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Sample records for radical stability directs

  1. Direct generation of oxygen-stabilized radicals by H• transfer from transition metal hydrides.

    PubMed

    Kuo, Jonathan L; Hartung, John; Han, Arthur; Norton, Jack R

    2015-01-28

    Transition-metal hydrides generate α-alkoxy radicals by H• transfer to enol ethers. We have measured the rate constant for transfer from CpCr(CO)3H to n-butyl vinyl ether and have examined the chemistry of radicals generated by such transfers. Radicals from appropriate substrates undergo 5-exo cyclization, with higher diastereoselectivity than the analogous all-carbon radicals. From such radicals it is straightforward to make substituted tetrahydrofurans. PMID:25569214

  2. Mechanically Stabilized Tetrathiafulvalene Radical Dimers

    SciTech Connect

    Coskun, Ali; Spruell, Jason M.; Barin, Gokhan; Fahrenbach, Albert C.; Forgan, Ross S.; Colvin, Michael T.; Carmieli, Raanan; Benitez, Diego; Tkatchouk, Ekaterina; Friedman, Douglas C.; Sarjeant, Amy A.; Wasielewski, Michael R.; Goddard, William A.; Stoddart, J. Fraser

    2011-01-01

    Two donor-acceptor [3]catenanes—composed of a tetracationic molecular square, cyclobis(paraquat-4,4'-biphenylene), as the π-electron deficient ring and either two tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) containing macrocycles or two TTF-butadiyne-containing macrocycles as the π-electron rich components—have been investigated in order to study their ability to form TTF radical dimers. It has been proven that the mechanically interlocked nature of the [3]catenanes facilitates the formation of the TTF radical dimers under redox control, allowing an investigation to be performed on these intermolecular interactions in a so-called “molecular flask” under ambient conditions in considerable detail. In addition, it has also been shown that the stability of the TTF radical-cation dimers can be tuned by varying the secondary binding motifs in the [3]catenanes. By replacing the DNP station with a butadiyne group, the distribution of the TTF radical-cation dimer can be changed from 60% to 100%. These findings have been established by several techniques including cyclic voltammetry, spectroelectrochemistry and UV-vis-NIR and EPR spectroscopies, as well as with X-ray diffraction analysis which has provided a range of solid-state crystal structures. The experimental data are also supported by high-level DFT calculations. The results contribute significantly to our fundamental understanding of the interactions within the TTF radical dimers.

  3. Competition of charge- versus radical-directed fragmentation of gas-phase protonated cysteine sulfinyl radicals.

    PubMed

    Love, Chasity B; Tan, Lei; Francisco, Joseph S; Xia, Yu

    2013-04-24

    The fragmentation behavior of various cysteine sulfinyl ions (intact, N-acetylated, and O-methylated), new members of the gas-phase amino acid radical ion family, was investigated by low-energy collision-induced dissociation (CID). The dominant fragmentation channel for the protonated cysteine sulfinyl radicals ((SO•)Cys) was the radical-directed Cα-Cβ homolytic cleavage, resulting in the formation of glycyl radical ions and loss of CH2SO. This channel, however, was not observed for protonated N-acetylated cysteine sulfinyl radicals (Ac-(SO•)Cys); instead, charge-directed H2O loss followed immediately by SH loss prevailed. Counterintuitively, the H2O loss did not derive from the carboxyl group but involved the sulfinyl oxygen, a proton, and a Cβ hydrogen atom. Theoretical calculations suggested that N-acetylation significantly increases the barrier (~14 kcal mol(-1)) for the radical-directed fragmentation channel because of its reduced capability to stabilize the thus-formed glycyl radical ions via the captodative effect. N-Acetylation also assists in moving the proton to the sulfinyl site, which reduces the barrier for H2O loss. Our studies demonstrate that for cysteine sulfinyl radical ions, the stability of the product ions (glycyl radical ions) and the location of the charge (proton) can significantly modulate the competition between radical- and charge-directed fragmentation. PMID:23527556

  4. The stabilization energies of polyenyl radicals

    NASA Astrophysics Data System (ADS)

    Luo, Yu-Ran; Holmes, John L.

    1994-10-01

    The resonance stabilization energies, Es, of polyenyl radicals can be estimated by the equation Es( N)=-13.2+[3.95-15.8(2) -2/ n] kcal mol -1, where N is the number of C, C-π bonds in the polyenyl radicals. This correlation has been extended for predicting the weakest HC, CC and COH bond dissociation energies in vitamin A and similar compounds.

  5. Designed metalloprotein stabilizes a semiquinone radical

    NASA Astrophysics Data System (ADS)

    Ulas, Gözde; Lemmin, Thomas; Wu, Yibing; Gassner, George T.; Degrado, William F.

    2016-04-01

    Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(II) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal-ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol-1). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry.

  6. Designed metalloprotein stabilizes a semiquinone radical

    PubMed Central

    Ulas, Gözde; Lemmin, Thomas; Wu, Yibing; Gassner, George T.; DeGrado, William F.

    2016-01-01

    Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(ii) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal–ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol−1). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry. PMID:27001731

  7. Designed metalloprotein stabilizes a semiquinone radical.

    PubMed

    Ulas, Gözde; Lemmin, Thomas; Wu, Yibing; Gassner, George T; DeGrado, William F

    2016-04-01

    Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(II) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal-ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol(-1)). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry. PMID:27001731

  8. Radical attached aluminum nanoclusters: an alternative way of cluster stabilization.

    PubMed

    Sengupta, Turbasu; Pal, Sourav

    2016-08-21

    The stability and electronic structure of radical attached aluminum nanoclusters are investigated using density functional theory (DFT). A detailed investigation shows good correlation between the thermodynamic stability of radical attached clusters and the stability of the attached radical anions. All other calculated parameters like HOMO-LUMO gap and charge transfer are also found to be consistent with the observed thermodynamic stabilities of the complexes. Investigation of the electronic structure of radical attached complexes further shows the presence of jellium structures within the core similar to the ligated clusters. Comparison with available experimental and theoretical data also proves the validity of superatomic complex theory for the radical attached clusters as well. Based on the evaluated thermodynamic parameters, selected radical attached clusters are observed to be more thermodynamically stable in comparison with experimentally synthesized ligated clusters. Stabilization of small metal clusters is one of the greatest challenges in current cluster science and the present investigation confirms the fact that radical attached clusters can provide a viable alternative to ligated clusters in the future. PMID:27435912

  9. Domino Fragmentations in Traceless Directing Groups of Radical Cascades: Evidence for the Formation of Alkoxy Radicals via C-O Scission.

    PubMed

    Harris, Trevor; Gomes, Gabriel Dos Passos; Clark, Ronald J; Alabugin, Igor V

    2016-07-15

    Direct evidence for the formation of alkoxy radicals is reported in radical cascades using traceless directing groups. Despite the possibility of hydrogen abstraction in the fragmenting step, followed by loss of R-OH, β-scission is preferred for the formation of alkoxy radicals. For the first time, the C-O radical was intermolecularly trapped using a silyl enol ether. Various C-X fragmenting groups were explored as possible traceless directing groups for the preparation of extended polyaromatics. Computational evidence shows that a combination of aromatization, steric and stereoelectronic effects assists the fragmentation to alkoxy radicals. Additionally, a new through-space interaction was discovered between O and Sn in the fragmentation as a specific transition state stabilizing effect. PMID:27304982

  10. The Radical Stabilization Energy of a Substituted Carbon-centered Free Radical Depends both on the Functionality of the Substituent and the Ordinality of the Radical

    SciTech Connect

    Poutsma, Marvin L

    2011-01-01

    Chemical intuition suggests that the stabilization of a carbon-centered free radical by a substituent X would be the greatest for a prim and least for a more stable tert radical because of saturation. However, analysis of a comprehensive recent set of bond dissociation energies computed by Coote and coworkers (Phys. Chem. Chem. Phys. 2010 12 9597) and transformed into radical stabilization energies (RSE) suggests that this supposition is often violated. The RSE for a given X depends not only on the nature of X but also on the ordinality (i.e., prim, sec, or tert) of the radical onto which it is substituted. For substituents that stabilize by electron delocalization but also contain electron-withdrawing centers, such as the carbonyl function, the stabilization of XCMe2 compared with HCMe2 is greater than for XCH2 compared with HCH2 . However, for substituents that stabilize by lone-pair electron donation, such as N or O centers, the order is strongly reversed. This contrast can be qualitatively rationalized by considering charge-separated VB contributors to the radical structure (R2C+ X- and R2C- X+ ) and the contrasting effects of methyl substituents on them. This conclusion is not dependent on the particular definition used for RSE.

  11. Haptoglobin Binding Stabilizes Hemoglobin Ferryl Iron and the Globin Radical on Tyrosine β145

    PubMed Central

    Schaer, Dominik J.; Buehler, Paul W.; Wilson, Michael T.; Reeder, Brandon J.; Silkstone, Gary; Svistunenko, Dimitri A.; Bulow, Leif; Alayash, Abdu I.

    2013-01-01

    Abstract Aim: Hemoglobin (Hb) becomes toxic when released from the erythrocyte. The acute phase protein haptoglobin (Hp) binds avidly to Hb and decreases oxidative damage to Hb itself and to the surrounding proteins and lipids. However, the molecular mechanism underpinning Hp protection is to date unclear. The aim of this study was to use electron paramagnetic resonance (EPR) spectroscopy, stopped flow optical spectrophotometry, and site-directed mutagenesis to explore the mechanism and specifically the role of specific tyrosine residues in this protection. Results: Following peroxide challenge Hb produces reactive oxidative intermediates in the form of ferryl heme and globin free radicals. Hp binding increases the steady state level of ferryl formation during Hb-catalyzed lipid peroxidation, while at the same time dramatically inhibiting the overall reaction rate. This enhanced ferryl stability is also seen in the absence of lipids and in the presence of external reductants. Hp binding is not accompanied by a decrease in the pK of ferryl protonation; the protonated ferryl species still forms, but is intrinsically less reactive. Ferryl stabilization is accompanied by a significant increase in the concentration of the peroxide-induced tyrosine free radical. EPR spectral parameters and mutagenesis studies suggest that this radical is located on tyrosine 145, the penultimate C-terminal amino acid on the beta Hb subunit. Innovation: Hp binding decreases both the ferryl iron and free radical reactivity of Hb. Conclusion: Hp protects against Hb-induced damage in the vasculature, not by preventing the primary reactivity of heme oxidants, but by rendering the resultant protein products less damaging. Antioxid. Redox Signal. 18, 2264–2273. PMID:22702311

  12. Tested Demonstrations: The Effect of Free Radical Stability on the Rate of Bromination of Hydrocarbons.

    ERIC Educational Resources Information Center

    Gilbert, George L., Ed.; And Others

    1980-01-01

    Presents a demonstration of the effect of alkyl free radical stability on the rate of free radical halogenation of hydrocarbons. The arenes toluene, ethylbenzene and comene are photobrominated comparatively, using an overhead projector both to provide a light source for the chemical reaction and to project the results on a screen. (CS)

  13. Spectroscopy and Ionization Thresholds of Isoelectronic 1-PHENYLALLYL and Benzylallenyl Resonance Stabilized Radicals

    NASA Astrophysics Data System (ADS)

    Sebree, Joshua A.; Kidwell, Nathan; Buchanan, Evan; Zwier, Timothy S.; Zgierski, Marek

    2011-06-01

    In recent years it has been proposed that resonance-stabilized radicals (RSRs) may play an important role as intermediates in the formation of polycyclic aromatic hydrocarbons (PAHs). RSRs gain extra stability by delocalizing the unpaired electron through a neighboring conjugated π-system. Because of this extra stability, RSRs are able to build up in concentration, allowing for the creation of larger, more complex systems through their recombination with other RSRs. Mass-selective two-color resonant two-photon ionization spectra of two RSRs, phenylallyl and benzylallenyl radicals, have been recorded under jet-cooled conditions. These two radicals, while sharing the same radical conjugation, have unique properties. The phenylallyl and benzylallenyl radicals were respectively produced via discharge of trans-β-methylstyrene and benzylallene in argon prior to supersonic expansion. The D0-D1 origin of the phenylallyl radical was found at 19204 wn and was found to have a strong vertical ionization energy of 6.905(2) eV. By comparison, the benzylallenyl radical has an origin at 19703 wn and, while showing similar Franck-Condon activity to phenylallyl, has an IP curve indicative of a large geometry change between the ground state and the ion 7.50(2) eV. Visible-visible holeburning was used to show that each radical exists in one conformeric form in the expansion. The CH stretch region of each radical was taken using D0-Resonant Ion Dip Infrared Spectroscopy in a novel four laser experiment. A combination of this and DFT calculations was used to show that each radical exists in a trans geometry.

  14. Electron exchange involving a sulfur-stabilized ruthenium radical cation.

    PubMed

    Shaw, Anthony P; Ryland, Bradford L; Norton, Jack R; Buccella, Daniela; Moscatelli, Alberto

    2007-07-01

    Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at -98 degrees C in CD2Cl2. PMID:17569530

  15. Stabilization of Superoxide and CO3- Radicals through Crystalliation of CaCO3

    NASA Astrophysics Data System (ADS)

    Meguro, Kazuhide; Ikeya, Motoji

    1993-08-01

    Unstable superoxide radicals (ga{=}2.010, gb{=}2.064, gc{=}2.049, and gd{=}2.006) and CO3- hole centers (gx{=}2.017, gy{=}2.011, and gz{=}2.002) were stabilized in CaCO3 when the inorganic material was crystallized from radical solution. The radicals surrounded by the lattice give strong electron spin resonance (ESR) signals at room temperature. The signal intensities of superoxide and CO3- radicals generated in H2O2 solution and doped in CaCO3 are much stronger than those obtained by adsorption. The color of radical-doped CaCO3 is different from that of the radical-adsorbed one. On heating the samples, the spectrum and the color of the radical-doped CaCO3 powder changed. The effects of impurities on the spectrum of radical-doped inorganic materials are studied. Some doping experiments have been conducted using other inorganic materials.

  16. Stabilization of superoxide and CO(-)3 radicals through crystallization of CaCO3

    NASA Astrophysics Data System (ADS)

    Meguro, Kazuhide; Ikeya, Motoji

    1993-08-01

    Unstable superoxide radicals (g(sub a) = 2.010, g(sub b) = 2.064, g(sub c) = 2.049, and g(sub d) = 2.066) and CO(-)3 hole centers (g(sub x) = 2.017, g(sub y) = 2.011, and g(sub z) = 2.002) were stabilized in CaCO3 when the inorganic material was crystallized from radical solution. The radicals surrounded by the lattice give strong electron spin resonance (ESR) signals at room temperature. The signal intensities of superoxide and CO(-)3 radicals generated in H2O2 solution and doped in CaCO are much stronger than those obtained by adsorption. The color of radical-doped CaCO3 is different from that of the radical-adsorbed one. On heating the samples, the spectrum and the color of the radical-doped CaCO3 powder changed. The effects of impurities on the spectrum of radical-doped inorganic materials are studied. Some doping experiments have been conducted using other inorganic materials.

  17. Charge-transfer-directed radical substitution enables para-selective C–H functionalization

    NASA Astrophysics Data System (ADS)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C–H functionalization requires selectivity for specific C–H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C–H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C–H functionalization reactions.

  18. Charge-transfer-directed radical substitution enables para-selective C-H functionalization.

    PubMed

    Boursalian, Gregory B; Ham, Won Seok; Mazzotti, Anthony R; Ritter, Tobias

    2016-08-01

    Efficient C-H functionalization requires selectivity for specific C-H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C-H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C-H functionalization reactions. PMID:27442288

  19. Stability and reactivity of free radicals: a physicochemical perspective with biological implications.

    PubMed

    Karogodina, Tatiana Yu; Sergeeva, Svetlana V; Stass, Dmitri V

    2011-01-01

    Several factors control the reactivity of radicals and can provide the strategies to convert highly reactive species into more persistent species that are easier to detect in an experiment. A reaction can only proceed if sufficient mobility and thermodynamic driving force are provided and the reaction is allowed by steric considerations and by electronic states of the reagents and products. A violation of at least one of these conditions can make the radical relatively stable. In certain cases, these factors occur naturally, in other situations, they can be purposefully manipulated to reduce the reactivity of highly reactive radicals, prolonging their lifetime and increasing their concentration. The discussed examples cover a vast range of lifetimes, from 10(-9) seconds to 10(9) years, at concentration levels down to 10(3) radicals per sample (10(-18) M), and stress that stability and reactivity are not independent notions and are the two sides of the same coin. PMID:21599439

  20. Sensing Magnetic Directions in Birds: Radical Pair Processes Involving Cryptochrome

    PubMed Central

    Wiltschko, Roswitha; Wiltschko, Wolfgang

    2014-01-01

    Birds can use the geomagnetic field for compass orientation. Behavioral experiments, mostly with migrating passerines, revealed three characteristics of the avian magnetic compass: (1) it works spontaneously only in a narrow functional window around the intensity of the ambient magnetic field, but can adapt to other intensities, (2) it is an “inclination compass”, not based on the polarity of the magnetic field, but the axial course of the field lines, and (3) it requires short-wavelength light from UV to 565 nm Green. The Radical Pair-Model of magnetoreception can explain these properties by proposing spin-chemical processes in photopigments as underlying mechanism. Applying radio frequency fields, a diagnostic tool for radical pair processes, supports an involvement of a radical pair mechanism in avian magnetoreception: added to the geomagnetic field, they disrupted orientation, presumably by interfering with the receptive processes. Cryptochromes have been suggested as receptor molecules. Cry1a is found in the eyes of birds, where it is located at the membranes of the disks in the outer segments of the UV-cones in chickens and robins. Immuno-histochemical studies show that it is activated by the wavelengths of light that allow magnetic compass orientation in birds. PMID:25587420

  1. Sensing magnetic directions in birds: radical pair processes involving cryptochrome.

    PubMed

    Wiltschko, Roswitha; Wiltschko, Wolfgang

    2014-09-01

    Birds can use the geomagnetic field for compass orientation. Behavioral experiments, mostly with migrating passerines, revealed three characteristics of the avian magnetic compass: (1) it works spontaneously only in a narrow functional window around the intensity of the ambient magnetic field, but can adapt to other intensities, (2) it is an "inclination compass", not based on the polarity of the magnetic field, but the axial course of the field lines, and (3) it requires short-wavelength light from UV to 565 nm Green. The Radical Pair-Model of magnetoreception can explain these properties by proposing spin-chemical processes in photopigments as underlying mechanism. Applying radio frequency fields, a diagnostic tool for radical pair processes, supports an involvement of a radical pair mechanism in avian magnetoreception: added to the geomagnetic field, they disrupted orientation, presumably by interfering with the receptive processes. Cryptochromes have been suggested as receptor molecules. Cry1a is found in the eyes of birds, where it is located at the membranes of the disks in the outer segments of the UV-cones in chickens and robins. Immuno-histochemical studies show that it is activated by the wavelengths of light that allow magnetic compass orientation in birds. PMID:25587420

  2. Future Directions of Structural Mass Spectrometry using Hydroxyl Radical Footprinting

    SciTech Connect

    J Kiselar; M Chance

    2011-12-31

    Hydroxyl radical protein footprinting coupled to mass spectrometry has been developed over the last decade and has matured to a powerful method for analyzing protein structure and dynamics. It has been successfully applied in the analysis of protein structure, protein folding, protein dynamics, and protein-protein and protein-DNA interactions. Using synchrotron radiolysis, exposure of proteins to a 'white' X-ray beam for milliseconds provides sufficient oxidative modification to surface amino acid side chains, which can be easily detected and quantified by mass spectrometry. Thus, conformational changes in proteins or protein complexes can be examined using a time-resolved approach, which would be a valuable method for the study of macromolecular dynamics. In this review, we describe a new application of hydroxyl radical protein footprinting to probe the time evolution of the calcium-dependent conformational changes of gelsolin on the millisecond timescale. The data suggest a cooperative transition as multiple sites in different molecular subdomains have similar rates of conformational change. These findings demonstrate that time-resolved protein footprinting is suitable for studies of protein dynamics that occur over periods ranging from milliseconds to seconds. In this review, we also show how the structural resolution and sensitivity of the technology can be improved as well. The hydroxyl radical varies in its reactivity to different side chains by over two orders of magnitude, thus oxidation of amino acid side chains of lower reactivity are more rarely observed in such experiments. Here we demonstrate that the selected reaction monitoring (SRM)-based method can be utilized for quantification of oxidized species, improving the signal-to-noise ratio. This expansion of the set of oxidized residues of lower reactivity will improve the overall structural resolution of the technique. This approach is also suggested as a basis for developing hypothesis

  3. The stability of allyl radicals following the photodissociation of allyl iodide at 193 nm.

    SciTech Connect

    Fan, H.; Pratt, S. T.; Chemistry

    2006-01-01

    The photodissociation of allyl iodide (C{sub 3}H{sub 5}I) at 193 nm was investigated by using a combination of vacuum-ultraviolet photoionization of the allyl radical, resonant multiphoton ionization of the iodine atoms, and velocity map imaging. The data provide insight into the primary C-I bond fission process and into the dissociative ionization of the allyl radical to produce C{sub 3}H{sup 3+}. The experimental results are consistent with the earlier results of Szpunar et al. [J. Chem. Phys. 119, 5078 (2003)], in that some allyl radicals with internal energies higher than the secondary dissociation barrier are found to be stable. This stability results from the partitioning of available energy between the rotational and vibrational degrees of freedom of the radical, the effects of a centrifugal barrier along the reaction coordinate, and the effects of the kinetic shift in the secondary dissociation of the allyl radical. The present results suggest that the primary dissociation of allyl iodide to allyl radicals plus I*({sup 2}P{sub 1/2}) is more important than previously suspected.

  4. The stability of allyl radicals following the photodissociation of allyl iodide at 193 nm.

    PubMed

    Fan, H; Pratt, S T

    2006-10-14

    The photodissociation of allyl iodide (C3H5I) at 193 nm was investigated by using a combination of vacuum-ultraviolet photoionization of the allyl radical, resonant multiphoton ionization of the iodine atoms, and velocity map imaging. The data provide insight into the primary C-I bond fission process and into the dissociative ionization of the allyl radical to produce C3H3+. The experimental results are consistent with the earlier results of Szpunar et al. [J. Chem. Phys. 119, 5078 (2003)], in that some allyl radicals with internal energies higher than the secondary dissociation barrier are found to be stable. This stability results from the partitioning of available energy between the rotational and vibrational degrees of freedom of the radical, the effects of a centrifugal barrier along the reaction coordinate, and the effects of the kinetic shift in the secondary dissociation of the allyl radical. The present results suggest that the primary dissociation of allyl iodide to allyl radicals plus I*(2P(1/2)) is more important than previously suspected. PMID:17042585

  5. Photodissociation of TEMPO-modified peptides: new approaches to radical-directed dissociation of biomolecules.

    PubMed

    Marshall, David L; Hansen, Christopher S; Trevitt, Adam J; Oh, Han Bin; Blanksby, Stephen J

    2014-03-14

    Radical-directed dissociation of gas phase ions is emerging as a powerful and complementary alternative to traditional tandem mass spectrometric techniques for biomolecular structural analysis. Previous studies have identified that coupling of 2-[(2,2,6,6-tetramethylpiperidin-1-oxyl)methyl]benzoic acid (TEMPO-Bz) to the N-terminus of a peptide introduces a labile oxygen-carbon bond that can be selectively activated upon collisional activation to produce a radical ion. Here we demonstrate that structurally-defined peptide radical ions can also be generated upon UV laser photodissociation of the same TEMPO-Bz derivatives in a linear ion-trap mass spectrometer. When subjected to further mass spectrometric analyses, the radical ions formed by a single laser pulse undergo identical dissociations as those formed by collisional activation of the same precursor ion, and can thus be used to derive molecular structure. Mapping the initial radical formation process as a function of photon energy by photodissociation action spectroscopy reveals that photoproduct formation is selective but occurs only in modest yield across the wavelength range (300-220 nm), with the photoproduct yield maximised between 235 and 225 nm. Based on the analysis of a set of model compounds, structural modifications to the TEMPO-Bz derivative are suggested to optimise radical photoproduct yield. Future development of such probes offers the advantage of increased sensitivity and selectivity for radical-directed dissociation. PMID:24473158

  6. Role of the Filters in the Formation and Stabilization of Semiquinone Radicals Collected from Cigarette Smoke

    PubMed Central

    Maskos, Zofia; Dellinger, Barry

    2013-01-01

    The fractional pyrolysis of Bright tobacco was performed in nitrogen atmosphere over the temperature range of 240 – 510 °C in a specially constructed, high temperature flow reactor system. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the free radicals in the initially produced total particular matter (TPM) and in TPM after exposure to ambient air (aging). Different filters have been used to collect TPM from tobacco smoke: cellulosic, cellulose nitrate, cellulose acetate, nylon, Teflon and Cambridge. The collection of the primary radicals (measured immediately after collection of TPM on filters), the formation and stabilization of the secondary radicals (defined as radicals formed during aging of TPM samples on the filters) depend significantly on the material of the filter. A mechanistic explanation about different binding capability of the filters decreasing in the order: cellulosic < cellulose nitrate < cellulose acetate < nylon ~ teflon is presented. Different properties were observed for the Cambridge filter. Specific care must be taken using the filters for identification of radicals from tobacco smoke to avoid artifacts in each case. PMID:24265513

  7. Thrust vectoring for lateral-directional stability

    NASA Technical Reports Server (NTRS)

    Peron, Lee R.; Carpenter, Thomas

    1992-01-01

    The advantages and disadvantages of using thrust vectoring for lateral-directional control and the effects of reducing the tail size of a single-engine aircraft were investigated. The aerodynamic characteristics of the F-16 aircraft were generated by using the Aerodynamic Preliminary Analysis System II panel code. The resulting lateral-directional linear perturbation analysis of a modified F-16 aircraft with various tail sizes and yaw vectoring was performed at several speeds and altitudes to determine the stability and control trends for the aircraft compared to these trends for a baseline aircraft. A study of the paddle-type turning vane thrust vectoring control system as used on the National Aeronautics and Space Administration F/A-18 High Alpha Research Vehicle is also presented.

  8. Direct Observation of Sulfur Radicals as Reaction Media in lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric D.; Pan, Huilin; Lu, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Zhiqun; Liaw, Bor Yann; Yu, Xiqian; Yang, Xiaoning; Zhang, Jiguang; Liu, Jun; Xiao, Jie

    2014-12-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge process follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials, it is revealed that the chemical and electrochemical reactions in Li-S cell are driven each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new insights to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  9. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    DOE PAGESBeta

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; et al

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-Smore » cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.« less

  10. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; Yang, Xiao-Qing; Zhang, Ji-Guang; Liu, Jun; Xiao, Jie

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-S cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  11. 14 CFR 27.177 - Static directional stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Static directional stability. 27.177... directional stability. (a) The directional controls must operate in such a manner that the sense and direction... sideslip angle versus directional control position curve may have a negative slope within a small range...

  12. 14 CFR 27.177 - Static directional stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Static directional stability. 27.177... directional stability. (a) The directional controls must operate in such a manner that the sense and direction... sideslip angle versus directional control position curve may have a negative slope within a small range...

  13. 14 CFR 27.177 - Static directional stability.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Static directional stability. 27.177... directional stability. (a) The directional controls must operate in such a manner that the sense and direction... sideslip angle versus directional control position curve may have a negative slope within a small range...

  14. In vivo triarylmethyl radical stabilization through encapsulation in Pluronic F-127 hydrogel

    NASA Astrophysics Data System (ADS)

    Abbas, Kahina; Boutier-Pischon, Audrey; Auger, Florian; Françon, Dominique; Almario, Antonio; Frapart, Yves-Michel

    2016-09-01

    In vivo electron paramagnetic resonance (EPR) imaging and spectroscopy are non-invasive technologies used to specifically detect and quantify paramagnetic species. However, the relative instability of spin probes such as triarylmethyl radicals limits their application to conduct oxygen quantification and mapping. In this study we encapsulated tetrathiatriarylmethyl radical (TAM; known as "Finland" probe) in Pluronic F-127 hydrogel (PF-127) in order to limit its degradation and evaluate its in vitro and in vivo EPR properties as a function of oxygen. Our results show that the EPR signal of encapsulated TAM in PF-127 hydrogel is similar to the one in solution. Although it is less sensitive to oxygen, it is suitable for oximetry. We also demonstrated that the incorporation of TAM in PF-127 hydrogel leads to an improved in vivo EPR stability of the radical under anesthesia. This new formulation enables high quality EPR imaging and oximetry and paves the way for the application of TAM radical-based probes in various biomedical fields.

  15. 14 CFR 29.177 - Static directional stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Static directional stability. 29.177... Static directional stability. (a) The directional controls must operate in such a manner that the sense... versus directional control position curve may have a negative slope within a small range of angles...

  16. 14 CFR 29.177 - Static directional stability.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Static directional stability. 29.177... Static directional stability. (a) The directional controls must operate in such a manner that the sense... versus directional control position curve may have a negative slope within a small range of angles...

  17. 14 CFR 29.177 - Static directional stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Static directional stability. 29.177... Static directional stability. (a) The directional controls must operate in such a manner that the sense... versus directional control position curve may have a negative slope within a small range of angles...

  18. Stability of eutectic interface during directional solidification

    SciTech Connect

    Han, S.H.

    1996-04-23

    Directional solidification of eutectic alloys shows different types of eutectic morphologies. These include lamellar, rod, oscillating and tilting modes. The growth of these morphologies occurs with a macroscopically planar interface. However, under certain conditions, the planar eutectic front becomes unstable and gives rise to a cellular or a dendritic structure. This instability leads to the cellular/dendritic structure of either a primary phase or a two-phase structure. The objective of this work is to develop a fundamental understanding of the instability of eutectic structure into cellular/dendritic structures of a single phase and of two-phases. Experimental studies have been carried out to examine the transition from a planar to two-phase cellular and dendritic structures in a ceramic system of Alumina-Zirconia (Al{sub 2}O{sub 3}-ZrO{sub 2}) and in a transparent organic system of carbon tetrabromide and hexachloroethane (CBr{sub 4}-C{sub 2}Cl{sub 6}). Several aspects of eutectic interface stability have been examined.

  19. Free radicals and SOD activity of jaw cyst. Direct measurement and spin trapping studies by ESR.

    PubMed

    Kimura, H; Simodate, H; Suzuki, M

    1990-01-01

    Free radicals produced in the fluid of jaw cysts were directly measured at room temperature using ESR. With these samples, SOD activity of the cyst fluid was measured by the ESR spin trapping method with DMPO as a trapping agent. Freeze-dried samples of cyst fluid showed a broad ESR signal at g = 2.005. Relative signal intensity of samples from jaw cysts with inflammation was higher than jaw cysts without inflammation. SOD activity of cyst fluid with high viscosity showed higher values than that of cyst fluid with low viscosity. We suggest that free radicals produced in jaw cyst damage tissues while higher SOD activity of cyst fluid play a role in a self-defense mechanism against free radicals. PMID:2167266

  20. Direct measurements of HOx radicals in the marine boundary layer: testing the current tropospheric chemistry mechanism.

    PubMed

    Kanaya, Yugo; Akimoto, Hajime

    2002-01-01

    OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in tropospheric chemistry. In spite of their importance, we had no choice but to trust their concentrations predicted by modeling studies based on known chemical processes. However, recent direct measurements of these radicals have enabled us to test and revise our knowledge of the processes by comparing the predicted and observed values of the radical concentrations. We developed a laser-induced fluorescence (LIF) instrument and successfully observed OH and HO(2) at three remote islands of Japan (Oki Island, Okinawa Island, and Rishiri Island). At Okinawa Island, the observed daytime level of HO(2) agreed closely with the model estimates, suggesting that the photochemistry at Okinawa is well described by the current chemistry mechanism. At Rishiri Island, in contrast, the observed daytime level of HO(2) was consistently much lower than the calculated values. We proposed that iodine chemistry, usually not incorporated into the mechanism, is at least partly responsible for the discrepancy in the results. At night, HO(2) was detected at levels greater than 1 pptv at all three islands, suggesting the presence of processes in the dark that produce radicals. We showed that ozone reactions with unsaturated hydrocarbons, including monoterpenes, could significantly contribute to radical production. PMID:12112871

  1. 213 nm Ultraviolet Photodissociation on Peptide Anions: Radical-Directed Fragmentation Patterns

    NASA Astrophysics Data System (ADS)

    Halim, Mohammad A.; Girod, Marion; MacAleese, Luke; Lemoine, Jérôme; Antoine, Rodolphe; Dugourd, Philippe

    2016-03-01

    Characterization of acidic peptides and proteins is greatly hindered due to lack of suitable analytical techniques. Here we present the implementation of 213 nm ultraviolet photodissociation (UVPD) in high-resolution quadrupole-Orbitrap mass spectrometer in negative polarity for peptide anions. Radical-driven backbone fragmentation provides 22 distinctive fragment ion types, achieving the complete sequence coverage for all reported peptides. Hydrogen-deficient radical anion not only promotes the cleavage of Cα-C bond but also stimulates the breaking of N-Cα and C-N bonds. Radical-directed loss of small molecules and specific side chain of amino acids are detected in these experiments. Radical containing side chain of amino acids (Tyr, Ser, Thr, and Asp) may possibly support the N-Cα backbone fragmentation. Proline comprising peptides exhibit the unusual fragment ions similar to reported earlier. Interestingly, basic amino acids such as Arg and Lys also stimulated the formation of abundant b and y ions of the related peptide anions. Loss of hydrogen atom from the charge-reduced radical anion and fragment ions are rationalized by time-dependent density functional theory (TDDFT) calculation, locating the potential energy surface (PES) of ππ* and repulsive πσ* excited states of a model amide system.

  2. 213 nm Ultraviolet Photodissociation on Peptide Anions: Radical-Directed Fragmentation Patterns.

    PubMed

    Halim, Mohammad A; Girod, Marion; MacAleese, Luke; Lemoine, Jérôme; Antoine, Rodolphe; Dugourd, Philippe

    2016-03-01

    Characterization of acidic peptides and proteins is greatly hindered due to lack of suitable analytical techniques. Here we present the implementation of 213 nm ultraviolet photodissociation (UVPD) in high-resolution quadrupole-Orbitrap mass spectrometer in negative polarity for peptide anions. Radical-driven backbone fragmentation provides 22 distinctive fragment ion types, achieving the complete sequence coverage for all reported peptides. Hydrogen-deficient radical anion not only promotes the cleavage of Cα-C bond but also stimulates the breaking of N-Cα and C-N bonds. Radical-directed loss of small molecules and specific side chain of amino acids are detected in these experiments. Radical containing side chain of amino acids (Tyr, Ser, Thr, and Asp) may possibly support the N-Cα backbone fragmentation. Proline comprising peptides exhibit the unusual fragment ions similar to reported earlier. Interestingly, basic amino acids such as Arg and Lys also stimulated the formation of abundant b and y ions of the related peptide anions. Loss of hydrogen atom from the charge-reduced radical anion and fragment ions are rationalized by time-dependent density functional theory (TDDFT) calculation, locating the potential energy surface (PES) of ππ* and repulsive πσ* excited states of a model amide system. PMID:26545767

  3. 14 CFR 29.177 - Static directional stability.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Static directional stability. 29.177 Section 29.177 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION... Static directional stability. (a) The directional controls must operate in such a manner that the...

  4. Structural basis for hydration dynamics in radical stabilization of bilin reductase mutants†#

    PubMed Central

    Kohler, Amanda C.; Gae, David D.; Richley, Michael A.; Stoll, Stefan; Gunn, Alexander; Lim, Sunghyuk; Martin, Shelley S.; Doukov, Tzanko I.; Britt, R. David; Ames, James B.; Lagarias, J. Clark; Fisher, Andrew J.

    2010-01-01

    Heme-derived linear tetrapyrroles (phytobilins) in phycobiliproteins and phytochromes perform critical light-harvesting and light-sensing roles in oxygenic photosynthetic organisms. A key enzyme in their biogenesis, phycocyanobilin:ferredoxin oxidoreductase (PcyA), catalyzes the overall four-electron reduction of biliverdin IXα to phycocyanobilin – the common chromophore precursor for both classes of biliproteins. This interconversion occurs via semi-reduced bilin radical intermediates that are profoundly stabilized by selected mutations of two critical catalytic residues, Asp105 and His88. To understand the structural basis for this stabilization and to gain insight into the overall catalytic mechanism, we report the high-resolution crystal structures of substrate-loaded Asp105Asn and His88Gln mutants of Synechocystis sp. PCC 6803 PcyA in the initial oxidized and one-electron reduced radical state. Unlike wild-type PcyA, both mutants possess a bilin-interacting axial water molecule that is ejected from the active site upon formation of the enzyme-bound neutral radical complex. Structural studies of both mutants also show that the side chain of Glu76 is unfavorably located for D-ring vinyl reduction. Based on these structures and companion 15N-1H long-range HMQC NMR analyses to assess the protonation state of histidine residues, we propose a new mechanistic scheme for PcyA-mediated reduction of both vinyl groups of biliverdin wherein an axial water molecule, that prematurely binds and ejects from both mutants upon one electron reduction, is required for catalytic turnover of the semi-reduced state. PMID:20557110

  5. The spinal accessory nerve plexus, the trapezius muscle, and shoulder stabilization after radical neck cancer surgery.

