Sample records for acceptors including feiii

  1. Anaerobic biodegradation of BTEX using Mn(IV) and Fe(III) as alternative electron acceptors.

    PubMed

    Villatoro-Monzón, W R; Mesta-Howard, A M; Razo-Flores, E

    2003-01-01

    Anaerobic BTEX biodegradation was tested in batch experiments using an anaerobic sediment as inoculum under Fe(III) and Mn(IV) reducing conditions. All BTEX were degraded under the conditions tested, specially under Mn(IV) reducing conditions, where benzene was degraded at a rate of 0.8 micromol l(-1) d(-1), significantly much faster than Fe(III) reducing conditions. Under Fe(III) reducing conditions, ethylbenzene was the compound that degraded at the faster rate of 0.19 micromol l(-1) d(-1). Mn(IV) reducing conditions are energetically more favourable than Fe(III), therefore, BTEX were more rapidly degraded under Mn(IV) reducing conditions. These results represent the first report of the degradation of benzene with Mn(IV) as the final electron acceptor. Amorphous manganese oxide is a natural widely distributed metal in groundwater, where it can be microbiologically reduced, leading to the degradation of monoaromatic compounds.

  2. Fe(III) and S0 reduction by Pelobacter carbinolicus

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.; Widma, P.K.

    1995-01-01

    There is a close phylogenetic relationship between Pelobacter species and members of the genera Desulfuromonas and Geobacter, and yet there has been a perplexing lack of physiological similarities. Pelobacter species have been considered to have a fermentative metabolism. In contrast, Desulfuromonas and Geobacter species have a respiratory metabolism with Fe(III) serving as the common terminal electron acceptor in all species. However, the ability of Pelobacter species to reduce Fe(III) had not been previously evaluated. When a culture of Pelobacter carbinolicus that had grown by fermentation of 2,3- butanediol was inoculated into the same medium supplemented with Fe(III), the Fe(III) was reduced. There was less accumulation of ethanol and more production of acetate in the presence of Fe(III). P. carbinolicus grew with ethanol as the sole electron donor and Fe(III) as the sole electron acceptor. Ethanol was metabolized to acetate. Growth was also possible on Fe(III) with the oxidation of propanol to propionate or butanol to butyrate if acetate was provided as a carbon source. P. carbinolicus appears capable of conserving energy to support growth from Fe(III) respiration as it also grew with H2 or formate as the electron donor and Fe(III) as the electron acceptor. Once adapted to Fe(III) reduction, P. carbinolicus could also grow on ethanol or H2 with S0 as the electron acceptor. P. carbinolicus did not contain detectable concentrations of the c-type cytochromes that previous studies have suggested are involved in electron transport to Fe(III) in other organisms that conserve energy to support growth from Fe(III) reduction. These results demonstrate that P. carbinolicus may survive in some sediments as an Fe(III) or S0 reducer rather than growing fermentatively on rare substrates or syntrophically as an ethanol-oxidizing acetogen. These studies also suggest that the ability to use Fe(III) as a terminal electron acceptor may be an important unifying feature of the

  3. Use of Fe(III) as an electron acceptor to recover previously uncultured hyperthermophiles: isolation and characterization of Geothermobacterium ferrireducens gen. nov., sp. nov.

    PubMed

    Kashefi, Kazem; Holmes, Dawn E; Reysenbach, Anna-Louise; Lovley, Derek R

    2002-04-01

    It has recently been recognized that the ability to use Fe(III) as a terminal electron acceptor is a highly conserved characteristic in hyperthermophilic microorganisms. This suggests that it may be possible to recover as-yet-uncultured hyperthermophiles in pure culture if Fe(III) is used as an electron acceptor. As part of a study of the microbial diversity of the Obsidian Pool area in Yellowstone National Park, Wyo., hot sediment samples were used as the inoculum for enrichment cultures in media containing hydrogen as the sole electron donor and poorly crystalline Fe(III) oxide as the electron acceptor. A pure culture was recovered on solidified, Fe(III) oxide medium. The isolate, designated FW-1a, is a hyperthermophilic anaerobe that grows exclusively by coupling hydrogen oxidation to the reduction of poorly crystalline Fe(III) oxide. Organic carbon is not required for growth. Magnetite is the end product of Fe(III) oxide reduction under the culture conditions evaluated. The cells are rod shaped, about 0.5 microm by 1.0 to 1.2 microm, and motile and have a single flagellum. Strain FW-1a grows at circumneutral pH, at freshwater salinities, and at temperatures of between 65 and 100 degrees C with an optimum of 85 to 90 degrees C. To our knowledge this is the highest temperature optimum of any organism in the Bacteria. Analysis of the 16S ribosomal DNA (rDNA) sequence of strain FW-1a places it within the Bacteria, most closely related to abundant but uncultured microorganisms whose 16S rDNA sequences have been previously recovered from Obsidian Pool and a terrestrial hot spring in Iceland. While previous studies inferred that the uncultured microorganisms with these 16S rDNA sequences were sulfate-reducing organisms, the physiology of the strain FW-1a, which does not reduce sulfate, indicates that these organisms are just as likely to be Fe(III) reducers. These results further demonstrate that Fe(III) may be helpful for recovering as-yet-uncultured microorganisms

  4. Dissimilatory Fe(III) reduction by the marine microorganism Desulfuromonas acetoxidans

    USGS Publications Warehouse

    Roden, E.E.; Lovley, D.R.

    1993-01-01

    The ability of the marine microorganism Desulfuromonas acetoxidans to reduce Fe(III) was investigated because of its close phylogenetic relationship with the freshwater dissimilatory Fe(III) reducer Geobacter metallireducens. Washed cell suspensions of the type strain of D. acetoxidans reduced soluble Fe(III)-citrate and Fe(III) complexed with nitriloacetic acid. The c-type cytochrome(s) of D. acetoxidans was oxidized by Fe(III)- citrate and Mn(IV)-oxalate, as well as by two electron acceptors known to support growth, colloidal sulfur and malate. D. acetoxidans grew in defined anoxic, bicarbonate-buffered medium with acetate as the sole electron donor and poorly crystalline Fe(III) or Mn(IV) as the sole electron acceptor. Magnetite (Fe3O4) and siderite (FeCO3) were the major end products of Fe(III) reduction, whereas rhodochrosite (MnCO3) was the end product of Mn(IV) reduction. Ethanol, propanol, pyruvate, and butanol also served as electron donors for Fe(III) reduction. In contrast to D. acetoxidans, G. metallireducens could only grow in freshwater medium and it did not conserve energy to support growth from colloidal S0 reduction. D. acetoxidans is the first marine microorganism shown to conserve energy to support growth by coupling the complete oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). Thus, D. acetoxidans provides a model enzymatic mechanism for Fe(III) or Mn(IV) oxidation of organic compounds in marine and estuarine sediments. These findings demonstrate that 16S rRNA phylogenetic analyses can suggest previously unrecognized metabolic capabilities of microorganisms.

  5. Growth of thermophilic and hyperthermophilic Fe(III)-reducing microorganisms on a ferruginous smectite as the sole electron acceptor.

    PubMed

    Kashefi, Kazem; Shelobolina, Evgenya S; Elliott, W Crawford; Lovley, Derek R

    2008-01-01

    Recent studies have suggested that the structural Fe(III) within phyllosilicate minerals, including smectite and illite, is an important electron acceptor for Fe(III)-reducing microorganisms in sedimentary environments at moderate temperatures. The reduction of structural Fe(III) by thermophiles, however, has not previously been described. A wide range of thermophilic and hyperthermophilic Archaea and Bacteria from marine and freshwater environments that are known to reduce poorly crystalline Fe(III) oxides were tested for their ability to reduce structural (octahedrally coordinated) Fe(III) in smectite (SWa-1) as the sole electron acceptor. Two out of the 10 organisms tested, Geoglobus ahangari and Geothermobacterium ferrireducens, were not able to conserve energy to support growth by reduction of Fe(III) in SWa-1 despite the fact that both organisms were originally isolated with solid-phase Fe(III) as the electron acceptor. The other organisms tested were able to grow on SWa-1 and reduced 6.3 to 15.1% of the Fe(III). This is 20 to 50% less than the reported amounts of Fe(III) reduced in the same smectite (SWa-1) by mesophilic Fe(III) reducers. Two organisms, Geothermobacter ehrlichii and archaeal strain 140, produced copious amounts of an exopolysaccharide material, which may have played an active role in the dissolution of the structural iron in SWa-1 smectite. The reduction of structural Fe(III) in SWa-1 by archaeal strain 140 was studied in detail. Microbial Fe(III) reduction was accompanied by an increase in interlayer and octahedral charges and some incorporation of potassium and magnesium into the smectite structure. However, these changes in the major element chemistry of SWa-1 smectite did not result in the formation of an illite-like structure, as reported for a mesophilic Fe(III) reducer. These results suggest that thermophilic Fe(III)-reducing organisms differ in their ability to reduce and solubilize structural Fe(III) in SWa-1 smectite and that SWa-1

  6. Dissimilatory Fe(III) and Mn(IV) reduction.

    PubMed Central

    Lovley, D R

    1991-01-01

    The oxidation of organic matter coupled to the reduction of Fe(III) or Mn(IV) is one of the most important biogeochemical reactions in aquatic sediments, soils, and groundwater. This process, which may have been the first globally significant mechanism for the oxidation of organic matter to carbon dioxide, plays an important role in the oxidation of natural and contaminant organic compounds in a variety of environments and contributes to other phenomena of widespread significance such as the release of metals and nutrients into water supplies, the magnetization of sediments, and the corrosion of metal. Until recently, much of the Fe(III) and Mn(IV) reduction in sedimentary environments was considered to be the result of nonenzymatic processes. However, microorganisms which can effectively couple the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV) have recently been discovered. With Fe(III) or Mn(IV) as the sole electron acceptor, these organisms can completely oxidize fatty acids, hydrogen, or a variety of monoaromatic compounds. This metabolism provides energy to support growth. Sugars and amino acids can be completely oxidized by the cooperative activity of fermentative microorganisms and hydrogen- and fatty-acid-oxidizing Fe(III) and Mn(IV) reducers. This provides a microbial mechanism for the oxidation of the complex assemblage of sedimentary organic matter in Fe(III)- or Mn(IV)-reducing environments. The available evidence indicates that this enzymatic reduction of Fe(III) or Mn(IV) accounts for most of the oxidation of organic matter coupled to reduction of Fe(III) and Mn(IV) in sedimentary environments. Little is known about the diversity and ecology of the microorganisms responsible for Fe(III) and Mn(IV) reduction, and only preliminary studies have been conducted on the physiology and biochemistry of this process. PMID:1886521

  7. Mechanisms for Fe(III) oxide reduction in sedimentary environments

    USGS Publications Warehouse

    Nevin, Kelly P.; Lovely, Derek R.

    2002-01-01

    Although it was previously considered that Fe(III)-reducing microorganisms must come into direct contact with Fe(III) oxides in order to reduce them, recent studies have suggested that electron-shuttling compounds and/or Fe(III) chelators, either naturally present or produced by the Fe(III)-reducing microorganisms themselves, may alleviate the need for the Fe(III) reducers to establish direct contact with Fe(III) oxides. Studies with Shewanella alga strain BrY and Fe(III) oxides sequestered within microporous beads demonstrated for the first time that this organism releases a compound(s) that permits electron transfer to Fe(III) oxides which the organism cannot directly contact. Furthermore, as much as 450 w M dissolved Fe(III) was detected in cultures of S. alga growing in Fe(III) oxide medium, suggesting that this organism releases compounds that can solublize Fe(III) from Fe(III) oxide. These results contrast with previous studies, which demonstrated that Geobacter metallireducens does not produce electron-shuttles or Fe(III) chelators. Some freshwater aquatic sediments and groundwaters contained compounds, which could act as electron shuttles by accepting electrons from G. metallireducens and then transferring the electrons to Fe(III). However, other samples lacked significant electron-shuttling capacity. Spectroscopic studies indicated that the electron-shuttling capacity of the waters was not only associated with the presence of humic substances, but water extracts of walnut, oak, and maple leaves contained electron-shuttling compounds did not appear to be humic substances. Porewater from a freshwater aquatic sediment and groundwater from a petroleum-contaminated aquifer contained dissolved Fe(III) (4-16 w M), suggesting that soluble Fe(III) may be available as an electron acceptor in some sedimentary environments. These results demonstrate that in order to accurately model the mechanisms for Fe(III) reduction in sedimentary environments it will be necessary

  8. Mechanisms of electron acceptor utilization: Implications for simulating anaerobic biodegradation

    USGS Publications Warehouse

    Schreiber, M.E.; Carey, G.R.; Feinstein, D.T.; Bahr, J.M.

    2004-01-01

    Simulation of biodegradation reactions within a reactive transport framework requires information on mechanisms of terminal electron acceptor processes (TEAPs). In initial modeling efforts, TEAPs were approximated as occurring sequentially, with the highest energy-yielding electron acceptors (e.g. oxygen) consumed before those that yield less energy (e.g., sulfate). Within this framework in a steady state plume, sequential electron acceptor utilization would theoretically produce methane at an organic-rich source and Fe(II) further downgradient, resulting in a limited zone of Fe(II) and methane overlap. However, contaminant plumes often display much more extensive zones of overlapping Fe(II) and methane. The extensive overlap could be caused by several abiotic and biotic processes including vertical mixing of byproducts in long-screened monitoring wells, adsorption of Fe(II) onto aquifer solids, or microscale heterogeneity in Fe(III) concentrations. Alternatively, the overlap could be due to simultaneous utilization of terminal electron acceptors. Because biodegradation rates are controlled by TEAPs, evaluating the mechanisms of electron acceptor utilization is critical for improving prediction of contaminant mass losses due to biodegradation. Using BioRedox-MT3DMS, a three-dimensional, multi-species reactive transport code, we simulated the current configurations of a BTEX plume and TEAP zones at a petroleum- contaminated field site in Wisconsin. Simulation results suggest that BTEX mass loss due to biodegradation is greatest under oxygen-reducing conditions, with smaller but similar contributions to mass loss from biodegradation under Fe(III)-reducing, sulfate-reducing, and methanogenic conditions. Results of sensitivity calculations document that BTEX losses due to biodegradation are most sensitive to the age of the plume, while the shape of the BTEX plume is most sensitive to effective porosity and rate constants for biodegradation under Fe(III)-reducing and

  9. Carbohydrate oxidation coupled to Fe(III) reduction, a novel form of anaerobic metabolism

    USGS Publications Warehouse

    Coates, J.D.; Councell, T.; Ellis, D.J.; Lovley, D.R.

    1998-01-01

    An isolate, designated GC-29, that could incompletely oxidize glucose to acetate and carbon dioxide with Fe(III) serving as the electron acceptor was recovered from freshwater sediments of the Potomac River, Maryland. This metabolism yielded energy to support cell growth. Strain GC-29 is a facultatively anaerobic, Gram-negative motile rod which, in addition to glucose, also used sucrose, lactate, pyruvate, yeast extract, casamino acids or H2 as alternative electron donors for Fe(III) reduction. Stain GC-29 could reduce NO-3, Mn(IV), U(VI), fumarate, malate, S2O32-, and colloidal S0 as well as the humics analog, 2,6-anthraquinone disulfonate. Analysis of the almost complete 16S rRNA sequence indicated that strain GC-29 belongs in the Shewanella genus in the epsilon subdivision of the Proteobacteria. The name Shewanella saccharophilia is proposed. Shewanella saccharophilia differs from previously described fermentative microorganisms that metabolize glucose with the reduction of Fe(III) because it transfers significantly more electron equivalents to Fe(III); acetate and carbon dioxide are the only products of glucose metabolism; energy is conserved from Fe(III) reduction; and glucose is not metabolized in the absence of Fe(III). The metabolism of organisms like S. saccharophilia may account for the fact that glucose is metabolized primarily to acetate and carbon dioxide in a variety of sediments in which Fe(III) reduction is the terminal electron accepting process.

  10. Growth of Iron(III)-Reducing Bacteria on Clay Minerals as the Sole Electron Acceptor and Comparison of Growth Yields on a Variety of Oxidized Iron Forms†

    PubMed Central

    Kostka, Joel E.; Dalton, Dava D.; Skelton, Hayley; Dollhopf, Sherry; Stucki, Joseph W.

    2002-01-01

    Smectite clay minerals are abundant in soils and sediments worldwide and are typically rich in Fe. While recent investigations have shown that the structural Fe(III) bound in clay minerals is reduced by microorganisms, previous studies have not tested growth with clay minerals as the sole electron acceptor. Here we have demonstrated that a pure culture of Shewanella oneidensis strain MR-1 as well as enrichment cultures of Fe(III)-reducing bacteria from rice paddy soil and subsurface sediments are capable of conserving energy for growth with the structural Fe(III) bound in smectite clay as the sole electron acceptor. Pure cultures of S. oneidensis were used for more detailed growth rate and yield experiments on various solid- and soluble-phase electron acceptors [smectite, Fe(III) oxyhydroxide FeOOH, Fe(III) citrate, and oxygen] in the same minimal medium. Growth was assessed as direct cell counts or as an increase in cell carbon (measured as particulate organic carbon). Cell counts showed that similar growth of S. oneidensis (108 cells ml−1) occurred with smectitic Fe(III) and on other Fe forms [amorphous Fe(III) oxyhydroxide, and Fe citrate] or oxygen as the electron acceptor. In contrast, cell yields of S. oneidensis measured as the increase in cell carbon were similar on all Fe forms tested while yields on oxygen were five times higher, in agreement with thermodynamic predictions. Over a range of particle loadings (0.5 to 4 g liter−1), the increase in cell number was highly correlated to the amount of structural Fe in smectite reduced. From phylogenetic analysis of the complete 16S rRNA gene sequences, a predominance of clones retrieved from the clay mineral-reducing enrichment cultures were most closely related to the low-G+C gram-positive members of the Bacteria (Clostridium and Desulfitobacterium) and the δ-Proteobacteria (members of the Geobacteraceae). Results indicate that growth with smectitic Fe(III) is similar in magnitude to that with Fe(III

  11. Importance of clay size minerals for Fe(III) respiration in a petroleum-contaminated aquifer

    USGS Publications Warehouse

    Shelobolina, Evgenya S.; Anderson, Robert T.; Vodyanitskii, Yury N.; Sivtsov, Anatolii V.; Yuretich, Richard; Lovely, Derek R.

    2004-01-01

    (III)-bearing clay size minerals were essential for microbial Fe(III) reduction and suggested that both potential sources of ‘bio-available’ Fe(III) in the clay size fraction, poorly crystalline Fe(III) hydroxides and structural Fe(III) of phyllosilicates, were important sources of electron acceptor for indigenous iron-reducing microorganisms in this aquifer.

  12. Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals

    PubMed Central

    White, Gaye F.; Shi, Zhi; Shi, Liang; Wang, Zheming; Dohnalkova, Alice C.; Marshall, Matthew J.; Fredrickson, James K.; Zachara, John M.; Butt, Julea N.; Richardson, David J.; Clarke, Thomas A.

    2013-01-01

    The mineral-respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decaheme cytochromes, MtrC and MtrA, brought together inside a transmembrane porin, MtrB, to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system containing a pool of internalized electron carriers was used to investigate how the topology of the MtrCAB complex relates to its ability to transport electrons across a lipid bilayer to externally located Fe(III) oxides. With MtrA facing the interior and MtrC exposed on the outer surface of the phospholipid bilayer, the established in vivo orientation, electron transfer from the interior electron carrier pool through MtrCAB to solid-phase Fe(III) oxides was demonstrated. The rates were 103 times higher than those reported for reduction of goethite, hematite, and lepidocrocite by S. oneidensis, and the order of the reaction rates was consistent with those observed in S. oneidensis cultures. In contrast, established rates for single turnover reactions between purified MtrC and Fe(III) oxides were 103 times lower. By providing a continuous flow of electrons, the proteoliposome experiments demonstrate that conduction through MtrCAB directly to Fe(III) oxides is sufficient to support in vivo, anaerobic, solid-phase iron respiration. PMID:23538304

  13. Isolation and Characterization of a Soluble NADPH-Dependent Fe(III) Reductase from Geobacter sulfurreducens

    PubMed Central

    Kaufmann, Franz; Lovley, Derek R.

    2001-01-01

    NADPH is an intermediate in the oxidation of organic compounds coupled to Fe(III) reduction in Geobacter species, but Fe(III) reduction with NADPH as the electron donor has not been studied in these organisms. Crude extracts of Geobacter sulfurreducens catalyzed the NADPH-dependent reduction of Fe(III)-nitrilotriacetic acid (NTA). The responsible enzyme, which was recovered in the soluble protein fraction, was purified to apparent homogeneity in a four-step procedure. Its specific activity for Fe(III) reduction was 65 μmol · min−1 · mg−1. The soluble Fe(III) reductase was specific for NADPH and did not utilize NADH as an electron donor. Although the enzyme reduced several forms of Fe(III), Fe(III)-NTA was the preferred electron acceptor. The protein possessed methyl viologen:NADP+ oxidoreductase activity and catalyzed the reduction of NADP+ with reduced methyl viologen as electron donor at a rate of 385 U/mg. The enzyme consisted of two subunits with molecular masses of 87 and 78 kDa and had a native molecular mass of 320 kDa, as determined by gel filtration. The purified enzyme contained 28.9 mol of Fe, 17.4 mol of acid-labile sulfur, and 0.7 mol of flavin adenine dinucleotide per mol of protein. The genes encoding the two subunits were identified in the complete sequence of the G. sulfurreducens genome from the N-terminal amino acid sequences derived from the subunits of the purified protein. The sequences of the two subunits had about 30% amino acid identity to the respective subunits of the formate dehydrogenase from Moorella thermoacetica, but the soluble Fe(III) reductase did not possess formate dehydrogenase activity. This soluble Fe(III) reductase differs significantly from previously characterized dissimilatory and assimilatory Fe(III) reductases in its molecular composition and cofactor content. PMID:11443080

  14. Enhanced reduction of Fe(III) oxides and methyl orange by Klebsiella oxytoca in presence of anthraquinone-2-disulfonate.

    PubMed

    Yu, Lei; Wang, Shi; Tang, Qing-Wen; Cao, Ming-Yue; Li, Jia; Yuan, Kun; Wang, Ping; Li, Wen-Wei

    2016-05-01

    Klebsiella oxytoca GS-4-08 is capable of azo dye reduction, but its quinone respiration and Fe(III) reduction abilities have not been reported so far. In this study, the abilities of this strain were reported in detail for the first time. As the biotic reduction of Fe(III) plays an important role in the biogeochemical cycles, two amorphous Fe(III) oxides were tested as the sole electron acceptor during the anaerobic respiration of strain GS-4-08. For the reduction of goethite and hematite, the biogenic Fe(II) concentrations reached 0.06 and 0.15 mM, respectively. Humic acid analog anthraquinone-2-disulfonate (AQS) was found to serve as an electron shuttle to increase the reduction of both methyl orange (MO) and amorphous Fe(III) oxides, and improve the dye tolerance of the strain. However, the formation of Fe(II) was not accelerated by biologically reduced AQS (B-AH2QS) because of the high bioavailability of soluble Fe(III). For the K. oxytoca strain, high soluble Fe(III) concentrations (above 1 mM) limit its growth and decolorization ability, while lower soluble Fe(III) concentrations produce an electron competition with MO initially, and then stimulate the decolorization after the electron couples of Fe(III)/Fe(II) are formed. With the ability to respire both soluble Fe(III) and insoluble Fe(III) oxides, this formerly known azo-reducer may be used as a promising model organism for the study of the interaction of these potentially competing processes in contaminated environments.

  15. Particle Aggregation During Fe(III) Bioreduction in Nontronite

    NASA Astrophysics Data System (ADS)

    Jaisi, D. P.; Dong, H.; Hi, Z.; Kim, J.

    2005-12-01

    This study was performed to evaluate the rate and mechanism of particle aggregation during bacterial Fe (III) reduction in different size fractions of nontronite and to investigate the role of different factors contributing to particle aggregation. To achieve this goal, microbial Fe(III) reduction experiments were performed with lactate as an electron donor, Fe(III) in nontronite as an electron acceptor, and AQDS as an electron shuttle in bicarbonate buffer using Shewanella putrefaceins CN32. These experiments were performed with and without Na- pyrophosphate as a dispersant in four size fractions of nontronite (0.12-0.22, 0.41-0.69, 0.73-0.96 and 1.42-1.8 mm). The rate of nontronite aggregation during the Fe(III) bioreduction was measured by analyzing particle size distribution using photon correlation spectroscopy (PCS) and SEM images analysis. Similarly, the changes in particle morphology during particle aggregation were determined by analyses of SEM images. Changes in particle surface charge were measured with electrophoretic mobility analyzer. The protein and carbohydrate fraction of EPS produced by cells during Fe(III) bioreduction was measured using Bradford and phenol-sulfuric acid extraction method, respectively. In the presence of the dispersant, the extent of Fe(III) bioreduction was 11.5-12.2% within the first 56 hours of the experiment. There was no measurable particle aggregation in control experiments. The PCS measurements showed that the increase in the effective diameter (95% percentile) was by a factor of 3.1 and 1.9 for particle size of 0.12-0.22 mm and 1.42-1.80 mm, respectively. The SEM image analyses also gave the similar magnitude of increase in particle size. In the absence of the dispersant, the extent of Fe(III) bioreduction was 13.4-14.5% in 56 hours of the experiment. The rate of aggregation was higher than that in the presence of the dispersant. The increase in the effective diameter (95% percentile) was by a factor of 13.6 and 4.1 for

  16. Growth of strain SES-3 with arsenate and other diverse electron acceptors

    USGS Publications Warehouse

    Laverman, A.M.; Blum, J.S.; Schaefer, J.K.; Phillips, E.J.P.; Lovley, D.R.; Oremland, R.S.

    1995-01-01

    The selenate-respiring bacterial strain SES-3 was able to use a variety of inorganic electron acceptors to sustain growth. SES-3 grew with the reduction of arsenate to arsenite, Fe(III) to Fe(II), or thiosulfate to sulfide. It also grew in medium in which elemental sulfur, Mn(IV), nitrite, trimethylamine N-oxide, or fumarate was provided as an electron acceptor. Growth on oxygen was microaerophilic. There was no growth with arsenite or chromate. Washed suspensions of cells grown on selenate or nitrate had a constitutive ability to reduce arsenate but were unable to reduce arsenite. These results suggest that strain SES-3 may occupy a niche as an environmental opportunist by being able to take advantage of a diversity of electron acceptors.

  17. The life cycle of iron Fe(III) oxide: impact of fungi and bacteria

    NASA Astrophysics Data System (ADS)

    Bonneville, Steeve

    2014-05-01

    Iron oxides are ubiquitous reactive constituents of soils, sediments and aquifers. They exhibit vast surface areas which bind a large array of trace metals, nutrients and organic molecules hence controlling their mobility/reactivity in the subsurface. In this context, understanding the "life cycle" of iron oxide in soils is paramount to many biogeochemical processes. Soils environments are notorious for their extreme heterogeneity and variability of chemical, physical conditions and biological agents at play. Here, we present studies investigating the role of two biological agents driving iron oxide dynamics in soils, root-associated fungi (mycorrhiza) and bacteria. Mycorrhiza filaments (hypha) grow preferentially around, and on the surface of nutrient-rich minerals, making mineral-fungi contact zones, hot-spots of chemical alteration in soils. However, because of the microscopic nature of hyphae (only ~ 5 µm wide for up to 1 mm long) and their tendency to strongly adhere to mineral surface, in situ observations of this interfacial micro-environment are scarce. In a microcosm, ectomycorrhiza (Paxillus involutus) was grown symbiotically with a pine tree (Pinus sylvestris) in the presence of freshly-cleaved biotite under humid, yet undersaturated, conditions typical of soils. Using spatially-resolved ion milling technique (FIB), transmission electron microscopy and spectroscopy (TEM/STEM-EDS), synchrotron based X-ray microscopy (STXM), we were able to quantify the speciation of Fe at the biotite-hypha interface. The results shows that substantial oxidation of biotite structural-Fe(II) into Fe(III) subdomains occurs at the contact zone between mycorrhiza and biotite. Once formed, iron(III) oxides can reductively dissolve under suboxic conditions via several abiotic and microbial pathways. In particular, they serve as terminal electron acceptors for the oxidation of organic matter by iron reducing bacteria. We aimed here to understand the role of Fe(III) mineral

  18. Anaerobic humus and Fe(III) reduction and electron transport pathway by a novel humus-reducing bacterium, Thauera humireducens SgZ-1.

    PubMed

    Ma, Chen; Yu, Zhen; Lu, Qin; Zhuang, Li; Zhou, Shun-Gui

    2015-04-01

    In this study, an anaerobic batch experiment was conducted to investigate the humus- and Fe(III)-reducing ability of a novel humus-reducing bacterium, Thauera humireducens SgZ-1. Inhibition tests were also performed to explore the electron transport pathways with various electron acceptors. The results indicate that in anaerobic conditions, strain SgZ-1 possesses the ability to reduce a humus analog, humic acids, soluble Fe(III), and Fe(III) oxides. Acetate, propionate, lactate, and pyruvate were suitable electron donors for humus and Fe(III) reduction by strain SgZ-1, while fermentable sugars (glucose and sucrose) were not. UV-visible spectra obtained from intact cells of strain SgZ-1 showed absorption peaks at 420, 522, and 553 nm, characteristic of c-type cytochromes (cyt c). Dithionite-reduced cyt c was reoxidized by Fe-EDTA and HFO (hydrous ferric oxide), which suggests that cyt c within intact cells of strain SgZ-1 has the ability to donate electrons to extracellular Fe(III) species. Inhibition tests revealed that dehydrogenases, quinones, and cytochromes b/c (cyt b/c) were involved in reduction of AQS (9, 10-anthraquinone-2-sulfonic acid, humus analog) and oxygen. In contrast, only NADH dehydrogenase was linked to electron transport to HFO, while dehydrogenases and cyt b/c were found to participate in the reduction of Fe-EDTA. Thus, various different electron transport pathways are employed by strain SgZ-1 for different electron acceptors. The results from this study help in understanding the electron transport processes and environmental responses of the genus Thauera.

  19. Microbial reduction of Fe(III) and turnover of acetate in Hawaiian soils.

    PubMed

    Küsel, Kirsten; Wagner, Christine; Trinkwalter, Tanja; Gössner, Anita S; Bäumler, Rupert; Drake, Harold L

    2002-04-01

    Soils contain anoxic microzones, and acetate is an intermediate during the turnover of soil organic carbon. Due to negligible methanogenic activities in well-drained soils, acetate accumulates under experimentally imposed short-term anoxic conditions. In contrast to forest, agricultural, and prairie soils, grassland soils from Hawaii rapidly consumed rather than formed acetate when incubated under anoxic conditions. Thus, alternative electron acceptors that might be linked to the anaerobic oxidation of soil organic carbon in Hawaiian soils were assessed. Under anoxic conditions, high amounts of Fe(II) were formed by Hawaiian soils as soon as soils were depleted of nitrate. Rates of Fe(II) formation for different soils ranged from 0.01 to 0.31 micromol (g dry weight soil)(-1) h(-1), but were not positively correlated to increasing amounts of poorly crystallized iron oxides. In general, sulfate-reducing and methanogenic activities were negligible. Supplemental acetate was rapidly oxidized to CO2 via the sequential reduction of nitrate and Fe(III) in grassland soil (obtained near Kaena State Park). Supplemental H2 stimulated the formation of Fe(II), but H2-utilizing acetogens appeared to also be involved in the consumption of H2. Approximately 270 micromol Fe(III) (g dry weight soil)(-1) was available for Fe(III)-reducing bacteria, and acetate became a stable end product when Fe(III) was depleted in long-term incubations. Most-probable-number estimates of H2- and acetate-utilizing Fe(III) reducers and of H2-utilizing acetogens were similar. These results indicate that (i) the microbial reduction of Fe(III) is an important electron-accepting process for the anaerobic oxidation of organic matter in Fe(III)-rich Hawaiian soils of volcanic origin, and (ii) acetate, formed by the combined activity of fermentative and acetogenic bacteria, is an important trophic link in anoxic microsites of these soils.

  20. Biodegradation of organic matter and anodic microbial communities analysis in sediment microbial fuel cells with/without Fe(III) oxide addition.

    PubMed

    Xu, Xun; Zhao, Qingliang; Wu, Mingsong; Ding, Jing; Zhang, Weixian

    2017-02-01

    To enhance the biodegradation of organic matter in sediment microbial fuel cell (SMFC), Fe(III) oxide, as an alternative electron acceptor, was added into the sediment. Results showed that the SMFC with Fe(III) oxide addition obtained higher removal efficiencies for organics than the SMFC without Fe(III) oxide addition and open circuit bioreactor, and produced a maximum power density (P max ) of 87.85mW/m 2 with a corresponding maximum voltage (V max ) of 0.664V. The alteration of UV-254 and specific ultraviolet absorbance (SUVA) also demonstrated the organic matter in sediments can be effectively removed. High-throughput sequencing of anodic microbial communities indicated that bacteria from the genus Geobacter were predominantly detected (21.23%) in the biofilm formed on the anode of SMFCs, while Pseudomonas was the most predominant genus (18.12%) in the presence of Fe(III) oxide. Additionally, compared with the open circuit bioreactor, more electrogenic bacteria attached to the biofilm of anode in SMFCs. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Microbial Fe(III) Oxide Reduction in Chocolate Pots Hot Springs, Yellowstone National Park

    NASA Astrophysics Data System (ADS)

    Fortney, N. W.; Roden, E. E.; Boyd, E. S.; Converse, B. J.

    2014-12-01

    Previous work on dissimilatory iron reduction (DIR) in Yellowstone National Park (YNP) has focused on high temperature, low pH environments where soluble Fe(III) is utilized as an electron acceptor for respiration. Much less attention has been paid to DIR in lower temperature, circumneutral pH environments, where solid phase Fe(III) oxides are the dominant forms of Fe(III). This study explored the potential for DIR in the warm (ca. 40-50°C), circumneutral pH Chocolate Pots hot springs (CP) in YNP. Most probable number (MPN) enumerations and enrichment culture studies confirmed the presence of endogenous microbial communities that reduced native CP Fe(III) oxides. Enrichment cultures demonstrated sustained DIR coupled to acetate and lactate oxidation through repeated transfers over ca. 450 days. Pyrosequencing of 16S rRNA genes indicated that the dominant organisms in the enrichments were closely affiliated with the well known Fe(III) reducer Geobacter metallireducens. Additional taxa included relatives of sulfate reducing bacterial genera Desulfohalobium and Thermodesulfovibrio; however, amendment of enrichments with molybdate, an inhibitor of sulfate reduction, suggested that sulfate reduction was not a primary metabolic pathway involved in DIR in the cultures. A metagenomic analysis of enrichment cultures is underway in anticipation of identifying genes involved in DIR in the less well-characterized dominant organisms. Current studies are aimed at interrogating the in situ microbial community at CP. Core samples were collected along the flow path (Fig. 1) and subdivided into 1 cm depth intervals for geochemical and microbiological analysis. The presence of significant quantities of Fe(II) in the solids indicated that DIR is active in situ. A parallel study investigated in vitro microbial DIR in sediments collected from three of the coring sites. DNA was extracted from samples from both studies for 16S rRNA gene and metagenomic sequencing in order to obtain a

  2. An Inner Membrane Cytochrome Required Only for Reduction of High Redox Potential Extracellular Electron Acceptors

    PubMed Central

    Levar, Caleb E.; Chan, Chi Ho; Mehta-Kolte, Misha G.

    2014-01-01

    ABSTRACT Dissimilatory metal-reducing bacteria, such as Geobacter sulfurreducens, transfer electrons beyond their outer membranes to Fe(III) and Mn(IV) oxides, heavy metals, and electrodes in electrochemical devices. In the environment, metal acceptors exist in multiple chelated and insoluble forms that span a range of redox potentials and offer different amounts of available energy. Despite this, metal-reducing bacteria have not been shown to alter their electron transfer strategies to take advantage of these energy differences. Disruption of imcH, encoding an inner membrane c-type cytochrome, eliminated the ability of G. sulfurreducens to reduce Fe(III) citrate, Fe(III)-EDTA, and insoluble Mn(IV) oxides, electron acceptors with potentials greater than 0.1 V versus the standard hydrogen electrode (SHE), but the imcH mutant retained the ability to reduce Fe(III) oxides with potentials of ≤−0.1 V versus SHE. The imcH mutant failed to grow on electrodes poised at +0.24 V versus SHE, but switching electrodes to −0.1 V versus SHE triggered exponential growth. At potentials of ≤−0.1 V versus SHE, both the wild type and the imcH mutant doubled 60% slower than at higher potentials. Electrodes poised even 100 mV higher (0.0 V versus SHE) could not trigger imcH mutant growth. These results demonstrate that G. sulfurreducens possesses multiple respiratory pathways, that some of these pathways are in operation only after exposure to low redox potentials, and that electron flow can be coupled to generation of different amounts of energy for growth. The redox potentials that trigger these behaviors mirror those of metal acceptors common in subsurface environments where Geobacter is found. PMID:25425235

  3. An inner membrane cytochrome required only for reduction of high redox potential extracellular electron acceptors

    DOE PAGES

    Levar, Caleb E.; Chan, Chi Ho; Mehta-Kolte, Misha G.; ...

    2014-10-28

    Dissimilatory metal-reducing bacteria, such as Geobacter sulfurreducens, transfer electrons beyond their outer membranes to Fe(III) and Mn(IV) oxides, heavy metals, and electrodes in electrochemical devices. In the environment, metal acceptors exist in multiple chelated and insoluble forms that span a range of redox potentials and offer different amounts of available energy. Despite this, metal-reducing bacteria have not been shown to alter their electron transfer strategies to take advantage of these energy differences. Disruption of imcH, encoding an inner membrane c-type cytochrome, eliminated the ability of G. sulfurreducens to reduce Fe(III) citrate, Fe(III)-EDTA, and insoluble Mn(IV) oxides, electron acceptors with potentialsmore » greater than 0.1 V versus the standard hydrogen electrode (SHE), but the imcH mutant retained the ability to reduce Fe(III) oxides with potentials of ≤–0.1 V versus SHE. The imcH mutant failed to grow on electrodes poised at +0.24 V versus SHE, but switching electrodes to –0.1 V versus SHE triggered exponential growth. At potentials of ≤–0.1 V versus SHE, both the wild type and the imcH mutant doubled 60% slower than at higher potentials. Electrodes poised even 100 mV higher (0.0 V versus SHE) could not trigger imcH mutant growth. These results demonstrate that G. sulfurreducens possesses multiple respiratory pathways, that some of these pathways are in operation only after exposure to low redox potentials, and that electron flow can be coupled to generation of different amounts of energy for growth. Redox potentials that trigger these behaviors mirror those of metal acceptors common in subsurface environments where Geobacter is found.« less

  4. Mechanisms for chelator stimulation of microbial Fe(III) -oxide reduction

    USGS Publications Warehouse

    Lovley, D.R.; Woodward, J.C.

    1996-01-01

    The mechanisms by which nitrilotriacetic acid (NTA) stimulated Fe(III) reduction in sediments from a petroleum-contaminated aquifer were investigated in order to gain insight into how added Fe(III) chelators stimulate the activity of hydrocarbon-degrading, Fe(III)-reducing microorganisms in these sediments, and how naturally occurring Fe(III) chelators might promote Fe(III) reduction in aquatic sediments. NTA solubilized Fe(III) from the aquifer sediments. NTA stimulation of microbial Fe(III) reduction did not appear to be the result of making calcium, magnesium, potassium, or trace metals more available to the microorganisms. Stimulation of Fe(III) reduction could not be attributed to NTA serving as a source of carbon or fixed nitrogen for Fe(III)-reducing bacteria as NTA was not degraded in the sediments. Studies with the Fe(III)-reducing microorganism, Geobacter metallireducens, and pure Fe(III)-oxide forms, demonstrated that NTA stimulated the reduction of a variety of Fe(III) forms, including highly crystalline Fe(III)-oxides such as goethite and hematite. The results suggest that NTA solubilization of insoluble Fe(III)-oxide is an important mechanism for the stimulation of Fe(III) reduction by NTA in aquifer sediments.

  5. Influence of humic acid imposed changes of ferrihydrite aggregation on microbial Fe(III) reduction

    NASA Astrophysics Data System (ADS)

    Amstaetter, Katja; Borch, Thomas; Kappler, Andreas

    2012-05-01

    Microbial reduction of Fe(III) minerals at neutral pH is faced by the problem of electron transfer from the cells to the solid-phase electron acceptor and is thought to require either direct cell-mineral contact, the presence of Fe(III)-chelators or the presence of electron shuttles, e.g. dissolved or solid-phase humic substances (HS). In this study we investigated to which extent the ratio of Pahokee Peat Humic Acids (HA) to ferrihydrite in the presence and absence of phosphate influences rates of Fe(III) reduction by Shewanella oneidensis MR-1 and the identity of the minerals formed. We found that phosphate generally decreased reduction rates by sorption to the ferrihydrite and surface site blocking. In the presence of low ferrihydrite concentrations (5 mM), the addition of HA helped to overcome this inhibiting effect by functioning as electron shuttle between cells and the ferrihydrite. In contrast, at high ferrihydrite concentrations (30 mM), the addition of HA did not lead to an increase but rather to a decrease in reduction rates. Confocal laser scanning microscopy images and ferrihydrite sedimentation behaviour suggest that the extent of ferrihydrite surface coating by HA influences the aggregation of the ferrihydrite particles and thereby their accessibility for Fe(III)-reducing bacteria. We further conclude that in presence of dissolved HA, iron reduction is stimulated through electron shuttling while in the presence of only sorbed HA, no stimulation by electron shuttling takes place. In presence of phosphate the stimulation effect did not occur until a minimum concentration of 10 mg/l of dissolved HA was reached followed by increasing Fe(III) reduction rates up to dissolved HA concentrations of approximately 240 mg/l above which the electron shuttling effect ceased. Not only Fe(III) reduction rates but also the mineral products changed in the presence of HA. Sequential extraction, XRD and 57Fe-Mössbauer spectroscopy showed that crystallinity and grain

  6. Spectral, thermal, XRD and SEM studies of charge-transfer complexation of hexamethylenediamine and three types of acceptors: π-, σ- and vacant orbital acceptors that include quinol, picric acid, bromine, iodine, SnCl4 and ZnCl2 acceptors

    NASA Astrophysics Data System (ADS)

    Adam, Abdel Majid A.; Refat, Moamen S.; Saad, Hosam A.

    2013-11-01

    In this work, structural, thermal, morphological and pharmacological characterization was performed on the interactions between a hexamethylenediamine (HMDA) donor and three types of acceptors to understand the complexation behavior of diamines. The three types of acceptors include π-acceptors (i.e., quinol (QL) and picric acid (PA)), σ-acceptors (i.e., bromine and iodine) and vacant orbital acceptors (i.e., tin(IV) tetrachloride (SnCl4) and zinc chloride (ZnCl2)). The characterization of the obtained CT complexes was performed using elemental analysis, infrared (IR), Raman, 1H NMR and electronic absorption spectroscopy, powder X-ray diffraction (XRD) and thermogravimetric (TG) analysis. Their morphologies were studied using scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). The biological activities of the obtained CT complexes were tested for their antibacterial activities. The complex containing the QL acceptor exhibited a remarkable electronic spectrum with a strong, broad absorption band, which had an observed λmax that was at a much longer wavelength than those of the free reactants. In addition, this complex exhibited strong antimicrobial activities against various bacterial and fungal strains compared to standard drugs. The complexes containing the PA, iodine, Sn(IV) and Zn(II) acceptors exhibited good thermal stability up to 240, 330, 275 and 295 °C, respectively. The complexes containing bromine, Sn(IV) and Zn(II) acceptors exhibited good crystallinity. In addition to its good crystallinity properties, the complex containing the bromine acceptor exhibits a remarkable morphology feature.

  7. Fe Isotope Fractionation During Fe(III) Reduction to Fe(II)

    NASA Astrophysics Data System (ADS)

    Baker, E. A.; Greene, S.; Hardin, E. E.; Hodierne, C. E.; Rosenberg, A.; John, S.

    2014-12-01

    The redox chemistry of Fe(III) and Fe(II) is tied to a variety of earth processes, including biological, chemical, or photochemical reduction of Fe(III) to Fe(II). Each process may fractionate Fe isotopes, but the magnitudes of the kinetic isotope effects have not been greatly explored in laboratory conditions. Here, we present the isotopic fractionation of Fe during reduction experiments under a variety of experimental conditions including photochemical reduction of Fe(III) bound to EDTA or glucaric acid, and chemical reduction of Fe-EDTA by sodium dithionite, hydroxylamine hydrochloride, Mn(II), and ascorbic acid. A variety of temperatures and pHs were tested. In all experiments, Fe(III) bound to an organic ligand was reduced in the presence of ferrozine. Ferrozine binds with Fe(II), forming a purple complex which allows us to measure the extent of reaction. The absorbance of the experimental solutions was measured over time to determine the Fe(II)-ferrozine concentration and thus the reduction rate. After about 5% of the Fe(III) was reduced, Fe(III)-EDTA and Fe(II)-ferrozine were separated using a C-18 column to which Fe(II)-ferrozine binds. The Fe(II) was eluted and purified through anion exchange chromatography for analysis of δ56Fe by MC-ICPMS. Preliminary results show that temperature and pH both affect reduction rate. All chemical reductants tested reduce Fe(III) at a greater rate as temperature increases. The photochemical reductant EDTA reduces Fe(III) at a greater rate under more acidic conditions. Comparison of the two photochemical reductants shows that glucaric acid reduces Fe(III) significantly faster than EDTA. For chemical reduction, the magnitude of isotopic fractionation depends on the reductant used. Temperature and pH also affect the isotopic fractionation of Fe. Experiments using chemical reductants show that an increase in temperature at low temperatures produces lighter 56Fe ratios, while at high temperatures some reductants produce heavier

  8. Control of Fe(III) site occupancy on the rate and extent of microbial reduction of Fe(III) in nontronite

    USGS Publications Warehouse

    Jaisi, Deb P.; Kukkadapu, R.K.; Eberl, D.D.; Dong, H.

    2005-01-01

    A quantitative study was performed to understand how Fe(III) site occupancy controls Fe(III) bioreduction in nontronite by Shewanella putrefaciens CN32. NAu-1 and NAu-2 were nontronites and contained Fe(III) in different structural sites with 16 and 23% total iron (w/w), respectively, with almost all iron as Fe(III). Mo??ssbauer spectroscopy showed that Fe(III) was present in the octahedral site in NAu-1 (with a small amount of goethite), but in both the tetrahedral and the octahedral sites in NAu-2. Mo??ssbauer data further showed that the octahedral Fe(III) in NAu-2 existed in at least two environments- trans (M1) and cis (M2) sites. The microbial Fe(III) reduction in NAu-1 and NAu-2 was studied in batch cultures at a nontronite concentration of 5 mg/mL in bicarbonate buffer with lactate as the electron donor. The unreduced and bioreduced nontronites were characterized by X-ray diffraction (XRD), Mo??ssbauer spectroscopy, and transmission electron microscopy (TEM). In the presence of an electron shuttle, anthraquinone-2,6-disulfonate (AQDS), the extent of bioreduction was 11%-16% for NAu-1 but 28%-32% for NAu-2. The extent of reduction in the absence of AQDS was only 5%-7% for NAu-1 but 14%-18% for NAu-2. The control experiments with heat killed cells and without cells did not show any appreciable reduction (<2%). The extent of reduction in experiments performed with a dialysis membrane to separate cells from clays (without AQDS) was 2%-3% for NAu-1 but 5%-7% for NAu-2, suggesting that cells probably released an electron shuttling compound and/or Fe(III) chelator. The reduction rate was also faster in NAu-2 than that in NAu-1. Mo??ssbauer data of the bioreduced nontronite materials indicated that the Fe(III) reduction in NAu-1 was mostly from the presence of goethite, whereas the reduction in NAu-2 was due to the presence of the tetrahedral and trans-octahedral Fe(III) in the structure. The measured aqueous Fe(II) was negligible. As a result of bioreduction, the

  9. Alkaline Fe(III) reduction by a novel alkali-tolerant Serratia sp. isolated from surface sediments close to Sellafield nuclear facility, UK.

    PubMed

    Thorpe, Clare L; Morris, Katherine; Boothman, Christopher; Lloyd, Jonathan R

    2012-02-01

    Extensive denitrification resulted in a dramatic increase in pH (from 6.8 to 9.5) in nitrate-impacted, acetate-amended sediment microcosms containing sediment representative of the Sellafield nuclear facility, UK. Denitrification was followed by Fe(III) reduction, indicating the presence of alkali-tolerant, metal-reducing bacteria. A close relative (99% 16S rRNA gene sequence homology) to Serratia liquefaciens dominated progressive enrichment cultures containing Fe(III)-citrate as the sole electron acceptor at pH 9 and was isolated aerobically using solid media. The optimum growth conditions for this facultatively anaerobic Serratia species were investigated, and it was capable of metabolizing a wide range of electron acceptors including oxygen, nitrate, FeGel, Fe-NTA and Fe-citrate and electron donors including acetate, lactate, formate, ethanol, glucose, glycerol and yeast extract at an optimum pH of c. 6.5 at 20 °C. The alkali tolerance of this strain extends the pH range of highly adaptable Fe(III)-reducing Serratia species from mildly acidic pH values associated with acid mine drainage conditions to alkali conditions representative of subsurface sediments stimulated for extensive denitrification and metal reduction. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

  10. Enzymatic versus nonenzymatic mechanisms for Fe(III) reduction in aquatic sediments

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.

    1991-01-01

    The potential for nonenzymatic reduction of Fe(III) either by organic compounds or by the development of a low redox potential during microbial metabolism was compared with direct, enzymatic Fe(III) reduction by Fe(III)-reducing microorganisms. At circumneutral pH, very few organic compounds nonenzymatically reduced Fe(III). In contrast, in the presence of the appropriate Fe(IH)-reducing microorganisms, most of the organic compounds examined could be completely oxidized to carbon dioxide with the reduction of Fe(III). Even for those organic compounds that could nonenzymatically reduce Fe(III), microbial Fe(III) reduction was much more extensive. The development of a low redox potential during microbial fermentation did not result in nonenzymatic Fe(III) reduction. Model organic compounds were readily oxidized in Fe(III)-reducing aquifer sediments, but not in sterilized sediments. These results suggest that microorganisms enzymatically catalyze most of the Fe(III) reduction in the Fe(III) reduction zone of aquatic sediments and aquifers.

  11. Fate of microbial metabolites of hydrocarbons in a coastal plain aquifer: The role of electron acceptors

    USGS Publications Warehouse

    Cozzarelli, I.M.; Herman, J.S.; Baedecker, M. Jo

    1995-01-01

    A combined field and laboratory study was undertaken to understand the distribution and geochemical conditions that influence the prevalence of low molecular weight organic acids in groundwater of a shallow aquifer contaminated with gasoline. Aromatic hydrocarbons from gasoline were degraded by microbially mediated oxidation-reduction reactions, including reduction of nitrate, sulfate, and Fe(III). The biogeochemical reactions changed overtime in response to changes in the hydrogeochemical conditions in the aquifer. Aliphatic and aromatic organic acids were associated with hydrocarbon degradation in anoxic zones of the aquifer. Laboratory microcosms demonstrated that the biogeochemical fate of specific organic acids observed in groundwater varied with the structure of the acid and the availability of electron acceptors. Benzoic and phenylacetic acid were degraded by indigenous aquifer microorganisms when nitrate was supplied as an electron acceptor. Aromatic acids with two or more methyl substituants on the benzene ring persisted under nitrate-reducing conditions. Although iron reduction and sulfate reduction were important processes in situ and occurred in the microcosms, these reactions were not coupled to the biological oxidation of aromatic organic acids that were added to the microcosms as electron donors. ?? 1995 American Chemical Society.

  12. Genome Scale Mutational Analysis of Geobacter sulfurreducens Reveals Distinct Molecular Mechanisms for Respiration and Sensing of Poised Electrodes versus Fe(III) Oxides.

    PubMed

    Chan, Chi Ho; Levar, Caleb E; Jiménez-Otero, Fernanda; Bond, Daniel R

    2017-10-01

    Geobacter sulfurreducens generates electrical current by coupling intracellular oxidation of organic acids to the reduction of proteins on the cell surface that are able to interface with electrodes. This ability is attributed to the bacterium's capacity to respire other extracellular electron acceptors that require contact, such as insoluble metal oxides. To directly investigate the genetic basis of electrode-based respiration, we constructed Geobacter sulfurreducens transposon-insertion sequencing (Tn-Seq) libraries for growth, with soluble fumarate or an electrode as the electron acceptor. Libraries with >33,000 unique insertions and an average of 9 insertions/kb allowed an assessment of each gene's fitness in a single experiment. Mutations in 1,214 different genomic features impaired growth with fumarate, and the significance of 270 genes unresolved by annotation due to the presence of one or more functional homologs was determined. Tn-Seq analysis of -0.1 V versus standard hydrogen electrode (SHE) electrode-grown cells identified mutations in a subset of genes encoding cytochromes, processing systems for proline-rich proteins, sensory networks, extracellular structures, polysaccharides, and metabolic enzymes that caused at least a 50% reduction in apparent growth rate. Scarless deletion mutants of select genes identified via Tn-Seq revealed a new putative porin-cytochrome conduit complex ( extABCD ) crucial for growth with electrodes, which was not required for Fe(III) oxide reduction. In addition, four mutants lacking components of a putative methyl-accepting chemotaxis-cyclic dinucleotide sensing network ( esnABCD ) were defective in electrode colonization but grew normally with Fe(III) oxides. These results suggest that G. sulfurreducens possesses distinct mechanisms for recognition, colonization, and reduction of electrodes compared to Fe(III) oxides. IMPORTANCE Since metal oxide electron acceptors are insoluble, one hypothesis is that cells sense and

  13. Reduction of Fe(III) colloids by Shewanella putrefaciens: A kinetic model

    NASA Astrophysics Data System (ADS)

    Bonneville, Steeve; Behrends, Thilo; van Cappellen, Philippe; Hyacinthe, Christelle; Röling, Wilfred F. M.

    2006-12-01

    A kinetic model for the microbial reduction of Fe(III) oxyhydroxide colloids in the presence of excess electron donor is presented. The model assumes a two-step mechanism: (1) attachment of Fe(III) colloids to the cell surface and (2) reduction of Fe(III) centers at the surface of attached colloids. The validity of the model is tested using Shewanella putrefaciens and nanohematite as model dissimilatory iron reducing bacteria and Fe(III) colloidal particles, respectively. Attachment of nanohematite to the bacteria is formally described by a Langmuir isotherm. Initial iron reduction rates are shown to correlate linearly with the relative coverage of the cell surface by nanohematite particles, hence supporting a direct electron transfer from membrane-bound reductases to mineral particles attached to the cells. Using internally consistent parameter values for the maximum attachment capacity of Fe(III) colloids to the cells, Mmax, the attachment constant, KP, and the first-order Fe(III) reduction rate constant, k, the model reproduces the initial reduction rates of a variety of fine-grained Fe(III) oxyhydroxides by S. putrefaciens. The model explains the observed dependency of the apparent Fe(III) half-saturation constant, Km∗, on the solid to cell ratio, and it predicts that initial iron reduction rates exhibit saturation with respect to both the cell density and the abundance of the Fe(III) oxyhydroxide substrate.

  14. Energetic Limitations on Microbial Respiration of Organic Compounds using Aqueous Fe(III) Complexes

    NASA Astrophysics Data System (ADS)

    Naughton, H.; Fendorf, S. E.

    2015-12-01

    Soil organic matter constitutes up to 75% of the terrestrial carbon stock. Microorganisms mediate the breakdown of organic compounds and the return of carbon to the atmosphere, predominantly through respiration. Microbial respiration requires an electron acceptor and an electron donor such as small fatty acids, organic acids, alcohols, sugars, and other molecules that differ in oxidation state of carbon. Carbon redox state affects how much energy is required to oxidize a molecule through respiration. Therefore, different organic compounds should offer a spectrum of energies to respiring microorganisms. However, microbial respiration has traditionally focused on the availability and reduction potential of electron acceptors, ignoring the organic electron donor. We found through incubation experiments that the organic compound serving as electron donor determined how rapidly Shewanella putrefaciens CN32 respires organic substrate and the extent of reduction of the electron acceptor. We simulated a range of energetically favorable to unfavorable electron acceptors using organic chelators bound to Fe(III) with equilibrium stability constants ranging from log(K) of 11.5 to 25.0 for the 1:1 complex, where more stable complexes are less favorable for microbial respiration. Organic substrates varied in nominal oxidation state of carbon from +2 to -2. The most energetically favorable substrate, lactate, promoted up to 30x more rapid increase in percent Fe(II) compared to less favorable substrates such as formate. This increased respiration on lactate was more substantial with less stable Fe(III)-chelate complexes. Intriguingly, this pattern contradicts respiration rate predicted by nominal oxidation state of carbon. Our results suggest that organic substrates will be consumed so long as the energetic toll corresponding to the electron donor half reaction is counterbalanced by the energy available from the electron accepting half reaction. We propose using the chemical

  15. Vaccine perception among acceptors and non-acceptors in Sokoto State, Nigeria.

    PubMed

    Murele, Bola; Vaz, Rui; Gasasira, Alex; Mkanda, Pascal; Erbeto, Tesfaye; Okeibunor, Joseph

    2014-05-30

    Vaccine perceptions among acceptors and non-acceptors of childhood vaccination were explored. Seventy-two care givers, among them, acceptors and non-acceptors were interviewed in-depth with an interview guide that assessed vaccine acceptance, social and personality factors, and health belief model (HBM) categories in relation to oral polio vaccine (perceived susceptibility, severity, cost barriers, general barriers, benefits, knowledge, and engagement in preventative health behaviours). Community leaders were purposively selected while parents were selected on the basis of availability while ensuring the different attitude to vaccines was covered. Results showed that the HBM framework was found to be appropriate for identifying and distinguishing vaccine acceptors and non-acceptors. In addition, the HBM categories of benefits and susceptibility were found to influence oral polio vaccine acceptance. Second, the opinion of family members about the oral polio vaccine moderated the relationship between number of social ties and vaccine acceptance. Further, oral polio vaccine acceptance was related to outbreaks of paralysis of any sort, but not aggregate scores of other preventative health behaviours. Implications of this study include the investigation of vaccine acceptance in a high risk population. Research was done to investigate vaccine acceptance. Copyright © 2014 Elsevier Ltd. All rights reserved.

  16. Humic substances as a mediator for microbially catalyzed metal reduction

    USGS Publications Warehouse

    Lovley, D.R.; Fraga, J.L.; Blunt-Harris, E. L.; Hayes, L.A.; Phillips, E.J.P.; Coates, J.D.

    1998-01-01

    The potential for humic substances to serve as a terminal electron acceptor in microbial respiration and to function as an electron shuttle between Fe(III)-reducing microorganisms and insoluble Fe(III) oxides was investigated. The Fe(III)-reducing microorganism Geobacter metallireducens conserved energy to support growth from electron transport to humics as evidenced by continued oxidation of acetate to carbon dioxide after as many as nine transfers in a medium with acetate as the electron donor and soil humic acids as the electron acceptor. Growth of G. metallireducens with poorly crystalline Fe(III) oxide as the electron acceptor was greatly stimulated by the addition of as little as 100 ??M of the humics analog, anthraquinone-2,6-disulfonate. Other quinones investigated, including lawsone, menadione, and anthraquinone-2-sulfonate, also stimulated Fe(III) oxide reduction. A wide phylogenetic diversity of microorganisms capable of Fe(III) reduction were also able to transfer electrons to humics. Microorganisms which can not reduce Fe(III) could not reduce humics. Humics stimulated the reduction of structural Fe(III) in clay and the crystalline Fe(III) forms, goethite and hematite. These results demonstrate that electron shuttling between Fe(III)-reducing microorganisms and Fe(III) via humics not only accelerates the microbial reduction of poorly crystalline Fe(III) oxide, but also can facilitate the reduction of Fe(III) forms that are not typically reduced by microorganisms in the absence of humics. Addition of humic substances to enhance electron shuttling between Fe(III)-reducing microorganisms and Fe(III) oxides may be a useful strategy to stimulate the remediation of soils and sediments contaminated with organic or metal pollutants.

  17. Microbial reduction of Fe(III) in acidic sediments: isolation of Acidiphilium cryptum JF-5 capable of coupling the reduction of Fe(III) to the oxidation of glucose.

    PubMed

    Küsel, K; Dorsch, T; Acker, G; Stackebrandt, E

    1999-08-01

    Acidiphilium species that are capable of coupling the reduction of Fe(III) to the complete oxidation of a large variety of substrates including glucose and H(2).

  18. Novel processes for anaerobic sulfate production from elemental sulfur by sulfate-reducing bacteria

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.

    1994-01-01

    Sulfate reducers and related organisms which had previously been found to reduce Fe(III) with H2 or organic electron donors oxidized S0 to sulfate when Mn(IV) was provided as an electron acceptor. Organisms catalyzing this reaction in washed cell suspensions included Desulfovibrio desulfuricans, Desulfomicrobium baculatum. Desulfobacterium autotrophicum, Desulfuromonas acetoxidans, and Geobacter metallireducens. These organisms produced little or no sulfate from S0 with Fe(III) as a potential electron acceptor or in the absence of an electron acceptor. In detailed studies with Desulfovibrio desulfuricans, the stoichiometry of sulfate and Mn(II) production was consistent with the reaction S0 + 3 MnO2 + 4H+ ???SO42- + 3Mn(II) + 2H2O. None of the organisms evaluated could be grown with S0 as the sole electron donor and Mn(IV) as the electron acceptor. In contrast to the other sulfate reducers evaluated, Desulfobulbus propionicus produced sulfate from S0 in the absence of an electron acceptor and Fe(III) oxide stimulated sulfate production. Sulfide also accumulated in the absence of Mn(IV) or Fe(III). The stoichiometry of sulfate and sulfide production indicated that Desulfobulbus propionicus disproportionates S0 as follows: 4S0 + 4H2O???SO42- + 3HS- + 5 H+. Growth of Desulfobulbus propionicus with S0 as the electron donor and Fe(III) as a sulfide sink and/or electron acceptor was very slow. The S0 oxidation coupled to Mn(IV) reduction described here provides a potential explanation for the Mn(IV)-dependent sulfate production that previous studies have observed in anoxic marine sediments. Desulfobulbus propionicus is the first example of a pure culture known to disproportionate S0.

  19. Geothrix fermentans Secretes Two Different Redox-Active Compounds To Utilize Electron Acceptors across a Wide Range of Redox Potentials

    PubMed Central

    Mehta-Kolte, Misha G.

    2012-01-01

    The current understanding of dissimilatory metal reduction is based primarily on isolates from the proteobacterial genera Geobacter and Shewanella. However, environments undergoing active Fe(III) reduction often harbor less-well-studied phyla that are equally abundant. In this work, electrochemical techniques were used to analyze respiratory electron transfer by the only known Fe(III)-reducing representative of the Acidobacteria, Geothrix fermentans. In contrast to previously characterized metal-reducing bacteria, which typically reach maximal rates of respiration at electron acceptor potentials of 0 V versus standard hydrogen electrode (SHE), G. fermentans required potentials as high as 0.55 V to respire at its maximum rate. In addition, G. fermentans secreted two different soluble redox-active electron shuttles with separate redox potentials (−0.2 V and 0.3 V). The compound with the lower midpoint potential, responsible for 20 to 30% of electron transfer activity, was riboflavin. The behavior of the higher-potential compound was consistent with hydrophilic UV-fluorescent molecules previously found in G. fermentans supernatants. Both electron shuttles were also produced when cultures were grown with Fe(III), but not when fumarate was the electron acceptor. This study reveals that Geothrix is able to take advantage of higher-redox-potential environments, demonstrates that secretion of flavin-based shuttles is not confined to Shewanella, and points to the existence of high-potential-redox-active compounds involved in extracellular electron transfer. Based on differences between the respiratory strategies of Geothrix and Geobacter, these two groups of bacteria could exist in distinctive environmental niches defined by redox potential. PMID:22843516

  20. Growth of Thermophilic and Hyperthermophilic Fe(III)-Reducing Microorganisms on a Ferruginous Smectite as the Sole Electron Acceptor▿

    PubMed Central

    Kashefi, Kazem; Shelobolina, Evgenya S.; Elliott, W. Crawford; Lovley, Derek R.

    2008-01-01

    Recent studies have suggested that the structural Fe(III) within phyllosilicate minerals, including smectite and illite, is an important electron acceptor for Fe(III)-reducing microorganisms in sedimentary environments at moderate temperatures. The reduction of structural Fe(III) by thermophiles, however, has not previously been described. A wide range of thermophilic and hyperthermophilic Archaea and Bacteria from marine and freshwater environments that are known to reduce poorly crystalline Fe(III) oxides were tested for their ability to reduce structural (octahedrally coordinated) Fe(III) in smectite (SWa-1) as the sole electron acceptor. Two out of the 10 organisms tested, Geoglobus ahangari and Geothermobacterium ferrireducens, were not able to conserve energy to support growth by reduction of Fe(III) in SWa-1 despite the fact that both organisms were originally isolated with solid-phase Fe(III) as the electron acceptor. The other organisms tested were able to grow on SWa-1 and reduced 6.3 to 15.1% of the Fe(III). This is 20 to 50% less than the reported amounts of Fe(III) reduced in the same smectite (SWa-1) by mesophilic Fe(III) reducers. Two organisms, Geothermobacter ehrlichii and archaeal strain 140, produced copious amounts of an exopolysaccharide material, which may have played an active role in the dissolution of the structural iron in SWa-1 smectite. The reduction of structural Fe(III) in SWa-1 by archaeal strain 140 was studied in detail. Microbial Fe(III) reduction was accompanied by an increase in interlayer and octahedral charges and some incorporation of potassium and magnesium into the smectite structure. However, these changes in the major element chemistry of SWa-1 smectite did not result in the formation of an illite-like structure, as reported for a mesophilic Fe(III) reducer. These results suggest that thermophilic Fe(III)-reducing organisms differ in their ability to reduce and solubilize structural Fe(III) in SWa-1 smectite and that SWa-1

  1. Exploring the biochemistry at the extracellular redox frontier of bacterial mineral Fe(III) respiration

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Richardson, David J.; Edwards, Marcus; White, Gaye F.

    2012-06-01

    Many species of the bacterial Shewanella genus are notable for their ability to respire in anoxic environments utilizing insoluble minerals of Fe(III) and Mn(IV) as extracellular electron acceptors. In Shewanella oneidensis, the process is dependent on the decahaem electron-transport proteins that lie at the extracellular face of the outer membrane where they can contact the insoluble mineral substrates. These extracellular proteins are charged with electrons provided by an inter-membrane electron-transfer pathway that links the extracellular face of the outer membrane with the inner cytoplasmic membrane and thereby intracellular electron sources. In the present paper, we consider the common structural featuresmore » of two of these outermembrane decahaem cytochromes, MtrC and MtrF, and bring this together with biochemical, spectroscopic and voltammetric data to identify common and distinct properties of these prototypical members of different clades of the outer-membrane decahaem cytochrome superfamily.« less

  2. Aluminum affects heterogeneous Fe(III) (Hydr)oxide nucleation, growth, and ostwald ripening.

    PubMed

    Hu, Yandi; Li, Qingyun; Lee, Byeongdu; Jun, Young-Shin

    2014-01-01

    Heterogeneous coprecipitation of iron and aluminum oxides is an important process for pollutant immobilization and removal in natural and engineered aqueous environments. Here, using a synchrotron-based small-angle X-ray scattering technique, we studied heterogeneous nucleation and growth of Fe(III) (hydr)oxide on quartz under conditions found in acid mine drainage (at pH = 3.7 ± 0.2, [Fe(3+)] = 10(-4) M) with different initial aqueous Al/Fe ratios (0:1, 1:1, and 5:1). Interestingly, although the atomic ratios of Al/Fe in the newly formed Fe(III) (hydr)oxide precipitates were less than 1%, the in situ particle size and volume evolutions of the precipitates on quartz were significantly influenced by aqueous Al/Fe ratios. At the end of the 3 h experiments, with aqueous Al/Fe ratios of 0:1, 1:1, and 5:1, the average radii of gyration of particles on quartz were 5.7 ± 0.3, 4.6 ± 0.1, and 3.7 ± 0.3 nm, respectively, and the ratio of total particle volumes on quartz was 1.7:3.4:1.0. The Fe(III) (hydr)oxide precipitates were poorly crystallized, and were positively charged in all solutions. In the presence of Al(3+), Al(3+) adsorption onto quartz changed the surface charge of quartz from negative to positive, which caused the slower heterogeneous growth of Fe(III) (hydr)oxide on quartz. Furthermore, Al affected the amount of water included in the Fe(III) (hydr)oxides, which can influence their adsorption capacity. This study yielded important information usable for pollutant removal not only in natural environments, but also in engineered water treatment processes.

  3. Acceptor Ionization Energies in GaN*

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Ban Chen, An

    2001-03-01

    The k.p Hamiltonian and a model potential are used to deduce the acceptor ionization energies in GaN from a systematic study of the chemical trend in GaAs, GaP, and InP. The acceptors studied include Be, Mg, Ca, Zn, and Cd on the cation sites and C, Si, and Ge on the anion sites. Our calculated acceptor ionization energies are estimated to be accurate to better than ten percent across the board. The ionization energies of C and Be (152 and 187 meV respectively) in wurtzite GaN are found to be lower than that of Mg (224 meV). The C was found to behave like the hydrogenic acceptor in all systems and it has the smallest ionization energy among all the acceptors studied.

  4. Rapid anaerobic benzene oxidation with a variety of chelated Fe(III) forms

    USGS Publications Warehouse

    Lovley, D.R.; Woodward, J.C.; Chapelle, F.H.

    1996-01-01

    Fe(III) chelated to such compounds as EDTA, N-methyliminodiacetie acid, ethanol diglycine, humic acids, and phosphates stimulated benzene oxidation coupled to Fe(III) reduction in anaerobic sediments from a petroleum- contaminated aquifer as effectively as or more effectively than nitrilotriacetic acid did in a previously demonstrated stimulation experiment. These results indicate that many forms of chelated Fe(III) might be applicable to aquifer remediation.

  5. Secondary mineral formation associated with respiration of nontronite, NAu-1 by iron reducing bacteria

    PubMed Central

    O'Reilly, S Erin; Watkins, Janet; Furukawa, Yoko

    2005-01-01

    Experimental batch and miscible-flow cultures were studied in order to determine the mechanistic pathways of microbial Fe(III) respiration in ferruginous smectite clay, NAu-1. The primary purpose was to resolve if alteration of smectite and release of Fe precedes microbial respiration. Alteration of NAu-1, represented by the morphological and mineralogical changes, occurred regardless of the extent of microbial Fe(III) reduction in all of our experimental systems, including those that contained heat-killed bacteria and those in which O2, rather than Fe(III), was the primary terminal electron acceptor. The solid alteration products observed under transmission electron microscopy included poorly crystalline smectite with diffuse electron diffraction signals, discrete grains of Fe-free amorphous aluminosilicate with increased Al/Si ratio, Fe-rich grains, and amorphous Si globules in the immediate vicinity of bacterial cells and extracellular polymeric substances. In reducing systems, Fe was also found as siderite. The small amount of Fe partitioned to the aqueous phase was primarily in the form of dissolved Fe(III) species even in the systems in which Fe(III) was the primary terminal electron acceptor for microbial respiration. From these observations, we conclude that microbial respiration of Fe(III) in our laboratory systems proceeded through the following: (1) alteration of NAu-1 and concurrent release of Fe(III) from the octahedral sheets of NAu-1; and (2) subsequent microbial respiration of Fe(III).

  6. Analysis of long-term bacterial vs. chemical Fe(III) oxide reduction kinetics

    NASA Astrophysics Data System (ADS)

    Roden, Eric E.

    2004-08-01

    Data from studies of dissimilatory bacterial (10 8 cells mL -1 of Shewanella putrefaciens strain CN32, pH 6.8) and ascorbate (10 mM, pH 3.0) reduction of two synthetic Fe(III) oxide coated sands and three natural Fe(III) oxide-bearing subsurface materials (all at ca. 10 mmol Fe(III) L -1) were analyzed in relation to a generalized rate law for mineral dissolution (J t/m 0 = k'(m/m 0) γ, where J t is the rate of dissolution and/or reduction at time t, m 0 is the initial mass of oxide, and m/m 0 is the unreduced or undissolved mineral fraction) in order to evaluate changes in the apparent reactivity of Fe(III) oxides during long-term biological vs. chemical reduction. The natural Fe(III) oxide assemblages demonstrated larger changes in reactivity (higher γ values in the generalized rate law) compared to the synthetic oxides during long-term abiotic reductive dissolution. No such relationship was evident in the bacterial reduction experiments, in which temporal changes in the apparent reactivity of the natural and synthetic oxides were far greater (5-10 fold higher γ values) than in the abiotic reduction experiments. Kinetic and thermodynamic considerations indicated that neither the abundance of electron donor (lactate) nor the accumulation of aqueous end-products of oxide reduction (Fe(II), acetate, dissolved inorganic carbon) are likely to have posed significant limitations on the long-term kinetics of oxide reduction. Rather, accumulation of biogenic Fe(II) on residual oxide surfaces appeared to play a dominant role in governing the long-term kinetics of bacterial crystalline Fe(III) oxide reduction. The experimental findings together with numerical simulations support a conceptual model of bacterial Fe(III) oxide reduction kinetics that differs fundamentally from established models of abiotic Fe(III) oxide reductive dissolution, and indicate that information on Fe(III) oxide reactivity gained through abiotic reductive dissolution techniques cannot be used to

  7. Fate of Cd during microbial Fe(III) mineral reduction by a novel and Cd-tolerant Geobacter species.

    PubMed

    Muehe, E Marie; Obst, Martin; Hitchcock, Adam; Tyliszczak, Tolek; Behrens, Sebastian; Schröder, Christian; Byrne, James M; Michel, F Marc; Krämer, Ute; Kappler, Andreas

    2013-12-17

    Fe(III) (oxyhydr)oxides affect the mobility of contaminants in the environment by providing reactive surfaces for sorption. This includes the toxic metal cadmium (Cd), which prevails in agricultural soils and is taken up by crops. Fe(III)-reducing bacteria can mobilize such contaminants by Fe(III) mineral dissolution or immobilize them by sorption to or coprecipitation with secondary Fe minerals. To date, not much is known about the fate of Fe(III) mineral-associated Cd during microbial Fe(III) reduction. Here, we describe the isolation of a new Geobacter sp. strain Cd1 from a Cd-contaminated field site, where the strain accounts for 10(4) cells g(-1) dry soil. Strain Cd1 reduces the poorly crystalline Fe(III) oxyhydroxide ferrihydrite in the presence of at least up to 112 mg Cd L(-1). During initial microbial reduction of Cd-loaded ferrihydrite, sorbed Cd was mobilized. However, during continuous microbial Fe(III) reduction, Cd was immobilized by sorption to and/or coprecipitation within newly formed secondary minerals that contained Ca, Fe, and carbonate, implying the formation of an otavite-siderite-calcite (CdCO3-FeCO3-CaCO3) mixed mineral phase. Our data shows that microbially mediated turnover of Fe minerals affects the mobility of Cd in soils, potentially altering the dynamics of Cd uptake into food or phyto-remediating plants.

  8. Electron transfer capacity dependence of quinone-mediated Fe(III) reduction and current generation by Klebsiella pneumoniae L17.

    PubMed

    Li, Xiaomin; Liu, Liang; Liu, Tongxu; Yuan, Tian; Zhang, Wei; Li, Fangbai; Zhou, Shungui; Li, Yongtao

    2013-06-01

    Quinone groups in exogenous electron shuttles can accelerate extracellular electron transfer (EET) from bacteria to insoluble terminal electron acceptors, such as Fe(III) oxides and electrodes, which are important in biogeochemical redox processes and microbial electricity generation. However, the relationship between quinone-mediated EET performance and electron-shuttling properties of the quinones remains incompletely characterized. This study investigates the effects of a series of synthetic quinones (SQs) on goethite reduction and current generation by a fermenting bacterium Klebsiella pneumoniae L17. In addition, the voltammetric behavior and electron transfer capacities (ETCs) of SQ, including electron accepting (EAC) and donating (EDC) capacities, is also examined using electrochemical methods. The results showed that SQ can significantly increase both the Fe(III) reduction rates and current outputs of L17. Each tested SQ reversibly accepted and donated electrons as indicated by the cyclic voltammograms. The EAC and EDC results showed that Carmine and Alizarin had low relative capacities of electron transfer, whereas 9,10-anthraquinone-2,6-disulfonic acid (AQDS), 2-hydroxy-1,4-naphthoquinone (2-HNQ), and 5-hydroxy-1,4-naphthoquinone (5-HNQ) showed stronger relative ETC, and 9,10-anthraquinone-2-carboxylic acid (AQC) and 9,10-anthraquinone-2-sulfonic acid (AQS) had high relative ETC. Enhancement of microbial goethite reduction kinetics and current outputs by SQ had a good linear relationship with their ETC, indicating that the effectiveness of quinone-mediated EET may be strongly dependent on the ETC of the quinones. Therefore, the presence of quinone compounds and fermenting microorganisms may increase the diversity of microbial populations that contribute to element transformation in natural environments. Moreover, ETC determination of different SQ would help to evaluate their performance for microbial EET under anoxic conditions. Copyright © 2013 Elsevier

  9. Stimulated anoxic biodegradation of aromatic hydrocarbons using Fe(III) ligands

    USGS Publications Warehouse

    Lovley, D.R.; Woodward, J.C.; Chapelle, F.H.

    1994-01-01

    Contamination of ground waters with water-soluble aromatic hydrocarbons, common components of petroleum pollution, often produces anoxic conditions under which microbial degradation of the aromatics is slow. Oxygen is often added to contaminated ground water to stimulate biodegradation, but this can be technically difficult and expensive. Insoluble Fe(III) oxides, which are generally abundant in shallow aquifers, are alternative potential oxidants, but are difficult for microorganisms to access. Here we report that adding organic ligands that bind to Fe(III) dramatically increases its bioavailability, and that in the presence of these ligands, rates of degradation of aromatic hydrocarbons in anoxic aquifer sediments are comparable to those in oxic sediments. We find that even benzene, which is notoriously refractory in the absence of oxygen, can be rapidly degraded. Our results suggest that increasing the bioavailability of Fe(III) by adding suitable ligands provides a potential alternative to oxygen addition for the bioremediation of petroleum-contaminated aquifers.Contamination of ground waters with water-soluble aromatic hydrocarbons, common components of petroleum pollution, often produces anoxic conditions under which microbial degradation of the aromatics is slow. Oxygen is often added to contaminated ground water to stimulate biodegradation, but this can be technically difficult and expensive. Insoluble Fe(III) oxides, which are generally abundant in shallow aquifers, are alternative potential oxidants, but are difficult for microorganisms to access. Here we report that adding organic ligands that bind to Fe(III) dramatically increases its bioavailability, and that in the presence of these ligands, rates of degradation of aromatic hydrocarbons in anoxic aquifer sediments are comparable to those in oxic sediments. We find that even benzene, which is notoriously refractory in the absence of oxygen, can be rapidly degraded. Our results suggest that increasing

  10. Microbial Reduction of Fe(III) and U(VI) in Aquifers: Simulations Exploring Coupled Effects of Heterogeneity and Fe(II) Sorption

    NASA Astrophysics Data System (ADS)

    Scheibe, T. D.; Fang, Y.; Roden, E. E.; Brooks, S. C.; Chien, Y.; Murray, C. J.

    2004-05-01

    Uranium is a significant groundwater contaminant at many former mining and processing sites. In its oxidized state, U(VI) is soluble and mobile, although strongly retarded by sorption to natural iron oxide surfaces. It has been demonstrated that commonly occurring subsurface microorganisms can reduce uranium and other metals when provided sufficient carbon as an electron donor. Reduced U(IV) precipitates as a solid phase; therefore biostimulation provides a potential strategy for in situ removal from contaminated groundwater. However, these biogeochemical reactions occur in the context of a complex heterogeneous environment in which flow and transport dynamics and abiotic reactions can have significant impacts. We have constructed a high-resolution numerical model of groundwater flow and multicomponent reactive transport that incorporates heterogeneity in hydraulic conductivity and initial Fe(III) distribution, microbial growth and transport dynamics, and effects of sorption or precipitation of biogenic Fe(II) on availability of Fe(III) as an electron acceptor. The biogeochemical reaction models and their parameters are based on laboratory experiments; the heterogeneous field-scale property distributions are based on interpretations of geophysical and other observations at a highly characterized field site. The model is being run in Monte Carlo mode to examine the controls that these factors exert on 1) the initial distribution of sorbed uranium in an oxic environment and 2) the reduction and immobilization of uranium upon introduction of a soluble electron donor.

  11. Release of 226Ra from uranium mill tailings by microbial Fe(III) reduction

    USGS Publications Warehouse

    Landa, E.R.; Phillips, E.J.P.; Lovley, D.R.

    1991-01-01

    Uranium mill tailings were anaerobically incubated in the presence of H2 with Alteromonas putrefaciens, a bacterium known to couple the oxidation of H2 and organic compounds to the reduction of Fe(III) oxides. There was a direct correlation between the extent of Fe(III) reduction and the accumulation of dissolved 226Ra. In sterile tailings in which Fe(III) was not reduced, there was negligible leaching of 226Ra. The behavior of Ba was similar to that of Ra in inoculated and sterile systems. These results demonstrate that under anaerobic conditions, microbial reduction of Fe(III) may result in the release of dissolved 226Ra from uranium mill tailings. ?? 1991.

