The α–β Transformation in Silicon Nitride Single Crystals

Single crystals of α-Si₃N₄ were annealed at 2000°–2150°C. The β phase was detected after annealing at 2150°C only when the crystals were surrounded by MgO·3Al₂O₃ or Y₂O₃ powders. On the other hand, no evidence of the α–β transformation was found when the crystals were annealed without additives. The solution–precipitation mechanism was concluded to be the dominant factor in the α–β transformation of Si₃N₄.     

Head‐to‐Head Prenyl Synthases in Pathogenic Bacteria

Many organisms contain head‐to‐head isoprenoid synthases; we investigated three such types of enzymes from the pathogens Neisseria meningitidis, Neisseria gonorrhoeae, and Enterococcus hirae. The E. hirae enzyme was found to produce dehydrosqualene, and we solved an inhibitor‐bound structure that revealed a fold similar to that of CrtM from Staphylococcus aureus. In contrast, the homologous proteins from Neisseria spp. carried out only the first half of the reaction, yielding presqualene diphosphate (PSPP). Based on product analyses, bioinformatics, and mutagenesis, we concluded that the Neisseria proteins were HpnDs (PSPP synthases). The differences in chemical reactivity to CrtM were due, at least in part, to the presence of a PSPP‐stabilizing arginine in the HpnDs, decreasing the rate of dehydrosqualene biosynthesis. These results show that not only S. aureus but also other bacterial pathogens contain head‐to‐head prenyl synthases, although their biological functions remain to be elucidated.     

A cobalt metal‐organic framework with small pore size for adsorptive separation of CO2 over N2 and CH4

In this study, a new cobalt‐based metal‐organic framework (MOF), [ (μ₃‐OH)₂(ipa)₅(C₃O₂)(DMF)₂] (CoIPA) was synthesized. The crystal structure analysis shows that CoIPA is constructed by Co₆(μ₃‐OH)₂ units linked by isophthalic acid forming a sxb topology and it possesses a small pore size of about 4 Å. The new MOF has been characterized using multiple experimental methods. Monte Carlo and Molecular Dynamic simulations were employed to investigate adsorption equilibrium and kinetics in terms of capacity and diffusivity of CO₂, N₂, and CH₄ on CoIPA. The gas adsorption isotherms collected experimentally were used to verify the simulation results. The activated CoIPA sample exhibits great gas separation ability at ambient conditions for CO₂/N₂ and CO₂/CH₄ with selectivity of around 61.4 and 11.7, respectively. The calculated self‐diffusion coefficients show a strong direction dependent diffusion behavior of target molecules. This high adsorption selectivity for both CO₂/N₂ and CO₂/CH₄ makes CoIPA a potential candidate for adsorptive CO₂ separation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4532–4540, 2017     

Comparison of N-Heterocyclic Aromatics Dibenzo[c,g]Carbazole and Dibenz[a,j]Acridine : Metabolism,DNA Binding and Mutation

N-Heterocyclic aromatics, such as carbazole and acridine derivatives, are environmental carcinogenic pollutants. Examples of these compounds are 7H-dibenzo[c,g]carbazole (DBC) and dibenz[a,j]acridine (DBA). The ionization potential (IP) for DBC is lower than for DBA. DBC is metabolized in lung and liver by way of phenols or directly through radical cations. DBC-induced liver and lung tumors have mutations in the 61^st codon of ras. DBA is metabolized in skin by way of a diol-epoxide of DBA. DBA-induced skin tumors have mutations in 12^th, 13^th and 61^st codons of ras. In summary, the metabolic activation of DBC proceeds through different adduction pattern pathways than does DBA and leads to different ras mutational spectra.     

Adhesion of CPO onto high modulus TPO: Lap-shear tests in conjunction with microscopy studies of the fracture surface structure

