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Sample records for acceptors including feiii

  1. Proteome of Geobacter sulfurreducens grown with Fe(III) oxide or Fe(III) citrate as the electron acceptor.

    SciTech Connect

    Ding, Y-H R.; Hixson, Kim K.; Aklujkar, Ma; Lipton, Mary S.; Smith, Richard D.; Lovley, Derek R.; Mester, Tunde

    2008-12-01

    e(III) oxides are the most abundant source of reducible Fe(III) by microorganisms in most soils and sediments, yet few studies on the physiology of Fe(III)-reducing microorganisms during growth on Fe(III) oxide have been conducted because of the technical difficulties in working with cell growth and harvest in the presence of Fe(III) oxides. Geobacter sulfurreducens is a representative of the Geobacter species that predominate in a variety of subsurface environments in which Fe(III) oxide is important. In order to better understand the physiology of Geobacter species during growth on Fe(III) oxide, the proteome of G. sulfurreducens grown on Fe(III) oxide was compared with the proteome of cells grown with soluble Fe(III) citrate. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) revealed 19 proteins that were more abundant during growth on Fe(III) oxide than on soluble Fe(III). These included proteins related to protein synthesis, electron transfer and energy production, oxidative stress, protein folding, outer membrane proteins, nitrogen metabolism and hypothetical proteins. Further analysis of the proteome with the accurate mass and time (AMT) tag method revealed additional proteins associated with growth on Fe(III) oxide. These included the outer-membrane c-type cytochrome, OmcS and OmcG, which genetic studies have suggested are required for Fe(III) oxide reduction. Furthermore, several other cytochromes, as yet unstudied, were detected to be significantly up regulated during growth on Fe(III) oxide and other proteins of unknown function were more abundant during growth on Fe(III) oxide than on soluble Fe(III). PilA, the structural protein for pili, which is required for Fe(III) oxide reduction, and other pilin-associated proteins were also more abundant during growth on Fe(III) oxide. Confirmation of the differential expression of proteins known to be important in Fe(III) oxide reduction was observed, and an additional number of previously

  2. Dissimilatory Reduction of Fe(III) and Other Electron Acceptors by a Thermus Isolate

    SciTech Connect

    Kieft, T. L.; Fredrickson, J. K.; Onstott, T. C.; Gorby, Y. A.; Kostandarithes, H. M.; Bailey, T. J.; Kennedy, D. W.; Li, S. W.; Plymale, A. E.; Spadoni, C. M.; Gray, M. S.

    1995-10-25

    A thermophilic bacterium that could use O{sub 2}, NO{sub 3}{sup -}, Fe(III), or S{sup o} as terminal electron acceptors for growth was isolated from groundwater sampled at 3.2 km depth in a South African gold mine. This organism, designated SA-01, clustered most closely with members of the genus Thermus, as determined by 16S rDNA gene sequence analysis. The 16S rDNA sequence of SA-01 was >98% similar to that of Thermus strain NMX2 A.1, which was previously isolated by other investigators from a thermal spring in New Mexico. Strain NMX2 A.1 was also able to reduce Fe(III) and other electron acceptors, whereas Thermus aquaticus (ATCC 25104) and Thermus filiformis (ATCC 43280) did not reduce NO{sub 3}{sup -} or Fe(III). Neither SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external electron acceptor was required for anaerobic growth. Thermus SA-01 reduced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could only reduce relatively small quantities (0.5 mM) of hydrous ferric oxide (HFO) except when the humic acid analog 2,6-anthraquinone disulfonate (AQDS) was added as an electron shuttle, in which case 10 mM Fe(III) was reduced. Fe(III)-NTA was reduced quantitatively to Fe(II), was coupled to the oxidation of lactate, and could support growth through three consecutive transfers. Suspensions of Thermus SA-01 cells also reduced Mn(IV), Co(III)-EDTA, Cr(VI), and AQDS. Mn(IV)-oxide was reduced in the presence of either lactate or H{sub 2}. Both strains were also able to mineralize NTA to CO{sub 2} and to couple its oxidation to Fe(III) reduction and growth. The optimum temperature for growth and Fe(III) reduction by Thermus SA-01 and NMX2 A.1 is approximately 65 C; optimum pH is 6.5 to 7.0. This is the first report of a Thermus sp. being able to couple the oxidation of organic compounds to the reduction of Fe, Mn or S.

  3. Dissimilatory reduction of Fe(III) and other electron acceptors by a Thermus isolate.

    PubMed

    Kieft, T L; Fredrickson, J K; Onstott, T C; Gorby, Y A; Kostandarithes, H M; Bailey, T J; Kennedy, D W; Li, S W; Plymale, A E; Spadoni, C M; Gray, M S

    1999-03-01

    A thermophilic bacterium that can use O2, NO3-, Fe(III), and S0 as terminal electron acceptors for growth was isolated from groundwater sampled at a 3.2-km depth in a South African gold mine. This organism, designated SA-01, clustered most closely with members of the genus Thermus, as determined by 16S rRNA gene (rDNA) sequence analysis. The 16S rDNA sequence of SA-01 was >98% similar to that of Thermus strain NMX2 A.1, which was previously isolated by other investigators from a thermal spring in New Mexico. Strain NMX2 A.1 was also able to reduce Fe(III) and other electron acceptors. Neither SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external electron acceptor was required for anaerobic growth. Thermus strain SA-01 reduced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could reduce only relatively small quantities (0.5 mM) of hydrous ferric oxide except when the humic acid analog 2,6-anthraquinone disulfonate was added as an electron shuttle, in which case 10 mM Fe(III) was reduced. Fe(III)-NTA was reduced quantitatively to Fe(II); reduction of Fe(III)-NTA was coupled to the oxidation of lactate and supported growth through three consecutive transfers. Suspensions of Thermus strain SA-01 cells also reduced Mn(IV), Co(III)-EDTA, Cr(VI), and U(VI). Mn(IV)-oxide was reduced in the presence of either lactate or H2. Both strains were also able to mineralize NTA to CO2 and to couple its oxidation to Fe(III) reduction and growth. The optimum temperature for growth and Fe(III) reduction by Thermus strains SA-01 and NMX2 A.1 is approximately 65 degrees C; their optimum pH is 6.5 to 7.0. This is the first report of a Thermus sp. being able to couple the oxidation of organic compounds to the reduction of Fe, Mn, or S.

  4. Dissimilatory Reduction of Fe(III) and Other Electron Acceptors by a Thermus Isolate

    PubMed Central

    Kieft, T. L.; Fredrickson, J. K.; Onstott, T. C.; Gorby, Y. A.; Kostandarithes, H. M.; Bailey, T. J.; Kennedy, D. W.; Li, S. W.; Plymale, A. E.; Spadoni, C. M.; Gray, M. S.

    1999-01-01

    A thermophilic bacterium that can use O2, NO3−, Fe(III), and S0 as terminal electron acceptors for growth was isolated from groundwater sampled at a 3.2-km depth in a South African gold mine. This organism, designated SA-01, clustered most closely with members of the genus Thermus, as determined by 16S rRNA gene (rDNA) sequence analysis. The 16S rDNA sequence of SA-01 was >98% similar to that of Thermus strain NMX2 A.1, which was previously isolated by other investigators from a thermal spring in New Mexico. Strain NMX2 A.1 was also able to reduce Fe(III) and other electron acceptors. Neither SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external electron acceptor was required for anaerobic growth. Thermus strain SA-01 reduced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could reduce only relatively small quantities (0.5 mM) of hydrous ferric oxide except when the humic acid analog 2,6-anthraquinone disulfonate was added as an electron shuttle, in which case 10 mM Fe(III) was reduced. Fe(III)-NTA was reduced quantitatively to Fe(II); reduction of Fe(III)-NTA was coupled to the oxidation of lactate and supported growth through three consecutive transfers. Suspensions of Thermus strain SA-01 cells also reduced Mn(IV), Co(III)-EDTA, Cr(VI), and U(VI). Mn(IV)-oxide was reduced in the presence of either lactate or H2. Both strains were also able to mineralize NTA to CO2 and to couple its oxidation to Fe(III) reduction and growth. The optimum temperature for growth and Fe(III) reduction by Thermus strains SA-01 and NMX2 A.1 is approximately 65°C; their optimum pH is 6.5 to 7.0. This is the first report of a Thermus sp. being able to couple the oxidation of organic compounds to the reduction of Fe, Mn, or S. PMID:10049886

  5. Shewanella oneidensis MR-1 mutants selected for their inability to produce soluble organic-Fe(III) complexes are unable to respire Fe(III) as anaerobic electron acceptor.

    PubMed

    Jones, Morris E; Fennessey, Christine M; DiChristina, Thomas J; Taillefert, Martial

    2010-04-01

    Recent voltammetric analyses indicate that Shewanella putrefaciens strain 200 produces soluble organic-Fe(III) complexes during anaerobic respiration of sparingly soluble Fe(III) oxides. Results of the present study expand the range of Shewanella species capable of producing soluble organic-Fe(III) complexes to include Shewanella oneidensis MR-1. Soluble organic-Fe(III) was produced by S. oneidensis cultures incubated anaerobically with Fe(III) oxides, or with Fe(III) oxides and the alternate electron acceptor fumarate, but not in the presence of O(2), nitrate or trimethylamine-N-oxide. Chemical mutagenesis procedures were combined with a novel MicroElectrode Screening Array (MESA) to identify four (designated Sol) mutants with impaired ability to produce soluble organic-Fe(III) during anaerobic respiration of Fe(III) oxides. Two of the Sol mutants were deficient in anaerobic growth on both soluble Fe(III)-citrate and Fe(III) oxide, yet retained the ability to grow on a suite of seven alternate electron acceptors. The rates of soluble organic-Fe(III) production were proportional to the rates of iron reduction by the S. oneidensis wild-type and Sol mutant strains, and all four Sol mutants retained wild-type siderophore production capability. Results of this study indicate that the production of soluble organic-Fe(III) may be an important intermediate step in the anaerobic respiration of both soluble and sparingly soluble forms of Fe(III) by S. oneidensis.

  6. Bioavailability of Fe(III) in Loess Sediments: An Important Source of Electron Acceptors

    SciTech Connect

    Bishop, Michael E.; Jaisi, Deb P.; Dong, Hailiang; Kukkadapu, Ravi K.; Ji, Junfeng

    2010-08-01

    A quantitative study was conducted to understand if Fe (III) in loess sediments is available for microbial respiration by using a common metal reducing bacterium, Shewanella putrefaciens, CN32. The loess samples were collected from three different sites: St. Louis (Peoria), Missouri, USA; Huanxia (HX) and Yanchang (YCH), Shanxi Province of China. Wet chemical analyses indicated that the total Fe concentration for the three samples was 1.69%, 2.76%, and 3.29%, respectively, of which 0.48%, 0.67%, and 1.27% was Fe(III). All unreduced loess sediments contained iron oxides and phyllosilicates (smectite, illite, chlorite, vermiculite), in addition to common minerals such as quartz, feldspar, plagioclase, calcite, and dolomite. Bioreduction experiments were performed at a loess concentration of 20 mg/mL using lactate as the sole electron donor, Fe(III) in loess as the sole electron acceptor in the presence and absence of anthraquinone-2, 6-disulfonate (AQDS) as an electron shuttle. Experiments were performed in non-growth (bicarbonate buffer) and growth (M1) media with a cell concentration of ~2.8 x 107 and 2.1 x 107 cells/mL, respectively. The unreduced and bioreduced solids were analyzed by X-ray diffraction (XRD), Mössbauer spectroscopy, diffuse reflection spectroscopy (DRS), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) methods. Despite many similarities among the three loess samples, the extent and rate of Fe (III) reduction varied significantly. For example, in presence of AQDS the extent of reduction in the non-growth experiment was 25% in HX, 34% in Peoria, and 38% in YCH. The extent of reduction in the growth experiment was 72% in HX, 94% in Peoria, and 56% in YCH. The extent of bioreduction was lower in absence of AQDS. Overall, AQDS and the M1 growth medium significantly enhanced the rate and extent of bioreduction. Fe(III) in iron oxides and Fe(III)-containing phyllosilicates was bioreduced. Biogenic illite, siderite, and

  7. 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

  8. 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

  9. Siderophores are not involved in Fe(III) solubilization during anaerobic Fe(III) respiration by Shewanella oneidensis MR-1.

    PubMed

    Fennessey, Christine M; Jones, Morris E; Taillefert, Martial; DiChristina, Thomas J

    2010-04-01

    Shewanella oneidensis MR-1 respires a wide range of anaerobic electron acceptors, including sparingly soluble Fe(III) oxides. In the present study, S. oneidensis was found to produce Fe(III)-solubilizing organic ligands during anaerobic Fe(III) oxide respiration, a respiratory strategy postulated to destabilize Fe(III) and produce more readily reducible soluble organic Fe(III). In-frame gene deletion mutagenesis, siderophore detection assays, and voltammetric techniques were combined to determine (i) if the Fe(III)-solubilizing organic ligands produced by S. oneidensis during anaerobic Fe(III) oxide respiration were synthesized via siderophore biosynthesis systems and (ii) if the Fe(III)-siderophore reductase was required for respiration of soluble organic Fe(III) as an anaerobic electron acceptor. Genes predicted to encode the siderophore (hydroxamate) biosynthesis system (SO3030 to SO3032), the Fe(III)-hydroxamate receptor (SO3033), and the Fe(III)-hydroxamate reductase (SO3034) were identified in the S. oneidensis genome, and corresponding in-frame gene deletion mutants were constructed. DeltaSO3031 was unable to synthesize siderophores or produce soluble organic Fe(III) during aerobic respiration yet retained the ability to solubilize and respire Fe(III) at wild-type rates during anaerobic Fe(III) oxide respiration. DeltaSO3034 retained the ability to synthesize siderophores during aerobic respiration and to solubilize and respire Fe(III) at wild-type rates during anaerobic Fe(III) oxide respiration. These findings indicate that the Fe(III)-solubilizing organic ligands produced by S. oneidensis during anaerobic Fe(III) oxide respiration are not synthesized via the hydroxamate biosynthesis system and that the Fe(III)-hydroxamate reductase is not essential for respiration of Fe(III)-citrate or Fe(III)-nitrilotriacetic acid (NTA) as an anaerobic electron acceptor.

  10. Mechanisms Involved in Fe(III) Respiration by the Hyperthermophilic Archaeon Ferroglobus placidus

    PubMed Central

    Smith, Jessica A.; Aklujkar, Muktak; Risso, Carla; Leang, Ching; Giloteaux, Ludovic

    2015-01-01

    The hyperthermophilic archaeon Ferroglobus placidus can utilize a wide variety of electron donors, including hydrocarbons and aromatic compounds, with Fe(III) serving as an electron acceptor. In Fe(III)-reducing bacteria that have been studied to date, this process is mediated by c-type cytochromes and type IV pili. However, there currently is little information available about how this process is accomplished in archaea. In silico analysis of the F. placidus genome revealed the presence of 30 genes coding for putative c-type cytochrome proteins (more than any other archaeon that has been sequenced to date), five of which contained 10 or more heme-binding motifs. When cell extracts were analyzed by SDS-PAGE followed by heme staining, multiple bands corresponding to c-type cytochromes were detected. Different protein expression patterns were observed in F. placidus cells grown on soluble and insoluble iron forms. In order to explore this result further, transcriptomic studies were performed. Eight genes corresponding to multiheme c-type cytochromes were upregulated when F. placidus was grown with insoluble Fe(III) oxide compared to soluble Fe(III) citrate as an electron acceptor. Numerous archaella (archaeal flagella) also were observed on Fe(III)-grown cells, and genes coding for two type IV pilin-like domain proteins were differentially expressed in Fe(III) oxide-grown cells. This study provides insight into the mechanisms for dissimilatory Fe(III) respiration by hyperthermophilic archaea. PMID:25662973

  11. Outer membrane-associated serine protease involved in adhesion of Shewanella oneidensis to Fe(III) oxides.

    PubMed

    Burns, Justin L; Ginn, Brian R; Bates, David J; Dublin, Steven N; Taylor, Jeanette V; Apkarian, Robert P; Amaro-Garcia, Samary; Neal, Andrew L; Dichristina, Thomas J

    2010-01-01

    The facultative anaerobe Shewanella oneidensis MR-1 respires a variety of anaerobic electron acceptors, including insoluble Fe(III) oxides. S. oneidensis employs a number of novel strategies for respiration of insoluble Fe(III) oxides, including localization of respiratory proteins to the cell outer membrane (OM). The molecular mechanism by which S. oneidensis adheres to and respires Fe(III) oxides, however, remains poorly understood. In the present study, whole cell fractionation and MALDI-TOF-MS/MS techniques were combined to identify a serine protease (SO3800) associated with the S. oneidensis OM. SO3800 contained predicted structural motifs similar to cell surface-associated serine proteases that function as bacterial adhesins in other gram-negative bacteria. The gene encoding SO3800 was deleted from the S. oneidensis genome, and the resulting mutant strain (DeltaSO3800) was tested for its ability to adhere to and respire Fe(III) oxides. DeltaSO3800 was severely impaired in its ability to adhere to Fe(III) oxides, yet retained wild-type Fe(III) respiratory capability. Laser Doppler velocimetry and cryoetch high-resolution SEM experiments indicated that DeltaSO3800 displayed a lower cell surface charge and higher amount of surface-associated exopolysaccharides. Results of this study indicate that S. oneidensis may respire insoluble Fe(III) oxides at a distance, negating the requirement for attachment prior to electron transfer.

  12. 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

  13. 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

  14. Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella Oneidensis MR-1

    PubMed Central

    Shi, Liang; Rosso, Kevin M.; Clarke, Tomas A.; Richardson, David J.; Zachara, John M.; Fredrickson, James K.

    2012-01-01

    In the absence of O2 and other electron acceptors, the Gram-negative bacterium Shewanella oneidensis MR-1 can use ferric [Fe(III)] (oxy)(hydr)oxide minerals as the terminal electron acceptors for anaerobic respiration. At circumneutral pH and in the absence of strong complexing ligands, Fe(III) oxides are relatively insoluble and thus are external to the bacterial cells. S. oneidensis MR-1 and related strains of metal-reducing Shewanella have evolved machinery (i.e., metal-reducing or Mtr pathway) for transferring electrons from the inner-membrane, through the periplasm and across the outer-membrane to the surface of extracellular Fe(III) oxides. The protein components identified to date for the Mtr pathway include CymA, MtrA, MtrB, MtrC, and OmcA. CymA is an inner-membrane tetraheme c-type cytochrome (c-Cyt) that belongs to the NapC/NrfH family of quinol dehydrogenases. It is proposed that CymA oxidizes the quinol in the inner-membrane and transfers the released electrons to MtrA either directly or indirectly through other periplasmic proteins. A decaheme c-Cyt, MtrA is thought to be embedded in the trans outer-membrane and porin-like protein MtrB. Together, MtrAB deliver the electrons through the outer-membrane to the MtrC and OmcA on the outmost bacterial surface. MtrC and OmcA are the outer-membrane decaheme c-Cyts that are translocated across the outer-membrane by the bacterial type II secretion system. Functioning as terminal reductases, MtrC and OmcA can bind the surface of Fe(III) oxides and transfer electrons directly to these minerals via their solvent-exposed hemes. To increase their reaction rates, MtrC and OmcA can use the flavins secreted by S. oneidensis MR-1 cells as diffusible co-factors for reduction of Fe(III) oxides. Because of their extracellular location and broad redox potentials, MtrC and OmcA can also serve as the terminal reductases for soluble forms of Fe(III). In addition to Fe(III) oxides, Mtr pathway is also involved in reduction of

  15. Microbial Reduction of Fe(III) under Alkaline Conditions Relevant to Geological Disposal

    PubMed Central

    Williamson, Adam J.; Morris, Katherine; Shaw, Sam; Byrne, James M.; Boothman, Christopher

    2013-01-01

    To determine whether biologically mediated Fe(III) reduction is possible under alkaline conditions in systems of relevance to geological disposal of radioactive wastes, a series of microcosm experiments was set up using hyperalkaline sediments (pH ∼11.8) surrounding a legacy lime working site in Buxton, United Kingdom. The microcosms were incubated for 28 days and held at pH 10. There was clear evidence for anoxic microbial activity, with consumption of lactate (added as an electron donor) concomitant with the reduction of Fe(III) as ferrihydrite (added as the electron acceptor). The products of microbial Fe(III) reduction were black and magnetic, and a range of analyses, including X-ray diffraction, transmission electron microscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism confirmed the extensive formation of biomagnetite in this system. The addition of soluble exogenous and endogenous electron shuttles such as the humic analogue anthraquinone-2,6-disulfonate and riboflavin increased both the initial rate and the final extent of Fe(III) reduction in comparison to the nonamended experiments. In addition, a soluble humic acid (Aldrich) also increased both the rate and the extent of Fe(III) reduction. These results show that microbial Fe(III) reduction can occur in conditions relevant to a geological disposal facility containing cement-based wasteforms that has evolved into a high pH environment over prolonged periods of time (>100,000 years). The potential impact of such processes on the biogeochemistry of a geological disposal facility is discussed, including possible coupling to the redox conditions and solubility of key radionuclides. PMID:23524677

  16. 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

  17. Shewanella putrefaciens produces an Fe(III)-solubilizing organic ligand during anaerobic respiration on insoluble Fe(III) oxides.

    PubMed

    Taillefert, Martial; Beckler, Jordon S; Carey, Elizabeth; Burns, Justin L; Fennessey, Christine M; DiChristina, Thomas J

    2007-11-01

    The mechanism of Fe(III) reduction was investigated using voltammetric techniques in anaerobic incubations of Shewanella putrefaciens strain 200 supplemented with Fe(III) citrate or a suite of Fe(III) oxides as terminal electron acceptor. Results indicate that organic complexes of Fe(III) are produced during the reduction of Fe(III) at rates that correlate with the reactivity of the Fe(III) phase and bacterial cell density. Anaerobic Fe(III) solubilization activity is detected with either Fe(III) oxides or Fe(III) citrate, suggesting that the organic ligand produced is strong enough to destabilize Fe(III) from soluble or solid Fe(III) substrates. Results also demonstrate that Fe(III) oxide dissolution is not controlled by the intrinsic chemical reactivity of the Fe(III) oxides. Instead, the chemical reaction between the endogenous organic ligand is only affected by the number of reactive surface sites available to S. putrefaciens. This report describes the first application of voltammetric techniques to demonstrate production of soluble organic-Fe(III) complexes by any Fe(III)-reducing microorganism and is the first report of a Fe(III)-solubilizing ligand generated by a metal-reducing member of the genus Shewanella.

  18. 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

  19. Availability of Fe(III) for Anaerobic Respiration across an Age Gradient of Drained Thaw Lake Basins in the Arctic Coastal Plain

    NASA Astrophysics Data System (ADS)

    Lipson, D.; Raab, T. K.; Bozzolo, F.; Emerson, C.; Hale, I.; Mauritz, M.; Miller, K.

    2010-12-01

    Our previous work demonstrated that Fe(III) reduction is an important respiratory pathway in a drained thaw lake basin (DTLB) of the Arctic coastal plain in northern Alaska (Lipson et al. 2010). When Fe(III) is available in anoxic environments that otherwise lack electron acceptors, it can act as a terminal electron acceptor, allowing anaerobic respiration to occur in favor of methanogenesis. Therefore, Fe(III) availability could be a key control over CO2 and CH4 emission from such ecosystems. Our previous work focused on a DTLB of medium age (50-300 years old). As DTLB’s age, the organic layer thickens, eventually to the point where the underlying mineral layers are buried completely in permafrost. The mineral layers are likely to be the source for the majority of Fe available for redox transformations by soil microbes. We therefore hypothesized that older basins with permanently frozen mineral layers would have lower Fe(III) availability than younger basins with active layers that include mineral material. To test this hypothesis we studied a gradient that comprised four DTLB, including young (<50 y), medium (50-300 y), old (300-2000 y) and ancient (2000-5500 y). We compared extractable Fe minerals in depth profiles from each DTLB, soluble Fe species in soil pore water, and other properties of soils and soil water. As expected, the youngest DTLB had the thinnest organic layer, a shallow mineral layer, and hence the largest total amount of HCl-extractable Fe(III) in the upper 25 cm. The medium DTLB had the lowest amounts of extractable Fe(III), while the old and ancient basins had intermediate amounts of extractable Fe(III). The amount of total Fe(III) present was related to the amount of mineral material found in the profile; the larger amounts in the old and ancient site relative to the medium site could be explained by cryoturbation, a process which mixes organic and mineral layers in older gelisols. S and Mn followed the same trends, but were orders of

  20. Molecular Underpinnings of Fe(III) Oxide Reduction by Shewanella oneidensis MR-1

    SciTech Connect

    Shi, Liang; Rosso, Kevin M.; Clarke, Thomas A.; Richardson, David J.; Zachara, John M.; Fredrickson, Jim K.

    2012-02-15

    In the absence of O2 and other electron acceptors, the Gram-negative bacterium Shewanella oneidensis MR-1 can use ferric [Fe(III)] (oxy)(hydr)oxide minerals as the terminal electron acceptors for anaerobic respiration. At circumneutral pH and in the absence of strong complexing ligands, Fe(III) oxides are relatively insoluble and thus are external to the bacterial cells. S. oneidensis MR-1 and related strains of metal-reducing Shewanella have evolved the machinery (i.e., metal-reducing or Mtr pathway) for transferring electrons from the inner-membrane, through the periplasm and across the outer-membrane to the surface of extracellular Fe(III) oxides. The protein components identified to date for the Mtr pathway include CymA, MtrA, MtrB, MtrC and OmcA. CymA is an inner-membrane tetraheme c-type cytochrome (c-Cyt) that belongs to the NapC/NrfH family of quinol dehydrogenases. It is proposed that CymA oxidizes the quinol in the inner-membrane and transfers the released electrons to redox proteins in the periplasm. Although the periplasmic proteins receiving electrons from CymA during Fe(III) oxidation have not been identified, they are believed to relay the electrons in the periplasm to MtrA. A decaheme c-Cyt, MtrA is thought to be embedded in the trans outer-membrane and porin-like protein MtrB. Together, MtrAB deliver the electrons through the outer-membrane to the MtrC and OmcA on the outmost bacterial surface. MtrC and OmcA are the outer-membrane decaheme c-Cyts that are translocated across the outer-membrane by the bacterial type II secretion system. Functioning as terminal reductases, MtrC and OmcA can bind the surface of Fe(III) oxides and transfer electrons directly to these minerals via their solvent-exposed hemes. To increase their reaction rates, MtrC and OmcA can use the flavins secreted by S. oneidensis MR-1 cells as diffusible co-factors for reduction of Fe(III) oxides. Because of their extracellular location and broad redox potentials, MtrC and OmcA can

  1. Advanced experimental analysis of controls on microbial Fe(III) oxide reduction. First year progress report

    SciTech Connect

    Roden, E.E.; Urrutia, M.M.

    1997-07-01

    'The authors have made considerable progress toward a number of project objectives during the first several months of activity on the project. An exhaustive analysis was made of the growth rate and biomass yield (both derived from measurements of cell protein production) of two representative strains of Fe(III)-reducing bacteria (Shewanellaalga strain BrY and Geobactermetallireducens) growing with different forms of Fe(III) as an electron acceptor. These two fundamentally different types of Fe(III)-reducing bacteria (FeRB) showed comparable rates of Fe(III) reduction, cell growth, and biomass yield during reduction of soluble Fe(III)-citrate and solid-phase amorphous hydrous ferric oxide (HFO). Intrinsic growth rates of the two FeRB were strongly influenced by whether a soluble or a solid-phase source of Fe(III) was provided: growth rates on soluble Fe(III) were 10--20 times higher than those on solid-phase Fe(III) oxide. Intrinsic FeRB growth rates were comparable during reduction of HF0 and a synthetic crystalline Fe(III) oxide (goethite). A distinct lag phase for protein production was observed during the first several days of incubation in solid-phase Fe(III) oxide medium, even though Fe(III) reduction proceeded without any lag. No such lag between protein production and Fe(III) reduction was observed during growth with soluble Fe(III). This result suggested that protein synthesis coupled to solid-phase Fe(III) oxide reduction in batch culture requires an initial investment of energy (generated by Fe(III) reduction), which is probably needed for synthesis of materials (e.g. extracellular polysaccharides) required for attachment of the cells to oxide surfaces. This phenomenon may have important implications for modeling the growth of FeRB in subsurface sedimentary environments, where attachment and continued adhesion to solid-phase materials will be required for maintenance of Fe(III) reduction activity. Despite considerable differences in the rate and pattern

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. Extracellular Electron Transfer to Fe(III) Oxides by the Hyperthermophilic Archaeon Geoglobus ahangari via a Direct Contact Mechanism

    PubMed Central

    Manzella, Michael P.; Reguera, Gemma

    2013-01-01

    The microbial reduction of Fe(III) plays an important role in the geochemistry of hydrothermal systems, yet it is poorly understood at the mechanistic level. Here we show that the obligate Fe(III)-reducing archaeon Geoglobus ahangari uses a direct-contact mechanism for the reduction of Fe(III) oxides to magnetite at 85°C. Alleviating the need to directly contact the mineral with the addition of a chelator or the electron shuttle anthraquinone-2,6-disulfonate (AQDS) stimulated Fe(III) reduction. In contrast, entrapment of the oxides within alginate beads to prevent cell contact with the electron acceptor prevented Fe(III) reduction and cell growth unless AQDS was provided. Furthermore, filtered culture supernatant fluids had no effect on Fe(III) reduction, ruling out the secretion of an endogenous mediator too large to permeate the alginate beads. Consistent with a direct contact mechanism, electron micrographs showed cells in intimate association with the Fe(III) mineral particles, which once dissolved revealed abundant curled appendages. The cells also produced several heme-containing proteins. Some of them were detected among proteins sheared from the cell's outer surface and were required for the reduction of insoluble Fe(III) oxides but not for the reduction of the soluble electron acceptor Fe(III) citrate. The results thus support a mechanism in which the cells directly attach and transfer electrons to the Fe(III) oxides using redox-active proteins exposed on the cell surface. This strategy confers on G. ahangari a competitive advantage for accessing and reducing Fe(III) oxides under the extreme physical and chemical conditions of hot ecosystems. PMID:23728807

  7. Proteins involved in electron transfer to Fe(III) and Mn(IV) oxides by Geobacter sulfurreducens and Geobacter uraniireducens.

    PubMed

    Aklujkar, M; Coppi, M V; Leang, C; Kim, B C; Chavan, M A; Perpetua, L A; Giloteaux, L; Liu, A; Holmes, D E

    2013-03-01

    Whole-genome microarray analysis of Geobacter sulfurreducens grown on insoluble Fe(III) oxide or Mn(IV) oxide versus soluble Fe(III) citrate revealed significantly different expression patterns. The most upregulated genes, omcS and omcT, encode cell-surface c-type cytochromes, OmcS being required for Fe(III) and Mn(IV) oxide reduction. Other electron transport genes upregulated on both metal oxides included genes encoding putative menaquinol : ferricytochrome c oxidoreductase complexes Cbc4 and Cbc5, periplasmic c-type cytochromes Dhc2 and PccF, outer membrane c-type cytochromes OmcC, OmcG and OmcV, multicopper oxidase OmpB, the structural components of electrically conductive pili, PilA-N and PilA-C, and enzymes that detoxify reactive oxygen/nitrogen species. Genes upregulated on Fe(III) oxide encode putative menaquinol : ferricytochrome c oxidoreductase complexes Cbc3 and Cbc6, periplasmic c-type cytochromes, including PccG and PccJ, and outer membrane c-type cytochromes, including OmcA, OmcE, OmcH, OmcL, OmcN, OmcO and OmcP. Electron transport genes upregulated on Mn(IV) oxide encode periplasmic c-type cytochromes PccR, PgcA, PpcA and PpcD, outer membrane c-type cytochromes OmaB/OmaC, OmcB and OmcZ, multicopper oxidase OmpC and menaquinone-reducing enzymes. Genetic studies indicated that MacA, OmcB, OmcF, OmcG, OmcH, OmcI, OmcJ, OmcM, OmcV and PccH, the putative Cbc5 complex subunit CbcC and the putative Cbc3 complex subunit CbcV are important for reduction of Fe(III) oxide but not essential for Mn(IV) oxide reduction. Gene expression patterns for Geobacter uraniireducens were similar. These results demonstrate that the physiology of Fe(III)-reducing bacteria differs significantly during growth on different insoluble and soluble electron acceptors and emphasize the importance of c-type cytochromes for extracellular electron transfer in G. sulfurreducens. PMID:23306674

  8. 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.

  9. Reductive biotransformation of Fe in shale limestone saprolite containing Fe(III) oxides and Fe(II)/Fe(III) phyllosilicates

    NASA Astrophysics Data System (ADS)

    Kukkadapu, Ravi K.; Zachara, John M.; Fredrickson, James K.; McKinley, James P.; Kennedy, David W.; Smith, Steven C.; Dong, Hailiang

    2006-07-01

    A <2.0-mm fraction of a mineralogically complex subsurface sediment containing goethite and Fe(II)/Fe(III) phyllosilicates was incubated with Shewanella putrefaciens (strain CN32) and lactate at circumneutral pH under anoxic conditions to investigate electron acceptor preference and the nature of the resulting biogenic Fe(II) fraction. Anthraquinone-2,6-disulfonate (AQDS), an electron shuttle, was included in select treatments to enhance bioreduction and subsequent biomineralization. The sediment was highly aggregated and contained two distinct clast populations: (i) a highly weathered one with "sponge-like" internal porosity, large mineral crystallites, and Fe-containing micas, and (ii) a dense, compact one with fine-textured Fe-containing illite and nano-sized goethite, as revealed by various forms of electron microscopic analyses. Approximately 10-15% of the Fe(III) TOT was bioreduced by CN32 over 60 d in media without AQDS, whereas 24% and 35% of the Fe(III) TOT was bioreduced by CN32 after 40 and 95 d in media with AQDS. Little or no Fe 2+, Mn, Si, Al, and Mg were evident in aqueous filtrates after reductive incubation. Mössbauer measurements on the bioreduced sediments indicated that both goethite and phyllosilicate Fe(III) were partly reduced without bacterial preference. Goethite was more extensively reduced in the presence of AQDS whereas phyllosilicate Fe(III) reduction was not influenced by AQDS. Biogenic Fe(II) resulting from phyllosilicate Fe(III) reduction remained in a layer-silicate environment that displayed enhanced solubility in weak acid. The mineralogic nature of the goethite biotransformation product was not determined. Chemical and cryogenic Mössbauer measurements, however, indicated that the transformation product was not siderite, green rust, magnetite, Fe(OH) 2, or Fe(II) adsorbed on phyllosilicate or bacterial surfaces. Several lines of evidence suggested that biogenic Fe(II) existed as surface associated phase on the residual goethite

  10. New Approaches to Characterizing Fe(III) Bioreduction by Hyperthermophiles: Combining Physiological Potential with Mineral Spectroscopies

    NASA Astrophysics Data System (ADS)

    Kashyap, S.; Sklute, E.; Dyar, M. D.; Holden, J. F.

    2015-12-01

    Fe(III) is a widely available electron acceptor in many mildly-reducing deep-sea hydrothermal vents and terrestrial hot springs. Dissimilatory iron reduction, or the extracellular reduction of Fe(III) to Fe(II), is an integral biogeochemical process at these sites. Most of what is known about microbial Fe(III) reduction, however, has been established for mesophiles rather than the hyperthermophiles that are ubiquitous in hot environments. Our study examines the rates and constraints of Fe(III) bioreduction by hyperthermophilic archaea in order to address the types of Fe(III) (oxyhydr)oxides that are favored for growth of hyperthermophiles, the rates of growth and Fe(II) production for these organisms, and the mineralogy of Fe(III) bioreduction and possible variations with electron acceptor. We synthesized a range of nanophase Fe(III) (oxyhydr)oxides (2-line-ferrihydrite, 6-line-ferrihydrite, lepidocrocite, hematite, goethite, maghemite and akaganéite) and examined cell growth and Fe(II) production rates of Pyrodictium sp. Su06 and Pyrobaculum islandicum on the different Fe(III) (oxyhydr)oxides at 90°C and 95°C, respectively. Two different aggregate sizes of 2-line ferrihydrite and one of 6-line ferrihydrite were used to understand the effect of mineral aggregate size and shape on bioreduction. Direct cell counts and ferrozine assays were used to monitor cell growth and Fe(II) production respectively. Transformed mineral products were characterized using Mössbauer and attenuated total reflectance (ATR) spectroscopies. Preliminary results suggest that Pyrodictium sp. Su06 can only utilize 2-line ferrihydrite, producing up to 35 mM Fe(II) for smaller aggregates, and 10 mM Fe(II) for larger aggregates. P. islandicum on the other hand, can reduce 2-line-ferrihydrite, goethite, and lepidocrocite, producing up to 8 mM Fe(II) with ferrihydrite, 7 mM with lepidocrocite, and 2 mM with goethite as an electron acceptor. Initial results from Mössbauer and ATR spectra

  11. 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. PMID:26762391

  12. Reduction of Fe(III), Mn(IV), and Toxic Metals at 100°C by Pyrobaculum islandicum

    PubMed Central

    Kashefi, Kazem; Lovley, Derek R.

    2000-01-01

    It has recently been noted that a diversity of hyperthermophilic microorganisms have the ability to reduce Fe(III) with hydrogen as the electron donor, but the reduction of Fe(III) or other metals by these organisms has not been previously examined in detail. When Pyrobaculum islandicum was grown at 100°C in a medium with hydrogen as the electron donor and Fe(III)-citrate as the electron acceptor, the increase in cell numbers of P. islandicum per mole of Fe(III) reduced was found to be ca. 10-fold higher than previously reported. Poorly crystalline Fe(III) oxide could also serve as the electron acceptor for growth on hydrogen. The stoichiometry of hydrogen uptake and Fe(III) oxide reduction was consistent with the oxidation of 1 mol of hydrogen resulting in the reduction of 2 mol of Fe(III). The poorly crystalline Fe(III) oxide was reduced to extracellular magnetite. P. islandicum could not effectively reduce the crystalline Fe(III) oxide minerals goethite and hematite. In addition to using hydrogen as an electron donor for Fe(III) reduction, P. islandicum grew via Fe(III) reduction in media in which peptone and yeast extract served as potential electron donors. The closely related species P. aerophilum grew via Fe(III) reduction in a similar complex medium. Cell suspensions of P. islandicum reduced the following metals with hydrogen as the electron donor: U(VI), Tc(VII), Cr(VI), Co(III), and Mn(IV). The reduction of these metals was dependent upon the presence of cells and hydrogen. The metalloids arsenate and selenate were not reduced. U(VI) was reduced to the insoluble U(IV) mineral uraninite, which was extracellular. Tc(VII) was reduced to insoluble Tc(IV) or Tc(V). Cr(VI) was reduced to the less toxic, less soluble Cr(III). Co(III) was reduced to Co(II). Mn(IV) was reduced to Mn(II) with the formation of manganese carbonate. These results demonstrate that biological reduction may contribute to the speciation of metals in hydrothermal environments and could

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

    PubMed

    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

    2013-04-16

    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 10(3) 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 10(3) 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.

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

    NASA Astrophysics Data System (ADS)

    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.

    2013-04-01

    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.

  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. 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.

  17. Enhanced natural attenuation of BTEX in the nitrate-reducing environment by different electron acceptors.

    PubMed

    Zhao, Yongsheng; Qu, Dan; Hou, Zhimin; Zhou, Rui

    2015-01-01

    Enhancing natural attenuation of benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater is a potential remediation technology. This study focused on selecting appropriate electron acceptors to promote BTEX degradation in a nitrate-reducing environment. Nitrate-reducing soil was obtained from simulated BTEX-contaminated column. Enhancing experiments were conducted in the microcosm with nitrate-reducing material and simulated BTEX-polluted groundwater to investigate the promoting feasibility of adding dissolved oxygen (DO), nitrate, chelated Fe(III), and sulphate as electron acceptors. The concentrations of BTEX, electron acceptors, and their reducing products were measured. The order of promoting BTEX degradation with four electron acceptors was nitrate>sulphate>chelated Fe(III)>DO, and the first-order decay coefficients were 0.0432, 0.0333, 0.0240, and 0.0155, respectively. Nitrate, sulphate, and chelated Fe(III) enhanced attenuation. Nitrate was the most effective electron acceptor under nitrate-reducing conditions. Selecting proper electron acceptor is significant in promoting BTEX degradation according to the biogeochemical characteristics of local underground environment.

  18. 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. PMID:22092936

  19. Shewanella oneidensis MR-1-Induced Fe(III) Reduction Facilitates Roxarsone Transformation.

    PubMed

    Chen, Guowei; Ke, Zhengchen; Liang, Tengfang; Liu, Li; Wang, Gang

    2016-01-01

    Although microbial activity and associated iron (oxy)hydroxides are known in general to affect the environmental dynamics of 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone), the mechanistic understanding of the underlying biophysico-chemical processes remains unclear due to limited experimental information. We studied how Shewanella oneidensis MR-1 -a widely distributed metal-reducing bacterium, in the presence of dissolved Fe(III), affects roxarsone transformations and biogeochemical cycling in a model aqueous system. The results showed that the MR-1 strain was able to anaerobically use roxarsone as a terminal electron acceptor and to convert it to a single product, 3-amino-4-hydroxybenzene arsonic acid (AHBAA). The presence of Fe(III) stimulated roxarsone transformation via MR-1-induced Fe(III) reduction, whereby the resulting Fe(II) acted as an efficient reductant for roxarsone transformation. In addition, the subsequent secondary Fe(III)/Fe(II) mineralization created conditions for adsorption of organoarsenic compounds to the yielded precipitates and thereby led to arsenic immobilization. The study provided direct evidence of Shewanella oneidensis MR-1-induced direct and Fe(II)-associated roxarsone transformation. Quantitative estimations revealed a candidate mechanism for the early-stage environmental dynamics of roxarsone in nature, which is essential for understanding the environmental dynamics of roxarsone and successful risk assessment. PMID:27100323

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

    SciTech Connect

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

    2013-04-16

    The mineral respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decaheme cytochromes brought together inside a transmembrane porin to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system that contains methyl viologen as an internalised electron carrier has been 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, direct electron transfer from the interior through MtrCAB to solid-phase Fe(III) oxides was demonstrated. The observed rates of conduction through the protein complex were 2 to 3 orders of magnitude higher than that observed in whole cells, demonstrating that direct electron exchange between MtrCAB and Fe(III) oxides is efficient enough to support in-vivo, anaerobic, solid phase iron respiration.

  1. Shewanella oneidensis MR-1-Induced Fe(III) Reduction Facilitates Roxarsone Transformation

    PubMed Central

    Chen, Guowei; Ke, Zhengchen; Liang, Tengfang; Liu, Li; Wang, Gang

    2016-01-01

    Although microbial activity and associated iron (oxy)hydroxides are known in general to affect the environmental dynamics of 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone), the mechanistic understanding of the underlying biophysico-chemical processes remains unclear due to limited experimental information. We studied how Shewanella oneidensis MR-1 –a widely distributed metal-reducing bacterium, in the presence of dissolved Fe(III), affects roxarsone transformations and biogeochemical cycling in a model aqueous system. The results showed that the MR-1 strain was able to anaerobically use roxarsone as a terminal electron acceptor and to convert it to a single product, 3-amino-4-hydroxybenzene arsonic acid (AHBAA). The presence of Fe(III) stimulated roxarsone transformation via MR-1-induced Fe(III) reduction, whereby the resulting Fe(II) acted as an efficient reductant for roxarsone transformation. In addition, the subsequent secondary Fe(III)/Fe(II) mineralization created conditions for adsorption of organoarsenic compounds to the yielded precipitates and thereby led to arsenic immobilization. The study provided direct evidence of Shewanella oneidensis MR-1-induced direct and Fe(II)-associated roxarsone transformation. Quantitative estimations revealed a candidate mechanism for the early-stage environmental dynamics of roxarsone in nature, which is essential for understanding the environmental dynamics of roxarsone and successful risk assessment. PMID:27100323

  2. 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

  3. 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

  4. Oxygen as Acceptor.

    PubMed

    Borisov, Vitaliy B; Verkhovsky, Michael I

    2015-01-01

    Like most bacteria, Escherichia coli has a flexible and branched respiratory chain that enables the prokaryote to live under a variety of environmental conditions, from highly aerobic to completely anaerobic. In general, the bacterial respiratory chain is composed of dehydrogenases, a quinone pool, and reductases. Substrate-specific dehydrogenases transfer reducing equivalents from various donor substrates (NADH, succinate, glycerophosphate, formate, hydrogen, pyruvate, and lactate) to a quinone pool (menaquinone, ubiquinone, and dimethylmenoquinone). Then electrons from reduced quinones (quinols) are transferred by terminal reductases to different electron acceptors. Under aerobic growth conditions, the terminal electron acceptor is molecular oxygen. A transfer of electrons from quinol to O₂ is served by two major oxidoreductases (oxidases), cytochrome bo₃ encoded by cyoABCDE and cytochrome bd encoded by cydABX. Terminal oxidases of aerobic respiratory chains of bacteria, which use O₂ as the final electron acceptor, can oxidize one of two alternative electron donors, either cytochrome c or quinol. This review compares the effects of different inhibitors on the respiratory activities of cytochrome bo₃ and cytochrome bd in E. coli. It also presents a discussion on the genetics and the prosthetic groups of cytochrome bo₃ and cytochrome bd. The E. coli membrane contains three types of quinones that all have an octaprenyl side chain (C₄₀). It has been proposed that the bo₃ oxidase can have two ubiquinone-binding sites with different affinities. "WHAT'S NEW" IN THE REVISED ARTICLE: The revised article comprises additional information about subunit composition of cytochrome bd and its role in bacterial resistance to nitrosative and oxidative stresses. Also, we present the novel data on the electrogenic function of appBCX-encoded cytochrome bd-II, a second bd-type oxidase that had been thought not to contribute to generation of a proton motive force in E

  5. Oxygen as Acceptor.

    PubMed

    Borisov, Vitaliy B; Verkhovsky, Michael I

    2015-01-01

    Like most bacteria, Escherichia coli has a flexible and branched respiratory chain that enables the prokaryote to live under a variety of environmental conditions, from highly aerobic to completely anaerobic. In general, the bacterial respiratory chain is composed of dehydrogenases, a quinone pool, and reductases. Substrate-specific dehydrogenases transfer reducing equivalents from various donor substrates (NADH, succinate, glycerophosphate, formate, hydrogen, pyruvate, and lactate) to a quinone pool (menaquinone, ubiquinone, and dimethylmenoquinone). Then electrons from reduced quinones (quinols) are transferred by terminal reductases to different electron acceptors. Under aerobic growth conditions, the terminal electron acceptor is molecular oxygen. A transfer of electrons from quinol to O₂ is served by two major oxidoreductases (oxidases), cytochrome bo₃ encoded by cyoABCDE and cytochrome bd encoded by cydABX. Terminal oxidases of aerobic respiratory chains of bacteria, which use O₂ as the final electron acceptor, can oxidize one of two alternative electron donors, either cytochrome c or quinol. This review compares the effects of different inhibitors on the respiratory activities of cytochrome bo₃ and cytochrome bd in E. coli. It also presents a discussion on the genetics and the prosthetic groups of cytochrome bo₃ and cytochrome bd. The E. coli membrane contains three types of quinones that all have an octaprenyl side chain (C₄₀). It has been proposed that the bo₃ oxidase can have two ubiquinone-binding sites with different affinities. "WHAT'S NEW" IN THE REVISED ARTICLE: The revised article comprises additional information about subunit composition of cytochrome bd and its role in bacterial resistance to nitrosative and oxidative stresses. Also, we present the novel data on the electrogenic function of appBCX-encoded cytochrome bd-II, a second bd-type oxidase that had been thought not to contribute to generation of a proton motive force in E

  6. Nontronite (NAu-1) Structure Associated with Microbial Fe(III) Reduction in Various Redox Conditions

    NASA Astrophysics Data System (ADS)

    Koo, T.; Kim, S.; Kim, J.

    2011-12-01

    Shewanella oneidensis MR-1 respires the structural Fe(III) of smectite and promotes illite formation in O2-free environment (Kostka et al., 1996, Kim et al., 2004). Since S. oneidensis is a facultative iron reducing bacterium, it is crucial to understand the structural changes induced by bio-reduction of structural Fe(III) in various redox conditions. Furthermore, the changes in cation exchange capacity (CEC) of bio-reduced nontronite upon the modification of mineral structure has not been extensively studied in terms of Fe-cycling. In this present study, we reported the evolution of nontronite structure at various time points in various redox conditions and corresponding CEC upon reduction and re-oxidation. S. oneidensis MR-1 was incubated in M1 medium with Na-lactate as the electron donor and Fe in nontronite (NAu-1) as the sole electron acceptor at pH 7 in anaerobic chamber for 3 hrs, 12 hrs, 1 day, 2 days, 4 days, 7 days, 14 days, and 21 days. O2 gas bubbling was then applied to the sample at each time point for 24 hours for re-oxidation. The triplet samples at each time point for both reduction and re-oxidation experiments were prepared. The extent of Fe(III) reduction measured by 1,10-phenanthroline method (Stucki and Anderson, 1981) indicated that the structural Fe(III) was reduced up to 8.8% of total Fe(III) within 21 days. XRD data with various treatments such as air dried, glycolated and lithium-saturated showed that K-nontronite may be formed because no discrete 10-Å illite peak was observed in Li-saturated sample upon glycolation. The CEC increased from 747 meg/kg to 1145 meg/kg during Fe(III) reduction and decreased to 954 meg/kg upon re-oxidation, supporting the possible formation of K-nontronite. The direct observation by electron microscopy verified the structural changes in nontonite in various redox conditions. The long-term experiment for 6 months, is in progress in anaerobic chamber, and results will be discussed. Kim, J. W., Dong, H., Seabaugh

  7. Inhibition of NO3− and NO2− Reduction by Microbial Fe(III) Reduction: Evidence of a Reaction between NO2− and Cell Surface-Bound Fe2+

    PubMed Central

    Coby, Aaron J.; Picardal, Flynn W.

    2005-01-01

    A recent study (D. C. Cooper, F. W. Picardal, A. Schimmelmann, and A. J. Coby, Appl. Environ. Microbiol. 69:3517-3525, 2003) has shown that NO3− and NO2− (NOx−) reduction by Shewanella putrefaciens 200 is inhibited in the presence of goethite. The hypothetical mechanism offered to explain this finding involved the formation of a Fe(III) (hydr)oxide coating on the cell via the surface-catalyzed, abiotic reaction between Fe2+ and NO2−. This coating could then inhibit reduction of NOx− by physically blocking transport into the cell. Although the data in the previous study were consistent with such an explanation, the hypothesis was largely speculative. In the current work, this hypothesis was tested and its environmental significance explored through a number of experiments. The inhibition of ∼3 mM NO3− reduction was observed during reduction of a variety of Fe(III) (hydr)oxides, including goethite, hematite, and an iron-bearing, natural sediment. Inhibition of oxygen and fumarate reduction was observed following treatment of cells with Fe2+ and NO2−, demonstrating that utilization of other soluble electron acceptors could also be inhibited. Previous adsorption of Fe2+ onto Paracoccus denitrificans inhibited NOx− reduction, showing that Fe(II) can reduce rates of soluble electron acceptor utilization by non-iron-reducing bacteria. NO2− was chemically reduced to N2O by goethite or cell-sorbed Fe2+, but not at appreciable rates by aqueous Fe2+. Transmission and scanning electron microscopy showed an electron-dense, Fe-enriched coating on cells treated with Fe2+ and NO2−. The formation and effects of such coatings underscore the complexity of the biogeochemical reactions that occur in the subsurface. PMID:16151113

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

    SciTech Connect

    Richardson, David J.; Edwards, Marcus; White, Gaye F.; Baiden, Nanakow; Hartshorne, Robert S.; Fredrickson, Jim K.; Shi, Liang; Zachara, John M.; Gates, Andrew J.; Butt, Julea N.; Clarke, Thomas

    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 features 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.

  9. 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

  10. Role of "electron shuttles" in the bioreduction of Fe(III) oxides in humid forest tropical soils.

    NASA Astrophysics Data System (ADS)

    Peretyazhko, T.; Sposito, G.

    2004-12-01

    Dissimilatory iron-reducing bacteria (DIRB) can reduce Fe(III) oxides either by direct contact between the organisms and the oxide surface or by indirect mechanisms not involving contact. These latter mechanisms can include (i) "electron shuttling" or (ii) soluble Fe(III) complexation with subsequent reduction. In the presence of humic substances, indirect Fe(III) reduction occurs, particularly by mechanism (i). Important electron-accepting groups in humic substances include quinone moieties, complexed Fe(III) and conjugated aromatic moieties. A model compound frequently used to study mechanism (i) is anthraquinone-2,6-disulfonate (AQDS), which is believed to function as an "electron shuttle" in a manner similar to humic substances. We are currently investigating Fe(III) reduction in humid tropical forest soils as affected by "electron shuttles," using AQDS and humic substances in our experiments. The soil samples were collected at the bottom of a toposequence in the Luquillo Experimental Forest, Puerto Rico. Development of anaerobic conditions in these soils occurs due to high precipitation and runoff water inputs. Fourteen-day anoxic incubations of soil suspensions amended with AQDS showed enhanced production of both soluble and particulate forms of Fe(II) as compared to non-amended soil suspensions. Our data indicated clearly that DIRB in the soil could utilize added "electron shuttles" effectively to reduce Fe(III). To examine factors controlling Fe(III) reduction by humic acid (HA), three IHSS HA samples (soil, peat and Leonardite) were both abiotically reduced by H2 treatment and microbially reduced by incubation with a filtrate from a soil suspension, then titrated with three different oxidants (iodine, cyanoferrate, and ferric citrate) to provide chemical and biological estimates of electron-accepting capacity at pH 5 and 7. The results will be discussed in terms of the three oxidants used, the properties of the HA samples, pH, and the effects of chemical

  11. 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.

  12. Competition between Methane and Alkylbenzenes for Electron Acceptors during Natural Attenuation of Crude Oil in the Subsurface

    NASA Astrophysics Data System (ADS)

    Bekins, B. A.; Amos, R. T.; Cozzarelli, I.; Voytek, M. A.

