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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Neutral rhenium( i ) tricarbonyl complexes with sulfur-donor ligands: anti-proliferative activity and cellular localization

Rhenium(I) tricarbonyl complexes are widely studied for their cell imaging properties and anti-cancer and anti-microbial activities, but the complexes with S-donor ligands remain relatively unexplored. A series of six fac-[Re(NN)(CO) 3 (SR)] complexes, where (NN) is 2,2'-bipyridyl (bipy) or 1,10-phenanthroline (phen), and RSH is a series of thiocarboxylic acid methyl esters, have been synthesized and characterized. Cellular uptake and anti-proliferative activities of these complexes in human breast cancer cell lines (MDA-MB-231 and MCF-7) were generally lower than those of the previously described fac-[Re(NN)(CO) 3 (OH 2 )]+ complexes; however, one of the complexes, fac-[Re(CO) 3 (phen)(SC(Ph)CH 2 C(O)OMe)] (3b), was active (IC 50 ~ 10 μM at 72 h treatment) in thiol-depleted MDA-MB-231 cells. Moreover, unlike fac-[Re(CO) 3 (phen)(OH 2 )]+, this complex did not lose activity in the presence of extracellular glutathione. Taken together these properties show promise for further development of 3b and its analogues as potential anti-cancer drugs for co-treatment with thiol-depleting agents. Conversely, the stable and non-toxic complex, fac-[Re(bipy)(CO) 3 (SC(Me)C(O)OMe)] (1a), predominantly localized in the lysosomes of MDA-MB-231 cells, as shown by live cell confocal microscopy (λ ex = 405 nm, λ em = 470–570 nm). It is strongly localized in a subset of lysosomes (25 μM Re, 4 h treatment), as shown by co-localization with a Lysotracker dye. Longer treatment times with 1a (25 μM Re for 48 h) resulted in partial migration of the probe into the mitochondria, as shown by co-localization with a Mitotracker dye. These properties make complex 1a an attractive target for further development as an organelle probe for multimodal imaging, including phosphorescence, carbonyl tag for vibrational spectroscopy, and Re tag for X-ray fluorescence microscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Olivine Weathering aud Sulfate Formation Under Cryogenic Conditions

High resolution photography and spectroscopy of the martian surface (MOC, HiRISE) from orbit has revolutionized our view of Mars with one of the most important discoveries being wide‐spread layered sedimentary deposits associated with sulfate minerals across the low to mid latitude regions of Mars. The mechanism for sulfate formation on Mars has been frequently attributed to playa‐like evaporative environments under prolonged warm conditions. An alternate view of the ancient martian climate contends that prolonged warm temperatures were never present and that the atmosphere and climate has been similar to modern conditions throughout most of its history. This view has had a difficult time explaining the sedimentary history of Mars and in particular the presence of sulfate minerals which seemingly need more water. We suggest here that mixtures of atmospheric aerosols, ice, and dust have the potential for creating small films of cryo‐concentrated acidic solutions that may represent an important unexamined environment for understanding weathering processes on Mars. This study seeks to test whether sulfate formation may be possible at temperatures well below 0degC in water limited environments removing the need for prolonged warm periods to form sulfates on early Mars. To test this idea we performed laboratory experiments to simulate weathering of mafic minerals under Mars‐like conditions. The weathering rates measured in this study suggest that fine grained olivine on Mars would weather into sulfate minerals in short time periods if they are exposed to H2SO4 aerosols at temperatures at or above ‐40degC. In this system, the strength of the acidic solution is maximized through eutectic freezing in an environment where the silicate minerals are extremely fine grained and have high surface areas. This provides an ideal environment despite the very low temperatures. On Mars the presence of large deposits of mixed ice and dust is undisputed. The presence of substantial sulfur‐rich volcanism, and sulfur‐rich surface deposits also makes it very likely that sulfate aerosols have also been an important component of the martian atmosphere. Thus mixtures of ice, dust, and sulfate aerosols are likely to have been common on the martian surface. Given the fact that it is not difficult to achieve surface temperatures above ‐40degC on Mars throughout its history, it seems likely that sulfate formation on Mars is controlled by the availability of sulfate aerosols and not by the martian climate. The current polar regions of Mars and Earth provide interesting analogs. Large regions of sulfaterich material have been detected on and around the modern north polar region of Mars. The prevalence of ice‐dust mixtures in this region and the existence of sulfates within the ice cap itself are strong evidence for the origin of the sulfates from inside the ice deposits. In addition sulfates have been found in ice deposits in Greenland and Mount Fuji on Earth that have been attributed to forming within the ice deposit. These sulfates can form either through interaction with dust particles in the atmosphere or through weathering inside the ice itself.

