Boron Separation by the Two—step Ion—Exchange for the Isotopic Measurement of Boron

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The Boron Conundrum: Which Principles Underlie the Formation of Large Hollow Boron Cages?

Extensive optimisation calculations are performed for the B₈₀ isomers in order to find out which principles underlie the formation of large hollow boron cages. Our analysis shows that the most stable isomers contain triangular B₁₀ or rhombohedral B₁₆ building blocks. The lowest‐energy isomer has C_3v symmetry and is characterised by a belt of three interconnected B₁₆ units and two separate B₁₀ units. At the B3LYP/6‐31G(d) level of theory, this newly discovered isomer is 2.29, 1.48, and 0.54 eV below the leapfrog B₈₀ of Szwacki et al., the T_h‐B₈₀ of Wang, and the D_3d‐B₈₀ of Pochet et al., respectively. Our C_3v isomer is therefore identified as the most stable hollow cage isomer of B₈₀ presently known. Its HOMO–LUMO gap of 1.6 eV approaches that of the leapfrog B₈₀. The leapfrog principle still remains a reliable scheme for producing boron cages with larger HOMO–LUMO gaps, whereas the thermodynamically most stable B₈₀ cages are formed when all pentagonal faces are capped. We show that large hollow cages of boron retain a preference for fullerene frames. The additional capping is in accordance with the following rules: preference for capping of pentagonal faces, formation of B₁₀ and/or B₁₆ units, homogeneous distribution of the hexagonal caps, and hole density approaching 1/9. Although our most stable B₈₀ isomer still remains higher in energy than the B₈₀ core–shell structure, we show that by applying the bonding principles to larger structures it is possible to construct boron cages with higher stabilisation energy per boron atom than the core–shell structure; a prototypical example is B₁₆₀. This clearly shows the continuous competition between the two suggested construction schemes, namely, the formation of multiple‐shell structures and hollow cages.     

Computational Evidence for the Smallest Boron Nanotube

One-dimensional boron nanostructures have being actively studied experimentally1 and theoretically2 in the recent years, due to their promising applications in field emission devices and high-temperature electronics. Amorphous3 and crystalline1 nanowires,…     

Boron–Ligand Cooperation: The Concept and Applications

The term boron–ligand cooperation was introduced to describe a specific mode of action by which certain metal-free systems activate chemical bonds. The main characteristic of this mode of action is that one covalently bound substituent at the boron is actively involved in the bond activation process and changes to a datively bound ligand in the course of the bond activation. Within this review, how the term boron–ligand cooperation evolved is reflected on and examples of bond activation by boron–ligand cooperation are discussed. It is furthermore shown that systems that operate via boron–ligand cooperation can complement the reactivity of classic intramolecular frustrated Lewis pairs and applications of this new concept for metal-free catalysis are summarized.     

Synthesis of Boron–Nitrogen–Phosphorus Compounds from N-Silylphosphoranimines

Two modes of reactivity of N-silylphosphoranimines have been utilized to prepare the title compounds containing either B–N=P or Si–N=P–N–B linkages. First, silicon-nitrogen bond cleavage reactions of the N-silylphosphoranimines, Me₃SiN=PMe(R)OCH₂CF₃ (1: R=Me, 2: R=Ph), with various chloroboranes gave the new N-borylphosphoranimines, Ph(Me₂N)B–N=PMe₂OCH₂CF₃ (2) and [(Me₃Si)₂N](Cl)B–N=PMe₂OCH₂CF₃ (10). In other cases, however, the expected B–N=P products were unstable and cyclic phosphazenes [Me(R)P=N]_3,4 were obtained. Second, deprotonation-substitution reactions of the aminophosphoranimines, Me₃SiN=P(R)Me–N(R)H, were used to prepare a series of novel (borylamino)-phosphoranimines, Me₃SiN=P(R)(Me)–N(R)–B(NMe₂)₂ (18: R=Me, R=t-Bu; 19: R=R=Me; 20: R=Ph, R=t-Bu; 21: R=Ph, R=Me) and Me₃SiN=PMe₂–N(t-Bu)–B(Ph)X (22: X=NMe₂, 23: X=OCH₂CF₃). All of the new boron–nitrogen–phosphorus products were fully characterized by multinuclear NMR (¹H, ¹³C, and ³¹P) spectroscopy and elemental analysis.     

