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Sample records for active reaction centers

  1. Nuclear Reaction Data Centers

    SciTech Connect

    McLane, V.; Nordborg, C.; Lemmel, H.D.; Manokhin, V.N.

    1988-01-01

    The cooperating Nuclear Reaction Data Centers are involved in the compilation and exchange of nuclear reaction data for incident neutrons, charged particles and photons. Individual centers may also have services in other areas, e.g., evaluated data, nuclear structure and decay data, reactor physics, nuclear safety; some of this information may also be exchanged between interested centers. 20 refs., 1 tab.

  2. Conversion of isoamyl alcohol over acid catalysts: Reaction dependence on nature of active centers

    SciTech Connect

    Babu, G.P.; Murthy, R.S.; Krishnan, V.

    1997-02-01

    Acid catalysts are known to catalyze the dehydration of alcohols. In addition some oxide catalysts with basic properties have also been shown to play an important role in such dehydration reactions. The dehydration of aliphatic alcohols to olefins has been studied in detail using alumina silica-alumina and zeolite catalysts. The olefin products further undergo isomerization in presence of acidic sites. The reaction of isoamyl alcohol on catalytic surfaces has not been investigated in greater detail. The dehydration of isoamyl alcohol is of considerable interest in fine chemicals. Isoamyl alcohol may also undergo dehydrogenation as observed in the case of n-butanol. The scope of the present work is to identify the nature of the active sites selective for dehydration and dehydrogenation of isoamyl alcohol and to modify the active sites to promote isomerization of dehydrated products. Four catalytic surfaces on which the acidic strength can be varied, as well as selectively suppressed, are chosen for this study. 17 refs., 1 fig., 3 tabs.

  3. Photosynthetic reaction centers in bacteria

    SciTech Connect

    Norris, J.R. Univ. of Chicago, IL ); Schiffer, M. )

    1990-07-30

    The photochemistry of photosynthesis begins in complexes called reaction centers. These have become model systems to study the fundamental process by which plants and bacteria convert and store solar energy as chemical free energy. In green plants, photosynthesis occurs in two systems, each of which contains a different reaction center, working in series. In one, known as photosystem 1, oxidized nicotinamide adenine dinucleotide phosphate (NADP[sup +]) is reduced to NADPH for use in a series of dark reactions called the Calvin cycle, named for Nobel Laureate Melvin Calvin, by which carbon dioxide is converted into useful fuels such as carbohydrates and sugars. In the other half of the photosynthetic machinery of green plants, called photosystem 2, water is oxidized to produce molecular oxygen. A different form of photosynthesis occurs in photosynthetic bacteria, which typically live at the bottom of ponds and feed on organic debris. Two main types of photosynthetic bacteria exist: purple and green. Neither type liberates oxygen from water. Instead, the bacteria feed on organic media or inorganic materials, such as sulfides, which are easier to reduce or oxidize than carbon dioxide or water. Perhaps in consequence, their photosynthetic machinery is simpler than that of green, oxygen-evolving plants and their primary photochemistry is better understood.

  4. Photochemical reaction centers from Rhodopseudomonas capsulata.

    PubMed

    Nieth, K F; Drews, G; Feick, R

    1975-09-30

    A photochemically active bacteriochlorophyll-protein complex (reaction center) has been isolated from the carotenoidless mutant A1a+ of Rhodopseudomonas capsulata by treatment of membranes with lauryl dimethyl amine oxide. Three proteins with molecular weights of 20,500, 24,000 and 28,000 (molar ratio 1:1:1) were detected in the reaction center preparations. After mild treatment of intracytoplasmic membranes with Na-dodecyl sulfate (0.5%, 30 degrees C, 1 min) succeeded by polyacrylamide gel electrophoresis two pigmented bands were obtained. Material of one fraction could be bleached reversibly by actinic light and contained two proteins with molecular weights of 20,500 and 24000. The second band is photochemically inactive.

  5. Site Energies of Active and Inactive Pheophytins in the Reaction Center of Photosystem II from Chlamydomonas Reinhardtii

    SciTech Connect

    Acharya, K.; Neupane, B.; Zazubovich, V.; Sayre, R. T.; Picorel, R.; Seibert, M.; Jankowiak, R.

    2012-03-29

    It is widely accepted that the primary electron acceptor in various Photosystem II (PSII) reaction center (RC) preparations is pheophytin {alpha} (Pheo {alpha}) within the D1 protein (Pheo{sub D1}), while Pheo{sub D2} (within the D2 protein) is photochemically inactive. The Pheo site energies, however, have remained elusive, due to inherent spectral congestion. While most researchers over the past two decades placed the Q{sub y}-states of Pheo{sub D1} and Pheo{sub D2} bands near 678-684 and 668-672 nm, respectively, recent modeling [Raszewski et al. Biophys. J. 2005, 88, 986-998; Cox et al. J. Phys. Chem. B 2009, 113, 12364-12374] of the electronic structure of the PSII RC reversed the assignment of the active and inactive Pheos, suggesting that the mean site energy of Pheo{sub D1} is near 672 nm, whereas Pheo{sub D2} ({approx}677.5 nm) and Chl{sub D1} ({approx}680 nm) have the lowest energies (i.e., the Pheo{sub D2}-dominated exciton is the lowest excited state). In contrast, chemical pigment exchange experiments on isolated RCs suggested that both pheophytins have their Q{sub y} absorption maxima at 676-680 nm [Germano et al. Biochemistry 2001, 40, 11472-11482; Germano et al. Biophys. J. 2004, 86, 1664-1672]. To provide more insight into the site energies of both Pheo{sub D1} and Pheo{sub D2} (including the corresponding Q{sub x} transitions, which are often claimed to be degenerate at 543 nm) and to attest that the above two assignments are most likely incorrect, we studied a large number of isolated RC preparations from spinach and wild-type Chlamydomonas reinhardtii (at different levels of intactness) as well as the Chlamydomonas reinhardtii mutant (D2-L209H), in which the active branch Pheo{sub D1} is genetically replaced with chlorophyll {alpha} (Chl {alpha}). We show that the Q{sub x}-/Q{sub y}-region site energies of Pheo{sub D1} and Pheo{sub D2} are {approx}545/680 nm and {approx}541.5/670 nm, respectively, in good agreement with our previous assignment

  6. Photosynthetic reaction center complexes from heliobacteria

    NASA Technical Reports Server (NTRS)

    Trost, J. T.; Vermaas, W. F. J.; Blankenship, R. E.

    1991-01-01

    The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus of this project is the family of newly discovered strictly anaerobic photosynthetic organisms known as Heliobacteria. These organisms are the only known photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reaction centers suggest that they might be the decendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes have been isolated from the photosynthetic bacteria Heliobacillus mobilis and Heliobacterium gestii. The absorption and fluorescence properties of membranes and reaction centers are almost identical, suggesting that a single pigment-protein complex serves as both antenna and reaction center. Experiments in progress include sequence determination of the 48,000 Mr reaction center protein, and evolutionary comparisons with other reaction center proteins.

  7. Photosynthetic reaction center complexes from heliobacteria

    NASA Technical Reports Server (NTRS)

    Trost, J. T.; Vermaas, W. F. J.; Blankenship, R. E.

    1991-01-01

    Photosynthetic reaction centers are pigment-protein complexes that are responsible for the transduction of light energy into chemical energy. Considerable evidence indicates that photosynthetic organisms were present very early in the evolution of life on Earth. The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus is on the family of newly discovered strictly anaerobic photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reactions centers suggest that they may be the descendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes were isolated from the photosynthetic bacteria, Heliobacillus mobilis and Heliobacterium gestii, by extraction of membranes with Deriphat 160C followed by differential centrifugation and sucrose density gradient centrifugation. Other aspects of this investigation are briefly discussed.

  8. Design of dinuclear manganese cofactors for bacterial reaction centers.

    PubMed

    Olson, Tien L; Espiritu, Eduardo; Edwardraja, Selvakumar; Simmons, Chad R; Williams, JoAnn C; Ghirlanda, Giovanna; Allen, James P

    2016-05-01

    A compelling target for the design of electron transfer proteins with novel cofactors is to create a model for the oxygen-evolving complex, a Mn4Ca cluster, of photosystem II. A mononuclear Mn cofactor can be added to the bacterial reaction center, but the addition of multiple metal centers is constrained by the native protein architecture. Alternatively, metal centers can be incorporated into artificial proteins. Designs for the addition of dinuclear metal centers to four-helix bundles resulted in three artificial proteins with ligands for one, two, or three dinuclear metal centers able to bind Mn. The three-dimensional structure determined by X-ray crystallography of one of the Mn-proteins confirmed the design features and revealed details concerning coordination of the Mn center. Electron transfer between these artificial Mn-proteins and bacterial reaction centers was investigated using optical spectroscopy. After formation of a light-induced, charge-separated state, the experiments showed that the Mn-proteins can donate an electron to the oxidized bacteriochlorophyll dimer of modified reaction centers, with the Mn-proteins having additional metal centers being more effective at this electron transfer reaction. Modeling of the structure of the Mn-protein docked to the reaction center showed that the artificial protein likely binds on the periplasmic surface similarly to cytochrome c2, the natural secondary donor. Combining reaction centers with exogenous artificial proteins provides the opportunity to create ligands and investigate the influence of inhomogeneous protein environments on multinuclear redox-active metal centers. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.

  9. Origin and evolution of photosynthetic reaction centers

    NASA Astrophysics Data System (ADS)

    Olson, John M.; Pierson, Beverly K.

    1987-09-01

    The prototype reaction center may have used protoporphyrin-IX associated with small peptides to transfer electrons or protons across the primitive cell membrane. The precursor of all contemporary reaction centers contained chlorophylla molecules as both primary electron donor and initial electron acceptor and an Fe-S center as secondary acceptor (RC-1 type). The biosynthetic pathway for chlorophylla evolved along with the evolution of a better organized reaction center associated with cytochromes and quinones in a primitive cyclic electron transport system. This reaction center probably functioned initially in photoassimilation, but was easily adapted to CO2 fixation using H2 and H2S as reductants. During this phase bacteriochlorophyllg may have evolved from chlorophylla in response to competition for light, and thereby initiated the gram-positive line of eubacteria. A second reaction center (RC-2) evolved from RC-1 between 3.5 and 2.5 Ga ago in response to the competition for reductants for CO2 fixation. The new organism containing RC-2 in series with RC-1 would have been able to use poor reducing agents such as the abundant aqueous ferrous ion in place of H2 and H2S. This new organism is proposed to be the common ancestor of all phototrophic eubacteria except those related to the gram-positive bacteria. All organisms containing bacteriochlorophylla lost either RC-1 or RC-2, while those organisms containing chlorophylla (ancestors of cyanobacteria) added a water-splitting enzyme to RC-2 between 3.0 and 2.5 Ga ago in order to use H2O in place of hydrated ferrous ion as electron donor for autotrophic photosynthesis.

  10. Type 1 reaction center of photosynthetic heliobacteria.

    PubMed

    Oh-oka, Hirozo

    2007-01-01

    The reaction center (RC) of heliobacteria contains iron-sulfur centers as terminal electron acceptors, analogous to those of green sulfur bacteria as well as photosystem I in cyanobacteria and higher plants. Therefore, they all belong to the so-called type 1 RCs, in contrast to the type 2 RCs of purple bacteria and photosystem II containing quinone molecules. Although the architecture of the heliobacterial RC as a protein complex is still unknown, it forms a homodimer made up of two identical PshA core proteins, where two symmetrical electron transfer pathways along the C2 axis are assumed to be equally functional. Electrons are considered to be transferred from membrane-bound cytochrome c (PetJ) to a special pair P800, a chlorophyll a-like molecule A0, (a quinone molecule A1) and a [4Fe-4S] center Fx and, finally, to 2[4Fe-4S] centers FA/FB. No definite evidence has been obtained for the presence of functional quinone acceptor A1. An additional interesting point is that the electron transfer reaction from cytochrome c to P800 proceeds in a collisional mode. It is highly dependent on the temperature, ion strength and/or viscosity in a reaction medium, suggesting that a heme-binding moiety fluctuates in an aqueous phase with its amino-terminus anchored to membranes. PMID:16842023

  11. Distributed Active Archive Center

    NASA Technical Reports Server (NTRS)

    Bodden, Lee; Pease, Phil; Bedet, Jean-Jacques; Rosen, Wayne

    1993-01-01

    The Goddard Space Flight Center Version 0 Distributed Active Archive Center (GSFC V0 DAAC) is being developed to enhance and improve scientific research and productivity by consolidating access to remote sensor earth science data in the pre-EOS time frame. In cooperation with scientists from the science labs at GSFC, other NASA facilities, universities, and other government agencies, the DAAC will support data acquisition, validation, archive and distribution. The DAAC is being developed in response to EOSDIS Project Functional Requirements as well as from requirements originating from individual science projects such as SeaWiFS, Meteor3/TOMS2, AVHRR Pathfinder, TOVS Pathfinder, and UARS. The GSFC V0 DAAC has begun operational support for the AVHRR Pathfinder (as of April, 1993), TOVS Pathfinder (as of July, 1993) and the UARS (September, 1993) Projects, and is preparing to provide operational support for SeaWiFS (August, 1994) data. The GSFC V0 DAAC has also incorporated the existing data, services, and functionality of the DAAC/Climate, DAAC/Land, and the Coastal Zone Color Scanner (CZCS) Systems.

  12. Incorporation of Photosynthetic Reaction Centers in the Membrane of Human Cells: Toward a New Tool for Optical Control of Cell Activity

    SciTech Connect

    Pennisi, Cristian P.; Jensen, Poul Erik; Zachar, Vladimir; Greenbaum, Elias; Yoshida, Ken

    2009-01-01

    The Photosystem I (PSI) reaction center is a photosynthetic membrane complex in which light-induced charge separation is accompanied by the generation of an electric potential. It has been recently proposed as a means to confer light sensitivity to cells possessing voltage-activated ion channels, but the feasibility of heterologous incorporation has not been demonstrated. In this work, methods of delivery and detection of PSI in the membrane of human cells are presented. Purified fractions of PSI were reconstituted in proteoliposomes that were used as vehicles for the membrane incorporation. A fluorescent impermeable dye was entrapped in the vesicles to qualitatively analyze the nature of the vesicle cell interaction. After incorporation, the localization and orientation of the complexes in the membrane was studied using immuno-fluorescence microscopy. The results showed complexes oriented as in native membranes, which were randomly distributed in clusters over the entire surface of the cell. Additionally, analysis of cell viability showed that the incorporation process does not damage the cell membrane. Taken together, the results of this work suggest that the mammalian cellular membrane is a reasonable environment for the incorporation of PSI complexes, which opens the possibility of using these molecular photovoltaic structures for optical control of cell activity.

  13. Supramolecular structures modeling photosynthetic reaction center function

    SciTech Connect

    Wasielewski, M.R.; Gaines, G.L. III; Gosztola, D.; Niemczyk, M.P.; Svec, W.A.

    1992-08-20

    Work in our laboratory has focused on the influence of solvent motion on the rates and energetics of photochemical charge separation in glassy solids. The efficiencies of many nonadiabatic electron transfer reactions involving photochemical electron donors with relatively low excited state energies, such as porphyrins and chlorophylls, are poor in the solid state. Recent work has shown that placing a porphyrin-acceptor system in a glassy solid at low temperature significantly raises the energy of ks ion-pair state. This destabilization can be as much as 0.8 eV relative to the ion pair state energy in a polar liquid. This contrasts sharply with photosynthetic reaction centers, which maintain medium-independent electron transfer rates with relatively small free energies of charge separation. Using this information we have set out to design photochemical systems that produce long-lived radical ion pairs in glassy solids with high quantum efficiency. These systems maintain their efficiency when placed in other glassy matrices, such as polymers. An important consequence of this effort is the design of molecules that minimize the electronic interaction between the oxidized donor and reduced acceptor. This minimization can be attained by careful design of the spacer groups linking the donor and acceptor and by using more than a single electron transfer step to increase the distance between the separated charges as is done in natural photosynthesis.

  14. Visitors Center activities

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Astronaut Katherine Hire and LEGO-Master Model Builders assisted children from Mississippi, Louisiana and Mississippi in the building of a 12-foot tall Space Shuttle made entirely from tiny LEGO bricks at the John C. Stennis Space Center Visitors Center in South Mississippi. The shuttle was part of an exhibit titled ' Travel in Space' World Show which depicts the history of flight and space travel from the Wright brothers to future generations of space vehicles. For more information concerning hours of operation or Visitors Center educational programs, call 1-800-237-1821 in Mississippi and Louisiana or (601) 688-2370.

  15. Visitors Center activities

    NASA Technical Reports Server (NTRS)

    1997-01-01

    More than 2,000 children and adults from Mississippi, Louisiana and Alabama recently build a 12-foot tall Space Shuttle made entirely from tiny LEGO bricks at the John C. Stennis Space Center Visitors Center in South Mississippi. The shuttle was part of an exhibit titled 'Travel in Space' World Show which depicts the history of flight and space travel from the Wright brothers to future generations of space vehicles. For more information concerning hours of operation or Visitors Center educational programs, call 1-800-237-1821 in Mississippi and Louisiana or (601) 688-2370.

  16. Multiantenna artificial photosynthetic reaction center complex.

    PubMed

    Terazono, Yuichi; Kodis, Gerdenis; Liddell, Paul A; Garg, Vikas; Moore, Thomas A; Moore, Ana L; Gust, Devens

    2009-05-21

    In order to ensure efficient utilization of the solar spectrum, photosynthetic organisms use a variety of antenna chromophores to absorb light and transfer excitation to a reaction center, where photoinduced charge separation occurs. Reported here is a synthetic molecular heptad that features two bis(phenylethynyl)anthracene and two borondipyrromethene antennas linked to a hexaphenylbenzene core that also bears two zinc porphyrins. A fullerene electron acceptor self-assembles to both porhyrins via dative bonds. Excitation energy is transferred very efficiently from all four antennas to the porphyrins. Singlet-singlet energy transfer occurs both directly and by a stepwise funnel-like pathway wherein excitation moves down a thermodynamic gradient. The porphyrin excited states donate an electron to the fullerene with a time constant of 3 ps to generate a charge-separated state with a lifetime of 230 ps. The overall quantum yield is close to unity. In the absence of the fullerene, the porphyrin excited singlet state donates an electron to a borondipyrromethene on a slower time scale. This molecule demonstrates that by incorporating antennas, it is possible for a molecular system to harvest efficiently light throughout the visible from ultraviolet wavelengths out to approximately 650 nm.

  17. The role played by acid and basic centers in the activity of biomimetic catalysts of the catalase, peroxidase, and monooxidase reactions

    NASA Astrophysics Data System (ADS)

    Magerramov, A. M.; Nagieva, I. T.

    2010-11-01

    The acid-basic centers of heterogeneous carriers of catalase, peroxidase, and monooxigenase biomimetics, in particular, iron protoporphyrin deposited on active or neutral aluminum magnesium silicate, were studied. The catalytic activity of biomimetics was stabilized, which allowed us not only to synthesize fairly effective biomimetics but also to clarify certain details of the mechanism of their action and perform a comparative analysis of the functioning of biomimetics and the corresponding enzymes.

  18. Conformationally Constrained Macrocyclic Diporphyrin-Fullerene Artificial Photosynthetic Reaction Center

    SciTech Connect

    Garg, Vikas; Kodis, Gerdenis; Chachisvilis, Mirianas; Hambourger, Michael; Moore, Ana L.; Moore, Thomas A.; Gust, Devens

    2011-02-14

    Photosynthetic reaction centers convert excitation energy from absorbed sunlight into chemical potential energy in the form of a charge-separated state. The rates of the electron transfer reactions necessary to achieve long-lived, high-energy charge-separated states with high quantum yields are determined in part by precise control of the electronic coupling among the chromophores, donors, and acceptors and of the reaction energetics. Successful artificial photosynthetic reaction centers for solar energy conversion have similar requirements. Control of electronic coupling in particular necessitates chemical linkages between active component moieties that both mediate coupling and restrict conformational mobility so that only spatial arrangements that promote favorable coupling are populated. Toward this end, we report the synthesis, structure, and photochemical properties of an artificial reaction center containing two porphyrin electron donor moieties and a fullerene electron acceptor in a macrocyclic arrangement involving a ring of 42 atoms. The two porphyrins are closely spaced, in an arrangement reminiscent of that of the special pair in bacterial reaction centers. The molecule is produced by an unusual cyclization reaction that yields mainly a product with C2 symmetry and trans-2 disubstitution at the fullerene. The macrocycle maintains a rigid, highly constrained structure that was determined by UV-vis spectroscopy, NMR, mass spectrometry, and molecular modeling at the semiempirical PM6 and DFT (B3LYP/6-31G**) levels. Transient absorption results for the macrocycle in 2-methyltetrahydrofuran reveal photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene to form a P•--C60•--P charge separated state with a time constant of 1.1 ps. Photoinduced electron transfer to the fullerene excited singlet state to form the same charge-separated state has a time constant of 15 ps. The

  19. Properties of photochemical reaction centers purified from Rhodopseudomonas gelatinosa.

    PubMed

    Clayton, B J; Clayton, R K

    1978-03-13

    Reaction centers were isolated from a carotenoidless mutant of Rhodopseudomonas gelatinosa by hydroxyapatite chromatography of purified chromatophores treated with lauryl dimethyl amine oxide. Absorption spectra and spectra of light-induced absorbance changes are similar to those of reaction centers from Rhodopseudomonas sphaeroides. The ratio of absorbance at 280 nm to that at 799 nm was 1.8 in the purest preparations. The extinction coefficient at the 799 nm absorption maximum was estimated to be 305 +/- 20 mM--1 . CM--1. The molecular weight based on protein and chromophore assays was found to be 1.5 . 10(5); the reaction center protein accounted for 6% of the total membrane protein. These reaction centers contained no cytochrome and showed just two components of apparent molecular weights 33 000 and 25 000 in polyacrylamide gel electrophoresis. The chromatophores contained 42 molecules of antenna bacteriochlorophyll for each reaction center.

  20. Evolution of a reaction center in an explosive material

    NASA Technical Reports Server (NTRS)

    Jackson, T. L.; Kapila, A. K.; Stewart, D. S.

    1989-01-01

    Consideration is given to the spatial structure and temporal evolution of a reaction center for a model involving Arrhenius kinetics. The center, which is characterized by peaks in pressure and temperature with little diminution in local density, is found to have one of two possible self-similar structures. The analysis uses a combination of asymptotics and numerics and terminates when pressure and temperature in the reaction center have peaked.

  1. Dispersed Polaron Simulations of Electron Transfer in Photosynthetic Reaction Centers

    NASA Astrophysics Data System (ADS)

    Warshel, A.; Chu, Z. T.; Parson, W. W.

    1989-10-01

    A microscopic method for simulating quantum mechanical, nuclear tunneling effects in biological electron transfer reactions is presented and applied to several electron transfer steps in photosynthetic bacterial reaction centers. In this ``dispersed polaron'' method the fluctuations of the protein and the electron carriers are projected as effective normal modes onto an appropriate reaction coordinate and used to evaluate the quantum mechanical rate constant. The simulations, based on the crystallographic structure of the reaction center from Rhodopseudomonas viridis, focus on electron transfer from a bacteriopheophytin to a quinone and the subsequent back-reaction. The rates of both of these reactions are almost independent of temperature or even increase with decreasing temperature. The simulations reproduce this unusual temperature dependence in a qualitative way, without the use of adjustable parameters for the protein's Franck-Condon factors. The observed dependence of the back-reaction on the free energy of the reaction also is reproduced, including the special behavior in the ``inverted region.''

  2. Germinal center B cells and mixed leukocyte reactions

    SciTech Connect

    Monfalcone, A.P.; Kosco, M.H.; Szakal, A.K.; Tew, J.G. )

    1989-09-01

    The present study was undertaken to determine if germinal center (GC) B cells are sufficiently activated to stimulate mixed leukocyte reactions (MLR). Percoll density fractionation and a panning technique with peanut agglutinin (PNA) were used to isolate GC B cells from the lymph nodes of immune mice. The GC B cells were treated with mitomycin C or irradiation and used to stimulate allogeneic or syngeneic splenic T cells in the MLR. Controls included high-density (HD) B cells prepared from spleens of the same mice and HD B cells activated with lipopolysaccharide (LPS) and dextran sulfate. GC B cells bound high amount sof PNA (i.e., PNAhi). Similarly, the LPS-dextran sulfate-activated B cells were PNAhi. Treatment with neuraminidase rendered the PNAlo HD B cells PNAhi. GC B cells and the LPS-dextran sulfate-activated HD B cells stimulated a potent MLR, while the untreated HD B cells did not. However, following neuraminidase treatment, the resulting PNAhi HD B cell population was able to induce an MLR. The PNA marker appeared to be an indicator of stimulatory activity, but incubating the cells with PNA to bind the cell surface ligand did not interfere with the MLR. GC B cells were also capable of stimulating a syngeneic MLR in most experiments although this was not consistently obtained. It appears that germinal centers represent a unique in vivo microenvironment that provides the necessary signals for B cells to become highly effective antigen-presenting cells.

  3. Bio-Photoelectrochemical Solar Cells Incorporating Reaction Center and Reaction Center Plus Light Harvesting Complexes

    NASA Astrophysics Data System (ADS)

    Yaghoubi, Houman

    Harvesting solar energy can potentially be a promising solution to the energy crisis now and in the future. However, material and processing costs continue to be the most important limitations for the commercial devices. A key solution to these problems might lie within the development of bio-hybrid solar cells that seeks to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. The bio-photoelectrochemical cell technologies exploit biomimetic means of energy conversion by utilizing plant-derived photosystems which can be inexpensive and ultimately the most sustainable alternative. Plants and photosynthetic bacteria harvest light, through special proteins called reaction centers (RCs), with high efficiency and convert it into electrochemical energy. In theory, photosynthetic RCs can be used in a device to harvest solar energy and generate 1.1 V open circuit voltage and ~1 mA cm-2 short circuit photocurrent. Considering the nearly perfect quantum yield of photo-induced charge separation, efficiency of a protein-based solar cell might exceed 20%. In practice, the efficiency of fabricated devices has been limited mainly due to the challenges in the electron transfer between the protein complex and the device electrodes as well as limited light absorption. The overarching goal of this work is to increase the power conversion efficiency in protein-based solar cells by addressing those issues (i.e. electron transfer and light absorption). This work presents several approaches to increase the charge transfer rate between the photosynthetic RC and underlying electrode as well as increasing the light absorption to eventually enhance the external quantum efficiency (EQE) of bio-hybrid solar cells. The first approach is to decrease the electron transfer distance between one of the redox active sites in the RC and the underlying electrode by direct attachment of the of protein complex

  4. Characterisation of reaction centers and their phospholipids from Rhodospirillum rubrum.

    PubMed

    Snozzi, M; Bachofen, R

    1979-05-01

    1. Reaction centers from Rhodospirillum rubrum have been extracted with the zwitterionic detergent lauryl dimethyl amine oxide. Subsequent purification has been achieved by gel filtration and ion-exchange chromatography. The pure reaction centers are composed of three protein subunits (L, M, H), bacteriocholorophyll and bacteriopheophytin in the ratio 2 : 1 and phospholipids. 2. The phospholipid composition has been found to be similar to that of whole chromatophore membrane, except that diphosphatidyl glycerol is present in higher amount in the isolated complex. When the detergent treatment of the chromatophore membrane is done in the presence of NaCl, a lower phospholipid content in isolated reaction centers has been found together with a lower stability in the association among the protein subunits. In this complex, the largest subunit H is easily split off and a LM complex is obtained. It is concluded that the phospholipids play an important role in the stability of reaction center complexes.

  5. [Protein fluorescence of photosynthetic reaction centers from Rhodopseudomonas sphaeroides].

    PubMed

    Zakharova, N I; Permiakov, E A; Fabian, M; Kononenko, A A; Chamorovskiĭ, S K

    1984-01-01

    Luminescence emitted by tryptophan residues of reaction center (RC) preparations was studied. The RG preparations were isolated from the photosynthetic bacterium Rhodopseudomonas sphaeroides by treatment with lauryl dimethyl amine oxide (LDAO). After excitation at lambda 280 nm the quantum yield of luminescence is 0,02. It is shown that 60% of tryptophanyls are located inside the protein globule in the surrounding of relaxating polar groups and the rest approximately 40% on the outer surface of the globule--predominantly in the positively charged region of the LDAO-RC protein--in the surrounding of protein-bound water molecules. There is a correlation between the pH dependencies of the position of the peak of luminescence from tryptophanyls and effectivity of electron transfer from the primary (quinone) to secondary acceptor. The two parameters are invariant at pH from 7 to 9 and vary at pH less than 7 and pH greater than 9. The phenomena responsible for the observed correlation are discussed on the basis of pH-dependent changes in the RC protein which govern electron transport activity at the reaction center.

  6. Artificial photosynthetic reaction centers coupled to light-harvesting antennas.

    PubMed

    Ghosh, Pulak Kumar; Smirnov, Anatoly Yu; Nori, Franco

    2011-12-01

    We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic system. The photosystem consists of a molecular triad (i.e., with a donor, a photosensitive unit, and an acceptor) coupled to four accessory light-harvesting-antenna pigments. The resonant energy transfer from the antennas to the artificial reaction center (the molecular triad) is described here by the Förster mechanism. We consider two different kinds of arrangements of the accessory light-harvesting pigments around the reaction center. The first arrangement allows direct excitation transfer to the reaction center from all the surrounding pigments. The second configuration transmits energy via a cascade mechanism along a chain of light-harvesting chromophores, where only one chromophore is connected to the reaction center. We show that the artificial photosynthetic system using the cascade energy transfer absorbs photons in a broader wavelength range and converts their energy into electricity with a higher efficiency than the system based on direct couplings between all the antenna chromophores and the reaction center.

  7. Evolution of heliobacteria: implications for photosynthetic reaction center complexes

    NASA Technical Reports Server (NTRS)

    Vermaas, W. F.; Blankenship, R. E. (Principal Investigator)

    1994-01-01

    The evolutionary position of the heliobacteria, a group of green photosynthetic bacteria with a photosynthetic apparatus functionally resembling Photosystem I of plants and cyanobacteria, has been investigated with respect to the evolutionary relationship to Gram-positive bacteria and cyanobacteria. On the basis of 16S rRNA sequence analysis, the heliobacteria appear to be most closely related to Gram-positive bacteria, but also an evolutionary link to cyanobacteria is evident. Interestingly, a 46-residue domain including the putative sixth membrane-spanning region of the heliobacterial reaction center protein show rather strong similarity (33% identity and 72% similarity) to a region including the sixth membrane-spanning region of the CP47 protein, a chlorophyll-binding core antenna polypeptide of Photosystem II. The N-terminal half of the heliobacterial reaction center polypeptide shows a moderate sequence similarity (22% identity over 232 residues) with the CP47 protein, which is significantly more than the similarity with the Photosystem I core polypeptides in this region. An evolutionary model for photosynthetic reaction center complexes is discussed, in which an ancestral homodimeric reaction center protein (possibly resembling the heliobacterial reaction center protein) with 11 membrane-spanning regions per polypeptide has diverged to give rise to the core of Photosystem I, Photosystem II, and of the photosynthetic apparatus in green, purple, and heliobacteria.

  8. The breakdown of vinyl ethers as a two-center synchronous reaction

    NASA Astrophysics Data System (ADS)

    Pokidova, T. S.; Shestakov, A. F.

    2009-11-01

    The experimental data on the molecular decomposition of vinyl ethers of various structures to alkanes and the corresponding aldehydes or ketones in the gas phase were analyzed using the method of intersecting parabolas. The enthalpies and kinetic parameters of decomposition were calculated for 17 reactions. The breakdown of ethers is a two-center concerted reaction characterized by a very high classical potential barrier to the thermally neutral reaction (180-190 kJ/mol). The kinetic parameters (activation energies and rate constants) of back reactions of the formation of vinyl ethers in the addition of aldehydes or ketones to alkanes were calculated using the method of intersecting parabolas. The factors that influenced the activation energy of the decomposition and formation of ethers were discussed. Quantum-chemical calculations of several vinyl ether decomposition reactions were performed. Ether formation reactions were compared with the formation of unsaturated alcohols as competitive reactions, which can occur in the interaction of carbonyl compounds with alkenes.

  9. Reaction of cytochrome c2 with photosynthetic reaction centers from Rhodopseudomonas viridis.

    PubMed

    Knaff, D B; Willie, A; Long, J E; Kriauciunas, A; Durham, B; Millett, F

    1991-02-01

    The reactions of Rhodopseudomonas viridis cytochrome c2 and horse cytochrome c with Rps. viridis photosynthetic reaction centers were studied by using both single- and double-flash excitation. Single-flash excitation of the reaction centers resulted in rapid photooxidation of cytochrome c-556 in the cytochrome subunit of the reaction center. The photooxidized cytochrome c-556 was subsequently reduced by electron transfer from ferrocytochrome c2 present in the solution. The rate constant for this reaction had a hyperbolic dependence on the concentration of cytochrome c2, consistent with the formation of a complex between cytochrome c2 and the reaction center. The dissociation constant of the complex was estimated to be 30 microM, and the rate of electron transfer within the 1:1 complex was 270 s-1. Double-flash experiments revealed that ferricytochrome c2 dissociated from the reaction center with a rate constant of greater than 100 s-1 and allowed another molecule of ferrocytochrome c2 to react. When both cytochrome c-556 and cytochrome c-559 were photooxidized with a double flash, the rate constant for reduction of both components was the same as that observed for cytochrome c-556 alone. The observed rate constant decreased by a factor of 14 as the ionic strength was increased from 5 mM to 1 M, indicating that electrostatic interactions contributed to binding. Molecular modeling studies revealed a possible cytochrome c2 binding site on the cytochrome subunit of the reaction center involving the negatively charged residues Glu-93, Glu-85, Glu-79, and Glu-67 which surround the heme crevice of cytochrome c-554.(ABSTRACT TRUNCATED AT 250 WORDS)

  10. Photosynthetic reaction center of green sulfur bacteria studied by EPR

    SciTech Connect

    Nitschke, W.; Rutherford, A.W. ); Fieler, U. )

    1990-04-24

    Membrane preparations of two species of the green sulfur bacteria Chlorobium have been studied be EPR. Three signals were detected which were attributed to iron-sulfur centers acting as electron acceptors in the photosynthetic reaction center. (1) A signal from a center designated F{sub B}, was photoinduced at 4K. (2) A similar signal, F{sub A}, was photoinduced in addition to the F{sub B} signal upon a short period of illumination at 200 K. (3) Further illumination at 200 K resulted in the appearance of a broad feature at g=1.78. This is attributed to the g{sub x} component of an iron-sulfur center designated F{sub X}. The designations of these signals as F{sub B}, F{sub A}, and F{sub X} are based on their spectroscopic similarities to signals in photosystem I (PS I). The orientation dependence of these EPR signals in ordered Chlorobium membrane multilayers is remarkably similar to that of their PS I homologues. A magnetic interaction between the reduced forms of F{sub B} and F{sub A} occurs, which is also very similar to that seen in PS I. The triplet state of P{sub 840}, the primary electron donor, could be photoinduced at 4 K in samples which had been preincubated with sodium dithionite and methyl viologen and then preilluminated at 200 K. The preillumination reduces the iron-sulfur centers while the preincubation is thought to result in the inactivation of an earlier electron acceptor. Orientation studies of the triplet signal in ordered multilayers indicate that the bacteriochlorophylls which act as the primary electron donor in Chlorobium are arranged with a structural geometry almost identical with that of the special pair in purple bacteria. The Chlorobium reaction center appears to be similar in some respects to both PS I and to the purple bacterial reaction center. This is discussed with regard to the evolution of the different types of reaction centers from a common ancestor.

  11. Modeling charge transfer in the photosynthetic reaction center

    NASA Astrophysics Data System (ADS)

    Pudlak, Michal; Pinčak, Richard

    2003-12-01

    In this work, we present a model to elucidate the unidirectionality of the primary charge-separation process in the bacterial reaction centers. We have used a model of three sites/molecules with electron transfer beginning at site 1 with an option to proceed to site 2 or site 3. We used a stochastic model with arbitrary correlation functions. We get the quantum yields of electron escape via the sites 2,3 in two limiting cases that correspond to a spectral density of underdamped and overdamped Brownian oscillator. In the fast modulation limit of an overdamped regime we get the effect, which was named “fear of death,” in which for strong enough sink parameters the electron has a tendency to avoid the place with greater sink. The presented model was used to provide a plausible explanation of the temperature dependence of the quantum yields of the Rhodobacter sphaeroides photosynthetic reaction center in the high-temperature regime.

  12. Purification of the photosynthetic reaction center from Heliobacterium modesticaldum.

    PubMed

    Sarrou, Iosifina; Khan, Zahid; Cowgill, John; Lin, Su; Brune, Daniel; Romberger, Steven; Golbeck, John H; Redding, Kevin E

    2012-03-01

    We have developed a purification protocol for photoactive reaction centers (HbRC) from Heliobacterium modesticaldum. HbRCs were purified from solubilized membranes in two sequential chromatographic steps, resulting in the isolation of a fraction containing a single polypeptide, which was identified as PshA by LC-MS/MS of tryptic peptides. All polypeptides reported earlier as unknown proteins (in Heinnickel et al., Biochemistry 45:6756-6764, 2006; Romberger et al., Photosynth Res 104:293-303, 2010) are now identified by mass spectrometry to be the membrane-bound cytochrome c (553) and four different ABC-type transporters. The purified PshA homodimer binds the following pigments: 20 bacteriochlorophyll (BChl) g, two BChl g', two 8(1)-OH-Chl a (F), and one 4,4'-diaponeurosporene. It lacks the PshB polypeptide binding the F(A) and F(B) [4Fe-4S] clusters. It is active in charge separation and exhibits a trapping time of 23 ps, as judged by time-resolved fluorescence studies. The charge recombination rate of the P(800) (+)F(X)(-) state is 10-15 ms, as seen before. The purified HbRC core was able to reduce cyanobacterial flavodoxin in the light, exhibiting a K (M) of 10 μM and a k (cat) of 9.5 s(-1) under near-saturating light. There are ~1.6 menaquinones per HbRC in the purified complex. Illumination of frozen HbRC in the presence of dithionite can cause creation of a radical at g = 2.0046, but this is not a semiquinone. Furthermore, we show that high-purity HbRCs are very stable in anoxic conditions and even remain active in the presence of oxygen under low light. PMID:22383054

  13. Reaction Rate Measurements at the National Criticality Experiments Research Center

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Bounds, J. A.; Brooks, G. H., Jr.; Favorite, J. A.; Goda, J. M.; Hayes, D. K.; Jackman, K. R.; Little, R. C.; Macinnes, M. R.; Myers, W. L.; Oldham, W. J.; Rundberg, R. S.; Sanchez, R. G.; Schake, A. R.; White, M. C.; Wilkerson, C. W., Jr.

    2014-09-01

    With the resumption of regular operations of the Los Alamos Critical Assemblies at the National Criticality Experiments Research Center (NCERC), located at the Nevada National Security Site, we have embarked upon a series of campaigns to restore the capability to perform integral reaction rate and fission product yield measurements using historical radiochemical methods. This talk will present an overview of the current and future experimental plans, including results from our experimental campaigns on the Comet/Zeus and Flattop assemblies.

  14. Manganese oxidation by modified reaction centers from Rhodobacter sphaeroides.

    PubMed

    Kálmán, L; LoBrutto, R; Allen, J P; Williams, J C

    2003-09-23

    The transfer of an electron from exogenous manganese (II) ions to the bacteriochlorophyll dimer, P, of bacterial reaction centers was characterized for a series of mutants that have P/P(+) midpoint potentials ranging from 585 to 765 mV compared to 505 mV for wild type. Light-induced changes in optical and EPR spectra of the mutants were measured to monitor the disappearance of the oxidized dimer upon electron donation by manganese in the presence of bicarbonate. The extent of electron transfer was strongly dependent upon the P/P(+) midpoint potential. The midpoint potential of the Mn(2+)/Mn(3+) couple was calculated to decrease linearly from 751 to 623 mV as the pH was raised from 8 to 10, indicating the involvement of a proton. The electron donation had a second order rate constant of approximately 9 x 10(4) M(-1) s(-1), determined from the linear increase in rate for Mn(2+) concentrations up to 200 microM. Weak dissociation constants of 100-200 microM were found. Quantitative EPR analysis of the six-line free Mn(2+) signal revealed that up to seven manganese ions were associated with the reaction centers at a 1 mM concentration of manganese. The association and the electron transfer between manganese and the reaction centers could be inhibited by Ca(2+) and Na(+) ions. The ability of reaction centers with high potentials to oxidize manganese suggests that manganese oxidation could have preceded water oxidation in the evolutionary development of photosystem II. PMID:12974637

  15. Dynamic response of a plane-symmetrical exothermic reaction center.

    NASA Technical Reports Server (NTRS)

    Meyer, J. W.; Oppenheim, A. K.

    1972-01-01

    ?sger,An analysis of the dynamic behavior of an idealized, plane-symmetrical exothermic reaction center is presented. The conservation equations for the reaction center are combined and yield a single integral equation expressing a nonlinear transfer function of the system for which the input is provided by a given time profile of the heat released per unit mass while the output gives the pressure pulse it generates under the restriction of plane-symmetrical motion. The solution is governed by a Daumk]hler number. For a given form of the exothermic power pulse profile, the dynamic behavior of the system is completely specified in terms of only this Daumk]hler number and the heat of reaction per unit mass of the combustible medium. Specific solutions are worked out for a set of typical elementary power pulse profiles, and the practical significance of the results is illustrated by their application to the problem of transition to detonation in an explosive gas.

  16. Protein Dynamics Control of Electron Transfer in Photosynthetic Reaction Centers from Rps. Sulfoviridis

    PubMed Central

    Medvedev, E. S.; Kotelnikov, A. I.; Barinov, A. V.; Psikha, B. L.; Ortega, J. M.; Popović, D. M.; Stuchebrukhov, A. A.

    2009-01-01

    In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi–Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4–0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed. PMID:18284231

  17. [Fernbank Science Center Environmental Activities].

    ERIC Educational Resources Information Center

    Shelton, Lewis

    This document is a compilation of environmental activities related directly to the environment in Georgia. A description of the physiographic characteristics of Georgia is presented upon which the activities that follow are based. These activities include soil, stream and forest investigations; meteorology activities; and plant and animal studies.…

  18. Photosynthetic reaction center as a quantum heat engine.

    PubMed

    Dorfman, Konstantin E; Voronine, Dmitri V; Mukamel, Shaul; Scully, Marlan O

    2013-02-19

    Two seemingly unrelated effects attributed to quantum coherence have been reported recently in natural and artificial light-harvesting systems. First, an enhanced solar cell efficiency was predicted and second, population oscillations were measured in photosynthetic antennae excited by sequences of coherent ultrashort laser pulses. Because both systems operate as quantum heat engines (QHEs) that convert the solar photon energy to useful work (electric currents or chemical energy, respectively), the question arises whether coherence could also enhance the photosynthetic yield. Here, we show that both effects arise from the same population-coherence coupling term which is induced by noise, does not require coherent light, and will therefore work for incoherent excitation under natural conditions of solar excitation. Charge separation in light-harvesting complexes occurs in a pair of tightly coupled chlorophylls (the special pair) at the heart of photosynthetic reaction centers of both plants and bacteria. We show the analogy between the energy level schemes of the special pair and of the laser/photocell QHEs, and that both population oscillations and enhanced yield have a common origin and are expected to coexist for typical parameters. We predict an enhanced yield of 27% in a QHE motivated by the reaction center. This suggests nature-mimicking architectures for artificial solar energy devices. PMID:23365138

  19. A multi-pathway model for photosynthetic reaction center.

    PubMed

    Qin, M; Shen, H Z; Yi, X X

    2016-03-28

    Charge separation occurs in a pair of tightly coupled chlorophylls at the heart of photosynthetic reaction centers of both plants and bacteria. Recently it has been shown that quantum coherence can, in principle, enhance the efficiency of a solar cell, working like a quantum heat engine. Here, we propose a biological quantum heat engine (BQHE) motivated by Photosystem II reaction center (PSII RC) to describe the charge separation. Our model mainly considers two charge-separation pathways which is more than that typically considered in the published literature. We explore how these cross-couplings increase the current and power of the charge separation and discuss the effects of multiple pathways in terms of current and power. The robustness of the BQHE against the charge recombination in natural PSII RC and dephasing induced by environments is also explored, and extension from two pathways to multiple pathways is made. These results suggest that noise-induced quantum coherence helps to suppress the influence of acceptor-to-donor charge recombination, and besides, nature-mimicking architectures with engineered multiple pathways for charge separations might be better for artificial solar energy devices considering the influence of environments. PMID:27036480

  20. A multi-pathway model for photosynthetic reaction center

    NASA Astrophysics Data System (ADS)

    Qin, M.; Shen, H. Z.; Yi, X. X.

    2016-03-01

    Charge separation occurs in a pair of tightly coupled chlorophylls at the heart of photosynthetic reaction centers of both plants and bacteria. Recently it has been shown that quantum coherence can, in principle, enhance the efficiency of a solar cell, working like a quantum heat engine. Here, we propose a biological quantum heat engine (BQHE) motivated by Photosystem II reaction center (PSII RC) to describe the charge separation. Our model mainly considers two charge-separation pathways which is more than that typically considered in the published literature. We explore how these cross-couplings increase the current and power of the charge separation and discuss the effects of multiple pathways in terms of current and power. The robustness of the BQHE against the charge recombination in natural PSII RC and dephasing induced by environments is also explored, and extension from two pathways to multiple pathways is made. These results suggest that noise-induced quantum coherence helps to suppress the influence of acceptor-to-donor charge recombination, and besides, nature-mimicking architectures with engineered multiple pathways for charge separations might be better for artificial solar energy devices considering the influence of environments.

  1. In vivo assessment of effect of phytotoxin tenuazonic acid on PSII reaction centers.

    PubMed

    Chen, Shiguo; Strasser, Reto Jörg; Qiang, Sheng

    2014-11-01

    Tenuazonic acid (TeA), a phytotoxin produced by the fungus Alternaria alternata isolated from diseased croftonweed (Ageratina adenophora), exhibits a strong inhibition in photosystem II (PSII) activity. In vivo chlorophyll fluorescence transients of the host plant croftonweed, show that the dominant effect of TeA is not on the primary photochemical reaction but on the biochemical reaction after QA. The most important action site of TeA is the QB site on the PSII electron-acceptor side, blocking electron transport beyond QA(-) by occupying the QB site in the D1 protein. However, TeA does not affect the antenna pigments, the energy transfer from antenna pigment molecules to reaction centers (RCs), and the oxygen-evolving complex (OEC) at the donor side of PSII. TeA severely inactivated PSII RCs. The fraction of non-QA reducing centers and non-QB reducing centers show a time- and concentration-dependent linear increase. Conversely, the amount of active QA or QB reducing centers declined sharply in a linear way. The fraction of non-QB reducing centers calculated from data of fluorescence transients is close to the number of PSII RCs with their QB site filled by TeA. An increase of the step-J level (VJ) in the OJIP fluorescence transients attributed to QA(-) accumulation due to TeA bound to the QB site is a typical characteristic response of the plants leaf with respect to TeA penetration.

  2. Structure-function investigations of bacterial photosynthetic reaction centers.

    PubMed

    Leonova, M M; Fufina, T Yu; Vasilieva, L G; Shuvalov, V A

    2011-12-01

    During photosynthesis light energy is converted into energy of chemical bonds through a series of electron and proton transfer reactions. Over the first ultrafast steps of photosynthesis that take place in the reaction center (RC) the quantum efficiency of the light energy transduction is nearly 100%. Compared to the plant and cyanobacterial photosystems, bacterial RCs are well studied and have relatively simple structure. Therefore they represent a useful model system both for manipulating of the electron transfer parameters to study detailed mechanisms of its separate steps as well as to investigate the common principles of the photosynthetic RC structure, function, and evolution. This review is focused on the research papers devoted to chemical and genetic modifications of the RCs of purple bacteria in order to study principles and mechanisms of their functioning. Investigations of the last two decades show that the maximal rates of the electron transfer reactions in the RC depend on a number of parameters. Chemical structure of the cofactors, distances between them, their relative orientation, and interactions to each other are of great importance for this process. By means of genetic and spectral methods, it was demonstrated that RC protein is also an essential factor affecting the efficiency of the photochemical charge separation. Finally, some of conservative water molecules found in RC not only contribute to stability of the protein structure, but are directly involved in the functioning of the complex.

  3. Energy Adventure Center. Activity Book.

    ERIC Educational Resources Information Center

    Carlton, Linda L.

    Energy activities are provided in this student activity book. They include: (1) an energy walk; (2) forms of energy in the home; (3) energy conversion; (4) constructing a solar hot dog cooker (with instructions for drawing a parabola); (5) interviewing senior citizens to learn about energy use in the past; (6) packaging materials; (7) insulation;…

  4. Rapid-flow resonance Raman spectroscopy of bacterial photosynthetic reaction centers.

    PubMed Central

    Shreve, A P; Cherepy, N J; Franzen, S; Boxer, S G; Mathies, R A

    1991-01-01

    Rapid-flow resonance Raman vibrational spectra of bacterial photosynthetic reaction centers from the R-26 mutant of Rhodobacter sphaeroides have been obtained by using excitation wavelengths (810-910 nm) resonant with the lowest energy, photochemically active electronic absorption. The technique of shifted excitation Raman difference spectroscopy is used to identify genuine Raman scattering bands in the presence of a large fluorescence background. The comparison of spectra obtained from untreated reaction centers and from reaction centers treated with the oxidant K3Fe(CN)6 demonstrates that resonance enhancement is obtained from the special pair. Relatively strong Raman scattering is observed for special pair vibrations with frequencies of 36, 94, 127, 202, 730, and 898 cm-1; other modes are observed at 71, 337, and 685 cm-1. Qualitative Raman excitation profiles are reported for some of the strong modes, and resonance enhancement is observed to occur throughout the near-IR absorption band of the special pair. These Raman data determine which vibrations are coupled to the optical absorption in the special pair and, thus, probe the nuclear motion that occurs after electronic excitation. Implications for the interpretation of previous hole-burning experiments and for the excited-state dynamics and photochemistry of reaction centers are discussed. PMID:1763034

  5. Primary charge separation in isolated photosystem II reaction centers

    SciTech Connect

    Seibert, M.; Toon, S. ); Govindjee ); O'Neil, M.P.; Wasielewski, M.R. )

    1992-08-24

    Primary charge-separation in isolated bacterial reaction center (RC) complex occurs in 2.8 ps at room temperature and 0.7--1.2 ps at 10 K. Because of similarities between the bacterial and photosystem II (PSII) RCs, it has been of considerable interest to obtain analogous charge-separation rates in the higher plant system. Our previous femtosecond transient absorption studies used PSII RC material stabilized with PEG or by exchanging dodecyl maltoside (DM) for Triton in the isolation procedure. These materials gave charge-separation 1/e times of 3.0 [plus minus] 0.6 ps at 4[degree]C and 1.4[plus minus] 0.2 ps at 15 K based on the risetime of transient absorption kinetics at 820 nm. These values were thought to represent the time required for formation of the P680[sup +]-Pheo[sup [minus

  6. The Hydrologic Cycle Distributed Active Archive Center

    NASA Technical Reports Server (NTRS)

    Hardin, Danny M.; Goodman, H. Michael

    1995-01-01

    The Marshall Space Flight Center Distributed Active Archive Center in Huntsville, Alabama supports the acquisition, production, archival and dissemination of data relevant to the study of the global hydrologic cycle. This paper describes the Hydrologic Cycle DAAC, surveys its principle data holdings, addresses future growth, and gives information for accessing the data sets.

  7. Ex vivo engineered immune organoids for controlled germinal center reactions

    PubMed Central

    Purwada, Alberto; Jaiswal, Manish K.; Ahn, Haelee; Nojima, Takuya; Kitamura, Daisuke; Gaharwar, Akhilesh K.; Cerchietti, Leandro; Singh, Ankur

    2015-01-01

    Ex vivo engineered three-dimensional organotypic cultures have enabled the real-time study and control of biological functioning of mammalian tissues. Organs of broad interest where its architectural, cellular, and molecular complexity has prevented progress in ex vivo engineering are the secondary immune organs. Ex vivo immune organs can enable mechanistic understanding of the immune system and more importantly, accelerate the translation of immunotherapies as well as a deeper understanding of the mechanisms that lead to their malignant transformation into a variety of B and T cell malignancies. However, till date, no modular ex vivo immune organ has been developed with an ability to control the rate of immune reaction through tunable design parameter. Here we describe a B cell follicle organoid made of nanocomposite biomaterials, which recapitulates the anatomical microenvironment of a lymphoid tissue that provides the basis to induce an accelerated germinal center (GC) reaction by continuously providing extracellular matrix (ECM) and cell–cell signals to naïve B cells. Compared to existing co-cultures, immune organoids provide a control over primary B cell proliferation with ~100-fold higher and rapid differentiation to the GC phenotype with robust antibody class switching. PMID:26072995

  8. Transcriptional analysis of the B cell germinal center reaction

    PubMed Central

    Klein, Ulf; Tu, Yuhai; Stolovitzky, Gustavo A.; Keller, Jeffrey L.; Haddad, Joseph; Miljkovic, Vladan; Cattoretti, Giorgio; Califano, Andrea; Dalla-Favera, Riccardo

    2003-01-01

    The germinal center (GC) reaction is crucial for T cell-dependent immune responses and is targeted by B cell lymphomagenesis. Here we analyzed the transcriptional changes that occur in B cells during GC transit (naïve B cells → centroblasts → centrocytes → memory B cells) by gene expression profiling. Naïve B cells, characterized by the expression of cell cycle-inhibitory and antiapoptotic genes, become centroblasts by inducing an atypical proliferation program lacking c-Myc expression, switching to a proapoptotic program, and down-regulating cytokine, chemokine, and adhesion receptors. The transition from GC to memory cells is characterized by a return to a phenotype similar to that of naïve cells except for an apoptotic program primed for both death and survival and for changes in the expression of cell surface receptors including IL-2 receptor β. These results provide insights into the dynamics of the GC reaction and represent the basis for the analysis of B cell malignancies. PMID:12604779

  9. Structural studies of iron and manganese in photosynthetic reaction centers

    SciTech Connect

    McDermott, A.E.

    1987-11-01

    Electron paramagnetic resonance (EPR) and x-ray absorption spectroscopy (XAS) were used to characterize components involved in the light reactions of photosynthetic reaction centers from spinach and a thermophilic cyanobacterium, Synechococcus sp.: center X, the low electron potential acceptor in Photosystem I (PS I) and the Mn complex involved in water oxidation and oxygen evolution. The dependence of its EPR amplitude on microwave power and temperature indicate an Orbach spin relaxation mechanism involving an excited state at 40 cm/sup -1/. This low energy contributes to its unusually anisotropic g-tensor. XAS of iron in PS I preparations containing ferredoxins A, B and X are consistent with a model with (4Fe-4S) ferredoxins, which are presumably centers A and B and (2Fe-2S) ferredoxins, which would be X. Illumination of dark-adapted Synechococcus PS II samples at 220 to 240 K results in the formation of the multiline EPR signal previously assigned as a Mn S/sub 2/ species, and g = 1.8 and 1.9 signals of Fe/sup 2 +/ Q/sub A//sup -/. In contrast to spinach, illumination at 110 to 160 K produces only a new EPR signal at g = 1.6 which we assign to another configuration of Fe/sup 2+ - Q/sup -/. Following illumination of a S/sub 1/ sample at 140 K or 215 K, the Mn x-ray absorption edge inflection energy changes from 6550 eV to 6551 eV, indicating an oxidation of Mn, and average valences greater than Mn(II). Concomitant changes in the shape of the pre-edge spectrum indicate oxidation of Mn(III) to Mn(IV). The Mn EXAFS spectrum of PS II from Synechococcus is similar in the S/sub 1/ and S/sub 2/ states, indicating O or N ligands at 1.75 +- 0.05 A, transition metal neighbor(s) at 2.75 +- 0.05 A, and N and O ligands at 2.2 A with heterogeneous bond lengths; these data demonstrate the presence of a di-..mu..-oxo bridged Mn structure. 202 refs., 40 figs., 7 tabs.

  10. Primary reactions in photosynthetic reaction centers of Rhodobacter sphaeroides - Time constants of the initial electron transfer

    NASA Astrophysics Data System (ADS)

    Dominguez, Pablo Nahuel; Himmelstoss, Matthias; Michelmann, Jeff; Lehner, Florian Thomas; Gardiner, Alastair T.; Cogdell, Richard J.; Zinth, Wolfgang

    2014-05-01

    The primary dynamics of reaction centers from Rhodobacter sphaeroides at room temperature are studied at low excitation intensities and low excitation rates. Analysis based on singular value decomposition yields three time constants in the picosecond range (ca. 1.2 ps, 3.5 ps and 220 ps). The spectral and temporal signatures are fully consistent with the step-wise electron transfer model published previously, with a first electron transfer to the bacteriochlorophyll with a time constant of 3.5 ps and a second 1.2 ps transfer to the bacteriopheophytin. No indications for adiabatic electron transfer are found in the time range >0.5 ps.

  11. Photocurrent generation in diamond electrodes modified with reaction centers.

    PubMed

    Caterino, Roberta; Csiki, Réka; Lyuleeva, Alina; Pfisterer, Jonas; Wiesinger, Markus; Janssens, Stoffel D; Haenen, Ken; Cattani-Scholz, Anna; Stutzmann, Martin; Garrido, Jose A

    2015-04-22

    Photoactive reaction centers (RCs) are protein complexes in bacteria able to convert sunlight into other forms of energy with a high quantum yield. The photostimulation of immobilized RCs on inorganic electrodes result in the generation of photocurrent that is of interest for biosolar cell applications. This paper reports on the use of novel electrodes based on functional conductive nanocrystalline diamond onto which bacterial RCs are immobilized. A three-dimensional conductive polymer scaffold grafted to the diamond electrodes enables efficient entrapment of photoreactive proteins. The electron transfer in these functional diamond electrodes is optimized through the use of a ferrocene-based electron mediator, which provides significant advantages such as a rapid electron transfer as well as high generated photocurrent. A detailed discussion of the generated photocurrent as a function of time, bias voltage, and mediators in solution unveils the mechanisms limiting the electron transfer in these functional electrodes. This work featuring diamond-based electrodes in biophotovoltaics offers general guidelines that can serve to improve the performance of similar devices based on different materials and geometries. PMID:25836362

  12. How to harvest solar energy with the photosynthetic reaction center

    NASA Astrophysics Data System (ADS)

    Balaeff, Alexander; Reyes, Justin

    Photosynthetic reaction center (PRC) is a protein complex that performs a key step in photosynthesis: the electron-hole separation driven by photon absorbtion. The PRC has a great promise for applications in solar energy harvesting and photosensing. Such applications, however, are hampered by the difficulty in extracting the photogenerated electric charge from the PRC. To that end, it was proposed to attach the PRC to a molecular wire through which the charge could be collected. In order to find the attachment point for the wire that would maximize the rate of charge outflow from the PRC, we performed a computational study of the PRC from the R. virdis bacterium. An ensemble of PRC structures generated by a molecular dynamics simulation was used to calculate the rate of charge transport from the site of initial charge separation to several trial sites on the protein surface. The Pathways model was used to calculate the charge transfer rate in each step of the network of heme co-factors through which the charge transport was presumed to proceed. A simple kinetic model was then used to determine the overall rate of the multistep charge transport. The calculations revealed several candidate sites for the molecular wire attachment, recommended for experimental verification.

  13. Primary charge separation in isolated photosystem II reaction centers

    SciTech Connect

    Seibert, M.; Toon, S.; Govindjee; O`Neil, M.P.; Wasielewski, M.R.

    1992-08-24

    Primary charge-separation in isolated bacterial reaction center (RC) complex occurs in 2.8 ps at room temperature and 0.7--1.2 ps at 10 K. Because of similarities between the bacterial and photosystem II (PSII) RCs, it has been of considerable interest to obtain analogous charge-separation rates in the higher plant system. Our previous femtosecond transient absorption studies used PSII RC material stabilized with PEG or by exchanging dodecyl maltoside (DM) for Triton in the isolation procedure. These materials gave charge-separation 1/e times of 3.0 {plus_minus} 0.6 ps at 4{degree}C and 1.4{plus_minus} 0.2 ps at 15 K based on the risetime of transient absorption kinetics at 820 nm. These values were thought to represent the time required for formation of the P680{sup +}-Pheo{sup {minus}} state. Recent results of Hastings et al. obtained at high data acquisition rates and low flash intensities, suggest that the Pheo{sup {minus}} state may form more slowly. In light of this work, we have carried out additional time domain studies of both electron transport and energy transfer phenomena in stabilized DM PSII RCs at room temperature. We used a 1-kHz repetition rate femtosecond transient absorption spectrometer with a 200 fs instrumental time resolution and compared the results with those obtained by others using frequency domain hole-burning techniques.

  14. Center for Radiation Research. 1990 technical activities

    SciTech Connect

    Kuyatt, C.E.

    1991-02-01

    The report summarizes research projects, measurement method development, calibration and testing and data evaluation activities that were carried out during Fiscal Year 1990 in the NIST Center for Radiation Research. These activities fall in the areas of radiometric physics, radiation sources and instrumentation, and ionizing radiation.

  15. Procedure for rapid isolation of photosynthetic reaction centers using cytochrome c affinity chromatography

    SciTech Connect

    Brudvig, G.W.; Worland, S.T.; Sauer, K.

    1983-02-01

    Horse heart cytochrome c linked to Sepharose 4B is used to purify reaction centers from Rhodopseudomonas sphaeroides R-26. This procedure allows for an initial recovery of 80-90% of the bacterial reaction centers present in chromatophore membranes. High purity reaction centers (A/sub 280//A/sub 802/ < 1.30) can be obtained with a 30% recovery. Reaction centers from wild-type Rps. sphaeroides and Rps. capsulata also bind to a cytochrome c column. Cytochrome c affinity chromatography can also be used to isolate photosystem I complexes from spinach chloroplasts.

  16. Structural consequences of the replacement of glycine M203 with aspartic acid in the reaction center from Rhodobacter sphaeroides.

    PubMed

    Fyfe, P K; Ridge, J P; McAuley, K E; Cogdell, R J; Isaacs, N W; Jones, M R

    2000-05-23

    Reaction centers with the double mutation Phe M197 to Arg and Gly M203 to Asp (FM197R/GM203D) have been crystallized from an antenna-deficient strain of Rhodobacter sphaeroides, and the structure has been determined at 2.7 A resolution. Unlike in reaction centers with a single FM197R mutation, the Arg M197 residue in the FM197R/GM203D reaction center adopts a position similar to that of the native Phe residue in the wild-type reaction center. Asp M203 is packed in such a way that the gamma-carboxy group interacts with the backbone carbonyl of Arg M197. The Asp M203 residue takes up part of the volume that is occupied in the wild-type reaction center by a water molecule. This water has been proposed to form a hydrogen bond interaction with the 9-keto carbonyl group of the active branch accessory bacteriochlorophyll, particularly when the primary donor bacteriochlorophylls are oxidized. The GM203D mutation therefore appears to remove the possibility of this hydrogen bond interaction by exclusion of this water molecule, as well as altering the local dielectric environment of the 9-keto carbonyl group. We examine whether the observed structural changes can provide new or alternative explanations for the absorbance and electron-transfer properties of reaction centers with the FM197R and GM203D mutations.

  17. Excited states of the 5-chlorophyll photosystem II reaction center

    SciTech Connect

    Jankowiak, R.; Raetsep, M.; Picorel, R.; Seibert, M.; Small, G.J.

    1999-11-04

    Results of 4.2 K hole burning, chemical reduction (sodium dithionite, in dark and with illumination), and oxidation (ferricyanide) experiments are reported for the isolated PS II reaction center containing five chlorophyll (Chl) molecules (RC-5). Q{sub y} states at 679.6 and 668.3 nm are identified as being highly localized on pheophytin a of the D{sub 1} branch (Pheo{sub 1}) and pheophytin a of the D{sub 2} branch (Pheo{sub 2}), respectively. The Pheo{sub 1}-Q{sub x} and Pheo{sub 2}-Q{sub x} transitions were found to lie on the low and high energy sides of the single Pheo-Q{sub x} absorption band, at 544.4 and 541.2 nm, respectively. The Q{sub y} band of the 684 nm absorbing Chl, which is more apparent in absorption in RC-5 than in RC-6 samples, is assigned to the peripheral Chl on the D{sub 1} side. The results are consistent with that peripheral Chl being Chl{sub z}. The results indicate that P680, the primary electron donor, is the main acceptor for energy transfer from the Pheo{sub 1}-Q{sub y} state and that excitation energy transfer from the Pheo{sub 1}-Q{sub y} state and P680* to the 684 nm Chl is inefficient. It is concluded that the procedure used to prepare RC-5 has only a small effect on the energies of the Q{sub y} states associated with the core cofactors of the 6-Chl RC as well as the 684 nm Chl. Implications of the results for the multimer model are considered. In that model the Q{sub y}-states of the core are significantly delocalized over several cofactors. The results presented provide no support for this model.

  18. Dual-face nucleoside scaffold featuring a stereogenic all-carbon quaternary center. Intramolecular silicon tethered group-transfer reaction.

    PubMed

    Tambutet, Guillaume; Becerril-Jiménez, Fabiola; Dostie, Starr; Simard, Ryan; Prévost, Michel; Mochirian, Philippe; Guindon, Yvan

    2014-11-01

    The design of a novel nucleoside scaffold that exhibits an all-carbon quaternary center is reported. This allows for both α- and β-anomers of a given 2'-deoxy-2',2'-difluoro nucleoside analog (NA) to have potential biological activity. Using an intramolecular atom-transfer reaction, an all-carbon quaternary center was obtained without the use of heavy metals and/or harsh conditions. The chemistry developed is efficient, easily scalable and leads to novel libraries of molecules.

  19. Relevance of the photosynthetic reaction center from purple bacteria to the structure of photosystem II

    SciTech Connect

    Michel, H.; Deisenhofer, J.

