Insertion Of Atoms Research Articles

Recent Advances in Electronic Structure Modifications of Layered Double Hydroxide (LDH) for the Water Splitting Application

AbstractElectrocatalytic water splitting is a feasible method for large‐scale hydrogen production. Recently, layered double hydroxides (LDH) have been identified as a possible candidate for accelerating the water splitting process. Nevertheless, certain structural alterations are necessary for immaculate LDH because of their weak electrocatalytic activity. These structural changes alter the local reaction environment by modulating the electronic structure of the metal center present in the LDH. This electronic structure tailoring is accomplished by a variety of processes, including heteroatom doping, single atom inclusion, cationic defect, oxygen vacancy creation, and heterostructure formation. Recently, there has been an uptick of advancement in this field, and it is necessary to summarize these developments. This review provides a concise summary of the current reports on the electronic structure manipulation of layered double hydroxide. The review begins by examining the local environmental changes of LDH resulting from the insertion of single atoms. Subsequently, we explore the charge transfer that occurs at the interface between LDH and other transition metal heterostructures. In addition, we explored the impact on the metal center near the vacancies on the basal plane of LDH. Finally, we presented a future perspective and guidance for advancing this field in electrocatalysis.

Direct oxygen insertion into C-C bond of styrenes with air.

Skeletal editing of single-atom insertion to basic chemicals has been demonstrated as an efficient strategy for the discovery of structurally diversified compounds. Previous endeavors in skeletal editing have successfully facilitated the insertion of boron, nitrogen, and carbon atoms. Given the prevalence of oxygen atoms in biologically active molecules, the direct oxygenation of C-C bonds through single-oxygen-atom insertion like Baeyer-Villiger reaction is of particular significance. Herein, we present an approach for the skeletal modification of styrenes using O2 via oxygen insertion, resulting in the formation of aryl ether frameworks under mild reaction conditions. The broad functional-group tolerance and the excellent chemo- and regioselectivity are demonstrated in this protocol. A preliminary mechanistic study indicates the potential involvement of 1,2-aryl radical migration in this reaction.

Structural order and disorder within novel antiferromagnetic RCrxGa3-yGey and R4Cr1-xGa12-yGey intermetallic compounds (R = Tb, Dy)

Single crystals of intermetallic phases RCrxGa3−yGey (R = Tb, Dy; x = 0.19–0.23, y = 0–0.4) and R4Cr1−xGa12−yGey (R = Tb, Dy; x = 0–0.13, y = 3–4) were grown from Ga flux ensuring the absence of magnetic impurities. The X-ray diffraction experiments revealed that the compounds belong to the family of filled AuCu3-type gallides. The compounds are formed upon the insertion of Cr atoms into E6 octahedral voids (E = Ga/Ge), which can occur in either disordered (RCrxGa3-yGey) or ordered (R4Cr1-xGa12-yGey) fashion. The unique feature of the obtained compounds is the strong correlation between the level of Ge doping and the Cr concentration in the phases, which allows one to control both the structural and magnetic ordering. At low Ge concentration, the cubic RCrxGa3-yGey phases form, which then experience tetragonal distortion upon the increase in the Ge content, and the cubic R4Cr1-xGa12-yGey 2×2×2 superstructures are formed at even higher Ge concentrations. The X-ray diffraction analysis also showed a presence of structural defects in the phases, which are caused by different size of empty E6 and filled CrE6 octahedra. Magnetic measurements of the single crystals of the cubic phases reveal antiferromagnetic ordering of the rare earth sublattice with the Neel temperatures decreasing upon Ge doping from 22 K for RCrxGa3 to 10 K for R4Cr1−xGa12−yGey. The Ge doping causes gradual decrease in the strength of antiferromagnetic R-R interactions ultimately leading to noncollinear magnetic structure in the superstructure R4Cr1−xGa12−yGey phases.

Pushing the Thickness Limit of the Giant Rashba Effect in Ferroelectric Semiconductor GeTe.

Ferroelectric Rashba semiconductors (FERSCs) such as α-GeTe are promising candidates for energy-efficient information technologies exploiting spin-orbit coupling (SOC) and are termed spin-orbitronics. In this work, the thickness limit of the Rashba-SOC effect in α-GeTe films is investigated. We demonstrate, using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations performed on pristine GeTe, that down to 1 nm, GeTe(111) films on a Sb-covered Si(111) substrate continuously exhibit a giant Rashba effect characterized, at 1 nm, by a constant of 5.2 ± 0.5 eV·Å. X-ray photoemission spectroscopy (XPS) allows the understanding of the persistence of the Rashba effect by evidencing a compensation of Ge vacancy defects resulting from the insertion of Sb interfacial atoms in the early stage growth of the GeTe(111) films.

