Structure Of Boron Research Articles

Thermogravimetric analysis of aromatic boronic acids for potential flame retardant applications

The need for non-halogenated flame retardants continues to increase as more information about the toxicity of halogenated flame retardants and their pyrolytic byproducts becomes available. One class of non-halogenated flame retardants, organic boronic acids, has been reported in a number of papers as having flame retardant effects for cellulosic fibers as well as synthetic polymers. To improve this performance, an understanding of how the structure of the boronic acid affects its flame-retardant properties as well as its thermal stability is necessary. Reported herein are experiments aimed at achieving precisely this understanding, by investigating the thermal stability and degradation pathways of a broad variety of boronic acids, and using the resulting data to develop rules about the relationship between boronic acid structure (number of boronic acid moieties; presence/absence of functional groups, etc.) and the compound’s thermal stability. These experiments highlight a number of boronic acids with exceptional thermal stability, with pyrene-1-boronic acid (compound 18) in particular showing stability up to 600 °C.

Highly Efficient Deep Blue Fluorescence Emitter Based on Highly Conjugated Boron Structure

Highly Efficient Deep Blue Fluorescence Emitter Based on Highly Conjugated Boron Structure

Highly Efficient Deep Blue Fluorescence Emitter Based on Highly Conjugated Boron Structure

Highly Efficient Deep Blue Fluorescence Emitter Based on Highly Conjugated Boron Structure

Effects of boron oxide composition, structure, and morphology on B4C formation via the SHS process in the B2O3–Mg – C ternary system

This study investigates the formation of B4C in the B2O3–Mg–C ternary system via a magnesiothermic reduction process using two kinds of boron oxide (B2O3) ‒ the commercial B2O3 and that synthesized from boric acid via the coupled chemical-thermal process. In addition to the raw materials, the products were subjected to XRD, FTIR, SEM, and FESEM analyses to determine the effects of microstructural and morphological properties of boron oxide as an important raw material, on B4C formation in the combustion synthesis process. For this purpose, powder mixtures of B2O3:Mg:C were prepared at a stoichiometric molar ratio of 2:6:1 and compacted into pellets using a uniaxial hydraulic press, which were subsequently subjected to the combustion synthesis process based on the self-propagating high-temperature synthesis (SHS). Finally, the samples thus obtained were leached in an aqueous hydrochloric acid solution. Analysis of the commercial B2O3 revealed the presence of large amounts of such by-products as magnesium borate (Mg3B2O6) and magnesium oxide (MgO) along with relatively small amounts of boron carbide after the leaching process, while those obtained for the chemically-thermally synthesized B2O3 showed a relatively large amount of B4C (from micron-sized particles to nanoparticles) together with a remaining carbon phase and very small amounts of magnesium borate as by-products. It can be, therefore, concluded that the changes in chemical composition and introduction of a hydrous HBO2 phase in the boron oxide in the B2O3–Mg–C mixture as well as its varied microstructure, morphology, and particle size have significant effects on the efficiency of B4C production through the SHS process.

Teamed boronate affinity-functionalized branched polyethyleneimine-modified magnetic nanoparticles for the selective capture of ginsenosides from rat plasma

Boronate-functionalized materials have been widely used for the selective separation and enrichment of glycoproteins and glycans. However, emerging boronic acid materials either use expensive boronic acid compounds containing electron-withdrawing groups combined with a graft structure or explore only simple methods for the synthesis of boronic acid structures with improved electron-withdrawing groups. In this study, polyethyleneimine (PEI)-assisted teamed boronate affinity (TBA)-functionalized magnetic nanoparticles (MNPs) (Fe3O4@PEI@TBA NPs) were designed to specifically capture trace ginsenosides from rat plasma under neutral conditions without requiring protein precipitation. The synergistic effect of the Fe3O4@PEI@TBA NPs exhibited higher affinity for ginsenosides (45.64 mg g−1) based on PEI dendrimer-assisted multivalent binding, the low pKa value of TBA and specific recognition sites. Additionally, the captured ginsenosides were quickly detected and characterized using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-MS) and an enriched in-house library. Compared to the 37 compounds identified using the methanol method, 63 ginsenoside prototypes and metabolites were successfully detected and identified in rat plasma by applying this novel integrated strategy. The strategy exhibited selectivity and identified more types and quantities of ginsenosides. Our study provided in-depth insight into the synergistic development of specific functional materials in combination with advanced analytical platforms for the selective capture and characterization of trace glycoconjugate families in analytical, engineering and biomedical fields under neutral conditions.