    PubMed Central

    Brown, H; Burns, S; Kaiser, C W

    1988-01-01

    A clinical and anatomic study of the spinal accessory, the eleventh cranial nerve, and trapezius muscle function of patients who had radical neck cancer surgery was conducted. This study was done not only to document the indispensibility of the trapezius muscle to shoulder-girdle stability, but also to clarify the role of the eleventh cranial nerve in the variable motor and sensory changes occurring after the loss of this muscle. Seventeen male patients, 49-69 years of age, (average of 60 years of age) undergoing a total of 23 radical neck dissections were examined for upper extremity function, particularly in regard to the trapezius muscle, and for subjective signs of pain. The eleventh nerve, usually regarded as the sole motor innervation to the trapezius, was cut in 17 instances because of tumor involvement. Dissection of four fresh and 30 preserved adult cadavers helped to reconcile the motor and sensory differences in patients who had undergone loss of the eleventh nerve. The dissections and clinical observations corroborate that the trapezius is a key part of a "muscle continuum" that stabilizes the shoulder. Variations in origins and insertions of the trapezius may influence its function in different individuals. As regards the spinal accessory nerve, it is concluded that varying motor and sensory connections form a plexus with the eleventh nerve, accounting, in part, for the variations in motor innervation and function of the trapezius, as well as for a variable spectrum of sensory changes when the eleventh nerve is cut. For this reason, it is suggested that the term "spinal accessory nerve plexus" be used to refer to the eleventh nerve when it is considered in the context of radical neck cancer surgery. Images Fig. 4. Fig. 6. Fig. 7. Fig. 8. PMID:3056289

  6. Stabilities of nitrogen containing heterocyclic radicals and geometrical influences on non-radiative processes in organic molecules

    NASA Technical Reports Server (NTRS)

    Evleth, E. M.

    1972-01-01

    Stabilities of nitrogen containing heterocyclic radicals were studied to detect radicals of the type R-N-R, and to theoretically rationalize their electronic structure. The computation of simple potential energy surfaces for ground and excited states is discussed along with the photophysical properties of indolizine. Methods of calculation and problems associated with the calculations are presented. Results, tables, diagrams, discussions, and references are included.

  7. Direct Excitation of the Reaction Coordinate: Overtone-Induced Predissociation of the Hydroxymethyl Radical

    NASA Astrophysics Data System (ADS)

    Reisler, Hanna; Ryazanov, Mikhail; Rodrigo, Chirantha P.

    2011-06-01

    The overtone-induced vibrational predissociation of the hydroxymethyl radical is achieved following excitation of the radical to the third O-H stretch overtone. The excited O-H stretch is also the bond that breaks; i.e. overtone excitation is in the reaction coordinate. The production of H atoms takes place via tunneling through the barrier to the H + formaldehyde channel. H-atom photofragment yield spectra in the region of the third overtone reveal two mixed bands with contributions from the third OH overtone and a combination band comprised of two quanta of OH stretch and one quantum of CH asymmetric stretch. Using velocity map imaging, sliced images of H-atom products are obtained with kinetic energy resolution sufficient to reveal the vibrational structure in the formaldehyde co-fragment. As expected, most of the formaldehyde molecules are born without vibrational excitation but some exhibit excitation in other modes, such as wagging and CO stretch. The rotational contours of the vibrational bands are well described by temperatures in the range 100-150 K. Slice imaging allows scanning the pump laser while monitoring H fragments in selected kinetic energy ranges, and in this way it is demonstrated that all the observed vibrational levels of formaldehyde have their parentage in the hydroxymethyl radical. The barrier to isomerization to methoxy is comparable to the barrier to direct dissociation and the role of isomerization is investigated by using partially deuterated radicals.

  8. 14 CFR 25.177 - Static lateral-directional stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Static lateral-directional stability. 25.177 Section 25.177 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.177 Static...

  9. 14 CFR 25.177 - Static lateral-directional stability.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Static lateral-directional stability. 25.177 Section 25.177 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.177 Static...

  10. Degradation pathways of lamotrigine under advanced treatment by direct UV photolysis, hydroxyl radicals, and ozone.

    PubMed

    Keen, Olya S; Ferrer, Imma; Michael Thurman, E; Linden, Karl G

    2014-12-01

    Lamotrigine is recently recognized as a persistent pharmaceutical in the water environment and wastewater effluents. Its degradation was studied under UV and ozone advanced oxidation treatments with reaction kinetics of lamotrigine with ozone (≈4 M(-1)s(-1)), hydroxyl radical [(2.1 ± 0.3) × 10(9)M(-1)s(-1)] and by UV photolysis with low and medium pressure mercury vapor lamps [quantum yields ≈0 and (2.7 ± 0.4)× 10(-4) respectively] determined. All constants were measured at pH 6 and at temperature ≈20°C. The results indicate that lamotrigine is slow to respond to direct photolysis or oxidation by ozone and no attenuation of the contaminant is expected in UV or ozone disinfection applications. The compound reacts rapidly with hydroxyl radicals indicating that advanced oxidation processes would be effective for its treatment. Degradation products were identified under each treatment process using accurate mass time-of-flight spectrometry and pathways of decay were proposed. The main transformation pathways in each process were: dechlorination of the benzene ring during direct photolysis; hydroxyl group addition to the benzene ring during the reaction with hydroxyl radicals; and triazine ring opening after reaction with ozone. Different products that form in each process may be to a varying degree less environmentally stable than the parent lamotrigine. In addition, a novel method of ozone quenching without addition of salts is presented. The new quenching method would allow subsequent mass spectrometry analysis without a solid phase extraction clean-up step. The method involves raising the pH of the sample to approximately 10 for a few seconds and lowering it back and is therefore limited to applications for which temporary pH change is not expected to affect the outcome of the analysis. PMID:25150682

  11. Choice of Bond Dissociation Enthalpies on which to Base the Stabilization Energies of Simple Radicals: DH(R-H)is Preferred because DH(R-Me) is Perturbed by Changes in Chain Branching

    SciTech Connect

    Poutsma, Marvin L

    2008-01-01

    The relative stabilization energies of radicals, SE(R ), along the simple series methyl/ethyl/i-propyl/t-butyl are known to vary in spread and even direction dependent on which dissociation enthalpies, DH(R-X), they are based on. Using a highly electronegative X is recognized as unwise, but it is not clear whether a choice of X = Me or X = R might not be preferred over the almost universal use of R = H. The enthalpies of isomerization of C4 radical pairs that vary only in the substitution pattern at the radical center but not in carbon skeleton illustrate that R = H is indeed the better choice. Comparisons in the context of recent predictive models for alkane and radical stability indicate that, while relative DH(R-H) values highlight the desired difference in substitution pattern at the radical center, relative DH(R-Me) values are perturbed by differences in skeletal branching or protobranching which are well-known to affect thermochemistry. As a result, SE(R ) values derived from relative DH(R-Me) values are consistently too small. The same pattern is illustrated for prim, sec, and tert allylic and benzylic radicals (larger SE(R )) and for the parent vinyl, phenyl, and ethynyl radicals (negative SE(R )).

  12. Infants Show Stability of Goal-Directed Imitation

    ERIC Educational Resources Information Center

    Sakkalou, Elena; Ellis-Davies, Kate; Fowler, Nia C.; Hilbrink, Elma E.; Gattis, Merideth

    2013-01-01

    Previous studies have reported that infants selectively reproduce observed actions and have argued that this selectivity reflects understanding of intentions and goals, or goal-directed imitation. We reasoned that if selective imitation of goal-directed actions reflects understanding of intentions, infants should demonstrate stability across…

  13. Stability and properties of the two-dimensional hexagonal boron nitride monolayer functionalized by hydroxyl (OH) radicals: a theoretical study.

    PubMed

    Wang, Hong-mei; Liu, Yue-jie; Wang, Hong-xia; Zhao, Jing-xiang; Cai, Qing-hai; Wang, Xuan-zhang

    2013-12-01

    Motivated by the great advance in graphene hydroxide--a versatile material with various applications--we performed density functional theory (DFT) calculations to study the functionalization of the two-dimensional hexagonal boron nitride (h-BN) sheet with hydroxyl (OH) radicals, which has been achieved experimentally recently. Particular attention was paid to searching for the most favorable site(s) for the adsorbed OH radicals on a h-BN sheet and addressing the roles of OH radical coverage on the stability and properties of functionalized h-BN sheet. The results indicate that, for an individual OH radica, the most stable configuration is that it is adsorbed on the B site of the h-BN surface with an adsorption energy of -0.88 eV and a magnetic moment of 1.00 μ(B). Upon adsorption of more than one OH radical on a h-BN sheet, however, these adsorbates prefer to adsorb in pairs on the B and its nearest N atoms from both sides of h-BN sheet without magnetic moment. An energy diagram of the average adsorption energy of OH radicals on h-BN sheet as a function of its coverage indicates that when the OH radical coverage reaches to 60 %, the functionalized h-BN sheet is the most stable among all studied configurations. More importantly, this configuration exhibits good thermal and dynamical stability at room temperature. Owing to the introduction of certain impurity levels, the band gap of h-BN sheet gradually decreases with increasing OH coverage, thereby enhancing its electrical conductivity. PMID:24092267

  14. Formation and Stabilization of Combustion-Generated, Environmentally Persistent Radicals on Ni(II)O Supported on a Silica Surface

    PubMed Central

    Vejerano, Eric; Lomnicki, Slawomir M.; Dellinger, Barry

    2013-01-01

    Previous studies have indicated Environmentally Persistent Free Radicals (EPFRs) are formed when hydroxyl- and chlorine-substituted aromatics chemisorbed on Cu(II)O and Fe(III)2O3 surfaces and were stabilized through their interactions with the surface metal cation. The current study reports our laboratory investigation on the formation and stabilization of EPFRs on an Ni(II)O surface. The EPFRs were produced by the chemisorption of adsorbates on the supported metal oxide surface and transfer of an electron from the adsorbate to the metal center, resulting in reduction of the metal cation. Depending on the temperature and the nature of the adsorbate, more than one type of organic radical was formed. A phenoxyl-type radical, with g-value between 2.0029 and 2.0044, and a semiquinone-type radical, with g-value from 2.0050 to as high as 2.0081, were observed. The half-lives on Ni(II)O were long and ranged from 1.5 to 5.2 days, which were similar to what were observed on Fe(III)2O3,. The yields of the EPFRs formed on Ni(II)O was ~ 8x higher than on Cu(II)O and ~50x higher than on Fe(III)2O3. PMID:22831558

  15. Formation and Stabilization of Environmentally Persistent Free Radicals Induced by the Interaction of Anthracene with Fe(III)-Modified Clays.

    PubMed

    Jia, Hanzhong; Nulaji, Gulimire; Gao, Hongwei; Wang, Fu; Zhu, Yunqing; Wang, Chuanyi

    2016-06-21

    Environmentally persistent free radicals (EPFRs) are occasionally detected in Superfund sites but the formation of EPFRs induced by polycyclic aromatic hydrocarbons (PAHs) is not well understood. In the present work, the formation of EPFRs on anthracene-contaminated clay minerals was quantitatively monitored via electron paramagnetic resonance (EPR) spectroscopy, and surface/interface-related environmental influential factors were systematically explored. The obtained results suggest that EPFRs are more readily formed on anthracene-contaminated Fe(III)-montmorillonite than in other tested systems. Depending on the reaction condition, more than one type of organic radicals including anthracene-based radical cations with g-factors of 2.0028-2.0030 and oxygenic carbon-centered radicals featured by g-factors of 2.0032-2.0038 were identified. The formed EPFRs are stabilized by their interaction with interlayer surfaces, and such surface-bound EPFRs exhibit slow decay with 1/e-lifetime of 38.46 days. Transformation pathway and possible mechanism are proposed on the basis of experimental results and quantum mechanical simulations. Overall, the formation of EPFRs involves single-electron-transfer from anthracene to Fe(III) initially, followed by H2O addition on formed aromatic radical cation. Because of their potential exposure in soil and atmosphere, such clay surface-associated EPFRs might induce more serious toxicity than PAHs and exerts significant impacts on human health. PMID:27224055

  16. Two tyrosyl radicals stabilize high oxidation states in cytochrome c oxidase for efficient energy conservation and proton translocation

    NASA Astrophysics Data System (ADS)

    Rousseau, Denis

    2012-02-01

    The reaction of hydrogen peroxide (H2O2) with oxidized bovine cytochrome c oxidase (bCcO) was studied by electron paramagnetic resonance (EPR) to determine the properties of radical intermediates. Two distinct radicals with widths of 12 and 46 G are directly observed by X-band CW-EPR in the reaction of bCcO with H2O2 at pH 6 and pH 8. High-frequency EPR (D-band) provides assignments to tyrosine for both radicals based on well-resolved g-tensors. The 46 G wide radical has extensive hyperfine structure and can be fit with parameters consistent with Y129. However, the 12 G wide radical has minimal hyperfine structure and can be fit using parameters unique to the post-translationally modified Y244 in CcO. The results are supported by mixed quantum mechanics and molecular mechanics calculations. This study reports spectroscopic evidence of a radical formed on the modified tyrosine in CcO and resolves the much debated controversy of whether the wide radical seen at low pH in the bovine system is a tyrosine or tryptophan. A model is presented showing how radical formation and migration may play an essential role in proton translocation. This work was done in collaboration with Michelle A. Yu, Tsuyoshi Egawa, Syun-Ru Yeh and Gary J. Gerfen from Albert Einstein College of Medicine; Kyoko Shinzawa-Itoh and Shinya Yoshikawa from the University of Hyogo; and Victor Guallar from the Barcelona Supercomputing Center.

  17. Potential role of stabilized Criegee radicals in sulfuric acid production in a high biogenic VOC environment.

    PubMed

    Kim, Saewung; Guenther, Alex; Lefer, Barry; Flynn, James; Griffin, Robert; Rutter, Andrew P; Gong, Longwen; Cevik, Basak Karakurt

    2015-03-17

    We present field observations made in June 2011 downwind of Dallas-Fort Worth, TX, and evaluate the role of stabilized Criegee radicals (sCIs) in gaseous sulfuric acid (H2SO4) production. Zero-dimensional model calculations show that sCI from biogenic volatile organic compounds composed the majority of the sCIs. The main uncertainty associated with an evaluation of H2SO4 production from the sCI reaction channel is the lack of experimentally determined reaction rates for sCIs formed from isoprene ozonolysis with SO2 along with systematic discrepancies in experimentally derived reaction rates between other sCIs and SO2 and water vapor. In general, the maximum of H2SO4 production from the sCI channel is found in the late afternoon as ozone increases toward the late afternoon. The sCI channel, however, contributes minor H2SO4 production compared with the conventional OH channel in the mid-day. Finally, the production and the loss rates of H2SO4 are compared. The application of the recommended mass accommodation coefficient causes significant overestimation of H2SO4 loss rates compared with H2SO4 production rates. However, the application of a lower experimental value for the mass accommodation coefficient provides good agreement between the loss and production rates of H2SO4. The results suggest that the recommended coefficient for the H2O surface may not be suitable for this relatively dry environment. PMID:25700170

  18. Extraordinary stability of naphthalenediimide radical ion and its ultra-electron-deficient precursor: strategic role of the phosphonium group.

    PubMed

    Kumar, Sharvan; Ajayakumar, M R; Hundal, Geeta; Mukhopadhyay, Pritam

    2014-08-27

    Stabilization of radical ions and highly electron-deficient systems under ambient conditions is of great significance. A new design concept is presented that applies the multifaceted features of the phosphonium group to achieve isolation of (a) the first naphthalenediimide (NDI) radical ion [(1a•+)BPh4(–)] as single crystals and (b) an ultra-electron-deficient NDI [(1a(2+))2BF4(–)] having the lowest LUMO level recorded for an NDI, overwhelming the formative tetracyanoquinodimethane (TCNQ) molecule. Both 1a•+ and 1a(2+) exhibit unprecedented stability to normal workup procedures, chromatography, and anion metathesis in open air. To our knowledge, this is the first instance where radical ions stable toward chromatography have been obtained, which is a noteworthy development in the field of synthetic radical chemistry. The crucial components of thermodynamic and kinetic stabilization, namely, the nonbonded P···O interaction, hypervalency, and propeller-like shape of the phosphonium groups in 1a(2+) and 1a•+, were substantiated by crystallography and theoretical studies. Natural bond orbital (NBO) calculations validated the P···O contact to be an nO → σP–C* orbital interaction. Spontaneous electron transfer reactions of 1a(2+) even in nonpolar solvents, anion−π interactions of 1a(2+) with the naphthalene core, and panchromism of 1a•+ are the other emergent properties. The high-yielding (∼90%) in situ synthesis of 1a•+ and the extraordinary stability fostered by the phosphonium group have the potential to turn hitherto unstable organic systems into a new genre of stable off-the-shelf systems. PMID:25093533

  19. Direct observation of roaming radicals in the thermal decomposition of acetaldehyde.

    SciTech Connect

    Sivaramakrishnan, R.; Michael, J. V.; Klippenstein, S. J.; Chemical Sciences and Engineering Division

    2010-01-21

    The thermal dissociation of acetaldehyde has been studied with the reflected shock tube technique using H(D)-atom atomic resonance absorption spectrometry detection. The use of an unreversed light source yields extraordinarily sensitive H atom detection. As a result, we are able to measure both the total decomposition rate and the branching to radical versus molecular channels. This branching provides a direct measure of the contribution from the roaming radical mechanism since the contributions from the usual tight transition states are predicted by theory to be negligible. The experimental observations also provide a measure of the rate coefficient for H + CH{sub 3}CHO. Another set of experiments employing C{sub 2}H{sub 5}I as an H-atom source provides additional data for this rate coefficient that extends to lower temperature. An evaluation of the available experimental results for H + CH{sub 3}CHO can be expressed by a three-parameter Arrhenius expression as k = 7.66 x 10{sup -20}T{sup 2.75} exp((-486 K)/T) cm{sup 3} molecule{sup -1} s{sup -1} (298-1415 K). Analogous experiments employing C{sub 2}D{sub 5}I as a D-atom source allow for the study of the isotopically substituted reaction. The present experiments are the only direct measure for this reaction rate constant, and the results can be expressed by an Arrhenius expression as k = 5.20 x 10{sup -10} exp((-4430 K)/T) cm{sup 3} molecule{sup -1} s{sup -1} (1151-1354 K). The H/D + CH{sub 3}CHO reactions are also studied with ab initio transition-state theory, and the results are in remarkably good agreement with the current experimental data.

  20. Stability of 2{radical} (2) {times}2{radical} (2) oxygen ordered superstructures in YBa{sub 2}Cu{sub 3}O{sub 6+x}

    SciTech Connect

    Aligia, A.A.; Koval, S.; Migoni, R.

    1998-01-01

    We have compared the ground-state energy of several observed or proposed {open_quotes}2{radical} (2) {times}2{radical} (2) oxygen ordered superstructures{close_quotes} [{open_quotes}herringbone{close_quotes} structures (HS{close_quote}s)], with those of {open_quotes}chain superstructures{close_quotes} (CS{close_quote}s) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa{sub 2}Cu{sub 3}O{sub 6+x}. The model Hamiltonian contains (i) the Madelung energy, (ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and (iii) covalency effects based on known results for t-J models in one and two dimensions. The optimum distribution of charge is determined, minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS{close_quote}s are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure and long-range Coulomb interactions are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation. {copyright} {ital 1998} {ital The American Physical Society}

  1. Reforming the EU Clinical Trials Directive: streamlining processes or a radical "new" agenda?.

    PubMed

    McHale, Jean V

    2013-09-01

    From its conception the EU Clinical Trials Directive met with controversy. Some saw it as an unnecessary inhibitor to scientific research, introducing bureaucracy which was unduly expensive, slowing down the clinical trial approval system. The Directive however also enshrined respect for fundamental rights in relation to clinical trials decision-making and impacted upon the domestic law of member states facilitating the alignment of trial review processes. Nearly a decade after its implementation the EU is moving towards implementation of further reform in this area, from a Directive to a Regulation, from a system placing the research ethics system at the heart of the clinical trials approval committee to one which does not and which represents a see change in international and domestic approaches to research ethics. This article critically examines the proposed reform of the regulation of clinical trials on medicinal product through the introduction of a new EU Regulation and asks whether this can be seen as a natural streamlining of processes or a radical new agenda in EU health law and regulation. PMID:23977734

  2. 14 CFR 27.177 - Static directional stability.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Static directional stability. 27.177 Section 27.177 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT Flight Flight Characteristics § 27.177...

  3. Triarylporphyrin meso-Oxy Radicals: Remarkable Chemical Stabilities and Oxidation to Oxophlorin π-Cations.

    PubMed

    Shimizu, Daiki; Oh, Juwon; Furukawa, Ko; Kim, Dongho; Osuka, Atsuhiro

    2015-12-16

    5-Hydroxy-10,15,20-triarylporphyrin (oxophlorin) and its Ni(II) and Zn(II) complexes were oxidized with PbO2 to give the corresponding porphyrin meso-oxy radicals as remarkably stable species. These radicals were fully characterized with X-ray diffraction analysis, UV/vis/NIR absorption and ESR spectroscopies, magnetic susceptibility measurement, electrochemical studies, and theoretical calculations. Free-base radical and its Ni(II) complex have been shown to exist as a monoradical in solution, while the Zn(II) complex exists in an equilibrium between monomer (doublet monoradical) and dimer (a non-Kekulé singlet biradicaloid) with a dimerization constant of KD = 3.0 × 10(5) M(-1) in noncoordinating CH2Cl2 but becomes a pyridine-coordinated monoradical upon addition of pyridine. Variable temperature magnetic susceptibility measurements of these radicals revealed different magnetic interactions in the solid-states, which has been interpreted in terms of their different packing structures in a microscopic sense. These radicals undergo one-electron oxidation and reduction in a reversible manner within narrow potential windows of 0.57-0.82 V. Finally, one-electron oxidation of Ni(II) and Zn(II) porphyrin meso-oxy radicals with tris(4-bromophenyl)aminium hexachloroantimonate furnished oxophlorin π-cations, which displayed nonaromatic closed-shell character, NIR absorption, and significant double bond character of the C-O bond. PMID:26609815

  4. The elimination of free radicals in irradiated UHMWPEs with and without vitamin E stabilization by annealing under pressure

    PubMed Central

    Oral, Ebru; Ghali, Bassem W.; Muratoglu, Orhun K.

    2013-01-01

    Radiation crosslinking of ultrahigh molecular weight polyethylene (UHMWPE) has been used to decrease the wear of joint implant bearing surfaces. While radiation crosslinking has been successful in decreasing femoral head penetration into UHMWPE acetabular liners in vivo, postirradiation thermal treatment of the polymer is required to ensure the oxidative stability of joint implants in the long term. Two types of thermal treatment have been used: (i) annealing below the melting point preserves the mechanical properties but the residual free radicals trapped in the crystalline regions are not completely eliminated, leading to oxidation in the long-term and (ii) annealing above the melting point (melting) eliminates the free radicals but leads to a decrease in mechanical properties through loss of crystallinity during the melting process. In this study, we hypothesized that free radicals could be reduced by annealing below the melting point under pressure effectively without melting due to the elevation of the melting point. By avoiding the complete melting of UHMWPE, mechanical properties would be preserved. Our hypothesis tested positive in that we found the radiation-induced free radicals to be markedly reduced (below the detection limit of state-of-the-art electron spin resonance) by thermal annealing under pressure in radiation crosslinked virgin UHMWPE and UHMWPE/vitamin-E blends without loss of mechanical properties. PMID:21381192

  5. The effect of free radical inhibitor on the sensitized radiation crosslinking and thermal processing stabilization of polyurethane shape memory polymers

    PubMed Central

    Hearon, Keith; Smith, Sarah E.; Maher, Cameron A.; Wilson, Thomas S.; Maitland, Duncan J.

    2012-01-01

    The effects of free radical inhibitor on the electron beam crosslinking and thermal processing stabilization of novel radiation crosslinkable polyurethane shape memory polymers (SMPs) blended with acrylic radiation sensitizers have been determined. The SMPs in this study possess novel processing capabilities—that is, the ability to be melt processed into complex geometries as thermoplastics and crosslinked in a secondary step using electron beam irradiation. To increase susceptibility to radiation crosslinking, the radiation sensitizer pentaerythritol triacrylate (PETA) was solution blended with thermoplastic polyurethane SMPs made from 2-butene-1,4-diol and trimethylhexamethylene diisocyanate (TMHDI). Because thermoplastic melt processing methods such as injection molding are often carried out at elevated temperatures, sensitizer thermal instability is a major processing concern. Free radical inhibitor can be added to provide thermal stabilization; however, inhibitor can also undesirably inhibit radiation crosslinking. In this study, we quantified both the thermal stabilization and radiation crosslinking inhibition effects of the inhibitor 1,4-benzoquinone (BQ) on polyurethane SMPs blended with PETA. Sol/gel analysis of irradiated samples showed that the inhibitor had little to no inverse effects on gel fraction at concentrations of 0-10,000 ppm, and dynamic mechanical analysis showed only a slight negative correlation between BQ composition and rubbery modulus. The 1,4-benzoquinone was also highly effective in thermally stabilizing the acrylic sensitizers. The polymer blends could be heated to 150°C for up to five hours or to 125°C for up to 24 hours if stabilized with 10,000 ppm BQ and could also be heated to 125°C for up to 5 hours if stabilized with 1000 ppm BQ without sensitizer reaction occurring. We believe this study provides significant insight into methods for manipulation of the competing mechanisms of radiation crosslinking and thermal

  6. Comparison of commercial uv lamps for radical oxidation and direct photolysis in water

    SciTech Connect

    Haag, W; Wang, F T

    1999-08-01

    Lawrence Livermore National Laboratory (LLNL) is charged with developing methods for treating contaminated sites and destroying waste organic compounds that are currently being accumulated, including Trimsol (machining oil), trichloroethene (ICE), tributyl phosphate (TBP), kerosene, and many other organics. These organics are sometimes present mixed with radioactive waste, and in these cases it is important to destroy the organics in such a way as to not increase the total volume of the waste and to ensure that no radioactivity is released in the process. Among the most promising techniques for treating aqueous mixed wastes are ultraviolet light (UV) oxidation and the molten salt process, as opposed to methods like incineration or supercritical water oxidation that might lead to air emissions of radioactivity if not very carefully controlled. The purpose of the present study was to compare the energy efficiency of various commercial UV lamp systems designed for photooxidation. Two type of tests were conducted: (1) direct photolysis of a chlorinated compound and (2) photolysis of hydrogen peroxide, which is an additive often used to photooxidize compounds that are not amenable to direct photolysis. The results should allow LLNL to select the most cost-effective system for treating wastes by UV- enhanced radical oxidation processes.

  7. Stability of superoxide radicals in glyme solvents for non-aqueous Li-O2 battery electrolytes.

    PubMed

    Schwenke, K Uta; Meini, Stefano; Wu, Xiaohan; Gasteiger, Hubert A; Piana, Michele

    2013-07-28

    Glyme-based electrolytes were studied for the use in lithium-air batteries because of their greater stability towards oxygen reduction reaction intermediates (e.g., superoxide anion radicals (O2˙(-))) produced upon discharge at the cathode compared to previously employed carbonate-based electrolytes. However, contradictory results of glyme stability tests employing KO2 as an O2˙(-) source were reported in the literature. For clarification, we investigated the reaction of KO2 with glymes of various chain lengths qualitatively using (1)H NMR and FTIR spectroscopy as well as more quantitatively using UV-Vis spectroscopy. During our experiments we found a huge impact of small quantities of impurities on the stability of the solvents. Therefore, we studied further the influence of impurities in the glymes on the cycling behavior of Li-O2 cells, demonstrating the large effect of electrolyte impurities on Li-O2 cell performance. PMID:23760527

  8. Stability of phenol and thiophenol radical cations - interpretation by comparative quantum chemical approaches

    NASA Astrophysics Data System (ADS)

    Hermann, R.; Naumov, S.; Mahalaxmi, G. R.; Brede, O.

    2000-07-01

    The deprotonation kinetics of phenol-type radical cations, formed via a very efficient electron transfer in the pulse radiolysis of non-polar solutions, for example n-chlorobutane, is governed mainly by electronic effects due to the nature of the phenol substituents, whereas steric effects are of minor importance; thiophenols, which are sulphur analogues of phenols, exhibit a similar behavior. Comparative quantum chemical calculations show that the calculated spin densities at the hetero atoms correlate well with the experimentally determined radical cation lifetimes. Not only the Density Functional Theory (DTF) B3LYP but also the semiempirical quantum chemical model PM3 can be applied for the open shell systems mentioned.

  9. Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP).

    PubMed

    Lu, Chunliang; Urban, Marek W

    2016-04-13

    Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10(6) g/mol) molecular weight pDMAEMA-b-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli. PMID:27002238

  10. Site-directed mutagenesis identifies a tyrosine radical involved in the photosynthesized oxygen-evolving system

    SciTech Connect

    Debus, R.J.; Barry, B.A.; Babcock, G.T.; McIntosh, L.

    1988-01-01

    Photosynthetic oxygen evolution takes place in the thylakoid protein complex known as photosystem II. The reaction center core of this photosystem, where photochemistry occurs, is a heterodimer of homologous polypeptides called D1 and D2. Besides chlorophyll and quinone, photosystem II contains other organic cofactors, including two known as Z and D. Z transfers electrons from the site of water oxidation to the oxidized reaction center primary donor, P/sub 680//sup +/, while D /center dot//sup +/ gives rise to the dark-stable EPR spectrum known as signal II. D/center dot//sup +/ has recently been shown to be a tyrosine radical. Z is probably a second tyrosine located in a similar environment. Indirect evidence indicates that Z and D are associated with the D1 and E2 polypeptides, respectively. To identify the specific tyrosine residue corresponding to D, the authors have changed Tyr-160 of the D2 polypeptide to phenylalanine by site-directed mutagenesis of a psbD gene in the cyanobacterium Synechocystis 6803. The resulting mutant grows photosynthetically, but it lacks the EPR signal of D/center dot//sup +/. The authors conclude that D is Tyr-160 of the D2 polypeptide. They suggest that the C/sub 2/ symmetry in photosystem II extends beyond P/sub 680/ to its immediate electron donor and conclude that Z is Try-161 of the D1 polypeptide.

  11. Development of Initiation Strategies for the Optimization and Stabilization of Brushes Formed by Surface-Initiated Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Bain, Erich D.

    Three challenges facing the continued development of the surface-initiated (SI) polymerization field are addressed. The first challenge is that surface-initiated free radical polymerization (SI-FRP) is currently under-represented in literature reports, despite the fact that SI-FRP offers several important advantages over surface-initiated controlled radical polymerization (SI-CRP) and represents a complementary approach. Recognizing that simple, efficient, and safer approaches to synthesizing effective surface free radical initiators are needed, we present a novel synthetic route to an azo type free radical initiator that forms self-assembled monolayers on oxide coated surfaces such as silicon and glass. The yield of the novel synthetic approach is approximately double that of the previous method, and the usage of cyanide is reduced dramatically. We characterize the decomposition kinetics of the initiator using differential scanning calorimetry, comparing it with other similar initiators. We characterize the surface properties of initiator layers on silicon using ellipsometry, water contact angle measurements, and x-ray photoelectron spectroscopy (XPS). We demonstrate the use of the initiator for SI-FRP as well as SI-CRP mechanisms including reverse atom transfer radical polymerization (RATRP) and reversible addition-fragmentation transfer (RAFT) polymerization. A second challenge facing the field of SI polymerization involves the stability of grafted polymer brushes in aqueous environments and under tension, both of which are commonly encountered in many applications. We hypothesize that the mechanism of brush degrafting involves hydrolysis of ester backbone units in the initiator, which are ubiquitous in surface-bound polymerization initiator systems. The novel initiator described herein is unique in that its backbone consists of a chemically stable alkane chain, free of esters or other easily hydrolysable groups. We present results of experiments demonstrating

  12. Are gait variability and stability measures influenced by directional changes?

    PubMed Central

    2014-01-01

    Background Many gait variability and stability measures have been proposed in the literature, with the aim to quantify gait impairment, degree of neuro-motor control and balance disorders in healthy and pathological subjects. These measures are often obtained from lower trunk acceleration data, typically acquired during rectilinear gait, but relevant experimental protocols and data processing techniques lack in standardization. Since directional changes represent an essential aspect of gait, the assessment of their influence on such measures is essential for standardization. In addition, their investigation is needed to evaluate the applicability of these measures in laboratory trials and in daily life activity analysis. A further methodological aspect to be standardized concerns the assessment of the sampling frequency, which could affect stability measures. The aim of the present study was hence to assess if gait variability and stability measures are affected by directional changes, and to evaluate the influence of sampling frequency of trunk acceleration data on the results. Methods Fifty-one healthy young adults performed a 6-minute walk test along a 30 m straight pathway, turning by 180 deg at each end of the pathway. Nine variability and stability measures (Standard deviation, Coefficient of variation, Poincaré plots, maximum Floquet multipliers, short-term Lyapunov exponents, Recurrence quantification analysis, Multiscale entropy, Harmonic ratio and Index of harmonicity) were calculated on stride duration and trunk acceleration data (acquired at 100 Hz and 200 Hz) coming from straight walking windows and from windows including both straight walking and the directional change. Results Harmonic ratio was the only measure that resulted to be affected by directional changes and sampling frequency, decreasing with the presence of a directional change task. HR was affected in the AP and V directions for the 200 Hz, but only in AP direction for the 100 Hz group

  13. Direct and quasi-direct band gap silicon allotropes with remarkable stability

    NASA Astrophysics Data System (ADS)

    He, Chaoyu; Zhang, Chunxiao; Li, Jin; Peng, Xiangyang; Meng, Lijun; Tang, Chao; Zhong, Jianxin

    In our present work, five previously proposed sp$^3$ carbon crystals were suggested as silicon allotropes and their stabilities, electronic and optical properties were investigated by first-principles method. We find that these allotropes with direct or quasi-direct band gaps in range of 1.2-1.6 eV are very suitable for applications in thin-film solar cells. They display strong adsorption coefficients in the visible range of the sunlight in comparison with diamond silicon. These five silicon allotropes are confirmed possessing positive dynamical stability and remarkable themodynamical stability close to that of diamond silicon. Especially, the direct band gap M585-silicon possessing energy higher than diamond silicon only 25 meV per atom is expected to be experimentally produced for thin-film solar cells.

  14. Human Cryptochrome-1 Confers Light Independent Biological Activity in Transgenic Drosophila Correlated with Flavin Radical Stability

    PubMed Central

    Vieira, Jacqueline; Jones, Alex R.; Danon, Antoine; Sakuma, Michiyo; Hoang, Nathalie; Robles, David; Tait, Shirley; Heyes, Derren J.; Picot, Marie; Yoshii, Taishi; Helfrich-Förster, Charlotte; Soubigou, Guillaume; Coppee, Jean-Yves; Klarsfeld, André; Rouyer, Francois; Scrutton, Nigel S.; Ahmad, Margaret

    2012-01-01

    Cryptochromes are conserved flavoprotein receptors found throughout the biological kingdom with diversified roles in plant development and entrainment of the circadian clock in animals. Light perception is proposed to occur through flavin radical formation that correlates with biological activity in vivo in both plants and Drosophila. By contrast, mammalian (Type II) cryptochromes regulate the circadian clock independently of light, raising the fundamental question of whether mammalian cryptochromes have evolved entirely distinct signaling mechanisms. Here we show by developmental and transcriptome analysis that Homo sapiens cryptochrome - 1 (HsCRY1) confers biological activity in transgenic expressing Drosophila in darkness, that can in some cases be further stimulated by light. In contrast to all other cryptochromes, purified recombinant HsCRY1 protein was stably isolated in the anionic radical flavin state, containing only a small proportion of oxidized flavin which could be reduced by illumination. We conclude that animal Type I and Type II cryptochromes may both have signaling mechanisms involving formation of a flavin radical signaling state, and that light independent activity of Type II cryptochromes is a consequence of dark accumulation of this redox form in vivo rather than of a fundamental difference in signaling mechanism. PMID:22427812

  15. Radical prostatectomy

    MedlinePlus

    Prostatectomy - radical; Radical retropubic prostatectomy; Radical perineal prostatectomy; Laparoscopic radical prostatectomy; LRP; Robotic-assisted laparoscopic prostatectomy; RALP; Pelvic lymphadenectomy; ...

