Synthesis and structural characterization of [PhE(BNMe2)2]2 (E = P or As): Six-Membered P2B4 and As2B4 Rings with Unusual Structures

The reaction of either Li₂PPh or Li₂AsPh with the diborane(4) derivative B₂(NMe₂)₂Br₂ affords the compounds [PhP(BNMe₂)₂]₂ ( 1 ) or [PhAs(BNMe₂)₂]₂ ( 2 ) in good yield. Both 1 and 2 have cyclic structures featuring non-planar P₂B₄ or As₂B₄ six-membered rings which have chair configurations. Although all four borons in each ring have planar coordination, the two phosphorus or arsenic centers have different degrees of pyramidalization. Bond distances within the rings indicate that the B? B, B? P or B? As bonds are single, whereas the exo-B? N bond lengths are consistent with significant π-bonding. The ring structures of 1 and 2 are in sharp contrast to the related boron-nitrogen species (t-BuN)₂N₄Me₄ which has a nido-N₂B₄ framework. The attempted synthesis of the nitrogen analogue of 1 or 2 by using a similar approach did not result in the isolation of [PhN(BNMe₂)₂]₂, instead the tetramino diborane(4) species [B(NMe₂)NHPh]₂ ( 3 ), which has a structure similar to other tetramine diborane(4) compounds, was isolated.     

Mechanical and transport properties of the poly(ethylene oxide)-poly(acrylic acid) double network hydrogel from molecular dynamic simulations

We used atomistic molecular dynamics (MD) simulations to investigate the mechanical and transport properties of the PEO-PAA double network (DN) hydrogel with 76 wt % water content. By analyzing the pair correlation functions for polymer-water pairs and for ion-water pairs and the solvent accessible surface area, we found that the solvation of polymer and ion in the DN hydrogel is enhanced in comparison with both PEO and PAA single network (SN) hydrogels. The effective mesh size of this DN hydrogel is smaller than that of the SN hydrogels with the same water content and the same molecular weight between the cross-linking points (Mc). Applying uniaxial extensions, we obtained the stress-strain curves for the hydrogels. This shows that the DN hydrogel has a sudden increase of stress above approximately 100% strain, much higher than the sum of the stresses of the two SN hydrogels at the same strain. This arises because PEO has a smaller Mc value than PAA, so that the PEO in the DN reaches fully stretched out at 100% strain that corresponds to 260% strain in the PEO SN (beyond this point, the bond stretching and the angle bending increase dramatically). We also calculated the diffusion coefficients of solutes such as D-glucose and ascorbic acid in the hydrogels, where we find that the diffusion coefficients of those solutes in the DN hydrogel are 60% of that in the PEO SN and 40% of that in the PAA SN due to its smaller effective mesh size.     

Overview of Synthetic Methods to Prepare Plasmonic Transition-Metal Nitride Nanoparticles

The search for new plasmonic materials that are low-cost, chemically and thermally stable, and exhibit low optical losses has garnered significant attention among researchers. Recently, metal nitrides have emerged as promising alternatives to conventional, noble-metal-based plasmonic materials, such as silver and gold. Many of the initial studies on metal nitrides have focused on computational prediction of the plasmonic properties of these materials. In recent years, several synthetic methods have been developed to enable empirical analysis. This review highlights synthetic techniques for the preparation of plasmonic metal nitride nanoparticles, which are predominantly free-standing, by using solid-state and solid–gas phase reactions, nonthermal and arc plasma methods, and laser ablation. The physical properties of the nanoparticles, such as shape, size, crystallinity, and optical response, obtained with such synthetic methods are also summarized.     

Antibody-catalyzed oxy-cope rearrangement: mechanism and origins of catalysis and stereoselectivity from DFT quantum mechanics and flexible docking

Density functional theory using B3LYP and flexible ligand docking methods were used to investigate the complete potential surface for the uncatalyzed and the AZ28 antibody-catalyzed oxy-Cope reaction of 2,5-diaryl-1,5-hexadien-3-ol derivatives. The reaction mechanism is stepwise, involving a cyclohexane diyl intermediate. Theoretical deuterium isotope effects match well with those from experiment. Gas-phase transition structures show mixed preferences for the axial vs equatorial hydroxyl group, while solvation favors the axial isomer. Specific phenyl group conformations are shown to be critical to transition-state stabilization (by up to 15 kcal/mol), and the effective conformation is not that found in the hapten used to generate the germline and affinity-matured AZ28 catalytic antibodies. Docking studies support greater transition-state binding than reactant binding. Docking studies also predict the S stereoselectivity of mature AZ28 and suggest that binding modes quite different from those of the hapten might play a role in catalysis, with specific focus on ligand hydrogen bonding to Asp(H101).     

