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1.
Environ Pollut ; 256: 113462, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31706772

RESUMO

Natural birnessite-like minerals are commonly enriched in various transitional metals (TMs), which greatly modify the mineral structure and properties. However few studies are yet conducted systematically on the effects of TM doping on birnessite reactivity towards Cr(III) oxidation. In the present study, the transformation behaviors of Cr(III) on Co-, Ni-, V-containing birnessites were investigated. Co and Ni doping generally decrease the mineral crystalline sizes and hydrodynamic sizes (DH) while V-doping greatly decreases the crystalline sizes but not the DH, owing to particle aggregation. Co and Ni firstly decrease and then increase the mineral zeta potentials (ζ) at pH4 while V decreases ζ. Electrochemical specific capacitances for Co-containing birnessites are gradually reduced, while those for Ni-doped birnessites are slightly reduced and for V-doped birnessites increased, which have a positively linear relationship with the amounts of Cr(III) oxidized by these samples. Cr(III) removal efficiencies from solution by these Co-, Ni- and V-containing birnessites are 26-51%, ∼62-72% and ∼96-100%, respectively, compared to ∼92% by pure birnessite. Cr(III) oxidation kinetics analysis demonstrates the gradual decrease of Mn(IV) and concurrent increase of Mn(III) and the adsorption of mainly Cr(III) on mineral surfaces. A negatively linear relationship exists between birnessite lateral sizes and the proportions of Mn(IV/III) consumed to oxidize Cr(III). Apparent initial Cr(III) oxidation rate (kobs) for Co-containing birnessites are greatly reduced, while those for Ni-doped samples moderately decreased and for V-doped samples first increased and then decreased. A positively or negatively linear relationship exists between kobs or the amount of Mn(II) released and the mineral Mn(IV) content respectively. Cr(III) oxidation probably initiates from layer edge sites of Ni-doped birnessites but the vacancies of Co- and V-containing birnessites. These results provide insights into the reaction mechanisms of Cr(III) with natural birnessite-like minerals.

2.
J Hazard Mater ; 385: 121562, 2020 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-31732334

RESUMO

The prevalence of construction and demolition (C&D) waste and the concurrent demand for construction aggregate presents the opportunity to recycle C&D waste materials as substitutes for virgin aggregate. Commonly, recycled concrete aggregate (RCA) is used as base course in pavement construction. Environmentally responsible applications of RCA must consider the high pH leachate and trace element leaching risks reported in the literature. This review presents the methodology, results, and limitations of existing laboratory and field investigations of RCA leachate chemistry. Long-term highway field studies of RCA leachate illustrate that an initially high leachate pH approaches neutral within approximately one to two years of construction. Conversely, laboratory investigations of RCA leachate pH using batch reactor leaching tests and column leaching tests measure consistently high leachate pH (pH > 10). The discrepancies between field and laboratory measurements of RCA leachate pH suggest that the current laboratory methodology inadequately describes leachate conditions in the field. The authors recommend that future laboratory investigations consider intermittent wetting and drying cycles, eliminate particle abrasion, employ relevant contact times, and consider additional environmental processes that reduce leachate pH such as soil acidity and carbonation.

3.
Environ Sci Process Impacts ; 21(1): 19-27, 2019 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-30542685

RESUMO

Bisphenol A (BPA) is an endocrine disrupting compound commonly found in natural waters at concentrations that are considered harmful for aquatic life. Manganese(iii/iv) oxides are strong oxidants capable of oxidizing organic and inorganic contaminants, including BPA. Here we use δ-MnO2 in stirred flow reactors to determine if higher influent BPA concentrations, or introduction rates, lead to increased polymer production. A major BPA oxidation product, 4-hydroxycumyl alcohol (HCA), is formed through radical coupling, and was therefore used as a metric for polymer production in this study. The influent BPA concentration in stirred flow reactors did not affect HCA yield, suggesting that polymeric production is not strongly dependent on influent concentrations. However, changes in influent BPA concentration affected BPA oxidation rates and the rate of δ-MnO2 reduction. Lower aqueous Mn(ii) production was observed in reactors at higher BPA introduction rates, suggesting that single-electron transfer and polymer production are favored under these conditions. However, an examination of Mn(ii) sorption during these reactions indicated that the length of the reaction, rather than BPA introduction rate, caused enhanced aqueous Mn(ii) production in reactors with low introduction rates and longer reaction times due to increased opportunity for disproportionation and comproportionation. This study demonstrates the importance of investigating both the organic and inorganic reactants in the aqueous and solid phases in this complex reaction.