Niles, Paul B.↗
DOE OSTI2025

Designing Peptide Fossils That Model the Evolution of the Bacterial Ferredoxin Fold

Electron transfer coupled to redox chemistry is at the heart of metabolism. The proteins responsible for moving electrons (protein electron carriers) must have emerged at the origin of life. The small iron–sulfur-binding bacterial ferredoxins were likely among these first proteins. Embedded within the ferredoxin sequence and structure is a symmetry that points to an ancient gene duplication event. Little is understood about the nature of ferredoxins prior to this duplication event or what environmental factors may have driven the selection for more complex forms. The deep-time molecular history of ferredoxins goes back billions of years and cannot be reconstructed by phylogenetic analyses based on amino acid sequences. Here, we use structure-guided protein design to model a fossil half-ferredoxin stage in the evolution of this fold, the semidoxins, and their symmetric full-length counterparts, the symdoxins. Semidoxin designs homodimerize, exhibiting structural, thermodynamic, and electrochemical behaviors in most cases identical to cognate symdoxins. However, the semi- and symdoxin fossil stages behave differently when incorporated into an in vivo electron transfer complementation assay. Both can support bacterial growth dependent on protein expression. Growth rates of bacteria expressing the semidoxins are much more sensitive to oxygen than those of bacteria expressing symdoxins. Motivated by the in vivo functionality of designed semidoxins, we identified putative naturally occurring semidoxins in extant anaerobic microorganisms. This is consistent with the observed in vivo oxygen sensitivity of the semidoxin designs. One natural semidoxin is shown to be folded and redox active. However, it exists as a mixture of monomers and dimers, suggesting a potential connection between semidoxins and even simpler single iron–sulfur cluster-binding peptides.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Promoting Atomically Dispersed MnN 4 Sites via Sulfur Doping for Oxygen Reduction: Unveiling Intrinsic Activity and Degradation in Fuel Cells

Carbon supported and nitrogen coordinated single Mn site catalysts (Mn-N-C) catalysts are the most desirable platinum group metal (PGM)-free cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their insignificant Fenton reactions (vs. Fe), earth abundances (vs. Co) and encouraging activity and stability. However, current Mn-N-C catalysts suffer from high over-potential due to low intrinsic activity and less dense MnN 4 sites. Herein, we present sulfur-doped Mn-N-C catalyst (Mn-N-C-S) synthesized through an effective adsorption-pyrolysis process. Using electron microscopy and X-ray absorption spectroscopy (XAS) techniques, we verify the uniform dispersion of MnN 4 sites and confirm the effect of S doping on the Mn-N coordination. The Mn-N-C-S catalyst exhibits a favorable oxygen reduction reaction (ORR) activity in acidic media relative to the S-free Mn-N-C catalyst. The corresponding membrane electrode assembly (MEA) generated a remarkable performance with a peak power density of 500 mW cm -2 under a realistic H 2 /air environment. The constant voltage tests of fuel cells confirm the much-enhanced stability of the Mn-N-C-S catalyst compared to the Fe-N-C and Fe-N-C-S catalysts. The electron microscopy and Fourier transform XAS analysis provide insights into catalyst degradation associated with Mn oxidation and agglomeration. The theoretical calculation elucidates that the promoted ORR activity is mainly attributed to the spatial effect stemmed from the repulsive interaction between the ORR intermediates and adjacent S do-pants.

