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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The Salmonella type III secretion system virulence effector forms a new hexameric chaperone assembly for export of effector/chaperone complexes

Bacteria hijack eukaryotic cells by injecting virulence effectors into host cytosol with a type III secretion system (T3SS). Effectors are targeted with their cognate chaperones to hexameric T3SS ATPase at the bacterial membrane's cytosolic face. In this issue of the Journal of Bacteriology , Roblin et al. (P. Roblin, F. Dewitte, V. Villeret, E. G. Biondi, and C. Bompard, J Bacteriol 197:688–698, 2015, http://dx.doi.org/10.1128/JB.02294-14) show that the T3SS chaperone SigE of Salmonella can form hexameric rings rather than dimers when bound to its cognate effector, SopB, implying a novel multimeric association for chaperone/effector complexes with their ATPase.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

How Does Metal Spin State Affect Electronic Communication in Mixed-Valence Dimers? Insights from Ultrafast Near-Infrared and Soft X-ray Transient Absorption Spectroscopy

Recent advancements in photocatalysis, photovoltaics, and quantum information science take advantage of electron spin, and determining how spin multiplicity affects electron transfer is key to understanding these phenomena. Here, in this study, we examine how metal spin state affects electronic communication in an organometallic mixed-valence dimer, ferrocenyl cobaltocenium ([Fe II Cp 2 Co III Cp 2 ] + ). This complex can be photoexcited from its low-spin singlet Fe II ground state to form intermediate-spin triplet Fe II and high-spin quintet Fe II excited states. Using femtosecond optical transient absorption (OTA) spectroscopy with visible (vis), near-infrared (NIR), and short-wave IR (SWIR) probes, supported by time-dependent density functional theory (TD-DFT) calculations, we measure Fe II Co III →Fe III Co II intervalence charge transfer (IVCT) bands in each of the Fe II spin states. Mulliken–Hush analysis of the excited-state IVCT bands was used to compute the electronic coupling between the metal centers in all three spin states, which increased as quintet < triplet < singlet. Meanwhile, the peak energy of the bands, and thus the ΔG of the IVCT transition, increased as triplet < quintet < singlet. Then, to directly probe the electronic structure at each metal center, we employed picosecond soft X-ray transient absorption (XTA) spectroscopy at the Fe and Co L 3 edges. Our results show that the low-spin and high-spin states of [Fe II Cp 2 Co III Cp 2 ] + are valence-localized, while the intermediate-spin state is partially delocalized. The differences in charge delocalization are attributed to differences in orbital occupation and geometry that affect the free energy and superexchange coupling.

Burke, John H. [Univ. of Illinois at Urbana-Champa↗
DOE OSTI2016

Activation of carbon dioxide by a terminal uranium–nitrogen bond in the gas-phase: a demonstration of the principle of microscopic reversibility

Activation of CO 2 is demonstrated by its spontaneous dissociative reaction with the gas-phase anion complex NUOCl 2 - , which can be considered as NUO + coordinated by two chloride anion ligands. This reaction was previously predicted by density functional theory to occur exothermically, without barriers above the reactant energy. In this paper, the present results demonstrate the validity of the prediction of microscopic reversibility, and provide a rare case of spontaneous dissociative addition of CO 2 to a gas-phase complex. The activation of CO 2 by NUOCl 2 - proceeds by conversion of a U[triple bond]N bond to a U[double bond]O bond and creation of an isocyanate ligand to yield the complex UO 2 (NCO)Cl 2 - , in which uranyl, UO 2 2+ , is coordinated by one isocyanate and two chloride anion ligands. This activation of CO 2 by a uranium(VI) nitride complex is distinctive from previous reports of oxidative insertion of CO 2 into lower oxidation state U(III) or U(IV) solid complexes, during which both C–O bonds remain intact. This unusual observation of spontaneous addition and activation of CO 2 by NUOCl 2 - is a result of the high oxophilicity of uranium. If the computed Gibbs free energy of the reaction pathway, rather than the energy, is considered, there are barriers above the reactant asymptotes such that the observed reaction should not proceed under thermal conditions. Finally, this result provides a demonstration that energy rather than Gibbs free energy determines reactivity under low-pressure bimolecular conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Soft-donor dipicolinamide derivatives for selective actinide( iii )/lanthanide( iii ) separation: the role of S- vs. O-donor sites