Study of the effect of local photon annealing on stress in silicon wafers

The effect of photon annealing on deformation in the crystal structure of boron doped Cz-Si wafers has been studied using triple crystal X-ray diffraction. Conventional annealing of the entire surface of double-side polished silicon wafers with halogen lamps (photon annealing mode) and rapid thermal annealing produce compression deformation. Annealing with special phototemplate providing for local annealing of multiple separated wafer areas (local photon annealing mode) at relatively low wafer temperatures (less than 55 °C) produces tensile deformation. This effect however is not observed if the reverse side of the annealed wafer contains a mechanical gettering layer. A mechanism explaining the experimental results has been suggested and can be used for the synthesis of charge pumps in photoelectric converter structures.

Nuclear Structure Effects in the Hyperfine Structure of Muonic Lithium, Beryllium, and Boron

Nuclear structure corrections to hyperfine splitting of energy levels in muonic lithium, beryllium, and boron ions are calculated. Account is taken of the contributions from the two-photon exchange amplitudes, including the vacuum polarization effect, and from the one-photon amplitude, which provide corrections to the nuclear structure and recoil of order $${{\alpha }^{5}}$$ and $${{\alpha }^{6}}$$ . Numerical results for different parametrizations of electromagnetic form factors are compared.

Silicon wafer strain under local photonic annealing

The effect of photon annealing on the occurrence of deformations in the crystal structure of boron−doped silicon wafers produced by the Czochralski (Cz−Si) was studied by the method of triple−X−ray diffraction. It was found that the traditional annealing of silicon wafers with polished surfaces on both sides by halogen lamps in Photonic Annealing (PA) and rapid thermal annealing modes (RTA) leads to compression deformation. The same process with the use of original photo− mask, which allows local processing produces multiple, spatially separated regions of the plate produced by Lосаl Photonic Annealing (LPA) at relatively low temperatures (less than 55 °C), gives rise to a tensile strain. This established effect is not observed if on the back side of the plates there is mechanical gettering layer. The mechanism explaining the experimental results can be used in the formation of the charge pump in the structure of the photo electric converters (PEC).

Outside help for a carbene catalyst

Organic Chemistry Metal catalysis is sometimes enhanced by secondary interactions with components that are not directly coordinated to the metal. Dhayalan et al. have explored this concept with metal-free organocatalysis. Specifically, they found that dynamically tethering a boronic acid to the periphery of an N-heterocyclic carbene catalyst raised enantioselectivity of a benzoin condensation. Furthermore, by applying a decision tree analysis correlating selectivity with parameters such as dipole moment and torsion angle, they efficiently optimized the boronic acid structure for gram-scale reactions. Nat. Chem. 11 , 543 (2019).

Synthesis and characterization of di-Schiff based boronic structures: Therapeutic investigation against cancer and implementation for antioxidant

In the present work, anticancer applications of boronic acid compounds containing di-Schiff groups were carried out. The synthesized compounds (((1Z,1′Z)-([1,1′-biphenyl]-4,4′-diylbis(azanylylidene))bis(methanylylidene))bis(4,1-phenylene))diboronic acid (1); (((1Z,1′Z)-([1,1′-biphenyl]-4,4′-diylbis(azanylylidene))bis(methanylylidene))bis(3,1-phenylene))diboronic acid (2); 2-((bis((E)-(4-boronobenzylidene)amino)methylene)amino)acetic acid (3); (((1E,1′E)-(naphthalene-1,8-diylbis(azanylylidene))bis(methanylylidene))bis(4,1-phenylene))diboronic acid (4) were characterized with 1H NMR, 13C NMR, FTIR, SEM-EDX, TGA and UV–Vis.These compounds containing the boronic acid group were investigated for their therapeutic effects on Ishikawa endometrial cancer cells. Solutions were prepared at diverse concentrations of each compound and applied in accordance with the biological process. It has been shown that the compounds obtained decrease cell viability of Ishikawa endometrial cancer cells at different percentages. The ((1E, 1′E)-(naphthalene-1,8-diylbis(azanylyldene))bis(methanylidene)bis(4,1-phenylene)diboronic acid (4) showed the highest activity among those (1–4) compounds. However, the antioxidant activity screening was also investigated by various methods such as CUPRAC, DPPH, and ABTS. Each has exhibited meaningful activity in different processes.

Predicting three-dimensional icosahedron-based boron B60

The icosahedron-based bulk boron structures have extremely chemical and structural complexity, and are usually semiconductors at ambient conditions. Here we predict bulk boron phases with a 60-atom orthorhombic unit cell from an ab initio evolutionary structure search, termed as ${\mathrm{B}}_{60}$. The metastable structures can be either a conductor or a semimetal depending on their interstitial atomic positions. In particular, an orthorhombic structure with $Pnma$ symmetry ($Pnma\ensuremath{-}{\mathrm{B}}_{60}$), consisting of ${\mathrm{B}}_{12}$ icosahedra and twisted interstitial two-atom wide boron ribbons, is identified to be a topological node-line semimetal with potential superior electronic transport. The band structure and simulated electron-diffraction pattern of $Pnma\ensuremath{-}{\mathrm{B}}_{60}$ are in satisfactory agreement with the experimental data, suggesting that it may exist in the form of nanomaterials.

