Search NASA⌕ Search

SEARCH · Search NASA

Results for “substrate selection”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Dynamic Conformational States Dictate Selectivity toward the Native Substrate in a Substrate-Permissive Acyltransferase

Hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase (HCT) is an essential acyltransferase that mediates flux through plant phenylpropanoid metabolism by catalyzing a reaction between p-coumaroyl-CoA and shikimate, yet it also exhibits broad substrate permissiveness in vitro. How do enzymes like HCT avoid functional derailment by cellular metabolites that qualify as non-native substrates? Here, we combine X-ray crystallography and molecular dynamics to reveal distinct dynamic modes of HCT under native and non-native catalysis. We find that essential electrostatic and hydrogen-bonding interactions between the ligand and active site residues, permitted by active site plasticity, are elicited more effectively by shikimate than by other non-native substrates. This work provides a structural basis for how dynamic conformational states of HCT favor native over non-native catalysis by reducing the number of futile encounters between the enzyme and shikimate.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Mechanisms of mTORC1 activation by RHEB and inhibition by PRAS40

The mechanistic target of rapamycin complex 1 (mTORC1) controls cell growth and metabolism in response to nutrients, energy levels, and growth factors. It contains the atypical kinase mTOR and the RAPTOR subunit that binds to the Tor signalling sequence (TOS) motif of substrates and regulators. mTORC1 is activated by the small GTPase RHEB (Ras homologue enriched in brain) and inhibited by PRAS40. Here we present the 3.0 ångström cryo-electron microscopy structure of mTORC1 and the 3.4 ångström structure of activated RHEB–mTORC1. RHEB binds to mTOR distally from the kinase active site, yet causes a global conformational change that allosterically realigns active-site residues, accelerating catalysis. Here, cancer-associated hyperactivating mutations map to structural elements that maintain the inactive state, and we provide biochemical evidence that they mimic RHEB relieving auto-inhibition. We also present crystal structures of RAPTOR–TOS motif complexes that define the determinants of TOS recognition, of an mTOR FKBP12–rapamycin-binding (FRB) domain–substrate complex that establishes a second substrate-recruitment mechanism, and of a truncated mTOR–PRAS40 complex that reveals PRAS40 inhibits both substrate-recruitment sites. These findings help explain how mTORC1 selects its substrates, how its kinase activity is controlled, and how it is activated by cancer-associated mutations.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Dynamic Phaeodactylum tricornutum exometabolites shape surrounding bacterial communities

Summary Roles of different ecological classes of algal exometabolites in regulating microbial community composition are not well understood. Here, we identify exometabolites from the model diatom Phaeodactylum tricornutum and demonstrate their potential to influence bacterial abundances. We profiled exometabolites across a time course of axenic algal growth using liquid chromatography–tandem mass spectrometry. We then investigated growth of 12 bacterial isolates on individual‐identified exometabolites. Lastly, we compared responses of a P. tricornutum ‐adapted enrichment community to additions of two contrasting metabolites: selective growth substrate 4‐hydroxybenzoic acid and putative signaling/facilitator molecule lumichrome. We identified 50 P. tricornutum metabolites and found distinct temporal accumulation patterns. Two exometabolites (of 12 tested) supported growth of distinct subsets of bacterial isolates. While algal exudates and algal presence drove similar changes in community composition compared with controls, exogenous 4‐hydroxybenzoic acid addition promoted increased abundances of taxa that utilized it in isolation, and also revealed the importance of factors relating to algal presence in regulating community composition. This work demonstrates that secretion of selective bacterial growth substrates represents one mechanism by which algal exometabolites can influence bacterial community composition and illustrates how the algal exometabolome has the potential to modulate bacterial communities as a function of algal growth.

4-hydroxybenzoic acid↗
NASA NTRS2002

Silicon-on-insulator (SOI) active pixel sensors with the photosite implemented in the substrate

Active pixel sensors for a high quality imager are fabricated using a silicon-on-insulator (SOI) process by integrating the photodetectors on the SOI substrate and forming pixel readout transistors on the SOI thin-film. The technique can include forming silicon islands on a buried insulator layer disposed on a silicon substrate and selectively etching away the buried insulator layer over a region of the substrate to define a photodetector area. Dopants of a first conductivity type are implanted to form a signal node in the photodetector area and to form simultaneously drain/source regions for a first transistor in at least a first one of the silicon islands. Dopants of a second conductivity type are implanted to form drain/source regions for a second transistor in at least a second one of the silicon islands. Isolation rings around the photodetector also can be formed when dopants of the second conductivity type are implanted. Interconnections among the transistors and the photodetector are provided to allow signals sensed by the photodetector to be read out via the transistors formed on the silicon islands.

