Enantioselective α-Boryl Carbene Transformations.

Carbenes, recognized as potent intermediates, enable unique chemical transformations, and organoborons are pivotal in diverse chemical applications. As a hybrid of carbene and the boryl group, α-boryl carbenes are promising intermediates for the construction of organoborons; unfortunately, such carbenes are hard to access and have low structural diversity with their asymmetric transformations largely uncharted. In this research, we utilized boryl cyclopropenes as precursors for the swift synthesis of α-boryl metal carbenes, a powerful category of intermediates for chiral organoboron synthesis. These α-boryl carbenes undergo a series of highly enantioselective transfer reactions, including B-H and Si-H insertion, cyclopropanation, and cyclopropanation/Cope rearrangement, catalyzed by a singular chiral copper complex. This approach opens paths to previously unattainable but easily transformable chiral organoborons, expanding both carbene and organoboron chemistry.

NSUN6 Regulates NM23-H1 Expression in an m5C Manner to Affect Epithelial-Mesenchymal Transition in Lung Cancer.

PURPOSE: The expression and regulatory mechanism of NSUN6 in lung cancer are still unclear. Our study explored whether NSUN6 mediates progression of lung cancer by affecting NM23-H1 expression in an m5C-dependent manner. METHODS: qRT-PCR, CCK-8, colony formation, transwell, and Western blot analysis were employed to probe the impact of NSUN6 on lung cancer cell proliferation, migration, and epithelial-mesenchymal transition (EMT). RMVar database was utilized to forecast the downstream genes of NSUN6. The mode of interaction between NSUN6 and NM23-H1 was determined by dot blot, luciferase assay, m5C RIP, and cell function assays. The effect of NSUN6 expression on tumor growth was verified in vivo. RESULTS: Expression of NSUN6 was reduced in lung cancer cells, and over-expression of NSUN6 restricted the proliferation of lung cancer cells, migration, and EMT. NSUN6 regulated NM23-H1 expression by modifying the 3'-UTR of NM23-H1 mRNA through m5C and inhibited lung cancer cell proliferation, migration, and EMT. In vivo experiments also showed that over-expression of NSUN6 inhibited the occurrence of lung cancer. CONCLUSION: NSUN6 regulates NM23-H1 expression in an m5C-dependent manner to affect EMT in lung cancer. Thus, NSUN6 may be considered as a potential therapeutic target for lung cancer.

Computational design of a reliable intermediate-band photovoltaic absorber based on diamond.

To reduce the wide bandgap of diamond and expand its applications in the photovoltaic fields, a diamond-based intermediate-band (IB) material C-Ge-V alloy was designed by first-principles calculations. By replacing some C with Ge and V in the diamond, the wide bandgap of the diamond can be reduced sharply and a reliable IB, which is mainly formed by the d states of V, can be formed in the bandgap. With the increase of Ge content, the total bandgap of the C-Ge-V alloy will be reduced and close to the optimal value of an IB material. At a relatively low atomic concentration of Ge (below 6.25%), the IB formed in the bandgap is partially filled and varies little with the concentration of Ge. When further increasing the content of Ge, the IB moves close to the conduction band and the electron filling in the IB increases. The 18.75% content of Ge might be the limitation to form an IB material, and the optimal content of Ge should be between 12.5% and 18.75%. Compared with the content of Ge, the distribution of Ge has a minor effect on the band structure of the material. The C-Ge-V alloy shows strong absorption for the sub-bandgap energy photons, and the absorption band generates a red-shift with the increase of Ge. This work will further expand the applications of diamond and be helpful to develop an appropriate IB material.

Theoretical identification of the superior anchoring effect and electrochemical performance of Ti2CS2 by single atom Zn doping for lithium-sulfur batteries.