The (p, ρ, T) of (methanol + benzene) and (methanol + ethylbenzene)

The (p, ρ, T) of methanol, ethylbenzene and (methanol + benzene) and (methanol + ethylbenzene) at temperatures between (290 and 500) K and pressures in the range (0.1 to 60) MPa have been measured with a magnetic suspension densimeter with an uncertainty of ±0.1%. Our measurements with methanol deviate from the literature values by less than 0.2%. The (p, ρ, T) measurements were fitted with experimental uncertainties by an empirical equation. The temperature and mole fraction dependence of the coefficients of the equation of state are presented.     

Asymmetric magnetization reversal in exchange-biased hysteresis loops

Polarized neutron reflectometry is used to probe the in-plane projection of the net-magnetization vector M--> of polycrystalline Fe films exchange coupled to twinned (110) MnF (2) or FeF (2) antiferromagnetic (AF) layers. The magnetization reversal mechanism depends upon the orientation of the cooling field with respect to the twinned microstructure of the AF, and whether the applied field is increased to (or decreased from) a positive saturating field; i.e. , the magnetization reversal is asymmetric. The reversal of the sample magnetization from one saturated state to the other occurs via either domain wall motion or magnetization rotation on opposite sides of the same hysteresis loop.     

On critical nets in $${\mathbb {R}}^k$$ R k

Geometriae Dedicata - Critical nets in $${\mathbb {R}}^k$$ (sometimes called geodesic nets) are embedded graph with the property that their embedding is a critical point of the total (edge) length...     

Conformational studies on heteroleptic trifluoromethyl‐substituted phenylboranes

Organoboranes carrying electron‐withdrawing substituents are commonly used as Lewis acidic catalysts or cocatalysts in a variety of organic processes. These Lewis acids also became popular through their application in `frustrated Lewis pairs', i.e. combinations of Lewis acids and bases that are unable to fully neutralize each other due to steric or electronic effects. We have determined the crystal and molecular structures of four heteroleptic arylboranes carrying 2‐(trifluoromethyl)phenyl, 2,6‐bis(trifluoromethyl)phenyl, 3,5‐bis(trifluoromethyl)phenyl or mesityl substituents. [3,5‐Bis(trifluoromethyl)phenyl]bis[2‐(trifluoromethyl)phenyl]borane, C₂₂H₁₁BF₁₂, (I), crystallizes with two molecules in the asymmetric unit which show very similar geometric parameters. In one of the two molecules, both trifluoromethyl groups of the 3,5‐bis(trifluoromethyl)phenyl substituent are disordered over two positions. In [3,5‐bis(trifluoromethyl)phenyl]bis[2,6‐bis(trifluoromethyl)phenyl]borane, C₂₄H₉BF₁₈, (II), only one of the two meta‐trifluoromethyl groups is disordered. In [2,6‐bis(trifluoromethyl)phenyl]bis[3,5‐bis(trifluoromethyl)phenyl]borane, C₂₄H₉BF₁₈, (III), both meta‐trifluoromethyl groups of only one 3,5‐bis(trifluoromethyl)phenyl ring are disordered. [3,5‐Bis(trifluoromethyl)phenyl]dimesitylborane, C₂₆H₂₅BF₆, (IV), carries only one meta‐trifluoromethyl‐substituted phenyl ring, with one of the two trifluoromethyl groups disordered over two positions. In addition to compounds (I)–(IV), the structure of bis[2,6‐bis(trifluoromethyl)phenyl]fluoroborane, C₁₆H₆BF₁₃, (V), is presented. None of the ortho‐trifluoromethyl groups is disordered in any of the five compounds. In all the structures, the boron centre is in a trigonal planar coordination. Nevertheless, the bond angles around this atom vary according to the bulkiness and mutual repulsion of the substituents of the phenyl rings. Also, the ortho‐trifluoromethyl‐substituted phenyl rings usually show longer B—C bonds and tend to be tilted out of the BC₃ plane by a higher degree than the phenyl rings carrying ortho H atoms. A comparison with related structures corroborates the conclusions regarding the geometric parameters of the boron centre drawn from the five structures in this paper. On the other hand, CF₃ groups in meta positions do not seem to have a marked effect on the geometry involving the boron centre. Furthermore, it has been observed for the structures reported here and those reported previously that for CF₃ groups in ortho positions of the aromatic ring, disorder of the F atoms is less probable than for CF₃ groups in meta or para positions of the ring.