Attack Of Water Molecule Research Articles

Theoretical insights on potential-dependent oxidation behaviors and antioxidant strategies of MXenes

Significant efforts have been devoted to investigating the oxidation of MXenes in various environments. However, the underlying mechanism of MXene oxidation and its dependence on the electrode potential remain poorly understood. Here we show the oxidation behavior of MXenes under the working conditions of electrochemical processes in terms of kinetics and thermodynamics by using constant-potential ab initio simulations. The theoretical results indicate that the potential effects can be attributed to the nucleophilic attack of water molecules on metal atoms, similar to that taking place in the Oxygen Evolution Reaction. Building upon these findings, we deduced the oxidation potential of the common MXenes, and proposed antioxidant strategies for MXene. Finally, we demonstrated that MBenes, the boron analogs of MXenes, may undergo a similar nucleophilic attack in water and inferred that molecule-induced Walden inversion is widely present in material reconstructions. This work contributes to a fundamental understanding MXene stability at the atomic level, and promotes the transition in materials discovery from trial-and-error synthesis to rational design.

Organic-inorganic hybrid cathode enabled by in-situ interface polymerization engineering boosts Zn2+ desolvation in aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have attracted considerable attention for application in large-scale energy storage systems. However, the progress of RAZIBs has been hindered by the sluggish reaction kinetics and poor structural stability, which are closely associated with the desolvation process of hydrated Zn2+. To overcome these issues, an in situ interfacial polymerization strategy is proposed to uniformly germinate a polyaniline (PANI) layer on α-MnO2 and form an organic–inorganic hybrid cathode (MnO2@PANI). Theoretical calculations and experimental characterizations disclose that the polyaniline layer equipped with hydrophilic functional groups can effectively trap the active water molecules to break the strong attraction between H2O and Zn2+, thereby facilitating the desolvation process of hydrated Zn2+, and regulating the Zn2+ diffusion kinetics and electrode reaction kinetics on the cathode/electrolyte surface. Meanwhile, the irreversible phase evolution and dissolution of active species are largely suppressed due to the PANI shell protecting the α-MnO2 from the attack of active water molecules. As a consequence, the organic–inorganic hybrid cathode exhibits 401.9 mAh/g after 200 cycles at a current density of 0.5 A/g and long-term durability over 1000 cycles at a current density of 2.0 A/g without irreversible phase transformation. This work provides insight into the regulation of the desolvation process for high performance aqueous energy storage systems.

Direct Synthesis of Artificial Esterase through Molecular Imprinting Using a Substrate-Mimicking Acylthiourea Template.

Most reported artificial esterases hydrolyze only activated esters. We here report a one-pot synthesis of artificial esterases via molecular imprinting. An acylthiourea template hydrogen bonds with 4-vinylbenzoic acid and coordinates to a polymerizable zinc complex inside a cross-linkable surfactant micelle. Double cross-linking of the micelle yields a polymeric nanoparticle catalyst that mimics a metalloenzyme to activate a water molecule for nucleophilic attack on the bound ester. The catalyst hydrolyzes both activated and unactivated esters under mild conditions with selectivity.

Molecular mechanism of thiocyanate dehydrogenase at atomic resolution

Some sulfur-oxidizing bacteria playing an important role in global geochemical cycles utilize thiocyanate as the sole source of energy and nitrogen. In these bacteria the process of thiocyanate into cyanate conversion is mediated by thiocyanate dehydrogenases — a recently discovered family of copper-containing enzymes with the three‑copper active site unique among the other copper proteins. To get a deeper insight into the structure and molecular mechanism of action of thiocyanate dehydrogenases we isolated, purified, and comprehensively characterized an enzyme from the bacterium Pelomicrobium methylotrophicum. High-resolution crystal structures of the thiocyanate dehydrogenase in the free state and in the complexes with the transition state analog, thiourea, and the closest substrate analog, selenocyanate, unveiled the fine details of molecular events occurring at the enzyme active site. During the reaction thiocyanate dehydrogenase undergoes profound conformational change that affects the position of the constituent copper ions and results in the activation of the attacking water molecule. The structure of the enzyme complex with the selenium atom bridged in-between two copper ions was obtained representing an important transient intermediate. Structures of the complexes with inhibitors supplemented with quantum chemical calculations clarify the role of copper ions and refine molecular mechanism of catalysis by thiocyanate dehydrogenase.

