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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Oxidation of dissolved elemental mercury by thiol compounds under anoxic conditions

Mercuric mercury, Hg(II), forms strong complexes with thiol compounds that commonly dominate Hg(II) speciation in natural freshwater. However, reactions between dissolved elemental Hg(0) and thiols are not well understood although these processes are likely to be important in determining Hg speciation and geochemical cycling in the environment. In this study, reaction rates and mechanisms between dissolved Hg(0) and a number of selected organic ligands with varying molecular structures and sulfur (S) oxidation states were determined to assess the role of these ligands in Hg(0) redox transformation. We found that all thiols caused oxidation of Hg(0) under anoxic conditions but, contrary to expectation, compounds with higher S-oxidation states (e.g., disulfide) than thiols exhibited little or no reactivity with Hg(0) at pH 7. The rate and extent of Hg(0) oxidation varied widely, with smaller aliphatic thiols showing the greatest degree of oxidation. The mechanism of the oxidation is attributed to a two-step process involving adsorption of Hg(0) to thiols followed by the charge transfer from Hg(0) to electron acceptors. These observations demonstrate a unique thiol-induced oxidation pathway of dissolved Hg(0), with important implications for the redox transformation, speciation, and bioavailability of Hg for microbial methylation in anoxic environments.

Zheng, Wang↗
DOE OSTI2021

Surface-Induced Deprotonation of Thiol Ligands Impacts the Optical Response of CdS Quantum Dots

Cadmium chalcogenide quantum dots (QDs) passivated by thiol-based ligands exhibit several advantages in their applications in lighting, sensing, and imaging technologies. However, their emission is sensitive to thiol concentrations, pH conditions, and temperatures. Using calculations based on the density functional theory, we identify conditions for thiol/thiolate equilibrium at the CdS QD surface that either eliminate or introduce optically inactive hole trap states favoring or disfavoring the emission. Our calculations indicate much weaker interactions between the QD and protonated species (thiols), compared to their deprotonated counterparts (thiolates). Additionally, the surface of CdS QD facilitates the partial deprotonation of thiols, leading to the formation of an additional stable networking conformation where the proton is shared between the ligand and the QD surface. Thiolates strongly reduce the optical intensity of low-energy transitions in CdS QDs, contributing thiolate-localized hole trap states at the QD band gap. However, networking between the thiols and the surface, as well as the presence of native ligands such as primary amines, stabilize such trap states brightening the lowest optical transitions. This explains the increased emission of thiol-passivated QDs at lower concentrations in neutral or acidic solutions. Surface-mediated bias toward deprotonated species and their contribution to optically inactive states also rationalizes irreversible emission quenching and bleaching in the CdSe/CdS QDs exposed to high temperatures or intensive laser pulse.

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

Coordination chemistry controls the thiol oxidase activity of the B 12 -trafficking protein CblC

The cobalamin or B 12 cofactor supports sulfur and one-carbon metabolism and the catabolism of odd-chain fatty acids, branched-chain amino acids, and cholesterol. CblC is a B 12 -processing enzyme involved in an early cytoplasmic step in the cofactor-trafficking pathway. It catalyzes the glutathione (GSH)-dependent dealkylation of alkylcobalamins and the reductive decyanation of cyanocobalamin. CblC from Caenorhabditis elegans (ceCblC) also exhibits a robust thiol oxidase activity, converting reduced GSH to oxidized GSSG with concomitant scrubbing of ambient dissolved O2. The mechanism of thiol oxidation catalyzed by ceCblC is not known. In this study, we demonstrate that novel coordination chemistry accessible to ceCblC-bound cobalamin supports its thiol oxidase activity via a glutathionyl-cobalamin intermediate. Deglutathionylation of glutathionyl-cobalamin by a second molecule of GSH yields GSSG. The crystal structure of ceCblC provides insights into how architectural differences at the α- and β-faces of cobalamin promote the thiol oxidase activity of ceCblC but mute it in wild-type human CblC. The R161G and R161Q mutations in human CblC unmask its latent thiol oxidase activity and are correlated with increased cellular oxidative stress disease. In summary, we have uncovered key architectural features in the cobalamin-binding pocket that support unusual cob(II)alamin coordination chemistry and enable the thiol oxidase activity of ceCblC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Nucleophilic Thiols Reductively Cleave Ether Linkages in Lignin Model Polymers and Lignin