25 ENERGY STORAGE↗
NASA NTRS1983

Advanced coal gasifier-fuel cell power plant systems design

Two advanced, high efficiency coal-fired power plants were designed, one utilizing a phosphoric acid fuel cell and one utilizing a molten carbonate fuel cell. Both incorporate a TRW Catalytic Hydrogen Process gasifier and regenerator. Both plants operate without an oxygen plant and without requiring water feed; they, instead, require makeup dolomite. Neither plant requires a shift converter; neither plant has heat exchangers operating above 1250 F. Both plants have attractive efficiencies and costs. While the molten carbonate version has a higher (52%) efficiency than the phosphoric acid version (48%), it also has a higher ($0.078/kWh versus $0.072/kWh) ten-year levelized cost of electricity. The phosphoric acid fuel cell power plant is probably feasible to build in the near term: questions about the TRW process need to be answered experimentally, such as weather it can operate on caking coals, and how effective the catalyzed carbon-dioxide acceptor will be at pilot scale, both in removing carbon dioxide and in removing sulfur from the gasifier.

Heller, M. E.↗
DOE OSTI2026

Effect of Antagonistic Binder–Catalyst Interactions on Catalytic Activity in Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries are a promising next-generation energy storage solution, as they can reduce reliance on critical transition metals while offering high energy densities. However, their deployment is hindered by low sulfur utilization and the formation/diffusion of lithium polysulfides (LiPSs). While transition-metal catalysts and polymeric binders have been independently developed to enhance redox kinetics and LiPS adsorption, their mutual compatibility has remained largely unexplored. We show here that binder-catalyst interactions can significantly impact catalytic performance. Employing TiO 2 as a generic catalyst, the electrochemical performance is shown to depend strongly on the binder environment. TiO 2 paired with lithiated polyacrylic acid (LiPAA) shows benign interactions, resulting in enhanced cycle life. In contrast, pairing TiO 2 with protonated PAA produces antagonistic interactions that hinder Li 2 S growth. A mechanistic analysis unveils that the carboxylic H atom in PAA promotes COO − coordination to Ti sites, occupying catalytic centers and suppressing LiPS adsorption, increasing charge transfer and diffusion resistances. This phenomenon is observed across multiple catalysts, indicating that COOH-functionalized binders may broadly hinder catalytic activity. Overall, this study underscores the need for holistic cathode design and identifies binder-catalyst compatibility as an important parameter for high-performance Li-S batteries.

25 ENERGY STORAGE↗
DOE OSTI2023

A conformational equilibrium in the nitrogenase MoFe protein with an α-V70I amino acid substitution illuminates the mechanism of H 2 formation