  12. Oxidation of tetracycline antibiotics induced by Fe(III) ions without light irradiation.

    PubMed

    Wang, Hui; Yao, Hong; Sun, Peizhe; Pei, Jin; Li, Desheng; Huang, Ching-Hua

    2015-01-01

    The presence of Fe(III) ions was found to induce degradation of three tetracycline antibiotics (TCs), tetracycline (TTC), oxytetracycline (OTC) and chlorotetracycline (CTC), in aqueous solutions without light. The presence of Fe(III) promoted the degradation of TCs in most experimental pH (5.0, 7.0 and 9.0) except at pH 9.0 for CTC. Degradation rate constants of TTC, OTC and CTC reached maximum ((6.2±0.5)×10(-3) h(-1), (10.6±0.1)×10(-3) h(-1) and (15.9±0.5)×10(-3) h(-1) at pH 7.0, 20 °C) when Fe(III):TC molar ratio was 1:1, 1:1 and 2:1, respectively. Such metal-to-ligand ratios agreed well with the most favorable complexation between Fe(III) and each TC. Compared to without metals, Fe(III) enhanced the degradation rate of TTC, OTC and CTC by up to 20.67, 7.07 and 2.30 times, respectively, in clean water matrix, and also promoted degradation of TCs in real surface water and wastewater matrices. The promoted degradation likely occurred via complexation of TCs and subsequent oxidation by Fe(III). Degradation results of CTC versus 4-epi-CTC suggested Fe(III) likely binds to TCs' C4 dimethylamino group. Toxicity of the complexes evaluated using Photobacterium phosphoreum T3 was increased after several hours of reaction, suggesting the transformation products may exert a stronger toxicity than parent TCs. This study identifies new oxidative transformation of TCs induced by Fe(III) ions without light irradiation, further supporting the important role of iron species in the environmental fate of TCs. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. Selective transport of Fe(III) using ionic imprinted polymer (IIP) membrane particle

    NASA Astrophysics Data System (ADS)

    Djunaidi, Muhammad Cholid; Jumina, Siswanta, Dwi; Ulbricht, Mathias

    2015-12-01

    The membrane particles was prepared from polyvinyl alcohol (PVA) and polymer IIP with weight ratios of 1: 2 and 1: 1 using different adsorbent templates and casting thickness. The permeability of membrane towards Fe(III) and also mecanism of transport were studied. The selectivity of the membrane for Fe(III) was studied by performing adsorption experiments also with Cr(III) separately. In this study, the preparation of Ionic Imprinted Polymer (IIP) membrane particles for selective transport of Fe (III) had been done using polyeugenol as functional polymer. Polyeugenol was then imprinted with Fe (III) and then crosslinked with PEGDE under alkaline condition to produce polyeugenol-Fe-PEGDE polymer aggregates. The agrregates was then crushed and sieved using mesh size of 80 and the powder was then used to prepare the membrane particles by mixing it with PVA (Mr 125,000) solution in 1-Methyl-2-pyrrolidone (NMP) solvent. The membrane was obtained after casting at a speed of 25 m/s and soaking in NaOH solution overnight. The membrane sheet was then cut and Fe(III) was removed by acid to produce IIP membrane particles. Analysis of the membrane and its constituent was done by XRD, SEM and size selectivity test. Experimental results showed the transport of Fe(III) was faster with the decrease of membrane thickness, while the higher concentration of template ion correlates with higher Fe(III) being transported. However, the transport of Fe(III) was slower for higher concentration of PVA in the membrane. IImparticles works through retarded permeation mechanism, where Fe(III) was bind to the active side of IIP. The active side of IIP membrane was dominated by the -OH groups. The selectivity of all IIP membranes was confirmed as they were all unable to transport Cr (III), while NIP (Non-imprinted Polymer) membrane was able transport Cr (III).

  14. Influence of Reactive Transport on the Reduction of U(VI) in the Presence of Fe(III) and Nitrate: Implications for U(VI) Immobilization by Bioremediation / Biobarriers- Final Report

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    B.D. Wood

    2007-01-01

    Subsurface contamination by metals and radionuclides represent some of the most challenging remediation problems confronting the Department of Energy (DOE) complex. In situ remediation of these contaminants by dissimilatory metal reducing bacteria (DMRB) has been proposed as a potential cost effective remediation strategy. The primary focus of this research is to determine the mechanisms by which the fluxes of electron acceptors, electron donors, and other species can be controlled to maximize the transfer of reductive equivalents to the aqueous and solid phases. The proposed research is unique in the NABIR portfolio in that it focuses on (i) the role ofmore » flow and transport in the initiation of biostimulation and the successful sequestration of metals and radionuclides [specifically U(VI)], (ii) the subsequent reductive capacity and stability of the reduced sediments produced by the biostimulation process, and (iii) the potential for altering the growth of biomass in the subsurface by the addition of specific metabolic uncoupling compounds. A scientifically-based understanding of these phenomena are critical to the ability to design successful bioremediation schemes. The laboratory research will employ Shewanella putrefaciens (CN32), a facultative DMRB that can use Fe(III) oxides as a terminal electron acceptor. Sediment-packed columns will be inoculated with this organism, and the reduction of U(VI) by the DMRB will be stimulated by the addition of a carbon and energy source in the presence of Fe(III). Separate column experiments will be conducted to independently examine: (1) the importance of the abiotic reduction of U(VI) by biogenic Fe(II); (2) the influence of the transport process on Fe(III) reduction and U(VI) immobilization, with emphasis on methods for controlling the fluxes of aqueous species to maximize uranium reduction; (3) the reductive capacity of biologically-reduced sediments (with respect to re-oxidation by convective fluxes of O2 and NO3

  15. Effect of dissimilatory Fe(III) reducers on bio-reduction and nickel-cobalt recovery from Sukinda chromite-overburden.

    PubMed

    Esther, Jacintha; Panda, Sandeep; Behera, Sunil K; Sukla, Lala B; Pradhan, Nilotpala; Mishra, Barada K

    2013-10-01

    The effect of an adapted dissimilatory iron reducing bacterial consortium (DIRB) towards bio-reduction of Sukinda chromite overburden (COB) with enhanced recovery of nickel and cobalt is being reported for the first time. The remarkable ability of DIRB to utilize Fe(III) as terminal electron acceptor reducing it to Fe(II) proved beneficial for treatment of COB as compared to previous reports for nickel leaching. XRD studies showed goethite as the major iron-bearing phase in COB. Under facultative anaerobic conditions, goethite was reduced to hematite and magnetite with the exposure of nickel oxide. FESEM studies showed DIRB to be associated with COB through biofilm formation with secondary mineral precipitates of magnetite deposited as tiny globular clusters on the extra polymeric substances. The morphological and mineralogical changes in COB, post DIRB application, yielded a maximum of 68.5% nickel and 80.98% cobalt in 10 days using 8M H2SO4. Copyright © 2013 Elsevier Ltd. All rights reserved.

  16. Role of Humic-Bound Iron as an Electron Transfer Agent in Dissimilatory Fe(III) Reduction

    PubMed Central

    Lovley, Derek R.; Blunt-Harris, Elizabeth L.

    1999-01-01

    The dissimilatory Fe(III) reducer Geobacter metallireducens reduced Fe(III) bound in humic substances, but the concentrations of Fe(III) in a wide range of highly purified humic substances were too low to account for a significant portion of the electron-accepting capacities of the humic substances. Furthermore, once reduced, the iron in humic substances could not transfer electrons to Fe(III) oxide. These results suggest that other electron-accepting moieties in humic substances, such as quinones, are the important electron-accepting and shuttling agents under Fe(III)-reducing conditions. PMID:10473447

  17. Microbial reduction of Fe(III) in the Fifthian and Muloorina illites: Contrasting extents and rates of bioreduction

    USGS Publications Warehouse

    Seabaugh, Jennifer L.; Dong, Hailiang; Kukkadapu, Ravi K.; Eberl, Dennis D.; Morton, John P.; Kim, J.

    2006-01-01

    Shewanella putrefaciens CN32 reduces Fe(III) within two illites which have different properties: the Fithian bulk fraction and the <0.2 m fraction of Muloorina. The Fithian illite contained 4.6% (w/w) total Fe, 81% of which was Fe(III). It was dominated by illite with some jarosite (∼32% of the total Fe(III)) and goethite (11% of the total Fe(III)). The Muloorina illite was pure and contained 9.2% Fe, 93% of which was Fe(III). Illite suspensions were buffered at pH 7 and were inoculated with CN32 cells with lactate as the electron donor. Select treatments included anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. Bioproduction of Fe(II) was determined by ferrozine analysis. The unreduced and bioreduced solids were characterized by Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. The extent of Fe(III) reduction in the bulk Fithian illite was enhanced by the presence of AQDS (73%) with complete reduction of jarosite and goethite and partial reduction of illite. Mössbauer spectroscopy and chemical extraction determined that 21–25% of illite-associated Fe(III) was bioreduced. The extent of bioreduction was less in the absence of AQDS (63%) and only jarosite was completely reduced with partial reduction of goethite and illite. The XRD and TEM data revealed no significant illite dissolution or biogenic minerals, suggesting that illite was reduced in the solid state and biogenic Fe(II) from jarosite and goethite was either released to aqueous solution or adsorbed onto residual solid surfaces. In contrast, only 1% of the structural Fe(III) in Muloorina illite was bioreduced. The difference in the extent and rate of bioreduction between the two illites was probably due to the difference in layer charge and the total structural Fe content between the Fithian illite (0.56 per formula) and Muloorina illite (0.87). There may be other factors contributing to the observed differences, such as expandability, surface area and the

  18. Calculations of acceptor ionization energies in GaN

    NASA Astrophysics Data System (ADS)

    Wang, H.; Chen, A.-B.

    2001-03-01

    The k.p Hamiltonian and a model potential are used to deduce the acceptor ionization energies in GaN from a systematic study of the chemical trend in GaAs, GaP, and InP. The acceptors studied include Be, Mg, Ca, Zn, and Cd on the cation sites and C, Si, and Ge on the anion sites. Our calculated acceptor ionization energies are estimated to be accurate to better than 10% across the board. The ionization energies of C and Be (152 and 187 meV, respectively) in wurtzite GaN are found to be lower than that of Mg (224 meV). The C was found to behave like the hydrogenic acceptor in all systems and it has the smallest ionization energy among all the acceptors studied.

  19. Fullerene-bisadduct acceptors for polymer solar cells.

    PubMed

    Li, Yongfang

    2013-10-01

    Polymer solar cells (PSCs) have drawn great attention in recent years for their simple device structure, light weight, and low-cost fabrication in comparison with inorganic semiconductor solar cells. However, the power-conversion efficiency (PCE) of PSCs needs to be increased for their future application. The key issue for improving the PCE of PSCs is the design and synthesis of high-efficiency conjugated polymer donors and fullerene acceptors for the photovoltaic materials. For the acceptor materials, several fullerene-bisadduct acceptors with high LUMO energy levels have demonstrated excellent photovoltaic performance in PSCs with P3HT as a donor. In this Focus Review, recent progress in high-efficiency fullerene-bisadduct acceptors is discussed, including the bisadduct of PCBM, indene-C60 bisadduct (ICBA), indene-C70 bisadduct (IC70BA), DMPCBA, NCBA, and bisTOQC. The LUMO levels and photovoltaic performance of these bisadduct acceptors with P3HT as a donor are summarized and compared. In addition, the applications of an ICBA acceptor in new device structures and with other conjugated polymer donors than P3HT are also introduced and discussed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. A hydrogen-oxidizing, Fe(III)-reducing microorganism from the Great Bay estuary, New Hampshire

    USGS Publications Warehouse

    Caccavo, F.; Blakemore, R.P.; Lovley, D.R.

    1992-01-01

    A dissimilatory Fe(III)- and Mn(IV)-reducing bacterium was isolated from bottom sediments of the Great Bay estuary, New Hampshire. The isolate was a facultatively anaerobic gram-negative rod which did not appear to fit into any previously described genus. It was temporarily designated strain BrY. BrY grew anaerobically in a defined medium with hydrogen or lactate as the electron donor and Fe(III) as the electron acceptor. BrY required citrate, fumarate, or malate as a carbon source for growth on H2 and Fe(III). With Fe(III) as the sole electron acceptor, BrY metabolized hydrogen to a minimum threshold at least 60-fold lower than the threshold reported for pure cultures of sulfate reducers. This finding supports the hypothesis that when Fe(III) is available, Fe(III) reducers can outcompete sulfate reducers for electron donors. Lactate was incompletely oxidized to acetate and carbon dioxide with Fe(III) as the electron acceptor. Lactate oxidation was also coupled to the reduction of Mn(IV), U(VI), fumarate, thiosulfate, or trimethylamine n-oxide under anaerobic conditions. BrY provides a model for how enzymatic metal reduction by respiratory metal-reducing microorganisms has the potential to contribute to the mobilization of iron and trace metals and to the immobilization of uranium in sediments of Great Bay Estuary.

  1. Amino group in Leptothrix sheath skeleton is responsible for direct deposition of Fe(III) minerals onto the sheaths.

    PubMed

    Kunoh, Tatsuki; Matsumoto, Syuji; Nagaoka, Noriyuki; Kanashima, Shoko; Hino, Katsuhiko; Uchida, Tetsuya; Tamura, Katsunori; Kunoh, Hitoshi; Takada, Jun

    2017-07-26

    Leptothrix species produce microtubular organic-inorganic materials that encase the bacterial cells. The skeleton of an immature sheath, consisting of organic exopolymer fibrils of bacterial origin, is formed first, then the sheath becomes encrusted with inorganic material. Functional carboxyl groups of polysaccharides in these fibrils are considered to attract and bind metal cations, including Fe(III) and Fe(III)-mineral phases onto the fibrils, but the detailed mechanism remains elusive. Here we show that NH 2 of the amino-sugar-enriched exopolymer fibrils is involved in interactions with abiotically generated Fe(III) minerals. NH 2 -specific staining of L. cholodnii OUMS1 detected a terminal NH 2 on its sheath skeleton. Masking NH 2 with specific reagents abrogated deposition of Fe(III) minerals onto fibrils. Fe(III) minerals were adsorbed on chitosan and NH 2 -coated polystyrene beads but not on cellulose and beads coated with an acetamide group. X-ray photoelectron spectroscopy at the N1s edge revealed that the terminal NH 2 of OUMS1 sheaths, chitosan and NH 2 -coated beads binds to Fe(III)-mineral phases, indicating interaction between the Fe(III) minerals and terminal NH 2 . Thus, the terminal NH 2 in the exopolymer fibrils seems critical for Fe encrustation of Leptothrix sheaths. These insights should inform artificial synthesis of highly reactive NH 2 -rich polymers for use as absorbents, catalysts and so on.

  2. New method for the direct determination of dissolved Fe(III) concentration in acid mine waters

    USGS Publications Warehouse

    To, T.B.; Nordstrom, D. Kirk; Cunningham, K.M.; Ball, J.W.; McCleskey, R. Blaine

    1999-01-01

    A new method for direct determination of dissolved Fe(III) in acid mine water has been developed. In most present methods, Fe(III) is determined by computing the difference between total dissolved Fe and dissolved Fe(II). For acid mine waters, frequently Fe(II) >> Fe(III); thus, accuracy and precision are considerably improved by determining Fe(III) concentration directly. The new method utilizes two selective ligands to stabilize Fe(III) and Fe(II), thereby preventing changes in Fe reduction-oxidation distribution. Complexed Fe(II) is cleanly removed using a silica-based, reversed-phase adsorbent, yielding excellent isolation of the Fe(III) complex. Iron(III) concentration is measured colorimetrically or by graphite furnace atomic absorption spectrometry (GFAAS). The method requires inexpensive commercial reagents and simple procedures that can be used in the field. Calcium(II), Ni(II), Pb(II), AI(III), Zn(II), and Cd(II) cause insignificant colorimetric interferences for most acid mine waters. Waters containing >20 mg of Cu/L could cause a colorimetric interference and should be measured by GFAAS. Cobalt(II) and Cr(III) interfere if their molar ratios to Fe(III) exceed 24 and 5, respectively. Iron(II) interferes when its concentration exceeds the capacity of the complexing ligand (14 mg/L). Because of the GFAAS elemental specificity, only Fe(II) is a potential interferent in the GFAAS technique. The method detection limit is 2 ??g/L (40 nM) using GFAAS and 20 ??g/L (0.4 ??M) by colorimetry.A new method for direct determination of dissolved Fe(III) in acid mine water has been developed. In most present methods, Fe(III) is determined by computing the difference between total dissolved Fe and dissolved Fe(II). For acid mine waters, frequently Fe(II)???Fe(III); thus, accuracy and precision are considerably improved by determining Fe(III) concentration directly. The new method utilizes two selective ligands to stabilize Fe(III) and Fe(II), thereby preventing changes

  3. Investigation of complexes tannic acid and myricetin with Fe(III)

    NASA Astrophysics Data System (ADS)

    Sungur, Şana; Uzar, Atike

    2008-01-01

    The pH dependence of the complexes was determined by both potentiometric and spectrophotometric studies. Stability constants and stoichiometries of the formed complexes were determined using slope ratio method. Fe(III) was formed complexes with tannic acid of various stoichiometries, which in the 1:1 molar ratio at pH < 3, in the 2:1 molar ratio at pH 3-7 and in the 4:1 molar ratio at pH > 7. Fe(III) was formed complexes with myricetin in the 1:2 molar ratio at pH 4 and 5 and in the 1:1 molar ratio at pH 6. Stability constant values were found to be 10 5 to 10 17 and 10 5 to 10 9 for Fe(III)-tannic acid complexes and Fe(III)-myricetin complexes. Both tannic acid and myricetin were possessed minimum affinities to Cu(II) and Zn(II). They had less affinity for Al(III) than for Fe(III).

  4. [Anaerobic reduction of humus/Fe (III) and electron transport mechanism of Fontibacter sp. SgZ-2].

    PubMed

    Ma, Chen; Yang, Gui-qin; Lu, Qin; Zhou, Shun-gui

    2014-09-01

    Humus and Fe(III) respiration are important extracellular respiration metabolism. Electron transport pathway is the key issue of extracellular respiration. To understand the electron transport properties and the environmental behavior of a novel Fe(III)- reducing bacterium, Fontibacter sp. SgZ-2, capacities of anaerobic humus/Fe(III) reduction and electron transport mechanisms with four electron acceptors were investigated in this study. The results of anaerobic batch experiments indicated that strain SgZ-2 had the ability to reduce humus analog [ 9,10-anthraquinone-2,6-disulfonic acid (AQDS) and 9,10-anthraquinone-2-sulfonic acid (AQS)], humic acids (HA), soluble Fe(III) (Fe-EDTA and Fe-citrate) and Fe(III) oxides [hydrous ferric oxide (HFO)]. Fermentative sugars (glucose and sucrose) were the most effective electron donors in the humus/Fe(III) reduction by strain SgZ-2. Additionally, differences of electron carrier participating in the process of electron transport with different electron acceptors (i. e. , oxygen, AQS, Fe-EDTA and HFO) were investigated using respiratory inhibitors. The results suggested that similar respiratory chain components were involved in the reducing process of oxygen and Fe-EDTA, including dehydrogenase, quinones and cytochromes b-c. In comparison, only dehydrogenase was found to participate in the reduction of AQS and HFO. In conclusion, different electron transport pathways may be employed by strain SgZ-2 between insoluble and soluble electron acceptors or among soluble electron acceptors. Preliminary models of electron transport pathway with four electron acceptors were proposed for strain SgZ-2, and the study of electron transport mechanism was explored to the genus Fontibacter. All the results from this study are expected to help understand the electron transport properties and the environmental behavior of the genus Fontibacter.

  5. Anaerobic Benzene Oxidation by Geobacter Species

    PubMed Central

    Bain, Timothy S.; Nevin, Kelly P.; Barlett, Melissa A.; Lovley, Derek R.

    2012-01-01

    The abundance of Geobacter species in contaminated aquifers in which benzene is anaerobically degraded has led to the suggestion that some Geobacter species might be capable of anaerobic benzene degradation, but this has never been documented. A strain of Geobacter, designated strain Ben, was isolated from sediments from the Fe(III)-reducing zone of a petroleum-contaminated aquifer in which there was significant capacity for anaerobic benzene oxidation. Strain Ben grew in a medium with benzene as the sole electron donor and Fe(III) oxide as the sole electron acceptor. Furthermore, additional evaluation of Geobacter metallireducens demonstrated that it could also grow in benzene-Fe(III) medium. In both strain Ben and G. metallireducens the stoichiometry of benzene metabolism and Fe(III) reduction was consistent with the oxidation of benzene to carbon dioxide with Fe(III) serving as the sole electron acceptor. With benzene as the electron donor, and Fe(III) oxide (strain Ben) or Fe(III) citrate (G. metallireducens) as the electron acceptor, the cell yields of strain Ben and G. metallireducens were 3.2 × 109 and 8.4 × 109 cells/mmol of Fe(III) reduced, respectively. Strain Ben also oxidized benzene with anthraquinone-2,6-disulfonate (AQDS) as the sole electron acceptor with cell yields of 5.9 × 109 cells/mmol of AQDS reduced. Strain Ben serves as model organism for the study of anaerobic benzene metabolism in petroleum-contaminated aquifers, and G. metallireducens is the first anaerobic benzene-degrading organism that can be genetically manipulated. PMID:23001648

  6. Hexanuclear Fe(III) wheels functionalized by amino-acetonitrile derivatives

    NASA Astrophysics Data System (ADS)

    Kravtsov, Victor Ch.; Malaestean, Iurie; Stingach, Eugenia P.; Duca, Gheorghe G.; Macaev, Fliur Z.; van Leusen, Jan; Kögerler, Paul; Hauser, Jürg; Krämer, Karl; Decurtins, Silvio; Liu, Shi-Xia; Ghosh, Ashta C.; Garcia, Yann; Baca, Svetlana G.

    2018-04-01

    Three new hexanuclear Fe(III) coordination wheels [Fe6Cl6(L1)6]·5(MeCN) (1), [Na0.5Fe6Cl6(L1)6](N3)0.5·4.5(MeCN) (2), and [Fe6Cl6(L2)6]·2(MeCN) (3) have been synthesized with new prepared amino-acetonitrile derivatives 2-[bis(2-hydroxyethyl)amino]acetonitrile hydrochloride (H2L1) and 3-[bis(2-hydroxyethyl)amino]propanenitrile hydrochloride (H2L2). They were structurally characterized by single-crystal X-ray diffraction. Mößbauer spectroscopy and magnetic susceptibility measurements indicate dominant antiferromagnetic behavior between the Fe(III) centers.

  7. The role of Shewanella oneidensis MR-1 outer surface structures in extracellular electron transfer

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bouhenni, Rachida; Vora, Gary J.; Biffinger, Justin C.

    2010-04-20

    Shewanella oneidensis is a facultative anaerobe that uses more than 14 different terminal electron acceptors for respiration. These include metal oxides and hydroxyoxides, and toxic metals such as uranium and chromium. Mutants deficient in metal reduction were isolated using the mariner transposon derivative, minihimar RB1. These included mutants with transposon insertions in the prepilin peptidase and type II secretion system genes. All mutants were deficient in Fe(III) and Mn(IV) reduction, and exhibited slow growth when DMSO was used as the electron acceptor. The genome sequence of S. oneidensis contains one prepilin peptidase gene, pilD. A similar prepilin peptidase that maymore » function in the processing of type II secretion prepilins was not found. Single and multiple chromosomal deletions of four putative type IV pilin genes did not affect Fe(III) and Mn(IV) reduction. These results indicate that PilD in S. oneidensis is responsible for processing both type IV and type II secretion prepilin proteins. Type IV pili do not appear to be required for Fe(III) and Mn(IV) reduction.« less

  8. Enrichment of Geobacter species in response to stimulation of Fe(III) reduction in sandy aquifer sediments

    USGS Publications Warehouse

    Snoeyenbos-West, O.L.; Nevin, K.P.; Anderson, R.T.; Lovely, D.R.

    2000-01-01

    Engineered stimulation of Fe(III) has been proposed as a strategy to enhance the immobilization of radioactive and toxic metals in metal-contaminated subsurface environments. Therefore, laboratory and field studies were conducted to determine which microbial populations would respond to stimulation of Fe(III) reduction in the sediments of sandy aquifers. In laboratory studies, the addition of either various organic electron donors or electron shuttle compounds stimulated Fe(III) reduction and resulted in Geobacter sequences becoming important constituents of the Bacterial 16S rDNA sequences that could be detected with PCR amplification and denaturing gradient gel electrophoresis (DGGE). Quantification of Geobacteraceae sequences with a PCR most-probable-number technique indicated that the extent to which numbers of Geobacter increased was related to the degree of stimulation of Fe(III) reduction. Geothrix species were also enriched in some instances, but were orders of magnitude less numerous than Geobacter species. Shewanella species were not detected, even when organic compounds known to be electron donors for Shewanella species were used to stimulate Fe(III) reduction in the sediments. Geobacter species were also enriched in two field experiments in which Fe(III) reduction was stimulated with the addition of benzoate or aromatic hydrocarbons. The apparent growth of Geobacter species concurrent with increased Fe(III) reduction suggests that Geobacter species were responsible for much of the Fe(III) reduction in all of the stimulation approaches evaluated in three geographically distinct aquifers. Therefore, strategies for subsurface remediation that involve enhancing the activity of indigenous Fe(III)-reducing populations in aquifers should consider the physiological properties of Geobacter species in their treatment design.

  9. Anaerobic oxidation of toluene, phenol, and p-cresol by the dissimilatory iron-reducing organism, GS-15

    USGS Publications Warehouse

    Lovley, D.R.; Lonergan, D.J.

    1990-01-01

    The dissimilatory Fe(III) reducer, GS-15, is the first microorganism known to couple the oxidation of aromatic compounds to the reduction of Fe(III) and the first example of a pure culture of any kind known to anaerobically oxidize an aromatic hydrocarbon, toluene. In this study, the metabolism of toluene, phenol, and p-cresol by GS-15 was investigated in more detail. GS-15 grew in an anaerobic medium with toluene as the sole electron donor and Fe(III) oxide as the electron acceptor. Growth coincided with Fe(III) reduction. [ring-14C]toluene was oxidized to 14CO2, and the stoichiometry of 14CO2 production and Fe(III) reduction indicated that GS-15 completely oxidized toluene to carbon dioxide with Fe(III) as the electron acceptor. Magnetite was the primary iron end product during toluene oxidation. Phenol and p-cresol were also completely oxidized to carbon dioxide with Fe(III) as the sole electron acceptor, and GS-15 could obtain energy to support growth by oxidizing either of these compounds as the sole electron donor. p-Hydroxybenzoate was a transitory extracellular intermediate of phenol and p-cresol metabolism but not of toluene metabolism. GS-15 oxidized potential aromatic intermediates in the oxidation of toluene (benzylalcohol and benzaldehyde) and p-cresol (p-hydroxybenzylalcohol and p-hydroxybenzaldehyde). The metabolism described here provides a model for how aromatic hydrocarbons and phenols may be oxidized with the reduction of Fe(III) in contaminated aquifers and petroleum-containing sediments.

  10. Reduction of structural Fe(III) in nontronite by methanogen Methanosarcina barkeri

    USGS Publications Warehouse

    Liu, D.; Dong, Hailiang H.; Bishop, M.E.; Wang, Hongfang; Agrawal, A.; Tritschler, S.; Eberl, D.D.; Xie, S.

    2011-01-01

    Clay minerals and methanogens are ubiquitous and co-exist in anoxic environments, yet it is unclear whether methanogens are able to reduce structural Fe(III) in clay minerals. In this study, the ability of methanogen Methanosarcina barkeri to reduce structural Fe(III) in iron-rich smectite (nontronite NAu-2) and the relationship between iron reduction and methanogenesis were investigated. Bioreduction experiments were conducted in growth medium using three types of substrate: H2/CO2, methanol, and acetate. Time course methane production and hydrogen consumption were measured by gas chromatography. M. barkeri was able to reduce structural Fe(III) in NAu-2 with H2/CO2 and methanol as substrate, but not with acetate. The extent of bioreduction, as measured by the 1,10-phenanthroline method, was 7-13% with H2/CO2 as substrate, depending on nontronite concentration (5-10g/L). The extent was higher when methanol was used as a substrate, reaching 25-33%. Methanogenesis was inhibited by Fe(III) reduction in the H2/CO2 culture, but enhanced when methanol was used. High charge smectite and biogenic silica formed as a result of bioreduction. Our results suggest that methanogens may play an important role in biogeochemical cycling of iron in clay minerals and may have important implications for the global methane budget. ?? 2010 Elsevier Ltd.

  11. Spectral, thermal and kinetic studies of charge-transfer complexes formed between the highly effective antibiotic drug metronidazole and two types of acceptors: σ- and π-acceptors

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; Saad, Hosam A.; Adam, Abdel Majid A.

    2015-04-01

    Understanding the interaction between drugs and small inorganic or organic molecules is critical in being able to interpret the drug-receptor interactions and acting mechanism of these drugs. A combined solution and solid state study was performed to describe the complexation chemistry of drug metronidazole (MZ) which has a broad-spectrum antibacterial activity with two types of acceptors. The acceptors include, σ-acceptor (i.e., iodine) and π-acceptors (i.e., dichlorodicyanobenzoquinone (DDQ), chloranil (CHL) and picric acid (PA)). The molecular structure, spectroscopic characteristics, the binding modes as well as the thermal stability were deduced from IR, UV-vis, 1H NMR and thermal studies. The binding ratio of complexation (MZ: acceptor) was determined to be 1:2 for the iodine acceptor and 1:1 for the DDQ, CHL or PA acceptor, according to the CHN elemental analyses and spectrophotometric titrations. It has been found that the complexation with CHL and PA acceptors increases the values of enthalpy and entropy, while the complexation with DDQ and iodine acceptors decreases the values of these parameters compared with the free MZ donor.

  12. Rapid photooxidation of Sb(III) in the presence of different Fe(III) species

    NASA Astrophysics Data System (ADS)

    Kong, Linghao; He, Mengchang; Hu, Xingyun

    2016-05-01

    The toxicity and mobility of antimony (Sb) are strongly influenced by the redox processes associated with Sb. Dissolved iron (Fe) is widely distributed in the environment as different species and plays a significant role in Sb speciation. However, the mechanisms of Sb(III) oxidation in the presence of Fe have remained unclear because of the complexity of Fe and Sb speciation. In this study, the mechanisms of Sb(III) photooxidation in the presence of different Fe species were investigated systematically. The photooxidation of Sb(III) occurred over a wide pH range, from 1 to 10. Oxygen was not a predominant or crucial factor in the Sb(III) oxidation process. The mechanism of Sb(III) photooxidation varied depending on the Fe(III) species. In acidic solution (pH 1-3), dichloro radicals (radCl2-) and hydroxyl radicals (radOH) generated by the photocatalysis of FeCl2+ and FeOH2+ were the main oxidants for Sb(III) oxidation. Fe(III) gradually transformed into the colloid ferric hydroxide (CFH) and ferrihydrite in circumneutral and alkaline solutions (pH 4-10). Photooxidation of Sb(III) occurred through electron transfer from Sb(III) to Fe(III) along with the reduction of Fe(III) to Fe(II) through a ligand-to-metal charge-transfer (LMCT) process. The photocatalysis of different Fe(III) species may play an important role in the geochemical cycle of Sb(III) in surface soil and aquatic environments.

  13. Intercalation of Coordinatively Unsaturated Fe(III) Ion within Interpenetrated Metal-Organic Framework MOF-5.

    PubMed

    Holmberg, Rebecca J; Burns, Thomas; Greer, Samuel M; Kobera, Libor; Stoian, Sebastian A; Korobkov, Ilia; Hill, Stephen; Bryce, David L; Woo, Tom K; Murugesu, Muralee

    2016-06-01

    Coordinatively unsaturated Fe(III) metal sites were successfully incorporated into the iconic MOF-5 framework. This new structure, Fe(III) -iMOF-5, is the first example of an interpenetrated MOF linked through intercalated metal ions. Structural characterization was performed with single-crystal and powder XRD, followed by extensive analysis by spectroscopic methods and solid-state NMR, which reveals the paramagnetic ion through its interaction with the framework. EPR and Mössbauer spectroscopy confirmed that the intercalated ions were indeed Fe(III) , whereas DFT calculations were employed to ascertain the unique pentacoordinate architecture around the Fe(III) ion. Interestingly, this is also the first crystallographic evidence of pentacoordinate Zn(II) within the MOF-5 SBU. This new MOF structure displays the potential for metal-site addition as a framework connector, thus creating further opportunity for the innovative development of new MOF materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Hydrogen and formate oxidation coupled to dissimilatory reduction of iron or manganese by Alteromonas putrefaciens

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.

    1989-01-01

    The ability of Alteromonas putrefaciens to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory Fe(III) or Mn(IV) reduction was investigated. A. putrefaciens grew with hydrogen, formate, lactate, or pyruvate as the sole electron donor and Fe(III) as the sole electron acceptor. Lactate and pyruvate were oxidized to acetate, which was not metabolized further. With Fe(III) as the electron acceptor, A. putrefaciens had a high affinity for hydrogen and formate and metabolized hydrogen at partial pressures that were 25-fold lower than those of hydrogen that can be metabolized by pure cultures of sulfate reducers or methanogens. The electron donors for Fe(III) reduction also supported Mn(IV) reduction. The electron donors for Fe(III) and Mn(IV) reduction and the inability of A. putrefaciens to completely oxidize multicarbon substrates to carbon dioxide distinguish A. putrefaciens from GS-15, the only other organism that is known to obtain energy for growth by coupling the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). The ability of A. putrefaciens to reduce large quantities of Fe(III) and to grow in a defined medium distinguishes it from a Pseudomonas sp., which is the only other known hydrogen-oxidizing, Fe(III)-reducing microorganism. Furthermore, A. putrefaciens is the first organism that is known to grow with hydrogen as the electron donor and Mn(IV) as the electron acceptor and is the first organism that is known to couple the oxidation of formate to the reduction of Fe(III) or Mn(IV). Thus, A. putrefaciens provides a much needed microbial model for key reactions in the oxidation of sediment organic matter coupled to Fe(III) and Mn(IV) reduction.

  15. Associative Memory Acceptors.

    ERIC Educational Resources Information Center

    Card, Roger

    The properties of an associative memory are examined in this paper from the viewpoint of automata theory. A device called an associative memory acceptor is studied under real-time operation. The family "L" of languages accepted by real-time associative memory acceptors is shown to properly contain the family of languages accepted by one-tape,…

  16. Characteristics of ovulation method acceptors: a cross-cultural assessment.

    PubMed

    Klaus, H; Labbok, M; Barker, D

    1988-01-01

    Five programs of instruction in the ovulation method (OM) in diverse geographic and cultural settings are described, and characteristics of approximately 200 consecutive OM acceptors in each program are examined. Major findings include: the religious background and family size of acceptors are variable, as is the level of previous contraceptive use. Acceptors are drawn from a wide range of socioeconomic and religious backgrounds; however, family planning intention was similarly distributed in all five countries. In sum, the ovulation method is accepted by persons from a variety of backgrounds within and between cultural setting.

  17. Fe(III) and Fe(II) induced photodegradation of nonylphenol polyethoxylate (NPEO) oligomer in aqueous solution and toxicity evaluation of the irradiated solution.

    PubMed

    Wang, Lei; Zhang, Junjie; Duan, Zhenghua; Sun, Hongwen

    2017-06-01

    Photodegradation of nonylphenol tri-ethoxylate (NPEO 3 ) in aqueous solution, and the effects of Fe(III) or Fe(II) were studied. The increasing degradation kinetics of NPEO 3 were observed when 500µM Fe(III) or Fe(II) was present in the solutions. Altered formation of NPEO oligomers with shorter EO chains, including nonyphenol (NP), NPEO 1 and NPEO 2 , was observed in water and in solutions containing Fe(III) or Fe(II). The molar percentage yields of NP and NPEO 1,2 production from NPEO 3 photodegradation were approximately 20% in NPEO 3 solution, while NPEO 3 solution with Fe(III), this percentage increased to approximately 50%. In solution with Fe(II), the molar balance between the photodegradation of NPEO 3 and the production of NP and NPEO 1,2 was observed. A luminescent bacterium, Vibrio fischeri, was used to identify changes in the toxicity of NPEO 3 solutions during the photodegradation process under different conditions, while dose addition (DA) model was used to estimate the toxicity of products. Toxicity of NPEO 3 /water solution increased significantly following the irradiation of UVA/UVB mixture. In contrast, obviously decreasing toxicity was observed when NPEO 3 underwent photodegradation in the presence of Fe(III). Copyright © 2017. Published by Elsevier Inc.

  18. Impact of Fe(III)-OM complexes and Fe(III) polymerization on SOM pools reactivity under different land uses

    NASA Astrophysics Data System (ADS)

    Giannetta, B.; Plaza, C.; Zaccone, C.; Siebecker, M. G.; Rovira, P.; Vischetti, C.; Sparks, D. L.

    2017-12-01

    Soil organic matter (SOM) protection and long-term accumulation are controlled by adsorption to mineral surfaces in different ways, depending on its molecular structure and pedo-climatic conditions. Iron (Fe) oxides are known to be key regulators of the soil carbon (C) cycle, and Fe speciation in soils is highly dependent on environmental conditions and chemical interactions with SOM. However, the molecular structure and hydrolysis of Fe species formed in association with SOM is still poorly described. We hypothesize the existence of two pools of Fe which interact with SOM: mononuclear Fe(III)-SOM complexes and precipitated Fe(III) hydroxides. To verify our hypothesis, we investigated the interactions between Fe(III) and physically isolated soil fractions by means of batch experiments at pH 7. Specifically, we examined the fine silt plus clay (FSi+C) fraction, obtained by ultrasonic dispersion and wet sieving. The soil samples spanned several land uses, including coniferous forest (CFS), grassland (GS), technosols (TS) and agricultural (AS) soils. Solid phase products and supernatants were analyzed for C and Fe content. X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis were also performed. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to assess the main C functional groups involved in C complexation and desorption experiments. Preliminary linear combination fitting (LCF) of Fe K-edge extended X-ray absorption fine structure (EXAFS) spectra suggested the formation of ferrihydrite-like polymeric Fe(III) oxides in reacted CFS and GS samples, with higher C and Fe concentration. Conversely, mononuclear Fe(III) OM complexes dominated the speciation for TS and AS samples, characterized by lower C and Fe concentration, inhibiting the hydrolysis and polymerization of Fe (III). This approach will help revealing the mechanisms by which SOM pools can control Fe(III) speciation, and will elucidate how both Fe

  19. Energy bands and acceptor binding energies of GaN

    NASA Astrophysics Data System (ADS)

    Xia, Jian-Bai; Cheah, K. W.; Wang, Xiao-Liang; Sun, Dian-Zhao; Kong, Mei-Ying

    1999-04-01

    The energy bands of zinc-blende and wurtzite GaN are calculated with the empirical pseudopotential method, and the pseudopotential parameters for Ga and N atoms are given. The calculated energy bands are in agreement with those obtained by the ab initio method. The effective-mass theory for the semiconductors of wurtzite structure is established, and the effective-mass parameters of GaN for both structures are given. The binding energies of acceptor states are calculated by solving strictly the effective-mass equations. The binding energies of donor and acceptor are 24 and 142 meV for the zinc-blende structure, 20 and 131, and 97 meV for the wurtzite structure, respectively, which are consistent with recent experimental results. It is proposed that there are two kinds of acceptor in wurtzite GaN. One kind is the general acceptor such as C, which substitutes N, which satisfies the effective-mass theory. The other kind of acceptor includes Mg, Zn, Cd, etc., the binding energy of these acceptors is deviated from that given by the effective-mass theory. In this report, wurtzite GaN is grown by the molecular-beam epitaxy method, and the photoluminescence spectra were measured. Three main peaks are assigned to the donor-acceptor transitions from two kinds of acceptors. Some of the transitions were identified as coming from the cubic phase of GaN, which appears randomly within the predominantly hexagonal material.

  20. Enzymatic iron and uranium reduction by sulfate-reducing bacteria

    USGS Publications Warehouse

    Lovley, D.R.; Roden, E.E.; Phillips, E.J.P.; Woodward, J.C.

    1993-01-01

    The potential for sulfate-reducing bacteria (SRB) to enzymatically reduce Fe(III) and U(VI) was investigated. Five species of Desulfovibrio as well as Desulfobacterium autotrophicum and Desulfobulbus propionicus reduced Fe(III) chelated with nitrilotriacetic acid as well as insoluble Fe(III) oxide. Fe(III) oxide reduction resulted in the accumulation of magnetite and siderite. Desulfobacter postgatei reduced the chelated Fe(III) but not Fe(III) oxide. Desulfobacter curvatus, Desulfomonile tiedjei, and Desulfotomaculum acetoxidans did not reduce Fe(III). Only Desulfovibrio species reduced U(VI). U(VI) reduction resulted in the precipitation of uraninite. None of the SRB that reduced Fe(III) or U(VI) appeared to conserve enough energy to support growth from this reaction. However, Desulfovibrio desulfuricans metabolized H2 down to lower concentrations with Fe(III) or U(VI) as the electron acceptor than with sulfate, suggesting that these metals may be preferred electron acceptors at the low H2 concentrations present in most marine sediments. Molybdate did not inhibit Fe(III) reduction by D. desulfuricans. This indicates that the inability of molybdate to inhibit Fe(III) reduction in marine sediments does not rule out the possibility that SRB are important catalysts for Fe(III) reduction. The results demonstrate that although SRB were previously considered to reduce Fe(III) and U(VI) indirectly through the production of sulfide, they may also directly reduce Fe(III) and U(VI) through enzymatic mechanisms. These findings, as well as our recent discovery that the So-reducing microorganism Desulfuromonas acetoxidans can reduce Fe(III), demonstrate that there are close links between the microbial sulfur, iron, and uranium cycles in anaerobic marine sediments. ?? 1993.

  1. Effect of the oxidation rate and Fe(II) state on microbial nitrate-dependent Fe(III) mineral formation

    USGS Publications Warehouse

    Senko, John M.; Dewers , Thomas A.; Krumholz, Lee R.

    2005-01-01

    A nitrate-dependent Fe(II)-oxidizing bacterium was isolated and used to evaluate whether Fe(II) chemical form or oxidation rate had an effect on the mineralogy of biogenic Fe(III) (hydr)oxides resulting from nitrate-dependent Fe(II) oxidation. The isolate (designated FW33AN) had 99% 16S rRNA sequence similarity to Klebsiella oxytoca. FW33AN produced Fe(III) (hydr)oxides by oxidation of soluble Fe(II) [Fe(II)sol] or FeS under nitrate-reducing conditions. Based on X-ray diffraction (XRD) analysis, Fe(III) (hydr)oxide produced by oxidation of FeS was shown to be amorphous, while oxidation of Fe(II)sol yielded goethite. The rate of Fe(II) oxidation was then manipulated by incubating various cell concentrations of FW33AN with Fe(II)sol and nitrate. Characterization of products revealed that as Fe(II) oxidation rates slowed, a stronger goethite signal was observed by XRD and a larger proportion of Fe(III) was in the crystalline fraction. Since the mineralogy of Fe(III) (hydr)oxides may control the extent of subsequent Fe(III) reduction, the variables we identify here may have an effect on the biogeochemical cycling of Fe in anoxic ecosystems.

  2. 2012 Gordon Research Conference, Electron donor-acceptor interactions, August 5-10 2012

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    McCusker, James

    The upcoming incarnation of the Gordon Research Conference on Electron Donor Acceptor Interactions will feature sessions on classic topics including proton-coupled electron transfer, dye-sensitized solar cells, and biological electron transfer, as well as emerging areas such as quantum coherence effects in donor-acceptor interactions, spintronics, and the application of donor-acceptor interactions in chemical synthesis.

  3. Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials.

    PubMed

    Wang, Qiang; Huang, Liping; Pan, Yuzhen; Quan, Xie; Li Puma, Gianluca

    2017-01-05

    The role of Fe(III) was investigated as an electron-shuttle mediator to enhance the reduction rate of the toxic heavy metal hexavalent chromium (Cr(VI)) in wastewaters, using microbial fuel cells (MFCs). The direct reduction of chromate (CrO 4 - ) and dichromate (Cr 2 O 7 2- ) anions in MFCs was hampered by the electrical repulsion between the negatively charged cathode and Cr(VI) functional groups. In contrast, in the presence of Fe(III), the conversion of Cr(VI) and the cathodic coulombic efficiency in the MFCs were 65.6% and 81.7%, respectively, 1.6 times and 1.4 folds as those recorded in the absence of Fe(III). Multiple analytical approaches, including linear sweep voltammetry, Tafel plot, cyclic voltammetry, electrochemical impedance spectroscopy and kinetic calculations demonstrated that the complete reduction of Cr(VI) occurred through an indirect mechanism mediated by Fe(III). The direct reduction of Cr(VI) with cathode electrons in the presence of Fe(III) was insignificant. Fe(III) played a critical role in decreasing both the diffusional resistance of Cr(VI) species and the overpotential for Cr(VI) reduction. This study demonstrated that the reduction of Cr(VI) in MFCs was effective in the presence of Fe(III), providing an alternative and environmentally benign approach for efficient remediation of Cr(VI) contaminated sites with simultaneous production of renewable energy. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. Acceptor and Excitation Density Dependence of the Ultrafast Polaron Absorption Signal in Donor-Acceptor Organic Solar Cell Blends.

    PubMed

    Zarrabi, Nasim; Burn, Paul L; Meredith, Paul; Shaw, Paul E

    2016-07-21

    Transient absorption spectroscopy on organic semiconductor blends for solar cells typically shows efficient charge generation within ∼100 fs, accounting for the majority of the charge carriers. In this Letter, we show using transient absorption spectroscopy on blends containing a broad range of acceptor content (0.01-50% by weight) that the rise of the polaron signal is dependent on the acceptor concentration. For low acceptor content (<10% by weight), the polaron signal rises gradually over ∼1 ps with most polarons generated after 200 fs, while for higher acceptor concentrations (>10%) most polarons are generated within 200 fs. The rise time in blends with low acceptor content was also found to be sensitive to the pump fluence, decreasing with increasing excitation density. These results indicate that the sub-100 fs rise of the polaron signal is a natural consequence of both the high acceptor concentrations in many donor-acceptor blends and the high excitation densities needed for transient absorption spectroscopy, which results in a short average distance between the exciton and the donor-acceptor interface.

  5. Acceptors in ZnO

    DOE PAGES

    Mccluskey, Matthew D.; Corolewski, Caleb; Lv, Jinpeng; ...

    2015-03-21

    Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence shows that these point defects have acceptor levels 3.2, 1.5, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO2 contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peakmore » in ZnO nanocrystals has been attributed to an acceptor, which may involve a zinc vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g = 2.0033 and g = 2.0075, along with an isotropic center at g = 2.0053.« less

  6. Thermodynamic Versus Surface Area Control of Microbial Fe(III) Oxide Reduction Kinetics

    NASA Astrophysics Data System (ADS)

    Roden, E. E.

    2003-12-01

    Recent experimental studies of synthetic and natural Fe(III) oxide reduction permit development of conceptual and quantitative models of enzymatic Fe(III) oxide reduction at circumneutral pH that can be compared to and contrasted with established models of abiotic mineral dissolution. The findings collectively support a model for controls on enzymatic reduction that differs fundamentally from those applied to abiotic reductive dissolution as a result of two basic phenomena: (1) the relatively minor influence of oxide mineralogical and thermodynamic properties on surface area-normalized rates of enzymatic reduction compared to abiotic reductive dissolution; and (2) the major limitation which sorption and/or surface precipitation of biogenic Fe(II) on residual oxide and Fe(III)-reducing bacterial cell surfaces poses to enzymatic electron transfer in the presence of excess electron donor. Parallel studies with two major Fe(III)-reducing bacteria genera (Shewanella and Geobacter) lead to common conclusions regarding the importance of these phenomena in regulating the rate and long-term extent of Fe(III) oxide reduction. Although the extent to which these phenomena can be traced to underlying kinetic vs. thermodynamic effects cannot be resolved with current information, models in which rates of enzymatic reduction are limited kinetically by the abundance of "available" oxide surface sites (as controlled by oxide surface area and the abundance of surface-bound Fe(II)) provide an adequate macroscopic description of controls on the initial rate and long-term extent of oxide reduction. In some instances, thermodynamic limitation posed by the accumulation of aqueous reaction end-products (i.e. Fe(II) and alkalinity) must also be invoked to explain observed long-term patterns of reduction. In addition, the abundance of Fe(III)-reducing microorganisms plays an important role in governing rates of reduction and needs to be considered in models of Fe(III) reduction in nonsteady

  7. Assessing bioavailability levels of metals in effluent-affected rivers: effect of Fe(III) and chelating agents on the distribution of metal speciation.

    PubMed

    Han, Shuping; Naito, Wataru; Masunaga, Shigeki

    To assess the effects of Fe(III) and anthropogenic ligands on the bioavailability of Ni, Cu, Zn, and Pb, concentrations of bioavailable metals were measured by the DGT (diffusive gradients in thin films) method in some urban rivers, and were compared with concentrations calculated by a chemical equilibrium model (WHAM 7.0). Assuming that dissolved Fe(III) (<0.45 μm membrane filtered) was in equilibrium with colloidal iron oxide, the WHAM 7.0 model estimated that bioavailable concentrations of Ni, Cu, and Zn were slightly higher than the corresponding values estimated assuming that dissolved Fe(III) was absent. In contrast, lower levels of free Pb were predicted by the WHAM 7.0 model when dissolved Fe(III) was included. Estimates showed that most of the dissolved Pb was present as colloidal iron-Pb complex. Ethylene-diamine-tetra-acetic acid (EDTA) concentrations at sampling sites were predicted from the relationship between EDTA and the calculated bioavailable concentration of Zn. When both colloidal iron and predicted EDTA concentrations were included in the WHAM 7.0 calculations, dissolved metals showed a strong tendency to form EDTA complexes, in the order Ni > Cu > Zn > Pb. With the inclusion of EDTA, bioavailable concentrations of Ni, Cu, and Zn predicted by WHAM 7.0 were different from those predicted considering only humic substances and colloidal iron.

  8. Online spectrophotometric determination of Fe(II) and Fe(III) by flow injection combined with low pressure ion chromatography

    NASA Astrophysics Data System (ADS)

    Chen, Shujuan; Li, Nan; Zhang, Xinshen; Yang, Dongjing; Jiang, Heimei

    2015-03-01

    A simple and new low pressure ion chromatography combined with flow injection spectrophotometric procedure for determining Fe(II) and Fe(III) was established. It is based on the selective adsorption of low pressure ion chromatography column to Fe(II) and Fe(III), the online reduction reaction of Fe(III) and the reaction of Fe(II) in sodium acetate with phenanthroline, resulting in an intense orange complex with a suitable absorption at 515 nm. Various chemical (such as the concentration of colour reagent, eluant and reductive agent) and instrumental parameters (reaction coil length, reductive coil length and wavelength) were studied and were optimized. Under the optimum conditions calibration graph of Fe(II)/Fe(III) was linear in the Fe(II)/Fe(III) range of 0.040-1.0 mg/L. The detection limit of Fe(III) and Fe(II) was respectively 3.09 and 1.55 μg/L, the relative standard deviation (n = 10) of Fe(II) and Fe(III) 1.89% and 1.90% for 0.5 mg/L of Fe(II) and Fe(III) respectively. About 2.5 samples in 1 h can be analyzed. The interfering effects of various chemical species were studied. The method was successfully applied in the determination of water samples.

  9. Next-generation organic photovoltaics based on non-fullerene acceptors

    NASA Astrophysics Data System (ADS)

    Cheng, Pei; Li, Gang; Zhan, Xiaowei; Yang, Yang

    2018-03-01

    Over the past three years, a particularly exciting and active area of research within the field of organic photovoltaics has been the use of non-fullerene acceptors (NFAs). Compared with fullerene acceptors, NFAs possess significant advantages including tunability of bandgaps, energy levels, planarity and crystallinity. To date, NFA solar cells have not only achieved impressive power conversion efficiencies of 13-14%, but have also shown excellent stability compared with traditional fullerene acceptor solar cells. This Review highlights recent progress on single-junction and tandem NFA solar cells and research directions to achieve even higher efficiencies of 15-20% using NFA-based organic photovoltaics are also proposed.

  10. Isolation of Geobacter species from diverse sedimentary environments

    USGS Publications Warehouse

    Coaxes, J.D.; Phillips, E.J.P.; Lonergan, D.J.; Jenter, H.; Lovley, D.R.

    1996-01-01

    In an attempt to better understand the microorganisms responsible for Fe(III) reduction in sedimentary environments, Fe(III)-reducing microorganisms were enriched for and isolated from freshwater aquatic sediments, a pristine deep aquifer, and a petroleum-contaminated shallow aquifer. Enrichments were initiated with acetate or toluene as the electron donor and Fe(III) as the electron acceptor. Isolations were made with acetate or benzoate. Five new strains which could obtain energy for growth by dissimilatory Fe(III) reduction were isolated. All five isolates are gram- negative strict anaerobes which grow with acetate as the electron donor and Fe(III) as the electron acceptor. Analysis of the 16S rRNA sequence of the isolated organisms demonstrated that they all belonged to the genus Geobacter in the delta subdivision of the Proteobacteria. Unlike the type strain, Geobacter metallireducens, three of the five isolates could use H2 as an electron donor fur Fe(III) reduction. The deep subsurface isolate is the first Fe(III) reducer shown to completely oxidize lactate to carbon dioxide, while one of the freshwater sediment isolates is only the second Fe(III) reducer known that can oxidize toluene. The isolation of these organisms demonstrates that Geobacter species are widely distributed in a diversity of sedimentary environments in which Fe(III) reduction is an important process.

  11. Comparative c-type cytochrome expression analysis in Shewanella oneidensis strain MR-1 and Anaeromyxobacter dehalogenans strain 2CP-C grown with soluble and insoluble oxidised metal electron acceptors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nissen, Silke; Liu, Xiaoxin; Chourey, Karuna

    2012-01-01

    The genomes of Shewanella oneidensis strain MR-1 and Anaeromyxobacter dehalogenans strain 2CP-C encode 40 and 69 putative c-type cytochrome genes, respectively. Deletion mutant and biochemical studies have assigned specific functions to a few c-type cytochromes involved in electron transfer to oxidised metals in Shewanella oneidensis strain MR-1. Although promising, the genetic approach is limited to gene deletions that produce a distinct phenotype, and organism for which a genetic system is available. To more comprehensively investigate and compare c-type cytochrome expression in Shewanella oneidensis strain MR-1 and Anaeromyxobacter dehalogenans strain 2CP-C, proteomic measurements were used to characterise lysates of cells grownmore » with soluble Fe(III) (as ferric citrate) and insoluble Mn(IV) (as MnO2) as electron acceptors. Strain MR-1 expressed 19 and 20, and strain 2CP-C expressed 27 and 25 c-type cytochromes when grown with Fe(III) and Mn(IV), respectively. The majority of c-type cytochromes (77% for strain MR-1 and 63% for strain 2CP-C) were expressed under both growth conditions; however, the analysis also revealed unique c-type cytochromes that were specifically expressed in cells grown with soluble Fe(III) or insoluble Mn(IV). Proteomic characterisation proved to be a promising approach for determining the c-type cytochrome complement expressed under different growth conditions, and will help elucidating the specific functions of more c-type cytochromes that are the basis for Shewanella and Anaeromyxobacter respiratory versatility.« less

  12. Single peak parameters technique for simultaneous measurements: Spectrophotometric sequential injection determination of Fe(II) and Fe(III).

    PubMed

    Kozak, J; Paluch, J; Węgrzecka, A; Kozak, M; Wieczorek, M; Kochana, J; Kościelniak, P

    2016-02-01

    Spectrophotometric sequential injection system (SI) is proposed to automate the method of simultaneous determination of Fe(II) and Fe(III) on the basis of parameters of a single peak. In the developed SI system, sample and mixture of reagents (1,10-phenanthroline and sulfosalicylic acid) are introduced into a vessel, where in an acid environment (pH≅3) appropriate compounds of Fe(II) and Fe(III) with 1,10-phenanthroline and sulfosalicylic acid are formed, respectively. Then, in turn, air, sample, EDTA and sample again, are introduced into a holding coil. After the flow reversal, a segment of air is removed from the system by an additional valve and as EDTA replaces sulfosalicylic acid forming a more stable colorless compound with Fe(III), a complex signal is registered. Measurements are performed at wavelength 530 nm. The absorbance measured at minimum of the negative peak and the area or the absorbance measured at maximum of the signal can be used as measures corresponding to Fe(II) and Fe(III) concentrations, respectively. The time of the peak registration is about 2 min. Two-component calibration has been applied to analysis. Fe(II) and Fe(III) can be determined within the concentration ranges of 0.04-4.00 and 0.1-5.00 mg L(-1), with precision less than 2.8% and 1.7% (RSD), respectively and accuracy better than 7% (RE). The detection limit is 0.04 and 0.09 mg L(-1) for Fe(II) and Fe(III), respectively. The method was applied to analysis of artesian water samples. Copyright © 2015 Elsevier B.V. All rights reserved.

  13. Microbiology and Biogeochemical Study of Underground Research Tunnel for the Geological Disposal of Nuclear Waste

    NASA Astrophysics Data System (ADS)

    Roh, Y.; Oh, J.; Seo, H.; Rhee, S.

    2007-12-01

    The Underground Research Tunnel (URT) located in Korea Atomic Energy Research Institute (KAERI), Daejeon, South Korea was recently constructed as an experimental site to study radionuclide transport, biogeochemistry, radionuclide-mineral interactions for the geological disposal of high level nuclear waste. Groundwater sampled from URT was used to examine microbial diversity and to enrich metal reducing bacteria for studying microbe- metal interactions. Genomic analysis indicated that the groundwater contained diverse microorganisms such as metal reducers, metal oxidizers, anaerobic denitrifying bacteria, and bacteria for reductive dechlorination. Metal- reducing bacteria enriched from the groundwater was used to study metal reduction and biomineralization. The metal-reducing bacteria enriched with acetate or lactate as the electron donors showed the bacteria reduced Fe(III)-citrate, Fe(III) oxyhydroxides, Mn(IV) oxide, and Cr(VI) as the electron acceptors. Preliminary study indicated that the enriched bacteria were able to use glucose, lactate, acetate, and hydrogen as electron donors while reducing Fe(III)-citrate or Fe(III) oxyhydroxide as the electron acceptor. The bacteria exhibited diverse mineral precipitation capabilities including the formation of magnetite, siderite, and rhodochrosite. The results indicated that Fe(III)- and metal-reducing communities are present in URT at the KAERI.

  14. Anaerobic electron acceptor chemotaxis in Shewanella putrefaciens

    NASA Technical Reports Server (NTRS)

    Nealson, K. H.; Moser, D. P.; Saffarini, D. A.

    1995-01-01

    Shewanella putrefaciens MR-1 can grow either aerobically or anaerobically at the expense of many different electron acceptors and is often found in abundance at redox interfaces in nature. Such redox interfaces are often characterized by very strong gradients of electron acceptors resulting from rapid microbial metabolism. The coincidence of S. putrefaciens abundance with environmental gradients prompted an examination of the ability of MR-1 to sense and respond to electron acceptor gradients in the laboratory. In these experiments, taxis to the majority of the electron acceptors that S. putrefaciens utilizes for anaerobic growth was seen. All anaerobic electron acceptor taxis was eliminated by the presence of oxygen, nitrate, nitrite, elemental sulfur, or dimethyl sulfoxide, even though taxis to the latter was very weak and nitrate and nitrite respiration was normal in the presence of dimethyl sulfoxide. Studies with respiratory mutants of MR-1 revealed that several electron acceptors that could not be used for anaerobic growth nevertheless elicited normal anaerobic taxis. Mutant M56, which was unable to respire nitrite, showed normal taxis to nitrite, as well as the inhibition of taxis to other electron acceptors by nitrite. These results indicate that electron acceptor taxis in S. putrefaciens does not conform to the paradigm established for Escherichia coli and several other bacteria. Carbon chemo-taxis was also unusual in this organism: of all carbon compounds tested, the only positive response observed was to formate under anaerobic conditions.

  15. Formation of Fe(III) oxyhydroxide colloids in freshwater and brackish seawater, with incorporation of phosphate and calcium

    NASA Astrophysics Data System (ADS)

    Gunnars, Anneli; Blomqvist, Sven; Johansson, Peter; Andersson, Christian

    2002-03-01

    The formation of Fe(III) oxyhydroxide colloids by oxidation of Fe(II) and their subsequent aggregation to larger particles were studied in laboratory experiments with natural water from a freshwater lake and a brackish coastal sea. Phosphate was incorporated in the solid phase during the course of hydrolysis of iron. The resulting precipitated amorphous Fe(III) oxyhydroxide phases were of varying composition, depending primarily on the initial dissolved Fe/P molar ratio, but with little influence by salinity or concentration of calcium ions. The lower limiting Fe/P ratio found for the solid phase suggests the formation of a basic Fe(III) phosphate compound with a stoichiometric Fe/P ratio of close to two. This implies that an Fe/P stoichiometry of ≈2 ultimately limits the capacity of precipitating Fe(III) to fix dissolved phosphate at oxic/anoxic boundaries in natural waters. In contrast to phosphorus, the uptake of calcium seemed to be controlled by sorption processes at the surface of the iron-rich particles formed. This uptake was more efficient in freshwater than in brackish water, suggesting that salinity restrains the uptake of calcium by newly formed Fe(III) oxyhydroxides in natural waters. Moreover, salinity enhanced the aggregation rate of the colloids formed. The suspensions were stabilised by the presence of organic matter, although this effect was less pronounced in seawater than in freshwater. Thus, in seawater of 6 to 33 ‰S, the removal of particles was fast (removal half time < 200 h), whereas the colloidal suspensions formed in freshwater were stable (removal half time > 900 h). Overall, oxidation of Fe(II) and removal of Fe(III) oxyhydroxide particles were much faster in seawater than in freshwater. This more rapid turnover results in lower iron availability in coastal seawater than in freshwater, making iron more likely to become a limiting element for chemical scavenging and biologic production.

  16. Mechanisms for Electron Transfer Through Pili to Fe(III) Oxide in Geobacter

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lovley, Derek R.

    The purpose of these studies was to aid the Department of Energy in its goal of understanding how microorganisms involved in the bioremediation of metals and radionuclides sustain their activity in the subsurface. This information is required in order to incorporate biological processes into decision making for environmental remediation and long-term stewardship of contaminated sites. The proposed research was designed to elucidate the mechanisms for electron transfer to Fe(III) oxides in Geobacter species because Geobacter species are abundant dissimilatory metal-reducing microorganisms in a diversity of sites in which uranium is undergoing natural attenuation via the reduction of soluble U(VI) tomore » insoluble U(IV) or when this process is artificially stimulated with the addition of organic electron donors. This study investigated the novel, but highly controversial, concept that the final conduit for electron transfer to Fe(III) oxides are electrically conductive pili. The specific objectives were to: 1) further evaluate the conductivity along the pili of Geobacter sulfurreducens and related organisms; 2) determine the mechanisms for pili conductivity; and 3) investigate the role of pili in Fe(III) oxide reduction. The studies demonstrated that the pili of G. sulfurreducens are conductive along their length. Surprisingly, the pili possess a metallic-like conductivity similar to that observed in synthetic organic conducting polymers such as polyaniline. Detailed physical analysis of the pili, as well as studies in which the structure of the pili was genetically modified, demonstrated that the metallic-like conductivity of the pili could be attributed to overlapping pi-pi orbitals of aromatic amino acids. Other potential mechanisms for conductivity, such as electron hopping between cytochromes associated with the pili were definitively ruled out. Pili were also found to be essential for Fe(III) oxide reduction in G. metallireducens. Ecological studies

  17. Geochemical control of microbial Fe(III) reduction potential in wetlands: Comparison of the rhizosphere to non-rhizosphere soil

    USGS Publications Warehouse

    Weiss, J.V.; Emerson, D.; Megonigal, J.P.

    2004-01-01

    We compared the reactivity and microbial reduction potential of Fe(III) minerals in the rhizosphere and non-rhizosphere soil to test the hypothesis that rapid Fe(III) reduction rates in wetland soils are explained by rhizosphere processes. The rhizosphere was defined as the area immediately adjacent to a root encrusted with Fe(III)-oxides or Fe plaque, and non-rhizosphere soil was 0.5 cm from the root surface. The rhizosphere had a significantly higher percentage of poorly crystalline Fe (66??7%) than non-rhizosphere soil (23??7%); conversely, non-rhizosphere soil had a significantly higher proportion of crystalline Fe (50??7%) than the rhizosphere (18??7%, P<0.05 in all cases). The percentage of poorly crystalline Fe(III) was significantly correlated with the percentage of FeRB (r=0.76), reflecting the fact that poorly crystalline Fe(III) minerals are labile with respect to microbial reduction. Abiotic reductive dissolution consumed about 75% of the rhizosphere Fe(III)-oxide pool in 4 h compared to 23% of the soil Fe(III)-oxide pool. Similarly, microbial reduction consumed 75-80% of the rhizosphere pool in 10 days compared to 30-40% of the non-rhizosphere soil pool. Differences between the two pools persisted when samples were amended with an electron-shuttling compound (AQDS), an Fe(III)-reducing bacterium (Geobacter metallireducens), and organic carbon. Thus, Fe(III)-oxide mineralogy contributed strongly to differences in the Fe(III) reduction potential of the two pools. Higher amounts of poorly crystalline Fe(III) and possibly humic substances, and a higher Fe(III) reduction potential in the rhizosphere compared to the non-rhizosphere soil, suggested the rhizosphere is a site of unusually active microbial Fe cycling. The results were consistent with previous speculation that rapid Fe cycling in wetlands is due to the activity of wetland plant roots. ?? 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.

  18. Non-fullerene electron acceptors for organic photovoltaic devices

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Jenekhe, Samson A.; Li, Haiyan; Earmme, Taeshik

    Non-fullerene electron acceptors for highly efficient organic photovoltaic devices are described. The non-fullerene electron acceptors have an extended, rigid, .pi.-conjugated electron-deficient framework that can facilitate exciton and charge derealization. The non-fullerene electron acceptors can physically mix with a donor polymer and facilitate improved electron transport. The non-fullerene electron acceptors can be incorporated into organic electronic devices, such as photovoltaic cells.

  19. Synthetic CO.sub.2 acceptor

    DOEpatents

    Lancet, Michael S.; Curran, George P.

    1981-08-18

    A synthetic CO.sub.2 acceptor consisting essentially of at least one compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix, the carrier having the general formula Ca.sub.5 (SiO.sub.4).sub.2 CO.sub.3. A method for producing the synthetic CO.sub.2 acceptor is also disclosed.

  20. Oxidation of aromatic contaminants coupled to microbial iron reduction

    USGS Publications Warehouse

    Lovley, D.R.; Baedecker, M.J.; Lonergan, D.J.; Cozzarelli, I.M.; Phillips, E.J.P.; Siegel, D.I.

    1989-01-01

    THE contamination of sub-surface water supplies with aromatic compounds is a significant environmental concern1,2. As these contaminated sub-surface environments are generally anaerobic, the microbial oxidation of aromatic compounds coupled to nitrate reduction, sulphate reduction and methane production has been studied intensively1-7. In addition, geochemical evidence suggests that Fe(III) can be an important electron acceptor for the oxidation of aromatic compounds in anaerobic groundwater. Until now, only abiological mechanisms for the oxidation of aromatic compounds with Fe(III) have been reported8-12. Here we show that in aquatic sediments, microbial activity is necessary for the oxidation of model aromatic compounds coupled to Fe(III) reduction. Furthermore, a pure culture of the Fe(III)-reducing bacterium GS-15 can obtain energy for growth by oxidizing benzoate, toluene, phenol or p-cresol with Fe(III) as the sole electron acceptor. These results extend the known physiological capabilities of Fe(III)-reducing organisms and provide the first example of an organism of any type which can oxidize an aromatic hydrocarbon anaerobically. ?? 1989 Nature Publishing Group.

  1. Microbiological and Geochemical Evidence of Fe(III) Reduction in the Rhizosphere (Root-Zone) of Wetland Plants

    NASA Astrophysics Data System (ADS)

    Weiss, J. V.; Megonigal, J. P.; Emerson, D.

    2002-05-01

    We have found that the Fe-oxide deposits (Fe-plaque) on wetland plant roots contain abundant microbes including Fe(II)-oxidizing bacteria (FeOB) (Appl. Environ. Microbiol. 1999, 65:2758-2761). In the current study, we investigated the potential for root Fe-plaque to serve as a substrate for Fe(III)-reducing bacteria (FeRB) and compared rates of Fe reduction between plaque and bulk soil. In a study at six wetland habitats located in the Mid-Atlantic region, abundances of FeRB in the rhizosphere of Typha spp. and the bulk soil were enumerated using the most probable number technique. In the rhizosphere, FeRB accounted for an average of 12% of the total cell number while in the soil they accounted for <1% of the total bacteria. We subsequently performed a sequential chemical extraction on both roots and soil to determine if FeRB abundances were driven by differences in the reducibility of Fe(III) in each environment. The roots contained a significantly higher percentage of amorphous Fe (77.4%; p<0.05 n=5 wetlands) than the bulk soil (33.8%); conversely, the soil also had significantly higher amounts of crystalline Fe (41.1%, p<0.05, n=5 wetlands) than the roots (8.1%). A significant correlation was observed between the percentage of amorphous Fe and the percentage of FeRB (r2=0.583; p<0.05). Since amorphous Fe is more readily reduced by microbes than crystalline Fe, these results suggested that the roots provide a good substrate for iron-reducing bacteria. To determine how differences in reducible Fe(III) might limit Fe reduction potential, we performed 12-day anaerobic incubations of roots and soil with Geobacter metallireducans, a common FeRB isolated from aquatic environments. Although Fe(III) reduction rates peaked at between 48 and 72 hours in both the roots and soils, the total amount of Fe(II) production in the root samples was significantly higher than that in the soil samples (350 μ moles g dry weight-1 vs. 153 μ moles g dry weight-1; p<0.05). All of these

  2. Mechanistic investigation of Fe(III) oxide reduction by low molecular weight organic sulfur species

    NASA Astrophysics Data System (ADS)

    Eitel, Eryn M.; Taillefert, Martial

    2017-10-01

    Low molecular weight organic sulfur species, often referred to as thiols, are known to be ubiquitous in aquatic environments and represent important chemical reductants of Fe(III) oxides. Thiols are excellent electron shuttles used during dissimilatory iron reduction, and in this capacity could indirectly affect the redox state of sediments, release adsorbed contaminants via reductive dissolution, and influence the carbon cycle through alteration of bacterial respiration processes. Interestingly, the reduction of Fe(III) oxides by thiols has not been previously investigated in environmentally relevant conditions, likely due to analytical limitations associated with the detection of thiols and their oxidized products. In this study, a novel electrochemical method was developed to simultaneously determine thiol/disulfide pair concentrations in situ during the reduction of ferrihydrite in batch reactors. First order rate laws with respect to initial thiol concentration were confirmed for Fe(III) oxyhydroxide reduction by four common thiols: cysteine, homocysteine, cysteamine, and glutathione. Zero order was determined for both Fe(III) oxyhydroxide and proton concentration at circumneutral pH. A kinetic model detailing the molecular mechanism of the reaction was optimized with proposed intermediate surface structures. Although metal oxide overall reduction rate constants were inversely proportional to the complexity of the thiol structure, the extent of metal reduction increased with structure complexity, indicating that surface complexes play a significant role in the ability of these thiols to reduce iron. Taken together, these results demonstrate the importance of considering the molecular reaction mechanism at the iron oxide surface when investigating the potential for thiols to act as electron shuttles during dissimilatory iron reduction in natural environments.

  3. Hydroxyl Radical Formation in Solutions of Fe(III) and Hydrogen Peroxide - Impact of Freezing and Thawing Process

    NASA Astrophysics Data System (ADS)

    Arakaki, T.; Kinjo, M.; Shiroma, K.; Shibata, M.; Miyake, T.; Hirakawa, T.; Sakugawa, H.

    2003-12-01

    Hydroxyl radical formation was studied by detecting concentration of formate in solutions of hydrated formaldehyde, HOOH, and Fe(III) or Cu(II). Oxidation of hydrated formaldehyde by OH radical is known to form formate. Formate formation increased by about 4 times when the solution underwent freezing and thawing. Although the reaction mechanisms are not clearly understood, we believe that the concentration effect of freezing enhanced the catalytic reactions between HOOH and Fe(III) or Cu(II) and the reduction of transition metals, i.e., Fe(III) to Fe(II) and Cu(II) to Cu(I). The concentration effect also enhanced reactions between Fe(II) and HOOH or Cu(I) and HOOH, which generated OH radical (freeze-Fenton reaction). Study of the effects of pH showed that formate formation was the highest at pH = 4.0, indicating that the speciation of Fe(III) affected the formation of formate. Concentration-dependent experiments demonstrated that Fe is probably the limiting agent under typical atmospheric conditions. Our results suggested that the freezing process could be an important source of hydroxyl radical in high cloud, winter fog, rime ice and freezing acidic rain, and more importantly, a potentially additional oxidation mechanism in the atmosphere.

  4. Acceptors in bulk and nanoscale ZnO

    NASA Astrophysics Data System (ADS)

    McCluskey, M. D.

    2012-02-01

    Zinc oxide (ZnO) is a semiconductor that emits bright UV light, with little wasted heat. This intrinsic feature makes it a promising material for energy-efficient white lighting, nano-lasers, and other optical applications. For devices to be competitive, however, it is necessary to develop reliable p-type doping. Although substitutional nitrogen has been considered as a potential p-type dopant for ZnO, theoretical and experimental work indicates that nitrogen is a deep acceptor and will not lead to p-type conductivity. This talk will highlight recent experiments on ZnO:N at low temperatures. A red/near-IR photoluminescence (PL) band is correlated with the presence of deep nitrogen acceptors. PL excitation (PLE) measurements show an absorption threshold of 2.26 eV, in good agreement with theory. Magnetic resonance experiments provide further evidence for this assignment. The results of these studies seem to rule out group-V elements as shallow acceptors in ZnO, contradicting numerous reports in the literature. If these acceptors do not work as advertised, is there a viable alternative? Optical studies on ZnO nanocrystals show some intriguing leads. At liquid-helium temperatures, a series of sharp IR absorption peaks arise from an unknown acceptor impurity. The data are consistent with a hydrogenic acceptor 0.46 eV above the valence band edge. While this binding energy is still too deep for many practical applications, it represents a significant improvement over the ˜ 1.3 eV binding energy for nitrogen acceptors. Nanocrystals present another twist. Due to their high surface-to-volume ratio, surface states are especially important. Specifically, electron-hole recombination at the surface give rises to a red luminescence band. From our PL and IR experiments, we have developed a ``unified'' model that attempts to explain acceptor and surface states in ZnO nanocrystals. This model could provide a useful framework for designing future nanoscale ZnO devices.

  5. Chemical trends for acceptor impurities in GaN

    NASA Astrophysics Data System (ADS)

    Neugebauer, Jörg; Van de Walle, Chris G.

    1999-03-01

    We present a comprehensive investigation of acceptor impurities in GaN, based on first-principles total-energy calculations. Two main factors are identified that determine acceptor incorporation: the strength of chemical bonding between the acceptor and its neighbors (which can be assessed by comparison with existing compounds) and the atomic size match between the acceptor and the host atom for which it substitutes. None of the candidates (Li, Na, K, Be, Zn, and Ca) exhibits characteristics which surpass those of Mg in all respects. Only Be emerges as a potential alternative dopant, although it may suffer from compensation by Be interstitial donors.

  6. Significance of a Posttranslational Modification of the PilA Protein of Geobacter sulfurreducens for Surface Attachment, Biofilm Formation, and Growth on Insoluble Extracellular Electron Acceptors.

    PubMed

    Richter, Lubna V; Franks, Ashley E; Weis, Robert M; Sandler, Steven J

    2017-04-15

    Geobacter sulfurreducens , an anaerobic metal-reducing bacterium, possesses type IV pili. These pili are intrinsic structural elements in biofilm formation and, together with a number of c -type cytochromes, are thought to serve as conductive nanowires enabling long-range electron transfer (ET) to metal oxides and graphite anodes. Here, we report that a posttranslational modification of a nonconserved amino acid residue within the PilA protein, the structural subunit of the type IV pili, is crucial for growth on insoluble extracellular electron acceptors. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry of the secreted PilA protein revealed a posttranslational modification of tyrosine-32 with a moiety of a mass consistent with a glycerophosphate group. Mutating this tyrosine into a phenylalanine inhibited cell growth with Fe(III) oxides as the sole electron acceptor. In addition, this amino acid substitution severely diminished biofilm formation on graphite surfaces and impaired current output in microbial fuel cells. These results demonstrate that the capability to attach to insoluble electron acceptors plays a crucial role for the cells' ability to utilize them. The work suggests that glycerophosphate modification of Y32 is a key factor contributing to the surface charge of type IV pili, influencing the adhesion of Geobacter to specific surfaces. IMPORTANCE Type IV pili are bacterial appendages that function in cell adhesion, virulence, twitching motility, and long-range electron transfer (ET) from bacterial cells to insoluble extracellular electron acceptors. The mechanism and role of type IV pili for ET in Geobacter sulfurreducens is still a subject of research. In this study, we identified a posttranslational modification of the major G. sulfurreducens type IV pilin, suggested to be a glycerophosphate moiety. We show that a mutant in which the glycerophosphate-modified tyrosine-32 is replaced with a phenylalanine has reduced abilities for

  7. Significance of a Posttranslational Modification of the PilA Protein of Geobacter sulfurreducens for Surface Attachment, Biofilm Formation, and Growth on Insoluble Extracellular Electron Acceptors

    PubMed Central

    Franks, Ashley E.; Weis, Robert M.; Sandler, Steven J.

    2017-01-01

    ABSTRACT Geobacter sulfurreducens, an anaerobic metal-reducing bacterium, possesses type IV pili. These pili are intrinsic structural elements in biofilm formation and, together with a number of c-type cytochromes, are thought to serve as conductive nanowires enabling long-range electron transfer (ET) to metal oxides and graphite anodes. Here, we report that a posttranslational modification of a nonconserved amino acid residue within the PilA protein, the structural subunit of the type IV pili, is crucial for growth on insoluble extracellular electron acceptors. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry of the secreted PilA protein revealed a posttranslational modification of tyrosine-32 with a moiety of a mass consistent with a glycerophosphate group. Mutating this tyrosine into a phenylalanine inhibited cell growth with Fe(III) oxides as the sole electron acceptor. In addition, this amino acid substitution severely diminished biofilm formation on graphite surfaces and impaired current output in microbial fuel cells. These results demonstrate that the capability to attach to insoluble electron acceptors plays a crucial role for the cells' ability to utilize them. The work suggests that glycerophosphate modification of Y32 is a key factor contributing to the surface charge of type IV pili, influencing the adhesion of Geobacter to specific surfaces. IMPORTANCE Type IV pili are bacterial appendages that function in cell adhesion, virulence, twitching motility, and long-range electron transfer (ET) from bacterial cells to insoluble extracellular electron acceptors. The mechanism and role of type IV pili for ET in Geobacter sulfurreducens is still a subject of research. In this study, we identified a posttranslational modification of the major G. sulfurreducens type IV pilin, suggested to be a glycerophosphate moiety. We show that a mutant in which the glycerophosphate-modified tyrosine-32 is replaced with a phenylalanine has reduced

  8. Microbial Anaerobic Ammonium Oxidation Under Iron Reducing Conditions, Alternative Electron Acceptors

    NASA Astrophysics Data System (ADS)

    Ruiz-Urigüen, M.; Jaffe, P. R.

    2015-12-01

    Autotrophic Acidimicrobiaceae-bacterium named A6 (A6), part of the Actinobacteria phylum have been linked to anaerobic ammonium (NH4+) oxidation under iron reducing conditions. These organisms obtain their energy by oxidizing NH4+ and transferring the electrons to a terminal electron acceptor (TEA). Under environmental conditions, the TEAs are iron oxides [Fe(III)], which are reduced to Fe(II), this process is known as Feammox. Our studies indicate that alternative forms of TEAs can be used by A6, e.g. iron rich clays (i.e. nontronite) and electrodes in bioelectrochemical systems such as Microbial Electrolysis Cells (MECs), which can sustain NH4+removal and A6 biomass production. Our results show that nontronite can support Feammox and promote bacterial cell production. A6 biomass increased from 4.7 x 104 to 3.9 x 105 cells/ml in 10 days. Incubations of A6 in nontronite resulted in up to 10 times more NH4+ removal and 3 times more biomass production than when ferrihydrite is used as the Fe(III) source. Additionally, Fe in nontronite can be reoxidized by aeration and A6 can reutilize it; however, Fe is still finite in the clay. In contrast, in MECs, A6 harvest electrons from NH4+ and use an anode as an unlimited TEA, as a result current is produced. We operated multiple MECs in parallel using a single external power source, as described by Call & Logan (2011). MECs were run with an applied voltage of 0.7V and different growing mediums always containing initial 5mM NH4+. Results show that current production is favored when anthraquinone-2,6-disulfonate (AQDS), an electron shuttled, is present in the medium as it facilitates the transfer of electrons from the bacterial cell to the anode. Additionally, A6 biomass increased from 1 x 104 to 9.77 x 105cells/ml in 14 days of operation. Due to Acidimicrobiaceae-bacterium A6's ability to use various TEAs, MECs represent an alternative, iron-free form, for optimized biomass production of A6 and its application in NH4

  9. Effective Tuning of Ketocyanine Derivatives through Acceptor Substitution.

    PubMed

    Poe, Ambata; Della Pelle, Andrea; Byrnes, Sean; Thayumanavan, S

    2015-05-18

    A series of ketocyanine derivatives possessing bis(diarylamino)fluorenyl donors and variable acceptors installed at the bridging carbon atom were synthesized to investigate how the electronic structure of the dye can be systemically tuned through stabilization of the cyanine-like character of the donor by increasing the acceptor strength. Analysis of the (1) H NMR spectra indicates that the "charge-separated" species dominates in these dyes, given that carbons possessing a positive or negative charge in the resonance structures of this state purposefully shift downfield or upfield, respectively, depending on the strength of the acceptor moiety. In DAA-Fl-PI, the acceptor strength and the gain of acceptor aromaticity indicates a predisposition of the separated state, indicated by asymmetry in the (1) H NMR spectrum, as well as uneven distribution of the HOMO on the fluorenyl donor. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Hybrid coconut seedlings, scholarships, and discount cards for family planning acceptors.

