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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Histidine-Mediated Ion Specific Effects Enable Salt Tolerance of a Pore-Forming Marine Antimicrobial Peptide

Antimicrobial peptides (AMPs) preferentially permeate prokaryotic membranes via electrostatic binding and membrane remodeling. Such action is drastically suppressed by high salt due to increased electrostatic screening, thus it is puzzling how marine AMPs can possibly work. We examine as a model system, piscidin-1, a histidine-rich marine AMP, and show that ion-histidine interactions play unanticipated roles in membrane remodeling at high salt: Histidines can simultaneously hydrogen-bond to a phosphate and coordinate with an alkali metal ion to neutralize phosphate charge, thereby facilitating multidentate bonds to lipid headgroups in order to generate saddle-splay curvature, a prerequisite to pore formation. A comparison among Na + , K + , and Cs + indicates that histidine-mediated salt tolerance is ion specific. Here we conclude that histidine plays a unique role in enabling protein/peptide-membrane interactions that occur in marine or other high-salt environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Role of Molecular Architecture on Ion Transport in Ethylene oxide-Based Polymer Electrolytes

This work aims to develop a detailed mechanistic understanding of the role of a graft polymer architecture on lithium ion (Li + ) transport in poly(ethylene oxide)-based polymer electrolytes. Specifically, we compare Li + transport in poly-(ethylene oxide) (PEO) versus poly(oligo oxyethylene methacrylate) (POEM) polymers doped with lithium bis( trifluoromethanesulfonyl) (LiTFSI) salts, using both experimental electrochemical characterization and molecular dynamics (MD) simulations. Furthermore, our results indicate that POEM exhibits a range of relaxation processes that cannot be interpreted solely in terms of glass-transition temperature (T g ) effects. Due to its side-chain architecture, the segmental relaxation of POEM is nonuniform across ether oxygens (EOs) and shows a more pronounced sensitivity to temperature above T g compared to PEO. Moreover, POEM also exhibits a nonuniform Li + coordination behavior, in which Li + is primarily solvated by two different chains in POEM, compared to a single chain in PEO. Li + transport in POEM occurs via two events with distinct characteristic times: a fast intrachain hopping along side chains and a slow interchain hopping between side chains. Taken together, the relaxation processes and ion transport mechanisms identified in POEM provide useful insights into design of more effective solid polymer electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Spectroscopic characterization of neptunium(VI), plutonium(VI), americium(VI) and neptunium(V) encapsulated in uranyl nitrate hexahydrate

The coordination of crystalline products resulting from the co-crystallization of Np(VI), Pu(VI), Am(VI), and Np(V) with uranyl nitrate hexahydrate (UNH) has been revealed through solid-state spectroscopic characterization via diffuse reflectance UV-Vis-NIR, SEM-EDS, and extended X-ray absorption fine structure (EXAFS). Density functional and multireference wavefunction calculations were performed to analyze the An(VI/V)O 2 (NO 3 ) 2 ·2H 2 O electronic structures and to help assign the observed transitions in the absorption spectra. EXAFS show a similar coordination between the U(VI) in UNH and Np(VI) and Pu(VI); while Am resulted in a similar coordination to Am(III), as reduction of Am(VI) occurred prior to EXAFS data being obtained. Here, the co-crystallization of the oxidized transuranic species—penta- and hexavalent—with UNH, represents a significant advance from not only a practical standpoint in providing an elegant solution for used nuclear fuel recycle, but also as an avenue to expand the fundamental understanding of the 5f electronic behavior in the solid-state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Chamber flux measurements at US-ORv located in Columbus, OH from 2010 to 2014

Closed and flow through chamber methane and carbon dioxide flux measurements were taken at different water depths, vegetation cover types, and times of day at the Wilma H. Schiermeier Olentangy River Wetland Research Park (ORWRP) from 2010 to 2014 to investigate the effects of these variables on gas exchange. The ORWRP consists of two urban experimental wetland basins constructed in 1994 within the footprint of the AmeriFlux tower US-ORv that was functional from 2011 to 2016. Chamber measurements are separated into flow through and closed chamber files (flow_through.csv, closed_chamber.csv) with location labels corresponding with coordinates listed in the metadata file (Location_ID.csv). All files are .csv and could be viewed or analyzed with Excel, MATLAB, Python, or R.

