Replacement Of Atom Research Articles

Bioorthogonal Activation of Deep Red Photoredox Catalysis Inducing Pyroptosis.

The revolutionary impact of photoredox catalytic processes has ignited novel avenues for exploration, empowering us to delve into nature in unprecedented ways and to pioneer innovative biotechnologies for therapy and diagnosis. However, integrating artificial photoredox catalysis into living systems presents significant challenges, primarily due to concerns over low targetability, low compatibility with complex biological environments, and the safety risks associated with photocatalyst toxicity. To address these challenges, herein, we present a novel bioorthogonally activatable photoredox catalysis approach. In this approach, potent photocatalyst selection via atom replacement of the rhodamine core yielded the bioorthogonally activatable photocatalyst (PC-Tz). The introduction of 1,2,4,5-tetrazine quenched its photocatalytic properties, which were restored upon an intracellular inverse electron-demand Diels-Alder (iEDDA) reaction with trans-cyclooctene (TCO) localized in mitochondria. This reaction led to remarkable photocatalytic oxidation of nicotinamide adenine dinucleotide (NADH), effectively manipulating the mitochondrial electron transport chain (ETC) under hypoxic conditions in cancer cells. Additionally, photocatalytic pyroptotic cell death was observed through a caspase-3/gasdermin E (GSDME) pathway, achieving notable antitumor efficacy and adenosine triphosphate (ATP) reduction in tumor cells. To the best of our knowledge, this represents the first example of bioorthogonally activatable photoredox catalysis, opening new avenues for chemists to spatiotemporally control activity in specific cell organelles without disrupting other native biological processes.

The Heteropolyacid-Catalyzed Conversion of Biomass Saccharides into High-Added-Value Products and Biofuels

The industrial processes used to produce paper and cellulose generate many lignocellulosic residues. These residues are usually burned to produce heat to supply the energy demands of other processes, increasing greenhouse gas emissions and resulting in a high environmental impact. Instead of burning these lignocellulosic residues, they can be converted into saccharides, which are feedstock for high-value products and biofuels. Keggin heteropolyacids are efficient catalysts for obtaining saccharides from cellulose and hemicellulose and converting them into bioproducts or biofuel. Furfural, 5-hydroxymethylfurfural, levulinic acid, and alkyl levulinates are important platform molecules obtained from saccharides and raw materials in the biorefinery processes used to produce fine chemicals and biofuels. This review discusses the significant progress achieved in the development of the processes based on heteropolyacid-catalyzed reactions to convert biomass and their residues into furfural, 5-hydroxymethylfurfural, levulinic acid, and alkyl levulinates in homogeneous and heterogeneous reaction conditions. The different modifications that can be performed to a Keggin HPA structure, such as the replacement of the central atom (P or Si) with B or Al, the doping of the heteropolyanion with metal cations, and a proton exchange with metal or organic cations, as well as their impact on the catalytic activity of HPAs, are detailed and discussed herein.

Atomically Tailored Zn-ZIF-8 via RuNi Nanoalloy Replacement for Improved Photocatalytic H2 Evolution.

In this study, we developed a solid-state atomic replacement method for metal catalysts, enabling the exchange of metal atoms between single atoms and nanoalloys to create new combinations of nanoalloys and single atoms. We observed that partial metal interchange occurred between the RuNi nanoalloy and Zn from the zeolitic imidazolate framework-8 (ZIF-8) on a carbon-nitrogen framework (CNF) at a high temperature of 900 °C, leading to the creation of RuZn nanoparticles and single nickel atoms (Ni-CN). Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analyses revealed that Ni is atomically dispersed within (RuZn)/Ni-CN. This finding confirms the migration of Zn and Ni during the pyrolysis of the RuNi@ZIF-8 precursor, providing definitive evidence of atomic replacement. Due to the synergistic influence of RuZn nanocrystals and Ni-CN, the resulting (RuZn)/Ni-CN multisite catalyst exhibited superior hydrogen evolution reaction (HER) ability compared to the conventional nanoalloy-based catalysts. Density functional theory calculations revealed that the integration of the (RuZn)n cluster on Ni surrounded with different N-coordinated carbon structures enhanced HER activity with the optimized (RuZn)n/NiN2C2 catalyst exhibiting a low ΔGH and improved electron charge redistribution, thereby promoting favorable hydrogen adsorption. Our findings provide valuable insights into the design and optimization of photocatalysts through atomic-level engineering, opening new avenues for efficient and sustainable energy conversion technologies.