As one of the promising next-generation energy storage systems, lithium-sulfur (Li-S) batteries have been the subject of much recent attention. However, the polysulfide shuttle effect remains problematic owing to the dissolution of intermediate polysulfide species in the electrolyte and the sluggish reaction dynamics in Li-S batteries. To overcome these issues, this work reports an effective strategy for enhancing the electrochemical performance of Li-S batteries using single atom Zn doping on the S-terminated Ti2C MXenes (Ti2-xZnxCS2). Spin-polarized density functional theory (DFT) calculations were performed to elucidate the interactions of lithium polysulfides (LiPSs) and the Ti2-xZnxCS2 surface in terms of geometric and electronic properties, as well as the delithiation process of Li2S on the Ti2-xZnxCS2 surface. It is found that doping single atom Zn could induce a new Lewis acid-based sites, which could provide proper affinity toward LiPSs. Combined with the metallic character, a low Li diffusion barrier and high catalytic activity for the delithiation process of Li2S, makes Ti2-xZnxCS2 a promising cathode material for Li-S batteries. The results demonstrate the importance of surface chemistry and the electronic structure of MXenes in LiPSs' adsorption and catalysis capability. We believe that our findings provide insights into the recent experimental results and guidance for the preparation and practical application of MXenes in Li-S batteries.

Iron-Catalyzed Stereoconvergent 1,4-Hydrosilylation of Conjugated Dienes.

Stereoconvergent transformation of E/Z mixtures of olefins to products with a single steric configuration is of great practical importance but hard to achieve. Herein, we report an iron-catalyzed stereoconvergent 1,4-hydrosilylation reactions of E/Z mixtures of readily available conjugated dienes for the synthesis of Z-allylsilanes with high regioselectivity and exclusive stereoselectivity. Mechanistic studies suggest that the reactions most likely proceed through a two-electron redox mechanism. The stereoselectivity of the reactions is ultimately determined by the crowded reaction cavity of the α-diimine ligand-modified iron catalyst, which forces the conjugated diene to coordinate with the iron center in a cis conformation, which in turn results in generation of an anti-π-allyl iron intermediate. The mechanism of this stereoconvergent transformation differs from previously reported mechanisms of other related reactions involving radicals or metal-hydride species.

Single-atom catalysts based on TiN for the electrocatalytic hydrogen evolution reaction: a theoretical study.

The electrocatalytic hydrogen evolution reaction (HER) for water splitting is crucial for the sustainable production of clean hydrogen fuel, while the high cost of Pt catalysts impedes its commercialization. Herein, we have performed a systematic theoretical study on the electrocatalytic HER over single-atom catalysts (SACs) based on low-cost TiN. Specifically, the TiN(100) surface with a Ti or N vacancy has been considered as the support. 20 transition-metal (TM) atoms and 3 nonmetallic atoms are embedded into the Ti or N vacancy, accordingly denoted as M@Tiv or M@Nv. All the single atoms can be stabilized by the surface vacancies, controlled by the adjustable chemical potential. Interestingly, for TM-embedded TiN(100), the hydrogen binding is much stronger over M@Nv than M@Tiv, which can be attributed to the more localized d states of the TM atoms anchored by the N vacancies, indicating a strong coordination effect. Among 43 catalysts, 10 (Ni, Zn, Nb, Mo, Rh@Tiv, and Au, Pd, W, Mo, B@Nv) were predicted to have high HER catalytic activity with near-zero hydrogen adsorption free energy. For the further gaseous hydrogen evolution, Zn@Tiv can adopt both Tafel (with an energy barrier of 0.68 eV) and Heyrovsky mechanisms, while the others may prefer the Heyrovsky mechanism. This work provides a promising strategy to realize cost-efficient electrocatalysts for the HER, and highlights the important role of the local coordination environment for SACs.

A Heterostructure Coupling of Bioinspired, Adhesive Polydopamine, and Porous Prussian Blue Nanocubics as Cathode for High-Performance Sodium-Ion Battery.