    1988-01-12

    Photosynthetic organisms are able to oxidize organic or inorganic compounds upon the absorption of light, and they use the extracted electron for the fixation of carbon dioxide. The most important oxidation product is oxygen due to the splitting of water. In eukaryotes these processes occur in photosystem II of chloroplasts. Among prokaryotes photosynthetic oxygen evolution is restricted to cyanobacteria and prochloron-type organisms. How water is split in the oxygen-evolving complex of photosystem II belongs to the most important question to be answered. The primary charge separation occurs in the reaction center of photosystem II. This reaction center is a complex consisting of peripheral and integral membrane proteins, several chlorophyll A molecules, two pheophytin A molecules, two and three plastoquinone molecules, and one non-heme iron atom. The location of the photosystem II reaction center is still a matter of debate. Nakatani et al. (l984) concluded from fluorescence measurements that a protein of apparent molecular weight 47,000 (CP47) is the apoprotein of the photosystem II reaction center. A different view emerged from work with the photosynthetic reaction centers from the purple bacteria. The amino acid sequence of the M subunit of the reaction center from Phodopseudomonas (Rps.) sphaeroides has sequence homologies with the D1 protein from spinach. A substantial amount of structural information can be obtained with the reaction center from Rhodopseudomonas viridis, which can be crystallized. Here the authors discuss the structure of the photosynthetic reaction center from the purple bacterium Rps. viridis and describe the role of those amino acids that are conserved between the bacterial and photosystem II reaction center.

  20. Catawba Science Center solar activities. Final report

    SciTech Connect

    1983-01-01

    Two demonstration solar water heaters were built. One was to be used at the Science Center and the other with traveling programs. This was completed and both units are being used for these programs which continue. We were able to build a library of 99 solar energy books and booklets that are available to the public for reference. We also conducted programs for 683 students of all ages. The culminating activity was the planned Energy Awareness Festival. This was held on September 26, 1981 and attracted 450 area citizens. We offered free exhibit space and hosted 17 exhibitors.

  1. Localisation of the subunits of the photosynthetic reaction centers in the chromatophore membrane of Rhodospirillum rubrum.

    PubMed

    Zürrer, H; Snozzi, M; Hanselmann, K; Bachofen, R

    1977-05-11

    Reaction centers were isolated with the detergent lauryl dimethyl amine oxide from chromatophore membranes of Rhodospirillum rubrum. The subunit composition of these reaction centers is similar to the one obtained from Rhodopseudomonas spheroides: three subunits with the molecular weights of 21 000, 24 000 and 29 000. Reaction centers prepared from chromatophores labeled with 131I were heavely labeled in their large subunit (H). The smaller subunits (L and M) contained only little label. Sonication during labeling yielded a slightly higher incorporation of 131I in subunit H compared to the smaller ones. It is concluded that the H protein is largely exposed at the cytoplasmic side of the membrane but might also be accessible for iodination on the inside of the membrane while the L and M proteins are almost completely embedded in the membrane. Iodination of spheroplasts results in only a slight binding of 131I to chromatophores and reaction centers.

  2. Protein structure, electron transfer and evolution of prokaryotic photosynthetic reaction centers

    NASA Technical Reports Server (NTRS)

    Blankenship, R. E.

    1994-01-01

    Photosynthetic reaction centers from a variety of organisms have been isolated and characterized. The groups of prokaryotic photosynthetic organisms include the purple bacteria, the filamentous green bacteria, the green sulfur bacteria and the heliobacteria as anoxygenic representatives as well as the cyanobacteria and prochlorophytes as oxygenic representatives. This review focuses on structural and functional comparisons of the various groups of photosynthetic reaction centers and considers possible evolutionary scenarios to explain the diversity of existing photosynthetic organisms.

  3. Nature of methane activation over oxide centers. Annual report, September 1987-September 1988

    SciTech Connect

    Marcelin, G.; Agarwal, S.K.; Migone, R.A.

    1988-10-01

    The oxidative coupling of methane was studied over alkali-promoted antimony oxide and lead-magnesia catalysts. Reaction studies were used in conjunction with bulk and surface characterization of the catalysts to attempt to characterize the active centers. It was found that both acidity and availability of strong oxidizing sites can influence the selectivities of the various products of the reaction.

  4. Photochemical reactions of metal nitrosyl complexes. Mechanisms of NO reactions with biologically relevant metal centers

    DOE PAGES

    Ford, Peter C.

    2001-01-01

    Tmore » he discoveries that nitric oxide (a.k.a. nitrogen monoxide) serves important roles in mammalian bioregulation and immunology have stimulated intense interest in the chemistry and biochemistry of NO and derivatives such as metal nitrosyl complexes. Also of interest are strategies to deliver NO to biological targets on demand. One such strategy would be to employ a precursor which displays relatively low thermal reactivity but is photochemically active to release NO.his proposition led us to investigate laser flash and continuous photolysis kinetics of nitrosyl complexes such as the Roussin's iron-sulfur-nitrosyl cluster anions Fe 2 S 2 ( NO ) 4 2 − and Fe 4 S 3 ( NO ) 7 − and several ruthenium salen and porphyrin nitrosyls.hese include studies using metal-nitrosyl photochemistry as a vehicle for delivering NO to hypoxic cell cultures in order to sensitize γ -radiation damage. Also studied were the rates and mechanisms of NO “on” reactions with model water soluble heme compounds, the ferriheme protein met-myoglobin and various ruthenium complexes using ns laser flash photolysis techniques. An overview of these studies is presented.« less

  5. Cross coupling reactions of polyfluoroarenes via C-F activation.

    PubMed

    Sun, Alex D; Love, Jennifer A

    2010-11-21

    This Perspective provides an overview of transition metal-catalyzed cross coupling reactions of polyfluoroarenes. When appropriate, stoichiometric C-F activation and subsequent reaction are briefly covered.

  6. Photosynthetic antennas and reaction centers: Current understanding and prospects for improvement

    SciTech Connect

    Blankenship, R.E.

    1996-09-01

    A brief introduction to the principles, structures and kinetic processes that take place in natural photosynthetic reaction center complexes is presented. Energy is first collected by an antenna system, and is transferred to a reaction center complex where primary electron transfer takes place. Secondary reactions lead to oxidation of water and reduction of CO{sub 2} in some classes of organisms. Antenna systems are highly regulated to maximize energy collection efficiency while avoiding photodamage. Some areas that are presently not well understood are listed.

  7. Stabilization of Isolated Photosystem II Reaction Center Complex in the Dark and in the Light Using Polyethylene Glycol and an Oxygen-Scrubbing System 1

    PubMed Central

    McTavish, Hugh; Picorel, Rafael; Seibert, Michael

    1989-01-01

    The photosystem II reaction center as isolated (O Nanba, K Satoh [1987] Proc Natl Acad Sci USA 84: 109-112) is quite dilute and very unstable. Precipitating the complex with polyethylene glycol and resuspending it in buffer without detergent concentrates the reaction center and greatly improves its stability at 4°C in the dark as judged by light-induced electron transport activity. Furthermore, a procedure was developed to minimize photodestruction of polyethylene-glycol-concentrated material at room temperature in the light. The ability to stabilize the photosystem II reaction center should facilitate future photophysical, biochemical, and structural studies of the complex. Images Figure 1 PMID:16666564

  8. Photoprotection of reaction centers: thermal dissipation of absorbed light energy vs charge separation in lichens.

    PubMed

    Heber, Ulrich; Soni, Vineet; Strasser, Reto J

    2011-05-01

    During desiccation, fluorescence emission and stable light-dependent charge separation in the reaction centers (RCs) of photosystem II (PSII) declined strongly in three different lichens: in Parmelia sulcata with an alga as the photobiont, in Peltigera neckeri with a cyanobacterium and in the tripartite lichen Lobaria pulmonaria. Most of the decline of fluorescence was caused by a decrease in the quantum efficiency of fluorescence emission. It indicated the activation of photoprotective thermal energy dissipation. Photochemical activity of the RCs was retained even after complete desiccation. It led to light-dependent absorption changes and found expression in reversible increases in fluorescence or in fluorescence quenching. Lowering the temperature changed the direction of fluorescence responses in P. sulcata. The observations are interpreted to show that reversible light-induced increases in fluorescence emission in desiccated lichens indicate the functionality of the RCs of PSII. Photoprotection is achieved by the drainage of light energy to dissipating centers outside the RCs before stable charge separation can take place. Reversible quenching of fluorescence by strong illumination is suggested to indicate the conversion of the RCs from energy conserving to energy dissipating units. This permits them to avoid photoinactivation. On hydration, re-conversion occurs to energy-conserving RCs.

  9. Molecular electronics of a single photosystem I reaction center: studies with scanning tunneling microscopy and spectroscopy.

    PubMed Central

    Lee, I; Lee, J W; Warmack, R J; Allison, D P; Greenbaum, E

    1995-01-01

    Thylakoids and photosystem I (PSI) reaction centers were imaged by scanning tunneling microscopy. The thylakoids were isolated from spinach chloroplasts, and PSI reaction centers were extracted from thylakoid membranes. Because thylakoids are relatively thick nonconductors, they were sputter-coated with Pd/Au before imaging. PSI photosynthetic centers and chemically platinized PSI were investigated without sputter-coating. They were mounted on flat gold substrates that had been treated with mercaptoacetic acid to help bind the proteins. With tunneling spectroscopy, the PSI centers displayed a semiconductor-like response with a band gap of 1.8 eV. Lightly platinized (platinized for 1 hr) centers displayed diode-like conduction that resulted in dramatic contrast changes between images taken with opposite bias voltages. The electronic properties of this system were stable under long-term storage. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 PMID:11607515

  10. Active damping with a reaction mass actuator

    NASA Technical Reports Server (NTRS)

    Spanos, John; O'Brien, John

    1992-01-01

    This paper presents analytical and experimental results in actively damping flexible structures with reaction mass actuators. A two degree of freedom spring-mass model of a flexible structure is analyzed and the key parameters of actuator mass participation and pole-zero separation are related to the maximum damping achievable from rate feedback control. The main conclusion of the paper is that the larger the pole-zero separation the larger the amount of damping that can be imparted to a structural mode. Laboratory experiments conducted on an 8-foot truss structure support the analytical predictions.

  11. Reengineering the optical absorption cross-section of photosynthetic reaction centers.

    PubMed

    Dutta, Palash K; Lin, Su; Loskutov, Andrey; Levenberg, Symon; Jun, Daniel; Saer, Rafael; Beatty, J Thomas; Liu, Yan; Yan, Hao; Woodbury, Neal W

    2014-03-26

    Engineered cysteine residues near the primary electron donor (P) of the reaction center from the purple photosynthetic bacterium Rhodobacter sphaeroides were covalently conjugated to each of several dye molecules in order to explore the geometric design and spectral requirements for energy transfer between an artificial antenna system and the reaction center. An average of 2.5 fluorescent dye molecules were attached at specific locations near P. The enhanced absorbance cross-section afforded by conjugation of Alexa Fluor 660 dyes resulted in a 2.2-fold increase in the formation of reaction center charge-separated state upon intensity-limited excitation at 650 nm. The effective increase in absorbance cross-section resulting from the conjugation of two other dyes, Alexa Fluor 647 and Alexa Fluor 750, was also investigated. The key parameters that dictate the efficiency of dye-to-reaction center energy transfer and subsequent charge separation were examined using both steady-state and time-resolved fluorescence spectroscopy as well as transient absorbance spectroscopy techniques. An understanding of these parameters is an important first step toward developing more complex model light-harvesting systems integrated with reaction centers. PMID:24568563

  12. Lipid binding to the carotenoid binding site in photosynthetic reaction centers.

    PubMed

    Deshmukh, Sasmit S; Tang, Kai; Kálmán, László

    2011-10-12

    Lipid binding to the carotenoid binding site near the inactive bacteriochlorophyll monomer was probed in the reaction centers of carotenoid-less mutant, R-26 from Rhodobacter sphaeroides. Recently, a marked light-induced change of the local dielectric constant in the vicinity of the inactive bacteriochlorophyll monomer was reported in wild type that was attributed to structural changes that ultimately lengthened the lifetime of the charge-separated state by 3 orders of magnitude (Deshmukh, S. S.; Williams, J. C.; Allen, J. P.; Kalman, L. Biochemistry 2011, 50, 340). Here in the R-26 reaction centers, the combination of light-induced structural changes and lipid binding resulted in a 5 orders of magnitude increase in the lifetime of the charge-separated state involving the oxidized dimer and the reduced primary quinone in proteoliposomes. Only saturated phospholipids with fatty acid chains of 12 and 14 carbon atoms long were bound successfully at 8 °C by cooling the reaction center protein slowly from room temperature. In addition to reporting a dramatic increase of the lifetime of the charge-separated state at physiologically relevant temperatures, this study reveals a novel lipid binding site in photosynthetic reaction center. These results shed light on a new potential application of the reaction center in energy storage as a light-driven biocapacitor since the charges separated by ∼30 Å in a low-dielectric medium can be prevented from recombination for hours.

  13. Oxygen Activation at Mononuclear Nonheme Iron Centers: A Superoxo Perspective

    PubMed Central

    Mukherjee, Anusree; Cranswick, Matthew A.; Chakraborti, Mrinmoy; Paine, Tapan K.; Fujisawa, Kiyoshi; Münck, Eckard; Que, Lawrence

    2010-01-01

    Dioxygen activation by iron enzymes is responsible for many metabolically important transformations in biology. Often a high-valent iron-oxo oxidant is proposed to form upon dioxygen activation at a mononuclear nonheme iron center, presumably via intervening iron-superoxo and iron-peroxo species. While iron(IV)-oxo intermediates have been trapped and characterized in enzymes and models, less is known of the putative iron(III)-superoxo species. Utilizing a synthetic model for the 2-oxoglutarate-dependent monoiron enzymes, [(TpiPr2)FeII(O2CC(O)CH3)], we have obtained indirect evidence for the formation of the putative iron(III)-superoxo species, which can undergo one-electron reduction, hydrogen-atom transfer, or conversion to an iron(IV)-oxo species, depending on the reaction conditions. These results demonstrate the various roles the iron(III)-superoxo species can play in the course of dioxygen activation at a nonheme iron center. PMID:20380464

  14. Time-resolved tryptophan fluorescence in photosynthetic reaction centers from Rhodobacter sphaeroides

    NASA Technical Reports Server (NTRS)

    Godik, V. I.; Blankenship, R. E.; Causgrove, T. P.; Woodbury, N.

    1993-01-01

    Tryptophan fluorescence of reaction centers isolated from Rhodobacter sphaeroides, both stationary and time-resolved, was studied. Fluorescence kinetics were found to fit best a sum of four discrete exponential components. Half of the initial amplitude was due to a component with a lifetime of congruent to 60 ps, belonging to Trp residues, capable of efficient transfer of excitation energy to bacteriochlorophyll molecules of the reaction center. The three other components seem to be emitted by Trp ground-state conformers, unable to participate in such a transfer. Under the influence of intense actinic light, photooxidizing the reaction centers, the yield of stationary fluorescence diminished by congruent to 1.5 times, while the number of the kinetic components and their life times remained practically unchanged. Possible implications of the observed effects for the primary photosynthesis events are considered.

  15. Activation Energy of Tantalum-Tungsten Oxide Thermite Reaction

    SciTech Connect

    Cervantes, O; Kuntz, J; Gash, A; Munir, Z

    2010-02-25

    The activation energy of a high melting temperature sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the High Pressure Spark Plasma Sintering (HPSPS) technique to 300 and 400 C to produce pellets with dimensions of 5 mm diameter by 1.5 mm height. A custom built ignition setup was developed to measure ignition temperatures at high heating rates (500-2000 C {center_dot} min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Unlike the 400 C samples, results show that the samples consolidated to 300 C undergo an abrupt change in temperature response prior to ignition. This change in temperature response has been attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465-670 C. The activation energy of the SG derived Ta-WO{sup 3} thermite composite consolidated to 300 and 400 C were determined to be 37.787 {+-} 1.58 kJ {center_dot} mol{sup -1} and 57.381 {+-} 2.26 kJ {center_dot} mol{sup -1}, respectively.

  16. Using synthetic model systems to understand charge separation and spin dynamics in photosynthetic reaction centers.

    SciTech Connect

    Wasielewski, M. R.

    1998-08-27

    Our current work in modeling reaction center dynamics has resulted in the observation of each major spin-dependent photochemical pathway that is observed in reaction centers. The development of new, simpler model systems has permitted us to probe deeply into the mechanistic issues that drive these dynamics. Based on these results we have returned to biomimetic chlorophyll-based electron donors to mimic these dynamics. Future studies will focus on the details of electronic structure and energetic of both the donor-acceptor molecules and their surrounding environment that dictate the mechanistic pathways and result in efficient photosynthetic charge separation.

  17. Electron paramagnetic resonance study of radiation damage in photosynthetic reaction center crystals.

    SciTech Connect

    Utschig, L. M.; Chemerisov, S. D.; Tiede, D. M.; Poluektov, O. G.; Chemical Sciences and Engineering Division

    2008-01-01

    Electron paramagnetic resonance (EPR) was used to simultaneously study radiation-induced cofactor reduction and damaging radical formation in single crystals of the bacterial reaction center (RC). Crystals of Fe-removed/Zn-replaced RC protein from Rhodobacter (R.) sphaeroides R26 were irradiated with varied radiation doses at cryogenic temperature and analyzed for radiation-induced free radical formation and alteration of light-induced photosynthetic electron transfer activity using high-field (HF) D-band (130 GHz) and X-band (9.5 GHz) EPR spectroscopies. These analyses show that the formation of radiation-induced free radicals saturated at doses 1 order of magnitude smaller than the amount of radiation at which protein crystals lose their diffraction quality, while light-induced RC activity was found to be lost at radiation doses at least 1 order of magnitude lower than the dose at which radiation-induced radicals exhibited saturation. HF D-band EPR spectra provide direct evidence for radiation-induced reduction of the quinones and possibly other cofactors. These results demonstrate that substantial radiation damage is likely to have occurred during X-ray diffraction data collection used for photosynthetic RC structure determination. Thus, both radiation-induced loss of photochemical activity in RC crystals and reduction of the quinones are important factors that must be considered when correlating spectroscopic and crystallographic measurements of quinone site structures.

  18. Activities of the Tandem Accelerator Center, University of Tsukuba

    NASA Astrophysics Data System (ADS)

    1993-10-01

    This annual report includes the research activities and the technical developments carried out at the Tandem Accelerator Center in University of Tsukuba for the period from April 1992 to March 1993. New experimental investigations were made on (1) nuclear spectroscopy was initiated by a new (gamma) ray spectrometer; (2) polarization phenomena in nuclear reactions; (3) the application of energetic heavy ions to solid state physics; (4) the behavior of self interstitial atoms and its migration mechanism in Mo metal; (5) the studies on electronic conduction of metal oxides and bronzes by NMR; (6) Moessbauer studies on Fe-Cr alloy and the RBS analysis of YBCO superconductor films; and (7) a new field was challenged on the micro cluster physics. Nuclear collective motion and the relativistic mean-field theory is also included in this report.

  19. A Light-Activated Reaction Manifold.

    PubMed

    Hiltebrandt, Kai; Elies, Katharina; D'hooge, Dagmar R; Blinco, James P; Barner-Kowollik, Christopher

    2016-06-01

    We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels.

  20. Protein modifications affecting triplet energy transfer in bacterial photosynthetic reaction centers.

    PubMed Central

    Laible, P D; Chynwat, V; Thurnauer, M C; Schiffer, M; Hanson, D K; Frank, H A

    1998-01-01

    The efficiency of triplet energy transfer from the special pair (P) to the carotenoid (C) in photosynthetic reaction centers (RCs) from a large family of mutant strains has been investigated. The mutants carry substitutions at positions L181 and/or M208 near chlorophyll-based cofactors on the inactive and active sides of the complex, respectively. Light-modulated electron paramagnetic resonance at 10 K, where triplet energy transfer is thermally prohibited, reveals that the mutations do not perturb the electronic distribution of P. At temperatures > or = 70 K, we observe reduced signals from the carotenoid in most of the RCs with L181 substitutions. In particular, triplet transfer efficiency is reduced in all RCs in which a lysine at L181 donates a sixth ligand to the monomeric bacteriochlorophyll B(B). Replacement of the native Tyr at M208 on the active side of the complex with several polar residues increased transfer efficiency. The difference in the efficiencies of transfer in the RCs demonstrates the ability of the protein environment to influence the electronic overlap of the chromophores and thus the thermal barrier for triplet energy transfer. PMID:9591686

  1. Assembly of a photosynthetic reaction center with ABA tri-block polymersomes: highlights on protein localization.

    PubMed

    Tangorra, R R; Operamolla, A; Milano, F; Hassan Omar, O; Henrard, J; Comparelli, R; Italiano, F; Agostiano, A; De Leo, V; Marotta, R; Falqui, A; Farinola, G M; Trotta, M

    2015-10-01

    The reconstitution of the integral membrane protein photosynthetic reaction center (RC) in polymersomes, i.e. artificial closed vesicles, was achieved by the micelle-to-vesicle transition technique, a very mild protocol based on size exclusion chromatography often used to drive the incorporation of proteins contemporarily to liposome formation. An optimized protocol was used to successfully reconstitute the protein in a fully active state in polymersomes formed by the tri-block copolymers PMOXA22-PDMS61-PMOXA22. The RC is very sensitive to its solubilizing environment and was used to probe the positioning of the protein in the vesicles. According to charge-recombination experiments and to the enzymatic activity assay, the RC is found to accommodate in the PMOXA22 region of the polymersome, facing the water bulk solution, rather than in the PDMS61 transmembrane-like region. Furthermore, polymersomes were found to preserve protein integrity efficiently as the biomimetic lipid bilayers but show a much longer temporal stability than lipid based vesicles.

  2. Native Mass Spectrometry Characterizes the Photosynthetic Reaction Center Complex from the Purple Bacterium Rhodobacter sphaeroides

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Harrington, Lucas B.; Lu, Yue; Prado, Mindy; Saer, Rafael; Rempel, Don; Blankenship, Robert E.; Gross, Michael L.

    2016-08-01

    Native mass spectrometry (MS) is an emerging approach to study protein complexes in their near-native states and to elucidate their stoichiometry and topology. Here, we report a native MS study of the membrane-embedded reaction center (RC) protein complex from the purple photosynthetic bacterium Rhodobacter sphaeroides. The membrane-embedded RC protein complex is stabilized by detergent micelles in aqueous solution, directly introduced into a mass spectrometer by nano-electrospray (nESI), and freed of detergents and dissociated in the gas phase by collisional activation. As the collision energy is increased, the chlorophyll pigments are gradually released from the RC complex, suggesting that native MS introduces a near-native structure that continues to bind pigments. Two bacteriochlorophyll a pigments remain tightly bound to the RC protein at the highest collision energy. The order of pigment release and their resistance to release by gas-phase activation indicates the strength of pigment interaction in the RC complex. This investigation sets the stage for future native MS studies of membrane-embedded photosynthetic pigment-protein and related complexes.

  3. Iron as a bound secondary electron donor in modified bacterial reaction centers.

    PubMed

    Kálmán, L; LoBrutto, R; Williams, J C; Allen, J P

    2006-11-21

    The binding and oxidation of ferrous iron were studied in wild-type reaction centers and in mutants that have been modified to be both highly oxidizing and able to bind manganese [Thielges et al. (2005) Biochemistry 44, 7389-7394]. After illumination of wild-type reaction centers, steady-state optical spectroscopy showed that the oxidized bacteriochlorophyll dimer, P+, could oxidize iron but only as a second-order reaction at iron concentrations above 100 microM. In the modified reaction centers, P+ was reduced by iron in the presence of sodium bicarbonate with dissociation constants of approximately 1 microM for two mutants with different metal-binding sites. Transient optical spectroscopy showed that P+ was rapidly reduced with first-order rates of 170 and 275 s-1 for the two mutants. The dependence of the amplitude of this rate on the iron concentration yielded a dissociation constant of approximately 1 microM for both mutants, in agreement with the steady-state determination. The oxidation of bound iron by P+ was confirmed by the observation of a light-induced EPR signal centered at g values of 2.2 and 4.3 and attributed to high-spin Fe3+. Bicarbonate was required at pH 7 for low dissociation constants for both iron and manganese binding. The similarity between iron and manganese binding in these mutants provides insight into general properties of metal-binding sites in proteins. PMID:17105205

  4. Mimicry of the radical pair and triplet states in photosynthetic reaction centers with a synthetic model

    SciTech Connect

    Wasielewski, M.R.; Greenfield, S.R.; Svec, W.A.

    1997-08-01

    Results are presented on a photosynthetic model system that closely mimics the spin dynamics of triplet state formation found in photosynthetic reaction centers. This research will make it possible to design new models to probe the mechanism of the primary events of photosynthesis.

  5. Activities of the Center for Space Construction

    NASA Technical Reports Server (NTRS)

    1993-01-01

    The Center for Space Construction (CSC) at the University of Colorado at Boulder is one of eight University Space Engineering Research Centers established by NASA in 1988. The mission of the center is to conduct research into space technology and to directly contribute to space engineering education. The center reports to the Department of Aerospace Engineering Sciences and resides in the College of Engineering and Applied Science. The college has a long and successful track record of cultivating multi-disciplinary research and education programs. The Center for Space Construction is prominent evidence of this record. At the inception of CSC, the center was primarily founded on the need for research on in-space construction of large space systems like space stations and interplanetary space vehicles. The scope of CSC's research has now evolved to include the design and construction of all spacecraft, large and small. Within this broadened scope, our research projects seek to impact the underlying technological basis for such spacecraft as remote sensing satellites, communication satellites, and other special purpose spacecraft, as well as the technological basis for large space platforms. The center's research focuses on three areas: spacecraft structures, spacecraft operations and control, and regolith and surface systems. In the area of spacecraft structures, our current emphasis is on concepts and modeling of deployable structures, analysis of inflatable structures, structural damage detection algorithms, and composite materials for lightweight structures. In the area of spacecraft operations and control, we are continuing our previous efforts in process control of in-orbit structural assembly. In addition, we have begun two new efforts in formal approach to spacecraft flight software systems design and adaptive attitude control systems. In the area of regolith and surface systems, we are continuing the work of characterizing the physical properties of lunar

  6. Structure-function studies of the photosynthetic reaction center using herbicides that compete for the quinone binding site

    SciTech Connect

    Bylina, E.J.

    1995-12-31

    Certain classes of herbicides act as competitive inhibitors of the photosynthetic reaction center. Genetic engineering techniques can be used to generate photosynthetic reaction centers which contain altered quinone binding sites. A genetic system for rapidly screening herbicides developed in the photosynthetic bacterium Rhodobacter capsulatus has been used to examine the effect of different s-triazine herbicides on the growth of bacteria containing reaction centers with altered quinone binding sites. Structural insights into herbicide binding have been obtained by determining the level of resistance or sensitivity to structurally related herbicides in these modified reaction centers.

  7. Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

    PubMed

    Sun, Chang; Carey, Anne-Marie; Gao, Bing-Rong; Wraight, Colin A; Woodbury, Neal W; Lin, Su

    2016-06-23

    It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination. PMID:27243380

  8. B cell responses to a peptide epitope. VII. Antigen-dependent modulation of the germinal center reaction.

    PubMed

    Agarwal, A; Nayak, B P; Rao, K V

    1998-12-01

    Germinal center responses to two analogous peptides, PS1CT3 and G32CT3, that differ in sequence only at one position within the B cell epitopic region were examined. In comparison with peptide PS1CT3, peptide G32CT3 elicited a poor germinal center response. By demonstrating equal facility of immune complexes with IgM and IgG Ab isotypes to seed germinal centers, we excluded differences in isotype profiles of early primary anti-PS1CT3 and anti-G32CT3 Ig as the probable cause. Quantitative differences in germinal center responses to the two peptides were also not due to either qualitative/quantitative differences in T cell priming or variation in the frequency of the early Ag-activated B cells induced. Rather, they resulted from qualitative differences in the nature of B cells primed. Analysis of early primary anti-PS1CT3 and anti-G32CT3 IgMs revealed that the latter population was of a distinctly lower affinity, implying the existence of an Ag affinity threshold that restricts germinal center recruitment of G32CT3-specific B cells. The impediment in anti-G32CT3 germinal center initiation could be overcome by making available an excess of Ag-activated Th cells at the time of immunization. This resulted in the appearance of a higher affinity population of G32CT3-specific B cells that, presumably, are now capable of seeding germinal centers. These data suggest that the strength of a germinal center reaction generated is Ag dependent. At least one regulatory parameter represents the quality of B cells that are initially primed.

  9. Telerobotic activities at Johnson Space Center

    NASA Technical Reports Server (NTRS)

    Price, Charles R.

    1989-01-01

    The Johnson Space Center telerobotic efforts span three major thrusts: (1) sustaining and expanding the capability of the Shuttle manipulator; (2) developing and integrating the multiple telerobotic system of the Space Station; and (3) fostering and applying research in all areas of telerobotics technology within the government, private, and academic sectors.

  10. Genetic probes of structure/function relationships in the Q{sub B} binding site of the photosynthetic reaction center

    SciTech Connect

    Hanson, D.K.; Tiede, D.M.; Nance, S.L.; Chang, Chong-Hwan; Schiffer, M.

    1991-06-25

    In photosynthetic reaction centers, a quinone molecule, Q{sub B}, is the terminal acceptor in light-induced electron transfer. The crystal structure of the reaction center implicates the protonatable amiho acid residues L212Glu and L213Asp in the binding of Q{sub B} to the reaction center and in proton transfer to the anionic forms of Q{sub B} generated by electron transfer from Q{sub A}. Here we report the construction of the double mutant L212Ala-L213Ala by site-specific mutagenesis, and the isolation and preliminary biophysical characterization of revertant and suppressor strains that have regained the ability to grow under photosynthetic conditions. Our results show that neither L212Glu nor L213Asp is essential for efficient light-induced electron or proton transfer in Rhodobacter capsulatus and that second-site mutations, located within the QB binding pocket or at a more distant site, can compensate for mutations at L212 and L213. Acquisition of a single negatively charged residue (at position L213, or on the other side of the binding pocket at position L225) or loss of a positively charged residue (at position M231) is sufficient to restore activity to the complex.

  11. A Light-Activated Reaction Manifold.

    PubMed

    Hiltebrandt, Kai; Elies, Katharina; D'hooge, Dagmar R; Blinco, James P; Barner-Kowollik, Christopher

    2016-06-01

    We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels. PMID:27151599

  12. Chemical trends in the activation energies of DX centers

    NASA Astrophysics Data System (ADS)

    Kumagai, O.; Kawai, H.; Mori, Y.; Kaneko, K.

    1984-12-01

    The activation energies of DX centers in AlGaAs doped with six different impurities (S, Se, Te, Si, Ge, and Sn) are measured by deep level transient spectroscopy. Remarkable trends are established, in which the activation energies of DX centers with group IV impurities become shallower as the mass number of the impurity increases, while those with group VI impurities remain constant.

  13. Marketing backgrounds and activities of community mental health center CEOs.

    PubMed

    Whyte, E G; Smith, M; Reidenbach, E N; Sharpe, T R

    1989-01-01

    More than 300 directors of community mental health centers responded to a survey concerning their marketing training and the marketing activities in which their centers had been engaged. Formal marketing training was found to be in the backgrounds of few of the respondents. The majority had not been engaged in a listing of marketing activities.

  14. 29 CFR 525.23 - Work activities centers.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 3 2012-07-01 2012-07-01 false Work activities centers. 525.23 Section 525.23 Labor... OF WORKERS WITH DISABILITIES UNDER SPECIAL CERTIFICATES § 525.23 Work activities centers. Nothing in these regulations shall be interpreted to prevent an employer from maintaining or establishing...

  15. 29 CFR 525.23 - Work activities centers.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 3 2011-07-01 2011-07-01 false Work activities centers. 525.23 Section 525.23 Labor... OF WORKERS WITH DISABILITIES UNDER SPECIAL CERTIFICATES § 525.23 Work activities centers. Nothing in these regulations shall be interpreted to prevent an employer from maintaining or establishing...

  16. 29 CFR 525.23 - Work activities centers.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 3 2010-07-01 2010-07-01 false Work activities centers. 525.23 Section 525.23 Labor... OF WORKERS WITH DISABILITIES UNDER SPECIAL CERTIFICATES § 525.23 Work activities centers. Nothing in these regulations shall be interpreted to prevent an employer from maintaining or establishing...

  17. Adult Basic Learning in an Activity Center: A Demonstration Approach.

    ERIC Educational Resources Information Center

    Metropolitan Adult Education Program, San Jose, CA.

    Escuela Amistad, an activity center in San Jose, California, is now operating at capacity, five months after its origin. Average daily attendance has been 125 adult students, 18-65, most of whom are females of Mexican-American background. Activities and services provided by the center are: instruction in English as a second language, home…

  18. Double Mutation in Photosystem II Reaction Centers and Elevated CO2 Grant Thermotolerance to Mesophilic Cyanobacterium

    PubMed Central

    Dinamarca, Jorge; Shlyk-Kerner, Oksana; Kaftan, David; Goldberg, Eran; Dulebo, Alexander; Gidekel, Manuel; Gutierrez, Ana; Scherz, Avigdor

    2011-01-01

    Photosynthetic biomass production rapidly declines in mesophilic cyanobacteria grown above their physiological temperatures largely due to the imbalance between degradation and repair of the D1 protein subunit of the heat susceptible Photosystem II reaction centers (PSIIRC). Here we show that simultaneous replacement of two conserved residues in the D1 protein of the mesophilic Synechocystis sp. PCC 6803, by the analogue residues present in the thermophilic Thermosynechococcus elongatus, enables photosynthetic growth, extensive biomass production and markedly enhanced stability and repair rate of PSIIRC for seven days even at 43°C but only at elevated CO2 (1%). Under the same conditions, the Synechocystis control strain initially presented very slow growth followed by a decline after 3 days. Change in the thylakoid membrane lipids, namely the saturation of the fatty acids is observed upon incubation for the different strains, but only the double mutant shows a concomitant major change of the enthalpy and entropy for the light activated QA−→QB electron transfer, rendering them similar to those of the thermophilic strain. Following these findings, computational chemistry and protein dynamics simulations we propose that the D1 double mutation increases the folding stability of the PSIIRC at elevated temperatures. This, together with the decreased impairment of D1 protein repair under increased CO2 concentrations result in the observed photothermal tolerance of the photosynthetic machinery in the double mutant PMID:22216094

  19. Targeted genetic inactivation of the photosystem I reaction center in the cyanobacterium Synechocystis sp. PCC 6803.

    PubMed

    Smart, L B; Anderson, S L; McIntosh, L

    1991-11-01

    We describe the first complete segregation of a targeted inactivation of psaA encoding one of the P700-chlorophyll a apoproteins of photosystem (PS) I. A kanamycin resistance gene was used to interrupt the psaA gene in the unicellular cyanobacterium Synechocystis sp. PCC 6803. Selection of a fully segregated mutant, ADK9, was performed under light-activated heterotrophic growth (LAHG) conditions; complete darkness except for 5 min of light every 24 h and 5 mM glucose. Under these conditions, wild-type cells showed a 4-fold decrease in chlorophyll (chl) per cell, primarily due to a decrease of PS I reaction centers. Evidence for the absence of PS I in ADK9 includes: the lack of EPR (electron paramagnetic resonance) signal I, from P700+; undetectable P700-apoprotein; greatly reduced whole-chain photosynthesis rates; and greatly reduced chl per cell, resulting in a turquoise blue phenotype. The PS I peripheral proteins PSA-C and PSA-D were not detected in this mutant. ADK9 does assemble near wild-type levels of functional PS II per cell, evidenced by: EPR signal II from YD+; high rates of oxygen evolution with 2,6-dichloro-p-benzoquinone (DCBQ), an electron acceptor from PS II; and accumulation of D1, a PS II core polypeptide. The success of this transformation indicates that this cyanobacterium may be utilized for site-directed mutagenesis of the PS I core.

  20. Photosynthetic electron transfer from reaction center pigment-protein complex in silica nanopores.

    PubMed

    Oda, Ippei; Iwaki, Masayo; Fujita, Daiju; Tsutsui, Yasutaka; Ishizaka, Souji; Dewa, Makiko; Nango, Mamoru; Kajino, Tsutomu; Fukushima, Yoshiaki; Itoh, Shigeru

    2010-08-17

    A photosynthetic reaction center (RC) pigment-protein complex purified from a thermophilic purple photosynthetic bacterium, Thermochromatium tepidum, was adsorbed to a folded-sheet silica mesoporous material (FSM). The RC has a molecular structure with a 7.0 x 5.0 x 13 nm diameter. The amount of RC adsorbed to the FSM compound with an average internal pore diameter of 7.9 nm (FSM(7.9)) was high at 0.29 gRC/gFSM, while that to the FSM(2.7) (2.7 nm diameter) was low at 0.02 gRC/gFSM, suggesting the specific binding of the RC into the 7.9 nm pores of FSM(7.9). An N(2)-adsorption isotherm study indicated the incorporation of the RC into the 7.9 nm pores. The RC inside FSM(7.9) showed absorption spectra in the visible and infrared regions similar to those of the RC in solution, indicating almost no structural changes induced by the adsorption. The RC-FSM(7.9) conjugate showed the high photochemical activity with the increased thermal stability up to 50 degrees C in the measurements by laser spectroscopy. The conjugates rapidly provided electrons to a dye in the outer medium or showed electric current on the ITO electrode upon the illumination. The RC-FSM conjugate will be useful for the construction of artificial photosynthetic systems and new photodevices. PMID:20695584

  1. Targeted genetic inactivation of the photosystem I reaction center in the cyanobacterium Synechocystis sp. PCC 6803.

    PubMed Central

    Smart, L B; Anderson, S L; McIntosh, L

    1991-01-01

    We describe the first complete segregation of a targeted inactivation of psaA encoding one of the P700-chlorophyll a apoproteins of photosystem (PS) I. A kanamycin resistance gene was used to interrupt the psaA gene in the unicellular cyanobacterium Synechocystis sp. PCC 6803. Selection of a fully segregated mutant, ADK9, was performed under light-activated heterotrophic growth (LAHG) conditions; complete darkness except for 5 min of light every 24 h and 5 mM glucose. Under these conditions, wild-type cells showed a 4-fold decrease in chlorophyll (chl) per cell, primarily due to a decrease of PS I reaction centers. Evidence for the absence of PS I in ADK9 includes: the lack of EPR (electron paramagnetic resonance) signal I, from P700+; undetectable P700-apoprotein; greatly reduced whole-chain photosynthesis rates; and greatly reduced chl per cell, resulting in a turquoise blue phenotype. The PS I peripheral proteins PSA-C and PSA-D were not detected in this mutant. ADK9 does assemble near wild-type levels of functional PS II per cell, evidenced by: EPR signal II from YD+; high rates of oxygen evolution with 2,6-dichloro-p-benzoquinone (DCBQ), an electron acceptor from PS II; and accumulation of D1, a PS II core polypeptide. The success of this transformation indicates that this cyanobacterium may be utilized for site-directed mutagenesis of the PS I core. Images PMID:1717264

  2. Temperature-dependent conformational changes in the bacteriopheophytins of Rhodobacter sphaeroides reaction centers.

    PubMed

    Peloquin, J M; Violette, C A; Frank, H A; Bocian, D F

    1990-05-22

    Resonance Raman (RR) spectra are reported for the photosynthetic reaction center (RC) protein from Rhodobacter sphaeroides 2.4.1. The spectra were obtained with a variety of excitation wavelengths, spanning the UV, violet, and yellow-green regions of the absorption spectrum, and at a number of temperatures ranging from 30 to 270 K. The RR data indicate that the frequencies of certain vibrational modes of the bacteriochlorin pigments in the RC shift with temperature. These shifts are reversible and do not depend on external factors such as solvent or detergent. The acetyl carbonyl bands exhibit the largest shifts with temperature. These shifts are attributed to thermal effects involving the torsional vibrations of the acetyl groups of several (or all) of the bacteriochlorins rather than to specific pigment-protein interactions. The frequency of the structure-sensitive skeletal mode near 1610 cm-1 of one of the two bacteriopheophytins (BPhs) in the RC is also sensitive to temperature. In contrast, no temperature sensitivity is observed for the analogous modes of the bacteriochlorophylls or other BPhs. Over the range 160-100 K, the skeletal mode of the BPh upshifts by approximately 4 cm-1. This upshift is attributed to a flattening of the macrocycle at low temperatures. It is suggested that the BPh active in the electron-transfer process is the pigment whose structure is temperature dependent. It is further suggested that such structural changes could be responsible in part for the temperature dependence of the electron-transfer rates in photosynthetic RCs.

  3. Constraints on Galactic Center Activity: A Search for Enhanced Galactic Center Lithium and Boron

    NASA Astrophysics Data System (ADS)

    Lubowich, D. A.; Turner, B. E.; Hobbs, L. M.

    1998-12-01

    The abundances of lithium and boron provide important information about big bang nucleosynthesis, Galactic chemical evolution, stellar evolution, and cosmic-ray spallation reactions. We conducted the first search for the ground-state hyperfine-structure transitions of Li I (2S1/2; F = 2-1 803 MHz) and B I (2P1/2; F = 2-1 732 MHz). We used the 43 m NRAO radio telescope to search for enhanced Galactic center (GC) Li and B expected from models of Galactic activity. We did not detect Li I or B I and obtained upper limits of N(Li I) < 1.9 × 1016 cm-2, (Li/H) < 3.9 × 10-8, N(B I) < 2.2 × 1018 cm-2, and (B/H) < 9.2 × 10-6 for the dense 20 km s-1 Sgr A molecular cloud where our largest sources of uncertainties are Li I/Li, B I/B, and N(H). Our observations imply (Li/H)GC < 22 (Li/H)disk, (Li/H)GC < 39 (Li/H)disk-spallation, (B/H)GC < 1.2 × 104 (B/H)disk, (B/H)GC < 1.5 × 104 (B/H)disk-spallation. For a simple model combining mass loss from AGB stars (only for Li), spallation reactions, and SN ν-nucleosynthesis, we estimate (Li/H)GC = 1.3 × 10-8 (13 times enhancement) and (B/H)GC = 7.4 × 10-9 (10 times enhancement). If Li is primarily produced via spallation reactions from a cosmic-ray proton flux φp(t) with the same energy and trapping as in the disk, then [\\smallint φp(t)dt]GC < 13[\\smallint φp(t)dt]disk. Comparing our results to AGN models, we conclude that the GC has not had an extended period of AGN activity containing a large cosmic-ray flux (LCR <= 1044 ergs s-1 for 108 yr), a large low-energy cosmic-ray flux (less than 100 times the disk flux), or a large γ-ray flux (Lγ < 1042 ergs s-1 for 109 yr). Furthermore, since any Galactic deuterium production will significantly enhance the abundances of Li and B, our results imply that there are no sources of D in the GC or Galaxy. Therefore, all the Galactic D originated from the infall of primordial matter with the current D/H reduced by astration and mixing.

  4. Two-dimensional free energy surfaces for primary electron transfer in a photosynthetic reaction center

    NASA Astrophysics Data System (ADS)

    Warshel, A.; Chu, Z. T.; Parson, W. W.

    1997-01-01

    Fushiki and Tachiya [Chem. Phys. Lett. 255 (1996) 83] recently analyzed the free energy surfaces of the initial electron-transfer processes in photosynthetic bacterial reaction centers. The authors state that when the results from simulations described by Warshel, Chu and Parson [Photochem. Photobiol. A: Chem. 82 (1994) 123] are analyzed using their formulation, the calculated energy of a key ion-pair state is inconsistent with experiment. They also state that previous analyses of the photosynthetic electron-transfer reactions had been limited to one-dimensional free energy surfaces. We show here that both these assertions are incorrect.

  5. Effective Absorption Cross-Sections in Porphyridium cruentum: Implications for Energy Transfer between Phycobilisomes and Photosystem II Reaction Centers.

    PubMed

    Ley, A C

    1984-02-01

    Effective absorption cross-sections for O(2) production by Porphyridium cruentum were measured at 546 and 596 nanometers. Although all photosystem II reaction centers are energetically coupled to phycobilisomes, any single phycobilisome acts as antenna for several photosystem II reaction centers. The cross-section measured in state I was 50% larger than that measured in state II.

  6. Evolution of reaction center mimics to systems capable of generating solar fuel.

    PubMed

    Sherman, Benjamin D; Vaughn, Michael D; Bergkamp, Jesse J; Gust, Devens; Moore, Ana L; Moore, Thomas A

    2014-05-01

    Capturing and converting solar energy via artificial photosynthesis offers an ideal way to limit society's dependence on fossil fuel and its myriad consequences. The development and study of molecular artificial photosynthetic reactions centers and antenna complexes and the combination of these constructs with catalysts to drive the photochemical production of a fuel helps to build the understanding needed for development of future scalable technologies. This review focuses on the study of molecular complexes, design of which is inspired by the components of natural photosynthesis, and covers research from early triad reaction centers developed by the group of Gust, Moore, and Moore to recent photoelectrochemical systems capable of using light to convert water to oxygen and hydrogen.

  7. Dynamical theory of primary processes of charge separation in the photosynthetic reaction center.

    PubMed

    Lakhno, Victor D

    2005-05-01

    A dynamical theory has been developed for primary separation of charges in the course of photosynthesis. The theory deals with both hopping and superexchange transfer mechanisms. Dynamics of electron transfer from dimeric bacteriochlorophyll to quinone has been calculated. The results obtained agree with experimental data and provide a unified explanation of both the hierarchy of the transfer time in the photosynthetic reaction center and the phenomenon of coherent oscillations accompanying the transfer process.

  8. Quantum nonequilibrium approach for fast electron transport in open systems: photosynthetic reaction centers.

    PubMed

    Pudlak, M; Pichugin, K N; Nazmitdinov, R G; Pincak, R

    2011-11-01

    Creation of electrons or excitons by external fields in a system with initially statistically independent unrelaxed vibrational modes leads to an initial condition term. The contribution of this term in the time convolution generalized master-equation approach is studied in the second order of the perturbation theory in path-integral formalism. The developed approach, applied for the analysis of dynamics in the photosynthetic reaction center, exhibits the key role of the initial condition terms at the primary stage of electron transfer.

  9. Simplicity in complexity: the photosynthetic reaction center performs as a simple 0.2 V battery.

    PubMed

    van Rotterdam, Bart J; Crielaard, Wim; van Stokkum, Ivo H M; Hellingwerf, Klaas J; Westerhoff, Hans V

    2002-01-01

    The photosynthetic reaction center is one of the most complicated molecular complexes. Transducing photon energy to a transmembrane electrochemical potential difference for protons, it is the direct or indirect energy source for virtually all life. We show here that it operates in a simple, battery-like manner, with a maximum potential of 0.20 V. Intriguingly this is only one fifth of the energy of the absorbed photon.

  10. Isolation and characterization of photosynthetic reaction centers from Rhodopseudomonas capsulata and Rhodopseudomonas sphaeroides

    SciTech Connect

    Worland, S.T.

    1984-09-01

    Reaction centers were isolated by affinity chromatography on equine cytochrome C. Peripheral proteins were removed with 0.05% LDAO. Absorption and EPR spectra and bleaching assays indicate that the reaction centers retained their electron donors and acceptors in the native environment. Three reaction center polypeptides were isolated and submitted for amino-terminal sequence determination. By comparing these sequences to those deduced from DNA, it was established that the M and L subunits are post-translationally modified to remove the aminoterminal Met, whereas the H subunit is not. Inhibition of O/sub 2/ evolution in photosystem II particles from spinach by naphthoquinone derivatives show O/sub 2/ inhibition by bromomethyl and acetoxymethyl derivatives but not with hydroxymethyl derivatives. Inhibition by acetoxymethyl derivatives in irreversible and dependent on illumination suggesting that reduction of the quinone is necessary. Therefore acetoxymethyl derivatives may be useful as suicide reagents for labelling quinone binding sites. Procedures were developed to extract one or both of the quinones present in reaction centers and preserve the integrity of the co-factor binding sites. The H and M subunits were cleaned using furmic acid. Both fragments were isolated from the H subunit, while the larger fragment was isolated from the M subunit. Electrophoretic mobilities of the isolated fragments agrees well with the expected molecular weights. The L subunit was digested with Staphylococcus areus vs protease. The pattern obtained was consistant with the potential sites of cleavage, but it was not possible to assign cleavage sites unambiguously. 112 references, 37 figures, 2 tables.

  11. Nuclear Reaction and Structure Databases of the National Nuclear Data Center

    SciTech Connect

    Pritychenko, B.; Arcilla, R.; Herman, M. W.; Oblozinsky, P.; Rochman, D.; Sonzogni, A. A.; Tuli, J. K.; Winchell, D. F.

    2006-03-13

    The National Nuclear Data Center (NNDC) collects, evaluates, and disseminates nuclear physics data for basic research and applied nuclear technologies. In 2004, the NNDC migrated all databases into modern relational database software, installed new generation of Linux servers and developed new Java-based Web service. This nuclear database development means much faster, more flexible and more convenient service to all users in the United States. These nuclear reaction and structure database developments as well as related Web services are briefly described.

  12. Kinetics and yields of bacteriochlorophyll fluorescence: redox and conformation changes in reaction center of Rhodobacter sphaeroides.

    PubMed

    Maróti, Péter

    2008-09-01

    Induction of the bacteriochlorophyll fluorescence under rectangular shape of intense laser diode illumination (1 W cm(-2), 808 nm) was measured over wide time range from 10 microseconds to 4 s in whole cells, chromatophore and isolated reaction center protein of wild type and carotenoid-less mutant (R-26.1) of purple photosynthetic bacterium Rhodobacter sphaeroides. While the antenna-containing species showed large and positive variable fluorescence (Fv) to initial fluorescence (F0) (Fv/F0 approximately 4.5 in whole cells), the isolated RC had negative change (Fv/F0 approximately -0.6) during photochemistry. In chromatophore from R-26.1, only seven times higher rate was measured than in isolated reaction center under identical experimental conditions. The enhancement effect of large antenna on the rate of photochemistry in chromatophore was partially compensated by the favorable pigment absorption properties in isolated RC. The transition from membrane bound to isolated form of the reaction center was probed by titration of zwitterionic detergent LDAO in chromatophore, and at 0.03% LDAO concentration, sharp change of the variable fluorescence was observed. The sudden drop was explained by the formation of LDAO micelles. After the photochemical phase, additional change of fluorescence yield could be observed in isolated RC considered as manifestation of long-living conformations of the trapped redox states of the protein characterized by non-exponential kinetics. Strong support was provided for use of the fluorescence induction to track structural and conformation changes at their earliest phases in chromatophores and isolated reaction centers.

  13. CFD Modeling Activities at the NASA Stennis Space Center

    NASA Technical Reports Server (NTRS)

    Allgood, Daniel

    2007-01-01

    A viewgraph presentation on NASA Stennis Space Center's Computational Fluid Dynamics (CFD) Modeling activities is shown. The topics include: 1) Overview of NASA Stennis Space Center; 2) Role of Computational Modeling at NASA-SSC; 3) Computational Modeling Tools and Resources; and 4) CFD Modeling Applications.

  14. Synthetic Antenna Functioning As Light Harvester in the Whole Visible Region for Enhanced Hybrid Photosynthetic Reaction Centers.

    PubMed

    Hassan Omar, Omar; la Gatta, Simona; Tangorra, Rocco Roberto; Milano, Francesco; Ragni, Roberta; Operamolla, Alessandra; Argazzi, Roberto; Chiorboli, Claudio; Agostiano, Angela; Trotta, Massimo; Farinola, Gianluca M

    2016-07-20

    The photosynthetic reaction center (RC) from the Rhodobacter sphaeroides bacterium has been covalently bioconjugated with a NIR-emitting fluorophore (AE800) whose synthesis was specifically tailored to act as artificial antenna harvesting light in the entire visible region. AE800 has a broad absorption spectrum with peaks centered in the absorption gaps of the RC and its emission overlaps the most intense RC absorption bands, ensuring a consistent increase of the protein optical cross section. The covalent hybrid AE800-RC is stable and fully functional. The energy collected by the artificial antenna is transferred to the protein via FRET mechanism, and the hybrid system outperforms by a noteworthy 30% the overall photochemical activity of the native protein under the entire range of visible light. This improvement in the optical characteristic of the photoenzyme demonstrates the effectiveness of the bioconjugation approach as a suitable route to new biohybrid materials for energy conversion, photocatalysis, and biosensing. PMID:27245093

  15. Synthetic Antenna Functioning As Light Harvester in the Whole Visible Region for Enhanced Hybrid Photosynthetic Reaction Centers.

    PubMed

    Hassan Omar, Omar; la Gatta, Simona; Tangorra, Rocco Roberto; Milano, Francesco; Ragni, Roberta; Operamolla, Alessandra; Argazzi, Roberto; Chiorboli, Claudio; Agostiano, Angela; Trotta, Massimo; Farinola, Gianluca M

    2016-07-20

    The photosynthetic reaction center (RC) from the Rhodobacter sphaeroides bacterium has been covalently bioconjugated with a NIR-emitting fluorophore (AE800) whose synthesis was specifically tailored to act as artificial antenna harvesting light in the entire visible region. AE800 has a broad absorption spectrum with peaks centered in the absorption gaps of the RC and its emission overlaps the most intense RC absorption bands, ensuring a consistent increase of the protein optical cross section. The covalent hybrid AE800-RC is stable and fully functional. The energy collected by the artificial antenna is transferred to the protein via FRET mechanism, and the hybrid system outperforms by a noteworthy 30% the overall photochemical activity of the native protein under the entire range of visible light. This improvement in the optical characteristic of the photoenzyme demonstrates the effectiveness of the bioconjugation approach as a suitable route to new biohybrid materials for energy conversion, photocatalysis, and biosensing.

  16. "JCE" Classroom Activity #111: Redox Reactions in Three Representations

    ERIC Educational Resources Information Center

    Nieves, Edgardo L. Ortiz; Barreto, Reizelie; Medina, Zuleika

    2012-01-01

    This activity introduces students to the concept of reduction-oxidation (redox) reactions. To help students obtain a thorough understanding of redox reactions, the concept is explored at three levels: macroscopic, submicroscopic, and symbolic. In this activity, students perform hands-on investigations of the three levels as they work at different…

  17. NASA Glenn Research Center Battery Activities Overview

    NASA Technical Reports Server (NTRS)

    Manzo, Michelle A.

    2009-01-01

    This paper will provide an overview of the planned energy storage systems for the Orion Spacecraft and the Aries rockets that will be used in the return journey to the Moon and GRC's involvement in their development. Technology development goals and approaches to provide batteries and fuel cells for the Altair Lunar Lander, the new space suit under development for extravehicular activities (EVA) on the Lunar surface, and the Lunar Surface Systems operations will also be discussed.

  18. Menaquinone-7 in the reaction center complex of the green sulfur bacterium Chlorobium vibrioforme functions as the electron acceptor A1.

    PubMed

    Kjaer, B; Frigaard, N U; Yang, F; Zybailov, B; Miller, M; Golbeck, J H; Scheller, H V

    1998-03-10

    Photosynthetically active reaction center complexes were prepared from the green sulfur bacterium Chlorobium vibrioforme NCIMB 8327, and the content of quinones was determined by extraction and high-performance liquid chromatography. The analysis showed a stoichiometry of 1.7 molecules of menaquinone-7/reaction center. No other quinones were detected in the isolated reaction centers, whereas membrane preparations also contained chlorobiumquinone. The possible involvement of quinones in electron transport was investigated by electron paramagnetic resonance (EPR) spectroscopy. A highly anisotropic radical was detected by Q-band EPR spectroscopy in both membranes and isolated reaction centers following dark reduction with sodium dithionite and photoaccumulation at 205 K. At 34 GHz, the EPR spectrum is characterized by a g tensor with gxx = 2.0063, gyy = 2.0052, gzz = 2.0020 and delta B of 0.7 mT, consistent with its identification as a quinone. This spectrum is highly similar in terms of g values and line widths to photoaccumulated A1- in photosystem I of Synechococcus sp. PCC 7002. The results indicate that menaquinone-7 in the green sulfur bacterial reaction center is analogous to phylloquinone in photosystem I.

  19. Hypersensitivity reactions to radiocontrast media: the role of complement activation.

    PubMed

    Szebeni, Janos

    2004-01-01

    Although intravenous use of radiocontrast media (RCM) for a variety of radiographic procedures is generally safe, clinically significant acute hypersensitivity reactions still occur in a significant percentage of patients. The mechanism of these anaphylactoid, or "pseudoallergic," reactions is complex, involving complement activation, direct degranulation of mast cells and basophils, and modulation of enzymes and proteolytic cascades in plasma. In this review, basic information on different RCMs and their reactogenicity is summarized and updated, and the prevalence, pathomechanism, prediction, prevention, treatment, and economic impact of hypersensitivity reactions are discussed. Particular attention is paid to the in vitro and in vivo evidence supporting complement activation as an underlying cause of RCM reactions.

  20. Formation of photosystem II reaction centers that work as energy sinks in lichen symbiotic Trebouxiophyceae microalgae.

    PubMed

    Guéra, Alfredo; Gasulla, Francisco; Barreno, Eva

    2016-04-01

    Lichens are poikilohydric symbiotic organisms that can survive in the absence of water. Photosynthesis must be highly regulated in these organisms, which live under continuous desiccation-rehydration cycles, to avoid photooxidative damage. Analysis of chlorophyll a fluorescence induction curves in the lichen microalgae of the Trebouxiophyceae Asterochloris erici and in Trebouxia jamesii (TR1) and Trebouxia sp. (TR9) phycobionts, isolated from the lichen Ramalina farinacea, shows differences with higher plants. In the presence of the photosynthetic electron transport inhibitor DCMU, the kinetics of Q(A) reduction is related to variable fluorescence by a sigmoidal function that approaches a horizontal asymptote. An excellent fit to these curves was obtained by applying a model based on the following assumptions: (1) after closure, the reaction centers (RCs) can be converted into "energy sink" centers (sRCs); (2) the probability of energy leaving the sRCs is very low or zero and (3) energy is not transferred from the antenna of PSII units with sRCs to other PSII units. The formation of sRCs units is also induced by repetitive light saturating pulses or at the transition from dark to light and probably requires the accumulation of reduced Q(A), as well as structural changes in the reaction centers of PSII. This type of energy sink would provide a very efficient way to protect symbiotic microalgae against abrupt changes in light intensity.

  1. Sequence of the core antenna domain from the anoxygenic phototroph Heliophilum fasciatum: implications for diversity of reaction center type I.

    PubMed

    Mix, Lucas J; Harmer, Tara L; Cavanaugh, Colleen M

    2004-06-01

    Broad variation among anoxygenic reaction centers makes it essential to consider a wide variety when considering the origins of photosynthesis. The photosynthetic core antenna domain in the gene pshA from Heliophilum fasciatum was sequenced doubling the number of core sequences available from heliobacteria. The sequence shares a pattern of hydrophobicity and histidine residues with the core antenna domain of pshA from Heliobacillus mobilis. Sequence identity between the two pshA sequences was 68%, indicating heliobacterial reaction centers show similar diversity to photosystem I throughout cyanobacteria and plastids. Thus, the diversity of anoxygenic phototrophic reaction centers may be greater than previously thought. PMID:15170240

  2. Sequence of the core antenna domain from the anoxygenic phototroph Heliophilum fasciatum: implications for diversity of reaction center type I.

    PubMed

    Mix, Lucas J; Harmer, Tara L; Cavanaugh, Colleen M

    2004-06-01

    Broad variation among anoxygenic reaction centers makes it essential to consider a wide variety when considering the origins of photosynthesis. The photosynthetic core antenna domain in the gene pshA from Heliophilum fasciatum was sequenced doubling the number of core sequences available from heliobacteria. The sequence shares a pattern of hydrophobicity and histidine residues with the core antenna domain of pshA from Heliobacillus mobilis. Sequence identity between the two pshA sequences was 68%, indicating heliobacterial reaction centers show similar diversity to photosystem I throughout cyanobacteria and plastids. Thus, the diversity of anoxygenic phototrophic reaction centers may be greater than previously thought.

  3. Immobilization and orientation of Photosystem I reaction centers on solid surfaces. Final report

    SciTech Connect

    1998-01-20

    The overall objective of this project was to test the potential for immobilization and orientation of Photosystem I reaction center protein on solid surfaces. In order to maximize the resources available for this work, bleomycin complexes were used as a test substrate. The reaction of [(H{sub 2}O)(NH{sub 3}){sub 5}Ru{sup II}]{sup 2+} with bleomycin forms at least two stable products following oxidation to the Ru(III) analog. Spectroscopic and electrochemical measurements indicate monodentate binding of [(NH{sub 3}){sub 5}Ru{sup III}] to the imidazole and pyrimidine moieties, with coordination to the latter involving the exocyclic amine nitrogen. DNA cleavage studies show the complexes to be ineffective in DNA strand scission.

  4. Structure of the reaction center from Rhodobacter sphaeroides R-26: the cofactors

    SciTech Connect

    Allen, J.P.; Feher, G.; Yeates, T.O.; Komiya, H.; Rees, D.C.

    1987-08-01

    The three-dimensional structure of the cofactors of the reaction center of Rhodobacter sphaeroides R-26 has been determined by x-ray diffraction and refined at a resolution of 2.8 A with an R value of 26%. The main features of the structure are similar to the ones determined for Rhodopseudomonas viridis. The cofactors are arranged along two branches, which are approximately related to each other by a 2-fold symmetry axis. The structure is well suited to produce light-induced charge separation across the membrane. Most of the structural features predicted from physical and biochemical measurements are confirmed by the x-ray structure.

  5. Brominated lipids identify lipid binding sites on the surface of the reaction center from Rhodobacter sphaeroides.

    PubMed

    Roszak, Aleksander W; Gardiner, Alastair T; Isaacs, Neil W; Cogdell, Richard J

    2007-03-20

    This study describes the use of brominated phospholipids to distinguish between lipid and detergent binding sites on the surface of a typical alpha-helical membrane protein. Reaction centers isolated from Rhodobacter sphaeroides were cocrystallized with added brominated phospholipids. X-ray structural analysis of these crystals has revealed the presence of two lipid binding sites from the characteristic strong X-ray scattering from the bromine atoms. These results demonstrate the usefulness of this approach to mapping lipid binding sites at the surface of membrane proteins.

  6. Animal-Centered Learning Activities in Pharmacy Education

    PubMed Central

    Lust, Elaine

    2006-01-01

    Objectives To assess the contribution of animal-centered activities to students achieving learning outcomes in a veterinary therapeutics course. Design Qualitative methods were used to assess the outcome of using “hands-on” animal interactions as tools of engagement in the course. Reflective commentary on animal-centered activities was collected and analyzed. Assessment Animal-centered learning activities are effective tools for engaging students and facilitating their understanding and application of veterinary therapeutic knowledge, skills, and attitudes. Analysis of qualitative data revealed themes of professional caring and caring behaviors as a direct result of animal-centered activities. Elements of empathy, caring, compassion, and self-awareness were strong undercurrents in student's comments. Conclusions Animal-centered learning activities provide an innovative learning environment for the application of veterinary pharmacy knowledge, skills, and attitudes directly to animal patients. The use of animals in the course is a successful active-learning technique to engage pharmacy students and assist them in developing caring attitudes and behaviors beneficial to future health care providers. PMID:17149415

  7. The Sugar Model: Autocatalytic Activity of the Triose Ammonia Reaction

    NASA Astrophysics Data System (ADS)

    Weber, Arthur L.

    2007-04-01

    Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior of the products was examined by measuring the effect of the crude triose ammonia reaction product on the kinetics of a second identical triose ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance of triose and the rate of formation of pyruvaldehyde, the product of triose dehydration. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of autocatalytic molecules.

  8. Fusion of liposomones and chromatophores of Rhodopseudomonas capsulata: effect on photosynthetic energy transfer between B875 and reaction center complexes

    SciTech Connect

    Takemoto, J.Y.; Schonhardt, T.; Golecki, J.R.; Drews, G.

    1985-06-01

    The photosynthetic chromatophore membranes of Rhodopseudomonas capsulata were fused with liposomes to investigate the effects of lipid dilution on energy transfer between the bacteriochlorophyll-protein complexes of this membrane. Freeze-fracture electron microscopy revealed that the fractions contained closed vesicles formed by the fusion of liposomes to chromatophores. Particles with 9-nm diameters on the P fracture faces did not appear to change in size with increasing lipid content, but the number of particles per membrane area decreased proportionally with increases in the lipid-to-protein ratio. The bacteriochlorophyll-to-protein ratios, electrophoretic polypeptide profiles on sodium dodecyl sulfate-polyacrylamide gels, and light-induced absorbance changes at 595 nm caused by photosynthetic reaction centers were not altered by fusion. The relative fluorescence emission intensities due to the B875 light-harvesting complex increased significantly with increasing lipid content, but no increases in fluorescence due to the B800-B850 light-harvesting complex were observed. Electron transport rates, measured as succinate-cytochrome c reductase activities, decreased with increased lipid content. The results indicate an uncoupling of energy transfer between the B875 light-harvesting and reaction center complexes with lipid dilution of the chromatophore membrane.

  9. Functional type 2 photosynthetic reaction centers found in the rare bacterial phylum Gemmatimonadetes.

    PubMed

    Zeng, Yonghui; Feng, Fuying; Medová, Hana; Dean, Jason; Koblížek, Michal

    2014-05-27

    Photosynthetic bacteria emerged on Earth more than 3 Gyr ago. To date, despite a long evolutionary history, species containing (bacterio)chlorophyll-based reaction centers have been reported in only 6 out of more than 30 formally described bacterial phyla: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, and Acidobacteria. Here we describe a bacteriochlorophyll a-producing isolate AP64 that belongs to the poorly characterized phylum Gemmatimonadetes. This red-pigmented semiaerobic strain was isolated from a freshwater lake in the western Gobi Desert. It contains fully functional type 2 (pheophytin-quinone) photosynthetic reaction centers but does not assimilate inorganic carbon, suggesting that it performs a photoheterotrophic lifestyle. Full genome sequencing revealed the presence of a 42.3-kb-long photosynthesis gene cluster (PGC) in its genome. The organization and phylogeny of its photosynthesis genes suggests an ancient acquisition of PGC via horizontal transfer from purple phototrophic bacteria. The data presented here document that Gemmatimonadetes is the seventh bacterial phylum containing (bacterio)chlorophyll-based phototrophic species. To our knowledge, these data provide the first evidence that (bacterio)chlorophyll-based phototrophy can be transferred between distant bacterial phyla, providing new insights into the evolution of bacterial photosynthesis. PMID:24821787

  10. Functional type 2 photosynthetic reaction centers found in the rare bacterial phylum Gemmatimonadetes

    PubMed Central

    Zeng, Yonghui; Feng, Fuying; Medová, Hana; Dean, Jason; Koblížek, Michal

    2014-01-01

    Photosynthetic bacteria emerged on Earth more than 3 Gyr ago. To date, despite a long evolutionary history, species containing (bacterio)chlorophyll-based reaction centers have been reported in only 6 out of more than 30 formally described bacterial phyla: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, and Acidobacteria. Here we describe a bacteriochlorophyll a-producing isolate AP64 that belongs to the poorly characterized phylum Gemmatimonadetes. This red-pigmented semiaerobic strain was isolated from a freshwater lake in the western Gobi Desert. It contains fully functional type 2 (pheophytin-quinone) photosynthetic reaction centers but does not assimilate inorganic carbon, suggesting that it performs a photoheterotrophic lifestyle. Full genome sequencing revealed the presence of a 42.3-kb–long photosynthesis gene cluster (PGC) in its genome. The organization and phylogeny of its photosynthesis genes suggests an ancient acquisition of PGC via horizontal transfer from purple phototrophic bacteria. The data presented here document that Gemmatimonadetes is the seventh bacterial phylum containing (bacterio)chlorophyll-based phototrophic species. To our knowledge, these data provide the first evidence that (bacterio)chlorophyll-based phototrophy can be transferred between distant bacterial phyla, providing new insights into the evolution of bacterial photosynthesis. PMID:24821787

  11. Isolated photosystem I reaction centers on a functionalized gated high electron mobility transistor.

    PubMed

    Eliza, Sazia A; Lee, Ida; Tulip, Fahmida S; Mostafa, Salwa; Greenbaum, Elias; Ericson, M Nance; Islam, Syed K

    2011-09-01

    In oxygenic plants, photons are captured with high quantum efficiency by two specialized reaction centers (RC) called Photosystem I (PS I) and Photosystem II (PS II). The captured photon triggers rapid charge separation and the photon energy is converted into an electrostatic potential across the nanometer-scale (~6 nm) reaction centers. The exogenous photovoltages from a single PS I RC have been previously measured using the technique of Kelvin force probe microscopy (KFM). However, biomolecular photovoltaic applications require two-terminal devices. This paper presents for the first time, a micro-device for detection and characterization of isolated PS I RCs. The device is based on an AlGaN/GaN high electron mobility transistor (HEMT) structure. AlGaN/GaN HEMTs show high current throughputs and greater sensitivity to surface charges compared to other field-effect devices. PS I complexes immobilized on the floating gate of AlGaN/GaN HEMTs resulted in significant changes in the device characteristics under illumination. An analytical model has been developed to estimate the RCs of a major orientation on the functionalized gate surface of the HEMTs. PMID:21926029

  12. Engineered Photosystem II reaction centers optimize photochemistry versus photoprotection at different solar intensities.

