Sample records for electron acceptor sulfate

  1. 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

  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. Biogenic hydroxysulfate green rust, a potential electron acceptor for SRB activity

    NASA Astrophysics Data System (ADS)

    Zegeye, Asfaw; Huguet, Lucie; Abdelmoula, Mustapha; Carteret, Cédric; Mullet, Martine; Jorand, Frédéric

    2007-11-01

    Microbiological reduction of a biogenic sulfated green rust (GR2(SO42-)), was examined using a sulfate reducing bacterium ( Desulfovibrio alaskensis). Experiments investigated whether GR2(SO42-) could serve as a sulfate source for D. alaskensis anaerobic respiration by analyzing mineral transformation. Batch experiments were conducted using lactate as the electron donor and biogenic GR2(SO42-) as the electron acceptor, at circumneutral pH in unbuffered medium. GR2(SO42-) transformation was monitored with time by X-ray diffraction (XRD), Transmission Mössbauer Spectroscopy (TMS), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The reduction of sulfate anions and the formation of iron sulfur mineral were clearly identified by XPS analyses. TMS showed the formation of additional mineral as green rust (GR) and vivianite. XRD analyses discriminated the type of the newly formed GR as GR1. The formed GR1 was GR1(CO32-) as indicated by DRIFTS analysis. Thus, the results presented in this study indicate that D. alaskensis cells were able to use GR2(SO42-) as an electron acceptor. GR1(CO32-), vivianite and an iron sulfur compound were formed as a result of GR2(SO42-) reduction by D. alaskensis. Hence, in environments where geochemical conditions promote biogenic GR2(SO42-) formation, this mineral could stimulate the anaerobic respiration of sulfate reducing bacteria.

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

    USGS Publications Warehouse

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

    1994-01-01

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

  5. 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

  6. Artificial electron acceptors decouple archaeal methane oxidation from sulfate reduction.

    PubMed

    Scheller, Silvan; Yu, Hang; Chadwick, Grayson L; McGlynn, Shawn E; Orphan, Victoria J

    2016-02-12

    The oxidation of methane with sulfate is an important microbial metabolism in the global carbon cycle. In marine methane seeps, this process is mediated by consortia of anaerobic methanotrophic archaea (ANME) that live in syntrophy with sulfate-reducing bacteria (SRB). The underlying interdependencies within this uncultured symbiotic partnership are poorly understood. We used a combination of rate measurements and single-cell stable isotope probing to demonstrate that ANME in deep-sea sediments can be catabolically and anabolically decoupled from their syntrophic SRB partners using soluble artificial oxidants. The ANME still sustain high rates of methane oxidation in the absence of sulfate as the terminal oxidant, lending support to the hypothesis that interspecies extracellular electron transfer is the syntrophic mechanism for the anaerobic oxidation of methane. Copyright © 2016, American Association for the Advancement of Science.

  7. Non-fullerene electron acceptors for organic photovoltaic devices

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

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

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

  8. 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.

  9. Electron acceptors for anaerobic oxidation of methane drive microbial community structure and diversity in mud volcanoes.

    PubMed

    Ren, Ge; Ma, Anzhou; Zhang, Yanfen; Deng, Ye; Zheng, Guodong; Zhuang, Xuliang; Zhuang, Guoqiang; Fortin, Danielle

    2018-04-06

    Mud volcanoes (MVs) emit globally significant quantities of methane into the atmosphere, however, methane cycling in such environments is not yet fully understood, as the roles of microbes and their associated biogeochemical processes have been largely overlooked. Here, we used data from high-throughput sequencing of microbial 16S rRNA gene amplicons from six MVs in the Junggar Basin in northwest China to quantify patterns of diversity and characterize the community structure of archaea and bacteria. We found anaerobic methanotrophs and diverse sulfate- and iron-reducing microbes in all of the samples, and the diversity of both archaeal and bacterial communities was strongly linked to the concentrations of sulfate, iron and nitrate, which could act as electron acceptors in anaerobic oxidation of methane (AOM). The impacts of sulfate/iron/nitrate on AOM in the MVs were verified by microcosm experiments. Further, two representative MVs were selected to explore the microbial interactions based on phylogenetic molecular ecological networks. The sites showed distinct network structures, key species and microbial interactions, with more complex and numerous linkages between methane-cycling microbes and their partners being observed in the iron/sulfate-rich MV. These findings suggest that electron acceptors are important factors driving the structure of microbial communities in these methane-rich environments. © 2018 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.

  10. 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.

  11. Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

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

    Haeggblom, M.M.; Rivera, M.D.; Young, L.Y.

    1993-04-01

    Methanogeneic conditions can promote the biodegradation of a number of halogenated aromatic compounds. This study, using sediments from freshwater and estuarine sites, is an evaluation of the anaerobic biodegradability of monochlorinated phenols and benzoic acids coupled to denitrification, sulfidogenesis, and methanogenesis. The results indicate that chlorinated phenols and benzoic acids are biodegradable under at least one set of anaerobic conditions. Metabolism depends both on the electron acceptor available and on the position of the chlorine substituent. Presence of alternative electron acceptors, nitrate, sulfate, and carbonate, can affect degradation rates and substrate specificities. Since contaminated sites usually have mixtures of wastes,more » bioremediation efforts may need to consider the activities of diverse anaerobic communities to carry out effective treatment of all components. 37 refs., 4 figs., 4 tabs.« less

  12. Impact of electron acceptor availability on the anaerobic oxidation of methane in coastal freshwater and brackish wetland sediments

    NASA Astrophysics Data System (ADS)

    Segarra, Katherine E. A.; Comerford, Christopher; Slaughter, Julia; Joye, Samantha B.

    2013-08-01

    Methane, a powerful greenhouse gas, is both produced and consumed in anoxic coastal sediments via microbial processes. Although the anaerobic oxidation of methane (AOM) is almost certainly an important process in coastal freshwater and salt marsh sediments, the factors that control the rates and pathways of AOM in these habitats are poorly understood. Here, we present the first direct measurements of AOM activity in freshwater (0 PSU) and brackish (25 PSU) wetland sediments. Despite disparate sulfate concentrations, both environments supported substantial rates of AOM. Higher sulfate reduction (SR) rates were measured in the freshwater site and SR at both sites was of sufficient magnitude to support the observed AOM activity. Laboratory incubations of freshwater and brackish tidal, wetland sediments amended with either nothing [control], sulfate, nitrate, manganese oxide (birnessite) or iron oxide (ferrihydrite) and supplied with a methane headspace were used to evaluate the impact(s) of electron acceptor availability on potential AOM rates. Maximum AOM rates in brackish slurries occurred in the sulfate amendments. In contrast, addition of sulfate and several possible electron acceptors to the freshwater slurries decreased AOM rates relative to the control. High ratios of AOM activity relative to SR activity in the nitrate, birnessite, and ferrihydrite treatments of both the brackish and freshwater slurries provided evidence of AOM decoupled from SR. This study demonstrates that both freshwater and brackish coastal wetland sediments support considerable rates of anaerobic methanotrophy and provides evidence for sulfate-independent AOM that may be coupled to nitrate, iron, or manganese reduction in both environments.

  13. An Overview of Electron Acceptors in Microbial Fuel Cells

    PubMed Central

    Ucar, Deniz; Zhang, Yifeng; Angelidaki, Irini

    2017-01-01

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

  14. Benzene oxidation coupled to sulfate reduction

    USGS Publications Warehouse

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

    1995-01-01

    Highly reduced sediments from San Diego Bay, Calif., that were incubated under strictly anaerobic conditions metabolized benzene within 55 days when they were exposed initially to I ??M benzene. The rate of benzene metabolism increased as benzene was added back to the benzene-adapted sediments. When a [14C]benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as 14CO2. Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of 14CO2 from [14C]benzene. Benzene metabolism stopped when the sediments became sulfate depleted, and benzene uptake resumed when sulfate was added again. The stoichiometry of benzene uptake and sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for benzene oxidation. Isotope trapping experiments performed with [14C]benzene revealed that there was no production of such potential extracellular intermediates of benzene oxidation as phenol, benzoate, p-hydroxybenzoate, cyclohexane, catechol, and acetate. The results demonstrate that benzene can be oxidized in the absence of O2, with sulfate serving as the electron acceptor, and suggest that some sulfate reducers are capable of completely oxidizing benzene to carbon dioxide without the production of extracellular intermediates. Although anaerobic benzene oxidation coupled to chelated Fe(III) has been documented previously, the study reported here provides the first example of a natural sediment compound that can serve as an electron acceptor for anaerobic benzene oxidation.

  15. Understanding the response of Desulfovibrio desulfuricans ATCC 27774 to the electron acceptors nitrate and sulfate - biosynthetic costs modulate substrate selection.

    PubMed

    Sousa, Joana R; Silveira, Célia M; Fontes, Pedro; Roma-Rodrigues, Catarina; Fernandes, Alexandra R; Van Driessche, Gonzalez; Devreese, Bart; Moura, Isabel; Moura, José J G; Almeida, M Gabriela

    2017-11-01

    Sulfate-reducing bacteria (SRB) are a diverse group of anaerobic microorganisms that obtain their energy from dissimilatory sulfate reduction. Some SRB species have high respiratory versatility due to the possible use of alternative electron acceptors. A good example is Desulfovibrio desulfuricans ATCC 27774, which grows in the presence of nitrate (end product: ammonium) with higher rates and yields to those observed in sulfate containing medium (end product: sulfide). In this work, the mechanisms supporting the respiratory versatility of D. desulfuricans were unraveled through the analysis of the proteome of the bacterium under different experimental conditions. The most remarkable difference in the two-dimensional gel electrophoresis maps is the high number of spots exclusively represented in the nitrate medium. Most of the proteins with increase abundance are involved in the energy metabolism and the biosynthesis of amino acids (or proteins), especially those participating in ammonium assimilation processes. qPCR analysis performed during different stages of the bacterium's growth showed that the genes involved in nitrate and nitrite reduction (napA and nrfA, respectively) have different expressions profiles: while napA did not vary significantly, nrfA was highly expressed at a 6h time point. Nitrite levels measured along the growth curve revealed a peak at 3h. Thus, the initial consumption of nitrate and concomitant production of nitrite must induce nrfA expression. The activation of alternative mechanisms for energy production, aside several N-assimilation metabolisms and detoxification processes, solves potential survival problems in adapting to different environments and contributes to higher bacterial growth rates. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. Total electron acceptor loading and composition affect hexavalent uranium reduction and microbial community structure in a membrane biofilm reactor.

    PubMed

    Ontiveros-Valencia, Aura; Zhou, Chen; Ilhan, Zehra Esra; de Saint Cyr, Louis Cornette; Krajmalnik-Brown, Rosa; Rittmann, Bruce E

    2017-11-15

    Molecular microbiology tools (i.e., 16S rDNA gene sequencing) were employed to elucidate changes in the microbial community structure according to the total electron acceptor loading (controlled by influent flow rate and/or medium composition) in a H 2 -based membrane biofilm reactor evaluated for removal of hexavalent uranium. Once nitrate, sulfate, and dissolved oxygen were replaced by U(VI) and bicarbonate and the total acceptor loading was lowered, slow-growing bacteria capable of reducing U(VI) to U(IV) dominated in the biofilm community: Replacing denitrifying bacteria Rhodocyclales and Burkholderiales were spore-producing Clostridiales and Natranaerobiales. Though potentially competing for electrons with U(VI) reducers, homo-acetogens helped attain steady U(VI) reduction, while methanogenesis inhibited U(VI) reduction. U(VI) reduction was reinstated through suppression of methanogenesis by addition of bromoethanesulfonate or by competition from SRB when sulfate was re-introduced. Predictive metagenome analysis further points out community changes in response to alterations in the electron-acceptor loading: Sporulation and homo-acetogenesis were critical factors for strengthening stable microbial U(VI) reduction. This study documents that sporulation was important to long-term U(VI) reduction, whether or not microorganisms that carry out U(VI) reduction mediated by cytochrome c 3 , such as SRB and ferric-iron-reducers, were inhibited. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

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

    Haeggblom, M.M.; Rivera, M.D.; Young, L.Y.

    1993-01-01

    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.)

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

    PubMed

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

    2018-05-15

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

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

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

    Zhang, T; Bain, TS; Barlett, MA

    2014-01-02

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

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

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

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

    2000-04-06

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

  1. Effect of sulfate on anaerobic reduction of nitrobenzene with acetate or propionate as an electron donor.

    PubMed

    Huang, Jingang; Wen, Yue; Ding, Ning; Xu, Yue; Zhou, Qi

    2012-09-15

    Sulfate is frequently found in wastewaters that contain nitrobenzene. To reveal the effect of sulfate on the reductive transformation of nitrobenzene to aniline--with acetate or propionate as potential electron donors in anaerobic systems--an acetate series (R1-R5) and a propionate series (R6-R10) were set up. Each of these was comprised of five laboratory-scale sequence batch reactors. The two series were amended with the same amount of nitrobenzene and electron donor electron equivalents, whereas with increasing sulfate concentrations. Results indicated that the presence of sulfate could depress nitrobenzene reduction. Such depression is linked to the inhibition of nitroreductase activity and/or the shift of electron flow. In the acetate series, although sulfate did not strongly compete with nitrobenzene for electron donors, noncompetitive inhibition of specific nitrobenzene reduction rates by sulfate was observed, with an inhibition constant of 0.40 mM. Propionate, which can produce intermediate H₂ as preferred reducing equivalent, is a more effective primary electron donor for nitrobenzene reduction as compared to acetate. In the propionate series, sulfate was found to be a preferential electron acceptor as compared to nitrobenzene, resulting in a quick depletion of propionate and then a likely termination of H₂-releasing under higher sulfate concentrations (R9 and R10). In such a situation, nitrobenzene reduction slowed down, occurring two-stage zero-order kinetics. Copyright © 2012 Elsevier Ltd. All rights reserved.

  2. SULFATE-REDUCING BACTERIA IN THE SEAGRASS RHIZOSPHERE

    EPA Science Inventory

    Seagrasses are rooted in anoxic sediments that support high levels of microbial activity including utilization of sulfate as a terminal electron acceptor which is reduced to sulfide. Sulfate reduction in seagrass bed sediments is stimulated by input of organic carbon through the ...

  3. 2012 Gordon Research Conference, Electron donor-acceptor interactions, August 5-10 2012

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

    McCusker, James

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

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

    PubMed Central

    2015-01-01

    Conspectus The active layer in a solution processed organic photovoltaic device comprises a light absorbing electron donor semiconductor, typically a polymer, and an electron accepting fullerene acceptor. Although there has been huge effort targeted to optimize the absorbing, energetic, and transport properties of the donor material, fullerenes remain as the exclusive electron acceptor in all high performance devices. Very recently, some new non-fullerene acceptors have been demonstrated to outperform fullerenes in comparative devices. This Account describes this progress, discussing molecular design considerations and the structure–property relationships that are emerging. The motivation to replace fullerene acceptors stems from their synthetic inflexibility, leading to constraints in manipulating frontier energy levels, as well as poor absorption in the solar spectrum range, and an inherent tendency to undergo postfabrication crystallization, resulting in device instability. New acceptors have to address these limitations, providing tunable absorption with high extinction coefficients, thus contributing to device photocurrent. The ability to vary and optimize the lowest unoccupied molecular orbital (LUMO) energy level for a specific donor polymer is also an important requirement, ensuring minimal energy loss on electron transfer and as high an internal voltage as possible. Initially perylene diimide acceptors were evaluated as promising acceptor materials. These electron deficient aromatic molecules can exhibit good electron transport, facilitated by close packed herringbone crystal motifs, and their energy levels can be synthetically tuned. The principal drawback of this class of materials, their tendency to crystallize on too large a length scale for an optimal heterojunction nanostructure, has been shown to be overcome through introduction of conformation twisting through steric effects. This has been primarily achieved by coupling two units together

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

    DOE PAGES

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

    2015-09-18

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

  6. 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.

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

    PubMed Central

    Meganathan, R; Schrementi, J

    1987-01-01

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

  8. Nitrate reduction in sulfate-reducing bacteria.

    PubMed

    Marietou, Angeliki

    2016-08-01

    Sulfate-reducing bacteria (SRBs) gain their energy by coupling the oxidation of organic substrate to the reduction of sulfate to sulfide. Several SRBs are able to use alternative terminal electron acceptors to sulfate such as nitrate. Nitrate-reducing SRBs have been isolated from a diverse range of environments. In order to be able to understand the significance of nitrate reduction in SRBs, we need to examine the ecology and physiology of the nitrate-reducing SRB isolates. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  9. The electronic properties of SWNTs intercalated by electron acceptors

    NASA Astrophysics Data System (ADS)

    Chernysheva, M. V.; Kiseleva, E. A.; Verbitskii, N. I.; Eliseev, A. A.; Lukashin, A. V.; Tretyakov, Yu. D.; Savilov, S. V.; Kiselev, N. A.; Zhigalina, O. M.; Kumskov, A. S.; Krestinin, A. V.; Hutchison, J. L.

    2008-05-01

    Here we report synthesis of Chal@SWNT nanocomposites (where Chal=S, Se and Te) and the impact of the intercalated electron-acceptor compounds on the electronic properties of SWNTs. The chalcogens were introduced to the channels of single-walled carbon nanotubes by molten media technique via impregnation of pre-opened SWNTs with melted guest compounds in vacuum. HRTEM imaging confirms the filling of nanotube channels by continuous nanostructures of corresponding chalcogens. The strong influence of incorporated matter on the electronic properties of the SWNTs was detected by Raman spectroscopy.

  10. Anaerobic oxidation of methane associated with sulfate reduction in a natural freshwater gas source

    PubMed Central

    Timmers, Peer HA; Suarez-Zuluaga, Diego A; van Rossem, Minke; Diender, Martijn; Stams, Alfons JM; Plugge, Caroline M

    2016-01-01

    The occurrence of anaerobic oxidation of methane (AOM) and trace methane oxidation (TMO) was investigated in a freshwater natural gas source. Sediment samples were taken and analyzed for potential electron acceptors coupled to AOM. Long-term incubations with 13C-labeled CH4 (13CH4) and different electron acceptors showed that both AOM and TMO occurred. In most conditions, 13C-labeled CO2 (13CO2) simultaneously increased with methane formation, which is typical for TMO. In the presence of nitrate, neither methane formation nor methane oxidation occurred. Net AOM was measured only with sulfate as electron acceptor. Here, sulfide production occurred simultaneously with 13CO2 production and no methanogenesis occurred, excluding TMO as a possible source for 13CO2 production from 13CH4. Archaeal 16S rRNA gene analysis showed the highest presence of ANME-2a/b (ANaerobic MEthane oxidizing archaea) and AAA (AOM Associated Archaea) sequences in the incubations with methane and sulfate as compared with only methane addition. Higher abundance of ANME-2a/b in incubations with methane and sulfate as compared with only sulfate addition was shown by qPCR analysis. Bacterial 16S rRNA gene analysis showed the presence of sulfate-reducing bacteria belonging to SEEP-SRB1. This is the first report that explicitly shows that AOM is associated with sulfate reduction in an enrichment culture of ANME-2a/b and AAA methanotrophs and SEEP-SRB1 sulfate reducers from a low-saline environment. PMID:26636551

  11. Fraction of Electrons Consumed in Electron Acceptor Reduction and Hydrogen Thresholds as Indicators of Halorespiratory Physiology

    PubMed Central

    Löffler, Frank E.; Tiedje, James M.; Sanford, Robert A.

    1999-01-01

    Measurements of the hydrogen consumption threshold and the tracking of electrons transferred to the chlorinated electron acceptor (fe) reliably detected chlororespiratory physiology in both mixed cultures and pure cultures capable of using tetrachloroethene, cis-1,2-dichloroethene, vinyl chloride, 2-chlorophenol, 3-chlorobenzoate, 3-chloro-4-hydroxybenzoate, or 1,2-dichloropropane as an electron acceptor. Hydrogen was consumed to significantly lower threshold concentrations of less than 0.4 ppmv compared with the values obtained for the same cultures without a chlorinated compound as an electron acceptor. The fe values ranged from 0.63 to 0.7, values which are in good agreement with theoretical calculations based on the thermodynamics of reductive dechlorination as the terminal electron-accepting process. In contrast, a mixed methanogenic culture that cometabolized 3-chlorophenol exhibited a significantly lower fe value, 0.012. PMID:10473415

  12. A novel aerobic sulfate reduction process in landfill mineralized refuse.

    PubMed

    Liu, Weijia; Long, Yuyang; Fang, Yuan; Ying, Luyao; Shen, Dongsheng

    2018-05-08

    It is thought that mineralized refuse could be excavated from almost-full landfill sites to provide space for the increasing burden of municipal solid waste. When excavating, however, the H 2 S emissions from the mineralized waste need to be considered carefully. In an attempt to understand how H 2 S emissions might change during this excavation process, we carried out a series of tests, including exposing anaerobic mineralized refuse to oxygen, isolating and determining possible functional bacteria, and characterizing the electron donors and/or acceptors. The results showed that H 2 S would be released when landfill mineralized refuse was exposed to oxygen (O 2 ), and could reach concentrations of 6 mg m -3 , which was 3 times the concentrations of H 2 S released from anaerobic mineralized refuse. Sulfur-metabolized microorganisms accounted for only 0.5% of the microbial functional bacteria (MFB) derived from the mineralized refuse when exposed to O 2 for 60 days, and SRB were not present. The MFB maintained H 2 S production by aerobic sulfate reduction using SO 4 2- and S 2 O 3 2- as electron acceptors, and sulfate-reducing rates of 16% and 55%, respectively, were achieved. Lactate and S 2 O 3 2- were the preferred electron donor and acceptor, respectively. By enhancing the carbon source and electron transfer, MFB may undergo strong aerobic sulfate reduction even at low abundances of sulfur-metabolized microorganisms. Copyright © 2018 Elsevier B.V. All rights reserved.

  13. The bioenergetics mechanisms and applications of sulfate-reducing bacteria in remediation of pollutants in drainage: A review.

    PubMed

    Li, Xin; Lan, Shi-Ming; Zhu, Zhong-Ping; Zhang, Chang; Zeng, Guang-Ming; Liu, Yun-Guo; Cao, Wei-Cheng; Song, Biao; Yang, Hong; Wang, Sheng-Fan; Wu, Shao-Hua

    2018-04-20

    Sulfate-reducing bacteria (SRB), a group of anaerobic prokaryotes, can use sulfur species as a terminal electron acceptor for the oxidation of organic compounds. They not only have significant ecological functions, but also play an important role in bioremediation of contaminated sites. Although numerous studies on metabolism and applications of SRB have been conducted, they still remain incompletely understood and even controversial. Fully understanding the metabolism of SRB paves the way for allowing the microorganisms to provide more beneficial services in bioremediation. Here we review progress in bioenergetics mechanisms and application of SRB including: (1) electron acceptors and donors for SRB; (2) pathway for sulfate reduction; (3) electron transfer in sulfate reduction; (4) application of SRB for economical and concomitant treatment of heavy metal, organic contaminants and sulfates. Moreover, current knowledge gaps and further research needs are identified. Copyright © 2018 Elsevier Inc. All rights reserved.

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

    PubMed

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

    2015-08-27

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

  15. 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.

  16. Diversity and degradation mechanism of an anaerobic bacterial community treating phenolic wastewater with sulfate as an electron acceptor.

    PubMed

    Guo, X J; Lu, Z Y; Wang, P; Li, H; Huang, Z Z; Lin, K F; Liu, Y D

    2015-10-01

    Petrochemical wastewater often contains high concentrations of phenol and sulfate that must be properly treated to meet discharge standards. This study acclimated anaerobic-activated sludge to treat saline phenolic wastewater with sulfate reduction and clarified the diversity and degradation mechanism of the microbial community. The active sludge in an upflow anaerobic sludge blanket (UASB) reactor could remove 90 % of phenol and maintain the effluent concentration of SO4 (2-) below 400 mg/L. Cloning and sequencing showed that Clostridium spp. and Desulfotomaculum spp. were major phenol-degrading bacteria. Phenol was probably degraded through the carboxylation pathway and sulfate reduction catalyzed by adenosine-5'-phosphosulfate (APS) reductase and dissimilatory sulfite reductase (DSR). A real-time polymerase chain reaction (RT-PCR) showed that as phenol concentration increased, the quantities of 16S rRNA gene, dsrB, and mcrA in the sludge all decreased. The relative abundance of dsrB dropped to 12.46 %, while that of mcrA increased to 56.18 %. The change in the electron flow ratio suggested that the chemical oxygen demand (COD) was removed mainly by sulfate-reducing bacteria under a phenol concentration of 420 mg/L, whereas it was removed mainly by methanogens above 630 mg/L.

  17. Impact of Organic Carbon Electron Donors on Microbial Community Development under Iron- and Sulfate-Reducing Conditions

    DOE PAGES

    Kwon, Man Jae; O’Loughlin, Edward J.; Boyanov, Maxim I.; ...

    2016-01-22

    Although iron- and sulfate-reducing bacteria in subsurface environments have crucial roles in biogeochemical cycling of C, Fe, and S, how specific electron donors impact the compositional structure and activity of native iron- and/or sulfate-reducing communities is largely unknown. To understand this better, we created bicarbonate-buffered batch systems in duplicate with three different electron donors (acetate, lactate, or glucose) paired with ferrihydrite and sulfate as the electron acceptors and inoculated them with subsurface sediment as the microbial inoculum. Sulfate and ferrihydrite reduction occurred simultaneously and were faster with lactate than with acetate. 16S rRNA-based sequence analysis of the communities over timemore » revealed that Desulfotomaculum was the major driver for sulfate reduction coupled with propionate oxidation in lactate-amended incubations. The reduction of sulfate resulted in sulfide production and subsequent abiotic reduction of ferrihydrite. In contrast, glucose promoted faster reduction of ferrihydrite, but without reduction of sulfate. Interestingly, the glucose-amended incubations led to two different biogeochemical trajectories among replicate bottles that resulted in distinct coloration (white and brown). The two outcomes in geochemical evolution might be due to the stochastic evolution of the microbial communities or subtle differences in the initial composition of the fermenting microbial community and its development via the use of different glucose fermentation pathways available within the community. Synchrotron-based x-ray analysis indicated that siderite and amorphous Fe(II) were formed in the replicate bottles with glucose, while ferrous sulfide and vivianite were formed with lactate or acetate. As a result, these data sets reveal that use of different C utilization pathways projects significant changes in microbial community composition over time that uniquely impact both the geochemistry and mineralogy of

  18. Impact of Organic Carbon Electron Donors on Microbial Community Development under Iron- and Sulfate-Reducing Conditions

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

    Kwon, Man Jae; O’Loughlin, Edward J.; Boyanov, Maxim I.

    Although iron- and sulfate-reducing bacteria in subsurface environments have crucial roles in biogeochemical cycling of C, Fe, and S, how specific electron donors impact the compositional structure and activity of native iron- and/or sulfate-reducing communities is largely unknown. To understand this better, we created bicarbonate-buffered batch systems in duplicate with three different electron donors (acetate, lactate, or glucose) paired with ferrihydrite and sulfate as the electron acceptors and inoculated them with subsurface sediment as the microbial inoculum. Sulfate and ferrihydrite reduction occurred simultaneously and were faster with lactate than with acetate. 16S rRNA-based sequence analysis of the communities over timemore » revealed that Desulfotomaculum was the major driver for sulfate reduction coupled with propionate oxidation in lactate-amended incubations. The reduction of sulfate resulted in sulfide production and subsequent abiotic reduction of ferrihydrite. In contrast, glucose promoted faster reduction of ferrihydrite, but without reduction of sulfate. Interestingly, the glucose-amended incubations led to two different biogeochemical trajectories among replicate bottles that resulted in distinct coloration (white and brown). The two outcomes in geochemical evolution might be due to the stochastic evolution of the microbial communities or subtle differences in the initial composition of the fermenting microbial community and its development via the use of different glucose fermentation pathways available within the community. Synchrotron-based x-ray analysis indicated that siderite and amorphous Fe(II) were formed in the replicate bottles with glucose, while ferrous sulfide and vivianite were formed with lactate or acetate. As a result, these data sets reveal that use of different C utilization pathways projects significant changes in microbial community composition over time that uniquely impact both the geochemistry and mineralogy of

  19. Impact of Organic Carbon Electron Donors on Microbial Community Development under Iron- and Sulfate-Reducing Conditions.

    PubMed

    Kwon, Man Jae; O'Loughlin, Edward J; Boyanov, Maxim I; Brulc, Jennifer M; Johnston, Eric R; Kemner, Kenneth M; Antonopoulos, Dionysios A

    2016-01-01

    Although iron- and sulfate-reducing bacteria in subsurface environments have crucial roles in biogeochemical cycling of C, Fe, and S, how specific electron donors impact the compositional structure and activity of native iron- and/or sulfate-reducing communities is largely unknown. To understand this better, we created bicarbonate-buffered batch systems in duplicate with three different electron donors (acetate, lactate, or glucose) paired with ferrihydrite and sulfate as the electron acceptors and inoculated them with subsurface sediment as the microbial inoculum. Sulfate and ferrihydrite reduction occurred simultaneously and were faster with lactate than with acetate. 16S rRNA-based sequence analysis of the communities over time revealed that Desulfotomaculum was the major driver for sulfate reduction coupled with propionate oxidation in lactate-amended incubations. The reduction of sulfate resulted in sulfide production and subsequent abiotic reduction of ferrihydrite. In contrast, glucose promoted faster reduction of ferrihydrite, but without reduction of sulfate. Interestingly, the glucose-amended incubations led to two different biogeochemical trajectories among replicate bottles that resulted in distinct coloration (white and brown). The two outcomes in geochemical evolution might be due to the stochastic evolution of the microbial communities or subtle differences in the initial composition of the fermenting microbial community and its development via the use of different glucose fermentation pathways available within the community. Synchrotron-based x-ray analysis indicated that siderite and amorphous Fe(II) were formed in the replicate bottles with glucose, while ferrous sulfide and vivianite were formed with lactate or acetate. These data sets reveal that use of different C utilization pathways projects significant changes in microbial community composition over time that uniquely impact both the geochemistry and mineralogy of subsurface environments.

  20. 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.

  1. 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

  2. An Electron-Deficient Building Block Based on the B←N Unit: An Electron Acceptor for All-Polymer Solar Cells.

    PubMed

    Dou, Chuandong; Long, Xiaojing; Ding, Zicheng; Xie, Zhiyuan; Liu, Jun; Wang, Lixiang

    2016-01-22

    A double B←N bridged bipyridyl (BNBP) is a novel electron-deficient building block for polymer electron acceptors in all-polymer solar cells. The B←N bridging units endow BNBP with fixed planar configuration and low-lying LUMO/HOMO energy levels. As a result, the polymer based on BNBP units (P-BNBP-T) exhibits high electron mobility, low-lying LUMO/HOMO energy levels, and strong absorbance in the visible region, which is desirable for polymer electron acceptors. Preliminary all-polymer solar cell (all-PSC) devices with P-BNBP-T as the electron acceptor and PTB7 as the electron donor exhibit a power conversion efficiency (PCE) of 3.38%, which is among the highest values of all-PSCs with PTB7 as the electron donor. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. COMPARISON OF HYDROGEN CONCENTRATIONS IN PCE-DEHALOGENATING AND SULFATE-REDUCING ESTUARINE SEDIMENTS

    EPA Science Inventory

    The primary transformation pathway for PCE in anoxic environments is through sequential reductive dehalogenation, and information concerning dehalogenation processes that occur in environments containing alternative electron acceptors (sulfate) is limited. Hydrogen is postulated ...

  4. 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

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

    PubMed

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

    2018-01-01

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

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

    PubMed Central

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

    2018-01-01

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

  7. Ultrafast above-threshold dynamics of the radical anion of a prototypical quinone electron-acceptor.

    PubMed

    Horke, Daniel A; Li, Quansong; Blancafort, Lluís; Verlet, Jan R R

    2013-08-01

    Quinones feature prominently as electron acceptors in nature. Their electron-transfer reactions are often highly exergonic, for which Marcus theory predicts reduced electron-transfer rates because of a free-energy barrier that occurs in the inverted region. However, the electron-transfer kinetics that involve quinones can appear barrierless. Here, we consider the intrinsic properties of the para-benzoquinone radical anion, which serves as the prototypical electron-transfer reaction product involving a quinone-based acceptor. Using time-resolved photoelectron spectroscopy and ab initio calculations, we show that excitation at 400 and 480 nm yields excited states that are unbound with respect to electron loss. These excited states are shown to decay on a sub-40 fs timescale through a series of conical intersections with lower-lying excited states, ultimately to form the ground anionic state and avoid autodetachment. From an isolated electron-acceptor perspective, this ultrafast stabilization mechanism accounts for the ability of para-benzoquinone to capture and retain electrons.

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

    NASA Astrophysics Data System (ADS)

    Lau, Maximilian Peter; Sander, Michael; Gelbrecht, Jörg; Hupfer, Michael

    2014-05-01

    Microbial respiration is a key driver of element cycling in oxic and anoxic environments. Upon depletion of oxygen as terminal electron acceptor (TEA), a number of anaerobic bacteria can employ alternative TEA for intracellular energy generation. Redox active quinone moieties in dissolved organic matter (DOM) are well known electron acceptors for microbial respiration. However, it remains unclear whether quinones in adsorbed and particulate OM accept electrons in a same way. In our studies we aim to understand the importance of natural organic matter (NOM) as electron acceptors for microbial energy gain and its possible implications for methanogenesis. Using a novel electrochemical approach, mediated electrochemical reduction and -oxidation, we can directly quantify reduced hydroquinone and oxidized quionone moieties in dissolved and particulate NOM samples. In a mesocosm experiment, we rewetted sediment and peat soil and followed electron transfer to the inorganic and organic electron acceptors over time. We found that inorganic and organic electron acceptor pools were depleted over the same timescales. More importantly, we showed that organic, NOM-associated electron accepting moieties represent as much as 21 40% of total TEA inventories. These findings support earlier studies that propose that the reduction of quinone moieties in particulate organic matter competitively suppresses methanogenesis in wetland soils. Our results indicate that electron transfer to organic, particulate TEA in inundated ecosystems has to be accounted for when establishing carbon budgets in and projecting greenhouse gas emissions from these systems.

  9. Global Distribution of Net Electron Acceptance in Subseafloor Sediment

    NASA Astrophysics Data System (ADS)

    Fulfer, V. M.; Pockalny, R. A.; D'Hondt, S.

    2017-12-01

    We quantified the global distribution of net electron acceptance rates (e-/m2/year) in subseafloor sediment (>1.5 meters below seafloor [mbsf]) using (i) a modified version of the chemical-reaction-rate algorithm by Wang et al. (2008), (ii) physical properties and dissolved oxygen and sulfate data from interstitial waters of sediment cores collected by the Ocean Drilling Program, Integrated Ocean Drilling Program, International Ocean Discovery Program, and U.S. coring expeditions, and (iii) correlation of net electron acceptance rates to global oceanographic properties. Calculated net rates vary from 4.8 x 1019 e-/m2/year for slowly accumulating abyssal clay to 1.2 x 1023 e-/m2/year for regions of high sedimentation rate. Net electron acceptance rate correlates strongly with mean sedimentation rate. Where sedimentation rate is very low (e.g., 1 m/Myr), dissolved oxygen penetrates more than 70 mbsf and is the primary terminal electron acceptor. Where sedimentation rate is moderate (e.g., 3 to 60 m/Myr), dissolved sulfate penetrates as far as 700 mbsf and is the principal terminal electron acceptor. Where sedimentation rate is high (e.g., > 60 m/Myr), dissolved sulfate penetrates only meters, but is the principal terminal electron acceptor in subseafloor sediment to the depth of sulfate penetration. Because microbial metabolism continues at greater depths than the depth of sulfate penetration in fast-accumulating sediment, complete quantification of subseafloor metabolic rates will require consideration of other chemical species.

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

    DOE PAGES

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

    2016-10-10

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

  11. An Exploratory Study on the Pathways of Cr (VI) Reduction in Sulfate-reducing Up-flow Anaerobic Sludge Bed (UASB) Reactor

    PubMed Central

    Qian, Jin; Wei, Li; Liu, Rulong; Jiang, Feng; Hao, Xiaodi; Chen, Guang-Hao

    2016-01-01

    Electroplating wastewater contains both Cr (VI) and sulfate. So Cr (VI) removal under sulfate-rich condition is quite complicated. This study mainly investigates the pathways for Cr (VI) removal under biological sulfate-reducing condition in the up-flow anaerobic sludge bed (UASB) reactor. Two potential pathways are found for the removal of Cr (VI). The first one is the sulfidogenesis-induced Cr (VI) reduction pathway (for 90% Cr (VI) removal), in which Cr (VI) is reduced by sulfide generated from biological reduction of sulfate. The second one leads to direct reduction of Cr (VI) which is utilized by bacteria as the electron acceptor (for 10% Cr (VI) removal). Batch test results confirmed that sulfide was oxidized to elemental sulfur instead of sulfate during Cr (VI) reduction. The produced extracellular polymeric substances (EPS) provided protection to the microbes, resulting in effective removal of Cr (VI). Sulfate-reducing bacteria (SRB) genera accounted for 11.1% of the total bacterial community; thus they could be the major organisms mediating the sulfidogenesis-induced reduction of Cr (VI). In addition, chromate-utilizing genera (e.g. Microbacterium) were also detected, which were possibly responsible for the direct reduction of Cr (VI) using organics as the electron donor and Cr (VI) as the electron acceptor. PMID:27021522

  12. TIO2 ADVANCED PHOTO-OXIDATION TECHNOLOGY: EFFECT OF ELECTRON ACCEPTORS

    EPA Science Inventory

    The effects of electron acceptors (additives) such as hydrogen peroxide, ammonium persulphate, potassium bromate and potassium peroxymonosulphate (ozone) on the TiO2 photocatalytic degradation of various organic pollutants were examined at various conditions. he individual and th...

  13. Increasing Saturated Electron-Drift Velocity in Donor-Acceptor Doped pHEMT Heterostructures

    NASA Astrophysics Data System (ADS)

    Protasov, D. Yu.; Gulyaev, D. V.; Bakarov, A. K.; Toropov, A. I.; Erofeev, E. V.; Zhuravlev, K. S.

    2018-03-01

    Field dependences of the electron-drift velocity in typical pseudomorphic high-electron-mobility transistor (pHEMT) heteroepitaxial structures (HESs) and in those with donor-acceptor doped (DApHEMT) heterostructures with quantum-well (QW) depth increased by 0.8-0.9 eV with the aid of acceptor layers have been studied by a pulsed technique. It is established that the saturated electron-drift velocity in DA-pHEMT-HESs is 1.2-1.3 times greater than that in the usual pHEMT-HESs. The electroluminescence (EL) spectra of DA-pHEMT-HESs do not contain emission bands related to the recombination in widebandgap layers (QW barriers). The EL intensity in these HESs is not saturated with increasing electric field. This is indicative of a suppressed real-space transfer of hot electrons from QW to barrier layers, which accounts for the observed increase in the saturated electron-drift velocity.

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

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

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

    1987-01-01

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

  15. Long-Lived Charge Separation at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors

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

    Kang, Hyun Suk; Sisto, Thomas J.; Peurifoy, Samuel

    Nonfullerene electron acceptors have facilitated a recent surge in the efficiencies of organic solar cells, although fundamental studies of the nature of exciton dissociation at interfaces with nonfullerene electron acceptors are still relatively sparse. Semiconducting single-walled carbon nanotubes (s-SWCNTs), unique one-dimensional electron donors with molecule-like absorption and highly mobile charges, provide a model system for studying interfacial exciton dissociation. Here, we investigate excited-state photodynamics at the heterojunction between (6,5) s-SWCNTs and two perylene diimide (PDI)-based electron acceptors. Each of the PDI-based acceptors, hPDI2-pyr-hPDI2 and Trip-hPDI2, is deposited onto (6,5) s-SWCNT films to form a heterojunction bilayer. Transient absorption measurements demonstratemore » that photoinduced hole/electron transfer occurs at the photoexcited bilayer interfaces, producing long-lived separated charges with lifetimes exceeding 1.0 us. Both exciton dissociation and charge recombination occur more slowly for the hPDI2-pyr-hPDI2 bilayer than for the Trip-hPDI2 bilayer. To explain such differences, we discuss the potential roles of the thermodynamic charge transfer driving force available at each interface and the different molecular structure and intermolecular interactions of PDI-based acceptors. As a result, detailed photophysical analysis of these model systems can develop the fundamental understanding of exciton dissociation between organic electron donors and nonfullerene acceptors, which has not been systematically studied.« less

  16. Long-Lived Charge Separation at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors

    DOE PAGES

    Kang, Hyun Suk; Sisto, Thomas J.; Peurifoy, Samuel; ...

    2018-04-13

    Nonfullerene electron acceptors have facilitated a recent surge in the efficiencies of organic solar cells, although fundamental studies of the nature of exciton dissociation at interfaces with nonfullerene electron acceptors are still relatively sparse. Semiconducting single-walled carbon nanotubes (s-SWCNTs), unique one-dimensional electron donors with molecule-like absorption and highly mobile charges, provide a model system for studying interfacial exciton dissociation. Here, we investigate excited-state photodynamics at the heterojunction between (6,5) s-SWCNTs and two perylene diimide (PDI)-based electron acceptors. Each of the PDI-based acceptors, hPDI2-pyr-hPDI2 and Trip-hPDI2, is deposited onto (6,5) s-SWCNT films to form a heterojunction bilayer. Transient absorption measurements demonstratemore » that photoinduced hole/electron transfer occurs at the photoexcited bilayer interfaces, producing long-lived separated charges with lifetimes exceeding 1.0 us. Both exciton dissociation and charge recombination occur more slowly for the hPDI2-pyr-hPDI2 bilayer than for the Trip-hPDI2 bilayer. To explain such differences, we discuss the potential roles of the thermodynamic charge transfer driving force available at each interface and the different molecular structure and intermolecular interactions of PDI-based acceptors. As a result, detailed photophysical analysis of these model systems can develop the fundamental understanding of exciton dissociation between organic electron donors and nonfullerene acceptors, which has not been systematically studied.« less

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2002-10-01

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

  19. 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...

  20. Interplay between barrier width and height in electron tunneling: photoinduced electron transfer in porphyrin-based donor-bridge-acceptor systems.

    PubMed

    Pettersson, Karin; Wiberg, Joanna; Ljungdahl, Thomas; Mårtensson, Jerker; Albinsson, Bo

    2006-01-12

    The rate of electron tunneling in molecular donor-bridge-acceptor (D-B-A) systems is determined both by the tunneling barrier width and height, that is, both by the distance between the donor and acceptor as well as by the energy gap between the donor and bridge moieties. These factors are therefore important to control when designing functional electron transfer systems, such as constructs for photovoltaics, artificial photosynthesis, and molecular scale electronics. In this paper we have investigated a set of D-B-A systems in which the distance and the energy difference between the donor and bridge states (DeltaEDB) are systematically varied. Zinc(II) and gold(III) porphyrins were chosen as electron donor and acceptor because of their suitable driving force for photoinduced electron transfer (-0.9 eV in butyronitrile) and well-characterized photophysics. We have previously shown, in accordance with the superexchange mechanism for electron transfer, that the electron transfer rate is proportional to the inverse of DeltaEDB in a series of zinc/gold porphyrin D-B-A systems with bridges of constant edge to edge distance (19.6 A) and varying DeltaEDB (3900-17 600 cm(-1)). Here, we use the same donor and acceptor but the bridge is shortened or extended giving a set of oligo-p-phenyleneethynylene bridges (OPE) with four different edge to edge distances ranging from 12.7 to 33.4 A. These two sets of D-B-A systems-ZnP-RB-AuP+ and ZnP-nB-AuP+-have one bridge in common, and hence, for the first time both the distance and DeltaEDB dependence of electron transfer can be studied simultaneously in a systematic way.

  1. Metabolic interactions in methanogenic and sulfate-reducing bioreactors.

    PubMed

    Stams, A J M; Plugge, C M; de Bok, F A M; van Houten, B H G W; Lens, P; Dijkman, H; Weijma, J

    2005-01-01

    In environments where the amount of electron acceptors is insufficient for complete breakdown of organic matter, methane is formed as the major reduced end product. In such methanogenic environments organic acids are degraded by syntrophic consortia of acetogenic bacteria and methanogenic archaea. Hydrogen consumption by methanogens is essential for acetogenic bacteria to convert organic acids to acetate and hydrogen. Several syntrophic cocultures growing on propionate and butyrate have been described. These syntrophic fatty acid-degrading consortia are affected by the presence of sulfate. When sulfate is present sulfate-reducing bacteria compete with methanogenic archaea for hydrogen and acetate, and with acetogenic bacteria for propionate and butyrate. Sulfate-reducing bacteria easily outcompete methanogens for hydrogen, but the presence of acetate as carbon source may influence the outcome of the competition. By contrast, acetoclastic methanogens can compete reasonably well with acetate-degrading sulfate reducers. Sulfate-reducing bacteria grow much faster on propionate and butyrate than syntrophic consortia.

  2. 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

  3. Geochemistry of dissolved inorganic carbon in a Coastal Plain aquifer. 1. Sulfate from confining beds as an oxidant in microbial CO2 production

    USGS Publications Warehouse

    Chapelle, F.H.; McMahon, P.B.

    1991-01-01

    A primary source of dissolved inorganic carbon (DIC) in the Black Creek aquifer of South Carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter. Groundwater chemistry data indicate, however, that the available mass of inorganic electron acceptors (oxygen, Fe(III), and sulfate) and observed methane production is inadequate to account for observed CO2 production. Although sulfate concentrations are low (approximately 0.05-0.10 mM) in aquifer water throughout the flow system, sulfate concentrations are greater in confining-bed pore water (0.4-20 mM). The distribution of culturable sulfate-reducing bacteria in these sediments suggests that this concentration gradient is maintained by greater sulfate-reducing activity in sands than in clays. Calculations based on Fick's Law indicate that possible rates of sulfate diffusion to aquifer sediments are sufficient to explain observed rates of CO2 production (about 10-5 mmoll-1 year-1), thus eliminating the apparent electron-acceptor deficit. Furthermore, concentrations of dissolved hydrogen in aquifer water are in the range characteristic of sulfate reduction (2-6 nM), which provides independent evidence that sulfate reduction is the predominant terminal electron-accepting process in this system. The observed accumulation of pyrite- and calcite-cemented sandstones at sand-clay interfaces is direct physical evidence that these processes have been continuing over the history of these sediments. ?? 1991.

  4. Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens

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

    Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R.

    2015-09-05

    The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than - 0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poisedmore » at - 0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ΔcbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below - 0.1 V vs. SHE.« less

  5. Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens.

    PubMed

    Zacharoff, Lori; Chan, Chi Ho; Bond, Daniel R

    2016-02-01

    The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than -0.1 V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poised at -0.1 V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50 mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ∆cbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below -0.1 V vs. SHE. Copyright © 2015. Published by Elsevier B.V.

  6. 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

  7. Negative Electron Transfer Dissociation Sequencing of 3-O-Sulfation-Containing Heparan Sulfate Oligosaccharides

    NASA Astrophysics Data System (ADS)

    Wu, Jiandong; Wei, Juan; Hogan, John D.; Chopra, Pradeep; Joshi, Apoorva; Lu, Weigang; Klein, Joshua; Boons, Geert-Jan; Lin, Cheng; Zaia, Joseph

    2018-03-01

    Among dissociation methods, negative electron transfer dissociation (NETD) has been proven the most useful for glycosaminoglycan (GAG) sequencing because it produces informative fragmentation, a low degree of sulfate losses, high sensitivity, and translatability to multiple instrument types. The challenge, however, is to distinguish positional sulfation. In particular, NETD has been reported to fail to differentiate 4-O- versus 6-O-sulfation in chondroitin sulfate decasaccharide. This raised the concern of whether NETD is able to differentiate the rare 3-O-sulfation from predominant 6-O-sulfation in heparan sulfate (HS) oligosaccharides. Here, we report that NETD generates highly informative spectra that differentiate sites of O-sulfation on glucosamine residues, enabling structural characterizations of synthetic HS isomers containing 3-O-sulfation. Further, lyase-resistant 3-O-sulfated tetrasaccharides from natural sources were successfully sequenced. Notably, for all of the oligosaccharides in this study, the successful sequencing is based on NETD tandem mass spectra of commonly observed deprotonated precursor ions without derivatization or metal cation adduction, simplifying the experimental workflow and data interpretation. These results demonstrate the potential of NETD as a sensitive analytical tool for detailed, high-throughput structural analysis of highly sulfated GAGs. [Figure not available: see fulltext.

  8. Electron Acceptors Based on α-Substituted Perylene Diimide (PDI) for Organic Solar Cells

    DOE PAGES

    Zhao, Donglin; Wu, Qinghe; Cai, Zhengxu; ...

    2016-02-20

    The ortho-position functionalized perylene diimide derivatives (αPPID, αPBDT) were synthesized and used as the electron acceptors in nonfullerene organic photovoltaics. Due to the good planarity of ortho-position functionalized PDI, the αPPID and αPBDT show strong tendency to form aggregate because of their enhanced intermolecular pie-pie interaction. Moreover, they maintain the pure domains and the same packing order as in the pure film if they are blended with PBT7-TH and the SCLC measurement also shows the high electron mobility. The inverted OPVs employing αPDI-based compounds as acceptor and PBT7-TH as the donor give the highest PCE of 4.92 % for αPBDTmore » based device and 3.61 % for αPPID based device, which is 39 % and 4 % higher than that for their counterpart βPBDT and βPPID. The charge separation study shows the more efficient exciton dissociation at interfaces between PDI based compounds and PBT7-TH. In conclusion, the results suggest that compared to beta-substituted ones, alpha-substituted PDI derivatives are more promising electron acceptors for OPV.« less

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  10. Decomposition of plant materials in marine sediment exposed to different electron acceptors (O 2, NO 3-, and SO 42-), with emphasis on substrate origin, degradation kinetics, and the role of bioturbation

    NASA Astrophysics Data System (ADS)

    Kristensen, Erik; Holmer, Marianne

    2001-02-01

    Carbon mineralization of fresh and aged diatoms ( Skeletonema costatum) and barley hay ( Hordeum vulgare) was followed for 23 to 35 d in sandy and silty sediment. By the use of a thin-layer flow-through technique, it was possible to expose the sediment selectively for oxygen, nitrate or sulfate as electron acceptors in the terminal oxidation of organic carbon. Decomposition took place in two basic stages. Mineralization of the rapidly leachable fraction of the fresh materials occurred rapidly and with the same constant rate regardless of the electron acceptor available, indicating that the dissolved organic carbon released initially was labile and readily available for all heterotrophic respirers. In the case of diatoms, decay of the remaining, more refractory, particulate fraction of fresh and aged diatoms were strikingly similar, although both were degraded 5 to 10 times faster under oxic than anoxic conditions. Most of the particulate remains of diatoms after leaching apparently belong to one fraction, which maintains the same degradability even after prolonged aging. With respect to hay, the late divergence in rates of aerobic and anaerobic decay (a factor of 4 to 5 for aged hay only after 20 d) indicated that the larger hay particles (<500 μm) became exhausted in labile organic matter much slower through time than fine-particulate diatoms (˜20 μm). Anaerobic carbon mineralization rates of diatoms and hay particulates with sulfate and nitrate as electron acceptors were similar or up to two times faster with sulfate. The generally low levels of dissolved organic carbon in all incubations after the initial leaching phase suggest that the limiting step of decomposition under both aerobic and anaerobic decay is the initial hydrolytic attack on the complex particulate remains. Based on a volumetric model, we show that the exposure of anoxic subsurface sediment containing partly degraded organic material to oxygen via irrigated worm burrows or by reworking may

  11. 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.

  12. Accelerated methanogenesis from aliphatic and aromatic hydrocarbons under iron- and sulfate-reducing conditions.

    PubMed

    Siegert, Michael; Cichocka, Danuta; Herrmann, Steffi; Gründger, Friederike; Feisthauer, Stefan; Richnow, Hans-Hermann; Springael, Dirk; Krüger, Martin

    2011-02-01

    The impact of four electron acceptors on hydrocarbon-induced methanogenesis was studied. Methanogenesis from residual hydrocarbons may enhance the exploitation of oil reservoirs and may improve bioremediation. The conditions to drive the rate-limiting first hydrocarbon-oxidizing steps for the conversion of hydrocarbons into methanogenic substrates are crucial. Thus, the electron acceptors ferrihydrite, manganese dioxide, nitrate or sulfate were added to sediment microcosms acquired from two brackish water locations. Hexadecane, ethylbenzene or 1-(13)C-naphthalene were used as model hydrocarbons. Methane was released most rapidly from incubations amended with ferrihydrite and hexadecane. Ferrihydrite enhanced only hexadecane-dependent methanogenesis. The rates of methanogenesis were negatively affected by sulfate and nitrate at concentrations of more than 5 and 1 mM, respectively. Metal-reducing Geobacteraceae and potential sulfate reducers as well as Methanosarcina were present in situ and in vitro. Ferrihydrite addition triggered the growth of Methanosarcina-related methanogens. Additionally, methane was removed concomitantly by anaerobic methanotrophy. ANME-1 and -2 methyl coenzyme M reductase genes were detected, indicating anaerobic methanotrophy as an accompanying process [Correction added 16 December after online publication: 'methyl coenzyme A' changed to 'methyl coenzyme M' in this sentence]. The experiments presented here demonstrate the feasibility of enhancing methanogenic alkane degradation by ferrihydrite or sulfate addition in different geological settings. © 2010 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

  13. Detection of Survival and Proliferation of Sulfate Reducers Under Simulated Martian Atmospheric and Soil Conditions

    NASA Astrophysics Data System (ADS)

    Mora, Sergio Mosquera

    Numerous studies have tried to determine the survivability and proliferation of microorganisms under simulated Martian conditions. Furthermore, most of them have been focused on the ability of these microbes to cope with high brines' salt (NaCl) concentrations inherent of the Martian surface. However, there are not studies related to the ability of bacteria to survive on subsurface environments that have increasing concentrations of sulfate compounds. For this research, a group of microorganisms known as sulfate-reducing bacteria or simply sulfate reducers were chosen due to their ability to use sulfate compounds as terminal electron acceptors to produce metabolic energy, their tolerance to low temperatures (psychrophilic microbes) and their anaerobic metabolism. Moreover, the principal purpose of this study was to determine the ability of sulfate reducers to carry active metabolism under conditions similar to those present on Mars subsurface (low temperature, high concentration of sulfate compounds, anoxic atmosphere-95% carbon dioxide, low nutrients availability, among others). Furthermore, we cultivated strains of Desulfotalea psychrophila, Desulfuromusa ferrireducens and Desulfotomaculum arcticum using different concentrations of minerals. The latter (CaSO 4, MgSO4, FeSO4 and Fe2(SO4) 3) are normally found as part of the Martian subsurface components and they can act as terminal electron acceptors in sulfate respiration. Moreover, PCR amplifications of the 16S rDNA gene and the dsrAB genes were performed in order to determine the growth and survivability of the three microorganisms tested. Finally, we were able to determine that they were metabolically active at the different types and mineral concentrations under study.

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

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

  15. Acceptor Percolation Determines How Electron-Accepting Additives Modify Transport of Ambipolar Polymer Organic Field-Effect Transistors.

    PubMed

    Ford, Michael J; Wang, Ming; Bustillo, Karen C; Yuan, Jianyu; Nguyen, Thuc-Quyen; Bazan, Guillermo C

    2018-06-18

    Organic field-effect transistors (OFETs) that utilize ambipolar polymer semiconductors can benefit from the ability of both electron and hole conduction, which is necessary for complementary circuits. However, simultaneous hole and electron transport in organic field-effect transistors result in poor ON/OFF ratios, limiting potential applications. Solution processing methods have been developed to control charge transport properties and transform ambipolar conduction to hole-only conduction. The electron-acceptor phenyl-C61-butyric acid methyl ester (PC 61 BM), when mixed in solution with an ambipolar semiconducting polymer, can reduce electron conduction. Unipolar p-type OFETs with high, well-defined ON/OFF ratios and without detrimental effects on hole conduction are achieved for a wide range of blend compositions, from 95:5 to 5:95 wt % semiconductor polymer:PC 61 BM. When introducing the alternative acceptor N, N'-bis(1-ethylpropyl)-3,4:9,10-perylenediimide (PDI), high ON/OFF ratios are achieved for 95:5 wt % semiconductor polymer:PDI; however, electron conduction increases for 50:50 and 5:95 wt % semiconductor polymer:PDI. As described within, we show that electron conduction is practically eliminated when additive domains do not percolate across the OFET channel, that is, electrons are "morphologically trapped". Morphologies were characterized by optical, electron, and atomic force microscopy as well as X-ray scattering techniques. PC 61 BM was substituted with an endohedral Lu 3 N fullerene, which enhanced contrast in electron microscopy and allowed for more detailed insight into the blend morphologies. Blends with alternative, nonfullerene acceptors further emphasize the importance of morphology and acceptor percolation, providing insights for such blends that control ambipolar transport and ON/OFF ratios.

  16. Succinic acid production from glycerol by Actinobacillus succinogenes using dimethylsulfoxide as electron acceptor.

    PubMed

    Carvalho, Margarida; Matos, Mariana; Roca, Christophe; Reis, Maria A M

    2014-01-25

    Glycerol, a highly abundant byproduct of the biodiesel industry, constitutes today a cheap feedstock for biobased succinic acid (SA) production. Actinobacillus succinogenes is one of the best SA producers. However, glycerol consumption by this biocatalyst is limited because of a redox imbalance during cell growth. The use of an external electron acceptor may improve the metabolism of SA synthesis by A. succinogenes in glycerol. In this study, the effect of dimethylsulfoxide (DMSO), an electron acceptor, on glycerol consumption and SA production by A. succinogenes under controlled fermentation conditions was investigated. Concentrations of DMSO between 1 and 4% (v/v) greatly promoted glycerol consumption and SA production by A. succinogenes. During fed-batch cultivation, SA concentration reached 49.62 g/L, with a product yield of 0.87 gSA/gGLR and a maximum production rate of 2.31 gSA/Lh, the highest values so far reported in the literature for A. succinogenes using glycerol as carbon source. These results show that using DMSO as external electron acceptor significantly promotes glycerol consumption and succinic acid production by A. succinogenes and may be used as a co-substrate, opening new perspectives for the use of glycerol by this biocatalyst. Copyright © 2013 Elsevier B.V. All rights reserved.

  17. Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

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

    Park, Changwon; Atalla, Viktor; Smith, Sean

    Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

  18. Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

    DOE PAGES

    Park, Changwon; Atalla, Viktor; Smith, Sean; ...

    2017-06-16

    Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

  19. Anaerobic biodegradability of alkylphenols and fuel oxygenates in the presence of alternative electron acceptors.

    PubMed

    Puig-Grajales, L; Tan, N G; van der Zee, F; Razo-Flores, E; Field, J A

    2000-11-01

    Alkylphenols and fuel oxygenates are important environmental pollutants produced by the petrochemical industry. A batch biodegradability test was conducted with selected ortho-substituted alkylphenols (2-cresol, 2,6-dimethylphenol and 2-ethylphenol), fuel oxygenates (methyl tert-butyl ether, ethyl tert-butyl ether and tert-amylmethyl ether) and tert-butyl alcohol (TBA) as model compounds. The ortho-substituted alkylphenols were not biodegraded after 100 days of incubation under methanogenic, sulfate-, or nitrate-reducing conditions. However, biodegradation of 2-cresol and 2-ethylphenol (150 mg l(-1)) was observed in the presence of Mn (IV) as electron acceptor. The biodegradation of these two compounds took place in less than 15 days and more than 90% removal was observed for both compounds. Mineralization was indicated since no UV-absorbing metabolites accumulated after 23 days of incubation. These alkylphenols were also slowly chemically oxidized by Mn (IV). No biodegradation of fuel oxygenates or TBA (1 g l(-1)) was observed after 80 or more days of incubation under methanogenic, Fe (III)-, or Mn (IV)-reducing conditions, suggesting that these compounds are recalcitrant under anaerobic conditions. The fuel oxygenates caused no toxicity towards acetoclastic methanogens activity in anaerobic granular sludge.

  20. Theoretical study of solvent effects on the electronic coupling matrix elements in rigidly linked donor-acceptor systems

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

    Cave, R.J.; Newton, M.D.; Kumar, K.

    1995-12-07

    The recently developed generalized Mulliken-Hush approach for the calculation of the electronic coupling matrix element for electron-transfer processes is applied to two rigidly linked donor-bridge-acceptor systems having dimethoxyanthracene as the donor and a dicarbomethoxycyclobutene unit as the acceptor. The dependence of the electronic coupling matrix element as a function of bridge type is examined with and without solvent molecules present. For clamp-shaped bridge structures solvent can have a dramatic effect on the electronic coupling matrix element. The behavior with variation of solvent is in good agreement with that observed experimentally for these systems. 23 refs., 2 tabs.

  1. Synthesis of an A-D-A type of molecule used as electron acceptor for improving charge transfer in organic solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Chao-Zhi; Gu, Shu-Duo; Shen, Dan; Yuan, Yang; Zhang, Mingdao

    2016-08-01

    Electron-accepting molecules play an important role in developing organic solar cells. A new type of A-D-A molecule, 3,6-di([7-(5-bromothiophen-2-yl)-1,5,2,4,6,8-dithiotetrazocin-3-yl]thiophen-2-yl)-9-(2-ethylhexyl)carbazole, was synthesized. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels are -3.55 and -5.85 eV, respectively. Therefore, the A-D-A type of compound could be used as electron acceptor for fabricating organic solar cell with a high open circuit voltage. Gibbs free energy (-49.2 kJ/mol) reveals that the process of A-D-A acceptor accepting an electron from poly(3-hexylthiophene) at excited state is spontaneous. The value of entropy (118 J/mol) in the process of an electron transferring from P3HT to the A-D-A acceptor at organic interface suggests that electrons generated from separation of electron-hole pairs at donor/acceptor interface would be delocalized efficiently. Therefore, the A-D-A molecule would be a potential acceptor for efficient organic BHJ solar cells.

  2. Evidence on Anaerobic Methane Oxidation (AOM) in a boreal cultivated peatland with natural and added electron acceptors

    NASA Astrophysics Data System (ADS)

    Dorodnikov, Maxim; Silvennoinen, Hanna; Martikainen, Pertti; Dörsch, Peter

    2015-04-01

    Anaerobic oxidation of methane (AOM) is a process of methane (CH4) consumption under anoxic conditions driven by microorganisms, which oxidize CH4 with various alternate electron acceptors (AEA): sulfate, nitrate, nitrite, metals-(Fe, Mn, Cu), organic compounds. AOM is common in marine ecosystems, where microbial sulfate reduction (SR) consumes most of the CH4 produced in sediments. Despite the global significance of AOM, the exact mechanisms and relevance of the process in terrestrial ecosystems are almost unknown. In the current study the occurrence of AOM was tested for two organic soil horizons (30 and 40 cm depth) and one mineral sub-soil (sand, 50 cm depth) of a cultivated boreal peatland (Linnansuo, Eastern Finland, energy crop Phalaris arundinacea - reed canarygrass) under controlled conditions with the addition of 13C-labeled CH4 and two common AEAs - SO4-2 and Fe+3. Concentrations of CH4, CO2 and O2 were continuously measured during 10 days of incubation and CO2 was sampled periodically under anaerobic conditions for stable 13C analysis. Oxygen dynamics revealed negligible O2 contamination during incubation and its trace amounts (0.05-0.8% from the atmospheric) were accounted in the net CH4 uptake. Application of 13C-enriched CH4 (4.9 atom%) allowed to track the label in CO2 as the end-product of AOM. The highest 13CO2 enrichment (up to 60‰) was observed in mineral sub-soil, however AOM was quantitatively more pronounced in the upper 30 cm horizon (2.1 vs. 0.2 μg CO2 g soil DW-1 in the 50 cm sub-soil). The highest AOM rate of 8.9 ng CO2 g soil DW-1 h-1 was estimated for the control treatment where no AEAs were added indicating sufficient amount of naturally available AEAs, likely organic compounds. This rate was 50 times more intensive (on the C basis) than the CH4 production potential of the same soil. In contrast, external AEAs decreased AOM rates but added Fe+3 stimulated decomposition of native SOM (as seen from the most depleted 13CO2 signatures

  3. [Effects of carbon sources, temperature and electron acceptors on biological phosphorus removal].

    PubMed

    Han, Yun; Xu, Song; Dong, Tao; Wang, Bin-Fan; Wang, Xian-Yao; Peng, Dang-Cong

    2015-02-01

    Effects of carbon sources, temperature and electron acceptors on phosphorus uptake and release were investigated in a pilot-scale oxidation ditch. Phosphorus uptake and release rates were measured with different carbon sources (domestic sewage, sodium acetate, glucose) at 25 degrees C. The results showed that the minimum phosphorus uptake and release rates of glucose were 5.12 mg x (g x h)(-1) and 6.43 mg x (g x h)(-1), respectively, and those of domestic sewage are similar to those of sodium acetate. Phosphorus uptake and release rates increased with the increase of temperature (12, 16, 20 and 25 degrees C) using sodium acetate as carbon sources. Anoxic phosphorus uptake rate decreased with added COD. Electron acceptors (oxygen, nitrate, nitrite) had significant effects on phosphorus uptake rate and their order was in accordance with oxygen > nitrate > nitrite. The mass ratio of anoxic P uptake and N consumption (P(uptake)/N (consumption)) of nitrate and nitrite were 0.96 and 0.65, respectively.