    PubMed

    Sumarsono

    1989-10-01

    Having learned from failed family planning (FP) incentive schemes in other countries, Indonesia implemented a reward system designed to popularize FP in the community. In order to overcome cultural opposition to FP, many countries in the 1970s opted to give incentives--money, materials, etc.--to new contraceptive acceptors and the FP workers who successfully recruited them. These countries, which oftentimes spent up to 1/4 of their program budget on incentives, saw rapid increases in the number of new acceptors. The results, however, only reflected a superficial acceptance of FP. When the incentives stopped, the number of acceptors dropped considerably. Recognizing this, the Indonesian government set out to increase FP acceptance by making the small family the norm in the community. And one of the approaches for doing so was a reward system. The goals of the reward program were: 1) to raise awareness of the recognition given to individuals or groups that have accepted FP; 2) to create pride among FP workers and new acceptors; and 3) to generate leadership in the community. Villages with high FP acceptance receive rewards such as deep-wells that provide clean water or income generating projects. Individuals also receive rewards that sometimes include hybrid coconut seedlings which, after 3 years, can yield up to 700 coconuts, which can provide a family with a significant supplemental income. The government also gives scholarships to children of FP acceptors. Also, the president of Indonesia publicly recognized family planning acceptors. In 1989, over 800,000 couples received awards for practicing contraception over the past 5-16 years.

  11. Sphaerotilus natans encrusted with nanoball-shaped Fe(III) oxide minerals formed by nitrate-reducing mixotrophic Fe(II) oxidation

    PubMed Central

    Park, Sunhwa; Kim, Dong-Hun; Lee, Ji-Hoon; Hur, Hor-Gil

    2014-01-01

    Ferrous iron has been known to function as an electron source for iron-oxidizing microorganisms in both anoxic and oxic environments. A diversity of bacteria has been known to oxidize both soluble and solid-phase Fe(II) forms coupled to the reduction of nitrate. Here, we show for the first time Fe(II) oxidation by Sphaerotilus natans strain DSM 6575T under mixotrophic condition. Sphaerotilus natans has been known to form a sheath structure enclosing long chains of rod-shaped cells, resulting in a thick biofilm formation under oxic conditions. Here, we also demonstrate that strain DSM 6575T grows mixotrophically with pyruvate, Fe(II) as electron donors and nitrate as an electron acceptor and single cells of strain DSM 6575T are dominant under anoxic conditions. Furthermore, strain DSM 6575T forms nanoball-shaped amorphous Fe(III) oxide minerals encrusting on the cell surfaces through the mixotrophic iron oxidation reaction under anoxic conditions. We propose that cell encrustation results from the indirect Fe(II) oxidation by biogenic nitrite during nitrate reduction and that causes the bacterial morphological change to individual rod-shaped single cells from filamentous sheath structures. This study extends the group of existing microorganisms capable of mixotrophic Fe(II) oxidation by a new strain, S. natans strain DSM 6575T, and could contribute to biogeochemical cycles of Fe and N in the environment. PMID:24965827

  12. Electron-Transfer Dynamics for a Donor-Bridge-Acceptor Complex in Ionic Liquids.

    PubMed

    DeVine, Jessalyn A; Labib, Marena; Harries, Megan E; Rached, Rouba Abdel Malak; Issa, Joseph; Wishart, James F; Castner, Edward W

    2015-08-27

    Intramolecular photoinduced electron transfer from an N,N-dimethyl-p-phenylenediamine donor bridged by a diproline spacer to a coumarin 343 acceptor was studied using time-resolved fluorescence measurements in three ionic liquids and in acetonitrile. The three ionic liquids have the bis[(trifluoromethyl)sulfonyl]amide anion paired with the tributylmethylammonium, 1-butyl-1-methylpyrrolidinium, and 1-decyl-1-methylpyrrolidinium cations. The dynamics in the two-proline donor-bridge-acceptor complex are compared to those observed for the same donor and acceptor connected by a single proline bridge, studied previously by Lee et al. (J. Phys. Chem. C 2012, 116, 5197). The increased conformational freedom afforded by the second bridging proline resulted in multiple energetically accessible conformations. The multiple conformations have significant variations in donor-acceptor electronic coupling, leading to dynamics that include both adiabatic and nonadiabatic contributions. In common with the single-proline bridged complex, the intramolecular electron transfer in the two-proline system was found to be in the Marcus inverted regime.

  13. How localized acceptors limit p-type conductivity in GaN

    NASA Astrophysics Data System (ADS)

    Lyons, John L.

    2013-03-01

    Despite the impressive development of GaN as an optoelectronic material, p-type conductivity is still limited. Only a single acceptor impurity, magnesium, is known to lead to p-type GaN. But Mg is far from a well-behaved acceptor. Hydrogen is known to passivate Mg, necessitating a post-growth anneal for acceptor activation. In addition, the ionization energy is quite large (~ 200 meV in GaN), meaning only a few percent of Mg acceptors are ionized at room temperature. Thus, hole conductivity is limited, and high concentrations of Mg are required to achieve moderately p-type GaN. Other acceptor impurities have not proven to be effective p-type dopants, for reasons that are still unresolved. Using advanced first-principles calculations based on a hybrid functional, we investigate the electrical and optical properties of the isolated Mg acceptor and its complexes with hydrogen in GaN, InN, and AlN.[2] We employ a technique that overcomes the band-gap-problem of traditional density functional theory, and allows for quantitative predictions of acceptor ionization energies and optical transition energies. Our results allow us to explain the deep or shallow nature of the Mg acceptor and its relation to the optical signals observed in Mg-doped GaN. We also revisit the properties of other group-II acceptors in GaN. We find that all cation-site acceptors show behavior similar to MgGa, and lead to highly localized holes. The ZnGa and BeGa acceptors have ionization energies that are even larger than that of Mg, making them ineffective dopants. All acceptors cause large lattice distortions in their neutral charge state, in turn leading to deep, broad luminescence signals that can serve as a means of experimentally verifying the deep nature of these acceptors. This work was performed in collaboration with Audrius Alkauskas, Anderson Janotti, and Chris G. Van de Walle. It was supported by the NSF and by the Solid State Lighting and Energy Center at UCSB.

  14. Shallow versus deep nature of Mg acceptors in nitride semiconductors

    NASA Astrophysics Data System (ADS)

    Lyons, John; Janotti, Anderson; van de Walle, Chris G.

    2012-02-01

    Although Mg doping is the only known method for achieving p-type conductivity in nitride semiconductors, Mg is not a perfect acceptor. Hydrogen is known to passivate the Mg acceptor, necessitating a post-growth anneal for acceptor activation. Furthermore, the acceptor ionization energy of Mg is relatively large (200 meV) in GaN, thus only a few percent of Mg acceptors are ionized at room temperature. Surprisingly, despite the importance of this impurity, open questions remain regarding the nature of the acceptor. Optical and magnetic resonance measurements on Mg-doped GaN indicate intriguing and complex behavior that depends on the growth, doping level, and thermal treatment of the samples. Motivated by these studies, we have revisited this topic by performing first-principles calculations based on a hybrid functional. We investigate the electrical and optical properties of the isolated Mg acceptor and its complexes with hydrogen in GaN, InN, and AlN. With the help of these advanced techniques we explain the deep or shallow nature of the Mg acceptor and its relation to optical signals often seen in Mg-doped GaN. We also explore the properties of the Mg acceptor in InN and AlN, allowing predictions of the behavior of the Mg dopant in ternary nitride alloys.

  15. Non-Fullerene Electron Acceptors for Use in Organic Solar Cells

    PubMed Central

    2015-01-01

    , forming dimers with a large intramolecular twist, which suppresses both nucleation and crystal growth. The generic design concept of rotationally symmetrical aromatic small molecules with extended π orbital delocalization, including polyaromatic hydrocarbons, phthalocyanines, etc., has also provided some excellent small molecule acceptors. In most cases, additional electron withdrawing functionality, such as imide or ester groups, can be incorporated to stabilize the LUMO and improve properties. New calamitic acceptors have been developed, where molecular orbital hybridization of electron rich and poor segments can be judiciously employed to precisely control energy levels. Conformation and intermolecular associations can be controlled by peripheral functionalization leading to optimization of crystallization length scales. In particular, the use of rhodanine end groups, coupled electronically through short bridged aromatic chains, has been a successful strategy, with promising device efficiencies attributed to high lying LUMO energy levels and subsequently large open circuit voltages. PMID:26505279

  16. Contrasting performance of donor-acceptor copolymer pairs in ternary blend solar cells and two-acceptor copolymers in binary blend solar cells.

    PubMed

    Khlyabich, Petr P; Rudenko, Andrey E; Burkhart, Beate; Thompson, Barry C

    2015-02-04

    Here two contrasting approaches to polymer-fullerene solar cells are compared. In the first approach, two distinct semi-random donor-acceptor copolymers are blended with phenyl-C61-butyric acid methyl ester (PC61BM) to form ternary blend solar cells. The two poly(3-hexylthiophene)-based polymers contain either the acceptor thienopyrroledione (TPD) or diketopyrrolopyrrole (DPP). In the second approach, semi-random donor-acceptor copolymers containing both TPD and DPP acceptors in the same polymer backbone, termed two-acceptor polymers, are blended with PC61BM to give binary blend solar cells. The two approaches result in bulk heterojunction solar cells that have the same molecular active-layer components but differ in the manner in which these molecular components are mixed, either by physical mixing (ternary blend) or chemical "mixing" in the two-acceptor (binary blend) case. Optical properties and photon-to-electron conversion efficiencies of the binary and ternary blends were found to have similar features and were described as a linear combination of the individual components. At the same time, significant differences were observed in the open-circuit voltage (Voc) behaviors of binary and ternary blend solar cells. While in case of two-acceptor polymers, the Voc was found to be in the range of 0.495-0.552 V, ternary blend solar cells showed behavior inherent to organic alloy formation, displaying an intermediate, composition-dependent and tunable Voc in the range from 0.582 to 0.684 V, significantly exceeding the values achieved in the two-acceptor containing binary blend solar cells. Despite the differences between the physical and chemical mixing approaches, both pathways provided solar cells with similar power conversion efficiencies, highlighting the advantages of both pathways toward highly efficient organic solar cells.

  17. Raw hematite based Fe(III) bio-reduction process for humified landfill leachate treatment.

    PubMed

    Li, Rui; Jiang, Yu; Xi, Beidou; Li, Mingxiao; Meng, Xiaoguang; Feng, Chuanping; Mao, Xuhui; Liu, Hongliang; Jiang, Yonghai

    2018-05-03

    Microorganisms from paddy soils and raw hematite are used for enhancing natural Fe(III) bio-reduction, in order to remove macromolecular organic pollutants from humified landfill leachate. Based on batch experiments, 60% of refractory organics can be adsorbed by hematite in 12 days. In the presence of Fe(III)-reducing bacteria, 489.60 ± 0.14 mg L -1 of dissolved organic matters can be degraded to 51.90 ± 3.96 mg L -1 within 50 days; twelve types of semi volatile organic compounds can be degraded; hereby, the reaction follows a first-order kinetics. Crystalline Fe(III) is transformed into the amorphous form and reduced to Fe(II), hydroquinone functional groups in the humic acid (HA) are transformed to quinone ones, and the formation of HA-hematite ligands is promoted. Comparing with most of the studies about electron shuttling of HA, the transformation of quinone in the HA to hydroquinone could not be observed in the present bio-system. Based on column evaluations, more than 93% of chemical oxygen demand (influent concentration of 658 ± 19 mg L -1 ) could be removed microbially under flow conditions, when the hydraulic retention time was 45 h. Raw hematite-based Fe(III) bio-reduction has a promising potential for the removal of humic and benzene series in humified landfill leachate. Copyright © 2018. Published by Elsevier B.V.

  18. Humic substance-mediated Fe(III) reduction by a fermenting Bacillus strain from the alkaline gut of a humus-feeding scarab beetle larva.

    PubMed

    Hobbie, Sven N; Li, Xiangzhen; Basen, Mirko; Stingl, Ulrich; Brune, Andreas

    2012-06-01

    Humus-feeding macroinvertebrates play an important role in the transformation of soil organic matter. Their diet contains significant amounts of redox-active components such as iron minerals and humic substances. In soil-feeding termites, acid-soluble Fe(III) and humic acids are almost completely reduced during gut passage. Here, we show that the reduction of Fe(III) and humic acids takes place also in the alkaline guts of scarab beetle larvae. Sterilized gut homogenates of Pachnoda ephippiata no longer converted Fe(III) to Fe(II), indicating an essential role of the gut microbiota in the process. From Fe(III)-reducing enrichment cultures inoculated with highly diluted gut homogenates, we isolated several facultatively anaerobic, alkali-tolerant bacteria that were closely related to metal-reducing isolates in the Bacillus thioparans group. Strain PeC11 showed a remarkable capacity for dissimilatory Fe(III) reduction, both at pH 7 and 10. Rates were strongly stimulated by the addition of the redox mediator 2,6-antraquinone disulfonate and by redox-active components in the fulvic-acid fraction of humus. Although the contribution of strain PeC11 to intestinal Fe(III) reduction in P. ephippiata remains to be further elucidated, our results corroborate the hypothesis that the lack of oxygen and the solubilization of humic substances in the extremely alkaline guts of humivorous soil fauna provide favorable conditions for the efficient reduction of Fe(III) and humic substances by a primarily fermentative microbiota. Copyright © 2012 Elsevier GmbH. All rights reserved.

  19. Organic solar cells based on non-fullerene acceptors

    NASA Astrophysics Data System (ADS)

    Hou, Jianhui; Inganäs, Olle; Friend, Richard H.; Gao, Feng

    2018-02-01

    Organic solar cells (OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.

  20. Identification of the lipopolysaccharide modifications controlled by the Salmonella PmrA/PmrB system mediating resistance to Fe(III) and Al(III)

    PubMed Central

    Nishino, Kunihiko; Hsu, Fong-Fu; Turk, John; Cromie, Michael J; Wösten, Marc M S M; Groisman, Eduardo A

    2006-01-01

    Iron is an essential metal but can be toxic in excess. While several homeostatic mechanisms prevent oxygen-dependent killing promoted by Fe(II), little is known about how cells cope with Fe(III), which kills by oxygen-independent means. Several Gram-negative bacterial species harbour a regulatory system – termed PmrA/PmrB – that is activated by and required for resistance to Fe(III). We now report the identification of the PmrA-regulated determinants mediating resistance to Fe(III) and Al(III) in Salmonella enterica serovar Typhimurium. We establish that these determinants remodel two regions of the lipopolysaccharide, decreasing the negative charge of this major constituent of the outer membrane. Remodelling entails the covalent modification of the two phosphates in the lipid A region with phosphoethanolamine and 4-aminoarabinose, which has been previously implicated in resistance to polymyxin B, as well as dephosphorylation of the Hep(II) phosphate in the core region by the PmrG protein. A mutant lacking the PmrA-regulated Fe(III) resistance genes bound more Fe(III) than the wild-type strain and was defective for survival in soil, suggesting that these PmrA-regulated lipopolysaccharide modifications aid Salmonella's survival and spread in non-host environments. PMID:16803591

  1. Methods for the synthesis of donor-acceptor cyclopropanes

    NASA Astrophysics Data System (ADS)

    Tomilov, Yu V.; Menchikov, L. G.; Novikov, R. A.; Ivanova, O. A.; Trushkov, I. V.

    2018-03-01

    The interest in cyclopropane derivatives is caused by the facts that, first, the three-carbon ring is present in quite a few natural and biologically active compounds and, second, compounds with this ring are convenient building blocks for the synthesis of diverse molecules (acyclic, alicyclic and heterocyclic). The carbon–carbon bonds in cyclopropane are kinetically rather inert; hence, they need to be activated to be involved in reactions. An efficient way of activation is to introduce vicinal electron-donating and electron-withdrawing substituents into the ring; these substrates are usually referred to as donor-acceptor cyclopropanes. This review gives a systematic account of the key methods for the synthesis of donor-acceptor cyclopropanes. The most important among them are reactions of nucleophilic alkenes with diazo compounds and iodonium ylides and approaches based on reactions of electrophilic alkenes with sulfur ylides (the Corey–Chaykovsky reaction). Among other methods used for this purpose, noteworthy are cycloalkylation of CH-acids, addition of α-halocarbonyl compounds to alkenes, cyclization via 1,3-elimination, reactions of alkenes with halocarbenes followed by reduction, the Simmons–Smith reaction and some other. The scope of applicability and prospects of various methods for the synthesis of donor-acceptor cyclopropanes are discussed. The bibliography includes 530 references.

  2. Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: the role of Fe(II) and Fe(III).

    PubMed

    Yan, Sen; Chen, Yongheng; Xiang, Wu; Bao, Zhengyu; Liu, Chongxuan; Deng, Baolin

    2014-12-01

    The role of Fe(II) and Fe(III) in U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed that U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.9 to 9.0. For instance, at pH 6.9 the observed U(VI) reduction rates decreased by 81% and 82% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) possibly acted as an electron shuttle to ferry the electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 could facilitate U(VI) reductive immobilization in the contaminated groundwater.

  3. Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: The role of Fe(II) and Fe(III)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yan, Sen; Chen, Yongheng; Xiang, Wu

    2014-12-01

    The role of Fe(II) and Fe(III) on U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.92 to 9.03. For instance, at pH 6.92 the observed U(VI) reduction rates decreased by 80.7% and 82.3% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can bemore » enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) probably acted as an electron shuttle to mediate the transfer of electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 can facilitate the U(VI) reductive immobilization in the contaminated groundwater.« less

  4. An Overview of Electron Acceptors in Microbial Fuel Cells

    PubMed Central

    Ucar, Deniz; Zhang, Yifeng; Angelidaki, Irini

    2017-01-01

    Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators. PMID:28469607

  5. Protection of Nitrate-Reducing Fe(II)-Oxidizing Bacteria from UV Radiation by Biogenic Fe(III) Minerals

    NASA Astrophysics Data System (ADS)

    Gauger, Tina; Konhauser, Kurt; Kappler, Andreas

    2016-04-01

    Due to the lack of an ozone layer in the Archean, ultraviolet radiation (UVR) reached early Earth's surface almost unattenuated; as a consequence, a terrestrial biosphere in the form of biological soil crusts would have been highly susceptible to lethal doses of irradiation. However, a self-produced external screen in the form of nanoparticular Fe(III) minerals could have effectively protected those early microorganisms. In this study, we use viability studies by quantifying colony-forming units (CFUs), as well as Fe(II) oxidation and nitrate reduction rates, to show that encrustation in biogenic and abiogenic Fe(III) minerals can protect a common soil bacteria such as the nitrate-reducing Fe(II)-oxidizing microorganisms Acidovorax sp. strain BoFeN1 and strain 2AN from harmful UVC radiation. Analysis of DNA damage by quantifying cyclobutane pyrimidine dimers (CPD) confirmed the protecting effect by Fe(III) minerals. This study suggests that Fe(II)-oxidizing microorganisms, as would have grown in association with mafic and ultramafic soils/outcrops, would have been able to produce their own UV screen, enabling them to live in terrestrial habitats on early Earth.

  6. Protection of Nitrate-Reducing Fe(II)-Oxidizing Bacteria from UV Radiation by Biogenic Fe(III) Minerals.

    PubMed

    Gauger, Tina; Konhauser, Kurt; Kappler, Andreas

    2016-04-01

    Due to the lack of an ozone layer in the Archean, ultraviolet radiation (UVR) reached early Earth's surface almost unattenuated; as a consequence, a terrestrial biosphere in the form of biological soil crusts would have been highly susceptible to lethal doses of irradiation. However, a self-produced external screen in the form of nanoparticular Fe(III) minerals could have effectively protected those early microorganisms. In this study, we use viability studies by quantifying colony-forming units (CFUs), as well as Fe(II) oxidation and nitrate reduction rates, to show that encrustation in biogenic and abiogenic Fe(III) minerals can protect a common soil bacteria such as the nitrate-reducing Fe(II)-oxidizing microorganisms Acidovorax sp. strain BoFeN1 and strain 2AN from harmful UVC radiation. Analysis of DNA damage by quantifying cyclobutane pyrimidine dimers (CPD) confirmed the protecting effect by Fe(III) minerals. This study suggests that Fe(II)-oxidizing microorganisms, as would have grown in association with mafic and ultramafic soils/outcrops, would have been able to produce their own UV screen, enabling them to live in terrestrial habitats on early Earth.

  7. Rise-Time of FRET-Acceptor Fluorescence Tracks Protein Folding

    PubMed Central

    Lindhoud, Simon; Westphal, Adrie H.; van Mierlo, Carlo P. M.; Visser, Antonie J. W. G.; Borst, Jan Willem

    2014-01-01

    Uniform labeling of proteins with fluorescent donor and acceptor dyes with an equimolar ratio is paramount for accurate determination of Förster resonance energy transfer (FRET) efficiencies. In practice, however, the labeled protein population contains donor-labeled molecules that have no corresponding acceptor. These FRET-inactive donors contaminate the donor fluorescence signal, which leads to underestimation of FRET efficiencies in conventional fluorescence intensity and lifetime-based FRET experiments. Such contamination is avoided if FRET efficiencies are extracted from the rise time of acceptor fluorescence upon donor excitation. The reciprocal value of the rise time of acceptor fluorescence is equal to the decay rate of the FRET-active donor fluorescence. Here, we have determined rise times of sensitized acceptor fluorescence to study the folding of double-labeled apoflavodoxin molecules and show that this approach tracks the characteristics of apoflavodoxinʼs complex folding pathway. PMID:25535076

  8. Characterization and Properties of Activated Carbon Prepared from Tamarind Seeds by KOH Activation for Fe(III) Adsorption from Aqueous Solution

    PubMed Central

    Mopoung, Sumrit; Moonsri, Phansiri; Palas, Wanwimon; Khumpai, Sataporn

    2015-01-01

    This research studies the characterization of activated carbon from tamarind seed with KOH activation. The effects of 0.5 : 1–1.5 : 1 KOH : tamarind seed charcoal ratios and 500–700°C activation temperatures were studied. FTIR, SEM-EDS, XRD, and BET were used to characterize tamarind seed and the activated carbon prepared from them. Proximate analysis, percent yield, iodine number, methylene blue number, and preliminary test of Fe(III) adsorption were also studied. Fe(III) adsorption was carried out by 30 mL column with 5–20 ppm Fe(III) initial concentrations. The percent yield of activated carbon prepared from tamarind seed with KOH activation decreased with increasing activation temperature and impregnation ratios, which were in the range from 54.09 to 82.03 wt%. The surface functional groups of activated carbon are O–H, C=O, C–O, –CO3, C–H, and Si–H. The XRD result showed high crystallinity coming from a potassium compound in the activated carbon. The main elements found in the activated carbon by EDS are C, O, Si, and K. The results of iodine and methylene blue adsorption indicate that the pore size of the activated carbon is mostly in the range of mesopore and macropore. The average BET pore size and BET surface area of activated carbon are 67.9764 Å and 2.7167 m2/g, respectively. Finally, the tamarind seed based activated carbon produced with 500°C activation temperature and 1.0 : 1 KOH : tamarind seed charcoal ratio was used for Fe(III) adsorption test. It was shown that Fe(III) was adsorbed in alkaline conditions and adsorption increased with increasing Fe(III) initial concentration from 5 to 20 ppm with capacity adsorption of 0.0069–0.019 mg/g. PMID:26689357

  9. A study of acceptors and non-acceptors of family planning methods among three tribal communities.

    PubMed

    Mutharayappa, R

    1995-03-01

    Primary data were collected from 399 currently married women of the Marati, Malekudiya, and Koraga tribes in the Dakshina Kannada district of Karnataka State in this study of the implementation of family planning programs in tribal areas. The Marati, Malekudiya, and Koraga tribes are three different endogamous tribal populations living in similar ecological conditions. Higher levels of literacy and a high rate of acceptance of family planning methods, however, have been observed among these tribes compared to the rest of the tribal population in the state. 46.4% of currently married women aged 15-49 years in the tribes were acceptors of family planning methods, having a mean 3.7 children. The majority of acceptors opted for tubectomy and vasectomy. The adoption of spacing methods is less common among tribal people. Most acceptors received their operations through government health facilities. They were motivated mainly by female health workers and received both cash and other incentives to accept family planning. The main reason for non-acceptance of family planning among non-acceptors was the desire to conceive and bear more children. The data indicate that most of the tribal households are nuclear families with household size more or less similar to that of the general population. They have a higher literacy rate than the rest of the tribal population in the state, with literacy levels between males and females and between the three tribes being quite different; the school enrollment ratio is relatively higher for both boys and girls.

  10. Method for producing and regenerating a synthetic CO.sub.2 acceptor

    DOEpatents

    Lancet, Michael S [Pittsburgh, PA; Curran, George P [Pittsburgh, PA; Gorin, Everett [San Rafael, CA

    1982-01-01

    A method for producing a synthetic CO.sub.2 acceptor by feeding a mixture of finely divided silica and at least one finely divided calcium compound selected from the group consisting of calcium oxide and calcium carbonate to a fluidized bed; operating the fluidized bed at suitable conditions to produce pellets of synthetic CO.sub.2 acceptor and recovering the pellets of synthetic CO.sub.2 acceptor from the fluidized bed. Optionally, spent synthetic CO.sub.2 acceptor can be charged to the fluidized bed to produce regenerated pellets of synthetic CO.sub.2 acceptor.

  11. Assessment of a New Type of Coin Acceptor

    DOT National Transportation Integrated Search

    1983-04-01

    An assessment of the Mars Money Systems Model CD 540-1 coin acceptor associated with farecard vendors was conducted at the Port Authority Transit Corp. as part of an appraisal of automatic fare collection (AFC) equipment. The Mars acceptor consistent...

  12. Alternansucrase acceptor reactions with D-tagatose and L-glucose.

    PubMed

    Côté, Gregory L; Dunlap, Christopher A; Appell, Michael; Momany, Frank A

    2005-02-07

    Alternansucrase (EC 2.4.1.140) is a d-glucansucrase that synthesizes an alternating alpha-(1-->3), (1-->6)-linked d-glucan from sucrose. It also synthesizes oligosaccharides via d-glucopyranosyl transfer to various acceptor sugars. Two of the more efficient monosaccharide acceptors are D-tagatose and L-glucose. In the presence of d-tagatose, alternansucrase produced the disaccharide alpha-d-glucopyranosyl-(1-->1)-beta-D-tagatopyranose via glucosyl transfer. This disaccharide is analogous to trehalulose. We were unable to isolate a disaccharide product from L-glucose, but the trisaccharide alpha-D-glucopyranosyl-(1-->6)-alpha-d-glucopyranosyl-(1-->4)-l-glucose was isolated and identified. This is analogous to panose, one of the structural units of pullulan, in which the reducing-end D-glucose residue has been replaced by its L-enantiomer. The putative L-glucose disaccharide product, produced by glucoamylase hydrolysis of the trisaccharide, was found to be an acceptor for alternansucrase. The disaccharide, alpha-D-glucopyranosyl-(1-->4)-L-glucose, was a better acceptor than maltose, previously the best known acceptor for alternansucrase. A structure comparison of alpha-D-glucopyranosyl-(1-->4)-L-glucose and maltose was performed through computer modeling to identify common features, which may be important in acceptor affinity by alternansucrase.

  13. Method for producing and regenerating a synthetic CO[sub 2] acceptor

    DOEpatents

    Lancet, M. S.; Curran, G. P.; Gorin, E.

    1982-05-18

    A method is described for producing a synthetic CO[sub 2] acceptor by feeding a mixture of finely divided silica and at least one finely divided calcium compound selected from the group consisting of calcium oxide and calcium carbonate to a fluidized bed; operating the fluidized bed at suitable conditions to produce pellets of synthetic CO[sub 2] acceptor and recovering the pellets of synthetic CO[sub 2] acceptor from the fluidized bed. Optionally, spent synthetic CO[sub 2] acceptor can be charged to the fluidized bed to produce regenerated pellets of synthetic CO[sub 2] acceptor. 1 fig.

  14. Environmentally-relevant concentrations of Al(III) and Fe(III) cations induce aggregation of free DNA by complexation with phosphate group.

    PubMed

    Qin, Chao; Kang, Fuxing; Zhang, Wei; Shou, Weijun; Hu, Xiaojie; Gao, Yanzheng

    2017-10-15

    Environmental persistence of free DNA is influenced by its complexation with other chemical species and its aggregation mechanisms. However, it is not well-known how naturally-abundant metal ions, e.g., Al(III) and Fe(III), influence DNA aggregation. This study investigated aggregation behaviors of model DNA from salmon testes as influenced by metal cations, and elucidated the predominant mechanism responsible for DNA aggregation. Compared to monovalent (K + and Na + ) and divalent (Ca 2+ and Mg 2+ ) cations, Al(III) and Fe(III) species in aqueous solution caused rapid DNA aggregations. The maximal DNA aggregation occurred at 0.05 mmol/L Al(III) or 0.075 mmol/L Fe(III), respectively. A combination of atomic force microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy revealed that Al(III) and Fe(III) complexed with negatively charged phosphate groups to neutralize DNA charges, resulting in decreased electrostatic repulsion and subsequent DNA aggregation. Zeta potential measurements and molecular computation further support this mechanism. Furthermore, DNA aggregation was enhanced at higher temperature and near neutral pH. Therefore, DNA aggregation is collectively determined by many environmental factors such as ion species, temperature, and solution pH. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Mapping the Relationship between Glycosyl Acceptor Reactivity and Glycosylation Stereoselectivity.

    PubMed

    van der Vorm, Stefan; van Hengst, Jacob M A; Bakker, Marloes; Overkleeft, Herman S; van der Marel, Gijsbert A; Codée, Jeroen D C

    2018-03-30

    The reactivity of both coupling partners-the glycosyl donor and acceptor-is decisive for the outcome of a glycosylation reaction, in terms of both yield and stereoselectivity. Where the reactivity of glycosyl donors is well understood and can be controlled through manipulation of the functional/protecting-group pattern, the reactivity of glycosyl acceptor alcohols is poorly understood. We here present an operationally simple system to gauge glycosyl acceptor reactivity, which employs two conformationally locked donors with stereoselectivity that critically depends on the reactivity of the nucleophile. A wide array of acceptors was screened and their structure-reactivity/stereoselectivity relationships established. By systematically varying the protecting groups, the reactivity of glycosyl acceptors can be adjusted to attain stereoselective cis-glucosylations. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  16. Defining donor and acceptor strength in conjugated copolymers

    NASA Astrophysics Data System (ADS)

    Hedström, Svante; Wang, Ergang; Persson, Petter

    2017-03-01

    The progress in efficiency of organic photovoltaic devices is largely driven by the development of new donor-acceptor (D-A) copolymers. The number of possible D-A combinations escalates rapidly with the ever-increasing number of donor and acceptor units, and the design process often involves a trial-and-error approach. We here present a computationally efficient methodology for the prediction of optical and electronic properties of D-A copolymers based on density functional theory calculations of donor- and acceptor-only homopolymers. Ten donors and eight acceptors are studied, as well as all of their 80 D-A copolymer combinations, showing absorption energies of 1.3-2.3 eV, and absorption strengths varying by up to a factor of 2.5. Focus lies on exhibited trends in frontier orbital energies, optical band gaps, and absorption intensities, as well as their relation to the molecular structure. Based on the results, we define the concept of donor and acceptor strength, and calculate this quantity for all investigated units. The light-harvesting capabilities of the 80 D-A copolymers were also assessed. This gives a valuable theoretical guideline to the design of D-A copolymers with the potential to reduce the synthesis efforts in the development of new polymers.

  17. Nanographenes as electron-deficient cores of donor-acceptor systems.

    PubMed

    Liu, Yu-Min; Hou, Hao; Zhou, Yan-Zhen; Zhao, Xin-Jing; Tang, Chun; Tan, Yuan-Zhi; Müllen, Klaus

    2018-05-15

    Conjugation of nanographenes (NGs) with electro-active molecules can establish donor-acceptor π-systems in which the former generally serve as the electron-donating moieties due to their electronic-rich nature. In contrast, here we report a series of reversed donor-acceptor structures are obtained by C-N coupling of electron-deficient perchlorinated NGs with electron-rich anilines. Selective amination at the vertexes of the NGs is unambiguously shown through X-ray crystallography. By varying the donating ability of the anilino groups, the optical and assembly properties of donor-acceptor NGs can be finely modulated. The electron-deficient concave core of the resulting conjugates can host electron-rich guest molecules by intermolecular donor-acceptor interactions and gives rise to charge-transfer supramolecular architectures.

  18. Separation and Determination of Fe(III) and Fe(II) in Natural and Waste Waters Using Silica Gel Sequentially Modified with Polyhexamethylene Guanidine and Tiron

    PubMed Central

    Maksimov, Nikolay; Trofimchuk, Anatoly; Zaporogets, Olga

    2017-01-01

    Silica gel, sequentially modified with polyhexamethylene guanidine and pyrocatechin-3,5-disulfonic acid (Tiron), was suggested for sorption separation and determination of Fe(III) and Fe(II). It was found that quantitative extraction of Fe(III) and its separation from Fe(II) were attained at pH 2.5–4.0, while quantitative extraction of Fe(II) was observed at pH 6.0–7.5. An intensive signal with g = 4.27, which is characteristic for Fe(III), appeared in EPR spectra of the sorbents after Fe(II) and Fe(III) sorption. During interaction between Fe(II) and Tiron, fixed on the sorbent surface, its oxidation up to Fe(III) occurred. Red-lilac complexes of the composition FeL3 were formed on the sorbent surface during sorption regardless of initial oxidation level of iron. Diffuse reflectance spectrum of surface complexes exhibited wide band with slightly expressed maxima at 480 and 510 nm. Procedures for separation and photometric determination of Fe(III) and Fe(II) at the joint presence and total Fe content determination as Fe(II) in waste and natural waters was developed. The limit of detection for iron was 0.05 μg per 0.100 g of the sorbent. The calibration graph was linear up to 20.0 μg of Fe per 0.100 g of the sorbent. The RSD in the determination of more than 0.2 μg of Fe was less than 0.06. PMID:29214095

  19. Organic Donor-Acceptor Complexes as Novel Organic Semiconductors.

    PubMed

    Zhang, Jing; Xu, Wei; Sheng, Peng; Zhao, Guangyao; Zhu, Daoben

    2017-07-18

    systematically controlled by changing the components. Finally, theoretical calculations based on cocrystals with unique stacking could widen our understanding of structure-property relationships and in turn help us design high-performance semiconductors based on DA complexes. In this Account, we focus on discussing organic DA complexes as a new class of semiconducting materials, including their design, growth methods, packing modes, charge-transport properties, and structure-property relationships. We have also fabricated and investigated devices based on these binary crystals. This interdisciplinary work combines techniques from the fields of self-assembly, crystallography, condensed-matter physics, and theoretical chemistry. Researchers have designed new complex systems, including donor and acceptor compounds that self-assemble in feasible ways into highly ordered cocrystals. We demonstrate that using this crystallization method can easily realize ambipolar or unipolar transport. To further improve device performance, we propose several design strategies, such as using new kinds of donors and acceptors, modulating the energy alignment of the donor (ionization potential, IP) and acceptor (electron affinity, EA) components, and extending the π-conjugated backbones. In addition, we have found that when we use molecular "doping" (2:1 cocrystallization), the charge-transport nature of organic semiconductors can be switched from hole-transport-dominated to electron-transport-dominated. We expect that the formation of cocrystals through the complexation of organic donor and acceptor species will serve as a new strategy to develop semiconductors for organic electronics with superior performances over their corresponding individual components.

  20. Fe(III) oxides accelerate microbial nitrate reduction and electricity generation by Klebsiella pneumoniae L17.

    PubMed

    Liu, Tongxu; Li, Xiaomin; Zhang, Wei; Hu, Min; Li, Fangbai

    2014-06-01

    Klebsiella pneumoniae L17 is a fermentative bacterium that can reduce iron oxide and generate electricity under anoxic conditions, as previously reported. This study reveals that K. pneumoniae L17 is also capable of dissimilatory nitrate reduction, producing NO2(-), NH4(+), NO and N2O under anoxic conditions. The presence of Fe(III) oxides (i.e., α-FeOOH, γ-FeOOH, α-Fe2O3 and γ-Fe2O3) significantly accelerates the reduction of nitrate and generation of electricity by K. pneumoniae L17, which is similar to a previous report regarding another fermentative bacterium, Bacillus. No significant nitrate reduction was observed upon treatment with Fe(2+) or α-FeOOH+Fe(2+), but a slight facilitation of nitrate reduction and electricity generation was observed upon treatment with L17+Fe(2+). This result suggests that aqueous Fe(II) or mineral-adsorbed Fe(II) cannot reduce nitrate abiotically but that L17 can catalyze the reduction of nitrate and generation of electricity in the presence of Fe(II) (which might exist as cell surface-bound Fe(II)). To rule out the potential effect of Fe(II) produced by L17 during microbial iron reduction, treatments with the addition of TiO2 or Al2O3 instead of Fe(III) oxides also exhibited accelerated microbial nitrate reduction and electricity generation, indicating that cell-mineral sorption did account for the acceleration effect. However, the acceleration caused by Fe(III) oxides is only partially attributed to the cell surface-bound Fe(II) and cell-mineral sorption but may be driven by the iron oxide conduction band-mediated electron transfer from L17 to nitrate or an electrode, as proposed previously. The current study extends the diversity of bacteria of which nitrate reduction and electricity generation can be facilitated by the presence of iron oxides and confirms the positive role of Fe(III) oxides on microbial nitrate reduction and electricity generation by particular fermentative bacteria in anoxic environments. Copyright

  1. Mineralogical and morphological constraints on the reduction of Fe(III) minerals by Geobacter sulfurreducens

    NASA Astrophysics Data System (ADS)

    Cutting, R. S.; Coker, V. S.; Fellowes, J. W.; Lloyd, J. R.; Vaughan, D. J.

    2009-07-01

    The biologically-mediated reduction of synthetic samples of the Fe(III)-bearing minerals hematite, goethite, lepidocrocite, feroxhyte, ford ferrihydrite, akaganeite and schwertmannite by Geobacter sulfurreducens has been investigated using microbiological techniques in conjunction with X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). This combination of approaches offers unique insights into the influence of subtle variations in the crystallinity of a given mineral on biogeochemical processes, and has highlighted the importance of (oxyhydr)oxide crystallite morphology in determining the changes occurring in a given mineral phase. Problems arising from normalising the biological Fe(III) reduction rates relative to the specific surface areas of the starting materials are also highlighted. These problems are caused primarily by particle aggregation, and compounded when using spectrophotometric assays to monitor reduction. For example, the initial rates of Fe(III) reduction observed for two synthetic feroxyhytes with different crystallinities (as shown by XRD and TEM studies) but almost identical surface areas, differ substantially. Both microbiological and high-resolution TEM studies show that hematite and goethite are susceptible to limited amounts of Fe(III) reduction, as evidenced by the accumulation of Fe(II) during incubation with G. sulfurreducens and the growth of nodular structures on crystalline goethite laths during incubation. Lepidocrocite and akaganeite readily transform into mixtures of magnetite and goethite, and XRD data indicate that the proportion of magnetite increases within the transformation products as the crystallinity of the starting material decreases. The presence of anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle increases both the initial rate and longer term extent of biological Fe(III) reduction for all of the synthetic minerals examined. High-resolution XPS indicates

  2. In Situ Remediation of a TCE-Contaminated Aquifer Using a Short Rotation Woody Crop Groundwater Treatment System

    DTIC Science & Technology

    2006-05-01

    excreting compounds containing organic carbon that is used as a food source for microorganisms ), there can be a direct comparison to in situ bioremediation ...Once DO is depleted, the process becomes anaerobic. Anaerobic microorganisms most often use available electron 3 acceptors in the following... microorganisms most often use available electron acceptors in the following order: nitrate, Fe(III) hydroxide, sulfate, and CO2 (Chapelle, 2000). In

  3. Depth-dependent geochemical and microbiological gradients in Fe(III) deposits resulting from coal mine-derived acid mine drainage

    PubMed Central

    Brantner, Justin S.; Haake, Zachary J.; Burwick, John E.; Menge, Christopher M.; Hotchkiss, Shane T.; Senko, John M.

    2014-01-01

    We evaluated the depth-dependent geochemistry and microbiology of sediments that have developed via the microbially-mediated oxidation of Fe(II) dissolved in acid mine drainage (AMD), giving rise to a 8–10 cm deep “iron mound” that is composed primarily of Fe(III) (hydr)oxide phases. Chemical analyses of iron mound sediments indicated a zone of maximal Fe(III) reducing bacterial activity at a depth of approximately 2.5 cm despite the availability of dissolved O2 at this depth. Subsequently, Fe(II) was depleted at depths within the iron mound sediments that did not contain abundant O2. Evaluations of microbial communities at 1 cm depth intervals within the iron mound sediments using “next generation” nucleic acid sequencing approaches revealed an abundance of phylotypes attributable to acidophilic Fe(II) oxidizing Betaproteobacteria and the chloroplasts of photosynthetic microeukaryotic organisms in the upper 4 cm of the iron mound sediments. While we observed a depth-dependent transition in microbial community structure within the iron mound sediments, phylotypes attributable to Gammaproteobacterial lineages capable of both Fe(II) oxidation and Fe(III) reduction were abundant in sequence libraries (comprising ≥20% of sequences) from all depths. Similarly, abundances of total cells and culturable Fe(II) oxidizing bacteria were uniform throughout the iron mound sediments. Our results indicate that O2 and Fe(III) reduction co-occur in AMD-induced iron mound sediments, but that Fe(II)-oxidizing activity may be sustained in regions of the sediments that are depleted in O2. PMID:24860562

  4. Recovery of Humic-Reducing Bacteria from a Diversity of Environments

    PubMed Central

    Coates, John D.; Ellis, Debra J.; Blunt-Harris, Elizabeth L.; Gaw, Catherine V.; Roden, Eric E.; Lovley, Derek R.

    1998-01-01

    To evaluate which microorganisms might be responsible for microbial reduction of humic substances in sedimentary environments, humic-reducing bacteria were isolated from a variety of sediment types. These included lake sediments, pristine and contaminated wetland sediments, and marine sediments. In each of the sediment types, all of the humic reducers recovered with acetate as the electron donor and the humic substance analog, 2,6-anthraquinone disulfonate (AQDS), as the electron acceptor were members of the family Geobacteraceae. This was true whether the AQDS-reducing bacteria were enriched prior to isolation on solid media or were recovered from the highest positive dilutions of sediments in liquid media. All of the isolates tested not only conserved energy to support growth from acetate oxidation coupled to AQDS reduction but also could oxidize acetate with highly purified soil humic acids as the sole electron acceptor. All of the isolates tested were also able to grow with Fe(III) serving as the sole electron acceptor. This is consistent with previous studies that have suggested that the capacity for Fe(III) reduction is a common feature of all members of the Geobacteraceae. These studies demonstrate that the potential for microbial humic substance reduction can be found in a wide variety of sediment types and suggest that Geobacteraceae species might be important humic-reducing organisms in sediments. PMID:9546186

  5. Impact of Thermal Annealing on Organic Photovoltaic Cells Using Regioisomeric Donor-Acceptor-Acceptor Molecules.

    PubMed

    Zhang, Tao; Han, Han; Zou, Yunlong; Lee, Ying-Chi; Oshima, Hiroya; Wong, Ken-Tsung; Holmes, Russell J

    2017-08-02

    We report a promising set of donor-acceptor-acceptor (D-A-A) electron-donor materials based on coplanar thieno[3,2-b]/[2,3-b]indole, benzo[c][1,2,5]thiadiazole, and dicyanovinylene, which are found to show broadband absorption with high extinction coefficients. The role of the regioisomeric electron-donating thienoindole moiety on the physical and structural properties is examined. Bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on the thieno[2,3-b]indole-based electron donor NTU-2, using C 70 as an electron acceptor, show a champion power conversion efficiency of 5.2% under AM 1.5G solar simulated illumination. This efficiency is limited by a low fill factor (FF), as has previously been the case in D-A-A systems. In order to identify the origin of the limited FF, further insight into donor layer charge-transport behavior is realized by examining planar heterojunction OPVs, with emphasis on the evolution of film morphology with thermal annealing. Compared to as-deposited OPVs that exhibit insufficient donor crystallinity, crystalline OPVs based on annealed thin films show an increase in the short-circuit current density, FF, and power conversion efficiency. These results suggest that that the crystallization of D-A-A molecules might not be realized spontaneously at room temperature and that further processing is needed to realize efficient charge transport in these materials.

  6. Satisfied IUD acceptors as family planning motivators in Sri Lanka.

    PubMed

    Fisher, A A; de Silva, V

    1986-01-01

    In this study, government midwives were teamed with currently satisfied IUD acceptors to strengthen field motivational and recruitment efforts. The objective was to increase the number of new IUD acceptors. In the experimental study areas, a total of 3,019 new IUD acceptors were recruited. Time series regression analysis revealed a significant difference between the experimental and comparison areas that was over and above what might be expected on the basis of the past history of differences between these two areas. These and other findings suggest that teaming currently satisfied acceptors with government field-workers can have a substantial impact on the recruitment of new family planning users.

  7. Influence of acceptor on charge mobility in stacked π-conjugated polymers

    NASA Astrophysics Data System (ADS)

    Sun, Shih-Jye; Menšík, Miroslav; Toman, Petr; Gagliardi, Alessio; Král, Karel

    2018-02-01

    We present a quantum molecular model to calculate mobility of π-stacked P3HT polymer layers with electron acceptor dopants coupled next to side groups in random position with respect to the linear chain. The hole density, the acceptor LUMO energy and the hybridization transfer integral between the acceptor and polymer were found to be very critical factors to the final hole mobility. For a dopant LUMO energy close and high above the top of the polymer valence band we have found a significant mobility increase with the hole concentration and with the dopant LUMO energy approaching the top of the polymer valence band. Higher mobility was achieved for small values of hybridization transfer integral between polymer and the acceptor, corresponding to the case of weakly bound acceptor. Strong couplings between the polymer and the acceptor with Coulomb repulsion interactions induced from the electron localizations was found to suppress the hole mobility.

  8. Measuring “Free” Iron Levels in Caenorhabditis Elegans Using Low-Temperature Fe(III) Electron Paramagnetic Resonance Spectroscopy

    PubMed Central

    Pate, Kira T.; Rangel, Natalie A.; Fraser, Brian; Clement, Matthew H. S.; Srinivasan, Chandra

    2007-01-01

    Oxidative stress, caused by free radicals within the body, has been associated with the process of aging and many human diseases. As free radicals, in particular superoxide, are difficult to measure, an alternative indirect method for measuring oxidative stress levels has been successfully used in E. coli and yeast. This method is based on a proposed connection between elevated superoxide levels and release of iron from solvent exposed [4Fe-4S] enzyme clusters, which eventually leads to an increase in hydroxyl radical production. In past studies using bacteria and yeast, a positive correlation was found between superoxide production or oxidative stress due to superoxide within the organism and EPR (electron paramagnetic resonance) detectable “free” iron levels. In the present study, we have developed a reliable and an efficient method for measuring “free” iron levels in C. elegans using low temperature Fe(III) EPR at g = 4.3. This method utilizes synchronized worm cultures grown on plates, which are homogenized and treated with desferrioxamine, an Fe(III) chelator, prior to packing the EPR tube. Homogenization was found not to alter “free” iron levels, while desferrioxamine treatment significantly raised these levels, indicating presence of both Fe(II) and Fe(III) in the “free” iron pool. The correlation between free radical levels and the observed “free” iron levels was examined by using heat stress and paraquat treatment. The intensity of the Fe(III) EPR signal and thus, the concentration of the “free” iron pool, varied with the treatments that altered radical levels without changing the total iron levels. This study provides the groundwork needed to uncover the correlation between oxidative stress, “free” iron levels, and longevity in C. elegans. PMID:17010298

  9. Mixed-valent [FeIV(mu-O)(mu-carboxylato)2FeIII]3+ core.

    PubMed

    Slep, Leonardo D; Mijovilovich, Ana; Meyer-Klaucke, Wolfram; Weyhermüller, Thomas; Bill, Eckhard; Bothe, Eberhard; Neese, Frank; Wieghardt, Karl

    2003-12-17

    The symmetrically ligated complexes 1, 2, and 3 with a (mu-oxo)bis(mu-acetato)diferric core can be one-electron oxidized electrochemically or chemically with aminyl radical cations [*NR3][SbCl6] in acetonitrile yielding complexes which contain the mixed-valent [(mu-oxo)bis(mu-acetato)iron(IV)iron(III)]3+ core: [([9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](ClO4)2 (1(ClO4)2), [(Me3[9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](PF6)2 (2(PF6)(2)), and [(tpb)(2FeIII2)(mu-O)(mu-CH3CO2)2] (3) where ([9]aneN3) is the neutral triamine 1,4,7-triazacyclononane and (Me3[9]aneN3) is its tris-N-methylated derivative, and (tpb)(-) is the monoanion trispyrazolylborate. The asymmetrically ligated complex [(Me3[9]aneN3)FeIII(mu-O)(mu-CH3CO2)2FeIII(tpb)](PF6) (4(PF6)) and its one-electron oxidized form [4ox]2+ have also been prepared. Finally, the known heterodinuclear species [(Me3[9]aneN3)CrIII(mu-O)(mu-CH3CO2)2Fe([9]aneN3)](PF6)2 (5(PF6)(2)) can also be one-electron oxidized yielding [5ox]3+ containing an iron(IV) ion. The structure of 4(PF6).0.5CH3CN.0.25(C2H5)2O has been determined by X-ray crystallography and that of [5ox]2+ by Fe K-edge EXAFS-spectroscopy (Fe(IV)-O(oxo): 1.69(1) A; Fe(IV)-O(carboxylato) 1.93(3) A, Fe(IV)-N 2.00(2) A) contrasting the data for 5 (Fe(III)-O(oxo) 1.80 A; Fe(III)-O(carboxylato) 2.05 A, Fe-N 2.20 A). [5ox]2+ has an St = 1/2 ground state whereas all complexes containing the mixed-valent [FeIV(mu-O)(mu-CH3CO2)2FeIII]3+ core have an St = 3/2 ground state. Mössbauer spectra of the oxidized forms of complexes clearly show the presence of low spin FeIV ions (isomer shift approximately 0.02 mm s(-1), quadrupole splitting approximately 1.4 mm s(-1) at 80 K), whereas the high spin FeIII ion exhibits delta approximately 0.46 mm s(-1) and DeltaE(Q) approximately 0.5 mm s(-1). Mössbauer, EPR spectral and structural parameters have been calculated by density functional theoretical methods at the BP86 and B3LYP levels. The exchange coupling constant, J, for diiron complexes

  10. Dissociation kinetics of Fe(III)- and Al(III)-natural organic matter complexes at pH 6.0 and 8.0 and 25 °C

    NASA Astrophysics Data System (ADS)

    Jones, Adele M.; Pham, A. Ninh; Collins, Richard N.; Waite, T. David

    2009-05-01

    The rate at which iron- and aluminium-natural organic matter (NOM) complexes dissociate plays a critical role in the transport of these elements given the readiness with which they hydrolyse and precipitate. Despite this, there have only been a few reliable studies on the dissociation kinetics of these complexes suggesting half-times of some hours for the dissociation of Fe(III) and Al(III) from a strongly binding component of NOM. First-order dissociation rate constants are re-evaluated here at pH 6.0 and 8.0 and 25 °C using both cation exchange resin and competing ligand methods for Fe(III) and a cation exchange resin method only for Al(III) complexes. Both methods provide similar results at a particular pH with a two-ligand model accounting satisfactorily for the dissociation kinetics results obtained. For Fe(III), half-times on the order of 6-7 h were obtained for dissociation of the strong component and 4-5 min for dissociation of the weak component. For aluminium, the half-times were on the order of 1.5 h and 1-2 min for the strong and weak components, respectively. Overall, Fe(III) complexes with NOM are more stable than analogous complexes with Al(III), implying Fe(III) may be transported further from its source upon dilution and dispersion.

  11. Polarized Neutron Diffraction to Probe Local Magnetic Anisotropy of a Low-Spin Fe(III) Complex.

    PubMed

    Ridier, Karl; Mondal, Abhishake; Boilleau, Corentin; Cador, Olivier; Gillon, Béatrice; Chaboussant, Grégory; Le Guennic, Boris; Costuas, Karine; Lescouëzec, Rodrigue

    2016-03-14

    We have determined by polarized neutron diffraction (PND) the low-temperature molecular magnetic susceptibility tensor of the anisotropic low-spin complex PPh4 [Fe(III) (Tp)(CN)3]⋅H2O. We found the existence of a pronounced molecular easy magnetization axis, almost parallel to the C3 pseudo-axis of the molecule, which also corresponds to a trigonal elongation direction of the octahedral coordination sphere of the Fe(III) ion. The PND results are coherent with electron paramagnetic resonance (EPR) spectroscopy, magnetometry, and ab initio investigations. Through this particular example, we demonstrate the capabilities of PND to provide a unique, direct, and straightforward picture of the magnetic anisotropy and susceptibility tensors, offering a clear-cut way to establish magneto-structural correlations in paramagnetic molecular complexes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence

    NASA Astrophysics Data System (ADS)

    Chábera, Pavel; Liu, Yizhu; Prakash, Om; Thyrhaug, Erling; Nahhas, Amal El; Honarfar, Alireza; Essén, Sofia; Fredin, Lisa A.; Harlang, Tobias C. B.; Kjær, Kasper S.; Handrup, Karsten; Ericson, Fredric; Tatsuno, Hideyuki; Morgan, Kelsey; Schnadt, Joachim; Häggström, Lennart; Ericsson, Tore; Sobkowiak, Adam; Lidin, Sven; Huang, Ping; Styring, Stenbjörn; Uhlig, Jens; Bendix, Jesper; Lomoth, Reiner; Sundström, Villy; Persson, Petter; Wärnmark, Kenneth

    2017-03-01

    Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3‧-dimethyl-1,1‧-bis(p-tolyl)-4,4‧-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(III) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

  13. Sphaerotilus natans encrusted with nanoball-shaped Fe(III) oxide minerals formed by nitrate-reducing mixotrophic Fe(II) oxidation.

    PubMed

    Park, Sunhwa; Kim, Dong-Hun; Lee, Ji-Hoon; Hur, Hor-Gil

    2014-10-01

    Ferrous iron has been known to function as an electron source for iron-oxidizing microorganisms in both anoxic and oxic environments. A diversity of bacteria has been known to oxidize both soluble and solid-phase Fe(II) forms coupled to the reduction of nitrate. Here, we show for the first time Fe(II) oxidation by Sphaerotilus natans strain DSM 6575(T) under mixotrophic condition. Sphaerotilus natans has been known to form a sheath structure enclosing long chains of rod-shaped cells, resulting in a thick biofilm formation under oxic conditions. Here, we also demonstrate that strain DSM 6575(T) grows mixotrophically with pyruvate, Fe(II) as electron donors and nitrate as an electron acceptor and single cells of strain DSM 6575(T) are dominant under anoxic conditions. Furthermore, strain DSM 6575(T) forms nanoball-shaped amorphous Fe(III) oxide minerals encrusting on the cell surfaces through the mixotrophic iron oxidation reaction under anoxic conditions. We propose that cell encrustation results from the indirect Fe(II) oxidation by biogenic nitrite during nitrate reduction and that causes the bacterial morphological change to individual rod-shaped single cells from filamentous sheath structures. This study extends the group of existing microorganisms capable of mixotrophic Fe(II) oxidation by a new strain, S. natans strain DSM 6575(T) , and could contribute to biogeochemical cycles of Fe and N in the environment. © 2014 The Authors. FEMS Microbiology Ecology published by John Wiley & Sons Ltd on behalf of Federation of European Microbiological Societies.

  14. Characteristics of contraceptive acceptors in an urban Nigerian setting.

    PubMed

    Ayangade, O

    1984-02-01

    Intensive efforts in promoting family planning concepts and contraceptive delivery in the Third World over the past two- and one-half decades have yielded only token dividends . This has occurred in Nigeria, despite the favorable government attitude. A study of the characteristics of current contraceptive acceptors showed an overwhelming percentage of acceptors are uneducated , married and from the lower socioeconomic class, a striking departure from usual expectations. Most acceptors prefer oral contraceptives. The status of acceptance of modern contraception by the educated population is still undetermined. Contraceptives appeared to be used primarily by women aged 30 and older in our population.

  15. Role of microbial activity in Fe(III) hydroxysulfate mineral transformations in an acid mine drainage-impacted site from the Dabaoshan Mine.

    PubMed

    Bao, Yanping; Guo, Chuling; Lu, Guining; Yi, Xiaoyun; Wang, Han; Dang, Zhi

    2018-03-01

    Fe(III) hydroxysulfate minerals are secondary minerals commonly found in acid mine drainage (AMD) sites and have a major impact on water and soil quality in these environments. While previous studies showed that the Fe(III) hydroxysulfate mineral transformation could be mediated by some bacterial strains under laboratory conditions, the role of indigenous microbial activity in Fe(III) hydroxysulfate mineral transformation in natural environment has received little attention. In this study, microcosms were constructed with AMD-affected river water and sediment from the Dabaoshan Mine that was either left unamended or enriched with nutrients (lactate, nitrogen, and phosphorus (LNP)) and biosynthetic minerals (schwertmannite or jarosite). The results show that microbial activity played a decisive role in the mineralogical transformation of schwertmannite/jarosite in the AMD-contaminated site when organic carbon was available. The accumulation of Fe(II) and sulfide in microcosms amended with LNP indicates that schwertmannite/jarosite transformation is mediated by microbial reduction. XRD, SEM and FTIR analyses suggest that schwertmannite was completely transformed to goethite in the Sch-LNP microcosms at the end of their incubation. Jarosite in the Jar-LNP microcosms was also transformed to goethite, but at a much slower rate than schwertmannite. Bacterial community analysis reveals that the stimulated indigenous bacteria promote the mineralogical transformation of schwertmannite/jarosite. Most of these bacteria, including Geobacter, Desulfosporosinus, Geothrix, Desulfurispora, Desulfovibrio, and Anaeromyxobacter, are known to reduce iron and/or sulfate. The mineralogical transformation of schwertmannite and jarosite exerts significant control on the geochemistry of AMD-contaminated systems. Copyright © 2018 Elsevier B.V. All rights reserved.

  16. Anaerobic methanotrophy in tidal wetland: Effects of electron acceptors

    NASA Astrophysics Data System (ADS)

    Lin, Li-Hung; Yu, Zih-Huei; Wang, Pei-Ling

    2016-04-01

    Wetlands have been considered to represent the largest natural source of methane emission, contributing substantially to intensify greenhouse effect. Despite in situ methanogenesis fueled by organic degradation, methanotrophy also plays a vital role in controlling the exact quantity of methane release across the air-sediment interface. As wetlands constantly experience various disturbances of anthropogenic activities, biological burrowing, tidal inundation, and plant development, rapid elemental turnover would enable various electron acceptors available for anaerobic methanotrophy. The effects of electron acceptors on stimulating anaerobic methanotrophy and the population compositions involved in carbon transformation in wetland sediments are poorly explored. In this study, sediments recovered from tidally influenced, mangrove covered wetland in northern Taiwan were incubated under the static conditions to investigate whether anaerobic methanotrophy could be stimulated by the presence of individual electron acceptors. Our results demonstrated that anaerobic methanotrophy was clearly stimulated in incubations amended with no electron acceptor, sulfate, or Fe-oxyhydroxide. No apparent methane consumption was observed in incubations with nitrate, citrate, fumarate or Mn-oxides. Anaerobic methanotrophy in incubations with no exogenous electron acceptor appears to proceed at the greatest rates, being sequentially followed by incubations with sulfate and Fe-oxyhydroxide. The presence of basal salt solution stimulated methane oxidation by a factor of 2 to 3. In addition to the direct impact of electron acceptor and basal salts, incubations with sediments retrieved from low tide period yielded a lower rate of methane oxidation than from high tide period. Overall, this study demonstrates that anaerobic methanotrophy in wetland sediments could proceed under various treatments of electron acceptors. Low sulfate content is not a critical factor in inhibiting methane

  17. Fluorescent and colorimetric molecular recognition probe for hydrogen bond acceptors.

    PubMed

    Pike, Sarah J; Hunter, Christopher A

    2017-11-22

    The association constants for formation of 1 : 1 complexes between a H-bond donor, 1-naphthol, and a diverse range of charged and neutral H-bond acceptors have been measured using UV/vis absorption and fluorescence emission titrations. The performance of 1-naphthol as a dual colorimetric and fluorescent molecular recognition probe for determining the H-bond acceptor (HBA) parameters of charged and neutral solutes has been investigated in three solvents. The data were employed to establish self-consistent H-bond acceptor parameters (β) for benzoate, azide, chloride, thiocyanate anions, a series of phosphine oxides, phosphate ester, sulfoxide and a tertiary amide. The results demonstrate both the transferability of H-bond parameters between different solvents and the utility of the naphthol-based dual molecular recognition probe to exploit orthogonal spectroscopic techniques to determine the HBA properties of neutral and charged solutes. The benzoate anion is the strongest HBA studied with a β parameter of 15.4, and the neutral tertiary amide is the weakest H-bond acceptor investigated with a β parameter of 8.5. The H-bond acceptor strength of the azide anion is higher than that of chloride (12.8 and 12.2 respectively), and the thiocyanate anion has a β value of 10.8 and thus is a significantly weaker H-bond acceptor than both the azide and chloride anions.

  18. Fe(II) sorption on pyrophyllite: Effect of structural Fe(III) (impurity) in pyrophyllite on nature of layered double hydroxide (LDH) secondary mineral formation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Starcher, Autumn N.; Li, Wei; Kukkadapu, Ravi K.

    Fe(II)-Al(III)-LDH (layered double hydroxide) phases have been shown to form from reactions of aqueous Fe(II) with Fe-free Al-bearing minerals (phyllosilicate/clays and Al-oxides). To our knowledge, the effect of small amounts of structural Fe(III) impurities in “neutral” clays on such reactions, however, were not studied. In this study to understand the role of structural Fe(III) impurity in clays, laboratory batch studies with pyrophyllite (10 g/L), an Al-bearing phyllosilicate, containing small amounts of structural Fe(III) impurities and 0.8 mM and 3 mM Fe(II) (both natural and enriched in 57Fe) were carried out at pH 7.5 under anaerobic conditions (4% H2 – 96%more » N2 atmosphere). Samples were taken up to 4 weeks for analysis by Fe-X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy. In addition to the precipitation of Fe(II)-Al(III)-LDH phases as observed in earlier studies with pure minerals (no Fe(III) impurities in the minerals), the analyses indicated formation of small amounts of Fe(III) containing solid(s), most probably hybrid a Fe(II)-Al(III)/Fe(III)-LDH phase. The mechanism of Fe(II) oxidation was not apparent but most likely was due to interfacial electron transfer from the sorbed Fe(II) to the structural Fe(III) and/or surface-sorption-induced electron-transfer from the sorbed Fe(II) to the clay lattice. Increase in the Fe(II)/Al ratio of the LDH with reaction time further indicated the complex nature of the samples. This research provides evidence for the formation of both Fe(II)-Al(III)-LDH and Fe(II)-Fe(III)/Al(III)-LDH-like phases during reactions of Fe(II) in systems that mimic the natural environments. Better understanding Fe phase formation in complex laboratory studies will improve models of natural redox systems.« less

  19. The Impact of Acceptor-Acceptor Homocoupling on the Optoelectronic Properties and Photovoltaic Performance of PDTSQxff Low Bandgap Polymers.

    PubMed

    Pirotte, Geert; Kesters, Jurgen; Cardeynaels, Tom; Verstappen, Pieter; D'Haen, Jan; Lutsen, Laurence; Champagne, Benoît; Vanderzande, Dirk; Maes, Wouter

    2018-04-22

    Push-pull-type conjugated polymers applied in organic electronics do not always contain a perfect alternation of donor and acceptor building blocks. Misscouplings can occur, which have a noticeable effect on the device performance. In this work, the influence of homocoupling on the optoelectronic properties and photovoltaic performance of PDTSQx ff polymers is investigated, with a specific focus on the quinoxaline acceptor moieties. A homocoupled biquinoxaline segment is intentionally inserted in specific ratios during the polymerization. These homocoupled units cause a gradually blue-shifted absorption, while the highest occupied molecular orbital energy levels decrease only significantly upon the presence of 75-100% of homocouplings. Density functional theory calculations show that the homocoupled acceptor unit generates a twist in the polymer backbone, which leads to a decreased conjugation length and a reduced aggregation tendency. The virtually defect-free PDTSQx ff affords a solar cell efficiency of 5.4%, which only decreases substantially upon incorporating a homocoupling degree over 50%. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Spatial structure of single and interacting Mn acceptors in GaAs

    NASA Astrophysics Data System (ADS)

    Koenraad, Paul

    2005-03-01

    Ferromagnetic semiconductors such as Ga1-xMnxAs are receiving a lot of attention at the moment because of their application in spintronic devices. However, despite intense study of deep acceptors in III-V semiconductors such as MnGa, little information has been obtained on their electronic properties at the atomic scale. Yet the spatial shape of the Mn acceptor state will influence the hole-mediated Mn-Mn coupling and thus all of the magnetic properties of ferromagnetic semiconductors such as Ga1-xMnxAs. This study presents an experimental and theoretical description of the spatial symmetry of the Mn acceptor wave-function in GaAs. We present measurements of the spatial mapping of the anisotropic wavefunction of a hole localized at a Mn acceptor. To achieve this, we have used the STM tip not only to image the Mn acceptor but also to manipulate its charge state A^0/A^- at room temperature. Within an envelope function effective mass model (EFM) the anisotropy in the acceptor wave-function can be traced to the influence of the cubic symmetry of the GaAs crystal which selects specific d-states that mix into the ground state due to the spin-orbit interaction in the valence band. Comparison with calculations based on a tight-binding model (TBM) for the Mn acceptor structure supports this conclusion. Using the same experimental and theoretical approach we furthermore explored the interaction between Mn acceptors directly by analyzing close Mn-Mn pairs, which were separated by less than 2 nm. We will discuss some implications of these results for Mn delta-doped layers grown on differently oriented growth surfaces.

  1. Uranium(VI) Reduction by Anaeromyxobacter dehalogenans Strain 2CP-C

    PubMed Central

    Wu, Qingzhong; Sanford, Robert A.; Löffler, Frank E.

    2006-01-01

    Previous studies demonstrated growth of Anaeromyxobacter dehalogenans strain 2CP-C with acetate or hydrogen as the electron donor and Fe(III), nitrate, nitrite, fumarate, oxygen, or ortho-substituted halophenols as electron acceptors. In this study, we explored and characterized U(VI) reduction by strain 2CP-C. Cell suspensions of fumarate-grown 2CP-C cells reduced U(VI) to U(IV). More-detailed growth studies demonstrated that hydrogen was the required electron donor for U(VI) reduction and could not be replaced by acetate. The addition of nitrate to U(VI)-reducing cultures resulted in a transitory increase in U(VI) concentration, apparently caused by the reoxidation of reduced U(IV), but U(VI) reduction resumed following the consumption of N-oxyanions. Inhibition of U(VI) reduction occurred in cultures amended with Fe(III) citrate, or citrate. In the presence of amorphous Fe(III) oxide, U(VI) reduction proceeded to completion but the U(VI) reduction rates decreased threefold compared to control cultures. Fumarate and 2-chlorophenol had no inhibitory effects on U(VI) reduction, and both electron acceptors were consumed concomitantly with U(VI). Since cocontaminants (e.g., nitrate, halogenated compounds) and bioavailable ferric iron are often encountered at uranium-impacted sites, the metabolic versatility makes Anaeromyxobacter dehalogenans a promising model organism for studying the complex interaction of multiple electron acceptors in U(VI) reduction and immobilization. PMID:16672509

  2. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

    DOE PAGES

    Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; ...

    2015-09-18

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealedmore » both electron and hole transfer processes at the donor–acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. As a result, this study describes a new motif for designing highly efficient acceptors for organic solar cells.« less

  3. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells.

    PubMed

    Zhong, Yu; Trinh, M Tuan; Chen, Rongsheng; Purdum, Geoffrey E; Khlyabich, Petr P; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Nam, Chang-Yong; Sfeir, Matthew Y; Black, Charles T; Steigerwald, Michael L; Loo, Yueh-Lin; Ng, Fay; Zhu, X-Y; Nuckolls, Colin

    2015-09-18

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells.

  4. Reduction of Fe(III), Cr(VI), U(VI), and Tc(VII) by Deinococcus radiodurans R1

    PubMed Central

    Fredrickson, J. K.; Kostandarithes, H. M.; Li, S. W.; Plymale, A. E.; Daly, M. J.

    2000-01-01

    Deinococcus radiodurans is an exceptionally radiation-resistant microorganism capable of surviving acute exposures to ionizing radiation doses of 15,000 Gy and previously described as having a strictly aerobic respiratory metabolism. Under strict anaerobic conditions, D. radiodurans R1 reduced Fe(III)-nitrilotriacetic acid coupled to the oxidation of lactate to CO2 and acetate but was unable to link this process to growth. D. radiodurans reduced the humic acid analog anthraquinone-2,6-disulfonate (AQDS) to its dihydroquinone form, AH2DS, which subsequently transferred electrons to the Fe(III) oxides hydrous ferric oxide and goethite via a previously described electron shuttle mechanism. D. radiodurans reduced the solid-phase Fe(III) oxides in the presence of either 0.1 mM AQDS or leonardite humic acids (2 mg ml−1) but not in their absence. D. radiodurans also reduced U(VI) and Tc(VII) in the presence of AQDS. In contrast, Cr(VI) was directly reduced in anaerobic cultures with lactate although the rate of reduction was higher in the presence of AQDS. The results are the first evidence that D. radiodurans can reduce Fe(III) coupled to the oxidation of lactate or other organic compounds. Also, D. radiodurans, in combination with humic acids or synthetic electron shuttle agents, can reduce U and Tc and thus has potential applications for remediation of metal- and radionuclide-contaminated sites where ionizing radiation or other DNA-damaging agents may restrict the activity of more sensitive organisms. PMID:10788374

  5. Investigating charge generation in polymer:non-fullerene acceptor bulk heterojunction films

    DOE PAGES

    Stoltzfus, Dani M.; Larson, Bryon W.; Zarrabi, Nasim; ...

    2018-01-31

    Non-fullerene acceptors are now capable of being used in high efficiency bulk heterojunction (BHJ) donor-acceptor organic solar cells. Acceptors comprising single or multiple linked chromophores have been used. We have developed a new non-fullerene molecular acceptor as well as two non-polymeric macromolecular materials that contain four equivalents of a similar chromophore, but can adopt different spatial arrangements of the chromophores. We compare the effect of having single and multiple chromophores within a macromolecule on the charge generation processes in P3HT:non-fullerene acceptor BHJ films using Transient Absorption Spectroscopy (TAS) and Time Resolved Microwave Conductivity (TRMC) measurements. It was found from themore » TAS measurements that at low weight percent (5 wt%) the single chromophore formed more polarons than the acceptors in which chromophores were linked, due to it having a more even distribution within the film. At higher concentrations (50 wt%) the trend was reversed due to the single chromophore forming crystalline domains, which reduced the interface area with the P3HT donor. The TRMC measurements showed that more mobile carriers were formed in the macromolecular acceptors when used at low concentrations in the blend and, independent of concentration, mobile carriers had a longer lifetime when compared to films containing the molecular material, which we ascribe to the charges being able to sample more than one chromophore and thus reduce recombination events.« less

  6. A voltammetric method for Fe(iii) in blood serum using a screen-printed electrode modified with a Schiff base ionophore.

    PubMed

    Mittal, Susheel K; Rana, Sonia; Kaur, Navneet; Banks, Craig E

    2018-05-23

    Herein, a potent electrochemical ionophore (SMS-2) based on a Schiff base has been used for the modification of a screen-printed electrode (SPE). The modified disposable electrode can selectively detect ferric ions in an aqueous medium. Redox behavior of the proposed strip was characterized using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Incorporation of the ligand in the ink of the SPE enhanced the analytical performance of the electrode, and its surface modification was confirmed by SEM and EDX analysis. Shifting/quenching of the cathodic peak potential of the ionophore after binding with Fe(iii) ions was used to detect and measure the ferric ion concentration. This sensor can identify Fe(iii) in the detection range from 0.625 μM to 7.5 μM. The modified SPE can selectively detect ferric ions in the presence of many other interfering ions and has been successfully used to determine the Fe(iii) content in blood serum samples. The metal-ionophore complex structure was optimized using DFT calculations to study the energetics of the metal-ionophore interactions.

  7. Spectrophotometric study of the charge-transfer and ion-pair complexation of methamphetamine with some acceptors

    NASA Astrophysics Data System (ADS)

    Shahdousti, Parvin; Aghamohammadi, Mohammad; Alizadeh, Naader

    2008-04-01

    The charge-transfer (CT) complexes of methamphetamine (MPA) as a n-donor with several acceptors including bromocresolgreen (BCG), bromocresolpurple (BCP), chlorophenolred (CPR), picric acid (PIC), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) have been studied spectrophotometrically in chloroform solutions in order to obtain some information about their stoichiometry and stability of complexation. The oscillator strengths, transition dipole moments and resonance energy of the complex in the ground state for all complexes have been calculated. Vertical ionization potential of MPA and electron affinity of acceptors were determined by ab initio calculation. The acceptors were also used to utilize a simple and sensitive extraction-spectrophotometric method for the determination of MPA. The method is based on the formation of 1:1 ion-pair association complexes of MPA with BCG, BCP and PIC in chloroform medium. Beer's plots were obeyed in a general concentration range of 0.24-22 μg ml -1 for the investigated drug with different acceptors. The proposed methods were applied successfully for the determination of MAP in pure and abuse drug with good accuracy and precision.

  8. Three holes bound to a double acceptor - Be(+) in germanium

    NASA Technical Reports Server (NTRS)

    Haller, E. E.; Mcmurray, R. E., Jr.; Falicov, L. M.; Haegel, N. M.; Hansen, W. L.

    1983-01-01

    A double acceptor binding three holes has been observed for the first time with photoconductive far-infrared spectroscopy in beryllium-doped germanium single crystals. This new center, Be(+), has a hole binding energy of about 5 meV and is only present when free holes are generated by ionization of either neutral shallow acceptors or neutral Be double acceptors. The Be(+) center thermally ionizes above 4 K. It disappears at a uniaxial stress higher than about a billion dyn/sq cm parallel to (111) as a result of the lifting of the valence-band degeneracy.

  9. Improving Photoconductance of Fluorinated Donors with Fluorinated Acceptors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Garner, Logan E.; Larson, Bryon; Oosterhout, Stefan

    2016-11-21

    This work investigates the influence of fluorination of both donor and acceptor materials on the generation of free charge carriers in small molecule donor/fullerene acceptor BHJ OPV active layers. A fluorinated and non-fluorinated small molecule analogue were synthesized and their optoelectronic properties characterized. The intrinsic photoconductance of blends of these small molecule donors was investigated using time-resolved microwave conductivity. Blends of the two donor molecules with a traditional non-fluorinated fullerene (PC70BM) as well as a fluorinated fullerene (C60(CF3)2-1) were investigated using 5% and 50% fullerene loading. We demonstrate for the first time that photoconductance in a 50:50 donor:acceptor BHJ blendmore » using a fluorinated fullerene can actually be improved relative to a traditional non-fluorinated fullerene by fluorinating the donor molecule as well.« less

  10. Acceptor binding energies in GaN and AlN

    NASA Astrophysics Data System (ADS)

    Mireles, Francisco; Ulloa, Sergio E.

    1998-08-01

    We employ effective-mass theory for degenerate hole bands to calculate the acceptor binding energies for Be, Mg, Zn, Ca, C, and Si substitutional acceptors in GaN and AlN. The calculations are performed through the 6×6 Rashba-Sheka-Pikus and the Luttinger-Kohn matrix Hamiltonians for wurtzite (WZ) and zinc-blende (ZB) crystal phases, respectively. An analytic representation for the acceptor pseudopotential is used to introduce the specific nature of the impurity atoms. The energy shift due to polaron effects is also considered in this approach. The ionization energy estimates are in very good agreement with those reported experimentally in WZ GaN. The binding energies for ZB GaN acceptors are all predicted to be shallower than the corresponding impurities in the WZ phase. The binding-energy dependence upon the crystal-field splitting in WZ GaN is analyzed. Ionization levels in AlN are found to have similar ``shallow'' values to those in GaN, but with some important differences which depend on the band structure parametrizations, especially the value of the crystal-field splitting used.

  11. Geobacter daltonii sp. nov., an Fe(III)- and uranium(VI)-reducing bacterium isolated from a shallow subsurface exposed to mixed heavy metal and hydrocarbon contamination.

    PubMed

    Prakash, Om; Gihring, Thomas M; Dalton, Dava D; Chin, Kuk-Jeong; Green, Stefan J; Akob, Denise M; Wanger, Greg; Kostka, Joel E

    2010-03-01

    An Fe(III)- and uranium(VI)-reducing bacterium, designated strain FRC-32(T), was isolated from a contaminated subsurface of the USA Department of Energy Oak Ridge Field Research Center (ORFRC) in Oak Ridge, Tennessee, where the sediments are exposed to mixed waste contamination of radionuclides and hydrocarbons. Analyses of both 16S rRNA gene and the Geobacteraceae-specific citrate synthase (gltA) mRNA gene sequences retrieved from ORFRC sediments indicated that this strain was abundant and active in ORFRC subsurface sediments undergoing uranium(VI) bioremediation. The organism belonged to the subsurface clade of the genus Geobacter and shared 92-98 % 16S rRNA gene and 75-81 % rpoB gene sequence similarities with other recognized species of the genus. In comparison to its closest relative, Geobacter uraniireducens Rf4(T), according to 16S rRNA gene sequence similarity, strain FRC-32(T) showed a DNA-DNA relatedness value of 21 %. Cells of strain FRC-32(T) were Gram-negative, non-spore-forming, curved rods, 1.0-1.5 microm long and 0.3-0.5 microm in diameter; the cells formed pink colonies in a semisolid cultivation medium, a characteristic feature of the genus Geobacter. The isolate was an obligate anaerobe, had temperature and pH optima for growth at 30 degrees C and pH 6.7-7.3, respectively, and could tolerate up to 0.7 % NaCl although growth was better in the absence of NaCl. Similar to other members of the Geobacter group, strain FRC-32(T) conserved energy for growth from the respiration of Fe(III)-oxyhydroxide coupled with the oxidation of acetate. Strain FRC-32(T) was metabolically versatile and, unlike its closest relative, G. uraniireducens, was capable of utilizing formate, butyrate and butanol as electron donors and soluble ferric iron (as ferric citrate) and elemental sulfur as electron acceptors. Growth on aromatic compounds including benzoate and toluene was predicted from preliminary genomic analyses and was confirmed through successive transfer with

  12. Harvesting visible light with MoO3 nanorods modified by Fe(iii) nanoclusters for effective photocatalytic degradation of organic pollutants.

    PubMed

    Alam, U; Kumar, S; Bahnemann, D; Koch, J; Tegenkamp, C; Muneer, M

    2018-02-07

    The photocatalytic performance of MoO 3 is limited due to its weak visible light absorption ability and quick recombination of charge carriers. In the present work, we report the facile synthesis of Fe(iii)-grafted MoO 3 nanorods using a hydrothermal method followed by an impregnation technique with the aim of enhancing the light harvesting ability and photocatalytic efficiency of MoO 3 . The prepared samples were characterized through the standard analytical techniques of XRD, SEM-EDS, TEM, XPS, UV-Vis-DRS, FT-IR, TG-DTA and PL spectrophotometry. XPS and TEM analyses reveal that Fe(iii) ions are successfully grafted onto the surface of the MoO 3 nanorod with intimate interfacial contact. The photocatalytic performances of the prepared samples were investigated by studying the degradation of methylene blue (MB), rhodamine B (RhB) and 4-nitrophenol (4-NP) under visible light irradiation. The surface-modified MoO 3 with Fe(iii) ions showed excellent photocatalytic activity towards the degradation of the above-mentioned pollutants, where Fe(iii) ions act as effective cocatalytic sites to produce hydroxyl radicals through multi-electron reduction of oxygen molecules. The improved photocatalytic activity could be ascribed to the effective separation of charge carriers and efficient production of hydroxyl radicals via the rapid capture of electrons by Fe(iii) through a well-known photoinduced interfacial charge transfer mechanism. Based on scavenger analysis study, a mechanism for the enhanced photocatalytic activity has been discussed and proposed. The concept of surface grafting onto large bandgap semiconductors with ubiquitous elements opens up a new avenue for the development of visible-light-responsive photocatalysts with excellent photocatalytic activity.

