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Sample records for atom transfer radical

  1. Living atom transfer radical polymerization of 4-acetoxystyrene

    DEFF Research Database (Denmark)

    Gao, Bo; Chen, Xianyi; Ivan, Bela

    1997-01-01

    Living atom transfer radical polymerization (ATRP) of 4-acetoxystyrene (1), a protected 4-vinylphenol, leading to poly(4-acetoxystyrene) with well-defined molecular weight and narrow molecular weight distribution was carried out in bulk with a,a'-dibromoxylene(2)/CuBr/2,2-bipyridine(bpy) as initi......Living atom transfer radical polymerization (ATRP) of 4-acetoxystyrene (1), a protected 4-vinylphenol, leading to poly(4-acetoxystyrene) with well-defined molecular weight and narrow molecular weight distribution was carried out in bulk with a,a'-dibromoxylene(2)/CuBr/2,2-bipyridine...

  2. Hemoglobin and Red Blood Cells Catalyze Atom Transfer Radical Polymerization

    OpenAIRE

    Silva Tilana B.; Spulber Mariana; Kocik Marzena K.; Seidi Farzad; Charan Himanshu; Rother Martin; Sigg Severin J.; Renggli Kasper; Kali Gergely; Bruns Nico

    2013-01-01

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity i.e. they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N isopropylacrylamide (NIPAAm) poly(ethylene glycol) methyl ether acrylate (PEGA) and poly(ethylene glycol) methyl eth...

  3. Hemoglobin and red blood cells catalyze atom transfer radical polymerization.

    Science.gov (United States)

    Silva, Tilana B; Spulber, Mariana; Kocik, Marzena K; Seidi, Farzad; Charan, Himanshu; Rother, Martin; Sigg, Severin J; Renggli, Kasper; Kali, Gergely; Bruns, Nico

    2013-08-12

    Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds.

  4. Palladium-Catalyzed Atom-Transfer Radical Cyclization at Remote Unactivated C(sp3)-H Sites: Hydrogen-Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates.

    Science.gov (United States)

    Ratushnyy, Maxim; Parasram, Marvin; Wang, Yang; Gevorgyan, Vladimir

    2018-03-01

    A novel mild, visible-light-induced palladium-catalyzed hydrogen atom translocation/atom-transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo- and heterocyclic structures. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. The pentafluorostyrene endeavours with atom transfer radical polymerization - quo vadis?

    DEFF Research Database (Denmark)

    Hvilsted, Søren

    2014-01-01

    The versatility of the atom transfer radical polymerization (ATRP) of pentafluorostyrene (FS) is comprehensively evaluated. The ATRP of a wide range of monomers derived from FS is likewise discussed with emphasis on the potential polymer applications. A large number of block and star copolymers...... centred around polypentafluorostyrene (PFS) and prepared primarily using the bromomacroinitiator concept is surveyed. Here the main emphasis is on the feasibility of the polymer design, but also the very many different applications are highlighted. The potential grafting onto PFS and PFS block copolymers...... by exploitation of the very labile para-fluorine demonstrates new material architecture possibilities through very mild reaction conditions. Finally the utility of PFS in various conducting materials is elaborated. The amphiphilic nature of PFS in triblock copolymers with polyethers has been exploited for Li+ ion...

  6. Organic thin film transistors with polymer brush gate dielectrics synthesized by atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Pinto, J.C.; Whiting, G.L.; Khodabakhsh, S.

    2008-01-01

    , synthesized by atom transfer radical polymerization (ATRP), were used to fabricate low voltage OFETs with both evaporated pentacene and solution deposited poly(3-hexylthiophene). The semiconductor-dielectric interfaces in these systems were studied with a variety of methods including scanning force microscopy...

  7. Polymer coating comprising 2-methoxyethyl acrylate units synthesized by surface-initiated atom transfer radical polymerization

    DEFF Research Database (Denmark)

    2011-01-01

    Source: US2012184029A The present invention relates to preparation of a polymer coating comprising or consisting of polymer chains comprising or consisting of units of 2-methoxyethyl acrylate synthesized by Surface-Initiated Atom Transfer Radical Polymerization (SI ATRP) such as ARGET SI ATRP...

  8. Surface-initiated Atom Transfer Radical Polymerization - a Technique to Develop Biofunctional Coatings

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren

    2009-01-01

    The initial formation of initiating sites for atom transfer radical polymerization (ATRP) on various polymer surfaces and numerous inorganic and metallic surfaces is elaborated. The subsequent ATRP grafting of a multitude of monomers from such surfaces to generate thin covalently linked polymer...

  9. Acrylamide Homopolymers and Acrylamide-N-Isopropylacrylamide Block Copolymers by Atomic Transfer Radical Polymerization in Water

    NARCIS (Netherlands)

    Wever, D. A. Z.; Raffa, P.; Picchioni, F.; Broekhuis, A. A.

    2012-01-01

    Atomic transfer radical polymerization (ATRP) of acrylamide has been accomplished in aqueous media at room temperature. By using methyl 2-chloropropionate (MeClPr) as the initiator and tris[2-(dimethylamino)ethyl]-amine (Me6TREN)/copper halogenide (CuX) as the catalyst system, different linear

  10. Novel fluorinated block copolymer architectures fuelled by atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Jankova, Katja; Hvilsted, Søren

    2005-01-01

    Block copolymers based on poly(pentafluorostyrene), PFS, in various numbers and of different lengths, and polystyrene are prepared by atom transfer radical polymerization (ATRP). Di- and triblock copolymers with varying amounts of PFS were synthesized employing either I phenylethylbromide or 1,4-...

  11. Surface-Initiated Atom Transfer Radical Polymerization from Electrospun Mats: An Alternative to Nafion

    DEFF Research Database (Denmark)

    Javakhishvili, Irakli; Dimitrov, Ivaylo; Tynelius, Oskar

    2017-01-01

    Proton exchange membranes for fuel cell applications are synthesized by surface-initiated(SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride-co-chlorotrifluoroethylene)is electrospun into 50 μm thick mat, which is then employed as multifunctionalinitiator for copper...

  12. Atom-Transfer Radical Addition to Unactivated Alkenes by using Heterogeneous Visible-Light Photocatalysis.

    Science.gov (United States)

    Mao, Liang-Liang; Cong, Huan

    2017-11-23

    Heterogeneous visible-light photocatalysis represents an important route toward the development of sustainable organic synthesis. In this study visible light-induced, heavy metal-free atom-transfer radical addition to unactivated terminal olefins is carried out by using the combination of heterogeneous titanium dioxide as photocatalyst and a hypervalent iodine(III) reagent as co-initiator. The reaction can be applied to a range of substrates with good functional-group tolerance under very mild conditions. In addition to a number of commonly used atom-transfer reagents, the relatively challenging chloroform is also suitable. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

    Directory of Open Access Journals (Sweden)

    Fabrice Chemla

    2013-02-01

    Full Text Available The formation of alkylidenezinc carbenoids by 1,4-addition/carbozincation of dialkylzincs or alkyl iodides based on zinc atom radical transfer, in the presence of dimethylzinc with β-(propargyloxyenoates having pendant iodo- and bromoalkynes, is disclosed. Formation of the carbenoid intermediate is fully stereoselective at −30 °C and arises from a formal anti-selective carbozincation reaction. Upon warming, the zinc carbenoid is stereochemically labile and isomerizes to its more stable form.

  14. Seawater uranium sorbents: preparation from a mesoporous copolymer initiator by atom-transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Yue, Yanfeng; Mayes, Richard T.; Fulvio, Pasquale F.; Sun, Xiao-Guang [Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Kim, Jungseung; Tsouris, Costas [Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Chen, Jihua [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Brown, Suree [Department of Chemistry, University of Tennessee, Knoxville, TN (United States); Dai, Sheng [Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN (United States); Department of Chemistry, University of Tennessee, Knoxville, TN (United States)

    2013-12-09

    Nanoporous template-free initiators for atom-transfer radical polymerization (ATRP) were synthesized with surface and framework initiator sites and tailorable pore structures. Polyacrylonitrile grown on one initiator was converted into polyamidoxime to generate a uranium sorbent for seawater extraction with a high uptake rate and capacity relative to those of nonwoven irradiation-grafted polyethylene-fiber composites. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Hydroperoxyl Radicals (HOO(.) ): Vitamin E Regeneration and H-Bond Effects on the Hydrogen Atom Transfer.

    Science.gov (United States)

    Cedrowski, Jakub; Litwinienko, Grzegorz; Baschieri, Andrea; Amorati, Riccardo

    2016-11-07

    Hydroperoxyl (HOO(.) ) and alkylperoxyl (ROO(.) ) radicals show a different behavior in H-atom-transfer processes. Both radicals react with an analogue of α-tocopherol (TOH), but HOO(.) , unlike ROO(.) , is able to regenerate TOH by a fast H-atom transfer: TO(.) +HOO(.) →TOH+O2 . The kinetic solvent effect on the H-atom transfer from TOH to HOO(.) is much stronger than that observed for ROO(.) because noncovalent interactions with polar solvents (Solv⋅⋅⋅HOO(.) ) destabilize the transition state. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. In situ AFM investigation of electrochemically induced surface-initiated atom-transfer radical polymerization.

    Science.gov (United States)

    Li, Bin; Yu, Bo; Zhou, Feng

    2013-02-12

    Electrochemically induced surface-initiated atom-transfer radical polymerization is traced by in situ AFM technology for the first time, which allows visualization of the polymer growth process. It affords a fundamental insight into the surface morphology and growth mechanism simultaneously. Using this technique, the polymerization kinetics of two model monomers were studied, namely the anionic 3-sulfopropyl methacrylate potassium salt (SPMA) and the cationic 2-(metharyloyloxy)ethyltrimethylammonium chloride (METAC). The growth of METAC is significantly improved by screening the ammonium cations by the addition of ionic liquid electrolyte in aqueous solution. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Hydrophilization of poly(ether ether ketone) films by surface-initiated atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Hvilsted, Søren

    2010-01-01

    Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) has been exploited to hydrophilize PEEK. The ketone groups on the PEEK surface were reduced to hydroxyl groups which were converted to bromoisobutyrate initiating sites for SI-ATRP. The modification steps were followed by contact...... angle measurements and XPS. Moreover, ATR FTIR has been used to confirm the formation of initiating groups. Grafting of PEGMA from PEEK was performed in aqueous solution. The presence of the PPEGMA grafts on PEEK was revealed by the thermograms from TGA whereas investigations with AFM rejected changes...

  18. Acrylamide Homopolymers and Acrylamide-N-Isopropylacrylamide Block Copolymers by Atomic Transfer Radical Polymerization in Water

    OpenAIRE

    Wever, D. A. Z.; Raffa, P.; Picchioni, F.; Broekhuis, A.A.

    2012-01-01

    Atomic transfer radical polymerization (ATRP) of acrylamide has been accomplished in aqueous media at room temperature. By using methyl 2-chloropropionate (MeClPr) as the initiator and tris[2-(dimethylamino)ethyl]-amine (Me6TREN)/copper halogenide (CuX) as the catalyst system, different linear polyacrylamides with apparent molecular weights up to >150 000 g/mol were synthesized with dispersities as low as 1.39. The molecular weights agreed well with the theoretical ones at relatively low-medi...

  19. Reactivity of hydropersulfides toward the hydroxyl radical unraveled: disulfide bond cleavage, hydrogen atom transfer, and proton-coupled electron transfer.

    Science.gov (United States)

    Anglada, Josep M; Crehuet, Ramon; Adhikari, Sarju; Francisco, Joseph S; Xia, Yu

    2018-02-14

    Hydropersulfides (RSSH) are highly reactive as nucleophiles and hydrogen atom transfer reagents. These chemical properties are believed to be key for them to act as antioxidants in cells. The reaction involving the radical species and the disulfide bond (S-S) in RSSH, a known redox-active group, however, has been scarcely studied, resulting in an incomplete understanding of the chemical nature of RSSH. We have performed a high-level theoretical investigation on the reactions of the hydroxyl radical (˙OH) toward a set of RSSH (R = -H, -CH 3 , -NH 2 , -C(O)OH, -CN, and -NO 2 ). The results show that S-S cleavage and H-atom abstraction are the two competing channels. The electron inductive effect of R induces selective ˙OH substitution at one sulfur atom upon S-S cleavage, forming RSOH and ˙SH for the electron donating groups (EDGs), whereas producing HSOH and ˙SR for the electron withdrawing groups (EWGs). The H-Atom abstraction by ˙OH follows a classical hydrogen atom transfer (hat) mechanism, producing RSS˙ and H 2 O. Surprisingly, a proton-coupled electron transfer (pcet) process also occurs for R being an EDG. Although for RSSH having EWGs hat is the leading channel, S-S cleavage can be competitive or even dominant for the EDGs. The overall reactivity of RSSH toward ˙OH attack is greatly enhanced with the presence of an EDG, with CH 3 SSH being the most reactive species found in this study (overall rate constant: 4.55 × 10 12 M -1 s -1 ). Our results highlight the complexity in RSSH reaction chemistry, the extent of which is closely modulated by the inductive effect of the substituents in the case of the oxidation by hydroxyl radicals.

  20. Functionalized polymer film surfaces via surface-initiated atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Y. [State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029 (China); Li, J.S. [College of Polymer Science and Engineering, Sichuan University, Chengdu 610065 (China); Yang, W.T. [State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029 (China); Xu, F.J., E-mail: xufj@mail.buct.edu.cn [State Key Laboratory of Chemical Resource Engineering, Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029 (China)

    2013-05-01

    The ability to manipulate and control the surface properties of polymer films, without altering the substrate properties, is crucial to their wide-spread applications. In this work, a simple one-step method for the direct immobilization of benzyl chloride groups (as the effective atom transfer radical polymerization (ATRP) initiators) on the polymer films was developed via benzophenone-induced coupling of 4-vinylbenzyl chloride (VBC). Polyethylene (PE) and nylon films were selected as examples of polymer films to illustrate the functionalization of film surfaces via surface-initiated ATRP. Functional polymer brushes of (2-dimethylamino)ethyl methacrylate, sodium 4-styrenesulfonate, 2-hydroxyethyl methacrylate and glycidyl methacrylate, as well as their block copolymer brushes, have been prepared via surface-initiated ATRP from the VBC-coupled PE or nylon film surfaces. With the development of a simple approach to the covalent immobilization of ATRP initiators on polymer film surfaces and the inherent versatility of surface-initiated ATRP, the surface functionality of polymer films can be precisely tailored. - Highlights: ► Atom transfer radical polymerization initiators were simply immobilized. ► Different functional polymer brushes were readily prepared. ► Their block copolymer brushes were also readily prepared.

  1. [Preparation of a novel polymer monolith using atom transfer radical polymerization method for solid phase extraction].

    Science.gov (United States)

    Shen, Ying; Qi, Li; Qiao, Juan; Mao, Lanqun; Chen, Yi

    2013-04-01

    In this study, a novel polymer monolith based solid phase extraction (SPE) material has been prepared by two-step atom transfer radical polymerization (ATRP) method. Firstly, employing ethylene glycol dimethacrylate (EDMA) as a cross-linker, a polymer monolith filled in a filter head has been in-situ prepared quickly under mild conditions. Then, the activators generated by electron transfer ATRP (ARGET ATRP) was used for the modification of poly(2-(dimethylamino)ethyl-methacrylate) (PDMAEMA) on the monolithic surface. Finally, this synthesized monolith for SPE was successfully applied in the extraction and enrichment of steroids. The results revealed that ATRP can be developed as a facile and effective method with mild reaction conditions for monolith construction and has the potential for preparing monolith in diverse devices.

  2. Surface Modification of Nanoporous 1,2-Polybutadiene by Atom Transfer Radical Polymerization or Click Chemistry

    DEFF Research Database (Denmark)

    Guo, Fengxiao; Jankova Atanasova, Katja; Schulte, Lars

    2010-01-01

    Surface-initiated atom transfer radical polymerization (ATRP) and click chemistry were used to obtain functional nanoporous polymers based oil nanoporous 1,2-polybutadiene (PB) with gyroid morphology. The ATRP monolith initiator was prepared by immobilizing bromoester initiators onto the pore walls...... through two different methodologies: (1) three-step chemical conversion of double bonds of PB into bromoisobutyrate, and (2) photochemical functionalization of PB with bromoisobutyrate groups. Azide functional groups were attached onto the pore walls before click reaction with alkynated MPEG. Following...... ATRP-grafting of hydrophilic polyacrylates and click of MPEG, the originally hydrophobic samples transformed into hydrophilic nanoporous materials. The successful modification was confirmed by infrared spectroscopy, contact angle measurements and measurements of spontaneous water uptake, while...

  3. On Surface-Initiated Atom Transfer Radical Polymerization Using Diazonium Chemistry To Introduce the Initiator Layer

    DEFF Research Database (Denmark)

    Iruthayaraj, Joseph; Chernyy, Sergey; Lillethorup, Mie

    2011-01-01

    of bromine shows a gradual transition from mushroom to brush-type conformation of the surface anchored chains in both polar and nonpolar reaction medium. Interestingly, it is revealed that very thick polymer brushes, on the order of 1 μm, can be obtained at high bromine content of the initiator layer......This work features the controllability of surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate, initiated by a multilayered 2-bromoisobutyryl moiety formed via diazonium chemistry. The thickness as a function of polymerization time has been studied by varying...... Cu(II)/Cu(I) complexes (L = Me(6)TREN, PMDETA, and BIPY). It is also observed that the ability of polymer brushes to reinitiate depends on the initial thickness and the solvent used for generating it....

  4. Seawater uranium sorbents. Preparation from a mesoporous copolymer initiator by atom-transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Yue, Yanfeng; Mayes, Richard T.; Fulvio, Pasquale F.; Sun, Xiao-Guang [Oak Ridge National Laboratory, TN (United States). Chemical Sciences Division; Kim, Jungseung; Tsouris, Costas [Oak Ridge National Laboratory, TN (United States). Energy and Transportation Science Division; Chen, Jihua [Oak Ridge National Laboratory, TN (United States). Center for Nanophase Materials Sciences; Brown, Suree [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry; Dai, Sheng [Oak Ridge National Laboratory, TN (United States). Chemical Sciences Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry

    2013-12-09

    From the sea to the reactor: Nanoporous template-free initiators for atom-transfer radical polymerization (ATRP) were synthesized with surface and framework initiator sites and tailorable pore structures. Polyacrylonitrile grown on one initiator was converted into polyamidoxime to generate a uranium sorbent for seawater extraction with a high uptake rate and capacity relative to those of nonwoven irradiation-grafted polyethylene-fiber composites. [German] Aus dem Meer in den Reaktor: Nanoporoese templatfreie Initiatoren fuer die radikalische Atomtransferpolymerisation (ATRP) mit einstellbarer Porenstruktur und Initiatorstellen an der Oberflaeche und im Geruestinneren wurden hergestellt. Auf einem Initiator erzeugtes Polyacrylnitril wurde in ein Polyamidoxim umgewandelt, um Uran aus Meerwasser zu extrahieren. Aufnahmerate und -kapazitaet waren hoch im Vergleich zu nichtverwobenen Kompositen aus Fasern und photochemisch aufgebrachtem Polyethylen.

  5. Modification of Jute Fibers with Polystyrene via Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Plackett, David; Jankova, Katja Atanassova; Egsgaard, Helge

    2005-01-01

    Atom transfer radical polymerization (ATRP) was investigated as a method of covalently bonding polystyrene to jute (Corchorus capsularis) and as a possible approach to fiber composites with enhanced properties. Jute fibers were modified with a brominated initiator and subsequently ATRP modified...... to attach polystyrene and then examined using SEM, DSC, TGA, FTIR, XPS, elemental analysis, and Py-GC-MS. These techniques confirmed that polystyrene had been covalently bound to the fibers and consequently ATRP-modified jute fiber mats were used to prepare hot-pressed polystyrene composites. Composite...... applications, we conclude that further optimization of the ATRP method is required, possibly targeting higher and more uniform loading of polystyrene on the fibers....