    2009-12-01

    At a crude-oil spill site near the town of Bemidji, MN, entrapped oil is present at residual saturations exceeding 10% in the vadose zone and floating at the water table at saturations of 30-60%. The degradable fraction of the light crude oil includes n-alkanes, aromatics, and alkyl-cyclohexanes. Together these compounds constitute a reduced carbon concentration at least 500 times greater than is present in the dissolved hydrocarbon groundwater plume comprised mainly of aromatics. Methanogenic degradation of the stationary oil body has been occurring for at least 20 years providing a continuous supply of methane emanating from the oil. Transport of methane away from the oil body occurs in both the vapor phase through the vadose zone and in the dissolved phase with the groundwater flow. Within the vadose zone the supply of oxygen and other electron acceptors from the surface is completely consumed by the process of methane oxidation in a zone 2-3 meters above the water table. In the groundwater, the 1 ppm contour of the methane plume extends beyond the 0.5 ppb contour for benzene, which is located at the aerobic/anaerobic boundary in the plume approximately 120 m downgradient of the oil body. Between 75 m and 120 m downgradient, methane concentrations decrease steadily from >0.6 mmol/L to <0.06 mmol/L, accompanied by increases in the δ13C-CH4 indicating that methane attenuation occurs through microbially-mediated oxidation. Anaerobic methane oxidation under iron-reducing conditions has recently been demonstrated by Beal et al. (Science, 325, 184, 2009) and is indicated at this site by several lines of evidence. In the methane oxidation zone, values of bioavailable Fe(III) extracted from the sediments averaged 8 mmol/kg (n=16), or >8 times the amount required to degrade 0.5 mmol methane, while all other electron acceptors together can account for complete oxidation of only 0.07 mmol (sulfate <0.06 mmol/L, dissolved oxygen <3 µmol/L, and nitrate <0.02 mmol

  13. 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

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

    2002-12-01

    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 (10(8) 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 delta-Proteobacteria (members of the Geobacteraceae). Results indicate that growth with smectitic Fe(III) is similar in magnitude to that with Fe(III

  14. 2012 ELECTRON DONOR-ACCEPTOR INTERACTIONS GORDON RESEARCH CONFERENCE, AUGUST 5-10, 2012

    SciTech Connect

    McCusker, James

    2012-08-10

    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.

  15. 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.; Bond, Daniel R.

    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

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

    SciTech Connect

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

    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 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. Redox potentials that trigger these behaviors mirror those of metal acceptors common in subsurface environments where Geobacter is found.

  17. Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor-Doped Pb-Based Ferroelectrics.

    PubMed

    Batuk, Dmitry; Batuk, Maria; Tsirlin, Alexander A; Hadermann, Joke; Abakumov, Artem M

    2015-12-01

    The defect chemistry of the ferroelectric material PbTiO3 after doping with Fe(III) acceptor ions is reported. Using advanced transmission electron microscopy and powder X-ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7% (material composition approximately ABO2.95), the oxygen vacancies are trapped into extended planar defects, specifically crystallographic shear planes. We investigate the evolution of these defects upon doping and unravel their detailed atomic structure using the formalism of superspace crystallography, thus unveiling their role in nonstoichiometry in the Pb-based perovskites.

  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. Evidence for the aquatic binding of arsenate by natural organic matter-suspended Fe(III)

    USGS Publications Warehouse

    Ritter, K.; Aiken, G.R.; Ranville, J.F.; Bauer, M. E.; Macalady, D.L.

    2006-01-01

    Dialysis experiments with arsenate and three different NOM samples amended with Fe(III) showed evidence confirming the formation of aquatic arsenate-Fe(III)-NOM associations. A linear relationship was observed between the amount of complexed arsenate and the Fe(III) content of the NOM. The dialysis results were consistent with complex formation through ferric iron cations acting as bridges between the negatively charged arsenate and NOM functional groups and/or a more colloidal association, in which the arsenate is bound by suspended Fe(III)-NOM colloids. Sequential filtration experiments confirmed that a significant proportion of the iron present at all Fe/C ratios used in the dialysis experiments was colloidal in nature. These colloids may include larger NOM species that are coagulated by the presence of chelated Fe(III) and/or NOM-stabilized ferric (oxy)hydroxide colloids, and thus, the solution-phase arsenate-Fe(III)-NOM associations are at least partially colloidal in nature. ?? 2006 American Chemical Society.

  20. Influence of Biogenic Fe(II) on the Extent of Microbial Reduction of Fe(III) in Clay Minerals Nontronite, Illite, and Chlorite

    SciTech Connect

    Jaisi, Deb P.; Dong, Hailiang; Liu, Chongxuan

    2007-03-01

    Microbial reduction of Fe(III) in clay minerals is an important process that affects properties of clay-rich materials and iron biogeochemical cycling in natural environments. Microbial reduction often ceases before all Fe(III) in clay minerals is exhausted. The factors causing the cessation are, however, not well understood. The objective of this study was to assess the role of biogenic Fe(II) in microbial reduction of Fe(III) in various clay minerals. Bioreduction experiments were performed in a batch system, where lactate was used as the sole electron donor, Fe(III) in clay minerals as the sole electron acceptor, and Shewanella putrefaciens CN32 as the mediator with and without an electron shuttle AQDS. Our results showed that bioreduction activity ceased within two weeks with variable extents of bioreduction of structural Fe(III) in clay minerals. When fresh CN32 cells were added to the old cultures (6 months), bioreduction resumed and extents increased. This result indicated that the previous cessation of Fe(III) bioreduction was not necessarily due to the exhaustion of bioavailable Fe(III) in the mineral structure, and suggested that the changes of cell physiology or solution chemistry, such as Fe(II) production during microbial reduction, affected the extent of bioreduction. To investigate the effect of Fe(II) production on Fe(III) bioreduction, a typical bioreduction process (consisting of lactate, clay, cells and AQDS) was separated into two steps: 1. AQDS was reduced by cells in the absence of clay but in the presence of variable Fe(II) concentrations; 2. reduction of Fe(III) in clays by biogenic AH2DS in the absence of cells. The inhibitory effect of Fe(II) on CN32 activity was confirmed. TEM analysis revealed a thick electron dense halo surrounding the cell surfaces that most likely resulted from Fe(II) sorption/precipitation. Such electron dense materials might have blocked or interfered electron transfers on cell surfaces. The inhibitory effect of Fe

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

    USGS Publications Warehouse

    Seabaugh, J.L.; Dong, H.; Kukkadapu, R.K.; Eberl, D.D.; Morton, J.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 Mo??ssbauer 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. Mo??ssbauer 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

  2. Dynamics of iron-acceptor-pair formation in co-doped silicon

    SciTech Connect

    Bartel, T.; Gibaja, F.; Graf, O.; Gross, D.; Kaes, M.; Heuer, M.; Kirscht, F.; Möller, C.; Lauer, K.

    2013-11-11

    The pairing dynamics of interstitial iron and dopants in silicon co-doped with phosphorous and several acceptor types are presented. The classical picture of iron-acceptor pairing dynamics is expanded to include the thermalization of iron between different dopants. The thermalization is quantitatively described using Boltzmann statistics and different iron-acceptor binding energies. The proper understanding of the pairing dynamics of iron in co-doped silicon will provide additional information on the electronic properties of iron-acceptor pairs and may become an analytical method to quantify and differentiate acceptors in co-doped silicon.

  3. Acceptors in ZnO

    SciTech Connect

    Mccluskey, Matthew D.; Corolewski, Caleb; Lv, Jinpeng; Tarun, Marianne C.; Teklemichael, Samuel T.; Walter, Eric D.; Norton, M. G.; Harrison, Kale W.; Ha, Su Y.

    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 peak 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.

  4. Acceptors in ZnO

    SciTech Connect

    McCluskey, Matthew D. Corolewski, Caleb D.; Lv, Jinpeng; Tarun, Marianne C.; Teklemichael, Samuel T.; Walter, Eric D.; Norton, M. Grant; Harrison, Kale W.; Ha, Su

    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 indicates these point defects have acceptor levels 3.2, 1.4, 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 MoO{sub 2} contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals is attributed to an acceptor, which may involve a Zn vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g{sub ⊥} = 2.0015 and g{sub //} = 2.0056, along with an isotropic center at g = 2.0035.

  5. Alkyl Chlorides as Hydrogen Bond Acceptors

    SciTech Connect

    Nadas, Janos I; Vukovic, Sinisa; Hay, Benjamin

    2012-01-01

    To gain an understanding of the role of an alkyl chloride as a hydrogen bond acceptor, geometries and interaction energies were calculated at the MP2/aug-cc-pVDZ level of theory for complexes between ethyl chloride and representative hydrogen donor groups. The results establish that these donors, which include hydrogen cyanide, methanol, nitrobenzene, pyrrole, acetamide, and N-methylurea, form X-H {hor_ellipsis} Cl hydrogen bonds (X = C, N, O) of weak to moderate strength, with {Delta}E values ranging from -2.8 to -5.3 kcal/mol.

  6. The influence of Fe(III) on oil biodegradation in excessively moistened soils and sediments

    NASA Astrophysics Data System (ADS)

    Vodyanitskii, Yu. N.; Trofimov, S. Ya.; Shoba, S. A.

    2015-07-01

    Soils are self-purified from oil slowly, in the north, in particular, where hydromorphic conditions and low temperatures hinder the process. Oxidation of oil hydrocarbons depends on the type of electron acceptors and decreases in the following sequence: denitrification > Mn4+ reduction > Fe3+ reduction > sulfate reduction > methanogenesis. Usually, not all of these redox reactions develop in contaminated excessively moistened soils and sediments. Fe(III) reduction and methanogenesis are the most common: the latter is manifested near the contamination source, while the former develops in less contaminated areas. Fe reduction hinders the methanogenesis. In oil-contaminated areas, Fe reduction is also combined with sulfate reduction, the latter intensifying Fe reduction due to the formation of iron sulfides. Concurrently with oil degradation in excessively moistened soils and sediments, the composition of iron compounds changes due to the increasing Fe(II) share magnetite, as well as siderite and ferrocalcite (in calcareous deposits), and iron sulfides (in S-containing medium) are formed.

  7. A putative multicopper protein secreted by an atypical type II secretion system involved in the reduction of insoluble electron acceptors in Geobacter sulfurreducens.

    PubMed

    Mehta, Teena; Childers, Susan E; Glaven, Richard; Lovley, Derek R; Mester, Tünde

    2006-08-01

    Extracellular electron transfer onto Fe(III) oxides in Geobacter sulfurreducens is considered to require proteins that must be exported to the outer surface of the cell. In order to investigate this, the putative gene for OxpG, the pseudopilin involved in a type II general secretion pathway of Gram-negative bacteria, was deleted. The mutant was unable to grow with insoluble Fe(III) oxide as the electron acceptor. Growth on soluble Fe(III) was not affected. An analysis of proteins that accumulated in the periplasm of the oxpG mutant, but not in the wild-type, led to the identification of a secreted protein, OmpB. OmpB is predicted to be a multicopper protein, with highest homology to the manganese oxidase, MofA, from Leptothrix discophora. OmpB contains a potential Fe(III)-binding site and a fibronectin type III domain, suggesting a possible role for this protein in accessing Fe(III) oxides. OmpB was localized to the membrane fraction of G. sulfurreducens and in the supernatant of growing cultures, consistent with the type II secretion system exporting OmpB. A mutant in which ompB was deleted had the same phenotype as the oxpG mutant, suggesting that the failure to export OmpB was responsible for the inability of the oxpG-deficient mutant to reduce Fe(III) oxide. This is the first report that proposes a role for a multicopper oxidase-like protein in an anaerobic organism. These results further emphasize the importance of outer-membrane proteins in Fe(III) oxide reduction and suggest that outer-membrane proteins other than c-type cytochromes are required for Fe(III) oxide reduction in Geobacter species. PMID:16849792

  8. 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.

  9. Soluble Iron as an In Situ Indicator of the Redox State of Humic Substances in Arctic Soil: Implications for Seasonal Regeneration of Oxidized Terminal Electron Acceptors

    NASA Astrophysics Data System (ADS)

    Lipson, D.; Zlamal, J. E.; Srinivas, A. J.; Raab, T. K.

    2014-12-01

    Ferric iron (Fe(III)) and humic substances (HS) are important terminal electron acceptors for anaerobic respiration in wet tundra soils of the Arctic Coastal Plain near Barrow, Alaska. These soils are rich in both solid phase Fe minerals (including oxides such as ferrihydrite and goethite and other minerals with reduced or mixed valence such as siderite and magnetite) and soluble Fe, chelated by siderophores and other small organic molecules. This latter pool may also include nanocolloidal Fe: extremely fine-grained minerals that pass through a 0.2 micron filter. Both the solid phase and aqueous Fe pools undergo seasonal changes in redox state as a result of biological reduction by Fe-reducing microorganisms and oxidation by a variety of potential mechanisms, both abiotic and biotic. These redox cycles of solid and aqueous pools are not in phase: solid phase Fe became progressively more reduced from mid- to late summer, while aqueous phase Fe became reduced over the first half of the summer. It is well-known that HS interact with Fe, and that HS can act as electron shuttles in the reduction of Fe oxides. In other ecosystems chelated Fe(III) has been incubated with soil samples and the resulting Fe(II) produced is used as an indicator of the reducing power of HS. In these Fe-rich Arctic soils, HS are continuously in contact with chelated Fe, and therefore we interpret the redox state of this pool as an indicator of HS redox status. To verify this we conducted redox titrations of extracted HS with both reduced and oxidized Fe chelates and showed that chelated Fe could interact with HS both as electron acceptor and donator. In a field experiment, the addition of oxidized humic acids to soils resulted in an immediate oxidation of the aqueous Fe pool within 24 hours, which we attribute to abiotic oxidation of Fe by HS, followed by a slow reduction of this pool over the next week, presumably due to biological Fe reduction of the HS/aqueous Fe pool. At the end of summer

  10. The structure and bonding of iron-acceptor pairs in silicon

    SciTech Connect

    Zhao, S.; Assali, L.V.C.; Kimerling, L.C.

    1995-08-01

    The highly mobile interstitial iron and Group III impurities (B, Al, Ga, In) form iron-acceptor pairs in silicon. Based on the migration kinetics and taking host silicon as a dielectric medium, we have simulated the pairing process in a static silicon lattice. Different from the conventional point charge ionic model, our phenomenological calculations include (1) a correction that takes into account valence electron cloud polarization which adds a short range, attractive interaction in the iron-acceptor pair bonding; and (2) silicon lattice relaxation due to the atomic size difference which causes a local strain field. Our model explains qualitatively (1) trends among the iron-acceptor pairs revealing an increase of the electronic state hole emission energy with increasing principal quantum number of acceptor and decreasing pair separation distance; and (2) the stable and metastable sites and configurational symmetries of the iron-acceptor pairs. The iron-acceptor pairing and bonding mechanism is also discussed.

  11. Higher excited states of acceptors in cubic semiconductors

    NASA Astrophysics Data System (ADS)

    Said, M.; Kanehisa, M. A.; Balkanski, M.

    1986-02-01

    For the first time, higher excited states of shallow acceptors up to the 3s and 4s states are calculated based on the Balderschi and Lipari theory including the cubic correction. The eigenvalues and eigenvectors of the effective mass Hamiltonian for shallow acceptor states were obtained by the finite element method. The resultant sparse matrix is diagonalized by a newly developed Saad's method based on Arnoldi's algorithm. Comparison with experimental spectra on ZnTe:Li and ZnTe:P gives best valence band parameters for ZnTe; μ = 0.60 and δ = 0.12.

  12. Donor-acceptor chemistry in the main group.

    PubMed

    Rivard, Eric

    2014-06-21

    This Perspective article summarizes recent progress from our laboratory in the isolation of reactive main group species using a general donor-acceptor protocol. A highlight of this program is the use of carbon-based donors in combination with suitable Lewis acidic acceptors to yield stable complexes of parent Group 14 element hydrides (e.g. GeH2 and H2SiGeH2). It is anticipated that this strategy could be extended to include new synthetic targets from throughout the Periodic Table with possible applications in bottom-up materials synthesis and main group element catalysis envisioned. PMID:24788390

  13. 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.

  14. Rapid Anaerobic Benzene Oxidation with a Variety of Chelated Fe(III) Forms.

    PubMed

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

    1996-01-01

    Fe(III) chelated to such compounds as EDTA, N-methyliminodiacetic 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.

  15. 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.

  16. Phthalimides as exceptionally efficient single electron transfer acceptors in reductive coupling reactions promoted by samarium diiodide.

    PubMed

    Vacas, Tatiana; Alvarez, Eleuterio; Chiara, Jose Luis

    2007-12-20

    Experimental and theoretical evidence shows that phthalimides are highly efficient single electron transfer acceptors in reactions promoted by samarium diiodide, affording ketyl radical anion intermediates, which participate in high-yielding inter- and intramolecular reductive coupling processes with different radicophiles including imides, oxime ethers, nitrones, and Michael acceptors.

  17. 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.

  18. Effect of nitrate enrichment and diatoms on the bioavailability of Fe(III) oxyhydroxide colloids in seawater.

    PubMed

    Liu, Feng-Jiao; Huang, Bang-Qin; Li, Shun-Xing; Zheng, Feng-Ying; Huang, Xu-Guang

    2016-03-01

    The photoconversion of colloidal iron oxyhydroxides was a significant source of bioavailable iron in coastal systems. Diatoms dominate phytoplankton communities in coastal and upwelling regions. Diatoms are often exposed to eutrophication. We investigated the effects of different species of diatom, cell density, illumination period, and nitrate additions on the bioavailability of Fe(III) oxy-hydroxide colloids in seawaters. With the increase of illumination period from 1 to 4 h, the ratios of concentrations of total dissolved Fe (DFe) to colloidal iron oxyhydroxides and Fe(II) to DFe increased up to 24.3% and 23.9% for seawater without coastal diatoms, 45.6% and 30.2% for Skeletonema costatum, 44.3% and 29.7% for Thalassiosira weissflogii, respectively. The photochemical activity of coastal diatoms themselves (excluding the dissolved organic matter secreted by algae) on the species transformation of iron in seawater (including the light-induced dissolution of Fe(III) oxyhydroxide colloids and the photo-reduction of Fe(III) into Fe(II)) was confirmed for the first time. There was no significant difference of the ability of S. costatum and Thalassiosira weissflogii on the photoconversion of colloidal iron oxyhydroxides. The photoproduction of dissolved Fe(II) and DFe in the seawater with or without diatoms could be depressed by the nitrate addition.

  19. Effect of nitrate enrichment and diatoms on the bioavailability of Fe(III) oxyhydroxide colloids in seawater.

    PubMed

    Liu, Feng-Jiao; Huang, Bang-Qin; Li, Shun-Xing; Zheng, Feng-Ying; Huang, Xu-Guang

    2016-03-01

    The photoconversion of colloidal iron oxyhydroxides was a significant source of bioavailable iron in coastal systems. Diatoms dominate phytoplankton communities in coastal and upwelling regions. Diatoms are often exposed to eutrophication. We investigated the effects of different species of diatom, cell density, illumination period, and nitrate additions on the bioavailability of Fe(III) oxy-hydroxide colloids in seawaters. With the increase of illumination period from 1 to 4 h, the ratios of concentrations of total dissolved Fe (DFe) to colloidal iron oxyhydroxides and Fe(II) to DFe increased up to 24.3% and 23.9% for seawater without coastal diatoms, 45.6% and 30.2% for Skeletonema costatum, 44.3% and 29.7% for Thalassiosira weissflogii, respectively. The photochemical activity of coastal diatoms themselves (excluding the dissolved organic matter secreted by algae) on the species transformation of iron in seawater (including the light-induced dissolution of Fe(III) oxyhydroxide colloids and the photo-reduction of Fe(III) into Fe(II)) was confirmed for the first time. There was no significant difference of the ability of S. costatum and Thalassiosira weissflogii on the photoconversion of colloidal iron oxyhydroxides. The photoproduction of dissolved Fe(II) and DFe in the seawater with or without diatoms could be depressed by the nitrate addition. PMID:26766021

  20. A genetic system for Geobacter metallireducens: role of the flagellin and pilin in the reduction of Fe(III) oxide

    SciTech Connect

    Tremblay, PL; Aklujkar, M; Leang, C; Nevin, KP; Lovley, D

    2011-11-27

    Geobacter metallireducens is an important model organism for many novel aspects of extracellular electron exchange and the anaerobic degradation of aromatic compounds, but studies of its physiology have been limited by a lack of techniques for gene deletion and replacement. Therefore, a genetic system was developed for G. metallireducens by making a number of modifications in the previously described approach for homologous recombination in Geobacter sulfurreducens. Critical modifications included, among others, a 3.5-fold increased in the quantity of electrotransformed linear DNA and the harvesting of cells at early-log. The Cre-lox recombination system was used to remove an antibiotic resistance cassette from the G. metallireducens chromosome permitting the generation of multiple mutations in the same strain. Deletion of the gene fliC, which encodes the flagellin protein, resulted in a strain that did not produce flagella, was non-motile, and was defective for the reduction of insoluble Fe(III). Deletion of pilA, which encodes the structural protein of the type IV pili, inhibited the production of lateral pili as well as Fe(III) oxide reduction and electron transfer to an electrode. These results demonstrate the importance of flagella and pili in the reduction of insoluble Fe(III) by G. metallireducens and provide methods for additional genetic-based approaches for the study of G. metallireducens.

  1. Reduction of Fe(III) with sulfite in natural waters

    NASA Astrophysics Data System (ADS)

    Millero, F. J.; Gonzalez-Davila, M.; Santana-Casiano, J. M.

    1995-04-01

    The Fe(III) in marine aerosols and rainwaters can be reduced to Fe(II) by photochemical processes and by reactions with sulfite. In this paper, measurements of the rates of reduction of nanomolar levels of Fe(III) with sulfite (without O2) have been determined in NaCl and seawater solutions as a function of temperature (0° to 40°C), pH (2 to 6.8), ionic strength (I = 0.1 to 6 M), and composition (Na+, Mg2+, Ca2+, F-, Cl-, Br-, HCO3-, SO42-). The overall rate constant (k, M-1 min-1) for the reaction, Fe>(III>)+S>(IV>)>→k products, is given by d[Fe(III)]/dt = -k[Fe(III)] [S(IV)]. The reaction was found to be first order with respect to Fe(III) and S(IV). The rate constants as a function of pH increased from a pH = 2 to 4 and decreased at higher pH. The effect of temperature and ionic strength on the rates could be represented by log k = log k0 + AI0.5/(1 + I0.5), where A = -1.1 in NaCl and -2.2 in seawater and log k0 = 25.39 - 6,323/T. The energy of activation was found by 121±6 kJ mol-1. The measured rates in seawater as a function of salinity were lower than the rates in NaCl at the same ionic strength. Measurements in NaCl solutions with added sea-salt ions (Mg2+, Ca2+, F-, Br-, and SO42-) at pH = 3.5 indicate that the formation of inert FeF2+ may be responsible for the lower rates. The effect of changes in the composition on the rates was interpreted by examining the speciation of Fe(III) and S(IV). This analysis indicates that the rate-determining steps from a pH of 2.5 to 4.0 are FeOH2+ + HSO3- ↔ HOFeSO3H + and HOFeSO3H+>⟶k1FeOH++HSO3· and at pH of 4 to 6, the reactions Fe(OH)2+ + HSO3- ↔ (HO)2FeSO3H and >(HO>)2FeSO3H>⟶k2Fe>(OH>)2+HSO3· become important. The changes in the concentration of FeOH2+ and HSO3- as a function of pH and composition can account for most of the changes in the rates. These kinetic studies indicate that the rates of reduction of Fe(III) with S(IV) in acidic water droplets at natural levels of S(IV) may be an important

  2. Bright Solid-State Emission of Disilane-Bridged Donor-Acceptor-Donor and Acceptor-Donor-Acceptor Chromophores.

    PubMed

    Shimada, Masaki; Tsuchiya, Mizuho; Sakamoto, Ryota; Yamanoi, Yoshinori; Nishibori, Eiji; Sugimoto, Kunihisa; Nishihara, Hiroshi

    2016-02-24

    The development of disilane-bridged donor-acceptor-donor (D-Si-Si-A-Si-Si-D) and acceptor-donor-acceptor (A-Si-Si-D-Si-Si-A) compounds is described. Both types of compound showed strong emission (λem =ca. 500 and ca. 400 nm, respectively) in the solid state with high quantum yields (Φ: up to 0.85). Compound 4 exhibited aggregation-induced emission enhancement in solution. X-ray diffraction revealed that the crystal structures of 2, 4, and 12 had no intermolecular π-π interactions to suppress the nonradiative transition in the solid state.

  3. 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

    2016-01-01

    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. PMID:27533864

  4. Reaction-based reactive transport modeling of Fe(III)

    SciTech Connect

    Kemner, K.M.; Kelly, S.D.; Burgos, Bill; Roden, Eric

    2006-06-01

    This research project (started Fall 2004) was funded by a grant to Argonne National Laboratory, The Pennsylvania State University, and The University of Alabama in the Integrative Studies Element of the NABIR Program (DE-FG04-ER63914/63915/63196). Dr. Eric Roden, formerly at The University of Alabama, is now at the University of Wisconsin, Madison. Our project focuses on the development of a mechanistic understanding and quantitative models of coupled Fe(III)/U(VI) reduction in FRC Area 2 sediments. This work builds on our previous studies of microbial Fe(III) and U(VI) reduction, and is directly aligned with the Scheibe et al. NABIR FRC Field Project at Area 2.

  5. The contribution of Fe(III) and humic acid reduction to ecosystem respiration in drained thaw lake basins of the Arctic Coastal Plain

    NASA Astrophysics Data System (ADS)

    Lipson, David A.; Raab, Theodore K.; Goria, Dominic; Zlamal, Jaime

    2013-04-01

    research showed that anaerobic respiration using iron (Fe) oxides as terminal electron acceptor contributed substantially to ecosystem respiration (ER) in a drained thaw lake basin (DTLB) on the Arctic coastal plain. As DTLBs age, the surface organic layer thickens, progressively burying the Fe-rich mineral layers. We therefore hypothesized that Fe(III) availability and Fe reduction would decline with basin age. We studied four DTLBs across an age gradient, comparing seasonal changes in the oxidation state of dissolved and extractable Fe pools and the estimated contribution of Fe reduction to ER. The organic layer thickness did not strictly increase with age for these four sites, though soil Fe levels decreased with increasing organic layer thickness. However, there were surprisingly high levels of Fe minerals in organic layers, especially in the ancient basin where cryoturbation may have transported Fe upward through the profile. Net reduction of Fe oxides occurred in the latter half of the summer and contributed an estimated 40-45% to ecosystem respiration in the sites with the thickest organic layers and 61-63% in the sites with the thinnest organic layers. All sites had high concentrations of soluble Fe(II) and Fe(III), explained by the presence of siderophores, and this pool became progressively more reduced during the first half of the summer. Redox titrations with humic acid (HA) extracts and chelated Fe support our view that this pattern indicates the reduction of HA during this interval. We conclude that Fe(III) and HA reductions contribute broadly to ER in the Arctic coastal plain.

  6. 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.

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

    USGS Publications Warehouse

    Jaisi, D.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

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

    NASA Astrophysics Data System (ADS)

    Jaisi, Deb P.; Kukkadapu, Ravi K.; Eberl, Dennis D.; Dong, Hailiang

    2005-12-01

    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). Mössbauer 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. Mössbauer 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), Mössbauer 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. Mössbauer 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. Nanowires, Capacitors, and Other Novel Outer-Surface Components Involved in Electron Transfer to Fe(III) Oxides in Geobacter Species

    SciTech Connect

    Lovley, Derek, R.

    2008-12-22

    The overall goal of this project was to better understand the mechanisms by which Geobacter species transfer electrons outside the cell onto Fe(III) oxides. The rationale for this study was that Geobacter species are often the predominant microorganisms involved in in situ uranium bioremediation and the growth and activity of the Geobacter species during bioremediation is primarily supported by electron transfer to Fe(III) oxides. These studies greatly expanded the understanding of electron transfer to Fe(III). Novel concepts developed included the potential role of microbial nanowires for long range electron transfer in Geobacter species and the importance of extracytoplasmic cytochromes functioning as capacitors to permit continued electron transfer during the hunt for Fe(III) oxide. Furthermore, these studies provided target sequences that were then used in other studies to tract the activity of Geobacter species in the subsurface through monitoring the abundance of gene transcripts of the target genes. A brief summary of the major accomplishments of the project is provided.

  10. Isolation and microbial reduction of Fe(III) phyllosilicates from subsurface sediments

    SciTech Connect

    Wu, Tao; Shelobolina, Evgenya S.; Xu, Huifang; Konishi, Hiromi; Kukkadapu, Ravi K.; Roden, Eric E.

    2012-10-12

    Fe(III)-bearing phyllosilicates can be important sources of Fe(III) for dissimilatory microbial iron reduction in clay-rich anoxic soils and sediments. The goal of this research was to isolate Fe(III) phyllosilicate phases, and if possible, Fe(III) oxide phases, from a weathered shale saprolite sediment in order to permit experimentation with each phase in isolation. Physical partitioning by density gradient centrifugation did not adequately separate phyllosilicate and Fe(III) oxide phases (primarily nanoparticulate goethite). Hence we examined the ability of chemical extraction methods to remove Fe(III) oxides without significantly altering the properties of the phyllosilicates. XRD analysis showed that extraction with oxalate alone or oxalate in the presence of added Fe(II) altered the structure of Fe-bearing phyllosilicates in the saprolite. In contrast, citrate-bicarbonate-dithionite (CBD) extraction at room temperature and 80C led to minimal alteration of phyllosilicate structures. Reoxidation of CDB-extracted sediment with H2O2 restored phyllosilicate structure (i.e. d-spacing) and redox speciation to conditions similar to that in the pristine sediment. The extent of microbial (Geobacter sulfurreducens) reduction of Fe(III) phyllosilicates isolated by CDB extraction (ca. 16 %) was comparable to what took place in pristine sediments as determined by Mossbauer spectroscopy (ca. 18 % reduction). These results suggest that materials isolated by CDB extraction and H2O2 reoxidation are appropriate targets for detailed studies of natural soil/sediment Fe(III) phyllosilicate reduction.

  11. Effects of Fe(III) and organic matter additions on methanogenic activity and Fe(III) reduction in boreal lake and wetland sediments

    NASA Astrophysics Data System (ADS)

    Karvinen, Anu; Lehtinen, Lotta; Kankaala, Paula

    2013-04-01

    We studied potential methane production and Fe(III) reduction activity in lake sediments and wetland peat sampled from 14 sites in southern and eastern Finland. The concentration of total iron in the sediments and peat varied between 0.5 and 1200 ppm and their organic matter content (loss of ignition) varied between 1-98% of dry weight. Also the effects of added amorphous Fe(III) oxyhydroxide and organic matter (ammoniumacetate and/or sodiumacetate) on methanogenic and Fe(III) reduction activities were studied in anaerobic laboratory incubations (in vitro) lasting 5-20 days at 15 °C in darkness. Potential methane production and the effects of iron and acetate additions were highly variable between lake and peatland sites. The highest methanogenic potential was generally measured in productive littoral sites, especially in those dominated by Phragmites australis vegetation stands. In these sediments the total iron concentrations were high and acetate additions clearly increased methane production whereas Fe(III) additions decreased it. Our results demonstrate that microbial Fe(III) reduction plays an important role in the anaerobic organic matter decomposition in many boreal lakes.

  12. Biostimulation of iron reduction and subsequent oxidation of sediment containing Fe-silicates and Fe-oxides: effect of redox cycling on Fe(III) bioreduction.

    PubMed

    Komlos, John; Kukkadapu, Ravi K; Zachara, John M; Jaffé, Peter R

    2007-07-01

    Sediment containing a mixture of iron (Fe)-phases, including Fe-oxides (mostly Al-goethite) and Fe-silicates (illites and vermiculite) was bioreduced in a long-term flow through column experiment followed by re-oxidation with dissolved oxygen. The objective of this study was (a) to determine the nature of the re-oxidized Fe(III), and (b) to determine how redox cycling of Fe would affect subsequent Fe(III)-bioavailability. In addition, the effect of Mn on Fe(III) reduction was explored.(57)Fe-Mössbauer spectroscopy measurements showed that biostimulation resulted in partial reduction (20%) of silicate Fe(III) to silicate Fe(II) while the reduction of goethite was negligible. Furthermore, the reduction of Fe in the sediment was uniform throughout the column. When, after biostimulation, 3900 pore volumes of a solution containing dissolved oxygen was pumped through the column over a period of 81 days, approximately 46% of the reduced silicate Fe(II) was re-oxidized to silicate Fe(III). The Mössbauer spectra of the re-oxidized sample were similar to that of pristine sediment implying that Fe-mineralogy of the re-oxidized sediment was mineralogically similar to that of the pristine sediment. In accordance to this, batch experiments showed that Fe(III) reduction occurred at a similar rate although time until Fe(II) buildup started was longer in the pristine sediment than re-oxidized sediment under identical seeding conditions. This was attributed to oxidized Mn that acted as a temporary redox buffer in the pristine sediment. The oxidized Mn was transformed to Mn(II) during bioreduction but, unlike silicate Fe(II), was not re-oxidized when exposed to oxygen.

  13. The Geoglobus acetivorans genome: Fe(III) reduction, acetate utilization, autotrophic growth, and degradation of aromatic compounds in a hyperthermophilic archaeon.

    PubMed

    Mardanov, Andrey V; Slododkina, Galina B; Slobodkin, Alexander I; Beletsky, Alexey V; Gavrilov, Sergey N; Kublanov, Ilya V; Bonch-Osmolovskaya, Elizaveta A; Skryabin, Konstantin G; Ravin, Nikolai V

    2015-02-01

    Geoglobus acetivorans is a hyperthermophilic anaerobic euryarchaeon of the order Archaeoglobales isolated from deep-sea hydrothermal vents. A unique physiological feature of the members of the genus Geoglobus is their obligate dependence on Fe(III) reduction, which plays an important role in the geochemistry of hydrothermal systems. The features of this organism and its complete 1,860,815-bp genome sequence are described in this report. Genome analysis revealed pathways enabling oxidation of molecular hydrogen, proteinaceous substrates, fatty acids, aromatic compounds, n-alkanes, and organic acids, including acetate, through anaerobic respiration linked to Fe(III) reduction. Consistent with the inability of G. acetivorans to grow on carbohydrates, the modified Embden-Meyerhof pathway encoded by the genome is incomplete. Autotrophic CO2 fixation is enabled by the Wood-Ljungdahl pathway. Reduction of insoluble poorly crystalline Fe(III) oxide depends on the transfer of electrons from the quinone pool to multiheme c-type cytochromes exposed on the cell surface. Direct contact of the cells and Fe(III) oxide particles could be facilitated by pilus-like appendages. Genome analysis indicated the presence of metabolic pathways for anaerobic degradation of aromatic compounds and n-alkanes, although an ability of G. acetivorans to grow on these substrates was not observed in laboratory experiments. Overall, our results suggest that Geoglobus species could play an important role in microbial communities of deep-sea hydrothermal vents as lithoautotrophic producers. An additional role as decomposers would close the biogeochemical cycle of carbon through complete mineralization of various organic compounds via Fe(III) respiration.

  14. The Geoglobus acetivorans Genome: Fe(III) Reduction, Acetate Utilization, Autotrophic Growth, and Degradation of Aromatic Compounds in a Hyperthermophilic Archaeon

    PubMed Central

    Mardanov, Andrey V.; Slododkina, Galina B.; Slobodkin, Alexander I.; Beletsky, Alexey V.; Gavrilov, Sergey N.; Kublanov, Ilya V.; Bonch-Osmolovskaya, Elizaveta A.; Skryabin, Konstantin G.

    2014-01-01

    Geoglobus acetivorans is a hyperthermophilic anaerobic euryarchaeon of the order Archaeoglobales isolated from deep-sea hydrothermal vents. A unique physiological feature of the members of the genus Geoglobus is their obligate dependence on Fe(III) reduction, which plays an important role in the geochemistry of hydrothermal systems. The features of this organism and its complete 1,860,815-bp genome sequence are described in this report. Genome analysis revealed pathways enabling oxidation of molecular hydrogen, proteinaceous substrates, fatty acids, aromatic compounds, n-alkanes, and organic acids, including acetate, through anaerobic respiration linked to Fe(III) reduction. Consistent with the inability of G. acetivorans to grow on carbohydrates, the modified Embden-Meyerhof pathway encoded by the genome is incomplete. Autotrophic CO2 fixation is enabled by the Wood-Ljungdahl pathway. Reduction of insoluble poorly crystalline Fe(III) oxide depends on the transfer of electrons from the quinone pool to multiheme c-type cytochromes exposed on the cell surface. Direct contact of the cells and Fe(III) oxide particles could be facilitated by pilus-like appendages. Genome analysis indicated the presence of metabolic pathways for anaerobic degradation of aromatic compounds and n-alkanes, although an ability of G. acetivorans to grow on these substrates was not observed in laboratory experiments. Overall, our results suggest that Geoglobus species could play an important role in microbial communities of deep-sea hydrothermal vents as lithoautotrophic producers. An additional role as decomposers would close the biogeochemical cycle of carbon through complete mineralization of various organic compounds via Fe(III) respiration. PMID:25416759

  15. Analysis of Shewanella oneidensis Membrane Protein Expression in Response to Electron Acceptor Availability

    SciTech Connect

    Giometti, Carol S.; Khare, Tripti; Verberkmoes, Nathan; O'Loughlin, Ed; Lindberg, Carl; Thompson, Melissa; Hettich, Robert

    2006-04-05

    Shewanella oneidensis MR-1, a gram negative metal-reducing bacterium, can utilize a large number of electron acceptors. In the natural environment, S. oneidensis utilizes insoluble metal oxides as well as soluble terminal electron acceptors. The purpose of this ERSP project is to identify differentially expressed proteins associated with the membranes of S. oneidensis MR-1 cells grown with different electron acceptors, including insoluble metal oxides. We hypothesize that through the use of surface labeling, subcellular fractionation, and a combination of proteome analysis tools, proteins involved in the reduction of different terminal electron acceptors will be elucidated. We are comparing the protein profiles from cells grown with the soluble electron acceptors oxygen and fumarate and with those from cells grown with the insoluble iron oxides goethite, ferrihydrite and lepidocrocite. Comparison of the cell surface proteins isolated from cells grown with oxygen or anaerobically with fumarate revealed an increase in the abundance of over 25 proteins in anaerobic cells, including agglutination protein and flagellin proteins along with the several hypothetical proteins. In addition, the surface protein composition of cells grown with the insoluble iron oxides varies considerably from the protein composition observed with either soluble electron acceptor as well as between the different insoluble acceptors.

  16. Oligosaccharide synthesis by dextransucrase: new unconventional acceptors.

    PubMed

    Demuth, Kristin; Jördening, Hans Joachim; Buchholz, Klaus

    2002-11-01

    The acceptor reactions of dextransucrase offer the potential for a targeted synthesis of a wide range of di-, tri- and higher oligosaccharides by the transfer of a glucosyl group from sucrose to the acceptor. We here report on results which show that the synthetic potential of this enzyme is not restricted to 'normal' saccharides. Additionally functionalized saccharides, such as alditols, aldosuloses, sugar acids, alkyl saccharides, and glycals, and rather unconventional saccharides, such as fructose dianhydride, may also act as acceptors. Some of these acceptors even turned out to be relatively efficient: alpha-D-glucopyranosyl-(1-->5)-D-arabinonic acid, alpha-D-glucopyranosyl-(1-->4)-D-glucitol, alpha-D-glucopyranosyl-(1-->6)-D-glucitol, alpha-D-glucopyranosyl-(1-->6)-D-mannitol, alpha-D-fructofuranosyl-beta-D-fructofuranosyl-(1,2':2,3')-dianhydride, 1,5-anhydro-2-deoxy-D-arabino-hex-1-enitol ('D-glucal'), and may therefore be of interest for future applications of the dextransucrase acceptor reaction.

  17. Photoconductivity in donor-acceptor heterojunction organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Renshaw, C. K.; Zimmerman, J. D.; Lassiter, B. E.; Forrest, S. R.

    2012-08-01

    Organic photovoltaics (OPVs) differ from ideal inorganic solar cells due to their pronounced voltage dependence under reverse bias. This feature is commonly modeled in an ad hoc fashion by including a parallel junction resistance (Rp) that bypasses the heterojunction energy barrier between donor and acceptor. The existence of a finite Rp has variously been attributed to rough interfaces, pinhole defects, or to the electric field dependence of the dissociation of polaron pairs that are bound at the heterojunction. Here we show that the voltage dependence of the photocurrent can also arise from photoconductivity resulting from exciton generation followed by dissociation into free polarons within the bulk of the donor and acceptor layers. The presence of photoconductivity of the active layers does not result in an increase in power conversion efficiency, and places a constraint on the maximum fill factor that can be achieved in an OPV cell.

  18. Solubilization of Fe(III) oxide-bound trace metals by a dissimilatory Fe(III) reducing bacterium

    NASA Astrophysics Data System (ADS)

    Zachara, John M.; Fredrickson, Jim K.; Smith, Steven C.; Gassman, Paul L.

    2001-01-01

    Trace metals associate with Fe(III) oxides as adsorbed or coprecipitated species, and consequently, the biogeochemical cycles of iron and the trace metals are closely linked. This communication investigated the solubilization of coprecipitated Co(III) and Ni(II) from goethite (α-FeOOH) during dissimilatory bacterial iron reduction to provide insights on biogeochemical factors controlling trace-element fluxes in anoxic environments. Suspensions of homogeneously substituted Co-FeOOH (50 mmol/L as Co 0.01Fe 0.99OOH; 57Co-labeled) in eight different buffer/media solutions were inoculated with a facultative, metal-reducing bacteria isolated from groundwater ( Shewanella putrefacians CN32), and incubated under strictly anaerobic conditions for periods up to 32 days. Lactate (30 mmol/L) was provided as an electron donor. Growth and non-growth promoting conditions were established by adding or withholding PO 4 and/or trace metals ( 60Co-labeled) from the incubation media. Anthraquinone disulfonate (AQDS; 100 μmol/L) was added to most suspensions as an electron shuttle to enhance bacterial reduction. Solutions were buffered at circumneutral pH with either PIPES or bicarbonate buffers. Solid and liquid samples were analyzed at intermediate and final time points for aqueous and sorbed/precipitated (by HCl extraction) Fe(II) and Co(II). The bioreduced solids were analyzed by X-ray diffraction and field-emission electron microscopy at experiment termination. Ni-FeOOH (Ni 0.01Fe 0.99OOH) was used for comparison in select experiments. Up to 45% of the metal containing FeOOH was bioreduced; growth-supporting conditions did not enhance reduction. The biogenic Fe(II) strongly associated with the residual Fe(III) oxide as an undefined sorbed phase at low fractional reduction in PIPES buffer, and as siderite (FeCO 3) in bicarbonate buffer or as vivianite [Fe 3(PO 4) 2 · 8H 2O] when P was present. Cobalt(III) was reduced to Co(II) in proportion to its mole ratio in the solid. The

  19. 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.

  20. Relationship between P and the most reactive fraction of Fe(III) oxyhydroxide in various aquatic and sedimentary environments

    NASA Astrophysics Data System (ADS)

    Anschutz, Pierre

    2014-05-01

    Phosphorus can experience a series of biogeochemical pathways. Primary P has an igneous origin and occurs mostly as apatite in bedrocks. Once P is dissolved as phosphate ion, it can incorporate organic matter or become adsorbed onto inorganic particles. The liberation of P from organic matter through bacterial respiration produces a subsequent flux back to the biota or a storage in Fe and Al oxyhydroxides, or in authigenic or biogenic phosphate minerals. The adsorption of phosphate on Fe- and Al-oxide and oxyhydroxide has been extensively studied in soil science because phosphorus is a limiting nutrient in terrestrial ecosystems, and sorptive removal of natural or fertilizer phosphorus impacts the production level of crops and forests. Fe(III) oxides/oxyhydroxides are subject to reductive dissolution, and consequently redox conditions play an important role in soil P-bioavailability. The main process of phosphorus removal from the aquatic systems is burial with sediments. Exchange between sediment and overlying water takes place through benthic biogeochemical processes, including organic-P mineralization, redox-driven Fe-P cycling, and benthic phosphorus efflux from sediments. A portion of the pore-water phosphate derived from organic matter mineralization may be adsorbed onto detrital or authigenic iron oxyhydroxides in the oxidized zone of the sediment. Once advected in the reduced zone of sediments through burial or bioturbation, the most reducible fraction of Fe(III) phase can be reduced and solubilized, leading to a release of phosphate. Eventually, P can be buried over long period as relict organic-P, P associated with refractory iron oxides, and apatite. Therefore, Fe-bound P is often the initial sink of P supplied by organic matter, but not the major final sink. Several techniques have been developed to extract P bound to Fe(III) phases. The citrate-dithionite buffered (CDB) solution is one of the most often used solution to measure Fe(III)-bound P. CDB

  1. Donor-acceptor heteroleptic open sandwiches.

    PubMed

    Merino, Gabriel; Beltrán, Hiram I; Vela, Alberto

    2006-02-01

    A series of donor-acceptor heteroleptic open sandwiches with formula CpM-M'Pyl (M = B, Al, Ga; M' = Li, Na; Cp = cyclopentadienyl; Pyl = pentadienyl) has been designed in silico using density functional theory. The most stable complexes are those containing boron as a donor atom. A molecular orbital analysis shows that the s character of the lone pair located at the group 13 element is mainly responsible for the complex stabilization. It is also found that the surrounding medium has a similar effect on these sandwiches such as in the "classical" donor-acceptor complexes, showing a decrement in the group 13 element-alkaline metal bond lengths.

  2. Dissimilatory Reduction of Cr(VI), Fe(III), and U(VI) by Cellulomonas Isolates

    SciTech Connect

    Smith, William Aaron; Apel, William Arnold; Peyton, B. M.; Petersen, J. N.; Sani, R.

    2002-10-01

    The reduction of Cr(VI), Fe(III), and U(VI) was studied using three recently isolated environmental Cellulomonas sp. (WS01, WS18, and ES5) and a known Cellulomonas strain (Cellulomonas flavigena ATCC 482) under anaerobic, non-growth conditions. In all cases, these cultures were observed to reduce Cr(VI), Fe(III), and U(VI). In 100 h, with lactate as electron donor, the Cellulomonas isolates (500 mg/l total cell protein) reduced nitrilotriacetic acid chelated Fe(III) [Fe(III)-NTA] from 5 mM to less than 2.2 mM, Cr(VI) from 0.2 mM to less than 0.001 mM, and U(VI) from 0.2 mM to less than 0.12 mM. All Cellulomonas isolates also reduced Cr(VI), Fe(III), and U(VI) in the absence of lactate, while no metal reduction was observed in either the cell-free or heat-killed cell controls. This is the first report of Cellulomonas sp. reducing Fe(III) and U(VI). Further, this is the first report of Cellulomonas spp. coupling the oxidation of lactate, or other unknown electron donors in the absence of lactate, to the reduction of Cr(VI), Fe(III), and U(VI).

  3. Electron transfer from humic substances to biogenic and abiogenic Fe(III) oxyhydroxide minerals.

    PubMed

    Piepenbrock, Annette; Schröder, Christian; Kappler, Andreas

    2014-01-01

    Microbial humic substance (HS) reduction and subsequent abiotic electron transfer from reduced HS to poorly soluble Fe(III) (oxyhydr)oxides, a process named electron shuttling, significantly increases microbial Fe(III) mineral reduction rates. However, the importance of electron shuttling in nature and notably the electron transfer from HS to biogenic Fe(III) (oxyhydr)oxides have thus far not been determined. In this study, we have quantified the rate and extent of electron transfer from reduced and nonreduced Pahokee Peat humic acids (PPHA) and fresh soil organic matter (SOM) extracts to both synthetic and environmentally relevant biogenic Fe(III) (oxyhydr)oxides. We found that biogenic Fe(III) minerals were reduced faster and to an equal or higher degree than their abiogenic counterparts. Differences were attributed to differences in crystallinity and the association of bacterial biomass with biogenic minerals. Compared to purified PPHA, SOM extract transferred fewer electrons per milligram of carbon and electron transfer was observed only to poorly crystalline ferrihydrite but not to more crystalline goethite. This indicates a difference in redox potential distribution of the redox-active functional groups in extracted SOM relative to the purified PPHA. Our results suggest that HS electron shuttling can also contribute to iron redox processes in environments where biogenic Fe(III) minerals are present.

  4. Dissimilatory reduction of Cr(VI), Fe(III), and U(VI) by Cellulomonas isolates.

    PubMed

    Sani, R K; Peyton, B M; Smith, W A; Apel, W A; Petersen, J N

    2002-10-01

    The reduction of Cr(VI), Fe(III), and U(VI) was studied using three recently isolated environmental Cellulomonas sp. (WS01, WS18, and ES5) and a known Cellulomonas strain ( Cellulomonas flavigena ATCC 482) under anaerobic, non-growth conditions. In all cases, these cultures were observed to reduce Cr(VI), Fe(III), and U(VI). In 100 h, with lactate as electron donor, the Cellulomonas isolates (500 mg/l total cell protein) reduced nitrilotriacetic acid chelated Fe(III) [Fe(III)-NTA] from 5 mM to less than 2.2 mM, Cr(VI) from 0.2 mM to less than 0.001 mM, and U(VI) from 0.2 mM to less than 0.12 mM. All Cellulomonas isolates also reduced Cr(VI), Fe(III), and U(VI) in the absence of lactate, while no metal reduction was observed in either the cell-free or heat-killed cell controls. This is the first report of Cellulomonas sp. reducing Fe(III) and U(VI). Further, this is the first report of Cellulomonas spp. coupling the oxidation of lactate, or other unknown electron donors in the absence of lactate, to the reduction of Cr(VI), Fe(III), and U(VI).

  5. Electron Donor Acceptor Interactions. Final Progress Report

    SciTech Connect

    2002-08-16

    The Gordon Research Conference (GRC) on Electron Donor Acceptor Interactions was held at Salve Regina University, Newport, Rhode Island, 8/11-16/02. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  6. Electron acceptor dependence of electron shuttle secretion and extracellular electron transfer by Shewanella oneidensis MR-1.

    PubMed

    Wu, Chao; Cheng, Yuan-Yuan; Li, Bing-Bing; Li, Wen-Wei; Li, Dao-Bo; Yu, Han-Qing

    2013-05-01

    Shewanella oneidensis MR-1 is an extensively studied dissimilatory metal-reducing bacterium with a great potential for bioremediation and electricity generation. It secretes flavins as electron shuttles which play an important role in extracellular electron transfer. However, the influence of various environmental factors on the secretion of flavins is largely unknown. Here, the effects of electron acceptors, including fumarate, ferrihydrite, Fe(III)-nitrilotriacetic acid (NTA), nitrate and trimethylamine oxide (TMAO), on the secretion of flavins were investigated. The level of riboflavin and riboflavin-5'-phosphate (FMN) secreted by S. oneidensis MR-1 varied considerably with different electron acceptors. While nitrate and ferrihydrite suppressed the secretion of flavins in relative to fumarate, Fe(III)-NTA and TMAO promoted such a secretion and greatly enhanced ferrihydrite reduction and electricity generation. This work clearly demonstrates that electron acceptors could considerably affect the secretion of flavins and consequent microbial EET. Such impacts of electron acceptors in the environment deserve more attention.

  7. Electron acceptor dependence of electron shuttle secretion and extracellular electron transfer by Shewanella oneidensis MR-1.

    PubMed

    Wu, Chao; Cheng, Yuan-Yuan; Li, Bing-Bing; Li, Wen-Wei; Li, Dao-Bo; Yu, Han-Qing

    2013-05-01

    Shewanella oneidensis MR-1 is an extensively studied dissimilatory metal-reducing bacterium with a great potential for bioremediation and electricity generation. It secretes flavins as electron shuttles which play an important role in extracellular electron transfer. However, the influence of various environmental factors on the secretion of flavins is largely unknown. Here, the effects of electron acceptors, including fumarate, ferrihydrite, Fe(III)-nitrilotriacetic acid (NTA), nitrate and trimethylamine oxide (TMAO), on the secretion of flavins were investigated. The level of riboflavin and riboflavin-5'-phosphate (FMN) secreted by S. oneidensis MR-1 varied considerably with different electron acceptors. While nitrate and ferrihydrite suppressed the secretion of flavins in relative to fumarate, Fe(III)-NTA and TMAO promoted such a secretion and greatly enhanced ferrihydrite reduction and electricity generation. This work clearly demonstrates that electron acceptors could considerably affect the secretion of flavins and consequent microbial EET. Such impacts of electron acceptors in the environment deserve more attention. PMID:23558182

  8. 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).

  9. Anaerobic Fe(II)-oxidizing bacteria show as resistance and immobilize as during Fe(III) mineral precipitation.

    PubMed

    Hohmann, Claudia; Winkler, Eva; Morin, Guillaume; Kappler, Andreas

    2010-01-01

    More than 100 million individuals worldwide are exposed to arsenic-contaminated water, making the investigation of arsenic mobility in aquatic systems of utmost importance. Iron (hydr)oxides play a key role in preventing arsenic release in aquifers and soils due to their strong arsenic sorption and are even used to remove arsenic in water treatment. Neutrophilic Fe(II)-oxidizing bacteria produce Fe(III) minerals and therefore have the potential to affect arsenic mobility. In the present study, we demonstrate that the metabolism of anaerobic nitrate-reducing and phototrophic Fe(II)-oxidizing bacteria is not significantly affected by arsenate concentrations of up to 500 muM (37.5 mg/L). Even in the presence of the more toxic arsenic species, arsenite, cell metabolism was significantly impaired only at the highest arsenite concentration (500 muM) for one of the Fe(II)-oxidizers. All Fe(II)-oxidizing bacteria tested effectively immobilized arsenic during Fe(II) oxidation (>96%), lowering the remaining dissolved arsenic concentrations to values close to or even lower than the current drinking water limit of 10 microg/L. Since the minerals formed by these bacteria included highly crystalline Fe(III) minerals that are hardly reducible by Fe(III)-reducing bacteria, stimulation of arsenic immobilization by Fe(II)-oxidizing bacteria can potentially support water treatment systems or even be applied as an effective remediation strategy. PMID:20039738

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

    USGS Publications Warehouse

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

    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

  11. Iron Isotope Fractionations Reveal a Finite Bioavailable Fe Pool for Structural Fe(III) Reduction in Nontronite.

    PubMed

    Shi, Bingjie; Liu, Kai; Wu, Lingling; Li, Weiqiang; Smeaton, Christina M; Beard, Brian L; Johnson, Clark M; Roden, Eric E; Van Cappellen, Philippe

    2016-08-16

    We report on stable Fe isotope fractionation during microbial and chemical reduction of structural Fe(III) in nontronite NAu-1. (56)Fe/(54)Fe fractionation factors between aqueous Fe(II) and structural Fe(III) ranged from -1.2 to +0.8‰. Microbial (Shewanella oneidensis and Geobacter sulfurreducens) and chemical (dithionite) reduction experiments revealed a two-stage process. Stage 1 was characterized by rapid reduction of a finite Fe(III) pool along the edges of the clay particles, accompanied by a limited release to solution of Fe(II), which partially adsorbed onto basal planes. Stable Fe isotope compositions revealed that electron transfer and atom exchange (ETAE) occurred between edge-bound Fe(II) and octahedral (structural) Fe(III) within the clay lattice, as well as between aqueous Fe(II) and structural Fe(III) via a transient sorbed phase. The isotopic fractionation factors decreased with increasing extent of reduction as a result of the depletion of the finite bioavailable Fe(III) pool. During stage 2, microbial reduction was inhibited while chemical reduction continued. However, further ETAE between aqueous Fe(II) and structural Fe(III) was not observed. Our results imply that the pool of bioavailable Fe(III) is restricted to structural Fe sites located near the edges of the clay particles. Blockage of ETAE distinguishes Fe(III) reduction of layered clay minerals from that of Fe oxyhydroxides, where accumulation of structural Fe(II) is much more limited. PMID:27291525

  12. Iron Isotope Fractionations Reveal a Finite Bioavailable Fe Pool for Structural Fe(III) Reduction in Nontronite.

    PubMed

    Shi, Bingjie; Liu, Kai; Wu, Lingling; Li, Weiqiang; Smeaton, Christina M; Beard, Brian L; Johnson, Clark M; Roden, Eric E; Van Cappellen, Philippe

    2016-08-16

    We report on stable Fe isotope fractionation during microbial and chemical reduction of structural Fe(III) in nontronite NAu-1. (56)Fe/(54)Fe fractionation factors between aqueous Fe(II) and structural Fe(III) ranged from -1.2 to +0.8‰. Microbial (Shewanella oneidensis and Geobacter sulfurreducens) and chemical (dithionite) reduction experiments revealed a two-stage process. Stage 1 was characterized by rapid reduction of a finite Fe(III) pool along the edges of the clay particles, accompanied by a limited release to solution of Fe(II), which partially adsorbed onto basal planes. Stable Fe isotope compositions revealed that electron transfer and atom exchange (ETAE) occurred between edge-bound Fe(II) and octahedral (structural) Fe(III) within the clay lattice, as well as between aqueous Fe(II) and structural Fe(III) via a transient sorbed phase. The isotopic fractionation factors decreased with increasing extent of reduction as a result of the depletion of the finite bioavailable Fe(III) pool. During stage 2, microbial reduction was inhibited while chemical reduction continued. However, further ETAE between aqueous Fe(II) and structural Fe(III) was not observed. Our results imply that the pool of bioavailable Fe(III) is restricted to structural Fe sites located near the edges of the clay particles. Blockage of ETAE distinguishes Fe(III) reduction of layered clay minerals from that of Fe oxyhydroxides, where accumulation of structural Fe(II) is much more limited.

