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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Structure and immunogenicity of a stabilized HIV-1 envelope trimer based on a group-M consensus sequence

Stabilized HIV-1 envelope glycoproteins (Env) that resemble the native Env are utilized in vaccination strategies aimed at inducing broadly neutralizing antibodies (bNAbs). To limit the exposure of rare isolate-specific antigenic residues/determinants we generated a SOSIP trimer based on a consensus sequence of all HIV-1 group M isolates (ConM). The ConM trimer displays the epitopes of most known bNAbs and several germline bNAb precursors. The crystal structure of the ConM trimer at 3.9Å resolution resembles that of the native Env trimer and its antigenic surface displays few rare residues. The ConM trimer elicits strong NAb responses against the autologous virus in rabbits and macaques that are significantly enhanced when it is presented on ferritin nanoparticles. The dominant NAb specificity is directed against an epitope at or close to the trimer apex. Immunogens based on consensus sequences might have utility in engineering vaccines against HIV-1 and other viruses.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Structural insights into the activation of metabotropic glutamate receptors

Metabotropic glutamate receptors are family C G-protein-coupled receptors. They form obligate dimers and possess extracellular ligand-binding Venus flytrap domains, which are linked by cysteine-rich domains to their 7-transmembrane domains. Spectroscopic studies show that signalling is a dynamic process, in which large-scale conformational changes underlie the transmission of signals from the extracellular Venus flytraps to the G protein-coupling domains—the 7-transmembrane domains—in the membrane. Here, using a combination of X-ray crystallography, cryo-electron microscopy and signalling studies, we present a structural framework for the activation mechanism of metabotropic glutamate receptor subtype 5. Our results show that agonist binding at the Venus flytraps leads to a compaction of the intersubunit dimer interface, thereby bringing the cysteine-rich domains into close proximity. Furthermore interactions between the cysteine-rich domains and the second extracellular loops of the receptor enable the rigid-body repositioning of the 7-transmembrane domains, which come into contact with each other to initiate signalling.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Atomic-Level Structural Dynamics of Polyoxoniobates during DMMP Decomposition

Ambient pressure in situ synchrotron-based spectroscopic techniques have been correlated to illuminate atomic-level details of bond breaking and formation during the hydrolysis of a chemical warfare nerve agent simulant over a polyoxometalate catalyst. Specifically, a Cs 8 [Nb 6 O 19 ] polyoxoniobate catalyst has been shown to react readily with dimethyl methylphosphonate (DMMP). The atomic-level transformations of all reactant moieties, the [Nb 6 O 19 ] 8- polyanion, its Cs + counterions, and the DMMP substrate, were tracked under ambient conditions by a combination of X-ray absorption fine structure spectroscopy, Raman spectroscopy, and X-ray diffraction. Results reveal that the reaction mechanism follows general base (in contrast to specific base) hydrolysis. Together with computational results, the work demonstrates that the ultimate fate of DMMP hydrolysis at the Cs 8 [Nb 6 O 19 ] catalyst is strong binding of the (methyl) methylphosphonic acid ((M)MPA) product to the polyanions, which ultimately inhibits catalytic turnover.

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

Magnetic and structural properties of the solid solution CuAl 2(1–x) Ga 2x O 4

CuAl 2 O 4 is a ternary oxide spinel with Cu 2+ ions (s = 1/2) primarily populating the A-site diamond sublattice. The compound is reported to display evidence of spin glass behavior but possess a non-frozen magnetic ground state below the transition temperature. On the other hand, the spinel CuGa 2 O 4 displays spin glass behavior at ~ 2.5 K with Cu 2+ ions more readily tending to the B-site pyrochlore sublattice. Therefore, we investigate the magnetic and structural properties of the solid solution CuAl 2(1-x) Ga 2x O 4 examining the evolution of the magnetic behavior as Al 3+ is replaced with a much larger Ga 3+ ion. Our results show that the Cu 2+ ions tend to migrate from tetrahedral to octahedral sites as the Ga 3+ ion concentration increases, resulting in a concomitant change in the glassy magnetic properties of the solution. Results indicate glassy behavior for much of the solution with a general trend towards decreasing magnetic frustration as the Cu 2+ ion shifts to the B-site. However, the x = 0.1 and 0.2 members of the system do not show glassy behavior down to our measurement limit (1.9 K) suggesting a delayed spin glass transition. We suggest that these two members are additional candidates for investigation to access highly frustrated exotic quantum states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Multiple crossovers between positive and negative magnetoresistance versus field due to fragile spin structure in metallic GdPd 3 [Oscillating magnetoresistance due to fragile spin structure in metallic GdPd 3 ]

