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The reaction chemistry and degradation mechanism of MnO2‐based cathodes remain controversial, which hinder their applications in energy storage. Herein, a conversion reaction between Zn4SO4·(OH)6·nH2O (ZSH) and ZnxMnO(OH)2 (ZMO) is proposed in ZnSO4‐based electrolytes. The conversion reaction is an important component of the reaction chemistry as well as the Zn2+/H+ intercalation/deintercalation reaction, which not only provides electrochemical capacity but also dominates the degradation of MnO2 cathodes. The massive accumulation of inactive ZMO seriously destroying the dynamic performance of MnO2 cathodes is deemed to be a principal trigger of the degradation mechanism. Intriguingly, the conversion reaction is sensitive to voltage, which can be activated by voltage modulation. Active ZMO generated in the activated conversion reaction is endowed with higher reversibility and electrooxidation, avoiding the accumulation of inactive ZMO and the decline of kinetic performance, which are evidenced by MnO2 and ZSH cathodes. Accordingly, superior cycling stability with a capacity retention of 89.1% after 2000 cycles is achieved at 2 A g−1 for the MnO2 cathode equipped with the activated conversion reaction. Impressively, the conversion reaction activated by voltage modulation is applicable to various crystal forms of MnO2 (α‐, β‐, γ‐, δ‐), which is significant for the ZIBs with a long lifespan. [ABSTRACT FROM AUTHOR]

The enzymatic biosynthesis of fragrance molecules from lignin fragments is an important reaction in biotechnology for the sustainable production of fine chemicals. In this work we investigated the biosynthesis of vanillin from lignostilbene by a nonheme iron dioxygenase using QM/MM and tested several suggested proposals via either an epoxide or dioxetane intermediate. Binding of dioxygen to the active site of the protein results in the formation of an iron(II)−superoxo species with lignostilbene cation radical. The dioxygenase mechanism starts with electrophilic attack of the terminal oxygen atom of the superoxo group on the central C=C bond of lignostilbene, and the second‐coordination sphere effects in the substrate binding pocket guide the reaction towards dioxetane formation. The computed mechanism is rationalized with thermochemical cycles and valence bond schemes that explain the electron transfer processes during the reaction mechanism. Particularly, the polarity of the protein and the local electric field and dipole moments enable a facile electron transfer and an exergonic dioxetane formation pathway. [ABSTRACT FROM AUTHOR]

The nonheme iron dioxygenase deoxypodophyllotoxin synthase performs an oxidative ring-closure reaction as part of natural product synthesis in plants. How the enzyme enables the oxidative ring-closure reaction of (-)-yatein and avoids substrate hydroxylation remains unknown. To gain insight into the reaction mechanism and understand the details of the pathways leading to products and by-products we performed a comprehensive computational study. The work shows that substrate is bound tightly into the substrate binding pocket with the C7'-H bond closest to the iron(IV)-oxo species. The reaction proceeds through a radical mechanism starting with hydrogen atom abstraction from the C7'-H position followed by ring-closure and a final hydrogen transfer to form iron(II)-water and deoxypodophyllotoxin. Alternative mechanisms including substrate hydroxylation and an electron transfer pathway were explored but found to be higher in energy. The mechanism is guided by electrostatic perturbations of charged residues in the second-coordination sphere that prevent alternative pathways. [ABSTRACT FROM AUTHOR]

