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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Efficient Mercury Capture Using Functionalized Porous Organic Polymer

The primary challenge in materials design and synthesis is achieving the balance between performance and economy for real-world application. Here, this issue is addressed by creating a thiol functionalized porous organic polymer (POP) using simple free radical polymerization techniques to prepare a cost-effective material with a high density of chelating sites designed for mercury capture and therefore environmental remediation. The resulting POP is able to remove aqueous and airborne mercury with uptake capacities of 1216 and 630 mg g -1 , respectively. The material demonstrates rapid kinetics, capable of dropping the mercury concentration from 5 ppm to 1 ppb, lower than the US Environmental Protection Agency's drinking water limit (2 ppb), within 10 min. Furthermore, the material has the added benefits of recyclability, stability in a broad pH range, and selectivity for toxic metals. These results are attributed to the material's physical properties, which include hierarchical porosity, a high density of chelating sites, and the material's robustness, which improve the thiol availability to bind with mercury as determined by X-ray photoelectron spectroscopy and X-ray absorption fine structure studies. Finally, the work provides promising results for POPs as an economical material for multiple environmental remediation applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Fatiguing contractions increase protein S-glutathionylation occupancy in mouse skeletal muscle

Protein S-glutathionylation is an important reversible post-translational modification implicated in redox signaling. Oxidative modifications to protein thiols can alter the activity of metabolic enzymes, transcription factors, kinases, phosphatases, and the function of contractile proteins. NADPH oxidase (NOX) associated reactive oxygen species (ROS), have been implicated in this redox signaling. However, the extent to which muscle contraction induces oxidative modifications in redox sensitive thiols is not known. In this study, we performed acute fatiguing contractions using an in vivo stimulation protocol on anesthetized CB6F1 (BALB/cBy x C57BL/6) mice. Contraction force and kinetics were monitored by a force transducer throughout the 15 minutes of fatiguing stimulations. The right (stimulated) and left (unstimulated) gastrocnemius were collected 60 minutes after the last stimulation and processed for redox proteomics assay for S-glutathionylation. Using a selective reduction with a glutaredoxin enzyme cocktail and resin-assisted capture technique, we quantified the levels of site-specific protein S-glutathionylation at rest and following fatiguing contractions in gastrocnemius muscles in adult mice. Redox proteomics revealed over 2,200 sites of S-glutathionylation modifications, of which 1290 were significantly increased after fatiguing contractions. Muscle contraction leads to the greatest increase in S-glutathionylation in the mitochondria and extracellular space and the smallest increase in the nucleus. Modification of proteins throughout the muscle fiber, including those associated with metabolism, muscle contraction, and stress response, are consistent with an important role for redox control of muscle physiology and adaptive processes. This study lays the groundwork for future investigation into the altered exercise adaptation associated with chronic conditions, such as sarcopenia, the age-related loss of muscle mass and function.

muscle contraction, Post-translational modificatio↗
DOE OSTI2021

Organic Modifiers Promote Furfuryl Alcohol Ring Hydrogenation via Surface Hydrogen-Bonding Interactions

Interactions between surface adsorbed species can affect catalyst reactivity, and thus, the ability to tune these interactions is of considerable importance. Deposition of organic modifiers provides one method of intentionally introducing controllable surface interactions onto catalyst surfaces. In this study, Pd/Al2O 3 catalysts were modified with either thiol or phosphonic acid (PA) ligands and tested in the hydrogenation of furanic species. The thiol modifiers were found to inhibit ring hydrogenation (RH) activity, with the degree of inhibition trending with the thiol surface coverage. This suggests that thiols do not strongly interact with the reactants and simply serve to block active sites on the Pd surface. PAs, on the other hand, were found to enhance RH when furfuryl alcohol (FA) was used as the reactant. Density functional theory calculations suggested that this enhancement was due to hydrogen-bonding interactions between FA-derived surface intermediates and PA modifiers. Here, installation of hydrogen-bonding groups on the Pd surface served to preferentially stabilize RH product states. Furthermore, the promotional effect on the RH of FA was observed to be greater when a higher-coverage PA was used, providing a rate more than twice that of the unmodified Pd/Al2O 3 . The results of this work suggest that organic ligands can be designed to impart tunable surface interactions on heterogeneous catalysts, providing an additional method of controlling catalytic performance.