  13. IR, UV-Vis, magnetic and thermal characterization of chelates of some catecholamines and 4-aminoantipyrine with Fe(III) and Cu(II)

    NASA Astrophysics Data System (ADS)

    Mohamed, Gehad G.; Zayed, M. A.; El-Dien, F. A. Nour; El-Nahas, Reham G.

    2004-07-01

    The dopamine derivatives participate in the regulation of wide variety of physiological functions in the human body and in medication life. Increase and/or decrease in the concentration of dopamine in human body reflect an indication for diseases such as Schizophrenia and/or Parkinson diseases. α-Methyldopa (α-MD) in tablets is used in medication of hypertension. The Fe(III) and Cu(II) chelates with coupled products of adrenaline hydrogen tartarate (AHT), levodopa (LD), α-MD and carbidopa (CD) with 4-aminoantipyrine (4-AAP) are prepared and characterized. Different physico-chemical methods like IR, magnetic and UV-Vis spectra are used to investigate the structure of these chelates. Fe(III) form 1:2 (M:catecholamines) chelates while Cu(II) form 1:1 chelates. Catecholamines behave as a bidentate mono- or dibasic ligands in binding to the metal ions. IR spectra show that the catecholamines are coordinated to the metal ions in a bidentate manner with O,O donor sites of the phenolic - OH. Magnetic moment measurements reveal the presence of Fe(III) chelates in octahedral geometry while the Cu(II) chelates are square planar. The thermal decomposition of Fe(III) and Cu(II) complexes is studied using thermogravimetric (TGA) and differential thermal analysis (DTA) techniques. The water molecules are removed in the first step followed immediately by decomposition of the ligand molecules. The activation thermodynamic parameters, such as, energy of activation, enthalpy, entropy and free energy change of the complexes are evaluated and the relative thermal stability of the complexes are discussed.

  14. Molecular structure and biological studies on Cr(III), Mn(II) and Fe(III) complexes of heterocyclic carbohydrazone ligand.

    PubMed

    Abu El-Reash, G M; El-Gammal, O A; Radwan, A H

    2014-01-01

    The chelating behavior of the ligand (H2APC) based on carbohydrazone core modified with pyridine end towards Cr(III), Mn(II) and Fe(III) ions have been examined. The (1)H NMR and IR data for H2APC revealed the presence of two stereoisomers syn and anti in both solid state and in solution in addition to the tautomeric versatility based on the flexible nature of the hydrazone linkage leading to varied coordination modes. The spectroscopic data confirmed that the ligand behaves as a monobasic tridentate in Cr(III) and Fe(III) complexes and as neutral tetradentate in Mn(II) complex. The electronic spectra as well as the magnetic measurements confirmed the octahedral geometry for all complexes. The bond length and angles were evaluated by DFT method using material studio program for all complexes. The thermal behavior and the kinetic parameters of degradation were determined using Coats-Redfern and Horowitz-Metzger methods. The antioxidant (DDPH and ABTS methods), anti-hemolytic and cytotoxic activities of the compounds have been screened. Cr(III) complex and H2APC showed the highest antioxidant activity using ABTS and DPPH methods. With respect to in vitro Ehrlich ascites assay, H2APC exhibited the potent activity followed by Fe(III) and Cr(III)complexes. Copyright © 2013 Elsevier B.V. All rights reserved.

  15. A Simple Small Size and Low Cost Sensor Based on Surface Plasmon Resonance for Selective Detection of Fe(III)

    PubMed Central

    Cennamo, Nunzio; Alberti, Giancarla; Pesavento, Maria; D'Agostino, Girolamo; Quattrini, Federico; Biesuz, Raffaela; Zeni, Luigi

    2014-01-01

    A simple, small size, and low cost sensor based on a Deferoxamine Self Assembled Monolayer (DFO-SAM) and Surface Plasmon Resonance (SPR) transduction, in connection with a Plastic Optical Fiber (POF), has been developed for the selective detection of Fe(III). DFO-SAM sensors based on appropriate electrochemical techniques can be frequently found in the scientific literature. In this work, we present the first example of a DFO-SAM sensor based on SPR in an optical fiber. The SPR sensing platform was realized by removing the cladding of a plastic optical fiber along half the circumference, spin coating a buffer of Microposit S1813 photoresist on the exposed core, and finally sputtering a thin gold film. The hydroxamate siderophore deferoxamine (DFO), having high binding affinity for Fe(III), is then used in its immobilized form, as self-assembled monolayer on the gold layer surface of the POF sensor. The results showed that the DFO-SAM-POF-sensor was able to sense the formation of the Fe(III)/DFO complex in the range of concentrations between 1 μm and 50 μm with a linearity range from 0 to 30 μm of Fe(III). The selectivity of the sensor was also proved by interference tests. PMID:24608007

  16. A simple small size and low cost sensor based on surface plasmon resonance for selective detection of Fe(III).

    PubMed

    Cennamo, Nunzio; Alberti, Giancarla; Pesavento, Maria; D'Agostino, Girolamo; Quattrini, Federico; Biesuz, Raffaela; Zeni, Luigi

    2014-03-07

    A simple, small size, and low cost sensor based on a Deferoxamine Self Assembled Monolayer (DFO-SAM) and Surface Plasmon Resonance (SPR) transduction, in connection with a Plastic Optical Fiber (POF), has been developed for the selective detection of Fe(III). DFO-SAM sensors based on appropriate electrochemical techniques can be frequently found in the scientific literature. In this work, we present the first example of a DFO-SAM sensor based on SPR in an optical fiber. The SPR sensing platform was realized by removing the cladding of a plastic optical fiber along half the circumference, spin coating a buffer of Microposit S1813 photoresist on the exposed core, and finally sputtering a thin gold film. The hydroxamate siderophore deferoxamine (DFO), having high binding affinity for Fe(III), is then used in its immobilized form, as self-assembled monolayer on the gold layer surface of the POF sensor. The results showed that the DFO-SAM-POF-sensor was able to sense the formation of the Fe(III)/DFO complex in the range of concentrations between 1 μm and 50 μm with a linearity range from 0 to 30 μm of Fe(III). The selectivity of the sensor was also proved by interference tests.

  17. Small molecule BODIPY dyes as non-fullerene acceptors in bulk heterojunction organic photovoltaics.

    PubMed

    Poe, Ambata M; Della Pelle, Andrea M; Subrahmanyam, Ayyagari V; White, William; Wantz, Guillaume; Thayumanavan, S

    2014-03-18

    A series of acceptor-donor-acceptor molecules containing terminal BODIPY moieties conjugated through the meso position were synthesized. Deep LUMO energy levels and good visible absorption led to their use as acceptors in bulk heterojunction solar cells. Inverted devices were fabricated, reaching efficiencies as high as 1.51%.

  18. Difference between resistance degradation of fixed valence acceptor (Mg) and variable valence acceptor (Mn)-doped BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Randall, Clive A.; Hur, Kang-Heon

    2010-09-01

    The difference in the resistance degradation behavior was investigated between fixed valence acceptor (Mg) and the variable valence acceptor (Mn)-doped BaTiO3 ceramics with an increase of each acceptor concentration. Coarse-grained specimens with uniform grain sizes and different acceptor concentrations were prepared. In the case of Mg-doped BaTiO3, the time to degradation systematically decreased with the increase in Mg concentration. In contrast, there is a systematically increased time to degradation with the increase in Mn concentration in Mn-doped BaTiO3. The fast degradation by the increase in Mg concentration directly corresponded to an increase in the Warburg impedance and ionic transference number (tion) associated with an increase in oxygen vacancy concentration ([VO••]). On the other hand, no distinct Warburg impedance or ionic conduction contribution could be observed with the increase in Mn concentration. It is supposed that the increase in [VO••] is negligible in spite of the increase in acceptor Mn concentration, when it is compared to Mg-doped BaTiO3. The much lower [VO••] and more dominant electron/hole trapping effect due to multivalence nature of Mn are supposed to cause such a contrary degradation behavior between Mg and Mn-doped BaTiO3. Reoxidation in a slightly reducing atmosphere (N2) showed better resistance to degradation behavior than in a oxidizing air atmosphere in both Mg and Mn-doped BaTiO3, which is anticipated to be an increase in the electron/hole trapping sites. All these behaviors could be explained by the low temperature defect chemical model that shows difference in the defect structure between Mg and Mn-doped BaTiO3, and its dependence on the oxygen partial pressure (pO2) during reoxidation and cooling. Not only the [VO••], but also the density of electron/hole trap sites, are believed to be crucial in controlling resistance degradation.

  19. Non-fullerene acceptors for organic solar cells

    NASA Astrophysics Data System (ADS)

    Yan, Cenqi; Barlow, Stephen; Wang, Zhaohui; Yan, He; Jen, Alex K.-Y.; Marder, Seth R.; Zhan, Xiaowei

    2018-03-01

    Non-fullerene acceptors (NFAs) are currently a major focus of research in the development of bulk-heterojunction organic solar cells (OSCs). In contrast to the widely used fullerene acceptors (FAs), the optical properties and electronic energy levels of NFAs can be readily tuned. NFA-based OSCs can also achieve greater thermal stability and photochemical stability, as well as longer device lifetimes, than their FA-based counterparts. Historically, the performance of NFA OSCs has lagged behind that of fullerene devices. However, recent developments have led to a rapid increase in power conversion efficiencies for NFA OSCs, with values now exceeding 13%, demonstrating the viability of using NFAs to replace FAs in next-generation high-performance OSCs. This Review discusses the important work that has led to this remarkable progress, focusing on the two most promising NFA classes to date: rylene diimide-based materials and materials based on fused aromatic cores with strong electron-accepting end groups. The key structure-property relationships, donor-acceptor matching criteria and aspects of device physics are discussed. Finally, we consider the remaining challenges and promising future directions for the NFA OSCs field.

  20. An overview of molecular acceptors for organic solar cells

    NASA Astrophysics Data System (ADS)

    Hudhomme, Piétrick

    2013-07-01

    Organic solar cells (OSCs) have gained serious attention during the last decade and are now considered as one of the future photovoltaic technologies for low-cost power production. The first dream of attaining 10% of power coefficient efficiency has now become a reality thanks to the development of new materials and an impressive work achieved to understand, control and optimize structure and morphology of the device. But most of the effort devoted to the development of new materials concerned the optimization of the donor material, with less attention for acceptors which to date remain dominated by fullerenes and their derivatives. This short review presents the progress in the use of non-fullerene small molecules and fullerene-based acceptors with the aim of evaluating the challenge for the next generation of acceptors in organic photovoltaics.

  1. Simulation study on the effects of chemical structure and molecular size on the acceptor strength in poly(3-hexylthiophene)-based copolymer with alternating donor and acceptor for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Rassamesard, Areefen; Pengpan, Teparksorn

    2017-02-01

    This research assessed the effects of various chemical structures and molecular sizes on the simulated geometric parameters, electron structures, and spectroscopic properties of single-chain complex alternating donor-acceptor (D-A) monomers and copolymers that are intended for use as photoactive layer in a polymer solar cell by using Kohn-Sham density functional theory with B3LYP exchange-correlation functional. The 3-hexylthiophene (3HT) was selected for electron donor, while eight chemicals, namely thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), benzothiadiazole (BT), thiadiazolothieno-pyrazine (TPD), oxadiazole (OXD) and 5-diphenyl-1,2,4-triazole (TAZ), were employed as electron acceptor functional groups. The torsional angle, bridge bond length, intramolecular charge transfer, energy levels, and molecular orbitals were analyzed. The simulation results reveal that the geometry and electron structure of donor-acceptor monomer and copolymer are significantly impacted by heterocyclic rings, heteroatoms, fused rings, degree of steric hindrance and coplanarity of the acceptor molecular structure. Planar conformation was obtained from the D copolymer, and a pseudo-planar structure with the TD copolymer. The TAZ acceptor exhibited strong steric hindrance due to its bulky structure and non-planarity of its structure. An analysis of the electron structures indicated that the degree of intramolecular electron-withdrawing capability had the rank order TAZ  <  Z  <  D  <  TPD  <  OXD  <  TP  <  BT  <  TD. The TD is indicated as the most effective acceptor among those that were simulated. However, the small energy gaps of TD as well as TPD copolymer indicate that these two copolymers can be used in transparent conducting materials. The copolymer based on BT acceptor exhibited good intramolecular charge transfer and absorbed at 656 nm wavelength which is close to the maximum flux of solar

  2. Direct involvement of ombB, omaB, and omcB genes in extracellular reduction of Fe(III) by Geobacter sulfurreducens PCA

    DOE PAGES

    Liu, Yimo; Fredrickson, Jim K.; Zachara, John M.; ...

    2015-10-01

    The tandem gene clusters orfR-ombB-omaB-omcB and orfS-ombC-omaC-omcC of the metal-reducing bacterium Geobacter sulfurreducens PCA are responsible for trans-outer membrane electron transfer during extracellular reduction of Fe(III)-citrate and ferrihydrite [a poorly crystalline Fe(III) oxide]. Each gene cluster encodes a putative transcriptional factor (OrfR/OrfS), a porin-like outer-membrane protein (OmbB/OmbC), a periplasmic c-type cytochrome (c-Cyt, OmaB/OmaC) and an outer-membrane c-Cyt (OmcB/OmcC). The individual roles of OmbB, OmaB and OmcB in extracellular reduction of Fe(III), however, have remained either uninvestigated or controversial. Here, we showed that replacements of ombB, omaB, omcB and ombB-omaB with an antibiotic gene in the presence of ombC-omaC-omcC had nomore » impact on reduction of Fe(III)-citrate by G. sulfurreducens PCA. Disruption of ombB, omaB, omcB and ombB-omaB in the absence of ombC-omaC-omcC, however, severely impaired the bacterial ability to reduce Fe(III)-citrate as well as ferrihydrite. These results unequivocally demonstrate an overlapping role of ombB-omaB-omcB and ombC-omaC-omcC in extracellular Fe(III) reduction by G. sulfurreducens PCA. Involvement of both ombB-omaB-omcB and ombC-omaC-omcC in extracellular Fe(III) reduction reflects the importance of these trans-outer membrane protein complexes in the physiology of this bacterium. Moreover, the kinetics of Fe(III)-citrate and ferrihydrite reduction by these mutants in the absence of ombC-omaC-omcC were nearly identical, which clearly show that OmbB, OmaB and OmcB contribute equally to extracellular Fe(III) reduction. Finally, orfS was found to have a negative impact on the extracellular reduction of Fe(III)-citrate and ferrihydrite in G. sulfurreducens PCA probably by serving as a transcriptional repressor.« less

  3. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers

    NASA Astrophysics Data System (ADS)

    Barrejón, Myriam; Gobeze, Habtom B.; Gómez-Escalonilla, María J.; Fierro, José Luis G.; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-01

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an

  4. A survey of acceptor dopants for β-Ga2O3

    NASA Astrophysics Data System (ADS)

    Lyons, John L.

    2018-05-01

    With a wide band gap, high critical breakdown voltage and commercially available substrates, Ga2O3 is a promising material for next-generation power electronics. Like most wide-band-gap semiconductors, obtaining better control over its electrical conductivity is critically important, but has proven difficult to achieve. Although efficient p-type doping in Ga2O3 is not expected, since theory and experiment indicate the self-trapping of holes, the full development of this material will require a better understanding of acceptor dopants. Here the properties of group 2, group 5 and group 12 acceptor impurities in β-Ga2O3 are explored using hybrid density functional calculations. All impurities are found to exhibit acceptor transition levels above 1.3 eV. After examining formation energies as a function of chemical potential, Mg (followed closely by Be) is determined to be the most stable acceptor species.

  5. Acceptor Products of Alternansucrase with Gentiobiose

    USDA-ARS?s Scientific Manuscript database

    In the presence of suitable acceptor molecules, dextransucrase makes a homologous series of oligosaccharides in which the isomers differ by a single glucosyl unit, whereas alternansucrase synthesizes one trisaccharide, two tetrasaccharides, etc. Previously, we showed that alternansucrase only forms...

  6. Isolation and Characterization of Microbes Mediating Thermodynamically Favorable Coupling of Anaerobic Oxidation of Methane and Metal Reduction

    NASA Astrophysics Data System (ADS)

    Glass, J. B.; Reed, B. C.; Sarode, N. D.; Kretz, C. B.; Bray, M. S.; DiChristina, T. J.; Stewart, F. J.; Fowle, D. A.; Crowe, S.

    2014-12-01

    Methane is the third most reduced environmentally relevant electron donor for microbial metabolisms after organic carbon and hydrogen. In anoxic ecosystems, the major sink for methane is anaerobic oxidation of methane (AOM) mediated by syntrophic microbial consortia that couple AOM to reduction of an oxidized electron acceptor to yield free energy. In marine sediments, AOM is generally coupled to reduction of sulfate despite an extremely small amount of free energy yield because sulfate is the most abundant electron acceptor in seawater. While AOM coupled to Fe(III) and Mn(IV) reduction (Fe- and Mn-AOM) is 10-30x more thermodynamically favorable than sulfate-AOM, and geochemical data suggests that it occurs in diverse environments, the microorganisms mediating Fe- and Mn-AOM remain unknown. Lake Matano, Indonesia is an ideal ecosystem to enrich for Fe- and Mn-AOM microbes because its anoxic ferruginous deep waters and sediments contain abundant Fe(III), Mn(IV) and methane, and extremely low sulfate and nitrate. Our research aims to isolate and characterize the microbes mediating Fe- and Mn-AOM from three layers of Lake Matano sediments through serial enrichment cultures in minimal media lacking nitrate and sulfate. 16S rRNA amplicon sequencing of sediment inoculum revealed the presence of the Fe(III)-reducing bacterium Geobacter (5-10% total microbial community in shallow sediment and 35-60% in deeper sediment) as well as 1-2% Euryarchaeota implicated in methane cycling, including ANME-1 and 2d and Methanosarcinales. After 90 days of primary enrichment, all three sediment layers showed high levels of Fe(III) reduction (60-90 μM Fe(II) d-1) in the presence of methane compared to no methane and heat-killed controls. Treatments with added Fe(III) as goethite contained higher abundances of Geobacter than the inoculum (60-80% in all layers), suggesting that Geobacter may be mediating Fe(III) reduction in these enrichments. Quantification of AOM rates is underway, and

  7. Donor assists acceptor binding and catalysis of human α1,6-fucosyltransferase.

    PubMed

    Kötzler, Miriam P; Blank, Simon; Bantleon, Frank I; Wienke, Martin; Spillner, Edzard; Meyer, Bernd

    2013-08-16

    α1,6-Core-fucosyltransferase (FUT8) is a vital enzyme in mammalian physiological and pathophysiological processes such as tumorigenesis and progress of, among others, non-small cell lung cancer and colon carcinoma. It was also shown that therapeutic antibodies have a dramatically higher efficacy if the α1,6-fucosyl residue is absent. However, specific and potent inhibitors for FUT8 and related enzymes are lacking. Hence, it is crucial to elucidate the structural basis of acceptor binding and the catalytic mechanism. We present here the first structural model of FUT8 in complex with its acceptor and donor molecules. An unusually large acceptor, i.e., a hexasaccharide from the core of N-glycans, is required as minimal structure. Acceptor substrate binding of FUT8 is being dissected experimentally by STD NMR and SPR and theoretically by molecular dynamics simulations. The acceptor binding site forms an unusually large and shallow binding site. Binding of the acceptor to the enzyme is much faster and stronger if the donor is present. This is due to strong hydrogen bonding between O6 of the proximal N-acetylglucosamine and an oxygen atom of the β-phosphate of GDP-fucose. Therefore, we propose an ordered Bi Bi mechanism for FUT8 where the donor molecule binds first. No specific amino acid is present that could act as base during catalysis. Our results indicate a donor-assisted mechanism, where an oxygen of the β-phosphate deprotonates the acceptor. Knowledge of the mechanism of FUT8 is now being used for rational design of targeted inhibitors to address metastasis and prognosis of carcinomas.

  8. Donor-Acceptor-Collector Ternary Crystalline Films for Efficient Solid-State Photon Upconversion.

    PubMed

    Ogawa, Taku; Hosoyamada, Masanori; Yurash, Brett; Nguyen, Thuc-Quyen; Yanai, Nobuhiro; Kimizuka, Nobuo

    2018-06-25

    It is pivotal to achieve efficient triplet-triplet annihilation based photon upconversion (TTA-UC) in the solid-state for enhancing potentials of renewable energy production devices. However, the UC efficiency of solid materials is largely limited by low fluorescence quantum yields that originate from the aggregation of TTA-UC chromophores, and also by severe back energy transfer from the acceptor singlet state to the singlet state of the triplet donor in the condensed state. In this work, to overcome these issues, we introduce a highly fluorescent singlet energy collector as the third component of donor-doped acceptor crystalline films, in which dual energy migration, i.e., triplet energy migration for TTA-UC and succeeding singlet energy migration for transferring energy to a collector, takes place. To demonstrate this scheme, a highly fluorescent singlet energy collector was added as the third component of donor-doped acceptor crystalline films. An anthracene-based acceptor containing alkyl chains and a carboxylic moiety is mixed with the triplet donor Pt(II) octaethylporphyrin (PtOEP) and the energy collector 2,5,8,11-tetra- tert-butylperylene (TTBP) in solution, and spin-coating of the mixed solution gives acceptor films of nanofibrous crystals homogeneously doped with PtOEP and TTBP. Interestingly, delocalized singlet excitons in acceptor crystals are found to diffuse effectively over the distance of ~37 nm. Thanks to this high diffusivity, only 0.5 mol% of doped TTBP can harvest most of the singlet excitons, which successfully doubles the solid-state fluorescent quantum yield of acceptor/TTBP blend films to 76%. Furthermore, since the donor PtOEP and the collector TTBP are separately isolated in the nanofibrous acceptor crystals, the singlet back energy transfer from the collector to the donor is effectively avoided. Such efficient singlet energy collection and inhibited back energy transfer processes result in a large increase of UC efficiency up to 9

  9. Photoinduced electron transfer in fixed distance chlorophyll-quinone donor-acceptor molecules

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wasielewski, M.R.; Johnson, D.G.; Svec, W.A.

    1987-01-01

    A series of fixed distance chlorophyll-quinone donor-acceptor molecules have been prepared. The donor consists of either methyl pyropheophorbide a or methyl pyrochlorophyllide a, while the acceptor is either benzoquinone or naphthoquinone. The acceptors are fused to a triptycene spacer group, which in turn is attached to the donors at their vinyl groups. Picosecond transient absorption measurements have been used to identify electron transfer from the lowest excited singlet state of the donor to the acceptor as the mechanism of fluorescence quenching in these molecules. The charge separation rate constants increase from 2 x 10/sup 10/ s/sup -1/ to 4 xmore » 10/sup 11/ s/sup -1/ as the free energy of charge separation increases, while the radical pair recombination rate constants decrease from 1.2 x 10/sup 11/ s/sup -1/ to 2 x 10/sup 9/ s/sup -1/ as the free energy of recombination increases. The resulting total reorganization energy lambda = 0.9 eV.« less

  10. Formation of Light Absorbing Soluble Secondary Organics and Insoluble Polymeric Particles from the Dark Reaction of Catechol and Guaiacol with Fe(III).

    PubMed

    Slikboer, Samantha; Grandy, Lindsay; Blair, Sandra L; Nizkorodov, Sergey A; Smith, Richard W; Al-Abadleh, Hind A

    2015-07-07

    Transition metals such as iron are reactive components of environmentally relevant surfaces. Here, dark reaction of Fe(III) with catechol and guaiacol was investigated in an aqueous solution at pH 3 under experimental conditions that mimic reactions in the adsorbed phase of water. Using UV-vis spectroscopy, liquid chromatography, mass spectrometry, elemental analysis, dynamic light scattering, and electron microscopy techniques, we characterized the reactants, intermediates, and products as a function of reaction time. The reactions of Fe(III) with catechol and guaiacol produced significant changes in the optical spectra of the solutions due to the formation of light absorbing secondary organics and colloidal organic particles. The primary steps in the reaction mechanism were shown to include oxidation of catechol and guaiacol to hydroxy- and methoxy-quinones. The particles formed within a few minutes of reaction and grew to micron-size aggregates after half an hour reaction. The mass-normalized absorption coefficients of the particles were comparable to those of strongly absorbing brown carbon compounds produced by biomass burning. These results could account for new pathways that lead to atmospheric secondary organic aerosol formation and abiotic polymer formation on environmental surfaces mediated by transition metals.

  11. Fe(III) reduction-mediated phosphate removal as vivianite (Fe3(PO4)2⋅8H2O) in septic system wastewater.

    PubMed

    Azam, Hossain M; Finneran, Kevin T

    2014-02-01

    Phosphate is a water contaminant from fertilizers, soaps, and detergents that enters municipal and onsite wastewater from households, businesses, and other commercial operations. Phosphate is a limiting nutrient for algae, and is one of the molecules that promotes eutrophication of water bodies. Phosphate is especially problematic in onsite wastewater because there are few removal mechanisms under normal operating conditions; a system must be amended specifically with compounds to bond to or adsorb phosphate in the septic tank or within the leach field. Vivianite (Fe3(PO4)2⋅8H2O) is a stable mineral formed from ferrous iron and phosphate, often as the result of Fe(III) reducing microbial activity. What was unknown was the concentration of phosphate that could be removed by this process, and whether it was relevant to mixed microbial systems like septic tank wastewater. Data presented here demonstrate that significant concentrations of phosphate (12-14mM) were removed as vivianite in growing cultures of Geobacter metallireducens strain GS-15. Vivianite precipitates were identified on the cell surfaces and within multi cell clusters using TEM-EDX; the mineral phases were directly characterized using XRD. Phosphate was also removed in dilute and raw (undiluted) septic wastewater amended with different forms of Fe(III) including solid phase and soluble Fe(III). Vivianite precipitates were recovered and identified using XRD, along with siderite (ferrous carbonate), which was expected given that the systems were likely bicarbonate buffered. These data demonstrate that ferric iron amendments in septic wastewater increase phosphate removal as the mineral vivianite, and this may be a good strategy for phosphate attenuation in the septic tank portion of onsite wastewater systems. Copyright © 2013 Elsevier Ltd. All rights reserved.

  12. Process for gasification using a synthetic CO.sub.2 acceptor

    DOEpatents

    Lancet, Michael S.; Curran, George P.

    1980-01-01

    A gasification process is disclosed using a synthetic CO.sub.2 acceptor consisting essentially of at least one compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix, the carrier having the general formula Ca.sub.5 (SiO.sub.4).sub.2 CO.sub.3. A method for producing the synthetic CO.sub.2 acceptor is also disclosed.

  13. Dye-Incorporated Polynaphthalenediimide Acceptor for Additive-Free High-Performance All-Polymer Solar Cells.

    PubMed

    Chen, Dong; Yao, Jia; Chen, Lie; Yin, Jingping; Lv, Ruizhi; Huang, Bin; Liu, Siqi; Zhang, Zhi-Guo; Yang, Chunhe; Chen, Yiwang; Li, Yongfang

    2018-04-16

    All-polymer solar cells (all-PSCs) can offer unique advantages for applications in flexible devices, and naphthalene diimide (NDI)-based polymer acceptors are the widely used polymer acceptors. However, their power conversion efficiency (PCE) still lags behind that of state-of-the-art polymer solar cells, due to low light absorption, suboptimal energy levels and the strong aggregation of the NDI-based polymer acceptor. Herein, a rhodanine-based dye molecule was introduced into the NDI-based polymer acceptor by simple random copolymerization and showed an improved light absorption coefficient, an up-shifted lowest unoccupied molecular orbital level and reduced crystallization. Consequently, additive-free all-PSCs demonstrated a high PCE of 8.13 %, which is one of the highest performance characteristics reported for all-PSCs to date. These results indicate that incorporating a dye into the n-type polymer gives insight into the precise design of high-performance polymer acceptors for all-PSCs. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Benzothiadiazole Versus Thiophene: Influence of the Auxiliary Acceptor on the Photovoltaic Properties of Donor-Acceptor-Based Copolymers.

    PubMed

    Li, Zongbo; Weng, Kangkang; Chen, Aihua; Sun, Xiaobo; Wei, Donghui; Yu, Mingming; Huo, Lijun; Sun, Yanming

    2018-01-01

    Two donor-acceptor (D-A) type conjugated copolymers, P1 and P2, are designed and synthesized. A classical benzothiadiazole acceptor is used to replace a thiophene unit in the polymer chain of P1 to obtain P2 terpolymer. Compared with P1, P2 exhibits broader absorption spectra, higher absorption coefficient, deeper lowest unoccupied molecular orbital level, and a relatively lower band gap. As a result, the P2-based solar cell exhibits a high power conversion efficiency (PCE) of 6.60%, with a short-circuit current (J sc ) of 12.43 mA cm -2 , and a fill factor (FF) of 73.1%, which are higher than those of the P1-based device with a PCE of 4.70%, a J sc of 9.43 mA cm -2 , and an FF of 61.6%. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Targeting ideal acceptor-donor materials based on hexabenzocoronene

    NASA Astrophysics Data System (ADS)

    Santos Silva, H.; Metz, Sebastian; Hiorns, Roger C.; Bégué, D.

    2018-06-01

    A series of new hybrid donor-acceptor materials based on hexabenzocoronenes (HBC) functionalized with electron donors is investigated by combining a variety of quantum mechanical and molecular dynamic methodologies for use in organic photovoltaic (OPV) devices. Segments of a low band gap alternating copolymer constructed of benzo[1,2-b;3,4-b]dithiophene and thieno[3,4-c]pyrrole-4,6-dione were attached to the conjugated HBC core. The copolymer was chosen for its known high performance in OPVs, and both moieties were singled out due to their exceptional resistance to photo-oxidation, an important requirement for such applications. The macromolecular topology of these systems are expected to induce supra-molecular columns, such as those common to discotic liquid crystals, conducive to the effective percolation of electrons in OPV devices. A challenge with these systems, that of the mixing of the electronic structures of the donor and acceptor moieties that result in excitonic losses and charge recombination, was diminished by trialling a range of linking units. It was found possible to propose ideal donor-acceptor structures with enhanced charge dissociations and transfers in the π-stacking direction for use in OPV and other organic electronic devices.

  16. Exploring the transferase activity of Ffase from Schwanniomyces occidentalis, a β-fructofuranosidase showing high fructosyl-acceptor promiscuity.

    PubMed

    Piedrabuena, David; Míguez, Noa; Poveda, Ana; Plou, Francisco J; Fernández-Lobato, María

    2016-10-01

    The β-fructofuranosidase from the yeast Schwanniomyces occidentalis (Ffase) produces the prebiotic sugars 6-kestose and 1-kestose by transfructosylation of sucrose, which makes it of biotechnological interest. In this study, the hydrolase and transferase activity of this enzyme was kinetically characterized and its potential to synthesize new fructosylated products explored. A total of 40 hydroxylated compounds were used as potential fructosyl-acceptor alternatives to sucrose. Only 17 of them, including some monosaccharides, disaccharides, and oligosaccharides as well as alditols and glycosides were fructosylated. The best alternative acceptors were the alditols. The major transfer product of the reaction including mannitol was purified and characterized as 1-O-β-D-fructofuranosyl-D-mannitol, whose maximum concentration reached 44 g/L, representing about 7.3 % of total compounds in the mixture and 89 % of all products generated by transfructosylation. The reactions including erythritol produced 35 g/L of an isomer mixture comprising 1- and 4-O-β-D-fructofuranosyl-D-erythritol. In addition, Ffase produced 24 g/L of the disaccharide blastose by direct fructosylation of glucose, which makes it the first enzyme characterized from yeast showing this ability. Thus, novel fructosylated compounds with potential applications in food and pharmaceutical industries can be obtained due to the Ffase fructosyl-acceptor promiscuity.

  17. Coexistence of spin crossover and magnetic ordering in a dendrimeric Fe(III) complex

    NASA Astrophysics Data System (ADS)

    Vorobeva, V. E.; Domracheva, N. E.; Pyataev, A. V.; Gruzdev, M. S.; Chervonova, U. V.

    2015-01-01

    The magnetic properties of a new dendrimeric spin crossover Fe(III) complex, [Fe(L)2]+PF6-, where L = 3,5-di[3,4,5-tris(tetradecyloxy) benzoyloxy]benzoyl-4-salicylidene-N-ethyl-N-ethylene-diamine, are reported for the first time. EPR studies show that this compound undergoes a gradual spin transition in the temperature range 70-300 K and has antiferromagnetic ordering below 10 K. Mössbauer spectroscopy at 5 K confirms the presence of magnetic ordering in the dendrimeric iron complex.

  18. Tetrahydrothiophene 1-oxide as an electron acceptor for Escherichia coli.

    PubMed Central

    Meganathan, R; Schrementi, J

    1987-01-01

    Escherichia coli used tetrahydrothiophene 1-oxide (THTO) as an electron acceptor for anaerobic growth with glycerol as a carbon source; the THTO was reduced to tetrahydrothiophene. Cell extracts also reduced THTO to tetrahydrothiophene in the presence of a variety of electron donors. Chlorate-resistant (chl) mutants (chlA, chlB, chlD, and chlE) were unable to grow with THTO as the electron acceptor. However, growth and THTO reduction by the chlD mutant were restored by high concentrations of molybdate. Similarly, mutants of E. coli that are blocked in the menaquinone (vitamin K2) biosynthetic pathway, i.e., menB, menC, and menD mutants, did not grow with THTO as an electron acceptor. Growth and THTO reduction were restored in these mutants by the presence of appropriate intermediates of the vitamin K biosynthetic pathway. PMID:3294808

  19. Perylene-Diimide Based Donor-Acceptor-Donor Type Small-Molecule Acceptors for Solution-Processable Organic Solar Cells

    NASA Astrophysics Data System (ADS)

    Ganesamoorthy, Ramasamy; Vijayaraghavan, Rajagopalan; Sakthivel, Pachagounder

    2017-12-01

    Development of nonfullerene acceptors plays an important role in the commercial availability of plastic solar cells. We report herein synthesis of bay-substituted donor-acceptor-donor (D-A-D)-type perylene diimide (PDI)-based small molecules (SM-1 to SM-4) by Suzuki coupling method and their use as acceptors in bulk heterojunction organic solar cells (BHJ-OSCs) with poly(3-hexylthiophene) (P3HT) polymer donor. We varied the number of electron-rich thiophene units and the solubilizing side chains and also evaluated the optical and electrochemical properties of the small molecules. The synthesized small molecules were confirmed by Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectroscopy (HR-MS). The small molecules showed extensive and strong absorption in the ultraviolet-visible (UV-Vis) region up to 750 nm, with bandgap (E_{{g}}^{{opt}} ) reduced below <2 eV. The energy levels of small molecules SM-1 to SM-4 were suitable for use as electron-accepting materials. The small molecules showed good thermal stability up to 300°C. BHJ-OSCs with SM-1 and P3HT polymer donor showed maximum power conversion efficiency (PCE) of 0.19% with V oc of 0.30 V, J sc of 1.72 mA cm-2, and fill factor (FF) of 37%. The PCE decreased with the number of thiophene units. The PCE of SM-2 was lower than that of SM-1. This difference in PCE can be explained by the higher aggregation tendency of the bithiophene compared with the thiophene unit. Introduction of the solubilizing group in the bay position increased the aggregation property, leading to much lower PCE than for the small molecules without solubilizing group.

  20. An Analytical Chemistry Experiment in Simultaneous Spectrophotometric Determination of Fe(III) and Cu(II) with Hexacyanoruthenate(II) Reagent.

    ERIC Educational Resources Information Center

    Mehra, M. C.; Rioux, J.

    1982-01-01

    Experimental procedures, typical observations, and results for the simultaneous analysis of Fe(III) and Cu(II) in a solution are discussed. The method is based on selective interaction between the two ions and potassium hexacyanoruthenate(II) in acid solution involving no preliminary sample preparations. (Author/JN)

  1. Fragment charge difference method for estimating donor-acceptor electronic coupling: Application to DNA π-stacks

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.; Rösch, Notker

    2002-09-01

    The purpose of this communication is two-fold. We introduce the fragment charge difference (FCD) method to estimate the electron transfer matrix element HDA between a donor D and an acceptor A, and we apply this method to several aspects of hole transfer electronic couplings in π-stacks of DNA, including systems with several donor-acceptor sites. Within the two-state model, our scheme can be simplified to recover a convenient estimate of the electron transfer matrix element HDA=(1-Δq2)1/2(E2-E1)/2 based on the vertical excitation energy E2-E1 and the charge difference Δq between donor and acceptor. For systems with strong charge separation, Δq≳0.95, one should resort to the FCD method. As favorable feature, we demonstrate the stability of the FCD approach for systems which require an approach beyond the two-state model. On the basis of ab initio calculations of various DNA related systems, we compared three approaches for estimating the electronic coupling: the minimum splitting method, the generalized Mulliken-Hush (GMH) scheme, and the FCD approach. We studied the sensitivity of FCD and GMH couplings to the donor-acceptor energy gap and found both schemes to be quite robust; they are applicable also in cases where donor and acceptor states are off resonance. In the application to π-stacks of DNA, we demonstrated for the Watson-Crick pair dimer [(GC),(GC)] how structural changes considerably affect the coupling strength of electron hole transfer. For models of three Watson-Crick pairs, we showed that the two-state model significantly overestimates the hole transfer coupling whereas simultaneous treatment of several states leads to satisfactory results.

  2. Microbial community composition during anaerobic mineralization of tert-butyl alcohol (TBA) in fuel-contaminated aquifer material.

    PubMed

    Wei, Na; Finneran, Kevin T

    2011-04-01

    Anaerobic mineralization of tert-butyl alcohol (TBA) and methyl tert-butyl ether (MTBE) were studied in sediment incubations prepared with fuel-contaminated aquifer material. Microbial community compositions in all incubations were characterized by amplified ribosomal DNA restriction analysis (ARDRA). The aquifer material mineralized 42.3±9.9% of [U-(14)C]-TBA to 14CO2 without electron acceptor amendment. Fe(III), sulfate, and Fe(III) plus anthraquinone-2,6-disulfonate addition also promoted U-[14C]-TBA mineralization at levels similar to those of the unamended controls. Nitrate actually inhibited TBA mineralization relative to unamended controls. In contrast to TBA, [U-(14)C]-MTBE was not significantly mineralized in 400 days regardless of electron acceptor amendment. Microbial community analysis indicated that the abundance of one dominant clone group correlated closely with anaerobic TBA mineralization. The clone was phylogenetically distinct from known aerobic TBA-degrading microorganisms, Fe(III)- or sulfate-reducing bacteria. It was most closely associated with organisms belonging to the alphaproteobacteria. Microbial communities were different in MTBE and TBA amended incubations. Shannon indices and Simpson indices (statistical community comparison tools) both demonstrated that microbial community diversity decreased in incubations actively mineralizing TBA, with distinct "dominant" clones developing. These data contribute to our understanding of anaerobic microbial transformation of fuel oxygenates in contaminated aquifer material and the organisms that may catalyze the reactions.

  3. Exploring the formation pathways of donor-acceptor catenanes in aqueous dynamic combinatorial libraries.

    PubMed

    Cougnon, Fabien B L; Au-Yeung, Ho Yu; Pantoş, G Dan; Sanders, Jeremy K M

    2011-03-09

    The discovery through dynamic combinatorial chemistry (DCC) of a new generation of donor-acceptor [2]catenanes highlights the power of DCC to access unprecedented structures. While conventional thinking has limited the scope of donor-acceptor catenanes to strictly alternating stacks of donor (D) and acceptor (A) aromatic units, DCC is demonstrated in this paper to give access to unusual DAAD, DADD, and ADAA stacks. Each of these catenanes has specific structural requirements, allowing control of their formation. On the basis of these results, and on the observation that the catenanes represent kinetic bottlenecks in the reaction pathway, we propose a mechanism that explains and predicts the structures formed. Furthermore, the spontaneous assembly of catenanes in aqueous dynamic systems gives a fundamental insight into the role played by hydrophobic effect and donor-acceptor interactions when building such complex architectures.

  4. Morphological study on small molecule acceptor-based organic solar cells with efficiencies beyond 7% (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Ma, Wei; Yan, He

    2015-10-01

    Despite the essential role of fullerenes in achieving best-performance organic solar cells (OSCs), fullerene acceptors have several drawbacks including poor light absorption, high-cost production and purification. For this reason, small molecule acceptor (SMA)-based OSCs have attracted much attention due to the easy tunability of electronic and optical properties of SMA materials. In this study, polymers with temperature dependent aggregation behaviors are combined with various small molecule acceptor materials, which lead to impressive power conversion efficiencies of up to 7.3%. The morphological and aggregation properties of the polymer:small molecule blends are studied in details. It is found that the temperature-dependent aggregation behavior of polymers allows for the processing of the polymer solutions at moderately elevated temperature, and more importantly, controlled aggregation and strong crystallization of the polymer during the film cooling and drying process. This results in a well-controlled and near-ideal polymer:small molecule morphology that is controlled by polymer aggregation during warm casting and thus insensitive to the choice of small molecules. As a result, several cases of highly efficient (PCE between 6-7.3%) SMA OSCs are achieved. The second part of this presentation will describe the morphology of a new small molecule acceptor with a unique 3D structure. The relationship between molecular structure and morphology is revealed.

  5. Interactions of the periplasmic binding protein CeuE with Fe(III) n-LICAM4- siderophore analogues of varied linker length

    NASA Astrophysics Data System (ADS)

    Wilde, Ellis J.; Hughes, Adam; Blagova, Elena V.; Moroz, Olga V.; Thomas, Ross P.; Turkenburg, Johan P.; Raines, Daniel J.; Duhme-Klair, Anne-Kathrin; Wilson, Keith S.

    2017-04-01

    Bacteria use siderophores to mediate the transport of essential Fe(III) into the cell. In Campylobacter jejuni the periplasmic binding protein CeuE, an integral part of the Fe(III) transport system, has adapted to bind tetradentate siderophores using a His and a Tyr side chain to complete the Fe(III) coordination. A series of tetradentate siderophore mimics was synthesized in which the length of the linker between the two iron-binding catecholamide units was increased from four carbon atoms (4-LICAM4-) to five, six and eight (5-, 6-, 8-LICAM4-, respectively). Co-crystal structures with CeuE showed that the inter-planar angles between the iron-binding catecholamide units in the 5-, 6- and 8-LICAM4- structures are very similar (111°, 110° and 110°) and allow for an optimum fit into the binding pocket of CeuE, the inter-planar angle in the structure of 4-LICAM4- is significantly smaller (97°) due to restrictions imposed by the shorter linker. Accordingly, the protein-binding affinity was found to be slightly higher for 5- compared to 4-LICAM4- but decreases for 6- and 8-LICAM4-. The optimum linker length of five matches that present in natural siderophores such as enterobactin and azotochelin. Site-directed mutagenesis was used to investigate the relative importance of the Fe(III)-coordinating residues H227 and Y288.

  6. Group III Acceptors with Shallow and Deep Levels in Silicon Carbide: ESR and ENDOR Studies

    NASA Astrophysics Data System (ADS)

    Il'in, I. V.; Uspenskaya, Yu. A.; Kramushchenko, D. D.; Muzafarova, M. V.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.

    2018-04-01

    Results of investigations of Group III acceptors (B, Al, and Ga) in crystals of silicon carbide using the most informative electron spin resonance and electron nuclear double resonance methods are presented. Structural models of the acceptors with shallow and deep levels are considered. In addition to the data obtained earlier, studies using high-frequency magnetic resonance were obtained, which allowed revealing orthorhombic deviations from the axial symmetry for the deep acceptors; theoretical analysis explains experimentally found shifts of g factors for the deep acceptors arising due to the orthorhombic deviations, which appear probably due to the Jahn-Teller effect.

  7. High-Performance All-Polymer Solar Cells Achieved by Fused Perylenediimide-Based Conjugated Polymer Acceptors.

    PubMed

    Yin, Yuli; Yang, Jing; Guo, Fengyun; Zhou, Erjun; Zhao, Liancheng; Zhang, Yong

    2018-05-09

    We report three n-type polymeric electron acceptors (PFPDI-TT, PFPDI-T, and PFPDI-Se) based on the fused perylene diimide (FPDI) and thieno[3,2- b]thiophene, thiophene, or selenophene units for all-polymer solar cells (all-PSCs). These FPDI-based polymer acceptors exhibit strong absorption between 350 and 650 nm with wide optical bandgap of 1.86-1.91 eV, showing good absorption compensation with the narrow bandgap polymer donor. The lowest unoccupied molecular orbital (LUMO) energy levels were located at around -4.11 eV, which are comparable with those of the fullerene derivatives and other small molecular electron acceptors. The conventional all-PSCs based on the three polymer acceptors and PTB7-Th as polymer donor gave remarkable power conversion efficiencies (PCEs) of >6%, and the PFPDI-Se-based all-PSC achieved the highest PCE of 6.58% with a short-circuit current density ( J sc ) of 13.96 mA/cm 2 , an open-circuit voltage ( V oc ) of 0.76 V, and a fill factor (FF) of 62.0%. More interestingly, our results indicate that the photovoltaic performances of the FPDI-based polymer acceptors are mainly determined by the FPDI unit with a small effect from the comonomers, which is quite different from the others reported rylenediimide-based polymer acceptors. This intriguing phenomenon is speculated as the huge geometry configuration of the FPDI unit, which minimizes the effect of the comonomer. These results highlight a promising future for the application of the FPDI-based polymer acceptors in the highly efficient all-PSCs.

  8. Enhanced biodegradation of cyclotetramethylenetetranitramine (HMX) under mixed electron-acceptor condition.

    PubMed

    Boopathy, R

    2001-02-01

    The biodegradation of cyclotetramethylenetetranitramine, commonly known as 'high melting explosive' (HMX), under various electron-acceptor conditions was investigated using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that the HMX was biodegraded under sulfate reducing, nitrate reducing, fermenting, methanogenic, and mixed electron accepting conditions. However, the rates of degradation varied among the various conditions studied. The fastest removal of HMX (from 22 ppm on day 0 to < 0.05 ppm on day 11) was observed under mixed electron-acceptor conditions, followed in order by sulfate reducing, fermenting, methanogenic, and nitrate reducing conditions. Under aerobic conditions, HMX was not biodegraded, which indicated that HMX degradation takes place under anaerobic conditions via reduction. HMX was converted to methanol and chloroform under mixed electron-acceptor conditions. This study showed evidence for HMX degradation under anaerobic conditions in a mixed microbial population system similar to any contaminated field sites, where a heterogeneous population exists.

  9. Ferric iron amendment increases Fe(III)-reducing microbial diversity and carbon oxidation in on-site wastewater systems.

    PubMed

    Azam, Hossain M; Finneran, Kevin T

    2013-01-01

    Onsite wastewater systems, or septic tanks, serve approximately 25% of the United States population; they are therefore a critical component of the total carbon balance for natural water bodies. Septic tanks operate under strictly anaerobic conditions, and fermentation is the dominant process driving carbon transformation. Nitrate, Fe(III), and sulfate reduction may be operating to a limited extent in any given septic tank. Electron acceptor amendments will increase carbon oxidation, but nitrate is toxic and sulfate generates corrosive sulfides, which may damage septic system infrastructure. Fe(III) reducing microorganisms transform all major classes of organic carbon that are dominant in septic wastewater: low molecular weight organic acids, carbohydrate monomers and polymers, and lipids. Fe(III) is not toxic, and the reduction product Fe(II) is minimally disruptive if the starting Fe(III) is added at 50-150 mg L(-1). We used (14)C radiolabeled acetate, lactate, propionate, butyrate, glucose, starch, and oleic acid to demonstrate that short and long-term carbon oxidation is increased when different forms of Fe(III) are amended to septic wastewater. The rates of carbon mineralization to (14)CO(2) increased 2-5 times (relative to unamended systems) in the presence of Fe(III). The extent of mineralization reached 90% for some carbon compounds when Fe(III) was present, compared to levels of 50-60% in the absence of Fe(III). (14)CH(4) was not generated when Fe(III) was added, demonstrating that this strategy can limit methane emissions from septic systems. Amplified 16S rDNA restriction analysis indicated that unique Fe(III)-reducing microbial communities increased significantly in Fe(III)-amended incubations, with Fe(III)-reducers becoming the dominant microbial community in several incubations. The form of Fe(III) added had a significant impact on the rate and extent of mineralization; ferrihydrite and lepidocrocite were favored as solid phase Fe(III) and chelated Fe(III

  10. Biodegradation of RDX by Stimulating Humic Substance- and Fe(III) - Reduction

    DTIC Science & Technology

    2007-06-19

    Sediments with Quinones and Humus as Terminal Electron Acceptors. Appl. Environ. Microbiol. 67:4471-4478. 10. Coates, J. D., D. J. Ellis, E. L...167. 57. Stevenson, F. J. 1982. Humus chemistry genesis, composition, reactions. Wiley Interscience, New York. 58. Stolz, J. F., D. R. Lovley, and

  11. Solvent as electron donor: Donor/acceptor electronic coupling is a dynamical variable

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Castner, E.W. Jr.; Kennedy, D.; Cave, R.J.

    2000-04-06

    The authors combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken-Hush (GMH) theory in the study of electron-transfer reactions and electron donor-acceptor interactions. The study focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state acceptors. The experimental results from femtosecond dynamical measurements fall into three categories: six coumarin acceptors reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 (7-(dimethylamino)-4-(trifluoromethyl)-coumarin), and reductive quenching dynamics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene. Applying a combination of molecular dynamicsmore » trajectories, semiempirical quantum mechanical calculations (of the relevant adiabatic electronic states), and GMH theory to the C152/DMA photoreaction, the authors calculate the electron donor/acceptor interaction parameter H{sub DA} at various time frames, H{sub DA} is strongly modulated by both inner-sphere and outer-sphere nuclear dynamics, leading us to conclude that H{sub DA} must be considered as a dynamical variable.« less

  12. Single molecule-level study of donor-acceptor interactions and nanoscale environment in blends

    NASA Astrophysics Data System (ADS)

    Quist, Nicole; Grollman, Rebecca; Rath, Jeremy; Robertson, Alex; Haley, Michael; Anthony, John; Ostroverkhova, Oksana

    2017-02-01

    Organic semiconductors have attracted considerable attention due to their applications in low-cost (opto)electronic devices. The most successful organic materials for applications that rely on charge carrier generation, such as solar cells, utilize blends of several types of molecules. In blends, the local environment strongly influences exciton and charge carrier dynamics. However, relationship between nanoscale features and photophysics is difficult to establish due to the lack of necessary spatial resolution. We use functionalized fluorinated pentacene (Pn) molecule as single molecule probes of intermolecular interactions and of the nanoscale environment in blends containing donor and acceptor molecules. Single Pn donor (D) molecules were imaged in PMMA in the presence of acceptor (A) molecules using wide-field fluorescence microscopy. Two sample configurations were realized: (i) a fixed concentration of Pn donor molecules, with increasing concentration of acceptor molecules (functionalized indenflouorene or PCBM) and (ii) a fixed concentration of acceptor molecules with an increased concentration of the Pn donor. The D-A energy transfer and changes in the donor emission due to those in the acceptor- modified polymer morphology were quantified. The increase in the acceptor concentration was accompanied by enhanced photobleaching and blinking of the Pn donor molecules. To better understand the underlying physics of these processes, we modeled photoexcited electron dynamics using Monte Carlo simulations. The simulated blinking dynamics were then compared to our experimental data, and the changes in the transition rates were related to the changes in the nanoscale environment. Our study provides insight into evolution of nanoscale environment during the formation of bulk heterojunctions.

  13. Sterilisation: characteristics of vasectomy acceptors in Delhi.

    PubMed

    Sarkar, N N

    1993-01-01

    The place of vasectomy within the sterilisation programme in Delhi over the period 1983-88 is reviewed and data on vasectomy acceptance and characteristics of acceptors are analysed. Findings suggest a need to improve the strategy for the promotion of vasectomy within the metropolis.

  14. [Effects of iron on azoreduction by Shewanella decolorationis S12].

    PubMed

    Chen, Xing-Juan; Xu, Mei-Ying; Sun, Guo-Ping

    2010-01-01

    The effects of soluble and insoluble Fe(III) on anaerobic azoreduction by Shewanella decolorationis S12 were examined in a series of experiments. Results showed that the effects of iron on anaerobic azoreduction depended on the solubility and concentration of the compounds. Azoreduction was inhibited by insoluble Fe(III) and 0.05-2 mmol/L Fe2 O3 all decelerated the azoreduction activity of 0.2 mmol/L amaranth, but the increase in the concentrations of Fe2O3 did not cause an increasing inhibition. Soluble Fe(III) of which concentration less than 0.4 mmol/L enhanced azoreduction activity of 0.2 mmol/L amaranth but there was no linear relationship between the concentration of soluble Fe(III) and azoreduction activity. Soluble Fe(III) of which concentration more than 1 mmol/L inhibited azoreduction activity of 0.2 mmol/L amaranth and an increasing concentration resulted in an increased inhibition. The inhibition was strengthened under the conditions of limited electron donor. On the other hand, soluble Fe(III) and Fe(II) could relieve the inhibition of azoreduction by dicumarol which blocked quinone cycle. It suggests that in addition to quinone cycle, there is a Fe(III) <--> Fe(II) cycle shuttling electrons in cytoplasmic and periplasmic environment. That is the reason why low concentration of soluble Fe(III) or Fe (II) can enhance azoreduction of S. decolorationis S12. It also indicates that insoluble Fe(III) and high concentration of soluble Fe(III) do compete with azo dye for electrons once it acts as electron acceptor. Thus, when iron and azo dye coexisted, iron could serve as an electron transfer agent or electron competitive inhibitor for anaerobic azoreduction under different conditions. High efficiency of azoreduction can be achieved through controlling the solubility and concentration of irons.

  15. Coupling of phonons with excitons bound to different donors and acceptors in hexagonal GaN

    NASA Astrophysics Data System (ADS)

    Korona, K. P.; Wysmoek, A.; Kuhl, J.; Kamiska, M.; Baranowski, J. M.; Look, D. C.; Park, S. S.

    2006-06-01

    Time-resolved measurements of GaN with different donors (oxygen or silicon) and acceptors (zinc or magnesium) showed pronounced bound exciton lines and their phonon replicas. The analysis included three phonon modes characteristic for the wurtzite (hexagonal) phase: A1(LO), E1(TO) and E2H. It was shown that relative amplitudes of replicas depended upon the chemical nature of the defects that the bind excitons. The replicas were stronger for acceptor- than for donor-related features. Huang-Rhys factors S = 0.06 +/- 0.02 and S = 0.025 +/- 0.01, were found for the A0X and the D0X LO replicas, respectively. A significant difference in phonon coupling to silicon and oxygen donor bound excitons has been observed.

  16. Amphorous hydrated Fe(III) sulfate: metastable product and bio-geochemical marker of iron oxidizing thiobacilli

    NASA Astrophysics Data System (ADS)

    Lazaroff, Norman; Jollie, John; Dugan, Patrick R.

    1998-07-01

    Chemolithotrophic iron oxidation by Thiobacillus ferrooxidans and other iron oxidizing thiobacilli produce an Fe(III) sulfato complex that polymerizes as x-ray amorphous filaments approximately 40 nm in diameter. The precursor complex in solutionis seen by ATR-FTIR spectroscopy to have a sulfate spectrum resembling the v(subscript 3) and v(subscript 1) vibrational modes of the precipitated polymer. Chemically similar precipitates prepared by oxidation of acid ferrous sulfate with hydrogen peroxide have a different micromorphology, higher iron/sulfur ratio and acid solubility than the bacterial product. They possess coalescing globular microstructures composed of compacted micro-fibrils. Scanning electron microscopy and diffuse reflectance FTIR show the formation of iron polymer on the surface of immobilized cells of T. ferrooxidans, oxidizing iron during the corrosion of steel. Although spatially separated form the steel coupons by a membrane filter, the cell walls become covered with tufts of amorphous hydrated Fe(III) sulfate. The metastable polymer is converted to crystalline goethite, lepidocrocite, and magnetite in that order, as the pH rises due to proton reduction at cathodic sites on the steel. The instability of the iron polymer to changes in pH is also evidenced by the loss of sulfate when washed with lithium hydroxide solution at pH 8. Under those conditions there is little change in micromorphology, but restoration of sulfate with sulfuric acid at pH 2.5, fails to re-establish the original chemical structure. Adding sulfate salts of appropriate cations to solutions of the Fe(III) sulfato complex or suspensions of its precipitated polymer in dilute sulfuric acid, result in dissociation of the metastable complex followed by crystallization of ferric ions and sulfate in jarosites. Jarosites and other derivatives of iron precipitation by iron oxidizing thiobacilli, form conspicuous deposits in areas of natural pyrite leaching. The role of iron oxidizing

  17. Bacterial manganese reduction and growth with manganese oxide as the sole electron acceptor

    NASA Technical Reports Server (NTRS)

    Myers, Charles R.; Nealson, Kenneth H.

    1988-01-01

    Microbes that couple growth to the reduction of manganese could play an important role in the biogeochemistry of certain anaerobic environments. Such a bacterium, Alteromonas putrefaciens MR-1, couples its growth to the reduction of manganese oxides only under anaerobic conditions. The characteristics of this reduction are consistent with a biological, and not an indirect chemical, reduction of manganese, which suggest that this bacterium uses manganic oxide as a terminal electron acceptor. It can also utilize a large number of other compounds as terminal electron acceptors; this versatility could provide a distinct advantage in environments where electron-acceptor concentrations may vary.

  18. Threshold-like complexation of conjugated polymers with small molecule acceptors in solution within the neighbor-effect model.

    PubMed

    Sosorev, Andrey Yu; Parashchuk, Olga D; Zapunidi, Sergey A; Kashtanov, Grigoriy S; Golovnin, Ilya V; Kommanaboyina, Srikanth; Perepichka, Igor F; Paraschuk, Dmitry Yu

    2016-02-14

    In some donor-acceptor blends based on conjugated polymers, a pronounced charge-transfer complex (CTC) forms in the electronic ground state. In contrast to small-molecule donor-acceptor blends, the CTC concentration in polymer:acceptor solution can increase with the acceptor content in a threshold-like way. This threshold-like behavior was earlier attributed to the neighbor effect (NE) in the polymer complexation, i.e., next CTCs are preferentially formed near the existing ones; however, the NE origin is unknown. To address the factors affecting the NE, we record the optical absorption data for blends of the most studied conjugated polymers, poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and poly(3-hexylthiophene) (P3HT), with electron acceptors of fluorene series, 1,8-dinitro-9,10-antraquinone (), and 7,7,8,8-tetracyanoquinodimethane () in different solvents, and then analyze the data within the NE model. We have found that the NE depends on the polymer and acceptor molecular skeletons and solvent, while it does not depend on the acceptor electron affinity and polymer concentration. We conclude that the NE operates within a single macromolecule and stems from planarization of the polymer chain involved in the CTC with an acceptor molecule; as a result, the probability of further complexation with the next acceptor molecules at the adjacent repeat units increases. The steric and electronic microscopic mechanisms of NE are discussed.

  19. Constraint-based modeling of carbon fixation and the energetics of electron transfer in Geobacter metallireducens.

    PubMed

    Feist, Adam M; Nagarajan, Harish; Rotaru, Amelia-Elena; Tremblay, Pier-Luc; Zhang, Tian; Nevin, Kelly P; Lovley, Derek R; Zengler, Karsten

    2014-04-01

    Geobacter species are of great interest for environmental and biotechnology applications as they can carry out direct electron transfer to insoluble metals or other microorganisms and have the ability to assimilate inorganic carbon. Here, we report on the capability and key enabling metabolic machinery of Geobacter metallireducens GS-15 to carry out CO2 fixation and direct electron transfer to iron. An updated metabolic reconstruction was generated, growth screens on targeted conditions of interest were performed, and constraint-based analysis was utilized to characterize and evaluate critical pathways and reactions in G. metallireducens. The novel capability of G. metallireducens to grow autotrophically with formate and Fe(III) was predicted and subsequently validated in vivo. Additionally, the energetic cost of transferring electrons to an external electron acceptor was determined through analysis of growth experiments carried out using three different electron acceptors (Fe(III), nitrate, and fumarate) by systematically isolating and examining different parts of the electron transport chain. The updated reconstruction will serve as a knowledgebase for understanding and engineering Geobacter and similar species.

  20. Triplet Tellurophene-Based Acceptors for Organic Solar Cells.

    PubMed

    Yang, Lei; Gu, Wenxing; Lv, Lei; Chen, Yusheng; Yang, Yufei; Ye, Pan; Wu, Jianfei; Hong, Ling; Peng, Aidong; Huang, Hui

    2018-01-22

    Triplet materials have been employed to achieve high-performing organic solar cells (OSCs) by extending the exciton lifetime and diffusion distances, while the triplet non-fullerene acceptor materials have never been reported for bulk heterojunction OSCs. Herein, for the first time, three triplet molecular acceptors based on tellurophene with different degrees of ring fusing were designed and synthesized for OSCs. Significantly, these molecules have long exciton lifetime and diffusion lengths, leading to efficient power conversion efficiency (7.52 %), which is the highest value for tellurophene-based OSCs. The influence of the extent of ring fusing on molecular geometry and OSCs performance was investigated to show the power conversion efficiencies (PCEs) continuously increased along with increasing the extent of ring fusing. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Molecular origin of photovoltaic performance in donor- block-acceptor all-conjugated block copolymers

    DOE PAGES

    Smith, Kendall A.; Lin, Yen -Hao; Mok, Jorge W.; ...

    2015-11-03

    All-conjugated block copolymers may be an effective route to self-assembled photovoltaic devices, but we lack basic information on the relationship between molecular characteristics and photovoltaic performance. Here, we synthesize a library of poly(3-hexylthiophene) (P3HT) block poly((9,9-dialkylfluorene)-2,7-diyl-alt-[4,7-bis(alkylthiophen-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (PFTBT) donor- block-acceptor all-conjugated block copolymers and carry out a comprehensive study of processing conditions, crystallinity, domain sizes, and side-chain structure on photovoltaic device performance. We find that all block copolymers studied exhibit an out-of-plane crystal orientation after deposition, and on thermal annealing at high temperatures the crystal orientation flips to an in-plane orientation. By varying processing conditions on polymer photovoltaic devices, we showmore » that the crystal orientation has only a modest effect (15-20%) on photovoltaic performance. The addition of side-chains to the PFTBT block is found to decrease photovoltaic power conversion efficiencies by at least an order of magnitude. Through grazing-incidence X-ray measurements we find that the addition of side-chains to the PFTBT acceptor block results in weak segregation and small (< 10 nm) block copolymer self-assembled donor and acceptor domains. This work is the most comprehensive to date on all-conjugated block copolymer systems and suggests that photovoltaic performance of block copolymers depends strongly on the miscibility of donor and acceptor blocks, which impacts donor and acceptor domain sizes and purity. Lastly, strategies for improving the device performance of block copolymer photovoltaics should seek to increase segregation between donor and acceptor polymer domains.« less

  2. Molecular origin of photovoltaic performance in donor- block-acceptor all-conjugated block copolymers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smith, Kendall A.; Lin, Yen -Hao; Mok, Jorge W.

    All-conjugated block copolymers may be an effective route to self-assembled photovoltaic devices, but we lack basic information on the relationship between molecular characteristics and photovoltaic performance. Here, we synthesize a library of poly(3-hexylthiophene) (P3HT) block poly((9,9-dialkylfluorene)-2,7-diyl-alt-[4,7-bis(alkylthiophen-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (PFTBT) donor- block-acceptor all-conjugated block copolymers and carry out a comprehensive study of processing conditions, crystallinity, domain sizes, and side-chain structure on photovoltaic device performance. We find that all block copolymers studied exhibit an out-of-plane crystal orientation after deposition, and on thermal annealing at high temperatures the crystal orientation flips to an in-plane orientation. By varying processing conditions on polymer photovoltaic devices, we showmore » that the crystal orientation has only a modest effect (15-20%) on photovoltaic performance. The addition of side-chains to the PFTBT block is found to decrease photovoltaic power conversion efficiencies by at least an order of magnitude. Through grazing-incidence X-ray measurements we find that the addition of side-chains to the PFTBT acceptor block results in weak segregation and small (< 10 nm) block copolymer self-assembled donor and acceptor domains. This work is the most comprehensive to date on all-conjugated block copolymer systems and suggests that photovoltaic performance of block copolymers depends strongly on the miscibility of donor and acceptor blocks, which impacts donor and acceptor domain sizes and purity. Lastly, strategies for improving the device performance of block copolymer photovoltaics should seek to increase segregation between donor and acceptor polymer domains.« less

  3. Energy transfer and correlations in cavity-embedded donor-acceptor configurations.

    PubMed

    Reitz, Michael; Mineo, Francesca; Genes, Claudiu

    2018-06-13

    The rate of energy transfer in donor-acceptor systems can be manipulated via the common interaction with the confined electromagnetic modes of a micro-cavity. We analyze the competition between the near-field short range dipole-dipole energy exchange processes and the cavity mediated long-range interactions in a simplified model consisting of effective two-level quantum emitters that could be relevant for molecules in experiments under cryogenic conditions. We find that free-space collective incoherent interactions, typically associated with sub- and superradiance, can modify the traditional resonant energy transfer scaling with distance. The same holds true for cavity-mediated collective incoherent interactions in a weak-coupling but strong-cooperativity regime. In the strong coupling regime, we elucidate the effect of pumping into cavity polaritons and analytically identify an optimal energy flow regime characterized by equal donor/acceptor Hopfield coefficients in the middle polariton. Finally we quantify the build-up of quantum correlations in the donor-acceptor system via the two-qubit concurrence as a measure of entanglement.

  4. Vacancy clustering and acceptor activation in nitrogen-implanted ZnO

    NASA Astrophysics Data System (ADS)

    Børseth, Thomas Moe; Tuomisto, Filip; Christensen, Jens S.; Monakhov, Edouard V.; Svensson, Bengt G.; Kuznetsov, Andrej Yu.

    2008-01-01

    The role of vacancy clustering and acceptor activation on resistivity evolution in N ion-implanted n -type hydrothermally grown bulk ZnO has been investigated by positron annihilation spectroscopy, resistivity measurements, and chemical profiling. Room temperature 220keV N implantation using doses in the low 1015cm-2 range induces small and big vacancy clusters containing at least 2 and 3-4 Zn vacancies, respectively. The small clusters are present already in as-implanted samples and remain stable up to 1000°C with no significant effect on the resistivity evolution. In contrast, formation of the big clusters at 600°C is associated with a significant increase in the free electron concentration attributed to gettering of amphoteric Li impurities by these clusters. Further annealing at 800°C results in a dramatic decrease in the free electron concentration correlated with activation of 1016-1017cm-3 acceptors likely to be N and/or Li related. The samples remain n type, however, and further annealing at 1000°C results in passivation of the acceptor states while the big clusters dissociate.

  5. Incorporating fluorinated moieties in fully conjugated donor-acceptor block copolymers

    NASA Astrophysics Data System (ADS)

    Lee, Youngmin; Wang, Qing; Gomez, Enrique D.

    Fully conjugated donor-acceptor block copolymers are promising candidates for photovoltaics due to their ability to microphase separate at length scales commensurate with exciton diffusion lengths. These materials can also serve as model systems to study the relationship between molecular structure, microstructure, and optoelectronic properties of conjugated polymers. The development of new donor-acceptor block copolymers relies on the manipulation of the chemical structure to fine tune properties and improve overall performance when employed in photovoltaic devices. To this end, we have demonstrated the incorporation of fluorinated moieties in conjugated block copolymers. The introduction of fluorine, a strong electron withdrawing element, is known to influence phase separation and the bandgap, and as a result, optoelectronic properties. Fluorine was introduced to the acceptor block of poly(3-hexylthiophene-2,5-diyl)-block-poly((9,9-bis(2-octyl)fluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5 ',5?-diyl) (P3HT- b-PFTBT). PFTBTs were prepared with di-fluorinated and mono-fluorinated TBT. We find that fluorination impacts the bandgap, morphology and performance in devices.

  6. Acceptor Specificity of the Pasteurella Hyaluronan and Chondroitin Synthases and Production of Chimeric Glycosaminoglycans*†

    PubMed Central

    Tracy, Breca S.; Avci, Fikri Y.; Linhardt, Robert J.; DeAngelis, Paul L.

    2014-01-01

    The hyaluronan (HA) synthase, PmHAS, and the chondroitin synthase, PmCS, from the Gram-negative bacterium Pasteurella multocida polymerize the glycosaminoglycan (GAG) sugar chains HA or chondroitin, respectively. The recombinant Escherichia coli-derived enzymes were shown previously to elongate exogenously supplied oligosaccharides of their cognate GAG (e.g. HA elongated by PmHAS). Here we show that oligosaccharides and polysaccharides of certain noncognate GAGs (including sulfated and iduronic acid-containing forms) are elongated by PmHAS (e.g. chondroitin elongated by PmHAS) or PmCS. Various acceptors were tested in assays where the synthase extended the molecule with either a single monosaccharide or a long chain (~102–4 sugars). Certain GAGs were very poor acceptors in comparison to the cognate molecules, but elongated products were detected nonetheless. Overall, these findings suggest that for the interaction between the acceptor and the enzyme (a) the orientation of the hydroxyl at the C-4 position of the hexosamine is not critical, (b) the conformation of C-5 of the hexuronic acid (glucuronic versus iduronic) is not crucial, and (c) additional negative sulfate groups are well tolerated in certain cases, such as on C-6 of the hexosamine, but others, including C-4 sulfates, were not or were poorly tolerated. In vivo, the bacterial enzymes only process unsulfated polymers; thus it is not expected that the PmCS and PmHAS catalysts would exhibit such relative relaxed sugar specificity by acting on a variety of animal-derived sulfated or epimerized GAGs. However, this feature allows the chemoenzymatic synthesis of a variety of chimeric GAG polymers, including mimics of proteoglycan complexes. PMID:17099217

  7. Influence of the local environment on Mn acceptors in GaAs

    NASA Astrophysics Data System (ADS)

    Lee, Donghun; Gohlke, David; Benjamin, Anne; Gupta, Jay A.

    2015-04-01

    As transistors continue to shrink toward nanoscale dimensions, their characteristics are increasingly dependent on the statistical variations of impurities in the semiconductor material. The scanning tunneling microscope (STM) can be used to not only study prototype devices with atomically precise placement of impurity atoms, but can also probe how the properties of these impurities depend on the local environment. Tunneling spectroscopy of Mn acceptors in GaAs indicates that surface-layer Mn act as a deep acceptor, with a hole binding energy that can be tuned by positioning charged defects nearby. Band bending induced by the tip or by these defects can also tune the ionization state of the acceptor complex, evident as a ring-like contrast in STM images. The interplay of these effects is explored over a wide range of defect distances, and understood using iterative simulations of tip-induced band bending.

  8. Next Generation Highly Conducting Organic Films Using Novel Donor-Acceptor Molecules for Opto-electronic Applications

    DTIC Science & Technology

    2010-06-01

    addition, a new class of donor molecules was invented in the course of the DRI program. 2.1 Polymer Based Donor-acceptor Material The following work by...average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data...information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information

  9. Photoinduced electron transfer between Fe(III) and adenosine triphosphate-BODIPY conjugates: Application to alkaline-phosphatase-linked immunoassay.

    PubMed

    Lin, Jia-Hui; Yang, Ya-Chun; Shih, Ya-Chen; Hung, Szu-Ying; Lu, Chi-Yu; Tseng, Wei-Lung

    2016-03-15

    Fluorescent boron dipyrromethene (BODIPY) analogs are often used as sensors for detecting various species because of their relatively high extinction coefficients, outstanding fluorescence quantum yields, photostability, and pH-independent fluorescence. However, there is little-to-no information in the literature that describes the use of BODIPY analogs for detecting alkaline phosphatase (ALP) activity and inhibition. This study discovered that the fluorescence of BODIPY-conjugated adenosine triphosphate (BODIPY-ATP) was quenched by Fe(III) ions through photoinduced electron transfer. The ALP-catalyzed hydrolysis of BODIPY-ATP resulted in the formation of BODIPY-adenosine and phosphate ions. The fluorescence of the generated BODIPY-adenosine was insensitive to the change in the concentration of Fe(III) ions. Thus, the Fe(III)-induced fluorescence quenching of BODIPY-ATP can be paired with its ALP-mediated dephosphorylation to design a turn-on fluorescence probe for ALP sensing. A method detection limit at a signal-to-noise ratio of 3 for ALP was estimated to be 0.02 units/L (~6 pM; 1 ng/mL). This probe was used for the screening of ALP inhibitors, including Na3VO4, imidazole, and arginine. Because ALP is widely used in enzyme-linked immunosorbent assays, the probe was coupled to an ALP-linked immunosorbent assay for the sensitive and selective detection of immunoglobulin G (IgG). The lowest detectable concentration for IgG in this system was 5 ng/mL. Compared with the use of 3,6-fluorescein diphosphate as a signal reporter in an ALP-linked immunosorbent assay, the proposed system provided comparable sensitivity, large linear range, and high stability over temperature and pH changes. Copyright © 2015 Elsevier B.V. All rights reserved.

  10. Enhanced nonlinear optical responses in donor-acceptor ionic complexes via photo induced energy transfer.

    PubMed

    Mamidala, Venkatesh; Polavarapu, Lakshminarayana; Balapanuru, Janardhan; Loh, Kian Ping; Xu, Qing-Hua; Ji, Wei

    2010-12-06

    By complexion of donor and acceptor using ionic interactions, the enhanced nonlinear optical responses of donor-acceptor ionic complexes in aqueous solution were studied with 7-ns laser pulses at 532 nm. The optical limiting performance of negatively charged gold nanoparticles or graphene oxide (Acceptor) was shown to be improved significantly when they were mixed with water-soluble, positively-charged porphyrin (Donor) derivative. In contrast, no enhancement was observed when mixing with negatively-charged porphyrin. Transient absorption studies of the donor-acceptor complexes confirmed that the addition of energy transfer pathway were responsible for excited-state deactivation, which results in the observed enhancement. Fluence, angle-dependent scattering and time correlated single photon counting measurements suggested that the enhanced nonlinear scattering due to faster nonradiative decay should play a major role in the enhanced optical limiting responses.

  11. Fundamental Studies on Donor-acceptor Conjugated Polymers Containing 'Heavy' Group 14 and Group 16 Elements

    NASA Astrophysics Data System (ADS)

    Gibson, Gregory Laird

    One advantage of conjugated polymers as organic materials is that their properties may be readily tuned through covalent modifications. This thesis presents studies on the structure-property relationships resulting from single- and double-atom substitutions on an alternating donor-acceptor conjugated polymer. Specifically, single selenium and tellurium atoms have been incorporated into the acceptor monomer in place of sulfur; silicon and germanium atoms have been substituted in place of carbon at the donor monomer bridge position. The carbon-donor/ tellurium-acceptor polymer was synthesized by a post-polymerization reaction sequence and demonstrated the utility of heavy group 16 atoms to red shift a polymer absorption spectrum. Density functional theory calculations point to a new explanation for this result invoking the lower heavy atom ionization energy and reduced aromaticity of acceptor monomers containing selenium and tellurium compared to sulfur. Absorption and emission experiments demonstrate that both silicon and germanium substitutions in the donor slightly blue shift the polymer absorption spectrum. Polymers containing sulfur in the acceptor are the strongest light absorbers of all polymers studied here. Molecular weight and phenyl end capping studies show that molecular weight appears to affect polymer absorption to the greatest degree in a medium molecular weight regime and that these effects have a significant aggregation component. Solar cell devices containing either the silicon- or germanium-donor/selenium-acceptor polymer display improved red light harvesting or hole mobility relative to their structural analogues. Overall, these results clarify the effects of single atom substitution on donor-acceptor polymers and aid in the future design of polymers containing heavy atoms.

  12. Internal structure of acceptor-bound excitons in wide-band-gap wurtzite semiconductors

    NASA Astrophysics Data System (ADS)

    Gil, Bernard; Bigenwald, Pierre; Paskov, Plamen P.; Monemar, Bo

    2010-02-01

    We describe the internal structure of acceptor-bound excitons in wurtzite semiconductors. Our approach consists in first constructing, in the context of angular momentum algebra, the wave functions of the two-hole system that fulfill Pauli’s exclusion’s principle. Second, we construct the acceptor-bound exciton states by adding the electron states in a similar manner that two-hole states are constructed. We discuss the optical selection rules for the acceptor-bound exciton recombination. Finally, we compare our theory with experimental data for CdS and GaN. In the specific case of CdS for which much experimental information is available, we demonstrate that, compared with cubic semiconductors, the sign of the short-range hole-exchange interaction is reversed and more than one order of magnitude larger. The whole set of data is interpreted in the context of a large value of the short-range hole-exchange interaction Ξ0=3.4±0.2meV . This value dictates the splitting between the ground-state line I1 and the other transitions. The values we find for the electron-hole spin-exchange interaction and of the crystal-field splitting of the two-hole state are, respectively, -0.4±0.1 and 0.2±0.1meV . In the case of GaN, the experimental data for the acceptor-bound excitons in the case of Mg and Zn acceptors, show more than one bound-exciton line. We discuss a possible assignment of these states.

  13. A Nonfullerene Small Molecule Acceptor with 3D Interlocking Geometry Enabling Efficient Organic Solar Cells.

    PubMed

    Lee, Jaewon; Singh, Ranbir; Sin, Dong Hun; Kim, Heung Gyu; Song, Kyu Chan; Cho, Kilwon

    2016-01-06

    A new 3D nonfullerene small-molecule acceptor is reported. The 3D interlocking geometry of the small-molecule acceptor enables uniform molecular conformation and strong intermolecular connectivity, facilitating favorable nanoscale phase separation and electron charge transfer. By employing both a novel polymer donor and a nonfullerene small-molecule acceptor in the solution-processed organic solar cells, a high-power conversion efficiency of close to 6% is demonstrated. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. General theory of excitation energy transfer in donor-mediator-acceptor systems.

    PubMed

    Kimura, Akihiro

    2009-04-21

    General theory of the excitation energy transfer (EET) in the case of donor-mediator-acceptor system was constructed by using generalized master equation (GME). In this theory, we consider the direct and indirect transitions in the EET consistently. Hence, our theory includes the quantum mechanical interference between the direct and indirect transitions automatically. Memory functions in the GME were expressed by the overlap integrals among the time-dependent emission spectrum of the donor, the absorption spectrum of the mediator, the time-dependent emission spectrum of the mediator, and the absorption spectrum of the acceptor. In the Markov limit of the memory functions, we obtained the rate of EET which consists of three terms due to the direct transition, the indirect transition, and the interference between them. We found that the interference works effectively in the limit of slow thermalization at the intermediate state. The formula of EET rate in this limit was expressed by the convolution of the EET interaction and optical spectra. The interference effect strongly depends on the width of the absorption spectrum of mediator molecule and the energy gap between the donor and the mediator molecules.

  15. Flexible biological arsenite oxidation utilizing NOx and O2 as alternative electron acceptors.

    PubMed

    Wang, Jie; Wan, Junfeng; Wu, Zihao; Li, Hongli; Li, Haisong; Dagot, Christophe; Wang, Yan

    2017-07-01

    The feasibility of flexible microbial arsenite (As III ) oxidation coupled with the reduction of different electron acceptors was investigated. The results indicated the acclimated microorganisms could oxidize As III with oxygen, nitrate and nitrite as the alternative electron acceptors. A series of batch tests were conducted to measure the kinetic parameters of As III oxidation and to evaluate the effects of environmental conditions including pH and temperature on the activity of biological As III oxidation dependent on different electron acceptors. Kinetic results showed that oxygen-dependent As III oxidation had the highest oxidation rate (0.59 mg As g -1  VSS min -1 ), followed by nitrate- (0.40 mg As g -1  VSS min -1 ) and nitrite-dependent As III oxidation (0.32 mg As g -1  VSS min -1 ). The kinetic data of aerobic As III oxidation were fitted well with the Monod kinetic model, while the Haldane substrate inhibition model was better applicable to describe the inhibition of anoxic As III oxidation. Both aerobic and anoxic As III oxidation performed the optimal activity at the near neutral pH. Besides, the optimal temperature for oxygen-, nitrate- and nitrite-dependent As III oxidation was 30 ± 1 °C, 40 ± 1 °C and 20 ± 1 °C, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

  16. The improved photovoltaic performance of phenothiazine-dithienopyrrole based dyes with auxiliary acceptors

    NASA Astrophysics Data System (ADS)

    Han, Ming-Liang; Zhu, Yi-Zhou; Liu, Shuang; Liu, Qing-Long; Ye, Dan; Wang, Bing; Zheng, Jian-Yu

    2018-05-01

    Incorporating alkyl chain decorated dithienopyrrole π-spacer with phenothiazine donor has proven to be efficient strategy for constructing novel dyes, which can achieve both large short-circuit current (Jsc) and high open-circuit voltage (Voc) in dye-sensitized solar cells (DSSCs). To promote the light harvesting capability, auxiliary acceptors including benzotriazole (BTZ), benzothiadiazole (BTD), and quinoxaline (Qu) have been inserted into the skeleton of dyes, and much improved Jsc have been realized. Meantime, the rational design of alkyl chains endows dyes JY53 and JY55 a good shielding effect from the penetration of electrolyte, guaranteeing a high Voc (over 810 mV) through retarding unwanted interfacial charge recombination. As a result, with the assistance of introduced auxiliary acceptors and alkyl chains, the photovoltaic performance of devices have been significantly improved, and dye JY55 has achieved an excellent power conversion efficiency (PCE) of 10.06% with Jsc of 19.18 mA cm-2, Voc of 829 mV, and FF of 0.63 under AM 1.5 G irradiation.

