whether short peptides could be used as a dissolving factor for such crystals. In order to identify peptides able to dissolve crystals of calcium pyrophosphate, we screened through a random library of peptides using a phage display. The first screening was designed to select phages able to bind the acidic part of alendronic acid (pyrophosphate analog). The second was a catalytic assay in the presence of crystals. The best-performing peptides were subsequently chemically synthesized and rechecked for catalytic properties. One peptide, named R25, turned out to possess some hydrolytic activity toward crystals. Its catalysis is Mg²⁺-dependent and also works against soluble species of pyrophosphate.     

Highly Stable Copper(I)–Thiacalix[4]arene-Based Frameworks for Highly Efficient Catalysis of Click Reactions in Water

Environmentally friendly metal–organic frameworks (MOFs) have gained considerable attention for their potential use as heterogeneous catalysts. Herein, two Cu^I-based MOFs, namely, [Cu₄Cl₄L] ⋅ CH₃OH ⋅ 1.5 H₂O ( 1-Cl ) and [Cu₄Br₄L] ⋅ DMF ⋅ 0.5 H₂O ( 1-Br ), were assembled with new functionalized thiacalix[4]arenes (L) and halogen anions X⁻ (X=Cl and Br) under solvothermal conditions. Remarkably, catalysts 1-Cl and 1-Br exhibit great stability in aqueous solutions over a wide pH range. Significantly, MOFs 1-Cl and 1-Br , as recycled heterogeneous catalysts, are capable of highly efficient catalysis for click reactions in water. The MOF structures, especially the exposed active Cu^I sites and 1D channels, play a key role in the improved catalytic activities. In particular, their catalytic activities in water are greatly superior to those in organic solvents or even in mixed solvents. This work proposes an attractive route for the design and self-assembly of environmentally friendly MOFs with high catalytic activity and reusability in water.     

One-Dimensional Covalent Organic Frameworks for the 2e− Oxygen Reduction Reaction

Two-dimensional covalent organic frameworks (2D COFs) are often employed for electrocatalytic systems because of their structural diversity. However, the efficiency of atom utilization is still in need of improvement, because the catalytic centers are located in the basal layers and it is difficult for the electrolytes to access them. Herein, we demonstrate the use of 1D COFs for the 2e⁻ oxygen reduction reaction (ORR). The use of different four-connectivity blocks resulted in the prepared 1D COFs displaying good crystallinity, high surface areas, and excellent chemical stability. The more exposed catalytic sites resulted in the 1D COFs showing large electrochemically active surface areas, 4.8-fold of that of a control 2D COF, and thus enabled catalysis of the ORR with a higher H₂O₂ selectivity of 85.8 % and activity, with a TOF value of 0.051 s⁻¹ at 0.2 V, than a 2D COF (72.9 % and 0.032 s⁻¹). This work paves the way for the development of COFs with low dimensions for electrocatalysis.     

Are Two Metal Ions Better than One? Mono- and Binuclear α-Diimine-Re(CO)3 Complexes with Proton-Responsive Ligands in CO2 Reduction Catalysis

Here, the reduction chemistry of mono- and binuclear α-diimine-Re(CO)₃ complexes with proton responsive ligands and their application in the electrochemically-driven CO₂ reduction catalysis are presented. The work was aimed to investigate the impact of 1) two metal ions in close proximity and 2) an internal proton source on catalysis. Therefore, three different Re complexes, a binuclear one with a central phenol unit, 3 , and two mononuclear, one having a central phenol unit, 1 , and one with a methoxy unit, 2 , were utilised. All complexes are active in the CO₂-to-CO conversion and CO is always the major product. The catalytic rate constant k_cat for all three complexes is much higher and the overpotential is lower in DMF/water mixtures than in pure DMF (DMF=N,N-dimethylformamide). Cyclic voltammetry (CV) studies in the absence of substrate revealed that this is due to an accelerated chloride ion loss after initial reduction in DMF/water mixtures in comparison to pure DMF. Chloride ion loss is necessary for subsequent CO₂ binding and this step is around ten times faster in the presence of water [ 2 : k^Cl(DMF)≈1.7 s⁻¹; k^Cl(DMF/H₂O)≈20 s⁻¹]. The binuclear complex 3 with a proton responsive phenol unit is more active than the mononuclear complexes. In the presence of water, the observed rate constant k_obs for 3 is four times higher than of 2 , in the absence of water even ten times. Thus, the two metal centres are beneficial for catalysis. Lastly, the investigation showed that the phenol unit has no impact on the rate of the catalysis, it even slows down the CO₂-to-CO conversion. This is due to an unproductive, competitive side reaction: After initial reduction, 1 and 3 loose either Cl⁻ or undergo a reductive OH deprotonation forming a phenolate unit. The phenolate could bind to the metal centre blocking the sixth coordination site for CO₂ activation. In DMF, O−H bond breaking and Cl⁻ ion loss have similar rate constants [ 1 : k^Cl(DMF)≈2 s⁻¹, k^OH≈1.5 s⁻¹], in water/DMF Cl⁻ loss is much faster. Thus, the effect on the catalytic rate is more pronounced in DMF. However, the acidic protons lower the overpotential of the catalysis by about 150 mV.     