The presented Review is focused on the latest research in the field of inorganic chemistry performed by the van Eldik group and his collaborators. The first part of the manuscript concentrates on the interaction of nitric oxide and its derivatives with biologically important compounds. We summarized mechanistic information on the interaction between model porphyrin systems (microperoxidase) and NO as well as the recent studies on the formation of nitrosylcobalamin (CblNO). The following sections cover the characterization of the Ru(II)/Ru(III) mixed‐valence ion‐pair complexes, including Ru(II)/Ru(III)(edta) complexes. The last part concerns the latest mechanistic information on the DFT techniques applications. Each section presents the most important results with the mechanistic interpretations. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is a versatile reductant that under the right conditions can react to form dioxygen in an electrochemical reaction. This reaction has a low carbon footprint and applications are being sought for batteries. In this work a computational study is presented on a recently reported nonheme iron(II) complex where we study mechanistic pathways leading to dioxygen formation from H2O2. The work shows that upon reduction of the iron(III)‐hydroperoxo species it rapidly leads through heterolytic cleavage of the dioxygen bond to form iron(IV)‐oxo(hydroxo). The dimerization reaction of two iron(IV)‐oxo(hydroxo) complexes then leads to formation of the dioxygen bond rapidly with small barriers. Dissociation of the dimer expels dioxygen in an exothermic reaction. An alternative mechanism through the formation of a μ‐1,2‐peroxo‐μ‐1,1‐hydroperoxodiiron(II) intermediate was also tested but found to be highly endergonic. These studies highlight the electrochemical feasibilities of nonheme iron(III)‐hydroperoxo complexes. [ABSTRACT FROM AUTHOR]

CO2 utilization is an important process in the chemical industry with great environmental power. In this work we show how CO2 and H2 can be reacted to form methanol on an iron(II) center and highlight the bottlenecks for the reaction and what structural features of the catalyst are essential for efficient turnover. The calculations predict the reactions to proceed through three successive reaction cycles that start with heterolytic cleavage of H2 followed by sequential hydride and proton transfer processes. The H2 splitting process is an endergonic process and hence high pressures will be needed to overcome this step and trigger the hydrogenation reaction. Moreover, H2 cleavage into a hydride and proton requires a metal to bind hydride and a nearby source to bind the proton, such as an amide or pyrazolyl group, which the scorpionate ligand used here facilitates. As such the computations highlight the non‐innocence of the ligand scaffold through proton shuttle from H2 to substrate as an important step in the reaction mechanism. [ABSTRACT FROM AUTHOR]

High‐valent metal‐oxo species play critical roles in enzymatic catalysis yet their properties are still poorly understood. In this work we report a combined experimental and computational study into biomimetic iron(IV)‐oxo and iron(III)‐oxo complexes with tight second‐coordination sphere environments that restrict substrate access. The work shows that the second‐coordination sphere slows the hydrogen atom abstraction step from toluene dramatically and the kinetics is zeroth order in substrate. However, the iron(II)‐hydroxo that is formed has a low reduction potential and hence cannot do OH rebound favorably. The tolyl radical in solution then reacts further with alternative reaction partners. By contrast, the iron(IV)‐oxo species reacts predominantly through OH rebound to form alcohol products. Our studies show that the oxidation state of the metal influences reactivities and selectivities with substrate dramatically and that enzymes will likely need an iron(IV) center to catalyze C−H hydroxylation reactions. [ABSTRACT FROM AUTHOR]

High‐valent iron(IV)‐oxo intermediates are versatile oxidants in the biotransformation of various substrates by metalloenzymes and catalyze essential reactions for human health as well as in the biodegradation of toxic organic pollutants in the environment. Herein, we report a biomimetic system that efficiently reacts with halophenols through defluorination reactions and characterize various short‐lived intermediates along the reaction mechanism. We study the reactivity pattern of a nonheme iron(IV)‐oxo species with a series of trihalophenols (X=F, Cl, Br). A combined experimental and computational study reveals that the oxidative dehalogenation of 2,4,6‐trifluorophenol is initiated with an H‐atom abstraction from the phenolic group by the iron(IV)‐oxo species resulting in the formation of a phenolate radical and an iron(III)‐hydroxo species. This iron(III)‐hydroxo species forms an adduct with the oxidized substrate with λmax at 558 nm which subsequently decays to give quinones as products. [ABSTRACT FROM AUTHOR]

