Search NASA⌕ Search

SEARCH · Search NASA

Results for “atomic chains”

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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Intramolecular Hydrogen Transfer from the Alpha-Carbon (Cα) and Backbone Amide Nitrogen (N{sub b}) to Form c- and y-Ions in Negative-Ion CID of Peptides

The source of hydrogen in the formation of c- and y-ions produced by intramolecular hydrogen transfer in negative-ion CID experiments with peptides has been examined using Cα-, Cβ-, and backbone amide (N{sub b})-deuterated peptides AAA(d3)AA, AAG(d2)AA, AAAG(d2)A, and AAAAA-d7, as well as five other peptides. The c- and y-ions produced by deuterium transfer from the deuterated residues were detected and identified by the exact m/z values obtained with a high-resolution orbitrap mass spectrometer. The rate of deuterium transfer obtained indicates that over 50% of the hydrogen was originated from the backbone amide nitrogen, with the residual hydrogen coming from the backbone Cα. It is clear that the hydrogen does not originate from the side chain Cβ. It is hypothesized that the intramolecular hydrogen transfer to form negative c- and y-ions takes place via 3-, 4-, 6-, 7-, 8-, and 9-membered ring transition states. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

First observation of a high-𝐾 band structure in 162 Er and implications in the context of the identical bands phenomenon

The first ever identification of a high-𝐾 band structure in 162 Er is reported. Based on a 𝐾 𝜋 = 7 (−) isomer, it is found to be identical in nature to the corresponding 𝐾 𝜋 = 7 − sequence in 164 Er up to its highest observed spin. Furthermore, the phenomenon of identical high-K bands built on a two-quasiparticle configuration in an isotopic chain is reported here for the first time. While this is a notable addition to the systematics of known identical bands in nuclei at normal deformation, a satisfactory global understanding of the phenomenon remains elusive.

150 ≤ A ≤ 189↗
DOE OSTI2019

Uniformly 15N-Labeled Recombinant Ricin A-chain as an Internal Retention Time Standard for Increased Confidence in Forensic Identification of Ricin by Untargeted Nanoflow Liquid Chromatography-Tandem Mass Spectrometry

Ricin, a toxic protein from the castor plant, is of forensic and biosecurity interest because of its high toxicity and common occurrence in crimes and attempted crimes. Qualitative methods to detect ricin are therefore needed. Untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics methods are well-suited because of their high speci-ficity. Specificity in LC-MS/MS comes from both the LC and MS components. However, modern untargeted proteomics methods often use nanoflow LC, which has less reproducible retention times than standard-flow LC, making it challenging to use retention time as a point of identification in a forensic assay. We address this challenge by using retention times rela-tive to a standard, namely uniformly 15N–labeled ricin A-chain produced recombinantly in a bacterial expression system. This material, added as an internal standard prior to trypsin digestion, produces a stable isotope labeled standard for every ricin tryptic peptide in the sample. We show that the MS signals for 15N and natural isotopic abundance ricin peptides are distinct, with mass shifts that correspond to the numbers of nitrogen atoms in each peptide or fragment. We also show that, as expected, labeled and unlabeled peptides coelute, with relative retention time differences of less than 0.2%.

ricin, mass spectrometry, isotope, nitrogen-15, re↗
DOE OSTI2018

Tailoring Surface Properties through in Situ Functionality Gradients in Reactively Modified Poly(2-vinyl-4,4-dimethyl azlactone) Thin Films

Generating physical or chemical gradients in thin-film scaffolds is an efficient approach for screening and optimizing an interfacial structure or chemical functionality to create tailored surfaces that are useful because of their wetting, antifouling, or barrier properties. In this paper, the relationship between the structure of poly(2-vinyl-4,4-dimethyl azlactone) (PVDMA) brushes created by the preferential assembly of poly(glycidyl methacrylate)-block-PVDMA diblock copolymers and the ability to chemically modify the PVDMA chains in situ to create a gradient in functionality are examined to investigate how the extent of functionalization affects the interfacial and surface properties. The introduction of a chemical gradient by controlled immersion allows reactive modification to generate position-dependent properties that are assessed by ellipsometry, attenuated total reflectance-Fourier transform infrared spectroscopy, contact angle measurements, and atomic force microscopy imaging. After functionalization of the azlactone rings with n-alkyl amines, ellipsometry confirms an increase in thickness and contact angle measurements support an increase in hydrophobicity along the substrate. These results are used to establish relationships between layer thickness, reaction time, position, and the extent of functionalization and demonstrate that gradual immersion into the functionalizing solution results in a linear change in chemical functionality along the surface. Finally, these findings broadly support efforts to produce tailored surfaces by in situ chemical modification, having application as tailored membranes, protein resistant surfaces, or sensors.