Minimum Energy Atomic Deposition: A novel, efficient atomistic simulation method for thin film growth

Thin-film growth is an area of research concerned with complex phenomena happening at atomic scales. Therefore, molecular simulation has been an important tool to confront experimental results to theoretical assumptions. However, the traditional thin film growth simulation methods, i.e., Molecular Dynamics (MD) and kinetic Monte-Carlo (kMC) and combinations thereof, suffer from limitations inherent to their design, i.e., limitations in system size and simulation time for MD and predetermined reaction rates and reaction sites for kMC. Consequently, it is practically impossible to simulate the evolution of polycrystalline growth resulting in ∼100nm thick films with realistic stress fields and defect structures, such as grain boundaries, stacking faults, etc. In this work, we propose a versatile and efficient atomistic simulation method (Minimum Energy Atomic Deposition) which works by direct insertion of atoms at points of minimal potential energy through efficient scanning of candidate positions and rapid relaxation of the system. This method allows simulating ≥100nm film thickness while mimicking experimental growth rates and high crystallinity and low-defect concentration and enables in-depth studies of atomic growth mechanisms, the evolution of crystal defects, and residual stress build-up. We demonstrate the efficiency and versatility of the method through the deposition of Al on Si, Al on Al, and Si on Si. The simulation results are systematically compared with experimental observations of thin-film deposition, yielding consistent observations. The method has been implemented in open-source LAMMPS software, making it easily accessible to the research community.

DFT insight into the structural, vibrational, and electronic properties of thin [110] Ge nanowires as anodic material for Li batteries

Germanium nanowires could be used to improve as anodic materials since their charge rate is better than that of the current graphite electrodes. In this work, we present a Density Functional Theory study of the effect of interstitial Li atoms on the vibrational, electronic, and mechanical properties of ultrathin hydrogen-passivated Ge nanowires (HGeNWs) with diamond structure, grown along the [110] crystallographic direction, and with a diameter of ∼14.4 Å. The interstitial Li atoms were placed at the tetrahedral positions (Td) reported as the more favorable ones. The phonon band structure of the HGeNWs reveals the existence of high frequency vibrations due to the hydrogen atoms at the nanowire surface. The effect of one interstitial Li atom in the nanowire leads to the apparition of three flat phonon bands almost independent of the collective vibrational states of the nanowire, reflecting a weak interaction between the Li atom and the neighboring ones; and a shift of the high vibrational modes to lower frequencies that results in more dispersive states. The electronic band structure confirms a transition from semiconducting to metallic behavior by adding a single Li interstitial atom per unit cell. The formation energies indicate that the nanowires with interstitial Li atoms are stable, and the average binding energy per Li atom slightly increases as a function of the concentration of Li atoms. The insertion of Li atoms in the nanowire leads to a volumetric expansion, without fracture or broken bonds. Even more, the redistribution of the electronic charge due to the Li atoms give the Ge-Ge bonds more axial elasticity and the values of the modulus of Young are almost constant for all studied concentrations of Li atoms. These theoretical results indicate an improvement of mechanical and electronic properties of Ge nanowires through the addition of interstitial Li atoms that could be important for their use as anodes in rechargeable Li batteries.

Electrochemical Performance of Niobium MXenes with Lanthanum.

MXenes are the newest class of two-dimensional nanomaterials characterized by large surface area, high conductivity, and hydrophilicity. To further improve their performance for use in energy storage devices, heteroatoms or functional groups can be inserted into the Mxenes' structure increasing their stability. This work proposes insertion of lanthanum atoms into niobium-MXene (Nb-MX/La) that was characterized in terms of morphogy, structure, and electrochemical behavior. The addition of La to the Nb-MXene structure was essential to increase the spacing between the layers, improving the interaction with the electrolyte and enabling charge/discharge cycling in a higher potential window and at higher current densities. Nb-MX/La achieved a specific capacitance of up to 157 mF cm-2, a specific capacity of 42 mAh cm-2 at 250 mV s-1, a specific power of 37.5 mW cm-2, and a specific energy of 14.1 mWh cm-2 after 1000 charge/discharge cycles at 50 mA cm-2.