    PubMed

    Vinyard, David J; Gimpel, Javier; Ananyev, Gennady M; Mayfield, Stephen P; Dismukes, G Charles

    2014-03-12

    The D1 protein of Photosystem II (PSII) provides most of the ligating amino acid residues for the Mn4CaO5 water-oxidizing complex (WOC) and half of the reaction center cofactors, and it is present as two isoforms in the cyanobacterium Synechococcus elongatus PCC 7942. These isoforms, D1:1 and D1:2, confer functional advantages for photosynthetic growth at low and high light intensities, respectively. D1:1, D1:2, and seven point mutations in the D1:2 background that are native to D1:1 were expressed in the green alga Chlamydomonas reinhardtii. We used these nine strains to show that those strains that confer a higher yield of PSII charge separation under light-limiting conditions (where charge recombination is significant) have less efficient photochemical turnover, measured in terms of both a lower WOC turnover probability and a longer WOC cycle period. Conversely, these same strains under light saturation (where charge recombination does not compete) confer a correspondingly faster O2 evolution rate and greater protection against photoinhibition. Taken together, the data clearly establish that PSII primary charge separation is a trade-off between photochemical productivity (water oxidation and plastoquinone reduction) and charge recombination (photoprotection). These trade-offs add up to a significant growth advantage for the two natural isoforms. These insights provide fundamental design principles for engineering of PSII reaction centers with optimal photochemical efficiencies for growth at low versus high light intensities.

  13. Stark effect spectroscopy of Rhodobacter sphaeroides and Rhodopseudomonas viridis reaction centers

    PubMed Central

    Lockhart, David J.; Boxer, Steven G.

    1988-01-01

    The nature of the initially excited state of the primary electron donor or special pair has been investigated by Stark effect spectroscopy for reaction centers from the photosynthetic bacteria Rhodopseudomonas viridis and Rhodobacter sphaeroides at 77 K. The data provide values for the magnitude of the difference in permanent dipole moment between the ground and excited state, [unk]Δμ[unk], and the angle [unk] between Δμ and the transition dipole moment for the electronic transition. [unk]Δμ[unk] and [unk] for the lowest-energy singlet electronic transition associated with the special pair primary electron donor were found to be very similar for the two species. [unk]Δμ[unk] for this transition is substantially larger than for the Qy transitions of the monomeric pigments in the reaction center or for pure monomeric bacteriochlorophylls, for which Stark data are also reported. We conclude that the excited state of the special pair has substantial charge-transfer character, and we suggest that charge separation in bacterial photosynthesis is initiated immediately upon photoexcitation of the special pair. Data for Rhodobacter sphaeroides between 340 and 1340 nm are presented and discussed in the context of the detection of charge-transfer states by Stark effect spectroscopy. PMID:16578825

  14. Isolated photosystem I reaction centers on a functionalized gated high electron mobility transistor.

    PubMed

    Eliza, Sazia A; Lee, Ida; Tulip, Fahmida S; Mostafa, Salwa; Greenbaum, Elias; Ericson, M Nance; Islam, Syed K

    2011-09-01

    In oxygenic plants, photons are captured with high quantum efficiency by two specialized reaction centers (RC) called Photosystem I (PS I) and Photosystem II (PS II). The captured photon triggers rapid charge separation and the photon energy is converted into an electrostatic potential across the nanometer-scale (~6 nm) reaction centers. The exogenous photovoltages from a single PS I RC have been previously measured using the technique of Kelvin force probe microscopy (KFM). However, biomolecular photovoltaic applications require two-terminal devices. This paper presents for the first time, a micro-device for detection and characterization of isolated PS I RCs. The device is based on an AlGaN/GaN high electron mobility transistor (HEMT) structure. AlGaN/GaN HEMTs show high current throughputs and greater sensitivity to surface charges compared to other field-effect devices. PS I complexes immobilized on the floating gate of AlGaN/GaN HEMTs resulted in significant changes in the device characteristics under illumination. An analytical model has been developed to estimate the RCs of a major orientation on the functionalized gate surface of the HEMTs.

  15. Modeling light-driven proton pumps in artificial photosynthetic reaction centers.

    PubMed

    Ghosh, Pulak Kumar; Smirnov, Anatoly Yu; Nori, Franco

    2009-07-21

    We study a model of a light-induced proton pump in artificial reaction centers. The model contains a molecular triad with four electron states (i.e., one donor state, two photosensitive group states, and one acceptor state) as well as a molecular shuttle having one electron and one proton-binding sites. The shuttle diffuses between the sides of the membrane and translocates protons energetically uphill: from the negative side to the positive side of the membrane, harnessing for this purpose the energy of the electron-charge separation produced by light. Using the methods of quantum transport theory we calculate the range of light intensity and transmembrane potentials that maximize both the light-induced proton current and the energy transduction efficiency. We also study the effect of temperature on proton pumping. The light-induced proton pump in our model gives a quantum yield of proton translocation of about 55%. Thus, our results explain previous experiments on these artificial photosynthetic reaction centers.

  16. Isolated Photosystem I Reaction Centers on a Functionalized Gated High Electron Mobility Transistor

    SciTech Connect

    Eliza, Sazia A.; Lee, Ida; Tulip, Fahmida S; Islam, Syed K; Mostafa, Salwa; Greenbaum, Elias; Ericson, Milton Nance

    2011-01-01

    In oxygenic plants, photons are captured with high quantum efficiency by two specialized reaction centers (RC) called Photosystem I (PS I) and Photosystem II (PS II). The captured photon triggers rapid charge separation and the photon energy is converted into an electrostatic potential across the nanometer-scale nm reaction centers. The exogenous photovoltages from a single PS I RC have been previously measured using the technique of Kelvin force probe microscopy (KFM). However, biomolecular photovoltaic applications require two-terminal devices. This paper presents for the first time, a micro-device for detection and characterization of isolated PS I RCs. The device is based on an AlGaN/GaN high electron mobility transistor (HEMT) structure. AlGaN/GaN HEMTs show high current throughputs and greater sensitivity to surface charges compared to other field-effect devices. PS I complexes immobilized on the floating gate of AlGaN/GaN HEMTs resulted in significant changes in the device characteristics under illumination. An analytical model has been developed to estimate the RCs of a major orientation on the functionalized gate surface of the HEMTs.

  17. Modulating the Redox Potential of the Stable Electron Acceptor, QB, in Mutagenized Photosystem II Reaction Centers.

    SciTech Connect

    Perrine, Zoee; Sayre, Richard

    2011-02-10

    One of the unique features of electron transfer processes in photosystem II (PSII) reaction centers (RC) is the exclusive transfer of electrons down only one of the two parallel cofactor branches. In contrast to the RC core polypeptides (psaA and psaB) of photosystem I (PSI), where electron transfer occurs down both parallel redox-active cofactor branches, there is greater protein-cofactor asymmetry between the PSII RC core polypeptides (D1 and D2). We have focused on the identification of protein-cofactor relationships that determine the branch along which primary charge separation occurs (P680+/pheophytin-(Pheo)). We have previously shown that mutagenesis of the strong hydrogen-bonding residue, D1-E130, to less polar residues (D1-E130Q,H,L) shifted the midpoint potential of the PheoD1/PheoD1- couple to more negative values, reducing the quantum yield of primary charge separation. We did not observe, however, electron transfer down the inactive branch in D1-E130 mutants. The protein residue corresponding to D1-E130 on the inactive branch is D2-Q129 which presumably has a reduced hydrogen-bonding interaction with PheoD2 relative to the D1-E130 residue with PheoD1. Analysis of the recent 2.9 Å cyanobacterial PSII crystal structure indicated, however, that the D2-Q129 residue was too distant from the PheoD2 headgroup to serve as a possible hydrogen bond donor and directly impact its midpoint potential as well as potentially determine the directionality of electron transfer. Our objective was to characterize the function of this highly conserved inactive branch residue by replacing it with a nonconservative leucine or a conservative histidine residue. Measurements of Chl fluorescence decay kinetics and thermoluminescence studies indicate that the mutagenesis of D2-Q129 decreases the redox gap between QA and QB due to a lowering of the redox potential of QB. The

  18. Induction and anisotropy of fluorescence of reaction center from photosynthetic bacterium Rhodobacter sphaeroides.

    PubMed

    Sipka, Gábor; Maróti, Péter

    2016-01-01

    Submillisecond dark-light changes of the yield (induction) and anisotropy of fluorescence under laser diode excitation were measured in the photosynthetic reaction center of the purple bacterium Rhodobacter sphaeroides. Narrow band (1-2 nm) laser diodes emitting at 808 and 865 nm were used to selectively excite the accessory bacteriochlorophyll (B, 800 nm) or the upper excitonic state of the bacteriochlorophyll dimer (P-, 810 nm) and the lower excitonic state of the dimer (P+, 865 nm), respectively. The fluorescence spectrum of the wild type showed two bands centered at 850 nm (B) and 910 nm (P-). While the monotonous decay of the fluorescence yield at 910 nm tracked the light-induced oxidation of the dimer, the kinetics of the fluorescence yield at 850 nm showed an initial rise before a decrease. The anisotropy of the fluorescence excited at 865 nm (P-) was very close to the limiting value (0.4) across the whole spectral range. The excitation of both B and P- at 808 nm resulted in wavelength-dependent depolarization of the fluorescence from 0.35 to 0.24 in the wild type and from 0.30 to 0.24 in the reaction center of triple mutant (L131LH-M160LH-M197FH). The additivity law of the anisotropies of the fluorescence species accounts for the wavelength dependence of the anisotropy. The measured fluorescence yields and anisotropies are interpreted in terms of very fast energy transfer from (1)B* to (1)P- (either directly or indirectly by internal conversion from (1)P+) and to the oxidized dimer.

  19. On the possibility of negative activation energies in bimolecular reactions

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1978-01-01

    The temperature dependence of the rate constants for model reacting systems was studied to understand some recent experimental measurements which imply the existence of negative activation energies. A collision theory model and classical trajectory calculations are used to demonstrate that the reaction probability can vary inversely with collision energy for bimolecular reactions occurring on attractive potential energy surfaces. However, this is not a sufficient condition to ensure that the rate constant has a negative temperature dependence. On the basis of these calculations, it seems unlikely that a true bimolecular reaction between neutral molecules will have a negative activation energy.

  20. Stereo and regioselectivity in ''Activated'' tritium reactions

    SciTech Connect

    Ehrenkaufer, R.L.E.; Hembree, W.C.; Wolf, A.P.

    1988-01-01

    To investigate the stereo and positional selectivity of the microwave discharge activation (MDA) method, the tritium labeling of several amino acids was undertaken. The labeling of L-valine and the diastereomeric pair L-isoleucine and L-alloisoleucine showed less than statistical labeling at the ..cap alpha..-amino C-H position mostly with retention of configuration. Labeling predominated at the single ..beta.. C-H tertiary (methyne) position. The labeling of L-valine and L-proline with and without positive charge on the ..cap alpha..-amino group resulted in large increases in specific activity (greater than 10-fold) when positive charge was removed by labeling them as their sodium carboxylate salts. Tritium NMR of L-proline labeled both as its zwitterion and sodium salt showed also large differences in the tritium distribution within the molecule. The distribution preferences in each of the charge states are suggestive of labeling by an electrophilic like tritium species(s). 16 refs., 5 tabs.

  1. Initial electron donor and acceptor in isolated Photosystem II reaction centers identified with femtosecond mid-IR spectroscopy

    PubMed Central

    Groot, Marie Louise; Pawlowicz, Natalia P.; van Wilderen, Luuk J. G. W.; Breton, Jacques; van Stokkum, Ivo H. M.; van Grondelle, Rienk

    2005-01-01

    Despite the apparent similarity between the plant Photosystem II reaction center (RC) and its purple bacterial counterpart, we show in this work that the mechanism of charge separation is very different for the two photosynthetic RCs. By using femtosecond visible-pump–mid-infrared probe spectroscopy in the region of the chlorophyll ester and keto modes, between 1,775 and 1,585 cm–1, with 150-fs time resolution, we show that the reduction of pheophytin occurs on a 0.6- to 0.8-ps time scale, whereas P+, the precursor state for water oxidation, is formed after ≈6 ps. We conclude therefore that in the Photosystem II RC the primary charge separation occurs between the “accessory chlorophyll” ChlD1 and the pheophytin on the so-called active branch. PMID:16135567

  2. The functional role of protein dynamics in photosynthetic reaction centers investigated by elastic and quasielastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Pieper, Jörg

    2015-01-01

    This short review summarizes our current knowledge about the functional relevance of protein dynamics in photosynthetic reaction centers. In the case of Photosystem II membrane fragments, elastic and quasielastic neutron scattering experiments reveal a dynamical transition at about 240 K corresponding to the activation of picosecond molecular motions. Likewise, a "freezing" of molecular dynamics is observed upon dehydration. Intriguingly, these effects correlate with the pronounced temperature- and hydration-dependence of specific electron transfer steps in Photosystem II indicating that molecular dynamics is an indispensable prerequisite for its function. Thus, electron transfer in Photosystem II appears to be a prototypical example for a dynamics-function correlation. Finally, the laser-neutron pump-probe technique is shown to permit in-situ monitoring of molecular dynamics in specific functional states of a protein in real time.

  3. Community Information and Services Centers: Concepts for Activation.

    ERIC Educational Resources Information Center

    Hopkins, Cleve

    An experimental program based on a study by the Department of Housing and Urban Development was activated to deliver services to urban residents via automated communications technology. Designed to contribute to improvement in the quality of life, the program of a Community Information and Services Center (CISC) included: outreach programs, i.e.,…

  4. Rate constants for aqueous-phase reactions of hydroxyl radical ({center_dot}OH) with aldehydes and ketones

    SciTech Connect

    Allen, J.M.; Allen, S.K.

    1995-12-31

    A wide variety of aldehydes and ketones are formed in the troposphere by the gas-phase oxidation of hydrocarbons. These compounds are expected to readily partition into cloud, fog, and aquated aerosol drops where they can participate in a variety of aqueous-phase reactions. It has been previously demonstrated by other researchers that aqueous-phase photochemical reactions involving aromatic aldehydes and ketones may lead to the formation of hydrogen peroxide. Hydrogen peroxide is an important oxidant for S(IV) and is also an {center_dot}OH precursor. Aldehydes and ketones may also participate in other aqueous-phase reactions within atmospheric water drops including reactions with {center_dot}OH. Rate constants for reactions involving {center_dot}OH in aqueous solutions have been reported for only a limited number of tropospheric aldehydes and ketones. The authors have measured the rate constants for aqueous-phase reactions of {center_dot}OH with several tropospheric aldehydes and ketones by the technique of competition kinetics. Hydroxyl radicals were generated by continuous illumination at 313 nm of an aqueous acidified solution containing Fe(ClO{sub 4}){sub 3}, an {center_dot}OH scavenger, the aldehyde or ketone whose rate constant was to be measured, and a standard for which the rate constant for reaction with {center_dot}OH is well known. Nitrobenzene was used as the standard in all experiments. Loss of the aldehyde or ketone and the standard were monitored by HPLC. Losses attributable to direct photolysis and dark reactions were minimal.

  5. AN OFF-CENTERED ACTIVE GALACTIC NUCLEUS IN NGC 3115

    SciTech Connect

    Menezes, R. B.; Steiner, J. E.; Ricci, T. V.

    2014-11-20

    NGC 3115 is an S0 galaxy that has always been considered to have a pure absorption-line spectrum. Some recent studies have detected a compact radio-emitting nucleus in this object, coinciding with the photometric center and with a candidate for the X-ray nucleus. This is evidence of the existence of a low-luminosity active galactic nucleus (AGN) in the galaxy, although no emission line has ever been observed. We report the detection of an emission-line spectrum of a type 1 AGN in NGC 3115, with an Hα luminosity of L {sub Hα} = (4.2 ± 0.4) × 10{sup 37} erg s{sup –1}. Our analysis revealed that this AGN is located at a projected distance of ∼0.''29 ± 0.''05 (corresponding to ∼14.3 ± 2.5 pc) from the stellar bulge center, which is coincident with the kinematic center of this object's stellar velocity map. The black hole corresponding to the observed off-centered AGN may form a binary system with a black hole located at the stellar bulge center. However, it is also possible that the displaced black hole is the merged remnant of the binary system coalescence, after the ''kick'' caused by the asymmetric emission of gravitational waves. We propose that certain features in the stellar velocity dispersion map are the result of perturbations caused by the off-centered AGN.

  6. Femtosecond infrared spectroscopy of reaction centers from Rhodobacter sphaeroides between 1000 and 1800 cm-1.

    PubMed Central

    Hamm, P; Zurek, M; Mäntele, W; Meyer, M; Scheer, H; Zinth, W

    1995-01-01

    Time-resolved pump-and-probe experiments of reaction centers of the purple bacterium Rhodobacter sphaeroides (R26) in the mid-IR region between 1000 and 1800 cm-1 are recorded with a time resolution of 300-400 fs. The difference spectra of the states P*, P+HA-, and P+QA- with respect to the ground state P predominantly reflect changes of the special pair. They show positive and negative bands due to changes of distinct vibrational modes superimposed on a broad background of enhanced absorption. A number of certain bands can be assigned to the special pair P, to the bacteriopheophytin HA, and to the quinone QA. The temporal evolution of the IR absorbance changes is well described by the time constants known from femtosecond spectroscopy of the electronic states. Differences occur only at very early times, which are indicative of fast vibrational relaxation with a time constant of a few hundred femtoseconds. PMID:7892185

  7. Origin of bimodal fluorescence enhancement factors of Chlorobaculum tepidum reaction centers on silver island films.

    PubMed

    Maćkowski, Sebastian; Czechowski, Nikodem; Ashraf, Khuram U; Szalkowski, Marcin; Lokstein, Heiko; Cogdell, Richard J; Kowalska, Dorota

    2016-08-01

    We focus on the spectral dependence of plasmon-induced enhancement of fluorescence of Chlorobaculum tepidum reaction centers. When deposited on silver island film, they exhibit up to a 60-fold increase in fluorescence. The dependence of enhancement factors on the excitation wavelength is not correlated with the absorption spectrum of the plasmonic structure. In particular, the presence of one (or multiple) trimers of the Fenna-Matthews-Olson (FMO) protein reveals itself in bimodal distribution of enhancement factors for the excitation at 589 nm, the wavelength corresponding to bacteriochlorophyll absorption of FMO and the core of the RC. We conclude that the structure of multichromophoric complexes can substantially affect the impact of plasmonic excitations, which is important in the context of assembling functional biohybrid systems.

  8. Origin of bimodal fluorescence enhancement factors of Chlorobaculum tepidum reaction centers on silver island films.

    PubMed

    Maćkowski, Sebastian; Czechowski, Nikodem; Ashraf, Khuram U; Szalkowski, Marcin; Lokstein, Heiko; Cogdell, Richard J; Kowalska, Dorota

    2016-08-01

    We focus on the spectral dependence of plasmon-induced enhancement of fluorescence of Chlorobaculum tepidum reaction centers. When deposited on silver island film, they exhibit up to a 60-fold increase in fluorescence. The dependence of enhancement factors on the excitation wavelength is not correlated with the absorption spectrum of the plasmonic structure. In particular, the presence of one (or multiple) trimers of the Fenna-Matthews-Olson (FMO) protein reveals itself in bimodal distribution of enhancement factors for the excitation at 589 nm, the wavelength corresponding to bacteriochlorophyll absorption of FMO and the core of the RC. We conclude that the structure of multichromophoric complexes can substantially affect the impact of plasmonic excitations, which is important in the context of assembling functional biohybrid systems. PMID:27406896

  9. Femtosecond infrared spectroscopy of reaction centers from Rhodobacter sphaeroides between 1000 and 1800 cm-1.

    PubMed

    Hamm, P; Zurek, M; Mäntele, W; Meyer, M; Scheer, H; Zinth, W

    1995-03-14

    Time-resolved pump-and-probe experiments of reaction centers of the purple bacterium Rhodobacter sphaeroides (R26) in the mid-IR region between 1000 and 1800 cm-1 are recorded with a time resolution of 300-400 fs. The difference spectra of the states P*, P+HA-, and P+QA- with respect to the ground state P predominantly reflect changes of the special pair. They show positive and negative bands due to changes of distinct vibrational modes superimposed on a broad background of enhanced absorption. A number of certain bands can be assigned to the special pair P, to the bacteriopheophytin HA, and to the quinone QA. The temporal evolution of the IR absorbance changes is well described by the time constants known from femtosecond spectroscopy of the electronic states. Differences occur only at very early times, which are indicative of fast vibrational relaxation with a time constant of a few hundred femtoseconds.

  10. Mimicry of the radical pair and triplet states in photosynthetic reaction centers with a synthetic model

    SciTech Connect

    Hasharoni, K.; Levanon, H.; Greenfield, S.R.; Gosztola, D.J.; Svec, W.A.; Wasiclewski, M.R. |

    1995-08-02

    Supramolecular systems synthesized to model the photosynthetic reaction center (RC) are designed to mimic several key properties of the RC protein. Thus far, most RC models fulfill only a subset of these criteria, with very few reports employing time-resolved electron paramagnetic resonance spectroscopy (TREPR). We now report TREPR results on a photosynthetic model system (1) in a nematic liquid crystal (LC) that does not contain the natural pigments, yet closely mimics the spin dynamics of triplet state formation found only in photosynthetic RCs. The design of supermolecule 1 follows criteria established for promoting high quantum yield charge separation in glassy media. The observation of this triplet state in 1 by TREPR demonstrates that most of the electronic states found in the primary photochemistry of photosynthetic RCs can be mimicked successfully in synthetic models interacting with LCs. 12 refs., 3 figs.

  11. Langley Research Center contributions in advancing active control technology

    NASA Technical Reports Server (NTRS)

    Abel, I.; Newsom, J. R.

    1981-01-01

    The application of active control technology to reduce aeroelastic response of aircraft structures offers a potential for significant payoffs in terms of aerodynamic efficiency and weight savings. Some of the contributions of the Langley Research Center in advancing active control technology are described. Contributions are categorized into the development of appropriate analysis tools, control law synthesis methodology, and experimental investigations aimed at verifying both analysis and synthesis methodology.

  12. The FMO protein is related to PscA in the reaction center of green sulfur bacteria.

    PubMed

    Olson, John M; Raymond, Jason

    2003-01-01

    The Fenna-Matthews-Olson protein is a water-soluble protein found only in green sulfur bacteria. Each subunit contains seven bacteriochlorophyll (BChl) a molecules wrapped in a string bag of protein consisting of mostly beta sheet. Most other chlorophyll-binding proteins are water-insoluble proteins containing membrane-spanning alpha helices. We compared an FMO consensus sequence to well-characterized, membrane-bound chlorophyll-binding proteins: L & M (reaction center proteins of proteobacteria), D1 & D2 (reaction center proteins of PS II), CP43 & CP47 (core proteins of PS II), PsaA & PsaB (reaction center proteins of PS I), PscA (reaction center protein of green sulfur bacteria), and PshA (reaction center protein of heliobacteria). We aligned the FMO sequence with the other sequences using the PAM250 matrix modified for His binding-site identities and found a signature sequence (LxHHxxxGxFxxF) common to FMO and PscA. (The two His residues are BChl a. binding sites in FMO.) This signature sequence is part of a 220-residue C-terminal segment with an identity score of 13%. PRSS (Probability of Random Shuffle) analysis showed that the 220-residue alignment is better than 96% of randomized alignments. This evidence supports the hypothesis that FMO protein is related to PscA. PMID:16228607

  13. 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.

  14. Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I.

    PubMed

    Trost, J T; Brune, D C; Blankenship, R E

    1992-01-01

    Photosynthetic reaction centers isolated from Heliobacillus mobilis exhibit a single major protein on SDS-PAGE of 47 000 Mr. Attempts to sequence the reaction center polypeptide indicated that the N-terminus is blocked. After enzymatic and chemical cleavage, four peptide fragments were sequenced from the Heliobacillus mobilis apoprotein. Only one of these sequences showed significant specific similarity to any of the protein and deduced protein sequences in the GenBank data base. This fragment is identical with 56% of the residues, including both cysteines, found in highly conserved region that is proposed to bind iron-sulfur center Fx in the Photosystem I reaction center peptide that is the psaB gene product. The similarity to the psaA gene product in this region is 48%. Redox titrations of laser-flash-induced photobleaching with millisecond decay kinetics on isolated reaction centers from Heliobacterium gestii indicate a midpoint potential of -414 mV with n = 2 titration behavior. In membranes, the behavior is intermediate between n = 1 and n = 2, and the apparent midpoint potential is -444 mV. This is compared to the behavior in Photosystem I, where the intermediate electron acceptor A1, thought to be a phylloquinone molecule, has been proposed to undergo a double reduction at low redox potentials in the presence of viologen redox mediators. These results strongly suggest that the acceptor side electron transfer system in reaction centers from heliobacteria is indeed analogous to that found in Photosystem I. The sequence similarities indicate that the divergence of the heliobacteria from the Photosystem I line occurred before the gene duplication and subsequent divergence that lead to the heterodimeric protein core of the Photosystem I reaction center.

  15. Large space antenna communications systems: Integrated Langley Research Center/Jet Propulsion Laboratory development activities. 2: Langley Research Center activities

    NASA Technical Reports Server (NTRS)

    Cambell, T. G.; Bailey, M. C.; Cockrell, C. R.; Beck, F. B.

    1983-01-01

    The electromagnetic analysis activities at the Langley Research Center are resulting in efficient and accurate analytical methods for predicting both far- and near-field radiation characteristics of large offset multiple-beam multiple-aperture mesh reflector antennas. The utilization of aperture integration augmented with Geometrical Theory of Diffraction in analyzing the large reflector antenna system is emphasized.

  16. Residual Water Modulates QA−-to-QB Electron Transfer in Bacterial Reaction Centers Embedded in Trehalose Amorphous Matrices

    PubMed Central

    Francia, Francesco; Palazzo, Gerardo; Mallardi, Antonia; Cordone, Lorenzo; Venturoli, Giovanni

    2003-01-01

    The role of protein dynamics in the electron transfer from the reduced primary quinone, QA−, to the secondary quinone, QB, was studied at room temperature in isolated reaction centers (RC) from the photosynthetic bacterium Rhodobacter sphaeroides by incorporating the protein in trehalose water systems of different trehalose/water ratios. The effects of dehydration on the reaction kinetics were examined by analyzing charge recombination after different regimes of RC photoexcitation (single laser pulse, double flash, and continuous light) as well as by monitoring flash-induced electrochromic effects in the near infrared spectral region. Independent approaches show that dehydration of RC-containing matrices causes reversible, inhomogeneous inhibition of QA−-to-QB electron transfer, involving two subpopulations of RCs. In one of these populations (i.e., active), the electron transfer to QB is slowed but still successfully competing with P+QA− recombination, even in the driest samples; in the other (i.e., inactive), electron transfer to QB after a laser pulse is hindered, inasmuch as only recombination of the P+QA− state is observed. Small residual water variations (∼7 wt %) modulate fully the relative fraction of the two populations, with the active one decreasing to zero in the driest samples. Analysis of charge recombination after continuous illumination indicates that, in the inactive subpopulation, the conformational changes that rate-limit electron transfer can be slowed by >4 orders of magnitude. The reported effects are consistent with conformational gating of the reaction and demonstrate that the conformational dynamics controlling electron transfer to QB is strongly enslaved to the structure and dynamics of the surrounding medium. Comparing the effects of dehydration on P+QA−→PQA recombination and QA−QB→QAQB− electron transfer suggests that conformational changes gating the latter process are distinct from those stabilizing the primary

  17. Highly Stable and Active Catalyst for Sabatier Reactions

    NASA Technical Reports Server (NTRS)

    Hu, Jianli; Brooks, Kriston P.

    2012-01-01

    Highly active Ru/TiO2 catalysts for Sabatier reaction have been developed. The catalysts have shown to be stable under repeated shutting down/startup conditions. When the Ru/TiO2 catalyst is coated on the engineered substrate Fe-CrAlY felt, activity enhancement is more than doubled when compared with an identically prepared engineered catalyst made from commercial Degussa catalyst. Also, bimetallic Ru-Rh/TiO2 catalysts show high activity at high throughput.

  18. Photocurrent Generation by Photosynthetic Purple Bacterial Reaction Centers Interfaced with a Porous Antimony-Doped Tin Oxide (ATO) Electrode.

    PubMed

    Carey, Anne-Marie; Zhang, HaoJie; Mieritz, Daniel; Volosin, Alex; Gardiner, Alastair T; Cogdell, Richard J; Yan, Hao; Seo, Dong-Kyun; Lin, Su; Woodbury, Neal W

    2016-09-28

    The ability to exchange energy and information between biological and electronic materials is critical in the development of hybrid electronic systems in biomedicine, environmental sensing, and energy applications. While sensor technology has been extensively developed to collect detailed molecular information, less work has been done on systems that can specifically modulate the chemistry of the environment with temporal and spatial control. The bacterial photosynthetic reaction center represents an ideal photonic component of such a system in that it is capable of modifying local chemistry via light-driven redox reactions with quantitative control over reaction rates and has inherent spectroscopic probes for monitoring function. Here a well-characterized model system is presented, consisting of a transparent, porous electrode (antimony-doped tin oxide) which is electrochemically coupled to the reaction center via a cytochrome c molecule. Upon illumination, the reaction center performs the 2-step, 2-electron reduction of a ubiquinone derivative which exchanges with oxidized quinone in solution. Electrons from the electrode then move through the cytochrome to reoxidize the reaction center electron donor. The result is a facile platform for performing redox chemistry that can be optically and electronically controlled in time and space.

  19. Photocurrent Generation by Photosynthetic Purple Bacterial Reaction Centers Interfaced with a Porous Antimony-Doped Tin Oxide (ATO) Electrode.

    PubMed

    Carey, Anne-Marie; Zhang, HaoJie; Mieritz, Daniel; Volosin, Alex; Gardiner, Alastair T; Cogdell, Richard J; Yan, Hao; Seo, Dong-Kyun; Lin, Su; Woodbury, Neal W

    2016-09-28

    The ability to exchange energy and information between biological and electronic materials is critical in the development of hybrid electronic systems in biomedicine, environmental sensing, and energy applications. While sensor technology has been extensively developed to collect detailed molecular information, less work has been done on systems that can specifically modulate the chemistry of the environment with temporal and spatial control. The bacterial photosynthetic reaction center represents an ideal photonic component of such a system in that it is capable of modifying local chemistry via light-driven redox reactions with quantitative control over reaction rates and has inherent spectroscopic probes for monitoring function. Here a well-characterized model system is presented, consisting of a transparent, porous electrode (antimony-doped tin oxide) which is electrochemically coupled to the reaction center via a cytochrome c molecule. Upon illumination, the reaction center performs the 2-step, 2-electron reduction of a ubiquinone derivative which exchanges with oxidized quinone in solution. Electrons from the electrode then move through the cytochrome to reoxidize the reaction center electron donor. The result is a facile platform for performing redox chemistry that can be optically and electronically controlled in time and space. PMID:27576015

  20. Activity in the Mission Control Center during Apollo 14

    NASA Technical Reports Server (NTRS)

    1971-01-01

    Two individuals are examining a seismic reading in the Mission Control Center's Apollo Lunar Surface Experiment Package (ALSEP) Room during the Apollo 14 S-IVB impact on the moon. Dr. Maurice Ewing (left) is the Director of the Lamont-Doherty Geological Observatory at Columbia University. David Lammlein, a Columbia graduate student, is on the right (17609); Partial view of activity in the Mission Operations Control Room in the Mission Control Center at the time the Apollo 14 S-IVB stage impacted on the lunar surface. The flight director's console in in the foregroune. Eugene F. Kranz, Chief of the Manned Spacecraft Center (MSC) Flight Control Division, is in the right foreground. Seated at the console is Glynn S. Lunney, Head of the Flight Directors Office, Flight Control Division. Facing the camera is Gerald D. Griffin, Flight Director of the Third (Gold) team (17610).

  1. Climate Change Adaptation Science Activities at NASA Johnson Space Center

    NASA Technical Reports Server (NTRS)

    Stefanov, William L.; Lulla, Kamlesh

    2012-01-01

    The Johnson Space Center (JSC), located in the southeast metropolitan region of Houston, TX is the prime NASA center for human spaceflight operations and astronaut training, but it also houses the unique collection of returned extraterrestrial samples, including lunar samples from the Apollo missions. The Center's location adjacent to Clear Lake and the Clear Creek watershed, an estuary of Galveston Bay, puts it at direct annual risk from hurricanes, but also from a number of other climate-related hazards including drought, floods, sea level rise, heat waves, and high wind events all assigned Threat Levels of 2 or 3 in the most recent NASA Center Disaster/Risk Matrix produced by the Climate Adaptation Science Investigator Working Group. Based on prior CASI workshops at other NASA centers, it is recognized that JSC is highly vulnerable to climate-change related hazards and has a need for adaptation strategies. We will present an overview of prior CASI-related work at JSC, including publication of a climate change and adaptation informational data brochure, and a Resilience and Adaptation to Climate Risks Workshop that was held at JSC in early March 2012. Major outcomes of that workshop that form a basis for work going forward are 1) a realization that JSC is embedded in a regional environmental and social context, and that potential climate change effects and adaptation strategies will not, and should not, be constrained by the Center fence line; 2) a desire to coordinate data collection and adaptation planning activities with interested stakeholders to form a regional climate change adaptation center that could facilitate interaction with CASI; 3) recognition that there is a wide array of basic data (remotely sensed, in situ, GIS/mapping, and historical) available through JSC and other stakeholders, but this data is not yet centrally accessible for planning purposes.

  2. Vehicle Engineering Development Activities at the Marshall Space Flight Center

    NASA Technical Reports Server (NTRS)

    Fisher, Mark F.; Champion, Robert H., Jr.

    1999-01-01

    New initiatives in the Space Transportation Directorate at the Marshall Space Flight Center include an emphasis on Vehicle Engineering to enhance the strong commitment to the Directorate's projects in the development of flight hardware and flight demonstrators for the advancement of space transportation technology. This emphasis can be seen in the activities of a newly formed organization in the Transportation Directorate, The Vehicle Subsystems Engineering Group. The functions and type of activities that this group works on are described. The current projects of this group are outlined including a brief description of the status and type of work that the group is performing. A summary section is included to describe future activities.

  3. Double group transfer reactions: role of activation strain and aromaticity in reaction barriers.

    PubMed

    Fernández, Israel; Bickelhaupt, F Matthias; Cossío, Fernando P

    2009-12-01

    Double group transfer (DGT) reactions, such as the bimolecular automerization of ethane plus ethene, are known to have high reaction barriers despite the fact that their cyclic transition states have a pronounced in-plane aromatic character, as indicated by NMR spectroscopic parameters. To arrive at a way of understanding this somewhat paradoxical and incompletely understood phenomenon of high-energy aromatic transition states, we have explored six archetypal DGT reactions using density functional theory (DFT) at the OLYP/TZ2P level. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity. In this model, the shape of the reaction profile DeltaE(zeta) and the height of the overall reaction barrier DeltaE( not equal)=DeltaE(zeta=zeta(TS)) is interpreted in terms of the strain energy DeltaE(strain)(zeta) associated with deforming the reactants along the reaction coordinate zeta plus the interaction energy DeltaE(int)(zeta) between these deformed reactants: DeltaE(zeta)=DeltaE(strain)(zeta)+DeltaE(int)(zeta). We also use an alternative fragmentation and a valence bond model for analyzing the character of the transition states. PMID:19852009

  4. O2 activation by binuclear Cu sites: Noncoupled versus exchange coupled reaction mechanisms

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Solomon, Edward I.

    2004-09-01

    Binuclear Cu proteins play vital roles in O2 binding and activation in biology and can be classified into coupled and noncoupled binuclear sites based on the magnetic interaction between the two Cu centers. Coupled binuclear Cu proteins include hemocyanin, tyrosinase, and catechol oxidase. These proteins have two Cu centers strongly magnetically coupled through direct bridging ligands that provide a mechanism for the 2-electron reduction of O2 to a µ-2:2 side-on peroxide bridged species. This side-on bridged peroxo-CuII2 species is activated for electrophilic attack on the phenolic ring of substrates. Noncoupled binuclear Cu proteins include peptidylglycine -hydroxylating monooxygenase and dopamine -monooxygenase. These proteins have binuclear Cu active sites that are distant, that exhibit no exchange interaction, and that activate O2 at a single Cu center to generate a reactive CuII/O2 species for H-atom abstraction from the C-H bond of substrates. O2 intermediates in the coupled binuclear Cu enzymes can be trapped and studied spectroscopically. Possible intermediates in noncoupled binuclear Cu proteins can be defined through correlation to mononuclear CuII/O2 model complexes. The different intermediates in these two classes of binuclear Cu proteins exhibit different reactivities that correlate with their different electronic structures and exchange coupling interactions between the binuclear Cu centers. These studies provide insight into the role of exchange coupling between the Cu centers in their reaction mechanisms.

  5. Photosynthetic oxygen evolution in mesoporous silica material: adsorption of photosystem II reaction center complex into 23 nm nanopores in SBA.

    PubMed

    Noji, Tomoyasu; Kamidaki, Chihiro; Kawakami, Keisuke; Shen, Jian-Ren; Kajino, Tsutomu; Fukushima, Yoshiaki; Sekitoh, Takeshi; Itoh, Shigeru

    2011-01-18

    An oxygen-evolving photosynthetic reaction center complex (PSII) was adsorbed into nanopores in SBA, a mesoporous silica compound. We purified the dimer of PSII complex from a thermophilic cyanobacterium, Thermosynechococcus vulcanus, which grows optimally at 57 °C. The thermally stable PSII dimeric complex has a diameter of 20 nm and a molecular mass of 756 kDa and binds more than 60 chlorophylls. The SBA particles, with average internal pore diameters of 15 nm (SBA(15)) and 23 nm (SBA(23)), adsorbed 4.7 and 15 mg of PSII/g SBA, respectively. Measurement with a confocal laser-scanning microscope indicated the adsorption of PSII to the surface and the inner space of the SBA(23) particles, indicating the adsorption of PSII into the 23 nm silica nanopores. PSII did not bind to the inner pores of SBA(15). PSII bound to SBA(23) showed the high and stable activity of a photosynthetic oxygen-evolving reaction, indicating the light-driven electron transport from water to the quinone molecules added in the outer medium. The PSII-SBA conjugate can be a new material for photosensors and artificial photosynthetic systems.

  6. Corrosion Activities at the NASA Kennedy Space Center

    NASA Technical Reports Server (NTRS)

    Heidersbach, Robert H.

    2002-01-01

    This report documents summer faculty fellow efforts in the corrosion test bed at the NASA Kennedy Space Center. During the summer of 2002 efforts were concentrated on three activities: a short course on corrosion control for KSC personnel, evaluation of commercial wash additives used for corrosion control on Army aircraft, and improvements in the testing of a new cathodic protection system under development at KSC.

  7. [On the influence of local molecular environment on the redox potential of electron transfer cofactors in bacterial photosynthetic reaction centers].

    PubMed

    Krasil'nikov, P M; Noks, P P; Rubin, A B

    2011-01-01

    The addition of cryosolvents (glycerol, dimethylsulfoxide) to a water solution containing bacterial photosynthetic reaction centers changes the redox potential of the bacteriochlorophyll dimer, but does not affect the redox potential of the quinone primary acceptor. It has been shown that the change in redox potential can be produced by changes of the electrostatic interactions between cofactors and the local molecular environment modified by additives entered into the solution. The degree of influence of a solvent on the redox potential of various cofactors is determined by degree of availability of these cofactors for molecules of solvent, which depends on the arrangement of cofactors in the structure of reaction centers.

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

    SciTech Connect

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

    1994-10-27

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

  9. Solid state NMR studies of photoinduced polarization in photosynthetic reaction centers: mechanism and simulations.

    PubMed

    McDermott, A; Zysmilich, M G; Polenova, T

    1998-03-01

    We simulate Photo-Chemically Induced Dynamic Nuclear Polarization in the 15N-solid-state NMR of 15N-labeled photosynthetic reaction centers using a Radical Pair Mechanism (RPM). According to the experimental data, the directly polarized nuclei include all eight nitrogens in the ground state of the bacteriochlorophyll special pair (P), and N-II in the bacteriopheophytin acceptor (H) [M.G. Zysmilich, A.E. McDermott, J. Am. Chem. Soc., 116 (1994) 8362-8363.] [M.G. Zysmilich, A. McDermott, J. Am. Chem. Soc., 118 (1996) 5867-5873.] [M.G. Zysmilich, A. McDermott, Proc. Natl. Acad. Sci. U.S.A., 93 (1996) 6857-6860.]; other signals are polarized in nonspecifically labeled samples, but the polarization apparently results from magnetization exchange with neighboring polarized nitrogens, and these are not treated in this work. Two quantitative models for the polarization associated with the RPM are presented and are used to test the validity of the proposal that this mechanism is cooperative in the reaction centers. The kinetic models can treat the steady state polarizations as well as the approach to steady state, and in principle could be expanded to include anisotropic effects, or pulse-probe experiments. Several features of the detailed simulations of the steady-state amplitudes and the kinetics of the approach to steady-state are compared with our data, including the signs and approximate absolute magnitudes of the polarization on the nitrogen nuclei in P and H(L), and the changes in the relative amplitudes with the change in the lifetime of the molecular triplet, photoaccumulation time, nuclear relaxation rate and illumination intensity. The simulations demonstrate that the polarization intensities are in qualitative agreement with those predicted for the RPM, including the curious observation of strong polariza-tion on the pheophytin acceptor for certain experimental conditions. However, this agreement requires efficient relaxation of the nitrogens on H(L) by 3P, due

  10. Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Jianjun; Wang, Jianji; Stell, George

    2006-10-01

    The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact.

  11. NASA Stennis Space Center Test Technology Branch Activities

    NASA Technical Reports Server (NTRS)

    Solano, Wanda M.

    2000-01-01

    This paper provides a short history of NASA Stennis Space Center's Test Technology Laboratory and briefly describes the variety of engine test technology activities and developmental project initiatives. Theoretical rocket exhaust plume modeling, acoustic monitoring and analysis, hand held fire imaging, heat flux radiometry, thermal imaging and exhaust plume spectroscopy are all examples of current and past test activities that are briefly described. In addition, recent efforts and visions focused on accomodating second, third, and fourth generation flight vehicle engine test requirements are discussed.

  12. Light induced transmembrane proton gradient in artificial lipid vesicles reconstituted with photosynthetic reaction centers.

    PubMed

    Milano, Francesco; Trotta, Massimo; Dorogi, Márta; Fischer, Béla; Giotta, Livia; Agostiano, Angela; Maróti, Péter; Kálmán, László; Nagy, László

    2012-06-01

    Photosynthetic reaction center (RC) is the minimal nanoscopic photoconverter in the photosynthetic membrane that catalyzes the conversion of solar light to energy readily usable for the metabolism of the living organisms. After electronic excitation the energy of light is converted into chemical potential by the generation of a charge separated state accompanied by intraprotein and ultimately transmembrane proton movements. We designed a system which fulfills the minimum structural and functional requirements to investigate the physico/chemical conditions of the processes: RCs were reconstituted in closed lipid vesicles made of selected lipids entrapping a pH sensitive indicator, and electron donors (cytochrome c₂ and K₄[Fe(CN)₆]) and acceptors (decylubiquinone) were added to sustain the photocycle. Thanks to the low proton permeability of our preparations, we could show the formation of a transmembrane proton gradient under illumination and low buffering conditions directly by measuring proton-related signals simultaneously inside and outside the vesicles. The effect of selected ionophores such as gramicidin, nigericin and valinomycin was used to gain more information on the transmembrane proton gradient driven by the RC photochemistry.

  13. Redox potential tuning through differential quinone binding in the photosynthetic reaction center of Rhodobacter sphaeroides.

    PubMed

    Vermaas, Josh V; Taguchi, Alexander T; Dikanov, Sergei A; Wraight, Colin A; Tajkhorshid, Emad

    2015-03-31

    Ubiquinone forms an integral part of the electron transport chain in cellular respiration and photosynthesis across a vast number of organisms. Prior experimental results have shown that the photosynthetic reaction center (RC) from Rhodobacter sphaeroides is only fully functional with a limited set of methoxy-bearing quinones, suggesting that specific interactions with this substituent are required to drive electron transport and the formation of quinol. The nature of these interactions has yet to be determined. Through parameterization of a CHARMM-compatible quinone force field and subsequent molecular dynamics simulations of the quinone-bound RC, we have investigated and characterized the interactions of the protein with the quinones in the Q(A) and Q(B) sites using both equilibrium simulation and thermodynamic integration. In particular, we identify a specific interaction between the 2-methoxy group of ubiquinone in the Q(B) site and the amide nitrogen of GlyL225 that we implicate in locking the orientation of the 2-methoxy group, thereby tuning the redox potential difference between the quinones occupying the Q(A) and Q(B) sites. Disruption of this interaction leads to weaker binding in a ubiquinone analogue that lacks a 2-methoxy group, a finding supported by reverse electron transfer electron paramagnetic resonance experiments of the Q(A)⁻Q(B)⁻ biradical and competitive binding assays. PMID:25734689

  14. Femtosecond coherent transient infrared spectroscopy of reaction centers from Rhodobacter sphaeroides.

    PubMed Central

    Maiti, S; Walker, G C; Cowen, B R; Pippenger, R; Moser, C C; Dutton, P L; Hochstrasser, R M

    1994-01-01

    Protein and cofactor vibrational dynamics associated with photoexcitation and charge separation in the photosynthetic reaction center were investigated with femto-second (300-400 fs) time-resolved infrared (1560-1960 cm-1) spectroscopy. The experiments are in the coherent transient limit where the quantum uncertainty principle governs the evolution of the protein vibrational changes. No significant protein relaxation accompanies charge separation, although the electric field resulting from charge separation modifies the polypeptide carbonyl spectra. The potential energy surfaces of the "special pair" P and the photoexcited singlet state P* and environmental perturbations on them are similar as judged from coherence transfer measurements. The vibrational dephasing time of P* modes in this region is 600 fs. A subpicosecond transient at 1665 cm-1 was found to have the kinetics expected for a sequential electron transfer process. Kinetic signatures of all other transient intermediates, P, P*, and P+, participating in the primary steps of photosynthesis were identified in the difference infrared spectra. PMID:7937956

  15. Induced conformational changes upon Cd2+ binding at photosynthetic reaction centers

    PubMed Central

    Ishikita, Hiroshi; Knapp, Ernst-Walter

    2005-01-01

    Cd2+ binding at the bacterial photosynthetic reaction center (bRC) from Rhodobacter sphaeroides is known to inhibit proton transfer (PT) from bulk solvent to the secondary quinone QB. To elucidate this mechanism, we calculated the pKa for residues along the water channels connecting QB with the stromal side based on the crystal structures of WT-bRC and Cd2+-bound bRC. Upon Cd2+ binding, we observed the release of two protons from His-H126/128 at the Cd2+ binding site and significant pKa shifts for residues along the PT pathways. Remarkably, Asp-L213 near QB, which is proposed to play a significant role in PT, resulted in a decrease in pKa upon Cd2+ binding. The direct electrostatic influence of the Cd2+-positive charge on these pKa shifts was small. Instead, conformational changes of amino acid side chains induced electrostatically by Cd2+ binding were the main mechanism for these pKa shifts. The long-range electrostatic influence over ≈12 Å between Cd2+ and Asp-L213 is likely to originate from a set of Cd2+-induced successive reorientations of side chains (Asp-H124, His-H126, His-H128, Asp-H170, Glu-H173, Asp-M17, and Asp-L210), which propagate along the PT pathways as a “domino” effect. PMID:16254054

  16. The protein's role in triplet energy transfer in bacterial reaction centers.

    SciTech Connect

    Laible, P. D.

    1998-08-14

    When photosynthetic organisms are subjected to high-light conditions in nature, electron transfer becomes blocked as the rate of conversion of light into charge-separated states in the reaction center (RC) exceeds the capacity of the soluble carriers involved in cyclic electron transfer. In that event, a well-characterized T{sub 0}-polarized triplet state {sup T}P, is formed on the primary donor, P, from the P{sup +}H{sub A}{sup {minus}} state (reviewed in [1]). In an aerobic or semi-aerobic environment, the major role of the carotenoid (C), also bound by the RC, is to quench {sup T}P prior to its sensitization of the {sup 1}{Delta}{sub g} singlet state of oxygen--a potentially damaging biological oxidant. The carotenoid performs this function efficiently in most bacterial RCs by rapidly accepting the triplet state from P and dissipating this excited-state energy into heat through internal conversion. The lowest-lying triplet states of P and the carotenoid are sufficiently different that {sup T}P can promote oxygen to its excited singlet state whereas {sup T}C can quench the {sup T}P state (reviewed in [2]).

  17. Spectral, photophysical, and stability properties of isolated photosystem II reaction center

    SciTech Connect

    Seibert, M.; Picorel, R.; Rubin, A.B.; Connolly, J.S. )

    1988-06-01

    Photosystem II reaction center (RC) preparations isolated from spinach (Spinacea oleracea) by the Nanba-Satoh procedure are quite labile, even at 4{degree}C in the dark. Simple spectroscopic criteria were developed to characterize the native state of the material. Degradation of the RC results in (a) blue-shifting of the red-most absorption maximum, (b) a shift of the 77 K fluorescence maximum from {approximately}682 nm to {approximately}670 nm, and (c) a shift of fluorescence lifetime components from 1.3-4 nanoseconds and >25 nanoseconds to {approximately}6-7 nanoseconds. Fluorescence properties at 77 K seem to be a more sensitive spectral indicator of the integrity of the material. The >25 nanosecond lifetime component is assigned to P680{sup +} Phenophytin{sup -}recombination luminescence, which suggest a correlation between the observed spectral shifts and the photochemical competence of the preparation. Substitution of lauryl maltoside for Triton X-100 immediately after RC isolation stabilizes the RCs and suggests that Triton may be responsible for the instability.

  18. A protein dynamics study of photosystem II: the effects of protein conformation on reaction center function.

    PubMed

    Vasil'ev, Sergej; Bruce, Doug

    2006-05-01

    Molecular dynamics simulations have been performed to study photosystem II structure and function. Structural information obtained from simulations was combined with ab initio computations of chromophore excited states. In contrast to calculations based on the x-ray structure, the molecular-dynamics-based calculations accurately predicted the experimental absorbance spectrum. In addition, our calculations correctly assigned the energy levels of reaction-center (RC) chromophores, as well as the lowest-energy antenna chlorophyll. The primary and secondary quinone electron acceptors, Q(A) and Q(B), exhibited independent changes in position over the duration of the simulation. Q(B) fluctuated between two binding sites similar to the proximal and distal sites previously observed in light- and dark-adapted RC from purple bacteria. Kinetic models were used to characterize the relative influence of chromophore geometry, site energies, and electron transport rates on RC efficiency. The fluctuating energy levels of antenna chromophores had a larger impact on quantum yield than did their relative positions. Variations in electron transport rates had the most significant effect and were sufficient to explain the experimentally observed multi-component decay of excitation in photosystem II. The implications of our results are discussed in the context of competing evolutionary selection pressures for RC structure and function.

  19. Early Bacteriopheophytin Reduction in Charge Separation in Reaction Centers of Rhodobacter sphaeroides

    PubMed Central

    Zhu, Jingyi; van Stokkum, Ivo H.M.; Paparelli, Laura; Jones, Michael R.; Groot, Marie Louise

    2013-01-01

    A question at the forefront of biophysical sciences is, to what extent do quantum effects and protein conformational changes play a role in processes such as biological sensing and energy conversion? At the heart of photosynthetic energy transduction lie processes involving ultrafast energy and electron transfers among a small number of tetrapyrrole pigments embedded in the interior of a protein. In the purple bacterial reaction center (RC), a highly efficient ultrafast charge separation takes place between a pair of bacteriochlorophylls: an accessory bacteriochlorophyll (B) and bacteriopheophytin (H). In this work, we applied ultrafast spectroscopy in the visible and near-infrared spectral region to Rhodobacter sphaeroides RCs to accurately track the timing of the electron on BA and HA via the appearance of the BA and HA anion bands. We observed an unexpectedly early rise of the HA− band that challenges the accepted simple picture of stepwise electron transfer with 3 ps and 1 ps time constants. The implications for the mechanism of initial charge separation in bacterial RCs are discussed in terms of a possible adiabatic electron transfer step between BA and HA, and the effect of protein conformation on the electron transfer rate. PMID:23746522

  20. Structural and preliminary molecular dynamics studies of the Rhodobacter sphaeroides reaction center and its mutant form L(M196)H + H(M202)L

    NASA Astrophysics Data System (ADS)

    Klyashtorny, V. G.; Fufina, T. Yu.; Vasilieva, L. G.; Shuvalov, V. A.; Gabdulkhakov, A. G.

    2014-07-01

    Pigment-protein interactions are responsible for the high efficiency of the light-energy transfer and conversion in photosynthesis. The reaction center (RC) from the purple bacterium Rhodobacter sphaeroides is the most convenient model for studying the mechanisms of primary processes of photosynthesis. Site-directed mutagenesis can be used to study the effect of the protein environment of electron-transfer cofactors on the optical properties, stability, pigment composition, and functional activity of RC. The preliminary analysis of RC was performed by computer simulation of the amino acid substitutions L(M196)H + H(M202)L at the pigment-protein interface and by estimating the stability of the threedimensional structure of the mutant RC by the molecular dynamics method. The doubly mutated reaction center was overexpressed, purified, and crystallized. The three-dimensional structure of this mutant was determined by X-ray crystallography and compared with the molecular dynamics model.

  1. Fission Activities of the Nuclear Reactions Group in Uppsala

    NASA Astrophysics Data System (ADS)

    Al-Adili, A.; Alhassan, E.; Gustavsson, C.; Helgesson, P.; Jansson, K.; Koning, A.; Lantz, M.; Mattera, A.; Prokofiev, A. V.; Rakopoulos, V.; Sjöstrand, H.; Solders, A.; Tarrío, D.; Österlund, M.; Pomp, S.

    This paper highlights some of the main activities related to fission of the nuclear reactions group at Uppsala University. The group is involved for instance in fission yield experiments at the IGISOL facility, cross-section measurements at the NFS facility, as well as fission dynamics studies at the IRMM JRC-EC. Moreover, work is ongoing on the Total Monte Carlo (TMC) methodology and on including the GEF fission code into the TALYS nuclear reaction code. Selected results from these projects are discussed.

  2. Air oxidation of hydrazine. 1. Reaction kinetics on natural kaolinites, halloysites, and model substituent layers with varying iron and titanium oxide and O- center contents

    NASA Technical Reports Server (NTRS)

    Coyne, L.; Mariner, R.; Rice, A.

    1991-01-01

    Air oxidation of hydrazine was studied by using a group of kaolinites, halloysites, and substituent oxides as models for the tetrahedral and octahedral sheets. The rate was found to be linear with oxygen. The stoichiometry showed that oxygen was the primary oxidant and that dinitrogen was the only important nitrogen-containing product. The rates on kaolinites were strongly inhibited by water. Those on three-dimensional silica and gibbsite appeared not to be. That on a supposedly layered silica formed from a natural kaolinite by acid leaching showed transitional behavior--slowed relative to that expected from a second-order reaction relative to that on the gibbsite and silica but faster than those on the kaolinites. The most striking result of the reaction was the marked increase in the rate of reaction of a constant amount of hydrazine as the amount of clay was increased. The increase was apparent (in spite of the water inhibition at high conversions) over a 2 order of magnitude variation of the clay weight. The weight dependence was taken to indicate that the role of the clay is very important, that the number of reactive centers is very small, or that they may be deactivated over the course of the reaction. In contrast to the strong dependence on overall amount of clay, the variation of amounts of putative oxidizing centers, such as structural Fe(III), admixed TiO2 or Fe2O3, or O- centers, did not result in alteration of the rate commensurate with the degree of variation of the entity in question. Surface iron does play some role, however, as samples that were pretreated with a reducing agent were less active as catalysts than the parent material. These results were taken to indicate either that the various centers interact to such a degree that they cannot be considered independently or that the reaction might proceed by way of surface complexation, rather than single electron transfers.

  3. Caffeine enhances micturition through neuronal activation in micturition centers.

    PubMed

    Cho, Young-Sam; Ko, Il-Gyu; Kim, Sung-Eun; Hwan, Lakkyong; Shin, Mal-Soon; Kim, Chang-Ju; Kim, Sang-Hoon; Jin, Jun-Jang; Chung, Jun-Young; Kim, Khae-Hawn

    2014-12-01

    Caffeine may promote incontinence through its diuretic effect, particularly in individuals with underlying detrusor overactivity, in addition to increasing muscle contraction of the bladder smooth muscle. Caffeine may also affect bladder function via central micturition centers, including the medial preoptic area, ventrolateral periaqueductal gray, and pontine micturition center. However, the biochemical mechanisms of caffeine in central micturition centers affecting bladder function remain unclear. In the present study, the effects of caffeine on the central micturition reflex were investigated by measuring the degree of neuronal activation, and by quantifying nerve growth factor (NGF) expression in rats. Following caffeine administration for 14 days, a urodynamic study was performed to assess the changes to bladder function. Subsequently, immunohistochemical staining to identify the expression of c‑Fos and NGF in the central micturition areas was performed. Ingestion of caffeine increased bladder smooth muscle contraction pressure and time as determined by cystometry. Expression levels of c‑Fos and NGF in all central micturition areas were significantly increased following the administration of caffeine. The effects on contraction pressure and time were the most potent and expression levels of c‑Fos and NGF were greatest at the lowest dose of caffeine. These results suggest that caffeine facilitates bladder instability through enhancing neuronal activation in the central micturition areas.

  4. Land processes distributed active archive center product lifecycle plan

    USGS Publications Warehouse

    Daucsavage, John C.; Bennett, Stacie D.

    2014-01-01

    The U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center and the National Aeronautics and Space Administration (NASA) Earth Science Data System Program worked together to establish, develop, and operate the Land Processes (LP) Distributed Active Archive Center (DAAC) to provide stewardship for NASA’s land processes science data. These data are critical science assets that serve the land processes science community with potential value beyond any immediate research use, and therefore need to be accounted for and properly managed throughout their lifecycle. A fundamental LP DAAC objective is to enable permanent preservation of these data and information products. The LP DAAC accomplishes this by bridging data producers and permanent archival resources while providing intermediate archive services for data and information products.

  5. Data Information for Global Change Studies: NASA's Distributed Active Archive Centers and Cooperating Data Centers

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The Earth Observing System (EOS) is an integral part of the National Aeronautics and Space Administration's (NASA's) Earth Science Enterprise (ESE). ESE is a long-term global change research program designed to improve our understanding of the Earth's interrelated processes involving the atmosphere, oceans, land surfaces, and polar regions. Data from EOS instruments and other Earth science measurement systems are useful in understanding the causes and processes of global climate change and the consequences of human activities. The EOS Data and Information System (EOSDIS) provides a structure for data management and user services for products derived from EOS satellite instruments and other NASA Earth science data. Within the EOSDIS framework, the Distributed Active Archive Centers (DAACs) have been established to provide expertise in one or more Earth science disciplines. The DAACs and cooperating data centers provide data and information services to support the global change research community. Much of the development of the DAACs has been in anticipation of the enormous amount of data expected from EOS instruments to be launched within the next two decades. Terra, the EOS flagship launched in December 1999, is the first of a series of EOS satellites to carry several instruments with multispectral capabilities. Some data products from these instruments are now available from several of the DAACs. These and other data products can be ordered through the EOS Data Gateway (EDG) and DAAC-specific online ordering systems.

  6. Quantitative determination of activation energies in mechanochemical reactions.

    PubMed

    Fischer, Franziska; Wenzel, Klaus-Jürgen; Rademann, Klaus; Emmerling, Franziska

    2016-08-17

    Mechanochemical reactions often result in 100% yields of single products, making purifying procedures obsolete. Mechanochemistry is also a sustainable and eco-friendly method. The ever increasing interest in this method is contrasted by a lack in mechanistic understanding of the mechanochemical reactivity and selectivity. Recent in situ investigations provided direct insight into formation pathways. However, the currently available theories do not predict temperature T as an influential factor. Here, we report the first determination of an apparent activation energy for a mechanochemical reaction. In a temperature-dependent in situ study the cocrystallisation of ibuprofen and nicotinamide was investigated as a model system. These experiments provide a pivotal step towards a comprehensive understanding of milling reaction mechanisms.

  7. A new mathematical solution for predicting char activation reactions

    USGS Publications Warehouse

    Rafsanjani, H.H.; Jamshidi, E.; Rostam-Abadi, M.

    2002-01-01

    The differential conservation equations that describe typical gas-solid reactions, such as activation of coal chars, yield a set of coupled second-order partial differential equations. The solution of these coupled equations by exact analytical methods is impossible. In addition, an approximate or exact solution only provides predictions for either reaction- or diffusion-controlling cases. A new mathematical solution, the quantize method (QM), was applied to predict the gasification rates of coal char when both chemical reaction and diffusion through the porous char are present. Carbon conversion rates predicted by the QM were in closer agreement with the experimental data than those predicted by the random pore model and the simple particle model. ?? 2002 Elsevier Science Ltd. All rights reserved.

  8. GHRC: NASAs Hazardous Weather Distributed Active Archive Center

    NASA Technical Reports Server (NTRS)

    Ramachandran, Rahul; Bugbee, Kaylin

    2016-01-01

    The Global Hydrology Resource Center (GHRC; ghrc.nsstc.nasa.gov) is one of NASA's twelve Distributed Active Archive Centers responsible for providing access to NASA's Earth science data to users worldwide. Each of NASA's twelve DAACs focuses on a specific science discipline within Earth science, provides data stewardship services and supports its research community's needs. Established in 1991 as the Marshall Space Flight Center DAAC and renamed GHRC in 1997, the data center's original mission focused on the global hydrologic cycle. However, over the years, data holdings, tools and expertise of GHRC have gradually shifted. In 2014, a User Working Group (UWG) was established to review GHRC capabilities and provide recommendations to make GHRC more responsive to the research community's evolving needs. The UWG recommended an update to the GHRC mission, as well as a strategic plan to move in the new direction. After a careful and detailed analysis of GHRC's capabilities, research community needs and the existing data landscape, a new mission statement for GHRC has been crafted: to provide a comprehensive active archive of both data and knowledge augmentation services with a focus on hazardous weather, its governing dynamical and physical processes, and associated applications. Within this broad mandate, GHRC will focus on lightning, tropical cyclones and storm-induced hazards through integrated collections of satellite, airborne, and in-situ data sets. The new mission was adopted at the recent 2015 UWG meeting. GHRC will retain its current name until such time as it has built substantial data holdings aligned with the new mission.

  9. 75 FR 49946 - National Drug Intelligence Center: Agency Information Collection Activities: Proposed Extension...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-16

    ... National Drug Intelligence Center: Agency Information Collection Activities: Proposed Extension With Change... Response System. The United States Department of Justice (DOJ), National Drug Intelligence Center (NDIC... Intelligence Center, Fifth Floor, 319 Washington Street, Johnstown, PA 15901. Written comments and...

  10. [Activities of Center for Nondestructive Evaluation, Iowa State University

    NASA Technical Reports Server (NTRS)

    Gray, Joe

    2002-01-01

    The final report of NASA funded activities at Iowa State University (ISU) for the period between 1/96 and 1/99 includes two main areas of activity. The first is the development and delivery of an x-ray simulation package suitable for evaluating the impact of parameters affects the inspectability of an assembly of parts. The second area was the development of images processing tools to remove reconstruction artifacts in x-ray laminagraphy images. The x-ray simulation portion of this work was done by J. Gray and the x-ray laminagraphy work was done by J. Basart. The report is divided into two sections covering the two activities respectively. In addition to this work reported the funding also covered NASA's membership in the NSF University/Industrial Cooperative Research Center.