  17. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT).

    PubMed

    Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

    2016-11-22

    The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La 3+ donor-doped, Fe 3+ acceptor-doped and La 3+ /Fe 3+ -co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

  18. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT)

    PubMed Central

    Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

    2016-01-01

    The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT. PMID:28774067

  19. Electron paramagnetic resonance study of neutral Mg acceptors in β-Ga2O3 crystals

    NASA Astrophysics Data System (ADS)

    Kananen, B. E.; Halliburton, L. E.; Scherrer, E. M.; Stevens, K. T.; Foundos, G. K.; Chang, K. B.; Giles, N. C.

    2017-08-01

    Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors ( M gGa0 ) in a β-Ga2O3 crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors ( M gGa- ). Unintentionally present Fe3+ (3d5) and Cr3+ (3d3) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion adjacent to an Mg ion at a sixfold-coordinated Ga site. These M gGa0 acceptors (S = 1/2) have a slightly anisotropic g matrix (principal values are 2.0038, 2.0153, and 2.0371). There is also partially resolved 69Ga and 71Ga hyperfine structure resulting from unequal interactions with the two Ga ions adjacent to the hole. With the magnetic field along the a direction, hyperfine parameters are 2.61 and 1.18 mT for the 69Ga nuclei at the two inequivalent neighboring Ga sites. The M gGa0 acceptors thermally convert back to their nonparamagnetic M gGa- charge state when the temperature of the crystal is raised above approximately 250 K.

  20. Local Intermolecular Order Controls Photoinduced Charge Separation at Donor/Acceptor Interfaces in Organic Semiconductors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Feier, Hilary M.; Reid, Obadiah G.; Pace, Natalie A.

    2016-03-23

    How free charge is generated at organic donor-acceptor interfaces is an important question, as the binding energy of the lowest energy (localized) charge transfer states should be too high for the electron and hole to escape each other. Recently, it has been proposed that delocalization of the electronic states participating in charge transfer is crucial, and aggregated or otherwise locally ordered structures of the donor or the acceptor are the precondition for this electronic characteristic. The effect of intermolecular aggregation of both the polymer donor and fullerene acceptor on charge separation is studied. In the first case, the dilute electronmore » acceptor triethylsilylhydroxy-1,4,8,11,15,18,22,25-octabutoxyphthalocyaninatosilicon(IV) (SiPc) is used to eliminate the influence of acceptor aggregation, and control polymer order through side-chain regioregularity, comparing charge generation in 96% regioregular (RR-) poly(3-hexylthiophene) (P3HT) with its regiorandom (RRa-) counterpart. In the second case, ordered phases in the polymer are eliminated by using RRa-P3HT, and phenyl-C61-butyric acid methyl ester (PC61BM) is used as the acceptor, varying its concentration to control aggregation. Time-resolved microwave conductivity, time-resolved photoluminescence, and transient absorption spectroscopy measurements show that while ultrafast charge transfer occurs in all samples, long-lived charge carriers are only produced in films with intermolecular aggregates of either RR-P3HT or PC61BM, and that polymer aggregates are just as effective in this regard as those of fullerenes.« less

  1. Impact of Group-II Acceptors on the Electrical and Optical Properties of GaN

    NASA Astrophysics Data System (ADS)

    Lyons, John L.; Janotti, Anderson; Van de Walle, Chris G.

    2013-08-01

    We explore the properties of group-II acceptors in GaN by performing hybrid density functional calculations. We find that MgGa gives rise to hole localization in zinc-blende GaN, similar to the behavior in the wurtzite phase. Alternative acceptor impurities, such as Zn and Be, also lead to localized holes in wurtzite GaN, and their ionization energies are larger than that of Mg. All these group-II acceptors also cause large lattice distortions in their neutral charge state, which in turn lead to deep and broad luminescence signals. We explore the consequences of these results for p-type doping.

  2. Design of Shallow Acceptors in GaN through Zinc-Magnium Codoping: First-Principles Calculation

    NASA Astrophysics Data System (ADS)

    Liu, Zhiqiang; Melton, Andrew G.; Yi, Xiaoyan; Wang, Jianwei; Kucukgok, Bahadir; Kang, Jun; Lu, Na; Wang, Junxi; Li, Jinmin; Ferguson, Ian

    2013-04-01

    In this work, we propose a novel approach to reduce the ionization energy of acceptors in GaN through Zn-Mg codoping. The characteristics of the defect states and the valence-band maximum (VBM) were investigated via first-principles calculation. Our results indicated that the original VBM of the host GaN could be altered by Zn-Mg codoping, thus improving the p-type dopability. We show that the calculated ionization energy ɛ(0/-) of the Zn-Mg acceptor is only 117 meV, which is about 90 meV shallower than that of the isolated Mg acceptor.

  3. Sulfur oxidation to sulfate coupled with electron transfer to electrodes by Desulfuromonas strain TZ1

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, T; Bain, TS; Barlett, MA

    2014-01-02

    Microbial oxidation of elemental sulfur with an electrode serving as the electron acceptor is of interest because this may play an important role in the recovery of electrons from sulfidic wastes and for current production in marine benthic microbial fuel cells. Enrichments initiated with a marine sediment inoculum, with elemental sulfur as the electron donor and a positively poised (+300 mV versus Ag/AgCl) anode as the electron acceptor, yielded an anode biofilm with a diversity of micro-organisms, including Thiobacillus, Sulfurimonas, Pseudomonas, Clostridium and Desulfuromonas species. Further enrichment of the anode biofilm inoculum in medium with elemental sulfur as the electronmore » donor and Fe(III) oxide as the electron acceptor, followed by isolation in solidified sulfur/Fe(III) medium yielded a strain of Desulfuromonas, designated strain TZ1. Strain TZ1 effectively oxidized elemental sulfur to sulfate with an anode serving as the sole electron acceptor, at rates faster than Desulfobulbus propionicus, the only other organism in pure culture previously shown to oxidize S with current production. The abundance of Desulfuromonas species enriched on the anodes of marine benthic fuel cells has previously been interpreted as acetate oxidation driving current production, but the results presented here suggest that sulfur-driven current production is a likely alternative.« less

  4. Structural, spectroscopic and thermal characterization of 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester and its Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes.

    PubMed

    Mohamed, Gehad G; El-Gamel, Nadia E A

    2005-04-01

    Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and UO(2)(II) complexes with the ligand 2-tert-butylaminomethylpyridine-6-carboxylic acid methylester (HL(2)) have been prepared and characterized by elemental analyses, molar conductance, magnetic moment, thermal analysis and spectral data. 1:1 M:HL(2) complexes, with the general formula [M(HL(2))X(2)].nH(2)O (where M = Co(II) (X = Cl, n = 0), Ni(II) (X = Cl, n = 3), Cu(II) (grey colour, X = AcO, n = 1), Cu(II) (yellow colour, X = Cl, n = 0) and Zn(II) (X = Br, n = 0). In addition, the Fe(III) and UO(2)(II) complexes of the type 1:2 M:HL(2) and with the formulae [Fe(L(2))(2)]Cl and [UO(2)(HL(2))(2)](NO(3))(2) are prepared. From the IR data, it is seen that HL(2) ligand behaves as a terdentate ligand coordinated to the metal ions via the pyridyl N, carboxylate O and protonated NH group; except the Fe(III) complex, it coordinates via the deprotonated NH group. This is supported by the molar conductance data, which show that all the complexes are non-electrolytes, while the Fe(III) and UO(2)(II) complexes are 1:1 electrolytes. IR and H1-NMR spectral studies suggest a similar behaviour of the Zn(II) complex in solid and solution states. From the solid reflectance spectral data and magnetic moment measurements, the complexes have a trigonal bipyramidal (Co(II), Ni(II), Cu(II) and Zn(II) complexes) and octahedral (Fe(III), UO(2)(II) complexes) geometrical structures. The thermal behaviour of the complexes is studied and the different dynamic parameters are calculated applying Coats-Redfern equation.

  5. Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

    NASA Astrophysics Data System (ADS)

    Singh, Prashant; Kumar, Pradeep; Katyal, Anju; Kalra, Rashmi; Dass, Sujata K.; Prakash, Satya; Chandra, Ramesh

    2010-03-01

    In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.

  6. Isolation of Phyllosilicate–Iron Redox Cycling Microorganisms from an Illite–Smectite Rich Hydromorphic Soil

    PubMed Central

    Shelobolina, Evgenya; Konishi, Hiromi; Xu, Huifang; Benzine, Jason; Xiong, Mai Yia; Wu, Tao; Blöthe, Marco; Roden, Eric

    2012-01-01

    The biogeochemistry of phyllosilicate–Fe redox cycling was studied in a Phalaris arundinacea (reed canary grass) dominated redoximorphic soil from Shovelers Sink, a small glacial depression near Madison, WI. The clay size fraction of Shovelers Sink soil accounts for 16% of the dry weight of the soil, yet contributes 74% of total Fe. The dominant mineral in the clay size fraction is mixed layer illite–smectite, and in contrast to many other soils and sediments, Fe(III) oxides are present in low abundance. We examined the Fe biogeochemistry of Shovelers Sink soils, estimated the abundance of Fe redox cycling microorganisms, and isolated in pure culture representative phyllosilicate–Fe oxidizing and reducing organisms. The abundance of phyllosilicate–Fe reducing and oxidizing organisms was low compared to culturable aerobic heterotrophs. Both direct isolation and dilution-to-extinction approaches using structural Fe(II) in Bancroft biotite as a Fe(II) source, and O2 as the electron acceptor, resulted in recovery of common rhizosphere organisms including Bradyrhizobium spp. and strains of Cupriavidus necator and Ralstonia solanacearum. In addition to oxidizing biotite and soluble Fe(II) with O2, each of these isolates was able to oxidize Fe(II) in reduced NAu-2 smectite with NO3- as the electron acceptor. Oxidized NAu-2 smectite or amorphous Fe(III) oxide served as electron acceptors for enrichment and isolation of Fe(III)-reducing microorganisms, resulting in recovery of a strain related to Geobacter toluenoxydans. The ability of the recovered microorganisms to cycle phyllosilicate–Fe was verified in an experiment with native Shovelers Sink clay. This study confirms that Fe in the native Shovelers Sink clay is readily available for microbial redox transformation and can be cycled by the Fe(III)-reducing and Fe(II)-oxidizing microorganisms recovered from the soil. PMID:22493596

  7. Isolation of phyllosilicate-iron redox cycling microorganisms from an illite-smectite rich hydromorphic soil.

    PubMed

    Shelobolina, Evgenya; Konishi, Hiromi; Xu, Huifang; Benzine, Jason; Xiong, Mai Yia; Wu, Tao; Blöthe, Marco; Roden, Eric

    2012-01-01

    The biogeochemistry of phyllosilicate-Fe redox cycling was studied in a Phalaris arundinacea (reed canary grass) dominated redoximorphic soil from Shovelers Sink, a small glacial depression near Madison, WI. The clay size fraction of Shovelers Sink soil accounts for 16% of the dry weight of the soil, yet contributes 74% of total Fe. The dominant mineral in the clay size fraction is mixed layer illite-smectite, and in contrast to many other soils and sediments, Fe(III) oxides are present in low abundance. We examined the Fe biogeochemistry of Shovelers Sink soils, estimated the abundance of Fe redox cycling microorganisms, and isolated in pure culture representative phyllosilicate-Fe oxidizing and reducing organisms. The abundance of phyllosilicate-Fe reducing and oxidizing organisms was low compared to culturable aerobic heterotrophs. Both direct isolation and dilution-to-extinction approaches using structural Fe(II) in Bancroft biotite as a Fe(II) source, and O(2) as the electron acceptor, resulted in recovery of common rhizosphere organisms including Bradyrhizobium spp. and strains of Cupriavidus necator and Ralstonia solanacearum. In addition to oxidizing biotite and soluble Fe(II) with O(2), each of these isolates was able to oxidize Fe(II) in reduced NAu-2 smectite with [Formula: see text] as the electron acceptor. Oxidized NAu-2 smectite or amorphous Fe(III) oxide served as electron acceptors for enrichment and isolation of Fe(III)-reducing microorganisms, resulting in recovery of a strain related to Geobacter toluenoxydans. The ability of the recovered microorganisms to cycle phyllosilicate-Fe was verified in an experiment with native Shovelers Sink clay. This study confirms that Fe in the native Shovelers Sink clay is readily available for microbial redox transformation and can be cycled by the Fe(III)-reducing and Fe(II)-oxidizing microorganisms recovered from the soil.

  8. Blinking fluorescence of single donor-acceptor pairs: important role of "dark'' states in resonance energy transfer via singlet levels.

    PubMed

    Osad'ko, I S; Shchukina, A L

    2012-06-01

    The influence of triplet levels on Förster resonance energy transfer via singlet levels in donor-acceptor (D-A) pairs is studied. Four types of D-A pair are considered: (i) two-level donor and two-level acceptor, (ii) three-level donor and two-level acceptor, (iii) two-level donor and three-level acceptor, and (iv) three-level donor and three-level acceptor. If singlet-triplet transitions in a three-level acceptor molecule are ineffective, the energy transfer efficiency E=I_{A}/(I_{A}+I_{D}), where I_{D} and I_{A} are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FT_{D}/(1+FT_{D}). Here F is the rate of energy transfer, and T_{D} is the donor fluorescence lifetime. In accordance with the last equation, 100% of the donor electronic energy can be transferred to an acceptor molecule at FT_{D}≫1. However, if singlet-triplet transitions in a three-level acceptor molecule are effective, the energy transfer efficiency is described by another theoretical equation, E(F)=F[over ¯](F)T_{D}/[1+F[over ¯](F)T_{D}]. Here F[over ¯](F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F[over ¯](F) are derived. In this case the energy transfer efficiency will be far from 100% even at FT_{D}≫1. The character of the intensity fluctuations of donor and acceptor fluorescence indicates which of the two equations for E(F) should be used to find the value of the rate F. Therefore, random time instants of photon emission in both donor and acceptor fluorescence are calculated by the Monte Carlo method for all four types of D-A pair. Theoretical expressions for start-stop correlators (waiting time distributions) in donor and acceptor fluorescence are derived. The probabilities w_{N}^{D}(t) and w_{N}^{A}(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy

  9. Synthesis and Characterization of Organic Dyes Containing Various Donors and Acceptors

    PubMed Central

    Wu, Tzi-Yi; Tsao, Ming-Hsiu; Chen, Fu-Lin; Su, Shyh-Gang; Chang, Cheng-Wen; Wang, Hong-Paul; Lin, Yuan-Chung; Ou-Yang, Wen-Chung; Sun, I-Wen

    2010-01-01

    New organic dyes comprising carbazole, iminodibenzyl, or phenothiazine moieties, respectively, as the electron donors, and cyanoacetic acid or acrylic acid moieties as the electron acceptors/anchoring groups were synthesized and characterized. The influence of heteroatoms on carbazole, iminodibenzyl and phenothiazine donors, and cyano-substitution on the acid acceptor is evidenced by spectral, electrochemical, photovoltaic experiments, and density functional theory calculations. The phenothiazine dyes show solar-energy-to-electricity conversion efficiency (η) of 3.46–5.53%, whereas carbazole and iminodibenzyl dyes show η of 2.43% and 3.49%, respectively. PMID:20162019

  10. Biological activity of Fe(III) aquo-complexes towards ferric chelate reductase (FCR).

    PubMed

    Escudero, Rosa; Gómez-Gallego, Mar; Romano, Santiago; Fernández, Israel; Gutiérrez-Alonso, Ángel; Sierra, Miguel A; López-Rayo, Sandra; Nadal, Paloma; Lucena, Juan J

    2012-03-21

    In this study we have obtained experimental evidence that confirms the high activity of aquo complexes III and IV towards the enzyme FCR, responsible for the reduction of Fe(III) to Fe(II) in the process of iron acquisition by plants. The in vivo FCR assays in roots of stressed cucumber plants have shown a higher efficiency of the family of complexes III and a striking structure-activity relationship with the nature of the substituent placed in a phenyl group far away from the metal center. The results obtained in this work demonstrate that all the aquo compounds tested interact efficiently with the enzyme FCR and hence constitute a new concept of iron chelates that could be of great use in agronomy.

  11. Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

    NASA Astrophysics Data System (ADS)

    Johnson, Brian; Kendrick, Mark J.; Ostroverkhova, Oksana

    2013-09-01

    We present a model that describes nanosecond (ns) time-scale photocurrent dynamics in functionalized anthradithiophene (ADT) films and ADT-based donor-acceptor (D/A) composites. By fitting numerically simulated photocurrents to experimental data, we quantify contributions of multiple pathways of charge carrier photogeneration to the photocurrent, as well as extract parameters that characterize charge transport (CT) in organic films including charge carrier mobilities, trap densities, hole trap depth, and trapping and recombination rates. In pristine ADT films, simulations revealed two competing charge photogeneration pathways: fast, occurring on picosecond (ps) or sub-ps time scales with efficiencies below 10%, and slow, which proceeds at the time scale of tens of nanoseconds, with efficiencies of about 11%-12%, at the applied electric fields of 40-80 kV/cm. The relative contribution of these pathways to the photocurrent was electric field dependent, with the contribution of the fast process increasing with applied electric field. However, the total charge photogeneration efficiency was weakly electric field dependent exhibiting values of 14%-20% of the absorbed photons. The remaining 80%-86% of the photoexcitation did not contribute to charge carrier generation at these time scales. In ADT-based D/A composites with 2 wt.% acceptor concentration, an additional pathway of charge photogeneration that proceeds via CT exciton dissociation contributed to the total charge photogeneration. In the composite with the functionalized pentacene (Pn) acceptor, which exhibits strong exciplex emission from a tightly bound D/A CT exciton, the contribution of the CT state to charge generation was small, ˜8%-12% of the total number of photogenerated charge carriers, dependent on the electric field. In contrast, in the composite with PCBM acceptor, the CT state contributed about a half of all photogenerated charge carriers. In both D/A composites, the charge carrier mobilities were

  12. Enhanced degradation of trichloroethene by calcium peroxide activated with Fe(III) in the presence of citric acid

    PubMed Central

    ZHANG, Xiang; GU, Xiaogang; LU, Shuguang; MIAO, Zhouwei; XU, Minhui; FU, Xiaori; DANISH, Muhammad; Brusseau, Mark L.; QIU, Zhaofu; SUI, Qian

    2017-01-01

    Trichloroethene (TCE) degradation by Fe(III)-activated calcium peroxide (CP) in the presence of citric acid (CA) in aqueous solution was investigated. The results demonstrated that the presence of CA enhanced TCE degradation significantly by increasing the concentration of soluble Fe(III) and promoting H2O2 generation. The generation of HO• and O2−• in both the CP/Fe(III) and CP/Fe(III)/CA systems was confirmed with chemical probes. The results of radical scavenging tests showed that TCE degradation was due predominantly o direct oxidation by HO•, while O2−• strengthened the generation of HO• by promoting Fe(III) transformation in the CP/Fe(III)/CA system. Acidic pH conditions were favorable for TCE degradation, and the TCE degradation rate decreased with increasing pH. The presence of Cl−, HCO3−, and humic acid (HA) inhibited TCE degradation to different extents for the CP/Fe(III)/CA system. Analysis of Cl− production suggested that TCE degradation in the CP/Fe(III)/CA system occurred through a dechlorination process. In summary, this study provided detailed information for the application of CA-enhanced Fe(III)-activated calcium peroxide for treating TCE contaminated groundwater. PMID:28959499

  13. Electron Spin Relaxation Rates for High-Spin Fe(III) in Iron Transferrin Carbonate and Iron Transferrin Oxalate

    PubMed Central

    Gaffney, Betty Jean; Eaton, Gareth R.; Eaton*, Sandra S.

    2005-01-01

    To optimize simulations of CW EPR spectra for high-spin Fe(III) with zero-field splitting comparable to the EPR quantum, information is needed on the factors that contribute to the line shapes and line widths. Continuous wave electron paramagnetic resonance (EPR) spectra obtained for iron transferrin carbonate from 4 to 150 K and for iron transferrin oxalate from 4 to 100 K did not exhibit significant temperature dependence of the line shape, which suggested that the line shapes were not relaxation determined. To obtain direct information concerning the electron spin relaxation rates, electron spin echo and inversion recovery EPR were used to measure T1 and Tm for the high-spin Fe(III) in iron transferrin carbonate and iron transferrin oxalate between 5 and 20–30 K. For comparison with the data for the transferrin complexes, relaxation times were obtained for tris(oxalato)ferrate(III). The relaxation rates are similar for the three complexes and do not exhibit a strong dependence on position in the spectrum. Extrapolation of the observed temperature dependence of the relaxation rates to higher temperatures gives values consistent with the conclusion that the CW line shapes are not relaxation determined up to 150 K. PMID:16429607

  14. Dissolution of Fe(III) (hydr) oxides by metal-EDTA complexes

    NASA Astrophysics Data System (ADS)

    Ngwack, Bernd; Sigg, Laura

    1997-03-01

    The dissolution of Fe(III)(hydr)oxides (goethite and hydrous ferric oxide) by metal-EDTA complexes occurs by ligand-promoted dissolution. The process is initiated by the adsorption of metal-EDTA complexes to the surface and is followed by the dissociation of the complex at the surface and the release of Fe(III)EDTA into solution. The dissolution rate is decreased to a great extent if EDTA is complexed by metals in comparison to the uncomplexed EDTA. The rate decreases in the order EDTA CaEDTA ≫ PbEDTA > ZnEDTA > CuEDTA > Co(II)EDTA > NiEDTA. Two different rate-limiting steps determine the dissolution process: (1) detachment of Fe(III) from the oxide-structure and (2) dissociation of the metal-EDTA complexes. In the case of goethite, step 1 is slower than step 2 and the dissolution rates by various metals are similar. In the case of hydrous ferric oxide, step 2 is rate-limiting and the effect of the complexed metal is very pronounced.

  15. Modification of Natural Zeolite with Fe(III) and Its Application as Adsorbent Chloride and Carbonate ions

    NASA Astrophysics Data System (ADS)

    Suhartana; Sukmasari, Emmanuella; Azmiyawati, Choiril

    2018-04-01

    The aim of the research is to natural zeolite with Fe(III) using anion exchange process to improve the anion exchange capacity. Natural zeolite was activated using HNO3 1 N and then mixed with FeCl3 solution and refluxed followed by oven and calcination at a temperature of 550°C. The influence of Fe(III) to zeolite was characterized by FTIR while presence of Fe in zeolite characterized by AAS. Zeolite and Zeolite-Fe adsorption capacity of chloride and carbonate anions were determined through adsorption test by variation of pH and contact time. In advanced, and then to determining the Fe adsorbed concentration at Zeolite using UV-Vis spectrophotometer. FTIR analysis result showed that the addition of Fe does not affect the zeolite’s structure but change the intensity of the zeolite spectra. The Fe concentration in Zeolite-Fe of 714 mg L-1, indicate that Fe was present in the zeolite. Both Zeolite and Zeolite-Fe adsorbtion results showed that optimum pH of Chloride anion is 2, with adsorption capacity 2,33 x 10-3 gg-1 and optimum contact time is 8 minutes. While Zeolite and Zeolite-Fe adsorbtion results showed that optimum pH of Carbonate anion is 5, with adsorption capacity 5,31 x 10-3 gg-1 and optimum contact time is 8 minutes.

  16. Preliminary study on the photoproduction of hydroxyl radicals in aqueous solution with Aldrich humic acid, algae and Fe(III) under high-pressure mercury lamp irradiation.

    PubMed

    Liu, Xianli; Xu, Dong; Wu, Feng; Liao, Zhenhuan; Liu, Jiantong; Deng, Nansheng

    2004-03-01

    Under a high-pressure mercury lamp (HPML) and using an exposure time of 4 h, the photoproduction of hydroxyl radicals (*OH) could be induced in an aqueous solution containing humic acid (HA). Hydroxyl radicals were determined by high-performance liquid chromatography using benzene as a probe. The results showed that *OH photoproduction increased from 1.80 to 2.74 microM by increasing the HA concentration from 10 to 40 mg L(-1) at an exposure time of 4 h (pH 6.5). Hydroxyl radical photoproduction in aqueous solutions of HA containing algae was greater than that in the aqueous solutions of HA without algae. The photoproduction of *OH in the HA solution with Fe(III) was greater than that of the solution without Fe(III) at pH ranging from 4.0 to 8.0. The photoproduction of *OH in HA solution with algae with or without Fe(III) under a 250 W HPML was greater than that under a 125 W HPML. The photoproduction of *OH in irradiated samples was influenced by the pH. The results showed that HPML exposure for 4 h in the 4-8 pH range led to the highest *OH photoproduction at pH 4.0.

  17. Electronic spectrum of non-tetrahedral acceptors in CdTe:Cl and CdTe:Bi,Cl single crystals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Krivobok, V. S., E-mail: krivobok@lebedev.ru; Moscow Institute of Physics and Technology; Nikolaev, S. N.

    2016-02-07

    The electronic spectra of complex acceptors in compensated CdTe:Cl, CdTe:Ag,Cl, and CdTe:Bi,Cl single crystals are studied using low-temperature photoluminescence (PL) measurements under both nonresonant and resonant excitation of distant donor–acceptor pairs (DAP). The wavelength modulation of the excitation source combined with the analysis of the differential PL signal is used to enhance narrow spectral features obscured because of inhomogeneous line broadening and/or excitation transfer for selectively excited DAPs. For the well-known tetrahedral (T{sub D}) Ag{sub Cd} acceptor, the energies of four excited states are measured, and the values obtained are shown to be in perfect agreement with the previous data.more » Moreover, splitting between the 2P{sub 3/2} (Γ{sub 8}) and 2S{sub 3/2} (Γ{sub 8}) states is clearly observed for Ag{sub Cd} centers located at a short distance (5–7 nm) from a hydrogen-like donor (Cl{sub Te}). This splitting results from the reduction of the T{sub D} symmetry taking place when the acceptor is a member of a donor–acceptor pair. For the Cl-related complex acceptor with an activation energy of ∼121 meV (A-center), the energies of eight excited states are measured. It is shown that this defect produces low-symmetry central-cell correction responsible for the strong splitting of S-like T{sub D} shells. The energy spectrum of the Bi-related shallow acceptor with an activation energy of ∼36 meV is measured as well. The spectrum obtained differs drastically from the hydrogen-like set of levels, which indicates the existence of repulsive low-symmetry perturbation of the hydrogen-like Coulomb potential. It is also shown that the spectra of selectively excited PL recorded for a macroscopic ensemble of distant donor–acceptor pairs allow one to detect the low symmetry of acceptors of a given type caused by their complex nature or by the Jahn–Teller distortion. This method does not require any additional (external) field

  18. Donor-bridge-acceptor energetics determine the distance dependence of electron tunneling in DNA

    NASA Astrophysics Data System (ADS)

    Lewis, Frederick D.; Liu, Jianqin; Weigel, Wilfried; Rettig, Wolfgang; Kurnikov, Igor V.; Beratan, David N.

    2002-10-01

    Electron transfer (ET) processes in DNA are of current interest because of their involvement in oxidative strand cleavage reactions and their relevance to the development of molecular electronics. Two mechanisms have been identified for ET in DNA, a single-step tunneling process and a multistep charge-hopping process. The dynamics of tunneling reactions depend on both the distance between the electron donor and acceptor and the nature of the molecular bridge separating the donor and acceptor. In the case of protein and alkane bridges, the distance dependence is not strongly dependent on the properties of the donor and acceptor. In contrast, we show here that the distance decay of DNA ET rates varies markedly with the energetics of the donor and acceptor relative to the bridge. Specifically, we find that an increase in the energy of the bridge states by 0.25 eV (1 eV = 1.602 × 1019 J) relative to the donor and acceptor energies for photochemical oxidation of nucleotides, without changing the reaction free energy, results in an increase in the characteristic exponential distance decay constant for the ET rates from 0.71 to 1.1 Å1. These results show that, in the small tunneling energy gap regime of DNA ET, the distance dependence is not universal; it varies strongly with the tunneling energy gap. These DNA ET reactions fill a "missing link" or transition regime between the large barrier (rapidly decaying) tunneling regime and the (slowly decaying) hopping regime in the general theory of bridge-mediated ET processes.

  19. Charge-transfer complexes of sulfamethoxazole drug with different classes of acceptors

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; El-Korashy, Sabry A.; El-Deen, Ibrahim M.; El-Sayed, Shaima M.

    2010-09-01

    The charge-transfer complexes of the donor sulfamethoxazole (SZ) with iodine (I 2), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil (CHL) and picric acid (PA) have been studied spectrophotometrically in chloroform or methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CT-complexes in case of four acceptors. The stoichiometry of the complexes was found to be 1:1 ratio by molar ratio method between donor and acceptor with maximum absorption bands (CT band). The data are discussed in terms of formation constant ( KCT), molar extinction coefficient ( ɛCT), standard free energy (Δ G°), oscillator strength (ƒ), transition dipole moment ( μ), resonance energy ( RN) and ionization potential ( ID). The results indicate that the formation constant ( KCT) for the complexes were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used. IR, 1H NMR, mass spectra, UV-Vis techniques, elemental analyses (CHN) and TG-DTG investigation were used to characterize the four sulfamethoxazole charge-transfer complexes.

  20. A method to quantify FRET stoichiometry with phasor plot analysis and acceptor lifetime ingrowth.

    PubMed

    Chen, WeiYue; Avezov, Edward; Schlachter, Simon C; Gielen, Fabrice; Laine, Romain F; Harding, Heather P; Hollfelder, Florian; Ron, David; Kaminski, Clemens F

    2015-03-10

    FRET is widely used for the study of protein-protein interactions in biological samples. However, it is difficult to quantify both the FRET efficiency (E) and the affinity (Kd) of the molecular interaction from intermolecular FRET signals in samples of unknown stoichiometry. Here, we present a method for the simultaneous quantification of the complete set of interaction parameters, including fractions of bound donors and acceptors, local protein concentrations, and dissociation constants, in each image pixel. The method makes use of fluorescence lifetime information from both donor and acceptor molecules and takes advantage of the linear properties of the phasor plot approach. We demonstrate the capability of our method in vitro in a microfluidic device and also in cells, via the determination of the binding affinity between tagged versions of glutathione and glutathione S-transferase, and via the determination of competitor concentration. The potential of the method is explored with simulations. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

  1. Generalization of the Förster resonance energy transfer theory for quantum mechanical modulation of the donor-acceptor coupling

    NASA Astrophysics Data System (ADS)

    Jang, Seogjoo

    2007-11-01

    The Förster resonance energy transfer theory is generalized for inelastic situations with quantum mechanical modulation of the donor-acceptor coupling. Under the assumption that the modulations are independent of the electronic excitation of the donor and the acceptor, a general rate expression is derived, which involves two dimensional frequency-domain convolution of the donor emission line shape, the acceptor absorption line shape, and the spectral density of the modulation of the donor-acceptor coupling. For two models of modulation, detailed rate expressions are derived. The first model is the fluctuation of the donor-acceptor distance, approximated as a quantum harmonic oscillator coupled to a bath of other quantum harmonic oscillators. The distance fluctuation results in additional terms in the rate, which in the small fluctuation limit depend on the inverse eighth power of the donor-acceptor distance. The second model is the fluctuation of the torsional angle between the two transition dipoles, which is modeled as a quantum harmonic oscillator coupled to a bath of quantum harmonic oscillators and causes sinusoidal modulation of the donor-acceptor coupling. The rate expression has new elastic and inelastic terms, depending sensitively on the value of the minimum energy torsional angle. Experimental implications of the present theory and some of the open theoretical issues are discussed.

  2. Hypothesis testing for the validation of the kinetic spectrophotometric methods for the determination of lansoprazole in bulk and drug formulations via Fe(III) and Zn(II) chelates.

    PubMed

    Rahman, Nafisur; Kashif, Mohammad

    2010-03-01

    Point and interval hypothesis tests performed to validate two simple and economical, kinetic spectrophotometric methods for the assay of lansoprazole are described. The methods are based on the formation of chelate complex of the drug with Fe(III) and Zn(II). The reaction is followed spectrophotometrically by measuring the rate of change of absorbance of coloured chelates of the drug with Fe(III) and Zn(II) at 445 and 510 nm, respectively. The stoichiometric ratio of lansoprazole to Fe(III) and Zn(II) complexes were found to be 1:1 and 2:1, respectively. The initial-rate and fixed-time methods are adopted for determination of drug concentrations. The calibration graphs are linear in the range 50-200 µg ml⁻¹ (initial-rate method), 20-180 µg ml⁻¹ (fixed-time method) for lansoprazole-Fe(III) complex and 120-300 (initial-rate method), and 90-210 µg ml⁻¹ (fixed-time method) for lansoprazole-Zn(II) complex. The inter-day and intra-day precision data showed good accuracy and precision of the proposed procedure for analysis of lansoprazole. The point and interval hypothesis tests indicate that the proposed procedures are not biased. Copyright © 2010 John Wiley & Sons, Ltd.

  3. Förster Resonance Energy Transfer between Quantum Dot Donors and Quantum Dot Acceptors

    PubMed Central

    Chou, Kenny F.; Dennis, Allison M.

    2015-01-01

    Förster (or fluorescence) resonance energy transfer amongst semiconductor quantum dots (QDs) is reviewed, with particular interest in biosensing applications. The unique optical properties of QDs provide certain advantages and also specific challenges with regards to sensor design, compared to other FRET systems. The brightness and photostability of QDs make them attractive for highly sensitive sensing and long-term, repetitive imaging applications, respectively, but the overlapping donor and acceptor excitation signals that arise when QDs serve as both the donor and acceptor lead to high background signals from direct excitation of the acceptor. The fundamentals of FRET within a nominally homogeneous QD population as well as energy transfer between two distinct colors of QDs are discussed. Examples of successful sensors are highlighted, as is cascading FRET, which can be used for solar harvesting. PMID:26057041

  4. Towards building artificial light harvesting complexes: enhanced singlet-singlet energy transfer between donor and acceptor pairs bound to albumins.

    PubMed

    Kumar, Challa V; Duff, Michael R

    2008-12-01

    Specific donor and acceptor pairs have been assembled in bovine serum albumin (BSA), at neutral pH and room temperature, and these dye-protein complexes indicated efficient donor to acceptor singlet-singlet energy transfer. For example, pyrene-1-butyric acid served as the donor and Coumarin 540A served as the acceptor. Both the donor and the acceptor bind to BSA with affinity constants in excess of 2x10(5) M(-1), as measured in absorption and circular dichroism (CD) spectral titrations. Simultaneous binding of both the donor and the acceptor chromophores was supported by CD spectra and one chromophore did not displace the other from the protein host, even when limited concentrations of the host were used. For example, a 1:1:1 complex between the donor, acceptor and the host can be readily formed, and spectral data clearly show that the binding sites are mutually exclusive. The ternary complexes (two different ligands bound to the same protein molecule) provided opportunities to examine singlet-singlet energy transfer between the protein-bound chromophores. Donor emission was quenched by the addition of the acceptor, in the presence of limited amounts of BSA, while no energy transfer was observed in the absence of the protein host, under the same conditions. The excitation spectra of the donor-acceptor-host complexes clearly show the sensitization of acceptor emission by the donor. Protein denaturation, as induced by the addition of urea or increasing the temperature to 360 K, inhibited energy transfer, which indicate that protein structure plays an important role. Sensitization also proceeded at low temperature (77 K) and diffusion of the donor or the acceptor is not required for energy transfer. Stern-Volmer quenching plots show that the quenching constant is (3.1+/-0.2)x10(4) M(-1), at low acceptor concentrations (<35 microM). Other albumins such as human and porcine proteins also served as good hosts for the above experiments. For the first time, non

  5. Magnetic and low temperature phonon studies of CoCr2O4 powders doped with Fe(III) and Ni(II) ions

    NASA Astrophysics Data System (ADS)

    Ptak, M.; Mączka, M.; Pikul, A.; Tomaszewski, P. E.; Hanuza, J.

    2014-04-01

    Extensive temperature-dependent phonon studies and low-temperature magnetic measurements of CoCr2-xFexO4 (for x=0.5, 1 and 2) and Co0.9Ni0.1Cr2O4 polycrystalline powders are presented. The main aim of these studies was to obtain information on phonon and structural properties of these compounds as well as strength of spin-phonon coupling in the magnetically ordered phases. IR and Raman spectra show that doping of CoCr2O4 with Fe(III) ions leads to broadening of bands and appearance of new bands due to the formation of inverted spinel structure. In contrast to this behavior, doping with 10 mol% of Ni(II) ions leads to weak increase of band width only. Magnetization measured as a function of temperature and external magnetic field showed that magnetic properties of Co0.9Ni0.1Cr2O4 sample are similar to those reported for pure CoCr2O4, i.e., partial substitution of Ni(II) for Co(II) leads to slight shift of the ferrimagnetic phase transition at TC and spiral spin order transition at TS towards lower values. The change of crystallization preference induced by incorporation of increasing concentration of Fe(III) ions in the spinel lattice causes significant increase of TC and decrease of TS. The latter transition disappears completely for higher concentrations of Fe(III). The performed temperature-dependent IR studies revealed interesting anomalous behavior of phonons below TC for CoCr1.5Fe0.5O4 and Co0.9Ni0.1Cr2O4, which was attributed to spin-phonon coupling.

  6. Acceptor number-dependent ultrafast photo-physical properties of push-pull chromophores using time-resolved methods

    NASA Astrophysics Data System (ADS)

    Chi, Xiao-Chun; Wang, Ying-Hui; Gao, Yu; Sui, Ning; Zhang, Li-Quan; Wang, Wen-Yan; Lu, Ran; Ji, Wen-Yu; Yang, Yan-Qiang; Zhang, Han-Zhuang

    2018-04-01

    Three push-pull chromophores comprising a triphenylamine (TPA) as electron-donating moiety and functionalized β-diketones as electron acceptor units are studied by various spectroscopic techniques. The time-correlated single-photon counting data shows that increasing the number of electron acceptor units accelerates photoluminescence relaxation rate of compounds. Transient spectra data shows that intramolecular charge transfer (ICT) takes place from TPA units to β-diketones units after photo-excitation. Increasing the number of electron acceptor units would prolong the generation process of ICT state, and accelerate the excited molecule reorganization process and the relaxation process of ICT state.

  7. Design of donor-acceptor copolymers for organic photovoltaic materials: a computational study.

    PubMed

    Turan, Haydar Taylan; Kucur, Oğuzhan; Kahraman, Birce; Salman, Seyhan; Aviyente, Viktorya

    2018-01-31

    80 different push-pull type organic chromophores which possess Donor-Acceptor (D-A) and Donor-Thiophene-Acceptor-Thiophene (D-T-A-T) structures have been systematically investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) at the B3LYP/6-311G* level. The introduction of thiophene (T) in the chain has allowed us to monitor the effect of π-spacers. Benchmark studies on the methodology have been carried out to predict the HOMO and LUMO energies and optical band gaps of the D-A systems accurately. The HOMO and LUMO energies and transition dipoles are seen to converge for tetrameric oligomers, and the latter have been used as optimal chain length to evaluate various geometrical and optoelectronic properties such as bond length alternations, distortion energies, frontier molecular orbital energies, reorganization energies and excited-state vertical transition of the oligomers. Careful analysis of our findings has allowed us to propose potential donor-acceptor couples to be used in organic photovoltaic cells.

  8. Arsenic cycling in hydrocarbon plumes: secondary effects of natural attenuation

    USGS Publications Warehouse

    Cozzarelli, Isabelle M.; Schreiber, Madeline E.; Erickson, Melinda L.; Ziegler, Brady A.

    2016-01-01

    Monitored natural attenuation is widely applied as a remediation strategy at hydrocarbon spill sites. Natural attenuation relies on biodegradation of hydrocarbons coupled with reduction of electron acceptors, including solid phase ferric iron (Fe(III)). Because arsenic (As) adsorbs to Fe-hydroxides, a potential secondary effect of natural attenuation of hydrocarbons coupled with Fe(III) reduction is a release of naturally occurring As to groundwater. At a crude-oil-contaminated aquifer near Bemidji, Minnesota, anaerobic biodegradation of hydrocarbons coupled to Fe(III) reduction has been well documented. We collected groundwater samples at the site annually from 2009 to 2013 to examine if As is released to groundwater and, if so, to document relationships between As and Fe inside and outside of the dissolved hydrocarbon plume. Arsenic concentrations in groundwater in the plume reached 230 µg/L, whereas groundwater outside the plume contained less than 5 µg/L As. Combined with previous data from the Bemidji site, our results suggest that (1) naturally occurring As is associated with Fe-hydroxides present in the glacially derived aquifer sediments; (2) introduction of hydrocarbons results in reduction of Fe-hydroxides, releasing As and Fe to groundwater; (3) at the leading edge of the plume, As and Fe are removed from groundwater and retained on sediments; and (4) downgradient from the plume, patterns of As and Fe in groundwater are similar to background. We develop a conceptual model of secondary As release due to natural attenuation of hydrocarbons that can be applied to other sites where an influx of biodegradable organic carbon promotes Fe(III) reduction.

  9. Fullerene derivatives as electron acceptors for organic photovoltaic cells.

    PubMed

    Mi, Dongbo; Kim, Ji-Hoon; Kim, Hee Un; Xu, Fei; Hwang, Do-Hoon

    2014-02-01

    Energy is currently one of the most important problems humankind faces. Depletion of traditional energy sources such as coal and oil results in the need to develop new ways to create, transport, and store electricity. In this regard, the sun, which can be considered as a giant nuclear fusion reactor, represents the most powerful source of energy available in our solar system. For photovoltaic cells to gain widespread acceptance as a source of clean and renewable energy, the cost per watt of solar energy must be decreased. Organic photovoltaic cells, developed in the past two decades, have potential as alternatives to traditional inorganic semiconductor photovoltaic cells, which suffer from high environmental pollution and energy consumption during production. Organic photovoltaic cells are composed of a blended film of a conjugated-polymer donor and a soluble fullerene-derivative acceptor sandwiched between a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-coated indium tin oxide positive electrode and a low-work-function metal negative electrode. Considerable research efforts aim at designing and synthesizing novel fullerene derivatives as electron acceptors with up-raised lowest unoccupied molecular orbital energy, better light-harvesting properties, higher electron mobility, and better miscibility with the polymer donor for improving the power conversion efficiency of the organic photovoltaic cells. In this paper, we systematically review novel fullerene acceptors synthesized through chemical modification for enhancing the photovoltaic performance by increasing open-circuit voltage, short-circuit current, and fill factor, which determine the performance of organic photovoltaic cells.

  10. Origin of high open-circuit voltage in a planar heterojunction solar cell containing a non-fullerene acceptor

    NASA Astrophysics Data System (ADS)

    Cheng, Nongyi; Peng, Yuelin; Andrew, Trisha L.

    2017-09-01

    Vapor-deposited, planar heterojunction organic solar cells containing a periflanthene donor and either a fullerene or non-fullerene acceptor are investigated. A high VOC of 1.16 V is observed in devices containing the non-fullerene, pyrrolo[3,4-c]pyrrole-1,4-dione, 3,6-bis(4-chlorophenyl)-2,5-dihydro acceptor, whereas analogous devices containing C60 only result in a VOC of 0.8 V. The measured band energy levels of the two different acceptors do not readily explain the observed difference. Small-perturbation transient photovoltage and transient photocurrent measurements reveal that interfacial charge recombination is comparatively slower for the non-fullerene acceptor, resulting in relatively higher Voc values.

  11. Charge transfer complex studies between some non-steroidal anti-inflammatory drugs and π-electron acceptors

    NASA Astrophysics Data System (ADS)

    Duymus, Hulya; Arslan, Mustafa; Kucukislamoglu, Mustafa; Zengin, Mustafa

    2006-12-01

    Charge transfer (CT) complexes of some non-steroidal anti-inflammatory drugs, naproxen and etodolac which are electron donors with some π-acceptors, such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), p-chloranil ( p-CHL), have been investigated spectrophotometrically in chloroform at 21 °C. The coloured products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptors. Beer's law is obeyed and colours were produced in non-aqueous media. All complexes were stable at least 2 h except for etodolac with DDQ stable for 5 min. The equilibrium constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters Δ H, Δ S, Δ G° were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptors were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands in all cases.

  12. Role of Crystallization in the Morphology of Polymer: Non-fullerene Acceptor Bulk Heterojunctions

    DOE PAGES

    O’Hara, Kathryn A.; Ostrowski, David P.; Koldemir, Unsal; ...

    2017-05-22

    Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages ( V OC). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. Themore » kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. In conclusion, this study reveals the need for complementary methods to investigate the morphology of BHJs.« less

  13. Role of Crystallization in the Morphology of Polymer: Non-fullerene Acceptor Bulk Heterojunctions

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    O’Hara, Kathryn A.; Ostrowski, David P.; Koldemir, Unsal

    Many high efficiency organic photovoltaics use fullerene-based acceptors despite their high production cost, weak optical absorption in the visible range, and limited synthetic variability of electronic and optical properties. To circumvent this deficiency, non-fullerene small-molecule acceptors have been developed that have good synthetic flexibility, allowing for precise tuning of optoelectronic properties, leading to enhanced absorption of the solar spectrum and increased open-circuit voltages ( V OC). We examined the detailed morphology of bulk heterojunctions of poly(3-hexylthiophene) and the small-molecule acceptor HPI-BT to reveal structural changes that lead to improvements in the fill factor of solar cells upon thermal annealing. Themore » kinetics of the phase transformation process of HPI-BT during thermal annealing were investigated through in situ grazing incidence wide-angle X-ray scattering studies, atomic force microscopy, and transmission electron microscopy. The HPI-BT acceptor crystallizes during film formation to form micron-sized domains embedded within the film center and a donor rich capping layer at the cathode interface reducing efficient charge extraction. Thermal annealing changes the surface composition and improves charge extraction. In conclusion, this study reveals the need for complementary methods to investigate the morphology of BHJs.« less

  14. Investigation of energy transfer between semiconducting polymer dot donors and hydrophilic and hydrophobic Cy5 acceptors

    NASA Astrophysics Data System (ADS)

    Lix, Kelsi; Algar, W. Russ

    2016-09-01

    Semiconducting polymer dots (Pdots) are rapidly emerging fluorescent probes for bioanalysis. Pdots have extraordinarily strong absorption and bright emission compared to other commonly used fluorescent probes, making them very attractive for applications involving Förster resonance energy transfer (FRET). Here, we investigated two FRET systems with green-emitting poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) Pdots as donors and two different Cyanine 5 (Cy5) dyes as acceptors. A hydrophilic sulfo-Cy5 dye was directly conjugated to the Pdot surface using carbodiimide chemistry, and a hydrophobic Cy5 dye was observed to spontaneously partition into the core of the Pdot. FRET was observed to depend on the acceptor dye concentration with both systems, and was characterized using a combination of fluorescence emission spectra, excitation spectra, and lifetime measurements. Much stronger quenching of Pdot emission and FRET-sensitized acceptor dye emission were observed for the hydrophobic Cy5 system, and these trends were attributed to reduced donor-acceptor distances in comparison to the hydrophilic sulfo-Cy5 system. Current limitations in the experimental format are discussed. The results show that Pdots are effective FRET donors for acceptor dyes located both within and at the surface of Pdots.

  15. Enhanced Efficiency in Fullerene-Free Polymer Solar Cell by Incorporating Fine-designed Donor and Acceptor Materials.

    PubMed

    Ye, Long; Sun, Kai; Jiang, Wei; Zhang, Shaoqing; Zhao, Wenchao; Yao, Huifeng; Wang, Zhaohui; Hou, Jianhui

    2015-05-06

    Among the diverse nonfullerene acceptors, perylene bisimides (PBIs) have been attracting much attention due to their excellent electron mobility and tunable molecular and electronic properties by simply engineering the bay and head linkages. Herein, guided by two efficient small molecular acceptors, we designed, synthesized, and characterized a new nonfullerene small molecule PPDI with fine-tailored alkyl chains. Notably, a certificated PCE of 5.40% is realized in a simple structured fullerene-free polymer solar cell comprising PPDI as the electron acceptor and a fine-tailored 2D-conjugated polymer PBDT-TS1 as the electron donor. Moreover, the device behavior, morphological feature, and origin of high efficiency in PBDT-TS1/PPDI-based fullerene-free PSC were investigated. The synchronous selection and design of donor and acceptor materials reported here offer a feasible strategy for realizing highly efficient fullerene-free organic photovoltaics.

  16. Stepwise Bay Annulation of Indigo for the Synthesis of Desymmetrized Electron Acceptors and Donor–Acceptor Constructs

    DOE PAGES

    Kolaczkowski, Matthew A.; He, Bo; Liu, Yi

    2016-10-10

    In this work, a selective stepwise annulation of indigo has been demonstrated as a means of providing both monoannulated and differentially double-annulated indigo derivatives. Disparate substitution of the electron accepting bay-annulated indigo system allows for fine control over both the electronic properties as well as donor-acceptor structural architectures. Optical and electronic properties were characterized computationally as well as through UV-vis absorption spectroscopy and cyclic voltammetry. Finally, this straightforward method provides a modular approach for the design of indigo-based materials with tailored optoelectronic properties.

  17. Iron and manganese in anaerobic respiration: environmental significance, physiology, and regulation

    NASA Technical Reports Server (NTRS)

    Nealson, K. H.; Saffarini, D.

    1994-01-01

    Dissimilatory iron and/or manganese reduction is known to occur in several organisms, including anaerobic sulfur-reducing organisms such as Geobacter metallireducens or Desulfuromonas acetoxidans, and facultative aerobes such as Shewanella putrefaciens. These bacteria couple both carbon oxidation and growth to the reduction of these metals, and inhibitor and competition experiments suggest that Mn(IV) and Fe(III) are efficient electron acceptors similar to nitrate in redox abilities and capable of out-competing electron acceptors of lower potential, such as sulfate (sulfate reduction) or CO2 (methanogenesis). Field studies of iron and/or manganese reduction suggest that organisms with such metabolic abilities play important roles in coupling the oxidation of organic carbon to metal reduction under anaerobic conditions. Because both iron and manganese oxides are solids or colloids, they tend to settle downward in aquatic environments, providing a physical mechanism for the movement of oxidizing potential into anoxic zones. The resulting biogeochemical metal cycles have a strong impact on many other elements including carbon, sulfur, phosphorous, and trace metals.

  18. Seasonal and spatial variation in soil chemistry and anaerobic processes in an Arctic ecosystem

    NASA Astrophysics Data System (ADS)

    Lipson, D.; Mauritz, M.; Bozzolo, F.; Raab, T. K.; Santos, M. J.; Friedman, E. F.; Rosenbaum, M.; Angenent, L.

    2009-12-01

    Drained thaw lake basins (DTLB) are the dominant landform in the Arctic coastal plain near Barrow, Alaska. Our previous work in a DTLB showed that Fe(III) and humic substances are important electron acceptors in anaerobic respiration, and play a significant role in the C cycle of these organic-rich soils. In the current study, we investigated seasonal and spatial patterns of availability of electron acceptors and labile substrate, redox conditions and microbial activity. Landscapes within DTLB contain complex, fine-scale topography arising from ice wedge polygons, which produce raised and lowered areas. One goal of our study was to determine the effects of microtopographic variation on the potential for Fe(III) reduction and other anaerobic processes. Additionally, the soil in the study site has a complex vertical structure, with an organic peat layer overlying a mineral layer, overlying permafrost. We described variations in soil chemistry across depth profiles into the permafrost. Finally, we installed an integrated electrode/potentiostat system to electrochemically monitor microbial activity in the soil. Topographically low areas differed from high areas in most of the measured variables: low areas had lower oxidation-reduction potential, higher pH and electrical conductivity. Soil pore water from low areas had higher concentrations of Fe(III), Fe(II), dissolved organic C (DOC), and aromaticity (UV absorbance at 260nm, “A260”). Low areas also had higher concentrations of dissolve CO2 and CH4 in soil pore water. Laboratory incubations of soil showed a trend toward higher potentials for Fe(III) reduction in topographically low areas. Clearly, ice wedge-induced microtopography exerts a strong control on microbial processes in this DTLB landscape, with increased anaerobic activity occurring in the wetter, depressed areas. Soil water extracted from 5-15 cm depth had higher concentrations of Fe(III), Fe(II), A260, and DOC compared to soil water sampled from 0-5cm

  19. tRNA acceptor stem and anticodon bases form independent codes related to protein folding

    PubMed Central

    Carter, Charles W.; Wolfenden, Richard

    2015-01-01

    Aminoacyl-tRNA synthetases recognize tRNA anticodon and 3′ acceptor stem bases. Synthetase Urzymes acylate cognate tRNAs even without anticodon-binding domains, in keeping with the possibility that acceptor stem recognition preceded anticodon recognition. Representing tRNA identity elements with two bits per base, we show that the anticodon encodes the hydrophobicity of each amino acid side-chain as represented by its water-to-cyclohexane distribution coefficient, and this relationship holds true over the entire temperature range of liquid water. The acceptor stem codes preferentially for the surface area or size of each side-chain, as represented by its vapor-to-cyclohexane distribution coefficient. These orthogonal experimental properties are both necessary to account satisfactorily for the exposed surface area of amino acids in folded proteins. Moreover, the acceptor stem codes correctly for β-branched and carboxylic acid side-chains, whereas the anticodon codes for a wider range of such properties, but not for size or β-branching. These and other results suggest that genetic coding of 3D protein structures evolved in distinct stages, based initially on the size of the amino acid and later on its compatibility with globular folding in water. PMID:26034281

  20. Tuning Optoelectronic Properties of Organic Semiconductors Via Donor-Acceptor Cocrystals and Interfacial Composites

    NASA Astrophysics Data System (ADS)

    Wang, Chen

    Organic donor-acceptor (D-A) interaction has attracted intensive research interest because of the promising applications in electronic devices and renewable energy. Depending on the interaction process, the optoelectronic properties of organic semiconductors may change dramatically. To improve their performance and expand the applications, we have investigated the structure-property relationship in D-A cocrystals and nanofibril composites. These materials provide unique D-A interface structures, thus allowing tunable charge transfer across the interface, which can be modified and controlled by exquisite molecule design and supramolecular assembly. In Chapter 2, we studied the fabrication, conductivity, and chemiresistive sensor performance of tetrathiafulvalene (TTF) - 7,7,8,8-tetracyanoquinodimethane (TCNQ) charge transfer cocrystal microfibers. Compared to TCNQ and TTF, TTF-TCNQ cocrystal has much higher conductivity under ambient conditions, due to the high yield of charge separation, which also induces high polarization at the interface, resulting in different binding intensity towards alkyl and aromatic amines. Based on this investment, we developed a TTF-TCNQ chemiresistive sensor to efficiently discriminate alkyl and aromatic amine vapors. In Chapter 3, we further designed a new series of D-A cocrystals, and studied the coassembly and optical properties. The cocrystal is composed of coronene and perylene diimide at 1:1 molar ratio and belongs to the triclinic system, as confirmed by X-ray analysis. The donor and acceptor molecules perform an alternate pi-pi stacking along the (100) direction, leading to the strong one-dimensional growth tendency of macroscopic cocrystal. Additionally, due to the charge transfer interaction, the cocrystal shows a new and largely red-shifted photoluminescence band, compared to the crystals of the components. In Chapter 4, we alternatively developed a series of donor-acceptor nanofibril composites, in which the donor and

  1. Partial androgen insensitivity syndrome caused by a deep intronic mutation creating an alternative splice acceptor site of the AR gene.

    PubMed

    Ono, Hiroyuki; Saitsu, Hirotomo; Horikawa, Reiko; Nakashima, Shinichi; Ohkubo, Yumiko; Yanagi, Kumiko; Nakabayashi, Kazuhiko; Fukami, Maki; Fujisawa, Yasuko; Ogata, Tsutomu

    2018-02-02

    Although partial androgen insensitivity syndrome (PAIS) is caused by attenuated responsiveness to androgens, androgen receptor gene (AR) mutations on the coding regions and their splice sites have been identified only in <25% of patients with a diagnosis of PAIS. We performed extensive molecular studies including whole exome sequencing in a Japanese family with PAIS, identifying a deep intronic variant beyond the branch site at intron 6 of AR (NM_000044.4:c.2450-42 G > A). This variant created the splice acceptor motif that was accompanied by pyrimidine-rich sequence and two candidate branch sites. Consistent with this, reverse transcriptase (RT)-PCR experiments for cycloheximide-treated lymphoblastoid cell lines revealed a relatively large amount of aberrant mRNA produced by the newly created splice acceptor site and a relatively small amount of wildtype mRNA produced by the normal splice acceptor site. Furthermore, most of the aberrant mRNA was shown to undergo nonsense mediated decay (NMD) and, if a small amount of aberrant mRNA may have escaped NMD, such mRNA was predicted to generate a truncated AR protein missing some functional domains. These findings imply that the deep intronic mutation creating an alternative splice acceptor site resulted in the production of a relatively small amount of wildtype AR mRNA, leading to PAIS.

  2. Field emission analysis of band bending in donor/acceptor heterojunction

    NASA Astrophysics Data System (ADS)

    Xing, Yingjie; Li, Shuai; Wang, Guiwei; Zhao, Tianjiao; Zhang, Gengmin

    2016-06-01

    The donor/acceptor heterojunction plays an important role in organic solar cells. An investigation of band bending in the donor/acceptor heterojunction is helpful in analysis of the charge transport behavior and for the improvement of the device performance. In this work, we report an approach for detection of band bending in a donor/acceptor heterojunction that has been prepared on a small and sharp tungsten tip. In situ field emission measurements are performed after the deposition process, and a linear Fowler-Nordheim plot is obtained from the fresh organic film surface. The thickness-dependent work function is then measured in the layer-by-layer deposited heterojunction. Several different types of heterojunction (zinc phthalocyanine (ZnPc)/C60, copper phthalocyanine (CuPc)/3,4,9,10-perylenetetracarboxylic bisbenzimidazole, and CuPc/C60) are fabricated and analyzed. The different charge transfer directions in the heterojunctions are distinguished by field emission measurements. The calculation method used to determine the band bending is then discussed in detail. A triple layer heterojunction (C60/ZnPc/CuPc) is also analyzed using this method. A small amount of band bending is measured in the outer CuPc layer. This method provides an independent reference method for determination of the band bending in an organic heterojunction that will complement photoemission spectroscopy and current-voltage measurement methods.

  3. FdC1 and Leaf-Type Ferredoxins Channel Electrons From Photosystem I to Different Downstream Electron Acceptors.

    PubMed

    Guan, Xiaoqian; Chen, Shuai; Voon, Chia Pao; Wong, Kam-Bo; Tikkanen, Mikko; Lim, Boon L

    2018-01-01

    Plant-type ferredoxins in Arabidopsis transfer electrons from the photosystem I to multiple redox-driven enzymes involved in the assimilation of carbon, nitrogen, and sulfur. Leaf-type ferredoxins also modulate the switch between the linear and cyclic electron routes of the photosystems. Recently, two novel ferredoxin homologs with extra C-termini were identified in the Arabidopsis genome (AtFdC1, AT4G14890; AtFdC2, AT1G32550). FdC1 was considered as an alternative electron acceptor of PSI under extreme ferredoxin-deficient conditions. Here, we showed that FdC1 could interact with some, but not all, electron acceptors of leaf-type Fds, including the ferredoxin-thioredoxin reductase (FTR), sulfite reductase (SiR), and nitrite reductase (NiR). Photoreduction assay on cytochrome c and enzyme assays confirmed its capability to receive electrons from PSI and donate electrons to the Fd-dependent SiR and NiR but not to the ferredoxin-NADP + oxidoreductase (FNR). Hence, FdC1 and leaf-type Fds may play differential roles by channeling electrons from photosystem I to different downstream electron acceptors in photosynthetic tissues. In addition, the median redox potential of FdC1 may allow it to receive electrons from FNR in non-photosynthetic plastids.

  4. FdC1 and Leaf-Type Ferredoxins Channel Electrons From Photosystem I to Different Downstream Electron Acceptors

    PubMed Central

    Guan, Xiaoqian; Chen, Shuai; Voon, Chia Pao; Wong, Kam-Bo; Tikkanen, Mikko; Lim, Boon L.

    2018-01-01

    Plant-type ferredoxins in Arabidopsis transfer electrons from the photosystem I to multiple redox-driven enzymes involved in the assimilation of carbon, nitrogen, and sulfur. Leaf-type ferredoxins also modulate the switch between the linear and cyclic electron routes of the photosystems. Recently, two novel ferredoxin homologs with extra C-termini were identified in the Arabidopsis genome (AtFdC1, AT4G14890; AtFdC2, AT1G32550). FdC1 was considered as an alternative electron acceptor of PSI under extreme ferredoxin-deficient conditions. Here, we showed that FdC1 could interact with some, but not all, electron acceptors of leaf-type Fds, including the ferredoxin-thioredoxin reductase (FTR), sulfite reductase (SiR), and nitrite reductase (NiR). Photoreduction assay on cytochrome c and enzyme assays confirmed its capability to receive electrons from PSI and donate electrons to the Fd-dependent SiR and NiR but not to the ferredoxin-NADP+ oxidoreductase (FNR). Hence, FdC1 and leaf-type Fds may play differential roles by channeling electrons from photosystem I to different downstream electron acceptors in photosynthetic tissues. In addition, the median redox potential of FdC1 may allow it to receive electrons from FNR in non-photosynthetic plastids. PMID:29670639

  5. Efficient Formation of Light-Absorbing Polymeric Nanoparticles from the Reaction of Soluble Fe(III) with C4 and C6 Dicarboxylic Acids.

    PubMed

    Tran, Ashley; Williams, Geoffrey; Younus, Shagufta; Ali, Nujhat N; Blair, Sandra L; Nizkorodov, Sergey A; Al-Abadleh, Hind A

    2017-09-05

    The role of transition metals in the formation and aging of secondary organic aerosol (SOA) from aliphatic and aromatic precursors in heterogeneous/multiphase reactions is not well understood. The reactivity of soluble Fe(III) toward known benzene photooxidation products that include fumaric (trans-butenedioic) and muconic (trans,trans-2,4-hexadienedioic) acids was investigated. Efficient formation of brightly colored nanoparticles was observed that are mostly rod- or irregular-shaped depending on the structure of the organic precursor. The particles were characterized for their optical properties, growth rate, elemental composition, iron content, and oxidation state. Results indicate that these particles have mass absorption coefficients on the same order as black carbon and larger than that of biomass burning aerosols. The particles are also amorphous in nature and consist of polymeric chains of Fe centers complexed to carboxylate groups. The oxidation state of Fe was found to be in between Fe(III) and Fe(II) in standard compounds. The organic reactant to iron molar ratio and pH were found to affect the particle growth rate. Control experiments using maleic acid (cis-butenedioic acid) and succinic acid (butanedioic acid) produced no particles. The formation of particles reported herein could account for new pathways that lead to SOA and brown carbon formation mediated by transition metals. In addition, the multiple chemically active components in these particles (iron, organics, and acidic groups) may have an effect on their chemical reactivity (enhanced uptake of trace gases, catalysis, and production of reactive oxygen species) and their likely poor cloud/ice nucleation properties.

  6. Metastable electronic populations and relaxation of Fe(I), Fe(II), and Fe(III) in MgO observed by Mössbauer emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Tuczek, F.; Spiering, H.; Gütlich, P.

    1990-06-01

    Magnetic-field Mössbauer emission spectra of 57Co in MgO single crystals covering a broad velocity range and measured up to high signal-to-noise ratios are presented. In accordance with a previous study, three charge states of 57Fe are found after 57Co(EC)57Fe (EC stands for electron capture). The evaluation of the Fe(III) fraction indicates nonthermalized populations of the 6A1 ground-state Zeeman levels. The field, temperature, and angular dependences of these populations are evaluated and display qualitative differences to the findings in 57Co/LiNbO3. The implications of the cubic symmetry on the spin-selective ground-state population are considered. In addition, a completely analogous phenomenon is evidenced for the first time within an Fe(II) electronic manifold, namely, the Γ5g ground state of Fe(II) in MgO, after the nuclear decay. In contrast to the Fe(III) case, these populations are not static within the Mössbauer time window. It turns out that the attainment of thermal equilibrium can be conveniently observed by changing the field value, evidencing a direct relaxation process at 4.2 K within Γ5g. The relaxation rates are compatible with static strain data; an initial alignment is observed. Finally, there is strong evidence that the Fe(I) fraction is also populated out of thermal equilibrium. In addition to these ground-state spectra, two features are present that may be attributed to metastable excited states of Fe(II) and Fe(III). It is described in detail how these various contributions can be disentangled.

  7. Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions

    NASA Astrophysics Data System (ADS)

    Tarazi, Leila; Narayanan, Nara; Sowell, John; Patonay, Gabor; Strekowski, Lucjan

    2002-01-01

    The spectral features of the squarylium dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is at 669 nm in tetrahydrofuran. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission maximum of the dye in tetrahydrofuran is at 676 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The detection limit is 6.24×10 -8 M for Fe(III) ion and 1.55×10 -8 M for Co(II) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant KS of the metal-dye complex was calculated to be 3.14×10 6 M -1 for the Fe-dye complex and 2.64×10 5 M -1 for the Co-dye complex.

  8. Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions.

    PubMed

    Tarazi, Leila; Narayanan, Nara; Sowell, John; Patonay, Gabor; Strekowski, Lucjan

    2002-01-15

    The spectral features of the squarylium dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is at 669 nm in tetrahydrofuran. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission maximum of the dye in tetrahydrofuran is at 676 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The detection limit is 6.24 x 10(-8) M for Fe(III) ion and 1.55 x 10(-8) M for Co(II) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant Ks of the metal-dye complex was calculated to be 3.14 x 10(6) M(-1) for the Fe-dye complex and 2.64 x 10(5) M(-1) for the Co-dye complex.

  9. Synthesis, spectroscopic, thermal and anticancer studies of metal-antibiotic chelations: Ca(II), Fe(III), Pd(II) and Au(III) chloramphenicol complexes

    NASA Astrophysics Data System (ADS)

    Al-Khodir, Fatima A. I.; Refat, Moamen S.

    2016-09-01

    Four Ca(II), Fe(III), Pd(II) and Au(III) complexes of chloramphenicol drug have been synthesized and well characterized using elemental analyses, (infrared, electronic, and 1H-NMR) spectra, magnetic susceptibility measurement, and thermal analyses. Infrared spectral data show that the chloramphenicol drug coordinated to Ca(II), Pd(II) and Au(III) metal ions through two hydroxyl groups with 1:1 or 1:2 M ratios, but Fe(III) ions chelated towards chloramphenicol drug via the oxygen and nitrogen atoms of amide group with 1:2 ratio based on presence of keto↔enol form. The X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) techniques were used to identify the nano-size particles of both iron(III) and gold(III) chloramphenicol complexes. The antimicrobial assessments of the chloramphenicol complexes were scanned and collected the results against of some kind of bacteria and fungi. The cytotoxic activity of the gold(III) complex was tested against the human colon carcinoma (HCT-116) and human hepatocellular carcinoma (HepG-2) tumor cell lines.

  10. Ultrafast photoinduced charge transport in Pt(II) donor-acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor.

    PubMed

    Sazanovich, Igor V; Best, Jonathan; Scattergood, Paul A; Towrie, Michael; Tikhomirov, Sergei A; Bouganov, Oleg V; Meijer, Anthony J H M; Weinstein, Julia A

    2014-12-21

    Visible light-induced charge transfer dynamics were investigated in a novel transition metal triad acceptor-chromophore-donor, (NDI-phen)Pt(II)(-C≡C-Ph-CH2-PTZ)2 (1), designed for photoinduced charge separation using a combination of time-resolved infrared (TRIR) and femtosecond electronic transient absorption (TA) spectroscopy. In 1, the electron acceptor is 1,4,5,8-naphthalene diimide (NDI), and the electron donor is phenothiazine (PTZ), and [(phen)Pt(-C≡C-Ph-)], where phen is 1,10-phenanthroline, represents the chromophoric core. The first excited state observed in 1 is a (3)MLCT/LL'CT, with {Pt(II)-acetylide}-to-phen character. Following that, charge transfer from the phen-anion onto the NDI subunit to form NDI(-)-phen-[Pt-(C≡C)2](+)-PTZ2 occurs with a time constant of 2.3 ps. This transition is characterised by appearance of the prominent NDI-anion features in both TRIR and TA spectra. The final step of the charge separation in 1 proceeds with a time constant of ∼15 ps during which the hole migrates from the [Pt-(C≡C)2] subunit to one of the PTZ groups. Charge recombination in 1 then occurs with two distinct time constants of 36 ns and 107 ns, corresponding to the back electron transfer to each of the two donor groups; a rather rare occurrence which manifests that the hole in the final charge-separated state is localised on one of the two donor PTZ groups. The assignment of the nature of the excited states and dynamics in 1 was assisted by TRIR investigations of the analogous previously reported ((COOEt)2bpy)Pt(C≡C-Ph-CH2-PTZ)2 (2), (J. E. McGarrah and R. Eisenberg, Inorg. Chem., 2003, 42, 4355; J. E. McGarrah, J. T. Hupp and S. N. Smirnov, J. Phys. Chem. A, 2009, 113, 6430) as well as (bpy)Pt(C≡C-Ph-C7H15)2, which represent the acceptor-free dyad, and the chromophoric core, respectively. Thus, the step-wise formation of the full charge-separated state on the picosecond time scale and charge recombination via tunnelling have been established; and

  11. Discriminating a deep gallium antisite defect from shallow acceptors in GaAs using supercell calculations

    DOE PAGES

    Schultz, Peter A.

    2016-03-01

    For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as B As. Thismore » systematic approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. Lastly, the properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.« less

  12. Diketopyrrolopyrrole-based π-bridged donor-acceptor polymer for photovoltaic applications.

    PubMed

    Li, Wenting; Lee, Taegweon; Oh, Soong Ju; Kagan, Cherie R

    2011-10-01

    We report the synthesis, properties, and photovoltaic applications of a new conjugated copolymer (C12DPP-π-BT) containing a donor group (bithiophene) and an acceptor group (2,5-didodecylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione), bridged by a phenyl group. Using cyclic voltammetry, we found the energy levels of C12DPP-π-BT are intermediate to common electron donor and acceptor photovoltaic materials, poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), respectively. Whereas P3HT and PCBM are exclusively electron donating or accepting, we predict C12DPP-π-BT may uniquely serve as either an electron donor or an acceptor when paired with PCBM or P3HT forming junctions with large built-in potentials. We confirmed the ambipolar nature of C12DPP-π-BT in space charge limited current measurements and in C12DPP-π-BT:PCBM and C12DPP-π-BT:P3HT bulk heterojunction solar cells, achieving power conversion efficiencies of 1.67% and 0.84%, respectively, under illumination of AM 1.5G (100 mW/cm(2)). Adding diiodooctane to C12DPP-π-BT:PCBM improved donor-acceptor inter-mixing and film uniformity, and therefore enhanced charge separation and overall device efficiency. Using higher-molecular-weight polymer C12DPP-π-BT in both C12DPP-π-BT:PCBM and C12DPP-π-BT:P3HT devices improved charge transport and hence the performance of the solar cells. In addition, we compared the structural and electronic properties of C12DPP-π-BT:PCBM and C12DPP-π-BT:P3HT blends, representing the materials classes of polymer:fullerene and polymer:polymer blends. In C12DPP-π-BT:PCBM blends, higher short circuit currents were obtained, consistent with faster charge transfer and balanced electron and hole transport, but lower open circuit voltages may be reduced by trap-assisted recombination and interfacial recombination losses. In contrast, C12DPP-π-BT:P3HT blends exhibit higher open circuit voltage, but short circuit currents were limited by charge transfer

  13. Carbon acceptor incorporation in GaAs grown by metalorganic chemical vapor deposition: Arsine versus tertiarybutylarsine

    NASA Astrophysics Data System (ADS)

    Watkins, S. P.; Haacke, G.

    1991-10-01

    Undoped p-type GaAs epilayers were grown by low-pressure metalorganic chemical vapor deposition (MOCVD) at 650 °C and 76 Torr using either arsine or tertiarybutylarsine (TBA), and trimethylgallium (TMG). Extremely high-purity precursors were used in order to eliminate extrinsic doping effects. Carbon acceptors from the TMG were the dominant residual electrical impurities under all growth conditions. Temperature-dependent Hall measurements were used to make a quantitative comparison of the carbon acceptor concentrations for arsine- and TBA-grown epilayers over a range of As partial pressures. For a given group V partial pressure, we report a significant reduction in carbon acceptor incorporation using TBA compared with arsine under identical growth conditions.

  14. Spectral engineering in π-conjugated polymers with intramolecular donor-acceptor interactions.

    PubMed

    Beaujuge, Pierre M; Amb, Chad M; Reynolds, John R

    2010-11-16

    With the development of light-harvesting organic materials for solar cell applications and molecular systems with fine-tuned colors for nonemissive electrochromic devices (e.g., smart windows, e-papers), a number of technical challenges remain to be overcome. Over the years, the concept of "spectral engineering" (tailoring the complex interplay between molecular physics and the various optical phenomena occurring across the electromagnetic spectrum) has become increasingly relevant in the field of π-conjugated organic polymers. Within the spectral engineering toolbox, the "donor-acceptor" approach uses alternating electron-rich and electron-deficient moieties along a π-conjugated backbone. This approach has proved especially valuable in the synthesis of dual-band and broadly absorbing chromophores with useful photovoltaic and electrochromic properties. In this Account, we highlight and provide insight into a present controversy surrounding the origin of the dual band of absorption sometimes encountered in semiconducting polymers structured using the "donor-acceptor" approach. Based on empirical evidence, we provide some schematic representations to describe the possible mechanisms governing the evolution of the two-band spectral absorption observed on varying the relative composition of electron-rich and electron-deficient substituents along the π-conjugated backbone. In parallel, we draw attention to the choice of the method employed to estimate and compare the absorption coefficients of polymer chromophores exhibiting distinct repeat unit lengths, and containing various extents of solubilizing side-chains along their backbone. Finally, we discuss the common assumption that "donor-acceptor" systems should have systematically lower absorption coefficients than their "all-donor" counterparts. The proposed models point toward important theoretical parameters which could be further explored at the macromolecular level to help researchers take full advantage of the

  15. Free-Standing Undoped ZnO Microtubes with Rich and Stable Shallow Acceptors

    PubMed Central

    Wang, Qiang; Yan, Yinzhou; Zeng, Yong; Lu, Yue; Chen, Liang; Jiang, Yijian

    2016-01-01

    Fabrication of reliable large-sized p-ZnO is a major challenge to realise ZnO-based electronic device applications. Here we report a novel technique to grow high-quality free-standing undoped acceptor-rich ZnO (A-ZnO) microtubes with dimensions of ~100 μm (in diameter) × 5 mm (in length) by optical vapour supersaturated precipitation. The A-ZnO exhibits long lifetimes (>1 year) against compensation/lattice-relaxation and the stable shallow acceptors with binding energy of ~127 meV are confirmed from Zn vacancies. The A-ZnO provides a possibility for a mimetic p-n homojunction diode with n+-ZnO:Sn. The high concentrations of holes in A-ZnO and electrons in n+-ZnO make the dual diffusion possible to form a depletion layer. The diode threshold voltage, turn-on voltage, reverse saturated current and reverse breakdown voltage are 0.72 V, 1.90 V, <10 μA and >15 V, respectively. The A-ZnO also demonstrates quenching-free donor-acceptor-pairs (DAP) emission located in 390–414 nm with temperature of 270–470 K. Combining the temperature-dependent DAP violet emission with native green emission, the visible luminescence of A-ZnO microtube can be modulated in a wide region of colour space across white light. The present work opens up new opportunities to achieve ZnO with rich and stable acceptors instead of p-ZnO for a variety of potential applications. PMID:27263856

  16. FRET two-hybrid assay by linearly fitting FRET efficiency to concentration ratio between acceptor and donor

    NASA Astrophysics Data System (ADS)

    Du, Mengyan; Yang, Fangfang; Mai, Zihao; Qu, Wenfeng; Lin, Fangrui; Wei, Lichun; Chen, Tongsheng

    2018-04-01

    We here introduce a fluorescence resonance energy transfer (FRET) two-hybrid assay method to measure the maximal donor(D)- and acceptor(A)-centric FRET efficiency (ED,max and EA,max) of the D-A complex and its stoichiometry by linearly fitting the donor-centric FRET efficiency (ED) to the acceptor-to-donor concentration ratio (RC) and acceptor-centric FRET efficiency (EA) to 1/RC, respectively. We performed this method on a wide-field fluorescence microscope for living HepG2 cells co-expressing FRET tandem constructs and free donor/acceptor and obtained correct ED, EA, and stoichiometry values of those tandem constructs. Evaluation on the binding of Bad with Bcl-XL in Hela cells showed that Bad interacted strongly with Bcl-XL to form a Bad-Bcl-XL complex on mitochondria, and one Bad interacted mainly with one Bcl-XL molecule in healthy cells, while with multiple (maybe 2) Bcl-XL molecules in apoptotic cells.

  17. Natural organic matter as electron acceptor: experimental evidence for its important role in anaerobic respiration

    NASA Astrophysics Data System (ADS)

    Lau, Maximilian Peter; Sander, Michael; Gelbrecht, Jörg; Hupfer, Michael

    2014-05-01

    Microbial respiration is a key driver of element cycling in oxic and anoxic environments. Upon depletion of oxygen as terminal electron acceptor (TEA), a number of anaerobic bacteria can employ alternative TEA for intracellular energy generation. Redox active quinone moieties in dissolved organic matter (DOM) are well known electron acceptors for microbial respiration. However, it remains unclear whether quinones in adsorbed and particulate OM accept electrons in a same way. In our studies we aim to understand the importance of natural organic matter (NOM) as electron acceptors for microbial energy gain and its possible implications for methanogenesis. Using a novel electrochemical approach, mediated electrochemical reduction and -oxidation, we can directly quantify reduced hydroquinone and oxidized quionone moieties in dissolved and particulate NOM samples. In a mesocosm experiment, we rewetted sediment and peat soil and followed electron transfer to the inorganic and organic electron acceptors over time. We found that inorganic and organic electron acceptor pools were depleted over the same timescales. More importantly, we showed that organic, NOM-associated electron accepting moieties represent as much as 21 40% of total TEA inventories. These findings support earlier studies that propose that the reduction of quinone moieties in particulate organic matter competitively suppresses methanogenesis in wetland soils. Our results indicate that electron transfer to organic, particulate TEA in inundated ecosystems has to be accounted for when establishing carbon budgets in and projecting greenhouse gas emissions from these systems.

  18. Acceptor Type Vacancy Complexes In As-Grown ZnO

    NASA Astrophysics Data System (ADS)

    Zubiaga, A.; Tuomisto, F.; Zuñiga-Pérez, J.

    2010-11-01

    One of the many technological areas that ZnO is interesting for is the construction of opto-electronic devices working in the blue-UV range as its large band gap (˜3.4 eV at 10 K) makes them suitable for that purpose. As-grown ZnO shows generally n-type conductivity partially due to the large concentration of unintentional shallow donors, like H, but impurities can also form complexes with acceptor type defects (Zn vacancy) leading to the creation of compensating defects. Recently, LiZn and NaZn acceptors have been measured and H could form similar type of defects. Doppler Broadening Positron Annihilation spectroscopy experimental results on the observation of Zn related vacancy complexes in ZnO thin films, as-grown, O implanted and Al doped will be presented. Results show that as-grown ZnO film show small Zn vacancy related complexed that could be related to presence of H as a unintentional doping element.

  19. Role of microbial Fe(III) reduction and solution chemistry in aggregation and settling of suspended particles in the Mississippi River Delta plain, Louisiana, USA

    USGS Publications Warehouse

    Jaisi, Deb P.; Ji, Shanshan; Dong, Hailiang; Blake, Ruth E.; Eberl, Dennis D.; Kim, Jinwook

    2008-01-01

    River-dominated delta areas are primary sites of active biogeochemical cycling, with productivity enhanced by terrestrial inputs of nutrients. Particle aggregation in these areas primarily controls the deposition of suspended particles, yet factors that control particle aggregation and resulting sedimentation in these environments are poorly understood. This study was designed to investigate the role of microbial Fe(III) reduction and solution chemistry in aggregation of suspended particles in the Mississippi Delta. Three representative sites along the salinity gradient were selected and sediments were collected from the sediment-water interface. Based on quantitative mineralogical analyses 88–89 wt.% of all minerals in the sediments are clays, mainly smectite and illite. Consumption of SO42− and the formation of H2S and pyrite during microbial Fe(III) reduction of the non-sterile sediments by Shewanella putrefaciens CN32 in artificial pore water (APW) media suggest simultaneous sulfate and Fe(III) reduction activity. The pHPZNPC of the sediments was ≤3.5 and their zeta potentials at the sediment-water interface pH (6.9–7.3) varied from −35 to −45 mV, suggesting that both edges and faces of clay particles have negative surface charge. Therefore, high concentrations of cations in pore water are expected to be a predominant factor in particle aggregation consistent with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Experiments on aggregation of different types of sediments in the same APW composition revealed that the sediment with low zeta potential had a high rate of aggregation. Similarly, addition of external Fe(II) (i.e. not derived from sediments) was normally found to enhance particle aggregation and deposition in all sediments, probably resulting from a decrease in surface potential of particles due to specific Fe(II) sorption. Scanning and transmission electron microscopy (SEM, TEM) images showed predominant face-to-face clay aggregation in

  20. Effect of π-bridge units on properties of A-π-D-π-A-type nonfullerene acceptors for organic solar cells.

    PubMed

    Wang, Yan-Ling; Li, Quan-Song; Li, Ze-Sheng

    2018-05-15

    Acceptor-π-donor-π-acceptor (A-π-D-π-A)-types of small molecules are very promising nonfullerene acceptors to overcome the drawbacks of fullerene derivatives such as the weak absorption ability and electronic adjustability. However, only few attempts have been made to develop π-bridge units to construct highly efficient acceptors in OSCs. Herein, taking the reported acceptor P1 as a reference, five small-structured acceptors (P2, P3, P4, P5, and P6) have been designed via the replacement of the π-bridge unit. A combination of quantum chemistry and Marcus theory approaches is employed to investigate the effect of different π-bridge units on the optical, electronic, and charge transport properties of P1-P6. The calculation results show that the designed molecules P2 and P5 can become potential acceptor replacements of P1 due to their red-shifted absorption bands, appropriate energy levels, low exciton binding energy, and high electron affinity and electron mobility. Additionally, compared with P3HT/P1, P3HT/P2 and P3HT/P5 exhibit stronger and wider absorption peaks, larger electron transfer distances (DCT), greater transferred charge amounts (Δq), and smaller overlaps (Λ), which shows that P2 and P5 have more significant electron transfer characteristics and favorable exciton dissociation capabilities for enhancing the short-circuit current density (JSC) and thus, they are potential acceptors in OSCs.