Silver-Catalyzed Single-Carbon Insertion of Indoles with Acetophenone N-Triftosylhydrazones.

Here, we report a silver carbene-enabled single-carbon insertion reaction of indoles via a one-pot, two-step sequence to deliver a dearomative quaternary center quinoline scaffold in a modular fashion. Specifically, we used N-triftosylhydrazones as masked donor-donor carbene precursors that facilitate the insertion of carbon atoms bearing various functional groups to the library of functionalized quinoline. Experimental and DFT evidence support the transient presence of a cyclopropane species and removal of protecting groups.

Elektrochemische Gerüst‐Editierung von Indolen durch Stickstoffatom‐Insertion mit nachhaltiger Sauerstoff‐Reduktionsreaktion

AbstractMolekulares Editieren hat in letzter Zeit stark an Bedeutung gewonnen und sich als einzigartiges Werkzeug für Late‐Stage Diversifizierungen erwiesen. Bislang waren für die Indol‐Editierung meist überstöchiometrische Mengen an teuren hochvalenten Iod(III)‐Reagenzien erforderlich. Im Gegensatz dazu zeigen wir hier, dass Elektrizität nachhaltige Stickstoffatom‐Insertionsreaktionen ermöglicht, um bio‐relevante Chinazolin‐Gerüste ohne stöchiometrische chemische Redox‐Abfallprodukte zu erhalten. Die Übergangsmetall freie Elektro‐Editierung wurde durch die Sauerstoff‐Reduktionsreaktion (ORR) ermöglicht und erwies sich in großem Maßstab als robust, wobei eine Vielzahl wertvoller funktioneller Gruppen toleriert wurden.

Insights into the nature of Zr-species in MFI-type Zr-metallosilicates by using bulk and surface techniques

The purpose of this study is to prepare Zr-metallosilicates with MFI-type framework via direct hydrothermal approach, by varying Si and Zr precursors. First, a set of routine characterization techniques was applied to confirm the presence of the targeted structure as well as their intrinsic properties. Results suggest the formation of MFI-type materials with large specific surface areas (up to 421 m2 g−1). Then, a combination of advanced spectroscopic techniques (XPS, ToF-SIMS, EPR), high-resolution microscopy, and periodic Density Functional Theory (DFT) calculations were applied to study their bulk and surface properties as well as the nature and localization of Zr-species. It appears that the insertion of zirconium atoms within a MFI framework is energetically unfavorable, leading to the formation of an amorphous silica-zirconia shell coating the zeolite crystals.

Room-temperature ferromagnetism in semimetallic Co-intercalated MoTe2

Fe-intercalated TaS2 prepared via the chemical intercalation of iron into van der Waals (vdW) layered 2H-TaS2 crystals enables hard ferromagnetic behavior, making it attractive for spintronic applications. However, the Curie transition at room temperature and no gate controllability in metallic TaS2 are still unfavorable. Here, we demonstrate the feasibility of realizing a ferromagnetic semimetal through the wet chemical intercalation of cobalt into semiconducting 2H-MoTe2, thereby leveraging its polymorphism. Transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy reveal the insertion of pure Co atoms within the vdW gap following the intercalation process. Co-intercalated MoTe2 (Co-MoTe2) demonstrates a conductivity of 1.5 orders of magnitude higher than that of 2H-MoTe2. This significant increase in the conductance facilitates the direct investigation of ferromagnetism through magnetotransport measurements. Co-MoTe2 exhibits a positive magnetoresistance of approximately 4 %, with hysteresis observed even at room temperature. Furthermore, density functional theory calculations corroborate the enhancement of the magnetoresistance ratio and Curie temperature, which is attributed to the ferromagnetism induced by local magnetic moments resulting from the incorporation of cobalt. This study paves the way for enhanced practical applications in future spintronics by demonstrating the effectiveness of integrating foreign magnetic atoms into the vdW gap, thereby increasing the operational temperature.

Electrochemical Skeletal Indole Editing via Nitrogen Atom Insertion by Sustainable Oxygen Reduction Reaction.

