- Department of Geosciences
Earth and Space Sciences Bldg.
Stony Brook University
Stony Brook, NY 11794-2100
Martin Schoonen
SUNY: Stony Brook University, Geosciences, Faculty Member
- Brookhaven National Laboratory, Environmental Sciences, Department Memberadd
- Astrobiology, Environmental Science, Geochemistry, Geosciences, Mineralogy, Semiconductors, and 10 moreSoil Science, Colloids and Surfaces, Trace element Geochemistry, Environmental Geochemistry (Environmental Studies), Colloid Science, Pyrite, Calcite, Sulfur Cycling, Hydrothermal Sulfides, and Iron Sulfideedit
- Professor Schoonen's research interests focus on the reactivity of earth materials under a wide range of conditions. ... moreProfessor Schoonen's research interests focus on the reactivity of earth materials under a wide range of conditions.
Schoonen's research group is currently working on three major projects: heterogeneous catalysis involving mineral surfaces; carbon capture and storage; and medical geology.
Heterogeneous Catalysis on Mineral Surfaces
While catalysis, or promotion of reactions, is extensively studied in the chemical community, geochemists are only now addressing the importance of catalysis and photocatalysis in geochemical systems. Most of Schoonen’s research has been directed at understanding the possible role of minerals in the conversion of relatively inert forms of biogenic elements (C, H, O, N, P, S) to small organic molecules or activated abiotic forms. Most of the recent effort in this area has been focused on studying the role of metal sulfides in the conversion of dinitrogen to ammonia in the context of the Origin of Life. Schoonen’s group is part of the Astrobiology Biogeocatalysis Research Center funded by NASA.
We use the same techniques and approaches to study reactions that are relevant to the degradation of contaminants. We are particularly interested in studying reactions that transfer electrons and create radicals. So, for example, we have studied the removal of crystal violet from solution. Crystal violet is widely used dye in the printing industry and textile industry. The cotton used for blue jeans is dyed using crystal violet or related cationic organic dyes.
Carbon Capture and Storage
Carbon capture and storage is one of the technologies being implemented around the world to eliminate carbon dioxide from emissions associated with the burning of fossil fuel. One option is to compress the gaseous waste stream into a supercritical liquid and inject it into deep saline aquifers. Schoonen’s group is conducted research on the reactivity of sulfur gases (mostly hydrogen sulfide and sulfur dioxide) which are expected to be co-injected along with carbon dioxide. The reactivity of the sulfur gases in subsurface environments dominated by supercritical carbon dioxide by itself or mixed with saline fluids is not understood. Schoonen’s group conducts experimental studies to simulate the subsurface conditions and monitors the changes in the mineralogy of the exposed sediments. Some of this work is done collaboratively with colleagues Teng-fong Wong, Department of Geosciences, Stony Brook, and Daniel Strongin, Department of Chemistry, Temple University. Schoonen’s research on carbon capture and storage is funded by the US Department of Energy.
Medical Geology
Schoonen’s group has been active in the emerging field of medical geology for about a decade. Research in the group focuses on mineral-driven radical formation and the interaction of minerals with biomolecules and human lung cells. The group has taken the lead in adapting a number of biomedial assays for use in mineral studies. Using these new methods, studies have been conducted on the role of pyrite in the development of black lung disease among coal miners and currently a study is being conducted to understand the effect of mineral dust on the health of soldiers stationed in Iraq and Afghanistan. Schoonen’s group works closely with colleagues in Pharmacological Sciences at Stony Brook as well as colleagues in the US Geological Survey. This research effort is primarily funded through an NSF- IGERT training grant. Schoonen is on the editorial board for the journal Environmental Geochemistry and Health.edit
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The purpose of this study was to simulate theoretical infrared (IR) spectra of halogenated acetate salts using density functional theory (DFT), and to calibrate those results with high-resolution ATR-FTIR spectra. Two types of spectra... more
The purpose of this study was to simulate theoretical infrared (IR) spectra of halogenated acetate salts using density functional theory (DFT), and to calibrate those results with high-resolution ATR-FTIR spectra. Two types of spectra were calculated: one of the solutes solvated in water droplets ranging in size from 15 to approximately 28 H(2)O molecules, and the other of a solvent molecule in equivalently sized (16-29 H(2)O molecules) droplets. The background-subtracted spectra, composed of solvated (halo)acetate spectra minus calculated solvent spectra, were compared with their experimental counterparts. Changes in the calculated IR spectra were used to determine the effects of dissolved salts on the structure of water. Calibrations of model dissolved salt spectra with observation were good; correlations of >0.90 were observed for all haloacetate species.
