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High-Pressure Synthesis of Bulk Cobalt Cementite, Co 3 C
Transition metal carbides find use in a wide range of advanced high-resilience applications including high-strength steels, heat shields, and deep-earth drills. However, carbides of the mid-to-late transition metals remain difficult to isolate and characterize on account of their metastability, which precludes the preparation of high-quality bulk single crystal samples using traditional solid-state methods. Herein, we report a combined computational and experimental survey of the cobalt-carbon binary system under high pressures and demonstrate that pressure offers a route toward the bulk synthesis of the metastable cementite-type cobalt carbide, Co 3 C, which under ambient conditions can only be prepared in low-dimensional thin film or nanoparticle forms. First-principles calculations reveal two competitive low-energy stoichiometric phases under ambient pressures - Pnnm-Co 2 C (Fe 2 C-type) and Pnma-Co 3 C (Fe 3 Ctype) - consistent with the known low-dimensional phases that have been studied for their promising magnetic properties. However, the calculated formation enthalpy of Pnma-Co 3 C decreases steadily with the applied pressure, while that of Pnnm-Co 2 C increases. Here, we pursue these results using high-pressure laser-heated synthesis methods coupled with in situ X-ray diffraction and observe the formation of Pnma-Co 3 C above 4.8 GPa. We determine the experimental bulk modulus of Co 3 C to be K o = 237 GPa (K p = 4.0). First-principles calculations of the phonon modes in Co 3 C reveal dynamical instabilities at ambient pressure that are absent under compression. These results offer a promising new route for the synthesis of rare-earth-free magnets.
Pathways of CdS Quantum Dot Degradation during Photocatalysis: Implications for Enhancing Stability and Efficiency for Organic Synthesis
CdS quantum dots (QDs) are widely employed as photocatalysts for reactions such as hydrogen evolution, and their degradation under aerobic aqueous conditions is well understood. However, despite evidence of aggregation and precipitation of CdS QD photocatalysts under anaerobic conditions, catalyst speciation and degradation under such conditions are underexplored. In this work, we demonstrate that during a reductive dehalogenation reaction, CdS QDs undergo surface ligand etching, which leads to a loss of colloidal stability and the formation of microcrystalline cadmium metal deposits. We hypothesize that this results from the accumulation of electrons on the QD surface. In addition, we demonstrate mild surface sulfur oxidation and the formation of an ammonium salt byproduct of a commonly used hole quencher. Furthermore, this work adds to our atomic-level understanding of the reactions occurring at the QD surface during photocatalysis, so that we can design more stable and efficient photocatalysts for organic synthesis.
Investigating and Optimizing the Lysate-Based Expression of Nonribosomal Peptide Synthetases Using a Reporter System
Lysate-based cell-free expression (CFE) systems are accessible platforms for expressing proteins that are difficult to synthesize in vivo, such as nonribosomal peptide synthetases (NRPSs). NRPSs are large (>100 kDa), modular enzyme complexes that synthesize bioactive peptide natural products. This synthetic process is analogous to transcription/translation (TX/TL) in lysates, resulting in potential resource competition between NRPS expression and NRPS activity in cell-free environments. Moreover, CFE conditions depend on the size and structure of the protein. Here, a reporter system for rapidly investigating and optimizing reaction environments for NRPS CFE is described. This strategy is demonstrated in E. coli lysate reactions using blue pigment synthetase A (BpsA), a model NRPS, carrying a C-terminal tetracysteine (TC) tag which forms a fluorescent complex with the biarsenical dye, FlAsH. A colorimetric assay was adapted for lysate reactions to detect the blue pigment product, indigoidine, of cell-free expressed BpsA-TC, confirming that the tagged enzyme is catalytically active. An optimized protocol for end point TC/FlAsH complex measurements in reactions enables quick comparisons of full-length BpsA-TC expressed under different reaction conditions, defining unique requirements for NRPS expression that are related to the protein’s catalytic activity and size. Importantly, these protein-dependent CFE conditions enable higher indigoidine titer and improve the expression of other monomodular NRPSs. Notably, these conditions differ from those used for the expression of superfolder GFP (sfGFP), a common reporter for optimizing lysate-based CFE systems, indicating the necessity for tailored reporters to optimize expression for specific enzyme classes. In conclusion, the reporter system is anticipated to advance lysate-based CFE systems for complex enzyme synthesis, enabling natural product discovery.