Here, studies on the phenomenon of magnetoresistance (MR) have produced intriguing and application-oriented outcomes for decades–colossal MR, giant MR and recently discovered extremely large MR of millions of percents in semimetals can be taken as examples. We report here the discovery of novel multiple sign changes versus applied magnetic field of the MR in the cubic intermetallic compound GdPd 3 . Our study shows that a very strong correlation between magnetic, electrical and magnetotransport properties is present in this compound. The magnetic structure in GdPd 3 is highly fragile since applied magnetic fields of moderate strength significantly alter the spin arrangement within the system–a behavior that manifests itself in the oscillating MR. Intriguing magnetotransport characteristics of GdPd 3 are appealing for field-sensitive device applications, especially if the MR oscillation could materialize at higher temperature by manipulating the magnetic interaction through perturbations caused by chemical substitutions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Assessment of electronic structure methods for the determination of the ground spin states of Fe( ii ), Fe( iii ) and Fe( iv ) complexes

Our ability to understand and simulate the reactions catalyzed by iron depends strongly on our ability to predict the relative energetics of spin states. In this work, we studied the electronic structures of Fe 2+ ion, gaseous FeO and 14 iron complexes using Kohn–Sham density functional theory with particular focus on determining the ground spin state of these species as well as the magnitudes of relevant spin-state energy splittings. The 14 iron complexes investigated in this work have hexacoordinate geometries of which seven are Fe(II), five are Fe(III) and two are Fe(IV) complexes. These are calculated using 20 exchange–correlation functionals. In particular, we use a local spin density approximation (LSDA) – GVWN5, four generalized gradient approximations (GGAs) – BLYP, PBE, OPBE and OLYP, two non-separable gradient approximations (NGAs) – GAM and N12, two meta-GGAs – M06-L and M11-L, a meta-NGA – MN15-L, five hybrid GGAs – B3LYP, B3LYP*, PBE0, B97-3 and SOGGA11-X, four hybrid meta-GGAs – M06, PW6B95, MPW1B95 and M08-SO and a hybrid meta-NGA – MN15. The density functional results are compared to reference data, which include experimental results as well as the results of diffusion Monte Carlo (DMC) calculations and ligand field theory estimates from the literature. For the Fe 2+ ion, all functionals except M11-L correctly predict the ground spin state to be quintet. However, quantitatively, most of the functionals are not close to the experimentally determined spin-state splitting energies. For FeO all functionals predict quintet to be the ground spin state. For the 14 iron complexes, the hybrid functionals B3LYP, MPW1B95 and MN15 correctly predict the ground spin state of 13 out of 14 complexes and PW6B95 gets all the 14 complexes right. Here, the local functionals, OPBE, OLYP and M06-L, predict the correct ground spin state for 12 out of 14 complexes. Two of the tested functionals are not recommended to be used for this type of study, in particular M08-SO and M11-L, because M08-SO systematically overstabilizes the high spin state, and M11-L systematically overstabilizes the low spin state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Visualization of structural evolution and phase distribution of a lithium vanadium oxide (Li 1.1 V 3 O 8 ) electrode via an operando and in situ energy dispersive X-ray diffraction technique

