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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Mechanism of Catalysis by L -Asparaginase

Two bacterial type II L -asparaginases, from Escherichia coli and Dickeya chrysanthemi, have played a critical role for more than 40 years as therapeutic agents against juvenile leukemias and lymphomas. Despite a long history of successful pharmacological applications and the apparent simplicity of the catalytic reaction, controversies still exist regarding major steps of the mechanism. In this report, we provide a detailed description of the reaction catalyzed by E. coli type II L -asparaginase (EcAII). Our model was developed on the basis of new structural and biochemical experiments combined with previously published data. The proposed mechanism is supported by quantum chemistry calculations based on density functional theory. In this work, we provide strong evidence that EcAII catalyzes the reaction according to the double-displacement (ping-pong) mechanism, with formation of a covalent intermediate. Several steps of catalysis by EcAII are unique when compared to reactions catalyzed by other known hydrolytic enzymes. Here, the reaction is initiated by a weak nucleophile, threonine, without direct assistance of a general base, although a distant general base is identified. Furthermore, tetrahedral intermediates formed during the catalytic process are stabilized by a never previously described motif. Although the scheme of the catalytic mechanism was developed only on the basis of data obtained from EcAII and its variants, this novel mechanism of enzymatic hydrolysis could potentially apply to most (and possibly all) L -asparaginases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Multisubstrate specificity shaped the complex evolution of the aminotransferase family across the tree of life

Aminotransferases (ATs) are an ancient enzyme family that play central roles in core nitrogen metabolism, essential to all organisms. However, many of the AT enzyme functions remain poorly defined, limiting our fundamental understanding of the nitrogen metabolic networks that exist in different organisms. Here, we traced the deep evolutionary history of the AT family by analyzing AT enzymes from 90 species spanning the tree of life (ToL). We found that each organism has maintained a relatively small and constant number of ATs. Mapping the distribution of ATs across the ToL uncovered that many essential AT reactions are carried out by taxon-specific AT enzymes due to wide-spread nonorthologous gene displacements. This complex evolutionary history explains the difficulty of homology-based AT functional prediction. Biochemical characterization of diverse aromatic ATs further revealed their broad substrate specificity, unlike other core metabolic enzymes that evolved to catalyze specific reactions today. Interestingly, however, we found that these AT enzymes that diverged over billion years share common signatures of multisubstrate specificity by employing different nonconserved active site residues. These findings illustrate that AT family enzymes had leveraged their inherent substrate promiscuity to maintain a small yet distinct set of multifunctional AT enzymes in different taxa. This evolutionary history of versatile ATs likely contributed to the establishment of robust and diverse nitrogen metabolic networks that exist throughout the ToL. The study provides a critical foundation to systematically determine diverse AT functions and underlying nitrogen metabolic networks across the ToL.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Phosphorus-rich stars with unusual abundances are challenging theoretical predictions

Almost all chemical elements have been made by nucleosynthetic reactions in various kind of stars and have been accumulated along our cosmic history. Among those elements, the origin of phosphorus is of extreme interest because it is known to be essential for life such as we know on Earth. However, current models of (Galactic) chemical evolution under-predict the phosphorus we observe in our Solar System. Here we report the discovery of 15 phosphorus-rich stars with unusual overabundances of O, Mg, Si, Al, and Ce. Phosphorus-rich stars likely inherit their peculiar chemistry from another nearby stellar source but their intriguing chemical abundance pattern challenge the present stellar nucleosynthesis theoretical predictions. Specific effects such as rotation or advanced nucleosynthesis in convective-reactive regions in massive stars represent the most promising alternatives to explain the existence of phosphorus-rich stars. The phosphorus-rich stars progenitors may significantly contribute to the phosphorus present on Earth today.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Nighttime OClO in the Winter Arctic Vortex