  13. 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

  14. Bioavailability of Fe(III) in natural soils and the impact on mobility of inorganic contaminants

    SciTech Connect

    Kosson, David S.; Cowan, Robert M.; Young, Lily Y.; Hacherl, Eric L.; Scala, David J.

    2002-10-03

    Inorganic contaminants, such as heavy metals and radionuclides, can adhere to insoluble Fe(III) minerals resulting in decreased mobility of these contaminants through subsurface environments. Dissimilatory Fe(III)-reducing bacteria (DIRB), by reducing insoluble Fe(III) to soluble Fe(II), may enhance contaminant mobility. The Savannah River Site, South Carolina (SRS), has been subjected to both heavy metal and radionuclide contamination. The overall objective of this project is to investigate the release of inorganic contaminants such as heavy metals and radionuclides that are bound to solid phase soil Fe complexes and to elucidate the mechanisms for mobilization of these contaminants that can be associated with microbial Fe(III) reduction. This is being accomplished by (i) using uncontaminated and contaminated soils from SRS as prototype systems, (ii) evaluating the diversity of DIRBs within the samples and isolating cultures for further study, (iii) using batch microcosms to evaluate the bioavailability of Fe(III) from pure minerals and SRS soils, (iv) developing kinetic and mass transfer models that reflect the system dynamics, and (v) carrying out soil column studies to elucidate the dynamics and interactions amongst Fe(III) reduction, remineralization and contaminant mobility.

  15. Availability and toxicity of Fe(II) and Fe(III) in Caco-2 cells*

    PubMed Central

    He, Wan-ling; Feng, Ying; Li, Xiao-li; Wei, Yan-yan; Yang, Xiao-e

    2008-01-01

    The objective of the present study was to compare the toxicity and availability of Fe(II) and Fe(III) to Caco-2 cells. Cellular damage was studied by measuring cell proliferation and lactate dehydrogenase (LDH) release. The activities of two major antioxidative enzymes [superoxide dismutase (SOD) and glutathione peroxidase (GPx)] and differentiation marker (alkaline phosphatase) were determined after the cells were exposed to different levels of iron salts. The cellular iron concentration was investigated to evaluate iron bioavailability. The results show that iron uptake of the cells treated with Fe(II) is significantly higher than that of the cells treated with Fe(III) (P<0.05). Fe(II) at a concentration >1.5 mmol/L was found to be more effective in reducing cellular viability than Fe(III). LDH release investigation suggests that Fe(II) can reduce stability of the cell membrane. The activities of SOD and GPx of the cells treated with Fe(II) were higher than those of the cells treated with Fe(III), although both of them increased with raising iron supply levels. The results indicate that both Fe(II) and Fe(III) could reduce the cellular antioxidase gene expression at high levels. PMID:18763303

  16. Cyanomethylbenzoic acid: an acceptor for donor-π-acceptor chromophores used in dye-sensitized solar cells.

    PubMed

    Xiang, Wanchun; Gupta, Akhil; Kashif, Muhammad Kalim; Duffy, Noel; Bilic, Ante; Evans, Richard A; Spiccia, Leone; Bach, Udo

    2013-02-01

    Sensing the sun: Incorporation of a cyanomethyl benzoic acid electron acceptor into donor-π-acceptor sensitizers for dye-sensitized-solar cell is shown to lead to devices with improved conversion efficiency when compared with more widely used cyanoacetic acid acceptor.

  17. 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

  18. An investigation of acceptor-doped grain boundaries in ?

    NASA Astrophysics Data System (ADS)

    Ravikumar, V.; Rodrigues, R. P.; Dravid, V. P.

    1996-07-01

    Grain boundary (GB) doped 0022-3727/29/7/014/img2 exhibits interesting electroceramic phenomena including varistor and barrier layer capacitor behaviour. We present here our investigation of GB acceptor-doped 0022-3727/29/7/014/img2 using analytical electron microscopy including electron holography. Mn was diffused into sintered polycrystalline 0022-3727/29/7/014/img2 to attain GBs which are rich in Mn. The presence and spatial extent of Mn at the GBs were analysed using x-ray emission spectroscopy (XES) and parallel electron energy loss spectroscopy (PEELS). The valence state of Mn was determined using PEELS to be predominantly +2. Finally, transmission high-energy electron holography was utilized to directly image and quantify the electrostatic potential and associated space-charge across the GBs directly. The holography results reveal a negatively charged GB with positive space-charge, indicating that Mn with a valence of +2 resides as an acceptor dopant on the Ti site at the GB core. The barrier height and local charge density distribution, including the Debye length, of the double Schottky barrier at the GB are derived from these holography results. This investigation demonstrates the usefulness of electron holography as a bulk-sensitive technique to probe the statics and dynamics of electrostatic field distribution and electrical charge across interfaces in technologically useful materials, and the need to employ diverse analytical techniques for such an investigation.

  19. Photophysics of Fe(III) complexes with fluorosalicylic acid isomers in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Pozdnyakov, Ivan P.; Melnikov, Alexey A.; Šípoš, Rastislav; Chekalin, Sergey V.; Šima, Jozef

    2016-09-01

    Transient absorption spectroscopy is used to study photophysical processes of 1:1 Fe(III) complexes with all four fluorosalicylic acid isomers (Fe-FSAs) in aqueous solutions. Excited states of Fe-FSAs decay to the ground electronic state with two time constants. The faster process is interpreted as internal conversion to the vibrationally hot electronic ground state and the slower one - as a combination of vibrational cooling and solvation of the ground state. The results obtained for Fe-FSAs and other previously investigated Fe(III) salicylato compounds allow us to reveal the main cause of photochemical stability of the complexes upon charge transfer band excitation.

  20. Binomial distribution-based quantitative measurement of multiple-acceptors fluorescence resonance energy transfer by partially photobleaching acceptor

    NASA Astrophysics Data System (ADS)

    Zhang, Lili; Yu, Huaina; Zhang, Jianwei; Chen, Tongsheng

    2014-06-01

    We report that binomial distribution depending on acceptor photobleaching degree can be used to characterize the proportions of various kinds of FRET (Fluorescence Resonance Energy Transfer) constructs resulted from partial acceptor photobleaching of multiple-acceptors FRET system. On this basis, we set up a rigorous quantitation theory for multiple-acceptors FRET construct named as Mb-PbFRET which is not affected by the imaging conditions and fluorophore properties. We experimentally validate Mb-PbFRET with FRET constructs consisted of one donor and two or three acceptors inside living cells on confocal and wide-field microscopes.

  1. Experimental investigation of donor-acceptor electron transfer and back transfer in solid solutions

    SciTech Connect

    Dorfman, R.C.; Lin, Y.; Fayer, M.D. )

    1989-08-24

    Electron transfer from an optically excited donor (rubrene) to randomly distributed acceptors (duroquinone) followed by electron back transfer in a rigid solution (sucrose octaacetate) has been studied experimentally. The forward electron-transfer process was observed by time-dependent fluorescence quenching measurements, while the electron back transfer from the radical anion to the radical cation was monitored by use of the picosecond transient grating technique. A statistical mechanics theory is used to describe the time-dependent dynamics of the system and to extract the forward- and back-transfer parameters from the data. The theory includes donor-acceptor and acceptor-acceptor excluded volume. It is found that the inclusion of excluded volume is necessary to obtain accurate transfer parameters. These parameters enable a detailed description of the electron transfer and recombination dynamics to be given. The agreement between theory and experiment is excellent. A variety of time-dependent properties of the system are calculated. These include the time-dependent ion populations and the probability that the ith acceptor is an ion as a function of time and distance. In addition, (R(t)) and ({tau}(t)), which are the average ion separation as a function of time and the average ion existence time as a function of ion separation, respectively, are calculated.

  2. Perfluorooctanoic acid degradation in the presence of Fe(III) under natural sunlight.

    PubMed

    Liu, Dandan; Xiu, Zongming; Liu, Fei; Wu, Gang; Adamson, Dave; Newell, Charles; Vikesland, Peter; Tsai, Ah-Lim; Alvarez, Pedro J

    2013-11-15

    Due to the high bond dissociation energy (BDE) of CF bonds (116 kcal/mol), perfluorooctanoic acid (PFOA) is a highly recalcitrant pollutant. Herein, we demonstrate a novel method to decompose PFOA in the presence of sunlight and ferric iron (Fe(III)). Under such conditions, 97.8 ± 1.7% of 50 μM PFOA decomposed within 28 days into shorter-chain intermediates and fluoride (F(-)), with an overall defluorination extent of 12.7 ± 0.5%. No PFOA was removed under visible light, indicating that UV radiation is required for PFOA decomposition. Spectroscopic analysis indicates that the decomposition reaction is likely initiated by electron-transfer from PFOA to Fe(III), forming Fe(II) and an unstable organic carboxyl radical. An alternative mechanism for the formation of this organic radical involves hydroxyl radicals, detected by electron paramagnetic resonance (EPR). The observation that PFOA can be degraded by Fe(III) under solar irradiation provides mechanistic insight into a possibly overlooked natural attenuation process. Because Fe(III) is abundant in natural waters and sunlight is essentially free, this work represents a potentially important step toward the development of simple and inexpensive remediation strategies for PFOA-contaminated water.

  3. 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.

  4. Simple flow injection method for simultaneous spectrophotometric determination of Fe(II) and Fe(III).

    PubMed

    Kozak, J; Jodłowska, N; Kozak, M; Kościelniak, P

    2011-09-30

    The method is based on spectrophotometric determination of Fe(II) and Fe(III) at a single wavelength (530 nm) with the use of a dedicated reversed-flow injection system. In the system, EDTA solution is injected into a carrier stream (HNO(3)) and then merged with a sample stream containing a mixture of sulfosalicylic acid and 1,10-phenanthroline as indicators. In an acid environment (pH≅3) the indicators form complexes with both Fe(III) and Fe(II), but EDTA replaces sulfosalicylic acid, forming a more stable colourless complex with Fe(III), whereas Fe(II) remains in a complex with 1,10-phenenthroline. As a result, the area and minimum of the characteristic peak can be exploited as measures corresponding to the Fe(III) and Fe(II) concentrations, respectively. The analytes were not found to affect each other's signals, hence two analytical curves were constructed with the use of a set of standard solutions, each containing Fe(II) and Fe(III). Both analytes were determined in synthetic samples within the concentration ranges of 0.05-4.0 and 0.09-6.0 mg L(-1), respectively, with precision less than 1.5 and 2.6% (RSD) and with accuracy less than 4.3 and 5.6% (RE). The method was applied to determination of the analytes in water samples collected from artesian wells and the results of the determination were consistent with those obtained using the ICP-OES technique.

  5. 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.

  6. The reaction of choline dehydrogenase with some electron acceptors.

    PubMed Central

    Barrett, M C; Dawson, A P

    1975-01-01

    1. The choline dehydrogenase (EC 1.1.99.1) WAS SOLUBILIZED FROM ACETONE-DRIED POWDERS OF RAT LIVER MITOCHONDRIA BY TREATMENT WITH Naja naja venom. 2. The kinetics of the reaction of enzyme with phenazine methosulphate and ubiquinone-2 as electron acceptors were investigated. 3. With both electron acceptors the reaction mechanism appears to involve a free, modified-enzyme intermediate. 4. With some electron acceptors the maximum velocity of the reaction is independent of the nature of the acceptor. With phenazine methosulphate and ubiquinone-2 as acceptors the Km value for choline is also independent of the nature of the acceptor molecule. 5. The mechanism of the Triton X-100-solubilized enzyme is apparently the smae as that for the snake venom solubilized enzyme. PMID:1218095

  7. The reaction of choline dehydrogenase with some electron acceptors.

    PubMed

    Barrett, M C; Dawson, A P

    1975-12-01

    1. The choline dehydrogenase (EC 1.1.99.1) WAS SOLUBILIZED FROM ACETONE-DRIED POWDERS OF RAT LIVER MITOCHONDRIA BY TREATMENT WITH Naja naja venom. 2. The kinetics of the reaction of enzyme with phenazine methosulphate and ubiquinone-2 as electron acceptors were investigated. 3. With both electron acceptors the reaction mechanism appears to involve a free, modified-enzyme intermediate. 4. With some electron acceptors the maximum velocity of the reaction is independent of the nature of the acceptor. With phenazine methosulphate and ubiquinone-2 as acceptors the Km value for choline is also independent of the nature of the acceptor molecule. 5. The mechanism of the Triton X-100-solubilized enzyme is apparently the smae as that for the snake venom solubilized enzyme.

  8. Electronic structure of acceptor-donor complexes in silicon

    NASA Astrophysics Data System (ADS)

    Atoro, E.; Ohama, Y.; Hayafuji, Y.

    2003-10-01

    The electronic structure of trimer acceptor-donor complexes in silicon Si clusters is studied using the ab initio discrete variational-Xα molecular-orbital (MO) method. The trimer complexes In2D (D=phosphorus P, arsenic As, antimony Sb, or bismuth Bi) consist of two indium In acceptor elements and a centered donor element D from the group V elements. Calculations are performed under the assumption that the three atoms are arranged in the nearest neighbor substitutional trimer configuration. Results indicate that the trimer complexes act as shallower acceptors having smaller ionization activation energies than In acceptor. The potential of In2D as an acceptor in Si is then discussed and In2D is proposed as a promising acceptor for the formation of channels and source/drains in ultralarge scaled integration.

  9. Charge and energy transfer in a bithiophene perylenediimide based donor-acceptor-donor system for use in organic photovoltaics.

    PubMed

    Wenzel, Jan; Dreuw, Andreas; Burghardt, Irene

    2013-07-28

    The elementary charge and excitation energy transfer steps in a novel symmetric donor-acceptor-donor triad first described in Roland et al. Phys. Chem. Chem. Phys., 2012, 14, 273, consisting of a central perylenediimide moiety as a potential electron acceptor and two identical electron rich bithiophene compounds, have been investigated using quantum chemical methodology. These elementary processes determine the applicability of such systems in photovoltaic devices. The molecular structure, excited states and the photo-physical properties are investigated using smaller model systems and including solvation effects. The donor and acceptor π-systems are separated by an ethyl bridge such that the molecular orbitals are either located on the donor or acceptor moiety making the identification of locally excited versus charge transfer states straightforward. Using excited state geometry optimizations, the mechanism of photo-initiated charge separation could be identified. Geometry relaxation in the excited donor state leads to a near-degeneracy with the locally excited acceptor state, entailing strong excitonic coupling and resonance energy transfer. This energy transfer process is driven by planarization and bond length alternation of the donor molecule. Geometry relaxation of the locally excited acceptor state in turn reveals a crossing with the energetically lowest charge transfer excited state. The energetic position of the latter depends in a sensitive fashion on the solvent. This provides an explanation of the sequential process observed in the experiment, favoring ultrafast (∼130 fs) formation of the excited acceptor state followed by slower (∼3 ps scale) formation of the charge separated state.

  10. 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.

  11. Non-fullerene electron acceptors for use in organic solar cells.

    PubMed

    Nielsen, Christian B; Holliday, Sarah; Chen, Hung-Yang; Cryer, Samuel J; McCulloch, Iain

    2015-11-17

    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

  12. Non-fullerene electron acceptors for use in organic solar cells.

    PubMed

    Nielsen, Christian B; Holliday, Sarah; Chen, Hung-Yang; Cryer, Samuel J; McCulloch, Iain

    2015-11-17

    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.

  13. 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

  14. Insights on the design and electron-acceptor properties of conjugated organophosphorus materials.

    PubMed

    Baumgartner, Thomas

    2014-05-20

    The development of conjugated organic materials has become a rapidly evolving field of research, particularly with a view toward practical applications in so-called organic electronics that encompass a variety of device types, such as OLEDs, OPVs, and OFETs. Almost all of these devices minimally require the presence of electron-donor and -acceptor components that act as p- and n-type semiconductors, respectively. Research over the past two decades has shown that while there is an abundant resource of organic p-type materials, suitable n-type species are few and far between. To overcome this severe bottleneck for the further development of organic electronics, researchers have identified organo-main-group avenues as valuable alternatives toward organic electron-acceptor materials that may ultimately be used as n-type components in practical devices. One particular element of interest in this context is phosphorus, which at first glance may not necessarily suggest such properties. In this Account, I provide detailed insights on the origin of the electron-acceptor properties of organophosphorus-based conjugated materials and include an overview of important molecular species that have been developed by my group and others. To this end, I explain that the electron-acceptor properties of conjugated organophosphorus materials originate from an interaction known as negative hyperconjugation. While this particular interaction creates a simply inductively withdrawing phosphoryl substituent for π-conjugated scaffolds, incorporation of a phosphorus atom as an integral part of a cyclic substructure within a π-conjugated system provides a much more complex, versatile, and consequently highly valuable tool for the tuning of the electron-acceptor properties of the materials. Notably, the degree of negative hyperconjugation can effectively be tailored in various ways via simple substitution at the phosphorus center. This is now well established for phosphole-based molecular

  15. Insights on the design and electron-acceptor properties of conjugated organophosphorus materials.

    PubMed

    Baumgartner, Thomas

    2014-05-20

    The development of conjugated organic materials has become a rapidly evolving field of research, particularly with a view toward practical applications in so-called organic electronics that encompass a variety of device types, such as OLEDs, OPVs, and OFETs. Almost all of these devices minimally require the presence of electron-donor and -acceptor components that act as p- and n-type semiconductors, respectively. Research over the past two decades has shown that while there is an abundant resource of organic p-type materials, suitable n-type species are few and far between. To overcome this severe bottleneck for the further development of organic electronics, researchers have identified organo-main-group avenues as valuable alternatives toward organic electron-acceptor materials that may ultimately be used as n-type components in practical devices. One particular element of interest in this context is phosphorus, which at first glance may not necessarily suggest such properties. In this Account, I provide detailed insights on the origin of the electron-acceptor properties of organophosphorus-based conjugated materials and include an overview of important molecular species that have been developed by my group and others. To this end, I explain that the electron-acceptor properties of conjugated organophosphorus materials originate from an interaction known as negative hyperconjugation. While this particular interaction creates a simply inductively withdrawing phosphoryl substituent for π-conjugated scaffolds, incorporation of a phosphorus atom as an integral part of a cyclic substructure within a π-conjugated system provides a much more complex, versatile, and consequently highly valuable tool for the tuning of the electron-acceptor properties of the materials. Notably, the degree of negative hyperconjugation can effectively be tailored in various ways via simple substitution at the phosphorus center. This is now well established for phosphole-based molecular

  16. 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. PMID:27171901

  17. 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.

  18. Quantum computing with acceptor spins in silicon

    NASA Astrophysics Data System (ADS)

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-01

    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 {T}2* 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.

  19. 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

  20. New acceptor-donor-acceptor (A-D-A) type copolymers for efficient organic photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Ghomrasni, S.; Ayachi, S.; Alimi, K.

    2015-01-01

    Three new conjugated systems alternating acceptor-donor-acceptor (A-D-A) type copolymers have been investigated by means of Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) at the 6-31g (d) level of theory. 4,4‧-Dimethoxy-chalcone, also called the 1,3-bis(4-methoxyphenyl)prop-2-en-1-one (BMP), has been used as a common acceptor moiety. It forced intra-molecular S⋯O interactions through alternating oligo-thiophene derivatives: 4-AlkylThiophenes (4-ATP), 4-AlkylBithiophenes (4-ABTP) and 4-Thienylene Vinylene (4-TEV) as donor moieties. The band gap, HOMO and LUMO electron distributions as well as optical properties were analyzed for each molecule. The fully optimized resulting copolymers showed low band gaps (2.2-2.8 eV) and deep HOMO energy levels ranging from -4.66 to -4.86 eV. A broad absorption [300-900 nm] covering the solar spectrum and absorption maxima ranges from 486 to 604 nm. In addition, organic photovoltaic cells (OPCs) based on alternating copolymers in bulk heterojunction (BHJ) composites with the 1-(3-methoxycarbonyl) propyl-1-phenyl-[6,6]-C61 (PCBM), as an acceptor, have been optimized. Thus, the band gap decreased to 1.62 eV, the power conversion efficiencies (PCEs) were about 3-5% and the open circuit voltage Voc of the resulting molecules decreased from 1.50 to 1.27 eV.

  1. 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

  2. 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

    SciTech Connect

    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 of 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-) and

  3. 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. PMID:12315968

  4. 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.

  5. Aromatic donor-acceptor interactions in non-polar environments.

    PubMed

    Prentice, Giles M; Pascu, Sofia I; Filip, Sorin V; West, Kevin R; Pantoş, G Dan

    2015-05-14

    We have evaluated the strength of aromatic donor-acceptor interactions between dialkyl naphthalenediimide and dialkoxynaphthalene in non-polar environments. (1)H NMR, UV-vis spectroscopy and isothermal titration calorimetry were used to characterise this interaction. We concluded that the strength of donor-acceptor interactions in heptane is sufficient to drive supramolecular assemblies in this and other aliphatic solvents. PMID:25875729

  6. Acceptor impurity activation in III-nitride light emitting diodes

    SciTech Connect

    Römer, Friedhard Witzigmann, Bernd

    2015-01-12

    In this work, the role of the acceptor doping and the acceptor activation and its impact on the internal quantum efficiency (IQE) of a Gallium Nitride (GaN) based multi-quantum well light emitting diode is studied by microscopic simulation. Acceptor impurities in GaN are subject to a high activation energy which depends on the presence of proximate dopant atoms and the electric field. A combined model for the dopant ionization and activation barrier reduction has been developed and implemented in a semiconductor carrier transport simulator. By model calculations, we demonstrate the impact of the acceptor activation mechanisms on the decay of the IQE at high current densities, which is known as the efficiency droop. A major contributor to the droop is the electron leakage which is largely affected by the acceptor doping.

  7. Requirement for a microbial consortium to completely oxidize glucose in Fe(III)- reducing sediments

    USGS Publications Warehouse

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

    1989-01-01

    In various sediments in which Fe(III) reduction was the terminal electron-accepting process, [14C]glucose was fermented to 14C-fatty acids in a manner similar to that observed in methanogenic sediments. These results are consistent with the hypothesis that, in Fe(III)-reducing sediments, fermentable substrates are oxidized to carbon dioxide by the combined activity of fermentative bacteria and fatty acid-oxidizing, Fe(III)-reducing bacteria.

  8. Microbial Fe(III) oxide reduction potential in Chocolate Pots hot spring, Yellowstone National Park.

    PubMed

    Fortney, N W; He, S; Converse, B J; Beard, B L; Johnson, C M; Boyd, E S; Roden, E E

    2016-05-01

    Chocolate Pots hot springs (CP) is a unique, circumneutral pH, iron-rich, geothermal feature in Yellowstone National Park. Prior research at CP has focused on photosynthetically driven Fe(II) oxidation as a model for mineralization of microbial mats and deposition of Archean banded iron formations. However, geochemical and stable Fe isotopic data have suggested that dissimilatory microbial iron reduction (DIR) may be active within CP deposits. In this study, the potential for microbial reduction of native CP Fe(III) oxides was investigated, using a combination of cultivation dependent and independent approaches, to assess the potential involvement of DIR in Fe redox cycling and associated stable Fe isotope fractionation in the CP hot springs. Endogenous microbial communities were able to reduce native CP Fe(III) oxides, as documented by most probable number enumerations and enrichment culture studies. Enrichment cultures demonstrated sustained DIR driven by oxidation of acetate, lactate, and H2 . Inhibitor studies and molecular analyses indicate that sulfate reduction did not contribute to observed rates of DIR in the enrichment cultures through abiotic reaction pathways. Enrichment cultures produced isotopically light Fe(II) during DIR relative to the bulk solid-phase Fe(III) oxides. Pyrosequencing of 16S rRNA genes from enrichment cultures showed dominant sequences closely affiliated with Geobacter metallireducens, a mesophilic Fe(III) oxide reducer. Shotgun metagenomic analysis of enrichment cultures confirmed the presence of a dominant G. metallireducens-like population and other less dominant populations from the phylum Ignavibacteriae, which appear to be capable of DIR. Gene (protein) searches revealed the presence of heat-shock proteins that may be involved in increased thermotolerance in the organisms present in the enrichments as well as porin-cytochrome complexes previously shown to be involved in extracellular electron transport. This analysis offers

  9. Microbial Reductive Transformation of Phyllosilicate Fe(III) and U(VI) in Fluvial Subsurface Sediments

    SciTech Connect

    Lee, Ji-Hoon; Fredrickson, Jim K.; Kukkadapu, Ravi K.; Boyanov, Maxim I.; Kemner, Kenneth M.; Lin, Xueju; Kennedy, David W.; Bjornstad, Bruce N.; Konopka, Allan; Moore, Dean A.; Resch, Charles T.; Phillips, Jerry L.

    2012-03-14

    The microbial reduction of Fe(III) and U(VI) were investigated in shallow aquifer sediments collected from subsurface Pleistocene flood deposits near the Hanford Reach of the Columbia River in Washington State. Increases in 0.5 N HCl-extractable Fe(II) were observed in incubated sediments and 57Fe Mössbauer spectroscopy revealed that Fe(III) associated with phyllosilicates and pyroxene was reduced to Fe(II). Aqueous uranium(VI) concentrations decreased in incubated Hanford sediments with the rate and extent being greater in sediment amended with organic carbon. X-ray absorption spectroscopy of bioreduced sediments indicated that 67-77% of the U signal was U(VI), probably as an adsorbed species associated with a new or modified reactive mineral phase. Phylotypes within the Deltaproteobacteria were more common in Hanford sediments incubated with U(VI) than without and in U(VI)-free incubations, members of the Clostridiales were dominant with sulfate-reducing phylotypes more common in the sulfate-amended sediments. These results demonstrate the potential for anaerobic reduction phyllosilicate Fe(III) and sulfate in Hanford unconfined aquifer sediments and biotransformations involving reduction and adsorption leading to decreased aqueous U concentrations.

  10. Enrichment of Geobacter Species in Response to Stimulation of Fe(III) Reduction in Sandy Aquifer Sediments.

    PubMed

    Snoeyenbos-West; Nevin; Anderson; Lovley

    2000-02-01

    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.

  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. PMID:24210595

  12. 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.

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

    PubMed

    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 515nm. 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 0.040-1.0mg/L. The detection limit of Fe(III) and Fe(II) was respectively 3.09 and 1.55μg/L, the relative standard deviation (n=10) of Fe(II) and Fe(III) 1.89% and 1.90% for 0.5mg/L of Fe(II) and Fe(III) respectively. About 2.5 samples in 1h can be analyzed. The interfering effects of various chemical species were studied. The method was successfully applied in the determination of water samples.

  14. Effect of Oxidation Rate and Fe(II) State on Microbial Nitrate-Dependent Fe(III) Mineral Formation

    PubMed Central

    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. PMID:16269756

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

    SciTech Connect

    Lovley, Derek R.

    2015-03-09

    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) to 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 demonstrated

  16. 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

  17. 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.

  18. Femtosecond transient grating studies of electron transfer in porphyrin and chlorophyll donor-acceptor molecules

    SciTech Connect

    Wiederrecht, G.P.; Svec, W.A.; Wasielewski, M.R.

    1994-04-01

    Transient grating studies of electron transfer in artificial photosynthetic systems are described. These systems include simple donor-acceptor molecules where the donor, a chlorophyll or porphyrin, is rigidly attached to an easily reduced species such as napthoquinone or benzoquinone. We have previously synthesized acceptor molecules which have well defined absorption bands upon reduction and are well removed from the excited and cationic states of porphyrins and chlorophylls. They also possess large molar extinction coefficients that dominate the spectra and have well defined polarization characteristics. These traits are ideal for polarization sensitive transient grating experiments which enable accurate determination of the angle of the transition dipole between the initial excitation and the acceptor probe, dynamic solvation effects on the charge separated species, and any time dependent rotation of the chromophores relative to each other. An example of the type of molecule utilized for these experiments is a free base porphyrin (HP) donor and a pyromellitic diimide (PI) acceptor directly bonded to the porphyrin ring.

  19. Effect of phosphate and sulfate on Ni repartitioning during Fe(II)-catalyzed Fe(III) oxide mineral recrystallization

    NASA Astrophysics Data System (ADS)

    Hinkle, Margaret A. G.; Catalano, Jeffrey G.

    2015-09-01

    Dissolved Fe(II) activates coupled oxidative growth and reductive dissolution of Fe(III) oxide minerals, causing recrystallization and the repartitioning of structurally-compatible trace metals. Phosphate and sulfate, two ligands common to natural aquatic systems, alter Fe(II) adsorption onto Fe(III) oxides and affect Fe(III) oxide dissolution and precipitation. However, the effect of these oxoanions on trace metal repartitioning during Fe(II)-catalyzed Fe(III) oxide recrystallization is unclear. The effects of phosphate and sulfate on Ni adsorption and Ni repartitioning during Fe(II)-catalyzed Fe(III) oxide recrystallization were investigated as such repartitioning may be affected by both Fe(II)-oxoanion and metal-oxoanion interactions. In most systems examined, phosphate alters Ni repartitioning during Fe(II)-catalyzed recrystallization to a larger extent than sulfate. Phosphate substantially enhances Ni adsorption onto hematite but decreases (nearly inhibiting) Fe(II)-catalyzed Ni incorporation into and release from this mineral. In the goethite system, however, phosphate suppresses Ni release but enhances Ni incorporation in the presence of aqueous Fe(II). In contrast, sulfate has little effect on macroscopic Ni adsorption and release of Ni from Fe(III) oxides, but substantially enhances Ni incorporation into goethite. This demonstrates that phosphate and sulfate have unique, mineral-specific interactions with Ni during Fe(II)-catalyzed Fe(III) oxide recrystallization. This research suggests that micronutrient bioavailability at redox interfaces in hematite-dominated systems may be especially suppressed by phosphate, while both oxoanions likely have limited effects in goethite-rich soils or sediments. Phosphate may also exert a large control on contaminant fate at redox interfaces, increasing Ni retention on iron oxide surfaces. These results further indicate that trace metal retention by iron oxides during lithification and later repartitioning during

  20. Nitrogen is a deep acceptor in ZnO

    DOE PAGES

    Tarun, M. C.; Iqbal, M. Zafar; McCluskey, M. D.

    2011-04-14

    Zinc oxide is a promising material for blue and UV solid-state lighting devices, among other applications. Nitrogen has been regarded as a potential p-type dopant for ZnO. However, recent calculations indicate that nitrogen is a deep acceptor. This paper presents experimental evidence that nitrogen is, in fact, a deep acceptor and therefore cannot produce p-type ZnO. A broad photoluminescence (PL) emission band near 1.7 eV, with an excitation onset of ~2.2 eV, was observed, in agreement with the deep-acceptor model of the nitrogen defect. Thus the deep-acceptor behavior can be explained by the low energy of the ZnO valence bandmore » relative to the vacuum level.« less

  1. Nitrogen is a deep acceptor in ZnO

    SciTech Connect

    Tarun, M. C.; Iqbal, M. Zafar; McCluskey, M. D.

    2011-04-14

    Zinc oxide is a promising material for blue and UV solid-state lighting devices, among other applications. Nitrogen has been regarded as a potential p-type dopant for ZnO. However, recent calculations indicate that nitrogen is a deep acceptor. This paper presents experimental evidence that nitrogen is, in fact, a deep acceptor and therefore cannot produce p-type ZnO. A broad photoluminescence (PL) emission band near 1.7 eV, with an excitation onset of ~2.2 eV, was observed, in agreement with the deep-acceptor model of the nitrogen defect. Thus the deep-acceptor behavior can be explained by the low energy of the ZnO valence band relative to the vacuum level.

  2. Electron Transfer Rate Maxima at Large Donor-Acceptor Distances.

    PubMed

    Kuss-Petermann, Martin; Wenger, Oliver S

    2016-02-01

    Because of their low mass, electrons can transfer rapidly over long (>15 Å) distances, but usually reaction rates decrease with increasing donor-acceptor distance. We report here on electron transfer rate maxima at donor-acceptor separations of 30.6 Å, observed for thermal electron transfer between an anthraquinone radical anion and a triarylamine radical cation in three homologous series of rigid-rod-like donor-photosensitizer-acceptor triads with p-xylene bridges. Our experimental observations can be explained by a weak distance dependence of electronic donor-acceptor coupling combined with a strong increase of the (outer-sphere) reorganization energy with increasing distance, as predicted by electron transfer theory more than 30 years ago. The observed effect has important consequences for light-to-chemical energy conversion. PMID:26800279

  3. New light on NO bonding in Fe(III) heme proteins from resonance Raman spectroscopy and DFT modeling.

    PubMed

    Soldatova, Alexandra V; Ibrahim, Mohammed; Olson, John S; Czernuszewicz, Roman S; Spiro, Thomas G

    2010-04-01

    Visible and ultraviolet resonance Raman (RR) spectra are reported for Fe(III)(NO) adducts of myoglobin variants with altered polarity in the distal heme pockets. The stretching frequencies of the Fe(III)-NO and N-O bonds, nu(FeN) and nu(NO), are negatively correlated, consistent with backbonding. However, the correlation shifts to lower nu(NO) for variants lacking a distal histidine. DFT modeling reproduces the shifted correlations and shows the shift to be associated with the loss of a lone-pair donor interaction from the distal histidine that selectively strengthens the N-O bond. However, when the model contains strongly electron-withdrawing substituents at the heme beta-positions, nu(FeN) and nu(NO) become positively correlated. This effect results from Fe(III)-N-O bending, which is induced by lone-pair donation to the N(NO) atom. Other mechanisms for bending are discussed, which likewise lead to a positive nu(FeN)/nu(NO) correlation, including thiolate ligation in heme proteins and electron-donating meso-substituents in heme models. The nu(FeN)/nu(NO) data for the Fe(III) complexes are reporters of heme pocket polarity and the accessibility of lone pair, Lewis base donors. Implications for biologically important processes, including NO binding, reductive nitrosylation, and NO reduction, are discussed. PMID:20218710

  4. New Light on NO Bonding in Fe(III) Heme Proteins from Resonance Raman Spectroscopy and DFT Modeling

    PubMed Central

    Soldatova, Alexandra V.; Ibrahim, Mohammed; Olson, John S.; Czernuszewicz, Roman S.; Spiro, Thomas G.

    2010-01-01

    Visible and ultraviolet resonance Raman (RR) spectra are reported for FeIII(NO) adducts of myoglobin variants with altered polarity in the distal heme pockets. The stretching frequencies of the FeIII–NO and N–O bonds, νFeN and νNO, are negatively correlated, consistent with backbonding. However, the correlation shifts to lower νNO for variants lacking a distal histidine. DFT modeling reproduces the shifted correlations, and shows the shift to be associated with the loss of a lone-pair donor interaction from the distal histidine that selectively strengthens the N–O bond. However, when the model contains strongly electron-withdrawing substituents at the heme β-positions, νFeN and νNO become positively correlated. This effect results from FeIII–N–O bending, which is induced by lone pair donation to the NNO atom. Other mechanisms for bending are discussed, which likewise lead to a positive νFeN/νNO correlation, including thiolate ligation in heme proteins and electron-donating meso-substituents in heme models. The νFeN/νNO data for the Fe(III) complexes are reporters of heme pocket polarity and the accessibility of lone pair, Lewis base donors. Implications for biologically important processes, including NO binding, reductive nitrosylation and NO reduction, are discussed. PMID:20218710

  5. Synthesis, Properties, and Design Principles of Donor-Acceptor Nanohoops.

    PubMed

    Darzi, Evan R; Hirst, Elizabeth S; Weber, Christopher D; Zakharov, Lev N; Lonergan, Mark C; Jasti, Ramesh

    2015-09-23

    We have synthesized a series of aza[8]cycloparaphenylenes containing one, two, and three nitrogens to probe the impact of nitrogen doping on optoelectronic properties and solid state packing. Alkylation of these azananohoops afforded the first donor-acceptor nanohoops where the phenylene backbone acts as the donor and the pyridinium units act as the acceptor. The impact on the optoelectronic properties was then studied experimentally and computationally to provide new insight into the effect of functionalization on nanohoops properties. PMID:27162989

  6. Synthesis, Properties, and Design Principles of Donor–Acceptor Nanohoops

    PubMed Central

    2015-01-01

    We have synthesized a series of aza[8]cycloparaphenylenes containing one, two, and three nitrogens to probe the impact of nitrogen doping on optoelectronic properties and solid state packing. Alkylation of these azananohoops afforded the first donor–acceptor nanohoops where the phenylene backbone acts as the donor and the pyridinium units act as the acceptor. The impact on the optoelectronic properties was then studied experimentally and computationally to provide new insight into the effect of functionalization on nanohoops properties. PMID:27162989

  7. 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

    2015-07-01

    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.

  8. Microbial Fe(III) oxide reduction potential in Chocolate Pots hot spring, Yellowstone National Park.

    PubMed

    Fortney, N W; He, S; Converse, B J; Beard, B L; Johnson, C M; Boyd, E S; Roden, E E

    2016-05-01

    Chocolate Pots hot springs (CP) is a unique, circumneutral pH, iron-rich, geothermal feature in Yellowstone National Park. Prior research at CP has focused on photosynthetically driven Fe(II) oxidation as a model for mineralization of microbial mats and deposition of Archean banded iron formations. However, geochemical and stable Fe isotopic data have suggested that dissimilatory microbial iron reduction (DIR) may be active within CP deposits. In this study, the potential for microbial reduction of native CP Fe(III) oxides was investigated, using a combination of cultivation dependent and independent approaches, to assess the potential involvement of DIR in Fe redox cycling and associated stable Fe isotope fractionation in the CP hot springs. Endogenous microbial communities were able to reduce native CP Fe(III) oxides, as documented by most probable number enumerations and enrichment culture studies. Enrichment cultures demonstrated sustained DIR driven by oxidation of acetate, lactate, and H2 . Inhibitor studies and molecular analyses indicate that sulfate reduction did not contribute to observed rates of DIR in the enrichment cultures through abiotic reaction pathways. Enrichment cultures produced isotopically light Fe(II) during DIR relative to the bulk solid-phase Fe(III) oxides. Pyrosequencing of 16S rRNA genes from enrichment cultures showed dominant sequences closely affiliated with Geobacter metallireducens, a mesophilic Fe(III) oxide reducer. Shotgun metagenomic analysis of enrichment cultures confirmed the presence of a dominant G. metallireducens-like population and other less dominant populations from the phylum Ignavibacteriae, which appear to be capable of DIR. Gene (protein) searches revealed the presence of heat-shock proteins that may be involved in increased thermotolerance in the organisms present in the enrichments as well as porin-cytochrome complexes previously shown to be involved in extracellular electron transport. This analysis offers

  9. 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.

  10. Nanowires, Capacitors, and Other Novel Outer-Surface Components Involved in Electron Transfer to Fe(III) Oxides in Geobacter Species

    SciTech Connect

    Lovley, Derek R.

    2005-06-01

    In the past year studies have primarily focused on elucidating the role of pili in electron transport to Fe(III) oxide in Geobacter sulfurreducens. As summarized in last year's report, it was previously found that pili are specifically expressed during growth on Fe(III) oxide and that Fe(III) oxide reduction is inhibited if the gene for the structural pilin protein is deleted. However, it was also found that a pilin-deficient mutant of G. sulfurreducens could attached to Fe(III) oxide as well as wild type.

  11. The interaction of phenolic acids with Fe(III) in the presence of citrate as studied by isothermal titration calorimetry.

    PubMed

    Yang, Senpei; Bai, Guangling; Chen, Lingli; Shen, Qun; Diao, Xianmin; Zhao, Guanghua

    2014-08-15

    Under physiological conditions, exogenous chelators such as polyphenols might interact with non-protein bound ferric complexes, such as Fe(III)-citrate. Additionally, Fe(III) and citrate are widely distributed in various fruits and vegetables which are also rich in phenolic acids. In this study, we focus on the interaction between phenolic acids (gallic acid, methyl gallate and protocatechuic acid) and Fe(III) in the presence of excessive citrate by isothermal titration calorimetry (ITC) for thermodynamic studies, and stopped-flow absorption spectrometry for fast kinetic studies. Results reveal that all of these three phenolic acids can bind to the Fe(III) with the same stoichiometry (3:1). Moreover, the binding constants of these three compounds with Fe(III) are greatly dependent on ligand structure, and are much higher than that of Fe(III)-citrate. Based on their stoichiometry and superhigh binding constants, it is most likely that these three phenolic acids can displace the citrate to bind with one iron(III) ion to form a stable octahedral geometric structure, albeit at different rates. These findings shed light on the interaction between phenolic acids and Fe(III) in the presence of citrate under either physiological conditions or in a food system.

  12. Analysis of nonlinear optical properties in donor–acceptor materials

    SciTech Connect

    Day, Paul N.; Pachter, Ruth; Nguyen, Kiet A.

    2014-05-14

    Time-dependent density functional theory has been used to calculate nonlinear optical (NLO) properties, including the first and second hyperpolarizabilities as well as the two-photon absorption cross-section, for the donor-acceptor molecules p-nitroaniline and dimethylamino nitrostilbene, and for respective materials attached to a gold dimer. The CAMB3LYP, B3LYP, PBE0, and PBE exchange-correlation functionals all had fair but variable performance when compared to higher-level theory and to experiment. The CAMB3LYP functional had the best performance on these compounds of the functionals tested. However, our comprehensive analysis has shown that quantitative prediction of hyperpolarizabilities is still a challenge, hampered by inadequate functionals, basis sets, and solvation models, requiring further experimental characterization. Attachment of the Au{sub 2}S group to molecules already known for their relatively large NLO properties was found to further enhance the response. While our calculations show a modest enhancement for the first hyperpolarizability, the enhancement of the second hyperpolarizability is predicted to be more than an order of magnitude.

  13. 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. PMID:26653493

  14. 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.

  15. Shoot-to-Root Signal Transmission Regulates Root Fe(III) Reductase Activity in the dgl Mutant of Pea.

    PubMed

    Grusak, M. A.; Pezeshgi, S.

    1996-01-01

    To understand the root, shoot, and Fe-nutritional factors that regulate root Fe-acquisition processes in dicotyledonous plants, Fe(III) reduction and net proton efflux were quantified in root systems of an Fe-hyperaccumulating mutant (dgl) and a parental (cv Dippes Gelbe Viktoria [DGV]) genotype of pea (Pisum sativum). Plants were grown with (+Fe treated) or without (-Fe treated) added Fe(III)-N,N'-ethylenebis[2-(2-hydroxyphenyl)-glycine] (2 [mu]M); root Fe(III) reduction was measured in solutions containing growth nutrients, 0.1 mM Fe(III)-ethylenediaminetetraacetic acid, and 0.1 mM Na2-bathophenanthrolinedisulfonic acid. Daily measurements of Fe(III) reduction (d 10-20) revealed initially low rates in +Fe-treated and -Fe-treated dgl, followed by a nearly 5-fold stimulation in rates by d 15 for both growth types. In DGV, root Fe(III) reductase activity increased only minimally by d 20 in +Fe-treated plants and about 3-fold in -Fe-treated plants, beginning on d 15. Net proton efflux was enhanced in roots of -Fe-treated DGV and both dgl growth types, relative to +Fe-treated DGV. In dgl, the enhanced proton efflux occurred prior to the increase in root Fe(III) reductase activity. Reductase studies using plants with reciprocal shoot:root grafts demonstrated that shoot expression of the dgl gene leads to the generation of a transmissible signal that enhances Fe(III) reductase activity in roots. The dgl gene product may alter or interfere with a normal component of a signal transduction mechanism regulating Fe homeostasis in plants.

  16. Electron acceptor-dependent respiratory and physiological stratifications in biofilms.

    PubMed

    Yang, Yonggang; Xiang, Yinbo; Sun, Guoping; Wu, Wei-Min; Xu, Meiying

    2015-01-01

    Bacterial respiration is an essential driving force in biogeochemical cycling and bioremediation processes. Electron acceptors respired by bacteria often have solid and soluble forms that typically coexist in the environment. It is important to understand how sessile bacteria attached to solid electron acceptors respond to ambient soluble alternative electron acceptors. Microbial fuel cells (MFCs) provide a useful tool to investigate this interaction. In MFCs with Shewanella decolorationis, azo dye was used as an alternative electron acceptor in the anode chamber. Different respiration patterns were observed for biofilm and planktonic cells, with planktonic cells preferred to respire with azo dye while biofilm cells respired with both the anode and azo dye. The additional azo respiration dissipated the proton accumulation within the anode biofilm. There was a large redox potential gap between the biofilms and anode surface. Changing cathodic conditions caused immediate effects on the anode potential but not on the biofilm potential. Biofilm viability showed an inverse and respiration-dependent profile when respiring with only the anode or azo dye and was enhanced when respiring with both simultaneously. These results provide new insights into the bacterial respiration strategies in environments containing multiple electron acceptors and support an electron-hopping mechanism within Shewanella electrode-respiring biofilms.

  17. Towards alternatives to anodic water oxidation: basket-handle thiolate Fe(III) porphyrins for electrocatalytic hydrocarbon oxidation.

    PubMed

    Li, Peiyi; Alenezi, Khalaf; Ibrahim, Saad K; Wright, Joseph A; Hughes, David L; Pickett, Christopher J

    2012-12-01

    Selective electrocatalytic oxidation of hydrocarbons to alcohols, epoxides or other (higher value) oxygenates should in principal present a useful complementary anodic half-cell reaction to cathodic generation of fuels from water or CO(2) viz. an alternative to oxygen evolution. A series of new basket-handle thiolate Fe(III) porphyrins have been synthesised and shown to mediate anodic oxidation of hydrocarbons, specifically adamantane hydroxylation and cyclooctene epoxidation. We compare yields obtained by electrochemical and chemical oxidation of the thiolate porphyrins and benchmark their behaviour against that of Fe(III) tetraphenyl porphyrin chloride and its tetrapentafluorophenyl analogue. PMID:22945754

  18. Phanta: A Non-Fluorescent Photochromic Acceptor for pcFRET

    PubMed Central

    Don Paul, Craig; Kiss, Csaba; Traore, Daouda A. K.; Gong, Lan; Wilce, Matthew C. J.; Devenish, Rodney J.; Bradbury, Andrew; Prescott, Mark

    2013-01-01

    We have developed an orange non-fluorescent photochromic protein (quantum yield, 0.003) we call Phanta that is useful as an acceptor in pcFRET applications. Phanta can be repeatedly inter-converted between the two absorbing states by alternate exposure to cyan and violet light. The absorption spectra of Phanta in one absorbing state shows excellent overlap with the emission spectra of a number of donor green fluorescent proteins including the commonly used EGFP. We show that the Phanta-EGFP FRET pair is suitable for monitoring the activation of caspase 3 in live cells using readily available instrumentation and a simple protocol that requires the acquisition of two donor emission images corresponding to Phanta in each of its photoswitched states. This the first report of a genetically encoded non-fluorescent acceptor for pcFRET. PMID:24098733

  19. Organic solar cells based on acceptor-functionalized diketopyrrolopyrrole derivatives

    NASA Astrophysics Data System (ADS)

    Ghosh, Sanjay S.; Serrano, Luis A.; Ebenhoch, Bernd; Rotello, Vincent M.; Cooke, Graeme; Samuel, Ifor D. W.

    2015-01-01

    The synthesis and characterization of three solution processable diketopyrrolopyrrole (DPP) derivatives featuring acceptor units attached to the core by alkyne linker units is reported. Cyclic voltammetry and density functional theory calculations indicate that the DPP derivatives possess similar HOMO and LUMO energies. Solar cells were fabricated by blending the synthesized DPP derivatives with [6,6]-phenyl-C71-butyrate methyl ester. The influence of donor:acceptor blend ratio, film thickness, annealing temperature, and annealing time on device performance was studied. Differences in device performance were related to atomic force microscopy measurements of the films. The highest power conversion efficiency of 1.76% was achieved for the DPP derivative functionalized with an aldehyde electron-withdrawing group with a 1∶0.7 donor:acceptor ratio when the active layer was annealed for 10 min at 110°C.

  20. Theory of Primary Photoexcitations in Donor-Acceptor Copolymers

    NASA Astrophysics Data System (ADS)

    Aryanpour, Karan; Dutta, Tirthankar; Huynh, Uyen N. V.; Vardeny, Zeev Valy; Mazumdar, Sumit

    2015-12-01

    We present a generic theory of primary photoexcitations in low band gap donor-acceptor conjugated copolymers. Because of the combined effects of strong electron correlations and broken symmetry, there is considerable mixing between a charge-transfer exciton and an energetically proximate triplet-triplet state with an overall spin singlet. The triplet-triplet state, optically forbidden in homopolymers, is allowed in donor-acceptor copolymers. For an intermediate difference in electron affinities of the donor and the acceptor, the triplet-triplet state can have a stronger oscillator strength than the charge-transfer exciton. We discuss the possibility of intramolecular singlet fission from the triplet-triplet state, and how such fission can be detected experimentally.

  1. TD-DFT study of the light-induced spin crossover of Fe(III) complexes.

    PubMed

    Saureu, Sergi; de Graaf, Coen

    2016-01-14

    Two light-induced spin-crossover Fe(III) compounds have been studied with time-dependent density functional theory (TD-DFT) to investigate the deactivation mechanism and the role of the ligand-field states as intermediates in this process. The B3LYP* functional has previously shown its ability to accurately describe (light-induced) spin-crossover in Fe(II) complexes. Here, we establish its performance for Fe(III) systems using [Fe(qsal)2](+) (Hqsal = 2-[(8-quinolinylimino)methyl]phenol) and [Fe(pap)2](+) (Hpap = 2-(2-pyridylmethyleneamino)phenol) as test cases comparing the B3LYP* results to experimental information and to multiconfigurational wave function results. In addition to rather accurate high spin (HS) and low spin (LS) state geometries, B3LYP* also predicts ligand-to-metal charge transfer (LMCT) states with large oscillator strength in the energy range where the UV-VIS spectrum shows an intense absorption band, whereas optically allowed π-π* excitations on the ligands were calculated at higher energy. Subsequently, we have generated a two-dimensional potential energy surface of the HS and LS states varying the Fe-N and Fe-O distances. LMCT and metal centered (MC) excited states were followed along the approximate minimal energy path that connects the minima of the HS and LS on this surface. The (2)LMCT state has a minimum in the same region as the initial LS state, where we also observe a crossing with the intermediate spin (IS) state. Upon the expansion of the coordination sphere of the Fe(III) ion, the IS state crosses with the HS state and further expansion of the coordination sphere leads to the excited spin state trapping as observed in experiment. The calculation of the intersystem crossing rates reveals that the deactivation from (2)LMCT → IS → HS competes with the (2)LMCT → IS → LS pathway, in line with the low efficiency encountered in experiments. PMID:26660866

  2. 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.

  3. Optical Spectroscopy of Acceptors in Semiconductors: I. Acceptor Complexes in Neutron Transmutation-Doped Silicon. I. Piezospectroscopy of Beryllium Double Acceptors in Germanium.

    NASA Astrophysics Data System (ADS)

    Labrec, Charles Raymond

    Substitutional group III impurities in group IV elemental semiconductors bind a hole from the valence band and are solid-state analogs of the hydrogen atom; likewise, group II impurities bind two holes and are analogs of the helium atom. In these materials, the electronic transitions from the acceptor s-like ground state to the p-like excited states are infrared active. A high-resolution Fourier transform spectrometer, and a liquid-helium cooled germanium bolometer and glass sample cryostat are ideally suited to study these effects. When silicon is exposed to neutron radiation, a fraction of the atoms are converted to phosphorus. After annealing, these impurity atoms occupy substitutional locations and are thus donors. When the initial crystal is p-type and the final phosphorus concentration is less than that of the acceptor, the sample is left p-type but highly compensated. This results in broadening of the transition lines. However, before complete annealing, it is discovered that a new, extremely shallow acceptor is formed, with an ionization energy of 28.24 meV, which is far shallower than any previously known. Neutral Be in Ge is known to be a double acceptor. Under uniaxial stress, the single hole (1s)^2 to (1s)(np) excitation spectrum shows splittings and polarization effects. These piezospectroscopic effects were observed for a compressive force vec F | (111) and vec F | (100). The phenomenological shear deformation potential constants have been deduced for the ground and excited states of the D transition.

  4. Effect of divalent cations on the kinetics of Fe(III) complexation by organic ligands in natural waters

    NASA Astrophysics Data System (ADS)

    Fujii, Manabu; Rose, Andrew L.; Waite, T. David; Omura, Tatsuo

    2008-03-01

    We have investigated the kinetics of Fe(III) complexation by several organic ligands including fulvic acid, citrate and ethylenediaminetetraacetic acid (EDTA). Particular attention was given to examination of the effect of competitive divalent cations (Me: Ca 2+ and Mg 2+) at concentrations typical of seawater on the complexation rate. All experiments were conducted in 0.5 M NaCl solution buffered with 2 mM bicarbonate at pH 8.0 in the absence and presence of Me (25 μM-250 mM). The rate constants of complex formation determined by using the competitive ligand (5-sulfosalicylic acid) method combined with visible spectrophotometry ranged from 3.3 × 10 4 to 3.2 × 10 6 M -1 s -1. The mechanism of complexation was then examined based on a kinetic model. When EDTA was used as a ligand, Me at concentrations comparable to the ligand markedly retarded the rate of iron complex formation due to the predominance of an adjunctive pathway (where iron-ligand complex is formed via direct association of iron to Me-ligand complex). In contrast, the competing effect of Me on iron complexation by citrate and fulvic acid was observed only when the Me concentration was in excess of the ligand by more than a factor of 10-1000. The kinetic model suggests that iron complexation by fulvic acid occurs predominantly via a disjunctive pathway (where iron complexation by ligand occurs after dissociation of Me from Me-ligand complex) at concentrations of divalent cations and natural organic matter typical of natural waters including seawater and freshwater.