Research Interests: Chemistry, Analytical Chemistry, Water, Quantum Theory, Medicine, and 15 moreInfrared spectroscopy, DFT, Calibration, Background Subtraction, Germanium, High Resolution, Infrared, Fourier transform infrared spectroscopy, Solutions, Molecule, Solvent, Sodium Compounds, Ions, Sodium Fluoride, and Solvents
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The reaction of FeS2 (pyrite) with gaseous H2O, O2, and H2O/O2 was investigated using horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR). Spectra were interpreted with the aid of hybrid molecular... more
The reaction of FeS2 (pyrite) with gaseous H2O, O2, and H2O/O2 was investigated using horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR). Spectra were interpreted with the aid of hybrid molecular orbital/density functional theory calculations of sulfate-iron hydroxide clusters. Reaction of pyrite in gaseous H2O led primarily to the formation of iron hydroxide on pyrite. Exposure of the pyrite to gaseous O2 after exposure to H2O vapor led to the formation of sulfur oxyanions that included SO42-. Isotopic labeling experiments showed that after this exposure sequence the oxygen in the sulfate product was primarily derived from the H2O reactant. If, however, pyrite was exposed to gaseous O2 prior to pure H2O vapor, both SO42- and iron oxyhydroxide became significant products. Isotopic rabeling experiments using the O2-then-H2O sequence showed that the oxygen in the SO42- product was derived from both H2O and O2. The results indicate that H2O and O2 exhibit a competitive adsorption on pyrite, with H2O blocking surface sites for O2 adsorption. The extent of oxygen incorporation from either the H2O or the O2 component into the surface-bound sulfur oxyanion product appears to be a strong function of the relative concentration ratio of the reactant H2O and O2.
Research Interests: Environmental Science, Geochemistry, Chemistry, Inorganic Chemistry, Water, and 15 moreMedicine, Multidisciplinary, Environmental science and technology, Adsorption, Sulfides, Pyrite, Iron, Sulfate, Sulfur, Oxygen, Fourier transform infrared spectroscopy, Environmental, Oxidation-Reduction, Hydroxide, and Isotope Labeling
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Research Interests: Environmental Science, Geology, Geochemistry, Geophysics, Chemistry, and 15 moreGeothermal Energy, Applied Geochemistry, Concentration, Depth, Balance, Acid Rock Drainage, Equilibrium, Geochemical, Fractionation, Boiling, Elevated Temperature, Binding Site, ENVIRONMENTAL SCIENCE AND MANAGEMENT, Gas, and Cinder
Experiments were conducted in an integrated ultra-high vacuum/ high-pressure apparatus. In short, samples could be scrutinized with surface science techniques, transferred to a reaction cell, exposed to liquid or gas, and transferred back... more
Experiments were conducted in an integrated ultra-high vacuum/ high-pressure apparatus. In short, samples could be scrutinized with surface science techniques, transferred to a reaction cell, exposed to liquid or gas, and transferred back to UHV for further analysis. At no time during this process was the sample exposed to the ambient atmosphere. UHV was obtained with cryogenic and turbomolecular pumps and the typical working base pressure of the UHV chamber was 6 × 10 Pa. X-ray photoelectron data were obtained with unmonochromatized Mg Kα radiation (1253.6 eV) as the excitation source and double pass cylindrical mirror analyzer (CMA, pass energy of 25 eV). 2p 3/2 and 2p1/2 contributions to each S 2p doublet used to fit spectra in this contribution have been constrained by a 2:1 peak area ratio, 1.8 eV separation, and 1.5 eV FWHM. Pyrite samples were mounted on a tantalum foil and this assembly was supported by (but not fastened so that it could be removed in-situ), and in electrica...