We present Li 1+n V 3 O 8 (n = 0–0.2) has been extensively investigated as a cathode material for Li ion batteries because of its superior electrochemical properties including high specific energy and good rate capability. In this paper, a synchrotron based energy dispersive X-ray diffraction (EDXRD) technique was employed to profile the phase transitions and the spatial phase distribution of a Li 1.1 V 3 O 8 electrode during electrochemical (de)lithiation in situ and operando. As annealing temperature during the preparation of the Li 1.1 V 3 O 8 material has a strong influence on the morphology and crystallinity, and consequently influences the electrochemical outcomes of the material, Li 1.1 V 3 O 8 materials prepared at two different temperatures, 500 and 300°C (LVO500 and LVO300), were employed in this study. The EDXRD spectra of LVO500 and LVO300 cells pre-discharged at C/18, C/40 and C/150 were recorded in situ, and phase localization and relative intensity of the peaks were compared. For cells discharged at the C/18 rate, although α and β phases were distributed uniformly within the LVO500 electrode, they were localized on two sides of the LVO300 electrode. Discharging rates of C/40 and C/150 led to homogeneous β phase formation in both LVO500 and LVO300 electrodes. Furthermore, the phase distribution as a function of position and (de)lithiation extent was mapped operando as the LVO500 cell was (de)lithiated. In conclusion, the operando data indicate that (1) the lithiation reaction initiated from the side of the electrode facing the Li anode and proceeded towards the side facing the steel can, (2) during discharge the phase transformation from a Li-poor to a Li-rich α phase and the formation of a β phase can proceed simultaneously in the electrode after the first formation of a β phase, and (3) the structural evolution occurring during charging is not the reverse of that during discharge and takes place homogenously throughout the electrode.

25 ENERGY STORAGE↗
DOE OSTI2017

Directed evolution of the periodic table: probing the electronic structure of late actinides

Recent investigations of the coordination chemistry and physical properties of berkelium (Z = 97) and californium (Z = 98) have revealed fundamental differences between post-curium elements and lighter members of the actinide series. This review highlights these developments and chronicles key findings and concepts from the last half-century that have helped usher in a new understanding of the evolution of electronic structure in the periodic table.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Structure and chemical stability in perovskite–polymer hybrid photovoltaic materials

Adding polymers to methylammonium lead iodide perovskite solar cell active layers has been previously shown to increase their chemical stability, but stabilization mechanisms in these hybrid materials are poorly understood. We report here on a structural and spectroscopic analysis in a number of perovskite–polymer hybrid materials and compare their stability. We observed that perovskite crystallite sizes decrease with the addition of polymers (polyethylene glycol, polyethyleneimine, poly(acrylic acid) and polyvinylpyrrolidone), and through the use of nanomechanical AFM showed phase contrast in the perovskite–polymer mixture. NMR and single-crystal growth experiments reveal that acid–base interactions, as well as facet-dependent interfacial interactions between perovskite and polymer, contribute to differences in stabilities of these hybrid materials. The polymers investigated tend to suppress the formation of a hydrate crystal phase that accelerates the degradation reaction, and we report that adding poly(acrylic acid) increases significantly the stability of perovskite films under humid air and ambient illumination. Under these controlled degradation conditions, perovskite–poly(acrylic acid) hybrid solar cells maintain stable efficiency for the first 3 days and then slowly degrade over the next 6 days under humid air and illumination, whereas control perovskite solar cells degrade entirely within the first 2 days. Furthermore, these results highlight the importance of choosing suitable functional groups in the polymer phase of perovskite hybrid solar cells to prolong their device lifetime.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Vibronic interaction in CO3- photo-detachment: Jahn-Teller effects beyond structural distortion and general formalisms for vibronic Hamiltonians in trigonal symmetries

Recently, the negative ion photoelectron spectrum of CO?? 3 was reported and the second lowest energy band is assigned to the close-lying 3E00 and 3E0 states that undergo Jahn-Teller distortions (Chem. Sci. 2016, 7, 1142). This assignment is based on the Born-Oppenheimer approximation and the assumption of a static Jahn-Teller eect that distorts the CO3 structure from D3h to C2v symmetry. In this work, we employ a 4 states 6 modes vibronic coupling model to investigate the triplet band and uncover the dynamic and non-adiabatic nature of the Jahn-Teller and pseudo- Jahn-Teller interactions in the triplet states. The apparent four peaks progression in the band is studied in depth, and is found to consist of more than four transitions. By comparing the simulated spectra using the full model and the reduced-dimension 2 states 2 modes models, we characterize those transitions. The origin of the complexities of the spectrum is traced to the C-O nonbonding character of the orbitals that lose electron in the photo-detachment process. Methodology-wise, we derive and present the formalisms for arbitrary order expansions of all bimodal trigonal Jahn-Teller and pseudo-Jahn-Teller Hamiltonians in vibrational coordinates.

Seidu, Issaka↗