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

    PubMed

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

    2017-07-01

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

  5. Microbial reduction of vanadium (V) in groundwater: Interactions with coexisting common electron acceptors and analysis of microbial community.

    PubMed

    Liu, Hui; Zhang, Baogang; Yuan, Heyang; Cheng, Yutong; Wang, Song; He, Zhen

    2017-12-01

    Vanadium (V) pollution in groundwater has posed serious risks to the environment and public health. Anaerobic microbial reduction can achieve efficient and cost-effective remediation of V(V) pollution, but its interactions with coexisting common electron acceptors such as NO 3 - , Fe 3+ , SO 4 2- and CO 2 in groundwater remain unknown. In this study, the interactions between V(V) reduction and reduction of common electron acceptors were examined with revealing relevant microbial community and identifying dominant species. The results showed that the presence of NO 3 - slowed down the removal of V(V) in the early stage of the reaction but eventually led to a similar reduction efficiency (90.0% ± 0.4% in 72-h operation) to that in the reactor without NO 3 - . The addition of Fe 3+ , SO 4 2- , or CO 2 decreased the efficiency of V(V) reduction. Furthermore, the microbial reduction of these coexisting electron acceptors was also adversely affected by the presence of V(V). The addition of V(V) as well as the extra dose of Fe 3+ , SO 4 2- and CO 2 decreased microbial diversity and evenness, whereas the reactor supplied with NO 3 - showed the increased diversity. High-throughput 16S rRNA gene pyrosequencing analysis indicated the accumulation of Geobacter, Longilinea, Syntrophobacter, Spirochaeta and Anaerolinea, which might be responsible for the reduction of multiple electron acceptors. The findings of this study have demonstrated the feasibility of anaerobic bioremediation of V(V) and the possible influence of coexisting electron acceptors commonly found in groundwater. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. Application of anaerobic ammonium-oxidizing consortium to achieve completely autotrophic ammonium and sulfate removal.

    PubMed

    Liu, Sitong; Yang, Fenglin; Gong, Zheng; Meng, Fangang; Chen, Huihui; Xue, Yuan; Furukawa, Kenji

    2008-10-01

    The simultaneous ammonium and sulfate removal was detected in an anammox reactor, consisted of ammonium oxidization with sulfate deoxidization, and subsequently traditional anammox process, in via of middle medium nitrite with solid sulfur and N2 as the terminal products. The pure anammox bacteria offered a great biotechnological potential for the completely autotrophic reaction indicated by batch tests. Denaturing gradient gel electrophoresis (DGGE) analysis further revealed that a new organism belonging to Planctomycetales was strongly enriched in the defined niche: the redox of ammonium and sulfate. The new species "Anammoxoglobussulfate" was so considered as holding a critical role in the ammonium oxidization with sulfate deoxidization to nitrite. Afterwards, the Planctomyces existing in the bacteria community performed the anammox process together to achieve the complete nitrogen and sulfate removal. The potential use of sulfate as electron acceptor for ammonium oxidizing widens the usage of anammox bacteria.

  7. Surface State Density Determines the Energy Level Alignment at Hybrid Perovskite/Electron Acceptors Interfaces.

    PubMed

    Zu, Fengshuo; Amsalem, Patrick; Ralaiarisoa, Maryline; Schultz, Thorsten; Schlesinger, Raphael; Koch, Norbert

    2017-11-29

    Substantial variations in the electronic structure and thus possibly conflicting energetics at interfaces between hybrid perovskites and charge transport layers in solar cells have been reported by the research community. In an attempt to unravel the origin of these variations and enable reliable device design, we demonstrate that donor-like surface states stemming from reduced lead (Pb 0 ) directly impact the energy level alignment at perovskite (CH 3 NH 3 PbI 3-x Cl x ) and molecular electron acceptor layer interfaces using photoelectron spectroscopy. When forming the interfaces, it is found that electron transfer from surface states to acceptor molecules occurs, leading to a strong decrease in the density of ionized surface states. As a consequence, for perovskite samples with low surface state density, the initial band bending at the pristine perovskite surface can be flattened upon interface formation. In contrast, for perovskites with a high surface state density, the Fermi level is strongly pinned at the conduction band edge, and only minor changes in surface band bending are observed upon acceptor deposition. Consequently, depending on the initial perovskite surface state density, very different interface energy level alignment situations (variations over 0.5 eV) are demonstrated and rationalized. Our findings help explain the rather dissimilar reported energy levels at interfaces with perovskites, refining our understanding of the operating principles in devices comprising this material.

  8. Electrodes as Terminal Electron Acceptors in Anaerobic Ammonium Oxidation

    NASA Astrophysics Data System (ADS)

    Ruiz-Urigüen, M.; Jaffe, P. R.

    2017-12-01

    Anaerobic ammonium (NH4+) oxidation under iron (Fe) reducing conditions is a microbial- mediated process known as Feammox. This is a novel pathway in the nitrogen cycle, and a key process for alleviating NH4+ accumulation in anoxic soils, wetlands, and wastewater. Acidimicrobiaceae-bacterium A6, phylum Actinobacteria, are one type of autotrophic bacteria linked to this process. The Feammox-bacteria obtain their energy by oxidizing NH4+ and transferring the electrons to a terminal electron acceptor (TEA). Under environmental conditions, iron oxides are the TEAs. However, in this study we show that electrodes in Microbial Electrolysis Cells (MECs) or electrodes set in the field can be used as TEAs by Feammox-bacteria. The potential difference between electrodes is the driving force for electron transfer, making the reaction energetically feasible. Our results show that MECs containing Feammox cultures can remove NH4+ up to 3.5 mg/L in less than 4 hours, compared to an average of 9 mg/L in 2 weeks when cultured under traditional conditions. Concomitantly, MECs produce an average current of 30.5 A/m3 whilst dead bacteria produced low (<2.7 A/m3) or no current. Furthermore, we have measured that A6 biomass increased from 5E4 cells/ml to 9.77E5 cells/ml in 2 weeks of operation, indicating the feasibility of growing A6 in MECs. Results from the electrodes in the field show higher percentage of electrogenic bacteria, including Acidimicrobiaceae-bacterium, on the more reducing electrode, compared to the more oxidized one. Our initial results also suggest that electrodes contained more Actinobacteria when compared to bulk soil. Electrodes as TEAs enhance electrogenic bacteria recovery and culturing. The use of MECs for the productions of Feammox-bacteria eliminates the dependence of Fe, a finite electron acceptor, therefore, allowing for continuous NH4+ removal. Finally, Fe-free Feammox-bacteria can be applied to reduce other metals of environmental concern; therefore

  9. Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

    PubMed

    Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

    2014-06-11

    Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

  10. Electron Donor-Acceptor Nature of the Ethanol-CO2 Dimer

    NASA Astrophysics Data System (ADS)

    McGuire, Brett A.; Martin-Drumel, Marie-Aline; McCarthy, Michael A.

    2017-08-01

    Supercritical CO2 is an appealing nontoxic, environmentally friendly solvent for the industrial extraction of many classes of compounds, from caffeine to natural product drug precursors to petrochemical impurities. Apolar in isolation, the ability of supercritical CO2 to dissolve polar species has been empirically shown to be greatly enhanced by the addition of a small molar percentage of a polar cosolvent, often ethanol. Computational work predicts that the isolated ethanol-CO2 complex can exist either in an electron-donor configuration or through a hydrogen-bonding one; yet, neither has been previously experimentally observed. Here, we demonstrate by rotational spectroscopy that the isolated, gas-phase ethanol-CO2 dimer is an electron donor-acceptor complex.

  11. Photoinduced electron transfer in a room temperature ionic liquid 1-butyl-3-methylimidazolium octyl sulfate micelle: a temperature dependent study.

    PubMed

    Sarkar, Souravi; Mandal, Sarthak; Pramanik, Rajib; Ghatak, Chiranjib; Rao, Vishal Govind; Sarkar, Nilmoni

    2011-05-19

    The effect of temperature on the dynamics of photoinduced electron transfer (PET) between different coumarin dyes and N,N-dimethyl aniline in a room temperature ionic liquid 1-butyl-3-methylimidazolium octyl sulfate ([C(4)mim][C(8)SO(4)]) micelle have been investigated using steady-state and time-resolved fluorescence quenching measurements at four different temperatures: 208, 298, 308, and 318 K. The quenching rates (k(q)(TR)) of the PET process in this micellar system are found to be lower than the PET rate in sodium dodecyl sulfate and Triton-X 100 micelle and almost comparable to the dodecyl trimethyl ammonium bromide and cetyl trimethyl ammonium bromide micelle due to larger donor–acceptor separation in the micellar phase. The temperature dependent PET rates are well correlated with the Arrhenius type of correlation for all the coumarin dyes. Marcus type of inversion in PET rates has been observed at relatively lower exergonicity, and the correlation plots gradually move upward with the increase of temperature. © 2011 American Chemical Society

  12. 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

  13. Modeling Reduction of Uranium U(VI) under Variable Sulfate Concentrations by Sulfate-Reducing Bacteria

    PubMed Central

    Spear, John R.; Figueroa, Linda A.; Honeyman, Bruce D.

    2000-01-01

    The kinetics for the reduction of sulfate alone and for concurrent uranium [U(VI)] and sulfate reduction, by mixed and pure cultures of sulfate-reducing bacteria (SRB) at 21 ± 3°C were studied. The mixed culture contained the SRB Desulfovibrio vulgaris along with a Clostridium sp. determined via 16S ribosomal DNA analysis. The pure culture was Desulfovibrio desulfuricans (ATCC 7757). A zero-order model best fit the data for the reduction of sulfate from 0.1 to 10 mM. A lag time occurred below cell concentrations of 0.1 mg (dry weight) of cells/ml. For the mixed culture, average values for the maximum specific reaction rate, Vmax, ranged from 2.4 ± 0.2 μmol of sulfate/mg (dry weight) of SRB · h−1) at 0.25 mM sulfate to 5.0 ± 1.1 μmol of sulfate/mg (dry weight) of SRB · h−1 at 10 mM sulfate (average cell concentration, 0.52 mg [dry weight]/ml). For the pure culture, Vmax was 1.6 ± 0.2 μmol of sulfate/mg (dry weight) of SRB · h−1 at 1 mM sulfate (0.29 mg [dry weight] of cells/ml). When both electron acceptors were present, sulfate reduction remained zero order for both cultures, while uranium reduction was first order, with rate constants of 0.071 ± 0.003 mg (dry weight) of cells/ml · min−1 for the mixed culture and 0.137 ± 0.016 mg (dry weight) of cells/ml · min−1 (U0 = 1 mM) for the D. desulfuricans culture. Both cultures exhibited a faster rate of uranium reduction in the presence of sulfate and no lag time until the onset of U reduction in contrast to U alone. This kinetics information can be used to design an SRB-dominated biotreatment scheme for the removal of U(VI) from an aqueous source. PMID:10966381

  14. Estimation of electronic coupling in π-stacked donor-bridge-acceptor systems: Correction of the two-state model

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.

    2006-02-01

    Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of Vda because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a π stack, where donor and acceptor are separated by a bridging unit, can be obtained as Ṽda=(E2-E1)μ12/Rda+(2E3-E1-E2)2μ13μ23/Rda2, where E1, E2, and E3 are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, μij is the transition dipole moments between the states i and j, and Rda is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

  15. Estimation of electronic coupling in pi-stacked donor-bridge-acceptor systems: correction of the two-state model.

    PubMed

    Voityuk, Alexander A

    2006-02-14

    Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of V(da) because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a pi stack, where donor and acceptor are separated by a bridging unit, can be obtained as V(da) = (E(2)-E(1))mu(12)R(da) + (2E(3)-E(1)-E(2))2mu(13)mu(23)R(da) (2), where E(1), E(2), and E(3) are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, mu(ij) is the transition dipole moments between the states i and j, and R(da) is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

  16. Desulfovibrio zosterae sp. nov., a new sulfate reducer isolated from surface-sterilized roots of the seagrass Zostera marina.

    PubMed

    Nielsen, J T; Liesack, W; Finster, K

    1999-04-01

    A sulfate-reducing bacterium, designated strain lacT, was isolated from surface-sterilized roots of the benthic macrophyte Zostera marina. Cells were motile by means of a single polar flagellum. Strain lacT utilized lactate, pyruvate, malate, ethanol, L-alanine, fumarate, choline and fructose with sulfate as electron acceptor. In addition, fumarate, pyruvate and fructose were also degraded without an external electron acceptor. Sulfate could be substituted with thiosulfate, sulfite and elemental sulfur. Optimal growth was observed between 32.5 and 34.5 degrees C, at an NaCl concentration of 0.2 M and in a pH range between 6.8 and 7.3. The G + C content of the DNA was 42.7 +/- 0.2 mol%. Desulfoviridin and catalase were present. Strain lacT contained c-type cytochromes. Comparative 16S rRNA gene sequence analysis and the fatty acid pattern grouped this isolate into the genus Desulfovibrio. However, strain lacT differs from all other described Desulfovibrio species on the bases of its 16S rRNA gene sequence, the G + C content, its cellular lipid pattern and the utilization pattern of substrates. These characteristics establish strain lacT (= DSM 11974T) as a novel species of the genus Desulfovibrio, for which the name Desulfovibrio zosterae sp. nov. is proposed.

  17. Bi-diketopyrrolopyrrole (Bi-DPP) as a novel electron accepting compound in low band gap π-conjugated donor–acceptor copolymers/oligomers

    PubMed Central

    Ahner, Johannes; Nowotny, Jürgen; Schubert, Ulrich S.; Hager, Martin D.

    2017-01-01

    Abstract The synthesis and characterization of a novel 2,5-diketopyrrolo[3,4-c]pyrrole(DPP)-based accepting building block with the scheme DPP-neutral small linker-DPP (Bi-DPP) is presented, which was utilized as electron accepting moiety for low band gap π-conjugated donor–acceptor copolymers as well as for a donor–acceptor small molecule. The electron accepting moiety Bi-DPP was prepared via a novel synthetic pathway by building up two DPP moieties step by step simultaneously starting from a neutral phenyl core unit. Characterization of the synthesized oligomeric and polymeric materials via cyclic voltammetry afford LUMO energy levels from −3.49 to −3.59 eV as well as HOMO energy levels from −5.07 to −5.34 eV resulting in low energy band gaps from 1.52 to 1.81 eV. Spin coating of the prepared donor–acceptor oligomers/polymers resulted in well-defined films. Moreover, UV–vis measurements of the investigated donor–acceptor systems showed a broad absorption over the whole visible region. It is demonstrated that Bi-DPP as an electron accepting moiety in donor–acceptor systems offer potential properties for organic solar cell devices. PMID:29491794

  18. Deducing the distribution of terminal electron-accepting processes in hydrologically diverse groundwater systems

    USGS Publications Warehouse

    Chapelle, Francis H.; McMahon, Peter B.; Dubrovsky, Neil M.; Fujii, Roger F.; Oaksford, Edward T.; Vroblesky, Don A.

    1995-01-01

    The distribution of microbially mediated terminal electron-accepting processes (TEAPs( was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor (nitrate, sulfate) consumption, intermediate product (hydrogen (H2)) concentrations, and final product (ferrous iron, sulfide, and methane) production. In each hydrologic system a determination of predominant TEAPs could be arrived at, but the level of confidence appropriate for each determination differed. In a portion of the lacustrine aquifer of the San Joaquin Valley, for example, all three indicators (sulfate concentrations decreasing, H2concentrations in the 1–2 nmol range, and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant TEAP, leading to a high degree of confidence in the determination. In portions of the Floridan aquifer and a petroleum hydrocarbon-contaminated aquifer, sulfate reduction and methanogenesis are indicated by production of sulfide and methane, and hydrogen oncentrations in the 1–4 nmol and 5–14 nmol range, respectively. However, because electron acceptor consumption could not be documented in these systems, less confidence is warranted in the TEAP determination. In the Black Creek aquifer, no pattern of sulfate consumption and sulfide production were observed, but H2 concentrations indicated sulfate reduction as the predominant TEAP. In this case, where just a single line of evidence is available, the least confidence in the TEAP diagnosis is justified. Because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes, it provides a better description of predominant redox processes in groundwater systems than more traditional Eh-based methods.

  19. Photoinduced electron transfer in rigidly linked dimethoxynapthalene-N-methylpyridinium donor-acceptor molecules

    NASA Astrophysics Data System (ADS)

    Clayton, Andrew H. A.; Ghiggino, Kenneth P.; Wilson, Gerard J.; Keyte, Peter J.; Paddon-Row, Michael N.

    1992-07-01

    Photoinduced electron transfer (ET) is studied in a series of novel molecules containing a dimethoxynaphthalene (DMN) donor and either a pyridine (P) or N-methylpyridinium (P-Me +) acceptor covalently linked via a rigid nonbornalogous bridge ( n sigma bonds in length). ET rates of the order of 10 10 s -1 were measured for the DMN- n-P-Me + series ( n = 4, 6), while no appreciable ET was observed for the DMN- n-P compounds. Electronic and nuclear factors are discussed and the results rationalized in terms of Marcus—Hush and non-adiabatic ET theories.

  20. Effects of Iron and Nitrogen Limitation on Sulfur Isotope Fractionation during Microbial Sulfate Reduction

    PubMed Central

    Ono, Shuhei; Bosak, Tanja

    2012-01-01

    Sulfate-reducing microbes utilize sulfate as an electron acceptor and produce sulfide that is depleted in heavy isotopes of sulfur relative to sulfate. Thus, the distribution of sulfur isotopes in sediments can trace microbial sulfate reduction (MSR), and it also has the potential to reflect the physiology of sulfate-reducing microbes. This study investigates the relationship between the availability of iron and reduced nitrogen and the magnitude of S-isotope fractionation during MSR by a marine sulfate-reducing bacterium, DMSS-1, a Desulfovibrio species, isolated from salt marsh in Cape Cod, MA. Submicromolar levels of iron increase sulfur isotope fractionation by about 50% relative to iron-replete cultures of DMSS-1. Iron-limited cultures also exhibit decreased cytochrome c-to-total protein ratios and cell-specific sulfate reduction rates (csSRR), implying changes in the electron transport chain that couples carbon and sulfur metabolisms. When DMSS-1 fixes nitrogen in ammonium-deficient medium, it also produces larger fractionation, but it occurs at faster csSRRs than in the ammonium-replete control cultures. The energy and reducing power required for nitrogen fixation may be responsible for the reverse trend between S-isotope fractionation and csSRR in this case. Iron deficiency and nitrogen fixation by sulfate-reducing microbes may lead to the large observed S-isotope effects in some euxinic basins and various anoxic sediments. PMID:23001667

  1. Electron acceptors for energy generation in microbial fuel cells fed with wastewaters: A mini-review.

    PubMed

    He, Chuan-Shu; Mu, Zhe-Xuan; Yang, Hou-Yun; Wang, Ya-Zhou; Mu, Yang; Yu, Han-Qing

    2015-12-01

    Microbial fuel cells (MFCs) have gained tremendous global interest over the last decades as a device that uses bacteria to oxidize organic and inorganic matters in the anode with bioelectricity generation and even for purpose of bioremediation. However, this prospective technology has not yet been carried out in field in particular because of its low power yields and target compounds removal which can be largely influenced by electron acceptors contributing to overcome the potential losses existing on the cathode. This mini review summarizes various electron acceptors used in recent years in the categories of inorganic and organic compounds, identifies their merits and drawbacks, and compares their influences on performance of MFCs, as well as briefly discusses possible future research directions particularly from cathode aspect. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Tumor cell membrane-targeting pH-dependent electron donor-acceptor fluorescence systems with low background signals.

    PubMed

    Han, Liang; Liu, Mingming; Ye, Deyong; Zhang, Ning; Lim, Ed; Lu, Jing; Jiang, Chen

    2014-03-01

    Minimizing the background signal is crucial for developing tumor-imaging techniques with sufficient specificity and sensitivity. Here we use pH difference between healthy tissues and tumor and tumor targeting delivery to achieve this goal. We synthesize fluorophore-dopamine conjugate as pH-dependent electron donor-acceptor fluorescence system. Fluorophores are highly sensitive to electron-transfer processes, which can alter their optical properties. The intrinsic redox properties of dopamine are oxidation of hydroquinone to quinone at basic pH and reduction of quinone to hydroquinone at acidic pH. Quinone can accept electron then quench fluorescence. We design tumor cell membrane-targeting carrier for delivery. We demonstrate quenched fluorophore-quinone can be specially transferred to tumor extracellular environment and tumor-accumulated fluorophore can be activated by acidic pH. These tumor-targeting pH-dependent electron donor-acceptor fluorescence systems may offer new opportunity for developing tumor-imaging techniques. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Highly Soluble Benzo[ghi]perylenetriimide Derivatives: Stable and Air-Insensitive Electron Acceptors for Artificial Photosynthesis.

    PubMed

    Chen, Hung-Cheng; Hsu, Chao-Ping; Reek, Joost N H; Williams, René M; Brouwer, Albert M

    2015-11-01

    A series of new benzo[ghi]perylenetriimide (BPTI) derivatives has been synthesized and characterized. These remarkably soluble BPTI derivatives show strong optical absorption in the range of λ=300-500 nm and have a high triplet-state energy of 1.67 eV. A cyanophenyl substituent renders BPTI such a strong electron acceptor (Ered =-0.11 V vs. the normal hydrogen electrode) that electron-trapping reactions with O2 and H2 O do not occur. The BPTI radical anion on a fluorine-doped tin oxide|TiO2 electrode is persistent up to tens of seconds (t1/2 =39 s) in air-saturated buffer solution. As a result of favorable packing, theoretical electron mobilities (10(-2) ∼10(-1) cm(2) V(-1) s(-1)) are high and similar to the experimental values observed for perylene diimide and C60 derivatives. Our studies show the potential of the cyanophenyl-modified BPTI compounds as electron acceptors in devices for artificial photosynthesis in water splitting that are also very promising nonfullerene electron-transport materials for organic solar cells. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  4. Nitrate is a preferred electron acceptor for growth of freshwater selenate-respiring bacteria

    USGS Publications Warehouse

    Steinberg, Nisan A.; Blum, Jodi Switzer; Hochstein , Lawrence; Oremland, Ronald S.

    1992-01-01

    An anaerobic, freshwater enrichment grew with either nitrate or selenate as an electron acceptor. With both ions present, nitrate reduction preceded selenate reduction. An isolate from the enrichment grew on either ion, but the presence of nitrate precluded the reduction of selenate. Stock cultures of denitrifiers grew anaerobically on nitrate but not on selenate.

  5. Polymer/Polymer Blend Solar Cells Using Tetraazabenzodifluoranthene Diimide Conjugated Polymers as Electron Acceptors

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

    Li, Haiyan; Hwang, Ye-Jin; Earmme, Taeshik

    2015-03-02

    Two n-type semiconducting polymers with alternating arylene (thiophene or selenophene)–tetraazabenzodifluoranthene diimide (BFI) donor–acceptor architecture have been investigated as new electron acceptors in polymer/polymer blend solar cells. The new selenophene-linked polymer, PBFI-S, has a significantly smaller optical band gap (1.13 eV) than the thiophene-linked PBFI-T (1.38 eV); however, both polymers have similar HOMO/LUMO energy levels determined from cyclic voltammetry. Blends of PBFI-T with the thiazolothiazole–dithienylsilole donor polymer (PSEHTT) gave a 2.60% power conversion efficiency (PCE) with a 7.34 mA/cm2 short-circuit current. In contrast, PBFI-S:PSEHTT blends had a 0.75% PCE with similarly reduced photocurrent and external quantum efficiency. Reduced free energy formore » charge transfer and reduced bulk electron mobility in PBFI-S:PSEHTT blends compared to PBFI-T:PSEHTT blends as well as significant differences in bulk film morphology are among the reasons for the large loss in efficiency in PBFI-S:PSEHTT blend solar cells.« less

  6. Dibenzothiophene-Substituted Fullerene Derivative as Electron Acceptor for Polymer Solar Cells.

    PubMed

    Kim, Hee Un; Park, Jong Baek; Hwang, Do-Hoon

    2016-05-01

    A new fullerene derivative, [6,6]-dibenzo[b,d]thiophene-C61-butyric acid methyl ester (DBTC61BM) was synthesized from C60 using tosylhydrazone, and used as an electron-acceptor material for poly(3-hexylthiophene) (P3HT)-based organic photovoltaic cells. The synthesized DBTC61BM was used to modify the basic structure of [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) by replacing the aromatic part with dibenzo[b,d]thiophene. The solubilities of DBTC61BM and PC61BM are similar; they have good solubilities in common organic solvents such as dichloromethane, chloroform, toluene, and 1,2-dichlorobenzene. The Stern-Volmer quenching constant (K(sv)) of DBTC61BM was 7.14 x 10(3) M(-1), and was correlated with the binding affinity between the fluorophore and a quencher. The lowest unoccupied molecular orbital energy level of DBTC61BM was -3.71 eV. The charge-carrier mobility of a P3HT:DBTC61BM blend film was determined using the space-charge-limited current method; the electron mobility value obtained for the P3HT:DBTC61BM blend film was 2.13 x 10(-4) cm2 V(-1) s(-1). Photovoltaic devices were fabricated using P3HT as the electron donor and DBTC61BM as the electron acceptor. Among the fabricated devices, photovoltaic cells with the structure ITO/PEDOT:PSS/P3HT:DBTC61BM/LiF/Al showed the highest power conversion efficiency, namely 3.23%, with an open-circuit voltage of 0.64 V, short-circuit-current density of 8.14 mA cm(-2), and fill factor of 0.59, under AM 1.5 G (100 mW cm(-2)) illumination.

  7. U(VI) bioreduction with emulsified vegetable oil as the electron donor--model application to a field test.

    PubMed

    Tang, Guoping; Watson, David B; Wu, Wei-Min; Schadt, Christopher W; Parker, Jack C; Brooks, Scott C

    2013-04-02

    We amended a shallow fast-flowing uranium (U) contaminated aquifer with emulsified vegetable oil (EVO) and subsequently monitored the biogeochemical responses for over a year. Using a biogeochemical model developed in a companion article (Tang et al., Environ. Sci. Technol.2013, doi: 10.1021/es304641b) based on microcosm tests, we simulated geochemical and microbial dynamics in the field test during and after the 2-h EVO injection. When the lab-determined parameters were applied in the field-scale simulation, the estimated rate coefficient for EVO hydrolysis in the field was about 1 order of magnitude greater than that in the microcosms. Model results suggested that precipitation of long-chain fatty acids, produced from EVO hydrolysis, with Ca in the aquifer created a secondary long-term electron donor source. The model predicted substantial accumulation of denitrifying and sulfate-reducing bacteria, and U(IV) precipitates. The accumulation was greatest near the injection wells and along the lateral boundaries of the treatment zone where electron donors mixed with electron acceptors in the groundwater. While electron acceptors such as sulfate were generally considered to compete with U(VI) for electrons, this work highlighted their role in providing electron acceptors for microorganisms to degrade complex substrates thereby enhancing U(VI) reduction and immobilization.

  8. Organic photovoltaic cells based on unconventional electron donor fullerene and electron acceptor copper hexadecafluorophthalocyanine

    NASA Astrophysics Data System (ADS)

    Yang, J. L.; Sullivan, P.; Schumann, S.; Hancox, I.; Jones, T. S.

    2012-01-01

    We demonstrate organic discrete heterojunction photovoltaic cells based on fullerene (C60) and copper hexadecafluorophthalocyanine (F16CuPc), in which the C60 and F16CuPc act as the electron donor and the electron acceptor, respectively. The C60/F16CuPc cells fabricated with conventional and inverted architectures both exhibit comparable power conversion efficiencies. Furthermore, we show that the photocurrent in both cells is generated by a conventional exciton dissociation mechanism rather than the exciton recombination mechanism recently proposed for a similar C60/F16ZnPc system [Song et al., J. Am. Chem. Soc. 132, 4554 (2010)]. These results demonstrate that new unconventional material systems are a potential way to fabricate organic photovoltaic cells with inverted as well as conventional architectures.

  9. 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.

  10. Desulfosoma caldarium gen. nov., sp. nov., a thermophilic sulfate-reducing bacterium from a terrestrial hot spring.

    PubMed

    Baena, Sandra; Perdomo, Natalia; Carvajal, Catalina; Díaz, Carolina; Patel, Bharat K C

    2011-04-01

    A thermophilic, sulfate-reducing bacterium, designated strain USBA-053(T), was isolated from a terrestrial hot spring located at a height of 2500 m in the Colombian Andes (5° 45' 33.29″ N 73° 6' 49.89″ W), Colombia. Cells of strain USBA-053(T) were oval- to rod-shaped, Gram-negative and motile by means of a single polar flagellum. The strain grew autotrophically with H(2) as the electron donor and heterotrophically on formate, propionate, butyrate, valerate, isovalerate, lactate, pyruvate, ethanol, glycerol, serine and hexadecanoic acid in the presence of sulfate as the terminal electron acceptor. The main end products from lactate degradation, in the presence of sulfate, were acetate, CO(2) and H(2)S. Strain USBA-053(T) fermented pyruvate in the absence of sulfate and grew optimally at 57 °C (growth temperature ranged from 50 °C to 62 °C) and pH 6.8 (growth pH ranged from 5.7 to 7.7). The novel strain was slightly halophilic and grew in NaCl concentrations ranging from 5 to 30 g l(-1), with an optimum at 25 g l(-1) NaCl. Sulfate, thiosulfate and sulfite were used as electron acceptors, but not elemental sulfur, nitrate or nitrite. The G+C content of the genomic DNA was 56±1 mol%. 16S rRNA gene sequence analysis indicated that strain USBA-053(T) was a member of the class Deltaproteobacteria, with Desulfacinum hydrothermale MT-96(T) as the closest relative (93 % gene sequence similarity). On the basis of physiological characteristics and phylogenetic analysis, it is suggested that strain USBA-053(T) represents a new genus and novel species for which the name Desulfosoma caldarium gen. nov., sp. nov. is proposed. The type strain of the type species is USBA-053(T) ( = KCTC 5670(T) = DSM 22027(T)).

  11. Structure and electronic properties of Alq3 derivatives with electron acceptor/donor groups at the C4 positions of the quinolate ligands: a theoretical study.

    PubMed

    Rao, Joshi Laxmikanth; Bhanuprakash, Kotamarthi

    2011-12-01

    The molecular structures of the ground (S(0)) and first singlet excited (S(1)) states of Alq3 derivatives in which pyrazolyl and 3-methylpyrazolyl groups are substituted at the C4 positions of the 8-hydroxyquinolate ligands as electron acceptors, and piperidinyl and N-methylpiperazinyl groups are substituted at the same positions as electron donors, have been optimized using the B3LYP/6-31G and CIS/6-31G methods, respectively. In order to analyze the electronic transitions in these derivatives, the frontier molecular orbital characteristics were analyzed systematically, and it was found that the highest occupied molecular orbital is localized on the A ligand while the lowest unoccupied molecular orbital is localized on the B ligand in their ground states, similar to what is seen for mer-Alq3. The absorption and emission spectra were evaluated at the TD-PBE0/6-31G level, and it was observed that electron acceptor substitution causes a red-shift in the emission spectra, which is also seen experimentally. The reorganization energies were calculated at the B3LYP/6-31G level and the results show that acceptor/donor substitution has a significant effect on the intrinsic charge mobilities of these derivatives as compared to mer-Alq3.

  12. Biochemistry, physiology and biotechnology of sulfate-reducing bacteria.

    PubMed

    Barton, Larry L; Fauque, Guy D

    2009-01-01

    Chemolithotrophic bacteria that use sulfate as terminal electron acceptor (sulfate-reducing bacteria) constitute a unique physiological group of microorganisms that couple anaerobic electron transport to ATP synthesis. These bacteria (220 species of 60 genera) can use a large variety of compounds as electron donors and to mediate electron flow they have a vast array of proteins with redox active metal groups. This chapter deals with the distribution in the environment and the major physiological and metabolic characteristics of sulfate-reducing bacteria (SRB). This chapter presents our current knowledge of soluble electron transfer proteins and transmembrane redox complexes that are playing an essential role in the dissimilatory sulfate reduction pathway of SRB of the genus Desulfovibrio. Environmentally important activities displayed by SRB are a consequence of the unique electron transport components or the production of high levels of H(2)S. The capability of SRB to utilize hydrocarbons in pure cultures and consortia has resulted in using these bacteria for bioremediation of BTEX (benzene, toluene, ethylbenzene and xylene) compounds in contaminated soils. Specific strains of SRB are capable of reducing 3-chlorobenzoate, chloroethenes, or nitroaromatic compounds and this has resulted in proposals to use SRB for bioremediation of environments containing trinitrotoluene and polychloroethenes. Since SRB have displayed dissimilatory reduction of U(VI) and Cr(VI), several biotechnology procedures have been proposed for using SRB in bioremediation of toxic metals. Additional non-specific metal reductase activity has resulted in using SRB for recovery of precious metals (e.g. platinum, palladium and gold) from waste streams. Since bacterially produced sulfide contributes to the souring of oil fields, corrosion of concrete, and discoloration of stonework is a serious problem, there is considerable interest in controlling the sulfidogenic activity of the SRB. The

  13. Microbial Diversity in Sulfate-Reducing Marine Sediment Enrichment Cultures Associated with Anaerobic Biotransformation of Coastal Stockpiled Phosphogypsum (Sfax, Tunisia)

    PubMed Central

    Zouch, Hana; Karray, Fatma; Armougom, Fabrice; Chifflet, Sandrine; Hirschler-Réa, Agnès; Kharrat, Hanen; Kamoun, Lotfi; Ben Hania, Wajdi; Ollivier, Bernard; Sayadi, Sami; Quéméneur, Marianne

    2017-01-01

    Anaerobic biotechnology using sulfate-reducing bacteria (SRB) is a promising alternative for reducing long-term stockpiling of phosphogypsum (PG), an acidic (pH ~3) by-product of the phosphate fertilizer industries containing high amounts of sulfate. The main objective of this study was to evaluate, for the first time, the diversity and ability of anaerobic marine microorganisms to convert sulfate from PG into sulfide, in order to look for marine SRB of biotechnological interest. A series of sulfate-reducing enrichment cultures were performed using different electron donors (i.e., acetate, formate, or lactate) and sulfate sources (i.e., sodium sulfate or PG) as electron acceptors. Significant sulfide production was observed from enrichment cultures inoculated with marine sediments, collected near the effluent discharge point of a Tunisian fertilizer industry (Sfax, Tunisia). Sulfate sources impacted sulfide production rates from marine sediments as well as the diversity of SRB species belonging to Deltaproteobacteria. When PG was used as sulfate source, Desulfovibrio species dominated microbial communities of marine sediments, while Desulfobacter species were mainly detected using sodium sulfate. Sulfide production was also affected depending on the electron donor used, with the highest production obtained using formate. In contrast, low sulfide production (acetate-containing cultures) was associated with an increase in the population of Firmicutes. These results suggested that marine Desulfovibrio species, to be further isolated, are potential candidates for bioremediation of PG by immobilizing metals and metalloids thanks to sulfide production by these SRB. PMID:28871244

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

    EPA Science Inventory

    Lab- and pilot-scale simultaneous nitrification, denitrification and phosphorus removal-sequencing batch reactors were operated under cyclic anaerobic and micro-aerobic conditions. The use of oxygen, nitrite, and nitrate as electron acceptors by Candidatus Accumulibacter phosphat...

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

    PubMed Central

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

    2014-01-01

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

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

    DOE PAGES

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

    2014-10-28

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

  17. Sulfate-Reducing Bacterium with Unusual Morphology and Pigment Content

    PubMed Central

    Jones, H. E.

    1971-01-01

    A dissimilatory sulfate-reducing bacterium was isolated which differed in morphology and pigment content from previously described species. The organism was mesophilic, obligately anaerobic, gram-negative, nonsporulating, long, and slender with one polar flagellum. Whole cells fluoresced red at neutral pH when excited with light at 365 nm owing to the presence of a pink pigment. Desulfoviridin was present. Reduced minus oxidized spectra of whole cells showed peaks in the position of a c-type cytochrome characteristic of Desulfovibrio species and peaks at about 629 and 603 nm. CO difference spectra showed the presence of a CO-binding pigment with a peak at 593 nm. Lactate and pyruvate supported growth in the presence of sulfate but not in its absence. Sulfate, sulfite, and thiosulfate served as electron acceptors for growth. Hydrogenase was present. The deoxyribonucleic acid had a buoyant density of 1.722 g/cm3 and a guanosine plus cystosine molar percentage of total bases calculated by two different methods of 61.2 or 63.2. Images PMID:4929856

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  19. Acceptors in ZnO

    DOE PAGES

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

    2015-03-21

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

  20. Oxygen-Dependent Growth of the Sulfate-Reducing Bacterium Desulfovibrio oxyclinae in Coculture with Marinobacter sp. Strain MB in an Aerated Sulfate-Depleted Chemostat

    PubMed Central

    Sigalevich, Pavel; Cohen, Yehuda

    2000-01-01

    A chemostat coculture of the sulfate-reducing bacterium Desulfovibrio oxyclinae and the facultatively aerobic heterotroph Marinobacter sp. strain MB was grown for 1 week under anaerobic conditions at a dilution rate of 0.05 h−1. It was then exposed to an oxygen flux of 223 μmol min−1 by gassing the growth vessel with 5% O2. Sulfate reduction persisted under these conditions, though the amount of sulfate reduced decreased by 45% compared to the amount reduced during the initial anaerobic mode. After 1 week of growth under these conditions, sulfate was excluded from the incoming medium. The sulfate concentration in the growth vessel decreased exponentially from 4.1 mM to 2.5 μM. The coculture consumed oxygen effectively, and no residual oxygen was detected during either growth mode in which oxygen was supplied. The proportion of D. oxyclinae cells in the coculture as determined by in situ hybridization decreased from 86% under anaerobic conditions to 70% in the microaerobic sulfate-reducing mode and 34% in the microaerobic sulfate-depleted mode. As determined by the most-probable-number (MPN) method, the numbers of viable D. oxyclinae cells during the two microaerobic growth modes decreased compared to the numbers during the anaerobic growth mode. However, there was no significant difference between the MPN values for the two modes when oxygen was supplied. The patterns of consumption of electron donors and acceptors suggested that when oxygen was supplied in the absence of sulfate and thiosulfate, D. oxyclinae performed incomplete aerobic oxidation of lactate to acetate. This is the first observation of oxygen-dependent growth of a sulfate-reducing bacterium in the absence of either sulfate or thiosulfate. Cells harvested during the microaerobic sulfate-depleted stage and exposed to sulfate and thiosulfate in a respiration chamber were capable of anaerobic sulfate and thiosulfate reduction. PMID:11055958

  1. Towards explaining excess CO2 production in wetlands - the roles of solid and dissolved organic matter as electron acceptors and of substrate quality

    NASA Astrophysics Data System (ADS)

    Knorr, Klaus-Holger; Gao, Chuanyu; Agethen, Svenja; Sander, Michael

    2017-04-01

    To understand carbon storage in water logged, anaerobic peatlands, factors controlling mineralization have been studied for decades. Temperature, substrate quality, water table position and the availability of electron acceptors for oxidation of organic carbon have been identified as major factors. However, many studies reported an excess carbon dioxide (CO2) production over methane (CH4) that cannot be explained by available electron acceptors, and peat soils did not reach strictly methanogenic conditions (i.e., a stoichiometric formation ratio of 1:1 of CO2 to CH4). It has been hypothesized that peat organic matter (OM) provides a previously unrecognized electron acceptor for microbial respiration, elevating CO2 to CH4 ratios. Microbial reduction of dissolved OM has been shown in the mid 90's, but only recently mediated electrochemical techniques opened the possibility to access stocks and changes in electron accepting capacities (EAC) of OM in dissolved and solid form. While it was shown that the EAC of OM follows redox cycles of microbial reduction and O2 reoxidation, changes in the EAC of OM were so far not related quantitatively to CO2 production. We therefore tested if CO2 production in anoxic peat incubations is balanced by the consumption of electron acceptors if EAC of OM is included. We set up anoxic incubations with peat and monitored production of CO2 and CH4, and changes in EAC of OM in the dissolved and solid phase over time. Interestingly, in all incubations, the EAC of dissolved OM was poorly related to CO2 and CH4 production. Instead, dissolved OM was rapidly reduced at the onset of the incubations and thereafter remained in reduced form. In contrast, the decrease in the EAC of particulate (i.e. non-dissolved) OM was closely linked to the observed production of non-methanogenic CO2. Thereby, the total EAC of the solid OM pool by far exceeded the EAC of the dissolved OM pool. Over the course of eight week incubations, measured decreases in the EAC

  2. Sulfur isotopic and proteomic profiles of sulfate reducers grown under differential steady-states

    NASA Astrophysics Data System (ADS)

    Leavitt, W.; Venceslau, S.; Waldbauer, J.; Smith, D. A.; Boidi, F. J.; Bradley, A. S.

    2016-12-01

    Microbial sulfate reducers (MSR) drive the Earth's biogeochemical sulfur cycle. At the heart of this energy metabolism is a cascade of redox transformations coupling organic carbon and/or hydrogen oxidation to the dissimilatory reduction of sulfate to sulfide. The product sulfide is depleted in the heavier isotopes of sulfur, relative to the reactant sulfate, consistent with a normal kinetic isotope effect. However, the magnitude of the net fractionation during MSR can range over a range of 70 permil, consistent with a multi-step set of reactions. This range in MSR fractionation has been shown to mainly depend on: i) the cell-specific sulfate reduction rate (csSRR), and ii) the ambient sulfate concentration. However, the fractionation under identical conditions differs among strains (Bradley et al. 2016. Geobio), and so must also be mediated by strain-specific processes, such as the nature and quantity of individual proteins involved in sulfate reduction, electron transport, and growth. In recent work we have examined the influence of electron donor, electron acceptor, and co-limitation under controlled steady-state culture conditions in order better inform models of MSR isotope fractionation, and the physiological and isotopic response to differential environmental forcings (e.g. Leavitt et al. (2013) PNAS). Recent models of the fractionation response to MSR rate (c.f. Bradley 2016; Wing & Halevy, 2016) make specific predictions for the responses of the cellular metabolome and proteome. Here we compare the steady-state S-isotopic fractionation and proteome of `fast' versus `slow' grown D. vulgaris, using replicate chemostats under electron donor limitation. We observe clear and statistically robust changes in some key central MSR and C-metabolism enzymes, though a host of the critical energy-transfer enzymes show no statistically discernable change. We discuss these results in light of recent theoretical advances and their relevance to modern and ancient

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

    PubMed

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

    2017-08-02

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

  4. Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors.

    PubMed

    Milanovsky, Georgy E; Petrova, Anastasia A; Cherepanov, Dmitry A; Semenov, Alexey Yu

    2017-09-01

    The reduction kinetics of the photo-oxidized primary electron donor P 700 in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P 700 , secondary quinone acceptor A 1 , iron-sulfur clusters and external electron donor and acceptors - methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl 2 NQ) and oxygen. PS I complexes containing various quinones in the A 1 -binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl 2 NQ) as well as F X -core complexes, depleted of terminal iron-sulfur F A /F B clusters, were studied. The acceleration of charge recombination in F X -core complexes by PhQ/PQ substitution indicates that backward ET from the iron-sulfur clusters involves quinone in the A 1 -binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P 700 + reduction with the kinetic model. The free energy gap ΔG 0 between F X and F A /F B clusters was estimated as -130 meV. The driving force of ET from A 1 to F X was determined as -50 and -220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A 1A -site, this reaction was found to be endergonic (ΔG 0  = +75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis-Menten kinetics. The second-order rate constants of ET from F A /F B , F X and Cl 2 NQ in the A 1 -site of PS I to external acceptors were estimated. The side production of superoxide radical in the A 1 -site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.

  5. Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence

    NASA Astrophysics Data System (ADS)

    Wong, Michael L.; Charnay, Benjamin D.; Gao, Peter; Yung, Yuk L.; Russell, Michael J.

    2017-10-01

    We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO3-) and nitrite (NO2-) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO2 and N2, will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H2O vapor will then produce acids such as HNO, HNO2, HNO3, and HO2NO2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO2 models, we calculate the NOx delivery to be 2.4 × 105, 6.5 × 108, and 1.9 × 108 molecules cm-2 s-1. After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life.

  6. Cation Effects on the Electron-Acceptor Side of Photosystem II.

    PubMed

    Khan, Sahr; Sun, Jennifer S; Brudvig, Gary W

    2015-06-18

    The normal pathway of electron transfer on the electron-acceptor side of photosystem II (PSII) involves electron transfer from quinone A, QA, to quinone B, QB. It is possible to redirect electrons from QA(-) to water-soluble Co(III) complexes, which opens a new avenue for harvesting electrons from water oxidation by immobilization of PSII on electrode surfaces. Herein, the kinetics of electron transfer from QA(-) to [Co(III)(terpy)2](3+) (terpy = 2,2';6',2″-terpyridine) are investigated with a spectrophotometric assay revealing that the reaction follows Michaelis-Menten saturation kinetics, is inhibited by cations, and is not affected by variation of the QA reduction potential. A negatively charged site on the stromal surface of the PSII protein complex, composed of glutamic acid residues near QA, is hypothesized to bind cations, especially divalent cations. The cations are proposed to tune the redox properties of QA through electrostatic interactions. These observations may thus explain the molecular basis of the effect of divalent cations like Ca(2+), Sr(2+), Mg(2+), and Zn(2+) on the redox properties of the quinones in PSII, which has previously been attributed to long-range conformational changes propagated from divalent cations binding to the Ca(II)-binding site in the oxygen-evolving complex on the lumenal side of the PSII complex.

  7. 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.

  8. Electron acceptor redox potential globally regulates transcriptomic profiling in Shewanella decolorationis S12

    NASA Astrophysics Data System (ADS)

    Lian, Yingli; Yang, Yonggang; Guo, Jun; Wang, Yan; Li, Xiaojing; Fang, Yun; Gan, Lixia; Xu, Meiying

    2016-08-01

    Electron acceptor redox potential (EARP) was presumed to be a determining factor for microbial metabolism in many natural and engineered processes. However, little is known about the potentially global effects of EARP on bacteria. In this study, we compared the physiological and transcriptomic properties of Shewanella decolorationis S12 respiring with different EARPs in microbial electrochemical systems to avoid the effects caused by the other physicochemical properties of real electron acceptor. Results showed that the metabolic activities of strain S12 were nonlinear responses to EARP. The tricarboxylic acid cycle for central carbon metabolism was down-regulated while glyoxylate shunt was up-regulated at 0.8 V compared to 0.2 and -0.2 V, which suggested that EARP is an important but not the only determinant for metabolic pathways of strain S12. Moreover, few cytochrome c genes were differentially expressed at different EARPs. The energy intensive flagella assembly and assimilatory sulfur metabolism pathways were significantly enriched at 0.8 V, which suggested strain S12 had stronger electrokinesis behavior and oxidative stress-response at high EARP. This study provides the first global information of EARP regulations on microbial metabolism, which will be helpful for understanding microorganism respiration.

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

    USGS Publications Warehouse

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

    1993-01-01

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

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

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

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

    2016-02-07

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

  11. Tuning the Rectification Ratio by Changing the Electronic Nature (Open-Shell and Closed-Shell) in Donor-Acceptor Self-Assembled Monolayers.

    PubMed

    Souto, Manuel; Yuan, Li; Morales, Dayana C; Jiang, Li; Ratera, Imma; Nijhuis, Christian A; Veciana, Jaume

    2017-03-29

    This Communication describes the mechanism of charge transport across self-assembled monolayers (SAMs) of two donor-acceptor systems consisting of a polychlorotriphenylmethyl (PTM) electron-acceptor moiety linked to an electron-donor ferrocene (Fc) unit supported by ultraflat template-stripped Au and contacted by a eutectic alloy of gallium and indium top contacts. The electronic and supramolecular structures of these SAMs were well characterized. The PTM unit can be switched between the nonradical and radical forms, which influences the rectification behavior of the junction. Junctions with nonradical units rectify currents via the highest occupied molecular orbital (HOMO) with a rectification ratio R = 99, but junctions with radical units have a new accessible state, a single-unoccupied molecular orbital (SUMO), which turns rectification off and drops R to 6.

  12. Fine-tuning of electronic properties in donor-acceptor conjugated polymers based on oligothiophenes

    NASA Astrophysics Data System (ADS)

    Imae, Ichiro; Sagawa, Hitoshi; Harima, Yutaka

    2018-03-01

    A novel series of donor-acceptor conjugated polymers having oligothiophenes with well-defined structures were synthesized and their optical, electrochemical, and photovoltaic properties were investigated. It was found that the absorption bands of polymers were red-shifted with increasing number of ethylenedioxy groups added to each oligothiophene unit and that their band edges reached over 1000 nm. The systematical fine-tuning of the electronic properties was achieved using the chemical structures of oligothiophene units. Photovoltaic cells based on polymer/(6,6)-phenyl C61 butyric acid methyl ester (PC61BM) exhibited power conversion efficiencies in the range from 0.004 to 1.10%, reflecting the electronic properties of the polymers.

  13. Degradation of phenol via phenylphosphate and carboxylation to 4-hydroxybenzoate by a newly isolated strain of the sulfate-reducing bacterium Desulfobacterium anilini.

    PubMed

    Ahn, Young-Beom; Chae, Jong-Chan; Zylstra, Gerben J; Häggblom, Max M

    2009-07-01

    A sulfate-reducing phenol-degrading bacterium, strain AK1, was isolated from a 2-bromophenol-utilizing sulfidogenic estuarine sediment enrichment culture. On the basis of phylogenetic analysis of the 16S rRNA gene and DNA homology, strain AK1 is most closely related to Desulfobacterium anilini strain Ani1 (= DSM 4660(T)). In addition to phenol, this organism degrades a variety of other aromatic compounds, including benzoate, 2-hydroxybenzoate, 4-hydroxybenzoate, 4-hydroxyphenylacetate, 2-aminobenzoate, 2-fluorophenol, and 2-fluorobenzoate, but it does not degrade aniline, 3-hydroxybenzoate, 4-cyanophenol, 2,4-dihydroxybenzoate, monohalogenated phenols, or monohalogenated benzoates. Growth with sulfate as an electron acceptor occurred with acetate and pyruvate but not with citrate, propionate, butyrate, lactate, glucose, or succinate. Strain AK1 is able to use sulfate, sulfite, and thiosulfate as electron acceptors. A putative phenylphosphate synthase gene responsible for anaerobic phenol degradation was identified in strain AK1. In phenol-grown cultures inducible expression of the ppsA gene was verified by reverse transcriptase PCR, and 4-hydroxybenzoate was detected as an intermediate. These results suggest that the pathway for anaerobic degradation of phenol in D. anilini strain AK1 proceeds via phosphorylation of phenol to phenylphosphate, followed by carboxylation to 4-hydroxybenzoate. The details concerning such reaction pathways in sulfidogenic bacteria have not been characterized previously.

  14. The ecophysiology of sulfur isotope fractionation by sulfate reducing bacteria in response to variable environmental conditions

    NASA Astrophysics Data System (ADS)

    Leavitt, W.; Bradley, A. S.; Johnston, D. T.; Pereira, I. A. C.; Venceslau, S.; Wallace, C.

    2014-12-01

    Microbial sulfate reducers (MSR) drive the Earth's biogeochemical sulfur cycle. At the heart of this energy metabolism is a cascade of redox transformations coupling organic carbon and/or hydrogen oxidation to the dissimilatory reduction of sulfate to sulfide. The sulfide produced is depleted in the heavier isotopes of sulfur relative to sulfate. The magnitude of discrimination (fractionation) depends on: i) the cell-specific sulfate reduction rate (csSRR, Kaplan & Rittenberg (1964) Can. J. Microbio.; Chambers et al. (1975) Can. J. Microbio; Sim et al. (2011) GCA; Leavitt et al. (2013) PNAS), ii) the ambient sulfate concentration (Harrison & Thode (1958) Research; Habicht et al. (2002) Science; Bradley et al. in review), iii) both sulfate and electron donor availability, or iv) an intrinsic physiological limitation (e.g. cellular division rate). When neither sulfate nor electron donor limits csSRR a more complex function relates the magnitude of isotope fractionation to cell physiology and environmental conditions. In recent and on-going work we have examined the importance of enzyme-specific fractionation factors, as well as the influence of electron donor or electron acceptor availability under carefully controlled culture conditions (e.g. Leavitt et al. (2013) PNAS). In light of recent advances in MSR genetics and biochemistry we utilize well-characterized mutant strains, along with a continuous-culture methodology (Leavitt et al. (2013) PNAS) to further probe the fractionation capacity of this metabolism under controlled physiological conditions. We present our latest findings on the magnitude of S and D/H isotope fractionation in both wild type and mutant strains. We will discuss these in light of recent theoretical advances (Wing & Halevy (2014) PNAS), examining the mode and relevance of MSR isotope fractionation in the laboratory to modern and ancient environmental settings, particularly anoxic marine sediments.

  15. Long-range electron transfer in zinc-phthalocyanine-oligo(phenylene-ethynylene)-based donor-bridge-acceptor dyads.

    PubMed

    Göransson, Erik; Boixel, Julien; Fortage, Jérôme; Jacquemin, Denis; Becker, Hans-Christian; Blart, Errol; Hammarström, Leif; Odobel, Fabrice

    2012-11-05

    In the context of long-range electron transfer for solar energy conversion, we present the synthesis, photophysical, and computational characterization of two new zinc(II) phthalocyanine oligophenylene-ethynylene based donor-bride-acceptor dyads: ZnPc-OPE-AuP(+) and ZnPc-OPE-C(60). A gold(III) porphyrin and a fullerene has been used as electron accepting moieties, and the results have been compared to a previously reported dyad with a tin(IV) dichloride porphyrin as the electron acceptor (Fortage et al. Chem. Commun. 2007, 4629). The results for ZnPc-OPE-AuP(+) indicate a remarkably strong electronic coupling over a distance of more than 3 nm. The electronic coupling is manifested in both the absorption spectrum and an ultrafast rate for photoinduced electron transfer (k(PET) = 1.0 × 10(12) s(-1)). The charge-shifted state in ZnPc-OPE-AuP(+) recombines with a relatively low rate (k(BET) = 1.0 × 10(9) s(-1)). In contrast, the rate for charge transfer in the other dyad, ZnPc-OPE-C(60), is relatively slow (k(PET) = 1.1 × 10(9) s(-1)), while the recombination is very fast (k(BET) ≈ 5 × 10(10) s(-1)). TD-DFT calculations support the hypothesis that the long-lived charge-shifted state of ZnPc-OPE-AuP(+) is due to relaxation of the reduced gold porphyrin from a porphyrin ring based reduction to a gold centered reduction. This is in contrast to the faster recombination in the tin(IV) porphyrin based system (k(BET) = 1.2 × 10(10) s(-1)), where the excess electron is instead delocalized over the porphyrin ring.

  16. Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence.

    PubMed

    Wong, Michael L; Charnay, Benjamin D; Gao, Peter; Yung, Yuk L; Russell, Michael J

    2017-10-01

    We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO 3 - ) and nitrite (NO 2 - ) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO 2 and N 2 , will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H 2 O vapor will then produce acids such as HNO, HNO 2 , HNO 3 , and HO 2 NO 2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO 2 models, we calculate the NOx delivery to be 2.4 × 10 5 , 6.5 × 10 8 , and 1.9 × 10 8 molecules cm -2 s -1 . After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life. Key Words: Nitrogen oxides-Nitrate-Nitrite-Photochemistry-Lightning-Emergence of life. Astrobiology 17, 975-983.

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

    PubMed Central

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

    2014-01-01

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

  18. A review on chemistry of a powerful organic electron acceptor 7, 7, 8, 8, tetracynoquinodimethane (TCNQ)

    NASA Astrophysics Data System (ADS)

    Singh, Yadunath

    2018-05-01

    Organic semiconductors have so far found extensive practical applications similar to inorganic semiconductors. Interest in these compounds has been stimulated by the synthesis of several powerful electron acceptors, such as tetracynoethylene (TCNE), 7, 7, 8, 8, tetracynoquinodimethane (TCNQ) and cyno-p-benzoquinone. In this connection TCNQ is of particular interest, due to presence of four powerful electron accepting groups in its molecule. Nucleophillic addition reactions, which are rarely encountered among unsaturated compounds, as well as addition reactions proceeding via a one electron transfer stage are characteristic of this substance.

  19. Dominance of sulfur-fueled iron oxide reduction in low-sulfate freshwater sediments.

    PubMed

    Hansel, Colleen M; Lentini, Chris J; Tang, Yuanzhi; Johnston, David T; Wankel, Scott D; Jardine, Philip M

    2015-11-01

    A central tenant in microbial biogeochemistry is that microbial metabolisms follow a predictable sequence of terminal electron acceptors based on the energetic yield for the reaction. It is thereby oftentimes assumed that microbial respiration of ferric iron outcompetes sulfate in all but high-sulfate systems, and thus sulfide has little influence on freshwater or terrestrial iron cycling. Observations of sulfate reduction in low-sulfate environments have been attributed to the presumed presence of highly crystalline iron oxides allowing sulfate reduction to be more energetically favored. Here we identified the iron-reducing processes under low-sulfate conditions within columns containing freshwater sediments amended with structurally diverse iron oxides and fermentation products that fuel anaerobic respiration. We show that despite low sulfate concentrations and regardless of iron oxide substrate (ferrihydrite, Al-ferrihydrite, goethite, hematite), sulfidization was a dominant pathway in iron reduction. This process was mediated by (re)cycling of sulfur upon reaction of sulfide and iron oxides to support continued sulfur-based respiration--a cryptic sulfur cycle involving generation and consumption of sulfur intermediates. Although canonical iron respiration was not observed in the sediments amended with the more crystalline iron oxides, iron respiration did become dominant in the presence of ferrihydrite once sulfate was consumed. Thus, despite more favorable energetics, ferrihydrite reduction did not precede sulfate reduction and instead an inverse redox zonation was observed. These findings indicate that sulfur (re)cycling is a dominant force in iron cycling even in low-sulfate systems and in a manner difficult to predict using the classical thermodynamic ladder.

  20. Dominance of sulfur-fueled iron oxide reduction in low-sulfate freshwater sediments

    PubMed Central

    Hansel, Colleen M; Lentini, Chris J; Tang, Yuanzhi; Johnston, David T; Wankel, Scott D; Jardine, Philip M

    2015-01-01

    A central tenant in microbial biogeochemistry is that microbial metabolisms follow a predictable sequence of terminal electron acceptors based on the energetic yield for the reaction. It is thereby oftentimes assumed that microbial respiration of ferric iron outcompetes sulfate in all but high-sulfate systems, and thus sulfide has little influence on freshwater or terrestrial iron cycling. Observations of sulfate reduction in low-sulfate environments have been attributed to the presumed presence of highly crystalline iron oxides allowing sulfate reduction to be more energetically favored. Here we identified the iron-reducing processes under low-sulfate conditions within columns containing freshwater sediments amended with structurally diverse iron oxides and fermentation products that fuel anaerobic respiration. We show that despite low sulfate concentrations and regardless of iron oxide substrate (ferrihydrite, Al-ferrihydrite, goethite, hematite), sulfidization was a dominant pathway in iron reduction. This process was mediated by (re)cycling of sulfur upon reaction of sulfide and iron oxides to support continued sulfur-based respiration—a cryptic sulfur cycle involving generation and consumption of sulfur intermediates. Although canonical iron respiration was not observed in the sediments amended with the more crystalline iron oxides, iron respiration did become dominant in the presence of ferrihydrite once sulfate was consumed. Thus, despite more favorable energetics, ferrihydrite reduction did not precede sulfate reduction and instead an inverse redox zonation was observed. These findings indicate that sulfur (re)cycling is a dominant force in iron cycling even in low-sulfate systems and in a manner difficult to predict using the classical thermodynamic ladder. PMID:25871933

  1. Desulfosporosinus acididurans sp. nov.: an acidophilic sulfate-reducing bacterium isolated from acidic sediments.

    PubMed

    Sánchez-Andrea, Irene; Stams, Alfons J M; Hedrich, Sabrina; Ňancucheo, Ivan; Johnson, D Barrie

    2015-01-01

    Three strains of sulfate-reducing bacteria (M1(T), D, and E) were isolated from acidic sediments (White river and Tinto river) and characterized phylogenetically and physiologically. All three strains were obligately anaerobic, mesophilic, spore-forming straight rods, stained Gram-negative and displayed variable motility during active growth. The pH range for growth was 3.8-7.0, with an optimum at pH 5.5. The temperature range for growth was 15-40 °C, with an optimum at 30 °C. Strains M1(T), D, and E used a wide range of electron donors and acceptors, with certain variability within the different strains. The nominated type strain (M1(T)) used ferric iron, nitrate, sulfate, elemental sulfur, and thiosulfate (but not arsenate, sulfite, or fumarate) as electron acceptors, and organic acids (formate, lactate, butyrate, fumarate, malate, and pyruvate), alcohols (glycerol, methanol, and ethanol), yeast extract, and sugars (xylose, glucose, and fructose) as electron donors. It also fermented some substrates such as pyruvate and formate. Strain M1(T) tolerated up to 50 mM ferrous iron and 10 mM aluminum, but was inhibited by 1 mM copper. On the basis of phenotypic, phylogenetic, and genetic characteristics, strains M1(T), D, and E represent a novel species within the genus Desulfosporosinus, for which the name Desulfosporosinus acididurans sp. nov. is proposed. The type strain is M1(T) (=DSM 27692(T) = JCM 19471(T)). Strain M1(T) was the first acidophilic SRB isolated, and it is the third described species of acidophilic SRB besides Desulfosporosinus acidiphilus and Thermodesulfobium narugense.

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

    NASA Astrophysics Data System (ADS)

    Rassamesard, Areefen; Pengpan, Teparksorn

    2017-02-01

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

  3. Impact of Temperature and Non-Gaussian Statistics on Electron Transfer in Donor-Bridge-Acceptor Molecules.

    PubMed

    Waskasi, Morteza M; Newton, Marshall D; Matyushov, Dmitry V

    2017-03-30

    A combination of experimental data and theoretical analysis provides evidence of a bell-shaped kinetics of electron transfer in the Arrhenius coordinates ln k vs 1/T. This kinetic law is a temperature analogue of the familiar Marcus bell-shaped dependence based on ln k vs the reaction free energy. These results were obtained for reactions of intramolecular charge shift between the donor and acceptor separated by a rigid spacer studied experimentally by Miller and co-workers. The non-Arrhenius kinetic law is a direct consequence of the solvent reorganization energy and reaction driving force changing approximately as hyperbolic functions with temperature. The reorganization energy decreases and the driving force increases when temperature is increased. The point of equality between them marks the maximum of the activationless reaction rate. Reaching the consistency between the kinetic and thermodynamic experimental data requires the non-Gaussian statistics of the donor-acceptor energy gap described by the Q-model of electron transfer. The theoretical formalism combines the vibrational envelope of quantum vibronic transitions with the Q-model describing the classical component of the Franck-Condon factor and a microscopic solvation model of the solvent reorganization energy and the reaction free energy.

  4. Spectrophotometric and spectroscopic studies of charge transfer complexes of p-toluidine as an electron donor with picric acid as an electron acceptor in different solvents

    NASA Astrophysics Data System (ADS)

    Singh, Neeti; Khan, Ishaat M.; Ahmad, Afaq

    2010-04-01

    The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as carbon tetrachloride, chloroform, dichloromethane acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant ( KCT), molar extinction coefficient ( ɛCT), standard free energy (Δ Go), oscillator strength ( f), transition dipole moment ( μEN), resonance energy ( RN) and ionization potential ( ID). The results indicate that the formation constant ( KCT) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used.