Assuntos
Compostos Benzidrílicos/química , Disruptores Endócrinos/química , Compostos de Manganês/química , Óxidos/química , Fenóis/química , Reatores Biológicos , Oxirredução , Tempo de Reação
4.
Environ Sci Technol ; 52(21): 12556-12562, 2018 11 06.
Artigo em Inglês | MEDLINE | ID: mdl-30351030

RESUMO

Soil lead (Pb) hazard level is contingent on bioavailability, but existing assays that estimate Pb bioavailability for human health risks are too expensive or otherwise inaccessible to many people that are impacted by Pb-contaminated soil. This study investigated the use of routine soil nutrient tests to estimate soil-Pb bioaccessibility as a surrogate measure of Pb bioavailability. A silt loam soil was spiked to a target concentration of 2000 mg Pb kg-1 with Pb(NO3)2 and amended with H3PO4 (varying P-to-Pb molar ratios) and KCl (Cl-to-P molar ratio of 2:5) to generate soils with similar total Pb concentrations but a range of Pb bioavailability (and bioaccessibility). Soils were extracted using Mehlich 3, Mehlich 1, Bray P1, Olsen, and  micronutrient (DTPA) methods, and the results were compared to U.S. Environmental Protection Agency method 1340 data as well as to extended X-ray absorption fine structure (EXAFS) spectroscopy. The Mehlich 3 and method 1340 treatment effect ratios were well-correlated ( r2 = 0.88, p ≤ 0.05), whereas Bray P1, DTPA, and Olsen results were more reflective of EXAFS data. Preliminary animal-feeding trials suggest that the Mehlich 3 is as effective as method 1340 at predicting the impact of P treatment on Pb relative bioavailability; however, both methods over-estimated the Pb hazard to mice in P-amended soil. Other routine soil tests that have heightened sensitivity to P amendment (e.g., Bray P1) may be promising candidates for Pb bioaccessibility assessment.


Assuntos
Poluentes do Solo , Solo , Animais , Disponibilidade Biológica , Poluição Ambiental , Humanos , Chumbo , Camundongos
5.
Environ Sci Technol ; 52(22): 13174-13183, 2018 11 20.
Artigo em Inglês | MEDLINE | ID: mdl-30354092

RESUMO

Recent studies have suggested the potential for release of iron (hydr)oxide-bound organic carbon (OC) during dissimilatory iron oxide reduction (DIR). However, the stability of iron (hydr)oxide-bound OC in the presence of a natural microbial consortium capable of driving both OC metabolism and DIR has not been resolved. Pure ferrihydrite (Fhy) and Fhy-humic acid coprecipitates (Fhy-HA) were inoculated with a small quantity of freshwater sediment and incubated under anoxic conditions in the presence and absence of H2 or glucose as electron donors for DIR. H2 promoted DIR led to release of ca. 1 mM dissolved organic carbon (DOC). However, comparable amounts of DOC were released from both pure Fhy and Fhy-HA, similar to DOC levels in mineral-free, inoculum-only controls. These results suggest that the observed DOC release during H2-promoted DIR originated from OC contained in the inoculum as opposed to the much larger pool (ca. 38 mM) of OC in the Fhy-HA. Thus, DIR preferentially released sorbed OC with low aromaticity (inoculum OC) versus highly aromatic OC (HA) coprecipitated with iron oxide. Our findings provide new insight into the extent and mechanisms by which DIR is likely to influence aqueous/solid-phase OC partitioning in anoxic soils and sediments.