  11. CHP REGIONAL APPLICATION CENTERS: ACTIVITIES AND SELECTED RESULTS

    SciTech Connect

    Schweitzer, Martin

    2010-08-01

    Between 2001 and 2005, the U.S. Department of Energy (DOE) created a set of eight Regional Application Centers (RACs) to facilitate the development and deployment of Combined Heat and Power (CHP) technologies. By utilizing the thermal energy that is normally wasted when electricity is produced at central generating stations, Combined Heat and Power installations can save substantial amounts of energy compared to more traditional technologies. In addition, the location of CHP facilities at or near the point of consumption greatly reduces or eliminates electric transmission and distribution losses. The regional nature of the RACs allows each one to design and provide services that are most relevant to the specific economic and market conditions in its particular geographic area. Between them, the eight RACs provide services to all 50 states and the District of Columbia. Through the end of the federal 2009 fiscal year (FY 2009), the primary focus of the RACs was on providing CHP-related information to targeted markets, encouraging the creation and adoption of public policies and incentives favorable to CHP, and providing CHP users and prospective users with technical assistance and support on specific projects. Beginning with the 2010 fiscal year, the focus of the regional centers broadened to include district energy and waste heat recovery and these entities became formally known as Clean Energy Application Centers, as required by the Energy Independence and Security Act (EISA) of 2007. In 2007, ORNL led a cooperative effort to establish metrics to quantify the RACs accomplishments. That effort began with the development of a detailed logic model describing RAC operations and outcomes, which provided a basis for identifying important activities and accomplishments to track. A data collection spreadsheet soliciting information on those activities for FY 2008 and all previous years of RAC operations was developed and sent to the RACs in the summer of 2008. This

  12. Antituberculosis activity of the molecular libraries screening center network library.

    PubMed

    Maddry, Joseph A; Ananthan, Subramaniam; Goldman, Robert C; Hobrath, Judith V; Kwong, Cecil D; Maddox, Clinton; Rasmussen, Lynn; Reynolds, Robert C; Secrist, John A; Sosa, Melinda I; White, E Lucile; Zhang, Wei

    2009-09-01

    There is an urgent need for the discovery and development of new antitubercular agents that target novel biochemical pathways and treat drug-resistant forms of the disease. One approach to addressing this need is through high-throughput screening of drug-like small molecule libraries against the whole bacterium in order to identify a variety of new, active scaffolds that will stimulate additional biological research and drug discovery. Through the Molecular Libraries Screening Center Network, the NIAID Tuberculosis Antimicrobial Acquisition and Coordinating Facility tested a 215,110-compound library against Mycobacterium tuberculosis strain H37Rv. A medicinal chemistry survey of the results from the screening campaign is reported herein.

  13. [Research activities in Kobe-Indonesia Collaborative Research Centers].

    PubMed

    Utsumi, Takako; Hayashi, Yoshitake; Hotta, Hak

    2013-01-01

    Kobe-Indonesia Collaborative Research Center was established in Institute of Tropical Disease (ITD), Airlangga University, Surabaya, Indonesia in 2007 under the program of ''Founding Research Centers for Emerging and Reemerging Infectious Diseases'' supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan, and then it has been under the Japan Initiative for Global Research Network on Infectious Diseases (J-GRID) since 2010. Japanese researchers have been stationed at ITD, conducting joint researches on influenza, viral hepatitis, dengue and infectious diarrhea. Also, another Japanese researcher has been stationed at Faculty of Medicine, University of Indonesia, Jakarta, carrying out joint researches on'' Identification of anti-hepatitis C virus (HCV) substances and development of HCV and dengue vaccines'' in collaboration with University of Indonesia and Airlangga University through the Science and Technology Research Partnership for Sustainable Development (SATREPS) supported by the Japan Science and Technology Agency (JST) and Japan International Cooperation Agency (JICA) since 2009. In this article, we briefly introduce the background history of Kobe University Research Center in Indonesia, and discuss the research themes and outcomes of J-GRID and SATREPS activities.

  14. Editors and author resource centers actively used by attendees

    NASA Astrophysics Data System (ADS)

    Major, Barbara

    2012-02-01

    At the 2011 Fall Meeting, as in previous years, the Editors Resource Center located on the second floor of Moscone West was buzzing with activity: editors talking with other editors, collaborating with associate editors, speaking with authors, and meeting with students. In addition, several editors took part in "Meet the Editor" informal sessions, a new feature introduced for the 2011 meeting to strengthen the partnership between authors and editors. The map "Where are you from?" (see photo), outside the Editors Resource Center, drew the attention of many attendees who were eager to place their colored dots on the map. The Author Resource Center, located in the AGU Marketplace, became a hub for AGU veteran authors and potential authors alike. Staff were there to answer both editorial and technical questions, especially the most frequent one: What happens after my paper is accepted? The running slideshow that described all aspects of the AGU publications program sparked a myriad of questions, which AGU staff were happy to answer.

  15. Architecture and evolution of Goddard Space Flight Center Distributed Active Archive Center

    NASA Technical Reports Server (NTRS)

    Bedet, Jean-Jacques; Bodden, Lee; Rosen, Wayne; Sherman, Mark; Pease, Phil

    1994-01-01

    The Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC) has been developed to enhance Earth Science research by improved access to remote sensor earth science data. Building and operating an archive, even one of a moderate size (a few Terabytes), is a challenging task. One of the critical components of this system is Unitree, the Hierarchical File Storage Management System. Unitree, selected two years ago as the best available solution, requires constant system administrative support. It is not always suitable as an archive and distribution data center, and has moderate performance. The Data Archive and Distribution System (DADS) software developed to monitor, manage, and automate the ingestion, archive, and distribution functions turned out to be more challenging than anticipated. Having the software and tools is not sufficient to succeed. Human interaction within the system must be fully understood to improve efficiency to improve efficiency and ensure that the right tools are developed. One of the lessons learned is that the operability, reliability, and performance aspects should be thoroughly addressed in the initial design. However, the GSFC DAAC has demonstrated that it is capable of distributing over 40 GB per day. A backup system to archive a second copy of all data ingested is under development. This backup system will be used not only for disaster recovery but will also replace the main archive when it is unavailable during maintenance or hardware replacement. The GSFC DAAC has put a strong emphasis on quality at all level of its organization. A Quality team has also been formed to identify quality issues and to propose improvements. The DAAC has conducted numerous tests to benchmark the performance of the system. These tests proved to be extremely useful in identifying bottlenecks and deficiencies in operational procedures.

  16. Charge separation, stabilization, and protein relaxation in photosystem II core particles with closed reaction center.

    PubMed

    Szczepaniak, M; Sander, J; Nowaczyk, M; Müller, M G; Rögner, M; Holzwarth, A R

    2009-01-01

    The fluorescence kinetics of cyanobacterial photosystem II (PSII) core particles with closed reaction centers (RCs) were studied with picosecond resolution. The data are modeled in terms of electron transfer (ET) and associated protein conformational relaxation processes, resolving four different radical pair (RP) states. The target analyses reveal the importance of protein relaxation steps in the ET chain for the functioning of PSII. We also tested previously published data on cyanobacterial PSII with open RCs using models that involved protein relaxation steps as suggested by our data on closed RCs. The rationale for this reanalysis is that at least one short-lived component could not be described in the previous simpler models. This new analysis supports the involvement of a protein relaxation step for open RCs as well. In this model the rate of ET from reduced pheophytin to the primary quinone Q(A) is determined to be 4.1 ns(-1). The rate of initial charge separation is slowed down substantially from approximately 170 ns(-1) in PSII with open RCs to 56 ns(-1) upon reduction of Q(A). However, the free-energy drop of the first RP is not changed substantially between the two RC redox states. The currently assumed mechanistic model, assuming the same early RP intermediates in both states of RC, is inconsistent with the presented energetics of the RPs. Additionally, a comparison between PSII with closed RCs in isolated cores and in intact cells reveals slightly different relaxation kinetics, with a approximately 3.7 ns component present only in isolated cores.

  17. Calculated coupling of electron and proton transfer in the photosynthetic reaction center of Rhodopseudomonas viridis.

    PubMed Central

    Lancaster, C R; Michel, H; Honig, B; Gunner, M R

    1996-01-01

    Based on new Rhodopseudomonas (Rp.) viridis reaction center (RC) coordinates with a reliable structure of the secondary acceptor quinone (QB) site, a continuum dielectric model and finite difference technique have been used to identify clusters of electrostatically interacting ionizable residues. Twenty-three residues within a distance of 25 A from QB (QB cluster) have been shown to be strongly electrostatically coupled to QB, either directly or indirectly. An analogous cluster of 24 residues is found to interact with QA (QA cluster). Both clusters extend to the cytoplasmic surface in at least two directions. However, the QB cluster differs from the QA cluster in that it has a surplus of acidic residues, more strong electrostatic interactions, is less solvated, and experiences a strong positive electrostatic field arising from the polypeptide backbone. Consequently, upon reduction of QA or QB, it is the QB cluster, and not the QA cluster, which is responsible for substoichiometric proton uptake at neutral pH. The bulk of the changes in the QB cluster are calculated to be due to the protonation of a tightly coupled cluster of the three Glu residues (L212, H177, and M234) within the QB cluster. If the lifetime of the doubly reduced state QB2- is long enough, Asp M43 and Ser L223 are predicted to also become protonated. The calculated complex titration behavior of the strongly interacting residues of the QB cluster and the resulting electrostatic response to electron transfer may be a common feature in proton-transferring membrane protein complexes. Images FIGURE 2 p2482-a FIGURE 6 FIGURE 8 FIGURE 10 PMID:8744288

  18. Optimizing multi-step B-side charge separation in photosynthetic reaction centers from Rhodobacter capsulatus.

    PubMed

    Faries, Kaitlyn M; Kressel, Lucas L; Dylla, Nicholas P; Wander, Marc J; Hanson, Deborah K; Holten, Dewey; Laible, Philip D; Kirmaier, Christine

    2016-02-01

    Using high-throughput methods for mutagenesis, protein isolation and charge-separation functionality, we have assayed 40 Rhodobacter capsulatus reaction center (RC) mutants for their P(+)QB(-) yield (P is a dimer of bacteriochlorophylls and Q is a ubiquinone) as produced using the normally inactive B-side cofactors BB and HB (where B is a bacteriochlorophyll and H is a bacteriopheophytin). Two sets of mutants explore all possible residues at M131 (M polypeptide, native residue Val near HB) in tandem with either a fixed His or a fixed Asn at L181 (L polypeptide, native residue Phe near BB). A third set of mutants explores all possible residues at L181 with a fixed Glu at M131 that can form a hydrogen bond to HB. For each set of mutants, the results of a rapid millisecond screening assay that probes the yield of P(+)QB(-) are compared among that set and to the other mutants reported here or previously. For a subset of eight mutants, the rate constants and yields of the individual B-side electron transfer processes are determined via transient absorption measurements spanning 100 fs to 50 μs. The resulting ranking of mutants for their yield of P(+)QB(-) from ultrafast experiments is in good agreement with that obtained from the millisecond screening assay, further validating the efficient, high-throughput screen for B-side transmembrane charge separation. Results from mutants that individually show progress toward optimization of P(+)HB(-)→P(+)QB(-) electron transfer or initial P*→P(+)HB(-) conversion highlight unmet challenges of optimizing both processes simultaneously. PMID:26658355

  19. The electronic behavior of a photosynthetic reaction center monitored by conductive atomic force microscopy.

    PubMed

    Mikayama, Takeshi; Iida, Kouji; Suemori, Yoshiharu; Dewa, Takehisa; Miyashita, Tokuji; Nango, Mamoru; Gardiner, Alastair T; Cogdell, Richard J

    2009-01-01

    The conductivity of a photosynthetic reaction center (RC) from Rhodobacter sphaeroides was measured with conductive atomic force microscopy (CAFM) on SAM-modified Au(111) substrates. 2-mercaptoethanol (2ME), 2-mercaptoacetic acid (MAC), 2-mercaptopyridine (2MP) and 4-mercaptopyridine (4MP) were prepared as SAM materials to investigate the stability and morphology of RCs on the substrate by using near-IR absorption spectroscopy and AFM, respectively. The clear presence of the three well known RC near-IR absorption peaks indicates that the RCs were native on the SAM-modified Au(111). Dense grains with various diameters of 5-20 nm, which corresponded to mixtures of single RCs up to aggregates of 10, were observed in topographs of RCs adsorbed on all the different SAM-modified Au(111) substrates. The size of currents obtained from the RC using a bare conductive cantilever were produced in the following order for SAM molecules: 2MP > 2ME > 4MP > MAC. A clear rectification of this current was observed for the modification of the Au(111) substrate with the pi-conjugated thiol, 2MP, indicating that 2MP was effective in both promoting the specific orientation of the RCs on the electrode and electron injection into the RC. Cyclic voltammetry measurements indicate that the 2MP is better mediator for the electron transfer between a quinone and substrate. The current with 2MP-modified cantilever was twice as high as that obtained with the Au-coated one alone, indicating that 2MP has an important role in lowering the electron injection barrier between special pair side of RC and gold electrode.

  20. Structural and spectropotentiometric analysis of Blastochloris viridis heterodimer mutant reaction center

    SciTech Connect

    Ponomarenko, Nina S.; Li, Liang; Marino, Antony R.; Tereshko, Valentina; Ostafin, Agnes; Popova, Julia A.; Bylina, Edward J.; Ismagilov, Rustem F.; Norris, Jr., James R.

    2010-07-22

    Heterodimer mutant reaction centers (RCs) of Blastochloris viridis were crystallized using microfluidic technology. In this mutant, a leucine residue replaced the histidine residue which had acted as a fifth ligand to the bacteriochlorophyll (BChl) of the primary electron donor dimer M site (HisM200). With the loss of the histidine-coordinated Mg, one bacteriochlorophyll of the special pair was converted into a bacteriopheophytin (BPhe), and the primary donor became a heterodimer supermolecule. The crystals had dimensions 400 x 100 x 100 {micro}m, belonged to space group P4{sub 3}2{sub 1}2, and were isomorphous to the ones reported earlier for the wild type (WT) strain. The structure was solved to a 2.5 {angstrom} resolution limit. Electron-density maps confirmed the replacement of the histidine residue and the absence of Mg. Structural changes in the heterodimer mutant RC relative to the WT included the absence of the water molecule that is typically positioned between the M side of the primary donor and the accessory BChl, a slight shift in the position of amino acids surrounding the site of the mutation, and the rotation of the M194 phenylalanine. The cytochrome subunit was anchored similarly as in the WT and had no detectable changes in its overall position. The highly conserved tyrosine L162, located between the primary donor and the highest potential heme C{sub 380}, revealed only a minor deviation of its hydroxyl group. Concomitantly to modification of the BChl molecule, the redox potential of the heterodimer primary donor increased relative to that of the WT organism (772 mV vs. 517 mV). The availability of this heterodimer mutant and its crystal structure provides opportunities for investigating changes in light-induced electron transfer that reflect differences in redox cascades.

  1. Spectral properties of chlorines and electron transfer with their participation in the photosynthetic reaction center of photosystem II

    NASA Astrophysics Data System (ADS)

    Shchupak, E. E.; Ivashin, N. V.

    2014-02-01

    Structural factors that provide localization of excited states and determine the properties of primary donor and acceptor of electron in the reaction center of photosystem II (PSII RC) are studied. The results of calculations using stationary and time-dependent density functional theory indicate an important role of protein environments of chlorophylls PA, PB, BA, and BB and pheophytins HA and HB in the area with a radius of no greater than ≤10 Å in the formation of excitonic states of PSII RC. When the neighboring elements are taken into account, the wavelength of long-wavelength Q y transition of chlorophyll molecules is varied by about 10 nm. The effect is less developed for pheophytin molecules (Δλ ≅ 2 nm). The following elements strongly affect energy of the transition: HisA198 and HisD197 amino-acid residues that serve as ligands of magnesium atoms affect PA and PB, respectively; MetA183 affects PA; MetA172 and MetD198 affect BA; water molecules that are located above the planes of the BA and BB macrocycles form H bonds with carbonyl groups; and phytol chains of PA and PB affect BA, BB, HA, and HB. The analysis of excitonic states, mutual positions of molecular orbitals of electron donors and acceptors, and matrix elements of electron transfer reaction shows that (i) charge separation between BA and HA and PB and BA is possible in the active A branch of cofactors of PSII RC and (ii) electron transfer is blocked at the BB - HB fragment in inactive B branch of PSII RC.

  2. Space weather activities at NOAA s Space Environment Center

    NASA Astrophysics Data System (ADS)

    Kunches, J.

    The NOAA Space Environment Center is the focal point for real-time space weather monitoring and prediction in the United States . The Space Weather Operations (SWO) division staffs a 24-hour/day operations center, through which both in-situ and remotely sensed data and imagery flow. These diverse data streams are analyzed continuously, and that information is applied to both predictions and specifications of various aspects of the space environment. These include the behavior of the geomagnetic field, the character of the ionosphere, and the strength of the near-earth radiation environment. Models are brought to bear in each of thes e areas, as SEC has an active research-to-operations transition effort. The Rapid Prototyping Center is the venue through which pertinent models and data must pass to be brought into the operational arena. The model outputs are then made available both internally and externally. SEC is a member of the International Space Environment Service (ISES), a partnership currently consisting of eleven nations. The mission of the ISES is to encourage and facilitate near-real-time international monitoring and prediction of the space environment by: the rapid exchange of space environment information; the standardization of the methodology for space environment observations and data reduction; the uniform publication of observations and statistics; and the application of standardized space environment products and services to assist users in reducing the impact of space weather on activities of human interest. An overview of the operational attributes of the SEC, and the function of the ISES, will be presented. Additional issues related to space weather customers, new data streams to be available in the near-term, and how these new data and imagery will be integrated int o operations will be discussed.

  3. The Land Processes Distributed Active Archive Center (LP DAAC)

    USGS Publications Warehouse

    Golon, Danielle K.

    2016-10-03

    The Land Processes Distributed Active Archive Center (LP DAAC) operates as a partnership with the U.S. Geological Survey and is 1 of 12 DAACs within the National Aeronautics and Space Administration (NASA) Earth Observing System Data and Information System (EOSDIS). The LP DAAC ingests, archives, processes, and distributes NASA Earth science remote sensing data. These data are provided to the public at no charge. Data distributed by the LP DAAC provide information about Earth’s surface from daily to yearly intervals and at 15 to 5,600 meter spatial resolution. Data provided by the LP DAAC can be used to study changes in agriculture, vegetation, ecosystems, elevation, and much more. The LP DAAC provides several ways to access, process, and interact with these data. In addition, the LP DAAC is actively archiving new datasets to provide users with a variety of data to study the Earth.

  4. Nanotube Activities at NASA-Johnson Space Center

    NASA Technical Reports Server (NTRS)

    Arepalli, Sivaram

    2004-01-01

    Nanotube activities at NASA-Johnson Space Center include production, purification, characterization as well as applications of single wall carbon nanotubes (SWCNTs). A parametric study of the pulsed laser ablation process is recently completed to monitor the effect of production parameters including temperature, buffer gas, flow rate, pressure, and laser fluence. Enhancement of production is achieved by rastering the graphite target and by increasing the target surface temperature with a cw laser. In-situ diagnostics during production included time resolved passive emission and laser induced fluorescence from the plume. The improvement of the purity by a variety of steps in the purification process is monitored by characterization techniques including SEM, TEM, Raman, UV-VIS-NIR and TGA. A recently established NASA-JSC protocol for SWCNT characterization is undergoing revision with feedback from nanotube community. Efforts at JSC over the past five years in composites have centered on structural polymer/nanotube systems. Recent activities broadened this focus to multifunctional materials, supercapacitors, fuel cells, regenerable CO2 absorbers, electromagnetic shielding, radiation dosimetry and thermal management systems of interest for human space flight. Preliminary tests indicate improvement of performance in most of these applications because of the large Surface area as well as high electrical and thermal conductivity exhibited by SWCNTs. Comparison with existing technologies and possible future improvements in the SWCNT materials sill be presented.

  5. Carbon Nanotube Activities at NASA-Johnson Space Center

    NASA Technical Reports Server (NTRS)

    Arepalli, Sivaram

    2006-01-01

    Research activities on carbon nanotubes at NASA-Johnson Space Center include production, purification, characterization and their applications for human space flight. In-situ diagnostics during nanotube production by laser oven process include collection of spatial and temporal data of passive emission and laser induced fluorescence from C2, C3 and Nickel atoms in the plume. Details of the results from the "parametric study" of the pulsed laser ablation process indicate the effect of production parameters including temperature, buffer gas, flow rate, pressure, and laser fluence. Improvement of the purity by a variety of steps in the purification process is monitored by characterization techniques including SEM, TEM, Raman, UV-VIS-NIR and TGA. A recently established NASA-JSC protocol for SWCNT characterization is undergoing revision with feedback from nanotube community. Efforts at JSC over the past five years in composites have centered on structural polymednanotube systems. Recent activities broadened this focus to multifunctional materials, supercapacitors, fuel cells, regenerable CO2 absorbers, electromagnetic shielding, radiation dosimetry and thermal management systems of interest for human space flight. Preliminary tests indicate improvement of performance in most of these applications because of the large surface area as well as high electrical and thermal conductivity exhibited by SWCNTs.

  6. Selective molecular recognition, C-H bond activation, and catalysis in nanoscale reaction vessels

    SciTech Connect

    Fiedler, Dorothea; Leung, Dennis H.; Raymond, Kenneth N.; Bergman, Robert G.

    2004-11-27

    Supramolecular chemistry represents a way to mimic enzyme reactivity by using specially designed container molecules. We have shown that a chiral self-assembled M{sub 4}L{sub 6} supramolecular tetrahedron can encapsulate a variety of cationic guests, with varying degrees of stereoselectivity. Reactive iridium guests can be encapsulated and the C-H bond activation of aldehydes occurs, with the host cavity controlling the ability of substrates to interact with the metal center based upon size and shape. In addition, the host container can act as a catalyst by itself. By restricting reaction space and preorganizing the substrates into reactive conformations, it accelerates the sigmatropic rearrangement of enammonium cations.

  7. Activity of formylphosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Jahansouz, H.; Kofron, J.L.; Smithers, G.W.; Himes, R.H.; Reed, G.H.

    1986-05-01

    Formylphosphate (FP), a putative enzyme-bound intermediate in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase, was synthesized from formylfluoride and Pi. Measurement of hydrolysis rates by /sup 31/P NMR showed that FP is very unstable with a half-life of 48 min at 20/sup 0/C and pH 7. At pH 7 hydrolysis occurs with O-P bond cleavage as shown by /sup 18/O incorporation from /sup 18/O-H/sub 2/O into Pi. The substrate activity of FP was tested in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase isolated from Clostridium cylindrosporum. MgATP + H/sub 4/folate + HCOO/sup -/ in equilibrium MgADP + Pi +N/sup 10/-formylH/sub 4/folate FP supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formylH/sub 4/folate is produced from H/sub 4/-folate and FP but only if ADP is present, and ATP is produced from FP and ADP but only if H/sub 4/folate is present. The requirements for H/sub 4/folate in the synthesis of ATP from ADP and FP and for ADP in the synthesis of N/sup 10/-formylH/sub 4/folate from FP and H/sub 4/folate, are consistent with past kinetic and isotope exchange studies which showed that the reaction proceeds by a sequential mechanism and that all three substrates must be present for any reaction to occur.

  8. Growing up Active: A Study into Physical Activity in Long Day Care Centers

    ERIC Educational Resources Information Center

    Cashmore, Aaron W.; Jones, Sandra C.

    2008-01-01

    The child care center is an ideal setting in which to implement strategies to promote physical activity and healthy weight, but there is a paucity of empirical evidence on factors that influence physical activity in these settings. The current study gathered initial qualitative data to explore these factors. Child care workers from five long day…

  9. Activity File of Learning Center and Classroom Multi-Cultural Activities.

    ERIC Educational Resources Information Center

    Riverside Unified School District, CA.

    The cards in this file are representative samples of the types of activities developed by teachers involved in a Title I funded learning center of multi-cultural classroom activities for elementary school students. The five cultures that are stuoied are those of blacks, Asian Americans, native Americans, Mexican Americans, and Anglos. A…

  10. Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(III) porphyrin and fullerene entities.

    PubMed

    Poddutoori, Prashanth K; Lim, Gary N; Sandanayaka, Atula S D; Karr, Paul A; Ito, Osamu; D'Souza, Francis; Pilkington, Melanie; van der Est, Art

    2015-07-28

    The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Ph(n)-py → AlPor-Ph(m)-C60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C60) entities. The C60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, k(CS) are in the range of 10(9)-10(11) s(-1), depending on the length of the bridges. The lifetimes of the charge-separated state TTF˙(+)-C₆₀˙⁻ obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 μs. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor β = 0.36 Å(-1) obtained from the exchange coupling values between TTF˙(+) and C₆₀˙⁻ is consistent with values reported in the literature for oligophenylene bridged TTF-C60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back

  11. Stigmatellin Probes the Electrostatic Potential in the QB Site of the Photosynthetic Reaction Center

    PubMed Central

    Gerencsér, László; Boros, Bogáta; Derrien, Valerie; Hanson, Deborah K.; Wraight, Colin A.; Sebban, Pierre; Maróti, Péter

    2015-01-01

    The electrostatic potential in the secondary quinone (QB) binding site of the reaction center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides determines the rate and free energy change (driving force) of electron transfer to QB. It is controlled by the ionization states of residues in a strongly interacting cluster around the QB site. Reduction of the QB induces change of the ionization states of residues and binding of protons from the bulk. Stigmatellin, an inhibitor of the mitochondrial and photosynthetic respiratory chain, has been proven to be a unique voltage probe of the QB binding pocket. It binds to the QB site with high affinity, and the pK value of its phenolic group monitors the local electrostatic potential with high sensitivity. Investigations with different types of detergent as a model system of isolated RC revealed that the pK of stigmatellin was controlled overwhelmingly by electrostatic and slightly by hydrophobic interactions. Measurements showed a high pK value (>11) of stigmatellin in the QB pocket of the dark-state wild-type RC, indicating substantial negative potential. When the local electrostatics of the QB site was modulated by a single mutation, L213Asp→Ala, or double mutations, L213Asp-L212Glu→Ala-Ala (AA), the pK of stigmatellin dropped to 7.5 and 7.4, respectively, which corresponds to a >210 mV increase in the electrostatic potential relative to the wild-type RC. This significant pK drop (ΔpK > 3.5) decreased dramatically to (ΔpK > 0.75) in the RC of the compensatory mutant (AA+M44Asn→AA+M44Asp). Our results indicate that the L213Asp is the most important actor in the control of the electrostatic potential in the QB site of the dark-state wild-type RC, in good accordance with conclusions of former studies using theoretical calculations or light-induced charge recombination assay. PMID:25606686

  12. Non-photochemical Fluorescence Quenching in Photosystem II Antenna Complexes by the Reaction Center Cation Radical.

    PubMed

    Paschenko, V Z; Gorokhov, V V; Grishanova, N P; Korvatovskii, B N; Ivanov, M V; Maksimov, E G; Mamedov, M D

    2016-06-01

    In direct experiments, rate constants of photochemical (kP) and non-photochemical (kP(+)) fluorescence quenching were determined in membrane fragments of photosystem II (PSII), in oxygen-evolving PSII core particles, as well as in core particles deprived of the oxygen-evolving complex. For this purpose, a new approach to the pulse fluorometry method was implemented. In the "dark" reaction center (RC) state, antenna fluorescence decay kinetics were measured under low-intensity excitation (532 nm, pulse repetition rate 1 Hz), and the emission was registered by a streak camera. To create a "closed" [P680(+)QA(-)] RC state, a high-intensity pre-excitation pulse (pump pulse, 532 nm) of the sample was used. The time advance of the pump pulse against the measuring pulse was 8 ns. In this experimental configuration, under the pump pulse, the [P680(+)QA(-)] state was formed in RC, whereupon antenna fluorescence kinetics was measured using a weak testing picosecond pulsed excitation light applied to the sample 8 ns after the pump pulse. The data were fitted by a two-exponential approximation. Efficiency of antenna fluorescence quenching by the photoactive RC pigment in its oxidized (P680(+)) state was found to be ~1.5 times higher than that of the neutral (P680) RC state. To verify the data obtained with a streak camera, control measurements of PSII complex fluorescence decay kinetics by the single-photon counting technique were carried out. The results support the conclusions drawn from the measurements registered with the streak camera. In this case, the fitting of fluorescence kinetics was performed in three-exponential approximation, using the value of τ1 obtained by analyzing data registered by the streak camera. An additional third component obtained by modeling the data of single photon counting describes the P680(+)Pheo(-) charge recombination. Thus, for the first time the ratio of kP(+)/kP = 1.5 was determined in a direct experiment. The mechanisms of higher

  13. Development of Secondary Archive System at Goddard Space Flight Center Version 0 Distributed Active Archive Center

    NASA Technical Reports Server (NTRS)

    Sherman, Mark; Kodis, John; Bedet, Jean-Jacques; Wacker, Chris; Woytek, Joanne; Lynnes, Chris

    1996-01-01

    The Goddard Space Flight Center (GSFC) version 0 Distributed Active Archive Center (DAAC) has been developed to support existing and pre Earth Observing System (EOS) Earth science datasets, facilitate the scientific research, and test EOS data and information system (EOSDIS) concepts. To ensure that no data is ever lost, each product received at GSFC DAAC is archived on two different media, VHS and digital linear tape (DLT). The first copy is made on VHS tape and is under the control of UniTree. The second and third copies are made to DLT and VHS media under a custom built software package named 'Archer'. While Archer provides only a subset of the functions available with commercial software like UniTree, it supports migration between near-line and off-line media and offers much greater performance and flexibility to satisfy the specific needs of a data center. Archer is specifically designed to maximize total system throughput, rather than focusing on the turn-around time for individual files. The commercial off the shelf software (COTS) hierarchical storage management (HSM) products evaluated were mainly concerned with transparent, interactive, file access to the end-user, rather than a batch-orientated, optimizable (based on known data file characteristics) data archive and retrieval system. This is critical to the distribution requirements of the GSFC DAAC where orders for 5000 or more files at a time are received. Archer has the ability to queue many thousands of file requests and to sort these requests into internal processing schedules that optimize overall throughput. Specifically, mount and dismount, tape load and unload cycles, and tape motion are minimized. This feature did not seem to be available in many COTS pacages. Archer also uses a generic tar tape format that allows tapes to be read by many different systems rather than the proprietary format found in most COTS packages. This paper discusses some of the specific requirements at GSFC DAAC, the

  14. Center of mass detection via an active pixel sensor

    NASA Technical Reports Server (NTRS)

    Yadid-Pecht, Orly (Inventor); Minch, Brad (Inventor); Pain, Bedabrata (Inventor); Fossum, Eric (Inventor)

    2002-01-01

    An imaging system for identifying the location of the center of mass (COM) in an image. In one aspect, an imaging system includes a plurality of photosensitive elements arranged in a matrix. A center of mass circuit coupled to the photosensitive elements includes a resistive network and a normalization circuit including at least one bipolar transistor. The center of mass circuit identifies a center of mass location in the matrix and includes: a row circuit, where the row circuit identifies a center of mass row value in each row of the matrix and identifies a row intensity for each row; a horizontal circuit, where the horizontal circuit identifies a center of mass horizontal value; and a vertical circuit, where the vertical circuit identifies a center of mass vertical value. The horizontal and vertical center of mass values indicate the coordinates of the center of mass location for the image.

  15. Center of mass detection via an active pixel sensor

    NASA Technical Reports Server (NTRS)

    Yadid-Pecht, Orly (Inventor); Minch, Brad (Inventor); Pain, Bedabrara (Inventor); Fossum, Eric (Inventor)

    2006-01-01

    An imaging system for identifying the location of the center of mass (COM) in an image. In one aspect, an imaging system includes a plurality of photosensitive elements arranged in a matrix. A center of mass circuit coupled to the photosensitive elements includes a resistive network and a normalization circuit including at least one bipolar transistor. The center of mass circuit identifies a center of mass location in the matrix and includes: a row circuit, where the row circuit identifies a center of mass row value in each row of the matrix and identifies a row intensity for each row; a horizontal circuit, where the horizontal circuit identifies a center of mass horizontal value; and a vertical circuit, where the vertical circuit identifies a center of mass vertical value. The horizontal and vertical center of mass values indicate the coordinates of the center of mass location for the image.

  16. Center of mass detection via an active pixel sensor

    NASA Technical Reports Server (NTRS)

    Yadid-Pecht, Orly (Inventor); Minch, Brad (Inventor); Pain, Bedabrata (Inventor); Fossum, Eric (Inventor)

    2005-01-01

    An imaging system for identifying the location of the center of mass (COM) in an image. In one aspect, an imaging system includes a plurality of photosensitive elements arranged in a matrix. A center of mass circuit coupled to the photosensitive elements includes a resistive network and a normalization circuit including at least one bipolar transistor. The center of mass circuit identifies a center of mass location in the matrix and includes: a row circuit, where the row circuit identifies a center of mass row value in each row of the matrix and identifies a row intensity for each row; a horizontal circuit, where the horizontal circuit identifies a center of mass horizontal value; and a vertical circuit, where the vertical circuit identifies a center of mass vertical value. The horizontal and vertical center of mass values indicate the coordinates of the center of mass location for the image.

  17. Isolation of a photosystem II reaction center consisting of D-1 and D-2 polypeptides and cytochrome b-559

    SciTech Connect

    Nanba, O.; Satoh, K.

    1987-01-01

    A photosystem II reaction center complex consisting of D-1 and D-2 polypeptides and cytochrome b-559 was isolated from spinach grana thylakoids, treated with 4% (wt/vol) Triton X-100, by ion-exchange chromatography using DEAE-Toyopearl 650S. The isolated complex appears to contain five chlorophyll a, two pheophytin a, one ..beta..-carotene, and one or two cytochrome b-559 heme(s) (molar ratio) and exhibits a reversible absorbance change attributable to the photochemical accumulation of reduced pheophytin typical for the intermediary electron acceptor of photosystem II reaction center. These results strongly suggest that the site of primary charge separation in photosystem II is located on the heterodimer composed of D-1 and D-2 subunits.

  18. Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(iii) porphyrin and fullerene entities

    NASA Astrophysics Data System (ADS)

    Poddutoori, Prashanth K.; Lim, Gary N.; Sandanayaka, Atula S. D.; Karr, Paul A.; Ito, Osamu; D'Souza, Francis; Pilkington, Melanie; van der Est, Art

    2015-07-01

    The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Phn-py --> AlPor-Phm-C60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(iii) porphyrin (AlPor) and fullerene (C60) entities. The C60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, kCS are in the range of 109-1011 s-1, depending on the length of the bridges. The lifetimes of the charge-separated state TTF&z.rad;+-C&z.rad;-60 obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 μs. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor β = 0.36 Å-1 obtained from the exchange coupling values between TTF&z.rad;+ and C&z.rad;-60 is consistent with values reported in the literature for oligophenylene bridged TTF-C60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back reaction

  19. Coherent Lidar Activities at NASA Langley Research Center

    NASA Technical Reports Server (NTRS)

    Kavaya, Michael J.; Amzajerdian, Farzin; Koch, Grady J.; Singh, Upendra N.; Yu, Jirong

    2007-01-01

    NASA Langley Research Center has been developing and using coherent lidar systems for many years. The current projects at LaRC are the Global Wind Observing Sounder (GWOS) mission preparation, the Laser Risk Reduction Program (LRRP), the Instrument Incubator Program (IIP) compact, rugged Doppler wind lidar project, the Autonomous precision Landing and Hazard detection and Avoidance Technology (ALHAT) project for lunar landing, and the Skywalker project to find and use thermals to extend UAV flight time. These five projects encompass coherent lidar technology development; characterization, validation, and calibration facilities; compact, rugged packaging; computer simulation; trade studies; data acquisition, processing, and display development; system demonstration; and space mission design. This paper will further discuss these activities at LaRC.

  20. Center-of-pressure movements during equine-assisted activities.

    PubMed

    Clayton, Hilary M; Kaiser, Leeann J; de Pue, Bonnie; Kaiser, Lana

    2011-01-01

    We compared anteroposterior and mediolateral range of motion and velocity of the center of pressure (COP) on the horse's back between riders without disabilities and riders with cerebral palsy. An electronic pressure mat was used to track COP movements beneath the saddle in 4 riders without disabilities and 4 riders with cerebral palsy. Comparisons between rider groups were made using the Mann-Whitney test (p < .05). The two rider groups differed significantly in anteroposterior range of COP motion, mediolateral range of COP motion, and mediolateral COP velocity. Anteroposterior COP velocity did not differ between groups. The results suggest that measurements of COP range of motion and velocity are potentially useful for monitoring changes in balance as an indicator of core stability during equine-assisted activities.

  1. Antituberculosis Activity of the Molecular Libraries Screening Center Network Library

    PubMed Central

    MADDRY, JOSEPH A.; ANANTHAN, SUBRAMANIAM; GOLDMAN, ROBERT C.; HOBRATH, JUDITH V.; KWONG, CECIL D.; MADDOX, CLINTON; RASMUSSEN, LYNN; REYNOLDS, ROBERT C.; SECRIST, JOHN A.; SOSA, MELINDA I.; WHITE, E. LUCILE; ZHANG, WEI

    2009-01-01

    SUMMARY There is an urgent need for the discovery and development of new antitubercular agents that target novel biochemical pathways and treat drug-resistant forms of the disease. One approach to addressing this need is through high-throughput screening of drug-like small molecule libraries against the whole bacterium in order to identify a variety of new, active scaffolds that will stimulate additional biological research and drug discovery. Through the Molecular Libraries Screening Center Network, the NIAID Tuberculosis Antimicrobial Acquisition and Coordinating Facility tested a 215,110-compound library against M. tuberculosis strain H37Rv. A medicinal chemistry survey of the results from the screening campaign is reported herein. PMID:19783214

  2. Complete reaction mechanisms of mercury oxidation on halogenated activated carbon.

    PubMed

    Rungnim, Chompoonut; Promarak, Vinich; Hannongbua, Supa; Kungwan, Nawee; Namuangruk, Supawadee

    2016-06-01

    The reaction mechanisms of mercury (Hg) adsorption and oxidation on halogenated activated carbon (AC) have been completely studied for the first time using density functional theory (DFT) method. Two different halogenated AC models, namely X-AC and X-AC-X (X=Cl, Br, I), were adopted. The results revealed that HgX is found to be stable-state on the AC edge since its further desorption from the AC as HgX, or further oxidation to HgX2, are energetically unfavorable. Remarkably, the halide type does not significantly affect the Hg adsorption energy but it strongly affects the activation energy barrier of HgX formation, which obviously increases in the order HgIBr-AC>Cl-AC. Thus, the study of the complete reaction mechanism is essential because the adsorption energy can not be used as a guideline for the rational material design in the halide impregnated AC systems. The activation energy is an important descriptor for the predictions of sorbent reactivity to the Hg oxidation process. PMID:26943019

  3. Microalloying of transition metal silicides by mechanical activation and field-activated reaction

    DOEpatents

    Munir, Zuhair A.; Woolman, Joseph N.; Petrovic, John J.

    2003-09-02

    Alloys of transition metal suicides that contain one or more alloying elements are fabricated by a two-stage process involving mechanical activation as the first stage and densification and field-activated reaction as the second stage. Mechanical activation, preferably performed by high-energy planetary milling, results in the incorporation of atoms of the alloying element(s) into the crystal lattice of the transition metal, while the densification and field-activated reaction, preferably performed by spark plasma sintering, result in the formation of the alloyed transition metal silicide. Among the many advantages of the process are its ability to accommodate materials that are incompatible in other alloying methods.

  4. Intramolecular C-H activation reactions of molybdenacyclobutanes.

    PubMed

    Graham, Peter M; Buschhaus, Miriam S A; Legzdins, Peter

    2006-07-19

    Molybdenacyclobutane complexes can be prepared by reaction of Cp*Mo(NO)(=CHCMe3) (formed spontaneously by loss of neopentane from Cp*Mo(NO)(CH2CMe3)2 (1) under ambient conditions) with cyclic olefins, including cyclopentene, cycloheptene, and cyclooctene. The cyclopentene metallacyclobutane orients the metallacycle bridgehead protons cis to each other. A trans arrangement is observed for the cyclooctene congener, and both cis and trans orientations occur for the cycloheptene species. The reaction of 1 with cyclohexene initially forms a metallacyclobutane that then undergoes an allylic C-H activation to form an allyl-alkyl-coupled product with the concomitant loss of H2. The analogous allyl-alkyl structure is also observed as the thermodynamic product for the reactions of cycloheptene and cyclooctene with 1. The cyclooctene allyl-alkyl compound (5C) can be converted to an eta2-diene complex by heating with pyridine. Alternatively, heating of 5C in the presence of a variety of olefins displaces the diene ligand that can then be isolated in its unbound state.

  5. Coupling of cytochrome and quinone turnovers in the photocycle of reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides.

    PubMed

    Osváth, S; Maróti, P

    1997-08-01

    A minimal kinetic model of the photocycle, including both quinone (Q-6) reduction at the secondary quinone-binding site and (mammalian) cytochrome c oxidation at the cytochrome docking site of isolated reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides, was elaborated and tested by cytochrome photooxidation under strong continuous illumination. The typical rate of photochemical excitation by a laser diode at 810 nm was 2.200 s-1, and the rates of stationary turnover of the reaction center (one-half of that of cytochrome photooxidation) were 600 +/- 70 s-1 at pH 6 and 400 +/- 50 s-1 at pH 8. The rate of turnover showed strong pH dependence, indicating the contribution of different rate-limiting processes. The kinetic limitation of the photocycle was attributed to the turnover of the cytochrome c binding site (pH < 6), light intensity and quinone/quinol exchange (6 < pH < 8), and proton-coupled second electron transfer in the quinone acceptor complex (pH > 8). The analysis of the double-reciprocal plot of the rate of turnover versus light intensity has proved useful in determining the light-independent (maximum) turnover rate of the reaction center (445 +/- 50 s-1 at pH 7.8).

  6. Determination of the primary charge separation rate in isolated photosystem II reaction centers with 500-fs time resolution

    PubMed Central

    Wasielewski, Michael R.; Johnson, Douglas G.; Seibert, Michael; Govindjee

    1989-01-01

    We have measured directly the rate of formation of the oxidized chlorophyll a electron donor (P680+) and the reduced electron acceptor pheophytin a- (Pheoa-) following excitation of isolated spinach photosystem II reaction centers at 4°C. The reaction-center complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure that stabilizes the protein complex. Transient absorption difference spectra were measured from 440 to 850 nm as a function of time with 500-fs resolution following 610-nm laser excitation. The formation of P680+-Pheoa- is indicated by the appearance of a band due to P680+ at 820 nm and corresponding absorbance changes at 505 and 540 nm due to formation of Pheoa-. The appearance of the 820-nm band is monoexponential with τ = 3.0 ± 0.6 ps. The time constant for decay of 1*P680, the lowest excited singlet state of P680, monitored at 650 nm, is τ = 2.6 ± 0.6 ps and agrees with that of the appearance of P680+ within experimental error. Treatment of the photosystem II reaction centers with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of Pheoa-, results in formation of a transient absorption spectrum due to 1*P680. We find no evidence for an electron acceptor that precedes the formation of Pheoa-. PMID:16594012

  7. Electronic structure of Q-A in reaction centers from Rhodobacter sphaeroides. I. Electron paramagnetic resonance in single crystals.

    PubMed Central

    Isaacson, R A; Lendzian, F; Abresch, E C; Lubitz, W; Feher, G

    1995-01-01

    The magnitude and orientation of the electronic g-tensor of the primary electron acceptor quinone radical anion, Q-A, has been determined in single crystals of zinc-substituted reaction centers of Rhodobacter sphaeroides R-26 at 275 K and at 80 K. To obtain high spectral resolution, EPR experiments were performed at 35 GHz and the native ubiquinone-10 (UQ10) in the reaction center was replaced by fully deuterated UQ10. The principal values and the direction cosines of the g-tensor axes with respect to the crystal axes a, b, c were determined. Freezing of the single crystals resulted in only minor changes in magnitude and orientation of the g-tensor. The orientation of Q-A as determined by the g-tensor axes deviates only by a few degrees (< or = 8 degrees) from the orientation of the neutral QA obtained from an average of four different x-ray structures of Rb. sphaeroides reaction centers. This deviation lies within the accuracy of the x-ray structure determinations. The g-tensor values measured in single crystals agree well with those in frozen solutions. Variations in g-values between Q-A, Q-B, and UQ10 radical ion in frozen solutions were observed and attributed to different environments. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 9 PMID:8527644

  8. Nucleotides as nucleophiles: reactions of nucleotides with phosphoimidazolide activated guanosine

    NASA Technical Reports Server (NTRS)

    Kanavarioti, A.; Rosenbach, M. T.; Hurley, T. B.

    1991-01-01

    An earlier study of the reaction of phosphoimidazolide activated nucleosides (ImpN) in aqueous phosphate buffers indicated two modes of reaction of the phosphate monoanion and dianion. The first mode is catalysis of the hydrolysis of the P-N bond in ImpN's which leads to imidazole and nucleoside 5'-monophosphate. The second represents a nucleophilic substitution of the imidazole to yield the nucleoside 5'-diphosphate. This earlier study thus served as a model for the reaction of ImpN with nucleoside monophosphates (pN) because the latter can be regarded as phosphate derivatives. In the present study we investigated the reaction of guanosine 5'-phosphate-2-methylimidazolide, 2-MeImpG, in the presence of pN (N = guanosine, adenosine and uridine) in the range 6.9 less than or equal to pH less than or equal to 7.7. We observed that pN's do act as nucleophiles to form NppG, and as general base to enhance the hydrolysis of the P-N bond in 2-MeImpG, i.e. pN show the same behavior as inorganic phosphate. The kinetic analysis yields the following rate constants for the dianion pN2-: knpN = 0.17 +/- 0.02 M-1 h-1 for nucleophilic attack and khpN = 0.11 +/- 0.07 M-1 h-1 for general base catalysis of the hydrolysis. These rate constants which are independent of the nucleobase compare with kp.2 = 0.415 M-1 h-1 and khp2. = 0.217 M-1 h-1 for the reactions of HPO4(2-). In addition, this study shows that under conditions where pN presumably form stacks, the reaction mechanism remains unchanged although in quantitative terms stacked pN are somewhat less reactive. Attack by the 2'-OH and 3'-OH groups of the ribose moiety in amounts greater than or equal to 1% is not observed; this is attributed to the large difference in nucleophilicity in the neutral pH range between the phosphate group and the ribose hydroxyls. This nucleophilicity rank is not altered by stacking.

  9. Ultrafast transient absorption studies on photosystem I reaction centers from Chlamydomonas reinhardtii. 2: mutations near the P700 reaction center chlorophylls provide new insight into the nature of the primary electron donor.

    PubMed

    Holzwarth, Alfred R; Müller, Marc G; Niklas, Jens; Lubitz, Wolfgang

    2006-01-15

    donor P700", are not oxidized in the first electron transfer process, but rather only in the secondary electron transfer step. We thus propose a new electron transfer mechanism for Photosystem I where the accessory Chl(s) function as the primary electron donor(s) and the A0 Chl(s) are the primary electron acceptor(s). This new mechanism also resolves in a straightforward manner the difficulty with the previous mechanism, where an electron would have to overcome a distance of approximately 14 A in <1 ps in a single step. If interpreted within a scheme of single-sided electron transfer, our data suggest that the B-branch is the active branch, although parallel A-branch activity cannot be excluded. All the mutations do affect to a varying extent the energy difference between the reaction center excited state RC* and the first radical pair and thus affect the rate constant of charge recombination. It is interesting to note that the new mechanism proposed is in fact analogous to the electron transfer mechanism in Photosystem II, where the accessory Chl also plays the role of the primary electron donor, rather than the special Chl pair P680 (Prokhorenko, V. and A. R. Holzwarth. 2000. J. Phys. Chem. B. 104:11563-11578). PMID:16258055

  10. Domino Michael-Michael and Aldol-Aldol Reactions: Diastereoselective Synthesis of Functionalized Cyclohexanone Derivatives Containing Quaternary Carbon Center.

    PubMed

    Ghorai, Manas K; Halder, Sandipan; Das, Subhomoy

    2015-10-01

    A simple strategy for the synthesis of highly functionalized cyclohexanone derivatives containing an all-carbon quaternary center from α-(aryl/alkyl)methylidene-β-keto esters or β-diketones via a K-enolate mediated domino Michael-Michael reaction sequence with moderate to good yield and excellent diastereoselectivity (de > 99%) is described. Interestingly, Li-base mediated reaction of α-arylmethylidene-β-diketones affords functionalized 3,5-dihydroxy cyclohexane derivatives as the kinetically controlled products via a domino aldol-aldol reaction sequence with excellent diastereoselectivity. Li-enolates of the β-keto esters or β-diketones undergo facile domino Michael-Michael reaction with nitro-olefins to afford the corresponding nitrocyclohexane derivatives in good yields and excellent diastereoselectivity (de > 99%). The formation of the products and the observed stereoselectivity were explained by plausible mechanisms and supported by extensive computational study. An asymmetric version of the protocol was explored with (L)-menthol derived nonracemic substrates, and the corresponding nonracemic cyclohexanone derivatives containing an all-carbon quaternary center were obtained with excellent stereoselectivity (de, ee > 99%).

  11. Overview of Active Flow Control at NASA Langley Research Center

    NASA Technical Reports Server (NTRS)

    Pack, L. G.; Joslin, R. D.

    1998-01-01

    The paper summarizes Active Flow Control projects currently underway at the NASA Langley Research Center. Technology development is being pursued within a multidisciplinary, cooperative approach, involving the classical disciplines of fluid mechanics, structural mechanics, material science, acoustics, and stability and control theory. Complementing the companion papers in this session, the present paper will focus on projects that have the goal of extending the state-of-the-art in the measurement, prediction, and control of unsteady, nonlinear aerodynamics. Toward this goal, innovative actuators, micro and macro sensors, and control strategies are considered for high payoff flow control applications. The target payoffs are outlined within each section below. Validation of the approaches range from bench-top experiments to wind-tunnel experiments to flight tests. Obtaining correlations for future actuator and sensor designs are implicit in the discussion. The products of the demonstration projects and design tool development from the fundamental NASA R&D level technology will then be transferred to the Applied Research components within NASA, DOD, and US Industry. Keywords: active flow control, separation control, MEMS, review

  12. ESR signal of the iron-sulfur center F(X) and its function in the homodimeric reaction center of Heliobacterium modesticaldum.

    PubMed

    Miyamoto, Ryo; Iwaki, Masayo; Mino, Hiroyuki; Harada, Jiro; Itoh, Shigeru; Oh-Oka, Hirozo

    2006-05-23

    Electron transfer in the membranes and the type I reaction center (RC) core protein complex isolated from Heliobacterium modesticaldum was studied by optical and ESR spectroscopy. The RC is a homodimer of PshA proteins. In the isolated membranes, illumination at 14 K led to accumulation of a stable ESR signal of the reduced iron-sulfur center F(B)(-) in the presence of dithiothreitol, and an additional 20 min illumination at 230 K induced the spin-interacting F(A)(-)/F(B)(-) signal at 14 K. During illumination at 5 K in the presence of dithionite, we detected a new transient signal with the following values: g(z)= 2.040, g(y)= 1.911, and g(x)= 1.896. The signal decayed rapidly with a 10 ms time constant after the flash excitation at 5 K and was attributed to the F(X)(-)-type center, although the signal shape was more symmetrical than that of F(X)(-) in photosystem I. In the purified RC core protein, laser excitation induced the absorption change of a special pair, P800. The flash-induced P800(+) signal recovered with a fast 2-5 ms time constant below 150 K, suggesting charge recombination with F(X)(-). Partial destruction of the RC core protein complex by a brief exposure to air increased the level of the P800(+)A(0)(-) state that gave a lifetime (t(1/2)) of 100 ns at 77 K. The reactions of F(X) and quinone were discussed on the basis of the three-dimensional structural model of RC that predicts the conserved F(X)-binding site and the quinone-binding site, which is more hydrophilic than that in the photosystem I RC. PMID:16700542

  13. Characterization of iron dinitrosyl species formed in the reaction of nitric oxide with a biological Rieske center.

    PubMed

    Tinberg, Christine E; Tonzetich, Zachary J; Wang, Hongxin; Do, Loi H; Yoda, Yoshitaka; Cramer, Stephen P; Lippard, Stephen J

    2010-12-29

    Reactions of nitric oxide with cysteine-ligated iron-sulfur cluster proteins typically result in disassembly of the iron-sulfur core and formation of dinitrosyl iron complexes (DNICs). Here we report the first evidence that DNICs also form in the reaction of NO with Rieske-type [2Fe-2S] clusters. Upon treatment of a Rieske protein, component C of toluene/o-xylene monooxygenase from Pseudomonas sp. OX1, with an excess of NO(g) or NO-generators S-nitroso-N-acetyl-D,L-pencillamine and diethylamine NONOate, the absorbance bands of the [2Fe-2S] cluster are extinguished and replaced by a new feature that slowly grows in at 367 nm. Analysis of the reaction products by electron paramagnetic resonance, Mössbauer, and nuclear resonance vibrational spectroscopy reveals that the primary product of the reaction is a thiolate-bridged diiron tetranitrosyl species, [Fe(2)(μ-SCys)(2)(NO)(4)], having a Roussin's red ester (RRE) formula, and that mononuclear DNICs account for only a minor fraction of nitrosylated iron. Reduction of this RRE reaction product with sodium dithionite produces the one-electron-reduced RRE, having absorptions at 640 and 960 nm. These results demonstrate that NO reacts readily with a Rieske center in a protein and suggest that dinuclear RRE species, not mononuclear DNICs, may be the primary iron dinitrosyl species responsible for the pathological and physiological effects of nitric oxide in such systems in biology.

  14. Electron transfer kinetics in purified reaction centers from the green sulfur bacterium Chlorobium tepidum studied by multiple-flash excitation.

    PubMed

    Kusumoto, N; Sétif, P; Brettel, K; Seo, D; Sakurai, H

    1999-09-14

    Reaction center preparations from the green sulfur bacterium Chlorobium tepidum, which contain monoheme cytochrome c, were studied by flash-absorption spectroscopy in the near-UV, visible, and near-infrared regions. The decay kinetics of the photooxidized primary donor P840(+), together with the amount of photooxidized cytochrome c, were analyzed along a series of four flashes spaced by 1 ms: 95% of the P840(+) was reduced by cytochrome c with a t(1/2) of approximately 65 micros after the first flash, 80% with a t(1/2) of approximately 100 micros after the second flash, and 23% with a t(1/2) of approximately 100 micros after the third flash; after the fourth flash, almost no cytochrome c oxidation occurred. The observed rates, the establishment of redox equilibrium after each flash, and the total amount of photooxidizable cytochrome c are consistent with the presence of two equivalent cytochrome c molecules per photooxidizable P840. The data are well fitted assuming a standard free energy change DeltaG degrees of -53 meV for electron transfer from one cytochrome c to P840(+), DeltaG degrees being independent of the oxidation state of the other cytochrome c. These observations support a model with two monoheme cytochromes c which are symmetrically arranged around the reaction center core. From the ratio of menaquinone-7 to the bacteriochlorophyll pigment absorbing at 663 nm, it was estimated that our preparations contain 0.6-1.2 menaquinone-7 molecules per reaction center. However, no transient signal due to menaquinone could be observed between 360 and 450 nm in the time window from 10 ns to 4 micros. No recombination reaction between the primary partners P840(+) and A(0)(-) could be detected under normal conditions. Such a recombination was observed (t(1/2) approximately 19 ns) under highly reducing conditions or after accumulation of three electrons on the acceptor side during a series of flashes, showing that the secondary acceptors can stabilize three electrons

  15. Circulating polymerase chain reaction chips utilizing multiple-membrane activation

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Hao; Chen, Yi-Yu; Liao, Chia-Sheng; Hsieh, Tsung-Min; Luo, Ching-Hsing; Wu, Jiunn-Jong; Lee, Huei-Huang; Lee, Gwo-Bin

    2007-02-01

    This paper reports a new micromachined, circulating, polymerase chain reaction (PCR) chip for nucleic acid amplification. The PCR chip is comprised of a microthermal control module and a polydimethylsiloxane (PDMS)-based microfluidic control module. The microthermal control modules are formed with three individual heating and temperature-sensing sections, each modulating a specific set temperature for denaturation, annealing and extension processes, respectively. Micro-pneumatic valves and multiple-membrane activations are used to form the microfluidic control module to transport sample fluids through three reaction regions. Compared with other PCR chips, the new chip is more compact in size, requires less time for heating and cooling processes, and has the capability to randomly adjust time ratios and cycle numbers depending on the PCR process. Experimental results showed that detection genes for two pathogens, Streptococcus pyogenes (S. pyogenes, 777 bps) and Streptococcus pneumoniae (S. pneumoniae, 273 bps), can be successfully amplified using the new circulating PCR chip. The minimum number of thermal cycles to amplify the DNA-based S. pyogenes for slab gel electrophoresis is 20 cycles with an initial concentration of 42.5 pg µl-1. Experimental data also revealed that a high reproducibility up to 98% could be achieved if the initial template concentration of the S. pyogenes was higher than 4 pg µl-1. The preliminary results of the current paper were presented at the 19th IEEE International Conference on Micro Electro Mechanical Systems (IEEE MEMS 2006), Istanbul, Turkey, 22-26 January, 2006.

  16. Fuel Cell Activities at the NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Kohout, Lisa L.; Lyons, Valerie (Technical Monitor)

    2002-01-01

    Fuel cells have a long history in space applications and may have potential application in aeronautics as well. A fuel cell is an electrochemical energy conversion device that directly transforms the chemical energy of a fuel and oxidant into electrical energy. Alkaline fuel cells have been the mainstay of the U.S. space program, providing power for the Apollo missions and the Space Shuttle. However, Proton Exchange Membrane (PEM) fuel cells offer potential benefits over alkaline systems and are currently under development for the next generation Reusable Launch Vehicle (RLV). Furthermore, primary and regenerative systems utilizing PEM technology are also being considered for future space applications such as surface power and planetary aircraft. In addition to these applications, the NASA Glenn Research Center is currently studying the feasibility of the use of both PEM and solid oxide fuel cells for low- or zero-emission electric aircraft propulsion. These types of systems have potential applications for high altitude environmental aircraft, general aviation and commercial aircraft, and high attitude airships. NASA Glenn has a unique set of capabilities and expertise essential to the successful development of advanced fuel cell power systems for space and aeronautics applications. NASA Glenn's role in past fuel cell development programs as well as current activities to meet these new challenges will be presented

  17. [Requests for active euthanasia: which reality in an oncology center.].

    PubMed

    Chvetzoff, G; Perret, M; Thevenet, G; Arbiol, E; Gobet, S; Saltel, P

    2009-09-01

    Euthanasia is a controversial issue in today's society. In countries where euthanasia is legal, it is mainly associated with people with cancer. We retrospectively studied the frequency and basis of patients' requests for active euthanasia in the oncology setting.MethodsRecurrent requests for euthanasia made by the patients of Leon-Berard cancer center (Lyon, France) between 2001 and 2003 were recorded by questioning the physicians and nurse supervisors in charge or by collecting information from the minutes of multidisciplinary palliative care meetings. We also collected information on the general health status of the patients, their motives and their evolution over time, as well as responses from caregivers.ResultsWe identified 16 requests for euthanasia. These involved 8 men, 7 women and 1 child (median age, 56 years), corresponding to 1% of the total deaths recorded during the period. In 2 cases, the request had come from the family only. The most frequent motives were psychological distress (38%), desire for self-autonomy (31%) and pain (31%). Half of the patients, particularly those striving for autonomy, persisted with their request until death, whereas 2 of 3 requests motivated by physical or psychological distress were not maintained. Sedation was administered to 3 patients in response to recurrent requests.ConclusionRequests for euthanasia in cancer patients are rare but may occur. Sometimes suffering is not relieved by palliative care and the request is maintained. Dealing with these patients puts caregivers in a difficult situation.

  18. Carbon Dioxide Information Analysis Center: FY 1991 activities

    SciTech Connect

    Cushman, R.M.; Stoss, F.W.

    1992-06-01

    During the course of a fiscal year, Oak Ridge National Laboratory`s Carbon Dioxide Information Analysis Center (CDIAC) distributes thousands of specially publications-numeric data packages (NDPs), computer model packages (CMPs), technical reports, public communication publications, newsletters, article reprints, and reference books-in response to requests for information related to global environmental issues, primarily those pertaining to climate change. CDIAC`s staff also provides technical responses to specific inquiries related to carbon dioxide (CO{sub 2}), other trace gases, and climate. Hundreds of referrals to other researchers, policy analysts, information specialists, or organizations are also facilitated by CDIAC`s staff. This report provides an account of the activities accomplished by CDIAC during the period October 1, 1990 to September 30, 1991. An organizational overview of CDIAC and its staff is supplemented by a detailed description of inquiries received and CDIAC`s response to those inquiries. An analysis and description of the preparation and distribution of numeric data packages, computer model packages, technical reports, newsletters, factsheets, specially publications, and reprints is provided. Comments and descriptions of CDIAC`s information management systems, professional networking, and special bilateral agreements are also described.

  19. Carbon Dioxide Information Analysis Center: FY 1991 activities

    SciTech Connect

    Cushman, R.M.; Stoss, F.W.

    1992-06-01

    During the course of a fiscal year, Oak Ridge National Laboratory's Carbon Dioxide Information Analysis Center (CDIAC) distributes thousands of specially publications-numeric data packages (NDPs), computer model packages (CMPs), technical reports, public communication publications, newsletters, article reprints, and reference books-in response to requests for information related to global environmental issues, primarily those pertaining to climate change. CDIAC's staff also provides technical responses to specific inquiries related to carbon dioxide (CO{sub 2}), other trace gases, and climate. Hundreds of referrals to other researchers, policy analysts, information specialists, or organizations are also facilitated by CDIAC's staff. This report provides an account of the activities accomplished by CDIAC during the period October 1, 1990 to September 30, 1991. An organizational overview of CDIAC and its staff is supplemented by a detailed description of inquiries received and CDIAC's response to those inquiries. An analysis and description of the preparation and distribution of numeric data packages, computer model packages, technical reports, newsletters, factsheets, specially publications, and reprints is provided. Comments and descriptions of CDIAC's information management systems, professional networking, and special bilateral agreements are also described.

  20. THE GALACTIC CENTER: NOT AN ACTIVE GALACTIC NUCLEUS

    SciTech Connect

    An, Deokkeun; Ramirez, Solange V.; Sellgren, Kris

    2013-06-01

    We present 10 {mu}m-35 {mu}m Spitzer spectra of the interstellar medium in the Central Molecular Zone (CMZ), the central 210 pc Multiplication-Sign 60 pc of the Galactic center (GC). We present maps of the CMZ in ionic and H{sub 2} emission, covering a more extensive area than earlier spectroscopic surveys in this region. The radial velocities and intensities of ionic lines and H{sub 2} suggest that most of the H{sub 2} 0-0 S(0) emission comes from gas along the line-of-sight, as found by previous work. We compare diagnostic line ratios measured in the Spitzer Infrared Nearby Galaxies Survey to our data. Previous work shows that forbidden line ratios can distinguish star-forming galaxies from low-ionization nuclear emission-line regions (LINERs) and active galactic nuclei (AGNs). Our GC line ratios agree with star-forming galaxies and not with LINERs or AGNs.

  1. Carbon Dioxide Information Analysis Center: FY 1992 activities

    SciTech Connect

    Cushman, R.M.; Stoss, F.W.

    1993-03-01

    During the course of a fiscal year, Oak Ridge National Laboratory`s Carbon Dioxide Information Analysis Center (CDIAC) distributes thousands of specialty publications-numeric data packages (NDPs), computer model packages (CMPs), technical reports, public communication publications, newsletters, article reprints, and reference books-in response to requests for information related to global environmental issues, primarily those pertaining to climate change. CDIACs staff also provides technical responses to specific inquiries related to carbon dioxide (CO{sub 2}), other trace gases, and climate. Hundreds of referrals to other researchers, policy analysts, information specialists, or organizations are also facilitated by CDIAC`s staff. This report provides an account of the activities accomplished by CDIAC during the period October 1, 1991 to September 30, 1992. An organizational overview of CDIAC and its staff is supplemented by a detailed description of inquiries received and CDIAC`s response to those inquiries. As analysis and description of the preparation and distribution of numeric data packages, computer model packages, technical reports, newsletters, fact sheets, specialty publications, and reprints is provided. Comments and descriptions of CDIAC`s information management systems, professional networking, and special bilateral agreements are also described.

  2. Activation of stratospheric chlorine by reactions in liquid sulphuric acid

    SciTech Connect

    Cox, R.A.; MacKenzie, A.R. ); Mueller, R.H.; Peter, Th.; Crutzen, P.J. )

    1994-06-22

    The authors discuss activation mechanisms for chlorine compounds in the stratosphere, based on laboratory measurements for the solubility and reaction rates of HOCl and HCl in H[sub 2]SO[sub 4] solutions, as found on aerosols in the stratosphere. Their interest is in the impact of the large increase in aerosol loading in the stratosphere in the winter on 1991-92 due to the Mt. Pinatubo eruption. While laboratory data is not available for the temperature range close to 190 K, they argue that should the solubility and hydrolysis rates be high enough, this excess aerosol density could have contributed a significant additional amount of reactive chlorine to the stratosphere.

  3. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water

    PubMed Central

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-01-01

    Splitting water for hydrogen production using light, or electrical energy, is the most developed ‘green technique’. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of −20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of −0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production. PMID:26541371

  4. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water

    NASA Astrophysics Data System (ADS)

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-11-01

    Splitting water for hydrogen production using light, or electrical energy, is the most developed ‘green technique’. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production.

  5. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water.

    PubMed

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-01-01

    Splitting water for hydrogen production using light, or electrical energy, is the most developed 'green technique'. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production. PMID:26541371

  6. Innovative Strategy on Hydrogen Evolution Reaction Utilizing Activated Liquid Water.

    PubMed

    Hwang, Bing-Joe; Chen, Hsiao-Chien; Mai, Fu-Der; Tsai, Hui-Yen; Yang, Chih-Ping; Rick, John; Liu, Yu-Chuan

    2015-11-06

    Splitting water for hydrogen production using light, or electrical energy, is the most developed 'green technique'. For increasing efficiency in hydrogen production, currently, the most exciting and thriving strategies are focused on efficient and inexpensive catalysts. Here, we report an innovative idea for efficient hydrogen evolution reaction (HER) utilizing plasmon-activated liquid water with reduced hydrogen-bonded structure by hot electron transfer. This strategy is effective for all HERs in acidic, basic and neutral systems, photocatalytic system with a g-C3N4 (graphite carbon nitride) electrode, as well as in an inert system with an ITO (indium tin oxide) electrode. Compared to deionized water, the efficiency of HER increases by 48% based on activated water ex situ on a Pt electrode. Increase in energy efficiency from activated water is 18% at a specific current yield of -20 mA in situ on a nanoscale-granulated Au electrode. Moreover, the onset potential of -0.023 V vs RHE was very close to the thermodynamic potential of the HER (0 V). The measured current density at the corresponding overpotential for HER in an acidic system was higher than any data previously reported in the literature. This approach establishes a new vista in clean green energy production.