We show that a nighttime profile of OClO in the Arctic vortex during the winter of 2000 is overestimated, by nearly a factor of 2, using an isentropic trajectory model constrained by observed profiles of ClOx (ClO + 2 X ClOOCl) and BrO. Calculated abundances of nighttime OClO are shown to be sensitive to the abundance of BrOx (BrO + BrCl), details of the air parcel history during the most recent sunrise/sunset transitions, and the BrCl yield from the reaction BrO + ClO. Many uncertainties are considered, and the discrepancy between measured and modeled nighttime OClO appears to be robust. This discrepancy suggests that production of OClO occurs more slowly than implied by standard photochemistry. If the yield of BrCl from the reaction of BrO + ClO is increased from 7% (JPL 2002 value) to 11% (near the upper limit of the uncertainty), good agreement is found between measured and modeled nighttime OClO. This study highlights the importance of accurate knowledge of BrO + ClO reaction kinetics as well as air parcel trajectories for proper interpretation of nighttime OClO. These factors have a considerably smaller impact on the interpretation of OClO observations obtained during twilight (90(deg) <=SZA <= 92(deg)), when photolytic processes are still active.

chlorine activation↗
NASA NTRS2016

Reaction of Basaltic Materials under High-Fidelity Venus Surface Conditions using the Glenn Extreme Environment Rig: First Results

Both historical and current investigations of Venus suggest that atmosphererock interactions play a critical role in the evolution of its atmosphere and crust. We have begun a series of systematic experiments designed to further our understanding of atmosphere-driven weathering and secondary mineralization of basaltic materials that may be occurring on Venus today. Our experiments expose representative igneous phases (mineral, glasses and rocks) to a high-fidelity simulation of Venus surface conditions using the NASA Glenn Extreme Environment Rig (GEER) located at the NASA Glenn Research Center in Cleveland, Ohio. GEER is a very large (800L) vessel capable of producing a long-term, high fidelity simulation of both the physical conditions (750 K and 92 bar) and atmospheric chemistry (down to the ppb-level) asso-ciated with the Venusian surface. As of this writing we have just finished the first of several planned experiments: a 42-day exposure of selected mineral, rocks and volcanic glasses. Our goal is to identify and prioritize the reactions taking place and better our understanding of their importance in Venus' climate history.

Venus surface↗
NASA NTRS1996

Hydrothermal systems as environments for the emergence of life

Analysis of the chemical disequilibrium provided by the mixing of hydrothermal fluids and seawater in present-day systems indicates that organic synthesis from CO2 or carbonic acid is thermodynamically favoured in the conditions in which hyperthermophilic microorganisms are known to live. These organisms lower the Gibbs free energy of the chemical mixture by synthesizing many of the components of their cells. Primary productivity is enormous in hydrothermal systems because it depends only on catalysis of thermodynamically favourable, exergonic reactions. It follows that hydrothermal systems may be the most favourable environments for life on Earth. This fact makes hydrothermal systems logical candidates for the location of the emergence of life, a speculation that is supported by genetic evidence that modern hyperthermophilic organisms are closer to a common ancestor than any other forms of life. The presence of hydrothermal systems on the early Earth would correspond to the presence of liquid water. Evidence that hydrothermal systems existed early in the history of Mars raises the possibility that life may have emerged on Mars as well. Redox reactions between water and rock establish the potential for organic synthesis in and around hydrothermal systems. Therefore, the single most important parameter for modelling the geochemical emergence of life on the early Earth or Mars is the composition of the rock which hosts the hydrothermal system.

Non-NASA Center↗
NASA NTRS1980

A model for gas phase chemistry in interstellar clouds. II - Nonequilibrium effects and effects of temperature and activation energies

The chemical evolution of diffuse and dense interstellar clouds is examined via the time-dependent model outlined by Prasad and Huntress (1980). This paper presents specific results for CH, CO, CH4, O2, CH2O, CN, C2, C2H, HC3N, and NH3. Comparison with observations and predictions of other contemporary models show that cloud temperature plays a very important role through the inverse temperature dependence of radiative association reactions and through activation energies in neutral reactions and selected ion-molecule reactions. The observed fractional abundance of CN with respect to H2 and more accurate recent laboratory data on CN + O and CN + O2 reactions suggest that there is an unidentified, yet efficient, mechanism for conversion of O and O2 into polyatomic species. C2H and HC3N are synthesized early in the history of dense clouds. The value of the fractional abundance of C2H remains high, because as the cloud cools down the activation energy in the C2H + O reaction closes down this most important loss channel. A rapidly decreasing fractional abundance of O with time can also accomplish the same result. The value of the fractional abundance of HC3N remains high because it is an unreactive molecule and probably does not condense readily onto grains.