Influence of Co Doping on Copper Nanoclusters for CO2 Electroreduction.

Copper stands out as one of the few metals capable of reducing carbon dioxide (CO2) beyond carbon monoxide (CO) and formic acid (HCOOH). Furthermore, substitutional doping in nanoclusters (NCs) has been expected to enhance their catalytic performance, even though our atomistic understanding of the influence of dopants is far from complete. Here, we investigate the effects induced by cobalt (Co) substitution doping in the Cu55 NC on the electroreduction of CO2 using density functional theory calculations combined with the computational hydrogen electrode model. We found that the replacement of a single copper atom in Cu55 by Co is energetically favorable, and it induces a drastic change in the density of states, for example, the appearance of a sharp peak near the Fermi level. The presence of a dopant atom on the surface increases the adsorption strength for all reaction intermediates, while also changing the preference of the adsorption site for selected species. The presence of the dopant atom on the surface of the particle hinders the production of CO in favor of more reduced products such as methane and methanol. From our analysis, it was observed that the catalyst will not suffer from poisoning by the OH species. However, our calculations predict that the catalysts will also enhance the formation of hydrogen in a competing reaction.

Bioisosteric Replacement in the Search for Biologically Active Compounds: Design, Synthesis and Anti-Inflammatory Activity of Novel [1,2,4]triazino[2,3-c]quinazolines.

Background: Designing novel biologically active compounds with anti-inflammatory properties based on condensed quinazolines is a significant area of interest in modern medicinal chemistry. In the present study, we describe the development of promising new bioactive molecules through the bioisosteric replacement of a carbon atom with a sulfur atom in anti-inflammatory agents, specifically 3-methyl-2-oxo-2H-[1,2,4]triazino[2,3-c]quinazolin-6-yl)butanoate. Methods: Design and synthetic studies have led to the series of previously unknown substituted 2-[((3-R-2-oxo-2H-[1,2,4]triazino[2,3-c]quinazolin-6-yl)methyl)thio]carboxylic acids and their esters. These compounds were synthesized by reacting 6-chloroalkyl-3-R-2H-[1,2,4]triazino[2,3-c]quinazolin-2-ones with sulfanylalkyl carboxylic acids and their functional derivatives. The purity and structure of the obtained compounds were confirmed using a set of physicochemical methods, including elemental analysis, HPLC-MS, and 1H NMR spectroscopy. Molecular modeling, predicted toxicity, drug-likeness, and pharmacokinetics data were used to select compounds for evaluation of their effects on acute aseptic inflammation (carrageenan-induced paw edema test) and on markers of the inflammatory process. Results: The compound 2-((1-(3-methyl-2-oxo-2H-[1,2,4]triazino[2,3-c]quinazolin-6-yl)ethyl)thio)acetic acid (compound 2e) was identified as the most active anti-inflammatory agent (AA = 53.41%), demonstrating significant inhibition of both paw edema development and the generation of pro-inflammatory cytokines and mediators. Conclusions: Results from docking studies and analysis of "structure-affinity" correlations revealed that these compounds are promising candidates for further modification and detailed investigation of their anti-inflammatory activity.

Synthesis, in vitro and in vivo biological evaluation of novel dual compounds targeting both acetylcholinesterase and serotonergic 5-HT4 receptors with potential interest in the treatment of Alzheimer's disease

In this work, we exemplified the “copride” family of drug candidates able to both inhibit acetylcholinesterase and to activate 5-HT4 receptors, with anti-amnesiant and promnesiant activities in mice. Twenty-one analogs of donecopride, the first-in class representative of the series, were synthesized exploring the influence on the biological activities of the substituents (methoxy, amine and chlorine) carried by its phenyl ring. This work was the support of an intensive structure-activity relationship study and allowed to obtain some interesting derivatives of donecopride. In this respect, the replacement of the methoxy group of the latter with a deuterated one led to deudonecopride. On the other hand, the replacement of the chlorine atom of donecopride by various halogen atoms was of particular interest, among which fluorine led to a potent analog, we called flucopride. The latter exhibited promising in vitro activities associated to excellent drugability parameters. Flucopride was consequently involved in in vivo studies such as a scopolamine-induced deficit model of working memory and in a novel object recognition test. Through these evaluations, flucopride demonstrated both its antiamnesiant and promnesiant capacities, which could make it a potential preclinical drug candidate for the treatment of Alzheimer's disease.