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Research Interests: Earth Sciences, Geology, Geochemistry, Chemistry, Inorganic Chemistry, and 13 moreMaterials Chemistry, Kinetics, Environmental Health, Environmental Chemistry, Reactive Oxygen Species, Pyrite, Catalysis and Reaction Engineering, Chalcopyrite, Hydrogen Peroxide, Emergent Behavior, Radical, Oxidation, and Hydroxyl Radical
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The reaction of nitrite (NO2(-)) and nitrate (NO3(-)) on nanometer-sized FeS particles was investigated in alkaline (initial pH = 10.3) solutions at reaction temperatures of 22, 70, and 120 °C using in situ attenuated total reflection... more
The reaction of nitrite (NO2(-)) and nitrate (NO3(-)) on nanometer-sized FeS particles was investigated in alkaline (initial pH = 10.3) solutions at reaction temperatures of 22, 70, and 120 °C using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and fluorescence spectroscopy that allowed an analysis of adsorbate complexation on the FeS and reaction product in the aqueous phase, respectively. ATR-FTIR showed that NO was a surface-bound intermediate on FeS during its exposure to NO2(-) at all three reaction temperatures. Ammonia/ammonium (NH3/NH4(+)) product was also produced when FeS was exposed to NO2(-) at the 70 °C and 120 °C reaction temperatures. Activation of NO3(-) to form surface-bound NO was experimentally observed to occur at 120 °C on FeS, but not at the lower reaction temperatures. Furthermore, NH3/NH4(+) product in the aqueous phase was only present during the reaction of FeS with NO3(-) at the highest temperature used in this study.
Research Interests: Geochemistry, Chemistry, Inorganic Chemistry, Origins of Life, Kinetics, and 14 moreNanoparticles, Chemical Evolution, Medicine, Biological Sciences, Nitrates, Nitrate, Temperature, Nitrite, Ammonia, Fourier transform infrared spectroscopy, Aqueous Solution, Hydrogen-Ion Concentration, Oxidation-Reduction, and Nitrites
ABSTRACT Hydrogen peroxide and hydroxyl radical are readily formed during the oxidation of pyrite with molecular oxygen over a wide range of pH conditions. However, pretreatment of the pyrite surface influences how much of the... more
ABSTRACT Hydrogen peroxide and hydroxyl radical are readily formed during the oxidation of pyrite with molecular oxygen over a wide range of pH conditions. However, pretreatment of the pyrite surface influences how much of the intermediates are formed and their fate. Acid-washed pyrite produces significant amounts of hydrogen peroxide and hydroxyl radical when suspended in air-saturated water. However, the hydrogen peroxide concentration shows an exponential decrease with time. Suspensions made with partially oxidized pyrite yield significantly lower amounts of hydrogen peroxide product. The presence of Fe(III)-oxide or Fe(III)-hydroxide patches facilitates the conversion of hydrogen peroxide to oxygen and water. Hence, the degree to which a pyrite surface is covered with patches of Fe(III)-oxide or Fe(III)-hydroxide patches is an important control on the concentration of hydrogen peroxide in solution.Hydrogen peroxide appears to be an important intermediate in the four-electron transfer from pyrite to molecular oxygen. Addition of catalase, an enzyme that decomposes hydrogen peroxide to water and molecular oxygen, to a pyrite suspension reduces the oxidation rate by 40%. By contrast, hydroxyl radical does not appear to play a significant role in the oxidation mechanism. It is estimated on the basis of a molecular oxygen and sulfate mass balance that 5–6% of the molecular oxygen is consumed without forming sulfate.
Research Interests: Engineering, Environmental Science, Geology, Geochemistry, Chemistry, and 14 morePhotochemistry, Acid Mine Drainage, Biological Sciences, Reactive Oxygen Species, Electron Transfer, Catalase, Pyrite, Enzyme, CHEMICAL SCIENCES, Hydrogen Peroxide, Oxygen, Mass Balance, Hydroxyl Radical, and partial oxidation
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Many waters sampled in Yellowstone National Park, both high-temperature (3094 °C) and low-temperature (030 °C), are acidsulfate type with pH values of 15. Sulfuric acid is the dominant component, especially as pH values decrease below... more
Many waters sampled in Yellowstone National Park, both high-temperature (3094 °C) and low-temperature (030 °C), are acidsulfate type with pH values of 15. Sulfuric acid is the dominant component, especially as pH values decrease below 3, and it forms from the oxidation of ...