Prasad, S. S.↗
DOE OSTI2021

Granick revisited: Synthesizing evolutionary and ecological evidence for the late origin of bacteriochlorophyll via ghost lineages and horizontal gene transfer

Photosynthesis—both oxygenic and more ancient anoxygenic forms—has fueled the bulk of primary productivity on Earth since it first evolved more than 3.4 billion years ago. However, the early evolutionary history of photosynthesis has been challenging to interpret due to the sparse, scattered distribution of metabolic pathways associated with photosynthesis, long timescales of evolution, and poor sampling of the true environmental diversity of photosynthetic bacteria. Here, we reconsider longstanding hypotheses for the evolutionary history of phototrophy by leveraging recent advances in metagenomic sequencing and phylogenetics to analyze relationships among phototrophic organisms and components of their photosynthesis pathways, including reaction centers and individual proteins and complexes involved in the multi-step synthesis of (bacterio)-chlorophyll pigments. We demonstrate that components of the photosynthetic apparatus have undergone extensive, independent histories of horizontal gene transfer. This suggests an evolutionary mode by which modular components of phototrophy are exchanged between diverse taxa in a piecemeal process that has led to biochemical innovation. We hypothesize that the evolution of extant anoxygenic photosynthetic bacteria has been spurred by ecological competition and restricted niches following the evolution of oxygenic Cyanobacteria and the accumulation of O 2 in the atmosphere, leading to the relatively late evolution of bacteriochlorophyll pigments and the radiation of diverse crown group anoxygenic phototrophs. This hypothesis expands on the classic “Granick hypothesis” for the stepwise evolution of biochemical pathways, synthesizing recent expansion in our understanding of the diversity of phototrophic organisms as well as their evolving ecological context through Earth history.

58 GEOSCIENCES↗
DOE OSTI2025

Understanding neutron capture processes in uranium deposits using combined U-Sm-Nd isotopic compositions

Valuable insights into the history and evolution of a geologic deposit can be found by investigating neutron capture reactions. Thermal neutron capture reactions occur within both the samarium (Sm) and the uranium (U) systems, where 149 Sm and 235 U can capture neutrons to become 150 Sm and 236 U, respectively. Although largely unexplored, paired measurements of 150 Sm and 236 U could be important for understanding neutron capture effects within uranium ore bodies, and such measurements are potentially useful in nuclear forensics for assessing a material's provenance or mineral exploration. In this work, we refined measurement procedures of Sm isotope compositions utilizing MC-ICPMS. While geologic reference materials were found to have indistinguishable Sm isotope compositions, we found significant isotope variations consistent with nuclear field shift among synthetic Sm standards. Here, this observation highlights that future high-precision Sm isotope investigations need to carefully evaluate synthetic standard(s) against geologic reference materials until an unfractionated and agreed-upon standard is identified. Here, we applied this method to a set of nine uranium ores from the South Australian Beverley North uranium deposits. Although 236 U excesses had been previously reported for these U ores, we found no measurable isotopic shifts in 149 Sm- 150 Sm at the current level of precision (±5 parts per million). One possible explanation for this disparity in the observed neutron capture signatures between U and Sm is that the source(s) of the U and Sm in these ores may be decoupled. This is consistent with the finding that these ores have variable 143 Nd/ 144 Nd, thus demonstrating that diverse sources were involved in the formation of the Beverley North deposits. Alternatively, this deposit may be too young (<50Ma) to have accumulated measurable neutron capture effects in Sm to be detected with the methods employed here.

Mineral exploration↗
DOE OSTI2022

Oxidation in laser-generated metal plumes

The temporal evolution of atoms and molecules in a laser-produced plasma was investigated using optical emission spectroscopy for several metal targets (i.e., Al, Ti, Fe, Zr, Nb, and Ta). Plasmas from metal targets were generated by focusing 1064 nm, 6 ns pulses from an Nd:YAG laser. Gas-phase oxidation/plasma chemistry was initiated by adding O2 (partial pressures up to ≈20%) to an N2 environment where the total background pressure was kept at a constant 1 atmosphere. Temporally resolved emission spectral features were used to track the gas-phase oxidation. The dynamics of atomic and molecular species were monitored using space-resolved time-of-flight emission spectroscopy. Our results highlight that the partial pressure of O2 strongly influences spectral features and molecular formation in laser-produced plasmas. Atoms and molecules co-exist in plasmas, although with different temporal histories depending on the target material due to differences in thermo- and plasma chemical reactions occurring in the plume.