  6. Effect of Reactant Concentration Variations on the Kinetics of Atom Transfer Radical Polymerization of Acrylonitrile

    Directory of Open Access Journals (Sweden)

    H. Roghani-Mamaqani

    2013-01-01

    Full Text Available Polyacrylontrile synthesis, via atom transfer radical polymerization, is studied in various initiator concentrations, transitional metal catalyst and different concentrations of CuBr2. The variations of monomer conversion and the lin-earity of semi-logarithmic kinetic profile which is the evidence of living polymerization and constant radical concentration in the reaction medium, were revealed by gas chromatography technique (GC. Gel permeation chromatography (GPC studies revealed that, the number average molecular weight increases linearly against monomer conversion, an indicative of living nature of the polymerization process. Additionally, the conversion, apparent rate constant and number average molecular weight increased with increased initiator concentration as well as the transitional metal complex concentration. However, addition of CuBr2 lowered conversion, kapp, and the number average molecular weight of polyacrylonitrile. Molecular weight distribution of synthesized polymers broadened with increased initiator concentration and also transitional metal complex concentration. However, addition of CuBr2 has resulted in narrower molecular weight distribution polyacrylonitrile. Moreover, all the samples experienced a drop in PDI value from nearly 2 to almost 1.1 as the reaction progressed.

  7. Synthesis of block copolymers by combination of atom transfer radical polymerization and visible light-induced free radical promoted cationic polymerization.

    Science.gov (United States)

    Kahveci, Muhammet U; Acik, Gokhan; Yagci, Yusuf

    2012-02-27

    A new synthetic approach for the preparation of block copolymers by mechanistic transformation from atom transfer radical polymerization (ATRP) to visible light-induced free radical promoted cationic polymerization is described. A series of halide end-functionalized polystyrenes with different molecular weights synthesized by ATRP were utilized as macro-coinitiators in dimanganese decacarbonyl [Mn(2) (CO)(10) ] mediated free radical promoted cationic photopolymerization of cyclohexene oxide or isobutyl vinyl ether. Precursor polymers and corresponding block copolymers were characterized by spectral, chromatographic, and thermal analyses. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Atom transfer radical polymerization preparation and photophysical properties of polypyridylruthenium derivatized polystyrenes.

    Science.gov (United States)

    Fang, Zhen; Ito, Akitaka; Keinan, Shahar; Chen, Zuofeng; Watson, Zoe; Rochette, Jason; Kanai, Yosuke; Taylor, Darlene; Schanze, Kirk S; Meyer, Thomas J

    2013-08-05

    A ruthenium containing polymer featuring a short carbonyl-amino-methylene linker has been prepared by atom transfer radical polymerization (ATRP). The polymer was derived from ATRP of the N-hydroxysuccinimide (NHS) derivative of p-vinylbenzoic acid, followed by an amide coupling reaction of the NHS-polystyrene with Ru(II) complexes derivatized with aminomethyl groups (i.e., [Ru(bpy)2(CH3-bpy-CH2NH2)](2+) where bpy is 2,2'-bipyridine, and CH3-bpy-CH2NH2 is 4-methyl-4'-aminomethyl-2,2'-bipyridine). The Ru-functionalized polymer structure was confirmed by using nuclear magnetic resonance and infrared spectroscopy, and the results suggest that a high loading ratio of polypyridylruthenium chromophores on the polystyrene backbone was achieved. The photophysical properties of the polymer were characterized in solution and in rigid ethylene glycol glasses. In solution, emission quantum yield and lifetime studies reveal that the polymer's metal-to-ligand charge transfer (MLCT) excited states are quenched relative to a model Ru complex chromophore. In rigid media, the MLCT-ground state band gap and lifetime are both increased relative to solution with time-resolved emission measurements revealing fast energy transfer hopping within the polymer. Molecular dynamics studies of the polymer synthesized here as well as similar model systems with various spatial arrangements of the pendant Ru complex chromophores suggest that the carbonyl-amino-methylene linker probed in our target polymer provides shorter Ru-Ru nearest-neighbor distances leading to an increased Ru*-Ru energy hopping rate, compared to those with longer linkers in counterpart polymers.

  9. A Kinetico-Mechanistic Study on CuII Deactivators Employed in Atom Transfer Radical Polymerization.

    Science.gov (United States)

    Zerk, Timothy J; Martinez, Manuel; Bernhardt, Paul V

    2016-10-03

    Copper complexes of tertiary amine ligands have emerged as the catalysts of choice in the extensively employed atom transfer radical polymerization (ATRP) protocol. The halide ligand substitution reactions of five-coordinate copper(II) complexes of tris[2-(dimethylamino)ethyl]amine (Me6tren), one of the most active ATRP catalysts, has been studied in a range of organic solvents using stopped-flow techniques. The kinetic and activation parameters indicate that substitution reactions on [CuII(Me6tren)X]+ (X- = Cl- and Br-) and [CuII(Me6tren)(Solv)]2+ (Solv = MeCN, DMF, DMSO, MeOH, EtOH) are dissociatively activated; this behavior is independent of the solvent used. Adjusting the effective concentration of the solvent by addition of an olefinic monomer to the solution does not affect the kinetics of the halide binding (kon) but can alter the outer-sphere association equilibrium constant (KOS) between reactants prior to the formal ligand substitution. Halide (X-/Y-) exchange reactions (X = Br and Y = Cl) involving the complex [Cu(Me6tren)X]+ and Y- reveal that the substitution is thermodynamically favored. The influence of solvent on the substitution reactions of [Cu(Me6tren)X]+ is complex; the more polar DMF confers a greater entropic driving force but larger enthalpic demands than MeCN. These substitution reactions are compared with those for copper(II) complexes bearing the tris[2-(diethylamino)ethyl]amine (Et6tren) and tris[2-(pyridyl)methyl]amine (tpa) ligands, which have also been used as catalysts for ATRP. Changing the ligand has a significant impact on the kinetics of X-/Y- exchange. These correlations are discussed in relation to the ability of five-coordinate [CuLX]+ complexes to deactivate radicals in ATRP.

  10. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Deng, Fengjie, E-mail: fengjiedeng@aliyun.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084 (China)

    2016-12-30

    Highlights: • Surface modification of ND with water soluble and biocompatible polymers. • Functionalized ND through metal free surface initiated ATRP. • The metal free surface initiated ATRP is rather simple and effective. • The ND-poly(MPC) showed high dispersibility and desirable biocompatibility. - Abstract: Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by {sup 1}H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  11. Sustainable Electrochemically-Mediated Atom Transfer Radical Polymerization with Inexpensive Non-Platinum Electrodes.

    Science.gov (United States)

    Fantin, Marco; Lorandi, Francesca; Isse, Abdirisak A; Gennaro, Armando

    2016-08-01

    Electrochemically-mediated atom transfer radical polymerization (eATRP) of oligo(ethylene oxide) methyl ether methacrylate in water is investigated on glassy carbon, Au, Ti, Ni, NiCr and SS304. eATRPs are performed both in divided and undivided electrochemical cells operating under either potentiostatic or galvanostatic mode. The reaction is fast, reaching high conversions in ≈4 h, and yields polymers with dispersity <1.2 and molecular weights close to the theoretical values. Most importantly, eATRP in a highly simplified setup (undivided cell under galvanostatic mode) with inexpensive nonnoble metals, such as NiCr and SS304, as cathode is well-controlled. Additionally, these electrodes neither release harmful ions in solution nor react directly with the CX chain end and can be reused several times. It is demonstrated that Pt can be replaced with cheaper, and more readily available materials without negatively affecting eATRP performance. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Synthesis of novel size exclusion chromatography support by surface initiated aqueous atom transfer radical polymerization.

    Science.gov (United States)

    Coad, Bryan R; Kizhakkedathu, Jayachandran N; Haynes, Charles A; Brooks, Donald E

    2007-11-06

    We report the use of aqueous surface-initiated atom transfer radical polymerization (SI-ATRP) to grow polymer brushes from a "gigaporous" polymeric chromatography support for use as a novel size exclusion chromatography medium. Poly(N,N-dimethylacrylamide) (PDMA) was grown from hydrolyzable surface initiators via SI-ATRP catalyzed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA)/CuCl. Grafted polymer was characterized semiquantitatively by ATR-FTIR and also cleaved and quantitatively characterized for mass, molecular weight, and polydispersity via analytical SEC/MALLS. The synthesis provides control over graft density and allows the creation of dense brushes. Incorporation of negative surface charge was found to be crucial for improving the initiation efficiency. As polymer molecular weight and density could be controlled through reaction conditions, the resulting low-polydispersity grafted polymer brush medium is shown to be suitable for use as a customizable size exclusion chromatography medium for investigating the principals of entropic interaction chromatography. All packed media investigated showed size-dependent partitioning of solutes, even for low graft density systems. Increasing the molecular weight of the grafts allowed solutes more access to the volume fraction in the column available for partitioning. Compared to low graft density media, increased graft density caused eluted solute probes to be retained less within the column and allowed for greater size discrimination of probes whose molecular weights were less than 10(4) kDa.

  13. Constructing Functional Ionic Membrane Surface by Electrochemically Mediated Atom Transfer Radical Polymerization

    Directory of Open Access Journals (Sweden)

    Fen Ran

    2016-01-01

    Full Text Available The sodium polyacrylate (PAANa contained polyethersulfone membrane that was fabricated by preparation of PES-NH2 via nonsolvent phase separation method, the introduction of bromine groups as active sites by grafting α-Bromoisobutyryl bromide, and surface-initiated electrochemically atom transfer radical polymerization (SI-eATRP of sodium acrylate (AANa on the surface of PES membrane. The polymerization could be controlled by reaction condition, such as monomer concentration, electric potential, polymerization time, and modifier concentration. The membrane surface was uniform when the monomer concentration was 0.9 mol/L, the electric potential was −0.12 V, the polymerization time was 8 h, and the modifier concentration was 2 wt.%. The membrane showed excellent hydrophilicity and blood compatibility. The water contact angle decreased from 84° to 68° and activated partial thromboplastin increased from 51 s to 84 s after modification of the membranes.

  14. Ultralow fouling polyacrylamide on gold surfaces via surface-initiated atom transfer radical polymerization.

    Science.gov (United States)

    Liu, Qingsheng; Singh, Anuradha; Lalani, Reza; Liu, Lingyun

    2012-04-09

    In this work, polyacrylamide is investigated as an ultralow fouling surface coating to highly resist protein adsorption, cell adhesion, and bacterial attachment. Polyacrylamide was grafted on gold surfaces via surface-initiated atom transfer radical polymerization (ATRP). Protein adsorption from a wide range of biological media, including single protein solutions of fibrinogen, bovine serum albumin, and lysozyme, dilute and undiluted human blood serum, and dilute and undiluted human blood plasma, was studied by surface plasmon resonance (SPR). Dependence of the protein resistance on polyacrylamide film thickness was examined. With the optimal film thickness, the adsorption amount of all three single proteins on polyacrylamide-grafted surfaces was polyacrylamide-grafted surfaces were 5, 6.5, 17, and 28 pg/mm(2), respectively, comparable (if not better) than the adsorption levels on poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) surfaces, the best antifouling materials known to date. The polyacrylamide-grafted surfaces were also shown strongly resistant to adhesion from bovine aortic endothelial cells and two bacterial species, Gram-positive Staphylococcus epidermidis ( S. epidermidis ) and Gram-negative Pseudomonas aeruginosa ( P. aeruginosa ). Strong hydrogen bond with water is considered the key attribute for the ultralow fouling properties of polyacrylamide. This is the first work to graft gold surfaces with polyacrylamide brushes via ATRP to achieve ultralow fouling surfaces, demonstrating that polyacrylamide is a promising alternative to traditional PEG-based antifouling materials.

  15. Efficient Functionalization of Polyethylene Fibers for the Uranium Extraction from Seawater through Atom Transfer Radical Polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Neti, Venkata S. [Chemical; Das, Sadananda [Chemical; Brown, Suree [Department; Janke, Christopher J. [Materials; Kuo, Li-Jung [Marine; Gill, Gary A. [Marine; Dai, Sheng [Chemical; Department; Mayes, Richard T. [Chemical

    2017-09-14

    Brush-on-brush structures are proposed as one method to overcome support effects in grafted polymers. Utilizing glycidyl methacrylate (GMA) grafted on polyethylene (PE) fibers using radiation-induced graft polymerization (RIGP) provides a hydrophilic surface on the hydrophobic PE. When integrated with atom transfer radical polymerization (ATRP), the grafting of acrylonitrile (AN) and hydroxyethyl acrylate (HEA) can be controlled and manipulated more easily than with RIGP. Poly(acrylonitrile)-co-poly(hydroxyethyl acrylate) chains were grown via ATRP on PE-GMA fibers to generate an adsorbent for the extraction of uranium from seawater. The prepared adsorbents in this study demonstrated promise (159.9 g- U/kg of adsorbent) in laboratory screening tests using a high uranium concentration brine and 1.24 g-U/Kg of adsorbent in the filtered natural seawater in 21-days. The modest capacity in 21- days exceeds previous efforts to generate brush-on-brush adsorbents by ATRP while manipulating the apparent surface hydrophilicity of the trunk material (PE).

  16. Synthesis of triblock and random copolymers of 4- acetoxystyrene and styrene by living atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Gao, Bo; Chen, Xianyi; Ivan, Bela

    1997-01-01

    Triblock copolymers containing polystyrene (PSt) and poly(4-acetoxystyrene) (PAcOSt) segments have been prepared by atom transfer radical polymerization (ATRP). In the first step one of the two monomers was polymerized in bulk using the initiating system alpha,alpha'-dibromo-p-xylene/CuBr/2...... weights and narrow molecular weight distributions. Polymerization of a mixture of equal molar amounts of the two monomers yielded a random copolymer with narrow molecular weight distribution....

  17. Water-assisted atom transfer radical polymerization of N-isopropylacrylamide: nature of solvent and temperature.

    Science.gov (United States)

    Ye, Jianding; Narain, Ravin

    2009-01-22

    We demonstrate here via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) at low temperature that the negative function of water in aqueous ATRP is significantly suppressed. By the addition of a small amount of water in a water-miscible organic solvent and maintaining low polymerization temperature, the ATRP of NIPAM is relatively fast and well controlled. We observed that the rate of the polymerization in pure organic solvent at a monomer concentration of 20 wt % is slow, and relatively low conversions were obtained. The low conversion of PNIPAM in pure alcoholic media (such as methanol, ethanol, and n-propanol) is attributed to the poor solubility of the resulting low molecular weight polymer in such solvents. The consequence is that the PNIPAM chains are aggregated, resulting in the inaccessibility of the embedded halide atom of the polymer chain ends by the copper catalyst. As expected, the ATRP of NIPAM in pure water was found to be fast and uncontrolled. These results have therefore prompted us to study the ATRP of NIPAM in aqueous-organic mixtures. Room temperature polymerization of NIPAM in mixed aqueous-organic solvent mixtures (organic:water = 4:1 or 3:1) revealed to be fast and uncontrolled. However, when the NIPAM polymerization was conducted at low temperature (0 degrees C) in such solvent systems, the polymerization turned out to be well-controlled as the molar masses progress linearly with conversion, and pseudo-first-order kinetic plots were obtained. Furthermore, monomodal GPC traces and narrow molecular weight distributions were obtained in all aqueous-organic solvent systems. Chain extension for aqueous ATRP of NIPAM revealed to proceed well at low temperature as compared to room temperature. Furthermore, we observe that the rates of the polymerization of NIPAM in different aqueous-organic mixtures follow the trend of polarity in the case of the polar aprotic solvents. However, in the case of polar protic solvent

  18. Ab initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization.

    Science.gov (United States)

    Lin, Ching Yeh; Coote, Michelle L; Gennaro, Armando; Matyjaszewski, Krzysztof

    2008-09-24

    High-level ab initio molecular orbital calculations are used to study the thermodynamics and electrochemistry relevant to the mechanism of atom transfer radical polymerization (ATRP). Homolytic bond dissociation energies (BDEs) and standard reduction potentials (SRPs) are reported for a series of alkyl halides (R-X; R = CH 2CN, CH(CH 3)CN, C(CH 3) 2CN, CH 2COOC 2H 5, CH(CH 3)COOCH 3, C(CH 3) 2COOCH 3, C(CH 3) 2COOC 2H 5, CH 2Ph, CH(CH 3)Ph, CH(CH 3)Cl, CH(CH 3)OCOCH 3, CH(Ph)COOCH 3, SO 2Ph, Ph; X = Cl, Br, I) both in the gas phase and in two common organic solvents, acetonitrile and dimethylformamide. The SRPs of the corresponding alkyl radicals, R (*), are also examined. The computational results are in a very good agreement with the experimental data. For all alkyl halides examined, it is found that, in the solution phase, one-electron reduction results in the fragmentation of the R-X bond to the corresponding alkyl radical and halide anion; hence it may be concluded that a hypothetical outer-sphere electron transfer (OSET) in ATRP should occur via concerted dissociative electron transfer rather than a two-step process with radical anion intermediates. Both the homolytic and heterolytic reactions are favored by electron-withdrawing substituents and/or those that stabilize the product alkyl radical, which explains why monomers such as acrylonitrile and styrene require less active ATRP catalysts than vinyl chloride and vinyl acetate. The rate constant of the hypothetical OSET reaction between bromoacetonitrile and Cu (I)/TPMA complex was estimated using Marcus theory for the electron-transfer processes. The estimated rate constant k OSET = approximately 10 (-11) M (-1) s (-1) is significantly smaller than the experimentally measured activation rate constant ( k ISET = approximately 82 M (-1) s (-1) at 25 degrees C in acetonitrile) for the concerted atom transfer mechanism (inner-sphere electron transfer, ISET), implying that the ISET mechanism is preferred. For

  19. PREPARATION OF BLOCK COPOLYMERS OF POLY(STYRENE) AND POLY(T-BUTYL ACRYLATE) OF VARIOUS MOLECULAR WEIGHTS AND ARCHITECTURES BY ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    Science.gov (United States)

    Block copolymers of polystyrene and poly(t-butyl acrylate) were prepared using atom transfer radical polymerization techniques. These polymers were synthesized with a CuBr/N,N,N,NHydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-oxyl Radical. A Kinetic and Theoretical Study.

    Science.gov (United States)

    DiLabio, Gino A; Franchi, Paola; Lanzalunga, Osvaldo; Lapi, Andrea; Lucarini, Fiorella; Lucarini, Marco; Mazzonna, Marco; Prasad, Viki Kumar; Ticconi, Barbara

    2017-06-16

    A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the quinolinimide-N-oxyl radical (QINO) was performed in CH3CN. The HAT rate constants are significantly higher than those observed with the phthalimide-N-oxyl radical (PINO) as a result of enthalpic and polar effects due to the presence of the N-heteroaromatic ring in QINO. The relevance of polar effects is supported by theoretical calculations conducted for the reactions of the two N-oxyl radicals with toluene, which indicate that the HAT process is characterized by a significant degree of charge transfer permitted by the π-stacking that occurs between the toluene and the N-oxyl aromatic rings in the transition state structures. An increase in the HAT reactivity of QINO was observed in the presence of 0.15 M HClO4 and 0.15 M Mg(ClO4)2 due to the protonation or complexation with the Lewis acid of the pyridine nitrogen that leads to a further decrease in the electron density in the N-oxyl radical. These results fully support the use of N-hydroxyquinolinimide as a convenient substitute for N-hydroxyphthalimide in the catalytic aerobic oxidations of aliphatic hydrocarbons characterized by relatively high C-H bond dissociation energies.

  1. Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide.

    Science.gov (United States)

    Kumar, Mukesh; Chung, Jin Suk; Hur, Seung Hyun

    2014-01-01

    We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a 'grafting from' technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures (T g) than those of pristine PMMA.