Regulating Ru−O Bonding Interactions by Ir Doping Boosts the Acid Oxygen Evolution Performance

AbstractHighly active and stable oxygen evolution reaction (OER) catalysts are crucial for the large‐scale application of proton exchange membrane water electrolyzers. However, the dynamic reconfiguration of the catalyst surface structure and active centers is still undefined, which greatly hinders the development and application of efficient OER catalysts. Herein, we report an Ir0.3Ru0.7Ox/C catalyst with a facile low‐temperature synthesis route, which can reach 10 mA cm−2 at an overpotential of 217 mV with a Tafel slope as low as 39.4 mV dec−1, and yields a mass activity 61 times that of commercial IrO2/C at an overpotential of 300 mV. The lattice oxygen structure of RuOx is stabilized by the introduction of Ir species, thus greatly promoting the OER activity and durability. Further in situ Raman reveals that RuOx emerges as the active species at high potentials, and Ru−O bonding interactions are enhanced with Ir regulation, stabilizing the solvation of Ru at high potentials and accelerating the nucleophilic attack of water molecules, leading to the improved OER performance. This work deepens the fundamental understanding of OER and offers an effective way to advance the utilization of Ru‐based OER catalysts.

High-valence metal-doped amorphous IrOx as active and stable electrocatalyst for acidic oxygen evolution reaction

Proton-exchange membrane water electrolysis, particularly driven by renewable electricity, is a sustainable strategy for green hydrogen production. However, developing highly active and stable electrocatalysts to accelerate the oxygen evolution reaction (OER) remains challenging. Herein, we introduce an effective strategy for constructing high-valence metal-doped IrOx with abundant oxygen vacancies, while simultaneously enhancing the catalytic activity and stability of the acidic OER. The synthesized Ta-doped IrOx (350-Ta@IrOx) exhibits ultramicroscopic nanoparticle morphology and abundant surface oxygen vacancies</a>, enabling a rapid OER process with a low overpotential of 223 mV at 10 mA cm-2 and 147.7 times higher mass activity (1207.4 A gIr−1) than that of commercial IrO2 at 1.55 V</a> versus the reversible hydrogen electrode. More importantly, 350-Ta@IrOx affords excellent stability with insignificant potential degradation after 500 h of electrolysis at 10 mA cm2, originating from the low operating potential and suppressed dissolution and oxidation of oxygen vacancy active sites via Ta doping. Density functional theory calculations suggest that Ta doping and oxygen defect engineering are effective in facilitating the nucleophilic attack of water molecules, thereby accelerating the rate-determining step toward high catalytic OER activity on Ta-doped IrOx. We anticipate that this study will provide an effective method to obtain active and stable electrocatalysts via high-valence metal doping.

A Novel Approach for Development of Stable Quasi‐Solid Lithium‐O2 Batteries: Assembly and Performances of Double Layer Gel Polymer Electrolytes

AbstractGel‐polymer electrolytes (GPEs) offer a suitable alternative to flammable organic liquid electrolytes in lithium‐oxygen batteries (LOBs) to address safety concerns. However, a major challenge with GPEs is their low ionic conductivity. To enhance the ionic conductivity of GPEs, active inorganic particles have been incorporated. To increase the ionic conductivity of GPE, active inorganic particles have been reinforced in GPE. While this increases the ionic conductivity, it also leads to blockage of the cathode porous structure and reduces the actual surface area of the cathode materials, resulting in poor battery performance. This study proposes a novel double‐layer polymer gel electrolyte (d‐GPE) that exhibits both high ionic conductivity and stability for quasi solid‐state LOBs. The double‐layer GPE consists of a bare GPE layer integrated in the cathode, and a composite GPE (c‐GPE, containing 5 wt. % lithium aluminum titanium phosphate (LATP)), which is in contact with Li anode and bare‐GPE. The produced double‐layer gel polymer electrolyte displays high reaction kinetic and better stability due to the excellent electrode/electrolyte interface and rapid oxygen diffusion in the air‐cathode. Furthermore, the d‐GPE electrolyte is resistant to fire and protects Li from dendrite growth and water molecules attack, indicating tremendous promise for the development of practical LOBs.