Skeletal molecular editing gained considerable recent momentum and emerged as a uniquely powerful tool for late-stage diversifications. Thus far, superstoichiometric amounts of costly hypervalent iodine(III) reagents were largely required for skeletal indole editing. In contrast, we herein show that electricity enables sustainable nitrogen atom insertion reactions to give bio-relevant quinazoline scaffolds without stoichiometric chemical redox-waste product. The transition metal-free electro-editing was enabled by the oxygen reduction reaction (ORR) and proved robust on scale, while tolerating a variety of valuable functional groups.

Atomic Tailoring of Ubiquitin Side Chains Influences E2‐Mediated Ubiquitin Chain Formation

AbstractUbiquitin (Ub) is a small, highly conserved protein essential for eukaryotic biology, and is unique in its formation of polyubiquitin chains by conjugation to one of its seven lysine side chains. Here we report that atomic tailoring of Ub side chains – i. e. the insertion, deletion, or replacement of specific atoms – has significant and unexpected consequences on the enzymatic conjugation of Ub oligomers by isopeptide bond formation mediated by E2 conjugating enzymes. These studies employed chemical synthesis and ligation methods to prepare numerous specifically tailored Ub monomers on multi‐milligram scales. While some modifications including N‐terminal acylation and methionine replacement did not affect protein folding or Ub chain formation with Ube2 K, other modifications had a pronounced effect of oligomerization with Ubc13/Mms2. We observed that Ala46Hse mutation obliterates the ability of this Ub monomer to accept another Ub at Lys63 in Ubc13‐mediated conjugations. Exhaustive replacement of all seven lysines with shorter surrogates Orn, Dab, or Dap essentially blocks Ub chain formation, and in the case of Dap, precludes proper folding of the Ub protein.

Au-doped PtCu2 nanonetworks with interface-rich for enhancing methanol electro-oxidation performance

Regulating the near-surface structure of platinum-based alloys by inserting transition metal atoms can significantly improve the electro-oxidative performance of small organic molecules. So far, it is rarely reported that a small amount of Au element is introduced into the interior of Pt-based alloys as an active auxiliary to adjust the electrocatalytic activity and stability of Pt-based alloys with special morphologies. Herein, a stable three-dimensional (3D) Au-doped PtCu2/C (Au–PtCu2/C) catalyst with nanonetwork structure and abundant interfaces has been successfully developed, in which the oxyphilic Cu atoms and stable Au atoms are implanted into the whole and inside of the Pt-based nanonetwork, respectively. Detailed physical characterizations of the Au–PtCu2/C catalyst illustrate that the insertion of Au atoms generates core-shell-like nanonetwork, highly-open structure, strong electronic effect, and sufficient active sites. The well-designed Au–PtCu2/C catalyst exhibits superior mass activity (MA) of 2355 mA·mgPt−1 and long-term durability of 500 cycles toward methanol oxidation reaction (MOR) in an acidic medium. Notably, the MA of the Au–PtCu2/C catalyst is 7.3 folds and 1.3 folds that of the Pt/C (322 mA·mgPt−1) and PtCu2/C (1821 mA·mgPt−1) catalysts, respectively. The kinetic and thermodynamics studies indicate that the Au–PtCu2/C catalyst is superior to PtCu2/C and Pt/C catalysts in reducing the electrochemical activation energy of MOR, promoting the mass transfer of methanol molecules, and enhancing electronic conductivity. This work proposes an advanced strategy to fabricate efficient and durable electrocatalyst with excellent electrocatalytic MOR performance, thereby enabling catalysts with special morphology to have greater application potential in direct methanol fuel cell.

Synthesis of Novel Polymers with Biodegradability by Main-Chain Editing of Chiral Polyketones.

Although the use of biodegradable plastics is suitable for unrecoverable, single-use plastic, their high production cost and much lower variety compared to commodity plastics limit their application. In this study, we developed a new polymer with potential biodegradability, poly(ketone/ester), synthesized from propylene and carbon monoxide. Propylene and carbon monoxide are easily available at low costs from fossil resources, and they can also be derived from biomass. Using an atom insertion reaction to the main chain of the polymer, the main-chain editing of the polymer molecule proceeded with up to 89% selectivity for atom insertion over main-chain cleavage.