Pain, Bedabrata↗
NASA NTRS2005

Silicon-on-insulator (SOI) active pixel sensors with the photosite implemented in the substrate

Active pixel sensors for a high quality imager are fabricated using a silicon-on-insulator (SOI) process by integrating the photodetectors on the SOI substrate and forming pixel readout transistors on the SOI thin-film. The technique can include forming silicon islands on a buried insulator layer disposed on a silicon substrate and selectively etching away the buried insulator layer over a region of the substrate to define a photodetector area. Dopants of a first conductivity type are implanted to form a signal node in the photodetector area and to form simultaneously drain/source regions for a first transistor in at least a first one of the silicon islands. Dopants of a second conductivity type are implanted to form drain/source regions for a second transistor in at least a second one of the silicon islands. Isolation rings around the photodetector also can be formed when dopants of the second conductivity type are implanted. Interconnections among the transistors and the photodetector are provided to allow signals sensed by the photodetector to be read out via the transistors formed on the silicon islands.

Zheng, Xinyu↗
NASA NTRS1991

Selective and low temperature synthesis of polycrystalline diamond

Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.

Ramesham, R.↗
DOE OSTI2024

Identification of carbohydrate gene clusters obtained from in vitro fermentations as predictive biomarkers of prebiotic responses

Prebiotic fibers are non-digestible substrates that modulate the gut microbiome by promoting expansion of microbes having the genetic and physiological potential to utilize those molecules. Although several prebiotic substrates have been consistently shown to provide health benefits in human clinical trials, responder and non-responder phenotypes are often reported. These observations had led to interest in identifying, a priori, prebiotic responders and non-responders as a basis for personalized nutrition. In this study, we conducted in vitro fecal enrichments and applied shotgun metagenomics and machine learning tools to identify microbial gene signatures from adult subjects that could be used to predict prebiotic responders and non-responders. Using short chain fatty acids as a targeted response, we identified genetic features, consisting of carbohydrate active enzymes, transcription factors and sugar transporters, from metagenomic sequencing of in vitro fermentations for three prebiotic substrates: xylooligosacharides, fructooligosacharides, and inulin. A machine learning approach was then used to select substrate-specific gene signatures as predictive features. These features were found to be predictive for XOS responders with respect to SCFA production in an in vivo trial. Our results confirm the bifidogenic effect of commonly used prebiotic substrates along with inter-individual microbial responses towards these substrates. We successfully trained classifiers for the prediction of prebiotic responders towards XOS and inulin with robust accuracy (≥ AUC 0.9) and demonstrated its utility in a human feeding trial. Overall, the findings from this study highlight the practical implementation of pre-intervention targeted profiling of individual microbiomes to stratify responders and non-responders.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Selective area growth of semiconductors using patterned sol-gel materials

Systems and methods for growing semiconductor materials on substrates by using patterned sol-gel materials are provided. According to a first aspect of the invention, a method includes forming a pattern of a sol-gel material on a first region of substrate, and depositing a semiconductor material on a second region of the substrate by selective area growth. The second region is adjacent to the first region.

Warren, Emily L.↗
DOE OSTI2018

Effect of bacterial inoculants on phytomining of metals from waste incineration bottom ash

Highlights: • Plants inoculated with PGP-bacteria were grown on waste incineration bottom ash. • Rhizobacteria Rhodococcus erythropolis P30 enhanced biomass of Nicotiana tabacum. • Selected PGP-strains enhanced biomass and nutritional status of Salix smithiana. • Strains enhancing growth on contaminated soil had a similar effect on bottom ash. • Bacterial inoculants did not enhance trace element accumulation in plants. - Abstract: Waste incineration bottom ash is considered a secondary resource for valuable trace elements (TE), which is currently neglected in most European countries. Phytomining could potentially recover valuable TE from such waste materials but is still at an exploratory stage with many challenges. The use of bioaugmentation to improve plant growth and TE accumulation of metal-tolerant high biomass plants growing on waste incineration bottom ash was evaluated. Bacterial strains that were previously isolated from rhizosphere, roots and contaminated soil were selected according to their plant growth promoting characteristics and tolerance to the bottom ash substrate. Those selected bacterial strains were tested for their beneficial effects on Nicotiana tabacum and Salix smithiana with regards to phytomining. The rhizobacterial strain Rhodococcus erythropolis P30 enhanced the shoot dry weight of N. tabacum by on average 57% compared to the control plants. Several bacterial inoculants enhanced biomass production and the nutritional status of S. smithiana. Moreover, those bacterial strains previously described to enhance biomass production of N. tabacum and members of the Salicaceae on TE-contaminated soils, also enhanced biomass production of these species on bottom ash. However, bacterial inoculants could not enhance trace element accumulation in plants.

