Helix sense of copoly(ethyl-l-aspartate-benzyl-l-aspartate)

Copoly(ethyl-L-aspartate-benzyl-L-aspartate)s with various compositions were prepared by ethylation of poly (β-benzyl-L-aspartate). Helix sense of copolyaspartates in chloroform solution was examined by optical rotatory dispersion and circular dichroism methods as a function of a degree of ethylation and temperature. Copolyaspartates of ethylation less than 35% exhibited the same left handed helix as that of poly (β-benzyl-L-aspartate), while copolymer of ethylation more than 70% assumed the right handed α-helical conformation like poly (β-ethyl-L-aspartate). Copolymers with the intermediate ethyl content of 35–70% indicated the reversal in helix sense from a right handed to a left handed helix with increasing temperature from ?20° to 60°C. The transition of reversal was reversibly observed and transition temperature rose with the increase of ethylation. In these intermediate copolymers, the mechanism of the reversal in helix sense was examined by circular dichroism and dielectric measurements. Three possibilities were postulated here for the conformation which should arise at the transition temperature of the reversal; First is the random conformation, second is the equimolar mixture of left and right handed α-helices in a chain, and the third is the equimolar mixture of left and right handed α helix chains. No observational circular dichroism spectra characteristic to random coil conformation and no remarkable change in residue dipole moment strongly suggested the third possibility.     

Corrosion of inconel 617 in HTGR grade helium

Corrosion of the primary circuit materials is one of the serious problems in High Temperature Gas-cooled Reactors (HTGR). In the present work, the effect of gaseous impurities in the helium coolant on the corrosion behavior of Inconel 617 has been studied at 1000 °C and atmospheric pressure for 1000 h. The helium gases used contained several impurities; H₂, H₂O, CH₄, CO, and CO₂. The corrosion behavior of alloying elements (Cr, Mo, Si, C) was strongly affected by the impurity concentration in helium and the extent of corrosion could be explained on the basis of the oxygen and carbon potentials in the gases used. Ryoji Watanabe, formerly Head of Nuclear Materials Division.     

Deterioration of electromotive force of chromel-alumel thermocouples in reducing atmospheres at high temperatures

The deterioration of electromotive force (emf) of Chromel-Alumel (CA) thermocouples in 80 pct H₂ + 15 pct CO + 5 pct CO₂ has been analyzed in terms of the corrosion behavior of Chromel. Emf of the CA thermocouple deteriorated drastically in 80 pct H₂ + 15 pct CO + 5 pct CO₂. After exposure for about 1000 hours at 900 °C, the decrease of emf was about 16 mV. The deterioration process could be separated into three terms. The first term, which has the smallest time constant of about 20 hours, was attributed to carbon deposition on the Chromel surface in the temperature range of 600 to 700 °C. The second term, which has a time constant of about 100 hours, was attributed to the severe internal oxidation of chromium in the temperature range of 500 to 800 °C. The third term, having the largest time constant of several thousand hours, might be attributed to the moderate and gradual preferential oxidation of chromium in Chromel in the range 800 to 900 °C. Boron nitride (BN) coating on CA thermocouples could reduce this deterioration of emf; the decrease of emf was improved to about 3 °C during 700 hours test at 900 °C.     

Basic study on heat rejection system using high heat flux micro channel evaporator

Thermal management system which can reject very high amount of heat by small thermal devices will be required for future space systems. Our purpose is to develop miniaturized heat rejection system that can reject more than 100 W/cm². In the evaporator, thin liquid film vaporization which can dissipate very high heat flux, was utilized. The liquid film is stabilized in micro-channels by capillary forces. The microchannels are fabricated by chemical etching on silicon and copper plate. Also miniaturized condenser which utilized droplet condensation was tested. Droplets were produced on a cooled plate covered by non-wetting coating. After we built a heat rejection system constructed by above mentioned evaporator and condenser, influence of heat flux, coolant flow rate, and inlet temperature on the temperature of the heater element were investigated. Water is used as working fluid. Heat flux of 100 W/cm² could be achieved for water inlet temperature in flow rate of 3.0 mL/min. The temperature of the heater element is kept constant at about 120°C.     