  7. More than Smile Sheets: Rasch Analysis of Training Reactions in a Medical Center

    ERIC Educational Resources Information Center

    McLinden, Daniel; Boone, William John

    2009-01-01

    Reaction questionnaires administered at the conclusion of a training program are a common method of evaluation. Because such questionnaires are often constructed and analyzed in an ad hoc manner, their usefulness is often difficult to gauge. However, if properly constructed and analyzed, such instruments can help to make clear the strengths and…

  8. Proton Reaction Data Library for Nuclear Activation (Medium Energy Nuclear Data Library.)

    2002-03-01

    Version 00 GROUPXS does file handling and processing of the double-differential continuum-emission cross sections stored in the new MF6 format of ENDF/VI. It treats the energy-angle data that are supposed to be represented by a Legendre-polynomial expansion in the center-of-mass system and can do the following: (1) Conversion of MF6 data from center-of-mass system to the laboratory system, with the possibility to continue the calculation with the options (2), (3), and (4). (2) Conversion ofmore » Legendre-polynomial representation into point-wise angular data, in MF6 format. (3) Conversion of data from MF6 into MF4 + MF5 (ENDF-V). (4) Calculation of group constants, scattering matrices and transfer matrices for arbitrary group structures with a fusion micro-flux weighting spectrum (PN-approximation). The code treats only continuum reaction types that are stored in the MF6 format with the restrictions as specified for the European Fusion File (EFF1). These restrictions are not inconvenient for the purpose of fusion neutronics calculations and they facilitate relatively simple processing . This neutron reaction data library can be used for nuclear activation and transmutation applications at energies up to 100 MeV.« less

  9. FTIR spectroscopy of the photoreduction of the bacteriopheophytin electron acceptor in reaction centers of Rb. sphaeroides and Rps. viridis.

    NASA Astrophysics Data System (ADS)

    Nabedryk, E.; Andrianambinintsoa, S.; Dejonghe, D.; Breton, J.

    1995-05-01

    The photoreduction of the bacteriopheophytin electron acceptor H A in reaction centers from Rhodobacter sphaeroides and Rhodopseudomonas viridis has been monitored by light-induced FTIR difference spectroscopy at 10°C, in the presence of reductant and mediator. The striking similarity of the H A-/H A spectra obtained for Rb. sphaeroides and Rps. viridis reflects comparable interactions of the bacteriopheophytin electron acceptor with the protein in both reaction centers and implies that the photoreduction of H A affects conserved amino acid residues. The H A-/H A spectra are interpreted by comparison with model compound spectra of the anion radicals of bacteriopheophytin a and b,a nd by analysis of 1H/2H isotope effects. The downshift of the 1677 cm -1 mode in Rb. sphaeroides (1681 cm -1 in Rps. viridis) reaction centers with respect to the model compound is interpreted in terms of a strongly perturbed 9-keto carbonyl of H A. This perturbation most probably originates from hydrogen bonding to Glu L104. At least part of the positive signal at 1591 cm -1 in Rb. sphaeroides and at 1601 cm -1 in Rps. viridis is assigned to the 9-keto carbonyl mode of H A-. From 1H/2H exchange experiments, it is proposed that the COO 1H side chain of Glu L104 contributes to the 1745-1735 cm -1 spectral range with the corresponding COO 2H signal displaced to lower frequencies and partly hidden under the 1732 cm -1 band.

  10. The Effect of Bacteriochlorophyll g Oxidation on Energy and Electron Transfer in Reaction Centers from Heliobacterium modesticaldum.

    PubMed

    Ferlez, Bryan; Dong, Weibing; Siavashi, Reza; Redding, Kevin; Hou, Harvey J M; Golbeck, John H; van der Est, Art

    2015-10-29

    The heliobacteria are a family of strictly anaerobic, Gram-positive, photoheterotrophs in the Firmicutes. They make use of a homodimeric type I reaction center (RC) that contains ∼20 antenna bacteriochlorophyll (BChl) g molecules, a special pair of BChl g' molecules (P800), two 8(1)-OH-Chl aF molecules (A0), a [4Fe-4S] iron-sulfur cluster (FX), and a carotenoid (4,4'-diaponeurosporene). It is known that in the presence of light and oxygen BChl g is converted to a species with an absorption spectrum identical to that of Chl a. Here, we show that main product of the conversion is 8(1)-OH-Chl aF. Smaller amounts of two other oxidized Chl aF species are also produced. In the presence of light and oxygen, the kinetics of the conversion are monophasic and temperature dependent, with an activation energy of 66 ± 2 kJ mol(-1). In the presence of oxygen in the dark, the conversion occurs in two temperature-dependent kinetic phases: a slow phase followed by a fast phase with an activation energy of 53 ± 1 kJ mol(-1). The loss of BChl g' occurs at the same rate as the loss of Bchl g; hence, the special pair converts at the same rate as the antenna Chl's. However, the loss of P800 photooxidiation and flavodoxin reduction is not linear with the loss of BChl g. In anaerobic RCs, the charge recombination between P800(+) and FX(-) at 80 K is monophasic with a lifetime of 4.2 ms, but after exposure to oxygen, an additional phase with a lifetime of 0.3 ms is observed. Transient EPR data show that the line width of P800(+) increases as BChl g is converted to Chl aF and the rate of electron transfer from A0 to FX, as estimated from the net polarization generated by singlet-triplet mixing during the lifetime of P800(+)A0(-), is unchanged. The transient EPR data also show that conversion of the BChl g results in increased formation of triplet states of both BChl g and Chl aF. The nonlinear loss of P800 photooxidiation and flavodoxin reduction, the biphasic backreaction kinetics, and

  11. Time-resolved electrochromism associated with the formation of quinone anions in the rhodobacter sphaeroides R26 reaction center

    SciTech Connect

    Tiede, D.M.; Vazquez, J.; Cordova, J.; Marone, P.A.

    1996-08-20

    The bacterial photosynthetic reaction center contains bacteriochlorophyll (Bchl) and bacteriochlorophyll (Bchl) and bacteriopheophytin (Bph) cofactors that provide natural probes of electrostatic fields within this protein. We have examined the electrochromic responses of these cofactors, resolved during the lifetimes of the quinone anion states, P{sup +}Q{sub A}{sup -Q}{sub B} and P{sup +}Q{sub A}Q{sub B}{sup -}, and measured as a function of temperature. These measurements provide information on the time-dependent variation in electrostatic field strength on the Bchl and Bph cofactors. Measurements in the near-infrared absorbance bands are described. 60 refs., 11 figs., 1 tab.

  12. Lamb shift in radical-ion pairs produces a singlet-triplet energy splitting in photosynthetic reaction centers

    NASA Astrophysics Data System (ADS)

    Vitalis, K. M.; Kominis, I. K.

    2014-09-01

    Radical-ion pairs, fundamental for understanding photosynthesis and the avian magnetic compass, were recently shown to be biological open quantum systems. We here show that the coupling of the radical-pair spin degrees of freedom to its decohering vibrational reservoir leads to a shift of the radical-pair magnetic energy levels. The Lamb shift Hamiltonian is diagonal in the singlet-triplet basis, and results in a singlet-triplet energy splitting physically indistinguishable from an exchange interaction. This could have significant implications for understanding the energy level structure and the dynamics of photosynthetic reaction centers.

  13. NUCLEAR REACTION AND STRUCTURE DATABASES OF THE NATIONAL NUCLEAR DATA CENTER.

    SciTech Connect

    PRITYCHENKO, B.; HERMAN, M.W.; MUGHABGHAB, S.F.; OBLOZINSKY, P.; SONZOGNI, A.A.

    2006-06-23

    We discuss nuclear data resources of the National Nuclear Data Center (NNDC) of relevance to nuclear astrophysics applications. These resources include databases, tools and powerful web service at www.nndc.bnl.gov. Our objective is to provide an overview of nuclear databases, related products and demonstrate nuclear astrophysics potential of the ENDF/B-VII beta2 library. A detailed discussion on the Maxwellian neutron capture cross sections obtained from the ENDF/B-VII beta2 library is presented.

  14. Reaction time-related activity reflecting periodic, task-specific cognitive control.

    PubMed

    Barber, Anita D; Pekar, James J; Mostofsky, Stewart H

    2016-01-01

    Reaction time (RT) is associated with increased amplitude of the Blood Oxygen-Level Dependent (BOLD) response in cognitive control regions. The current study examined whether the Primary Condition (PC) effect and RT-BOLD effect both reflect the same cognitive control processes. In addition, RT-BOLD effects were examined in two Go/No-go tasks with different demands to determine whether RT-related activity is task-dependent, reflecting the recruitment of task-specific cognitive processes. Data simulations showed that RT-related activity could be distinguished from that of the primary condition if it is mean-centered. In that case, RT-related activity reflects periodically-engaged processes rather than "time-on-task" (ToT). RT-related activity was mostly distinct from that of the primary Go contrast, particularly for the perceptual decision task. Therefore, RT effects can reflect additional cognitive processes that are not captured by the PC contrast consistent with a periodic-engagement account. RT-BOLD effects occurred in a separate set of regions for the two tasks. For the task requiring a perceptual decision, RT-related activity occurred within occipital and posterior parietal regions supporting visual attention. For the task requiring a working memory decision, RT-related activity occurred within fronto-parietal regions supporting the maintenance and retrieval of task representations. The findings suggest that RT-related activity reflects task-specific processes that are periodically-engaged, particularly during less demanding tasks. PMID:26318935

  15. Synthesis of highly active and dual-functional electrocatalysts for methanol oxidation and oxygen reduction reactions

    NASA Astrophysics Data System (ADS)

    Zhao, Qi; Zhang, Geng; Xu, Guangran; Li, Yingjun; Liu, Baocang; Gong, Xia; Zheng, Dafang; Zhang, Jun; Wang, Qin

    2016-12-01

    The promising Pt-based ternary catalyst is crucial for polymer electrolyte membrane fuel cells (PEMFCs) due to improving catalytic activity and durability for both methanol oxidation reaction and oxygen reduction reaction. In this work, a facile strategy is used for the synthesis ternary RuMPt (M = Fe, Co, Ni, and Cu) nanodendrities catalysts. The ternary RuMPt alloys exhibit enhanced specific and mass activity, positive half-wave potential, and long-term stability, compared with binary Pt-based alloy and the commercial Pt/C catalyst, which is attributed to the high electron density and upshifting of the d-band center for Pt atoms, and synergistic catalytic effects among Pt, M, and Ru atoms by introducing a transition metal. Impressively, the ternary RuCoPt catalyst exhibits superior mass activity (801.59 mA mg-1) and positive half-wave potential (0.857 V vs. RHE) towards MOR and ORR, respectively. Thus, the RuMPt nanocomposite is a very promising material to be used as dual electrocatalyst in the application of PEMFCs.

  16. Magnetic-field-induced orientation of photosynthetic reaction centers as revealed by time-resolved W-band EPR of spin-correlated radical pairs

    SciTech Connect

    Berthold, T.; Bechtold, M.; Heinen, U.; Link, G.; Poluektov, O.; Utschig, L.; Tang, J.; Thurnauer, M.C.; Kothe, G.

    1999-12-09

    The spin-polarized W-band EPR spectra of the secondary radical pair in plant photosystem 1 indicate a magnetic-field-induced orientation of the photosynthetic reaction centers in the field of the EPR spectrometer. This orientation arises due to the anisotropy of the diamagnetic susceptibility of the reaction center protein. Analysis of the angular-dependent EPR spectra on the basis of the spin-correlated radical pair concept provides new information on the cofactor arrangement in plant photosystem 1.

  17. 77 FR 70211 - Agency Information Collection Activities (Call Center Satisfaction Survey) Under OMB Review

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-11-23

    ... AFFAIRS Agency Information Collection Activities (Call Center Satisfaction Survey) Under OMB Review AGENCY....'' SUPPLEMENTARY INFORMATION: Title: VBA Call Center Satisfaction Survey. OMB Control Number: 2900-0744. Type of... VA call centers will provide VBA with three key benefits to: (1) Identify what is most important...

  18. 34 CFR 426.7 - What activities does the Secretary fund under the Agriculture Action Centers?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Agriculture Action Centers? 426.7 Section 426.7 Education Regulations of the Offices of the Department of... DEMONSTRATION PROGRAM General § 426.7 What activities does the Secretary fund under the Agriculture Action Centers? The Secretary supports model Agriculture Action Centers that provide improved access...

  19. 34 CFR 426.7 - What activities does the Secretary fund under the Agriculture Action Centers?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Agriculture Action Centers? 426.7 Section 426.7 Education Regulations of the Offices of the Department of... DEMONSTRATION PROGRAM General § 426.7 What activities does the Secretary fund under the Agriculture Action Centers? The Secretary supports model Agriculture Action Centers that provide improved access...

  20. 34 CFR 426.7 - What activities does the Secretary fund under the Agriculture Action Centers?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Agriculture Action Centers? 426.7 Section 426.7 Education Regulations of the Offices of the Department of... DEMONSTRATION PROGRAM General § 426.7 What activities does the Secretary fund under the Agriculture Action Centers? The Secretary supports model Agriculture Action Centers that provide improved access...

  1. Low temperature absorption, fluorescence, and hole-burning spectroscopy of photosystem II reaction center complex containing 1 and 2 carotenoides

    NASA Astrophysics Data System (ADS)

    Dědic, R.; Lovčinský, M.; Pšenčík, J.; Vácha, M.; Vácha, F.; Hála, J.

    1999-05-01

    Well defined photosystem II reaction centers from Pisum sativum containing 5 or 6 chlorophyll a (Chl a), 2 pheophytine a (Pheo a), and 1 or 2 β-carotene ( β Car) molecules were prepared by using immobilized metal affinity chromatography. Samples containing 6 Chl a and 1 or 2 β-Car and containing 5 Chl a and 1 β-Car were measured using low temperature absorption, fluorescence and hole-burning spectroscopy. Absorption bands of the β Car (462, 490, and 508 nm) can be clearly distinguished next to the Soret absorption band of Chl a at low temperature. Their relative intensities strongly depend on Chl/Car ratio. The shapes of fluorescence bands are the same for all samples. Persistent spectral holes were burnt into both absorption and fluorescence spectra. This technique provides lifetime of excited state τ1 and Huang-Rhys factor S. Values of τ1 correspond to two picoseconds energy transfer in reaction centers. Huang-Rhys factor S=0.4 appears to be the same for all studied samples.

  2. Spin densities from subsystem density-functional theory: Assessment and application to a photosynthetic reaction center complex model

    SciTech Connect

    Solovyeva, Alisa; Pavanello, Michele; Neugebauer, Johannes

    2012-05-21

    Subsystem density-functional theory (DFT) is a powerful and efficient alternative to Kohn-Sham DFT for large systems composed of several weakly interacting subunits. Here, we provide a systematic investigation of the spin-density distributions obtained in subsystem DFT calculations for radicals in explicit environments. This includes a small radical in a solvent shell, a {pi}-stacked guanine-thymine radical cation, and a benchmark application to a model for the special pair radical cation, which is a dimer of bacteriochlorophyll pigments, from the photosynthetic reaction center of purple bacteria. We investigate the differences in the spin densities resulting from subsystem DFT and Kohn-Sham DFT calculations. In these comparisons, we focus on the problem of overdelocalization of spin densities due to the self-interaction error in DFT. It is demonstrated that subsystem DFT can reduce this problem, while it still allows to describe spin-polarization effects crossing the boundaries of the subsystems. In practical calculations of spin densities for radicals in a given environment, it may thus be a pragmatic alternative to Kohn-Sham DFT calculations. In our calculation on the special pair radical cation, we show that the coordinating histidine residues reduce the spin-density asymmetry between the two halves of this system, while inclusion of a larger binding pocket model increases this asymmetry. The unidirectional energy transfer in photosynthetic reaction centers is related to the asymmetry introduced by the protein environment.

  3. The effect of an applied electric field on the charge recombination kinetics in reaction centers reconstituted in planar lipid bilayers.

    PubMed Central

    Gopher, A; Blatt, Y; Schönfeld, M; Okamura, M Y; Feher, G; Montal, M

    1985-01-01

    Reaction Centers (RCs) from the photosynthetic bacterium Rhodopseudomonas sphaeroides were incorporated in planar bilayers made from monolayers derived from liposomes reconstituted with purified RCs. The photocurrents associated with the charge recombination process between the reduced primary quinone (QA-) and the oxidized bacteriochlorophyll donor (D+) were measured as a function of voltage (-150 mV less than V less than 150 mV) applied across the bilayer. When QA was the native ubiquinone (UQ) the charge recombination was voltage independent. However, when UQ was replaced by anthraquinone (AQ), the recombination time depended on the applied voltage V according to the relation tau = 8.5 X 10(-3) eV/0.175S. These results were explained by a simple model in which the charge recombination from UQ- proceeds directly to D+ while that from AQ occurs via a thermally activated intermediate state, D+I-QA, where I is the intermediate acceptor. The voltage dependence arises from an electric field induced change in the energy gap, delta G0, between the states D+I-QA and D+IQA-. This model is supported by the measured temperature dependence of the charge recombination time, which for RCs with AQ gave a value of delta G0 = 340 +/- 20 meV. In contrast, delta G0 for RCs with UQ as the primary acceptor, is sufficiently large (approximately 550 meV) so that even in the presence of the field, the direct pathway dominates. The voltage dependence shows that the electron transfer from I- to QA is electrogenic. From a quantitative analysis of the voltage dependence on the recombination rate it was concluded that the component of the distance between I and QA along the normal to the membrane is about one-seventh of the thickness of the membrane. This implies that the electron transfer from I to Q contributes at least one-seventh to the potential generated by the charge separation between D+ and QA-. PMID:3902109

  4. Activities and Products at IVS combination center at BKG

    NASA Astrophysics Data System (ADS)

    Bachmann, S.; Lösler, M.

    2013-08-01

    The IVS combination center is primarily responsible to provide rapid EOP products based on observation campaigns twice a week and a long-term EOP series which is updated four times a year. Besides EOP products, methods and analysis of combined station coordinates and source positions are evolving and new products are developed in order to expand the range of combined VLBI products. Within the last year the combination center continuously worked on several improvements and refinements of the combination procedure: outlier test have been improved, the detection of unsuitable sessions in order to improve the stability of the results, the modeling of station coordinates of the reference frame generation and the data presentation on the combination centers website. Besides the routine combination of 24h VLBI sessions, several other projects have been developed, e.g. the preparation of the latest VLBI reference frame (VTRF) including the calculation of station height variations and baseline lengths generation derived by the combination of station coordinates. The combination center is furthermore intensely working on the combination of source coordinates and on providing user friendly online analysis tools on the combination centers website in order to meet the user requirements.

  5. Activities, accomplishments and research progress of the Center for Theoretical Geoplasma Physics, Center for Space Research, Massachusetts Inst. of Technology

    NASA Astrophysics Data System (ADS)

    Chang, Tom

    1992-02-01

    This annual report contains a detailed description of the activities, accomplishments, and research progress of the MIT Center for Theoretical Geoplasma Physics established under the University Research Initiative Program by AFOSR. During this second phase of the program, the Center has made definite strides toward the goals prescribed in the renewal proposal. The Center now has a staff of twenty-five (25) faculty, research scientists, postdoctoral, graduate and undergraduate students and visiting scientists. Members of the Center published forty-eight (48) scientific papers and five (5) books and proceedings, delivered forty (40) invited lectures and fifty-one (51) contributed papers. We have initiated a number of new research activities to complement our other ongoing research programs. Some of our research efforts have already been utilized by Dr. J. R. Jasperse's group at the Geophysics Directorate of the Phillips Laboratory in practical space technology applications relevant to the missions of the Air Force. In addition to the Phillips Laboratory, the Center has interacted with numerous research organizations and universities. The research publications are generally the direct product of such interactions.

  6. Isolation and Characterization of Homodimeric Type-I Reaction Center Complex from Candidatus Chloracidobacterium thermophilum, an Aerobic Chlorophototroph*

    PubMed Central

    Tsukatani, Yusuke; Romberger, Steven P.; Golbeck, John H.; Bryant, Donald A.

    2012-01-01

    The recently discovered thermophilic acidobacterium Candidatus Chloracidobacterium thermophilum is the first aerobic chlorophototroph that has a type-I, homodimeric reaction center (RC). This organism and its type-I RCs were initially detected by the occurrence of pscA gene sequences, which encode the core subunit of the RC complex, in metagenomic sequence data derived from hot spring microbial mats. Here, we report the isolation and initial biochemical characterization of the type-I RC from Ca. C. thermophilum. After removal of chlorosomes, crude membranes were solubilized with 0.1% (w/v) n-dodecyl β-d-maltoside, and the RC complex was purified by ion-exchange chromatography. The RC complex comprised only two polypeptides: the reaction center core protein PscA and a 22-kDa carotenoid-binding protein denoted CbpC. The absorption spectrum showed a large, broad absorbance band centered at ∼483 nm from carotenoids as well as smaller Qy absorption bands at 672 and 812 nm from chlorophyll a and bacteriochlorophyll a, respectively. The light-induced difference spectra of whole cells, membranes, and the isolated RC showed maximal bleaching at 840 nm, which is attributed to the special pair and which we denote as P840. Making it unique among homodimeric type-I RCs, the isolated RC was photoactive in the presence of oxygen. Analyses by optical spectroscopy, chromatography, and mass spectrometry revealed that the RC complex contained 10.3 bacteriochlorophyll aP, 6.4 chlorophyll aPD, and 1.6 Zn-bacteriochlorophyll aP′ molecules per P840 (12.8:8.0:2.0). The possible functions of the Zn-bacteriochlorophyll aP′ molecules and the carotenoid-binding protein are discussed. PMID:22184116

  7. Electron Transfer in Bacterial Reaction Centers with the Photoactive Bacteriopheophytin Replaced by a Bacteriochlorophyll through Coordinating Ligand Substitution.

    PubMed

    Pan, Jie; Saer, Rafael; Lin, Su; Beatty, J Thomas; Woodbury, Neal W

    2016-09-01

    The influence of amino acid substitutions at position M214 (M-subunit, residue 214) on the rate and pathway of electron transfer involving the bacteriopheophytin cofactor, HA, in a bacterial photosynthetic reaction center has been explored in a series of Rhodobacter sphaeroides mutants. The M214 leucine (L) residue of the wild type was replaced with histidine (H), glutamine (Q), and asparagine (N), creating the mutants M214LH, M214LQ, and M214LN, respectively. As has been reported previously for M214LH, each of these mutations resulted in a bacteriochlorophyll molecule in place of a bacteriopheophytin in the HA pocket, forming so-called β-type mutants (in which the HA cofactor is called βA). In addition, these mutations changed the properties of the surrounding protein environment in terms of charge distribution and the amino acid side chain volume. Electron transfer reactions from the excited primary donor P to the acceptor QA were characterized using ultrafast transient absorption spectroscopic techniques. Similar to that of the previously characterized M214LH (β mutant), the strong energetic mixing of the P(+)BA(-) and P(+)βA(-) states (the mixed anion is denoted I(-)) increased the rate of charge recombination between P(+) and I(-) in competition with the I(-) → QA forward reaction. This reduced the overall yield of charge separation forming the P(+)QA(-) state. While the kinetics of the primary electron transfer forming P(+)I(-) were essentially identical in all three β mutants, the rates of the βA(-) (I(-)) → QA electron transfer in M214LQ and M214LH were very similar but quite different from that of the M214LN mutant. The observed yield changes and the differences in kinetics are correlated more closely with the volume of the mutated amino acid than with their charge characteristics. These results are consistent with those of previous studies of a series of M214 mutants with different sizes of amino acid side chains that did not alter the HA

  8. STS-26 simulation activities in JSC Mission Control Center (MCC)

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Overall view of JSC Mission Control Center (MCC) Bldg 30 Flight Control Room (FCR) during Flight Day 1 of STS-26 integrated simulations in progress between MCC and JSC Mission Simulation and Training Facility Bldg 5 fixed-base (FB) shuttle mission simulator (SMS).

  9. STS-26 simulation activities in JSC Mission Control Center (MCC)

    NASA Technical Reports Server (NTRS)

    1987-01-01

    In JSC Mission Control Center (MCC) Bldg 30 Flight Control Room (FCR), astronauts John O. Creighton (right) and L. Blaine Hammond review their notes while serving as spacecraft communicators (CAPCOMs) for STS-26 simulations in progress between MCC and JSC Mission Simulation and Training Facility Bldg 5 fixed-base (FB) shuttle mission simulator (SMS).

  10. STS-26 simulation activities in JSC Mission Control Center (MCC)

    NASA Technical Reports Server (NTRS)

    1987-01-01

    In JSC Mission Control Center (MCC) Bldg 30 Flight Control Room (FCR), flight directors (FDs) Lee Briscoe (left) and Charles W. Shaw, seated at FD console, view front visual display monitors during STS-26 simulations in progress between MCC and JSC Mission Simulation and Training Facility Bldg 5 fixed-base (FB) shuttle mission simulator (SMS).

  11. Development of various reaction abilities and their relationships with favorite play activities in preschool children.

    PubMed

    Miyaguchi, Kazuyoshi; Demura, Shinich; Sugiura, Hiroki; Uchiyama, Masanobu; Noda, Masahiro

    2013-10-01

    This study examines the development of various reaction movements in preschool children and the relationship between reaction times and favorite play activities. The subjects were 167 healthy preschool children aged 4-6 (96 boys and 71 girls). This study focused on the reaction times of the upper limbs (reaction 1: release; reaction 2: press) and the whole body (reaction 3: forward jump). The activities frequently played in preschools are largely divided into dynamic play activities (tag, soccer, gymnastics set, dodge ball, and jump rope) and static play activities (drawing, playing house, reading, playing with sand, and building blocks). The subjects chose 3 of 10 cards picturing their favorite play activities, depicting 10 different activities. All intraclass correlation coefficients of measured reaction times were high (0.73-0.79). In addition, each reaction time shortened with age. Reaction 1 showed a significant and low correlation with reaction 3 (r = 0.37). The effect size of the whole body reaction time was the largest. Whole body reaction movement, which is largely affected by the exercise output function, develops remarkably in childhood. Children who liked "tag" were faster in all reaction times. The children who chose "soccer" were faster in reactions 2 and 3. In contrast, children who liked "playing house" tended to have slower reaction times. Dynamic activities, such as tag and soccer, promote development of reaction speed and agility in movements involving the whole body. Preschool teachers and physical educators should re-examine the effect of tag and use it periodically as one of the exercise programs to avoid unexpected falls and injuries in everyday life. PMID:23302758

  12. Physical activity in the EPIC-Italy centers.

    PubMed

    Salvini, Simonetta; Saieva, Calogero; Ciardullo, Anna Vittoria; Panico, Salvatore; Masala, Giovanna; Assedi, Melania; Berrino, Franco; Pala, Valeria; Frasca, Graziella; Tumino, Rosario; Veglia, Fabrizio; Sacerdote, Carlotta; Palli, Domenico

    2003-01-01

    The European Prospective Investigation into Cancer and nutrition offers the opportunity to explore patterns of physical activity in a large series of healthy adults enrolled in the different local cohorts of the Italian section of the European EPIC project. Physical activity is considered one of the means by which chronic disease could be prevented. Subjects in the EPIC study completed a life-style questionnaire, with a section dedicated to the assessment of physical activity at work and during leisure time. Time spent in the various activities was transformed into an index of physical activity (physical activity level, PAL) and an activity index that includes intense activity (PAL; intense activity included). Quintiles of these indexes were computed in order to observe the distribution of subject characteristics according to levels of physical activity. In general, the population was characterized by low levels of physical activity at work, with more than 50% of the sample reporting sedentary occupations. During leisure time, only a small percentage of subjects compensated for the inactivity at work by engaging in energy-consuming activities. In particular, organized fitness activities were reported by a small percentage of people, whereas walking was the most common sort of physical activity. Specific types of activity seemed to characterize subjects in the different areas of the country, reflecting local traditions or specific living situations. Detailed information about physical activity habits, together with a description of other characteristics, could help in designing physical activity promotion programs in different Italian populations and age groups.

  13. Symmetry-related mutants in the quinone binding sites of the reaction center -- The effects of changes in charge distribution

    SciTech Connect

    Hanson, D.K.; Schiffer, M.

    1997-09-01

    To probe the structural elements that contribute to the functional asymmetries of the two ubiquinone{sub 10}binding pockets in the reaction center of Rhodobacter capsulatus, the authors targeted the L212Glu-L213Asp (near Q{sub B}) and the M246Ala-M247Ala (near Q{sub A}) pairs of symmetry-related residues for site-specific mutagenesis. They have constructed site-specific mutants that eliminate the sequence differences at these positions (L212Glu-L213Asp{yields}Ala-Ala or M246Ala-M247Ala{yields}Glu-Asp), and have reversed that asymmetry by constructing a quadruple-mutant strain, RQ (L212Glu-L213Asp-M246Ala-M247Ala{yields}Ala-Ala-Glu-Asp). The mutations were designed to change the charge distribution in the quinone-binding region of the reaction center; none of the strains is capable of photosynthetic growth. In photocomponent phenotypic revertants of the RQ strain, second-site mutations which affect Q{sub B} function are coupled to mutations in the Q{sub A} site which restore an Ala or substitute a Tyr at the M247 site; one strain carries an additional Met{yields}Glu substitution at M260 near Q{sub A}. All of the RQ revertants retain the engineered M246Ala{yields}Glu mutation in the Q{sub A} site as well as the L212Ala-L213Ala mutations in the Q{sub B} site. Kinetic characterization of the RQ revertants will give them an idea of what structural and functional elements are important for restoring efficiency to electron and proton transfer pathways in the RQRC, which is far from native. To date, these preliminary results underscore the importance of an asymmetric distribution of polar amino acids in the quinone binding pockets and its influence on the functional properties of the reaction center.

  14. Two-Dimensional Electronic Spectroscopy of the Photosystem II D1D2-cyt.b559 Reaction Center Complex

    NASA Astrophysics Data System (ADS)

    Myers, Jeffrey Allen

    Two-dimensional electronic spectroscopy (2DES) is a powerful new technique for examining the electronic and vibronic couplings and dynamics of chemical, semiconductor, and biological samples. We present several technical innovations in the implementation of 2DES. We have performed two-color 2DES experiments, extending the technique's ability to study energy transfer to states at frequencies far from the initial absorption. We have demonstrated 2DES in the pump-probe geometry using a pulse-shaper. This method eliminates many technical challenges inherent to previous implementations of 2DES, making it a more widely accessible technique. To broaden the available frequency information, we have demonstrated 2DES with a continuum probe pulse. We have utilized this method to observe vibrational wavepacket dynamics in a laser dye, demonstrating that these dynamics modulate 2D lineshapes and must be accounted for in modelling 2DES data. We perform 2DES studies on the Qy band of the D1D2-cyt.b559 reaction center of plant photosystem II. This reaction center is the core oxygen-evolving complex in plant photosynthesis, taking in light energy and forming a charge separated state capable of splitting water. Understanding the relationship between the structure and function has both fundamental importance and applications to improving artificial light-harvesting. Traditional spectroscopy methods have been unable to completely resolve the time-ordering of energy and charge transfer events or the degree of electronic coupling between chromophores due to severe spectral congestion in the Q y band. 2DES extends previous methods by frequency-resolving an additional dimension to reveal the degree of static disorder and electronic coupling, as well as a detailed picture of energy and charge transfer dynamics that will allow tests of excitonic models of the reaction center. Our data show direct evidence of electronic coupling and rapid sub-ps energy transfer between "blue" and "red

  15. Energy Adventure Center. Activity Book. Revised [and Expanded] Edition.

    ERIC Educational Resources Information Center

    Wichita Unified School District 259, KS.

    A variety of energy activities are provided, including instructions for and questions related to energy films. The activities are organized into five sections. Section 1 (work) includes an activity focusing on movement and change. Section 2 (forms of energy) includes activities related to mechanical (movement), radiant (light), chemical (burning),…

  16. Physical Activity in Child-Care Centers: Do Teachers Hold the Key to the Playground?

    ERIC Educational Resources Information Center

    Copeland, Kristen A.; Kendeigh, Cassandra A.; Saelens, Brian E.; Kalkwarf, Heidi J.; Sherman, Susan N.

    2012-01-01

    Many (56%) US children aged 3-5 years are in center-based childcare and are not obtaining recommended levels of physical activity. In order to determine what child-care teachers/providers perceived as benefits and barriers to children's physical activity in child-care centers, we conducted nine focus groups and 13 one-on-one interviews with 49…

  17. 34 CFR 350.22 - What activities must a Rehabilitation Research and Training Center conduct?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... DISABILITY AND REHABILITATION RESEARCH PROJECTS AND CENTERS PROGRAM What Rehabilitation Research and Training Centers Does the Secretary Assist? § 350.22 What activities must a Rehabilitation Research and Training... 34 Education 2 2010-07-01 2010-07-01 false What activities must a Rehabilitation Research...

  18. 34 CFR 350.32 - What activities must a Rehabilitation Engineering Research Center conduct?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 34 Education 2 2011-07-01 2010-07-01 true What activities must a Rehabilitation Engineering... DISABILITY AND REHABILITATION RESEARCH PROJECTS AND CENTERS PROGRAM What Rehabilitation Engineering Research Centers Does the Secretary Assist? § 350.32 What activities must a Rehabilitation Engineering...

  19. 34 CFR 350.22 - What activities must a Rehabilitation Research and Training Center conduct?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 34 Education 2 2011-07-01 2010-07-01 true What activities must a Rehabilitation Research and... DISABILITY AND REHABILITATION RESEARCH PROJECTS AND CENTERS PROGRAM What Rehabilitation Research and Training Centers Does the Secretary Assist? § 350.22 What activities must a Rehabilitation Research and...

  20. 34 CFR 350.32 - What activities must a Rehabilitation Engineering Research Center conduct?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 2 2012-07-01 2012-07-01 false What activities must a Rehabilitation Engineering... DISABILITY AND REHABILITATION RESEARCH PROJECTS AND CENTERS PROGRAM What Rehabilitation Engineering Research Centers Does the Secretary Assist? § 350.32 What activities must a Rehabilitation Engineering...

  1. Probing the Active Center of Benzaldehyde Lyase with Substitutions and the Pseudosubstrate Analogue Benzoylphosphonic Acid Methyl Ester

    SciTech Connect

    Brandt, Gabriel S.; Nemeria, Natalia; Chakraborty, Sumit; McLeish, Michael J.; Yep, Alejandra; Kenyon, George L.; Petsko, Gregory A.; Jordan, Frank; Ringe, Dagmar

    2008-07-28

    Benzaldehyde lyase (BAL) catalyzes the reversible cleavage of (R)-benzoin to benzaldehyde utilizing thiamin diphosphate and Mg{sup 2+} as cofactors. The enzyme is important for the chemoenzymatic synthesis of a wide range of compounds via its carboligation reaction mechanism. In addition to its principal functions, BAL can slowly decarboxylate aromatic amino acids such as benzoylformic acid. It is also intriguing mechanistically due to the paucity of acid-base residues at the active center that can participate in proton transfer steps thought to be necessary for these types of reactions. Here methyl benzoylphosphonate, an excellent electrostatic analogue of benzoylformic acid, is used to probe the mechanism of benzaldehyde lyase. The structure of benzaldehyde lyase in its covalent complex with methyl benzoylphosphonate was determined to 2.49 {angstrom} (Protein Data Bank entry 3D7K) and represents the first structure of this enzyme with a compound bound in the active site. No large structural reorganization was detected compared to the complex of the enzyme with thiamin diphosphate. The configuration of the predecarboxylation thiamin-bound intermediate was clarified by the structure. Both spectroscopic and X-ray structural studies are consistent with inhibition resulting from the binding of MBP to the thiamin diphosphate in the active centers. We also delineated the role of His29 (the sole potential acid-base catalyst in the active site other than the highly conserved Glu50) and Trp163 in cofactor activation and catalysis by benzaldehyde lyase.

  2. Probing the active center of benzaldehyde lyase with substitutions and the pseudosubstrate analogue benzoylphosphonic acid methyl ester.

    PubMed

    Brandt, Gabriel S; Nemeria, Natalia; Chakraborty, Sumit; McLeish, Michael J; Yep, Alejandra; Kenyon, George L; Petsko, Gregory A; Jordan, Frank; Ringe, Dagmar

    2008-07-22

    Benzaldehyde lyase (BAL) catalyzes the reversible cleavage of ( R)-benzoin to benzaldehyde utilizing thiamin diphosphate and Mg (2+) as cofactors. The enzyme is important for the chemoenzymatic synthesis of a wide range of compounds via its carboligation reaction mechanism. In addition to its principal functions, BAL can slowly decarboxylate aromatic amino acids such as benzoylformic acid. It is also intriguing mechanistically due to the paucity of acid-base residues at the active center that can participate in proton transfer steps thought to be necessary for these types of reactions. Here methyl benzoylphosphonate, an excellent electrostatic analogue of benzoylformic acid, is used to probe the mechanism of benzaldehyde lyase. The structure of benzaldehyde lyase in its covalent complex with methyl benzoylphosphonate was determined to 2.49 A (Protein Data Bank entry 3D7K ) and represents the first structure of this enzyme with a compound bound in the active site. No large structural reorganization was detected compared to the complex of the enzyme with thiamin diphosphate. The configuration of the predecarboxylation thiamin-bound intermediate was clarified by the structure. Both spectroscopic and X-ray structural studies are consistent with inhibition resulting from the binding of MBP to the thiamin diphosphate in the active centers. We also delineated the role of His29 (the sole potential acid-base catalyst in the active site other than the highly conserved Glu50) and Trp163 in cofactor activation and catalysis by benzaldehyde lyase.

  3. Photosynthetic antenna-reaction center mimicry with a covalently linked monostyryl boron-dipyrromethene-aza-boron-dipyrromethene-C60 triad.

    PubMed

    Shi, Wen-Jing; El-Khouly, Mohamed E; Ohkubo, Kei; Fukuzumi, Shunichi; Ng, Dennis K P

    2013-08-19

    An efficient functional mimic of the photosynthetic antenna-reaction center has been designed and synthesized. The model contains a near-infrared-absorbing aza-boron-dipyrromethene (ADP) that is connected to a monostyryl boron-dipyrromethene (BDP) by a click reaction and to a fullerene (C60 ) using the Prato reaction. The intramolecular photoinduced energy and electron-transfer processes of this triad as well as the corresponding dyads BDP-ADP and ADP-C60 have been studied with steady-state and time-resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge-separated states. Such calculations show that electron transfer from the singlet excited ADP ((1) ADP*) to C60 yielding ADP(.+) -C60 (.-) is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from (1) BDP* to ADP in the dyad BDP-ADP and electron transfer from (1) ADP* to C60 in the dyad ADP-C60 . Sequential energy and electron transfer have also been clearly observed in the triad BDP-ADP-C60 . By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10(11)  s(-1) ). The dynamics of electron transfer through (1) ADP* has also been studied by monitoring the formation of C60 radical anion at 1000 nm. A fast charge-separation process from (1) ADP* to C60 has been detected, which gives the relatively long-lived BDP-ADP(.+) C60 (.-) with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge-separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state

  4. Ligand Displacement Reaction Paths in a Diiron Hydrogenase Active Site Model Complex.

    PubMed

    Blank, Jan H; Moncho, Salvador; Lunsford, Allen M; Brothers, Edward N; Darensbourg, Marcetta Y; Bengali, Ashfaq A

    2016-08-26

    The mechanism and energetics of CO, 1-hexene, and 1-hexyne substitution from the complexes (SBenz)2 [Fe2 (CO)6 ] (SBenz=SCH2 Ph) (1-CO), (SBenz)2 [Fe2 (CO)5 (η(2) -1-hexene)] (1-(η(2) -1-hexene)), and (SBenz)2 [Fe2 (CO)5 (η(2) -1-hexyne)] (1-(η(2) -1-hexyne)) were studied by using time-resolved infrared spectroscopy. Exchange of both CO and 1-hexyne by P(OEt)3 and pyridine, respectively, proceeds by a bimolecular mechanism. As similar activation enthalpies are obtained for both reactions, the rate-determining step in both cases is assumed to be the rotation of the Fe(CO)2 L (L=CO or 1-hexyne) unit to accommodate the incoming ligand. The kinetic profile for the displacement of 1-hexene is quite different than that for the alkyne and, in this case, both reaction channels, that is, dissociative (SN 1) and associative (SN 2), were found to be competitive. Because DFT calculations predict similar binding enthalpies of alkene and alkyne to the iron center, the results indicate that the bimolecular pathway in the case of the alkyne is lower in free energy than that of the alkene. In complexes of this type, subtle changes in the departing ligand characteristics and the nature of the mercapto bridge can influence the exchange mechanism, such that more than one reaction pathway is available for ligand substitution. The difference between this and the analogous study of (μ-pdt)[Fe(CO)3 ]2 (pdt=S(CH2 )3 S) underscores the unique characteristics of a three-atom S-S linker in the active site of diiron hydrogenases. PMID:27482938

  5. Synchronizing Substrate Activation Rates in Multicomponent Reactions with Metal-Organic Framework Catalysts.

    PubMed

    Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles

    2016-05-01

    A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In8 (OH)6 (popha)6 (H2 O)4 ]⋅3 H2 O (InPF-16), [In(popha)(2,2'-bipy)]⋅3 H2 O (InPF-17), [In3 (OH)3 (popha)2 (4,4'-bipy)]⋅4 H2 O (InPF-18), [In2 (popha)2 (4,4'-bipy)2 ]⋅3 H2 O (InPF-19), [In(OH)(Hpopha)]⋅0.5 (1,7-phen) (InPF-20), and [In(popha)(1,10-phen)]⋅4 H2 O (InPF-21) (InPF=indium polymeric framework, H3 popha=5-(4-carboxy-2-nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent-free cyanosilylation of carbonyl compounds, the one pot Passerini 3-component (P-3CR) and the Ugi 4-component (U-4CR) reactions. In addition, InPF-17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α-aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven-coordinated indium framework of the catalyst InPF-17. This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF-based heterogeneous catalyst for multicomponent reactions.

  6. Modeling of the D1/D2 proteins and cofactors of the photosystem II reaction center: implications for herbicide and bicarbonate binding.

    PubMed Central

    Xiong, J.; Subramaniam, S.; Govindjee

    1996-01-01

    A three-dimensional model of the photosystem II (PSII) reaction center from the cyanobacterium Synechocystis sp. PCC 6803 was generated based on homology with the anoxygenic purple bacterial photosynthetic reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis, for which the X-ray crystallographic structures are available. The model was constructed with an alignment of D1 and D2 sequences with the L and M subunits of the bacterial reaction center, respectively, and by using as a scaffold the structurally conserved regions (SCRs) from bacterial templates. The structurally variant regions were built using a novel sequence-specific approach of searching for the best-matched protein segments in the Protein Data Bank with the "basic local alignment search tool" (Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ, 1990, J Mol Biol 215:403-410), and imposing the matching conformational preference on the corresponding D1 and D2 regions. The structure thus obtained was refined by energy minimization. The modeled D1 and D2 proteins contain five transmembrane alpha-helices each, with cofactors (4 chlorophylls, 2 pheophytins, 2 plastoquinones, and a non-heme iron) essential for PSII primary photochemistry embedded in them. A beta-carotene, considered important for PSII photoprotection, was also included in the model. Four different possible conformations of the primary electron donor P680 chlorophylls were proposed, one based on the homology with the bacterial template and the other three on existing experimental suggestions in literature. The P680 conformation based on homology was preferred because it has the lowest energy. Redox active tyrosine residues important for P680+ reduction as well as residues important for PSII cofactor binding were analyzed. Residues involved in interprotein interactions in the model were also identified. Herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was also modeled in the plastoquinone QB binding niche using the

  7. Aerospace Battery Activities at NASA/Goddard Space Flight Center

    NASA Technical Reports Server (NTRS)

    Rao, Gopalakrishna M.

    2006-01-01

    Goddard Space Flight Center has "pioneered" rechargeable secondary battery design, test, infusion and in-orbit battery management among NASA installations. Nickel cadmium batteries of various designs and sizes have been infused for LEO, GEO and Libration Point spacecraft. Nickel-Hydrogen batteries have currently been baselined for the majority of our missions. Li-Ion batteries from ABSL, JSB, SaFT and Lithion have been designed and tested for aerospace application.

  8. Activities in Aeroelasticity at NASA Langley Research Center

    NASA Technical Reports Server (NTRS)

    Perry, Boyd, III; Noll, Thomas E.

    1997-01-01

    This paper presents the results of recently-completed research and presents status reports of current research being performed within the Aeroelasticity Branch of the NASA Langley Research Center. Within the paper this research is classified as experimental, analytical, and theoretical aeroelastic research. The paper also describes the Langley Transonic Dynamics Tunnel, its features, capabilities, a new open-architecture data acquisition system, ongoing facility modifications, and the subsequent calibration of the facility.

  9. STS-26 simulation activities in JSC Mission Control Center (MCC)

    NASA Technical Reports Server (NTRS)

    1987-01-01

    In JSC Mission Control Center (MCC) Bldg 30 Flight Control Room (FCR), flight controller Granvil A. Pennington, leaning on console, listens to communications during the STS-26 integrated simulations in progress between MCC and JSC Mission Simulation and Training Facility Bldg 5 fixed-base (FB) shuttle mission simulator (SMS). MCC FCR visual displays are seen in background. Five veteran astronauts were in the FB-SMS rehearsing their roles for the scheduled June 1988 flight aboard Discovery, Orbiter Vehicle (OV) 103.

  10. Research on Social Stability Mechanisms Based on Activation Energy and Gradual Activation Reaction Theory

    NASA Astrophysics Data System (ADS)

    Ning, Miao; Gu, Jifa

    This paper draws a comparison between social stability and chemical reaction process, and brings forward the concept of “social temperature” and “activation energy of social agent”. It is considered that social temperature turns out to be the macro symptom of social average energy, and its unceasing up-climbing roots in the energy accumulation of “inferiorization” process of social system; that “activation energy of social agent” stands for the social energy or temperature where individuals or groups reach the limit of their psychological bearing ability. This paper, basing on above concepts, elaborates on and demonstrates the gradual activation reaction mechanisms of social stability by a lot of concrete examples. It is thought that there is a threshold value for social stability, and the society will be unstable if social temperature goes higher than this value; that the larger the social average activation energy is, the higher the temperature threshold value of social stability will be; and considering that different groups have different activation energy, those fragile groups with low activation energy are often the risk source which might pose a threat to social stability.

  11. Comparison of reaction centers from Rhodobacter sphaeroides and rhodopseudomonas viridis: Overall archistecture and protein-pigment interactions

    SciTech Connect

    Elkabbani, Ossama; Chang, Chonghwan; Tiede, D.; Norris, J.; Schiffer, M. )

    1991-06-04

    Photosynthetic reaction centers (RCs) from the photosynthetic bacteria Rhodobacter sphaeroides and Rhodopseudomonas viridis are protein complexes closely related in both structure and function. The structure of the Rps. viridis RC was used to determine the structure of the RC from Rb. sphaeroides. Small but meaningful differences between the positions of the helices and the cofactors in the two complexes were identified. The distances between helices A{sub L} adn A{sub M}, between B{sub L} and B{sub M}, and between bacteriopheophytins BP{sub L} and BP{sub M} are significantly shorter in Rps. viridis than they are in Rb. sphaeroides RCs. There are a number of differences in the amino acid residues that surround the cofactors; some of these residues form hydrogen bonds with the cofactors. Differences in chemical properties of the two RCs.

  12. Low-temperature (77 K) phosphorescence of triplet chlorophyll in isolated reaction centers of photosystem II.

    PubMed

    Neverov, Konstantin V; Krasnovsky, Alexander A; Zabelin, Alexey A; Shuvalov, Vladimir A; Shkuropatov, Anatoly Ya

    2015-08-01

    Phosphorescence characterized by the main emission band at 952 ± 1 nm (1.30 eV), the lifetime of 1.5 ± 0.1 ms and the quantum yield nearly equal to that for monomeric chlorophyll a in aqueous detergent dispersions, has been detected in isolated reaction centers (RCs) of spinach photosystem II at 77 K. The excitation spectrum shows maxima corresponding to absorption bands of chlorophyll a, pheophytin a, and β-carotene. The phosphorescence intensity strongly depends upon the redox state of RCs. The data suggest that the phosphorescence signal originates from the chlorophyll triplet state populated via charge recombination in the radical pair [Formula: see text].

  13. Comments on the optical lineshape function: Application to transient hole-burned spectra of bacterial reaction centers

    SciTech Connect

    Reppert, Mike; Kell, Adam; Pruitt, Thomas; Jankowiak, Ryszard

    2015-03-07

    The vibrational spectral density is an important physical parameter needed to describe both linear and non-linear spectra of multi-chromophore systems such as photosynthetic complexes. Low-temperature techniques such as hole burning (HB) and fluorescence line narrowing are commonly used to extract the spectral density for a given electronic transition from experimental data. We report here that the lineshape function formula reported by Hayes et al. [J. Phys. Chem. 98, 7337 (1994)] in the mean-phonon approximation and frequently applied to analyzing HB data contains inconsistencies in notation, leading to essentially incorrect expressions in cases of moderate and strong electron-phonon (el-ph) coupling strengths. A corrected lineshape function L(ω) is given that retains the computational and intuitive advantages of the expression of Hayes et al. [J. Phys. Chem. 98, 7337 (1994)]. Although the corrected lineshape function could be used in modeling studies of various optical spectra, we suggest that it is better to calculate the lineshape function numerically, without introducing the mean-phonon approximation. New theoretical fits of the P870 and P960 absorption bands and frequency-dependent resonant HB spectra of Rb. sphaeroides and Rps. viridis reaction centers are provided as examples to demonstrate the importance of correct lineshape expressions. Comparison with the previously determined el-ph coupling parameters [Johnson et al., J. Phys. Chem. 94, 5849 (1990); Lyle et al., ibid. 97, 6924 (1993); Reddy et al., ibid. 97, 6934 (1993)] is also provided. The new fits lead to modified el-ph coupling strengths and different frequencies of the special pair marker mode, ω{sub sp}, for Rb. sphaeroides that could be used in the future for more advanced calculations of absorption and HB spectra obtained for various bacterial reaction centers.

  14. Learning by Doing: Engaging Students through Learner-Centered Activities

    ERIC Educational Resources Information Center

    Smart, Karl L.; Csapo, Nancy

    2007-01-01

    With a shift of focus from teaching to learning in higher education, teachers often look for strategies to involve students actively in the learning process, especially since numerous studies have demonstrated that a student's active involvement in the learning process enhances learning. Active learning has resulted in positive learning outcomes.…

  15. Insight into the reaction mechanisms for oxidative addition of strong σ bonds to an Al(i) center.

    PubMed

    Zhang, Xiangfei; Cao, Zexing

    2016-06-21

    The oxidation addition of a series of σ H-X bonds (X = H, B, C, Si, N, P, and O) to a single Al(i) supported by a (NacNac)(-) bidentate ligand ((NacNac)(-) = [ArNC(Me)CHC(Me)NAr](-) and Ar = 2,6-(i)Pr2C6H3) has been explored through extensive DFT calculations. The presented results show that activation and addition of these σ bonds follow various reaction mechanisms, in which hydride transfer, proton transfer, and Al-X bond coupling steps are involved. The predicted free energy barriers for these oxidative additions range from 8 to 32 kcal mol(-1), and all the reactions are remarkably favorable thermodynamically. However, sterically hindered ligands, for most reactants, make the formation of the initial reactant complex difficult and may reduce the efficiency of the reaction. Calculations reveal a strong dependence of the reaction mechanism and low-energy channel on the bonding features of X-H and the local structural environments. PMID:27249667

  16. Dynamic and reversible self-assembly of photoelectrochemical complexes based on lipid bilayer disks, photosynthetic reaction centers, and single-walled carbon nanotubes.

    PubMed

    Boghossian, Ardemis A; Choi, Jong Hyun; Ham, Moon-Ho; Strano, Michael S

    2011-03-01

    An aqueous solution containing photosynthetic reaction centers (RCs), membrane scaffold proteins (MSPs), phospholipids, and single-walled carbon nanotubes (SWCNTs) solubilized with the surfactant sodium cholate (SC) reversibly self-assembles into a highly ordered structure upon dialysis of the latter. The resulting structure is photoelectrochemically active and consists of 4-nm-thick lipid bilayer disks (nanodisks, NDs) arranged parallel to the surface of the SWCNT with the RC housed within the bilayer such that its hole injecting site faces the nanotube surface. The structure can be assembled and disassembled autonomously with the addition or removal of surfactant. We model the kinetic and thermodynamic forces that drive the dynamics of this reversible self-assembly process. The assembly is monitored using spectrofluorimetry during dialysis and subsequent surfactant addition and used to fit a kinetic model to determine the forward and reverse rate constants of ND and ND-SWCNT formation. The calculated ND and ND-SWCNT forward rate constants are 79 mM(-1) s(-1) and 5.4 × 10(2) mM(-1) s(-1), respectively, and the reverse rate constants are negligible over the dialysis time scale. We find that the reaction is not diffusion-controlled since the ND-SWCNT reaction, which consists of entities with smaller diffusion coefficients, has a larger reaction rate constant. Using these rate parameters, we were able to develop a kinetic phase diagram for the formation of ND-SWCNT complexes, which indicates an optimal dialysis rate of approximately 8 × 10(-4) s(-1). We also fit the model to cyclic ND-SWCNT assembly and disassembly experiments and hence mimic the thermodynamic forces used in regeneration processes detailed previously. Such forces may form the basis of both synthetic and natural photoelectrochemical complexes capable of dynamic component replacement and repair.

  17. Activation energy for a model ferrous-ferric half reaction from transition path sampling.

    PubMed

    Drechsel-Grau, Christof; Sprik, Michiel

    2012-01-21

    Activation parameters for the model oxidation half reaction of the classical aqueous ferrous ion are compared for different molecular simulation techniques. In particular, activation free energies are obtained from umbrella integration and Marcus theory based thermodynamic integration, which rely on the diabatic gap as the reaction coordinate. The latter method also assumes linear response, and both methods obtain the activation entropy and the activation energy from the temperature dependence of the activation free energy. In contrast, transition path sampling does not require knowledge of the reaction coordinate and directly yields the activation energy [C. Dellago and P. G. Bolhuis, Mol. Simul. 30, 795 (2004)]. Benchmark activation energies from transition path sampling agree within statistical uncertainty with activation energies obtained from standard techniques requiring knowledge of the reaction coordinate. In addition, it is found that the activation energy for this model system is significantly smaller than the activation free energy for the Marcus model, approximately half the value, implying an equally large entropy contribution.

  18. Recent Activities of Tsukuba Correlator/Analysis Center

    NASA Astrophysics Data System (ADS)

    Kokado, K.; Kurihara, S.; Kawabata, R.; Nozawa, K.

    2012-12-01

    The Geospatial Information Authority of Japan (GSI) has been a member of IVS and taken charge of a Network Station and an IVS Correlator since 1998. In addition, GSI became an IVS Operational Analysis Center in January 2010.The Tsukuba Correlator takes charge of correlation work for approximately 100 IVS-INT02 (INT2) sessions and 10 Japanese domestic sessions every year. In 2011, the number of INT2 sessions dramatically increased, because INT2 sessions were observed twice a day during the weekend from April 2011 to January 2012 due to the change in position of the Tsukuba 32-m antenna by the 2011 earthquake off the Pacific coast of Tohoku. The role of the Tsukuba VLBI Analysis Center is to produce ultra-rapid dUT1 measurements, sessions with the goal of obtaining a dUT1 solution within 30 minutes after the end of the observation session. The data processing system at the Tsukuba Correlator and Analysis Center was dramatically improved to achieve rapid data processing. It enabled us to shorten the data processing time to one-sixth and to process the IVS VLBI data in near real-time. In 2011, we processed the ultra-rapid dUT1 measurements with the Onsala or Wettzell stations from INT2 sessions or IVS 24-hour sessions, such as R1, RD or T2 sessions. The most successful sessions for ultra-rapid dUT1 measurement was the CONT11 sessions which were a campaign of 15 days of continuous VLBI sessions. During these sessions, we succeeded in estimating continuous dUT1 solutions in near real-time for 15 days.

  19. Recent activities of the Priroda State Remote Sensing Center

    USGS Publications Warehouse

    Morrison, J.L.; Bond, A.R.

    1989-01-01

    At present the Priroda State Remote Sensing Center is the largest entity in the USSR responsible for the receipt and processing of space imagery. Besides the aforementioned consulting and training functions, Priroda, upon user request: a) processes multispectral, band-specific, and other remote sensing imagery and supplies a broad range of primary and derivative information in the form of image copies [prints and transparencies] and digital products; and b) cooperates with other GUGK bodies in the compilation of thematic map series on diverse topics. -from Authors

  20. Integration of photoswitchable proteins, photosynthetic reaction centers and semiconductor/biomolecule hybrids with electrode supports for optobioelectronic applications.

    PubMed

    Wang, Fuan; Liu, Xiaoqing; Willner, Itamar

    2013-01-18

    Light-triggered biological processes provide the principles for the development of man-made optobioelectronic systems. This Review addresses three recently developed topics in the area of optobioelectronics, while addressing the potential applications of these systems. The topics discussed include: (i) the reversible photoswitching of the bioelectrocatalytic functions of redox proteins by the modification of proteins with photoisomerizable units or by the integration of proteins with photoisomerizable environments; (ii) the integration of natural photosynthetic reaction centers with electrodes and the construction of photobioelectrochemical cells and photobiofuel cells; and (iii) the synthesis of biomolecule/semiconductor quantum dots hybrid systems and their immobilization on electrodes to yield photobioelectrochemical and photobiofuel cell elements. The fundamental challenge in the tailoring of optobioelectronic systems is the development of means to electrically contact photoactive biomolecular assemblies with the electrode supports. Different methods to establish electrical communication between the photoactive biomolecular assemblies and electrodes are discussed. These include the nanoscale engineering of the biomolecular nanostructures on surfaces, the development of photoactive molecular wires and the coupling of photoinduced electron transfer reactions with the redox functions of proteins. The different possible applications of optobioelectronic systems are discussed, including their use as photosensors, the design of biosensors, and the construction of solar energy conversion and storage systems.

  1. Mutation-induced perturbation of the special pair P840 in the homodimeric reaction center in green sulfur bacteria.

    PubMed

    Azai, Chihiro; Sano, Yuko; Kato, Yuki; Noguchi, Takumi; Oh-oka, Hirozo

    2016-01-01

    Homodimeric photosynthetic reaction centers (RCs) in green sulfur bacteria and heliobacteria are functional homologs of Photosystem (PS) I in oxygenic phototrophs. They show unique features in their electron transfer reactions; however, detailed structural information has not been available so far. We mutated PscA-Leu688 and PscA-Val689 to cysteine residues in the green sulfur bacterium Chlorobaculum tepidum; these residues were predicted to interact with the special pair P840, based on sequence comparison with PS I. Spectroelectrochemical measurements showed that the L688C and V689C mutations altered a near-infrared difference spectrum upon P840 oxidation, as well as the redox potential of P840. Light-induced Fourier transform infrared difference measurements showed that the L688C mutation induced a differential signal of the S-H stretching vibration in the P840(+)/P840 spectrum, as reported in P800(+)/P800 difference spectrum in a heliobacterial RC. Spectral changes in the 13(1)-keto C=O region, caused by both mutations, revealed corresponding changes in the electronic structure of P840 and in the hydrogen-bonding interaction at the 13(1)-keto C=O group. These results suggest that there is a common spatial configuration around the special pair sites among type 1 RCs. The data also provided evidence that P840 has a symmetric electronic structure, as expected from a homodimeric RC. PMID:26804137

  2. Mutation-induced perturbation of the special pair P840 in the homodimeric reaction center in green sulfur bacteria

    PubMed Central

    Azai, Chihiro; Sano, Yuko; Kato, Yuki; Noguchi, Takumi; Oh-oka, Hirozo

    2016-01-01

    Homodimeric photosynthetic reaction centers (RCs) in green sulfur bacteria and heliobacteria are functional homologs of Photosystem (PS) I in oxygenic phototrophs. They show unique features in their electron transfer reactions; however, detailed structural information has not been available so far. We mutated PscA-Leu688 and PscA-Val689 to cysteine residues in the green sulfur bacterium Chlorobaculum tepidum; these residues were predicted to interact with the special pair P840, based on sequence comparison with PS I. Spectroelectrochemical measurements showed that the L688C and V689C mutations altered a near-infrared difference spectrum upon P840 oxidation, as well as the redox potential of P840. Light-induced Fourier transform infrared difference measurements showed that the L688C mutation induced a differential signal of the S-H stretching vibration in the P840+/P840 spectrum, as reported in P800+/P800 difference spectrum in a heliobacterial RC. Spectral changes in the 131-keto C=O region, caused by both mutations, revealed corresponding changes in the electronic structure of P840 and in the hydrogen-bonding interaction at the 131-keto C=O group. These results suggest that there is a common spatial configuration around the special pair sites among type 1 RCs. The data also provided evidence that P840 has a symmetric electronic structure, as expected from a homodimeric RC. PMID:26804137

  3. Tumor Suppressor Interferon-Regulatory Factor 1 Counteracts the Germinal Center Reaction Driven by a Cancer-Associated Gammaherpesvirus

    PubMed Central

    Mboko, Wadzanai P.; Olteanu, Horatiu; Ray, Avijit; Xin, Gang; Darrah, Eric J.; Kumar, Suresh N.; Kulinski, Joseph M.; Cui, Weiguo; Dittel, Bonnie N.; Gauld, Stephen B.

    2015-01-01

    ABSTRACT Gammaherpesviruses are ubiquitous pathogens that are associated with the development of B cell lymphomas. Gammaherpesviruses employ multiple mechanisms to transiently stimulate a broad, polyclonal germinal center reaction, an inherently mutagenic stage of B cell differentiation that is thought to be the primary target of malignant transformation in virus-driven lymphomagenesis. We found that this gammaherpesvirus-driven germinal center expansion was exaggerated and lost its transient nature in the absence of interferon-regulatory factor 1 (IRF-1), a transcription factor with antiviral and tumor suppressor functions. Uncontrolled and persistent expansion of germinal center B cells led to pathological changes in the spleens of chronically infected IRF-1-deficient animals. Additionally, we found decreased IRF-1 expression in cases of human posttransplant lymphoproliferative disorder, a malignant condition associated with gammaherpesvirus infection. The results of our study define an unappreciated role for IRF-1 in B cell biology and provide insight into the potential mechanism of gammaherpesvirus-driven lymphomagenesis. IMPORTANCE Gammaherpesviruses establish lifelong infection in most adults and are associated with B cell lymphomas. While the infection is asymptomatic in many hosts, it is critical to identify individuals who may be at an increased risk of virus-induced cancer. Such identification is currently impossible, as the host risk factors that predispose individuals toward viral lymphomagenesis are poorly understood. The current study identifies interferon-regulatory factor 1 (IRF-1) to be one of such candidate host factors. Specifically, we found that IRF-1 enforces long-term suppression of an inherently mutagenic stage of B cell differentiation that gammaherpesviruses are thought to target for transformation. Correspondingly, in the absence of IRF-1, chronic gammaherpesvirus infection induced pathological changes in the spleens of infected animals

  4. Activated by Combined Magnrtic Field Gravitropic Reaction Reply on Nanodose of Biologicaly Active Compounds

    NASA Astrophysics Data System (ADS)

    Sheykina, Nadezhda; Bogatina, Nina

    The new science direction nanotechnologies initiated a big jump in the pharmacology and medicine. This leads to the big development of homeopathy. The most interest appeared while investigating of the reaction of biological object on the nano dose of iologically substances. The changing of concentration (in nmol/l) of biologically active material is also possible during weak energy action. For instance, weak combined magnetic field may change a little the concentration of ions that are oriented parallel to the external magnetic field and, by the analogy with said above, lead to the similar effects. Simple estimations give the value for the threshold to the magnetic field by two orders smaller than the geomagnetic field. By this investigation we wanted to understand whether the analogy in the action of nano dose of biologically active substances and weak combined magnetic field presents and whether the action of one of these factors may be replaced by other one. The effect of one of biologically active substances NPA (Naphtyl-Phtalame Acid) solution with the concentration 0.01 mol/l on the gravitropic reaction of cress roots was investigated. It was shown that its effect was the inhibition of cress roots gravitropic reaction. The same inhibition was achieved by the combined magnetic field action on the cress roots, germinated in water. The alternative component of the combined magnetic field coincided formally with the cyclotron frequency of NPA ions. So the analogy in the action of nano dose of biologically active substances and weak combined magnetic field was shown. The combined magnetic field using allows to decrease sufficiently the dose of biologically active substances. This fact can be of great importance in pharmacy and medicine.

  5. Self-assembled biomimetic nanoreactors II: Noble metal active centers

    NASA Astrophysics Data System (ADS)

    McTaggart, Matt; Malardier-Jugroot, Cecile; Jugroot, Manish

    2015-09-01

    The structure and stability of polymer-metal nanoreactors is detailed, including a complete characterization of the first successful synthesis of stable, dispersible, atomically thin gold nanosheets. Further developments in the synthesis of monodisperse, ∼2.5 nm platinum nanoclusters in aqueous solution and ambient conditions are described and pH stability of the composite material is established. The facile nanoreactor synthesis, environmentally friendly reaction conditions, and structural stability makes these biomimetic systems attractive for applications ranging from chemical detoxification to nanoelectronics.

  6. Fluorescence decay kinetics of wild type and D2-H117N mutant photosystem II reaction centers isolated from Chlamydomonas reinhardtii

    SciTech Connect

    Johnston, H.G.; Want, J.; Ruffle, S.V.; Sayre, R.T.; Gustafson, T.L.

    2000-05-18

    The authors compare the chlorophyll fluorescence decay kinetics of the wild type and the D2-H117N mutant photosystem II reaction centers isolated from Chlamydomonas reinhardtii. The histidine residue located at site 117 on the D2 polypeptide of photosystem II is a proposed binding site for one of two peripheral accessory chlorophylls located in the reaction center complex. The peripheral accessory chlorophylls are thought to be coupled with the primary electron donor, P680, and thus involved in energy transfer with P680. The conservative replacement of the histidine residue with an asparagine residue allows the chlorophyll to remain bound to the reaction center. However, slight changes in the structural organization of the reaction center may exist that can affect the energy transfer kinetics. The authors show that the D2-H117N mutation causes a shift in the 20--30 ps lifetime component that has been associated with energy equilibration among coupled chlorophylls in the photosystem II reaction center.

  7. Activities of the Structures Division, Lewis Research Center

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The purpose of the NASA Lewis Research Center, Structures Division's 1990 Annual Report is to give a brief, but comprehensive, review of the technical accomplishments of the Division during the past calendar year. The report is organized topically to match the Center's Strategic Plan. Over the years, the Structures Division has developed the technology base necessary for improving the future of aeronautical and space propulsion systems. In the future, propulsion systems will need to be lighter, to operate at higher temperatures and to be more reliable in order to achieve higher performance. Achieving these goals is complex and challenging. Our approach has been to work cooperatively with both industry and universities to develop the technology necessary for state-of-the-art advancement in aeronautical and space propulsion systems. The Structures Division consists of four branches: Structural Mechanics, Fatigue and Fracture, Structural Dynamics, and Structural Integrity. This publication describes the work of the four branches by three topic areas of Research: (1) Basic Discipline; (2) Aeropropulsion; and (3) Space Propulsion. Each topic area is further divided into the following: (1) Materials; (2) Structural Mechanics; (3) Life Prediction; (4) Instruments, Controls, and Testing Techniques; and (5) Mechanisms. The publication covers 78 separate topics with a bibliography containing 159 citations. We hope you will find the publication interesting as well as useful.