Lignin may serve as a renewable feedstock for the production of chemicals and fuels if mild, scalable processes for its depolymerization can be devised. The use of small organic thiols represents a bioinspired strategy to cleave the β–O–4 bond, the most common linkage in lignin. In the present study, synthetic β–O–4 linked polymers were treated with organic thiols, yielding up to 90 % cleaved monomer products. Lignin extracted from poplar was also treated with organic thiols resulting in molecular weight reductions as high as 65 % (Mn) in oxidized lignin. Thiol–based cleavage of other lignin linkages was also explored in small–molecule model systems to uncover additional potential pathways by which thiols might depolymerize lignin. The success of thiol–mediated cleavage on model dimers, polymers, and biomass–derived lignin illustrates the potential utility of small redox–active molecules to penetrate complex polymer matrices for depolymerization and subsequent valorization of lignin into fuels and chemicals.

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

Selective Electrocatalytic Reduction of CO 2 into CO at Small, Thiol-Capped Au/Cu Nanoparticles

The electrochemical CO 2 reduction reaction (CO 2 RR) is a promising approach for converting fossil fuel emissions into environmentally sustainable chemicals and fuels. The ability to control the surface structure of CO 2 RR nanocatalysts provides an opportunity to tune product selectivity. Bimetallic gold–copper catalysts have been identified as emerging electrocatalyst candidates, but Cu incorporation typically lowers product selectivity compared with pure Au. Here we show sustained CO selectivity and activity up to 49% Cu content in small (<2 nm), thiol-capped Au/Cu nanoparticles (NPs). Bimetallic NPs containing 49% Cu selectivity converted CO 2 into CO with 100 ± 6% CO Faradaic efficiency and average mass activity of ~500 mA/mg during a 12 h electrolysis experiment at –0.8 V vs RHE. Au/Cu NPs synthesized without thiol ligands selectively produced H 2 , whereas larger (>10 nm), thermally dethiolated Au/Cu NPs produced a wider product distribution including H 2 , CO, and C 2 H 4 . Density functional theory (DFT) modeling of CO 2 RR and H 2 evolution at realistic, thiol-capped Au/Cu NP structures indicated that copper–thiol surface structures sustained CO selectivity by stabilizing key *CO intermediates while making *H binding less favorable. Calculations also predicted that removing a significant fraction of the thiol ligands would increase *CO binding strength such that desorption of CO product molecules could become the most thermodynamically challenging step. This result, coupled with increased *H stability on dethiolated nanoclusters, points to decreased CO 2 RR selectivity for small, ligand-free catalysts, which is in line with experimental observations from our group and others. Here, our results demonstrate that thiol-ligand surface structures can sustain the CO selectivity of bimetallic Au/Cu NPs and reduce precious metal requirements for CO 2 RR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Resin-assisted enrichment of thiols as a general strategy for proteomic profiling of cysteine-based reversible modifications

Reversible modifications on cysteine thiols play a significant role in redox signaling and regulation. A number of reversible redox modifications, including disulfide formation, S-nitrosylation, and S-glutathionylation, have been recognized for their significance in various physiological and pathological processes. Here we describe in detail a resin-assisted thiol-affinity enrichment protocol for both biochemical and proteomics applications. This protocol serves as a general approach for specific isolation of thiol-containing proteins or peptides derived from reversible redox-modified proteins. This approach utilizes thiol-affinity resins to directly capture thiol-containing proteins or peptides through a disulfide exchange reaction followed by on-resin protein digestion and on-resin multiplexed isobaric labeling to facilitate LC-MS/MS based quantitative site-specific analysis of redox modifications. The overall approach requires a much simpler workflow with increased specificity compared to the commonly used biotin switch technique. By coupling different selective reduction strategies, the resin-assisted approach provides the researcher with a useful tool capable of enriching different types of reversible modifications on protein thiols. Procedures for selective enrichment and analyses of S-nitrosylation and total reversible cysteine oxidation are presented to demonstrate the utility of this general strategy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Methods for lignin depolymerization using thiols