  2. Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

    Directory of Open Access Journals (Sweden)

    Yannick Borguet

    2010-12-01

    Full Text Available The tandem catalysis of ring-closing metathesis/atom transfer radical reactions was investigated with the homobimetallic ruthenium–indenylidene complex [(p-cymeneRu(μ-Cl3RuCl(3-phenyl-1-indenylidene(PCy3] (1 to generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic γ-lactams and lactones from α,ω-diene substrates bearing trihaloacetamide or trichloroacetate functionalities. The individual steps were carefully monitored by 1H and 31P NMR spectroscopies in order to understand the intimate details of the catalytic cycles. Polyhalogenated substrates and the ethylene released upon metathesis induced the clean transformation of catalyst precursor 1 into the Ru(II–Ru(III mixed-valence compound [(p-cymeneRu(μ-Cl3RuCl2(PCy3], which was found to be an efficient promoter for atom transfer radical reactions under the adopted experimental conditions.

  3. Expanded corn starch as a versatile material in atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate.

    Science.gov (United States)

    Bansal, Ankushi; Kumar, Arvind; Latha, Patnam Padma; Ray, Siddharth Sankar; Chatterjee, Alok Kumar

    2015-10-05

    Polymerization of styrene (St) and methyl methacrylate (MMA) was performed by surface initiated (SI) and activator generated by electron transfer (AGET) systems of atom transfer radical polymerization (ATRP) using renewable expanded corn starch (ECS) as a support. This prepared ECS is found to have V type crystallinity with 50 m(2)g(-1) surface area (<1m(2)g(-1) for corn starch (CS)) and average pore volume of 0.43 cm(3)g(-1) (<0.1cm(3)g(-1) for CS). In SI-ATRP, hydroxyl groups on ECS were converted into macro-initiator by replacing with 2-bromoisobutyryl bromide (BIBB) with a 0.06 degree of substitution determined from NMR. In AGET-ATRP, CuBr2/ligand complex get adsorbed on ECS (Cu(II)/ECS=10 wt.%) to catalyze the polymerization. Synthesized PS/PMMA was characterized by SEM, FT-IR, (1)H NMR. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. Poly(vinyl acetate-Based Block Copolymer/Clay Nanocomposites Prepared by In Situ Atom Transfer Radical Polymerization

    Directory of Open Access Journals (Sweden)

    M.A. Semsarzadeh

    2009-12-01

    Full Text Available Atom transfer radical polymerization of styrene (St and methyl methacrylate (MMA was performed at 90oC in the absence and presence of nanoclay (Cloisite 30B. Trichloromethyl-terminated poly(vinyl acetate telomerand CuCl/ PMDETA were used as a macroinitiator and catalyst system, respectively. The experimental results showed that the atom transfer radical polymerization of St and MMA in the absence or presence of nanoclay proceeds via a controlled/living mode. It was observed that nanoclay significantly enhances the homopolymerization rate of MMA, which was attributed to the activated conjugated C=C bond of MMA monomer via interaction between the carbonyl group of MMA monomer and the hydroxyl moiety (Al-O-H of nanoclay as well as the effect of nanoclay on the dynamic equilibrium between the active (macro radicals and dormant species.Homopolymerization rate of St (a non-coordinative monomer with nanoclay decreased slightly in the presence of nanoclay. This could be explained by insertion of a portion of macroinitiator into the clay galleries, where no sufficient St monomer exists due to the low compatibility or interaction of St monomer with nanoclay to react with the macroinitiator. The results obtained from XRD, TEM and TGA analyses were fully in agreement with the kinetic data. Structure of the poly(vinyl acetate-bpolystyrene nanocomposite was found to be a combination of stacking layers and exfoliated structures while poly(vinyl acetate-b-poly(methyl methacryale nanocomposite had an exfoliated structure. This difference in the structure of nanocomposites was attributed to the different capability of the monomers (styrene and methyl methacrylate to react with the hydroxyl moiety (Al-O-H of nanoclay.

  5. New method for exploring deactivation kinetics in copper-catalyzed atom-transfer-radical reactions.

    Science.gov (United States)

    Zerk, Timothy J; Bernhardt, Paul V

    2014-11-03

    Copper polyamine complexes are among the most utilized catalysts for controlled radical polymerization reactions. Copper(I) complexes may react reversibly with an alkyl halide to form an alkyl radical, which promotes polymerization, and a copper(II) halido complex in a step known as activation. The kinetics of the reverse reaction between the alkyl radical and higher oxidation-state copper complex (deactivation) are less studied because these reactions approach diffusion-controlled rates, and it is difficult to isolate or quantify the concentration of the alkyl radical (R(•)) in situ. Herein we report a broadly applicable electrochemical technique for simultaneously measuring the kinetics of deactivation and kinetics of activation.

  6. Bottom-Up Fabrication of Nanopatterned Polymers on DNA Origami by In Situ Atom-Transfer Radical Polymerization.

    Science.gov (United States)

    Tokura, Yu; Jiang, Yanyan; Welle, Alexander; Stenzel, Martina H; Krzemien, Katarzyna M; Michaelis, Jens; Berger, Rüdiger; Barner-Kowollik, Christopher; Wu, Yuzhou; Weil, Tanja

    2016-05-04

    Bottom-up strategies to fabricate patterned polymers at the nanoscale represent an emerging field in the development of advanced nanodevices, such as biosensors, nanofluidics, and nanophotonics. DNA origami techniques provide access to distinct architectures of various sizes and shapes and present manifold opportunities for functionalization at the nanoscale with the highest precision. Herein, we conduct in situ atom-transfer radical polymerization (ATRP) on DNA origami, yielding differently nanopatterned polymers of various heights. After cross-linking, the grafted polymeric nanostructures can even stably exist in solution without the DNA origami template. This straightforward approach allows for the fabrication of patterned polymers with low nanometer resolution, which provides access to unique DNA-based functional hybrid materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Polymeric nanocapsules with controllable crosslinking degree via combination of surface-initiated atom transfer radical polymerisation and photocrosslinking techniques.

    Science.gov (United States)

    Liu, Peng; Mu, Bin; Du, Pengcheng; Hong, Zhilai

    2013-06-01

    The crosslinked polystyrene nanocapsules with controllable crosslinking degree have been prepared by the ultraviolet (UV)-induced photocrosslinking of the polystyrene grafted silica nanoparticles (SN-PS), which was obtained by the surface-initiated atom transfer radical polymerisation of styrene from the modified silica nanoparticle templates, after the silica templates were etched with hydrofluoric acid. The effect of the UV-irradiating time on the inner diameter of the nanocapsules, and the degree of crosslinking and the thickness of the shells was investigated. The dynamic light scattering results showed that the degree of crosslinking of the obtained nanocapsules increased with the prolongation of the UV-irradiation time, therefore the inner diameter of the nanocapsules increased. However, the percentage of grafting of the crosslinked polymer shells decreased with increasing the UV-irradiation time because of the photodecomposition of the polystyrene grafted during the UV-irradiated crosslinking process, according to the thermogravimetric analysis.

  8. Simulation of temperature effect on the structure control of polystyrene obtained by atom-transfer radical polymerization

    Directory of Open Access Journals (Sweden)

    Roniérik Pioli Vieira

    Full Text Available Abstract This paper uses a new kinetic modeling and simulations to analyse the effect of temperature on the polystyrene properties obtained by atom-transfer radical polymerization (ATRP. Differently from what has been traditionaly published in ATRP modeling works, it was considered “break” reactions in the mechanism aiming to reproduce the process at high temperatures. Results suggest that there is an upper limit temperature (130 °C, above which the polymer architecture loses the control. In addition, for the system considered in this work, the optimum operating temperature was 100 °C, because at this temperature polymer with very low polydispersity index is obtained, at considerable fast polymerization rate. Therefore, this present paper provides not only a tool to study ATRP processes by simulations, but also a tool for analysis and optimization, being a basis for future works dealing with this monomer and process.

  9. Phenyl Benzo[b]phenothiazine as a Visible Light Photoredox Catalyst for Metal-Free Atom Transfer Radical Polymerization.

    Science.gov (United States)

    Dadashi-Silab, Sajjad; Pan, Xiangcheng; Matyjaszewski, Krzysztof

    2017-05-02

    This paper reports use of phenyl benzo[b]phenothiazine (Ph-benzoPTZ) as a visible light-induced metal-free atom transfer radical polymerization (ATRP) photoredox catalyst. Well-controlled polymerizations of various methacrylate monomers were conducted under a 392 nm visible light LED using Ph-benzoPTZ to activate different alkyl halides. The use of the photocatalyst enabled temporal control over the growth of polymer chains during intermittent on/off periods. The polymerization was initiated and progressed only under stimulation by light and completely stopped in the absence of light. Block copolymers were synthesized to demonstrate high retention of chain end fidelity in the polymers and livingness of the process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Achieving highly effective nonfouling performance for surface-grafted poly(HPMA) via atom-transfer radical polymerization.

    Science.gov (United States)

    Zhao, Chao; Li, Lingyan; Zheng, Jie

    2010-11-16

    Human blood plasma and serum pose significant challenges to implanted devices because of highly unfavorable nonspecific protein adsorption on the surface. In this work, we introduce an improved two-step method to immobilize initiator thiols on a gold substrate for the surface-initiated atom-transfer radical polymerization (SI-ATRP) of hydroxypropyl methacrylate (HPMA). We investigate protein adsorption from a single-protein solution, diluted (10%) and undiluted (100%) human blood plasma, and serum on the poly(HPMA) brushes with different film thicknesses using surface plasmon resonance (SPR) sensors. SPR results show a correlation between antifouling properties and film thickness; that is, the poly(HPMA) brushes exhibit high protein resistance at medium film thicknesses of ∼25-40 nm (e.g. HPMA) brush also demonstrates its high resistance to fibroblast adhesion. This work provides an alternative surface polymerization approach to preparing effective antifouling poly(HPMA) materials for potential applications in blood-contacting medical devices.

  11. Synthesis of tri-block copolymers through reverse atom transfer radical polymerization of methyl methacrylate using polyurethane macroiniferter

    Directory of Open Access Journals (Sweden)

    2008-08-01

    Full Text Available Reverse atom transfer radical polymerization was successfully used for the first time to synthesis tri-block copolymers. Poly (methyl methacrylate-block-polyurethane-block-poly (methyl methacrylate tri-block copolymers were synthesized using tetraphenylethane-based polyurethane as a macroiniferter, copper(II halide as a catalyst and N, N, N′, N″, N″-pentamethyldiethylenetriamine as a ligand. Controlled nature of the polymerization was confirmed by the linear increase of number average molecular weight with increasing conversion. Mole contents of poly (methyl methacrylate present in the tri-block copolymers were calculated using proton nuclear magnetic resonance spectroscopy and the results were comparable with the gel permeation chromatography results. Differential scanning calorimetric results confirmed the presence of two different types of blocks in the tri-block copolymers.

  12. Conventional and atom transfer radical copolymerization of phenoxycarbonylmethyl methacrylate-styrene and thermal behavior of their copolymers

    Directory of Open Access Journals (Sweden)

    2007-08-01

    Full Text Available The atom transfer radical polymerization (ATRP of phenoxycarbonylmethyl methacrylate (PCMMA with styrene (St were performed in bulk at 110°C in the presence of ethyl 2-bromoacetate, cuprous(Ibromide (CuBr, and N,N,N’,N”,N”-pentamethyldiethyltriamine. Also, a series conventional free-radical polymerization (CFRP of PCMMA and styrene were carried out in the presence of 2,2’-azobisisobutyronitrile in 1,4-dioxane solvent at 60°C. The structure of homo and copolymers was characterized by IR, 1H and 13C-NMR techniques. The composition of the copolymers was calculated by 1H-NMR spectra. The average-molecular weight of the copolymers were investigated by Gel Permeation Chromatography (GPC. For copolymerization system, their monomer reactivity ratios were obtained by using both Kelen-Tüdõs and Fineman-Ross equations. Thermal analysis measurements of homo- and copolymers prepared CFRP and ATRP methods were measured by TGA-50 and DSC-50. Blends of poly(PCMMA and poly(St obtained via ATRP method have been prepared by casting films from dichlorormethane solution. The blends were characterized by differential scanning calorimetry. The initial decomposition temperatures of the resulting copolymers increased with increasing mole fraction of St.

  13. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jingjing, E-mail: jjwang1@hotmail.com; Wei, Jun

    2016-09-30

    Highlights: • Crosslinked hydrogel brushes were grafted from SS surfaces for marine antifouling. • All brush-coated SS surfaces could effectively reduce the adhesion of biofouling. • The antifouling efficacy increased with the crosslinking density of hydrogels. - Abstract: Crosslinked hydrogel brushes were grafted from stainless steel (SS) surfaces for marine antifouling. The brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) respectively with different fractions of crosslinker in the feed. The grafted layers prepared with different thickness were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and water contact angle measurements. With the increase in the fraction of crosslinker in the feed, the thickness of the grafted layer increased and the surface became smooth. All the brush-coated SS surfaces could effectively reduce the adhesion of bacteria and microalgae and settlement of barnacle cyprids, as compared to the pristine SS surface. The antifouling efficacy of the PEGMA polymer (PPEGMA)-grafted surface was higher than that of the MPC polymer (PMPC)-grafted surfaces. Furthermore, the crosslinked hydrogel brush-grafted surfaces exhibited better fouling resistance than the non-crosslinked polymer brush-grafted surfaces, and the antifouling efficacy increased with the crosslinking density. These hydrogel coatings of low toxicity and excellent anti-adhesive characteristics suggested their useful applications as environmentally friendly antifouling coatings.

  14. Light-Mediated Atom Transfer Radical Polymerization of Semi-Fluorinated (Meth)acrylates: Facile Access to Functional Materials.

    Science.gov (United States)

    Discekici, Emre H; Anastasaki, Athina; Kaminker, Revital; Willenbacher, Johannes; Truong, Nghia P; Fleischmann, Carolin; Oschmann, Bernd; Lunn, David J; Read de Alaniz, Javier; Davis, Thomas P; Bates, Christopher M; Hawker, Craig J

    2017-04-26

    A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me6-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (Đ ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results disclosed herein should create opportunities across a variety of fields that exploit fluorine-containing polymers for tailored bulk, interfacial, and solution properties.

  15. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    Science.gov (United States)

    Wang, Jingjing; Wei, Jun

    2016-09-01

    Crosslinked hydrogel brushes were grafted from stainless steel (SS) surfaces for marine antifouling. The brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) respectively with different fractions of crosslinker in the feed. The grafted layers prepared with different thickness were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and water contact angle measurements. With the increase in the fraction of crosslinker in the feed, the thickness of the grafted layer increased and the surface became smooth. All the brush-coated SS surfaces could effectively reduce the adhesion of bacteria and microalgae and settlement of barnacle cyprids, as compared to the pristine SS surface. The antifouling efficacy of the PEGMA polymer (PPEGMA)-grafted surface was higher than that of the MPC polymer (PMPC)-grafted surfaces. Furthermore, the crosslinked hydrogel brush-grafted surfaces exhibited better fouling resistance than the non-crosslinked polymer brush-grafted surfaces, and the antifouling efficacy increased with the crosslinking density. These hydrogel coatings of low toxicity and excellent anti-adhesive characteristics suggested their useful applications as environmentally friendly antifouling coatings.

  16. A DFT Study of R-X Bond Dissociation Enthalpies of Relevance to the Initiation Process of Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Gillies, Malcolm Bjørn; Matyjaszewski, Krzysztof; Norrby, Per-Ola

    2003-01-01

    DFT calculations at the B3P86/6-31G** level have been carried out to derive the bond dissociation energies (BDE) and free energies for a number of R-X systems (X ) Cl, Br, I, N3, and S2-CNMe2) that have been or can potentially be used as initiators for atom transfer radical polymerization (ATRP)....

  17. Acrylamide-b-N-isopropylacrylamide block copolymers : Synthesis by atomic transfer radical polymerization in water and the effect of the hydrophilic-hydrophobic ratio on the solution properties

    NARCIS (Netherlands)

    Wever, Diego Armando Z.; Ramalho, Graham; Picchioni, Francesco; Broekhuis, Antonius Augustinus

    2014-01-01

    A series of block copolymers of acrylamide and N-isopropylacrylamide (NIPAM) characterized by different ratios between the length of the two blocks have been prepared through atomic transfer radical polymerization in water at room temperature. The solution properties of the block copolymers were

  18. Hydrophilization of Poly(ether ether ketone) Films by Surface-initiated Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Eskimergen, Rüya; Burkrinsky, J.T.

    2008-01-01

    and confirmed by ATR FTIR, water contact ang;le, and Thermal Gravimetric Analysis (TGA). The surface topography was evaluated by "Atomic Force Microscopy (AFM). X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the degree of functionalization. The performed modification allowed for successful...

  19. Nitroxide mediated and atom transfer radical graft polymerization of atactic polymers onto syndiotactic polystyrene

    Directory of Open Access Journals (Sweden)

    M. Abbasian

    2012-06-01

    Full Text Available 'Living' radical graft polymerization was employed to prepare graft copolymers with nitroxide-mediated arylated syndiotactic polystyrene as the backbone and polystyrene (PS, poly(p-methylstyrene (PMS and poly(methylmethacrylate (PMMA as branches. A two-stage process has been developed to synthesize the macroinitiator. First, syndiotactic polystyrene (sPS was modified by the Friedel-Crafts reaction to introduce chlorine; second, the chlorine groups were converted to nitroxide mediated groups by coupling with 1-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO-OH. The resulting macroinitiator (sPS-TEMPO for 'living' free radical polymerization was then heated in the presence of styrene and p-methylstyrene to form graft and block copolymers. We used the obtained copolymer and N-bromosuccinimide as brominating agent to achieve polymers with bromine groups. This brominated copolymer was used as a macroinitiator for polymerizing methyl methacrylate in the presence of the CuBr/bpy catalyst system. The formation of the graft and block copolymers was confirmed by DSC, ¹H NMR and FTIR spectroscopy. This approach using macroinitiators is an effective method for the preparation of new materials.

  20. In situ development of self-reinforced cellulose nanocrystals based thermoplastic elastomers by atom transfer radical polymerization.

    Science.gov (United States)

    Yu, Juan; Wang, Chunpeng; Wang, Jifu; Chu, Fuxiang

    2016-05-05

    Recently, the utilization of cellulose nanocrystals (CNCs) as a reinforcing material has received a great attention due to its high elastic modulus. In this article, a novel strategy for the synthesis of self-reinforced CNCs based thermoplastic elastomers (CTPEs) is presented. CNCs were first surface functionalized with an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP). Subsequently, SI-ATRP of methyl methacrylate (MMA) and butyl acrylate (BA) was carried out in the presence of sacrificial initiator to form CTPEs in situ. The CTPEs together with the simple blends of CNCs and linear poly(MMA-co-BA) copolymer (P(MMA-co-BA)) were characterized for comparative study. The results indicated that P(MMA-co-BA) was successfully grafted onto the surface of CNCs and the compatibility between CNCs and the polymer matrix in CTPEs was greatly enhanced. Specially, the CTPEs containing 2.15wt% CNCs increased Tg by 19.2°C and tensile strength by 100% as compared to the linear P(MMA-co-BA). Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. In Situ Investigation of Electrochemically Mediated Surface-Initiated Atom Transfer Radical Polymerization by Electrochemical Surface Plasmon Resonance.

    Science.gov (United States)

    Chen, Daqun; Hu, Weihua

    2017-04-18

    Electrochemically mediated atom transfer radical polymerization (eATRP) initiates/controls the controlled/living ATRP chain propagation process by electrochemically generating (regenerating) the activator (lower-oxidation-state metal complex) from deactivator (higher-oxidation-state metal complex). Despite successful demonstrations in both of the homogeneous polymerization and heterogeneous systems (namely, surface-initiated ATRP, SI-ATRP), the eATRP process itself has never been in situ investigated, and important information regarding this process remains unrevealed. In this work, we report the first investigation of the electrochemically mediated SI-ATRP (eSI-ATRP) by rationally combining the electrochemical technique with real-time surface plasmon resonance (SPR). In the experiment, the potential of a SPR gold chip modified by the self-assembled monolayer of the ATRP initiator was controlled to electrochemically reduce the deactivator to activator to initiate the SI-ATRP, and the whole process was simultaneously monitored by SPR with a high time resolution of 0.1 s. It is found that it is feasible to electrochemically trigger/control the SI-ATRP and the polymerization rate is correlated to the potential applied to the gold chip. This work reveals important kinetic information for eSI-ATRP and offers a powerful platform for in situ investigation of such complicated processes.