  5. Tetrathiafulvalene-based mixed-valence acceptor-donor-acceptor triads: a joint theoretical and experimental approach.

    PubMed

    Calbo, Joaquín; Aragó, Juan; Otón, Francisco; Lloveras, Vega; Mas-Torrent, Marta; Vidal-Gancedo, José; Veciana, Jaume; Rovira, Concepció; Ortí, Enrique

    2013-12-01

    This work presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)-based acceptor-donor-acceptor triads (BQ-TTF-BQ and BTCNQ-TTF-BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano-p-quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum-chemical calculations. Emphasis is placed on the mixed-valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ-TTF-BQ and BTCNQ-TTF-BTCNQ triads in their radical anion states behave as class-II mixed-valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc-pVTZ), taking into account the solvent effects, predict charge-localised species (BQ(.-)-TTF-BQ and BTCNQ(.-)-TTF-BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ-TTF-BTCNQ anion, in accordance with the more electron-withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low-energy, broad absorption bands observed experimentally for the BQ-TTF-BQ and BTCNQ-TTF-BTCNQ radical anions are associated with the intervalence charge transfer (IV-CT) electronic transition and two nearby donor-to-acceptor CT excitations. The study highlights the molecular efficiency of the electron-donor TTF unit as a molecular wire connecting two acceptor redox centres.

  6. Heterocyclic tri-urea isocyanurate bridged groups modified periodic mesoporous organosilica synthesized for Fe(III) adsorption

    SciTech Connect

    Rana, Vijay Kumar; Selvaraj, M.; Parambadath, Surendran; Chu, Sang-Wook; Park, Sung Soo; Mishra, Satyendra; Singh, Raj Pal; Ha, Chang-Sik

    2012-10-15

    To achieve a high level of heavy metal adsorption, 1,1 Prime ,1 Double-Prime -(1,3,5-triazine-2,4,6-triyl)tris(3-(3-(triethoxysilyl)propyl)urea) (TTPU) was synthesized as a novel melamine precursor and incorporated on the silica surface of periodic mesoporous organosilica (PMO). The melamine modified PMOs (MPMOs) were synthesized under acidic conditions using TTPU, tetraethylorthosilicate (TEOS) and Pluronic P123 as a template and the modified PMOs were characterized using the relevant instrumental techniques. The characteristic materials were used as adsorbents for the adsorption of Fe(III) ions. Fe(III) adsorption studies revealed MPMO-7.5 to be a good absorbent with higher adsorption efficiency than other MPMOs. - Graphical Abstract: A new organosilica precursor, TTPU, has been successfully synthesized and characterized to incorporate on the silica surface of periodic mesoporous organosilica (PMO). The melamine modified PMOs (MPMOs), in particular, the MPMO-7.5 was found to exhibit good adsorption efficiency for Fe(III). Highlights: Black-Right-Pointing-Pointer Synthesis of new melamine modified periodic mesoporous organosilicas (MPMOs). Black-Right-Pointing-Pointer A new organosilica precursor, TTPU, has been successfully synthesized for the MPMOs. Black-Right-Pointing-Pointer The MPMOs were characterized by the relevant instrumental techniques. Black-Right-Pointing-Pointer MPMO-7.5 exhibits higher adsorption efficiency for Fe(III) ions than other MPMOs.

  7. Does As(III) interact with Fe(II), Fe(III) and organic matter through ternary complexes?

    PubMed

    Catrouillet, Charlotte; Davranche, Mélanie; Dia, Aline; Bouhnik-Le Coz, Martine; Demangeat, Edwige; Gruau, Gérard

    2016-05-15

    Up until now, only a small number of studies have been dedicated to the binding processes of As(III) with organic matter (OM) via ionic Fe(III) bridges; none was interested in Fe (II). Complexation isotherms were carried out with As(III), Fe(II) or Fe(III) and Leonardite humic acid (HA). Although PHREEQC/Model VI, implemented with OM thiol groups, reproduced the experimental datasets with Fe(III), the poor fit between the experimental and modeled Fe(II) data suggested another binding mechanism for As(III) to OM. PHREEQC/Model VI was modified to take various possible As(III)-Fe(II)-OM ternary complex conformations into account. The complexation of As(III) as a mononuclear bidentate complex to a bidentate Fe(II)-HA complex was evidenced. However, the model needed to be improved since the distribution of the bidentate sites appeared to be unrealistic with regards to the published XAS data. In the presence of Fe(III), As(III) was bound to thiol groups which are more competitive with regards to the low density of formed Fe(III)-HA complexes. Based on the new data and previously published results, we propose a general scheme describing the various As(III)-Fe-MO complexes that are able to form in Fe and OM-rich waters. PMID:26939079

  8. New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique.

    PubMed

    Kozak, J; Gutowski, J; Kozak, M; Wieczorek, M; Kościelniak, P

    2010-05-23

    The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength lambda=530 nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic "cut off" peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 2(2) factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1-3.0 and 0.9-3.5 mg L(-1) of both analytes, respectively.

  9. A comparative study for the ion exchange of Fe(III) and Zn(II) on zeolite NaY.

    PubMed

    Ostroski, Indianara C; Barros, Maria A S D; Silva, Edson A; Dantas, João H; Arroyo, Pedro A; Lima, Oswaldo C M

    2009-01-30

    The uptake capacity of Fe(III) and Zn(II) ions in NaY zeolite was investigated. Experiments were carried out in a fixed bed column at 30 degrees C, pH 3.5 and 4.5 for Fe(III) and Zn(II), respectively, and an average particle size of 0.180 mm. In order to minimize the diffusional resistances the influence of flow rate on the breakthrough curves at feed concentrations of 1.56 meq/L for Fe(III) and 0.844 meq/L for Zn(II) was investigated. Flow rate of the minimal resistance in the bed according to mass transfer parameter were 2.0 mL/min for iron and 8.0 mL/min for zinc ions. Freundlich and Langmuir isotherm models have been used to represent the column equilibrium data. The iron dynamic isotherm was successfully modeled by the Langmuir equation and this mathematical model described well the experimental breakthrough curves for feed concentrations from 0.1 up to 3.5 meq/L. The zinc dynamic isotherm was successfully modeled by the Freundlich equation. This equilibrium model was applied to mathematical model. Experimental breakthrough curves could be predicted. Experiments were also carried out in a batch reactor to investigate the kinetics adsorption of the ions Fe(III) and Zn(II). Langmuir kinetic model fit well both experimental data.

  10. C-H-Activated Direct Arylation of Strong Benzothiadiazole and Quinoxaline-Based Electron Acceptors.

    PubMed

    Zhang, Junxiang; Parker, Timothy C; Chen, Wayne; Williams, LaRita; Khrustalev, Victor N; Jucov, Evgheni V; Barlow, Stephen; Timofeeva, Tatiana V; Marder, Seth R

    2016-01-15

    Electron acceptors are important components of π-conjugated materials, but the strong electron-withdrawing properties of the required synthetic intermediates often make them poor substrates in synthetic schemes designed around conventional organometallic cross-coupling. Here, strong benzodiimine-based acceptors, including 5,6-difluoro[2,1,3]benzothiadiazole, 5,6-dicyano[2,1,3]benzothiadiazole, 5,6-dicyanobenzo[d][1,2,3]triazole, 6,7-dicyanoquinoxaline, and 6,7-dinitroquinoxaline, are shown to undergo facile palladium-catalyzed C-H direct arylation with a variety of bromoarenes in moderate to high yields. The electrochemical characteristics of di-2-thienyl derivatives synthesized using this methodology are compared and suggest that, in an electron-transfer sense, 5,6-dicyano[2,1,3]benzothiadiazole is a comparably strong acceptor to benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole. The synthetic results suggest that high electron-withdrawing ability, which has traditionally limited reaction yields and structural variety in organic electronic materials, may be advantageous when employing C-H activated direct arylation in certain circumstances.

  11. The Impact of Ionizing Radiation on the Microbial Reduction of Fe(III)

    NASA Astrophysics Data System (ADS)

    Brown, A.; Correa, E. S.; Xu, Y.; Vaughan, D. J.; Pimblott, S. M.; Goodacre, R.; Lloyd, J. R.

    2014-12-01

    Biogeochemical processes mediated by Fe(III)-reducing bacteria have the potential to impact on the post-closure evolution of a geological disposal facility (GDF) for radioactive waste. However, the organisms promoting these processes will likely be subject to significant radiation fluxes. Therefore, the impact of acute doses of ionizing radiation on the physiological status of the model Fe(III)-reducing bacterium Shewanella oneidensis was assessed. FT-IR spectroscopy and MALDI-TOF-MS suggested that the metabolic response to radiation is underpinned by alterations to lipids and proteins. Furthermore, the irradiated phenotype exhibits enhanced Fe(III)-reduction. The impact of radiation on the extracellular environment was also assessed. Exposure to gamma radiation caused activation of ferrihydrite and hematite for enzymatic reduction by S. oneidensis. TEM, SAED and Mössbauer spectroscopy revealed that this effect was a result of radiation induced changes to crystallinity leading to an increase in bioavailability of Fe(III) for respiration. To assess the impact of radiation on sediment microbial communities, a series of microcosm experiments were constructed and gamma irradiated over a two month period. Sediments irradiated at a dose rate of 0.5 Gy h-1 exhibited enhanced Fe(III) reduction despite receiving doses potentially lethal to indigenous microorganisms, whilst biogeochemical processes in sediments irradiated with 30 Gy h-1 were only partially restricted. Despite this, 16S rRNA gene pyrosequencing revealed significant dose-dependent shifts in the microbial communities in tandem with changes in microcosm biogeochemical profiles. Collectively, these results indicate that, despite significant total absorbed doses, biogeochemical processes will likely not be restricted by dose rates expected in a deep geological repository. Indeed, electron accepting processes in such environments may even be stimulated by radiation.

  12. Mechanisms of Sb(III) Photooxidation by the Excitation of Organic Fe(III) Complexes.

    PubMed

    Kong, Linghao; He, Mengchang

    2016-07-01

    Organic Fe(III) complexes are widely distributed in the aqueous environment, which can efficiently generate free radicals under light illumination, playing a significant role in heavy metal speciation. However, the potential importance of the photooxidation of Sb(III) by organic Fe(III) complexes remains unclear. Therefore, the photooxidation mechanisms of Sb(III) were comprehensively investigated in Fe(III)-oxalate, Fe(III)-citrate and Fe(III)-fulvic acid (FA) solutions by kinetic measurements and modeling. Rapid photooxidation of Sb(III) was observed in an Fe(III)-oxalate solution over the pH range of 3 to 7. The addition of tert-butyl alcohol (TBA) as an ·OH scavenger quenched the Sb(III) oxidation, suggesting that ·OH is an important oxidant for Sb(III). However, the incomplete quenching of Sb(III) oxidation indicated the existence of other oxidants, presumably an Fe(IV) species in irradiated Fe(III)-oxalate solution. In acidic solutions, ·OH may be formed by the reaction of Fe(II)(C2O4) with H2O2, but a hypothetical Fe(IV) species may be generated by the reaction of Fe(II)(C2O4)2(2-) with H2O2 at higher pH. Kinetic modeling provides a quantitative explanation of the results. Evidence for the existence of ·OH and hypothetical Fe(IV) was also observed in an irradiated Fe(III)-citrate and Fe(III)-FA system. This study demonstrated an important pathway of Sb(III) oxidation in surface waters. PMID:27267512

  13. Decarboxylative 1,4-Addition of α-Oxocarboxylic Acids with Michael Acceptors Enabled by Photoredox Catalysis.

    PubMed

    Wang, Guang-Zu; Shang, Rui; Cheng, Wan-Min; Fu, Yao

    2015-10-01

    Enabled by iridium photoredox catalysis, 2-oxo-2-(hetero)arylacetic acids were decarboxylatively added to various Michael acceptors including α,β-unsaturated ester, ketone, amide, aldehyde, nitrile, and sulfone at room temperature. The reaction presents a new type of acyl Michael addition using stable and easily accessible carboxylic acid to formally generate acyl anion through photoredox-catalyzed radical decarboxylation. PMID:26366608

  14. Three Redox States of a Diradical Acceptor-Donor-Acceptor Triad: Gating the Magnetic Coupling and the Electron Delocalization.

    PubMed

    Souto, Manuel; Lloveras, Vega; Vela, Sergi; Fumanal, Maria; Ratera, Imma; Veciana, Jaume

    2016-06-16

    The diradical acceptor-donor-acceptor triad 1(••), based on two polychlorotriphenylmethyl (PTM) radicals connected through a tetrathiafulvalene(TTF)-vinylene bridge, has been synthesized. The generation of the mixed-valence radical anion, 1(•-), and triradical cation species, 1(•••+), obtained upon electrochemical reduction and oxidation, respectively, was monitored by optical and ESR spectroscopy. Interestingly, the modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes have been rationalized by theoretical calculations.

  15. 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.

  16. Covalent non-fused tetrathiafulvalene-acceptor systems.

    PubMed

    Pop, Flavia; Avarvari, Narcis

    2016-06-28

    Covalent donor-acceptor (D-A) systems have significantly contributed to the development of many organic materials and to molecular electronics. Tetrathiafulvalene (TTF) represents one of the most widely studied donor precursors and has been incorporated into the structure of many D-A derivatives with the objective of obtaining redox control and modulation of the intramolecular charge transfer (ICT), in order to address switchable emissive systems and to take advantage of its propensity to form regular stacks in the solid state. In this review, we focus on the main families of non-fused TTF-acceptors, which are classified according to the nature of the acceptor: nitrogen-containing heterocycles, BODIPY, perylenes and electron poor unsaturated hydrocarbons, as well as radical acceptors. We describe herein the most representative members of each family with a brief mention of their synthesis and a special focus on their D-A characteristics. Special attention is given to ICT and its modulation, fluorescence quenching and switching, photoconductivity, bistability and spin distribution by discussing and comparing spectroscopic and electrochemical features, photophysical properties, solid-state properties and theoretical calculations. PMID:27193500

  17. Fine structure of the Mn acceptor in GaAs

    NASA Astrophysics Data System (ADS)

    Krainov, I. V.; Debus, J.; Averkiev, N. S.; Dimitriev, G. S.; Sapega, V. F.; Lähderanta, E.

    2016-06-01

    We reveal the electronic level structure of the Mn acceptor, which consists of a valence-band hole bound to an Mn2 + ion, in presence of applied uniaxial stress and an external magnetic field in bulk GaAs. Resonant spin-flip Raman scattering is used to measure the g factor of the AMn0 center in the ground and excited states with the total angular momenta F =1 and F =2 and characterize the optical selection rules of the spin-flip transitions between these Mn-acceptor states. We determine the random stress fields near the Mn acceptor, the constant of the antiferromagnetic exchange interaction between the valence-band holes and the electrons of the inner Mn2 + shell as well as the deformation potential for the exchange energy. The p -d exchange energy, in particular, decreases significantly with increasing compressive stress. By combining the experimental Raman study with the developed theoretical model on the scattering efficiency, in which also the random local and external uniaxial stresses and magnetic field are considered, the fine structure of the Mn acceptor is determined in full detail.

  18. Transformation of Tetracycline Antibiotics and Fe(II) and Fe(III) Species Induced by Their Complexation.

    PubMed

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

    2016-01-01

    Tetracycline antibiotics (TCs) are frequently detected micropollutants and are known to have a strong tendency to complex with metal ions such as Fe(II) and Fe(III) in aquatic environments. Experiments with Fe(II) and TCs showed that the complexation of Fe(II) with tetracycline (TTC), oxytetracycline (OTC), or chlorotetracycline (CTC) could lead to the accelerated oxidation of Fe(II) and the promoted degradation of TCs simultaneously. The reaction started with complexation of Fe(II) with TC followed by oxidation of the Fe(II)-TC complex by dissolved oxygen to generate a Fe(III)-TC complex and reactive oxygen species (ROS). The ROS (primarily ·OH) then degraded TC. The oxidation rate constants of Fe(II) in the Fe(II)-H2L and Fe(II)-HL complexes were 0.269 and 1.511 min(-1), respectively, at ambient conditions (pH 7, 22 °C, and PO2 of 0.21 atm), which were about 60 and 350 times of the oxidation rate of uncomplexed Fe(II). Humic acids (HA) compete with TCs for Fe(II), but the effect was negligible at moderate HA concentrations (≤10 mg·L(-1)). Experiments with Fe(III) and TCs showed that the complexation of Fe(III) with TC could generate oxidized TC and Fe(II) without the need of oxygen at a relatively slower rate compared to the reaction involving Fe(II), O2, and TCs. These findings indicate the mutually influenced environmental transformation of TCs and Fe(II) and Fe(III) induced by their complexation. These newly identified reactions could play an important role in affecting the environmental fate of TCs and cycling of Fe(II) and Fe(III) in TCs-contaminated water and soil systems. PMID:26618388

  19. Development of imide- and imidazole-containing electron acceptors for use in donor-acceptor conjugated compounds and polymers

    NASA Astrophysics Data System (ADS)

    Li, Duo

    Conjugated organic compounds and polymers have attracted significant attention due to their potential application in electronic devices as semiconducting materials, such as organic solar cells (OSCs). In order to tune band gaps, donor-acceptor (D-A) structure is widely used, which has been proved to be one of the most effective strategies. This thesis consists of three parts: 1) design, syntheses and characterization of new weak acceptors based on imides and the systematic study of the structure-property relationship; (2) introduction of weak and strong acceptors in one polymer to achieve a broad coverage of light absorption and improve the power conversion efficiency (PCE); (3) modification of benzothiadiazole (BT) acceptor in order to increase the electron withdrawing ability. Imide-based electron acceptors, 4-(5-bromothiophen-2-y1)-2-(2-ethylhexyl)-9- phenyl- 1H-benzo[f]isoindole-1,3(2H)-dione (BIDO-1) and 4,9-bis(5-bromothiophen-2-yl)-2-(2-ethylhexyl)-benzo[f]isoindole-1,3-dione (BIDO-2), were designed and synthesized. In this design, naphthalene is selected as its main core to maintain a planar structure, and thienyl groups are able to facilitate the bromination reaction and lower the band gap. BIDO-1 and BIDO-2 were successfully coupled with different donors by both Suzuki cross-coupling and Stille cross-coupling reactions. Based on the energy levels and band gaps of the BIDO-containing compounds and polymers, BIDO-1 and BIDO-2 are proved to be weak electron acceptors. Pyromellitic diimide (PMDI) was also studied and found to be a stronger electron acceptor than BIDO . In order to obtain broad absorption coverage, both weak acceptor ( BIDO-2) and strong acceptor diketopyrrolopyrrole (DPP) were introduced in the same polymer. The resulting polymers show two absorption bands at 400 and 600 nm and two emission peaks at 500 and 680 nm. The band gaps of the polymers are around 1.6 eV, which is ideal for OSC application. The PCE of 1.17% was achieved. Finally

  20. 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

  1. Acceptor conductivity in bulk zinc oxide (0001) crystals

    NASA Astrophysics Data System (ADS)

    Adekore, Bababunmi Tolu

    ZnO is a promising wide bandgap semiconductor. Its renowned and prominent properties as its bandgap of 3.37eV at 4.2K; its very high excitonic binding energy, 60meV; its high melting temperature, 2248K constitute the basis for the recently renewed and sustained scientific interests in the material. In addition to the foregoing, the availability of bulk substrates of industrially relevant sizes provides important opportunities such as homoepitaxial deposition of the material which is a technological asset in the production of efficient optoelectronic and electronic devices. The nemesis of wide bandgap materials cannot be more exemplified than in ZnO. The notorious limitation of asymmetric doping and the haunting plague of electrically active point defects dim the bright future of the material. In this case, the search for reliable and consistent acceptor conductivity in bulk substrates has been hitherto, unsuccessful. In the dissertation that now follows, our efforts have been concerted in the search for a reliable acceptor. We have carefully investigated the science of point defects in the material, especially those responsible for the high donor conductivity. We also investigated and herein report variety of techniques of introducing acceptors into the material. We employ the most relevant and informative characterization techniques in verifying both the intended conductivity and the response of intrinsic crystals to variation in temperature and strain. And finally we explain deviations, where they exist, from ideal acceptor characteristics. Our work on reliable acceptor has been articulated in four papers. The first establishing capacitance based methods of monitoring electrically active donor defects. The second investigates the nature of anion acceptors on the oxygen sublattice. A study similar to the preceding study was conducted for cation acceptors on the zinc sublattice and reported in the third paper. Finally, an analysis of the response of the crystal to

  2. Modelling transport and degradation of de-icing chemicals in soil, assuming Monod kinetics with multiple electron-acceptors

    NASA Astrophysics Data System (ADS)

    Schotanus, D.; Meeussen, J. C. L.; van der Ploeg, M. J.; van der Zee, S. E. A. T. M.

    2012-04-01

    De-icing chemicals that contain propylene glycol are used at Oslo airport during winter time. A fraction of these chemicals is spilled on the runway and can be transported rapidly in the sandy soil in spring during snowmelt. Better insight into the chemical and physical processes that govern the fate of these chemicals in soil will help to estimate potential effects on the large unconfined aquifer in this area, and makes it possible to evaluate potential remedial actions. Micro-organisms in the soil can degrade propylene glycol, for which they need electron-acceptors. Under aerobic conditions, oxygen will be used as an electron-acceptor. From experiments, it is known that also anaerobic degradation occurs in this soil. During snowmelt, high infiltration rates can lead to locally saturated soil. In these parts, oxygen diffusion is limited and thus anaerobic conditions will occur. In these anaerobic regions, other electron-acceptors, such as manganese-oxides that are present in this soil, are used. However, frequent propylene glycol application may lead to a depletion of manganese-oxides and so to increased persistence and migration of propylene glycol in soil. To prevent this depletion and to enhance biodegradation, other electron-acceptors can be applied at the soil surface. Examples are the application of nitrate to the soil surface, and air injection. Model calculations could help to estimate required concentrations. The objectives of this study are 1) to create the reactive model, 2) to use this model to evaluate which parameters are determining leaching fluxes of propylene glycol from the soil, and 3) to evaluate the effectiveness of the different remediation strategies. Therefore, transient water flow, kinetic degradation, and redox chemistry were combined in one model. Degradation is modelled with Monod kinetics using multiple electron-acceptors. Oxygen diffusion in the gas phase, biomass growth, and oxidation and reduction of the important electron-acceptors

  3. Fourier-transform photoluminescence spectroscopy of excitons bound to group-III acceptors in silicon: Uniaxial stress

    NASA Astrophysics Data System (ADS)

    Karasyuk, V. A.; Thewalt, M. L. W.; An, S.; Lightowlers, E. C.

    1997-12-01

    Photoluminescence of excitons bound to Al, Ga, In, and Tl acceptors in Si crystals subjected to <001>, <111>, or <110> uniaxial stress was studied at liquid-He temperatures with 0.0025-meV spectral resolution. The deformation-potential constants of the group-III acceptors in the ground state are (in eV) b=-1.01+/-0.02, d=-3.31+/-0.06 for Al, b=-1.03+/-0.02, d=-3.10+/-0.06 for Ga, b=-0.43+/-0.01, d=-2.41+/-0.05 for In, and b=-0.30+/-0.03, d=-1.95+/-0.2 for Tl. The shear deformation-potential constant for electrons in acceptor bound excitons Ξu=8.6 eV for all group-III acceptors within an experimental error of +/-0.15 eV for Al, Ga, and In, and +/-0.8 eV for Tl. The order of the valley-orbit states in Tl bound excitons is Γ1, Γ3, Γ5 with the Γ5 energy 1.21 meV above Γ1, and 0.10 meV above Γ3. All details of the spectra including positions, relative amplitudes, and polarizations of the components have been explained on the basis of a simple model of acceptor bound excitons with holes in the J=0 state taking into account the valley-orbit splitting and the spin-orbit coupling of the electron. Significant deviations from the theoretical predictions were observed only for very small strains producing acceptor splittings comparable with the intrinsic zero-stress splitting.

  4. 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

    SciTech Connect

    Nissen, Silke; Liu, Xiaoxin; Chourey, Karuna; Hettich, Robert {Bob} L; Wagner, Darlene D; Pffifner, Susan; Loeffler, Frank E

    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 grown 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.

  5. Structure of Fe(III) precipitates generated by the electrolytic dissolution of Fe(0) in the presence of groundwater ions

    NASA Astrophysics Data System (ADS)

    van Genuchten, Case M.; Peña, Jasquelin; Amrose, Susan E.; Gadgil, Ashok J.

    2014-02-01

    We apply Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and pair distribution function (PDF) analysis of high-energy X-ray scattering to investigate the effects of bivalent cation-oxyanion pairs on the structure of Fe(III) precipitates formed from the oxidation of Fe(II) generated by the electrolytic dissolution of Fe(0) electrodes. We found that Fe(II) oxidation in the presence of weakly adsorbing electrolytes (NaCl, CaCl2, MgCl2) leads to pseudo-lepidocrocite (Lp; γ-FeOOH), a poorly crystalline version of Lp with low sheet-stacking coherence. In the absence of bivalent cations, P and As(V) have similar uptake behavior, but different effects on the average Fe(III) precipitate structure: pseudo-Lp dominates in the presence of P, whereas a disordered ferrihydrite-like precipitate akin to hydrous ferric oxide (HFO) is the dominant phase that forms in the presence of As(V). Despite its lower affinity for Fe(III) precipitates, Si leads to Si-HFO in all conditions tested. The presence of 1 mM Ca2+ or Mg2+ enhances oxyanion uptake, destabilizes the colloidally stable oxyanion-bearing particle suspensions and, in some P and As(V) electrolytes, results in more crystalline precipitates. The trends in oxyanion uptake and Fe(III) precipitate structure in the presence of Ca2+/Mg2+ suggest a systematic decrease in the strength of bivalent cation:oxyanion interaction in the order of Ca2+ > Mg2+ and P > As(V) ≫ Si. Using the PDF technique, we identify the polyhedral linkages that contribute to the intermediate structures (>6 Å) of disordered, nanoscale oxyanion-bearing Fe(III) precipitate samples. Our results suggest that oxyanions present during Fe(III) polymerization bind to corner-sharing Fe surface sites leading to a precipitate surface deficient in corner-sharing Fe, whereas the edge- and corner-sharing Fe sites in the precipitate core likely remain intact.

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

    PubMed

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

    2016-08-21

    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.

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

    PubMed

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

    2016-08-21

    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. PMID:27305145

  8. Interface effects on acceptor qubits in silicon and germanium.

    PubMed

    Abadillo-Uriel, J C; Calderón, M J

    2016-01-15

    Dopant-based quantum computing implementations often require the dopants to be situated close to an interface to facilitate qubit manipulation with local gates. Interfaces not only modify the energies of the bound states but also affect their symmetry. Making use of the successful effective mass theory we study the energy spectra of acceptors in Si or Ge taking into account the quantum confinement, the dielectric mismatch and the central cell effects. The presence of an interface puts constraints to the allowed symmetries and leads to the splitting of the ground state in two Kramers doublets (Mol et al 2015 Appl. Phys. Lett. 106 203110). Inversion symmetry breaking also implies parity mixing which affects the allowed optical transitions. Consequences for acceptor qubits are discussed. PMID:26618443

  9. Free Carrier Generation in Organic Photovoltaic Bulk Heterojunctions of Conjugated Polymers with Molecular Acceptors: Planar versus Spherical Acceptors

    SciTech Connect

    Nardes, Alexandre M.; Ferguson, Andrew J.; Wolfer, Pascal; Gui, Kurt; Burn, Paul L.; Meredith, Paul; Kopidakis, Nikos

    2014-03-05

    We present a comparative study of the photophysical performance of the prototypical fullerene derivative PC61BM with a planar small-molecule acceptor in an organic photovoltaic device. The small-molecule planar acceptor is 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile, termed K12. We discuss photoinduced free charge-carrier generation and transport in blends of PC61BM or K12 with poly(3-n-hexylthiophene) (P3HT), surveying literature results for P3HT:PC61BM and presenting new results on P3HT:K12. For both systems we also review previous work on film structure and correlate the structural and photophysical results. In both cases, a disordered mixed phase is formed between P3HT and the acceptor, although the photophysical properties of this mixed phase differ markedly for PC61BM and K12. In the case of PC61BM the mixed phase acts as a free carrier generation region that can efficiently shuttle carriers to the pure polymer and fullerene domains. As a result, the vast majority of excitons quenched in P3HT:PC61BM blends yield free carriers detected by the contactless time-resolved microwave conductivity (TRMC) method. In contrast, approximately 85 % of the excitons quenched in P3HT:K12 do not result in free carriers over the nanosecond timescale of the TRMC experiment. We attribute this to poor electron-transport properties in the mixed P3HT:K12 phase. Here, we propose that the observed differences can be traced to the respective shapes of PC61BM and K12: the three-dimensional nature of the fullerene cage facilitates coupling between PC61BM molecules irrespective of their relative orientation, whereas for K12 strong electronic coupling is only expected for molecules oriented with their π systems parallel to each other. Comparison between the eutectic compositions of the P3HT:PC61BM and P3HT:K12 shows that the former contains enough fullerene to form a percolation pathway for electrons, whereas the latter contains a sub

  10. Free carrier generation in organic photovoltaic bulk heterojunctions of conjugated polymers with molecular acceptors: planar versus spherical acceptors.

    PubMed

    Nardes, Alexandre M; Ferguson, Andrew J; Wolfer, Pascal; Gui, Kurt; Burn, Paul L; Meredith, Paul; Kopidakis, Nikos

    2014-06-01

    A comparative study of the photophysical performance of the prototypical fullerene derivative PC61BM with a planar small-molecule acceptor in an organic photovoltaic device is presented. The small-molecule planar acceptor is 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile, termed K12. We discuss photoinduced free charge-carrier generation and transport in blends of PC61BM or K12 with poly(3-n-hexylthiophene) (P3HT), surveying literature results for P3HT:PC61BM and presenting new results on P3HT:K12. For both systems we also review previous work on film structure and correlate the structural and photophysical results. In both cases, a disordered mixed phase is formed between P3HT and the acceptor, although the photophysical properties of this mixed phase differ markedly for PC61BM and K12. In the case of PC61BM the mixed phase acts as a free carrier generation region that can efficiently shuttle carriers to the pure polymer and fullerene domains. As a result, the vast majority of excitons quenched in P3HT:PC61BM blends yield free carriers detected by the contactless time-resolved microwave conductivity (TRMC) method. In contrast, approximately 85% of the excitons quenched in P3HT:K12 do not result in free carriers over the nanosecond timescale of the TRMC experiment. We attribute this to poor electron-transport properties in the mixed P3HT:K12 phase. We propose that the observed differences can be traced to the respective shapes of PC61BM and K12: the three-dimensional nature of the fullerene cage facilitates coupling between PC61BM molecules irrespective of their relative orientation, whereas for K12 strong electronic coupling is only expected for molecules oriented with their π systems parallel to each other. Comparison between the eutectic compositions of the P3HT:PC61BM and P3HT:K12 shows that the former contains enough fullerene to form a percolation pathway for electrons, whereas the latter contains a sub

  11. Free carrier generation in organic photovoltaic bulk heterojunctions of conjugated polymers with molecular acceptors: planar versus spherical acceptors.

    PubMed

    Nardes, Alexandre M; Ferguson, Andrew J; Wolfer, Pascal; Gui, Kurt; Burn, Paul L; Meredith, Paul; Kopidakis, Nikos

    2014-06-01

    A comparative study of the photophysical performance of the prototypical fullerene derivative PC61BM with a planar small-molecule acceptor in an organic photovoltaic device is presented. The small-molecule planar acceptor is 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile, termed K12. We discuss photoinduced free charge-carrier generation and transport in blends of PC61BM or K12 with poly(3-n-hexylthiophene) (P3HT), surveying literature results for P3HT:PC61BM and presenting new results on P3HT:K12. For both systems we also review previous work on film structure and correlate the structural and photophysical results. In both cases, a disordered mixed phase is formed between P3HT and the acceptor, although the photophysical properties of this mixed phase differ markedly for PC61BM and K12. In the case of PC61BM the mixed phase acts as a free carrier generation region that can efficiently shuttle carriers to the pure polymer and fullerene domains. As a result, the vast majority of excitons quenched in P3HT:PC61BM blends yield free carriers detected by the contactless time-resolved microwave conductivity (TRMC) method. In contrast, approximately 85% of the excitons quenched in P3HT:K12 do not result in free carriers over the nanosecond timescale of the TRMC experiment. We attribute this to poor electron-transport properties in the mixed P3HT:K12 phase. We propose that the observed differences can be traced to the respective shapes of PC61BM and K12: the three-dimensional nature of the fullerene cage facilitates coupling between PC61BM molecules irrespective of their relative orientation, whereas for K12 strong electronic coupling is only expected for molecules oriented with their π systems parallel to each other. Comparison between the eutectic compositions of the P3HT:PC61BM and P3HT:K12 shows that the former contains enough fullerene to form a percolation pathway for electrons, whereas the latter contains a sub

  12. Quantum confined acceptors and donors in InSe nanosheets

    SciTech Connect

    Mudd, G. W.; Patanè, A. Makarovsky, O.; Eaves, L.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Fay, M. W.; Zólyomi, V.; Falko, V.

    2014-12-01

    We report on the radiative recombination of photo-excited carriers bound at native donors and acceptors in exfoliated nanoflakes of nominally undoped rhombohedral γ-polytype InSe. The binding energies of these states are found to increase with the decrease in flake thickness, L. We model their dependence on L using a two-dimensional hydrogenic model for impurities and show that they are strongly sensitive to the position of the impurities within the nanolayer.

  13. An extended Foerster-Dexter model for correlated donor-acceptor placement in solid state materials

    NASA Astrophysics Data System (ADS)

    Rotman, S. R.; Hartmann, F. X.

    1987-09-01

    The current theory of donor-acceptor interactions in solid-state materials is based on a random distribution of donors and acceptors through the crystal. In this paper, we present a model to calculate the observable transfer rates for the correlated positioning of donors and acceptors in laser materials. Chemical effects leading to such correlations are discussed.

  14. 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.

  15. Income-generating activities for family planning acceptors.

    PubMed

    1989-07-01

    The Income Generating Activities program for Family Planning Acceptors was introduced in Indonesia in 1979. Capital input by the Indonesian National Family Planning Coordination Board and the UN Fund for Population Activities was used to set up small businesses by family planning acceptors. In 2 years, when the businesses become self-sufficient, the loans are repaid, and the money is used to set up new family planning acceptors in business. The program strengthens family planning acceptance, improves the status of women, and enhances community self-reliance. The increase in household income generated by the program raises the standards of child nutrition, encourages reliance on the survival of children, and decreases the value of large families. Approximately 18,000 Family Planning-Income Generating Activities groups are now functioning all over Indonesia, with financial assistance from the central and local governments, the World Bank, the US Agency for International Development, the UN Population Fund, the Government of the Netherlands, and the Government of Australia through the Association of South East Asian Nations.

  16. Virtual screening of electron acceptor materials for organic photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Halls, Mathew D.; Djurovich, Peter J.; Giesen, David J.; Goldberg, Alexander; Sommer, Jonathan; McAnally, Eric; Thompson, Mark E.

    2013-10-01

    Virtual screening involves the generation of structure libraries, automated analysis to predict properties related to application performance and subsequent screening to identify lead systems and estimate critical structure-property limits across a targeted chemical design space. This approach holds great promise for informing experimental discovery and development efforts for next-generation materials, such as organic semiconductors. In this work, the virtual screening approach is illustrated for nitrogen-substituted pentacene molecules to identify systems for development as electron acceptor materials for use in organic photovoltaic (OPV) devices. A structure library of tetra-azapentacenes (TAPs) was generated by substituting four nitrogens for CH at 12 sites on the pentacene molecular framework. Molecular properties (e.g. ELUMO, Eg and μ) were computed for each candidate structure using hybrid DFT at the B3LYP/6-311G** level of theory. The resulting TAPs library was then analyzed with respect to intrinsic properties associated with OPV acceptor performance. Marcus reorganization energies for charge transport for the most favorable TAP candidates were then calculated to further determine suitability as OPV electron acceptors. The synthesis, characterization and OPV device testing of TAP materials is underway, guided by these results.

  17. Design directed self-assembly of donor-acceptor polymers.

    PubMed

    Marszalek, Tomasz; Li, Mengmeng; Pisula, Wojciech

    2016-09-21

    Donor-acceptor polymers with an alternating array of donor and acceptor moieties have gained particular attention during recent years as active components of organic electronics. By implementation of suitable subunits within the conjugated backbone, these polymers can be made either electron-deficient or -rich. Additionally, their band gap and light absorption can be precisely tuned for improved light-harvesting in solar cells. On the other hand, the polymer design can also be modified to encode the desired supramolecular self-assembly in the solid-state that is essential for an unhindered transport of charge carriers. This review focuses on three major factors playing a role in the assembly of donor-acceptor polymers on surfaces which are (1) nature, geometry and substitution position of solubilizing alkyl side chains, (2) shape of the conjugated polymer defined by the backbone curvature, and (3) molecular weight which determines the conjugation length of the polymer. These factors adjust the fine balance between attractive and repulsive forces and ensure a close polymer packing important for an efficient charge hopping between neighboring chains. On the microscopic scale, an appropriate domain formation with a low density of structural defects in the solution deposited thin film is crucial for the charge transport. The charge carrier transport through such thin films is characterized by field-effect transistors as basic electronic elements. PMID:27440174

  18. 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.

  19. 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.

  20. 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.

  1. SERS Activity of Silver Nanoparticles Functionalized with A Desferrioxamine B Derived Ligand for FE(III) Binding and Sensing

    NASA Astrophysics Data System (ADS)

    Galinetto, P.; Taglietti, A.; Pasotti, L.; Pallavicini, P.; Dacarro, G.; Giulotto, E.; Grandi, M. S.

    2016-01-01

    We report the SERS activity of colloidal silver nanoparticles functionalized with a ligand, derived from the siderophore desferrioxamine B (desferal, DFO), an iron chelator widely used in biological and medical applications. The ligand was equipped with a sulfur-containing moiety to ensure optimal binding with silver surfaces. By means of Raman and SERS effects we monitored the route of material preparation from the modified DFO-S molecule to the colloidal aggregates. The results indicate that the functionalization of the chelating agent does not affect its binding ability towards Fe(III). The resulting functionalized silver nanoparticles are a promising SERS tag for operation in biological environments. The Fe-O stretching signature, arising when DFO-S grafted to silver nanoparticles binds Fe(III), could provide a tool for cation sensing in solution.

  2. Biochar-Facilitated Reduction of Crystalline Fe(III) in Hematite

    NASA Astrophysics Data System (ADS)

    Xu, S.; Yang, Y.; Roden, E. E.; Tang, Y.; Huang, R.; Adhikari, D.

    2015-12-01

    Pyrogenic organic matter is a significant component of soil organic matter, the transformation of which may play a crucial role in the coupled redox cycles of carbon and iron. However, scant information is available for the role of pyrogenic carbon in the redox cycle of iron. Herein, we studied the influences of wheat straw-derived biochar on the microbial reduction of hematite by Shewanella oneidensis MR-1. In the presence of 10 mg/L biochar, microbial reduction of hematite was substantially accelerated by 41% to 142%. Reduction of hematite was enhanced to similar degrees by aqueous biochar with the concentration of 1-3 mg C/L. Importance of the aqueous biochar was also supported by the response of enhancement of Fe reduction to the dose of biochar particles, closely linked to the change in aqueous biochar concentration rather than the amount of total biochar particles. Microbiologically pre-reduced biochar reduced hematite abiotically, demonstrating the electron shuttling capacity of aqueous biochar for hematite reduction. On the other side, biochar particles sorbed Fe(II) and consequently decreased the accumulation of Fe(II) in solution to facilitate the reduction of hematite further. We reported for the first time the biochar-facilitated microbial reduction of crystalline Fe(III), through electron shuttling processes mediated by aqueous biochar and complexation of Fe(II) by biochar particles. Such impacted redox cycles of Fe would be important for the soil environment with relatively high content of indigenous pyrogenic carbon or substantial application of biochar.

  3. Antioxidant, tautomerism and antibacterial studies of Fe(III)-1,2,4-triazole based complexes

    NASA Astrophysics Data System (ADS)

    Kharadi, G. J.

    2013-06-01

    New Fe(III) complexes have been synthesized by the reactions of ferric nitrate with Schiff base derived from 3-substituted phenyl-4-amino-5-hydrazino-1,2,4-triazole and indoline-2,3-dione. All these complexes are soluble in DMF and DMSO; low molar conductance values indicate that they are non-electrolytes. Elemental analyses suggest that the complexes have 1:1 stoichiometry of the type [FeLn(H2O)(OH)]·xH2O. Structural and spectroscopic properties have been studied on the basis of elemental analyses, infrared spectra, 1H and 13H NMR spectra, electronic spectra, magnetic measurements and FAB mass spectra. FT-IR, 1H and 13H NMR studies reveal that the ligand (Ln) exists in the tautomeric enol form in both the states with intramolecular hydrogen bonding. Magnetic moment and reflectance spectral studies reveal that an octahedral geometry has been assigned to all the prepared complexes. FRAP values indicate that all the compounds have a ferric reducing antioxidant power. The compounds 2 and 3 showed relatively high antioxidant activity while compound 1 and 4 shows poor antioxidant power. Also good antimicrobial activities of the complexes against Staphylococcus aureus, Bacillus subtilis, Serratia marcescens, Pseudomonas aeruginosa and Escherichia coli have been found compared to its free ligands.

  4. Measuring "free" iron levels in Caenorhabditis elegans using low-temperature Fe(III) electron paramagnetic resonance spectroscopy.

    PubMed

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

    2006-11-15

    Oxidative stress, caused by free radicals within the body, has been associated with the process of aging and many human diseases. Because free radicals, in particular superoxide, are difficult to measure, an alternative indirect method for measuring oxidative stress levels has been used successfully in Escherichia 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 that 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 electron paramagnetic resonance (EPR) detectable "free" iron levels. In the current study, we have developed a reliable and efficient method for measuring "free" iron levels in Caenorhabditis elegans using low-temperature Fe(III) EPR at g=4.3. This method uses synchronized worm cultures grown on plates that 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, whereas desferrioxamine treatment significantly raised these levels, indicating the 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 among oxidative stress, "free" iron levels, and longevity in C. elegans.

  5. Evaluation of siderite and magnetite formation in BIFs by pressure-temperature experiments of Fe(III) minerals and microbial biomass

    NASA Astrophysics Data System (ADS)

    Halama, Maximilian; Swanner, Elizabeth D.; Konhauser, Kurt O.; Kappler, Andreas

    2016-09-01

    Anoxygenic phototrophic Fe(II)-oxidizing bacteria potentially contributed to the deposition of Archean banded iron formations (BIFs), before the evolution of cyanobacterially-generated molecular oxygen (O2), by using sunlight to oxidize aqueous Fe(II) and precipitate Fe(III) (oxyhydr)oxides. Once deposited at the seafloor, diagenetic reduction of the Fe(III) (oxyhydr)oxides by heterotrophic bacteria produced secondary Fe(II)-bearing minerals, such as siderite (FeCO3) and magnetite (Fe3O4), via the oxidation of microbial organic carbon (i.e., cellular biomass). During deeper burial at temperatures above the threshold for life, thermochemical Fe(III) reduction has the potential to form BIF-like minerals. However, the role of thermochemical Fe(III) reduction of primary BIF minerals during metamorphism, and its impact on mineralogy and geochemical signatures in BIFs, is poorly understood. Consequently, we simulated the metamorphism of the precursor and diagenetic iron-rich minerals (ferrihydrite, goethite, hematite) at low-grade metamorphic conditions (170 °C, 1.2 kbar) for 14 days by using (1) mixtures of abiotically synthesized Fe(III) minerals and either microbial biomass or glucose as a proxy for biomass, and (2) using biogenic minerals formed by phototrophic Fe(II)-oxidizing bacteria. Mössbauer spectroscopy and μXRD showed that thermochemical magnetite formation was limited to samples containing ferrihydrite and glucose, or goethite and glucose. No magnetite was formed from Fe(III) minerals when microbial biomass was present as the carbon and electron sources for thermochemical Fe(III) reduction. This could be due to biomass-derived organic molecules binding to the mineral surfaces and preventing solid-state conversion to magnetite. Mössbauer spectroscopy revealed siderite contents of up to 17% after only 14 days of incubation at elevated temperature and pressure for all samples with synthetic Fe(III) minerals and biomass, whereas 6% of the initial Fe(III) was

  6. [FI-KR non-separated method coupled with FAAS for the determination of Fe(II) and Fe(III) in water].

    PubMed

    Wang, Zhong-yuan; Zhang, Hong-kang; Fang, Hong-da; Su, Yao-dong; Mittal, Gauri S

    2012-03-01

    An FI-KR non-separated method coupled with FAAS for the determination of Fe(II) and Fe(III) was developed. With 60 s of sampling at a flow rate of 6.0 mL x min(-1), EF of 41 for Fe(III) and 9 for Fe(II) were obtained. The precision (RSD, n = 11) for Fe(III) and Fe(II) was 2.3% and 3.1% at the 0.04 mg x L(-1) level respectively. When 0.1 per thousand phi TEA was used as masking reagent, the recovery rate for Fe(III) and Fe(II) was from 97% to 101% and from 96% to 100% respectively.

  7. 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.

  8. 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. PMID:27027418

  9. 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

  10. Fe(III) doped and grafted PbTiO{sub 3} film photocathode with enhanced photoactivity for hydrogen production

    SciTech Connect

    Hu, Yuxiang; Dong, Wen; Zheng, Fengang; Fang, Liang; Shen, Mingrong

    2014-08-25

    The photoelectrochemical activity of the PbTiO{sub 3} film photocathode deposited on indium tin oxide-coated quartz substrate was significantly improved through modifying the film surface by both the Fe(III) doping and grafting. Doping the PbTiO{sub 3} with Fe(III) ions narrows its band gap thus increases the visible light utilization, while the surface-grafted Fe(III) ions on the doped PbTiO{sub 3} surface are helpful to improve the charge transfer on the photocathode/electrolyte interface. Consequently, the photocurrent was increased from 38 μA/cm{sup 2} to 220 μA/cm{sup 2} under the irradiation of 100 mW/cm{sup 2} Xe lamp by using 0.1M Na{sub 2}SO{sub 4} as an electrolyte and zero-potential versus saturated calomel as a reference electrode. The corresponding increase in open circuit voltage was 0.95–1.11 V.

  11. Redox potentials of Ti(IV) and Fe(III) complexes provide insights into titanium biodistribution mechanisms.

    PubMed

    Parker Siburt, Claire J; Lin, Emily M; Brandt, Sara J; Tinoco, Arthur D; Valentine, Ann M; Crumbliss, Alvin L

    2010-09-01

    Transferrin, the human iron transport protein, binds Ti(IV) even more tightly than it binds Fe(III). However, the fate of titanium bound to transferrin is not well understood. Here we present results which address the fate of titanium once bound to transferrin. We have determined the redox potentials for a series of Ti(IV) complexes and have used these data to develop a linear free energy relationship (LFER) correlating Ti(IV) <==> Ti(III) redox processes with Fe(III) <==> Fe(II) redox processes. This LFER enables us to compare the redox potentials of Fe(III) complexes and Ti(IV) complexes that mimic the active site of transferrin and allows us to predict the redox potential of titanium-transferrin. Using cyclic voltammetry and discontinuous metalloprotein spectroelectrochemistry (dSEC) in conjunction with the LFER, we report that the redox potential of titanium-transferrin is lower than -600 mV (lower than that of iron-transferrin) and is predicted to be ca. -900 mV vs. NHE (normal hydrogen electrode). We conclude that Ti(IV)/Ti(III) reduction in titanium-transferrin is not accessible by biological reducing agents. This observation is discussed in the context of current hypotheses concerning the role of reduction in transferrin mediated iron transport. PMID:20569990

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Kinetics of DCE and VC mineralization under methanogenic and Fe(III)- reducing conditions

    USGS Publications Warehouse

    Bradley, P.M.; Chapelle, F.H.

    1997-01-01

    The kinetics of anaerobic mineralization of DCE and VC under mathanogenic and Fe(III)-reducing conditions as a function of dissolved contaminant concentration were evaluated. Microorganisms indigenous to creek bed sediments, where groundwater contaminated with chlorinated ethenes continuously discharges, demonstrated significant mineralization of DCE and VC under methanogenic and Fe(III)- reducing conditions. Over 37 days, the recovery of [1,214C]VC radioactivity as 14CO2 ranged from 5% to 44% and from 8% to 100% under methanogenic and Fe(III)-reducing conditions, respectively. The recovery of [1,2-14C]DCE radioactivity as 14CO2 ranged from 4% to 14% and did not vary significantly between methanogenic and Fe(III)reducing conditions. VC mineralization was described by Michaelis- Menten kinetics. Under methanogenic conditions, V(max) was 0.19 ?? 0.01 ??mol L-1 d-1 and the half-saturation constant, k(m), was 7.6 ?? 1.7 ??M. Under Fe(III)-reducing conditions, V(max) was 0.76 ?? 0.07 ??mol L-1 d-1 and k(m) was 1.3 ?? 0.5 ??M. In contrast, DCE mineralization could be described by first-order kinetics. The first-order degradation rate constant for DCE mineralization was 0.6 ?? 0.2% d-1 under methanogenic and Fe(III)-reducing conditions. The results indicate that the kinetics of chlorinated ethane mineralization can vary significantly with the specific contaminant and the predominant redox conditions under which mineralization occurs.

  17. 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

  18. Nanostructured donor-acceptor self assembly with improved photoconductivity.

    PubMed

    Saibal, B; Ashar, A Z; Devi, R Nandini; Narayan, K S; Asha, S K

    2014-11-12

    Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly.

  19. Nanostructured donor-acceptor self assembly with improved photoconductivity.

    PubMed

    Saibal, B; Ashar, A Z; Devi, R Nandini; Narayan, K S; Asha, S K

    2014-11-12

    Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly. PMID:25283356

  20. Incorporation of Cu Acceptors in ZnO Nanocrystals

    SciTech Connect

    Oo, W.M.H.; Mccluskey, Matthew D.; Huso, Jesse; Morrison, J.; Bergman, Leah; Engelhard, Mark H.; Saraf, Laxmikant V.

    2010-09-16

    Doping of semiconductor nanocrystals is an important problem in nanomaterials research. Using infrared (IR) and x-ray photoelectron spectroscopy (XPS), we have observed Cu acceptor dopants that were intentionally introduced into ZnO nanocrystals. The incorporation of Cu2+ dopants increased as the diameter of the nanocrystals was increased from ~3 to 5 nm. Etching the nanocrystals with acetic acid revealed a core-shell structure, where a 2-nm lightly doped core is surrounded by a heavily doped shell. These observations are consistent with the trapped dopant model, in which dopant atoms stick to the surface of the core and are overgrown by the nanocrystal material.

  1. Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors

    SciTech Connect

    Hartshorne, Robert S.; Jepson, Brian N.; Clarke, Thomas A.; Field, Sarah J.; Fredrickson, Jim K.; Zachara, John M.; Shi, Liang; Butt, Julea N.; Richardson, David

    2007-09-04

    Abstract MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV–vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately *500 mV (vs. the standard hydrogen electrode). Across this potential window the UV– vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled lowspin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate.

  2. 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.

  3. 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. PMID:27229725

  4. Controlling charge separation and recombination by chemical design in donor-acceptor dyads.

    PubMed

    Liu, Li; Eisenbrandt, Pierre; Roland, Thomas; Polkehn, Matthias; Schwartz, Pierre-Olivier; Bruchlos, Kirsten; Omiecienski, Beatrice; Ludwigs, Sabine; Leclerc, Nicolas; Zaborova, Elena; Léonard, Jérémie; Méry, Stéphane; Burghardt, Irene; Haacke, Stefan

    2016-07-21

    Conjugated donor-acceptor block co-oligomers that self-organize into D-A mesomorphic arrays have raised increasing interest due to their potential applications in organic solar cells. We report here a combined experimental and computational study of charge transfer (CT) state formation and recombination in isolated donor-spacer-acceptor oligomers based on bisthiophene-fluorene (D) and perylene diimide (A), which have recently shown to self-organize to give a mesomorphic lamellar structure at room temperature. Using femtosecond transient absorption spectroscopy and Time-Dependent Density Functional Theory in combination with the Marcus-Jortner formalism, the observed increase of the CT lifetimes is rationalized in terms of a reduced electronic coupling between D and A brought about by the chemical design of the donor moiety. A marked dependence of the CT lifetime on solvent polarity is observed, underscoring the importance of electrostatic effects and those of the environment at large. The present investigation therefore calls for a more comprehensive design approach including the effects of molecular packing. PMID:27341086

  5. Dissimilatory reduction of extracellular electron acceptors in anaerobic respiration.

    PubMed

    Richter, Katrin; Schicklberger, Marcus; Gescher, Johannes

    2012-02-01

    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.

  6. Functional analysis of a C. elegans trans-splice acceptor.

    PubMed Central

    Conrad, R; Liou, R F; Blumenthal, T

    1993-01-01

    The rol-6 gene is trans-spliced to the 22 nt leader, SL1, 173 nt downstream of the transcription start. We have analyzed splicing in transformants carrying extrachromosomal arrays of rol-6 with mutations in the trans-splice acceptor site. This site is a close match to the consensus, UUUCAG, that is highly conserved in both trans-splice and intron acceptor sites in C. elegans. When the trans-splice site was inactivated by mutating the perfectly-conserved AG, trans-splicing still occurred, but at a cryptic site 20 nt upstream. We tested the frequency with which splicing switched from the normal site to the cryptic site when the pyrimidines at this site were changed to A's. Since most C. elegans 3' splice sites lack an obvious polypyrimidine tract, we hypothesized that these four pyrimidines might play this role, and indeed mutation of these bases caused splicing to switch to the cryptic site. We also demonstrated that a major reason the downstream site is normally favored is because it occurs at a boundary between A+U rich and non-A+U rich RNA. When the RNA between the two splice sites was made less A+U rich, splicing occurred preferentially at the upstream site. Images PMID:8451190

  7. 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

  8. Donor-acceptor complexation and dehydrogenation chemistry of aminoboranes.

    PubMed

    Malcolm, Adam C; Sabourin, Kyle J; McDonald, Robert; Ferguson, Michael J; Rivard, Eric

    2012-12-01

    A series of formal donor-acceptor adducts of aminoborane (H(2)BNH(2)) and its N-substituted analogues (H(2)BNRR') were prepared: LB-H(2)BNRR'(2)-BH(3) (LB = DMAP, IPr, IPrCH(2) and PCy(3); R and R' = H, Me or tBu; IPr = [(HCNDipp)(2)C:] and Dipp = 2,6-iPr(2)C(6)H(3)). To potentially access complexes of molecular boron nitride, LB-BN-LA (LA = Lewis acid), preliminary dehydrogenation chemistry involving the parent aminoborane adducts LB-H(2)BNH(2)-BH(3) was investigated using [Rh(COD)Cl](2), CuBr, and NiBr(2) as dehydrogenation catalysts. In place of isolating the intended dehydrogenated BN donor-acceptor complexes, the formation of borazine was noted as a major product. Attempts to prepare the fluoroarylborane-capped aminoborane complexes, LB-H(2)BNH(2)-B(C(6)F(5))(3), are also described. PMID:23153209

  9. Effect of desferrioxamine B and Suwannee River fulvic acid on Fe(III) release and Cr(III) desorption from goethite

    NASA Astrophysics Data System (ADS)

    Stewart, Angela G.; Hudson-Edwards, Karen A.; Dubbin, William E.