  16. Direct measurement of methyl radicals in a methane/air flame at atmospheric pressure by radar REMPI.

    PubMed

    Wu, Yue; Bottom, Andrew; Zhang, Zhili; Ombrello, Timothy M; Katta, Viswanath R

    2011-11-21

    We report the direct measurements of methyl radicals (CH(3)) in methane/air flames at atmospheric pressure by using coherent microwave Rayleigh scattering (Radar) from Resonance Enhanced Multi-Photon Ionization (REMPI), also known as the Radar REMPI technique. A tunable dye laser was used to selectively induce the (2 + 1) REMPI ionization of methyl radicals (CH(3), 3p(2)A(2)('')0(0)(0) band) in a near adiabatic and premixed laminar methane/air flame, generated by a Hencken burner. In situ measurements of the REMPI electrons were made by non-intrusively using a microwave homodyne transceiver detection system. The REMPI spectrum of the CH(3) radical was obtained and a spatial distribution of the radicals limited by focused laser beam geometry, approximately 20 µm normal to the flame front and 2.4 mm parallel to the flame, was determined. The measured CH(3) was in good agreement with numerical simulations performed using the detailed kinetic mechanism of GRI-3.0. To the authors' knowledge, these experiments represent the first directly-measured spatially-resolved CH(3) in a flame at atmospheric pressure. PMID:22109424

  17. Direct Evidence for PCB Destruction in the Subtropical Troposphere by OH Radicals

    NASA Astrophysics Data System (ADS)

    Mandalakis, M.; Berresheim, H.; Stephanou, E.

    2003-04-01

    Although polychlorinated biphenyls (PCBs) production and use were banned by the mid-1970s, PCBs are ubiquitous pollutants in nearly all environmental compartments. Because of their high persistence and toxicity PCBs can pose toxic effects on animals and humans, decades after their release into the environment. It has been supported that warm temperatures at the tropical and subtropical regions of the earth favor the volatilization of PCBs, which are subsequently transported to colder areas of high latitude. This process, known as "global distillation effect", could cause an enhancement of PCB concentrations in the plant biomass and the marine mammals of Earth's polar regions. It has been experimentally established, that chemical reactions of PCBs with OH radicals might be the dominant loss processes in the atmosphere1. Nevertheless, PCBs atmospheric removal by OH radicals has never been positively demonstrated under real atmospheric conditions, mainly due to the difficulties to measure simultaneously the concentration of OH radicals and PCBs in the atmosphere. By applying elaborated sampling and analytical techniques2,3, under real atmospheric conditions, we achieved the simultaneous determination of OH radicals and PCBs congeners and demonstrated for the first time that PCB removal from the troposphere of subtropical regions is due to a large extent to reactions with OH radicals. References 1. Anderson, P. N. &Hites, R. A. OH radical reactions: The major removal pathway for polychlorinated biphenyls from the atmosphere. Environ. Sci. Technol. 30, 1756-1763 (1996). 2. Berresheim, H., Elste, T., Plass-Dülmer, C., Eisele, F. L. &Tanner, D. J. Chemical ionization mass spectrometer for long-term measurements of atmospheric OH and H2SO4. Int. J. Mass Spectrom. 202, 91-109 (2000). 3. Mandalakis, M., M. Tsapakis, and E.G. Stephanou, Optimization and application of high-resolution gas chromatography with ion trap tandem mass spectrometry to the determination of

  18. Stability of water-stable C60 clusters to OH radical oxidation and hydrated electron reduction.

    PubMed

    Lee, Jaesang; Song, Weihua; Jang, Seung S; Fortner, John D; Alvarez, Pedro J J; Cooper, William J; Kim, Jae-Hong

    2010-05-15

    Reactions of water-stable C(60) clusters (nC(60)) in water with OH radicals (*OH) and hydrated electrons (e(aq)(-)), generated by steady-state gamma-radiation, were observed and characterized. Ordered C(60) clusters were relatively recalcitrant to highly reactive *OH and e(aq)(-) species, with only a fraction of carbons oxidized and reduced, respectively. Pulse radiolysis suggested that the reactions of nC(60) with OH* and e(aq)(-) were diffusion limited, with rate constants of (7.34 +/- 0.31) x 10(9) M(-1) s(-1) and (2.34 +/- 0.02) x 10(10) M(-1) s(-1), respectively. Quantum mechanical calculations of binding energy of the C(60)-OH adduct as a function of C(60) clustering degree indicate, despite an initial fast reaction, a slower overall conversion due to thermodynamic instability of C(60)-OH intermediates. The results imply that ordered clustering of C(60) in the aqueous phase significantly hinders C(60)'s fundamental reactivity with radical species. PMID:20397700

  19. Directional dependence of surface morphological stability of heteroepitaxial layers

    NASA Astrophysics Data System (ADS)

    Obayashi, Y.; Shintani, K.

    1998-09-01

    Surface morphological stability in coherent heteroepitaxial layers is analyzed focusing on the directional dependence of surface undulations created by surface diffusion. The critical stability condition is defined in terms of the free energy of the system which is assumed to be the sum of the elastic strain energy and the surface free energy. The displacement and stress fields of the semi-infinite anisotropic solid with the slightly undulating surface are calculated by using the surface admittance tensor and the vector complex potential function. Numerical results for the Si1-xGex/Si systems show that the critical wavelength of the <100> surface undulations is smaller than that of the <110> surface undulations, which means that surface undulations are likely to be formed in the <100> directions. It is also found that the critical wavelength decreases with the increase of Ge fraction. These tendencies are in good agreement with the observations in annealing experiments for the Si1-xGex/Si systems in the literature. If the substrate is assumed to be rigid, the range of layer thickness where the system is absolutely stable against a surface undulation of any wavelength exists. Finally, the growth rate of the amplitude of surface undulations is estimated from an evolution equation for the surface shape. It is shown that even if anisotropy is taken into account, the growth rate of the amplitude takes the maximum value when the wavelength is 4/3 times the critical wavelength, which is the same as in the isotropic approximation.

  20. Redox reactivity in propolis: direct detection of free radicals in basic medium and interaction with hemoglobin.

    PubMed

    Mot, Augustin-Catalin; Damian, Grigore; Sarbu, Costel; Silaghi-Dumitrescu, Radu

    2009-01-01

    Propolis is one of many natural products with known antioxidant properties. The present work aims to investigate the intimate molecular-level mechanisms of this antioxidant reactivity. Electron paramagnetic resonance (EPR)-detectable free radical signals are described here for the first time in propolis extracts. The shape of these signals and the conditions in which they were obtained, point to polyphenolic flavonoids as the sites of the radicals. An inverse correlation between antioxidant capacity and free radical signal intensity is shown. The free radical reactivity of propolis is also illustrated by the effect it exerts on the biologically-relevant peroxide reactivity of hemoglobin. A new test of antioxidant ability in natural extracts such as propolis is proposed, based on modulation of the ascorbate peroxidase activity of hemoglobin (HAPX). Results of this test correlate well with those obtained via traditional methods such as those based on DPPH (2,2-diphenyl-1-picrylhydrazyl), or on ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid). PMID:20003712

  1. Novel Synthesis of Surface-Grafted Radical Initiator With Improved Stability and Yield

    NASA Astrophysics Data System (ADS)

    Bain, Erich; Dawes, Keith; Hu, Xinfang; Gorman, Christopher; Srogl, Jiri; Genzer, Jan

    2012-02-01

    Polymers grafted at interfaces are attractive for applications including antifouling coatings, biologically functionalized materials, and responsive surfaces. The ``grafting from'' approach to form densely packed brushes involves functionalizing a substrate with initiating moieties, and carrying out polymerization, e.g., surface-inititated free-radical polymerization (SI-FRP). Azo initiators for SI-FRP are commonly synthesized by a low-yielding route requiring large amounts of potassium cyanide. Those initiators are linked to a substrate by means of an ester group, rendering tethered polymers susceptible to degrafting by hydrolysis. We present a novel synthetic route to an asymmetric azo initiator, whose yield is nearly double that of previous syntheses. Cyanide usage in the new method is reduced by 72 percent. The spacer linking the initiator to a substrate contains only carbon-carbon bonds, resulting in stable brushes. Results are demonstrated for SI-FRP as well as reverse ATRP and RAFT.

  2. Efficient radical cation stabilization of PANI-ZnO and PANI-ZnO-GO composites and its optical activity

    NASA Astrophysics Data System (ADS)

    Mathavan, T.; Divya, A.; Archana, J.; Ramasubbu, A.; Benial, A. Milton Franklin; Jothirajan, M. A.

    2016-05-01

    Polyaniline (PANI) and its composites PANI-ZnO (Zinc oxide) and PANI-ZnO-GO (Graphene oxide) were successfully constructed. These materials were characterized by electron spin resonance (ESR) technique and ultraviolet visible spectrometry. The parameters such as line width, g-factor and spin concentration were deduced from ESR spectra, from the results the radical cation stabilization of PANI, PANI-ZnO and PANI-ZnO-GO composites were compared by the polaron and bipolaron formation. The absorption features obtained in the UV absorption spectra reveal the band gap of these modified PANI composites and also predicted the information of increasing and decreasing features of signal intensity and spin concentration.

  3. New insights into the aquatic photochemistry of fluoroquinolone antibiotics: Direct photodegradation, hydroxyl-radical oxidation, and antibacterial activity changes.

    PubMed

    Ge, Linke; Na, Guangshui; Zhang, Siyu; Li, Kai; Zhang, Peng; Ren, Honglei; Yao, Ziwei

    2015-09-15

    The ubiquity and photoreactivity of fluoroquinolone antibiotics (FQs) in surface waters urge new insights into their aqueous photochemical behavior. This study concerns the photochemistry of 6 FQs: ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin and enrofloxacin. Methods were developed to calculate their solar direct photodegradation half-lives (td,E) and hydroxyl-radical oxidation half-lives (tOH,E) in sunlit surface waters. The td,E values range from 0.56 min to 28.8 min at 45° N latitude, whereas tOH,E ranges from 3.24h to 33.6h, suggesting that most FQs tend to undergo fast direct photolysis rather than hydroxyl-radical oxidation in surface waters. However, a case study for levofloxacin and sarafloxacin indicated that the hydroxyl-radical oxidation induced risky photochlorination and resulted in multi-degradation pathways, such as piperazinyl hydroxylation and clearage. Changes in the antibacterial activity of FQs caused by photodegradation in various waters were further examined using Escherichia coli, and it was found that the activity evolution depended on primary photodegradation pathways and products. Primary intermediates with intact FQ nuclei retained significant antibacterial activity. These results are important for assessing the fate and risk of FQs in surface waters. PMID:25956144

  4. Direct Evidence of Solution-Mediated Superoxide Transport and Organic Radical Formation in Sodium-Oxygen Batteries.

    PubMed

    Xia, Chun; Fernandes, Russel; Cho, Franklin H; Sudhakar, Niranjan; Buonacorsi, Brandon; Walker, Sean; Xu, Meng; Baugh, Jonathan; Nazar, Linda F

    2016-09-01

    Advanced large-scale electrochemical energy storage requires cost-effective battery systems with high energy densities. Aprotic sodium-oxygen (Na-O2) batteries offer advantages, being comprised of low-cost elements and possessing much lower charge overpotential and higher reversibility compared to their lithium-oxygen battery cousins. Although such differences have been explained by solution-mediated superoxide transport, the underlying nature of this mechanism is not fully understood. Water has been suggested to solubilize superoxide via formation of hydroperoxyl (HO2), but direct evidence of these HO2 radical species in cells has proven elusive. Here, we use ESR spectroscopy at 210 K to identify and quantify soluble HO2 radicals in the electrolyte-cold-trapped in situ to prolong their lifetime-in a Na-O2 cell. These investigations are coupled to parallel SEM studies that image crystalline sodium superoxide (NaO2) on the carbon cathode. The superoxide radicals were spin-trapped via reaction with 5,5-dimethyl-pyrroline N-oxide at different electrochemical stages, allowing monitoring of their production and consumption during cycling. Our results conclusively demonstrate that transport of superoxide from cathode to electrolyte leads to the nucleation and growth of NaO2, which follows classical mechanisms based on the variation of superoxide content in the electrolyte and its correlation with the crystallization of cubic NaO2. The changes in superoxide content upon charge show that charge proceeds through the reverse solution process. Furthermore, we identify the carbon-centered/oxygen-centered alkyl radicals arising from attack of these solubilized HO2 species on the diglyme solvent. This is the first direct evidence of such species, which are likely responsible for electrolyte degradation. PMID:27498623

  5. Tuning the Reactivity of Radical through a Triplet Diradical Cu(II) Intermediate in Radical Oxidative Cross-Coupling

    PubMed Central

    Zhou, Liangliang; Yi, Hong; Zhu, Lei; Qi, Xiaotian; Jiang, Hanpeng; Liu, Chao; Feng, Yuqi; Lan, Yu; Lei, Aiwen

    2015-01-01

    Highly selective radical/radical cross-coupling is paid more attention in bond formations. However, due to their intrinsic active properties, radical species are apt to achieve homo-coupling instead of cross-coupling, which makes the selective cross-coupling as a great challenge and almost untouched. Herein a notable strategy to accomplish direct radical/radical oxidative cross-coupling has been demonstrated, that is metal tuning a transient radical to a persistent radical intermediate followed by coupling with another transient radical. Here, a transient nitrogen-centered radical is tuned to a persistent radical complex by copper catalyst, followed by coupling with a transient allylic carbon-centered radical. Firstly, nitrogen-centered radical generated from N-methoxybenzamide stabilized by copper catalyst was successfully observed by EPR. Then DFT calculations revealed that a triplet diradical Cu(II) complex formed from the chelation N-methoxybenzamide nitrogen-centered radical to Cu(II) is a persistent radical species. Moreover, conceivable nitrogen-centered radical Cu(II) complex was observed by high-resolution electrospray ionization mass spectrometry (ESI-MS). Ultimately, various allylic amides derivatives were obtained in good yields by adopting this strategy, which might inspire a novel and promising landscape in radical chemistry. PMID:26525888

  6. Tuning the Reactivity of Radical through a Triplet Diradical Cu(II) Intermediate in Radical Oxidative Cross-Coupling

    NASA Astrophysics Data System (ADS)

    Zhou, Liangliang; Yi, Hong; Zhu, Lei; Qi, Xiaotian; Jiang, Hanpeng; Liu, Chao; Feng, Yuqi; Lan, Yu; Lei, Aiwen

    2015-11-01

    Highly selective radical/radical cross-coupling is paid more attention in bond formations. However, due to their intrinsic active properties, radical species are apt to achieve homo-coupling instead of cross-coupling, which makes the selective cross-coupling as a great challenge and almost untouched. Herein a notable strategy to accomplish direct radical/radical oxidative cross-coupling has been demonstrated, that is metal tuning a transient radical to a persistent radical intermediate followed by coupling with another transient radical. Here, a transient nitrogen-centered radical is tuned to a persistent radical complex by copper catalyst, followed by coupling with a transient allylic carbon-centered radical. Firstly, nitrogen-centered radical generated from N-methoxybenzamide stabilized by copper catalyst was successfully observed by EPR. Then DFT calculations revealed that a triplet diradical Cu(II) complex formed from the chelation N-methoxybenzamide nitrogen-centered radical to Cu(II) is a persistent radical species. Moreover, conceivable nitrogen-centered radical Cu(II) complex was observed by high-resolution electrospray ionization mass spectrometry (ESI-MS). Ultimately, various allylic amides derivatives were obtained in good yields by adopting this strategy, which might inspire a novel and promising landscape in radical chemistry.

  7. Tuning the Reactivity of Radical through a Triplet Diradical Cu(II) Intermediate in Radical Oxidative Cross-Coupling.

    PubMed

    Zhou, Liangliang; Yi, Hong; Zhu, Lei; Qi, Xiaotian; Jiang, Hanpeng; Liu, Chao; Feng, Yuqi; Lan, Yu; Lei, Aiwen

    2015-01-01

    Highly selective radical/radical cross-coupling is paid more attention in bond formations. However, due to their intrinsic active properties, radical species are apt to achieve homo-coupling instead of cross-coupling, which makes the selective cross-coupling as a great challenge and almost untouched. Herein a notable strategy to accomplish direct radical/radical oxidative cross-coupling has been demonstrated, that is metal tuning a transient radical to a persistent radical intermediate followed by coupling with another transient radical. Here, a transient nitrogen-centered radical is tuned to a persistent radical complex by copper catalyst, followed by coupling with a transient allylic carbon-centered radical. Firstly, nitrogen-centered radical generated from N-methoxybenzamide stabilized by copper catalyst was successfully observed by EPR. Then DFT calculations revealed that a triplet diradical Cu(II) complex formed from the chelation N-methoxybenzamide nitrogen-centered radical to Cu(II) is a persistent radical species. Moreover, conceivable nitrogen-centered radical Cu(II) complex was observed by high-resolution electrospray ionization mass spectrometry (ESI-MS). Ultimately, various allylic amides derivatives were obtained in good yields by adopting this strategy, which might inspire a novel and promising landscape in radical chemistry. PMID:26525888

  8. Quantitative assessment on the contribution of direct photolysis and radical oxidation in photochemical degradation of 4-chlorophenol and oxytetracycline.

    PubMed

    Liu, Yiqing; He, Xuexiang; Fu, Yongsheng; Dionysiou, Dionysios D

    2016-07-01

    In UV-254 nm/H2O2 advanced oxidation process (AOP), the potential degradation pathways for organic pollutants include (1) hydrolysis, (2) direct H2O2 oxidation, (3) UV direct photolysis, and (4) hydroxyl radical (HO(•)) reaction. In this study, the contribution of these pathways was quantitatively assessed in the photochemical destruction of 4-chlorophenol (4-CP), demonstrating pathways (3) and (4) to be predominantly responsible for the removal of 4-CP by UV/H2O2 in 50 mM phosphate buffer solution. Increasing reaction pH could significantly enhance the contribution of direct photolysis in UV/H2O2 process. The contribution of HO(•) oxidation was improved with increasing initial H2O2 concentration probably due to the increased formation of HO(•). Presence of sodium carbonate (Na2CO3) as in UV/H2O2/Na2CO3 system promoted the degradation of 4-CP, with carbonate radical (CO3 (•-)) reaction and direct photolysis identified to be the main contributing pathways. The trends in the contribution of each factor were further evaluated and validated on the degradation of the antibiotic compound oxytetracycline (OTC). This study provides valuable information on the relative importance of different reaction pathways on the photochemical degradation of organic contaminants such as 4-CP and OTC in the presence and absence of a CO3 (•-) precursor. PMID:27055892

  9. N-substituted phenothiazine derivatives: how the stability of the neutral and radical cation forms affects overcharge performance in lithium-ion batteries.

    PubMed

    Narayana, Kishore Anand; Casselman, Matthew D; Elliott, Corrine F; Ergun, Selin; Parkin, Sean R; Risko, Chad; Odom, Susan A

    2015-04-27

    Phenothiazine and five N-substituted derivatives were evaluated as electrolyte additives for overcharge protection in LiFePO4 /synthetic graphite lithium-ion batteries. We report on the stability and reactivity of both the neutral and radical-cation forms of these six compounds. While three of the compounds show extensive overcharge protection, the remaining three last for only one to a few cycles. UV/Vis studies of redox shuttle stability in the radical cation form are consistent with the overcharge performance: redox shuttles with spectra that show little change over time exhibit extensive overcharge performance, whereas those with changing spectra have limited overcharge protection. In one case, we determined that a C-N bond cleaves upon oxidation, forming the phenothiazine radical cation and leading to premature overcharge protection failure; in another case, poor solubility appears to limit protection. PMID:25504135

  10. 14 CFR 23.177 - Static directional and lateral stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... stability, as shown by the tendency to recover from a wings level sideslip with the rudder free, must be... stability, as shown by the tendency to raise the low wing in a sideslip with the aileron controls free,...

  11. Liquid falling films: linear stability and direct numerical simulation

    NASA Astrophysics Data System (ADS)

    Schmidt, Patrick; O'Naraigh, Lennon; Valluri, Prashant; Lucquiaud, Mathieu

    2013-11-01

    Interfacial instability of falling liquid films in counter-current contact with a turbulent gas phase is investigated by means of an Orr-Sommerfeld analysis. This study is complemented by a full energy budget analysis, identifying the key mechanisms of the instability. This gives first insight into the dynamic behaviour of the two-phase system, which is relevant for a wide range of technical applications, such as absorption and distillation. The linear stability analysis is also used to identify the operating limits of a counter-current operation i.e. the so-called loading and flooding limits. In addition, the results of this analysis are benchmark for direct numerical simulations using the newly launched Two-Phase Level Set (http://sourceforge.net/projects/tpls/) solver. High resolution DNS is used to obtain detailed knowledge of important mechanisms at play, especially with regard to interfacial instability and transient system behaviour, which can help to design more efficient mass transfer equipment such as structured packings. Sulzer Chemtech Ltd, EPSRC, Energy Technology Partnership.

  12. Effect of hydrogen pressure on free radicals in direct coal liquefaction/coprocessing

    SciTech Connect

    Seehra, M.S.; Ibrahim, M.M.

    1995-12-31

    The objective of this study was to investigate the coprocessing of coal with waste tires and commingled plastics and to characterize the relevant catalysts, using high pressure/high temperature in-situ ESR (Electron Spin Resonance) spectroscopy. The recent results from high pressure ESR spectroscopy are emphasized. During this period, considerable progress was made in developing the high pressure capabilities in in-situ ESR spectroscopy and new results carried out in 1000 psi of H{sub 2}gas are presented. In these experiments, sapphire tubes were used to contain the high pressures at temperatures up to 500{degrees}C. Results of the experiments carried out under 1000 psi of H{sub 2} are compared with those under 1000 psi of non-interacting argon and with the earlier experiments in flowing H{sub 2} gas where the volatiles are removed by the flowing gas. In these experiments, the free radical density N of the Blind Canyon coal was measured at each temperature and pressure by double integration of the ESR signal and calibrating it against a standard. The details of the experimental apparatus and procedures have been described in earlier publications.

  13. The production mechanisms of OH radicals in a pulsed direct current plasma jet

    SciTech Connect

    Liu, X. Y.; Pei, X. K.; Lu, X. P.; Liu, D. W.; Ostrikov, K.

    2014-09-15

    The production mechanism of OH radicals in a pulsed DC plasma jet is studied by a two-dimensional (2-D) plasma jet model and a one-dimensional (1-D) discharge model. For the plasma jet in the open air, electron-impact dissociation of H{sub 2}O, electron neutralization of H{sub 2}O{sup +}, as well as dissociation of H{sub 2}O by O(1D) are found to be the main reactions to generate the OH species. The contribution of the dissociation of H{sub 2}O by electron is more than the others. The additions of N{sub 2}, O{sub 2}, air, and H{sub 2}O into the working gas increase the OH density outside the tube slightly, which is attributed to more electrons produced by Penning ionization. On the other hand, the additions of O{sub 2} and H{sub 2}O into the working gas increase the OH density inside the tube substantially, which is attributed to the increased O (1D) and H{sub 2}O concentration, respectively. The gas flow will transport high density OH out of the tube during pulse off period. It is also shown that the plasma chemistry and reactivity can be effectively controlled by the pulse numbers. These results are supported by the laser induced fluorescence measurements and are relevant to several applications of atmospheric-pressure plasmas in health care, medicine, and materials processing.

  14. On the Electronic Spectroscopy of Closed Shell Cations Derived from Resonance Stabilized Radicals: Insights from Theory and Franck-Condon Analysis

    NASA Astrophysics Data System (ADS)

    Troy, Tyler P.; Kable, Scott H.; Schmidt, Timothy W.; Reid, Scott A.

    2012-06-01

    Recent attention has been directed on closed shell aromatic cations as potential carriers of the diffuse interstellar bands. The spectra of mass-selected, matrix-isolated benzylium and tropylium cations were recently reported [Nagy, A., Fulara, J., Garkusha, I. and Maier, J. P. (2011), Angew. Chem. Int. Ed., 50: 3022-3025]. The benzylium spectrum shows an extended progression in a low frequency (510 cm-1) ring distortion mode. Modeling of the benzylium spectrum using (TD)DFT and MCSCF-PT2 methods in concert with multidimensional Franck-Condon (FC) analysis is found to yield excellent agreement with the experimental spectrum. We extended this analysis to larger (2 and 3 ring) PAH cations derived from resonance stabilized radicals, which are predicted to show strong S0 → Sn transitions in the visible region. The FC progression is significantly quenched in the larger species, and our results for 1-napthylmethylium are in excellent agreement with very recent experiments [Nagy, A., Fulara, J., and Maier, J. P. (2011), J. Am. Chem. Soc., 133, 19796]. Since carriers of the DIBs should exhibit spectra dominated by a single vibronic transition, our results demonstrate that closed-shell cations may present spectra with the required properties. Furthermore, the calculated ionization energies of a range of CSCs were found to be in the 13-14 eV range, consistent with variations in behaviour of the DIB carriers with respect to various astrophysical environments.

  15. Direct observation of unimolecular decay of CH3CH2CHOO Criegee intermediates to OH radical products

    NASA Astrophysics Data System (ADS)

    Fang, Yi; Liu, Fang; Klippenstein, Stephen J.; Lester, Marsha I.

    2016-07-01

    The unimolecular decay of carbonyl oxide intermediates, known as Criegee intermediates, produced in alkene ozonolysis is a significant source of OH radicals in the troposphere. Here, the rate of appearance of OH radical products is examined directly in the time-domain for a prototypical alkyl-substituted Criegee intermediate, CH3CH2CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice-Ramsperger-Kassel-Marcus calculations of the microcanonical unimolecular decay rate for CH3CH2CHOO are also carried out at energies in the vicinity of the barrier for 1,4 hydrogen atom transfer that leads to OH products. Tunneling through the barrier, derived from high level electronic structure calculations, contributes significantly to the decay rate. Infrared transitions of CH3CH2CHOO are identified in the CH stretch overtone region, which are detected by ultraviolet laser-induced fluorescence of the resultant OH products. The features observed are attributed to CH vibrational excitations and conformational forms utilizing insights from theory. Both experiment and theory yield unimolecular decay rates for CH3CH2CHOO of ca. 107 s-1, which are slower than those obtained for syn-CH3CHOO or (CH3)2COO reported previously [Fang et al., J. Chem. Phys. 144, 061102 (2016)] at similar energies. Master equation modeling is also utilized to predict the thermal decay rate of CH3CH2CHOO under atmospheric conditions, giving a rate of 279 s-1 at 298 K.

  16. Direct observation of unimolecular decay of CH3CH2CHOO Criegee intermediates to OH radical products.

    PubMed

    Fang, Yi; Liu, Fang; Klippenstein, Stephen J; Lester, Marsha I

    2016-07-28

    The unimolecular decay of carbonyl oxide intermediates, known as Criegee intermediates, produced in alkene ozonolysis is a significant source of OH radicals in the troposphere. Here, the rate of appearance of OH radical products is examined directly in the time-domain for a prototypical alkyl-substituted Criegee intermediate, CH3CH2CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice-Ramsperger-Kassel-Marcus calculations of the microcanonical unimolecular decay rate for CH3CH2CHOO are also carried out at energies in the vicinity of the barrier for 1,4 hydrogen atom transfer that leads to OH products. Tunneling through the barrier, derived from high level electronic structure calculations, contributes significantly to the decay rate. Infrared transitions of CH3CH2CHOO are identified in the CH stretch overtone region, which are detected by ultraviolet laser-induced fluorescence of the resultant OH products. The features observed are attributed to CH vibrational excitations and conformational forms utilizing insights from theory. Both experiment and theory yield unimolecular decay rates for CH3CH2CHOO of ca. 10(7) s(-1), which are slower than those obtained for syn-CH3CHOO or (CH3)2COO reported previously [Fang et al., J. Chem. Phys. 144, 061102 (2016)] at similar energies. Master equation modeling is also utilized to predict the thermal decay rate of CH3CH2CHOO under atmospheric conditions, giving a rate of 279 s(-1) at 298 K. PMID:27475366

  17. Reductive Umpolung of Carbonyl Derivatives with Visible-Light Photoredox Catalysis: Direct Access to Vicinal Diamines and Amino Alcohols via α-Amino Radicals and Ketyl Radicals.

    PubMed

    Fava, Eleonora; Millet, Anthony; Nakajima, Masaki; Loescher, Sebastian; Rueping, Magnus

    2016-06-01

    Visible-light-mediated photoredox-catalyzed aldimine-aniline and aldehyde-aniline couplings have been realized. The reductive single electron transfer (SET) umpolung of various carbonyl derivatives enabled the generation of intermediary ketyl and α-amino radical anions, which were utilized for the synthesis of unsymmetrically substituted 1,2-diamines and amino alcohols. PMID:27136443

  18. Direct formation of the C5'-radical in the sugar-phosphate backbone of DNA by high-energy radiation.

    PubMed

    Adhikary, Amitava; Becker, David; Palmer, Brian J; Heizer, Alicia N; Sevilla, Michael D

    2012-05-24

    Neutral sugar radicals formed in DNA sugar-phosphate backbone are well-established as precursors of biologically important damage such as DNA strand scission and cross-linking. In this work, we present electron spin resonance (ESR) evidence showing that the sugar radical at C5' (C5'(•)) is one of the most abundant (ca. 30%) sugar radicals formed by γ- and Ar ion-beam irradiated hydrated DNA samples. Taking dimethyl phosphate as a model of sugar-phosphate backbone, ESR and theoretical (DFT) studies of γ-irradiated dimethyl phosphate were carried out. CH(3)OP(O(2)(-))OCH(2)(•) is formed via deprotonation from the methyl group of directly ionized dimethyl phosphate at 77 K. The formation of CH(3)OP(O(2)(-))OCH(2)(•) is independent of dimethyl phosphate concentration (neat or in aqueous solution) or pH. ESR spectra of C5'(•) found in DNA and of CH(3)OP(O(2)(-))OCH(2)(•) do not show an observable β-phosphorus hyperfine coupling (HFC). Furthermore, C5'(•) found in DNA does not show a significant C4'-H β-proton HFC. Applying the DFT/B3LYP/6-31G(d) method, a study of conformational dependence of the phosphorus HFC in CH(3)OP(O(2)(-))OCH(2)(•) shows that in its minimum energy conformation, CH(3)OP(O(2)(-))OCH(2)(•), has a negligible β-phosphorus HFC. On the basis of these results, the formation of radiation-induced C5'(•) is proposed to occur via a very rapid deprotonation from the directly ionized sugar-phosphate backbone, and the rate of this deprotonation must be faster than that of energetically downhill transfer of the unpaired spin (hole) from ionized sugar-phosphate backbone to the DNA bases. Moreover, C5'(•) in irradiated DNA is found to be in a conformation that does not exhibit β-proton or β-phosphorus HFCs. PMID:22553971

  19. Role of the reaction of stabilized Criegee intermediates with peroxy radicals in particle formation and growth in air.

    PubMed

    Zhao, Yue; Wingen, Lisa M; Perraud, Véronique; Greaves, John; Finlayson-Pitts, Barbara J

    2015-05-21

    Ozonolysis of alkenes is an important source of secondary organic aerosol (SOA) in the atmosphere. However, the mechanisms by which stabilized Criegee intermediates (SCI) react to form and grow the particles, and in particular the contributions from oligomers, are not well understood. In this study, ozonolysis of trans-3-hexene (C6H12), as a proxy for small alkenes, was investigated with an emphasis on the mechanisms of particle formation and growth. Ozonolysis experiments were carried out both in static Teflon chambers (18-20 min reaction times) and in a glass flow reactor (24 s reaction time) in the absence and presence of OH or SCI scavengers, and under different relative humidity (RH) conditions. The chemical composition of polydisperse and size-selected SOA particles was probed using different mass spectrometric techniques and infrared spectroscopy. Oligomers having SCI as the chain unit are found to be the dominant components of such SOA particles. The formation mechanism for these oligomers suggested by our results follows the sequential addition of SCI to organic peroxy (RO2) radicals, in agreement with previous studies by Moortgat and coworkers. Smaller particles are shown to have a relatively greater contribution from longer oligomers. Higher O/C ratios are observed in smaller particles and are similar to those of oligomers resulting from RO2 + nSCI, supporting a significant role for longer oligomers in particle nucleation and early growth. Under atmospherically relevant RH of 30-80%, water vapor suppresses oligomer formation through scavenging SCI, but also enhances particle nucleation. Under humid conditions, or in the presence of formic or hydrochloric acid as SCI scavengers, peroxyhemiacetals are formed by the acid-catalyzed particle phase reaction between oligomers from RO2 + nSCI and a trans-3-hexene derived carbonyl product. In contrast to the ozonolysis of trans-3-hexene, oligomerization involving RO2 + nSCI does not appear to be prevalent in the

  20. Perturbative stability along the supersymmetric directions of the landscape

    SciTech Connect

    Sousa, Kepa

    2015-02-01

    We consider the perturbative stability of non-supersymmetric configurations in N=1 supergravity models with a spectator sector not involved in supersymmetry breaking. Motivated by the supergravity description of complex structure moduli in Large Volume Compactifications of type IIB-superstrings, we concentrate on models where the interactions are consistent with the supersymmetric truncation of the spectator fields, and we describe their couplings by a random ensemble of generic supergravity theories. We characterise the mass spectrum of the spectator fields in terms of the statistical parameters of the ensemble and the geometry of the scalar manifold. Our results show that the non-generic couplings between the spectator and the supersymmetry breaking sectors can stabilise all the tachyons which typically appear in the spectator sector before including the supersymmetry breaking effects, and we find large regions of the parameter space where the supersymmetric sector remains stable with probability close to one. We discuss these results about the stability of the supersymmetric sector in two physically relevant situations: non-supersymmetric Minkowski vacua, and slow-roll inflation driven by the supersymmetry breaking sector. For the class of models we consider, we have reproduced the regimes in which the KKLT and Large Volume Scenarios stabilise all supersymmetric moduli. We have also identified a new regime in which the supersymmetric sector is stabilised at a very robust type of dS minimum without invoking a large mass hierarchy.

  1. Perturbative stability along the supersymmetric directions of the landscape

    NASA Astrophysics Data System (ADS)

    Sousa, Kepa; Ortiz, Pablo

    2015-02-01

    We consider the perturbative stability of non-supersymmetric configurations in Script N=1 supergravity models with a spectator sector not involved in supersymmetry breaking. Motivated by the supergravity description of complex structure moduli in Large Volume Compactifications of type IIB-superstrings, we concentrate on models where the interactions are consistent with the supersymmetric truncation of the spectator fields, and we describe their couplings by a random ensemble of generic supergravity theories. We characterise the mass spectrum of the spectator fields in terms of the statistical parameters of the ensemble and the geometry of the scalar manifold. Our results show that the non-generic couplings between the spectator and the supersymmetry breaking sectors can stabilise all the tachyons which typically appear in the spectator sector before including the supersymmetry breaking effects, and we find large regions of the parameter space where the supersymmetric sector remains stable with probability close to one. We discuss these results about the stability of the supersymmetric sector in two physically relevant situations: non-supersymmetric Minkowski vacua, and slow-roll inflation driven by the supersymmetry breaking sector. For the class of models we consider, we have reproduced the regimes in which the KKLT and Large Volume Scenarios stabilise all supersymmetric moduli. We have also identified a new regime in which the supersymmetric sector is stabilised at a very robust type of dS minimum without invoking a large mass hierarchy.

  2. A computational study on directional stability of chine-shaped forebodies at high-alpha

    NASA Technical Reports Server (NTRS)

    Ravi, R.; Mason, William H.

    1992-01-01

    CFD is employed to study the flowfields over chine-shaped forebodies at low-speed high-angle-of-attack conditions with sideslip. This study is conducted to define forebody geometries that provide good directional stability characteristics under these conditions. An analytically defined generic forebody model is developed and a systematic examination of forebody shapes is performed to determine which shapes promote a positive contribution to directional stability at high-alpha. Results of the initial parametric study and some guidelines for aerodynamic design to promote positive directional stability are presented.

  3. Model of diffusion-assisted direct laser writing by means of nanopolymerization in the presence of radical quencher

    SciTech Connect

    Pikulin, Alexander Bityurin, Nikita; Sokolov, Viktor I.