Assuntos
Substâncias Húmicas , Solo , Compostos Férricos , Ferro , Minerais
6.
Environ Sci Technol ; 52(10): 5691-5699, 2018 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-29658273

RESUMO

Dissimilatory iron-reducing bacteria (DIRB) are known to use humic substances (HS) as electron shuttles for dissimilatory iron reduction (DIR) by transferring electrons to HS-quinone moieties, which in turn rapidly reduce Fe(III) oxides. However, the potential for HS to serve as a source of organic carbon (OC) that can donate electrons for DIR is unknown. We studied whether humic acids (HA) and humins (HM) recovered from peat soil by sodium pyrophosphate extraction could serve as both electron shuttles and electron donors for DIR by freshwater sediment microorganisms. Both HA and HM served as electron shuttles in cultures amended with glucose. However, only HA served as an electron donor for DIR. Metagenomes from HA-containing cultures had an overrepresentation of genes involved in polysaccharide and to a lesser extent aromatic compound degradation, suggesting complex OC metabolism. Genomic searches for the porin-cytochrome complex involved in DIR resulted in matches to Ignavibacterium/Melioribacter, DIRB capable of polymeric OC metabolism. These results indicate that such taxa may have played a role in both DIR and decomposition of complex OC. Our results suggest that decomposition of HS coupled to DIR and other anaerobic pathways could play an important role in soil and sediment OC metabolism.


Assuntos
Elétrons , Substâncias Húmicas , Compostos Férricos , Ferro , Oxirredução
7.
J Environ Sci (China) ; 65: 282-292, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29548399

RESUMO

Hexagonal turbostratic birnessite, with the characteristics of high contents of vacancies, varying amounts of structural and adsorbed Mn3+, and small particle size, undergoes strong adsorption reactions with trace metal (TM) contaminants. While the interactions of TM, i.e., Zn2+, with birnessite are well understood, the effect of birnessite structural characteristics on the coordination and stability of Zn2+ on the mineral surfaces under proton attack is as yet unclear. In the present study, the effects of a series of synthesized hexagonal turbostratic birnessites with different Mn average oxide states (AOSs) on the coordination geometry of adsorbed Zn2+ and its stability under acidic conditions were investigated. With decreasing Mn AOS, birnessite exhibits smaller particle sizes and thus larger specific surface area, higher amounts of layer Mn3+ and thus longer distances for the first MnO and MnMn shells, but a low quantity of available vacancies and thus low adsorption capacity for Zn2+. Zn K-edge EXAFS spectroscopy demonstrates that birnessite with low Mn AOS has smaller adsorption capacity but more tetrahedral Zn (IVZn) complexes on vacancies than octahedral (VIZn) complexes, and Zn2+ is more unstable under acidic conditions than that adsorbed on birnessite with high Mn AOS. High Zn2+ loading favors the formation of VIZn complexes over IVZn complexes, and the release of Zn2+ is faster than at low loading. These results will deepen our understanding of the interaction mechanisms of various TMs with natural birnessites, and the stability and thus the potential toxicity of heavy metal pollutants sequestered by engineered nano-sized metal oxide materials.


Assuntos
Poluentes Ambientais/química , Manganês/química , Modelos Químicos , Óxidos/química , Zinco/química , Manganês/classificação , Oxirredução
8.
J Environ Qual ; 47(1): 139-146, 2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29415106

RESUMO

9,10-Anthraquinone-2,6-disulfonic acid (AQDS) is commonly used as a model species to examine the influence of quinones on different biogeochemical cycles. The reduced form of this quinone, AHDS, can donate electrons to the toxic metal species Cr(VI), leading to the precipitation of less soluble Cr(III) phases. Due to the environmental abundance of Fe(III) (oxyhydr)oxides, such as goethite (α-FeOOH), it is important to study the role of these mineral phases on the electron transfer reaction between AHDS and Cr(VI). In this study, this electron transfer reaction is examined in the presence and absence of goethite at three different ratios of AHDS/Cr(VI). Ultraviolet-visible spectroscopy is used to qualitatively assess the oxidation state of AQDS during reactions with goethite. Iron K-edge and Cr K-edge X-ray absorption spectroscopy are used to examine the role of goethite in electron transfer and identify Cr(III) phases that form. Goethite inhibits the extent of Cr(VI) reduction to Cr(III), most notably at the highest ratio of AHDS/Cr(VI) investigated. Production of semiquinone radical species may limit electron transfer and decrease the yields of Fe(II) and Cr(III), both in the presence and absence of goethite. Understanding abiotic electron transfer reactions that occur in systems with multiple redox active species is important to determine the contribution of abiotic redox reactions to Fe biogeochemical cycling in natural soils.