Selectivity for An(III) vs. Ln(III) binding and extraction with dipicolinamide analogs containing the C=O vs. C=S groups was investigated in solution and the gas-phase, and by DFT calculations. The results reflect higher selectivity for complex formation and extraction for Am(III) vs. Eu(III) for the softer dithioamide vs. the diamide ligand, while in CH 3 CN the diamide binds more strongly than the thioamide to several Ln(III), forming 1:1 complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Control of cerium oxidation state through metal complex secondary structures

A series of alkali metal cerium diphenylhydrazido complexes, M x (py) y [Ce(PhNNPh) 4 ], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation. The resulting electronic structures of the heterobimetallic cerium diphenylhydrazido complexes were found to be strongly dependent on the identity of the alkali metal cations. When M = Li + or Na + , the cerium(III) starting material was oxidized with concomitant reduction of 1,2-diphenylhydrazine to aniline. Reduction of 1,2-diphenylhydrazine was not observed when M = K + , and the complex remained in the cerium(III) oxidation state. Oxidation of the cerium(III) diphenylhydrazido complex to the Ce( IV ) diphenylhydrazido one was achieved through a simple cation exchange reaction of the alkali metals. As a result, UV-Vis spectroscopy, FTIR spectroscopy, electrochemistry, magnetic susceptibility, and DFT studies were used to probe the oxidation state and the electronic changes that occurred at the metal centre.

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

Transient Triamidoamine Neptunium(V)–Mono(Imido) Complexes: C–H Activations and Hydrogen Atom Transfer Driven by Effective Nuclear Charge

Metal-mono(imido) linkages have been known for seven decades, and they are found in transition metal, main group, lanthanide, thorium, and uranium complexes. However, transuranium-mono(imido) complexes remain unknown in any scenario. Here, we present evidence for transient neptunium(V)–mono(imido) complexes. Treatment of [Np III (Tren TIPS )] (1, Tren TIPS = {N(CH 2 CH 2 NSiPr i 3 ) 3 } 3– ) with N 3 R (R = SiMe 3 ; 1-adamantyl, Ad) results in N 2 evolution and dark purple solutions consistent with the formation of [Np V (Tren TIPS )(NR)] (3NpNR). However, solutions of 3NpNR rapidly turn orange, where for R = SiMe 3 the isolated 1:1 products are [Np IV (Tren TIPS ){N(H)SiMe 3 }] (4a) and [Np IV (Tren TIPS-2H ){N(H)SiMe 3 }] (4b, Tren TIPS-2H = {N(CH 2 CH 2 NS i Pri 3 ) 2 (NCH 2 CH 2 NSiPr i 2 C[Me]=CH 2 )} 3– ). The latter contains a dehydrogenated-Pr i vinyl functionality accounting for the source of the two amido H atoms. The reaction for R = Ad proceeds similarly, but only [Np IV (Tren TIPS ){N(H)Ad}] (5a) could be unequivocally confirmed, though its isolation suggests generality of the imido-to-amido functional group transformation. Complexes 4a/4b exhibit slow relaxation of their magnetization, adding to the small number of transuranium single ion magnets. Experimental and computational analysis suggests that the amido products are formed by C–H activation and two sequential hydrogen atom transfer reactions involving a three-step proton-coupled electron-transfer sequence of H • radical abstraction, electron transfer, then another H • radical abstraction step. In contrast to transient 3NpNR, the 5f 2 uranium(IV)-imido complex [K(2.2.2-cryptand)][U IV (Tren TIPS )(NSiMe 3 )] (8UNSiMe 3 ) is robust, even in boiling THF, suggesting the transience of 5f 2 3NpNR is not due to the 5f n -count but the increased effective nuclear charge of neptunium vs uranium. This work highlights divergence of uranium- and neptunium-imido stabilities, emphasizing that the latter is an inherently challenging synthetic target.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Crystal Structure of a CRISPR RNA-guided Surveillance Complex Bound to a ssDNA Target

