Covalent Bonds Research Articles

Highly Refractive Transparent Half‐Heuslers for Near Infrared Optics and Their Material Design

AbstractAdvanced control of light focusing, reflection, and transmission is possible with highly refractive transparent materials; however, such materials are difficult to discover because of the negative correlation between the refractive index and the optical band gap. This study elucidates half‐Heuslers as highly refractive transparent materials, considering their densely packed crystal structures comprising both covalent and ionic bonds with d orbitals. Theoretical calculations revealed that 22 ternary half‐Heusler systems (αβγ) exhibited higher refractive indices with wider band gaps than conventional high‐refractive‐index‐transparent materials in the near‐infrared region. The key to achieving a high index and wide gap is aligning α‐d and β‐d levels within a small lattice frame given by small γ elements to the verge of forming Γ‐point conduction band minimum. Experimental examinations revealed that α and γ elements with low and high melting points are preferred for the thin‐film preparation of the well‐ordered half‐Heuslers. Highly refractive transparent half‐Heuslers and their material designs expedite post‐silicon technology for controlling near‐infrared light.

Peripheral Substitution Engineering of MR-TADF Emitters Embedded With B‒N Covalent Bond Towards Efficient BT.2020 Blue Electroluminescence.

Compared with the classical boron/nitrogen (B/N) doped ones, multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters embedded with B-N covalent bond behave a significantly blue-shifted narrowband TADF, and thus show a greater potential in ultrapure blue organic light-emitting diodes (OLEDs). As a proof of concept, herein a peripheral substitution engineering is demonstrated based on such a B‒N embedded parent core. The simple approach is found to ensure easy synthesis via a one-pot lithium-free borylation-annulation, manipulate the excited states through different electronic coupling between core and substituent, and introduce the steric hindrance to minimize the unwanted spectral broadening. Impressively, ultrapure blue OLEDs are realized to give a high external quantum efficiency of 20.3% together with Commission Internationale de l'Éclairage coordinates of (0.152, 0.046). The performance is well competent with those of B/N doped MR-TADF emitters, clearly highlighting that the B‒N embedded framework is a novel promising paradigm towards efficient BT.2020 blue standard.

Investigation on mechanism of mechanical activation and chemical reactions in CMP of diamond assisted by hydroxyl free radicals

Chemical mechanical polishing (CMP) is a crucial manufacturing process for diamond substrate applications. However, due to the extremely high hardness and chemical stability of diamond, its CMP efficiency is extremely low. This study aims to achieve microscopic simulation of atomic oxidation removal at the three-phase interface between diamond abrasive particle, diamond substrate, and hydroxyl free radicals (∙OH) aqueous solution. The mechanical activation behavior, microscopic mechanism, and feasibility of elementary reactions in the ∙OH aqueous solution environment was studied using various perspectives of radial distribution function, central atomic coordination state, atomic bonding and removal forms, energy, electron orbitals, and density functional theory (DFT). The simulation results indicate that during the process of diamond atomic oxidation removal, the atomic density at the first adjacent position centered on one atom decreases, and the stable covalent bond structure is disrupted, resulting in an amorphous phase transition. The chemical adsorption reaction generates C-O and C–H bonds. The C atoms mainly separate from the diamond substrate by the forming products such as carbon monoxide (CO), carbon dioxide (CO2), and carbon chains. The mechanical activation behavior indirectly reduces the activation energy of chemical reactions, while increasing the absolute value of adsorption energy and improving the ability of chemical adsorption solution atoms H and O, as well as ∙OH groups. Based on DFT, it has been verified that the intrusion process of ∙OH groups in the elementary reactions involving the typical product C*O2 is an exothermic reaction that can occur spontaneously, and the energy barrier needs to be overcome by the mechanical action of abrasive particles. At the same time, the energetics of the oxidation of diamond C atoms to generate C*O2 have successfully confirmed that the combined action of ∙OH and diamond abrasive particles is expected to achieve efficient oxidation removal and finishing polishing of diamond atoms.