Metal-Free C−H Borylation of N-Heteroarenes by Boron Trifluoride

Organoboron compounds are essential reagents in modern C−C coupling reactions. Their synthesis via catalytic C−H borylation by main group elements is emerging as a powerful tool alternative to transition metal based catalysis. Herein, a straightforward metal-free synthesis of aryldifluoroboranes from BF₃ and heteroarenes is reported. The reaction is assisted by sterically hindered amines and catalytic amounts of thioureas. According to computational studies the reaction proceeds via frustrated Lewis pair (FLP) mechanism. The obtained aryldifluoroboranes are further stabilized against destructive protodeborylation by converting them to the corresponding air stable tetramethylammonium organotrifluoroborates.     

Anisotropic Boron–Carbon Hetero-Nanosheets for Ultrahigh Energy Density Supercapacitors

A 2D boron nanosheet that exhibits high theoretical capacitance, around four times that of graphene, is a significant supercapacitor electrode. However, its bulk structure with low interlaminar conduction and porosity restricts the charge transfer, ion diffusion, and energy density. Herein, we develop a new 2D hetero-nanosheet made of anisotropic boron–carbon nanosheets (ABCNs) by B−C chemical bonds via gas-phase exfoliation and condensation bottom-up strategy. The ABCNs are constructed into high flexible supercapacitor electrode by microfluidic electrospinning. The ABCN electrode greatly promotes smooth migration and excessive storage of electrolyte ions due to large interlayer conductivity, ionic pathways, and accessible surfaces. The flexible supercapacitor delivers ultrahigh volumetric energy density of 167.05 mWh cm⁻³ and capacitance of 534.5 F cm⁻³. A wearable energy-sensor system is designed to stably monitor physiological signals.     

Boron in coral skeletons determined by prompt γ-ray analysis

A systematic and non-destructive technique is proposed for the determination of boron in coral samples by neutron-induced prompt γ-ray analysis (PGA) using a thermal neutron guide beam of the JRR-3M reactor. About 50–150 mg samples in sealed FEP film were irradiated and measured for 5000 s in the PGA system at a neutron flux of 2.4 × 10⁷ n cm⁻² s⁻¹. In order to determine B content in coral skeletons, the Doppler-broadened γ-ray peak of 478 keV (¹⁰B) was used together with the correction of interference from the Na-peak of 472 keV. The analytical precision was ~3% for the JCp-1 coral standard. The data (n = 56) obtained by the present method showed a range of B content from 40.7 to 76.9 ppm which is similar to reported values. Boron in corals showed the highest levels in Rukan-sho (Okinawa) with an average B content of 62.5 ppm, whereas corals collected from Mizugama (Okinawa), Cebu (the Philippines) and Khang Khao (Thailand) exhibited B contents of 56.5, 53.0 and 45.7 ppm, respectively. The uptake of boron by living corals may be influenced by seawater pH related to higher seawater B(OH)₄⁻. In this paper we discuss factors controlling the B levels in corals.     

The Electro‐Oxidation of Formaldehyde at a Boron‐Doped Diamond Electrode

Abstract

The characteristics of the boron‐doped diamond (BDD) electrode in this work were studied by atomic force microscope (AFM), scanning electron microscopy, and Raman spectroscopy. The electro‐oxidation of formaldehyde at the BDD electrode in 0.5 M K₂SO₄ with different pH was studied by cyclic voltammetry and amperometry. There is no significant oxidation peak of formaldehyde in acidic solution because the oxidation of formaldehyde is at the potential range of water discharge. However, in neutral solution, there is a well‐defined oxidation peak at about +2.2 V vs. Ag/AgCl. The relation between the response current and formaldehyde concentration is linear behavior at the concentration range from 50 to 600 µM. Besides, in neutral solution, the oxidation of formaldehyde is dominated by indirect oxidation at lower formaldehyde concentration, and it is dominated by direct oxidation at higher concentration. Finally, in alkaline solution, the oxidation of formaldehyde is dominated by indirect oxidation caused by a powerful oxidant and is related to the ratio of the amounts of formaldehyde and OH molecules at the BDD electrode surface.     