    2016-04-01

    Siderophores are biogenic chelating ligands that facilitate the solubilisation of Fe(III) and form stable complexes with a range of contaminant metals and therefore may significantly affect their biogeochemical cycling. Desferrioxamine B (DFOB) is a trihydroxamate siderophore that acts synergistically with fulvic acid and low molecular weight organic ligands to release Fe from Fe(III) oxides. We report the results of batch dissolution experiments in which we determine the rates of Cr(III) desorption and Fe(III) release from Cr(III)-treated synthetic goethite as influenced by DFOB, by fulvic acid, and by the two compounds in combination. We observed that adsorbed Cr(III) at 3% surface coverage significantly reduced Fe(III) release from goethite for all combinations of DFOB and fulvic acid. When DFOB (270 μM) was the only ligand present, dissolved Fe(III) and Cr(III) increased approximately 1000-fold and 16-fold, respectively, as compared to the ligand-free system, a difference we attribute to the slow rate of water exchange of Cr(III). Suwannee River fulvic acid (SRFA) acts synergistically with DFOB by (i) reducing the goethite surface charge leading to increased HDFOB+ surface excess and by (ii) forming aqueous Fe(III)-SRFA species whose Fe(III) is subsequently removed by DFOB to yield aqueous Fe(III)-DFOB complexes. These observations shed new light on the synergistic relationship between DFOB and fulvic acid and reveal the mechanisms of Fe(III) acquisition available to plants and micro-organisms in Cr(III) contaminated environments.

  10. Synthesis and characterization of dopamine substitue tripodal trinuclear [(salen/salophen/salpropen)M] (Mdbnd Cr(III), Mn(III), Fe(III) ions) capped s-triazine complexes: Investigation of their thermal and magnetic properties

    NASA Astrophysics Data System (ADS)

    Uysal, Şaban; Koç, Ziya Erdem

    2016-04-01

    In this work, we aimed to synthesize and characterize a novel tridirectional ligand including three catechol groups and its novel tridirectional-trinuclear triazine core complexes. For this purpose, we used melamine (2,4,6-triamino-1,3,5-triazine) (MA) as starting material. 2,4,6-tris(4-carboxybenzimino)-1,3,5-triazine (II) was synthesized by the reaction of an equivalent melamine (I) and three equivalent 4-carboxybenzaldehyde. 4,4‧,4″-((1E,1‧E,1″E)-((1,3,5-triazine-2,4,6-triyl)tris(azanylylidene))tris(methanylylidene))tris(N-(3,4-dihydroxyphenethyl)benzamide) L (IV) was synthesized by the reaction of one equivalent (II) and three equivalent dopamine (3,4-dihydroxyphenethylamine) (DA) by using two different methods. (II, III, IV) and nine novel trinuclear Cr(III), Mn(III) and Fe(III) complexes of (IV) were characterized by means of elemental analyses, 1H NMR, FT-IR spectrometry, LC-MS (ESI+) and thermal analyses. The metal ratios of the prepared complexes were performed using Atomic Absorption Spectrophotometry (AAS). We also synthesized novel tridirectional-trinuclear systems and investigated their effects on magnetic behaviors of [salen, salophen, salpropen Cr(III)/Mn(III)/Fe(III)] capped complexes. The complexes were determined to be low-spin distorted octahedral Mn(III) and Fe(III), and distorted octahedral Cr(III) all bridged by catechol group.

  11. A new combined process for efficient removal of Cu(II) organic complexes from wastewater: Fe(III) displacement/UV degradation/alkaline precipitation.

    PubMed

    Xu, Zhe; Gao, Guandao; Pan, Bingcai; Zhang, Weiming; Lv, Lu

    2015-12-15

    Efficient removal of heavy metals complexed with organic ligands from water is still an important but challenging task now. Herein, a novel combined process, i.e., Fe(III)-displacement/UV degradation/alkaline precipitation (abbreviated as Fe(III)/UV/OH) was developed to remove copper-organic complexes from synthetic solution and real electroplating effluent, and other processes including alkaline precipitation, Fe(III)/OH, UV/OH were employed for comparison. By using the Fe(III)/UV/OH process, some typical Cu(II) complexes, such as Cu(II)-ethylenediaminetetraacetic acid (EDTA), Cu(II)-nitrilotriacetic acid (NTA), Cu(II)-citrate, Cu(II)-tartrate, and Cu(II)-sorbate, each at 19.2 mg Cu/L initially, were efficiently removed from synthetic solution with the residual Cu below 1 mg/L. Simultaneously, 30-48% of total organic carbon was eliminated with exception of Cu(II)-sorbate. Comparatively, the efficiency of other processes was much lower than the Fe(III)/UV/OH process. With Cu(II)-citrate as the model complex, the optimal conditions for the combined process were obtained as: initial pH for Fe(III) displacement, 1.8-5.4; molar ratio of [Fe]/[Cu], 4:1; UV irradiation, 10 min; precipitation pH, 6.6-13. The mechanism responsible for the process involved the liberation of Cu(II) ions from organic complexes as a result of Fe(III) displacement, decarboxylation of Fe(III)-ligand complexes subjected to UV irradiation, and final coprecipitation of Cu(II) and Fe(II)/Fe(III) ions. Up to 338.1 mg/L of Cu(II) in the electroplating effluent could be efficiently removed by the process with the residual Cu(II) below 1 mg/L and the removal efficiency of ∼99.8%, whereas direct precipitation by using NaOH could only result in total Cu(II) removal of ∼8.6%. In addition, sunlight could take the place of UV to achieve similar removal efficiency with longer irradiation time (90 min).

  12. Heterogeneous Reduction of PuO2 with Fe(II): Importance of the Fe(III) Reaction Product

    SciTech Connect

    Felmy, Andrew R.; Moore, Dean A.; Rosso, Kevin M.; Qafoku, Odeta; Rai, Dhanpat; Buck, Edgar C.; Ilton, Eugene S.

    2011-05-01

    Abstract Heterogeneous reduction of actinides in higher and more soluble oxidation states to lower more insoluble oxidation states by reductants such as Fe(II) has been the subject of intensive study for more than two decades. However, Fe(II)-induced reduction of sparingly soluble Pu(IV) to the more soluble lower oxidation state Pu(III) has been much less studied even though such reactions can potentially increase the mobility of Pu in the subsurface. Thermodynamic calculations are presented that show how differences in the free energy of various possible solid-phase Fe(III) reaction products can greatly influence aqueous Pu(III) concentrations resulting from reduction of PuO2(am) by Fe(II). We present the first experimental evidence that reduction of PuO2(am) to Pu(III) by Fe(II) was enhanced when the Fe(III) mineral goethite was spiked into the reaction. The effect of goethite on reduction of Pu(IV) was demonstrated by measuring the time-dependence of total aqueous Pu concentration, its oxidation state, and system pe/pH. We also re-evaluated established protocols for determining Pu(III) [(Pu(III) + Pu(IV)) - Pu(IV)] by using thenoyltrifluoroacetone (TTA) in toluene extractions; the study showed that it is important to eliminate dissolved oxygen from the TTA solutions for accurate determinations. More broadly, this study highlights the importance of the Fe(III) reaction product in actinide reduction rate and extent by Fe(II).

  13. Theory of Triplet Excitation Transfer in the Donor-Oxygen-Acceptor System: Application to Cytochrome b6f.

    PubMed

    Petrov, Elmar G; Robert, Bruno; Lin, Sheng Hsien; Valkunas, Leonas

    2015-10-20

    Theoretical consideration is presented of the triplet excitation dynamics in donor-acceptor systems in conditions where the transfer is mediated by an oxygen molecule. It is demonstrated that oxygen may be involved in both real and virtual intramolecular triplet-singlet conversions in the course of the process under consideration. Expressions describing a superexchange donor-acceptor coupling owing to a participation of the bridging twofold degenerate oxygen's virtual singlet state are derived and the transfer kinetics including the sequential (hopping) and coherent (distant) routes are analyzed. Applicability of this theoretical description to the pigment-protein complex cytochrome b6f, by considering the triplet excitation transfer from the chlorophyll a molecule to distant β-carotene, is discussed. PMID:26488665

  14. Binding characteristics of homogeneous molecularly imprinted polymers for acyclovir using an (acceptor-donor-donor)-(donor-acceptor-acceptor) hydrogen-bond strategy, and analytical applications for serum samples.

    PubMed

    Wu, Suqin; Tan, Lei; Wang, Ganquan; Peng, Guiming; Kang, Chengcheng; Tang, Youwen

    2013-04-12

    This paper demonstrates a novel approach to assembling homogeneous molecularly imprinted polymers (MIPs) based on mimicking multiple hydrogen bonds between nucleotide bases by preparing acyclovir (ACV) as a template and using coatings grafted on silica supports. (1)H NMR studies confirmed the AAD-DDA (A for acceptor, D for donor) hydrogen-bond array between template and functional monomer, while the resultant monodisperse molecularly imprinted microspheres (MIMs) were evaluated using a binding experiment, high performance liquid chromatography (HPLC), and solid phase extraction. The Langmuir isothermal model and the Langmuir-Freundlich isothermal model suggest that ACV-MIMs have more homogeneous binding sites than MIPs prepared through normal imprinting. In contrast to previous MIP-HPLC columns, there were no apparent tailings for the ACV peaks, and ACV-MIMs had excellent specific binding properties with a Ka peak of 3.44 × 10(5)M(-1). A complete baseline separation is obtained for ACV and structurally similar compounds. This work also successfully used MIMs as a specific sorbent for capturing ACV from serum samples. The detection limit and mean recovery of ACV was 1.8 ng/mL(-1) and 95.6%, respectively, for molecularly imprinted solid phase extraction coupled with HPLC. To our knowledge, this was the first example of MIPs using AAD-DDA hydrogen bonds.

  15. Donor-Acceptor-Type Semiconducting Polymers Consisting of Benzothiadiazole Derivatives as Electron-Acceptor Units for Organic Photovoltaic Cells.

    PubMed

    Kim, Hee Su; Park, Jong Baek; Kim, Ji-Hoon; Hwang, Do-Hoon

    2015-11-01

    We synthesized two fused pentacyclic donor-acceptor structures, where the two different outer electron rich thiophene (DTPBT) and electron poor benzene (ICTh) moieties are covalently bonded to the central electron-deficient benzothiadiazole core by two nitrogen bridges. These new electron-acceptor DTPBT and ICTh building blocks were copolymerized with fluorene, as the electron donor group, via Suzuki coupling polymerization, to produce two new alternating copolymers, PFDTPBT and PFICTh, respectively. The average molecular weights of the synthesized polymers were determined by GPC. The number-average molecular weights of PFDTPBT and PFICTh were 19,000 (PDI = 2.5) and 20,000 (PDI = 4.0), respectively. The optical bandgap energies of the polymers were measured from their absorption onsets to be 2.15 and 2.55 eV, depending on the polymer structure. The HOMO energy levels of the polymers were determined, by measuring the oxidation onsets of the polymer films by cyclic voltammetry. The measured HOMO energy levels of PFDTPBT and PFICTh were -5.10 and -5.57 eV, respectively. When the polymers were blended with PC71BM, as the active layer for bulk-heterojunction photovoltaic devices, power conversion efficiencies were 2.08% and 0.34%, respectively, under AM 1.5 G (100 mW cm(-2)) conditions.

  16. Stimuli responsive hybrid magnets: tuning the photoinduced spin-crossover in Fe(III) complexes inserted into layered magnets.

    PubMed

    Clemente-León, Miguel; Coronado, Eugenio; López-Jordà, Maurici; Waerenborgh, João C; Desplanches, Cédric; Wang, Hongfeng; Létard, Jean-François; Hauser, Andreas; Tissot, Antoine

    2013-06-12

    The insertion of a [Fe(sal2-trien)](+) complex cation into a 2D oxalate network in the presence of different solvents results in a family of hybrid magnets with coexistence of magnetic ordering and photoinduced spin-crossover (LIESST effect) in compounds [Fe(III)(sal2-trien)][Mn(II)Cr(III)(ox)3]·CHCl3 (1·CHCl3), [Fe(III)(sal2-trien)][Mn(II)Cr(III)(ox)3]·CHBr3 (1·CHBr3), and [Fe(III)(sal2-trien)][Mn(II)Cr(III)(ox)3]·CH2Br2 (1·CH2Br2). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn(II) and Cr(III) ions linked through oxalate ligands and a layer of [Fe(sal2-trien)](+) complexes and solvent molecules (CHCl3, CHBr3, or CH2Br2) intercalated between the 2D oxalate network. The magnetic properties and Mössbauer spectroscopy indicate that they undergo long-range ferromagnetic ordering at 5.6 K and a spin crossover of the intercalated [Fe(sal2-trien)](+) complexes at different temperatures T1/2. The three compounds present a LIESST effect with a relaxation temperature TLIESST inversely proportional to T1/2. The isostructural paramagnetic compound, [Fe(III)(sal2-trien)][Zn(II)Cr(III)(ox)3]·CH2Cl2 (2·CH2Cl2) was also prepared. This compound presents a partial spin crossover of the inserted Fe(III) complex as well as a LIESST effect. Finally, spectroscopic characterization of the Fe(III) doped compound [Ga0.99Fe0.01(sal2trien)][Mn(II)Cr(III)(ox)3]·CH2Cl2 (3·CH2Cl2) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated Fe(III) complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an Fe(III) compound.

  17. A Strongly Spin-Frustrated Fe(III) 7 Complex with a Canted Intermediate Spin Ground State of S=7/2 or 9/2.

    PubMed

    Mondal, Kartik Chandra; Mereacre, Valeriu; Kostakis, George E; Lan, Yanhua; Anson, Christopher E; Prisecaru, Ion; Waldmann, Oliver; Powell, Annie K

    2015-07-20

    A disk-shaped [Fe(III) 7 (Cl)(MeOH)6 (μ3 -O)3 (μ-OMe)6 (PhCO2 )6 ]Cl2 complex with C3 symmetry has been synthesised and characterised. The central tetrahedral Fe(III) is 0.733 Å above the almost co-planar Fe(III) 6 wheel, to which it is connected through three μ3 -oxide bridges. For this iron-oxo core, the magnetic susceptibility analysis proposed a Heisenberg-Dirac-van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The (57) Fe Mössbauer (MS) analysis verifies that the central Fe(III) ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral Fe(III) ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology.

  18. Effects of microbial iron reduction and oxidation on the immobilization and mobilization of copper in synthesized Fe(III) minerals and Fe-rich soils.

    PubMed

    Hu, Chaohua; Zhang, Youchi; Zhang, Lei; Luo, Wensui

    2014-04-01

    The effects of microbial iron reduction and oxidation on the immobilization and mobilization of copper were investigated in a high concentration of sulfate with synthesized Fe(III) minerals and red earth soils rich in amorphous Fe (hydr)oxides. Batch microcosm experiments showed that red earth soil inoculated with subsurface sediments had a faster Fe(III) bioreduction rate than pure amorphous Fe(III) minerals and resulted in quicker immobilization of Cu in the aqueous fraction. Coinciding with the decrease of aqueous Cu, SO4(2-) in the inoculated red earth soil decreased acutely after incubation. The shift in the microbial community composite in the inoculated soil was analyzed through denaturing gradient gel electrophoresis. Results revealed the potential cooperative effect of microbial Fe(III) reduction and sulfate reduction on copper immobilization. After exposure to air for 144 h, more than 50% of the immobilized Cu was remobilized from the anaerobic matrices; aqueous sulfate increased significantly. Sequential extraction analysis demonstrated that the organic matter/sulfide-bound Cu increased by 52% after anaerobic incubation relative to the abiotic treatment but decreased by 32% after oxidation, indicating the generation and oxidation of Cu-sulfide coprecipitates in the inoculated red earth soil. These findings suggest that the immobilization of copper could be enhanced by mediating microbial Fe(III) reduction with sulfate reduction under anaerobic conditions. The findings have an important implication for bioremediation in Cucontaminated and Fe-rich soils, especially in acid-mine-drainage-affected sites.

  19. Fe(III) fertilization mitigating net global warming potential and greenhouse gas intensity in paddy rice-wheat rotation systems in China.

    PubMed

    Liu, Shuwei; Zhang, Ling; Liu, Qiaohui; Zou, Jianwen

    2012-05-01

    A complete accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) affected by Fe(III) fertilizer application was examined in typical annual paddy rice-winter wheat rotation cropping systems in southeast China. Annual fluxes of soil carbon dioxide (CO(2)), methane (CH(4)) and nitrous oxide (N(2)O) were measured using static chamber method, and the net ecosystem exchange of CO(2) (NEE) was determined by the difference between soil CO(2) emissions (R(H)) and net primary production (NPP). Fe(III) fertilizer application significantly decreased R(H) without adverse effects on NPP of rice and winter wheat. Fe(III) fertilizer application decreased seasonal CH(4) by 27-44%, but increased annual N(2)O by 65-100%. Overall, Fe(III) fertilizer application decreased the annual NGHGB and GHGI by 35-47% and 30-36%, respectively. High grain yield and low greenhouse gas intensity can be reconciled by Fe(III) fertilizer applied at the local recommendation rate in rice-based cropping systems.

  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. Generation of Nitrogen Acceptors in ZnO using Pulse Thermal Processing

    SciTech Connect

    Xu, Jun; Ott, Ronald D; Sabau, Adrian S; Pan, Zhengwei; Xiu, Faxian; Liu, Jilin; Erie, Jean-Marie; Norton, David P

    2008-01-01

    Bipolar doping in wide bandgap semiconductors is difficult to achieve under equilibrium conditions because of the spontaneous formation of compensating defects and unfavorable energetics for dopant substitution. In this work, we explored the use of rapid pulse thermal processing for activating nitrogen dopants into acceptor states in ZnO. Low-temperature photoluminescence spectra revealed both acceptor-bound exciton (A{sup 0}X) and donor-acceptor pair emissions, which present direct evidence for acceptors generated after pulse thermal processing of nitrogen-doped ZnO. This work suggests that pulse thermal processing is potentially an effective method for p-type doping of ZnO.

  2. Synthesis of charged bis-heteroaryl donor-acceptor (D-A+) NLO-phores coupling (π-deficient-π-excessive) heteroaromatic rings.

    PubMed

    Ramirez, Marco Antonio; Custodio, Raul; Cuadro, Ana M; Alvarez-Builla, Julio; Clays, Koen; Asselberghs, Inge; Mendicuti, Francisco; Castaño, Obis; Andrés, José L; Vaquero, Juan J

    2013-11-01

    Charged chromophores based on heteroaromatic cations were prepared by reaction of alkylazinium salts with N-heteroarylstannanes under Stille conditions. This approach provides easy access to potential single donor D-A(+) chromophores in which the acceptor moiety A(+) is the pyridinium cation and the donors are different π-excessive N-heterocycles. The β hyperpolarizabilities were measured in hyper-Rayleigh scattering experiments and the experimental data are supported by a theoretical analysis that combines a variety of computational procedures, including density functional theory and correlated Hartree-Fock-based methods. In some chromophores, the absence of a bridge between donor and acceptor fragments increases the NLO properties.

  3. Quantum information processing using acceptors in silicon and phonon entanglement

    NASA Astrophysics Data System (ADS)

    Clark, Susan; Reinke, Charles; McGuinness, Hayden; El-Kady, Ihab

    2014-03-01

    Quantum computing with large numbers of qubits remains challenging due to the decoherence and complexity that arise as more qubits are added to a system. Here I propose a new platform for semiconductor quantum computing which may be robust to common sources of decoherence and may not be difficult to fabricate repeatedly. This system consists of a hole bound to an acceptor in silicon which has been implanted in the center of a mechanical cavity (similar to a photonic crystal cavity) and connected to other cavities by a system of waveguides. I will outline a basic entangling gate and calculations showing the promise of this platform as the ideal qubit. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U. S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  4. Beyond fullerenes: design of nonfullerene acceptors for efficient organic photovoltaics.

    PubMed

    Li, Haiyan; Earmme, Taeshik; Ren, Guoqiang; Saeki, Akinori; Yoshikawa, Saya; Murari, Nishit M; Subramaniyan, Selvam; Crane, Matthew J; Seki, Shu; Jenekhe, Samson A

    2014-10-15

    New electron-acceptor materials are long sought to overcome the small photovoltage, high-cost, poor photochemical stability, and other limitations of fullerene-based organic photovoltaics. However, all known nonfullerene acceptors have so far shown inferior photovoltaic properties compared to fullerene benchmark [6,6]-phenyl-C60-butyric acid methyl ester (PC60BM), and there are as yet no established design principles for realizing improved materials. Herein we report a design strategy that has produced a novel multichromophoric, large size, nonplanar three-dimensional (3D) organic molecule, DBFI-T, whose π-conjugated framework occupies space comparable to an aggregate of 9 [C60]-fullerene molecules. Comparative studies of DBFI-T with its planar monomeric analogue (BFI-P2) and PC60BM in bulk heterojunction (BHJ) solar cells, by using a common thiazolothiazole-dithienosilole copolymer donor (PSEHTT), showed that DBFI-T has superior charge photogeneration and photovoltaic properties; PSEHTT:DBFI-T solar cells combined a high short-circuit current (10.14 mA/cm(2)) with a high open-circuit voltage (0.86 V) to give a power conversion efficiency of 5.0%. The external quantum efficiency spectrum of PSEHTT:DBFI-T devices had peaks of 60-65% in the 380-620 nm range, demonstrating that both hole transfer from photoexcited DBFI-T to PSEHTT and electron transfer from photoexcited PSEHTT to DBFI-T contribute substantially to charge photogeneration. The superior charge photogeneration and electron-accepting properties of DBFI-T were further confirmed by independent Xenon-flash time-resolved microwave conductivity measurements, which correctly predict the relative magnitudes of the conversion efficiencies of the BHJ solar cells: PSEHTT:DBFI-T > PSEHTT:PC60BM > PSEHTT:BFI-P2. The results demonstrate that the large size, multichromophoric, nonplanar 3D molecular design is a promising approach to more efficient organic photovoltaic materials.

  5. Recent advances in photoinduced donor/acceptor copolymerization

    NASA Astrophysics Data System (ADS)

    Jönsson, S.; Viswanathan, K.; Hoyle, C. E.; Clark, S. C.; Miller, C.; Morel, F.; Decker, C.

    1999-05-01

    Photoinitiated free radical polymerization of donor (D)/acceptor (A) type monomers has gained considerable interest due to the possibility to efficiently photopolymerize non-acrylate based systems. Furthermore, this photoinduced alternating copolymerization can be accomplished without the presence of a conventional free radical generating photoinitiator. In the past, we have shown that the structural influences in the direct photolysis of N-Alkyl and N-Arylmaleimides as well as their corresponding ground state charge transfer complexes (CTC) with suitable donors have carefully been investigated. For certain combinations of A and D type monomers, a direct photolysis of the ground state complex or the excitation of the acceptor, followed by the formation of an exciplex, has been shown to initiate the copolymerization. Herein, we show that the main route of initiation is based on inter or intra molecular H-abstraction from an excited state maleimide, whereby no exciplex formation takes place. H-abstraction will predominantly take place in systems where easily abstractable hydrogens are present. Our laser flash photolysis investigation, ESR [1] (A. Hiroshi, I. Takasi, T. Nosi, Macromol. Chem. 190 (1989) 2821) and phosphorescence emissions [2,3] (K.S. Chen, T. Foster, J.K.S. Wan, J. Phys. Chem. 84 (1980) 2473; C.J. Seliskar, S.P. McGlynn, J. Chem. Phys. 55 (1971) 4337) studies show that triplet excited states of N-alkyl substituted maleimides (RMI), which are well known strong precursors for direct H-abstractions from aliphatic ethers and secondary alcohols, are formed upon excitation. Rates of copolymerization and degrees of conversion for copolymerization of maleimide/vinyl ether pairs in air and nitrogen have been measured as a function of hydrogen abstractability of the excited triplet state MI as well as the influence of concentration and hydrogen donating effect of the hydrogen donor.

  6. 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

  7. The Influence of the Amide Linkage in the Fe(III) -Binding Properties of Catechol-Modified Rosamine Derivatives.

    PubMed

    Queirós, Carla; Leite, Andreia; G M Couto, Maria; Cunha-Silva, Luís; Barone, Giampaolo; de Castro, Baltazar; Rangel, Maria; M N Silva, André; M G Silva, Ana

    2015-10-26

    The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave-assisted coupling reactions of carboxyl- or amine-substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively). The ligands were characterized by means of NMR spectroscopy, mass-spectrometry, and DFT calculations and X-ray crystallography studies for RosCat1. The influence of the amide linkage on the photophysical properties of the fluorescent ligands was assessed in different solvents and showed a higher fluorescence quantum yield for RosCat1. The coordination chemistry of these ligands with a Fe(III) center has been rationalized by mass-spectrometric analysis and semiempirical calculations. Octahedral Fe(III) complexes were obtained by the chelation of three RosCat1 or RosCat2 ligands. Interestingly, the unconventional amide connectivity in RosCat1 imposes the formation of an eight-membered ring on the chelate complex through a "salicylate-type" mode of coordination.

  8. Effect of different solutes, natural organic matter, and particulate Fe(III) on ferrate(VI) decomposition in aqueous solutions.

    PubMed

    Jiang, Yanjun; Goodwill, Joseph E; Tobiason, John E; Reckhow, David A

    2015-03-01

    This study investigated the impacts of buffer ions, natural organic matter (NOM), and particulate Fe(III) on ferrate(VI) decomposition and characterized Fe(VI) decomposition kinetics and exposure in various waters. Homogeneous and heterogeneous Fe(VI) decomposition can be described as a second- and first-order reaction with respect to Fe(VI), respectively. Fe(VI) decay was catalyzed by Fe(VI) decomposition products. Solutes capable of forming complexes with iron hydroxides retarded Fe(VI) decay. Fractionation of the resulting solutions from Fe(VI) self-decay and ferric chloride addition in borate- and phosphate-buffered waters showed that phosphate could sequester Fe(III). The nature of the iron precipitate from Fe(VI) decomposition was different from that of freshly precipitated ferric hydroxide from ferric chloride solutions. The stabilizing effects of different solutes on Fe(VI) are in the following order: phosphate > bicarbonate > borate. The constituents of colored and alkaline waters (NOM and bicarbonate) inhibited the catalytic effects of Fe(VI) decomposition products and stabilized Fe(VI) in natural waters. Because of the stabilizing effects of solutes, moderate doses of Fe(VI) added to natural waters at pH 7.5 resulted in exposures that have been shown to be effective for inactivation of target pathogens. Preformed ferric hydroxide was less effective than freshly dosed ferric chloride in accelerating Fe(VI) decomposition.

  9. Formation and movement of Fe(III) in horse spleen, H- and L-recombinant ferritins. A fluorescence study.

    PubMed Central

    Cavallo, S.; Mei, G.; Stefanini, S.; Rosato, N.; Finazzi-Agrò, A.; Chiancone, E.

    1998-01-01

    Iron oxidation and incorporation into apoferritins of different subunit composition, namely the recombinant H and L homopolymers and the natural horse spleen heteropolymer (10-15% H), have been followed by steady-state and time-resolved fluorescence. After aerobic addition of 100 Fe(II) atoms/polymer, markedly different kinetic profiles are observed. In the rL-homopolymer a slow monotonic fluorescence quenching is observed which reflects binding, slow oxidation at the threefold apoferritin channels, and diffusion into the protein cavity. In the rH-homopolymer a fast fluorescence quenching is followed by a partial, slow recovery. The two processes have been attributed to Fe(II) binding and oxidation at the ferroxidase centers and to Fe(III) released into the cavity, respectively. The fluorescence kinetics of horse spleen apoferritin is dominated by the H chain contribution and resembles that of the H homopolymer. It brings out clearly that the rate of the overall process is limited by the rate at which Fe(III) leaves the ferroxidase centers of the H chains where binding of incoming Fe(II) and its oxidation take place. The data obtained upon stepwise addition of iron and the results of optical absorption measurements confirm this picture. The correspondence between steady-state and time-resolved data is remarkably good; this is manifest when the latter are used to calculate the change in fluorescence intensity as apparent in the steady-state measurements. PMID:9521120

  10. The Influence of the Amide Linkage in the Fe(III) -Binding Properties of Catechol-Modified Rosamine Derivatives.

    PubMed

    Queirós, Carla; Leite, Andreia; G M Couto, Maria; Cunha-Silva, Luís; Barone, Giampaolo; de Castro, Baltazar; Rangel, Maria; M N Silva, André; M G Silva, Ana

    2015-10-26

    The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave-assisted coupling reactions of carboxyl- or amine-substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively). The ligands were characterized by means of NMR spectroscopy, mass-spectrometry, and DFT calculations and X-ray crystallography studies for RosCat1. The influence of the amide linkage on the photophysical properties of the fluorescent ligands was assessed in different solvents and showed a higher fluorescence quantum yield for RosCat1. The coordination chemistry of these ligands with a Fe(III) center has been rationalized by mass-spectrometric analysis and semiempirical calculations. Octahedral Fe(III) complexes were obtained by the chelation of three RosCat1 or RosCat2 ligands. Interestingly, the unconventional amide connectivity in RosCat1 imposes the formation of an eight-membered ring on the chelate complex through a "salicylate-type" mode of coordination. PMID:26493881

  11. Efficiency improvement of new Tetrathienoacene-based dyes by enhancing donor, acceptor and bridge units, a theoretical study

    NASA Astrophysics Data System (ADS)

    Tavangar, Zahra; Zareie, Nazanin

    2016-10-01

    A series of metal free Tetrathienoacene-based (TTA-based) organic dyes are designed and investigated as sensitizers for application in dye sensitized solar cells (DSSCs). Density function theory and time dependent density function theory calculations were performed on these dyes at vacuum and orthodichlorobenzene as the solvent. Effects of changing π-conjugation bridges and different functional groups in acceptor and donor units were investigated. UV-Vis absorption spectra were simulated to show the wavelength shifting and absorption properties. Inserting nitro and acyl chloride functional groups in acceptor and NH2 in donor units leads to the reduction of HOMO-LUMO gap by lowering the lowest unoccupied molecular orbital (LUMO) energy level and raising the highest occupied molecular orbital (HOMO) energy level and the increase in effective parameters in DSSC' efficiency. The results show that changing spacer units from thiophene to furan has a great effect on electronic structure and absorption spectra. Investigation of the electron distributions of frontier orbitals shows the HOMO and LUMO localization in donor and acceptor, respectively. Some key parameters that were studied here include light harvesting efficiency, free energy of electron injection and open circuit photo-voltage.

  12. Modeling the Effect of External Carbon Source Addition under Different Electron Acceptor Conditions in Biological Nutrient Removal Activated Sludge Systems.

    PubMed

    Hu, Xiang; Wisniewski, Kamil; Czerwionka, Krzysztof; Zhou, Qi; Xie, Li; Makinia, Jacek

    2016-02-16

    The aim of this study was to expand the International Water Association Activated Sludge Model No. 2d (ASM2d) to predict the aerobic/anoxic behavior of polyphosphate accumulating organisms (PAOs) and "ordinary" heterotrophs in the presence of different external carbon sources and electron acceptors. The following new aspects were considered: (1) a new type of the readily biodegradable substrate, not available for the anaerobic activity of PAOs, (2) nitrite as an electron acceptor, and (3) acclimation of "ordinary" heterotrophs to the new external substrate via enzyme synthesis. The expanded model incorporated 30 new or modified process rate equations. The model was evaluated against data from several, especially designed laboratory experiments which focused on the combined effects of different types of external carbon sources (acetate, ethanol and fusel oil) and electron acceptors (dissolved oxygen, nitrate and nitrite) on the behavior of PAOs and "ordinary" heterotrophs. With the proposed expansions, it was possible to improve some deficiencies of the ASM2d in predicting the behavior of biological nutrient removal (BNR) systems with the addition of external carbon sources, including the effect of acclimation to the new carbon source. PMID:26783836

  13. Modeling the Effect of External Carbon Source Addition under Different Electron Acceptor Conditions in Biological Nutrient Removal Activated Sludge Systems.

    PubMed

    Hu, Xiang; Wisniewski, Kamil; Czerwionka, Krzysztof; Zhou, Qi; Xie, Li; Makinia, Jacek

    2016-02-16

    The aim of this study was to expand the International Water Association Activated Sludge Model No. 2d (ASM2d) to predict the aerobic/anoxic behavior of polyphosphate accumulating organisms (PAOs) and "ordinary" heterotrophs in the presence of different external carbon sources and electron acceptors. The following new aspects were considered: (1) a new type of the readily biodegradable substrate, not available for the anaerobic activity of PAOs, (2) nitrite as an electron acceptor, and (3) acclimation of "ordinary" heterotrophs to the new external substrate via enzyme synthesis. The expanded model incorporated 30 new or modified process rate equations. The model was evaluated against data from several, especially designed laboratory experiments which focused on the combined effects of different types of external carbon sources (acetate, ethanol and fusel oil) and electron acceptors (dissolved oxygen, nitrate and nitrite) on the behavior of PAOs and "ordinary" heterotrophs. With the proposed expansions, it was possible to improve some deficiencies of the ASM2d in predicting the behavior of biological nutrient removal (BNR) systems with the addition of external carbon sources, including the effect of acclimation to the new carbon source.

  14. Shared-intermediates in the biosynthesis of thio-cofactors: Mechanism and functions of cysteine desulfurases and sulfur acceptors.

    PubMed

    Black, Katherine A; Dos Santos, Patricia C

    2015-06-01

    Cysteine desulfurases utilize a PLP-dependent mechanism to catalyze the first step of sulfur mobilization in the biosynthesis of sulfur-containing cofactors. Sulfur activation and integration into thiocofactors involve complex mechanisms and intricate biosynthetic schemes. Cysteine desulfurases catalyze sulfur-transfer reactions from l-cysteine to sulfur acceptor molecules participating in the biosynthesis of thio-cofactors, including Fe-S clusters, thionucleosides, thiamin, biotin, and molybdenum cofactor. The proposed mechanism of cysteine desulfurases involves the PLP-dependent cleavage of the C-S bond from l-cysteine via the formation of a persulfide enzyme intermediate, which is considered the hallmark step in sulfur mobilization. The subsequent sulfur transfer reaction varies with the class of cysteine desulfurase and sulfur acceptor. IscS serves as a mecca for sulfur incorporation into a network of intertwined pathways for the biosynthesis of thio-cofactors. The involvement of a single enzyme interacting with multiple acceptors, the recruitment of shared-intermediates partaking roles in multiple pathways, and the participation of Fe-S enzymes denote the interconnectivity of pathways involving sulfur trafficking. In Bacillus subtilis, the occurrence of multiple cysteine desulfurases partnering with dedicated sulfur acceptors partially deconvolutes the routes of sulfur trafficking and assigns specific roles for these enzymes. Understanding the roles of promiscuous vs. dedicated cysteine desulfurases and their partnership with shared-intermediates in the biosynthesis of thio-cofactors will help to map sulfur transfer events across interconnected pathways and to provide insight into the hierarchy of sulfur incorporation into biomolecules. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.

  15. Paramagnetic centers in particulate formed from the oxidative pyrolysis of 1-methylnaphthalene in the presence of Fe(III)2O3 nanoparticles

    PubMed Central

    Herring, Paul; Khachatryan, Lavrent; Lomnicki, Slawomir; Dellinger, Barry

    2015-01-01

    The identity of radical species associated with particulate formed from the oxidative pyrolysis of 1-methylnaphthalene (1-MN) was investigated using low temperature matrix isolation electron paramagnetic resonance spectroscopy (LTMI-EPR), a specialized technique that provided a method of sampling and analysis of the gas-phase paramagnetic components. A superimposed EPR signal was identified to be a mixture of organic radicals (carbon and oxygen-centered) and soot. The carbon-centered radicals were identified as a mixture of the resonance-stabilized indenyl, cyclopentadienyl, and naphthalene 1-methylene radicals through the theoretical simulation of the radical’s hyperfine structure. Formation of these radical species was promoted by the addition of Fe(III)2O3 nanoparticles. Enhanced formation of resonance stabilized radicals from the addition of Fe(III)2O3 nanoparticles can account for the observed increased sooting tendency associated with Fe(III)2O3 nanoparticle addition. PMID:25673882

  16. Synthesis of Imine-Naphthol Tripodal Ligand and Study of Its Coordination Behaviour towards Fe(III), Al(III), and Cr(III) Metal Ions

    PubMed Central

    Kaur, Kirandeep

    2014-01-01

    A hexadentate Schiff base tripodal ligand is synthesized by the condensation of tris (2-aminoethyl) amine with 2-hydroxy-1-naphthaldehyde and characterized by various spectroscopic techniques like UV-VIS, IR, NMR, MASS, and elemental analysis. The solution studies by potentiometric and spectrophotometric methods are done at 25 ± 1°C, µ = 0.1 M KCl, to calculate the protonation constants of the ligand and formation constants of metal complexes formed by the ligand with Fe(III), Al(III), and Cr(III) metal ions. The affinity of the ligand towards Fe(III) is compared with deferiprone (a drug applied for iron intoxication) and transferrin (the main Fe(III) binding protein in plasma). Structural analysis of the ligand and the metal complexes was done using semiempirical PM6 method. Electronic and IR spectra are calculated by semiempirical methods and compared with experimental one. PMID:25294978

  17. Synthesis of Imine-Naphthol Tripodal Ligand and Study of Its Coordination Behaviour towards Fe(III), Al(III), and Cr(III) Metal Ions.

    PubMed

    Kaur, Kirandeep; Baral, Minati

    2014-01-01

    A hexadentate Schiff base tripodal ligand is synthesized by the condensation of tris (2-aminoethyl) amine with 2-hydroxy-1-naphthaldehyde and characterized by various spectroscopic techniques like UV-VIS, IR, NMR, MASS, and elemental analysis. The solution studies by potentiometric and spectrophotometric methods are done at 25 ± 1°C, µ = 0.1 M KCl, to calculate the protonation constants of the ligand and formation constants of metal complexes formed by the ligand with Fe(III), Al(III), and Cr(III) metal ions. The affinity of the ligand towards Fe(III) is compared with deferiprone (a drug applied for iron intoxication) and transferrin (the main Fe(III) binding protein in plasma). Structural analysis of the ligand and the metal complexes was done using semiempirical PM6 method. Electronic and IR spectra are calculated by semiempirical methods and compared with experimental one. PMID:25294978

  18. Synthesis of Imine-Naphthol Tripodal Ligand and Study of Its Coordination Behaviour towards Fe(III), Al(III), and Cr(III) Metal Ions.

    PubMed

    Kaur, Kirandeep; Baral, Minati

    2014-01-01

    A hexadentate Schiff base tripodal ligand is synthesized by the condensation of tris (2-aminoethyl) amine with 2-hydroxy-1-naphthaldehyde and characterized by various spectroscopic techniques like UV-VIS, IR, NMR, MASS, and elemental analysis. The solution studies by potentiometric and spectrophotometric methods are done at 25 ± 1°C, µ = 0.1 M KCl, to calculate the protonation constants of the ligand and formation constants of metal complexes formed by the ligand with Fe(III), Al(III), and Cr(III) metal ions. The affinity of the ligand towards Fe(III) is compared with deferiprone (a drug applied for iron intoxication) and transferrin (the main Fe(III) binding protein in plasma). Structural analysis of the ligand and the metal complexes was done using semiempirical PM6 method. Electronic and IR spectra are calculated by semiempirical methods and compared with experimental one.

  19. 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

    2015-02-01

    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.

  20. Photoaffinity labelling of methyltransferase enzymes with S-adenosylmethionine: effects of methyl acceptor substrates.

    PubMed

    Hurst, J H; Billingsley, M L; Lovenberg, W

    1984-07-31

    Radioactivity from 3H-[methyl]-S-adenosyl-L-methionine (AdoMet) was covalently bound to protein-O-carboxylmethyltransferase and phenylethanolamine N-methyltransferase following 10-15 min irradiation by short-wave ultraviolet light. This photoaffinity binding of 3H-[methyl]-AdoMet was blocked by S-adenosylhomocysteine and sinefungin, but was not affected by 5 mM dithiothreitol. The binding was also inhibited by including methyl acceptors such as calmodulin (protein-O-carboxylmethyltransferase) or phenylethanolamine (phenylethanolamine N-methyltransferase) in the photoaffinity incubation. Staphlococcus V8 protease digests of 3H-[methyl]-AdoMet/enzyme complexes revealed that the primary structure around the AdoMet binding site is different in these two enzymes. Thus, protein-O-carboxylmethyltransferase, a large molecule methyltransferase, can covalently bind 3H-[methyl]-AdoMet in a manner similar to that of phenylethanolamine-N-methyltransferase.

  1. Physical and reactive extraction equilibria of penicillin G in a hydrogen-bond acceptor solvent system.

    PubMed

    Lee, Sang Cheol

    2006-01-01

    Physical and reactive extraction equilibria of penicillin G were investigated experimentally and theoretically in the existence of n-butyl acetate as a hydrogen-bond acceptor solvent. Physical extraction equilibrium experiments were carried out varying the pH of aqueous phase and overall penicillin concentration. We compared the experimental data with the calculated results from four physical extraction equilibrium models suggested here and obtained the most reasonable model. Also, penicillin G was reactively extracted using Amberlite LA-2 in n-butyl acetate. The experimental variables were pH of the aqueous phase, overall amine concentration, and overall penicillin concentration. A combined equilibrium model including our physical extraction equilibrium expression and the reactive extraction equilibrium expression suggested by Reschke and Schügerl was used so as to analyze the current reactive extraction equilibrium system. The calculated results from the reactive extraction equilibrium model were in good agreement with the experimental data.

  2. 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

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

    PubMed

    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 m(2)/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.

  4. Simultaneous spectrophotometric determination of Fe(III) and Al(III) using orthogonal signal correction-partial least squares calibration method after solidified floating organic drop microextraction.

    PubMed

    Rohani Moghadam, Masoud; Haji Shabani, Ali Mohammad; Dadfarnia, Shayessteh

    2015-01-25

    A solidified floating organic drop microextraction (SFODME) procedure was developed for the simultaneous extraction and preconcentration of Fe(III) and Al(III) from water samples. The method was based on the formation of cationic complexes between Fe(III) and Al(III) and 3,5,7,2',4'-pentahydroxyflavone (morin) which were extracted into 1-undecanol as ion pairs with perchlorate ions. The absorbance of the extracted complexes was then measured in the wavelength range of 300-450 nm. Finally, the concentration of each metal ion was determined by the use of the orthogonal signal correction-partial least squares (OSC-PLS) calibration method. Several experimental parameters that may be affected on the extraction process such as the type and volume of extraction solvent, pH of the aqueous solution, morin and perchlorate concentration and extraction time were optimized. Under the optimum conditions, Fe(III) and Al(III) were determined in the ranges of 0.83-27.00 μg L(-1) (R(2)=0.9985) and 1.00-32.00 μg L(-1) (R(2)=0.9979) of Fe(III) and Al(III), respectively. The relative standard deviations (n=6) at 12.80 μg L(-1) of Fe(III) and 17.00 μg L(-)(1) of Al(III) were 3.2% and 3.5%, respectively. An enhancement factors of 102 and 96 were obtained for Fe(III) and Al(III) ions, respectively. The procedure was successfully applied to determination of iron and aluminum in steam and water samples of thermal power plant; and the accuracy was assessed through the recovery experiments and independent analysis by electrothermal atomic absorption spectroscopy (ETAAS). PMID:25168229

  5. Simultaneous spectrophotometric determination of Fe(III) and Al(III) using orthogonal signal correction-partial least squares calibration method after solidified floating organic drop microextraction

    NASA Astrophysics Data System (ADS)

    Rohani Moghadam, Masoud; Haji Shabani, Ali Mohammad; Dadfarnia, Shayessteh

    2015-01-01

    A solidified floating organic drop microextraction (SFODME) procedure was developed for the simultaneous extraction and preconcentration of Fe(III) and Al(III) from water samples. The method was based on the formation of cationic complexes between Fe(III) and Al(III) and 3,5,7,2‧,4‧-pentahydroxyflavone (morin) which were extracted into 1-undecanol as ion pairs with perchlorate ions. The absorbance of the extracted complexes was then measured in the wavelength range of 300-450 nm. Finally, the concentration of each metal ion was determined by the use of the orthogonal signal correction-partial least squares (OSC-PLS) calibration method. Several experimental parameters that may be affected on the extraction process such as the type and volume of extraction solvent, pH of the aqueous solution, morin and perchlorate concentration and extraction time were optimized. Under the optimum conditions, Fe(III) and Al(III) were determined in the ranges of 0.83-27.00 μg L-1 (R2 = 0.9985) and 1.00-32.00 μg L-1 (R2 = 0.9979) of Fe(III) and Al(III), respectively. The relative standard deviations (n = 6) at 12.80 μg L-1 of Fe(III) and 17.00 μg L-1 of Al(III) were 3.2% and 3.5%, respectively. An enhancement factors of 102 and 96 were obtained for Fe(III) and Al(III) ions, respectively. The procedure was successfully applied to determination of iron and aluminum in steam and water samples of thermal power plant; and the accuracy was assessed through the recovery experiments and independent analysis by electrothermal atomic absorption spectroscopy (ETAAS).

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

    PubMed

    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 m(2)/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

  7. 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.

  8. Fresh look at electron-transfer mechanisms via the donor/acceptor bindings in the critical encounter complex.

    PubMed

    Rosokha, Sergiy V; Kochi, Jay K

    2008-05-01

    . First, Q < 1 identifies one extreme mechanism owing to slow electron-transfer rates that result from the dominance of the intrinsic activation barrier (lambdaT) between the encounter and successor complexes. At the other extreme of Q > or = 1, the overwhelming dominance of the resonance stabilization (H(DA)) predicts the odd-electron mobility between the donor and acceptor to occur without an activation barrier such that bimolecular electron transfer is coincident with their diffusional encounter. In between lies a potentially infinite set of states, 0 < Q < 1 with opposing attractive and destabilizing forces that determine the location of the bound transition states along the reaction coordinate. Three prototypical potential-energy surfaces evolve as a result of progressively increasing the donor/acceptor bindings (H(DA)) extant in the precursor complex (at constant lambdaT). In these cases, the "outer-sphere" mechanism is limited by the weak donor/acceptor coupling that characterizes the now classical Marcus outer-sphere mechanism. Next, the "inner-sphere" mechanism derives from moderate (localized) donor/acceptor bindings and includes the mechanistic concept of the bridged-activated complex introduced by Taube for a wide variety of ligand-based redox dyads. Finally, the "interior" mechanism is also another subclass of the Taube (inner-sphere) classification, and it lies at the other extreme of very fast electron-transfer rate processes (heretofore unrecognized), arising from the spontaneous annihilation of the donor/acceptor dyad to the delocalized (electron-transfer) complex as it descends barrierlessly into the chemical "black hole" that is rate-limited solely by diffusion. PMID:18380446

  9. 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

  10. Gene and protein expression profiles of Shewanella oneidensis during anaerobic growth with different electron acceptors.

    SciTech Connect

    Beliaev, A. S.; Thompson, D. K.; Khare, T.; Lim, H.; Brandt, C. C.; Li, G.; Murray, A. E.; Heidelberg, J. F.; Giometti, C. S.; Yates, J., III; Nealson, K. H.; Tiedje, J. M.; Zhou, J.; Biosciences Division; ORNL; Scripps Research Inst.; Michigan State Univ.; The Inst. for Genomic Research; Jet Propulsion Laboratory; California Inst. of Tech.

    2002-01-01

    Changes in mRNA and protein expression profiles of Shewanella oneidenesis MR-1 during switch from aerobic to fumarate-, Fe(III)-, or nitrate-reducing conditions were examined using DNA microarrays and two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). In response to changes in growth conditions, 121 of the 691 arrayed genes displayed at least a two-fold difference in transcript abundance as determined by microarray analysis. Genes involved in aerobic respiration encoding cytochrome c and d oxidases and TCA cycle enzymes were repressed under anaerobic conditions. Genes induced during anaerobic respiration included those involved in cofactor biosynthesis and assembly (moaACE, ccmHF, nosD, cysG), substrate transport (cysUP, cysTWA, dcuB), and anaerobic energy metabolism (dmsAB, psrC, pshA, hyaABC, hydA). Transcription of genes encoding a periplasmic nitrate reductase (napBHGA), cytochrome c{sub 552}, and prismane was elevated 8- to 56-fold in response to the presence of nitrate, while cymA, ifcA, and frdA were specifically induced three- to eightfold under fumarate-reducing conditions. The mRNA levels for two oxidoreductase-like genes of unknown function and several cell envelope genes involved in multidrug resistance increased two- to fivefold specifically under Fe(III)-reducing conditions. Analysis of protein expression profiles under aerobic and anaerobic conditions revealed 14 protein spots that showed significant differences in abundance on 2-D gels. Protein identification by mass spectrometry indicated that the expression of prismane, dihydrolipoamide succinyltransferase, and alcaligin siderophore biosynthesis protein correlated with the microarray data.

  11. Gene and protein expression profiles of Shewanella oneidensis during anaerobic growth with different electron acceptors.

    PubMed

    Beliaev, Alex S; Thompson, Dorothea K; Khare, Tripti; Lim, Hanjo; Brandt, Craig C; Li, Guangshan; Murray, Alison E; Heidelberg, John F; Giometti, Carol S; Yates, John; Nealson, Kenneth H; Tiedje, James M; Zhoui, Jizhong

    2002-01-01

    Changes in mRNA and protein expression profiles of Shewanella oneidenesis MR-1 during switch from aerobic to fumarate-, Fe(III)-, or nitrate-reducing conditions were examined using DNA microarrays and two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). In response to changes in growth conditions, 121 of the 691 arrayed genes displayed at least a two-fold difference in transcript abundance as determined by microarray analysis. Genes involved in aerobic respiration encoding cytochrome c and d oxidases and TCA cycle enzymes were repressed under anaerobic conditions. Genes induced during anaerobic respiration included those involved in cofactor biosynthesis and assembly (moaACE, ccmHF, nosD, cysG), substrate transport (cysUP, cysTWA, dcuB), and anaerobic energy metabolism (dmsAB, psrC, pshA, hyaABC, hydA). Transcription of genes encoding a periplasmic nitrate reductase (napBHGA), cytochrome c552, and prismane was elevated 8- to 56-fold in response to the presence of nitrate, while cymA, ifcA, and frdA were specifically induced three- to eightfold under fumarate-reducing conditions. The mRNA levels for two oxidoreductase-like genes of unknown function and several cell envelope genes involved in multidrug resistance increased two- to fivefold specifically under Fe(III)-reducing conditions. Analysis of protein expression profiles under aerobic and anaerobic conditions revealed 14 protein spots that showed significant differences in abundance on 2-D gels. Protein identification by mass spectrometry indicated that the expression of prismane, dihydrolipoamide succinyltransferase, and alcaligin siderophore biosynthesis protein correlated with the microarray data. PMID:11881834

  12. The effect of intermolecular donor?acceptor energy transfer on emission anisotropy in uniaxially oriented polymer films

    NASA Astrophysics Data System (ADS)

    Sadownik, M.; Bojarski, Piotr

    2004-10-01

    Excitation energy transport between donors and acceptors is studied for uniaxially stretched and unstretched poly(vinyl) alcohol films. Donor emission anisotropy courses versus acceptor concentration as well as donor-acceptor emission anisotropy spectra occurred quite different in stretched and unstretched films. Upon donor excitation the total emission anisotropy rapidly decreases when passing from the donor to the acceptor fluorescence band in disordered systems. However, such a pronounced effect has not been found in partly ordered films. Donors and acceptors exhibit highly preferential mutual orientation in strongly ordered films resulting in the preservation of acceptor emission anisotropy.

  13. Physiological and electrochemical effects of different electron acceptors on bacterial anode respiration in bioelectrochemical systems.

    PubMed

    Yang, Yonggang; Xiang, Yinbo; Xia, Chunyu; Wu, Wei-Min; Sun, Guoping; Xu, Meiying

    2014-07-01

    To understand the interactions between bacterial electrode respiration and the other ambient bacterial electron acceptor reductions, alternative electron acceptors (nitrate, Fe2O3, fumarate, azo dye MB17) were added singly or multiply into Shewanella decolorationis microbial fuel cells (MFCs). All the added electron acceptors were reduced simultaneously with current generation. Adding nitrate or MB17 resulted in more rapid cell growth, higher flavin concentration and higher biofilm metabolic viability, but lower columbic efficiency (CE) and normalized energy recovery (NER) while the CE and NER were enhanced by Fe2O3 or fumarate. The added electron acceptors also significantly influenced the cyclic voltammetry profile of anode biofilm probably via altering the cytochrome c expression. The highest power density was observed in MFCs added with MB17 due to the electron shuttle role of the naphthols from MB17 reduction. The results provided important information for MFCs applied in practical environments where contains various electron acceptors.

  14. Excitation energy transfer in partly ordered polymer films differing in donor and acceptor transition moments orientation

    NASA Astrophysics Data System (ADS)

    Synak, A.; Bojarski, P.; Sadownik, M.; Kułak, L.; Gryczynski, I.; Grobelna, B.; Rangełowa-Jankowska, S.; Jankowski, D.; Kubicki, A.

    2016-09-01

    Based on spectroscopic measurements selected properties of nonradiative Förster energy transport are studied in uniaxially stretched polyvinyl alcohol thin films for three systems differing in donor and acceptor transition moments orientation relative to the axis of stretching. In particular, donor - acceptor emission anisotropy spectra yield completely different regularities for these systems in uniaxially stretched films, whereas they are similar in unstretched films. In particular it is shown that acceptor fluorescence can be either strongly polarized after nonradiative energy transfer in stretched films or depolarized depending on the angular distribution of acceptor transition moments in the matrix. Donor and acceptor emission anisotropy decays exhibit similar regularities to those of steady-state measurements. The obtained results are analyzed with the help of Monte Carlo simulations.