EARTH SCIENCE > ATMOSPHERE > ATMOSPHERIC CHEMISTRY↗
DOE OSTI2023

Porous Salts as Platforms for Heterogeneous Catalysis

In this study, the preparation of a new class of reactive porous solids, prepared via straightforward salt metathesis reactions, is described here. Reaction of the dimethylammonium salt of a magnesium-based porous coordination cage with the chloride salt of [Cr II Cl(Me 4 cyclam)] + affords a porous solid with concomitant removal of dimethylammonium chloride. The salt consists of the ions combined in the expected ratio based on their charge as confirmed by UV–vis and X-ray photoelectron spectroscopies, ion chromatography (IC), and inductively coupled plasma mass spectrometry (ICP-MS). The porous salt boasts a Brunauer-Emmett-Teller (BET) surface area of 213 m 2 g -1 . Single crystal X-ray diffraction reveals the chromium(II) cations in the structure reside in the interstitial space between porous cages. Importantly, the chromium(II) centers, previously shown to react with O 2 to afford reactive chromium(III)-superoxide adducts, are still accessible in the solid state as confirmed by UV–vis spectroscopy. The site-isolated reactive centers have competence toward hydrogen atom abstraction chemistry and display significantly increased stability and reactivity as compared to dissolved ions.

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

Hierarchically Porous Carbons with Highly Curved Surfaces for Hosting Single Metal FeN 4 Sites as Outstanding Oxygen Reduction Catalysts

Iron–nitrogen–carbon (Fe₋N₋C) materials have emerged as a promising alternative to platinum-group metals for catalyzing the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells. However, their low intrinsic activity and stability are major impediments. Herein, an Fe₋N–C electrocatalyst with dense FeN 4 sites on hierarchically porous carbons with highly curved surfaces (denoted as FeN 4 - hc C) is reported. The FeN 4 - hc C catalyst displays exceptional ORR activity in acidic media, with a high half-wave potential of 0.85 V (versus reversible hydrogen electrode) in 0.5 m H 2 SO 4 . When integrated into a membrane electrode assembly, the corresponding cathode displays a high maximum peak power density of 0.592 W cm -2 and demonstrates operating durability over 30 000 cycles under harsh H 2 /air conditions, outperforming previously reported Fe–N₋C electrocatalysts. These experimental and theoretical studies suggest that the curved carbon support fine-tunes the local coordination environment, lowers the energies of the Fe d-band centers, and inhibits the adsorption of oxygenated species, which can enhance the ORR activity and stability. This work provides new insight into the carbon nanostructure–activity correlation for ORR catalysis. It also offers a new approach to designing advanced single-metal-site catalysts for energy-conversion applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Z-Contrast Enhancement in Au–Pt Nanocatalysts by Correlative X-ray Absorption Spectroscopy and Electron Microscopy: Implications for Composition Determination

The properties of bimetallic nanoparticles (BNPs) vary widely as a function of their composition and size distributions. X-ray absorption fine structure analysis is commonly used to characterize their structure, but its application to elements that are close to each other in the periodic table is hampered by poor Z-contrast. For this study, we trained an artificial neural network to recognize the partial coordination numbers in AuPt NPs synthesized via peptide templating using their X-ray absorption near-edge structure spectra. This approach, combined with scanning transmission electron microscopy analysis, revealed unique details of this prototype catalytic system that has different forms of heterogeneities at both the intra- and inter-particle levels. Our method based on the enhancement of Z-contrast of metal species will have implications for compositional studies of BNPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Heterometallic Ce IV / V V Oxo Clusters with Adjustable Catalytic Reactivities

Heterometallic Ce IV /M oxo clusters are underexplored yet and can benefit from synergistic properties from combining cerium and other metal cations to produce efficient redox catalysts. Herein, we designed and synthesized a series of new Ce 12 V 6 oxo clusters with different capping ligands: Ce 12 V 6 -SO 4 , Ce 12 V 6 -OTs (OTs: toluenesulfonic acid), and Ce 12 V 6 -NBSA (NBSA: nitrobenzenesulfonic acid). Single crystal X-ray diffraction (SCXRD) for all three structures reveals a Ce 12 V 6 cubane core formulated [Ce 12 (VO) 6 O 24 ] 18+ with cerium on the edges of the cube, vanadyl capping the faces, and sulfate on the corners. While infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV–vis), electrospray ionization mass spectrometry (ESI-MS), and proton nuclear magnetic resonance ( 1 H NMR) proved the successful coordination of the organic ligands to the Ce 12 V 6 core, liquid phase 51 V NMR and small-angle X-ray scattering (SAXS) confirmed the integrity of the clusters in the organic solutions. Furthermore, functionalization of the Ce 12 V 6 core with organic ligands both provides increased solubility in term of homogeneous application and introduces porosity to the assemblies of Ce 12 V 6 -OTs and Ce 12 V 6 -NBSA in term of heterogeneous application, thus allowing more catalytic sites to be accessible and improving reactivity as compared to the nonporous and less soluble Ce 12 V 6 -SO 4 . Meanwhile, the coordinated ligands also influenced the electronic environment of the catalytic sites, in turn affecting the reactivity of the cluster, which we probed by the selective oxidation of 2-chloroethyl ethyl sulfide (CEES). Furthermore, this work provides a strategy to make full use of the catalytic sites within a class of inorganic sulfate capped clusters via organic ligand introduction.