In prokaryotes, RNA derived from type I and type III CRISPR loci direct large ribonucleoprotein complexes to destroy invading bacteriophage and plasmids. In Escherichia coli, this 405-kilodalton complex is called Cascade. We report the crystal structure of Cascade bound to a single-stranded DNA (ssDNA) target at a resolution of 3.03 angstroms. The structure reveals that the CRISPR RNA and target strands do not form a double helix but instead adopt an underwound ribbon-like structure. This noncanonical structure is facilitated by rotation of every sixth nucleotide out of the RNA-DNA hybrid and is stabilized by the highly interlocked organization of protein subunits. These studies provide insight into both the assembly and the activity of this complex and suggest a mechanism to enforce fidelity of target binding.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

V‐Groove Si Nanopatterning for the Direct Epitaxy of Orientation‐Patterned III–V Nonlinear Optical Crystals

Orientation‐patterned (OP) III–V semiconductors—used as quasi‐phase‐matched crystals for nonlinear optics applications—are typically epitaxially grown on expensive III–V substrates using a complex process requiring three separate epitaxy steps. In this work, a method is demonstrated for growing orientation‐patterned III–V crystals on Si substrates through V‐groove nanopatterning and a single epitaxial growth. V‐groove Si allows for suppression of random antiphase domain formation that is typical of III–V growth on (001)‐oriented Si through the use of (111)‐faceted trenches patterned on (001)‐oriented Si substrates. By alternating the directions of the V‐groove trenches between [110] and [10], antiphase boundaries can be selectively induced at the boundaries between the two directions of trenches due to the difference in symmetry between the III–V material and Si. This approach allows for a greatly simplified process for growing OP‐III‐Vs and more broadly is a new, robust approach for precisely patterning antiphase boundaries of arbitrary shape and length scales down to 50 nm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Room temperature crystal field splitting of curium resolved by circularly polarized luminescence spectroscopy

Coordination of Cm(III) with a chiral decadentate ligand N,N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]-1,2-diaminocyclohexane (tpadac) generated complexes with strong luminescence allowing for the unprecedented measurement of well-resolved Cm(III) circularly polarized luminescence spectra. Quantitative resolution of the electronic structure of the [Cm(tpadac)][K] complexes was achieved at room temperature, highlighting the strength of the combination of luminescence and circularly polarized luminescence spectroscopies to unravel the fundamental electronic structure of Cm(III). These results are a clear demonstration that these spectroscopies are powerful yet simple tools for the fundamental understanding of electronic structure, which opens the door to future investigations of other Cm(III) complexes in geometries relevant to nuclear applications, and even other 5f-elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Conformational flexibility of BECN1: Essential to its key role in autophagy and beyond: BECN1 Structure and Mechanism

BECN1 (Beclin 1), a highly conserved eukaryotic protein, is a key regulator of autophagy, a cellular homeostasis pathway, and also participates in vacuolar protein sorting, endocytic trafficking, and apoptosis. BECN1 is important for embryonic development, the innate immune response, tumor suppression, and protection against neurodegenerative disorders, diabetes, and heart disease. BECN1 mediates autophagy as a core component of the class III phosphatidylinositol 3-kinase complexes. However, the exact mechanism by which it regulates the activity of these complexes, or mediates its other diverse functions is unclear. BECN1 interacts with several diverse protein partners, perhaps serving as a scaffold or interaction hub for autophagy. Based on extensive structural, biophysical and bioinformatics analyses, BECN1 consists of an intrinsically disordered region (IDR), which includes a BH3 homology domain (BH3D); a flexible helical domain (FHD); a coiled-coil domain (CCD); and a β-α-repeated autophagy-specific domain (BARAD). Each of these BECN1 domains mediates multiple diverse interactions that involve concomitant conformational changes. Thus, BECN1 conformational flexibility likely plays a key role in facilitating diverse protein interactions. Further, BECN1 conformation and interactions are also modulated by numerous post-translational modifications. A better structure-based understanding of the interplay between different BECN1 conformational and binding states, and the impact of post-translational modifications will be essential to elucidating the mechanism of its multiple biological roles.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Tris(carbene)borates; alternatives to cyclopentadienyls in organolanthanide chemistry

The chemistry of the tris-carbene anion phenyltris(3-alkyl-imidazoline-2-yliden-1-yl)borate, [C3 Me ] - ligand, is initiated for f-block metal cations. Neutral, molecular complexes of the form Ln(C3) 2 I are formed for cerium(III), while a separated ion pair [Ln(C3) 2 ]I forms for ytterbium(III). DFT/QTAIM computational analyses of the complexes and related tridentate tris(pyrazolyl)borate (Tp) – supported analogs demonstrates the anticipated strength of the σ donation and confirms greater covalency in the metal–carbon bonds of the [C3 Me ] - complexes in comparison with those in the Tp Me,Me complexes. The DFT calculations demonstrate the crucial role of THF solvent in accurately reproducing the contrasting molecular and ion-pair geometries observed experimentally for the Ce and Yb complexes.