  2. Preparation of magnetic molecularly imprinted polymers by atom transfer radical polymerization for the rapid extraction of avermectin from fish samples.

    Science.gov (United States)

    You, Xiaoxiao; Gao, Lei; Qin, Dongli; Chen, Ligang

    2017-01-01

    A novel and highly efficient approach to obtain magnetic molecularly imprinted polymers is described to detect avermectin in fish samples. The magnetic molecularly imprinted polymers were synthesized by surface imprinting polymerization using magnetic multiwalled carbon nanotubes as the support materials, atom transfer radical polymerization as the polymerization method, avermectin as template, acrylamide as functional monomer, and ethylene glycol dimethacrylate as crosslinker. The characteristics of the magnetic molecularly imprinted polymers were assessed by using transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, vibrating sample magnetometry, X-ray diffraction, and thermogravimetric analysis. The binding characteristics of magnetic molecularly imprinted polymers were researched through isothermal adsorption experiment, kinetics adsorption experiment, and the selectivity experiment. Coupled with ultra high performance liquid chromatography and tandem mass spectrometry, the extraction conditions of the magnetic molecularly imprinted polymers as adsorbents for avermectin were investigated in detail. The recovery of avermectin was 84.2-97.0%, and the limit of detection was 0.075 μg/kg. Relative standard deviations of intra- and inter-day precisions were in the range of 1.7-2.9% and 3.4-5.6%, respectively. The results demonstrated that the extraction method not only has high selectivity and accuracy, but also is convenient for the determination of avermectin in fish samples. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Rational preparation of dibenzothiophene-imprinted polymers by surface imprinting technique combined with atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Wenming [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Liu, Lukuan [School of the Environment, Jiangsu University, Zhenjiang 212013 (China); Zhou, Zhiping, E-mail: zhouzp@ujs.edu.cn [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Liu, Hong [Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130023 (China); Xie, Binze; Xu, Wanzhen [School of the Environment, Jiangsu University, Zhenjiang 212013 (China)

    2013-10-01

    A computational simulation method is introduced to simulate the dibenzothiophene-monomer pre-assembly system of molecular imprinted polymers. The interaction type and intensity between dibenzothiophene and monomer are discussed from the binding energy and spatial position distribution. The simulation and analysis results indicate that the amount of the function monomer is not the more the better in preparing molecular imprinted polymers. Based on the above results, a novel dibenzothiophene-imprinted polymers with the favorable specific adsorption effect was prepared by surface imprinting technique combined with atom transfer radical polymerization. This combined technologies are used for preparing a desulfurization adsorbent for the first time. Various measures were selected to characterize the structure and morphology of the prepared adsorbent. The characterization results show that the adsorbent has suitable features for further adsorption process. A series of static adsorption experiments were conducted to analyze its adsorption performance. The adsorption process follows Elovich model by the kinetic analysis and Sips equation by the isothermal analysis. The approach we described will provide another opportunity in the deep desulfurization field.

  4. Surface modification of glycidyl-containing poly(methyl methacrylate) microchips using surface-initiated atom-transfer radical polymerization.

    Science.gov (United States)

    Sun, Xuefei; Liu, Jikun; Lee, Milton L

    2008-02-01

    Fabrication of microfluidic systems from polymeric materials is attractive because of simplicity and low cost. Unfortunately, the surfaces of many polymeric materials can adsorb biological samples. Therefore, it is necessary to modify their surfaces before these polymeric materials can be used for separation and analysis. Oftentimes it is difficult to modify polymeric surfaces because of their resistance to chemical reaction. Recently, we introduced a surface-reactive acrylic polymer, poly(glycidyl methacrylate-co-methyl methacrylate) (PGMAMMA), which can be modified easily and is suitable for fabrication of microfluidic devices. Epoxy groups on the surface can be activated by air plasma treatment, hydrolysis, or aminolysis. In this work, the resulting hydroxyl or amino groups were reacted with 2-bromoisobutylryl bromide to introduce an initiator for surface-initiated atom-transfer radical polymerization (SI-ATRP). Polyethylene glycol (PEG) layers grown on the surface using this method were uniform, hydrophilic, stable, and resistant to protein adsorption. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize activated polymer surfaces, initiator-bound surfaces, and PEG-grafted surfaces. We obtained excellent capillary electrophoresis (CE) separations of proteins and peptides with the PEG-modified microchips. A separation efficiency of 4.4 x 10(4) plates for a 3.5 cm long separation channel was obtained.

  5. Polymer brushes on single-walled carbon nanotubes by atom transfer radical polymerization of n-butyl methacrylate.

    Science.gov (United States)

    Qin, Shuhui; Qin, Dongqi; Ford, Warren T; Resasco, Daniel E; Herrera, Jose E

    2004-01-14

    Polymer brushes with single-walled carbon nanotubes (SWNT) as backbones were synthesized by grafting n-butyl methacrylate (nBMA) from the ends and sidewalls of SWNT via atom transfer radical polymerization (ATRP). Carboxylic acid groups on SWNT were formed by nitric acid oxidation. The ATRP initiators were covalently attached to the SWNT by esterification of 2-hydroxyethyl 2'-bromopropionate with carboxylic acid groups. Methyl 2-bromopropionate (MBP) was added as free initiator during the brush preparation to control growth of the brushes and to monitor the polymerization kinetics. Size-exclusion chromatography (SEC) results show that the molecular weight of free poly(n-butyl methacrylate) (PnBMA) increased linearly with nBMA monomer conversion. PnBMA cleaved from the SWNT after high conversion had the same molecular weight as PnBMA produced in solution. Thermogravimetric analyses (TGA) show that the amount of PnBMA grown from the SWNT increased linearly with the molecular weight of the free PnBMA. The most highly PnBMA-functionalized SWNT dissolve in 1,2-dichlorobenzene, chloroform, and tetrahydrofuran, and solubility increases with the amount of PnBMA bound to SWNT. Near-infrared and Raman spectra indicate that the side walls of the SWNT were lightly functionalized by the nitric acid treatment and that the degree of functionalization of the SWNT did not change significantly during the formation of initiator or during the polymerization. Atomic force microscopy (AFM) images show contour lengths of the SWNT brushes on a mica surface from 200 nm to 2.0 microm and an average height of the backbone of 2-3 nm, indicating that the bundles of original SWNT were broken into individual tubes by functionalization and polymerization.

  6. Chain conformation and nano-patterning of polymer brushes prepared by surface-initiated atom transfer radical polymerization

    Science.gov (United States)

    Gao, Xiang

    Over the past decade, the development of surface-initiated living polymerization methods has brought a breakthrough to surface modification owing to their control ability. Surface-initiated atom transfer radical polymerization (si-ATRP), as the most popular one, has been widely employed to give novel polymer structures and functionalities to various surfaces for the purposes of tailoring surface properties, introducing new functions, or preparing so-called "smart surfaces", which can respond to external stimuli such as solvent type, pH, temperature, electric and magnetic fields etc. In this thesis, the mechanistic study of the si-ATRP was first carried out through modeling to gain good understanding of si-ATRP. Si-ATRP was then employed to prepare different types of polymer brushes to produce "smart surfaces". The kinetic model was developed using the method of moment. Combined with experimental data, a quantitative analysis was carried out for the si-ATRP mechanism. All information of grafted polymer chains, including active chain concentration, radical concentration, chain length, polydispersity, was illustrated. A new radical termination mechanism, termed as migration-termination, was proposed for si-ATRP. Si-ATRP was then employed to graft poly(oligo(ethylene glycol) methacrylate) (POEGMA) block poly(methyl methacrylate) (PMMA) brushes on silicon wafer surfaces. Simple solvent treatment gave nanoscale patterns via the phase segregation of POEGMA and PMMA segments. Various patterns including spherical aggregates, wormlike aggregates, stripe patterns, perforated layers and complete overlayers, were obtained by adjusting the upper block layer thickness. Furthermore, these nanopatterns had a unique stimuli-responsive property, i.e., switching between different morphologies reversibly after being treated with selective solvents. POEGMA-block-poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) brushes, having two hydrophilic segments, were synthesized

  7. Preparation of a novel polymer monolith with functional polymer brushes by two-step atom-transfer radical polymerization for trypsin immobilization.

    Science.gov (United States)

    Li, Nan; Zheng, Wei; Shen, Ying; Qi, Li; Li, Yaping; Qiao, Juan; Wang, Fuyi; Chen, Yi

    2014-12-01

    Novel porous polymer monoliths grafted with poly{oligo[(ethylene glycol) methacrylate]-co-glycidyl methacrylate} brushes were fabricated via two-step atom-transfer radical polymerization and used as a trypsin-based reactor in a continuous flow system. This is the first time that atom-transfer radical polymerization technique was utilized to design and construct polymer monolith bioreactor. The prepared monoliths possessed excellent permeability, providing fast mass transfer for enzymatic reaction. More importantly, surface properties, which were modulated via surface-initiated atom-transfer radical polymerization, were found to have a great effect on bioreactor activities based on Michaelis-Menten studies. Furthermore, three model proteins were digested by the monolith bioreactor to a larger degree within dramatically reduced time (50 s), about 900 times faster than that by free trypsin (12 h). The proposed method provided a platform to prepare porous monoliths with desired surface properties for immobilizing various enzymes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Novel UV Initiator for Functionalization of Multiwalled Carbon Nanotubes by Atom Transfer Radical Polymerization Applied on Two Different Grades of Nanotubes

    DEFF Research Database (Denmark)

    Daugaard, Anders Egede; Jankova Atanasova, Katja; Bøgelund, J.

    2010-01-01

    A novel nonoxidative method for preparation of functionalized multiwalled carbon nanotubes (MWCNT) has been developed based on a UV sensitive initiator for atom transfer radical polymerization (ATRP). The method has been investigated with respect to ligands and polymerization time for the prepara......A novel nonoxidative method for preparation of functionalized multiwalled carbon nanotubes (MWCNT) has been developed based on a UV sensitive initiator for atom transfer radical polymerization (ATRP). The method has been investigated with respect to ligands and polymerization time...... for the preparation of polystyrene functionalized MWCNT. It was found that pentamethyldiethylenetriamine (PMDETA) gave superior results with higher loading in shorter polymerization time. A comparative study of the method applied on two different grades of nonoxidized MWCNT has been performed, illustrating large...

  9. Protein adsorption resistance of PVP-modified polyurethane film prepared by surface-initiated atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Huihui; Qian, Bin; Zhang, Wei [Shanghai Key Laboratory of Functional Materials Chemistry and Research Center of Analysis and Test, East China University of Science and Technology, Shanghai 200237 (China); Lan, Minbo, E-mail: minbolan@ecust.edu.cn [Shanghai Key Laboratory of Functional Materials Chemistry and Research Center of Analysis and Test, East China University of Science and Technology, Shanghai 200237 (China); State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237 (China)

    2016-02-15

    Highlights: • Antifouling PVP brushes were successfully grafted on PU films by SI-ATRP. • The effect of polymerization time on surface property and topography was studied. • Hydrophilicity and protein fouling resistance of PVP–PU films were greatly promoted. • Competitive adsorption of three proteins on PVP–PU films was evaluated. - Abstract: An anti-fouling surface of polyurethane (PU) film grafted with Poly(N-vinylpyrrolidone) (PVP) was prepared through surface-initiated atom transfer radical polymerization (SI-ATRP). And the polymerization time was investigated to obtain PU films with PVP brushes of different lengths. The surface properties and protein adsorption of modified PU films were evaluated. The results showed that the hydrophilicity of PU–PVP films were improved with the increase of polymerization time, which was not positive correlation with the surface roughness due to the brush structure. Additionally, the protein resistance performance was promoted when prolonging the polymerization time. The best antifouling PU–PVP (6.0 h) film reduced the adsoption level of bovine serum albumin (BSA), lysozyme (LYS), and brovin serum fibrinogen (BFG) by 93.4%, 68.3%, 85.6%, respectively, compared to the unmodified PU film. The competitive adsorption of three proteins indicated that LYS preferentially adsorbed on the modified PU film, while BFG had the lowest adsorption selectivity. And the amount of BFG on PU–PVP (6.0 h) film reduced greatly to 0.08 μg/cm{sup 2}, which was almost one-tenth of its adsorption from the single-protein system. Presented results suggested that both hydrophilicity and surface roughness might be the important factors in all cases of protein adsorption, and the competitive or selective adsorption might be related to the size of the proteins, especially on the non-charged films.

  10. Combining Polymers with the Functionality of Proteins: New Concepts for Atom Transfer Radical Polymerization, Nanoreactors and Damage Self-reporting Materials

    OpenAIRE

    Bruns Nico; Lörcher Samuel; Makyla Katarzyna; Pollard Jonas; Renggli Kasper; Spulber Mariana

    2013-01-01

    Proteins are macromolecules with a great diversity of functions. By combining these biomolecules with polymers exciting opportunities for new concepts in polymer sciences arise. This highlight exemplifies the aforementioned with current research results of our group. We review our discovery that the proteins horseradish peroxidase and hemoglobin possess ATRPase activity i.e. they catalyze atom transfer radical polymerizations. Moreover a permeabilization method for polymersomes is presented w...

  11. Investigation of the Mechanism of Electron Capture and Electron Transfer Dissociation of Peptides with a Covalently Attached Free Radical Hydrogen Atom Scavenger.

    Science.gov (United States)

    Sohn, Chang Ho; Yin, Sheng; Peng, Ivory; Loo, Joseph A; Beauchamp, J L

    2015-11-15

    The mechanisms of electron capture and electron transfer dissociation (ECD and ETD) are investigated by covalently attaching a free-radical hydrogen atom scavenger to a peptide. The 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) radical was chosen as the scavenger due to its high hydrogen atom affinity (ca. 280 kJ/mol) and low electron affinity (ca. 0.45 ev), and was derivatized to the model peptide, FQX TEMPO EEQQQTEDELQDK. The X TEMPO residue represents a cysteinyl residue derivatized with an acetamido-TEMPO group. The acetamide group without TEMPO was also examined as a control. The gas phase proton affinity (882 kJ/mol) of TEMPO is similar to backbone amide carbonyls (889 kJ/mol), minimizing perturbation to internal solvation and sites of protonation of the derivatized peptides. Collision induced dissociation (CID) of the TEMPO tagged peptide dication generated stable odd-electron b and y type ions without indication of any TEMPO radical induced fragmentation initiated by hydrogen abstraction. The type and abundance of fragment ions observed in the CID spectra of the TEMPO and acetamide tagged peptides are very similar. However, ECD of the TEMPO labeled peptide dication yielded no backbone cleavage. We propose that a labile hydrogen atom in the charge reduced radical ions is scavenged by the TEMPO radical moiety, resulting in inhibition of N-C α backbone cleavage processes. Supplemental activation after electron attachment (ETcaD) and CID of the charge-reduced precursor ion generated by electron transfer of the TEMPO tagged peptide dication produced a series of b + H (b H ) and y + H (y H ) ions along with some c ions having suppressed intensities, consistent with stable O-H bond formation at the TEMPO group. In summary, the results indicate that ECD and ETD backbone cleavage processes are inhibited by scavenging of a labile hydrogen atom by the localized TEMPO radical moiety. This observation supports the conjecture that ECD and ETD processes involve long

  12. Surface-Initiated Atom Transfer Radical Polymerization of Magnetite Nanoparticles with Statistical Poly(tert-butyl acrylate)-poly(poly(ethylene glycol) methyl ether methacrylate) Copolymers

    OpenAIRE

    Patcharin Kanhakeaw; Boonjira Rutnakornpituk; Uthai Wichai; Metha Rutnakornpituk

    2015-01-01

    This work presented the surface modification of magnetite nanoparticle (MNP) with poly[(t-butyl acrylate)-stat-(poly(ethylene glycol) methyl ether methacrylate)] copolymers (P[(t-BA)-stat-PEGMA]) via a surface-initiated “grafting from” atom transfer radical polymerization (ATRP). Loading molar ratio of t-BA to PEGMA was systematically varied (100 : 0, 75 : 25, 50 : 50, and 25 : 75, resp.) such that the degree of hydrophilicity of the copolymers, affecting the particle dispersibility in water,...

  13. A manganese(V)-oxo π-cation radical complex: influence of one-electron oxidation on oxygen-atom transfer.

    Science.gov (United States)

    Prokop, Katharine A; Neu, Heather M; de Visser, Sam P; Goldberg, David P

    2011-10-12

    One-electron oxidation of Mn(V)-oxo corrolazine 2 affords 2(+), the first example of a Mn(V)(O) π-cation radical porphyrinoid complex, which was characterized by UV-vis, EPR, LDI-MS, and DFT methods. Access to 2 and 2(+) allowed for a direct comparison of their reactivities in oxygen-atom transfer (OAT) reactions. Both complexes are capable of OAT to PPh(3) and RSR substrates, and 2(+) was found to be a more potent oxidant than 2. Analysis of rate constants and activation parameters, together with DFT calculations, points to a concerted OAT mechanism for 2(+) and 2 and indicates that the greater electrophilicity of 2(+) likely plays a dominant role in enhancing its reactivity. These results are relevant to comparisons between Compound I and Compound II in heme enzymes.

  14. Combining polymers with the functionality of proteins: new concepts for atom transfer radical polymerization, nanoreactors and damage self-reporting materials.

    Science.gov (United States)

    Bruns, Nico; Lörcher, Samuel; Makyła, Katarzyna; Pollarda, Jonas; Renggli, Kasper; Spulber, Mariana

    2013-01-01

    Proteins are macromolecules with a great diversity of functions. By combining these biomolecules with polymers, exciting opportunities for new concepts in polymer sciences arise. This highlight exemplifies the aforementioned with current research results of our group. We review our discovery that the proteins horseradish peroxidase and hemoglobin possess ATRPase activity, i.e. they catalyze atom transfer radical polymerizations. Moreover, a permeabilization method for polymersomes is presented, where the photo-reaction of an α-hydroxyalkylphenone with block copolymer vesicles yields enzyme-containing nanoreactors. A further intriguing possibility to obtain functional nanoreactors is to enclose a polymerization catalyst into the thermosome, a protein cage from the family of chaperonins. Last but not least, fluorescent proteins are discussed as mechanoresponsive molecular sensors that report microdamages within fiber-reinforced composite materials.

