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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The antimalarial compound ELQ ‐400 is an unusual inhibitor of the bc 1 complex, targeting both Q o and Q i sites

Inhibitors of the mitochondrial respiratory chain cytochrome bc 1 complex, such as the antimalarial atovaquone and ELQ ‐300, and many well‐studied compounds, are classified as either Q o or Q i site inhibitors based on their site of action. Here, we investigated the site of action of ELQ ‐400 that showed an unusual behaviour, being effective against parasites resistant to the Q o site inhibitor atovaquone or to the Q i site inhibitor ELQ ‐300. Analysis of yeast mutants and comparison with atovaquone and other ELQ s strongly suggest that ELQ ‐400 targets both Q o and Q i sites. Dual site inhibition would be particularly efficient as it would lower the risk of acquired resistance. However, such compounds are seldom found, which could be explained by structural and mechanistic differences between the sites.

Song, Zehua↗
DOE OSTI2019

Highly Efficient Blue OLEDs Based on Metal‐Assisted Delayed Fluorescence Pd(II) Complexes

Abstract A series of metal‐assisted delayed fluorescence (MADF) palladium(II) complexes, PdN1N, PdN1N‐dm, and PdN6N, are studied. Their 77 K photoluminescence emission spectra show a narrow primary emission peak at 464, 466, and 470 nm, respectively, with small vibronic peaks characteristic of many phosphorescent emitters. At room temperature (300 K), the dominant emission peaks for PdN1N, PdN1N‐dm, and PdN6N are slightly redshifted to 472, 470, and 476 nm, respectively. In the meantime, a broad sideband is also shown between 410 and 450 nm due to the MADF process. A blue device employing PdN1N‐dm demonstrates an electroluminescence emission peak at 476 nm and the maximum external quantum efficiency (EQE) of 25.1%. The high maximum EQE of the blue organic light‐emitting diode (OLED) device indicates that both the phosphorescence and the delayed fluorescence are very efficient. In addition, a stable OLED device of PdN1N‐dm gives a maximum EQE of 9.8% and the estimated operational lifetime LT 70 of 350 h at the practical luminance of 100 cd m −2 .

Zhu, Zhi‐Qiang↗
DOE OSTI2015

Synthesis and Characterization of a Triphos Ligand Derivative and the Corresponding Pd II Complexes: Triphos Ligand Derivative and Corresponding Pd II Complexes

The synthesis of the new bis(2-(diphenylphosphino)ethyl)methylhydroxyphosphine tridentate phosphine ligand, LCH2OH/Ph, is reported. The ligand reacts with [Pd(Cl)2(PhCN)2 to form [Pd(LCH2OH/Ph)Cl]Cl. Exchange of the chloride ions for triflate (OTf–) using AgOTf yielded pure [Pd(LCH2OH/Ph)OTf]OTf. In addition to spectral characterization the free ligand, LCH2OH/Ph, and Pd(II) complex, [Pd(LCH2OH/Ph)OTf]OTf, are structurally characterized. This research was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences, and Geosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated by Battelle for DOE.

Miller, Deanna L.↗
DOE OSTI2013

Intersubunit communication in the dihydroorotase-aspartate transcarbamoylase complex of Aquifex aeolicus : Intersubunit Communication in a Pyrimidine Biosynthetic Complex

Aspartate transcarbamoylase and dihydroorotase, enzymes that catalyze the second and third step in de novo pyrimidine biosynthesis, are associated in dodecameric complexes in Aquifex aeolicus and many other organisms. The architecture of the dodecamer is ideally suited to channel the intermediate, carbamoyl aspartate from its site of synthesis on the ATC subunit to the active site of DHO, which catalyzes the next step in the pathway, because both reactions occur within a large, internal solvent-filled cavity. Channeling usually requires that the reactions of the enzymes are coordinated so that the rate of synthesis of the intermediate matches its rate of utilization. The linkage between the ATC and DHO subunits was demonstrated by showing that the binding of the bisubstrate analog, N-phosphonacetyl-L-aspartate to the ATC subunit inhibits the activity of the distal DHO subunit. Structural studies identified a DHO loop, loop A, interdigitating between the ATC domains that would be expected to interfere with domain closure essential for ATC catalysis. Mutation of the DHO residues in loop A that penetrate deeply between the two ATC domains inhibits the ATC activity by interfering with the normal reciprocal linkage between the two enzymes. Moreover, a synthetic peptide that mimics that part of the DHO loop that binds between the two ATC domains was found to be an allosteric or noncompletive ATC inhibitor (K i = 22 μM). A model is proposed suggesting that loop A is an important component of the functional linkage between the enzymes.