Study of α-V70I-substituted nitrogenase MoFe protein identified Fe6 of FeMo-cofactor (Fe 7 S 9 MoC-homocitrate) as a critical N 2 binding/reduction site. Freeze-trapping this enzyme during Ar turnover captured the key catalytic intermediate in high occupancy, denoted E 4 (4H), which has accumulated 4[e — /H + ] as two bridging hydrides, Fe2–H–Fe6 and Fe3–H–Fe7, and protons bound to two sulfurs. E 4 (4H) is poised to bind/reduce N 2 as driven by mechanistically-coupled H 2 reductive-elimination of the hydrides. This process must compete with ongoing hydride protonation (HP), which releases H 2 as the enzyme relaxes to state E 2 (2H), containing 2[e — /H + ] as a hydride and sulfur-bound proton; accumulation of E 4 (4H) in α-V70I is enhanced by HP suppression. EPR and 95 Mo ENDOR spectroscopies now show that resting-state α-V70I enzyme exists in two conformational states, both in solution and as crystallized, one with wild type (WT)-like FeMo-co and one with perturbed FeMo-co. These reflect two conformations of the Ile residue, as visualized in a reanalysis of the X-ray diffraction data of α-V70I and confirmed by computations. EPR measurements show delivery of 2[e — /H + ] to the E 0 state of the WT MoFe protein and to both α-V70I conformations generating E 2 (2H) that contains the Fe3–H–Fe7 bridging hydride; accumulation of another 2[e — /H + ] generates E 4 (4H) with Fe2–H–Fe6 as the second hydride. E 4 (4H) in WT enzyme and a minority α-V70I E 4 (4H) conformation as visualized by QM/MM computations relax to resting-state through two HP steps that reverse the formation process: HP of Fe2–H–Fe6 followed by slower HP of Fe3–H–Fe7, which leads to transient accumulation of E 2 (2H) containing Fe3–H–Fe7. In the dominant α-V70I E 4 (4H) conformation, HP of Fe2–H–Fe6 is passively suppressed by the positioning of the Ile sidechain; slow HP of Fe3–H–Fe7 occurs first and the resulting E 2 (2H) contains Fe2–H–Fe6. Importantly, it is this HP suppression in E 4 (4H) that enables α-V70I MoFe to accumulate E 4 (4H) in high occupancy. In addition, HP suppression in α-V70I E 4 (4H) kinetically unmasks hydride reductive-elimination without N 2 -binding, a process that is precluded in WT enzyme.

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

Parametric study of operating conditions of an SO 2 -depolarized electrolyzer

Large-scale hydrogen generation is needed to satisfy both existing commercial demands and the realization of a hydrogen economy. The hybrid sulfur cycle has the potential to meet this goal without the use of fossil fuels. The ability to model and predict how the electrolyzer step of the cycle is affected by independent and interdependent variables is vital to maximizing the efficiency of the overall cycle. Herein, we report that our parametric study of the SO 2 -depolarized electrolyzer, representing one half of the overall reaction cycle, has identified desirable conditions and will help guide further development for operation that will achieve the benchmarks for economic feasibility. We discuss the interactions among the inlet flow rates, applied current, and cell temperature and pressure, on the resulting cell voltage and acid concentration in the liquid product stream. For example, we find that using a sulfonated polybenzimidazole (s-PBI) membrane and a platinum catalyst, a constant current density of either 0.5 A cm -2 , 0.75 A cm -2 , or 1 A cm -2 with an acid concentration of 65 wt% H 2 SO 4 can be produced at a cell voltage of 0.59 V, 0.63 V, and 0.67 V, respectively, by maintaining a cell temperature of 130 °C, a pressure of 2 bar, and a water-to-SO 2 stoichiometry of 2.77. Finally, we discuss directions for future research based on the findings in this manuscript.

08 HYDROGEN↗
DOE OSTI2020

Node-Accessible Zirconium MOFs

High-stability, zirconium-based metal–organic frameworks are attractive as heterogeneous catalysts and as model supports for uniform arrays of subsequently constructed heterogeneous catalysts—for example, MOF-node-grafted metal–oxy and metal–sulfur clusters. For hexa-Zr(IV)-MOFs characterized by nodes that are less than 12-connected, sites not used for linkers are ideally occupied by reactive and displaceable OH/H 2 O pairs. Here, the desired pairs are ideal for grafting the aforementioned catalytic clusters, while aqua-ligand lability renders them effective for exposing highly Lewis-acidic Zr(IV) sites (catalytic sites) to candidate reactants. New single-crystal X-ray studies of an eight-connected Zr-MOF, NU-1000, reveal that conventional activation fully removes modulator ligands, but replaces them with three node-blocking formate ligands (from solvent decomposition) and only one OH/H 2 O pair, not four—a largely overlooked complication that now appears to be general for Zr-MOFs. Here we describe an alternative activation protocol that effectively removes modulators, avoids formate, and installs the full complement of terminal OH/H 2 O pairs. It does so via an unusual isolatable intermediate featuring eight aqua ligands and four non-ligated chlorides—again as supported by single-crystal X-ray data. We find that complete replacement of node-blocking modulators/formate with the originally envisioned OH/OH 2 pairs has striking consequences; here we touch upon just three. First, elimination of unrecognized formate renders aqua ligands much more thermally labile, enabling open Zr(IV) sites to be obtained at lower temperature. Second, in the absence of formate, which otherwise links and locks pairs of node Zr(IV) ions, reversible removal of aqua ligands engenders reversible contraction of MOF meso- and micropores, as evidenced by X-ray diffraction. Third, formate replacement with OH/OH 2 pairs renders NU-1000 ca.10× more active for catalytic hydrolytic degradation of a representative simulant of G-type chemical warfare agents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1985