Kautz, Elizabeth J. (ORCID:0000000263389223)↗
DOE OSTI2023

Xanthine Oxidase—A Personal History

A personal perspective is provided regarding the work in several laboratories, including the author’s, that has established the reaction mechanism of xanthine oxidase and related enzymes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2009

Old Faithful Model for Radiolytic Gas-Driven Cryovolcanism at Enceladus

A new model is presented on how chemically driven cryovolcanism might contribute to episodic outgassing at the icy moon Enceladus and potentially elsewhere including Europa and Kuiper Belt Objects. Exposed water ices can become oxidized from radiolytic chemical alteration of near-surface water ice by space environment irradiation. In contact with primordially abundant reductants such as NH3, CH4, and other hydrocarbons, the product oxidants can react exothermically to produce volatile gases driving cryovolcanism via gas-piston forces on any subsurface liquid reservoirs. Radiolytic oxidants such as H2O2 and O2 can continuously accumulate deep in icy regoliths and be conveyed by rheological flows to subsurface chemical reaction zones over million-year time scales indicated by cratering ages for active regions of Enceladus and Europa. Surface blanketing with cryovolcanic plume ejecta would further accelerate regolith burial of radiolytic oxidants. Episodic heating from transient gravitational tides, radioisotope decay, impacts, or other geologic events might occasionally accelerate chemical reaction rates and ignite the exothermic release of cumulative radiolytic oxidant energy. The time history for the suggested "Old Faithful" model of radiolytic gas-driven cryovolcanism at Enceladus and elsewhere therefore consists of long periods of chemical energy accumulation punctuated by much briefer episodes of cryovolcanic activity. The most probable sequence for detection of activity in the current epoch is a long evolutionary phase of slow but continuous oxidant accumulation over billions of years followed by continuous but variable high activity over the past 10(exp 7)-10(exp 8) years. Detectable cryovolcanic activity could then later decline due to near-total oxidation of the rheologically accessible ice crust and depletion the accessible reductant abundances, as may have already occurred for Europa in the more intense radiation environment of Jupiter's magnetosphere. Astrobiological potential of Enceladus could correspondingly be higher than at Europa due to a less extreme state of oxidation and greater residual abundance of organics.

Cooper, John F.↗
NASA NTRS2010

Carbon Isotopes of Alkanes in Hydrothermal Abiotic Organic Synthesis Processes at High Temperatures and Pressures: An Experimental Study

Observation of methane in the Martian atmosphere has been reported by different detection techniques [1-4]. With more evidence showing extensive water-rock interaction in Martian history [5-7], abiotic formation by Fischer-Tropsch Type (FTT) synthesis during serpentization reactions may be one possible process responsible for methane generation on Mars [8, 9]. While the experimental studies performed to date leave little doubt that chemical reactions exist for the abiotic synthesis of organic compounds by mineral surface-catalyzed reactions [10-12], little is known about the reaction pathways by which CO2 and/or CO are reduced under hydrothermal conditions. Carbon and hydrogen isotope measurements of alkanes have been used as an effective tool to constrain the origin and reaction pathways of hydrocarbon formation. Alkanes generated by thermal breakdown of high molecular weight organic compounds have carbon and hydrogen isotopic signatures completely distinct from those formed abiotically [13-15]. Recent experimental studies, however, showed that different abiogenic hydrocarbon formation processes (e.g., polymerization vs. depolymerization) may have different carbon and hydrogen isotopic patterns [16]. Results from previous experiments studying decomposition of higher molecular weight organic compounds (lignite) also suggested that pressure could be a crucial factor affecting fractionation of carbon isotopes [17]. Under high pressure conditions, no experimental data are available describing fractionation of carbon isotope during mineral catalyzed FTT synthesis. Thus, hydrothermal experiments present an excellent opportunity to provide the requisite carbon isotope data. Such data can also be used to identify reaction pathways of abiotic organic synthesis under experimental conditions.