09 BIOMASS FUELS↗
DOE OSTI2014

Proteomic Identification and Quantification of S-glutathionylation in Mouse Macrophages Using Resin-Assisted Enrichment and Isobaric Labeling

Protein S-glutathionylation (SSG) is an important regulatory posttranslational modification of protein cysteine (Cys) thiol redox switches, yet the role of specific cysteine residues as targets of modification is poorly understood. We report a novel quantitative mass spectrometry (MS)-based proteomic method for site-specific identification and quantification of S-glutathionylation across different conditions. Briefly, this approach consists of initial blocking of free thiols by alkylation, selective reduction of glutathionylated thiols and enrichment using thiol affinity resins, followed by on-resin tryptic digestion and isobaric labeling with iTRAQ (isobaric tags for relative and absolute quantitation) for MS-based identification and quantification. The overall approach was validated by application to RAW 264.7 mouse macrophages treated with different doses of diamide to induce glutathionylation. A total of 1071 Cys-sites from 690 proteins were identified in response to diamide treatment, with ~90% of the sites displaying >2-fold increases in SSG-modification compared to controls.. This approach was extended to identify potential SSG modified Cys-sites in response to H2O2, an endogenous oxidant produced by activated macrophages and many pathophysiological stimuli. The results revealed 364 Cys-sites from 265 proteins that were sensitive to S-glutathionylation in response to H2O2 treatment. These proteins covered a range of molecular types and molecular functions with free radical scavenging, and cell death and survival included as the most significantly enriched functional categories. Overall the results demonstrate that our approach is effective for site-specific identification and quantification of S-glutathionylated proteins. The analytical strategy also provides a unique approach to determining the major pathways and cell processes most susceptible to glutathionylation at a proteome-wide scale.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Organosilane-assisted selective etching strategy for fabrication of hollow/rattle-type mesoporous organosilica nanospheres

Highlights: • Effective fabrication of organic hollow/rattle-type mesoporous organosilica. • The addition of CTES could increase the porosity of the materials. • Pore-making agent (CTES) could be removed by alkali treatment without additional step. - Abstract: A facile strategy to fabricate hollow or rattle-type mesoporous silica nanospheres (HMSNs or RMSNs) with organic functional groups and porous shell was developed. Herein, thiol-HMSNs were obtained via treating vinyl-SiO{sub 1.5} @cyano&thiol-SiO{sub 1.5} prepared by using 3-mercaptopropyltrimethoxysilane (MPTMS) as organosilane precursor, vinyltriethoxysilane (VTES) as sacrificial template precursor and cyanoethyltriethoxysilane (CTES) as pore-making agent. In this method, CTES was co-condensed with MPTMS to form hybrid shell and played an important role in the formation of pore structures. When the volume ratio of MPTMS to CTES was 1:1, well-defined thiol-HMSNs with a specific surface area of 295.6 m{sup 2} g{sup −1} and pore volume of 0.51 cm{sup 3} g{sup −1} could be obtained. Moreover, [email protected] could also be synthesized through this method from three-layered structures (thiocyanato-SiO{sub 1.5} @vinyl-SiO{sub 1.5} @cyano&thiol-SiO{sub 1.5}). The as-prepared RMSNs presented good performance for the adsorption of 2, 4-dichloropheno in water. And this selective etching strategy was versatile and might be extended to fabricate more valuable organic hollow/rattle-type composites for different applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

TiO 2 Nanoparticles Enabling Photocatalytic Desulfurization for C–C Coupling Reaction Using Visible Light