Bioorthogonal chemistry involves selective biocompatible reactions between functional groups that are not normally present in biology. It has been used to probe biomolecules in living systems, and has advanced biomedical strategies such as diagnostics and therapeutics. In this review, the challenges and opportunities encountered when translating in vitro bioorthogonal approaches to in vivo settings are presented, with a focus on methods to deliver the bioorthogonal reaction components. These methods include metabolic bioengineering, active targeting, passive targeting, and simultaneously used strategies. The suitability of bioorthogonal ligation reactions and bond cleavage reactions for in vivo applications is critically appraised, and practical considerations such as the optimum scheduling regimen in pretargeting approaches are discussed. Finally, we present our own perspectives for this area and identify what, in our view, are the key challenges that must be overcome to maximise the impact of these approaches. [ABSTRACT FROM AUTHOR]

Organic chemistry (OC) appears to be an unstructured and confusing subject to many learners. Reaction mechanisms often seem to be an additional challenge rather than a helpful guideline. Comparable problems were also found for OC as a science at the beginning of the 20th century. One turning point was the systematic application of physical principles on organic reactions through Ingold and coworkers. Kinetic measurements implied for example that in nucleophilic substitution reactions the elimination of the leaving group and the attack of the nucleophile could either occur at the same time or stepwise. In this work the historic insights are made accessible for school lessons by easy experiments suitable for school students. A fictional audio diary of Hilda Ingold is proposed as a history lift to make learners realize that in principle different reaction pathways are possible for one reaction type. [ABSTRACT FROM AUTHOR]

Taurine/α‐ketoglutarate dioxygenase is an important enzyme that takes part in the cysteine catabolism process in the human body and selectively hydroxylates taurine at the C1‐position. Recent computational studies showed that in the gas‐phase the C2−H bond of taurine is substantially weaker than the C1−H bond, yet no evidence exists of 2‐hydroxytaurine products. To this end, a detailed computational study on the selectivity patterns in TauD was performed. The calculations show that the second‐coordination sphere and the protonation states of residues play a major role in guiding the enzyme to the right selectivity. Specifically, a single proton on an active site histidine residue can change the regioselectivity of the reaction through its electrostatic perturbations in the active site and effectively changes the C1−H and C2−H bond strengths of taurine. This is further emphasized by many polar and hydrogen bonding interactions of the protein cage in TauD with the substrate and the oxidant that weaken the pro‐R C1−H bond and triggers a chemoselective reaction process. The large cluster models reproduce the experimental free energy of activation excellently. [ABSTRACT FROM AUTHOR]

Aryloxyalkanoate dioxygenases are unique herbicide biodegrading nonheme iron enzymes found in plants and hence, from environmental and agricultural point of view they are important and valuable. However, they often are substrate specific and little is known on the details of the mechanism and the substrate scope. To this end, we created enzyme models and calculate the mechanism for 2,4‐dichlorophenoxyacetic acid biodegradation and 2‐methyl substituted analogues by density functional theory. The work shows that the substrate binding is tight and positions the aliphatic group close to the metal center to enable a chemoselective reaction mechanism to form the C2‐hydroxy products, whereas the aromatic hydroxylation barriers are well higher in energy. Subsequently, we investigated the metabolism of R‐ and S‐methyl substituted inhibitors and show that these do not react as efficiently as 2,4‐dichlorophenoxyacetic acid substrate due to stereochemical clashes in the active site and particularly for the R‐isomer give high rebound barriers. [ABSTRACT FROM AUTHOR]

This rosarium article relates the adventure started 50 years ago of a computational chemist who was interested in molecules; what are they, what are their shape and how do they react. The story describes results, still valid today, obtained with highly simplified models of chemical reality and elementary computational methods and the gain resulting from the use of better models and more elaborate computational methods. It was necessary to select examples. In this presentation, focus is on hydride and dihydrogen complexes as well as on nucleophiles. Nucleophiles were considered as free hydrides in gas phase at the start of the rosarium while the Grignard reaction is treated with ab initio molecular mechanisms at the end of it. [ABSTRACT FROM AUTHOR]