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

Dual Orbital Degeneracy Lifting in a Strongly Correlated Electron System

The local structure of NaTiSi 2 O 6 is examined across its Ti-dimerization orbital-assisted Peierls transition at 210 K. An atomic pair distribution function approach evidences local symmetry breaking preexisting far above the transition. The analysis unravels that, on warming, the dimers evolve into a short range orbital degeneracy lifted (ODL) state of dual orbital character, persisting up to at least 490 K. The ODL state is correlated over the length scale spanning ~ 6 sites of the Ti zigzag chains. Results imply that the ODL phenomenology extends to strongly correlated electron systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1988

Thermochemical stabilities and vibrational spectra of isomers of the chlorine oxide dimer

Molecular orbital calculations were performed to determine the relative thermochemical stabilities and IR vibrational spectra of isomers of the ClO dimer. Two straight-chain isomers (ClOOCl and ClOClO) and one branched species (ClClO2) were identified as energy minima on the Cl2O2 potential surface. It is shown that ClOOCl and ClClO2 are comparable in terms of stability, while ClOClO is about 11 kcal/mol higher in energy. The IR spectra obtained by Molina and Molina (1987) as a result of the reaction of chlorine atoms with ClO precursors are consistent with the production of the two most stable forms of Cl2O2.

Mcgrath, M. P.↗
DOE OSTI2019

Tissue-Specific Peculiarities of Vibration-Induced Hypoxia in Rabbit Liver and Kidney

Activity of the energy production systems in rabbit liver and kidney under conditions of unfavorable vibration exposure was studied by the polarography method using a galvanic-type closed oxygen sensor. The rate of oxidation of endogenous substrates by mitochondria was determined by the tissue and was 5.2±0.6 and 8.13±1.4 (ng-atom O)×min{sup —1}×mg{sup —1} protein for liver and kidney of intact animals, respectively. After 21 vibration sessions against the background of inhibition of NAD-dependent substrate oxidation in liver mitochondria, the rate metabolism of exogenous succinic acid increased by 44% and then decreased with prolongation of the effect, which indicated impaired function of the respiratory chain. Similar fluctuations of the parameters were revealed in kidney mitochondria, though their amplitude was lower. The study of bioenergetic mechanisms of hypoxia in various tissues makes it possible to determine the targets for the pharmacological action of antihypoxic drugs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Characterisation of magnesium silicate hydrate phases (M-S-H): A combined approach using synchrotron-based absorption-spectroscopy and ab initio calculations

The formation of magnesium-silicate-hydrate (M-S-H) phases has been observed at the interface between cement and argillaceous rock formations. In this study the atomic structure of M-S-H and magnesium-calcium-silicate-hydrate (M-C-S-H, a mixing with Ca) was performed by Mg K-edge X-ray absorption spectroscopy combined with ab-initio calculations. The results show that all magnesium containing phases have a TOT phyllosilicate structure with silica defects creating end of silica chains and an interlayer composed of Mg bound to hydroxide groups. Significant differences are observable between the M-S-H and the M-C-S-H. Firstly, the M-C-S-H phases have an enlarged structure compared to the M-S-H phases. Secondly, the results indicate that at least two geometrically distinct Mg octahedral sites are present for all phases. It is concluded that the Mg octahedra are attached to both Si tetrahedra in a manner similarly to that in talc and, to hydroxide groups in a manner similar to that in brucite.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of Initiator Density, Catalyst Concentration, and Surface Curvature on the Uniformity of Polymers Grafted from Spherical Nanoparticles