Expanding the β-substitution reactions of serine synthase through mutagenesis of aromatic active site residues

The Gram-negative bacterium, Fusobacterium nucleatum, possesses a fold II type pyridoxal 5′-phosphate-dependent enzyme that catalyzes the reversible β-replacement of l-cysteine and l-serine, generating H2S and H2O, respectively. This enzyme, termed serine synthase (FN1055), contains an active site Asp232 that serves as a general base in the activation of a water molecule for nucleophilic attack of the ⍺-aminoacrylate intermediate. A network of hydrophobic residues surrounding Asp232 are key to catalysis as they increase the basicity of the side chain. However, these residues severely restrict the range of nucleophilic substrates that can react with the ⍺-aminoacrylate, making the enzyme an ineffective biocatalyst for noncanonical amino acid biosynthesis. Herein, we systematically substituted four aromatic active residues (Trp99, Phe125, Phe148 and Phe234) to an alanine to determine their catalytic importance in serine/cysteine synthase reactions and if their substitution could broaden the scope of nucleophiles that could react with the ⍺-aminoacrylate intermediate. All four single site mutants W99A, F125A, F148A, and F234A could form the ⍺-aminoacrylate intermediate upon reaction with either l-cysteine or l-serine; however, the rate constant associated with the elimination of the β-hydroxyl group from l-serine was 150 to 200-fold lower in the F125A and F148A variants. Substitution of Phe125 and Phe148, situated ∼3–4 Å from the general base, also abolished the serine synthase reaction due to their inability to activate a water molecule for nucleophilic attack of the ⍺-aminoacrylate. Overall, the mutational studies indicate that the clustering of aromatic residues disproportionately benefits the serine synthase reaction as they increase the binding affinity for l-cysteine, decrease the binding of the product, l-serine, and promote the activation of a water molecule. Notably, the aminoacrylate species present in F125A and F148A was able to react with thiophenol, signifying that serine synthase has biocatalytic potential in the synthesis of noncanonical amino acids.

Catalytic deAMPylation in AMPylation-inhibitory/assistant forms of FICD protein.

DeAMPylation, as a reversible reaction of AMPylation and mediated by the endoplasmic reticulum-localized enzyme FICD (filamentation induced by cAMP domain protein, also known as HYPE), is an important process in protein posttranslational modifications (PTMs). Elucidating the function and catalytic details of FICD is of vital importance to provide a comprehensive understanding of protein folding homeostasis. However, the detailed deAMPylation mechanism is still unclear. Furthermore, the role of a conserved glutamine (Glu234), that plays an inhibitory role in the AMPylation response, is still an open question in the deAMPylation process. In the present work, the elaborated deAMPylation mechanisms with AMPylation-inhibitory/assistant forms of FICD (wild type and Glu234Ala mutant) were investigated based on the QM(DFT)/MM MD approach. The results revealed that deAMPylation was triggered by proton transfer from protonated histidine (His363) to AMPylated threonine, instead of a nucleophilic attack of water molecules adding to the phosphorus of AMP. The free energy barrier of deAMPylation in the wild type (∼17.3kcal/mol) is consistent with that in the Glu234Ala mutant of FICD (∼17.1kcal/mol), suggesting that the alteration of the Glu234 residue does not affect the deAMPylation reaction and indirectly verifying the inducement of deAMPylation in FICD. In the wild type, the proton in the nucleophilic water molecule is transferred to Glu234, whereas it is delivered to Asp367 through the hydrogen-bond network of coordinated water molecules in the Glu234Ala mutant. The present findings were inspirational for understanding the catalytic and inhibitory mechanisms of FICD-mediated AMP transfer, paving the way for further studies on the physiological role of FICD protein.

