Electroreduction of organic compounds. 31. Electroreduction of 2- and 3-Chlorodibenzofuran in Deuterated Methanol

The cathodic reduction of dibenzofuran ( 2 ), 2-chlorodibenzofuran ( 4 ), and 3-chlorodibenzofuran ( 1 ) in deuterated methanol is investigated. The Birch-type reduction product 1,4-dibenzofuran ( 3 ) is formed from 1 via 2 , whereas 2-chloro-1,4-dihydrodibenzofuran ( 5 ) is obtained as by-product besides 3 from 4 as starting compound. Deuterium is only incorporated into the reduction products if CH₃OD or CD₃OD but not if CD₃OH are used. This observation is strongly indicative of a polar mechanism involving protonation rather than a radical mechanism with hydrogen atom abstraction to be operative.     

Cellulose-binding domains: potential for purification of complex proteins

The endoglucanase CenA and the exoglucanase Cex from Cellulomonasfimi each contain a discrete cellulose-binding domain (CBD),at the amino-terminus or carboxyl-terminus respectively. Thegene fragment encoding the CBD can be fused to the gene of aprotein of interest. Using this approach hybrid proteins canbe engineered which bind reversibly to cellulose and exhibitthe biological activity of the protein partner. Alkaline phosphatase(PhoA) from Escherichia coli, and a ß-glucosidase(Abg) from an Agrobacterium sp. are dimeric proteins. The fusionpolypeptides CenA-PhoA and Abg-CBC_cex are sensitive to proteolysisat the junctions between the fusion partners. Proteolysis resultsin a mixture of homo- and heterodimers; these bind to celluloseif one or both of the monomers carry a CBD, e.g. CenA-PhoA/CenA-PhoAand CenA-PhoA/PhoA. CBD fusion polypeptides could be used inthis way to purify polypeptides which associate with the fusionpartner.     

The characteristic curvature (Cc) definition and its use in assessing Cc for single ionic surfactants

The hydrophilic–lipophilic-difference (HLD) is a set of empirical equations that correlate the formulation conditions at phase inversion (HLD = 0). Based on partition studies for nonionic surfactants, the HLD can be interpreted as a normalized chemical potential difference between the surfactant dissolved in water and oil. The net-average curvature (NAC) model extrapolates this interpretation into a curvature form that has been used to fit and predict the phase behavior of surfactant-oil–water (SOW) systems. The curvature interpretation led to renaming the HLD surfactant parameter, sigma (σ), as the characteristic curvature (Cc). This work tests the validity of the curvature interpretation of the HLD, and the Cc concept, for single ionic surfactants and the use of this concept as a method to assess the Cc without the use of reference surfactants or alcohols. To this end, the net curvature of six anionic and two cationic surfactants was evaluated from solubilization data at the characteristic condition of 25°C, no added cosolvent, in the presence of an oil mixture with equivalent alkane carbon number (EACN) of zero, and as a function of salinity. These studies showed that the original HLD equation for ionic surfactant could not be interpreted as chemical potential or curvature because a salinity prefactor (coefficient) “bi” was missing. The revised equation, HLD_bi = bi∙ln(S)-k_bi∙EACN+Cc_bi -a_Tbi∙(T-25°C), could now be interpreted as a curvature expression, and it was demonstrated that Cc could be obtained from curvature using the expression Cc = Cc_bi/bi. This single surfactant method produces uncertainties that, for most surfactants, ranged from 0.2 to 1 Cc units, similar to the uncertainty obtained with the conventional method of Cc determination using mixtures of test and reference surfactants.     

Stress rupture of SiC/SiC composite tubes under high-temperature steam

SiC-fiber–reinforced SiC matrix composite cladding for light water reactor fuel elements must withstand high-temperature steam oxidation in a loss-of-coolant accident scenario (LOCA). Current composite designs include an outer monolithic SiC layer, in part, to increase steam oxidation resistance. However, it is not clear how such a structure would behave under high-temperature steam in the case when the monolithic layer cracks and carbon interphases and SiC fibers are exposed to the environment. To fill this knowledge gap, stress-rupture tests of prototypic SiC composite cladding at 1000°C under steam and inert environments were conducted. The applied stress was ∼120 MPa, which was beyond the initial cracking stress. The failure lifetime under steam was 400–1300 s, while 75% of the composite specimens did not fail after 3 h of total exposure under inert gases. Microstructural observations suggest that steam oxidation activated slow crack growth in the fibers, which led to failure of the composite. The results from this study suggest that stress rupture in steam environments could be a limiting factor of the cladding under reactor LOCA conditions.     