Sulfur reduction in sediments of marine and evaporite environments

Transformations of sulfur in sediments of ponds ranging in salinities from that of normal seawater to those of brines saturated with sodium chloride were examined. The chemistry of the sediment and pore waters were focused on with emphasis on the fate of sulfate reduction. The effects of increasing salinity on both forms of sulfur and microbial activity were determined. A unique set of chemical profiles and sulfate-reducing activity was found for the sediments of each of the sites examined. The quantity of organic matter in the salt pond sediments was significantly greater than that occurring in the adjacent intertidal site. The total quantitative and qualitative distribution of volatile fatty acids was also greater in the salt ponds. Volatile fatty acids increased with salinity.

Klug, M. J.↗
NASA NTRS1996

Low Crossover Polymer Electrolyte Membranes for Direct Methanol Fuel Cells

Direct Methanol Fuel Cells (DMFC's) using polymer electrolyte membranes are promising power sources for portable and vehicular applications. State of the art technology using Nafion(R) 117 membranes (Dupont) are limited by high methanol permeability and cost, resulting in reduced fuel cell efficiencies and impractical commercialization. Therefore, much research in the fuel cell field is focused on the preparation and testing of low crossover and cost efficient polymer electrolyte membranes. The University of Southern California in cooperation with the Jet Propulsion Laboratory is focused on development of such materials. Interpenetrating polymer networks are an effective method used to blend polymer systems without forming chemical links. They provide the ability to modify physical and chemical properties of polymers by optimizing blend compositions. We have developed a novel interpenetrating polymer network based on poly (vinyl - difluoride)/cross-linked polystyrenesulfonic acid polymer composites (PVDF PSSA). Sulfonation of polystyrene accounts for protonic conductivity while the non-polar, PVDF backbone provides structural integrity in addition to methanol rejection. Precursor materials were prepared and analyzed to characterize membrane crystallinity, stability and degree of interpenetration. USC JPL PVDF-PSSA membranes were also characterized to determine methanol permeability, protonic conductivity and sulfur distribution. Membranes were fabricated into membrane electrode assemblies (MEA) and tested for single cell performance. Tests include cell performance over a wide range of temperatures (20 C - 90 C) and cathode conditions (ambient Air/O2). Methanol crossover values are measured in situ using an in-line CO2 analyzer.

Prakash, G. K. Surya↗
DOE OSTI2022

Templating Bicarbonate in the Second Coordination Sphere Enhances Electrochemical CO 2 Reduction Catalyzed by Iron Porphyrins

Bicarbonate-based electrolytes are ubiquitous in aqueous electrochemical CO 2 reduction, particularly in heterogenous catalysis, where they demonstrate improved catalytic performance relative to other buffers. In contrast, the presence of bicarbonate in organic electrolytes and its roles in homogeneous electrocatalysis remain underexplored. Here, we investigate the influence of bicarbonate on iron porphyrin-catalyzed electrochemical CO 2 reduction. In this work, we show that bicarbonate is a viable proton donor in organic electrolyte (p K a = 20.8 in dimethyl sulfoxide) and that urea pendants in the second coordination sphere can be used to template bicarbonate in the vicinity of a molecular iron porphyrin catalyst. The templated binding of bicarbonate increases its acidity, resulting in a 1500-fold enhancement in catalytic rates relative to unmodified parent iron porphyrin. This work emphasizes the importance of bicarbonate speciation in wet organic electrolytes and establishes second-sphere bicarbonate templating as a design strategy to harness this adventitious acid and enhance CO 2 reduction catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structural basis for catalysis by human lipoyl synthase