  15. Ultrasound-modulated fluorescence based on donor-acceptor-labeled microbubbles

    PubMed Central

    Liu, Yuan; Feshitan, Jameel A.; Wei, Ming-Yuan; Borden, Mark A.; Yuan, Baohong

    2015-01-01

    Abstract. A fluorescence resonance energy transfer (FRET)-based microbubble contrast agent system was designed to experimentally demonstrate the concept of ultrasound-modulated fluorescence (UMF). Microbubbles were simultaneously labeled with donor and acceptor fluorophores on the surface to minimize self-quenching and maximize FRET. In response to ultrasound, the quenching efficiency was greatly modulated by changing the distance between the donor and acceptor molecules through microbubble size oscillations. Both donors and acceptors exhibited UMF on individual microbubbles. The UMF strength of the donor was more significant compared to that of the acceptor. Furthermore, the UMF of the donor was observed from a microbubble solution in a turbid media. This study exploits the feasibility of donor–acceptor labeled microbubbles as UMF contrast agents. PMID:25789423

  16. Regulation of human dihydrodiol dehydrogenase by Michael acceptor xenobiotics.

    PubMed

    Ciaccio, P J; Jaiswal, A K; Tew, K D

    1994-06-01

    A human oxidoreductase (H-37) that is overexpressed in ethacrynic acid-resistant HT29 colon cells (Ciaccio, P. J., Stuart, J.E., and Tew, K.D. (1993) Mol. Pharmacol. 43, 845-853) has been identified as a dihydrodiol dehydrogenase. Translated protein from a dihydrodiol dehydrogenase cDNA isolated from a library prepared from ethacrynic acid-resistant HT29 cell poly(A+) RNA was recognized by anti-H-37 IgG and was identical in molecular weight with H-37. The isolated cDNA was identical in both nucleotide and amino acid sequences with the recently cloned liver dihydrodiol dehydrogenase (Stolz, A., Hammond, L., Lou, H., Takikawa, H., Ronk, M., and Shively, J.E. (1993) J. Biol. Chem. 268, 10448-10457). Using this cDNA as probe, we have examined its induction by Michael acceptors. The steady state dihydrodiol dehydrogenase mRNA level in the ethacrynic acid-resistant line was increased 30-fold relative to that of wild-type cells. Twenty-four hour treatment of wild-type cells with ethacrynic acid or dimethyl maleate increased mRNA 10-fold and 5-fold, respectively. These changes are accompanied by both increased protein expression and increased NADP-dependent 1-acenaphthenol oxidative activity in cell cytosol. In gel shift assays, compared to wild type controls, increased binding of NAD(P)H quinone oxidoreductase human antioxidant response element (hARE) DNA to redox labile protein complexes present in treated and resistant cell nuclear extract was observed. Ethacrynic acid induced CAT activity 2-fold in Hepa1 cells stably transfected with NAD(P)H quinone oxidoreductase hARE-tk-CAT chimeric gene construct. Thus, dihydrodiol dehydrogenase protein is inducible by de novo synthesis from mRNA by structurally related monofunctional inducer Michael acceptors. Altered in vitro binding of nuclear protein to the hARE is indirect evidence for the involvement of an element similar to hARE in the regulation of dihydrodiol dehydrogenase by these agents. PMID:7515059

  17. Evidence for ligand hydrolysis and Fe(III) reduction in the dissolution of goethite by desferrioxamine-B

    NASA Astrophysics Data System (ADS)

    Simanova, Anna A.; Persson, Per; Loring, John S.

    2010-12-01

    Desferrioxamine-B (DFOB) is a bacterial trihydroxamate siderophore and probably the most studied to date. However, the manner in which DFOB adsorbs at mineral surfaces and promotes dissolution is still under discussion. Here we investigated the adsorption and dissolution reactions in the goethite-DFOB system using both in situ infrared spectroscopic and quantitative analytical methods. Experiments were carried out at a total DFOB concentration of 1 μmol/m 2, at pH 6, and in the absence of visible light. Our infrared spectroscopic results indicated that the adsorption of DFOB was nearly complete after a 4-h reaction time. In an attempt to determine the coordination mode at the goethite surface, we compared the spectrum of adsorbed DFOB after a 4-h reaction time to the spectra of model aqueous species. However, this approach proved too simplistic in the case of such a complex ligand as DFOB, and we suggest that a more detailed investigation (IR in D 2O, EXAFS of adsorbed model complexes) is needed to elucidate the structure of the adsorbed siderophore. Between a 4-h and 4-day reaction time, we observed the growth of carboxylate stretching bands at 1548 and 1404 cm -1, which are indicators of DFOB hydrolysis. Acetate, a product of DFOB hydrolysis at its terminal hydroxamate group, was quantified by ion chromatography. Its rate of formation was linear and nearly the same as the rate of Fe(III) dissolution. The larger hydrolysis product, a hydroxylamine fragment, was not detected by LC-MS. However, a signal due to the oxidized form of this fragment, a nitroso compound, was found to increase linearly with time, which is an indirect indication for Fe(III) reduction. Based on these findings, we propose that DFOB undergoes metal-enhanced hydrolysis at the mineral surface followed by the reduction of surface Fe(III). While Fe(II) was not detected in solution, this is likely because it remains adsorbed at the goethite surface or becomes buried in the goethite crystal by

  18. Potassium acceptor doping of ZnO crystals

    SciTech Connect

    Parmar, Narendra S. Lynn, K. G.; Corolewski, Caleb D.; McCluskey, Matthew D.

    2015-05-15

    ZnO bulk single crystals were doped with potassium by diffusion at 950°C. Positron annihilation spectroscopy confirms the filling of zinc vacancies and a different trapping center for positrons. Secondary ion mass spectroscopy measurements show the diffusion of potassium up to 10 μm with concentration ∼1 × 10{sup 16} cm{sup −3}. IR measurements show a local vibrational mode (LVM) at 3226 cm{sup −1}, at a temperature of 9 K, in a potassium doped sample that was subsequently hydrogenated. The LVM is attributed to an O–H bond-stretching mode adjacent to a potassium acceptor. When deuterium substitutes for hydrogen, a peak is observed at 2378 cm{sup −1}. The O-H peak is much broader than the O-D peak, perhaps due to an unusually low vibrational lifetime. The isotopic frequency ratio is similar to values found in other hydrogen complexes. Potassium doping increases the resistivity up to 3 orders of magnitude at room temperature. The doped sample has a donor level at 0.30 eV.

  19. Molecular insights into the terminal energy acceptor in cyanobacterial phycobilisome.

    PubMed

    Gao, Xiang; Wei, Tian-Di; Zhang, Nan; Xie, Bin-Bin; Su, Hai-Nan; Zhang, Xi-Ying; Chen, Xiu-Lan; Zhou, Bai-Cheng; Wang, Zhi-Xin; Wu, Jia-Wei; Zhang, Yu-Zhong

    2012-09-01

    The linker protein L(CM) (ApcE) is postulated as the major component of the phycobilisome terminal energy acceptor (TEA) transferring excitation energy from the phycobilisome to photosystem II. L(CM) is the only phycobilin-attached linker protein in the cyanobacterial phycobilisome through auto-chromophorylation. However, the underlying mechanism for the auto-chromophorylation of L(CM) and the detailed molecular architecture of TEA is still unclear. Here, we demonstrate that the N-terminal phycobiliprotein-like domain of L(CM) (Pfam00502, LP502) can specifically recognize phycocyanobilin (PCB) by itself. Biochemical assays indicated that PCB binds into the same pocket in LP502 as that in the allophycocyanin α-subunit and that Ser152 and Asp155 play a vital role in LP502 auto-chromophorylation. By carefully conducting computational simulations, we arrived at a rational model of the PCB-LP502 complex structure that was supported by extensive mutational studies. In the PCB-LP502 complex, PCB binds into a deep pocket of LP502 with a distorted conformation, and Ser152 and Asp155 form several hydrogen bonds to PCB fixing the PCB Ring A and Ring D. Finally, based on our results, the dipoles and dipole-dipole interactions in TEA are analysed and a molecular structure for TEA is proposed, which gives new insights into the energy transformation mechanism of cyanobacterial phycobilisome. PMID:22758351

  20. Swift Electrofluorochromism of Donor-Acceptor Conjugated Polytriphenylamines.

    PubMed

    Sun, Jingwei; Liang, Ziqi

    2016-07-20

    Electrofluorochromic (EFC) materials, which exhibit electrochemically controllable fluorescence, hold great promise in optoelectronic devices and biological analysis. Here we design such donor-acceptor (D-A) conjugated polymers-P(TPACO) and P(TCEC)-that contain the same electron-rich and oxidizable polytriphenylamine (PTPA) as π-backbone, yet with different electron-deficient ketone and cyano units as pendant groups, respectively. They both exhibit solvatochromic effects due to intrinsic characteristics of intramolecular charge transfer (ICT). Compared to P(TPACO), P(TCEC) shows stronger ICT, which leads to higher electrochemical oxidation potential and lower ion diffusion coefficient. Moreover, both polymers present simultaneous electrochromic (EC) and EFC behaviors with multistate display and remarkably rapid fluorescence response. The response time of P(TPACO) is as short as 0.19 s, nearly 4-fold faster than that of P(TCEC) (0.92 s). Such rapid response is found to be determined by the ion diffusion coefficient which is associated with the ICT nature. Finally, the EFC display device based on P(TPACO) is successfully demonstrated, which shows green fluorescence ON/OFF switching upon applied potentials. This work has successfully demonstrated that swift EFCs can be achieved by rational modulation of the ICT effect in such D-A conjugated polymers. PMID:27347724

  1. Poly(trifluoromethyl)azulenes: structures and acceptor properties

    SciTech Connect

    Clikeman, Tyler T.; Bukovsky, Eric V.; Kuvychko, Igor V.; San, Long K.; Deng, Shihu; Wang, Xue B.; Chen, Yu-Sheng; Strauss, Steven H.; Boltalina, Olga 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 of a π-stacked donor-acceptor complex of a trifluoromethyl azulene with donor pyrene.

  2. Biosynthesis, characterization and biological evalutation of Fe(III) and Cu(II) complexes of neoaspergillic acid, a hydroxamate siderophore produced by co-cultures of two marine-derived mangrove epiphytic fungi.

    PubMed

    Zhu, Feng; Wu, Jingshu; Chen, Guangying; Lu, Weihong; Pan, Jiahui

    2011-08-01

    A hydroxamate siderophore, neoaspergillic acid (1), and a red pigment, ferrineoaspergillin (2) which is an Fe(III) complex of 1, were produced by co-cultures of two epiphytic fungi from a rotten fruit of the mangrove Avicennia marina from the South China Sea, and a new Cu(II) complex of 1, designated as cuprineoaspergillin (3), was also prepared by treatment of 1 with cupric acetate. All the compounds (1-3) were characterized by physical and chemical techniques, including 1H NMR, ESIMS, and photoelectron energy spectra. In the bioassays, compounds 1-3 showed significant inhibitory activities against selected Gram-positive and Gram-negative bacteria, and compound 1 also exhibited moderate inhibitory activities against human cancer cell lines SPC-A-1, BEL-7402, SGC-7901 and K562.

  3. The role of multihaem cytochromes in the respiration of nitrite in Escherichia coli and Fe(III) in Shewanella oneidensis

    SciTech Connect

    Clarke, Thomas A.; Holley, Tracey; Hartshorne, Robert S.; Fredrickson, Jim K.; Zachara, John M.; Shi, Liang; Richardson, David

    2008-10-01

    The periplasmic nitrite reductase system from Escherichia coli and the extracellular Fe(III) reductase system from Shewanella oneidensis contain multihaem c-type cytochromes as electron carriers and terminal reductases. The position and orientation of the haem cofactors in multihaem cytochromes from different bacteria often show significant conservation despite different arrangements of the polypeptide chain. We propose that the decahaem cytochromes of the iron reductase system MtrA, MtrC and OmcA comprise pentahaem ‘modules’ similar to the electron donor protein, NrfB, from E. coli. To demonstrate this, we have isolated and characterized the N-terminal pentahaem module of MtrA by preparing a truncated form containing five covalently attached haems. UV–visible spectroscopy indicated that all five haems were low-spin, consistent with the presence of bis-His ligand co-ordination as found in full-length MtrA.

  4. The role of multihaem cytochromes in the respiration of nitrite in Escherichia coli and Fe(III) in Shewanella oneidensis.

    PubMed

    Clarke, Thomas A; Holley, Tracey; Hartshorne, Robert S; Fredrickson, Jim K; Zachara, John M; Shi, Liang; Richardson, David J

    2008-10-01

    The periplasmic nitrite reductase system from Escherichia coli and the extracellular Fe(III) reductase system from Shewanella oneidensis contain multihaem c-type cytochromes as electron carriers and terminal reductases. The position and orientation of the haem cofactors in multihaem cytochromes from different bacteria often show significant conservation despite different arrangements of the polypeptide chain. We propose that the decahaem cytochromes of the iron reductase system MtrA, MtrC and OmcA comprise pentahaem 'modules' similar to the electron donor protein, NrfB, from E. coli. To demonstrate this, we have isolated and characterized the N-terminal pentahaem module of MtrA by preparing a truncated form containing five covalently attached haems. UV-visible spectroscopy indicated that all five haems were low-spin, consistent with the presence of bis-His ligand co-ordination as found in full-length MtrA.

  5. Nanostructured Fe(III) catalysts for water oxidation assembled with the aid of organic acid salt electrolytes

    NASA Astrophysics Data System (ADS)

    Zhao, Qiang; Li, Dandan; Gao, Guofeng; Yuan, Wen; Hao, Genyan; Li, Jinping

    2016-11-01

    We describe the preparation of three partially ordered iron-based catalyst films (Fe-OAc, Fe-Pro, Fe-But) with nanoporous structure by electrodeposition from organate electrolytes containing Fe2+. The anions of the organic acids assisted the partial ordering of the nanostructured Fe(III) catalysts for water oxidation. A model involving an electrical double layer is invoked to explain the role of the organate electrolyte system in their formation. Analytical results have revealed the main component of the iron-based films to be a β-FeOOH structure. The Fe-But catalyst catalyzed water oxidation in 0.1 m potassium carbonate solution with an average activity of 1.48 mA cm-2 and an overpotential of 433 mV.

  6. Redox cycling of Fe(II) and Fe(III) in magnetite by Fe-metabolizing bacteria.

    PubMed

    Byrne, James M; Klueglein, Nicole; Pearce, Carolyn; Rosso, Kevin M; Appel, Erwin; Kappler, Andreas

    2015-03-27

    Microorganisms are a primary control on the redox-induced cycling of iron in the environment. Despite the ability of bacteria to grow using both Fe(II) and Fe(III) bound in solid-phase iron minerals, it is currently unknown whether changing environmental conditions enable the sharing of electrons in mixed-valent iron oxides between bacteria with different metabolisms. We show through magnetic and spectroscopic measurements that the phototrophic Fe(II)-oxidizing bacterium Rhodopseudomonas palustris TIE-1 oxidizes magnetite (Fe3O4) nanoparticles using light energy. This process is reversible in co-cultures by the anaerobic Fe(III)-reducing bacterium Geobacter sulfurreducens. These results demonstrate that Fe ions bound in the highly crystalline mineral magnetite are bioavailable as electron sinks and electron sources under varying environmental conditions, effectively rendering magnetite a naturally occurring battery.

  7. Redox cycling of Fe(II) and Fe(III) in magnetite by Fe-metabolizing bacteria

    NASA Astrophysics Data System (ADS)

    Byrne, James M.; Klueglein, Nicole; Pearce, Carolyn; Rosso, Kevin M.; Appel, Erwin; Kappler, Andreas

    2015-03-01

    Microorganisms are a primary control on the redox-induced cycling of iron in the environment. Despite the ability of bacteria to grow using both Fe(II) and Fe(III) bound in solid-phase iron minerals, it is currently unknown whether changing environmental conditions enable the sharing of electrons in mixed-valent iron oxides between bacteria with different metabolisms. We show through magnetic and spectroscopic measurements that the phototrophic Fe(II)-oxidizing bacterium Rhodopseudomonas palustris TIE-1 oxidizes magnetite (Fe3O4) nanoparticles using light energy. This process is reversible in co-cultures by the anaerobic Fe(III)-reducing bacterium Geobacter sulfurreducens. These results demonstrate that Fe ions bound in the highly crystalline mineral magnetite are bioavailable as electron sinks and electron sources under varying environmental conditions, effectively rendering magnetite a naturally occurring battery.

  8. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  9. On-line solid-phase extraction and multisyringe flow injection analysis of Al(III) and Fe(III) in drinking water.

    PubMed

    Vanloot, Pierre; Branger, Catherine; Margaillan, André; Brach-Papa, Christophe; Boudenne, Jean-Luc; Coulomb, Bruno

    2007-11-01

    A new analytical method was developed for on-line monitoring of residual coagulants (aluminium and iron salts) in potable water. The determination was based on a sequential procedure coupling an extraction/enrichment step of the analytes onto a modified resin and a spectrophotometric measurement of a surfactant-sensitized binary complex formed between eluted analytes and Chrome Azurol S. The optimization of the solid phase extraction was performed using factorial design and a Doehlert matrix considering six variables: sample percolation rate, sample metal concentration, flow-through sample volume (all three directly linked to the extraction step), elution flow rate, concentration and volume of eluent (all three directly linked to the elution step). A specific reagent was elaborated for sensitive and specific spectrophotometric determination of Al(III) and Fe(III), by optimizing surfactant and ligand concentrations and buffer composition. The whole procedure was automated by a multisyringe flow injection analysis (MSFIA) system. Detection limits of 4.9 and 5.6 microg L(-1) were obtained for Al(III) and Fe(III) determination , respectively, and the linear calibration graph up to 300 microg L(-1) (both for Al(III) and Fe(III)) was well adapted to the monitoring of drinking water quality. The system was successfully applied to the on-site determination of Al(III) and Fe(III) at the outlet of two water treatment units during two periods of the year (winter and summer conditions).

  10. 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)

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

    SciTech Connect

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

    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 be 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.

  12. 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

  13. Pyrimidone-based series of glucokinase activators with alternative donor-acceptor motif.

    PubMed

    Filipski, Kevin J; Guzman-Perez, Angel; Bian, Jianwei; Perreault, Christian; Aspnes, Gary E; Didiuk, Mary T; Dow, Robert L; Hank, Richard F; Jones, Christopher S; Maguire, Robert J; Tu, Meihua; Zeng, Dongxiang; Liu, Shenping; Knafels, John D; Litchfield, John; Atkinson, Karen; Derksen, David R; Bourbonais, Francis; Gajiwala, Ketan S; Hickey, Michael; Johnson, Theodore O; Humphries, Paul S; Pfefferkorn, Jeffrey A

    2013-08-15

    Glucokinase activators are a class of experimental agents under investigation as a therapy for Type 2 diabetes mellitus. An X-ray crystal structure of a modestly potent agent revealed the potential to substitute the common heterocyclic amide donor-acceptor motif for a pyridone moiety. We have successfully demonstrated that both pyridone and pyrimidone heterocycles can be used as a potent donor-acceptor substituent. Several sub-micromolar analogs that possess the desired partial activator profile were synthesized and characterized. Unfortunately, the most potent activators suffered from sub-optimal pharmacokinetic properties. Nonetheless, these donor-acceptor motifs may find utility in other glucokinase activator series or beyond.

  14. 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.

  15. A KAP study on MTP acceptors and their contraceptive practice.

    PubMed

    Roy, M; Lahiri, B C; Ghosh, B N

    1978-01-01

    From the point of view of the family planning program, it is necessary to determine whether a medical termination of pregnancy has a learning effect on a woman's subsequent fertility control behavior. In order to determine the knowledge and attitude of medical termination of pregnancy (MTP) acceptors towards abortion and their pre and post abortion contraceptive practices, a study was conducted during January to December 1975 in a family planning clinic in North Calcutta. 300 consecutive cases admitted to the hospital for abortions were the study subjects - the MTP group. They were subjected to repeated interviews in the ward before and after the abortion and were followed up at home within 6-10 months after the discharge from the hospital. 300 women who attended the antenatal clinic of the same hospital during the same period were selected for comparison by systematic sampling. There is no statistically significant difference in the social characteristics of the 2 groups except that the MTP group was from a comparatively poorer economic class. 13.3% of the MTP group had "good" knowledge of physiology of reproduction in contrast to only 5.0% in the comparison group. Only 52% of the MTP group and 63% in the comparison group failed to have even an "average" knowledge of this area. Nearly 55% of the MTP group and 65% of the comparison group had never practiced family planning. Over 55% of the MTP group had poor knowledge about abortion; the most important soruce of their knowledge was their neighbors. 78.7% of the cases considered MTP to be a sinful act. The primary reason for deciding to have an abortion was socioeconomic. Over 27.6% of the cases were using contraceptives to avoid the present pregnancy. The difference is statistically significant suggesting a positive learning effect of MTP on contraceptive behavior of women seeking abortions.

  16. Fluorescence quenching in an organic donor-acceptor dyad: a first principles study.

    PubMed

    Körzdörfer, T; Tretiak, S; Kümmel, S

    2009-07-21

    Perylene bisimide and triphenyl diamine are prototypical organic dyes frequently used in organic solar cells and light emitting devices. Recent Forster-resonant-energy-transfer experiments on a bridged organic dyad consisting of triphenyl diamine as an energy-donor and perylene bisimide as an energy-acceptor revealed a strong fluorescence quenching on the perylene bisimide. This quenching is absent in a solution of free donors and acceptors and thus attributed to the presence of the saturated CH(2)O(CH(2))(12)-bridge. We investigate the cause of the fluorescence quenching as well as the special role of the covalently bound bridge by means of time dependent density functional theory and molecular dynamics. The conformational dynamics of the bridged system leads to a charge transfer process between donor and acceptor that causes the acceptor fluorescence quenching. PMID:19624200

  17. Interface-induced heavy-hole/light-hole splitting of acceptors in silicon

    SciTech Connect

    Mol, J. A.; Salfi, J.; Simmons, M. Y.; Rogge, S.; Rahman, R.; Hsueh, Y.; Klimeck, G.; Miwa, J. A.

    2015-05-18

    The energy spectrum of spin-orbit coupled states of individual sub-surface boron acceptor dopants in silicon have been investigated using scanning tunneling spectroscopy at cryogenic temperatures. The spatially resolved tunnel spectra show two resonances, which we ascribe to the heavy- and light-hole Kramers doublets. This type of broken degeneracy has recently been argued to be advantageous for the lifetime of acceptor-based qubits [R. Ruskov and C. Tahan, Phys. Rev. B 88, 064308 (2013)]. The depth dependent energy splitting between the heavy- and light-hole Kramers doublets is consistent with tight binding calculations, and is in excess of 1 meV for all acceptors within the experimentally accessible depth range (<2 nm from the surface). These results will aid the development of tunable acceptor-based qubits in silicon with long coherence times and the possibility for electrical manipulation.

  18. Dinitrogen extrusion from enoldiazo compounds under thermal conditions: synthesis of donor-acceptor cyclopropenes.

    PubMed

    Deng, Yongming; Jing, Changcheng; Doyle, Michael P

    2015-08-21

    Donor-acceptor cyclopropenes are formed quantitatively or in high yield from enoldiazoacetates and enoldiazoacetamides under moderate thermal conditions. They are more versatile than their corresponding enoldiazocarbonyl compounds as carbene precursors.

  19. Preparation and spectroscopic studies on charge-transfer complexes of 2-hydroxypyridine with electron acceptors

    NASA Astrophysics Data System (ADS)

    Gaballa, Akmal S.

    2013-07-01

    The CT-interactions of electron acceptors such as iodine (I2), chloranilic acid (H2CA) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) with 2-hydroxypyridine (HPyO) have been investigated in the defined solvent. The data indicate the formation of CT-complexes with the general formula [(HPyO)(acceptor)]. The 1:1 stoichiometry of the (HPyO)-acceptors were based on elemental analysis, IR spectra and thermogravimetric analysis of the solid CT-complexes along with the photometric titration measurements for the reactions. The formation constants (KCT) for the CT-complexes are shown to be strongly dependent on the type and structure of the electron acceptors. Factors affecting the CT-processes are discussed.

  20. Preparation and spectroscopic studies on charge-transfer complexes of famciclovir drug with different electron acceptors

    NASA Astrophysics Data System (ADS)

    Gaballa, Akmal S.; Teleb, Said M.; Nour, El-Metwally

    2012-09-01

    The CT-interaction of electron acceptors such as chloranilic acid (H2CA), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and and 7,7',8,8'-tetracyano-p-quinodimethane (TCNQ) with the antiviral drug famciclovir (FCV) have been investigated spectrophotometrically in the defined solvent. The data indicate the formation of CT-complexes with the general formula [(FCV)(acceptor)]. The 1:1 stoichiometry of the (FCV)-acceptors were based on elemental analysis, IR spectra and thermogravimetric analysis of the solid CT-complexes along with the photometric titration measurements for the reactions. The formation constants (KCT) for the CT-complexes are shown to be strongly dependent on the type and structure of the electron acceptor. Factors affecting the CT-processes such as redox potentials and steric hinderance of reactants are discussed.

  1. Computational design of donor-bridge-acceptor systems exhibiting pronounced quantum interference effects.

    PubMed

    Gorczak, Natalie; Renaud, Nicolas; Galan, Elena; Eelkema, Rienk; Siebbeles, Laurens D A; Grozema, Ferdinand C

    2016-03-01

    Quantum interference is a well-known phenomenon that dictates charge transport properties of single molecule junctions. However, reports on quantum interference in donor-bridge-acceptor molecules are scarce. This might be due to the difficulties in meeting the conditions for the presence of quantum interference in a donor-bridge-acceptor system. The electronic coupling between the donor, bridge, and acceptor moieties must be weak in order to ensure localised initial and final states for charge transfer. Yet, it must be strong enough to allow all bridge orbitals to mediate charge transfer. We present the computational route to the design of a donor-bridge-acceptor molecule that features the right balance between these contradicting requirements and exhibits pronounced interference effects.

  2. 34 CFR 303.15 - Include; including.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 34 Education 2 2010-07-01 2010-07-01 false Include; including. 303.15 Section 303.15 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF SPECIAL EDUCATION AND REHABILITATIVE SERVICES, DEPARTMENT OF EDUCATION EARLY INTERVENTION PROGRAM FOR INFANTS AND TODDLERS...

  3. Curved Oligophenylenes as Donors in Shape-Persistent Donor-Acceptor Macrocycles with Solvatofluorochromic Properties.

    PubMed

    Kuwabara, Takuya; Orii, Jun; Segawa, Yasutomo; Itami, Kenichiro

    2015-08-10

    Many optoelectronic organic materials are based on donor-acceptor (D-A) systems with heteroatom-containing electron donors. Herein, we introduce a new molecular design for all-carbon curved oligoparaphenylenes as donors, which results in the generation of unique shape-persistent D-A macrocycles. Two types of acceptor-inserted cycloparaphenylenes were synthesized. These macrocycles display positive solvatofluorochromic properties owing to their D-A characteristics, which were confirmed by theoretical and electrochemical studies. PMID:26140706

  4. Experiments probing the viability of donor-acceptor norbornenes for (5 + 2)-annulation.

    PubMed

    Walker, Morgan M; Goodman, C Guy; Johnson, Jeffrey S

    2014-10-01

    This Note details experiments that probe the mechanism by which donor-acceptor norbornene systems epimerize. A number of mechanistic studies indicate that epimerization in these systems occurs via a Lewis acid catalyzed retro-Diels-Alder/Diels-Alder sequence, rather than bond rotation in an intimate ion pair. These results suggest that, under the reaction conditions examined, the ring strain present in norbornene is inadequate to induce zwitterion formation analogous to that observed with donor-acceptor cyclopropanes.

  5. New acceptor centers of the background impurities in p-CdZnTe

    SciTech Connect

    Plyatsko, S. V. Rashkovetskyi, L. V.

    2013-07-15

    Low-temperature photoluminescence data are used to study the redistribution of the background impurities and host components of p-CdZnTe single crystals with a resistivity of 1-50 {Omega} cm upon their interaction with infrared laser radiation. The effect of widening of the band gap and the formation of new acceptor centers in response to laser-stimulated changes in the system of intrinsic defects are established. The activation energy of the new acceptor centers is determined.

  6. 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.

  7. Fast Carrier Formation from Acceptor Exciton in Low-Gap Organic Photovotalic

    NASA Astrophysics Data System (ADS)

    Yonezawa, Kouhei; Kamioka, Hayato; Yasuda, Takeshi; Han, Liyuan; Moritomo, Yutaka

    2012-04-01

    Bulk heterojunction (BHJ) based on a donor (D) polymer and an acceptor (A) fullerene derivative is a promising organic photovoltaic. Here, we investigated the femtosecond charge dynamics after acceptor excitation in poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b '] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl

  8. Effects of size restriction on donor-acceptor recombination in AgBr

    NASA Astrophysics Data System (ADS)

    Rodney, Paul J.; Marchetti, Alfred P.; Fauchet, Philippe M.

    2000-08-01

    The behavior of donor-acceptor (DA) recombination luminescence in quantum confined AgBr has been investigated. The DA luminescence decay, after pulsed excitation, became longer lived as the nanocluster size decreased. This result differs from theoretical expectations and from observations with AgI nanoclusters. The DA lifetime increase with decreasing size is due to an increase in yield and lifetime of ``free'' excitons that slowly dissociate into ``close'' donor-acceptor pairs, giving rise to an ``exciton dribbling'' effect.

  9. Benzodipyrrole-based Donor-Acceptor-type Boron Complexes as Tunable Near-infrared-Absorbing Materials.

    PubMed

    Nakamura, Tomoya; Furukawa, Shunsuke; Nakamura, Eiichi

    2016-07-20

    Benzodipyrrole-based donor-acceptor boron complexes were designed and synthesized as near-infrared-absorbing materials. The electron-rich organic framework combined with the Lewis acidic boron co-ordination enabled us to tune the LUMO energy level and the HOMO-LUMO gap (i.e.,the absorption wavelength) by changing the organic acceptor units, the number of boron atoms, and the substituents on the boron atoms.

  10. Nanosecond intersystem crossing times in fullerene acceptors: implications for organic photovoltaic diodes.

    PubMed

    Chow, Philip C Y; Albert-Seifried, Sebastian; Gélinas, Simon; Friend, Richard H

    2014-07-23

    Triplet-exciton formation through intersystem crossing of photogenerated singlet excitons in fullerene acceptors can compete with charge generation in organic photovoltaic diodes. This article reports the intersystem crossing timescale (τISC ) of the most commonly used fullerene acceptors, PC60 BM and PC70 BM, in solutions and in spin-coated films. These times are on the nanosecond timescale, and are longer than the characteristic times for charge generation (τd ).

  11. Study of characteristics of condom-acceptors using condom as first choice and alternative method of contraception in 1981-1987 at the NPFDB, GHKL.

    PubMed

    Low Boon Song

    1990-06-01

    Factors influencing condom acceptance were studied and compared in 2 groups of condom-acceptors--those using condoms as a 1st method of contraception and those using condoms as an alternative method of contraception. Data was obtained by reviewing the condom-acceptor cards during 1981-1987 at the General Hospital in Kuala Lumpur, Malaysia; 208 cards for the 1st group and 230 for the 2nd group were included in the study. Statistical analysis was conducted to determine characteristics influencing condom-use. AGe of wife, duration of marriage, number of living children, wife's level of education and socioeconomic status were identified as factors influencing condom acceptance. No significant difference was observed between the 2 group concerning their purpose of contraception. Age of wife had a significant influence on the use of condoms as contraception. Age of wife had a significant influence on the use of condoms as contraception; 74.5% of group 1 users were 31 years and 56.5% of group 2 users were 30 years. A very significant relationship also exist between condom use and duration of marriage and number of living children; condom-acceptors using condoms as the 1st method of contraception did so within 9 years of marriage (85.6%) and practiced condom use when they had 2 of children (73.6%) while those who used condoms subsequently were married 10 years (46.5%) and did so after having 3 or children (57.8%). Significant differences were observed between groups in higher socioeconomic status and higher level of education. With 7 or more years of education, a significant proportion of condom-acceptors used condoms as a 1st method of contraception as compared with those who used it as a subsequent method of contraception. For the higher socioeconomic, a significant number of acceptors used condoms as a 1st method of contraception.

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

    PubMed Central

    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

    2015-01-01

    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. PMID:26382113

  13. Beyond Fullerenes: Designing Alternative Molecular Electron Acceptors for Solution-Processable Bulk Heterojunction Organic Photovoltaics.

    PubMed

    Sauvé, Geneviève; Fernando, Roshan

    2015-09-17

    Organic photovoltaics (OPVs) are promising candidates for providing a low cost, widespread energy source by converting sunlight into electricity. Solution-processable active layers have predominantly consisted of a conjugated polymer donor blended with a fullerene derivative as the acceptor. Although fullerene derivatives have been the acceptor of choice, they have drawbacks such as weak visible light absorption and poor energy tuning that limit overall efficiencies. This has recently fueled new research to explore alternative acceptors that would overcome those limitations. During this exploration, one question arises: what are the important design principles for developing nonfullerene acceptors? It is generally accepted that acceptors should have high electron affinity, electron mobility, and absorption coefficient in the visible and near-IR region of the spectra. In this Perspective, we argue that alternative molecular acceptors, when blended with a conjugated polymer donor, should also have large nonplanar structures to promote nanoscale phase separation, charge separation and charge transport in blend films. Additionally, new material design should address the low dielectric constant of organic semiconductors that have so far limited their widespread application.

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

    DOE PAGES

    Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; Chen, Rongsheng; Purdum, Geoffrey E.; Khlyabich, Petr P.; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; et al

    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

  15. Differences in gene expression of human xylosyltransferases and determination of acceptor specificities for various proteoglycans

    SciTech Connect

    Roch, Christina; Kuhn, Joachim; Kleesiek, Knut; Goetting, Christian

    2010-01-01

    The xylosyltransferase (XT) isoforms XT-I and XT-II initiate the posttranslational glycosaminoglycan (GAG) synthesis. Here, we determined the relative expression of both isoforms in 33 human cell lines. The majority of tested cell lines showed dominant XYLT2 gene expression, while only in 23132/87, JAR, NCI-H510A and THP-1 was the XT-I mRNA expression higher. Nearly equal expression levels were detected in six cell lines. Additionally, to shed light on putative differences in acceptor specificities the acceptor properties of potential acceptor sequences were determined. Peptides were expressed as glutathione-S-transferase fusion proteins containing putative or known GAG attachment sites of in vivo proteoglycans. Kinetic analysis showed that K{sub m} and V{sub max} values for XT-I mediated xylosylation were slightly higher than those for XT-II, and that XT-I showed a lesser stringency concerning the acceptor sequence. Mutagenesis of the bikunin peptide sequence in the G-S-G attachment site and flanking regions generated potential acceptor molecules. Here, mutations on the N-terminal side and the attachment site were found to be more susceptible to a loss of acceptor function than mutations in the C-terminus. Altogether the known consensus sequence a-a-a-a-G-S-G-a-a/G-a ('a' representing Asp or Glu) for XT-I mediated xylosylation could be approved and additionally extended to apply to XT-II as well.

  16. A new classification of the amino acid side chains based on doublet acceptor energy levels.

    PubMed Central

    Sneddon, S F; Morgan, R S; Brooks, C L

    1988-01-01

    We describe a new classification of the amino acid side chains based on the potential energy level at which each will accept an extra (doublet) electron. The doublet acceptor energy level, and the doublet acceptor orbital were calculated using semiempirical INDO/2-UHF molecular orbital theory. The results of these calculations show that the side chains fall into four groups. We have termed these groups repulsive, insulating, semiconducting, and attractive in accordance with where each lies on the relative energy scale. We use this classification to examine the role of residues between the donor and acceptor in modulating the rate and mechanism of electron transfer in proteins. With the calculated acceptor levels, we construct a potential barrier for those residues between the donor and acceptor. It is the area beneath this barrier that determines the decay of electronic coupling between donor and acceptor, and thus the transfer rate. We have used this schematic approach to characterize the four electron transfer pathways in myoglobin recently studied by Mayo et al. (Mayo, S.L., W.R. Ellis, R.J. Crutchley, and H.B. Gray. 1986. Science [Wash. DC]. 233:948-952). PMID:3342271

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

    SciTech Connect

    Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; Chen, Rongsheng; Purdum, Geoffrey E.; Khlyabich, Petr P.; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; 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. As a result, this study describes a new motif for designing highly efficient acceptors for organic solar cells.

  18. 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.

  19. 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

    2015-01-01

    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. PMID:26382113

  20. Acceptor sites for retroviral integrations map near DNase I-hypersensitive sites in chromatin.

    PubMed Central

    Vijaya, S; Steffen, D L; Robinson, H L

    1986-01-01

    Seven cellular loci with acceptor sites for retroviral integrations have been mapped for the presence of DNase I-hypersensitive sites in chromatin. Integrations in three of these loci, chicken c-erbB, rat c-myc, and a rat locus, dsi-1, had been selected for in retrovirus-induced tumors. Of the remaining four, two, designated dsi-3 and dsi-4, harbored acceptor sites for apparently unselected integrations of Moloney murine leukemia virus in a Moloney murine leukemia virus-induced thymoma, and two, designated C and F, harbored unselected acceptor sites for Moloney murine leukemia virus integrations in a rat fibroblast cell line. Each acceptor site mapped to within 500 base pairs of a DNase I-hypersensitive site. In the analyses of the unselected integrations, six hypersensitive sites were observed in 39 kilobases of DNA. The four acceptor sites in this DNA were localized between 0.05 and 0.43 kilobases of a hypersensitive site. The probability of this close association occurring by chance was calculated to be extremely low. Hypersensitive sites were mapped in cells representing the lineage in which integration had occurred as well as in an unrelated lineage. In six of the seven acceptor loci hypersensitive sites could not be detected in the unrelated lineage. Our results indicate that retroviruses preferentially integrate close to DNase I-hypersensitive sites and that many of these sites are expressed in some but not all cells. Images PMID:3490582

  1. Candidatus Accumulibacter phosphatis clades enriched under cyclic anaerobic and microaerobic conditions simultaneously use different electron acceptors.

    PubMed

    Camejo, Pamela Y; Owen, Brian R; Martirano, Joseph; Ma, Juan; Kapoor, Vikram; Santo Domingo, Jorge; McMahon, Katherine D; Noguera, Daniel R

    2016-10-01

    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 phosphatis during the micro-aerobic stage was investigated. A complete clade-level characterization of Accumulibacter in both reactors was performed using newly designed qPCR primers targeting the polyphosphate kinase gene (ppk1). In the lab-scale reactor, limited-oxygen conditions led to an alternated dominance of Clade IID and IC over the other clades. Results from batch tests when Clade IC was dominant (i.e., >92% of Accumulibacter) showed that this clade was capable of using oxygen, nitrite and nitrate as electron acceptors for P uptake. A more heterogeneous distribution of clades was found in the pilot-scale system (Clades IIA, IIB, IIC, IID, IA, and IC), and in this reactor, oxygen, nitrite and nitrate were also used as electron acceptors coupled to phosphorus uptake. However, nitrite was not an efficient electron acceptor in either reactor, and nitrate allowed only partial P removal. The results from the Clade IC dominated reactor indicated that either organisms in this clade can simultaneously use multiple electron acceptors under micro-aerobic conditions, or that the use of multiple electron acceptors by Clade IC is due to significant microdiversity within the Accumulibacter clades defined using the ppk1 gene. PMID:27340814

  2. 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

  3. Conduction electrons in acceptor-doped GaAs/GaAlAs heterostructures: a review

    NASA Astrophysics Data System (ADS)

    Zawadzki, Wlodek; Raymond, Andre; Kubisa, Maciej

    2016-05-01

    We review magneto-optical and magneto-transport effects in GaAs/GaAlAs heterostructures doped in GaAlAs barriers with donors, providing two-dimensional (2D) electron gas (2DEG) in GaAs quantum wells (QWS), and additionally doped with smaller amounts of acceptors (mostly Be atoms) in the vicinity of 2DEG. One may also deal with residual acceptors (mostly C atoms). The behavior of such systems in the presence of a magnetic field differs appreciably from those doped in the vicinity of 2DEG with donors. Three subjects related to the acceptor-doped heterostructures are considered. First is the problem of bound states of conduction electrons confined to the vicinity of negatively charged acceptors by the joint effect of a QW and an external magnetic field parallel to the growth direction. A variational theory of such states is presented, demonstrating that an electron turning around a repulsive center has discrete energies above the corresponding Landau levels. Experimental evidence for the discrete electron energies comes from the work on interband photo-magneto-luminescence, intraband cyclotron resonance and quantum magneto-transport (the Quantum Hall and Shubnikov-de Haas effects). An electron rain-down effect at weak electric fields and a boil-off effect at strong electric fields are introduced. It is demonstrated, both theoretically and experimentally, that a negatively charged acceptor can localize more than one electron. The second subject describes experiment and theory of asymmetric quantized Hall and Shubnikov-de Haas plateaus in acceptor-doped GaAs/GaAlAs heterostructures. It is shown that the main features of the plateau asymmetry can be attributed to asymmetric density of Landau states in the presence of acceptors. However, at high magnetic fields, the rain-down effect is also at work. The third subject deals with the so-called disorder modes (DMs) in the cyclotron resonance of conduction electrons. The DMs originate from random distributions of negatively

  4. Impact of donor-acceptor geometry and metal chelation on photophysical properties and applications of triarylboranes.

    PubMed

    Hudson, Zachary M; Wang, Suning

    2009-10-20

    Three-coordinate organoboron compounds have recently found a wide range of applications in materials chemistry as nonlinear optical materials, chemical sensors, and emitters for organic light-emitting diodes (OLEDs). These compounds are excellent electron acceptors due to the empty p(pi) orbital on the boron center. When accompanied by electron donors such as amines, these molecules possess large electronic dipoles, which promote donor-acceptor charge-transfer upon excitation with light. Because of this, donor-acceptor triarylboranes are often highly luminescent both in the solid state and in solution. In this Account, we describe our research to develop donor-acceptor triarylboranes as efficient blue emitters for OLEDs. Through the use of hole-transporting donor groups such as 1-napthylphenylamines, we have prepared multifunctional triarylboranes that can act as the emissive, electron transport, or hole transport layers in OLEDs. We have also examined donor-acceptor compounds based on 2,2'-dipyridylamine or 7-azaindolyl donors, several of which have fluorescent quantum efficiencies approaching 100%. We are also investigating the chemistry of metal-containing triarylboranes. Our studies show that the electron-deficient boryl group can greatly facilitate metal-to-ligand charge-transfer transitions and phosphorescence. In addition, electronegative linker groups such as 2,2'-bipyridine can act in synergy with metal chelation to greatly improve the electron-accepting ability and Lewis acidity of triarylboranes. Donor-acceptor triarylboranes developed in our laboratory can also serve as a series of "switch-on" sensors for fluoride ions. When the donor and acceptor are linked by rigid naphthyl or nonrigid silane linkers, donor-acceptor conjugation is disrupted and charge transfer occurs primarily through space. The binding of fluoride ions to the boron center disrupts this charge transfer, activating alternative pi --> pi* transitions in the molecule and changing the

  5. The role of Fe(III) modified montmorillonite on fluoride mobility: adsorption experiments and competition with phosphate.

    PubMed

    Bia, Gonzalo; De Pauli, Carlos P; Borgnino, Laura

    2012-06-15

    Fluoride adsorption onto Fe(III) modified montmorillonite was investigated using batch experiments. The effect of reaction time, pH, ionic strength and phosphate, as a competitive anion, was evaluated. Kinetics indicated that adsorption obeys a pseudo-first-order rate law which involves two steps. The fast one (bulk transport/surface reaction) occurs instantaneously. The slower (diffusion in pores) takes hours to complete. The adsorption rate increases by increasing the fluoride concentration and by decreasing pH. The presence of phosphate reduces fluoride adsorption and reveals that both ions are in competition for surface sites. The reduction in fluoride adsorption when phosphate is present depends on the order of adsorbate addition. The higher fluoride adsorption occurs when both anions are added simultaneously, whereas when either fluoride or phosphate is added first, the fluoride adsorption is lower. The presence of fluoride does not have a measurable effect on phosphate adsorption. The results obtained contribute to our understanding of the mobility of fluoride in surface water which has naturally high levels of fluoride, in both the presence and absence of phosphate.

  6. Synthesis, spectroscopic and theoretical studies of two novel tripodal imine-phenol ligands and their complexation with Fe(III)

    NASA Astrophysics Data System (ADS)

    Kanungo, B. K.; Baral, Minati; Sahoo, Suban K.; Muthu, S. E.

    2009-10-01

    Two novel tripodal imine-phenol ligands, cis, cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L 1) and of cis, cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me 3-TMACHSAL, L 2) have been synthesized and characterized by elemental analyses and various spectral (UV-vis, IR and 1H and 13C NMR) data. The complexation reactions of the ligands with H + and Fe(III) were investigated by potentiometric and spectrophotometric methods at an ionic strength of 0.1 M KCl and 25 ± 1 °C in aqueous medium. Three protonation constants each for ligands L 1 and L 2 were determined and were used as input data to evaluate the formation constants of the metal complexes. Formations of metal complexes of the types FeLH 3, FeLH 2, FeLH, FeL and FeLH -1 were depicted in solution. Experimental evidences suggested for a formation of tris(iminophenolate) type metal complex by the ligands. The ligand L 1 showed higher affinity towards iron(III) than L 2. The pFe value related to L 1 (pFe = 20.14) is approximately four units higher than L 2 (pFe = 16.41) at pH = 7.4. The structures of the metal complexes were proposed through the molecular mechanics calculation using MM3 force field followed by semi-empirical PM3 method.

  7. Crystal structure of the coordination polymer [FeIII 2{PtII(CN)4}3

    PubMed Central

    Seredyuk, Maksym; Muñoz, M. Carmen; Real, José A.; Iskenderov, Turganbay S.

    2015-01-01

    The title complex, poly[dodeca-μ-cyanido-diiron(III)triplat­inum(II)], [FeIII 2{PtII(CN)4}3], has a three-dimensional polymeric structure. It is built-up from square-planar [PtII(CN)4]2− anions (point group symmetry 2/m) bridging cationic [FeIIIPtII(CN)4]+ ∞ layers extending in the bc plane. The FeII atoms of the layers are located on inversion centres and exhibit an octa­hedral coordination sphere defined by six N atoms of cyanide ligands, while the PtII atoms are located on twofold rotation axes and are surrounded by four C atoms of the cyanide ligands in a square-planar coordination. The geometrical preferences of the two cations for octa­hedral and square-planar coordination, respectively, lead to a corrugated organisation of the layers. The distance between neighbouring [FeIIIPtII(CN)4]+ ∞ layers corresponds to the length a/2 = 8.0070 (3) Å, and the separation between two neighbouring PtII atoms of the bridging [PtII(CN)4]2− groups corresponds to the length of the c axis [7.5720 (2) Å]. The structure is porous with accessible voids of 390 Å3 per unit cell. PMID:25705468

  8. Paenibacillus guangzhouensis sp. nov., an Fe(III)- and humus-reducing bacterium from a forest soil.

    PubMed

    Li, Jibing; Lu, Qin; Liu, Ting; Zhou, Shungui; Yang, Guiqin; Zhao, Yong

    2014-11-01

    A Gram-reaction-variable, rod-shaped, motile, facultatively aerobic and endospore-forming bacterium, designated strain GSS02(T), was isolated from a forest soil. Strain GSS02(T) was capable of reducing humic substances and Fe(III) oxides. Strain GSS02(T) grew optimally at 35 °C, at pH 78 and in the presence of 1% NaCl. The predominant menaquinone was MK-7. The major cellular fatty acids were anteiso-C(15:0) and iso-C(16:0) and the polar lipid profile contained mainly phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol, with moderate amounts of two unknown aminophospholipids and a minor amount of one unknown lipid. The DNA G+C content was 53.4 mol%. Comparative 16S rRNA gene sequence analysis showed that strain GSS02(T) was related most closely to Paenibacillus terrigena JCM 21741(T) (98.1% similarity). Mean DNA-DNA relatedness between strain GSS02(T) and P. terrigena JCM 21741(T) was 58.8 ± 0.5%. The phylogenetic, chemotaxonomic and phenotypic results clearly demonstrated that strain GSS02(T) belongs to the genus Paenibacillus and represents a novel species, for which the name Paenibacillus guangzhouensis sp. nov. is proposed. The type strain is GSS02(T) ( =KCTC 33171(T) =CCTCC AB 2013236(T)).

  9. Triazole bridges as versatile linkers in electron donor-acceptor conjugates

    PubMed Central

    de Miguel, Gustavo; Wielopolski, Mateusz; Schuster, David I.; Fazio, Michael A; Lee, Olivia P.; Haley, Christopher K.; Ortiz, Angy L.; Echegoyen, Luis; Clark, Timothy; Guldi, Dirk M.

    2011-01-01

    Aromatic triazoles have been frequently used as π-conjugated linkers in intramolecular electron transfer processes. To gain a deeper understanding of the electron mediating function of triazoles, we have synthesized a family of new triazole-based electron donor-acceptor conjugates. We have connected porphyrins and fullerenes through a central triazole moiety – (ZnP-Tri-C60) – each with a single change in their connection through the linker. An extensive photophysical and computational investigation reveals that the electron transfer dynamics – charge separation and charge recombination – in the different ZnP-Tri-C60 conjugates reflect a significant influence of the connectivity at the triazole linker. Except for m4m-ZnP-Tri-C60 17, the conjugates exhibit through-bond electron transfer with varying rate constants. Since the through-bond distance is nearly equal in the ZnP-Tri-C60 conjugates, the variation in charge separation and charge recombination dynamics is mainly associated with the electronic properties of the conjugates, including orbital energies, electron affinity, and the energies of the excited states. The changes of the electronic couplings are, in turn, a consequence of the different connectivity patterns at the triazole moieties. PMID:21702513

  10. The donor-acceptor approach allows a black-to-transmissive switching polymeric electrochrome

    NASA Astrophysics Data System (ADS)

    Beaujuge, P. M.; Ellinger, S.; Reynolds, J. R.

    2008-10-01

    In the context of the fast-growing demand for innovative high-performance display technologies, the perspective of manufacturing low-cost functional materials that can be easily processed over large areas or finely printed into individual pixels, while being mechanically deformable, has motivated the development of novel electronically active organic components fulfilling the requirements for flexible displays and portable applications. Among all technologies relying on a low-power stimulated optical change, non-emissive organic electrochromic devices (ECDs) offer the advantage of being operational under a wide range of viewing angles and lighting conditions spanning direct sunlight as desired for various applications including signage, information tags and electronic paper. Combining mechanical flexibility, high contrast ratios and fast response times, along with colour tunability through structural control, polymeric electrochromes constitute the most attractive organic electronics for tomorrow's reflective/transmissive ECDs and displays. Although red, blue and most recently green electrochromic polymers (ECPs) required for additive primary colour space were investigated, attempts to make saturated black ECPs have not been reported, probably owing to the complexity of designing materials absorbing effectively over the whole visible spectrum. Here, we report on the use of the donor-acceptor approach to make the first neutral-state black polymeric electrochrome. Processable black-to-transmissive ECPs promise to affect the development of both reflective and transmissive ECDs by providing lower fabrication and processing costs through printing, spraying and coating methods, along with good scalability when compared with their traditional inorganic counterparts.

  11. Abundances of Hyperthermophilic Autotrophic Fe(III) Oxide Reducers and Heterotrophs in Hydrothermal Sulfide Chimneys of the Northeastern Pacific Ocean ▿ †

    PubMed Central

    Ver Eecke, Helene C.; Kelley, Deborah S.; Holden, James F.

    2009-01-01

    The abundances of hyperthermophilic heterotrophs, methanogens, and autotrophic reducers of amorphous Fe(III) oxide in 18 samples of deep-sea hydrothermal vent sulfide chimneys of the Endeavour Segment were measured. The results indicate that conditions favor the growth of iron reducers toward the interiors of these deposits and that of heterotrophs toward the outer surfaces near high-temperature polychaete worms (Paralvinella sulfincola). PMID:18978076

  12. Wet oxidative method for removal of 2,4,6-trichlorophenol in water using Fe(III), Co(II), Ni(II) supported MCM41 catalysts.

    PubMed

    Chaliha, Suranjana; Bhattacharyya, Krishna Gopal

    2008-02-11

    Chlorophenols in water are resistant to biological oxidation and they have to be destroyed by chemical oxidation. In the present work, Fe(III), Co(II) and Ni(II) incorporated MCM41 mesoporous solids were used as catalysts for oxidation of 2,4,6-trichlorophenol in water with or without the oxidant, H(2)O(2). The catalysts were prepared by impregnation and were characterized by XRD and FTIR measurements. The parent MCM41, Fe(III), Co(II) and Ni(II) impregnated MCM41 had cation exchange capacity of 20.5, 25.5, 24.2, 26.0 mequiv./100g, respectively. The catalysts were used after calcination at 773-873 K for 5 h. The reactions were carried out in a high pressure stirred reactor at 0.2 MPa (autogenous) and 353 K under various reaction conditions. The conversion achieved with Fe(III), Co(II) and Ni(II) incorporated MCM41 in 5h is respectively 59.4, 50.0 and 65.6% with 2,4,6-TCP:H(2)O(2) molar ratio of 1:1, and 60.2, 60.9 and 68.8% in absence of H(2)O(2). The oxidation has a first order rate coefficient of (1.2-4.8)x10(-3)min(-1). The results show that introduction of Fe(III), Co(II) and Ni(II) into MCM-41 through impregnation produces very effective catalysts for wet oxidation of 2,4,6-trichlorophenol.

  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. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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 1H 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.

  16. Thermodynamics of metal cation binding by a solid soil-derived humic acid: binding of Fe(III), Pb(II), and Cu(II).

    PubMed

    Ghabbour, Elham A; Shaker, Medhat; El-Toukhy, Ahmed; Abid, Ismail M; Davies, Geoffrey

    2006-04-01

    Metal binding and release by solid humic acids (HAs) in soils and sediments can affect metal mobility and bioavailability. Isotherms for tight binding of Fe(III), Pb(II) and Cu(II) by a solid humic acid at pH2.0 fit the Langmuir binding model. Low pH was chosen to protonate the HA carboxylate groups and avoid metal cation hydrolysis. Binding of Fe(III), Pb(II) and Cu(II) occurs in one detectable step labeled A. Site capacities nu(A) are temperature-independent from 10.0 to 40.0 degrees C and point to binding by charge-neutralization to form solid complexes M(OOC-R)(n)(s), where n appears to be 2 for Pb(II) and 3 for Fe(III). Thermodynamic data pairs (DeltaH(A), DeltaS(A)) for metal binding are linearly correlated with previous data for Ca(II), Co(II) and Mg(II) binding by solid HAs.