Yi Liu answers questions about 15 years of research on covalent organic frameworks
The article is an interview with Dr. Yi Liu. Dr. Liu is the facility director at the Molecular Foundry, Lawrence Berkeley National Laboratory. Trained as a supramolecular chemist and after a postdoctoral stay and working on click chemistry in Sharpless’s group he started his independent research career working on organic electronics, porous materials, and covalent organic frameworks (COFs). His aim is to develop nanostructured electronic materials through the design, synthesis and manipulation of tailor-made molecular constituents. He answers questions about research on covalent organic frameworks.
Mechanical performance of co-deposited immiscible Cu–Ta thin films
Abstract The immiscible alloy Cu–Ta has the potential for enhanced mechanical performance in applications as a functional coating. To establish baseline mechanical properties, four Cu–Ta films were co-sputtered at the temperatures 23, 400, 600, and 800 °C and tested with nanoindentation at strain rates 5 $$\times $$ × 10 −3 s −1 to 10 s −1 . Each film had a unique microstructure morphology. The hardness and elastic modulus of the four films were insensitive to strain rate changes. Instead, the measured properties were spatially dependent, particularly in the 600 and 800 °C films. In those two films, there is a bimodal deformation behavior due to Cu-agglomeration under protruding grains and planar Ta-rich regions. Increasing the indentation depth revealed shear band suppression which is related to a homogenous distribution of flow stresses for all four microstructure morphologies. Finally, the Cu–Ta hardness appeared to follow a rule-of-mixtures when compared to extrapolated data of Cu and Ta monolithic films.
Data-driven analysis of text-mined seed-mediated syntheses of gold nanoparticles
Gold nanoparticle synthesis recipes were extracted from the literature to obtain data-driven hypotheses for synthesis outcome morphology and size. Used images from https://Flaticon.com.
Multiscale characterization, modeling and simulation of packed bed reactor for direct conversion of syngas to dimethyl ether
A multiscale computational approach to examine direct DME synthesis in a packed bed reactor composed of Cu/ZnO/Al 2 O 3 and γ-Al 2 O 3 catalysts.
Additive manufacturing of high explosives with inert dilution for wave shaping and detonation velocity grading
The performance of a high explosive charge is highly influenced by the detonation velocity and any inherent internal structure. Additively manufactured (AM) high explosive charges allow for a precisely engineered internal structure and the selective placement of discrete or graded volumes of a tailored material, which are unachievable by conventional means. The dilution of a solid explosive by an inert additive for detonation velocity reduction is herein evaluated for a method of material extrusion called a direct-ink-write AM, where an 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane-based ultraviolet -curable energetic-binder paste explosive was diluted by the inert density mock 5-iodo-2′-deoxyuridine for use in the manufacture of multi-material explosive charges. The explosive ink was characterized for printing by rheological and particle size measurements, and the detonation velocities for 0–40 wt. % inert diluent were found to have a continuous linear reduction in detonation velocity down to 14.3% difference. A two-component 3D plane wave explosive lens with 8.038 km/s “fast” and 7.491 km/s “slow” diluted ink in an internal cone demonstrated a reduced time of breakout at the output face from 361 to 53 ns. A linearly graded “fast–slow–fast” cylinder was successfully printed and fired, showing engineered control along the length of the charge as the detonation velocity dropped from 7.851 to 6.700 km/s and then recovered to 7.241 km/s. The extreme control over the internal composition of a high explosive charge via a dual-material extruder/mixer challenges conventional manufacturing approaches and opens new avenues for engineered detonation wavefronts, high explosive charge performance, and new applications.