Prussian blue (PB) and its analogues are recognized as promising cathodes for rechargeable batteries intended for application in low-cost and large-scale electric energy storage. With respect to PB cathodes, however, their intrinsic crystal regularity, vacancies, and coordinated water will lead to low specific capacity and poor rate performance, impeding their application. Herein, nanocubic porous Nax FeFe(CN)6 coated with polydopamine (PDA) as a coupling layer to improve its electrochemical performance is reported, inspired by the excellent adhesive property of PDA. As a cathode for sodium-ion batteries, the Nax FeFe(CN)6 electrode coupled with PDA delivers a reversible capacity of 93.8 mA h g-1 after 500 cycles at 0.2 A g-1 , and a discharge capacity of 72.6 mA h g-1 at 5.0 A g-1 . The sodium storage mechanism of this Nax FeFe(CN)6 coupled with PDA is revealed via in situ Raman spectroscopy. The first-principles computational results indicate that FeII sites in PB prefer to couple with the robust PDA layer to stabilize the PB structure. Moreover, the sodium-ion migration in the PB structure is enhanced after coating with PDA, thus improving the sodium storage properties. Both experiments and computational simulations present guidelines for the rational design of nanomaterials as electrodes for energy storage devices.

Transition metal embedded C3N monolayers as promising catalysts for the hydrogen evolution reaction.

Transition metal (TM) doped or TM, N co-doped carbon materials have attracted increasing attention as efficient catalysts for the hydrogen evolution reaction (HER), to replace Pt or reduce the usage of Pt. By using first-principles calculations, the TM-embedded C3N monolayer (TM@C3N) has been theoretically investigated for HER, for which eighteen TMs are selected from the 3d, 4d, and 5d rows. The M-CC catalysts, with the TM atom embedded into the C-C double atomic vacancy, are the most stable among the various TM@C3N materials. All the M-CC catalysts show metallic conductivity and high thermal stability. The hydrogen binding free energy for the M-CC catalysts can be optimized to be close to 0 eV by choosing a suitable TM, and the kinetic barrier under the Tafel mechanism for further gaseous hydrogen evolution can be reduced to as low as 0.58 eV. These results suggest that the HER catalytic activities of the M-CC catalysts are likely comparable or even higher than those of the well-explored MoS2 nanostructures or Pt catalysts. Moreover, the HER activities of the M-CC catalysts can be illustrated by the electronic state distribution near the Fermi level of the catalytically active sites. This study provides a new possibility for cost-efficient HER catalysts of high activity and for the application of C3N nanostructures.

Novel two-dimensional tetragonal vanadium carbides and nitrides as promising materials for Li-ion batteries.

Two-dimensional (2D) materials, owing to their unique properties, have shown great potential for energy storage. In this work, we predict two types of new 2D transition metal carbides and nitrides, namely, tetragonal V2C2 and V2N2 (tetr-V2C2 and tetr-V2N2) monolayer sheets. Comprehensive first-principle calculations show that these two 2D systems exhibit dynamic (thermal) stabilities and intrinsic metallic nature. Compared with the commercialized graphite anode material, tetr-V2C2 and tetr-V2N2 monolayer sheets exhibit lower Li diffusion barrier of 89 and 94 meV, higher theoretical capacity of 412 and 425 mA h g-1 and lower average open circuit of 0.468 and 0.583 V, respectively. Combining those advanced features, our proposed tetr-V2C2 and tetr-V2N2 monolayer sheets are both promising candidates as anode materials for lithium-ion batteries (LIBs) in the future.

Novel structures of two-dimensional tungsten boride and their superconductivity.

Two-dimensional (2D) superconductors, which can be widely applied in optoelectronic and microelectronic devices, have gained renewed attention in recent years. Based on the crystal structure prediction method and first-principles calculations, we obtain four novel 2D tungsten boride structures of tetr-, hex-, and tri-W2B2 and hex-WB4 and investigate their bonding types, electronic properties, phonon dispersions and electron-phonon coupling (EPC). The results show that both tetr- and hex-W2B2 are intrinsic phonon-mediated superconductors with a superconducting transition temperature (Tc) of 7.8 and 1.5 K, respectively, while tri-W2B2 and hex-WB4 are normal metals. We demonstrate that carrier doping as well as biaxial strain can soften the low-frequency phonon modes and enhance the strength of the EPC. While the Tc of tetr-W2B2 can be increased to 15.4 K under a compressive strain of -2%, the Tc of hex-W2B2 can be enhanced to 5.9 K by a tensile strain of +4%. With the inclusion of spin-orbit couping (SOC), the value of Tc decreases by 38.5% in our systems. Furthermore, we explore the stabilities and mechanical properties of tetr- and hex-W2B2 and indicate that they may be prepared by growing on ZnS(100) and ZnS(111), respectively. Our findings provide novel 2D superconducting materials and will stimulate more efforts in this filed.