  5. Reactions of vitamin A with acceptors of electrons. Interactions with iodine and the formation of iodide

    PubMed Central

    Lucy, J. A.; Lichti, F. Ulrike

    1969-01-01

    1. The reactions of retinol and retinoic acid with iodine were investigated since knowledge of the chemical reactions of vitamin A with acceptors of electrons may shed light on its biochemical mode of action. 2. Colloidal retinol, but not retinoic acid, reacts with iodine to yield a blue–green complex that rapidly decomposes, giving iodide and an unknown species with λmax. at 870mμ. 3. In addition, both retinol and retinoic acid reduce iodine to iodide by a reaction that does not involve an intermediate coloured complex; this reaction appears to yield unstable carbonium ion derivatives of the vitamin. 4. The presence of water greatly facilitates the production of iodide from vitamin A and iodine. 5. Possible chemical pathways involved in these reactions are discussed. 6. It is suggested that the chemical properties of retinol and retinoic acid that underlie their biochemical behaviour might be apparent only when the molecules are at a lipid–water interface, and that vitamin A might be expected to react with a number of different electron acceptors in vivo. PMID:5801297

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

    NASA Astrophysics Data System (ADS)

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

    2018-02-01

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

  7. Cytochrome components of nitrate- and sulfate-respiring Desulfovibrio desulfuricans ATCC 27774.

    PubMed Central

    Liu, M C; Costa, C; Coutinho, I B; Moura, J J; Moura, I; Xavier, A V; LeGall, J

    1988-01-01

    Three multiheme c-type cytochromes--the tetraheme cytochrome c3 (molecular weight [MW] 13,500), a dodecaheme cytochrome c (MW 40,800), and a "split-Soret" cytochrome c (MW 51,540), which is a dimer with 2 hemes per subunit (MW 26,300)--were isolated from the soluble fraction of Desulfovibrio desulfuricans (ATCC 27774) grown under nitrate- or sulfate-respiring conditions. Two of them, the dodecaheme and the split-Soret cytochromes, showed no similarities to any of the c-type cytochromes isolated from other sulfate-reducing bacteria, while the tetraheme cytochrome c3 appeared to be analogous to the cytochrome c3 found in other sulfate-reducing bacteria. For all three multiheme c-type cytochromes isolated, the homologous proteins from nitrate- and sulfate-grown cells were indistinguishable in amino acid composition, physical properties, and spectroscopic characteristics. It therefore appears that the same c-type cytochrome components are present when D. desulfuricans ATCC 27774 cells are grown under either condition. This is in contrast to the considerable difference found in Pseudomonas perfectomarina (Liu et al., J. Bacteriol. 154:278-286, 1983), a marine denitrifier, when the cells are grown on nitrate or oxygen as the terminal electron acceptor. In addition, two spectroscopy methods capable of revealing minute structural variations in proteins provided identical information about the tetraheme cytochrome c3 from nitrate-grown and sulfate-grown cells. PMID:2848008

  8. Degradation of TCE, Cr(VI), sulfate, and nitrate mixtures by granular iron in flow-through columns under different microbial conditions.

    PubMed

    Gandhi, Sumeet; Oh, Byung-Taek; Schnoor, Jerald L; Alvarez, Pedro J J

    2002-04-01

    Flow-through aquifer columns packed with a middle layer of granular iron (Fe0) were used to study the applicability and limitations of bio-enhanced Fe0 barriers for the treatment of contaminant mixtures in groundwater. Concentration profiles along the columns showed extensive degradation of hexavalent chromium Cr(VI), nitrate, sulfate, and trichloroethene (TCE), mainly in the Fe0 layer. One column was bioaugmented with Shevanella algae BRY, an iron-reducing bacterium that could enhance Fe0 reactivity by reductive dissolution of passivating iron oxides. This strain did not enhance Cr(VI), which was rapidly reduced by iron, leaving little room for improvement by microbial participation. Nevertheless, BRY-enhanced nitrate removal (from 15% to 80%), partly because this strain has a wide range of electron acceptors, including nitrate. Sulfate was removed (55%) only in a column that was bioaugmented with a mixed culture containing sulfate-reducing bacteria. Apparently, these bacteria used H2 (produced by Fe0 corrosion) as electron donor to respire sulfate. Most of the TCE was degraded in the zone containing Fe0 (50-70%), and bioaugmentation with BRY slightly increased the removal efficiency to about 80%. Microbial colonization of the Fe0 surface was confirmed by scanning electron microscopy.

  9. Hydrogen concentrations as an indicator of the predominant terminal electron-accepting reactions in aquatic sediments

    USGS Publications Warehouse

    Lovley, D.R.; Goodwin, S.

    1988-01-01

    Factors controlling the concentration of dissolved hydrogen gas in anaerobic sedimentary environments were investigated. Results, presented here or previously, demonstrated that, in sediments, only microorganisms catalyze the oxidation of H2 coupled to the reduction of nitrate, Mn(IV), Fe(III), sulfate, or carbon dioxide. Theoretical considerations suggested that, at steady-state conditions, H2 concentrations are primarily dependent upon the physiological characteristics of the microorganism(s) consuming the H2 and that organisms catalyzing H2 oxidation, with the reduction of a more electrochemically positive electron acceptor, can maintain lower H2 concentrations than organisms using electron acceptors which yield less energy from H2 oxidation. The H2 concentrations associated with the specified predominant terminal electron-accepting reactions in bottom sediments of a variety of surface water environments were: methanogenesis, 7-10 nM; sulfate reduction, 1-1.5 nM; Fe(III) reduction, 0.2 nM; Mn(IV) or nitrate reduction, less than 0.05 nM. Sediments with the same terminal electron acceptor for organic matter oxidation had comparable H2 concentrations, despite variations in the rate of organic matter decomposition, pH, and salinity. Thus, each terminal electron-accepting reaction had a unique range of steady-state H2 concentrations associated with it. Preliminary studies in a coastal plain aquifer indicated that H2 concentrations also vary in response to changes in the predominant terminal electron-accepting process in deep subsurface environments. These studies suggest that H2 measurements may aid in determining which terminal electron-accepting reactions are taking place in surface and subsurface sedimentary environments. ?? 1988.

  10. Algae as an electron donor promoting sulfate reduction for the bioremediation of acid rock drainage.

    PubMed

    Ayala-Parra, Pedro; Sierra-Alvarez, Reyes; Field, Jim A

    2016-11-05

    This study assessed bioremediation of acid rock drainage in simulated permeable reactive barriers (PRB) using algae, Chlorella sorokiniana, as the sole electron donor for sulfate-reducing bacteria. Lipid extracted algae (LEA), the residues of biodiesel production, were compared with whole cell algae (WCA) as an electron donor to promote sulfate-reducing activity. Inoculated columns containing anaerobic granular sludge were fed a synthetic medium containing H2SO4 and Cu(2+). Sulfate, sulfide, Cu(2+) and pH were monitored throughout the experiment of 123d. Cu recovered in the column packing at the end of the experiment was evaluated using sequential extraction. Both WCA and LEA promoted 80% of sulfate removal (12.7mg SO4(2-) d(-1)) enabling near complete Cu removal (>99.5%) and alkalinity generation raising the effluent pH to 6.5. No noteworthy sulfate reduction, alkalinity formation and Cu(2+) removal were observed in the endogenous control. In algae amended-columns, Cu(2+) was precipitated with biogenic H2S produced by sulfate reduction. Formation of CuS was evidenced by sequential extraction and X-ray diffraction. LEA and WCA provided similar levels of electron donor based on the COD balance. The results demonstrate an innovative passive remediation system using residual algae biomass from the biodiesel industry. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Influence of nitrate, sulfate and operational parameters on the bioreduction of perchlorate using an up-flow packed bed reactor at high salinity.

    PubMed

    Chung, J; Shin, S; Oh, J

    2010-05-01

    In this study we have investigated whether electron acceptors, such as nitrate or sulphate ions, competitively inhibit the reduction of perchlorate in brine in continuous up-flow packed bed bioreactors. The effect of pH and hydraulic retention time (HRT) on the reduction of perchlorate at high salinity has also been examined. Reduction of perchlorate was found to be only moderately influenced by nitrate (under 163 mg N L-'), implying that there was no significant microbial competition for electron acceptors. As a result of microbial diversity, there were few differences between microbial communities fed with a variety of media, suggesting that most nitrate-reducing bacteria are able to reduce perchlorate at high salinity. Reduction of perchlorate was almost complete at relatively high sulfate levels (1000 mg L(-1)), neutral pH (6-8) and relatively long HRTs (> 10 h).

  12. Formate Metabolism in Shewanella oneidensis Generates Proton Motive Force and Prevents Growth without an Electron Acceptor.

    PubMed

    Kane, Aunica L; Brutinel, Evan D; Joo, Heena; Maysonet, Rebecca; VanDrisse, Chelsey M; Kotloski, Nicholas J; Gralnick, Jeffrey A

    2016-04-01

    Shewanella oneidensis strain MR-1 is a facultative anaerobe that thrives in redox-stratified environments due to its ability to utilize a wide array of terminal electron acceptors. Conversely, the electron donors utilized by S. oneidensis are more limited and include products of primary fermentation such as lactate, pyruvate, formate, and hydrogen. Lactate, pyruvate, and hydrogen metabolisms inS. oneidensis have been described previously, but little is known about the role of formate oxidation in the ecophysiology of these bacteria. Formate is produced by S. oneidensis through pyruvate formate lyase during anaerobic growth on carbon sources that enter metabolism at or above the level of pyruvate, and the genome contains three gene clusters predicted to encode three complete formate dehydrogenase complexes. To determine the contribution of each complex to formate metabolism, strains lacking one, two, or all three annotated formate dehydrogenase gene clusters were generated and examined for growth rates and yields on a variety of carbon sources. Here, we report that formate oxidation contributes to both the growth rate and yield of S. oneidensis through the generation of proton motive force. Exogenous formate also greatly accelerated growth on N-acetylglucosamine, a carbon source normally utilized very slowly by S. oneidensis under anaerobic conditions. Surprisingly, deletion of all three formate dehydrogenase gene clusters enabled growth of S. oneidensis using pyruvate in the absence of a terminal electron acceptor, a mode of growth never before observed in these bacteria. Our results demonstrate that formate oxidation is a fundamental strategy under anaerobic conditions for energy conservation inS. oneidensis. Shewanella species have garnered interest in biotechnology applications for their ability to respire extracellular terminal electron acceptors, such as insoluble iron oxides and electrodes. While much effort has gone into studying the proteins for

  13. 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

  14. Photosensitized electron transfer processes in SiO2 colloids and sodium lauryl sulfate micellar systems: Correlation of quantum yields with interfacial surface potentials

    PubMed Central

    Laane, Colja; Willner, Itamar; Otvos, John W.; Calvin, Melvin

    1981-01-01

    The effectiveness of negatively charged colloidal SiO2 particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO4) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS0) with tris(2,2′-bipyridinium)ruthenium(II) [Ru(bipy)32+] as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS[unk]) in the SiO2 colloid compared with 0.005 in the homogeneous system and 0.0086 in a NaLauSO4 micellar solution. The higher quantum yields obtained with the SiO2 colloidal system are attributed to substantial stabilization against back reaction of the intermediate photoproducts—i.e., Ru(bipy)33+ and PVS[unk]—by electrostatic repulsion of the reduced electron acceptor from the negatively charged particle surface. The binding properties of the SiO2 particles and NaLauSO4 micelles were investigated by flow dialysis. The results show that the sensitizer binds to both interfaces and that the SiO2 interface is characterized by a much higher surface potential than the micellar interface (≈-170 mV vs. -85 mV). The effect of ionic strength on the surface potential was estimated from the Gouy-Chapman theory, and the measured quantum yields of photosensitized electron transfer were correlated with surface potential at different ionic strengths. This correlation shows that the quantum yield is not affected by surface potentials smaller than ≈-40 mV. At larger potentials, the quantum yield increases rapidly. The quantum yield obtained in the micellar system at different strengths fits nicely on the correlation curve for the colloid SiO2 system. These results indicate that the surface potential is the dominant factor in the quantum yield improvement for PVS0 reduction. PMID:16593095

  15. Electronic tuning of the lability of Pt(II) complexes through pi-acceptor effects. Correlations between thermodynamic, kinetic, and theoretical parameters.

    PubMed

    Hofmann, Andreas; Jaganyi, Deogratius; Munro, Orde Q; Liehr, Günter; van Eldik, Rudi

    2003-03-10

    pi-Acceptor effects are often used to account for the unusual high lability of [Pt(terpy)L]((2)(-)(n)+) (terpy = 2,2':6',2' '-terpyridine) complexes. To gain further insight into this phenomenon, the pi-acceptor effect was varied systematically by studying the lability of [Pt(diethylenetriamine)OH(2)](2+) (aaa), [Pt(2,6-bis-aminomethylpyridine)OH(2)](2+) (apa), [Pt(N-(pyridyl-2-methyl)-1,2-diamino-ethane)OH(2)](2+) (aap), [Pt(bis(2-pyridylmethyl)amine)OH(2)](2+) (pap), [Pt(2,2'-bipyridine)(NH(3))(OH(2))](2+) (app), and [Pt(terpy)OH(2)](2+) (ppp). The crystal structure of the apa precursor [Pt(2,6-bis-aminomethylpyridine)Cl]Cl.H(2)O was determined. The substitution of water by a series of nucleophiles, viz. thiourea, N,N-dimethylthiourea, N,N,N',N'-tetramethylthiourea, I(-), and SCN(-), was studied under pseudo-first-order conditions as a function of concentration, pH, temperature, and pressure, using stopped-flow techniques. The data enable an overall comparison of the substitution behavior of these complexes, emphasizing the role played by the kinetic cis and trans pi-acceptor effects. The results indicate that the cis pi-acceptor effect is larger than the trans pi-acceptor effect, and that the pi-acceptor effects are multiplicative. DFT calculations at the B3LYP/LACVP level of theory show that, by the addition of pi-acceptor ligands to the metal, the positive charge on the metal center increases, and the energy separation of the frontier molecular orbitals (E(LUMO) - E(HOMO)) of the ground state Pt(II) complexes decreases. The calculations collectively support the experimentally observed additional increase in reactivity when two pi-accepting rings are adjacent to each other (app and ppp), which is ascribed to "electronic communication" between the pyridine rings. The results furthermore indicate that the pK(a) value of the platinum bound water molecule is controlled by the pi-accepting nature of the chelate system and reflects the electron density around the

  16. Targeting ideal acceptor-donor materials based on hexabenzocoronene

    NASA Astrophysics Data System (ADS)

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

    2018-06-01

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

  17. Distribution of iron- and sulfate-reducing bacteria across a coastal acid sulfate soil (CASS) environment: implications for passive bioremediation by tidal inundation.

    PubMed

    Ling, Yu-Chen; Bush, Richard; Grice, Kliti; Tulipani, Svenja; Berwick, Lyndon; Moreau, John W

    2015-01-01

    Coastal acid sulfate soils (CASS) constitute a serious and global environmental problem. Oxidation of iron sulfide minerals exposed to air generates sulfuric acid with consequently negative impacts on coastal and estuarine ecosystems. Tidal inundation represents one current treatment strategy for CASS, with the aim of neutralizing acidity by triggering microbial iron- and sulfate-reduction and inducing the precipitation of iron-sulfides. Although well-known functional guilds of bacteria drive these processes, their distributions within CASS environments, as well as their relationships to tidal cycling and the availability of nutrients and electron acceptors, are poorly understood. These factors will determine the long-term efficacy of "passive" CASS remediation strategies. Here we studied microbial community structure and functional guild distribution in sediment cores obtained from 10 depths ranging from 0 to 20 cm in three sites located in the supra-, inter- and sub-tidal segments, respectively, of a CASS-affected salt marsh (East Trinity, Cairns, Australia). Whole community 16S rRNA gene diversity within each site was assessed by 454 pyrotag sequencing and bioinformatic analyses in the context of local hydrological, geochemical, and lithological factors. The results illustrate spatial overlap, or close association, of iron-, and sulfate-reducing bacteria (SRB) in an environment rich in organic matter and controlled by parameters such as acidity, redox potential, degree of water saturation, and mineralization. The observed spatial distribution implies the need for empirical understanding of the timing, relative to tidal cycling, of various terminal electron-accepting processes that control acid generation and biogeochemical iron and sulfur cycling.

  18. Impact of Temperature and Non-Gaussian Statistics on Electron Transfer in Donor–Bridge–Acceptor Molecules

    DOE PAGES

    Waskasi, Morteza M.; Newton, Marshall D.; Matyushov, Dmitry V.

    2017-03-16

    A combination of experimental data and theoretical analysis provides evidence of a bell-shaped kinetics of electron transfer in the Arrhenius coordinates ln k vs 1/T . This kinetic law is a temperature analog of the familiar Marcus bell-shaped dependence based on ln k vs the reaction free energy. These results were obtained for reactions of intramolecular charge shift between the donor and acceptor separated by a rigid spacer studied experimentally by Miller and co-workers. The non-Arrhenius kinetic law is a direct consequence of the solvent reorganization energy and reaction driving force changing approximately as hyperbolic functions with temperature. The reorganizationmore » energy decreases and the driving force increases when temperature is increased. The point of equality between them marks the maximum of the activationless reaction rate. Reaching the consistency between the kinetic and thermodynamic experimental data requires the non-Gaussian statistics of the donor-acceptor energy gap described by the Q-model of electron transfer. Furthermore, the theoretical formalism combines the vibrational envelope of quantum vibronic transitions with the Q-model describing the classical component of the Franck-Condon factor and a microscopic solvation model of the solvent reorganization energy and the reaction free energy.« less

  19. Spectrophotometric and spectroscopic studies of charge transfer complexes of p-toluidine as an electron donor with picric acid as an electron acceptor in different solvents.

    PubMed

    Singh, Neeti; Khan, Ishaat M; Ahmad, Afaq

    2010-04-01

    The charge transfer complexes of the donor p-toluidine with pi-acceptor picric acid have been studied spectrophotometrically in various solvents such as carbon tetrachloride, chloroform, dichloromethane acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K(CT)), molar extinction coefficient (epsilon(CT)), standard free energy (DeltaG(o)), oscillator strength (f), transition dipole moment (mu(EN)), resonance energy (R(N)) and ionization potential (I(D)). The results indicate that the formation constant (K(CT)) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used. Copyright 2010 Elsevier B.V. All rights reserved.

  20. Organic solar cells based on non-fullerene acceptors

    NASA Astrophysics Data System (ADS)

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

    2018-02-01

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

  1. Effective Tuning of Ketocyanine Derivatives through Acceptor Substitution.

    PubMed

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

    2015-05-18

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

  2. Hexuronic Acid Stereochemistry Determination in Chondroitin Sulfate Glycosaminoglycan Oligosaccharides by Electron Detachment Dissociation

    NASA Astrophysics Data System (ADS)

    Leach, Franklin E.; Ly, Mellisa; Laremore, Tatiana N.; Wolff, Jeremy J.; Perlow, Jacob; Linhardt, Robert J.; Amster, I. Jonathan

    2012-09-01

    Electron detachment dissociation (EDD) has previously provided stereo-specific product ions that allow for the assignment of the acidic C-5stereochemistry in heparan sulfate glycosaminoglycans (GAGs), but application of the same methodology to an epimer pair in the chondroitin sulfate glycoform class does not provide the same result. A series of experiments have been conducted in which glycosaminoglycan precursor ions are independently activated by electron detachment dissociation (EDD), electron induced dissociation (EID), and negative electron transfer dissociation (NETD) to assign the stereochemistry in chondroitin sulfate (CS) epimers and investigate the mechanisms for product ion formation during EDD in CS glycoforms. This approach allows for the assignment of electronic excitation products formed by EID and detachment products to radical pathways in NETD, both of which occur simultaneously during EDD. The uronic acid stereochemistry in electron detachment spectra produces intensity differences when assigned glycosidic and cross-ring cleavages are compared. The variations in the intensities of the doubly deprotonated 0,2X3 and Y3 ions have been shown to be indicative of CS-A/DS composition during the CID of binary mixtures. These ions can provide insight into the uronic acid composition of binary mixtures in EDD, but the relative abundances, although reproducible, are low compared with those in a CID spectrum acquired on an ion trap. The application of principal component analysis (PCA) presents a multivariate approach to determining the uronic acid stereochemistry spectra of these GAGs by taking advantage of the reproducible peak distributions produced by electron detachment.

  3. Inhibitory Effects of Sulfate and Nitrate Reduction on Reductive Dechlorination of PCP in a Flooded Paddy Soil

    PubMed Central

    Xu, Yan; Xue, Lili; Ye, Qi; Franks, Ashley E.; Zhu, Min; Feng, Xi; Xu, Jianming; He, Yan

    2018-01-01

    Pentachlorophenol (PCP) is highly toxic and persistent in soils. Bioreduction of PCP often co-occurs with varying concentrations of sulfate and nitrate in flooded paddy soils where each can act as an electron acceptor. Anaerobic soil microcosms were constructed to evaluate the influence of sulfate and nitrate amendments and their redox processes. Microcosms with varying sulfate and nitrate concentrations demonstrated an inhibitory effect on reductive dechlorination of PCP compared to an untreated control. Compared to nitrate, sulfate exhibited a more significant impact on PCP dechlorination, as evidenced by a lower maximum reaction rate and a longer time to reach the maximum reaction rate. Dechlorination of PCP was initiated at the ortho-position, and then at the para- and meta-positions to form 3-CP as the final product in all microcosms. Deep sequencing of microbial communities in the microcosms revealed a strong variation in bacterial taxon among treatments. Specialized microbial groups, such as the genus of Desulfovibrio responding to the addition of sulfate, had a potential to mediate the competitive microbial dechlorination of PCP. Our results provide an insight into the competitive microbial-mediated reductive dechlorination of PCP in natural flooded soil or sediment environments. PMID:29643842

  4. Ultrafast Electron Transfer across a Nanocapsular Wall: Coumarins as Donors, Viologen as Acceptor, and Octa Acid Capsule as the Mediator.

    PubMed

    Chuang, Chi-Hung; Porel, Mintu; Choudhury, Rajib; Burda, Clemens; Ramamurthy, V

    2018-01-11

    Results of our study on ultrafast electron transfer (eT) dynamics from coumarins (coumarin-1, coumarin-480, and coumarin-153) incarcerated within octa acid (OA) capsules as electron donors to methyl viologen dissolved in water as acceptor are presented. Upon photoexcitation, coumarin inside the OA capsule transfers an electron to the acceptor electrostatically attached to the capsule leading to a long-lived radical-ion pair separated by the OA capsular wall. This charge-separated state returns to the neutral ground state via back electron transfer on the nanosecond time scale. This system allows for ultrafast electron transfer processes through a molecular wall from the apolar capsular interior to the highly polar (aqueous) environment on the femtosecond time scale. Employing femtosecond transient absorption spectroscopy, distinct rates of both forward (1-25 ps) and backward eT (700-1200 ps) processes were measured. Further understanding of the energetics is provided using Rehm-Weller analysis for the investigated photoinduced eT reactions. The results provide the rates of the eT across a molecular wall, akin to an isotropic solution, depending on the standard free energy of the reaction. The insights from this work could be utilized in the future design of efficient electron transfer processes across interfaces separating apolar and polar environments.

  5. Biodegradation of pharmaceuticals and endocrine disruptors with oxygen, nitrate, manganese (IV), iron (III) and sulfate as electron acceptors

    NASA Astrophysics Data System (ADS)

    Schmidt, Natalie; Page, Declan; Tiehm, Andreas

    2017-08-01

    Biodegradation of pharmaceuticals and endocrine disrupting compounds was examined in long term batch experiments for a period of two and a half years to obtain more insight into the effects of redox conditions. A mix including lipid lowering agents (e.g. clofibric acid, gemfibrozil), analgesics (e.g. diclofenac, naproxen), beta blockers (e.g. atenolol, propranolol), X-ray contrast media (e.g. diatrizoic acid, iomeprol) as well as the antiepileptic carbamazepine and endocrine disruptors (e.g. bisphenol A, 17α-ethinylestradiol) was analyzed in batch tests in the presence of oxygen, nitrate, manganese (IV), iron (III), and sulfate. Out of the 23 selected substances, 14 showed a degradation of > 50% of their initial concentrations under aerobic conditions. The beta blockers propranolol and atenolol and the analgesics pentoxifylline and naproxen showed a removal of > 50% under anaerobic conditions. In particular naproxen proved to be degradable with oxygen and under most anaerobic conditions, i.e. with manganese (IV), iron (III), or sulfate. The natural estrogens estriol, estrone and 17β-estradiol showed complete biodegradation under aerobic and nitrate-reducing conditions, with a temporary increase of estrone during transformation of estriol and 17β-estradiol. Transformation of 17β-estradiol under Fe(III)-reducing conditions resulted in an increase of estriol as well. Concentrations of clofibric acid, carbamazepine, iopamidol and diatrizoic acid, known for their recalcitrance in the environment, remained unchanged.

  6. Anaerobic oxidation of ethene coupled to sulfate reduction in microcosms and enrichment cultures.

    PubMed

    Fullerton, Heather; Crawford, Michael; Bakenne, Ademola; Freedman, David L; Zinder, Stephen H

    2013-01-01

    Ethene is considered recalcitrant under anaerobic conditions, but biological reduction to ethane and oxidation to CO2 have been reported; however, little is known about these processes or the organisms carrying them out. In this report we describe sulfate dependent ethene consumption in microcosms prepared with sediments from a freshwater canal. A first dose of 0.6 mmol/L ethene was consumed within 77 days, and a second dose was largely consumed twelve days later. Material from this microcosm was transferred into growth medium with ethene as the only electron donor (except for trace amounts of vitamins) and sulfate as the electron acceptor. Four doses of ethene were consumed at increasing rates, and the cultures have been transferred at least eight times in this medium. Conversion of [(14)C]ethene primarily to (14)CO2 was demonstrated in fifth and sixth generation cultures, as well as production of sulfide in other cultures, confirming the ethene/sulfate couple. Ovoid cells 1-2 μm in diameter were found in cultures containing ethene and sulfate, and quantitative PCR showed large increases in bacterial 16S rRNA gene copy number. Over half of a 16S rRNA gene clone library from a sixth-generation culture was a phylotype with a sequence ca. 90% identical with a clade of Deltaproteobacteria that includes Desulfovirga adipica and several Syntrophobacter spp. These studies have solidified the concept that deficits in mass balances for chloroethene fate in sulfate reducing zones of contaminated groundwater sites may be due to ethene oxidation, and suggest a unique phylotype is involved in this process.

  7. Self-assembly properties of semiconducting donor-acceptor-donor bithienyl derivatives of tetrazine and thiadiazole-effect of the electron accepting central ring.

    PubMed

    Zapala, Joanna; Knor, Marek; Jaroch, Tomasz; Maranda-Niedbala, Agnieszka; Kurach, Ewa; Kotwica, Kamil; Nowakowski, Robert; Djurado, David; Pecaut, Jacques; Zagorska, Malgorzata; Pron, Adam

    2013-11-26

    Scanning tunneling microscopy was used to study the effect of the electron-accepting unit and the alkyl substituent's position on the type and extent of 2D supramolecular organization of penta-ring donor-acceptor-donor (DAD) semiconductors, consisting of either tetrazine or thiadiazole central acceptor ring symmetrically attached to two bithienyl groups. Microscopic observations of monomolecular layers on HOPG of four alkyl derivatives of the studied adsorbates indicate significant differences in their 2D organizations. Ordered monolayers of thiadiazole derivatives are relatively loose and, independent of the position of alkyl substituents, characterized by large intermolecular separation of acceptor units in the adjacent molecules located in the face-to-face configuration. The 2D supramolecular architecture in both derivatives of thiadiazole is very sensitive to the alkyl substituent's position. Significantly different behavior is observed for derivatives of tetrazine (which is a stronger electron acceptor). Stronger intermolecular DA interactions in these adsorbates generate an intermolecular shift in the monolayer, which is a dominant factor determining the 2D structural organization. As a consequence of this molecular arrangement, tetrazine groups (A segments) face thiophene rings (D segments) of the neighboring molecules. Monolayers of tetrazine derivatives are therefore much more densely packed and characterized by similar π-stacking of molecules independently of the position of alkyl substituents. Moreover, a comparative study of 3D supramolecular organization, deduced from the X-ray diffraction patterns, is also presented clearly confirming the polymorphism of the studied adsorbates.

  8. Synthesis and photophysical properties of new catenated electron donor-acceptor materials with magnesium and free base porphyrins as donors and C60 as the acceptor

    NASA Astrophysics Data System (ADS)

    Kirner, Sabrina V.; Guldi, Dirk M.; Megiatto, Jackson D., Jr.; Schuster, David I.

    2014-12-01

    A new series of nanoscale electron donor-acceptor systems with [2]catenane architectures has been synthesized, incorporating magnesium porphyrin (MgP) or free base porphyrin (H2P) as electron donor and C60 as electron acceptor, surrounding a central tetrahedral Cu(i)-1,10-phenanthroline (phen) complex. Model catenated compounds incorporating only one or none of these photoactive moieties were also prepared. The synthesis involved the use of Sauvage's metal template protocol in combination with the 1,3-dipolar cycloaddition of azides and alkynes (``click chemistry''), as in other recent reports from our laboratories. Ground state electron interactions between the individual constituents was probed using electrochemistry and UV-vis absorption spectroscopy, while events occurring following photoexcitation in tetrahydrofuran (under both aerobic and anaerobic conditions) at various wavelengths were followed by means of time-resolved transient absorption and emission spectroscopies on the femtosecond and nanosecond time scales, respectively, complemented by measurements of quantum yields for generation of singlet oxygen. From similar studies with model catenates containing one or neither of the chromophores, the events following photoexcitation could be elucidated. The results were compared with those previously reported for analogous catenates based on zinc porphyrin (ZnP). It was determined that a series of energy transfer (EnT) and electron transfer (ET) processes take place in the present catenates, ultimately generating long-distance charge separated (CS) states involving oxidized porphyrin and reduced C60 moieties, with lifetimes ranging from 400 to 1060 nanoseconds. Shorter lived short-distance CS states possessing oxidized copper complexes and reduced C60, with lifetimes ranging from 15 to 60 ns, were formed en route to the long-distance CS states. The dynamics of the ET processes were analyzed in terms of their thermodynamic driving forces. It was clear that

  9. Tuning the Electron-Transport and Electron-Accepting Abilities of Dyes through Introduction of Different π-Conjugated Bridges and Acceptors for Dye-Sensitized Solar Cells.

    PubMed

    Li, Yuanzuo; Sun, Chaofan; Song, Peng; Ma, Fengcai; Yang, Yanhui

    2017-02-17

    A series of dyes, containing thiophene and thieno[3,2-b]thiophene as π-conjugated bridging units and six kinds of groups as electron acceptors, were designed for dye-sensitized solar cells (DSSCs). The ground- and excited-state properties of the designed dyes were investigated by using density functional theory (DFT) and time-dependent DFT, respectively. Moreover, the parameters affecting the short-circuit current density and open-circuit voltage were calculated to predict the photoelectrical performance of each dye. In addition, the charge difference density was presented through a three-dimensional (3D) real-space analysis method to investigate the electron-injection mechanism in the complexes. Our results show that the longer conjugated bridge would inhibit the intramolecular charge transfer, thereby affecting the photoelectrical properties of DSSCs. Similarly, owing to the lowest chemical hardness, largest electron-accepting ability, dipole moment (μnormal ) and the change in the energy of the TiO 2 conduction band (ΔECB ), the dye with a (E)-3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylic acid (TCA) acceptor group would exhibit the most significant photoelectrical properties among the designed dyes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Tuning the electronic and optical properties of NDT-based conjugated polymers by adopting fused heterocycles as acceptor units: a theoretical study.

    PubMed

    Cheng, Na; Zhang, Changqiao; Liu, Yongjun

    2017-08-01

    Donor-acceptor conjugated polymers have been successfully applied in bulk heterojunction solar cell devices. Tuning their donor and acceptor units allows the design of new polymers with desired electronic and optical properties. Here, to screen new candidate polymers based on a newly synthesized donor unit, dithieo[2,3-d:2',3'-d']naphtho[1,2-b:3,4-b']dithiophene (NDT), a series of model polymers with different acceptor units were designed and denoted NDT-A 0 to NDT-A 12 , and the structures and optical properties of those polymers were investigated using DFT and TDDFT calculations. The results of the calculations revealed that the electronic and optical properties of these polymers depend on the acceptor unit present; specifically, their HOMO energies ranged from -4.89 to -5.38 eV, their HOMO-LUMO gaps ranged from 1.30 to 2.80 eV, and their wavelengths of maximum absorption ranged from 538 to 1212 nm. The absorption spectra of NDT-A 1 to NDT-A 6 , NDT-A 8 , NDT-A 9 , and NDT-A 12 occur within the visible region (<900 nm), indicating that these polymers are potential candidates for use in solar cells. On the other hand, the absorption spectra of NDT-A 7 , NDT-A 10 , and NDT-A 11 extend much further into the near-infrared region, implying that they absorb near-infrared light. These polymers could meet the requirements of donor units for use in tandem and ternary solar cells. Graphical abstract Theoretical calculations by TD-DFT reveal that the optical properties of NDT-based conjugated polymers can be well tuned by adopting different acceptor units, and these ploymers are potential donor materials for tandem and ternary solar cells.

  11. Biodegradation of pharmaceuticals and endocrine disruptors with oxygen, nitrate, manganese (IV), iron (III) and sulfate as electron acceptors.

    PubMed

    Schmidt, Natalie; Page, Declan; Tiehm, Andreas

    2017-08-01

    Biodegradation of pharmaceuticals and endocrine disrupting compounds was examined in long term batch experiments for a period of two and a half years to obtain more insight into the effects of redox conditions. A mix including lipid lowering agents (e.g. clofibric acid, gemfibrozil), analgesics (e.g. diclofenac, naproxen), beta blockers (e.g. atenolol, propranolol), X-ray contrast media (e.g. diatrizoic acid, iomeprol) as well as the antiepileptic carbamazepine and endocrine disruptors (e.g. bisphenol A, 17α-ethinylestradiol) was analyzed in batch tests in the presence of oxygen, nitrate, manganese (IV), iron (III), and sulfate. Out of the 23 selected substances, 14 showed a degradation of >50% of their initial concentrations under aerobic conditions. The beta blockers propranolol and atenolol and the analgesics pentoxifylline and naproxen showed a removal of >50% under anaerobic conditions. In particular naproxen proved to be degradable with oxygen and under most anaerobic conditions, i.e. with manganese (IV), iron (III), or sulfate. The natural estrogens estriol, estrone and 17β-estradiol showed complete biodegradation under aerobic and nitrate-reducing conditions, with a temporary increase of estrone during transformation of estriol and 17β-estradiol. Transformation of 17β-estradiol under Fe(III)-reducing conditions resulted in an increase of estriol as well. Concentrations of clofibric acid, carbamazepine, iopamidol and diatrizoic acid, known for their recalcitrance in the environment, remained unchanged. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  12. Microbial fuel cell operation using monoazo and diazo dyes as terminal electron acceptor for simultaneous decolourisation and bioelectricity generation.

    PubMed

    Oon, Yoong-Sin; Ong, Soon-An; Ho, Li-Ngee; Wong, Yee-Shian; Oon, Yoong-Ling; Lehl, Harvinder Kaur; Thung, Wei-Eng; Nordin, Noradiba

    2017-03-05

    Monoazo and diazo dyes [New coccine (NC), Acid orange 7 (AO7), Reactive red 120 (RR120) and Reactive green 19 (RG19)] were employed as electron acceptors in the abiotic cathode of microbial fuel cell. The electrons and protons generated from microbial organic oxidation at the anode which were utilized for electrochemical azo dye reduction at the cathodic chamber was successfully demonstrated. When NC was employed as the electron acceptor, the chemical oxygen demand (COD) removal and dye decolourisation efficiencies obtained at the anodic and cathodic chamber were 73±3% and 95.1±1.1%, respectively. This study demonstrated that the decolourisation rates of monoazo dyes were ∼50% higher than diazo dyes. The maximum power density in relation to NC decolourisation was 20.64mW/m 2 , corresponding to current density of 120.24mA/m 2 . The decolourisation rate and power output of different azo dyes were in the order of NC>AO7>RR120>RG19. The findings revealed that the structure of dye influenced the decolourisation and power performance of MFC. Azo dye with electron-withdrawing group at para substituent to azo bond would draw electrons from azo bond; hence the azo dye became more electrophilic and more favourable for dye reduction. Copyright © 2016 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2018-04-01

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

  14. The separation distance distribution in electron-donor-acceptor systems and the wavelength dependence of free ion yields

    NASA Astrophysics Data System (ADS)

    Zhou, Jinwei; Findley, Bret R.; Braun, Charles L.; Sutin, Norman

    2001-06-01

    We recently reported that free radical ion quantum yields for electron-donor-acceptor (EDA) systems of alkylbenzenes-tetracyanoethylene (TCNE) exhibit a remarkable wavelength dependence in dichloromethane, a medium polarity solvent. We proposed that weak absorption by long-distance, unassociated or "random" D⋯A pairs is mainly responsible for the free radical ion yield. Here a model for the wavelength dependence of the free ion yield is developed for four systems in which differing degrees of EDA complex formation are present: 1,3,5-tri-tert-butylbenzene-TCNE in which only random pairs exist due to the bulky groups on the electron donor, and toluene—TCNE, 1,3,5-triethylbenzene-TCNE and 1,3,5-trimethylbenzene-TCNE. Mulliken-Hush theory is used to determine the excitation distance distribution of unassociated, random pairs at different wavelengths. For each absorption distribution, free radical ion yields at different wavelengths are then calculated using Onsager's result for the ion separation probability. Encouraging agreement between the calculated yields and our experimental results is obtained. As far as we are aware, this is the first time that photoexcitation of unassociated donor/acceptor pairs has been invoked as the source of separated radical ion pairs.

  15. Phenothiazine-anthraquinone donor-acceptor molecules: synthesis, electronic properties and DFT-TDDFT computational study.

    PubMed

    Zhang, Wen-Wei; Mao, Wei-Li; Hu, Yun-Xia; Tian, Zi-Qi; Wang, Zhi-Lin; Meng, Qing-Jin

    2009-09-17

    Two donor-acceptor molecules with different pi-electron conjugative units, 1-((10-methyl-10H-phenothiazin-3-yl)ethynyl)anthracene-9,10-dione (AqMp) and 1,1'-(10-methyl-10H-phenothiazine-3,7-diyl)bis(ethyne-2,1-diyl)dianthracene-9,10-dione (Aq2Mp), have been synthesized and investigated for their photochemical and electrochemical properties. Density functional theory (DFT) calculations provide insights into their molecular geometry, electronic structures, and properties. These studies satisfactorily explain the electrochemistry of the two compounds and indicate that larger conjugative effect leads to smaller HOMO-LUMO gap (Eg) in Aq2Mp. Both compounds show ICT and pi --> pi* transitions in the UV-visible range in solution, and Aq2Mp has a bathochromic shift and shows higher oscillator strength of the absorption, which has been verified by time-dependent DFT (TDDFT) calculations. The differences between AqMp and Aq2Mp indicate that the structural and conjugative effects have great influence on the electronic properties of the molecules.

  16. (Per)Chlorate-Reducing Bacteria Can Utilize Aerobic and Anaerobic Pathways of Aromatic Degradation with (Per)Chlorate as an Electron Acceptor

    PubMed Central

    Carlström, Charlotte I.; Loutey, Dana; Bauer, Stefan; Clark, Iain C.; Rohde, Robert A.; Iavarone, Anthony T.; Lucas, Lauren

    2015-01-01

    ABSTRACT The pathways involved in aromatic compound oxidation under perchlorate and chlorate [collectively known as (per)chlorate]-reducing conditions are poorly understood. Previous studies suggest that these are oxygenase-dependent pathways involving O2 biogenically produced during (per)chlorate respiration. Recently, we described Sedimenticola selenatireducens CUZ and Dechloromarinus chlorophilus NSS, which oxidized phenylacetate and benzoate, two key intermediates in aromatic compound catabolism, coupled to the reduction of perchlorate or chlorate, respectively, and nitrate. While strain CUZ also oxidized benzoate and phenylacetate with oxygen as an electron acceptor, strain NSS oxidized only the latter, even at a very low oxygen concentration (1%, vol/vol). Strains CUZ and NSS contain similar genes for both the anaerobic and aerobic-hybrid pathways of benzoate and phenylacetate degradation; however, the key genes (paaABCD) encoding the epoxidase of the aerobic-hybrid phenylacetate pathway were not found in either genome. By using transcriptomics and proteomics, as well as by monitoring metabolic intermediates, we investigated the utilization of the anaerobic and aerobic-hybrid pathways on different electron acceptors. For strain CUZ, the results indicated utilization of the anaerobic pathways with perchlorate and nitrate as electron acceptors and of the aerobic-hybrid pathways in the presence of oxygen. In contrast, proteomic results suggest that strain NSS may use a combination of the anaerobic and aerobic-hybrid pathways when growing on phenylacetate with chlorate. Though microbial (per)chlorate reduction produces molecular oxygen through the dismutation of chlorite (ClO2−), this study demonstrates that anaerobic pathways for the degradation of aromatics can still be utilized by these novel organisms. PMID:25805732

  17. 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

  18. Reconstructing metabolic pathways of a member of the genus Pelotomaculum suggesting its potential to oxidize benzene to carbon dioxide with direct reduction of sulfate.

    PubMed

    Dong, Xiyang; Dröge, Johannes; von Toerne, Christine; Marozava, Sviatlana; McHardy, Alice C; Meckenstock, Rainer U

    2017-03-01

    The enrichment culture BPL is able to degrade benzene with sulfate as electron acceptor and is dominated by an organism of the genus Pelotomaculum. Members of Pelotomaculum are usually known to be fermenters, undergoing syntrophy with anaerobic respiring microorganisms or methanogens. By using a metagenomic approach, we reconstructed a high-quality genome (∼2.97 Mbp, 99% completeness) for Pelotomaculum candidate BPL. The proteogenomic data suggested that (1) anaerobic benzene degradation was activated by a yet unknown mechanism for conversion of benzene to benzoyl-CoA; (2) the central benzoyl-CoA degradation pathway involved reductive dearomatization by a class II benzoyl-CoA reductase followed by hydrolytic ring cleavage and modified β-oxidation; (3) the oxidative acetyl-CoA pathway was utilized for complete oxidation to CO2. Interestingly, the genome of Pelotomaculum candidate BPL has all the genes for a complete sulfate reduction pathway including a similar electron transfer mechanism for dissimilatory sulfate reduction as in other Gram-positive sulfate-reducing bacteria. The proteome analysis revealed that the essential enzymes for sulfate reduction were all formed during growth with benzene. Thus, our data indicated that, besides its potential to anaerobically degrade benzene, Pelotomaculum candidate BPL is the first member of the genus that can perform sulfate reduction. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  19. Self-Assembly of Electron Donor-Acceptor-Based Carbazole Derivatives: Novel Fluorescent Organic Nanoprobes for Both One- and Two-Photon Cellular Imaging.

    PubMed

    Zhang, Jinfeng; Chen, Wencheng; Kalytchuk, Sergii; Li, King Fai; Chen, Rui; Adachi, Chihaya; Chen, Zhan; Rogach, Andrey L; Zhu, Guangyu; Yu, Peter K N; Zhang, Wenjun; Cheah, Kok Wai; Zhang, Xiaohong; Lee, Chun-Sing

    2016-05-11

    In this study, we report fluorescent organic nanoprobes with intense blue, green, and orange-red emissions prepared by self-assembling three carbazole derivatives into nanorods/nanoparticles. The three compounds consist of two or four electron-donating carbazole groups linked to a central dicyanobenzene electron acceptor. Steric hindrance from the carbazole groups leads to noncoplanar 3D molecular structures favorable to fluorescence in the solid state, while the donor-acceptor structures endow the molecules with good two-photon excited emission properties. The fluorescent organic nanoprobes exhibit good water dispersibility, low cytotoxicity, superior resistance against photodegradation and photobleaching. Both one- and two-photon fluorescent imaging were shown in the A549 cell line. Two-photon fluorescence imaging with the fluorescent probes was demonstrated to be more effective in visualizing and distinguishing cellular details compared to conventional one-photon fluorescence imaging.

  20. The electronic structure and second-order nonlinear optical properties of donor-acceptor acetylenes - A detailed investigation of structure-property relationships

    NASA Technical Reports Server (NTRS)

    Stiegman, A. E.; Graham, Eva; Khundkar, Lutfur R.; Perry, Joseph W.; Cheng, L.-T.; Perry, Kelly J.

    1991-01-01

    A series of donor-acceptor acetylene compounds was synthesized in which systematic changes in both the conjugation length and the donor-acceptor strength were made. The effect of these structural changes on the spectroscopic and electronic properties of the molecules and, ultimately, on the measured second-order molecular hyperpolarizabilities (beta) was investigated. It was found that increases in the donor-acceptor strength resulted in increases in the magnitude of beta. For this class of molecules, the increase is dominated by the energy of the intramolecular charge-transfer transition, while factors such as the ground to excited-state dipole moment change and the transition-moment integral are much less important. Increasing the conjugation length from one to two acetylene linkers did not result in an increase in the value of beta; however, beta increased sharply in going from two acetylenes to three. This increase is attributed to the superposition of several nearly isoenergetic excited states.

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

    NASA Astrophysics Data System (ADS)

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

    2018-04-01

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

  2. Non-fullerene acceptors for organic solar cells

    NASA Astrophysics Data System (ADS)

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

    2018-03-01

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

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

    PubMed

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

    2017-04-15

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

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

    PubMed Central

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

    2017-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  6. 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.

  7. Transcriptional analysis of Shewanella oneidensis MR-1 with an electrode compared to Fe(III)citrate or oxygen as terminal electron acceptor

    USDA-ARS?s Scientific Manuscript database

    Background. Shewanella oneidensis is a target of extensive research efforts in the fields of bioelectrochemical systems and bioremediation because of its versatile metabolic capabilities, especially in regards to the respiration with extracellular electron acceptors. Here, we took a global approach ...

  8. The nitrogen cycle in anaerobic methanotrophic mats of the Black Sea is linked to sulfate reduction and biomass decomposition.

    PubMed

    Siegert, Michael; Taubert, Martin; Seifert, Jana; von Bergen-Tomm, Martin; Basen, Mirko; Bastida, Felipe; Gehre, Matthias; Richnow, Hans-Hermann; Krüger, Martin

    2013-11-01

    Anaerobic methanotrophic (ANME) mats host methane-oxidizing archaea and sulfate-reducing prokaryotes. Little is known about the nitrogen cycle in these communities. Here, we link the anaerobic oxidation of methane (AOM) to the nitrogen cycle in microbial mats of the Black Sea by using stable isotope probing. We used four different (15)N-labeled sources of nitrogen: dinitrogen, nitrate, nitrite and ammonium. We estimated the nitrogen incorporation rates into the total biomass and the methyl coenzyme M reductase (MCR). Dinitrogen played an insignificant role as nitrogen source. Assimilatory and dissimilatory nitrate reduction occurred. High rates of nitrate reduction to dinitrogen were stimulated by methane and sulfate, suggesting that oxidation of reduced sulfur compounds such as sulfides was necessary for AOM with nitrate as electron acceptor. Nitrate reduction to dinitrogen occurred also in the absence of methane as electron donor but at six times slower rates. Dissimilatory nitrate reduction to ammonium was independent of AOM. Ammonium was used for biomass synthesis under all conditions. The pivotal enzyme in AOM coupled to sulfate reduction, MCR, was synthesized from nitrate and ammonium. Results show that AOM coupled to sulfate reduction along with biomass decomposition drive the nitrogen cycle in the ANME mats of the Black Sea and that MCR enzymes are involved in this process. © 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

  9. Pilot scale application of nanosized iron oxides as electron acceptors for bioremediation

    NASA Astrophysics Data System (ADS)

    Bosch, Julian; Fritzsche, Andreas; Frank-Fahle, Beatrice; Lüders, Tilmann; Höss, Sebastian; Eisenmann, Heinrich; Held, Thomas; Totsche, Kai U.; Meckenstock, Rainer U.

    2014-05-01

    Microbial reduction of ferric iron is a major biogeochemical process in groundwater aquifer ecosystems and often associated with the degradation of organic contaminants, as bacteria couple iron reduction to the oxidation reduced carbon like e.g. BTEX. Yet in general the low bioavailability of natural iron oxides limits microbial reduction rates. However, nanosized iron oxides have an unequally enhanced bioavailability and reactivity compared to their respective bulk, macro-sized, and more crystalline materials. At the same time, nanosized iron oxides can be produced in stable colloidal suspensions, permitting efficient injections into contaminated aquifers. We examined the reactivity of nanosized synthetic colloidal iron oxides in microbial iron reduction. Application of colloidal nanoparticles led to a strong and sustainable enhancement of microbial reaction rates in batch experiments and sediment columns. Toluene oxidation was increased five-fold as compared to bulk, non-colloidal ferrihydrite as electron acceptor. Furthermore, we developed a unique approach for custom-tailoring the subsurface mobility of these particles after being injected into a contaminant plume. In a field pilot application, we injected 18 m3 of an iron oxide nanoparticle solution into a BTEX contaminated aquifer with a maximum excess pressure as low as 0.2 bar. The applied suspension showed a superior subsurface mobility, creating a reactive zone of 4 m height (corresponding to the height of the confined aquifer) and 6 m in diameter. Subsequent monitoring of BTEX, microbial BTEX degradation metabolites, ferrous iron generation, stable isotopes fractionation, microbial populations, and methanogenesis demonstrated the strong impact of our approach. Mathematic processed X-ray diffractograms and FTIR spectra provided a semi-quantitatively estimate of the long-term fate of the iron oxide colloids in the aquifer. Potential environmental risks of the injection itself were monitored with

  10. Theory for electron transfer from a mixed-valence dimer with paramagnetic sites to a mononuclear acceptor

    NASA Astrophysics Data System (ADS)

    Bominaar, E. L.; Achim, C.; Borshch, S. A.

    1999-06-01

    Polynuclear transition-metal complexes, such as Fe-S clusters, are the prosthetic groups in a large number of metalloproteins and serve as temporary electron storage units in a number of important redox-based biological processes. Polynuclearity distinguishes clusters from mononuclear centers and confers upon them unique properties, such as spin ordering and the presence of thermally accessible excited spin states in clusters with paramagnetic sites, and fractional valencies in clusters of the mixed-valence type. In an earlier study we presented an effective-mode (EM) analysis of electron transfer from a binuclear mixed-valence donor with paramagnetic sites to a mononuclear acceptor which revealed that the cluster-specific attributes have an important impact on the kinetics of long-range electron transfer. In the present study, the validity of these results is tested in the framework of more detailed theories which we have termed the multimode semiclassical (SC) model and the quantum-mechanical (QM) model. It is found that the qualitative trends in the rate constant are the same in all treatments and that the semiclassical models provide a good approximation of the more rigorous quantum-mechanical description of electron transfer under physiologically relevant conditions. In particular, the present results corroborate the importance of electron transfer via excited spin states in reactions with a low driving force and justify the use of semiclassical theory in cases in which the QM model is computationally too demanding. We consider cases in which either one or two donor sites of a dimer are electronically coupled to the acceptor. In the case of multiconnectivity, the rate constant for electron transfer from a valence-delocalized (class-III) donor is nonadditive with respect to transfer from individual metal sites of the donor and undergoes an order-of-magnitude change by reversing the sign of the intradimer metal-metal resonance parameter (β). In the case of

  11. Fluorescent carbon quantum dots synthesized by chemical vapor deposition: An alternative candidate for electron acceptor in polymer solar cells

    NASA Astrophysics Data System (ADS)

    Cui, Bo; Yan, Lingpeng; Gu, Huimin; Yang, Yongzhen; Liu, Xuguang; Ma, Chang-Qi; Chen, Yongkang; Jia, Husheng

    2018-01-01

    Excitation-wavelength-dependent blue-greenish fluorescent carbon quantum dots (CQDs) with graphite structure were synthesized by chemical vapor deposition (CVD) method. In comparison with those synthesized by hydrothermal method (named H-CQDs), C-CQDs have less hydrophilic terminal groups, showing good solubility in common organic solvents. Furthermore, these synthesized C-CQDs show a low LUMO energy level (LUMO = -3.84 eV), which is close to that of phenyl-C61-butyric acid methyl ester (PC61BM, LUMO = -4.01 eV), the most widely used electron acceptor in polymer solar cells. Photoluminescence quenching of the poly(3-hexylthiophene-2,5-diyl):C-CQDs blended film (P3HT:C-CQDs) indicated that a photo-induced charge transfer between P3HT and C-CQDs occurs in such a composite film. Bulk heterojunction solar cells using C-CQDs as electron acceptors or doping materials were fabricated and tested. High fill factors were achieved for these C-CQDs based polymer solar cells, demonstrating that CQDs synthesized by CVD could be alternative to the fullerene derivatives for applying in polymer solar cells.

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

    PubMed

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

    2015-05-06

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

  13. The genetic basis of energy conservation in the sulfate-reducing bacterium Desulfovibrio alaskensis G20

    DOE PAGES

    Price, Morgan N.; Ray, Jayashree; Wetmore, Kelly M.; ...

    2014-10-31

    Sulfate-reducing bacteria play major roles in the global carbon and sulfur cycles, but it remains unclear how reducing sulfate yields energy. To determine the genetic basis of energy conservation, we measured the fitness of thousands of pooled mutants of Desulfovibrio alaskensis G20 during growth in 12 different combinations of electron donors and acceptors. We show that ion pumping by the ferredoxin:NADH oxidoreductase Rnf is required whenever substrate-level phosphorylation is not possible. The uncharacterized complex Hdr/flox-1 (Dde_1207:13) is sometimes important alongside Rnf and may perform an electron bifurcation to generate more reduced ferredoxin from NADH to allow further ion pumping. Similarly,more » during the oxidation of malate or fumarate, the electron-bifurcating transhydrogenase NfnAB-2 (Dde_1250:1) is important and may generate reduced ferredoxin to allow additional ion pumping by Rnf. During formate oxidation, the periplasmic [NiFeSe] hydrogenase HysAB is required, which suggests that hydrogen forms in the periplasm, diffuses to the cytoplasm, and is used to reduce ferredoxin, thus providing a substrate for Rnf. We found that during hydrogen utilization, the transmembrane electron transport complex Tmc is important and may move electrons from the periplasm into the cytoplasmic sulfite reduction pathway. Finally, mutants of many other putative electron carriers have no clear phenotype, which suggests that they are not important under our growth conditions, although we cannot rule out genetic redundancy.« less

  14. The genetic basis of energy conservation in the sulfate-reducing bacterium Desulfovibrio alaskensis G20

    PubMed Central

    Price, Morgan N.; Ray, Jayashree; Wetmore, Kelly M.; Kuehl, Jennifer V.; Bauer, Stefan; Deutschbauer, Adam M.; Arkin, Adam P.

    2014-01-01

    Sulfate-reducing bacteria play major roles in the global carbon and sulfur cycles, but it remains unclear how reducing sulfate yields energy. To determine the genetic basis of energy conservation, we measured the fitness of thousands of pooled mutants of Desulfovibrio alaskensis G20 during growth in 12 different combinations of electron donors and acceptors. We show that ion pumping by the ferredoxin:NADH oxidoreductase Rnf is required whenever substrate-level phosphorylation is not possible. The uncharacterized complex Hdr/flox-1 (Dde_1207:13) is sometimes important alongside Rnf and may perform an electron bifurcation to generate more reduced ferredoxin from NADH to allow further ion pumping. Similarly, during the oxidation of malate or fumarate, the electron-bifurcating transhydrogenase NfnAB-2 (Dde_1250:1) is important and may generate reduced ferredoxin to allow additional ion pumping by Rnf. During formate oxidation, the periplasmic [NiFeSe] hydrogenase HysAB is required, which suggests that hydrogen forms in the periplasm, diffuses to the cytoplasm, and is used to reduce ferredoxin, thus providing a substrate for Rnf. During hydrogen utilization, the transmembrane electron transport complex Tmc is important and may move electrons from the periplasm into the cytoplasmic sulfite reduction pathway. Finally, mutants of many other putative electron carriers have no clear phenotype, which suggests that they are not important under our growth conditions, although we cannot rule out genetic redundancy. PMID:25400629

  15. Reactive Black 5 as electron donor and/or electron acceptor in dual chamber of solar photocatalytic fuel cell.

    PubMed

    Khalik, Wan Fadhilah; Ho, Li-Ngee; Ong, Soon-An; Voon, Chun-Hong; Wong, Yee-Shian; Yusuf, Sara Yasina; Yusoff, NikAthirah; Lee, Sin-Li

    2018-07-01

    The role of azo dye Reactive Black 5 (RB5) as an electron donor and/or electron acceptor could be distinguished in dual chamber of photocatalytic fuel cell (PFC). The introduction of RB5 in anode chamber increased the voltage generation in the system since degradation of RB5 might produce electrons which also would transfer through external circuit to the cathode chamber. The removal efficiency of RB5 with open and closed circuit was 8.5% and 13.6%, respectively and removal efficiency for open circuit was low due to the fact that recombination of electron-hole pairs might happen in anode chamber since without connection to the cathode, electron cannot be transferred. The degradation of RB5 in cathode chamber with absence of oxygen showed that electrons from anode chamber was accepted by dye molecules to break its azo bond. The presence of oxygen in cathode chamber would improve the oxygen reduction rate which occurred at Platinum-loaded carbon (Pt/C) cathode electrode. The V oc , J sc and P max for different condition of ultrapure water at cathode chamber also affected their fill factor. The transportation of protons to cathode chamber through Nafion membrane could decrease the pH of ultrapure water in cathode chamber and undergo hydrogen evolution reaction in the absence of oxygen which then increased degradation rate of RB5 as well as its electricity generation. Copyright © 2018 Elsevier Ltd. All rights reserved.

  16. Negative Electron Transfer Dissociation Sequencing of Increasingly Sulfated Glycosaminoglycan Oligosaccharides on an Orbitrap Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Leach, Franklin E.; Riley, Nicholas M.; Westphall, Michael S.; Coon, Joshua J.; Amster, I. Jonathan

    2017-09-01

    The structural characterization of sulfated glycosaminoglycan (GAG) carbohydrates remains an important target for analytical chemists attributable to challenges introduced by the natural complexity of these mixtures and the defined need for molecular-level details to elucidate biological structure-function relationships. Tandem mass spectrometry has proven to be the most powerful technique for this purpose. Previously, electron detachment dissociation (EDD), in comparison to other methods of ion activation, has been shown to provide the largest number of useful cleavages for de novo sequencing of GAG oligosaccharides, but such experiments are restricted to Fourier transform ion cyclotron resonance mass spectrometers (FTICR-MS). Negative electron transfer dissociation (NETD) provides similar fragmentation results, and can be achieved on any mass spectrometry platform that is designed to accommodate ion-ion reactions. Here, we examine for the first time the effectiveness of NETD-Orbitrap mass spectrometry for the structural analysis of GAG oligosaccharides. Compounds ranging in size from tetrasaccharides to decasaccharides were dissociated by NETD, producing both glycosidic and cross-ring cleavages that enabled the location of sulfate modifications. The highly-sulfated, heparin-like synthetic GAG, ArixtraTM, was also successfully sequenced by NETD. In comparison to other efforts to sequence GAG chains without fully ionized sulfate constituents, the occurrence of sulfate loss peaks is minimized by judicious precursor ion selection. The results compare quite favorably to prior results with electron detachment dissociation (EDD). Significantly, the duty cycle of the NETD experiment is sufficiently short to make it an effective tool for on-line separations, presenting a straightforward path for selective, high-throughput analysis of GAG mixtures. [Figure not available: see fulltext.

  17. 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

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

    PubMed Central

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

    2002-01-01

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

  19. Covalently Bound Clusters of Alpha-Substituted PDI—Rival Electron Acceptors to Fullerene for Organic Solar Cells

    DOE PAGES

    Wu, Qinghe; Zhao, Donglin; Schneider, Alexander M.; ...

    2016-05-24

    Here, a cluster type of electron acceptor, TPB, bearing four α-perylenediimides (PDIs), was developed, in which the four PDIs form a cross-like molecular conformation while still partially conjugated with the BDT-Th core. The blend TPB:PTB7-Th films shows favorable morphology and efficient charge dissociation. The inverted solar cells exhibited the highest PCE of 8.47 % with the extraordinary high J sc values (>18 mA/cm 2), comparable with those of the corresponding PC 71BM/PBT7-Th based solar cells.

  20. The ETHANOL-CO_2 Dimer is AN Electron Donor-Acceptor Complex

    NASA Astrophysics Data System (ADS)

    McGuire, Brett A.; Martin-Drumel, Marie-Aline; McCarthy, Michael C.

    2017-06-01

    Supercritical (sc) CO_2 is a common industrial solvent for the extraction of caffeine, nicotine, petrochemicals, and natural products. The ability of apolar scCO_2 to dissolve polar solutes is greatly enhanced by the addition of a polar co-solvent, often methanol or ethanol. Experimental and theoretical work show that methanol interactions in scCO_2 are predominantly hydrogen bonding, while the gas-phase complex is an electron donor-acceptor (EDA) configuration. Ethanol, meanwhile, is predicted to form EDA complexes both in scCO_2 and in the gas phase, but there have been no experimental measurements to support this conclusion. Here, we report a combined chirped-pulse and cavity FTMW study of the ethanol-CO_2 complex. Comparison with theory indicates the EDA complex is dominant under our experimental conditions. We confirm the structure with isotopic substitution, and derive a semi-experimental equilibrium structure. Our results are consistent with theoretical predictions that the linearity of the CO_2 subgroup is broken by the complexation interaction.

  1. Effect of π-bridge units on properties of A-π-D-π-A-type nonfullerene acceptors for organic solar cells.

    PubMed

    Wang, Yan-Ling; Li, Quan-Song; Li, Ze-Sheng

    2018-05-15

    Acceptor-π-donor-π-acceptor (A-π-D-π-A)-types of small molecules are very promising nonfullerene acceptors to overcome the drawbacks of fullerene derivatives such as the weak absorption ability and electronic adjustability. However, only few attempts have been made to develop π-bridge units to construct highly efficient acceptors in OSCs. Herein, taking the reported acceptor P1 as a reference, five small-structured acceptors (P2, P3, P4, P5, and P6) have been designed via the replacement of the π-bridge unit. A combination of quantum chemistry and Marcus theory approaches is employed to investigate the effect of different π-bridge units on the optical, electronic, and charge transport properties of P1-P6. The calculation results show that the designed molecules P2 and P5 can become potential acceptor replacements of P1 due to their red-shifted absorption bands, appropriate energy levels, low exciton binding energy, and high electron affinity and electron mobility. Additionally, compared with P3HT/P1, P3HT/P2 and P3HT/P5 exhibit stronger and wider absorption peaks, larger electron transfer distances (DCT), greater transferred charge amounts (Δq), and smaller overlaps (Λ), which shows that P2 and P5 have more significant electron transfer characteristics and favorable exciton dissociation capabilities for enhancing the short-circuit current density (JSC) and thus, they are potential acceptors in OSCs.

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

    PubMed Central

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

    2010-01-01

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

  3. 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.

  4. High Magnetic Susceptibility in a Highly Saline Sulfate-Rich Aquifer Undergoing Biodegradation of Hydrocarbon Results from Sulfate Reduction.

    NASA Astrophysics Data System (ADS)

    Atekwana, E. A.; Enright, A.; Ntarlagiannis, D.; Slater, L. D.; Bernier, R.; Beaver, C. L.; Rossbach, S.

    2016-12-01

    We investigated the chemical and stable carbon isotope composition of groundwater in a highly saline aquifer contaminated with hydrocarbon. Our aim to evaluate hydrocarbon degradation and to constrain the geochemical conditions that generated high anomalous magnetic susceptibility (MS) signatures observed at the water table interface. The occurrence of high MS in the water table fluctuating zone has been attributed to microbial iron reduction, suggesting the use of MS as a proxy for iron cycling. The highly saline aquifer had total dissolved solids concentrations of 3.7 to 29.3 g/L and sulfate concentrations of 787 to 37,100 mg/L. We compared our results for groundwater locations with high hydrocarbon contamination (total petroleum hydrocarbon (TPH) >10 mg/L), at lightly contaminated (TPH <10 mg/L) and locations with no contaminations. Our results for the terminal electron acceptors (TEAs) dissolved oxygen (DO), nitrate (NO3-), dissolved iron (Fe2+) , dissolved manganese (Mn2+), sulfate (SO42-) and methane (CH4) suggest a chemically heterogeneous aquifer, probably controlled by heterogeneous distribution of TEAs and contamination (type of hydrocarbon, phase and age of contamination). The concentrations of dissolved inorganic carbon (DIC) ranged from 67 to 648 mg C/L and the stable carbon isotope (δ13CDIC) ranged from -30.0‰ to 1.0 ‰ and DIC-δ13CDIC modeling indicates that the carbon in the DIC is derived primarily from hydrocarbon degradation. The concentrations of Fe2+ in the aquifer ranged from 0.1 to 55.8 mg/L, but was mostly low, averaging 2.7+10.9 mg/L. Given the low Fe2+ [AE1] in the aqueous phase and the high MS at contaminated locations, we suggest that the high MS observed does not arise from iron reduction but rather from sulfate reduction. Sulfate reduction produces H2S which reacts with Fe2+ to produce ferrous sulfide (Fe2+S) or the mixed valence greigite (Fe2+Fe3+2S4). We conclude that in highly saline aquifers with high concentrations of sulfate

  5. Defining donor and acceptor strength in conjugated copolymers

    NASA Astrophysics Data System (ADS)

    Hedström, Svante; Wang, Ergang; Persson, Petter

    2017-03-01

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

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

    PubMed

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

    2015-02-04

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

  7. BIOREMEDIATION AT WOOD-PRESERVING SITES

    EPA Science Inventory

    The removal of organic compounds from ground water during bioremediation at wood-preserving sites is a function of the stoichiometric demand for electron acceptors (oxygen, nitrate, and sulfate) to metabolize the organic contaminants and the supply of the electron acceptors in th...