  17. Natural input of arsenic into a coral-reef ecosystem by hydrothermal fluids and its removal by Fe(III) oxyhydroxides

    SciTech Connect

    Pichler, T.; Veizer, J.; Hall, G.E.M.

    1999-05-01

    The coral reef that circles Ambitle Island, Papua New Guinea, is exposed to the discharge of a hot, mineralized hydrothermal fluid. The hydrothermal fluids have a pH of {approximately}6 and are slightly reducing and rich in As. Seven individual vents discharge an estimated 1500 g of As per day into an area of approximately 50 x 100 m that has an average depth of 6 m. Despite the amount of As released into the bay, corals, clams, and fish do not show a response to the elevated values. The authors analyzed hydrothermal precipitates for their chemical and mineralogical composition in order to determine As sinks. Two mechanisms efficiently control and buffer the As concentration: (1) dilution by seawater and (2) incorporation in and adsorption on Fe(III) oxyhydroxides that precipitate when the hydrothermal fluids mix with ambient seawater. Fe(III) oxyhydroxides contain up to 76,000 ppm As, by an order of magnitude the highest As values found in a natural marine environment. Following adsorption, As is successfully retained in the Fe(III) oxyhydroxide deposits because oxidizing conditions prevail and high As activity allows for the formation of discrete As minerals, such as claudetite, arsenic oxide, and scorodite.

  18. The transformation of ferrihydrite in the presence of trace Fe(II): The effect of the ammonia, amine and the coordination ions of Fe(III)

    SciTech Connect

    Liu Hui; Yang Lijuan; Ma Miaorui; Li Ping; Wei Yu

    2010-03-15

    This work examined Fe(II)-induced transformation of ferrihydrite in the presence of ammonia, amine and the coordination ions of Fe(III). Our earlier results showed that ferrihydrite transformed into the mixture of lepidocrocite, goethite and/or hematite in the presence of trace Fe(II) and absence of ammonia and similar species. However, the formation of lepidocrocite was restrained when using ammonia as precipitants. When introducing some amines (e.g. ethanolamine and diethanolamine) and some coordination ions (e.g. F{sup -} and C{sub 2}O{sub 4}{sup 2-} ions) into the reaction system, a similar effect on the transformation of ferrihydrite was found. Probably, the complexes formed between Fe(III) and those additives favor the formation of goethite. At the same time, the introduction of these additives hinders Fe(II) from interacting with ferrihydrite, which makes the catalytic dissolution of ferrihydrite be limited, thus, the formation of lepidocrocite be restrained. - Graphical Abstract: Fe(II)-induced transformation of ferrihydrite in the presence of ammonia, amine and coordination ions of Fe(III) was studied. The introduction of the additives favors the formation of goethite.

  19. Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

    SciTech Connect

    Fonari, A.; Corbin, N. S.; Coropceanu, V. E-mail: coropceanu@gatech.edu; Vermeulen, D.; McNeil, L. E.; Goetz, K. P.; Jurchescu, O. D.; Bredas, J. L. E-mail: coropceanu@gatech.edu

    2015-12-14

    We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoretical Raman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.

  20. Conformation-selective coordination-driven self-assembly of a ditopic donor with Pd(II) acceptors.

    PubMed

    Howlader, Prodip; Mukherjee, Sandip; Saha, Rajat; Mukherjee, Partha Sarathi

    2015-12-21

    Coordination-driven self-assembly of 3-(5-(pyridin-3-yl)-1H-1,2,4-triazol-3-yl)pyridine (L) was investigated with 90°cis-blocked Pd(II) acceptors and tetratopic Pd(NO3)2. Although the ligand is capable of binding in several different conformations (acting as a ditopic donor through the pyridyl nitrogens), the experimental results (including X-ray structures) showed that it adopts a particular conformation when it binds with 90°cis-blocked Pd(II) acceptors (two available sites) to yield [2 + 2] self-assembled macrocycles. On the other hand, with Pd(NO3)2 (where four available sites are present) a different conformer of the same donor was selectively bound to form a molecular cubic cage. The experimental findings were corroborated well with the density functional theory (B3LYP) calculations. The tetratopic Pd(NO3)2 yielded a [6 + 12] self-assembled Pd6L12 molecular cube, which contains a potential void occupied by nitrate and perchlorate ions. Being a triazole based ligand, the free space inside the cage is enriched with several sp(2) hybridised nitrogen atoms with lone pairs of electrons to act as Lewis basic sites. Knoevenagel condensation reactions of several aromatic aldehydes with active methylene compounds were successfully performed in reasonably high yields in the presence of the cage. PMID:26544720

  1. Taming hot CF3 radicals: incrementally tuned families of polyarene acceptors for air-stable molecular optoelectronics

    SciTech Connect

    Kuvychko, Igor V.; Castro, Karlee P.; Deng, Shihu; Wang, Xue B.; Strauss, Steven H.; Boltalina, Olga V.

    2013-04-26

    Breakthroughs in molecular optoelectronics await the availability of new families of air-stable polyaromatic hydrocarbon (PAH) acceptors with incrementally- and predictably-tunable electron affinities and structures capable of inducing desirable solid-state morphologies in hybrid materials. Although the addition of electron withdrawing groups to PAHs has been studied for decades, producing new compounds from time to time, a generic one-step synthetic methodology applicable to potentially all PAH substrates has been, until now, an impossible dream. We herein report that at least seventeen common PAHs and polyheterocyclics can be trifluoromethylated by a new procedure to yield families of PAH(CF3)n acceptors with (i) n = 4-8, (ii) multiple isomers for particular n values, (iii) gas-phase experimental electron affinities as high as 3.32 eV and shifted from the respective PAH precursor as a linear function of n, and (iv) various solid-state morphologies, including the ability to form alternating π stacked hybrid crystals with aromatic donors.

  2. 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.

  3. Catalytic reaction of cytokinin dehydrogenase: preference for quinones as electron acceptors.

    PubMed Central

    Frébortová, Jitka; Fraaije, Marco W; Galuszka, Petr; Sebela, Marek; Pec, Pavel; Hrbác, Jan; Novák, Ondrej; Bilyeu, Kristin D; English, James T; Frébort, Ivo

    2004-01-01

    The catalytic reaction of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was studied in detail using the recombinant flavoenzyme from maize. Determination of the redox potential of the covalently linked flavin cofactor revealed a relatively high potential dictating the type of electron acceptor that can be used by the enzyme. Using 2,6-dichlorophenol indophenol, 2,3-dimethoxy-5-methyl-1,4-benzoquinone or 1,4-naphthoquinone as electron acceptor, turnover rates with N6-(2-isopentenyl)adenine of approx. 150 s(-1) could be obtained. This suggests that the natural electron acceptor of the enzyme is quite probably a p-quinone or similar compound. By using the stopped-flow technique, it was found that the enzyme is rapidly reduced by N6-(2-isopentenyl)adenine (k(red)=950 s(-1)). Re-oxidation of the reduced enzyme by molecular oxygen is too slow to be of physiological relevance, confirming its classification as a dehydrogenase. Furthermore, it was established for the first time that the enzyme is capable of degrading aromatic cytokinins, although at low reaction rates. As a result, the enzyme displays a dual catalytic mode for oxidative degradation of cytokinins: a low-rate and low-substrate specificity reaction with oxygen as the electron acceptor, and high activity and strict specificity for isopentenyladenine and analogous cytokinins with some specific electron acceptors. PMID:14965342

  4. Nature of the attractive interaction between proton acceptors and organic ring systems.

    PubMed

    Arras, Emmanuel; Seitsonen, Ari Paavo; Klappenberger, Florian; Barth, Johannes V

    2012-12-14

    Systematic ab initio calculations are combined with a deconvolution of electrostatic contributions to analyze the interplay between potential hydrogen bond acceptors and organic rings with C(sp(2))-H groups (benzene, pyridine and cyclopentadiene). A distinct anisotropic interaction between the ring systems and the electron lone pairs of cyanide, water and other acceptor species is revealed that favors the in-plane orientation of the proton acceptor group. In the attractive regime this interaction carries a pronounced electrostatic signature. By decomposing the electrostatic contribution into parts attributed to different subunits of the ring systems we demonstrate that a major proportion of the interaction energy gain is originating from the non-adjacent moieties, that are not in close contact with. This behavior holds equally for homocyclic, heterocyclic and non-aromatic rings but contrasts that of the ethyne molecule, taken as reference for a weak hydrogen bond donor clearly exhibiting the expected localized character. The ring interaction requires the presence of π-electron clouds and typically results in an interaction energy gain of 40 to 80 meV. Our findings suggest the proton acceptor-ring interaction as a new category of intermolecular non-covalent interactions.

  5. Effect of acceptor (Mg) concentration on the electrical resistance at room and high (200 deg. C) temperatures of acceptor (Mg)-doped BaTiO{sub 3} ceramics

    SciTech Connect

    Yoon, Seok-Hyun; Hong, Min-Hee; Hong, Jeong-Oh; Kim, Young-Tae; Hur, Kang-Heon

    2007-09-01

    The behaviors of the electrical resistance at room and high (200 deg. C) temperatures of acceptor (Mg)-doped BaTiO{sub 3} ceramics with the increase of acceptor concentration were investigated. A series of coarse-grained specimens with different acceptor concentrations that were sintered at various oxygen partial pressures was prepared. The critical acceptor concentrations, beyond which the room temperature resistance increases abruptly, were experimentally evaluated and they were found to increase with a decrease in oxygen partial pressure during sintering. Each defect and electron concentrations at sintering and room temperature as a function of acceptor concentration were theoretically calculated. The results calculated could explain the experimentally observed behavior of the resistance versus acceptor concentration. The high (200 deg. C) temperature resistances under high electric field showed resistance degradation critically depending on acceptor concentration in the very small concentration range below {approx}0.1 mol %, which occurred easily with the increase of acceptor concentration. It was explained that such behavior was caused by the variation of potential barrier of grain boundaries for the migration of oxygen vacancies as a function of acceptor concentration.

  6. Probing charge and energy transfer process at the donor-acceptor interface of semiconductor nanostructures with simultaneous photocurrent-optical microscopy

    NASA Astrophysics Data System (ADS)

    Gao, Yongqian; Acharya, Krishna; Galande, Charudatta; Ajayan, Pulickel; Mohite, Aditya; Dattelbaum, Andrew; Hollingsworth, Jennifer; Htoon, Han; Los Alamos Natioal Lab Team; Rice Univerisity Collaboration

    2013-03-01

    Understanding and control of charge and energy transfer (CT & ET) processes happening at the donor-acceptor interface of colloidal semiconductor nanostructures play a critical role in defining the performance of many exploratory photo-voltaic devices. Ultrafast dynamics of CT and ET processes in semiconductor nanostrucutres can be investigated effectively by time and energy resolved PL spectroscopy. However a full understanding on impact of these process on device performance demand direct correlation of these dynamical measurements with photocurrent measurements that probe the separation and transport of charges. To this end we develop simultaneous optical and electrical characterization approaches capable of performing scanning photocurrent microscopy and various single nanostructure optical spectroscopies (e.g. photoluminescence (PL), Raman, time resolved PL) simultaneously. We will present application of this technique on various donor/acceptor interfaces including graphene oxide/CdSe nanowire and TiO2 nanocrystals/CdSe nanowire interfaces.

  7. 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.; Shi, Liang

    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

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

    SciTech Connect

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

    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 no 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.

  9. Synthesis, spectroscopic properties, and photoconductivity of black absorbers consisting of pt(bipyridine)(dithiolate) charge transfer complexes in the presence and absence of nitrofluorenone acceptors.

    PubMed

    Browning, Charles; Hudson, Joshua M; Reinheimer, Eric W; Kuo, Fang-Ling; McDougald, Roy N; Rabaâ, Hassan; Pan, Hongjun; Bacsa, John; Wang, Xiaoping; Dunbar, Kim R; Shepherd, Nigel D; Omary, Mohammad A

    2014-11-19

    The diimine-dithiolato ambipolar complexes Pt(dbbpy)(tdt) and Pt(dmecb)(bdt) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt(2-) = 3,4-toluenedithiolate; dmecb = 4,4'-dimethoxyester-2,2'-bipyridine; bdt(2-) = benzene-1,2-dithiolate) are prepared herein. Pt(dmecb)(bdt) exhibits photoconductivity that remains constant (photocurrent density of 1.6 mA/cm(2) from a 20 nm thin film) across the entire visible region of the solar spectrum in a Schottky diode device structure. Pt(dbbpy)(tdt) acts as donor when combined with the strong nitrofluorenone acceptors 2,7-dinitro-9-fluorenone (DNF), 2,4,7-trinitro-9-fluorenone (TRNF), or 2,4,5,7-tetranitro-9-fluorenone (TENF). Supramolecular charge transfer stacks form and exhibit various donor-acceptor stacking patterns. The crystalline solids are "black absorbers" that exhibit continuous absorptions spanning the entire visible region and significant ultraviolet and near-infrared wavelengths, the latter including long wavelengths that the donor or acceptor molecules alone do not absorb. Absorption spectra reveal the persistence of donor-acceptor interactions in solution, as characterized by low-energy donor/acceptor charge transfer (DACT) bands. Crystal structures show closely packed stacks with distances that underscore intermolecular DACT. (1)H NMR provides further evidence of DACT, as manifested by upfield shifts of aromatic protons in the binary adducts versus their free components, whereas 2D nuclear Overhauser effect spectroscopy (NOESY) spectra suggest coupling between dithiolate donor protons with nitrofluorenone acceptor protons, in correlation with the solid-state stacking. The NMR spectra also show significant peak broadening, indicating some paramagnetism verified by magnetic susceptibility data. Solid-state absorption spectra reveal further red shifts and increased relative intensities of DACT bands for the solid adducts vs solution, suggesting cooperativity of the DACT phenomenon in the solid state, as further

  10. Proficiency of acceptor-donor-acceptor organic dye with spiro-MeOTAD HTM on the photovoltaic performance of dye sensitized solar cell

    NASA Astrophysics Data System (ADS)

    Ramavenkateswari, K.; Venkatachalam, P.

    2016-08-01

    This work investigates the proficiency of acceptor-donor-acceptor (A-D-A) organic dye Diisopropyl azodicarboxylate (DIAC) as photosensitizer on the photovoltaic parameters of silver (Ag) doped TiO2 photoanode dye-sensitized solar cells (DSSCs) with quasi-solid state electrolyte/hole transport material (HTM) spiro-MeOTAD. TNSs (TiO2 nanosticks) photoanodes are prepared through sol-gel method and hydrothermal technique. X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and BET measurement were used to characterize the structure and morphology of TiO2 nanostructures. The Diisopropyl azodicarboxylate organic dye with TNPs-Ag@TNSs composite photoanode structure and spiro-MeOTAD HTM exhibited better power conversion efficiency (PCE). [Figure not available: see fulltext.

  11. Proficiency of acceptor-donor-acceptor organic dye with spiro-MeOTAD HTM on the photovoltaic performance of dye sensitized solar cell

    NASA Astrophysics Data System (ADS)

    Ramavenkateswari, K.; Venkatachalam, P.

    2016-09-01

    This work investigates the proficiency of acceptor-donor-acceptor (A-D-A) organic dye Diisopropyl azodicarboxylate (DIAC) as photosensitizer on the photovoltaic parameters of silver (Ag) doped TiO2 photoanode dye-sensitized solar cells (DSSCs) with quasi-solid state electrolyte/hole transport material (HTM) spiro-MeOTAD. TNSs (TiO2 nanosticks) photoanodes are prepared through sol-gel method and hydrothermal technique. X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and BET measurement were used to characterize the structure and morphology of TiO2 nanostructures. The Diisopropyl azodicarboxylate organic dye with TNPs-Ag@TNSs composite photoanode structure and spiro-MeOTAD HTM exhibited better power conversion efficiency (PCE).

  12. Effect of cathode electron acceptors on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell.

    PubMed

    Cai, Jing; Zheng, Ping; Mahmood, Qaisar

    2016-01-01

    The current investigation reports the effect of cathode electron acceptors on simultaneous sulfide and nitrate removal in two-chamber microbial fuel cells (MFCs). Potassium permanganate and potassium ferricyanide were common cathode electron acceptors and evaluated for substrate removal and electricity generation. The abiotic MFCs produced electricity through spontaneous electrochemical oxidation of sulfide. In comparison with abiotic MFC, the biotic MFC showed better ability for simultaneous nitrate and sulfide removal along with electricity generation. Keeping external resistance of 1,000 Ω, both MFCs showed good capacities for substrate removal where nitrogen and sulfate were the main end products. The steady voltage with potassium permanganate electrodes was nearly twice that of with potassium ferricyanide. Cyclic voltammetry curves confirmed that the potassium permanganate had higher catalytic activity than potassium ferricyanide. The potassium permanganate may be a suitable choice as cathode electron acceptor for enhanced electricity generation during simultaneous treatment of sulfide and nitrate in MFCs. PMID:26901739

  13. 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

  14. Photovoltaic enhancement of organic solar cells by a bridged donor-acceptor block copolymer approach

    NASA Astrophysics Data System (ADS)

    Sun, Sam-Shajing; Zhang, Cheng; Ledbetter, Abram; Choi, Soobum; Seo, Kang; Bonner, Carl E.; Drees, Martin; Sariciftci, Niyazi Serdar

    2007-01-01

    The authors show that a photovoltaic device composed of a -donor-bridge-acceptor-bridge- type block copolymer thin film exhibits a significant performance improvement over its corresponding donor/acceptor blend (Voc increased from 0.14to1.10V and Jsc increased from 0.017 to 0.058mA/cm2) under identical conditions, where donor is an alkyl derivatized poly-p-phenylenevinylene (PPV) conjugated block, acceptor is a sulfone-alkyl derivatized PPV conjugated block, and bridge is a nonconjugated and flexible unit. The authors attribute such improvement to the block copolymer intrinsic nanophase separation and molecular self-assembly that results in the reduction of the exciton and carrier losses.

  15. Mg acceptors in GaN: Dependence of the /g-anisotropy on the doping concentration

    NASA Astrophysics Data System (ADS)

    Hofmann, Detlev M.; Burkhardt, Wolfgang; Leiter, Frank; Walter von Förster; Alves, Helder; Hofstaetter, Albrecht; Meyer, Bruno K.; Romanov, Nikolai G.; Amano, Hiroshi; Akasaki, Isamu

    1999-12-01

    Mg acceptors in GaN epitaxial layers grown by metal-organic vapour-phase epitaxy were investigated by optically detected magnetic resonance (ODMR) spectroscopy. The magnetic resonances were detected on the magnetic circular dichroism (MCD) of the acceptor bound exciton (Mg0X) in the near bandgap region, and in the infrared spectral range on the MCD of the hole ionisation transition Mg0+hν→Mg-+hVB. The observed g-values of the Mg0 acceptors range for g|| from 2.102 to 2.065 and for g⊥ from 1.94 to 2.00, respectively. These variations depend on the Mg doping concentration.

  16. Rational design of two-dimensional molecular donor-acceptor nanostructure arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Jia Lin; Zhong, Shu; Zhong, Jian Qiang; Niu, Tian Chao; Hu, Wen Ping; Wee, Andrew Thye Shen; Chen, Wei

    2015-02-01

    The construction of long-range ordered organic donor-acceptor nanostructure arrays over microscopic areas supported on solid substrates is one of the most challenging tasks towards the realization of molecular nanodevices. They can also be used as ideal model systems to understand light induced charge transfer, charge separation and energy conversion processes and mechanisms at the nanometer scale. The aim of this paper is to highlight recent advances and progress in this topic. Special attention is given to two different strategies for the construction of organic donor-acceptor nanostructure arrays, namely (i) molecular self-assembly on artificially patterned or pre-defined molecular surface nanotemplates and (ii) molecular nanostructure formation steered via directional and selective intermolecular interactions. The interfacial charge transfer and the energy level alignment of these donor-acceptor nanostructures are also discussed.

  17. Spectroscopic studies of charge transfer complexes between colchicine and some π acceptors

    NASA Astrophysics Data System (ADS)

    Arslan, Mustafa; Duymus, Hulya

    2007-07-01

    Charge transfer complexes between colchicine as donor and π acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), p-chloranil ( p-CHL) have been studied spectrophotometrically in dichloromethane at 21 °C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used.

  18. Pyridine as proton acceptor in the concerted proton electron transfer oxidation of phenol.

    PubMed

    Bonin, Julien; Costentin, Cyrille; Robert, Marc; Savéant, Jean-Michel

    2011-06-01

    Taking pyridine as a prototypal example of biologically important nitrogen bases involved in proton-coupled electron transfers, it is shown with the example of the photochemically triggered oxidation of phenol by Ru(III)(bpy)(3) that this proton acceptor partakes in a concerted pathway whose kinetic characteristics can be extracted from the overall kinetic response. The treatment of these data, implemented by the results of a parallel study carried out in heavy water, allowed the determination of the intrinsic kinetic characteristics of this proton acceptor. Comparison of the reorganization energies and of the pre-exponential factors previously derived for hydrogen phosphate and water (in water) as proton acceptors suggests that, in the case of pyridine, the proton charge is delocalized over a primary shell of water molecules firmly bound to the pyridinium cation. PMID:21499600

  19. Design of reversible, cysteine-targeted Michael acceptors guided by kinetic and computational analysis.

    PubMed

    Krishnan, Shyam; Miller, Rand M; Tian, Boxue; Mullins, R Dyche; Jacobson, Matthew P; Taunton, Jack

    2014-09-10

    Electrophilic probes that covalently modify a cysteine thiol often show enhanced pharmacological potency and selectivity. Although reversible Michael acceptors have been reported, the structural requirements for reversibility are poorly understood. Here, we report a novel class of acrylonitrile-based Michael acceptors, activated by aryl or heteroaryl electron-withdrawing groups. We demonstrate that thiol adducts of these acrylonitriles undergo β-elimination at rates that span more than 3 orders of magnitude. These rates correlate inversely with the computed proton affinity of the corresponding carbanions, enabling the intrinsic reversibility of the thiol-Michael reaction to be tuned in a predictable manner. We apply these principles to the design of new reversible covalent kinase inhibitors with improved properties. A cocrystal structure of one such inhibitor reveals specific noncovalent interactions between the 1,2,4-triazole activating group and the kinase. Our experimental and computational study enables the design of new Michael acceptors, expanding the palette of reversible, cysteine-targeted electrophiles.

  20. Donor-Acceptor Heterojunction Configurations Based on DNA-Multichromophore Arrays.

    PubMed

    Nakamura, Mitsunobu; Tsuto, Koji; Jomura, Ayumi; Takada, Tadao; Yamana, Kazushige

    2015-08-10

    Multichromophore arrays of bis(2-thienyl)diketopyrrolopyrrole (DPP) and naphthalenediimide (NDI) with two Zn(II) -cyclens were constructed using thymidine DNA as a scaffold through the binding of the Zn(II) -cyclens with thymine bases. We demonstrate photocurrent generation in a donor-acceptor heterojunction configuration consisting of the DPP (donor) and NDI (acceptor) arrays co-immobilized on an Au electrode. The co-immobilized electrode exhibited good photocurrent responses because of the efficient charge separation between the DPP and NDI arrays. In contrast, an immobilized electrode consisting of randomly assembled DPP-NDI arrays generated no photocurrent response because DPP formed ground-state charge-transfer complexes with NDI in the randomly assembled arrays. Therefore, our approach to generate donor-acceptor heterojunctions based on DNA-multichromophore arrays is a useful method to efficiently generate photocurrent. PMID:26179473

  1. Pyridine as proton acceptor in the concerted proton electron transfer oxidation of phenol.

    PubMed

    Bonin, Julien; Costentin, Cyrille; Robert, Marc; Savéant, Jean-Michel

    2011-06-01

    Taking pyridine as a prototypal example of biologically important nitrogen bases involved in proton-coupled electron transfers, it is shown with the example of the photochemically triggered oxidation of phenol by Ru(III)(bpy)(3) that this proton acceptor partakes in a concerted pathway whose kinetic characteristics can be extracted from the overall kinetic response. The treatment of these data, implemented by the results of a parallel study carried out in heavy water, allowed the determination of the intrinsic kinetic characteristics of this proton acceptor. Comparison of the reorganization energies and of the pre-exponential factors previously derived for hydrogen phosphate and water (in water) as proton acceptors suggests that, in the case of pyridine, the proton charge is delocalized over a primary shell of water molecules firmly bound to the pyridinium cation.

  2. 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.

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

    DOE PAGES

    Smith, Kendall A.; Lin, Yen -Hao; Mok, Jorge W.; Yager, Kevin G.; Strzalka, Joseph; Nie, Wanyi; Mohite, Aditya D.; Verduzco, Rafael

    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 show thatmore » 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

  4. 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.

  5. 2010 Electron Donor-Acceptor Interactions Gordon Research Conference, August 8 - 13, 2010.

    SciTech Connect

    Gerald Meyer

    2010-08-18

    The Gordon Research Conference on Electron Donor Acceptor Interactions (GRC EDAI) presents and advances the current frontiers in experimental and theoretical studies of Electron Transfer Processes and Energy Conversion. The fundamental concepts underpinning the field of electron transfer and charge transport phenomena are understood, but fascinating experimental discoveries and novel applications based on charge transfer processes are expanding the discipline. Simultaneously, global challenges for development of viable and economical alternative energy resources, on which many researchers in the field focus their efforts, are now the subject of daily news headlines. Enduring themes of this conference relate to photosynthesis, both natural and artificial, and solar energy conversion. More recent developments include molecular electronics, optical switches, and nanoscale charge transport structures of both natural (biological) and man-made origin. The GRC EDAI is one of the major international meetings advancing this field, and is one of the few scientific meetings where fundamental research in solar energy conversion has a leading voice. The program includes sessions on coupled electron transfers, molecular solar energy conversion, biological and biomimetic systems, spin effects, ultrafast reactions and technical frontiers as well as electron transport in single molecules and devices. In addition to disseminating the latest advances in the field of electron transfer processes, the conference is an excellent forum for scientists from different disciplines to meet and initiate new directions; for scientists from different countries to make contacts; for young scientists to network and establish personal contacts with other young scientists and with established scientists who, otherwise, might not have the time to meet young people. The EDAI GRC also features an interactive atmosphere with lively poster sessions, a few of which are selected for oral presentations.

  6. Evidence for Microbial Fe(III) Reduction in Anoxic, Mining-Impacted Lake Sediments (Lake Coeur d'Alene, Idaho)

    PubMed Central

    Cummings, David E.; March, Anthony W.; Bostick, Benjamin; Spring, Stefan; Caccavo, Frank; Fendorf, Scott; Rosenzweig, R. Frank

    2000-01-01

    Mining-impacted sediments of Lake Coeur d'Alene, Idaho, contain more than 10% metals on a dry weight basis, approximately 80% of which is iron. Since iron (hydr)oxides adsorb toxic, ore-associated elements, such as arsenic, iron (hydr)oxide reduction may in part control the mobility and bioavailability of these elements. Geochemical and microbiological data were collected to examine the ecological role of dissimilatory Fe(III)-reducing bacteria in this habitat. The concentration of mild-acid-extractable Fe(II) increased with sediment depth up to 50 g kg−1, suggesting that iron reduction has occurred recently. The maximum concentrations of dissolved Fe(II) in interstitial water (41 mg liter−1) occurred 10 to 15 cm beneath the sediment-water interface, suggesting that sulfidogenesis may not be the predominant terminal electron-accepting process in this environment and that dissolved Fe(II) arises from biological reductive dissolution of iron (hydr)oxides. The concentration of sedimentary magnetite (Fe3O4), a common product of bacterial Fe(III) hydroxide reduction, was as much as 15.5 g kg−1. Most-probable-number enrichment cultures revealed that the mean density of Fe(III)-reducing bacteria was 8.3 × 105 cells g (dry weight) of sediment−1. Two new strains of dissimilatory Fe(III)-reducing bacteria were isolated from surface sediments. Collectively, the results of this study support the hypothesis that dissimilatory reduction of iron has been and continues to be an important biogeochemical process in the environment examined. PMID:10618217

  7. Bacteria attenuation by iron electrocoagulation governed by interactions between bacterial phosphate groups and Fe(III) precipitates.

    PubMed

    Delaire, Caroline; van Genuchten, Case M; Amrose, Susan E; Gadgil, Ashok J

    2016-10-15

    Iron electrocoagulation (Fe-EC) is a low-cost process in which Fe(II) generated from an Fe(0) anode reacts with dissolved O2 to form (1) Fe(III) precipitates with an affinity for bacterial cell walls and (2) bactericidal reactive oxidants. Previous work suggests that Fe-EC is a promising treatment option for groundwater containing arsenic and bacterial contamination. However, the mechanisms of bacteria attenuation and the impact of major groundwater ions are not well understood. In this work, using the model indicator Escherichia coli (E. coli), we show that physical removal via enmeshment in EC precipitate flocs is the primary process of bacteria attenuation in the presence of HCO3(-), which significantly inhibits inactivation, possibly due to a reduction in the lifetime of reactive oxidants. We demonstrate that the adhesion of EC precipitates to cell walls, which results in bacteria encapsulation in flocs, is driven primarily by interactions between EC precipitates and phosphate functional groups on bacteria surfaces. In single solute electrolytes, both P (0.4 mM) and Ca/Mg (1-13 mM) inhibited the adhesion of EC precipitates to bacterial cell walls, whereas Si (0.4 mM) and ionic strength (2-200 mM) did not impact E. coli attenuation. Interestingly, P (0.4 mM) did not affect E. coli attenuation in electrolytes containing Ca/Mg, consistent with bivalent cation bridging between bacterial phosphate groups and inorganic P sorbed to EC precipitates. Finally, we found that EC precipitate adhesion is largely independent of cell wall composition, consistent with comparable densities of phosphate functional groups on Gram-positive and Gram-negative cells. Our results are critical to predict the performance of Fe-EC to eliminate bacterial contaminants from waters with diverse chemical compositions.

  8. Effect of Electronic Acceptor Segments on Photophysical Properties of Low-Band-Gap Ambipolar Polymers

    PubMed Central

    Li, Yuanzuo; Cui, Jingang; Zhao, Jianing; Liu, Jinglin; Song, Peng; Ma, Fengcai

    2013-01-01

    Stimulated by a recent experimental report, charge transfer and photophysical properties of donor-acceptor ambipolar polymer were studied with the quantum chemistry calculation and the developed 3D charge difference density method. The effects of electronic acceptor strength on the structure, energy levels, electron density distribution, ionization potentials, and electron affinities were also obtained to estimate the transporting ability of hole and electron. With the developed 3D charge difference density, one visualizes the charge transfer process, distinguishes the role of molecular units, and finds the relationship between the role of DPP and excitation energy for the three polymers during photo-excitation. PMID:23365549

  9. 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.

  10. Assessing the regioselectivity of OleD-catalyzed glycosylation with a diverse set of acceptors.

    PubMed

    Zhou, Maoquan; Hamza, Adel; Zhan, Chang-Guo; Thorson, Jon S

    2013-02-22

    To explore the acceptor regioselectivity of OleD-catalyzed glucosylation, the products of OleD-catalyzed reactions with 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.

  11. 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.

  12. Hexachloroiridate IV as an Electron Acceptor for a Plasmalemma Redox System in Maize Roots 1

    PubMed Central

    Lüthen, Hartwig; Böttger, Michael

    1988-01-01

    Hexachloroiridate IV, a new artificial electron acceptor for the constitutive plant plasma membrane redox system has been investigated. It appeared not to permeate through biological membranes. Due to its higher redox potential, it is a more powerful electron acceptor than hexacyanoferrate III (ferricyanide) and even micromolar concentrations are rapidly reduced. Hexachloroiridate IV increased H+ efflux over a concentration range of 0.05 to 0.1 millimolar. Lower concentrations slightly inhibited proton extrusion. Calcium stimulated both proton and electron transfer rates. Like hexacyanoferrate III-reduction, irridate reduction was inhibited by auxin. PMID:16666029

  13. Through-Solvent Tunneling in Donor-Bridge-Acceptor Molecules Containing a Molecular Cleft.

    PubMed

    Graff, B M; Lamont, D N; Parker, M F L; Bloom, B P; Schafmeister, C E; Waldeck, D H

    2016-08-01

    Photoinduced electron transfer is used to investigate the solvent-mediated electron tunneling between electron donor and acceptor groups in polar solvents. Bis-peptide scaffolds are used to control the spatial positioning of electron donor and acceptor groups and create a molecular cleft. The photoinduced electron transfer is studied for two different cleft sizes, and the electronic coupling is found to be controlled by the nature of the solvent and the ability of the molecular cleft to accommodate it, as well as interact directly with it. These studies demonstrate the importance of electron tunneling through nonbonded contacts and reveal a strategy for examining such tunneling pathways in polar solvents. PMID:27401503

  14. Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

    PubMed Central

    Schmid, Thibault E; Drissi-Amraoui, Sammy; Crévisy, Christophe; Baslé, Olivier

    2015-01-01

    Summary The copper-catalyzed asymmetric conjugate addition (ACA) of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as it enables in a straightforward manner the sequential generation of two or more stereogenic centers. In the last decade, various chiral copper-based catalysts were evaluated in combination with different nucleophiles and Michael acceptors, and have unambiguously demonstrated their usefulness in the control of the regio- and enantioselectivity of the addition. The aim of this review is to report recent breakthroughs achieved in this challenging field. PMID:26734090

  15. Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors.

    PubMed

    Schmid, Thibault E; Drissi-Amraoui, Sammy; Crévisy, Christophe; Baslé, Olivier; Mauduit, Marc

    2015-01-01

    The copper-catalyzed asymmetric conjugate addition (ACA) of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as it enables in a straightforward manner the sequential generation of two or more stereogenic centers. In the last decade, various chiral copper-based catalysts were evaluated in combination with different nucleophiles and Michael acceptors, and have unambiguously demonstrated their usefulness in the control of the regio- and enantioselectivity of the addition. The aim of this review is to report recent breakthroughs achieved in this challenging field.

  16. Magnetic field effect on the Coulomb interaction of acceptors in semimagnetic quantum dot

    SciTech Connect

    Kalpana, P.; Merwyn, A.; Nithiananthi, P.; Jayakumar, K.; Reuben, Jasper D.

    2015-06-24

    The Coulomb interaction of holes in a Semimagnetic Cd{sub 1-x}Mn{sub x}Te / 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.

  17. Linking Microbial Dynamics and Physicochemical Processes in High-temperature Acidic Fe(III)- Mineralizing Systems

    NASA Astrophysics Data System (ADS)

    Inskeep, W.

    2014-12-01

    Microbial activity is responsible for the mineralization of Fe(III)-oxides in high-temperature chemotrophic communities that flourish within oxygenated zones of low pH (2.5 - 4) geothermal outflow channels (Yellowstone National Park, WY). High-temperature Fe(II)-oxidizing communities contain several lineages of Archaea, and are excellent model systems for studying microbial interactions and spatiotemporal dynamics across geochemical gradients. We hypothesize that acidic Fe(III)-oxide mats form as a result of constant interaction among primary colonizers including Hydrogenobaculum spp. (Aquificales) and Metallosphaera spp. (Sulfolobales), and subsequent colonization by archaeal heterotrophs, which vary in abundance as a function of oxygen, pH and temperature. We are integrating a complementary suite of geochemical, stable isotope, genomic, proteomic and modeling analyses to study the role of microorganisms in Fe(III)-oxide mat development, and to elucidate the primary microbial interactions that are coupled with key abiotic events. Curated de novo assemblies of major phylotypes are being used to analyze additional -omics datasets from these microbial mats. Hydrogenobaculum spp. (Aquificales) are the dominant bacterial population(s) present, and predominate during early mat development (< 30 d). Other Sulfolobales populations known to oxidize Fe(II) and fix carbon dioxide (e.g., Metallosphaera spp.) represent a secondary stage of mat development (e.g., 14 - 30 d). Hydrogenobaculum filaments appear to promote the nucleation and subsequent mineralization of Fe(III)-oxides, which likely affect the growth and turnover rates of these organisms. Other heterotrophs colonize Fe(III)-oxide mats during succession (> 30 d), including novel lineages of Archaea and representatives within the Crenarchaeota, Euryarchaeota, Thaumarchaeota and Nanoarchaeota. In situ oxygen consumption rates show that steep gradients occur within the top 1 mm of mat surface, and which correlate with

  18. Synthesis, characterization and stability of Cr(III) and Fe(III) hydroxides.

    PubMed

    Papassiopi, N; Vaxevanidou, K; Christou, C; Karagianni, E; Antipas, G S E

    2014-01-15

    Chromium is a common contaminant of soils and aquifers and constitutes a major environmental problem. In nature, chromium usually exists in the form of two oxidation states, trivalent, Cr(III), which is relatively innocuous for biota and for the aquatic environment, and hexavalent, Cr(VI) which is toxic, carcinogenic and very soluble. Accordingly, the majority of wastewater and groundwater treatment technologies, include a stage where Cr(VI) is reduced to Cr(III), in order to remove chromium from the aqueous phase and bind the element in the form of environmentally stable solid compounds. In the absence of iron the final product is typically of the form Cr(OH)3·xH2O whereas in the presence of iron the precipitate is a mixed Fe(1-x)Crx(OH)3 phase. In this study, we report on the synthesis, characterisation and stability of mixed (Fex,Cr1-x)(OH)3 hydroxides as compared to the stability of Cr(OH)3. We established that the plain Cr(III) hydroxide, abiding to the approximate molecular formula Cr(OH)3·3H2O, was crystalline, highly soluble, i.e. unstable, with a tendency to transform into the stable amorphous hydroxide Cr(OH)3(am) phase. Mixed Fe0.75Cr0.25(OH)3 hydroxides were found to be of the ferrihydrite structure, Fe(OH)3, and we correlated their solubility to that of a solid solution formed by plain ferrihydrite and the amorphous Cr(III) hydroxide. Both our experimental results and thermodynamic calculations indicated that mixed Fe(III)-Cr(III) hydroxides are more effective enhancers of groundwater quality, in comparison to the plain amorphous or crystalline Cr(III) hydroxides, the latter found to have a solubility typically higher than 50μg/l (maximum EU permitted Cr level in drinking water), while the amorphous Cr(OH)3(am) phase was within the drinking water threshold in the range 5.7

  19. Evidence that bank vole PrP is a universal acceptor for prions.

    PubMed

    Watts, Joel C; Giles, Kurt; Patel, Smita; Oehler, Abby; DeArmond, Stephen J; Prusiner, Stanley B

    2014-04-01

    Bank voles are uniquely susceptible to a wide range of prion strains isolated from many different species. To determine if this enhanced susceptibility to interspecies prion transmission is encoded within the sequence of the bank vole prion protein (BVPrP), we inoculated Tg(M109) and Tg(I109) mice, which express BVPrP containing either methionine or isoleucine at polymorphic codon 109, with 16 prion isolates from 8 different species: humans, cattle, elk, sheep, guinea pigs, hamsters, mice, and meadow voles. Efficient disease transmission was observed in both Tg(M109) and Tg(I109) mice. For instance, inoculation of the most common human prion strain, sporadic Creutzfeldt-Jakob disease (sCJD) subtype MM1, into Tg(M109) mice gave incubation periods of ∼200 days that were shortened slightly on second passage. Chronic wasting disease prions exhibited an incubation time of ∼250 days, which shortened to ∼150 days upon second passage in Tg(M109) mice. Unexpectedly, bovine spongiform encephalopathy and variant CJD prions caused rapid neurological dysfunction in Tg(M109) mice upon second passage, with incubation periods of 64 and 40 days, respectively. Despite the rapid incubation periods, other strain-specified properties of many prion isolates--including the size of proteinase K-resistant PrPSc, the pattern of cerebral PrPSc deposition, and the conformational stability--were remarkably conserved upon serial passage in Tg(M109) mice. Our results demonstrate that expression of BVPrP is sufficient to engender enhanced susceptibility to a diverse range of prion isolates, suggesting that BVPrP may be a universal acceptor for prions. PMID:24699458

  20. 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...

  1. Engineering of glucoside acceptors for the regioselective synthesis of beta-(1-->3)-disaccharides with glycosynthases.

    PubMed

    Marton, Zsuzanna; Tran, Vinh; Tellier, Charles; Dion, Michel; Drone, Jullien; Rabiller, Claude

    2008-11-24

    Glycosynthase mutants obtained from Thermotogamaritima were able to catalyze the regioselective synthesis of aryl beta-D-Galp-(1-->3)-beta-D-Glcp and aryl beta-D-Glcp-(1-->3)-beta-D-Glcp in high yields (up to 90 %) using aryl beta-D-glucosides as acceptors. The need for an aglyconic aryl group was rationalized by molecular modeling calculations, which have emphasized a high stabilizing interaction of this group by stacking with W312 of the enzyme. Unfortunately, the deprotection of the aromatic group of the disaccharides was not possible without partial hydrolysis of the glycosidic bond. The replacement of aryl groups by benzyl ones could offer the opportunity to deprotect the anomeric position under very mild conditions. Assuming that benzyl acceptors could preserve the stabilizing stacking, benzyl beta-d-glucoside firstly assayed as acceptor resulted in both poor yields and poor regioselectivity. Thus, we decided to undertake molecular modeling calculations in order to design which suitable substituted benzyl acceptors could be used. This study resulted in the choice of 2-biphenylmethyl beta-D-glucopyranoside. This choice was validated experimentally, since the corresponding beta-(1-->3) disaccharide was obtained in good yields and with a high regioselectivity. At the same time, we have shown that phenyl 1-thio-beta-D-glucopyranoside was also an excellent substrate leading to similar results as those obtained with the O-phenyl analogue. The NBS deprotection of the S-phenyl group afforded the corresponding disaccharide quantitatively.

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

    PubMed

    Carter, Charles W; Wolfenden, Richard

    2015-06-16

    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.

  3. Synthesis of rapeseed biodiesel using short-chained alkyl acetates as acyl acceptor.

    PubMed

    Jeong, Gwi-Taek; Park, Don-Hee

    2010-05-01

    In this study, we conducted experiments using a response surface methodology to determine the optimal reaction conditions for the enzymatic synthesis of biodiesel from rapeseed oil and short-chained alkyl acetates, such as methyl acetate or ethyl acetate, as the acyl acceptor at 40 degrees C. Based on our response surface methodology experiments, the optimal reaction conditions for the synthesis of biodiesel were as follows: methyl acetate as acyl acceptor, catalyst concentration of 16.50%, oil-to-methyl acetate molar ratio of 1:12.44, and reaction time of 19.70 h; ethyl acetate as acyl acceptor, catalyst concentration of 16.95%, oil-to-ethyl acetate molar ratio of 1:12.56, and reaction time of 19.73 h. The fatty acid ester content under the above conditions when methyl acetate and ethyl acetate were used as the acyl acceptor was 58.0% and 62.6%, respectively. The statistical method described in this study can be applied to effectively optimize the enzymatic conditions required for biodiesel production with short-chained alkyl acetates.

  4. Photoluminescence study of Be acceptors in GaInNAs epilayers

    NASA Astrophysics Data System (ADS)

    Tsai, Y.; Barman, B.; Scrace, T.; Petrou, A.; Fukuda, M.; Sellers, I. R.; Leroux, M.; Khalfioui, M. A.

    2014-03-01

    We have studied the photoluminescence (PL) spectra from MBE grown GaInNAs epilayers doped p-type with Beryllium acceptors. The measurements were carried out in the 5 K - 70 K temperature range and in magnetic fields (B) up to 7 tesla. The PL spectra contain two features at T = 5 K: The exciton at 1093 meV and a second broader feature at 1058 meV. The intensity of this feature decreases with increasing temperature and disappears completely by 70K while the excitonic feature persists. The emission at 1058meV is identified as the conduction band to Beryllium acceptor transition. If we take into account the binding energy of the exciton [3] we get a value of 23 meV for the Beryllium acceptor binding energy. The acceptor related transition was studied as a function of magnetic field; the energy of this transition has a linear dependence on B with a slope of 055 meV/T. Research supported by Amethyst Research In. through the State of Oklahoma, ONAP program.

  5. Dominant effects of first monolayer energetics at donor/acceptor interfaces on organic photovoltaics.

    PubMed

    Izawa, Seiichiro; Nakano, Kyohei; Suzuki, Kaori; Hashimoto, Kazuhito; Tajima, Keisuke

    2015-05-20

    Energy levels of the first monolayer are manipulated at donor/acceptor interfaces in planar heterojunction organic photovoltaics by using molecular self-organization. A "cascade" energy landscape allows thermal-activation-free charge generation by photoirradiation, destabilizes the energy of the interfacial charge-transfer state, and suppresses bimolecular charge recombination, resulting in a higher open-circuit voltage and fill factor.

  6. 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

  7. Measuring drug saturation solubility in thin polymer films: use of a thin acceptor layer.

    PubMed

    Kunst, Anders; Lee, Geoffrey

    2015-03-15

    The saturation solubility of scopolamine base in two pressure sensitive adhesive DURO-TAKs has been determined using the 5-layer laminate technique. The acceptor layer had a thickness of less than 25 μm to promote a rapid partitioning equilibrium. With DURO-TAK 87-2510 the saturation solubility is 5.2 ± 0.6% w/w when measured after 7 days. With DURO-TAK 87-4098 the saturation solubility is slightly higher, 7.9 ± 0.7% w/w after 7 days. These values remained constant up to approximately 30 days' experimental time. In both cases the acceptor was free of crystalline material at the end of the experiment. This strongly suggests that that equilibrium had been reached between the saturated solution in the acceptor layer and the crystalline drug still present in the donor layer. The addition of light liquid paraffin to the acceptor produced a solubilizing effect with 87-4098 but not 87-2510. We recommend some experimental conditions that we consider to be necessary to achieve a reliable and accurate result with this technique. If performed correctly, it can give a feasible result.

  8. Isotope effect on electron paramagnetic resonance of boron acceptors in silicon

    NASA Astrophysics Data System (ADS)

    Stegner, A. R.; Tezuka, H.; Andlauer, T.; Stutzmann, M.; Thewalt, M. L. W.; Brandt, M. S.; Itoh, K. M.

    2010-09-01

    The fourfold degeneracy of the boron acceptor ground state in silicon, which is easily lifted by any symmetry-breaking perturbation, allows for a strong inhomogeneous broadening of the boron-related electron paramagnetic resonance (EPR) lines, e.g., by a random distribution of local strains. However, since EPR of boron acceptors in externally unstrained silicon was reported initially, neither the line shape nor the magnitude of the residual broadening observed in samples with high-crystalline purity were compatible with the low concentrations of carbon and oxygen point defects, being the predominant source of random local strain. Adapting a theoretical model which has been applied to understand the acceptor ground-state splitting in the absence of a magnetic field as an effect due to the presence of different silicon isotopes, we show that local fluctuations of the valence-band edge due to different isotopic configurations in the vicinity of the boron acceptors can quantitatively account for all inhomogeneous broadening effects in high-purity Si with a natural isotope composition. Our calculations show that such an isotopic perturbation also leads to a shift in the g value of different boron-related resonances, which we could verify in our experiments. Further, our results provide an independent test and verification of the valence-band offsets between the different Si isotopes determined in previous works.

  9. Nonequilibrium phenomena in charge recombination of excited donor-acceptor complexes and free energy gap law.

    PubMed

    Yudanov, Vladislav V; Mikhailova, Valentina A; Ivanov, Anatoly I

    2010-12-23

    The charge recombination dynamics of excited donor-acceptor complexes in polar solvents has been investigated within the framework of the stochastic approach. The model involves the excited state formation by the pump pulse and accounts for the reorganization of a number of intramolecular high-frequency vibrational modes, for their relaxation as well as for the solvent reorganization following nonexponential relaxation. The hot transitions accelerate the charge recombination in the low exergonic region and suppress it in the region of moderate exothermicity. This straightens the dependence of the logarithm of the charge recombination rate constant on the free energy gap to the form that can be fitted to the experimental data. The free energy dependence of the charge recombination rate constant can be well fitted to the multichannel stochastic model if the donor-acceptor complexes are separated into a few groups with different values of the electronic coupling. The model provides correct description of the nonexponential charge recombination dynamics in excited donor-acceptor complexes, in particular, nearly exponential recombination in perylene-tetracyanoethylene complex in acetonitrile. It appears that majority of the initially excited donor-acceptor complexes recombines in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state in the area of the low and moderate exothermicity.

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

    NASA Astrophysics Data System (ADS)

    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 GaA s 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 BA s. This 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. 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.

  11. 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.

  12. Photocurrent generation through electron-exciton interaction at the organic semiconductor donor/acceptor interface.

    PubMed

    Chen, Lijia; Zhang, Qiaoming; Lei, Yanlian; Zhu, Furong; Wu, Bo; Zhang, Ting; Niu, Guoxi; Xiong, Zuhong; Song, Qunliang

    2013-10-21

    In this work, we report our effort to understand the photocurrent generation that is contributed via electron-exciton interaction at the donor/acceptor interface in organic solar cells (OSCs). Donor/acceptor bi-layer heterojunction OSCs, of the indium tin oxide/copper phthalocyanine (CuPc)/fullerene (C60)/molybdenum oxide/Al type, were employed to study the mechanism of photocurrent generation due to the electron-exciton interaction, where CuPc and C60 are the donor and the acceptor, respectively. It is shown that the electron-exciton interaction and the exciton dissociation processes co-exist at the CuPc/C60 interface in OSCs. Compared to conventional donor/acceptor bi-layer OSCs, the cells with the above configuration enable holes to be extracted at the C60 side while electrons can be collected at the CuPc side, resulting in a photocurrent in the reverse direction. The photocurrent thus observed is contributed to primarily by the charge carriers that are generated by the electron-exciton interaction at the CuPc/C60 interface, while charges derived from the exciton dissociation process also exist at the same interface. The mechanism of photocurrent generation due to electron-exciton interaction in the OSCs is further investigated, and it is manifested by the transient photovoltage characteristics and the external quantum efficiency measurements. PMID:24002235

  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. Synthesis of rapeseed biodiesel using short-chained alkyl acetates as acyl acceptor.

    PubMed

    Jeong, Gwi-Taek; Park, Don-Hee

    2010-05-01

    In this study, we conducted experiments using a response surface methodology to determine the optimal reaction conditions for the enzymatic synthesis of biodiesel from rapeseed oil and short-chained alkyl acetates, such as methyl acetate or ethyl acetate, as the acyl acceptor at 40 degrees C. Based on our response surface methodology experiments, the optimal reaction conditions for the synthesis of biodiesel were as follows: methyl acetate as acyl acceptor, catalyst concentration of 16.50%, oil-to-methyl acetate molar ratio of 1:12.44, and reaction time of 19.70 h; ethyl acetate as acyl acceptor, catalyst concentration of 16.95%, oil-to-ethyl acetate molar ratio of 1:12.56, and reaction time of 19.73 h. The fatty acid ester content under the above conditions when methyl acetate and ethyl acetate were used as the acyl acceptor was 58.0% and 62.6%, respectively. The statistical method described in this study can be applied to effectively optimize the enzymatic conditions required for biodiesel production with short-chained alkyl acetates. PMID:19802734

  15. 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 BAs. This systematicmore » 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

  16. Limited Cash Flow on Slot Machines: Effects of Prohibition of Note Acceptors on Adolescent Gambling Behaviour

    ERIC Educational Resources Information Center

    Hansen, Marianne; Rossow, Ingeborg

    2010-01-01

    This study addresses the impact of prohibition of note acceptors on gambling behaviour and gambling problems among Norwegian adolescents. Data comprised school surveys at three time points; 2004 and 2005 (before intervention) and 2006 (after intervention). Net samples comprised 20.000 students aged 13-19 years at each data collection. Identical…

  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. Rhodanine dye-based small molecule acceptors for organic photovoltaic cells.

    PubMed

    Kim, Yujeong; Song, Chang Eun; Moon, Sang-Jin; Lim, Eunhee

    2014-08-01

    The solution-processable small molecules based on carbazole or fluorene containing rhodanine dyes at both ends were synthesized and introduced as acceptors in organic photovoltaic cells. The high energy levels of their lowest unoccupied molecular orbitals resulted in a power conversion efficiency of 3.08% and an open circuit voltage of up to 1.03 V.

  19. Time dependence of donor-acceptor electron transfer and back transfer in solid solution

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Dorfman, R. C.; Fayer, M. D.

    1989-01-01

    Electron transfer from an optically excited donor to randomly distributed acceptors followed by electron back transfer is treated theoretically for donors and acceptors in a rigid solution. The forward electron transfer process is described in terms of the excited state population probabilityPex(t) of the donor molecules, while the electron back transfer from the radical anion to the radical cation is characterized by Pct(t), the donor cation state population probability. Exact expressions for the ensemble averages and are derived. Numerical calulations are presented for the cation probabilities, the average cation-anion separation distance , and the average cation existence time <τ(R)>, using parameters which characterize the forward and back transfer distance dependent rates. Relationships among , and the intermolecular interaction parameters provide detailed insights into the distance and time dependence of the flow of electron probability in an ensemble of donors and acceptors. The theoretical expressions can be used to calculate experimental observables. In particular, picosecond transient grating experiments are analyzed, and it is shown that by combining grating experiments (or other ground state recovery experiments) with fluorescence experiments it is possible to obtain the intermolecular interaction parameters for both forward and back transfer and a detailed description of the dynamics. The calculations presented here for rigid solutions are the precursor to the inclusion of diffusive motion of donors and acceptors to describe the dynamics of coupled electron transfer and back transfer in liquid solutions.

  20. Solution-grown organic single-crystalline donor-acceptor heterojunctions for photovoltaics.

    PubMed

    Li, Hanying; Fan, Congcheng; Fu, Weifei; Xin, Huolin L; Chen, Hongzheng

    2015-01-12

    Organic single crystals are ideal candidates for high-performance photovoltaics due to their high charge mobility and long exciton diffusion length; however, they have not been largely considered for photovoltaics due to the practical difficulty in making a heterojunction between donor and acceptor single crystals. Here, we demonstrate that extended single-crystalline heterojunctions with a consistent donor-top and acceptor-bottom structure throughout the substrate can be simply obtained from a mixed solution of C60 (acceptor) and 3,6-bis(5-(4-n-butylphenyl)thiophene-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (donor). 46 photovoltaic devices were studied with the power conversion efficiency of (0.255±0.095)% under 1 sun, which is significantly higher than the previously reported value for a vapor-grown organic single-crystalline donor-acceptor heterojunction (0.007%). As such, this work opens a practical avenue for the study of organic photovoltaics based on single crystals.