Controllable Skeletal and Peripheral Editing of Pyrroles with Vinylcarbenes

AbstractThe skeletal editing of azaarenes through insertion, deletion, or swapping of single atoms has recently gained considerable momentum in chemical synthesis. Here, we describe a practical skeletal editing strategy using vinylcarbenes in situ generated from trifluoromethyl vinyl N‐triftosylhydrazones, leading to the first dearomative skeletal editing of pyrroles through carbon‐atom insertion. Furthermore, depending on the used catalyst and substrate, three types of peripheral editing reactions of pyrroles are also disclosed: α‐ or γ‐selective C−H insertion, and [3+2] cycloaddition. These controllable molecular editing reactions provide a powerful platform for accessing medicinally relevant CF3‐containing N‐heterocyclic frameworks, such as 2,5‐dihydropyridines, piperidines, azabicyclo[3.3.0]octadienes, and allylated pyrroles from readily available pyrroles. Mechanistic insights from experiments and density functional theory (DFT) calculations shed light on the origin of substrate‐ or catalyst‐controlled chemo‐ and regioselectivity as well as the reaction mechanism.

Controllable Skeletal and Peripheral Editing of Pyrroles with Vinylcarbenes.

The skeletal editing of azaarenes through insertion, deletion, or swapping of single atoms has recently gained considerable momentum in chemical synthesis. Here, we describe a practical skeletal editing strategy using vinylcarbenes in situ generated from trifluoromethyl vinyl N-triftosylhydrazones, leading to the first dearomative skeletal editing of pyrroles through carbon-atom insertion. Furthermore, depending on the used catalyst and substrate, three types of peripheral editing reactions of pyrroles are also disclosed: α- or γ-selective C-H insertion, and [3+2] cycloaddition. These controllable molecular editing reactions provide a powerful platform for accessing medicinally relevant CF3-containing N-heterocyclic frameworks, such as 2,5-dihydropyridines, piperidines, azabicyclo[3.3.0]octadienes, and allylated pyrroles from readily available pyrroles. Mechanistic insights from experiments and density functional theory (DFT) calculations shed light on the origin of substrate- or catalyst-controlled chemo- and regioselectivity as well as the reaction mechanism.

Atomic-scale oxygen-vacancy engineering in Sub-2 nm thin Al2O3/MgO memristors

Ultrathin (sub-2 nm) Al2O3/MgO memristors were recently developed using an in vacuo atomic layer deposition (ALD) process that minimizes unintended defects and prevents undesirable leakage current. These memristors provide a unique platform that allows oxygen vacancies (VO) to be inserted into the memristor with atomic precision and study how this affects the formation and rupture of conductive filaments (CFs) during memristive switching. Herein, we present a systematic study on three sets of ultrathin Al2O3/MgO memristors with VO-doping via modular MgO atomic layer insertion into an otherwise pristine insulating Al2O3 atomic layer stack (ALS) using an in vacuo ALD. At a fixed memristor thickness of 17 Al2O3/MgO atomic layers (∼1.9 nm), the properties of the memristors were found to be affected by the number and stacking pattern of the MgO atomic layers in the Al2O3/MgO ALS. Importantly, the trend of reduced low-state resistance and the increasing appearance of multi-step switches with an increasing number of MgO atomic layers suggests a direct correlation between the dimension and dynamic evolution of the conducting filaments and the VO concentration and distribution. Understanding such a correlation is critical to an atomic-scale control of the switching behavior of ultrathin memristors.

Drug design via single-carbon atom insertion

Drug design via single-carbon atom insertion

Controlled Ring Opening of a Tetracyclic Tetraphosphane with Twofold Metallocene Bridging.

A direct route to a doubly ferrocene bridged tetracyclic tetraphosphane 1 was developed via reductive coupling of Fe(CpPCl2)2 (2 a), where a chlorine terminated linear P4-compound 3 could be identified as an intermediate. Selective P-P bond activation was further achieved by reacting 1 with elemental selenium or [Cp*Al]4, where regioselective insertion of Se or Al atoms resulted in ferrocenylene bridged [P4Se] (4) or [P4Al] (7) moieties. Compound 7 can be transformed to a hydrogen terminated linear P4 species, 8, with protic solvents. Methylation of compound 1 with MeOTf, proceeds via intermediate formation of monomethylated species 5, which gradually produced Me2-terminated dicationic 6, again containing a linear P4-unit. Besides spectroscopic characterization, the structural details of compounds 1, 4, 6, and 8 could be determined by SC-XRD. Moreover, DFT calculations were used to rationalize the reactivity of 1, derived compounds and intermediates. As a key feature, 1 undergoes ring opening polymerization to a linear polyphosphane 9.