Biochemical and Structural Analyses Shed Light on the Mechanisms of RadD DNA Binding and Its ATPase from Escherichia coli

DNA double-strand breaks (DSBs) are the most perilous and harmful type of DNA damage and can cause tumorigenesis or cell death if left repaired with an error or unrepaired. RadD, a member of the SF2 family, is a recently discovered DNA repair protein involved in the repair of DSBs after radiation or chemical damage. However, the function of RadD in DNA repair remains unclear. Here, we determined the crystal structures of RadD/ATPγS and RadD/ATP complexes and revealed the novel mechanism of RadD binding to DNA and ATP hydrolysis with biochemical data. In the RadD catalytic center, the Gly34 and Gly36 on the P-loop are key residues for ATP binding besides the conserved amino acids Lys37 and Arg343 in the SF2 family. If any of them mutate, then RadD loses ATPase activity. Asp117 polarizes the attacking water molecule, which then starts a nucleophilic reaction toward γ-phosphate, forming the transition state. Lys68 acts as a pocket switch to regulate substrate entry and product release. We revealed that the C-terminal peptide of single-stranded DNA-binding protein (SSB) binds the RadD C-terminal domain (CTD) and promotes the RadD ATPase activity. Our mutagenesis studies confirmed that the residues Arg428 on the zinc finger domain (ZFD) and Lys488 on the CTD of RadD are the key sites for binding branched DNA. Using the Coot software combined with molecular docking, we propose a RadD-binding DNA model for the DNA damage repair process.

Stabilizing the MXene by Ion Confinement Shielding in a Wide Temperature Range

Herein, the environmental stability of MXenes aqueous solution in a wide temperature range is successfully enhanced by a mechanism of ion‐confined shielding. Combined with experiments and molecular dynamics simulation, it is found that, in an aqueous solution, a confinement shielding layer formed by the electrostatic adsorption of the introduced hydronium ion onto the electronegative surface of nanosheets, which efficiently constrains free water molecules near the nanosheet surface through hydration, and prevents nanosheets from an attack of water molecules and dissolved oxygen through its steric hindrance effect. Moreover, the hydronium ions could induce the aggregation of nanosheets and further reduce the active surface area of exposed Ti3C2Tx. Under the aforementioned synergistic effect, the storage duration allowing Ti3C2Tx aqueous solution to keep stable is extended to 100 days at 25 °C and 30 days at 60 °C, respectively. In addition, hydronium ion has the advantages of low cost, environmentally friendly, and easy recovery. It also shows an excellent protection effect at low concentration, such as 2 mol L−1. The present study provides guidance for the prolongation of life of the MXenes device working under long‐term or high‐temperature aqueous conditions and the selection of electrolytes for supercapacitors.

Fluorine Substitution Promotes Air-Stability of P'2-Type Layered Cathodes for Sodium-Ion Batteries.

As one of the most promising cathode materials in sodium-ion batteries, manganese-based layered oxides have aroused wide attention due to their high specific capacity and plentiful reserves. However, they are plagued by poor air stability rooting in water/Na+ exchange and adverse structural reconstruction, hindering their practical applications. Herein, it is demonstrated that utilizing fluorine to substitute oxygen atoms can narrow the interlayer spacing of novel P'2-Na0.67 MnO1.97 F0.03 (NMOF) cathode material, which resists the attack of water molecules, significantly prolonging exposure time in air. Density functional theory (DFT) calculation results indicate that fluorine substitution alleviates the insertion of water molecules and spontaneous extraction of Na+ effectively. Benefiting from the structural modulation, NMOF can deliver a high specific capacity of 227.1mAhg-1 at 20mAg-1 and a promising capacity retention of 84.0% after 100 cycles at 200mAg-1 . This facile and available strategy provides a feasible way to strengthen the air-stability and expands the scope of practical applications of layered oxide cathodes.