Evidence for the metal-cofactor independence of an RNA phosphodiester-cleaving DNA enzyme

Background: RNA and DNA are polymers that lack the diversity of chemical functionalities that make proteins so suited to biological catalysis. All naturally occurring ribozymes (RNA catalysts) that catalyze the formation, transfer and hydrolysis of phosphodiesters require metal-ion cofactors for their catalytic activity. We wished to investigate whether, and to what extent, DNA molecules could catalyze the cleavage (by either hydrolysis or transesterification) of a ribonucleotide phosphodiester in the absence of divalent or higher-valent metal ions or, indeed, any other cofactors.Results: We performed in vitro selection and amplification experiments on a library of random-sequence DNA that incorporated a single ribonucleotide, a suitable site for cleavage. Following 12 cycles of selection and amplification, a ‘first generation’ of DNA enzymes (DNAzymes) cleaved their internal ribonucleotide phosphodiesters at rates ∼ 10⁷-fold faster than the spontaneous rate of cleavage of the dinucleotide ApA in the absence of divalent cations. Re-selection from a partially randomized DNA pool yielded ‘second generation’ DNAzymes that self-cleaved at rates of ∼ 0.01 min⁻¹ (a 10⁸-fold rate enhancement over the cleavage rate of ApA). The properties of these selected catalysts were different in key respects from those of metal-utilizing ribozymes and DNAzymes. The catalyzed cleavage took place in the presence of different chelators and ribonuclease inhibitors. Trace-metal analysis of the reaction buffer (containing very high purity reagents) by inductively coupled plasma-optical emission spectrophotometry indicated that divalent or higher-valent metal ions do not mediate catalysis by the DNAzymes.Conclusions: Our results indicate that, although ribozymes are sometimes regarded generically to be metalloenzymes, the nucleic acid components of ribozymes may play a substantial role in the overall catalysis. Given that metal cofactors increase the rate of catalysis by ribozymes only ∼ 10²−10³-fold above that of the DNAzyme described in this paper, it is conceivable that substrate positioning, transition-state stabilization or general acid/base catalysis by the nucleic acid components of ribozymes and DNAzymes may contribute significantly to their overall catalytic performance.     

Effect of Building Block Transformation in Covalent Triazine-Based Frameworks for Enhanced CO2 Uptake and Metal-Free Heterogeneous Catalysis

Covalent triazine frameworks (CTFs) have provided a unique platform in functional material design for a wide range of applications. This work reports a series of new CTFs with two new heteroaromatic building blocks (pyrazole and isoxazole groups) through a building-block transformation approach aiming for carbon capture and storage (CCS) and metal-free catalysis. The CTFs were synthesized from their respective building blocks [(4,4′-(1H-pyrazole-3,5-diyl)dibenzonitrile (pyz) and 4,4′-(isoxazole-3,5-diyl)dibenzonitrile (isox))] under ionothermal conditions using ZnCl₂. Both of the building blocks were designed by an organic transformation of an acetylacetone containing dinitrile linker to pyrazole and isoxazole groups, respectively. Due to this organic transformation, (i) linker aromatization, (ii) higher surface areas and nitrogen contents, (iii) higher aromaticity, and (iv) higher surface basicity was achieved. Due to these enhanced properties, CTFs were explored for CO₂ uptake and metal-free heterogeneous catalysis. Among all, the isox-CTF, synthesized at 400 °C, showed the highest CO₂ uptake (4.92 mmol g⁻¹ at 273 K and 2.98 mmol g⁻¹ at 298 K at 1 bar). Remarkably, these CTFs showed excellent metal-free catalytic activity for the aerobic oxidation of benzylamine at mild reaction conditions. On studying the properties of the CTFs, it was observed that organic transformations and ligand aromatization of the materials are crucial factor to tune the important parameters that influence the CO₂ uptake and the catalytic activity. Overall, this work highlights the substantial effect of designing new CTF materials by building-block organic transformations resulting in better properties for CCS applications and heterogeneous catalysis.     