Repairing single and double atomic vacancies in a C3N monolayer with CO or NO molecules: a first-principles study.

Even the simplest point defect in a two-dimensional (2D) material can have a significant influence on its electronic, magnetic, and chemical properties. Defect repairing in 2D materials has been a focus of concern in recent years. Based on first-principles calculations, the repair of C and N single vacancies with CO or NO molecules in a C3N monolayer has been studied. The repair process consists of two steps, i.e., filling of the vacancy with the first molecule and removal of the extra O atom by a second molecule. Overall, the repair processes of C and N single vacancies by CO or NO molecules are both thermodynamically and kinetically favorable, as evidenced by the significant energy released and the small energy barriers. In addition, the electronic and magnetic properties and the chemical activity of the C3N monolayer before and after the defect repair have been studied systematically. In addition to single vacancies, the repair of double vacancies with CO was also studied; this process is much less kinetically favorable than the case of single vacancies. This study provides useful insight into the effects of simple atomic vacancies on the physical and chemical properties of the C3N 2D semiconductor and also presents a promising strategy for repairing vacancies.

Manganese-Doped CeO2 Nanocubes for Catalytic Combustion of Chlorobenzene: An Experimental and Density Functional Theory Study.

Manganese oxide (MnOx) supported on CeO2 nanocubes (MnOx/CeO2) were synthesized and tested for the catalytic combustion of chlorobenzene (CB), which was taken as a model compound of chlorinated volatile organic compounds (CVOCs). The catalytic activity tests demonstrated that MnOx/CeO2 nanocube catalysts exhibited a catalytic activity significantly better than that of bare CeO2 nanocubes, indicating MnOx plays a significant role for CB oxidation. To illustrate the effect of MnOx on the CeO2 nanocubes, experimental and theoretical methods such as density functional theory (DFT) calculations were carried out. Experimental characterization testified that the introduction of MnOx to CeO2 nanocubes brought the facile reduction of cerium species, larger amount of Oα species and oxygen vacancies, which lead to the enhanced catalytic performance of MnOx/CeO2 nanocube. Furthermore, DFT calculations clearly validated that MnOx/CeO2 (100) models could form the oxygen vacancies more easily, and CB molecules were preferentially adsorbed on the MnOx/CeO2 (100) models than on the CeO2 (100) models, which facilitated the easier formation of C-O* bond; this facile bond formation enabled faster CB decomposition into COx, thereby a higher CB conversion on the MnOx/CeO2 (100) could be found. Therefore, the vital role of MnOx can be successfully elucidated by both experimental and theoretical methods. Hence, this finding can be utilized for enhanced catalytic performance of CeO2 nanocube catalysts for the CVOCs elimination.

Mechanisms of direct hydrogen peroxide synthesis on silicon and phosphorus dual-doped graphene: a DFT-D study.

Hydrogen peroxide (H2O2) is an important chemical commodity, with demand growing significantly in chemical synthesis due to its green characteristics. The mechanisms of the direct synthesis of hydrogen peroxide (DSHP) on metal-free silicon and phosphorus dual-doped graphene (Si-P-G) catalyst, based on a dispersion-corrected density functional theory (DFT-D) method, are systematically investigated. The most stable Si-P-G catalyst is presented, with the local region of dopants shown to play an important role in the adsorption and reduction of oxygen. A two-electron pathway is probable for DSHP on Si-P-G according to kinetic and thermodynamic analyses. The hydrogenation of O2 to OOH is the rate-limiting step, with a small barrier energy of 0.66 eV, and the potential energy surface is downhill by Gibbs free energy calculations. All results indicate that Si-P-G is a novel catalyst with high activity and good selectivity for DSHP.