Porphyrinic metal–organic framework@alumina nanocomposite fluorescent probe: Two-stage stimuli-responsive behavior and phosphate sensing

Phosphate (PO 4 3− ) is not only a typical indicator of water quality monitoring but also a well-established essential nutrient in biological systems. The quantification of PO 4 3− is of great importance for environment protection and human health. Herein, a novel two-stage stimuli-responsive MOF nanocomposite fluorescent probe was proposed for PO 4 3− sensing. This MOF nanocomposite is composed of an inner two-dimensional (2D) Zr-BTB (BTB = 1,3,5-tris(4-carboxyphenyl)benzene) nanosheet-anchoring TCPP (TCPP = tetrakis(4-carboxyphenyl)porphyrin) MOF and an outer amorphous Al 2 O 3 film, namely PMOF@Al 2 O 3 . Due to the protective effect of Al 2 O 3 , it possesses excellent stability in water. Meanwhile, the Al 2 O 3 nanolayer on the surface can be selectively destroyed by low concentrations of PO 4 3− , exposing the water-unstable PMOF, and water molecules attack Zr nodes, causing the release of free TCPP and resulting in near-infrared fluorescence. And, high concentrations of PO 4 3− will also attack Zr nodes, which will not only separate TCPP molecules, but also lead to the structure collapse of MOF. The PMOF@Al 2 O 3 shows a fast (10 min) and highly selective response to PO 4 3− with two linear ranges and the detection limit is as low as 0.16 μM. Moreover, this MOF nanoprobe was successfully used for PO 4 3− detection in the seawater and the intracellular imaging of PO 4 3− . 1. A novel Al 2 O 3 -protected 2D porphyrinic MOF nanocomposite fluorescent probe was successfully synthesized. 2. PMOF@Al 2 O 3 presented high water stability, fast response, selectivity and sensitivity to phosphate. 3. The two-stage stimuli-responsive sensing mechanism was proposed. 4. PMOF@Al 2 O 3 was used for phosphate detection in the seawater and the intracellular imaging of phosphate.

Surfactant-assisted synthesis of water-stable cobalt-imidazole metal organic frameworks as signal probes for chemiluminescent immunoassay

Application of metal-organic frameworks (MOFs) as signal probes for immunoassay has been greatly hampered by their chemical instability in aqueous solutions. To reduce the attack of water molecules and improve the water stability of MOFs, cetyltrimethyl ammonium bromide (CTAB) was used as a capping reagent to form a hydrophobic protective layer on the surface of MOFs. The Co-MOFs synthesized with CTAB-assisted approach (CTAB-Co-MOFs) can keep stable in water for no less than 45 days, while the stationary duration of those without CTAB assistance is only 3 days. The CTAB-Co-MOFs can vastly catalyze the reaction between luminol and H2O2, and generate very intensive chemiluminescent (CL) emission. The results of mechanism study show that CTAB-Co-MOFs are capable of promoting the generation of reactive oxygen species. Attributing to the improved water stability and outstanding catalytic activity of CTAB-Co-MOFs, a competitive immunoassay method was established for detecting acetamiprid by adopting them as CL probes. It shows a linear range of 0.01–25 ng mL-1 and a detection limit of 4.77 pg mL-1 (3σ). Successful detection of herbal medicines spiked with acetamiprid validated the accuracy of the CTAB-Co-MOFs-based immunoassay method. This work implies the possibility of using water-stable CTAB-Co-MOFs for tracing biological binding events.

Theoretical Analysis of the Catalytic Hydrolysis Mechanism of HCN over Cu-ZSM-5

HCN catalytic hydrolysis mechanism over Cu-ZSM-5 was investigated based on the density functional theory (DFT) with 6-31++g (d, p) basis set. Five paths (A, B, C, D, and E) were designed. For path A and path B, the first step is the nucleophilic attack of water molecule. Next, the hydrogen atom of H2O is transferred to the nitrogen atom first for path A, while in path B, the hydrogen atom of the HCN is first transferred to the nitrogen atom. In path C, HCN isomerizes to HNC initially, and the remaining steps are similar to that of path A. The H atom of HCN shifts to Cu-ZSM-5 initially in path D, and the H atom is transferred to N atom subsequently. The last step is the attack on water molecule. The first step for path E is similar to that of path D. The next step is the attack on water molecule, in which the H atom of water molecule shifts to N atom, and the H on Cu-ZSM-5 shifts to the N atom. Meanwhile, the H atom of oxygen atom is transferred to the N atom. The results show that path C is the most favorable path, with the lowest free energy barrier (35.45 kcal/mol). The results indicate that the Cu-ZSM-5 strongly reduces the energy barrier of HCN and isomerizes to HNC, making it an effective catalyst for HCN hydrolysis.