Embedded-atom method interatomic potential for boron nanostructures

Parameters of embedded-atom method interatomic potential for boron are presented in this paper. The potential parameters were determined by means of ab initio data for boron cluster B20, triangular boron sheet, and body-centered cubic structure. The potential has been tested against basic properties of various boron structures. They are face-centered cubic, diamond-like, body-centered tetragonal, icosahedron B12 and icosahedral chain structures. One can conclude that the proposed potential provides a reasonable representation of the interatomic interaction in boron nanostructures, and it is intended for use in large-scale molecular dynamics simulations of boron nanomaterials.

From Two- to Three-Dimensional van der Waals Layered Structures of Boron Crystals: An Ab Initio Study.

A remarkable recent advancement has been the successful synthesis of two-dimensional boron monolayers on metal substrates. However, although up to 16 possible bulk allotropes of boron have been reported, none of them possess van der Waals (vdW) layered structures. In this work, starting from the experimentally synthesized monolayer boron sheet (β12 borophene), we explored the possibility for forming vdW layered bulk boron. We found that two β12 borophene sheets cannot form a stable vdW bilayer structure, as covalent-like B–B bonds are formed between them because of the peculiar bonding. Interestingly, when the covalently bonded bilayer borophene sheets are stacked on top of each other, three-dimensional (3D) layered structures are constructed via vdW interlayer interactions, rather than covalent. The 3D vdW layered structures were found to be dynamically stable. The interlayer binding energy is about 20 meV/Å2, which is close to the weakly bound graphene layers in graphite (∼16 meV/Å2). Furthermore, the density functional theory predicted electronic band structure testifies that these vdW bulk boron crystals can behave as good conductors. The insights obtained from this work suggest an opportunity to discover new vdW layered structures of bulk boron, which is expected to be crucial to numerous applications ranging from microelectronic devices to energy storage devices.

Two-dimensional antiferromagnetic boron form first principles

A new two-dimensional (2D) antiferromagnetic semiconducting boron structure, named as M-B28, is predicted using ab initio evolutionary structure searching. First-principles calculations show that M-B28 has a lower energy than other 2D magnetic boron structures and is dynamically stable. The unpaired electrons from the caps of B26 clusters lead to magnetism in M-B28, while making its highest valence band flat and isolated. The Néel temperature and mechanical properties of M-B28 are evaluated with the Ising model and strain-stress method, respectively, revealing a transition temperature of 32 K and the ideal strengths of 43.7 N/m along x direction and 38.5 N/m along y direction.

Protein Substrates for Reaction Discovery: Site-Selective Modification with Boronic Acid Reagents.

Chemical modification of natural proteins must navigate difficult selectivity questions in a complex polyfunctional aqueous environment, within a narrow window of acceptable conditions. Limits on solvent mixtures, pH, and temperature create challenges for most synthetic methods. While a protein's complex polyfunctional environment undoubtedly creates challenges for traditional reactions, we wondered if it also might create opportunities for pursuing new bioconjugation reactivity directly on protein substrates. This Account describes our efforts to date to discover and develop new and useful reactivity for protein modification by starting from an open-ended screen of potential transition-metal catalysts for boronic acid reactivity with a model protein substrate. By starting from a broad screen, we were hoping to take advantage of the very many potential reactive sites on even a small model protein. And perhaps more importantly, whole proteins as reaction screening substrates might exhibit uniquely reactive local environments, the results of a dense combination of functional groups that would be nearly impossible to mimic in a small-molecule context. This effort has resulted in the discovery of four new protein modification reactions with boronic acid reagents, including a remarkable modification of specific backbone N-H bonds. This histidine-directed Chan-Lam coupling, based on specific proximity of an imidazole and two amide groups, is one important example of powerful reactivity that depends on a combination of functional groups that proteins make possible. Other bioconjugation reactions uncovered include a three-component tyrosine metalation with rhodium(III), a nickel-catalyzed cysteine arylation, and an unusual ascorbate-mediated oxidative process for N-terminal modification. The remarkably broad scope of reactivity types encountered in this work is a testament to the breadth of boronic acid reactivity. It is also a demonstration of the diverse reactivities that are possible by the combined alteration of boronic acid structure and metal promoter. The discovery of specific backbone modification chemistry has been a broadly empowering reactivity. Pyroglutamate, a naturally occurring posttranslational modification, exhibits remarkably high reactivity in histidine-directed backbone modification, which allows us to treat pyroglutamate as a reactive bioorthogonal handle that is readily incorporated into proteins of interest by natural machinery. In another research direction, the development of a vinylogous photocleavage system has allowed us to view backbone modification as a photocaging modification which is released by exposure to light.