A promising single atom catalyst for CO oxidation: Ag on boron vacancies of h-BN sheets.

Single atom catalysts (SACs) have attracted broad research interest in recent years due to their importance in various fields, such as environmental protection and energy conversion. Here, we discuss the mechanisms of CO oxidation to CO2 over single Ag atoms supported on hexagonal boron-nitride sheets (Ag1/BN) through systematic van der Waals inclusive density functional theory (DFT-D) calculations. The Ag adatom can be anchored onto a boron defect (VB), as suggested by the large energy barrier of 3.12 eV for Ag diffusion away from the VB site. Three possible mechanisms (i.e., Eley-Rideal, Langmuir-Hinshelwood, and termolecular Eley-Rideal) of CO oxidation over Ag1/BN are investigated. Due to "CO-Promoted O2 Activation", the termolecular Eley-Rideal (TER) mechanism is the most relevant one for CO oxidation over Ag1/BN and the rate-limiting reaction barrier is only 0.33 eV. More importantly, the first principles molecular dynamics simulations confirm that CO oxidation via the TER mechanism may easily occur at room temperature. Analyses with the inclusion of temperature and entropy effects further indicate that the CO oxidation via the TER mechanism over Ag1/BN is thermodynamically favorable in a broad range of temperatures.

Interaction between H2O, N2, CO, NO, NO2 and N2O molecules and a defective WSe2 monolayer.

In this study, the interaction between gas molecules, including H2O, N2, CO, NO, NO2 and N2O, and a WSe2 monolayer containing an Se vacancy (denoted as VSe) has been theoretically studied. Theoretical results show that H2O and N2 molecules are highly prone to be physisorbed on the VSe surface. The presence of the Se vacancy can significantly enhance the sensing ability of the WSe2 monolayer toward H2O and N2 molecules. In contrast, CO and NO molecules highly prefer to be molecularly chemisorbed on the VSe surface with the non-oxygen atom occupying the Se vacancy site. Furthermore, the exposed O atoms of the molecularly chemisorbed CO or NO can react with additional CO or NO molecules, to produce C-doped or N-doped WSe2 monolayers. The calculated energies suggest that the filling of the CO or NO molecule and the removal of the exposed O atom are both energetically and dynamically favorable. Electronic structure calculations show that the WSe2 monolayers are p-doped by the CO and NO molecules, as well as the C and N atoms. However, only the NO molecule and N atom doped WSe2 monolayers exhibit significantly improved electronic structures compared with VSe. The NO2 and N2O molecules will dissociate directly to form an O-doped WSe2 monolayer, for which the defect levels due to the Se vacancy can be completely removed. The calculated energies suggest that although the dissociation processes for NO2 and N2O molecules are highly exothermic, the N2O dissociation may need to operate at an elevated temperature compared with room temperature, due to its large energy barrier of ∼1 eV.

CO oxidation catalyzed by the single Co atom embedded hexagonal boron nitride nanosheet: a DFT-D study.

A single metal atom stabilized on two dimensional materials (such as graphene and h-BN) exhibits extraordinary activity in the oxidation of CO. The oxidation of CO by molecular O2 on a single cobalt atom embedded in a hexagonal boron nitride monolayer (h-BN) is investigated using first-principles calculations with dispersion-correction. It is found that the single Co atom prefers to reside in a boron vacancy and possesses great stability. There are three mechanisms for CO oxidation: the traditional Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms and the termolecular Eley-Rideal (TER) mechanism proposed recently. Given the relatively small reaction barriers of the rate-limiting steps for the ER, LH and TER mechanisms (0.59, 0.55 and 0.41 eV, respectively), all three mechanisms are able to occur at low temperature. The current study may provide useful clues to develop low cost single atom catalysts.