Thiol dioxygenases are important enzymes for human health; they are involved in the detoxification and catabolism of toxic thiol‐containing natural products such as cysteine. As such, these enzymes have relevance to the development of Alzheimer's and Parkinson's diseases in the brain. Recent crystal structure coordinates of cysteine and 3‐mercaptopropionate dioxygenase (CDO and MDO) showed major differences in the second‐coordination spheres of the two enzymes. To understand the difference in activity between these two analogous enzymes, we created large, active‐site cluster models. We show that CDO and MDO have different iron(III)‐superoxo‐bound structures due to differences in ligand coordination. Furthermore, our studies show that the differences in the second‐coordination sphere and particularly the position of a positively charged Arg residue results in changes in substrate positioning, mobility and enzymatic turnover. Furthermore, the substrate scope of MDO is explored with cysteinate and 2‐mercaptosuccinic acid and their reactivity is predicted. [ABSTRACT FROM AUTHOR]

Reaction monitoring by electrospray ionization mass spectrometry (ESI‐MS) is a popular method for investigation of reaction mechanisms. Here, we present a new approach based on a coupling between a modular capillary flow reactor and ESI‐MS. The flow reactor allows a sequential adding of the reactants. We demonstrate the approach for oxidation of Ph2S by ArIO catalyzed by [(TPA)Fe(TfO)2] (ArIO=2‐(tBuSO2)C6H4IO, TPA=tris(2‐pyridylmethyl)amine, TfO−=triflate). In steps, we could follow the formation of the reactive iron(IV)oxo complexes, then the oxygen transfer reaction from the iron(IV)oxo to the sulfide, and finally the reoxidation of the iron complexes. The flow reactor also allows kinetic experiments by changing relative concentrations of the reactants. We could analyze in detail the formation of various [(TPA)FeIVO(X)]2+/+ complexes (X=MeCN, ArI, ArIO, TfO−) and compare their relative reactivity with Ph2S. The [(TPA)FeIVO(MeCN)]2+ complex is the most reactive complex for the oxygen atom transfer reaction whilst [(TPA)FeIVO(ArIO)]2+ prevails in solution under catalytic conditions. [ABSTRACT FROM AUTHOR]

The quantum calculation gives the insight of reaction mechanism in chemistry. In this work, we predict hydrogen evolution reaction (HER) mechanism in Ni(abt)2 (abt = 2‐aminobenzenethiolate) catalyst. Using density functional theory (DFT) and coupled‐cluster singles, doubles and perturbative triples (CCSD(T)) methods, we demonstrate the potential energy surface (PES) for the HER reaction result with two intermediate states (IM) and transition states (TS). Our result shows that the hydrogen atoms are migrated to Ni atom one by one from each of two amino groups. It indicates that the HER reaction in Ni(abt)2 occurs following the ligand‐assisted metal‐centered H2 production. Finally, two hydrogen atoms are merged in Ni atom site which generates hydrogen molecule. This would be meaningful prediction to understand the role of metal catalyst in HER reaction pathway. [ABSTRACT FROM AUTHOR]

This article, titled "Mechanism of CO2 Reduction to Methanol with H2 on an Iron(II)-scorpionate Catalyst," explores the reaction mechanism of a homogeneous catalyst that binds H2 and CO2 on an iron(II)-scorpionate complex. Through calculations, it is determined that the iron complex can cleave H2 into a hydride and proton, which then bind to different sites on the complex. CO2 is subsequently reduced through a series of hydride and proton transfer steps, ultimately resulting in the formation of methanol products. The full research article provides more detailed information on this topic. [Extracted from the article]

Bioorthogonal chemistry, click chemistry, in vivo, metabolic glycoengineering Keywords: bioorthogonal chemistry; click chemistry; in vivo; metabolic glycoengineering EN bioorthogonal chemistry click chemistry in vivo metabolic glycoengineering 1 1 1 04/10/23 20230406 NES 230406 Bioorthogonal reactions are biocompatible reactions that enable the study of biomolecules in living organisms. [Extracted from the article]