Microstructural and mechanical properties of high-strength geopolymer based on Martian soil simulant

Geopolymers made from simulated Martian regolith would suffer from exhibit poor engineering properties, rendering them unsuitable as base materials. To improve the mechanical properties of geopolymers, this study prepared a new Martian soil simulant named DH-1. DH-1- based geopolymers were synthesized using Al2O3 (Al group) and metakaolin (MK group) as modifying agents. The durability of geopolymers with ultraviolet (UV) radiation was assessed under simulated Martian atmospheric conditions. The results indicated that the UCS and FS of both the Al and MK groups increased with curing time, with maximum UCS and FS of 55.27 MPa and 15.16 MPa, respectively. The UCS and FS of the Al and MK groups exhibited a two-phase change. The inflection points for rapid to slow in the UCS and FS occurred on day 28 for the Al group and day 14 for the MK group. The addition of Al2O3 and metakaolin promoted the replacement of silicon atoms by aluminum atoms in the silica-oxygen group, producing more gels product. After UV irradiation, the UCS and FS of the geopolymer decreased by 13 % and 44 %, respectively. Furthermore, the geopolymers underwent carbonation, with new cracks forming due to the combined effects of UV exposure, causing strength reduction.

Flexible Hybrid Membrane with Synergistic Exciton Dynamics for Excessive 280 h of Durably Piezo-Photocatalytic H2O-to-H2 Conversion.

Solar-driven H2O-to-H2 conversion is a feasible artificial photoconversion technology for clean energy production. However, low photon utilization efficiency has become a major obstacle limiting the practical application of this technology. Herein, a metal atomic replacement (Sb→Ni) is conducted to disintegrate bulk Sb2S3 nanorods and synchronously grow the NiS nanolayers, and a flower-like Sb2S3-NiS nanocomposite with high BET specific surface area and synergistic exciton dynamics is constructed for simulated solar (SSL)-driven H2O-to-H2 conversion. The optimal Sb2S3-NiS nanocomposite is compounded with polyvinylidene fluoride (PVDF) to prepare a flexible PVDF/Sb2S3-NiS (PSN) hybrid membrane with stable structure and excellent recyclability via an electrospinning method. Due to the synergistically interacted organic-inorganic interface and high porosity, it is conducive to the exposure of effective active sites, exciton conduction and mass transfer and exchange, thereby an outstanding alkaline (Ph=13.0) H2O-to-H2 conversion activity with a 0.06% of solar-to-hydrogen efficiency and over 280 h (70 cycles) of durable recycling is achieved under the collaborative drives of SSL and weak ultrasound (40 Hz). This study raises a state-of-the-art membrane material for solar-driven panel reaction technology.

Impact of Alkoxy Side Chains on the Quinoxaline-Based Electron Acceptors for Efficient Organic Solar Cells.

In this work, three alkoxy-substituted quinoxaline core-based small-molecule acceptors (BQO-F, BQDO-F, and BQDO-Cl) are developed to elucidate the impact of ethoxy substituents on the physicochemical and photoelectric properties. Comparative analysis reveals that dialkoxy-substituted BQDO-F has a more planar molecular skeleton, a red-shifted absorption spectrum, upshifted energy levels, stronger crystallinity, and reduced energetic disorder compared to the monoalkoxy-substituted BQO-F. Although the replacement of fluorine atoms with chlorine atoms on the end-capped units of BQDO-F leads to a bathochromically shifted absorption spectrum, the resulting molecule BQDO-Cl shows worse π-π packing order compared to BQDO-F. Benefiting from the more favorable active layer morphology and improved carrier dynamics, the PBDB-T:BQDO-F-based organic solar cell achieves a much higher power conversion efficiency (PCE) of 16.41% compared to that of 14.48% obtained in the BQO-F-based device. In comparison with the BQDO-F-based device, the higher voltage loss of the BQDO-Cl-based device results in a lower PCE of 15.89%. The results clarify the effects of ethoxy substituents and end-capped substitutions of quinoxaline core-based small-molecule acceptors on efficient organic solar cells.