Structural elucidation of the cis -prenyltransferase NgBR/DHDDS complex reveals insights in regulation of protein glycosylation
Cis-prenyltransferase (cis-PTase) catalyzes the rate-limiting step in the synthesis of glycosyl carrier lipids required for protein glycosylation in the lumen of endoplasmic reticulum. Here, we report the crystal structure of the human NgBR/DHDDS complex, which represents an atomic resolution structure for any heterodimeric cis-PTase. The crystal structure sheds light on how NgBR stabilizes DHDDS through dimerization, participates in the enzyme’s active site through its C-terminal -RXG- motif, and how phospholipids markedly stimulate cis-PTase activity. Comparison of NgBR/DHDDS with homodimeric cis-PTase structures leads to a model where the elongating isoprene chain extends beyond the enzyme’s active site tunnel, and an insert within the α3 helix helps to stabilize this energetically unfavorable state to enable long-chain synthesis to occur. These data provide unique insights into how heterodimeric cis-PTases have evolved from their ancestral, homodimeric forms to fulfill their function in long-chain polyprenol synthesis.
Asymmetric photoenzymatic incorporation of fluorinated motifs into olefins
Enzymes capable of assimilating fluorinated feedstocks are scarce. This situation poses a challenge for the biosynthesis of fluorinated compounds used in pharmaceuticals, agrochemicals, and materials. We developed a photoenzymatic hydrofluoroalkylation that integrates fluorinated motifs into olefins. The photoinduced promiscuity of flavin-dependent ene-reductases enables the generation of carbon-centered radicals from iodinated fluoroalkanes, which are directed by the photoenzyme to engage enantioselectively with olefins. This approach facilitates stereocontrol through interaction between a singular fluorinated unit and the enzyme, securing high enantioselectivity at β, γ, or δ positions of fluorinated groups through enzymatic hydrogen atom transfer—a process that is notably challenging with conventional chemocatalysis. Furthermore, this work advances enzymatic strategies for integrating fluorinated chemical feedstocks and opens avenues for asymmetric synthesis of fluorinated compounds.
Investigations of Dimensionally-Constrained Fermions
This project dealt with the investigation of bulk condensed matter materials that contain low-dimensional substructures. The main focus was materials with one-dimensional conducting or magnetic chains. This report describes the activities undertaken during the course of this project.
Development of Bismuth and Platinum Bi-Metallic Nanoparticles to Enhance Melt Wire Temperature Resolution
Advanced manufacturing (AM) based on direct-write (DW) technologies has emerged as the predominant enabler for the fabrication of active and passive sensors to be deployed in harsh operating environments seen in a nuclear reactor. Recently, Idaho National Laboratory and Boise State University have recently established capabilities to incorporate advanced manufacturing (AM) methods to accelerate, modernize and enhance functionality of nuclear sensors and instrumentation to achieve the goal of enhancing the safety and efficiency of nuclear reactors. A significant thrust of this work includes the development of nuclear relevant feedstock materials compatible with a variety of direct-write processes for the development, fabrication and testing of AM sensors for peak temperature detection and neutron flux monitoring. For this report, bismuth and bismuth/platinum (BiPt) bi-metallic nanoparticles were synthesized using wet chemical approaches to develop bi-metallic feedstock materials to enhance the sensitivity of melt wires for peak temperature detection. Nanoparticle characterization was performed with Transmission Electron Microscopy (TEM) for nanoparticle composition and size, Transmission X-Ray Diffraction Fluorescence (TXRF) for nanoparticle composition, and Differential Scanning Calorimetry to elucidate the melting point of BiPt bi-metallic nanoparticles. Preliminary results indicate bi-metallic BiPt nanoparticles as a viable pathway for fabricating high resolution AM melt wires.
