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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Dual domain recognition determines SARS-CoV-2 PLpro selectivity for human ISG15 and K48-linked di-ubiquitin

The Papain-like protease (PLpro) is a domain of a multi-functional, non-structural protein 3 of coronaviruses. PLpro cleaves viral polyproteins and posttranslational conjugates with poly-ubiquitin and protective ISG15, composed of two ubiquitin-like (UBL) domains. Across coronaviruses, PLpro showed divergent selectivity for recognition and cleavage of posttranslational conjugates despite sequence conservation. We show that SARS-CoV-2 PLpro binds human ISG15 and K48-linked di-ubiquitin (K48-Ub 2 ) with nanomolar affinity and detect alternate weaker-binding modes. Crystal structures of untethered PLpro complexes with ISG15 and K48-Ub 2 combined with solution NMR and cross-linking mass spectrometry revealed how the two domains of ISG15 or K48-Ub 2 are differently utilized in interactions with PLpro. Analysis of protein interface energetics predicted differential binding stabilities of the two UBL/Ub domains that were validated experimentally. We emphasize how substrate recognition can be tuned to cleave specifically ISG15 or K48-Ub 2 modifications while retaining capacity to cleave mono-Ub conjugates. These results highlight alternative druggable surfaces that would inhibit PLpro function.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Cryo-EM captures the coordination of asymmetric electron transfer through a di-copper site in DPOR

Enzymes that catalyze long-range electron transfer (ET) reactions often function as higher order complexes that possess two structurally symmetrical halves. The functional advantages for such an architecture remain a mystery. Using cryoelectron microscopy we capture snapshots of the nitrogenase-like dark-operative protochlorophyllide oxidoreductase (DPOR) during substrate binding and turnover. DPOR catalyzes reduction of the C17 = C18 double bond in protochlorophyllide during the dark chlorophyll biosynthetic pathway. DPOR is composed of electron donor (L-protein) and acceptor (NB-protein) component proteins that transiently form a complex in the presence of ATP to facilitate ET. NB-protein is an α 2 β 2 heterotetramer with two structurally identical halves. However, our structures reveal that NB-protein becomes functionally asymmetric upon substrate binding. Asymmetry results in allosteric inhibition of L-protein engagement and ET in one half. Residues that form a conduit for ET are aligned in one half while misaligned in the other. An ATP hydrolysis-coupled conformational switch is triggered once ET is accomplished in one half. These structural changes are then relayed to the other half through a di-nuclear copper center at the tetrameric interface of the NB-protein and leads to activation of ET and substrate reduction. These findings provide a mechanistic blueprint for regulation of long-range electron transfer reactions.

Computational biophysics↗
DOE OSTI2022

The impact of the electric field of metal ions on the vibrations and internal hydrogen bond strength in alkali metal ion di- and triglycine complexes

Using infrared predissociation spectroscopy of cryogenic ions, we revisit the vibrational spectra of alkali metal ion (Li+, Na+, K+) di- and triglycine complexes. We assign their most stable conformation, which involves metal ion coordination to all C=O groups and an internal NH⋯NH2 hydrogen bond in the peptide backbone. An analysis of the spectral shifts of the OH and C=O stretching vibrations across the different metal ions and peptide chain lengths shows that these are largely caused by the electric field of the metal ion, which varies in strength as a function of the square of the distance. The metal ion–peptide interaction also remotely modulates the strength of internal hydrogen bonding in the peptide backbone via the weakening of the amide C=O bond, resulting in a decrease in internal hydrogen bond strength from Li+ > Na+ > K+.

Chemistry↗
DOE OSTI2026

A simplified di-homodyne transient grating spectroscopy system utilizing polarization

Here, a modification to the di-homodyne transient grating spectroscopy optical arrangement is presented that removes the need to individually align two spatially separated probe laser beams. This work details the novel application of a single probe beam that utilizes birefringent materials to produce two optically homodyned signals with a relative phase shift of π radians. This arrangement effectively simplifies the alignment to one probe beam and removes the relative phase shift ambiguity between each homodyned signal. Several example measurements for tungsten, titanium, molybdenum, and silicon are shown to illustrate the utility of the new optical system.

