Electrochemical investigation of chromium nanocarbide coated Ti–6Al–4V and Co–Cr–Mo alloy substrates

This study investigated the electrochemical behavior of chromium nano-carbide cermet coating applied on Ti–6Al–4V and Co–Cr–Mo alloys for potential application as wear and corrosion resistant bearing surfaces. The cermet coating consisted of a highly heterogeneous combination of carbides embedded in a metal matrix. The main factors studied were the effect of substrate (Ti–6Al–4V vs. Co–Cr–Mo), solution conditions (physiological vs. 1 M H₂O₂ of pH 2), time of immersion (1 vs. 24 h) and post coating treatments (passivation and gamma sterilization). The coatings were produced with high velocity oxygen fuel (HVOF) thermal spray technique at atmospheric conditions to a thickness of 250 μm then ground and polished to a finished thickness of 100 μm and gamma sterilized. Native Ti–6Al–4V and Co–Cr–Mo alloys were used as controls. The corrosion behavior was evaluated using potentiodynamic polarization, mechanical abrasion and electrochemical impedance spectroscopy under physiologically representative test solution conditions (phosphate buffered saline, pH 7.4, 37 °C) as well as harsh corrosion environments (pH ～ 2, 1 M H₂O₂, T = 65 °C). Severe environmental conditions were used to assess how susceptible coatings are to conditions that derive from possible crevice-like environments, and the presence of inflammatory species like H₂O₂. SEM analysis was performed on the coating surface and cross-section. The results show that the corrosion current values of the coatings (0.4–4 μA/cm²) were in a range similar to Co–Cr–Mo alloy. The heterogeneous microstructure of the coating influenced the corrosion performance. It was observed that the coating impedances for all groups decreased significantly in aggressive environments compared with neutral and also dropped over exposure time. The low frequency impedances of coatings were lower than controls. Among the coated samples, passivated nanocarbide coating on Co–Cr–Mo alloy displayed the least corrosion resistance. However, all the coated materials demonstrated higher corrosion resistance to mechanical abrasion compared to the native alloys.     

Influence of an Electric Field on the Burning Behavior of Solid Fuels and Propellants

An experimental study on the effects of an applied external electric field on the combustion behavior of solid fuels and solid propellants has been conducted. In an opposed flow burning configuration, application of an electric field was shown to extinguish a paraffin fuel and gaseous oxygen flame over a broad range of operating conditions. When subjected to the electric field, burning paraffin fuel strands were found to extinguish at various axial locations relative to the exit of the oxidizer gas jet. Extinguishment location was found to be a function of field strength as well as electrode surface area, while changes in polarity did not significantly alter the results. In addition, the combustion behaviors of two composite solid rocket propellants were studied while subjected to an external electric field. Both propellants were based on HTPB/AP combinations, with one propellant containing aluminum and the other being non‐aluminized. Application of an electric field to the composite solid rocket propellant strands demonstrated decreases in propellant burning rate under all operating conditions for both propellants including changes in polarity. The flame structure of the aluminized propellant was examined closely as the luminosity, flame length, and flame width varied significantly with field strength and burning location of the strand relative to the electrodes.     

Targeting tumour proliferation with a small-molecule inhibitor of AICAR transformylase homodimerization

Aminoimidazole carboxamide ribonucleotide transformylase/ inosine monophosphate cyclohydrolase (ATIC) is a bifunctional homodimeric enzyme that catalyzes the last two steps of de novo purine biosynthesis. Homodimerization of ATIC, a protein–protein interaction with an interface of over 5000 Ų, is required for its aminoimidazole carboxamide ribonucleotide (AICAR) transformylase activity, with the active sites forming at the interface of the interacting proteins. Here, we report the development of a small‐molecule inhibitor of AICAR transformylase that functions by preventing the homodimerization of ATIC. The compound is derived from a previously reported cyclic hexapeptide inhibitor of AICAR transformylase (with a K_i of 17 μM ), identified by high‐throughput screening. The active motif of the cyclic peptide is identified as an arginine‐tyrosine dipeptide, a capped analogue of which inhibits AICAR transformylase with a K_i value of 84 μM . A library of nonnatural analogues of this dipeptide was designed, synthesized, and assayed. The most potent compound inhibits AICAR transformylase with a K_i value of 685 nM , a 25‐fold improvement in activity from the parent cyclic peptide. The potential for this AICAR transformylase inhibitor in cancer therapy was assessed by studying its effect on the proliferation of a model breast cancer cell line. Using a nonradioactive proliferation assay and live cell imaging, a dose‐dependent reduction in cell numbers and cell division rates was observed in cells treated with our ATIC dimerization inhibitor.     