  1. Conformation and geometry of cyclopropane rings having π-acceptor substituents: a theoretical and database study.

    PubMed

    Cruz-Cabeza, Aurora J; Allen, Frank H

    2011-02-01

    The 3e' orbitals of cyclopropane have the correct symmetry to interact with low-lying unoccupied orbitals of π-acceptor substituents and maximum overlap occurs when the two orbital systems are parallel, i.e. when the π-acceptor bisects the ring in projection down the substituent bond. Since the cyclopropyl group is a common component of active pharmaceutical and agrochemical ingredients, it is important that these strong conjugative interactions are well modelled by computational techniques, and clearly represented in experimental crystal structures. Here we show that torsion angle distributions derived from crystal structure data in the Cambridge Structural Database are in excellent correspondence with torsional energy profiles computed using density functional theory (DFT) for a range of substituents: -COOR, -CONR(2), -NO(2), vinyl and phenyl. We also show that crystal structure information is invaluable in modelling conformations of compounds that contain multiply substituted rings, where steric interactions require some substituents to adopt energetically disfavoured conformations. Further, conjugative interactions with π-acceptors lead to significant asymmetry in the cyclopropane ring bond lengths and again the experimental and computational results are in excellent agreement. Such asymmetry effects are additive, and this explains bond-length variations in cyclopropane rings bearing two or more π-acceptor substituents. PMID:21245544

  2. A Dithienosilole-Benzooxadiazole Donor-Acceptor Copolymer for Utility in Organic Solar Cells

    SciTech Connect

    Caputo, Bruno J. A.; Welch, Gregory C.; Kamkar, Daniel A.; Henson, Zachary B.; Nguyen, Thuc-Quyen; Bazan, Guillermo C.

    2011-04-20

    A systematic evaluation of a novel conjugated polymer, bearing alkyl side chains on both the donor and acceptor units, is conducted using nanoscale characterization techniques and device fabrication. How to manage the use of solvent additives to achieve power-conversion efficiencies of up to 3.7% is demonstrated.

  3. Three component assemblies by orthogonal H-bonding and donor-acceptor charge-transfer interaction.

    PubMed

    Kar, Haridas; Ghosh, Suhrit

    2014-02-01

    Three component supramolecular assemblies from a mixture of an aromatic donor (D), acceptor (A) and external structure directing agent (ESDA) are achieved by orthogonal noncovalent interactions involving two different types of H-bonding and alternate D-A stacking. An ESDA containing amide or urea produces a charge-transfer gel and sol, respectively, owing to their contrasting morphology. PMID:24309620

  4. 2004 Electron Donor Acceptor Interactions Gordon Conference - August 8-13, 2004

    SciTech Connect

    GUILFORD JONES BOSTON UNIVERSITY PHOTONICS CENTER 8 ST. MARY'S ST BOSTON, MA 02215

    2005-09-14

    The 2004 Gordon Conference on Donor/Acceptor Interactions will take place at Salve Regina University in Newport, Rhode Island on August 8-13, 2004. The conference will be devoted to the consequences of charge interaction and charge motion in molecular and materials systems.

  5. Microbial Community Succession during Lactate Amendment and Electron Acceptor Limitation Reveals a Predominance of Metal-Reducing Pelosinus spp.

    PubMed Central

    Mosher, Jennifer J.; Phelps, Tommy J.; Podar, Mircea; Hurt, Richard A.; Campbell, James H.; Drake, Meghan M.; Moberly, James G.; Schadt, Christopher W.; Brown, Steven D.; Hazen, Terry C.; Arkin, Adam P.; Palumbo, Anthony V.; Faybishenko, Boris A.

    2012-01-01

    The determination of the success of in situ bioremediation strategies is complex. By using controlled laboratory conditions, the influence of individual variables, such as U(VI), Cr(VI), and electron donors and acceptors on community structure, dynamics, and the metal-reducing potential can be studied. Triplicate anaerobic, continuous-flow reactors were inoculated with Cr(VI)-contaminated groundwater from the Hanford, WA, 100-H area, amended with lactate, and incubated for 95 days to obtain stable, enriched communities. The reactors were kept anaerobic with N2 gas (9 ml/min) flushing the headspace and were fed a defined medium amended with 30 mM lactate and 0.05 mM sulfate with a 48-h generation time. The resultant diversity decreased from 63 genera within 12 phyla to 11 bacterial genera (from 3 phyla) and 2 archaeal genera (from 1 phylum). Final communities were dominated by Pelosinus spp. and to a lesser degree, Acetobacterium spp., with low levels of other organisms, including methanogens. Four new strains of Pelosinus were isolated, with 3 strains being capable of Cr(VI) reduction while one also reduced U(VI). Under limited sulfate, it appeared that the sulfate reducers, including Desulfovibrio spp., were outcompeted. These results suggest that during times of electron acceptor limitation in situ, organisms such as Pelosinus spp. may outcompete the more-well-studied organisms while maintaining overall metal reduction rates and extents. Finally, lab-scale simulations can test new strategies on a smaller scale while facilitating community member isolation, so that a deeper understanding of community metabolism can be revealed. PMID:22267668

  6. Pump apparatus including deconsolidator

    SciTech Connect

    Sonwane, Chandrashekhar; Saunders, Timothy; Fitzsimmons, Mark Andrew

    2014-10-07

    A pump apparatus includes a particulate pump that defines a passage that extends from an inlet to an outlet. A duct is in flow communication with the outlet. The duct includes a deconsolidator configured to fragment particle agglomerates received from the passage.

  7. New conjugated molecular scaffolds based on [2,2]paracyclophane as electron acceptors for organic photovoltaic cells.

    PubMed

    Yang, Yang; Zhang, Guanxin; Yu, Chenmin; He, Chang; Wang, Jianguo; Chen, Xin; Yao, Jingjing; Liu, Zitong; Zhang, Deqing

    2014-09-01

    Two conjugated molecules with a [2,2]paracyclophane core were designed as non-fullerene electron acceptors for photovoltaic cells. Using as the donor, a high power conversion efficiency (2.69%) is achieved for the blending thin film of with , which is relatively high for solution-processed OPVs based on small molecular non-fullerene acceptors and as the electron donor.

  8. 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.

  9. Photoinduced electron transfer between donors and acceptors on micelle surfaces

    NASA Astrophysics Data System (ADS)

    Weidemaier, Kristin; Tavernier, H. L.; Chu, K. T.; Fayer, M. D.

    1997-09-01

    Fluorescence time-dependence and fluorescence yield data are used to examine photoinduced electron transfer between N,N-dimethylaniline and octadecylrhodamine B on the surfaces of dodecyltrimethylammonium bromide (DTAB) and Triton X-100 micelles. The data are analyzed with a detailed theory that includes diffusion of the chromophores over the micelle surface and models the reaction rate by a distance-dependent Marcus form. Good agreement between theory and experiment is obtained for reasonable choices of the transfer parameters for DTAB. However, for Triton X-100, there is reasonable agreement between theory and experiment only for values of the parameters that verge on unphysical. Possible explanations are discussed.

  10. Adsorption of atrazine, hydroxyatrazine, deethylatrazine, and deisopropylatrazine onto Fe(III) polyhydroxy cations intercalated vermiculite and montmorillonite.

    PubMed

    Abate, Gilberto; Masini, Jorge Cesar

    2005-03-01

    This paper describes the modification of the clay minerals vermiculite (VT) and montmorillonite (MT) by intercalating Fe(III) polymers of different [OH(-)]:[Fe(III)] ratios with the aim of removing atrazine (AT) and its metabolites deethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (ATOH) from aqueous solution. An enhancement of adsorption capacity was observed for both intercalated clay minerals in comparison to the potassium-saturated materials (KVT or KMT). The results showed that different [OH(-)]:[Fe(III)] molar ratios had a small influence on the adsorption capacity, as well as in the basal spacing, BET surface area, and porosity. For the lowest initial concentrations of AT, DIA, and ATOH (0.050 mg L(-)(1)) studied, the modified VT adsorbed almost 80% of AT and DIA, while ATOH was removed at concentration levels below the detection limit of the technique, implying in at least 99.5% of sorption. Weak interaction between intercalated VT and DEA was observed, although a significant adsorption enhancement occurred in comparison to KVT. Within a 24 h interval, desorption of AT and DIA in aqueous medium reached levels close to 20% of the amount initially adsorbed, while for ATOH only 3% of the adsorbed compound was desorbed. The adsorption capacity of the Fe(III)-intercalated VT decreased after the first adsorption/desorption cycle, implying that the material is not suitable for reutilization. The intercalated MT was a powerful sorbent for AT, DEA, DIA, and ATOH, removing all of these chemicals from solution almost quantitatively (sorption greater than 99.5%), even at initial concentrations as high as 1.0 mg L(-)(1). Additionally, desorption of AT, ATOH, and DIA in water was not measurable up to the tube corresponding to the initial concentration of 1.0 mg L(-)(1), suggesting strong irreversible binding of these compounds to the intercalated MT materials. Desorption of DEA from the intercalated MT was between 5 and 30%. Unlike what was observed

  11. 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

  12. Optical modulator including grapene

    DOEpatents

    Liu, Ming; Yin, Xiaobo; Zhang, Xiang

    2016-06-07

    The present invention provides for a one or more layer graphene optical modulator. In a first exemplary embodiment the optical modulator includes an optical waveguide, a nanoscale oxide spacer adjacent to a working region of the waveguide, and a monolayer graphene sheet adjacent to the spacer. In a second exemplary embodiment, the optical modulator includes at least one pair of active media, where the pair includes an oxide spacer, a first monolayer graphene sheet adjacent to a first side of the spacer, and a second monolayer graphene sheet adjacent to a second side of the spacer, and at least one optical waveguide adjacent to the pair.

  13. A New Family of Anionic Fe(III) Spin Crossover Complexes Featuring a Weak-Field N2O4 Coordination Octahedron.

    PubMed

    Takahashi, Kazuyuki; Kawamukai, Kiko; Okai, Mitsunobu; Mochida, Tomoyuki; Sakurai, Takahiro; Ohta, Hitoshi; Yamamoto, Takashi; Einaga, Yasuaki; Shiota, Yoshihito; Yoshizawa, Kazunari

    2016-01-22

    Unprecedented anionic Fe(III) spin crossover (SCO) complexes involving a weak-field O,N,O-tridentate ligand were discovered. The SCO transition was evidenced by the temperature variations in magnetic susceptibility, Mössbauer spectrum, and coordination structure. The DFT calculations suggested that larger coefficients on the azo group in the HOMO-1 of a ligand might contribute to the enhancement of a ligand-field splitting energy. The present anionic SCO complex also exhibited the light- induced excited-spin-state trapping effect. PMID:26642040

  14. A demonstration model for a selective and recyclable uptake of metals from water: Fe(III) ions complexation and release by a supported natural fluorescent chelator.

    PubMed

    Mureseanu, M; Renard, G; Galarneau, A; Lerner, D A

    2003-06-13

    We describe here the preliminary stage of development of a process aiming at the selective uptake and release of metal ions from water. The process envisioned involves the encapsulation of highly selective natural chelates secreted by bacteria or other living species in mesoporous solids that could be used as usual resins. To demonstrate the feasibility of the concept, we use a model system involving pyoverdin, a natural Fe(III) ions chelator from a Pseudomonas fluorescens strain, encapsulated in a mesoporous templated silica. For this model study, the native fluorescence of the chelator allows a simpler follow-up and quantification of the uptake and release processes. PMID:18969073

  15. 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, D.P.; Ji, S.; Dong, H.; Blake, R.E.; Eberl, D.D.; Kim, J.

    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 SO421 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 native

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

    PubMed

    Liu, Yimo; Fredrickson, James K; Zachara, John M; Shi, Liang

    2015-01-01

    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 no 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 suggests that absence of any protein subunit eliminates function of OmaB/OmbB/OmcB protein complex. 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. PMID:26483786

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

    PubMed Central

    Liu, Yimo; Fredrickson, James K.; Zachara, John M.; Shi, Liang

    2015-01-01

    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 no 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 suggests that absence of any protein subunit eliminates function of OmaB/OmbB/OmcB protein complex. 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. PMID:26483786

  18. Exquisite 1D Assemblies Arising from Rationally Designed Asymmetric Donor-Acceptor Architectures Exhibiting Aggregation-Induced Emission as a Function of Auxiliary Acceptor Strength.

    PubMed

    Singh, Roop Shikha; Mukhopadhyay, Sujay; Biswas, Arnab; Pandey, Daya Shankar

    2016-01-11

    One-dimensional nanostructures with aggregation-induced emission (AIE) properties have been fabricated to keep the pace with growing demand from optoelectronics applications. The compounds 2-[4-(4-methylpiperazin-1-yl)benzylidene]malononitrile (PM1), 2-{4-[4-(pyridin-2-yl)piperazin-1-yl]-benzylidene}malononitrile (PM2), and 2-{4-[4-(pyrimidin-2-yl)piperazin-1-yl]benzylidene}malononitrile (PM3) have been designed and synthesized by melding piperazine and dicyanovinylene to investigate AIE in an asymmetric donor-acceptor (D-A) construct of A'-D-π-A- topology. The synthetic route has been simplified by using phenylpiperazine as a weak donor (D), dicyanovinylene as an acceptor (A), and pyridyl/pyrimidyl groups (PM2/PM3) as auxiliary acceptors (A'). It has been established that A' plays a vital role in triggering AIE in these compounds because the same D-A construct led to aggregation-caused quenching upon replacing A' with an electron-donating ethyl group (PM1). Moreover, the effect of restricted intramolecular rotation and twisted intramolecular charge transfer on the mechanism of AIE has also been investigated. Furthermore, it has been clearly shown that the optical disparities of these A'-D-π-A architectures are a direct consequence of comparative A' strength. Single-crystal X-ray analyses provided justification for role of intermolecular interactions in aggregate morphology. Electrochemical and theoretical studies affirmed the effect of the A' strength on the overall properties of the A'-D-π-A system.

  19. 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.

  20. Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I

    NASA Technical Reports Server (NTRS)

    Trost, J. T.; Brune, D. C.; Blankenship, R. E.

    1992-01-01

    Photosynthetic reaction centers isolated from Heliobacillus mobilis exhibit a single major protein on SDS-PAGE of 47 000 Mr. Attempts to sequence the reaction center polypeptide indicated that the N-terminus is blocked. After enzymatic and chemical cleavage, four peptide fragments were sequenced from the Heliobacillus mobilis apoprotein. Only one of these sequences showed significant specific similarity to any of the protein and deduced protein sequences in the GenBank data base. This fragment is identical with 56% of the residues, including both cysteines, found in highly conserved region that is proposed to bind iron-sulfur center Fx in the Photosystem I reaction center peptide that is the psaB gene product. The similarity to the psaA gene product in this region is 48%. Redox titrations of laser-flash-induced photobleaching with millisecond decay kinetics on isolated reaction centers from Heliobacterium gestii indicate a midpoint potential of -414 mV with n = 2 titration behavior. In membranes, the behavior is intermediate between n = 1 and n = 2, and the apparent midpoint potential is -444 mV. This is compared to the behavior in Photosystem I, where the intermediate electron acceptor A1, thought to be a phylloquinone molecule, has been proposed to undergo a double reduction at low redox potentials in the presence of viologen redox mediators. These results strongly suggest that the acceptor side electron transfer system in reaction centers from heliobacteria is indeed analogous to that found in Photosystem I. The sequence similarities indicate that the divergence of the heliobacteria from the Photosystem I line occurred before the gene duplication and subsequent divergence that lead to the heterodimeric protein core of the Photosystem I reaction center.

  1. Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I.

    PubMed

    Trost, J T; Brune, D C; Blankenship, R E

    1992-01-01

    Photosynthetic reaction centers isolated from Heliobacillus mobilis exhibit a single major protein on SDS-PAGE of 47 000 Mr. Attempts to sequence the reaction center polypeptide indicated that the N-terminus is blocked. After enzymatic and chemical cleavage, four peptide fragments were sequenced from the Heliobacillus mobilis apoprotein. Only one of these sequences showed significant specific similarity to any of the protein and deduced protein sequences in the GenBank data base. This fragment is identical with 56% of the residues, including both cysteines, found in highly conserved region that is proposed to bind iron-sulfur center Fx in the Photosystem I reaction center peptide that is the psaB gene product. The similarity to the psaA gene product in this region is 48%. Redox titrations of laser-flash-induced photobleaching with millisecond decay kinetics on isolated reaction centers from Heliobacterium gestii indicate a midpoint potential of -414 mV with n = 2 titration behavior. In membranes, the behavior is intermediate between n = 1 and n = 2, and the apparent midpoint potential is -444 mV. This is compared to the behavior in Photosystem I, where the intermediate electron acceptor A1, thought to be a phylloquinone molecule, has been proposed to undergo a double reduction at low redox potentials in the presence of viologen redox mediators. These results strongly suggest that the acceptor side electron transfer system in reaction centers from heliobacteria is indeed analogous to that found in Photosystem I. The sequence similarities indicate that the divergence of the heliobacteria from the Photosystem I line occurred before the gene duplication and subsequent divergence that lead to the heterodimeric protein core of the Photosystem I reaction center.

  2. Listening to Include

    ERIC Educational Resources Information Center

    Veck, Wayne

    2009-01-01

    This paper attempts to make important connections between listening and inclusive education and the refusal to listen and exclusion. Two lines of argument are advanced. First, if educators and learners are to include each other within their educational institutions as unique individuals, then they will need to listen attentively to each other.…

  3. Elevated NK sensitivity of Raji cells carrying acceptor-bound C3 fragments.

    PubMed

    Kai, C; Sármay, G; Ramos, O; Yefenof, E; Klein, E

    1988-05-01

    The majority of cell lines derived from Burkitt lymphomas carry CR2 on their plasma membrane cell lines of haematopoietic origin can activate C3 present in human serum through the alternative pathway. However, only the lines that carry CR2 were shown to bind C3 fragments. This bond can be either fixation to acceptor sites or attachment to the CR. Our studies with Raji cells showed that when the possibility for the covalent acceptor bond was eliminated by using methylamine (MA)- or zymosan-treated serum, considerably lower amounts of C3 were bound. In the zymosan-treated serum C3 fragments are present that can bind to receptors but their capacity for acceptor bond is absent. These results indicate that when Raji cell are incubated in human serum some of the generated C3 fragments are bound to acceptors and a lower proportion through the specific interaction with complement receptors. Pretreatment of the CR2 carrying cell lines with human serum elevated their sensitivity to the lytic effect of human blood lymphocytes. We showed in this work that MA-treated serum did not induce this elevation. Zymosan-treated serum under conditions that excluded activation of the residual native C3 molecules, i.e., in the presence of EDTA, did not have the enhancing effect either. These results suggest that the increased lytic efficiency imposed by human serum was due to cleavage of C3 molecules by Raji and fixation of the C3 fragments by acceptor sites. Natural killer cells carry CR3; therefore it is likely that the attached C3 fragments bind also to the effector cells. The C3 molecules could elevate thereby the avidity between the target and the lytic lymphocytes. The observation that C3 fragments are not bound to the surface of CR2 negative lines in spite of their capacity to activate C3 suggests that the receptor molecule is either involved in the activation and/or serves also as an acceptor. PMID:3359489

  4. One pot/two donors/one diol give one differentiated trisaccharide: powerful evidence for reciprocal donor-acceptor selectivity (RDAS).

    PubMed

    Fraser-Reid, Bert; López, J Cristóbal; Radhakrishnan, K V; Nandakumar, M V; Gómez, Ana M; Uriel, Clara

    2002-09-21

    Three component, one-pot reactions involving equimolar amounts of the acceptor diol and both armed and disarmed donors presented simultaneously, produce a single double-differential glycosidation product; this phenomenon provides evidence for Reciprocal Donor Acceptor Selectivity (RDAS).

  5. 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; Tulk, Christopher A.; Molaison, Jamie J.; Feygenson, Mikhail; Yang, Wenge; Guthrie, Malcolm; Mao, Hokwang

    2015-09-14

    The addition polymerization of charged monomers like C≡C2– 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 K3Fe(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 K3Fe(CN)6 under external pressure are investigated by in situ neutron diffraction, in situ X-ray absorption fine structure (XAFS), and neutron pair distributionmore » 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

  6. Photoinductive activity of humic acid fractions with the presence of Fe(III): the role of aromaticity and oxygen groups involved in fractions.

    PubMed

    Ou, Xiaoxia; Chen, Shuo; Quan, Xie; Zhao, Huimin

    2008-06-01

    Relationship between the photoinductive activity and the properties of humic acids (HA) fractions were investigated with and without Fe(III). Three fractions were separated based on the molecular weight (M(w)) and were obtained following the order of M(w): F(A)>F(B)>F(C). Compared to F(A) and F(B), photodegradation of atrazine under simulated sunlight was much faster in solution containing F(C), whose structure was dominated by greater aromaticity, more oxygen groups and fluorophores. The interaction of HA fractions and Fe(III) was studied using fluorescence spectrometry and F(C) had the largest quenching constant. The capacity of electron transfer, estimated from the amount of photoformed Fe(II), was also highest for F(C). Thus, the Fe(III)-F(C) complex was efficient in phototransformation of atrazine in nearly neutral aqueous solutions. These results suggest that the aromaticity and oxygen groups content of HA exert great influence on the binding ability of metals and on the fate of pollutants in natural waters.

  7. 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

  8. INVESTIGATION OF THE TRANSFORMATION OF URANIUM UNDER IRON-REDUCING CONDITIONS: REDUCTION OF UVI BY BIOGENIC FEII/FEIII HYDROXIDE (GREEN RUST)

    SciTech Connect

    O'Loughlin, Edward J.; Scherer, Michelle M.; Kemner, Kenneth M.

    2006-12-31

    The recent identification of green rusts (GRs) as products of the reduction of FeIII oxyhydroxides by dissimilatory iron-reducing bacteria, coupled with the ability of synthetic (GR) to reduce UVI species to insoluble UO2, suggests that biogenic green rusts (BioGRs) may play an important role in the speciation (and thus mobility) of U in FeIII-reducing environments. The objective of our research was to examine the potential for BioGR to affect the speciation of U under FeIII-reducing conditions. To meet this objective, we designed and executed a hypothesis-driven experimental program to identify key factors leading to the formation of BioGRs as products of dissimilatory FeIII reduction, to determine the key factors controlling the reduction of UVI to UIV by GRs, and to identify the resulting U-bearing mineral phases. The results of this research significantly increase our understanding of the coupling of biotic and abiotic processes with respect to the speciation of U in iron-reducing environments. In particular, the reduction of UVI to UIV by BioGR with the subsequent formation of U-bearing mineral phases may be effective for immobilizing U in suboxic subsurface environments. This information has direct applications to contaminant transport modeling and bioremediation engineering for natural or enhanced in situ remediation of subsurface contamination.

  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. K 3 Fe(CN) 6 under External Pressure: Dimerization of CN Coupled with Electron Transfer to Fe(III)

    SciTech Connect

    Li, Kuo; Zheng, Haiyan; Wang, Lijuan; Tulk, Christopher A.; Molaison, Jamie J.; Feygenson, Mikhail; Yang, Wenge; Guthrie, Malcolm; Mao, Hokwang

    2015-09-14

    The addition polymerization of charged monomers like C≡C2– 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 K3Fe(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 K3Fe(CN)6 under external pressure are investigated by in situ neutron diffraction, in situ X-ray absorption fine structure (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.

  11. 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.

  12. New calcareous soil-alginate composites for efficient uptake of Fe(III), Mn(II) and As(V) from water.

    PubMed

    El-Sherbiny, Ibrahim M; Abdel-Hamid, Mohammed I; Rashad, Mohamed; Ali, Abdelnaser S M; Azab, Yehia A

    2013-07-25

    In the present study, various grades of sodium alginates were extracted from different brown macro-algae and their characteristics were investigated using FTIR, UV-vis and EA. The alginates were used in combination with different proportions of calcareous soil to develop new composite microparticles as potential sorbents for efficient uptake of Fe(III), Mn(II) and As(V) from water. Under the investigated conditions (1g of composite equilibrated in 100ml of standard metal ion solution), the composites have removed almost 100% of Fe(III) in the concentration range of 0.5-16.0 mg l(-1). Soil, alginate and composites exhibited the highest removal (about 89%) of Mn(II) at 0.5 mg l(-1). Reasonable removal efficiency (50-60%) was recorded at 0.5 mg l(-1) of As(V) whereas, increasing the initial As(V) concentration resulted in marked decrease in removal efficiency. The collected equilibrium data were also fitted to both Langmuir and Freundlich isotherms for all the developed composites. PMID:23768586

  13. Binding of the Trace Elements: Cu(II) and Fe(III) to the Native and Modified Nutritive Potato Starches Studied by EPR

    NASA Astrophysics Data System (ADS)

    Śmigielska, H.; Lewandowicz, G.; Goslar, J.; Hoffmann, S. K.

    2006-08-01

    The Cu(II) and Fe(III) ions have been adsorbed by four potato starches of different degrees of oxidation (different numbers of COOH groups replacing host CH2OH groups): native (no oxidized), white (pudding) with oxidation degree of 0.04%, gelating (0.1%), and LUBOX starch (0.5%). Concentration of the ions in starches was determined from atomic absorption and EPR spectrum intensity. For small concentration of the adsorbed ions (below 4 mg/g) nearly all ions are adsorbed from the solution. EPR shows that adsorbed copper(II) ions are chemically bonded to the starch molecules (preferably) at COOH sites and uniformly dispersed in the starch structure. The complexes are typical of octahedral or square-quadratic coordination with spin-Hamiltonian parameters gǁ=2.373, g⊥= 2.080, Aǁ=12.1 mT, A⊥=1.0 mT. For higher concentrations the Cu(II) displays a tendency to clustering. Iron(III) ions are introduced into starch in a form of clusters mainly, even for the smallest concentration. The highest concentrations of both Cu(II) and Fe(III) were observed in LUBOX starch having the highest degree of oxidation.

  14. M(III)Dy(III)3 (M = Fe(III), Co(III)) complexes: three-blade propellers exhibiting slow relaxation of magnetization.

    PubMed

    Xu, Gong-Feng; Gamez, Patrick; Tang, Jinkui; Clérac, Rodolphe; Guo, Yun-Nan; Guo, Yang

    2012-05-21

    [Dy(III)(HBpz(3))(2)](2+) moieties (HBpz(3)(-) = hydrotris(pyrazolyl)borate) and a 3d transition-metal ion (Fe(III) or Co(III)) have been rationally assembled using an dithiooxalato dianion ligand into 3d-4f [MDy(3)(HBpz(3))(6)(dto)(3)]·4CH(3)CN·2CH(2)Cl(2) (M = Fe (1), Co (2) complexes. Single-crystal X-ray studies reveal that three eight-coordinated Dy(III) centers in a square antiprismatic coordination environment are connecting to a central octahedral trivalent Fe or Co ion forming a propeller-type complex. The dynamics of the magnetization in the two isostructural compounds, modulated by the nature of the central M(III) metal ion, are remarkably different despite their analogous direct current (dc) magnetic properties. The slow relaxation of the magnetization observed for 2 mainly originates from isolated Dy ions, since a diamagnetic Co(III) metal ion links the magnetic Dy(III) ions. In the case of 1, the magnetic interaction between S = 1/2 Fe(III) ion and the three Dy(III) magnetic centers, although weak, generates a complex energy spectrum of magnetic states with low-lying excited states that induce a smaller energy gap than for 2 and thus a faster relaxation of the magnetization.

  15. A Geobacter sulfurreducens Strain Expressing Pseudomonas aeruginosa Type IV Pili Localizes OmcS on Pili but Is Deficient in Fe(III) Oxide Reduction and Current Production

    PubMed Central

    Liu, Xing; Tremblay, Pier-Luc; Malvankar, Nikhil S.; Nevin, Kelly P.; Vargas, Madeline

    2014-01-01

    The conductive pili of Geobacter species play an important role in electron transfer to Fe(III) oxides, in long-range electron transport through current-producing biofilms, and in direct interspecies electron transfer. Although multiple lines of evidence have indicated that the pili of Geobacter sulfurreducens have a metal-like conductivity, independent of the presence of c-type cytochromes, this claim is still controversial. In order to further investigate this phenomenon, a strain of G. sulfurreducens, designated strain PA, was constructed in which the gene for the native PilA, the structural pilin protein, was replaced with the PilA gene of Pseudomonas aeruginosa PAO1. Strain PA expressed and properly assembled P. aeruginosa PilA subunits into pili and exhibited a profile of outer surface c-type cytochromes similar to that of a control strain expressing the G. sulfurreducens PilA. Surprisingly, the strain PA pili were decorated with the c-type cytochrome OmcS in a manner similar to the control strain. However, the strain PA pili were 14-fold less conductive than the pili of the control strain, and strain PA was severely impaired in Fe(III) oxide reduction and current production. These results demonstrate that the presence of OmcS on pili is not sufficient to confer conductivity to pili and suggest that there are unique structural features of the G. sulfurreducens PilA that are necessary for conductivity. PMID:24296506

  16. Fe(III) Reduction and U(VI) Immobilization by Paenibacillus sp. Strain 300A, Isolated from Hanford 300A Subsurface Sediments

    SciTech Connect

    Ahmed, B.; Cao, B.; McLean, Jeffrey S.; Ica, Tuba; Dohnalkova, Alice; Istanbullu, Ozlem; Paksoy, Akin; Fredrickson, Jim K.; Beyenal, Haluk

    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 also 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.

  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.

  18. 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.

  19. Click and chemically triggered declick reactions through reversible amine and thiol coupling via a conjugate acceptor

    NASA Astrophysics Data System (ADS)

    Diehl, Katharine L.; Kolesnichenko, Igor V.; Robotham, Scott A.; Bachman, J. Logan; Zhong, Ye; Brodbelt, Jennifer S.; Anslyn, Eric V.

    2016-10-01

    The coupling and decoupling of molecular units is a fundamental undertaking of organic chemistry. Herein we report the use of a very simple conjugate acceptor, derived from Meldrum's acid, for the sequential ‘clicking’ together of an amine and a thiol in aqueous conditions at neutral pH. Subsequently, this linkage can be ‘declicked’ by a chemical trigger to release the original amine and thiol undisturbed. The reactivity differs from that of other crosslinking agents because the selectivity for sequential functionalization derives from an altering of the electrophilicity of the conjugate acceptor on the addition of the amine. We describe the use of the procedure to modify proteins, create multicomponent libraries and synthesize oligomers, all of which can be declicked to their starting components in a controlled fashion when desired. Owing to the mild reaction conditions and ease of use in a variety of applications, the method is predicted to have wide utility.

  20. Alteration of the Donor/Acceptor Spectrum of the (S)-Amine Transaminase from Vibrio fluvialis

    PubMed Central

    Genz, Maika; Vickers, Clare; van den Bergh, Tom; Joosten, Henk-Jan; Dörr, Mark; Höhne, Matthias; Bornscheuer, Uwe T.

    2015-01-01

    To alter the amine donor/acceptor spectrum of an (S)-selective amine transaminase (ATA), a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417) was created. A 3DM-derived alignment comprising fold class I pyridoxal-5′-phosphate (PLP)-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal), as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions. PMID:26569229

  1. Alteration of the Donor/Acceptor Spectrum of the (S)-Amine Transaminase from Vibrio fluvialis.

    PubMed

    Genz, Maika; Vickers, Clare; van den Bergh, Tom; Joosten, Henk-Jan; Dörr, Mark; Höhne, Matthias; Bornscheuer, Uwe T

    2015-01-01

    To alter the amine donor/acceptor spectrum of an (S)-selective amine transaminase (ATA), a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417) was created. A 3DM-derived alignment comprising fold class I pyridoxal-5'-phosphate (PLP)-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal), as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions. PMID:26569229

  2. Electrostatic interaction of pi-acidic amides with hydrogen-bond acceptors.

    PubMed

    Li, Yi; Snyder, Lawrence B; Langley, David R

    2003-10-01

    Interactions between N-methylacetamide (NMA) and N-methylated derivatives of uracil, isocyanurate and barbituric acid have been studied using ab initio methods at the local MP2/6-31G** level of theory. The results were compared to similar interactions between the oxygen atom of NMA and the pi-clouds of perfluorobenzene, quinone and trimethyltriazine. The pi-acidic amides of isocyanurate and barbituric acid were found to interact with a hydrogen bond acceptor primarily through electrostatic attractions. These groups may be used as alternatives of a hydrogen bond donor to complement a hydrogen bond acceptor or an anion in molecular recognition and drug design. Examples of such interactions were identified through a search of the CSD database.

  3. 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

    2016-09-01

    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. PMID:27552302

  4. Cooperative luminescence quenching on many-particle acceptors in disordered media

    NASA Astrophysics Data System (ADS)

    Basiev, T. T.; Basieva, I. T.

    2012-06-01

    Many-body cooperative energy transfer is an important process in biology, medicine, photosynthesis, rare-earth-doped laser materials, responsible for up- and down-conversion of energy, optical excitation sensitization and relaxation. We present an analytical solution for long-time asymptotic of static luminescence quenching kinetics due to cooperative energy transfer to ensembles of acceptors comprised of two-, three-, and more particles. For cooperative energy transfer and cooperative luminescence quenching to n-body acceptors we have discovered a new law of power d/(nS-(n-1)d) time dependence (d=1,2,3 is the space dimension, S=6,8,10 is the multipolarty of interaction: dipole-dipole, dipole-quadrupole, or quadrupole-quadrupole). The detailed numerical simulation of cooperative quenching by Monte-Carlo method confirms the theoretical result.

  5. Effects of acceptors on halogenated organic compound biotransformations in a biofilm column

    SciTech Connect

    Cobb, G.D.; Bouwer, E.J. )

    1991-06-01

    The transformability of trihalomethanes, carbon tetrachloride, 1,1,1-trichlorethane, 1,2-dibromomethane, tetrachlorethylene, dibromochloropropane, and chlorinated benzenes was evaluated by a biofilm utilizing a mixture of primary electron acceptors (oxygen, nitrate, and sulfate). These compounds at concentrations commonly found in groundwater were continuously administered for 4 years to a biofilm column reactor that resembled polluted groundwater environments. Acetate was the primary substrate to support microbial growth. Sequential biofilm zones or aerobic respiration, denitrification, and sulfate reduction developed within the column. Transformation of the halogenated aliphatic compounds coincided with the onset of sulfate in the column feed decreased the steady-state removals for several of the halogenated aliphatic compounds. These results suggest that sulfate was an important primary electron acceptor. Aerobic transformations of the chlorinated benzenes were incomplete due to the rapid depletion of oxygen and limited aerobic zone at the column inlet.

  6. Acceptor states in heteroepitaxial CdHgTe films grown by molecular-beam epitaxy

    SciTech Connect

    Mynbaev, K. D.; Shilyaev, A. V. Bazhenov, N. L.; Izhnin, A. I.; Izhnin, I. I.; Mikhailov, N. N.; Varavin, V. S.; Dvoretsky, S. A.

    2015-03-15

    The photoluminescence method is used to study acceptor states in CdHgTe heteroepitaxial films (HEFs) grown by molecular-beam epitaxy. A comparison of the photoluminescence spectra of HEFs grown on GaAs substrates (CdHgTe/GaAs) with the spectra of CdHgTe/Si HEFs demonstrates that acceptor states with energy depths of about 18 and 27 meV are specific to CdHgTe/GaAs HEFs. The possible nature of these states and its relation to the HEF synthesis conditions and, in particular, to the vacancy doping occurring under conditions of a mercury deficiency during the course of epitaxy and postgrowth processing are discussed.

  7. Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

    SciTech Connect

    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, 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.

  8. Evolution of the electron mobility in polymer solar cells with different fullerene acceptors.

    PubMed

    Gao, Dong; Djukic, Brandon; Shi, Weiqing; Bridges, Colin R; Kozycz, Lisa M; Seferos, Dwight S

    2013-08-28

    We investigate the evolution of the electron mobility of two different acceptors, [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) and indene-C60 bisadduct (ICBA), in a poly(3-hexylthiophene) blend solar cell during a prolonged thermal aging process. High electron mobility does not correlate with the best device performance in our study of the P3HT:PC71BM and P3HT:ICBA systems. Very little changes are observed in the polymer crystallinity as a function of time. The evolution of the acceptor appears to be the dominant factor that leads to long-term changes in the device performance. The electron mobility evolves differently in PC71BM and ICBA systems, which highlights the importance of the fullerene molecular structure. PMID:23845022

  9. Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

    SciTech Connect

    Haeggblom, M.M.; Rivera, M.D.; Young, L.Y.

    1993-01-01

    Nitrate, sulfate, and carbonate were used as electron acceptors to examine the anaerobic biodegradability of chlorinated aromatic compounds in estuarine and freshwater sediments. The respective denitrifying, sulfidogenic, and methanogenic enrichment cultures were established on each of the monochlorinated phenol and monochlorinated benzoic acid isomers, using sediment from the upper (freshwater) and lower (estuarine) Hudson River and the East River (estuarine) as source materials. Utilization of each chlorophenol and chlorobenzoate isomer was observed under at least one reducing condition; however, no single reducing condition permitted the metabolism of all six compounds tested. The anaerobic biodegradation of the chlorophenols and chlorobenzoates depended on the electron acceptor available and on the position of the chlorine substituent. In general, similar activities were observed under the different reducing conditions in both the freshwater and estuarine sediments.

  10. Optoelectronic properties and charge transfer in donor-acceptor all-conjugated diblock copolymers.

    SciTech Connect

    Botiz, I.; Schaller, R. D.; Verduzco, R.; Darling, S. B.

    2011-05-12

    All-conjugated block copolymers, which can self-assemble into well-ordered morphologies, provide exciting opportunities to rationally design and control the nanoscale organization of electron-donor and electron-acceptor moieties in optoelectronic active layers. Here we report on the steady-state and time-resolved optical characterization of block copolymer films and solutions containing poly(3-hexylthiophene) as the donor block and poly(9,9-dioctylfluorene) with and without copolymerization with benzothiadiazole as the acceptor block. Transient absorption measurements suggest rapid charge transfer occurs in both systems, with higher efficiency observed in the latter composition. These results indicate that this class of materials has promise in preparing highly ordered bulk heterojunction all-polymer organic photovoltaic devices.

  11. Construction of an upconversion nanoprobe with few-atom silver nanoclusters as the energy acceptor.

    PubMed

    Xiao, Yan; Zeng, Lingyu; Xia, Tian; Wu, Zhengjun; Liu, Zhihong

    2015-04-27

    Herein we report that few-atom silver nanoclusters (Ag NCs) can be effective energy acceptors for upconversion phosphors (UCPs). A luminescence resonance energy transfer (LRET) probe for biothiols was constructed by decorating UCPs with dithiol-stabilized Ag NCs. Owing to the unique properties of ultrasmall NCs, properties which bridge the gap between those of small molecules and those of nanoparticles, the use of approximately 1.9 nm Ag NCs as energy acceptors endows the probe with high energy-transfer efficiency, good biocompatibility, and flexibility. The UCP-Ag NC nanoprobe enables rapid and robust target assay in solutions. It was also uploaded into living cells and used to detect intracellular biothiol levels with high discrimination. Moreover, the probe shows transportability in vivo and can be used for tissue imaging. The facile growth of few-atom metal NCs on diverse templates may enable the development of various nanoprobes combining UCPs and metal NCs.

  12. Donor-acceptor-pair emission in fluorescent 4H-SiC grown by PVT method

    SciTech Connect

    Liu, Xi Zhuo, Shi-Yi; Gao, Pan; Huang, Wei; Yan, Cheng-Feng; Shi, Er-Wei

    2015-04-15

    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 crystal in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.

  13. Synthesis of dithiafulvene-quinone donor-acceptor systems: isolation of a Michael adduct.

    PubMed

    Lissau, Henriette; Jevric, Martyn; Madsen, Anders Østergaard; Nielsen, Mogens Brøndsted

    2015-06-01

    π-Conjugated donor-acceptor systems based on dithiafulvene (DTF) donor units and various acceptor units have attracted attention for their linear and nonlinear optical properties. The reaction between p-benzoquinone and a 1,3-dithiole phosphonium salt, deprotonated by lithium hexamethyldisilazide (LiHMDS), gave a product mixture from which the Michael adduct [systematic name: dimethyl 2-(3-hydroxy-6-oxocyclohexa-2,4-dien-1-ylidene)-2H-1,3-dithiole-4,5-dicarboxylate], C13H10O6S2, was isolated. It is likely that one of the unidentified products obtained previously by others from related reactions could be a similar Michael adduct.

  14. 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.

  15. XeF(2) /fluoride acceptors as versatile one-electron oxidants.

    PubMed

    Poleschner, Helmut; Seppelt, Konrad

    2013-12-01

    No phlogiston but xenon is released when XeF2 /F(-) acceptors act as new one-electron oxidants. F(-) acceptors are Lewis acids BF3 , B(C6 F5 )3 , and Al{OC(CF3 )3 }3 , and silyl derivatives TfOSiMe3 , Tf2 NSiMe3 , Me3 Si(+)  B(C6 F5 )4 (-) , and Me3 Si(+)  CHB11 Cl11 (-) . The anions BF4 (-) , TfO(-) , Tf2 N(-) , FB(C6 F5 )3 (-) , FAl{OC(CF3 )3 }3 (-) , B(C6 F5 )4 (-) , or CHB11 Cl11 (-) can be introduced into oxidation products of R2 E2 (E=S, Se, Te), [FeCp2 ], [(FeCpS)4 ], tetrathiafulvalene, thianthrene, and (2,4-Br2 C6 H3 )3 N. PMID:24127390

  16. Influence of different electron donors and acceptors on dehalorespiration of tetrachloroethene by Desulfitobacterium frappieri TCE1

    SciTech Connect

    Gerritse, J.; Drzyzga, O.; Kloetstra, G.; Keijmel, M.; Wiersum, L.P.; Hutson, R.; Collins, M.D.; Gottschal, J.C.

    1999-12-01

    Strain TCE1, a strictly anaerobic bacterium that can grow by reductive dechlorination of tetrachloroethene (PCE) and trichloroethane (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 {micro}m 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 H{sub 2}, format, 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 format and H{sub 2}) are oxidized to acetate and CO{sub 2}. 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. 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 fumate or nitrate.

  17. 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

  18. 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.

  19. Neutral nitrogen acceptors in ZnO: The {sup 67}Zn hyperfine interactions

    SciTech Connect

    Golden, E. M.; Giles, N. C.; Evans, S. M.; Halliburton, L. E.

    2014-03-14

    Electron paramagnetic resonance (EPR) is used to characterize the {sup 67}Zn hyperfine interactions associated with neutral nitrogen acceptors in zinc oxide. Data are obtained from an n-type bulk crystal grown by the seeded chemical vapor transport method. Singly ionized nitrogen acceptors (N{sup −}) initially present in the crystal are converted to their paramagnetic neutral charge state (N{sup 0}) during exposure at low temperature to 442 or 633 nm laser light. The EPR signals from these N{sup 0} acceptors are best observed near 5 K. Nitrogen substitutes for oxygen ions and has four nearest-neighbor cations. The zinc ion along the [0001] direction is referred to as an axial neighbor and the three equivalent zinc ions in the basal plane are referred to as nonaxial neighbors. For axial neighbors, the {sup 67}Zn hyperfine parameters are A{sub ‖} = 37.0 MHz and A{sub ⊥} = 8.4 MHz with the unique direction being [0001]. For nonaxial neighbors, the {sup 67}Zn parameters are A{sub 1} = 14.5 MHz, A{sub 2} = 18.3 MHz, and A{sub 3} = 20.5 MHz with A{sub 3} along a [101{sup ¯}0] direction (i.e., in the basal plane toward the nitrogen) and A{sub 2} along the [0001] direction. These {sup 67}Zn results and the related {sup 14}N hyperfine parameters provide information about the distribution of unpaired spin density at substitutional neutral nitrogen acceptors in ZnO.

  20. 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

  1. Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends

    PubMed Central

    Zhou, Ye; Han, Su-Ting; Yan, Yan; Zhou, Li; Huang, Long-Biao; Zhuang, Jiaqing; Sonar, Prashant; Roy, V. A. L.

    2015-01-01

    Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices. PMID:26029856

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

    PubMed

    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

  3. 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

  4. Donor-acceptor organo-imido polyoxometalates: high transparency, high activity redox-active NLO chromophores.

    PubMed

    Al-Yasari, Ahmed; Van Steerteghem, Nick; El Moll, Hani; Clays, Koen; Fielden, John

    2016-02-21

    We show that polyoxometalates (POMs) are an excellent redox-active acceptor on which to base high performance 2(nd) order non-linear optical (NLO) chromophores. This is demonstrated through three new organoimido-Lindqvist derivatives with HRS β0-values exceeding those of any dipolar organic system with comparable donor, π-system and absorption profile. Thus, organoimido POMs may provide a new generation of high performance, high transparency, and potentially redox-switchable NLO materials. PMID:26815652

  5. Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

    SciTech Connect

    Haeggblom, M.M.; Rivera, M.D.; Young, L.Y.

    1993-01-01

    Nitrate, sulfate, and carbonate were used as electron acceptors to examine the anaerobic biodegradability of chlorinated aromatic compounds in estuarine and freshwater sediments. The respective denitrifying, sulfidogenic, and methanogenic enrichment cultures were established on each of the monochlorinated phenol and monochlorinated benzoic acid isomers, using sediment from the upper (freshwater) and lower (estuarine) Hudson River and the East River (estuarine) as source materials. (Copyright (c) 1993 American Society for Microbiology.)

  6. Well-defined star-shaped donor-acceptor conjugated molecules for organic resistive memory devices.

    PubMed

    Wu, Hung-Chin; Zhang, Jicheng; Bo, Zhishan; Chen, Wen-Chang

    2015-09-28

    Solution processable star-shaped donor-acceptor (D-A) conjugated molecules (TPA-T-NI and TPA-3T-NI) with an electron-donating triphenylamine (TPA) core, three thienylene or terthienylene spacers, and three 1.8-naphthalimide (NI) electron-withdrawing end-groups are explored for the first time as charge storage materials for resistor-type memory devices owing to the efficient electric charge transfer and trapping.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  9. Well-defined star-shaped donor-acceptor conjugated molecules for organic resistive memory devices.

    PubMed

    Wu, Hung-Chin; Zhang, Jicheng; Bo, Zhishan; Chen, Wen-Chang

    2015-09-28

    Solution processable star-shaped donor-acceptor (D-A) conjugated molecules (TPA-T-NI and TPA-3T-NI) with an electron-donating triphenylamine (TPA) core, three thienylene or terthienylene spacers, and three 1.8-naphthalimide (NI) electron-withdrawing end-groups are explored for the first time as charge storage materials for resistor-type memory devices owing to the efficient electric charge transfer and trapping. PMID:26255879

  10. Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends.

    PubMed

    Zhou, Ye; Han, Su-Ting; Yan, Yan; Zhou, Li; Huang, Long-Biao; Zhuang, Jiaqing; Sonar, Prashant; Roy, V A L

    2015-01-01

    Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices.

  11. Donor-acceptor organo-imido polyoxometalates: high transparency, high activity redox-active NLO chromophores.

    PubMed

    Al-Yasari, Ahmed; Van Steerteghem, Nick; El Moll, Hani; Clays, Koen; Fielden, John

    2016-02-21

    We show that polyoxometalates (POMs) are an excellent redox-active acceptor on which to base high performance 2(nd) order non-linear optical (NLO) chromophores. This is demonstrated through three new organoimido-Lindqvist derivatives with HRS β0-values exceeding those of any dipolar organic system with comparable donor, π-system and absorption profile. Thus, organoimido POMs may provide a new generation of high performance, high transparency, and potentially redox-switchable NLO materials.

  12. Structure and function of the ARH family of ADP-ribose-acceptor hydrolases

    PubMed Central

    Mashimo, Masato; Kato, Jiro; Moss, Joel

    2014-01-01

    ADP-ribosylation is a post-translational protein modification, in which ADP-ribose is transferred from nicotinamide adenine dinucleotide (NAD+) to specific acceptors, thereby altering their activities. The ADP-ribose transfer reactions are divided into mono- and poly-(ADP-ribosyl)ation. Cellular ADP-ribosylation levels are tightly regulated by enzymes that transfer ADP-ribose to acceptor proteins (e.g. ADP-ribosyltransferases, poly-(ADP-ribose) polymerases (PARP)) and those that cleave the linkage between ADP-ribose and acceptor (e.g. ADP-ribosyl-acceptor hydrolases (ARH), poly-(ADP-ribose) glycohydrolases (PARG)), thereby constituting an ADP-ribosylation cycle. This review summarizes current findings related to the ARH family of proteins. This family comprises three members (ARH1-3) with similar size (39 kDa) and amino acid sequence. ARH1 catalyzes the hydrolysis of the N-glycosidic bond of mono-(ADP-ribosyl)ated arginine. ARH3 hydrolyzes poly-(ADP-ribose) (PAR) and O-acetyl-ADP-ribose. The different substrate specificities of ARH1 and ARH3 contribute to their unique roles in the cell. Based on a phenotype analysis of ARH1−/− and ARH3−/− mice, ARH1 is involved in the action by bacterial toxins as well as in tumorigenesis. ARH3 participates in the degradation of PAR that is synthesized by PARP1 in response to oxidative stress-induced DNA damage; this hydrolytic reaction suppresses PAR-mediated cell death, a pathway termed parthanatos. PMID:24746921

  13. Molecular assembly of amino acid interlinked, topologically symmetric, π-complementary donor-acceptor-donor triads.

    PubMed

    Avinash, M B; Sandeepa, K V; Govindaraju, T

    2013-01-01

    Amino acid interlinked pyrene and naphthalenediimide (NDI) based novel donor-acceptor-donor (D-A-D) triads are designed to exploit their topological symmetry and complementary π-character for facile charge-transfer complexation. Consequently, free-floating high-aspect-ratio supercoiled nanofibres and hierarchical helical bundles of triads are realized by modulating the chemical functionality of interlinking amino acids. PMID:23946856

  14. Dynamic combinatorial synthesis of a catenane based on donor–acceptor interactions in water

    PubMed Central

    Au-Yeung, Ho Yu; Pantoş, G. Dan; Sanders, Jeremy K. M.

    2009-01-01

    A new type of neutral donor–acceptor [2]-catenane, containing both complementary units in the same ring was synthesized from a dynamic combinatorial library in water. The yield of the water soluble [2]-catenane is enhanced by increasing either building-block concentrations or ionic strength, or by the addition of an electron-rich template. NMR spectroscopy demonstrates that the template is intercalated between the 2 electron-deficient naphthalenediimide units of the catenane. PMID:19171892

  15. 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.

  16. Influence of defect structure on ferroelectric aging in donor-acceptor hybrid-doped PZT

    NASA Astrophysics Data System (ADS)

    Anil, A.; Vani, K.; Kumar, V.

    2016-06-01

    In the present work, we report the aging effect in manganese (Mn) and niobium (Nb) hybrid-doped PZT composition. Interestingly, it is observed that the ferroelectric aging depends on the acceptor/donor ratio. In hybrid-doped PZT, at high donor dopant concentrations, aging is not observed. The underlying mechanism is correlated with the defect chemistry of the system. It is also observed that tuning the defect chemistry is an effective strategy to realize piezoceramics with enhanced dielectric and piezoelectric characteristics.

  17. Observation of selective plasmon-exciton coupling in nonradiative energy transfer: donor-selective versus acceptor-selective plexcitons.

    PubMed

    Ozel, Tuncay; Hernandez-Martinez, Pedro Ludwig; Mutlugun, Evren; Akin, Onur; Nizamoglu, Sedat; Ozel, Ilkem Ozge; Zhang, Qing; Xiong, Qihua; Demir, Hilmi Volkan

    2013-07-10

    We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Förster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs (i.e., donor-selective) or to only the acceptor QDs (i.e., acceptor-selective). Using layer-by-layer assembled colloidal QD nanocrystal solids with metal nanoparticles integrated at carefully designed spacing, we demonstrate the ability to enable/disable the coupled plasmon-exciton (plexciton) formation distinctly at the donor (exciton departing) site or at the acceptor (exciton feeding) site of our choice, while not hindering the donor exciton-acceptor exciton interaction but refraining from simultaneous coupling to both sites of the donor and the acceptor in the FRET process. In the case of donor-selective plexciton, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors, both of which shorten the donor lifetime. This consequently enhanced the acceptor emission by a factor of 1.93. On the other hand, in the complementary case of acceptor-selective plexciton we observed a 2.70-fold emission enhancement in the acceptor QDs, larger than the acceptor emission enhancement of the donor-selective plexciton, as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Here we present the comparative results of theoretical modeling of the donor- and acceptor-selective plexcitons of nonradiative energy transfer developed here for the first time, which are in excellent agreement with the systematic experimental characterization. Such an ability to modify and control energy transfer through mastering plexcitons is of fundamental importance, opening up new applications for quantum dot embedded plexciton devices along with the development of new

  18. Observation of selective plasmon-exciton coupling in nonradiative energy transfer: donor-selective versus acceptor-selective plexcitons.

    PubMed

    Ozel, Tuncay; Hernandez-Martinez, Pedro Ludwig; Mutlugun, Evren; Akin, Onur; Nizamoglu, Sedat; Ozel, Ilkem Ozge; Zhang, Qing; Xiong, Qihua; Demir, Hilmi Volkan

    2013-07-10

    We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Förster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs (i.e., donor-selective) or to only the acceptor QDs (i.e., acceptor-selective). Using layer-by-layer assembled colloidal QD nanocrystal solids with metal nanoparticles integrated at carefully designed spacing, we demonstrate the ability to enable/disable the coupled plasmon-exciton (plexciton) formation distinctly at the donor (exciton departing) site or at the acceptor (exciton feeding) site of our choice, while not hindering the donor exciton-acceptor exciton interaction but refraining from simultaneous coupling to both sites of the donor and the acceptor in the FRET process. In the case of donor-selective plexciton, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors, both of which shorten the donor lifetime. This consequently enhanced the acceptor emission by a factor of 1.93. On the other hand, in the complementary case of acceptor-selective plexciton we observed a 2.70-fold emission enhancement in the acceptor QDs, larger than the acceptor emission enhancement of the donor-selective plexciton, as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Here we present the comparative results of theoretical modeling of the donor- and acceptor-selective plexcitons of nonradiative energy transfer developed here for the first time, which are in excellent agreement with the systematic experimental characterization. Such an ability to modify and control energy transfer through mastering plexcitons is of fundamental importance, opening up new applications for quantum dot embedded plexciton devices along with the development of new

  19. Design of Reversible, Cysteine-Targeted Michael Acceptors Guided by Kinetic and Computational Analysis

    PubMed Central

    2015-01-01

    Electrophilic probes that covalently modify a cysteine thiol often show enhanced pharmacological potency and selectivity. Although reversible Michael acceptors have been reported, the structural requirements for reversibility are poorly understood. Here, we report a novel class of acrylonitrile-based Michael acceptors, activated by aryl or heteroaryl electron-withdrawing groups. We demonstrate that thiol adducts of these acrylonitriles undergo β-elimination at rates that span more than 3 orders of magnitude. These rates correlate inversely with the computed proton affinity of the corresponding carbanions, enabling the intrinsic reversibility of the thiol-Michael reaction to be tuned in a predictable manner. We apply these principles to the design of new reversible covalent kinase inhibitors with improved properties. A cocrystal structure of one such inhibitor reveals specific noncovalent interactions between the 1,2,4-triazole activating group and the kinase. Our experimental and computational study enables the design of new Michael acceptors, expanding the palette of reversible, cysteine-targeted electrophiles. PMID:25153195

  20. tRNA acceptor-stem and anticodon bases embed separate features of amino acid chemistry.

    PubMed

    Carter, Charles W; Wolfenden, Richard

    2016-01-01

    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.