Assessment of Neutrophil Gelatinase Associated Lipocalin in Children with Acute Gastroenteritis and Dehydration to Identify Early Signs of Acute Kidney Injury

Background: Gastroenteritis often correlates with acute kidney injury (AKI) in children who are hospitalized. The primary diagnostic test for acute kidney injury (AKI) in modern times is serum creatinine (SCr), which increases in the presence of AKI and is eliminated by glomerular filtration. SCr is an unsuitable biomarker for renal sickness because it lacks specificity and a slow response to disease severity or treatment changes. NGAL, or neutrophil gelatinase-associated lipocalin, is a molecular weight of 25 kDa protein and forms a covalent bond with neutrophil gelatinase. Elevations in NGAL levels due to kidney injury have important predictive value and may forecast the onset of acute kidney injury (AKI) 24-72 hours before an increase in diagnostic serum creatinine (SCr) values. Aim and objectives: This study aims to determine whether plasma NGAL concentrations in mild, moderate, or severe dehydrated acute gastroenteritis patients may indicate acute kidney damage (AKI). The research will investigate whether acute renal injury and plasma NGAL concentrations are connected. Patients and methods: The cross-sectional design was employed in this study and included 80 patients who attended the pediatric gastrointestinal clinic at Babylon Children's Hospital. Between November 2022 and June 2023, all patients had gastroenteritis symptoms accompanied by different dehydration levels. Results: Patients with severe dehydration had considerable higher level of NGAL than those with mild to moderate dehydration (p<0.001). There was a notable inverse relationship (p = 0.046) between the NGAL level and potassium but a considerable direct link (p<0.001) between the NGAL level and creatinine. However, no significant correlation was seen between the NGAL level and urea (p = 0.404 and 0.062, respectively). The confidence range for the area under the curve (AUC) is 0.940 to 0.981, with a confidence level of 95%. The p-value is less than 0.001. The sensitivity is 88%. An accuracy of 88.4% has been attained. The NGAL cut-off point is 3.9832. Conclusion: An analysis of plasma neutrophil gelatinase-associated lipocalin (NGAL) in individuals with gastroenteritis and varied degrees of dehydration indicated a clear and direct link between the two parameters. Specifically, when dehydration worsened, the average NGAL value increased

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The syntheses of poly[2]catenane gels reported to date all rely on the polymer as the backbone. We reported poly[2]catenane gels prepared by entirely sequential self‐assembly of small molecules via noncovalent and dynamic covalent bonds. Due to the presence of hydrogen bonds in the poly[2]catenane gels, the gels also possessed stimulus responsiveness and self‐healing properties. More details are discussed in the article by Ji et al. on pages 2699—2704. image

Bioreceptors’ immobilization by hydrogen bonding interactions and differential pulse voltammetry for completely label-free electrochemical biosensors

Label-free electrochemical biosensors show great potential for the development of point-of-care devices (POCDs) for environmental and clinical applications. These sensors operate with shorter analysis times and are more economic than the labelled ones. Here, four completely label-free biosensors without electron transfer mediators were developed for hepatitis B virus (HBV) detection. The approach consisted in (i) the modification of gold surfaces with cysteamine (CT) or cysteine (CS) linkers, (ii) the subsequent antibody (Ab) immobilization, either directly by hydrogen bonding (HB) interactions or by covalent bonds (CB) using additional reagents, and (iii) measuring the biosensor response by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The electrode surfaces at each stage of the modification process were characterised by X-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). The combination of Ab immobilization by HB with the DPV analysis displayed improved repeatability, lower interference to serum matrix and similar limits of detection and quantification than the traditional biosensors that immobilize the Ab via CB and use EIS as readout technique. The Ab immobilization by HB is shown as a simple, efficient and low-cost alternative to CB ones, while DPV was faster and showed better performance than EIS. The CT-HB biosensor displayed the lowest limits of detection and quantification of 0.14 and 0.46 ng/mL, respectively, a 0.46–12.5 ng/mL linear analytical range, and 100% of recovery for 1/10 human serum media during HBV surface antigen detection by DPV. Even, it preserved the initial sensing capability after 7 days of its fabrication.Graphical abstract

Construction of bispecific antibodies by specific pairing between the heavy chain and the light chain using removable SpyCatcher/SnoopCatcher units