Tetrapyrrolic macrocycles self-organization into floating layers and sensory properties of their Langmuir-Schaefer films

The influence of the chemical structure of the 5,10,15,20-tetraphenylporphyrin (I) and 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (II) on their supramolecular organization in floating layers at the air/water interface and sensor properties in Langmuir-Schaefer films has been investigated. It was shown that a minor change in the macrocycle structure (namely, the replacement of a single nitrogen atom from the center to the periphery of macrocycle) has a considerable effect on the surface properties and hysteresis processes of the floating layers. Using the Bruster angle microscopy, it was established that both porphyrins aggregate even before the compression of their floating layers begins. The aggregation is more pronounced in porphyrin I. The analysis of hysteresis loops showed that the formation of a floating layer by the modified porphyrin II requires approximately 100 times more energy than for the unmodified porphyrin I. Using the Langmuir-Schaefer (LS) method, the floating layers were transferred onto solid substrates and the resulting thin films were analyzed by atomic force microscopy, scanning electron microscopy, polarization optical microscopy, and spectrophotometry. The combination of these methods revealed a general tendency of the porphyrins to form 3D structures on the surface of LS-films. The study of the basic properties of the porphyrin's LS-films showed that both porphyrins are diprotonated. The protonation process in porphyrin II occurs at a concentration of HClO4 that is 1000 times lower than that observed in porphyrin I. The greater tendency to protonation of porphyrin II is caused by the availability of both nitrogen atoms (the external nitrogen atom located at the macrocycle periphery and the internal nitrogen atom, which becomes more assesible to interactions due to the distortion of the macrocycle). As for the sensor properties of LS-films for iodide ion in aqueous solutions, it was observed that the diprotonated form of porphyrin I exhibited higher sensitivity due to a more developed film surface because of the presence of a greater number of 3D aggregates. The data obtained can be used in the development of efficient pH-controlled thin-film sensor materials for halide ions.

The role of spacer heteroatomic fragment in spectroscopic and luminescent behaviour of phenyl-substituted phthalocyanine complexes

Peripheral phenyl-substituted metal phthalocyanines with thio and oxa substitution in the spacer bridge fragment were obtained in the work. Spectroscopic properties were studied for the obtained complexes, and the main patterns of behavior and characteristics change depending on the solvent and the nature of the spacer atom. It is shown that the replacement of an oxygen atom in the bridge fragment of a peripheral substituent with a sulfur atom leads to a change in the values of the fluorescence quantum yields. It was revealed that the presence of a spacer fragment is one of the key factors that strongly influence both the solubility of phthalocyanine complexes and their aggregation behavior in various solvents.

First-Principles Investigation on Ru-Doped Janus WSSe Monolayer for Adsorption of Dissolved Gases in Transformer Oil: A Novel Sensing Candidate Exploration.

Using first-principles theory, this work purposes Ru-doped Janus WSSe (Ru-WSSe) monolayer as a potential gas sensor for detection of three typical gas species (CO, C2H2, and C2H4), in order to evaluate the operation status of the oil-immersed transformers. The Ru-doping behavior on the WSSe surface is analyzed, giving rise to the preferred doping site by the replacement of a Se atom with the formation energy of 0.01 eV. The gas adsorption of three gas species onto the Ru-WSSe monolayer is conducted, and chemisorption is identified for all three gas systems with the adsorption energy following the order: CO (-2.22 eV) > C2H2 (-2.01 eV) > C2H4 (-1.70 eV). Also, the modulated electronic properties and the frontier molecular orbital are investigated to uncover the sensing mechanism of Ru-WSSe monolayer upon three typical gases. Results reveal that the sensing responses of the Ru-WSSe monolayer, based on the variation of energy gap, to CO, C2H2, and C2H4 molecules are calculated to be 1.67 × 106, 2.10 × 105, and 9.61 × 103, respectively. Finally, the impact of the existence of O2 molecule for gas adsorption and sensing is also analyzed to uncover the potential of Ru-WSSe monolayer for practical application in the air atmosphere. The obtained high electrical responses manifest strong potential as a resistive sensor for detection of three gases. The findings hold practical implications for the development of novel gas sensing materials based on Janus WSSe monolayer. We anticipate that our results will inspire further research in this domain, particularly for applications in electrical engineering where the reliable detection of fault gases is paramount for maintaining the integrity and safety of power systems.

Explored the potential of Rb2SeX6 (X=Cl, Br) double perovskites for energy harvesting devices: A DFT study