  15. High-performance liquid chromatographic method to evaluate the hydrogen atom transfer during reaction between 1,1-diphenyl-2-picryl-hydrazyl radical and antioxidants

    Energy Technology Data Exchange (ETDEWEB)

    Boudier, Ariane; Tournebize, Juliana [CITHEFOR - EA 3452, Faculte de Pharmacie, Nancy-Universite, 5 Rue Albert Lebrun, BP 80403, 54001 Nancy Cedex (France); Bartosz, Grzegorz [Department of Molecular Biophysics, University of Lodz, Lodz (Poland); El Hani, Safae; Bengueddour, Rachid [Laboratoire de Nutrition et Sante, Biology Department, Faculty of Sciences, Ibn Tofail University, Kenitra (Morocco); Sapin-Minet, Anne [CITHEFOR - EA 3452, Faculte de Pharmacie, Nancy-Universite, 5 Rue Albert Lebrun, BP 80403, 54001 Nancy Cedex (France); Leroy, Pierre, E-mail: pierre.leroy@pharma.uhp-nancy.fr [CITHEFOR - EA 3452, Faculte de Pharmacie, Nancy-Universite, 5 Rue Albert Lebrun, BP 80403, 54001 Nancy Cedex (France)

    2012-01-20

    Highlights: Black-Right-Pointing-Pointer Both 1,1-diphenyl-2-picrylhydrazyl radical and its product measurement by HPLC. Black-Right-Pointing-Pointer Lowest limit of detection by monitoring 1,1-diphenyl-2-picryl-hydrazine. Black-Right-Pointing-Pointer Adsorption problem of the radical on HPLC parts have been pointed out. - Abstract: 1,1-Diphenyl-2-picrylhydrazyl (DPPH{center_dot}) is a stable nitrogen centred radical widely used to evaluate direct radical scavenging properties of various synthetic or natural antioxidants (AOs). The bleaching rate of DPPH{center_dot} absorbance at 515 nm is usually monitored for this purpose. In order to avoid the interference of complex coloured natural products used as antioxidant supplements or cosmetics, HPLC systems have been reported as alternative techniques to spectrophotometry. They also rely upon measurement of DPPH{center_dot} quenching rate and none of them permits to identify and measure 1,1-diphenyl-2-picryl-hydrazine (DPPH-H), the reduced product of DPPH{center_dot} resulting from hydrogen atom transfer (HAT), which is the main mechanism of the reaction between DPPH{center_dot} and AOs. We presently report an HPLC method devoted to the simultaneous measurement of DPPH{center_dot} and DPPH-H. Both were fully separated on a C18 column eluted with acetonitrile-10 mM ammonium citrate buffer pH 6.8 (70:30, v/v) and detected at 330 nm. Adsorption process of DPPH{center_dot} onto materials of the HPLC system was pointed out. Consequently, the linearity range observed for DPPH{center_dot} was restricted, thus a much lower limit of detection was obtained for DPPH-H than for DPPH{center_dot} using standards (0.02 and 14 {mu}M, respectively). The method was applied to three commonly used AOs, i.e. Trolox{sup Registered-Sign }, ascorbic acid and GSH, and compared with spectrophotometry. Further application to complex matrices (cell culture media, vegetal extracts) and nanomaterials demonstrated (i) its usefulness because of

  16. Synthesis and Characterization of Surface Grafted Poly(N-isopropylacrylamide) and Poly(Carboxylic Acid)- Iron Particles via Atom Transfer Radical Polymerization for Biomedical Applications.

    Science.gov (United States)

    Sutrisno, Joko; Fuchs, Alan; Evrensel, Cahit

    2014-07-15

    This research relates to the preparation and characterization of surface grafted poly(N-isopropylacrylamide) and poly(carboxylic acid)-micron-size iron particles via atom transfer radical polymerization (ATRP). The surface grafted polymers-iron particles result in multifunctional materials which can be used in biomedical applications. The functionalities consist of cell targeting, imaging, drug delivery, and immunological response. The multifunctional materials are synthesized in two steps. First, surface grafting is used to place polymer molecules on the iron particles surface. The second step, is conjugation of the bio-molecules onto the polymer backbone. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy were used to confirm the presence of polymers on the iron particles. The thickness of the grafted polymers and glass transition temperature of the surface grafted polymers were determined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The covalent bond between grafted polymers and iron particles caused higher glass transition temperature as compared with non-grafted polymers. The ability to target the bio-molecule and provide fluorescent imaging was simulated by conjugation of rat immunoglobulin and fluorescein isothiocyanate (FITC) labeled anti-rat. The fluorescence intensity was determined using flow cytometry and conjugated IgG-FITC anti-rat on iron particles which was imaged using a fluorescence microscopy.

  17. Synthesis and Characterization of Surface Grafted Poly(N-isopropylacrylamide) and Poly(Carboxylic Acid)– Iron Particles via Atom Transfer Radical Polymerization for Biomedical Applications

    Science.gov (United States)

    Sutrisno, Joko; Fuchs, Alan; Evrensel, Cahit

    2014-01-01

    This research relates to the preparation and characterization of surface grafted poly(N-isopropylacrylamide) and poly(carboxylic acid)–micron-size iron particles via atom transfer radical polymerization (ATRP). The surface grafted polymers–iron particles result in multifunctional materials which can be used in biomedical applications. The functionalities consist of cell targeting, imaging, drug delivery, and immunological response. The multifunctional materials are synthesized in two steps. First, surface grafting is used to place polymer molecules on the iron particles surface. The second step, is conjugation of the bio-molecules onto the polymer backbone. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy were used to confirm the presence of polymers on the iron particles. The thickness of the grafted polymers and glass transition temperature of the surface grafted polymers were determined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The covalent bond between grafted polymers and iron particles caused higher glass transition temperature as compared with non-grafted polymers. The ability to target the bio-molecule and provide fluorescent imaging was simulated by conjugation of rat immunoglobulin and fluorescein isothiocyanate (FITC) labeled anti-rat. The fluorescence intensity was determined using flow cytometry and conjugated IgG-FITC anti-rat on iron particles which was imaged using a fluorescence microscopy. PMID:25382869

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

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiao, E-mail: wangxiao@dlpu.edu.cn [School of Textile and Materials Engineering, Dalian Polytechnic University, Dalian, Liaoning Province (China); Zhang, Yue; Lv, Lihua; Cui, Yongzhu; Wei, Chunyan [School of Textile and Materials Engineering, Dalian Polytechnic University, Dalian, Liaoning Province (China); Pang, Guibing [School of Mechanical Engineering and Automation, Dalian Polytechnic University, Dalian, Liaoning Province (China)

    2016-02-15

    Graphical abstract: - Highlights: • Adsorbed anionic dye molecules are conducive to preferential growth of (0 0 1) plane of Mg(OH){sub 2} crystal for Mg(OH){sub 2} pigments. • Uniform coverage of nanosized Mg(OH){sub 2} pigments on fiber surface is achieved via surface-initiated ATRP. • About 4 wt% of Mg(OH){sub 2} pigment on fiber surface shortens nearly half of burning time of cellulose. - Abstract: Mg(OH){sub 2} flame retardant hybrid pigment is synthesized through simultaneous solution precipitation and adsorption of anionic dyes (C.I. Acid Red 6). The Mg(OH){sub 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){sub 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){sub 2} crystals and affect the formation of lamella-like Mg(OH){sub 2} crystals. The cellulose fiber grafted with modified Mg(OH){sub 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.

  19. Synthesis and characterization of TiO{sub 2}/Ag/polymer ternary nanoparticles via surface-initiated atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jung Tae; Koh, Joo Hwan; Seo, Jin Ah [Department of Chemical and Biomolecular Engineering, Yonsei University, 262 Seongsanno, Seodaemun-gu, Seoul 120-749 (Korea, Republic of); Cho, Yong Soo [Department of Materials Science and Engineering, Yonsei University, 262 Seongsanno, Seodaemun-gu, Seoul 120-749 (Korea, Republic of); Kim, Jong Hak, E-mail: jonghak@yonsei.ac.kr [Department of Chemical and Biomolecular Engineering, Yonsei University, 262 Seongsanno, Seodaemun-gu, Seoul 120-749 (Korea, Republic of)

    2011-08-01

    We report on the novel ternary hybrid materials consisting of semiconductor (TiO{sub 2}), metal (Ag) and polymer (poly(oxyethylene methacrylate) (POEM)). First, a hydrophilic polymer, i.e. POEM, was grafted from TiO{sub 2} nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. These TiO{sub 2}-POEM brush nanoparticles were used to template the formation of Ag nanoparticles by introduction of a AgCF{sub 3}SO{sub 3} precursor and a NaBH{sub 4} aqueous solution for reduction process. Successful grafting of polymeric chains from the surface of TiO{sub 2} nanoparticles and the in situ formation of Ag nanoparticles within the polymeric chains were confirmed using transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FT-IR spectroscopy also revealed the specific interaction of Ag nanoparticles with the C=O groups of POEM brushes. This study presents a simple route for the in situ synthesis of both metal and polymer confined within the semiconductor, producing ternary hybrid inorganic-organic nanomaterials.

  20. Preparation of a magnetic molecularly imprinted polymer by atom-transfer radical polymerization for the extraction of parabens from fruit juices.

    Science.gov (United States)

    You, Xiaoxiao; Piao, Chungying; Chen, Ligang

    2016-07-01

    A silica-based surface magnetic molecularly imprinted polymer for the selective recognition of parabens was prepared using a facile and general method that combined atom-transfer radical polymerization with surface imprinting technique. The prepared magnetic molecularly imprinted polymer was characterized by transmission electron microscopy, Fourier transform infrared spectrometry and physical property measurement. The isothermal adsorption experiment and kinetics adsorption experiment investigated the adsorption property of magnetic molecularly imprinted polymer to template molecule. The four parabens including methylparaben, ethylparaben, propylparaben, and butylparaben were used to assess the rebinding selectivity. An extraction method, which used magnetic molecularly imprinted polymer as adsorbents coupled with high-performance liquid chromatography for the determination of the four parabens in fruit juice samples was developed. Under the optimal conditions, the limits of detections of the four parabens were 0.028, 0.026, 0.021, and 0.026 mg/L, respectively. The precision expressed as relative standard deviation ranging from 2.6 to 8.9% was obtained. In all three fortified levels, recoveries of parabens were in the range of 72.5-89.4%. The proposed method has been applied to different fruit juice samples including orange juice, grape juice, apple juice and peach juice, and satisfactory results were obtained. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine

    Directory of Open Access Journals (Sweden)

    Jing Lin

    2015-11-01

    Full Text Available Pentablock copolymers PMA-PPO-PEO-PPO-PMA synthesized via atom transfer radical polymerization (ATRP were self-assembled with varying amounts of γ-CDs to prepare poly(pseudorotaxanes (PPRs. When the concentration of γ-CDs was lower, the central PEO segment served as a shell of the micelles and was preferentially bent to pass through the γ-CD cavity to construct double-chain-stranded tight-fit PPRs characterized by a channel-like crystal structure. With an increase in the amount of γ-CDs added, they began to accommodate the poly(methyl acrylate (PMA segments dissociated from the core of the micelles. When more γ-CDs were threaded and slipped over the segments, the γ-CDs were randomly distributed along the pentablock copolymer chain to generate single-chain-stranded loose-fit PPRs and showed no characteristic channel-like crystal structure. All the self-assembly processes of the pentablock copolymers resulted in the formation of hydrogels. After endcapping via in situ ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC, these single-chain-stranded loose-fit PPRs were transformed into conformational identical polyrotaxanes (PRs. The structures of the PPRs and PRs were characterized by means of 1H NMR, GPC, 13C CP/MAS NMR, 2D 1H NOESY NMR, FTIR, WXRD, TGA and DSC analyses.

  2. Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine

    Science.gov (United States)

    Lin, Jing; Kong, Tao; Ye, Lin; Zhang, Ai-ying

    2015-01-01

    Summary Pentablock copolymers PMA-PPO-PEO-PPO-PMA synthesized via atom transfer radical polymerization (ATRP) were self-assembled with varying amounts of γ-CDs to prepare poly(pseudorotaxanes) (PPRs). When the concentration of γ-CDs was lower, the central PEO segment served as a shell of the micelles and was preferentially bent to pass through the γ-CD cavity to construct double-chain-stranded tight-fit PPRs characterized by a channel-like crystal structure. With an increase in the amount of γ-CDs added, they began to accommodate the poly(methyl acrylate) (PMA) segments dissociated from the core of the micelles. When more γ-CDs were threaded and slipped over the segments, the γ-CDs were randomly distributed along the pentablock copolymer chain to generate single-chain-stranded loose-fit PPRs and showed no characteristic channel-like crystal structure. All the self-assembly processes of the pentablock copolymers resulted in the formation of hydrogels. After endcapping via in situ ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC), these single-chain-stranded loose-fit PPRs were transformed into conformational identical polyrotaxanes (PRs). The structures of the PPRs and PRs were characterized by means of 1H NMR, GPC, 13C CP/MAS NMR, 2D 1H NOESY NMR, FTIR, WXRD, TGA and DSC analyses. PMID:26732122

  3. Enhanced and selective adsorption of mercury ions on chitosan beads grafted with polyacrylamide via surface-initiated atom transfer radical polymerization.

    Science.gov (United States)

    Li, Nan; Bai, Renbi; Liu, Changkun

    2005-12-06

    Enhanced and selective removal of mercury ions was achieved with chitosan beads grafted with polyacrylamide (chitosan-g-polyacrylamide) via surface-initiated atom transfer radical polymerization (ATRP). The chitosan-g-polyacrylamide beads were found to have significantly greater adsorption capacities and faster adsorption kinetics for mercury ions than the chitosan beads. At pH 4 and with initial mercury concentrations of 10-200 mg/L, the chitosan-g-polyacrylamide beads can achieve a maximum adsorption capacity of up to 322.6 mg/g (in comparison with 181.8 mg/g for the chitosan beads) and displayed a short adsorption equilibrium time of less than 60 min (compared to more than 15 h for the chitosan beads). Coadsorption experiments with both mercury and lead ions showed that the chitosan-g-polyacrylamide beads had excellent selectivity in the adsorption of mercury ions over lead ions at pH polyacrylamide beads can be effectively desorbed in a perchloric acid solution, and the regenerated beads can be reused almost without any loss of adsorption capacity.

  4. Surface-Initiated Atom Transfer Radical Polymerization of Magnetite Nanoparticles with Statistical Poly(tert-butyl acrylate-poly(poly(ethylene glycol methyl ether methacrylate Copolymers

    Directory of Open Access Journals (Sweden)

    Patcharin Kanhakeaw

    2015-01-01

    Full Text Available This work presented the surface modification of magnetite nanoparticle (MNP with poly[(t-butyl acrylate-stat-(poly(ethylene glycol methyl ether methacrylate] copolymers (P[(t-BA-stat-PEGMA] via a surface-initiated “grafting from” atom transfer radical polymerization (ATRP. Loading molar ratio of t-BA to PEGMA was systematically varied (100 : 0, 75 : 25, 50 : 50, and 25 : 75, resp. such that the degree of hydrophilicity of the copolymers, affecting the particle dispersibility in water, can be fine-tuned. The reaction progress in each step of the synthesis was monitored via Fourier transform infrared spectroscopy (FTIR. The studies in the reaction kinetics indicated that PEGMA had higher reactivity than that of t-BA in the copolymerizations. Gel permeation chromatography (GPC indicated that the molecular weights of the copolymers increased with the increase of the monomer conversion. Transmission electron microscopy (TEM revealed that the particles were spherical with averaged size of 8.1 nm in diameter. Dispersibility of the particles in water was apparently improved when the copolymers were coated as compared to P(t-BA homopolymer coating. The percentages of MNP and the copolymer in the composites were determined via thermogravimetric analysis (TGA and their magnetic properties were investigated via vibrating sample magnetometry (VSM.

  5. Poly(glycidyl methacrylate) grafted CdSe quantum dots by surface-initiated atom transfer radical polymerization: Novel synthesis, characterization, properties, and cytotoxicity studies

    Energy Technology Data Exchange (ETDEWEB)

    Bach, Long Giang; Islam, Md. Rafiqul [Department of Imaging System Engineering, Pukyong National University, Busan 608-737 (Korea, Republic of); Lee, Doh Chang [Department of Chemical and Biomolecular Engineering, KAIST Institute for the Nanocentury (KINC), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of); Lim, Kwon Taek, E-mail: ktlim@pknu.ac.kr [Department of Imaging System Engineering, Pukyong National University, Busan 608-737 (Korea, Republic of)

    2013-10-15

    A novel approach for the synthesis of poly(glycidyl methacrylate) grafted CdSe quantum dot (QDs) (PGMA-g-CdSe) was developed. The PGMA-g-CdSe nanohybrids were synthesized by the surface-initiated atom transfer radical polymerization of glycidyl methacrylate from the surface of the strategic initiator, CdSe-BrIB QDs prepared by the interaction of 2-bromoisobutyryl bromide (BrIB) and CdSe-OH QDs. The structure, morphology, and optical property of the PGMA-g-CdSe nanohybrids were analyzed by FT-IR, XPS, TGA, XRD, TEM, and PL. The as-synthesized PGMA-g-CdSe nanohybrids having multi-epoxide groups were employed for the direct coupling of biotin via ring-opening reaction of the epoxide groups to afford the Biotin-f-PGMA-g-CdSe nanobioconjugate. The covalent immobilization of biotin onto PGMA-g-CdSe was confirmed by FT-IR, XPS, and EDX. Biocompatibility and imaging properties of the Biotin-f-PGMA-g-CdSe were investigated by MTT bioassay and PL analysis, respectively. The cell viability study suggested that the biocompatibility was significantly enhanced by the functionalization of CdSe QDs by biotin and PGMA.

  6. A combination of "thiol-ene" click chemistry and surface initiated atom transfer radical polymerization: Fabrication of boronic acid functionalized magnetic graphene oxide composite for enrichment of glycoproteins.

    Science.gov (United States)

    Su, Jie; He, Xiwen; Chen, Langxing; Zhang, Yukui

    2018-04-01

    An efficient glycoproteins enrichment platform is one of vital preprocessing steps in biomarker research and in particular glycoproteomics. In this work, a well-defined boronic acid functionalized magnetic graphene oxide nanocomposite (Fe3O4-GO@PAAPBA) was synthesized for the selective enrichment of glycoproteins from complex biological samples via a novel strategy based on the "thiol-ene" click chemistry and surface initiated atom transfer radical polymerization (SI-ATRP). The initiator of ATRP was anchored to the surface of substrate through "thiol-ene" click reaction. The product Fe3O4-GO@PAAPBA was successfully synthesized in following SI-ATRP. The Fe3O4-GO@PAAPBA nanocomposite was characterized by transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and thermogravimetric analysis. The adsorption capacity of Fe3O4-GO@PAAPBA towards ovalbumin (OVA) and transferrin (Trf) is 471mgg-1 and 450mgg-1, respectively. The nanocomposite also featured good selectivity to glycoproteins in the mixture of glycoproteins and non-glycoproteins at alkaline (pH 9.0) and physiological conditions (pH 7.4). Furthermore, it can be applied to extract glycoproteins directly from egg white samples. These results have indicated that Fe3O4-GO@PAAPBA was a potential affinity material in glycoprotein analysis. Copyright © 2017 Elsevier B.V. All rights reserved.

  7. Surface polyPEGylation of Eu3+ doped luminescent hydroxyapatite nanorods through the combination of ligand exchange and metal free surface initiated atom transfer radical polymerization

    Science.gov (United States)

    Zeng, Guangjian; Liu, Meiying; Heng, Chunning; Huang, Qiang; Mao, Liucheng; Huang, Hongye; Hui, Junfeng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-01

    The Eu3+ doped luminescent hydroxyapatite (HAp) nanorods with uniform size and morphology can be synthesized by hydrothermal route. However, these HAp nanorods are coated by hydrophobic oleylamine, which makes them difficult to be dispersed in aqueous solution and impede their biomedical applications. In this work, Eu3+ doped luminescent polymers functionalized HAp nanorods were prepared through the combination of ligand exchange reaction and metal free surface initiated atom transfer radical polymerization (ATRP) method. In this procedure, the amino group functionalized HAp nanorods were first prepared by ligand exchange reaction using adenosine monophosphate (AMP) as ligand. Then the Br-containing initiators (HAp-Br) were introduced onto the surface of HAp-AMP nanorods through the amidation reaction. Finally, polymers functionalized HAp nanorods were prepared by metal free ATRP method using poly(ethylene glycol) methacrylate (PEGMA) as monomer and 10-phenylphenothiazine (PTH) as organic photocatalyst. The properties of these obtained HAp nanocomposites (HAP-polyPEGMA nanorods) were characterized by means of transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis in detail. The cell imaging of these HAP-polyPEGMA nanorods was examined using laser scanning confocal microscope to evaluate their biomedical applications. We demonstrated for the first time that hydrophobic luminescent HAp nanorods can be functionalized with polyPEGMA through the combination of ligand exchange reaction and metal free surface initiated ATRP. As compared with the traditional ATRP, the metal free ATRP can overcome the toxic and fluorescence quenching effects of metal catalysts such as copper ions. More importantly, the strategy described in this work should also be utilized for fabrications of many other luminescent polymer nanocomposites due to its good monomer adoptability.

  8. Synthesis of multirecognition magnetic molecularly imprinted polymer by atom transfer radical polymerization and its application in magnetic solid-phase extraction.