During the production of bispecific antibodies (bsAbs), nonspecific pairing results in low yields of target bsAb molecules, an issue known as the “mispairing problem.” Several antibody engineering techniques have been developed to overcome mispairing issues. Here, we introduce “bsAb by external pairing and excision” (BAPE), a novel chain pairing method that induces specific chain pairing by fusing external SpyCatcher/Tag and SnoopCatcher/Tag units. These tags are then removed via protease cleavage. In this study, we applied this method to force the correct pairings of heavy and light chains while the heavy-chain pairing was achieved by the Knobs-into-Holes mutation. We then confirmed the formation of interchain bridges with covalent isopeptide bonds. Both anti-CD3/anti-Her2 and anti-CD3/anti-EGFR bsAbs displayed satisfactory target binding activities and in vitro cell-killing activity with activated T-cells.

Implementation of frozen density embedding in CP2K and OpenMolcas: CASSCF wavefunctions embedded in a Gaussian and plane wave DFT environment.

Most chemical processes happen at a local scale where only a subset of molecular orbitals is directly involved and only a subset of covalent bonds may be rearranged. To model such reactions, Density Functional Theory (DFT) is often inadequate, and the use of computationally more expensive correlated wavefunction (WF) methods is required for accurate results. Mixed-resolution approaches backed by quantum embedding theory have been used extensively to approach this imbalance. Based on the frozen density embedding freeze-and-thaw algorithm, we describe an approach to embed complete active space self-consistent field simulations run in the OpenMolcas code in a DFT environment calculated in CP2K without requiring any external tools. This makes it possible to study a local, active part of a chemical system in a larger and relatively static environment with a computational cost balanced between the accuracy of a WF method and the efficiency of DFT, which we test on environment-subsystem pairs. Finally, we apply the implementation to an oxygen molecule leaving an aluminum (111) surface and a ruthenium(IV) oxide (110) surface.

Distance-Dependent Magnetization Modulation Induced by Inter-Superatomic Interactions in Cr-Doped Au6Te12Se8 Dimers

Abstract Individual superatoms were assembled into more complicated nanostructures for diversify their physical properties. Magnetism of assembled superatoms remains, however, ambiguous, particularly in terms of its distance dependence. Here, we report density functional theory calculations on the distance-dependent magnetism of transition metal embedded Au6Te8Se12 (ATS) superatomic dimers. Among the four considered transition metals, which include V, Cr, Mn and Fe, the Cr-embedded Au6Te12Se8 (Cr@ATS) is identified as the most suitable for exploring the inter-superatomic distance-dependent magnetism. We thus focused on Cr@ATS superatomic dimers and found an inter-superatomic magnetization-distance oscillation where three transitions occur for magnetic ordering and/or anisotropy at different inter-superatomic distances. As the inter-superatomic distance elongates, a ferromagnetism (FM)-to-antiferromagnetic (AFM) transition and a sequential AFM-to-FM transition occur, ascribed to competitions among Pauli repulsion and kinetic-energy-gains in formed inter-superatomic Cr-Au-Au-Cr covalent bonds and Te-Te quasi-covalent bonds. For the third transition, in-plane electronic hybridization contributes to the stabilization of the AFM configuration. This work unveils two mechanisms for tuning magnetism through non-covalent interactions and provides a strategy for manipulating magnetism in superatomic assemblies.

Electrochemical conversion of CO2 via C−X bond formation: recent progress and perspective

With the depletion of traditional energy sources and growing environmental concerns, it is becoming increasingly urgent to develop green, low-emission renewable energy technologies to replace fossil fuel-driven methods that emit carbon dioxide (CO2). Currently, the electrochemical production of high-value-added chemicals and fuels from CO2 has aroused great interest from scientists. However, to make full use of CO2 for the preparation of chemicals, it is necessary to expand the range of electrosynthesis methods, in particular by expanding reaction pathways through the reaction of CO2 with different substrates. In general, CO2 can form new covalent bonds with substrate molecules through the formation of C−X bonds, including C−H, C−C, C−N, C−O, and C−S bonds, which would expand the range of possible products by diversifying the reaction pathway. In this review, we focus on the research progress in electrochemical conversion of CO2 through C−X bond formation. We start by examining fundamentals of the reactions and summarizing the reaction modes. Next, we discuss the electrosynthesis of C−X bonds (C−H, C−C, C−N, C−O, C−S) using CO2 and different substrate molecules. Finally, (i) strategies for the design and activity optimization of catalyst materials and (ii) the future development of forming five types of bonds from CO2 and small molecules are discussed, along with an outlook on their future research prospects.