Abstract Lipoic acid is an essential cofactor in five mitochondrial multiprotein complexes. In each complex, it is tethered in an amide linkage to the side chain of a conserved lysyl residue on a lipoyl carrier protein or lipoyl domain to afford the lipoyl cofactor. Lipoyl synthase catalyzes the last step in the biosynthesis of the lipoyl cofactor, the addition of two sulfur atoms to carbons 6 and 8 of an octanoyllysyl residue of the H protein, the lipoyl carrier protein of the glycine cleavage system. Lipoyl synthase, a member of the radical S-adenosylmethionine superfamily, contains two [Fe 4 S 4 ] clusters, one of which is sacrificed during catalysis to supply the appended sulfur atoms. Herein, we use X-ray crystallography to characterize several stages in lipoyl synthase catalysis and present a structure of an intermediate wherein the enzyme is cross-linked to the H protein substrate through a 6-mercaptooctanoyl ligand to a [Fe 3 S 4 ] cluster.

Science & Technology - Other Topics↗
DOE OSTI2021

Mineralogy-dependent sulfide oxidation via polysulfide and thiosulfate pathways during weathering of mixed-sulfide bearing mine waste rock

Tracking the S oxidation pathway in sulfide-bearing mine waste-rock piles is complicated by variations in water content, O 2 and Fe 3+ concentrations, microbial diversity, mineralogy, the occurrence of a variety of S species associated with incomplete oxidation, and nonlinear coupling between physicochemical processes. Synchrotron-based S K-edge X-ray absorption near edge structure (XANES) spectroscopy facilitates the identification and quantification of S species (i.e., S 2– , $S_{2}O_{2}^{2–}$, S 8 , $S_{2}O_{3}^{2–}$, and $S_{2}O_{4}^{2–}$) in a weathered mine waste-rock pile containing pyrite, sphalerite, galena, pyrrhotite, and chalcopyrite. Mineralogy-dependent polysulfide and thiosulfate pathways both affect the S oxidation within the waste-rock pile. Currently, the polysulfide pathway, with S 8 as the intermediate S species, generates high concentrations of dissolved metals (from the rapid oxidation of monosulfides including sphalerite, galena, pyrrhotite, and chalcopyrite). As these monosulfides are depleted, the thiosulfate pathway of pyrite oxidation, including intermediate oxidation products (i.e., S 8 and $S_{2}O_{3}^{2–}$), will become the dominant oxidation pathway, resulting in the potential for generation of additional acidic drainage. This information highlights the importance of identifying the sulfide-mineral oxidation reaction pathways when attempting to estimate acid generation potential, and when developing remediation strategies for the storage and management of sulfide-bearing waste rock.

58 GEOSCIENCES↗
NASA NTRSDate not supplied

Joint Assimilation of CO, O3, NO2, SO2, PM, AOD, NH4, PAN, and HNO3 in Support of the Tropospheric Regional Atmospheric Composition and Emissions Reanalysis (2005 - 2024) (TRACER-I)