  8. Electron-transfer and acid-base properties of a two-electron oxidized form of quaterpyrrole that acts as both an electron donor and an acceptor.

    PubMed

    Zhang, Min; E, Wenbo; Ohkubo, Kei; Sanchez-Garcia, David; Yoon, Dae-Wi; Sessler, Jonathan L; Fukuzumi, Shunichi; Kadish, Karl M

    2008-02-21

    Electron-transfer interconversion between the four-electron oxidized form of a quaterpyrrole (abbreviated as P4 for four pyrroles) and the two-electron oxidized form (P4H2) as well as between P4H2 and its fully reduced form (P4H4) bearing analogous substituents in the alpha- and beta-pyrrolic positions was studied by means of cyclic voltammetry and UV-visible spectroelectrochemistry combined with ESR and laser flash photolysis measurements. The two-electron oxidized form, P4H2, acts as both an electron donor and an electron acceptor. The radical cation (P4H2*+) and radical anion (P4H2*-) are both produced by photoinduced electron transfer from dimeric 1-benzyl-1,4-dihydronicotinamide to P4H2, whereas the cation radical form of the compound is also produced by electron-transfer oxidation of P4H2 with [Ru(bpy)3]3+. The ESR spectra of P4H2*+ and P4H2*- were recorded at low temperature and exhibit spin delocalization over all four pyrrole units. Thus, the two-electron oxidized form of the quaterpyrrole (P4H2) displays redox and electronic features analogous to those seen in the case of porphyrins and may be considered as a simple, open-chain model of this well-studied tetrapyrrolic macrocycle. The dynamics of deprotonation from P4H2*+ and disproportionation of P4H2 were examined by laser flash photolysis measurements of photoinduced electron-transfer oxidation and reduction of P4H2, respectively.

  9. Spectrophotometric and spectroscopic studies of charge transfer complex of 1-Naphthylamine as an electron donor with picric acid as an electron acceptor in different polar solvents

    NASA Astrophysics Data System (ADS)

    Singh, Neeti; Ahmad, Afaq

    2010-08-01

    The charge transfer complex of 1-Naphthylamine as a donor with π-acceptor picric acid has been studied spectrophotometrically in different solvents at room temperature. The results indicate that the formation of charge transfer complex is high in less polar solvent. The stoichiometry of the complex was found to be 1:1 by straight line method. The data are analysed in terms of formation constant ( KCT), molar extinction coefficient ( ɛCT), standard free energy (Δ G o), oscillator strength ( ƒ), transition dipole moment ( μ EN), resonance energy ( R N) and ionization potential ( I D). It is concluded that the formation constant ( KCT) of the complex is found to be depends upon the nature of both electron acceptor and donor and also on the polarity of solvents. Further the charge transfer molecular complex between picric acid and 1-Naphthylamine is stabilized by hydrogen bonding.

  10. The iron-sulfur cluster of electron transfer flavoprotein-ubiquinone oxidoreductase is the electron acceptor for electron transfer flavoprotein.

    PubMed

    Swanson, Michael A; Usselman, Robert J; Frerman, Frank E; Eaton, Gareth R; Eaton, Sandra S

    2008-08-26

    Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) accepts electrons from electron transfer flavoprotein (ETF) and reduces ubiquinone from the ubiquinone pool. It contains one [4Fe-4S] (2+,1+) and one FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. In the porcine protein, threonine 367 is hydrogen bonded to N1 and O2 of the flavin ring of the FAD. The analogous site in Rhodobacter sphaeroides ETF-QO is asparagine 338. Mutations N338T and N338A were introduced into the R. sphaeroides protein by site-directed mutagenesis to determine the impact of hydrogen bonding at this site on redox potentials and activity. The mutations did not alter the optical spectra, EPR g-values, spin-lattice relaxation rates, or the [4Fe-4S] (2+,1+) to FAD point-dipole interspin distances. The mutations had no impact on the reduction potential for the iron-sulfur cluster, which was monitored by changes in the continuous wave EPR signals of the [4Fe-4S] (+) at 15 K. For the FAD semiquinone, significantly different potentials were obtained by monitoring the titration at 100 or 293 K. Based on spectra at 293 K the N338T mutation shifted the first and second midpoint potentials for the FAD from +47 and -30 mV for wild type to -11 and -19 mV, respectively. The N338A mutation decreased the potentials to -37 and -49 mV. Lowering the midpoint potentials resulted in a decrease in the quinone reductase activity and negligible impact on disproportionation of ETF 1e (-) catalyzed by ETF-QO. These observations indicate that the FAD is involved in electron transfer to ubiquinone but not in electron transfer from ETF to ETF-QO. Therefore, the iron-sulfur cluster is the immediate acceptor from ETF.

  11. The Iron-Sulfur Cluster of Electron Transfer Flavoprotein-Ubiquinone Oxidoreductase Is the Electron Acceptor for Electron Transfer Flavoprotein†

    PubMed Central

    Swanson, Michael A.; Usselman, Robert J.; Frerman, Frank E.; Eaton, Gareth R.; Eaton, Sandra S.

    2009-01-01

    Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) accepts electrons from electron transfer flavoprotein (ETF) and reduces ubiquinone from the ubiquinone pool. It contains one [4Fe-4S]2+,1+ and one FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. In the porcine protein, threonine 367 is hydrogen bonded to N1 and O2 of the flavin ring of the FAD. The analogous site in Rhodobacter sphaeroides ETF-QO is asparagine 338. Mutations N338T and N338A were introduced into the R. sphaeroides protein by site-directed mutagenesis to determine the impact of hydrogen bonding at this site on redox potentials and activity. The mutations did not alter the optical spectra, EPR g-values, spin-lattice relaxation rates, or the [4Fe-4S]2+,1+ to FAD point-dipole interspin distances. The mutations had no impact on the reduction potential for the iron-sulfur cluster, which was monitored by changes in the continuous wave EPR signals of the [4Fe-4S]+ at 15 K. For the FAD semiquinone, significantly different potentials were obtained by monitoring the titration at 100 or 293 K. Based on spectra at 293 K the N338T mutation shifted the first and second midpoint potentials for the FAD from +47 and -30 mV for wild type to -11 and -19 mV, respectively. The N338A mutation decreased the potentials to -37 and -49 mV. Lowering the midpoint potentials resulted in a decrease in the quinone reductase activity and negligible impact on disproportionation of ETF1e- catalyzed by ETF-QO. These observations indicate that the FAD is involved in electron transfer to ubiquinone but not in electron transfer from ETF to ETF-QO. Therefore, the iron-sulfur cluster is the immediate acceptor from ETF. PMID:9585549

  12. Metabolic potential of a Novel Gram-Negative, Spore-forming, and Putatively Sulfate-Reducing Bacterium in the Continental Subsurface

    NASA Astrophysics Data System (ADS)

    Lau, C. Y. M.; Becraft, E. D.; Cason, E. D.; Borgonie, G.; Kieft, T. L.; Li, L.; van Heerden, E.; Jarett, J.; Woyke, T.; Stepanauskas, R.; Onstott, T. C.

    2017-12-01

    Anaerobic sulfate reduction is among the most thermodynamically favorable biochemical reactions in the deep subsurface environments. Phylogenetically and functionally diverse sulfate-reducing bacteria (SRB) within Deltaproteobacteria and Firmicutes have been reported. However, only few of them have been isolated in pure cultures for detailed physiological characterization. Previous studies showed that fracture fluid samples from the 1 km-deep borehole DR5IPC (Driefontein gold mine, South Africa) harbored novel SRB, as indicated by the low percentages (84% and 90%) of identity of the 16S ribosomal RNA clone sequences to known SRB. To overcome the challenge of low cultivability, we employed next-generation sequencing to unveil the metabolic potential of these novel SRB. Metagenomic assembly and binning yielded seven >50% complete genomes including a methylotrophic SRB belonging to Deltaproteobacteria (DR5_3) and two draft genomes representing an uncultivated phylum, tentatively "Driefonteinae" (DR5_4 and DR5_5). They accounted for 3%, 2% and 18% of all metagenomic reads. Three single-cell assembled genomes (SAGs) sharing 99% of average nucleotide identity (ANI) with DR5_5 were obtained. Analysis of the protein-coding genes in DR5_5 and related SAGs indicated that "Driefonteinae" possesses dissimilatory sulfite reductase genes (dsrAB), suggesting that sulfate would be the terminal electron acceptor. Whereas it may use diverse electron acceptors such as carbon monoxide, acetate, lactate and formate. A near-complete collection of genes for Wood-Ljungdahl pathway and genes for partial pentose phosphate pathway, glycolysis and tricarboxylic acid cycle further showed that "Driefonteinae" may live a mixotrophic life style. It is evident that archaeal genes related to methanogens were acquired through horizontal gene transfer. Phenotypically, "Driefonteinae" has a Gram-negative cell wall and flagella. The ability of forming spores would enable this microorganism to endure

  13. Diversity and composition of sulfate- and sulfite-reducing prokaryotes as affected by marine-freshwater gradient and sulfate availability.

    PubMed

    Fan, Lan-Feng; Tang, Sen-Lin; Chen, Chang-Po; Hsieh, Hwey-Lian

    2012-01-01

    Sulfate- and sulfite-reducing prokaryotes (SSRP) communities play a key role in both sulfur and carbon cycles. In estuarine ecosystems, sulfate concentrations change with tides and could be limited in tidal freshwater reach or deep sediments. In a subtropical estuary of northern Taiwan in December 2007, we examined the compositional changes of SSRP communities. We examined three sites: from the lower estuarine brackish-water reach (site GR and mangrove vegetation site, GM) to the upper estuarine tidal freshwater reach (site HR), as well as from surface to a 50-cm depth. The partial sequence of sulfite reductase (dsrB) genes was used as a molecular marker of SSRP, linked to polymerase chain reaction and denaturing gradient gel electrophoresis (DGGE) techniques. SSRP communities of the DGGE profiles varied with sites according to one-way analyses of similarities (Global R = 0.69, P = 0.001). Using cluster analysis, the DGGE profile was found to show site-specific clusters and a distinct depth zonation (five, six, and two SSRP communities at the GM, GR, and HR sites, respectively). SSRP composition was highly correlated to the combination of salinity, reduced sulfur, and total organic carbon contents (BIO-ENV analysis, r ( s ) = 0.56). After analyzing a total of 35 dsrB sequences in the DGGE gel, six groups with 15 phylotypes were found, which were closely related to marine-freshwater gradient. Moreover, sequences neighboring sulfite-reducing prokaryotes were observed, in addition to those affiliated to sulfate-reducing prokaryotes. Four phylotypes harvested in HR resembled the genus Desulfitobacterium, a sulfite-reducing prokaryote, which failed to use sulfate as an electron acceptor and were active in freshwater and sulfate-limited habitat. The other five phylotypes in the HR reach belonged to the sulfate-reducing prokaryotes of the genera Desulfatiferula, Desulfosarcina, Desulfovibrio, and Desulfotomaculum, which appeared to tolerate low salinity and

  14. Anaerobic biodegradation of nonylphenol in river sediment under nitrate- or sulfate-reducing conditions and associated bacterial community.

    PubMed

    Wang, Zhao; Yang, Yuyin; Dai, Yu; Xie, Shuguang

    2015-04-09

    Nonylphenol (NP) is a commonly detected pollutant in aquatic ecosystem and can be harmful to aquatic organisms. Anaerobic degradation is of great importance for the clean-up of NP in sediment. However, information on anaerobic NP biodegradation in the environment is still very limited. The present study investigated the shift in bacterial community structure associated with NP degradation in river sediment microcosms under nitrate- or sulfate-reducing conditions. Nearly 80% of NP (100 mg kg(-1)) could be removed under these two anaerobic conditions after 90 or 110 days' incubation. Illumina MiSeq sequencing analysis indicated that Proteobacteria, Firmicutes, Bacteroidetes and Chloroflexi became the dominant phylum groups with NP biodegradation. The proportion of Gammaproteobacteria, Deltaproteobacteria and Choloroflexi showed a marked increase in nitrate-reducing microcosm, while Gammaproteobacteria and Firmicutes in sulfate-reducing microcosm. Moreover, sediment bacterial diversity changed with NP biodegradation, which was dependent on type of electron acceptor. Copyright © 2014 Elsevier B.V. All rights reserved.

  15. Methods for the synthesis of donor-acceptor cyclopropanes

    NASA Astrophysics Data System (ADS)

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

    2018-03-01

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

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

    PubMed

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

    2018-04-22

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

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

    PubMed

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

    2017-07-18

    Organic donor-acceptor (DA) complexes have attracted wide attention in recent decades, resulting in the rapid development of organic binary system electronics. The design and synthesis of organic DA complexes with a variety of component structures have mainly focused on metallicity (or even superconductivity), emission, or ferroelectricity studies. Further efforts have been made in high-performance electronic investigations. The chemical versatility of organic semiconductors provides DA complexes with a great number of possibilities for semiconducting applications. Organic DA complexes extend the semiconductor family and promote charge separation and transport in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In OFETs, the organic complex serves as an active layer across extraordinary charge pathways, ensuring the efficient transport of induced charges. Although an increasing number of organic semiconductors have been reported to exhibit good p- or n-type properties (mobilities higher than 1 or even 10 cm 2 V -1 s -1 ), critical scientific challenges remain in utilizing the advantages of existing semiconductor materials for more and wider applications while maintaining less complicated synthetic or device fabrication processes. DA complex materials have revealed new insight: their unique molecular packing and structure-property relationships. The combination of donors and acceptors could offer practical advantages compared with their unimolecular materials. First, growing crystals of DA complexes with densely packed structures will reduce impurities and traps from the self-assembly process. Second, complexes based on the original structural components could form superior mixture stacking, which can facilitate charge transport depending on the driving force in the coassembly process. Third, the effective use of organic semiconductors can lead to tunable band structures, allowing the operation mode (p- or n-type) of the transistor to be

  18. EPR studies of the vitamin K 1 semiquinone radical anion. Comparison to the electron acceptor A 1 in green plant photosystem I

    NASA Astrophysics Data System (ADS)

    Thurnauer, Marion C.; Brown, James W.; Gast, P.; Feezel, Laura L.

    Suggestions that the electron acceptor, A 1, in Photosystem I is a quinone have come from both optical and epr experiments. Vitamin K 1 (phylloquinone) is present in the PSI complex with a stoichiometry of two molecules per reaction center. In order to determine if A 1 can be identified with vitamin K 1, X-band and Q-band epr properties of the vitamin K 1 radical anion in frozen alcohol solutions are examined. The results are compared to the epr properties that have been observed for the reduced A 1 acceptor in vivo. The g-values obtained for the vitamin K 1 radical anion are consistent with identifying A 1 with vitamin K 1.

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

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

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

    2016-03-23

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

  20. Synthesis, and spectroscopic studies of charge transfer complex of 1,2-dimethylimidazole as an electron donor with π-acceptor 2,4-dinitro-1-naphthol in different polar solvents

    NASA Astrophysics Data System (ADS)

    Miyan, Lal; Khan, Ishaat M.; Ahmad, Afaq

    2015-07-01

    The charge transfer (CT) complex of 1,2-dimethylimidazole (DMI) as an electron donor with π acceptor 2,4-dinitro-1-naphthol (DNN) has been studied spectrophotometrically in different solvents like chloroform, acetonitrile, methanol, methylene chloride, etc. at room temperature. The CT complex which is formed through the transfer of lone pair electrons from DMI to DNN exhibits well resolved CT bands and the regions of these bands were remarkably different from those of the donor and acceptor. The stoichiometry of the CT complex was found to be 1:1 by a straight-line method between donor and acceptor with maximum absorption bands. The novel CT complex has been characterized by FTIR, TGA-DTA, powder XRD, 1H NMR and 13C NMR spectroscopic techniques. The Benesi-Hildebrand equation has been used to determine the formation constant (KCT), molar extinction coefficient (εCT), standard gibbs free energy (ΔG°) and other physical parameters of the CT complex. The formation constant recorded higher values and molar extinction coefficient recorded lower values in chloroform compared with methylene chloride, methanol and acetonitrile, confirming the strong interaction between the molecular orbital's of donor and acceptor in the ground state in less polar solvent. This CT complex has been studied by absorption spectra of donor 1,2-dimethylimidazole (DMI) and acceptor 2,4-dinitro-1-naphthol (DNN) by using the spectrophotometric technique in various solvents at room temperature.

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

    PubMed

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

    2014-05-30

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-01-01

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

  3. Microbial Community Composition and Functional Capacity in a Terrestrial Ferruginous, Sulfate-Depleted Mud Volcano

    PubMed Central

    Tu, Tzu-Hsuan; Wu, Li-Wei; Lin, Yu-Shih; Imachi, Hiroyuki; Lin, Li-Hung; Wang, Pei-Ling

    2017-01-01

    Terrestrial mud volcanoes (MVs) are an important natural source of methane emission. The role of microbial processes in methane cycling and organic transformation in such environments remains largely unexplored. In this study, we aim to uncover functional potentials and community assemblages across geochemical transitions in a ferruginous, sulfate-depleted MV of eastern Taiwan. Geochemical profiles combined with 16S rRNA gene abundances indicated that anaerobic oxidation of methane (AOM) mediated by ANME-2a group coincided with iron/manganese reduction by Desulfuromonadales at shallow depths deprived of sulfate. The activity of AOM was stimulated either by methane alone or by methane and a range of electron acceptors, such as sulfate, ferrihydrite, and artificial humic acid. Metagenomic analyses revealed that functional genes for AOM and metal reduction were more abundant at shallow intervals. In particular, genes encoding pili expression and electron transport through multi-heme cytochromes were prevalent, suggesting potential intercellular interactions for electron transport involved in AOM. For comparison, genes responsible for methanogenesis and degradation of chitin and plant-derived molecules were more abundant at depth. The gene distribution combined with the enhanced proportions of 16S rRNA genes related to methanogens and heterotrophs, and geochemical characteristics suggest that particulate organic matter was degraded into various organic entities that could further fuel in situ methanogenesis. Finally, genes responsible for aerobic methane oxidation were more abundant in the bubbling pool and near-surface sediments. These methane oxidizers account for the ultimate attenuation of methane discharge into the atmosphere. Overall, our results demonstrated that various community members were compartmentalized into stratified niches along geochemical gradients. These community members form a metabolic network that cascades the carbon transformation from the

  4. Microbial Community Composition and Functional Capacity in a Terrestrial Ferruginous, Sulfate-Depleted Mud Volcano.

    PubMed

    Tu, Tzu-Hsuan; Wu, Li-Wei; Lin, Yu-Shih; Imachi, Hiroyuki; Lin, Li-Hung; Wang, Pei-Ling

    2017-01-01

    Terrestrial mud volcanoes (MVs) are an important natural source of methane emission. The role of microbial processes in methane cycling and organic transformation in such environments remains largely unexplored. In this study, we aim to uncover functional potentials and community assemblages across geochemical transitions in a ferruginous, sulfate-depleted MV of eastern Taiwan. Geochemical profiles combined with 16S rRNA gene abundances indicated that anaerobic oxidation of methane (AOM) mediated by ANME-2a group coincided with iron/manganese reduction by Desulfuromonadales at shallow depths deprived of sulfate. The activity of AOM was stimulated either by methane alone or by methane and a range of electron acceptors, such as sulfate, ferrihydrite, and artificial humic acid. Metagenomic analyses revealed that functional genes for AOM and metal reduction were more abundant at shallow intervals. In particular, genes encoding pili expression and electron transport through multi-heme cytochromes were prevalent, suggesting potential intercellular interactions for electron transport involved in AOM. For comparison, genes responsible for methanogenesis and degradation of chitin and plant-derived molecules were more abundant at depth. The gene distribution combined with the enhanced proportions of 16S rRNA genes related to methanogens and heterotrophs, and geochemical characteristics suggest that particulate organic matter was degraded into various organic entities that could further fuel in situ methanogenesis. Finally, genes responsible for aerobic methane oxidation were more abundant in the bubbling pool and near-surface sediments. These methane oxidizers account for the ultimate attenuation of methane discharge into the atmosphere. Overall, our results demonstrated that various community members were compartmentalized into stratified niches along geochemical gradients. These community members form a metabolic network that cascades the carbon transformation from the

  5. Thermodesulfobacterium geofontis sp. nov., a hyperthermophilic, sulfate-reducing bacterium isolated from Obsidian Pool, Yellowstone National Park

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

    Hamilton-Brehm, Scott D.; Gibson, Robert A.; Green, Stefan J.

    2013-01-24

    A novel sulfate-reducing bacterium designated OPF15T was isolated from Obsidian Pool, Yellowstone National Park, Wyoming. The phylogeny of 16S rRNA and functional genes (dsrAB) placed the organism within the family Thermodesulfobacteriaceae. The organism displayed hyperthermophilic temperature requirements for growth with a range of 70 90 C and an optimum of 83 C. Optimal pH was around 6.5 7.0 and the organism required the presence of H2 or formate as an electron donor and CO2 as a carbon source. Electron acceptors supporting growth included sulfate, thiosulfate, and elemental sulfur. Lactate, acetate, pyruvate, benzoate, oleic acid, and ethanol did not serve asmore » electron donors. Membrane lipid analysis revealed diacyl glycerols and acyl/ether glycerols which ranged from C14:0 to C20:0. Alkyl chains present in acyl/ether and diether glycerol lipids ranged from C16:0 to C18:0. Straight, iso- and anteiso-configurations were found for all lipid types. The presence of OPF15T was also shown to increase cellulose consumption during co-cultivation with Caldicellulosiruptor obsidiansis, a fermentative, cellulolytic extreme thermophile isolated from the same environment. On the basis of phylogenetic, phenotypic, and structural analyses, Thermodesulfobacterium geofontis sp. nov. is proposed as a new species with OPF15T representing the type strain.« less

  6. Thermodesulfobacterium geofontis sp. nov., a hyperthermophilic, sulfate-reducing bacterium isolated from Obsidian Pool, Yellowstone National Park.

    PubMed

    Hamilton-Brehm, Scott D; Gibson, Robert A; Green, Stefan J; Hopmans, Ellen C; Schouten, Stefan; van der Meer, Marcel T J; Shields, John P; Damsté, Jaap S S; Elkins, James G

    2013-03-01

    A novel sulfate-reducing bacterium designated OPF15(T) was isolated from Obsidian Pool, Yellowstone National Park, Wyoming. The phylogeny of 16S rRNA and functional genes (dsrAB) placed the organism within the family Thermodesulfobacteriaceae. The organism displayed hyperthermophilic temperature requirements for growth with a range of 70-90 °C and an optimum of 83 °C. Optimal pH was around 6.5-7.0 and the organism required the presence of H2 or formate as an electron donor and CO2 as a carbon source. Electron acceptors supporting growth included sulfate, thiosulfate, and elemental sulfur. Lactate, acetate, pyruvate, benzoate, oleic acid, and ethanol did not serve as electron donors. Membrane lipid analysis revealed diacyl glycerols and acyl/ether glycerols which ranged from C14:0 to C20:0. Alkyl chains present in acyl/ether and diether glycerol lipids ranged from C16:0 to C18:0. Straight, iso- and anteiso-configurations were found for all lipid types. The presence of OPF15(T) was also shown to increase cellulose consumption during co-cultivation with Caldicellulosiruptor obsidiansis, a fermentative, cellulolytic extreme thermophile isolated from the same environment. On the basis of phylogenetic, phenotypic, and structural analyses, Thermodesulfobacterium geofontis sp. nov. is proposed as a new species with OPF15(T) representing the type strain.

  7. Biodegradation of munitions compounds by a sulfate reducing bacterial enrichment culture

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

    Boopathy, R.; Manning, J.

    1997-08-01

    The degradation of several munitions compounds was studied. The compounds included 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine, 2,4,6-trinitrobenzene (TNB), and 2,4-dinitrotoluene. All of the compounds studied were degraded by the sulfate reducing bacterial (SRB) enrichment culture. The SRB culture did not use the munitions compounds as their sole source of carbon. However, all the munitions compounds tested served as the sole source of nitrogen for the SRB culture. Degradation of munitions compounds was achieved by a co-metabolic process. The SRB culture used a variety of carbon sources including pyruvate, ethanol, formate, lactate, and H{sub 2}-CO{sub 2}. The SRB culture was an incompletemore » oxidizer, unable to carry out the terminal oxidation of organic substrates to CO{sub 2} as the sole product, and it did not use acetate or methanol as a carbon source. In addition to serving as nitrogen sources, the munitions compounds also served as electron acceptors in the absence of sulfate. A soil slurry experiment with 5% and 10% munitions compounds-contaminated soil showed that the contaminant TNT was metabolized by the SRB culture in the presence of pyruvate as electron donor. This culture may be useful in decontaminating munitions compounds-contaminated soil and water under anaerobic conditions.« less

  8. Evidence of Sulfate-Dependent Anaerobic Methane Oxidation within an Area Impacted by Coalbed Methane-Related Gas Migration

    NASA Astrophysics Data System (ADS)

    Wolfe, A. L.; Wikin, R. T.

    2017-12-01

    We evaluated water quality characteristics in the northern Raton Basin of Colorado and documented the response of the Poison Canyon aquifer system several years after upward migration of methane gas occurred from the deeper Vermejo Formation coalbed production zone. Over a 17-month study period, water samples were obtained from domestic water wells and monitoring wells located within the impacted area, and analyzed for 245 constituents, including organic compounds, nutrients, major and trace elements, dissolved gases, and isotopic tracers for carbon, sulfur, oxygen, and hydrogen. Multiple lines of evidence suggest that sulfate-dependent methane biodegradation, which involves the oxidation of methane (CH4) to carbon dioxide (CO2) using sulfate (SO42-) as the terminal electron acceptor, is occurring: (i) consumption of methane and sulfate and production of sulfide and bicarbonate, (ii) methane loss coupled to production of higher molecular weight (C2+) gaseous hydrocarbons, (iii) patterns of 13C enrichment and depletion in methane and dissolved inorganic carbon, and (iv) a systematic shift in sulfur and oxygen isotope ratios of sulfate, indicative of microbial sulfate reduction. Groundwater-methane attenuation is linked to the production of dissolved sulfide, and elevated dissolved sulfide concentrations represent an undesirable secondary water quality impact. The biogeochemical response of the aquifer system has not mobilized naturally occurring trace metals, including arsenic, chromium, cobalt, nickel, and lead, likely due to the microbial production of hydrogen sulfide, which favors stabilization of metals in aquifer solids.

  9. Relationship between microbial sulfate reduction rates and sulfur isotopic fractionation

    NASA Astrophysics Data System (ADS)

    Matsu'Ura, F.

    2009-12-01

    Sulfate reduction is one of the common processes to obtain energy for certain types of microorganisms.They use hydrogen gas or organic substrates as electron donor and sulfates as electron acceptor, and reduce sulfates to sulfides. Sulfate reducing microbes extend across domains Archea and Bacteria, and are believed to be one of the earliest forms of terrestrial life (Shen 2004). The origin of 34S-depleted (light) sulfide sulfur, especially δ34S < -30 ‰, around hydrothermal vents or beneath the sea-floor is speculated to be the products of sulfate reducers. But laboratory experiments using sulfate reducers fail to produce such light sulfur, and many models were proposed to explain the discrepancy. Canfield et al. (2006) proposed so-called "standard model" based on previous studies. The standard model explained the reason for the large fractionation by temperature dependence of sulfur isotopic fractionation factor and rate of sulfate reduction, which indicated the growth conditions of microbes. However, they failed to prove their model by their other experiments (Canfield et al., 2006). In this study, I performed laboratory culture experiment of sulfate reducing bacteria (SRB) to explain the 34S-depleted sulfide sulfur. [Experiments] To compare the result with Canfield et al. (2006), I used Desulfovibrio desulfuricans for my laboratory culture experiment. D. desulfuricans was inoculated into glass vials, which contain 40ml of liquid culture media slightly modified from DSMZ #63 medium.Excess amount of Fe (II) is added to the DSMZ#63 medium to precipitate sulfide as iron sulfide. The vials were incubated at 25°C, 30°C, and 37°C, respectively. 21 vials were used for one temperature and sulfide and sulfate was collected from each three glass vials at every 12 hours from 72 hours to 144 hours after start of incubation. The sulfide was precipitated as iron sulfide and the sulfate was precipitated as barite. Sulfur isotope compositions of sulfate and sulfide were

  10. Anaerobic oxidation of methane coupled to thiosulfate reduction in a biotrickling filter.

    PubMed

    Cassarini, Chiara; Rene, Eldon R; Bhattarai, Susma; Esposito, Giovanni; Lens, Piet N L

    2017-09-01

    Microorganisms from an anaerobic methane oxidizing sediment were enriched with methane gas as the substrate in a biotrickling filter (BTF) using thiosulfate as electron acceptor for 213days. Thiosulfate disproportionation to sulfate and sulfide were the dominating sulfur conversion process in the BTF and the sulfide production rate was 0.5mmoll -1 day -1 . A specific group of sulfate reducing bacteria (SRB), belonging to the Desulforsarcina/Desulfococcus group, was enriched in the BTF. The BTF biomass showed maximum sulfate reduction rate (0.38mmoll -1 day -1 ) with methane as sole electron donor, measured in the absence of thiosulfate in the BTF. Therefore, a BTF fed with thiosulfate as electron acceptor can be used to enrich SRB of the DSS group and activate the inoculum for anaerobic oxidation of methane coupled to sulfate reduction. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. STUDIES ON THERMOPHILIC SULFATE-REDUCING BACTERIA II.

    PubMed Central

    Akagi, J. M.; Campbell, L. Leon

    1961-01-01

    Akagi, J. M. (Western Reserve University, Cleveland, Ohio) and L. Leon Campbell. Studies on thermophilic sulfate-reducing bacteria. II. Hydrogenase activity of Clostridium nigrificans. J. Bacteriol. 82:927–932. 1961.—The hydrogenase of Clostridium nigrificans has been found to be associated with the cell-free particulate fraction which can be sedimented at 105,000 × g in 1 hr. The specific activity of this fraction was increased 2 to 3 fold over that of the crude extract. It was not found possible to liberate the enzyme from the particulate fraction by methods of enzymatic digestion, chemical extraction, or physical disruption. The optimum temperature for H2 utilization using benzyl viologen as an electron acceptor was found to be 55 C, and the optimum pH range was 7 to 8. Employing metal complexing agents it was found that the enzyme required Fe++ ions for H2 utilization. In contrast, Fe++ ions were not required to catalyze the evolution of H2 from reduced methyl viologen. The role of Fe++ ions in the hydrogenase activity of this organism is discussed. PMID:13859876

  12. 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

  13. A survey of acceptor dopants for β-Ga2O3

    NASA Astrophysics Data System (ADS)

    Lyons, John L.

    2018-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Ganesamoorthy, Ramasamy; Vijayaraghavan, Rajagopalan; Sakthivel, Pachagounder

    2017-12-01

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

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

    PubMed

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

    2018-05-09

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

  16. Effects of formate binding on the quinone-iron electron acceptor complex of photosystem II.

    PubMed

    Sedoud, Arezki; Kastner, Lisa; Cox, Nicholas; El-Alaoui, Sabah; Kirilovsky, Diana; Rutherford, A William

    2011-02-01

    EPR was used to study the influence of formate on the electron acceptor side of photosystem II (PSII) from Thermosynechococcus elongatus. Two new EPR signals were found and characterized. The first is assigned to the semiquinone form of Q(B) interacting magnetically with a high spin, non-heme-iron (Fe²(+), S=2) when the native bicarbonate/carbonate ligand is replaced by formate. This assignment is based on several experimental observations, the most important of which were: (i) its presence in the dark in a significant fraction of centers, and (ii) the period-of-two variations in the concentration expected for Q(B)(•-) when PSII underwent a series of single-electron turnovers. This signal is similar but not identical to the well-know formate-modified EPR signal observed for the Q(A)(•-)Fe²(+) complex (W.F.J. Vermaas and A.W. Rutherford, FEBS Lett. 175 (1984) 243-248). The formate-modified signals from Q(A)(•-)Fe²(+) and Q(B)(•-)Fe²(+) are also similar to native semiquinone-iron signals (Q(A)(•-)Fe²(+)/Q(B)(•-)Fe²(+)) seen in purple bacterial reaction centers where a glutamate provides the carboxylate ligand to the iron. The second new signal was formed when Q(A)(•-) was generated in formate-inhibited PSII when the secondary acceptor was reduced by two electrons. While the signal is reminiscent of the formate-modified semiquinone-iron signals, it is broader and its main turning point has a major sub-peak at higher field. This new signal is attributed to the Q(A)(•-)Fe²(+) with formate bound but which is perturbed when Q(B) is fully reduced, most likely as Q(B)H₂ (or possibly Q(B)H(•-) or Q(B)(²•-)). Flash experiments on formate-inhibited PSII monitoring these new EPR signals indicate that the outcome of charge separation on the first two flashes is not greatly modified by formate. However on the third flash and subsequent flashes, the modified Q(A)(•-)Fe²(+)Q(B)H₂ signal is trapped in the EPR experiment and there is a marked

  17. New acceptor-bridge-donor strategy for enhancing NLO response with long-range excess electron transfer from the NH2...M/M3O donor (M = Li, Na, K) to inside the electron hole cage C20F19 acceptor through the unusual σ chain bridge (CH2)4.

    PubMed

    Bai, Yang; Zhou, Zhong-Jun; Wang, Jia-Jun; Li, Ying; Wu, Di; Chen, Wei; Li, Zhi-Ru; Sun, Chia-Chung

    2013-04-04

    Using the strong electron hole cage C20F19 acceptor, the NH2...M/M3O (M = Li, Na, and K) complicated donors with excess electron, and the unusual σ chain (CH2)4 bridge, we construct a new kind of electride molecular salt e(-)@C20F19-(CH2)4-NH2...M(+)/M3O(+) (M = Li, Na, and K) with excess electron anion inside the hole cage (to be encapsulated excess electron-hole pair) serving as a new A-B-D strategy for enhancing nonlinear optical (NLO) response. An interesting push-pull mechanism of excess electron generation and its long-range transfer is exhibited. The excess electron is pushed out from the (super)alkali atom M/M3O by the lone pair of NH2 in the donor and further pulled inside the hole cage C20F19 acceptor through the efficient long σ chain (CH2)4 bridge. Owing to the long-range electron transfer, the new designed electride molecular salts with the excess electron-hole pair exhibit large NLO response. For the e(-)@C20F19-(CH2)4-NH2...Na(+), its large first hyperpolarizability (β0) reaches up to 9.5 × 10(6) au, which is about 2.4 × 10(4) times the 400 au for the relative e(-)@C20F20...Na(+) without the extended chain (CH2)4-NH2. It is shown that the new strategy is considerably efficient in enhancing the NLO response for the salts. In addition, the effects of different bridges and alkali atomic number on β0 are also exhibited. Further, three modulating factors are found for enhancing NLO response. They are the σ chain bridge, bridge-end group with lone pair, and (super)alkali atom. The new knowledge may be significant for designing new NLO materials and electronic devices with electrons inside the cages. They may also be the basis of establishing potential organic chemistry with electron-hole pair.

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

    PubMed

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

    2011-10-01

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

  19. Analysis of fast chlorophyll fluorescence rise (O-K-J-I-P) curves in green fruits indicates electron flow limitations at the donor side of PSII and the acceptor sides of both photosystems.

    PubMed

    Kalachanis, Dimitrios; Manetas, Yiannis

    2010-07-01

    Limited evidence up to now indicates low linear photosynthetic electron flow and CO(2) assimilation rates in non-foliar chloroplasts. In this investigation, we used chlorophyll fluorescence techniques to locate possible limiting steps in photosystem function in exposed, non-stressed green fruits (both pericarps and seeds) of three species, while corresponding leaves served as controls. Compared with leaves, fruit photosynthesis was characterized by less photon trapping and less quantum yields of electron flow, while the non-photochemical quenching was higher and potentially linked to enhanced carotenoid/chlorophyll ratios. Analysis of fast chlorophyll fluorescence rise curves revealed possible limitations both in the donor (oxygen evolving complex) and the acceptor (Q(A)(-)--> intermediate carriers) sides of photosystem II (PSII) indicating innately low PSII photochemical activity. On the other hand, PSI was characterized by faster reduction of its final electron acceptors and their small pool sizes. We argue that the fast reductive saturation of final PSI electron acceptors may divert electrons back to intermediate carriers facilitating a cyclic flow around PSI, while the partial inactivation of linear flow precludes strong reduction of plastoquinone. As such, the photosynthetic attributes of fruit chloroplasts may act to replenish the ATP lost because of hypoxia usually encountered in sink organs with high diffusive resistance to gas exchange.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed

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

    2016-01-06

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

  2. The Iron-Sulfur Cluster of Electron Transfer Flavoprotein-ubiquinone Oxidoreductase (ETF-QO) is the Electron Acceptor for Electron Transfer Flavoprotein†

    PubMed Central

    Swanson, Michael A.; Usselman, Robert J.; Frerman, Frank E.; Eaton, Gareth R.; Eaton, Sandra S.

    2011-01-01

    Electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) accepts electrons from electron-transfer flavoprotein (ETF) and reduces ubiquinone from the ubiquinone-pool. It contains one [4Fe-4S]2+,1+ and one FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. In the porcine protein, threonine 367 is hydrogen bonded to N1 and O2 of the flavin ring of the FAD. The analogous site in Rhodobacter sphaeroides ETF-QO is asparagine 338. Mutations N338T and N338A were introduced into the R. sphaeroides protein by site-directed mutagenesis to determine the impact of hydrogen bonding at this site on redox potentials and activity. The mutations did not alter the optical spectra, EPR g-values, spin-lattice relaxation rates, or the [4Fe-4S]2+,1+ to FAD point-dipole interspin distances. The mutations had no impact on the reduction potential for the iron-sulfur cluster, which was monitored by changes in the continuous wave EPR signals of the [4Fe-4S]+ at 15 K. For the FAD semiquinone, significantly different potentials were obtained by monitoring the titration at 100 or 293 K. Based on spectra at 293 K the N338T mutation shifted the first and second midpoint potentials for the FAD from +47 mV and −30 mV for wild type to −11 mV and −19 mV, respectively. The N338A mutation decreased the potentials to −37 mV and −49 mV. Lowering the midpoint potentials resulted in a decrease in the quinone reductase activity and negligible impact on disproportionation of ETF1e− catalyzed by ETF-QO. These observations indicate that the FAD is involved in electron transfer to ubiquinone, but not in electron transfer from ETF to ETF-QO. Therefore the iron-sulfur cluster is the immediate acceptor from ETF. PMID:18672901

  3. An Efficient, "Burn in" Free Organic Solar Cell Employing a Nonfullerene Electron Acceptor.

    PubMed

    Cha, Hyojung; Wu, Jiaying; Wadsworth, Andrew; Nagitta, Jade; Limbu, Saurav; Pont, Sebastian; Li, Zhe; Searle, Justin; Wyatt, Mark F; Baran, Derya; Kim, Ji-Seon; McCulloch, Iain; Durrant, James R

    2017-09-01

    A comparison of the efficiency, stability, and photophysics of organic solar cells employing poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'″-di(2-octyldodecyl)-2,2';5',2″;5″,2'″-quaterthiophen-5,5'″-diyl)] (PffBT4T-2OD) as a donor polymer blended with either the nonfullerene acceptor EH-IDTBR or the fullerene derivative, [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM) as electron acceptors is reported. Inverted PffBT4T-2OD:EH-IDTBR blend solar cell fabricated without any processing additive achieves power conversion efficiencies (PCEs) of 9.5 ± 0.2%. The devices exhibit a high open circuit voltage of 1.08 ± 0.01 V, attributed to the high lowest unoccupied molecular orbital (LUMO) level of EH-IDTBR. Photoluminescence quenching and transient absorption data are employed to elucidate the ultrafast kinetics and efficiencies of charge separation in both blends, with PffBT4T-2OD exciton diffusion kinetics within polymer domains, and geminate recombination losses following exciton separation being identified as key factors determining the efficiency of photocurrent generation. Remarkably, while encapsulated PffBT4T-2OD:PC 71 BM solar cells show significant efficiency loss under simulated solar irradiation ("burn in" degradation) due to the trap-assisted recombination through increased photoinduced trap states, PffBT4T-2OD:EH-IDTBR solar cell shows negligible burn in efficiency loss. Furthermore, PffBT4T-2OD:EH-IDTBR solar cells are found to be substantially more stable under 85 °C thermal stress than PffBT4T-2OD:PC 71 BM devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    NASA Astrophysics Data System (ADS)

    Koenraad, Paul

    2005-03-01

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

  5. Realizing high-rate sulfur reduction under sulfate-rich conditions in a biological sulfide production system to treat metal-laden wastewater deficient in organic matter.

    PubMed

    Sun, Rongrong; Zhang, Liang; Zhang, Zefeng; Chen, Guang-Hao; Jiang, Feng

    2017-12-22

    Biological sulfur reduction can theoretically produce sufficient sulfide to effectively remove and recover heavy metals in the treatment of organics-deficient sulfate-rich metal-laden wastewater such as acid mine drainage and metallurgic wastewater, using 75% less organics than biological sulfate reduction. However, it is still unknown whether sulfur reduction can indeed compete with sulfate reduction, particularly under high-strength sulfate conditions. The aim of this study was to investigate the long-term feasibility of biological sulfur reduction under high sulfate conditions in a lab-scale sulfur-reducing biological sulfide production (BSP) system with sublimed sulfur added. In the 169-day trial, an average sulfide production rate (SPR) as high as 47 ± 9 mg S/L-h was achieved in the absence of sulfate, and the average SPR under sulfate-rich conditions was similar (53 ± 10 mg S/L-h) when 1300 mg S/L sulfate were fed with the influent. Interestingly, sulfate was barely reduced even at such a high strength and contributed to only 1.5% of total sulfide production. Desulfomicrobium was identified as the predominant sulfidogenic bacterium in the bioreactor. Batch tests further revealed that this sulfidogenic bacteria used elemental sulfur as the electron acceptor instead of the highly bioavailable sulfate, during which polysulfide acted as an intermediate, leading to an even higher bioavailability of sulfur than sulfate. The pathway of sulfur to sulfide conversion via polysulfide in the presence of both sulfur and sulfate was discussed. Collectively, when conditions favor polysulfide formation, sulfur reduction can be a promising and attractive technology to realize a high-rate and low-cost BSP process for treating sulfate-rich metal-laden wastewater. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. High-throughput screening to identify selective inhibitors of microbial sulfate reduction (and beyond)

    NASA Astrophysics Data System (ADS)

    Carlson, H. K.; Coates, J. D.; Deutschbauer, A. M.

    2015-12-01

    The selective perturbation of complex microbial ecosystems to predictably influence outcomes in engineered and industrial environments remains a grand challenge for geomicrobiology. In some industrial ecosystems, such as oil reservoirs, sulfate reducing microorganisms (SRM) produce hydrogen sulfide which is toxic, explosive and corrosive. Current strategies to selectively inhibit sulfidogenesis are based on non-specific biocide treatments, bio-competitive exclusion by alternative electron acceptors or sulfate-analogs which are competitive inhibitors or futile/alternative substrates of the sulfate reduction pathway. Despite the economic cost of sulfidogenesis, there has been minimal exploration of the chemical space of possible inhibitory compounds, and very little work has quantitatively assessed the selectivity of putative souring treatments. We have developed a high-throughput screening strategy to target SRM, quantitatively ranked the selectivity and potency of hundreds of compounds and identified previously unrecognized SRM selective inhibitors and synergistic interactions between inhibitors. Once inhibitor selectivity is defined, high-throughput characterization of microbial community structure across compound gradients and identification of fitness determinants using isolate bar-coded transposon mutant libraries can give insights into the genetic mechanisms whereby compounds structure microbial communities. The high-throughput (HT) approach we present can be readily applied to target SRM in diverse environments and more broadly, could be used to identify and quantify the potency and selectivity of inhibitors of a variety of microbial metabolisms. Our findings and approach are relevant for engineering environmental ecosystems and also to understand the role of natural gradients in shaping microbial niche space.

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

  8. Cytochromes and iron sulfur proteins in sulfur metabolism of phototrophic bacteria

    NASA Technical Reports Server (NTRS)

    Fischer, U.

    1985-01-01

    Dissimilatory sulfur metabolism in phototrophic sulfur bacteria provides the bacteria with electrons for photosynthetic electron transport chain and, with energy. Assimilatory sulfate reduction is necessary for the biosynthesis of sulfur-containing cell components. Sulfide, thiosulfate, and elemental sulfur are the sulfur compounds most commonly used by phototrophic bacteria as electron donors for anoxygenic photosynthesis. Cytochromes or other electron transfer proteins, like high-potential-iron-sulfur protein (HIPIP) function as electron acceptors or donors for most enzymatic steps during the oxidation pathways of sulfide or thiosulfate. Yet, heme- or siroheme-containing proteins themselves undergo enzymatic activities in sulfur metabolism. Sirohemes comprise a porphyrin-like prosthetic group of sulfate reductase. eenzymatic reactions involve electron transfer. Electron donors or acceptors are necessary for each reaction. Cytochromes and iron sulfur problems, are able to transfer electrons.

  9. Fused-Ring Acceptors with Asymmetric Side Chains for High-Performance Thick-Film Organic Solar Cells.

    PubMed

    Feng, Shiyu; Zhang, Cai'e; Liu, Yahui; Bi, Zhaozhao; Zhang, Zhe; Xu, Xinjun; Ma, Wei; Bo, Zhishan

    2017-11-01

    A kind of new fused-ring electron acceptor, IDT-OB, bearing asymmetric side chains, is synthesized for high-efficiency thick-film organic solar cells. The introduction of asymmetric side chains can increase the solubility of acceptor molecules, enable the acceptor molecules to pack closely in a dislocated way, and form favorable phase separation when blended with PBDB-T. As expected, PBDB-T:IDT-OB-based devices exhibit high and balanced hole and electron mobility and give a high power conversion efficiency (PCE) of 10.12%. More importantly, the IDT-OB-based devices are not very sensitive to the film thickness, a PCE of 9.17% can still be obtained even the thickness of active layer is up to 210 nm. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Characterization of 16S rRNA genes from oil field microbial communities indicates the presence of a variety of sulfate-reducing, fermentative, and sulfide-oxidizing bacteria.

    PubMed

    Voordouw, G; Armstrong, S M; Reimer, M F; Fouts, B; Telang, A J; Shen, Y; Gevertz, D

    1996-05-01

    Oil field bacteria were characterized by cloning and sequencing of PCR-amplified 16S rRNA genes. A variety of gram-negative, sulfate-reducing bacteria was detected (16 members of the family Desulfovibrionaceae and 8 members of the family Desulfobacteriaceae). In contrast, a much more limited number of anaerobic, fermentative, or acetogenic bacteria was found (one Clostridium sp., one Eubacterium sp., and one Synergistes sp.). Potential sulfide oxidizers and/or microaerophiles (Thiomicrospira, Arcobacter, Campylobacter, and Oceanospirillum spp.) were also detected. The first two were prominently amplified from uncultured production water DNA and represented 28 and 47% of all clones, respectively. Growth on media containing sulfide as the electron donor and nitrate as the electron acceptor and designed for the isolation of Thiomicrospira spp. gave only significant enrichment of the Campylobacter sp., which was shown to be present in different western Canadian oil fields. This newly discovered sulfide oxidizer may provide a vital link in the oil field sulfur cycle by reoxidizing sulfide formed by microbial sulfate or sulfur reduction.

  11. Characterization of 16S rRNA genes from oil field microbial communities indicates the presence of a variety of sulfate-reducing, fermentative, and sulfide-oxidizing bacteria.

    PubMed Central

    Voordouw, G; Armstrong, S M; Reimer, M F; Fouts, B; Telang, A J; Shen, Y; Gevertz, D

    1996-01-01

    Oil field bacteria were characterized by cloning and sequencing of PCR-amplified 16S rRNA genes. A variety of gram-negative, sulfate-reducing bacteria was detected (16 members of the family Desulfovibrionaceae and 8 members of the family Desulfobacteriaceae). In contrast, a much more limited number of anaerobic, fermentative, or acetogenic bacteria was found (one Clostridium sp., one Eubacterium sp., and one Synergistes sp.). Potential sulfide oxidizers and/or microaerophiles (Thiomicrospira, Arcobacter, Campylobacter, and Oceanospirillum spp.) were also detected. The first two were prominently amplified from uncultured production water DNA and represented 28 and 47% of all clones, respectively. Growth on media containing sulfide as the electron donor and nitrate as the electron acceptor and designed for the isolation of Thiomicrospira spp. gave only significant enrichment of the Campylobacter sp., which was shown to be present in different western Canadian oil fields. This newly discovered sulfide oxidizer may provide a vital link in the oil field sulfur cycle by reoxidizing sulfide formed by microbial sulfate or sulfur reduction. PMID:8633860

  12. 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,…

  13. 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

  14. Effect of sulfate and nitrate on acetate conversion by anaerobic microorganisms in a freshwater sediment.

    PubMed

    Scholten, Johannes C M; Bodegom, Peter M; Vogelaar, Jaap; Ittersum, Alexander; Hordijk, Kees; Roelofsen, Wim; Stams, Alfons J M

    2002-12-01

    Acetate is quantitatively the most important substrate for methane production in a freshwater sediment in The Netherlands. In the presence of alternative electron acceptors the conversion of acetate by methanogens was strongly inhibited. By modelling the results, obtained in experiments with and without (13)C-labelled acetate, we could show that the competition for acetate between methanogens and sulfate reducers is the main cause of inhibition of methanogenesis in the sediment. Although nitrate led to a complete inhibition of methanogenesis, acetate-utilising nitrate-reducing bacteria hardly competed with methanogens for the available acetate in the presence of nitrate. Most-probable-number enumerations showed that methanogens (2x10(8) cells cm(-3) sediment) and sulfate reducers (2x10(8) cells cm(-3) sediment) were the dominant acetate-utilising organisms in the sediment, while numbers of acetate-utilising nitrate reducers were very low (5x10(5) cells cm(-3) sediment). However, high numbers of sulfide-oxidising nitrate reducers were detected. Denitrification might result in the formation of toxic products. We speculate that the accumulation of low concentrations of NO (<0.2 mM) may result in an inhibition of methanogenesis.

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

    PubMed

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

    2003-01-01

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

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

    DOE PAGES

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

    2017-05-22

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

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

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

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

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

  18. Development of a glucose sensor employing quick and easy modification method with mediator for altering electron acceptor preference.

    PubMed

    Hatada, Mika; Loew, Noya; Inose-Takahashi, Yuka; Okuda-Shimazaki, Junko; Tsugawa, Wakako; Mulchandani, Ashok; Sode, Koji

    2018-06-01

    Enzyme based electrochemical biosensors are divided into three generations according to their type of electron transfer from the cofactors of the enzymes to the electrodes. Although the 3rd generation sensors using direct electron transfer (DET) type enzymes are ideal, the number of enzyme types which possess DET ability is limited. In this study, we report of a glucose sensor using mediator-modified glucose dehydrogenase (GDH), that was fabricated by a new quick-and-easy method using the pre-functionalized amine reactive phenazine ethosulfate (arPES). Thus mediator-modified GDH obtained the ability to transfer electrons to bulky electron acceptors as well as electrodes. The concentration of glucose was successfully measured using electrodes with immobilized PES-modified GDH, without addition of external electron mediators. Therefore, continuous monitoring systems can be developed based on this "2.5th generation" electron transfer principle utilizing quasi-DET. Furthermore, we successfully modified two other diagnostically relevant enzymes, glucoside 3-dehydrogenase and lactate oxidase, with PES. Therefore, various kinds of diagnostic enzymes can achieve quasi-DET ability simply by modification with arPES, suggesting that continuous monitoring systems based on the 2.5th generation principle can be developed for various target molecules. Copyright © 2018 Elsevier B.V. All rights reserved.

  19. Sulfate-reducing bacteria: Microbiology and physiology

    NASA Technical Reports Server (NTRS)

    Peck, H. D.

    1985-01-01

    The sulfate reducing bacteria, the first nonphotosynthetic anaerobic bacteria demonstrated to contain c type cytochromes, perform electron transfer coupled to phosphorylation. A new bioenergetic scheme for the formation of a proton gradient for growth of Desulfovibrio on organic substrates and sulfate involving vectors electron transfer and consistent with the cellular localization of enzymes and electron transfer components was proposed. Hydrogen is produced in the cytoplasm from organic substrates and, as a permease molecule diffuses rapidly across the cytoplasmic membrane, it is oxidized to protons and electrons by the periplasmic hydrogenase. The electrons only are transferred across the cytoplasmic membrane to the cytoplasm where they are used to reduce sulfate to sulfide. The protons are used for transport or to drive a reversible ATPOSE. The net effect is the transfer of protons across the cytoplasmic membrane with the intervention of a proton pump. This type of H2 cycling is relevant to the bioenergetics of other types of anaerobic microorganisms.

  20. Growth of magnetotactic sulfate-reducing bacteria in oxygen concentration gradient medium.

    PubMed

    Lefèvre, Christopher T; Howse, Paul A; Schmidt, Marian L; Sabaty, Monique; Menguy, Nicolas; Luther, George W; Bazylinski, Dennis A

    2016-12-01

    Although dissimilatory sulfate-reducing bacteria (SRB) are generally described as strictly anaerobic organisms with regard to growth, several reports have shown that some SRB, particularly Desulfovibrio species, are quite resistant to O 2 . For example, SRB remain viable in many aerobic environments while some even reduce O 2 to H 2 O. However, reproducible aerobic growth of SRB has not been unequivocally documented. Desulfovibrio magneticus is a SRB that is also a magnetotactic bacterium (MTB). MTB biomineralize magnetosomes which are intracellular, membrane-bounded, magnetic iron mineral crystals. The ability of D. magneticus to grow aerobically in several different media under air where an O 2 concentration gradient formed, or under O 2 -free N 2 gas was tested. Under air, cells grew as a microaerophilic band of cells at the oxic-anoxic interface in media lacking sulfate. These results show that D. magneticus is capable of aerobic growth with O 2 as a terminal electron acceptor. This is the first report of consistent, reproducible aerobic growth of SRB. This finding is critical in determining important ecological roles SRB play in the environment. Interestingly, the crystal structure of the magnetite crystals of D. magneticus grown under microaerobic conditions showed significant differences compared with those produced anaerobically providing more evidence that environmental parameters influence magnetosome formation. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

  1. Characterization of a new thermophilic sulfate-reducing bacterium Thermodesulfovibrio yellowstonii, gen. nov. and sp. nov.: its phylogenetic relationship to Thermodesulfobacterium commune and their origins deep within the bacterial domain

    NASA Technical Reports Server (NTRS)

    Henry, E. A.; Devereux, R.; Maki, J. S.; Gilmour, C. C.; Woese, C. R.; Mandelco, L.; Schauder, R.; Remsen, C. C.; Mitchell, R.

    1994-01-01

    A thermophilic sulfate-reducing vibrio isolated from thermal vent water in Yellowstone Lake, Wyoming, USA is described. The gram-negative, curved rod-shaped cells averaged 0.3 micrometer wide and 1.5 micrometers long. They were motile by means of a single polar flagellum. Growth was observed between 40 degrees and 70 degrees C with optimal growth at 65 degrees C. Cultures remained viable for one year at 27 degrees C although spore-formation was not observed. Sulfate, thiosulfate and sulfite were used as electron acceptors. Sulfur, fumarate and nitrate were not reduced. In the presence of sulfate, growth was observed only with lactate, pyruvate, hydrogen plus acetate, or formate plus acetate. Pyruvate was the only compound observed to support fermentative growth. Pyruvate and lactate were oxidized to acetate. Desulfofuscidin and c-type cytochromes were present. The G + C content was 29.5 mol%. The divergence in the 16 S ribosomal RNA sequences between the new isolate and Thermodesulfobacterium commune suggests that these two thermophilic sulfate-reducing bacteria represent different genera. These two bacteria depict a lineage that branches deeply within the Bacteria domain and which is clearly distinct from previously defined phylogenetic lines of sulfate-reducing bacteria. Strain YP87 is described as the type strain of the new genus and species Thermodesulfovibrio yellowstonii.

  2. Small-Molecule Acceptor Based on the Heptacyclic Benzodi(cyclopentadithiophene) Unit for Highly Efficient Nonfullerene Organic Solar Cells.

    PubMed

    Kan, Bin; Feng, Huanran; Wan, Xiangjian; Liu, Feng; Ke, Xin; Wang, Yanbo; Wang, Yunchuang; Zhang, Hongtao; Li, Chenxi; Hou, Jianhui; Chen, Yongsheng

    2017-04-05

    A new nonfullerene small molecule with acceptor-donor-acceptor (A-D-A) structure, namely, NFBDT, based on a heptacyclic benzodi(cyclopentadithiophene) (FBDT) unit using benzo[1,2-b:4,5-b']dithiophene as the core unit, was designed and synthesized. Its absorption ability, energy levels, thermal stability, as well as photovoltaic performances were fully investigated. NFBDT exhibits a low optical bandgap of 1.56 eV resulting in wide and efficient absorption that covered the range from 600 to 800 nm, and suitable energy levels as an electron acceptor. With the widely used and successful wide bandgap polymer PBDB-T selected as the electron donor material, an optimized PCE of 10.42% was obtained for the PBDB-T:NFBDT-based device with an outstanding short-circuit current density of 17.85 mA cm -2 under AM 1.5G irradiation (100 mW cm -2 ), which is so far among the highest performance of NF-OSC devices. These results demonstrate that the BDT unit could also be applied for designing NF-acceptors, and the fused-ring benzodi(cyclopentadithiophene) unit is a prospective block for designing new NF-acceptors with excellent performance.

  3. Studies on the electron acceptors of photosystem two

    NASA Astrophysics Data System (ADS)

    Bowden, Simon John

    The differences in temperature dependent behaviour and microwave power saturation characteristics between the g=1.9 and g=1.8 QA -Fe2+ signals are described. The dependence of these behaviourial differences on the presence or absence of bicarbonate is emphasised. By studying the EPR signals of QA-Fe2+, Q-Fe2+, Q-Fe2+TBTQ- and the oxidised non-haem iron I have found that detergent solubilisation of BBY PS2 preparations with the detergent OGP, at pH 6.0, results in loss of bicarbonate binding. New preparations, including a dodecylmaltoside prepared CP47, CP4 3, D1, D2, cytochrome bgsg complex, are described which at pH 7.5 retain native bicarbonate binding. These preparations provide a new system for studies into the "bicarbonate effect" because bicarbonate depletion can now be achieved without displacement by another anion. The new OGP particles have been used to investigate both the split pheophytin signal and the two step redox titration phenomenon associated with this signal. The low potential step of the titration was concluded to be independent of the QA/QA- mid-point potential but was found to be linked to the ability to photoreduce pheophytin; once the low potential component, suggested here to be the fluorescence quencher QL, was reduced, pheophytin photoreduction increased. A model is described to explain the two step titration and, from analysis of the signal splitting in +/- HCO3- samples, a possible structural role for bicarbonate is proposed. I have probed the structure of the PS2 electron acceptor region with the protease trypsin. The QA, iron-semiquinone; oxidised non-haem iron and cytochrome bss, EPR signals were all found to be susceptible to trypsin damage, while oxygen evolution with ferricyanide was enhanced by protease treatment. The protective effect of calcium ions against trypsin damage was demonstrated and a possible Ca2+ binding site in the binding region identified.

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

    PubMed

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

    2016-07-21

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

  5. Sulfate- and Sulfur-Reducing Bacteria as Terrestrial Analogs for Microbial Life on Jupiter's Satellite Io

    NASA Technical Reports Server (NTRS)

    Pikuta, Elena V.; Hoover, Richard B.; Six, N. Frank (Technical Monitor)

    2001-01-01

    Observations from the Voyager and Galileo spacecraft have revealed Jupiter's moon Io to be the most volcanically active body of our Solar System. The Galileo Near Infrared Imaging Spectrometer (NIMS) detected extensive deposits of sulfur compounds, elemental sulfur and SO2 frost on the surface of Io. There are extreme temperature variations on Io's surface, ranging from -130 C to over 2000 C at the Pillan Patera volcanic vent. The active volcanoes, fumaroles, calderas, and lava lakes and vast sulfur deposits on this frozen moon indicate that analogs of sulfur- and sulfate-reducing bacteria might inhabit Io. Hence Io may have great significance to Astrobiology. Earth's life forms that depend on sulfur respiration are members of two domains: Bacteria and Archaea. Two basic links of the biogeochemical sulfur cycle of Earth have been studied: 1) the sulfur oxidizing process (occurring at aerobic conditions) and 2) the process of sulfur-reduction to hydrogen sulfide (anaerobic conditions). Sulfate-reducing bacteria (StRB) and sulfur-reducing bacteria (SrRB) are responsible for anaerobic reducing processes. At the present time the systematics of StRB include over 112 species distributed into 35 genera of Bacteria and Archaea. Moderately thermophilic and mesophilic SrRB belong to the Bacteria. The hyperthermophilic SrRB predominately belong to the domain Archaea and are included in the genera: Pyrodictium, Thermoproteus, Pyrobaculum, Thermophilum, Desulfurococcus, and Thermodiscus. The StRB and SrRB use a wide spectrum of substrates as electron donors for lithotrophic and heterotrophic type nutrition. The electron acceptors for the StRB include: sulfate, thiosulfate, sulfite, sulfur, arsenate, dithionite, tetrathionate, sulfur monoxide, iron, nitrite, selenite, fumarate, oxygen, carbon dioxide, and chlorine-containing phenol compounds. The Sulfate- and Sulfur-reducing bacteria are widely distributed in anaerobic ecosystems, including extreme environments like hot springs

  6. Photoinduced electron transfer across a molecular wall: coumarin dyes as donors and methyl viologen and TiO2 as acceptors.

    PubMed

    Porel, Mintu; Klimczak, Agnieszka; Freitag, Marina; Galoppini, Elena; Ramamurthy, V

    2012-02-21

    Coumarins C-153, C-480, and C-1 formed 1:2 (guest:host) complexes with a water-soluble cavitand having eight carboxylic acid groups (OA) in aqueous borate buffer solution. The complexes were photoexcited in the presence of electron acceptors (methyl viologen, MV(2+), or TiO(2)) to probe the possibility of electron transfer between a donor and an acceptor physically separated by a molecular wall. In solution at basic pH, the dication MV(2+) was associated to the exterior of the complex C-153@OA(2), as suggested by diffusion constants (~1.2 × 10(-6) cm(2)/s) determined by DOSY NMR. The fluorescence of C-153@OA(2) was quenched in the presence of increasing amounts of MV(2+) and Stern-Volmer plots of I(o)/I and τ(o)/τ vs [MV(2+)] indicated that the quenching was static. As per FT-IR-ATR spectra, the capsule C-153@OA(2) was bound to TiO(2) nanoparticle films. Selective excitation (λ(exc) = 420) of the above bound complex resulted in fluorescence quenching. When adsorbed on insulating ZrO(2) nanoparticle films, excitation of the complex resulted in a broad fluorescence spectrum centered at 500 nm and consistent with C-153 being within the lipophilic capsule interior. Consistent with the above results, colloidal TiO(2) quenched the emission while colloidal ZrO(2) did not.

  7. Start-up of simultaneous removal of ammonium and sulfate from an anaerobic ammonium oxidation (anammox) process in an anaerobic up-flow bioreactor.