Assuntos
Cromo/química , Compostos de Ferro/química , Minerais/química , Poluentes do Solo/química , Elétrons , Compostos Férricos , Oxirredução
9.
Appl Environ Microbiol ; 83(16)2017 08 15.
Artigo em Inglês | MEDLINE | ID: mdl-28600318

RESUMO

Hydrologic exchange plays a critical role in biogeochemical cycling within the hyporheic zone (the interface between river water and groundwater) of riverine ecosystems. Such exchange may set limits on the rates of microbial metabolism and impose deterministic selection on microbial communities that adapt to dynamically changing dissolved organic carbon (DOC) sources. This study examined the response of attached microbial communities (in situ colonized sand packs) from groundwater, hyporheic, and riverbed habitats within the Columbia River hyporheic corridor to "cross-feeding" with either groundwater, river water, or DOC-free artificial fluids. Our working hypothesis was that deterministic selection during in situ colonization would dictate the response to cross-feeding, with communities displaying maximal biomass and respiration when supplied with their native fluid source. In contrast to expectations, the major observation was that the riverbed colonized sand had much higher biomass and respiratory activity, as well as a distinct community structure, compared with those of the hyporheic and groundwater colonized sands. 16S rRNA gene amplicon sequencing revealed a much higher proportion of certain heterotrophic taxa as well as significant numbers of eukaryotic algal chloroplasts in the riverbed colonized sand. Significant quantities of DOC were released from riverbed sediment and colonized sand, and separate experiments showed that the released DOC stimulated respiration in the groundwater and piezometer colonized sand. These results suggest that the accumulation and degradation of labile particulate organic carbon (POC) within the riverbed are likely to release DOC, which may enter the hyporheic corridor during hydrologic exchange, thereby stimulating microbial activity and imposing deterministic selective pressure on the microbial community composition.IMPORTANCE The influence of river water-groundwater mixing on hyporheic zone microbial community structure and function is an important but poorly understood component of riverine biogeochemistry. This study employed an experimental approach to gain insight into how such mixing might be expected to influence the biomass, respiration, and composition of hyporheic zone microbial communities. Colonized sands from three different habitats (groundwater, river water, and hyporheic) were "cross-fed" with either groundwater, river water, or DOC-free artificial fluids. We expected that the colonization history would dictate the response to cross-feeding, with communities displaying maximal biomass and respiration when supplied with their native fluid source. By contrast, the major observation was that the riverbed communities had much higher biomass and respiration, as well as a distinct community structure compared with those of the hyporheic and groundwater colonized sands. These results highlight the importance of riverbed microbial metabolism in organic carbon processing in hyporheic corridors.


Assuntos
Bactérias/metabolismo , Água Subterrânea/microbiologia , Rios/microbiologia , Bactérias/classificação , Bactérias/genética , Bactérias/crescimento & desenvolvimento , Ecossistema , Sedimentos Geológicos/microbiologia , Água Subterrânea/química , Rios/química , Microbiologia da Água
10.
Environ Sci Technol ; 51(11): 6053-6062, 2017 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-28445042

RESUMO

Bisphenol A (BPA) is an endocrine-disrupting compound widely used in the plastic industry and found in natural waters at concentrations considered harmful for aquatic life. BPA is susceptible to oxidation by Mn(III/IV) oxides, which are commonly found in near-surface environments. Here, we quantify BPA oxidation rates and the formation of its predominant product, 4-hydroxycumyl alcohol (HCA), in tandem with transformation of a synthetic, Mn(III)-rich δ-MnO2. To investigate the effect of Mn oxide structural changes on BPA oxidation rate, 12 sequential additions of 80 µM BPA are performed at pH 7. During the additions, BPA oxidation rate decreases by 3 orders of magnitude, and HCA yield decreases from 40% to 3%. This is attributed to the accumulation of interlayer Mn(II/III) produced during the reaction, as observed using X-ray absorption spectroscopy, as well as additional spectroscopic and wet chemical techniques. HCA is oxidized at a rate that is 12.6 times slower than BPA and accumulates in solution. These results demonstrate that BPA degradation by environmentally relevant Mn(III/IV) oxides is inhibited by the buildup of solid-phase Mn(II/III), specifically in interlayer sites. Nevertheless, Mn oxides may limit BPA migration in near-surface environments and have potential for use in drinking and wastewater treatment.