    Science.gov (United States)

    Kong, Xiang-Jin; Zheng, Chao; Lan, Yao-Han; Chi, Shuai-Shuai; Dong, Qian; Liu, Hao-Long; Peng, Chao; Dong, Lin-Yi; Xu, Liang; Wang, Xian-Hua

    2018-01-01

    In this work, we reported an effective method for the synthesis of a multirecognition magnetic molecularly imprinted polymer (MMIP) with atom transfer radical polymerization (ATRP), using 2,4-diamino-6-methyl-1,3,5-triazine as pseudo-template. The resulting MMIP was characterized in detail by Fourier transform-infrared (FT-IR) spectra, scanning electron microscopy (SEM), thermogravimetic analysis (TGA), and vibrating sample magnetometry (VSM). These results indicated the successful synthesis of MMIP with sufficient thermal stability and magnetic properties. The adsorption experiments were carried out to evaluate the specific selectivity of MMIP related to the spatial structure of target molecules. The MMIP exhibited multirecognition ability and excellent binding capability for melamine (MEL), cyromazine (CYR), triamterene (TAT), diaveridine (DVD), and trimethoprim (TME), and the apparent maximum number of binding sites (Q max) was 77.5, 75.2, 72.5, 69.9, and 70.4 μmol g-1, respectively. The multirecognition MMIP not only possessed adequate magnetic responsiveness for fast separation but also avoided the risk of template leakage on trace component analysis. Therefore, it was suitable for serving as a magnetic solid-phase extraction (MSPE) adsorbent. MSPE coupled with high-performance liquid chromatography analysis was applied to enrich and separate five target molecules from three samples. Recoveries for all target molecules ranged from 81.6 to 91.5% with relative standard deviations of no more than 4.1% (n = 3). Graphical abstract Multirecognition property of magnetic molecularly imprinted polymer prepared with pseudo template.

  9. Hydrogen-atom transfer in reactions of organic radicals with [Co-II(por)](center dot) (por = porphyrinato) and in subsequent addition of [Co(H)(por)] to olefins

    NARCIS (Netherlands)

    de Bruin, B.; Dzik, W.I.; Li, S.; Wayland, B.B.

    2009-01-01

    The mechanisms for hydrogen-atom transfer from the cyanoisopropyl radical C-center dot(CH3)(2)CN to [Co-II(por)](center dot) (yielding [Co-III(H)(por)] and CH2=C(CH3)(CN); por = porphyrinato) and the insertion of vinyl acetate (CH2=CHOAc) into the Co-H bond of [Co(H)(por)] (giving

  10. Evaluation of acrylate-based block copolymers prepared by atom transfer radical polymerization as matrices for paclitaxel delivery from coronary stents.

    Science.gov (United States)

    Richard, Robert E; Schwarz, Marlene; Ranade, Shrirang; Chan, A Ken; Matyjaszewski, Krzysztof; Sumerlin, Brent

    2005-01-01

    Acrylate-based block copolymers, synthesized by atom transfer radical polymerization (ATRP) processes, were evaluated as drug delivery matrices for the controlled release of paclitaxel from coronary stents. The polymers were multiblock copolymers consisting of poly(butyl acrylate) or poly(lauryl acrylate) soft blocks and hard blocks composed of poly(methyl methacrylate), poly(isobornyl acrylate), or poly(styrene) homo- or copolymers. Depending on the ratio of hard to soft blocks in the copolymers, coating formulations were produced that possessed variable elastomeric properties, resulting in stent coatings that maintained their integrity when assessed by scanning electron microscopy (SEM) imaging of overexpanded stents. In vitro paclitaxel release kinetics from coronary stents coated with these copolymers typically showed an early burst followed by sustained release behavior, which permitted the elution of the majority of the paclitaxel over a 10-day time period. It was determined that neither the nature of the polyacrylate (n-butyl or lauryl) nor that of the hard block appeared to affect the release kinetics of paclitaxel at a loading of 25% drug by weight, whereas some effects were observed at lower drug loading levels. Differential scanning calorimetry (DSC) analysis indicated that the paclitaxel was at least partially miscible with the poly(n-butyl acrylate) phase of those block copolymers. The copolymers were also evaluated for sterilization stability by exposing both the copolymer alone and copolymer/paclitaxel coated stents to e-beam radiation at doses of 1-3 times the nominal dose used for medical device sterilization (25 kGy). It was found that the copolymers containing blocks bearing quaternary carbons within the polymer backbone were less stable to the radiation and showed a decrease in molecular weight as determined by gel-permeation chromatography. Conversely, those without quaternary carbons showed no significant change in molecular weight when

  11. Surface polyPEGylation of Eu{sup 3+} doped luminescent hydroxyapatite nanorods through the combination of ligand exchange and metal free surface initiated atom transfer radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Guangjian; Liu, Meiying [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Heng, Chunning [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Shaanxi Key Laboratory of Degradable Biomedical Materials, Shaanxi R& D Center of Biomaterials and Fermentation Engineering, School of Chemical and Engineering, Northwest University, Xi’an 710069 (China); Huang, Qiang; Mao, Liucheng; Huang, Hongye [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Hui, Junfeng [Shaanxi Key Laboratory of Degradable Biomedical Materials, Shaanxi R& D Center of Biomaterials and Fermentation Engineering, School of Chemical and Engineering, Northwest University, Xi’an 710069 (China); Deng, Fengjie, E-mail: fengjiedeng@aliyun.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and The Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing 100084 (China)

    2017-03-31

    Highlights: • Surface modification of HAp nanorods through the combination of ligand exchange reaction and metal free SI-ATRP. • HAp-polyPEGMA displayed high water dispersibility, good biocompatibility and biological imaging capability. • Metal free ATRP can overcome the toxic and fluorescence quenching effects of metal catalysts of conventional ATRP. - Abstract: The Eu{sup 3+} doped luminescent hydroxyapatite (HAp) nanorods with uniform size and morphology can be synthesized by hydrothermal route. However, these HAp nanorods are coated by hydrophobic oleylamine, which makes them difficult to be dispersed in aqueous solution and impede their biomedical applications. In this work, Eu{sup 3+} doped luminescent polymers functionalized HAp nanorods were prepared through the combination of ligand exchange reaction and metal free surface initiated atom transfer radical polymerization (ATRP) method. In this procedure, the amino group functionalized HAp nanorods were first prepared by ligand exchange reaction using adenosine monophosphate (AMP) as ligand. Then the Br-containing initiators (HAp-Br) were introduced onto the surface of HAp-AMP nanorods through the amidation reaction. Finally, polymers functionalized HAp nanorods were prepared by metal free ATRP method using poly(ethylene glycol) methacrylate (PEGMA) as monomer and 10-phenylphenothiazine (PTH) as organic photocatalyst. The properties of these obtained HAp nanocomposites (HAP-polyPEGMA nanorods) were characterized by means of transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis in detail. The cell imaging of these HAP-polyPEGMA nanorods was examined using laser scanning confocal microscope to evaluate their biomedical applications. We demonstrated for the first time that hydrophobic luminescent HAp nanorods can be functionalized with polyPEGMA through the combination of ligand exchange reaction and metal free surface

  12. Preparation of bi-layer-polymer coated silica using atom transfer radical polymerization and its application as restricted access phase for HPLC separation of hydrophobic molecules in biological fluids.

    Science.gov (United States)

    Xu, Dan; Dong, Xiangchao; Zhang, Haiyan; Wang, Huaisong; Jiang, Ping; Zhang, Min

    2012-07-01

    A novel restricted access material was prepared by surface initiated atom transfer radical polymerization. The bi-layer-polymer structures were created on the surface of silica layer-by-layer. The inner layer was composed of poly(styrene-co-divinylbenzene), which was grafted first for binding small molecules based on hydrophobic and π-π interactions. The poly(styrene-co-divinylbenzene) bonded silica has good selectivity for aromatic hydrocarbons. It also has hydrophobicity and column efficiency similar to a C(18) bonded silica. The material has shown good ability of protein exclusion after grafting hydrophilic polymer on the external surface while its hydrophobicity and selectivity do not have obvious change. It demonstrated that the material is still qualified for hydrophobic extraction. In the study, the relations between the polymer structures and chromatographic properties of the materials were investigated. The synthetic conditions were optimized. The results have shown that the material prepared in the study has application potential in the HPLC analysis of hydrophobic molecules from biological samples by direct injection. It demonstrated that atom transfer radical polymerization can be used as a method in the preparation of restricted access material. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Structure and Reactivity of the Glutathione Radical Cation: Radical Rearrangement from the Cysteine Sulfur to the Glutamic Acid alpha-Carbon Atom

    NARCIS (Netherlands)

    Osburn, S.; Berden, G.; Oomens, J.; Gulyuz, K.; Polfer, N.C.; O'Hair, R.A.J.; Ryzhov, V.

    2013-01-01

    A gas-phase radical rearrangement through intramolecular hydrogen-atom transfer (HAT) was studied in the glutathione radical cation, [-ECG](+.), which was generated by a homolytic cleavage of the protonated S-nitrosoglutathione. Ion-molecule reactions suggested that the radical migrates from the

  14. A New Global Potential Energy Surface for the Hydroperoxyl Radical, HO2: Reaction Coefficients for H + O2 and Vibrational Splittings for H Atom Transfer

    Science.gov (United States)

    Dateo, Christopher E.; Arnold, James O. (Technical Monitor)

    1994-01-01

    A new analytic global potential energy surface describing the hydroperoxyl radical system H((sup 2)S) + O2(X (sup 3)Sigma((sup -)(sub g))) (reversible reaction) HO2 ((X-tilde) (sup 2)A'') (reversible reaction) O((sup 3)P) + O H (X (sup 2)Pi) has been fitted using the ab initio complete active space SCF (self-consistent-field)/externally contracted configuration interaction (CASSCF/CCI) energy calculations of Walch and Duchovic. Results of quasiclassical trajectory studies to determine the rate coefficients of the forward and reverse reactions at combustion temperatures will be presented. In addition, vibrational energy levels were calculated using the quantum DVR-DGB (discrete variable representation-distributed Gaussian basis) method and the splitting due to H atom migration is investigated. The material of the proposed presentation was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.

  15. Efficient transfer of francium atoms

    Science.gov (United States)

    Aubin, Seth; Behr, John; Gorelov, Alexander; Pearson, Matt; Tandecki, Michael; Collister, Robert; Gwinner, Gerald; Shiells, Kyle; Gomez, Eduardo; Orozco, Luis; Zhang, Jiehang; Zhao, Yanting; FrPNC Collaboration

    2016-05-01

    We report on the progress of the FrPNC collaboration towards Parity Non Conservation Measurements (PNC) using francium atoms at the TRIUMF accelerator. We demonstrate efficient transfer (higher than 40%) to the science vacuum chamber where the PNC measurements will be performed. The transfer uses a downward resonant push beam from the high-efficiency capture magneto optical trap (MOT) towards the science chamber where the atoms are recaptured in a second MOT. The transfer is very robust with respect to variations in the parameters (laser power, detuning, alignment, etc.). We accumulate a growing number of atoms at each transfer pulse (limited by the lifetime of the MOT) since the push beam does not eliminate the atoms already trapped in the science MOT. The number of atoms in the science MOT is on track to meet the requirements for competitive PNC measurements when high francium rates (previously demonstrated) are delivered to our apparatus. The catcher/neutralizer for the ion beam has been tested reliably to 100,000 heating/motion cycles. We present initial tests on the direct microwave excitation of the ground hyperfine transition at 45 GHz. Support from NSERC and NRC from Canada, NSF and Fulbright from USA, and CONACYT from Mexico.

  16. Structural and medium effects on the reactions of the cumyloxyl radical with intramolecular hydrogen bonded phenols. The interplay between hydrogen-bonding and acid-base interactions on the hydrogen atom transfer reactivity and selectivity.

    Science.gov (United States)

    Salamone, Michela; Amorati, Riccardo; Menichetti, Stefano; Viglianisi, Caterina; Bietti, Massimo

    2014-07-03

    A time-resolved kinetic study on the reactions of the cumyloxyl radical (CumO(•)) with intramolecularly hydrogen bonded 2-(1-piperidinylmethyl)phenol (1) and 4-methoxy-2-(1-piperidinylmethyl)phenol (2) and with 4-methoxy-3-(1-piperidinylmethyl)phenol (3) has been carried out. In acetonitrile, intramolecular hydrogen bonding protects the phenolic O-H of 1 and 2 from attack by CumO(•) and hydrogen atom transfer (HAT) exclusively occurs from the C-H bonds that are α to the piperidine nitrogen (α-C-H bonds). With 3 HAT from both the phenolic O-H and the α-C-H bonds is observed. In the presence of TFA or Mg(ClO4)2, protonation or Mg(2+) complexation of the piperidine nitrogen removes the intramolecular hydrogen bond in 1 and 2 and strongly deactivates the α-C-H bonds of the three substrates. Under these conditions, HAT to CumO(•) exclusively occurs from the phenolic O-H group of 1-3. These results clearly show that in these systems the interplay between intramolecular hydrogen bonding and Brønsted and Lewis acid-base interactions can drastically influence both the HAT reactivity and selectivity. The possible implications of these findings are discussed in the framework of the important role played by tyrosyl radicals in biological systems.

  17. Tuning the Solubility of Copper Complex in Atom Transfer Radical Self-Condensing Vinyl Polymerizations to Control Polymer Topology via One-Pot to the Synthesis of Hyperbranched Core Star Polymers

    Directory of Open Access Journals (Sweden)

    Zong-Cheng Chen

    2014-09-01

    Full Text Available In this paper, we propose a simple one-pot methodology for proceeding from atom transfer reaction-induced conventional free radical polymerization (AT-FRP to atom transfer self-condensing vinyl polymerization (AT-SCVP through manipulation of the catalyst phase homogeneity (i.e., CuBr/2,2'-bipyridine (CuBr/Bpy in a mixture of styrene (St, 4-vinyl benzyl chloride (VBC, and ethyl 2-bromoisobutyrate. Tests of the solubilities of CuBr/Bpy and CuBr2/Bpy under various conditions revealed that both temperature and solvent polarity were factors affecting the solubility of these copper complexes. Accordingly, we obtained different polymer topologies when performing AT-SCVP in different single solvents. We investigated two different strategies to control the polymer topology in one-pot: varying temperature and varying solvent polarity. In both cases, different fractions of branching revealed the efficacy of varying the polymer topology. To diversify the functionality of the peripheral space, we performed chain extensions of the resulting hyperbranched poly(St-co-VBC macroinitiator (name as: hbPSt MI with either St or tBA (tert-butyl acrylate. The resulting hyperbranched core star polymer had high molecular weights (hbPSt-g-PSt: Mn = 25,000, Đ = 1.77; hbPSt-g-PtBA: Mn = 27,000, Đ = 1.98; hydrolysis of the tert-butyl groups of the later provided a hyperbranched core star polymer featuring hydrophilic poly(acrylic acid segments.

  18. Cu(II)-mediated atom transfer radical polymerization of methyl methacrylate via a strategy of thermo-regulated phase-separable catalysis in a liquid/liquid biphasic system: homogeneous catalysis, facile heterogeneous separation, and recycling.

    Science.gov (United States)

    Pan, Jinlong; Zhang, Bingjie; Jiang, Xiaowu; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2014-09-01

    A strategy of thermo-regulated phase-separable catalysis (TPSC) is applied to the Cu(II)-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in a p-xylene/PEG-200 biphasic system. Initiators for continuous activator regeneration ATRP (ICAR ATRP) are used to establish the TPSC-based ICAR ATRP system using water-soluble TPMA as a ligand, EBPA as an initiator, CuBr2 as a catalyst, and AIBN as a reducing agent. By heating to 70 °C, unlimited miscibility of both solvents is achieved and the polymerization can be carried out under homogeneous conditions; then on cooling to 25 °C, the mixture separates into two phases again. As a result, the catalyst complex remains in the PEG-200 phase while the obtained polymers stay in the p-xylene phase. The catalyst can therefore be removed from the resultant polymers by easily separating the two different layers and can be reused again. It is important that well-defined PMMA with a controlled molecular weight and narrow molecular weight distribution could be obtained using this TPSC-based ICAR ATRP system. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Synthesis of Monodisperse Silica Particles Grafted with Concentrated Ionic Liquid-Type Polymer Brushes by Surface-Initiated Atom Transfer Radical Polymerization for Use as a Solid State Polymer Electrolyte

    Directory of Open Access Journals (Sweden)

    Takashi Morinaga

    2016-04-01

    Full Text Available A polymerizable ionic liquid, N,N-diethyl-N-(2-methacryloylethyl-N-methylammonium bis(trifluoromethylsulfonylimide (DEMM-TFSI, was polymerized via copper-mediated atom transfer radical polymerization (ATRP. The polymerization proceeded in a living manner producing well-defined poly(DEMM-TFSI of target molecular weight up to about 400 K (including a polycation and an counter anion. The accurate molecular weight as determined by a GPC analysis combined with a light scattering measurement, and the molecular weight values obtained exhibited good agreement with the theoretical values calculated from the initial molar ratio of DEMM-TFSI and the monomer conversion. Surface-initiated ATRP on the surface of monodisperse silica particles (SiPs with various diameters was successfully performed, producing SiPs grafted with well-defined poly(DEMM-TFSI with a graft density as high as 0.15 chains/nm2. Since the composite film made from the silica-particle-decorated polymer brush and ionic liquid shows a relatively high ionic conductivity, we have evaluated the relationship between the grafted brush chain length and the ionic conductivity.

  20. Synthesis of Novel μ-Star Copolymers with Poly(N-Octyl Benzamide) and Poly(ε-Caprolactone) Miktoarms through Chain-Growth Condensation Polymerization, Styrenics-Assisted Atom Transfer Radical Coupling, and Ring-Opening Polymerization.

    Science.gov (United States)

    Huang, Chih-Feng; Aimi, Junko; Lai, Kuan-Yu

    2017-02-01

    Star copolymers are known to phase separate on the nanoscale, providing useful self-assembled morphologies. In this study, the authors investigate synthesis and assembly behavior of miktoarm star (μ-star) copolymers. The authors employ a new strategy for the synthesis of unprecedented μ-star copolymers presenting poly(N-octyl benzamide) (PBA) and poly(ε-caprolactone) (PCL) arms: a combination of chain-growth condensation polymerization, styrenics-assisted atom transfer radical coupling, and ring-opening polymerization. Gel permeation chromatography, mass-analyzed laser desorption/ionization mass spectrometry, and (1) H NMR spectroscopy reveal the successful synthesis of a well-defined (PBA11 )2 -(PCL15 )4 μ-star copolymer (Mn,NMR ≈ 12 620; Đ = 1.22). Preliminary examination of the PBA2 PCL4 μ-star copolymer reveals assembled nanofibers having a uniform diameter of ≈20 nm. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)- co -chlorinated Poly(vinyl chloride) (PVC- co -CPVC) Fiber

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Suree; Yue, Yanfeng; Kuo, Li-Jung; Mehio, Nada; Li, Meijun; Gill, Gary; Tsouris, Costas; Mayes, Richard T.; Saito, Tomonori; Dai, Sheng

    2016-04-20

    The need to secure future supplies of energy attracts researchers in several countries to a vast resource of nuclear energy fuel: uranium in seawater (estimated at 4.5 billion tons in seawater). In this study, we developed effective adsorbent fibers for the recovery of uranium from seawater via atom-transfer radical polymerization (ATRP) from a poly- (vinyl chloride)-co-chlorinated poly(vinyl chloride) (PVC-co-CPVC) fiber. ATRP was employed in the surface graft polymerization of acrylonitrile (AN) and tert-butyl acrylate (tBA), precursors for uranium-interacting functional groups, from PVC-co-CPVC fiber. The [tBA]/[AN] was systematically varied to identify the optimal ratio between hydrophilic groups (from tBA) and uranyl-binding ligands (from AN). The best performing adsorbent fiber, the one with the optimal [tBA]/[AN] ratio and a high degree of grafting (1390%), demonstrated uranium adsorption capacities that are significantly greater than those of the Japan Atomic Energy Agency (JAEA) reference fiber in natural seawater tests (2.42-3.24 g/kg in 42 days of seawater exposure and 5.22 g/kg in 49 days of seawater exposure, versus 1.66 g/kg in 42 days of seawater exposure and 1.71 g/kg in 49 days of seawater exposure for JAEA). Adsorption of other metal ions from seawater and their corresponding kinetics were also studied. The grafting of alternative monomers for the recovery of uranium from seawater is now under development by this versatile technique of ATRP.