In this study, we employed Density Functional Theory (DFT) to comprehensively analyze the structural, mechanical, electronic, optical, and transport characteristics of Rb2SeX6 (X=Cl, Br) double perovskite halides. Our investigation aimed to assess the stability and suitability of these materials for energy harvesting devices. To evaluate material stability, we performed optimization and mechanical calculations. The computed bulk modulus indicated that the Rb2SeX6 (X=Cl, Br) compounds possess mechanical stability. Nevertheless, both compounds satisfied stability requirements for cubic structures, ensuring their potential utility. Using the modified Beck-Johnson approximation, we determined the indirect electronic band gaps to be within the range of 2.15 eV to 2.61 eV. These values indicate that the indirect band gaps of Rb2SeX6 (X=Cl, Br) compounds fall within the visible region due to the strong orbital coupling of the cations. Notably, the conduction band minimum mainly consists of Se-4p elements, while the valence band maximum predominantly comprises X-3p elements. Furthermore, the replacement of halogen atoms significantly influences the optical characteristics of the double perovskites. We observed that the complex dielectric function advocates the maximum electron transition and absorption efficiency when photon energy (eV) subjected on the Rb2SeX6 (X=Cl, Br) compounds. Further, considered the transport properties against temperature, chemical potential, and carriers’ concentrations. These findings emphasize the potential of Rb2SeX6 (X=Cl, Br) compounds double perovskites for energy harvesting applications. In conclusion, our study highlights the favorable properties and stability of Rb2SeX6 (X=Cl, Br) double perovskites, as revealed through DFT analysis. These materials exhibit desirable electronic and optical characteristics, making them promising candidates for energy harvesting devices.

Insights from Ca2+→Sr2+ substitution on the mechanism of O-O bond formation in photosystem II.

In recent years, there has been a steady interest in unraveling the intricate mechanistic details of water oxidation mechanism in photosynthesis. Despite the substantial progress made over several decades, a comprehensive understanding of the precise kinetics underlying O-O bond formation and subsequent evolution remains elusive. However, it is well-established that the oxygen evolving complex (OEC), specifically the CaMn4O5 cluster, plays a crucial role in O-O bond formation, undergoing a series of four oxidative events as it progresses through the S-states of the Kok cycle. To gain further insights into the OEC, researchers have explored the substitution of the Ca2+ cofactor with strontium (Sr), the sole atomic replacement capable of retaining oxygen-evolving activity. Empirical investigations utilizing spectroscopic techniques such as XAS, XRD, EPR, FTIR, and XANES have been conducted to probe the structural consequences of Ca2+→Sr2+ substitution. In parallel, the development of DFT and QM/MM computational models has explored different oxidation and protonation states, as well as variations in ligand coordination at the catalytic center involving amino acid residues. In this review, we critically evaluate and integrate these computational and spectroscopic approaches, focusing on the structural and mechanistic implications of Ca2+→Sr2+ substitution in PS II. We contribute DFT modelling and simulate EXAFS Fourier transforms of Sr-substituted OEC, analyzing promising structures of the S3 state. Through the combination of computational modeling and spectroscopic investigations, valuable insights have been gained, developing a deeper understanding of the photosynthetic process.

Design of an Oxide Monolayer with High ZT by a Strong Anharmonicity Unit.

In this paper, a new strategy to obtain a transition-metal oxide (TMO) thermoelectric monolayer is demonstrated. We show that the TMO thermoelectric monolayer can be achieved by the replacement of a transition-metal atom with a cluster, which is composed of heavy transition atoms with abundant valence electrons. Specifically, the transition-metal atom in the XO2 (X = Ti, Zr, Hf) monolayer is replaced by the [Ag6]4+ cluster and a stable structure Ag6O2 is achieved. Due to the abundant valence electrons in the [Ag6]4+ cluster unit, n-type Ag6O2 has high electrical conductivity, which leads to a satisfactory power factor. More importantly, Ag6O2 has an extremely low phonon thermal conductivity of 0.16 W·m-1·K-1, which is one of the lowest values in thermoelectric materials. An in-depth study reveals that the extremely low value originates from the strong phonon anharmonicity and weak metal bond of the [Ag6]4+ cluster unit. Due to the satisfactory power factor and ultralow phonon thermal conductivity, Ag6O2 has high ZT at 300-700 K, and the maximum ZT is 3.77, corresponding to an energy conversion efficiency of 22.24%. Our results demonstrate that replacement of the transition-metal atom by an appropriate cluster is a good way to obtain a TMO thermoelectric monolayer.

