Intrinsic Reactivity Research Articles

Accelerating Li+/Li redox through the regulation of the electric double layer for efficient lithium metal anodes

High performance lithium metal anode is of great importance to achieve batteries with high energy density. Due to the intrinsic high reactivity of Li metal anode and the insufficient understanding of lithium redox at the Li/electrolyte interface, the fast and dendrite-free Li metal deposition still remains a grand challenge. In this work, we accelerate Li+/Li redox through the regulation of the electric double layer (EDL), in which 2-Mercaptopyridine (2-MP), a conjugated weak-base molecule with stable electrochemical properties, can be specifically adsorbed on Li metal surface and promote charge transfer. It fundamentally avoided the formation of Li metal dendrites and enabled fast Li plating/stripping process, leading to uniform Li deposition as well as superior cycling performances of batteries. This work provides a significant contribution to the understanding of battery chemistry at the electrode/electrolyte interface.

Developing the Ascorbic Acid Test: A Candidate Standard Tool for Characterizing the Intrinsic Reactivity of Metallic Iron for Water Remediation

Granular metallic iron (gFe0) materials have been widely used for eliminating a wide range of pollutants from aqueous solutions over the past three decades. However, the intrinsic reactivity of gFe0 is rarely evaluated and existing methods for such evaluations have not been standardized. The aim of the present study was to develop a simple spectrophotometric method to characterize the intrinsic reactivity of gFe0 based on the extent of iron dissolution in an ascorbic acid (AA—0.002 M or 2 mM) solution. A modification of the ethylenediaminetetraacetic acid method (EDTA method) is suggested for this purpose. Being an excellent chelating agent for FeII and a reducing agent for FeIII, AA sustains the oxidative dissolution of Fe0 and the reductive dissolution of FeIII oxides from gFe0 specimens. In other words, Fe0 dissolution to FeII ions is promoted while the further oxidation to FeIII ions is blocked. Thus, unlike the EDTA method that promotes Fe0 oxidation to FeIII ions, the AA method promotes only the formation of FeII species, despite the presence of dissolved O2. The AA test is more accurate than the EDTA test and is considerably less expensive. Eight selected gFe0 specimens (ZVI1 through ZVI8) with established diversity in intrinsic reactivity were tested in parallel batch experiments (for 6 days) and three of these specimens (ZVI1, ZVI3, ZVI5) were further tested for iron leaching in column experiments (for 150 days). Results confirmed the better suitability (e.g., accuracy in assessing Fe0 dissolution) of the AA test relative to the EDTA test as a powerful screening tool to select materials for various field applications. Thus, the AA test should be routinely used to characterize and rationalize the selection of gFe0 in individual studies.

Dual Photochemical H-Atom Transfer & Cobalt Catalysis for the Desaturative Synthesis of Phenols from Cyclohexanones.

Phenols are integral aromatic molecules widely encountered in the structure of natural products and routinely utilised for the synthesis of high-value materials. Accessing highly substituted derivatives can often be difficult especially when their functionalization pattern does not match the intrinsic reactivity leveraged by electrophilic aromatic substitution (SEAr) chemistry. Here we provide an alternative and mechanistically distinct approach for phenol synthesis using saturated cyclohexanone precursors. This process operates at ambient temperature, under simple purple light irradiation, and features a dual catalytic manifold carrying four sequential H-atom transfer processes.

Dualkatalytisch‐Photochemische H‐Atomtransfer/Kobaltkatalysesequenz Ermöglicht Desaturative Synthese von Phenolen aus Cyclohexanonen

AbstractPhenole gehören zu den grundlegendsten aromatischen Strukturen, die nicht nur in einer Vielzahl von Naturstoffen zu finden sind, sondern auch routinemäßig für die Herstellung von wertvollen Produkten eingesetzt werden. Die Synthese hochsubstituierter Phenolderivate kann jedoch äußerst komplex sein, wenn das gewünschte Substitutionsmuster nicht durch die dirigierenden Effekte der elektrophilen aromatischen Substitution (SEAr) erreicht werden kann. In diesem Aufsatz präsentieren wir einen alternativen und mechanistisch einzigarten Ansatz zur Phenolsynthese, der saturierte Cyclohexanone als Ausgangsstoffe verwendet. Dieser bei Raumtemperatur ablaufende Prozess wird durch die Nutzung von violettem Licht ermöglicht und kennzeichnet sich durch den Einsatz einer Anthrachinon‐Kobalt‐Dualkatalyse, welcher vier aufeinanderfolgende Wasserstoffatomtransfers ermöglicht.