Unrevealing the Proteolytic Activity of RgpB Gingipain from Computational Simulations.

Alzheimer's disease represents one of the greatest medical concerns for today's population and health services. Its multifactorial inherent nature represents a challenge for its treatment and requires the development of a broad spectrum of drugs. Recently, the cysteine protease gingipain RgpB has been related to neurodegenerative diseases, including Alzheimer's disease, and its inhibition appears to be a promising neuroprotective strategy. Given these features, a computational study that integrates molecular dynamics (MD) simulations with classical and hybrid quantum mechanics/molecular mechanics (QM/MM) potentials was carried out to unravel the atomistic details of RgpB activity. First, a preliminary study based on principal component analysis (PCA), determined the protonation state of the Cys/His catalytic dyad, as well as the crucial role of a flexible loop that favors reactive interactions of the catalytic residues and the peptide in the precatalytic state in its closed conformation. Then, different mechanisms were explored by means of QM/MM MD simulations. The most favorable mechanism consists of two stages. First is an acylation stage that takes place in two steps where, initially, the sulfur atom of the C244 residue attacks the carbonylic carbon of the peptide and the proton of the C244 residue is transferred to the amino group of the peptide in a concerted manner. Subsequently, the peptide bond is broken, and a fragment of the peptide is released. After that, the deacylation stage takes place in a single step where a water molecule attacks the carbonylic carbon of the peptide and a proton of the water is transferred to the C244 residue. The free energy barrier of the rate limiting step is in very good agreement with available experimental data. The mechanism exhibits an unusual role of H211 residue compared with other cysteine proteases but a crucial role of the peptide in triggering the catalysis. Notably, the atomic and energetic particularities found represent a significant contribution to the comprehension of the reaction mechanism and a great opportunity for the design of efficient inhibitors of gingipain RgpB.

The Role of Conserved Residues in the DEDDh Motif: the Proton-Transfer Mechanism of HIV-1 RNase H

RNase H is a prototypical example for two-metal-ion catalysis in enzymes. An RNase H activity cleaving the ribonucleic acid (RNA) backbone of a DNA/RNA hybrid is present not only in important drug targets, such as the HIV-1 reverse transcriptase, but also in many other nucleases, such as Homo sapiens (Hs) and Escherichia coli (Ec) RNase H or, notably, in enzymes that are part of the CRISPR gene editing molecular machinery. Despite its importance, the reaction mechanism uncovering the proton-transfer events is not yet understood. In particular, it is not known, which group is the proton donor for the leaving group. Moreover, several different proton acceptors were proposed, and the exact identity of the proton acceptor is also elusive. Here, we revisit the mechanism for RNAse H, whereby we find that the highly conserved Glu residue of the DDE motif acts as a proton donor via a mechanism further stabilized by the 2′O atom of the sugar. Additionally, we also describe an alternative proton-transfer mechanism via a conserved catalytic His residue to deprotonate the attacking water molecule. Furthermore, our quantum mechanics/molecular mechanics (QM/MM) calculations combining Hamiltonian replica exchange with a finite-temperature string method provide an accurate free-energy profile for the reaction catalyzed by the HIV-1 RNase H. Our reported pathway is consistent with kinetic data obtained for mutant HIV-1, Hs, and Ec RNase H, with the calculated pKa values of the DEDD residues and with crystallographic studies. The overall reaction barrier of ∼19 kcal mol–1, encountered in the phosphate-cleavage step, matches the slow experimental rate of ∼1–100 min–1. Additionally, using molecular dynamics (MD) calculations, we sample the recently identified binding site for a third transient divalent metal ion in the vicinity of the scissile phosphate in the product complex. Our results account for the experimental observation of a third metal ion facilitating product release in an Aquifex aeolicus RNase III crystal structure and the Bh RNase H in crystallo reaction. Taken together, we provide a molecular mechanism of the nuclease catalytic reaction that is likely common for the broad family of two-metal-ion catalytic phosphate-cleaving enzymes with a DDE motif.