Polymer-grafted nanoparticles (PGNPs) are versatile hybrid materials whose properties critically depend on brush dimensions, uniformity, and grafting density. Herein, we systematically investigated how initiator density, catalyst concentration, and nanoparticle curvature govern the growth of poly(methyl methacrylate) (PMMA) brushes grafted from spherical SiO 2 nanoparticles via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). By tuning the initiator density through a combination of “active” and “dummy” silane initiators anchored on the nanoparticles’ surface and controlling the catalyst concentration, we reveal that increased initiator crowding and smaller surface curvature amplify steric hindrance, leading to decreased initiation efficiency and broader molecular weight distributions. Correlation with the corresponding unattached chains by ARGET ATRP suggests the presence of permanently inaccessible (“buried”) initiation sites, which are a characteristic of surface-grafted systems. At sufficient Cu catalyst concentrations, uniform brush growth is attained across different initiator densities, whereas decreased catalyst concentrations accentuate nonconcurrent initiation and propagation. These findings provide mechanistic insights into the interplay of initiator density, catalyst concentration, and surface curvature, offering design principles for tailoring the PGNP architecture. These results can guide the structural engineering of densely grafted surfaces, including nanoparticles and flat substrates, for applications in nanocomposites, photonics, and functional coatings.

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

Mapping the scattered family tree of fission neutrons

A statistically predicted tendency for neutrons produced inside fission reactors to form in clusters can cause asymmetrical energy production that is counterbalanced, at least in part, by the spontaneous fission of radioactive material in the reactor. This neutron-clustering effect theory has been demonstrated in a nuclear reactor for the first time and was described in an article published by Los Alamos National Laboratory. The findings of a study supported by the Department of Energy’s Nuclear Criticality Safety Program, funded through the National Nuclear Security Administration, and carried out in collaboration with two French nuclear agencies—the Institute for Radiological Protection and Nuclear Safety (IRSN) and the Atomic Energy Commission (CEA)—could improve reactor safety and lead to more accurate simulations, according to LANL. The team found that a complete die-off was avoided in the small reactor because spontaneous fission—nuclear splitting of radioactive material inside reactors that is not caused by direct impact from a fission neutron—creates more neutrons. The balance of fission chain reactions and spontaneous fission lessens the impact of energy bursts created by clustering neutrons.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

The molecular mechanism of robust macrophage immune responses induced by PEGylated molybdenum disulfide

Molybdenum disulfide (MoS 2 ), a representative hexagonal transition metal dichalcogenide (TMD), has been extensively exploited in biomedical applications due to its unique physicochemical properties and biocompatibility. However, the lack of adequate data regarding how MoS 2 activates immunological responses of macrophages remains a key concern for its risk assessment. Here, we employ a combined theoretical and experimental approach to investigate the interactions of MoS 2 and PEGylated MoS 2 (MoS 2 -PEG) with macrophages. We first perform molecular dynamics simulations to examine the atomic-detailed interactions of MoS 2 and MoS 2 -PEG nanoflakes with a realistic model of the macrophage membrane. We show that a small MoS 2 nanoflake (edge length of 2.86 nm) is capable of penetrating the macrophage membrane independent of its concentration. We also demonstrate that when initiated with a corner point-on configuration, the surface-bound PEG chains of MoS 2 -PEG hinder its membrane insertion process, leading to a prolonged passage through the membrane. Moreover, when placed in a face-on arrangement initially, the MoS 2 -PEG exhibits a lower binding free energy than pristine MoS 2 after its adsorption on the membrane surface. The PEG chains can even insert and get buried in the outer leaflet of the membrane, providing additional contact for membrane adsorption. Our flow cytometric experiments then show that the responses of macrophages to either MoS 2 -PEG or MoS 2 are significantly higher than that of the control (no nanomaterial stimulus), with MoS 2 -PEG eliciting stronger cytokine secretion than the pristine MoS 2 . The characteristics of slower/prolonged membrane penetration and stronger membrane adsorption of MoS 2 -PEG compared to pristine MoS 2 explain why it triggers more sustained stimulation and higher cytokine secretion in macrophages as observed in our experiments. Our findings reveal the underlying molecular mechanism of how MoS 2 -PEG influences the immune responses and suggest its potential applications in nanomedicine involving immune stimulation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Structural elucidation of the cis -prenyltransferase NgBR/DHDDS complex reveals insights in regulation of protein glycosylation

