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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Zinc Adsorption and Hydration Structures at Yttria-Stabilized Zirconia Surfaces

Zinc adsorption and interfacial hydration on yttria-stabilized zirconia (YSZ) surfaces in contact with aqueous zinc solutions at room temperature and neutral pH have been probed, with combined specular high-resolution X-ray reflectivity and element-specific (Zn) resonant anomalous X-ray reflectivity techniques. The total and partial zinc-Specific electron density profiles in the surface normal direction show the detailed interfacial hydration structures with zinc adsorption: Strongly depending on its crystallographic orientations, the YSZ (110) surface adsorbs zinc species only within adsorbed water layers above the terminal plane, while on (111) surface, zinc further-penetrates the substrate (below the terminal plane). Considering that both surfaces are enriched with oxygen vacancies and metal-depleted sites; on which chemisorbed water species are expected, the observed contrast indicates that specific zinc adsorption is controlled strongly by the intrinsic surface chemistry that results from orientation-dependent interfacial structures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Coupling to short linear motifs creates versatile PME-1 activities in PP2A holoenzyme demethylation and inhibition

Protein phosphatase 2A (PP2A) holoenzymes target broad substrates by recognizing short motifs via regulatory subunits. PP2A methylesterase 1 (PME-1) is a cancer-promoting enzyme and undergoes methylesterase activation upon binding to the PP2A core enzyme. Here, we showed that PME-1 readily demethylates different families of PP2A holoenzymes and blocks substrate recognition in vitro. The high-resolution cryoelectron microscopy structure of a PP2A-B56 holoenzyme–PME-1 complex reveals that PME-1 disordered regions, including a substrate-mimicking motif, tether to the B56 regulatory subunit at remote sites. They occupy the holoenzyme substrate-binding groove and allow large structural shifts in both holoenzyme and PME-1 to enable multipartite contacts at structured cores to activate the methylesterase. B56 interface mutations selectively block PME-1 activity toward PP2A-B56 holoenzymes and affect the methylation of a fraction of total cellular PP2A. The B56 interface mutations allow us to uncover B56-specific PME-1 functions in p53 signaling. Our studies reveal multiple mechanisms of PME-1 in suppressing holoenzyme functions and versatile PME-1 activities derived from coupling substrate-mimicking motifs to dynamic structured cores.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Protective effects of non–catalytic proteins on endoglucanase activity at air and lignin interfaces

The manner in which added non-catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated that a reduction in the non-specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air–liquid interface provide rationale. This work investigated root causes including effects of the air–liquid interface on non-catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air–liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non-enzymatic protein (bovine serum albumin [BSA] or soy proteins ) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%–50% of its activity due to an air–liquid interface in the presence of lignin while addition of non-enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. Finally, these results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Bioenergetic consequences of compromised mitochondrial DNA repair in the mouse heart

Highlights: • Loss of mitochondrial DNA repair compromises bioenergetic efficiency. • Impairments in bioenergetic efficiency result from ETS stoichiometry shifts. • Bioenergetic flux in Polg{sup m/m} mitochondria favors accelerated electron leak. The progeroid phenotype of mitochondrial DNA (mtDNA) mutator mice has been nebulously attributed to general mitochondrial ‘dysfunction’, though few studies have rigorously defined the bioenergetic consequences of accumulating mtDNA mutations. Comprehensive mitochondrial diagnostics was employed to interrogate the bioenergetic properties of isolated cardiac mitochondria from mtDNA mutator mice and wild type littermates. Assessment of respiratory flux in conjunction with parallel measurements of mitochondrial free energy all point to the cause of respiratory flux limitations observed in mtDNA mutator mouse mitochondria being due to impairments within the energy transduction step catalyzed by the electron transport system in which NADH/NAD{sup +} free energy is transduced to the proton motive force (ΔP). The primary bioenergetic consequence of this limitation appears to be hyper-reduction of NAD(P)H/NAD(P){sup +} redox poise across multiple substrate conditions, particularly evident at moderate to high respiration rates. This hyper-reduced phenotype appears to result from specific reductions in both complex I and complex IV expression, presumably due to compromised mtDNA integrity. Translation of these findings to the working heart would suggest that the primary biological consequence of accumulated mtDNA damage is accelerated electron leak driven by an increase in electron redox pressure for a given rate of oxygen consumption.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Screening and modular design for metabolic pathway optimization

