BN Compounds Research Articles

Adsorption of H, NH x, BH x and BBr x on a (110) surface of c-BN: A quantum-mechanical DFT study

The adsorption of H, NH x , BH x and BBr x ( x = 1, 2 and 3) on hydrogen-terminated (110) surfaces of c-BN has been investigated theoretically. Density Functional Theory (DFT) methods were used in order to study the adsorption processes of these different species on both nitrogen and boron sites at the surfaces. With one exception, all adsorption processes were found to be exothermic and in the order; BBr· ≫ BH 2· ≈H· > BH· ≫ NH· ≈ BBr 2· > NH 2· ≫ BH 3· > NH 3· > BBr 3· for a nitrogen site, and NH 2· > NH· > BBr· > H· > BH· > BH 2· ≈ BBr 2· ≫ BBr 3· ≈ NH 3· ≈BH 3· for a boron site. The exception was NH 3 being bonded to a surface N site, for which the reaction was slightly endothermic. The various modeling parameters that were used in the calculations of these adsorption energies have been chosen by performing series of extensive test calculations, in which the effect of these parameters (e.g. template size, vacuum depth, atom constraints) on bond-strength have been carefully estimated. Moreover, a semi-empirical method has been evaluated with the purpose to study the usefulness of this type of method for the polar BN compound.

Synthesis of N‐Benzylated Anilines from the Reaction of Anilines and Benzyl Chloroformate

Reactions of benzyl chloroformate with a series of substituted anilines produced N‐carbobenzyloxy “CBZ” products along with the unexpected N‐benzylated “Bn” compounds. Reaction of aniline, 1a, gave the CBZ, or 2a, and Bn, or 3a, products in 29% and 14% yield, respectively. For 2‐nitro‐, 2‐bromo‐, and 2‐bromo‐5‐nitroanilines, the N‐benzylated compounds were produced exclusively. However, 2‐methoxy‐, 4‐bromo, 4‐iodo, and 4‐ethylanilines gave mainly CBZ products. Other compounds reported in this study gave mixtures of the two products. For 4‐chloro‐3‐nitroaniline, in addition to the Bn and CBZ products (53% and 14% yield, respectively), a N,N‐dibenzylated product was isolated in 27% yield. Collectively, the results indicated that electron‐withdrawing groups, particularly at the ortho position, directed the formation of Bn compounds, whilst electron‐donating groups, especially at the ortho and para positions, favored the synthesis of CBZ products.

Synthesis of N‐Benzylated Anilines from the Reaction of Anilines and Benzyl Chloroformate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Prediction study of elastic properties under pressure effect for zincblende BN, AlN, GaN and InN

We have performed a first-principles full-potential augmented-plane wave plus local orbitals (FP-APW+lo) calculations with density functional theory in local density approximation, in aim to determine and predict the pressure dependence of elastic constants of BN, AlN, GaN and InN compounds. From our results, we sustain the idea of no evidence that the soft acoustic mode is responsible for the phase transition.

On the cubic boron nitride crystallization in fluid systems

For the fluid-containing systems the position of the low-temperature boundary of the cBN crystallization region in the p,T-diagram of boron nitride is defined either by the line of the incongruent melting of the BN compound with the solvent, or by the kinetics of the cBN nucleation and crystal growth. The position of the high-temperature boundary of the p,T-region of cBN crystallization is always defined by kinetics factors.

Bond modification of BCN films on Ni substrate

We show that the composition for boron–carbon–nitrogen (BCN) ternary films can be tailored by controlling the quantities of the carbon and BN plumes together with the use of in situ nitrogen ion bombardment. At 800°C, BCN films with composition of BC2N are obtained on Si (100) substrates. However, Fourier transformed infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements indicate that these films are carbon doped BN compounds (BN:C), in which, phase separation of the carbon and BN phases occurred. On the other hand, hybridized BCN films can be deposited on Ni substrates under similar synthesis conditions. In such a case, the carbon and BN phases are hybridized through the carbon nitride and boron carbide bonds. These films appeared in fibrous nanostructures as observed by field emission scanning electron microscopy (FESEM). Evidence indicates that the Ni substrate acts as a sink for the carbon and forces the carbon composites to grow on top of the B and N atoms. By this means, bond hybridization between the carbon and BN phases occurred.