Assuntos
Compostos Benzidrílicos/química , Fenóis/química , Poluentes Químicos da Água/química , Compostos de Manganês , Oxirredução , Óxidos
11.
Environ Sci Technol ; 50(7): 3580-8, 2016 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-26949922

RESUMO

Oscillations between reducing and oxidizing conditions are observed at the interface of anaerobic/oxic and anaerobic/anoxic environments, and are often stimulated by an alternating flux of electron donors (e.g., organic carbon) and electron acceptors (e.g., O2 and NO3(-)). In iron (Fe) rich soils and sediments, these oscillations may stimulate the growth of both Fe-reducing bacteria (FeRB) and Fe-oxidizing bacteria (FeOB), and their metabolism may induce cycling between Fe(II) and Fe(III), promoting the transformation of Fe (hydr)oxide minerals. Here, we examine the mineralogical evolution of lepidocrocite and ferrihydrite, and the adaptation of a natural microbial community to alternating Fe-reducing (anaerobic with addition of glucose) and Fe-oxidizing (with addition of nitrate or air) conditions. The growth of FeRB (e.g., Geobacter) is stimulated under anaerobic conditions in the presence of glucose. However, the abundance of these organisms depends on the availability of Fe(III) (hydr)oxides. Redox cycling with nitrate results in decreased Fe(II) oxidation thereby decreasing the availability of Fe(III) for FeRB. Additionally, magnetite is detected as the main product of both lepidocrocite and ferrihydrite reduction. In contrast, introduction of air results in increased Fe(II) oxidation, increasing the availability of Fe(III) and the abundance of Geobacter. In the lepidocrocite reactors, Fe(II) oxidation by dissolved O2 promotes the formation of ferrihydrite and lepidocrocite, whereas in the ferrihydrite reactors we observe a decrease in magnetite stoichiometry (e.g., oxidation). Understanding Fe (hydr)oxide transformation under environmentally relevant redox cycling conditions provides insight into nutrient availability and transport, contaminant mobility, and microbial metabolism in soils and sediments.


Assuntos
Bactérias/metabolismo , Compostos Férricos/metabolismo , Minerais/metabolismo , Nitratos/farmacologia , Oxigênio/farmacologia , Microbiologia do Solo , Bactérias/efeitos dos fármacos , Geobacter/efeitos dos fármacos , Geobacter/metabolismo , Glucose/farmacologia , Ferro/metabolismo , Oxirredução/efeitos dos fármacos , Óxidos/metabolismo
12.
Environ Sci Process Impacts ; 16(6): 1247-66, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24791271

RESUMO

Naturally occurring manganese (Mn(iii/iv)) oxides are ubiquitous in a wide range of environmental settings and play a key role in numerous biogeochemical cycles. In addition, Mn(iii/iv) oxides are powerful oxidants that are capable of oxidizing a wide range of compounds. This review critically assesses the reactivity of Mn oxides with organic contaminants. Initial work with organic reductants employed high concentrations of model compounds (e.g., substituted phenols and anilines) and emphasized the reductive dissolution of the Mn oxides. Studies with lower concentrations of organic contaminants demonstrate that Mn oxides are capable of oxidizing a wide range of compounds (e.g., antibacterial agents, endocrine disruptors, and pesticides). Both model compounds and organic contaminants undergo similar reaction mechanisms on the oxide surface. The oxidation rates of organic compounds by manganese oxides are dependent upon solution conditions, such as pH and the presence of cations, anions, or dissolved organic matter. Similarly, physicochemical properties of the minerals used affect the rates of organic compound oxidation, which increase with the average oxidation state, redox potential, and specific surface area of the Mn oxides. Due to their reactivity with contaminants under environmentally relevant conditions, Mn oxides may oxidize contaminants in soils and/or be applied in water treatment applications.