Ethical Conduct in Chemical Research and Publishing

In recent years the incidence of scientific misconduct has increased. While the direct responsibility lies with the individual researcher, the educational role of mentors and research institutions needs rethinking and renewal. Researchers, principal investigators, departments, institutions, funding agencies, chemical societies, publishers, scientific journal editors, referees and editorial board members all have responsibilities in order to maintain the integrity of chemistry within the scientific community and to restore the confidence of the general public in chemistry as a responsible contributor to the solutions of the global problems facing mankind in this century.     

Fabrication of porous low crystalline calcite block by carbonation of calcium hydroxide compact

Calcium carbonate (CaCO₃) has been widely used as a bone substitute material because of its excellent tissue response and good resorbability. In this experimental study, we propose a new method obtaining porous CaCO₃ monolith for an artificial bone substitute. In the method, calcium hydroxide compacts were exposed to carbon dioxide saturated with water vapor at room temperature. Carbonation completed within 3 days and calcite was the only product. The mechanical strength of CaCO₃ monolith increased with carbonation period and molding pressure. Development of mechanical strength proceeded through two steps; the first rapid increase by bonding with calcite layer formed at the surface of calcium hydroxide particles and the latter increase by the full conversion of calcium hydroxide to calcite. The latter process was thought to be controlled by the diffusion of CO₂ through micropores in the surface calcite layer. Porosity of calcite blocks thus prepared had 36.8–48.1% depending on molding pressure between 1 MPa and 5 MPa. We concluded that the present method may be useful for the preparation of bone substitutes or the preparation of source material for bone substitutes since this method succeeded in fabricating a low-crystalline, and thus a highly reactive, porous calcite block.     

Lidar characterization of crystalline silica generation and transport from a sand and gravel plant

Light detection and ranging (Lidar) remote sensing two-dimensional vertical and horizontal scans collected downwind of a sand and gravel plant were used to evaluate the generation and transport of geologic fugitive dust emitted by quarry operations. The lidar data give unsurpassed spatial resolution of the emitted dust, but lack quantitative particulate matter (PM) mass concentration data. Estimates of the airborne PM10 and crystalline silica concentrations were determined using linear relationships between point monitor PM10 and quartz content data with the lidar backscatter signal collected from the point monitor location. Lidar vertical profiles at different distances downwind from the plant were used to quantify the PM10 and quartz horizontal fluxes at 2-m vertical resolution as well as off-site emission factors. Emission factors on the order of 65-110 kg of PM10 (10-30 kg quartz) per daily truck activity or 2-4 kg/t product shipped (0.5-1 kg quartz/t) were quantified for this facility. The lidar results identify numerous elevated plumes at heights >30 m and maximum plume heights of 100 m that cannot be practically sampled by conventional point sampler arrays. The PM10 and quartz mass flux was greatest at 10-25 m height and decreased with distance from the main operation. Measures of facility activity were useful for explaining differences in mass flux and emission rates between days. The study results highlight the capabilities of lidar remote sensing for determining the spatial distribution of fugitive dust emitted by area sources with intermittent and spatially diverse dust generation rates.     

Asymmetric Hydrogenation of Ketones with Polymer‐Bound BINAP/Diamine Ruthenium Catalysts

The BINAP/1,2‐diphenylethylenediamine RuCl₂ complexes bound to a polystyrene resin act as precatalysts for asymmetric hydrogenation of various simple ketones. The enantioselectivity, turnover number, and turnover frequency are comparable to those attained under homogeneous conditions.     

Opportunities for Expanding Encoded Chemical Diversification and Improving Hit Enrichment in mRNA-Displayed Peptide Libraries

DNA-encoded small-molecule libraries and mRNA displayed peptide libraries both use numerically large pools of oligonucleotide-tagged molecules to identify potential hits for protein targets. They differ dramatically, however, in the ‘drug-likeness’ of the molecules that each can be used to discover. We give here an overview of the two techniques, comparing some advantages and disadvantages of each, and suggest areas where particularly mRNA display can benefit from adopting advances developed with DNA-encoded small molecule libraries. We outline cases where chemical modification of the peptide library has already been used in mRNA display, and survey opportunities to expand this using examples from DNA-encoded small molecule libraries. We also propose potential opportunities for encoding such reactions within the mRNA/cDNA tag of an mRNA-displayed peptide library to allow a more diversity-oriented approach to library modification. Finally, we outline alternate approaches for enriching target-binding hits from a pooled and tagged library, and close by detailing several examples of how an adjusted mRNA-display based approach could be used to discover new ‘drug-like’ modified small peptides.