  1. Long-Lived Charge Separation at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kang, Hyun Suk; Sisto, Thomas J.; Peurifoy, Samuel

    Nonfullerene electron acceptors have facilitated a recent surge in the efficiencies of organic solar cells, although fundamental studies of the nature of exciton dissociation at interfaces with nonfullerene electron acceptors are still relatively sparse. Semiconducting single-walled carbon nanotubes (s-SWCNTs), unique one-dimensional electron donors with molecule-like absorption and highly mobile charges, provide a model system for studying interfacial exciton dissociation. Here, we investigate excited-state photodynamics at the heterojunction between (6,5) s-SWCNTs and two perylene diimide (PDI)-based electron acceptors. Each of the PDI-based acceptors, hPDI2-pyr-hPDI2 and Trip-hPDI2, is deposited onto (6,5) s-SWCNT films to form a heterojunction bilayer. Transient absorption measurements demonstratemore » that photoinduced hole/electron transfer occurs at the photoexcited bilayer interfaces, producing long-lived separated charges with lifetimes exceeding 1.0 us. Both exciton dissociation and charge recombination occur more slowly for the hPDI2-pyr-hPDI2 bilayer than for the Trip-hPDI2 bilayer. To explain such differences, we discuss the potential roles of the thermodynamic charge transfer driving force available at each interface and the different molecular structure and intermolecular interactions of PDI-based acceptors. As a result, detailed photophysical analysis of these model systems can develop the fundamental understanding of exciton dissociation between organic electron donors and nonfullerene acceptors, which has not been systematically studied.« less

  2. Cyan-emitting and orange-emitting fluorescent proteins as a donor/acceptor pair for fluorescence resonance energy transfer.

    PubMed

    Karasawa, Satoshi; Araki, Toshio; Nagai, Takeharu; Mizuno, Hideaki; Miyawaki, Atsushi

    2004-07-01

    GFP (green fluorescent protein)-based FRET (fluorescence resonance energy transfer) technology has facilitated the exploration of the spatio-temporal patterns of cellular signalling. While most studies have used cyan- and yellow-emitting FPs (fluorescent proteins) as FRET donors and acceptors respectively, this pair of proteins suffers from problems of pH-sensitivity and bleeding between channels. In the present paper, we demonstrate the use of an alternative additional donor/acceptor pair. We have cloned two genes encoding FPs from stony corals. We isolated a cyan-emitting FP from Acropara sp., whose tentacles exhibit cyan coloration. Similar to GFP from Renilla reniformis, the cyan FP forms a tight dimeric complex. We also discovered an orange-emitting FP from Fungia concinna. As the orange FP exists in a complex oligomeric structure, we converted this protein into a monomeric form through the introduction of three amino acid substitutions, recently reported to be effective for converting DsRed into a monomer (Clontech). We used the cyan FP and monomeric orange FP as a donor/acceptor pair to monitor the activity of caspase 3 during apoptosis. Due to the close spectral overlap of the donor emission and acceptor absorption (a large Förster distance), substantial pH-resistance of the donor fluorescence quantum yield and the acceptor absorbance, as well as good separation of the donor and acceptor signals, the new pair can be used for more effective quantitative FRET imaging.

  3. Long-Lived Charge Separation at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors

    DOE PAGES

    Kang, Hyun Suk; Sisto, Thomas J.; Peurifoy, Samuel; ...

    2018-04-13

    Nonfullerene electron acceptors have facilitated a recent surge in the efficiencies of organic solar cells, although fundamental studies of the nature of exciton dissociation at interfaces with nonfullerene electron acceptors are still relatively sparse. Semiconducting single-walled carbon nanotubes (s-SWCNTs), unique one-dimensional electron donors with molecule-like absorption and highly mobile charges, provide a model system for studying interfacial exciton dissociation. Here, we investigate excited-state photodynamics at the heterojunction between (6,5) s-SWCNTs and two perylene diimide (PDI)-based electron acceptors. Each of the PDI-based acceptors, hPDI2-pyr-hPDI2 and Trip-hPDI2, is deposited onto (6,5) s-SWCNT films to form a heterojunction bilayer. Transient absorption measurements demonstratemore » that photoinduced hole/electron transfer occurs at the photoexcited bilayer interfaces, producing long-lived separated charges with lifetimes exceeding 1.0 us. Both exciton dissociation and charge recombination occur more slowly for the hPDI2-pyr-hPDI2 bilayer than for the Trip-hPDI2 bilayer. To explain such differences, we discuss the potential roles of the thermodynamic charge transfer driving force available at each interface and the different molecular structure and intermolecular interactions of PDI-based acceptors. As a result, detailed photophysical analysis of these model systems can develop the fundamental understanding of exciton dissociation between organic electron donors and nonfullerene acceptors, which has not been systematically studied.« less

  4. A novel method for determination of alpha1,6fucosyltransferase activity using a reducing oligosaccharide from egg yolk as a specific acceptor.

    PubMed

    Yazawa, S; Kochibe, N; Nishimura, T; Shima, C; Takai, I; Adachi, M; Asao, T; Hada, T; Enoki, Y; Juneja, L R

    1998-09-01

    A new method for determination of alpha1,6fucosyltransferase activity has been described. Recently, the disialyl-biantennary undecasaccharide was prepared in high yield from egg yolk [(1996), Carbohydr Lett 2: 137-42]. By treatment of this oligosaccharide with neuraminidase and beta-galactosidase, we readily obtained an asialo-agalacto-biantennary heptasaccharide (GlcNAcbeta 1,2Manalpha1,6[GlcNAcbeta1,2Manalpha1,3]Manbeta1 ,4GlcNAcbeta1,4GlcNAc). Using this asialo-agalacto-oligosaccharide as an acceptor, fucosyltransferases from human plasma and extracts of various human hepatoma cell lines were assayed in the presence of GDP-[3H]fucose. The reaction mixture was applied to a column of GlcNAc-binding, Psathyrella velutina lectin coupled gel. All the fucosylated acceptor were bound to the column which was eluted with 50 mM GlcNAc. Structural analyses revealed that only the innermost GlcNAc residue of the acceptor was fucosylated through an alpha1,6-linkage, and the oligosaccharide prepared could be used as a specific acceptor for alpha1,6fucosyltransferase. The present method was used to screen plasma alpha1,6fucosyltransferase in several patient groups, and significantly elevated activities were found in samples from patients with liver diseases, including chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma.

  5. Small-Molecule Acceptor Based on the Heptacyclic Benzodi(cyclopentadithiophene) Unit for Highly Efficient Nonfullerene Organic Solar Cells.

    PubMed

    Kan, Bin; Feng, Huanran; Wan, Xiangjian; Liu, Feng; Ke, Xin; Wang, Yanbo; Wang, Yunchuang; Zhang, Hongtao; Li, Chenxi; Hou, Jianhui; Chen, Yongsheng

    2017-04-05

    A new nonfullerene small molecule with acceptor-donor-acceptor (A-D-A) structure, namely, NFBDT, based on a heptacyclic benzodi(cyclopentadithiophene) (FBDT) unit using benzo[1,2-b:4,5-b']dithiophene as the core unit, was designed and synthesized. Its absorption ability, energy levels, thermal stability, as well as photovoltaic performances were fully investigated. NFBDT exhibits a low optical bandgap of 1.56 eV resulting in wide and efficient absorption that covered the range from 600 to 800 nm, and suitable energy levels as an electron acceptor. With the widely used and successful wide bandgap polymer PBDB-T selected as the electron donor material, an optimized PCE of 10.42% was obtained for the PBDB-T:NFBDT-based device with an outstanding short-circuit current density of 17.85 mA cm -2 under AM 1.5G irradiation (100 mW cm -2 ), which is so far among the highest performance of NF-OSC devices. These results demonstrate that the BDT unit could also be applied for designing NF-acceptors, and the fused-ring benzodi(cyclopentadithiophene) unit is a prospective block for designing new NF-acceptors with excellent performance.

  6. Modular supramolecular approach for co-crystallization of donors and acceptors into ordered networks

    DOEpatents

    Stupp, Samuel I.; Stoddart, J. Fraser; Shveyd, Alex K.; Tayi, Alok S.; Sue, Andrew C. H.; Narayanan, Ashwin

    2016-09-20

    Organic charge-transfer (CT) co-crystals in a mixed stack system are disclosed, wherein a donor molecule (D) and an acceptor molecule (A) occupy alternating positions (DADADA) along the CT axis. A platform is provided which amplifies the molecular recognition of donors and acceptors and produces co-crystals at ambient conditions, wherein the platform comprises (i) a molecular design of the first constituent (.alpha.-complement), (ii) a molecular design of the second compound (.beta.-complement), and (iii) a solvent system that promotes co-crystallization.

  7. Modular supramolecular approach for co-crystallization of donors and acceptors into ordered networks

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stupp, Samuel I.; Stoddart, J. Fraser; Shveyd, Alexander K.

    Organic charge-transfer (CT) co-crystals in a mixed stack system are disclosed, wherein a donor molecule (D) and an acceptor molecule (A) occupy alternating positions (DADADA) along the CT axis. A platform is provided which amplifies the molecular recognition of donors and acceptors and produces co-crystals at ambient conditions, wherein the platform comprises (i) a molecular design of the first constituent (.alpha.-complement), (ii) a molecular design of the second compound (.beta.-complement), and (iii) a solvent system that promotes co-crystallization.

  8. TIO2 ADVANCED PHOTO-OXIDATION TECHNOLOGY: EFFECT OF ELECTRON ACCEPTORS

    EPA Science Inventory

    The effects of electron acceptors (additives) such as hydrogen peroxide, ammonium persulphate, potassium bromate and potassium peroxymonosulphate (ozone) on the TiO2 photocatalytic degradation of various organic pollutants were examined at various conditions. he individual and th...

  9. Discriminating a deep defect from shallow acceptors in supercell calculations: gallium antisite in GaAs

    NASA Astrophysics Data System (ADS)

    Schultz, Peter

    To make reliable first principles predictions of defect energies in semiconductors, it is crucial to discriminate between effective-mass-like defects--for which existing supercell methods fail--and deep defects--for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a framework of level occupation patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BAs. This systematic analysis determines that the gallium antisite is inconsistent with a shallow state, and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, predicting that the Ga antisite is a deep double acceptor and has two donor states, one of which might be accidentally shallow. -- Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  10. Magnetic field effect on the Coulomb interaction of acceptors in semimagnetic quantum dot

    NASA Astrophysics Data System (ADS)

    Kalpana, P.; Merwyn, A.; Reuben, Jasper D.; Nithiananthi, P.; Jayakumar, K.

    2015-06-01

    The Coulomb interaction of holes in a Semimagnetic Cd1-xMnxTe / CdTe Spherical and Cubical Quantum Dot (SMQD) in a magnetic field is studied using variational approach in the effective mass approximation. Since these holes in QD show a pronounced collective behavior, while distinct single particle phenomena is suppressed, their interaction in confined potential becomes very significant. It has been observed that acceptor-acceptor interaction is more in cubical QD than in spherical QD which can be controlled by the magnetic field. The results are presented and discussed.

  11. Medium-Bandgap Small-Molecule Donors Compatible with Both Fullerene and Nonfullerene Acceptors.

    PubMed

    Huo, Yong; Yan, Cenqi; Kan, Bin; Liu, Xiao-Fei; Chen, Li-Chuan; Hu, Chen-Xia; Lau, Tsz-Ki; Lu, Xinhui; Sun, Chun-Lin; Shao, Xiangfeng; Chen, Yongsheng; Zhan, Xiaowei; Zhang, Hao-Li

    2018-03-21

    Much effort has been devoted to the development of new donor materials for small-molecule organic solar cells due to their inherent advantages of well-defined molecular weight, easy purification, and good reproducibility in photovoltaic performance. Herein, we report two small-molecule donors that are compatible with both fullerene and nonfullerene acceptors. Both molecules consist of an (E)-1,2-di(thiophen-2-yl)ethane-substituted (TVT-substituted) benzo[1,2-b:4,5-b']dithiophene (BDT) as the central unit, and two rhodanine units as the terminal electron-withdrawing groups. The central units are modified with either alkyl side chains (DRBDT-TVT) or alkylthio side chains (DRBDT-STVT). Both molecules exhibit a medium bandgap with complementary absorption and proper energy level offset with typical acceptors like PC 71 BM and IDIC. The optimized devices show a decent power conversion efficiency (PCE) of 6.87% for small-molecule organic solar cells and 6.63% for nonfullerene all small-molecule organic solar cells. Our results reveal that rationally designed medium-bandgap small-molecule donors can be applied in high-performance small-molecule organic solar cells with different types of acceptors.

  12. Arsenic Cycling in Hydrocarbon Plumes: Secondary Effects of Natural Attenuation.

    PubMed

    Cozzarelli, Isabelle M; Schreiber, Madeline E; Erickson, Melinda L; Ziegler, Brady A

    2016-01-01

    Monitored natural attenuation is widely applied as a remediation strategy at hydrocarbon spill sites. Natural attenuation relies on biodegradation of hydrocarbons coupled with reduction of electron acceptors, including solid phase ferric iron (Fe(III)). Because arsenic (As) adsorbs to Fe-hydroxides, a potential secondary effect of natural attenuation of hydrocarbons coupled with Fe(III) reduction is a release of naturally occurring As to groundwater. At a crude-oil-contaminated aquifer near Bemidji, Minnesota, anaerobic biodegradation of hydrocarbons coupled to Fe(III) reduction has been well documented. We collected groundwater samples at the site annually from 2009 to 2013 to examine if As is released to groundwater and, if so, to document relationships between As and Fe inside and outside of the dissolved hydrocarbon plume. Arsenic concentrations in groundwater in the plume reached 230 µg/L, whereas groundwater outside the plume contained less than 5 µg/L As. Combined with previous data from the Bemidji site, our results suggest that (1) naturally occurring As is associated with Fe-hydroxides present in the glacially derived aquifer sediments; (2) introduction of hydrocarbons results in reduction of Fe-hydroxides, releasing As and Fe to groundwater; (3) at the leading edge of the plume, As and Fe are removed from groundwater and retained on sediments; and (4) downgradient from the plume, patterns of As and Fe in groundwater are similar to background. We develop a conceptual model of secondary As release due to natural attenuation of hydrocarbons that can be applied to other sites where an influx of biodegradable organic carbon promotes Fe(III) reduction. © 2015, National Ground Water Association.

  13. Development and Characterization of New Donor-Acceptor Conjugated Polymers and Fullerene Nanoparticles for High Performance Bulk Heterojunction Solar Cells

    DTIC Science & Technology

    2011-01-14

    thieno[3,4-c] pyrrole -4,6-dione (TPD)–based donor–acceptor polymer, PBTTPD, that exhibits high crystallinity and a low-lying highest occupied molecular...release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT Bithiophene/thieno[3,4-c] pyrrole -4,6-dione (TPD)?based donor?acceptor polymer...nearby fullerene acceptors. The electron-deficient thieno[3,4-c] pyrrole -4,6-dione (TPD) moiety exhibits a symmetric, rigidly fused, coplanar

  14. Mechanism of radiative recombination in acceptor-doped bulk GaN crystals

    NASA Astrophysics Data System (ADS)

    Godlewski, M.; Suski, T.; Grzegory, I.; Porowski, S.; Bergman, J. P.; Chen, W. M.; Monemar, B.

    1999-12-01

    Optical and electrical properties of acceptor-doped bulk GaN crystals are discussed. Though introducing Zn and Ca to bulk GaN does not significantly change electron concentration, it results in the appearance of a blue photoluminescence band accompanying the relatively strong yellow band usually present. Highly resistive GaN : Mg crystals are obtained when high amount of Mg is introduced to the Ga melt during high-pressure synthesis. Change of electrical properties of Mg-doped bulk crystals is accompanied by the appearance of a strong blue emission of GaN similar to that in Ca- and Zn-doped crystals. Optically detected magnetic resonance investigations indicate a multi-band character of this blue emission and suggest possible mechanism of compensation in acceptor-doped bulk GaN.

  15. Comparison of lactate, formate, and propionate as hydrogen donors for the reductive dehalogenation of trichloroethene in a continuous-flow column

    NASA Astrophysics Data System (ADS)

    Azizian, Mohammad F.; Marshall, Ian P. G.; Behrens, Sebastian; Spormann, Alfred M.; Semprini, Lewis

    2010-04-01

    A continuous-flow column study was conducted to analyze the reductive dehalogenation of trichloroethene (TCE) with aquifer material with high content of iron oxides. The column was bioaugmented with the Point Mugu (PM) culture, which is a mixed microbial enrichment culture capable of completely transforming TCE to ethene (ETH). We determined whether lactate, formate, or propionate fermentation resulted in more effective dehalogenation. Reductive dehalogenation, fermentation, and sulfate, Fe(III), and Mn(IV) reduction were all exhibited within the column. Different steady-states of dehalogenation were achieved based on the concentration of substrates added, with effective transformation to ETH obtained when ample electron donor equivalents were provided. Most of the metabolic reducing equivalents were channeled to sulfate, Fe(III), and Mn(IV) reduction. When similar electron reducing equivalents were added, the most effective dehalogenation was achieved with formate, with 14% of the electron equivalents going towards dehalogenation reactions, compared to 6.5% for lactate and 9.6% for propionate. Effective dehalogenation was maintained over 1000 days of column operation. Over 90% of electron equivalents added could be accounted for by the different electron accepting processes in the column, with 50% associated with soluble and precipitated Fe(II) and Mn(II). Bulk Fe(III) and Mn(IV) reduction was rather associated with lactate and propionate addition than formate addition. Sulfate reduction was a competing electron acceptor reaction with all three electron donors. DNA was extracted from solid coupon samples obtained during the course of the experiment and analyzed using 16S rRNA gene clone libraries and quantitative PCR. Lactate and propionate addition resulted in a significant increase in Geobacter, Spirochaetes, and Desulfitobacterium phylotypes relative to " Dehalococcoides" when compared to formate addition. Results from the molecular biological analyses support

  16. Fused-Ring Acceptors with Asymmetric Side Chains for High-Performance Thick-Film Organic Solar Cells.

    PubMed

    Feng, Shiyu; Zhang, Cai'e; Liu, Yahui; Bi, Zhaozhao; Zhang, Zhe; Xu, Xinjun; Ma, Wei; Bo, Zhishan

    2017-11-01

    A kind of new fused-ring electron acceptor, IDT-OB, bearing asymmetric side chains, is synthesized for high-efficiency thick-film organic solar cells. The introduction of asymmetric side chains can increase the solubility of acceptor molecules, enable the acceptor molecules to pack closely in a dislocated way, and form favorable phase separation when blended with PBDB-T. As expected, PBDB-T:IDT-OB-based devices exhibit high and balanced hole and electron mobility and give a high power conversion efficiency (PCE) of 10.12%. More importantly, the IDT-OB-based devices are not very sensitive to the film thickness, a PCE of 9.17% can still be obtained even the thickness of active layer is up to 210 nm. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Redox potential as a master variable controlling pathways of metal reduction by Geobacter sulfurreducens

    PubMed Central

    Levar, Caleb E; Hoffman, Colleen L; Dunshee, Aubrey J; Toner, Brandy M; Bond, Daniel R

    2017-01-01

    Geobacter sulfurreducens uses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of –0.10 V vs the standard hydrogen electrode, whereas the ImcH-dependent pathway operates only above this value. Here, we provide evidence that G. sulfurreducens also requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)-(oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high-potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment. PMID:28045456

  18. Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

    NASA Astrophysics Data System (ADS)

    Stübner, R.; Scheffler, L.; Kolkovsky, Vl.; Weber, J.

    2016-05-01

    In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are EC-0.06 eV (E42) and EC-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier for electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB configuration, where one H atom is directly bound to carbon in the anti-bonding position.

  19. Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing

    PubMed Central

    Li, Ning; Perea, José Darío; Kassar, Thaer; Richter, Moses; Heumueller, Thomas; Matt, Gebhard J.; Hou, Yi; Güldal, Nusret S.; Chen, Haiwei; Chen, Shi; Langner, Stefan; Berlinghof, Marvin; Unruh, Tobias; Brabec, Christoph J.

    2017-01-01

    The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. Here we demonstrate an abnormal strong burn-in degradation in highly efficient polymer solar cells caused by spinodal demixing of the donor and acceptor phases, which dramatically reduces charge generation and can be attributed to the inherently low miscibility of both materials. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. A theoretical calculation of the molecular parameters and construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells. PMID:28224984

  20. Doping of germanium and silicon crystals with non-hydrogenic acceptors for far infrared lasers

    DOEpatents

    Haller, Eugene E.; Brundermann, Erik

    2000-01-01

    A method for doping semiconductors used for far infrared lasers with non-hydrogenic acceptors having binding energies larger than the energy of the laser photons. Doping of germanium or silicon crystals with beryllium, zinc or copper. A far infrared laser comprising germanium crystals doped with double or triple acceptor dopants permitting the doped laser to be tuned continuously from 1 to 4 terahertz and to operate in continuous mode. A method for operating semiconductor hole population inversion lasers with a closed cycle refrigerator.

  1. Making highly conductive ZnO: creating donors and destroying acceptors

    NASA Astrophysics Data System (ADS)

    Look, D. C.; Leedy, K. D.

    2012-02-01

    We obtain room-temperature resistivities as low as ρ =1.4 x 10-4 Ω-cm in transparent Ga-doped ZnO grown on Al2O3 by pulsed laser deposition (PLD) at 200 °C in 10 mTorr of pure Ar and then annealed in a Zn enfivironment. Donor ND and acceptor NA concentrations are calculated from a recently developed scattering theory that is valid for any degenerate semiconductor material and requires only two input parameters, mobility μ and carrier concentration n measured at any temperature in the range 5 - 300 K. By comparison with SIMS and positron annihilation measurements, it has been shown that the donors in these samples are mostly GaZn, as expected, but that the acceptors are point defects, Zn vacancies VZn. PLD growth in Ar at 200 °C produces a high concentration of donors [GaZn] = 1.4 x 1021 cm-3, but VZn acceptors are produced at the same time, due to self-compensation. Fortunately, a large fraction of the VZn can be eliminated by annealing in a Zn environment. The theory gives ND and NA, and thus [GaZn] and [VZn], at each step of the growth and annealing process. For convenience, the theory is presented graphically, as plots of μ vs n at various values of compensation ratio K = NA/ND. From the value of K corresponding to the experimental values of μ and n, it is possible to calculate ND = n/(1 - K) and NA = nK/(1 - K).

  2. The presence of codon-anticodon pairs in the acceptor stem of tRNAs.

    PubMed Central

    Rodin, S; Rodin, A; Ohno, S

    1996-01-01

    A total of 1268 available (excluding mitochondrial) tRNA sequences was used to reconstruct the common consensus image of their acceptor domains. Its structure appeared as a 11-bp-long double-stranded palindrome with complementary triplets in the center, each flanked by the 3'-ACCD and NGGU-5' motifs on each strand (D, base determinator). The palindrome readily extends up to the modern tRNA-like cloverleaf passing through an intermediate hairpin having in the center the single-stranded triplet, in supplement to its double-stranded precursor. The latter might represent an original anticodon-codon pair mapped at 1-2-3 positions of the present-day tRNA acceptors. This conclusion is supported by the striking correlation: in pairs of consensus tRNAs with complementary anticodons, their bases at the 2nd position of the acceptor stem were also complementary. Accordingly, inverse complementarity was also evident at the 71st position of the acceptor stem. With a single exception (tRNA(Phe)-tRNA(Glu) pair), the parallelism is especially impressive for the pairs of tRNAs recognized by aminoacyl-tRNA synthetases (aaRS) from the opposite classes. The above complementarity still doubly presented at the key central position of real single-stranded anticodons and their hypothetical double-stranded precursors is consistent with our previous data pointing to the double-strand use of ancient RNAs in the origin of the main actors in translation- tRNAs with complementary anticodons and the two classes of aaRS. Images Fig. 3 Table 2 Fig. 4 PMID:8643439

  3. Dissimilatory Reduction of Extracellular Electron Acceptors in Anaerobic Respiration

    PubMed Central

    Richter, Katrin; Schicklberger, Marcus

    2012-01-01

    An extension of the respiratory chain to the cell surface is necessary to reduce extracellular electron acceptors like ferric iron or manganese oxides. In the past few years, more and more compounds were revealed to be reduced at the surface of the outer membrane of Gram-negative bacteria, and the list does not seem to have an end so far. Shewanella as well as Geobacter strains are model organisms to discover the biochemistry that enables the dissimilatory reduction of extracellular electron acceptors. In both cases, c-type cytochromes are essential electron-transferring proteins. They make the journey of respiratory electrons from the cytoplasmic membrane through periplasm and over the outer membrane possible. Outer membrane cytochromes have the ability to catalyze the last step of the respiratory chains. Still, recent discoveries provided evidence that they are accompanied by further factors that allow or at least facilitate extracellular reduction. This review gives a condensed overview of our current knowledge of extracellular respiration, highlights recent discoveries, and discusses critically the influence of different strategies for terminal electron transfer reactions. PMID:22179232

  4. Ultrafast above-threshold dynamics of the radical anion of a prototypical quinone electron-acceptor.

    PubMed

    Horke, Daniel A; Li, Quansong; Blancafort, Lluís; Verlet, Jan R R

    2013-08-01

    Quinones feature prominently as electron acceptors in nature. Their electron-transfer reactions are often highly exergonic, for which Marcus theory predicts reduced electron-transfer rates because of a free-energy barrier that occurs in the inverted region. However, the electron-transfer kinetics that involve quinones can appear barrierless. Here, we consider the intrinsic properties of the para-benzoquinone radical anion, which serves as the prototypical electron-transfer reaction product involving a quinone-based acceptor. Using time-resolved photoelectron spectroscopy and ab initio calculations, we show that excitation at 400 and 480 nm yields excited states that are unbound with respect to electron loss. These excited states are shown to decay on a sub-40 fs timescale through a series of conical intersections with lower-lying excited states, ultimately to form the ground anionic state and avoid autodetachment. From an isolated electron-acceptor perspective, this ultrafast stabilization mechanism accounts for the ability of para-benzoquinone to capture and retain electrons.

  5. New anthracene derivatives as triplet acceptors for efficient green-to-blue low-power upconversion.

    PubMed

    Liang, Zuo-Qin; Sun, Bin; Ye, Chang-Qing; Wang, Xiao-Mei; Tao, Xu-Tang; Wang, Qin-Hua; Ding, Ping; Wang, Bao; Wang, Jing-Jing

    2013-10-21

    Three new anthracene derivatives [2-chloro-9,10-dip-tolylanthracene (DTACl), 9,10-dip-tolylanthracene-2-carbonitrile (DTACN), and 9,10-di(naphthalen-1-yl)anthracene-2-carbonitrile (DNACN)] were synthesized as triplet acceptors for low-power upconversion. Their linear absorption, single-photon-excited fluorescence, and upconversion fluorescence properties were studied. The acceptors exhibit high fluorescence yields in DMF. Selective excitation of the sensitizer Pd(II)octaethylporphyrin (PdOEP) in solution containing DTACl, DTACN, or DNA-CN at 532 nm with an ultralow excitation power density of 0.5 W cm(-2) results in anti-Stokes blue emission. The maximum upconversion quantum yield (Φ(UC) =17.4%) was obtained for the couple PdOEP/DTACl. In addition, the efficiency of the triplet-triplet energy transfer process was quantitatively studied by quenching experiments. Experimental results revealed that a highly effective acceptor for upconversion should combine high fluorescence quantum yields with efficient quenching of the sensitizer triplet. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Interactions of chloride and formate at the donor and the acceptor side of photosystem II.

    PubMed

    Jajoo, Anjana; Bharti, Sudhakar; Kawamori, Asako

    2005-02-01

    Chloride is required for the maximum activity of the oxygen evolving complex (OEC) while formate inhibits the function of OEC. On the basis of the measurements of oxygen evolution rates and the S(2) state multiline EPR signal, an interaction between the action of chloride and formate at the donor side of PS II has been suggested. Moreover, the Fe(2)+Q-A EPR signals were measured to investigate a common binding site of both these anions at the PS II acceptor side. Other monovalent anions like bromide, nitrate etc. could influence the effects of formate to a small extent at the donor side of PS II, but not significantly at the acceptor side of PS II. The results presented in this paper clearly suggest a competitive binding of formate and chloride at the PS II acceptor side.

  7. J-V and C-V investigation of the effect of small molecular fullerene and non-fullerene acceptors for CH3NH3PbI3 perovskite solar cell

    NASA Astrophysics Data System (ADS)

    Zheng, Yanqiong; Wang, Chao; Yu, Junle; Yang, Fang; Zhang, Jing; Wei, Bin; Li, Weishi

    2017-11-01

    To find the ideal acceptors for perovskite solar cells (PSCs) and get insight into the dielectric property at the interface between perovskite and acceptor, series of small molecular fullerene and non-fullerene acceptors were comparatively investigated. Fullerene acceptors based PSCs show higher performance than non-fullerene acceptors based PSCs. However, the perylene tetracarboxylic diimide based PSC has achieved a η PCE of 4.70%, implying that it is a promising acceptor candidate for PSCs because of its suitable energy level, high electron mobility, and smooth surface. By employing double acceptors of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM)/C60 or PCBM/3,4,9,10-perylenetetracarboxylic bisbenzimidazole, the PSC stability is greatly improved even without performance enhancement. The perovskite (Pero)/PCBM film shows smooth surface, suggesting that PCBM penetrates into the Pero layer. The hydrophobicity trend of Pero/acceptor composite films is same as the device performance by judging from the water contact angle, and Pero/PCBM as well as Pero/C60 show higher hydrophobicity than other Pero/small-molecular-acceptor composite films. Capacitance-voltage characteristics of the series of single and double acceptor based PSCs were measured. The double acceptor based PSCs show larger depletion layer width (W d) than single acceptor based PSCs. Meanwhile, the defect density (N A) in Pero layer for single acceptor based PSCs is larger than that for double acceptor based PSCs, implying better n-doping of Pero layer by using a single acceptor.

  8. K 3 Fe(CN) 6 under External Pressure: Dimerization of CN – Coupled with Electron Transfer to Fe(III)

    DOE PAGES

    Li, Kuo; Zheng, Haiyan; Wang, Lijuan; ...

    2015-09-14

    The addition polymerization of charged monomers like C≡C 2– and C≡N– is scarcely seen at ambient conditions but can progress under external pressure with their conductivity significantly enhanced, which expands the research field of polymer science to inorganic salts. Moreover, the reaction pressures of transition metal cyanides like Prussian blue and K 3Fe(CN) 6 are much lower than that of alkali cyanides. To figure out the effect of the transition metal on the reaction, the crystal structure and electronic structure of K 3Fe(CN) 6 under external pressure are investigated by in situ neutron diffraction, in situ X-ray absorption fine structuremore » (XAFS), and neutron pair distribution functions (PDF) up to ~15 GPa. The cyanide anions react following a sequence of approaching–bonding–stabilizing. The Fe(III) brings the cyanides closer which makes the bonding progress at a low pressure (2–4 GPa). At ~8 GPa, an electron transfers from the CN to Fe(III), reduces the charge density on cyanide ions, and stabilizes the reaction product of cyanide. Finally, from this study we can conclude that bringing the monomers closer and reducing their charge density are two effective routes to decrease the reaction pressure, which is important for designing novel pressure induced conductor and excellent electrode materials.« less

  9. Photo-switchable Donor-Acceptor (D-A) Dyad Interfacial Self-Assembled Monolayers for Organic Photovoltaic Cells

    DTIC Science & Technology

    2015-11-05

    AFRL-AFOSR-VA-TR-2015-0396 (HBCU) Photo-switchable Donor-Acceptor for Organic Photovoltaic Cells Luis Echegoyen UNIVERSITY OF TEXAS AT EL PASO Final...Acceptor (D-A) Dyad Interfacial Self-Assembled Monolayers for Organic Photovoltaic Cells 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA9550-12-1-0053 5c...demonstrated using impedance spectroscopy for several triphenylamine-fullerene dyads, but their performance in photovoltaic devices was not remarkable, likely

  10. Ternary Organic Solar Cells Based on Two Compatible Nonfullerene Acceptors with Power Conversion Efficiency >10.

    PubMed

    Liu, Tao; Guo, Yuan; Yi, Yuanping; Huo, Lijun; Xue, Xiaonan; Sun, Xiaobo; Fu, Huiting; Xiong, Wentao; Meng, Dong; Wang, Zhaohui; Liu, Feng; Russell, Thomas P; Sun, Yanming

    2016-12-01

    Two different nonfullerene acceptors and one copolymer are used to fabricate ternary organic solar cells (OSCs). The two acceptors show unique interactions that reduce crystallinity and form a homogeneous mixed phase in the blend film, leading to a high efficiency of ≈10.3%, the highest performance reported for nonfullerene ternary blends. This work provides a new approach to fabricate high-performance OSCs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Quantum computing with acceptor spins in silicon.

    PubMed

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-17

    The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time [Formula: see text] as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si.

  12. Wide-range light-harvesting donor-acceptor assemblies through specific intergelator interactions via self-assembly.

    PubMed

    Samanta, Suman K; Bhattacharya, Santanu

    2012-12-03

    We have synthesized two new low-molecular-mass organogelators based on tri-p-phenylene vinylene derivatives, one of which could be designated as the donor whereas the other one is an acceptor. These were prepared specifically to show the intergelator interactions at the molecular level by using donor-acceptor self-assembly to achieve appropriate control over their macroscopic properties. Intermolecular hydrogen-bonding, π-stacking, and van der Waals interactions operate for both the individual components and the mixtures, leading to the formation of gels in the chosen organic solvents. Evidence for intergelator interactions was acquired from various spectroscopic, microscopic, thermal, and mechanical investigations. Due to the photochromic nature of these molecules, interesting photophysical properties, such as solvatochromism and J-type aggregation, were clearly observed. An efficient energy transfer was exhibited by the mixture of donor-acceptor assemblies. An array of four chromophores was built up by inclusion of two known dyes (anthracene and rhodamine 6G) for the energy-transfer studies. Interestingly, an energy-transfer cascade was observed in the assembly of four chromophores in a particular order (anthracene-donor-acceptor-rhodamine 6G), and if one of the components was removed from the assembly the energy transfer process was discontinued. This allowed the build up of a light-harvesting process with a wide range. Excitation at one end produces an emission at the other end of the assembly. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Stübner, R.; Scheffler, L.; Kolkovsky, Vl., E-mail: kolkov@ifpan.edu.pl

    In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are E{sub C}-0.06 eV (E42) and E{sub C}-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier formore » electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH{sub 1AB} configuration, where one H atom is directly bound to carbon in the anti-bonding position.« less

  14. Symmetry-breaking charge transfer in a zinc chlorodipyrrin acceptor for high open circuit voltage organic photovoltaics.

    PubMed

    Bartynski, Andrew N; Gruber, Mark; Das, Saptaparna; Rangan, Sylvie; Mollinger, Sonya; Trinh, Cong; Bradforth, Stephen E; Vandewal, Koen; Salleo, Alberto; Bartynski, Robert A; Bruetting, Wolfgang; Thompson, Mark E

    2015-04-29

    Low open-circuit voltages significantly limit the power conversion efficiency of organic photovoltaic devices. Typical strategies to enhance the open-circuit voltage involve tuning the HOMO and LUMO positions of the donor (D) and acceptor (A), respectively, to increase the interfacial energy gap or to tailor the donor or acceptor structure at the D/A interface. Here, we present an alternative approach to improve the open-circuit voltage through the use of a zinc chlorodipyrrin, ZCl [bis(dodecachloro-5-mesityldipyrrinato)zinc], as an acceptor, which undergoes symmetry-breaking charge transfer (CT) at the donor/acceptor interface. DBP/ZCl cells exhibit open-circuit voltages of 1.33 V compared to 0.88 V for analogous tetraphenyldibenzoperyflanthrene (DBP)/C60-based devices. Charge transfer state energies measured by Fourier-transform photocurrent spectroscopy and electroluminescence show that C60 forms a CT state of 1.45 ± 0.05 eV in a DBP/C60-based organic photovoltaic device, while ZCl as acceptor gives a CT state energy of 1.70 ± 0.05 eV in the corresponding device structure. In the ZCl device this results in an energetic loss between E(CT) and qV(OC) of 0.37 eV, substantially less than the 0.6 eV typically observed for organic systems and equal to the recombination losses seen in high-efficiency Si and GaAs devices. The substantial increase in open-circuit voltage and reduction in recombination losses for devices utilizing ZCl demonstrate the great promise of symmetry-breaking charge transfer in organic photovoltaic devices.

  15. 9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor.

    PubMed

    Bin, Haijun; Yang, Yankang; Zhang, Zhi-Guo; Ye, Long; Ghasemi, Masoud; Chen, Shanshan; Zhang, Yindong; Zhang, Chunfeng; Sun, Chenkai; Xue, Lingwei; Yang, Changduk; Ade, Harald; Li, Yongfang

    2017-03-29

    In the last two years, polymer solar cells (PSCs) developed quickly with n-type organic semiconductor (n-OSs) as acceptor. In contrast, the research progress of nonfullerene organic solar cells (OSCs) with organic small molecule as donor and the n-OS as acceptor lags behind. Here, we synthesized a D-A structured medium bandgap organic small molecule H11 with bithienyl-benzodithiophene (BDTT) as central donor unit and fluorobenzotriazole as acceptor unit, and achieved a power conversion efficiency (PCE) of 9.73% for the all organic small molecules OSCs with H11 as donor and a low bandgap n-OS IDIC as acceptor. A control molecule H12 without thiophene conjugated side chains on the BDT unit was also synthesized for investigating the effect of the thiophene conjugated side chains on the photovoltaic performance of the p-type organic semiconductors (p-OSs). Compared with H12, the 2D-conjugated H11 with thiophene conjugated side chains shows intense absorption, low-lying HOMO energy level, higher hole mobility and ordered bimodal crystallite packing in the blend films. Moreover, a larger interaction parameter (χ) was observed in the H11 blends calculated from Hansen solubility parameters and differential scanning calorimetry measurements. These special features combined with the complementary absorption of H11 donor and IDIC acceptor resulted in the best PCE of 9.73% for nonfullerene all small molecule OSCs up to date. Our results indicate that fluorobenzotriazole based 2D conjugated p-OSs are promising medium bandgap donors in the nonfullerene OSCs.

  16. Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Scherer, Michelle

    2016-08-31

    During this project, we investigated Fe electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clay minerals. We used selective chemical extractions, enriched Fe isotope tracer experiments, computational molecular modeling, and Mössbauer spectroscopy. Our findings indicate that structural Fe(III) in clay minerals is reduced by aqueous Fe(II) and that electron transfer occurs when Fe(II) is sorbed to either basal planes and edge OH-groups of clay mineral. Findings from highly enriched isotope experiments suggest that up to 30 % of the Fe atoms in the structure of some clay minerals exhanges with aqueous Fe(II). First principles calculations usingmore » a small polaron hopping approach suggest surprisingly fast electron mobility at room temperature in a nontronite clay mineral and are consistent with temperature dependent Mössbauer data Fast electron mobility suggests that electrons may be able to conduct through the mineral fast enough to enable exchange of Fe between the aqueous phase and clay mineral structure. over the time periods we observed. Our findings suggest that Fe in clay minerals is not as stable as previously thought.« less

  17. Electron Acceptors Based on α-Substituted Perylene Diimide (PDI) for Organic Solar Cells

    DOE PAGES

    Zhao, Donglin; Wu, Qinghe; Cai, Zhengxu; ...

    2016-02-20

    The ortho-position functionalized perylene diimide derivatives (αPPID, αPBDT) were synthesized and used as the electron acceptors in nonfullerene organic photovoltaics. Due to the good planarity of ortho-position functionalized PDI, the αPPID and αPBDT show strong tendency to form aggregate because of their enhanced intermolecular pie-pie interaction. Moreover, they maintain the pure domains and the same packing order as in the pure film if they are blended with PBT7-TH and the SCLC measurement also shows the high electron mobility. The inverted OPVs employing αPDI-based compounds as acceptor and PBT7-TH as the donor give the highest PCE of 4.92 % for αPBDTmore » based device and 3.61 % for αPPID based device, which is 39 % and 4 % higher than that for their counterpart βPBDT and βPPID. The charge separation study shows the more efficient exciton dissociation at interfaces between PDI based compounds and PBT7-TH. In conclusion, the results suggest that compared to beta-substituted ones, alpha-substituted PDI derivatives are more promising electron acceptors for OPV.« less

  18. Hydrogen depassivation of the magnesium acceptor by beryllium in p-type GaN

    NASA Astrophysics Data System (ADS)

    Wang, Chihsiang; Wang, Xiao; Zhang, Qiming

    2010-05-01

    Under nitrogen-rich growth conditions, the present ab initio study predicts that hydrogen passivation is more effective on the acceptor Be instead of Mg in a co-doped p-type GaN. The formation energy is 0.24 eV for (H-Be Ga) complex, and 0.46 eV for (H-Mg Ga) complex. Congruently, the binding energy is 1.40 eV for (H-Be Ga), and 0.60 eV for (H-Mg Ga). Owing to the lower binding energy, (H-Mg Ga) is not thermally stable. As Be is incorporated in Mg-doped GaN, a (H-Mg Ga) may release a H + cation at relatively elevated temperatures. Consequently, the H + diffuses swiftly away from a Mg -Ga, across a barrier of 1.17 eV, towards a Be -Ga and forms a stable (H-Be Ga) with it. The activation of Mg acceptors can be thus facilitated. In this view, the process of hydrogen depassivation of the Mg acceptor by Be can convert the as-grown high-resistivity Mg-doped GaN into a p-conducting material, as observed in the experiments.

  19. Crystal structure of K0.75[Fe(II) 3.75Fe(III) 1.25(HPO3)6]·0.5H2O, an open-framework iron phosphite with mixed-valent Fe(II)/Fe(III) ions.

    PubMed

    Larrea, Edurne S; Mesa, José Luis; Legarra, Estibaliz; Aguayo, Andrés Tomás; Arriortua, Maria Isabel

    2016-01-01

    Single crystals of the title compound, potassium hexa-phosphito-penta-ferrate(II,III) hemihydrate, K0.75[Fe(II) 3.75Fe(III) 1.25(HPO3)6]·0.5H2O, were grown under mild hydro-thermal conditions. The crystal structure is isotypic with Li1.43[Fe(II) 4.43Fe(III) 0.57(HPO3)6]·1.5H2O and (NH4)2[Fe(II) 5(HPO3)6] and exhibits a [Fe(II) 3.75Fe(III) 1.25(HPO3)6](0.75-) open framework with disordered K(+) (occupancy 3/4) as counter-cations. The anionic framework is based on (001) sheets of two [FeO6] octa-hedra (one with point group symmetry 3.. and one with point group symmetry .2.) linked along [001] through [HPO3](2-) oxoanions. Each sheet is constructed from 12-membered rings of edge-sharing [FeO6] octa-hedra, giving rise to channels with a radius of ca 3.1 Å where the K(+) cations and likewise disordered water mol-ecules (occupancy 1/4) are located. O⋯O contacts between the water mol-ecule and framework O atoms of 2.864 (5) Å indicate hydrogen-bonding inter-actions of medium strength. The infrared spectrum of the compound shows vibrational bands typical for phosphite and water groups. The Mössbauer spectrum is in accordance with the presence of Fe(II) and Fe(III) ions.

  20. Ternary Polymer Solar Cells based on Two Acceptors and One Donor for Achieving 12.2% Efficiency.

    PubMed

    Zhao, Wenchao; Li, Sunsun; Zhang, Shaoqing; Liu, Xiaoyu; Hou, Jianhui

    2017-01-01

    Ternary polymer solar cells are fabricated based on one donor PBDB-T and two acceptors (a methyl-modified small-molecular acceptor (IT-M) and a bis-adduct of Bis[70]PCBM). A high power conversion efficiency of 12.2% can be achieved. The photovoltaic performance of the ternary polymer solar cells is not sensitive to the composition of the blend. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Investigations on the charge transfer mechanism at donor/acceptor interfaces in the quest for descriptors of organic solar cell performance.

    PubMed

    Muraoka, Azusa; Fujii, Mikiya; Mishima, Kenji; Matsunaga, Hiroki; Benten, Hiroaki; Ohkita, Hideo; Ito, Shinzaburo; Yamashita, Koichi

    2018-05-07

    Herein, we theoretically and experimentally investigated the mechanisms of charge separation processes of organic thin-film solar cells. PTB7, PTB1, and PTBF2 have been chosen as donors and PC 71 BM has been chosen as an acceptor considering that effective charge generation depends on the difference between the material combinations. Experimental results of transient absorption spectroscopy show that the hot process is a key step for determining external quantum efficiency (EQE) in these systems. From the quantum chemistry calculations, it has been found that EQE tends to increase as the transferred charge, charge transfer distance, and variation of dipole moments between the ground and excited states of the donor/acceptor complexes increase; this indicates that these physical quantities are a good descriptor to assess the donor-acceptor charge transfer quality contributing to the solar cell performance. We propose that designing donor/acceptor interfaces with large values of charge transfer distance and variation of dipole moments of the donor/acceptor complexes is a prerequisite for developing high-efficiency polymer/PCBM solar cells.

  2. Impact of Microcystis aeruginosa Exudate on the Formation and Reactivity of Iron Oxide Particles Following Fe(II) and Fe(III) Addition.

    PubMed

    Garg, Shikha; Wang, Kai; Waite, T David

    2017-05-16

    Impact of the organic exudate secreted by a toxic strain of Microcystis aeruginosa on the formation, aggregation, and reactivity of iron oxides that are formed on addition of Fe(II) and Fe(III) salts to a solution of the exudate is investigated in this study. The exudate has a stabilizing effect on the particles formed with decreased aggregation rate and increased critical coagulant concentration required for diffusion-limited aggregation to occur. These results suggest that the presence of algal exudates from Microcystis aeruginosa may significantly influence particle aggregation both in natural water bodies where Fe(II) oxidation results in oxide formation and in water treatment where Fe(III) salts are commonly added to aid particle growth and contaminant capture. The exudate also affects the reactivity of iron oxide particles formed with exudate coated particles undergoing faster dissolution than bare iron oxide particles. This has implications to iron availability, especially where algae procure iron via dissolution of iron oxide particles as a result of either reaction with reducing moieties, light-mediated ligand to metal charge transfer and/or reaction with siderophores. The increased reactivity of exudate coated particles is attributed, for the most part, to the smaller size of these particles, higher surface area and increased accessibility of surface sites.

  3. Central action of dendrotoxin: selective reduction of a transient K conductance in hippocampus and binding to localized acceptors.

    PubMed

    Halliwell, J V; Othman, I B; Pelchen-Matthews, A; Dolly, J O

    1986-01-01

    Dendrotoxin, a small single-chain protein from the venom of Dendroaspis angusticeps, is highly toxic following intracerebroventricular injection into rats. Voltage-clamp analysis of CA1 neurons in hippocampal slices, treated with tetrodotoxin, revealed that nanomolar concentrations of dendrotoxin reduce selectively a transient, voltage-dependent K conductance. Epileptiform activity known to be induced by dendrotoxin can be attributed to such an action. Membrane currents not affected directly by the toxin include (i) Ca-activated K conductance; (ii) noninactivating voltage-dependent K conductance; (iii) inactivating and noninactivating Ca conductances; (iv) persistent inward (anomalous) rectifier current. Persistence of the effects of the toxin when Cd was included to suppress spontaneous transmitter release indicates a direct action on the neuronal membrane. Using biologically active, 125I-labeled dendrotoxin, protein acceptor sites of high affinity were detected on cerebrocortical synaptosomal membranes and sections of rat brain. In hippocampus, toxin binding was shown autoradiographically to reside in synapse-rich and white matter regions, with lower levels in cell body layers. This acceptor is implicated in the action of toxin because its affinities for dendrotoxin congeners are proportional to their central neurotoxicities and potencies in reducing the transient, voltage-dependent K conductance.

  4. (3+3)-Annulation of Donor-Acceptor Cyclopropanes with Diaziridines.

    PubMed

    Trushkov, Igor V; Chagarovskiy, Alexey O; Vasin, Vladimir S; Kuznetsov, Vladimir V; Ivanova, Olga A; Rybakov, Victor B; Shumsky, Alexey N; Makhova, Nina N

    2018-06-23

    The first example of (3+3)-annulation of two different three-membered rings is reported herein. Donor-acceptor cyclopropanes in reaction with diaziridines were found to afford perhydropyridazine derivatives in high yields and diastereoselectivity under mild Lewis acid catalysis. The disclosed reaction is applicable for the broad substrate scope and exhibits an excellent functional group tolerance. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Fe(III) reduction and U(VI) immobilization by Paenibacillus sp. strain 300A, isolated from Hanford 300A subsurface sediments.

    PubMed

    Ahmed, Bulbul; Cao, Bin; McLean, Jeffrey S; Ica, Tuba; Dohnalkova, Alice; Istanbullu, Ozlem; Paksoy, Akin; Fredrickson, Jim K; Beyenal, Haluk

    2012-11-01

    A facultative iron-reducing [Fe(III)-reducing] Paenibacillus sp. strain was isolated from Hanford 300A subsurface sediment biofilms that was capable of reducing soluble Fe(III) complexes [Fe(III)-nitrilotriacetic acid and Fe(III)-citrate] but unable to reduce poorly crystalline ferrihydrite (Fh). However, Paenibacillus sp. 300A was capable of reducing Fh in the presence of low concentrations (2 μM) of either of the electron transfer mediators (ETMs) flavin mononucleotide (FMN) or anthraquinone-2,6-disulfonate (AQDS). Maximum initial Fh reduction rates were observed at catalytic concentrations (<10 μM) of either FMN or AQDS. Higher FMN concentrations inhibited Fh reduction, while increased AQDS concentrations did not. We also found that Paenibacillus sp. 300A could reduce Fh in the presence of natural ETMs from Hanford 300A subsurface sediments. In the absence of ETMs, Paenibacillus sp. 300A was capable of immobilizing U(VI) through both reduction and adsorption. The relative contributions of adsorption and microbial reduction to U(VI) removal from the aqueous phase were ∼7:3 in PIPES [piperazine-N,N'-bis(2-ethanesulfonic acid)] and ∼1:4 in bicarbonate buffer. Our study demonstrated that Paenibacillus sp. 300A catalyzes Fe(III) reduction and U(VI) immobilization and that these reactions benefit from externally added or naturally existing ETMs in 300A subsurface sediments.

  6. Fe(III) Reduction and U(VI) Immobilization by Paenibacillus sp. Strain 300A, Isolated from Hanford 300A Subsurface Sediments

    PubMed Central

    Ahmed, Bulbul; Cao, Bin; McLean, Jeffrey S.; Ica, Tuba; Dohnalkova, Alice; Istanbullu, Ozlem; Paksoy, Akin; Fredrickson, Jim K.

    2012-01-01

    A facultative iron-reducing [Fe(III)-reducing] Paenibacillus sp. strain was isolated from Hanford 300A subsurface sediment biofilms that was capable of reducing soluble Fe(III) complexes [Fe(III)-nitrilotriacetic acid and Fe(III)-citrate] but unable to reduce poorly crystalline ferrihydrite (Fh). However, Paenibacillus sp. 300A was capable of reducing Fh in the presence of low concentrations (2 μM) of either of the electron transfer mediators (ETMs) flavin mononucleotide (FMN) or anthraquinone-2,6-disulfonate (AQDS). Maximum initial Fh reduction rates were observed at catalytic concentrations (<10 μM) of either FMN or AQDS. Higher FMN concentrations inhibited Fh reduction, while increased AQDS concentrations did not. We also found that Paenibacillus sp. 300A could reduce Fh in the presence of natural ETMs from Hanford 300A subsurface sediments. In the absence of ETMs, Paenibacillus sp. 300A was capable of immobilizing U(VI) through both reduction and adsorption. The relative contributions of adsorption and microbial reduction to U(VI) removal from the aqueous phase were ∼7:3 in PIPES [piperazine-N,N′-bis(2-ethanesulfonic acid)] and ∼1:4 in bicarbonate buffer. Our study demonstrated that Paenibacillus sp. 300A catalyzes Fe(III) reduction and U(VI) immobilization and that these reactions benefit from externally added or naturally existing ETMs in 300A subsurface sediments. PMID:22961903

  7. Fe(III) Reduction and U(VI) Immobilization by Paenibacillus sp. Strain 300A, Isolated from Hanford 300A Subsurface Sediments

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ahmed, B.; Cao, B.; McLean, Jeffrey S.

    2012-11-07

    A facultative iron-reducing (Fe(III)-reducing) Paenibacillus sp. strain was isolated from Hanford 300A subsurface sediment biofilms that was capable of reducing soluble Fe(III) complexes (Fe(III)-NTA and Fe(III)-citrate) but unable to reduce poorly crystalline ferrihydrite (Fh). However, Paenibacillus sp. 300A was capable of reducing Fh in the presence of low concentrations (2 µM) of either of electron transfer mediators (ETMs) flavin mononucleotide (FMN) or anthraquinone-2,6-disulfonate (AQDS). Maximum initial Fh reduction rates were observed at catalytic concentrations (<10 µM) of either FMN or AQDS. Higher FMN concentrations inhibited Fh reduction, while increased AQDS concentrations did not. We found that Paenibacillus sp. 300A alsomore » could reduce Fh in the presence of natural ETMs from Hanford 300A subsurface sediments. In the absence of ETMs, Paenibacillus sp. 300A was capable of immobilizing U(VI) through both reduction and adsorption. The relative contributions of adsorption and microbial reduction to U(VI) removal from the aqueous phase were ~7:3 in PIPES and ~1:4 in bicarbonate buffer. Our study demonstrated that Paenibacillus sp. 300A catalyzes Fe(III) reduction and U(VI) immobilization and that these reactions benefit from externally added or naturally existing ETMs in 300A subsurface sediments.« less

  8. Fraction of Electrons Consumed in Electron Acceptor Reduction and Hydrogen Thresholds as Indicators of Halorespiratory Physiology

    PubMed Central

    Löffler, Frank E.; Tiedje, James M.; Sanford, Robert A.

    1999-01-01

    Measurements of the hydrogen consumption threshold and the tracking of electrons transferred to the chlorinated electron acceptor (fe) reliably detected chlororespiratory physiology in both mixed cultures and pure cultures capable of using tetrachloroethene, cis-1,2-dichloroethene, vinyl chloride, 2-chlorophenol, 3-chlorobenzoate, 3-chloro-4-hydroxybenzoate, or 1,2-dichloropropane as an electron acceptor. Hydrogen was consumed to significantly lower threshold concentrations of less than 0.4 ppmv compared with the values obtained for the same cultures without a chlorinated compound as an electron acceptor. The fe values ranged from 0.63 to 0.7, values which are in good agreement with theoretical calculations based on the thermodynamics of reductive dechlorination as the terminal electron-accepting process. In contrast, a mixed methanogenic culture that cometabolized 3-chlorophenol exhibited a significantly lower fe value, 0.012. PMID:10473415

  9. Charge Transfer and Collection in Dilute Organic Donor-Acceptor Heterojunction Blends.

    PubMed

    Ding, Kan; Liu, Xiao; Forrest, Stephen R

    2018-05-09

    Experimental and theoretical approaches are used to understand the role of nanomorphology on exciton dissociation and charge collection at dilute donor-acceptor (D-A) organic heterojunctions (HJs). Specifically, two charge transfer (CT) states in D-A mixed HJs comprising nanocrystalline domains of tetraphenyldibenzoperiflanthene (DBP) as the donor and C 70 as the acceptor are unambiguously related to the nanomorphology of the mixed layer. Alternating DBP:C 70 multilayer stacks are used to identify and control the optical properties of the CT states, as well as to simulate the dilute mixed heterojunctions. A kinetic Monte Carlo model along with photoluminescence spectroscopy and scanning transmission electron microscopy are used to quantitatively evaluate the layer morphology under various growth conditions. As a result, we are able to understand the counterintuitive observation of high charge extraction efficiency and device performance of DBP:C 70 mixed layer photovoltaics at surprisingly low (∼10%) donor concentrations.

  10. Assessing the Regioselectivity of OleD-Catalyzed Glycosylation with a Diverse Set of Acceptors

    PubMed Central

    Zhou, Maoquan; Hamza, Adel; Zhan, Chang-Guo; Thorson, Jon S.

    2013-01-01

    To explore the acceptor regioselectivity of OleD-catalyzed glucosylation, the products of OleD-catalyzed reactions with the six structurally diverse acceptors - flavones (daidzein), isoflavones (flavopiridol), stilbenes (resveratrol), indole alkaloids (10-hydroxycamptothecin), and steroids (2-methoxyestradiol) - were determined. This study highlights the first synthesis of flavopiridol and 2-methoxyestradiol glucosides and confirms the ability of OleD to glucosylate both aromatic and aliphatic nucleophiles. In all cases, molecular dynamics simulations were consistent with the determined product distribution and suggest the potential to develop a virtual screening model to identify additional OleD substrates. PMID:23360118

  11. Synthesis, magnetic, spectral, and antimicrobial studies of Cu(II), Ni(II) Co(II), Fe(III), and UO 2(II) complexes of a new Schiff base hydrazone derived from 7-chloro-4-hydrazinoquinoline

    NASA Astrophysics Data System (ADS)

    El-Behery, Mostafa; El-Twigry, Haifaa

    2007-01-01

    A new hydrazone ligand, HL, was prepared by the reaction of 7-chloro-4-hydrazinoquinoline with o-hydroxybenzaldehyde. The ligand behaves as monoprotic bidentate. This was accounted for as the ligand contains a phenolic group and its hydrogen atom is reluctant to be replaced by a metal ion. The ligand reacted with Cu(II), Ni(II), Co(II), Fe(III), and UO 2(II) ions to yield mononuclear complexes. In the case of Fe(III) ion two complexes, mono- and binuclear complexes, were obtained in the absence and presence of LiOH, respectively. Also, mixed ligand complexes were obtained from the reaction of the metal cations Cu(II), Ni(II) and Fe(III) with the ligand (HL) and 8-hydroxyquinoline (8-OHqu) in the presence of LiOH, in the molar ratio 1:1:1:1. It is clear that 8-OHqu behaves as monoprotic bidentate ligand in such mixed ligand complexes. The ligand, HL, and its metal complexes were characterized by elemental analyses, IR, UV-vis, mass, and 1H NMR spectra, as well as magnetic moment, conductance measurements, and thermal analyses. All complexes have octahedral configurations except Cu(II) complex which has an extra square-planar geometry, while Ni(II) mixed complex has also formed a tetrahedral configuration and UO 2(II) complex which formed a favorable pentagonal biprymidial geometry. Magnetic moment of the binuclear Fe(III) complex is quite low compared to calculated value for two iron ions complex and thus shows antiferromagnetic interactions between the two adjacent ferric ions. The HL and metal complexes were tested against one stain Gram positive bacteria ( Staphylococcus aureus), Gram negative bacteria ( Escherichia coli), and fungi ( Candida albicans). The tested compounds exhibited higher antibacterial acivities.

  12. Development of a C3-symmetric benzohydroxamate tripod: Trimetallic complexation with Fe(III), Cr(III) and Al(III)

    NASA Astrophysics Data System (ADS)

    Baral, Minati; Gupta, Amit; Kanungo, B. K.

    2016-06-01

    The design, synthesis and physicochemical characterization of a C3-symmetry Benzene-1,3,5-tricarbonylhydroxamate tripod, noted here as BTHA, are described. The chelator was built from a benzene as an anchor, symmetrically extended by three hydroxamate as ligating moieties, each bearing O, O donor sites. A combination of absorption spectrophotometry, potentiometry and theoretical investigations are used to explore the complexation behavior of the ligand with some trivalent metal ions: Fe(III), Cr(III), and Al(III). Three protonation constants were calculated for the ligand in a pH range of 2-11 in a highly aqueous medium (9:1 H2O: DMSO). A high rigidity in the molecular structure restricts the formation of 1:1 (M/L) metal encapsulation but shows a high binding efficiency for a 3:1 metal ligand stoichiometry giving formation constant (in β unit) 28.73, 26.13 and 19.69 for [M3L]; Mdbnd Fe(III), Al(III) and Cr(III) respectively, and may be considered as an efficient Fe-carrier. The spectrophotometric study reveals of interesting electronic transitions occurred during the complexation. BTHA exhibits a peak at 238 nm in acidic pH and with the increase of pH, a new peak appeared at 270 nm. A substantial shifting in both of the peaks in presence of the metal ions implicates a s coordination between ligand and metal ions. Moreover, complexation of BTHA with iron shows three distinct colors, violet, reddish orange and yellow in different pH, enables the ligand to be considered for the use as colorimetric sensor.

  13. The formation of light absorbing insoluble organic compounds from the reaction of biomass burning precursors and Fe(III)

    NASA Astrophysics Data System (ADS)

    Lavi, Avi; Lin, Peng; Bhaduri, Bhaskar; Laskin, Alexander; Rudich, Yinon

    2017-04-01

    Dust particles and volatile organic compounds from fuel or biomass burning are two major components that affect air quality in urban polluted areas. We characterized the products from the reaction of soluble Fe(III), a reactive transition metal originating from dust particles dissolution processes, with phenolic compounds , namely, guaiacol, syringol, catechol, o- and p- cresol that are known products of incomplete fuel and biomass combustion but also from other natural sources such as humic compounds degradation. We found that under acidic conditions comparable to those expected on a dust particle surface, phenolic compounds readily react with dissolved Fe(III), leading to the formation of insoluble polymeric compounds. We characterized the insoluble products by x-ray photoelectron microscopy, UV-Vis spectroscopy, mass spectrometry, elemental analysis and thermo-gravimetric analysis. We found that the major chromophores formed are oligomers (from dimers to pentamers) of the reaction precursors that efficiently absorb light between 300nm and 500nm. High variability of the mass absorption coefficient of the reaction products was observed with catechol and guaiacol showing high absorption at the 300-500nm range that is comparable to that of brown carbon (BrC) from biomass burning studies. The studied reaction is a potential source for the in-situ production of secondary BrC material under dark conditions. Our results suggest a reaction path for the formation of bio-available iron in coastal polluted areas where dust particles mix with biomass burning pollution plumes. Such mixing can occur, for instance in the coast of West Africa or North Africa during dust and biomass burning seasons

  14. Fluorinated arene, imide and unsaturated pyrrolidinone based donor acceptor conjugated polymers: Synthesis, structure-property and device studies

    NASA Astrophysics Data System (ADS)

    Liyanage, Arawwawala Don Thilanga

    After the discovery of doped polyacetylene, organic semiconductor materials are widely studied as high impending active components in consumer electronics. They have received substantial consideration due to their potential for structural tailoring, low cost, large area and mechanically flexible alternatives to common inorganic semiconductors. To acquire maximum use of these materials, it is essential to get a strong idea about their chemical and physical nature. Material chemist has an enormous role to play in this novel area, including development of efficient synthetic methodologies and control the molecular self-assembly and (opto)-electronic properties. The body of this thesis mainly focuses on the substituent effects: how different substituents affect the (opto)-electronic properties of the donor-acceptor (D-A) conjugated polymers. The main priority goes to understand, how different alkyl substituent effect to the polymer solubility, crystallinity, thermal properties (e.g.: glass transition temperature) and morphological order. Three classes of D-A systems were extensively studied in this work. The second chapter mainly focuses on the synthesis and structure-property study of fluorinated arene (TFB) base polymers. Here we used commercially available 1,4-dibromo-2,3,5,6-tetrafluorobenzene (TFB) as the acceptor material and prepare several polymers using 3,3'-dialkyl(3,3'-R2T2) or 3,3'-dialkoxy bithiophene (3,3'-RO2T2) units as electron donors. A detail study was done using 3,3'-bithiophene donor units incorporating branched alkoxy-functionalities by systematic variation of branching position and chain length. The study allowed disentangling the branching effects on (i) aggregation tendency, intermolecular arrangement, (iii) solid state optical energy gaps, and (iv) electronic properties in an overall consistent picture, which might guide future polymer synthesis towards optimized materials for opto-electronic applications. The third chapter mainly focused on

  15. Spectroscopic studies of Fe(III) ion-exchanged ETS-10 and ETAS-10 molecular sieves

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sommerfeld, D.A.; Ellis, W.R. Jr.; Eyring, E.M.

    1992-11-26

    Two new titanium silicate molecular sieves, designated ETS-10 and ETAS-10, have been ion-exchanged with Fe(III). Both products exhibit prominent EPR signals, at g = 6.0 and 4.3, that are assigned to populations of ferric iron on the surface and in the interior cavities, respectively, of the molecular sieve microcrystals. Corollary XPS measurements on these samples indicate that a substantial fraction of the surface iron is present as Fe(II). Chemical modification procedures have been explored in an effort to produce ion-exchanged materials containing no exterior iron. Acid treatment (pH 1.0) proved to be an effective means of achieving this goal inmore » the case of ETS-10-based materials. ETAS-10-based samples do not retain their crystallinity under these conditions. 35 refs., 4 figs., 2 tabs.« less

  16. Effect of hydrogen on Ca and Mg acceptors in GaN

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lee, J.W.; Pearton, S.J.; Zolper, J.C.

    The influence of minority carrier injection on the reactivation of hydrogen passivated Mg in GaN at 175 C has been investigated in p-n junction diodes. The dissociation of the neutral MgH complexes is greatly enhanced in the presence of minority carrier and the reactivation process follows second order kinetics. Conventional annealing under zero-bias conditions does not produce Mg-H dissociation until temperatures {ge} 450 C. These results provide an explanation for the e-beam induced reactivation of Mg acceptors in hydrogenated GaN. Exposure to a hydrogen plasma at 250 C of p-type GaN (Ca) prepared by either Ca{sup +} or Ca{sup +}more » plus P{sup +} coimplantation leads to a reduction in sheet carrier density of approximately an order of magnitude (1.6 {times} 10{sup 12} cm{sup {minus}2} to 1.8 {times} 10{sup 11} cm{sup {minus}2}), and an accompanying increase in hole mobility (6 cm{sup 2}/Vs to 18 cm{sup 2}/Vs). The passivation process can be reversed by post-hydrogenation annealing at 400--500 C under a N{sub 2} ambient. This reactivation of the acceptors is characteristic of the formation of neutral (Ca-H) complexes in the GaN. The thermal stability of the passivation is similar to that of Mg-H complexes in material prepared in the same manner (implantation) with similar initial doping levels. Hydrogen passivation of acceptor dopants in GaN appears to be a ubiquitous phenomenon, as it is in other p-type semiconductors.« less

  17. Giant first hyperpolarizabilities of donor-acceptor substituted graphyne: An ab initio study.

    PubMed

    Chakraborti, Himadri

    2016-01-15

    Graphyne (Gy), a theoretically proposed material, has been utilized, for the first time, in a phenomenal donor-Gy-acceptor (D-Gy-A) structure to plan a superior nonlinear optical material. Owing to the extraordinary character of graphyne, this conjugate framework shows strikingly extensive static first hyperpolarizability (β(tot)) up to 128×10(-30) esu which is an enormous improvement than that of the bare graphyne. The donor-acceptor separation plays a key role in the change of β(tot) value. The π-conjugation of graphyne backbone has spread throughout some of the D-A attached molecules and leads to a low band gap state. Finally, two level model clarifies that the molecule having low transition energy should have high first hyperpolarizability. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. Lack of electricity production by Pelobacter carbinolicus indicates that the capacity for Fe(III) oxide reduction does not necessarily confer electron transfer ability to fuel cell anodes.

    PubMed

    Richter, Hanno; Lanthier, Martin; Nevin, Kelly P; Lovley, Derek R

    2007-08-01

    The ability of Pelobacter carbinolicus to oxidize electron donors with electron transfer to the anodes of microbial fuel cells was evaluated because microorganisms closely related to Pelobacter species are generally abundant on the anodes of microbial fuel cells harvesting electricity from aquatic sediments. P. carbinolicus could not produce current in a microbial fuel cell with electron donors which support Fe(III) oxide reduction by this organism. Current was produced using a coculture of P. carbinolicus and Geobacter sulfurreducens with ethanol as the fuel. Ethanol consumption was associated with the transitory accumulation of acetate and hydrogen. G. sulfurreducens alone could not metabolize ethanol, suggesting that P. carbinolicus grew in the fuel cell by converting ethanol to hydrogen and acetate, which G. sulfurreducens oxidized with electron transfer to the anode. Up to 83% of the electrons available in ethanol were recovered as electricity and in the metabolic intermediate acetate. Hydrogen consumption by G. sulfurreducens was important for ethanol metabolism by P. carbinolicus. Confocal microscopy and analysis of 16S rRNA genes revealed that half of the cells growing on the anode surface were P. carbinolicus, but there was a nearly equal number of planktonic cells of P. carbinolicus. In contrast, G. sulfurreducens was primarily attached to the anode. P. carbinolicus represents the first Fe(III) oxide-reducing microorganism found to be unable to produce current in a microbial fuel cell, providing the first suggestion that the mechanisms for extracellular electron transfer to Fe(III) oxides and fuel cell anodes may be different.

  19. Chemopreventive Agents from Physalis minima Function as Michael Reaction Acceptors

    PubMed Central

    Men, Ruizhi; Li, Ning; Ding, Chihong; Tang, Yingzhan; Xing, Yachao; Ding, Wanjing; Ma, Zhongjun

    2016-01-01

    Background: The fruits of some varieties of genus Physalis have been used as delicious fruits and functional food in the Northeast of China. Materials and Methods: To reveal the functional material basis, we performed bioactivity-guided phytochemical research and chemopreventive effect assay of the constituents from Physalis minima. Results: It was demonstrated that the ethyl acetate extract of P. minima L. (EEPM) had potential quinone reductase (QR) inducing activity with induction ratio (IR, QR induction activity) value of 1.47 ± 0.24, and glutathione binding property as potential Michael reaction acceptors (with an α, β-unsaturated ketone moiety). Furthermore, bioactivity-guided phytochemical research led eight compounds (1–8), which were elucidated as 3-isopropyl-5-acetoxycyclohexene-2-one-1 (1), isophysalin B (2), physalin G (3), physalin D (4), physalin I (5), physordinose B (6), stigmasterol-3-O-β-D-glucopyranoside (7) and 5α-6β-dihydroxyphysalin R (8) on the basis of nuclear magnetic resonance spectroscopy analyses and HRESIMS. Then, isophysalin B (2) and physordinose B (6) showed significant QR inducing activity with IR value of 2.80 ± 0.19 and 2.38 ± 0.46, respectively. SUMMARY An ultra-performance liquid chromatographic method with glutathione as the substrate was used to detect the Michael reaction acceptors in extracts of Physalis minima (EPM)We investigated the chemical constituents of EPM guided by biological activity methodIsophysalin B (1) and physordinose B (6) showed strong quinone reductase inducing activity with induction ratio values of 2.80 ± 0.19 and 2.38 ± 0.46This study generated useful information for consumers and many encourage researchers to utilize edible fruits from Physalis as a source of phytochemicals Abbreviations used: EPM: Extracts of Physalis minima, EEPM: Ethyl acetate extract of Physalis minima L., GSH: Glutathione, MRAs: Michael reaction acceptors, QR: Quinone reductase. PMID:27279713

  20. Synthesis, characterization and physicochemical studies of new chelating resin 1, 8-(3, 6-dithiaoctyl)-4-polyvinylbenzenesulphonate (dpvbs) and its metallopolymer Cu(II), Ni(II), Co(II) and Fe(III) complexes

    NASA Astrophysics Data System (ADS)

    Khalil, Tarek E.; Elbadawy, Hemmat A.; El-Dissouky, Ali

    2018-02-01

    A new chelating resin, 1,8-(3,6-dithiaoctyl)-4-polyvinylbenzenesulphonate (dpvbs) has been synthesized by coupling Amberlite XAD-16 with (2,2‧-ethylenedithio) diethanol using pyridine/CH2Cl2 mixture as a solvent. The chelating resin and its metallopolymer Cu(II), Ni(II), Co(II) and Fe(III) complexes have been synthesized and characterized by EDS, SEM, XPS, elemental analysis, spectral (IR, UV/Vis, EPR). The thermal analysis of the resin and its metallopolymer complexes indicated an endothermic spontaneous sorption mechanism with the liberation of water of hydration of the metal ions and that adsorbed by the free resin. At the solid liquid interface, the degrees of freedom increased during the sorption of the metal ions onto the resin. The surface area of polymer support and its metallopolymer complexes are estimated by (BJH) method. The batch equilibrium method was used for studying the metal sorption and selectivity at different pH values and different contact times at room temperature. ICP-AES was used to estimate the metal capacity of the resin for sorption of Cu(II), Ni(II), Co(II) and Fe(III) from aqueous solutions utilizing the batch equilibrium method. The sorption tendency of the metal ions by the resin was found to be: Cu(II) > Fe(III) > Co(II) > Ni(II). Adsorption kinetics was found to be fit the pseudo-second order model.

  1. Hydrogen concentrations as an indicator of the predominant terminal electron-accepting reactions in aquatic sediments

    USGS Publications Warehouse

    Lovley, D.R.; Goodwin, S.

    1988-01-01

    Factors controlling the concentration of dissolved hydrogen gas in anaerobic sedimentary environments were investigated. Results, presented here or previously, demonstrated that, in sediments, only microorganisms catalyze the oxidation of H2 coupled to the reduction of nitrate, Mn(IV), Fe(III), sulfate, or carbon dioxide. Theoretical considerations suggested that, at steady-state conditions, H2 concentrations are primarily dependent upon the physiological characteristics of the microorganism(s) consuming the H2 and that organisms catalyzing H2 oxidation, with the reduction of a more electrochemically positive electron acceptor, can maintain lower H2 concentrations than organisms using electron acceptors which yield less energy from H2 oxidation. The H2 concentrations associated with the specified predominant terminal electron-accepting reactions in bottom sediments of a variety of surface water environments were: methanogenesis, 7-10 nM; sulfate reduction, 1-1.5 nM; Fe(III) reduction, 0.2 nM; Mn(IV) or nitrate reduction, less than 0.05 nM. Sediments with the same terminal electron acceptor for organic matter oxidation had comparable H2 concentrations, despite variations in the rate of organic matter decomposition, pH, and salinity. Thus, each terminal electron-accepting reaction had a unique range of steady-state H2 concentrations associated with it. Preliminary studies in a coastal plain aquifer indicated that H2 concentrations also vary in response to changes in the predominant terminal electron-accepting process in deep subsurface environments. These studies suggest that H2 measurements may aid in determining which terminal electron-accepting reactions are taking place in surface and subsurface sedimentary environments. ?? 1988.

  2. Acceptors in ZnO nanocrystals: A reinterpretation

    NASA Astrophysics Data System (ADS)

    Gehlhoff, W.; Hoffmann, A.

    2012-12-01

    In a recent article, Teklemichael et al. reported on the identification of an uncompensated acceptor in ZnO nanocrystals using infrared spectroscopy and electron paramagnetic resonance (EPR) in the dark and under illumination. Most of their conclusions, interpretations, and suggestions turned out to be erroneous. The observed EPR signals were interpreted to originate from axial and nonaxial VZn-H defects. We show that the given interpretation of the EPR results is based on misinterpretations of EPR spectra arising from defects in nanocrystals. The explanation of the infrared absorption lines is in conflict with recent results of valence band ordering and valence band splitting.

  3. Effect of Fe(III) on 1,1,2,2-tetrachloroethane degradation and vinyl chloride accumulation in wetland sediments of the Aberdeen proving ground

    USGS Publications Warehouse

    Jones, E.J.P.; Voytek, M.A.; Lorah, M.M.

    2004-01-01

    1,1,2,2-Tetrachloroethane (TeCA) contaminated groundwater at the Aberdeen Proving Ground discharges through an anaerobic wetland in West Branch Canal Creek, MD, where dechlorination occurred. Two microbially mediated pathways, dichloroelimination and hydrogenolysis, account for most of the TeCA degradation at this site. The dichloroelimination pathways led to the formation of vinyl chloride (VC), a recalcitrant carcinogen of great concern. The effect of adding Fe(III) to TeCA-amended microcosms of wetland sediment was studied. Differences were identified in the TeCA degradation pathway between microcosms treated with amorphous ferric oxyhydroxide (AFO-treated) and untreated (no AFO) microcosms. TeCA degradation was accompanied by a lower accumulation of VC in AFO-treated microcosms than no AFO microcosms. The microcosm incubations and subsequent experiments with the microcosm materials showed that AFO treatment resulted in lower production of VC by shifting TeCA degradation from dichloroelimination pathways to production of a greater proportion of chlorinated ethane products, and decreasing the microbial capability to produce VC from 1,2-dichloroethylene. VC degradation was not stimulated in the presence of Fe(III). Rather, VC degradation occurred readily under methanogenic conditions and was inhibited under Fe(III)-reducing conditions.

  4. Succinic acid production from glycerol by Actinobacillus succinogenes using dimethylsulfoxide as electron acceptor.

    PubMed

    Carvalho, Margarida; Matos, Mariana; Roca, Christophe; Reis, Maria A M

    2014-01-25

    Glycerol, a highly abundant byproduct of the biodiesel industry, constitutes today a cheap feedstock for biobased succinic acid (SA) production. Actinobacillus succinogenes is one of the best SA producers. However, glycerol consumption by this biocatalyst is limited because of a redox imbalance during cell growth. The use of an external electron acceptor may improve the metabolism of SA synthesis by A. succinogenes in glycerol. In this study, the effect of dimethylsulfoxide (DMSO), an electron acceptor, on glycerol consumption and SA production by A. succinogenes under controlled fermentation conditions was investigated. Concentrations of DMSO between 1 and 4% (v/v) greatly promoted glycerol consumption and SA production by A. succinogenes. During fed-batch cultivation, SA concentration reached 49.62 g/L, with a product yield of 0.87 gSA/gGLR and a maximum production rate of 2.31 gSA/Lh, the highest values so far reported in the literature for A. succinogenes using glycerol as carbon source. These results show that using DMSO as external electron acceptor significantly promotes glycerol consumption and succinic acid production by A. succinogenes and may be used as a co-substrate, opening new perspectives for the use of glycerol by this biocatalyst. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. Electrodes as Terminal Electron Acceptors in Anaerobic Ammonium Oxidation

    NASA Astrophysics Data System (ADS)

    Ruiz-Urigüen, M.; Jaffe, P. R.

    2017-12-01

    Anaerobic ammonium (NH4+) oxidation under iron (Fe) reducing conditions is a microbial- mediated process known as Feammox. This is a novel pathway in the nitrogen cycle, and a key process for alleviating NH4+ accumulation in anoxic soils, wetlands, and wastewater. Acidimicrobiaceae-bacterium A6, phylum Actinobacteria, are one type of autotrophic bacteria linked to this process. The Feammox-bacteria obtain their energy by oxidizing NH4+ and transferring the electrons to a terminal electron acceptor (TEA). Under environmental conditions, iron oxides are the TEAs. However, in this study we show that electrodes in Microbial Electrolysis Cells (MECs) or electrodes set in the field can be used as TEAs by Feammox-bacteria. The potential difference between electrodes is the driving force for electron transfer, making the reaction energetically feasible. Our results show that MECs containing Feammox cultures can remove NH4+ up to 3.5 mg/L in less than 4 hours, compared to an average of 9 mg/L in 2 weeks when cultured under traditional conditions. Concomitantly, MECs produce an average current of 30.5 A/m3 whilst dead bacteria produced low (<2.7 A/m3) or no current. Furthermore, we have measured that A6 biomass increased from 5E4 cells/ml to 9.77E5 cells/ml in 2 weeks of operation, indicating the feasibility of growing A6 in MECs. Results from the electrodes in the field show higher percentage of electrogenic bacteria, including Acidimicrobiaceae-bacterium, on the more reducing electrode, compared to the more oxidized one. Our initial results also suggest that electrodes contained more Actinobacteria when compared to bulk soil. Electrodes as TEAs enhance electrogenic bacteria recovery and culturing. The use of MECs for the productions of Feammox-bacteria eliminates the dependence of Fe, a finite electron acceptor, therefore, allowing for continuous NH4+ removal. Finally, Fe-free Feammox-bacteria can be applied to reduce other metals of environmental concern; therefore

  6. Properties of Mg and Zn acceptors in MOVPE GaN as studied by optically detected magnetic resonance

    NASA Astrophysics Data System (ADS)

    Kunzer, M.; Baur, J.; Kaufmann, U.; Schneider, J.; Amano, H.; Akasaki, I.