We uncover a surface-mediated mechanism for visible-light-driven photocatalytic desulfurization of thiols on titanium dioxide (TiO 2 ) nanoparticles under LED illumination (>420 nm). Combined diffuse reflectance, infrared, and cryogenic electron paramagnetic resonance spectroscopy verify the formation of a surface thiol–Ti charge-transfer complex that introduces visible-light absorption into an otherwise UV-active reaction system. Selective photoexcitation of this surface complex drives interfacial charge transfer, directly activating the adsorbed thiol and inducing C–S bond scission without the band gap excitation of TiO 2 . The resulting carbon-centered radical intermediates are intercepted by styrene to form C–C coupling products. These results uncover a distinct surface-mediated photocatalytic mechanism in which charge-transfer complex formation governs both light absorption and chemical activation, providing a mechanistic framework for extending visible-light reactivity to wide-bandgap metal oxide photocatalysts.

addition of carbon radical to vinyl groups↗
DOE OSTI2017

Synthesis of thioether-containing carbosilane dendrimers with sterically shielded sulfur atoms

Carbosilane thiols were synthesized as the first- and second-generation (in silicon) dendrons. It was demonstrated that the resulting bulky thiols successfully undergo the thiol—ene addition to third-generation polyallyl carbosilane dendrimer as a photoinitiated radical reaction to give the corresponding thioether-containing derivatives with sterically shielded sulfur atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Gamma-glutamylcysteine protects ergothioneine-deficient Mycobacterium tuberculosis mutants against oxidative and nitrosative stress

Highlights: • EgtA is essential for gamma-glutamylcysteine biosynthesis. • EgtE is not essential for ergothioneine biosynthesis. • EgtC is partially compensated for in ergothioneine biosynthesis. • The production of gamma-glutamylcysteine is elevated in thiol-deficient M. tuberculosis mutants. • Gamma-glutamylcysteine protects thiol-deficient M. tuberculosis mutants. Mycobacterium tuberculosis (M.tb.), the causative agent of tuberculosis (TB), cannot synthesize GSH, but synthesizes two major low molecular weight thiols namely mycothiol (MSH) and ergothioneine (ERG). Gamma-glutamylcysteine (GGC), an intermediate in GSH synthesis, has been implicated in the protection of lactic acid bacteria from oxidative stress in the absence of GSH. In mycobacteria, GGC is an intermediate in ERG biosynthesis, and its formation is catalysed by EgtA (GshA). GGC is subsequently used by EgtB in the formation of hercynine-sulphoxide-GGC. In this study, M.tb. mutants harbouring unmarked, in-frame deletions in each of the fives genes involved in ERG biosynthesis (egtA, egtB, egtC, egtD and egtE) or a marked deletion of the mshA gene (required for MSH biosynthesis) were generated. Liquid chromatography tandem mass spectrometry analyses (LC-MS) revealed that the production of GGC was elevated in the MSH-deficient and the ERG-deficient mutants. The ERG-deficient ΔegtB mutant which accumulated GGC was more resistant to oxidative and nitrosative stress than the ERG-deficient, GGC-deficient ΔegtA mutant. This implicates GGC in the detoxification of reactive oxygen and nitrogen species in M.tb.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Furoxans (1,2,5-Oxadiazole-N-Oxides) as Novel NO Mimetic Neuroprotective and Procognitive Agents

Furoxans (1,2,5-oxadiazole-N-oxides) are thiol-bioactivated NO-mimetics that have not hitherto been studied in the CNS. Incorporation of varied substituents adjacent to the furoxan ring system led to modulation of reactivity toward bioactivation, studied by HPLC-MS/MS analysis of reaction products. Attenuated reactivity unmasked the cytoprotective actions of NO in contrast to the cytotoxic actions of higher NO fluxes reported previously for furoxans. Neuroprotection was observed in primary neuronal cell cultures following oxygen glucose deprivation (OGD). Neuroprotective activity was observed to correlate with thiol-dependent bioactivation to produce NO{sub 2}{sup -}, but not with depletion of free thiol itself. Neuroprotection was abrogated upon cotreatment with a sGC inhibitor, ODQ, thus supporting activation of the NO/sGC/CREB signaling cascade by furoxans. Long-term potentiation (LTP), essential for learning and memory, has been shown to be potentiated by NO signaling, therefore, a peptidomimetic furoxan was tested in hippocampal slices treated with oligomeric amyloid-{beta} peptide (A{beta}) and was shown to restore synaptic function. The novel observation of furoxan activity of potential therapeutic use in the CNS warrants further studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Transition voltages of vacuum-spaced and molecular junctions with Ag and Pt electrodes