Accelerating crystal structure prediction by machine-learning interatomic potentials with active learning

In this letter we propose a new methodology for crystal structure prediction, which is based on the evolutionary algorithm USPEX and the machine-learning interatomic potentials actively learning on-the-fly. Our methodology allows for an automated construction of an interatomic interaction model from scratch replacing the expensive DFT with a speedup of several orders of magnitude. Predicted low-energy structures are then tested on DFT, ensuring that our machine-learning model does not introduce any prediction error. We tested our methodology on a problem of prediction of carbon allotropes, dense sodium structures and boron allotropes including those which have more than 100 atoms in the primitive cell. All the the main allotropes have been reproduced and a new 54-atom structure of boron have been found at very modest computational efforts.

Tailoring the hybrid network structure of boron nitride/carbon nanotube to achieve thermally conductive poly(vinylidene fluoride) composites

Abstract In this work, three kinds of boron nitride (BN) particles with different sizes were combined with carbon nanotubes (CNTs) to prepare the poly(vinylidene fluoride) (PVDF) composites. The dispersion states and the hybrid network structure of fillers were investigated. The results showed that the dispersion states of CNTs were greatly influenced by the size of BN particles. Relatively high density of hybrid network structure of fillers was obtained in the ternary composites containing the smallest BN particles (0.16 μm), while the composites containing the biggest BN platelets (22.02 μm) showed the low density of the hybrid network structure. Thermal conductivity measurements showed that BN particles with moderate size (8.70 μm) were the most appropriate filler to construct the highly efficient thermal conductive path with CNTs and in this condition, the ternary composites exhibited the highest thermal conductivity.

Electronic structure of boron and nitrogen doped isomeric graphene nanoflakes

Electronic properties of nitrogen and boron doped isomeric graphene nanoflakes have been explored using dispersion corrected B3LYP functional and CASSCF methods. The most thermodynamically stable isomers of nitrogen and boron doped systems contain phenalene and azulene motifs substituted in positions 7 and 9, respectively. Nitrogen doping promotes nanoflake planarity, increases singlet-triplet gap and a band gap, while boron doping promotes dome shaped nanoflake geometry, polyradicalic ground state, reduces singlet-triplet gap. Isomeric nanoflakes are less sensitive to doping compared to graphene nanoflakes. Nitrogen is a weak n type dopant for isomeric nanoflakes, while boron cannot be considered as a p type dopant. This effect is explained by non-uniform electron density distribution in pristine isomeric nanoflakes as compared to graphene nanoflakes.

Effect of Net Charge on the Relative Stability of 2D Boron Allotropes.

We study the effect of electron doping on the bonding character and stability of two-dimensional (2D) structures of elemental boron, called borophene, which is known to form many stable allotropes. Our ab initio calculations for the neutral system reveal previously unknown stable 2D ϵ-B and ω-B structures. We find that the chemical bonding characteristic in this and other boron structures is strongly affected by extra charge. Beyond a critical degree of electron doping, the most stable allotrope changes from ϵ-B to a buckled honeycomb structure. Additional electron doping, mimicking a transformation of boron to carbon, causes a gradual decrease in the degree of buckling of the honeycomb lattice that can be interpreted as piezoelectric response. Net electron doping can be achieved by placing borophene in direct contact with layered electrides such as Ca2N. We find that electron doping can be doubled by changing from the B/Ca2N bilayer to the Ca2N/B/Ca2N sandwich geometry.

Effects of single and double nickel doping on boron clusters: stabilization of tubular structures in BnNim, n = 2-22, m = 1, 2.

A systematic investigation on structure, relative stabilities, dissociation behavior and bonding of the singly and doubly Ni doped boron clusters BnNim with n = 2-22 and m = 1-2, was carried out using density functional theory (TPSSh functional) calculations. Calculated results indicate that for n < 14, BnNim structures are generally formed by capping Ni atom(s) on the edge or the surface of the pure boron Bn frameworks. From n = 14, the Ni dopants exert stronger effects in such a way that the most stable isomers BnNim adopt the shape of the related double ring tubular boron structures. With n ≥ 20, the Bn double ring appears to possess a large enough volume to entirely enclose the Ni2 dimer. The B14Ni and B22Ni2 turn out to be remarkable species with enhanced thermodynamic stability with larger average binding energies along with surprising geometric structures. Their higher thermodynamic stability can be understood in terms of the MO energy levels predicted by a hollow cylinder model, and other electronic properties. The (2 0 2)-orbital derived from the model of particle in a hollow cylinder appears to play a key role in the stabilization of the boron double ring.