    2015-12-15

    Diffusion-assisted direct laser writing (DA-DLW) by multiphoton polymerization has been recently shown to be one of the most promising methods for the high-resolution 3D nanofabrication [I. Sakellari, et al., ACS Nano 6, 2302 (2012)]. The improvement of the writing spatial resolution has been observed under certain conditions when the mobile radical quencher (polymerization inhibitor) is added to the photosensitive composition. In this work, we present a theoretical study of this method, focusing on the resolution capabilities and optimal writing parameters. The laser beam absorption in the polymerizable composition causes the localized depletion of the quencher molecules. If the quencher depletion is balanced by its diffusion from the outside of the focal volume, the quasi-stationary non-equillibrium concentration spatial profile with zero minimum can be obtained. The polymer is then effectively formed only in the domain where the quencher is depleted. The spatially-distributed quencher, in this case, has the effect similar to that of the vortex beam in STimulated Emission Microscopy (STED)

  4. Chemistry of carotenoid neutral radicals.

    PubMed

    Ligia Focsan, A; Magyar, Adam; Kispert, Lowell D

    2015-04-15

    Proton loss from the carotenoid radical cations (Car(+)) to form neutral radicals (#Car) was investigated by numerous electrochemical, EPR, ENDOR and DFT studies described herein. The radical cation and neutral radicals were formed in solution electrochemically and stabilized on solid silica-alumina and MCM-41 matrices. Carotenoid neutral radicals were recently identified in Arabidopsis thaliana plant and photosystem II samples. Deprotonation at the terminal ends of a zeaxanthin radical cation could provide a secondary photoprotection pathway which involves quenching excited state chlorophyll by the long-lived zeaxanthin neutral radicals formed. PMID:25687648

  5. Radicalization and Radical Catalysis of Biomass Sugars: Insights from First-principles Studies

    PubMed Central

    Yang, Gang; Zhu, Chang; Zou, Xianli; Zhou, Lijun

    2016-01-01

    Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions. PMID:27405843

  6. Radicalization and Radical Catalysis of Biomass Sugars: Insights from First-principles Studies

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Zhu, Chang; Zou, Xianli; Zhou, Lijun

    2016-07-01

    Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions.

  7. Radicalization and Radical Catalysis of Biomass Sugars: Insights from First-principles Studies.

    PubMed

    Yang, Gang; Zhu, Chang; Zou, Xianli; Zhou, Lijun

    2016-01-01

    Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions. PMID:27405843

  8. [Anti-radical activity of products of processing of holothurian Cucumaria japonica and their practical application for lipid stabilization].

    PubMed

    Tabakaeva, O V; Kalenik, T K; Tabakaev, A V

    2015-01-01

    Products of technological and biotechnological modification (acid and enzymatic hydrolyzates and hydrothermal extracts) of the holothurian Cucumariajaponica from the Far East region are the complex multicomponent systems containing biologically active agents of a sea origin that has to provide them biological activity. The research objective consisted in quantitative studying of anti-radical properties of acid, enzymatic hydrolyzates and hydrothermal extracts from soft fabrics of a holothurian from the Far East region (Cucumaria japonica) and their influence on oxidation of lipids in fat emulsion products. The reaction with stable free 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical was used as a model system. Radical relating activity of hydrolyzates and extracts from Cucumaria japonica varied over a wide range from 48 to 78%. The maximum radical binding activity was noted for acid hydrolyzates. The activity of the hydrolyzate from a nimbus and feelers of Cucumaria japonica was comparable with activity of ionol. It has been defined that levels of manifestation of anti-radical activity depended on a way of technological and biotechnological processing of raw materials. Studying of fractional composition of melanoidins of hydrolyzates and extracts from Cucumaria japonica established that they can be divided into fractions--with molecular masses about 10,000 and 1000 Da. The maximum content of melanoidins has been defined in fraction weighing about 1000 Da. Introduction of acid, enzymatic hydrolyzates and hydrothermal extracts from Cucumaria japonica in the composition of oil-fat emulsion systems allowed to slow down processes of lipid oxidation and triglyceride hydrolysis in mayonnaise. Introduction of hydrolyzates and hydrothermal extracts from Cucumaria japonica in an oil-fat emulsion product allowed to reduce peroxide value by 22-45%, acid value by 12-35% on the 90th days of storage. Acid hydrolysates of Cucumaria Japonica most significantly reduce the rate of

  9. Beta-Carotene chemical stability in nanoemulsions was improved by stabilized with Beta-Lactoglobulin-Catechin conjugates through free radical method

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Beta-lactoglobulin (BLG)-catechin conjugates were prepared by a free radical method and investigated with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), electrospray ionization-mass spectrometry (ESI-MS), and far-UV circular dichroism (CD). Covalent binding between BLG and cat...

  10. Towards reducing DBP formation potential of drinking water by favouring direct ozone over hydroxyl radical reactions during ozonation.

    PubMed

    De Vera, Glen Andrew; Stalter, Daniel; Gernjak, Wolfgang; Weinberg, Howard S; Keller, Jurg; Farré, Maria José

    2015-12-15

    When ozonation is employed in advanced water treatment plants to produce drinking water, dissolved organic matter reacts with ozone (O3) and/or hydroxyl radicals (OH) affecting disinfection byproduct (DBP) formation with subsequently used chlorine-based disinfectants. This study presents the effects of varying exposures of O3 and •OH on DBP concentrations and their associated toxicity generated after subsequent chlorination. DBP formation potential tests and in vitro bioassays were conducted after batch ozonation experiments of coagulated surface water with and without addition of tertiary butanol (t-BuOH, 10 mM) and hydrogen peroxide (H2O2, 1 mg/mg O3), and at different pH (6-8) and transferred ozone doses (0-1 mg/mg TOC). Although ozonation led to a 24-37% decrease in formation of total trihalomethanes, haloacetic acids, haloacetonitriles, and trihaloacetamides, an increase in formation of total trihalonitromethanes, chloral hydrate, and haloketones was observed. This effect however was less pronounced for samples ozonated at conditions favoring molecular ozone (e.g., pH 6 and in the presence of t-BuOH) over •OH reactions (e.g., pH 8 and in the presence of H2O2). Compared to ozonation only, addition of H2O2 consistently enhanced formation of all DBP groups (20-61%) except trihalonitromethanes. This proves that •OH-transformed organic matter is more susceptible to halogen incorporation. Analogously, adsorbable organic halogen (AOX) concentrations increased under conditions that favor •OH reactions. The ratio of unknown to known AOX, however, was greater at conditions that promote direct O3 reactions. Although significant correlation was found between AOX and genotoxicity with the p53 bioassay, toxicity tests using 4 in vitro bioassays showed relatively low absolute differences between various ozonation conditions. PMID:26378731

  11. Effect of nucleobase sequence on the proton-transfer reaction and stability of the guanine-cytosine base pair radical anion.

    PubMed

    Chen, Hsing-Yin; Yeh, Shu-Wen; Hsu, Sodio C N; Kao, Chai-Lin; Dong, Teng-Yuan

    2011-02-21

    The formation of base pair radical anions is closely related to many fascinating research fields in biology and chemistry such as radiation damage to DNA and electron transport in DNA. However, the relevant knowledge so far mainly comes from studies on isolated base pair radical anions, and their behavior in the DNA environment is less understood. In this study, we focus on how the nucleobase sequence affects the properties of the guanine-cytosine (GC) base pair radical anion. The energetic barrier and reaction energy for the proton transfer along the N(1)(G)-H···N(3)(C) hydrogen bond and the stability of GC˙(-) (i.e., electron affinity of GC) embedded in different sequences of base-pair trimer were evaluated using density functional theory. The computational results demonstrated that the presence of neighboring base pairs has an important influence on the behavior of GC˙(-) in the gas phase. The excess electron was found to be localized on the embedded GC and the charge leakage to neighboring base pairs was very minor in all of the investigated sequences. Accordingly, the sequence behavior of the proton-transfer reaction and the stability of GC˙(-) is chiefly governed by electrostatic interactions with adjacent base pairs. However, the effect of base stacking, due to its electrostatic nature, is severely screened upon hydration, and thus, the sequence dependence of the properties of GC˙(-) in aqueous environment becomes relatively weak and less than that observed in the gas phase. The effect of geometry relaxation associated with neighboring base pairs as well as the possibility of proton transfer along the N(2)(G)-H···O(2)(C) channel have also been investigated. The implications of the present findings to the electron transport and radiation damage of DNA are discussed. PMID:21152551

  12. Spin-trapping studies of peroxynitrite decomposition and of 3-morpholinosydnonimine N-ethylcarbamide autooxidation: direct evidence for metal-independent formation of free radical intermediates.

    PubMed

    Augusto, O; Gatti, R M; Radi, R

    1994-04-01

    Decomposition of peroxynitrite, the reaction product of superoxide and nitric oxide, was studied by electron paramagnetic resonance (EPR)-spin-trapping experiments with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Proton-catalyzed decomposition of peroxynitrite at pH 7.5 resulted in the formation of the DMPO-hydroxyl radical adduct (DMPO-OH). Yields were low as DMPO-OH decomposes by direct reactions with peroxynitrite anion and nitrogen dioxide. The yield of DMPO-OH greatly increased in the presence of glutathione or cysteine. Both thiols inhibited the DMPO-OH signal decay by scavenging excess peroxynitrite anion and presumably nitrogen dioxide yielded during peroxynitrite decomposition. In turn, the reactions of peroxynitrite with either glutathione or cysteine resulted in the formation of thiyl radicals, detectable as the corresponding DMPO adduct. Systematic spin-trapping studies of peroxynitrite decomposition in the presence of glutathione established that DMPO-hydroxyl radical adduct formation was metal independent, occurring in a metal-free buffer and being unaffected by diethylene-triaminepentaacetic acid. Also, quantitative competition experiments with ethanol and formate demonstrated that the oxidant generated during peroxynitrite decomposition reacts with rate constants similar to those expected for free hydroxyl radical and forming the same free radical intermediates, alpha-ethyl-hydroxy and carbon dioxide radicals, respectively. Similar spin-trapping results were obtained in studies of the autooxidation of 3-morpholinosydnonimine, a sydnonimine which generates a flux of both superoxide and nitric oxide. The obtained results contribute for the understanding of the reactivity of peroxynitrite, a transient intermediate of emerging biological significance. PMID:8161194

  13. Theoretical investigations of reactions of some radicals with HO sub 2. 1. Hydrogen abstractions by direct mechanisms

    SciTech Connect

    Toohey, D.W.; Anderson, J.G. )

    1989-02-09

    Ab initio quantum mechanical methods are used to calculate saddle-point geometries and energies for hydrogen abstractions from HO{sub 2} by N, ClO, O, Cl, H, OH, and F assuming direct attack at the hydrogen atom. Results are consistent with bond energy-bond order principles and indicate that activation energies for these reactions should decrease with increasing exothermicity of reaction. In addition, the large rate constant for OH + HO{sub 2} {yields} H{sub 2}O + O{sub 2} is interpreted to be due to long-range dipole-dipole attraction, leading ultimately to formation of a hydrogen bond and to stabilization of an early transition state. Results for the ClO + HO{sub 2} {yields} HOCl + O{sub 2} reaction suggest a dual mechanism dominated by direct abstraction at high temperatures and by elimination from a stable intermediate at lower temperatures, perhaps the only reaction in this series which does so. These results are in good agreement with current experimental rate data.

  14. The formation and stability of the superoxide radical (O2-) on rock-forming minerals: Band gaps, hydroxylation state, and implications for Mars oxidant chemistry

    NASA Astrophysics Data System (ADS)

    Zent, Aaron P.; Ichimura, Andrew S.; Quinn, Richard C.; Harding, Heather K.

    2008-09-01

    We have examined the generation and stability of O2 - on TiO2 and albite, a common Na feldspar. We were not able to produce thermally stable superoxide on albite, in contrast to the results of Yen et al., who reported the generation of O2 - that was stable up to 200°C on labradorite, another common feldspar. The superoxide radical did form under UV irradiation at 77 K on albite that was not dehydrated but decayed rapidly at room temperature. On dehydrated albite, no superoxide signal was observed. We studied the kinetics of O2 - decomposition on hydrated albite and derived an activation energy, E a = 15.2 kJ/mol. Assuming pseudo first-order kinetics, a simple thermal model of Mars' regolith demonstrates that the surface O2 - population does not go to zero overnight; superoxide extinction at the surface is only complete when the seasonal CO2 cap covers the surface and surface photolysis is inhibited. Depending on the specific quantum efficiency of the e-/h+ generation process, a finite, non-equilibrium population of O2 - should be observable on Martian surface materials throughout the Martian year. However, on the basis of our inability to generate stable O2 - on hydrated albite via direct UV irradiation, we do not believe that this mechanism is capable of explaining the O2 release in the Viking Gas Exchange (GEx) results, since O2 release in that case was observed even after samples had been stored for 143 sols in the dark at 10°C, then heated to 145°C for 3 hours. At least two other potential pathways to the generation of O2 - are identified in this article. The first possibility is that metal oxides common on the Martian surface, particularly hematite, may be photoactive on Mars and play a role analogous to TiO2 in surface catalysis. Secondly, we found that superoxide that formed during the sorption or drying of a 1% H2O2 solution on TiO2, and potentially other oxides seems to be stable indefinitely.

  15. Direct measurement of intracellular free Ca2+ in rat peritoneal macrophages: correlation with oxygen-radical production.

    PubMed Central

    Hallett, M B; Campbell, A K

    1983-01-01

    A novel method has been developed, based on osmotic lysis of intracellular pinocytotic vesicles, to introduce the Ca2+-activated photoprotein obelin into the cytoplasm of rat peritoneal macrophages. The change in osmolarity of the incubating medium necessary to induce lysis of the pinocytotic vesicles did not significantly affect the viability or responsiveness of the cells. The method enabled on average 3 fl of external medium to be introduced into each cell. Macrophages loaded with photoprotein had a resting intracellular Ca2+ concentration of 0.24 +/- 0.02 microM, calculated from the obelin consumption rate. The calcium ionophore, A23187, induced a prolonged rise in intracellular Ca2+ and also stimulated oxygen-radical production, monitored by luminol-dependent chemiluminescence. The chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine, 1 microM, produced a transient increase in cytoplasmic Ca2+ which reached a plateau of 1.2 +/- 0.64 microM (n = 7) and declined with a half-time of approximately 40 sec. Unopsonized particles, latex beads (diameter = 1 micron), did not produce any detectable rise in intracellular Ca2+. Incorporation of a calcium chelator EGTA-ethylene-glycol-bis-(aminoethylether) tetra-acetate--into the cytoplasm abolished the transient intracellular Ca2+ rise induced by chemotactic peptide. Oxygen-radical production was also abolished. However, oxygen radical production induced by unopsonized particles was unaffected by intracellular EGTA. It was concluded that oxygen-radical production detected by chemiluminescence can be triggered by a rise in intracellular Ca2+. Chemotactic peptide induces oxygen-radical production by this mechanism. However, unopsonized particles induce oxygen-radical production by a mechanism independent of a rise in intracellular Ca2+. Images Figure 1 PMID:6414943

  16. Stabilities of nitrogen containing heterocyclic radicals and geometrical influences on non-radiative processes in organic molecules

    NASA Technical Reports Server (NTRS)

    Evleth, E. M.

    1971-01-01

    Theoretical and experimental work on generating radicals by removal of a hydrogen atom from pyrrole, imidazole, indole, and carbazole is reported. Photophysical studies on indolizine and related aza-derivatives show that materials having large S2-S1 energy gaps might exhibit upper state fluorescence. Photodecomposition quantum yields of a series of sterically hindered p-aminobenzene diazonium cations in water were found structurally and wavelength dependent and unquenched in aqueous sodium bromide solutions. Photodecomposition of diazonium materials did not produce a metastable species with a longer lifetime than 1 msec.

  17. Beta-carotene chemical stability in Nanoemulsions was improved by stabilized with beta-lactoglobulin-catechin conjugates through free radical method.

    PubMed

    Yi, Jiang; Zhang, Yuzhu; Liang, Rong; Zhong, Fang; Ma, Jianguo

    2015-01-14

    Beta-lactoglobulin (BLG)–catechin conjugates were prepared by a free radical method and investigated with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), electrospray ionization–mass spectrometry (ESI-MS), and far-UV circular dichroism (CD). Covalent binding between BLG and catechin were confirmed with SDS-PAGE and ESI-MS. About 93% of beta-lactoglobulin was conjugated with catechin or catecin fragments according to the gel intensity analysis software. Far-UV CD results showed that the content of β-sheet decreased with a corresponding increase in unordered structures after grafting. Both nanoemulsions with mean particle size between 160 and 170 nm were prepared. Both the rate of particle growth and the total beta-carotene (BC) loss at 50 °C were significantly greater than at 4 and 25 °C. The retention rates of BC in nanoemulsions were 27.8% and 48.6% for BLG and BLG–catechin conjugates, respectively, after 30 days of storage at 50 °C. The BC retention encapsulated in nanoemulsion was significantly improved using BLG–catechin conjugates, compared with BLG alone. The increase of BC retention in nanoemulsions encapsulated with BLG–catechin conjugates was due to the significant improvement of antioxidative properties (reducing power, free radical scavenging activity, and hydroxyl radical scavenging activity) of BLG after covalent binding with catechin. The results indicated that the proteins modified with polyphenols can be widely used in a labile bioactive compounds encapsulation delivery system. PMID:25514513

  18. An extension of A-stability to alternating direction implicit methods

    NASA Technical Reports Server (NTRS)

    Warming, R. F.; Beam, R. M.

    1978-01-01

    An alternating direction implicit (ADI) scheme was constructed by the method of approximate factorization. An A-stable linear multistep method (LMM) was used to integrate a model two-dimensional hyperbolic-parabolic partial differential equation. Sufficient conditions for the A-stability of the LMM were determined by applying the theory of positive real functions to reduce the stability analysis of the partial differential equations to a simple algebraic test. A linear test equation for partial differential equations is defined and then used to analyze the stability of approximate factorization schemes. An ADI method for the three-dimensional heat equation is also presented.

  19. Rheology and stability kinetics of bare silicon nanoparticle inks for low-cost direct printing

    SciTech Connect

    More, Priyesh V.; Jeong, Sunho; Seo, Yeong-Hui; Ryu, Beyong-Hwan; Choi, Youngmin; Kim, Seong Jip; Nahm, Sahn

    2013-12-16

    Highly dispersed and stable silicon nanoparticles ink is formulated for its application in direct printing or printable electronics. These dispersions are prepared from free-standing silicon nanoparticles which are not capped with any organic ligand, making it suitable for electronic applications. Silicon nanoparticles dispersions are prepared by suspending the nanoparticles in benzonitrile or ethanol by using polypropylene glycol (PPG) as a binder. All the samples show typical shear thinning behavior while the dispersion samples show low viscosities signifying good quality dispersion. Such thinning behavior favors in fabrication of dense films with spin-coating or patterns with drop casting. The dispersion stability is monitored by turbiscan measurements showing good stability for one week. A low-cost direct printing method for dispersion samples is also demonstrated to obtain micro-sized patterns. Low electrical resistivity of resulting patterns, adjustable viscosity and good stability makes these silicon nanoparticles dispersions highly applicable for direct printing process.

  20. Rheology and stability kinetics of bare silicon nanoparticle inks for low-cost direct printing

    NASA Astrophysics Data System (ADS)

    More, Priyesh V.; Jeong, Sunho; Seo, Yeong-Hui; Kim, Seong Jip; Nahm, Sahn; Ryu, Beyong-Hwan; Choi, Youngmin

    2013-12-01

    Highly dispersed and stable silicon nanoparticles ink is formulated for its application in direct printing or printable electronics. These dispersions are prepared from free-standing silicon nanoparticles which are not capped with any organic ligand, making it suitable for electronic applications. Silicon nanoparticles dispersions are prepared by suspending the nanoparticles in benzonitrile or ethanol by using polypropylene glycol (PPG) as a binder. All the samples show typical shear thinning behavior while the dispersion samples show low viscosities signifying good quality dispersion. Such thinning behavior favors in fabrication of dense films with spin-coating or patterns with drop casting. The dispersion stability is monitored by turbiscan measurements showing good stability for one week. A low-cost direct printing method for dispersion samples is also demonstrated to obtain micro-sized patterns. Low electrical resistivity of resulting patterns, adjustable viscosity and good stability makes these silicon nanoparticles dispersions highly applicable for direct printing process.

  1. Direct {anti b}b production in {anti p}p collisions at {radical}s = 1.8 TeV

    SciTech Connect

    Lamoureux, J.

    1993-12-31

    The first measurement of bottom quark production in the forward detector at CDF is presented in this thesis. Events from the 1988/89 Fermilab collider run were selected with forward muons with nearby jets to form a bottom quark tag. The efficiency and acceptance of the detector are then taken into account and the number of events is turned into a cross section: {sigma}(p{sub t}{sup b} > 20 GeV, 1.9 < {vert_bar}{eta}{sup b}{vert_bar} < 2.5) = (124. {+-} 35. {+-} 76.) nb. The contribution from direct bottom quarks is {sigma}(p{sub t}{sup b} > 20 GeV, p{sub t}{sup {anti b}} > 15 GeV, 1.9 < {vert_bar}{eta}{sup b}{vert_bar} < 2.5) = (100. {+-} 30.{sub {minus}31.}{sup +30.}) nb.

  2. System for imposing directional stability on a rocket-propelled vehicle

    NASA Technical Reports Server (NTRS)

    Perkins, H. (Inventor)

    1976-01-01

    An improved system for use in imposing directional stability on a rocket-propelled vehicle is described. The system includes a pivotally supported engine-mounting platform, a gimbal ring mounted on the platform and adapted to pivotally support a rocket engine and an hydraulic actuator connected to the platform for imparting selected pivotal motion. An accelerometer and a signal comparator circuit for providing error intelligence indicative of aberration in vehicle acceleration is included along with an actuator control circuit connected with the actuator and responsive to error intelligence for imparting pivotal motion to the platform. Relocation of the engine's thrust vector is thus achieved for imparting directional stability to the vehicle.

  3. Catalytic surface radical in dye-decolorizing peroxidase: a computational, spectroscopic and site-directed mutagenesis study

    PubMed Central

    Linde, Dolores; Pogni, Rebecca; Cañellas, Marina; Lucas, Fátima; Guallar, Victor; Baratto, Maria Camilla; Sinicropi, Adalgisa; Sáez-Jiménez, Verónica; Coscolín, Cristina; Romero, Antonio; Medrano, Francisco Javier; Ruiz-Dueñas, Francisco J.; Martínez, Angel T.

    2014-01-01

    Dye-decolorizing peroxidase (DyP) of Auricularia auricula-judae has been expressed in Escherichia coli as a representative of a new DyP family, and subjected to mutagenic, spectroscopic, crystallographic and computational studies. The crystal structure of DyP shows a buried haem cofactor, and surface tryptophan and tyrosine residues potentially involved in long-range electron transfer from bulky dyes. Simulations using PELE (Protein Energy Landscape Exploration) software provided several binding-energy optima for the anthraquinone-type RB19 (Reactive Blue 19) near the above aromatic residues and the haem access-channel. Subsequent QM/MM (quantum mechanics/molecular mechanics) calculations showed a higher tendency of Trp-377 than other exposed haem-neighbouring residues to harbour a catalytic protein radical, and identified the electron-transfer pathway. The existence of such a radical in H2O2-activated DyP was shown by low-temperature EPR, being identified as a mixed tryptophanyl/tyrosyl radical in multifrequency experiments. The signal was dominated by the Trp-377 neutral radical contribution, which disappeared in the W377S variant, and included a tyrosyl contribution assigned to Tyr-337 after analysing the W377S spectra. Kinetics of substrate oxidation by DyP suggests the existence of high- and low-turnover sites. The high-turnover site for oxidation of RB19 (kcat> 200 s−1) and other DyP substrates was assigned to Trp-377 since it was absent from the W377S variant. The low-turnover site/s (RB19 kcat ~20 s−1) could correspond to the haem access-channel, since activity was decreased when the haem channel was occluded by the G169L mutation. If a tyrosine residue is also involved, it will be different from Tyr-337 since all activities are largely unaffected in the Y337S variant. PMID:25495127

  4. Lactoferrin Directly Scavenges Hydroxyl Radicals and Undergoes Oxidative Self-Degradation: A Possible Role in Protection against Oxidative DNA Damage

    PubMed Central

    Ogasawara, Yuki; Imase, Megumi; Oda, Hirotsugu; Wakabayashi, Hiroyuki; Ishii, Kazuyuki

    2014-01-01

    In this study, we examined the protective effect of lactoferrin against DNA damage induced by various hydroxyl radical generation systems. Lactoferrin (LF) was examined with regard to its potential role as a scavenger against radical oxygen species using bovine milk LF. Native LF, iron-saturated LF (holo-LF), and apolactoferrin (apo-LF) effectively suppressed strand breaks in plasmid DNA due to hydroxyl radicals produced by the Fenton reaction. In addition, both native LF and holo-LF clearly protected calf thymus DNA from fragmentation due to ultraviolet irradiation in the presence of H2O2. We also demonstrated a protective effect of all three LF molecules against 8-hydroxydeoxyguanosine (8-OHdG) formation in calf thymus DNA following ultraviolet (UV) irradiation with H2O2. Our results clearly indicate that native LF has reactive oxygen species-scavenging ability, independent of its nature as a masking component for transient metals. We also demonstrated that the protective effect of LF against oxidative DNA damage is due to degradation of LF itself, which is more susceptible to degradation than other bovine milk proteins. PMID:24424315

  5. Direct fiber comb stabilization to a gas-filled hollow-core photonic crystal fiber.

    PubMed

    Wu, Shun; Wang, Chenchen; Fourcade-Dutin, Coralie; Washburn, Brian R; Benabid, Fetah; Corwin, Kristan L

    2014-09-22

    We have isolated a single tooth from a fiber laser-based optical frequency comb for nonlinear spectroscopy and thereby directly referenced the comb. An 89 MHz erbium fiber laser frequency comb is directly stabilized to the P(23) (1539.43 nm) overtone transition of (12)C(2)H(2) inside a hollow-core photonic crystal fiber. To do this, a single comb tooth is isolated and amplified from 20 nW to 40 mW with sufficient fidelity to perform saturated absorption spectroscopy. The fractional stability of the comb, ~7 nm away from the stabilized tooth, is shown to be 6 × 10(-12) at 100 ms gate time, which is over an order of magnitude better than that of a comb referenced to a GPS-disciplined Rb oscillator. PMID:25321837

  6. Direct observation of the low-spin Fe(III)-NO(radical) intermediate state during rebinding of NO to photodeligated ferric cytochrome c.

    PubMed

    Park, Jaeheung; Lee, Taegon; Lim, Manho

    2013-10-10

    Nitrosylated ferric heme is autoreduced readily to the more stable Fe(II)-NO adduct, but it is stabilized in NO-carrier heme proteins where maintaining the Fe(III) oxidation state is crucial for efficient NO delivery. Density functional theory calculations by Lehnert and co-workers have shown that a NO-bound ferric model heme has a low-spin (LS) Fe(III)-NO(radical) state that might be critical for efficient NO transport by NO-carrier heme proteins. Recently, the elusive LS Fe(III)-NO(radical) state was observed as an electronic intermediate state during geminate rebinding (GR) of NO to ferric myoglobin (Mb(III)). Cytochrome c (Cytc), a ubiquitous heme protein, is useful for generalizing the presence of the LS Fe(III)-NO(radical) state. Photoexcitation dynamics of NO-bound ferric Cytc (Cytc(III)NO) was probed after excitation of Cytc(III)NO in D2O solution at 294 K with a 575 nm pulse using femtosecond vibrational spectroscopy. The time-resolved spectra displayed several weak absorption bands in the 1900-1800 cm(-1) range and a dominant bleach at 1917 cm(-1), the position of the absorption at equilibrium. Two absorptions, with 37 cm(-1) isotope shift of (15)NO, shifted toward higher energy and narrowed with an average time constant of 8 ps, indicating that they arose from thermally and/or vibrationally excited NO in the ground electronic state of Cytc(III)NO. Three absorption bands, showing 33 cm(-1) isotope shift of (15)NO and peaked at 1865, 1836, and 1807 cm(-1), were assigned to the deligated NO residing in the interior of the protein, to the rebound Cytc(III)NO in the LS Fe(III)-NO(radical) state, and to the vibrationally excited NO of Cytc(III)NO in the LS Fe(III)-NO(radical) state, respectively. The quantum yield for NO deligation of Cytc(III)NO by a 575 nm photon was 0.8 ± 0.1. Most of the deligated NO showed non-exponential GR, and the GR kinetics was described by exp(-(t/7 ps)(0.7)). Every rebound Cytc(III)NO formed the LS Fe(III)-NO(radical) state that

  7. Hypersonic lateral and directional stability characteristics of aeroassist flight experiment configuration in air and CF4

    NASA Technical Reports Server (NTRS)

    Micol, John R.; Wells, William L.

    1993-01-01

    Hypersonic lateral and directional stability characteristics measured on a 60 deg half-angle elliptical cone, which was raked at an angle of 73 deg from the cone centerline and with an ellipsoid nose (ellipticity equal to 2.0 in the symmetry plane), are presented for angles of attack from -10 to 10 deg. The high normal-shock density ratio of a real gas was simulated by tests at a Mach number of 6 in air and CF4 (density ratio equal to 5.25 and 12.0, respectively). Tests were conducted in air at Mach 6 and 10 and in CF4 at Mach 6 to examine the effects of Mach number, Reynolds number, and normal-shock density ratio. Changes in Mach number from 6 to 10 in air or in Reynolds number by a factor of 4 at Mach 6 had a negligible effect on lateral and directional stability characteristics. Variations in normal-shock density ratio had a measurable effect on lateral and directional aerodynamic coefficients, but no significant effect on lateral and directional stability characteristics. Tests in air and CF4 indicated that the configuration was laterally and directionally stable through the test range of angle of attack.

  8. Structures and stabilities of hemi-bonded vs proton-transferred isomers of dimer radical cation systems (XH3sbnd YH3)+ (X,Y = N, P, As)

    NASA Astrophysics Data System (ADS)

    Ji, Li Fei; Li, An Yong; Li, Zhuo Zhe

    2015-01-01

    Structures, bonding and relative stabilities of the radical dimer cations (XH3sbnd YH3)+ (X,Y = N, P, As) have been studied theoretically. Two kinds of structures (hemi-bonded and proton-transferred isomers) are obtained for each system. For (NH3sbnd N/P/AsH3)+ the stable conformer is the proton-transferred structure; for (PH3sbnd PH3)+ and (AsH3sbnd AsH3)+ the stable structure is the hemi-bonded one; for (PH3sbnd AsH3)+ three proton-transferred and one hemi-bonded isomers were found with the stability order: (Hsbnd PH3+⋯AsH2) I > (H3PH+⋯AsH2) II > (H3P⋯AsH3+) > (H3AsH+⋯PH2) III. The hemi-bonds have large interaction energies 25.2-35.1 kcal/mol and are partially covalent in nature, while the proton-transferred structures have moderate interaction energies 6.5-22.2 kcal/mol.

  9. Enhancement of the organic solvent-stability of the LST-03 lipase by directed evolution.

    PubMed

    Kawata, Takuya; Ogino, Hiroyasu

    2009-01-01

    LST-03 lipase from an organic solvent-tolerant Pseudomonas aeruginosa LST-03 has high stability and activity in the presence of various organic solvents. In this research, enhancement of organic solvent-stability of LST-03 lipase was attempted by directed evolution. The structural gene of the LST-03 lipase was amplified by the error prone-PCR method. Organic solvent-stability of the mutated lipases was assayed by formation of a clear zone of agar which contained dimethyl sulfoxide (DMSO) and tri-n-butyrin and which overlaid a plate medium. And the organic solvent-stability was also confirmed by measuring the half-life of activity in the presence of DMSO. Four mutated enzymes were selected on the basis of their high organic solvent-stability in the presence of DMSO. The organic solvent-stabilities of mutated LST-03 lipase in the presence of various organic solvents were measured and their mutated amino acid residues were identified. The half-lives of the LST-03-R65 lipase in the presence of cyclohexane and n-decane were about 9 to 11-fold longer than those of the wild-type lipase, respectively. Some substituted amino acid residues of mutated LST-03 lipases have been located at the surface of the enzyme molecules, while some other amino acid residues have been changed from neutral to basic residues. PMID:19731302

  10. Direct observation of multimer stabilization in the mechanical unfolding pathway of a protein undergoing oligomerization.

    PubMed

    Scholl, Zackary N; Yang, Weitao; Marszalek, Piotr E

    2015-02-24

    Understanding how protein oligomerization affects the stability of monomers in self-assembled structures is crucial to the development of new protein-based nanomaterials and protein cages for drug delivery. Here, we use single-molecule force spectroscopy (AFM-SMFS), protein engineering, and computer simulations to evaluate how dimerization and tetramerization affects the stability of the monomer of Streptavidin, a model homotetrameric protein. The unfolding force directly relates to the folding stability, and we find that monomer of Streptavidin is mechanically stabilized by 40% upon dimerization, and that it is stabilized an additional 24% upon tetramerization. We also find that biotin binding increases stability by another 50% as compared to the apo-tetrameric form. We used the distribution of unfolding forces to extract properties of the underlying energy landscape and found that the distance to the transition state is decreased and the barrier height is increased upon multimerization. Finally, we investigated the origin of the strengthening by ligand binding. We found that, rather than being strengthened through intramolecular contacts, it is strengthened due to the contacts provided by the biotin-binding loop that crosses the interface between the dimers. PMID:25639698

  11. Direct production of OH radicals upon CH overtone activation of (CH{sub 3}){sub 2}COO Criegee intermediates

    SciTech Connect

    Liu, Fang; Beames, Joseph M.; Lester, Marsha I.

    2014-12-21

    Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH{sub 3}){sub 2}COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol{sup −1}) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features, indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X{sup 2}Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH{sub 3}){sub 2}COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH{sub 3}CHOO and its unimolecular decay to OH products [F. Liu, J. M. Beames, A. S. Petit, A. B. McCoy, and M. I. Lester, Science 345, 1596 (2014)].

  12. Some effects of nonlinear variation in the directional-stability and damping-in-yawing derivatives on the lateral stability of an airplane

    NASA Technical Reports Server (NTRS)

    Sternfield, Leonard

    1951-01-01

    A theoretical investigation has been made to determine the effect of nonlinear stability derivatives on the lateral stability of an airplane. Motions were calculated on the assumption that the directional-stability and the damping-in-yawing derivatives are functions of the angle of sideslip. The application of the Laplace transform to the calculation of an airplane motion when certain types of nonlinear derivatives are present is described in detail. The types of nonlinearities assumed correspond to the condition in which the values of the directional-stability and damping-in-yawing derivatives are zero for small angle of sideslip.

  13. Effects of antioxidants and additional emulsifiers on the stability of emulsified milk fat in the photo/radical oxidation system.

    PubMed

    Yamamoto, Yukihiro; Hiyama, Shinichiro; Takase, Yoshihiko; Kadowaki, Akio; Hara, Setsuko

    2014-01-01

    The effects of antioxidants on the oxidative deterioration of emulsified oils and fats differ depending on the oxidation conditions, oils and fats used, and type of emulsifier. In this study, milk fat was emulsified to obtain water-oil (O/W) emulsion using Tween20 as emulsifier. The antioxidative effects of several antioxidants with various lipophilic properties, such as δ-tocopherol (Toc), epigallocatechin gallate (EGCg), quercetin (Qu), green tea extract (GTE), and rooibos tea extract (RTE) were investigated, the effects of additional emulsifiers such as polyglycerol and sucrose esters of fatty acids on the oxidation stability of the emulsion were also investigated. Under oxidative conditions of 30°C in 650 lx, Toc was more effective than GTE in suppressing the increase of the peroxide value (PV, meq/kg) of the emulsified milk fat. Under these oxidative conditions, the antioxidative effect of GTE was enhanced by the addition of polyglycerol and sucrose esters of fatty acids. Under the oxidative conditions at 40°C in dark with 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) or 2,2'-azobis (2,4-dimethylvaleronitrile) (AMVN), Toc showed the most antioxidative effect on suppression of the increase of PV and anisidine value (AnV) of the emulsified milk fat. Furthermore, additional emulsifiers also showed suppressive effects on the increase of the PV and AnV of the emulsified milk fat even without any antioxidants. The effects of additional emulsifiers on the oxidative stability of O/W emulsions were enhanced with antioxidants such as Toc, EGCg, and Qu. PMID:25174675

  14. Designing and building nanowires: directed nanocrystal self-assembly into radically branched and zigzag PbS nanowires

    NASA Astrophysics Data System (ADS)

    Xu, Fan; Ma, Xin; Gerlein, L. Felipe; Cloutier, Sylvain G.

    2011-07-01

    Lead sulfide nanowires with controllable optoelectronic properties would be promising building blocks for various applications. Here, we report the hot colloidal synthesis of radically branched and zigzag nanowires through self-attachment of star-shaped and octahedral nanocrystals in the presence of multiple surfactants. We obtained high-quality single-crystal nanowires with uniform diameter along the entire length, and the size of the nanowire can be tuned by tailoring the reaction parameters. This slow oriented attachment provides a better understanding of the intricacies of this complex nanocrystal assembly process. Meanwhile, these self-assembled nanowire structures have appealing lateral conformations with narrow side arms or highly faceted edges, where strong quantum confinement can occur. Consequently, the single-crystal nanowire structures exhibit strong photoluminescence in the near-infrared region with a large blue-shift compared to the bulk material.