Geometric stability and reaction activity of Pt clusters adsorbed graphene substrates for catalytic CO oxidation.

The geometric stabilities, electronic structures and catalytic properties of tetrahedral Pt4 clusters anchored on graphene substrates are investigated using the first-principles methods. It is found that the small Pt4 clusters adsorbed on pristine graphene substrates easily interconvert between structural isomers by the small energy barriers, while the structural interconversion of Pt4 clusters on the defective graphene and oxygen-doped graphene (O-graphene) have the large energy barriers. Compared to other graphene substrates, the Pt4 clusters supported on the O-graphene substrate (Pt4/O-graphene) have the least geometrical distortion and the high symmetry of the Pt4 cluster can enhance the sensitivity of reactive gases. Moreover, the sequential reactions of CO oxidation on Pt4/O-graphene are investigated for comparison. Compared with the coadsorption reaction of CO and O2 molecules, the dissociative adsorption of O2 as a starting step has a small energy barrier (0.07 eV) and is followed through the Eley-Rideal reaction with an energy barrier of 0.42 eV (CO + Oads → CO2). The results provide valuable guidance for fabricating graphene-based catalysts as anode materials, and explore the microscopic mechanism of the CO oxidation reaction on atomic-scale catalysts.

Single Pt atom stabilized on nitrogen doped graphene: CO oxidation readily occurs via the tri-molecular Eley-Rideal mechanism.

Single-atom catalysts, especially with single Pt atoms, have attracted more and more attention due to their high catalytic activity for CO oxidation. The outstanding stability and catalytic activity of a single Pt atom supported on nitrogen doped graphene (Pt/NG) are revealed using first-principles calculations. We find that the stability of a Pt atom on the NG can be promoted by picking an appropriate doping configuration. The exceptionally stable Pt/NG catalyst exhibits excellent catalytic activity for CO oxidation via a new tri-molecular Eley-Rideal mechanism (2CO + O2 → OCO-OCO → 2CO2) with an energy barrier of 0.16 eV for the rate-limiting step of OCO-OCO dissociation, which is more preferable than the other two normal Langmuir-Hinshelwood and Eley-Rideal mechanisms.

Direct CO oxidation by lattice oxygen on the SnO2(110) surface: a DFT study.

As a noble-metal-free catalyst for CO oxidation, SnO2 has sparked worldwide interest owing to its highly reactive lattice oxygen atoms and low cost. The current density functional theory (DFT) results demonstrate the process of CO oxidation by lattice oxygen on the SnO2(110) surface and the recovery of the reduced surface by O2. It is found that CO can be easily oxidized on the SnO2(110) surface following the Mars-van Krevelen mechanism. The adsorbed oxygen turns into various oxygen species by transferring electron(s) to the chemisorbed oxygen, which is only found on the partially reduced SnO2-x surface, but not on the perfect SnO2(110) surface: O2(gas) ↔ O2(ad) ↔ O2(-)(ad) ↔ O2(2-)(ad) ↔ O(2-)(lattice) + O(-)(ad). The calculated stretching frequencies would help to distinguish the various adsorbed species observed in experiment and of course help in the assignment of vibrational modes in the experimental spectra.

A density function theory study on the NO reduction on nitrogen doped graphene.

The mechanisms for the catalytic reduction of NO on the metal-free nitrogen doped graphene (NG) support are investigated using the density function theory (DFT) calculations both with and without the van der Waals (vdW) correction. The results indicate that the dimer mechanism is more facile than the direct decomposition mechanism. In the dimer mechanism, a three-step reaction is identified: (i) the coupling of two NO molecules into a (NO)2 dimer, followed by (ii) the dissociation of the (NO)2 dimer into N2O + Oad, then (iii) the O adatom is taken away easily by the subsequent NO. Once the NO2 is desorbed, the remaining N2O can be reduced readily by NO on NG. The reaction processes are also confirmed from the first principles molecular dynamics simulations. The results suggest that the NG is an efficient metal-free catalyst for catalytic reduction of NO.