Simmonds, M. J. [Univ. of California, San Diego, C↗
DOE OSTI2020

Synthesis, characterization, and computational modeling of 6,6'-(((2-hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) modified group 4 metal alkoxides

The coordination behavior of the tridentate alkoxy ligand 6,6'-(((2-hydroxyethyl)azanediyl)bis(methylene)) bis(2,4-di-tert-butylphenol) (termed H 3 -AM-DBP 2 ) with group 4 metal alkoxides ([M(OR) 4 ]) in a 1:1 ratio was previously found to generate [(ONep)Ti(κ 4 (O,O’,O”,N)-AM-DBP2)] and [(OR)Zr(κ 4 (μ-O,O’,O”,N)-AM-DBP 2 )] 2 (M = Zr, Hf). Additional studies revealed that increasing the stoichiometric ratio to 1:2 H3-AM-DBP 2 :[M(OR) 4 ] led to the isolation of [(ONep)Ti(κ 4 (μ-O,O’,O”,N)-AM-DBP2)(μ-ONep)Ti(ONep) 3 ] (1)•tol, [(OBu t)Zr(κ 4 (μ-O,O’,O”,N)-AM-DBP2)(μ-OBu t)Zr(OBu t )3] (2) and [(OBu t)Hf(κ 4 (μ-O,O’,O”,N)-AM-DBP2)(μ-OBu t )Hf(OBu t ) 3 ] (3). The asymmetric dinuclear complexes of 1-3 resemble the chelation of a [M(OR) 4 ] moiety to a “(OR)M(κ 4 (O,O’,O”,N)-AM-DBP 2 )” fragment. The metal complexed by the AM-DBP 2 ligand has a pseudo octahedral geometry while the other metal adopts an intermediate trigonal bipyramidal (TBP-5)/square base pyramidal (SBP-5) geometry for 1 but a distorted SBP-5 for both 2 and 3. The structure and properties of 1-3 were analyzed by computational modeling and fully characterized by standard analytical methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Extraction of Neptunium, Plutonium, Americium, Zirconium, and Technetium by Di-(2-Ethylhexyl)- Iso -Butyramide (DEH i BA) at High Metal Loadings

Increased focus on carbon neutral energy has generated a resurgence of interest in nuclear power, and in particular advanced reactors which are likely to utilize high assay low enriched uranium (HALEU). This in turn could increase the economic attractiveness of recovering still partially enriched uranium from used nuclear fuel. Concomitant to development of advanced reactors, advanced reprocessing schemes should be developed which address the disadvantages to well established reprocessing schemes. The present study focuses on using di-(2-ethylhexyl)-iso-butyramide (DEHiBA) under high metal loading conditions for the reprocessing of used nuclear fuel. The elements examined in the study include the dominant transuranic actinides (Np, Pu, Am) as well as the often-problematic Tc and Zr. Further, by increasing the concentration of the extractant from the more commonly reported 1.0 M – 1.5 M, the extraction of hexavalent actinides is substantially increased, while maintaining effective rejection of tri, tetra, and pentavalent actinides, particularly in the presence of high loadings of uranium. In conclusion, the extraction of Zr by 1.5 M DEHiBA is noted to be negligible by comparison to tributyl phosphate (TBP), however the coextraction of Tc with U is observed to be nominally twice the quantity that is extracted by TBP indicating a need for effective Tc management.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Constraining the Higgs potential with neural simulation-based inference for di-Higgs production

Determining the form of the Higgs potential is one of the most exciting challenges of modern particle physics. Higgs pair production directly probes the Higgs self-coupling and should be observed in the near future at the High-Luminosity LHC. We explore how to improve the sensitivity to physics beyond the Standard Model through per-event kinematics for di-Higgs events. In particular, we employ machine learning through simulation-based inference to estimate per-event likelihood ratios and gauge potential sensitivity gains from including this kinematic information. In terms of the Standard Model Effective Field Theory, we find that adding a limited number of observables can help to remove degeneracies in Wilson coefficient likelihoods and significantly improve the experimental sensitivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Di-$\pi^0$ correlations in p+p, p+Al and p+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at STAR

The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di- \pi^0 π 0 produced at forward pseudorapidity ( 2.6<\eta<4.0 2.6 < η < 4.0 ) in p+ p + p p , p+ p + \mathrm{Al} A l and p+ p + \mathrm{Au} A u collisions at a center-of-mass energy per nucleon-nucleon pair of 200 GeV. A clear suppression of the correlated away-side yields is observed in p+ p + \mathrm{Au} A u and for the first time in p+ p + \mathrm{Al} A l collisions, compared with the p p + + p p data. The enhanced suppression found in p+ p + \mathrm{Au} A u with respect to p+ p + \mathrm{Al} A l collisions exhibits the saturation scale ( Q_s^2 Q s 2 ) dependence on the mass number A A . The observed suppression of back-to-back pairs as a function of event activity and transverse momentum points to non-linear gluon dynamics arising at high parton densities.