  15. Calculation of the relative geometry of tRNAs in the ribosome from directed hydroxyl-radical probing data.

    PubMed Central

    Joseph, S; Whirl, M L; Kondo, D; Noller, H F; Altman, R B

    2000-01-01

    The many interactions of tRNA with the ribosome are fundamental to protein synthesis. During the peptidyl transferase reaction, the acceptor ends of the aminoacyl and peptidyl tRNAs must be in close proximity to allow peptide bond formation, and their respective anticodons must base pair simultaneously with adjacent trinucleotide codons on the mRNA. The two tRNAs in this state can be arranged in two nonequivalent general configurations called the R and S orientations, many versions of which have been proposed for the geometry of tRNAs in the ribosome. Here, we report the combined use of computational analysis and tethered hydroxyl-radical probing to constrain their arrangement. We used Fe(II) tethered to the 5' end of anticodon stem-loop analogs (ASLs) of tRNA and to the 5' end of deacylated tRNA(Phe) to generate hydroxyl radicals that probe proximal positions in the backbone of adjacent tRNAs in the 70S ribosome. We inferred probe-target distances from the resulting RNA strand cleavage intensities and used these to calculate the mutual arrangement of A-site and P-site tRNAs in the ribosome, using three different structure estimation algorithms. The two tRNAs are constrained to the S configuration with an angle of about 45 degrees between the respective planes of the molecules. The terminal phosphates of 3'CCA are separated by 23 A when using the tRNA crystal conformations, and the anticodon arms of the two tRNAs are sufficiently close to interact with adjacent codons in mRNA. PMID:10688361

  16. Stability analysis of direct contact heat exchangers subject to system perturbations. Final report, Task 2

    SciTech Connect

    Jacobs, H.R.

    1985-01-01

    This report includes a project summary, copies of two papers resulting from the work and the Ph.D. Dissertation of Dr. Mehdi Golafshani entitled, ''Stability of a Direct Contact Heat Exchanger''. Specifically, the work deals with the operational stability of a spray column type heat exchanger subject to disturbances typical of those which can occur for geothermal applications. A computer program was developed to solve the one-dimensional transient two-phase flow problem and it was applied to the design of a spray column. The operation and design of the East Mesa 500kW/sub e/ direct contactor was assessed. It is shown that the heat transfer is governed by the internal resistance of the dispersed phase. In fact, the performance is well-represented by diffusion of heat within the drops. 5 refs.

  17. Uncoupling of increased cellular oxidative stress and myocardial ischemia reperfusion injury by directed sarcolemma stabilization

    PubMed Central

    Martindale, Joshua J.; Metzger, Joseph M.

    2014-01-01

    Myocardial ischemia/reperfusion (I/R) injury is a major clinical problem leading to cardiac dysfunction and myocyte death. It is widely held that I/R causes damage to membrane phospholipids, and is a significant mechanism of cardiac I/R injury. Molecular dissection of sarcolemmal damage in I/R, however, has been difficult to address experimentally. We studied here cardiac I/R injury under conditions targeting gain- or loss-of sarcolemma integrity. To implement gain-in-sarcolemma integrity during I/R, synthetic copolymer-based sarcolemmal stabilizers (CSS), including Poloxamer 188 (P188), were used as a tool to directly stabilize the sarcolemma. Consistent with the hypothesis of sarcolemmal stabilization, cellular markers of necrosis and apoptosis evident in untreated myocytes were fully blocked in sarcolemma stabilized myocytes. Unexpectedly, sarcolemmal stabilization of adult cardiac myocytes did not affect the status of myocyte-generated oxidants or lipid peroxidation in two independent assays. We also investigated the loss of sarcolemmal integrity using two independent genetic mouse models, dystrophin-deficient mdx or dysferlin knockout (Dysf KO) mice. Both models of sarcolemmal loss-of-function were severely affected by I/R injury ex vivo, and this was lessened by CSS. In vivo studies also showed that infarct size was significantly reduced in CSS-treated hearts. Mechanistically, these findings support a model whereby I/R-mediated increased myocyte oxidative stress is uncoupled from myocyte injury. Because the sarcolemma stabilizers used here do not transit across the myocyte membrane this is evidence that intracellular targets of oxidants are not sufficiently altered to affect cell death when sarcolemma integrity is preserved by synthetic stabilizers. These findings, in turn, suggest that sarcolemma destabilization, and consequent Ca2+ mishandling, as a focal initiating mechanism underlying myocardial I/R injury. PMID:24362314

  18. Direct epoxidation of propylene over stabilized Cu(+) surface sites on titanium-modified Cu2O.

    PubMed

    Yang, Xiaofang; Kattel, Shyam; Xiong, Ke; Mudiyanselage, Kumudu; Rykov, Sergei; Senanayake, Sanjaya D; Rodriguez, José A; Liu, Ping; Stacchiola, Dario J; Chen, Jingguang G

    2015-10-01

    Direct propylene epoxidation by O2 is a challenging reaction because of the strong tendency for complete combustion. Results from the current study demonstrate that by generating highly dispersed and stabilized Cu(+) active sites in a TiCuOx mixed oxide the epoxidation selectivity can be tuned. The TiCuOx surface anchors the key surface intermediate, an oxametallacycle, leading to higher selectivity for epoxidation of propylene. PMID:26215635

  19. Direct Epoxidation of Propylene over Stabilized Cu+ Surface Sites on Ti Modified Cu2O

    DOE PAGESBeta

    Yang, X.; Kattel, S.; Xiong, K.; Mudiyanselage, K.; Rykov, S.; Senanayake, S. D.; Rodriguez, J. A.; Liu, P.; Stacchiola, D. J.; Chen, J. G.

    2015-07-17

    Direct propylene epoxidation by O2 is a challenging reaction because of the strong tendency for complete combustion. Results from the current study demonstrate the feasibility to tune the epoxidation selectivity by generating highly dispersed and stabilized Cu+ active sites in a TiCuOx mixed oxide. The TiCuOx surface anchors the key surface intermediate, oxametallacycle, leading to higher selectivity for epoxidation of propylene.

  20. Development and validation of a simple high performance thin layer chromatography method combined with direct 1,1-diphenyl-2-picrylhydrazyl assay to quantify free radical scavenging activity in wine.

    PubMed

    Agatonovic-Kustrin, Snezana; Morton, David W; Yusof, Ahmad P

    2016-04-15

    The aim of this study was to: (a) develop a simple, high performance thin layer chromatographic (HPTLC) method combined with direct 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay to rapidly assess and compare free radical scavenging activity or anti-oxidant activity for major classes of polyphenolics present in wines; and (b) to investigate relationship between free radical scavenging activity to the total polyphenolic content (TPC) and total antioxidant capacity (TAC) in the wine samples. The most potent free radical scavengers that we tested for in the wine samples were found to be resveratrol (polyphenolic non-flavonoid) and rutin (flavonoid), while polyphenolic acids (caffeic acid and gallic acid) although present in all wine samples were found to be less potent free radical scavengers. Therefore, the total antioxidant capacity was mostly affected by the presence of resveratrol and rutin, while total polyphenolic content was mostly influenced by the presence of the less potent free radical scavengers gallic and caffeic acids. PMID:26616951

  1. Hi-alpha forebody design. Part 2: Determination of body shapes for positive directional stability

    NASA Technical Reports Server (NTRS)

    Ravi, R.; Mason, William H.

    1991-01-01

    Computational Fluid Dynamics (CFD) has been used to study aircraft forebody flowfields at low speed high angle-of-attack conditions with sideslip. The purpose is to define forebody geometries which provide good directional stability characteristics under these conditions. The flows of the F-5A forebody and Erickson forebody were recomputed with better and refined grids. The results were obtained using a modified version of cfl3d to solve either the Euler equations or the Reynolds equations employing a form of the Baldwin-Lomax turbulence model. Based on those results, we conclude that current CFD methods can be used to investigate the aerodynamic characteristics of forebodies to achieve desirable high angle-of-attack characteristics. An analytically defined generic forebody model is described, and a systematic study of forebody shapes was then conducted to determine which shapes promote a positive contribution to directional stability at high angle-of-attack. A novel way of presenting the results is used to illustrate how the positive contribution arises. Based on the results of this initial parametric study, some guidelines for aerodynamic design to promote positive directional stability are presented.

  2. A computational examination of directional stability for smooth and chined forebodies at high-alpha

    NASA Technical Reports Server (NTRS)

    Ravi, Ramakrishnan; Mason, William H.

    1992-01-01

    Computational Fluid Dynamics (CFD) has been used to study aircraft forebody flowfields at low-speed, angle-of-attack conditions with sideslip. The purpose is to define forebody geometries which provide good directional stability characteristics under these conditions. The flows over the experimentally investigated F-5A forebody and chine type configuration, previously computed by the authors, were recomputed with better grid topology and resolution. The results were obtained using a modified version of CFL3D (developed at NASA Langley) to solve either the Euler equations or the Reynolds equations employing the Baldwin-Lomax turbulence model with the Degani-Schiff modification to account for massive crossflow separation. Based on the results, it is concluded that current CFD methods can be used to investigate the aerodynamic characteristics of forebodies to achieve desirable high angle-of-attack characteristics. An analytically defined generic forebody model is described, and a parametric study of various forebody shapes was then conducted to determine which shapes promote a positive contribution to directional stability at high angle-of-attack. An unconventional approach for presenting the results is used to illustrate how the positive contribution arises. Based on the results of this initial parametric study, some guidelines for aerodynamic design to promote positive directional stability are presented.

  3. Direct-current cathodic vacuum arc system with magnetic-field mechanism for plasma stabilization

    SciTech Connect

    Zhang, H.-S.; Komvopoulos, K.

    2008-07-15

    Filtered cathodic vacuum arc (FCVA) deposition is characterized by plasma beam directionality, plasma energy adjustment via substrate biasing, macroparticle filtering, and independent substrate temperature control. Between the two modes of FCVA deposition, namely, direct current (dc) and pulsed arc, the dc mode yields higher deposition rates than the pulsed mode. However, maintaining the dc arc discharge is challenging because of its inherent plasma instabilities. A system generating a special configuration of magnetic field that stabilizes the dc arc discharge during film deposition is presented. This magnetic field is also part of the out-of-plane magnetic filter used to focus the plasma beam and prevent macroparticle film contamination. The efficiency of the plasma-stabilizing magnetic-field mechanism is demonstrated by the deposition of amorphous carbon (a-C) films exhibiting significantly high hardness and tetrahedral carbon hybridization (sp{sup 3}) contents higher than 70%. Such high-quality films cannot be produced by dc arc deposition without the plasma-stabilizing mechanism presented in this study.

  4. Direct-current cathodic vacuum arc system with magnetic-field mechanism for plasma stabilization.

    PubMed

    Zhang, H-S; Komvopoulos, K

    2008-07-01

    Filtered cathodic vacuum arc (FCVA) deposition is characterized by plasma beam directionality, plasma energy adjustment via substrate biasing, macroparticle filtering, and independent substrate temperature control. Between the two modes of FCVA deposition, namely, direct current (dc) and pulsed arc, the dc mode yields higher deposition rates than the pulsed mode. However, maintaining the dc arc discharge is challenging because of its inherent plasma instabilities. A system generating a special configuration of magnetic field that stabilizes the dc arc discharge during film deposition is presented. This magnetic field is also part of the out-of-plane magnetic filter used to focus the plasma beam and prevent macroparticle film contamination. The efficiency of the plasma-stabilizing magnetic-field mechanism is demonstrated by the deposition of amorphous carbon (a-C) films exhibiting significantly high hardness and tetrahedral carbon hybridization (sp3) contents higher than 70%. Such high-quality films cannot be produced by dc arc deposition without the plasma-stabilizing mechanism presented in this study. PMID:18681714

  5. Lateral-directional stability and control characteristics of the Quiet Short-Haul Research Aircraft (QSRA)

    NASA Technical Reports Server (NTRS)

    Stephenson, Jack D.; Jeske, James A.; Hardy, Gordon H.

    1990-01-01

    The results are presented of flight experiments to determine the lateral-directional stability and control characteristics of the Quiet Short-Haul Research Aircraft (QSRA), an experimental aircraft designed to furnish information on various aerodynamic characteristics of a transport type of airplane that makes use of the upper-surface blown (USB) flap technology to achieve short takeoff and landing (STOL) performance. The flight program designed to acquire the data consisted of maneuvers produced by rudder and control-wheel inputs with the airplane in several configurations that had been proposed for landing approach and takeoff operation. The normal stability augmentation system was not engaged during these maneuvers. Time-history records from the maneuvers were analyzed with a parameter estimation procedure to extract lateral-directional stability and control derivatives. For one aircraft configuration in which the USB flaps were deflected 50 deg, several maneuvers were performed to determine the effects of varying the average angle of attack, varying the thrust coefficient, and setting the airplane's upper surface spoilers at a 13 deg symmetrical bias angle . The effects on the lateral characteristics of deflecting the spoilers were rather small and generally favorable. The data indicate that for one test, conducted at low thrust (a thrust coefficient of 0.38), compared with results from tests at thrust coefficients of 0.77 and larger, there was a significant decrease in the lateral control effectiveness, in the yaw damping and in the directional derivative. The directional derivative was also decreased (by about 30 percent) when the average angle of attack of the test was increased from 3 to 16 deg.

  6. Direct Grout Stabilization of High Cesium Salt Waste: Cesium Leaching Studies

    SciTech Connect

    Langton, C.A.

    1999-09-19

    'The direct grout alternative is a viable option for treatment/stabilization and disposal of salt waste containing Cs-137 concentrations of 1-3 Ci/gal. The significant difference between these waste solutions is that the high cesium salt solution will contain between 1 and 3 Curies of Cs-137 per gallon compared to a negligible amount in the current salt solution. This difference will require special engineering and shielding for a direct grout processing facility and disposal units to achieve acceptable radiation exposure conditions. The higher cesium concentrations in the direct grout also require that the cesium leaching be evaluated as a function of curing temperature. ANS 16.1 leaching results and distribution ratios (approximations of distribution coefficients) as a function of temperature are presented in this report.'

  7. Determination of direct photolysis rate constants and OH radical reactivity of representative odour compounds in brewery broth using a continuous flow-stirred photoreactor

    NASA Astrophysics Data System (ADS)

    Jürgens, Marion; Jacob, Fritz; Ekici, Perihan; Friess, Albrecht; Parlar, Harun

    A method based on photolysis was developed for the appropriate treatment of organic pollutants in air exhausting from breweries upon wort decoction, and thereby causing smell nuisance. A continuous flow stirred photoreactor was built-up exclusively, allowing OH radicals to react with selected odorous compounds contained in exhaust vapours, such as: 2-methylpropanal, 3-methylbutanal, 2-methylbutanal, 3-methyl-1-butanol, n-hexanal, 2-methylbutyl isobutyrate, 2-undecanone, phenyl acetaldehyde, myrcene, limonene, linalool, humulene, dimethylsulphide, and dimethyltrisulphide. These substances were quantified in brewery broth before and after UV irradiation using high-resolution gas chromatography-mass spectrometry (HRGC-MS). For odour analysis, high-resolution gas chromatography-flame ionisation detection (HRGC-FID) coupled with sensory methods was used. Determined quantum yields of about 10 -3 for phenyl acetaldehyde, myrcene, and humulene pointed out that direct photolysis contributed to their decay. Quantum yields of below 10 -4 for the other substances indicated that UV irradiation did not contribute significantly to their degradation processes. Hydroxyl radical reaction rate constants and Henry constants of organic compounds were also measured. Substances accompanied with low Henry constants converted rapidly, whereas those with higher ones, relatively slowly. Determined aroma values concluded that after UV-H 2O 2 treatment, only dimethylsulphide and myrcene remained as important odorous compounds, but in significantly reduced concentrations. The UV-H 2O 2 treatment of brewery broth has been proved effective to reduce smell-irritating substances formed upon wort decoction.

  8. High p{sub T} direct photon and {pi}{sup 0} triggered azimuthal jet correlations and measurement of k{sub T} for isolated direct photons in p+p collisions at {radical}(s)=200 GeV

    SciTech Connect

    Adare, A.; Bickley, A. A.; Ellinghaus, F.; Glenn, A.; Kinney, E.; Kiriluk, K.; Nagle, J. L.; Seele, J.; Wysocki, M.; Afanasiev, S.; Isupov, A.; Litvinenko, A.; Malakhov, A.; Peresedov, V.; Rukoyatkin, P.; Zolin, L.; Aidala, C.; Ajitanand, N. N.; Alexander, J.; Chung, P.

    2010-10-01

    Correlations of charged hadrons of 1direct photons and {pi}{sup 0} mesons in the range 5direct photon-associated hadron spectrum as well as its charge asymmetry are found to be consistent with a sample dominated by quark-gluon Compton scattering. No significant evidence of fragmentation photon correlated production is observed within experimental uncertainties.

  9. Morphological stability analysis of directional solidification into an oscillatory fluid layer

    NASA Astrophysics Data System (ADS)

    Volfson, Dmitri; Viñals, Jorge

    2001-12-01

    We study the stability of a planar solid-melt boundary during directional solidification of a binary alloy when the solid is being periodically vibrated in the direction parallel to the boundary (or equivalently, under a far field uniform and oscillatory flow parallel to the planar boundary). The analysis is motivated by directional solidification experiments under the low level residual acceleration field characteristic of a microgravity environment, and possible effects on crystal growth in space. It is known that periodic modulation of the solid-melt interface under the conditions stated induces second order stationary streaming flows within a boundary layer adjacent to the interface, the thickness of which is the same as the wavelength of the modulation. We derive an effective solute transport equation by averaging over the fast time scale of the oscillatory flow, and obtain the resulting dispersion relation for a small disturbance of a planar interface. We find both regions of stationary and oscillatory instability. For small ratios of the viscous to solutal layer thicknesses, s, the flow generally destabilizes the planar interface. For s≃1, the flow stabilizes the stationary branch, but it can also excite an oscillatory instability. For large s, the effect of the flow is small.

  10. Directional versus Stabilizing Selection for Developmental Time in Natural and Laboratory Populations of Flour Beetles.

    PubMed

    Dawson, P S

    1975-08-01

    Artificial selection for fast development is successful in long-established laboratory populations of Tribolium, but not in strains recently derived from natural populations. It is shown that selection against fast development in dense, synchronized cultures operates through cannibalism of early pupae by larvae. Since standard husbandry procedures for laboratory strains involve the periodic creation of dense, synchronized cultures, it is suggested that these populations are subjected to stabilizing selection for intermediate developmental time. Natural populations, on the other hand, are probably subjected to directional selection for rapid development. PMID:17248688

  11. Direct Formation of the C5′-Radical in the Sugar-Phosphate Backbone of DNA by High Energy Radiation

    PubMed Central

    Adhikary, Amitava; Becker, David; Palmer, Brian J.; Heizer, Alicia N.; Sevilla, Michael D.

    2012-01-01

    Neutral sugar radicals formed in DNA sugar-phosphate backbone are well-established as precursors of biologically important damage such as DNA-strand scission and crosslinking. In this work, we present electron spin resonance (ESR) evidence showing that the sugar radical at C5′ (C5′•) is one of the most abundant (ca. 30%) sugar radicals formed by γ- and Ar ion-beam irradiated hydrated DNA samples. Taking dimethyl phosphate as a model of sugar-phosphate backbone, ESR and theoretical (DFT) studies of γ-irradiated dimethyl phosphate were carried out. CH3OP(O2−)OCH2• is formed via deprotonation from the methyl group of directly ionized dimethyl phosphate at 77 K. Formation of CH3OP(O2−)OCH2• is independent of dimethyl phosphate concentration (neat or in aqueous solution) or pH. ESR spectra of C5′• found in DNA and of CH3OP(O2−)OCH2• do not show an observable β-phosphorous hyperfine coupling (HFC). Further, C5′• found in DNA does not show a significant C4′-H β–proton HFC. Applying the DFT/B3LYP/6-31G(d) method, a study of conformational dependence of the phosphorous HFC in CH3OP(O2−)OCH2• shows that in its minimum energy conformation, CH3OP(O2−)OCH2• has a negligible β-phosphorous HFC. Based on these results, formation of radiation-induced C5′• is proposed to occur via a very rapid deprotonation from the directly ionized sugar-phosphate backbone and rate of this deprotonation must be faster than that of energetically downhill transfer of the unpaired spin (hole) from ionized sugar-phosphate backbone to the DNA bases. Moreover, C5′• in irradiated DNA is found to be in a conformation that does not exhibit β proton or β phosphorous HFCs. PMID:22553971

  12. Improving Kinetic or Thermodynamic Stability of an Azoreductase by Directed Evolution

    PubMed Central

    Brissos, Vânia; Gonçalves, Nádia; Melo, Eduardo P.; Martins, Lígia O.

    2014-01-01

    Protein stability arises from a combination of factors which are often difficult to rationalise. Therefore its improvement is better addressed through directed evolution than by rational design approaches. In this study, five rounds of mutagenesis/recombination followed by high-throughput screening (≈10,000 clones) yielded the hit 1B6 showing a 300-fold higher half life at 50°C than that exhibited by the homodimeric wild type PpAzoR azoreductase from Pseudomonas putida MET94. The characterization using fluorescence, calorimetry and light scattering shows that 1B6 has a folded state slightly less stable than the wild type (with lower melting and optimal temperatures) but in contrast is more resistant to irreversible denaturation. The superior kinetic stability of 1B6 variant was therefore related to an increased resistance of the unfolded monomers to aggregation through the introduction of mutations that disturbed hydrophobic patches and increased the surface net charge of the protein. Variants 2A1 and 2A1-Y179H with increased thermodynamic stability (10 to 20°C higher melting temperature than wild type) were also examined showing the distinctive nature of mutations that lead to improved structural robustness: these occur in residues that are mostly involved in strengthening the solvent-exposed loops or the inter-dimer interactions of the folded state. PMID:24475252

  13. Radical Hysterectomy

    MedlinePlus

    ... the base of her partner’s penis during intercourse. Orgasm after radical hysterectomy Women who have had a ... the surgery will affect their ability to have orgasms. This has not been studied a great deal, ...

  14. The Stability of Double White Dwarf Binaries Undergoing Direct-Impact Accretion

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Frank, Juhan; Tohline, Joel E.; D'Souza, Mario C. R.

    2007-12-01

    We present numerical simulations of dynamically unstable mass transfer in a double white dwarf binary with initial mass ratio q=0.4. The binary components are approximated as polytropes of index n=3/2, and the initially synchronously rotating, semidetached equilibrium binary is evolved hydrodynamically, with the gravitational potential being computed through the solution of Poisson's equation. Upon initiating deep contact in our baseline simulation, the mass transfer rate grows by more than an order of magnitude over approximately 10 orbits, as would be expected for dynamically unstable mass transfer. However, the mass transfer rate then reaches a peak value, the binary expands, and the mass transfer event subsides. The binary must therefore have crossed the critical mass ratio for stability against dynamical mass transfer. Despite the initial loss of orbital angular momentum into the spin of the accreting star, we find that the accretor's spin saturates and that angular momentum is returned to the orbit more efficiently than has been previously suspected for binaries in the direct-impact accretion mode. To explore this surprising result, we directly measure the critical mass ratio for stability by imposing artificial angular momentum loss at various rates to drive the binary to an equilibrium mass transfer rate. For one of these driven evolutions, we attain equilibrium mass transfer and deduce that, effectively, qcrit has evolved to approximately 2/3. Despite the absence of a fully developed disk, tidal interactions appear to be effective in returning excess spin angular momentum to the orbit.

  15. Direct mass measurements above uranium bridge the gap to the island of stability.

    PubMed

    Block, M; Ackermann, D; Blaum, K; Droese, C; Dworschak, M; Eliseev, S; Fleckenstein, T; Haettner, E; Herfurth, F; Hessberger, F P; Hofmann, S; Ketelaer, J; Ketter, J; Kluge, H-J; Marx, G; Mazzocco, M; Novikov, Yu N; Plass, W R; Popeko, A; Rahaman, S; Rodríguez, D; Scheidenberger, C; Schweikhard, L; Thirolf, P G; Vorobyev, G K; Weber, C

    2010-02-11

    The mass of an atom incorporates all its constituents and their interactions. The difference between the mass of an atom and the sum of its building blocks (the binding energy) is a manifestation of Einstein's famous relation E = mc(2). The binding energy determines the energy available for nuclear reactions and decays (and thus the creation of elements by stellar nucleosynthesis), and holds the key to the fundamental question of how heavy the elements can be. Superheavy elements have been observed in challenging production experiments, but our present knowledge of the binding energy of these nuclides is based only on the detection of their decay products. The reconstruction from extended decay chains introduces uncertainties that render the interpretation difficult. Here we report direct mass measurements of trans-uranium nuclides. Located at the farthest tip of the actinide species on the proton number-neutron number diagram, these nuclides represent the gateway to the predicted island of stability. In particular, we have determined the mass values of (252-254)No (atomic number 102) with the Penning trap mass spectrometer SHIPTRAP. The uncertainties are of the order of 10 keV/c(2) (representing a relative precision of 0.05 p.p.m.), despite minute production rates of less than one atom per second. Our experiments advance direct mass measurements by ten atomic numbers with no loss in accuracy, and provide reliable anchor points en route to the island of stability. PMID:20148034

  16. A novel method to directionally stabilize enzymes together with redox mediators by electrodeposition.

    PubMed

    Shi, Wentao; Lin, Nansen; Song, Yilin; Liu, Chunxiu; Zhou, Shuai; Cai, Xinxia

    2014-01-15

    This paper depicts a novel method to directionally stabilize enzymes together with redox mediators by electrodeposition. Chitosan was used as a stabilizing matrix. By electrochemical removal of local H(+), chitosan close to working electrode became locally insoluble, and enzymes and redox mediators in chitosan were stabilized. The microelectrode on home-made microelectrode array (MEA) served as the working electrode. Three model enzymes--horseradish peroxidase (HRP), glucose oxidase (GOD), and glutamate oxidase (GlOD)--were used to fabricate different biosensors, and the redox mediator model was a poly(vinylpyridine) complex of Os(bpy)2Cl and a diepoxide (PVP-Os). Biosensors fabricated by the method exhibited very high performance. For HRP biosensor fabricated by this method, the sensitivity was 5.274 nA μM(-1) mm(-2), with linear detection range (LDR) of 2-220 μM and limit of detection (LOD) of 1 μM (S/N=3); for GOD biosensor, the sensitivity was 2.65 nA μM(-1) mm(-2), with LDR of 4-500 μM and LOD of 2 μM (S/N=3); for GlOD biosensor, the sensitivity was 0.33 nA μM(-1)mm(-2), with LDR of 4-500 μM and LOD of 2 μM (S/N=3). Since this method is very simple and especially suitable for directionally introducing enzymes and redox mediators onto microelectrode without contaminating other sites in the same microenvironment, it could be used for fabricating in vivo or in vitro 2nd generation biosensors in μm-scale, especially in neuroscience. PMID:23974156

  17. In vivo copper-mediated free radical production: an ESR spin-trapping study

    NASA Astrophysics Data System (ADS)

    Kadiiska, Maria B.; Mason, Ronald P.

    2002-04-01

    Copper has been suggested to facilitate oxidative tissue injury through a free radical-mediated pathway analogous to the Fenton reaction. By applying the electron spin resonance (ESR) spin-trapping technique, evidence for hydroxyl radical formation in vivo was obtained in rats treated simultaneously with copper and ascorbic acid or paraquat. A secondary radical spin-trapping technique was used in which the hydroxyl radical formed the methyl radical upon reaction with dimethylsulfoxide. The methyl radical was then detected by ESR spectroscopy as its adduct with the spin trap phenyl- N- t-butyl- nitrone (PBN). In contrast, lipid derived radical was detected in vivo in copper-challenged, vitamin E and selenium-deficient rats. These findings support the proposal that dietary selenium and vitamin E can protect against lipid peroxidation and copper toxicity. Since copper excreted into the bile from treated animals is expected to be maintained in the Cu(I) state (by ascorbic acid or glutathione), a chelating agent that would redox-stablilize it in the Cu(I) state was used to prevent ex vivo redox chemistry. Bile samples were collected directly into solutions of bathocuproinedisulfonic acid, a Cu(I)-stabilizing agent, and 2,2'-dipyridyl, a Fe(II)-stabilizing agent. If these precautions were not taken, radical adducts generated ex vivo could be mistaken for radical adducts produced in vivo and excreted into the bile.

  18. Direct Grout Stabilization of High Cesium Salt Waste: Salt Alternative Phase III Feasibility Study

    SciTech Connect

    Langton, C.A.

    1998-12-07

    The direct grout alternative is a viable option for treatment/stabilization and disposal of salt waste containing Cs-137 concentrations of 1-3 Ci/gal. The composition of the direct grout salt solution is higher in sodium salts and contains up to a few hundred ppm Cs-137 more than the current reference salt solution. However it is still similar to the composition of the current reference salt solution. Consequently, the processing, setting, and leaching properties (including TCLP for Cr and Hg) of the direct grout and current saltstone waste forms are very similar. The significant difference between these waste solutions is that the high cesium salt solution will contain between 1 and 3 Curies of Cs-137 per gallon compared to a negligible amount in the current salt solution. This difference will require special engineering and shielding for a direct grout processing facility and disposal units to achieve acceptable radiation exposure conditions. The Cs-137 concentration in the direct grout salt solution will also affect the long-term curing temperature of the waste form since 4.84 Watts of energy are generated per 1000 Ci of Cs-137. The temperature rise of the direct grout during long-term curing has been calculated by A. Shaddy, SRTC.1 The effect of curing temperature on the strength, leaching and physical durability of the direct grout saltstone is described in this report. At the present time, long term curing at 90 degrees C appears to be unacceptable because of cracking which will affect the structural integrity as evaluated in the immersion test. (The experiments conducted in this feasibility study do not address the effect of cracking on leaching of contaminants other than Cr, Hg, and Cs.) No cracking of the direct grout or reference saltstone waste forms was observed for samples cured at 70 degrees C. At the present time the implications of waste form cracking at elevated curing temperatures has not been fully addressed. The direct grout falls within the

  19. High-speed fuel tracer fluorescence and OH radical chemiluminescence imaging in a spark-ignition direct-injection engine.

    PubMed

    Smith, James D; Sick, Volker

    2005-11-01

    An innovative technique has been demonstrated to achieve crank-angle-resolved planar laser-induced fluorescence (PLIF) of fuel followed by OH* chemiluminescence imaging in a firing direct-injected spark-ignition engine. This study used two standard KrF excimer lasers to excite toluene for tracking fuel distribution. The intensified camera system was operated at single crank-angle resolution at 2000 revolutions per minute (RPM) for 500 consecutive cycles. Through this work, it has been demonstrated that toluene and OH* can be imaged through the same optical setup while similar signal levels are obtained from both species, even at these high rates. The technique is useful for studying correlations between fuel distribution and subsequent ignition and flame propagation without the limitations of phase-averaging imaging approaches. This technique is illustrated for the effect of exhaust gas recirculation on combustion and will be useful for studies of misfire causes. Finally, a few general observations are presented as to the effect of preignition fuel distribution on subsequent combustion. PMID:16270557

  20. Enhanced Production of Direct Photons in Au+Au Collisions at {radical}(s{sub NN})=200 GeV and Implications for the Initial Temperature

    SciTech Connect

    Adare, A.; Bickley, A. A.; Ellinghaus, F.; Kelly, S.; Kinney, E.; Nagle, J. L.; Seele, J.; Wysocki, M.; Afanasiev, S.; Isupov, A.; Litvinenko, A.; Malakhov, A.; Peresedov, V.; Rukoyatkin, P.; Zolin, L.; Aidala, C.; Bjorndal, M. T.; Chi, C. Y.; Cole, B. A.; D'Enterria, D.

    2010-04-02

    The production of e{sup +}e{sup -} pairs for m{sub e}{sup +}{sub e}{sup -}<0.3 GeV/c{sup 2} and 1radical}(s{sub NN})=200 GeV. An enhanced yield above hadronic sources is observed. Treating the excess as photon internal conversions, the invariant yield of direct photons is deduced. In central Au+Au collisions, the excess of the direct photon yield over p+p is exponential in transverse momentum, with an inverse slope T=221{+-}19{sup stat{+-}}19{sup syst} MeV. Hydrodynamical models with initial temperatures ranging from T{sub init{approx}}300-600 MeV at times of {approx}0.6-0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at {approx}170 MeV.

  1. STABILITY OF THE DIRECTLY IMAGED MULTIPLANET SYSTEM HR 8799: RESONANCE AND MASSES

    SciTech Connect

    Fabrycky, Daniel C.; Murray-Clay, Ruth A.

    2010-02-20

    A new era of directly imaged extrasolar planets has produced a three-planet system, where the masses of the planets have been estimated by untested cooling models. We point out that the nominal circular, face-on orbits of the planets lead to a dynamical instability in {approx}10{sup 5} yr, a factor of at least 100 shorter than the estimated age of the star. Reduced planetary masses produce stability only for unreasonably small planets ({approx}<2 M{sub Jup}). Relaxing the face-on assumption, but still requiring circular orbits while fitting the observed positions, makes the instability time even shorter. A promising solution is that the inner two planets have a 2:1 commensurability between their periods, and they avoid close encounters with each other through this resonance. The fact that the inner resonance has lasted until now, in spite of the perturbations of the outer planet, leads to a limit {approx}<10 M{sub Jup} on the masses unless the outer two planets are also engaged in a 2:1 mean-motion resonance. In a double resonance, which is consistent with the current data, the system could survive until now even if the planets have masses of {approx}20 M{sub Jup}. Apsidal alignment can further enhance the stability of a mean-motion resonant system. A completely different dynamical configuration, with large eccentricities and large mutual inclinations among the planets, is possible but finely tuned.

  2. Linear stability analysis and direct numerical simulation of two layer channel flow

    NASA Astrophysics Data System (ADS)

    Sahu, Kirti; Govindarajan, Rama; Tripathi, Manoj

    2015-11-01

    We study the stability of two-fluid flow through a plane channel at Reynolds numbers of a hundred to a thousand. The two fluids have the same density but different viscosities. The fluids, when miscible, are separated from each other by a mixed layer of small but finite thickness, across which viscosity changes from that of one fluid to that of the other. When immiscible, the interface is sharp. Our study spans a range of Schmidt numbers, viscosity ratios and location and thickness of the mixed layer. Our two-dimensional linear stability results predict well the behaviour displayed by our three-dimensional direct numerical simulations at early times. In both linear and non-linear regimes, the miscible flow is more unstable than the corresponding immiscible one, and the miscible flow breaks spanwise symmetry more readily to go into three-dimensionality. We show that the miscible flow over our range of parameters is always significantly more unstable than the corresponding immiscible case.