Discovery of a spirocyclic 3-bromo-4,5-dihydroisoxazole covalent inhibitor of hGAPDH with antiproliferative activity against pancreatic cancer cells

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key glycolytic enzyme, plays a crucial role in the energy metabolism of cancer cells and has been proposed as a valuable target for the development of anticancer agents. Among a series of 5-substituted 3-bromo-4,5-dihydroisoxazole (BDHI) derivatives, we identified the spirocyclic compound 11, which is able to covalently inactivate recombinant human GAPDH (hGAPDH) with a faster reactivity than koningic acid, one of the most potent hGAPDH inhibitors known to date. Computational studies confirmed that conformational rigidification is crucial to stabilize the interaction of the inhibitor with the binding site, thus favoring the subsequent covalent bond formation. Investigation of intrinsic warhead reactivity at different pH disclosed the negligible reactivity of 11 with free thiols, highlighting its ability to selectively react with the activated cysteine of hGAPDH with respect to other sulfhydryl groups. Compound 11 strongly reduced cancer cell growth in four different pancreatic cancer cell lines and its antiproliferative activity correlated well with the intracellular inhibition of hGAPDH. Overall, our results qualify 11 as a potent hGAPDH covalent inhibitor with a moderate drug-like reactivity that could be further exploited to develop anticancer agents.

Visible-Light Promoted Radical Fluoroalkylation of O- and N-Substituted Alkenes.

Interaction of enol ethers enol acetates, enamides and enamines with fluorinated reagents may be considered as a reliable method for the synthesis of organofluorine compounds. While classic nucleophile/electrophile substitution or addition mechanisms cannot be realized for coupling of these components, their intrinsic reactivities are revealed with the aid of photoredox catalysis. A combination of these electron donating and accepting components provides a perfect balance needed for individual redox steps, which in some cases may proceed even without a photocatalyst. The same electronic factors also support the key C,C-bond forming event involving addition of fluorinated radical at the electron rich double bond.

Stabilizing Fe in intermetallic L10-PtAuFe nanoparticles with strong Au-Fe bond to boost oxygen reduction reaction activity and durability

The intrinsic reactivity of PtM alloys during the catalysis of oxygen reduction reactions (ORRs) under acidic conditions is deactivated by the unavoidable leaching of cocatalyst M. Herein, we propose an unprecedented “Au-stabilized strategy” to stabilize the Fe atoms in L10-PtAuFe via a strong Au-Fe bond. Simultaneously, the introduction of Au atoms regulates the Pt atomic electronic structure and increases resistance to Pt atomic oxidation, which is beneficial to further boost ORR activity and stability. As a result, the as-obtained L10-PtAuFe exhibits minimal loss of mass activity after accelerated durability tests and is far superior to L10-PtFe and commercial Pt/C. In addition, L10-PtAuFe shows fantastic ORR activity, with a 7.3-fold improvement in mass activity and a 4.5-fold increase in specific activity compared to that of commercial Pt/C. This novel Au-stabilized strategy provides a new avenue to stabilize the M atoms in L10-PtM alloys and further enhance their ORR activity and stability.

Oxidative Assemblies of Flavonoids Dimers – Synthesis of Dehydrodicatechin A

AbstractCatechin and quercetin were subjected to different oxidative conditions. Reagents such as silver oxide, potassium ferricyanide or PIDA (phenyliodine diacetate), as well as electrochemical and photocatalytic conditions were evaluated. From quercetin, the formation of a dimer resulting from an oxa‐Diels‐Alder has been systematically observed. From catechin, dehydrodicatechin A was obtained by the action of silver oxide in a toluene/acetone mixture. Complementary experiments in the presence of catechol gave information on the mechanisms of formation. Products resulting from these reactions have already been identified in plants and beverages made from plants and are supposed to result from the oxidation of flavonoids. This reactivity exploration provides a better understanding of the role of catechols in the formation of natural compounds arising from the dimerization of flavonoids during oxidative process. These results shed some light on the intrinsic reactivity of catechin and quercetin.

Progress of Azametallacyclopentadienes in the New Century.

As the key intermediates in metal-promoted/catalyzed C-C bond coupling reactions of nitriles and alkynes, azametallacyclopentadienes, M(N=CR1 -CR2 =CR3 ), are an important class of azametallacycles. Although the first authentic azametallacyclopentadienes were documented in 1986, their chemistry towards solid-state structures, intrinsic reactivity, and synthetic application was rarely investigated for a long time. At the beginning of this century, seminal works about the applications of azametallacyclopentadienes in the synthesis of heterocycles, including multi-substituted pyridines, isoquinolines, furans, and pyrroles were reported. Subsequently, a series of new complexes with this motif, namely the Group 4, aluminum, actinide, and rare-earth azametallacyclopentadienes were isolated and structurally characterized. Among them, the rare-earth azametallacyclopentadiene expresses high reactivity towards unsaturated molecules, such as nitriles, isocyanides, and Mo(CO)6 to provide novel fused metallacycles. In this Concept, we reviewed the advances in the preparation, reactivity, and synthetic application of azametallacyclopentadienes in the past twenty years.