Assuntos
Poluentes Ambientais/química , Compostos de Manganês/química , Compostos Orgânicos/química , Óxidos/química , Modelos Químicos , Oxirredução , Eliminação de Resíduos Líquidos , Purificação da Água
13.
Environ Sci Technol ; 46(21): 11601-9, 2012 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-23050862

RESUMO

Layered, poorly crystalline Mn(IV)O(2) phases are abundant in the environment. These mineral phases may rapidly oxidize Cr(III) to more mobile and toxic Cr(VI) in soils. There is still, however, little knowledge of how Cr(III) oxidation by Mn(IV)O(2) proceeds at the microscopic and molecular levels. Therefore, the sorption mechanisms of Cr(III) and Cr(VI) on Random Stacked Birnessite (RSB), δ-MnO(2), and Acid Birnessite (AB) were determined by Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). These three synthetic Mn(IV)O(2), which are poorly crystalline phases and have layered structures, were reacted with 50 mM Cr(III) at pH 2.5, 3, and 3.5 before being analyzed by EXAFS. The results indicated that Cr(VI) was loosely sorbed as an outer-sphere complex on Mn(IV)O(2), while Cr(III) was tightly sorbed as an inner-sphere complex. Further research is needed to understand why Cr(III) stopped being significantly oxidized by Mn(IV)O(2) after 30 min. This study, however, demonstrated that the formation of a Cr surface precipitate is not necessarily responsible for the cessation in Cr(III) oxidation. Indeed, no Cr surface precipitate was detected at the microscopic and molecular levels on Mn(IV)O(2) surfaces reacted with Cr(III) for 1 h, although the Cr(III) oxidation ceased before 1 h of reaction at most employed experimental conditions.


Assuntos
Cromo/química , Compostos de Manganês/química , Óxidos/química , Cristalização , Concentração de Íons de Hidrogênio , Oxirredução , Espectroscopia por Absorção de Raios X
14.
Environ Sci Technol ; 46(21): 11594-600, 2012 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-23050871

RESUMO

The Cr(III)-oxidizing capacity of three layered poorly crystalline Mn(IV)O(2) phases, i.e. δ-MnO(2), Random Stacked Birnessite (RSB), and Acid Birnessite (AB), was determined in real-time and in situ, using Quick X-ray Absorption Fine Structure Spectroscopy (Q-XAFS). The results obtained with this technique, which allows the measurement of the total amount of Cr(VI) produced in the system, indicated that the Cr(III) oxidation reaction had ceased between 30 min and 1 h under most experimental conditions. However, this cessation was not observed with a traditional batch technique, which only allows the measurement of Cr(VI) present in solution and thus neglects the amount of Cr(VI) that may be sorbed to Mn(IV)O(2). This study also demonstrated that the Mn(IV)O(2) phase oxidizing the highest amount of Cr(III), which is positively charged in solution, was the mineral featuring the most negatively charged surface. Also, the results indicated that the presence of Mn(II) and/or Mn(III) impurities inside the Mn(IV)O(2) structure could enhance the mineral's capacity to oxidize Cr(III). The information provided in this study will be useful in predicting the capabilities of naturally occurring Mn oxide minerals, which are similar to the three synthetic Mn(IV)O(2) investigated, to oxidize Cr(III) to toxic and mobile Cr(VI) in the soil of contaminated sites.


Assuntos
Cromo/química , Compostos de Manganês/química , Óxidos/química , Cristalização , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , Espectroscopia por Absorção de Raios X
15.
J Enzyme Inhib Med Chem ; 27(6): 784-94, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-22085139

RESUMO

Trypanothione reductase (TR) is found in the trypanosomatid parasites, where it catalyses the NADPH-dependent reduction of the glutathione analogue, trypanothione, and is a key player in the parasite's defenses against oxidative stress. TR is a promising target for the development of antitrypanosomal drugs; here, we report our synthesis and evaluation of compounds 3-5 as low micromolar Trypanosoma cruzi TR inhibitors. Although 4 and 5 were designed as potential irreversible inhibitors, these compounds, as well as 3, displayed reversible competitive inhibition. Compound 3 proved to be the most potent inhibitor, with a K(i) = 2 µM.