  3. Peptidyl Prolyl Isomerase PIN1 Directly Binds to and Stabilizes Hypoxia-Inducible Factor-1α.

    PubMed

    Han, Hyeong-Jun; Kwon, Nayoung; Choi, Min-A; Jung, Kyung Oh; Piao, Juan-Yu; Ngo, Hoang Kieu Chi; Kim, Su-Jung; Kim, Do-Hee; Chung, June-Key; Cha, Young-Nam; Youn, Hyewon; Choi, Bu Young; Min, Sang-Hyun; Surh, Young-Joon

    2016-01-01

    Peptidyl prolyl isomerase (PIN1) regulates the functional activity of a subset of phosphoproteins through binding to phosphorylated Ser/Thr-Pro motifs and subsequently isomerization of the phosphorylated bonds. Interestingly, PIN1 is overexpressed in many types of malignancies including breast, prostate, lung and colon cancers. However, its oncogenic functions have not been fully elucidated. Here, we report that PIN1 directly interacts with hypoxia-inducible factor (HIF)-1α in human colon cancer (HCT116) cells. PIN1 binding to HIF-1α occurred in a phosphorylation-dependent manner. We also found that PIN1 interacted with HIF-1α at both exogenous and endogenous levels. Notably, PIN1 binding stabilized the HIF-1α protein, given that their levels were significantly increased under hypoxic conditions. The stabilization of HIF-1α resulted in increased transcriptional activity, consequently upregulating expression of vascular endothelial growth factor, a major contributor to angiogenesis. Silencing of PIN1 or pharmacologic inhibition of its activity abrogated the angiogenesis. By utilizing a bioluminescence imaging technique, we were able to demonstrate that PIN1 inhibition dramatically reduced the tumor volume in a subcutaneous mouse xenograft model and angiogenesis as well as hypoxia-induced transcriptional activity of HIF-1α. These results suggest that PIN1 interacting with HIF-1α is a potential cancer chemopreventive and therapeutic target. PMID:26784107

  4. Peptidyl Prolyl Isomerase PIN1 Directly Binds to and Stabilizes Hypoxia-Inducible Factor-1α

    PubMed Central

    Han, Hyeong-jun; Kwon, Nayoung; Choi, Min-A; Jung, Kyung Oh; Piao, Juan-Yu; Ngo, Hoang Kieu Chi; Kim, Su-Jung; Kim, Do-Hee; Chung, June-Key; Cha, Young-Nam; Youn, Hyewon; Choi, Bu Young; Min, Sang-Hyun; Surh, Young-Joon

    2016-01-01

    Peptidyl prolyl isomerase (PIN1) regulates the functional activity of a subset of phosphoproteins through binding to phosphorylated Ser/Thr-Pro motifs and subsequently isomerization of the phosphorylated bonds. Interestingly, PIN1 is overexpressed in many types of malignancies including breast, prostate, lung and colon cancers. However, its oncogenic functions have not been fully elucidated. Here, we report that PIN1 directly interacts with hypoxia-inducible factor (HIF)-1α in human colon cancer (HCT116) cells. PIN1 binding to HIF-1α occurred in a phosphorylation-dependent manner. We also found that PIN1 interacted with HIF-1α at both exogenous and endogenous levels. Notably, PIN1 binding stabilized the HIF-1α protein, given that their levels were significantly increased under hypoxic conditions. The stabilization of HIF-1α resulted in increased transcriptional activity, consequently upregulating expression of vascular endothelial growth factor, a major contributor to angiogenesis. Silencing of PIN1 or pharmacologic inhibition of its activity abrogated the angiogenesis. By utilizing a bioluminescence imaging technique, we were able to demonstrate that PIN1 inhibition dramatically reduced the tumor volume in a subcutaneous mouse xenograft model and angiogenesis as well as hypoxia-induced transcriptional activity of HIF-1α. These results suggest that PIN1 interacting with HIF-1α is a potential cancer chemopreventive and therapeutic target. PMID:26784107

  5. Stability robustness improvement of direct eigenspace assignment based feedback systems using singular value sensitivities

    NASA Technical Reports Server (NTRS)

    Garg, Sanjay

    1989-01-01

    A methodology to improve the stability robustness of feedback control systems designed using direct eigenspace assignment techniques is presented. The method consists of considering the sensitivity of the minimum singular value of the return difference transfer matrix at the plant input to small changes in the desired closed-loop eigenvalues and the specified elements of the desired closed-loop eigenvectors. Closed-form expressions for the gradient of the minimum return difference singular value with respect to desired closed-loop eigenvalue and eigenvector parameters are derived. Closed-form expressions for the gradients of the control feedback gains with respect to the specified eigenspace parameters are obtained as an intermediate step. The use of the gradient information to improve the guaranteed gain and phase margins in eigenspace assignment based designs is demonstrated by application to an advanced fighter aircraft.

  6. Directed evolution of a G protein-coupled receptor for expression, stability, and binding selectivity

    PubMed Central

    Sarkar, Casim A.; Dodevski, Igor; Kenig, Manca; Dudli, Stefan; Mohr, Anja; Hermans, Emmanuel; Plückthun, Andreas

    2008-01-01

    We outline a powerful method for the directed evolution of integral membrane proteins in the inner membrane of Escherichia coli. For a mammalian G protein-coupled receptor, we arrived at a sequence with an order-of-magnitude increase in functional expression that still retains the biochemical properties of wild type. This mutant also shows enhanced heterologous expression in eukaryotes (12-fold in Pichia pastoris and 3-fold in HEK293T cells) and greater stability when solubilized and purified, indicating that the biophysical properties of the protein had been under the pressure of selection. These improvements arise from multiple small contributions, which would be difficult to assemble by rational design. In a second screen, we rapidly pinpointed a single amino acid substitution in wild type that abolishes antagonist binding while retaining agonist-binding affinity. These approaches may alleviate existing bottlenecks in structural studies of these targets by providing sufficient quantities of stable variants in defined conformational states. PMID:18812512

  7. A computational study of the F-5A forebody emphasizing directional stability

    NASA Technical Reports Server (NTRS)

    Mason, William H.; Ravi, R.

    1991-01-01

    CFD has been used to study the F-5A forebody flowfield at high angle-of-attack combined with sideslip. The classic wind tunnel experiment demonstrating the dominant contribution of the F-5A forebody to directional stability at high angle-of-attack has been simulated computationally over an angle-of-attack range from 10 deg to 45 deg. The key wind tunnel trend for C (n-beta) was obtained computationally using the code known as cfl3d to solve the Reynolds' equations using a modified form of the Baldwin-Lomax turbulence model. The computations provide detailed and fascinating insights into the physics of flowfield. The results of the investigation show that CFD has reached a level of development where computational methods can be used for high angle-of-attack aerodynamic design.

  8. Direct osmolyte-macromolecule interactions confer entropic stability to folded states.

    PubMed

    Rodríguez-Ropero, Francisco; van der Vegt, Nico F A

    2014-07-01

    Protective osmolytes are chemical compounds that shift the protein folding/unfolding equilibrium toward the folded state under osmotic stresses. The most widely considered protection mechanism assumes that osmolytes are depleted from the protein's first solvation shell, leading to entropic stabilization of the folded state. However, recent theoretical and experimental studies suggest that protective osmolytes may directly interact with the macromolecule. As an exemplary and experimentally well-characterized system, we herein discuss poly(N-isopropylacrylamide) (PNiPAM) in water whose folding/unfolding equilibrium shifts toward the folded state in the presence of urea. On the basis of molecular dynamics simulations of this specific system, we propose a new microscopic mechanism that explains how direct osmolyte-macromolecule interactions confer stability to folded states. We show that urea molecules preferentially accumulate in the first solvation shell of PNiPAM driven by attractive van der Waals dispersion forces with the hydrophobic isopropyl groups, leading to the formation of low entropy urea clouds. These clouds provide an entropic driving force for folding, resulting in preferential urea binding to the folded state and a decrease of the lower folding temperature in agreement with experiment. The simulations further indicate that thermodynamic nonideality of the bulk solvent opposes this driving force and may lead to denaturation, as illustrated by simulations of PNiPAM in aqueous solutions with dimethylurea. The proposed mechanism provides a new angle on relations between the properties of protecting and denaturing osmolytes, salting-in or salting-out effects, and solvent nonidealities. PMID:24927256

  9. O-GlcNAcylation stabilizes β-catenin through direct competition with phosphorylation at threonine 41

    PubMed Central

    Olivier-Van Stichelen, Stéphanie; Dehennaut, Vanessa; Buzy, Armelle; Zachayus, Jean-Luc; Guinez, Céline; Mir, Anne-Marie; El Yazidi-Belkoura, Ikram; Copin, Marie-Christine; Boureme, Didier; Loyaux, Denis; Ferrara, Pascual; Lefebvre, Tony

    2014-01-01

    Dysfunctions in Wnt signaling increase β-catenin stability and are associated with cancers, including colorectal cancer. In addition, β-catenin degradation is decreased by nutrient-dependent O-GlcNAcylation. Human colon tumors and colons from mice fed high-carbohydrate diets exhibited higher amounts of β-catenin and O-GlcNAc relative to healthy tissues and mice fed a standard diet, respectively. Administration of the O-GlcNAcase inhibitor thiamet G to mice also increased colonic expression of β-catenin. By ETD-MS/MS, we identified 4 O-GlcNAcylation sites at the N terminus of β-catenin (S23/T40/T41/T112). Furthermore, mutation of serine and threonine residues within the D box of β-catenin reduced O-GlcNAcylation by 75%. Interestingly, elevating O-GlcNAcylation in human colon cell lines drastically reduced phosphorylation at T41, a key residue of the D box responsible for β-catenin stability. Analyses of β-catenin O-GlcNAcylation mutants reinforced T41 as the most crucial residue that controls the β-catenin degradation rate. Finally, inhibiting O-GlcNAcylation decreased the β-catenin/α-catenin interaction necessary for mucosa integrity, whereas O-GlcNAcase silencing improved this interaction. These results suggest that O-GlcNAcylation regulates not only the stability of β-catenin, but also affects its localization at the level of adherens junctions. Accordingly, we propose that O-GlcNAcylation of β-catenin is a missing link between the glucose metabolism deregulation observed in metabolic disorders and the development of cancer.—Olivier-Van Stichelen, S., Dehennaut, V., Buzy, A., Zachayus, J.-L., Guinez, C., Mir, A.-M., El Yazidi-Belkoura, I., Copin, M.-C., Boureme, D., Loyaux, D., Ferrara, P., Lefebvre, T. O-GlcNAcylation stabilizes β-catenin through direct competition with phosphorylation at threonine 41. PMID:24744147

  10. Which trunk inclination directions best predict multidirectional-seated limits of stability among individuals with spinal cord injury?

    PubMed Central

    Gauthier, Cindy; Gagnon, Dany; Jacquemin, Géraldine; Duclos, Cyril; Masani, Kei; Popovic, Milos R.

    2012-01-01

    Objective To determine which trunk inclination directions most accurately predict multidirectional-seated limits of stability among individuals with spinal cord injury (SCI). Design Predictive study using cross-sectional data. Setting Pathokinesiology Laboratory. Participants Twenty-one individuals with complete or incomplete sensorimotor SCI affecting various vertebral levels participated in this study. Interventions Participants were instructed to lean their trunk as far as possible in eight directions, separated by 45° intervals, while seated on an instrumented chair with their feet positioned on force plates. Outcomes measures Eight direction-specific stability indices (DSIs) were used to define an overall stability index (OSI) (limits of stability). Results All DSIs significantly correlated with the OSI (r = 0.816–0.925). A protocol that only tests the anterior, left postero-lateral, and right lateral trunk inclinations accurately predicts multidirectional-seated postural stability (R2 = 0.98; P < 0.001). Conclusion Multidirectional-seated postural stability can be predicted almost perfectly by evaluating trunk inclinations performed toward the anterior, left postero-lateral, and right lateral directions. PMID:23031171

  11. Reliable Quantum Chemical Prediction of the Localized/Delocalized Character of Organic Mixed-Valence Radical Anions. From Continuum Solvent Models to Direct-COSMO-RS.

    PubMed

    Renz, Manuel; Kess, Martin; Diedenhofen, Michael; Klamt, Andreas; Kaupp, Martin

    2012-11-13

    A recently proposed quantum-chemical protocol for the description of the character of organic mixed-valence (MV) compounds, close from both sides to the localized/delocalized borderline, is evaluated and extended for a series of dinitroaryl radical anions 1-6. A combination of global hybrid functionals with exact-exchange admixtures of 35% (BLYP35) or 42% (BMK) with appropriate solvent modeling allows an essentially quantitative treatment of, for example, structural symmetry-breaking in Robin/Day class II systems, thermal electron transfer (ET) barriers, and intervalence charge-transfer (IV-CT) excitation energies, while covering also the delocalized class III cases. Global hybrid functionals with lower exact-exchange admixtures (e.g., B3LYP, M05, or M06) provide a too delocalized description, while functionals with higher exact-exchange admixtures (M05-2X, M06-2X) provide a too localized one. The B2PLYP double hybrid gives reasonable structures but far too small barriers in class II cases. The CAM-B3LYP range hybrid gives somewhat too high ET barriers and IV-CT energies, while the range hybrids ωB97X and LC-BLYP clearly exhibit too much exact exchange. Continuum solvent models describe the situation well in most aprotic solvents studied. The transition of 1,4-dinitrobenzene anion 1 from a class III behavior in aprotic solvents to a class II behavior in alcohols is not recovered by continuum solvent models. In contrast, it is treated faithfully by the novel direct conductor-like screening model for real solvents (D-COSMO-RS). The D-COSMO-RS approach, the TURBOMOLE implementation of which is reported, also describes accurately the increased ET barriers of class II systems 2 and 3 in alcohols as compared to aprotic solvents and can distinguish at least qualitatively between different aprotic solvents with identical or similar dielectric constants. The dominant role of the solvent environment for the ET character of these MV radical anions is emphasized, as in

  12. Production of sulfate radical from peroxymonosulfate induced by a magnetically separable CuFe2O4 spinel in water: efficiency, stability, and mechanism.

    PubMed

    Zhang, Tao; Zhu, Haibo; Croué, Jean-Philippe

    2013-03-19

    A simple, nonhazardous, efficient and low energy-consuming process is desirable to generate powerful radicals from peroxymonosulfate (PMS) for recalcitrant pollutant removal. In this work, the production of radical species from PMS induced by a magnetic CuFe(2)O(4) spinel was studied. Iopromide, a recalcitrant model pollutant, was used to investigate the efficiency of this process. CuFe(2)O(4) showed higher activity and 30 times lower Cu(2+) leaching (1.5 μg L(-1) per 100 mg L(-1)) than a well-crystallized CuO at the same dosage. CuFe(2)O(4) maintained its activity and crystallinity during repeated batch experiments. In comparison, the activity of CuO declined significantly, which was ascribed to the deterioration in its degree of crystallinity. The efficiency of the PMS/CuFe(2)O(4) was highest at neutral pH and decreased at acidic and alkaline pHs. Sulfate radical was the primary radical species responsible for the iopromide degradation. On the basis of the stoichiometry of oxalate degradation in the PMS/CuFe(2)O(4), the radical production yield from PMS was determined to be near 1 mol/mol. The PMS decomposition involved an inner-sphere complexation with the oxide's surface Cu(II) sites. In situ characterization of the oxide surface with ATR-FTIR and Raman during the PMS decomposition suggested that surface Cu(II)-Cu(III)-Cu(II) redox cycle was responsible for the efficient sulfate radical generation from PMS. PMID:23439015

  13. Selective stabilization of microtubules oriented toward the direction of cell migration.

    PubMed Central

    Gundersen, G G; Bulinski, J C

    1988-01-01

    A small subset of the microtubule (MT) array in many cultured cells does not exhibit the rapid turnover (t 1/2 approximately equal to 10 min) shown by most cellular MTs. The function of the stable class of MTs is unknown and has been confounded by the apparent lack of organization of stable MTs within cells. Using an antibody against detyrosinated tubulin, a post-translationally modified form of tubulin that accumulates in stable MTs, we localized the stable MTs in mouse 3T3 cells induced to initiate directional migration by experimental wounding of confluent monolayers. Immediately after monolayer wounding, the distribution of stable MTs in cells at the wound edge resembled that in cells in the monolayer interior; most cells either contained randomly distributed stable MTs or lacked them entirely. However, by 20 min after wounding, cells at the wound margin began to generate an asymmetric MT array, with virtually all stable MTs oriented toward the cell edge in contact with the wound. Two hours after monolayer wounding, greater than or equal to 80% of cells at the wound margin had generated this polarized array of stable MTs, and the array was maintained for at least 12 hr. MTs in the polarized array showed enhanced resistance to depolymerization by nocodazole, thus providing an independent test of their stability. Formation of the polar array of stable MTs appeared to precede onset of cell migration and closely paralleled reorientation of the MT-organizing center. These results show that cultured cells can remodel their MT array rapidly in response to an extracellular signal and suggest that selective stabilization of MTs is an early event in the generation of cellular asymmetry. Images PMID:3413068

  14. Direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability in rhizosphere of trifoliate orange.

    PubMed

    Wu, Qiang-Sheng; Cao, Ming-Qin; Zou, Ying-Ning; He, Xin-hua

    2014-01-01

    To test direct and indirect effects of glomalin, mycorrhizal hyphae, and roots on aggregate stability, perspex pots separated by 37-μm nylon mesh in the middle were used to form root-free hyphae and root/hyphae chambers, where trifoliate orange (Poncirus trifoliata) seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in the root/hyphae chamber. Both fungal species induced significantly higher plant growth, root total length, easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP), and mean weight diameter (an aggregate stability indicator). The Pearson correlation showed that root colonization or soil hyphal length significantly positively correlated with EE-GRSP, difficultly-extractable GRSP (DE-GRSP), T-GRSP, and water-stable aggregates in 2.00-4.00, 0.50-1.00, and 0.25-0.50 mm size fractions. The path analysis indicated that in the root/hyphae chamber, aggregate stability derived from a direct effect of root colonization, EE-GRSP or DE-GRSP. Meanwhile, the direct effect was stronger by EE-GRSP or DE-GRSP than by mycorrhizal colonization. In the root-free hyphae chamber, mycorrhizal-mediated aggregate stability was due to total effect but not direct effect of soil hyphal length, EE-GRSP and T-GRSP. Our results suggest that GRSP among these tested factors may be the primary contributor to aggregate stability in the citrus rhizosphere. PMID:25059396

  15. MOF-5-Polystyrene: Direct Production from Monomer, Improved Hydrolytic Stability, and Unique Guest Adsorption.

    PubMed

    Gamage, Nipuni-Dhanesha H; McDonald, Kyle A; Matzger, Adam J

    2016-09-19

    An unprecedented mode of reactivity of Zn4 O-based metal-organic frameworks (MOFs) offers a straightforward and powerful approach to polymer-hybridized porous solids. The concept is illustrated with the production of MOF-5-polystyrene wherein polystyrene is grafted and uniformly distributed throughout MOF-5 crystals after heating in pure styrene for 4-24 h. The surface area and polystyrene content of the material can be fine-tuned by controlling the duration of heating styrene in the presence of MOF-5. Polystyrene grafting significantly alters the physical and chemical properties of pristine MOF-5, which is evident from the unique guest adsorption properties (solvatochromic dye uptake and improved CO2 capacity) as well as the dramatically improved hydrolytic stability of composite. Based on the fact that MOF-5 is the best studied member of the structure class, and has been produced at scale by industry, these findings can be directly leveraged for a range of current applications. PMID:27555362

  16. LMO2 Oncoprotein Stability in T-Cell Leukemia Requires Direct LDB1 Binding

    PubMed Central

    Layer, Justin H.; Alford, Catherine E.; McDonald, W. Hayes

    2015-01-01

    LMO2 is a component of multisubunit DNA-binding transcription factor complexes that regulate gene expression in hematopoietic stem and progenitor cell development. Enforced expression of LMO2 causes leukemia by inducing hematopoietic stem cell-like features in T-cell progenitor cells, but the biochemical mechanisms of LMO2 function have not been fully elucidated. In this study, we systematically dissected the LMO2/LDB1-binding interface to investigate the role of this interaction in T-cell leukemia. Alanine scanning mutagenesis of the LIM interaction domain of LDB1 revealed a discrete motif, R320LITR, required for LMO2 binding. Most strikingly, coexpression of full-length, wild-type LDB1 increased LMO2 steady-state abundance, whereas coexpression of mutant proteins deficient in LMO2 binding compromised LMO2 stability. These mutant LDB1 proteins also exerted dominant negative effects on growth and transcription in diverse leukemic cell lines. Mass spectrometric analysis of LDB1 binding partners in leukemic lines supports the notion that LMO2/LDB1 function in leukemia occurs in the context of multisubunit complexes, which also protect the LMO2 oncoprotein from degradation. Collectively, these data suggest that the assembly of LMO2 into complexes, via direct LDB1 interaction, is a potential molecular target that could be exploited in LMO2-driven leukemias resistant to existing chemotherapy regimens. PMID:26598604

  17. Microstructural stability of directionally solidified eutectic NiAl-Mo under static and thermal cycling conditions

    SciTech Connect

    Kush, M.T.; Holmes, J.W.; Gibala, R.

    1997-12-31

    The quasi-binary eutectic NiAl-9% Mo with faceted molybdenum fibers was subjected to both thermal annealing conditions and to annealing under thermal cycling conditions to determine the microstructural stability of this alloy. The static temperature tests were run at 0.85T{sub M}--0.97T{sub M} in an argon gas atmosphere. The thermal cycling tests were performed between temperatures of 700 C and 1,200 C by induction heating disk-shaped specimens in an argon gas atmosphere using time-temperature heating and cooling profiles to approximate potential engine applications. To quantify microstructural changes, the fiber size and size distribution and number of fibers per unit area were measured as a function of time at temperature. The overall results demonstrate that the directionally solidified eutectic NiAl-9Mo subjected to thermal fatigue conditions exhibits cell boundary coarsening and large shape changes, whereas the microstructure under static stress-free annealing is stable.

  18. Direct ab initio dynamics studies on the hydrogen-abstraction reactions of OH radicals with HOX (X = F, Cl, and Br).

    PubMed

    Wang, Li; Liu, Jing-Yao; Li, Ze-Sheng; Sun, Chia-Chung

    2004-03-01

    The hydrogen abstract reactions of OH radicals with HOF (R1), HOCl (R2), and HOBr (R3) have been studied systematically by a dual-level direct-dynamics method. The geometries and frequencies of all the stationary points are optimized at the MP2/6-311+G(2d, 2p) level of theory. A hydrogen-bonded complex is located at the product channel for the OH + HOBr reaction. To improve the energetics information along the minimum energy path (MEP), single-point energy calculations are carried out at the CCSD(T)/6-311++G(3df, 3pd) level of theory. Interpolated single-point energy (ISPE) method is employed to correct the energy profiles for the three reactions. It is found that neither the barrier heights (DeltaE) nor the H-O bond dissociation energies [D(H-O)] exhibit any clear-cut linear correlations with the halogen electronegative. The decrease of DeltaE and D(H-O) for the three reactions are in order of HOF > HOBr > HOCl. Rate constants for each reaction are calculated by canonical variational transition-state theory (CVT) with a small-curvature tunneling correction (SCT) within 200-2000 K. The agreement of the rate constants with available experimental values for reactions R2 and R3 at 298 K is good. Our results show that the variational effect is small while the tunneling correction has an important contribution in the calculation of rate constants in the low-temperature range. Due to the lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available. PMID:14735573

  19. A Stability Study of Ni/Yttria-Stabilized Zirconia Anode for Direct Ammonia Solid Oxide Fuel Cells.

    PubMed

    Yang, Jun; Molouk, Ahmed Fathi Salem; Okanishi, Takeou; Muroyama, Hiroki; Matsui, Toshiaki; Eguchi, Koichi

    2015-12-30

    In recent years, solid oxide fuel cells fueled with ammonia have been attracting intensive attention. In this work, ammonia fuel was supplied to the Ni/yttria-stabilized zirconia (YSZ) cermet anode at 600 and 700 °C, and the change of electrochemical performance and microstructure under the open-circuit state was studied in detail. The influence of ammonia exposure on the microstructure of Ni was also investigated by using Ni/YSZ powder and Ni film deposited on a YSZ disk. The obtained results demonstrated that Ni in the cermet anode was partially nitrided under an ammonia atmosphere, which considerably roughened the Ni surface. Moreover, the destruction of the anode support layer was confirmed for the anode-supported cell upon the temperature cycling test between 600 and 700 °C because of the nitriding phenomenon of Ni, resulting in severe performance degradation. PMID:26642379

  20. Direct kinetic study of radical transformation reaction Me sub 2 COH + Ph sub 2 CO yields Me sub 2 CO + Ph sub 2 COH

    SciTech Connect

    Demeter, A.; Berces, T. )

    1991-02-07

    Reaction Me{sub 2}COH + Ph{sub 2}CO {yields} Me{sub 2}CO + Ph{sub 2}COH (5) was studied by laser flash photolysis under such experimental conditions where the changes in the concentrations of ketyl radicals with reaction time were controlled by this radical transformation process. Diphenylketyl radical concentration profiles were obtained by monitoring transient absorption at 540 nm and the rate coefficient k{sub 5} was extracted from that part of the concentration trajectory which was determined solely by reaction 5. Thus, k{sub 5} = (3.6 {plus minus} 0.6) {times} 10{sup 5} dm{sup 3} mol{sup {minus}1} s{sup {minus}1} was determined at 298 K in acetonitrile, which is higher than the two recently reported values derived from quantum yields measured under steady-state conditions. A reaction mechanism for the radical transformation process (5) is proposed in which hydrogen-bonded species formed from ketyl radical and benzophenone participate.

  1. Roaming Radicals

    NASA Astrophysics Data System (ADS)

    Bowman, Joel M.; Shepler, Benjamin C.

    2011-05-01

    Roaming is a recently verified unusual pathway to molecular products from unimolecular dissociation of an energized molecule. Here we present the evidence for this pathway for H2CO and CH3CHO. Theoretical analysis shows that this path visits the plateau region of the potential energy surface near dissociation to radical products. It is not clear whether roaming is a distinct isolated pathway, in addition to the conventional one via the well-known molecular saddle-point transition state. Evidence is presented to suggest that the two pathways may originate from a single, but highly complicated, dividing surface. Other examples of unusual reaction dynamics are also reviewed.

  2. Stability of 5,5-dimethyl-1-pyrroline-N-oxide as a spin-trap for quantification of hydroxyl radicals in processes based on Fenton reaction.

    PubMed

    Fontmorin, J M; Burgos Castillo, R C; Tang, W Z; Sillanpää, M

    2016-08-01

    Fenton reaction was used to produce hydroxyl radicals under conditions similar to AOPs with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap agent in electron paramagnetic resonance (EPR) analysis. A theoretical kinetics model was developed to determine conditions under which the spin-adduct DMPO-OH is not further oxidized by Fe(3+) and excessive radicals, so that hydroxyl radicals concentration could be accurately inferred. Experiments were designed based upon the model and H2O2 and Fe(2+) concentrations were varied from 1 to 100 mM and from 0.1 to 10 mM, respectively, with a constant H2O2: Fe(2+) ratio of 10:1. Results confirmed that DMPO concentration should be at least 20 times higher than the concentration of H2O2 and 200 times higher than iron concentration to produce stable DMPO-OH EPR signal. When DMPO: H2O2 ratio varied from 1 to 10, DMPO-OH could generate intermediates and be further oxidized leading to the apparition of an additional triplet. This signal was attributed to a paramagnetic dimer: its structure and a formation mechanism were proposed. Finally, the utilization of sodium sulfite and catalase to terminate Fenton reaction was discussed. Catalase appeared to be compatible with DMPO. However, sodium sulfite should be avoided since it reacted with DMPO-OH to form DMPO-SO3. PMID:27132196

  3. Performance, methanol tolerance and stability of Fe-aminobenzimidazole derived catalyst for direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Sebastián, David; Serov, Alexey; Artyushkova, Kateryna; Atanassov, Plamen; Aricò, Antonino S.; Baglio, Vincenzo

    2016-07-01

    Highly active and durable non-platinum group metals (non-PGM) catalyst based on iron-nitrogen-carbon (Fe-N-C) for the oxygen reduction reaction (ORR) derived from pyrolyzed Fe-aminobenzimidazole (Fe-ABZIM) was synthesized by sacrificial support method (SSM), and characterized by several physical-chemical techniques: scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller method and X-ray photoelectron spectroscopy. In half-cell electrochemical configuration, the Fe-ABZIM catalyst presented a significant improvement of ORR activity with respect to a recently reported non-PGM formulation based on Fe-aminoantipyrine, with an enhancement of half-wave potential of about 85 mV in O2-saturated sulfuric acid solution. To the moment, the gap with respect to a benchmark Pt/C catalyst was about 90 mV. The Fe-ABZIM catalyst showed a remarkably high tolerance to methanol, resulting in superior ORR performance compared to Pt/C at methanol concentrations higher than 0.02 M. In direct methanol fuel cell (DMFC) good performances were also obtained. A durability test (100 h) at 90 °C, feeding 5 M methanol, was carried out. A certain decrease of performance was recorded, amounting to -0.20 mW cm-2 h-1 at the very beginning of test and -0.05 mW cm-2 h-1 at the end. However, the Fe-ABZIM is more adequate than previously reported formulations in terms of both ORR activity and stability.

  4. Non-covalent interaction between dietary stilbenoids and human serum albumin: Structure-affinity relationship, and its influence on the stability, free radical scavenging activity and cell uptake of stilbenoids.

    PubMed

    Cao, Hui; Jia, Xueping; Shi, Jian; Xiao, Jianbo; Chen, Xiaoqing

    2016-07-01

    Dietary stilbenoids are associated with many benefits for human health, which depend on their bioavailability and bioaccessibility. The stilbenoid-human serum albumin (HSA) interactions are investigated to explore the structure-affinity relationship and influence on the stability, free radical scavenging activity and cell uptake of stilbenoids. The structure-affinity relationship of the stilbenoids-HSA interaction was found as: (1) the methoxylation enhanced the affinity, (2) an additional hydroxyl group increases the affinity and (3) the glycosylation significantly weakened the affinity. HSA obviously masked the free radical scavenging potential of stilbenoids. The stabilities of stilbenoids in different medium were determined as: HSA solution>human plasma>Dulbecco's modified Eagle's medium. It appears that the milk enhanced the cell uptake of stilbenoids with multi-hydroxyl groups and weakened the cell uptake of stilbenoids with methoxyl group on EA.hy 926 endothelial cells. The stilbenoids are hardly absorbed by human umbilical vein endothelial cells in the presence of milk. PMID:26920308

  5. Effects of craniocervical flexion exercise on upper-limb postural stability during a goal-directed pointing task

    PubMed Central

    Yong, Min-Sik; Lee, Hae-Yong; Ryu, Young-Uk; Lee, Mi-Young

    2015-01-01

    [Purpose] This study investigated the effects of craniocervical flexion exercise on upper-limb postural stability by measuring upper-limb postural tremor during a goal-directed pointing task. [Subjects and Methods] Twenty-four subjects were randomly assigned to the exercise or control group. The exercise group performed craniocervical flexion exercise four days per week for five weeks. Upper-limb postural tremor was measured by using a three-dimensional electromagnetic motion tracking system (trakSTAR™, Ascension Technology Corporation, Burlington, VT, USA) during a goal-directed pointing task. [Results] In the exercise group, the range and velocity of the trajectories of the shoulder, wrist, and finger in the lateral direction improved significantly. However, no significant changes were observed in the control group. [Conclusion] Craniocervical flexion exercise reduces the range and velocity of upper-limb postural tremor, thereby increasing postural stability. PMID:26180368

  6. Reduced Graphene Oxide-Ag3PO4 Heterostructure: A Direct Z-Scheme Photocatalyst for Augmented Photoreactivity and Stability.

    PubMed

    Samal, Alaka; Das, D P; Nanda, K K; Mishra, B K; Das, J; Dash, A

    2016-02-18

    A visible light driven, direct Z-scheme reduced graphene oxide-Ag3PO4 (RGO-Ag3 PO4 ) heterostructure was synthesized by means of a simple one-pot photoreduction route by varying the amount of RGO under visible light illumination. The reduction of graphene oxide (GO) and growth of Ag3PO4 took place simultaneously. The effect of the amount of RGO on the textural properties and photocatalytic activity of the heterostructure was investigated under visible light illumination. Furthermore, total organic carbon (TOC) analysis confirmed 97.1 % mineralization of organic dyes over RGO-Ag3PO4 in just five minutes under visible-light illumination. The use of different quenchers in the photomineralization suggested the presence of hydroxyl radicals ((.)OH), superoxide radicals ((.)O2 (-)), and holes (h(+)), which play a significant role in the mineralization of organic dyes. In addition to that, clean hydrogen fuel generation was also observed with excellent reusability. The 4 RGO-Ag3PO4 heterostructure has a high H2 evolution rate of 3690 μmol h(-1)  g(-1), which is 6.15 times higher than that of RGO. PMID:26639552

  7. SIRT1 deacetylates and stabilizes hypoxia-inducible factor-1α (HIF-1α) via direct interactions during hypoxia.

    PubMed

    Joo, Hyun-Yoo; Yun, Miyong; Jeong, Jaemin; Park, Eun-Ran; Shin, Hyun-Jin; Woo, Seon Rang; Jung, Jin Kyu; Kim, Yong-Min; Park, Joong-Jean; Kim, Joon; Lee, Kee-Ho

    2015-07-10

    Upon shift to a hypoxic environment, cellular HIF-1α protein is stabilized, with a rapid decline in oxygen-sensitive hydroxylation. Several additional post-translational modifications of HIF-1α are critical in controlling protein stability during hypoxia. In the present study, we showed that SIRT1 stabilizes HIF-1α via direct binding and deacetylation during hypoxia. SIRT1 depletion or inactivation led to reduced hypoxic HIF-1α accumulation, accompanied by an increase in HIF-1α acetylation. Impaired HIF-1α accumulation was recovered upon inhibition of 26S proteasome activity, indicating that SIRT1 is essential for HIF-1α stabilization during hypoxia. Consistently, HIF-1α accumulation was enhanced upon overexpression of wild-type SIRT1, but not its dominant-negative form. SIRT1-mediated accumulation of HIF-1α protein led to increased expression of HIF-1α target genes, including VEGF, GLUT1 and MMP2, and ultimate promotion of cancer cell invasion. These findings collectively imply that hypoxic HIF-1α stabilization requires SIRT1 activation. Furthermore, SIRT1 protection of HIF-1α from acetylation may be a prerequisite for stabilization and consequent enhancement of cell invasion. PMID:25979359

  8. Homolytic dissociation of the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and structures and stabilities of the related radicals Me2NCSn* (n = 1-4).

    PubMed

    Steudel, Ralf; Steudel, Yana; Mak, Adrian Matthew; Wong, Ming Wah

    2006-12-01

    The homolytic dissociation of the important vulcanization accelerator tetramethylthiuram disulfide (TMTD) has been studied by ab initio calculations according to the G3X(MP2) and G3X(MP2)-RAD theories. Homolytic cleavage of the SS bond requires a low enthalpy of 150.0 kJ mol-1, whereas 268.0 kJ mol-1 is needed for the dissociation of one of the C-S single bonds. To cleave one of the SS bonds of the corresponding trisulfide (TMTT) requires 191.1 kJ mol-1. Me2NCS2* is a particularly stable sulfur radical as reflected in the low S-H bond dissociation enthalpy of the corresponding acid Me2NC(=S)SH (301.7 kJ mol-1). Me2NCS2* (2B2) is a sigma radical characterized by the unpaired spin density shared equally between the two sulfur atoms and by a 4-center (NCS2) delocalized pi system. The ESR g-tensors of the radicals Me2NCSn* (n = 1-3) have been calculated. Both TMTD and the mentioned radicals form stable chelate complexes with a Li+ cation, which here serves as a model for the zinc ions used in accelerated rubber vulcanization. Although the binding energy of the complex [Li(TMTD)]+ is larger than that of the isomeric species [Li(S2CNMe2)2]+ (12), the dissociation enthalpy of TMTD as a ligand is smaller (125.5 kJ mol-1) than that of free TMTD. In other words, the homolytic dissociation of the SS bonds of TMTD is facilitated by the presence of Li+ ions. The sulfurization of TMTD in the presence of Li+ to give the paramagnetic complex [Li(S3CNMe2)2]+ is strongly exothermic. These results suggest that TMTD reacts with naked zinc ions as well as with the surface atoms of solid zinc oxide particles in an analogous manner producing highly reactive complexes, which probably initiate the crosslinking process during vulcanization reactions of natural or synthetic rubber accelerated by TMTD/ZnO. PMID:17137356

  9. Effect of polar solvents on beta-carotene radical precursor.

    PubMed

    Tian, Yu-Xi; Han, Rui-Min; Zhang, Jian-Ping; Skibsted, Leif H

    2008-03-01

    Beta-carotene forms radicals in chloroform upon photo-excitation (i) in the femtosecond time-scale by direct electron ejection into chloroform and (ii) in the microsecond time-scale by secondary reactions with chloroform radicals formed in the faster reactions. The precursor for beta-carotene radical cation decays in a second-order reaction in the mixed solvents, with a rate decreasing for increasing dielectric constant of cosolvent (acetic acid < ethanol < acetonitrile approximately methanol). The precursor is assigned as an ion pair from which the beta-carotene radical cation is formed in neat chloroform, but in more polar solvents it reacts at least partly through disproportionation in a bimolecular reaction promoted by the presence of ions. The stabilization of the radical precursor by increased solvent polarity, allowing for deactivation of the precursor by an alternative reaction channel, is discussed in relation to the balance of pro- and antioxidative properties of beta-carotene at lipid/water interfaces. PMID:18344123

  10. Enhancement of oxidative stability of the subtilisin nattokinase by site-directed mutagenesis expressed in Escherichia coli.

    PubMed

    Weng, MeiZhi; Zheng, ZhongLiang; Bao, Wei; Cai, YongJun; Yin, Yan; Zou, GuoLin; Zou, GouLin

    2009-11-01

    Nattokinase (subtilisin NAT, NK) is a bacterial serine protease with strong fibrinolytic activity and it is a potent cardiovascular drug. In medical and commercial applications, however, it is susceptible to chemical oxidation, and subsequent inactivation or denaturation. Here we show that the oxidative stability of NK was substantially increased by optimizing the amino acid residues Thr(220) and Met(222), which were in the vicinity of the catalytic residue Ser(221) of the enzyme. Two nonoxidative amino acids (Ser and Ala) were introduced at these sites using site-directed mutagenesis. Active enzymes were successfully expressed in Escherichia coli with periplasmic secretion and enzymes were purified to homogeneity. The purified enzymes were analyzed with respect to oxidative stability, kinetic parameters, fibrinolytic activity and thermal stability. M222A mutant was found to have a greatly increased oxidative stability compared with wild-type enzyme and it was resistant to inactivation by more than 1 M H(2)O(2), whereas the wild-type enzyme was inactivated by 0.1 M H(2)O(2) (t(1/2) approximately 11.6 min). The other mutant (T220S) also showed an obvious increase in antioxidative ability. Molecular dynamic simulations on wild-type and T220S mutant proteins suggested that a hydrogen bond was formed between Ser(220) and Asn(155), and the spatial structure of Met(222) was changed compared with the wild-type. The present study demonstrates the feasibility of improving oxidative stability of NK by site-directed mutagenesis and shows successful protein engineering cases to improve stability of NK as a potent therapeutic agent. PMID:19631297

  11. Calculation of lateral-directional stability derivatives for wing-body combinations with and without jet-interaction effects

    NASA Technical Reports Server (NTRS)

    Lan, C. E.