Electron Transfer Energy and Hydrogen Atom Transfer Energy-Based Linear Free Energy Relationships for Predicting the Rate Constants of Munition Constituent Reduction by Hydroquinones.

No single linear free energy relationship (LFER) exists that can predict reduction rate constants of all munition constituents (MCs). To address this knowledge gap, we measured the reduction rates of MCs and their surrogates including nitroaromatics [NACs; 2,4,6-trinitrotoluene (TNT), 2,4-dinitroanisole (DNAN), 2-amino-4,6-dinitrotoluene (2-A-DNT), 4-amino-2,6-dinitrotoluene (4-A-DNT), and 2,4-dinitrotoluene (DNT)], nitramines [hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and nitroguanidine (NQ)], and azoles [3-nitro-1,2,4-triazol-5-one (NTO) and 3,4-dinitropyrazole (DNP)] by three dithionite-reduced quinones (lawsone, AQDS, and AQS). All MCs/NACs were reduced by the hydroquinones except NQ. Hydroquinone and MC speciations were varied by controlling pH, permitting the application of a speciation model to determine second-order rate constants (k) from observed pseudo-first-order rate constants. The intrinsic reactivity of MCs (oxidants) decreased upon deprotonation, while the opposite was true for hydroquinones (reductants). The rate constants spanned ∼6 orders of magnitude in the order NTO ≈ TNT > DNP > DNT ≈ DNAN ≈ 2-A-DNT > DNP- > 4-A-DNT > NTO- > RDX. LFERs developed using density functional theory-calculated electron transfer and hydrogen atom transfer energies and reported one-electron reduction potentials successfully predicted k, suggesting that these structurally diverse MCs/NACs are all reduced by hydroquinones through the same mechanism and rate-limiting step. These results increase the applicability of LFER models for predicting the fate and half-lives of MCs and related nitro compounds in reducing environments.

Imperfect narrow escape problem.

We consider the kinetics of the imperfect narrow escape problem, i.e., the time it takes for a particle diffusing in a confined medium of generic shape to reach and to be adsorbed by a small, imperfectly reactive patch embedded in the boundary of the domain, in two or three dimensions. Imperfect reactivity is modeled by an intrinsic surface reactivity κ of the patch, giving rise to Robin boundary conditions. We present a formalism to calculate the exact asymptotics of the mean reaction time in the limit of large volume of the confining domain. We obtain exact explicit results in the two limits of large and small reactivities of the reactive patch, and a semianalytical expression in the general case. Our approach reveals an anomalous scaling of the mean reaction time as the inverse square root of the reactivity in the large-reactivity limit, valid for an initial position near the extremity of the reactive patch. We compare our exact results with those obtained within the "constant flux approximation"; we show that this approximation turns out to give exactly the next-to-leading-order term of the small-reactivity limit, and provides a good approximation of the reaction time far from the reactive patch for all reactivities, but not in the vicinity of the boundary of the reactive patch due to the above-mentioned anomalous scaling. These results thus provide a general framework to quantify the mean reaction times for the imperfect narrow escape problem.

Monosubstituted Doublet Sn(I) Radical Featuring Substantial Unquenched Orbital Angular Momentum

Due to their intrinsic high reactivity, isolation of heavier analogues of carbynes remains a great challenge. Here, we report the synthesis and characterization of a neutral monosubstituted Sn(I) radical (2) supported by a sterically hindered hydrindacene ligand, which represents the first tin analogue of a free carbyne. Different from all Sn(I/III) species reported thus far, the presence of a sole Sn-C σ bond in 2 renders the remaining two Sn 5p orbitals energetically almost degenerate, of which one is singly occupied and the other is empty. Consequently, its S = 1/2 ground state possesses two-fold orbital pseudo-degeneracy and substantial unquenched orbital angular momentum, as evidenced by one component of its g matrix (1.957, 1.896, and 1.578) being considerably less than 2. Consistent with this unique electronic structure, 2 can bind to an N-heterocyclic carbene to afford a neutral two-coordinate Sn(I) radical and initiate a one-electron transfer to benzophenone to furnish a Sn(II)-ketyl radical anion adduct. As a manifestation of its Sn-centered radical nature, 2 reacts with diphenyl diselenide and p-benzoquinone to form Sn-S and Sn-O bonds, respectively.