Enhancement of the response speed of CIGS-based photodetector by Te-doping

Cu(In,Ga)Se2 (CIGS) based devices are promising candidates for high performance photodetector applications. The present work investigated the effects of Te-doping on the properties of CIGS layers and studied the performance of photodetectors (PDs) fabricated on these films. The films were vacuum evaporated on glass substrates and their morphological, structural and optical properties were evaluated after an annealing step at 550ºC. Morphological data indicated that undoped CIGS films had non-uniform surface features with large grains separated by nanoparticles. Addition of 6.6 % Te improved the morphology and yielded a smoother layer. Further increase in Te concentration showed appreciable reduction in surface feature size and shape. X-ray diffraction patterns showed that increasing the Te amount in CIGS caused a shift in the XRD peaks towards smaller angles pointing to replacement of Se atoms by Te. Peak splitting at higher Te samples suggested a graded structure with Se and Te amounts changing through the thickness of the film. Raman analysis demonstrated formation of CuInGa(Se,Te)2 (CIGST) compound. According to Tauc’s approximation, CIGS films with and without Te atoms possessed two energy band gaps of Eg1 and Eg2 that were in the ranges of 1.10–1.28 eV and 1.16–1.36 eV, respectively. Electrical data obtained from photodetector devices showed a responsivity of 4.44×10−1 A/W and a detectivity of 8.01×107 Jones for Te-free material, while the rise/fall times were measured as 34/148 ms. A much faster response speed of 19/20 ms was reached for devices fabricated on films with 10.2 % Te. This work demonstrated, for the first time, the fabrication low-cost and high-performance metal-semiconductor-metal (MSM) type CIGST-based PDs.

Noncanonical Amino Acids in Biocatalysis.

In recent years, powerful genetic code reprogramming methods have emerged that allow new functional components to be embedded into proteins as noncanonical amino acid (ncAA) side chains. In this review, we will illustrate how the availability of an expanded set of amino acid building blocks has opened a wealth of new opportunities in enzymology and biocatalysis research. Genetic code reprogramming has provided new insights into enzyme mechanisms by allowing introduction of new spectroscopic probes and the targeted replacement of individual atoms or functional groups. NcAAs have also been used to develop engineered biocatalysts with improved activity, selectivity, and stability, as well as enzymes with artificial regulatory elements that are responsive to external stimuli. Perhaps most ambitiously, the combination of genetic code reprogramming and laboratory evolution has given rise to new classes of enzymes that use ncAAs as key catalytic elements. With the framework for developing ncAA-containing biocatalysts now firmly established, we are optimistic that genetic code reprogramming will become a progressively more powerful tool in the armory of enzyme designers and engineers in the coming years.

EVOLUTION OF ELECTRONIC PROPERTIES ALONG THE PATH FROM COVALENT TO TETREL BOND IN THE SYNTHESIS OF TETRAPHENYL SUBSTITUTED COMPOUNDS

The evolution of the electronic characteristics of chemical bonds formed and broken along the path of the bimolecular nucleophilic substitution reaction at a tetrahedral central atom, which is the Tt = C, Si, Ge atom, is analyzed. For this purpose, the reaction paths of the step-by-step replacement of the chlorine atom with the phenyl fragment have been modeled, and the energy characteristics of the equilibrium initial, transition and nal states were obtained within the framework of DFT. For different reaction centers, which are atoms of the carbon group (Tt), changes in electron density distributions, shifts in the positions of the extremes of the total static and electrostatic potential for the forming C-Tt and breaking Tt-Cl bonds along the reaction path are compared. Quantitative criteria have been re ned that determine the region of existence of a typical noncovalent tetrel bond Tt...Cl, allowing it to be distinguished from a covalent one. Establishment of the properties of the transition state stabilizing tetrel bond may be useful for monitoring the ef cient synthesis of covalent organic framework precursors.

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.

Simulation of electrical rectification effect in two-dimensional MoSe2/WSe2 lateral heterostructures

Two-dimensional (2D) transition metal dichalcogenides lateral heterostructures exhibit excellent performance in electrics and optics. The electron transport of the heterostructures can be effectively regulated by ingenious design. In this study, we construct a monolayer MoSe2/WSe2 lateral heterostructure, covalently connecting monolayer MoSe2 and monolayer WSe2. Using the Extended Huckel Theory method, we explored current-voltage characteristics under varied conditions, including altering carrier density, atomic replacement and interface angles. Calculations demonstrate a significant electrical rectification ratio (ERR) ranging from 200 to 800. Additionally, Employing Density Functional Theory with non-equilibrium Green’s function method, we investigated electronic properties, attributing the rectification effect to electronic state distribution differences, asymmetric transmission coefficients and band bending of projected local density of states. The expandability of the interfacial energy barrier enhances the rectification effect through adjustments in carrier concentration, atomic replacements and interface size. However, these enhancements introduce challenges such as increased electron-boundary scattering and reduced ambipolarity, resulting in a lower ERR. This study provides valuable theoretical insights for optimizing 2D electronic diode devices, offering avenues for precise control of the rectification effect.