Citric acid/sucrose-modified pMDI for constructing high-performance straw particleboard based on multiple cross-linked networks

Polymeric diphenylmethane diisocyanate (pMDI) is an indispensable material used to produce straw particleboard. However, prolonged exposure to high concentrations of pMDI significantly increases the health risks to relevant professionals. Herein, we report a strategy for reducing safety hazards by partially replacing the pMDI with a bio-based adhesive. An adhesive with multiple cross-linked networks were synthesized using citric acid (CA), sucrose (SU), and pMDI first, and then applied to the preparation of straw particleboard. The amide and esterification reactions between the adhesives and rice straw particles form covalent bonds, enhancing boards adhesion and water resistance. Furthermore, acidic conditions provided by citric acid facilitate to convert SU into 5-hydroxymethyl furfural (5-HMF), which plays a positive role in straw adhesion. Adhesives made with 2.4 % pMDI, 8 %, and 4.8 % SU were used to bond particleboard, achieving internal bond strength, bending strength and elastic modulus of 0.57 MPa, 25.87 MPa, and 3.77 GPa, respectively, whose mechanical properties are comparable to the particleboard prepared with 4 % pMDI. The board showed superb mechanical performances, mould resistance, as well as water resistance. The CA/SU-modified pMDI adhesive system shows significant potential and promising application value in straw particleboard.

Controllable structure, super adhesion, multifunctional, conductive pressure-sensitive adhesive for electronic skin: Enhancing cohesion by cellulose-derived covalent crosslinking

Ensuring firm adhesion to the skin is essential for improving the detection of temperature and movement signals in electronic skin (E-skin). Self-adhesive eutectogel, an ideal material for E-skin, could act as an innovative pressure-sensitive adhesives (PSAs) that can be easily applied through simple pressing without requiring heating or irradiation. Herein, we synthesized a cellulose-derived polymer crosslinking agent (MCCAC) to create a eutectogel-based conductive PSA (CPSA). The MCCAC formed strong covalent bonds with polymer chains, significantly enhancing the cohesion of the CPSAs. As a result, the CPSAs exhibited high tensile lap-shear strength (99.5 kPa) among self-adhesive eutectogels. Unlike the construction of double-network structures, this method included a straightforward chemical reaction and a cohesion-enhancing strategy, and could adjust crosslinking density by changing the MCCAC content. The preparation process was simple, and the products were controllable. More importantly, this cohesion-enhancing strategy did not compromise the fluidity of polymer chains, which ensured that CPSAs maintain effective interfacial adhesion to adhere on skin, offering exceptional capabilities for capturing body temperature signals (−3.66 %/℃) as well as applications in motion detection and information transmission. This work resolved the cohesion and interfacial adhesion imbalances observed in previous self-adhesive eutectogels and provided a promising approach for designing the novel cellulose-reinforced CPSA for E-skins.

Static disorder in perovskite-type proton-conducting oxides BaSn1-xMxO3-x/2-(y/2)H2O (M = Ga, Sc, In, Y, La): a novel approach based on statistical analysis of numerous DFT simulated structures.