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

Nonequilibrium design strategies for functional colloidal assemblies

Here, we use a nonequilibrium variational principle to optimize the steady-state, shear-induced interconversion of self-assembled nanoclusters of DNA-coated colloids. Employing this principle within a stochastic optimization algorithm allows us to identify design strategies for functional materials. We find that far-from-equilibrium shear flow can significantly enhance the flux between specific colloidal states by decoupling trade-offs between stability and reactivity required by systems in equilibrium. For isolated nanoclusters, we find nonequilibrium strategies for amplifying transition rates by coupling a given reaction coordinate to the background shear flow. We also find that shear flow can be made to selectively break detailed balance and maximize probability currents by coupling orientational degrees of freedom to conformational transitions. For a microphase consisting of many nanoclusters, we study the flux of colloids hopping between clusters. We find that a shear flow can amplify the flux without a proportional compromise on the microphase structure. This approach provides a general means of uncovering design principles for nanoscale, autonomous, functional materials driven far from equilibrium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Boat-Dragged Riverbed and Mid-Column Water Quality along the Hanford Reach in the Columbia River Shorelines

This dataset contains water quality measurements used to identify sites of hydrologic exchange (i.e.hydrologic exchange flows; HEFs) in the Columbia River near Richland, WA by looking for anomalies in temperature and electrical conductivity (EC) along the bed of the river in February, June, July, August, and November 2017. These are ultimately the ‘ends’ of HEFs as they are locations of subsurface inflow to the river. This dataset contains dissolved oxygen (DO) measurements at 1-min intervals; temperature, EC, depth, and GPS coordinates at 1-second intervals; and N-NO3 at 2-min intervals along the river bed and mid-column water. DO measurements are included in this dataset for completeness but were not used in the analysis of HEFs due to the relatively long time interval of collection.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R 3 Si + Species

The silylium-like surface species [ i Pr 3 Si][(R F O) 3 Al-OSi≡)] activates (N^N)Pd(CH 3 )Cl (N^N=Ar-N=CMeMeC=N-Ar, Ar=2,6-bis(diphenylmethyl)-4-methylbenzene) by chloride ion abstraction to form [(N^N)Pd-CH 3 ][(R F O) 3 Al-OSi≡)] ( 1 ). A combination of FTIR, solid-state NMR spectroscopy, and reactions with CO or vinyl chloride establish that 1 shows similar reactivity patterns as (N^N)Pd(CH 3 )Cl activated with Na[B(Ar F ) 4 ]. Multinuclear 13 C{ 27 Al} RESPDOR and 1 H{ 19 F} S-REDOR experiments are consistent with a weakly coordinated ion-pair between (N^N)Pd-CH 3 + and [(R F O) 3 Al-OSi≡)]. 1 catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd-CH 3 ] + in solution and incorporates up to 0.4% methyl acrylate in copolymerization reactions. 1 produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Ab Initio Molecular Dynamics Study of the Reduction of Acetone by the Hydrated Electron

We have investigated the reaction dynamics of the reduction of acetone by the solvated electron in water using ab initio molecular dynamics simulations at 298 and 373 K. The rate constants derived from the simulations are consistent with experimental observations that the reaction has a low activation energy. Detailed analyses carried out to shed light on the mechanism of the reaction show that solvent reorganization plays a key role as a reaction coordinate, as expected from the Marcus electron transfer theory. Furthermore, constrained density functional theory calculations indicate that the electronic coupling is large, placing the reaction in the adiabatic limit. Indeed, the activation energies and rate constants of the simulations are in accordance with the predictions of adiabatic Marcus theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Molecular Origins of Temperature-Dependent X-ray Absorption in YAG:Dy

The absorption and emission of X-rays in dysprosium-doped yttrium aluminum garnet (YAG:Dy) has produced unexpected thermographic behavior, which is investigated using a combination of finite temperature ab initio molecular dynamic simulations, structural characterization, and electronic structure calculations of X-ray characteristics. Calculated average peak X-ray absorption spectra (XAS) from simulations between 300 and 600 K result in peak intensity loss due to thermalization effects, matching experimentally measured behavior of YAG:Dy. Here, investigation of atomic snapshots indicates structural factors that correlated with the X-ray behavior, with the first Y–O coordination sphere identified as the primary structural feature unique to high XAS intensity as calculated by radial and pair distribution functions.