    PubMed

    Yang, Zhiquan; Zhou, Shaoqi; Sun, Yanbo

    2009-09-30

    A laboratory testing of simultaneous removal of ammonium and sulfate (SRAS) was studied from an anammox process in an anaerobic bioreactor filled with granular activated carbon. Two different phases of experiment were investigated to start up the SRAS process, and final batch tests were performed to analyze the SRAS process. The experiment included an anammox process and an SRAS process. During the anammox process, the highest removal efficiency of ammonium and nitrite was up to 97 and 98%, respectively. After 160 days in the stationary phase of anammox process, the ratio of ammonium to nitrite consumption was approximately 1:1.15, which is much higher than 1:1.32 in the traditional anammox process. The extra electron acceptor, such as sulfate, was thought to react with ammonium by bacteria. Synthetic wastewater containing ammonium chlorine and sodium sulfate was used as the feed for the bioreactor in the second phase of experiment. During the SRAS process, the influent concentrations of ammonium and sulfate were controlled to be 50-60 and 210-240 mg L(-1) respectively. After start-up and acclimatization of this process for 60 days, the average effluent concentrations of ammonium and sulfate were 30 and 160 mg L(-1), respectively. The simultaneous ammonium and sulfate removal was detected in the reactor. In order to further validate the biochemical interaction between ammonium and sulfate, batch tests was carried out. Abiotic tests were carried out to demonstrate that the pure chemical action between ammonium and sulfate without microorganism was not possible. Biotic assays with different ammonium and sulfate concentrations were further investigated that high concentrations of ammonium and sulfate could promote simultaneous removal of ammonium and sulfate. And elemental sulfur and nitrogen gas as the products measured in the SRAS process helped to demonstrate the occurrence of new interaction between nitrogen and sulfur. The new process of SRAS in the inorganic

  8. Anaerobic Degradation of Ethylbenzene by a New Type of Marine Sulfate-Reducing Bacterium

    PubMed Central

    Kniemeyer, Olaf; Fischer, Thomas; Wilkes, Heinz; Glöckner, Frank Oliver; Widdel, Friedrich

    2003-01-01

    Anaerobic degradation of the aromatic hydrocarbon ethylbenzene was studied with sulfate as the electron acceptor. Enrichment cultures prepared with marine sediment samples from different locations showed ethylbenzene-dependent reduction of sulfate to sulfide and always contained a characteristic cell type that formed gas vesicles towards the end of growth. A pure culture of this cell type, strain EbS7, was isolated from sediment from Guaymas Basin (Gulf of California). Complete mineralization of ethylbenzene coupled to sulfate reduction was demonstrated in growth experiments with strain EbS7. Sequence analysis of the 16S rRNA gene revealed a close relationship between strain EbS7 and the previously described marine sulfate-reducing strains NaphS2 and mXyS1 (similarity values, 97.6 and 96.2%, respectively), which grow anaerobically with naphthalene and m-xylene, respectively. However, strain EbS7 did not oxidize naphthalene, m-xylene, or toluene. Other compounds utilized by strain EbS7 were phenylacetate, 3-phenylpropionate, formate, n-hexanoate, lactate, and pyruvate. 1-Phenylethanol and acetophenone, the characteristic intermediates in anaerobic ethylbenzene degradation by denitrifying bacteria, neither served as growth substrates nor were detectable as metabolites by gas chromatography-mass spectrometry in ethylbenzene-grown cultures of strain EbS7. Rather, (1-phenylethyl)succinate and 4-phenylpentanoate were detected as specific metabolites in such cultures. Formation of these intermediates can be explained by a reaction sequence involving addition of the benzyl carbon atom of ethylbenzene to fumarate, carbon skeleton rearrangement of the succinate moiety (as a thioester), and loss of one carboxyl group. Such reactions are analogous to those suggested for anaerobic n-alkane degradation and thus differ from the initial reactions in anaerobic ethylbenzene degradation by denitrifying bacteria which employ dehydrogenations. PMID:12570993

  9. Biodegradation of BTEX and Other Petroleum Hydrocarbons by Enhanced and Controlled Sulfate Reduction

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

    Song Jin

    High concentrations of sulfide in the groundwater at a field site near South Lovedale, OK, were inhibiting sulfate reducing bacteria (SRB) that are known to degrade contaminants including benzene, toluene, ethylbenzene, and m+p-xylenes (BTEX). Microcosms were established in the laboratory using groundwater and sediment collected from the field site and amended with various nutrient, substrate, and inhibitor treatments. All microcosms were initially amended with FeCl{sub 2} to induce FeS precipitation and, thereby, reduce sulfide concentrations. Complete removal of BTEX was observed within 39 days in treatments with various combinations of nutrient and substrate amendments. Results indicate that elevated concentration ofmore » sulfide is a limiting factor to BTEX biodegradation at this site, and that treating the groundwater with FeCl{sub 2} is an effective remedy to facilitate and enhance BTEX degradation by the indigenous SRB population. On another site in Moore, OK, studies were conducted to investigate barium in the groundwater. BTEX biodegradation by SRB is suspected to mobilize barium from its precipitants in groundwater. Data from microcosms demonstrated instantaneous precipitation of barium when sulfate was added; however, barium was detected redissolving for a short period and precipitating eventually, when active sulfate reduction was occurring and BTEX was degraded through the process. SEM elemental spectra of the evolved show that sulfur was not present, which may exclude BaSO{sub 4} and BaS as a possible precipitates. The XRD analysis suggests that barium probably ended in BaS complexing with other amorphous species. Results from this study suggest that SRB may be able to use the sulfate from barite (BaSO{sub 4}) as an electron acceptor, resulting in the release of free barium ions (Ba{sup 2+}), and re-precipitate it in BaS, which exposes more toxicity to human and ecological health.« less

  10. Role of protein sulfation in vasodilation induced by minoxidil sulfate, a K+ channel opener

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

    Meisheri, K.D.; Oleynek, J.J.; Puddington, L.

    Evidence from contractile, radioisotope ion flux and electrophysiological studies suggest that minoxidil sulfate (MNXS) acts as a K+ channel opener in vascular smooth muscle. This study was designed to examine possible biochemical mechanisms by which MNXS exerts such an effect. Experiments performed in the isolated rabbit mesenteric artery (RMA) showed that MNXS, 5 microM, but not the parent compound minoxidil, was a potent vasodilator. Whereas the relaxant effects of an another K+ channel opener vasodilator, BRL-34915 (cromakalim), were removed by washing with physiological saline solution, the effects of MNXS persisted after repeated washout attempts. Furthermore, after an initial exposure ofmore » segments of intact RMA to (35S) MNXS, greater than 30% of the radiolabel was retained 2 hr after removal of the drug. In contrast, retention of radiolabel was not detected with either (3H)MNXS (label on the piperidine ring of MNXS) or (3H)minoxidil (each less than 3% after a 2-hr washout). These data suggested that the sulfate moiety from MNXS was closely associated with the vascular tissue. To determine if proteins were the acceptors of sulfate from MNXS, intact RMAs were incubated with (35S)MNXS, and then 35S-labeled proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and analyzed by fluorography. Preferential labeling of a 116 kD protein was detected by 2 and 5 min of treatment. A 43 kD protein (resembling actin) also showed significant labeling. A similar profile of 35S-labeled proteins was observed in (35S) MNXS-treated A7r5 rat aortic smooth muscle cells, suggesting that the majority of proteins labeled by (35S)MNXS in intact RMA were components of smooth muscle cells.« less

  11. Validation Testing a Contaminant Transport and Natural Attenuation Simulation Model Using Field Data.

    DTIC Science & Technology

    1995-12-01

    reactions . The following figure shows the relationship of common electron acceptors with regard to their redox potential. Redox Potential (pH = 7) in...Model 8 Fuel-Spill Plume Profile 8 Hydrocarbon Biodegradation 1° Oxygen 11 Anaerobic Electron Acceptors 12 Redox Potential *4 Contaminants of...Biodegradation Reactions 21 Oxygen Reactions 21 Nitrate 22 Manganese (IV) 22 Iron (III) 23 Sulfate 24 in Page Intrinsic Bioremediation Model

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

    DTIC Science & Technology

    2006-05-01

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

  13. Development and Characterization of New Donor-Acceptor Conjugated Polymers and Fullerene Nanoparticles for High Performance Bulk Heterojunction Solar Cells

    DTIC Science & Technology

    2011-01-14

    thieno[3,4-c] pyrrole -4,6-dione (TPD)–based donor–acceptor polymer, PBTTPD, that exhibits high crystallinity and a low-lying highest occupied molecular...release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT Bithiophene/thieno[3,4-c] pyrrole -4,6-dione (TPD)?based donor?acceptor polymer...nearby fullerene acceptors. The electron-deficient thieno[3,4-c] pyrrole -4,6-dione (TPD) moiety exhibits a symmetric, rigidly fused, coplanar

  14. A role for a lithium-inhibited Golgi nucleotidase in skeletal development and sulfation

    PubMed Central

    Frederick, Joshua P.; Tafari, A. Tsahai; Wu, Sheue-Mei; Megosh, Louis C.; Chiou, Shean-Tai; Irving, Ryan P.; York, John D.

    2008-01-01

    Sulfation is an important biological process that modulates the function of numerous molecules. It is directly mediated by cytosolic and Golgi sulfotransferases, which use 3′-phosphoadenosine 5′-phosphosulfate to produce sulfated acceptors and 3′-phosphoadenosine 5′-phosphate (PAP). Here, we identify a Golgi-resident PAP 3′-phosphatase (gPAPP) and demonstrate that its activity is potently inhibited by lithium in vitro. The inactivation of gPAPP in mice led to neonatal lethality, lung abnormalities resembling atelectasis, and dwarfism characterized by aberrant cartilage morphology. The phenotypic similarities of gPAPP mutant mice to chondrodysplastic models harboring mutations within components of the sulfation pathway lead to the discovery of undersulfated chondroitin in the absence of functional enzyme. Additionally, we observed loss of gPAPP leads to perturbations in the levels of heparan sulfate species in lung tissue and whole embryos. Our data are consistent with a model that clearance of the nucleotide product of sulfotransferases within the Golgi plays an important role in glycosaminoglycan sulfation, provide a unique genetic basis for chondrodysplasia, and define a function for gPAPP in the formation of skeletal elements derived through endochondral ossification. PMID:18695242

  15. Kinetics of sulfate and hydrogen uptake by the thermophilic sulfate-reducing bacteria Thermodesulfobacterium sp. strain JSP and Thermodesulfovibrio sp. strain R1Ha3

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

    Sonne-Hansen, J.; Ahring, B.K.; Westermann, P.

    1999-03-01

    Dissimilatory sulfate reduction and methanogenesis are the main terminal processes in the anaerobic food chain. Both the sulfate-reducing bacteria (SRB) and the methane-producing archaea (MPA) use acetate and hydrogen as substrates and, therefore, compete for common electron donors in sulfate-containing natural environments. Due to a higher affinity for the electron donors acetate and hydrogen, SRB outcompete MPA for these compounds whenever sulfate is present in sufficient concentrations. Half-saturation constants (K{sub m}), maximum uptake rates (V{sub max}), and threshold concentrations for sulfate and hydrogen were determined for two thermophilic sulfate-reducing bacteria (SRB) in an incubation system without headspace. K{sub m} valuesmore » determined for the thermophilic SRB were similar to the constants described for mesophilic SRB isolated from environments with low sulfate concentrations.« less

  16. 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

  17. Acceptor Ionization Energies in GaN*

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Ban Chen, An

    2001-03-01

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

  18. Desulfonatronum paiuteum sp. nov.: A New Alkaliphilic, Sulfate-Reducing Bacterium, Isolated from Soda Mono Lake, California

    NASA Technical Reports Server (NTRS)

    Pikuta, Elena; Hoover, Richard B.; Marsic, Damien; Whitman, William; Cleland, David; Krader, Paul; Six, N. Frank (Technical Monitor)

    2002-01-01

    A novel alkaliphilic, sulfate reducing bacterium strain MLF1(sup T) was isolated from sediments of soda Mono Lake, California. Gram-negative vibrion cells, motile by singular polar flagellum, with sizes 0.5 - 0.6x 1.2 - 2.0 micron occurred singly, in pairs or short spirilla. Growth was observed over the temperature range of +15 C to +48 C (optimum +37 C), NaCl concentration range is greater than 1 - 7 %, wt/vol (optimum 3 %, wt/vol) and pH range 7.8 - 10.5 (optimum pH 9.0 - 9.4). The novel isolate is strictly alkaliphilic, requires high carbonate concentration in medium, obligately anaerobic and catalase negative. As electron donors strain MLF1(sup T) uses hydrogen, formate, ethanol. Sulfate, sulfite, and thiosulfate (but not sulfur or nitrate) can be used as electron acceptors. The sole end product of growth on formate was H2S. Strain MLF1(sup T) is resistant to kanamycin and gentamycin, but sensitive to chloramphenicol and tetracycline. Na2MoO4 inhibits growth of strain MLF1(sup T). The sum of G+C in DNA is 63.1 mol% (by HPLC method). On the basis of physiological and molecular properties, the isolate was considered as novel species of genus Desulfonatronum; and the name Desulfonatronum paiuteum sp. nov., is proposed (type strain MLF1(sup T) = ATCC BAA-395(sup T) = DSMZ 14708(sup T).

  19. 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

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

    NASA Astrophysics Data System (ADS)

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

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

  1. Electronic structure and properties of unsubstituted rhodamine in different electron states

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

    Artyukhov, V.Ya.

    1988-04-01

    An analysis is given of the electron density distribution, dipole moment variation, and proton acceptor properties of unsubstituted rhodamine molecules in different electron states. It is shown that the electron density redistribution between the pyronine and benzoin parts of rhodamine may be large and strongly affect the molecular properties. In one of the electron transitions (S/sub 4/) producing the third absorption band the proton acceptor power markedly increases, giving rise to a protonated form under suitable conditions.

  2. Electronic structure and properties of unsubstituted rhodamine in different electron states

    NASA Astrophysics Data System (ADS)

    Artyukhov, V. Ya.

    1987-10-01

    An analysis is given of the electron density distribution, dipole moment variation, and proton acceptor properties of unsubstituted rhodamine molecules in different electron states. It is shown that the electron density redistribution between the pyronine and benzoin parts of rhodamine may be large and strongly affect the molecular properties. In one of the electron transitions (S4) producing the third absorption band the proton acceptor power markedly increases, giving rise to a protonated form under suitable conditions.

  3. Reverse Methanogenesis and Respiration in Methanotrophic Archaea

    PubMed Central

    Koehorst, Jasper J.; Jetten, Mike S. M.; Stams, Alfons J. M.

    2017-01-01

    Anaerobic oxidation of methane (AOM) is catalyzed by anaerobic methane-oxidizing archaea (ANME) via a reverse and modified methanogenesis pathway. Methanogens can also reverse the methanogenesis pathway to oxidize methane, but only during net methane production (i.e., “trace methane oxidation”). In turn, ANME can produce methane, but only during net methane oxidation (i.e., enzymatic back flux). Net AOM is exergonic when coupled to an external electron acceptor such as sulfate (ANME-1, ANME-2abc, and ANME-3), nitrate (ANME-2d), or metal (oxides). In this review, the reversibility of the methanogenesis pathway and essential differences between ANME and methanogens are described by combining published information with domain based (meta)genome comparison of archaeal methanotrophs and selected archaea. These differences include abundances and special structure of methyl coenzyme M reductase and of multiheme cytochromes and the presence of menaquinones or methanophenazines. ANME-2a and ANME-2d can use electron acceptors other than sulfate or nitrate for AOM, respectively. Environmental studies suggest that ANME-2d are also involved in sulfate-dependent AOM. ANME-1 seem to use a different mechanism for disposal of electrons and possibly are less versatile in electron acceptors use than ANME-2. Future research will shed light on the molecular basis of reversal of the methanogenic pathway and electron transfer in different ANME types. PMID:28154498

  4. Anaerobic hydrocarbon and fatty acid metabolism by syntrophic bacteria and their impact on carbon steel corrosion.

    PubMed

    Lyles, Christopher N; Le, Huynh M; Beasley, William Howard; McInerney, Michael J; Suflita, Joseph M

    2014-01-01

    The microbial metabolism of hydrocarbons is increasingly associated with the corrosion of carbon steel in sulfate-rich marine waters. However, how such transformations influence metal biocorrosion in the absence of an electron acceptor is not fully recognized. We grew a marine alkane-utilizing, sulfate-reducing bacterium, Desulfoglaeba alkanexedens, with either sulfate or Methanospirillum hungatei as electron acceptors, and tested the ability of the cultures to catalyze metal corrosion. Axenically, D. alkanexedens had a higher instantaneous corrosion rate and produced more pits in carbon steel coupons than when the same organism was grown in syntrophic co-culture with the methanogen. Since anaerobic hydrocarbon biodegradation pathways converge on fatty acid intermediates, the corrosive ability of a known fatty acid-oxidizing syntrophic bacterium, Syntrophus aciditrophicus was compared when grown in pure culture or in co-culture with a H2-utilizing sulfate-reducing bacterium (Desulfovibrio sp., strain G11) or a methanogen (M. hungatei). The instantaneous corrosion rates in the cultures were not substantially different, but the syntrophic, sulfate-reducing co-culture produced more pits in coupons than other combinations of microorganisms. Lactate-grown cultures of strain G11 had higher instantaneous corrosion rates and coupon pitting compared to the same organism cultured with hydrogen as an electron donor. Thus, if sulfate is available as an electron acceptor, the same microbial assemblages produce sulfide and low molecular weight organic acids that exacerbated biocorrosion. Despite these trends, a surprisingly high degree of variation was encountered with the corrosion assessments. Differences in biomass, initial substrate concentration, rates of microbial activity or the degree of end product formation did not account for the variations. We are forced to ascribe such differences to the metallurgical properties of the coupons.

  5. Anaerobic hydrocarbon and fatty acid metabolism by syntrophic bacteria and their impact on carbon steel corrosion

    PubMed Central

    Lyles, Christopher N.; Le, Huynh M.; Beasley, William Howard; McInerney, Michael J.; Suflita, Joseph M.

    2014-01-01

    The microbial metabolism of hydrocarbons is increasingly associated with the corrosion of carbon steel in sulfate-rich marine waters. However, how such transformations influence metal biocorrosion in the absence of an electron acceptor is not fully recognized. We grew a marine alkane-utilizing, sulfate-reducing bacterium, Desulfoglaeba alkanexedens, with either sulfate or Methanospirillum hungatei as electron acceptors, and tested the ability of the cultures to catalyze metal corrosion. Axenically, D. alkanexedens had a higher instantaneous corrosion rate and produced more pits in carbon steel coupons than when the same organism was grown in syntrophic co-culture with the methanogen. Since anaerobic hydrocarbon biodegradation pathways converge on fatty acid intermediates, the corrosive ability of a known fatty acid-oxidizing syntrophic bacterium, Syntrophus aciditrophicus was compared when grown in pure culture or in co-culture with a H2-utilizing sulfate-reducing bacterium (Desulfovibrio sp., strain G11) or a methanogen (M. hungatei). The instantaneous corrosion rates in the cultures were not substantially different, but the syntrophic, sulfate-reducing co-culture produced more pits in coupons than other combinations of microorganisms. Lactate-grown cultures of strain G11 had higher instantaneous corrosion rates and coupon pitting compared to the same organism cultured with hydrogen as an electron donor. Thus, if sulfate is available as an electron acceptor, the same microbial assemblages produce sulfide and low molecular weight organic acids that exacerbated biocorrosion. Despite these trends, a surprisingly high degree of variation was encountered with the corrosion assessments. Differences in biomass, initial substrate concentration, rates of microbial activity or the degree of end product formation did not account for the variations. We are forced to ascribe such differences to the metallurgical properties of the coupons. PMID:24744752

  6. Desulfomusa hansenii gen. nov., sp. nov., a novel marine propionate-degrading, sulfate-reducing bacterium isolated from Zostera marina roots.

    PubMed

    Finster, K; Thomsen, T R; Ramsing, N B

    2001-11-01

    The physiology and phylogeny of a novel sulfate-reducing bacterium, isolated from surface-sterilized roots of the marine macrophyte Zostera marina, are presented. The strain, designated P1T, was enriched and isolated in defined oxygen-free, bicarbonate-buffered, iron-reduced seawater medium with propionate as sole carbon source and electron donor and sulfate as electron acceptor. Strain P1T had a rod-shaped, slightly curved cell morphology and was motile by means of a single polar flagellum. Cells generally aggregated in clumps throughout the growth phase. High CaCl2 (10 mM) and MgCl2 (50 mM) concentrations were required for optimum growth. In addition to propionate, strain P1T utilized fumarate, succinate, pyruvate, ethanol, butanol and alanine. Oxidation of propionate was incomplete and acetate was formed in stoichiometric amounts. Strain P1T thus resembles members of the sulfate-reducing genera Desulfobulbus and Desulforhopalus, which both oxidize propionate incompletely and form acetate in addition to CO2. However, sequence analysis of the small-subunit rDNA and the dissimilatory sulfite reductase gene revealed that strain P1T was unrelated to the incomplete oxidizers Desulfobulbus and Desulforhopalus and that it constitutes a novel lineage affiliated with the genera Desulfococcus, Desulfosarcina, Desulfonema and 'Desulfobotulus'. Members of this branch, with the exception of 'Desulfobotulus sapovorans', oxidize a variety of substrates completely to CO2. Strain P1T (= DSM 12642T = ATCC 700811T) is therefore proposed as Desulfomusa hansenii gen. nov., sp. nov. Strain p1T thus illustrates the difficulty of extrapolating rRNA similarities to physiology and/or ecological function.

  7. Sulfur speciation and stable isotope trends of water-soluble sulfates in mine tailings profiles.

    PubMed

    Dold, Bernhard; Spangenberg, Jorge E

    2005-08-01

    ) with a delta34S approximately -0.7 per thousand as the most probable sulfate source. The gradual decrease of delta18O(SO4) values from the surface to the oxidation front in the tailings impoundments at Piuquenes (from -4.5 per thousand to -8.6 per thousand Vienna Standard Mean Ocean Water, V-SMOW) and at Cauquenes (from -1.3 per thousand to -3.5 per thousand) indicates the increasing importance of ferric iron as the main electron acceptor in the oxidation of pyrite. The different delta18O(SO4) values between the tailings impoundments studied here reflect the local climates.

  8. Desulfovibrio oceani subsp. oceani sp. nov., subsp. nov. and Desulfovibrio oceani subsp. galateae subsp. nov., novel sulfate-reducing bacteria isolated from the oxygen minimum zone off the coast of Peru.

    PubMed

    Finster, Kai W; Kjeldsen, Kasper U

    2010-03-01

    Two deltaproteobacterial sulfate reducers, designated strain I.8.1(T) and I.9.1(T), were isolated from the oxygen minimum zone water column off the coast of Peru at 400 and 500 m water depth. The strains were Gram-negative, vibrio-shaped and motile. Both strains were psychrotolerant, grew optimally at 20 degrees C at pH 7.0-8.0 and at 2.5-3.5% NaCl (w/v). The strains grew by utilizing hydrogen/acetate, C(3-4) fatty acids, amino acids and glycerol as electron acceptors for sulfate reduction. Fumarate, lactate and pyruvate supported fermentative growth. Sulfate, sulfite, thiosulfate and taurin supported growth as electron acceptors. Both strains were catalase-positive and highly oxygen-tolerant, surviving 24 days of exposure to atmospheric concentrations. MK6 was the only respiratory quinone. The most prominent cellular fatty acid was iso-17:1-omega9c (18%) for strain I.8.1(T) and iso-17:0-omega9c (14%) for strain I.9.1(T). The G+C contents of their genomic DNA were 45-46 mol%. Phylogenetic analysis of 16S rRNA and dsrAB gene sequences showed that both strains belong to the genus Desulfovibrio. Desulfovibrio acrylicus DSM 10141(T) and Desulfovibrio marinisediminis JCM 14577(T) represented their closest validly described relatives with pairwise 16S rRNA gene sequence identities of 98-99%. The level of DNA-DNA hybridization between strains I.8.1(T) and I.9.1(T) was 30-38%. The two strains shared 10-26% DNA-DNA relatedness with D. acrylicus. Based on a polyphasic investigation it is proposed that strains I.8.1(T) and I.9.1(T) represent a novel species for which the name Desulfovibrio oceani sp. nov. is proposed with the two subspecies D. oceani subsp. oceani (type strain, I.8.1(T) = DSM 21390(T) = JCM 15970(T)) and D. oceani subsp. galateae (type strain, I.9.1(T) = DSM 21391(T) = JCM 15971(T)).

  9. Distinguishing between Dexter and rapid sequential electron transfer in covalently linked donor-acceptor assemblies.

    PubMed

    Soler, Monica; McCusker, James K

    2008-04-09

    with the lack of enhanced emission at temperatures below the glass-to-fluid transition of the solvent and the absence of visible absorption features associated with the Mn(II)2 core allows for a definitive assignment of Dexter transfer as the dominant excited-state reaction pathway. A similar conclusion was reached for complex 3 based in part on the smaller driving force for electron transfer (DeltaG0(ET) = -0.1 eV), the increase in probability of Dexter transfer due to the closer proximity of the donor excited state to the dimanganese acceptor, and a lack of emission from the compound upon formation of an optical glass at 80 K. Electronic coupling constants for Dexter transfer were determined to be approximately 10 cm(-1) and approximately 0.15 cm(-1) in complexes 3 and 4, respectively, indicating that the change in spatial localization of the excited state from the bridge (complex 3) to the periphery of the chromophore (complex 4) results in a decrease in electronic coupling to the dimanganese core of nearly 2 orders of magnitude. In addition to providing insight into the influence of donor/acceptor proximity on exchange energy transfer, this study underscores the utility of variable-temperature measurements in cases where Dexter and electron-transfer mechanisms can lead to indistinguishable spectroscopic observables.

  10. Chemical Fucosylation of a Polysaccharide: A Semisynthetic Access to Fucosylated Chondroitin Sulfate.

    PubMed

    Laezza, Antonio; Iadonisi, Alfonso; Castro, Cristina De; De Rosa, Mario; Schiraldi, Chiara; Parrilli, Michelangelo; Bedini, Emiliano

    2015-07-13

    Chemical O-glycosylation of polysaccharides is an almost unexplored reaction. This is mainly due to the difficulties in derivatizing such complex biomacromolecules in a quantitative manner and with a fine control of the obtained structural parameters. In this work, chondroitin raw material from a microbial source was chemo- and regioselectively protected to give two polysaccharide intermediates, that acted in turn as glycosyl acceptors in fucosylation reactions. Further manipulations on the fucosylated polysaccharides, including multiple de-O-benzylation and sulfation, furnished for the first time nonanimal sourced fucosylated chondroitin sulfates (fCSs)-polysaccharides obtained so far exclusively from sea cucumbers (Echinoidea, Holothuroidea) and showing several very interesting biological activities. A semisynthetic fCS was characterized from a structural point of view by means of 2D-NMR techniques, and preliminarily assayed in an anticoagulant test.

  11. Detection and characterization of a dehalogenating microorganism by terminal restriction fragment length polymorphism fingerprinting of 16S rRNA in a sulfidogenic, 2-bromophenol-utilizing enrichment.

    PubMed

    Fennell, Donna E; Rhee, Sung-Keun; Ahn, Young-Beom; Häggblom, Max M; Kerkhof, Lee J

    2004-02-01

    Terminal restriction fragment length polymorphism analysis of reverse-transcribed 16S rRNA during periods of community flux was used as a tool to delineate the roles of the members of a 2-bromophenol-degrading, sulfate-reducing consortium. Starved, washed cultures were amended with 2-bromophenol plus sulfate, 2-bromophenol plus hydrogen, phenol plus sulfate, or phenol with no electron acceptor and were monitored for substrate use. In the presence of sulfate, 2-bromophenol and phenol were completely degraded. In the absence of sulfate, 2-bromophenol was dehalogenated and phenol accumulated. Direct terminal restriction fragment length polymorphism fingerprinting of the 16S rRNA in the various subcultures indicated that phylotype 2BP-48 (a Desulfovibrio-like sequence) was responsible for the dehalogenation of 2-bromophenol. A stable coculture was established which contained predominantly 2BP-48 and a second Desulfovibrio-like bacterium (designated BP212 based on terminal restriction fragment length polymorphism fingerprinting) that was capable of dehalogenating 2-bromophenol to phenol. Strain 2BP-48 in the coculture could couple reductive dehalogenation to growth with 2-bromophenol, 2,6-dibromophenol, or 2-iodophenol and lactate or formate as the electron donor. In addition to halophenols, strain 2BP-48 appears to use sulfate, sulfite, and thiosulfate as electron acceptors and is capable of simultaneous sulfidogenesis and reductive dehalogenation in the presence of sulfate.

  12. Detection and Characterization of a Dehalogenating Microorganism by Terminal Restriction Fragment Length Polymorphism Fingerprinting of 16S rRNA in a Sulfidogenic, 2-Bromophenol-Utilizing Enrichment

    PubMed Central

    Fennell, Donna E.; Rhee, Sung-Keun; Ahn, Young-Beom; Häggblom, Max M.; Kerkhof, Lee J.

    2004-01-01

    Terminal restriction fragment length polymorphism analysis of reverse-transcribed 16S rRNA during periods of community flux was used as a tool to delineate the roles of the members of a 2-bromophenol-degrading, sulfate-reducing consortium. Starved, washed cultures were amended with 2-bromophenol plus sulfate, 2-bromophenol plus hydrogen, phenol plus sulfate, or phenol with no electron acceptor and were monitored for substrate use. In the presence of sulfate, 2-bromophenol and phenol were completely degraded. In the absence of sulfate, 2-bromophenol was dehalogenated and phenol accumulated. Direct terminal restriction fragment length polymorphism fingerprinting of the 16S rRNA in the various subcultures indicated that phylotype 2BP-48 (a Desulfovibrio-like sequence) was responsible for the dehalogenation of 2-bromophenol. A stable coculture was established which contained predominantly 2BP-48 and a second Desulfovibrio-like bacterium (designated BP212 based on terminal restriction fragment length polymorphism fingerprinting) that was capable of dehalogenating 2-bromophenol to phenol. Strain 2BP-48 in the coculture could couple reductive dehalogenation to growth with 2-bromophenol, 2,6-dibromophenol, or 2-iodophenol and lactate or formate as the electron donor. In addition to halophenols, strain 2BP-48 appears to use sulfate, sulfite, and thiosulfate as electron acceptors and is capable of simultaneous sulfidogenesis and reductive dehalogenation in the presence of sulfate. PMID:14766602

  13. Reduction of electron accumulation at InN(0001) surfaces via saturation of surface states by potassium and oxygen as donor- or acceptor-type adsorbates

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

    Eisenhardt, A.; Reiß, S.; Krischok, S., E-mail: stefan.krischok@tu-ilmenau.de

    2014-01-28

    The influence of selected donor- and acceptor-type adsorbates on the electronic properties of InN(0001) surfaces is investigated implementing in-situ photoelectron spectroscopy. The changes in work function, surface band alignment, and chemical bond configurations are characterized during deposition of potassium and exposure to oxygen. Although an expected opponent charge transfer characteristic is observed with potassium donating its free electron to InN, while dissociated oxygen species extract partial charge from the substrate, a reduction of the surface electron accumulation occurs in both cases. This observation can be explained by adsorbate-induced saturation of free dangling bonds at the InN resulting in the disappearancemore » of surface states, which initially pin the Fermi level and induce downward band bending.« less

  14. NOx in the Atmosphere of Early Earth as Electron Acceptors for Life

    NASA Astrophysics Data System (ADS)

    Wong, M. L.; Charnay, B.; Gao, P.; Yung, Y. L.; Russell, M. J.

    2015-12-01

    We quantify the amount of NOx produced in the Hadean atmosphere and available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO3-) and nitrite (NO2-) are the most attractive high-potential electron acceptors for driving the highly endergonic reactions at the entry points to autotrophic metabolic pathways at submarine alkaline hydrothermal vents (Ducluzeau, 2008; Russell, 2014). The Hadean atmosphere, dominated by CO2 and N2, will produce nitric oxide (NO) when shocked by lightning and impacts (Ducluzeau, 2008; Nna Mvondo, 2001). Photochemical reactions involving NO and H2O vapor will then produce acids such as HNO3 and HNO2 that rain into the ocean and dissociate into NO3- and NO2-. Previous work suggests that 1018 g of NOx can be produced in a million years or so, satisfying the need for micromolar concentrations of NO3- and NO2- in the ocean (Ducluzeau, 2008). But because this number is controversial, we present new calculations based on a novel combination of early-Earth GCM and photochemical modeling, calculating the sources and sinks for fixed nitrogen. Finally, it is notable that lightning has been detected on Venus and Mars along with evidence of atmospheric NO; in the distant past, could NOx have been created and available for the emergence of life on numerous wet, rocky worlds?

  15. A mathematical model for the interactive behavior of sulfate-reducing bacteria and methanogens during anaerobic digestion.

    PubMed

    Ahammad, S Ziauddin; Gomes, James; Sreekrishnan, T R

    2011-09-01

    Anaerobic degradation of waste involves different classes of microorganisms, and there are different types of interactions among them for substrates, terminal electron acceptors, and so on. A mathematical model is developed based on the mass balance of different substrates, products, and microbes present in the system to study the interaction between methanogens and sulfate-reducing bacteria (SRB). The performance of major microbial consortia present in the system, such as propionate-utilizing acetogens, butyrate-utilizing acetogens, acetoclastic methanogens, hydrogen-utilizing methanogens, and SRB were considered and analyzed in the model. Different substrates consumed and products formed during the process also were considered in the model. The experimental observations and model predictions showed very good prediction capabilities of the model. Model prediction was validated statistically. It was observed that the model-predicted values matched the experimental data very closely, with an average error of 3.9%.

  16. Characterization of the specificities of human blood group H gene-specified alpha 1,2-L-fucosyltransferase toward sulfated/sialylated/fucosylated acceptors: evidence for an inverse relationship between alpha 1,2-L-fucosylation of Gal and alpha 1,6-L-fucosylation of asparagine-linked GlcNAc.

    PubMed

    Chandrasekaran, E V; Jain, R K; Larsen, R D; Wlasichuk, K; Matta, K L

    1996-07-09

    The assembly of complex structures bearing the H determinant was examined by characterizing the specificities of a cloned blood group H gene-specified alpha 1,2-L-fucosyltransferase (FT) toward a variety of sulfated, sialylated, or fucosylated Gal beta 1,3/4GlcNAc beta- or Gal beta 1,3GalNAc alpha-based acceptor structures. (a) As compared to the basic type 2, Gal beta 1,4GlcNAc beta-(K(m) = 1.67 mM), the basic type 1 was 137% active (K(m) = 0.83 mM). (b) On C-6 sulfation of Gal, type 1 became 142.1% active and type 2 became 223.0% active (K(m) = 0.45 mM). (c) On C-6 sulfation of GlcNAc, type 2 showed 33.7% activity. (d) On C-3 or C-4 fucosylation of GlcNAc, both types 1 and 2 lost activity. (e) Type 1 showed 70.8% and 5.8% activity, respectively, on C-6 and C-4 O-methylation of GlcNAc. (f) Type 1 retained 18.8% activity on alpha 2,6-sialylation of GlcNAc. (g) Terminal type 1 or 2 of extended chain had lower activity. (h) With Gal in place of GlcNAc in type 1, the activity became 43.2%. (i) Compounds with terminal alpha 1,3-linked Gal were inactive. (j) Gal beta 1,3GalNAc alpha- (the T-hapten) was approximately 0.4-fold as active as Gal beta 1,4GlcNAc beta-. (k) C-6 sulfation of Gal on the T-hapten did not affect the acceptor activity. (l) C-6 sulfation of GalNAc decreased the activity to 70%, whereas on C-6 sulfation of both Gal and GalNAc the T-hapten lost the acceptor ability. (m) C-6 sialylation of GalNAc also led to inactivity. (n) beta 1,6 branching from GalNAc of the T-hapten by a GlcNAc residue or by units such as Gal beta 1, 4GlcNAc-, Gal beta 1,4(Fuc alpha 1,3)GlcNAc-, or 3-sulfoGal beta 1,4GlcNAc- resulted in 111.9%, 282.8%, 48.3%, and 75.3% activities, respectively. (o) The enhancement of enzyme affinity by a sulfo group on C-6 of Gal was demonstrated by an increase (approximately 5-fold) in the K(m) for Gal beta 1,4GlcNAc beta 1,6(Gal beta 1,3)GalNAc alpha-O-Bn in presence of 6-sulfoGal beta 1,- 4GlcNAc beta-O-Me (3.0 mM). (p) Among the two sites in

  17. Electronic structure and normal vibrations of the 1-ethyl-3-methylimidazolium ethyl sulfate ion pair.

    PubMed

    Dhumal, Nilesh R; Kim, Hyung J; Kiefer, Johannes

    2011-04-21

    Electronic and structural properties of the ion pair 1-ethyl-3-methylimidazolium ethyl sulfate are studied using density functional methods. Three locally stable conformers of the ion pair complex are considered to analyze molecular interactions between its cation and anion. Manifestations of these interactions in the vibrational spectra are discussed and compared with experimental IR and Raman spectroscopy data. NBO analysis and difference electron density coupled with molecular electron density topography are used to interpret the frequency shifts of the normal vibrations of the ion pair, compared to the free anion and cation. Excitation energies of low-lying singlet excited states of the conformers are also studied. The density functional theory results are found to be in a reasonable agreement with experimental UV/vis absorption spectra.

  18. 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.

  19. Thermodesulfobacterium hveragerdense sp. nov., and Thermodesulfovibrio islandicus sp. nov., two thermophilic sulfate reducing bacteria isolated from a Icelandic hot spring.

    PubMed

    Sonne-Hansen, J; Ahring, B K

    1999-12-01

    Two thermophilic non-sporeforming sulfate-reducing bacteria (SRB) were isolated from microbial mats collected from an Icelandic hot spring. Strain JSP was a gram negative rod, with an average cell size of 2.8 x 0.5 microm. No flagella were found. Growth occurred between 55 and 74 degrees C with an optimum between 70 and 74 degrees C at pH 7.0. The G+C content was 40 mol%. Strain R1Ha3 was a gram negative vibrio-shaped rod with an average cell size of 1.7 x 0.4 microm. Motility was observed mediated by one polar flagellum. The growth optimum at pH 7.0 was 65 degrees C, and growth occurred between 45 and 70 degrees C. The G+C content was 38 mol%. In the presence of sulfate, both strains used lactate, pyruvate and H2 as electron donors. In addition, strain R1Ha3 used formate. Pyruvate was the only substrate supporting fermentative growth of both strains. Growth occurred with sulfate as well as thiosulfate as electron acceptors. Furthermore, strain R1Ha3 reduced nitrate and strain JSP reduced sulfite. Neither of the strains were able to oxidize lactate completely to CO2 and neither of the strains contained desulfoviridin. 16S rDNA sequencing placed strain JSP in the genus Thermodesulfobacterium and strain R1Ha3 in the genus Thermodesulfovibrio. Based on the DNA-DNA hybridization studies and differences in morphology and physiology to their closest relatives the two new isolates were considered as new species. Strain JSP is named Thermodesulfobacterium hveragerdense and strain R1Ha3 Thermodesulfovibrio islandicus.

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  1. Removing organic matter from sulfate-rich wastewater via sulfidogenic and methanogenic pathways.

    PubMed

    Vilela, Rogerio Silveira; Damianovic, Márcia Helena Rissato Zamariolli; Foresti, Eugenio

    2014-01-01

    The simultaneous organic matter removal and sulfate reduction in synthetic sulfate-rich wastewater was evaluated for various chemical oxygen demand (COD)/sulfate ratios applied in a horizontal-flow anaerobic immobilized sludge (HAIS) reactor. At higher COD/sulfate ratios (12.5 and 7.5), the removal of organic matter was stable, likely due to methanogenesis. A combination of sulfate reduction and methanogenesis was clearly established at COD/sulfate ratios of 3.0 and 1.9. At a COD/sulfate ratio of 1.0, the organic matter removal was likely influenced by methanogenesis inhibition. The quantity of sulfate removed at a COD/sulfate ratio of 1.0 was identical to that obtained at a ratio of 1.9, indicating a lack of available electron donors for sulfidogenesis. The sulfate reduction and organic matter removal were not maximized at the same COD/sulfate ratio; therefore, competitive inhibition must be the predominant mechanism in establishing an electron flow.

  2. Isolation of sulfate-reducing bacteria from the terrestrial deep subsurface and description of Desulfovibrio cavernae sp. nov.

    PubMed

    Sass, Henrik; Cypionka, Heribert

    2004-09-01

    Deep subsurface sandstones in the area of Berlin (Germany) located 600 to 1060 m below the surface were examined for the presence of viable microorganisms. The in situ temperatures at the sampling sites ranged from 37 to 45 degrees C. Investigations focussed on sulfate-reducing bacteria able to grow on methanol and triethylene glycol, which are added as chemicals to facilitate the long-term underground storage of natural gas. Seven strains were isolated from porewater brines in the porous sandstone. Three of them were obtained with methanol (strains H1M, H3M, and B1M), three strains with triethylene glycol (strains H1T, B1T, and B2T) and one strain with a mixture of lactate, acetate and butyrate (strain H1-13). Due to phenotypic properties six isolates could be identified as members of the genus Desulfovibrio, and strain B2T as a Desulfotomaculum. The salt tolerance and temperature range for growth indicated that the isolates originated from the indigenous deep subsurface sandstones. They grew in mineral media reflecting the in situ ionic composition of the different brines, which contained 1.5 to 190 g NaCl x l(-1) and high calcium and magnesium concentrations. The Desulfovibrio strains grew at temperatures between 20 and 50 degrees C, while the Desulfotomaculum strain was thermophilic and grew between 30 and 65 degrees C. The strains utilized a broad spectrum of electron donors and acceptors. They grew with carbon compounds like lactate, pyruvate, formate, n-alcohols (C1-C5), glycerol, ethylene glycol, malate, succinate, and fumarate. Some strains even utilized glucose as electron donor and carbon source. All strains were able to use sulfate, sulfite and nitrate as electron acceptors. Additionally, three Desulfovibrio strains reduced manganese oxide, the Desulfotomaculum strain reduced manganese oxide, iron oxide, and elemental sulfur. The 16S rRNA analysis revealed that the isolates belong to three different species. The strains H1T, H3M and B1M could be

  3. Possibility to Use Hydrothermally Synthesized CuFeS2 Nanocomposite as an Acceptor in Hybrid Solar Cell

    NASA Astrophysics Data System (ADS)

    Sil, Sayantan; Dey, Arka; Halder, Soumi; Datta, Joydeep; Ray, Partha Pratim

    2018-01-01

    Here we have approached the plausible use of CuFeS2 nanocomposite as an acceptor in organic-inorganic hybrid solar cell. To produce CuFeS2 nanocomposite, hydrothermal strategy was employed. The room-temperature XRD pattern approves the synthesized material as CuFeS2 with no phase impurity (JCPDS Card no: 37-0471). The elemental composition of the material was analyzed from the TEM-EDX data. The obtained selected area electron diffraction (SAED) planes harmonized with the XRD pattern of the synthesized product. Optical band gap (4.14 eV) of the composite from UV-Vis analysis depicts that the synthesized material is belonging to wide band gap semiconductor family. The HOMO (- 6.97 eV) and LUMO (- 2.93 eV) positions from electrochemical study reveal that there is a possibility of electron transfer from MEH-PPV to CuFeS2. The optical absorption and photoluminescence spectra of MEH-PPV:CuFeS2 (donor:acceptor) composite were recorded sequentially by varying weight ratios. The monotonic blue shifting of the absorption peak position indicated the interaction between donor and acceptor materials. The possibility of electron transfer from donor (MEH-PPV) to acceptor (CuFeS2) was approved with photoluminescence analysis. Subsequently, we have fabricated a hybrid solar cell by incorporating CuFeS2 nanocomposite with MEH-PPV in open atmosphere and obtained 0.3% power conversion efficiency.

  4. Shewanella oneidensis MR-1 chemotaxis proteins and electron-transport chain components essential for congregation near insoluble electron acceptors.

    PubMed

    Harris, H Wayne; El-Naggar, Mohamed Y; Nealson, Kenneth H

    2012-12-01

    Shewanella oneidensis MR-1 cells utilize a behaviour response called electrokinesis to increase their speed in the vicinity of IEAs (insoluble electron acceptors), including manganese oxides, iron oxides and poised electrodes [Harris, El-Naggar, Bretschger, Ward, Romine, Obraztsova and Nealson (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 326-331]. However, it is not currently understood how bacteria remain in the vicinity of the IEA and accumulate both on the surface and in the surrounding medium. In the present paper, we provide results indicating that cells that have contacted the IEAs swim faster than those that have not recently made contact. In addition, fast-swimming cells exhibit an enhancement of swimming reversals leading to rapid non-random accumulation of cells on, and adjacent to, mineral particles. We call the observed accumulation near IEAs 'congregation'. Congregation is eliminated by the loss of a critical gene involved with EET (extracellular electron transport) (cymA, SO_4591) and is altered or eliminated in several deletion mutants of homologues of genes that are involved with chemotaxis or energy taxis in Escherichia coli. These genes include chemotactic signal transduction protein (cheA-3, SO_3207), methyl-accepting chemotaxis proteins with the Cache domain (mcp_cache, SO_2240) or the PAS (Per/Arnt/Sim) domain (mcp_pas, SO_1385). In the present paper, we report studies of S. oneidensis MR-1 that lend some insight into how microbes in this group can 'sense' the presence of a solid substrate such as a mineral surface, and maintain themselves in the vicinity of the mineral (i.e. via congregation), which may ultimately lead to attachment and biofilm formation.

  5. Donor-π-Acceptor Polymer with Alternating Triarylborane and Triphenylamine Moieties.

    PubMed

    Li, Haiyan; Jäkle, Frieder

    2010-05-12

    A luminescent main chain donor-π-acceptor-type polymer (4) was prepared via organometallic polycondensation reaction followed by post modification. With both electron-rich amine and electron-deficient borane moieties embedded in the main chain, 4 exhibits an interesting ambipolar character: it can be reduced and oxidized electrochemically at moderate potentials and shows a strong solvatochromic effect in the emission spectra. Complexation studies show that 4 selectively binds to fluoride and cyanide; quantitative titration with cyanide reveals a two-step binding process. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Identification of the dominant sulfate-reducing bacterial partner of anaerobic methanotrophs of the ANME-2 clade.

    PubMed

    Schreiber, Lars; Holler, Thomas; Knittel, Katrin; Meyerdierks, Anke; Amann, Rudolf

    2010-08-01

    The anaerobic oxidation of methane (AOM) with sulfate as terminal electron acceptor is mediated by consortia of methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). Whereas three clades of ANME have been repeatedly studied with respect to phylogeny, key genes and genomic capabilities, little is known about their sulfate-reducing partner. In order to identify the partner of anaerobic methanotrophs of the ANME-2 clade, bacterial 16S rRNA gene libraries were constructed from cultures highly enriched for ANME-2a and ANME-2c in consortia with Deltaproteobacteria of the Desulfosarcina/Desulfococcus group (DSS). Phylogenetic analysis of those and publicly available sequences from AOM sites supported the hypothesis by Knittel and colleagues that the DSS partner belongs to the diverse SEEP-SRB1 cluster. Six subclusters of SEEP-SRB1, SEEP-SRB1a to SEEP-SRB1f, were proposed and specific oligonucleotide probes were designed. Using fluorescence in situ hybridization on samples from six different AOM sites, SEEP-SRB1a was identified as sulfate-reducing partner in up to 95% of total ANME-2 consortia. SEEP-SRB1a cells exhibited a rod-shaped, vibrioid, or coccoid morphology and were found to be associated with subgroups ANME-2a and ANME-2c. Moreover, SEEP-SRB1a was also detected in 8% to 23% of ANME-3 consortia in Haakon Mosby Mud Volcano sediments, previously described to be predominantly associated with SRB of the Desulfobulbus group. SEEP-SRB1a contributed to only 0.3% to 0.7% of all single cells in almost all samples indicating that these bacteria are highly adapted to a symbiotic relationship with ANME-2. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

  7. Mechanism of radiative recombination in acceptor-doped bulk GaN crystals

    NASA Astrophysics Data System (ADS)

    Godlewski, M.; Suski, T.; Grzegory, I.; Porowski, S.; Bergman, J. P.; Chen, W. M.; Monemar, B.

    1999-12-01

    Optical and electrical properties of acceptor-doped bulk GaN crystals are discussed. Though introducing Zn and Ca to bulk GaN does not significantly change electron concentration, it results in the appearance of a blue photoluminescence band accompanying the relatively strong yellow band usually present. Highly resistive GaN : Mg crystals are obtained when high amount of Mg is introduced to the Ga melt during high-pressure synthesis. Change of electrical properties of Mg-doped bulk crystals is accompanied by the appearance of a strong blue emission of GaN similar to that in Ca- and Zn-doped crystals. Optically detected magnetic resonance investigations indicate a multi-band character of this blue emission and suggest possible mechanism of compensation in acceptor-doped bulk GaN.

  8. The role of amino acid electron-donor/acceptor atoms in host-cell binding peptides is associated with their 3D structure and HLA-binding capacity in sterile malarial immunity induction

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

    Patarroyo, Manuel E., E-mail: mepatarr@mail.com; Universidad Nacional de Colombia, Bogota; Almonacid, Hannia

    Highlights: Black-Right-Pointing-Pointer Fundamental residues located in some HABPs are associated with their 3D structure. Black-Right-Pointing-Pointer Electron-donor atoms present in {beta}-turn, random, distorted {alpha}-helix structures. Black-Right-Pointing-Pointer Electron-donor atoms bound to HLA-DR53. Black-Right-Pointing-Pointer Electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. -- Abstract: Plasmodium falciparum malaria continues being one of the parasitic diseases causing the highest worldwide mortality due to the parasite's multiple evasion mechanisms, such as immunological silence. Membrane and organelle proteins are used during invasion for interactions mediated by high binding ability peptides (HABPs); these have amino acids which establish hydrogen bonds between them in some of theirmore » critical binding residues. Immunisation assays in the Aotus model using HABPs whose critical residues had been modified have revealed a conformational change thereby enabling a protection-inducing response. This has improved fitting within HLA-DR{beta}1{sup Asterisk-Operator} molecules where amino acid electron-donor atoms present in {beta}-turn, random or distorted {alpha}-helix structures preferentially bound to HLA-DR53 molecules, whilst HABPs having amino acid electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. This data has great implications for vaccine development.« less

  9. Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property

    NASA Astrophysics Data System (ADS)

    Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

    2015-01-01

    An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1.An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05915h

  10. 5' modification of duplex DNA with a ruthenium electron donor-acceptor pair using solid-phase DNA synthesis

    NASA Technical Reports Server (NTRS)

    Frank, Natia L.; Meade, Thomas J.

    2003-01-01

    Incorporation of metalated nucleosides into DNA through covalent modification is crucial to measurement of thermal electron-transfer rates and the dependence of these rates with structure, distance, and position. Here, we report the first synthesis of an electron donor-acceptor pair of 5' metallonucleosides and their subsequent incorporation into oligonucleotides using solid-phase DNA synthesis techniques. Large-scale syntheses of metal-containing oligonucleotides are achieved using 5' modified phosporamidites containing [Ru(acac)(2)(IMPy)](2+) (acac is acetylacetonato; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (3) and [Ru(bpy)(2)(IMPy)](2+) (bpy is 2,2'-bipyridine; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (4). Duplexes formed with the metal-containing oligonucleotides exhibit thermal stability comparable to the corresponding unmetalated duplexes (T(m) of modified duplex = 49 degrees C vs T(m) of unmodified duplex = 47 degrees C). Electrochemical (3, E(1/2) = -0.04 V vs NHE; 4, E(1/2) = 1.12 V vs NHE), absorption (3, lambda(max) = 568, 369 nm; 4, lambda(max) = 480 nm), and emission (4, lambda(max) = 720 nm, tau = 55 ns, Phi = 1.2 x 10(-)(4)) data for the ruthenium-modified nucleosides and oligonucleotides indicate that incorporation into an oligonucleotide does not perturb the electronic properties of the ruthenium complex or the DNA significantly. In addition, the absence of any change in the emission properties upon metalated duplex formation suggests that the [Ru(bpy)(2)(IMPy)](2+)[Ru(acac)(2)(IMPy)](2+) pair will provide a valuable probe for DNA-mediated electron-transfer studies.

  11. Fullerene-bisadduct acceptors for polymer solar cells.

    PubMed

    Li, Yongfang

    2013-10-01

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

  12. Electron acceptor-based regulation of microbial greenhouse gas production from thawing permafrost

    NASA Astrophysics Data System (ADS)

    Bak, Ebbe; Jones, Eleanor; Yde, Jacob; Hodson, Andy; Mallon, Gunnar; Fisnter, Kai

    2017-04-01

    Permafrost contains about 35% of the global soil organic carbon (0-3 m depth). As a consequence of global warming, the active layer thickness is steadily increasing and its organic carbon is becoming available for degradation, causing a concomitant release of CO2 and CH4. The climate forcing feedbacks of permafrost thaw are determined by the rate of organic carbon degradation and to which degree it is released as CO2 or CH4. Methane is produced under anoxic conditions, but the factors that regulate its production are poorly constrained. In this study, we investigate how CH4 production is influenced by the presence of competing anaerobic processes with focus on the role of iron and sulfate reduction. We have collected permafrost cores to 2.2 meters depth from three different lowland sites in Adventdalen on Svalbard. From these cores, we have prepared anoxic batch incubation for each 25 cm depth interval and followed the production of CO2 and CH4 as well as the iron and sulfate reduction. This approach allows us to monitor the rate of the CO2 and CH4 production as well as to investigate the correlation between CH4 production and competing anaerobic respiration processes in the active layer as well in the permafrost. These investigations are accompanied by characterization of the carbon, iron and sulfate content in the soil and will be followed by characterization of the microbial community structure. The aim of this study is to get a better understanding of how the availability of sulfate and iron and the microbial community structure regulate the production of CO2 and CH4 in thawing permafrost, and to elucidate how the rate of the organic carbon degradation changes with depth in permafrost-affected soils. This study improves our understanding of climate feedback mechanisms operating during permafrost thaw.

  13. 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.

  14. The link between the microbial ecology, gene expression, and biokinetics of denitrifying polyphosphate-accumulating systems under different electron acceptor combinations.

    PubMed

    Vieira, A; Ribera-Guardia, A; Marques, R; Barreto Crespo, M T; Oehmen, A; Carvalho, G

    2018-06-02

    The emission of the greenhouse gas nitrous oxide (N 2 O) can occur during biological nutrient removal. Denitrifying enhanced biological phosphorus removal (d-EBPR) systems are an efficient means of removing phosphate and nitrogen, performed by denitrifying polyphosphate-accumulating organisms (d-PAOs). The aim of this work was to study the effect of various combinations of electron acceptors, nitrate (NO 3 - ), nitrite (NO 2 - ), and N 2 O, on the denitrification pathway of a d-EBPR system. Batch tests were performed with different electron acceptor combinations, to explore the denitrification pathway. Reverse transcriptase-qPCR (RT-qPCR) and high-throughput sequencing, combined with chemical analysis, were used to study gene expression, microbial diversity, and denitrification kinetics. The potential for N 2 O production was greater than the potential for its reduction in most tests. A strong correlation was observed between the N 2 O reduction rate and the relative gene expression of nitrous oxide reductase per nitrite reductase (nosZ/(nirS + nirK)), suggesting that the expression of denitrifying marker genes is a strong predictor of the N 2 O reduction rate. The d-EBPR community maintained a core population with low variations throughout the study. Furthermore, phylogenetic analyses of the studied marker genes revealed that the organisms actively involved in denitrification were closely related to Thauera sp., Candidatus Accumulibacter phosphatis, and Candidatus Competibacter denitrificans. Moreover, Competibacter-related OTUs seem to be important contributors to the N 2 O reduction capacity of the system, likely scavenging the N 2 O produced by other organisms. Overall, this study contributes to a better understanding of the microbial biochemistry and the genetics involving biological denitrification removal, important to minimize N 2 O emissions in wastewater treatment plants.

  15. Two-Electron Transfer Pathways.

    PubMed

    Lin, Jiaxing; Balamurugan, D; Zhang, Peng; Skourtis, Spiros S; Beratan, David N

    2015-06-18

    The frontiers of electron-transfer chemistry demand that we develop theoretical frameworks to describe the delivery of multiple electrons, atoms, and ions in molecular systems. When electrons move over long distances through high barriers, where the probability for thermal population of oxidized or reduced bridge-localized states is very small, the electrons will tunnel from the donor (D) to acceptor (A), facilitated by bridge-mediated superexchange interactions. If the stable donor and acceptor redox states on D and A differ by two electrons, it is possible that the electrons will propagate coherently from D to A. While structure-function relations for single-electron superexchange in molecules are well established, strategies to manipulate the coherent flow of multiple electrons are largely unknown. In contrast to one-electron superexchange, two-electron superexchange involves both one- and two-electron virtual intermediate states, the number of virtual intermediates increases very rapidly with system size, and multiple classes of pathways interfere with one another. In the study described here, we developed simple superexchange models for two-electron transfer. We explored how the bridge structure and energetics influence multielectron superexchange, and we compared two-electron superexchange interactions to single-electron superexchange. Multielectron superexchange introduces interference between singly and doubly oxidized (or reduced) bridge virtual states, so that even simple linear donor-bridge-acceptor systems have pathway topologies that resemble those seen for one-electron superexchange through bridges with multiple parallel pathways. The simple model systems studied here exhibit a richness that is amenable to experimental exploration by manipulating the multiple pathways, pathway crosstalk, and changes in the number of donor and acceptor species. The features that emerge from these studies may assist in developing new strategies to deliver multiple

  16. Acceptor Type Vacancy Complexes In As-Grown ZnO

    NASA Astrophysics Data System (ADS)

    Zubiaga, A.; Tuomisto, F.; Zuñiga-Pérez, J.

    2010-11-01

    One of the many technological areas that ZnO is interesting for is the construction of opto-electronic devices working in the blue-UV range as its large band gap (˜3.4 eV at 10 K) makes them suitable for that purpose. As-grown ZnO shows generally n-type conductivity partially due to the large concentration of unintentional shallow donors, like H, but impurities can also form complexes with acceptor type defects (Zn vacancy) leading to the creation of compensating defects. Recently, LiZn and NaZn acceptors have been measured and H could form similar type of defects. Doppler Broadening Positron Annihilation spectroscopy experimental results on the observation of Zn related vacancy complexes in ZnO thin films, as-grown, O implanted and Al doped will be presented. Results show that as-grown ZnO film show small Zn vacancy related complexed that could be related to presence of H as a unintentional doping element.

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

    NASA Astrophysics Data System (ADS)

    Jang, Seogjoo

    2007-11-01

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

  18. Acceptors in ZnO nanocrystals: A reinterpretation

    NASA Astrophysics Data System (ADS)

    Gehlhoff, W.; Hoffmann, A.

    2012-12-01

    In a recent article, Teklemichael et al. reported on the identification of an uncompensated acceptor in ZnO nanocrystals using infrared spectroscopy and electron paramagnetic resonance (EPR) in the dark and under illumination. Most of their conclusions, interpretations, and suggestions turned out to be erroneous. The observed EPR signals were interpreted to originate from axial and nonaxial VZn-H defects. We show that the given interpretation of the EPR results is based on misinterpretations of EPR spectra arising from defects in nanocrystals. The explanation of the infrared absorption lines is in conflict with recent results of valence band ordering and valence band splitting.

  19. Preparation, spectroscopic and structural studies on charge-transfer complexes of 2,9-dimethyl-1,10-phenanthroline with some electron acceptors

    NASA Astrophysics Data System (ADS)

    Gaballa, Akmal S.; Wagner, Christoph; Teleb, Said M.; Nour, El-Metwally; Elmosallamy, M. A. F.; Kaluđerović, Goran N.; Schmidt, Harry; Steinborn, Dirk

    2008-03-01

    Charge-transfer (CT) complexes formed in the reactions of 2,9-dimethyl-1,10-phenanthroline (Me 2phen) with some acceptors such as chloranil (Chl), picric acid (HPA) and chloranilic acid (H 2CA) have been studied in the defined solvent at room temperature. Based on elemental analysis and infrared spectra of the solid CT-complexes along with the photometric titration curves for the reactions, obtained data indicate the formation of 1:1 charge-transfer complexes [(Me 2phen)(Chl)] ( 1), [(Me 2phenH)(PA)] ( 2) and [(Me 2phenH)(HCA)] ( 3), respectively, was proposed. In the three complexes, infrared and 1H NMR spectroscopic data indicate a charge-transfer interaction and as far as complexes 2 and 3 are concerned this interaction is associated with a hydrogen bonding. The formation constants for the complexes ( KC) were shown to be dependent upon the nature of the electron acceptors used. The X-ray structure of complex 3 indicate the formation of dimeric units [Me 2phenH] 2[(HCA) 2] in which the two anions (HCA) - are connected by two O-H⋯O hydrogen bonds whereas the cations and anions are joined together by strong three-center (bifurcated) N-H⋯O hydrogen bonds. Furthermore, the cations are arranged in a π-π stacking.

  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. Pyrosequencing analysis yields comprehensive assessment of microbial communities in pilot-scale two-stage membrane biofilm reactors.

    PubMed

    Ontiveros-Valencia, Aura; Tang, Youneng; Zhao, He-Ping; Friese, David; Overstreet, Ryan; Smith, Jennifer; Evans, Patrick; Rittmann, Bruce E; Krajmalnik-Brown, Rosa

    2014-07-01

    We studied the microbial community structure of pilot two-stage membrane biofilm reactors (MBfRs) designed to reduce nitrate (NO3(-)) and perchlorate (ClO4(-)) in contaminated groundwater. The groundwater also contained oxygen (O2) and sulfate (SO4(2-)), which became important electron sinks that affected the NO3(-) and ClO4(-) removal rates. Using pyrosequencing, we elucidated how important phylotypes of each "primary" microbial group, i.e., denitrifying bacteria (DB), perchlorate-reducing bacteria (PRB), and sulfate-reducing bacteria (SRB), responded to changes in electron-acceptor loading. UniFrac, principal coordinate analysis (PCoA), and diversity analyses documented that the microbial community of biofilms sampled when the MBfRs had a high acceptor loading were phylogenetically distant from and less diverse than the microbial community of biofilm samples with lower acceptor loadings. Diminished acceptor loading led to SO4(2-) reduction in the lag MBfR, which allowed Desulfovibrionales (an SRB) and Thiothrichales (sulfur-oxidizers) to thrive through S cycling. As a result of this cooperative relationship, they competed effectively with DB/PRB phylotypes such as Xanthomonadales and Rhodobacterales. Thus, pyrosequencing illustrated that while DB, PRB, and SRB responded predictably to changes in acceptor loading, a decrease in total acceptor loading led to important shifts within the "primary" groups, the onset of other members (e.g., Thiothrichales), and overall greater diversity.

  2. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  3. Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT

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

    Baruah, Tunna; Garnica, Amanda; Paggen, Marina

    2016-04-14

    We study the electronic structure of C{sub 60} fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Ourmore » results show that all functionalized fullerenes with an exception of the C{sub 60}-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C{sub 60} fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C{sub 61}-butyric acid methyl ester (PCBM)-P3MT complex.« less

  4. Influence of Bicarbonate, Sulfate, and Electron Donors on Biological reduction of Uranium and Microbial Community Composition

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

    Luo, Wensui; Zhou, Jizhong; Wu, Weimin

    2007-01-01

    A microcosm study was performed to investigate the effect of ethanol and acetate on uranium(VI) biological reduction and microbial community changes under various geochemical conditions. Each microcosm contained an uranium-contaminated sediment (up to 2.8 g U/kg) suspended in buffer with bicarbonate at concentrations of either 1 mM or 40 mM and sulfate at either 1.1 or 3.2 mM. Ethanol or acetate was used as an electron donor. Results indicate that ethanol yielded in significantly higher U(VI) reduction rates than acetate. A low bicarbonate concentration (1 mM) was favored for U(VI) bioreduction to occur in sediments, but high concentrations of bicarbonatemore » (40 mM) and sulfate (3.2 mM) decreased the reduction rates of U(VI). Microbial communities were dominated by species from the Geothrix genus and Proteobacteria phylum in all microcosms. However, species in the Geobacteraceae family capable of reducing U(VI) were significantly enriched by ethanol and acetate in low bicarbonate buffer. Ethanol increased the population of unclassified Desulfuromonales, while acetate increased the population of Desulfovibrio. Additionally, species in the Geobacteraceae family were not enriched in high bicarbonate buffer, but the Geothrix and the unclassified Betaproteobacteria species were enriched. This study concludes that ethanol could be a better electron donor than acetate for reducing U(VI) under given experimental conditions, and electron donor and geoundwater geochemistry alter microbial communities responsible for U(VI) reduction.« less

  5. Recharge processes drive sulfate reduction in an alluvial aquifer contaminated with landfill leachate

    USGS Publications Warehouse

    Scholl, M.A.; Cozzarelli, I.M.; Christenson, S.C.