09 BIOMASS FUELS↗
DOE OSTI2024

Bench-Scale Development of a Novel Direct Air Capture Technology Using High-Capacity Structured Sorbents

The work performed under this project has resulted into development of a DAC technology utilizing a structured sorbent to capture CO 2 from ambient air with a key innovation of direct Joule heating of the sorbent for CO 2 desorption. A working SMA, fully integrated with an electrically resistive heating layer, high surface area support, and high CO 2 capacity sorbent coated onto a commercial ceramic monolithic substrate, was successfully developed and demonstrated over >200 adsorption-desorption cycles in a high-fidelity bench test unit directly using ambient air. A cordierite-based monolith was selected as a substrate owing to its high surface area, low bulk density, low heat capacity, and commercial availability. Reaction kinetics study conducted during this project led to development of a promoter for the base Na 2 CO 3 sorbent that could be incorporated into the sorbent to enhance to achieve higher CO 2 adsorption/desorption rates, greater working capacity, and reduced regeneration temperature. An accelerated aging study was conducted in a TGA to determine sorbent stability and no degradation in the sorbent performance was observed even after 250 adsorption-desorption cycles. An electrically resistive heating layer was developed with tunable electrical properties. The heating layer was coated onto the selected cordierite substrate. Aging studies performed showed the electrical properties and heating performance was stable after 500 heating and cooling cycles. The collective findings on the selected cordierite substrate, robust heating layer, promoter and sorbent selection were used to synthesize a full, 6”x6” SMA for bench-scale testing. The bench-scale DAC system was constructed to test full size SMAs using real ambient air for adsorption and joule heating for regeneration. After completing shakedown and commissioning of the 1 kg/day of CO 2 capacity DAC bench unit, an extended operation was performed to complete over 230 cycles with the full size SMA. This testing showed no observable degradation in sorbent performance. A detailed process model, TEA and LCA were developed for a conceptual 100,000 TPY CO 2 removal DAC facility. The LCA results show the net CO 2 e emissions from the DAC system are highly dependent on the electricity source. All other factors, including SMA manufacturing, materials for facility enclosure, etc., are minor cost contributors compared to the energy consumption required for CO 2 removal. With the successful development and validation of the SMA for the sustained performance for CO 2 removal from ambient air with joule heated regeneration in this project, a fully integrated 1 TPY bench-scale DAC system is currently in development with the support of DOE/FECM (DE-FE0032243). The project objective is to demonstrate the engineering design of the DAC system to produce a continuous, high purity CO 2 stream from ambient air. This project will address and validate key engineering features of the DAC system including the gas sealing mechanism and panels, enclosure and air contactor design, and automation sequence to achieve continuous CO 2 production.

42 ENGINEERING↗
NASA NTRS1995

Weightless Environment Training Facility (WETF) Materials Coating Evaluation, Volume 1

The Weightless Environment Training Facility Material Coating Evaluation project has included preparing, coating, testing, and evaluating 800 test panels of three differing substrates. Ten selected coating systems were evaluated in six separate exposure environments and subject to three tests for physical properties. Substrate materials were identified, the manner of surface preparation described, and exposure environments defined. Exposure environments included immersion exposure, cyclic exposure, and field exposure. Cyclic exposures, specifically QUV-Weatherometer and the KTA Envirotest were found to be the most agressive of the environments included in the study when all three evaluation criteria are considered. This was found to result primarily from chalking of the coatings under ultraviolet (UV) light exposure. Volumes 2 and 3 hold the 5 appendices to this report.