C versus O Protonation in Zincate Anions: A Simple Gas-Phase Model for the Surprising Kinetic Stability of Organometallics.

For better understanding the intrinsic reactivity of organozinc reagents, we have examined the protolysis of the isolated zincate ions Et3 Zn- , Et2 Zn(OH)- , and Et2 Zn(OH)2 Li- by 2,2,2-trifluoroethanol in the gas phase. The protonation of the hydroxy groups and the release of water proceed much more efficiently than the protonation of the ethyl groups and the liberation of ethane. Quantum-chemical computations and statistical-rate theory calculations fully reproduce the experimental findings and attribute the lower reactivity of the more basic ethyl moiety to higher intrinsic barriers, which override the thermodynamic preference for its protonation. Thus, our minimalistic gas-phase model provides evidence for the intrinsically low reactivity of organozinc reagents toward proton donors and helps to explain their remarkable kinetic stability against moisture and even protic media.

Comparative study on the effects of heating rate on char gasification behaviors by thermogravimetric analyzer and high-temperature stage microscope under non-isothermal condition

Understanding the intrinsic gasification reactivity and kinetics of coal char is vital in the process optimization, reactor design, and scaling of industrial gasifiers. Thermogravimetric analyzer (TGA) and visual high-temperature stage microscope (HTSM) were developed to investigate the mass loss and morphological evolution of coal char under non-isothermal conditions at different heating rates of 2.5, 5, and 10 °C/min, respectively. The gasification reactivity and kinetics obtained from different systems were comprehensively compared with the consideration of heating rate. Results showed that the consumption of carbon matrix and sintering could be responsible for the appearance of two reaction rate peaks in the rapid reaction stage in the HTSM experiments. As the heating rate increased from 2.5 to 10 °C/min, the limitation of heat and mass transfer and shortened residence time were conducive to the increase of observed reactivity and characteristic temperatures. Also, more serious diffusion and limitation could be responsible for the lower reactivity monitored by TGA and the difference in increasing amplitude of characteristic temperatures. Kissinger-Akahira-Sunosen (KAS) iso-conversional method was efficiently proposed to predict the gasification process. The activation energy varied with the carbon conversion, and then the average activation energies determined by TGA and HTSM were 191.51 and 199.01 kJ/mol, respectively. The evidence proved powerfully that the results close to the intrinsic behaviors could be provided by HTSM due to lower diffusion and limitation from heat and mass transfer.

Aluminum-Catalyzed Cross Selective C3–N1′ Coupling Reactions of N-Methoxyindoles with Indoles

C3–N1′ bond formation of bisindoles has been a great challenge due to the intrinsic reactivity of indoles as both C3 and N1-nucleophilic character. Herein, we demonstrate an C3–N1′ cross-coupling reaction of indoles using N-methoxyindoles as N-electrophilic indole reagents in the presence of Lewis acid. The bisindoles generated in this transformation are latent C3-nucleophile, allowing them to be used as strategic intermediates in sequential C3–N1′–C3′–N1″ triindole formations. The potential synthetic usefulness of this sequential transformation was highlighted upon application to the construction of C3–N1 looped polyindoles.

Revealing the Effect of High Ni Content in Li-Rich Cathode Materials: Mitigating Voltage Decay or Increasing Intrinsic Reactivity.

Li-rich layeredoxides are considered as one of the most promising cathode materials for secondary lithium batteries due to their high specific capacities, buttheissueofcontinuous voltage decay during cycling hinders their market entry. Increasing the Ni content in Li-rich materials is assumed to be an effective way to address this issue and attracts recent research interests. However, a high Ni content may induce increased intrinsic reactivity of materials, resulting in severe side reactions with the electrolyte. Thus, a comprehensive study to differentiate the two effects of the Ni content on the cell performance with Li-rich cathode is carried out in this work. Herein, it is demonstrated that a properly dosed amount of Ni can effectively suppress the voltage decay in Li-rich cathodes, while over-loading of Ni, on the contrary, can cause structural instability, Ni dissolution, and nonuniform Li deposition during cycling as well as severe oxygen loss. This work offers a deep understanding on the impacts of Ni content in Li-rich materials, which can be a good guidance for the future design of such cathodes for high energy density lithium batteries.