    2006-01-01

    Natural attenuation of contaminants in groundwater depends on an adequate supply of electron acceptors to stimulate biodegradation. In an alluvial aquifer contaminated with leachate from an unlined municipal landfill, the mechanism of recharge infiltration was investigated as a source of electron acceptors. Water samples were collected monthly at closely spaced intervals in the top 2 m of the saturated zone from a leachate-contaminated well and an uncontaminated well, and analyzed for ??18O, ??2H, non-volatile dissolved organic carbon (NVDOC), SO42-, NO3- and Cl-. Monthly recharge amounts were quantified using the offset of the ??18O or ??2H from the local meteoric water line as a parameter to distinguish water types, as evaporation and methanogenesis caused isotopic enrichment in waters from different sources. Presence of dissolved SO42- in the top 1 to 2??m of the saturated zone was associated with recharge; SO42- averaged 2.2??mM, with maximum concentrations of 15??mM. Nitrate was observed near the water table at the contaminated site at concentrations up to 4.6??mM. Temporal monitoring of ??2H and SO42- showed that vertical transport of recharge carried SO42- to depths up to 1.75??m below the water table, supplying an additional electron acceptor to the predominantly methanogenic leachate plume. Measurements of ??34S in SO42- indicated both SO42- reduction and sulfide oxidation were occurring in the aquifer. Depth-integrated net SO42- reduction rates, calculated using the natural Cl- gradient as a conservative tracer, ranged from 7.5 ?? 10- 3 to 0.61??mM??d- 1 (over various depth intervals from 0.45 to 1.75??m). Sulfate reduction occurred at both the contaminated and uncontaminated sites; however, median SO42- reduction rates were higher at the contaminated site. Although estimated SO42- reduction rates are relatively high, significant decreases in NVDOC were not observed at the contaminated site. Organic compounds more labile than the leachate NVDOC may be

  6. Magnetic field enhanced electroluminescence in organic light emitting diodes based on electron donor-acceptor exciplex blends

    NASA Astrophysics Data System (ADS)

    Baniya, Sangita; Basel, Tek; Sun, Dali; McLaughlin, Ryan; Vardeny, Zeev Valy

    2016-03-01

    A useful process for light harvesting from injected electron-hole pairs in organic light emitting diodes (OLED) is the transfer from triplet excitons (T) to singlet excitons (S) via reverse intersystem crossing (RISC). This process adds a delayed electro-luminescence (EL) emission component that is known as thermally activated delayed fluorescence (TADF). We have studied electron donor (D)/acceptor(A) blends that form an exciplex manifold in which the energy difference, ΔEST between the lowest singlet (S1) and triplet (T1) levels is relatively small (<100 meV), and thus allows RISC at ambient temperature. We found that the EL emission in OLED based on the exciplex blend is enhanced up to 40% by applying a relatively weak magnetic field of 50 mT at ambient. Moreover the MEL response is activated with activation energy similar that of the EL emission. This suggests that the large magneto-EL originates from an additional spin-mixing channel between singlet and triplet states of the generated exciplexes, which is due to TADF. We will report on the MEL dependencies on the temperature, bias voltage, and D-A materials for optimum OLED performance. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

  7. Effects of various pretreatments on biological sulfate reduction with waste activated sludge as electron donor and waste activated sludge diminution under biosulfidogenic condition.

    PubMed

    Sheng, Yuxing; Cao, Hongbin; Li, Yuping; Zhang, Yi

    2010-07-15

    The current study focused on the influences of various pretreatments, including alkaline, ultrasonic and thermal pretreatments on biological sulfate reduction with waste activated sludge (WAS) as sole electron donor. Our results showed that thermal and ultrasonic pretreatments increased the sulfate reduction percentage by 14.8% and 7.1%, respectively, compared with experiment with raw WAS, while alkaline pretreatment decreased the sulfate reduction percentage by 46%. By analyzing the WAS structure, particle size distribution, organic component, and enzyme activity after different pretreatments, we studied the effects of these pretreatments on WAS as well as on the mechanisms of how biological sulfate reduction was affected. The reduction of WAS and variation of WAS structure in the process of sulfate reduction were investigated. Our results showed that biosulfidogenesis was an efficient method of diminishing WAS, and various pretreatments could enhance the reduction efficiency of volatile solid in the WAS. 2010 Elsevier B.V. All rights reserved.

  8. Redox potentials of primary electron acceptor quinone molecule (QA)- and conserved energetics of photosystem II in cyanobacteria with chlorophyll a and chlorophyll d.

    PubMed

    Allakhverdiev, Suleyman I; Tsuchiya, Tohru; Watabe, Kazuyuki; Kojima, Akane; Los, Dmitry A; Tomo, Tatsuya; Klimov, Vyacheslav V; Mimuro, Mamoru

    2011-05-10

    In a previous study, we measured the redox potential of the primary electron acceptor pheophytin (Phe) a of photosystem (PS) II in the chlorophyll d-dominated cyanobacterium Acaryochloris marina and a chlorophyll a-containing cyanobacterium, Synechocystis. We obtained the midpoint redox potential (E(m)) values of -478 mV for A. marina and -536 mV for Synechocystis. In this study, we measured the redox potentials of the primary electron acceptor quinone molecule (Q(A)), i.e., E(m)(Q(A)/Q(A)(-)), of PS II and the energy difference between [P680·Phe a(-)·Q(A)] and [P680·Phe a·Q(A)(-)], i.e., ΔG(PhQ). The E(m)(Q(A)/Q(A)(-)) of A. marina was determined to be +64 mV without the Mn cluster and was estimated to be -66 to -86 mV with a Mn-depletion shift (130-150 mV), as observed with other organisms. The E(m)(Phe a/Phe a(-)) in Synechocystis was measured to be -525 mV with the Mn cluster, which is consistent with our previous report. The Mn-depleted downshift of the potential was measured to be approximately -77 mV in Synechocystis, and this value was applied to A. marina (-478 mV); the E(m)(Phe a/Phe a(-)) was estimated to be approximately -401 mV. These values gave rise to a ΔG(PhQ) of -325 mV for A. marina and -383 mV for Synechocystis. In the two cyanobacteria, the energetics in PS II were conserved, even though the potentials of Q(A)(-) and Phe a(-) were relatively shifted depending on the special pair, indicating a common strategy for electron transfer in oxygenic photosynthetic organisms.

  9. Pronounced Effects of a Triazine Core on Photovoltaic Performance-Efficient Organic Solar Cells Enabled by a PDI Trimer-Based Small Molecular Acceptor.

    PubMed

    Duan, Yuwei; Xu, Xiaopeng; Yan, He; Wu, Wenlin; Li, Zuojia; Peng, Qiang

    2017-02-01

    A novel-small molecular acceptor with electron-deficient 1,3,5-triazine as the core and perylene diimides as the arms is developed as the acceptor material for efficient bulk heterojunction organic solar cells with an efficiency of 9.15%. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Calculations of acceptor ionization energies in GaN

    NASA Astrophysics Data System (ADS)

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

    2001-03-01

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

  11. Dissimilatory arsenate reduction with sulfide as electron donor: Experiments with Mono Lake water and isolation of strain MLMS-1, a chemoautotrophic arsenate respirer

    USGS Publications Warehouse

    Hoeft, S.E.; Kulp, T.R.; Stolz, J.F.; Hollibaugh, J.T.; Oremland, R.S.

    2004-01-01

    Anoxic bottom water from Mono Lake, California, can biologically reduce added arsenate without any addition of electron donors. Of the possible in situ inorganic electron donors present, only sulfide was sufficiently abundant to drive this reaction. We tested the ability of sulfide to serve as an electron donor for arsenate reduction in experiments with lake water. Reduction of arsenate to arsenite occurred simultaneously with the removal of sulfide. No loss of sulfide occurred in controls without arsenate or in sterilized samples containing both arsenate and sulfide. The rate of arsenate reduction in lake water was dependent on the amount of available arsenate. We enriched for a bacterium that could achieve growth with sulfide and arsenate in a defined, mineral medium and purified it by serial dilution. The isolate, strain MLMS-1, is a gram-negative, motile curved rod that grows by oxidizing sulfide to sulfate while reducing arsenate to arsenite. Chemoautotrophy was confirmed by the incorporation of H14CO3- into dark-incubated cells, but preliminary gene probing tests with primers for ribulose-1,5-biphosphate carboxylase/oxygenase did not yield PCR-amplified products. Alignment of 16S rRNA sequences indicated that strain MLMS-1 was in the ??-Proteobacteria, located near sulfate reducers like Desulfobulbus sp. (88 to 90% similarity) but more closely related (97%) to unidentified sequences amplified previously from Mono Lake. However, strain MLMS-1 does not grow with sulfate as its electron acceptor.

  12. Effect of sudden addition of PCE and bioreactor coupling to ZVI filters on performance of fluidized bed bioreactors operated in simultaneous electron acceptor modes.

    PubMed

    Moreno-Medina, C U; Poggi-Varaldo, Hector M; Breton-Deval, L; Rinderknecht-Seijas, N

    2017-11-01

    The present work evaluated the effects of (i) feeding a water contaminated with 80 mg/L PCE to bioreactors seeded with inoculum not acclimated to PCE, (ii) coupling ZVI side filters to bioreactors, and (iii) working in different biological regimes, i.e., simultaneous methanogenic aeration and simultaneous methanogenic-denitrifying regimes, on fluidized bed bioreactor performance. Simultaneous electron acceptors refer to the simultaneous presence of two compounds operating as final electron acceptors in the biological respiratory chain (e.g., use of either O 2 or NO 3 - in combination with a methanogenic environment) in a bioreactor or environmental niche. Four lab-scale, mesophilic, fluidized bed bioreactors (bioreactors) were implemented. Two bioreactors were operated as simultaneous methanogenic-denitrifying (MD) units, whereas the other two were operated in partially aerated methanogenic (PAM) mode. In the first period, all bioreactors received a wastewater with 1 g chemical oxygen demand of methanol per liter (COD-methanol/L). In a second period, all the bioreactors received the wastewater plus 80 mg perchloroethylene (PCE)/L; at the start of period 2, one MD and one PAM were coupled to side sand-zero valent iron filters (ZVI). All bioreactors were inoculated with a microbial consortium not acclimated to PCE. In this work, the performance of the full period 1 and the first 60 days of period 2 is reported and discussed. The COD removal efficiency and the nitrate removal efficiency of the bioreactors essentially did not change between period 1 and period 2, i.e., upon PCE addition. On the contrary, specific methanogenic activity in PAM bioreactors (both with and without coupled ZVI filter) significantly decreased. This was consistent with a sharp fall of methane productivity in those bioreactors in period 2. During period 2, PCE removals in the range 86 to 97 % were generally observed; the highest removal corresponded to PAM bioreactors along with the

  13. Acetate Production from Oil under Sulfate-Reducing Conditions in Bioreactors Injected with Sulfate and Nitrate

    PubMed Central

    Callbeck, Cameron M.; Agrawal, Akhil

    2013-01-01

    Oil production by water injection can cause souring in which sulfate in the injection water is reduced to sulfide by resident sulfate-reducing bacteria (SRB). Sulfate (2 mM) in medium injected at a rate of 1 pore volume per day into upflow bioreactors containing residual heavy oil from the Medicine Hat Glauconitic C field was nearly completely reduced to sulfide, and this was associated with the generation of 3 to 4 mM acetate. Inclusion of 4 mM nitrate inhibited souring for 60 days, after which complete sulfate reduction and associated acetate production were once again observed. Sulfate reduction was permanently inhibited when 100 mM nitrate was injected by the nitrite formed under these conditions. Pulsed injection of 4 or 100 mM nitrate inhibited sulfate reduction temporarily. Sulfate reduction resumed once nitrate injection was stopped and was associated with the production of acetate in all cases. The stoichiometry of acetate formation (3 to 4 mM formed per 2 mM sulfate reduced) is consistent with a mechanism in which oil alkanes and water are metabolized to acetate and hydrogen by fermentative and syntrophic bacteria (K. Zengler et al., Nature 401:266–269, 1999), with the hydrogen being used by SRB to reduce sulfate to sulfide. In support of this model, microbial community analyses by pyrosequencing indicated SRB of the genus Desulfovibrio, which use hydrogen but not acetate as an electron donor for sulfate reduction, to be a major community component. The model explains the high concentrations of acetate that are sometimes found in waters produced from water-injected oil fields. PMID:23770914

  14. Acetate production from oil under sulfate-reducing conditions in bioreactors injected with sulfate and nitrate.

    PubMed

    Callbeck, Cameron M; Agrawal, Akhil; Voordouw, Gerrit

    2013-08-01

    Oil production by water injection can cause souring in which sulfate in the injection water is reduced to sulfide by resident sulfate-reducing bacteria (SRB). Sulfate (2 mM) in medium injected at a rate of 1 pore volume per day into upflow bioreactors containing residual heavy oil from the Medicine Hat Glauconitic C field was nearly completely reduced to sulfide, and this was associated with the generation of 3 to 4 mM acetate. Inclusion of 4 mM nitrate inhibited souring for 60 days, after which complete sulfate reduction and associated acetate production were once again observed. Sulfate reduction was permanently inhibited when 100 mM nitrate was injected by the nitrite formed under these conditions. Pulsed injection of 4 or 100 mM nitrate inhibited sulfate reduction temporarily. Sulfate reduction resumed once nitrate injection was stopped and was associated with the production of acetate in all cases. The stoichiometry of acetate formation (3 to 4 mM formed per 2 mM sulfate reduced) is consistent with a mechanism in which oil alkanes and water are metabolized to acetate and hydrogen by fermentative and syntrophic bacteria (K. Zengler et al., Nature 401:266-269, 1999), with the hydrogen being used by SRB to reduce sulfate to sulfide. In support of this model, microbial community analyses by pyrosequencing indicated SRB of the genus Desulfovibrio, which use hydrogen but not acetate as an electron donor for sulfate reduction, to be a major community component. The model explains the high concentrations of acetate that are sometimes found in waters produced from water-injected oil fields.

  15. Chemical trends for acceptor impurities in GaN

    NASA Astrophysics Data System (ADS)

    Neugebauer, Jörg; Van de Walle, Chris G.

    1999-03-01

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

  16. Desulfonatronum thiodismutans sp. nov., a novel alkaliphilic, sulfate-reducing bacterium capable of lithoautotrophic growth.

    PubMed

    Pikuta, Elena V; Hoover, Richard B; Bej, Asim K; Marsic, Damien; Whitman, William B; Cleland, David; Krader, Paul

    2003-09-01

    A novel alkaliphilic, sulfate-reducing bacterium, strain MLF1(T), was isolated from sediments of soda Mono Lake, California. Gram-negative vibrio-shaped cells were observed, which were 0.6-0.7x1.2-2.7 micro m in size, motile by a single polar flagellum and occurred singly, in pairs or as short spirilla. Growth was observed at 15-48 degrees C (optimum, 37 degrees C), >1-7 % NaCl, w/v (optimum, 3 %) and pH 8.0-10.0 (optimum, 9.5). The novel isolate is strictly alkaliphilic, requires a high concentration of carbonate in the growth medium and is obligately anaerobic and catalase-negative. As electron donors, strain MLF1(T) uses hydrogen, formate and ethanol. Sulfate, sulfite and thiosulfate (but not sulfur or nitrate) can be used as electron acceptors. The novel isolate is a lithoheterotroph and a facultative lithoautotroph that is able to grow on hydrogen without an organic source of carbon. Strain MLF1(T) is resistant to kanamycin and gentamicin, but sensitive to chloramphenicol and tetracycline. The DNA G+C content is 63.0 mol% (HPLC). DNA-DNA hybridization with the most closely related species, Desulfonatronum lacustre Z-7951(T), exhibited 51 % homology. Also, the genome size (1.6x10(9) Da) and T(m) value of the genomic DNA (71+/-2 degrees C) for strain MLF1(T) were significantly different from the genome size (2.1x10(9) Da) and T(m) value (63+/-2 degrees C) for Desulfonatronum lacustre Z-7951(T). On the basis of physiological and molecular properties, the isolate was considered to be a novel species of the genus Desulfonatronum, for which the name Desulfonatronum thiodismutans sp. nov. is proposed (the type strain is MLF1(T)=ATCC BAA-395(T)=DSM 14708(T)).

  17. Desulfonatronum Thiodismutans sp. nov., a Novel Alkaliphilic, Sulfate-reducing Bacterium Capable of Lithoautotrophic Growth

    NASA Technical Reports Server (NTRS)

    Pikuta, Elena V.; Hoover, Richard B.; Bej, Asim K.; Marsic, Damien; Whitman, William B.; Cleland, David; Krader, Paul

    2003-01-01

    A novel alkaliphilic, sulfate-reducing bacterium, strain MLF1(sup T), was isolated from sediments of soda Mono Lake, California. Gram-negative vibrio-shaped cells were observed, which were 0.6-0.7 x 1.2-2.7 microns in size, motile by a single polar flagellum and occurred singly, in pairs or as short spirilla. Growth was observed at 15-48 C (optimum, 37 C), > 1-7 % NaCI, w/v (optimum, 3%) and pH 8.0-10.0 (optimum, 9.5). The novel isolate is strictly alkaliphilic, requires a high concentration of carbonate in the growth medium and is obligately anaerobic and catalase-negative. As electron donors, strain MLF1(sup T) uses hydrogen, formate and ethanol. Sulfate, sulfite and thiosulfate (but not sulfur or nitrate) can be used as electron acceptors. The novel isolate is a lithoheterotroph and a facultative lithoautotroph that is able to grow on hydrogen without an organic source of carbon. Strain MLF1(sup T) is resistant to kanamycin and gentamicin, but sensitive to chloramphenicol and tetracycline. The DNA G+C content is 63.0 mol% (HPLC). DNA-DNA hybridization with the most closely related species, Desulfonatronum lacustre Z-7951(sup T), exhibited 51 % homology. Also, the genome size (1.6 x 10(exp 9) Da) and T(sub m) value of the genomic DNA (71 +/- 2 C) for strain MLF1(sup T) were significantly different from the genome size (2.1 x 10(exp 9) Da) and T(sub m) value (63 +/- 2 C) for Desulfonatronum lacustre Z-7951(sup T). On the basis of physiological and molecular properties, the isolate was considered to be a novel species of the genus Desulfonatronum, for which the name Desulfonatronum thiodismutans sp. nov. is proposed (the type strain is MLF1(sup T) = ATCC BAA-395(sup T) = DSM 14708(sup T)).

  18. Sulfated modification and anti-tumor activity of laminarin.

    PubMed

    Ji, Chen-Feng; Ji, Yu-Bin; Meng, DE-You

    2013-11-01

    The aim of this study was to investigate the sulfated modification of laminarin and the changes in structure and antitumor activity. The chlorosulfonic acid-pyridine method was applied for sulfated modification. The molecular weights of laminarin and laminarin sulfate (LAMS) were measured by high-performance liquid chromatography (HPLC), and IR and NMR spectra were also recorded. The surface conformations of laminarin and LAMS were observed with a scanning electron microscope. The antitumor activities of the two polysaccharides were also evaluated using an MTT assay. LAMS with a sulfate content of 45.92% and a molecular weight of 16,000 was synthesized. The IR spectra of laminarin and LAMS showed the characteristic absorption peaks of a polysaccharide, and LAMS also had the characteristic absorption peaks of sulfate moieties. The NMR spectra showed that laminarin and LAMS had β-(1→3) glycosidic bonds forming the main chain, and sulfate substitution was at the hydroxyl groups of C 2 and C 6 . Under the scanning electron microscope, there were clear differences in surface conformation between laminarin and LAMS; laminarin was cloud-like and spongy, while LAMS was block-like and flaky. The MTT results showed that laminarin and LAMS had inhibitory effects on LoVo cell growth, and the antitumor activity of LAMS was higher than that of laminarin at the same concentration. This suggests that sulfated modification was able to change the laminarin structure and markedly enhance the antitumor activity.

  19. Dissimilatory arsenate reduction with sulfide as the electron donor--Experiments with Mono Lake water and isolation of strain MLMS-1, a chemoautotrophic arsenate-respirer

    USGS Publications Warehouse

    Hoeft, Shelley E.; Kulp, Thomas R.; Stolz, John F.; Hollibaugh, James T.; Oremland, Ronald S.

    2004-01-01

    Anoxic bottom water from Mono Lake, California, can biologically reduce added arsenate without any addition of electron donors. Of the possible in situ inorganic electron donors present, only sulfide was sufficiently abundant to drive this reaction. We tested the ability of sulfide to serve as an electron donor for arsenate reduction in experiments with lake water. Reduction of arsenate to arsenite occurred simultaneously with the removal of sulfide. No loss of sulfide occurred in controls without arsenate or in sterilized samples containing both arsenate and sulfide. The rate of arsenate reduction in lake water was dependent on the amount of available arsenate. We enriched for a bacterium that could achieve growth with sulfide and arsenate in a defined, mineral medium and purified it by serial dilution. The isolate, strain MLMS-1, is a gram-negative, motile curved rod that grows by oxidizing sulfide to sulfate while reducing arsenate to arsenite. Chemoautotrophy was confirmed by the incorporation of H14CO3− into dark-incubated cells, but preliminary gene probing tests with primers for ribulose-1,5-biphosphate carboxylase/oxygenase did not yield PCR-amplified products. Alignment of 16S rRNA sequences indicated that strain MLMS-1 was in the δ-Proteobacteria, located near sulfate reducers like Desulfobulbus sp. (88 to 90% similarity) but more closely related (97%) to unidentified sequences amplified previously from Mono Lake. However, strain MLMS-1 does not grow with sulfate as its electron acceptor.

  20. Carbonate and sulfate minerals in the Chassigny meteorite

    NASA Technical Reports Server (NTRS)

    Wentworth, Susan J.; Gooding, James L.

    1991-01-01

    SO2 and CO2 from pyrolysis and combustion of bulk Chassigny and infrared traces of sulfate and carbonate minerals have been previously reported. Using scanning electron microscopy (SEM) and energy-dispersive x ray spectrometry (EDS), portions of these samples are searched, and a Ca-sulfate/carbonate association is confirmed.

  1. Desulfoplanes formicivorans gen. nov., sp. nov., a novel sulfate-reducing bacterium isolated from a blackish meromictic lake, and emended description of the family Desulfomicrobiaceae.

    PubMed

    Watanabe, Miho; Kojima, Hisaya; Fukui, Manabu

    2015-06-01

    A novel sulfate-reducing bacterium, designated strain Pf12BT, was isolated from sediment of meromictic Lake Harutori in Japan. Cells were vibroid (1.0 × 3.0-4.0 μm), motile and Gram-stain-negative. For growth, the optimum pH was 7.0-7.5 and the optimum temperature was 42-45 °C. Strain Pf12BT used sulfate, thiosulfate and sulfite as electron acceptors. The G+C content of the genomic DNA was 55.4 mol%. Major cellular fatty acids were C16 : 0 and C18 : 0. The strain was desulfoviridin-positive. Phylogenetic analysis based on the 16S rRNA gene revealed that the novel strain belonged to the order Desulfovibrionales in the class Deltaproteobacteria. The closest relative was Desulfomicrobium baculatum DSM 4028T with which it shared 91 % 16S rRNA gene sequence similarity. On the basis of phylogenetic and phenotypic characterization, a novel species of a new genus belonging to the family Desulfomicrobiaceae is proposed, Desulfoplanes formicivorans gen. nov., sp. nov. The type strain of Desulfoplanes formicivorans is Pf12BT ( = NBRC 110391T = DSM 28890T).

  2. Theoretical characterization of photoinduced electron transfer in rigidly linked donor-acceptor molecules: the fragment charge difference and the generalized Mulliken-Hush schemes

    NASA Astrophysics Data System (ADS)

    Lee, Sheng-Jui; Chen, Hung-Cheng; You, Zhi-Qiang; Liu, Kuan-Lin; Chow, Tahsin J.; Chen, I.-Chia; Hsu, Chao-Ping

    2010-10-01

    We calculate the electron transfer (ET) rates for a series of heptacyclo[6.6.0.02,6.03,13.014,11.05,9.010,14]-tetradecane (HCTD) linked donor-acceptor molecules. The electronic coupling factor was calculated by the fragment charge difference (FCD) [19] and the generalized Mulliken-Hush (GMH) schemes [20]. We found that the FCD is less prone to problems commonly seen in the GMH scheme, especially when the coupling values are small. For a 3-state case where the charge transfer (CT) state is coupled with two different locally excited (LE) states, we tested with the 3-state approach for the GMH scheme [30], and found that it works well with the FCD scheme. A simplified direct diagonalization based on Rust's 3-state scheme was also proposed and tested. This simplified scheme does not require a manual assignment of the states, and it yields coupling values that are largely similar to those from the full Rust's approach. The overall electron transfer (ET) coupling rates were also calculated.

  3. Tailorable PC71 BM Isomers: Using the Most Prevalent Electron Acceptor to Obtain High-Performance Polymer Solar Cells.

    PubMed

    Zhan, Xin-Xing; Zhang, Xin; Dai, Si-Min; Li, Shu-Hui; Lu, Xu-Zhai; Deng, Lin-Long; Xie, Su-Yuan; Huang, Rong-Bin; Zheng, Lan-Sun

    2016-12-23

    Despite being widely used as electron acceptor in polymer solar cells, commercially available PC 71 BM (phenyl-C 71 -butyric acid methyl ester) usually has a "random" composition of mixed regioisomers or stereoisomers. Here PC 71 BM has been isolated into three typical isomers, α-, β 1 - and β 2 -PC 71 BM, to establish the isomer-dependent photovoltaic performance on changing the ternary composition of α-, β 1 - and β 2 -PC 71 BM. Mixing the isomers in a ratio of α/β 1 /β 2 =8:1:1 resulted in the best power conversion efficiency (PCE) of 7.67 % for the polymer solar cells with PTB7:PC 71 BM as photoactive layer (PTB7=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

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

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

    Clikeman, Tyler T.; Bukovsky, Eric V.; Kuvychko, Igor V.

    2014-07-10

    Azulene is a non-alternant, non-benzenoid aromatic hydrocarbon with an intense blue colour, a dipole moment of 1.0 D,1 positive electron affinity, and an “anomalous” emission from the second excited state in violation of Kasha’s rule.2,3 Azulene’s unique properties have potential uses in molecular switches,4,5 molecular diodes,6 organic photovoltaics,7 and charge transfer complexes.8-12 Introduction of electron-withdrawing groups to the azulenic core, such as CN,8,13,14 halogens,15-19 and CF3,20,21 can enhance certain electrical and photophysical properties. In this work, we report six new trifluoromethyl derivatives of azulene (AZUL), three isomers of AZUL(CF3)3 and three isomers of AZUL(CF3)4, and the first X-ray structure ofmore » a π-stacked donor-acceptor complex of a trifluoromethyl azulene with donor pyrene.« less

  5. Medium-Bandgap Small-Molecule Donors Compatible with Both Fullerene and Nonfullerene Acceptors.

    PubMed

    Huo, Yong; Yan, Cenqi; Kan, Bin; Liu, Xiao-Fei; Chen, Li-Chuan; Hu, Chen-Xia; Lau, Tsz-Ki; Lu, Xinhui; Sun, Chun-Lin; Shao, Xiangfeng; Chen, Yongsheng; Zhan, Xiaowei; Zhang, Hao-Li

    2018-03-21

    Much effort has been devoted to the development of new donor materials for small-molecule organic solar cells due to their inherent advantages of well-defined molecular weight, easy purification, and good reproducibility in photovoltaic performance. Herein, we report two small-molecule donors that are compatible with both fullerene and nonfullerene acceptors. Both molecules consist of an (E)-1,2-di(thiophen-2-yl)ethane-substituted (TVT-substituted) benzo[1,2-b:4,5-b']dithiophene (BDT) as the central unit, and two rhodanine units as the terminal electron-withdrawing groups. The central units are modified with either alkyl side chains (DRBDT-TVT) or alkylthio side chains (DRBDT-STVT). Both molecules exhibit a medium bandgap with complementary absorption and proper energy level offset with typical acceptors like PC 71 BM and IDIC. The optimized devices show a decent power conversion efficiency (PCE) of 6.87% for small-molecule organic solar cells and 6.63% for nonfullerene all small-molecule organic solar cells. Our results reveal that rationally designed medium-bandgap small-molecule donors can be applied in high-performance small-molecule organic solar cells with different types of acceptors.

  6. Differences in the efficiency of reductive activation of methionine synthase and exogenous electron acceptors between the common polymorphic variants of human methionine synthase reductase.

    PubMed

    Olteanu, Horatiu; Munson, Troy; Banerjee, Ruma

    2002-11-12

    Methionine synthase reductase (MSR) catalyzes the conversion of the inactive form of human methionine synthase to the active state of the enzyme. This reaction is of paramount physiological importance since methionine synthase is an essential enzyme that plays a key role in the methionine and folate cycles. A common polymorphism in human MSR has been identified (66A --> G) that leads to replacement of isoleucine with methionine at residue 22 and has an allele frequency of 0.5. Another polymorphism is 524C --> T, which leads to the substitution of serine 175 with leucine, but its allele frequency is not known. The I22M polymorphism is a genetic determinant for mild hyperhomocysteinemia, a risk factor for cardiovascular disease. In this study, we have examined the kinetic properties of the M22/S175 and I22/S175 and the I22/L175 and I22/S175 pairs of variants. EPR spectra of the semiquinone forms of variants I22/S175 and M22/S175 are indistinguishable and exhibit an isotropic signal at g = 2.00. In addition, the electronic absorption and reduction stoichiometries with NADPH are identical in these variants. Significantly, the variants activate methionine synthase with the same V(max); however, a 3-4-fold higher ratio of MSR to methionine synthase is required to elicit maximal activity with the M22/S175 and I22/L175 variant versus the I22/S175 enzyme. Differences are also observed between the variants in the efficacies of reduction of the artificial electron acceptors: ferricyanide, 2,6-dichloroindophenol, 3-acetylpyridine adenine dinucleotide phosphate, menadione, and the anticancer drug doxorubicin. These results reveal differences in the interactions between the natural and artificial electron acceptors and MSR variants in vitro, which are predicted to result in less efficient reductive repair of methionine synthase in vivo.

  7. Biogeochemical controls on interactions of microbial iron and sulfate reduction

    NASA Astrophysics Data System (ADS)

    Kirk, M. F.; Paper, J. M.; Haller, B. R.; Shodunke, G. O.; Marquart, K. A.; Jin, Q.

    2016-12-01

    Although iron and sulfate reduction are two of the most common microbial electron accepting processes in anoxic settings, the relative influences of environmental factors that guide interactions between each are poorly known. Identifying these factors is a key to predicting how those interactions will respond to future environmental changes. In this study, we used semi-continuous bioreactors to examine the influence of pH, electron donor flux, and sulfate availability. The reactors contained 100 mL of aqueous media and 1 g of marsh sediment amended with goethite (1 mmol). One set of reactors received acidic media (pH 6) while the other set received alkaline media (pH 7.5). Media for both sets of reactors included acetate (0.25 and 1 mM), which served as an electron donor, and sulfate (2.5 mM). We also included sets of sulfate-deficient and acetate-deficient control reactors. We maintained a fluid residence time of 35 days in the reactors by sampling and feeding them every seven days during the 91-day incubation. Our results show that, under the conditions tested, pH had a larger influence on the balance between each reaction than acetate concentration. In acidic reactors, the molar amount of iron reduced exceeded the amount of sulfate reduced by a factor of 3 in reactors receiving media with 0 and 0.25 mM acetate and a factor of 2 in reactors receiving 1 mM acetate. Under alkaline conditions, iron and sulfate were reduced in nearly equal proportions, regardless of influent acetate concentration. Results from sulfate-deficient control reactors show that the presence of sulfate reduction increased the extent of iron reduction in all reactors, but particularly those with alkaline pH. Under acidic conditions, the amount of iron reduced was greater by a factor of 1.2 if sulfate reduction occurred simultaneously than if it did not. Under alkaline conditions, that factor increased to 8.2. Hence, pH influenced the extent to which sulfate reduction promoted iron reduction.

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

    NASA Astrophysics Data System (ADS)

    Lyons, John L.

    2013-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  10. Anaerobic aquifer transformations of 2,4-Dinitrophenol under different terminal electron accepting conditions

    USGS Publications Warehouse

    Krumholz, L.R.; Suflita, J.M.

    1997-01-01

    We evaluated the susceptibility of 2,4-dinitrophenol (2,4-DNP) and 2,4-diaminophenol to anaerobic biodegradation in aquifer slurries. Aquifer microorganisms depleted 2,4-DNP at rates of 25, 9 and 0.4 μM/day under methanogenic, sulfate-reducing and nitrate-reducing conditions, respectively. Rates of abiotic, 2,4-DNP loss in autoclaved control incubations were 7.2, 6.2 and 0.95 μM/day respectively. Abiotic, 2,4-DNP reduction was especially important as the first step in its transformation. 2-Amino-4-nitrophenol was produced by this process, but this compound was further metabolized in methanogenic and sulfate-reducing aquifer slurries. This partially reduced compound persisted in autoclaved controls and in the nitrate-reducing aquifer slurries. Aquifer slurries incubated with either 2,4-DNP or 2,4-diaminophenol produced methane when incubated with no other electron acceptor suggesting that mineralization had occurred under these conditions. In parallel experiments, aquifer slurries amended with 2,6-dinitrophenol or picric acid did not produce methane at levels above the substrate unamended controls.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  12. 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.

  13. Photoinduced Charge Transfer and Electrochemical Properties of Triphenylamine Ih-Sc3N@C80 Donor-Acceptor Conjugates

    PubMed Central

    Pinzón, Julio R.; Gasca, Diana C.; Shankara, Gayathri. S; Bottari, Giovanni; Torres, Tomás; Guldi, Dirk M.; Echegoyen, Luis

    2009-01-01

    Two isomeric [5,6]-pyrrolidine-Ih-Sc3N@C80 electron donor acceptor conjugates containing triphenylamine (TPA) as the donor system were synthesized. Electrochemical and photophysical studies of the novel conjugates were made and compared with those of their C60 analogues, in order to determine i) the effect of the linkage position (N-substituted versus 2-substituted pyrrolidine) of the donor system in the formation of photoinduced charge separated states, ii) the thermal stability towards the retro-cycloaddition reaction and iii) the effect of changing C60 for Ih-Sc3N@C80 as the electron acceptor. It was found that when the donor is connected to the pyrrolidine nitrogen atom, the resulting dyad produces a significantly longer lived radical pair than the corresponding 2-substituted isomer for both the C60 and Ih-Sc3N@C80 dyads. In addition to that, the N-substituted TPA-Ih-Sc3N@C80 dyad has much better thermal stability than the 2-subtituted one. Finally, the Ih-Sc3N@C80 dyads have considerably longer lived charge separated states than their C60 analogues, thus approving the advantage of using Ih-Sc3N@C80 instead of C60 as the acceptor for the construction of fullerene based donor acceptor conjugates. These findings are important for the design and future application of Ih-Sc3N@C80 dyads as materials for the construction of plastic organic solar cells. PMID:19445462

  14. Anaerobic degradation of a mixture of MtBE, EtBE, TBA, and benzene under different redox conditions.

    PubMed

    van der Waals, Marcelle J; Pijls, Charles; Sinke, Anja J C; Langenhoff, Alette A M; Smidt, Hauke; Gerritse, Jan

    2018-04-01

    The increasing use of biobased fuels and fuel additives can potentially change the typical fuel-related contamination in soil and groundwater. Anaerobic biotransformation of the biofuel additive ethyl tert-butyl ether (EtBE), as well as of methyl tert-butyl ether (MtBE), benzene, and tert-butyl alcohol (TBA, a possible oxygenate metabolite), was studied at an industrially contaminated site and in the laboratory. Analysis of groundwater samples indicated that in the field MtBE was degraded, yielding TBA as major product. In batch microcosms, MtBE was degraded under different conditions: unamended control, with medium without added electron acceptors, or with ferrihydrite or sulfate (with or without medium) as electron acceptor, respectively. Degradation of EtBE was not observed under any of these conditions tested. TBA was partially depleted in parallel with MtBE. Results of microcosm experiments with MtBE substrate analogues, i.e., syringate, vanillate, or ferulate, were in line with the hypothesis that the observed TBA degradation is a cometabolic process. Microcosms with ferulate, syringate, isopropanol, or diethyl ether showed EtBE depletion up to 86.5% of the initial concentration after 83 days. Benzene was degraded in the unamended controls, with medium without added electron acceptors and with ferrihydrite, sulfate, or chlorate as electron acceptor, respectively. In the presence of nitrate, benzene was only degraded after addition of an anaerobic benzene-degrading community. Nitrate and chlorate hindered MtBE, EtBE, and TBA degradation.

  15. Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex.

    PubMed

    Lennox, J Christian; Dempsey, Jillian L

    2017-11-22

    A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru 3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pK a units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

  16. Charge Transfer and Collection in Dilute Organic Donor-Acceptor Heterojunction Blends.

    PubMed

    Ding, Kan; Liu, Xiao; Forrest, Stephen R

    2018-05-09

    Experimental and theoretical approaches are used to understand the role of nanomorphology on exciton dissociation and charge collection at dilute donor-acceptor (D-A) organic heterojunctions (HJs). Specifically, two charge transfer (CT) states in D-A mixed HJs comprising nanocrystalline domains of tetraphenyldibenzoperiflanthene (DBP) as the donor and C 70 as the acceptor are unambiguously related to the nanomorphology of the mixed layer. Alternating DBP:C 70 multilayer stacks are used to identify and control the optical properties of the CT states, as well as to simulate the dilute mixed heterojunctions. A kinetic Monte Carlo model along with photoluminescence spectroscopy and scanning transmission electron microscopy are used to quantitatively evaluate the layer morphology under various growth conditions. As a result, we are able to understand the counterintuitive observation of high charge extraction efficiency and device performance of DBP:C 70 mixed layer photovoltaics at surprisingly low (∼10%) donor concentrations.

  17. Energy bands and acceptor binding energies of GaN

    NASA Astrophysics Data System (ADS)

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

    1999-04-01

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

  18. Early diagenesis in the sediments of the Congo deep-sea fan dominated by massive terrigenous deposits: Part III - Sulfate- and methane- based microbial processes

    NASA Astrophysics Data System (ADS)

    Pastor, L.; Toffin, L.; Decker, C.; Olu, K.; Cathalot, C.; Lesongeur, F.; Caprais, J.-C.; Bessette, S.; Brandily, C.; Taillefert, M.; Rabouille, C.

    2017-08-01

    Geochemical profiles (SO42-, H2S, CH4, δ13CH4) and phylogenetic diversity of Archaea and Bacteria from two oceanographic cruises dedicated to the lobes sediments of the Congo deep-sea fan are presented in this paper. In this area, organic-rich turbidites reach 5000 m and allow the establishment of patchy cold-seep-like habitats including microbial mats, reduced sediments, and vesicomyid bivalves assemblages. These bivalves live in endosymbiosis with sulfur-oxidizing bacteria and use sulfides to perform chemosynthesis. In these habitats, unlike classical abyssal sediments, anoxic processes are dominant. Total oxygen uptake fluxes and methane fluxes measured with benthic chambers are in the same range as those of active cold-seep environments, and oxygen is mainly used for reoxidation of reduced compounds, especially in bacterial mats and reduced sediments. High concentrations of methane and sulfate co-exist in the upper 20 cm of sediments, and evidence indicates that sulfate-reducing microorganisms and methanogens co-occur in the shallow layers of these sediments. Simultaneously, anaerobic oxidation of methane (AOM) with sulfate as the electron acceptor is evidenced by the presence of ANMEs (ANaerobic MEthanotroph). Dissolved sulfide produced through the reduction of sulfate is reoxidized through several pathways depending on the habitat. These pathways include vesicomyid bivalves uptake (adults or juveniles in the bacterial mats habitats), reoxidation by oxygen or iron phases within the reduced sediment, or reoxidation by microbial mats. Sulfide uptake rates by vesicomyids measured in sulfide-rich sea water (90±18 mmol S m-2 d-1) were similar to sulfide production rates obtained by modelling the sulfate profile with different bioirrigation constants, highlighting the major control of vesicomyids on sulfur cycle in their habitats.

  19. Organic electronic devices with multiple solution-processed layers

    DOEpatents

    Forrest, Stephen R.; Lassiter, Brian E.; Zimmerman, Jeramy D.

    2015-08-04

    A method of fabricating a tandem organic photosensitive device involves depositing a first layer of an organic electron donor type material film by solution-processing of the organic electron donor type material dissolved in a first solvent; depositing a first layer of an organic electron acceptor type material over the first layer of the organic electron donor type material film by a dry deposition process; depositing a conductive layer over the interim stack by a dry deposition process; depositing a second layer of the organic electron donor type material over the conductive layer by solution-processing of the organic electron donor type material dissolved in a second solvent, wherein the organic electron acceptor type material and the conductive layer are insoluble in the second solvent; depositing a second layer of an organic electron acceptor type material over the second layer of the organic electron donor type material film by a dry deposition process, resulting in a stack.

  20. Single Stage Tandem Mass Spectrometry Assignment of the C-5 Uronic Acid Stereochemistry in Heparan Sulfate Tetrasaccharides using Electron Detachment Dissociation

    NASA Astrophysics Data System (ADS)

    Agyekum, Isaac; Zong, Chengli; Boons, Geert-Jan; Amster, I. Jonathan

    2017-09-01

    The analysis of heparan sulfate (HS) glycosaminoglycans presents many challenges, due to the high degree of structural heterogeneity arising from their non-template biosynthesis. Complete structural elucidation of glycosaminoglycans necessitates the unambiguous assignments of sulfo modifications and the C-5 uronic acid stereochemistry. Efforts to develop tandem mass spectrometric-based methods for the structural analysis of glycosaminoglycans have focused on the assignment of sulfo positions. The present work focuses on the assignment of the C-5 stereochemistry of the uronic acid that lies closest to the reducing end. Prior work with electron-based tandem mass spectrometry methods, specifically electron detachment dissociation (EDD), have shown great promise in providing stereo-specific product ions, such as the B3 ´ -CO2, which has been found to distinguish glucuronic acid (GlcA) from iduronic acid (IdoA) in some HS tetrasaccharides. The previously observed diagnostic ions are generally not observed with 2- O-sulfo uronic acids or for more highly sulfated heparan sulfate tetrasaccharides. A recent study using electron detachment dissociation and principal component analysis revealed a series of ions that correlate with GlcA versus IdoA for a set of 2- O-sulfo HS tetrasaccharide standards. The present work comprehensively investigates the efficacy of these ions for assigning the C-5 stereochemistry of the reducing end uronic acid in 33 HS tetrasaccharides. A diagnostic ratio can be computed from the sum of the ions that correlate to GlcA to those that correlate to IdoA. [Figure not available: see fulltext.

  1. Evidence of the Zn vacancy acting as the dominant acceptor in n-type ZnO.

    PubMed

    Tuomisto, F; Ranki, V; Saarinen, K; Look, D C

    2003-11-14

    We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (E(el)=2 MeV, fluence 6 x 10(17) cm(-2)) ZnO samples. The Zn vacancies are identified at concentrations of [V(Zn)] approximately 2 x 10(15) cm(-3) in the as-grown material and [V(Zn)] approximately 2 x 10(16) cm(-3) in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.

  2. On vibrational circular dichroism chirality transfer in electron donor-acceptor complexes: a prediction for the quinine···BF3 system.

    PubMed

    Rode, Joanna E; Jamróz, Michał H; Dobrowolski, Jan Cz; Sadlej, Joanna

    2012-08-02

    Vibrational circular dichroism (VCD) chirality transfer occurs when an achiral molecule interacts with a chiral one and becomes VCD-active. Unlike for H-bonds, for organic electron donor-acceptor (EDA) complexes this phenomenon remains almost unknown. Here, the VCD chirality transfer from chiral quinine to achiral BF3 is studied at the B3LYP/aug-cc-pVDZ level. Accessibility of four quinine electron donor sites changes with conformation. Therefore, the quinine conformational landscape was explored and a considerable agreement between X-ray and the most stable conformer geometries was achieved. The BF3 complex through the aliphatic quinuclidine N atom is definitely dominating and is predicted to be easily recognizable in the VCD spectrum. Out of several VCD chirality transfer modes, the ν(s)(BF3) mode, the most intense in the entire VCD spectrum, satisfies the VCD mode robustness criterion and can be used for monitoring the chirality transfer phenomenon in quinine···BF3 system.

  3. Modeling donor/acceptor interactions: Combined roles of theory and computation

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

    Newton, M.D.

    2000-03-05

    An extended superexchange model for electron transfer (ET) matrix elements (H{sub DA}) has been formulated as a superposition of McConnell-type pathways and implemented by combined use of configuration interaction wave functions (obtained using the INDO/s model of Zerner and co-workers) and the generalized Muliken-Hush formulation of charge-localized diabatic states. Applications are made for et (and hold transfer) in several donor/bridge/acceptor radical anion (and cation) systems, (DBA){sup {+-}}, allowing detailed comparison with experimental H{sub DA} estimates. For the case of oligo phenylene ethynylene (OPE) bridges, the role of {pi} and {sigma} electronic manifolds for different distributions of phenylene torsion angles ismore » analyzed in detail.« less

  4. Evidence for Redox Mechanisms in Organometallic Chemisorption and Reactivity on Sulfated Metal Oxides

    DOE PAGES

    Klet, Rachel C.; Kaphan, David M.; Liu, Cong; ...

    2018-04-09

    The chemical and electronic interactions of organometallic species with metal oxide support materials are of fundamental importance for the development of new classes of catalytic materials. Chemisorption of Cp*(PMe 3)IrMe 2 on sulfated alumina (SA) and sulfated zirconia (SZ) led to an unexpected redox mechanism for deuteration of the ancillary Cp* ligand. Evidence for this oxidative mechanism was provided by studying the analogous homogeneous reactivity of the organometallic precursors toward trityl cation ([Ph 3C] +), a Lewis acid known to effect formal hydride abstraction by one-electron oxidation followed by hydrogen abstraction. Organometallic deuterium incorporation was found to be correlated withmore » surface sulfate concentration as well as the extent of dehydration under thermal activation conditions of SA and SZ supports. Surface sulfate concentration dependence, in conjunction with a computational study of surface electron affinity, indicates an electron-deficient pyrosulfate species as the redox-active moiety. Furthermore, these results provide further evidence for the ability of sulfated metal oxides to participate in redox chemistry not only toward organometallic complexes but also in the larger context of their application as catalysts for the transformation of light alkanes.« less

  5. Evidence for Redox Mechanisms in Organometallic Chemisorption and Reactivity on Sulfated Metal Oxides

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

    Klet, Rachel C.; Kaphan, David M.; Liu, Cong

    The chemical and electronic interactions of organometallic species with metal oxide support materials are of fundamental importance for the development of new classes of catalytic materials. Chemisorption of Cp*(PMe 3)IrMe 2 on sulfated alumina (SA) and sulfated zirconia (SZ) led to an unexpected redox mechanism for deuteration of the ancillary Cp* ligand. Evidence for this oxidative mechanism was provided by studying the analogous homogeneous reactivity of the organometallic precursors toward trityl cation ([Ph 3C] +), a Lewis acid known to effect formal hydride abstraction by one-electron oxidation followed by hydrogen abstraction. Organometallic deuterium incorporation was found to be correlated withmore » surface sulfate concentration as well as the extent of dehydration under thermal activation conditions of SA and SZ supports. Surface sulfate concentration dependence, in conjunction with a computational study of surface electron affinity, indicates an electron-deficient pyrosulfate species as the redox-active moiety. Furthermore, these results provide further evidence for the ability of sulfated metal oxides to participate in redox chemistry not only toward organometallic complexes but also in the larger context of their application as catalysts for the transformation of light alkanes.« less

  6. Spin-Polarization-Induced Preedge Transitions in the Sulfur K-Edge XAS Spectra of Open-Shell Transition-Metal Sulfates: Spectroscopic Validation of σ-Bond Electron Transfer.

    PubMed

    Frank, Patrick; Szilagyi, Robert K; Gramlich, Volker; Hsu, Hua-Fen; Hedman, Britt; Hodgson, Keith O

    2017-02-06

    Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M II (itao)(SO 4 )(H 2 O) 0,1 ] (M = Co, Ni, Cu) and [Cu(Me 6 tren)(SO 4 )] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO 4 )] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO 4 )] but not of [Cu(Me 6 tren)(SO 4 )] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [M II (SO 4 )(H 2 O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-down (β) spin orbitals of the sulfate ligand, inducing negative spin density at the sulfate sulfur. Ground-state DFT calculations show that sulfur 3p character then mixes into metal 4s and 4p valence orbitals and various combinations of ligand antibonding orbitals, producing measurable sulfur XAS transitions. TDDFT calculations confirm the presence of XAS preedge features 0.5-2 eV below the rising sulfur K-edge energy. The 2472.1 eV feature arises when orbitals at lower energy than the frontier occupied orbitals with S 3p character mix with the copper(II) electron hole. Transmission of spin polarization and thus of radical character through several bonds between the sulfur and electron hole provides a new mechanism for the counterintuitive appearance of preedge transitions in the XAS spectra of transition-metal oxoanion ligands in the absence of any direct metal-absorber bond. The 2472.1 eV transition is evidence for further radicalization from copper(II), which

  7. Spin-Polarization-Induced Preedge Transitions in the Sulfur K-Edge XAS Spectra of Open-Shell Transition-Metal Sulfates: Spectroscopic Validation of σ-Bond Electron Transfer

    DOE PAGES

    Frank, Patrick; Szilagyi, Robert K.; Gramlich, Volker; ...

    2017-01-09

    Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [M II(itao)(SO 4)(H 2O) 0,1] (M = Co, Ni, Cu) and [Cu(Me 6tren)(SO 4)] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal–sulfur bond, while the XAS preedge of [Zn(itao)(SO 4)] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO 4)] but not of [Cu(Me 6tren)(SO 4)] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [M II(SO 4)(Hmore » 2O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-down (β) spin orbitals of the sulfate ligand, inducing negative spin density at the sulfate sulfur. Ground-state DFT calculations show that sulfur 3p character then mixes into metal 4s and 4p valence orbitals and various combinations of ligand antibonding orbitals, producing measurable sulfur XAS transitions. TDDFT calculations confirm the presence of XAS preedge features 0.5–2 eV below the rising sulfur K-edge energy. The 2472.1 eV feature arises when orbitals at lower energy than the frontier occupied orbitals with S 3p character mix with the copper(II) electron hole. Transmission of spin polarization and thus of radical character through several bonds between the sulfur and electron hole provides a new mechanism for the counterintuitive appearance of preedge transitions in the XAS spectra of transition-metal oxoanion ligands in the absence of any direct metal–absorber bond. The 2472.1 eV transition is evidence for further radicalization from copper(II), which

  8. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, R.; Calvin, M.

    1984-01-24

    The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospholipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transferring electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

  9. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, Roland; Calvin, Melvin

    1984-01-01

    The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospho-lipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transfering electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

  10. Micro-SHINE Uranyl Sulfate Irradiations at the Linac

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

    Youker, Amanda J.; Kalensky, Michael; Chemerisov, Sergey

    2016-08-01

    Peroxide formation due to water radiolysis in a uranyl sulfate solution is a concern for the SHINE Medical Technologies process in which Mo-99 is generated from the fission of dissolved low enriched uranium. To investigate the effects of power density and fission on peroxide formation and uranyl-peroxide precipitation, uranyl sulfate solutions were irradiated using a 50-MeV electron linac as part of the micro-SHINE experimental setup. Results are given for uranyl sulfate solutions with both high and low enriched uranium irradiated at different linac powers.

  11. Tunable Rh 2(II,II) Light Absorbers as Excited State Electron Donors and Acceptors Accessible with Red/Near-IR Irradiation

    DOE PAGES

    Whittemore, Tyler; Millet, Agustin; Sayre, Hannah; ...

    2018-04-04

    In this study, a series of dirhodium(II,II) paddlewheeel complexes of the type cis-[Rh 2(μ-DTolF) 2(μ-L) 2][BF 4] 2, where DTolF = N,N'-di(p-tolyl)formamidinate and L = 1,8-naphthyridine (np), 2-(pyridin-2-yl)-1,8-naphthyridine (pynp), 2-(quinolin-2-yl)-1,8-naphthyridine (qnnp), and 2-(1,8-naphthyridin-2-yl)quinoxaline (qxnp), were synthesized and characterized. These molecules feature new tridentate ligands that concomitantly bridge the dirhodium core and cap the axial positions. The complexes absorb light strongly throughout the ultraviolet/visible range and into the near-infrared region and exhibit relatively long-lived triplet excited-state lifetimes. Both the singlet and triplet excited states exhibit metal/ligand-to-ligand charge transfer (ML-LCT) in nature as determined by transient absorption spectroscopy and spectroelectrochemistry measurements. Whenmore » irradiated with low-energy light, these black dyes are capable of undergoing reversible bimolecular electron transfer both to the electron acceptor methyl viologen and from the electron donor p-phenylenediamine. Photoinduced charge transfer in the latter was inaccessible with previous Rh 2(II,II) complexes. Finally, these results underscore the fact that the excited state of this class of molecules can be readily tuned for electron-transfer reactions upon simple synthetic modification and highlight their potential as excellent candidates for p- and n-type semiconductor applications and for improved harvesting of low-energy light to drive useful photochemical reactions.« less

  12. Tunable Rh 2(II,II) Light Absorbers as Excited State Electron Donors and Acceptors Accessible with Red/Near-IR Irradiation

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

    Whittemore, Tyler; Millet, Agustin; Sayre, Hannah

    In this study, a series of dirhodium(II,II) paddlewheeel complexes of the type cis-[Rh 2(μ-DTolF) 2(μ-L) 2][BF 4] 2, where DTolF = N,N'-di(p-tolyl)formamidinate and L = 1,8-naphthyridine (np), 2-(pyridin-2-yl)-1,8-naphthyridine (pynp), 2-(quinolin-2-yl)-1,8-naphthyridine (qnnp), and 2-(1,8-naphthyridin-2-yl)quinoxaline (qxnp), were synthesized and characterized. These molecules feature new tridentate ligands that concomitantly bridge the dirhodium core and cap the axial positions. The complexes absorb light strongly throughout the ultraviolet/visible range and into the near-infrared region and exhibit relatively long-lived triplet excited-state lifetimes. Both the singlet and triplet excited states exhibit metal/ligand-to-ligand charge transfer (ML-LCT) in nature as determined by transient absorption spectroscopy and spectroelectrochemistry measurements. Whenmore » irradiated with low-energy light, these black dyes are capable of undergoing reversible bimolecular electron transfer both to the electron acceptor methyl viologen and from the electron donor p-phenylenediamine. Photoinduced charge transfer in the latter was inaccessible with previous Rh 2(II,II) complexes. Finally, these results underscore the fact that the excited state of this class of molecules can be readily tuned for electron-transfer reactions upon simple synthetic modification and highlight their potential as excellent candidates for p- and n-type semiconductor applications and for improved harvesting of low-energy light to drive useful photochemical reactions.« less

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

    USGS Publications Warehouse

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

    1992-01-01

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

  14. THz emission of donor and acceptor doped GaAs/AlGaAs quantum well structures with inserted thin AlAs monolayer

    NASA Astrophysics Data System (ADS)

    van Dommelen, Paphavee; Daengngam, Chalongrat; Kalasuwan, Pruet

    2018-04-01

    In this paper, we explore THz range optical intersubband transition energies in a donor doped quantum well of a GaAs/AlGaAs system as a function of the insertion position of an AlAs monolayer in the GaAs quantum well. In simulated models, the optical transition energies between electron subband levels 1 and 2 were higher in the doped structure than in the undoped structure. This may be because the envelope wave function of the second electron subband strongly overlapped the envelope wave function of the first electron subband and influenced the optical intersubband transition between the two levels in the THz range. At different levels of bias voltage at the Schottky barrier on the donor doped structure, the electric field in the growth direction of the structure linearly increased the further away the AlAs monolayer was placed from the reference position. We also simulated the optical transition energies between acceptor energy levels of the acceptor doped structure as a function of the insertion position of the AlAs monolayer. The acceptor doped structure induced THz range emission whereas the undoped structure induced mid-IR emission.

  15. Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

    NASA Astrophysics Data System (ADS)

    Stübner, R.; Scheffler, L.; Kolkovsky, Vl.; Weber, J.

    2016-05-01

    In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are EC-0.06 eV (E42) and EC-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier for electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB configuration, where one H atom is directly bound to carbon in the anti-bonding position.

  16. Calcium sulfate crystallization along citrus root channels in a Florida soil exhibiting acid sulfate properties

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

    Syslo, S.K.; Myhre, D.L.; Harris, W.G.

    1988-02-01

    The authors observed euhedral crystals in Manatee soil in a citrus grove in St. Lucie County, Florida. The material was identified as gypsum (CaSO/sub 4/ /times/ 2H/sub 2/O) using x-ray diffraction and infrared spectra. Photomicrography and scanning electron microscopy revealed that gypsum accumulated both in old root channels and within citrus root tissue of the Btg horizon. The subsurface horizons had elevated sulfate levels, a low initial pH, a drop (0.5 unit) in pH upon air-drying. Electrical conductivity paralleled the concentration of water-soluble sulfate. High levels of calcium and sulfate occurred for horizons above the water table. This accumulation ismore » attributed to groundwater bearing these ions and subsequently discharging them to the overlying soil. Dead citrus roots appear to act as wicks to aid water transfer from lower to higher horizons. The roots and their empty channels provide spaces in which the gypsum can precipitate if the concentrations of calcium and sulfate in the evaporating groundwater exceed the solubility product of gypsum.« less

  17. A High-Efficiency Organic Solar Cell Enabled by the Strong Intramolecular Electron Push-Pull Effect of the Nonfullerene Acceptor.

    PubMed

    Li, Wanning; Ye, Long; Li, Sunsun; Yao, Huifeng; Ade, Harald; Hou, Jianhui

    2018-04-01

    Besides broadening of the absorption spectrum, modulating molecular energy levels, and other well-studied properties, a stronger intramolecular electron push-pull effect also affords other advantages in nonfullerene acceptors. A strong push-pull effect improves the dipole moment of the wings in IT-4F over IT-M and results in a lower miscibility than IT-M when blended with PBDB-TF. This feature leads to higher domain purity in the PBDB-TF:IT-4F blend and makes a contribution to the better photovoltaic performance. Moreover, the strong push-pull effect also decreases the vibrational relaxation, which makes IT-4F more promising than IT-M in reducing the energetic loss of organic solar cells. Above all, a power conversion efficiency of 13.7% is recorded in PBDB-TF:IT-4F-based devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Excited state dynamics can be used to probe donor-acceptor distances for H-tunneling reactions catalyzed by flavoproteins.

    PubMed

    Hardman, Samantha J O; Pudney, Christopher R; Hay, Sam; Scrutton, Nigel S

    2013-12-03

    In enzyme systems where fast motions are thought to contribute to H-transfer efficiency, the distance between hydrogen donor and acceptor is a very important factor. Sub-ångstrom changes in donor-acceptor distance can have a large effect on the rate of reaction, so a sensitive probe of these changes is a vital tool in our understanding of enzyme function. In this study we use ultrafast transient absorption spectroscopy to investigate the photoinduced electron transfer rates, which are also very sensitive to small changes in distance, between coenzyme analog, NAD(P)H4, and the isoalloxazine center in the model flavoenzymes morphinone reductase (wild-type and selected variants) and pentaerythritol tetranitrate reductase (wild-type). It is shown that upon addition of coenzyme to the protein the rate of photoinduced electron transfer is increased. By comparing the magnitude of this increase with existing values for NAD(P)H4-FMN distances, based on charge-transfer complex absorbance and experimental kinetic isotope effect reaction data, we show that this method can be used as a sensitive probe of donor-acceptor distance in a range of enzyme systems. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  19. C–H arylation of unsubstituted furan and thiophene with acceptor bromides: access to donor–acceptor–donor-type building blocks for organic electronics.

    PubMed

    Matsidik, Rukiya; Martin, Johannes; Schmidt, Simon; Obermayer, Johannes; Lombeck, Florian; Nübling, Fritz; Komber, Hartmut; Fazzi, Daniele; Sommer, Michael

    2015-01-16

    Pd-catalyzed direct arylation (DA) reaction conditions have been established for unsubstituted furan (Fu) and thiophene (Th) with three popular acceptor building blocks to be used in materials for organic electronics, namely 4,7-dibromo-2,1,3-benzothiadiazole (BTBr2), N,N′-dialkylated 2,6-dibromonaphthalene-1,4,5,8-bis(dicarboximide) (NDIBr2), and 1,4-dibromotetrafluorobenzene (F4Br2). Reactions with BTBr2, F4Br2, and NDIBr2 require different solvents to obtain high yields. The use of dimethylacetamide (DMAc) is essential for the successful coupling of BTBr2 and F4Br2, but detrimental for NDIBr2, as the electron-deficient NDI core is prone to nucleophilic core substitution in DMAc as solvent but not in toluene. NDIFu2 is much more planar compared to NDITh2, resulting in an enhanced charge-transfer character, which makes it an interesting building block for conjugated systems designed for organic electronics. This study highlights direct arylation as a simple and inexpensive method to construct a series of important donor–acceptor–donor building blocks to be further used for the preparation of a variety of conjugated materials.

  20. Bio-reduction of N-nitrosodimethylamine (NDMA) using a hydrogen-based membrane biofilm reactor.

    PubMed

    Chung, Jinwook; Ahn, Chang-Hoon; Chen, Zhuo; Rittmann, Bruce E

    2008-01-01

    N-Nitrosodimethylamine (NDMA) is a disinfection by-product shown to be carcinogenic, mutagenic, and teratogenic. A feasible detoxification pathway for NDMA is a three-step bio-reduction that leads to ammonia and dimethylamine. This study examines the bio-reduction of NDMA in a H2-based membrane biofilm reactor (MBfR) that also is active in nitrate and sulfate reductions. In particular, the study investigates the effects of H2 availability and the relative loadings of NDMA, nitrate, and sulfate, which potentially are competing electron acceptors. The results demonstrate that NDMA was bio-reduced to a major extent (i.e., at least 96%) in a H2-based MBfR in which the electron-equivalent fluxes from H2 oxidation were dominated by nitrate and sulfate reductions. NDMA reduction kinetics responded to NDMA concentration, H2 pressure, and the presence of competing acceptors. The most important factor controlling NDMA-reduction kinetics was the H2 availability, controlled primarily by the H2 pressure, and secondarily by competition from nitrate reduction.

  1. Effect of donor to acceptor ratio on electrochemical and spectroscopic properties of oligoalkylthiophene 1,3,4-oxadiazole derivatives.

    PubMed

    Kurowska, Aleksandra; Zassowski, Pawel; Kostyuchenko, Anastasia S; Zheleznova, Tatyana Yu; Andryukhova, Kseniya V; Fisyuk, Alexander S; Pron, Adam; Domagala, Wojciech

    2017-11-15

    A structure-property study across a series of donor-acceptor-donor structures composed of mono- and bi-(1,3,4-oxadiazole) units symmetrically substituted with alkyl functionalized bi-, ter- and quaterthiophene segments is presented. Synthetically tailoring the ratio of electron-withdrawing 1,3,4-oxadiazole to electron-releasing thiophene units and their alkyl grafting pattern permitted us to scrutinize the impact of these structural factors on the redox, absorptive and emissive properties of these push-pull molecules. Contrasting trends of redox potentials were observed, with the oxidation potential closely following the donor-to-acceptor ratio, whereas the reduction potential being tuned independently by either the number of acceptor units or the conjugation length of the donor-acceptor system. Increasing the thiophene unit contribution delivered a shift from blue to green luminescence, while the structural rigidity afforded by intramolecular non-covalent interactions between 1,3,4-oxadiazole and the thiophene moieties has been identified as the prime factor determining the emission efficiency of these molecules. All six structures investigated electro-polymerize easily, yielding electroactive and electrochromic polymers. The polymer doping process is largely influenced by the length of the oligothiophene repeating unit and the alkyl chain grafting density. Polymers with relatively short oligothiophene segments are able to support polarons and polaron-pairs, whereas those with segments longer than six thiophene units could also stabilize diamagnetic charge carries - bipolarons. Increasing the alkyl chain grafting density improved the reversibility and broadened the working potential window of the p-doping process. Stable radical anions have also been investigated, bringing detailed information about the conjugation pattern of these electron-surplus species. This study delivers interesting clues towards the conscious structural design of bespoke frontier energy

  2. A theoretical probe on the non-covalent interactions of sulfadoxine drug with pi-acceptors

    NASA Astrophysics Data System (ADS)

    Sandhiya, L.; Senthilkumar, K.

    2014-09-01

    A detailed analysis of the interaction between an antimalarial drug sulfadoxine and four pi-acceptors, tetrachloro-catechol, picric acid, chloranil, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone is presented in this study. The interaction of the amine, amide, methoxy, Csbnd H groups and π electron density of the drug molecule with the acceptors are studied using DFT method at M06-2X level of theory with 6-31G(d,p) basis set. The interaction energy of the complexes is calculated using M06-2X, M06-HF, B3LYP-D and MP2 methods with 6-31G(d,p) basis set. The role of weak interactions on the formation and stability of the complexes is discussed in detail. The two aromatic platforms of sulfadoxine play a major role in determining the stability of the complexes. The electron density difference maps have been plotted for the most stable drug interacting complexes to understand the changes in electron density delocalization upon the complex formation. The nature of the non-covalent interaction has been addressed from NCI plot. The infrared spectra calculated at M06-2X/6-31G(d,p) level of theory is used to characterize the most stable complexes. The SDOX-pi acceptor complexation leads to characteristic changes in the NMR spectra. The 13C, 1H, 17O and 15N NMR chemical shifts have been calculated using GIAO method at M06-2X/6-311+G(d,p)//M06-2X/6-31G(d,p) level of theory. The results obtained from this study confirm the role of non-covalent interactions on the function of the sulfadoxine drug.