Biological conversion of substrate sugars to a variety of products is an increasingly popular option for chemical transformation due to its high specificity and because of significant interest in the use of renewable feedstocks. Yet, pathway optimization through metabolic engineering is often needed to make such molecules economically at a relevant scale. Employing effective methods to search and narrow the immense pathway parameter space is essential to meet performance metrics such as high titer, yield and productivity with efficiency. This review focuses on two practices that increase the likelihood of finding a more advantageous pathway solution: implementing a screen to identify high producers and utilizing modular pathway design to streamline engineering efforts. While screens seek to couple product titer with a high-throughput measurement output, modular design aims to rationally construct pathways to allow parallel optimization of various units. Both of these methodologies have proven widely successful in metabolic engineering, with combinations of them resulting in synergistic enhancements to pathway optimization. This review will specifically illustrate their utility for microbially derived acid and alcohol products, which are of interest as fuels and value added products.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

In situ oxidation of reduced graphene oxide membranes by peracetic acid for dye desalination

Graphene oxide (GO) membranes with tunable interlayer spacings are of interest for dye removal from salty textile wastewater, and the membranes are often reduced to improve their stability, which inevitably lowers water permeance. Herein, we demonstrate that reduced GO (rGO) membranes can be facilely modified using peracetic acid (PAA) in situ to dramatically enhance water permeance while retaining dye rejection. Specifically, PAA-modified membranes (PrGO) are synthesized by vacuum-filtering hydrazine-reduced rGO nanosheets onto Nylon substrate and then exposing them to PAA solutions. The effects of the rGO layer thickness, PAA content, and PAA exposure time on the membrane chemistry, nanostructures, and salt/dye separation properties are thoroughly examined. For example, the PAA oxidation of a 100 nm-thick rGO membrane for 10 min increases water permeance by 180 %, from 35 to 93 Liter m −2 h −1 bar −1 , and decreases Na 2 SO 4 rejection from 10 % to 3.3 % while retaining the rejection of Congo red at ≈99.7 %. The PrGO membranes exhibit stable water permeance and >99 % dye rejection in multi-cycle tests in a crossflow system, surpassing state-of-the-art GO membranes and showcasing their potential for practical applications.

Dye desalination↗
DOE OSTI2019

Protection of GaInP 2 Photocathodes by Direct Photoelectrodeposition of MoS x Thin Films

Catalytic MoS x thin films have been directly photoelectrodeposited on GaInP 2 photocathodes for stable photoelectrochemical hydrogen generation. Specifically, the MoSx deposition conditions were controlled to obtain 8-10 nm films directly on p-GaInP 2 substrates without ancillary protective layers. The films were nominally composed of MoS 2 , with additional MoO x S y and MoO 3 species detected and showed no long-range crystalline order. The as-deposited material showed excellent catalytic activity toward the hydrogen evolution reaction relative to bare p-GaInP 2 . Notably, no appreciable photocurrent reduction was incurred by the addition of the photoelectrodeposited MoSx catalyst to the GaInP 2 photocathode under light-limited operating conditions, highlighting the advantageous optical properties of the film. The MoS x catalyst also imparted enhanced durability toward photoelectrochemical hydrogen evolution in acidic conditions, maintaining nearly 85% of the initial photocurrent after 50 h of electrolysis. In total, this work demonstrates a simple method for producing dual-function catalyst/protective layers directly on high-performance, planar III-V photoelectrodes for photoelectrochemical energy conversion.

14 SOLAR ENERGY↗
DOE OSTI2026

Using Novosphingobium aromaticivorans for Concurrent Production of Intracellular and Extracellular Products from Aromatics Extracted from Poplar Biomass

Achieving high biochemical production in biotransformations of renewable resources requires using concentrated cultures that not only generate the product of interest but also produce abundant microbial cell waste. We explored the concept of gaining value from microbial cells by producing intracellular products in tandem with a desired extracellular product. Specifically, we engineered a strain ofNovosphingobium aromaticivorans to extracellularly produce 2-pyrone-4,6-dicarboxylic acid (PDC) from aromatic substrates and to intracellularly accumulate astaxanthin along with coenzyme Q 10 , all of which are products of industrial interest. Achieving the goal of concurrent production of intracellular and extracellular products required the creative application of bioreactor engineering principles. Although a continuously fed membrane bioreactor (MBR) maximized extracellular product biosynthesis, it had a negative effect on intracellular product accumulation. However, operating the MBR as a sequencing batch reactor (MBR-SBR) with a step-feed resulted in stable concurrent production of both extracellular and intracellular products. With aromatics extracted from poplar biomass, we achieved productivities of 1.14 g of PDC/L-h for the extracellular product and 0.04 mg of astaxanthin/L-h and 0.64 mg of CoQ 10 /L-h for intracellular products, respectively. Our findings demonstrate that the mode of operation of a bioreactor impacts the simultaneous production of intracellular and extracellular products byN. aromaticivorans.