Source record↗
DOE OSTI2018

Control of Polar Orientation and Lattice Strain in Epitaxial BaTiO 3 Films on Silicon

Conventional strain engineering of epitaxial ferroelectric oxide thin films is based on the selection of substrates with a suitable lattice parameter. In this work, we show that the variation of oxygen pressure during pulsed laser deposition is a flexible strain engineering method for epitaxial ferroelectric BaTiO 3 films either on perovskite substrates or on Si(001) wafers. This unconventional growth strategy permits continuous tuning of strain up to high levels (ε > 0.8%) in films greater than one hundred nanometers thick, as well as selecting the polar axis orientation to be either parallel or perpendicular to the substrate surface plane.

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

J-domain proteins interaction with neurodegenerative disease-related proteins

HSP70 chaperones, J-domain proteins (JDPs) and nucleotide exchange factors (NEF) form functional networks that have the ability to prevent and reverse the aggregation of proteins associated with neurodegenerative diseases. JDPs can interact with specific substrate proteins, hold them in a refolding-competent conformation and target them to specific HSP70 chaperones for remodeling. Thereby, JDPs select specific substrates and constitute an attractive target for pharmacological intervention of neurodegenerative diseases. This, under the condition that the exact mechanism of JDPs interaction with specific substrates is unveiled. In this review, we provide an overview of the structural and functional variety of JDPs that interact with neurodegenerative disease-associated proteins and we highlight those studies that identified specific residues, domains or regions of JDPs that are crucial for substrate binding.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Complete replacement of Arabidopsis oil-producing enzymes with heterologous diacylglycerol acyltransferases

Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) and phospholipid:diacylglycerol acyltransferase 1 (PDAT1) share responsibility for triacylglycerol (TAG) biosynthesis, and their selectivities control TAG fatty acid (FA) compositions. For rational metabolic engineering of seed oils, replacing endogenous TAG biosynthesis with exogenous enzymes containing different substrate FA selectivities is desirable; however, the dgat1-1/pdat1-2 double mutant is pollen lethal. Here, we evaluated the ability of 3 DGAT1s, from phylogenetically diverse plants with distinct TAG assembly processes, to completely replace endogenous TAG biosynthesis in Arabidopsis ( Arabidopsis thaliana ). We transformed dgat1-1 mutant plants with expression constructs for DGAT1 s from Camelina sativa , Physaria fendleri , and castor ( Ricinus communis ). Transgene expression was properly “contextualized” by using a previously determined minimum necessary expression unit containing the promoter/5′ UTR and first intron of native AtDGAT1 ; both of these DNA elements are essential for pollen expression. Next, we crossed homozygous lines with a DGAT1/DGAT1/PDAT1/pdat1-2 parent. C. sativa and P. fendleri DGAT1s restored the FA compositions and transcriptional differences of dgat1-1 to near wild-type and rescued the dgat1-1/pdat1-2 pollen lethality. R. communis DGAT1 was active in dgat1-1 seeds but produced unique oil profiles and alterations in the expression of lipid metabolic genes; it also failed to rescue dgat1-1/pdat1-2 lethality. This study confirms that the promoter and first intron of AtDGAT1 can modulate the expression of foreign DGAT1 genes to fit the correct spatiotemporal profile necessary for completely replacing endogenous TAG biosynthesis. Furthermore, it demonstrates an additional layer of unexpected enzyme incompatibility between oilseed lineages, which may complicate bioengineering approaches that seek to replace essential genes with orthologs.

McGuire, Sean T. [Washington State Univ., Pullman,↗
NASA NTRS1990

Space Station long term lubrication analysis. Phase 1 preliminary tribological survey

Increases in the size, complexity, and life requirements of satellites and space vehicles have put increasing demands on the lubrication requirements for trouble-free service. Since the development costs of large systems are high, long lives with minimum maintenance are dictated. The Space Station represents the latest level of size and complexity in satellite development; it will be nearly 100 meters in major dimensions and will have a life requirement of thirty years. It will have numerous mechanisms critical to its success, some of which will be exposed to the space environment. Designing long-life lubrication systems and choosing appropriate lubricants for these systems will be necessary for their meeting the requirements and for avoiding failures with associated dependent mechanisms. The purpose of this program was to identify the various critical mechanisms and review their designs during the overall design and development stage so that problem areas could be avoided or minimized prior to the fabrication of hardware. The specific objectives were fourfold: (1) to perform a tribology survey of the Space Station for the purpose of documenting each wear point as to materials involved, environmental conditions, and operating characteristics; (2) to review each wear point (point of relative motion) as to the lubrication used and substrate materials selected in the context of its operating characteristics and the environmental conditions imposed; (3) to make recommendations for improvement in areas where the lubricant chosen and/or where the substrate (materials of the wear couple) are not considered optimum for the application; and (4) to make or recommend simulated or full scale tests in tribological areas where the state-of-the-art is being advanced, in areas where new designs are obviously being employed and a critical review would indicate that problems are a strong possibility, and/or where excessive wear, a malfunction, or excessive leakage would create fluid systems problems or contamination of exposed optical equipment.