Cis-prenyltransferase (cis-PTase) catalyzes the rate-limiting step in the synthesis of glycosyl carrier lipids required for protein glycosylation in the lumen of endoplasmic reticulum. Here, we report the crystal structure of the human NgBR/DHDDS complex, which represents an atomic resolution structure for any heterodimeric cis-PTase. The crystal structure sheds light on how NgBR stabilizes DHDDS through dimerization, participates in the enzyme’s active site through its C-terminal -RXG- motif, and how phospholipids markedly stimulate cis-PTase activity. Comparison of NgBR/DHDDS with homodimeric cis-PTase structures leads to a model where the elongating isoprene chain extends beyond the enzyme’s active site tunnel, and an insert within the α3 helix helps to stabilize this energetically unfavorable state to enable long-chain synthesis to occur. These data provide unique insights into how heterodimeric cis-PTases have evolved from their ancestral, homodimeric forms to fulfill their function in long-chain polyprenol synthesis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Crystal structure of brimonidine hydrogen tartrate, (C 11 H 11 BrN 5 )(HC 4 H 4 O 6 )

The crystal structure of brimonidine hydrogen tartrate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Brimonidine hydrogen tartrate crystallizes in space groupP2 1 (#4) witha= 7.56032(2),b= 7.35278(2),c= 30.10149(9) Å,β= 90.1992(2)°,V= 1673.312(10) Å 3 , andZ= 4 at 295 K. The crystal structure consists of alternating layers of cations and anions parallel to theab-plane. Each of the hydrogen tartrate anions is linked to itself by very strong charge-assisted O–H⋯O hydrogen bonds into chains along thea-axis. Each hydroxyl group of each tartrate acts as a donor in an O–H⋯O or O–H⋯N hydrogen bond. One of these is intramolecular, but the other three are intermolecular. These hydrogen bonds link the hydrogen tartrate anions into layers parallel to theab-plane and also link the anion–cation layers. The protonated N atoms act as donors in N–H⋯O or N–H⋯N hydrogen bonds to the carboxyl groups of the tartrates and to a ring nitrogen atom. These link the cations and anions, as well as providing cation–cation links. The amino N atoms of the cations form N–H⋯O hydrogen bonds to hydroxyl groups of the anions. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®)

Materials Science↗
DOE OSTI2020

CryoEM structure of the low-complexity domain of hnRNPA2 and its conversion to pathogenic amyloid

hnRNPA2 is a human ribonucleoprotein (RNP) involved in RNA metabolism. It forms fibrils both under cellular stress and in mutated form in neurodegenerative conditions. Previous work established that the C-terminal low-complexity domain (LCD) of hnRNPA2 fibrillizes under stress, and missense mutations in this domain are found in the disease multisystem proteinopathy (MSP). However, little is known at the atomic level about the hnRNPA2 LCD structure that is involved in those processes and how disease mutations cause structural change. Here we present the cryo-electron microscopy (cryoEM) structure of the hnRNPA2 LCD fibril core and demonstrate its capability to form a reversible hydrogel in vitro containing amyloid-like fibrils. Whereas these fibrils, like pathogenic amyloid, are formed from protein chains stacked into β-sheets by backbone hydrogen bonds, they display distinct structural differences: the chains are kinked, enabling non-covalent cross-linking of fibrils and disfavoring formation of pathogenic steric zippers. Both reversibility and energetic calculations suggest these fibrils are less stable than pathogenic amyloid. Moreover, the crystal structure of the disease-mutation-containing segment (D290V) of hnRNPA2 suggests that the replacement fundamentally alters the fibril structure to a more stable energetic state. These findings illuminate how molecular interactions promote protein fibril networks and how mutation can transform fibril structure from functional to a pathogenic form.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Lipid composition dictates serum stability of reconstituted high-density lipoproteins: implications for in vivo applications