Structural and Mechanistic Insights into C-S Bond Formation in Gliotoxin.

Glutathione‐S‐transferases (GSTs) usually detoxify xenobiotics. The human pathogenic fungus Aspergillus fumigatus however uses the exceptional GST GliG to incorporate two sulfur atoms into its virulence factor gliotoxin. Because these sulfurs are essential for biological activity, glutathionylation is a key step of gliotoxin biosynthesis. Yet, the mechanism of carbon−sulfur linkage formation from a bis‐hydroxylated precursor is unresolved. Here, we report structures of GliG with glutathione (GSH) and its reaction product cyclo[‐l‐Phe‐l‐Ser]‐bis‐glutathione, which has been purified from a genetically modified A. fumigatus strain. The structures argue for stepwise processing of first the Phe and second the Ser moiety. Enzyme‐mediated dehydration of the substrate activates GSH and a helix dipole stabilizes the resulting anion via a water molecule for the nucleophilic attack. Activity assays with mutants validate the interactions of GliG with the ligands and enrich our knowledge about enzymatic C−S bond formation in gliotoxin and epipolythiodioxopiperazine (ETP) natural compounds in general.

Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst.

Despite their technological importance for water splitting, the reaction mechanisms of most water oxidation catalysts (WOCs) are poorly understood. This paper combines theoretical and experimental methods to reveal mechanistic insights into the reactivity of the highly active molecular manganese vanadium oxide WOC [Mn4V4O17(OAc)3]3− in aqueous acetonitrile solutions. Using density functional theory together with electrochemistry and IR-spectroscopy, we propose a sequential three-step activation mechanism including a one-electron oxidation of the catalyst from [Mn23+Mn24+] to [Mn3+Mn34+], acetate-to-water ligand exchange, and a second one-electron oxidation from [Mn3+Mn34+] to [Mn44+]. Analysis of several plausible ligand exchange pathways shows that nucleophilic attack of water molecules along the Jahn–Teller axis of the Mn3+ centers leads to significantly lower activation barriers compared with attack at Mn4+ centers. Deprotonation of one water ligand by the leaving acetate group leads to the formation of the activated species [Mn4V4O17(OAc)2(H2O)(OH)]− featuring one H2O and one OH ligand. Redox potentials based on the computed intermediates are in excellent agreement with electrochemical measurements at various solvent compositions. This intricate interplay between redox chemistry and ligand exchange controls the formation of the catalytically active species. These results provide key reactivity information essential to further study bio-inspired molecular WOCs and solid-state manganese oxide catalysts.

Enhancing stability of CsPbBr3 nanocrystals light‐emitting diodes through polymethylmethacrylate physical adsorption

AbstractBoosting the efficiency and lifetime of all inorganic metal halide perovskite nanocrystals (PeNCs) based light‐emitting diodes (PeLEDs) will promote the application of PeNCs in displays and lighting. However, achieving high‐stability CsPbBr3 NCs is still a critical challenge. In this study, a physical adsorption of polymethylmethacrylate (PMMA) on the surface of CsPbBr3 NCs is proven effective to enhance CsPbBr3 NCs stability by reducing the surface energy and preventing the attack of water and oxygen molecules. It also alleviates the energy transfer between neighboring NCs and greatly reduces the thin film roughness by suppressing the agglomeration of the CsPbBr3 NCs within films. Specifically, compared with CsPbBr3 NCs without PMMA adsorption, the photostability under the illumination of continuous ultraviolet light (96 hours) and storage stability under 0 °C (60 days) of the proposed CsPbBr3 NCs with PMMA adsorption are therefore improved by &gt;10 times and four times, respectively. Moreover, since the energy transfer between CsPbBr3 NCs and the agglomeration of CsPbBr3 NCs within films have been suppressed dramatically by the physical absorbed PMMA, the maximum luminance of as‐fabricated LED devices is promoted from 5000 to 13,800 cd m−2 with alleviated roll‐off effect. The operational lifetime of the LED devices is also improved by 5.7 times owing to PMMA preventing the attack of water and oxygen molecules.