    1997-02-01

    We have studied the photoluminescence (PL) and optically detected magnetic resonance (ODMR) of undoped, n-doped and p-doped thin wurtzite GaN layers grown by metal-organic chemical vapor deposition on sapphire substrates. The ODMR data obtained for undoped. Mg-doped and Zn-doped GaN layers provide an insight into the recombination mechanisms responsible for the broad yellow (2.25 eV), the violet (3.15 eV) and the blue (2.8 eV) PL bands, respectively. The ODMR results for Mg and Zn also show that these acceptors do not behave effective mass like and indicate that the acceptor hole is mainly localized in the nearest neighbor shell surrounding the acceptor core. In addition concentration effects in heavily doped GaN:Mg have been studied.

  7. Alternative initial proton acceptors for the D pathway of Rhodobacter sphaeroides cytochrome c oxidase

    PubMed Central

    Varanasi, Lakshman; Hosler, Jonathan

    2011-01-01

    In order to characterize protein structures that control proton uptake, forms of cytochrome c oxidase (CcO) containing a carboxyl or a thiol group in line with the initial, internal waters of the D pathway for proton transfer have been assayed in the presence and absence of subunit III. Subunit III provides approximately half of the protein surrounding the entry region of the D pathway. The mutant N139D-D132N contains a carboxyl group 6Å within the D pathway and lacks the normal, surface-exposed proton acceptor, Asp-132. With subunit III, the steady-state activity of this mutant is slow but once subunit III is removed its activity is the same as wild-type CcO lacking subunit III (∼1800 H+ s-1). Thus, a carboxyl group ∼25% within the pathway enhances proton uptake even though the carboxyl has no direct contact with bulk solvent. Protons from solvent apparently move to internal Asp-139 through a short file of waters, normally blocked by subunit III. Cysteine-139 also supports rapid steady-state proton uptake, demonstrating that an anion other than a carboxyl can attract and transfer protons into the D pathway. When both Asp-132 and Asp/Cys-139 are present, the removal of subunit III increases CcO activity to rates greater than that of normal CcO due to simultaneous proton uptake by two initial acceptors. The results show how the environment of the initial proton acceptor for the D pathway in these CcO forms dictates the pH range of CcO activity, with implications for the function of Asp-132, the normal proton acceptor. PMID:21344856

  8. Donor acceptor electronic couplings in π-stacks: How many states must be accounted for?

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.

    2006-04-01

    Two-state model is commonly used to estimate the donor-acceptor electronic coupling Vda for electron transfer. However, in some important cases, e.g. for DNA π-stacks, this scheme fails to provide accurate values of Vda because of multistate effects. The Generalized Mulliken-Hush method enables a multistate treatment of Vda. In this Letter, we analyze the dependence of calculated electronic couplings on the number of the adiabatic states included in the model. We suggest a simple scheme to determine this number. The superexchange correction of the two-state approximation is shown to provide good estimates of the electronic coupling.

  9. tRNA acceptor-stem and anticodon bases embed separate features of amino acid chemistry

    PubMed Central

    Carter, Charles W.; Wolfenden, Richard

    2016-01-01

    abstract The universal genetic code is a translation table by which nucleic acid sequences can be interpreted as polypeptides with a wide range of biological functions. That information is used by aminoacyl-tRNA synthetases to translate the code. Moreover, amino acid properties dictate protein folding. We recently reported that digital correlation techniques could identify patterns in tRNA identity elements that govern recognition by synthetases. Our analysis, and the functionality of truncated synthetases that cannot recognize the tRNA anticodon, support the conclusion that the tRNA acceptor stem houses an independent code for the same 20 amino acids that likely functioned earlier in the emergence of genetics. The acceptor-stem code, related to amino acid size, is distinct from a code in the anticodon that is related to amino acid polarity. Details of the acceptor-stem code suggest that it was useful in preserving key properties of stereochemically-encoded peptides that had developed the capacity to interact catalytically with RNA. The quantitative embedding of the chemical properties of amino acids into tRNA bases has implications for the origins of molecular biology. PMID:26595350

  10. Two Well-Miscible Acceptors Work as One for Efficient Fullerene-Free Organic Solar Cells.

    PubMed

    Yu, Runnan; Zhang, Shaoqing; Yao, Huifeng; Guo, Bing; Li, Sunsun; Zhang, Hao; Zhang, Maojie; Hou, Jianhui

    2017-07-01

    High-performance ternary organic solar cells are fabricated by using a wide-bandgap polymer donor (bithienyl-benzodithiophene-alt-fluorobenzotriazole copolymer, J52) and two well-miscible nonfullerene acceptors, methyl-modified nonfullerene acceptor (IT-M) and 2,2'-((2Z,2'Z)-((5,5'-(4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydros-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-5,2-diyl))bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IEICO). The two acceptors with complementary absorption spectra and similar lowest unoccupied molecular orbital levels show excellent compatibility in the blend due to their very similar chemical structures. Consequently, the obtained ternary organic solar cells (OSC) exhibits a high efficiency of 11.1%, with an enhanced short-circuit current density of 19.7 mA cm -2 and a fill factor of 0.668. In this ternary system, broadened absorption, similar output voltages, and compatible morphology are achieved simultaneously, demonstrating a promising strategy to further improve the performance of ternary OSCs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R.

    2015-09-05

    The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than - 0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poisedmore » at - 0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ΔcbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below - 0.1 V vs. SHE.« less

  12. Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens.

    PubMed

    Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R

    2016-02-01

    The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than -0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poised at -0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ∆cbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below -0.1 V vs. SHE. Copyright © 2015. Published by Elsevier B.V.

  13. Intramolecular Charge-Transfer Interaction of Donor-Acceptor-Donor Arrays Based on Anthracene Bisimide.

    PubMed

    Iwanaga, Tetsuo; Ogawa, Marina; Yamauchi, Tomokazu; Toyota, Shinji

    2016-05-20

    We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor-acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki-Miyaura and Sonogashira coupling reactions, respectively. In UV-vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600-650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.

  14. Estimation of electronic coupling in π-stacked donor-bridge-acceptor systems: Correction of the two-state model

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.

    2006-02-01

    Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of Vda because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a π stack, where donor and acceptor are separated by a bridging unit, can be obtained as Ṽda=(E2-E1)μ12/Rda+(2E3-E1-E2)2μ13μ23/Rda2, where E1, E2, and E3 are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, μij is the transition dipole moments between the states i and j, and Rda is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

  15. Estimation of electronic coupling in pi-stacked donor-bridge-acceptor systems: correction of the two-state model.

    PubMed

    Voityuk, Alexander A

    2006-02-14

    Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of V(da) because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a pi stack, where donor and acceptor are separated by a bridging unit, can be obtained as V(da) = (E(2)-E(1))mu(12)R(da) + (2E(3)-E(1)-E(2))2mu(13)mu(23)R(da) (2), where E(1), E(2), and E(3) are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, mu(ij) is the transition dipole moments between the states i and j, and R(da) is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

  16. Light-induced noncentrosymmetry in acceptor-donor-substituted azobenzene solutions

    NASA Astrophysics Data System (ADS)

    Zhao, Jiang; Si, Jinhai; Wang, Yougui; Ye, Peixian; Fu, Xingfa; Qiu, Ling; Shen, Yuquan

    1995-10-01

    Light-induced noncentrosymmetry was achieved experimentally in acceptor-donor-substituted azobenzene solutions and observed by phase-matched nondegenerate six-wave mixing. The microscopic origin of the induced noncentrosymmetry was found to be orientational hole burning, which was distinguished directly with net orientation of molecules by experimental observations. The decay time of the induced noncentrosymmetry depended on the rotational orientation time of the sample's molecule, which varied linearly with the viscosity of the solvent.

  17. Comparison of lactate, formate, and propionate as hydrogen donors for the reductive dehalogenation of trichloroethene in a continuous-flow column.

    PubMed

    Azizian, Mohammad F; Marshall, Ian P G; Behrens, Sebastian; Spormann, Alfred M; Semprini, Lewis

    2010-04-01

    A continuous-flow column study was conducted to analyze the reductive dehalogenation of trichloroethene (TCE) with aquifer material with high content of iron oxides. The column was bioaugmented with the Point Mugu (PM) culture, which is a mixed microbial enrichment culture capable of completely transforming TCE to ethene (ETH). We determined whether lactate, formate, or propionate fermentation resulted in more effective dehalogenation. Reductive dehalogenation, fermentation, and sulfate, Fe(III), and Mn(IV) reduction were all exhibited within the column. Different steady-states of dehalogenation were achieved based on the concentration of substrates added, with effective transformation to ETH obtained when ample electron donor equivalents were provided. Most of the metabolic reducing equivalents were channeled to sulfate, Fe(III), and Mn(IV) reduction. When similar electron reducing equivalents were added, the most effective dehalogenation was achieved with formate, with 14% of the electron equivalents going towards dehalogenation reactions, compared to 6.5% for lactate and 9.6% for propionate. Effective dehalogenation was maintained over 1000 days of column operation. Over 90% of electron equivalents added could be accounted for by the different electron accepting processes in the column, with 50% associated with soluble and precipitated Fe(II) and Mn(II). Bulk Fe(III) and Mn(IV) reduction was rather associated with lactate and propionate addition than formate addition. Sulfate reduction was a competing electron acceptor reaction with all three electron donors. DNA was extracted from solid coupon samples obtained during the course of the experiment and analyzed using 16S rRNA gene clone libraries and quantitative PCR. Lactate and propionate addition resulted in a significant increase in Geobacter, Spirochaetes, and Desulfitobacterium phylotypes relative to "Dehalococcoides" when compared to formate addition. Results from the molecular biological analyses support

  18. Bi-diketopyrrolopyrrole (Bi-DPP) as a novel electron accepting compound in low band gap π-conjugated donor–acceptor copolymers/oligomers

    PubMed Central

    Ahner, Johannes; Nowotny, Jürgen; Schubert, Ulrich S.; Hager, Martin D.

    2017-01-01

    Abstract The synthesis and characterization of a novel 2,5-diketopyrrolo[3,4-c]pyrrole(DPP)-based accepting building block with the scheme DPP-neutral small linker-DPP (Bi-DPP) is presented, which was utilized as electron accepting moiety for low band gap π-conjugated donor–acceptor copolymers as well as for a donor–acceptor small molecule. The electron accepting moiety Bi-DPP was prepared via a novel synthetic pathway by building up two DPP moieties step by step simultaneously starting from a neutral phenyl core unit. Characterization of the synthesized oligomeric and polymeric materials via cyclic voltammetry afford LUMO energy levels from −3.49 to −3.59 eV as well as HOMO energy levels from −5.07 to −5.34 eV resulting in low energy band gaps from 1.52 to 1.81 eV. Spin coating of the prepared donor–acceptor oligomers/polymers resulted in well-defined films. Moreover, UV–vis measurements of the investigated donor–acceptor systems showed a broad absorption over the whole visible region. It is demonstrated that Bi-DPP as an electron accepting moiety in donor–acceptor systems offer potential properties for organic solar cell devices. PMID:29491794

  19. Distinctive acceptor-end structure and other determinants of Escherichia coli tRNAPro identity.

    PubMed Central

    McClain, W H; Schneider, J; Gabriel, K

    1994-01-01

    The previously uncharacterized determinants of the specificity of tRNAPro for aminoacylation (tRNAPro identity) were defined by a computer comparison of all Escherichia coli tRNA sequences and tested by a functional analysis of amber suppressor tRNAs in vivo. We determined the amino acid specificity of tRNA by sequencing a suppressed protein and the aminoacylation efficiency of tRNA by examining the steady-state level of aminoacyl-tRNA. On substituting nucleotides derived from the acceptor end and variable pocket of tRNAPro for the corresponding nucleotides in a tRNAPhe gene, the identity of the resulting tRNA changed substantially but incompletely to that of tRNAPro. The redesigned tRNAPhe was weakly active and aminoacyl-tRNA was not detected. Ethyl methanesulfonate mutagenesis of the redesigned tRNAPhe gene produced a mutant with a wobble pair in place of a base pair in the end of the acceptor-stem helix of the transcribed tRNA. This mutant exhibited both a tRNAPro identity and substantial aminoacyl-tRNA. The results speak for the importance of a distinctive conformation in the acceptor-stem helix of tRNAPro for aminoacylation by the prolyl-tRNA synthetase. The anticodon also contributes to tRNAPro identity but is not necessary in vivo. Images PMID:8127693

  20. Investigation of the donor and acceptor range for chiral carboligation catalyzed by the E1 component of the 2-oxoglutarate dehydrogenase complex

    PubMed Central

    Patel, Hetalben; Shim, Da Jeong; Farinas, Edgardo T.; Jordan, Frank

    2013-01-01

    The potential of thiamin diphosphate (ThDP)-dependent enzymes to catalyze C-C bond forming (carboligase) reactions with high enantiomeric excess has been recognized for many years. Here we report the application of the E1 component of the Escherichia coli 2-oxoglutarate dehydrogenase multienzyme complex in the synthesis of chiral compounds with multiple functional groups in good yield and high enantiomeric excess, by varying both the donor substrate (different 2-oxo acids) and the acceptor substrate (glyoxylate, ethyl glyoxylate and methyl glyoxal). Major findings include the demonstration that the enzyme can accept 2-oxovalerate and 2-oxoisovalerate in addition to its natural substrate 2-oxoglutarate, and that the tested acceptors are also acceptable in the carboligation reaction, thereby very much expanding the repertory of the enzyme in chiral synthesis. PMID:24277992

  1. Synthesis of an A-D-A type of molecule used as electron acceptor for improving charge transfer in organic solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Chao-Zhi; Gu, Shu-Duo; Shen, Dan; Yuan, Yang; Zhang, Mingdao

    2016-08-01

    Electron-accepting molecules play an important role in developing organic solar cells. A new type of A-D-A molecule, 3,6-di([7-(5-bromothiophen-2-yl)-1,5,2,4,6,8-dithiotetrazocin-3-yl]thiophen-2-yl)-9-(2-ethylhexyl)carbazole, was synthesized. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels are -3.55 and -5.85 eV, respectively. Therefore, the A-D-A type of compound could be used as electron acceptor for fabricating organic solar cell with a high open circuit voltage. Gibbs free energy (-49.2 kJ/mol) reveals that the process of A-D-A acceptor accepting an electron from poly(3-hexylthiophene) at excited state is spontaneous. The value of entropy (118 J/mol) in the process of an electron transferring from P3HT to the A-D-A acceptor at organic interface suggests that electrons generated from separation of electron-hole pairs at donor/acceptor interface would be delocalized efficiently. Therefore, the A-D-A molecule would be a potential acceptor for efficient organic BHJ solar cells.

  2. Template Dimerization Promotes an Acceptor Invasion-Induced Transfer Mechanism during Human Immunodeficiency Virus Type 1 Minus-Strand Synthesis

    PubMed Central

    Balakrishnan, Mini; Roques, Bernard P.; Fay, Philip J.; Bambara, Robert A.

    2003-01-01

    The biochemical mechanism of template switching by human immunodeficiency virus type 1 (HIV-1) reverse transcriptase and the role of template dimerization were examined. Homologous donor-acceptor template pairs derived from the HIV-1 untranslated leader region and containing the wild-type and mutant dimerization initiation sequences (DIS) were used to examine the efficiency and distribution of transfers. Inhibiting donor-acceptor interaction was sufficient to reduce transfers in DIS-containing template pairs, indicating that template dimerization, and not the mere presence of the DIS, promotes efficient transfers. Additionally, we show evidence that the overall transfer process spans an extended region of the template and proceeds through a two-step mechanism. Transfer is initiated through an RNase H-facilitated acceptor invasion step, while synthesis continues on the donor template. The invasion then propagates towards the primer terminus by branch migration. Transfer is completed with the translocation of the primer terminus at a site distant from the invasion point. In our system, most invasions initiated before synthesis reached the DIS. However, transfer of the primer terminus predominantly occurred after synthesis through the DIS. The two steps were separated by 60 to 80 nucleotides. Sequence markers revealed the position of primer terminus switch, whereas DNA oligomers designed to block acceptor-cDNA interactions defined sites of invasion. Within the region of homology, certain positions on the template were inherently more favorable for invasion than others. In templates with DIS, the proximity of the acceptor facilitates invasion, thereby enhancing transfer efficiency. Nucleocapsid protein enhanced the overall efficiency of transfers but did not alter the mechanism. PMID:12663778

  3. TERMINAL ELECTRON ACCEPTOR MASS BALANCE: LIGHT NONAQUEOUS PHASE LIQUIDS AND NATURAL ATTENUATION

    EPA Science Inventory

    Nonaqueous phase liquids (NAPLs) in subsurface systems contain a relatively large amount of biodegradable organic material. During the biochemical oxidation of the organic compounds in the NAPL, electrons are transferred to terminal electron acceptors (TEA) (i.e., O2, NO3-, Mn(I...

  4. Increasing Saturated Electron-Drift Velocity in Donor-Acceptor Doped pHEMT Heterostructures

    NASA Astrophysics Data System (ADS)

    Protasov, D. Yu.; Gulyaev, D. V.; Bakarov, A. K.; Toropov, A. I.; Erofeev, E. V.; Zhuravlev, K. S.

    2018-03-01

    Field dependences of the electron-drift velocity in typical pseudomorphic high-electron-mobility transistor (pHEMT) heteroepitaxial structures (HESs) and in those with donor-acceptor doped (DApHEMT) heterostructures with quantum-well (QW) depth increased by 0.8-0.9 eV with the aid of acceptor layers have been studied by a pulsed technique. It is established that the saturated electron-drift velocity in DA-pHEMT-HESs is 1.2-1.3 times greater than that in the usual pHEMT-HESs. The electroluminescence (EL) spectra of DA-pHEMT-HESs do not contain emission bands related to the recombination in widebandgap layers (QW barriers). The EL intensity in these HESs is not saturated with increasing electric field. This is indicative of a suppressed real-space transfer of hot electrons from QW to barrier layers, which accounts for the observed increase in the saturated electron-drift velocity.

  5. Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Park, Changwon; Atalla, Viktor; Smith, Sean

    Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

  6. Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

    DOE PAGES

    Park, Changwon; Atalla, Viktor; Smith, Sean; ...

    2017-06-16

    Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

  7. Synthesis and evaluation of NLO properties of π-conjugated donor-acceptor systems bearing pyrrole and thiophene heterocycles

    NASA Astrophysics Data System (ADS)

    Castro, M. Cidália R.; Fonseca, A. Maurício C.; Belsley, M.; Raposo, M. Manuela M.

    2011-05-01

    Two series of novel push-pull heterocyclic azo dyes have been synthesized and characterized. The two series of compounds were based on different combinations of π-conjugated bridges (bithiophene and thienylpyrrole) which also act simultaneously as donor groups, together with diazo(benzo)thiazolyl as acceptor moieties. Their thermal stability and electrochemical behavior were characterized, while hyper-Rayleigh scattering (HRS) was employed to evaluate their second-order nonlinear optical properties. The results of these studies have been critically analyzed together with several thienylpyrrole azo dyes reported earlier from our laboratories in which the thienylpyrrole system was used as the donor group functionalized with aryl and (benzo)thiazolyldiazene as acceptor moiety. The measured molecular first hyperpolarizabilities and the observed linear optical and redox behavior showed strong variations in function of the heterocyclic spacers used (bithiophene or thienylpyrrole) and were also sensitive to the acceptor strength of the diazenehetero(aryl) moiety.

  8. Effect of Fe(III) on 1,1,2,2-Tetrachloroethane degradation and vinyl chloride accumulation in wetland sediments of the Aberdeen Proving Ground

    USGS Publications Warehouse

    Jones, Elizabeth; Voytek, Mary; Lorah, Michelle

    2004-01-01

    1,1,2,2-Tetrachloroethane (TeCA) contaminated groundwater at the Aberdeen Proving Ground discharges through an anaerobic wetland in West Branch Canal Creek (MD), where dechlorination occurs. Two microbially mediated pathways, dichloroelimination and hydrogenolysis, account for most of the TeCA degradation at this site. The dichloroelimination pathways lead to the formation of vinyl chloride (VC), a recalcitrant carcinogen of great concern. The goal of this investigation was to determine whether microbially-available Fe(III) in the wetland surface sediment influenced the fate of TeCA and its daughter products. Differences were identified in the TeCA degradation pathway between microcosms treated with amorphous ferric oxyhydroxide (AFO-treated) and untreated (no AFO) microcosms. TeCA degradation was accompanied by a lower accumulation of VC in AFO-treated microcosms than untreated microcosms. The microcosm incubations and subsequent experiments with the microcosm materials showed that AFO treatment resulted in lower production of VC by (1) shifting TeCA degradation from dichloroelimination pathways to production of a greater proportion of chlorinated ethane products, and (2) decreasing the microbial capability to produce VC from 1,2-dichloroethene (DCE). VC degradation was not stimulated in the presence of Fe(III). Rather, VC degradation occurred readily under methanogenic conditions and was inhibited under Fe(III)-reducing conditions.

  9. An Unfused-Core-Based Nonfullerene Acceptor Enables High-Efficiency Organic Solar Cells with Excellent Morphological Stability at High Temperatures.

    PubMed

    Li, Shuixing; Zhan, Lingling; Liu, Feng; Ren, Jie; Shi, Minmin; Li, Chang-Zhi; Russell, Thomas P; Chen, Hongzheng

    2018-02-01

    Most nonfullerene acceptors developed so far for high-performance organic solar cells (OSCs) are designed in planar molecular geometry containing a fused-ring core. In this work, a new nonfullerene acceptor of DF-PCIC is synthesized with an unfused-ring core containing two cyclopentadithiophene (CPDT) moieties and one 2,5-difluorobenzene (DFB) group. A nearly planar geometry is realized through the F···H noncovalent interaction between CPDT and DFB for DF-PCIC. After proper optimizations, the OSCs with DF-PCIC as the acceptor and the polymer PBDB-T as the donor yield the best power conversion efficiency (PCE) of 10.14% with a high fill factor of 0.72. To the best of our knowledge, this efficiency is among the highest values for the OSCs with nonfullerene acceptors owning unfused-ring cores. Furthermore, no obvious morphological changes are observed for the thermally treated PBDB-T:DF-PCIC blended films, and the relevant devices can keep ≈70% of the original PCEs upon thermal treatment at 180 °C for 12 h. This tolerance of such a high temperature for so long time is rarely reported for fullerene-free OSCs, which might be due to the unique unfused-ring core of DF-PCIC. Therefore, the work provides new idea for the design of new nonfullerene acceptors applicable in commercial OSCs in the future. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Synthesis, spectroscopy, and binding constants of ketocatechol-containing iminodiacetic acid and its Fe(III), Cu(II), and Zn(II) complexes and reaction of Cu(II) complex with H₂O₂ in aqueous solution.

    PubMed

    Gao, Jiaojiao; Xing, Feifei; Bai, Yueling; Zhu, Shourong

    2014-06-07

    A new neuromelanin-like ketocatechol-containing iminodiacetic acid ligand, (N-(3,4-dihydroxyl)phenacylimino)diacetic acid (H4L), which is also quite similar to compounds found in insect cuticle, has been synthesized and characterized. The X-ray crystal structure of H4L has been successfully determined. Proton binding and coordination with Fe(III), Cu(II), and Zn(II) have been studied by potentiometric titrations and UV-vis spectrophotometry in aqueous solution. UV spectra of H4L in the absence and presence of different metal ions indicate complexes formed with the catechol moiety of H4L in aqueous solution. Visible spectra and NMR reveal that H4L with Fe(III), Cu(II), and Zn(II) can all give stable mono-(ML) and dinuclear complexes [M(ML)]. Fe(III) can also form {Fe(FeL)2} and {Fe(FeL)3} species with sufficient base. The process is accompanied by a drastic color change from light blue to deep-blue to wine-red. The Fe(III)-Cu(II) heteronuclear complex also exists in aqueous solution whose spectra are similar to the homonuclear Fe(III) complex. However, the spectra of {Fe(CuL)} shifted to a longer wavelength and {Fe(CuL)2} and {Fe(CuL)3} shifted to a shorter wavelength. Keto-enol tautomerism was observed in weak basic aqueous solution as indicated by (1)H NMR spectra. The reaction products of Cu(II) complex with H2O2 depend on the H2O2 concentration and pH value. Low concentrations of H2O2 oxidize H4L to a series of semiquinone and quinone compounds with absorption maxima at 314-400 nm, while a high concentration of H2O2 oxidizes H4L to colorless muconic acid derivatives. NaIO4 gives different oxidase products, but no 2,4,5-trihydroxyphenylalanine quinone (TPQ)-like hydroxyquinone can be found.

  11. Dual nature of acceptors in GaN and ZnO: The curious case of the shallow MgGa deep state

    NASA Astrophysics Data System (ADS)

    Lany, Stephan; Zunger, Alex

    2010-04-01

    Employing a Koopmans corrected density functional method, we find that the metal-site acceptors Mg, Be, and Zn in GaN and Li in ZnO bind holes in deep levels that are largely localized at single anion ligand atoms. In addition to this deep ground state (DGS), we observe an effective-masslike delocalized state that can exist as a short lived shallow transient state (STS). The Mg dopant in GaN represents the unique case where the ionization energy of the localized deep level exceeds only slightly that of the shallow effective-mass acceptor, which explains why Mg works so exceptionally well as an acceptor dopant.

  12. Magnesium acceptor in gallium nitride. II. Koopmans-tuned Heyd-Scuseria-Ernzerhof hybrid functional calculations of its dual nature and optical properties

    NASA Astrophysics Data System (ADS)

    Demchenko, D. O.; Diallo, I. C.; Reshchikov, M. A.

    2018-05-01

    The problem of magnesium acceptor in gallium nitride is that experimental photoluminescence measurements clearly reveal a shallow defect state, while most theoretical predictions favor a localized polaronic defect state. To resolve this contradiction, we calculate properties of magnesium acceptor using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, tuned to fulfill the generalized Koopmans condition. We test Koopmans tuning of HSE for defect calculations in GaN using two contrasting test cases: a deep state of gallium vacancy and a shallow state of magnesium acceptor. The obtained parametrization of HSE allows calculations of optical properties of acceptors using neutral defect-state eigenvalues, without relying on corrections due to charged defects in periodic supercells. Optical transitions and vibrational properties of M gGa defect are analyzed to bring the dual (shallow and deep) nature of this defect into accord with experimental photoluminescence measurements of the ultraviolet band in Mg-doped GaN samples.

  13. Regulation of lecithin-cholesterol acyltransferase reaction by acyl acceptors and demonstration of its "idling" reaction.

    PubMed

    Czarnecka, H; Yokoyama, S

    1993-09-15

    The mechanism for regulation of cholesterol esterification by lecithin-cholesterol acyltransferase (LCAT) was studied using the highly isolated enzyme from pig plasma. In the reaction with phosphatidylcholine small unilamellar vesicles, cholesterol, water, diacylglycerol, and lysophosphatidylcholine were all potent acceptors of an acyl group cleaved from the sn-2 position of egg phosphatidylcholine, generating cholesteryl ester, free fatty acid, triglyceride, and phosphatidylcholine, respectively. All of these reactions required activation by human apolipoprotein A-I, suggesting that this activation leads to the deacylation of phosphatidylcholine. Those acceptors competed against each other in this vesicle reaction system, and cholesterol was the most potent acyl acceptor. Lysophosphatidylcholine that was endogenously generated by deacylation of phosphatidylcholine in the first step of the LCAT reaction was also a good acyl acceptor, showing that the reaction is always partly "idling." Bovine serum albumin partially inhibited this idling reaction in a concentration-dependent manner up to 80% at 0.60 mM. The above results were essentially reproducible with high density lipoprotein, except that cholesterol is less potent than lysophosphatidylcholine in accepting the acyl group under the condition used. Unlike the apolipoprotein A-I-activated reaction, cholesterol was esterified only slightly by the LCAT reaction on low density lipoprotein and, consequently, did not compete against lysophosphatidylcholine for generation of phosphatidylcholine. Thus, apoB may activate LCAT in a very different manner from apoA-I. The rate of esterification of lysophosphatidylcholine on low density lipoprotein was one-tenth of that on the vesicles and on high density lipoprotein. Thus, LCAT is active on low density lipoprotein but mostly idling as deacylating and reacylating glycerophospholipids.

  14. Analysis of the pH-Dependent Fe(III) Ion Chelating Activity of Anthocyanin Extracted from Black Soybean [Glycine max (L.) Merr.] Coats.

    PubMed

    Xie, Yanli; Zhu, Xiaolu; Li, Yuan; Wang, Chen

    2018-02-07

    The Fe(III) chelating activity of anthocyanin extracted from black soybean coats was investigated at pH 3.0, 5.0, 6.5, 7.0, and 7.4 with fluorescence spectroscopy and microscale thermophoresis (MST). Cyanidin-3-glucoside (C3G) was determined to be 98% of the total anthocyanin by high-performance liquid chromatography. The binding affinity (K a ) exhibited significant pH-dependent behavior: K a was 9.7167 × 10 4 , 1.0837 × 10 4 , 1.4284 × 10 4 , 5.4550 × 10 4 , and 3.0269 × 10 4 M -1 at pH 3.0, 5.0, 6.5, 7.0, and 7.4, respectively (p < 0.05). The MST data showed that ΔG < 0 and ΔH < 0, demonstrating that chelation is spontaneous and exothermic. Because both ΔH and ΔS < 0, the chelation involves hydrogen bonds and/or van der Waals forces for pH 3.0, 5.0, and 6.5. Electrostatic interactions contributed to chelation at pH 7.0 and 7.4 with ΔH < 0 and ΔS > 0. With the formation of chelates, C3G improved the solubility of Fe(III) at pH 6.5, 7.0, and 7.4 to enhance the ferric ion bioavailability, except for aggregation observed at pH 5.0.

  15. Evidence of the Zn vacancy acting as the dominant acceptor in n-type ZnO.

    PubMed

    Tuomisto, F; Ranki, V; Saarinen, K; Look, D C

    2003-11-14

    We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (E(el)=2 MeV, fluence 6 x 10(17) cm(-2)) ZnO samples. The Zn vacancies are identified at concentrations of [V(Zn)] approximately 2 x 10(15) cm(-3) in the as-grown material and [V(Zn)] approximately 2 x 10(16) cm(-3) in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.

  16. Microbial reduction of vanadium (V) in groundwater: Interactions with coexisting common electron acceptors and analysis of microbial community.

    PubMed

    Liu, Hui; Zhang, Baogang; Yuan, Heyang; Cheng, Yutong; Wang, Song; He, Zhen

    2017-12-01

    Vanadium (V) pollution in groundwater has posed serious risks to the environment and public health. Anaerobic microbial reduction can achieve efficient and cost-effective remediation of V(V) pollution, but its interactions with coexisting common electron acceptors such as NO 3 - , Fe 3+ , SO 4 2- and CO 2 in groundwater remain unknown. In this study, the interactions between V(V) reduction and reduction of common electron acceptors were examined with revealing relevant microbial community and identifying dominant species. The results showed that the presence of NO 3 - slowed down the removal of V(V) in the early stage of the reaction but eventually led to a similar reduction efficiency (90.0% ± 0.4% in 72-h operation) to that in the reactor without NO 3 - . The addition of Fe 3+ , SO 4 2- , or CO 2 decreased the efficiency of V(V) reduction. Furthermore, the microbial reduction of these coexisting electron acceptors was also adversely affected by the presence of V(V). The addition of V(V) as well as the extra dose of Fe 3+ , SO 4 2- and CO 2 decreased microbial diversity and evenness, whereas the reactor supplied with NO 3 - showed the increased diversity. High-throughput 16S rRNA gene pyrosequencing analysis indicated the accumulation of Geobacter, Longilinea, Syntrophobacter, Spirochaeta and Anaerolinea, which might be responsible for the reduction of multiple electron acceptors. The findings of this study have demonstrated the feasibility of anaerobic bioremediation of V(V) and the possible influence of coexisting electron acceptors commonly found in groundwater. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Non-enzymatic U(VI) interactions with biogenic mackinawite

    NASA Astrophysics Data System (ADS)

    Veeramani, H.; Qafoku, N. P.; Kukkadapu, R. K.; Murayama, M.; Hochella, M. F.

    2011-12-01

    Reductive immobilization of hexavalent uranium [U(VI)] by stimulation of dissimilatory metal and/or sulfate reducing bacteria (DMRB or DSRB) has been extensively researched as a remediation strategy for subsurface U(VI) contamination. These bacteria derive energy by reducing oxidized metals as terminal electron acceptors, often utilizing organic substrates as electron donors. Thus, when evaluating the potential for in-situ uranium remediation in heterogeneous subsurface media, it is important to understand how the presence of alternative electron acceptors such as Fe(III) and sulfate affect U(VI) remediation and the long term behavior and reactivity of reduced uranium. Iron, an abundant subsurface element, represents a substantial sink for electrons from DMRB, and the reduction of Fe(III) leads to the formation of dissolved Fe(II) or to reactive biogenic Fe(II)- and mixed Fe(II)/Fe(III)- mineral phases. Consequently, abiotic U(VI) reduction by reactive forms of biogenic Fe(II) minerals could be a potentially important process for uranium immobilization. In our study, the DMRB Shewanella putrefaciens CN32 was used to synthesize a biogenic Fe(II)-bearing sulfide mineral: mackinawite, that has been characterized by XRD, SEM, HRTEM and Mössbauer spectroscopy. Batch experiments involving treated biogenic mackinawite and uranium (50:1 molar ratio) were carried out at room temperature under strict anoxic conditions. Following complete removal of uranium from solution, the biogenic mackinawite was analyzed by a suite of analytical techniques including XAS, HRTEM and Mössbauer spectroscopy to determine the speciation of uranium and investigate concomitant Fe(II)-phase transformation. Determining the speciation of uranium is critical to success of a remediation strategy. The present work elucidates non-enzymatic/abiotic molecular scale redox interactions between biogenic mackinawite and uranium.

  18. The defect and transport properties of acceptor doped TlBr: role of dopant exsolution and association.

    PubMed

    Bishop, Sean R; Tuller, Harry L; Ciampi, Guido; Higgins, William; Engel, Johanna; Churilov, Alexei; Shah, Kanai S

    2012-08-07

    The role of acceptor dopants (S and Se) in controlling the ionic conductivity of single crystal TlBr, grown by the vertical Bridgman method, was examined as a function of temperature with the aid of impedance spectroscopy. Several features in the conductivity were identified and related to acceptor dopant-Br vacancy association, acceptor dopant exsolution, and Br vacancy mobility. The corresponding enthalpies for these processes were extracted from the data and were found to be equal to H(a) = 0.42 ± 0.07 eV, H(sol) = 1.55 ± 0.18 eV and H(m,Br) = 0.31 ± 0.02 eV respectively, the latter consistent with earlier studies on donor doped and undoped TlBr. A long term conductivity decay in the extrinsic region, attributed to S or Se exsolution, was observed. The time constant associated with exsolution was found to be thermally activated with an activation energy of 0.47 ± 0.1 eV. Estimates for Se solubility at different temperatures are provided.

  19. [Effects of carbon sources, temperature and electron acceptors on biological phosphorus removal].

    PubMed

    Han, Yun; Xu, Song; Dong, Tao; Wang, Bin-Fan; Wang, Xian-Yao; Peng, Dang-Cong

    2015-02-01

    Effects of carbon sources, temperature and electron acceptors on phosphorus uptake and release were investigated in a pilot-scale oxidation ditch. Phosphorus uptake and release rates were measured with different carbon sources (domestic sewage, sodium acetate, glucose) at 25 degrees C. The results showed that the minimum phosphorus uptake and release rates of glucose were 5.12 mg x (g x h)(-1) and 6.43 mg x (g x h)(-1), respectively, and those of domestic sewage are similar to those of sodium acetate. Phosphorus uptake and release rates increased with the increase of temperature (12, 16, 20 and 25 degrees C) using sodium acetate as carbon sources. Anoxic phosphorus uptake rate decreased with added COD. Electron acceptors (oxygen, nitrate, nitrite) had significant effects on phosphorus uptake rate and their order was in accordance with oxygen > nitrate > nitrite. The mass ratio of anoxic P uptake and N consumption (P(uptake)/N (consumption)) of nitrate and nitrite were 0.96 and 0.65, respectively.

  20. Asymmetric intramolecular α-cyclopropanation of aldehydes using a donor/acceptor carbene mimetic

    PubMed Central

    Luo, Chaosheng; Wang, Zhen; Huang, Yong

    2015-01-01

    Enantioselective α-alkylation of carbonyl is considered as one of the most important processes for asymmetric synthesis. Common alkylation agents, that is, alkyl halides, are notorious substrates for both Lewis acids and organocatalysts. Recently, olefins emerged as a benign alkylating species via photo/radical mechanisms. However, examples of enantioselective alkylation of aldehydes/ketones are scarce and direct asymmetric dialkylation remains elusive. Here we report an intramolecular α-cyclopropanation reaction of olefinic aldehydes to form chiral cyclopropane aldehydes. We demonstrate that an α-iodo aldehyde can function as a donor/acceptor carbene equivalent, which engages in a formal [2+1] annulation with a tethered double bond. Privileged bicyclo[3.1.0]hexane-type scaffolds are prepared in good optical purity using a chiral amine. The synthetic utility of the products is demonstrated by versatile transformations of the bridgehead formyl functionality. We expect the concept of using α-iodo iminium as a donor/acceptor carbene surrogate will find wide applications in chemical reaction development. PMID:26644194

  1. Self-assembly of Metallamacrocycles Employing a New Benzil-based Organometallic Bisplatinum(II) Acceptor.

    PubMed

    Roy, Bijan; Shanmugaraju, Sankarasekaran; Saha, Rupak; Mukherjee, Partha Sarathi

    2015-01-01

    A benzil-based semi-rigid dinuclear-organometallic acceptor 4,4'-bis[trans-Pt(PEt(3))(2)(NO(3))(ethynyl)]benzil (bisPt-NO(3)) containing a Pt-ethynyl functionality was synthesized in good yield and characterized by multinuclear NMR ((1)H, (31)P, and (13)C), electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray diffraction analysis of the iodide analogue bisPt-I. The stoichiometric (1:1) combination of the acceptor bisPt-NO(3) separately with four different ditopic donors (L(1)-L(4); L(1) = 9-ethyl-3,6-di(1H-imidazol-1-yl)-9H-carbazole, L(2) = 1,4-bis((1H-imidazol-1-yl)methyl)benzene, L(3) = 1,3-bis((1H-imidazol-1-yl)methyl)benzene and L(4) = 9,10-bis((1H-imidazol-1-yl) methyl)anthracene) yielded four [2 + 2] self-assembled metallacycles M(1)-M(4) in quantitative yields, respectively. All these newly synthesized assemblies were characterized by various spectroscopic techniques (NMR, IR, ESI-MS) and their sizes/shapes were predicted through geometry optimization employing the PM6 semi-empirical method. The benzil moiety was introduced in the backbone of the acceptor bisPt-NO(3) due to the interesting structural feature of long carbonyl C-C bond (∼1.54 Å), which enabled us to probe the role of conformational flexibility on size and shapes of the resulting coordination ensembles.

  2. Donor-Acceptor Distance Sampling Enhances the Performance of "Better than Nature" Nicotinamide Coenzyme Biomimetics.

    PubMed

    Geddes, Alexander; Paul, Caroline E; Hay, Sam; Hollmann, Frank; Scrutton, Nigel S

    2016-09-07

    Understanding the mechanisms of enzymatic hydride transfer with nicotinamide coenzyme biomimetics (NCBs) is critical to enhancing the performance of nicotinamide coenzyme-dependent biocatalysts. Here the temperature dependence of kinetic isotope effects (KIEs) for hydride transfer between "better than nature" NCBs and several ene reductase biocatalysts is used to indicate transfer by quantum mechanical tunneling. A strong correlation between rate constants and temperature dependence of the KIE (ΔΔH(⧧)) for H/D transfer implies that faster reactions with NCBs are associated with enhanced donor-acceptor distance sampling. Our analysis provides the first mechanistic insight into how NCBs can outperform their natural counterparts and emphasizes the need to optimize donor-acceptor distance sampling to obtain high catalytic performance from H-transfer enzymes.

  3. A Coupling of Benzamides and Donor/Acceptor Diazo–Compounds to form γ-Lactams via Rh(III)–Catalyzed C–H Activation

    PubMed Central

    Hyster, Todd K.; Ruhl, Kyle E.; Rovis, Tomislav

    2013-01-01

    The coupling of O-pivaloyl benzhydroxamic acids with donor/acceptor diazo compounds provides iso-indolones in high yield. The reaction tolerates a broad range of benzhydroxamic acids and diazo compounds including substituted 2,2,2-trifluorodiazo ethanes. Mechanistic experiments suggest that C–H activation is turnover limiting and irreversible, while insertion of the diazo compound favors electron deficient substrates. PMID:23548055

  4. Vanguard family planning acceptors in Senegal.

    PubMed

    Nichols, D; Ndiaye, S; Burton, N; Janowitz, B; Gueye, L; Gueye, M

    1985-01-01

    This study examines contraceptive use among clients at the three clinics providing family planning services in Dakar, Senegal in early 1983. Most clients first became interested in family planning following the birth of a child, and most are interested in spacing future pregnancies, although one-third state that they want no more children. The clinic itself was found to be an important determinant of the type of contraceptive used, with only the government-operated clinic providing a balance between IUDs, oral contraceptives, and barrier methods. Nearly half of the clients interviewed said that a lack of knowledge about contraception is the reason for the low contraceptive prevalence rates among Senegalese women; another frequently cited reason was the opposition of the husband. Most clients reported the broadcast media to be the best means of providing family planning information to potential acceptors.

  5. Structural characterization of a family of cytochromes c{sub 7} involved in Fe(III) respiration by Geobacter sulfurreducens.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Pokkuluri, P. R.; Londer, Y. Y.; Yang, X.

    2010-02-01

    Periplasmic cytochromes c{sub 7} are important in electron transfer pathway(s) in Fe(III) respiration by Geobacter sulfurreducens. The genome of G. sulfurreducens encodes a family of five 10-kDa, three-heme cytochromes c{sub 7}. The sequence identity between the five proteins (designated PpcA, PpcB, PpcC, PpcD, and PpcE) varies between 45% and 77%. Here, we report the high-resolution structures of PpcC, PpcD, and PpcE determined by X-ray diffraction. This new information made it possible to compare the sequences and structures of the entire family. The triheme cores are largely conserved but are not identical. We observed changes, due to different crystal packing, inmore » the relative positions of the hemes between two molecules in the crystal. The overall protein fold of the cytochromes is similar. The structure of PpcD differs most from that of the other homologs, which is not obvious from the sequence comparisons of the family. Interestingly, PpcD is the only cytochrome c{sub 7} within the family that has higher abundance when G. sulfurreducens is grown on insoluble Fe(III) oxide compared to ferric citrate. The structures have the highest degree of conservation around 'heme IV'; the protein surface around this heme is positively charged in all of the proteins, and therefore all cytochromes c{sub 7} could interact with similar molecules involving this region. The structures and surface characteristics of the proteins near the other two hemes, 'heme I' and 'heme III', differ within the family. The above observations suggest that each of the five cytochromes c{sub 7} could interact with its own redox partner via an interface involving the regions of heme I and/or heme III; this provides a possible rationalization for the existence of five similar proteins in G. sulfurreducens.« less

  6. Halocarbons as hydrogen bond acceptors: a spectroscopic study of haloethylbenzenes (PhCH2CH2X, X = F, Cl, Br) and their hydrate clusters.

    PubMed

    Robertson, Patrick A; Villani, Luigi; Dissanayake, Uresha L M; Duncan, Luke F; Abbott, Belinda M; Wilson, David J D; Robertson, Evan G

    2018-03-28

    The electronic spectra of 2-bromoethylbenzene and its chloro and fluoro analogues have been recorded by resonant two-photon ionisation (R2PI) spectroscopy. Anti and gauche conformers have been assigned by rotational band contour analysis and IR-UV ion depletion spectroscopy in the CH region. Hydrate clusters of the anti conformers have also been observed, allowing the role of halocarbons as hydrogen bond acceptors to be examined in this context. The donor OH stretch of water bound to chlorine is red-shifted by 36 cm -1 , or 39 cm -1 in the case of bromine. Although classed as weak H-bond acceptors, halocarbons are favourable acceptor sites compared to π systems. Fluorine stands out as the weakest H-bond acceptor amongst the halogens. Chlorine and bromine are also weak H-bond acceptors, but allow for more geometric lability, facilitating complimentary secondary interactions within the host molecule. Ab initio and DFT quantum chemical calculations, both harmonic and anharmonic, aid the structural assignments and analysis.

  7. In vitro fermentation of alternansucrase raffinose acceptor products by human gut bacteria

    USDA-ARS?s Scientific Manuscript database

    In this work, in vitro fermentation of alternansucrase raffinose acceptor products, previously fractionated according to their degree of polymerization (DP; from DP4 to DP10) was carried out using pH-controlled small scale batch cultures at 37ºC under anaerobic conditions with human faeces. Bifidog...

  8. Low molecular weight carboxylic acids in oxidizing porphyry copper tailings.

    PubMed

    Dold, Bernhard; Blowes, David W; Dickhout, Ralph; Spangenberg, Jorge E; Pfeifer, Hans-Rudolf

    2005-04-15

    The distribution of low molecular weight carboxylic acids (LMWCA) was investigated in pore water profiles from two porphyry copper tailings impoundments in Chile (Piuquenes at La Andina and Cauquenes at El Teniente mine). The objectives of this study were (1) to determine the distribution of LMWCA, which are interpreted to be the metabolic byproducts of the autotroph microbial community in this low organic carbon system, and (2) to infer the potential role of these acids in cycling of Fe and other elements in the tailings impoundments. The speciation and mobility of iron, and potential for the release of H+ via hydrolysis of the ferric iron, are key factors in the formation of acid mine drainage in sulfidic mine wastes. In the low-pH oxidation zone of the Piuquenes tailings, Fe(III) is the dominant iron species and shows high mobility. LMWCA, which occur mainly between the oxidation front down to 300 cm below the tailings surface at both locations (e.g., max concentrations of 0.12 mmol/L formate, 0.17 mmol/L acetate, and 0.01 mmol/L pyruvate at Piuquenes and 0.14 mmol/L formate, 0.14 mmol/L acetate, and 0.006 mmol/L pyruvate at Cauquenes), are observed at the same location as high Fe concentrations (up to 71.2 mmol/L Fe(II) and 16.1 mmol/L Fe(III), respectively). In this zone, secondary Fe(III) hydroxides are depleted. Our data suggest that LMWCA may influence the mobility of iron in two ways. First, complexation of Fe(III), through formation of bidentate Fe(III)-LMWCA complexes (e.g., pyruvate, oxalate), may enhance the dissolution of Fe(III) (oxy)hydroxides or may prevent precipitation of Fe(III) (oxy)hydroxides. Soluble Fe(III) chelate complexes which may be mobilized downward and convert to Fe(II) by Fe(III) reducing bacteria. Second, monodentate LMWCA (e.g., acetate and formate) can be used by iron-reducing bacteria as electron donors (e.g., Acidophilum spp.), with ferric iron as the electron acceptor. These processes may, in part, explain the low abundances

  9. Electronic tuning of the lability of Pt(II) complexes through pi-acceptor effects. Correlations between thermodynamic, kinetic, and theoretical parameters.

    PubMed

    Hofmann, Andreas; Jaganyi, Deogratius; Munro, Orde Q; Liehr, Günter; van Eldik, Rudi

    2003-03-10

    pi-Acceptor effects are often used to account for the unusual high lability of [Pt(terpy)L]((2)(-)(n)+) (terpy = 2,2':6',2' '-terpyridine) complexes. To gain further insight into this phenomenon, the pi-acceptor effect was varied systematically by studying the lability of [Pt(diethylenetriamine)OH(2)](2+) (aaa), [Pt(2,6-bis-aminomethylpyridine)OH(2)](2+) (apa), [Pt(N-(pyridyl-2-methyl)-1,2-diamino-ethane)OH(2)](2+) (aap), [Pt(bis(2-pyridylmethyl)amine)OH(2)](2+) (pap), [Pt(2,2'-bipyridine)(NH(3))(OH(2))](2+) (app), and [Pt(terpy)OH(2)](2+) (ppp). The crystal structure of the apa precursor [Pt(2,6-bis-aminomethylpyridine)Cl]Cl.H(2)O was determined. The substitution of water by a series of nucleophiles, viz. thiourea, N,N-dimethylthiourea, N,N,N',N'-tetramethylthiourea, I(-), and SCN(-), was studied under pseudo-first-order conditions as a function of concentration, pH, temperature, and pressure, using stopped-flow techniques. The data enable an overall comparison of the substitution behavior of these complexes, emphasizing the role played by the kinetic cis and trans pi-acceptor effects. The results indicate that the cis pi-acceptor effect is larger than the trans pi-acceptor effect, and that the pi-acceptor effects are multiplicative. DFT calculations at the B3LYP/LACVP level of theory show that, by the addition of pi-acceptor ligands to the metal, the positive charge on the metal center increases, and the energy separation of the frontier molecular orbitals (E(LUMO) - E(HOMO)) of the ground state Pt(II) complexes decreases. The calculations collectively support the experimentally observed additional increase in reactivity when two pi-accepting rings are adjacent to each other (app and ppp), which is ascribed to "electronic communication" between the pyridine rings. The results furthermore indicate that the pK(a) value of the platinum bound water molecule is controlled by the pi-accepting nature of the chelate system and reflects the electron density around the

  10. Surface State Density Determines the Energy Level Alignment at Hybrid Perovskite/Electron Acceptors Interfaces.

    PubMed

    Zu, Fengshuo; Amsalem, Patrick; Ralaiarisoa, Maryline; Schultz, Thorsten; Schlesinger, Raphael; Koch, Norbert

    2017-11-29

    Substantial variations in the electronic structure and thus possibly conflicting energetics at interfaces between hybrid perovskites and charge transport layers in solar cells have been reported by the research community. In an attempt to unravel the origin of these variations and enable reliable device design, we demonstrate that donor-like surface states stemming from reduced lead (Pb 0 ) directly impact the energy level alignment at perovskite (CH 3 NH 3 PbI 3-x Cl x ) and molecular electron acceptor layer interfaces using photoelectron spectroscopy. When forming the interfaces, it is found that electron transfer from surface states to acceptor molecules occurs, leading to a strong decrease in the density of ionized surface states. As a consequence, for perovskite samples with low surface state density, the initial band bending at the pristine perovskite surface can be flattened upon interface formation. In contrast, for perovskites with a high surface state density, the Fermi level is strongly pinned at the conduction band edge, and only minor changes in surface band bending are observed upon acceptor deposition. Consequently, depending on the initial perovskite surface state density, very different interface energy level alignment situations (variations over 0.5 eV) are demonstrated and rationalized. Our findings help explain the rather dissimilar reported energy levels at interfaces with perovskites, refining our understanding of the operating principles in devices comprising this material.

  11. Photoinduced Charge Transfer and Electrochemical Properties of Triphenylamine Ih-Sc3N@C80 Donor-Acceptor Conjugates

    PubMed Central

    Pinzón, Julio R.; Gasca, Diana C.; Shankara, Gayathri. S; Bottari, Giovanni; Torres, Tomás; Guldi, Dirk M.; Echegoyen, Luis

    2009-01-01

    Two isomeric [5,6]-pyrrolidine-Ih-Sc3N@C80 electron donor acceptor conjugates containing triphenylamine (TPA) as the donor system were synthesized. Electrochemical and photophysical studies of the novel conjugates were made and compared with those of their C60 analogues, in order to determine i) the effect of the linkage position (N-substituted versus 2-substituted pyrrolidine) of the donor system in the formation of photoinduced charge separated states, ii) the thermal stability towards the retro-cycloaddition reaction and iii) the effect of changing C60 for Ih-Sc3N@C80 as the electron acceptor. It was found that when the donor is connected to the pyrrolidine nitrogen atom, the resulting dyad produces a significantly longer lived radical pair than the corresponding 2-substituted isomer for both the C60 and Ih-Sc3N@C80 dyads. In addition to that, the N-substituted TPA-Ih-Sc3N@C80 dyad has much better thermal stability than the 2-subtituted one. Finally, the Ih-Sc3N@C80 dyads have considerably longer lived charge separated states than their C60 analogues, thus approving the advantage of using Ih-Sc3N@C80 instead of C60 as the acceptor for the construction of fullerene based donor acceptor conjugates. These findings are important for the design and future application of Ih-Sc3N@C80 dyads as materials for the construction of plastic organic solar cells. PMID:19445462

  12. Possibility to Use Hydrothermally Synthesized CuFeS2 Nanocomposite as an Acceptor in Hybrid Solar Cell

    NASA Astrophysics Data System (ADS)

    Sil, Sayantan; Dey, Arka; Halder, Soumi; Datta, Joydeep; Ray, Partha Pratim

    2018-01-01

    Here we have approached the plausible use of CuFeS2 nanocomposite as an acceptor in organic-inorganic hybrid solar cell. To produce CuFeS2 nanocomposite, hydrothermal strategy was employed. The room-temperature XRD pattern approves the synthesized material as CuFeS2 with no phase impurity (JCPDS Card no: 37-0471). The elemental composition of the material was analyzed from the TEM-EDX data. The obtained selected area electron diffraction (SAED) planes harmonized with the XRD pattern of the synthesized product. Optical band gap (4.14 eV) of the composite from UV-Vis analysis depicts that the synthesized material is belonging to wide band gap semiconductor family. The HOMO (- 6.97 eV) and LUMO (- 2.93 eV) positions from electrochemical study reveal that there is a possibility of electron transfer from MEH-PPV to CuFeS2. The optical absorption and photoluminescence spectra of MEH-PPV:CuFeS2 (donor:acceptor) composite were recorded sequentially by varying weight ratios. The monotonic blue shifting of the absorption peak position indicated the interaction between donor and acceptor materials. The possibility of electron transfer from donor (MEH-PPV) to acceptor (CuFeS2) was approved with photoluminescence analysis. Subsequently, we have fabricated a hybrid solar cell by incorporating CuFeS2 nanocomposite with MEH-PPV in open atmosphere and obtained 0.3% power conversion efficiency.

  13. Quantitative measurements of magnetic polaron binding on acceptors in CdMnTe alloys

    NASA Astrophysics Data System (ADS)

    Nhung, Tran Hong; Planel, R.

    1983-03-01

    The acceptor binding energy is measured as a function of Temperature and composition in Cd1-x Mnx Te alloys, by time resolved spectroscopy. The Bound magnetic polaron effect is measured and compared with a theory accouting for magnetic saturation and fluctuations.

  14. Very low band gap thiadiazoloquinoxaline donor-acceptor polymers as multi-tool conjugated polymers.

    PubMed

    Steckler, Timothy T; Henriksson, Patrik; Mollinger, Sonya; Lundin, Angelica; Salleo, Alberto; Andersson, Mats R

    2014-01-29

    Here we report on the synthesis of two novel very low band gap (VLG) donor-acceptor polymers (Eg ≤ 1 eV) and an oligomer based on the thiadiazoloquinoxaline acceptor. Both polymers demonstrate decent ambipolar mobilities, with P1 showing the best performance of ∼10(-2) cm(2) V(-1) s(-1) for p- and n-type operation. These polymers are among the lowest band gap polymers (≲0.7 eV) reported, with a neutral λmax = 1476 nm (P2), which is the farthest red-shifted λmax reported to date for a soluble processable polymer. Very little has been done to characterize the electrochromic aspects of VLG polymers; interestingly, these polymers actually show a bleaching of their neutral absorptions in the near-infrared region and have an electrochromic contrast up to 30% at a switching speed of 3 s.

  15. Hydrophobic interactions in donor-disulphide-acceptor (DSSA) probes looking beyond fluorescence resonance energy transfer theory.

    PubMed

    Sanjeeva, Shilpa Kammaradi; Korrapati, Swathi; Nair, Chandrasekhar B; Rao, P V Subba; Pullela, Phani Kumar; Vijayalakshmi, U; Siva, Ramamoorthy

    2014-07-01

    Donor-linker-acceptor (DSSA) is a concept in fluorescence chemistry with acceptor being a fluorescent compound (FRET) or quencher. The DSSA probes used to measure thiol levels in vitro and in vivo. The reduction potential of these dyes are in the range of -0.60 V, much lower than the best thiol reductant reported in literature, the DTT (-0.33 V). DSSA disulphide having an unusually low reduction potential compared to the typical thiol reductants is a puzzle. Secondly, DSSA probes have a cyclized rhodamine ring as acceptor which does not have any spectral overlap with fluorescein, but quenches its absorbance and fluorescence. To understand the structural features of DSSA probes, we have synthesized DSSANa and DSSAOr. The calculated reduction potential of these dyes suggest that DSSA probes have an alternate mechanism from the FRET based quenching, namely hydrophobic interaction or dye to dye quenching. The standard reduction potential change with increasing complexity and steric hindrance of the molecule is small, suggesting that ultra- low Eo' has no contribution from the disulphide linker and is based on structural interactions between fluorescein and cyclized rhodamine. Our results help to understand the DSSA probe quenching mechanism and provide ways to design fluorescent probes.

  16. Amorphous carbon nanoparticle used as novel resonance energy transfer acceptor for chemiluminescent immunoassay of transferrin.

    PubMed

    Gao, Hongfei; Wang, Wenwen; Wang, Zhenxing; Han, Jing; Fu, Zhifeng

    2014-03-28

    Amorphous carbon nanoparticles (ACNPs) showing highly efficient quenching of chemiluminescence (CL) were prepared from candle soot with a very simple protocol. The prepared ACNP was employed as the novel energy acceptor for a chemiluminescence resonance energy transfer (CRET)-based immunoassay. In this work, ACNP was linked with transferrin (TRF), and horseradish peroxidase (HRP) was conjugated to TRF antibody (HRP-anti-TRF). The immunoreaction rendered the distance between the ACNP acceptor and the HRP-catalyzed CL emitter to be short enough for CRET occurring. In the presence of TRF, this antigen competed with ACNP-TRF for HRP-anti-TRF, thus led to the decreased occurrence of CRET. A linear range of 20-400 ng mL(-1) and a limit of detection of 20 ng mL(-1) were obtained in this immunoassay. The proposed method was successfully applied for detection of TRF levels in human sera, and the results were in good agreement with ELISA method. Moreover, the ACNPs show higher energy transfer efficiency than other conventional nano-scaled energy acceptors such as graphene oxide in CRET assay. It is anticipated that this approach can be developed for determination of other analytes with low cost, simple manipulation and high specificity. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Production and Isomeric Distribution of Xanthylium Cation Pigments and Their Precursors in Wine-like Conditions: Impact of Cu(II), Fe(II), Fe(III), Mn(II), Zn(II), and Al(III).

    PubMed

    Guo, Anque; Kontoudakis, Nikolaos; Scollary, Geoffrey R; Clark, Andrew C

    2017-03-22

    This study establishes the influence of Cu(II), Fe(II), Fe(III), Zn(II), Al(III), and Mn(II) on the oxidative production of xanthylium cations from (+)-catechin and either tartaric acid or glyoxylic acid in model wine systems. The reaction was studied at 25 °C using UHPLC and LC-HRMS for the analysis of phenolic products and their isomeric distribution. In addition to the expected products, a colorless product, tentatively assigned as a lactone, was detected for the first time. The results show the importance of Fe ions and a synergistic influence of Mn(II) in degrading tartaric acid to glyoxylic acid, whereas the other metal ions had minimal activity in this mechanistic step. Fe(II) and Fe(III) were shown to mediate the (+)-catechin-glyoxylic acid addition reaction, a role previously attributed to only Cu(II). Importantly, the study demonstrates that C-8 addition products of (+)-catechin are promoted by Cu(II), whereas C-6 addition products are promoted by Fe ions.

  18. In situ expression of nifD in Geobacteraceae in subsurface sediments

    USGS Publications Warehouse

    Holmes, Dawn E.; Nevin, Kelly P.; Lovely, Derek R.

    2004-01-01

    In order to determine whether the metabolic state of Geobacteraceae involved in bioremediation of subsurface sediments might be inferred from levels of mRNA for key genes, in situ expression of nifD, a highly conserved gene involved in nitrogen fixation, was investigated. When Geobacter sulfurreducens was grown without a source of fixed nitrogen in chemostats with acetate provided as the limiting electron donor and Fe(III) as the electron acceptor, levels of nifD transcripts were 4 to 5 orders of magnitude higher than in chemostat cultures provided with ammonium. In contrast, the number of transcripts of recA and the 16S rRNA gene were slightly lower in the absence of ammonium. The addition of acetate to organic- and nitrogen-poor subsurface sediments stimulated the growth of Geobacteraceae and Fe(III) reduction, as well as the expression of nifD in Geobacteraceae. Levels of nifD transcripts in Geobacteraceae decreased more than 100-fold within 2 days after the addition of 100 μM ammonium, while levels of recA and total bacterial 16S rRNA in Geobacteraceae remained relatively constant. Ammonium amendments had no effect on rates of Fe(III) reduction in acetate-amended sediments or toluene degradation in petroleum-contaminated sediments, suggesting that other factors, such as the rate that Geobacteraceae could access Fe(III) oxides, limited Fe(III) reduction. These results demonstrate that it is possible to monitor one aspect of the in situ metabolic state of Geobacteraceae species in subsurface sediments via analysis of mRNA levels, which is the first step toward a more global analysis of in situ gene expression related to nutrient status and stress response during bioremediation by Geobacteraceae.

  19. The electronic properties of SWNTs intercalated by electron acceptors

    NASA Astrophysics Data System (ADS)

    Chernysheva, M. V.; Kiseleva, E. A.; Verbitskii, N. I.; Eliseev, A. A.; Lukashin, A. V.; Tretyakov, Yu. D.; Savilov, S. V.; Kiselev, N. A.; Zhigalina, O. M.; Kumskov, A. S.; Krestinin, A. V.; Hutchison, J. L.

    2008-05-01

    Here we report synthesis of Chal@SWNT nanocomposites (where Chal=S, Se and Te) and the impact of the intercalated electron-acceptor compounds on the electronic properties of SWNTs. The chalcogens were introduced to the channels of single-walled carbon nanotubes by molten media technique via impregnation of pre-opened SWNTs with melted guest compounds in vacuum. HRTEM imaging confirms the filling of nanotube channels by continuous nanostructures of corresponding chalcogens. The strong influence of incorporated matter on the electronic properties of the SWNTs was detected by Raman spectroscopy.

  20. Acceptor Percolation Determines How Electron-Accepting Additives Modify Transport of Ambipolar Polymer Organic Field-Effect Transistors.

    PubMed

    Ford, Michael J; Wang, Ming; Bustillo, Karen C; Yuan, Jianyu; Nguyen, Thuc-Quyen; Bazan, Guillermo C

    2018-06-18

    Organic field-effect transistors (OFETs) that utilize ambipolar polymer semiconductors can benefit from the ability of both electron and hole conduction, which is necessary for complementary circuits. However, simultaneous hole and electron transport in organic field-effect transistors result in poor ON/OFF ratios, limiting potential applications. Solution processing methods have been developed to control charge transport properties and transform ambipolar conduction to hole-only conduction. The electron-acceptor phenyl-C61-butyric acid methyl ester (PC 61 BM), when mixed in solution with an ambipolar semiconducting polymer, can reduce electron conduction. Unipolar p-type OFETs with high, well-defined ON/OFF ratios and without detrimental effects on hole conduction are achieved for a wide range of blend compositions, from 95:5 to 5:95 wt % semiconductor polymer:PC 61 BM. When introducing the alternative acceptor N, N'-bis(1-ethylpropyl)-3,4:9,10-perylenediimide (PDI), high ON/OFF ratios are achieved for 95:5 wt % semiconductor polymer:PDI; however, electron conduction increases for 50:50 and 5:95 wt % semiconductor polymer:PDI. As described within, we show that electron conduction is practically eliminated when additive domains do not percolate across the OFET channel, that is, electrons are "morphologically trapped". Morphologies were characterized by optical, electron, and atomic force microscopy as well as X-ray scattering techniques. PC 61 BM was substituted with an endohedral Lu 3 N fullerene, which enhanced contrast in electron microscopy and allowed for more detailed insight into the blend morphologies. Blends with alternative, nonfullerene acceptors further emphasize the importance of morphology and acceptor percolation, providing insights for such blends that control ambipolar transport and ON/OFF ratios.

  1. An Electron-Deficient Building Block Based on the B←N Unit: An Electron Acceptor for All-Polymer Solar Cells.

    PubMed

    Dou, Chuandong; Long, Xiaojing; Ding, Zicheng; Xie, Zhiyuan; Liu, Jun; Wang, Lixiang

    2016-01-22

    A double B←N bridged bipyridyl (BNBP) is a novel electron-deficient building block for polymer electron acceptors in all-polymer solar cells. The B←N bridging units endow BNBP with fixed planar configuration and low-lying LUMO/HOMO energy levels. As a result, the polymer based on BNBP units (P-BNBP-T) exhibits high electron mobility, low-lying LUMO/HOMO energy levels, and strong absorbance in the visible region, which is desirable for polymer electron acceptors. Preliminary all-polymer solar cell (all-PSC) devices with P-BNBP-T as the electron acceptor and PTB7 as the electron donor exhibit a power conversion efficiency (PCE) of 3.38%, which is among the highest values of all-PSCs with PTB7 as the electron donor. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Spectroscopic studies of multiple charge transfer complexes of p-toluidine with π-acceptor picric acid in different polar solvents

    NASA Astrophysics Data System (ADS)

    Singh, Neeti; Ahmad, Afaq

    2010-04-01

    The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in less polar solvent is high. The stoichiometry of the complex was found to be 1: 1 ratio by straight line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant ( K CT), molar extinction coefficient (ɛCT), standard free energy (Δ G°), oscillator strength ( f), transition dipole moment (μEN), resonance energy ( R N) and ionization potential ( I D). The results indicate that the formation constant ( K CT) for the complex were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used.

  3. Process of negative-muon-induced formation of an ionized acceptor center ({sub μ}A){sup –} in crystals with the diamond structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Belousov, Yu. M., E-mail: theorphys@phystech.edu

    The formation of an ionized acceptor center by a negative muon in crystals with the diamond structure is considered. The negative muon entering a target is captured by a nucleus, forming a muonic atom {sub μ}A coupled to a lattice. The appearing radiation-induced defect has a significant electric dipole moment because of the violation of the local symmetry of the lattice and changes the phonon spectrum of the crystal. The ionized acceptor center is formed owing to the capture of an electron interacting with the electric dipole moment of the defect and with the radiation of a deformation-induced local-mode phonon.more » Upper and lower bounds of the formation rate of the ionized acceptor center in diamond, silicon, and germanium crystals are estimated. It is shown that the kinetics of the formation of the acceptor center should be taken into account when processing μSR experimental data.« less

  4. Reinforced self-assembly of donor-acceptor π-conjugated molecules to DNA templates by dipole-dipole interactions together with complementary hydrogen bonding interactions for biomimetics.

    PubMed

    Yang, Wanggui; Chen, Yali; Wong, Man Shing; Lo, Pik Kwan

    2012-10-08

    One of the most important criteria for the successful DNA-templated polymerization to generate fully synthetic biomimetic polymers is to design the complementary structural monomers, which assemble to the templates strongly and precisely before carrying polymerization. In this study, water-soluble, laterally thymine-substituted donor-acceptor π-conjugated molecules were designed and synthesized to self-assemble with complementary oligoadenines templates, dA(20) and dA(40), into stable and tubular assemblies through noncovalent interactions including π-π stacking, dipole-dipole interactions, and the complementary adenine-thymine (A-T) hydrogen-bonding. UV-vis, fluorescence, circular dichroism (CD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) techniques were used to investigate the formation of highly robust nanofibrous structures. Our results have demonstrated for the first time that the dipole-dipole interactions are stronger and useful to reinforce the assembly of donor-acceptor π-conjugated molecules to DNA templates and the formation of the stable and robust supramolecular nanofibrous complexes together with the complementary hydrogen bonding interactions. This provides an initial step toward DNA-templated polymerization to create fully synthetic DNA-mimetic polymers for biotechnological applications. This study also presents an opportunity to precisely position donor-acceptor type molecules in a controlled manner and tailor-make advanced materials for various biotechnological applications.

  5. Current Production and Metal Oxide Reduction by Shewanella oneidensis MR-1 Wild Type and Mutants▿ †

    PubMed Central

    Bretschger, Orianna; Obraztsova, Anna; Sturm, Carter A.; Chang, In Seop; Gorby, Yuri A.; Reed, Samantha B.; Culley, David E.; Reardon, Catherine L.; Barua, Soumitra; Romine, Margaret F.; Zhou, Jizhong; Beliaev, Alexander S.; Bouhenni, Rachida; Saffarini, Daad; Mansfeld, Florian; Kim, Byung-Hong; Fredrickson, James K.; Nealson, Kenneth H.

    2007-01-01

    Shewanella oneidensis MR-1 is a gram-negative facultative anaerobe capable of utilizing a broad range of electron acceptors, including several solid substrates. S. oneidensis MR-1 can reduce Mn(IV) and Fe(III) oxides and can produce current in microbial fuel cells. The mechanisms that are employed by S. oneidensis MR-1 to execute these processes have not yet been fully elucidated. Several different S. oneidensis MR-1 deletion mutants were generated and tested for current production and metal oxide reduction. The results showed that a few key cytochromes play a role in all of the processes but that their degrees of participation in each process are very different. Overall, these data suggest a very complex picture of electron transfer to solid and soluble substrates by S. oneidensis MR-1. PMID:17644630

  6. Modulation Doping of Silicon using Aluminium-induced Acceptor States in Silicon Dioxide

    PubMed Central

    König, Dirk; Hiller, Daniel; Gutsch, Sebastian; Zacharias, Margit; Smith, Sean

    2017-01-01

    All electronic, optoelectronic or photovoltaic applications of silicon depend on controlling majority charge carriers via doping with impurity atoms. Nanoscale silicon is omnipresent in fundamental research (quantum dots, nanowires) but also approached in future technology nodes of the microelectronics industry. In general, silicon nanovolumes, irrespective of their intended purpose, suffer from effects that impede conventional doping due to fundamental physical principles such as out-diffusion, statistics of small numbers, quantum- or dielectric confinement. In analogy to the concept of modulation doping, originally invented for III-V semiconductors, we demonstrate a heterostructure modulation doping method for silicon. Our approach utilizes a specific acceptor state of aluminium atoms in silicon dioxide to generate holes as majority carriers in adjacent silicon. By relocating the dopants from silicon to silicon dioxide, Si nanoscale doping problems are circumvented. In addition, the concept of aluminium-induced acceptor states for passivating hole selective tunnelling contacts as required for high-efficiency photovoltaics is presented and corroborated by first carrier lifetime and tunnelling current measurements. PMID:28425460

  7. 48-spot single-molecule FRET setup with periodic acceptor excitation

    NASA Astrophysics Data System (ADS)

    Ingargiola, Antonino; Segal, Maya; Gulinatti, Angelo; Rech, Ivan; Labanca, Ivan; Maccagnani, Piera; Ghioni, Massimo; Weiss, Shimon; Michalet, Xavier

    2018-03-01

    Single-molecule Förster resonance energy transfer (smFRET) allows measuring distances between donor and acceptor fluorophores on the 3-10 nm range. Solution-based smFRET allows measurement of binding-unbinding events or conformational changes of dye-labeled biomolecules without ensemble averaging and free from surface perturbations. When employing dual (or multi) laser excitation, smFRET allows resolving the number of fluorescent labels on each molecule, greatly enhancing the ability to study heterogeneous samples. A major drawback to solution-based smFRET is the low throughput, which renders repetitive measurements expensive and hinders the ability to study kinetic phenomena in real-time. Here we demonstrate a high-throughput smFRET system that multiplexes acquisition by using 48 excitation spots and two 48-pixel single-photon avalanche diode array detectors. The system employs two excitation lasers allowing separation of species with one or two active fluorophores. The performance of the system is demonstrated on a set of doubly labeled double-stranded DNA oligonucleotides with different distances between donor and acceptor dyes along the DNA duplex. We show that the acquisition time for accurate subpopulation identification is reduced from several minutes to seconds, opening the way to high-throughput screening applications and real-time kinetics studies of enzymatic reactions such as DNA transcription by bacterial RNA polymerase.

  8. Effects of hydrogen on acceptor activation in ternary nitride semiconductors

    DOE PAGES

    Fioretti, Angela N.; Stokes, Adam; Young, Matthew R.; ...

    2017-02-09

    Doping control is necessary to unlock the scientific and technological potential of many materials, including ternary II-IV-nitride semiconductors, which are closely related to binary GaN. In particular, ZnSnN 2 has been reported to have degenerate doping density, despite bandgap energies that are well suited for solar energy conversion. Here, we show that annealing Zn-rich Zn 1+xSn 1-xN 2 grown with added hydrogen reduces its free electron density by orders of magnitude, down to 4 x 10 16 cm -3. This experimental observation can be explained by hydrogen passivation of acceptors in Zn 1+xSn 1-xN 2 during growth, lowering the drivingmore » force for unintentional donor formation. Lastly, these results indicate that the doping control principles used in GaN can be translated to ZnSnN 2, suggesting that other strategies used in binary III-Vs can be applied to accelerate the technological development of ternary II-IV-N 2 materials.« less

  9. Theoretical study of solvent effects on the electronic coupling matrix elements in rigidly linked donor-acceptor systems

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cave, R.J.; Newton, M.D.; Kumar, K.

    1995-12-07

    The recently developed generalized Mulliken-Hush approach for the calculation of the electronic coupling matrix element for electron-transfer processes is applied to two rigidly linked donor-bridge-acceptor systems having dimethoxyanthracene as the donor and a dicarbomethoxycyclobutene unit as the acceptor. The dependence of the electronic coupling matrix element as a function of bridge type is examined with and without solvent molecules present. For clamp-shaped bridge structures solvent can have a dramatic effect on the electronic coupling matrix element. The behavior with variation of solvent is in good agreement with that observed experimentally for these systems. 23 refs., 2 tabs.

  10. Pronounced Effects of a Triazine Core on Photovoltaic Performance-Efficient Organic Solar Cells Enabled by a PDI Trimer-Based Small Molecular Acceptor.

    PubMed

    Duan, Yuwei; Xu, Xiaopeng; Yan, He; Wu, Wenlin; Li, Zuojia; Peng, Qiang

    2017-02-01

    A novel-small molecular acceptor with electron-deficient 1,3,5-triazine as the core and perylene diimides as the arms is developed as the acceptor material for efficient bulk heterojunction organic solar cells with an efficiency of 9.15%. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Structural classification of RAO3( MO) n compounds ( R =Sc, In, Y, or lanthanides; A =Fe(III), Ga, Cr, or Al; M =divalent cation; n = 1-11)

    NASA Astrophysics Data System (ADS)

    Kimizuka, Noboru; Mohri, Takahiko

    1989-01-01

    A series of new compounds RAO3( MO) n ( n = 1-11) having spinel, YbFe 2O 4, or InFeO 3(ZnO) n types of structures were newly synthesized ( R =Sc, In, Y, Lu, Yb, Tm, or Er; A =Fe(III), Ga, Cr, or Al; M =Mg, Mn, Fe(II), Co, Ni, Zn, or Cd) at elevated temperatures. The conditions of synthesis and the lattice constants for these compounds are reported. The stacking sequences of the InO 1.5, (FeZn)O 2.5, and ZnO layers for InFeO 3(ZnO) 10 and the TmO 1.5, (AlZn)O 2.5, and ZnO layers for TmAlO 3(ZnO) 11 are presented, respectively. The crystal structures of the( RAO3) m( MO) n phases ( R =Sc, In, Y, or lanthanide elements; A =Fe(III), Ga, Cr, or Al; M =divalent cation elements; m and n =integer) are classified into four crystal structure types (K 2NiF 4, CaFe 2O 4, YbFe 2O 4, and spinel), based upon the constituent cations R, A, and M

  12. Benzene oxidation coupled to sulfate reduction

    USGS Publications Warehouse

    Lovley, D.R.; Coates, J.D.; Woodward, J.C.; Phillips, E.J.P.

    1995-01-01

    Highly reduced sediments from San Diego Bay, Calif., that were incubated under strictly anaerobic conditions metabolized benzene within 55 days when they were exposed initially to I ??M benzene. The rate of benzene metabolism increased as benzene was added back to the benzene-adapted sediments. When a [14C]benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as 14CO2. Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of 14CO2 from [14C]benzene. Benzene metabolism stopped when the sediments became sulfate depleted, and benzene uptake resumed when sulfate was added again. The stoichiometry of benzene uptake and sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for benzene oxidation. Isotope trapping experiments performed with [14C]benzene revealed that there was no production of such potential extracellular intermediates of benzene oxidation as phenol, benzoate, p-hydroxybenzoate, cyclohexane, catechol, and acetate. The results demonstrate that benzene can be oxidized in the absence of O2, with sulfate serving as the electron acceptor, and suggest that some sulfate reducers are capable of completely oxidizing benzene to carbon dioxide without the production of extracellular intermediates. Although anaerobic benzene oxidation coupled to chelated Fe(III) has been documented previously, the study reported here provides the first example of a natural sediment compound that can serve as an electron acceptor for anaerobic benzene oxidation.

  13. Magnetic resonance studies of the Mg acceptor in thick free-standing and thin-film GaN

    NASA Astrophysics Data System (ADS)

    Zvanut, Mary Ellen

    Mg, the only effective p-type dopant for the nitrides, substitutes for Ga and forms an acceptor with a defect level of about 0.16 eV. The magnetic resonance of such a center should be highly anisotropic, yet early work employing both optically detected magnetic resonance (ODMR) and electron paramagnetic resonance (EPR) spectroscopies revealed a defect with a nearly isotropic g-tensor. The results were attributed to crystal fields caused by compensation and/or strain typical of the heteroepitaxially grown films. The theory was supported by observation of the expected highly anisotropic ODMR signature in homoepitaxially grown films in which dislocation-induced non-uniform strain and compensation are reduced. The talk will review EPR measurements of thin films and describe new work which takes advantage of the recently available thick free-standing GaN:Mg substrates grown by hydride vapor phase epitaxy (HVPE) and high nitrogen pressure solution growth (HNPS). Interestingly, the films and HVPE substrates exhibit characteristically different types of EPR signals, and no EPR response could be induced in the HNPS substrates, with or without illumination. In the heteroepitaxial films, a curious angular dependent line-shape is observed in addition to the nearly isotropic g-tensor characteristic of the Mg-related acceptor. On the other hand, the free-standing HVPE crystals reveal a clear signature of a highly anisotropic shallow acceptor center. Comparison with SIMS measurements implies a direct relation to the Mg impurity, and frequency-dependent EPR studies demonstrate the influence of the anisotropic crystal fields. Overall, the measurements of the thick free-standing crystals show that the Mg acceptor is strongly affected by the local environment. The ODMR was performed by Evan Glaser, NRL and the free-standing Mg-doped HVPE crystals were grown by Jacob Leach, Kyma Tech. The work at UAB is supported by NSF Grant No. DMR-1308446.

  14. Spectroscopic studies on the interaction of cimetidine drug with biologically significant σ- and π-acceptors

    NASA Astrophysics Data System (ADS)

    Pandeeswaran, M.; Elango, K. P.

    2010-05-01

    Spectroscopic studies revealed that the interaction of cimetidine drug with electron acceptors iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted through the initial formation of ionic intermediate to charge transfer (CT) complex. The CT-complexes of the interactions have been characterized using UV-vis, 1H NMR, FT-IR and GC-MS techniques. The formation of triiodide ion, I 3-, is further confirmed by the observation of the characteristic bands in the far IR spectrum for non-linear I 3- ion with C s symmetry at 156 and 131 cm -1 assigned to νas(I-I) and νs(I-I) of the I-I bond and at 73 cm -1 due to bending δ(I 3-). The rate of formation of the CT-complexes has been measured and discussed as a function of relative permittivity of solvent and temperature. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants and this observation was further supported by spectral studies. Based on the spectroscopic results plausible mechanisms for the interaction of the drug with the chosen acceptors were proposed and discussed and the point of attachment of the multifunctional cimetidine drug with these acceptors during the formation of CT-complex has been established.

  15. Improvement of DNA adenylation using T4 DNA ligase with a template strand and a strategically mismatched acceptor strand

    PubMed Central

    Patel, Maha P.; Baum, Dana A.; Silverman, Scott K.

    2008-01-01

    DNA with a 5′-adenylpyrophosphoryl cap (5′-adenylated DNA; AppDNA) is an activated form of DNA that is the biochemical intermediate of the reactions catalyzed by DNA ligase, RNA ligase, polynucleotide kinase, and other nucleic acid modifying enzymes. 5′-Adenylated DNA is also useful for in vitro selection experiments. Efficient preparation of 5′-adenylated DNA is therefore desirable for several biochemical applications. Here we have developed a DNA adenylation procedure that uses T4 DNA ligase and is more reliable than a previously reported approach that used the 5′-phosphorylated donor DNA substrate to be adenylated, a DNA template, and ATP but no acceptor strand. Our improved DNA adenylation procedure uses the above components as well as an acceptor strand that has a strategically chosen C-T acceptor-template mismatch directly adjacent to the adenylation site. This mismatch permits adenylation of the donor DNA substrate but largely suppresses subsequent ligation of the donor with the acceptor, as assayed on nine different DNA substrates that collectively have all four DNA nucleotides represented at each of the first two positions. The new DNA adenylation procedure is successful using either laboratory-prepared or commercial T4 DNA ligase and works well on the preparative (2 nmol) scale for all nine of the test DNA substrates. PMID:18022669

  16. Thermophily in the Geobacteraceae: Geothermobacter ehrlichii gen. nov., sp. nov., a novel thermophilic member of the Geobacteraceae from the "Bag City" hydrothermal vent.