Assuntos
Glutationa/análogos & derivados , NADH NADPH Oxirredutases/antagonistas & inibidores , NADP/química , Espermidina/análogos & derivados , Tripanossomicidas/síntese química , Trypanosoma cruzi/química , Desenho de Drogas , Ensaios Enzimáticos , Escherichia coli/genética , Glutationa/química , Cinética , Espectroscopia de Ressonância Magnética , Mimetismo Molecular , Proteínas Recombinantes/antagonistas & inibidores , Espectroscopia de Infravermelho com Transformada de Fourier , Espermidina/química , Especificidade por Substrato , Tripanossomicidas/química , Trypanosoma cruzi/enzimologia
16.
Environ Sci Technol ; 45(21): 9218-23, 2011 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-21950706

RESUMO

Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese oxides (Mn oxides) have the ability to decrease overall As mobility both by oxidizing toxic arsenite (As(III)) to less toxic arsenate (As(V)), and by sorbing As. However, the effect of competing ions on the mobility of As sorbed on Mn-oxide surfaces is not well understood. In this study, desorption of As(V) and As(III) from a poorly crystalline phyllomanganate (δ-MnO(2)) by two environmentally significant ions is investigated using a stirred-flow technique and X-ray absorption spectroscopy (XAS). As(III) is not observed in solution after desorption under any conditions used in this study, agreeing with previous studies showing As sorbed on Mn-oxides exists only as As(V). However, some As(V) is desorbed from the δ-MnO(2) surface under all conditions studied, while neither desorptive used in this study completely removes As(V) from the δ-MnO(2) surface.


Assuntos
Arsênico/química , Arsenitos/química , Compostos de Manganês/química , Manganês/química , Óxidos/química , Adsorção , Oxirredução , Espectroscopia por Absorção de Raios X
17.
Environ Sci Technol ; 45(10): 4249-55, 2011 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-21513267

RESUMO

This study determined Cd speciation and release kinetics in a Cd-Zn cocontaminated alkaline paddy soil, under various flooding periods and draining conditions, by employing synchrotron-based techniques, and a stirred-flow kinetic method. Results revealed that varying flooding periods and draining conditions affected Cd speciation and its release kinetics. Linear least-squares fitting (LLSF) of bulk X-ray absorption fine structure (XAFS) spectra of the air-dried, and the 1 day-flooded soil samples, showed that at least 50% of Cd was bound to humic acid. Cadmium carbonates were found as the major species at most flooding periods, while a small amount of cadmium sulfide was found after the soils were flooded for longer periods. Under all flooding and draining conditions, at least 14 mg/kg Cd was desorbed from the soil after a 2-hour desorption experiment. The results obtained by micro X-ray fluorescence (µ-XRF) spectroscopy showed that Cd was less associated with Zn than Ca, in most soil samples. Therefore, it is more likely that Cd and Ca will be present in the same mineral phases rather than Cd and Zn, although the source of these two latter elements may originate from the same surrounding Zn mines in the Mae Sot district.


Assuntos
Cádmio/química , Inundações/estatística & dados numéricos , Poluentes do Solo/química , Solo/química , Cádmio/análise , Concentração de Íons de Hidrogênio , Cinética , Modelos Químicos , Poluentes do Solo/análise , Movimentos da Água , Espectroscopia por Absorção de Raios X
18.
Environ Sci Technol ; 44(22): 8460-6, 2010 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-20977202

RESUMO

Manganese-oxides (Mn-oxides) are quite reactive, with respect to arsenite (As(III)) oxidation. However, studies regarding the pathways of As(III) oxidation, over a range of time scales, by poorly crystalline Mn-oxides, are lacking. In stirred-flow experiments, As(III) oxidation by δ-MnO2 (a poorly crystalline form of hexagonal birnessite) is initially rapid but slows appreciably after several hours of reaction. Mn(II) is the only reduced product of δ-MnO2 formed by As(III) oxidation during the initial, most rapid phase of the reaction. There seems to be evidence that the formation of Mn(III) observed in previous studies is a result of conproportionation of Mn(II) sorbed onto Mn(IV) reaction sites rather than from direct reduction of Mn(IV) by As(III).The only evidence of arsenic (As) sorption during As(III) oxidation by δ-MnO2 is during the first 10 h of reaction, and As sorption is greater when As(V) and Mn(II) occur simultaneously in solution. Our findings indicate that As(III) oxidation by poorly crystalline δ-MnO2 involves several simultaneous reactions and reinforces the importance of studying reaction mechanisms over time.