The disclosure relates to a method for depolymerizing lignin. The method includes reacting a lignin compound with a thiol compound to depolymerize the lignin compound and to form a depolymerized lignin product having a reduced molecular weight relative to the lignin compound prior to reacting. The method can further include forming an oxidized thiol reaction product between two thiol groups from one or more thiol compounds, and then reducing the oxidized thiol reaction product to re-form or regenerate the thiol compound for further lignin depolymerization.

09 BIOMASS FUELS↗
DOE OSTI2020

Highly Tunable Thiol-Ene Photoresins for Volumetric Additive Manufacturing

Volumetric additive manufacturing (VAM) forms complete 3D objects in a single photocuring operation without layering defects, enabling 3D printed polymer parts with mechanical properties similar to their bulk material counterparts. This study presents the first report of VAM-printed thiol-ene resins. With well-ordered molecular networks, thiol-ene chemistry accesses polymer materials with a wide range of mechanical properties, moving VAM beyond the limitations of commonly used acrylate formulations. Since free-radical thiol-ene polymerization is not inhibited by oxygen, the nonlinear threshold response required in VAM is introduced by incorporating 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a radical scavenger. Tuning of the reaction kinetics is accomplished by balancing inhibitor and initiator content. Coupling this with quantitative measurements of the absorbed volumetric optical dose allows control of polymer conversion and gelation during printing. Importantly, this work thereby establishes the first comprehensive framework for spatial–temporal control over volumetric energy distribution, demonstrating structures 3D printed in thiol-ene resin by means of tomographic volumetric VAM. Mechanical characterization of this thiol-ene system, with varied ratios of isocyanurate and triethylene glycol monomers, reveals highly tunable mechanical response far more versatile than identical acrylate-based resins. This broadens the range of materials and properties available for VAM, taking another step toward high-performance printed polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Pore surface engineering in a zirconium metal–organic framework via thiol-ene reaction

A porous olefin-functionalized Zr(IV)-based metal–organic framework, denoted as UiO-68-allyl, has been constructed. Our results clearly demonstrated that the surface of UiO-68-allyl could be decorated with organic molecule (ethanethiol) via thiol-ene reaction. More importantly, the crystallinity of the framework were maintained during the post-synthetic modification process. However, the microporosity of the framework is retained but the surface area decreased, due to the grafting of ethylthio groups into the pores. From our studies, we can conclude that the strategy of post-synthetic modification of UiO-68-allyl via thiol-ene reaction may be general. Furthermore, we may anchor other desired functional group onto the pore walls in Zr-MOFs via thiol-ene reaction, enabling more potential applications. - graphical abstract: In this manuscript, we reported the post-synthetic modification of an olefin-functionalized Zr(IV)-based metal–organic framework via thiol-ene reaction. - Highlights: • A porous olefin-functionalized Zr(IV)-based metal–organic framework has been constructed. • The surface of olefin-functionalized Zr-MOF could be decorated with organic molecules via thiol-ene reaction. • The crystallinity and permanent porosity of the framework were maintained during the post-synthetic modification process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Important Roles of Thiols in Methylmercury Uptake and Translocation by Rice Plants