Combinatorial and High-Throughput Materials Synthesis to Advanced Nuclear Materials Discovery
Poster for end of LDRD project
Assessing the Effectiveness of Large-Scale Environmental Restoration: Challenges and Opportunities
A recent National Academies consensus report addresses monitoring and assessment of cumulative effects of large-scale and multiple restoration projects within the context of long-term environmental change. Fines and penalties from the Deepwater Horizon oil spill in the Gulf of Mexico (GoM) have supported hundreds of restoration projects at spatial scales not often possible in the past. Here, in this paper, the report committee members and staff provide personal reflections from our time working on the study. We found that gaps in data collection, issues with data accessibility, and a lack of synthesis and analysis are hindering the ability to answer a basic question: What are the impacts of these many restoration efforts on improving ecosystem health and productivity in the GoM at the regional and Gulf wide scale? Restoration efforts are occurring in environments where many trends are changing and exhibiting higher variability than in the past, suggesting that previously successful restoration practices may no longer be adequate to compensate for the effects of environmental changes and variability. Our proposed approach to these challenges includes employing emerging monitoring technologies; using conceptual models; devising an adaptive management framework; rethinking restoration outcome goals; assessing cumulative effects; and undertaking rigorous synthesis and analysis of existing information on long-term environmental trends and restoration efforts. Restoration scientists and practitioners working in the GoM have an unprecedented opportunity to demonstrate large-scale environmental recovery if advances in monitoring, synthesis, assessment, and action are taken quickly. We are cautiously optimistic that, with mid-course adjustments, continued progress toward large-scale environmental recovery is possible.
A Tethered Formation Flying Concept for the SPECS Mission
The Sub-millimeter Probe of the Evolution of Cosmic Structure (SPECS) is a bold new mission concept designed to address fundamental questions about the Universe, including how the first stars formed from primordial material, and the first galaxies from pre-galactic structures, how the galaxies evolve over time, and what the cosmic history of energy release, heavy element synthesis, and dust formation is. Half of the luminosity and 98% of the post Big-Bang photons exit in the sub-millimeter range. The spectrum of our own Milky Way Galaxy shows this, and many galaxies have even more pronounced long-wavelength emissions. There can be no doubt that revolutionary science will be enabled when we have tools to study the sub-millimeter sky with Hubble- Space-Telescope-class resolution and sensitivity. Ideally, a very large telescope with an effective aperture approaching one kilometer in diameter would be needed to obtain such high quality angular resolution at these long wavelengths. However, a single aperture one kilometer in diameter would not only be very difficult to build and maintain at the cryogenic temperatures required for good seeing, but could actually turn out to be serious overkill. Because cosmic sub-millimeter photons are plentiful and the new detectors will be sensitive, the observations needed to address the questions posed above can be made with an interferometer using well established aperture synthesis techniques. Possibly as few as three 3-4 meter diameter mirrors flying in precision formation could be used to collect the light. To mitigate the need for a great deal of propellant, tethers may be needed as well. A spin-stabilized, tethered formation is a possible configuration requiring a more advanced form of formation flying controller, where dynamics are coupled due to the existence of the tethers between nodes in the formation network. The paper presents one such concept, a proposed configuration for a mission concept which combines the best features of structure, tethers and formation flying to meet the ambitious requirements necessary to make a future SPECS mission a success.
Multicomponent Nanoparticle Synthesis for Advanced Manufactured Melt Wire Development
Additive manufacturing (AM) based direct-write technologies have emerged as a predominant enabler for the fabrication of advanced passive sensors in-pile applications. This work continues previous efforts with the modification and optimization of synthesis methods for multi-component nanoparticle systems used to support the development, fabrication and testing of AM sensors for peak temperature detection. For this report, bismuth, bismuth/platinum, tin, tin/silver, tin/zinc, indium, and indium/silver bi-metallic nanoparticles were synthesized using the wet chemical methods. The nanoparticles were then characterized with x-ray fluorescence to evaluate the elemental composition and differential scanning to determine the melting point and mass loss of the samples. Results continue to show that bi-metallic nanoparticles are a viable pathway for the fabrication of high-resolution AM melt wires.