Over-production of 5-enolpyruvylshikimate-3-phosphate synthase in Escherichia coli: use of the T7 promoter

5-Enolpyruvylshikimate-3-phosphate (EPSP) synthase, the productof the Escherichia coli aroA gene, has been overproduced inE.coli BL21(DE3) under the control of the T7 gene 10 promoterand ribosome binding site, to a level of {small tilde}50% oftotal cell protein. EPSP synthase is the primary target of thepost-emergence herbicide, glyphosate, commonly known as Roundup^TM.A simple two step purification is described, which results in99% pure homogeneous protein (as determined by PAGE). The integrityof the protein has been compared with previously characterizedprotein from .E.coli AB2829(pKD501) by determination of itskinetic parameters, N-terminal protein and DNA sequences, aminoacid analysis and ¹³C-NMR spectroscopy. This new overproducingstrain readily provides the gram quantities of highly pure proteinrequired for NMR studies of the active site and the developmentof novel time-resolved solid-state NMR techniques currentlyunderway in this laboratory.     

Aluminum Phosphates Derived from Alumina and Alumina-Sol–Gel Systems

Aluminum phosphate products formed by the reactions of alumina and alumina-gel systems with acidic phosphates were analyzed. Drying of alumina-gel to form microcrystalline boehmite and conversion to γ-alumina by thermal treatment was indicated by the appearance of octahedral, pentacoordinate, or tetrahedral sites, which were established using ²⁷Al magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Crystalline aluminum phosphate products and amorphous material were identified using this technique. α-alumina and heat-treated alumina-gel that were reacted with phosphate in an Al:P ratio of 1:1 yielded dramatically different aluminum orthophosphate:aluminum metaphosphate product ratios of 8.2:1 and 1:1.1, respectively. When alumina-gel was heat-treated with phosphate, an abundance of aluminum orthophosphate, aluminum metaphosphate, and hydrated aluminum phosphate products were affected by varying conditions of temperature and time of heat treatment and by the amount of phosphate present. An α-alumina/alumina-gel composite sol–gel phase that was reacted with phosphoric acid (H₃PO₄) in a Al:P ratio of 1:1 exhibited an increased quantity of aluminum metaphosphate products compared with an α-alumina:H₃PO₄ ratio of 1:1 and a higher percentage of reaction (79%) compared with the reactions of an α-alumina:H₃PO₄ ratio of 1:1 or an alumina-gel:H₃PO₄ ratio of 1:1. The morphologies of aluminum triphosphate hydrate and aluminum metaphosphate product phases were observed using scanning electron microscopy.     

Identification of Two Sex Pheromone Components of the Potato Aphid, Macrosiphum euphorbiae (Thomas)

Females of the potato aphid Macrosiphum euphorbiae exhibit typical calling behavior, with virgin female oviparae raising their back legs off the substrate to release sex pheromone from glands on the tibia. Airborne collections from calling oviparae were analyzed by GC and GC-MS to determine if, like the majority of aphids examined to date, they produced (1R,4aS,7S,7aR)-nepetalactol (1) and (4aS,7S,7aR)-nepetalactone (2). Both components were present and produced in ratios that varied with age from 4:1 to 2:1. The relative stereochemical configurations of these components were determined by GC-coinjection of the aphid-derived sample with synthetic standards on both HP-1 and DB-Wax GC columns. The absolute stereochemical configuration of the nepetalactol (determined from approximately 15 microg of material in an air entrainment sample) was determined as (1R,4aS,7S,7aR)-1 by derivatization of the aphid sample with (S)-(+)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride (Mosher's acid chloride) to generate a diastereoisomer that was compared to synthetic samples by NMR spectroscopy and GC. In bioassays in the wind tunnel, M. euphorbiae males responded to potato plants with oviparae but not to unattacked plants or those infested with parthenogenetically reproducing apterae. In no-choice laboratory bioassays, the same level of male response was observed to virgins and to the 3:1-5:1 synthetic blends of nepetalactol (1):nepetalactone (2). However, the time taken to reach the source was significantly less to virgin females than to the synthetic pheromone blends. In all cases, males walked rather than flew to the source. Males showed lower responses to a 1:1 synthetic mixture and did not respond to either of the components when presented alone. Under field conditions, few M. euphorbiae males were captured in traps baited with different ratios of the synthetic pheromone. Possible reasons for the different responses under laboratory and field conditions are discussed.     