Research Interests: Geology, Geochemistry, Chemistry, Kinetics, Mine Water, and 15 moreEnvironmental Chemistry, Applied Geochemistry, Concentration, Models, Depth, Balance, High Temperature, Acid Rock Drainage, Equilibrium, Fractionation, Low Temperature, Boiling, Elevated Temperature, ENVIRONMENTAL SCIENCE AND MANAGEMENT, and Gas
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The stage for the origin of life may have been set during a period that was as short as 20 million years within the rst 100 million years after the formation of the Moon (at ~4.5 Ga). The atmosphere at that time contained more carbon... more
The stage for the origin of life may have been set during a period that was as short as 20 million years within the rst 100 million years after the formation of the Moon (at ~4.5 Ga). The atmosphere at that time contained more carbon dioxide than at any other period thereafter. Carbon dioxide sustained greenhouse conditions, accelerated the weathering of a primitive crust, and may have led to conditions conducive to forming the building blocks of life. The conversion of inorganic carbon and nitrogen to the essential building blocks of life may have been facilitated by clays, zeolites, sul des, and metal alloys that had been formed as the crust reacted with a warm and carbonated (seltzer) ocean. Geochemical modeling constrains the conditions favorable for the formation of these potential mineral catalysts.
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United States soldiers are returning from the Greater Middle East with respiratory illnesses ranging from new onset asthma to constrictive bronchiolitis. The etiologies of the diseases are unknown. A study was conducted to determine the... more
United States soldiers are returning from the Greater Middle East with respiratory illnesses
ranging from new onset asthma to constrictive bronchiolitis. The etiologies of the diseases are unknown. A
study was conducted to determine the possible role of local mineral dust in the development of abnormal
respiratory illnesses in soldiers during and after deployment in Iraq. A dust sample obtained in proximity to a
burn pit in Camp Victory, Iraq (Camp Victory dust) was characterized both chemically and mineralogically.
For comparison, a dust sample from Fort Irwin, California (Fort Irwin dust) was also collected. The ability of the
dust samples to generate reactive oxygen species (ROS) was quantified, as well as their ability to generate an
inflammatory stress response (ISR) in human lung epithelial cells. Both samples are composed of common
silicate and carbonate minerals and contain heavy metals with concentration ranges expected for mineral
dust. The ISR generated by each sample was within the range of inert material with the minimal stress
generated associated with the carbonate phases. The findings based on this one sample suggest that the
origin of the disease is not driven by the particles ability to generate ROS. However, it is likely that particle
overload and associated complications, or endotoxin contributes extensively to pathogenesis.
Citation:
Harrington, A. D., M. P. Schmidt,
A. M. Szema, K. Galdanes, S. E. Tsirka,
T. Gordon, and M. A. A. Schoonen
(2017), The role of Iraqi dust in
inducing lung injury in United States
soldiers—An interdisciplinary study,
GeoHealth, 1, doi:10.1002/
2017GH000071.
ranging from new onset asthma to constrictive bronchiolitis. The etiologies of the diseases are unknown. A
study was conducted to determine the possible role of local mineral dust in the development of abnormal
respiratory illnesses in soldiers during and after deployment in Iraq. A dust sample obtained in proximity to a
burn pit in Camp Victory, Iraq (Camp Victory dust) was characterized both chemically and mineralogically.
For comparison, a dust sample from Fort Irwin, California (Fort Irwin dust) was also collected. The ability of the
dust samples to generate reactive oxygen species (ROS) was quantified, as well as their ability to generate an
inflammatory stress response (ISR) in human lung epithelial cells. Both samples are composed of common
silicate and carbonate minerals and contain heavy metals with concentration ranges expected for mineral
dust. The ISR generated by each sample was within the range of inert material with the minimal stress
generated associated with the carbonate phases. The findings based on this one sample suggest that the
origin of the disease is not driven by the particles ability to generate ROS. However, it is likely that particle
overload and associated complications, or endotoxin contributes extensively to pathogenesis.
Citation:
Harrington, A. D., M. P. Schmidt,
A. M. Szema, K. Galdanes, S. E. Tsirka,
T. Gordon, and M. A. A. Schoonen
(2017), The role of Iraqi dust in
inducing lung injury in United States
soldiers—An interdisciplinary study,
GeoHealth, 1, doi:10.1002/
2017GH000071.
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The formation of hydroxyl radicals was studied in mixed pyrite-chalcopyrite dispersions in water using the conversion rate of adenine as a proxy for hydroxyl radical formation rate. Experiments were conducted as a function of pH, presence... more
The formation of hydroxyl radicals was studied in mixed pyrite-chalcopyrite dispersions in water using the conversion rate
of adenine as a proxy for hydroxyl radical formation rate. Experiments were conducted as a function of pH, presence of phosphate
buffer, surface loading, and pyrite-to-chalcopyrite ratio.