The transition voltage of vacuum-spaced and molecular junctions constructed with Ag and Pt electrodes is investigated by non-equilibrium Green's function formalism combined with density functional theory. Our calculations show that, similarly to the case of Au-vacuum-Au previously studied, the transition voltages of Ag and Pt metal-vacuum-metal junctions with atomic protrusions on the electrode surface are determined by the local density of states of the p-type atomic orbitals of the protrusion. Since the energy position of the Pt 6p atomic orbitals is higher than that of the 5p/6p of Ag and Au, the transition voltage of Pt-vacuum-Pt junctions is larger than that of both Ag-vacuum-Ag and Au-vacuum-Au junctions. When one moves to analyzing asymmetric molecular junctions constructed with biphenyl thiol as central molecule, then the transition voltage is found to depend on the specific bonding site for the sulfur atom in the thiol group. In particular agreement with experiments, where the largest transition voltage is found for Ag and the smallest for Pt, is obtained when one assumes S binding at the hollow-bridge site on the Ag/Au(111) surface and at the adatom site on the Pt(111) one. This demonstrates the critical role played by the linker-electrode binding geometry in determining the transition voltage of devices made of conjugated thiol molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Reverse Self-Assembly: (111)-Oriented Gold Crystallization at Alkylthiol Monolayer Templates

It has long been known that thiol-terminated molecules self-assemble as commensurate monolayers on Au(111) surfaces. By spreading floating octadecanethiol monolayers on aqueous solutions of chloroauric acid (HAuCl{sub 4}) and using x rays to reduce the gold ions as well as to probe the structure, we have observed the nucleation of (111)-oriented Au nanoparticles at thiol surfaces. This process may be similar to the formation of biogenic gold by bacteria. The thiol monolayer acts as a 'soft template,' changing its structure as Au crystals form so that there is a {radical}3 x {radical}3 commensurate relationship.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Enhanced removal of aqueous hexavalent chromium (Cr(VI)) as a nuclear industry water contaminant by a polymer-modified activated carbon - 18354

Cr (VI) is produced through industrial processes including nuclear activities. It is one of the highly toxic pollutants defined by US EPA, classified as a know human carcinogen. Some of the health effects caused by Cr (VI) exposure are: severe skin and eye damage, nose, throat and lung irritations, damage to the mucous membranes results in ulcers. At Hanford and Savannah River nuclear sites in the United States, the chromium concentration vary from 20 - 30,000 μg/L in water. The maximum level of Cr(VI) for drinking water has been regulated by California Environmental Protection Agency (Cal/EPA) at 0.01 mg/L. Activated carbon (AC) is a widely-used adsorbent for water treatment. However, AC has a limited selectivity for chromium species. Thiol compounds (R-S-H) have also been reported to reduce Cr(VI) to Cr(III) which is harmless. To enhance the removal efficiency of chromium, polysulfide rubber polymer containing thiol was synthesized and coated on Activated Carbon (AC-PSR). Polymer coating on activated carbon enhances its sorption capacity by increasing the chromium binding sites. Conclusions: Polysulfide rubber polymer successfully coated on granular activated carbon. AC-PSR provided greater Cr(VI) removal capacity, due to the reduction of Cr(VI) to Cr(III) by thiol compounds in PSR, as well as physical adsorption onto AC. Future Work: Investigating intra-particle diffusion mechanism of of Cr(VI) in AC-PSR. Evaluating reusability of AC-PSR. Investigating the competition of mercury and chromium ions to be adsorbed onto AC-PSR.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

A Naked-Eye Visible and Fluorescence 'Turn-On' Probe for Acetylcholinesterase Assay and the Discrimination of Biothiols

We demonstrate the utility of 4-chloro-7-nitrobenzofurazan (NBD-Cl), a simple, low-cost probe, for colorimetrically and fluorescently detecting and differentiating similar thiol species, including cysteine, homocysteine, and glutathione, as well as for assaying acetylcholinesterase (AChE) activity. This assay is a potential tool for investigating thiol functions in disease and diagnosis, and for screening AChE inhibitors. We envision that this versatile probe, which is commercially available and inexpensive, will be useful for further elucidating the roles of thiols in biology and also shows applicability for analysis of AChE inhibitors in physiological samples.