Perovskite-type proton-conducting oxides inherently include defects such as substitutional aliovalent cations, oxide ion vacancies, and interstitial protons. These defects introduce static disorder into their crystal structures. To investigate such disorder in BaSn1-xMxO3-x/2-(y/2)H2O (M = Ga, Sc, In, Y, La), we employ a novel approach based on density functional theory (DFT) simulations. This approach involves the structural optimization of a large number of relatively small, randomly constructed supercells, followed by statistical analysis of their geometric, energetic, and vibrational properties. Our key findings are as follows. The structural disorder becomes more pronounced as the dopant concentration increases, and as the dopant ionic radius increases from Sc to La. The O-H covalent bond lengths, as well as the number densities, of hydrogen atoms display clearly different distributions depending on whether the hydrogen atoms are trapped by aliovalent cations or not. The hydrogen-trapping energies appear to decrease as the geometric similarity of O-H covalent bonds between trapped and untrapped hydrogen atoms increases. Hydrogen atoms simultaneously trapped by more than one dopant atom exhibit considerable stability, potentially hindering proton diffusion at high dopant concentrations. The O-H stretching wavenumber decreases as the O-H covalent bond length increases, showing a very strong and nearly linear correlation between the two. The simulated IR absorption spectra show semi-quantitative agreement with the measured spectra. These new findings demonstrate the effectiveness of the present 'statistical' approach for investigating static disorder.

Soft-Rigid Construction of Mechanically Robust, Thermally Stable, and Self-Healing Polyimine Networks with Strongly Recyclable Adhesion.

Reversible and recyclable thermosets have garnered increasing attention for their smart functionality and sustainability. However, they still face challenges in balancing comprehensive performance and dynamic features. Herein, silicon (Si)─oxygen (O) and imidazole units covalent bonds are coupled to generate a new class of bio-polyimines (Bio-Si-PABZs), to endow them with high performance and excellent reprocessing capability and acid-degradability. By tailoring the molar content of diamines, this Bio-Si-PABZs displayed both a markedly high glass transition temperature (162°C) and a high char yield at 800°C in an oxygen atmosphere (73.1%). These Bio-Si-PABZs with their favorable properties outperformed various previously reported polyimines and competed effectively with commercial fossil-based polycarbonate. Moreover, the scratch (≈10µm) on the surface of samples can be self-healing within only 2min, and an effective "Bird Nest"-to-"Torch" recycling can also be achieved through free amines solution. Most importantly, a bio-based siloxane adhesive derived from the intermediate Bio-Si-PABZ-1 by acidic degradation demonstrated broad and robust adhesion in various substrates, with values reaching up to ≈3.5MPa. For the first time, this study lays the scientific groundwork for designing robust and recyclable polyimine thermosets with Si─O and imidazole units, as well as converting plastic wastes into thermal-reversibility and renewable adhesives.

Mechanical properties of diamane: Orientation dependence of strength and fracture strain

Diamane, the two-dimensional counterpart of diamond, is very promising for novel electronic and nanomechanical devices, which requires additional studies on their physical and mechanical properties. In the present work, the orientation dependence of diamane strength with the detailed analysis of the deformation behavior was carried out by molecular dynamics. Two stacks of diamane layers covered with hydrogen with different chirality θ from 0 to 30° were considered. The atomic stacking of diamane has no effect on its strength. It was found that diamane strength depends non-monotonously on the diamane chirality: the highest strength was found for θ = 10°. The fracture strain decreases with the increase of chiral angle from 0 to 20° and does not change for chirality from 20 to 30°. However, the Young’s modulus does not depend on the diamane chirality. The main deformation mechanisms were revealed: elongation of covalent bonds and rotation of valence angles. For chiral angles from 0 to 20°, the diamane chirality can be controllably changed during tension which results in the increase in fracture strength and strain. The obtained results allow a better understanding of the effect of the diamane morphology on their mechanical properties for future applications.

Complete conversion of eucalyptus wood to dynamic covalent networks: An in-situ plasticising strategy

Ongoing innovation in bio-based plastics aims to meet more economical and diverse societal needs. However, the dependence on a single biomass source and the generally inadequate wet stability and moisture mechanical properties of traditional bio-based plastics severely limit their competitiveness. We have developed a high mechanical performance, fully bio-based, thermoset in-suit plastic from an almost worthless agricultural and forestry waste (eucalyptus) through a simple and environmentally friendly deconstruction-reconstruction strategy. In this process, the hydrogen and covalent bonds in the lignin and cellulose of eucalyptus are broken and then reorganised through dynamic covalent bonds. The resulting eucalyptus-based plastic exhibits high mechanical strength, excellent water resistance, UV ageing resistance, photothermal performance and light/heat controllable shape memory properties. By preserving the original structure of the lignin and cellulose, its natural degradability is ensured. This strategy for developing full-component plastics from solid agricultural and forestry waste offers a new approach to producing more competitive fully bio-based plastics.