  3. Multivariate Analysis of Electron Detachment Dissociation and Infrared Multiphoton Dissociation Mass Spectra of Heparan Sulfate Tetrasaccharides Differing Only in Hexuronic acid Stereochemistry

    NASA Astrophysics Data System (ADS)

    Oh, Han Bin; Leach, Franklin E.; Arungundram, Sailaja; Al-Mafraji, Kanar; Venot, Andre; Boons, Geert-Jan; Amster, I. Jonathan

    2011-03-01

    The structural characterization of glycosaminoglycan (GAG) carbohydrates by mass spectrometry has been a long-standing analytical challenge due to the inherent heterogeneity of these biomolecules, specifically polydispersity, variability in sulfation, and hexuronic acid stereochemistry. Recent advances in tandem mass spectrometry methods employing threshold and electron-based ion activation have resulted in the ability to determine the location of the labile sulfate modification as well as assign the stereochemistry of hexuronic acid residues. To facilitate the analysis of complex electron detachment dissociation (EDD) spectra, principal component analysis (PCA) is employed to differentiate the hexuronic acid stereochemistry of four synthetic GAG epimers whose EDD spectra are nearly identical upon visual inspection. For comparison, PCA is also applied to infrared multiphoton dissociation spectra (IRMPD) of the examined epimers. To assess the applicability of multivariate methods in GAG mixture analysis, PCA is utilized to identify the relative content of two epimers in a binary mixture.

  4. 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

  5. Constraining pathways of microbial mediation for carbonate concretions of the Miocene Monterey Formation using carbonate-associated sulfate

    NASA Astrophysics Data System (ADS)

    Loyd, Sean J.; Berelson, William M.; Lyons, Timothy W.; Hammond, Douglas E.; Corsetti, Frank A.

    2012-02-01

    Carbonate concretions can form as a result of organic matter degradation within sediments. However, the ability to determine specific processes and timing relationships to particular concretions has remained elusive. Previously employed proxies (e.g., carbon and oxygen isotopes) cannot uniquely distinguish among diagenetic alkalinity sources generated by microbial oxidation of organic matter using oxygen, nitrate, metal oxides, and sulfate as electron acceptors, in addition to degradation by thermal decarboxylation. Here, we employ concentrations of carbonate-associated sulfate (CAS) and δ 34S CAS (along with more traditional approaches) to determine the specific nature of concretion authigenesis within the Miocene Monterey Formation. Integrated geochemical analyses reveal that at least three specific organo-diagenetic reaction pathways can be tied to concretion formation and that these reactions are largely sample-site specific. One calcitic concretion from the Phosphatic Shale Member at Naples Beach yields δ 34S CAS values near Miocene seawater sulfate (˜+22‰ VCDT), abundant CAS (ca. 1000 ppm), depleted δ 13C carb (˜-11‰ VPDB), and very low concentrations of Fe (ca. 700 ppm) and Mn (ca. 15 ppm)—characteristics most consistent with shallow formation in association with organic matter degradation by nitrate, iron-oxides and/or minor sulfate reduction. Cemented concretionary layers of the Phosphatic Shale Member at Shell Beach display elevated δ 34S CAS (up to ˜+37‰), CAS concentrations of ˜600 ppm, mildly depleted δ 13C carb (˜-6‰), moderate amounts of Mn (ca. 250 ppm), and relatively low Fe (ca. 1700 ppm), indicative of formation in sediments dominated by sulfate reduction. Finally, concretions within a siliceous host at Montaña de Oro and Naples Beach show minimal CAS concentrations, positive δ 13C values, and the highest concentrations of Fe (ca. 11,300 ppm) and Mn (ca. 440 ppm), consistent with formation in sediments experiencing

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

    PubMed Central

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

    2014-01-01

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

  7. Production of Methane During Anaerobic Degradation of Ethanol in Gasoline

    EPA Science Inventory

    Field and laboratory studies show that the natural biodegradation of benzene may be inhibited by the presence of ethanol. Preferential biodegradation of ethanol can consume electron acceptors such as sulfate, nitrate, or oxygen that are needed for BTEX biodegradation. An additi...

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

    PubMed

    Mutharayappa, R

    1995-03-01

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

  9. Electron Capture Dissociation of Divalent Metal-adducted Sulfated N-Glycans Released from Bovine Thyroid Stimulating Hormone

    NASA Astrophysics Data System (ADS)

    Zhou, Wen; Håkansson, Kristina

    2013-11-01

    Sulfated N-glycans released from bovine thyroid stimulating hormone (bTSH) were ionized with the divalent metal cations Ca2+, Mg2+, and Co by electrospray ionization (ESI). These metal-adducted species were subjected to infrared multiphoton dissociation (IRMPD) and electron capture dissociation (ECD) and the corresponding fragmentation patterns were compared. IRMPD generated extensive glycosidic and cross-ring cleavages, but most product ions suffered from sulfonate loss. Internal fragments were also observed, which complicated the spectra. ECD provided complementary structural information compared with IRMPD, and all observed product ions retained the sulfonate group, allowing sulfonate localization. To our knowledge, this work represents the first application of ECD towards metal-adducted sulfated N-glycans released from a glycoprotein. Due to the ability of IRMPD and ECD to provide complementary structural information, the combination of the two strategies is a promising and valuable tool for glycan structural characterization. The influence of different metal ions was also examined. Calcium adducts appeared to be the most promising species because of high sensitivity and ability to provide extensive structural information.

  10. Effects of chlorate on the sulfation process of Trypanosoma cruzi glycoconjugates. Implication of parasite sulfates in cellular invasion.

    PubMed

    Ferrero, Maximiliano R; Soprano, Luciana L; Acosta, Diana M; García, Gabriela A; Esteva, Mónica I; Couto, Alicia S; Duschak, Vilma G

    2014-09-01

    Sulfation, a post-translational modification which plays a key role in various biological processes, is inhibited by competition with chlorate. In Trypanosoma cruzi, the agent of Chagas' disease, sulfated structures have been described as part of glycolipids and we have reported sulfated high-mannose type oligosaccharides in the C-T domain of the cruzipain (Cz) glycoprotein. However, sulfation pathways have not been described yet in this parasite. Herein, we studied the effect of chlorate treatment on T. cruzi with the aim to gain some knowledge about sulfation metabolism and the role of sulfated molecules in this parasite. In chlorate-treated epimastigotes, immunoblotting with anti-sulfates enriched Cz IgGs (AS-enriched IgGs) showed Cz undersulfation. Accordingly, a Cz mobility shift toward higher isoelectric points was observed in 2D-PAGE probed with anti-Cz antibodies. Ultrastructural membrane abnormalities and a significant decrease of dark lipid reservosomes were shown by electron microscopy and a significant decrease in sulfatide levels was confirmed by TLC/UV-MALDI-TOF-MS analysis. Altogether, these results suggest T. cruzi sulfation occurs via PAPS. Sulfated epitopes in trypomastigote and amastigote forms were evidenced using AS-enriched IgGs by immunoblotting. Their presence on trypomastigotes surface was demonstrated by flow cytometry and IF with Cz/dCz specific antibodies. Interestingly, the percentage of infected cardiac HL-1 cells decreased 40% when using chlorate-treated trypomastigotes, suggesting sulfates are involved in the invasion process. The same effect was observed when cells were pre-incubated with dCz, dC-T or an anti-high mannose receptor (HMR) antibody, suggesting Cz sulfates and HMR are also involved in the infection process by T. cruzi. Copyright © 2014 Elsevier B.V. All rights reserved.

  11. 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…

  12. 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.

  13. Selenium as an electron acceptor during the catalytic mechanism of thioredoxin reductase.

    PubMed

    Lothrop, Adam P; Snider, Gregg W; Ruggles, Erik L; Patel, Amar S; Lees, Watson J; Hondal, Robert J

    2014-02-04

    accelerate this exchange reaction by being a good leaving group (attack at the sulfur atom) or by being a good electrophile (attack at the selenium atom). Here we provide strong evidence that the selenium atom is attacked in this exchange step. This was shown by creating a mutant enzyme containing a Gly-Gly-Seccoo- motif that had 0.5% of the activity of the wild-type enzyme. This mutant lacks the adjacent, resolving Cys residue, which acts by attacking the mixed selenosulfide bond that occurs between the enzyme and substrate. A similar result was obtained when Sec was replaced with homocysteine. These results highlight the role of selenium as an electron acceptor in the catalytic mechanism of thioredoxin reductase as well as its established role as a donor of an electron to the substrate.

  14. Assessment of a New Type of Coin Acceptor

    DOT National Transportation Integrated Search

    1983-04-01

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

  15. Glucosamine Sulfate

    MedlinePlus

    ... Glucosamine Sulphate KCl, Glucosamine-6-Phosphate, GS, Mono-Sulfated Saccharide, Poly-(1->3)-N-Acetyl-2-Amino- ... Sulfate de Glucosamine, Sulfate de Glucosamine 2KCl, SG, Sulfated Monosaccharide, Sulfated Saccharide, Sulfato de Glucosamina. Glucosamine Hydrochloride ...

  16. J-V and C-V investigation of the effect of small molecular fullerene and non-fullerene acceptors for CH3NH3PbI3 perovskite solar cell

    NASA Astrophysics Data System (ADS)

    Zheng, Yanqiong; Wang, Chao; Yu, Junle; Yang, Fang; Zhang, Jing; Wei, Bin; Li, Weishi

    2017-11-01

    To find the ideal acceptors for perovskite solar cells (PSCs) and get insight into the dielectric property at the interface between perovskite and acceptor, series of small molecular fullerene and non-fullerene acceptors were comparatively investigated. Fullerene acceptors based PSCs show higher performance than non-fullerene acceptors based PSCs. However, the perylene tetracarboxylic diimide based PSC has achieved a η PCE of 4.70%, implying that it is a promising acceptor candidate for PSCs because of its suitable energy level, high electron mobility, and smooth surface. By employing double acceptors of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM)/C60 or PCBM/3,4,9,10-perylenetetracarboxylic bisbenzimidazole, the PSC stability is greatly improved even without performance enhancement. The perovskite (Pero)/PCBM film shows smooth surface, suggesting that PCBM penetrates into the Pero layer. The hydrophobicity trend of Pero/acceptor composite films is same as the device performance by judging from the water contact angle, and Pero/PCBM as well as Pero/C60 show higher hydrophobicity than other Pero/small-molecular-acceptor composite films. Capacitance-voltage characteristics of the series of single and double acceptor based PSCs were measured. The double acceptor based PSCs show larger depletion layer width (W d) than single acceptor based PSCs. Meanwhile, the defect density (N A) in Pero layer for single acceptor based PSCs is larger than that for double acceptor based PSCs, implying better n-doping of Pero layer by using a single acceptor.

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

    PubMed

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

    2005-02-07

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

  18. Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property.

    PubMed

    Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

    2015-02-07

    An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10(-3) cm(2) V(-1) s(-1) and an electron mobility of 1.40 × 10(-3) cm(2) V(-1) s(-1).

  19. 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.

  20. Magneto-ionic phase control in a quasi-layered donor/acceptor metal-organic framework by means of a Li-ion battery system

    NASA Astrophysics Data System (ADS)

    Taniguchi, Kouji; Narushima, Keisuke; Yamagishi, Kayo; Shito, Nanami; Kosaka, Wataru; Miyasaka, Hitoshi

    2017-06-01

    Electrical magnetism control is realized in a Li-ion battery system through a redox reaction involving ion migrations; “magneto-ionic control”. A quasi-layered metal-organic framework compound with a cross-linked π-conjugated/unconjugated one-dimensional chain motifs composed of electron-donor/acceptor units is developed as the cathode material. A change in magnetic phase from paramagnetic to ferrimagnetic is demonstrated by means of electron-filling control for the acceptor units via insertion of Li+-ions into pores in the material. The transition temperature is as high as that expected for highly π-conjugated layered systems, indicating an extension of π-conjugated exchange paths by rearranging coordination bonds in the first discharge process.

  1. Design, Synthesis, Structural and Spectroscopic Studies of Push-Pull Two-Photon Absorbing Chromophores with Acceptor Groups of Varying Strength

    PubMed Central

    Morales, Alma R.; Frazer, Andrew; Woodward, Adam W.; Ahn-White, Hyo-Yang; Fonari, Alexandr; Tongwa, Paul; Timofeeva, Tatiana; Belfield, Kevin D.

    2013-01-01

    A new series of unsymmetrical diphenylaminofluorene-based chromophores with various strong π-electron acceptors were synthesized and fully characterized. The systematic alteration of the structural design facilitated the investigation of effects such as molecular symmetry and strength of electron-donating and/or withdrawing termini have on optical nonlinearity. In order to determine the electronic and geometrical properties of the novel compounds, a thorough investigation was carried out by a combination of linear and nonlinear spectroscopic techniques, single crystal X-ray diffraction, and quantum chemical calculations. Finally, on the basis of two-photon absorption (2PA) cross sections, the general trend for π -electron accepting ability, i.e., ability to accept charge transfer from diphenylamine was: 2-pyran-4-ylidene malononitrile (pyranone) > dicyanovinyl > bis(dicyanomethylidene)indane > 1-(thiophen-2-yl)propenone > dicyanoethylenyl > 3-(thiophen-2-yl)propenone. An analog with the 2-pyran-4-ylidene malononitrile acceptor group exhibited a nearly three-fold enhancement of the 2PA< δ (1650 GM at 840 nm), relative to other members of the series. PMID:23305555

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

    DTIC Science & Technology

    2010-06-01

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

  3. Effects of sulfate on microcystin production, photosynthesis, and oxidative stress in Microcystis aeruginosa.

    PubMed

    Chen, Lei; Gin, Karina Y H; He, Yiliang

    2016-02-01

    Increasing sulfate in freshwater systems, caused by human activities and climate change, may have negative effects on aquatic organisms. Microcystis aeruginosa (M. aeruginosa) is both a major primary producer and a common toxic cyanobacterium, playing an important role in the aquatic environment. This study first investigated the effects of sulfate on M. aeruginosa. The experiment presented here aims at analyzing the effects of sulfate on physiological indices, molecular levels, and its influencing mechanism. The results of our experiment showed that sulfate (at 40, 80, and 300 mg L(-1)) inhibited M. aeruginosa growth, increased both intracellular and extracellular toxin contents, and enhanced the mcyD transcript level. Sulfate inhibited the photosynthesis of M. aeruginosa, based on the decrease in pigment content and the down-regulation of photosynthesis-related genes after sulfate exposure. Furthermore, sulfate decreased the maximum electron transport rate, causing the cell to accumulate surplus electrons and form reactive oxygen species (ROS). Sulfate also increased the malondialdehyde (MDA) content, which showed that sulfate damaged the cytomembrane. This damage contributed to the release of intracellular toxin to the culture medium. Although sulfate increased superoxide dismutase (SOD) activities, expression of sod, and total antioxidant capacity in M. aeruginosa, it still overwhelmed the antioxidant system since the ROS level simultaneously increased, and finally caused oxidative stress. Our results indicate that sulfate has direct effects on M. aeruginosa, inhibits photosynthesis, causes oxidative stress, increases toxin production, and affects the related genes expression in M. aeruginosa.

  4. SULFATE REDUCTION IN GROUNDWATER: CHARACTERIZATION AND APPLICATIONS FOR REMEDIATION

    PubMed Central

    Miao, Z.; Brusseau, M. L.; Carroll, K. C.; Carreón-Diazconti, C.; Johnson, B.

    2013-01-01

    Sulfate is ubiquitous in groundwater, with both natural and anthropogenic sources. Sulfate reduction reactions play a significant role in mediating redox conditions and biogeochemical processes for subsurface systems. They also serve as the basis for innovative in-situ methods for groundwater remediation. An overview of sulfate reduction in subsurface environments is provided, along with a brief discussion of characterization methods and applications for addressing acid mine drainage. We then focus on two innovative, in-situ methods for remediating sulfate-contaminated groundwater, the use of zero-valent iron (ZVI) and the addition of electron-donor substrates. The advantages and limitations associated with the methods are discussed, with examples of prior applications. PMID:21947714

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

    PubMed

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

    2018-03-30

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

  6. Synthesis of the oligosaccharides related to branching sites of fucosylated chondroitin sulfates from sea cucumbers.

    PubMed

    Ustyuzhanina, Nadezhda E; Fomitskaya, Polina A; Gerbst, Alexey G; Dmitrenok, Andrey S; Nifantiev, Nikolay E

    2015-02-02

    Natural anionic polysaccharides fucosylated chondroitin sulfates (FCS) from sea cucumbers attract great attention nowadays due to their ability to influence various biological processes, such as blood coagulation, thrombosis, angiogenesis, inflammation, bacterial and viral adhesion. To determine pharmacophore fragments in FCS we have started systematic synthesis of oligosaccharides with well-defined structure related to various fragments of these polysaccharides. In this communication, the synthesis of non-sulfated and selectively O-sulfated di- and trisaccharides structurally related to branching sites of FCS is described. The target compounds are built up of propyl β-d-glucuronic acid residue bearing at O-3 α-l-fucosyl or α-l-fucosyl-(1→3)-α-l-fucosyl substituents. O-Sulfation pattern in the fucose units of the synthetic targets was selected according to the known to date holothurian FCS structures. Stereospecific α-glycoside bond formation was achieved using 2-O-benzyl-3,4-di-O-chloroacetyl-α-l-fucosyl trichloroacetimidate as a donor. Stereochemical outcome of the glycosylation was explained by the remote participation of the chloroacetyl groups with the formation of the stabilized glycosyl cations, which could be attacked by the glycosyl acceptor only from the α-side. The experimental results were in good agreement with the SCF/MP2 calculated energies of such participation. The synthesized oligosaccharides are regarded as model compounds for the determination of a structure-activity relationship in FCS.

  7. Synthesis of the Oligosaccharides Related to Branching Sites of Fucosylated Chondroitin Sulfates from Sea Cucumbers

    PubMed Central

    Ustyuzhanina, Nadezhda E.; Fomitskaya, Polina A.; Gerbst, Alexey G.; Dmitrenok, Andrey S.; Nifantiev, Nikolay E.

    2015-01-01

    Natural anionic polysaccharides fucosylated chondroitin sulfates (FCS) from sea cucumbers attract great attention nowadays due to their ability to influence various biological processes, such as blood coagulation, thrombosis, angiogenesis, inflammation, bacterial and viral adhesion. To determine pharmacophore fragments in FCS we have started systematic synthesis of oligosaccharides with well-defined structure related to various fragments of these polysaccharides. In this communication, the synthesis of non-sulfated and selectively O-sulfated di- and trisaccharides structurally related to branching sites of FCS is described. The target compounds are built up of propyl β-d-glucuronic acid residue bearing at O-3 α-l-fucosyl or α-l-fucosyl-(1→3)-α-l-fucosyl substituents. O-Sulfation pattern in the fucose units of the synthetic targets was selected according to the known to date holothurian FCS structures. Stereospecific α-glycoside bond formation was achieved using 2-O-benzyl-3,4-di-O-chloroacetyl-α-l-fucosyl trichloroacetimidate as a donor. Stereochemical outcome of the glycosylation was explained by the remote participation of the chloroacetyl groups with the formation of the stabilized glycosyl cations, which could be attacked by the glycosyl acceptor only from the α-side. The experimental results were in good agreement with the SCF/MP2 calculated energies of such participation. The synthesized oligosaccharides are regarded as model compounds for the determination of a structure-activity relationship in FCS. PMID:25648510

  8. Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

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

    Stübner, R.; Scheffler, L.; Kolkovsky, Vl., E-mail: kolkov@ifpan.edu.pl

    In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are E{sub C}-0.06 eV (E42) and E{sub C}-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier formore » electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH{sub 1AB} configuration, where one H atom is directly bound to carbon in the anti-bonding position.« less

  9. Donors, Acceptors, and Traps in AlGaN and AlGaN/GaN Epitaxial Layers

    DTIC Science & Technology

    2006-07-31

    the background. 3.3 Positron annihilation spectroscopy (PAS): acceptor-type defects Positrons injected into defect-free GaN are annihilated by electrons...electron concentration n, and the average Ga-vacancy VGa concentration deduced from positron annihilation spectroscopy . 0.09 3.47 3.46 - 3.45 •ŗ.47225...of this paper, are often investigated by deep level transient spectroscopy (DLTS), and the usual analysis of DLTS data is based on the assumption that

  10. Enrichment and characterization of sulfate reducing, naphthalene degrading microorganisms

    NASA Astrophysics Data System (ADS)

    Steffen, Kümmel; Florian-Alexander, Herbst; Márcia, Duarte; Dietmar, Pieper; Jana, Seifert; Bergen Martin, von; Hans-Hermann, Richnow; Carsten, Vogt

    2014-05-01

    Polycyclic aromatic hydrocarbons (PAH) are pollutants of great concern due to their potential toxicity, mutagenicity and carcinogenicity. PAH are widely distributed in the environment by accidental discharges during the transport, use and disposal of petroleum products, and during forest and grass fires. Caused by their hydrophobic nature, PAH basically accumulate in sediments from where they are slowly released into the groundwater. Although generally limited by the low water solubility of PAH, microbial degradation is one of the major mechanisms leading to the complete clean-up of PAH-contaminated sites. Whereas organisms and biochemical pathways responsible for the aerobic breakdown of PAH are well known, anaerobic PAH biodegradation is less understood; only a few anaerobic PAH degrading cultures have been described. We studied the anaerobic PAH degradation in a microcosm approach to enrich anaerobic PAH degraders. Anoxic groundwater and sediment samples were used as inoculum. Groundwater samples were purchased from the erstwhile gas works facility and a former wood impregnation site. In contrast, sources of sediment samples were a former coal refining area and an old fuel depot. Samples were incubated in anoxic mineral salt medium with naphthalene as sole carbon source and sulfate as terminal electron acceptor. Grown cultures were characterized by feeding with 13C-labeled naphthalene, 16S rRNA gene sequencing using an Illumina® approach, and functional proteome analyses. Finally, six enrichment cultures able to degrade naphthalene under anoxic conditions were established. First results point to a dominance of identified sequences affiliated to the freshwater sulfate-reducing strain N47, which is a known anaerobic naphthalene degrader, in four out of the six enrichments. In those enrichments, peptides related to the pathway of anoxic naphthalene degradation in N47 were abundant. Overall the data underlines the importance of Desulfobacteria for natural

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

    NASA Astrophysics Data System (ADS)

    Wang, Chen

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

  12. Improvement of photovoltaic performance by substituent effect of donor and acceptor structure of TPA-based dye-sensitized solar cells.

    PubMed

    Inostroza, Natalia; Mendizabal, Fernando; Arratia-Pérez, Ramiro; Orellana, Carlos; Linares-Flores, Cristian

    2016-01-01

    We report a computational study of a series of organic dyes built with triphenylamine (TPA) as an electron donor group. We designed a set of six dyes called (TPA-n, where n = 0-5). In order to enhance the electron-injection process, the electron-donor effect of some specific substituent was studied. Thus, we gave insights into the rational design of organic TPA-based chromophores for use in dye-sensitized solar cells (DSSCs). In addition, we report the HOMO, LUMO, the calculated excited state oxidized potential E(dye*)(eV) and the free energy change for electron-injection ΔGinject(eV), and the UV-visible absorption bands for TPA-n dyes by a time-dependent density functional theory (TDDFT) procedure at the B3LYP and CAM-B3LYP levels with solvent effect. The results demonstrate that the introduction of the electron-acceptor groups produces an intramolecular charge transfer showing a shift of the absorption wavelengths of TPA-n under studies. Graphical Abstract Several organic dyes TPA-n with different donors and acceptors are modeled. A strong conjugation acrros the donor and anchoring groips (TPA-n) bas been studied. Candidate TPA-3 shows a promising results.

  13. Vitamin C-sulfate inhibits mineralization in chondrocyte cultures: a caveat

    NASA Technical Reports Server (NTRS)

    Boskey, A. L.; Blank, R. D.; Doty, S. B.

    2001-01-01

    Differentiating chick limb-bud mesenchymal cell micro-mass cultures routinely mineralize in the presence of 10% fetal calf serum, antibiotics, 4 mM inorganic phosphate (or 2.5 mM beta-glycerophosphate), 0.3 mg/ml glutamine and either 25 microg/ml vitamin C or 5-12 microg/ml vitamin C-sulfate. The failure of these cultures to produce a mineralized matrix (assessed by electron microscopy, 45Ca uptake and Fourier transform infrared microscopy) led to the evaluation of each of these additives. We report here that the "stable" vitamin C-sulfate (ascorbic acid-2-sulfate) causes increased sulfate incorporation into the cartilage matrix. Furthermore, the release of sulfate from the vitamin C derivative appears to be responsible for the inhibition of mineral deposition, as demonstrated in cultures with equimolar amounts of vitamin C and sodium sulfate.

  14. Design principle for efficient charge separation at the donor-acceptor interface for high performance organic solar cell device

    NASA Astrophysics Data System (ADS)

    Nie, Wanyi; Gupta, Gautam; Crone, Brian; Wang, Hsing-Lin; Mohite, Aditya; MPA-11 Material synthesis and integrated device Team; MPA-chemistry Team

    2014-03-01

    The performance of donor (D) /acceptor (A) structure based organic electronic devices, such as solar cell, light emitting devices etc., relays on the charge transfer process at the interface dramatically. In organic solar cell, the photo-induced electron-hole pair is tightly bonded and will form a charge transfer (CT) state at the D/A interface after dissociation. There is a large chance for them to recombine through CT state and thus is a major loss that limit the overall performance. Here, we report three different strategies that allow us to completely suppress the exciplex (or charge transfer state) recombination between any D/A system. We observe that the photocurrent increases by 300% and the power conversion efficiency increases by 4-5 times simply by inserting a spacer layer in the form of an a) insulator b) Oliogomer or using a c) heavy atom at the donor-acceptor interface in a P3HT/C60 bilayer device. By using those different functional mono layers, we successfully suppressed the exciplex recombination in evidence of increased photocurrent and open circuit voltage. Moreover, these strategies are applicable universally to any donor-acceptor interface. And we demonstrated such strategies in a bulk-heterojunction device which improved the power conversion efficiency from 3.5% up to 4.6%.

  15. Energy Gradients Structure Microbial Communities Across Sediment Horizons in Deep Marine Sediments of the South China Sea

    PubMed Central

    Graw, Michael F.; D'Angelo, Grace; Borchers, Matthew; Thurber, Andrew R.; Johnson, Joel E.; Zhang, Chuanlun; Liu, Haodong; Colwell, Frederick S.

    2018-01-01

    The deep marine subsurface is a heterogeneous environment in which the assembly of microbial communities is thought to be controlled by a combination of organic matter deposition, electron acceptor availability, and sedimentology. However, the relative importance of these factors in structuring microbial communities in marine sediments remains unclear. The South China Sea (SCS) experiences significant variability in sedimentation across the basin and features discrete changes in sedimentology as a result of episodic deposition of turbidites and volcanic ashes within lithogenic clays and siliceous or calcareous ooze deposits throughout the basin's history. Deep subsurface microbial communities were recently sampled by the International Ocean Discovery Program (IODP) at three locations in the SCS with sedimentation rates of 5, 12, and 20 cm per thousand years. Here, we used Illumina sequencing of the 16S ribosomal RNA gene to characterize deep subsurface microbial communities from distinct sediment types at these sites. Communities across all sites were dominated by several poorly characterized taxa implicated in organic matter degradation, including Atribacteria, Dehalococcoidia, and Aerophobetes. Sulfate-reducing bacteria comprised only 4% of the community across sulfate-bearing sediments from multiple cores and did not change in abundance in sediments from the methanogenic zone at the site with the lowest sedimentation rate. Microbial communities were significantly structured by sediment age and the availability of sulfate as an electron acceptor in pore waters. However, microbial communities demonstrated no partitioning based on the sediment type they inhabited. These results indicate that microbial communities in the SCS are structured by the availability of electron donors and acceptors rather than sedimentological characteristics. PMID:29696012

  16. Enhancement in Open-Circuit Voltage in Organic Solar Cells by Using Ladder-Type Nonfullerene Acceptors

    DOE PAGES

    Cai, Zhengxu; Zhao, Donglin; Sharapov, Valerii; ...

    2018-03-28

    The open-circuit voltage (V oc) loss has always been a major factor in lowering power conversion efficiencies (PCEs) in bulk heterojunction organic photovoltaic cells (OPVs). A method to improve the V oc is indispensable to achieve high PCEs. Here in this paper, we investigated a series of perylene diimide-based ladder-type molecules as electron acceptors in nonfullerene OPVs. The D-A ladder-type structures described here lock our pi-systems into a planar structure and eliminate bond twisting associated with linear conjugated systems. This enlarges the interface energy gap (ΔE DA), extends electronic delocalization, and hence improves the V oc. More importantly, these devicesmore » showed an increase in V oc without compromising either the J sc or the FF. C5r exhibited a strong intermolecular interaction and a PCE value of 6.1%. Moreover, grazing-incident wide-angle X-ray scattering analysis and atomic force microscopy images suggested that our fused-ring acceptors showed a suitable domain size and uniform blend films, which were not affected by their rigid molecular structures.« less

  17. Enhancement in Open-Circuit Voltage in Organic Solar Cells by Using Ladder-Type Nonfullerene Acceptors.

    PubMed

    Cai, Zhengxu; Zhao, Donglin; Sharapov, Valerii; Awais, Mohammad A; Zhang, Na; Chen, Wei; Yu, Luping

    2018-04-25

    The open-circuit voltage ( V oc ) loss has always been a major factor in lowering power conversion efficiencies (PCEs) in bulk heterojunction organic photovoltaic cells (OPVs). A method to improve the V oc is indispensable to achieve high PCEs. In this paper, we investigated a series of perylene diimide-based ladder-type molecules as electron acceptors in nonfullerene OPVs. The D-A ladder-type structures described here lock our π-systems into a planar structure and eliminate bond twisting associated with linear conjugated systems. This enlarges the interface energy gap (Δ E DA ), extends electronic delocalization, and hence improves the V oc . More importantly, these devices showed an increase in V oc without compromising either the J sc or the FF. C5r exhibited a strong intermolecular interaction and a PCE value of 6.1%. Moreover, grazing-incident wide-angle X-ray scattering analysis and atomic force microscopy images suggested that our fused-ring acceptors showed a suitable domain size and uniform blend films, which were not affected by their rigid molecular structures.

  18. Enhancement in Open-Circuit Voltage in Organic Solar Cells by Using Ladder-Type Nonfullerene Acceptors

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

    Cai, Zhengxu; Zhao, Donglin; Sharapov, Valerii

    The open-circuit voltage (V oc) loss has always been a major factor in lowering power conversion efficiencies (PCEs) in bulk heterojunction organic photovoltaic cells (OPVs). A method to improve the V oc is indispensable to achieve high PCEs. Here in this paper, we investigated a series of perylene diimide-based ladder-type molecules as electron acceptors in nonfullerene OPVs. The D-A ladder-type structures described here lock our pi-systems into a planar structure and eliminate bond twisting associated with linear conjugated systems. This enlarges the interface energy gap (ΔE DA), extends electronic delocalization, and hence improves the V oc. More importantly, these devicesmore » showed an increase in V oc without compromising either the J sc or the FF. C5r exhibited a strong intermolecular interaction and a PCE value of 6.1%. Moreover, grazing-incident wide-angle X-ray scattering analysis and atomic force microscopy images suggested that our fused-ring acceptors showed a suitable domain size and uniform blend films, which were not affected by their rigid molecular structures.« less

  19. An Inexpensive Co-Intercalated Layered Double Hydroxide Composite with Electron Donor-Acceptor Character for Photoelectrochemical Water Splitting

    PubMed Central

    Zheng, Shufang; Lu, Jun; Yan, Dongpeng; Qin, Yumei; Li, Hailong; Evans, David G.; Duan, Xue

    2015-01-01

    In this paper, the inexpensive 4,4-diaminostilbene-2,2-disulfonate (DAS) and 4,4-dinitro-stilbene-2,2- disulfonate (DNS) anions with arbitrary molar ratios were successfully co-intercalated into Zn2Al-layered double hydroxides (LDHs). The DAS(50%)-DNS/LDHs composite exhibited the broad UV-visible light absorption and fluorescence quenching, which was a direct indication of photo-induced electron transfer (PET) process between the intercalated DAS (donor) and DNS (acceptor) anions. This was confirmed by the matched HOMO/LUMO energy levels alignment of the intercalated DAS and DNS anions, which was also compatible for water splitting. The DAS(50%)-DNS/LDHs composite was fabricated as the photoanode and Pt as the cathode. Under the UV-visible light illumination, the enhanced photo-generated current (4.67 mA/cm2 at 0.8 V vs. SCE) was generated in the external circuit, and the photoelectrochemical water split was realized. Furthermore, this photoelectrochemical water splitting performance had excellent crystalline, electrochemical and optical stability. Therefore, this novel inorganic/organic hybrid photoanode exhibited potential application prospect in photoelectrochemical water splitting. PMID:26174201

  20. Design and Construction of Experiment for Direct Electron Irradiation of Uranyl Sulfate Solution: Bubble Formation and Thermal Hydraulics Studies

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

    Chemerisov, Sergey; Gromov, Roman; Makarashvili, Vakho

    Argonne is assisting SHINE Medical Technologies in developing SHINE, a system for producing fission-product 99Mo using a D/T-accelerator to produce fission in a non-critical target solution of aqueous uranyl sulfate. We have developed an experimental setup for studying thermal-hydraulics and bubble formation in the uranyl sulfate solution to simulate conditions expected in the SHINE target solution during irradiation. A direct electron beam from the linac accelerator will be used to irradiate a 20 L solution (sector of the solution vessel). Because the solution will undergo radiolytic decomposition, we will be able to study bubble formation and dynamics and effects ofmore » convection and temperature on bubble behavior. These experiments will serve as a verification/ validation tool for the thermal-hydraulic model. Utilization of the direct electron beam for irradiation allows homogeneous heating of a large solution volume and simplifies observation of the bubble dynamics simultaneously with thermal-hydraulic data collection, which will complement data collected during operation of the miniSHINE experiment. Irradiation will be conducted using a 30-40 MeV electron beam from the high-power linac accelerator. The total electron-beam power will be 20 kW, which will yield a power density on the order of 1 kW/L. The solution volume will be cooled on the front and back surfaces and central tube to mimic the geometry of the proposed SHINE solution vessel. Also, multiple thermocouples will be inserted into the solution vessel to map thermal profiles. The experimental design is now complete, and installation and testing are in progress.« less

  1. A Bacterial Multidomain NAD-Independent d-Lactate Dehydrogenase Utilizes Flavin Adenine Dinucleotide and Fe-S Clusters as Cofactors and Quinone as an Electron Acceptor for d-Lactate Oxidization

    PubMed Central

    Jiang, Tianyi; Guo, Xiaoting; Yan, Jinxin; Zhang, Yingxin; Wang, Yujiao; Zhang, Manman; Sheng, Binbin; Ma, Cuiqing; Xu, Ping

    2017-01-01

    ABSTRACT Bacterial membrane-associated NAD-independent d-lactate dehydrogenase (Fe-S d-iLDH) oxidizes d-lactate into pyruvate. A sequence analysis of the enzyme reveals that it contains an Fe-S oxidoreductase domain in addition to a flavin adenine dinucleotide (FAD)-containing dehydrogenase domain, which differs from other typical d-iLDHs. Fe-S d-iLDH from Pseudomonas putida KT2440 was purified as a His-tagged protein and characterized in detail. This monomeric enzyme exhibited activities with l-lactate and several d-2-hydroxyacids. Quinone was shown to be the preferred electron acceptor of the enzyme. The two domains of the enzyme were then heterologously expressed and purified separately. The Fe-S cluster-binding motifs predicted by sequence alignment were preliminarily verified by site-directed mutagenesis of the Fe-S oxidoreductase domain. The FAD-containing dehydrogenase domain retained 2-hydroxyacid-oxidizing activity, although it decreased compared to the full Fe-S d-iLDH. Compared to the intact enzyme, the FAD-containing dehydrogenase domain showed increased catalytic efficiency with cytochrome c as the electron acceptor, but it completely lost the ability to use coenzyme Q10. Additionally, the FAD-containing dehydrogenase domain was no longer associated with the cell membrane, and it could not support the utilization of d-lactate as a carbon source. Based on the results obtained, we conclude that the Fe-S oxidoreductase domain functions as an electron transfer component to facilitate the utilization of quinone as an electron acceptor by Fe-S d-iLDH, and it helps the enzyme associate with the cell membrane. These functions make the Fe-S oxidoreductase domain crucial for the in vivo d-lactate utilization function of Fe-S d-iLDH. IMPORTANCE Lactate metabolism plays versatile roles in most domains of life. Lactate utilization processes depend on certain enzymes to oxidize lactate to pyruvate. In recent years, novel bacterial lactate-oxidizing enzymes have been

  2. Halocarbons as hydrogen bond acceptors: a spectroscopic study of haloethylbenzenes (PhCH2CH2X, X = F, Cl, Br) and their hydrate clusters.

    PubMed

    Robertson, Patrick A; Villani, Luigi; Dissanayake, Uresha L M; Duncan, Luke F; Abbott, Belinda M; Wilson, David J D; Robertson, Evan G

    2018-03-28

    The electronic spectra of 2-bromoethylbenzene and its chloro and fluoro analogues have been recorded by resonant two-photon ionisation (R2PI) spectroscopy. Anti and gauche conformers have been assigned by rotational band contour analysis and IR-UV ion depletion spectroscopy in the CH region. Hydrate clusters of the anti conformers have also been observed, allowing the role of halocarbons as hydrogen bond acceptors to be examined in this context. The donor OH stretch of water bound to chlorine is red-shifted by 36 cm -1 , or 39 cm -1 in the case of bromine. Although classed as weak H-bond acceptors, halocarbons are favourable acceptor sites compared to π systems. Fluorine stands out as the weakest H-bond acceptor amongst the halogens. Chlorine and bromine are also weak H-bond acceptors, but allow for more geometric lability, facilitating complimentary secondary interactions within the host molecule. Ab initio and DFT quantum chemical calculations, both harmonic and anharmonic, aid the structural assignments and analysis.

  3. Simultaneous quantification of cholesterol sulfate, androgen sulfates, and progestagen sulfates in human serum by LC-MS/MS.

    PubMed

    Sánchez-Guijo, Alberto; Oji, Vinzenz; Hartmann, Michaela F; Traupe, Heiko; Wudy, Stefan A

    2015-09-01

    Steroids are primarily present in human fluids in their sulfated forms. Profiling of these compounds is important from both diagnostic and physiological points of view. Here, we present a novel method for the quantification of 11 intact steroid sulfates in human serum by LC-MS/MS. The compounds analyzed in our method, some of which are quantified for the first time in blood, include cholesterol sulfate, pregnenolone sulfate, 17-hydroxy-pregnenolone sulfate, 16-α-hydroxy-dehydroepiandrosterone sulfate, dehydroepiandrosterone sulfate, androstenediol sulfate, androsterone sulfate, epiandrosterone sulfate, testosterone sulfate, epitestosterone sulfate, and dihydrotestosterone sulfate. The assay was conceived to quantify sulfated steroids in a broad range of concentrations, requiring only 300 μl of serum. The method has been validated and its performance was studied at three quality controls, selected for each compound according to its physiological concentration. The assay showed good linearity (R(2) > 0.99) and recovery for all the compounds, with limits of quantification ranging between 1 and 80 ng/ml. Averaged intra-day and between-day precisions (coefficient of variation) and accuracies (relative errors) were below 10%. The method has been successfully applied to study the sulfated steroidome in diseases such as steroid sulfatase deficiency, proving its diagnostic value. This is, to our best knowledge, the most comprehensive method available for the quantification of sulfated steroids in human blood. Copyright © 2015 by the American Society for Biochemistry and Molecular Biology, Inc.

  4. Design of a New Fused-Ring Electron Acceptor with Excellent Compatibility to Wide-Bandgap Polymer Donors for High-Performance Organic Photovoltaics.

    PubMed

    Liu, Wenrui; Zhang, Jianyun; Zhou, Zichun; Zhang, Dongyang; Zhang, Yuan; Xu, Shengjie; Zhu, Xiaozhang

    2018-05-16

    Fused-ring electron acceptors (FREAs) have recently received intensive attention. Besides the continuing development of new FREAs, the demand for FREAs featuring good compatibility to donor materials is becoming more and more urgent, which is highly desirable for screening donor materials and achieving new breakthroughs. In this work, a new FREA is developed, ZITI, featuring an octacyclic dithienocyclopentaindenoindene central core. The core is designed by linking 2,7-dithienyl substituents and indenoindene with small methylene groups, in which the indeno[1,2-b]thiophene-2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile part provides a large and unoccupied π-surface. Most notably, ZITI possesses an excellent compatibility with commercially available polymer donors, delivering very high power conversion efficiencies of over 13%. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Formation of tellurium nanocrystals during anaerobic growth of bacteria that use Te oxyanions as respiratory electron acceptors

    USGS Publications Warehouse

    Baesman, S.M.; Bullen, T.D.; Dewald, J.; Zhang, Dongxiao; Curran, S.; Islam, F.S.; Beveridge, T.J.; Oremland, R.S.

    2007-01-01

    Certain toxic elements support the metabolism of diverse prokaryotes by serving as respiratory electron acceptors for growth. Here, we demonstrate that two anaerobes previously shown to be capable of respiring oxyanions of selenium also achieve growth by reduction of either tellurate [Te(VI)] or tellurite [Te(IV)] to elemental tellurium [Te(0)]. This reduction achieves a sizeable stable-Te-isotopic fractionation (isotopic enrichment factor [??] = -0.4 to -1.0 per ml per atomic mass unit) and results in the formation of unique crystalline Te(0) nanoarchitectures as end products. The Te(0) crystals occur internally within but mainly externally from the cells, and each microorganism forms a distinctly different structure. Those formed by Bacillus selenitireducens initially are nanorods (???10-nm diameter by 200-nm length), which cluster together, forming larger (???1,000-nm) rosettes composed of numerous individual shards (???100-nm width by 1,000-nm length). In contrast, Sulfurospirillium barnesii forms extremely small, irregularly shaped nanospheres (diameter < 50 nm) that coalesce into larger composite aggregates. Energy-dispersive X-ray spectroscopy and selected area electron diffraction indicate that both biominerals are composed entirely of Te and are crystalline, while Raman spectroscopy confirms that they are in the elemental state. These Te biominerals have specific spectral signatures (UV-visible light, Raman) that also provide clues to their internal structures. The use of microorganisms to generate Te nanomaterials may be an alternative for bench-scale syntheses. Additionally, they may also generate products with unique properties unattainable by conventional physical/chemical methods. Copyright ?? 2007, American Society for Microbiology. All Rights Reserved.

  6. Chlorinated Electron Acceptor Abundance Drives Selection of Dehalococcoides mccartyi (D. mccartyi) Strains in Dechlorinating Enrichment Cultures and Groundwater Environments

    PubMed Central

    Pérez-de-Mora, Alfredo; Lacourt, Anna; McMaster, Michaye L.; Liang, Xiaoming; Dworatzek, Sandra M.; Edwards, Elizabeth A.

    2018-01-01

    Dehalococcoides mccartyi (D. mccartyi) strains differ primarily from one another by the number and identity of the reductive dehalogenase homologous catalytic subunit A (rdhA) genes within their respective genomes. While multiple rdhA genes have been sequenced, the activity of the corresponding proteins has been identified in only a few cases. Examples include the enzymes whose substrates are groundwater contaminants such as trichloroethene (TCE), cis-dichloroethene (cDCE) and vinyl chloride (VC). The associated rdhA genes, namely tceA, bvcA, and vcrA, along with the D. mccartyi 16S rRNA gene are often used as biomarkers of growth in field samples. In this study, we monitored an additional 12 uncharacterized rdhA sequences identified in the metagenome in the mixed D. mccartyi-containing culture KB-1 to monitor population shifts in more detail. Quantitative PCR (qPCR) assays were developed for 15 D. mccartyi rdhA genes and used to measure population diversity in 11 different sub-cultures of KB-1, each enriched on different chlorinated ethenes and ethanes. The proportion of rdhA gene copies relative to D. mccartyi 16S rRNA gene copies revealed the presence of multiple distinct D. mccartyi strains in each culture, many more than the two strains inferred from 16S rRNA analysis. The specific electron acceptor amended to each culture had a major influence on the distribution of D. mccartyi strains and their associated rdhA genes. We also surveyed the abundance of rdhA genes in samples from two bioaugmented field sites (Canada and United Kingdom). Growth of the dominant D. mccartyi strain in KB-1 was detected at the United Kingdom site. At both field sites, the measurement of relative rdhA abundances revealed D. mccartyi population shifts over time as dechlorination progressed from TCE through cDCE to VC and ethene. These shifts indicate a selective pressure of the most abundant chlorinated electron acceptor, as was also observed in lab cultures. These results also

  7. Spectroscopic studies of multiple charge transfer complexes of p-toluidine with π-acceptor picric acid in different polar solvents

    NASA Astrophysics Data System (ADS)

    Singh, Neeti; Ahmad, Afaq

    2010-04-01

    The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in less polar solvent is high. The stoichiometry of the complex was found to be 1: 1 ratio by straight line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant ( K CT), molar extinction coefficient (ɛCT), standard free energy (Δ G°), oscillator strength ( f), transition dipole moment (μEN), resonance energy ( R N) and ionization potential ( I D). The results indicate that the formation constant ( K CT) for the complex were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used.

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

    PubMed

    Fisher, A A; de Silva, V

    1986-01-01

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

  9. On chirality transfer in electron donor-acceptor complexes. A prediction for the sulfinimine···BF3 system.

    PubMed

    Rode, Joanna E; Dobrowolski, Jan Cz

    2012-01-01

    Stabilization energies of the electron donor-acceptor sulfinimine···BF(3) complexes calculated at either the B3LYP/aug-cc-pVTZ or the MP2/aug-cc-pVTZ level do not allow to judge, whether the N- or O-atom in sulfinimine is stronger electron-donor to BF(3) . The problem seems to be solvable because chirality transfer phenomenon between chiral sulfinimine and achiral BF(3) is expected to be vibrational circular dichroism (VCD) active. Moreover, the bands associated with the achiral BF(3) molecule are predicted to be the most intense in the entire spectrum. However, the VCD band robustness analyses show that most of the chirality transfer modes of BF(3) are unreliable. Conversely, variation of VCD intensity with change of intermolecular distance, angle, and selected dihedrals between the complex partners shows that to establish the robustness of chirality transfer mode. It is also necessary to determine the influence of the potential energy surface (PES) shape on the VCD intensity. At the moment, there is still no universal criterion for the chirality transfer mode robustness and the conclusions formulated based on one system cannot be directly transferred even to a quite similar one. However, it is certain that more attention should be focused on relation of PES shape and the VCD mode robustness problem. Copyright © 2011 Wiley Periodicals, Inc.

  10. Simultaneous quantification of cholesterol sulfate, androgen sulfates, and progestagen sulfates in human serum by LC-MS/MS[S

    PubMed Central

    Sánchez-Guijo, Alberto; Oji, Vinzenz; Hartmann, Michaela F.; Traupe, Heiko; Wudy, Stefan A.

    2015-01-01

    Steroids are primarily present in human fluids in their sulfated forms. Profiling of these compounds is important from both diagnostic and physiological points of view. Here, we present a novel method for the quantification of 11 intact steroid sulfates in human serum by LC-MS/MS. The compounds analyzed in our method, some of which are quantified for the first time in blood, include cholesterol sulfate, pregnenolone sulfate, 17-hydroxy-pregnenolone sulfate, 16-α-hydroxy-dehydroepiandrosterone sulfate, dehydroepiandrosterone sulfate, androstenediol sulfate, androsterone sulfate, epiandrosterone sulfate, testosterone sulfate, epitestosterone sulfate, and dihydrotestosterone sulfate. The assay was conceived to quantify sulfated steroids in a broad range of concentrations, requiring only 300 μl of serum. The method has been validated and its performance was studied at three quality controls, selected for each compound according to its physiological concentration. The assay showed good linearity (R2 > 0.99) and recovery for all the compounds, with limits of quantification ranging between 1 and 80 ng/ml. Averaged intra-day and between-day precisions (coefficient of variation) and accuracies (relative errors) were below 10%. The method has been successfully applied to study the sulfated steroidome in diseases such as steroid sulfatase deficiency, proving its diagnostic value. This is, to our best knowledge, the most comprehensive method available for the quantification of sulfated steroids in human blood. PMID:26239050

  11. Studies of Luminescence Performance on Carbazole Donor and Quinoline Acceptor Based Conjugated Polymer.

    PubMed

    Upadhyay, Anjali; S, Karpagam

    2016-03-01

    We report on the synthesis of conjugated polymer (CV-QP) containing carbazole (donor) and quinoline (acceptor) using Wittig methodology. The structural, optical and thermal properties of the polymer were investigated by FT-IR, NMR, GPC, UV, PL, cyclic voltammetry, atomic force microscopy (AFM) and thermogravimetric analysis (TGA). The polymer exhibits thermal stability upto 200 °C and shows good solubility in common organic solvents. The polymer has optical absorption band in a thin film at 360 nm and emission band formed at 473 nm. The optical energy band gap was found to be 2.69 eV as calculated from the onset absorption edge. Fluorescence quenching of the polymer CV-QP was found by using DMA (electron donor) and DMTP (electron acceptor). AFM image indicated that triangular shaped particles were observed and the particle size was found as 1.1 μm. The electrochemical studies of CV-QP reveal that, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the CV-QP are 6.35 and 3.70 eV, which indicated that the polymers are expected to provide charge transporting properties for the development of polymer light-emitting diodes (PLEDs).

  12. Synthesis and characterization of donor-acceptor copolymers carrying triphenylamine units for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Neumann, Katharina; Thelakkat, Mukundan

    2012-09-01

    The synthesis and analysis of solution processable polymers for organic solar cells is crucial for innovative solar cell technologies such as printing processes. In the field of donor materials for photovoltaic applications, polymers based on tetraphenylamine (TPA) are well known hole conducting materials. Here, we synthesized two conjugated TPA containing copolymers via Suzuki polycondensation. We investigated the tuning of the energy levels of the TPA based polymers by two different concepts. Firstly, we introduced an acceptor unit in the side chain. The main-chain of this copolymer was built from TPA units. The resulting copolymer 2-(4-((4'-((4-(2-ethylhexyloxy)phenyl)(paratolyl) amino)biphenyl-4-yl)(para-tolyl)amino)benzylidene) malononitrile P1 showed a broader absorption up to 550 nm. Secondly, we used a donor-acceptor concept by synthesizing a copolymer with alternating electron donating TPA and electron withdrawing Thieno[3,4-b]thiophene ester units. Consequently, the absorption maximum in the copolymer octyl-6-(4-((4-(2-ethylhexyloxy)phenyl)(p-tolyl)amino)phenyl)-4-methylthieno[3,4-b]thiophene-2-carboxylate P2 was red shifted to 580 nm. All three polymers showed high thermal stability. By UV-vis and Cyclic voltammetry measurements the optical and electrochemical properties of the polymers were analyzed.

  13. Sulfate-reducing anaerobic ammonium oxidation as a potential treatment method for high nitrogen-content wastewater.

    PubMed

    Rikmann, Ergo; Zekker, Ivar; Tomingas, Martin; Tenno, Taavo; Menert, Anne; Loorits, Liis; Tenno, Toomas

    2012-07-01

    After sulfate-reducing ammonium oxidation (SRAO) was first assumed in 2001, several works have been published describing this process in laboratory-scale bioreactors or occurring in the nature. In this paper, the SRAO process was performed using reject water as a substrate for microorganisms and a source of NH(4) (+), with SO(4) (2-) being added as an electron acceptor. At a moderate temperature of 20°C in a moving bed biofilm reactor (MBBR) sulfate reduction along with ammonium oxidation were established. In an upflow anaerobic sludge blanket reactor (UASBR) the SRAO process took place at 36°C. Average volumetric TN removal rates of 0.03 kg-N/m³/day in the MBBR and 0.04 kg-N/m³/day in the UASBR were achieved, with long-term moderate average removal efficiencies, respectively. Uncultured bacteria clone P4 and uncultured planctomycete clone Amx-PAn30 were detected from the biofilm of the MBBR, from sludge of the UASBR uncultured Verrucomicrobiales bacterium clone De2102 and Uncultured bacterium clone ATB-KS-1929 were found also. The stoichiometrical ratio of NH(4) (+) removal was significantly higher than could be expected from the extent of SO(4) (2-) reduction. This phenomenon can primarily be attributed to complex interactions between nitrogen and sulfur compounds and organic matter present in the wastewater. The high NH(4) (+) removal ratio can be attributed to sulfur-utilizing denitrification/denitritation providing the evidence that SRAO is occurring independently and is not a result of sulfate reduction and anammox. HCO(3) (-) concentrations exceeding 1,000 mg/l were found to have an inhibiting effect on the SRAO process. Small amounts of hydrazine were naturally present in the reaction medium, indicating occurrence of the anammox process. Injections of anammox intermediates, hydrazine and hydroxylamine, had a positive effect on SRAO process performance, particularly in the case of the UASBR.

  14. Design and Synthesis of Novel Block Copolymers for Efficient Opto-Electronic Applications

    NASA Technical Reports Server (NTRS)

    Sun, Sam-Shajing; Fan, Zhen; Wang, Yiqing; Taft, Charles; Haliburton, James; Maaref, Shahin

    2002-01-01

    It has been predicted that nano-phase separated block copolymer systems containing electron rich donor blocks and electron deficient acceptor blocks may facilitate the charge carrier separation and migration in organic photovoltaic devices due to improved morphology in comparison to polymer blend system. This paper presents preliminary data describing the design and synthesis of a novel Donor-Bridge-Acceptor (D-B-A) block copolymer system for potential high efficient organic optoelectronic applications. Specifically, the donor block contains an electron donating alkyloxy derivatized polyphenylenevinylene (PPV), the acceptor block contains an electron withdrawing alkyl-sulfone derivatized polyphenylenevinylene (PPV), and the bridge block contains an electronically neutral non-conjugated aliphatic hydrocarbon chain. The key synthetic strategy includes the synthesis of each individual block first, then couple the blocks together. While the donor block stabilizes and facilitates the transport of the holes, the acceptor block stabilizes and facilitates the transport of the electrons, the bridge block is designed to hinder the probability of electron-hole recombination. Thus, improved charge separation and stability are expected with this system. In addition, charge migration toward electrodes may also be facilitated due to the potential nano-phase separated and highly ordered block copolymer ultra-structure.

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

    PubMed

    Klaus, H; Labbok, M; Barker, D

    1988-01-01

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

  16. 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.

  17. Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review

    PubMed Central

    Buckel, Wolfgang; Thauer, Rudolf K.

    2018-01-01

    , NfnB with bound FAD, or HdrA harboring FAD. All these flavoproteins are cytoplasmic except for the membrane-associated protein FixABCX. The organisms—in which they have been found—are strictly anaerobic microorganisms except for the aerobe A. vinelandii. The electron-bifurcating complexes are involved in a variety of processes such as butyric acid fermentation, methanogenesis, acetogenesis, anaerobic lactate oxidation, dissimilatory sulfate reduction, anaerobic- dearomatization, nitrogen fixation, and CO2 fixation. They contribute to energy conservation via the energy-converting ferredoxin: NAD+ reductase complex Rnf or the energy-converting ferredoxin-dependent hydrogenase complex Ech. This Review describes how this mechanism was discovered. PMID:29593673

  18. Monitoring structural transformation of hydroxy-sulphate green rust in the presence of sulphate reducing bacteria

    NASA Astrophysics Data System (ADS)

    Abdelmoula, M.; Zegeye, A.; Jorand, F.; Carteret, C.

    2006-01-01

    The activities of bacterial consortia enable organisms to maximize their metabolic capabilities. This article assesses the synergetic relationship between iron reducing bacteria (IRB), Shewanella putrefaciens and sulphate reducing bacteria (SRB) Desulfovibrio alaskensis. Thus, the aim of this study was first to form a biogenic hydroxy-sulpahte green rust GR2( {text{SO}}_{{text{4}}} ^{{2 - }} ) through the bioreduction of lepidocrocite by S. putrefaciens and secondly to investigate if sulfate anions intercalated in the biogenic GR2( {text{SO}}_{{text{4}}} ^{{2 - }} ) could serve as final electron acceptor for a sulfate reducing bacterium, D. alaskensis. The results indicate that the IRB lead to the formation of GR2( {text{SO}}_{{text{4}}} ^{{2 - }} ) and this mineral serve as an electron acceptor for SRB. GR2( {text{SO}}_{{text{4}}} ^{{2 - }} ) precipitation and its transformation was demonstrated by using X-ray diffraction (DRX), Mössbauer spectroscopy (TMS) and transmission electron spectroscopy (TEM). These observations point out the possible acceleration of steel corrosion in marine environment in presence of IRB/SRB consortia.

  19. Process of negative-muon-induced formation of an ionized acceptor center ({sub μ}A){sup –} in crystals with the diamond structure

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

    Belousov, Yu. M., E-mail: theorphys@phystech.edu

    The formation of an ionized acceptor center by a negative muon in crystals with the diamond structure is considered. The negative muon entering a target is captured by a nucleus, forming a muonic atom {sub μ}A coupled to a lattice. The appearing radiation-induced defect has a significant electric dipole moment because of the violation of the local symmetry of the lattice and changes the phonon spectrum of the crystal. The ionized acceptor center is formed owing to the capture of an electron interacting with the electric dipole moment of the defect and with the radiation of a deformation-induced local-mode phonon.more » Upper and lower bounds of the formation rate of the ionized acceptor center in diamond, silicon, and germanium crystals are estimated. It is shown that the kinetics of the formation of the acceptor center should be taken into account when processing μSR experimental data.« less

  20. The surface properties of Shewanella putrefaciens 200 and S. oneidensis MR-1: the effect of pH and terminal electron acceptors.

    PubMed

    Furukawa, Yoko; Dale, Jason R

    2013-04-08

    We investigated the surface characteristics of two strains of Shewanella sp., S. oneidensis MR-1 and S. putrefaciens 200, that were grown under aerobic conditions as well as under anaerobic conditions with trimethylamine oxide (TMAO) as the electron acceptor. The investigation focused on the experimental determination of electrophoretic mobility (EPM) under a range of pH and ionic strength, as well as by subsequent modeling in which Shewanella cells were considered to be soft particles with water- and ion-permeable outermost layers. The soft layer of p200 is significantly more highly charged (i.e., more negative) than that of MR-1. The effect of electron acceptor on the soft particle characteristics of Shewanella sp. is complex. The fixed charge density, which is a measure of the deionized and deprotonated functional groups in the soft layer polymers, is slightly greater (i.e., more negative) for aerobically grown p200 than for p200 grown with TMAO. On the other hand, the fixed charge density of aerobically grown MR1 is slightly less than that of p200 grown with TMAO. The effect of pH on the soft particle characteristics is also complex, and does not exhibit a clear pH-dependent trend. The Shewanella surface characteristics were attributed to the nature of the outermost soft layer, the extracellular polymeric substances (EPS) in case of p200 and lypopolysaccharides (LPS) in case of MR1 which generally lacks EPS. The growth conditions (i.e., aerobic vs. anaerobic TMAO) have an influence on the soft layer characteristics of Shewanella sp. cells. Meanwhile, the clear pH dependency of the mechanical and morphological characteristics of EPS and LPS layers, observed in previous studies through atomic force microscopy, adhesion tests and spectroscopies, cannot be corroborated by the electrohydrodynamics-based soft particle characteristics which does not exhibited a clear pH dependency in this study. While the electrohydrodynamics-based soft-particle model is a useful tool

  1. Optical orientation of electrons in compensated semiconductors

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

    Kokurin, I. A., E-mail: kokorinia@math.mrsu.ru; Petrov, P. V.; Averkiev, N. S.

    2013-09-15

    The theory of the optical orientation of charge carriers in compensated III-V semiconductors and quantum wells for the case where electrons are excited to the conduction band from Mn-charged acceptor states is presented. It is shown that, in GaAs/AlGaAs quantum wells, the degree of the spin orientation of conduction-band electrons in this excitation scheme can be as high as 85%. This spin-orientation enhancement results from an increase in the heavy-hole contribution to the acceptor state in the vicinity of the defect center rather than from level splitting caused by quantum confinement. It is shown that the degree of circular polarizationmore » of the photoluminescence emitted upon the recombination of electrons thermalized at the bottom of the band with holes occupying the acceptor ground state in a quantum well can exceed 70%.« less

  2. Iron Reduction and Carbonate Precipitation by Shewanella oneidensis

    NASA Astrophysics Data System (ADS)

    Zeng, Z.; Tice, M. M.

    2011-12-01

    This study is to contribute to better understanding of how Archean microbes induced carbonate diagenesis in mats and stromatolites. Previous studies showed sulfate reduction, a common promoter of carbonate precipitation in modern mats[1], is likely to have been less effective in Archean mats in marine fluids lower in sulfate[2]. Alternatively, iron reduction produces far more alkalinity per unit carbon respired than sulfate reduction. Therefore, we hypothesize iron reduction can promote much more carbonate precipitation than sulfate reduction. Our study might also have some relevance to banded iron formation on which microbial iron reduction played a potential role[3]. To test our hypothesis, Shewanella oneidensis MR-1, a dissimilatory iron reducing bacterium will be cultured anaerobically (79%N2, 20%CO2 and 1%H2) in basal medium to trigger iron reduction. Lactate will be used as electron donor, and the electron acceptor will be fresh ferrihydrite. Culture medium will be added with various metal ions, such as Ca2+ and Mg2+, to obtain potential carbonate precipitate. Escherichia coli (with fumarate added as an electron acceptor) will be used to provide a comparison to live but non-iron- reduction cells. After 20 days incubation, precipitate will be collected, washed and identified by X-ray diffraction (XRD). Besides, iron reduction rate (ferrozine assay)[4], PH and amount of precipitate (carbonate and oxidize fractions)[5] will be measured over time to well understand how S. oneidensis drives carbonate precipitation.

  3. Assessing the High Temperature, High Pressure Subsurface for Anaerobic Methane Oxidation

    NASA Astrophysics Data System (ADS)

    Harris, R. L.; Bartlett, D.; Byrnes, A. W.; Walsh, K. M.; Lau, C. Y. M.; Onstott, T. C.