  8. Directionality of Electron Transfer in Type I Reaction Center Proteins: High-Frequency EPR Study of PS I with Removed Iron-Sulfur Centers.

    PubMed

    Poluektov, Oleg G; Utschig, Lisa M

    2015-10-29

    A key step of photosynthetic solar energy conversion involves rapid light-induced sequential electron-transfer steps that result in the formation of a stabilized charge-separated state. These primary reactions take place in large integral membrane reaction center (RC) proteins, wherein a series of donor/acceptor cofactors are specifically positioned for efficient electron transfer. RCs can be divided in two classes, Type I and Type II and examples of both types, photosystem I (PS I) and photosystem II (PS II), are involved in the oxygenic photosynthesis of higher plants, cyanobacteria, and algae. High-resolution X-ray crystal structures reveal that PS I and PS II contain two nearly symmetric branches of redox cofactors, termed the A and B branches. While unidirectional ET along the A branch in Type II RCs is well established, there is still a debate of whether primary photochemistry in Type I RCs is unidirectional along the A branch or bidirectional proceeding down both of the A and B branches. Light-induced electron transfer through the B branch has been observed in genetically modified PS I and in native PS I pretreated with strong reducing conditions to reduce three [4Fe-4S] clusters, the terminal electron acceptors of PS I; however, the extent of asymmetry of ET along both cofactor branches remains an open question. To prove that bidirectional ET in PS I is not simply an artifact of a reducing environment or genetic modification and to determine the degree of PS I ET asymmetry, we have examined biochemically modified Synechococcus leopoliensis PS I RCs, wherein the [4Fe-4S] clusters FX, FA, and FB have been removed to prevent secondary ET from phylloquinones (A1A/A1B) to FX. For these Fe-removed proteins, we observe that ET along both the A and B branches occurs with a ratio close to 1. Together with previously reported data, the concomitant structural and kinetic information obtained with HF EPR unambiguously proves the bidirectional nature of ET in PS I over

  9. Recent Activities on the Embrace Space Weather Regional Warning Center: the New Space Weather Data Center

    NASA Astrophysics Data System (ADS)

    Denardini, Clezio Marcos; Dal Lago, Alisson; Mendes, Odim; Batista, Inez S.; SantAnna, Nilson; Gatto, Rubens; Takahashi, Hisao; Costa, D. Joaquim; Banik Padua, Marcelo; Campos Velho, Haroldo

    2016-07-01

    On August 2007 the National Institute for Space Research started a task force to develop and operate a space weather program, which is known by the acronyms Embrace that stands for the Portuguese statement "Estudo e Monitoramento BRAasileiro de Clima Espacial" Program (Brazilian Space Weather Study and Monitoring program). The mission of the Embrace/INPE program is to monitor the Solar-Terrestrial environment, the magnetosphere, the upper atmosphere and the ground induced currents to prevent effects on technological and economic activities. The Embrace/INPE system monitors the physical parameters of the Sun-Earth environment, such as Active Regions (AR) in the Sun and solar radiation by using radio telescope, Coronal Mass Ejection (CME) information by satellite and ground-based cosmic ray monitoring, geomagnetic activity by the magnetometer network, and ionospheric disturbance by ionospheric sounders and using data collected by four GPS receiver network, geomagnetic activity by a magnetometer network, and provides a forecasting for Total Electronic Content (TEC) - 24 hours ahead - using a version of the SUPIM model which assimilates the two latter data using nudging approach. Most of these physical parameters are daily published on the Brazilian space weather program web portal, related to the entire network sensors available. Regarding outreach, it has being published a daily bulletin in Portuguese and English with the status of the space weather environment on the Sun, the Interplanetary Medium and close to the Earth. Since December 2011, all these activities are carried out at the Embrace Headquarter, a building located at the INPE's main campus. Recently, a comprehensive data bank and an interface layer are under commissioning to allow an easy and direct access to all the space weather data collected by Embrace through the Embrace web Portal. The information being released encompasses data from: (a) the Embrace Digisonde Network (Embrace DigiNet) that monitors

  10. [History and activities of the Rescue Coordination Center].

    PubMed

    Hausman, A

    1983-01-01

    The founder and first director of the C.C.R. enumerates the principles that led to the conception and the achievement of the C.C.R. He reviews the principal rescue activities during these 25 years and mentions the development of supplementary activities on safety, ergonomics and respiratory protection during the last few years.

  11. Direct observation of the active center for methane dehydroaromatization using an ultrahigh field 95Mo NMR spectroscopy.

    PubMed

    Zheng, Heng; Ma, Ding; Bao, Xinhe; Hu, Jian Zhi; Kwak, Ja Hun; Wang, Yong; Peden, Charles H F

    2008-03-26

    The use of an ultrahigh magnetic field spectrometer and 95Mo isotope enrichment facilitate the direct observation of the local structure of Mo species on Mo/zeolite catalysts by 95Mo NMR. Top trace: The experimental 95Mo NMR spectrum of 6Mo/HZSM-5. Bottom traces: The simulated overall spectrum (orange), the spectral component corresponding to MoO3 (purple), and the component corresponding to the exchanged Mo species (green). The exchanged Mo species proved to be the active center for the methane dehydroaromatization (MDA) reaction.

  12. Brain Activity, Personality Traits and Affect: Electrocortical Activity in Reaction to Affective Film Stimuli

    NASA Astrophysics Data System (ADS)

    Makvand Hosseini, Sh.; Azad Fallah, P.; Rasoolzadeh Tabatabaei, S. K.; Ghannadyan Ladani, S. H.; Heise, C.

    We studied the patterns of activation over the cerebral cortex in reaction to affective film stimuli in four groups of extroverts, introverts, neurotics and emotionally stables. Measures of extraversion and neuroticism were collected and resting EEG was recorded from 40 right handed undergraduate female students (19-23) on one occasion for five 30s periods in baseline condition and in affective states. Mean log-transformed absolute alpha power was extracted from 12 electrode sites and analyzed. Patterns of activation were different in personality groups. Different patterns of asymmetries were observed in personality groups in reaction to affective stimuli. Results were partly consistent with approach and withdrawal model and provided supportive evidence for the role of right frontal asymmetry in negative affects in two groups (introverts and emotionally stables) as well as the role of right central asymmetry (increase on right and decrease on left) in active affective states (anxiety and happiness) in all personality groups. Results were also emphasized on the role of decrease activity relative to baseline in cortical regions (bilaterally in frontal and unilaterally in left parietal and temporal regions) in moderating of positive and negative emotion.

  13. [Activities of Goddard Earth Sciences and Technology Center, Maryland University

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The Goddard Space Flight Center (GSFC) is recognized as a world leader in the application of remote sensing and modeling aimed at improving knowledge of the Earth system. The Goddard Earth Sciences Directorate plays a central role in NASA's Earth Observing System and the U.S. Global Change Research Program. Goddard Earth Sciences and Technology (GEST) is organized as a cooperative agreement with the GSFC to promote excellence in the Earth sciences, and is a consortium of universities and corporations (University of Maryland Baltimore County, Howard University, Hampton University, Caelum Research Corporation and Northrop Grumman Corporation). The aim of this new program is to attract and introduce promising students in their first or second year of graduate studies to Oceanography and Earth system science career options through hands-on instrumentation research experiences on coastal processes at NASA's Wallops Flight Facility on the Eastern Shore of Virginia.

  14. Report on Advanced Life Support Activities at Kennedy Space Center

    NASA Technical Reports Server (NTRS)

    Wheeler, Raymond M.

    2004-01-01

    Plant studies at Kennedy Space Center last year focused on selecting cultivars of lettuce, tomato, and pepper for further testing as crops for near-term space flight applications. Other testing continued with lettuce, onion, and radish plants grown at different combinations of light (PPF), temperature, and CO2 concentration. In addition, comparisons of mixed versus mono culture approaches for vegetable production were studied. Water processing testing focused on the development and testing of a rotating membrane bioreactor to increase oxygen diffusion levels for reducing total organic carbon levels and promoting nitrification. Other testing continued to study composting testing for food wastes (NRA grant) and the use of supplemental green light with red/blue LED lighting systems for plant production (NRC fellowship).

  15. Craving love? Enduring grief activates brain's reward center.

    PubMed

    O'Connor, Mary-Frances; Wellisch, David K; Stanton, Annette L; Eisenberger, Naomi I; Irwin, Michael R; Lieberman, Matthew D

    2008-08-15

    Complicated Grief (CG) occurs when an individual experiences prolonged, unabated grief. The neural mechanisms distinguishing CG from Noncomplicated Grief (NCG) are unclear, but hypothesized mechanisms include both pain-related activity (related to the social pain of loss) and reward-related activity (related to attachment behavior). Bereaved women (11 CG, 12 NCG) participated in an event-related functional magnetic resonance imaging scan, during grief elicitation with idiographic stimuli. Analyses revealed that whereas both CG and NCG participants showed pain-related neural activity in response to reminders of the deceased, only those with CG showed reward-related activity in the nucleus accumbens (NA). This NA cluster was positively correlated with self-reported yearning, but not with time since death, participant age, or positive/negative affect. This study supports the hypothesis that attachment activates reward pathways. For those with CG, reminders of the deceased still activate neural reward activity, which may interfere with adapting to the loss in the present. PMID:18559294

  16. Recent and Future Stratospheric Balloon Activities at Esrange Space Center

    NASA Astrophysics Data System (ADS)

    Kemi, Stig

    Esrange Space Center located in northern Sweden has during 45 years been a leading launch site for both sounding rockets and stratospheric balloons. We have a unique combination of maintaining both stratospheric balloons and sounding rockets launch operations. Most balloon flights are normally handled inside Scandinavia but since 2005 PersonNamesemi-circular flights are performed with recovery in northern Canada. The Swedish Government and Swedish National Space Board are now finaliz-ing an agreement with Russia for peaceful uPersonNamese of space, which will permit circumpolar balloon flights. Within this agreement we will soon be able to of-fer the science community long duration balloon flights with durations for PersonNameseveral weeks. The balloon operations at Esrange Space Center are yearly expanding. Both NASA and CNES have long term plans for balloon flights from northern Sweden. We have also received a request from JAXA for future balloon missions. To handle balloon campaigns with large numbers of payloads or build up for two different campaigns a new big assembly hall will be ready for use at the beginning of 2011. January 24 we made an historical balloon flight in a very cold stratosphere with a Zodiac metricconverterProductID402?000 m3402ü ınbsp;000 m3402 000 m3 balloon carrying a 750kg gondola with the German Mipas-B/Telis instrument. The balloon reached 34kms alti-tude after a carefully piloted ascent in temperature levels down to -89 degrees Centigrade. The scientists received unique data during the 13 hours and 30 minutes long sailing at different altitudes during slow descent. The payload was recovered in very good condition 80 kms from the border between country-regionFinland and Russia.

  17. Ultrafast and ultraslow oxygen atom transfer reactions between late metal centers.

    PubMed

    Fortner, Kevin C; Laitar, David S; Muldoon, John; Pu, Lihung; Braun-Sand, Sonja B; Wiest, Olaf; Brown, Seth N

    2007-01-24

    Oxotrimesityliridium(V), (mes)3Ir=O (mes = 2,4,6-trimethylphenyl), and trimesityliridium(III), (mes)3Ir, undergo extremely rapid degenerate intermetal oxygen atom transfer at room temperature. At low temperatures, the two complexes conproportionate to form (mes)3Ir-O-Ir(mes)3, the 2,6-dimethylphenyl analogue of which has been characterized crystallographically. Variable-temperature NMR measurements of the rate of dissociation of the mu-oxo dimer combined with measurements of the conproportionation equilibrium by low-temperature optical spectroscopy indicate that oxygen atom exchange between iridium(V) and iridium(III) occurs with a rate constant, extrapolated to 20 degrees C, of 5 x 107 M-1 s-1. The oxotris(imido)osmium(VIII) complex (ArN)3Os=O (Ar = 2,6-diisopropylphenyl) also undergoes degenerate intermetal atom transfer to its deoxy partner, (ArN)3Os. However, despite the fact that its metal-oxygen bond strength and reactivity toward triphenylphosphine are nearly identical to those of (mes)3Ir=O, the osmium complex (ArN)3Os=O transfers its oxygen atom 12 orders of magnitude more slowly to (ArN)3Os than (mes)3Ir=O does to (mes)3Ir (kOsOs = 1.8 x 10-5 M-1 s-1 at 20 degrees C). Iridium-osmium cross-exchange takes place at an intermediate rate, in quantitative agreement with a Marcus-type cross relation. The enormous difference between the iridium-iridium and osmium-osmium exchange rates can be rationalized by an analogue of the inner-sphere reorganization energy. Both Ir(III) and Ir(V) are pyramidal and can form pyramidal iridium(IV) with little energetic cost in an orbitally allowed linear approach. Conversely, pyramidalization of the planar tris(imido)osmium(VI) fragment requires placing a pair of electrons in an antibonding orbital. The unique propensity of (mes)3Ir=O to undergo intermetal oxygen atom transfer allows it to serve as an activator of dioxygen in cocatalyzed oxidations, for example, acting with osmium tetroxide to catalyze the aerobic

  18. Site-specific and compensatory mutations imply unexpected pathways for proton delivery to the QB binding site of the photosynthetic reaction center.

    PubMed Central

    Hanson, D K; Tiede, D M; Nance, S L; Chang, C H; Schiffer, M

    1993-01-01

    In photosynthetic reaction centers, a quinone molecule, QB, is the terminal acceptor in light-induced electron transfer. The protonatable residues Glu-L212 and Asp-L213 have been implicated in the binding of QB and in proton transfer to QB anions generated by electron transfer from the primary quinone QA. Here we report the details of the construction of the Ala-L212/Ala-L213 double mutant strain by site-specific mutagenesis and show that its photosynthetic incompetence is due to an inability to deliver protons to the QB anions. We also report the isolation and biophysical characterization of a collection of revertant and suppressor strains that have regained the photosynthetic phenotype. The compensatory mutations that restore function are diverse and show that neither Glu-L212 nor Asp-L213 is essential for efficient light-induced electron or proton transfer in Rhodobacter capsulatus. Second-site mutations, located within the QB binding pocket or at more distant sites, can compensate for mutations at L212 and L213 to restore photocompetence. Acquisition of a single negatively charged residue (at position L213, across the binding pocket at position L225, or outside the pocket at M43) or loss of a positively charged residue (at position M231) is sufficient to restore proton transfer activity to the complex. The proton transport pathways in the suppressor strains cannot, in principle, be identical to that of the wild type. The apparent mutability of this pathway suggests that the reaction center can serve as a model system to study the structural basis of protein-mediated proton transport. PMID:8105468

  19. A journey into the active center of nitrogenase.

    PubMed

    Hu, Yilin; Ribbe, Markus W

    2014-08-01

    Nitrogenase catalyzes the reduction of N2 to NH3, a key step in the global nitrogen cycle. This article describes our journey toward the definition of a complete molecular structure of the active site of nitrogenase, with an emphasis on the discovery of the interstitial carbide and the radical SAM-dependent insertion of this atom into the active FeMo cofactor site of nitrogenase.

  20. Formation of quaternary stereogenic centers by copper-catalyzed asymmetric conjugate addition reactions of alkenylaluminums to trisubstituted enones.

    PubMed

    Müller, Daniel; Alexakis, Alexandre

    2013-11-01

    Alkenylaluminums undergo asymmetric copper-catalyzed conjugate addition (ACA) to β-substituted enones allowing the formation of stereogenic all-carbon quaternary centers. Phosphinamine-copper complexes proved to be particularly active and selective compared with phosphoramidite ligands. After extensive optimization, high enantioselectivities (up to 96% ee) were obtained for the addition of alkenylalanes to β-substituted enones. Two strategies for the generation of the requisite alkenylaluminums were explored allowing for the introduction of aryl- and alkyl-substituted alkenyl nucleophiles. Moreover, alkyl-substituted phosphinamine (SimplePhos) ligands were identified for the first time as highly efficient ligands for the Cu-catalyzed ACA.

  1. Reaction of germinal centers in the T-cell-independent response to the bacterial polysaccharide alpha(1-->6)dextran.

    PubMed Central

    Wang, D; Wells, S M; Stall, A M; Kabat, E A

    1994-01-01

    Primary immunization of BALB/c mice with alpha(1-->6)dextran (DEX), a native bacterial polysaccharide, induces an unexpected pattern of splenic B-cell responses. After a peak of antibody-secreting B-cell response at day 4, deposition of dextran-anti-dextran immune complexes, as revealed by staining with both dextran and antibodies to dextran, occurs and persists in splenic follicles until at least the fourth week after immunization. Antigen-specific B cells appear and proliferate in such follicles, leading by day 11 to development of DEX-specific germinal centers as characterized by the presence of distinct regions of DEX+ peanut agglutinin-positive (PNA+) cells. At this time, fluorescence-activated cell sorter analysis also reveals the appearance of a distinct population of DEX+ PNA+ splenic B cells. In contrast, DEX+ PNA- cells, characterized by intense cytoplasmic staining, are present outside of splenic follicles, peak at day 4 to day 5, and persist until at least day 28. The frequency of these cells correlates with DEX-specific antibody-secreting cells, as detected by the ELISA-spot assay. Thus, in addition to the expected plasma cellular response, the typical T-cell-independent type II antigen, DEX, surprisingly also elicits the formation of antigen-specific germinal centers. These observations raise fundamental questions about the roles of germinal centers in T-cell-independent immune responses. Images PMID:7511812

  2. An Interactive Classroom Activity Demonstrating Reaction Mechanisms and Rate-Determining Steps

    ERIC Educational Resources Information Center

    Jennings, Laura D.; Keller, Steven W.

    2005-01-01

    An interactive classroom activity that includes two-step reaction of unwrapping and eating chocolate candies is described which brings not only the reaction intermediate, but also the reactants and products into macroscopic view. The qualitative activation barriers of both steps can be adjusted independently.

  3. Physical Activity and Beverages in Home- and Center-Based Child Care Programs

    ERIC Educational Resources Information Center

    Tandon, Pooja S.; Garrison, Michelle M.; Christakis, Dimitri A.

    2012-01-01

    Objective: To describe and compare obesity prevention practices related to physical activity and beverages in home- and center-based child care programs. Methods: A telephone survey of licensed home- and center-based child care programs in Florida, Massachusetts, Michigan, and Washington between October and December 2008. Results: Most programs…

  4. Report on the Activities of the Single Parent Resource Center, 1975-1976.

    ERIC Educational Resources Information Center

    Childcare Switchboard / Single Parent Resource Center, San Francisco, CA.

    This report provides a model for the provision of social services to single parents. The activities the center provides include drop-in support groups, workshops on single parent issues, a single parent magazine, individual counseling and community outreach. The report briefly specifies the goals of the center and the rationale behind its…

  5. Social Inequalities in Body Weight and Physical Activity: Exploring the Role of Fitness Centers

    ERIC Educational Resources Information Center

    McLaren, Lindsay; Rock, Melanie J.; McElgunn, Jamie

    2012-01-01

    Fitness centers are a viable option for physical activity, particularly in climates with significant weather variation. Due to variation in economic and social expressions of exclusivity, fitness centers may have some relation to social inequalities in physical inactivity and related health outcomes; thus, our objective was to explore this…

  6. GREENHOUSE GAS (GHG) MITIGATION AND MONITORING TECHNOLOGY PERFORMANCE: ACTIVITIES OF THE GHG TECHNOLOGY VERIFICATION CENTER

    EPA Science Inventory

    The paper discusses greenhouse gas (GHG) mitigation and monitoring technology performance activities of the GHG Technology Verification Center. The Center is a public/private partnership between Southern Research Institute and the U.S. EPA's Office of Research and Development. It...

  7. Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Zheng, Chong

    2004-08-19

    Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation. PMID:15330667

  8. Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Zheng, Chong

    2004-08-19

    Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.

  9. Transmission research activities at NASA Lewis Research Center

    NASA Technical Reports Server (NTRS)

    Lewicki, D. G.

    1990-01-01

    A joint research program, to advance the technology of rotorcraft transmissions, consists of analytical and experimental efforts to achieve the overall goals of reducing transmission weight and noise, while increasing life and reliability. Recent activities in the areas of transmission and related component research are highlighted. Current areas include specific technologies in support of military rotary wing aviation, gearing technology, transmission noise reduction studies, a recent interest in gearbox diagnostics, and advanced transmission system studies. Results of recent activities are presented along with near term research plans.

  10. Diffusion-controlled reaction rate to an active site

    NASA Astrophysics Data System (ADS)

    Traytak, S. D.

    1995-02-01

    The diffusion-controlled reactions of chemically anisotropic reactants are treated for the simplest model of Solc and Stockmayer (Intern. J. Chem. Kinet. 5 (1973) 733) in the absence of rotational diffusion. Using the dual series relations approach we can find the effective steric factor with any necessary accuracy. A few simple analytical approximations for the effective steric factor are proposed. The derived results we compare with the relevant analytical approximations and numerical calculations available in the literature.

  11. Ultrastructure - function relationship in Chlamydomonas reinhartii thylakoids, by means of a comparison between the wild type and the F34 mutant which lacks the photosystem II reaction center.

    PubMed

    Olive, J; Wollman, F A; Bennoun, P; Recouvreur, M

    1979-08-31

    The F34 mutant strain of Chlamydomonas reinhartii is deficient in photosystem II reaction centers. The E fracture faces of the thylakoid membranes of this mutant show a considerable reduction in the number of particles present ant in their size compared with the wild type. We conclude that the polypeptides associated with photosystem II reaction centers, which are missing in SDS polyacrylamide gel electrophoresis patterns of proteins from this mutant strain, are part of the EF particles and are required for assembly of these particles. PMID:492157

  12. Effects of reaction time variability and age on brain activity during Stroop task performance.

    PubMed

    Tam, Angela; Luedke, Angela C; Walsh, Jeremy J; Fernandez-Ruiz, Juan; Garcia, Angeles

    2015-09-01

    Variability in reaction time during task performance may reflect fluctuations in attention and cause reduced performance in goal-directed tasks, yet it is unclear whether the mechanisms behind this phenomenon change with age. Using fMRI, we tested young and cognitively healthy older adults with the Stroop task to determine whether aging affects the neural mechanisms underlying intra-individual reaction time variability. We found significant between-group differences in BOLD activity modulated by reaction time. In older adults, longer reaction times were associated with greater activity in frontoparietal attentional areas, while in younger adults longer reaction times were associated with greater activity in default mode network areas. Our results suggest that the neural correlates of reaction time variability change with healthy aging, reinforcing the concept of functional plasticity to maintain high cognitive function throughout the lifespan.

  13. Kidspiration[R] for Inquiry-Centered Activities

    ERIC Educational Resources Information Center

    Shaw, Edward L., Jr.; Baggett, Paige V.; Salyer, Barbara

    2004-01-01

    Computer technology can be integrated into science inquiry activities to increase student motivation and enhance and expand scientific thinking. Fifth-grade students used the visual thinking tools in the Kidspiration[R] software program to generate and represent a web of hypotheses around the question, "What affects the distance a marble rolls?"…

  14. Robotics-Centered Outreach Activities: An Integrated Approach

    ERIC Educational Resources Information Center

    Ruiz-del-Solar, Javier

    2010-01-01

    Nowadays, universities are making extensive efforts to attract prospective students to the fields of electrical, electronic, and computer engineering. Thus, outreach is becoming increasingly important, and activities with schoolchildren are being extensively carried out as part of this effort. In this context, robotics is a very attractive and…

  15. An Interdisciplinary, Computer-Centered Approach to Active Learning.

    ERIC Educational Resources Information Center

    Misale, Judi M.; And Others

    1996-01-01

    Describes a computer-assisted, interdisciplinary course in decision making developed to promote student participation and critical thinking. Students participate in 20 interactive exercises that utilize and illustrate psychological and economic concepts. Follow-up activities include receiving background information, group discussions, text…

  16. Hydrogen bonding and spin density distribution in the Qb semiquinone of bacterial reaction centers and comparison with the Qa site.

    PubMed

    Martin, Erik; Samoilova, Rimma I; Narasimhulu, Kupala V; Lin, Tzu-Jen; O'Malley, Patrick J; Wraight, Colin A; Dikanov, Sergei A

    2011-04-13

    In the photosynthetic reaction center from Rhodobacter sphaeroides, the primary (Q(A)) and secondary (Q(B)) electron acceptors are both ubiquinone-10, but with very different properties and functions. To investigate the protein environment that imparts these functional differences, we have applied X-band HYSCORE, a 2D pulsed EPR technique, to characterize the exchangeable protons around the semiquinone (SQ) in the Q(A) and Q(B) sites, using samples of (15)N-labeled reaction centers, with the native high spin Fe(2+) exchanged for diamagnetic Zn(2+), prepared in (1)H(2)O and (2)H(2)O solvent. The powder HYSCORE method is first validated against the orientation-selected Q-band ENDOR study of the Q(A) SQ by Flores et al. (Biophys. J.2007, 92, 671-682), with good agreement for two exchangeable protons with anisotropic hyperfine tensor components, T, both in the range 4.6-5.4 MHz. HYSCORE was then applied to the Q(B) SQ where we found proton lines corresponding to T ≈ 5.2, 3.7 MHz and T ≈ 1.9 MHz. Density functional-based quantum mechanics/molecular mechanics (QM/MM) calculations, employing a model of the Q(B) site, were used to assign the observed couplings to specific hydrogen bonding interactions with the Q(B) SQ. These calculations allow us to assign the T = 5.2 MHz proton to the His-L190 N(δ)H···O(4) (carbonyl) hydrogen bonding interaction. The T = 3.7 MHz spectral feature most likely results from hydrogen bonding interactions of O1 (carbonyl) with both Gly-L225 peptide NH and Ser-L223 hydroxyl OH, which possess calculated couplings very close to this value. The smaller 1.9 MHz coupling is assigned to a weakly bound peptide NH proton of Ile-L224. The calculations performed with this structural model of the Q(B) site show less asymmetric distribution of unpaired spin density over the SQ than seen for the Q(A) site, consistent with available experimental data for (13)C and (17)O carbonyl hyperfine couplings. The implications of these interactions for Q

  17. Delayed hemolytic transfusion reaction in adult sickle-cell disease: presentations, outcomes, and treatments of 99 referral center episodes.

    PubMed

    Habibi, Anoosha; Mekontso-Dessap, Armand; Guillaud, Constance; Michel, Marc; Razazi, Keyvan; Khellaf, Mehdi; Chami, Btissam; Bachir, Dora; Rieux, Claire; Melica, Giovanna; Godeau, Bertrand; Galacteros, Frédéric; Bartolucci, Pablo; Pirenne, France

    2016-10-01

    Delayed hemolytic transfusion reaction (DHTR) is one of the most feared complications of sickle-cell disease (SCD). We retrospectively analyzed the clinical and biological features, treatments and outcomes of 99 DHTRs occurring in 69 referral center patients over 12 years. The first clinical signs appeared a median of 9.4 [IQR, 3-22] days after the triggering transfusion (TT). The most frequent DHTR-related clinical manifestation was dark urine/hemoglobinuria (94%). Most patients (89%) had a painful vaso-occlusive crisis and 50% developed a secondary acute chest syndrome (ACS). The median [IQR] hemoglobin-concentration nadir was 5.5 [4.5-6.3] g/dL and LDH peak was 1335 [798-2086] IU/L. Overall mortality was 6%. None of the patients had been receiving chronic transfusions. Among these DHTRs, 61% were developed in previously immunized patients, 28% in patients with prior DHTR. Among Abs detected after the TT in 62% of the episodes, half are classically considered potentially harmful. No association could be established between clinical severity and immunohematological profile and/or the type and specificity of Abs detected after the TT. Management consisted of supportive care alone (53%) or with adjunctive measures (47%), including recombinant erythropoietin and sometimes rituximab and/or immunosuppressants. Additional transfusions were either ineffective or worsened hemolysis. In some cases, severe intravascular hemolysis can be likely responsible for the vascular reaction and high rates of ACS, pulmonary hypertension and (multi)organ failure. In conclusion, clinicians and patients must recognize early DHTR signs to avoid additional transfusions. For patients with a history of RBC immunization or DHTR, transfusion indications should be restricted. Am. J. Hematol. 91:989-994, 2016. © 2016 Wiley Periodicals, Inc. PMID:27348613

  18. B-side charge separation in bacterial photosynthetic reaction centers: nanosecond time scale electron transfer from HB- to QB.

    PubMed

    Kirmaier, Christine; Laible, Philip D; Hanson, Deborah K; Holten, Dewey

    2003-02-25

    We report time-resolved optical measurements of the primary electron transfer reactions in Rhodobacter capsulatus reaction centers (RCs) having four mutations: Phe(L181) --> Tyr, Tyr(M208) --> Phe, Leu(M212) --> His, and Trp(M250) --> Val (denoted YFHV). Following direct excitation of the bacteriochlorophyll dimer (P) to its lowest excited singlet state P, electron transfer to the B-side bacteriopheophytin (H(B)) gives P(+)H(B)(-) in approximately 30% yield. When the secondary quinone (Q(B)) site is fully occupied, P(+)H(B)(-) decays with a time constant estimated to be in the range of 1.5-3 ns. In the presence of excess terbutryn, a competitive inhibitor of Q(B) binding, the observed lifetime of P(+)H(B)(-) is noticeably longer and is estimated to be in the range of 4-8 ns. On the basis of these values, the rate constant for P(+)H(B)(-) --> P(+)Q(B)(-) electron transfer is calculated to be between approximately (2 ns)(-)(1) and approximately (12 ns)(-)(1), making it at least an order of magnitude smaller than the rate constant of approximately (200 ps)(-)(1) for electron transfer between the corresponding A-side cofactors (P(+)H(A)(-) --> P(+)Q(A)(-)). Structural and energetic factors associated with electron transfer to Q(B) compared to Q(A) are discussed. Comparison of the P(+)H(B)(-) lifetimes in the presence and absence of terbutryn indicates that the ultimate (i.e., quantum) yield of P(+)Q(B)(-) formation relative to P is 10-25% in the YFHV RC.

  19. Calculated protein and proton motions coupled to electron transfer: electron transfer from QA- to QB in bacterial photosynthetic reaction centers.

    PubMed

    Alexov, E G; Gunner, M R

    1999-06-29

    Reaction centers from Rhodobacter sphaeroides were subjected to Monte Carlo sampling to determine the Boltzmann distribution of side-chain ionization states and positions and buried water orientation and site occupancy. Changing the oxidation states of the bacteriochlorophyll dimer electron donor (P) and primary (QA) and secondary (QB) quinone electron acceptors allows preparation of the ground (all neutral), P+QA-, P+QB-, P0QA-, and P0QB- states. The calculated proton binding going from ground to other oxidation states and the free energy of electron transfer from QA-QB to form QAQB- (DeltaGAB) compare well with experiment from pH 5 to pH 11. At pH 7 DeltaGAB is measured as -65 meV and calculated to be -80 meV. With fixed protein positions as in standard electrostatic calculations, DeltaGAB is +170 meV. At pH 7 approximately 0.2 H+/protein is bound on QA reduction. On electron transfer to QB there is little additional proton uptake, but shifts in side chain protonation and position occur throughout the protein. Waters in channels leading from QB to the surface change site occupancy and orientation. A cluster of acids (GluL212, AspL210, and L213) and SerL223 near QB play important roles. A simplified view shows this cluster with a single negative charge (on AspL213 with a hydrogen bond to SerL233) in the ground state. In the QB- state the cluster still has one negative charge, now on the more distant AspL210. AspL213 and SerL223 move so SerL223 can hydrogen bond to QB-. These rearrangements plus other changes throughout the protein make the reaction energetically favorable.

  20. 77 FR 69604 - Agency Information Collection Activities; Comment Request; Educational Opportunity Centers...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-11-20

    ... Agency Information Collection Activities; Comment Request; Educational Opportunity Centers Program (EOC... respondents, including through the use of information technology. Please note that written comments received in response to this notice will be considered public records. Title of Collection:...

  1. 77 FR 20887 - Proposed Information Collection (National Acquisition Center Customer Response Survey) Activity...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-06

    ... AFFAIRS Proposed Information Collection (National Acquisition Center Customer Response Survey) Activity; Comment Request AGENCY: Office of Acquisition and Logistics, Department of Veterans Affairs. ACTION: Notice. SUMMARY: The Office of Acquisition and Logistics (OAL), Department of Veterans Affairs (VA),...

  2. 77 FR 38398 - Agency Information Collection (National Acquisition Center Customer Response Survey) Activities...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-27

    ... AFFAIRS Agency Information Collection (National Acquisition Center Customer Response Survey) Activities Under OMB Review AGENCY: Office of Acquisition and Logistics, Department of Veterans Affairs. ACTION... notice announces that the Office of Acquisition and Logistics, Department of Veterans Affairs,...

  3. Classroom Activities: Simple Strategies to Incorporate Student-Centered Activities within Undergraduate Science Lectures

    PubMed Central

    Lom, Barbara

    2012-01-01

    The traditional science lecture, where an instructor delivers a carefully crafted monolog to a large audience of students who passively receive the information, has been a popular mode of instruction for centuries. Recent evidence on the science of teaching and learning indicates that learner-centered, active teaching strategies can be more effective learning tools than traditional lectures. Yet most colleges and universities retain lectures as their central instructional method. This article highlights several simple collaborative teaching techniques that can be readily deployed within traditional lecture frameworks to promote active learning. Specifically, this article briefly introduces the techniques of: reader’s theatre, think-pair-share, roundtable, jigsaw, in-class quizzes, and minute papers. Each technique is broadly applicable well beyond neuroscience courses and easily modifiable to serve an instructor’s specific pedagogical goals. The benefits of each technique are described along with specific examples of how each technique might be deployed within a traditional lecture to create more active learning experiences. PMID:23494568

  4. UAS Related Activities at NASA's Dryden Flight Research Center

    NASA Technical Reports Server (NTRS)

    Bauer, Jeffrey E.

    2009-01-01

    NASA s Dryden Flight Research Center is completing its refurbishment and initial flights of one the pre-production Global Hawk aircraft it received from the U.S. Air Force. NASA Dryden has an agreement with the Global Hawk s manufacturer, Northrop Grumman, to partner in the refurbishment and flight operations of the vehicles. The National Oceanic and Atmospheric Administration (NOAA) has also partnered on the project and is assisting NASA with project management and pilot responsibilities for the aircraft. NASA and NOAA will be using the Global Hawks to conduct earth science research. The earth science community is increasing utilizing UAS of all sizes and capabilities to collect important data on a variety of issues including important global climate change issues. To pursue the data collection needs of the science community there is a growing demand for international collaboration with respect to operating UAS in global airspace. Operations of NASA s Ikhana aircraft continued this past year. The Ikhana is a modified Predator B UAS. A UAS dedicated to research at NASA Dryden is the X-48B blended wing body research aircraft. Flight tests with the 500- pound, remotely piloted test vehicle are now in a block 4 phase involving parameter identification and maneuvers to research the limits of the engine in stall situations. NASA s participation in the blended wing body research effort is focused on fundamental, advanced flight dynamics and structural design concepts within the Subsonic Fixed Wing project, part of the Fundamental Aeronautics program managed through NASA s Aeronautics Research Mission Directorate. Potential benefits of the aircraft include increased volume for carrying capacity, efficient aerodynamics for reduced fuel burn and possibly significant reductions in noise due to propulsion integration options. NASA Dryden continues to support the UAS industry by facilitating access to three specially designated test areas on Edwards Air Force Base for the

  5. Beyond active learning: a case study of teaching practices in an occupation-centered curriculum.

    PubMed

    Hooper, Barbara

    2006-01-01

    Although occupation-centered curricula are highly promoted, the teaching processes that convey such designs remain unclear. This case study elucidated occupation-centered teaching practices. Interview and observational data were collected over 8 weeks, and analysis involved coding transcriptions, data matrices, concept maps, journaling, and writing. Participants augmented active learning strategies with strategies that linked course topics to the subject of occupation. The use of linking strategies suggested that: (a) course content was treated as two-tiered; (b) neither content nor instructional processes were inherently occupation-centered; and (c) subject-centered education strengthens social learning theories. Although curricula may appear occupation-centered based on a curriculum description and course content, ultimately "linking opportunities" in the classroom constitute an essential feature that demarcates a program as occupation-centered.

  6. City Kids and City Critters! Activities for Urban Explorers from the Houston Arboretum & Nature Center.

    ERIC Educational Resources Information Center

    Roberts, Janet Wier; Huelbig, Carole

    This guide contains activities from the Houston Arboretum and Nature Center programs for children ages 8 to 12 years. The multisensory activities help students improve their observational skills and utilize activity sheets, journals, and hands-on projects to involve them. Children observe, draw, and photograph animals in their natural settings and…

  7. Kinetics of acrylamide formation/elimination reactions as affected by water activity.

    PubMed

    De Vleeschouwer, Kristel; Van der Plancken, Iesel; Van Loey, Ann; Hendrickx, Marc E

    2007-01-01

    The influence of water activity on the kinetics of acrylamide formation and elimination reaction was investigated using low-moisture equimolar asparagine-glucose model systems, which were heated at temperatures between 120 and 200 degrees C for variable heating times. To determine the water content corresponding to the water activities tested, a sorption moisture isotherm was constructed experimentally. The acrylamide concentrations measured at different water activities could be modeled on the basis of a reaction scheme including not only acrylamide formation and elimination reactions but also an alternative Maillard reaction between both reactants. The corresponding rate constants and activation energies were estimated using nonlinear regression analysis. Whereas the rate constant for acrylamide formation varied only slightly with the initial water activity of the model system, the elimination rate constant showed a clear minimum around a water activity of 0.82. The opposite trend, namely, a maximum at a water activity of 0.82, was found for the Maillard reaction rate constant as a function of water activity, which confirms data from literature. The activation energies for the different reactions changed in a comparable way as the corresponding rate constant with water activity. PMID:17503764

  8. Molecular characterization of PsbW, a nuclear-encoded component of the photosystem II reaction center complex in spinach.

    PubMed Central

    Lorković, Z J; Schröder, W P; Pakrasi, H B; Irrgang, K D; Herrmann, R G; Oelmüller, R

    1995-01-01

    We describe the isolation and characterization of cDNAs encoding the precursor polypeptide of the 6.1-kDa polypeptide associated with the reaction center core of the photosystem II complex from spinach. PsbW, the gene encoding this polypeptide, is present in a single copy per haploid genome. The mature polypeptide with 54 amino acid residues is characterized by a hydrophobic transmembrane segment, and, although an intrinsic membrane protein, it carries a bipartite transit peptide of 83 amino acid residues which directs the N terminus of the mature protein into the chloroplast lumen. Thylakoid integration of this polypeptide does not require a delta pH across the membrane, nor is it azide-sensitive, suggesting that the polypeptide chain inserts spontaneously in an as yet unknown way. The PsbW mRNA levels are light regulated. Similar to cytochrome b559 and PsbS, but different from the chlorophyll-complexing polypeptides D1, D2, CP43, and CP47 of photosystem II, PsbW is present in etiolated spinach seedlings. Images Fig. 1 Fig. 4 Fig. 5 Fig. 6 PMID:7568046

  9. Charge Recombination and Protein Dynamics in Bacterial Photosynthetic Reaction Centers Entrapped in a Sol-Gel Matrix

    PubMed Central

    Kriegl, Jan M.; Forster, Florian K.; Nienhaus, G. Ulrich

    2003-01-01

    Many proteins can be immobilized in silica hydrogel matrices without compromising their function, making this a suitable technique for biosensor applications. Immobilization will in general affect protein structure and dynamics. To study these effects, we have measured the P+QA− charge recombination kinetics after laser excitation of QB-depleted wild-type photosynthetic reaction centers from Rhodobacter sphaeroides in a tetramethoxysilane (TMOS) sol-gel matrix and, for comparison, also in cryosolvent. The nonexponential electron transfer kinetics observed between 10 and 300 K were analyzed quantitatively using the spin boson model for the intrinsic temperature dependence of the electron transfer and an adiabatic change of the energy gap and electronic coupling caused by protein motions in response to the altered charge distributions. The analysis reveals similarities and differences in the TMOS-matrix and bulk-solvent samples. In both preparations, electron transfer is coupled to the same spectrum of low frequency phonons. As in bulk solvent, charge-solvating protein motions are present in the TMOS matrix. Large-scale conformational changes are arrested in the hydrogel, as evident from the nonexponential kinetics even at room temperature. The altered dynamics is likely responsible for the observed changes in the electronic coupling matrix element. PMID:12944298

  10. EPR and ENDOR Investigation of Rhodosemiquinone in Bacterial Reaction Centers Formed by B-Branch Electron Transfer

    PubMed Central

    Paddock, M. L.; Flores, M.; Isaacson, R.; Shepherd, J. N.

    2010-01-01

    In photosynthetic bacteria, light-induced electron transfer takes place in a protein called the reaction center (RC) leading to the reduction of a bound ubiquinone molecule, QB, coupled with proton binding from solution. We used electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) to study the magnetic properties of the protonated semiquinone, an intermediate proposed to play a role in proton coupled electron transfer to QB. To stabilize the protonated semiquinone state, we used a ubiquinone derivative, rhodoquinone, which as a semiquinone is more easily protonated than ubisemiquinone. To reduce this low-potential quinone we used mutant RCs modified to directly reduce the quinone in the QB site via B-branch electron transfer (Paddock et al. in Biochemistry 44:6920–6928, 2005). EPR and ENDOR signals were observed upon illumination of mutant RCs in the presence of rhodoquinone. The EPR signals had g values characteristic of rhodosemiquinone (gx = 2.0057, gy = 2.0048, gz ∼ 2.0018) at pH 9.5 and were changed at pH 4.5. The ENDOR spectrum showed couplings due to solvent exchangeable protons typical of hydrogen bonds similar to, but different from, those found for ubisemiquinone. This approach should be useful in future magnetic resonance studies of the protonated semiquinone. PMID:20157643

  11. Role of Intramolecular Vibrations in Long-Range Electron Transfer between Pheophytin and Ubiquinone in Bacterial Photosynthetic Reaction Centers

    PubMed Central

    Borrelli, Raffaele; Di Donato, Mariangela; Peluso, Andrea

    2005-01-01

    The dynamics of the elementary electron transfer step between pheophytin and primary ubiquinone in bacterial photosynthetic reaction centers is investigated by using a discrete state approach, including only the intramolecular normal modes of vibration of the two redox partners. The whole set of normal coordinates of the acceptor and donor groups have been employed in the computations of the Hamiltonian matrix, to reliably account both for shifts and mixing of the normal coordinates, and for changes in vibrational frequencies upon ET. It is shown that intramolecular modes provide not only a discrete set of states more strongly coupled to the initial state but also a quasicontinuum of weakly coupled states, which account for the spreading of the wave packet after ET. The computed transition probabilities are sufficiently high for asserting that electron transfer from bacteriopheophytin to the primary quinone can occur via tunneling solely promoted by intramolecular modes; the transition times, computed for different values of the electronic energy difference and coupling term, are of the same order of magnitude (102 ps) of the observed one. PMID:15894646

  12. Reaction Control System Thruster Cracking Consultation: NASA Engineering and Safety Center (NESC) Materials Super Problem Resolution Team (SPRT) Findings

    NASA Technical Reports Server (NTRS)

    MacKay, Rebecca A.; Smith, Stephen W.; Shah, Sandeep R.; Piascik, Robert S.

    2005-01-01

    The shuttle orbiter s reaction control system (RCS) primary thruster serial number 120 was found to contain cracks in the counter bores and relief radius after a chamber repair and rejuvenation was performed in April 2004. Relief radius cracking had been observed in the 1970s and 1980s in seven thrusters prior to flight; however, counter bore cracking had never been seen previously in RCS thrusters. Members of the Materials Super Problem Resolution Team (SPRT) of the NASA Engineering and Safety Center (NESC) conducted a detailed review of the relevant literature and of the documentation from the previous RCS thruster failure analyses. It was concluded that the previous failure analyses lacked sufficient documentation to support the conclusions that stress corrosion cracking or hot-salt cracking was the root cause of the thruster cracking and lacked reliable inspection controls to prevent cracked thrusters from entering the fleet. The NESC team identified and performed new materials characterization and mechanical tests. It was determined that the thruster intergranular cracking was due to hydrogen embrittlement and that the cracking was produced during manufacturing as a result of processing the thrusters with fluoride-containing acids. Testing and characterization demonstrated that appreciable environmental crack propagation does not occur after manufacturing.

  13. Evolutionary origins of the photosynthetic water oxidation cluster: bicarbonate permits Mn(2+) photo-oxidation by anoxygenic bacterial reaction centers.

    PubMed

    Khorobrykh, Andrei; Dasgupta, Jyotishman; Kolling, Derrick R J; Terentyev, Vasily; Klimov, Vyacheslav V; Dismukes, G Charles

    2013-09-23

    The enzyme that catalyzes water oxidation in oxygenic photosynthesis contains an inorganic cluster (Mn4 CaO5 ) that is universally conserved in all photosystem II (PSII) protein complexes. Its hypothesized precursor is an anoxygenic photobacterium containing a type 2 reaction center as photo-oxidant (bRC2, iron-quinone type). Here we provide the first experimental evidence that a native bRC2 complex can catalyze the photo-oxidation of Mn(2+) to Mn(3+) , but only in the presence of bicarbonate concentrations that allows the formation of (bRC2)Mn(2+) (bicarbonate)1-2 complexes. Parallel-mode EPR spectroscopy was used to characterize the photoproduct, (bRC2)Mn(3+) (CO3 (2-) ), based on the g tensor and (55) Mn hyperfine splitting. (Bi)carbonate coordination extends the lifetime of the Mn(3+) photoproduct by slowing charge recombination. Prior electrochemical measurements show that carbonate complexation thermodynamically stabilizes the Mn(3+) product by 0.9-1 V relative to water ligands. A model for the origin of the water oxidation catalyst is presented that proposes chemically feasible steps in the evolution of oxygenic PSIIs, and is supported by literature results on the photoassembly of contemporary PSIIs.

  14. Attitudinal Effects of a Student-Centered Active Learning Environment

    NASA Astrophysics Data System (ADS)

    Oliver-Hoyo, Maria T.; Allen, Deedee

    2005-06-01

    The importance of attitudes toward science has risen from widely accepted assumptions that achievement and attitude are positively interdependent and that affective variables are as important as cognitive variables in molding student learning. This report examines the effect on student attitudes toward learning chemistry in an active learning environment that has incorporated elements believed to positively influence student attitudes toward science including cooperative learning, hands-on activities, real-world applications, and engaging technology. These elements were considered for synergetic effects and not as individual contributors to the overall results. Two different sections of the same general chemistry course participated. The lecture setting was used as the control. Residualized gain scores were used to compare net changes in student attitudes. Data were analyzed for possible differences in gain for different academic majors. Anxiety in chemistry was monitored for the two class settings in three areas, learning in chemistry, chemistry evaluation, and chemical handling. Qualitative student feedback was also collected and is summarized in this report on the attitudinal aspects of instruction.

  15. Activation of defence reactions in Solanaceae: where is the specificity?

    PubMed

    Desender, Sabine; Andrivon, Didier; Val, Florence

    2007-01-01

    When a potential pathogen attempts to infect a plant, biochemical and molecular communication takes place and leads to the induction of plant defence mechanisms. In the case of efficient defence, visible symptoms are restricted and the pathogen does not multiply (incompatible interaction); when defence is inefficient, the plant becomes rapidly infected (compatible interaction). During the last 30 years, a growing body of knowledge on plant-pathogen interactions has been gathered, and a large number of studies investigate the induction of various plant defence reactions by pathogens or by pathogen-derived compounds. However, as most papers focus on incompatible interactions, there is still a lack of understanding about the similarities and differences between compatible and incompatible situations. This review targets the question of specificity in Solanaceae-pathogen interactions, by comparing defence patterns in plants challenged with virulent or avirulent pathogens (or with pathogen-associated molecular patterns from these). A special emphasis is made on analysing whether defence reactions in Solanaceae depend primarily on the type of elicitor, on the plant genotype/species, or on the type of interaction (compatible or incompatible).

  16. Constraint based scheduling for the Goddard Space Flight Center distributed Active Archive Center's data archive and distribution system

    NASA Technical Reports Server (NTRS)

    Short, Nick, Jr.; Bedet, Jean-Jacques; Bodden, Lee; Boddy, Mark; White, Jim; Beane, John

    1994-01-01

    The Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC) has been operational since October 1, 1993. Its mission is to support the Earth Observing System (EOS) by providing rapid access to EOS data and analysis products, and to test Earth Observing System Data and Information System (EOSDIS) design concepts. One of the challenges is to ensure quick and easy retrieval of any data archived within the DAAC's Data Archive and Distributed System (DADS). Over the 15-year life of EOS project, an estimated several Petabytes (10(exp 15)) of data will be permanently stored. Accessing that amount of information is a formidable task that will require innovative approaches. As a precursor of the full EOS system, the GSFC DAAC with a few Terabits of storage, has implemented a prototype of a constraint-based task and resource scheduler to improve the performance of the DADS. This Honeywell Task and Resource Scheduler (HTRS), developed by Honeywell Technology Center in cooperation the Information Science and Technology Branch/935, the Code X Operations Technology Program, and the GSFC DAAC, makes better use of limited resources, prevents backlog of data, provides information about resources bottlenecks and performance characteristics. The prototype which is developed concurrently with the GSFC Version 0 (V0) DADS, models DADS activities such as ingestion and distribution with priority, precedence, resource requirements (disk and network bandwidth) and temporal constraints. HTRS supports schedule updates, insertions, and retrieval of task information via an Application Program Interface (API). The prototype has demonstrated with a few examples, the substantial advantages of using HTRS over scheduling algorithms such as a First In First Out (FIFO) queue. The kernel scheduling engine for HTRS, called Kronos, has been successfully applied to several other domains such as space shuttle mission scheduling, demand flow manufacturing, and avionics communications

  17. Estimating Youth Locomotion Ground Reaction Forces Using an Accelerometer-Based Activity Monitor

    PubMed Central

    Neugebauer, Jennifer M.; Hawkins, David A.; Beckett, Laurel

    2012-01-01

    To address a variety of questions pertaining to the interactions between physical activity, musculoskeletal loading and musculoskeletal health/injury/adaptation, simple methods are needed to quantify, outside a laboratory setting, the forces acting on the human body during daily activities. The purpose of this study was to develop a statistically based model to estimate peak vertical ground reaction force (pVGRF) during youth gait. 20 girls (10.9±0.9 years) and 15 boys (12.5±0.6 years) wore a Biotrainer AM over their right hip. Six walking and six running trials were completed after a standard warm-up. Average AM intensity (g) and pVGRF (N) during stance were determined. Repeated measures mixed effects regression models to estimate pVGRF from Biotrainer activity monitor acceleration in youth (girls 10–12, boys 12–14 years) while walking and running were developed. Log transformed pVGRF had a statistically significant relationship with activity monitor acceleration, centered mass, sex (girl), type of locomotion (run), and locomotion type-acceleration interaction controlling for subject as a random effect. A generalized regression model without subject specific random effects was also developed. The average absolute differences between the actual and predicted pVGRF were 5.2% (1.6% standard deviation) and 9% (4.2% standard deviation) using the mixed and generalized models, respectively. The results of this study support the use of estimating pVGRF from hip acceleration using a mixed model regression equation. PMID:23133564

  18. Centering perspectives on Black women, hair politics, and physical activity.

    PubMed

    Versey, H Shellae

    2014-05-01

    As researchers categorize issues facing Black women's health, obesity and physical exercise continue to be significant topics of debate. General interventions targeted toward Black women to address obesity and increase physical exercise have been largely ineffective. In this article, I situate the current public health discourse on obesity and related interventions within a sociocultural context of body appearance, with a specific focus on hair. Why do some African American women feel such strong ties to their hair that they will avoid exercise? What can be done to understand this phenomenon and address alternatives that may make both hair maintenance and regular exercise feasible? I map a theoretical argument for why hair matters for some women, and discuss how physical activity intervention strategies might be improved by considering such complexities.

  19. Synthesis of multisubstituted pyrroles from doubly activated cyclopropanes using an iron-mediated oxidation domino reaction.

    PubMed

    Zhang, Zhiguo; Zhang, Wei; Li, Junlong; Liu, Qingfeng; Liu, Tongxin; Zhang, Guisheng

    2014-11-21

    An alternative route has been developed for the construction of multisubstituted pyrrole derivatives from readily available, doubly activated cyclopropanes and anilines using an iron-mediated oxidation domino reaction (i.e., sequential ring-opening, cyclization, and dehydrogenation reactions). This reaction uses readily available reactants and is tolerant of a broad range of substrates, with the desired products being formed in good to excellent yields. PMID:25330125

  20. Abnormal germinal center reactions in systemic lupus erythematosus demonstrated by blockade of CD154-CD40 interactions

    PubMed Central

    Grammer, Amrie C.; Slota, Rebecca; Fischer, Randy; Gur, Hanan; Girschick, Hermann; Yarboro, Cheryl; Illei, Gabor G.; Lipsky, Peter E.

    2003-01-01

    To determine the role of CD154-CD40 interactions in the B cell overactivity exhibited by patients with active systemic lupus erythematosus (SLE), CD19+ peripheral B cells were examined before and after treatment with humanized anti-CD154 mAb (BG9588, 5c8). Before treatment, SLE patients manifested activated B cells that expressed CD154, CD69, CD38, CD5, and CD27. Cells expressing CD38, CD5, or CD27 disappeared from the periphery during treatment with anti-CD154 mAb, and cells expressing CD69 and CD154 disappeared from the periphery during the post-treatment period. Before treatment, active-SLE patients had circulating CD38bright Ig-secreting cells that were not found in normal individuals. Disappearance of this plasma cell subset during treatment was associated with decreases in anti–double-stranded DNA (anti-dsDNA) Ab levels, proteinuria, and SLE disease activity index. Consistent with this finding, peripheral B cells cultured in vitro spontaneously proliferated and secreted Ig in a manner that was inhibited by anti-CD154 mAb. Finally, the CD38+/++IgD+, CD38+++, and CD38+IgD– B cell subsets present in the peripheral blood also disappeared following treatment with humanized anti-CD154. Together, these results indicate that patients with active lupus nephritis exhibit abnormalities in the peripheral B cell compartment that are consistent with intensive germinal center activity, are driven via CD154-CD40 interactions, and may reflect or contribute to the propensity of these patients to produce autoantibodies. PMID:14617752

  1. Abnormal germinal center reactions in systemic lupus erythematosus demonstrated by blockade of CD154-CD40 interactions.

    PubMed

    Grammer, Amrie C; Slota, Rebecca; Fischer, Randy; Gur, Hanan; Girschick, Hermann; Yarboro, Cheryl; Illei, Gabor G; Lipsky, Peter E

    2003-11-01

    To determine the role of CD154-CD40 interactions in the B cell overactivity exhibited by patients with active systemic lupus erythematosus (SLE), CD19+ peripheral B cells were examined before and after treatment with humanized anti-CD154 mAb (BG9588, 5c8). Before treatment, SLE patients manifested activated B cells that expressed CD154, CD69, CD38, CD5, and CD27. Cells expressing CD38, CD5, or CD27 disappeared from the periphery during treatment with anti-CD154 mAb, and cells expressing CD69 and CD154 disappeared from the periphery during the post-treatment period. Before treatment, active-SLE patients had circulating CD38 (bright) Ig-secreting cells that were not found in normal individuals. Disappearance of this plasma cell subset during treatment was associated with decreases in anti-double-stranded DNA (anti-dsDNA) Ab levels, proteinuria, and SLE disease activity index. Consistent with this finding, peripheral B cells cultured in vitro spontaneously proliferated and secreted Ig in a manner that was inhibited by anti-CD154 mAb. Finally, the CD38(+/++)IgD(+), CD38(+++), and CD38(+)IgD(-) B cell subsets present in the peripheral blood also disappeared following treatment with humanized anti-CD154. Together, these results indicate that patients with active lupus nephritis exhibit abnormalities in the peripheral B cell compartment that are consistent with intensive germinal center activity, are driven via CD154-CD40 interactions, and may reflect or contribute to the propensity of these patients to produce autoantibodies.

  2. [Automation of immunohematologic testing activities at French blood transfusion centers].

    PubMed

    Muller, A; Girard, M

    1983-11-01

    In May 1982, a questionnaire was sent to all of the 170 French Blood Transfusion Services (BTS), on behalf of the French Society of Blood Transfusion. The purpose was to determine the types of automated equipment used for immunohematological controls, the way in which they are used and the result of automation and computerization in daily laboratory operations. We received 135 replies (80%). A generalized conclusion can be drawn from the collected information. 50% of the respondents are neither automated nor computerized. 30% are both automated and computerized. 10% are automated but not computerized and 8% are not automated but are computerized. In the field of automated serology there is an increased tendency to complete the ABO/Rh testing by Cc D Ee and Kell phenotyping. The use of computers allows the current test determination to be compared with previous donation data. However, no fully automated equipment, which can conduct antibody screening, exists, cost effectively, in small or average BTS. In France, there has been a significant increase in automation between 1970 and 1980 but only the most important BTS have carried out automation at the same time as computerization. The smaller BTS have usually become automated without becoming computerized. In 1978, Codabar was first used. This has been one of the principal advances of the last 10 years, allowing all the users of automation to start moving towards complete computerization. This advance was assisted by the use of prepackaged software. This questionnaire also determined that the current emphasis is now to computerize administrative and management activities before laboratory activities. This survey has been conducted during a turning point of the automation of French BTS. It shows that they are, on the whole, satisfied with their automation. As far as the safety and the efficiency of the service are concerned, it is only fair to consider that the main purposes of the automation have been achieved. But

  3. Coevolution between human's anticancer activities and functional foods from crop origin center in the world.

    PubMed

    Zeng, Ya-Wen; Du, Juan; Pu, Xiao-Ying; Yang, Jia-Zhen; Yang, Tao; Yang, Shu-Ming; Yang, Xiao-Meng

    2015-01-01

    Cancer is the leading cause of death around the world. Anticancer activities from many functional food sources have been reported in years, but correlation between cancer prevalence and types of food with anticancer activities from crop origin center in the world as well as food source with human migration are unclear. Hunger from food shortage is the cause of early human evolution from Africa to Asia and later into Eurasia. The richest functional foods are found in crop origin centers, housing about 70% in the world populations. Crop origin centers have lower cancer incidence and mortality in the world, especially Central Asia, Middle East, Southwest China, India and Ethiopia. Asia and Africa with the richest anticancer crops is not only the most important evolution base of humans and origin center of anticancer functional crop, but also is the lowest mortality and incidence of cancers in the world. Cancer prevention of early human migrations was associated with functional foods from crop origin centers, especially Asia with four centers and one subcenter of crop origin, accounting for 58% of the world population. These results reveal that coevolution between human's anticancer activities associated with functional foods for crop origin centers, especially in Asia and Africa. PMID:25824728

  4. NNDC Stand: Activities and Services of the National Nuclear Data Center

    SciTech Connect

    Pritychenko, B.; Arcilla, R.; Burrows, T.W.; Dunford, C.L.; Herman, M.W.; McLane, V.; Oblozinsky, P.; Sonzogni, A.A.; Tuli, J.K.; Winchell, D.F.

    2005-05-24

    The National Nuclear Data Center (NNDC) collects, evaluates, and disseminates nuclear physics data for basic nuclear research, applied nuclear technologies including energy, shielding, medical and homeland security. In 2004, to answer the needs of nuclear data users community, NNDC completed a project to modernize data storage and management of its databases and began offering new nuclear data Web services. The principles of database and Web application development as well as related nuclear reaction and structure database services are briefly described.

  5. Kinetics of H+ ion binding by the P+QA-state of bacterial photosynthetic reaction centers: rate limitation within the protein.

    PubMed Central

    Maróti, P; Wraight, C A

    1997-01-01

    The kinetics of flash-induced H+ ion binding by isolated reaction centers (RCs) of Rhodobacter sphaeroides, strain R-26, were measured, using pH indicators and conductimetry, in the presence of terbutryn to block electron transfer between the primary and secondary quinones (QA and QB), and in the absence of exogenous electron donors to the oxidized primary donor, P+, i.e., the P+QA-state. Under these conditions, proton binding by RCs is to the protein rather than to any of the cofactors. After light activation to form P+QA-, the kinetics of proton binding were monoexponential at all pH values studied. At neutral pH, the apparent bimolecular rate constant was close to the diffusional limit for proton transfer in aqueous solution (approximately 10(11) M-1 s-1), but increased significantly in the alkaline pH range (e.g., 2 x 10(13) M-1 s-1 at pH 10). The average slope of the pH dependence was -0.4 instead of -1.0, as might be expected for a H+ diffusion-controlled process. High activation energy (0.54 eV at pH 8.0) and weak viscosity dependence showed that H+ ion uptake by RCs is not limited by diffusion. The salt dependence of the H+ ion binding rate and the pK values of the protonatable amino acid residues of the reaction center implicated surface charge influences, and Gouy-Chapman theory provided a workable description of the ionic effects as arising from modulation of the pH at the surface of the RC. Incubation in D2O caused small increases in the pKs of the protonatable groups and a small, pH (pD)-dependent slowing of the binding rate. The salt, pH, temperature, viscosity, and D2O dependences of the proton uptake by RCs in the P+QA- state were accounted for by three considerations: 1) parallel pathways of H+ delivery to the RC, contributing to the observed (net) H+ disappearance; 2) rate limitation of the protonation of target groups within the protein by conformational dynamics; and 3) electrostatic influences of charged groups in the protein, via the surface p

  6. Kinetics of H+ ion binding by the P+QA-state of bacterial photosynthetic reaction centers: rate limitation within the protein.

    PubMed

    Maróti, P; Wraight, C A

    1997-07-01

    The kinetics of flash-induced H+ ion binding by isolated reaction centers (RCs) of Rhodobacter sphaeroides, strain R-26, were measured, using pH indicators and conductimetry, in the presence of terbutryn to block electron transfer between the primary and secondary quinones (QA and QB), and in the absence of exogenous electron donors to the oxidized primary donor, P+, i.e., the P+QA-state. Under these conditions, proton binding by RCs is to the protein rather than to any of the cofactors. After light activation to form P+QA-, the kinetics of proton binding were monoexponential at all pH values studied. At neutral pH, the apparent bimolecular rate constant was close to the diffusional limit for proton transfer in aqueous solution (approximately 10(11) M-1 s-1), but increased significantly in the alkaline pH range (e.g., 2 x 10(13) M-1 s-1 at pH 10). The average slope of the pH dependence was -0.4 instead of -1.0, as might be expected for a H+ diffusion-controlled process. High activation energy (0.54 eV at pH 8.0) and weak viscosity dependence showed that H+ ion uptake by RCs is not limited by diffusion. The salt dependence of the H+ ion binding rate and the pK values of the protonatable amino acid residues of the reaction center implicated surface charge influences, and Gouy-Chapman theory provided a workable description of the ionic effects as arising from modulation of the pH at the surface of the RC. Incubation in D2O caused small increases in the pKs of the protonatable groups and a small, pH (pD)-dependent slowing of the binding rate. The salt, pH, temperature, viscosity, and D2O dependences of the proton uptake by RCs in the P+QA- state were accounted for by three considerations: 1) parallel pathways of H+ delivery to the RC, contributing to the observed (net) H+ disappearance; 2) rate limitation of the protonation of target groups within the protein by conformational dynamics; and 3) electrostatic influences of charged groups in the protein, via the surface pH.

  7. Ligand-free Heck reaction: Pd(OAc)2 as an active catalyst revisited.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Yang, Zhi

    2003-09-19

    Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K(3)PO(4) and N,N-dimethylacetamide being the optimal base and solvent, respectively. PMID:12968913

  8. An Activation Energy Experiment for a Second-Order Reaction in a Single Laboratory Period.

    ERIC Educational Resources Information Center

    Barile, Raymond C.; Michiels, Leo P.

    1983-01-01

    Describes modification of a chemical reaction to a single 4 1/2-hour laboratory period. Reaction kinetics between 2, 4-initrochlorobenzene and piperidine to form 2, 4-dinitrophenyl-piperidine and piperidinium hydrochloride are followed conductometrically at three temperatures to obtain data to calculate activation parameters. (Author/JN)

  9. Ligand-free Heck reaction: Pd(OAc)2 as an active catalyst revisited.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Yang, Zhi

    2003-09-19

    Palladium acetate was shown to be an extremely active catalyst for the Heck reaction of aryl bromides. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K(3)PO(4) and N,N-dimethylacetamide being the optimal base and solvent, respectively.

  10. Social inequalities in body weight and physical activity: exploring the role of fitness centers.

    PubMed

    McLaren, Lindsay; Rock, Melanie J; McElgunn, Jamie

    2012-03-01

    Fitness centers are a viable option for physical activity, particularly in climates with significant weather variation. Due to variation in economic and social expressions ofexclusivity, fitness centers may have some relation to social inequalities in physical inactivity and related health outcomes; thus, our objective was to explore this relation. Using publicly available data and guided by Bourdieu's theory of habitus, we classified fitness centers in Calgary, Canada, on three dimensions of exclusivity (economic, social, and appearance). We found that, although some highly exclusive centers exist, most demonstrated low exclusivity based on our dimensions. An overall contribution of centers to inequalities appears to be limited; however, caution is warranted in light of cutbacks to municipal budgets that can have an impact on publicly funded facilities.

  11. High energy halogen atom reactions activated by nuclear transformations. Progress report, February 15, 1979-February 14, 1980

    SciTech Connect

    Rack, E.P.

    1980-02-01

    The program consists of six interrelated areas: (1) Reactions of iodine with alkenes and alkynes activated by radiative neutron capture and isomeric transition in low pressure gaseous systems employing additives and rare gas moderators, high pressure, and liquid systems. Special attention was given to the reactivity of excited complex formation and structural effects of electrophilic iodine attack on various pi-bond systems. (2) The gas-to-condensed phase transition in halogen high energy chemistry. Current interest involves the study of caging effects of an ice lattice on recombination reactions involving neutron-irradiated frozen aqueous solutions of halogenated organic and biochemical solutes in order to learn more about kinetic energy effects, halogen size, solute molecule size, steric effects and hydrogen bonding within an ice lattice cage. (3) Systematics of halogen hot atom reactions. The reactions of /sup 80m/Br, /sup 80/Br, /sup 82m/Br + /sup 82/Br, /sup 82/Br, /sup 82/Br, /sup 128/I, /sup 130/I, and /sup 130m/I + /sup 130/I activated by radiative neutron capture or isomeric transition in hydrocarbons and halo-substituted alkanes in low pressure and high pressure gaseous systems employing additives and rare gas moderators are currently being studied. (4) Mathematical and computer simulation studies of caging events within an ice lattice are being investigated. (5) At Brookhaven National Laboratory, cyclotron-produced chlorine and fluorine hot atoms substitution reactions with molecules possessing a single chiral center are under investigation to determine the role of hot atom kinetic energy, halogen atom, enantioner structure, steric effects and phase on the extent of substitution by retention of configuration or by Walden inversion. (6) The applications of high energy techniques and concepts to neutron activation analysis for trace element determinations in biological systems was continued.