Fu, Qi↗
NASA NTRS2011

Selected Lessons Learned in Space Shuttle Orbiter Propulsion and Power Subsystems

Over its 30 years of space flight history, plus the nearly 10 years of design, development test and evaluation, the Space Shuttle Orbiter is full of lessons learned in all of its numerous and complex subsystems. In the current paper, only selected lessons learned in the areas of the Orbiter propulsion and power subsystems will be described. The particular Orbiter subsystems include: Auxiliary Power Unit (APU), Hydraulics and Water Spray Boiler (WSB), Mechanical Flight Controls, Main Propulsion System (MPS), Fuel Cells and Power Reactant and Storage Devices (PRSD), Orbital Maneuvering System (OMS), Reaction Control System (RCS), Electrical Power Distribution (EPDC), electrical wiring and pyrotechnics. Given the complexity and extensive history of each of these subsystems, and the limited scope of this paper, it is impossible to include most of the lessons learned; instead the attempt will be to present a selected few or key lessons, in the judgment of the authors. Each subsystem is presented separate, beginning with an overview of the hardware and their function, a short description of a few historical problems and their lessons, followed by a more comprehensive table listing of the major subsystem problems and lessons. These tables serve as a quick reference for lessons learned in each subsystem. In addition, this paper will establish common lessons across subsystems as well as concentrate on those lessons which are deemed to have the highest applicability to future space flight programs.

Hernandez, Francisco J.↗
DOE OSTI2020

An image-driven machine learning approach to kinetic modeling of a discontinuous precipitation reaction

Micrograph quantification is an essential component of several materials science studies. Machine learning methods, in particular convolutional neural networks, have previously demonstrated performance in image recognition tasks across several disciplines (e.g. materials science, medical imaging, facial recognition). Here, we apply these well-established methods to develop an approach to microstructure quantification for kinetic modeling of a discontinuous precipitation reaction in a case study on the uranium-molybdenum system. Prediction of material processing history based on image data (classification), calculation of area fraction of phases present in the micrographs (segmentation), and kinetic modeling from segmentation results were performed. Results indicate that convolutional neural networks represent microstructure image data well, and segmentation using the k-means clustering algorithm yields results that agree well with manually annotated images. Classification accuracies of original and segmented images are both 94% for a 5-class classification problem. Kinetic modeling results agree well with previously reported data using manual thresholding. The image quantification and kinetic modeling approach developed and presented here aims to reduce researcher bias introduced into the characterization process, and allows for leveraging information in limited image data sets.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Primary igneous carbon in ureilites - Petrological implications

The ureilite meteorites are carbonaceous olivine-pyroxene achondrites. They typically contain up to 4 wt.% carbon (carbonaceous matrix) as graphite, diamond, and lonsdaleite. Shock degradation has effectively obliterated primary textures in the carbonaceous matrix of previously described ureilites, a factor that has hampered efforts to explain the origin of this material. In contrast, the Antarctic ureilite ALHA78019 displays perfectly preserved primary textures in the carbonaceous matrix characterized by euhedral graphite blades intergrown with Fe-Ni metal and sulfide (diamonds are absent). This petrographic feature suggests that most graphite in ureilites originated by crystallization from a C-rich metallic phase. Assuming that fO2 is controlled by C-CO-CO2 reactions, the compositions of silicates and metals in ureilites imply a two-stage redox history. The noble gases and rare earths of ureilites are discussed in light of this model.

Berkely, J. L.↗
NASA NTRS1993

Carbonate formation on Mars: Latest experiments

Laboratory simulations of Martian CO2 storage address whether carbonate formation could have reduced CO2 pressure from a hypothetical greater than 1 bar to the present 7 mbar in less than or equal to 3 to 4 billion years. This problem is addressed with experiments and analysis designed to verify and improve previous kinetic measurements, reaction mechanisms, and product characterizations, with the goal of improving existing models of Martian CO2 history. A sensitive manometer monitored the pressure drop of CO2 due to uptake by powdered silicate for periods of 3 to 100+ days. Pressure drops for diopside 1 and basalt show rapid short-term (approximately one day) CO2 uptake and considerably slower long-term pressure drops. Curves for diopside 2, olivine 1, and olivine 2 are qualitatively similar to those for diopside 1, whereas quartz and plagioclase show near-zero short-term pressure drops and very slow long-term signals, indistinguishable from a leak (less than 10(exp 11) mol/sq m/s).

Stephens, S. K.↗
NASA NTRS2002

RNA-Catalyzed RNA Ligation on an External RNA Template

Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside '5-triphosphates onto the '3 end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.

McGinness, Kathleen E.↗