  2. Well-defined iron complexes as efficient catalysts for "green" atom-transfer radical polymerization of styrene, methyl methacrylate, and butyl acrylate with low catalyst loadings and catalyst recycling.

    Science.gov (United States)

    Nakanishi, So-Ichiro; Kawamura, Mitsunobu; Kai, Hidetomo; Jin, Ren-Hua; Sunada, Yusuke; Nagashima, Hideo

    2014-05-05

    Environmentally friendly iron(II) catalysts for atom-transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N-trialkylated-1,4,9-triazacyclononane (R3 TACN) ligands. Two types of structures were confirmed by crystallography: "[(R3 TACN)FeX2 ]" complexes with relatively small R groups have ionic and dinuclear structures including a [(R3 TACN)Fe(μ-X)3 Fe(R3 TACN)](+) moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R3 TACN)FeX2 ]n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)3 TACN}FeBr2 ] (4 b) was the best catalyst for the well-controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Fundamentals of Atom Transfer Radical Polymerization

    Science.gov (United States)

    Coessens, Veerle M. C.; Matyjaszewski, Krzysztof

    2010-01-01

    Today's market increasingly demands sophisticated materials for advanced technologies and high-value applications, such as nanocomposites, optoelectronic, or biomedical materials. Therefore, the demand for well-defined polymers with very specific molecular architecture and properties increases. Until recently, these kinds of polymers could only be…

  4. Electron Transfer from Azide Radical to Histidine Generates ...

    African Journals Online (AJOL)

    The formation of histidinyl radical (HR), which is a product of electron transfer reaction between histidine and some free radicals, was studied by pulse radiolysis. The reaction between histidine and azide radicals was found to produce HR, which has a distinct absorption spectrum with peaks at 300, 480 and 520 nm.

  5. Preparation of Transparent Bulk TiO2/PMMA Hybrids with Improved Refractive Indices via an in Situ Polymerization Process Using TiO2 Nanoparticles Bearing PMMA Chains Grown by Surface-Initiated Atom Transfer Radical Polymerization.

    Science.gov (United States)

    Maeda, Satoshi; Fujita, Masato; Idota, Naokazu; Matsukawa, Kimihiro; Sugahara, Yoshiyuki

    2016-12-21

    Transparent TiO2/PMMA hybrids with a thickness of 5 mm and improved refractive indices were prepared by in situ polymerization of methyl methacrylate (MMA) in the presence of TiO2 nanoparticles bearing poly(methyl methacrylate) (PMMA) chains grown using surface-initiated atom transfer radical polymerization (SI-ATRP), and the effect of the chain length of modified PMMA on the dispersibility of modified TiO2 nanoparticles in the bulk hybrids was investigated. The surfaces of TiO2 nanoparticles were modified with both m-(chloromethyl)phenylmethanoyloxymethylphosphonic acid bearing a terminal ATRP initiator and isodecyl phosphate with a high affinity for common organic solvents, leading to sufficient dispersibility of the surface-modified particles in toluene. Subsequently, SI-ATRP of MMA was achieved from the modified surfaces of the TiO2 nanoparticles without aggregation of the nanoparticles in toluene. The molecular weights of the PMMA chains cleaved from the modified TiO2 nanoparticles increased with increases in the prolonging of the polymerization period, and these exhibited a narrow distribution, indicating chain growth controlled by SI-ATRP. The nanoparticles bearing PMMA chains were well-dispersed in MMA regardless of the polymerization period. Bulk PMMA hybrids containing modified TiO2 nanoparticles with a thickness of 5 mm were prepared by in situ polymerization of the MMA dispersion. The transparency of the hybrids depended significantly on the chain length of the modified PMMA on the nanoparticles, because the modified PMMA of low molecular weight induced aggregation of the TiO2 nanoparticles during the in situ polymerization process. The refractive indices of the bulk hybrids could be controlled by adjusting the TiO2 content and could be increased up to 1.566 for 6.3 vol % TiO2 content (1.492 for pristine PMMA).

  6. Hydropersulfides: H-Atom Transfer Agents Par Excellence.

    Science.gov (United States)

    Chauvin, Jean-Philippe R; Griesser, Markus; Pratt, Derek A

    2017-05-10

    Hydropersulfides (RSSH) are formed endogenously via the reaction of the gaseous biotransmitter hydrogen sulfide (H 2 S) and disulfides (RSSR) and/or sulfenic acids (RSOH). RSSH have been investigated for their ability to store H 2 S in vivo and as a line of defense against oxidative stress, from which it is clear that RSSH are much more reactive to two-electron oxidants than thiols. Herein we describe the results of our investigations into the H-atom transfer chemistry of RSSH, contrasting it with the well-known H-atom transfer chemistry of thiols. In fact, RSSH are excellent H-atom donors to alkyl (k ∼ 5 × 10 8 M -1 s -1 ), alkoxyl (k ∼ 1 × 10 9 M -1 s -1 ), peroxyl (k ∼ 2 × 10 6 M -1 s -1 ), and thiyl (k > 1 × 10 10 M -1 s -1 ) radicals, besting thiols by as little as 1 order and as much as 4 orders of magnitude. The inherently high reactivity of RSSH to H-atom transfer is based largely on thermodynamic factors; the weak RSS-H bond dissociation enthalpy (∼70 kcal/mol) and the associated high stability of the perthiyl radical make the foregoing reactions exothermic by 15-34 kcal/mol. Of particular relevance in the context of oxidative stress is the reactivity of RSSH to peroxyl radicals, where favorable thermodynamics are bolstered by a secondary orbital interaction in the transition state of the formal H-atom transfer that drives the inherent reactivity of RSSH to match that of α-tocopherol (α-TOH), nature's premier radical-trapping antioxidant. Significantly, the reactivity of RSSH eclipses that of α-TOH in H-bond-accepting media because of their low H-bond acidity (α 2 H ∼ 0.1). This affords RSSH a unique versatility compared to other highly reactive radical-trapping antioxidants (e.g., phenols, diarylamines, hydroxylamines, sulfenic acids), which tend to have high H-bond acidities. Moreover, the perthiyl radicals that result are highly persistent under autoxidation conditions and undergo very rapid dimerization (k = 5 × 10 9 M -1 s -1 ) in

  7. Enhanced binding capacity of boronate affinity adsorbent via surface modification of silica by combination of atom transfer radical polymerization and chain-end functionalization for high-efficiency enrichment of cis-diol molecules

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Wei; He, Maofang; Wang, Chaozhan; Wei, Yinmao, E-mail: ymwei@nwu.edu.cn

    2015-07-30

    Boronate affinity materials have been widely used for specific separation and preconcentration of cis-diol molecules, but most do not have sufficient capacity due to limited binding sites on the material surface. In this work, we prepared a phenylboronic acid-functionalized adsorbent with a high binding capacity via the combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and chain-end functionalization. With this method, the terminal chlorides of the polymer chains were used fully, and the proposed adsorbent contains dense boronic acid polymers chain with boronic acid on the chain end. Consequently, the proposed adsorbent possesses excellent selectivity and a high binding capacity of 513.6 μmol g{sup −1} for catechol and 736.8 μmol g{sup −1} for fructose, which are much higher than those of other reported adsorbents. The dispersed solid-phase extraction (dSPE) based on the prepared adsorbent was used for extraction of three cis-diol drugs (i.e., epinephrine, isoprenaline and caffeic acid isopropyl ester) from plasma; the eluates were analyzed by HPLC-UV. The reduced amount of adsorbent (i.e., 2.0 mg) could still eliminate interferences efficiently and yielded a recovery range of 85.6–101.1% with relative standard deviations ranging from 2.5 to 9.7% (n = 5). The results indicated that the proposed strategy could serve as a promising alternative to increase the density of surface functional groups on the adsorbent; thus, the prepared adsorbent has the potential to effectively enrich cis-diol substances in real samples. - Highlights: • Boronate adsorbent is prepared via ATRP and chain-end functionalization. • The adsorbent has quite high binding capacity for cis-diols. • Binding capacity is easily manipulated by ATRP condition. • Chain-end functionalization can improve binding capacity significantly. • Reduced adsorbent is consumed in dispersed solid-phase extraction of cis-diols.

  8. Studies of Atomic Free Radicals Stored in a Cryogenic Environment

    Science.gov (United States)

    Lee, David M.; Hubbard, Dorthy (Technical Monitor); Alexander, Glen (Technical Monitor)

    2003-01-01

    Impurity-Helium Solids are porous gel-like solids consisting of impurity atoms and molecules surrounded by thin layers of solid helium. They provide an ideal medium for matrix isolation of free radicals to prevent recombination and store chemical energy. In this work electron spin resonance, nuclear magnetic resonance, X-ray diffraction, and ultrasound techniques have all been employed to study the properties of these substances. Detailed studies via electron spin resonance of exchange tunneling chemical reactions involving hydrogen and deuterium molecular and atomic impurities in these solids have been performed and compared with theory. Concentrations of hydrogen approaching the quantum solid criterion have been produced. Structured studies involving X ray diffraction, ultrasound, and electron spin resonance have shown that the impurities in impurity helium solids are predominantly contained in impurity clusters, with each cluster being surrounded by thin layers of solid helium.

  9. FROM ATOM TRANSFER RADICAL ADDITION TO ATOM TRANSFER RADICAL POLYMERIZATION. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  10. Manipulating Energy Transfer in Conjugated Polymers using Radical Mediators

    Science.gov (United States)

    Wilcox, Daniel; Mukherjee, Sanjoy; Boudouris, Bryan

    Previous efforts have demonstrated that polymers containing open-shell moieties can be used to improve the performance of organic electronic devices (e.g., organic field-effect transistors (OFETs) and photovoltaic devices). However, the exact mechanism of how these redox-active radical polymers improve the performance of these next-generation devices has yet to be described in full. Here, we take the first steps towards elucidating this full picture by demonstrating that the galvinoxyl radical can be used as an electron acceptor for a common electron-donating macromolecule. First, galvinoxyl was used as a fluorescence quencher for poly(3-hexylthiophene) (P3HT) with quenching performance on par with that of oft-used fullerene derivatives. This effect was caused by photoinduced electron transfer between the two materials. Additionally, the galvinoxyl radical was used as an active layer dopant for P3HT OFETs. By increasing the P3HT carrier density through spontaneous electron transfer, the behavior of the device was changed from that of an intrinsic semiconductor to that of a highly-doped semiconductor. Thus, these initial studies lay the foundation for a paradigm where open-shell entities are used to dope conjugated polymer semiconductors for high-performance device applications.

  11. Electron predators are hydrogen atom traps. Effects of aryl groups on N-C(α) bond dissociations of peptide radicals.

    Science.gov (United States)

    Tureček, František

    2010-11-01

    Effects of substituted aryl groups on dissociations of peptide aminoketyl radicals were studied computationally for model tetrapeptide intermediates GXD(•) G where X was a cysteine residue that was derivatized by S-(3-nitrobenzyl), S-(3-cyanobenzyl), S-(3,5-dicyanobenzyl), S-(2,3,4,5,6-pentafluorobenzyl), and S-benzyl groups. The aminoketyl radical was placed within the Asp amide group. Aminoketyl radicals having the S-(3-nitrobenzyl) group were found to undergo spontaneous and highly exothermic migration of the hydroxyl hydrogen atom onto the nitro group in conformers allowing interaction between these groups. Competing reaction channels were investigated for aminoketyl radicals having the S-(3-cyanobenzyl) and S-(3,5-dicyanobenzyl) groups, e.g. H-atom migration to the C and N atoms of the C≡N group, migration to the C-4 position of the phenyl ring, and dissociation of the radical-activated NC(α) bond between the Asp and Gly residues. RRKM kinetic analysis on the combined B3LYP and ROMP2/6-311++G(2d,p) potential energy surface indicated > 99% H-atom transfer to the C≡N group forming a stable iminyl intermediate. The NC(α) bond dissociation was negligible. In contrast, peptides with the S-(2,3,4,5,6-pentafluorobenzyl) and S-benzyl groups showed preferential NC(α) bond dissociation that outcompeted H-atom migration to the C-4 position and fluorine substituents in the phenyl ring. These computational results are used to suggest an alternative mechanism for the quenching effect on electron-based peptide backbone dissociations of benzyl groups with electron-withdrawing substitutents, as reported recently. Copyright © 2010 John Wiley & Sons, Ltd.

  12. Understanding Hydrogen Atom Transfer: from Bond Strengths to Marcus Theory

    Science.gov (United States)

    MAYER, JAMES M.

    2010-01-01

    CONSPECTUS Hydrogen atom transfer (HAT) is one of the most fundamental chemical reactions: A–H + B → A + H–B. It is a key step in a wide range of chemical, environmental, and biological processes. Traditional HAT involves p-block radicals such as tBuO• abstracting H• from organic molecules. More recently, it has been recognized that many transition metal species undergo HAT. This has led to a broader perspective, with HAT viewed as one type of proton-coupled electron transfer (PCET). When transition metal complexes oxidize substrates by removing H• (≡ e– and H+), typically the electron transfers to the metal and the proton transfers to a ligand. Two examples are shown in the Figure: iron-imidazolinate and vanadium-oxo complexes. Although such reagents do not “look like” main group radicals, they have the same pattern of reactivity. For instance, their HAT rate constants parallel the A–H bond strengths within a series of similar reactions. Just like main group radicals, they abstract H• much faster from O–H bonds than from C–H bonds of the same strength. This shows that driving force is not the only determinant of reactivity. We have found that HAT reactivity is well described using a Marcus-theory approach. In the simplest model, the cross relation, kAH/B = (kAH/AkBH/BKeqf)½, predicts the rate constant for AH + B in terms of the self-exchange rate constants (kAH/A for AH + A) and the equilibrium constant. For a variety of transition metal oxidants, kAH/B is predicted within one or two orders of magnitude with only a few exceptions. For 36 organic reactions of oxyl radicals, kAH/B is predicted with an average deviation of a factor of 3.8, and within a factor of 5 for all but six of the reactions. These reactions involve both O–H or C–H bonds, occur either in water or organic solvents, and over a range of 1028 in Keq and 1013 in kAH/B. The treatment of organic reactions of O–H bonds includes the well-established kinetic solvent

  13. An environmental transfer hub for multimodal atom probe tomography.

    Science.gov (United States)

    Perea, Daniel E; Gerstl, Stephan S A; Chin, Jackson; Hirschi, Blake; Evans, James E

    2017-01-01

    Environmental control during transfer between instruments is required for samples sensitive to air or thermal exposure to prevent morphological or chemical changes prior to analysis. Atom probe tomography is a rapidly expanding technique for three-dimensional structural and chemical analysis, but commercial instruments remain limited to loading specimens under ambient conditions. In this study, we describe a multifunctional environmental transfer hub allowing controlled cryogenic or room-temperature transfer of specimens under atmospheric or vacuum pressure conditions between an atom probe and other instruments or reaction chambers. The utility of the environmental transfer hub is demonstrated through the acquisition of previously unavailable mass spectral analysis of an intact organic molecule made possible via controlled cryogenic transfer into the atom probe using the hub. The ability to prepare and transfer specimens in precise environments promises a means to access new science across many disciplines from untainted samples and allow downstream time-resolved in situ atom probe studies.

  14. An environmental transfer hub for multimodal atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Perea, Daniel E.; Gerstl, Stephan S. A.; Chin, Jackson; Hirschi, Blake; Evans, James. E.

    2017-05-02

    Environmental control during transfer between instruments is required for specimens sensitive to air or thermal exposure to prevent morphological or chemical changes. Atom Probe Tomography is an expanding technique but commercial instruments remain limited to loading under ambient conditions. Here we describe a multifunctional environmental transfer hub allowing controlled cryogenic, atmospheric and vacuum transfer between an Atom Probe and other instruments containing separate chambers to allow downstream time-resolved in-situ studies.

  15. TRANSITION METAL CATALYZED ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  16. ATOM TRANSFER RADICAL POLYMERIZATION IN SUPERCRITICAL CARBON DIOXIDE. (R826735)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  17. Synthesis of Amphiphilic Copolymwers by Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Hansen, Natanya Majbritt Louie

    2007-01-01

    Fluorerede polymerer besidder en række enestående egenskaber såsom god biokom-patibilitet og lav overfladeenergi såvel som god kemisk og termisk stabilitet. Målsæt-ningen for denne afhandling var at fremstille fluorerede polymerer og copolymerer, der potentielt kunne finde anvendelse som biokompa...... luftfugtighed fra copolymerer af 3FM og MMA, hvilket resulterede i meget hydrofobe overflader med statiske kontaktvinkler for vand på op til 144°....

  18. COPPER(I)-CATALYZED ATOM TRANSFER RADICAL POLYMERIZATIONS. (R826735)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  19. Formation of long-lived radicals on proteins by radical transfer from heme enzymes--a common process?

    DEFF Research Database (Denmark)

    Ostdal, H; Andersen, H J; Davies, Michael Jonathan

    1999-01-01

    investigated using horseradish peroxidase (HRP)/H2O2, in the presence and absence of added tyrosine. Incubation of HRP with H2O2 and bovine or human serum albumins, in the presence and absence of tyrosine, gave long-lived albumin-derived radicals as detected by EPR spectroscopy. Evidence has been obtained...... for these albumin radicals being located on buried tyrosine residues on the basis of blocking experiments. The effect of protein conformation on radical transfer has been investigated using partial proteolytic digestion prior to protein oxidation. With HRP/H2O2/BSA and Fe(III)Mb/H2O2/BSA increased radical...... concentrations were observed after limited digestion, although this effect was less marked with the HRP/H2O2/BSA system than with Fe(III)Mb/H2O2/BSA, consistent with different modes of radical transfer. More extensive digestion of BSA decreased the radical concentration to levels below those detected with native...

  20. Charge transfer for slow H atoms interacting with Al: Atomic levels and linewidths

    Science.gov (United States)

    Merino, J.; Lorente, N.; Pou, P.; Flores, F.

    1996-10-01

    The charge transfer of slow H atoms colliding with an Al(100) surface is studied by means of a linear combination of atomic orbitals method with local-density many-body contributions. The method is developed in order to calculate atomic levels and associated linewidths. Unlike previous theories, the present method is able to study the effect of the corrugation of the surface, together with the self-consistent potentials involved. This leads to a shift of atomic levels nonlinear on the external charge, contrary to the traditionally assumed image shift. The method works best at very short distances, where the strong coupling between atom and surface promotes molecular orbitals. Thus, the theory expounded in this work can describe the charge-transfer processes of systems in which the atomic levels are near the band edges, as protons scattered off aluminum.

  1. International atomic time and time transfer

    Science.gov (United States)

    Lewandowski, Wlodzimierz

    Global Navigation Satellite Systems (GNSS) keep a central role in the international timekeeping. American Global Positioning System (GPS) is a navigation system that has proven itself to be a reliable source of positioning for both the military community and the civilian community. But, little known by many, is the fact that GPS has proven itself to be an important and valuabe utility to the timekeeping community (Lewandowski et al. 1999). GPS is a versatile and global tool which can be used to both distribute time to an arbitrary number of users and synchronise clocks over large distances with a high degree of precision and accuracy. Similar performance can be obtained with Russian Global Navigation Satellite System (GLONASS). It is expected in the near future satellites of a new European navigation system GALILEO might bring some important opportunities for international timekeeping. This paper after a brief introduction to international timekeeping focuses on the description of recent progress in time transfer techniques using GNSS satellites.

  2. Nonradiative charge transfer in collisions of protons with rubidium atoms

    Science.gov (United States)

    Yan, Ling-Ling; Qu, Yi-Zhi; Liu, Chun-Hua; Zhang, Yu; Wang, Jian-Guo; Buenker, Robert J.