Residual stress versus microstructural effects on the strength and toughness of phase-separated PbO–B2O3–Al2O3 glasses

A few authors have reasonably proposed that liquid–liquid phase-separated (LLPS) glasses could show improved fracture strength, S_f, and toughness, K_Ic, as the second phase could provide a barrier to crack propagation via deflection, bowing, trapping, or bridging. Due to the associated tensile or compressive residual stresses, the second phase could also act as a toughening or a weakening mechanism. In this work, we investigated five glasses of the PbO–B₂O₃–Al₂O₃ system spanning across the miscibility gap: Four of them undergo LLPS—three are binodal (two B₂O₃-rich and one PbO-rich) and one is spinodal—and one does not show LLPS (composition outside the miscibility gap). Their compositions were designed in such a way that the amorphous particles are under compressive residual stresses in some and under tensile residual stresses in others. The following mechanical properties were determined: the Vickers hardness, ball on three balls (B3B) strength, and toughness, K_Ic-SEVNB (single-edge V-notch beam [SEVNB]). The microstructures and compositions were analyzed using scanning electron microscopy with energy-dispersive X-ray spectrometry. The spinodal glass showed, by far, the best mechanical properties. Its K_Ic-SEVNB = 1.6 ± 0.1 MPa m^1/2, which embodies an increase of almost 50% over the B₂O₃-rich binodal composition, and 90% considering the PbO-rich binodal composition. Moreover, its fracture strength, S_f = 166 ± 7 MPa, is one of the highest ones ever reported for an LLPS glass. Fracture analyses evidenced that the spinodal composition exhibited the lowest net stress at the fracture point. Moreover, calculations indicate that the internal residual stress level is the lowest in the spinodal glass. The overall results indicate that the microstructural effect of the spinodal glass is the most significant factor for its superior mechanical properties. This work corroborates the idea that LLPS provides a feasible and stimulating solution to improve the mechanical properties of glasses.     

On the Determination of the Concentration of Crystal Nuclei in Glasses by DSC

An interesting technique was proposed by Ray et al. over a decade ago to determine the number density of nucleation sites, N_q, or the nucleation rate, I(T), in glasses that exhibit internal nucleation. Their approach is based on the measurement of the areas under the differential scanning calorimetry (DSC) crystallization peaks of partially crystallized glass samples. In this study, we review their method and test a modified equation recently proposed by some of us, which also takes into account the crystal morphology and impingement. We compare N_q obtained with both methods for a Li₂O·2SiO₂ glass. Small glass monoliths were treated at 620°C for different time periods for crystal growth, without any nucleation treatment, and subsequently analyzed by DSC up to 800°C. We thus estimated N_q from the area under the DSC crystallization peaks. The corrected approach resulted in N_q values which were not affected by the pair of growth times chosen, as expected, but the obtained values were two‐ to fivefold lower than those calculated with the Ray model. Taking into account previously reported nucleation rates and the corresponding induction periods as a function of temperature (for specimens of the same glass batch), we estimated the number of nuclei formed during the DSC heating/cooling steps, and also measured them by optical microscopy (OM). Finally, we compared the obtained values from OM with the N_q values determined by the DSC method. The N_q resulting from the original and new equations were approximately two orders of magnitude larger than those experimentally determined for the same glass using optical microscopy. This difference is attributed to the formation of new nuclei during the heating and cooling paths of the DSC runs and to surface crystallization, which are not taken into account in the DSC expressions.     

An Overview of Synergistic Data Tools for Biological Scrutiny

A network of biological databases is reviewed, supplying a framework for studies of human genes and the association of their genomic variations with human phenotypes. The network is composed of GeneCards, the human gene compendium, which provides comprehensive information on all known and predicted human genes, along with its suite members GeneDecks and GeneLoc. Two databases are shown that address genes and variations focusing on olfactory reception (HORDE) and transduction (GOSdb). In the realm of disease scrutiny, we portray MalaCards, a novel comprehensive database of human diseases and their annotations. Also shown is GeneKid, a tool aimed at generating novel kidney disease biomarkers using systems biology, as well as Xome, a database for whole-exome next-generation DNA sequences for human diseases in the Israeli population. Finally, we show LifeMap Discovery, a database of embryonic development, stem cell research and regenerative medicine, which links to both GeneCards and MalaCards.     