A lap-shear test was employed to investigate the failure mechanism of a chlorinated polyolefin (CPO) coating on a high-modulus thermoplastic olefin (TPO) substrate fabricated as a blend of a highly crystalline Ziegler-Natta isotactic polypropylene (iPP) and a crystalline metallocene poly(ethylene-butene) (9 wt% butene, EB9) impact modifier. The CPO was a chlorinated polypropylene containing 20 wt% Cl. The results showed that the fracture strength increased with increasing EB9 content in TPO blends. They also showed that the presence of xylene vapor during the bake step improved the adhesion between CPO and iPP itself (by 40%), but had a much smaller effect for the TPOs. Optical and transmission electronic microscopy images revealed a well-defined skin layer approximately 230 μm thick at the mold surface of the injection molded substrates. For the 25 wt% EB9 blend (TPO₂₅), this skin layer consists of thin fibers of EB trapped in a transcrystalline iPP matrix, with crystalline lamellae propagating from the matrix across the EB9 domains. Laser scanning confocal fluorescence microscopy (LCFM) and scanning electron microscopy images of iPP/CPO/iPP samples indicate that failure occurred close to the interface between the CPO and the iPP substrate, and, during fracture, the CPO layer maintained its original thickness. For the TPO/CPO/TPO sandwich samples, the fracture surfaces themselves were much rougher than that between CPO and iPP. Substantial deformation of the CPO layer was seen in the fractured samples, and failure was due primarily to cohesive fracture of the CPO in the region adjacent to the TPO substrate. From the perspective of newly introduced environmental regulations restricting aromatic hydrocarbons in automotive coatings, the most important result was the strong adhesion between CPO and TPO₂₅, with little difference between the samples exposed to xylene vapor and those not exposed to xylene.     

Magnetic resonance studies of cement based materials in inhomogeneous magnetic fields

Single-sided magnets give hope that Nuclear Magnetic Resonance (NMR) might in future be used for in situ characterisation of hydration and water transport in the surface layers of concrete slabs. Towards that end, a portable NMR-MOUSE (MObile Universal Surface Explorer) has been used to follow the hydration of gypsum based plaster, a Portland cement paste and concrete mortar. The results compare favourably to those obtained using a standard laboratory bench-top spectrometer. Further, stray field imaging (STRAFI) based methods have been used with embedded NMR detector coils to study water transport across a mortar/topping interface. The measured signal amplitudes are found to correlate with varying sample conditions.     

Photochemical free-volume generation in poly(methyl methacrylate) photoresists

The dissolution rates of poly(methyl methacrylate) [PMMA] thin films on quartz substrates are studied by a combination of laser interferometry and fluorescence quenching methods. In this way one can monitor the penetration, rate of the solvent (2-butanone, 2-pentanone) into the film. When these films were prepared containing 2 to 8 percent Meldrum's diazo (1) as a dopant, the dopant acted as a mild retarder of film dissolution. Upon irradiation at 254 nm, 1 is converted to CO, N₂ + acetone, and this process leads to a pronounced acceleration' of the PMMA film dissolution rate.     

Iron antimony oxide selective oxidation catalysts – an inelastic neutron scattering study

The inelastic neutron scattering spectra of allyl iodide (3-iodopropene, CH₂=CHCH₂I) and allylpalladium chloride, and allyl iodide dosed onto activated iron(III) oxide and iron antimonate catalysts at room temperature have been determined to characterise the adsorbed allyl species. The spectra are energy loss vibrational spectra in the range 16–4000 cm⁻¹. Allyl iodide is not decomposed on the surface and interacts through the localised C = C bond, more strongly with iron antimonate than with iron(III) oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Elastic Constants of Erbia Single Crystals

The elastic properties of single-crystalline erbia (Er₂O₃) at room temperature have been investigated using resonant ultrasound spectroscopy. The three independent stiffness constants of anisotropic Er₂O₃ cubic type-C crystals have been measured. The values of the stiffness constants were c ₁₁= 256.4 GPa, c ₁₂= 146.8 GPa, and c ₄₄= 75.2 GPa. From the stiffness constants, the estimated values for dense polycrystalline erbia for Young's modulus, the shear modulus, the bulk modulus, and Poisson's ratio at room temperature were 179 GPa, 67 GPa, 183.3 GPa, and 0.337, respectively. The value of Young's modulus is a minimum along [001] and a maximum along [111]. The value of the shear modulus is independent of the direction in the (001) and (111) planes, whereas it decreases in (11¯0) from 75 GPa along [001] to 55 GPa along [110].     

Cl electrosorption on Ag(1 0 0): Lateral interactions and electrosorption valency from comparison of Monte Carlo simulations with chronocoulometry experiments

We present Monte Carlo simulations using an equilibrium lattice-gas model for the electrosorption of Cl on Ag(1 0 0) single-crystal surfaces. Fitting the simulated isotherms to chronocoulometry experiments, we extract parameters such as the electrosorption valency γ and the next-nearest-neighbor lateral interaction energy ϕ_nnn. Both coverage-dependent and coverage-independent γ were previously studied, assuming a constant ϕ_nnn [I. Abou Hamad, Th. Wandlowski, G. Brown, P.A. Rikvold, J. Electroanal. Chem. 554–555 (2003) 211]. Here, a self-consistent, entirely electrostatic picture of the lateral interactions with a coverage-dependent ϕ_nnn is developed, and a relationship between ϕ_nnn and γ is investigated for Cl on Ag(1 0 0).