    1977-01-01

    A theoretical method is presented for predicting the lateral-directional stability derivatives of wing-body combinations with or without the blowing jet effect. The fuselage effect is accounted for by the axial distribution of vortex multiplets. Comparison of the predicted results with experiments and other theoretical methods show good agreement for configurations without the blowing jet. More applicable experimental data with blowing jets are needed to establish the accuracy of the theory.

  12. Dual high-resolution α-glucosidase and radical scavenging profiling combined with HPLC-HRMS-SPE-NMR for identification of minor and major constituents directly from the crude extract of Pueraria lobata.

    PubMed

    Liu, Bingrui; Kongstad, Kenneth T; Qinglei, Sun; Nyberg, Nils T; Jäger, Anna K; Staerk, Dan

    2015-02-27

    The crude methanol extract of Pueraria lobata was investigated by dual high-resolution α-glucosidase inhibition and radical scavenging profiling combined with hyphenated HPLC-HRMS-SPE-NMR. Direct analysis of the crude extract without preceding purification was facilitated by combining chromatograms from two analytical-scale HPLC separations of 120 and 600 μg on-column, respectively. High-resolution α-glucosidase and radical scavenging profiles were obtained after microfractionation of the eluate in 96-well microplates. This allowed full bioactivity profiling of individual peaks in the HPLC chromatogram of the crude methanol extract. Subsequent HPLC-HRMS-SPE-NMR analysis allowed identification of 21 known compounds in addition to two new compounds, i.e., 3'-methoxydaidzein 8-C-[α-D-apiofuranosyl-(1→6)]-β-D-glucopyranoside and 6″-O-malonyl-3'-methoxydaidzin, as well as an unstable compound tentatively identified as 3'-de-O-methylpuerariafuran. PMID:25679337

  13. Measurements of the Lateral and Directional Stability and Control Characteristics of a P-51H Airplane (AAF No. 44-64164)

    NASA Technical Reports Server (NTRS)

    Kraft, Christopher C., Jr.; Reeder, J. P.

    1948-01-01

    Flight tests of a P-51H airplane with two different vertical-tail assemblies were made to determine lateral and directional stability and control characteristics. The airplane had satisfactory directional stability in the landing, approach, and wave-off conditions with either tail. In the power-on clean and glide conditions, however, the airplane had weak directional stability with the original tail. The production tail, which had a 7-inch fin extension and a shorter span rudder, improved the directional stability in the power-on clean and glide conditions, but the stability was still weak in the power-on clean condition. Increased altitude in either case caused a slight decrease in the stability. The rudder-trim-force change with speed with either vertical-tail assembly was high. The general aileron control characteristics were satisfactory but the aileron effectiveness failed to meet the Army handling-qualities requirements.

  14. Optimizing wind farm layout via LES-calibrated geometric models inclusive of wind direction and atmospheric stability effects

    NASA Astrophysics Data System (ADS)

    Archer, Cristina; Ghaisas, Niranjan

    2015-04-01

    The energy generation at a wind farm is controlled primarily by the average wind speed at hub height. However, two other factors impact wind farm performance: 1) the layout of the wind turbines, in terms of spacing between turbines along and across the prevailing wind direction; staggering or aligning consecutive rows; angles between rows, columns, and prevailing wind direction); and 2) atmospheric stability, which is a measure of whether vertical motion is enhanced (unstable), suppressed (stable), or neither (neutral). Studying both factors and their complex interplay with Large-Eddy Simulation (LES) is a valid approach because it produces high-resolution, 3D, turbulent fields, such as wind velocity, temperature, and momentum and heat fluxes, and it properly accounts for the interactions between wind turbine blades and the surrounding atmospheric and near-surface properties. However, LES are computationally expensive and simulating all the possible combinations of wind directions, atmospheric stabilities, and turbine layouts to identify the optimal wind farm configuration is practically unfeasible today. A new, geometry-based method is proposed that is computationally inexpensive and that combines simple geometric quantities with a minimal number of LES simulations to identify the optimal wind turbine layout, taking into account not only the actual frequency distribution of wind directions (i.e., wind rose) at the site of interest, but also atmospheric stability. The geometry-based method is calibrated with LES of the Lillgrund wind farm conducted with the Software for Offshore/onshore Wind Farm Applications (SOWFA), based on the open-access OpenFOAM libraries. The geometric quantities that offer the best correlations (>0.93) with the LES results are the blockage ratio, defined as the fraction of the swept area of a wind turbine that is blocked by an upstream turbine, and the blockage distance, the weighted distance from a given turbine to all upstream turbines

  15. Temporal Variability and Stability in Infant-Directed Sung Speech: Evidence for Language-Specific Patterns

    ERIC Educational Resources Information Center

    Falk, Simone

    2011-01-01

    In this paper, sung speech is used as a methodological tool to explore temporal variability in the timing of word-internal consonants and vowels. It is hypothesized that temporal variability/stability becomes clearer under the varying rhythmical conditions induced by song. This is explored cross-linguistically in German--a language that exhibits a…

  16. Temporal variability and stability in infant-directed sung speech: evidence for language-specific patterns.

    PubMed

    Falk, Simone

    2011-06-01

    In this paper, sung speech is used as a methodological tool to explore temporal variability in the timing of word-internal consonants and vowels. It is hypothesized that temporal variability/stability becomes clearer under the varying rhythmical conditions induced by song.This is explored crosslinguistically in German - a language that exhibits a potential vocalic quantity distinction - and the non-quantity languages French and Russian. Songs by non-professional singers, i.e. parents that sang to their infants aged 2 to 13 months in a non-laboratory setting, were recorded and analyzed.Vowel and consonant durations at syllable contacts of trochaic word types with CVCV or CV:CV structure were measured under varying rhythmical conditions. Evidence is provided that in German non-professional singing, the two syllable structures can be differentiated by two distinct temporal variability patterns: vocalic variability (and consonantal stability) was found to be dominant in CV:CV structures whereas consonantal variability (and vocalic stability) was characteristic for CVCV structures. In French and Russian, however, only vocalic variability seemed to apply.Additionally, findings suggest that the different temporal patterns found in German were also supported by the stability pattern at the tonal level. These results point to subtle (supra) segmental timing mechanisms in sung speech that affect temporal targets according to the specific prosodic nature of the language in question. PMID:21848078

  17. Longitudinal Double Spin Asymmetry and Cross Section for Direct Photon Production Measured at Mid-rapidity in Polarized {radical}(s) = 200 GeV pp Collisions at PHENIX

    SciTech Connect

    Bennett, Robert

    2009-08-04

    Direct photon production in pp collisions at RHIC is one of the important channels PHENIX will employ to determine the polarized gluon distribution {delta}G. The direct photon A{sub LL} is linear in {delta}G, therefore sensitive to its sign and magnitude. To establish the applicability of perturbative Quantum Chromodynamics (pQCD) to this process, we present a comparison of the direct photon unpolarized cross section, with next-to-leading order pQCD calculations. We then evaluate the double helicity spin asymmetries, A{sub LL}, from these data and compare with theoretical models. We present results and the current status the analysis of 2005 and 2006 data sets.

  18. Improvement of the directional stability of passenger car trailer couplings with actively controlled steering

    NASA Astrophysics Data System (ADS)

    Desens, Jens

    The stabilization of pendulum oscillations of passenger car trailer couplings, using active steering, was examined. A linear model of the couplings was presented. Each axle was provided with a controller. The controllers were optimized, with regard to necessary sensors, in order to minimize costs. The rear and the front axles were provided with a control unit in order to compute the potential prevailing in the active steering of several axles. It was shown that the passenger car rear axle was the most suitable for coupling stabilization. The experiment was simulated, using a complex coupling model. The developed controller allowed the passenger car trailer to be driven at a speed higher than 150 km per hour.

  19. THERMOCHEMISTRY OF HYDROCARBON RADICALS

    SciTech Connect

    Kent M. Ervin, Principal Investigator

    2004-08-17

    Gas phase negative ion chemistry methods are employed to determine enthalpies of formation of hydrocarbon radicals that are important in combustion processes and to investigate the dynamics of ion-molecule reactions. Using guided ion beam tandem mass spectrometry, we measure collisional threshold energies of endoergic proton transfer and hydrogen atom transfer reactions of hydrocarbon molecules with negative reagent ions. The measured reaction threshold energies for proton transfer yield the relative gas phase acidities. In an alternative methodology, competitive collision-induced dissociation of proton-bound ion-molecule complexes provides accurate gas phase acidities relative to a reference acid. Combined with the electron affinity of the R {center_dot} radical, the gas phase acidity yields the RH bond dissociation energy of the corresponding neutral molecule, or equivalently the enthalpy of formation of the R{center_dot} organic radical, using equation: D(R-H) = {Delta}{sub acid}H(RH) + EA(R) - IE(H). The threshold energy for hydrogen abstraction from a hydrocarbon molecule yields its hydrogen atom affinity relative to the reagent anion, providing the RH bond dissociation energy directly. Electronic structure calculations are used to evaluate the possibility of potential energy barriers or dynamical constrictions along the reaction path, and as input for RRKM and phase space theory calculations. In newer experiments, we have measured the product velocity distributions to obtain additional information on the energetics and dynamics of the reactions.

  20. Improvement of stability and enzymatic activity by site-directed mutagenesis of E. coli asparaginase II.

    PubMed

    Verma, Shikha; Mehta, Ranjit Kumar; Maiti, Prasanta; Röhm, Klaus-Heinrich; Sonawane, Avinash

    2014-07-01

    Bacterial asparaginases (EC 3.5.1.1) have attracted considerable attention because enzymes of this group are used in the therapy of certain forms of leukemia. Class II asparaginase from Escherichia coli (EcA), a homotetramer with a mass of 138 kDa, is especially effective in cancer therapy. However, the therapeutic potential of EcA is impaired by the limited stability of the enzyme in vivo and by the induction of antibodies in the patients. In an attempt to modify the properties of EcA, several variants with amino acid replacements at subunit interfaces were constructed and characterized. Chemical and thermal denaturation analysis monitored by activity, fluorescence, circular dichroism, and differential scanning calorimetry showed that certain variants with exchanges that weaken dimer-dimer interactions exhibited complex denaturation profiles with active dimeric and/or inactive monomeric intermediates appearing at low denaturant concentrations. By contrast, other EcA variants showed considerably enhanced activity and stability as compared to the wild-type enzyme. Thus, even small changes at a subunit interface may markedly affect EcA stability without impairing its catalytic properties. Variants of this type may have a potential for use in the asparaginase therapy of leukemia. PMID:24721562

  1. Stability of formation control using a consensus protocol under directed communications with two time delays and delay scheduling

    NASA Astrophysics Data System (ADS)

    Cepeda-Gomez, Rudy; Olgac, Nejat

    2016-01-01

    We consider a linear algorithm to achieve formation control in a group of agents which are driven by second-order dynamics and affected by two rationally independent delays. One of the delays is in the position and the other in the velocity information channels. These delays are taken as constant and uniform throughout the system. The communication topology is assumed to be directed and fixed. The formation is attained by adding a supplementary control term to the stabilising consensus protocol. In preparation for the formation control logic, we first study the stability of the consensus, using the recent cluster treatment of characteristic roots (CTCR) paradigm. This effort results in a unique depiction of the non-conservative stability boundaries in the domain of the delays. However, CTCR requires the knowledge of the potential stability switching loci exhaustively within this domain. The creation of these loci is done in a new surrogate coordinate system, called the 'spectral delay space (SDS)'. The relative stability is also investigated, which has to do with the speed of reaching consensus. This step leads to a paradoxical control design concept, called the 'delay scheduling', which highlights the fact that the group behaviour may be enhanced by increasing the delays. These steps lead to a control strategy to establish a desired group formation that guarantees spacing among the agents. Example case studies are presented to validate the underlying analytical derivations.

  2. Optimisation of ultrasound-assisted extraction of oil from papaya seed by response surface methodology: oil recovery, radical scavenging antioxidant activity, and oxidation stability.

    PubMed

    Samaram, Shadi; Mirhosseini, Hamed; Tan, Chin Ping; Ghazali, Hasanah Mohd; Bordbar, Sara; Serjouie, Alireza

    2015-04-01

    The present study aimed to investigate the effects of ultrasound-assisted extraction (UAE) condition on the yield, antioxidant activity and stability of the oil from papaya seed. The studied ultrasound variables were time, temperature, ultrasound power and solvent to sample ratio. The main goal was to optimise UAE condition providing the highest recovery of papaya seed oil with the most desirable antioxidant activity and stability. The interaction of ultrasound variables had the most and least significant effects on the antioxidant activity and stability, respectively. Ultrasound-assisted extraction provided a relatively high oil recovery (∼ 73%) from papaya seed. The strongest antioxidant activity was achieved by the extraction at the elevated temperature using low solvent to sample ratio. The optimum ultrasound extraction was set at the elevated temperature (62.5 °C) for 38.5 min at high ultrasound power (700 W) using medium solvent to sample ratio (∼ 7:1 v/w). The optimum point was practically validated. PMID:25442517

  3. Direct association between diet and the stability of human atherosclerotic plaque.

    PubMed

    Gonçalves, Isabel; Andersson Georgiadou, Elisavet; Mattsson, Sören; Skog, Göran; Pedro, Luís; Fernandes E Fernandes, José; Dias, Nuno; Engström, Gunnar; Nilsson, Jan; Stenström, Kristina

    2015-01-01

    Mediterranean diet has been suggested to explain why coronary heart disease mortality is lower in southern than northern Europe. Dietary habits can be revealed by isotope ratio mass spectrometry (IRMS) measurement of carbon (δ(13)C) and nitrogen (δ(15)N) in biological tissues. To study if diet is associated with human plaque stability, atherosclerotic plaques from carotid endarterectomy on 56 patients (21 Portuguese and 35 Swedish) were analysed by IRMS and histology. Plaque components affecting rupture risk were measured. Swedish plaques had more apoptosis, lipids and larger cores, as well as fewer proliferating cells and SMC than the Portuguese, conferring the Swedish a more rupture-prone phenotype. Portuguese plaques contained higher δ(13)C and δ(15)N than the Swedish, indicating that Portuguese plaques were more often derived from marine food. Plaque δ(13)C correlated with SMC and proliferating cells, and inversely with lipids, core size, apoptosis. Plaque δ(15)N correlated with SMC and inversely with lipids, core size and apoptosis. This is the first observational study showing that diet is reflected in plaque components associated with its vulnerability. The Portuguese plaques composition is consistent with an increased marine food intake and those plaques are more stable than those from Swedish patients. Marine-derived food is associated with plaque stability. PMID:26490319

  4. Direct association between diet and the stability of human atherosclerotic plaque

    PubMed Central

    Gonçalves, Isabel; Andersson Georgiadou, Elisavet; Mattsson, Sören; Skog, Göran; Pedro, Luís; Fernandes e Fernandes, José; Dias, Nuno; Engström, Gunnar; Nilsson, Jan; Stenström, Kristina

    2015-01-01

    Mediterranean diet has been suggested to explain why coronary heart disease mortality is lower in southern than northern Europe. Dietary habits can be revealed by isotope ratio mass spectrometry (IRMS) measurement of carbon (δ13C) and nitrogen (δ15N) in biological tissues. To study if diet is associated with human plaque stability, atherosclerotic plaques from carotid endarterectomy on 56 patients (21 Portuguese and 35 Swedish) were analysed by IRMS and histology. Plaque components affecting rupture risk were measured. Swedish plaques had more apoptosis, lipids and larger cores, as well as fewer proliferating cells and SMC than the Portuguese, conferring the Swedish a more rupture-prone phenotype. Portuguese plaques contained higher δ13C and δ15N than the Swedish, indicating that Portuguese plaques were more often derived from marine food. Plaque δ13C correlated with SMC and proliferating cells, and inversely with lipids, core size, apoptosis. Plaque δ15N correlated with SMC and inversely with lipids, core size and apoptosis. This is the first observational study showing that diet is reflected in plaque components associated with its vulnerability. The Portuguese plaques composition is consistent with an increased marine food intake and those plaques are more stable than those from Swedish patients. Marine-derived food is associated with plaque stability. PMID:26490319

  5. Direct force measurement of the stability of poly(ethylene glycol)-polyethylenimine graft films.

    PubMed

    Nnebe, Ijeoma M; Tilton, Robert D; Schneider, James W

    2004-08-15

    The stability and passivity of poly(ethylene glycol)-polyethylenimine (PEG-PEI) graft films are important for their use as antifouling coatings in a variety of biotechnology applications. We have used AFM colloidal-probe force measurements combined with optical reflectometry to characterize the surface properties and stability of PEI and dense PEG-PEI graft films on silica. Initial contact between bare silica probes and PEI-modified surfaces yields force curves that exhibit a long-range electrostatic repulsion and short-range attraction between the surfaces, indicating spontaneous desorption of PEI in the aqueous medium. Further transfer of PEI molecules to the probe occurs with subsequent application of forces between FR = 300 and 500 microN/m. The presence of PEG reduces the adhesive properties of the PEI surface and prevents transfer of PEI molecules to the probe with continuous contact, though an initial desorption of PEI still occurs. Glutaraldehyde crosslinking of the graft films prevents both the initial desorption and subsequent transfer of the PEI, resulting in sustained attractive interaction forces of electrostatic origin between the negatively charged probe and the positively charged copolymer graft films. PMID:15271557

  6. Calculation of lateral-directional stability derivatives of wings by a nonplanar quasi-vortex-lattice method

    NASA Technical Reports Server (NTRS)

    Lan, C. E.

    1981-01-01

    The nonplanar quasi-vortex-lattice method is applied to the calculation of lateral-directional stability derivatives of wings with and without vortex-lift effect. Results for conventional configurations and those with winglets, V-tail, etc. are compared with available data. All rolling moment derivatives are found to be accurately predicted. The prediction of side force and yawing moment derivatives for some configurations is not as accurate. Causes of the discrepancy are discussed. A user's manual for the program and the program listing are also included.

  7. Entry dynamics of space shuttle orbiter with lateral-directional stability and control uncertainties at supersonic and hypersonic speeds

    NASA Technical Reports Server (NTRS)

    Stone, H. W.; Powell, R. W.

    1977-01-01

    A six-degree-of-freedom simulation analysis was conducted to examine the effects of the lateral-directional static aerodynamic stability and control uncertainties on the performance of the automatic (no manual inputs) entry-guidance and control systems of the space shuttle orbiter. To establish the acceptable boundaries of the uncertainties, the static aerodynamic characteristics were varied either by applying a multiplier to the aerodynamic parameter or by adding an increment. Control-system modifications were identified that decrease the sensitivity to off-nominal aerodynamics. With these modifications, the acceptable aerodynamic boundaries were determined.

  8. Histidine-rich stabilized polyplexes for cMet-directed tumor-targeted gene transfer

    NASA Astrophysics Data System (ADS)

    Kos, Petra; Lächelt, Ulrich; Herrmann, Annika; Mickler, Frauke Martina; Döblinger, Markus; He, Dongsheng; Krhač Levačić, Ana; Morys, Stephan; Bräuchle, Christoph; Wagner, Ernst

    2015-03-01

    Overexpression of the hepatocyte growth factor receptor/c-Met proto oncogene on the surface of a variety of tumor cells gives an opportunity to specifically target cancerous tissues. Herein, we report the first use of c-Met as receptor for non-viral tumor-targeted gene delivery. Sequence-defined oligomers comprising the c-Met binding peptide ligand cMBP2 for targeting, a monodisperse polyethylene glycol (PEG) for polyplex surface shielding, and various cationic (oligoethanamino) amide cores containing terminal cysteines for redox-sensitive polyplex stabilization, were assembled by solid-phase supported syntheses. The resulting oligomers exhibited a greatly enhanced cellular uptake and gene transfer over non-targeted control sequences, confirming the efficacy and target-specificity of the formed polyplexes. Implementation of endosomal escape-promoting histidines in the cationic core was required for gene expression without additional endosomolytic agent. The histidine-enriched polyplexes demonstrated stability in serum as well as receptor-specific gene transfer in vivo upon intratumoral injection. The co-formulation with an analogous PEG-free cationic oligomer led to a further compaction of pDNA polyplexes with an obvious change of shape as demonstrated by transmission electron microscopy. Such compaction was critically required for efficient intravenous gene delivery which resulted in greatly enhanced, cMBP2 ligand-dependent gene expression in the distant tumor.Overexpression of the hepatocyte growth factor receptor/c-Met proto oncogene on the surface of a variety of tumor cells gives an opportunity to specifically target cancerous tissues. Herein, we report the first use of c-Met as receptor for non-viral tumor-targeted gene delivery. Sequence-defined oligomers comprising the c-Met binding peptide ligand cMBP2 for targeting, a monodisperse polyethylene glycol (PEG) for polyplex surface shielding, and various cationic (oligoethanamino) amide cores containing

  9. Direct and indirect effects of unilateral divorce law on marital stability.

    PubMed

    Kneip, Thorsten; Bauer, Gerrit; Reinhold, Steffen

    2014-12-01

    Previous research examining the impact of unilateral divorce law (UDL) on the prevalence of divorce has provided mixed results. Studies based on cross-sectional cross-country/cross-state survey data have received criticism for disregarding unobserved heterogeneity across countries, as have studies using country-level panel data for failing to account for possible mediating mechanisms at the micro level. We seek to overcome both shortcomings by using individual-level event-history data from 11 European countries (SHARELIFE) and controlling for unobserved heterogeneity over countries and cohorts. We find that UDL in total increased the incidence of marital breakdown by about 20 %. This finding, however, neglects potential selection effects into marriage. Accordingly, the estimated effect of unilateral divorce laws becomes much larger when we control for age at marriage, which is used as indicator for match quality. Moreover, we find that UDL particularly affects marital stability in the presence of children. PMID:25354572

  10. Comparison of Critical Trajectory Methods for Direct CCT Computation for Transient Stability

    NASA Astrophysics Data System (ADS)

    Priyadi, Ardyono; Yorino, Naoto; Sasaki, Yutaka; Tanaka, Masahide; Fujiwara, Takuma; Zoka, Yoshifumi; Kakui, Hironori; Takeshita, Mitsuhiro

    This paper studies new techniques for critical trajectory method, a recent new method proposed by the authors for obtaining critical clearing time (CCT) for transient stability analysis. A specific feature of the proposed method lies in its ability to provide exact CCT without approximations since no such methods have existed so far. The method is based on the computation of the critical trajectory, which is defined as the trajectory that starts from a point on a fault-on trajectory at CCT and reaches an end point. There are a few possible methods for the treatment of the end point conditions, computational performances of the methods are investigated in terms of accuracy of CCT and computational efficiency. It is shown that the proposed methods successfully provide the exact CCT that agrees with the conventional numerical simulation method.

  11. The direct criterion of Newcomb for the ideal MHD stability of an axisymmetric toroidal plasma

    NASA Astrophysics Data System (ADS)

    Glasser, A. H.

    2016-07-01

    A method is presented for determining the ideal magnetohydrodynamic stability of an axisymmetric toroidal plasma, based on a toroidal generalization of the method developed by Newcomb for fixed-boundary modes in a cylindrical plasma. For toroidal mode number n ≠ 0 , the stability problem is reduced to the numerical integration of a high-order complex system of ordinary differential equations, the Euler-Lagrange equation for extremizing the potential energy, for the coupled amplitudes of poloidal harmonics m as a function of the radial coordinate ψ in a straight-fieldline flux coordinate system. Unlike the cylindrical case, different poloidal harmonics couple to each other, which introduces coupling between adjacent singular intervals. A boundary condition is used at each singular surface, where m = nq and q ( ψ ) is the safety factor, to cross the singular surface and continue the solutions beyond it. Fixed-boundary instability is indicated by the vanishing of a real determinant of a Hermitian complex matrix constructed from the fundamental matrix of solutions, the generalization of Newcomb's crossing criterion. In the absence of fixed-boundary instabilities, an M × M plasma response matrix W P , with M the number of poloidal harmonics used, is constructed from the Euler-Lagrange solutions at the plasma-vacuum boundary. This is added to a vacuum response matrix W V to form a total response matrix W T . The existence of negative eigenvalues of W T indicates the presence of free-boundary instabilities. The method is implemented in the fast and accurate DCON code.

  12. Preparation of Mg(OH)2 hybrid pigment by direct precipitation and graft onto cellulose fiber via surface-initiated atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Wang, Xiao; Zhang, Yue; Lv, Lihua; Cui, Yongzhu; Wei, Chunyan; Pang, Guibing

    2016-02-01

    Mg(OH)2 flame retardant hybrid pigment is synthesized through simultaneous solution precipitation and adsorption of anionic dyes (C.I. Acid Red 6). The Mg(OH)2 hybrid pigment bearing vinyl groups after surface silane modification is immobilized onto the surface of bromo end-functional cellulose fiber by atom transfer radical polymerization (ATRP). The morphology and structure of Mg(OH)2 pigments and cellulose fibers grafted with modified pigments are characterized. The thermal properties, flammability and color fastness of cellulose fibers grafted with modified pigments are measured. The results reveal that anionic dye molecules are adsorbed onto Mg(OH)2 crystals and affect the formation of lamella-like Mg(OH)2 crystals. The cellulose fiber grafted with modified Mg(OH)2 hybrid pigment absorbs about four times heat more than original cellulose fiber with about 4% immobilization ratio of pigment, which shortens nearly half of afterflame time and afterglow time.

  13. The nucleus prepositus hypoglossi contributes to head direction cell stability in rats.

    PubMed

    Butler, William N; Taube, Jeffrey S

    2015-02-11

    Head direction (HD) cells in the rat limbic system fire according to the animal's orientation independently of the animal's environmental location or behavior. These HD cells receive strong inputs from the vestibular system, among other areas, as evidenced by disruption of their directional firing after lesions or inactivation of vestibular inputs. Two brainstem nuclei, the supragenual nucleus (SGN) and nucleus prepositus hypoglossi (NPH), are known to project to the HD network and are thought to be possible relays of vestibular information. Previous work has shown that lesioning the SGN leads to a loss of spatial tuning in downstream HD cells, but the NPH has historically been defined as an oculomotor nuclei and therefore its role in contributing to the HD signal is less clear. Here, we investigated this role by recording HD cells in the anterior thalamus after either neurotoxic or electrolytic lesions of the NPH. There was a total loss of direction-specific firing in anterodorsal thalamus cells in animals with complete NPH lesions. However, many cells were identified that fired in bursts unrelated to the animals' directional heading and were similar to cells seen in previous studies that damaged vestibular-associated areas. Some animals with significant but incomplete lesions of the NPH had HD cells that were stable under normal conditions, but were unstable under conditions designed to minimize the use of external cues. These results support the hypothesis that the NPH, beyond its traditional oculomotor function, plays a critical role in conveying vestibular-related information to the HD circuit. PMID:25673848

  14. The Nucleus Prepositus Hypoglossi Contributes to Head Direction Cell Stability in Rats

    PubMed Central

    Butler, William N.

    2015-01-01

    Head direction (HD) cells in the rat limbic system fire according to the animal's orientation independently of the animal's environmental location or behavior. These HD cells receive strong inputs from the vestibular system, among other areas, as evidenced by disruption of their directional firing after lesions or inactivation of vestibular inputs. Two brainstem nuclei, the supragenual nucleus (SGN) and nucleus prepositus hypoglossi (NPH), are known to project to the HD network and are thought to be possible relays of vestibular information. Previous work has shown that lesioning the SGN leads to a loss of spatial tuning in downstream HD cells, but the NPH has historically been defined as an oculomotor nuclei and therefore its role in contributing to the HD signal is less clear. Here, we investigated this role by recording HD cells in the anterior thalamus after either neurotoxic or electrolytic lesions of the NPH. There was a total loss of direction-specific firing in anterodorsal thalamus cells in animals with complete NPH lesions. However, many cells were identified that fired in bursts unrelated to the animals' directional heading and were similar to cells seen in previous studies that damaged vestibular-associated areas. Some animals with significant but incomplete lesions of the NPH had HD cells that were stable under normal conditions, but were unstable under conditions designed to minimize the use of external cues. These results support the hypothesis that the NPH, beyond its traditional oculomotor function, plays a critical role in conveying vestibular-related information to the HD circuit. PMID:25673848

  15. The location of protein S8 and surrounding elements of 16S rRNA in the 70S ribosome from combined use of directed hydroxyl radical probing and X-ray crystallography.

    PubMed Central

    Lancaster, L; Culver, G M; Yusupova, G Z; Cate, J H; Yusupov, M M; Noller, H F

    2000-01-01

    Ribosomal protein S8, which is essential for the assembly of the central domain of 16S rRNA, is one of the most thoroughly studied RNA-binding proteins. To map its surrounding RNA in the ribosome, we carried out directed hydroxyl radical probing of 16S rRNA using Fe(II) tethered to nine different positions on the surface of protein S8 in 70S ribosomes. Hydroxyl radical-induced cleavage was observed near the classical S8-binding site in the 620 stem, and flanking the other S8-footprinted regions of the central domain at the three-helix junction near position 650 and the 825 and 860 stems. In addition, cleavage near the 5' terminus of 16S rRNA, in the 300 region of its 5' domain, and in the 1070 region of its 3'-major domain provide information about the proximity to S8 of RNA elements not directly involved in its binding. These data, along with previous footprinting and crosslinking results, allowed positioning of protein S8 and its surrounding RNA elements in a 7.8-A map of the Thermus thermophilus 70S ribosome. The resulting model is in close agreement with the extensive body of data from previous studies using protein-protein and protein-RNA crosslinking, chemical and enzymatic footprinting, and genetics. PMID:10836793

  16. Dynamics of Radical-Mediated Enzyme Catalyses

    NASA Astrophysics Data System (ADS)

    Warncke, Kurt

    1997-11-01

    An emergent class of enzymes harnesses the extreme reactivity of electron-deficient free radical species to perform some of the most difficult reactions in biology. The regio- and stereo-selectivity achieved by these enzymes defies long-held ideas that radical reactions are non-specific. The common primary step in these catalyses is metal- or metallocenter-assisted generation of an electron-deficient organic "initiator radical". The initiator radical abstracts a hydrogen atom from the substrate, opening a new reaction channel for rearrangement to the product. Our aim is to elucidate the detailed molecular mechanisms of the radical pair separation and radical rearrangement steps. Radical pair separation and substrate radical rearrangement are tracked by using time-resolved (10-7 to 10-3 s) techniques of pulsed-electron paramagnetic resonance spectroscopy (FT-EPR, ESEEM). Synchronous time-evolution of the reactions is attained by triggering with a visible laser pulse. Transient non-Boltzmann population of the states of the spin-coupled systems, and resultant electron spin polarization, facilitates study at or near room temperature under conditions where the enzymes are operative. The systems examined include ethanolamine deaminase, a vitamin B12 coenzyme-dependent enzyme, ribonucleotide reductase and photosynthetic reaction centers. The electronic and nuclear structural and kinetic information obtained from the pulsed-EPR studies is used to address how the initiator radicals are stabilized against deleterious recombination with the metal, and to distinguish the participation of concerted versus sequential rearrangement pathways.

  17. Structural Characterization of Hydroxyl Radical Adducts in Aqueous Media

    NASA Astrophysics Data System (ADS)

    Janik, Ireneusz; Tripathi, G. N. R.

    2015-06-01

    The oxidation by the hydroxyl (OH) radical is one of the most widely studied reactions because of its central role in chemistry, biology, organic synthesis, and photocatalysis in aqueous environments, wastewater treatment, and numerous other chemical processes. Although the redox potential of OH is very high, direct electron transfer (ET) is rarely observed. If it happens, it mostly proceeds through the formation of elusive OH adduct intermediate which facilitates ET and formation of hydroxide anion. Using time resolved resonance Raman technique we structurally characterized variety of OH adducts to sulfur containing organic compounds, halide ions as well as some metal cations. The bond between oxygen of OH radical and the atom of oxidized molecule differs depending on the nature of solute that OH radical reacts with. For most of sulfur containing organics, as well as halide and pseudo-halide ions, our observation suggested that this bond has two-center three-electron character. For several metal aqua ions studied, the nature of the bond depends on type of the cation being oxidized. Discussion on spectral parameters of all studied hydroxyl radical adducts as well as the role solvent plays in their stabilization will be presented.

  18. The stability of Taylor bubbles in large-diameter tubes: direct numerical simulations

    NASA Astrophysics Data System (ADS)

    Dhanjal, Amanjalot; Saravan-Butler, Maya; Smith, Sydney; Yang, Junfeng; Matar, Omar

    2015-11-01

    Slug flow corresponds to intermittent Taylor bubbles and liquid slugs, and is widely observed in the oil-and-gas industry. The fluctuating flow rate caused by Taylor bubbles is problematical; thus, the destabilisation of this regime would be beneficial. To gain better understanding of this regime in vertical tubes, three-dimensional CFD simulations of Taylor air bubble rise in initially stagnant water and progressively larger diameter tubes, are carried out. Tubes with diameters in the range of 0.032m-0.290m and a height of 2m are considered. The topology of the Taylor bubbles and their rise velocity are predicted and validated against experimental results. Our results suggest that the wake of leading bubbles plays a key role in the deformation and break-up of trailing bubbles. Motivated by these results, the effect of bubble separation distance, and aspect ratio, on bubble stability and the slug flow regime is investigated. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.

  19. Direct measurement of human ankle stiffness during quiet standing: the intrinsic mechanical stiffness is insufficient for stability

    PubMed Central

    Loram, Ian D; Lakie, Martin

    2002-01-01

    During quiet standing the human ‘inverted pendulum’ sways irregularly. In previous work where subjects balanced a real inverted pendulum, we investigated what contribution the intrinsic mechanical ankle stiffness makes to achieve stability. Using the results of a plausible model, we suggested that intrinsic ankle stiffness is inadequate for providing stability. Here, using a piezo-electric translator we applied small, unobtrusive mechanical perturbations to the foot while the subject was standing freely. These short duration perturbations had a similar size and velocity to movements which occur naturally during quiet standing, and they produced no evidence of any stretch reflex response in soleus, or gastrocnemius. Direct measurement confirms our earlier conclusion; intrinsic ankle stiffness is not quite sufficient to stabilise the body or pendulum. On average the directly determined intrinsic stiffness is 91 ± 23 % (mean ± s.d.) of that necessary to provide minimal stabilisation. The stiffness was substantially constant, increasing only slightly with ankle torque. This stiffness cannot be neurally regulated in quiet standing. Thus we attribute this stiffness to the foot, Achilles’ tendon and aponeurosis rather than the activated calf muscle fibres. Our measurements suggest that the triceps surae muscles maintain balance via a spring-like element which is itself too compliant to guarantee stability. The implication is that the brain cannot set ankle stiffness and then ignore the control task because additional modulation of torque is required to maintain balance. We suggest that the triceps surae muscles maintain balance by predictively controlling the proximal offset of the spring-like element in a ballistic-like manner. PMID:12482906

  20. Radical Behaviorism and Buddhism: Complementarities and Conflicts

    ERIC Educational Resources Information Center

    Diller, James W.; Lattal, Kennon A.

    2008-01-01

    Comparisons have been made between Buddhism and the philosophy of science in general, but there have been only a few attempts to draw comparisons directly with the philosophy of radical behaviorism. The present review therefore considers heretofore unconsidered points of comparison between Buddhism and radical behaviorism in terms of their…

  1. VORSTAB: A computer program for calculating lateral-directional stability derivatives with vortex flow effect

    NASA Technical Reports Server (NTRS)

    Lan, C. Edward

    1985-01-01

    A computer program based on the Quasi-Vortex-Lattice Method of Lan is presented for calculating longitudinal and lateral-directional aerodynamic characteristics of nonplanar wing-body combination. The method is based on the assumption of inviscid subsonic flow. Both attached and vortex-separated flows are treated. For the vortex-separated flow, the calculation is based on the method of suction analogy. The effect of vortex breakdown is accounted for by an empirical method. A summary of the theoretical method, program capabilities, input format, output variables and program job control set-up are described. Three test cases are presented as guides for potential users of the code.