In their Review (DOI: 10.1002/chem.202203942), M. M. A. Mitry, F. Greco and H. M. I. Osborn critically appraise the suitability of bioorthogonal reactions for in vivo applications. Keywords: bioorthogonal chemistry; click chemistry; in vivo; metabolic glycoengineering EN bioorthogonal chemistry click chemistry in vivo metabolic glycoengineering 1 1 1 04/10/23 20230406 NES 230406 B Bioorthogonal chemistry b refers to reactions that can proceed in biological systems without interfering with biological processes. [Extracted from the article]

Keywords: Antiscalants; Crystal Engineering; Green Chemistry; Reaction Mechanisms; Solid-State REDOR NMR EN Antiscalants Crystal Engineering Green Chemistry Reaction Mechanisms Solid-State REDOR NMR 1 1 1 09/28/22 20221004 NES 221004 B Amorphous calcium carbonate b (ACC) is a pivotal precursor in biomineralization, central to geological and industrial calcification. In their Research Article (e202208475), Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. decode the underlying molecular mechanisms that regulate both prenucleation cluster and solution composition and proceed outside the established conceptional framework. In their Research Article (e202208475), Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. decode the underlying molecular mechanisms that regulate both prenucleation cluster and solution composition and proceed outside the established conceptional framework. [Extracted from the article]

Keywords: Antiscalants; Crystal Engineering; Green Chemistry; Reaction Mechanisms; Solid-State REDOR NMR EN Antiscalants Crystal Engineering Green Chemistry Reaction Mechanisms Solid-State REDOR NMR 1 1 1 09/28/22 20221004 NES 221004 B Amorphes Kalziumcarbonat b (ACC) ist ein wichtiger Vorläufer in der Biomineralisierung und von zentraler Bedeutung für die geologische und industrielle Kalzifizierung. Einige kleine organische Moleküle haben die Fähigkeit, die Bildung, Zusammensetzung und Stabilität von ACC stark zu beeinflussen. In ihrem Forschungsartikel (e202208475) entschlüsseln Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. die zugrundeliegenden molekularen Mechanismen, die sowohl die Pränukleation als auch die Zusammensetzung der Lösung regulieren. [Extracted from the article]

Keywords: density functional calculations; guanidines mechanochemistry; microwave chemistry; reaction mechanisms EN density functional calculations guanidines mechanochemistry microwave chemistry reaction mechanisms 1 1 1 04/07/22 20220405 NES 220405 The cover picture shows the two-step synthesis of Boc-2-amino-quinazolin-4(3 I H i )-ones starting from aromatic amines by utilization of mechanochemical and microwave methods. Cover Picture: Consecutive Utilization of Mechanochemical and Microwave Methods for the Synthesis of Boc-2-amino-quinazolin-4(3H)-ones and DFT Study of Mechanism 6 -Diazaelectrocyclization Process (ChemistrySelect 13/2022) Density functional calculations, guanidines mechanochemistry, microwave chemistry, reaction mechanisms. [Extracted from the article]

Keywords: historic problem-oriented teaching method; reaction mechanisms in organic chemistry; nucleophilic substitution; reaction kinetics; experiment for school students; Historisch-problemorientierter Unterricht; Reaktionsmechanismen der organischen Chemie; Nukleophile Substitution; Reaktionskinetik; Schülerexperiment EN historic problem-oriented teaching method reaction mechanisms in organic chemistry nucleophilic substitution reaction kinetics experiment for school students DE Historisch-problemorientierter Unterricht Reaktionsmechanismen der organischen Chemie Nukleophile Substitution Reaktionskinetik Schülerexperiment 53 53 1 03/07/22 20220301 NES 220301 B Das Titelbild b zeigt im Hintergrund Christopher Ingold, Edward Hughes und Hilda Ingold (abgebildet mit Erlaubnis der Royal Society of Chemistry nach Chem. Historic problem-oriented teaching method, reaction mechanisms in organic chemistry, nucleophilic substitution, reaction kinetics, experiment for school students Pölloth, Häfner und Schwarzer erschließen in ihrem Beitrag die historische Erforschung von Reaktionsmechanismen durch einfache Experimente und einen I history lift i für den Schulunterricht. [Extracted from the article]