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

Oriented Electrostatic Effects on O 2 and CO 2 Reduction by a Polycationic Iron Porphyrin

Next-generation energy technologies require improved methods for rapid and efficient chemical-to-electrical energy transformations. One new approach has been to include atomically-positioned, electrostatic motifs in molecular catalysts to stabilize high-energy, charged intermediates. For example, an iron porphyrin bearing four cationic, ortho-N,N,N-trimethylanilinium groups (o-[N(CH 3 ) 3 ] + ) has recently been used to catalyze the complex, multi-step O 2 and CO 2 reduction reactions (ORR and CO 2 RR) with fast rates and at low overpotentials. The success of this catalyst is attributed, at least in part, to specific charge-charge interactions between the atomically-positioned o-[N(CH 3 ) 3 ] + groups and the bound substrate. However, by nature of the mono-ortho substitution pattern, there are four possible atropisomers of this metalloporphyrin and thus four unique electrostatic environments. This work reports that each of the four individual atropisomers catalyzes both the ORR and CO 2 RR with fast rates and low overpotentials. The maximum turnover frequencies (TOF max ) vary among the atropisomers, by a factor of 60 for the ORR and a factor of 5 for CO 2 RR. For the ORR, the αβαβ isomer is the fastest and has the highest overpotential, while for the CO 2 RR, the order is reversed and the αααα isomer is the fastest and has the highest overpotential. The role of charge-positioning is complex and can affect more than a single step such as CO 2 binding. These data offer a first-of-a-kind perspective on atomically positioned charge and highlight the significance of high charge density, rather than orientation, on the thermodynamics and kinetics of multistep molecular electrochemical transformations.

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

Unraveling the Role of Transport, Electrocatalysis, and Surface Science in the Solid Oxide Fuel Cell Cathode Oxygen Reduction Reaction

This final report for project FE0009656 covers the period from 10/01/2012 to 09/30/2015 and covers research accomplishments on the effects of carbon dioxide on the surface composition and structure of cathode materials for solid oxide fuel cells (SOFCs), specifically La1-xSrxFeyCo1- yO3-δ (LSCF). Epitaxially deposited thin films of LSCF on various single-crystal substrates have revealed the selective segregation of strontium to the surface thereby resulting in a surface enrichment of strontium. The near surface compositional profile in the films have been measured using total x-ray fluorescence (TXRF), and show that the kinetics of strontium segregation are higher at higher partial pressures of carbon dioxide. Once the strontium segregates to the surface, it leads to the formation of precipitates of SrO which convert to SrCO3 in the presence of even modest concentrations of carbon dioxide in the atmosphere. This has important implications for the performance of SOFCs which is discussed in this report. These experimental observations have also been verified by Density Functional Theory calculations (DFT) which predict the conditions under which SrO and SrCO3 can occur in LSCF. Furthermore, a few cathode compositions which have received attention in the literature as alternatives to LSCF cathodes have been studied in this work and shown to be thermodynamically unstable under the operating conditions of the SOFCs.