Ab initio molecular dynamics↗
DOE OSTI2022

Direct Observation of Ammonia Storage in UiO-66 Incorporating Cu(II) Binding Sites

The presence of active sites in metal–organic framework (MOF) materials can control and affect their performance significantly in adsorption and catalysis. However, revealing the interactions between the substrate and active sites in MOFs at atomic precision remains a challenging task. Here, we report the direct observation of binding of NH 3 in a series of UiO-66 materials containing atomically dispersed defects and open Cu(I) and Cu(II) sites. While all MOFs in this series exhibit similar surface areas (1111–1135 m 2 g –1 ), decoration of the -OH site in UiO-66-defect with Cu(II) results in a 43% enhancement of the isothermal uptake of NH 3 at 273 K and 1.0 bar from 11.8 in UiO-66-defect to 16.9 mmol g –1 in UiO-66-Cu II . A 100% enhancement of dynamic adsorption of NH 3 at a concentration level of 630 ppm from 2.07 mmol g –1 in UiO-66-defect to 4.15 mmol g –1 in UiO-66-Cu II at 298 K is observed. In situ neutron powder diffraction, inelastic neutron scattering, and electron paramagnetic resonance, solid-state nuclear magnetic resonance, and infrared spectroscopies, coupled with modeling reveal that the enhanced NH 3 uptake in UiO-66-Cu II originates from a {Cu(II)···NH 3 } interaction, with a reversible change in geometry at Cu(II) from near-linear to trigonal coordination. This work represents the first example of structural elucidation of NH 3 binding in MOFs containing open metal sites and will inform the design of new efficient MOF sorbents by targeted control of active sites for NH 3 capture and storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Towards complete assignment of the infrared spectrum of the protonated water cluster H + (H 2 O) 21

The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase water clusters H + (H 2 O) n extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H + (H 2 O) 21 cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Excited-state structure of copper phenanthroline-based photosensitizers

Cu diimine complexes present a noble metal free alternative to classical Ru, Re, Ir and Pt based photosensitizers in solution photochemistry, photoelectrochemical or dye-sensitized solar cells. Optimization of these dyes requires understanding of factors governing the key photochemical properties: excited state lifetime and emission quantum yield. The involvement of exciplex formation in the deactivation of the photoexcited state is a key question. Here, we investigate the excited-state structure of [Cu(dmp) 2 ] + and [Cu(dsbtmp) 2 ] + (dmp = 2,9-dimethyl-1,10-phenanthroline, dsbtmp = 2,9-di-sec-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) using pump–probe X-ray absorption spectroscopy (XAS) and DFT. Features of XAS that distinguish flattened tetrahedral site and 5-coordinated geometry with an additional solvent near Cu(II) center are identified. Pump–probe XAS demonstrates that for both complexes the excited state is 4-coordinated. For [Cu(dmp) 2 ] + the exciplex is 0.24 eV higher in energy than the flattened triplet state, therefore it can be involved in deactivation pathways as a non-observable state that forms slower than it decays. For [Cu(dsbtmp) 2 ] + the excited-state structure is characterized by Cu–N distances of 1.98 and 2.07 Å and minor distortions, leading to a 3 orders of magnitude longer excited-state lifetime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The Institute for Nuclear Science to Inspire the next Generation of a Highly Trained workforce (INSIGHT) at FRIB

The proposed INSIGHT Center at FRIB has two objectives: (1) provide a center to support and coordinate a nationwide traineeship effort; and (2) offer traineeships at FRIB by leveraging its scientific opportunities. This will provide an environment to: (i) recruit and retain undergraduate students in (nuclear) physics and sustain and/or increase their interest, confidence, and enthusiasm in this field; (ii) provide participants with a toolset to become effective independent researchers who pursue further research opportunities as undergraduates; and (iii) encourage participants to pursue graduate studies and potential careers in nuclear science, or related STEM fields.

07 ISOTOPE AND RADIATION SOURCES↗