Differential Activity of Plasma and Vacuolar Membrane Transporters Contributes to Genotypic Differences in Salinity Tolerance in a Halophyte Species,Chenopodium quinoa

Halophytes species can be used as a highly convenient model system to reveal key ionic and molecular mechanisms that confer salinity tolerance in plants. Earlier, we reported that quinoa (Chenopodium quinoa Willd.), a facultative C3 halophyte species, can efficiently control the activity of slow (SV) and fast (FV) tonoplast channels to match specific growth conditions by ensuring that most of accumulated Na⁺ is safely locked in the vacuole (Bonales-Alatorre et al. (2013) Plant Physiology). This work extends these finding by comparing the properties of tonoplast FV and SV channels in two quinoa genotypes contrasting in their salinity tolerance. The work is complemented by studies of the kinetics of net ion fluxes across the plasma membrane of quinoa leaf mesophyll tissue. Our results suggest that multiple mechanisms contribute towards genotypic differences in salinity tolerance in quinoa. These include: (i) a higher rate of Na⁺ exclusion from leaf mesophyll; (ii) maintenance of low cytosolic Na⁺ levels; (iii) better K⁺ retention in the leaf mesophyll; (iv) a high rate of H⁺ pumping, which increases the ability of mesophyll cells to restore their membrane potential; and (v) the ability to reduce the activity of SV and FV channels under saline conditions. These mechanisms appear to be highly orchestrated, thus enabling the remarkable overall salinity tolerance of quinoa species.     

SEM and AFM characterization of surface of two RMGICs for degradation before and after modification with bioactive glass ceramic

Objectives: The aim of this study was to evaluate the effect of bioactive glass–ceramic particles (Biosilicate®) addition on surface nanoroughness and topography of Resin-modified glass ionomer cements (RMGICs).

Methods: Experimental materials were made by incorporating 2 wt% of Biosilicate® into Fuji II LC® (FL) and Vitremer® (VT) powders. Disks of RMGICs (with and without Biosilicate®) measuring 0.5 cm (diameter) × 0.5 mm (thickness) were fabricated and polished. Samples were stored at 37 °C in dry or immersed in distilled water for 30 days. Digital images (20 × 20 μm) from the surfaces were obtained by means of an atomic force microscopy. Three images were acquired for each sample, and four nanoroughness measurements were performed in each image. Nanoroughness (Ra, nm) was assessed by Nanoscope Software V7. Data were analyzed with ANOVA and Student–Newman–Keuls multiple comparisons (p < 0.05). SEM images were obtained for surface topography analysis.

Results: FL was significantly rougher than VT (p < 0.05) in wet and dry conditions. The addition of Biosilicate® increased the surface roughness in VT and decreased in FL, regardless of the storage media (p ≤ 0.05). No differences existed between materials and storage conditions after Biosilicate® addition. Significance: The Biosilicate® particles addition produced changes on the surface nanoroughness of the RMGICs. These changes depended on the particles size of the original cements in dry conditions. In water storage, dissolution of the Biosilicate® particles, a silica-rich gel formation, and a hydroxyl carbonate apatite precipitation on the surface of the materials changed the nanoroughness surface. FL was the roughest in both conditions.

Significance: The Biosilicate® particles addition produced changes on the surface nanoroughness of the RMGICs. These changes depended on the particles size of the original cements in dry conditions. In water storage, dissolution of the Biosilicate® particles, a silica-rich gel formation, and a hydroxyl carbonate apatite precipitation on the surface of the materials changed the nanoroughness surface. FL was the roughest in both conditions.     

Process development for the laser powder bed fusion of WC-Ni Cermets using sintered-agglomerated powder

Although ceramic particle-metal matrix materials (i.e., cermets) can offer superior performance, manufacturing these materials via conventional means is difficult compared to the manufacturing of metal alloys. This study leverages the laser powder bed fusion (LPBF) process to additively manufacture dense tungsten carbide (WC)-17 wt.% nickel (Ni) composite specimens using novel spherical, sintered-agglomerated composite powder. A range of processing parameters yielding high-density specimens was discovered using a sequential series of experiments comprised of single bead, multi-layer, and cylindrical builds. Cylinders with a relative density >99% were fabricated and characterized in terms of microstructure, chemical composition, and hardness. Scanning electron microscopy images show favorable wetting between the Ni binder and carbide particles without any phase segregation and laser processing increased the average carbide particle size. Energy dispersive X-ray and X-ray diffraction analyses detected traces of secondary products after laser processing. For samples processed at high energy densities, complex carbides and carbon agglomerate phases were detected. The maximum hardness of 60.38 Rockwell C is achieved in the printed samples. The successful builds in this study open the way for LPBF of dense WC-Ni parts with a large workable laser power-laser velocity processing window.