25 ENERGY STORAGE↗
DOE OSTI2018

Safety Evaluation of Nitric Acid Reactions with Polysaccharides

The hazards of polysaccharides in a transuranic (TRU) waste drum exposed to nitric acid (HNO3) and metal nitrate salts have been evaluated, based on considerations of how complex nitrogen redox cycles carry out the aqueous phase oxidation of alcohols and related organic functional groups. Of particular emphasis is how these exothermic reactions, coupled with a positive feedback loop inherent to nitrogen redox chemistry, can initiate an autocatalytic thermal runaway and explosive gas generation. This poses the most significant hazard for a TRU waste drum under ambient conditions where acidic solution may be present, either in small quantities as free liquid or sorbed within a solid matrix. Regarding specific mechanistic details, nitric acid is an extremely potent oxidant but is remarkably inert, rarely interacting directly with oxidizable substrates, instead exerting its vast potential energy through lower oxidation state reactants such as nitrogen dioxide (NO 2 ) and nitrous acid (HNO 2 ). These lower oxidation states of nitrogen are generated from the slow self-decomposition of nitric acid, as a result of which oxidation reactions involving nitric acid that have not been preloaded with these reactants commonly experience a quiescent induction period. It is the end of this induction period when exothermic reactivity increases rapidly that the system is most vulnerable to autocatalytic thermal runaway. Metal nitrate salts promote this ambient temperature solution chemistry (cf. traditional oxidizer properties of metal nitrate salts, which operate in the solid state at elevated temperatures) by releasing nitric acid into the system. Although less reactive than alcohols by virtue of extensive hydrogen bonding, carbohydrates are oxidized by nitric acid through the same fundamental mechanisms, potentially proceeding through a series of oxidation steps. For polymeric carbohydrates (polysaccharides) the chemistry is complicated by a variety of competing side reactions, including acid-catalyzed hydrolytic depolymerization to more reactive (ultimately monomeric) units, as well as other degradation reactions promoted by radical mechanisms. For this reason, polysaccharides that are more susceptible to hydrolysis such as starches are more reactive than cellulose, with the attendant microbial population in starch based kitty litter adding a special aspect of reactivity. A spectrum of nitrogen containing gas products is generated from polysaccharide oxidation by nitric acid depending on the reaction conditions - for example, fuel lean mixtures tend towards producing more oxidized gases such as NO 2 , and thus favor an autocatalytic cycle, relative to fuel rich conditions that produce lower oxidation state gases such as nitrous oxide (N 2 O). These nitrogen based gases may be accompanied by variable quantities of carbon dioxide (CO 2 ), which may be generated from small molecule (e.g., oxalic acid) oxidation or from decarboxylation of previously oxidized functional groups.

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

Safety Evaluation of Nitric Acid Reactions with Polysaccharides

The hazards of polysaccharides in a transuranic (TRU) waste drum exposed to nitric acid (HNO 3 ) and metal nitrate salts have been evaluated, based on considerations of how complex nitrogen redox cycles carry out the aqueous phase oxidation of alcohols and related organic functional groups. Of particular emphasis is how these exothermic reactions, coupled with a positive feedback loop inherent to nitrogen redox chemistry, can initiate an autocatalytic thermal runaway and explosive gas generation. This poses the most significant hazard for a TRU waste drum under ambient conditions where acidic solution may be present, either in small quantities as free liquid or sorbed within a solid matrix. Regarding specific mechanistic details, nitric acid is an extremely potent oxidant but is remarkably inert, rarely interacting directly with oxidizable substrates, instead exerting its vast potential energy through lower oxidation state reactants such as nitrogen dioxide (NO 2 ) and nitrous acid (HNO 2 ). These lower oxidation states of nitrogen are generated from the slow self-decomposition of nitric acid, as a result of which oxidation reactions involving nitric acid that have not been preloaded with these reactants commonly experience a quiescent induction period. It is the end of this induction period when exothermic reactivity increases rapidly that the system is most vulnerable to autocatalytic thermal runaway. Metal nitrate salts promote this ambient temperature solution chemistry (cf. traditional oxidizer properties of metal nitrate salts, which operate in the solid state at elevated temperatures) by releasing nitric acid into the system.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Novel Microbial Based Enzymatic CO 2 Fixation Mechanisms

The broad, long term goal of the research is to provide insight into the mechanism of novel carboxylation reactions catalyzed by enzymes involved in bacterial alkene, ketone, and epoxide metabolism. Novel convergent pathways in the model microorganism Xanthobacter autotrophicus have been described in which epoxides produced by alkene oxidation and ketones produced by the oxidation of alcohols are further carboxylated and utilized in energy yielding pathways. Both alkene/epoxide and alcohol/ketone pathways involve distinct carboxylases with unique molecular properties and cofactor requirements that represent alternative mechanisms of CO 2 fixation. The main focus and aims of this project is to provide structural basis for the mechanistic understanding of the reactions catalyzed by 2-ketopropyl coenzyme M oxidoreductase / carboxylase and acetone carboxylase, the terminal steps in the convergent pathways of alkene/epoxide and alcohol ketone metabolism in X. autotrophicus strain Py2. Interestingly, coenzyme M (CoM), the simplest known organic coenzyme, has been shown to have a central role in the pathway of alkene/epoxide carboxylation. Prior to this discovery CoM was thought only to be involved in methanogenesis in archaea. In addition to the carboxylation mechanisms, we are examining the enzymology of the biosynthesis of CoM in bacteria and we have already determined that it is biochemically distinct from that of CoM synthesized by methanogens. The proposed studies will reveal new and unique insights into CO 2 fixation pathways and carboxylation chemistry. We are utilizing a multidisciplinary approach involving kinetic studies, site-specific amino acid substitution studies, and the determination of high-resolution structures of enzymes in the presence of substrate analogs and mechanism base inhibitors to ascertain information concerning the biochemical mechanisms of enzyme catalyzed reactions. Within the context of the mission of the Department of Energy and the core activities of the Energy Biosciences, the results obtained in the study will reveal new insights into these novel carboxylation reactions and will provide the basis for the comparison of the mechanism of these interesting enzymes to other well-characterized biological mechanisms for CO 2 fixation and carboxylation. Knowledge concerning the mechanism of these enzymes provides the basis for an increased fundamental understanding of carboxylation chemistry that could contribute to future mechanisms for CO 2 capture and fixation and, in turn, to mitigating the effects of increasing concentrations of CO 2 on global climate change.