    2017-12-01

    The anaerobic oxidation of methane (AOM) is an important sink in the global methane (CH4) budget. ANMEs are known to oxidize CH4 either independently or in consortia with bacteria, coupling the reduction of electron acceptors such as, SO42-, NO2-, NO3-, Mn4+, or Fe3+. To further constrain the contribution of AOM to the global CH4 budget, it is important to assess unexplored environments where AOM is thermodynamically possible such as the high pressure, high temperature deep biosphere. Provided plausible electron acceptor availability, increased temperature and pCH4 yield favorable Gibbs free energies for AOM reactions and the production of ATP (Fig. 1). To date, only sulfate-dependent AOM metabolism has been documented under high temperature conditions (50-72˚C), and AOM has not been assessed above 10.1 MPa. Given that ANMEs share close phylogenetic and metabolic heritage with methanogens and that the most heat-tolerant microorganism known is a barophilic methanogen, there possibly exist thermophilic ANMEs. Here we describe preliminary results from high pressure, high temperature stable isotope tracer incubation experiments on deep biosphere samples. Deep sub-seafloor sediments collected by IODP 370 from the Nankai Trough (257 - 865 m below seafloor) and deep fracture fluid from South Africa (1339 m below land surface) were incubated anaerobically in hydrostatic pressure vessels at 40 MPa in simulated in situ temperatures (40˚ - 80˚C). Sediments and fracture fluid were incubated in sulfate-free artificial seawater, a 2:98 13CH4:N2 headspace, and treated with one of the potential electron acceptors listed above in addition to kill and endogenous activity (i.e. no added electron acceptor) controls. Stable isotope analysis of dissolved inorganic carbon (DIC) suggests that AOM occurred within 60 days of incubation for all investigated electron acceptors and temperatures except 50˚C. Sulfate-dependent AOM rates are consistent with those previously reported in the

  4. Contorted Organic Semiconductors for Molecular Electronics

    NASA Astrophysics Data System (ADS)

    Zhong, Yu

    This thesis focuses on the synthesis, properties and applications of two types of contorted organic molecules: contorted molecular ribbons and conjugated corrals. We utilized the power of reaction chemistry to writing information into conjugated molecules with contorted structures and studied "structure-property" relationships. The unique properties of the molecules were expressed in electronic and optoelectronic devices such as field-effect transistors, solar cells, photodetectors, etc. In Chapter 2, I describe the design and synthesis of a new graphene ribbon architecture that consists of perylenediimide (PDI) subunits fused together by ethylene bridges. We created a prototype series of oligomers consisting of the dimer, trimer, and tetramer. The steric congestion at the fusion point between the PDI units creates helical junctions, and longer oligomers form helical ribbons. Thin films of these oligomers form the active layer in n-type field effect transistors. UV-vis spectroscopy reveals the emergence of an intense long-wavelength transition in the tetramer. From DFT calculations, we find that the HOMO-2 to LUMO transition is isoenergetic with the HOMO to LUMO transition in the tetramer. We probe these transitions directly using femtosecond transient absorption spectroscopy. The HOMO-2 to LUMO transition electronically connects the PDI subunits with the ethylene bridges, and its energy depends on the length of the oligomer. In Chapter 3, I describe an efficiency of 6.1% for a solution processed non-fullerene solar cell using a helical PDI dimer as the electron acceptor. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces, indicating that charge carriers are created from photogenerated excitons in both the electron donor and acceptor phases. Light-intensity-dependent current?voltage measurements suggested different recombination rates under short-circuit and open-circuit conditions. In

  5. Reduced Sulfation of Chondroitin Sulfate but Not Heparan Sulfate in Kidneys of Diabetic db/db Mice

    PubMed Central

    Reine, Trine M.; Grøndahl, Frøy; Jenssen, Trond G.; Hadler-Olsen, Elin; Prydz, Kristian

    2013-01-01

    Heparan sulfate proteoglycans are hypothesized to contribute to the filtration barrier in kidney glomeruli and the glycocalyx of endothelial cells. To investigate potential changes in proteoglycans in diabetic kidney, we isolated glycosaminoglycans from kidney cortex from healthy db/+ and diabetic db/db mice. Disaccharide analysis of chondroitin sulfate revealed a significant decrease in the 4-O-sulfated disaccharides (D0a4) from 65% to 40%, whereas 6-O-sulfated disaccharides (D0a6) were reduced from 11% to 6%, with a corresponding increase in unsulfated disaccharides. In contrast, no structural differences were observed in heparan sulfate. Furthermore, no difference was found in the molar amount of glycosaminoglycans, or in the ratio of hyaluronan/heparan sulfate/chondroitin sulfate. Immunohistochemical staining for the heparan sulfate proteoglycan perlecan was similar in both types of material but reduced staining of 4-O-sulfated chondroitin and dermatan was observed in kidney sections from diabetic mice. In support of this, using qRT-PCR, a 53.5% decrease in the expression level of Chst-11 (chondroitin 4-O sulfotransferase) was demonstrated in diabetic kidney. These results suggest that changes in the sulfation of chondroitin need to be addressed in future studies on proteoglycans and kidney function in diabetes. PMID:23757342

  6. Reduced sulfation of chondroitin sulfate but not heparan sulfate in kidneys of diabetic db/db mice.

    PubMed

    Reine, Trine M; Grøndahl, Frøy; Jenssen, Trond G; Hadler-Olsen, Elin; Prydz, Kristian; Kolset, Svein O

    2013-08-01

    Heparan sulfate proteoglycans are hypothesized to contribute to the filtration barrier in kidney glomeruli and the glycocalyx of endothelial cells. To investigate potential changes in proteoglycans in diabetic kidney, we isolated glycosaminoglycans from kidney cortex from healthy db/+ and diabetic db/db mice. Disaccharide analysis of chondroitin sulfate revealed a significant decrease in the 4-O-sulfated disaccharides (D0a4) from 65% to 40%, whereas 6-O-sulfated disaccharides (D0a6) were reduced from 11% to 6%, with a corresponding increase in unsulfated disaccharides. In contrast, no structural differences were observed in heparan sulfate. Furthermore, no difference was found in the molar amount of glycosaminoglycans, or in the ratio of hyaluronan/heparan sulfate/chondroitin sulfate. Immunohistochemical staining for the heparan sulfate proteoglycan perlecan was similar in both types of material but reduced staining of 4-O-sulfated chondroitin and dermatan was observed in kidney sections from diabetic mice. In support of this, using qRT-PCR, a 53.5% decrease in the expression level of Chst-11 (chondroitin 4-O sulfotransferase) was demonstrated in diabetic kidney. These results suggest that changes in the sulfation of chondroitin need to be addressed in future studies on proteoglycans and kidney function in diabetes.

  7. Assembly of coupled redox fuel cells using copper as electron acceptors to generate power and its in-situ retrieval

    PubMed Central

    Zhang, Hui-Min; Xu, Wei; Li, Gang; Liu, Zhan-Meng; Wu, Zu-Cheng; Li, Bo-Geng

    2016-01-01

    Energy extraction from waste has attracted much interest nowadays. Herein, a coupled redox fuel cell (CRFC) device using heavy metals, such as copper, as an electron acceptor is assembled to testify the recoveries of both electricity and the precious metal without energy consumption. In this study, a NaBH4-Cu(II) CRFC was employed as an example to retrieve copper from a dilute solution with self-electricity production. The properties of the CRFC have been characterized, and the open circuit voltage was 1.65 V with a maximum power density of 7.2 W m−2 at an initial Cu2+ concentration of 1,600 mg L−1 in the catholyte. 99.9% of the 400 mg L−1 copper was harvested after operation for 24 h, and the product formed on the cathode was identified as elemental copper. The CRFC demonstrated that useful chemicals were recovered and the electricity contained in the chemicals was produced in a self-powered retrieval process. PMID:26877144

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

    PubMed

    Ayangade, O

    1984-02-01

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

  9. Physiological function of hydrogen metabolism during growth of sulfidogenic bacteria on organic substrates.

    PubMed Central

    Lupton, F S; Conrad, R; Zeikus, J G

    1984-01-01

    Desulfovibrio vulgaris Madison and Thermodesulfobacterium commune contained functionally distinct hydrogenase activities, one which exchanged 3H2 into 3H2O and was inhibited by carbon monoxide and a second activity which produced H2 in the presence of CO. Cell suspensions of D. vulgaris used either lactate, pyruvate, or CO as the electron donor for H2 production in the absence of sulfate. Both sulfidogenic species produced and consumed hydrogen as a trace gas during growth on lactate or pyruvate as electron donors and on thiosulfate or sulfate as electron acceptors. Higher initial levels of hydrogen were detected during growth on lactate-sulfate than on pyruvate-sulfate. D. vulgaris but not T. commune also produced and then consumed CO during growth on organic electron donors and sulfate or thiosulfate. High partial pressures of exogenous H2 inhibited growth and substrate consumption when D. vulgaris was cultured on pyruvate alone but not when it was metabolizing pyruvate plus sulfate or lactate plus sulfate. The data are discussed in relation to supporting two different models for the physiological function of H2 metabolism during growth of sulfidogenic bacteria on organic electron donors plus sulfate. A trace H2 transformation model is proposed for control of redox processes during growth on either pyruvate or lactate plus sulfate, and an obligate H2 cycling model is proposed for chemiosmotic energy coupling during growth on CO plus sulfate. PMID:6480553

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

    PubMed

    Pike, Sarah J; Hunter, Christopher A

    2017-11-22

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

  11. Impact on electronic structure of donor/acceptor blend in organic photovoltaics by decontamination of molybdenum-oxide surface

    NASA Astrophysics Data System (ADS)

    Ito, Yuta; Akaike, Kouki; Fukuda, Takeshi; Sato, Daisuke; Fuse, Takuya; Iwahashi, Takashi; Ouchi, Yukio; Kanai, Kaname

    2018-05-01

    Molybdenum oxide (MoOx) is widely used as the hole-transport layer in bulk-heterojunction organic photovoltaics (BHJ-OPVs). During the fabrication of solution-processed BHJ-OPVs on vacuum-deposited MoOx film, the film must be exposed to N2 atmosphere in a glove box, where the donor/acceptor blends are spin-coated from a mixed solution. Employing photoelectron spectroscopy, we reveal that the exposure of the MoOx film to such atmosphere contaminates the MoOx surface. Annealing the contaminated MoOx film at 160 °C for 5 min, prior to spin-coating the blend film, can partially remove the carbon and oxygen adsorbed on the MoOx surface during the exposure of MoOx. However, the contamination layer on the MoOx surface does not affect the energy-level alignment at the interface between MoOx and the donor/acceptor blend. Hence, significant improvement in the performance of BHJ-OPVs by mildly annealing the MoOx layer, which was previously reported, can be explained by the reduction of undesired contamination.

  12. Modulation Doping of Silicon using Aluminium-induced Acceptor States in Silicon Dioxide

    PubMed Central

    König, Dirk; Hiller, Daniel; Gutsch, Sebastian; Zacharias, Margit; Smith, Sean

    2017-01-01

    All electronic, optoelectronic or photovoltaic applications of silicon depend on controlling majority charge carriers via doping with impurity atoms. Nanoscale silicon is omnipresent in fundamental research (quantum dots, nanowires) but also approached in future technology nodes of the microelectronics industry. In general, silicon nanovolumes, irrespective of their intended purpose, suffer from effects that impede conventional doping due to fundamental physical principles such as out-diffusion, statistics of small numbers, quantum- or dielectric confinement. In analogy to the concept of modulation doping, originally invented for III-V semiconductors, we demonstrate a heterostructure modulation doping method for silicon. Our approach utilizes a specific acceptor state of aluminium atoms in silicon dioxide to generate holes as majority carriers in adjacent silicon. By relocating the dopants from silicon to silicon dioxide, Si nanoscale doping problems are circumvented. In addition, the concept of aluminium-induced acceptor states for passivating hole selective tunnelling contacts as required for high-efficiency photovoltaics is presented and corroborated by first carrier lifetime and tunnelling current measurements. PMID:28425460

  13. Assessment of the performance of SMFCs in the bioremediation of PAHs in contaminated marine sediments under different redox conditions and analysis of the associated microbial communities.

    PubMed

    Hamdan, Hamdan Z; Salam, Darine A; Hari, Ananda Rao; Semerjian, Lucy; Saikaly, Pascal

    2017-01-01

    The biodegradation of naphthalene, 2-methylnaphthalene and phenanthrene was evaluated in marine sediment microbial fuel cells (SMFCs) under different biodegradation conditions, including sulfate reduction as a major biodegradation pathway, employment of anode as terminal electron acceptor (TEA) under inhibited sulfate reducing bacteria activity, and combined sulfate and anode usage as electron acceptors. A significant removal of naphthalene and 2-methylnaphthalene was observed at early stages of incubation in all treatments and was attributed to their high volatility. In the case of phenanthrene, a significant removal (93.83±1.68%) was measured in the closed circuit SMFCs with the anode acting as the main TEA and under combined anode and sulfate reduction conditions (88.51±1.3%). A much lower removal (40.37±3.24%) was achieved in the open circuit SMFCs operating with sulfate reduction as a major biodegradation pathway. Analysis of the anodic bacterial community using 16S rRNA gene pyrosequencing revealed the enrichment of genera with potential exoelectrogenic capability, namely Geoalkalibacter and Desulfuromonas, on the anode of the closed circuit SMFCs under inhibited SRB activity, while they were not detected on the anode of open circuit SMFCs. These results demonstrate the role of the anode in enhancing PAHs biodegradation in contaminated marine sediments and suggest a higher system efficiency in the absence of competition between microbial redox processes (under SRB inhibition), namely due to the anode enrichment with exoelectrogenic bacteria, which is a more energetically favorable mechanism for PAHs oxidation than sulfate. Copyright © 2016. Published by Elsevier B.V.

  14. Energy for biologic sulfate reduction in a hydrothermally formed ocean on Europa

    NASA Astrophysics Data System (ADS)

    Zolotov, Mikhail Y.; Shock, Everett L.

    2003-04-01

    Formation of a sulfate-bearing ocean on Jupiter's satellite Europa by quenched hydrothermal fluids provides a source of metabolic energy for low-temperature sulfate-reducing organisms that use dissolved H2 as an electron donor. Inhibition of thermodynamically favorable sulfate reduction in cooled hydrothermal fluids creates the potential for biologic reduction. Both high temperature and reduced conditions of ocean-forming hydrothermal solutions favor sulfate reduction in quenched fluids. The maximum amount of energy available to support autotrophic sulfate reduction is on the order of a few kilojoules per kilogram of water and is limited by the low abundances of either H2 or sulfate in ocean-forming fluids. Although this irreplaceable energy source might have supported early life on Europa, maintenance of biologic sulfate reduction throughout the ocean's history would require a supply of organic compounds from endogenic sources or from the satellite's surface.

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

    NASA Astrophysics Data System (ADS)

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

    2018-03-01

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

  16. Isolation from Estuarine Sediments of a Desulfovibrio Strain Which Can Grow on Lactate Coupled to the Reductive Dehalogenation of 2,4,6-Tribromophenol

    PubMed Central

    Boyle, Alfred W.; Phelps, Craig D.; Young, L. Y.

    1999-01-01

    Strain TBP-1, an anaerobic bacterium capable of reductively dehalogenating 2,4,6-tribromophenol to phenol, was isolated from estuarine sediments of the Arthur Kill in the New York/New Jersey harbor. It is a gram-negative, motile, vibrio-shaped, obligate anaerobe which grows on lactate, pyruvate, hydrogen, and fumarate when provided sulfate as an electron acceptor. The organism accumulates acetate when grown on lactate and sulfate, contains desulfoviridin, and will not grow in the absence of NaCl. It will not utilize acetate, succinate, propionate, or butyrate for growth via sulfate reduction. When supplied with lactate as an electron donor, strain TBP-1 will utilize sulfate, sulfite, sulfur, and thiosulfate for growth but not nitrate, fumarate, or acrylate. This organism debrominates 2-, 4-, 2,4-, 2,6-, and 2,4,6-bromophenol but not 3- or 2,3-bromophenol or monobrominated benzoates. It will not dehalogenate monochlorinated, fluorinated, or iodinated phenols or chlorinated benzoates. Together with its physiological characteristics, its 16S rRNA gene sequence places it in the genus Desulfovibrio. The average growth yield of strain TBP-1 grown on a defined medium supplemented with lactate and 2,4,6-bromophenol is 3.71 mg of protein/mmol of phenol produced, and the yield was 1.42 mg of protein/mmol of phenol produced when 4-bromophenol was the electron acceptor. Average growth yields (milligrams of protein per millimole of electrons utilized) for Desulfovibrio sp. strain TBP-1 grown with 2,4,6-bromophenol, 4-bromophenol, or sulfate are 0.62, 0.71, and 1.07, respectively. Growth did not occur when either lactate or 2,4,6-bromophenol was omitted from the growth medium. These results indicate that Desulfovibrio sp. strain TBP-1 is capable of growth via halorespiration. PMID:10049873

  17. Conjugated block copolymers as model materials to examine charge transfer in donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Gomez, Enrique; Aplan, Melissa; Lee, Youngmin

    Weak intermolecular interactions and disorder at junctions of different organic materials limit the performance and stability of organic interfaces and hence the applicability of organic semiconductors to electronic devices. The lack of control of interfacial structure has also prevented studies of how driving forces promote charge photogeneration, leading to conflicting hypotheses in the organic photovoltaic literature. Our approach has focused on utilizing block copolymer architectures -where critical interfaces are controlled and stabilized by covalent bonds- to provide the hierarchical structure needed for high-performance organic electronics from self-assembled soft materials. For example, we have demonstrated control of donor-acceptor heterojunctions through microphase-separated conjugated block copolymers to achieve 3% power conversion efficiencies in non-fullerene photovoltaics. Furthermore, incorporating the donor-acceptor interface within the molecular structure facilitates studies of charge transfer processes. Conjugated block copolymers enable studies of the driving force needed for exciton dissociation to charge transfer states, which must be large to maximize charge photogeneration but must be minimized to prevent losses in photovoltage in solar cell devices. Our work has systematically varied the chemical structure, energetics, and dielectric constant to perturb charge transfer. As a consequence, we predict a minimum dielectric constant needed to minimize the driving force and therefore simultaneously maximize photocurrent and photovoltage in organic photovoltaic devices.

  18. Ultrafast electron and hole transfer dynamics of a solar cell dye containing hole acceptors on mesoporous TiO2 and Al2O3.

    PubMed

    Scholz, Mirko; Flender, Oliver; Boschloo, Gerrit; Oum, Kawon; Lenzer, Thomas

    2017-03-08

    The stability of dye cations against recombination with conduction band electrons in mesoporous TiO 2 electrodes is a key property for improving light harvesting in dye-sensitised solar cells. Using ultrafast transient broadband absorption spectroscopy, we monitor efficient intramolecular hole transfer in the solar cell dye E6 having two peripheral triarylamine acceptors. After photoexcitation, two hole transfer mechanisms are identified: a concerted mechanism for electron injection and hole transfer (2.4 ps) and a sequential mechanism with time constants of 3.9 ps and 30 ps. This way the dye retards unwanted recombination with a TiO 2 conduction band electron by quickly moving the hole further away from the surface. Contact of the E6/TiO 2 surface with the solvent acetonitrile has almost no influence on the electron injection and hole transfer kinetics. Fast hole transfer (2.8 ps) is also observed on a "non-injecting" Al 2 O 3 surface generating a radical cation-radical anion species with a lifetime of 530 ps. The findings confirm the good intramolecular hole transfer properties of this dye on both thin films. In contrast, intramolecular hole transfer does not occur in the mid-polar organic solvent methyl acetate. This is confirmed by TDDFT calculations suggesting a polarity-induced reduction of the driving force for hole transfer. In methyl acetate, only the relaxation of the initially photoexcited core chromophore is observed including solvent relaxation processes of the electronically excited state S 1 /ICT.

  19. Nanobelt formation of magnesium hydroxide sulfate hydrate via a soft chemistry process.

    PubMed

    Zhou, Zhengzhi; Sun, Qunhui; Hu, Zeshan; Deng, Yulin

    2006-07-13

    The nanobelt formation of magnesium hydroxide sulfate hydrate (MHSH) via a soft chemistry approach using carbonate salt and magnesium sulfate as reactants was successfully demonstrated. X-ray diffraction (XRD), energy dispersion X-ray spectra (EDS), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis revealed that the MHSH nanobelts possessed a thin belt structure (approximately 50 nm in thickness) and a rectangular cross profile (approximately 200 nm in width). The MHSH nanobelts suffered decomposition under electron beam irradiation during TEM observation and formed MgO with the pristine nanobelt morphology preserved. The formation process of the MHSH nanobelts was studied by tracking the morphology of the MHSH nanobelts during the reaction. A possible chemical reaction mechanism is proposed.

  20. Hypochlorite-Mediated Modulation of Photoinduced Electron Transfer in a Phenothiazine-Boron dipyrromethene Electron Donor-Acceptor Dyad: A Highly Water Soluble "Turn-On" Fluorescent Probe for Hypochlorite.

    PubMed

    Soni, Disha; Duvva, Naresh; Badgurjar, Deepak; Roy, Tapta Kanchan; Nimesh, Surendra; Arya, Geeta; Giribabu, Lingamallu; Chitta, Raghu

    2018-04-16

    A highly water-soluble phenothiazine (PTZ)-boron dipyrromethene (BODIPY)-based electron donor-acceptor dyad (WS-Probe), which contains BODIPY as the signaling antennae and PTZ as the OCl - reactive group, was designed and used as a fluorescent chemosensor for the detection of OCl - . Upon addition of incremental amounts of NaOCl, the quenched fluorescence of WS-Probe was enhanced drastically, which indicated the inhibition of reductive photoinduced electron transfer (PET) from PTZ to 1 BODIPY*; the detection limit was calculated to be 26.7 nm. Selectivity studies with various reactive oxygen species, cations, and anions revealed that WS-Probe was able to detect OCl - selectively. Steady-state fluorescence studies performed at varied pH suggested that WS-Probe can detect NaOCl and exhibits maximum fluorescence in the pH range of 7 to 8, similar to physiological conditions. ESI-MS analysis and 1 H NMR spectroscopy titrations showed the formation of sulfoxide as the major oxidized product upon addition of hypochlorite. More interestingly, when WS-Probe was treated with real water samples, the fluorescence response was clearly visible with tap water and disinfectant, which indicated the presence of OCl - in these samples. The in vitro cell viability assay performed with human embryonic kidney 293 (HEK 293) cells suggested that WS-probe is non-toxic up to 10 μm and implicates the use of the probe for biological applications. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    DOE PAGES

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

    2018-01-31

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

  2. Sulfate-reducing bacteria in rice field soil and on rice roots.

    PubMed

    Wind, T; Stubner, S; Conrad, R

    1999-05-01

    Rice plants that were grown in flooded rice soil microcosms were examined for their ability to exhibit sulfate reducing activity. Washed excised rice roots showed sulfate reduction potential when incubated in anaerobic medium indicating the presence of sulfate-reducing bacteria. Rice plants, that were incubated in a double-chamber (phylloshpere and rhizosphere separated), showed potential sulfate reduction rates in the anoxic rhizosphere compartment. These rates decreased when oxygen was allowed to penetrate through the aerenchyma system of the plants into the anoxic root compartment, indicating that sulfate reducers on the roots were partially inhibited by oxygen or that sulfate was regenerated by oxidation of reduced S-compounds. The potential activity of sulfate reducers on rice roots was consistent with MPN enumerations showing that H2-utilizing sulfate-reducing bacteria were present in high numbers on the rhizoplane (4.1 x 10(7) g-1 root fresh weight) and in the adjacent rhizosperic soil (2.5 x 10(7) g-1 soil dry weight). Acetate-oxidizing sulfate reducers, on the other hand, showed highest numbers in the unplanted bulk soil (1.9 x 10(6) g-1 soil dry weight). Two sulfate reducing bacteria were isolated from the highest dilutions of the MPN series and were characterized physiologically and phylogenetically. Strain F1-7b which was isolated from the rhizoplane with H2 as electron donor was related to subgroup II of the family Desulfovibrionaceae. Strain EZ-2C2, isolated from the rhizoplane on acetate, grouped together with Desulforhabdus sp. and Syntrophobacter wolinii. Other strains of sulfate-reducing bacteria originated from bulk soil of rice soil microcosms and were isolated using different electron donors. From these isolates, strains R-AcA1, R-IbutA1, R-PimA1 and R-AcetonA170 were Gram-positive bacteria which were affiliated with the genus Desulfotomaculum. The other isolates were members of subgroup II of the Desulfovibrionaceae (R-SucA1 and R-LacA1), were

  3. 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.

  4. Improving Photoconductance of Fluorinated Donors with Fluorinated Acceptors

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

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

    2016-11-21

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

  5. Acceptor binding energies in GaN and AlN

    NASA Astrophysics Data System (ADS)

    Mireles, Francisco; Ulloa, Sergio E.

    1998-08-01

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

  6. Sulfate-mediated electrooxidation of X-ray contrast media on boron-doped diamond anode.

    PubMed

    Radjenovic, Jelena; Petrovic, Mira

    2016-05-01

    Recently, electrochemical activation of sulfate ions to sulfate radical species and nonradically activated persulfate has been demonstrated at boron-doped diamond (BDD) anode, which enhanced the electrooxidation kinetics of several persistent contaminants. In this study, we investigated the transformation pathways of two X-ray contrast media (ICM), diatrizoate and iopromide, in electrooxidation at BDD anode using sulfate and inert nitrate anolyte. Sulfate anolyte yielded a seven-fold increase in apparent rate constants for ICM oxidation compared to inert nitrate anolyte, and a two-fold increase for the removal of organic carbon. Higher iodine release was observed in electrooxidation of diatrizoate compared to iopromide. In the case of diatrizoate, around 80% of deiodination efficiency was achieved in both anolytes. Deiodination efficiency of iopromide was somewhat lower in nitrate anolyte (≤75%) and significantly reduced in sulfate anolyte (≤46%) due to a larger steric hindrance of alkyl side chains. Moreover, a considerable lag phase of iopromide deiodination was observed in sulfate anolyte, indicating that initial oxidation reactions took place almost exclusively at the alkyl side chains. Several transformation products (TPs) of ICM were identified in electrooxidation in sulfate anolyte, and only three TPs in the case of nitrate anolyte. The main mechanistic steps in the oxidation of iopromide were H-abstraction and bond cleavage in the alkyl side chains. Diatrizoate was mainly transformed through oxidative cleavage of iodine substituent and inter-molecular cyclization. Two hydroxylamine derivatives of iopromide and a nitro-derivative of diatrizoate were observed in sulfate anolyte. These products have not been reported previously for hydroxyl radical-mediated oxidation of ICM. Given that electron-transfer mechanism is more typical for sulfate than for hydroxyl radicals, formation of hydroxylamine and nitro-derivatives of ICM was assigned to one-electron

  7. Photoinduced intercomponent excited-state decays in a molecular dyad made of a dinuclear rhenium(I) chromophore and a fullerene electron acceptor unit.

    PubMed

    Nastasi, Francesco; Puntoriero, Fausto; Natali, Mirco; Mba, Miriam; Maggini, Michele; Mussini, Patrizia; Panigati, Monica; Campagna, Sebastiano

    2015-05-01

    A novel molecular dyad, 1, made of a dinuclear {[Re2(μ-X)2(CO)6(μ-pyridazine)]} component covalently-linked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties - including pump-probe transient absorption spectroscopy in the visible and near-infrared region - have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((3)MLLCT) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.

  8. Efficient Förster resonance energy transfer in 1,2,3-triazole linked BODIPY-Zn(II) meso-tetraphenylporphyrin donor-acceptor arrays.

    PubMed

    Leonardi, Matthew J; Topka, Michael R; Dinolfo, Peter H

    2012-12-17

    Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC) reactivity was successfully employed to synthesize three donor-acceptor energy transfer (EnT) arrays that contain one (Dyad), three (Tetrad) and four (Pentad) 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) donors connected to a Zn-tetraphenylporphyrin acceptor via 1,2,3-triazole linkages. The photophysical properties of the three arrays, along with individual donor and acceptor chromophores, were investigated by UV-vis absorption and emission spectroscopy, fluorescence lifetimes, and density functional theory (DFT) electronic structure modeling. Comparison of the UV-vis absorption spectra and frontier molecular orbitals from DFT calculations of the three arrays with ZnTPP, ZnTTrzlP, and Trzl-BODIPY shows that the electronic structure of the chromophores is essentially unperturbed by the 1,2,3-triazole linkage. Time-dependent DFT (TDDFT) calculations on the Dyad reproduce the absorption spectra in THF and show no evidence of excited state mixing of the donor and acceptor. The BODIPY singlet excited state emission is significantly quenched in all three arrays, consistent with EnT to the porphyrin core, with efficiencies of 95.8, 97.5, and 97.2% for the Dyad, Tetrad, and Pentad, respectively. Fluorescence excitation spectra of the three arrays, measured at the porphyrin emission, mirror the absorption profile of both the porphyrin and BODIPY chromophores and are consistent with the Förster resonance energy transfer (FRET) mechanism. Applying Förster theory to the spectroscopic data of the chromophores gives EnT efficiency estimates that are in close agreement with experimental values, suggesting that the through-space mechanism plays a dominant role in the three arrays.

  9. Synthesis of nano-crystalline hydroxyapatite and ammonium sulfate from phosphogypsum waste

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

    Mousa, Sahar, E-mail: dollyriri@yahoo.com; King Abdulaziz University, Science and Art College, Chemistry Department, Rabigh Campus, P.O. Box:344, Postal code: 21911 Rabigh; Hanna, Adly

    2013-02-15

    Graphical abstract: TEM micrograph of dried HAP at 800 °C. -- Abstract: Phosphogypsum (PG) waste which is derived from phosphoric acid manufacture by using wet method was converted into hydroxyapatite (HAP) and ammonium sulfate. Very simple method was applied by reacting PG with phosphoric acid in alkaline medium with adjusting pH using ammonia solution. The obtained nano-HAP was dried at 80 °C and calcined at 600 °C and 900 °C for 2 h. Both of HAP and ammonium sulfate were characterized by X-ray diffraction (XRD) and infrared spectroscopy (IR) to study the structural evolution. The thermal behavior of nano-HAP wasmore » studied; the particle size and morphology were estimated by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). All the results showed that HAP nano-crystalline and ammonium sulfate can successfully be produced from phosphogypsum waste.« less

  10. Processes controlling the fate of chloroethenes emanating from DNAPL aged sources in river-aquifer contexts.

    PubMed

    Puigserver, Diana; Cortés, Amparo; Viladevall, Manuel; Nogueras, Xènia; Parker, Beth L; Carmona, José M

    2014-11-01

    This work dealt with the physical and biogeochemical processes that favored the natural attenuation of chloroethene plumes of aged sources located close to influent rivers in the presence of co-contaminants, such as nitrate and sulfate. Two working hypotheses were proposed: i) Reductive dechlorination is increased in areas where the river-aquifer relationship results in the groundwater dilution of electron acceptors, the reduction potential of which exceeds that of specific chloroethenes; ii) zones where silts predominate or where textural changes occur are zones in which biodegradation preferentially takes place. A field site on a Quaternary alluvial aquifer at Torelló, Catalonia (Spain) was selected to validate these hypotheses. This aquifer is adjacent to an influent river, and its redox conditions favor reductive dechlorination. The main findings showed that the low concentrations of nitrate and sulfate due to dilution caused by the input of surface water diminish the competition for electrons between microorganisms that reduce co-contaminants and chloroethenes. Under these conditions, the most bioavailable electron acceptors were PCE and metabolites, which meant that their biodegradation was favored. This led to the possibility of devising remediation strategies based on bioenhancing natural attenuation. The artificial recharge with water that is low in nitrates and sulfates may favor dechlorinating microorganisms if the redox conditions in the mixing water are sufficiently maintained as reducing and if there are nutrients, electron donors and carbon sources necessary for these microorganisms. Copyright © 2014 Elsevier B.V. All rights reserved.

  11. Diphenylphenoxy-Thiophene-PDI Dimers as Acceptors for OPV Applications with Open Circuit Voltage Approaching 1 Volt.

    PubMed

    Stenta, Caterina; Molina, Desiré; Viterisi, Aurélien; Montero-Rama, María Pilar; Pla, Sara; Cambarau, Werther; Fernández-Lázaro, Fernando; Palomares, Emilio; Marsal, Lluis F; Sastre-Santos, Ángela

    2018-03-30

    Two new perylenediimides (PDIs) have been developed for use as electron acceptors in solution-processed bulk heterojunction solar cells. The compounds were designed to exhibit maximal solubility in organic solvents, and reduced aggregation in the solid state. In order to achieve this, diphenylphenoxy groups were used to functionalize a monomeric PDI core, and two PDI dimers were bridged with either one or two thiophene units. In photovoltaic devices prepared using PDI dimers and a monomer in conjunction with PTB7, it was found that the formation of crystalline domains in either the acceptor or donor was completely suppressed. Atomic force microscopy, X-ray diffraction, charge carrier mobility measurements and recombination kinetics studies all suggest that the lack of crystallinity in the active layer induces a significant drop in electron mobility. Significant surface recombination losses associated with a lack of segregation in the material were also identified as a significant loss mechanism. Finally, the monomeric PDI was found to have sub-optimum LUMO energy matching the cathode contact, thus limiting charge carrier extraction. Despite these setbacks, all PDIs produced high open circuit voltages, reaching almost 1 V in one particular case.

  12. Bi-anchoring organic sensitizers of type D-(π-A)2 comprising thiophene-2-acetonitrile as π-spacer and malonic acid as electron acceptor for dye sensitized solar cell applications

    NASA Astrophysics Data System (ADS)

    Reddy, Gachumale Saritha; Ramkumar, Sekar; Asiri, Abdullah M.; Anandan, Sambandam

    2015-06-01

    Two new bi-anchoring organic sensitizers of type D-(π-A)2 comprising the identical π-spacer (thiophene-2-acetonitrile) and electron acceptor (malonic acid) but different aryl amine as electron donors (diphenylamine and carbazole) were synthesized, characterized and fabricated metal free dye-sensitized solar cell devices. The intra molecular charge transfer property and electrochemical property of these dyes were investigated by molecular absorption, emission, cyclic voltammetric experiments and in addition, quantum chemical calculation studies were performed to provide sufficient driving force for the electron injection into the conduction band of TiO2 which leads to efficient charge collection. Among the fabricated devices, carbazole based device exhibits high current conversion efficiency (η = 4.7%) with a short circuit current density (JSC) 15.3 mA/cm2, an open circuit photo voltage (VOC) of 0.59 V and a fill factor of 0.44 under AM 1.5 illumination (85 mW/cm2) compared to diphenylamine based device.

  13. New insight into sludge reduction induced by different substrate allocation strategy between oxygen and nitrate/nitrite as terminal electron acceptor.

    PubMed

    Yan, Peng; Guo, Jin-Song; Xu, Yu-Feng; Chen, You-Peng; Wang, Jing; Liu, Zhi-Ping; Fang, Fang

    2018-06-01

    Sludge reduction based on regulating substrate allocation between catabolism and anabolism as a strategy is proposed to reduce energy and chemicals consumption during wastewater treatment. The results indicated that a sludge reduction of 14.8% and excellent nutrient removal were simultaneously achieved in the low dissolved oxygen (LDO) activated sludge system with a hydraulic retention time of 24 h at 25 °C. Denitrifiers comprised nearly 1/4 of all microorganisms in the system. These denitrifiers converted NO x - to N 2 obtaining a lower biomass yield. The oxidoreductase activity proteins in the LDO sample was more than twice that of the normal DO sample, indicating that catabolism was stimulated by NO x - when replacing O 2 as electron acceptor. Less substrate was used for cell synthesis in the LDO system. Stable sludge reduction without extra energy and chemicals inputs was achieved by regulating the substrate allocation by inducing the bacteria to utilize NO x - instead of O 2 . Copyright © 2018 Elsevier Ltd. All rights reserved.

  14. Creating Graphitic Carbon Nitride Based Donor-π-Acceptor-π-Donor Structured Catalysts for Highly Photocatalytic Hydrogen Evolution.

    PubMed

    Li, Kui; Zhang, Wei-De

    2018-03-01

    Conjugated polymers with tailored donor-acceptor units have recently attracted considerable attention in organic photovoltaic devices due to the controlled optical bandgap and retained favorable separation of charge carriers. Inspired by these advantages, an effective strategy is presented to solve the main obstructions of graphitic carbon nitride (g-C 3 N 4 ) photocatalyst for solar energy conversion, that is, inefficient visible light response and insufficient separation of photogenerated electrons and holes. Donor-π-acceptor-π-donor polymers are prepared by incorporating 4,4'-(benzoc 1,2,5 thiadiazole-4,7-diyl) dianiline (BD) into the g-C 3 N 4 framework (UCN-BD). Benefiting from the visible light band tail caused by the extended π conjugation, UCN-BD possesses expanded visible light absorption range. More importantly, the BD monomer also acts as an electron acceptor, which endows UCN-BD with a high degree of intramolecular charge transfer. With this unique molecular structure, the optimized UCN-BD sample exhibits a superior performance for photocatalytic hydrogen evolution upon visible light illumination (3428 µmol h -1 g -1 ), which is nearly six times of that of the pristine g-C 3 N 4 . In addition, the photocatalytic property remains stable for six cycles in 3 d. This work provides an insight into the synthesis of g-C 3 N 4 -based D-π-A-π-D systems with highly visible light response and long lifetime of intramolecular charge carriers for solar fuel production. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. The impact of biostimulation on the fate of sulfate and associated sulfur dynamics in groundwater

    NASA Astrophysics Data System (ADS)

    Miao, Ziheng; Carreón-Diazconti, Concepcion; Carroll, Kenneth C.; Brusseau, Mark L.

    2014-08-01

    The impact of electron-donor addition on sulfur dynamics for a groundwater system with low levels of metal contaminants was evaluated with a pilot-scale biostimulation test conducted at a former uranium mining site. Geochemical and stable-isotope data collected before, during, and after the test were analyzed to evaluate the sustainability of sulfate reducing conditions induced by the test, the fate of hydrogen sulfide, and the impact on aqueous geochemical conditions. The results of site characterization activities conducted prior to the test indicated the absence of measurable bacterial sulfate reduction. The injection of an electron donor (ethanol) induced bacterial sulfate reduction, as confirmed by an exponential decrease of sulfate concentration in concert with changes in oxidation-reduction potential, redox species, alkalinity, production of hydrogen sulfide, and fractionation of δ34S-sulfate. High, stoichiometrically-equivalent hydrogen sulfide concentrations were not observed until several months after the start of the test. It is hypothesized that hydrogen sulfide produced from sulfate reduction was initially sequestered in the form of iron sulfides until the exhaustion of readily reducible iron oxides within the sediment. The fractionation of δ34S for sulfate was atypical, wherein the enrichment declined in the latter half of the experiment. It was conjectured that mixing effects associated with the release of sulfate from sulfate minerals associated with the sediments, along with possible sulfide re-oxidation contributed to this behavior. The results of this study illustrate the biogeochemical complexity that is associated with in-situ biostimulation processes involving bacterial sulfate reduction.

  16. THE IMPACT OF BIOSTIMULATION ON THE FATE OF SULFATE AND ASSOCIATED SULFUR DYNAMICS IN GROUNDWATER

    PubMed Central

    Miao, Ziheng; Carreón-Diazconti, Concepcion; Carroll, Kenneth C.; Brusseau, Mark L.

    2014-01-01

    The impact of electron-donor addition on sulfur dynamics for a groundwater system with low levels of metal contaminants was evaluated with a pilot-scale biostimulation test conducted at a former uranium mining site. Geochemical and stable-isotope data collected before, during, and after the test were analyzed to evaluate the sustainability of sulfate reducing conditions induced by the test, the fate of hydrogen sulfide, and the impact on aqueous geochemical conditions. The results of site characterization activities conducted prior to the test indicated the absence of measurable bacterial sulfate reduction. The injection of an electron donor (ethanol) induced bacterial sulfate reduction, as confirmed by an exponential decrease of sulfate concentration in concert with changes in oxidation-reduction potential, redox species, alkalinity, production of hydrogen sulfide, and fractionation of δ34S-sulfate. High, stoichiometrically-equivalent hydrogen sulfide concentrations were not observed until several months after the start of the test. It is hypothesized that hydrogen sulfide produced from sulfate reduction was initially sequestered in the form of iron sulfides until the exhaustion of readily reducible iron oxides associated with the sediment. The fractionation of δ34S for sulfate was atypical, wherein the enrichment declined in the latter half of the experiment. It was conjectured that mixing effects associated with the release of sulfate from sulfate minerals associated with the sediments, along with possible sulfide re-oxidation contributed to this behavior. The results of this study illustrate the biogeochemical complexity that is associated with in-situ biostimulation processes involving bacterial sulfate reduction. PMID:25016586

  17. Molecular design of novel fullerene-based acceptors for enhancing the open circuit voltage in polymer solar cells

    NASA Astrophysics Data System (ADS)

    Tajbakhsh, Mahmood; Kariminasab, Mohaddeseh; Ganji, Masoud Darvish; Alinezhad, Heshmatollah

    2017-12-01

    Organic solar cells, especially bulk hetero-junction polymer solar cells (PSCs), are the most successful structures for applications in renewable energy. The dramatic improvement in the performance of PSCs has increased demand for new conjugated polymer donors and fullerene derivative acceptors. In the present study, quantum chemical calculations were performed for several representative fullerene derivatives in order to determine their frontier orbital energy levels and electronic structures, thereby helping to enhance their performance in PSC devices. We found correlations between the theoretical lowest unoccupied molecular orbital levels and electrophilicity index of various fullerenes with the experimental open circuit voltage of photovoltaic devices according to the poly(3-hexylthiophene) (P3HT):fullerene blend. The correlations between the structure and descriptors may facilitate screening of the best fullerene acceptor for the P3HT donor. Thus, we considered fullerenes with new functional groups and we predicted the output factors for the corresponding P3HT:fullerene blend devices. The results showed that fullerene derivatives based on thieno-o-quinodimethane-C60 with a methoxy group will have enhanced photovoltaic properties. Our results may facilitate the design of new fullerenes and the development of favorable acceptors for use in photovoltaic applications.

  18. A helical perylene diimide-based acceptor for non-fullerene organic solar cells: synthesis, morphology and exciton dynamics

    NASA Astrophysics Data System (ADS)

    Chen, Li; Wu, Mingliang; Shao, Guangwei; Hu, Jiahua; He, Guiying; Bu, Tongle; Yi, Jian-Peng; Xia, Jianlong

    2018-05-01

    Helical perylene diimide-based (hPDI) acceptors have been established as one of the most promising candidates for non-fullerene organic solar cells (OSCs). In this work, we report a novel hPDI-based molecule, hPDI2-CN2, as an electron acceptor for OSCs. Combining the hPDI2-CN2 with a low-bandgap polymeric donor (PTB7-Th), the blending film morphology exhibited high sensitivity to various treatments (such as thermal annealing and addition of solvent additives), as evidenced by atomic force microscope studies. The power conversion efficiency (PCE) was improved from 1.42% (as-cast device) to 2.76% after thermal annealing, and a PCE of 3.25% was achieved by further addition of 1,8-diiodooctane (DIO). Femtosecond transient absorption (TA) spectroscopy studies revealed that the improved thin-film morphology was highly beneficial for the charge carrier transport and collection. And a combination of fast exciton diffusion rate and the lowest recombination rate contributed to the best performance of the DIO-treated device. This result further suggests that the molecular conformation needs to be taken into account in the design of perylene diimide-based acceptors for OSCs.

  19. Effect of sulfate ions on the crystallization and photocatalytic activity of TiO2/diatomite composite photocatalyst

    NASA Astrophysics Data System (ADS)

    Zhang, Jinjun; Wang, Xiaoyan; Wang, Jimei; Wang, Jing; Ji, Zhijiang

    2016-01-01

    TiO2 nanoparticles were immobilized on diatomite by hydrolysis-deposition method using titanium tetrachloride as precursor. The effect of sulfate ions on the crystallization and photocatalytic activity of TiO2/diatomite composite photocatalyst was characterized by TG-DSC, XRD, BET surface area, SEM, FT-IR spectroscopy, XPS and UV-vis diffuse reflectance spectra. The results indicate that addition of a small amount of sulfate ions promotes the formation of anatase phase and inhibits the transformation from anatase to rutile. On the other hand, sulfate ions immobilized on the surface of TiO2/diatomite have strong affinity for electrons, capturing the photo-generated electrons, which hinders the recombination of electrons and holes.

  20. Copper sulfates as cathode materials for Li batteries

    NASA Astrophysics Data System (ADS)

    Schwieger, Jonathan N.; Kraytsberg, Alexander; Ein-Eli, Yair

    As lithium battery technology sets out to bridge the gap between portable electronics and the electrical automotive industry, cathode materials still stand as the bottleneck regarding performances. In the realm of highly attractive polyanion-type structures as high-voltage cathode materials, the sulfate group (SO 4) 2- possesses an acknowledged superiority over other contenders in terms of open circuit voltage arising from the inductive effect of strong covalent S-O bonds. In parallel, novel lithium insertion mechanisms are providing alternatives to traditional intercalation, enabling reversible multi-electron processes securing high capacities. Combining both of these advantageous features, we report here the successful electrochemical reactivity of copper sulfate pentahydrate (CuSO 4·5H 2O) with respect to lithium insertion via a two-electron displacement reaction entailing the extrusion of metallic copper at a dual voltage of 3.2 V and 2.7 V followed by its reversible insertion at 3.5 V and 3.8 V. At this stage, cyclability was still shown to be limited due to the irreversible degradation to a monohydrate structure owing to constitutional water loss.

  1. Immunocytochemistry of cell surface heparan sulfate proteoglycan in mouse tissues. A light and electron microscopic study.

    PubMed

    Hayashi, K; Hayashi, M; Jalkanen, M; Firestone, J H; Trelstad, R L; Bernfield, M

    1987-10-01

    The core protein of the proteoglycan at the cell surface of NMuMG mouse mammary epithelial cells bears both heparan and chondroitin sulfate chains and is recognized by the monoclonal antibody 281-2. Using this antibody and the peroxidase-antiperoxidase staining technique in adult mouse tissues, we found that the antibody recognizes the antigen in a highly restricted distribution, staining a variety of epithelial cells but no cells derived from embryonic mesoderm or neural crest. The antibody fails to stain any stromal (mesenchymal) or neuronal cells, with the exception of plasma cells and Leydig cells. Squamous and transitional epithelia stain intensely over their entire surfaces, whereas cuboidal and columnar epithelia stain moderately and only at the lateral surface of the basal cells. Within squamous and transitional epithelial tissues that undergo physiological regeneration (e.g., epidermis), the most superficial and differentiated cell types fail to stain. Within glandular and branched epithelia (e.g., pancreas), the secretory alveolar cells fail to stain. When evaluated by electron microscopy, granular deposits of stain are seen on the plasma membrane, especially on lateral surfaces, but none are noted within the cells or the basement membrane. These results indicate that in adult tissues the core protein of this heparan sulfate-rich proteoglycan is expressed almost exclusively at epithelial cell surfaces. Expression appears to be lost as the cells become either mature or highly differentiated.

  2. Nickel recovery from electronic waste II electrodeposition of Ni and Ni-Fe alloys from diluted sulfate solutions.

    PubMed

    Robotin, B; Ispas, A; Coman, V; Bund, A; Ilea, P

    2013-11-01

    This study focuses on the electrodeposition of Ni and Ni-Fe alloys from synthetic solutions similar to those obtained by the dissolution of electron gun (an electrical component of cathode ray tubes) waste. The influence of various parameters (pH, electrolyte composition, Ni(2+)/Fe(2+) ratio, current density) on the electrodeposition process was investigated. Scanning electron microscopy (SEM) and X-ray fluorescence analysis (XRFA) were used to provide information about the obtained deposits' thickness, morphology, and elemental composition. By controlling the experimental parameters, the composition of the Ni-Fe alloys can be tailored towards specific applications. Complementarily, the differences in the nucleation mechanisms for Ni, Fe and Ni-Fe deposition from sulfate solutions have been evaluated and discussed using cyclic voltammetry and potential step chronoamperometry. The obtained results suggest a progressive nucleation mechanism for Ni, while for Fe and Ni-Fe, the obtained data points are best fitted to an instantaneous nucleation model. Copyright © 2013 Elsevier Ltd. All rights reserved.

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

    PubMed

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

    2014-09-01

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

  4. Osm1 facilitates the transfer of electrons from Erv1 to fumarate in the redox-regulated import pathway in the mitochondrial intermembrane space

    PubMed Central

    Neal, Sonya E.; Dabir, Deepa V.; Wijaya, Juwina; Boon, Cennyana; Koehler, Carla M.

    2017-01-01

    Prokaryotes have aerobic and anaerobic electron acceptors for oxidative folding of periplasmic proteins. The mitochondrial intermembrane space has an analogous pathway with the oxidoreductase Mia40 and sulfhydryl oxidase Erv1, termed the mitochondrial intermembrane space assembly (MIA) pathway. The aerobic electron acceptors include oxygen and cytochrome c, but an acceptor that can function under anaerobic conditions has not been identified. Here we show that the fumarate reductase Osm1, which facilitates electron transfer from fumarate to succinate, fills this gap as a new electron acceptor. In addition to microsomes, Osm1 localizes to the mitochondrial intermembrane space and assembles with Erv1 in a complex. In reconstitution studies with reduced Tim13, Mia40, and Erv1, the addition of Osm1 and fumarate completes the disulfide exchange pathway that results in Tim13 oxidation. From in vitro import assays, mitochondria lacking Osm1 display decreased import of MIA substrates, Cmc1 and Tim10. Comparative reconstitution assays support that the Osm1/fumarate couple accepts electrons with similar efficiency to cytochrome c and that the cell has strategies to coordinate expression of the terminal electron acceptors. Thus Osm1/fumarate is a new electron acceptor couple in the mitochondrial intermembrane space that seems to function in both aerobic and anaerobic conditions. PMID:28814504

  5. Magnesium acceptor in gallium nitride. I. Photoluminescence from Mg-doped GaN

    NASA Astrophysics Data System (ADS)

    Reshchikov, M. A.; Ghimire, P.; Demchenko, D. O.

    2018-05-01

    Defect-related photoluminescence (PL) is analyzed in detail for n -type, p -type, and semi-insulating Mg-doped GaN grown by different techniques. The ultraviolet luminescence (UVL) band is the dominant PL band in conductive n -type and p -type GaN:Mg samples grown by hydride vapor phase epitaxy (HVPE) and molecular beam epitaxy. The UVL band in undoped and Mg-doped GaN samples is attributed to the shallow M gGa acceptor with the ionization energy of 223 meV. In semi-insulating GaN:Mg samples, very large shifts of the UVL band (up to 0.6 eV) are observed with variation of temperature or excitation intensity. The shifts are attributed to diagonal transitions, likely due to potential fluctuations or near-surface band bending. The blue luminescence (B LMg ) band is observed only in GaN:Mg samples grown by HVPE or metalorganic chemical vapor deposition when the concentration of Mg exceeds 1019c m-3 . The B LMg band is attributed to electron transitions from an unknown deep donor to the shallow M gGa acceptor. Basic properties of the observed PL are explained with a phenomenological model.

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

    PubMed

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

    2014-03-18

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

  7. Volatile fatty acids as substrates for iron and sulfate reduction in Arctic marine sediments, Svalbard

    NASA Astrophysics Data System (ADS)

    Finke, N.; Vandieken, V.; Jorgensen, B. B.

    2006-12-01

    Anaerobic degradation of complex organic material in aquatic systems is a multi-step process. The metabolic products of fermentative bacteria serve as electron donors for the terminal oxidizing bacteria. In marine sediments, iron reduction and sulfate reduction are generally the most important terminal oxidation processes in the upper anoxic zone [1]. Microorganisms that reduce iron and sulfate may use a broad range of electron donors, yet the list of potential substrates provides little information about the substrates used in situ by these organisms. Investigations on the electron donors for sulfate reducers in marine sediments have shown that volatile fatty acids (VFA), and in particular acetate, together with hydrogen are the major substrates (e.g. [2-4]). Similar investigations for iron reduction or simultaneous iron and sulfate reduction are lacking for marine sediments. Furthermore, most of these studies were made in temperate sediments and little is known about the substrates for sulfate reducers in permanently cold sediments, which account for >90% of the ocean floor [5]. We investigated the relative contributions of iron reduction and sulfate reduction to the terminal oxidation of organic carbon and the importance of acetate, lactate, propionate, and isobutyrate as electron donors for iron and sulfate reduction in permanently cold, Arctic sediments from Svalbard. In the surface layer (0-2 cm) sulfate reduction accounted for 2/3 of the organic carbon oxidation (determined as DIC production), the remaining 1/3 were attributed to iron reduction. In the 5-9 cm layer sulfate reduction was the sole important terminal oxidation step. The contribution of acetate to terminal oxidation was determined by radiotracer incubation as well as from the accumulation after the inhibition of sulfate reduction by selenate. The rates determined with the two methods varied by less than 20%. Acetate turnover, determined with the tracer incubations, accounted for 10 and 40% of

  8. Evaluating microbial chemical choices: The ocean chemistry basis for the competition between use of O2 or NO3- as an electron acceptor

    NASA Astrophysics Data System (ADS)

    Brewer, Peter G.; Hofmann, Andreas F.; Peltzer, Edward T.; Ussler, William, III

    2014-05-01

    The traditional ocean chemical explanation for the emergence of suboxia is that once O2 levels decline to about 10 μmol kg-1 then onset of NO3- reduction occurs. This piece of ocean chemical lore is well founded in observations and is typically phrased as a microbial choice and not as an obligate requirement. The argument based on O2 levels alone could also be phrased as being dependent on an equivalent amount of NO3- that would yield the same energy gain. This description is based on the availability of the electron acceptor: but the oxidation reactions are usually written out as free energy yield per mole of organic matter, thus not addressing the oxidant availability constraint invoked by ocean scientists. Here we show that the argument can be phrased simply as competing rate processes dependent on the free energy yield ratio per amount of electron acceptor obtained, and thus the [NO3-]:[O2] molar ratio is the critical variable. The rate at which a microbe can acquire either O2 or NO3- to carry out the oxidation reactions is dependent on both the concentration in the bulk ocean, and on the diffusivity within the microbial external molecular boundary layer. From the free energy yield calculations combined with the ~25% greater diffusivity of the O2 molecule we find that the equivalent energy yield occurs at a ratio of about 3.8 NO3-:O2 for a typical Redfield ratio reaction, consistent with an ocean where NO3- reduction onset occurs at about 10 μmol O2:40 μmol NO3-, and the reactions then proceed in parallel along a line of this slope until the next energy barrier is approached. Within highly localized microbial consortia intensely reducing pockets may occur in a bulk ocean containing finite low O2 levels; and the local flux of reduced species from strongly reducing shelf sediments will perturb the large scale water column relationship. But all localized reactions drive towards maximal energy gain from their immediate diffusive surroundings, thus the ocean

  9. An overview of molecular acceptors for organic solar cells

    NASA Astrophysics Data System (ADS)

    Hudhomme, Piétrick

    2013-07-01

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

  10. Effects of electron acceptors on soluble reactive phosphorus in the overlying water during algal decomposition.

    PubMed

    Wang, Jinzhi; Jiang, Xia; Zheng, Binghui; Niu, Yuan; Wang, Kun; Wang, Wenwen; Kardol, Paul

    2015-12-01

    Endogenous phosphorus (P) release from sediments is an important factor to cause eutrophication and, hence, algal bloom in lakes in China. Algal decomposition depletes dissolved oxygen (DO) and causes anaerobic conditions and therefore increases P release from sediments. As sediment P release is dependent on the iron (Fe) cycle, electron acceptors (e.g., NO3 (-), SO4 (2-), and Mn(4+)) can be utilized to suppress the reduction of Fe(3+) under anaerobic conditions and, as such, have the potential to impair the release of sediment P. Here, we used a laboratory experiment to test the effects of FeCl3, MnO2, and KNO3 on soluble reactive phosphorus (SRP) concentration and related chemical variables in the overlying water column during algal decomposition at different algal densities. Results showed that algal decomposition significantly depleted DO and thereby increased sediment Fe-bound P release. Compared with the control, addition of FeCl3 significantly decreased water SRP concentration through inhibiting sediment P release. Compared with FeCl3, addition of MnO2 has less potential to suppress sediment P release during algal decomposition. Algal decomposition has the potential for NO3 (-) removal from aquatic ecosystem through denitrification and by that alleviates the suppressing role of NO3 (-) on sediment P release. Our results indicated that FeCl3 and MnO2 could be efficient in reducing sediment P release during algal decomposition, with the strongest effect found for FeCl3; large amounts of NO3 (-) were removed from the aquatic ecosystem through denitrification during algal decomposition. Moreover, the amounts of NO3 (-) removal increased with increasing algal density.

  11. Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems

    PubMed Central

    Teuscher, Joël; Brauer, Jan C.; Stepanov, Andrey; Solano, Alicia; Boziki, Ariadni; Chergui, Majed; Wolf, Jean-Pierre; Rothlisberger, Ursula; Banerji, Natalie; Moser, Jacques-E.

    2017-01-01

    Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research “Molecular Ultrafast Science and Technology,” a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here. PMID:29308415

  12. Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems.

    PubMed

    Teuscher, Joël; Brauer, Jan C; Stepanov, Andrey; Solano, Alicia; Boziki, Ariadni; Chergui, Majed; Wolf, Jean-Pierre; Rothlisberger, Ursula; Banerji, Natalie; Moser, Jacques-E

    2017-11-01

    Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research "Molecular Ultrafast Science and Technology," a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.

  13. Spectroscopic studies on the interaction of cimetidine drug with biologically significant σ- and π-acceptors

    NASA Astrophysics Data System (ADS)

    Pandeeswaran, M.; Elango, K. P.

    2010-05-01

    Spectroscopic studies revealed that the interaction of cimetidine drug with electron acceptors iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted through the initial formation of ionic intermediate to charge transfer (CT) complex. The CT-complexes of the interactions have been characterized using UV-vis, 1H NMR, FT-IR and GC-MS techniques. The formation of triiodide ion, I 3-, is further confirmed by the observation of the characteristic bands in the far IR spectrum for non-linear I 3- ion with C s symmetry at 156 and 131 cm -1 assigned to νas(I-I) and νs(I-I) of the I-I bond and at 73 cm -1 due to bending δ(I 3-). The rate of formation of the CT-complexes has been measured and discussed as a function of relative permittivity of solvent and temperature. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants and this observation was further supported by spectral studies. Based on the spectroscopic results plausible mechanisms for the interaction of the drug with the chosen acceptors were proposed and discussed and the point of attachment of the multifunctional cimetidine drug with these acceptors during the formation of CT-complex has been established.

  14. Intracellular metabolite levels shape sulfur isotope fractionation during microbial sulfate respiration

    PubMed Central

    Wing, Boswell A.; Halevy, Itay

    2014-01-01

    We present a quantitative model for sulfur isotope fractionation accompanying bacterial and archaeal dissimilatory sulfate respiration. By incorporating independently available biochemical data, the model can reproduce a large number of recent experimental fractionation measurements with only three free parameters: (i) the sulfur isotope selectivity of sulfate uptake into the cytoplasm, (ii) the ratio of reduced to oxidized electron carriers supporting the respiration pathway, and (iii) the ratio of in vitro to in vivo levels of respiratory enzyme activity. Fractionation is influenced by all steps in the dissimilatory pathway, which means that environmental sulfate and sulfide levels control sulfur isotope fractionation through the proximate influence of intracellular metabolites. Although sulfur isotope fractionation is a phenotypic trait that appears to be strain specific, we show that it converges on near-thermodynamic behavior, even at micromolar sulfate levels, as long as intracellular sulfate reduction rates are low enough (<<1 fmol H2S⋅cell−1⋅d−1). PMID:25362045

  15. Pseudodesulfovibrio hydrargyri sp. nov., a mercury-methylating bacterium isolated from a brackish sediment.

    PubMed

    Ranchou-Peyruse, Magali; Goñi-Urriza, Marisol; Guignard, Marion; Goas, Marjorie; Ranchou-Peyruse, Anthony; Guyoneaud, Rémy

    2018-05-01

    The strain BerOc1 T was isolated from brackish sediments contaminated with hydrocarbons and heavy metals. This strain has been used as a model strain of sulfate-reducer to study the biomethylation of mercury. The cells are vibrio-shaped, motile and not sporulated. Phylogeny and physiological traits placed this strain within the genus Pseudodesulfovibrio. Optimal growth was obtained at 30 °C, 1.5 % NaCl and pH 6.0-7.4. The estimated G+C content of the genomic DNA was 62.6 mol%. BerOc1 T used lactate, pyruvate, fumarate, ethanol and hydrogen. Terminal electron acceptors used were sulfate, sulfite, thiosulfate and DMSO. Only pyruvate could be used without a terminal electron acceptor. The major fatty acids were C18 : 0, anteiso-C15 : 0, C16 : 0 and C18 : 1ω7. The name Pseudodesulfovibrio hydrargyri sp. nov. is proposed for the type strain BerOc1 T (DSM 10384 T =JCM 31820 T ).

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

    NASA Technical Reports Server (NTRS)

    Nealson, K. H.; Saffarini, D.

    1994-01-01

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

  17. A detailed experimental and theoretical investigation of the role of cyano groups in the π-bridged acceptor of sensitizers for use in dye-sensitized solar cells (DSCs).

    PubMed

    Xu, Qinqin; Yang, Guang; Ren, Yu; Lu, Futai; Zhang, Nuonuo; Qamar, Muhammad; Yang, Manlin; Zhang, Bao; Feng, Yaqing

    2017-11-01

    Three donor-π conjugated unit-acceptor (D-π-A) type zinc porphyrin sensitizers LX1, LX2 and LX3 bearing meso acrylic acid, α-cyanoacrylic acid, and α-cyanopentadienoic acid, respectively, as the π-bridged acceptors were designed and synthesized for use in dye-sensitized solar cells (DSCs). The interesting role of the cyano group attached to the α position of the acrylic and pentadienoic acid acceptor was investigated. It was shown that even though the introduction of the cyano group and the elongation of the π-bridge can both increase the light-harvesting as indicated by the UV-vis absorption spectra, the relevant cell performance dropped significantly. The photo to power conversion efficiencies (PCEs) of the devices increase in the order of LX1 > LX2 > LX3, with the highest PCE of 6.04% achieved for the LX1-based cell, which bears acrylic acid as the π-bridged acceptor. To further explore the effect of -CN and -CH[double bond, length as m-dash]CH- on the interaction between the absorbed dye and TiO 2 substrates, their density of states (DOS) and partial density of states (PDOS), as well as electronic properties were investigated in detail using theoretical calculations. The results suggest that introducing the -CN group into the acceptor and extending the conjugation of the π-bridge have decreased the LUMO levels of the dyes, leading to weak interfacial coupling, low electron injection driving force, low J sc , and thus poor cell performance.

  18. Morphological, structural, and spectral characteristics of amorphous iron sulfates

    PubMed Central

    Sklute, E. C.; Jensen, H. B.; Rogers, A. D.; Reeder, R. J.

    2018-01-01

    Current or past brine hydrologic activity on Mars may provide suitable conditions for the formation of amorphous ferric sulfates. Once formed, these phases would likely be stable under current Martian conditions, particularly at low- to mid-latitudes. Therefore, we consider amorphous iron sulfates (AIS) as possible components of Martian surface materials. Laboratory AIS were created through multiple synthesis routes and characterized with total X-ray scattering, thermogravimetric analysis, scanning electron microscopy, visible/near-infrared (VNIR), thermal infrared (TIR), and Mössbauer techniques. We synthesized amorphous ferric sulfates (Fe(III)2(SO4)3 · ~ 6–8H2O) from sulfate-saturated fluids via vacuum dehydration or exposure to low relative humidity (<11%). Amorphous ferrous sulfate (Fe(II)SO4 · ~1H2O) was synthesized via vacuum dehydration of melanterite. All AIS lack structural order beyond 11 Å. The short-range (<5 Å) structural characteristics of amorphous ferric sulfates resemble all crystalline reference compounds; structural characteristics for the amorphous ferrous sulfate are similar to but distinct from both rozenite and szomolnokite. VNIR and TIR spectral data for all AIS display broad, muted features consistent with structural disorder and are spectrally distinct from all crystalline sulfates considered for comparison. Mössbauer spectra are also distinct from crystalline phase spectra available for comparison. AIS should be distinguishable from crystalline sulfates based on the position of their Fe-related absorptions in the visible range and their spectral characteristics in the TIR. In the NIR, bands associated with hydration at ~1.4 and 1.9 μm are significantly broadened, which greatly reduces their detectability in soil mixtures. AIS may contribute to the amorphous fraction of soils measured by the Curiosity rover. PMID:29675340

  19. Localized sulfate-reducing zones in a coastal plain aquifer

    USGS Publications Warehouse

    Brown, C.J.; Coates, J.D.; Schoonen, M.A.A.

    1999-01-01

    High concentrations of dissolved iron in ground water of coastal plain or alluvial aquifers contribute to the biofouling of public supply wells for which treatment and remediation is costly. Many of these aquifers, however, contain zones in which microbial sulfate reduction and the associated precipitation of iron-sulfide minerals decreases iron mobility. The principal water-bearing aquifer (Magothy Aquifer of Cretaceous age) in Suffolk County, New York, contains localized sulfate-reducing zones in and near lignite deposits, which generally are associated with clay lenses. Microbial analyses of core samples amended with [14C]-acetate indicate that microbial sulfate reduction is the predominant terminal-electron-accepting process (TEAP) in poorly permeable, lignite-rich sediments at shallow depths and near the ground water divide. The sulfate-reducing zones are characterized by abundant lignite and iron-sulfide minerals, low concentrations of Fe(III) oxyhydroxides, and by proximity to clay lenses that contain pore water with relatively high concentrations of sulfate and dissolved organic carbon. The low permeability of these zones and, hence, the long residence time of ground water within them, permit the preservation and (or) allow the formation of iron-sulfide minerals, including pyrite and marcasite. Both sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) are present beneath and beyond the shallow sulfate-reducing zones. A unique Fe(III)-reducing organism, MD-612, was found in core sediments from a depth of 187 m near the southern shore of Long Island. The distribution of poorly permeable, lignite-rich, sulfate-reducing zones with decreased iron concentration is varied within the principal aquifer and accounts for the observed distribution of dissolved sulfate, iron, and iron sulfides in the aquifer. Locating such zones for the placement of production wells would be difficult, however, because these zones are of limited aerial extent.

  20. Long-distance electron transfer by cable bacteria in aquifer sediments

    PubMed Central

    Müller, Hubert; Bosch, Julian; Griebler, Christian; Damgaard, Lars Riis; Nielsen, Lars Peter; Lueders, Tillmann; Meckenstock, Rainer U

    2016-01-01

    The biodegradation of organic pollutants in aquifers is often restricted to the fringes of contaminant plumes where steep countergradients of electron donors and acceptors are separated by limited dispersive mixing. However, long-distance electron transfer (LDET) by filamentous ‘cable bacteria' has recently been discovered in marine sediments to couple spatially separated redox half reactions over centimeter scales. Here we provide primary evidence that such sulfur-oxidizing cable bacteria can also be found at oxic–anoxic interfaces in aquifer sediments, where they provide a means for the direct recycling of sulfate by electron transfer over 1–2-cm distance. Sediments were taken from a hydrocarbon-contaminated aquifer, amended with iron sulfide and saturated with water, leaving the sediment surface exposed to air. Steep geochemical gradients developed in the upper 3 cm, showing a spatial separation of oxygen and sulfide by 9 mm together with a pH profile characteristic for sulfur oxidation by LDET. Bacterial filaments, which were highly abundant in the suboxic zone, were identified by sequencing of 16S rRNA genes and fluorescence in situ hybridization (FISH) as cable bacteria belonging to the Desulfobulbaceae. The detection of similar Desulfobulbaceae at the oxic–anoxic interface of fresh sediment cores taken at a contaminated aquifer suggests that LDET may indeed be active at the capillary fringe in situ. PMID:27058505