  12. The Sugar Model: Autocatalytic Activity of the Triose-Ammonia Reaction

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    2006-01-01

    Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior of the products was examined by measuring the effect of the crude triose-ammonia reaction product on the kinetics of a second identical triose-ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance of triose and the rate formation of pyruvaldehyde, the product of triose dehydration. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of autocatalytic molecules.

  13. Nanoreactors for simultaneous remote thermal activation and optical monitoring of chemical reactions.

    PubMed

    Vázquez-Vázquez, Carmen; Vaz, Belén; Giannini, Vincenzo; Pérez-Lorenzo, Moisés; Alvarez-Puebla, Ramon A; Correa-Duarte, Miguel A

    2013-09-18

    We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress.

  14. The sugar model: autocatalytic activity of the triose-ammonia reaction.

    PubMed

    Weber, Arthur L

    2007-04-01

    Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior of the products was examined by measuring the effect of the crude triose-ammonia reaction product on the kinetics of a second identical triose-ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance of triose and the rate of formation of pyruvaldehyde, the product of triose dehydration. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of autocatalytic molecules. PMID:17225954

  15. Quality-Assurance Plan for Water-Quality Activities in the USGS Ohio Water Science Center

    USGS Publications Warehouse

    Francy, Donna S.; Shaffer, Kimberly H.

    2008-01-01

    In accordance with guidelines set forth by the Office of Water Quality in the Water Resources Discipline of the U.S. Geological Survey, a quality-assurance plan has been written for use by the Ohio Water Science Center in conducting water-quality activities. This quality-assurance plan documents the standards, policies, and procedures used by the Ohio Water Science Center for activities related to the collection, processing, storage, analysis, and publication of water-quality data. The policies and procedures documented in this quality-assurance plan for water-quality activities are meant to complement the Ohio Water Science Center quality-assurance plans for water-quality monitors, the microbiology laboratory, and surface-water and ground-water activities.

  16. Primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of Mars

    USGS Publications Warehouse

    Anderson, R.C.; Dohm, J.M.; Golombek, M.P.; Haldemann, A.F.C.; Franklin, B.J.; Tanaka, K.L.; Lias, J.; Peer, B.

    2001-01-01

    Five main stages of radial and concentric structures formed around Tharsis from the Noachian through the Amazonian as determined by geologic mapping of 24,452 structures within the stratigraphic framework of Mars and by testing their radial and concentric orientations. Tectonic activity peaked in the Noachian (stage 1) around the largest center, Claritas, an elongate center extending more than 20?? in latitude and defined by about half of the total grabens which are concentrated in the Syria Planum, Thaumasia, and Tempe Terra regions. During the Late Noachian and Early Hesperian (stage 2), extensional structures formed along the length of present-day Valles Marineris and in Thaumasia (with a secondary concentration near Warrego Vallis) radial to a region just to the south of the central margin of Valles Marineris. Early Hesperian (stage 3) radial grabens in Pavonis, Syria, Ulysses, and Tempe Terra and somewhat concentric wrinkle ridges in Lunae and Solis Plana and in Thaumasia, Sirenum, Memnonia, and Amazonis are centered northwest of Syria with secondary centers at Thaumasia, Tempe Terra, Ulysses Fossae, and western Valles Marineris. Late Hesperian/Early Amazonian (stage 4) structures around Alba Patera, the northeast trending alignment of Tharsis Montes, and Olympus Mons appears centered on Alba Patera. Stage 5 structures (Middle-Late Amazonian) represent the last pulse of Tharsis-related activity and are found around the large shield volcanoes and are centered near Pavonis Mons. Tectonic activity around Tharsis began in the Noachian and generally decreased through geologic time to the Amazonian. Statistically significant radial distributions of structures formed during each stage, centered at different locations within the higher elevations of Tharsis. Secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout Tharsis. Copyright 2001 by

  17. The FX iron-sulfur cluster serves as the terminal bound electron acceptor in heliobacterial reaction centers.

    PubMed

    Romberger, Steven P; Golbeck, John H

    2012-03-01

    Phototrophs of the family Heliobacteriaceae contain the simplest known Type I reaction center (RC), consisting of a homodimeric (PshA)(2) core devoid of bound cytochromes and antenna proteins. Unlike plant and cyanobacterial Photosystem I in which the F(A)/F(B) protein, PsaC, is tightly bound to P(700)-F(X) cores, the RCs of Heliobacterium modesticaldum contain two F(A)/F(B) proteins, PshBI and PshBII, which are loosely bound to P(800)-F(X) cores. These two 2[4Fe-4S] ferredoxins have been proposed to function as mobile redox proteins, reducing downstream metabolic partners much in the same manner as does [2Fe-2S] ferredoxin or flavodoxin (Fld) in PS I. Using P(800)-F(X) cores devoid of PshBI and PshBII, we show that iron-sulfur cluster F(X) directly reduces Fld without the involvement of F(A) or F(B) (Fld is used as a proxy for soluble redox proteins even though a gene encoding Fld is not identified in the H. modesticaldum genome). The reduction of Fld is suppressed by the addition of PshBI or PshBII, an effect explained by competition for the electron on F(X). In contrast, P(700)-F(X) cores require the presence of the PsaC, and hence, the F(A)/F(B) clusters for Fld (or ferredoxin) reduction. Thus, in H. modesticaldum, the interpolypeptide F(X) cluster serves as the terminal bound electron acceptor. This finding implies that the homodimeric (PshA)(2) cores should be capable of donating electrons to a wide variety of yet-to-be characterized soluble redox partners. PMID:22297911

  18. Multiple Scattering X-Ray Absorption Studies of Zn2+ Binding Sites in Bacterial Photosynthetic Reaction Centers

    PubMed Central

    Giachini, Lisa; Francia, Francesco; Mallardi, Antonia; Palazzo, Gerardo; Carpenè, Emilio; Boscherini, Federico; Venturoli, Giovanni

    2005-01-01

    Binding of transition metal ions to the reaction center (RC) protein of the photosynthetic bacterium Rhodobacter sphaeroides has been previously shown to slow light-induced electron and proton transfer to the secondary quinone acceptor molecule, QB. On the basis of x-ray diffraction at 2.5 Å resolution a site, formed by AspH124, HisH126, and HisH128, has been identified at the protein surface which binds Cd2+ or Zn2+. Using Zn K-edge x-ray absorption fine structure spectroscopy we report here on the local structure of Zn2+ ions bound to purified RC complexes embedded into polyvinyl alcohol films. X-ray absorption fine structure data were analyzed by combining ab initio simulations and multiparameter fitting; structural contributions up to the fourth coordination shell and multiple scattering paths (involving three atoms) have been included. Results for complexes characterized by a Zn to RC stoichiometry close to one indicate that Zn2+ binds two O and two N atoms in the first coordination shell. Higher shell contributions are consistent with a binding cluster formed by two His, one Asp residue, and a water molecule. Analysis of complexes characterized by ∼2 Zn ions per RC reveals a second structurally distinct binding site, involving one O and three N atoms, not belonging to a His residue. The local structure obtained for the higher affinity site nicely fits the coordination geometry proposed on the basis of x-ray diffraction data, but detects a significant contraction of the first shell. Two possible locations of the second new binding site at the cytoplasmic surface of the RC are proposed. PMID:15613631

  19. Clinical utility of panfungal polymerase chain reaction for the diagnosis of invasive fungal disease: a single center experience.

    PubMed

    Trubiano, J A; Dennison, A M; Morrissey, C O; Chua, K Y; Halliday, C L; Chen, S C-A; Spelman, D

    2016-02-01

    The role of panfungal polymerase chain reaction (PCR) assays for diagnosis of invasive fungal disease (IFD) is inadequately defined. We describe the use of an internal transcribed spacer 1 (ITS-1) region-directed panfungal PCR in this context at a tertiary referral transplant center. A retrospective review of patients at Alfred Health, Melbourne, Australia (2009-2014) who had clinical samples referred for panfungal PCR testing was conducted. Baseline patient characteristics, antifungal drug history, fungal culture/histopathology, and radiology results were recorded. For bronchoalveolar lavage (BAL) fluid samples, identification of a fungus other than a Candida spp. was defined as a potential pathogen.Of 138 panfungal PCR tests (108 patients), 41 (30%) were positive for a fungal product. Ninety-seven percent (134/138) of specimens were from immunocompromised hosts. Thirteen percent (19/138) of panfungal PCR positive results were for potential pathogens and potential pathogens were detected more frequently in tissue as compared with BAL (12/13 vs. 6/26; P = .0001). No positive panfungal PCR results were obtained from CSF specimens. If histopathology examination was negative, panfungal PCR identified a potential pathogen in only 12% (11/94) of specimens. For the 20 culture negative/histopathology positive specimens, diagnosis of IFD to causative species level by panfungal PCR occurred in 35% (6/20).Sterile site specimens, in particular tissue, were more frequently panfungal PCR positive for potential pathogens than BAL. The utility of panfungal PCR appears greatest in tissue specimens, as an adjunct to histopathology to improve diagnostic sensitivity and specificity. Based on the results of this study we are now only testing tissue specimens by panfungal PCR.

  20. Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides.

    PubMed

    Husu, Ivan; Giustini, Mauro; Colafemmina, Giuseppe; Palazzo, Gerardo; Mallardi, Antonia

    2011-09-01

    The bacterial reaction center (RC) has become a reference model in the study of the diverse interactions of quinones with electron transfer complexes. In these studies, the RC functionality was probed through flash-induced absorption changes where the state of the primary donor is probed by means of a continuous measuring beam and the electron transfer is triggered by a short intense light pulse. The single-beam set-up implies the use as reference of the transmittance measured before the light pulse. Implicit in the analysis of these data is the assumption that the measuring beam does not elicit the protein photochemistry. At variance, measuring beam is actinic in nature at almost all the suitable wavelengths. In this contribution, the analytical modelling of the time evolution of neutral and charge-separated RCs has been performed. The ability of measuring light to elicit RC photochemistry induces a first order growth of the charge-separated state up to a steady state that depends on the light intensity and on the occupation of the secondary quinone (Q(B)) site. Then the laser pulse pumps all the RCs in the charge-separated state. The following charge recombination is still affected by the measuring beam. Actually, the kinetics of charge recombination measured in RC preparation with the Q(B) site partially occupied are two-exponential. The rate constant of both fast and slow phases depends linearly on the intensity of the measuring beam while their relative weights depend not only on the fractions of RC with the Q(B) site occupied but also on the measuring light intensity itself.

  1. Local electrostatic field induced by the carotenoid bound to the reaction center of the purple photosynthetic bacterium Rhodobacter sphaeroides.

    PubMed

    Yanagi, Kazuhiro; Shimizu, Madoka; Hashimoto, Hideki; Gardiner, Alastair T; Roszak, Aleksander W; Cogdell, Richard J

    2005-01-20

    Electroabsorption (EA) spectra were recorded in the region of the reaction center (RC) Qy absorption bands of bacteriochlorophyll (Bchl) and bacteriopheophytin, to investigate the effect of carotenoid (Car) on the electrostatic environment of the RCs of the purple bacterium Rhodobacter (Rb.) sphaeroides. Two different RCs were prepared from Rb. sphaeroides strain R26.1 (R26.1-RC); R26.1 RC lacking Car and a reconstituted RC (R26.1-RC+ Car) prepared by incorporating a synthetic Car (3,4-dihydrospheroidene). Although there were no detectable differences between these two RCs in their near infrared (NIR) absorption spectra at 79 and 293 K, or in their EA spectra at 79 K, significant differences were detected in their EA spectra at 293 K. Three nonlinear optical parameters of each RC were determined in order to evaluate quantitatively these differences; transition dipole-moment polarizability and hyperpolarizability (D factor), the change in polarizability upon photoexcitation (Deltaalpha), and the change in dipole-moment upon photoexcitation (Deltamu). The value of D or Deltaalpha determined for each absorption band of the two RC samples showed similar values at 77 or 293 K. However, the Deltamu values of the special pair Bchls (P) and the monomer Bchls absorption bands showed significant differences between the two RCs at 293 K. X-ray crystallography of the two RCs has revealed that a single molecule of the solubilizing detergent LDAO occupies part of the carotenoid binding site in the absence of a carotenoid. The difference in the value of Deltamu therefore represents the differential effect of the detergent LDAO and the carotenoid on P. The change of electrostatic field around P induced by the presence of Car was determined to be 1.7 x 10(5) [V/cm], corresponding to a approximately 10% change in the electrostatic field around P.

  2. Cyclotriphosphazene appended porphyrins and fulleropyrrolidine complexes as supramolecular multiple photosynthetic reaction centers: steady and excited states photophysical investigation.

    PubMed

    Nair, Vishnu Sukumaran; Pareek, Yogita; Karunakaran, Venugopal; Ravikanth, Mangalampalli; Ajayaghosh, Ayyappanpillai

    2014-06-01

    New multiple photosynthetic reaction centers were constructed from cyclophosphazene decorated multiporphyrin chromophores and a fulleropyrrolidine having a pyridine ligand (FPY). The excited state electron transfer in the self-assembled donor-acceptor assembly was investigated by using steady state absorption and emission, time-resolved emission spectroscopy and nanosecond laser flash photolysis. The effect of metal (Zn(2+)) coordination to porphyrin units in the multiporphyrin arrays on cyclophosphazine scaffold (P3N3Zn) was studied by comparing with metal free porphyrin assembly on a cyclophosphazene scaffold (P3N3). In P3N3Zn, the decrease of absorption and fluorescence intensity and the lowering of the amplitude of longer fluorescence lifetime with increase of FPY concentration reflect the formation of a ground state complex with an association constant of ∼14,910 M(-1). When compared to the metal-free complex P3N3, the metal-coordinated derivative P3N3Zn exhibited shortening of the singlet and triplet state lifetimes and lowering of the singlet and triplet quantum yields. The cause of the decrease of the triplet quantum yields by insertion of zinc metal is discussed along with the possible non-planarity of the porphyrin ring. From the fluorescence lifetime measurements for the P3N3Zn-FPY mixture, it is proposed that self-assembly of the donor-acceptor complex leads to charge separated species with a rate constant of 7.1 × 10(9) s(-1). The decrease of triplet state intensity and lifetime of the P3N3Zn in the P3N3Zn-FPY complex from the nanosecond transient absorption studies support the occurrence of intermolecular electron transfer in the triplet state.

  3. Carbon Dioxide Information Analysis Center and World Data Center-A for atmospheric trace gases: FY 1993 activities

    SciTech Connect

    Cushman, R.M.; Stoss, F.W. |

    1994-01-01

    During the course of a fiscal year, Oak Ridge National Laboratory`s Carbon Dioxide Information Analysis Center (CDIAC) distributes thousands of specialty publications-numeric data packages (NDPs), computer model packages (CMPs), technical reports, public communication publications, newsletters, article reprints, and reference books-in response to requests for information related to global environmental issues, primarily those pertaining to climate change. CDIAC`s staff also provide technical responses to specific inquiries related to carbon dioxide (CO{sub 2}), other trace gases, and climate. Hundreds of referrals to other researchers, policy analysts, information specialists, or organizations are also facilitated by CDIAC`s staff. This report provides an account of the activities accomplished by CDIAC (including World Data Center-A for Atmospheric Trace Gases) during the period October 1, 1992, to September 30, 1993. An organizational overview of CDIAC and its staff is supplemented by a detailed description of inquiries received and CDIAC`s response to those inquiries. An analysis and description of the preparation and distribution of NDPS, CMPS, technical reports, newsletters, fact sheets, specialty publications, and reprints are provided. Comments and descriptions of CDIAC`s information management systems, professional networking, and special bilateral agreements are also presented.

  4. Learner-Centered Activities from the DVD-Format "Crouching Tiger, Hidden Dragon."

    ERIC Educational Resources Information Center

    Lin, Li-Yun

    This paper demonstrates how Taiwanese English-as-a-Second-Language (ESL) college teachers and students collaborate and negotiate to design various learner-centered activities based on the Chinese film, "Crouching Tiger, Hidden Dragon." These activities are intended to enhance students' listening and speaking abilities. The paper demonstrates eight…

  5. Active-Learning versus Teacher-Centered Instruction for Learning Acids and Bases

    ERIC Educational Resources Information Center

    Sesen, Burcin Acar; Tarhan, Leman

    2011-01-01

    Background and purpose: Active-learning as a student-centered learning process has begun to take more interest in constructing scientific knowledge. For this reason, this study aimed to investigate the effectiveness of active-learning implementation on high-school students' understanding of "acids and bases". Sample: The sample of this study was…

  6. Activities. A Collection of Things to Do at the Environmental Learning Center, Isabella, Minnesota.

    ERIC Educational Resources Information Center

    Environmental Learning Center, Isabella, Minn.

    A collection of activities used successfully at the Environmental Learning Center in Isabella, Minnesota, are contained in this guide. Areas of study are perception and communication, mapping, weather, snow, soil, aquatics, trees, and animals. Within these areas is a number of related activities, each to be adapted to the appropriate grade level.…

  7. SPECIAL ACTIVITIES SUPPLEMENTAL TO AND RELATED TO THE ART PROGRAM AT DEEP RIVER OUTDOOR EDUCATION CENTER.

    ERIC Educational Resources Information Center

    Gary City Public School System, IN.

    A CURRICULUM GUIDE DEALING WITH VARIOUS SUBJECT AREAS WAS PREPARED FOR POSSIBLE STUDY ACTIVITIES THAT WOULD USE THE LEARNING RESOURCES AVAILABLE AT THE DEEP RIVER OUTDOOR EDUCATION CENTER IN GARY, INDIANA. ACTIVITIES GUIDES ARE PRESENTED FOR (1) ART ACTITIVIES RELATED TO DESIGN, COLOR, LANDSCAPE REPRESENTATION, PAPER CONSTRUCTION, DRAWING, PRINT…

  8. A Work Sampling Study of Provider Activities in School-Based Health Centers

    ERIC Educational Resources Information Center

    Mavis, Brian; Pearson, Rachel; Stewart, Gail; Keefe, Carole

    2009-01-01

    Background: The purpose of this study was to describe provider activities in a convenience sample of School-Based Health Centers (SBHCs). The goal was to determine the relative proportion of time that clinic staff engaged in various patient care and non-patient care activities. Methods: All provider staff at 4 urban SBHCs participated in this…

  9. De novo-designed metallopeptides with type 2 copper centers: modulation of reduction potentials and nitrite reductase activities.

    PubMed

    Yu, Fangting; Penner-Hahn, James E; Pecoraro, Vincent L

    2013-12-01

    Enzymatic reactions involving redox processes are highly sensitive to the local electrostatic environment. Despite considerable effort, the complex interactions among different influential factors in native proteins impede progress toward complete understanding of the structure-function relationship. Of particular interest is the type 2 copper center Cu(His)3, which may act as an electron transfer center in peptidylglycine α-hydroxylating monooxygenase (PHM) or a catalytic center in copper nitrite reductase (CuNiR). A de novo design strategy is used to probe the effect of modifying charged amino acid residues around, but not directly bound to, a Cu(His)3 center embedded in three-stranded coiled coils (TRI-H)3 [TRI-H = Ac-G WKALEEK LKALEEK LKALEEK HKALEEK G-NH2]. Specifically, the peptide TRI-EH (=TRI-HK22E) alters an important lysine to glutamate just above the copper binding center. With a series of TRI-EH peptides mutated below the metal center, we use a variety of spectroscopies (EPR, UV-vis, XAS) to show a direct impact on the protonation equilibria, copper binding affinities, reduction potentials, and nitrite reductase activities of these copper-peptide complexes. The potentials at a specific pH vary by 100 mV, and the nitrite reductase activities range over a factor of 4 in rates. We also observe that the affinities, potentials, and catalytic activities are strongly influenced by the pH conditions (pH 5.8-7.4). In general, Cu(II) affinities for the peptides are diminished at low pH values. The interplay among these factors can lead to a 200 mV shift in reduction potential across these peptides, which is determined by the pH-dependent affinities of copper in both oxidation states. This study illustrates the strength of de novo protein design in elucidating the influence of ionizable residues on a particular redox system, an important step toward understanding the factors that govern the properties of this metalloenzyme with a goal of eventually improving the

  10. De novo designed metallopeptides with type 2 copper centers: modulation of reduction potentials and nitrite reductase activities

    PubMed Central

    Yu, Fangting; Penner-Hahn, James E.; Pecoraro, Vincent L.

    2014-01-01

    Enzymatic reactions involving redox processes are highly sensitive to the local electrostatic environment. Despite considerable effort, the complex interactions between different influential factors in native proteins impede progress towards complete understanding of the structure-function relationship. Of particular interest is the type 2 copper center Cu(His)3, which may act as an electron transfer center in peptidylglycine α-hydroxylating monooxygenase (PHM) or a catalytic center in copper nitrite reductase (CuNiR). A de novo design strategy is used to probe the effect of modifying charged amino acid residues around, but not directly bound to, a Cu(His)3 center embedded in three-stranded coiled coils (TRI-H)3 [TRI-H = Ac-G WKALEEK LKALEEK LKALEEK HKALEEK G-NH2]. Specifically, the peptide TRI-EH [TRI-EH = TRI-HK22E] alters an important lysine to glutamate just above the copper binding center. With a series of TRI-EH peptides mutated below the metal center, we use a variety of spectroscopies (EPR, UV-Vis, XAS) to show a direct impact on the protonation equilibria, copper binding affinities, reduction potentials and nitrite reductase activities of these copper-peptide complexes. The potentials at a specific pH vary by 100 mV and nitrite reductase activity ranges over a factor of four in rates. We also observe that affinities, potentials and catalytic activities are strongly influenced by pH conditions (pH 5.8 ~ 7.4). In general, Cu(II) affinities for the peptides are diminished at low pH values. The interplay between these factors can lead to a 200 mV shift in reduction potentials across these peptides, which is determined by the pH-dependent affinities of copper in both oxidation states. This study illustrates the strength of de novo protein design in elucidating the influence of ionizable residues on a particular redox system, an important step towards understanding the factors that govern the properties of this metalloenzyme with a goal of eventually improving

  11. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  12. Interaction between Cytochrome c2 and Photosynthetic Reaction Center from Rhodobacter sphaeroides: Role of Inter- Protein Hydrogen Bonds in Binding and Electron Transfer †

    PubMed Central

    Abresch, Edward C.; Paddock, Mark L.; Villalobos, Miguel; Chang, Charlene; Okamura, Melvin Y.

    2008-01-01

    The role of short-range hydrogen bond interactions at the interface between electron transfer proteins cytochrome c2 (cyt) and reaction center (RC) from Rb. sphaeroides was studied by mutation (to Ala) of RC residues Asn M187, Asn M188 and Gln L258 which form inter-protein hydrogen bonds to cyt in the cyt:RC complex. The largest decrease in binding constant KA (8-fold) for single mutation was observed for Asn M187, which forms an intra-protein hydrogen bond to the key residue Tyr L162 in the center of the contact region having low solvent accessibility. Interaction between Asn M187 and Tyr L162 was also implicated in binding by double mutation of the two residues. The hydrogen bond mutations did not significantly change the second order rate constant, k2 , indicating the mutations did not change the association rate for forming the cyt:RC complex, but increased the dissociation rate. The first order electron transfer rate, ke, for the cyt:RC complex was reduced by up to a factor of 4 (for Asn M187). The changes in ke were correlated with the changes in binding affinity but were not accompanied by increases in activation energy. We conclude that short-range hydrogen bond interactions contribute to the close packing of residues in the central contact region between the cyt and RC near Asn M187 and Tyr L162. The close packing contributes to fast electron transfer by increasing the electronic coupling and contributes to the binding energy holding the cyt in position for times long enough for electron transfer to occur. PMID:19053264

  13. Kinetic phases in the electron transfer from P+QA-QB to P+QAQB- and the associated processes in Rhodobacter sphaeroides R-26 reaction centers.

    PubMed

    Li, J; Gilroy, D; Tiede, D M; Gunner, M R

    1998-03-01

    Electron transfer from P+QA-QB to form P+QAQB- was measured in Rhodobacter sphaeroides R-26 reaction centers (RCs) where the native primary quinone, ubiquinone-10 (UQA), was replaced by 2-methyl-3-phytyl-1,4-naphthoquinone (MQA). The native secondary quinone, UQ-10, was retained as UQB. The difference spectrum of the semiquinone MQA- minus UQB- absorption is very similar to that of MQ- minus UQ- in solution (398-480 nm). Thus, the absorption change provides a direct monitor of the electron transfer from MQA- to UQB. In contrast, when both QA and QB are UQ-10 the spectral difference between UQA- and UQB- arises from electrochromic responses of RC chromophores. Three kinetic processes are seen in the near UV (390-480 nm) and near-IR (740-820 nm). Analysis of the time-correlated spectra support the conclusion that the changes at tau1 approximately 3 micros are mostly due to electron transfer, electron transfer and charge compensation are mixed in tau2 approximately 80 micros, while little or no electron transfer occurs at 200-600 micros (tau3) in MQAUQB RCs. The 80-micros rate has been previously observed, while the fast component has not. The fast phase represents 60% of the electron-transfer reaction (398 nm). The activation energy for electron transfer is DeltaG approximately 3.5 kcal/mol for both tau1 and tau2 between 0 and 30 degrees C. In isolated RCs with UQA, if there is any fast component, it appears to be faster and less important than in the MQA reconstituted RCs.

  14. Combined activation strain model and energy decomposition analysis methods: a new way to understand pericyclic reactions.

    PubMed

    Fernández, Israel

    2014-05-01

    The recently introduced activation strain model (ASM) has allowed us to gain more insight into the intimacies of different fundamental processes in chemistry. In combination with the energy decomposition analysis (EDA) method, we have nowadays a very useful tool to quantitatively understand the physical factors that govern the activation barriers of reactions within organic and organometallic chemistry. In this Perspective article, we present selected illustrative examples of the application of this method to pericyclic reactions (Diels-Alder and double group transfer reactions) to show that this methodology nicely complements other more traditional, widely used theoretical methods.

  15. Highly active copper-network catalyst for the direct aldol reaction.

    PubMed

    Ohta, Hidetoshi; Uozumi, Yasuhiro; Yamada, Yoichi M A

    2011-09-01

    The development of a highly active solid-phase catechol-copper network catalyst for direct aldol reaction is described. The catalyst was prepared from an alkyl-chain-linked bis(catechol) and a copper(II) complex. The direct aldol reaction between carbonyl compounds (aldehydes and ketones) and methyl isocyanoacetate was carried out using 0.1-1 mol% [Cu] catalyst to give the corresponding oxazolines at yields of up to 99% and a trans/cis ratio of >99:1. The catalyst was reused with no loss of catalytic activity. A plausible reaction pathway is also described. PMID:21751405

  16. Synthesis of marine polyacetylenes callyberynes A-C by transition-metal-catalyzed cross-coupling reactions to sp centers.

    PubMed

    López, Susana; Fernandez-Trillo, Francisco; Midón, Pilar; Castedo, Luis; Saa, Carlos

    2006-03-31

    Efficient total syntheses of the sponge-derived hydrocarbon polyacetylenes callyberynes A-C have been achieved using metal-catalyzed cross-coupling reactions of highly unsaturated 1,3-diyne fragments as the key steps, namely: Cadiot-Chodkiewicz reaction under Alami's optimized conditions (sp-sp), sequential Sonogashira reaction of a cis,cis-divinyl dihalide (sp2-sp), and Kumada-Corriu reaction of an unactivated alkyl iodide (sp3-sp). This last approach constitutes the first application of a metal-catalyzed sp3-sp Kumada-Corriu cross-coupling reaction to the synthesis of a natural product.

  17. Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

    DOEpatents

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2010-08-03

    A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

  18. Electronic structure of the Mn-cofactor of modified bacterial reaction centers measured by electron paramagnetic resonance and electron spin echo envelope modulation spectroscopies.

    PubMed

    Tufts, A A; Flores, M; Olson, T L; Williams, J C; Allen, J P

    2014-05-01

    The electronic structure of a Mn(II) ion bound to highly oxidizing reaction centers of Rhodobacter sphaeroides was studied in a mutant modified to possess a metal binding site at a location comparable to the Mn4Ca cluster of photosystem II. The Mn-binding site of the previously described mutant, M2, contains three carboxylates and one His at the binding site (Thielges et al., Biochemistry 44:389-7394, 2005). The redox-active Mn-cofactor was characterized using electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies. In the light without bound metal, the Mn-binding mutants showed an EPR spectrum characteristic of the oxidized bacteriochlorophyll dimer and reduced quinone whose intensity was significantly reduced due to the diminished quantum yield of charge separation in the mutant compared to wild type. In the presence of the metal and in the dark, the EPR spectrum measured at the X-band frequency of 9.4 GHz showed a distinctive spin 5/2 Mn(II) signal consisting of 16 lines associated with both allowed and forbidden transitions. Upon illumination, the amplitude of the spectrum is decreased by over 80 % due to oxidation of the metal upon electron transfer to the oxidized bacteriochlorophyll dimer. The EPR spectrum of the Mn-cofactor was also measured at the Q-band frequency of 34 GHz and was better resolved as the signal was composed of the six allowed electronic transitions with only minor contributions from other transitions. A fit of the Q-band EPR spectrum shows that the Mn-cofactor is a high spin Mn(II) species (S = 5/2) that is six-coordinated with an isotropic g-value of 2.0006, a weak zero-field splitting and E/D ratio of approximately 1/3. The ESEEM experiments showed the presence of one (14)N coordinating the Mn-cofactor. The nitrogen atom is assigned to a His by comparing our ESEEM results to those previously reported for Mn(II) ions bound to other proteins and on the basis of the X-ray structure of the M2

  19. Characterization of the strongly coupled, low-frequency vibrational modes of the special pair of photosynthetic reaction centers via isotopic labeling of the cofactors

    SciTech Connect

    Czarnecki, K.; Diers, J.R.; Bocian, D.F.; Chynwat, V.; Erickson, J.P.; Frank, H.A.

    1997-01-15

    Low-frequency (50-425-cm{sup -1}), near-infrared-excitation resonance Raman (RR) spectra are reported for bacterial photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides in which the bacteriochlorophyll (BChl) and bacteriopheophytin (BPh) cofactors are labeled with {sup 15}N or {sup 26}Mg. The focus of the study is the identification of the very low-frequency modes of the dimer of BChls (P) which are strongly coupled to the P{sup *} electronic transition which initiates the primary charge separation process in RCs. In order to gain a complete picture of the vibrational characteristics, the low-frequency RR spectra of the accessory BChls and the BPhs were examined in addition to those of P. The RR spectra of the isotopically labeled cofactors in the RCs were compared with one another and with the spectra obtained for solid-film samples of isolated, isotopically labeled BChl and BPh. Based on these comparisons and the predictions of semiempirical normal coordinate calculations, a self-consistent set of assignments has been developed for all the RR active modes of the different BChl and BPh cofactors in the RC which are observed in the very low-frequency regime (50-250 cm{sup -1}). The assignments indicate that the strongly coupled, low-frequency modes of P all involve either deformations localized on pyrrole ring I or the macrocycle core. 45 refs., 10 figs., 3 tabs.

  20. Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

    DOE PAGES

    Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; Shen, Bo; Wu, Liheng; Zhang, Sen; Lu, Gang; Wu, Zhongbiao; Sun, Shouheng

    2015-10-04

    We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly, our study offersmore » a general approach to enhance Pd catalysis in acid for ORB.« less

  1. Core/shell face-centered tetragonal FePd/Pd nanoparticles as an efficient non-Pt catalyst for the oxygen reduction reaction

    SciTech Connect

    Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; Shen, Bo; Wu, Liheng; Zhang, Sen; Lu, Gang; Wu, Zhongbiao; Sun, Shouheng

    2015-10-04

    We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly, our study offers a general approach to enhance Pd catalysis in acid for ORB.

  2. Two-step mechanism of photodamage to photosystem II: step 1 occurs at the oxygen-evolving complex and step 2 occurs at the photochemical reaction center.

    PubMed

    Ohnishi, Norikazu; Allakhverdiev, Suleyman I; Takahashi, Shunichi; Higashi, Shoichi; Watanabe, Masakatsu; Nishiyama, Yoshitaka; Murata, Norio

    2005-06-14

    Under strong light, photosystem II (PSII) of oxygenic photosynthetic organisms is inactivated, and this phenomenon is called photoinhibition. In a widely accepted model, photoinhibition is induced by excess light energy, which is absorbed by chlorophyll but not utilized in photosynthesis. Using monochromatic light from the Okazaki Large Spectrograph and thylakoid membranes from Thermosynechococcus elongatus, we observed that UV and blue light inactivated the oxygen-evolving complex much faster than the photochemical reaction center of PSII. These observations suggested that the light-induced damage was associated with a UV- and blue light-absorbing center in the oxygen-evolving complex of PSII. The action spectrum of the primary event in photodamage to PSII revealed the strong effects of UV and blue light and differed considerably from the absorption spectra of chlorophyll and thylakoid membranes. By contrast to the photoinduced inactivation of the oxygen-evolving complex in untreated thylakoid membranes, red light efficiently induced inactivation of the PSII reaction center in Tris-treated thylakoid membranes, and the action spectrum resembled the absorption spectrum of chlorophyll. Our observations suggest that photodamage to PSII occurs in two steps. Step 1 is the light-induced inactivation of the oxygen-evolving complex. Step 2, occurring after step 1 is complete, is the inactivation of the PSII reaction center by light absorbed by chlorophyll. We confirmed our model by illumination of untreated thylakoid membranes with blue and UV light, which inactivated the oxygen-evolving complex, and then with red light, which inactivated the photochemical reaction center.

  3. The rate of second electron transfer to QB(-) in bacterial reaction center of impaired proton delivery shows hydrogen-isotope effect.

    PubMed

    Maróti, Ágnes; Wraight, Colin A; Maróti, Péter

    2015-02-01

    The 2nd electron transfer in reaction center of photosynthetic bacterium Rhodobacter sphaeroides is a two step process in which protonation of QB(-) precedes interquinone electron transfer. The thermal activation and pH dependence of the overall rate constants of different RC variants were measured and compared in solvents of water (H2O) and heavy water (D2O). The electron transfer variants where the electron transfer is rate limiting (wild type and M17DN, L210DN and H173EQ mutants) do not show solvent isotope effect and the significant decrease of the rate constant of the second electron transfer in these mutants is due to lowering the operational pKa of QB(-)/QBH: 4.5 (native), 3.9 (L210DN), 3.7 (M17DN) and 3.1 (H173EQ) at pH7. On the other hand, the proton transfer variants where the proton transfer is rate limiting demonstrate solvent isotope effect of pH-independent moderate magnitude (2.11±0.26 (WT+Ni(2+)), 2.16±0.35 (WT+Cd(2+)) and 2.34±0.44 (L210DN/M17DN)) or pH-dependent large magnitude (5.7 at pH4 (L213DN)). Upon deuteration, the free energy and the enthalpy of activation increase in all proton transfer variants by about 1 kcal/mol and the entropy of activation becomes negligible in L210DN/M17DN mutant. The results are interpreted as manifestation of equilibrium and kinetic solvent isotope effects and the structural, energetic and kinetic possibility of alternate proton delivery pathways are discussed.

  4. A Mesoporous Indium Metal-Organic Framework: Remarkable Advances in Catalytic Activity for Strecker Reaction of Ketones.

    PubMed

    Reinares-Fisac, Daniel; Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles; Gándara, Felipe

    2016-07-27

    With the aim of developing new highly porous, heterogeneous Lewis acid catalysts for multicomponent reactions, a new mesoporous metal-organic framework, InPF-110 ([In3O(btb)2(HCOO)(L)], (H3btb = 1,3,5-tris(4-carboxyphenyl)benzene acid, L = methanol, water, or ethanol), has been prepared with indium as the metal center. It exhibits a Langmuir surface area of 1470 m(2) g(-1), and its structure consists of hexagonal pores with a 2.8 nm aperture, which allows the diffusion of multiple substrates. This material presents a large density of active metal sites resulting in outstanding catalytic activity in the formation of substituted α-aminonitriles through the one-pot Strecker reaction of ketones. In this respect, InPF-110 stands out compared to other catalysts for this reaction due to the small catalyst loadings required, and without the need for heat or solvents. Furthermore, X-ray single crystal diffraction studies clearly show the framework-substrate interaction through coordination to the accessible indium sites. PMID:27420904

  5. Boron-doped graphene as promising support for platinum catalyst with superior activity towards the methanol electrooxidation reaction

    NASA Astrophysics Data System (ADS)

    Sun, Yongrong; Du, Chunyu; An, Meichen; Du, Lei; Tan, Qiang; Liu, Chuntao; Gao, Yunzhi; Yin, Geping

    2015-12-01

    We report the synthesis of boron-doped graphene by thermally annealing the mixture of graphene oxide and boric acid, and its usage as the support of Pt catalyst towards the methanol oxidation reaction. The composition, structure and morphology of boron-doped graphene and its supported Pt nanoparticles (Pt/BG) are characterized by transmission electron microscopy, inductively coupled plasma mass spectrometry, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. It is revealed that boron atoms are doped into graphene network in the form of BC2O and BCO2 bonds, which lead to the increase in defect sites and facilitate the subsequent deposition of Pt nanoparticles. Therefore, the Pt/BG catalyst presents smaller particle size and narrower size distribution than the graphene supported Pt (Pt/G) catalyst. When evaluated as the electrocatalyst for the methanol oxidation reaction, the Pt/BG catalyst exhibits excellent electrochemical activity and stability demonstrated by cyclic voltammetry and chronoamperometry tests. The enhanced activity is mainly ascribed to the electronic interaction between boron-doped graphene and Pt nanoparticles, which lowers the d-band center of Pt and thus weakens the absorption of the poisoning intermediate CO. Our work provides an alternative approach of improving the reaction kinetics for the oxidation of small organic molecules.

  6. A Mesoporous Indium Metal-Organic Framework: Remarkable Advances in Catalytic Activity for Strecker Reaction of Ketones.

    PubMed

    Reinares-Fisac, Daniel; Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles; Gándara, Felipe

    2016-07-27

    With the aim of developing new highly porous, heterogeneous Lewis acid catalysts for multicomponent reactions, a new mesoporous metal-organic framework, InPF-110 ([In3O(btb)2(HCOO)(L)], (H3btb = 1,3,5-tris(4-carboxyphenyl)benzene acid, L = methanol, water, or ethanol), has been prepared with indium as the metal center. It exhibits a Langmuir surface area of 1470 m(2) g(-1), and its structure consists of hexagonal pores with a 2.8 nm aperture, which allows the diffusion of multiple substrates. This material presents a large density of active metal sites resulting in outstanding catalytic activity in the formation of substituted α-aminonitriles through the one-pot Strecker reaction of ketones. In this respect, InPF-110 stands out compared to other catalysts for this reaction due to the small catalyst loadings required, and without the need for heat or solvents. Furthermore, X-ray single crystal diffraction studies clearly show the framework-substrate interaction through coordination to the accessible indium sites.

  7. Activation energy for a model ferrous-ferric half reaction from transition path sampling

    NASA Astrophysics Data System (ADS)

    Drechsel-Grau, Christof; Sprik, Michiel

    2012-01-01

    Activation parameters for the model oxidation half reaction of the classical aqueous ferrous ion are compared for different molecular simulation techniques. In particular, activation free energies are obtained from umbrella integration and Marcus theory based thermodynamic integration, which rely on the diabatic gap as the reaction coordinate. The latter method also assumes linear response, and both methods obtain the activation entropy and the activation energy from the temperature dependence of the activation free energy. In contrast, transition path sampling does not require knowledge of the reaction coordinate and directly yields the activation energy [C. Dellago and P. G. Bolhuis, Mol. Simul. 30, 795 (2004), 10.1080/08927020412331294869]. Benchmark activation energies from transition path sampling agree within statistical uncertainty with activation energies obtained from standard techniques requiring knowledge of the reaction coordinate. In addition, it is found that the activation energy for this model system is significantly smaller than the activation free energy for the Marcus model, approximately half the value, implying an equally large entropy contribution.

  8. Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.

    PubMed

    Becker, Julia; Modl, Tanja; Gessner, Viktoria H

    2014-09-01

    The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. PMID:25047390

  9. Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.

    PubMed

    Becker, Julia; Modl, Tanja; Gessner, Viktoria H

    2014-09-01

    The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis.

  10. Study of spin centers in nanocrystalline titanium dioxide with a high degree of photocatalytic activity

    SciTech Connect

    Konstantinova, E. A.; Gayvoronskiy, V. Ya.; Timoshenko, V. Yu.; Kashkarov, P. K.

    2010-08-15

    Electron spin resonance spectroscopy is used to study the effects of illumination and changes in temperature on spin centers in nanocrystalline anatase powders synthesized by sol-gel methods with various complexing agents. A correlation between the concentration of oxygen radicals at the surface and the rate of photocatalytic decomposition of organic compounds in the presence of TiO{sub 2} is observed. It is shown that the concentration of centers active in the electron spin resonance spectra can be used for monitoring the photocatalytic activity of TiO{sub 2}.

  11. Formation of P{sup +}Q{sub B}{sup -} via B-branch electron transfer in mutant reaction centers.

    SciTech Connect

    Laible, P. D.

    1998-08-14

    The crystallographic observation of two symmetry-related branches of electron transfer cofactors in the structure of the bacterial reaction center (RC) 13 years ago [1] remains an enigma in light of experimental observations that show that only the A branch is active in the initial electron transfer steps in wild-type RCs. Unidirectional electron flow has been attributed to localized asymmetries between the A and B branches that lead to differences in: (1) the electronic couplings of the cofactors [2]; (2) the relative electrostatic environments of the cofactors, caused by amino acid differences which modulate the free energies of their charge-separated states [3] and/or create a higher dielectric constant on the active side, resulting in a stronger static field for stabilizing A-branch charge transfer states [4,5]. Some photo-induced bleaching of H{sub B} has been observed, in wild-type RCs following trapping of HA{sub A}{sup {minus}}[6], and in ''hybrid'' RCs where the redox potentials of cofactors were manipulated by pigment exchange [7] or mutagenesis [8]. Transient bleaching of the 530-nm band of H{sub B} was more easily observed in the hybrid RCs because the H{sub A} transition at 545 nm was shifted to {approximately}600 nm due to incorporation of a bacteriochlorophyll, designated ''{beta}'', at the H{sub A} site. No experiments to detect further electron transfer to Q{sub B} were done with either type of modified RCs. Many site-specific mutagenesis experiments have given us insight into the nature and magnitude of the effects that amino acid side chains can exert in tuning the relative energy levels of the cofactors to optimize the balance between forward and reverse reactions, and the large distances through which some of these effects are manifested. In this paper, we show that in mutant RCs of Rhodobacter capsulatus, P{sup +}Q{sub B}{sup {minus}} can be formed in the absence of prior formation of P{sup +}Q{sub A}{sup {minus}}, solely through activity of B

  12. Luminescence induced by dehydration of kaolin - Association with electron-spin-active centers and with surface activity for dehydration-polymerization of glycine

    NASA Technical Reports Server (NTRS)

    Coyne, L.; Hovatter, W.; Sweeney, M.

    1983-01-01

    Experimental data concerning emission of light upon dehydration as a function of preheating and pre-gamma-irradiation are correlated with reported studies of electron-spin resonance (ESR) activity after similar pretreatments. The effect of these pretreatments on the kaolin-promoted incorporation of glycine into peptide oligomers in a wet/cold, hot/dry fluctuating environment is compared to their effect on the ESR and luminescent signals. The existence of spectroscopically active centers appears to be loosely anticorrelated with reaction yield; these yields are increased by increasing the overall energy content of the material. It is concluded that some part of the chemical yield is produced by a mechanism involving intrinsic, excited electronic states of the clay crystal lattice. These states may be derived from thermally, interfacially, and/or mechanically induced charge reorganization within interspersed energy levels in the band structure of the material.

  13. Active Hemovigilance Significantly Improves Reporting of Acute Non-infectious Adverse Reactions to Blood Transfusion.

    PubMed

    Agnihotri, Naveen; Agnihotri, Ajju

    2016-09-01

    One of the key purposes of a hemovigilance program is to improve reporting of transfusion related adverse events and subsequent data-driven improvement in blood transfusion (BT) practices. We conducted a study over 3 years to assess the impact of healthcare worker training and an active feedback programme on reporting of adverse reactions to BTs. All hospitalized patients who required a BT were included in the study. Healthcare workers involved in BT to patients were sensitized and trained in adverse reaction reporting by conducting training sessions and meetings. All the transfused patients were 'actively' monitored for any acute adverse reaction by using a uniquely coded blood issue form. A total of 18,914 blood components transfused to 5785 different patients resulted in 61 adverse reaction episodes. This incidence of 0.32 % in our study was found to be significantly higher (p < 0.005) than that reported from the same region in the past. Red blood cell units were the most frequently transfused component and thus most commonly involved in an adverse reaction (42.6 %), however apheresis platelets had the highest chance of reaction per unit transfused (0.66 %). There was no mortality associated with the BT during the study period. An active surveillance program significantly improves reporting and management of adverse reactions to BTs. PMID:27429527

  14. DISCOVERY OF THE RECOMBINING PLASMA IN THE SOUTH OF THE GALACTIC CENTER: A RELIC OF THE PAST GALACTIC CENTER ACTIVITY?

    SciTech Connect

    Nakashima, S.; Nobukawa, M.; Uchida, H.; Tanaka, T.; Tsuru, T. G.; Koyama, K.; Murakami, H.; Uchiyama, H.

    2013-08-10

    We report Suzaku results for soft X-ray emission to the south of the Galactic center (GC). The emission (hereafter {sup G}C South{sup )} has an angular size of {approx}42' Multiplication-Sign 16' centered at (l, b) {approx} (0. Degree-Sign 0, - 1. Degree-Sign 4) and is located in the largely extended Galactic ridge X-ray emission (GRXE). The X-ray spectrum of GC South exhibits emission lines from highly ionized atoms. Although the X-ray spectrum of the GRXE can be well fitted with a plasma in collisional ionization equilibrium (CIE), that of GC South cannot be fitted with a plasma in CIE, leaving hump-like residuals at {approx}2.5 and 3.5 keV, which are attributable to the radiative recombination continua of the K-shells of Si and S, respectively. In fact, GC South spectrum is well fitted with a recombination-dominant plasma model; the electron temperature is 0.46 keV while atoms are highly ionized (kT = 1.6 keV) in the initial epoch, and the plasma is now in a recombining phase at a relaxation scale (plasma density Multiplication-Sign elapsed time) of 5.3 Multiplication-Sign 10{sup 11} s cm{sup -3}. The absorption column density of GC South is consistent with that toward the GC region. Thus, GC South is likely to be located in the GC region ({approx}8 kpc distance). The size of the plasma, the mean density, and the thermal energy are estimated to be {approx}97 pc Multiplication-Sign 37 pc, 0.16 cm{sup -3}, and 1.6 Multiplication-Sign 10{sup 51} erg, respectively. We discuss possible origins of the recombination-dominant plasma as a relic of past activity in the GC region.

  15. Titanium oxynitride interlayer to influence oxygen reduction reaction activity and corrosion stability of Pt and Pt-Ni alloy.

    PubMed

    Tan, XueHai; Wang, Liya; Zahiri, Beniamin; Kohandehghan, Alireza; Karpuzov, Dimitre; Lotfabad, Elmira Memarzadeh; Li, Zhi; Eikerling, Michael H; Mitlin, David

    2015-01-01

    A key advancement target for oxygen reduction reaction catalysts is to simultaneously improve both the electrochemical activity and durability. To this end, the efficacy of a new highly conductive support that comprises of a 0.5 nm titanium oxynitride film coated by atomic layer deposition onto an array of carbon nanotubes has been investigated. Support effects for pure platinum and for a platinum (50 at %)/nickel alloy have been considered. Oxynitride induces a downshift in the d-band center for pure platinum and fundamentally changes the platinum particle size and spatial distribution. This results in major enhancements in activity and corrosion stability relative to an identically synthesized catalyst without the interlayer. Conversely, oxynitride has a minimal effect on the electronic structure and microstructure, and therefore, on the catalytic performance of platinum-nickel. Calculations based on density functional theory add insight with regard to compositional segregation that occurs at the alloy catalyst-support interface.

  16. Resolution and reconstitution of a bound Fe-S protein from the photosynthetic reaction center of Heliobacterium modesticaldum.

    PubMed

    Heinnickel, Mark; Shen, Gaozhong; Agalarov, Rufat; Golbeck, John H

    2005-07-26

    The photosynthetic reaction center of Heliobacterium modesticaldum (HbRC) was isolated from membranes using n-dodecyl beta-D-maltopyranoside followed by sucrose density ultracentrifugation. The low-temperature EPR spectra of whole cells, isolated membranes, and HbRC complexes are similar, showing a single Fe-S cluster with g values of 2.067, 1.933, and 1.890 after illumination at 20 K, and a complex spectrum attributed to exchange interaction from two Fe-S clusters after illumination during freezing. The protein containing the Fe-S clusters was removed from the HbRC by washing it with 1.0 M NaCl and purified by ultrafiltration over a 30 kDa cutoff membrane. Analysis of the filtrate by SDS-PAGE showed a major band at approximately 8 kDa that was weakly stained with Coomassie Brilliant Blue and strongly stained with silver. The optical spectrum of the oxidized Fe-S protein shows a maximum at 410 nm, and the EPR spectrum of the reduced Fe-S protein shows a complex set of resonances similar to those found in 2[4Fe-4S] ferredoxins. The HbRC core was purified by DEAE ion-exchange chromatography and resolved by SDS-PAGE. The purified HbRC was composed of a band at ca. 40 kDa, which is identified as PshA, and several additional proteins. The isolated Fe-S protein rebinds spontaneously to purified HbRC cores, and the light-induced EPR signals of the Fe-S clusters are recovered. The flash-induced kinetics of the HbRC complex show two kinetic phases at room temperature, one with a lifetime of 75 ms and the other with a lifetime of 15 ms. The 75 ms component is lost when the Fe-S protein is removed from the HbRC complex, and it is regained when the Fe-S protein is rebound to HbRC cores. Thus, the 75 ms kinetic phase is derived from recombination of a terminal Fe-S cluster with P798(+), and the 15 ms kinetic phase is derived from recombination with an earlier acceptor, probably F(X). We suggest that the bound Fe-S protein present in the HbRC be designated PshB. PMID:16026168

  17. Modulation of the fluorescence yield in heliobacterial cells by induction of charge recombination in the photosynthetic reaction center.

    PubMed

    Redding, Kevin E; Sarrou, Iosifina; Rappaport, Fabrice; Santabarbara, Stefano; Lin, Su; Reifschneider, Kiera T

    2014-05-01

    Heliobacteria contain a very simple photosynthetic apparatus, consisting of a homodimeric type I reaction center (RC) without a peripheral antenna system and using the unique pigment bacteriochlorophyll (BChl) g. They are thought to use a light-driven cyclic electron transport pathway to pump protons, and thereby phosphorylate ADP, although some of the details of this cycle are yet to be worked out. We previously reported that the fluorescence emission from the heliobacterial RC in vivo was increased by exposure to actinic light, although this variable fluorescence phenomenon exhibited very different characteristics to that in oxygenic phototrophs (Collins et al. 2010). Here, we describe the underlying mechanism behind the variable fluorescence in heliobacterial cells. We find that the ability to stably photobleach P800, the primary donor of the RC, using brief flashes is inversely correlated to the variable fluorescence. Using pump-probe spectroscopy in the nanosecond timescale, we found that illumination of cells with bright light for a few seconds put them in a state in which a significant fraction of the RCs underwent charge recombination from P800 (+)A0 (-) with a time constant of ~20 ns. The fraction of RCs in the rapidly back-reacting state correlated very well with the variable fluorescence, indicating that nearly all of the increase in fluorescence could be explained by charge recombination of P800 (+)A0 (-), some of which regenerated the singlet excited state. This hypothesis was tested directly by time-resolved fluorescence studies in the ps and ns timescales. The major decay component in whole cells had a 20-ps decay time, representing trapping by the RC. Treatment of cells with dithionite resulted in the appearance of a ~18-ns decay component, which accounted for ~0.6 % of the decay, but was almost undetectable in the untreated cells. We conclude that strong illumination of heliobacterial cells can result in saturation of the electron acceptor pool

  18. Modulation of the fluorescence yield in heliobacterial cells by induction of charge recombination in the photosynthetic reaction center.

    PubMed

    Redding, Kevin E; Sarrou, Iosifina; Rappaport, Fabrice; Santabarbara, Stefano; Lin, Su; Reifschneider, Kiera T

    2014-05-01

    Heliobacteria contain a very simple photosynthetic apparatus, consisting of a homodimeric type I reaction center (RC) without a peripheral antenna system and using the unique pigment bacteriochlorophyll (BChl) g. They are thought to use a light-driven cyclic electron transport pathway to pump protons, and thereby phosphorylate ADP, although some of the details of this cycle are yet to be worked out. We previously reported that the fluorescence emission from the heliobacterial RC in vivo was increased by exposure to actinic light, although this variable fluorescence phenomenon exhibited very different characteristics to that in oxygenic phototrophs (Collins et al. 2010). Here, we describe the underlying mechanism behind the variable fluorescence in heliobacterial cells. We find that the ability to stably photobleach P800, the primary donor of the RC, using brief flashes is inversely correlated to the variable fluorescence. Using pump-probe spectroscopy in the nanosecond timescale, we found that illumination of cells with bright light for a few seconds put them in a state in which a significant fraction of the RCs underwent charge recombination from P800 (+)A0 (-) with a time constant of ~20 ns. The fraction of RCs in the rapidly back-reacting state correlated very well with the variable fluorescence, indicating that nearly all of the increase in fluorescence could be explained by charge recombination of P800 (+)A0 (-), some of which regenerated the singlet excited state. This hypothesis was tested directly by time-resolved fluorescence studies in the ps and ns timescales. The major decay component in whole cells had a 20-ps decay time, representing trapping by the RC. Treatment of cells with dithionite resulted in the appearance of a ~18-ns decay component, which accounted for ~0.6 % of the decay, but was almost undetectable in the untreated cells. We conclude that strong illumination of heliobacterial cells can result in saturation of the electron acceptor pool

  19. Binding of nitrite and its reductive activation to nitric oxide at biomimetic copper centers.

    PubMed

    Monzani, E; Anthony, G J; Koolhaas, A; Spandre, A; Leggieri, E; Casella, L; Gullotti, M; Nardin, G; Randaccio, L; Fontani, M; Zanello, P; Reedijk, J

    2000-04-01

    analyzed. The mechanism of reductive activation of nitrite to nitric oxide by the Cu(I) complexes of 1-bb, 2-bb, and ddah has been studied. The reaction requires two protons per molecule of nitrite and Cu(I). Kinetic experiments show that the reaction is first order in [Cu(I)] and [H+] and exhibits saturation behavior with respect to nitrite concentration. The kinetic data show that [Cu(2-bb)]+ is more efficient than [Cu(1-bb)]+ and [Cu(ddah)]+ in reducing nitrite. PMID:10819470

  20. Analysis of ground reaction force and electromyographic activity of the gastrocnemius muscle during double support.

    PubMed

    Sousa, Andreia S P; Santos, Rubim; Oliveira, Francisco P M; Carvalho, Paulo; Tavares, João Manuel R S

    2012-05-01

    Mechanisms associated with energy expenditure during gait have been extensively researched and studied. According to the double-inverted pendulum model energy expenditure is higher during double support, as lower limbs need to work to redirect the centre of mass velocity. This study looks into how the ground reaction force of one limb affects the muscle activity required by the medial gastrocnemius of the contralateral limb during step-to-step transition. Thirty-five subjects were monitored as to the medial gastrocnemius electromyographic activity of one limb and the ground reaction force of the contralateral limb during double support. After determination of the Pearson correlation coefficient (r), a moderate correlation was observed between the medial gastrocnemius electromyographic activity of the dominant leg and the vertical (Fz) and anteroposterior (Fy) components of ground reaction force of the non-dominant leg (r = 0.797, p < 0.000 1; r = -0.807, p < 0.000 1). A weak and moderate correlation was observed between the medial gastrocnemius electromyographic activity of the non-dominant leg and the Fz and Fy of the dominant leg, respectively (r = 0.442, p = 0.018; r = -0.684 p < 0.000 1). The results obtained suggest that during double support, ground reaction force is associated with the electromyographic activity of the contralateral medial gastrocnemius and that there is an increased dependence between the ground reaction force of the non-dominant leg and the electromyographic activity of the dominant medial gastrocnemius. PMID:22720393

  1. Developing novel organocatalyzed aldol reactions for the enantioselective synthesis of biologically active molecules

    PubMed Central

    Bhanushali, Mayur; Zhao, Cong-Gui

    2011-01-01

    Aldol reaction is one of the most important methods for the formation of carbon-carbon bonds. Because of its significance and usefulness, asymmetric versions of this reaction have been realized with different approaches in the past. Over the last decade, the area of organocatalysis has made significant progresses. As one of most studied reactions in organocatalyses, organocatalyzed aldol reaction has emerged as a powerful tool for the synthesis of a large number of useful products in optically enriched forms. In this review, we summarize our efforts on the development of novel organocatalyzed aldol reactions for the enantioselective synthesis of biological active molecules. Literatures closely related to our studies are also covered. PMID:21918584

  2. New tetragonal form of reaction centers from Rhodobacter sphaeroides and the involvement of a manganese ion at a crystal contact point

    PubMed Central

    Uyeda, G.; Cámara-Artigas, A.; Williams, J. C.; Allen, J. P.

    2005-01-01

    Crystals have been obtained of wild-type reaction centers from Rhodobacter sphaeroides using manganese chloride as a precipitating agent. The crystals belong to the tetragonal space group P4222, with unit-cell parameters a = b = 207.8, c = 107.5 Å. The crystal structure has been determined to a resolution limit of 4.6 Å using a previously determined structure of the reaction center as a molecular-replacement model. The calculated electron-density maps show the presence of a manganese ion at one of the crystal contact points bridging two symmetry-related histidine residues, suggesting that the metal plays a key role in facilitating the crystallization of the protein in this form. PMID:16511142

  3. Reconstitution of photosynthetic energy conservation. II. Photophosphorylation in liposomes containing photosystem-I reaction center and chloroplast coupling-factor complex.

    PubMed

    Hauska, G; Samoray, D; Orlich, G; Nelson, N

    1980-10-01

    Photophosphorylation has been reconstituted in a liposomal system containing reaction centers of photosystem I and coupling-factor complex, both highly purified from spinach chloroplasts. This energy-converting model system was put together by diluting the preparation of the coupling-factor complex with an aqueous suspension of proteolipid vesicles, preformed from photosystem-I reaction centers and soybean phospholipids by sonication. In the presence of reduced N-methyl-phenazonium methosulfate the system catalyzed photophosphorylation with rates up to 50 mumol ATP formed x mg chlorophyll-1 x h-1, which was sensitive to uncouplers and to N,N'-dicyclohexyl-carbodiimide. The properties of the system in comparison to chloroplasts is discussed. PMID:6450680

  4. Catalytic activation of carbohydrates as formaldehyde equivalents for Stetter reaction with enones.

    PubMed

    Zhang, Junmin; Xing, Chong; Tiwari, Bhoopendra; Chi, Yonggui Robin

    2013-06-01

    We disclose the first catalytic activation of carbohydrates as formaldehyde equivalents to generate acyl anions as one-carbon nucleophilic units for a Stetter reaction. The activation involves N-heterocyclic carbene (NHC)-catalyzed C-C bond cleavage of carbohydrates via a retro-benzoin-type process to generate the acyl anion intermediates. This Stetter reaction constitutes the first success in generating formal formaldehyde-derived acyl anions as one-carbon nucleophiles for non-self-benzoin processes. The renewable nature of carbohydrates, accessible from biomass, further highlights the practical potential of this fundamentally interesting catalytic activation.

  5. Integration of telencephalic Wnt and hedgehog signaling center activities by Foxg1.

    PubMed

    Danesin, Catherine; Peres, João N; Johansson, Marie; Snowden, Victoria; Cording, Amy; Papalopulu, Nancy; Houart, Corinne

    2009-04-01

    The forebrain is patterned along the dorsoventral (DV) axis by Sonic Hedgehog (Shh). However, previous studies have suggested the presence of an Shh-independent mechanism. Our study identifies Wnt/beta-catenin-activated from the telencephalic roof-as an Shh-independent pathway that is essential for telencephalic pallial (dorsal) specification during neurulation. We demonstrate that the transcription factor Foxg1 coordinates the activity of two signaling centers: Foxg1 is a key downstream effector of the Shh pathway during induction of subpallial (ventral) identity, and it inhibits Wnt/beta-catenin signaling through direct transcriptional repression of Wnt ligands. This inhibition restricts the dorsal Wnt signaling center to the roof plate and consequently limits pallial identities. Concomitantly to these roles, Foxg1 controls the formation of the compartment boundary between telencephalon and basal diencephalon. Altogether, these findings identify a key direct target of Foxg1, and uncover a simple molecular mechanism by which Foxg1 integrates two opposing signaling centers.

  6. Atmospheric chemistry of the reaction ClO + O2 reversible reaction ClO (center dot) O2: Where it stands, what needs to be done, and why?

    NASA Technical Reports Server (NTRS)

    Prasad, Sheo S.; Lee, Timothy J.

    1994-01-01

    Possible existence and chemistry of ClO (center dot) O2 was originally proposed to explain the Norrish-Neville effect that O2 suppresses chlorine photosensitized loss of ozone. It was also thought that ClO (center dot) O2 might have some atmospheric chemistry significance. Recently, doubts have been cast on this proposal, because certain laboratory data seem to imply that the equilibrium constant of the title reaction is so small that ClO (center dot) O2 may be too unstable to matter. However, those data create only a superficial illusion to that effect, because on a closer analysis they do not disprove a moderately stable and chemically significant ClO (center dot) O2. Furthermore, our state-of-the-science accurate computational chemistry calculations also suggest that ClO (center dot) O2 may be a weakly bound ClOOO radical with a reactive (2)A ground electronic state. There is therefore a need to design and perform definitive experimental tests of the existence and chemistry of the ClO (center dot) O2 species, which we discuss and which have the potential to mediate the chlorine-catalyzed stratospheric ozone depletion.

  7. Dephosphorylation of Photosystem II Reaction Center Proteins in Plant Photosynthetic Membranes as an Immediate Response to Abrupt Elevation of Temperature1

    PubMed Central

    Rokka, Anne; Aro, Eva-Mari; Herrmann, Reinhold G.; Andersson, Bertil; Vener, Alexander V.

    2000-01-01

    Kinetic studies of protein dephosphorylation in photosynthetic thylakoid membranes revealed specifically accelerated dephosphorylation of photosystem II (PSII) core proteins at elevated temperatures. Raising the temperature from 22°C to 42°C resulted in a more than 10-fold increase in the dephosphorylation rates of the PSII reaction center proteins D1 and D2 and of the chlorophyll a binding protein CP43 in isolated spinach (Spinacia oleracea) thylakoids. In contrast the dephosphorylation rates of the light harvesting protein complex and the 9-kD protein of the PSII (PsbH) were accelerated only 2- to 3-fold. The use of a phospho-threonine antibody to measure in vivo phosphorylation levels in spinach leaves revealed a more than 20-fold acceleration in D1, D2, and CP43 dephosphorylation induced by abrupt elevation of temperature, but no increase in light harvesting protein complex dephosphorylation. This rapid dephosphorylation is catalyzed by a PSII-specific, intrinsic membrane protein phosphatase. Phosphatase assays, using intact thylakoids, solubilized membranes, and the isolated enzyme, revealed that the temperature-induced lateral migration of PSII to the stroma-exposed thylakoids only partially contributed to the rapid increase in the dephosphorylation rate. Significant activation of the phosphatase coincided with the temperature-induced release of TLP40 from the membrane into thylakoid lumen. TLP40 is a peptidyl-prolyl cis-trans isomerase, which acts as a regulatory subunit of the membrane phosphatase. Thus dissociation of TLP40 caused by an abrupt elevation in temperature and activation of the membrane protein phosphatase are suggested to trigger accelerated repair of photodamaged PSII and to operate as possible early signals initiating other heat shock responses in chloroplasts. PMID:10938368

  8. ACTIVE: a program to calculate and plot reaction rates from ANISN calculated fluxes

    SciTech Connect

    Judd, J.L.

    1981-12-01

    The ACTIVE code calculates spatial heating rates, tritium production rates, neutron reaction rates, and energy spectra from particle fluxes calculated by ANISN. ACTIVE has a variety of input options including the capability to plot all calculated spatial distributions. The code was primarily designed for use with fusion first wall/blanket systems, but could be applied to any one-dimensional problem.

  9. Nucleophilic substitution at centers other than carbon: reaction at the chlorine of N-chloroacetanilides with triethylamine as the nucleophile

    SciTech Connect

    Underwood, G.R.; Dietze, P.E.

    1984-12-28

    The reaction between triethylamine (TEA) and a series of para-substituted N-chloroacetanilides has been studied in aqueous solution buffered to pHs between 1 and 5. The exclusive product derived from the aromatic moiety is the corresponding acetanilide. The reaction occurs via two parallel pseudo-second-order paths, one acid catalyzed (the Orton-like mechanism), the other uncatalyzed. The uncatalyzed reaction is accelerated by the presence of electron-withdrawing substituents on the aromatic ring and can best be represented as nucleophilic displacement at chlorine. It therefore appears to be the prototype of a convenient class of reactions for the study of displacement reactions at chlorine. The rho value for this reaction is 3.87, indicating substantial negative charge buildup in the aromatic ring during of the transition state. The acid-catalyzed reaction is more complex, presumable involving a protonation equilibrium for the N-chloroacetanilide prior to the rate-determining step similar to that in the Orton reaction. 15 references, 2 figures, 3 tables.

  10. (BB)-Carboryne Complex of Ruthenium: Synthesis by Double B–H Activation at a Single Metal Center

    PubMed Central

    2016-01-01

    The first example of a transition metal (BB)-carboryne complex containing two boron atoms of the icosahedral cage connected to a single exohedral metal center (POBBOP)Ru(CO)2 (POBBOP = 1,7-OP(i-Pr)2-2,6-dehydro-m-carborane) was synthesized by double B–H activation within the strained m-carboranyl pincer framework. Theoretical calculations revealed that the unique three-membered (BB)>Ru metalacycle is formed by two bent B–Ru σ-bonds with the concomitant increase of the bond order between the two metalated boron atoms. The reactivity of the highly strained electron-rich (BB)-carboryne fragment with small molecules was probed by reactions with electrophiles. The carboryne–carboranyl transformations reported herein represent a new mode of cooperative metal–ligand reactivity of boron-based complexes. PMID:27526855

  11. (BB)-Carboryne Complex of Ruthenium: Synthesis by Double B-H Activation at a Single Metal Center.