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

Evaluation of engineered sorbents for the sorption of mercury from contaminated bank soils: a column study

Abstract As a global environmental pollutant, mercury (Hg) threatens our water resources and presents a substantial risk to human health. The rate and extent of immobilization of Hg 2+ (hereafter, Hg) on engineered sorbents (Thiol-SAMMS®, pine biochar, SediMite™, Organoclay™ PM-199, and quartz sand as a control) was evaluated using flow-through column experiments. The effectiveness of the sorbents was based on (1) the percentage of Hg removed in relation to the total amount of Hg passing the sorbent column, and (2) the rate of Hg uptake compared to the nonreactive tracer bromide (Br − ). All sorbents removed Hg to a certain extent, but none of the sorbents removed all the Hg introduced to the columns. Thiol-SAMMS showed the highest mean percentage of Hg removed (87% ± 2.9%), followed by Organoclay PM-199 (71% ± 0.4%), pine biochar (57% ± 22.3%), SediMite (61% ± 0.8%), and the control quartz sand (11% ± 5.6%). Thiol-SAMMS was the only sorbent to exhibit retardation of Hg in comparison to the conservative tracer Br − . For the remaining sorbents, Br − along with low concentrations of Hg were eluted within the first 3 pore volumes, indicating limited retardation of Hg. Overall, removal of Hg by sorbents was substantial, suggesting that sorbents might be suitable for deployment in contaminated environments. High concentrations of DOM leaching from the soil columns likely influenced the speciation of Hg and inhibited sorption to the sorbents. Incomplete removal of Hg by any sorbent suggests that additional optimization is needed to increase efficiency.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Direct determination of the redox status of cysteine residues in proteins in vivo

Highlights: • A new DNA-maleimide which is cleaved by UV irradiation, DNA-PCMal, was developed. • DNA-PCMal can be used like DNA-Mal to analyze the redox state of cysteine residues. • It is useful for detecting the thiol redox status of a protein in vivo by Western blotting method. • Thus, DNA-PCMal can be a powerful tool for redox proteomics analysis. - Abstract: The redox states of proteins in cells are key factors in many cellular processes. To determine the redox status of cysteinyl thiol groups in proteins in vivo, we developed a new maleimide reagent, a photocleavable maleimide-conjugated single stranded DNA (DNA-PCMal). The DNA moiety of DNA-PCMal is easily removed by UV-irradiation, allowing DNA-PCMal to be used in Western blotting applications. Thereby the state of thiol groups in intracellular proteins can be directly evaluated. This new maleimide compound can provide information concerning redox proteins in vivo, which is important for our understanding of redox networks in the cell.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Resin-assisted Enrichment of N-terminal Peptides for Characterizing Proteolytic Processing

Proteolytic processing is a ubiquitous, irreversible posttranslational modification that plays an important role in cellular regulation in all living organisms. Herein we report a resin-assisted positive selection method for specifically enriching protein N-terminal peptides to facilitate the characterization of proteolytic processing events by liquid chromatography-tandem mass spectrometry. In this approach, proteins are initially reduced and alkylated and their lysine residues are converted to homoarginines. Then, protein N-termini are selectively converted to reactive thiol groups. We demonstrate that these sequential reactions were achieved with nearly quantitative efficiencies. Thiol-containing N-terminal peptides are then captured (>98% efficiency) by a thiol-affinity resin, a significant improvement over the traditional avidin/biotin enrichment. Application to cell lysates of Aspergillus niger, a filamentous fungus of interest for biomass degradation, enabled the identification of 1672 unique protein N-termini and proteolytic cleavage sites from 690 unique proteins.

Environmental Molecular Sciences Laboratory↗