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

Novel sterol binding domains in bacteria

Sterol lipids are widely present in eukaryotes and play essential roles in signaling and modulating membrane fluidity. Although rare, some bacteria also produce sterols, but their function in bacteria is not known. Moreover, many more species, including pathogens and commensal microbes, acquire or modify sterols from eukaryotic hosts through poorly understood molecular mechanisms. The aerobic methanotroph Methylococcus capsulatus was the first bacterium shown to synthesize sterols, producing a mixture of C-4 methylated sterols that are distinct from those observed in eukaryotes. C-4 methylated sterols are synthesized in the cytosol and localized to the outer membrane, suggesting that a bacterial sterol transport machinery exists. Until now, the identity of such machinery remained a mystery. In this study, we identified three novel proteins that may be the first examples of transporters for bacterial sterol lipids. The proteins, which all belong to well-studied families of bacterial metabolite transporters, are predicted to reside in the inner membrane, periplasm, and outer membrane of M. capsulatus, and may work as a conduit to move modified sterols to the outer membrane. Quantitative analysis of ligand binding revealed their remarkable specificity for 4-methylsterols, and crystallographic structures coupled with docking and molecular dynamics simulations revealed the structural bases for substrate binding by two of the putative transporters. Their striking structural divergence from eukaryotic sterol transporters signals that they form a distinct sterol transport system within the bacterial domain. Finally, bioinformatics revealed the widespread presence of similar transporters in bacterial genomes, including in some pathogens that use host sterol lipids to construct their cell envelopes. The unique folds of these bacterial sterol binding proteins should now guide the discovery of other proteins that handle this essential metabolite.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1981

Electronic depth micrometer

Device for measuring depth or thickness reads distance of penetration by small-diameter probe. It was developed specifically to measure thickness of wet (uncured) insulation applied to Space Shuttle structures; thin probes penetrate wet insulation to substrate, and reference surface on gage is then positioned against outer surface of insulation to measure its thickness. Gage is easy to use, even by workers wearing gloves or other protective clothing, and allows remote reading and recording of production data.

Major, R. K.↗
NASA NTRS2004

Cloning and Characterization of an alpha-amylase Gene from the Hyperthermophilic Archaeon Thermococcus Thioreducens

The gene encoding an extracellular alpha-amylase, TTA, from the hyperthermophilic archaeon Thermococcus thioreducens was cloned and expressed in Escherichia coli. Primary structural analysis revealed high similarity with other a-amylases from the Thermococcus and Pyrococcus genera, as well as the four highly conserved regions typical for a-amylases. The 1374 bp gene encodes a protein of 457 amino acids, of which 435 constitute the mature protein preceded by a 22 amino acid signal peptide. The molecular weight of the purified recombinant enzyme was estimated to be 43 kDa by denaturing gel electrophoresis. Maximal enzymatic activity of recombinant TTA was observed at 90 C and pH 5.5 in the absence of exogenous Ca(2+), and the enzyme was considerably stable even after incubation at 90 C for 2 hours. The thermostability at 90 and 102 C was enhanced in the presence of 5 mM Ca(2+). The extraordinarily high specific activity (about 7.4 x 10(exp 3) U/mg protein at 90 C, pH 5.5 with soluble starch as substrate) together with its low pH optimum makes this enzyme an interesting candidate for starch processing applications.

Bernhardsdotter, Eva C. M. J.↗