NASA Ames Research Center is collaborating with the NOAA Chemical Systems Laboratory (NOAA/CSL), the NASA Jet Propulsion Laboratory (JPL), the NASA Goddard Modeling and Assimilation Office, and the National Center for Atmospheric Research to prepare a 20-year Tropospheric Regional Atmospheric Composition and Emissions Reanalysis (2005 – 2024) (TRACER-I) for the continental United States during the summer ozone (O3) and wildfire seasons (April to October). TRACER-I will be a regional complement to JPL’s global Tropospheric Chemistry Reanalyses II and III. We will use WRF-Chem/DART with NOAA/CSL’s WRF-Chem setup at 12 km x 12 km horizontal resolution, 51 vertical levels, and 30 ensemble members. We will assimilate: (i) conventional meteorological observations; (ii) EPA’s Air Quality System in situ measurements of carbon monoxide (CO), O3, nitrogen dioxide (NO2), sulfur dioxide (SO2), particulate matter (PM) with diameters less than 10 µm (PM10), and PM with diameters less than 2.5 µm (PM2.5); and (iii) MOPITT, MODIS, OMI, TROPOMI, GOME-2a, MLS, TES, SCIAMACHY, CrIS, and TEMPO total/partial column and/or profile retrievals of CO, O3, NO2, SO2, aerosol optical depth (AOD), formaldehyde (HCHO), ammonia (NH4), peroxyacetyl nitrate (PAN), and/or nitric acid (HNO3) with 3-hr cycling. We will present an overview of this project, its status, and available results (likely the analysis of sensitivity experiment results from the assimilation/emissions estimation system).

data assimilation↗
NASA NTRS2005

Effects of Volcanoes on the Natural Environment

The primary focus of this project has been on the development of techniques to study the thermal and gas output of volcanoes, and to explore our options for the collection of vegetation and soil data to enable us to assess the impact of this volcanic activity on the environment. We originally selected several volcanoes that have persistent gas emissions and/or magma production. The investigation took an integrated look at the environmental effects of a volcano. Through their persistent activity, basaltic volcanoes such as Kilauea (Hawaii) and Masaya (Nicaragua) contribute significant amounts of sulfur dioxide and other gases to the lower atmosphere. Although primarily local rather than regional in its impact, the continuous nature of these eruptions means that they can have a major impact on the troposphere for years to decades. Since mid-1986, Kilauea has emitted about 2,000 tonnes of sulfur dioxide per day, while between 1995 and 2000 Masaya has emotted about 1,000 to 1,500 tonnes per day (Duffel1 et al., 2001; Delmelle et al., 2002; Sutton and Elias, 2002). These emissions have a significant effect on the local environment. The volcanic smog ("vog" ) that is produced affects the health of local residents, impacts the local ecology via acid rain deposition and the generation of acidic soils, and is a concern to local air traffic due to reduced visibility. Much of the work that was conducted under this NASA project was focused on the development of field validation techniques of volcano degassing and thermal output that could then be correlated with satellite observations. In this way, we strove to develop methods by which not only our study volcanoes, but also volcanoes in general worldwide (Wright and Flynn, 2004; Wright et al., 2004). Thus volcanoes could be routinely monitored for their effects on the environment. The selected volcanoes were: Kilauea (Hawaii; 19.425 N, 155.292 W); Masaya (Nicaragua; 11.984 N, 86.161 W); and Pods (Costa Rica; 10.2OoN, 84.233 W).

Mouginis-Mark, Peter J.↗
NASA NTRS1988

The evolution of glutathione metabolism in phototrophic microorganisms

The low molecular weight thiol composition of a variety of phototropic microorganisms is examined in order to ascertain how evolution of glutathione (GSH) production is related to the evolution of oxygenic photosynthesis. Cells were extracted in the presence of monobromobimane (mBBr) to convert thiols (RSH) to fluorescent derivatives (RSmB) which were analyzed by high performance liquid chromatography (HPLC). Significant levels of GSH were not found in green sulfur bacteria. Substantial levels were present in purple bacteria, cyanobacteria, and eukaryotic algae. Other thiols measured included cysteine, gamma-glutamylcysteine, thiosulfate, coenzyme A, and sulfide. Many of the organisms also exhibited a marked ability to reduce mBBr to syn-(methyl,methyl)bimane, an ability which was quenched by treatment with 2-pyridyl disulfide or 5,5 prime-bisdithio - (2-nitrobenzoic acid) prior to reaction with mBBr. These observations indicate the presence of a reducing system capable of electron transfer to mBBr and reduction of reactive disulfides. The distribution of GSH in phototropic eubacteria indicates that GSH synthesis evolved at or around the time that oxygenic photosynthesis evolved.

Fahey, Robert C.↗