Characterization of zirconia specimens fabricated by ceramic on-demand extrusion

The Ceramic On-Demand Extrusion (CODE) process is a novel additive manufacturing method for fabricating dense (~99% of theoretical density) ceramic components from aqueous, high solids loading pastes (>50?vol%). In this study, 3?mol% Y₂O₃ stabilized zirconia (3YSZ) specimens were fabricated using the CODE process. The specimens were then dried in a humidity-controlled environmental chamber and afterwards sintered under atmospheric conditions. Mechanical properties of the sintered specimens were examined using ASTM standard test techniques, including density, Young’s modulus, flexural strength, Weibull modulus, fracture toughness, and Vickers hardness. The microstructure was analyzed and grain size measured using scanning electron microscopy. The results were compared with those from Direct Inkjet Printing, Selective Laser Sintering, Lithography-based Ceramic Manufacturing (LCM), and other extrusion-based processes, and indicated that zirconia specimens produced by CODE exhibit superior mechanical properties among the additive manufacturing processes. Several sample components were produced to demonstrate CODE’s capability for fabricating geometrically complex ceramic components. The surface roughness of these components was also examined.     

Conductivity Measurement Using Four Linear Electrodes Embedded Inside a Rectangular Sample

Using solid materials prepared by melting or sintering allows inert metal electrodes to be embedded inside the solid. The I–V relations for four linear electrodes embedded inside a rectangular sample are evaluated. Two cases are considered: (a) a sample with uniform electronic (electron/hole) conductivity and (b) the electron/hole partial current in a sample that is a mixed ionic-electronic conductor with a nonuniform electron/hole distribution. Equations are derived which allow the determination of the conductivity from four-electrode measurements if a pure electronic conductor is considered or if a mixed ionic-electronic conductor is considered with the ionic current being blocked.     

In Vivo Delivery and Activation of Masked Fluorogenic Hydrolase Substrates by Endogenous Hydrolases in C. elegans

Protein expression and localization are often studied in vivo by tagging molecules with green fluorescent protein (GFP), yet subtle changes in protein levels are not easily detected. To develop a sensitive in vivo method to amplify fluorescence signals and allow cell‐specific quantification of protein abundance changes, we sought to apply an enzyme‐activated cellular fluorescence system in vivo by delivering ester‐masked fluorophores to Caenorhabditis elegans neurons expressing porcine liver esterase (PLE). To aid uptake into sensory neuron membranes, we synthesized two novel fluorogenic hydrolase substrates with long hydrocarbon tails. Recombinant PLE activated these fluorophores in vitro. In vivo activation occurred in sensory neurons, along with potent activation in intestinal lysosomes quantifiable by imaging and microplate and partially attributable to gut esterase 1 (GES‐1) activity. These data demonstrate the promise of biorthogonal hydrolases and their fluorogenic substrates as in vivo neuronal imaging tools and for characterizing endogenous C. elegans hydrolase substrate specificities.     

Decoupled Roles for the Atypical,Bifurcated Binding Pocket of the ybfF Hydrolase

Serine hydrolases have diverse intracellular substrates, biological functions, and structural plasticity, and are thus important for biocatalyst design. Amongst serine hydrolases, the recently described ybfF enzyme family are promising novel biocatalysts with an unusual bifurcated substrate‐binding cleft and the ability to recognize commercially relevant substrates. We characterized in detail the substrate selectivity of a novel ybfF enzyme from Vibrio cholerae (Vc‐ybfF) by using a 21‐member library of fluorogenic ester substrates. We assigned the roles of the two substrate‐binding clefts in controlling the substrate selectivity and folded stability of Vc‐ybfF by comprehensive substitution analysis. The overall substrate preference of Vc‐ybfF was for short polar chains, but it retained significant activity with a range of cyclic and extended esters. This broad substrate specificity combined with the substitutional analysis demonstrates that the larger binding cleft controls the substrate specificity of Vc‐ybfF. Key selectivity residues (Tyr116, Arg120, Tyr209) are also located at the larger binding pocket and control the substrate specificity profile. In the structure of ybfF the narrower binding cleft contains water molecules prepositioned for hydrolysis, but based on substitution this cleft showed only minimal contribution to catalysis. Instead, the residues surrounding the narrow binding cleft and at the entrance to the binding pocket contributed significantly to the folded stability of Vc‐ybfF. The relative contributions of each cleft of the binding pocket to the catalytic activity and folded stability of Vc‐ybfF provide a valuable map for designing future biocatalysts based on the ybfF scaffold.