    PubMed

    Eleazer, Bennett J; Smith, Mark D; Popov, Alexey A; Peryshkov, Dmitry V

    2016-08-24

    The first example of a transition metal (BB)-carboryne complex containing two boron atoms of the icosahedral cage connected to a single exohedral metal center (POBBOP)Ru(CO)2 (POBBOP = 1,7-OP(i-Pr)2-2,6-dehydro-m-carborane) was synthesized by double B-H activation within the strained m-carboranyl pincer framework. Theoretical calculations revealed that the unique three-membered (BB)>Ru metalacycle is formed by two bent B-Ru σ-bonds with the concomitant increase of the bond order between the two metalated boron atoms. The reactivity of the highly strained electron-rich (BB)-carboryne fragment with small molecules was probed by reactions with electrophiles. The carboryne-carboranyl transformations reported herein represent a new mode of cooperative metal-ligand reactivity of boron-based complexes. PMID:27526855

  12. Light-driven amino acid uptake in Streptococcus cremoris or Clostridium acetobutylicum membrane vesicles fused with liposomes containing bacterial reaction centers

    SciTech Connect

    Crielaard, W.; Driessen, A.J.; Molenaar, D.; Hellingwerf, K.J.; Konings, W.N.

    1988-04-01

    Reaction centers of the phototrophic bacterium Rhodopseudomonas palustris were introduced as proton motive force-generating systems in membrane vesicles of two anaerobic bacteria. Liposomes containing reaction center-light-harvesting complex I pigment protein complexes were fused with membrane vesicles of Streptococcus cremoris or Clostridium acetobutylicum by freeze-thawing and sonication. Illumination of these fused membranes resulted in the generation of a proton motive force of approximately -110 mV. The magnitude of the proton motive force in these membranes could be varied by changing the light intensity. As a result of this proton motive force, amino acid transport into the fused membranes could be observed. The initial rate of leucine transport by membrane vesicles of S. cremoris increased exponentially with the proton motive force. An H+/leucine stoichiometry of 0.8 was determined from the steady-state level of leucine accumulation and the proton motive force, and this stoichiometry was found to be independent of the magnitude of the proton motive force. These results indicate that the introduction of bacterial reaction centers in membrane vesicles by the fusion procedure yields very attractive model systems for the study of proton motive force-consuming processes in membrane vesicles of (strict) anaerobic bacteria.

  13. Photosynthetic reaction center mimicry: low reorganization energy driven charge stabilization in self-assembled cofacial zinc phthalocyanine dimer-fullerene conjugate.

    PubMed

    D'Souza, Francis; Maligaspe, Eranda; Ohkubo, Kei; Zandler, Melvin E; Subbaiyan, Navaneetha K; Fukuzumi, Shunichi

    2009-07-01

    By employing well-defined self-assembly methods, a biomimetic bacterial photosynthetic reaction center complex has been constructed, and photoinduced electron transfer originating in this supramolecular donor-acceptor conjugate has been investigated. The biomimetic model of the bacterial "special pair" donor, a cofacial zinc phthalocyanine dimer, was formed via potassium ion induced dimerization of 4,5,4',5',4'', 5'',4''',5'''-zinc tetrakis(1,4,7,10,13-pentaoxatridecamethylene)phthalocyanine. The dimer was subsequently self-assembled with functionalized fullerenes via "two-point" binding involving axial coordination and crown ether-alkyl ammonium cation complexation to form the donor-acceptor pair, mimicking the noncovalently bound entities of the bacterial photosynthetic reaction center. The adopted self-assembly methodology yielded a supramolecular complex of higher stability with defined geometry and orientation as revealed by the binding constant and computational optimized structure. Unlike the previously reported porphyrin analog, the present phthalocyanine macrocycle based model system exhibited superior electron-transfer properties including formation of a long-lived charge-separated state, a key step of the photosynthetic light energy conversion process. Detailed analysis of the kinetic data in light of the Marcus theory of electron transfer revealed that small reorganization energy of the relatively rigid phthalocyanine is primarily responsible for slower charge-recombination process. The importance of the cofacial dimer in stabilizing the charge-separated state is borne out in the present all-supramolecular "reaction center" donor-acceptor mimic.

  14. Catalysts for cross-coupling reactions with non-activated alkyl halides.

    PubMed

    Frisch, Anja C; Beller, Matthias

    2005-01-21

    Despite the problems inherent to metal-catalyzed cross-coupling reactions with alkyl halides, these reactions have become increasingly important during the last few years. Detailed mechanistic investigations have led to a variety of novel procedures for the selective cross-coupling of non-activated alkyl halides bearing beta hydrogen atoms with a variety of organometallic nucleophiles under mild reaction conditions. This Minireview highlights selected examples of metal-catalyzed coupling methods and is intended to encourage chemists to exploit the potential of these approaches in organic synthesis.

  15. Molecular Complexity via C–H Activation: A Dehydrogenative Diels-Alder Reaction

    PubMed Central

    Stang, Erik M.; White, M. Christina

    2011-01-01

    Traditionally, C–H oxidation reactions install oxidized functionality onto a preformed molecular skeleton, resulting in a local molecular change. The use of C–H activation chemistry to construct complex molecular scaffolds is a new area with tremendous potential in synthesis. We report a Pd(II)/bis-sulfoxide catalyzed dehydrogenative Diels-Alder reaction that converts simple terminal olefins into complex cycloadducts in a single operation. PMID:21842902

  16. Molecular complexity via C-H activation: a dehydrogenative Diels-Alder reaction.

    PubMed

    Stang, Erik M; White, M Christina

    2011-09-28

    Traditionally, C-H oxidation reactions install oxidized functionality onto a preformed molecular skeleton, resulting in a local molecular change. The use of C-H activation chemistry to construct complex molecular scaffolds is a new area with tremendous potential in synthesis. We report a Pd(II)/bis-sulfoxide-catalyzed dehydrogenative Diels-Alder reaction that converts simple terminal olefins into complex cycloadducts in a single operation.

  17. Introductory Astronomy Student-Centered Active Learning at The George Washington University

    NASA Astrophysics Data System (ADS)

    Cobb, Bethany

    2014-01-01

    The Physics Department at the George Washington University has been successfully using student-centered active learning (SCALE-UP) in physics classes since 2008. In Fall 2011, we began implementing introductory (non-majors) astronomy classes taught in the student-centered active learning mode. Class time is devoted to engaging in hands-on activities and laboratories, and tackling thought-provoking questions and problems. Students work together in small groups to gain a deeper understanding of the material. Multiple instructors circulate to answer questions and engage students in additional contemplation of the material. Research has shown that students who are engaged in this manner have an increased conceptual understanding and are better able to solve problems. This talk will describe our methods, our successes and the associated challenges of integrating active learning into courses entitled “Stars, Planets and Life” and “Introduction to the Cosmos.”

  18. Research and technology activities at Ames Research Center's Biomedical Research Division

    NASA Technical Reports Server (NTRS)

    Martello, N.

    1985-01-01

    Various research and technology activities at Ames Research Center's Biomedical Research Division are described. Contributions to the Space Administration's goals in the life sciences include descriptions of research in operational medicine, cardiovascular deconditioning, motion sickness, bone alterations, muscle atrophy, fluid and electrolyte changes, radiation effects and protection, behavior and performance, gravitational biology, and life sciences flight experiments.

  19. Students´ Perspectives on eLearning Activities in Person-Centered, Blended Learning Settings

    ERIC Educational Resources Information Center

    Haselberger, David; Motsching, Renate

    2016-01-01

    Blended or hybrid learning has become a frequent practice in higher education. In this article our primary research interest was to find out how students perceived eLearning activities in blended learning courses based on the person-centered paradigm. Through analyzing the content of a series of semi-structured interviews we found out that…

  20. Nutrition and Physical Activity Practices in Childcare Centers versus Family Childcare Homes

    ERIC Educational Resources Information Center

    Natale, Ruby; Page, Monica; Sanders, Lee

    2014-01-01

    Obesity rates among preschool-aged children have doubled in the past 10 years, and 60% of these children spend the majority of their day in childcare facilities. Few studies have examined the quality of nutrition and physical activity practices in childcare centers as compared to family childcare homes. The purpose of this study is to determine if…

  1. 34 CFR 350.22 - What activities must a Rehabilitation Research and Training Center conduct?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 2 2012-07-01 2012-07-01 false What activities must a Rehabilitation Research and Training Center conduct? 350.22 Section 350.22 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF SPECIAL EDUCATION AND REHABILITATIVE SERVICES, DEPARTMENT OF...

  2. 34 CFR 350.22 - What activities must a Rehabilitation Research and Training Center conduct?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 34 Education 2 2013-07-01 2013-07-01 false What activities must a Rehabilitation Research and Training Center conduct? 350.22 Section 350.22 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF SPECIAL EDUCATION AND REHABILITATIVE SERVICES, DEPARTMENT OF...

  3. 34 CFR 350.22 - What activities must a Rehabilitation Research and Training Center conduct?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 34 Education 2 2014-07-01 2013-07-01 true What activities must a Rehabilitation Research and Training Center conduct? 350.22 Section 350.22 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF SPECIAL EDUCATION AND REHABILITATIVE SERVICES, DEPARTMENT OF...

  4. 34 CFR 656.3 - What activities define a comprehensive or undergraduate National Resource Center?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 34 Education 3 2014-07-01 2014-07-01 false What activities define a comprehensive or undergraduate National Resource Center? 656.3 Section 656.3 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF POSTSECONDARY EDUCATION, DEPARTMENT OF EDUCATION NATIONAL RESOURCE...

  5. 34 CFR 656.3 - What activities define a comprehensive or undergraduate National Resource Center?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 3 2012-07-01 2012-07-01 false What activities define a comprehensive or undergraduate National Resource Center? 656.3 Section 656.3 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF POSTSECONDARY EDUCATION, DEPARTMENT OF EDUCATION NATIONAL RESOURCE...

  6. 34 CFR 656.3 - What activities define a comprehensive or undergraduate National Resource Center?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 34 Education 3 2010-07-01 2010-07-01 false What activities define a comprehensive or undergraduate National Resource Center? 656.3 Section 656.3 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF POSTSECONDARY EDUCATION, DEPARTMENT OF EDUCATION NATIONAL RESOURCE...

  7. Can Physical Education and Physical Activity Outcomes Be Developed Simultaneously Using a Game-Centered Approach?

    ERIC Educational Resources Information Center

    Miller, Andrew; Christensen, Erin; Eather, Narelle; Gray, Shirley; Sproule, John; Keay, Jeanne; Lubans, David

    2016-01-01

    The primary objective of this study was to evaluate the efficacy of a pilot intervention using a game-centered approach for improvement of physical activity (PA) and physical education (PE) outcomes simultaneously, and if this had an impact on enjoyment of PE. A group-randomized controlled trial with a 7-week wait-list control group was conducted…

  8. Individual Information-Centered Approach for Handling Physical Activity Missing Data

    ERIC Educational Resources Information Center

    Kang, Minsoo; Rowe, David A.; Barreira, Tiago V.; Robinson, Terrance S.; Mahar, Matthew T.

    2009-01-01

    The purpose of this study was to validate individual information (II)-centered methods for handling missing data, using data samples of 118 middle-aged adults and 91 older adults equipped with Yamax SW-200 pedometers and Actigraph accelerometers for 7 days. We used a semisimulation approach to create six data sets: three physical activity outcome…

  9. Formation of active sites for oxygen reduction reactions by transformation of nitrogen functionalities in nitrogen-doped carbon nanotubes.

    PubMed

    Sharifi, Tiva; Hu, Guangzhi; Jia, Xueen; Wågberg, Thomas

    2012-10-23

    Heat treating nitrogen-doped multiwalled carbon nanotubes containing up to six different types of nitrogen functionalities transforms particular nitrogen functionalities into other types which are more catalytically active toward oxygen reduction reactions (ORR). In the first stage, the unstable pyrrolic functionalities transform into pyridinic functionalities followed by an immediate transition into quaternary center and valley nitrogen functionalities. By measuring the electrocatalytic oxidation reduction current for the different samples, we achieve information on the catalytic activity connected to each type of nitrogen functionality. Through this, we conclude that quaternary nitrogen valley sites, N-Q(valley), are the most active sites for ORR in N-CNTs. The number of electrons transferred in the ORR is determined from ring disk electrode and rotating ring disk electrode measurements. Our measurements indicate that the ORR processes proceed by a direct four-electron pathway for the N-Q(valley) and the pyridinic sites while it proceeds by an indirect two-electron pathway via hydrogen peroxide at the N-Q(center) sites. Our study gives both insights on the mechanism of ORR on different nitrogen functionalities in nitrogen-doped carbon nanostructures and it proposes how to treat samples to maximize the catalytic efficiency of such samples.

  10. Identifying the active site in nitrogen-doped graphene for the VO2+/VO2(+) redox reaction.

    PubMed

    Jin, Jutao; Fu, Xiaogang; Liu, Qiao; Liu, Yanru; Wei, Zhiyang; Niu, Kexing; Zhang, Junyan

    2013-06-25

    Nitrogen-doped graphene sheets (NGS), synthesized by annealing graphite oxide (GO) with urea at 700-1050 °C, were studied as positive electrodes in a vanadium redox flow battery. The NGS, in particular annealed at 900 °C, exhibited excellent catalytic performance in terms of electron transfer (ET) resistance (4.74 ± 0.51 and 7.27 ± 0.42 Ω for the anodic process and cathodic process, respectively) and reversibility (ΔE = 100 mV, Ipa/Ipc = 1.38 at a scan rate of 50 mV s(-1)). Detailed research confirms that not the nitrogen doping level but the nitrogen type in the graphene sheets determines the catalytic activity. Among four types of nitrogen species doped into the graphene lattice including pyridinic-N, pyrrolic-N, quaternary nitrogen, and oxidic-N, quaternary nitrogen is verified as a catalytic active center for the [VO](2+)/[VO2](+) couple reaction. A mechanism is proposed to explain the electrocatalytic performance of NGS for the [VO](2+)/[VO2](+) couple reaction. The possible formation of a N-V transitional bonding state, which facilitates the ET between the outer electrode and reactant ions, is a key step for its high catalytic activity.

  11. Acridine orange staining reaction as an index of physiological activity in Escherichia coli

    NASA Technical Reports Server (NTRS)

    McFeters, G. A.; Singh, A.; Byun, S.; Callis, P. R.; Williams, S.

    1991-01-01

    The assumption that the acridine orange (AO) color reaction may be used as an index of physiological activity was investigated in laboratory grown Escherichia coli. Spectrofluorometric observations of purified nucleic acids, ribosomes and the microscopic color of bacteriophage-infected cells stained with AO confirmed the theory that single-stranded nucleic acids emit orange to red fluorescence while those that are double-stranded fluoresce green in vivo. Bacteria growing actively in a rich medium could be distinguished from cells in stationary phase by the AO reaction. Cells from log phase appeared red, whereas those in stationary phase were green. However, this differentiation was not seen when the bacteria were grown in a minimal medium or when a variation of the staining method was used. Also, shifting bacteria in stationary phase to starvation conditions rapidly changed their AO staining reaction. Boiling and exposure to lethal concentrations of azide and formalin resulted in stationary-phase cells that appeared red after staining but bacteria killed with chlorine remained green. These findings indicate that the AO staining reaction may be suggestive of physiological activity under defined conditions. However, variables in staining and fixation procedures as well as uncertainties associated with mixed bacterial populations in environmental samples may produce results that are not consistent with the classical interpretation of this reaction. The importance of validating the putative physiological implications of this staining reaction is stressed.

  12. Thermal Technology Development Activities at the Goddard Space Flight Center - 2001

    NASA Technical Reports Server (NTRS)

    Butler, Dan

    2002-01-01

    This presentation provides an overview of thermal technology development activities carried out at NASA's Goddard Space Flight Center during 2001. Specific topics covered include: two-phase systems (heat pipes, capillary pumped loops, vapor compression systems and phase change materials), variable emittance systems, advanced coatings, high conductivity materials and electrohydrodynamic (EHD) thermal coatings. The application of these activities to specific space missions is also discussed.

  13. Paris Observatory Analysis Center (OPAR): Report on Activities, January - December 2012

    NASA Technical Reports Server (NTRS)

    Lambert, Sebastien; Barache, Christophe

    2013-01-01

    We report on activities of the Paris Observatory VLBI Analysis Center (OPAR) for calendar year 2012 concerning the development of operational tasks, the development of our Web site, and various other activities: monitoring of the Earth's free core nutation, measuring of the post-seismic displacements of some stations, and the analysis of the recent IVS R&D sessions, including observations of quasars close to the Sun.

  14. Biogenic synthesis of palladium nanoparticles using Pulicaria glutinosa extract and their catalytic activity towards the Suzuki coupling reaction.

    PubMed

    Khan, Mujeeb; Khan, Merajuddin; Kuniyil, Mufsir; Adil, Syed Farooq; Al-Warthan, Abdulrahman; Alkhathlan, Hamad Z; Tremel, Wolfgang; Tahir, Muhammad Nawaz; Siddiqui, Mohammed Rafiq H

    2014-06-28

    Green synthesis of nanomaterials finds the edge over chemical methods due to its environmental compatibility. Herein, we report a facile and eco-friendly method for the synthesis of palladium (Pd) nanoparticles (NPs) using an aqueous solution of Pulicaria glutinosa, a plant widely found in a large region of Saudi Arabia, as a bioreductant. The as-prepared Pd NPs were characterized using ultraviolet-visible (UV-vis) spectroscopy, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform-infrared spectroscopy (FT-IR). The hydroxyl groups of the plant extract (PE) molecules were found mainly responsible for the reduction and growth of Pd NPs. FT-IR analysis confirmed the dual role of the PE, both as a bioreductant as well as a capping ligand, which stabilizes the surface of Pd NPs. The crystalline nature of the Pd NPs was identified using XRD analysis which confirmed the formation of a face-centered cubic structure (JCPDS: 87-0641, space group: Fm3m (225)). Furthermore, the as-synthesized Pd NPs demonstrated excellent catalytic activity towards the Suzuki coupling reaction under aqueous and aerobic conditions. Kinetic studies of the catalytic reaction monitored using GC confirmed that the reaction completes in less than 5 minutes.

  15. Visible-Light-Mediated Generation of Nitrogen-Centered Radicals: Metal-Free Hydroimination and Iminohydroxylation Cyclization Reactions.

    PubMed

    Davies, Jacob; Booth, Samuel G; Essafi, Stephanie; Dryfe, Robert A W; Leonori, Daniele

    2015-11-16

    The formation and use of iminyl radicals in novel and divergent hydroimination and iminohydroxylation cyclization reactions has been accomplished through the design of a new class of reactive O-aryl oximes. Owing to their low reduction potentials, the inexpensive organic dye eosin Y could be used as the photocatalyst of the organocatalytic hydroimination reaction. Furthermore, reaction conditions for a unique iminohydroxylation were identified; visible-light-mediated electron transfer from novel electron donor-acceptor complexes of the oximes and Et3N was proposed as a key step of this process.

  16. X-ray imaging of chemically active valence electrons during a pericyclic reaction.

    PubMed

    Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

    2014-11-26

    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions.

  17. X-ray imaging of chemically active valence electrons during a pericyclic reaction

    PubMed Central

    Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

    2014-01-01

    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions. PMID:25424639

  18. Spatiotemporal regulation of chemical reaction kinetics of cell surface molecules by active remodeling of cortical actin

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Bhaswati; Chaudhuri, Abhishek; Gowrishankar, Kripa; Mayor, Satyajit; Rao, Madan

    2010-03-01

    Cell surface proteins such as lipid tethered GPI-anchored proteins and Ras-proteins are distributed as monomers and nanoclusters on the surface of living cells. Recent work from our laboratory suggests that the spatial distribution and dynamics of formation and breakup of these nanoclusters is controlled by the active remodeling dynamics of the underlying cortical actin. To explain these observations, we propose a novel mechanism of nanoclustering, involving the transient binding to and advection along constitutively occuring ``asters'' of cortical actin. Here we study the consequences of such active actin based clustering, in the context of chemical reactions involving conformational changes of cell surface proteins. We find that active remodeling of cortical actin, can give rise to a dramatic increase in the reaction efficiency and output levels. In general, such actin driven clustering of membrane proteins could be a cellular mechanism to spatiotemporally regulate and amplify local chemical reaction rates, in the context of signalling and endocytosis.

  19. Active Site Dependent Reaction Mechanism over Ru/CeO2 Catalyst toward CO2 Methanation.

    PubMed

    Wang, Fei; He, Shan; Chen, Hao; Wang, Bin; Zheng, Lirong; Wei, Min; Evans, David G; Duan, Xue

    2016-05-18

    Oxygen vacancy on the surface of metal oxides is one of the most important defects which acts as the reactive site in a variety of catalytic reactions. In this work, operando spectroscopy methodology was employed to study the CO2 methanation reaction catalyzed by Ru/CeO2 (with oxygen vacancy in CeO2) and Ru/α-Al2O3 (without oxygen vacancy), respectively, so as to give a thorough understanding on active site dependent reaction mechanism. In Ru/CeO2 catalyst, operando XANES, IR, and Raman were used to reveal the generation process of Ce(3+), surface hydroxyl, and oxygen vacancy as well as their structural evolvements under practical reaction conditions. The steady-state isotope transient kinetic analysis (SSITKA)-type in situ DRIFT infrared spectroscopy undoubtedly substantiates that CO2 methanation undergoes formate route over Ru/CeO2 catalyst, and the formate dissociation to methanol catalyzed by oxygen vacancy is the rate-determining step. In contrast, CO2 methanation undergoes CO route over Ru surface in Ru/α-Al2O3 with the absence of oxygen vacancy, demonstrating active site dependent catalytic mechanism toward CO2 methanation. In addition, the catalytic activity evaluation and the oscillating reaction over Ru/CeO2 catalyst further prove that the oxygen vacancy catalyzes the rate-determining step with a much lower activation temperature compared with Ru surface in Ru/α-Al2O3 (125 vs 250 °C).

  20. Center for Multiscale Plasma Dynamics: Report on Activities (UCLA/MIT), 2009-2010

    SciTech Connect

    Troy Carter

    2011-04-18

    The final 'phaseout' year of the CMPD ended July 2010; a no cost extension was requested until May 2011 in order to enable the MIT subcontract funds to be fully utilized. Research progress over this time included verification and validation activities for the BOUT and BOUT++ code, studies of spontaneous reconnection in the VTF facility at MIT, and studies of the interaction between Alfven waves and drift waves in LAPD. The CMPD also hosted the 6th plasma physics winter school in 2010 (jointly with the NSF frontier center the Center for Magnetic Self-Organization, significant funding came from NSF for this most recent iteration of the Winter School).

  1. Identifying reaction intermediates and catalytic active sites through in situ characterization techniques

    SciTech Connect

    Foster, Andrew J.; Lobo, Raul F

    2010-01-01

    This tutorial review centers on recent advances and applications of experimental techniques that help characterize surface species and catalyst structures under in situ conditions. We start by reviewing recent applications of IR spectroscopy of working catalysis, emphasizing newer approaches such as Sum Frequency Generation and Polarization Modulation-infrared reflection absorption spectroscopy. This is followed by a section on solid-state NMR spectroscopy for the detection of surface species and reaction intermediates. These two techniques provide information mainly about the concentration and identity of the prevalent surface species. The following sections center on methods that provide structural and chemical information about the catalyst surface. The increasingly important role of high-pressure X-ray photoelectron spectroscopy in catalyst characterization is evident from the new and interesting information obtained on supported catalysts as presented in recent reports. X-Ray absorption spectroscopy (XANES and EXAFS) is used increasingly under reaction conditions to great advantage, although is inherently limited to systems where the bulk of the species in the sample are surface species. However, the ability of X-rays to penetrate the sample has been used cleverly by a number of groups to understand how changing reaction conditions change the structure and composition of surface atoms on supported catalyst.

  2. Gas-phase activation and reaction dynamics of chiral ion-dipole complexes.

    PubMed

    Filippi, Antonello; Speranza, Maurizio

    2003-11-01

    A family of enantiomerically pure oxonium ions, that is O-protonated 1-aryl-1-methoxyethanes, has been generated in the gas phase by the (CH(3))(2)Cl(+) methylation of the corresponding 1-arylethanols. Some information on their reaction dynamics was obtained from a detailed kinetic study of their inversion of configuration and dissociation. The activation parameters of the inversion reaction are found to obey two different isokinetic relationships depending upon the nature and the position of the substituents in the oxonium ions. In contrast, the activation parameters of the dissociation reaction obey a single isokinetic relationship. The inversion and dissociation rate constants do not follow simple linear free-energy relationships. This complicated kinetic picture has been rationalized in terms of different activation dynamics in gaseous CH(3)Cl, which, in turn, determine the reaction dynamics of the oxonium ion. When the predominant activation of the oxonium ion involves resonant energy exchange from the 1015 cm(-1) CH(3) rocking mode of unperturbed CH(3)Cl, the inversion reaction proceeds through the dynamically most favored TS, characterized by the unassisted C(alpha)bond;O bond elongation. When, instead, the activation of the oxonium ions requires the formation of an intimate encounter complex with CH(3)Cl, the inversion reaction takes place via the energetically most favored TS, characterized by multiple coordination of the CH(3)OH moiety with the H(alpha) and H(ortho) atoms of the benzylic residue. The activation dynamics operating in the intimate encounter complex with CH(3)Cl is also responsible for the dissociation of most selected oxonium ions.

  3. Introductory Astronomy Student-Centered Active Learning at the George Washington University

    NASA Astrophysics Data System (ADS)

    Cobb, B. E.

    2014-07-01

    The Physics Department at the George Washington University has been successfully using student-centered active learning (SCALE-UP) in physics classes since 2008. Recently (since fall 2011), we have been developing and implementing introductory (non-majors) astronomy classes taught in the student-centered active learning mode. Class time is devoted to engaging in hands-on activities and laboratories and tackling questions and problems in a workbook. Students work in small groups, and multiple instructors circulate to answer questions and engage students in the material. Research has shown that students who are engaged in this manner have an increased conceptual understanding of the material. In developing our “Stars, Planets and Life” course into an interactive class, we encountered many challenges, but there have also been positive outcomes. Improvements to this class are ongoing, and in fall of 2013 we will begin full implementation of SCALE-UP in our “Introduction to the Cosmos” course.

  4. Assessment of DFT methods for computing activation energies of Mo/W-mediated reactions.

    PubMed

    Hu, Lianrui; Chen, Hui

    2015-10-13

    Using high level ab initio coupled cluster calculations as reference, the performances of 15 commonly used density functionals (DFs) on activation energy calculations for typical Mo/W-mediated reactions have been systematically assessed for the first time in this work. The selected representative Mo/W-mediated reactions cover a wide range from enzymatic reactions to organometallic reactions, which include Mo-catalyzed aldehyde oxidation (aldehyde oxidoreductase), Mo-catalyzed dimethyl sulfoxide (DMSO) reduction (DMSO reductase), W-catalyzed acetylene hydration (acetylene hydratase), Mo/W-mediated olefin metathesis, Mo/W-mediated olefin epoxidation, W-mediated alkyne metathesis, and W-mediated C-H bond activation. Covering both Mo- and W-mediated reactions, four DFs of B2GP-PLYP, M06, B2-PLYP, and B3LYP are uniformly recommended with and without DFT empirical dispersion correction. Among these four DFs, B3LYP is notably improved in performance by DFT empirical dispersion correction. In addition to the absolute value of calculation error, if the trend of DFT results is also a consideration, B2GP-PLYP, B2-PLYP, and M06 keep better performance than other functionals tested and constitute our final recommendation of DFs for both Mo- and W-mediated reactions. PMID:26574251

  5. Differences in the Abilities to Mechanically Eliminate Activation Energies for Unimolecular and Bimolecular Reactions

    PubMed Central

    Kochhar, Gurpaul S.; Mosey, Nicholas J.

    2016-01-01

    Mechanochemistry, i.e. the application of forces, F, at the molecular level, has attracted significant interest as a means of controlling chemical reactions. The present study uses quantum chemical calculations to explore the abilities to mechanically eliminate activation energies, ΔE‡, for unimolecular and bimolecular reactions. The results demonstrate that ΔE‡ can be eliminated for unimolecular reactions by applying sufficiently large F along directions that move the reactant and/or transition state (TS) structures parallel to the zero-F reaction coordinate, S0. In contrast, eliminating ΔE‡ for bimolecular reactions requires the reactant to undergo a force-induced shift parallel to S0 irrespective of changes in the TS. Meeting this requirement depends upon the coupling between F and S0 in the reactant. The insights regarding the differences in eliminating ΔE‡ for unimolecular and bimolecular reactions, and the requirements for eliminating ΔE‡, may be useful in practical efforts to control reactions mechanochemically. PMID:26972114

  6. Relationships among performance of lateral cutting maneuver from lateral sliding and hip extension and abduction motions, ground reaction force, and body center of mass height.

    PubMed

    Shimokochi, Yohei; Ide, Daishi; Kokubu, Masahiro; Nakaoji, Tetsu

    2013-07-01

    Basketball players have to move laterally and quickly change their movement directions, especially during defensive moves. This study aimed to investigate how frontal and sagittal plane hip movements relate to fastness and quickness of lateral cutting maneuvers from sliding. Three-dimensional biomechanical data were obtained for 28 female college basketball players while they performed lateral cutting maneuvers using their left leg after 2 lateral sliding steps. The lateral cutting index (LCIndex) expressing fastness and quickness of lateral cutting maneuvers, peak hip abduction and extension velocities immediately before foot contact, hip abduction and extension velocities at foot contact, peak horizontal ground reaction force, frontal plane ground reaction force angle, and sacrum center of mass position were calculated. Simple and stepwise regression analyses were conducted to predict LCIndex. The former showed that greater maximum hip extension velocity (p = 0.03) and lesser hip abduction velocity (p = 0.04) as well as smaller ground reaction force angle (p = 0.001) and lower sacrum center of mass position (p = 0.001) at foot contact led to better LCIndex. The latter showed that sacrum center of mass position at foot contact and hip extension velocity explained 35.3% (p < 0.01) and 7.3% (p = 0.088) of variance in LCIndex, respectively. Our results did not suggest that hip abductor function is important for lateral sliding moves, instead suggesting that faster hip extension motions to kick the ground and lowering the body center of mass are crucial for better lateral deceleration-acceleration motions.

  7. Activities in the Spacelab Payload Operations Control Center (SL POCC) During the STS-42 IML-1

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The primary payload for Space Shuttle Mission STS-42, launched January 22, 1992, was the International Microgravity Laboratory-1 (IML-1), a pressurized manned Spacelab module. The goal of IML-1 was to explore in depth the complex effects of weightlessness of living organisms and materials processing. Around-the-clock research was performed on the human nervous system's adaptation to low gravity and effects of microgravity on other life forms such as shrimp eggs, lentil seedlings, fruit fly eggs, and bacteria. Materials processing experiments were also conducted, including crystal growth from a variety of substances such as enzymes, mercury iodide, and a virus. The Huntsville Operations Support Center (HOSC) Spacelab Payload Operations Control Center (SL POCC) at the Marshall Space Flight Center (MSFC) was the air/ground communication channel used between the astronauts and ground control teams during the Spacelab missions. Featured are activities in the SL POCC during STS-42, IML-1 mission.

  8. Design of an experiment to study optically-active centers in diamond nanoparticles

    NASA Astrophysics Data System (ADS)

    Singh, Ankit; Tiwari, Kunal; Sharma, Suresh

    2012-03-01

    The silicon-vacancy (SiV) and nitrogen-vacancy (NV) complexes in diamond nanoparticles (NPs) are optically active centers, which produce single photon events. These centers may be formed when a silicon atom from the silicon substrate often used in CVD growth or nitrogen from impurities in the feed gas ends up next to a vacancy in the diamond lattice. Because of their stability and high quantum efficiency, SiV and NV centers in diamond NPs are attractive for applications in quantum computing, optics, biotechnology, and medicine. We briefly review our recently published results on diamond NPs, describe the design of an experimental system for carrying out in-situ optical spectroscopy and time-correlation measurements, and show preliminary photoluminescence data.

  9. The Influence of Elastic Strain on Catalytic Activity in the Hydrogen Evolution Reaction.

    PubMed

    Yan, Kai; Maark, Tuhina Adit; Khorshidi, Alireza; Sethuraman, Vijay A; Peterson, Andrew A; Guduru, Pradeep R

    2016-05-17

    Understanding the role of elastic strain in modifying catalytic reaction rates is crucial for catalyst design, but experimentally, this effect is often coupled with a ligand effect. To isolate the strain effect, we have investigated the influence of externally applied elastic strain on the catalytic activity of metal films in the hydrogen evolution reaction (HER). We show that elastic strain tunes the catalytic activity in a controlled and predictable way. Both theory and experiment show strain controls reactivity in a controlled manner consistent with the qualitative predictions of the HER volcano plot and the d-band theory: Ni and Pt's activities were accelerated by compression, while Cu's activity was accelerated by tension. By isolating the elastic strain effect from the ligand effect, this study provides a greater insight into the role of elastic strain in controlling electrocatalytic activity. PMID:27079940

  10. MuA Transposase: Organizing Two Reactions With One Active Site

    NASA Astrophysics Data System (ADS)

    Goldhaber-Gordon, Ilana; Baker, Tania A.

    2002-03-01

    Transposases are unusual proteins, performing at least two types of chemical reaction with a single active site. In the first reaction, the transposase cleaves the 3' end of a transposon DNA sequence. In the second reaction, the transposase transfers the cleaved 3' end into a new DNA molecule called the target. The final product is the transposon DNA attached by its 3' strands to the target DNA. The two reactions, DNA cleavage and DNA strand transfer, are chemically very similar, raising the question of how transposases avoid unintentionally cleaving the target. We have now observed that at least one transposase, the MuA protein, can cleave a target DNA --- when in the presence of a transposon DNA with a special (dideoxy nucleotide) termination. By exploring the protein's ability to cleave the target DNA under these unusual circumstances, we are learning how it prevents target cleavage when working with more standard DNA substrates.

  11. A new approach for the photosynthetic antenna-reaction center complex with a model organized around an s-triazine linker.

    PubMed

    Kuhri, Susanne; Charalambidis, Georgios; Angaridis, Panagiotis A; Lazarides, Theodore; Pagona, Georgia; Tagmatarchis, Nikos; Coutsolelos, Athanassios G; Guldi, Dirk M

    2014-02-10

    Two new artificial mimics of the photosynthetic antenna-reaction center complex have been designed and synthesized (BDP-H2 P-C60 and BDP-ZnP-C60). The resulting electron-donor/acceptor conjugates contain a porphyrin (either in its free-base form (H2P) or as Zn-metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C60-X-NH2 (X=spacer). In both cases, the three different components were connected by s-triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star-type arrangement of the three photo- and redox-active components around the central s-triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy- and electron-transfer properties of the resulting electron-donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP-H2P-C60 and BDP-ZnP-C60 with those of BDP-H2P, BDP-ZnP and BDP-C60, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H2P or ZnP. This is then followed by an electron transfer to C60, yielding the formation of the singlet charge-separated states, namely BDP-H2(·+) -C60(·-) and BDP-ZnP(·+)-C60(·-). As such, the sequence of energy transfer and electron transfer in the

  12. Earth Science Data Archive and Access at the NASA/Goddard Space Flight Center Distributed Active Archive Center (DAAC)

    NASA Technical Reports Server (NTRS)

    Leptoukh, Gregory

    1999-01-01

    The Goddard Distributed Active Archive Center (DAAC), as an integral part of the Earth Observing System Data and Information System (EOSDIS), is the official source of data for several important earth remote sensing missions. These include the Sea-viewing Wide-Field-of-view Sensor (SeaWiFS) launched in August 1997, the Tropical Rainfall Measuring Mission (TRMM) launched in November 1997, and the Moderate Resolution Imaging Spectroradiometer (MODIS) scheduled for launch in mid 1999 as part of the EOS AM-1 instrumentation package. The data generated from these missions supports a host of users in the hydrological, land biosphere and oceanographic research and applications communities. The volume and nature of the data present unique challenges to an Earth science data archive and distribution system such as the DAAC. The DAAC system receives, archives and distributes a large number of standard data products on a daily basis, including data files that have been reprocessed with updated calibration data or improved analytical algorithms. A World Wide Web interface is provided allowing interactive data selection and automatic data subscriptions as distribution options. The DAAC also creates customized and value-added data products, which allow additional user flexibility and reduced data volume. Another significant part of our overall mission is to provide ancillary data support services and archive support for worldwide field campaigns designed to validate the results from the various satellite-derived measurements. In addition to direct data services, accompanying documentation, WWW links to related resources, support for EOSDIS data formats, and informed response to inquiries are routinely provided to users. The current GDAAC WWW search and order system is being restructured to provide users with a simplified, hierarchical access to data. Data Browsers have been developed for several data sets to aid users in ordering data. These Browsers allow users to specify

  13. Insights on activation enthalpy for non-Schmid slip in body-centered cubic metals

    DOE PAGES

    Hale, Lucas M.; Lim, Hojun; Zimmerman, Jonathan A.; Battaile, Corbett C.; Weinberger, Christopher R.

    2014-12-18

    We use insights gained from atomistic simulation to develop an activation enthalpy model for dislocation slip in body-centered cubic iron. Furthermore, using a classical potential that predicts dislocation core stabilities consistent with ab initio predictions, we quantify the non-Schmid stress-dependent effects of slip. The kink-pair activation enthalpy is evaluated and a model is identified as a function of the general stress state. Thus, our model enlarges the applicability of the classic Kocks activation enthalpy model to materials with non-Schmid behavior.

  14. In Situ Imidazole Activation of Ribonucleotides for Abiotic RNA Oligomerization Reactions

    NASA Astrophysics Data System (ADS)

    Burcar, Bradley T.; Jawed, Mohsin; Shah, Hari; McGown, Linda B.

    2015-06-01

    The hypothesis that RNA played a significant role in the origin of life requires effective and efficient abiotic pathways to produce RNA oligomers. The most successful abiotic oligomerization reactions to date have utilized high-energy, modified, or pre-activated ribonucleotides to generate strands of RNA up to 50-mers in length. In spite of their success, these modifications and pre-activation reactions significantly alter the ribonucleotides in ways that are highly unlikely to have occurred on a prebiotic Earth. This research seeks to address this problem by exploring an aqueous based method for activating the canonical ribonucleotides in situ using 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and imidazole. The reactions were run with and without a montmorillonite clay catalyst and compared to reactions that used ribonucleotides that were pre-activated with imidazole. The effects of pH and ribonucleotide concentration were also investigated. The results demonstrate the ability of in situ activation of ribonucleotides to generate linear RNA oligomers in solution, providing an alternative route to produce RNA for use in prebiotic Earth scenarios.

  15. Ground reaction forces, kinematics, and muscle activations during the windmill softball pitch.

    PubMed

    Oliver, Gretchen D; Plummer, Hillary

    2011-07-01

    The aims of the present study were to examine quantitatively ground reaction forces, kinematics, and muscle activations during the windmill softball pitch, and to determine relationships between knee valgus and muscle activations, ball velocity and muscle activation as well as ball velocity and ground reaction forces. It was hypothesized that there would be an inverse relationship between degree of knee valgus and muscle activation, a direct relationship between ground reaction forces and ball velocity, and non-stride leg muscle activations and ball velocity. Ten female windmill softball pitchers (age 17.6 ± 3.47 years, stature 1.67 ± 0.07 m, weight 67.4 ± 12.2 kg) participated. Dependent variables were ball velocity, surface electromyographic (sEMG), kinematic, and kinetic data while the participant was the independent variable. Stride foot contact reported peak vertical forces of 179% body weight. There were positive relationships between ball velocity and ground reaction force (r = 0.758, n = 10, P = 0.029) as well as ball velocity and non-stride leg gluteus maximus (r = 0.851, n = 10, P = 0.007) and medius (r = 0.760, n = 10, P = 0.029) muscle activity, while there was no notable relationship between knee valgus and muscle activation. As the windmill softball pitcher increased ball velocity, her vertical ground reaction forces also increased. Proper conditioning of the lumbopelvic-hip complex, including the gluteals, is essential for injury prevention. From the data presented, it is evident that bilateral strength and conditioning of the gluteal muscle group is salient in the windmill softball pitch as an attempt to decrease incidence of injury.

  16. The role of surface reactions on the active and selective catalyst design for bioethanol steam reforming

    NASA Astrophysics Data System (ADS)

    Benito, M.; Padilla, R.; Serrano-Lotina, A.; Rodríguez, L.; Brey, J. J.; Daza, L.

    In order to study the role of surface reactions involved in bioethanol steam reforming mechanism, a very active and selective catalyst for hydrogen production was analysed. The highest activity was obtained at 700 °C, temperature at which the catalyst achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. It also exhibited a very high hydrogen production efficiency, higher than 4.5 mol H 2 per mol of EtOH fed. The catalyst was operated at a steam to carbon ratio (S/C) of 4.8, at 700 °C and atmospheric pressure. No by-products, such as ethylene or acetaldehyde were observed. In order to consider a further application in an ethanol processor, a long-term stability test was performed under the conditions previously reported. After 750 h, the catalyst still exhibited a high stability and selectivity to hydrogen production. Based on the intermediate products detected by temperature programmed desorption and reaction (TPD and TPR) experiments, a reaction pathway was proposed. Firstly, the adsorbed ethanol is dehydrogenated to acetaldehyde producing hydrogen. Secondly, the adsorbed acetaldehyde is transformed into acetone via acetic acid formation. Finally, acetone is reformed to produce hydrogen and carbon dioxide, which were the final reaction products. The promotion of such reaction sequence is the key to develop an active, selective and stable catalyst, which is the technical barrier for hydrogen production by ethanol reforming.

  17. Distinct mechanisms for DNA cleavage by myoglobin with a designed heme active center.

    PubMed

    Zhao, Yuan; Du, Ke-Jie; Gao, Shu-Qin; He, Bo; Wen, Ge-Bo; Tan, Xiangshi; Lin, Ying-Wu

    2016-03-01

    Heme proteins perform diverse biological functions, of which myoglobin (Mb) is a representative protein. In this study, the O2 carrier Mb was shown to cleave double stranded DNA upon aerobic dithiothreitol-induced reduction, which is fine-tuned by an additional distal histidine, His29 or His43, engineered in the heme active center. Spectroscopic (UV-vis and EPR) and inhibition studies suggested that free radicals including singlet oxygen and hydroxyl radical are responsible for efficient DNA cleavage via an oxidative cleavage mechanism. On the other hand, L29E Mb, with a distinct heme active center involving three water molecules in the met form, was found to exhibit an excellent DNA cleavage activity that was not depending on O2. Inhibition and ligation studies demonstrated for the first time that L29E Mb cleaves double stranded DNA into both the nicked circular and linear forms via a hydrolytic cleavage mechanism, which resembles native endonucleases. This study provides valuable insights into the distinct mechanisms for DNA cleavage by heme proteins, and lays down a base for creating artificial DNA endonucleases by rational design of heme proteins. Moreover, this study suggests that the diverse functions of heme proteins can be fine-tuned by rational design of the heme active center with a hydrogen-bonding network.

  18. Assessment of food, nutrition, and physical activity practices in Oklahoma child-care centers.

    PubMed

    Sisson, Susan B; Campbell, Janis E; May, Kellie B; Brittain, Danielle R; Monroe, Lisa A; Guss, Shannon H; Ladner, Jennifer L

    2012-08-01

    The purpose of the current study was to determine the obesogenic practices in all-day child-care centers caring for preschool-aged children. This study used a cross-sectional, self-reported survey mailed to centers across Oklahoma (n=314). Frequency of responses and χ(2) were calculated comparing region and star rating. Items where the majority of centers frequently report best practices include: daily fruits served (76%), daily nonfried vegetables served (71%), rarely/never served sugary drinks (92%), rarely/never used food to encourage good behaviors (88%), staff join children at table most of the time (81%), staff rarely eat different foods in view of children (69%), visible self-serve or request availability of water (93%), regular informal communication about healthy eating (86%), opportunities for outdoor play (95%), not withholding activity for punishment (91%), accessible play equipment (59% to 80% for different types of equipment), and minimization of extended sitting time (78%). Practices where centers can improve include increasing variety of vegetables (18%), reducing frequency of high-fat meats served (74% serve more than once per week), increasing high-fiber and whole-grain foods (35% offer daily), serving style of "seconds" (28% help kids determine whether they are still hungry), nonfood holiday celebrations (44% use nonfood treats), having toys and books that encourage healthy eating (27%) and physical activity (25%) in all rooms in the center, a standard nutrition (21%) and physical education (50%) curriculum, and following a written physical activity policy (43%). Practitioners can use these data to develop benchmarks and interventions, as this was the first study to assess statewide obesogenic practices in child care.

  19. Characterizing Active Site Conformational Heterogeneity along the Trajectory of an Enzymatic Phosphoryl Transfer Reaction.

    PubMed

    Zeymer, Cathleen; Werbeck, Nicolas D; Zimmermann, Sabine; Reinstein, Jochen; Hansen, D Flemming

    2016-09-12

    States along the phosphoryl transfer reaction catalyzed by the nucleoside monophosphate kinase UmpK were captured and changes in the conformational heterogeneity of conserved active site arginine side-chains were quantified by NMR spin-relaxation methods. In addition to apo and ligand-bound UmpK, a transition state analog (TSA) complex was utilized to evaluate the extent to which active site conformational entropy contributes to the transition state free energy. The catalytically essential arginine side-chain guanidino groups were found to be remarkably rigid in the TSA complex, indicating that the enzyme has evolved to restrict the conformational freedom along its reaction path over the energy landscape, which in turn allows the phosphoryl transfer to occur selectively by avoiding side reactions. PMID:27534930

  20. Organocatalytic chemo- and regioselective oxyarylation of styrenes via a cascade reaction: remote activation of hydroxyl groups.

    PubMed

    Zhang, Yu-Chen; Jiang, Fei; Wang, Shu-Liang; Shi, Feng; Tu, Shu-Jiang

    2014-07-01

    The first organocatalytic oxyarylation of styrenes has been established through a cascade of vinylogous Michael addition/alkoxyl transfer reactions of o- or p-hydroxylstyrenes with quinone imine ketals. The process leads to a highly chemo- and regioselective oxyarylation of styrenes and provides access to m-alkylated anilines in generally high yields and excellent diastereoselectivity (up to 99% yield, >95:5 dr). An investigation of the reaction pathway revealed that the existence and position of the hydroxyl group of styrene played crucial roles in the cascade reaction, suggesting that the two reactants were simultaneously activated by binaphthyl-derived phosphoric acid via hydrogen bonding interactions and long-distance conjugative effects. In addition, the activating group of the hydroxyl functionality in the products can be easily removed or transformed, demonstrating the applicability and utility of this strategy in styrene oxyarylation and in the synthesis of styrene-based compounds.

  1. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen–Popper, Dion–Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  2. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen-Popper, Dion-Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  3. Characterizing Active Site Conformational Heterogeneity along the Trajectory of an Enzymatic Phosphoryl Transfer Reaction

    PubMed Central

    Zeymer, Cathleen; Werbeck, Nicolas D.; Zimmermann, Sabine

    2016-01-01

    Abstract States along the phosphoryl transfer reaction catalyzed by the nucleoside monophosphate kinase UmpK were captured and changes in the conformational heterogeneity of conserved active site arginine side‐chains were quantified by NMR spin‐relaxation methods. In addition to apo and ligand‐bound UmpK, a transition state analog (TSA) complex was utilized to evaluate the extent to which active site conformational entropy contributes to the transition state free energy. The catalytically essential arginine side‐chain guanidino groups were found to be remarkably rigid in the TSA complex, indicating that the enzyme has evolved to restrict the conformational freedom along its reaction path over the energy landscape, which in turn allows the phosphoryl transfer to occur selectively by avoiding side reactions. PMID:27534930

  4. Chemoselective Boron-Catalyzed Nucleophilic Activation of Carboxylic Acids for Mannich-Type Reactions.

    PubMed

    Morita, Yuya; Yamamoto, Tomohiro; Nagai, Hideoki; Shimizu, Yohei; Kanai, Motomu

    2015-06-10

    The carboxyl group (COOH) is an omnipresent functional group in organic molecules, and its direct catalytic activation represents an attractive synthetic method. Herein, we describe the first example of a direct catalytic nucleophilic activation of carboxylic acids with BH3·SMe2, after which the acids are able to act as carbon nucleophiles, i.e. enolates, in Mannich-type reactions. This reaction proceeds with a mild organic base (DBU) and exhibits high levels of functional group tolerance. The boron catalyst is highly chemoselective toward the COOH group, even in the presence of other carbonyl moieties, such as amides, esters, or ketones. Furthermore, this catalytic method can be extended to highly enantioselective Mannich-type reactions by using a (R)-3,3'-I2-BINOL-substituted boron catalyst.

  5. Employing Magnetic Levitation to Monitor Reaction Kinetics and Measure Activation Energy

    ERIC Educational Resources Information Center

    Benz, Lauren; Cesafsky, Karen E.; Le, Tran; Park, Aileen; Malicky, David

    2012-01-01

    This article describes a simple and inexpensive undergraduate-level kinetics experiment that uses magnetic levitation to monitor the progress and determine the activation energy of a condensation reaction on a polymeric solid support. The method employs a cuvette filled with a paramagnetic solution positioned between two strong magnets. The…

  6. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  7. Oxidation of flavonoids by hypochlorous acid: reaction kinetics and antioxidant activity studies.

    PubMed

    Krych-Madej, Justyna; Stawowska, Katarzyna; Gebicka, Lidia

    2016-08-01

    Flavonoids, plant polyphenols, ubiquitous components of human diet, are excellent antioxidants. Hypochlorous acid (HOCl), produced by activated neutrophils, is highly reactive chlorinating and oxidizing species. It has been reported earlier that flavonoids are chlorinated by HOCl. Here we show that flavonoids from flavonol subclass are also oxidized by HOCl, but only if the latter is in a large molar excess (≥ 10). The kinetics of this reaction was studied by stopped-flow spectrophotometry, at different pH. We found that flavonols were oxidized by HOCl with the rate constants of the order of 10(4)-10(5) M(-1) s(-1) at pH 7.5. Antioxidant activity of HOCl-modified flavonoids was measured by 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) method. Slightly higher antioxidant activity, compared to parent compounds, was observed for flavonols after their reaction with equimolar or moderate excess of HOCl whereas flavonols treated with high molar excess of HOCl exhibited decrease in antioxidant activity. The mechanism of flavonoid reaction with HOCl at physiological pH is proposed, and biological consequences of this reaction are discussed. PMID:27225705

  8. In-situ resource utilization activities at the NASA Space Engineering Research Center

    NASA Technical Reports Server (NTRS)

    Ramohalli, Kumar

    1992-01-01

    The paper describes theoretical and experimental research activities at the NASA Space Engineering Research Center aimed at realizing significant cost savings in space missions through the use of locally available resources. The fundamental strategy involves idea generation, scientific screening, feasibility demonstrations, small-scale process plant design, extensive testing, scale-up to realistic production rates, associated controls, and 'packaging', while maintaining sufficient flexibility to respond to national needs in terms of specific applications. Aside from training, the principal activities at the Center include development of a quantitative figure-of-merit to quickly assess the overall mission impact of individual components that constantly change with advancing technologies, extensive tests on a single-cell test bed to produce oxygen from carbon dioxide, and the use of this spent stream to produce methane.

  9. Research Activities at Plasma Research Laboratory at NASA Ames Research Center

    NASA Technical Reports Server (NTRS)

    Sharma, S. P.; Rao, M. V. V. S.; Meyyappan, Meyya

    2000-01-01

    In order to meet NASA's requirements for the rapid development and validation of future generation electronic devices as well as associated materials and processes, enabling technologies are being developed at NASA-Ames Research Center using a multi-discipline approach. The first step is to understand the basic physics of the chemical reactions in the area of plasma reactors and processes. Low pressure glow discharges are indispensable in the fabrication of microelectronic circuits. These plasmas are used to deposit materials and also etch fine features in device fabrication. However, many plasma-based processes suffer from stability and reliability problems leading to a compromise in performance and a potentially increased cost for the semiconductor manufacturing industry. Although a great deal of laboratory-scale research has been performed on many of these processing plasmas, little is known about the gas-phase and surface chemical reactions that are critical in many etch and deposition processes, and how these reactions are influenced by the variation in operating conditions. Such a lack of understanding has hindered the development of process models that can aid in the scaling and improvement of plasma etch and deposition systems. Our present research involves the study of such plasmas. An inductively-coupled plasma (ICP) source in place of the standard upper electrode assembly of the Gaseous Electronics Conference (GEC) radio-frequency (RF) Reference Cell is used to investigate the discharge characteristics. This ICP source generates plasmas with higher electron densities and lower operating pressures than obtainable with the original parallel-plate version of the GEC Cell. This expanded operating regime is more relevant to new generations of industrial plasma systems being used by the microelectronics industry. The research goal is to develop an understanding of the physical phenomena involved in plasma processing and to measure much needed fundamental

  10. Organocatalytic enantioselective tandem aldol-cyclization reaction of α-isothiocyanato imides and activated carbonyl compounds

    PubMed Central

    Guang, Jie; Zhao, Cong-Gui

    2011-01-01

    The organocatalytic enantioselective tandem aldol-cyclization reactions of α-isothiocyanato imides and activated carbonyl compounds, such as isatins, an α-ketolactone and a 1,2-dione, have been studied with cinchona alkaloid-derived thiourea-catalysts. This methodology provided an easy way to access enantiomerically enriched spirobicyclic thiocarbamates with high yields and good to excellent stereoselectivity, which have been demonstrated to be useful precursors for the synthesis of biologically active molecules. PMID:21921975

  11. Adverse reactions of Methylphenidate in children with attention deficit-hyperactivity disorder: Report from a referral center

    PubMed Central

    Khajehpiri, Zahra; Mahmoudi-Gharaei, Javad; Faghihi, Toktam; Karimzadeh, Iman; Khalili, Hossein; Mohammadi, Mostafa

    2014-01-01

    Objective: The aim of the current study was to determine various aspects of methylphenidate adverse reactions in children with attention deficit-hyperactivity disorder (ADHD) in Iran. Methods: During the 6 months period, all children under methylphenidate treatment alone or along with other agents attending a university-affiliated psychology clinic were screened regarding all subjective and objective adverse drug reactions (ADRs) of methylphenidate. Causality and seriousness of detected ADRs were assessed by relevant World Health Organization definitions. The Schumock and Thornton questionnaire was used to determine preventability of ADRs. Findings: Seventy-one patients including 25 girls and 46 boys with ADHD under methylphenidate treatment were enrolled within the study period. All (100%) ADHD children under methylphenidate treatment developed at least one ADR. Anorexia (74.3%), irritability (57.1%), and insomnia (47.2%) were the most frequent methylphenidate-related adverse reactions. Except for one, all other detected ADRs were determined to be mild. In addition, no ADR was considered to be preventable and serious. Conclusion: Our data suggested that although methylphenidate related adverse reactions were common in children with ADHD, but they were mainly mild and nonserious. PMID:25535621

  12. Probing the Energy Transfer Dynamics of Photosynthetic Reaction Center Complexes Through Hole-Burning and Single-Complex Spectroscopy

    SciTech Connect

    Riley, Kerry Joseph

    2007-01-01

    Photosynthesis is the process by which light energy is used to drive reactions that generate sugars to supply energy for cellular processes. It is one of the most important fundamental biological reactions and occurs in both prokaryotic (e.g. bacteria) and eukaryotic (e.g. plants and algae) organisms. Photosynthesis is also remarkably intricate, requiring the coordination of many different steps and reactions in order to successfully transform absorbed solar energy into a biochemical usable form of energy. However, the net reaction for all photosynthetic organisms can be reduced to the following, deceptively general, equation developed by Van Niel[1] H2 - D + Aimplieshv A - H2 + D where H2-D is the electron donor, e.g. H2O, H2S. A is the electron acceptor, e.g. CO2, and A-H2 is the synthesized sugar. Amazingly, this simple net equation is responsible for creating the oxidizing atmosphere of Earth and the recycling of CO2, both of which are necessary for the sustainment of the global ecosystem.

  13. Societal Values and Policies May Curtail Preschool Children’s Physical Activity in Child Care Centers

    PubMed Central

    Sherman, Susan N.; Kendeigh, Cassandra A.; Kalkwarf, Heidi J.; Saelens, Brian E.

    2012-01-01

    BACKGROUND AND OBJECTIVES: Three-fourths of US preschool-age children are in child care centers. Children are primarily sedentary in these settings, and are not meeting recommended levels of physical activity. Our objective was to identify potential barriers to children’s physical activity in child care centers. METHODS: Nine focus groups with 49 child care providers (55% African American) were assembled from 34 centers (inner-city, suburban, Head Start, and Montessori) in Cincinnati, Ohio. Three coders independently analyzed verbatim transcripts for themes. Data analysis and interpretation of findings were verified through triangulation of methods. RESULTS: We identified 3 main barriers to children’s physical activity in child care: (1) injury concerns, (2) financial, and (3) a focus on “academics.” Stricter licensing codes intended to reduce children's injuries on playgrounds rendered playgrounds less physically challenging and interesting. In addition, some parents concerned about potential injury, requested staff to restrict playground participation for their children. Small operating margins of most child care centers limited their ability to install abundant playground equipment. Child care providers felt pressure from state mandates and parents to focus on academics at the expense of gross motor play. Because children spend long hours in care and many lack a safe place to play near their home, these barriers may limit children's only opportunity to engage in physical activity. CONCLUSIONS: Societal priorities for young children—safety and school readiness—may be hindering children’s physical development. In designing environments that optimally promote children’s health and development, child advocates should think holistically about potential unintended consequences of policies. PMID:22218842

  14. Catalytic Activity-d-Band Center Correlation for the O2 Reduction on Platinum in Alkaline Solutions

    SciTech Connect

    Lima,F.; Zhang, J.; Shao, M.; Sasaki, K.; Vukmirovic, M.; Ticianelli, E.; Adzic, R.

    2007-01-01

    We determined, by the rotating disk electrode technique, the kinetics of the oxygen-reduction reaction (ORR) on the surfaces of single crystals of Au(111), Ag(111), Pd(111), Rh(111), Ir(111), and Ru(0001), on Pt monolayers deposited on their surfaces, and also on nanoparticles of these metals dispersed on high-surface-area carbon. Plotting the correlation between the experimentally determined activities of these three types of electrocatalysts with the calculated metal d-band center energies,{var_epsilon}{sub d}, revealed a volcano-type dependence. In all cases, the electronic properties of the metal electrocatalysts, represented by the {var_epsilon}{sub d} value, were used for elucidating the metal-dependent catalytic activities, and establishing their electronic properties-the ORR kinetics relationship. Pt(111), Pt/C, and Pt/Pd(111) were found to top their corresponding volcano plots. Pd in alkaline solutions showed particularly high activity, suggesting it may offer potential replacement for Pt in fuel cells.

  15. Person-Centered, Physical Activity for Patients with Low Back Pain: Piloting Service Delivery.

    PubMed

    Bloxham, Saul; Barter, Phil; Scragg, Slafka; Peers, Charles; Jane, Ben; Layden, Joe

    2016-01-01

    Low back pain (LBP) is one of the most common and costly conditions in industrialized countries. Exercise therapy has been used to treat LBP, although typically using only one mode of exercise. This paper describes the method and initial findings of a person-centered, group physical activity programme which featured as part of a multidisciplinary approach to treating LBP. Six participants (aged 50.7 ± 17 years) completed a six-week physical activity programme lasting two hours per week. A multicomponent approach to physical activity was adopted which included aerobic fitness, core activation, muscular strength and endurance, Nordic Walking, flexibility and exercise gaming. In addition, participants were required to use diary sheets to record physical activity completed at home. Results revealed significant (p < 0.05) improvements in back strength (23%), aerobic fitness (23%), negative wellbeing (32%) and disability (16%). Person's Correlation Coefficient analysis revealed significant (p < 0.05) relationships between improvement in perceived pain and aerobic fitness (r = 0.93). It was concluded that a person-centered, multicomponent approach to physical activity may be optimal for supporting patients who self-manage LBP. PMID:27417616

  16. Person-Centered, Physical Activity for Patients with Low Back Pain: Piloting Service Delivery

    PubMed Central

    Bloxham, Saul; Barter, Phil; Scragg, Slafka; Peers, Charles; Jane, Ben; Layden, Joe

    2016-01-01

    Low back pain (LBP) is one of the most common and costly conditions in industrialized countries. Exercise therapy has been used to treat LBP, although typically using only one mode of exercise. This paper describes the method and initial findings of a person-centered, group physical activity programme which featured as part of a multidisciplinary approach to treating LBP. Six participants (aged 50.7 ± 17 years) completed a six-week physical activity programme lasting two hours per week. A multicomponent approach to physical activity was adopted which included aerobic fitness, core activation, muscular strength and endurance, Nordic Walking, flexibility and exercise gaming. In addition, participants were required to use diary sheets to record physical activity completed at home. Results revealed significant (p < 0.05) improvements in back strength (23%), aerobic fitness (23%), negative wellbeing (32%) and disability (16%). Person’s Correlation Coefficient analysis revealed significant (p < 0.05) relationships between improvement in perceived pain and aerobic fitness (r = 0.93). It was concluded that a person-centered, multicomponent approach to physical activity may be optimal for supporting patients who self-manage LBP. PMID:27417616

  17. Effect of the pyrrole polymerization mechanism on the antioxidative activity of nonenzymatic browning reactions.

    PubMed

    Hidalgo, Francisco J; Nogales, Fátima; Zamora, Rosario

    2003-09-10

    The present investigation was undertaken to study how the antioxidative activity (AA) of nonenzymatic browning reactions is changing at the same time that the browning (by the pyrrole polymerization mechanism) is being produced. The antioxidative activities of eight model pyrroles (pyrrole, 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, 2-acetylpyrrole, 2-acetyl-1-methylpyrrole, pyrrole-2-carboxaldehyde, and 1-methyl-2-pyrrolecarboxaldehyde) as well as the browning reaction of 2-(1-hydroxyethyl)-1-methylpyrrole (HMP) and the dimer (DIM) produced during HMP browning were determined. The results obtained suggest that the AAs observed in nonenzymatic browning reactions are the result of the AAs of the different oxidized lipid/amino acid reaction products formed. Thus, the different pyrrole derivatives produced in these reactions had different AAs, and the highest AAs were observed for alkyl-substituted pyrroles without free alpha-positions. Because some of these pyrrole derivatives are implicated in nonenzymatic browning production and this browning production implies the loss of hydroxyl groups and the transformation of some pyrroles with one type of substitution into others, changes in AA during browning production were observed, and the resulting DIM derivative was more antioxidant than HMP or higher polymers. These results explain the AA observed in fatty acid/protein mixtures after slight oxidation and suggest that, when the pyrrole polymerization mechanism is predominant, slightly browned samples may be more antioxidant than samples in which nonenzymatic browning has been highly developed. PMID:12952422

  18. Nucleophilic reactions at a vinylic center. XVI. Investigation of the nucleophilic exchange of fluorine in. beta. -fluoroacrylonitriles by the MINDO/3 method

    SciTech Connect

    Shainyan, B.A.

    1986-01-10

    The potential energy surfaces of the reactions of F/sup -/ with cis- and trans-..beta..-fluoroacrylonitriles were calculated by the MINDO/3 method. It was shown that three reaction paths can be realized in the system, i.e., attack by the nucleophile at the ..beta..-carbon atom, the elimination of a proton from the ..cap alpha.. position, and the elimination of a proton from the ..beta.. position. All three reaction paths are exothermic in the gas phase, and the elimination of the proton from the ..cap alpha.. position is 70 kJ/mole more favorable than from the ..beta.. position. Allowance for the effect of the medium in terms of an unconcerted solvation model modes not lead to the appearance of an activation barrier, in contrast to the reactions of anions with ethylene.

  19. Features of the electronic structure of the active center of an HbS molecule

    NASA Astrophysics Data System (ADS)

    Novoselov, D. Yu.; Korotin, Dm. M.; Anisimov, V. I.

    2016-01-01

    Features of the electronic structure of the nonprotein part of the mutant form of the human hemoglobin molecule, HbS, are studied along with the magnetic state of the iron ion that is the "nucleus" of the active center of the molecule. It is found that the mutant form of the HbS molecule differs from a normal hemoglobin molecule by the distortion of the local environment of the iron ion, which changes the energy level splitting by a crystal field. As a result of ab initio calculations, the magnetic transition in the iron atom from the high-spin state to the low-spin state upon the addition of molecular oxygen to hemoglobin molecule is reproduced. It is established for the first time that a change in the crystal and electronic structure of the active center as a result of a mutation can lead to a substantial change in the energy of the bond between the active center of the hemoglobin molecule and an oxygen molecule.

  20. Substrate activity of synthetic formyl phosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Smithers, G.W.; Jahansouz, H.; Kofron, J.L.; Himes, R.H.; Reed, G.H.

    1987-06-30

    Formyl phosphate, a putative enzyme-bound intermediate in the reaction catalyzed by formyltetrahydrofolate synthetase (EC 6.3.4.3), was synthesized from formyl fluoride and inorganic phosphate, and the product was characterized by /sup 31/P, /sup 1/H, and /sup 13/C nuclear magnetic resonance (NMR). Measurement of hydrolysis rates by /sup 31/P NMR indicates that formyl phosphate is particularly labile, with a half-life of 48 min in a buffered neutral solution at 20 /sup 0/C. At pH 7, hydrolysis occurs with P-O bond cleavage, as demonstrated by /sup 18/O incorporation from H/sub 2//sup 18/O into P/sub i/, while at pH 1 and pH 13 hydrolysis occurs with C-O bond cleavage. The substrate activity of formyl phosphate was tested in the reaction catalyzed by formyltetrahydrofolate synthetase isolated from Clostridium cylindrosporum. Formyl phosphate supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formyltetrahydrofolate is produced from tetrahydrofolate and formyl phosphate in a reaction mixture that contains enzyme, Mg(II), and ADP, and ATP is produced from formyl phosphate and ADP with enzyme, Mg(II), and tetrahydrofolate present. The requirements for ADP and for tetrahydrofolate as cofactors in these reactions are consistent with previous steady-state kinetic and isotope exchange studies, which demonstrated that all substrate subsites must be occupied prior to catalysis. The k/sub cat/ values for both the forward and reverse directions, with formyl phosphate as the substrate, are much lower than those for the normal forward and reverse reactions. Kinetic analysis of the formyl phosphate supported reactions indicates that the low steady-state rates observed for the synthetic intermediate are most likely due to the sequential nature of the normal reaction.