The results indicate that hydroxyl radical formation rate in mixed systems is non-linear with respect to the rates in the pure
endmember dispersions. The only exception is a set of experiments in which phosphate buffer is used. In the presence of phosphate
buffer, the hydroxyl radical formation is suppressed in mixtures and the rate is close to that predicted based on the reaction
kinetics of the pure endmembers.
The non-linear hydroxyl radical formation in dispersions containing mixtures of pyrite and chalcopyrite is likely the result
of two complementary processes. One is the fact that pyrite and chalcopyrite form a galvanic couple. In this arrangement,
chalcopyrite oxidation is accelerated, while pyrite passes electrons withdrawn from chalcopyrite to molecular oxygen, the oxidant.
The incomplete reduction of molecular oxygen leads to the formation of hydrogen peroxide and hydroxyl radical. The
galvanic coupling appears to be augmented by the fact that chalcopyrite generates a significant amount of hydrogen peroxide
upon dispersal in water. This hydrogen peroxide is then available for conversion to hydroxyl radical, which appears to be
facilitated by pyrite as chalcopyrite itself produces only minor amounts of hydroxyl radical. In essence, pyrite is a ‘‘cofactor”
that facilitates the conversion of hydrogen peroxide to hydroxyl radical. This conversion reaction is a surfacemediated
reaction.
Given that hydroxyl radical is one of the most reactive species in nature, the formation of hydroxyl radicals in aqueous
systems containing chalcopyrite and pyrite has implications for the stability of organic molecules, biomolecules, the viability
of microbes, and exposure to dust containing the two metal sulfides may present a health burden.
of adenine as a proxy for hydroxyl radical formation rate. Experiments were conducted as a function of pH, presence of phosphate
buffer, surface loading, and pyrite-to-chalcopyrite ratio.
The results indicate that hydroxyl radical formation rate in mixed systems is non-linear with respect to the rates in the pure
endmember dispersions. The only exception is a set of experiments in which phosphate buffer is used. In the presence of phosphate
buffer, the hydroxyl radical formation is suppressed in mixtures and the rate is close to that predicted based on the reaction
kinetics of the pure endmembers.
The non-linear hydroxyl radical formation in dispersions containing mixtures of pyrite and chalcopyrite is likely the result
of two complementary processes. One is the fact that pyrite and chalcopyrite form a galvanic couple. In this arrangement,
chalcopyrite oxidation is accelerated, while pyrite passes electrons withdrawn from chalcopyrite to molecular oxygen, the oxidant.
The incomplete reduction of molecular oxygen leads to the formation of hydrogen peroxide and hydroxyl radical. The
galvanic coupling appears to be augmented by the fact that chalcopyrite generates a significant amount of hydrogen peroxide
upon dispersal in water. This hydrogen peroxide is then available for conversion to hydroxyl radical, which appears to be
facilitated by pyrite as chalcopyrite itself produces only minor amounts of hydroxyl radical. In essence, pyrite is a ‘‘cofactor”
that facilitates the conversion of hydrogen peroxide to hydroxyl radical. This conversion reaction is a surfacemediated
reaction.
Given that hydroxyl radical is one of the most reactive species in nature, the formation of hydroxyl radicals in aqueous
systems containing chalcopyrite and pyrite has implications for the stability of organic molecules, biomolecules, the viability
of microbes, and exposure to dust containing the two metal sulfides may present a health burden.