Boron difluoride formazanate dye for high-efficiency NIR-Ⅱ fluorescence imaging-guided cancer photothermal therapy

The small molecular second near-infrared(NIR-Ⅱ, 1000–1700 nm) dye-based nanotheranostics can concurrently combine deep-tissue photodiagnosis with in situ phototherapy, which occupies a vital position in the early detection and precise treatment of tumors. However, the development of small molecular NIR-Ⅱ dyes is still challenging due to the limited electron acceptors and cumbersome synthetic routes.Herein, we report a novel molecular electron acceptor, boron difluoride formazanate(BDF). Based on...     

Ion Exchange Extraction of Boron from Aqueous Fluids by Amberlite IRA 743 Resin

The ion exchange characteristics d Amherlite IRA 743 resin for extracting boron from aqueous fluids have been investigated in detail. The results show that AmherHte IRA 743 resin, a boron specific ion exchange resin, can quantitatively extract boron as the B (OH)4- spedes from weakly basle solution. Some exchangeable anions such as CI- and SO4^2- are present, resulting in an increase in pH value of the loeded solution within the nan, and the boron in natural aqueous fluids with low nH is also extracted by Amberlite IRA 743 resin. However, the voiume of loaded solution must be restricted. The maximum voiume of loaded solution giving quantitative extraction of boron decreases for sample soh.,tiom of lower pH value. Warm HCI solution is more effective than room temperature HCI solution for eluting boron from Amberllte IRA 743 resin.     

Electrosynthesis of Zirconium Boride from Cryolite–Alumina Melts Containing Zirconium and Boron Oxides

Electrosynthesis of zirconium boride from cryolite–alumina melts containing zirconium and boron oxides is studied. A thermodynamic estimate of the synthesis feasibility and cyclic voltammetry data prove that the synthesis involves one stage. Electrolytic ZrB₂coatings on nickel are obtained.     

1, 1‐Dianthrimide as a Reagent for the Spectrophotometric Determination of Boron

Abstract

The optimum conditions for the formation of the blue 1:1 complex by the reaction of 1, 1‐dianthrimide and boric acid in 95% by weight sulfuric acid have been determined. The effect of certain diverse ions are reported. The procedure is applicable to the determination of 1 to 10 μ of boron.     

Boron environments in Pyrex® glass--a high resolution, Double-Rotation NMR and thermodynamic modelling study

It is shown, using the important technological glass Pyrex? as an example, that 1D and 2D (11)B Double-Rotation (DOR) NMR experiments, in combination with thermodynamic modelling, are able to provide unique structural information about complex glasses. (11)B DOR NMR has been applied to Pyrex? glass in order to remove both dipolar and quadrupolar broadening of the NMR lines, leading to high resolution spectra that allow unambiguous, accurate peak fitting to be carried out, of particular importance in the case of the 3-coordinated [BO(3)] (B3) trigonal planar environments. The data obtained are of sufficient quality that they can be used to test the distributions of borate and borosilicate superstructural units predicted by the thermodynamics-based Model of Associated Solutions. The model predicts the dominant boron-containing chemical groupings in Pyrex? glass to be those associated with B(2)O(3) and sodium tetraborate (with smaller amounts of sodium triborate, sodium diborate, sodium pentaborate, danburite and reedmergnerite). Excellent agreement is found between model and experiment provided the (11)B peaks with isotropic chemical shifts of -1.4 ppm and 0.5 ppm are assigned to B4 species from borosilicate units ([B(OSi)(4)] and [B(OSi)(3)(OB)]) and borate superstructural units (mainly triborate rings with some pentaborate and diborate) respectively. The peaks with isotropic shifts of 14 ppm and 18.1 ppm are then assigned to B3 in borate superstructural units (mainly triborate and pentaborate along with connecting B3) and boroxol rings respectively. The assignments of the DOR NMR peaks, are supported by the presence of cross-peaks in (11)B spin-diffusion DOR NMR spectra which can be used to develop a structural model in which B(2)O(3)-like regions are linked, via borate and borosilicate superstructural units, to the majority silica network. Pyrex? is thus shown to have a heterogeneous structure, with distinct molecular groupings that are far removed from a random distribution of network polyhedra with only short-range order.     