Evans, Hedeel Guy↗
DOE OSTI2019

Triphenylene‐Derived Electron Acceptors and Donors on Ag(111): Formation of Intermolecular Charge‐Transfer Complexes with Common Unoccupied Molecular States

Abstract Over the past years, ultrathin films consisting of electron donating and accepting molecules have attracted increasing attention due to their potential usage in optoelectronic devices. Key parameters for understanding and tuning their performance are intermolecular and molecule–substrate interactions. Here, the formation of a monolayer thick blend of triphenylene‐based organic donor and acceptor molecules from 2,3,6,7,10,11‐hexamethoxytriphenylene (HAT) and 1,4,5,8,9,12‐hexaazatriphenylenehexacarbonitrile (HATCN), respectively, on a silver (111) surface is reported. Scanning tunneling microscopy and spectroscopy, valence and core level photoelectron spectroscopy, as well as low‐energy electron diffraction measurements are used, complemented by density functional theory calculations, to investigate both the electronic and structural properties of the homomolecular as well as the intermixed layers. The donor molecules are weakly interacting with the Ag(111) surface, while the acceptor molecules show a strong interaction with the substrate leading to charge transfer and substantial buckling of the top silver layer and of the adsorbates. Upon mixing acceptor and donor molecules, strong hybridization occurs between the two different molecules leading to the emergence of a common unoccupied molecular orbital located at both the donor and acceptor molecules. The donor acceptor blend studied here is, therefore, a compelling candidate for organic electronics based on self‐assembled charge‐transfer complexes.

Müller, Kathrin↗
DOE OSTI2015

A numerical approach for simulating fluid structure interaction of flexible thin shells undergoing arbitrarily large deformations in complex domains

We present a new numerical methodology for simulating fluid–structure interaction (FSI) problems involving thin flexible bodies in an incompressible fluid. The FSI algorithm uses the Dirichlet–Neumann partitioning technique. The curvilinear immersed boundary method (CURVIB) is coupled with a rotation-free finite element (FE) model for thin shells enabling the efficient simulation of FSI problems with arbitrarily large deformation. Turbulent flow problems are handled using large-eddy simulation with the dynamic Smagorinsky model in conjunction with a wall model to reconstruct boundary conditions near immersed boundaries. The CURVIB and FE solvers are coupled together on the flexible solid–fluid interfaces where the structural nodal positions, displacements, velocities and loads are calculated and exchanged between the two solvers. Loose and strong coupling FSI schemes are employed enhanced by the Aitken acceleration technique to ensure robust coupling and fast convergence especially for low mass ratio problems. The coupled CURVIB-FE-FSI method is validated by applying it to simulate two FSI problems involving thin flexible structures: 1) vortex-induced vibrations of a cantilever mounted in the wake of a square cylinder at different mass ratios and at low Reynolds number; and 2) the more challenging high Reynolds number problem involving the oscillation of an inverted elastic flag. For both cases the computed results are in excellent agreement with previous numerical simulations and/or experiential measurements. Grid convergence tests/studies are carried out for both the cantilever and inverted flag problems, which show that the CURVIB-FE-FSI method provides their convergence. Finally, the capability of the new methodology in simulations of complex cardiovascular flows is demonstrated by applying it to simulate the FSI of a tri-leaflet, prosthetic heart valve in an anatomic aorta and under physiologic pulsatile conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Characterisation of a complex thin walled structure fabricated by selective laser melting using a ferritic oxide dispersion strengthened steel

Oxide dispersion strengthened (ODS) alloys exhibit superior mechanical and physical properties due to the presence of nanoscopic Y(Al, Ti) oxide precipitates, but their manufacturing process is complex. The present study is aimed at further investigation of the application of an alternative, Additive Manufacturing (AM) technique, Selective Laser Melting (SLM), to the production of consolidated ODS alloy components. Mechanically alloyed PM2000 (ODS-FeCrAl) powders have been consolidated and a fine dispersion of Y-containing precipitates were observed in an as built thin-walled component, but these particles were typically poly-crystalline and contained a variety of elements including O, Al, Ti, Cr and Fe. Application of post-build heat treatments resulted in the modification of particle structures and compositions; in the annealed condition most precipitates were transformed to single crystal yttrium aluminium oxides. During the annealing treatment, precipitate distributions homogenised and localised variations in number density were diminished. The resulting volume fractions of those precipitates were 25–40% lower than have been reported in conventionally processed PM2000, which was attributed to Y-rich slag-like surface features and inclusions formed during SLM. - Highlights: • A wall structure was grown from ODS steel powder using selective laser melting. • A fine dispersion of nano-precipitates was apparent in as-build material. • Precipitates were multi-phased containing several elements, e.g. O, Ti, Al, Fe, Cr, Y. • Post-build annealing changed those into typically single-crystalline Y–Al–O. • The anneal also reduced and stabilised the volume fraction of precipitates to ~ 0.006.

36 MATERIALS SCIENCE↗