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Oxidation of silicon nanoclusters depending on temperature and oxygen pressure is explored from first principles using the evolutionary algorithm, structural and thermodynamic analysis. From our calculations of 90 SinOm clusters we found... more
Oxidation of silicon nanoclusters depending on temperature and oxygen pressure is explored from first principles using the evolutionary algorithm, structural and thermodynamic analysis. From our calculations of 90 SinOm clusters we found that at normal conditions oxidation does not stop at the stoichiometric SiO2 composition, as it does in bulk silicon, but goes further placing extra oxygen atoms on the cluster surface. These extra atoms are magnetic, responsible for light emission and relevant to reactive oxygen species. We argue that the super-oxidation effect is size-independent and discuss its relevance to nanotechnology and miscellaneous applications, including biomedical ones
Sergey Lepeshkin, Vladimir Baturin, Evgeny Tikhonov, Nikita Matsko, Yurii Uspenskii, Anastasia Naumova, Oleg D. Feya, Martin Schoonen and Artem R Oganov
Sergey Lepeshkin, Vladimir Baturin, Evgeny Tikhonov, Nikita Matsko, Yurii Uspenskii, Anastasia Naumova, Oleg D. Feya, Martin Schoonen and Artem R Oganov
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With extreme heat events projected to increase in frequency, duration and magnitude, understanding their impacts on large urban centers and their neighboring areas has become increasingly important. Studying these events in cities... more
With extreme heat events projected to increase in frequency, duration and magnitude, understanding their impacts on large urban centers and their neighboring areas has become increasingly important. Studying these events in cities requires a level of spatial detail that is not traditionally found in reanalysis and station data sets, and thus the use of techniques such as dynamical downscaling becomes essential. This study uses the Weather Research and Forecast model version 3.5 as a regional climate model to perform dynamical downscaling of 32 km resolution North American Regional Reanalysis in order to study the sensitivity of key climate variables such as surface temperatures and surface fluxes to the presence of New York City during the heat wave event of July 2010. The sensitivity experiment consists of three simulations: a control run using unaltered land use index, a forest run with a modified land use index and soil moisture profile, and a run using the Building Energy Parame...
The effect of phospholipid on the biogeochemistry of pyrite oxidation, which leads to acid mine drainage (AMD) chemistry in the environment, was investigated. Metagenomic analyses were carried out to understand how the microbial community... more
The effect of phospholipid on the biogeochemistry of pyrite oxidation, which leads to acid mine drainage (AMD) chemistry in the environment, was investigated. Metagenomic analyses were carried out to understand how the microbial community structure, which developed during the oxidation of pyrite-containing coal mining overburden/waste rock (OWR), was affected by the presence of adsorbed phospholipid. Using columns packed with OWR (with and without lipid adsorption), the release of sulfate (SO4(2-)) and soluble iron (FeTot) was investigated. Exposure of lipid-free OWR to flowing pH-neutral water resulted in an acidic effluent with a pH range of 2-4.5 over a 3-year period. The average concentration of FeTot and SO4(2-) in the effluent was ≥20 and ≥30 mg/L, respectively. In contrast, in packed-column experiments where OWR was first treated with phospholipid, the effluent pH remained at ∼6.5 and the average concentrations of FeTot and SO4(2-) were ≤2 and l.6 mg/L, respectively. 16S rDNA metagenomic pyrosequencing analysis of the microbial communities associated with OWR samples revealed the development of AMD-like communities dominated by acidophilic sulfide-oxidizing bacteria on untreated OWR samples, but not on refuse pretreated with phospholipid.
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Reactive oxygen species including hydroxyl radicals can cause oxidative stress and mutations. Inhaled particulate matter can trigger formation of hydroxyl radicals, which have been implicated as one of the causes of particulate-induced... more
Reactive oxygen species including hydroxyl radicals can cause oxidative stress and mutations. Inhaled particulate matter can trigger formation of hydroxyl radicals, which have been implicated as one of the causes of particulate-induced lung disease. The extreme reactivity of hydroxyl radicals presents challenges to their detection and quantification. Here, three fluorescein derivatives [aminophenyl fluorescamine (APF), amplex ultrared, and dichlorofluorescein (DCFH)] and two radical species, proxyl fluorescamine and tempo-9-ac have been compared for their usefulness to measure hydroxyl radicals generated in two different systems: a solution containing ferrous iron and a suspension of pyrite particles. APF, amplex ultrared, and DCFH react similarly to the presence of hydroxyl radicals. Proxyl fluorescamine and tempo-9-ac do not react with hydroxyl radicals directly, which reduces their sensitivity. Since both DCFH and amplex ultrared will react with reactive oxygen species other than...
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The broad goals of our study were to identify processes by which organic molecules may have been destroyed or altered on early Earth, thus affecting the total inventory of organics available for prebiotic synthesis reactions.