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

Pinning of energy transitions of defects, complexes, and surface states in AlGaN alloys

In this work, we determine the dependence of the defect transition energies, electronic bands, and surface charge neutrality levels in AlGaN. With Vacuum level as reference, we show that energy transitions of localized defects and the surface Fermi level are independent of the alloy composition as electronic bands diverge with the increase in the bandgap as a function of alloy composition. The invariance of localized states on the alloy composition creates a convenient internal reference energy with respect to which other energy states may be measured. We demonstrate a higher generality to the universality rule with the independence of deep transition states of otherwise shallow donor type defects [(+1/+3) transition for VN] and defect complexes (C N +Si III ) in addition to the earlier predicted independent nature of mid-gap states when they are either the antibonding state between cationic impurities and host anion or acceptors at anion sites.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis and crystal and molecular structure of three heterometallic polymeric compounds (Ln{sub 2}[LnGe{sub 6}(μ-Oedph){sub 6}(μ-O){sub 3}(μ-OH){sub 3}(H{sub 2}O){sub 4}] · xH{sub 2}O){sub n} [Ln = Nd, x ∼ 26 (I); Er, x ∼ 24 (II); Tm, x ∼ 20 (III); H{sub 4}Oedph = 1-hydroxyethylidenediphosphonic acid]

The synthesis and X-ray diffraction study of three heterometallic compounds of general formula (Ln{sub 2}[LnGe{sub 6}(μ-Oedph){sub 6}(μ-O){sub 3}(μ-OH){sub 3}(H{sub 2}O){sub 4}] · xH{sub 2}O){sub n} [Ln = Nd, x ∼ 26 (I); Er, x ∼ 24 (II); Tm, x ∼20 (III); H{sub 4}Oedph = 1-hydroxyethylidenediphosphonic acid] are performed. The basis element of structures I–III is a hexanuclear complex anion [Ge(μ-Oedph)(μ-O){sub 0.5}(μ-OH){sub 0.5}]{sub 6}{sup 9−}, in which bridging hydroxo and oxo ligands are statistically disordered with equally probability. Hexameric units are connected by Ln1(H{sub 2}O){sub 4} fragments into a framework whose channels are completely populated by disordered lanthanide atoms and water molecules.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Polk Carbon Storage Complex CarbonSAFE Phase 3 (Final Scientific/Technical Report)

This report summarizes the workplan, technical progress, and high-level findings for the Polk Carbon Storage Complex (PCSC) CarbonSAFE Phase III project. The project was designed to advance a commercial-scale geologic CO 2 storage by drilling and completing two characterization wells to strengthen an already-submitted Underground Injection Control (UIC) Class VI permit application, acquiring new subsurface data, advancing National Environmental Policy Act (NEPA) requirements, progressing CO 2 transportation engineering, and developing commercial and community engagement frameworks.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

The human coronavirus HCoV-229E S-protein structure and receptor binding

The coronavirus S-protein mediates receptor binding and fusion of the viral and host cell membranes. In HCoV-229E, its receptor binding domain (RBD) shows extensive sequence variation but how S-protein function is maintained is not understood. Reported are the X-ray crystal structures of Class III-V RBDs in complex with human aminopeptidase N (hAPN), as well as the electron cryomicroscopy structure of the 229E S-protein. The structures show that common core interactions define the specificity for hAPN and that the peripheral RBD sequence variation is accommodated by loop plasticity. The results provide insight into immune evasion and the cross-species transmission of 229E and related coronaviruses. We also find that the 229E S-protein can expose a portion of its helical core to solvent. This is undoubtedly facilitated by hydrophilic subunit interfaces that we show are conserved among coronaviruses. These interfaces likely play a role in the S-protein conformational changes associated with membrane fusion.

59 BASIC BIOLOGICAL SCIENCES↗