We report the bioaccumulation of the neurotoxin methylmercury (MeHg) in rice is a significant concern due to its potential risk to humans. Thiols have been known to affect MeHg bioavailability in microorganisms, but how thiols influence MeHg accumulation in rice plants remains unknown. Here, we investigated effects of common low-molecular-weight thiols, including cysteine (Cys), glutathione (GSH), and penicillamine (PEN), on MeHg uptake and translocation by rice plants. Results show that rice roots can rapidly take up MeHg, and this process is influenced by the types and concentrations of thiols in the system. The presence of Cys facilitated MeHg uptake by roots and translocation to shoots, while GSH could only promote MeHg uptake, but not translocation, by roots. Conversely, PEN significantly inhibited MeHg uptake and translocation to shoots. Using labeled 13 Cys assays, we also found that MeHg uptake was coupled with Cys accumulation in rice roots. Moreover, analyses of comparative transcriptomics revealed that key genes associated with metallothionein and SULTR transporter families may be involved in MeHg uptake. These findings provide new insights into the uptake and translocation of MeHg in rice plants and suggest potential roles of thiol attributes in affecting MeHg bioavailability and bioaccumulation in rice.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Probing the thiol-gold planar interface by spin polarized tunneling

Reports of induced magnetism at thiol-gold interface have generated considerable recent interest. In these studies, the sample magnetization was generally measured by superconducting quantum interference device magnetometry which has limitation in determining surface and interface magnetism. In this work, we have fabricated planar tunnel junctions incorporating a thiol-gold interface. An observed room temperature humidity effect together with low temperature inelastic electron tunneling spectroscopy confirmed the existence of a thiol-gold interface in the organic-inorganic hybrid heterostructure. Spin polarized tunneling measurements were performed to probe the spin polarization at the thiol-gold interface; however, the obtained spin polarized tunneling spectra indicate no measurable spin polarization at the thiol-gold interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The use of a mercury biosensor to evaluate the bioavailability of mercury-thiol complexes and mechanisms of mercury uptake in bacteria

We discuss as mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS) 2 ) and Hg-glutathione (Hg(GSH) 2 ) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH) 2 was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Redox and Thiols in Archaea

Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.

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

Proteome-wide Light/Dark Modulation of Thiol Oxidation in Cyanobacteria Revealed by Quantitative Site-Specific Redox Proteomics

Reversible protein thiol oxidation is an essential regulatory mechanism of photosynthesis, metabolism, and gene expression in photosynthetic organisms. Herein, we present the first proteome-wide quantitative site-specific profiling of in vivo dynamics of thiol oxidation modulated by light/dark in cyanobacterium Synechocystis sp. PCC 6803, an oxygenic photosynthetic prokaryote. Our proteomic approach integrates resin-assisted enrichment with isobaric labeling to enable site-specific and quantitative measurements of reversibly oxidized thiols. The redox dynamics of ~2,200 cysteine sites from 1,060 proteins under different conditions (light, dark, and in the presence of a photosystem II inhibitor DCMU) were quantified. The results revealed broad proteome-wide changes in thiol oxidation in many key biological processes including photosynthesis, carbon fixation, and glycolysis. Moreover, the redox sensitivity data provides a good prediction of potential functional cysteine sites for proteins of interest. Together, our findings provided significant novel insights into the broad redox regulation of photosynthetic organisms.

redox proteomics, photosynthesis, Synechocystis 68↗
DOE OSTI2024

Embedding Thiols into Choline Phosphate Polymer Zwitterions

Abstract The compositional scope of polymer zwitterions has grown significantly in recent years and now offers designer synthetic materials that are broadly applicable across numerous areas, including supracolloidal structures, electronic materials interfaces, and macromolecular therapeutics. Among recent developments in polymer zwitterion syntheses are those that allow insertion of reactive functionality directly into the zwitterionic moiety, yielding new monomer and polymer structures that hold potential for maximizing the impact of zwitterions on the macromolecular materials chemistry field. This manuscript describes the preparation of zwitterionic choline phosphate (CP) methacrylates containing either aromatic or aliphatic thiols embedded directly into the zwitterionic moiety. The polymerization of these functional CP methacrylates by reversible addition‐fragmentation chain‐transfer methodology yields polymeric zwitterionic thiols containing protected thiol functionality in the zwitterionic units. After polymerization, the protected thiols are liberated to yield thiol‐rich polymer zwitterions which serve as precursors to subsequent reactions that produce polymer networks as well as polymer‐protein bioconjugates.