Dufrane, K. F.↗
NASA NTRS2003

Structure, Function, Self-Assembly and Origin of Simple Membrane Proteins

Integral membrane proteins perform such essential cellular functions as transport of ions, nutrients and waste products across cell walls, transduction of environmental signals, regulation of cell fusion, recognition of other cells, energy capture and its conversion into high-energy compounds. In fact, 30-40% of genes in modem organisms codes for membrane proteins. Although contemporary membrane proteins or their functional assemblies can be quite complex, their transmembrane fragments are usually remarkably simple. The most common structural motif for these fragments is a bundle of alpha-helices, but occasionally it could be a beta-barrel. In a series of molecular dynamics computer simulations we investigated self-organizing properties of simple membrane proteins based on these structural motifs. Specifically, we studied folding and insertion into membranes of short, nonpolar or amphiphatic peptides. We also investigated glycophorin A, a peptide that forms sequence-specific dimers, and a transmembrane aggregate of four identical alpha-helices that forms an efficient and selective voltage-gated proton channel was investigated. Many peptides are attracted to water-membrane interfaces. Once at the interface, nonpolar peptides spontaneously fold to a-helices. Whenever the sequence permits, peptides that contain both polar and nonpolar amino also adopt helical structures, in which polar and nonpolar amino acid side chains are immersed in water and membrane, respectively. Specific identity of side chains is less important. Helical peptides at the interface could insert into the membrane and adopt a transmembrane conformation. However, insertion of a single helix is unfavorable because polar groups in the peptide become completely dehydrated upon insertion. The unfavorable free energy of insertion can be regained by spontaneous association of peptides in the membrane. The first step in this process is the formation of dimers, although the most common are aggregates of 4-7 helices. The helices could arrange themselves such that they formed pores capable of transporting ions and small molecules across membranes. Stability of transmembrane aggregates of simple proteins is often only marginal and, therefore, it can be regulated by environmental signals or small sequence modifications in the region of interhelical interactions. A key step in the earliest evolution of membrane proteins was the emergence of selectivity for specific substrates. Many channels could become selective if one or only a few properly chosen amino acids are properly placed along the channel, acting as filters or gates. This is a convenient evolutionary solution because it does not require imposing conditions on the whole sequence.

Pohorille, Andrew↗
NASA NTRS2007

Genesis Contingency Planning and Mishap Recovery: The Sample Curation View

Planning for sample preservation and curation was part of mission design from the beginning. One of the scientific objectives for Genesis included collecting samples of three regimes of the solar wind in addition to collecting bulk solar wind during the mission. Collectors were fabricated in different thicknesses for each regime of the solar wind and attached to separate frames exposed to the solar wind during specific periods of solar activity associated with each regime. The original plan to determine the solar regime sampled for specific collectors was to identify to which frame the collector was attached. However, the collectors were dislodged during the hard landing making identification by frame attachment impossible. Because regimes were also identified by thickness of the collector, the regime sampled is identified by measuring fragment thickness. A variety of collector materials and thin films applied to substrates were selected and qualified for flight. This diversity provided elemental measurement in more than one material, mitigating effects of diffusion rates and/or radiation damage. It also mitigated against different material and substrate strengths resulting in differing effects of the hard landing. For example, silicon crystal substrates broke into smaller fragments than sapphire-based substrates and diamond surfaces were more resilient to flying debris damage than gold. The primary responsibility of the curation team for recovery was process documentation. Contingency planning for the recovery phase expanded this responsibility to include not only equipment to document, but also gather, contain and identify samples from the landing area and the recovered spacecraft. The team developed contingency plans for various scenarios as part of mission planning that included topographic maps to aid in site recovery and identification of different modes of transport and purge capability depending on damage. A clean tent, set-up at Utah Test & Training Range to control the environment for processing the sample return capsule and cleanly installing a nitrogen purge to the canister, was used to control the environment for extracting collector fragments from the damaged canister and to document and package over 10,000 collector fragments.

Stansbery, E. K.↗