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Nelsen's four-point method of separating oxidants and reductants has been tested to evaluate its applicability to proton-coupled electron-transfer reactions. An... more
Nelsen's four-point method of separating oxidants and reductants has been tested to evaluate its applicability to proton-coupled electron-transfer reactions. An efficient computational method was developed to determine rate-limiting steps in complex, multistep redox reactions. Geochemical redox reactions are rarely single-step, and by identifying the rate-limiting steps, computational time can be greatly reduced. The reaction of superoxide and ferrous oxide was selected as a test case for its simplicity and its importance in environmental radical generation chemistry (Fenton's reaction). Two approaches, one quantum mechanical and the other semiempirical, were compared. In both approaches, hybrid density functional theory (DFT) was used with the B3LYP/6-31+G(d,p) basis set and a polarized continuum model of the solvent to minimize the structures and determine the energies. In the quantum mechanical case, DFT was used to determine both the Gibbs free energies and the values for the intrinsic component of the reorganization energy of possible combinations of reactants and products. In the latter, experimental DeltaG(f) values were combined with calculated intrinsic reorganization energy values. The computational results matched the relative difference in rate barriers between the reduction of superoxide by ferrous iron above and below pH 4.8. In the acidic pH range, the proton is coupled to the electron transfer, whereas in the neutral case, the proton initiates the electron transfer.
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Studies are presented that investigate the adsorption and binding of CH3OH and H2O on the atomically clean (100) crystallographic plane of pyrite, FeS2. Temperature programmed desorption suggests that both reactants adsorb molecularly at... more
Studies are presented that investigate the adsorption and binding of CH3OH and H2O on the atomically clean (100) crystallographic plane of pyrite, FeS2. Temperature programmed desorption suggests that both reactants adsorb molecularly at 90 K and desorb thermally between 170 and 400 K depending on the surface coverage. Photoemission of adsorbed xenon (PAX) suggests that the surface of pyrite is
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The purpose of this study was to simulate theoretical infrared (IR) spectra of halogenated acetate salts using density functional theory (DFT), and to calibrate those results with high-resolution ATR-FTIR spectra. Two types of spectra... more
The purpose of this study was to simulate theoretical infrared (IR) spectra of halogenated acetate salts using density functional theory (DFT), and to calibrate those results with high-resolution ATR-FTIR spectra. Two types of spectra were calculated: one of the solutes solvated in water droplets ranging in size from 15 to approximately 28 H(2)O molecules, and the other of a solvent molecule in equivalently sized (16-29 H(2)O molecules) droplets. The background-subtracted spectra, composed of solvated (halo)acetate spectra minus calculated solvent spectra, were compared with their experimental counterparts. Changes in the calculated IR spectra were used to determine the effects of dissolved salts on the structure of water. Calibrations of model dissolved salt spectra with observation were good; correlations of >0.90 were observed for all haloacetate species.
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The reaction of nitrite (NO 2 −) and nitrate (NO 3 −) on nanometer-sized FeS particles was investigated in alkaline (initial pH=10.3) solutions at reaction temperatures of 22, 70, and 120 °C using in situ attenuated total reflection... more
The reaction of nitrite (NO 2 −) and nitrate (NO 3 −) on nanometer-sized FeS particles was investigated in alkaline (initial pH=10.3) solutions at reaction temperatures of 22, 70, and 120 °C using in situ attenuated total reflection Fourier transform infrared spectros-copy (ATR-FTIR) and fluorescence spectroscopy that allowed an analysis of adsorbate complexation on the FeS and reaction product in the aqueous phase, respectively. ATR-FTIR showed that NO was a surface-bound intermediate on FeS during its exposure to NO 2 − at all three reaction temperatures. Ammonia/ammonium (NH 3 /NH 4 +) product was also produced when FeS was exposed to NO 2 − at the 70 °C and 120 °C reaction temperatures. Activation of NO 3 − to form surface-bound NO was experimentally observed to occur at 120 °C on FeS, but not at the lower reaction temperatures. Furthermore, NH 3 /NH 4 + product in the aqueous phase was only present during the reaction of FeS with NO 3 − at the highest temperature used in this study.
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... FM Michel,* SM Antao, PJ Chupas, PL Lee, JB Parise, and MAA Schoonen . ... 29-31 Table 4. Refinement Results a. parameter, FeS-A (1 ) b, FeS-B (1), FeS-C (1), FeS-D (1), FeS-E (1), FeS-F (2), Rietveld parameters b, CeO 2... more
... FM Michel,* SM Antao, PJ Chupas, PL Lee, JB Parise, and MAA Schoonen . ... 29-31 Table 4. Refinement Results a. parameter, FeS-A (1 ) b, FeS-B (1), FeS-C (1), FeS-D (1), FeS-E (1), FeS-F (2), Rietveld parameters b, CeO 2 (1), CeO 2 (2). ...