  2. Deposition and properties of yttria-stabilized zirconia thin films using reactive direct current magnetron sputtering

    SciTech Connect

    Thiele, E.S.; Wang, L.S.; Mason, T.O.; Barnett, S.A. . Dept. of Materials Science Northwestern Univ., Evanston, IL . Materials Research Center)

    1991-11-01

    Yttria-stabilized zirconia (YSZ) thin films were deposited by reactive magnetron sputter deposition from a composite Zr--Y target in Ar--O{sub 2} mixtures. Hysteresis was observed as a function of oxygen flow rate {ital f}. For a discharge current of 0.4 A and a total pressure {ital P} of 5 mTorr, for example, the target oxidized at {ital f}{gt}2.3 ml/min, with the reverse transition from an oxidized to a metallic target surface occurring at 1.95 ml/min. The deposition rate was 2.7 {mu}m/h in the metallic mode and 0.1 {mu}m/h in the oxide mode. Fully oxidized (Y{sub 2}O{sub 3}){sub 0.1}(ZrO{sub 2}){sub 0.9} was obtained for {ital f}{gt}2.0 ml/min, even in the metallic mode. While films deposited with {ital P}=3--20 mTorr were continuous, for {ital P}{gt}20 mTorr crazing was apparent as expected for a ceramic film in a tensile stress state. For {ital P}{lt}3 mTorr, the films delaminated due to excessive compressive stress. X-ray diffraction and electron microscopy results showed that the films were polycrystalline cubic YSZ with a columnar structure and an average grain diameter of 15 nm. Fully dense films were obtained at a deposition temperature of 350 {degree}C. Temperature-dependent impedance spectroscopy analysis of YSZ films with Ag electrodes showed that the oxygen ion conductivity was as expected for YSZ.

  3. Direct Observation of Transient Surface Species during Ge Nanowire Growth and Their Influence on Growth Stability.

    PubMed

    Sivaram, Saujan V; Shin, Naechul; Chou, Li-Wei; Filler, Michael A

    2015-08-12

    Surface adsorbates are well-established choreographers of material synthesis, but the presence and impact of these short-lived species on semiconductor nanowire growth are largely unknown. Here, we use infrared spectroscopy to directly observe surface adsorbates, hydrogen atoms and methyl groups, chemisorbed to the nanowire sidewall and show they are essential for the stable growth of Ge nanowires via the vapor-liquid-solid mechanism. We quantitatively determine the surface coverage of hydrogen atoms during nanowire growth by comparing ν(Ge-H) absorption bands from operando measurements (i.e., during growth) to those after saturating the nanowire sidewall with hydrogen atoms. This method provides sub-monolayer chemical information at relevant reaction conditions while accounting for the heterogeneity of sidewall surface sites and their evolution during elongation. Our findings demonstrate that changes to surface bonding are critical to understand Ge nanowire synthesis and provide new guidelines for rationally selecting catalysts, forming heterostructures, and controlling dopant profiles. PMID:26147949

  4. Selective Radical-Radical Cross-Couplings: Design of a Formal β-Mannich Reaction.

    PubMed

    Jeffrey, Jenna L; Petronijević, Filip R; MacMillan, David W C

    2015-07-01

    A direct β-coupling of cyclic ketones with imines has been accomplished via the synergistic combination of photoredox catalysis and organocatalysis. Transient β-enaminyl radicals derived from ketones via enamine and oxidative photoredox catalysis readily combine with persistent α-amino radicals in a highly selective hetero radical-radical coupling. This novel pathway to γ-aminoketones is predicated upon the use of DABCO as both a base and an electron transfer agent. This protocol also formally allows for the direct synthesis of β-Mannich products via a chemoselective three-component coupling of aryl aldehydes, amines, and ketones. PMID:26075347

  5. TRIM32 modulates pluripotency entry and exit by directly regulating Oct4 stability.

    PubMed

    Bahnassawy, Lamia'a; Perumal, Thanneer M; Gonzalez-Cano, Laura; Hillje, Anna-Lena; Taher, Leila; Makalowski, Wojciech; Suzuki, Yutaka; Fuellen, Georg; del Sol, Antonio; Schwamborn, Jens Christian

    2015-01-01

    Induced pluripotent stem cells (iPSCs) have revolutionized the world of regenerative medicine; nevertheless, the exact molecular mechanisms underlying their generation and differentiation remain elusive. Here, we investigated the role of the cell fate determinant TRIM32 in modulating such processes. TRIM32 is essential for the induction of neuronal differentiation of neural stem cells by poly-ubiquitinating cMyc to target it for degradation resulting in inhibition of cell proliferation. To elucidate the role of TRIM32 in regulating somatic cell reprogramming we analysed the capacity of TRIM32-knock-out mouse embryonic fibroblasts (MEFs) in generating iPSC colonies. TRIM32 knock-out MEFs produced a higher number of iPSC colonies indicating a role for TRIM32 in inhibiting this cellular transition. Further characterization of the generated iPSCs indicated that the TRIM32 knock-out iPSCs show perturbed differentiation kinetics. Additionally, mathematical modelling of global gene expression data revealed that during differentiation an Oct4 centred network in the wild-type cells is replaced by an E2F1 centred network in the TRIM32 deficient cells. We show here that this might be caused by a TRIM32-dependent downregulation of Oct4. In summary, the data presented here reveal that TRIM32 directly regulates at least two of the four Yamanaka Factors (cMyc and Oct4), to modulate cell fate transitions. PMID:26307407

  6. TRIM32 modulates pluripotency entry and exit by directly regulating Oct4 stability

    PubMed Central

    Bahnassawy, Lamia’a; Perumal, Thanneer M.; Gonzalez-Cano, Laura; Hillje, Anna-Lena; Taher, Leila; Makalowski, Wojciech; Suzuki, Yutaka; Fuellen, Georg; Sol, Antonio del; Schwamborn, Jens Christian

    2015-01-01

    Induced pluripotent stem cells (iPSCs) have revolutionized the world of regenerative medicine; nevertheless, the exact molecular mechanisms underlying their generation and differentiation remain elusive. Here, we investigated the role of the cell fate determinant TRIM32 in modulating such processes. TRIM32 is essential for the induction of neuronal differentiation of neural stem cells by poly-ubiquitinating cMyc to target it for degradation resulting in inhibition of cell proliferation. To elucidate the role of TRIM32 in regulating somatic cell reprogramming we analysed the capacity of TRIM32-knock-out mouse embryonic fibroblasts (MEFs) in generating iPSC colonies. TRIM32 knock-out MEFs produced a higher number of iPSC colonies indicating a role for TRIM32 in inhibiting this cellular transition. Further characterization of the generated iPSCs indicated that the TRIM32 knock-out iPSCs show perturbed differentiation kinetics. Additionally, mathematical modelling of global gene expression data revealed that during differentiation an Oct4 centred network in the wild-type cells is replaced by an E2F1 centred network in the TRIM32 deficient cells. We show here that this might be caused by a TRIM32-dependent downregulation of Oct4. In summary, the data presented here reveal that TRIM32 directly regulates at least two of the four Yamanaka Factors (cMyc and Oct4), to modulate cell fate transitions. PMID:26307407

  7. Effect of gas-containing microspheres and echo contrast agents on free radical formation by ultrasound.

    PubMed

    Kondo, T; Misík, V; Riesz, P

    1998-09-01

    Stabilized microbubbles (microspheres) are widely used to enhance the contrast of ultrasound imaging. Our data provide direct evidence that the contrast agents, Levovist, PVC-AN (polyvinylidene chloride-acrylonitryl copolymer), and Albunex (compared to 5% human albumin), at concentrations comparable to those used for ultrasound imaging, enhance H2O2 production (through the superoxide-dependent pathway) in air-saturated aqueous solutions exposed to 47 kHz ultrasound above the cavitation threshold. These agents also act as scavengers of .H atoms and .OH radicals, thus lowering H2O2 formation (by recombination of .OH radicals) in argon-saturated solutions. EPR spin trapping also reveals that secondary radicals derived from the contrast agents are produced by reactions with .H and .OH which are formed by pyrolysis of water inside cavitation bubbles. In addition, the contrast agents themselves undergo pyrolysis reactions in the cavitation bubbles as demonstrated by formation of methyl radicals. Possible deleterious consequences of the formation of sonochemical intermediates may have to be assessed, particularly since some of the echo contrast agents have been shown to lower the cavitation threshold of diagnostic ultrasound. Unlike the microspheres formed from organic molecules, inorganic microspheres, Eccospheres, because of their stability and inert nature with respect to participation in free radical processes, appear to be suitable tools for enhancing the yields of aqueous sonochemical reactions. PMID:9741598

  8. Radical prostatectomy - discharge

    MedlinePlus

    ... prostatectomy - discharge; Laparoscopic radical prostatectomy - discharge; LRP - discharge; Robotic-assisted laparoscopic prostatectomy - discharge ; RALP - discharge; Pelvic lymphadenectomy - ...

  9. Direct force measurements reveal that protein Tau confers short-range attractions and isoform-dependent steric stabilization to microtubules

    PubMed Central

    Chung, Peter J.; Choi, Myung Chul; Miller, Herbert P.; Feinstein, H. Eric; Raviv, Uri; Li, Youli; Wilson, Leslie; Feinstein, Stuart C.; Safinya, Cyrus R.

    2015-01-01

    Microtubules (MTs) are hollow cytoskeletal filaments assembled from αβ-tubulin heterodimers. Tau, an unstructured protein found in neuronal axons, binds to MTs and regulates their dynamics. Aberrant Tau behavior is associated with neurodegenerative dementias, including Alzheimer’s. Here, we report on a direct force measurement between paclitaxel-stabilized MTs coated with distinct Tau isoforms by synchrotron small-angle X-ray scattering (SAXS) of MT-Tau mixtures under osmotic pressure (P). In going from bare MTs to MTs with Tau coverage near the physiological submonolayer regime (Tau/tubulin-dimer molar ratio; ΦTau = 1/10), isoforms with longer N-terminal tails (NTTs) sterically stabilized MTs, preventing bundling up to PB ∼ 10,000–20,000 Pa, an order of magnitude larger than bare MTs. Tau with short NTTs showed little additional effect in suppressing the bundling pressure (PB ∼ 1,000–2,000 Pa) over the same range. Remarkably, the abrupt increase in PB observed for longer isoforms suggests a mushroom to brush transition occurring at 1/13 < ΦTau < 1/10, which corresponds to MT-bound Tau with NTTs that are considerably more extended than SAXS data for Tau in solution indicate. Modeling of Tau-mediated MT–MT interactions supports the hypothesis that longer NTTs transition to a polyelectrolyte brush at higher coverages. Higher pressures resulted in isoform-independent irreversible bundling because the polyampholytic nature of Tau leads to short-range attractions. These findings suggest an isoform-dependent biological role for regulation by Tau, with longer isoforms conferring MT steric stabilization against aggregation either with other biomacromolecules or into tight bundles, preventing loss of function in the crowded axon environment. PMID:26542680

  10. Site-directed mutagenesis of tobacco anionic peroxidase: Effect of additional aromatic amino acids on stability and activity.

    PubMed

    Poloznikov, A A; Zakharova, G S; Chubar, T A; Hushpulian, D M; Tishkov, V I; Gazaryan, I G

    2015-08-01

    Tobacco anionic peroxidase (TOP) is known to effectively catalyze luminol oxidation without enhancers, in contrast to horseradish peroxidase (HRP). To pursue structure-activity relationship studies for TOP, two amino acids have been chosen for mutation, namely Thr151, close to the heme plane, and Phe140 at the entrance to the active site pocket. Three mutant forms TOP F140Y, T151W and F140Y/T151W have been expressed in Escherichia coli, and reactivated to yield active enzymes. Single-point mutations introducing additional aromatic amino acid residues at the surface of TOP exhibit a significant effect on the enzyme catalytic activity and stability as judged by the results of steady-state and transient kinetics studies. TOP T151W is up to 4-fold more active towards a number of aromatic substrates including luminol, whereas TOP F140Y is 2-fold more stable against thermal inactivation and 8-fold more stable in the reaction course. These steady-state observations have been rationalized with the help of transient kinetic studies on the enzyme reaction with hydrogen peroxide in a single turnover regime. The stopped-flow data reveal (a) an increased stability of F140Y Compound I towards hydrogen peroxide, and thus, a higher operational stability as compared to the wild-type enzyme, and (b) a lesser leakage of oxidative equivalents from TOP T151W Compound I resulting in the increased catalytic activity. The results obtained show that TOP unique properties can be further improved for practical applications by site-directed mutagenesis. PMID:25957835

  11. Sunlight and free radicals

    NASA Astrophysics Data System (ADS)

    Tidwell, Thomas

    2013-08-01

    Thomas Tidwell reflects on the overlooked -- but prescient -- proposal by the British chemists Arthur Downes and Thomas Blunt for photochemical free-radical formation, decades before Moses Gomberg launched the field of radical chemistry by preparing triphenylmethyl, the first stable organic radical.

  12. Uniformity of spherical shock wave dynamically stabilized by two successive laser profiles in direct-drive inertial confinement fusion implosions

    SciTech Connect

    Temporal, M.; Canaud, B.; Garbett, W. J.; Ramis, R.

    2015-10-15

    The implosion uniformity of a directly driven spherical inertial confinement fusion capsule is considered within the context of the Laser Mégajoule configuration. Two-dimensional (2D) hydrodynamic simulations have been performed assuming irradiation with two laser beam cones located at 49° and 131° with respect to the axis of symmetry. The laser energy deposition causes an inward shock wave whose surface is tracked in time, providing the time evolution of its non-uniformity. The illumination model has been used to optimize the laser intensity profiles used as input in the 2D hydro-calculations. It is found that a single stationary laser profile does not maintain a uniform shock front over time. To overcome this drawback, it is proposed to use two laser profiles acting successively in time, in order to dynamically stabilize the non-uniformity of the shock front.

  13. Sub-kilohertz linewidth narrowing of a mid-infrared optical parametric oscillator idler frequency by direct cavity stabilization.

    PubMed

    Ricciardi, I; Mosca, S; Parisi, M; Maddaloni, P; Santamaria, L; De Natale, P; De Rosa, M

    2015-10-15

    We stabilize the idler frequency of a singly resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-Perot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10(3)  Hz(2)/Hz is reached on average, with a Gaussian linewidth of 920 Hz over 100 ms, which reveals the potential for reaching spectral purity down to the hertz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance. PMID:26469609

  14. Uniformity of spherical shock wave dynamically stabilized by two successive laser profiles in direct-drive inertial confinement fusion implosions

    NASA Astrophysics Data System (ADS)

    Temporal, M.; Canaud, B.; Garbett, W. J.; Ramis, R.

    2015-10-01

    The implosion uniformity of a directly driven spherical inertial confinement fusion capsule is considered within the context of the Laser Mégajoule configuration. Two-dimensional (2D) hydrodynamic simulations have been performed assuming irradiation with two laser beam cones located at 49° and 131° with respect to the axis of symmetry. The laser energy deposition causes an inward shock wave whose surface is tracked in time, providing the time evolution of its non-uniformity. The illumination model has been used to optimize the laser intensity profiles used as input in the 2D hydro-calculations. It is found that a single stationary laser profile does not maintain a uniform shock front over time. To overcome this drawback, it is proposed to use two laser profiles acting successively in time, in order to dynamically stabilize the non-uniformity of the shock front.

  15. On the time behaviour of the concentration of pyrazinium radical cations in the early stage of the Maillard reaction

    NASA Astrophysics Data System (ADS)

    Stoesser, Reinhard; Klein, Jeannette; Peschke, Simone; Zehl, Andrea; Cämmerer, Bettina; Kroh, Lothar W.

    2007-08-01

    During the early stage of the Maillard reaction pyrazinium radical cations were detected by ESR within the reaction system D-glucose/glycine. The spectra were characterized by completely resolved hyperfine structure. The partial pressure of oxygen and the radical concentrations were measured directly in the reaction mixture by ESR using solutions of the spin probe TEMPOL and of DPPH, respectively. There are quantitative and qualitative relations of the actual concentration of the radical ions to the partial pressure of oxygen, the temperature-time regime and the mechanical mixing of the reaction system. These macroscopic parameters significantly affect both the induction period and the velocity of the time-dependent formation of free radicals. From in situ variations of p(O 2) and p(Ar) including the connected mixing effects caused by the passing the gases through the reaction mixture, steric and chemical effects of the stabilization of the radical ions were established. The determination of suitable and relevant conditions for stabilization and subsequent radical reactions contributes to the elucidation of the macroscopically known antioxidant activity of Maillard products.

  16. Vinculin directly binds zonula occludens-1 and is essential for stabilizing connexin-43-containing gap junctions in cardiac myocytes

    PubMed Central

    Zemljic-Harpf, Alice E.; Godoy, Joseph C.; Platoshyn, Oleksandr; Asfaw, Elizabeth K.; Busija, Anna R.; Domenighetti, Andrea A.; Ross, Robert S.

    2014-01-01

    ABSTRACT Vinculin (Vcl) links actin filaments to integrin- and cadherin-based cellular junctions. Zonula occludens-1 (ZO-1, also known as TJP1) binds connexin-43 (Cx43, also known as GJA1), cadherin and actin. Vcl and ZO-1 anchor the actin cytoskeleton to the sarcolemma. Given that loss of Vcl from cardiomyocytes causes maldistribution of Cx43 and predisposes cardiomyocyte-specific Vcl-knockout mice with preserved heart function to arrhythmia and sudden death, we hypothesized that Vcl and ZO-1 interact and that loss of this interaction destabilizes gap junctions. We found that Vcl, Cx43 and ZO-1 colocalized at the intercalated disc. Loss of cardiomyocyte Vcl caused parallel loss of ZO-1 from intercalated dics. Vcl co-immunoprecipitated Cx43 and ZO-1, and directly bound ZO-1 in yeast two-hybrid studies. Excision of the Vcl gene in neonatal mouse cardiomyocytes caused a reduction in the amount of Vcl mRNA transcript and protein expression leading to (1) decreased protein expression of Cx43, ZO-1, talin, and β1D-integrin, (2) reduced PI3K activation, (3) increased activation of Akt, Erk1 and Erk2, and (4) cardiomyocyte necrosis. In summary, this is the first study showing a direct interaction between Vcl and ZO-1 and illustrates how Vcl plays a crucial role in stabilizing gap junctions and myocyte integrity. PMID:24413171

  17. Slow oscillating transcranial direct current stimulation during sleep has a sleep-stabilizing effect in chronic insomnia: a pilot study.

    PubMed

    Saebipour, Mohammad R; Joghataei, Mohammad T; Yoonessi, Ali; Sadeghniiat-Haghighi, Khosro; Khalighinejad, Nima; Khademi, Soroush

    2015-10-01

    Recent evidence suggests that lack of slow-wave activity may play a fundamental role in the pathogenesis of insomnia. Pharmacological approaches and brain stimulation techniques have recently offered solutions for increasing slow-wave activity during sleep. We used slow (0.75 Hz) oscillatory transcranial direct current stimulation during stage 2 of non-rapid eye movement sleeping insomnia patients for resonating their brain waves to the frequency of sleep slow-wave. Six patients diagnosed with either sleep maintenance or non-restorative sleep insomnia entered the study. After 1 night of adaptation and 1 night of baseline polysomnography, patients randomly received sham or real stimulation on the third and fourth night of the experiment. Our preliminary results show that after termination of stimulations (sham or real), slow oscillatory transcranial direct current stimulation increased the duration of stage 3 of non-rapid eye movement sleep by 33 ± 26 min (P = 0.026), and decreased stage 1 of non-rapid eye movement sleep duration by 22 ± 17.7 min (P = 0.028), compared with sham. Slow oscillatory transcranial direct current stimulation decreased stage 1 of non-rapid eye movement sleep and wake time after sleep-onset durations, together, by 55.4 ± 51 min (P = 0.045). Slow oscillatory transcranial direct current stimulation also increased sleep efficiency by 9 ± 7% (P = 0.026), and probability of transition from stage 2 to stage 3 of non-rapid eye movement sleep by 20 ± 17.8% (P = 0.04). Meanwhile, slow oscillatory transcranial direct current stimulation decreased transitions from stage 2 of non-rapid eye movement sleep to wake by 12 ± 6.7% (P = 0.007). Our preliminary results suggest a sleep-stabilizing role for the intervention, which may mimic the effect of sleep slow-wave-enhancing drugs. PMID:26014344

  18. Contemporary Radical Prostatectomy

    PubMed Central

    Fu, Qiang; Moul, Judd W.; Sun, Leon

    2011-01-01

    Purpose. Patients diagnosed with clinically localized prostate cancer have more surgical treatment options than in the past. This paper focuses on the procedures' oncological or functional outcomes and perioperative morbidities of radical retropubic prostatectomy, radical perineal prostatectomy, and robotic-assisted laparoscopic radical prostatectomy. Materials and Methods. A MEDLINE/PubMed search of the literature on radical prostatectomy and other new management options was performed. Results. Compared to the open procedures, robotic-assisted radical prostatectomy has no confirmed significant difference in most literatures besides less blood loss and blood transfusion. Nerve sparing is a safe means of preserving potency on well-selected patients undergoing radical prostatectomy. Positive surgical margin rates of radical prostatectomy affect the recurrence and survival of prostate cancer. The urinary and sexual function outcomes have been vastly improved. Neoadjuvant treatment only affects the rate of positive surgical margin. Adjuvant therapy can delay and reduce the risk of recurrence and improve the survival of the high risk prostate cancer. Conclusions. For the majority of patients with organ-confined prostate cancer, radical prostatectomy remains a most effective approach. Radical perineal prostatectomy remains a viable approach for patients with morbid obesity, prior pelvic surgery, or prior pelvic radiation. Robot-assisted laparoscopic prostatectomy (RALP) has become popular among surgeons but has not yet become the firmly established standard of care. Long-term data have confirmed the efficacy of radical retropubic prostatectomy with disease control rates and cancer-specific survival rates. PMID:22110994

  19. Bacterial Fucose-Rich Polysaccharide Stabilizes MAPK-Mediated Nrf2/Keap1 Signaling by Directly Scavenging Reactive Oxygen Species during Hydrogen Peroxide-Induced Apoptosis of Human Lung Fibroblast Cells

    PubMed Central

    Roy Chowdhury, Sougata; Sinha, Tridib Kumar; Sen, Ramkrishna; Basak, Ratan Kumar; Adhikari, Basudam; Bhattacharyya, Arindam

    2014-01-01

    Continuous free radical assault upsets cellular homeostasis and dysregulates associated signaling pathways to promote stress-induced cell death. In spite of the continuous development and implementation of effective therapeutic strategies, limitations in treatments for stress-induced toxicities remain. The purpose of the present study was to determine the potential therapeutic efficacy of bacterial fucose polysaccharides against hydrogen peroxide (H2O2)-induced stress in human lung fibroblast (WI38) cells and to understand the associated molecular mechanisms. In two different fermentation processes, Bacillus megaterium RB-05 biosynthesized two non-identical fucose polysaccharides; of these, the polysaccharide having a high-fucose content (∼42%) conferred the maximum free radical scavenging efficiency in vitro. Structural characterizations of the purified polysaccharides were performed using HPLC, GC-MS, and 1H/13C/2D-COSY NMR. H2O2 (300 µM) insult to WI38 cells showed anti-proliferative effects by inducing intracellular reactive oxygen species (ROS) and by disrupting mitochondrial membrane permeability, followed by apoptosis. The polysaccharide (250 µg/mL) attenuated the cell death process by directly scavenging intracellular ROS rather than activating endogenous antioxidant enzymes. This process encompasses inhibition of caspase-9/3/7, a decrease in the ratio of Bax/Bcl2, relocalization of translocated Bax and cytochrome c, upregulation of anti-apoptotic members of the Bcl2 family and a decrease in the phosphorylation of MAPKs (mitogen activated protein kinases). Furthermore, cellular homeostasis was re-established via stabilization of MAPK-mediated Nrf2/Keap1 signaling and transcription of downstream cytoprotective genes. This molecular study uniquely introduces a fucose-rich bacterial polysaccharide as a potential inhibitor of H2O2-induced stress and toxicities. PMID:25412177

  20. Bacterial fucose-rich polysaccharide stabilizes MAPK-mediated Nrf2/Keap1 signaling by directly scavenging reactive oxygen species during hydrogen peroxide-induced apoptosis of human lung fibroblast cells.

    PubMed

    Roy Chowdhury, Sougata; Sengupta, Suman; Biswas, Subir; Sinha, Tridib Kumar; Sen, Ramkrishna; Basak, Ratan Kumar; Adhikari, Basudam; Bhattacharyya, Arindam

    2014-01-01

    Continuous free radical assault upsets cellular homeostasis and dysregulates associated signaling pathways to promote stress-induced cell death. In spite of the continuous development and implementation of effective therapeutic strategies, limitations in treatments for stress-induced toxicities remain. The purpose of the present study was to determine the potential therapeutic efficacy of bacterial fucose polysaccharides against hydrogen peroxide (H2O2)-induced stress in human lung fibroblast (WI38) cells and to understand the associated molecular mechanisms. In two different fermentation processes, Bacillus megaterium RB-05 biosynthesized two non-identical fucose polysaccharides; of these, the polysaccharide having a high-fucose content (∼ 42%) conferred the maximum free radical scavenging efficiency in vitro. Structural characterizations of the purified polysaccharides were performed using HPLC, GC-MS, and (1)H/(13)C/2D-COSY NMR. H2O2 (300 µM) insult to WI38 cells showed anti-proliferative effects by inducing intracellular reactive oxygen species (ROS) and by disrupting mitochondrial membrane permeability, followed by apoptosis. The polysaccharide (250 µg/mL) attenuated the cell death process by directly scavenging intracellular ROS rather than activating endogenous antioxidant enzymes. This process encompasses inhibition of caspase-9/3/7, a decrease in the ratio of Bax/Bcl2, relocalization of translocated Bax and cytochrome c, upregulation of anti-apoptotic members of the Bcl2 family and a decrease in the phosphorylation of MAPKs (mitogen activated protein kinases). Furthermore, cellular homeostasis was re-established via stabilization of MAPK-mediated Nrf2/Keap1 signaling and transcription of downstream cytoprotective genes. This molecular study uniquely introduces a fucose-rich bacterial polysaccharide as a potential inhibitor of H2O2-induced stress and toxicities. PMID:25412177

  1. A Mechanochemical Switch to Control Radical Intermediates

    PubMed Central

    2015-01-01

    B12-dependent enzymes employ radical species with exceptional prowess to catalyze some of the most chemically challenging, thermodynamically unfavorable reactions. However, dealing with highly reactive intermediates is an extremely demanding task, requiring sophisticated control strategies to prevent unwanted side reactions. Using hybrid quantum mechanical/molecular mechanical simulations, we follow the full catalytic cycle of an AdoB12-dependent enzyme and present the details of a mechanism that utilizes a highly effective mechanochemical switch. When the switch is “off”, the 5′-deoxyadenosyl radical moiety is stabilized by releasing the internal strain of an enzyme-imposed conformation. Turning the switch “on,” the enzyme environment becomes the driving force to impose a distinct conformation of the 5′-deoxyadenosyl radical to avoid deleterious radical transfer. This mechanochemical switch illustrates the elaborate way in which enzymes attain selectivity of extremely chemically challenging reactions. PMID:24846280

  2. A mechanochemical switch to control radical intermediates.

    PubMed

    Brunk, Elizabeth; Kellett, Whitney F; Richards, Nigel G J; Rothlisberger, Ursula

    2014-06-17

    B₁₂-dependent enzymes employ radical species with exceptional prowess to catalyze some of the most chemically challenging, thermodynamically unfavorable reactions. However, dealing with highly reactive intermediates is an extremely demanding task, requiring sophisticated control strategies to prevent unwanted side reactions. Using hybrid quantum mechanical/molecular mechanical simulations, we follow the full catalytic cycle of an AdoB₁₂-dependent enzyme and present the details of a mechanism that utilizes a highly effective mechanochemical switch. When the switch is "off", the 5'-deoxyadenosyl radical moiety is stabilized by releasing the internal strain of an enzyme-imposed conformation. Turning the switch "on," the enzyme environment becomes the driving force to impose a distinct conformation of the 5'-deoxyadenosyl radical to avoid deleterious radical transfer. This mechanochemical switch illustrates the elaborate way in which enzymes attain selectivity of extremely chemically challenging reactions. PMID:24846280

  3. Identifying the tobacco related free radicals by UPCC-QTOF-MS with radical trapping method in mainstream cigarette smoke.

    PubMed

    Wang, Ying; Liu, Misha; Zhu, Yingjing; Cheng, Kuan; Da Wu; Liu, Baizhan; Li, Fengting

    2016-11-01

    Tobacco related free radicals (TFRs) in the cigarette smoke are specific classes of hazardous compounds that merit concern. In this study, we developed a hybrid method to identify TFRs directly based on ultra-performance convergence chromatography with a quadrupole time-of-flight mass spectrometry (UPCC-QTOF MS) combined spin trapping technique. The short-lived TFRs were stabilized successfully in situ through spin trapping procedure and UPCC was applied to facilitate efficient separation of complex derivative products. Coupling of orthogonal partial least squares discriminant analysis (OPLS-DA), UPCC-QTOF MS system enabled us to identify specific potential TFRs with exact chemical formula. Moreover, computational stimulations have been carried out to evaluate the optimized stability of TFRs. This work is a successful demonstration for the application of an advanced hyphenated technique for separation of TFRs with short detection time (less than 7min) and high throughput. PMID:27591593

  4. Measurement of Flying Qualities of a Dehavilland Mosquito F-8 Airplane (AAF No. 43-334960) I: Lateral and Directional Stability and Control Characteristics

    NASA Technical Reports Server (NTRS)

    Gray, W.E.; Talmage, D.B.; Crane, H.L.

    1945-01-01

    The data presented have no bearing on performance characteristics of airplane, which were considered exceptionally good in previous tests. Some of the undesirable features of lateral and directional stability and control characteristics of the F-8 are listed. Directional stability, with rudder fixed, did not sufficiently restrict aileron yaw; rudder control was inadequate during take-off and landing, and was insufficient to fly airplane with one engine; in clean condition, power of ailerons was slightly below minimum value specified; it was difficult to trim airplane in rough air.

  5. A computer program for calculating symmetrical aerodynamic characteristics and lateral-directional stability derivatives of wing-body combinations with blowing jets

    NASA Technical Reports Server (NTRS)

    Lan, C. E.; Mehrotra, S. C.; Fox, C. H., Jr.

    1978-01-01

    The necessary information for using a computer program to calculate the aerodynamic characteristics under symmetrical flight conditions and the lateral-directional stability derivatives of wing-body combinations with upper-surface-blowing (USB) or over-wing-blowing (OWB) jets are described. The following new features were added to the program: (1) a fuselage of arbitrary body of revolution has been included. The effect of wing-body interference can now be investigated, and (2) all nine lateral-directional stability derivatives can be calculated. The program is written in FORTRAN language and runs on CDC Cyber 175 and Honeywell 66/60 computers.

  6. X-29A Lateral-Directional Stability and Control Derivatives Extracted From High-Angle-of-Attack Flight Data

    NASA Technical Reports Server (NTRS)

    Iliff, Kenneth W.; Wang, Kon-Sheng Charles Wang

    1996-01-01

    The lateral-directional stability and control derivatives of the X-29A number 2 are extracted from flight data over an angle-of-attack range of 4 degrees to 53 degrees using a parameter identification algorithm. The algorithm uses the linearized aircraft equations of motion and a maximum likelihood estimator in the presence of state and measurement noise. State noise is used to model the uncommanded forcing function caused by unsteady aerodynamics over the aircraft at angles of attack above 15 degrees. The results supported the flight-envelope-expansion phase of the X-29A number 2 by helping to update the aerodynamic mathematical model, to improve the real-time simulator, and to revise flight control system laws. Effects of the aircraft high gain flight control system on maneuver quality and the estimated derivatives are also discussed. The derivatives are plotted as functions of angle of attack and compared with the predicted aerodynamic database. Agreement between predicted and flight values is quite good for some derivatives such as the lateral force due to sideslip, the lateral force due to rudder deflection, and the rolling moment due to roll rate. The results also show significant differences in several important derivatives such as the rolling moment due to sideslip, the yawing moment due to sideslip, the yawing moment due to aileron deflection, and the yawing moment due to rudder deflection.

  7. Direct Measurements of the Mechanical Stability of Zinc-Thiolate Bonds in Rubredoxin by Single-Molecule Atomic Force Microscopy

    PubMed Central

    Zheng, Peng; Li, Hongbin

    2011-01-01

    Zinc (Zn) is one of the most abundant metals and is essential for life. Through ligand interactions, often with thiolate from cysteine residues in proteins, Zn can play important structural roles in organizing protein structure and augmenting protein folding and stability. However, it is difficult to separate the contributions of Zn-ligand interactions from those originating from intrinsic protein folding in experimental studies of Zn-containing metalloproteins, which makes the study of Zn-ligand interactions in proteins challenging. Here, we used single-molecule force spectroscopy to directly measure the mechanical rupture force of the Zn-thiolate bond in Zn-rubredoxin. Our results show that considerable force is needed to rupture Zn-thiolate bonds (∼170 pN, which is significantly higher than the force necessary to rupture the coordination bond between Zn and histidines). To our knowledge, our study not only provides new information about Zn-thiolate bonds in rubredoxin, it also opens a new avenue for studying metal-ligand bonds in proteins using single-molecule force spectroscopy. PMID:21943428

  8. Investigation of the active site and the conformational stability of nucleoside diphosphate kinase by site-directed mutagenesis.

    PubMed

    Tepper, A D; Dammann, H; Bominaar, A A; Véron, M

    1994-12-23

    Nucleoside-diphosphate kinase (EC 2.7.4.6) catalyzes phosphate exchange between nucleoside triphosphates and nucleoside diphosphates. Its 17 kDa subunits are highly conserved throughout evolution in both sequence and tertiary structure. Using site-directed mutagenesis we investigated the function of 8 amino acids (Lys16, Tyr56, Arg92, Thr98, Arg109, Asn119, Ser124, and Glu133) that are totally conserved among all nucleoside diphosphate kinases known to date. The mutant proteins all show decreased specific activity and support roles for these residues in catalysis, substrate binding, or both, as was previously proposed on the basis of the x-ray structure (Moréra, S., Lascu, I., Dumas, C., LeBras, G., Briozzo, P., Véron, M., and Janin, J. (1994) Biochemistry 33, 459-467). Furthermore, residues Lys16, Arg109, and Asn 119 were identified to play important roles in conformational stability or subunit interactions. We show that Lys16 and Asn119 form a rigid structure that is important for enzymatic function and that Arg109, known to interact with the phosphate moiety of the substrate, also plays an important role in subunit association. The dual roles of Lys16, Arg109, and Asn119 in both substrate binding and subunit assembly provide further evidence for a functional coupling between catalytic activity and quaternary structure in nucleoside diphosphate kinase. PMID:7798215

  9. Influence of the external torques in the angle between the spin axis and the Sun direction for spin stabilized satellite

    NASA Astrophysics Data System (ADS)

    Motta, G. B.; Zanardi, M. C.

    2015-10-01

    The goal of this paper is the study of the influence of the environmental torques in the angle between the spin axis and the Sun direction (solar aspect angle) for spin stabilized satellite. The theory uses a cylindrical satellite in an illumined orbit, considering the gravity gradient, aerodynamic, solar radiation, residual magnetic and eddy current torques. The mathematic model for each torque is shown. The dynamic equations are represented in a reference system fixed in the satellite and described by spin velocity and the right ascension and declination angles of the spin axis. An analytical solution for the spin velocity and the attitude angles is used to study the behavior of the solar aspect angle. The theory is applied for the real data of the Brazilian Satellite of Data Collection - SCD1 and SCD2. Two approaches are presented. The results agree with the real satellite behavior for specific time simulation. Then the theory has consistency and can be applied to predict the behavior of the solar aspect angle.

  10. Stability-indicating simultaneous determination of paracetamol and three of its related substances using a direct GC/MS method.

    PubMed

    Belal, Tarek; Awad, Tamer; Clark, C Randall

    2009-01-01

    A simple, direct, and selective stability-indicating GC/MS procedure was developed for the simultaneous determination of paracetamol (PR) and three of its related substances: 4-aminophenol (4-AP), acetanilide (AD), and 4'-chloroacetanilide (4-CA). The method involved resolution of the underivatized compounds using a 100% dimethylpolysiloxane (Rtx-1) column, and MS detection was carried out in the electron-impact mode. The four compounds were completely resolved in less than 11 min. The fragmentation pathways for the four compounds were described, and the structures of the major fragment ions peaks were proposed. Quantification of the analytes was based on measuring their peak areas. The reliability and analytical performance of the proposed method including linearity, range, precision, accuracy, and detection and quantification limits were statistically validated. Calibration curves were linear over the ranges 75-500, 25-350, 25-350, and 25-350 microg/mL for PR, 4-AP, AD, and 4-CA, respectively. The proposed method was successfully applied for the determination of PR and its related substances in laboratory-prepared mixtures of different proportions. Also, it was applied for the assay of PR in several commercially available pharmaceutical formulations with recoveries of 98.95-100.76%. PMID:20166578