Assuntos
Arsenitos/química , Compostos de Manganês/química , Óxidos/química , Adsorção , Cristalização , Oxirredução
19.
Environ Sci Technol ; 44(22): 8467-72, 2010 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-20977204

RESUMO

Arsenite (As(III)) oxidation by manganese oxides (Mn-oxides) serves to detoxify and, under many conditions, immobilize arsenic (As) by forming arsenate (As(V)). As(III) oxidation by Mn(IV)-oxides can be quite complex, involving many simultaneous forward reactions and subsequent back reactions. During As(III) oxidation by Mn-oxides, a reduction in oxidation rate is often observed, which is attributed to Mn-oxide surface passivation. X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) data show that Mn(II) sorption on a poorly crystalline hexagonal birnessite (δ-MnO2) is important in passivation early during reaction with As(III). Also, it appears that Mn(III) in the δ-MnO2 structure is formed by conproportionation of sorbed Mn(II) and Mn(IV) in the mineral structure. The content of Mn(III) within the δ-MnO2 structure appears to increase as the reaction proceeds. Binding of As(V) to δ-MnO2 also changes as Mn(III) becomes more prominent in the δ-MnO 2 structure. The data presented indicate that As(III) oxidation and As(V) sorption by poorly crystalline δ-MnO2 is greatly affected by Mn oxidation state in the δ-MnO2 structure.


Assuntos
Arsenitos/química , Compostos de Manganês/química , Óxidos/química , Espectroscopia por Absorção de Raios X , Difração de Raios X , Adsorção , Cristalização , Oxirredução
20.
Appl Environ Microbiol ; 76(20): 6778-86, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-20729318

RESUMO

Massively parallel sequencing has provided a more affordable and high-throughput method to study microbial communities, although it has mostly been used in an exploratory fashion. We combined pyrosequencing with a strict indicator species statistical analysis to test if bacteria specifically responded to ethanol injection that successfully promoted dissimilatory uranium(VI) reduction in the subsurface of a uranium contamination plume at the Oak Ridge Field Research Center in Tennessee. Remediation was achieved with a hydraulic flow control consisting of an inner loop, where ethanol was injected, and an outer loop for flow-field protection. This strategy reduced uranium concentrations in groundwater to levels below 0.126 µM and created geochemical gradients in electron donors from the inner-loop injection well toward the outer loop and downgradient flow path. Our analysis with 15 sediment samples from the entire test area found significant indicator species that showed a high degree of adaptation to the three different hydrochemical-created conditions. Castellaniella and Rhodanobacter characterized areas with low pH, heavy metals, and low bioactivity, while sulfate-, Fe(III)-, and U(VI)-reducing bacteria (Desulfovibrio, Anaeromyxobacter, and Desulfosporosinus) were indicators of areas where U(VI) reduction occurred. The abundance of these bacteria, as well as the Fe(III) and U(VI) reducer Geobacter, correlated with the hydraulic connectivity to the substrate injection site, suggesting that the selected populations were a direct response to electron donor addition by the groundwater flow path. A false-discovery-rate approach was implemented to discard false-positive results by chance, given the large amount of data compared.


Assuntos
Bactérias/classificação , Bactérias/genética , Biodiversidade , Microbiologia Ambiental , Metagenoma , Sulfatos/metabolismo , Urânio/metabolismo , Bactérias/metabolismo , Análise por Conglomerados , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Sequenciamento de Nucleotídeos em Larga Escala , Dados de Sequência Molecular , Oxirredução , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Poluentes Radioativos do Solo/metabolismo , Tennessee
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