Biomimetic design of elastomers with improved mechanical properties by integrating hydrogen bonds with covalent crosslinking bonds

It is an important issue for rubber to realize reinforcement and expand application gallery in material science and engineering. In the present work, we initiated a bioinspired design to introduce sacrificial hydrogen bonds by post-modifying sulfur crosslinked carboxyl nitrile rubber with pendent urazole through triazolinedione “click” chemistry. The post-modification of the crosslinked rubber can not only avoid adverse effect of the grafted urazoles on rubber vulcanization, but also enable to evaluate the effect of sacrificial hydrogen bonds on the rubber based on a consistent covalent network. Under external stress, the hydrogen bonds between the urazoles can function as sacrificial bonds that would rupture prior to covalent bonds, during which enormous energy is dissipated and meanwhile facilitates the rubber chain orientation. In light of the unique energy dissipating mechanism, the modulus, ultimate stress, and toughness of the hydrogen bonds and sulfur bonds dual-crosslinked rubber material are improved simultaneously without sacrificing the stretchability, and these properties can be easily manipulated by varying the grafting ratio of urazoles.

High-Strength and Self-Healing Polyurethane Based on Dynamic Covalent Bonds for Concrete Protection

High-Strength and Self-Healing Polyurethane Based on Dynamic Covalent Bonds for Concrete Protection

Mechanical energy at the origins of life

Mechanical energy at the origins of life Did mechanical energy power life’s origins before chemical energy such as ATP was available?. Mechanobiology is a hot topic in science today, with special issues on the subject in scientific journals. Was mechanical energy a way to form chemical bonds before the origin of life made mechanobiology possible? This makes a lot of sense, because life was not around yet to synthesize ATP (adenosine triphosphate), the chemical energy molecule that powers many of the processes of life. With mechanochemistry, molecules are simply smashed together to form covalent bonds between them (Figure 1). Mica sheets provide mechanical energy at their split edges and bubbles between the sheets (1-3), as shown in this photograph of a piece of mica (Figure 2) and the diagram of mica in Figure 3.

Biomimetic joints inspired soft and hard combined 2D diamond solvent-free nanofluids with multi-layer structure for superior lubrication

The articulating joints consist of a three-layer lubricating structure, which combines soft and hard materials, including cartilage, polymer brushes, and a hydration layer. This structure leverages the synergistic effects of fluid and boundary lubrication to maintain ultra-low friction under different pressures on the same frictional surface. In this study, a biomimetic multilayer lubricating structure inspired by joint tissues is constructed using single-crystalline diamond nanosheets (SCND) as the hard phase material. Through a facile chemical reduction method and employing polydopamine (PDA) as a "bridge", a soft phase material is deposited onto the SCND surface to produce diamond composite silver nanocomposites (SCND@PDA@Ag). Subsequently, two solvent-free SCND@PDA@Ag nanofluids are prepared by grafting organic canopy substances onto the SCND@PDA@Ag surface via ionic bonds or covalent bonds, referred to as SCND@PDA@Ag-ionic bonding nanofluid and SCND@PDA@Ag-covalent bonding nanofluid, respectively. The findings reveal that the SCND@PDA@Ag-covalent bonding solvent-free nanofluid exhibits superior lubricating performance for steel/SiC contacts. The friction coefficient and wear rate for steel/SiC are significantly reduced by 93.2 % and 63.1 %, respectively, compared to dry friction, it's noteworthy that these results outperform those achieved by individual components of the lubricant. During the friction process, SCND and silver particles on the surface of SCND@PDA@Ag-covalent bonding solvent-free nanofluid work together to enhance lubrication synergistically. Furthermore, silver particles on the surface of SCND are released and fill into the worn surface, providing a repairing effect. This study highlights that the design of soft-hard multilayer structures offers a novel approach for researching nanocomposite materials in the field of tribology.