Atomically Dispersed Metals on Nanodiamond-Derived Hybrid Materials for Heterogeneous Catalysis

ConspectusSupported metal catalyst, has been one of the most important systems in the field of heterogeneous catalysis. The great complexity of both the compositions and structures of such supported metal catalysts provides a great degree of freedom for tuning their catalytic properties, which has essentially triggered the explosive growth in research on design and control active metals’ surface structures for decades. An ideal metal catalyst theoretically features maximum active sites and optimal intrinsic reactivity to facilitate a desired chemical reaction. Inspired by the catalytic concepts brought by natural enzymes and homogeneous catalysis, the fabrication of heterogeneous catalysts with atomically dispersed metal atoms has attracted much attention and been extensively explored in recent years.Atomically dispersed metal catalysts (ADMCs) including single-atom catalyst (SACs) and fully exposed cluster catalyst (FECCs), as shining stars in heterogeneous catalysts have recently drawn much attention. The advantages of ADMCs mainly include the following three aspects: (1) the fully exposed active metal atoms can realize the utmost atomic utilization efficiency and reduce the cost of catalysts; (2) the geometric and electronic structure can be effectively regulated by altering the coordination environments of metal atoms and then further tuning the catalytic performance in terms of activity, selectivity, and stability; (3) the precisely designed structures provide a promising platform for digging the structure–performance relationships of active sites with the assistance of theoretical calculations. Owing to these advantages, ADMCs have been used in thermal-catalysis, electrocatalysis, photocatalysis, etc. until now.In this Account, a summary of recent progress regarding ADMCs for heterogeneous thermal catalysis in our group will be presented from the following aspects. First, an overview of great opportunities brought by nanodiamond and its derivatives as substrates for anchoring atomically dispersed metals (ADMs) and tailoring their structures. Next, our recent progress in achieving desirable catalytic performance, including activity, selectivity, and stability over nanodiamond–graphene (ND@G) supported ADMCs will be introduced in detail. Finally, a brief outlook regarding the development directions for ADMCs by discussing current challenges and opportunities will be proposed. It is hoped that this Account can inspire the development of the rational design and various application of ADMCs.

Kinetic Impacts of Defect Sites in Metal–Organic Framework Catalysts under Varied Driving Forces

Defects in metal–organic frameworks (MOFs) primarily manifest as missing linkers or metal nodes induced through synthesis, post-synthetic modification, and/or exposure to reaction conditions. By changing the nature of active site(s) and perturbing crystalline frameworks, defects confer physicochemical alterations to MOF catalysts that may promote or inhibit intrinsic reactivity, electron transfer and excitation, and mass transport. However, the complexity and dynamic character of defects often obfuscate the structure–function relations needed to permit rational catalyst design. Here, highlights of recent studies examining the impact of MOF defects in thermo-, photo-, and electrocatalytic systems pertinent to energy applications demonstrate progress toward identifying defect impacts on MOF catalysis, particularly for widely studied zirconium-based frameworks. Moreover, the combination of ex situ and operando/in situ defect identification and quantification will be paramount in future research to improve the mechanistic understanding of MOF-catalyzed systems for energy conversion but also extends to MOF energy storage, photovoltaics, and gas separations/storage applications.

Photocatalytic C−H Amination of Electron‐rich Aromatic Hydrocarbons by Carbon Nitride Photocatalysis

AbstractConstruction of C−N bond is a central process in organic synthesis. Typically, it relies on noble‐metal catalysts and prefunctionalized substrates, such as aryl halides. Alternative and more appealing method is a direct C−H amination of hydrocarbons that is based on intrinsic reactivity of the in situ generated radical cations, which are more electrophilic compared to their closed‐shell precursors. In this work, we employ potassium poly(heptazine imide) (K‐PHI), a graphitic carbon nitride semiconductor, to enable C−H amination of electron rich aromatic hydrocarbons with NH3 and pyrazole under oxidative conditions. Screening of oxidants, indicate those molecules that are able to accept not only electrons, but also protons, such as O2, PhNO2 and Ph2S2, mediate the reaction. As such, multisite proton‐coupled electron transfer (MS‐PCET) from the photocharged state of K‐PHI to the acceptor of electrons and protons is the key element in the studied photocatalytic process.

Tweezer-Based C-H Oxidation Catalysts Overriding the Intrinsic Reactivity of Aliphatic Ammonium Substrates.

The site-selective C-H oxygenation of alkyl chains as well as deactivated positions remains a great challenge for chemists. Here, we report the synthesis and application of four new supramolecular tweezer-based oxidation catalysts. They consist of the well-explored M(pdp/mcp) oxidation moiety and a molecular tweezer capable of binding ammonium salts. All catalysts display preferential oxidation of the strongly deactivated C3/C4 positions, however to different degrees. Furthermore, the best performing catalyst Fe(pdp)Twe was explored with an expanded substrate scope. It was demonstrated that the deactivated positions C3/C4 are also preferentially oxidized in these cases.