[HP(HNCH2CH2)3N]NO3: an efficient homogeneous and solid-supported promoter for aza and thia-Michael reactions and for Strecker reactions

In the presence of a catalytic amount of an azaphosphatrane nitrate salt, amines and thiols react readily with Michael acceptors. The salt is also an efficient promoter for the one pot synthesis of α-amino and α-amidonitriles. By anchoring the salt to Merrifield Resin, a reusable heterogeneous catalyst is obtained for these reactions. Evidence is presented for catalysis being attributable solely to the NO₃⁻ ion.     

Suzuki–Miyaura Cross-Coupling of Bromotryptophan Derivatives at Ambient Temperature

Mild reaction conditions are highly desirable for bio-orthogonal side chain derivatizations of amino acids, peptides or proteins due to the sensitivity of these substrates. Transition metal catalysed cross-couplings such as Suzuki–Miyaura reactions are highly versatile, but usually require unfavourable reaction conditions, in particular, when applied with aryl bromides. Ligand-free solvent-stabilised Pd-nanoparticles represent an efficient and sustainable alternative to conventional phosphine-based catalysts, because the cross-coupling can be performed at considerably lower temperature. We report on the application of such a highly reactive heterogeneous catalyst for the Suzuki–Miyaura cross-coupling of brominated tryptophan derivatives. The solvent-stabilised Pd-nanoparticles are even more efficient than the literature-known ADHP-Pd precatalyst. Interestingly, the latter also leads to the formation of quasi-homogeneous Pd-nanoparticles as the catalytic species. One advantage of our approach is the compatibility with aqueous and aerobic conditions at near-ambient temperatures and short reaction times of only 2 h. The influence of different N^α-protecting groups, boronic acids as well as the impact of different amino acid side chains in bromotryptophan-containing peptides has been studied. Notably, a surprising acceleration of the catalysis was observed when palladium-coordinating side chains were present in proximal positions.     

Cooperative catalysis and critical decomposition distances in water oxidation by tris(ethylenediamine)ruthenium (III) complex confined in a Nafion membrane

The activity of tris(ethylenediamine)ruthenium (III) complex, [Ru(en)₃]³⁺, as a water oxidation catalyst was studied in a homogeneous aqueous solution and a heterogeneous Nafion (Nf) membrane. In the aqueous solution, the apparent catalytic activity (k_app (s⁻¹)) decreased monotonously with the concentration due to a bimolecular decomposition of the complex. The bimolecular decomposition of the complex was remarkably suppressed by incorporating it into a Nf membrane. An optimum complex concentration for k_app in the Nf membrane was exhibited, which was explained both by a cooperative catalysis and a bimolecular decomposition of the complex. The k_app in the Nf membrane was analyzed in terms of an intrinsic catalytic activity (k_O2 (s⁻¹)) of the complex, a cooperative catalysis distance (r_co (nm)) and a critical decomposition distance (r_d (nm)) between them based on intermolecular distance distribution to obtain the k_O2=8.5×10⁻⁵ s⁻¹, r_co=1.44 nm and r_d=1.07 nm. The results in the [Ru(en)₃]³⁺ system were compared with those obtained in the [Ru(NH₃)₆]³⁺ system.     

Generation and Stabilization of a Dinickel Catalyst in a Metal-Organic Framework for Selective Hydrogenation Reactions

Although many monometallic active sites have been installed in metal–organic frameworks (MOFs) for catalytic reactions, there are no effective strategies to generate bimetallic catalysts in MOFs. Here we report the synthesis of a robust, efficient, and reusable MOF catalyst, MOF-NiH, by adaptively generating and stabilizing dinickel active sites using the bipyridine groups in MOF-253 with the formula of Al(OH)(2,2′-bipyridine-5,5′-dicarboxylate) for Z-selective semihydrogenation of alkynes and selective hydrogenation of C=C bonds in α,β-unsaturated aldehydes and ketones. Spectroscopic studies established the dinickel complex (bpy⋅⁻)Ni^II(μ₂-H)₂Ni^II(bpy⋅⁻) as the active catalyst. MOF-NiH efficiently catalyzed selective hydrogenation reactions with turnover numbers of up to 192 and could be used in five cycles of hydrogenation reactions without catalyst leaching or significant decrease of catalytic activities. The present work uncovers a synthetic strategy toward solution-inaccessible Earth-abundant bimetallic MOF catalysts for sustainable catalysis.