Chu, Xiaoxuan↗
DOE OSTI2025

Characterization of Performance Degradation Mechanisms in Low-Cost High Throughput DI-O3 Layer for Passivated Contact Silicon Solar Cells

Characterization and mitigating performance limiting defects in Silicon (Si) PV is one of key areas to be addressed to improve PV hardware costs and energy yield in order to lower the levelized cost of energy (LCOE) of installed PV cost to $0.02/kWh. As Si PV cells efficiencies have surpassed 22% and approaching 23%, the recombination at the metal contacts have become the focus point to be addressed. Passivated contact technologies—having a heterojunction with a band-gap larger than silicon between the metal and silicon—have emerged as a great potential for future highand ultrahigh-efficiency solar cells, as it concurrently reduces recombination and increases carrier selectivity, by incorporating thin films within the contact structure. Passivated contact Si solar cell technologies use a wide variety of tunnel layers—playing a crucial role to passivate metal contacts and tunnel charge carriers—including stoichiometric silicon oxide (SiO 2 ) grown by thermal oxidation and Low-Pressure Chemical Vapor Deposition (LPCVD) technique and silicon oxide (SiO x ) by hot nitric acid. However, thorough investigations on understanding the failure and performance degradation mechanisms associated with tunnel layers are still limited to date. Unlocking those degradation characteristics in crucial tunnel layers could improve the reliability and energy yield of passivated contact Si solar cells. Besides, the technique of growing aforementioned tunneling layers are low throughput, and requires high temperature processes and/or a vacuum environment. In this project, we investigated the performance degradation mechanisms of a low-cost high-throughput ozonated oxide (DI-O 3 ) tunnel layer for the passivated contact Si solar cells.

14 SOLAR ENERGY↗
DOE OSTI2022

In Situ Microstructure Characterization of Potassium Di-Phosphate (KDP) Densification during Cold Sintering

In order for ceramic additive manufacturing (AM) to achieve its full potential, it is increasingly important to develop a more rigorous understanding of fundamental phenomena that govern the kinetics and thermodynamics of ceramic AM processes. In the case of additive build processes, such as direct ink write and ceramic extrusion, methods for densifying the resulting green-body product need to be considered to complement the efficiencies of ceramics AM, itself. One densification route, at least for monolithic components, built layer-by-layer, is offered by the recently developed cold sintering process, whereby high-density final product is achieved through addition of a small amount of liquid solvent and application of modest uniaxial compressive stress at relatively low temperature. In situ small-angle X-ray scattering methods and X-ray diffraction have been applied to characterize and quantify the pore morphology evolution during cold sintering for a model system: potassium di-phosphate, KH 2 PO 4 (KDP). It is shown that both temperature and applied stress affect the densification rate, but stress has a stronger effect on the evolving morphology. A regime with an approximate linear densification rate can be identified, yielding an effective densification activation energy of ≈90 kJ/mol.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Zeolite-Stabilized Di- and Tetranuclear Molybdenum Sulfide Clusters Form Stable Catalytic Hydrogenation Sites

Supercages of faujasite (FAU)-type zeolites serve as a robust scaffold for stabilizing dinuclear (Mo 2 S 4 ) and tetranuclear (Mo 4 S 4 ) molybdenum sulfide clusters. The FAU-encaged Mo 4 S 4 clusters have a distorted cubane structure similar to the FeMo-cofactor in nitrogenase. Both clusters possess one unpaired electron per Mo atom. Additionally, they show identical catalytic activity per sulfide cluster. Their catalytic activity is stable (> 150 h) for ethene hydrogenation, while layered MoS 2 structures deactivate significantly under the same reaction conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