Polymer Science↗
DOE OSTI2025

Selective Adsorption of Thiol-Containing Molecules on Copper Sulfide Surfaces via Molecule–Surface Disulfide Bridges

Recent results in the fields of nanoenhanced agriculture and expanding interest in prebiotic chemistry have placed increased emphasis on understanding the chemically selective interaction of small molecules with the surfaces of metal sulfides. Here, we present an integrated experimental and computational study of the interaction of thiol-containing molecules with copper sulfide (covellite) surfaces in aqueous media. In situ Fourier-transform infrared (FTIR) measurements and ex situ X-ray photoelectron spectroscopy (XPS) measurements show that molecules bearing free thiol groups, including glutathione and cysteine, bind strongly to CuS (covellite) nanoparticles and to CuS (001) single crystals, while control studies show that similar molecules lacking the free thiol group exhibit much less binding. Additional experiments show that these thiol-containing molecules interact transiently with CuO nanoparticle surfaces but are readily removed by rinsing. The FTIR and XPS experiments demonstrate that adsorption of molecular thiols to CuS surfaces occurs in a chemically selective manner. Further experimental studies and density functional calculations show that the preferred mode of binding is through the surface S atoms, forming a Solid–S–S–Molecule disulfide linkage. While the role of disulfide linkages in controlling structure and function of proteins and other biomolecules is widely known, the formation of surface disulfide linkages as a motif for covalent molecular binding at surfaces has not been established previously.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and Optical Properties of Thiol Functionalized CdSe/ZnS (Core/Shell) Quantum Dots by Ligand Exchange

The colloidal photoluminescent quantum dots (QDs) of CdSe (core) and CdSe/ZnS (core/shell) were synthesized at different temperatures with different growth periods. The optical properties (i.e., UV/Vis spectra and photoluminescent emission spectra) of the resulting QDs were investigated. The CdSe/ZnS QDs exhibited higher photoluminescent (PL) efficiency and stability than their corresponding CdSe core QDs. Ligand exchange with various thiol molecules was performed to replace the initial surface passivation ligands, that is, trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), and the optical properties of the surface-modified QDs were studied. The thiol ligand molecules used included 1,4-benzenedimethanethiol, 1,16-hexadecanedithiol, 1,11-undecanedithiol, 11-mercapto-1-undecanol, and 1,8 octanedithiol. After the thiol functionalization, the CdSe/ZnS QDs exhibited significantly enhanced PL efficiency and storage stability. Besides surface passivation effect, such enhanced performance of thiol-functionalized QDs could be due to self-assembly formation of dimer/trimer clusters, in which QDs are linked by dithiol molecules. Effects of ligand concentration, type of ligand, and heating on the thiol stabilization of QDs were also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Thiol-based pathways in the thylakoid lumen and their role in photoprotection

The long-term goal of this research is to elaborate the catalysis of thiol-disulfide transactions in the thylakoid lumen, a compartment required for transducing energy via photophosphorylation. The molecular identity of the redox players catalyzing thiol-disulfide exchanges, their relevant targets of action in vivo and how thiol-disulfide chemistry in general controls photosynthesis are the experimental questions this research aims to address. Through previous work, we documented the requirement of catalyzed disulfide formation and reduction for the biogenesis of two photosynthetic enzymes, namely Photosystem II and the cytochrome b6f complex. We established that dedicated trans-thylakoid pathways operate in these processes by delivering reducing and oxidizing power to cysteine-containing subunits of the photosynthetic complexes, which are localized in the lumen compartment. Here we focused on CCDA, CCS4 and CCS5/HCF164, the components of the disulfide-reducing pathway which maintains the heme binding cysteines of apoforms of plastid cytochrome c in the reduced form prior to covalent heme ligation. We showed that CCS4 and CCS5 operate in functionally redundant pathways for the supply of reducing power and postulate a role for CCS4 in recruiting the source of reductants to CCDA or controlling the CCDA-dependent transduction of reducing equivalents. We also demonstrate the disulfide reducing pathway operates to counter thiol oxidation of the heme-binding cysteines by disulfide forming enzyme LTO1 in the thylakoid lumen.

59 BASIC BIOLOGICAL SCIENCES↗