Nanolipoprotein particles (NLPs) are reconstituted high-density lipoproteins, consisting of a phospholipid bilayer stabilized by an apolipoprotein scaffold protein. This class of nanoparticle has been a vital tool in the study of membrane proteins, and in recent years has been increasingly used for in vivo applications. Previous studies demonstrated that the composition of the lipid bilayer component affects the stability of these particles in serum solutions. In the current study, NLPs assembled with phosphatidylcholine lipids featuring different acyl chain structures were systematically tested to understand the effect that lipid composition has on NLP stability in both neat serum and cell culture media supplemented with 10% serum by volume. The time at which 50% of the particles dissociate, as well as the fraction of the initial population that remains resistant to dissociation, were correlated to key parameters obtained from all-atom simulations of the corresponding lipid bilayers. A significant correlation was observed between the compressibility modulus of the lipid bilayer and particle stability in these complex biological milieu. These results can be used as a reference to tune the stability of these versatile biological nanoparticles for in vitro and in vivo applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2026

Molecular-Level Insights into the Influence of Ionic Liquids on the Structure and Dynamics of Neutral and Charged Polyimides

We use all-atom molecular dynamics simulations to investigate how increasing ionic functionalization influences polyimide (PI) behavior in ionic liquid (IL) solvation environments. Here, we examine three polymer systems with varying charge densities: a neutral polyimide [N−PI] containing imidazole rings and progressively introduce charge through quaternization to create singly [C−PI] + and doubly charged [C−2PI] 2+ variants across a wide range of IL concentration (0−90 wt %). Through comprehensive structural, mechanical, and electrostatic analyses, we reveal that polymer charge density plays a central role in shaping IL organization and interaction with the polymer matrix. At low IL content, charged systems exhibit strong electrostatic complexation, leading to chain compaction, localized ESP environments, and elevated dielectric constants. As IL concentration increases, the effect of the different polymer charge states becomes less significant. Notably, an intermediate composition regime at approximately 50 wt % IL is associated with changes in IL-rich domain connectivity and overall system behavior across all three PI systems.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Wide Band Gap Polymer with a Deep Highest Occupied Molecular Orbital Level Enables 14.2% Efficiency in Polymer Solar Cells

To simultaneously achieve low photon energy loss ( E loss ) and broad spectral response, the molecular design of the wide band gap (WBG) donor polymer with a deep HOMO level is of critical importance in fullerene-free polymer solar cells (PSCs). Herein, we developed a new benzodithiophene unit, i.e., DTBDT-EF, and conducted systematic investigations on a WBG DTBDT-EF-based donor polymer, namely, PDTB-EF-T. Due to the synergistic electron-withdrawing effect of the fluorine atom and ester group, PDTB-EF-T exhibits a higher oxidation potential, i.e., a deeper HOMO level (ca. –5.5 eV) than most well-known donor polymers. Hence, a high open-circuit voltage of 0.90 V was obtained when paired with a fluorinated small molecule acceptor (IT-4F), corresponding to a low E loss of 0.62 eV. Furthermore, side-chain engineering demonstrated that subtle side-chain modulation of the ester greatly influences the aggregation effects and molecular packing of polymer PDTB-EF-T. With the benefits of the stronger interchain π–π interaction, the improved ordering structure, and thus the highest hole mobility, the most symmetric charge transport and reduced recombination are achieved for the linear decyl-substituted PDTB-EF-T (P2)-based PSCs, leading to the highest short-circuit current density and fill factor (FF). Due to the high Flory–Huggins interaction parameter (χ), surface-directed phase separation occurs in the P2:IT-4F blend, which is supported by X-ray photoemission spectroscopy results and cross-sectional transmission electron microscope images. By taking advantage of the vertical phase distribution of the P2:IT-4F blend, a high power conversion efficiency (PCE) of 14.2% with an outstanding FF of 0.76 was recorded for inverted devices. Lastly, these results demonstrate the great potential of the DTBDT-EF unit for future organic photovoltaic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