Core-level photoabsorption study of defects and metastable bonding configurations in boron nitride

Boron nitride is an interesting material for technological applications and for fundamental solid state physics investigations. It is a compound isoelectronic with carbon and, like carbon can possess sp{sup 2} and sp{sup 3} bonded phases resembling graphite and diamond. BN crystallizes in the sp{sup 2}-bonded hexagonal (h-BN), rhombohedral (r-BN) and turbostratic phases, and in the sp{sup 3}-bonded cubic (c-BN) and wurtzite (w-BN) phases. A new family of materials is obtained when replacing C-C pairs in graphite with isoelectronic B-N pairs, resulting in C{sub 2}BN compounds. Regarding other boron compounds, BN is exceptional in the sense that it has standard two-center bonds with conventional coordination numbers, while other boron compounds (e.g. B{sub 4}C) are based on the boron icosahedron unit with three-center bonds and high coordination numbers. The existence of several allotropic forms and fullerene-like structures for BN suggests a rich variety of local bonding and poses the questions of how this affects the local electronic structure and how the material accommodates the stress induced in the transition regions between different phases. One would expect point defects to play a crucial role in stress accommodation, but these must also have a strong influence in the electronic structure, since the B-N bondmore » is polar and a point defect will thus be a charged structure. The study of point defects in relationship to the electronic structure is of fundamental interest in these materials. Recently, the authors have shown that Near-Edge X-ray Absorption Fine Structure (NEXAFS) is sensitive to point defects in h-BN, and to the formation of metastable phases even in amorphous materials. This is significant since other phase identification techniques like vibrational spectroscopies or x-ray diffraction yield ambiguous results for nanocrystalline and amorphous samples. Serendipitously, NEXAFS also combines chemical selectivity with point defect sensitivity.« less

Inhibition of radiation-induced up-regulation of leukocyte adhesion to endothelial cells with the platelet-activating factor inhibitor, BN52021

Purpose : The inflammatory process is likely involved in normal tissue damage after radiation exposure, yet few studies have directly evaluated the factors that might be involved in the regulation of inflammation after irradiation in vivo. We tested the hypothesis that platelet-activating factor, a neutrophil agonist synthesized by endothelial cells, is involved in the upregulation of radiation-induced leukocyte-endothelial cell interactions by using an inhibitor of its receptor, BN52021. Methods and Materials : Fischer-344 rats with dorsal skin-fold window chambers were randomized to three experimental groups: control (sham irradiation); 6 Gy radiation; and 6 Gy + BN52021. BN52021 (0.5 mg/kg) was administered 5 min prior to 6 Gy radiation. Leukocytes were stained in vivo with i.v acridine orange for visualization with fluorescent microscopy. Venous vessel diameters were measured and numbers of rolling leukocytes were counted per 30-s period. The number of adhering leukocytes per unit surface area was also determined. Differences among that three experimental groups for rolling and adhering leukocytes were analyzed using a mixed-effects linear model with vessel shear rate used as a covariate. Results are reported as means ± standard errors. Results : Irradiation caused upregulation of leukocyte rolling, as compared with sham-treated controls ( p = 0.04): the BN compound in addition to radiation did not downregulate this effect. Irradiation also upregulated leukocyte adhesion ( p < 0.001), but the addition of BN52021 prior to irradiation blocked this effect. The drug did not affect heart rate or blood pressure. Conclusions : These results support the hypothesis that radiation-induced upregulation of leukocyte adhesion is mediated by platelet-activating factor. These results are consistent with prior reports that platelet-activating factor is not involved in leukocyte rolling, which involves separate families of adhesion molecules from those that regulate adhesion. BN52021, a ginkolide, or other related drugs might provide a useful pharmacological means to prevent or ameliorate inflammatory pathways that are invoked after radiation exposure.

A theoretical study on the boron—nitrogen bond in aminoborane (BH 2 · NH 2), diaminoborane (BH(NH 2) 2) and aminodifluoroborane (BF 2 · NH 2)

Results of ab initio SCF calculations for aminoborane (BH 2 · NH 2), diaminoborane (BH(NH 2) 2) and aminodifluoroborane (BF 2 · NH 2) are presented. The equilibrium geometries, rotational constants and vibrational frequencies of these species have been determined by calculation. Several molecular electronic properties have been computed and compared with each other to elucidate the electronic structure of the boron—nitrogen bond in those related aliphatic BN compounds. An appreciable amount of the double bond character found and the direction of the calculated dipole moment vector, from nitrogen to boron (positive to negative), in BH 2 · NH 2 and BF 2 · NH 2 give rise to the proposal to adopt BH 2 ⇋NH 2 and BF 2⇋NH 2 as an adequate representation of the BN bond in these molecules.