    PubMed

    Kashefi, Kazem; Holmes, Dawn E; Baross, John A; Lovley, Derek R

    2003-05-01

    Little is known about the microbiology of the "Bag City" hydrothermal vent, which is part of a new eruption site on the Juan de Fuca Ridge and which is notable for its accumulation of polysaccharide on the sediment surface. A pure culture, designated strain SS015, was recovered from a vent fluid sample from the Bag City site through serial dilution in liquid medium with malate as the electron donor and Fe(III) oxide as the electron acceptor and then isolation of single colonies on solid Fe(III) oxide medium. The cells were gram-negative rods, about 0.5 micro m by 1.2 to 1.5 micro m, and motile and contained c-type cytochromes. Analysis of the 16S ribosomal DNA (rDNA) sequence of strain SS015 placed it in the family Geobacteraceae in the delta subclass of the Proteobacteria. Unlike previously described members of the Geobacteraceae, which are mesophiles, strain SS015 was a thermophile and grew at temperatures of between 35 and 65 degrees C, with an optimum temperature of 55 degrees C. Like many previously described members of the Geobacteraceae, strain SS015 grew with organic acids as the electron donors and Fe(III) or nitrate as the electron acceptor, with nitrate being reduced to ammonia. Strain SS015 was unique among the Geobacteraceae in its ability to use sugars, starch, or amino acids as electron donors for Fe(III) reduction. Under stress conditions, strain SS015 produced copious quantities of extracellular polysaccharide, providing a model for the microbial production of the polysaccharide accumulation at the Bag City site. The 16S rDNA sequence of strain SS015 was less than 94% similar to the sequences of previously described members of the Geobacteraceae; this fact, coupled with its unique physiological properties, suggests that strain SS015 represents a new genus in the family Geobacteraceae. The name Geothermobacter ehrlichii gen. nov., sp. nov., is proposed (ATCC BAA-635 and DSM 15274). Although strains of Geobacteraceae are known to be the predominant

  17. Electron acceptors for energy generation in microbial fuel cells fed with wastewaters: A mini-review.

    PubMed

    He, Chuan-Shu; Mu, Zhe-Xuan; Yang, Hou-Yun; Wang, Ya-Zhou; Mu, Yang; Yu, Han-Qing

    2015-12-01

    Microbial fuel cells (MFCs) have gained tremendous global interest over the last decades as a device that uses bacteria to oxidize organic and inorganic matters in the anode with bioelectricity generation and even for purpose of bioremediation. However, this prospective technology has not yet been carried out in field in particular because of its low power yields and target compounds removal which can be largely influenced by electron acceptors contributing to overcome the potential losses existing on the cathode. This mini review summarizes various electron acceptors used in recent years in the categories of inorganic and organic compounds, identifies their merits and drawbacks, and compares their influences on performance of MFCs, as well as briefly discusses possible future research directions particularly from cathode aspect. Copyright © 2015 Elsevier Ltd. All rights reserved.

  18. Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Haeggblom, M.M.; Rivera, M.D.; Young, L.Y.

    1993-04-01

    Methanogeneic conditions can promote the biodegradation of a number of halogenated aromatic compounds. This study, using sediments from freshwater and estuarine sites, is an evaluation of the anaerobic biodegradability of monochlorinated phenols and benzoic acids coupled to denitrification, sulfidogenesis, and methanogenesis. The results indicate that chlorinated phenols and benzoic acids are biodegradable under at least one set of anaerobic conditions. Metabolism depends both on the electron acceptor available and on the position of the chlorine substituent. Presence of alternative electron acceptors, nitrate, sulfate, and carbonate, can affect degradation rates and substrate specificities. Since contaminated sites usually have mixtures of wastes,more » bioremediation efforts may need to consider the activities of diverse anaerobic communities to carry out effective treatment of all components. 37 refs., 4 figs., 4 tabs.« less

  19. Donor-acceptor-pair emission in fluorescent 4H-SiC grown by PVT method

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Xi, E-mail: liuxi@mail.sic.ac.cn; Zhuo, Shi-Yi; Gao, Pan

    Fluorescent SiC, which contains donor and acceptor impurities with optimum concentrations, can work as a phosphor for visible light emission by donor-acceptor-pair (DAP) recombination. In this work, 3 inch N-B-Al co-doped fluorescent 4H-SiC crystals are prepared by PVT method. The p-type fluorescent 4H-SiC with low aluminum doping concentration can show intensive yellow-green fluorescence at room temperature. N-B DAP peak wavelength shifts from 578nm to 525nm and weak N-Al DAP emission occurred 403/420 nm quenches, when the temperature increases from 4K to 298K. The aluminum doping induces higher defect concentration in the fluorescent crystal and decreases optical transmissivity of the crystalmore » in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.« less

  20. Molecular design of novel fullerene-based acceptors for enhancing the open circuit voltage in polymer solar cells

    NASA Astrophysics Data System (ADS)

    Tajbakhsh, Mahmood; Kariminasab, Mohaddeseh; Ganji, Masoud Darvish; Alinezhad, Heshmatollah

    2017-12-01

    Organic solar cells, especially bulk hetero-junction polymer solar cells (PSCs), are the most successful structures for applications in renewable energy. The dramatic improvement in the performance of PSCs has increased demand for new conjugated polymer donors and fullerene derivative acceptors. In the present study, quantum chemical calculations were performed for several representative fullerene derivatives in order to determine their frontier orbital energy levels and electronic structures, thereby helping to enhance their performance in PSC devices. We found correlations between the theoretical lowest unoccupied molecular orbital levels and electrophilicity index of various fullerenes with the experimental open circuit voltage of photovoltaic devices according to the poly(3-hexylthiophene) (P3HT):fullerene blend. The correlations between the structure and descriptors may facilitate screening of the best fullerene acceptor for the P3HT donor. Thus, we considered fullerenes with new functional groups and we predicted the output factors for the corresponding P3HT:fullerene blend devices. The results showed that fullerene derivatives based on thieno-o-quinodimethane-C60 with a methoxy group will have enhanced photovoltaic properties. Our results may facilitate the design of new fullerenes and the development of favorable acceptors for use in photovoltaic applications.

  1. A helical perylene diimide-based acceptor for non-fullerene organic solar cells: synthesis, morphology and exciton dynamics

    NASA Astrophysics Data System (ADS)

    Chen, Li; Wu, Mingliang; Shao, Guangwei; Hu, Jiahua; He, Guiying; Bu, Tongle; Yi, Jian-Peng; Xia, Jianlong

    2018-05-01

    Helical perylene diimide-based (hPDI) acceptors have been established as one of the most promising candidates for non-fullerene organic solar cells (OSCs). In this work, we report a novel hPDI-based molecule, hPDI2-CN2, as an electron acceptor for OSCs. Combining the hPDI2-CN2 with a low-bandgap polymeric donor (PTB7-Th), the blending film morphology exhibited high sensitivity to various treatments (such as thermal annealing and addition of solvent additives), as evidenced by atomic force microscope studies. The power conversion efficiency (PCE) was improved from 1.42% (as-cast device) to 2.76% after thermal annealing, and a PCE of 3.25% was achieved by further addition of 1,8-diiodooctane (DIO). Femtosecond transient absorption (TA) spectroscopy studies revealed that the improved thin-film morphology was highly beneficial for the charge carrier transport and collection. And a combination of fast exciton diffusion rate and the lowest recombination rate contributed to the best performance of the DIO-treated device. This result further suggests that the molecular conformation needs to be taken into account in the design of perylene diimide-based acceptors for OSCs.

  2. Michael acceptor containing drugs are a novel class of 5-lipoxygenase inhibitor targeting the surface cysteines C416 and C418.

    PubMed

    Maucher, Isabelle V; Rühl, Michael; Kretschmer, Simon B M; Hofmann, Bettina; Kühn, Benjamin; Fettel, Jasmin; Vogel, Anja; Flügel, Karsten T; Manolikakes, Georg; Hellmuth, Nadine; Häfner, Ann-Kathrin; Golghalyani, Vahid; Ball, Ann-Katrin; Piesche, Matthias; Matrone, Carmela; Geisslinger, Gerd; Parnham, Michael J; Karas, Michael; Steinhilber, Dieter; Roos, Jessica; Maier, Thorsten J

    2017-02-01

    Recently, we published that nitro-fatty acids (NFA) are potent electrophilic molecules which inhibit 5-lipoxygenase (5-LO) by interacting catalytically with cysteine residues next to a substrate entry channel. The electrophilicity is derived from an intramolecular Michael acceptor moiety consisting of an electron-withdrawing group in close proximity to a double bond. The potential of the Michael acceptor moiety to interact with functionally relevant cysteines of proteins potentially renders them effective and sustained enzyme activity modulators. We screened a large library of naturally derived and synthetic electrophilic compounds to investigate whether other types of Michael acceptor containing drugs suppress 5-LO enzyme activity. The activity was measured by assessing the effect on the 5-LO product formation of intact human polymorphonuclear leukocytes. We demonstrated that a number of structurally different compounds were suppressive in the activity assays and showed that Michael acceptors of the quinone and nitro-alkene group produced the strongest inhibition of 5-LO product formation. Reactivity with the catalytically relevant cysteines 416 and 418 was confirmed using mutated recombinant 5-LO and mass spectrometric analysis (MALDI-MS). In the present study, we show for the first time that a number of well-recognized naturally occurring or synthetic anti-inflammatory compounds carrying a Michael acceptor, such as thymoquinone (TQ), the paracetamol metabolite NAPQI, the 5-LO inhibitor AA-861, and bardoxolone methyl (also known as RTA 402 or CDDO-methyl ester) are direct covalent 5-LO enzyme inhibitors that target the catalytically relevant cysteines 416 and 418. Copyright © 2016 Elsevier Inc. All rights reserved.

  3. Magnesium acceptor in gallium nitride. I. Photoluminescence from Mg-doped GaN

    NASA Astrophysics Data System (ADS)

    Reshchikov, M. A.; Ghimire, P.; Demchenko, D. O.

    2018-05-01

    Defect-related photoluminescence (PL) is analyzed in detail for n -type, p -type, and semi-insulating Mg-doped GaN grown by different techniques. The ultraviolet luminescence (UVL) band is the dominant PL band in conductive n -type and p -type GaN:Mg samples grown by hydride vapor phase epitaxy (HVPE) and molecular beam epitaxy. The UVL band in undoped and Mg-doped GaN samples is attributed to the shallow M gGa acceptor with the ionization energy of 223 meV. In semi-insulating GaN:Mg samples, very large shifts of the UVL band (up to 0.6 eV) are observed with variation of temperature or excitation intensity. The shifts are attributed to diagonal transitions, likely due to potential fluctuations or near-surface band bending. The blue luminescence (B LMg ) band is observed only in GaN:Mg samples grown by HVPE or metalorganic chemical vapor deposition when the concentration of Mg exceeds 1019c m-3 . The B LMg band is attributed to electron transitions from an unknown deep donor to the shallow M gGa acceptor. Basic properties of the observed PL are explained with a phenomenological model.

  4. A charge carrier transport model for donor-acceptor blend layers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fischer, Janine, E-mail: janine.fischer@iapp.de; Widmer, Johannes; Koerner, Christian

    2015-01-28

    Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C{sub 60} in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for themore » characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (E{sub t} = 0.14 eV, N{sub t} = 1.2 × 10{sup 18 }cm{sup −3}) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.« less

  5. Multiplexed interfacial transduction of nucleic acid hybridization using a single color of immobilized quantum dot donor and two acceptors in fluorescence resonance energy transfer.

    PubMed

    Algar, W Russ; Krull, Ulrich J

    2010-01-01

    A multiplexed solid-phase assay for the detection of nucleic acid hybridization was developed on the basis of a single color of immobilized CdSe/ZnS quantum dot (QD) as a donor in fluorescence resonance energy transfer (FRET). This work demonstrated that two channels of detection did not necessitate two different QD donors. Two probe oligonucleotides were coimmobilized on optical fibers modified with QDs, and a sandwich assay was used to associate the acceptor dyes with interfacial hybridization events without target labeling. FRET-sensitized acceptor emission provided an analytical signal that was concentration dependent down to 10 nM. Changes in the ratio of coimmobilized probe oligonucleotides were found to yield linear changes in the relative amounts of acceptor emission. These changes were compared to previous studies that used mixed films of two QD donors for two detection channels. The analysis indicated that probe dilution effects were primarily driven by changes in acceptor number density and that QD dilution effects or changes in mean donor-acceptor distance were secondary. Hybridization kinetics were found to be consistent between different ratios of coimmobilized probes, suggesting that hybridization in this type of system occurred via the accepted model for solid-phase hybridization, where adsorption and then diffusion at the solid interface drove hybridization.

  6. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  7. Nitrate is a preferred electron acceptor for growth of freshwater selenate-respiring bacteria

    USGS Publications Warehouse

    Steinberg, Nisan A.; Blum, Jodi Switzer; Hochstein , Lawrence; Oremland, Ronald S.

    1992-01-01

    An anaerobic, freshwater enrichment grew with either nitrate or selenate as an electron acceptor. With both ions present, nitrate reduction preceded selenate reduction. An isolate from the enrichment grew on either ion, but the presence of nitrate precluded the reduction of selenate. Stock cultures of denitrifiers grew anaerobically on nitrate but not on selenate.

  8. Thiophene-based rhodamine as selectivef luorescence probe for Fe(III) and Al(III) in living cells.

    PubMed

    Wang, Kun-Peng; Chen, Ju-Peng; Zhang, Si-Jie; Lei, Yang; Zhong, Hua; Chen, Shaojin; Zhou, Xin-Hong; Hu, Zhi-Qiang

    2017-09-01

    The thiophene-modified rhodamine 6G (GYJ) has been synthesized as a novel chemosensor. The sensor has sufficiently high selectivity and sensitivity for the detection of Fe 3+ and Al 3+ ions (M 3+ ) by fluorescence and ultraviolet spectroscopy with a strong ability for anti-interference performance. The binding ratio of M 3+ -GYJ complex was determined to be 2:1 according to the Job's plot. The binding constants for Fe 3+ and Al 3+ were calculated to be 3.91 × 10 8 and 5.26 × 10 8  M -2 , respectively. All these unique features made it particularly favorable for cellular imaging applications. The obvious fluorescence microscopy experiments demonstrated that the probes could contribute to the detection of Fe 3+ and Al 3+ in related cells and biological organs with satisfying resolution. Graphical abstract GYJ has high selectivity and sensitivity for the detection of Fe(III) and Al(III) with the binding ratio of 2:1.

  9. Interaction of Vimang (Mangifera indica L. extract) with Fe(III) improves its antioxidant and cytoprotecting activity.

    PubMed

    Pardo-Andreu, Gilberto L; Sánchez-Baldoquín, Carlos; Avila-González, Rizette; Yamamoto, Edgar T Suzuki; Revilla, Andrés; Uyemura, Sérgio Akira; Naal, Zeki; Delgado, René; Curti, Carlos

    2006-11-01

    A standard aqueous stem bark extract from selected species of Mangifera indica L. (Anacardiaceae)--Vimang, whose major polyphenolic component is mangiferin, displays potent in vitro and in vivo antioxidant activity. The present study provides evidence that the Vimang-Fe(III) mixture is more effective at scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radicals, as well as in protecting against t-butyl hydroperoxide-induced mitochondrial lipid peroxidation and hypoxia/reoxygenation-induced hepatocytes injury, compared to Vimang alone. Voltammetric assays demonstrated that Vimang, in line with the high mangiferin content of the extract, behaves electrochemically like mangiferin, as well as interacts with Fe(III) in close similarity with mangiferin's interaction with the cation. These results justify the high efficiency of Vimang as an agent protecting from iron-induced oxidative damage. We propose Vimang as a potential therapy against the deleterious action of reactive oxygen species generated during iron-overload, such as that occurring in diseases like beta-thalassemia, Friedreich's ataxia and haemochromatosis.

  10. Polymer/Polymer Blend Solar Cells Using Tetraazabenzodifluoranthene Diimide Conjugated Polymers as Electron Acceptors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Li, Haiyan; Hwang, Ye-Jin; Earmme, Taeshik

    2015-03-02

    Two n-type semiconducting polymers with alternating arylene (thiophene or selenophene)–tetraazabenzodifluoranthene diimide (BFI) donor–acceptor architecture have been investigated as new electron acceptors in polymer/polymer blend solar cells. The new selenophene-linked polymer, PBFI-S, has a significantly smaller optical band gap (1.13 eV) than the thiophene-linked PBFI-T (1.38 eV); however, both polymers have similar HOMO/LUMO energy levels determined from cyclic voltammetry. Blends of PBFI-T with the thiazolothiazole–dithienylsilole donor polymer (PSEHTT) gave a 2.60% power conversion efficiency (PCE) with a 7.34 mA/cm2 short-circuit current. In contrast, PBFI-S:PSEHTT blends had a 0.75% PCE with similarly reduced photocurrent and external quantum efficiency. Reduced free energy formore » charge transfer and reduced bulk electron mobility in PBFI-S:PSEHTT blends compared to PBFI-T:PSEHTT blends as well as significant differences in bulk film morphology are among the reasons for the large loss in efficiency in PBFI-S:PSEHTT blend solar cells.« less

  11. Donor-π-Acceptor Polymer with Alternating Triarylborane and Triphenylamine Moieties.

    PubMed

    Li, Haiyan; Jäkle, Frieder

    2010-05-12

    A luminescent main chain donor-π-acceptor-type polymer (4) was prepared via organometallic polycondensation reaction followed by post modification. With both electron-rich amine and electron-deficient borane moieties embedded in the main chain, 4 exhibits an interesting ambipolar character: it can be reduced and oxidized electrochemically at moderate potentials and shows a strong solvatochromic effect in the emission spectra. Complexation studies show that 4 selectively binds to fluoride and cyanide; quantitative titration with cyanide reveals a two-step binding process. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. The significance of microbial processes in hydrogeology and geochemistry

    USGS Publications Warehouse

    Chapelle, F.H.

    2000-01-01

    Microbial processes affect the chemical composition of groundwater and the hydraulic properties of aquifers in both contaminated and pristine groundwater systems. The patterns of water-chemistry changes that occur depend upon the relative abundance of electron donors and electron acceptors. In many pristine aquifers, where microbial metabolism is limited by the availability of electron donors (usually organic matter), dissolved inorganic carbon (DIC) accumulates slowly along aquifer flow paths and available electron acceptors are consumed sequentially in the order dissolved oxygen > nitrate > Fe(III) > sulfate > CO2 (methanogenesis). In aquifers contaminated by anthropogenic contaminants, an excess of available organic carbon often exists, and microbial metabolism is limited by the availability of electron acceptors. In addition to changes in groundwater chemistry, the solid matrix of the aquifer is affected by microbial processes. The production of carbon dioxide and organic acids can lead to increased mineral solubility, which can lead to the development of secondary porosity and permeability. Conversely, microbial production of carbonate, ferrous iron, and sulfide can result in the precipitation of secondary calcite or pyrite cements that reduce primary porosity and permeability in groundwater systems.

  13. Transpeptidation reactions of a specific substrate catalyzed by the streptomyces R61 DD-peptidase: characterization of a chromogenic substrate and acyl acceptor design.

    PubMed

    Kumar, Ish; Pratt, R F

    2005-08-02

    The Streptomyces R61 dd-peptidase, a functional model for penicillin-binding proteins, catalyzes the hydrolysis and aminolysis of d-alanyl-d-alanine-terminating peptides by specific amines. In vivo, this reaction completes bacterial cell wall biosynthesis. For in vitro studies of this enzyme to date, various nonspecific acyl-donor substrates have been employed. Recently, however, a peptidoglycan-mimetic peptide substrate, glycyl-l-alpha-amino-epsilon-pimelyl-d-alanyl-d-alanine, has been described that is much more specific for this enzyme. In this paper, we describe the synthesis and kinetic characterization of an analogous thiolester substrate, 3-(N-glycyl-l-cysteinyl)-propanoyl-d-alanyl-d-thiolactate, that the enzyme hydrolyzes and aminolyzes very efficiently (k(cat)/K(m) = 1.0 x 10(7) s(-)(1) M(-)(1)). Direct or indirect, by means of a thiol trap, spectrophotometric monitoring of the reactions of this substrate is readily achieved. Deacylation of the enzyme is rate-determining under substrate saturation conditions, and therefore the aminolysis reaction can be directly studied. The results show that d-amino acids and certain Gly-l-Xaa dipeptides and tripeptides may act as acyl acceptors at the active site of the enzyme. d-Phenylalanine and Gly-l-Phe were the most effective d-amino acid and dipeptide acceptors, respectively. On the basis of the dual specificity of the active site for acceptors (d-amino acids and Gly-l-Xaa peptides), "dual function" acceptors were designed and synthesized. Two of these, aminomalon-(N-ethyl)amide and aminomalon-(N-phenethyl)amide, were particularly effective. It did seem, however, that the observed rates of reaction of these very effective acceptors may be limited by some common, possibly physical, step. More extended, peptidoglycan-like, acceptors were found to be essentially unreactive. The reasons for this counterintuitive behavior are discussed.

  14. Donor/acceptor nanoparticle pair-based singlet oxygen channeling homogenous chemiluminescence immunoassay for quantitative determination of bisphenol A.

    PubMed

    Hou, Changjiang; Zhao, Lixia; Geng, Fanglan; Wang, Dan; Guo, Liang-Hong

    2016-12-01

    Bisphenol A (BPA) is widely used in consumer products such as plastic bottles and food containers. It has become a ubiquitous environmental contaminant and poses a serious risk to human health. A rapid, sensitive, and high-throughput method for detecting BPA is therefore desirable. Herein, a donor/acceptor nanoparticle pair-based singlet oxygen channeling chemiluminescence homogenous immunoassay is developed for the determination of BPA. The donor nanoparticles were modified with phthalocyanine as a photosensitizer and were then coated with streptavidin. The acceptor nanoparticles were doped with thioxene derivatives and Eu(III) as a chemiluminescence emitter and then coated with anti-BPA antibody. Under light irradiation, oxygen near the donor surface transforms to singlet oxygen ( 1 O 2 ), which migrates to the acceptor and reacts with it, generating luminescence. Because 1 O 2 has a very short lifetime, luminescence is generated only when the donor and acceptor are in close proximity. This occurs when they are brought together by the antigen/antibody and streptavidin/biotin reaction. Based on this singlet oxygen channeling mechanism, a competitive homogenous chemiluminescence immunoassay for BPA was developed on 384 microplates. The assay exhibited linear detection over the range 10-1000 ng/mL and a limit of detection of 2.9 ng/mL. The intra- and inter-assay precisions were both below 5.1 %. The average recoveries of three spiked samples in tap and river water samples were in the range 95.5-121.0 %, in agreement with values obtained using high-performance liquid chromatography. The homogeneous assay is rapid, low cost, sensitive, and allows high-throughput, so is well suited for screening large numbers of environmental samples. Graphical abstract Principle of the singlet oxygen channeling homogenous chemiluminescence competitive immunoassay based on nanoparticle pairs for determination of BPA.

  15. Selecting the spin crossover profile with controlled crystallization of mononuclear Fe(iii) polymorphs.

    PubMed

    Vicente, Ana I; Ferreira, Liliana P; Carvalho, Maria de Deus; Rodrigues, Vítor H N; Dîrtu, Marinela M; Garcia, Yann; Calhorda, Maria José; Martinho, Paulo N

    2018-05-08

    Two polymorphic species of the [Fe(5-Br-salEen)2]ClO4 compound were obtained, each of them being selectively recovered after evaporation of the solvent at a controlled rate. While polymorph 1a is formed during slow evaporation, fast evaporation favors polymorph 1b. The importance of the evaporation rate was recognized after detailed studies of the reaction temperature, solvent evaporation rate and crystallization temperature effects. The complex in the new polymorphic form 1a showed an abrupt spin crossover at 172 K with a small 1 K hysteresis window and over a narrow 10 K range. 57Fe Mössbauer spectroscopy and differential scanning calorimetry, complemented by X-ray studies for both the high-spin and low-spin forms, were used to further characterize the new polymorphic phase 1a. Both polymorphs are based on the same Fe(iii) complex cation hydrogen bonded to the perchlorate anion. These units are loosely bound in the crystals via weak interactions. In the new polymorph 1a, the hydrogen bonds are stronger, while the weak hydrogen and halogen bonds, as well as π-π stacking, create a cooperative network, not present in 1b, responsible for the spin transition profile.

  16. Geobacter sulfurreducens sp. nov., a hydrogen- and acetate-oxidizing dissimilatory metal-reducing microorganism.

    PubMed Central

    Caccavo, F; Lonergan, D J; Lovley, D R; Davis, M; Stolz, J F; McInerney, M J

    1994-01-01

    A dissimilatory metal- and sulfur-reducing microorganism was isolated from surface sediments of a hydrocarbon-contaminated ditch in Norman, Okla. The isolate, which was designated strain PCA, was an obligately anaerobic, nonfermentative nonmotile, gram-negative rod. PCA grew in a defined medium with acetate as an electron donor and ferric PPi, ferric oxyhydroxide, ferric citrate, elemental sulfur, Co(III)-EDTA, fumarate, or malate as the sole electron acceptor. PCA also coupled the oxidation of hydrogen to the reduction of Fe(III) but did not reduce Fe(III) with sulfur, glucose, lactate, fumarate, propionate, butyrate, isobutyrate, isovalerate, succinate, yeast extract, phenol, benzoate, ethanol, propanol, or butanol as an electron donor. PCA did not reduce oxygen, Mn(IV), U(VI), nitrate, sulfate, sulfite, or thiosulfate with acetate as the electron donor. Cell suspensions of PCA exhibited dithionite-reduced minus air-oxidized difference spectra which were characteristic of c-type cytochromes. Phylogenetic analysis of the 16S rRNA sequence placed PCA in the delta subgroup of the proteobacteria. Its closest known relative is Geobacter metallireducens. The ability to utilize either hydrogen or acetate as the sole electron donor for Fe(III) reduction makes strain PCA a unique addition to the relatively small group of respiratory metal-reducing microorganisms available in pure culture. A new species name, Geobacter sulfurreducens, is proposed. Images PMID:7527204

  17. Petrophilic, Fe(III) Reducing Exoelectrogen Citrobacter sp. KVM11, Isolated From Hydrocarbon Fed Microbial Electrochemical Remediation Systems

    PubMed Central

    Venkidusamy, Krishnaveni; Hari, Ananda Rao; Megharaj, Mallavarapu

    2018-01-01

    Exoelectrogenic biofilms capable of extracellular electron transfer are important in advanced technologies such as those used in microbial electrochemical remediation systems (MERS) Few bacterial strains have been, nevertheless, obtained from MERS exoelectrogenic biofilms and characterized for bioremediation potential. Here we report the identification of one such bacterial strain, Citrobacter sp. KVM11, a petrophilic, iron reducing bacterial strain isolated from hydrocarbon fed MERS, producing anodic currents in microbial electrochemical systems. Fe(III) reduction of 90.01 ± 0.43% was observed during 5 weeks of incubation with Fe(III) supplemented liquid cultures. Biodegradation screening assays showed that the hydrocarbon degradation had been carried out by metabolically active cells accompanied by growth. The characteristic feature of diazo dye decolorization was used as a simple criterion for evaluating the electrochemical activity in the candidate microbe. The electrochemical activities of the strain KVM11 were characterized in a single chamber fuel cell and three electrode electrochemical cells. The inoculation of strain KVM11 amended with acetate and citrate as the sole carbon and energy sources has resulted in an increase in anodic currents (maximum current density) of 212 ± 3 and 359 ± mA/m2 with respective coulombic efficiencies of 19.5 and 34.9% in a single chamber fuel cells. Cyclic voltammetry studies showed that anaerobically grown cells of strain KVM11 are electrochemically active whereas aerobically grown cells lacked the electrochemical activity. Electrobioremediation potential of the strain KVM11 was investigated in hydrocarbonoclastic and dye detoxification conditions using MERS. About 89.60% of 400 mg l-1 azo dye was removed during the first 24 h of operation and it reached below detection limits by the end of the batch operation (60 h). Current generation and biodegradation capabilities of strain KVM11 were examined using an initial

  18. Petrophilic, Fe(III) Reducing Exoelectrogen Citrobacter sp. KVM11, Isolated From Hydrocarbon Fed Microbial Electrochemical Remediation Systems.

    PubMed

    Venkidusamy, Krishnaveni; Hari, Ananda Rao; Megharaj, Mallavarapu

    2018-01-01

    Exoelectrogenic biofilms capable of extracellular electron transfer are important in advanced technologies such as those used in microbial electrochemical remediation systems (MERS) Few bacterial strains have been, nevertheless, obtained from MERS exoelectrogenic biofilms and characterized for bioremediation potential. Here we report the identification of one such bacterial strain, Citrobacter sp. KVM11, a petrophilic, iron reducing bacterial strain isolated from hydrocarbon fed MERS, producing anodic currents in microbial electrochemical systems. Fe(III) reduction of 90.01 ± 0.43% was observed during 5 weeks of incubation with Fe(III) supplemented liquid cultures. Biodegradation screening assays showed that the hydrocarbon degradation had been carried out by metabolically active cells accompanied by growth. The characteristic feature of diazo dye decolorization was used as a simple criterion for evaluating the electrochemical activity in the candidate microbe. The electrochemical activities of the strain KVM11 were characterized in a single chamber fuel cell and three electrode electrochemical cells. The inoculation of strain KVM11 amended with acetate and citrate as the sole carbon and energy sources has resulted in an increase in anodic currents (maximum current density) of 212 ± 3 and 359 ± mA/m 2 with respective coulombic efficiencies of 19.5 and 34.9% in a single chamber fuel cells. Cyclic voltammetry studies showed that anaerobically grown cells of strain KVM11 are electrochemically active whereas aerobically grown cells lacked the electrochemical activity. Electrobioremediation potential of the strain KVM11 was investigated in hydrocarbonoclastic and dye detoxification conditions using MERS. About 89.60% of 400 mg l -1 azo dye was removed during the first 24 h of operation and it reached below detection limits by the end of the batch operation (60 h). Current generation and biodegradation capabilities of strain KVM11 were examined using an initial

  19. Poly(trifluoromethyl)azulenes: structures and acceptor properties

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Clikeman, Tyler T.; Bukovsky, Eric V.; Kuvychko, Igor V.

    2014-07-10

    Azulene is a non-alternant, non-benzenoid aromatic hydrocarbon with an intense blue colour, a dipole moment of 1.0 D,1 positive electron affinity, and an “anomalous” emission from the second excited state in violation of Kasha’s rule.2,3 Azulene’s unique properties have potential uses in molecular switches,4,5 molecular diodes,6 organic photovoltaics,7 and charge transfer complexes.8-12 Introduction of electron-withdrawing groups to the azulenic core, such as CN,8,13,14 halogens,15-19 and CF3,20,21 can enhance certain electrical and photophysical properties. In this work, we report six new trifluoromethyl derivatives of azulene (AZUL), three isomers of AZUL(CF3)3 and three isomers of AZUL(CF3)4, and the first X-ray structure ofmore » a π-stacked donor-acceptor complex of a trifluoromethyl azulene with donor pyrene.« less

  20. Dissipative exciton transfer in donor-bridge-acceptor systems: numerical renormalization group calculation of equilibrium properties.

    PubMed

    Tornow, Sabine; Tong, Ning-Hua; Bulla, Ralf

    2006-07-05

    We present a detailed model study of exciton transfer processes in donor-bridge-acceptor (DBA) systems. Using a model which includes the intermolecular Coulomb interaction and the coupling to a dissipative environment we calculate the phase diagram, the absorption spectrum as well as dynamic equilibrium properties with the numerical renormalization group. This method is non-perturbative and therefore allows one to cover the full parameter space, especially the case when the intermolecular Coulomb interaction is of the same order as the coupling to the environment and perturbation theory cannot be applied. For DBA systems with up to six sites we found a transition to the localized phase (self-trapping) depending on the coupling to the dissipative environment. We discuss various criteria which favour delocalized exciton transfer.

  1. Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property

    NASA Astrophysics Data System (ADS)

    Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

    2015-01-01

    An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1.An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05915h

  2. Influence of Different Electron Donors and Acceptors on Dehalorespiration of Tetrachloroethene by Desulfitobacterium frappieri TCE1

    PubMed Central

    Gerritse, Jan; Drzyzga, Oliver; Kloetstra, Geert; Keijmel, Mischa; Wiersum, Luit P.; Hutson, Roger; Collins, Matthew D.; Gottschal, Jan C.

    1999-01-01

    Strain TCE1, a strictly anaerobic bacterium that can grow by reductive dechlorination of tetrachloroethene (PCE) and trichloroethene (TCE), was isolated by selective enrichment from a PCE-dechlorinating chemostat mixed culture. Strain TCE1 is a gram-positive, motile, curved rod-shaped organism that is 2 to 4 by 0.6 to 0.8 μm and has approximately six lateral flagella. The pH and temperature optima for growth are 7.2 and 35°C, respectively. On the basis of a comparative 16S rRNA sequence analysis, this bacterium was identified as a new strain of Desulfitobacterium frappieri, because it exhibited 99.7% relatedness to the D. frappieri type strain, strain PCP-1. Growth with H2, formate, l-lactate, butyrate, crotonate, or ethanol as the electron donor depends on the availability of an external electron acceptor. Pyruvate and serine can also be used fermentatively. Electron donors (except formate and H2) are oxidized to acetate and CO2. When l-lactate is the growth substrate, strain TCE1 can use the following electron acceptors: PCE and TCE (to produce cis-1,2-dichloroethene), sulfite and thiosulfate (to produce sulfide), nitrate (to produce nitrite), and fumarate (to produce succinate). Strain TCE1 is not able to reductively dechlorinate 3-chloro-4-hydroxyphenylacetate. The growth yields of the newly isolated bacterium when PCE is the electron acceptor are similar to those obtained for other dehalorespiring anaerobes (e.g., Desulfitobacterium sp. strain PCE1 and Desulfitobacterium hafniense) and the maximum specific reductive dechlorination rates are 4 to 16 times higher (up to 1.4 μmol of chloride released · min−1 · mg of protein−1). Dechlorination of PCE and TCE is an inducible process. In PCE-limited chemostat cultures of strain TCE1, dechlorination is strongly inhibited by sulfite but not by other alternative electron acceptors, such as fumarate or nitrate. PMID:10583967

  3. The electronic structure and second-order nonlinear optical properties of donor-acceptor acetylenes - A detailed investigation of structure-property relationships

    NASA Technical Reports Server (NTRS)

    Stiegman, A. E.; Graham, Eva; Khundkar, Lutfur R.; Perry, Joseph W.; Cheng, L.-T.; Perry, Kelly J.

    1991-01-01

    A series of donor-acceptor acetylene compounds was synthesized in which systematic changes in both the conjugation length and the donor-acceptor strength were made. The effect of these structural changes on the spectroscopic and electronic properties of the molecules and, ultimately, on the measured second-order molecular hyperpolarizabilities (beta) was investigated. It was found that increases in the donor-acceptor strength resulted in increases in the magnitude of beta. For this class of molecules, the increase is dominated by the energy of the intramolecular charge-transfer transition, while factors such as the ground to excited-state dipole moment change and the transition-moment integral are much less important. Increasing the conjugation length from one to two acetylene linkers did not result in an increase in the value of beta; however, beta increased sharply in going from two acetylenes to three. This increase is attributed to the superposition of several nearly isoenergetic excited states.

  4. Probing the Donor and Acceptor Substrate Specificity of the Gamma-Glutamyl Transpeptidase

    DTIC Science & Technology

    2012-01-17

    glutathione can function as a source of cysteine. Mutant strains of F. tularensis that lack functional GGT have been shown to have impaired intracellular...conservation of structure and function between human and bacterial GGT homologues, significant differences in acceptor substrate and inhibitor preferences are...with the lowest value of MODELER objective function . The three-dimensional (3D) fold of the generated models was verified with PROSA II,40 and

  5. Shedding light on the photostability of two intermolecular charge-transfer complexes between highly fluorescent bis-1,8-naphthalimide dyes and some π-acceptors: A spectroscopic study in solution and solid states

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; Ismail, Lamia A.; Adam, Abdel Majid A.

    2015-01-01

    Given the great importance of the various uses of 1,8-naphthalimides in the trends of biology, medicine and industry, the current study focused on extending the scope of these dyes by introducing some of their charge-transfer (CT) complexes. For this purpose, two highly fluorescent bis-1,8-naphthalimide dyes and their complexes with some π-acceptors have been synthesized and characterized spectroscopically. The π-acceptors include picric acid (PA), chloranilic acid (CLA), tetracyanoquinodimethane (TCNQ) and dichlorodicyanobenzoquinone (DDQ). The molecular structure, spectroscopic and fluorescence properties as well as the binding modes were deduced from IR, UV-vis and 1H NMR spectral studies. The binding ratio of complexation was determined to be 1:1 according to the elemental analyses and photometric titrations. It has been found that the order of acceptance ability for the different acceptors is TCNQ > DDQ > CLA > PA. The photostability of 1,8-naphthalimide dye as a donor and its charge-transfer complex doped in polymethyl methacrylate/PMMA were exposed to UV-Vis radiation and the change in the absorption spectra was achieved at different times during irradiation period.

  6. Excited state dynamics can be used to probe donor-acceptor distances for H-tunneling reactions catalyzed by flavoproteins.

    PubMed

    Hardman, Samantha J O; Pudney, Christopher R; Hay, Sam; Scrutton, Nigel S

    2013-12-03

    In enzyme systems where fast motions are thought to contribute to H-transfer efficiency, the distance between hydrogen donor and acceptor is a very important factor. Sub-ångstrom changes in donor-acceptor distance can have a large effect on the rate of reaction, so a sensitive probe of these changes is a vital tool in our understanding of enzyme function. In this study we use ultrafast transient absorption spectroscopy to investigate the photoinduced electron transfer rates, which are also very sensitive to small changes in distance, between coenzyme analog, NAD(P)H4, and the isoalloxazine center in the model flavoenzymes morphinone reductase (wild-type and selected variants) and pentaerythritol tetranitrate reductase (wild-type). It is shown that upon addition of coenzyme to the protein the rate of photoinduced electron transfer is increased. By comparing the magnitude of this increase with existing values for NAD(P)H4-FMN distances, based on charge-transfer complex absorbance and experimental kinetic isotope effect reaction data, we show that this method can be used as a sensitive probe of donor-acceptor distance in a range of enzyme systems. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  7. Part I. Synthesis and characterization of donor-pi-acceptor compounds with pentadienyl-bridged indoline and tetrahydroquinoline donors and aldehyde and thiobarbituric acid acceptors Part II. Longitudinal study comparing online versus face-to-face course delivery in introductory chemistry

    NASA Astrophysics Data System (ADS)

    Greco, Patrick F.

    Part I. The design and development of organic second-order nonlinear optical (NLO) materials have attracted much interest due to their applications in optoelectronic devices and modern communications technology. Donor-pi-acceptor compounds, D-(CH=CH)n-A, often exhibit hyperpolarizability that results in laser frequency doubling (second harmonic generation) and spectroscopic solvatochromism. To study the effect of donor amine geometry upon properties associated with second-order NLO behavior in simple donor-pi-acceptor compounds, equilibrium geometries and hyperpolarizabilities (beta) for donor-acceptor polyenes with amine donors were calculated at several levels of computational theory. Two new molecules with donors that only differ by one methylene group were chosen for comparison. Thus, 5-(N-methylindolin-5-yl)-2, 4-pentadienal (1a) and 5-(N-methyl-2, 3, 4-trihydroquinolin-6-yl)-2, 4-pentadienal (2a) were synthesized in two steps from starting materials described in the literature. These aldehydes were converted into stronger acceptors in one step to give diethylthiobarbituric acid derivatives 1c and 2c, as well as tricyanofuran derivatives 1d and 2d. Positive UV solvatochromism was observed in all three derivatives. NMR solvatochromism was most pronounced in 1c, and 2c vs. 1a and 2a as measured by changes in chemical shifts. Additionally, coupling constants showed more conjugation in 1c and 2c, where 1a and 2a showed less conjugation. Finally, differential scanning calorimetry and thermal gravimetric analysis were used to compare decomposition and melting temperatures of these compounds to determine their stability. Aldehydes, 1a and 2a had distinct melting points, while the 1c, 2c, 1d, and 2d derivatives decomposed at temperatures above 150 °C. Part II. This longitudinal study focused on an introductory chemistry course taught using two different modes of delivery: online and face-to-face (FtF). The sections of the course using the different delivery modes

  8. Influence of Oxygen and Nitrate on Fe (Hydr)oxide Mineral Transformation and Soil Microbial Communities during Redox Cycling.

    PubMed

    Mejia, Jacqueline; Roden, Eric E; Ginder-Vogel, Matthew

    2016-04-05

    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.

  9. Anaerobic Oxidation of Benzene by the Hyperthermophilic Archaeon Ferroglobus placidus▿†

    PubMed Central

    Holmes, Dawn E.; Risso, Carla; Smith, Jessica A.; Lovley, Derek R.

    2011-01-01

    Anaerobic benzene oxidation coupled to the reduction of Fe(III) was studied in Ferroglobus placidus in order to learn more about how such a stable molecule could be metabolized under strict anaerobic conditions. F. placidus conserved energy to support growth at 85°C in a medium with benzene provided as the sole electron donor and Fe(III) as the sole electron acceptor. The stoichiometry of benzene loss and Fe(III) reduction, as well as the conversion of [14C]benzene to [14C]carbon dioxide, was consistent with complete oxidation of benzene to carbon dioxide with electron transfer to Fe(III). Benzoate, but not phenol or toluene, accumulated at low levels during benzene metabolism, and [14C]benzoate was produced from [14C]benzene. Analysis of gene transcript levels revealed increased expression of genes encoding enzymes for anaerobic benzoate degradation during growth on benzene versus growth on acetate, but genes involved in phenol degradation were not upregulated during growth on benzene. A gene for a putative carboxylase that was more highly expressed in benzene- than in benzoate-grown cells was identified. These results suggest that benzene is carboxylated to benzoate and that phenol is not an important intermediate in the benzene metabolism of F. placidus. This is the first demonstration of a microorganism in pure culture that can grow on benzene under strict anaerobic conditions and for which there is strong evidence for degradation of benzene via clearly defined anaerobic metabolic pathways. Thus, F. placidus provides a much-needed pure culture model for further studies on the anaerobic activation of benzene in microorganisms. PMID:21742914

  10. Multi-reverse flow injection analysis integrated with multi-optical sensor for simultaneous determination of Mn(II), Fe(II), Cu(II) and Fe(III) in natural waters.

    PubMed

    Youngvises, Napaporn; Suwannasaroj, Kittigan; Jakmunee, Jaroon; AlSuhaimi, Awadh

    2017-05-01

    Multi-reverse flow injection analysis (Mr-FIA) integrated with multi-optical sensor was developed and optimized for the simultaneous determination of multi ions; Mn(II), Fe(II), Cu(II) and Fe(III) in water samples. The sample/standard solutions were propelled making use of a four channels peristaltic pump whereas 4 colorimetric reagents specific for the metal ions were separately injected in sample streams using multi-syringe pump. The color zones that formed in the individual mixing coils were then streamed into multi-channels spectrometer, which comprised of four flows through cell and four pairs of light emitting diode and photodiode, whereby signals were measured concurrently. The linearity range (along with detection limit, µgL -1 ) was 0.050-3.0(16), 0.30-2.0 (11), 0.050-1.0(12) and 0.10-1.0(50)mgL -1 , for Mn(II), Fe(II), Cu(II) and Fe(III), respectively. In the interim, the correlation coefficients were 0.9924-0.9942. The percentages relative standard deviation was less than 3. The proposed system was applied successfully to determine targeted metal ions simultaneously in natural water with high sample throughput and low reagent consumption, thus it satisfies the criteria of Green Analytical Chemistry (GAC) and its goals. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Role of an organic carbon-rich soil and Fe(III) reduction in reducing the toxicity and environmental mobility of chromium(VI) at a COPR disposal site.

    PubMed

    Ding, Weixuan; Stewart, Douglas I; Humphreys, Paul N; Rout, Simon P; Burke, Ian T

    2016-01-15

    Cr(VI) is an important contaminant found at sites where chromium ore processing residue (COPR) is deposited. No low cost treatment exists for Cr(VI) leaching from such sites. This study investigated the mechanism of interaction of alkaline Cr(VI)-containing leachate with an Fe(II)-containing organic matter rich soil beneath the waste. The soil currently contains 0.8% Cr, shown to be present as Cr(III)(OH)3 in EXAFS analysis. Lab tests confirmed that the reaction of Cr(VI) in site leachate with Fe(II) present in the soil was stoichiometrically correct for a reductive mechanism of Cr accumulation. However, the amount of Fe(II) present in the soil was insufficient to maintain long term Cr(VI) reduction at historic infiltration rates. The soil contains a population of bacteria dominated by a Mangroviflexus-like species, that is closely related to known fermentative bacteria, and a community capable of sustaining Fe(III) reduction in alkaline culture. It is therefore likely that in situ fermentative metabolism supported by organic matter in the soil produces more labile organic substrates (lactate was detected) that support microbial Fe(III) reduction. It is therefore suggested that addition of solid phase organic matter to soils adjacent to COPR may reduce the long term spread of Cr(VI) in the environment. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  12. Tuning the electronic and optical properties of NDT-based conjugated polymers by adopting fused heterocycles as acceptor units: a theoretical study.

    PubMed

    Cheng, Na; Zhang, Changqiao; Liu, Yongjun

    2017-08-01

    Donor-acceptor conjugated polymers have been successfully applied in bulk heterojunction solar cell devices. Tuning their donor and acceptor units allows the design of new polymers with desired electronic and optical properties. Here, to screen new candidate polymers based on a newly synthesized donor unit, dithieo[2,3-d:2',3'-d']naphtho[1,2-b:3,4-b']dithiophene (NDT), a series of model polymers with different acceptor units were designed and denoted NDT-A 0 to NDT-A 12 , and the structures and optical properties of those polymers were investigated using DFT and TDDFT calculations. The results of the calculations revealed that the electronic and optical properties of these polymers depend on the acceptor unit present; specifically, their HOMO energies ranged from -4.89 to -5.38 eV, their HOMO-LUMO gaps ranged from 1.30 to 2.80 eV, and their wavelengths of maximum absorption ranged from 538 to 1212 nm. The absorption spectra of NDT-A 1 to NDT-A 6 , NDT-A 8 , NDT-A 9 , and NDT-A 12 occur within the visible region (<900 nm), indicating that these polymers are potential candidates for use in solar cells. On the other hand, the absorption spectra of NDT-A 7 , NDT-A 10 , and NDT-A 11 extend much further into the near-infrared region, implying that they absorb near-infrared light. These polymers could meet the requirements of donor units for use in tandem and ternary solar cells. Graphical abstract Theoretical calculations by TD-DFT reveal that the optical properties of NDT-based conjugated polymers can be well tuned by adopting different acceptor units, and these ploymers are potential donor materials for tandem and ternary solar cells.

  13. Candidatus Accumulibacter phosphatis clades enriched under cyclic anaerobic and microaerobic conditions simultaneously use different electron acceptors

    EPA Science Inventory

    Lab- and pilot-scale simultaneous nitrification, denitrification and phosphorus removal-sequencing batch reactors were operated under cyclic anaerobic and micro-aerobic conditions. The use of oxygen, nitrite, and nitrate as electron acceptors by Candidatus Accumulibacter phosphat...

  14. Complete genome of Thauera humireducens SgZ-1, a potential bacterium for environmental remediation and wastewater treatment.

    PubMed

    Ma, Chen; Yang, Guiqin; Zhang, Qun; Zhuang, Li; Zhou, Shungui

    2016-05-10

    Thauera humireducens SgZ-1(T) (KACC 16524(T)=CCTCC M2011497(T)), isolated from the anode biofilm of a microbial fuel cell, is able to grow under anaerobic conditions via the oxidation of various organic compounds coupled to the reduction of humus, Fe(III) species and nitrate. Addtionally, the strain has the ability to produce exopolysaccharide (EPS). Here, we report the complete genome sequence of T. humiruducens SgZ-1(T), which is relevant to metabolism of electron donors and acceptors for environmental remediation and wastewater treatment. Copyright © 2016. Published by Elsevier B.V.

  15. Constraint-Based Modeling of Carbon Fixation and the Energetics of Electron Transfer in Geobacter metallireducens

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Feist, AM; Nagarajan, H; Rotaru, AE

    2014-04-24

    Geobacter species are of great interest for environmental and biotechnology applications as they can carry out direct electron transfer to insoluble metals or other microorganisms and have the ability to assimilate inorganic carbon. Here, we report on the capability and key enabling metabolic machinery of Geobacter metallireducens GS-15 to carry out CO2 fixation and direct electron transfer to iron. An updated metabolic reconstruction was generated, growth screens on targeted conditions of interest were performed, and constraint-based analysis was utilized to characterize and evaluate critical pathways and reactions in G. metallireducens. The novel capability of G. metallireducens to grow autotrophically withmore » formate and Fe(III) was predicted and subsequently validated in vivo. Additionally, the energetic cost of transferring electrons to an external electron acceptor was determined through analysis of growth experiments carried out using three different electron acceptors (Fe(III), nitrate, and fumarate) by systematically isolating and examining different parts of the electron transport chain. The updated reconstruction will serve as a knowledgebase for understanding and engineering Geobacter and similar species. Author Summary The ability of microorganisms to exchange electrons directly with their environment has large implications for our knowledge of industrial and environmental processes. For decades, it has been known that microbes can use electrodes as electron acceptors in microbial fuel cell settings. Geobacter metallireducens has been one of the model organisms for characterizing microbe-electrode interactions as well as environmental processes such as bioremediation. Here, we significantly expand the knowledge of metabolism and energetics of this model organism by employing constraint-based metabolic modeling. Through this analysis, we build the metabolic pathways necessary for carbon fixation, a desirable property for industrial chemical

  16. Large Spatially Resolved Rectification in a Donor–Acceptor Molecular Heterojunction

    DOE PAGES

    Smerdon, Joseph A.; Giebink, Noel C.; Guisinger, Nathan P.; ...

    2016-03-10

    Here, we demonstrate that rectification ratios (RR) of ≳250 (≳1000) at biases of 0.5 V (1.2 V) are achievable at the two-molecule limit for donor–acceptor bilayers of pentacene on C 60 on Cu using scanning tunneling spectroscopy and microscopy. Using first-principles calculations, we show that the system behaves as a molecular Schottky diode with a tunneling transport mechanism from semiconducting pentacene to Cu- hybridized metallic C 60. Low-bias RRs vary by two orders-of-magnitude at the edge of these molecular heterojunctions due to increased Stark shifts and confinement effects.

  17. Application Of Bacterial Iron Reduction For The Removal Of Iron Impurities From Industrial Silica Sand And Kaolin

    NASA Astrophysics Data System (ADS)

    Zegeye, A.; Yahaya, S.; Fialips, C. I.; White, M.; Manning, D. A.; Gray, N.

    2008-12-01

    Biogeochemical evidence exists to support the potential importance of crystalline or amorphous Fe minerals as electron acceptor for Fe reducing bacteria in soils and subsurface sediments. This microbial metabolic activity can be exploited as alternative method in different industrial applications. For instance, the removal of ferric iron impurities from minerals for the glass and paper industries currently rely on physical and chemical treatments having substantial economical and environmental disadvantages. The ability to remove iron by other means, such as bacterial iron reduction, may reduce costs, allow lower grade material to be mined, and improve the efficiency of mineral processing. Kaolin clay and silica sand are used in a wide range of industrial applications, particularly in paper, ceramics and glass manufacturing. Depending on the geological conditions of deposition, they are often associated with iron (hydr)oxides that are either adsorbed to the mineral surfaces or admixed as separate iron bearing minerals. In this study, we have examined the Fe(III) removal efficiency from kaolin and silica sand by a series of iron- reducing bacteria from the Shewanella species (S. alga BrY, S. oneidensis MR-1, S. putrefaciens CN32 and S. putrefaciens ATCC 8071) in the presence of anthraquinone 2,6 disulfonate (AQDS). We have also investigated the effectiveness of a natural organic matter, extracted with the silica sand, as a substitute to AQDS for enhancing Fe(III) reduction kinetics. The microbial reduction of Fe(III) was achieved using batch cultures under non-growth conditions. The rate and the extent of Fe(III) reduction was monitored as a function of the initial Fe(III) content, Shewanella species and temperature. The bacterially- treated minerals were analyzed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) to observe any textural and mineralogical transformation. The whiteness and ISO brightness of the kaolin was also measured by

  18. Novel indole-based inhibitors of IMPDH: introduction of hydrogen bond acceptors at indole C-3.

    PubMed

    Watterson, Scott H; Dhar, T G Murali; Ballentine, Shelley K; Shen, Zhongqi; Barrish, Joel C; Cheney, Daniel; Fleener, Catherine A; Rouleau, Katherine A; Townsend, Robert; Hollenbaugh, Diane L; Iwanowicz, Edwin J

    2003-04-07

    The development of a series of novel indole-based inhibitors of 5'-inosine monophosphate dehydrogenase (IMPDH) is described. Various hydrogen bond acceptors at C-3 of the indole were explored. The synthesis and the structure-activity relationships (SARs) derived from in vitro studies are outlined.

  19. A microbial fuel cell operating at low pH using an acidophile, Acidiphilium cryptum.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Borole, Abhijeet P; Cesar, Scott A; O'Neill, Hugh Michael

    2008-01-01

    A microbial fuel cell using an acidophilic microorganism, Acidiphilium cryptum, as the anode biocatalyst was investigated. The mode of electron transfer by this organism to the electrode was studied. Electricity production in the presence of a mediator was demonstrated using its natural electron acceptor, iron, as well as phenosafranin as the electron mediating agent. Production of Fe(II), as a result of iron reduction, at a pH of 4.0 or below was found to support electricity production. Accumulation of the oxidized iron, Fe(III) as a result of electron donation to the electrode, however, restricted higher current output. Addition of nitrilotriacetic acidmore » helped resolve the problem by redissolution of deposited Fe(III). Further, use of phenosafranin as a secondary mediator resulted in improvement in power output. At a cell loading equivalent to OD600 of 1.0, a power output of 12.7 mW/m2 was obtained in a two-chamber air-sparged fuel cell. Potential for direct electron transfer was also investigated but not detected under the conditions studied.« less

  20. Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

    PubMed

    Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

    2015-12-17

    The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length.

  1. Effect of donor to acceptor ratio on electrochemical and spectroscopic properties of oligoalkylthiophene 1,3,4-oxadiazole derivatives.

    PubMed

    Kurowska, Aleksandra; Zassowski, Pawel; Kostyuchenko, Anastasia S; Zheleznova, Tatyana Yu; Andryukhova, Kseniya V; Fisyuk, Alexander S; Pron, Adam; Domagala, Wojciech

    2017-11-15

    A structure-property study across a series of donor-acceptor-donor structures composed of mono- and bi-(1,3,4-oxadiazole) units symmetrically substituted with alkyl functionalized bi-, ter- and quaterthiophene segments is presented. Synthetically tailoring the ratio of electron-withdrawing 1,3,4-oxadiazole to electron-releasing thiophene units and their alkyl grafting pattern permitted us to scrutinize the impact of these structural factors on the redox, absorptive and emissive properties of these push-pull molecules. Contrasting trends of redox potentials were observed, with the oxidation potential closely following the donor-to-acceptor ratio, whereas the reduction potential being tuned independently by either the number of acceptor units or the conjugation length of the donor-acceptor system. Increasing the thiophene unit contribution delivered a shift from blue to green luminescence, while the structural rigidity afforded by intramolecular non-covalent interactions between 1,3,4-oxadiazole and the thiophene moieties has been identified as the prime factor determining the emission efficiency of these molecules. All six structures investigated electro-polymerize easily, yielding electroactive and electrochromic polymers. The polymer doping process is largely influenced by the length of the oligothiophene repeating unit and the alkyl chain grafting density. Polymers with relatively short oligothiophene segments are able to support polarons and polaron-pairs, whereas those with segments longer than six thiophene units could also stabilize diamagnetic charge carries - bipolarons. Increasing the alkyl chain grafting density improved the reversibility and broadened the working potential window of the p-doping process. Stable radical anions have also been investigated, bringing detailed information about the conjugation pattern of these electron-surplus species. This study delivers interesting clues towards the conscious structural design of bespoke frontier energy

  2. A theoretical probe on the non-covalent interactions of sulfadoxine drug with pi-acceptors

    NASA Astrophysics Data System (ADS)

    Sandhiya, L.; Senthilkumar, K.

    2014-09-01

    A detailed analysis of the interaction between an antimalarial drug sulfadoxine and four pi-acceptors, tetrachloro-catechol, picric acid, chloranil, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone is presented in this study. The interaction of the amine, amide, methoxy, Csbnd H groups and π electron density of the drug molecule with the acceptors are studied using DFT method at M06-2X level of theory with 6-31G(d,p) basis set. The interaction energy of the complexes is calculated using M06-2X, M06-HF, B3LYP-D and MP2 methods with 6-31G(d,p) basis set. The role of weak interactions on the formation and stability of the complexes is discussed in detail. The two aromatic platforms of sulfadoxine play a major role in determining the stability of the complexes. The electron density difference maps have been plotted for the most stable drug interacting complexes to understand the changes in electron density delocalization upon the complex formation. The nature of the non-covalent interaction has been addressed from NCI plot. The infrared spectra calculated at M06-2X/6-31G(d,p) level of theory is used to characterize the most stable complexes. The SDOX-pi acceptor complexation leads to characteristic changes in the NMR spectra. The 13C, 1H, 17O and 15N NMR chemical shifts have been calculated using GIAO method at M06-2X/6-311+G(d,p)//M06-2X/6-31G(d,p) level of theory. The results obtained from this study confirm the role of non-covalent interactions on the function of the sulfadoxine drug.

  3. Synthesis, chemical reactivity as Michael acceptors, and biological potency of monocyclic cyanoenones, novel and highly potent anti-inflammatory and cytoprotective agents.

    PubMed

    Zheng, Suqing; Santosh Laxmi, Y R; David, Emilie; Dinkova-Kostova, Albena T; Shiavoni, Katherine H; Ren, Yanqing; Zheng, Ying; Trevino, Isaac; Bumeister, Ronald; Ojima, Iwao; Wigley, W Christian; Bliska, James B; Mierke, Dale F; Honda, Tadashi

    2012-05-24

    Novel monocyclic cyanoenones examined to date display unique features regarding chemical reactivity as Michael acceptors and biological potency. Remarkably, in some biological assays, the simple structure is more potent than pentacyclic triterpenoids (e.g., CDDO and bardoxolone methyl) and tricycles (e.g., TBE-31). Among monocyclic cyanoenones, 1 is a highly reactive Michael acceptor with thiol nucleophiles. Furthermore, an important feature of 1 is that its Michael addition is reversible. For the inhibition of NO production, 1 shows the highest potency. Notably, its potency is about three times higher than CDDO, whose methyl ester (bardoxolone methyl) is presently in phase III clinical trials. For the induction of NQO1, 1 also demonstrated the highest potency. These results suggest that the reactivity of these Michael acceptors is closely related to their biological potency. Interestingly, in LPS-stimulated macrophages, 1 causes apoptosis and inhibits secretion of TNF-α and IL-1β with potencies that are higher than those of bardoxolone methyl and TBE-31.

  4. Chemical trend of acceptor levels of Be, Mg, Zn, and Cd in GaAs, GaP, InP and GaN

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Chen, An-Ban

    2000-03-01

    We are investigating the “shallow” acceptor levels in the III-nitride semiconductors theoretically. The k·p Hamiltonians and a model central-cell impurity potential have been used to evaluate the ordering of the ionization energies of impurities Be, Mg, Zn, and Cd in GaN. The impurity potential parameters were obtained from studying the same set of impurities in GaAs. These parameters were then transferred to the calculation for other hosts, leaving only one adjustable screening parameter for each host. This procedure was tested in GaP and InP and remarkably good results were obtained. When applied to GaN, this procedure produced a consistent set of acceptor levels with different k·p Hamiltonians. The calculated ionization energies for Be, Mg, Zn and Cd acceptors in GaN are respectively145, 156, 192, and 312 meV for the zincblende structure, and 229, 250, 320, and 510 meV for the wurtzite structure. These and other results will be discussed.

  5. Biogenic hydroxysulfate green rust, a potential electron acceptor for SRB activity

    NASA Astrophysics Data System (ADS)

    Zegeye, Asfaw; Huguet, Lucie; Abdelmoula, Mustapha; Carteret, Cédric; Mullet, Martine; Jorand, Frédéric

    2007-11-01

    Microbiological reduction of a biogenic sulfated green rust (GR2(SO42-)), was examined using a sulfate reducing bacterium ( Desulfovibrio alaskensis). Experiments investigated whether GR2(SO42-) could serve as a sulfate source for D. alaskensis anaerobic respiration by analyzing mineral transformation. Batch experiments were conducted using lactate as the electron donor and biogenic GR2(SO42-) as the electron acceptor, at circumneutral pH in unbuffered medium. GR2(SO42-) transformation was monitored with time by X-ray diffraction (XRD), Transmission Mössbauer Spectroscopy (TMS), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The reduction of sulfate anions and the formation of iron sulfur mineral were clearly identified by XPS analyses. TMS showed the formation of additional mineral as green rust (GR) and vivianite. XRD analyses discriminated the type of the newly formed GR as GR1. The formed GR1 was GR1(CO32-) as indicated by DRIFTS analysis. Thus, the results presented in this study indicate that D. alaskensis cells were able to use GR2(SO42-) as an electron acceptor. GR1(CO32-), vivianite and an iron sulfur compound were formed as a result of GR2(SO42-) reduction by D. alaskensis. Hence, in environments where geochemical conditions promote biogenic GR2(SO42-) formation, this mineral could stimulate the anaerobic respiration of sulfate reducing bacteria.

  6. Design principle for efficient charge separation at the donor-acceptor interface for high performance organic solar cell device

    NASA Astrophysics Data System (ADS)

    Nie, Wanyi; Gupta, Gautam; Crone, Brian; Wang, Hsing-Lin; Mohite, Aditya; MPA-11 Material synthesis and integrated device Team; MPA-chemistry Team

    2014-03-01

    The performance of donor (D) /acceptor (A) structure based organic electronic devices, such as solar cell, light emitting devices etc., relays on the charge transfer process at the interface dramatically. In organic solar cell, the photo-induced electron-hole pair is tightly bonded and will form a charge transfer (CT) state at the D/A interface after dissociation. There is a large chance for them to recombine through CT state and thus is a major loss that limit the overall performance. Here, we report three different strategies that allow us to completely suppress the exciplex (or charge transfer state) recombination between any D/A system. We observe that the photocurrent increases by 300% and the power conversion efficiency increases by 4-5 times simply by inserting a spacer layer in the form of an a) insulator b) Oliogomer or using a c) heavy atom at the donor-acceptor interface in a P3HT/C60 bilayer device. By using those different functional mono layers, we successfully suppressed the exciplex recombination in evidence of increased photocurrent and open circuit voltage. Moreover, these strategies are applicable universally to any donor-acceptor interface. And we demonstrated such strategies in a bulk-heterojunction device which improved the power conversion efficiency from 3.5% up to 4.6%.

  7. All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers.

    PubMed

    Zhou, Nanjia; Dudnik, Alexander S; Li, Ting I N G; Manley, Eric F; Aldrich, Thomas J; Guo, Peijun; Liao, Hsueh-Chung; Chen, Zhihua; Chen, Lin X; Chang, Robert P H; Facchetti, Antonio; Olvera de la Cruz, Monica; Marks, Tobin J

    2016-02-03

    The influence of the number-average molecular weight (Mn) on the blend film morphology and photovoltaic performance of all-polymer solar cells (APSCs) fabricated with the donor polymer poly[5-(2-hexyldodecyl)-1,3-thieno[3,4-c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophen-2-yl)thiophene)] (PTPD3T) and acceptor polymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2); N2200) is systematically investigated. The Mn effect analysis of both PTPD3T and N2200 is enabled by implementing a polymerization strategy which produces conjugated polymers with tunable Mns. Experimental and coarse-grain modeling results reveal that systematic Mn variation greatly influences both intrachain and interchain interactions and ultimately the degree of phase separation and morphology evolution. Specifically, increasing Mn for both polymers shrinks blend film domain sizes and enhances donor-acceptor polymer-polymer interfacial areas, affording increased short-circuit current densities (Jsc). However, the greater disorder and intermixed feature proliferation accompanying increasing Mn promotes charge carrier recombination, reducing cell fill factors (FF). The optimized photoactive layers exhibit well-balanced exciton dissociation and charge transport characteristics, ultimately providing solar cells with a 2-fold PCE enhancement versus devices with nonoptimal Mns. Overall, it is shown that proper and precise tuning of both donor and acceptor polymer Mns is critical for optimizing APSC performance. In contrast to reports where maximum power conversion efficiencies (PCEs) are achieved for the highest Mns, the present two-dimensional Mn optimization matrix strategy locates a PCE "sweet spot" at intermediate Mns of both donor and acceptor polymers. This study provides synthetic methodologies to predictably access conjugated polymers with desired Mn and highlights the importance of optimizing Mn for both polymer

  8. All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhou, Nanjia; Dudnik, Alexander S.; Li, Ting I. N. G.

    2016-01-21

    The influence of the number-average molecular weight (Mn) on the blend film morphology and photovoltaic performance of all-polymer solar cells (APSCs) fabricated with the donor polymer poly[5-(2-hexyldodecyl)-1,3-thieno[3,4-c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophen-2-yl)thiophene)] (PTPD3T) and acceptor polymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2); N2200) is systematically investigated. The Mn effect analysis of both PTPD3T and N2200 is enabled by implementing a polymerization strategy which produces conjugated polymers with tunable Mns. Experimental and coarse-grain modeling results reveal that systematic Mn variation greatly influences both intrachain and interchain interactions and ultimately the degree of phase separation and morphology evolution. Specifically, increasing Mn for both polymers shrinks blend film domain sizes and enhancesmore » donor–acceptor polymer–polymer interfacial areas, affording increased short-circuit current densities (Jsc). However, the greater disorder and intermixed feature proliferation accompanying increasing Mn promotes charge carrier recombination, reducing cell fill factors (FF). The optimized photoactive layers exhibit well-balanced exciton dissociation and charge transport characteristics, ultimately providing solar cells with a 2-fold PCE enhancement versus devices with nonoptimal Mns. Overall, it is shown that proper and precise tuning of both donor and acceptor polymer Mns is critical for optimizing APSC performance. In contrast to reports where maximum power conversion efficiencies (PCEs) are achieved for the highest Mns, the present two-dimensional Mn optimization matrix strategy locates a PCE “sweet spot” at intermediate Mns of both donor and acceptor polymers. This study provides synthetic methodologies to predictably access conjugated polymers with desired Mn and highlights the importance of optimizing Mn for

  9. All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhou, Nanjia; Dudnik, Alexander S.; Li, Ting I. N. G.

    2015-12-31

    ABSTRACT: The influence of the number-average molecular weight (Mn) on the blend film morphology and photovoltaic performance of all-polymer solar cells (APSCs) fabricated with the donor polymer poly[5-(2-hexyldodecyl)-1,3-thieno[3,4- c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophen-2-yl)- thiophene)] (PTPD3T) and acceptor polymer poly{[N,N'- bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)- 2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2); N2200) is systematically investigated. The M n effect analysis of both PTPD3T and N2200 is enabled by implementing a polymerization strategy which produces conjugated polymers with tunable M ns. Experimental and coarse-grain modeling results reveal that systematic M n variation greatly influences both intrachain and interchain interactions and ultimately the degree of phase separation and morphology evolution. Specifically, increasing M n formore » both polymers shrinks blend film domain sizes and enhances donor-acceptor polymer-polymer interfacial areas, affording increased short-circuit current densities (J sc). However, the greater disorder and intermixed feature proliferation accompanying increasing M n promotes charge carrier recombination, reducing cell fill factors (FF). The optimized photoactive layers exhibit well-balanced exciton dissociation and charge transport characteristics, ultimately providing solar cells with a 2-fold PCE enhancement versus devices with nonoptimal M ns. Overall, it is shown that proper and precise tuning of both donor and acceptor polymer M ns is critical for optimizing APSC performance. In contrast to reports where maximum power conversion efficiencies (PCEs) are achieved for the highest M ns, the present two-dimensional M n optimization matrix strategy locates a PCE “sweet spot” at intermediate Mns of both donor and acceptor polymers. This study provides synthetic methodologies to predictably access conjugated polymers with desired M n and highlights the importance of

  10. Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors.

    PubMed

    Milanovsky, Georgy E; Petrova, Anastasia A; Cherepanov, Dmitry A; Semenov, Alexey Yu

    2017-09-01

    The reduction kinetics of the photo-oxidized primary electron donor P 700 in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P 700 , secondary quinone acceptor A 1 , iron-sulfur clusters and external electron donor and acceptors - methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl 2 NQ) and oxygen. PS I complexes containing various quinones in the A 1 -binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl 2 NQ) as well as F X -core complexes, depleted of terminal iron-sulfur F A /F B clusters, were studied. The acceleration of charge recombination in F X -core complexes by PhQ/PQ substitution indicates that backward ET from the iron-sulfur clusters involves quinone in the A 1 -binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P 700 + reduction with the kinetic model. The free energy gap ΔG 0 between F X and F A /F B clusters was estimated as -130 meV. The driving force of ET from A 1 to F X was determined as -50 and -220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A 1A -site, this reaction was found to be endergonic (ΔG 0  = +75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis-Menten kinetics. The second-order rate constants of ET from F A /F B , F X and Cl 2 NQ in the A 1 -site of PS I to external acceptors were estimated. The side production of superoxide radical in the A 1 -site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.

  11. A comparative study of thermochemical and cold plasma treatment on lignin-based activated carbon for adsorbing Fe(III)

    NASA Astrophysics Data System (ADS)

    Shi, Shukai; Wang, Xin; Chen, Weimin; Chen, Minzhi; Zhou, Xiaoyan

    2018-05-01

    The as-prepared lignin-based activated carbon (LAC) was post-treated by urea and radio-frequency cold plasma separately. The obtained results demonstrated that the BET surface and total volumes of the LAC and plasma-treated LACs were greater than the urea-modified sample. The analysis of surface elemental composition showed that the nitrogen content of urea-modified LAC and nitrogen plasma-treated LAC are 3.79% and 2.62% higher than that of original LAC respectively, while the oxygen content of air plasma-treated LAC is 10.23% higher than that of original LAC. The Fe(III) ions adsorbed studies with pseudo-second order kinetic model revealed that urea-modified LAC had faster chemisorption rates while air plasma-treated LAC had larger adsorption capacity within 3 h. Moreover, the adsorption capacity and chemisorption rates of LAC post-treated by nitrogen plasma are inferior to the air plasma-treated LAC.

  12. Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

    PubMed

    Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

    2014-06-11

    Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

  13. Ternary Nonfullerene Polymer Solar Cells with 12.16% Efficiency by Introducing One Acceptor with Cascading Energy Level and Complementary Absorption.

    PubMed

    Jiang, Weigang; Yu, Runnan; Liu, Zhiyang; Peng, Ruixiang; Mi, Dongbo; Hong, Ling; Wei, Qiang; Hou, Jianhui; Kuang, Yongbo; Ge, Ziyi

    2018-01-01

    A novel small-molecule acceptor, (2,2'-((5E,5'E)-5,5'-((5,5'-(4,4,9,9-tetrakis(5-hexylthiophen-2-yl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(4-(2-ethylhexyl)thiophene-5,2-diyl))bis(methanylylidene)) bis(3-hexyl-4-oxothiazolidine-5,2-diylidene))dimalononitrile (ITCN), end-capped with electron-deficient 2-(3-hexyl-4-oxothiazolidin-2-ylidene)malononitrile groups, is designed, synthesized, and used as the third component in fullerene-free ternary polymer solar cells (PSCs). The cascaded energy-level structure enabled by the newly designed acceptor is beneficial to the carrier transport and separation. Meanwhile, the three materials show a complementary absorption in the visible region, resulting in efficient light harvesting. Hence, the PBDB-T:ITCN:IT-M ternary PSCs possess a high short-circuit current density (J sc ) under an optimal weight ratio of donors and acceptors. Moreover, the open-circuit voltage (V oc ) of the ternary PSCs is enhanced with an increase of the third acceptor ITCN content, which is attributed to the higher lowest unoccupied molecular orbital energy level of ITCN than that of IT-M, thus exhibits a higher V oc in PBDB-T:ITCN binary system. Ultimately, the ternary PSCs achieve a power conversion efficiency of 12.16%, which is higher than the PBDB-T:ITM-based PSCs (10.89%) and PBDB-T:ITCN-based ones (2.21%). This work provides an effective strategy to improve the photovoltaic performance of PSCs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Self-assembly properties of semiconducting donor-acceptor-donor bithienyl derivatives of tetrazine and thiadiazole-effect of the electron accepting central ring.

    PubMed

    Zapala, Joanna; Knor, Marek; Jaroch, Tomasz; Maranda-Niedbala, Agnieszka; Kurach, Ewa; Kotwica, Kamil; Nowakowski, Robert; Djurado, David; Pecaut, Jacques; Zagorska, Malgorzata; Pron, Adam

    2013-11-26

    Scanning tunneling microscopy was used to study the effect of the electron-accepting unit and the alkyl substituent's position on the type and extent of 2D supramolecular organization of penta-ring donor-acceptor-donor (DAD) semiconductors, consisting of either tetrazine or thiadiazole central acceptor ring symmetrically attached to two bithienyl groups. Microscopic observations of monomolecular layers on HOPG of four alkyl derivatives of the studied adsorbates indicate significant differences in their 2D organizations. Ordered monolayers of thiadiazole derivatives are relatively loose and, independent of the position of alkyl substituents, characterized by large intermolecular separation of acceptor units in the adjacent molecules located in the face-to-face configuration. The 2D supramolecular architecture in both derivatives of thiadiazole is very sensitive to the alkyl substituent's position. Significantly different behavior is observed for derivatives of tetrazine (which is a stronger electron acceptor). Stronger intermolecular DA interactions in these adsorbates generate an intermolecular shift in the monolayer, which is a dominant factor determining the 2D structural organization. As a consequence of this molecular arrangement, tetrazine groups (A segments) face thiophene rings (D segments) of the neighboring molecules. Monolayers of tetrazine derivatives are therefore much more densely packed and characterized by similar π-stacking of molecules independently of the position of alkyl substituents. Moreover, a comparative study of 3D supramolecular organization, deduced from the X-ray diffraction patterns, is also presented clearly confirming the polymorphism of the studied adsorbates.

  15. Economical and accurate protocol for calculating hydrogen-bond-acceptor strengths.

    PubMed

    El Kerdawy, Ahmed; Tautermann, Christofer S; Clark, Timothy; Fox, Thomas

    2013-12-23

    A series of density functional/basis set combinations and second-order Møller-Plesset calculations have been used to test their ability to reproduce the trends observed experimentally for the strengths of hydrogen-bond acceptors in order to identify computationally efficient techniques for routine use in the computational drug-design process. The effects of functionals, basis sets, counterpoise corrections, and constraints on the optimized geometries were tested and analyzed, and recommendations (M06-2X/cc-pVDZ and X3LYP/cc-pVDZ with single-point counterpoise corrections or X3LYP/aug-cc-pVDZ without counterpoise) were made for suitable moderately high-throughput techniques.

  16. Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence

    NASA Astrophysics Data System (ADS)

    Wong, Michael L.; Charnay, Benjamin D.; Gao, Peter; Yung, Yuk L.; Russell, Michael J.

    2017-10-01

    We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO3-) and nitrite (NO2-) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO2 and N2, will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H2O vapor will then produce acids such as HNO, HNO2, HNO3, and HO2NO2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO2 models, we calculate the NOx delivery to be 2.4 × 105, 6.5 × 108, and 1.9 × 108 molecules cm-2 s-1. After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life.

  17. Organic Materials in the Undergraduate Laboratory: Microscale Synthesis and Investigation of a Donor-Acceptor Molecule

    ERIC Educational Resources Information Center

    Pappenfus, Ted M.; Schliep, Karl B.; Dissanayake, Anudaththa; Ludden, Trevor; Nieto-Ortega, Belen; Lopez Navarrete, Juan T.; Ruiz Delgado, M. Carmen; Casado, Juan

    2012-01-01

    A series of experiments for undergraduate courses (e.g., organic, physical) have been developed in the area of small molecule organic materials. These experiments focus on understanding the electronic and redox properties of a donor-acceptor molecule that is prepared in a convenient one-step microscale reaction. The resulting intensely colored…

  18. Formate Metabolism in Shewanella oneidensis Generates Proton Motive Force and Prevents Growth without an Electron Acceptor.

    PubMed

    Kane, Aunica L; Brutinel, Evan D; Joo, Heena; Maysonet, Rebecca; VanDrisse, Chelsey M; Kotloski, Nicholas J; Gralnick, Jeffrey A

    2016-04-01

    Shewanella oneidensis strain MR-1 is a facultative anaerobe that thrives in redox-stratified environments due to its ability to utilize a wide array of terminal electron acceptors. Conversely, the electron donors utilized by S. oneidensis are more limited and include products of primary fermentation such as lactate, pyruvate, formate, and hydrogen. Lactate, pyruvate, and hydrogen metabolisms inS. oneidensis have been described previously, but little is known about the role of formate oxidation in the ecophysiology of these bacteria. Formate is produced by S. oneidensis through pyruvate formate lyase during anaerobic growth on carbon sources that enter metabolism at or above the level of pyruvate, and the genome contains three gene clusters predicted to encode three complete formate dehydrogenase complexes. To determine the contribution of each complex to formate metabolism, strains lacking one, two, or all three annotated formate dehydrogenase gene clusters were generated and examined for growth rates and yields on a variety of carbon sources. Here, we report that formate oxidation contributes to both the growth rate and yield of S. oneidensis through the generation of proton motive force. Exogenous formate also greatly accelerated growth on N-acetylglucosamine, a carbon source normally utilized very slowly by S. oneidensis under anaerobic conditions. Surprisingly, deletion of all three formate dehydrogenase gene clusters enabled growth of S. oneidensis using pyruvate in the absence of a terminal electron acceptor, a mode of growth never before observed in these bacteria. Our results demonstrate that formate oxidation is a fundamental strategy under anaerobic conditions for energy conservation inS. oneidensis. Shewanella species have garnered interest in biotechnology applications for their ability to respire extracellular terminal electron acceptors, such as insoluble iron oxides and electrodes. While much effort has gone into studying the proteins for

  19. Formate Metabolism in Shewanella oneidensis Generates Proton Motive Force and Prevents Growth without an Electron Acceptor

    PubMed Central

    Kane, Aunica L.; Brutinel, Evan D.; Joo, Heena; Maysonet, Rebecca; VanDrisse, Chelsey M.; Kotloski, Nicholas J.

    2016-01-01

    ABSTRACT Shewanella oneidensis strain MR-1 is a facultative anaerobe that thrives in redox-stratified environments due to its ability to utilize a wide array of terminal electron acceptors. Conversely, the electron donors utilized by S. oneidensis are more limited and include products of primary fermentation such as lactate, pyruvate, formate, and hydrogen. Lactate, pyruvate, and hydrogen metabolisms in S. oneidensis have been described previously, but little is known about the role of formate oxidation in the ecophysiology of these bacteria. Formate is produced by S. oneidensis through pyruvate formate lyase during anaerobic growth on carbon sources that enter metabolism at or above the level of pyruvate, and the genome contains three gene clusters predicted to encode three complete formate dehydrogenase complexes. To determine the contribution of each complex to formate metabolism, strains lacking one, two, or all three annotated formate dehydrogenase gene clusters were generated and examined for growth rates and yields on a variety of carbon sources. Here, we report that formate oxidation contributes to both the growth rate and yield of S. oneidensis through the generation of proton motive force. Exogenous formate also greatly accelerated growth on N-acetylglucosamine, a carbon source normally utilized very slowly by S. oneidensis under anaerobic conditions. Surprisingly, deletion of all three formate dehydrogenase gene clusters enabled growth of S. oneidensis using pyruvate in the absence of a terminal electron acceptor, a mode of growth never before observed in these bacteria. Our results demonstrate that formate oxidation is a fundamental strategy under anaerobic conditions for energy conservation in S. oneidensis. IMPORTANCE Shewanella species have garnered interest in biotechnology applications for their ability to respire extracellular terminal electron acceptors, such as insoluble iron oxides and electrodes. While much effort has gone into studying the

  20. Humic acids as electron acceptors for anaerobic microbial oxidation of vinyl chloride and dichloroethene

    USGS Publications Warehouse

    Bradley, P.M.; Chapelle, F.H.; Lovley, D.R.

    1998-01-01

    Anaerobic oxidation of [1,2-14C]vinyl chloride and [1,2- 14C]dichloroethene to 14CO2 under humic acid-reducing conditions was demonstrated. The results indicate that waterborne contaminants can be oxidized by using humic acid compounds as electron acceptors and suggest that natural aquatic systems have a much larger capacity for contaminant oxidation than previously thought.