Cu-Catalyzed Asymmetric Kinetic Boron Conjugate Addition of γ-Substituted α,β-Unsaturated γ-Lactams

Chiral α,β-unsaturated γ-lactams bearing simple γ- substituents are found in biologically active molecules and natural products, however, their synthesis still remains difficult. Herein, we report an efficient kinetic resolution (KR) of γ-substituted α,β-unsaturated γ-lactams via a Cu-catalyzed asymmetric boron conjugate addition, which also leads to the efficient synthesis of chiral β-hydroxy-γ-lactams with β,γ-stereogenic carbon centers. The KR proceeded smoothly with a wide range of γ-alkyl or aryl substituted substrates including those bearing aromatic heterocycles and different N-protected substrates in up to 347 of s value. Their highly versatile transformations, synthetic utility in biologically active molecules, and inhibitory activities against cisplatin-sensitive ovarian cancer cell A2780 have also been demonstrated. Differing from the well-known mechanism involving Cu−B species in Cu-catalyzed boron conjugate additions, our mechanistic studies using density functional theory (DFT) calculations and experiments indicate that a Lewis acid Cu^I-catalyzed mechanism is the likely pathway in the catalytic reaction.     

Boron Tunneling in the “Weak” Bond-Stretch Isomerization of N−B Lewis Adducts

Some nitrile-boron halide adducts exhibit a double-well potential energy surface with two distinct minima: a “long bond” geometry (LB, a van der Waals interaction mostly based on electrostatics, but including a residual charge transfer component) and a “short bond” structure (SB, a covalent dative bond). This behavior can be considered as a “weak” form of bond stretch isomerism. Our computations reveal that complexes RCN−BX₃ (R=CH₃, FCH₂, BrCH₂, and X=Cl, Br) exhibit a fast interconversion from LB to SB geometries even close to the absolute zero thanks to a boron atom tunneling mechanism. The computed half-lives of the meta-stable LB compounds vary between minutes to nanoseconds at cryogenic conditions. Accordingly, we predict that the long bond structures are practically impossible to isolate or characterize, which agrees with previous matrix-isolation experiments.     

Observation of Transition-Metal–Boron Triple Bonds in IrB2O− and ReB2O−

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π→BR back-donation, despite the electron deficiency of boron. An electron-precise metal–boron triple bond was first observed in BiB₂O⁻ [Bi≡B−B≡O]⁻ in which both boron atoms can be viewed as sp-hybridized and the [B−BO]⁻ fragment is isoelectronic to a carbyne (CR). To search for the first electron-precise transition-metal-boron triple-bond species, we have produced IrB₂O⁻ and ReB₂O⁻ and investigated them by photoelectron spectroscopy and quantum-chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂O⁻ has a closed-shell bent structure (C_s, ¹A′) with BO⁻ coordinated to an Ir≡B unit, (⁻OB)Ir≡B, whereas ReB₂O⁻ is linear (C_∞v, ³Σ⁻) with an electron-precise Re≡B triple bond, [Re≡B−B≡O]⁻. The results suggest the intriguing possibility of synthesizing compounds with electron-precise M≡B triple bonds analogous to classical carbyne systems.     

Ab initio Studies on Boron Clusters and Their Corresponding Boranes with T_d,O_h and I_h Symmetries

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Square‐Wave Voltammetry Determination of Aspartame in Dietary Products Using a Boron‐Doped Diamond Electrode

Abstract

The use of square‐wave voltammetry in conjunction with a cathodically pretreated boron‐doped diamond electrode for the analytical determination of aspartame in dietary products is described. In this determination, the samples were analyzed without previous treatment in a 0.5 mol l^?1 H₂SO₄ solution. A single oxidation peak at a potential of 1.6 V vs. Ag/AgCl (3.0 mol l^?1 KCl) with the characteristics of an irreversible reaction was obtained. The analytical curve was linear in the aspartame concentration range 9.9×10^?6 to 5.2×10^?5 mol l^?1 with a detection limit of 2.3×10^?7 mol l^?1. The relative standard deviation (n=5) obtained was smaller than 0.2% for the 1.0×10^?4 mol l^?1 aspartame solution. The proposed method was applied with success to the determination of aspartame in several dietary products and the results were similar to those obtained using an HPLC method at 95% confidence level.