    2012-06-01

    The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10-3 keV-10 keV. The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region. The importance of rotational coupling for chargetransfer process is stressed. Compared with the radiative charge-transfer process, nonradiative charge transfer is a dominant mechanism at energies above 15 eV. The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail. The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

  3. Kinetics of the reaction of iodine atoms with HO sub 2 radicals

    Energy Technology Data Exchange (ETDEWEB)

    Jenkin, M.E.; Cox, R.A. (Harwell Laboratory, Oxfordshire (England)); Mellouki, A.; Le Bras, G.; Poulet, G. (CNRS, Orleans (France))

    1990-04-05

    The rate coefficient (k{sub 7}) for the reaction of iodine atoms with HO{sub 2} radicals, I + HO{sub 2} {yields} HI + O{sub 2}, has been measured directly with use of the discharge-flow/EPR technique, and the molecular-modulation/UV-absorption spectroscopy technique. Discharge-flow measurements were made under pseudo-first-order conditions with iodine atoms in large excess over HO{sub 2}. Molecular-modulation measurements were made with iodine atoms in excess over HO{sub 2}, but the I + HO{sub 2} reaction was occurring in competition with the self-reaction of HO{sub 2}. The potential significance of this reaction as a sink for iodine in the troposphere and other aspects of tropospheric iodine chemistry are considered with a simple model of the atmospheric boundary layer.

  4. Hydrogen atom transfer reactions in thiophenol: photogeneration of two new thione isomers.

    Science.gov (United States)

    Reva, Igor; Nowak, Maciej J; Lapinski, Leszek; Fausto, Rui

    2015-02-21

    Photoisomerization reactions of monomeric thiophenol have been investigated for the compound isolated in low-temperature argon matrices. The initial thiophenol population consists exclusively of the thermodynamically most stable thiol form. Phototransformations were induced by irradiation of the matrices with narrowband tunable UV light. Irradiation at λ > 290 nm did not induce any changes in isolated thiophenol molecules. Upon irradiation at 290-285 nm, the initial thiol form of thiophenol converted into its thione isomer, cyclohexa-2,4-diene-1-thione. This conversion occurs by transfer of an H atom from the SH group to a carbon atom at the ortho position of the ring. Subsequent irradiation at longer wavelengths (300-427 nm) demonstrated that this UV-induced hydrogen-atom transfer is photoreversible. Moreover, upon irradiation at 400-425 nm, the cyclohexa-2,4-diene-1-thione product converts, by transfer of a hydrogen atom from the ortho to para position, into another thione isomer, cyclohexa-2,5-diene-1-thione. The latter thione isomer is also photoreactive and is consumed if irradiated at λ atom-transfer isomerization reactions dominate the unimolecular photochemistry of thiophenol confined in a solid argon matrix. A set of low-intensity infrared bands, observed in the spectra of UV irradiated thiophenol, indicates the presence of a phenylthiyl radical with an H- atom detached from the SH group. Alongside the H-atom-transfer and H-atom-detachment processes, the ring-opening photoreaction occurred in cyclohexa-2,4-diene-1-thione by the cleavage of the C-C bond at the alpha position with respect to the thiocarbonyl C[double bond, length as m-dash]S group. The resulting open-ring conjugated thioketene adopts several isomeric forms, differing by orientations around single and double bonds. The species photogenerated upon UV irradiation of thiophenol were identified by comparison of their experimental infrared spectra with the spectra theoretically calculated for

  5. Efficient inter-trap transfer of cold francium atoms

    Science.gov (United States)

    Zhang, J.; Collister, R.; Shiells, K.; Tandecki, M.; Aubin, S.; Behr, J. A.; Gomez, E.; Gorelov, A.; Gwinner, G.; Orozco, L. A.; Pearson, M. R.; Zhao, Y.

    2016-12-01

    We report on the status of the FrPNC experiments and summarize our plans for measurements of parity non-conservation (PNC) in a sample of cold francium. The FrPNC collaboration has commissioned a laser cooling apparatus at the TRIUMF accelerator that collects and cools francium atoms for PNC experiments. We have recently demonstrated the robust, high efficiency transfer (50 %) of laser cooled francium atoms to a second laser cooling apparatus, located 0.7 m below the first, where the PNC experiments will be conducted.

  6. Efficient inter-trap transfer of cold francium atoms

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, J. [University of Maryland and National Institute of Standards and Technology, Department of Physics, Joint Quantum Institute (United States); Collister, R.; Shiells, K. [University of Manitoba, Department of Physics and Astronomy (Canada); Tandecki, M. [TRIUMF (Canada); Aubin, S., E-mail: saaubi@wm.edu [College of William and Mary, Department of Physics (United States); Behr, J. A. [TRIUMF (Canada); Gomez, E. [Universidad Autónoma de San Luis Potosí, Instituto de Física (Mexico); Gorelov, A. [TRIUMF (Canada); Gwinner, G. [University of Manitoba, Department of Physics and Astronomy (Canada); Orozco, L. A. [University of Maryland and National Institute of Standards and Technology, Department of Physics, Joint Quantum Institute (United States); Pearson, M. R. [TRIUMF (Canada); Zhao, Y. [Shanxi University, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy (China)

    2016-12-15

    We report on the status of the FrPNC experiments and summarize our plans for measurements of parity non-conservation (PNC) in a sample of cold francium. The FrPNC collaboration has commissioned a laser cooling apparatus at the TRIUMF accelerator that collects and cools francium atoms for PNC experiments. We have recently demonstrated the robust, high efficiency transfer (50 %) of laser cooled francium atoms to a second laser cooling apparatus, located 0.7 m below the first, where the PNC experiments will be conducted.

  7. Integration of CuAAC Polymerization and Controlled Radical Polymerization into Electron Transfer Mediated "Click-Radical" Concurrent Polymerization.

    Science.gov (United States)

    Xue, Wentao; Wang, Jie; Wen, Ming; Chen, Gaojian; Zhang, Weidong

    2017-03-01

    The successful chain-growth copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization employing Cu(0)/pentamethyldiethylenetriamine (PMDETA) and alkyl halide as catalyst is first investigated by a combination of nuclear magnetic resonance, gel-permeation chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In addition, the electron transfer mediated "click-radical" concurrent polymerization utilizing Cu(0)/PMDETA as catalyst is successfully employed to generate well-defined copolymers, where controlled CuAAC polymerization of clickable ester monomer is progressed in the main chain acting as the polymer backbone, the controlled radical polymerization (CRP) of acrylic monomer is carried out in the side chain. Furthermore, it is found that there is strong collaborative effect and compatibility between CRP and CuAAC polymerization to improve the controllability. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. The coordination and atom transfer chemistry of titanium porphyrin complexes

    Energy Technology Data Exchange (ETDEWEB)

    Hays, James Allen [Iowa State Univ., Ames, IA (United States)

    1993-11-05

    Preparation, characterization, and reactivity of (η2- alkyne)(meso-tetratolylpoprphrinato)titanium(II) complexes are described, along with inetermetal oxygen atom transfer reactions involving Ti(IV) and Ti(III) porphyrin complexes. The η2- alkyne complexes are prepared by reaction of (TTP)TiCl2 with LiAlH4 in presence of alkyne. Structure of (OEP)Ti(η2-Ph-C≡C-Ph) (OEP=octaethylporphryin) was determined by XRD. The compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Structure of (TTP)Ti(4-picoline)2 was also determined by XRD. Reaction of (TTP)Ti=O with (OEP)Ti-Cl yields intermetal O/Cl exchange, which is a one-electron redox process mediated by O atom transfer. Also a zero-electron redox process mediated by atom transfer is observed when (TTP)TiCl2 is reacted with (OEP)Ti=O.

  9. Symmetric large momentum transfer for atom interferometry with BECs

    Science.gov (United States)

    Abend, Sven; Gebbe, Martina; Gersemann, Matthias; Rasel, Ernst M.; Quantus Collaboration

    2017-04-01

    We develop and demonstrate a novel scheme for a symmetric large momentum transfer beam splitter for interferometry with Bose-Einstein condensates. Large momentum transfer beam splitters are a key technique to enhance the scaling factor and sensitivity of an atom interferometer and to create largely delocalized superposition states. To realize the beam splitter, double Bragg diffraction is used to create a superposition of two symmetric momentum states. Afterwards both momentum states are loaded into a retro-reflected optical lattice and accelerated by Bloch oscillations on opposite directions, keeping the initial symmetry. The favorable scaling behavior of this symmetric acceleration, allows to transfer more than 1000 ℏk of total differential splitting in a single acceleration sequence of 6 ms duration while we still maintain a fraction of approx. 25% of the initial atom number. As a proof of the coherence of this beam splitter, contrast in a closed Mach-Zehnder atom interferometer has been observed with up to 208 ℏk of momentum separation, which equals a differential wave-packet velocity of approx. 1.1 m/s for 87Rb. The presented work is supported by the CRC 1128 geo-Q and the DLR with funds provided by the Federal Ministry of Economic Affairs and Energy (BMWi) due to an enactment of the German Bundestag under Grant No. DLR 50WM1552-1557 (QUANTUS-IV-Fallturm).

  10. Study of the transfer of electrons and hydrogen atoms between substituted p-benzoquinone triplets and diphenylamine by flash-photolysis methods

    Energy Technology Data Exchange (ETDEWEB)

    Levin, P.P.; Kokrashvili, T.A.

    1981-01-01

    The primary and secondary aromatic amines quench the triplet states of carbonyl compounds through processes involving the transfer of charges and hydrogen atoms. The interaction of the benzophenone triplet with primary and secondary aromatic amines involves a one-step transfer of H atoms, and leads to the formation of ketyl and aminyl radicals in both polar and nonpolar solvents. The triplet state of 2,6-diphenyl-1,4-benzoquinone can be quenched through diphenylamine (DPA), a secondary aromatic amine, the quenching mechanism involving a diffusion-limited transfer of both charges and H atoms. The processes of electron and H atom transfer are in competition here, proceeding independently in the collision complex. Neutral radicals and short-lived radical-ion pairs (t approx. 100 nsec) are formed as the result of quenching in low-polarity solvents. Both neutral and charged radicals are formed through quenching in acetonitrile, but only radical-ions are formed through quenching in alcoholic solution. Only charged radicals are formed through quenching of duroquinone by DPA in ethanol-water mixtures. An understanding of the factors determining the mechanism of carbonyl compound triplet state quenching by electron and H atom donors can be obtained through a study of the effect of the structures of the reacting molecules, and the solvent, on the kinetics of the transfer processes. The present work has used flash photolysis methods to study the intermediates formed during the quenching of the triplet states of the p-benzoquinones by DFA in solvents of various polarities.

  11. Kinetic study of the 7-endo selective radical cyclization of N-tert-butyl-o-bromobenzylmethacryl amides: kinetic investigation of the cyclization and 1,7-hydrogen transfer of aromatic radicals.

    Science.gov (United States)

    Kamimura, Akio; Kotake, Tomoko; Ishihara, Yuriko; So, Masahiro; Hayashi, Takahiro

    2013-04-19

    A kinetic investigation of the radical cyclization of N-tert-butyl-o-bromobenzylmethacryl amides to give 2-benzazepines via 7-endo selective cyclization was undertaken. The aryl radical generated from the amide precursor by treatment with Bu3SnH gave the three compounds, which are a 7-endo cyclized adduct, a 6-exocyclized adduct, and a reduced product. The cyclization reactions under various Bu3SnH concentrations were traced by GC analysis. The 7-endo/6-exo selectivity was constant irrespective of variation in Bu3SnH concentration. These results revealed that regioselectivity is controlled in a kinetic manner and that there is no possibility of a neophyl rearrangement. The use of Bu3SnD revealed that 1,7-hydrogen transfer, in which an aryl radical abstracts a hydrogen atom from the methallylic methyl group, occurs during the reaction. Hydrogen abstraction from toluene, the reaction solvent, was also observed. The 1,7-transfer rate depended on the Bu3SnX (X = H or D), and the reaction kinetics was examined. The k(H)/k(D) value for the hydrogen abstraction of aryl radical from Bu3SnX (X = H or D) was estimated using 4-bromoanisol. The utilization of these values revealed the overall reaction kinetics and relative rates for the cyclization and reduction by Bu3SnX (X = H or D). Kinetic parameters for hydrogen abstraction from toluene by aryl radicals were also estimated.

  12. Hydrogen atom transfer reactions of imido manganese(V) corrole: one reaction with two mechanistic pathways.

    Science.gov (United States)

    Zdilla, Michael J; Dexheimer, Jennifer L; Abu-Omar, Mahdi M

    2007-09-19

    Hydrogen atom transfer (HAT) reactions of (tpfc)MnNTs have been investigated (tpfc = 5,10,15-tris(pentafluorophenyl)corrole and Ts = p-toluenesulfonate). 9,10-Dihydroanthracene and 1,4-dihydrobenzene reduce (tpfc)MnNTs via HAT with second-order rate constants 0.16 +/- 0.03 and 0.17 +/- 0.01 M(-1) s(-1), respectively, at 22 degrees C. The products are the respective arenes, TsNH(2) and (tpfc)Mn(III). Conversion of (tpfc)MnNTs to (tpfc)Mn by reaction with dihydroanthracene exhibits isosbestic behavior, and formation of 9,9',10,10'-tetrahydrobianthracene is not observed, suggesting that the intermediate anthracene radical rebounds in a second fast step without accumulation of a Mn(IV) intermediate. The imido complex (tpfc)Mn(V)NTs abstracts a hydrogen atom from phenols as well. For example, 2,6-di-tert-butyl phenol is oxidized to the corresponding phenoxyl radical with a second-order rate constant of 0.32 +/- 0.02 M(-1) s(-1) at 22 degrees C. The other products from imido manganese(V) are TsNH(2) and the trivalent manganese corrole. Unlike reaction with dihydroarenes, when phenols are used isosbestic behavior is not observed, and formation of (tpfc)Mn(IV)(NHTs) is confirmed by EPR spectroscopy. A Hammett plot for various p-substituted 2,6-di-tert-butyl phenols yields a V-shaped dependence on sigma, with electron-donating substituents exhibiting the expected negative rho while electron-withdrawing substituents fall above the linear fit (i.e., positive rho). Similarly, a bond dissociation enthalpy (BDE) correlation places electron-withdrawing substituents above the well-defined negative slope found for the electron-donating substituents. Thus two mechanisms are established for HAT reactions in this system, namely, concerted proton-electron transfer and proton-gated electron transfer in which proton transfer is followed by electron transfer.

  13. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    KAUST Repository

    Alsam, Amani Abdu

    2015-09-02

    We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

  14. Radical-Molecule Reaction Mechanisms: Role of Electron Delocalization, Complex Formation, and Intramolecular Energy Transfer.

    Science.gov (United States)

    Dubey, Manvendra Krishna

    This thesis presents: (1) measurements of the kinetics of the reactions of the OH radical with several molecules by the discharge flow technique, (2) reactivity trend analysis, electronic structure, and transition state calculations, (3) molecular beam electric deflection experiments of hot polyatomics. A synthesis of these studies demonstrates that radical-molecule reactions frequently involve an indirect mechanism and are not necessarily direct, activated, bimolecular processes. Indirect mechanisms arise when the reactant frontier orbitals do not transform to the product configuration. Compact reactivity trends among homologous reaction sets are defined by the difference between the ionization potential of the electron donor and the electron affinity of the electron acceptor and show that charge-transfer stabilizations (rather than thermodynamics) govern radical-molecule reactivity. A multiple transition state model is developed to predict the mixed bimolecular/termolecular kinetics implicit in the indirect mechanism. The fundamental assumption of rapid intramolecular energy redistribution in the energized complex in the model is validated by our electric deflection studies. Model calculations for the rm OH + HNO_3to H_2O + NO_3 reaction reproduce the small A factor, negative activation energy, and pressure dependence of the rate. They elucidate the reaction mechanism in molecular detail. The OH first bonds to either the O or N atom of HNO_3 to form an energized complex, which subsequently suffers one of three fates: dissociation to reactants via a loose transition state, dissociation to products via a tight transition state with a negative threshold, or collisional stabilization. These processes compete to determine the overall kinetics. Isotopic scrambling rates are predicted. Our model predicts faster rates than the NASA recommendation at low temperatures with potential consequences for stratospheric photochemistry. The rate constants of the reactions of OH

  15. A crystalline singlet phosphinonitrene: a nitrogen atom-transfer agent.

    Science.gov (United States)

    Dielmann, Fabian; Back, Olivier; Henry-Ellinger, Martin; Jerabek, Paul; Frenking, Gernot; Bertrand, Guy

    2012-09-21

    A variety of transition metal-nitrido complexes (metallonitrenes) have been isolated and studied in the context of modeling intermediates in biological nitrogen fixation by the nitrogenase enzymes and the industrial Haber-Bosch hydrogenation of nitrogen gas into ammonia. In contrast, nonmetallic nitrenes have so far only been spectroscopically observed at low temperatures, despite their intermediacy in a range of organic reactions. Here, we report the synthesis of a bis(imidazolidin-2-iminato)phosphinonitrene, which is stable at room temperature in solution and can even be isolated in the solid state. The bonding between phosphorus and nitrogen is analogous to that observed for metallonitrenes. We also show that this nitrido phosphorus derivative can be used to transfer a nitrogen atom to organic fragments, a difficult task for transition metal-nitrido complexes.

  16. Temperature-dependent kinetics of charge transfer, hydrogen-atom transfer, and hydrogen-atom expulsion in the reaction of CO+ with CH4 and CD4.

    Science.gov (United States)

    Melko, Joshua J; Ard, Shaun G; Johnson, Ryan S; Shuman, Nicholas S; Guo, Hua; Viggiano, Albert A

    2014-09-18

    We have determined the rate constants and branching ratios for the reactions of CO(+) with CH4 and CD4 in a variable-temperature selected ion flow tube. We find that the rate constants are collisional for all temperatures measured (193-700 K for CH4 and 193-500 K for CD4). For the CH4 reaction, three product channels are identified, which include charge transfer (CH4(+) + CO), H-atom transfer (HCO(+) + CH3), and H-atom expulsion (CH3CO(+) + H). H-atom transfer is slightly preferred to charge transfer at low temperature, with the charge-transfer product increasing in contribution as the temperature is increased (H-atom expulsion is a minor product for all temperatures). Analogous products are identified for the CD4 reaction. Density functional calculations on the CO(+) + CH4 reaction were also conducted, revealing that the relative temperature dependences of the charge-transfer and H-atom transfer pathways are consistent with an initial charge transfer followed by proton transfer.

  17. Tape transfer atomization patterning of liquid alloys for microfluidic stretchable wireless power transfer.

    Science.gov (United States)

    Jeong, Seung Hee; Hjort, Klas; Wu, Zhigang

    2015-02-12

    Stretchable electronics offers unsurpassed mechanical compliance on complex or soft surfaces like the human skin and organs. To fully exploit this great advantage, an autonomous system with a self-powered energy source has been sought for. Here, we present a new technology to pattern liquid alloys on soft substrates, targeting at fabrication of a hybrid-integrated power source in microfluidic stretchable electronics. By atomized spraying of a liquid alloy onto a soft surface with a tape transferred adhesive mask, a universal fabrication process is provided for high quality patterns of liquid conductors in a meter scale. With the developed multilayer fabrication technique, a microfluidic stretchable wireless power transfer device with an integrated LED was demonstrated, which could survive cycling between 0% and 25% strain over 1,000 times.

  18. Tape Transfer Atomization Patterning of Liquid Alloys for Microfluidic Stretchable Wireless Power Transfer

    Science.gov (United States)

    Jeong, Seung Hee; Hjort, Klas; Wu, Zhigang

    2015-02-01

    Stretchable electronics offers unsurpassed mechanical compliance on complex or soft surfaces like the human skin and organs. To fully exploit this great advantage, an autonomous system with a self-powered energy source has been sought for. Here, we present a new technology to pattern liquid alloys on soft substrates, targeting at fabrication of a hybrid-integrated power source in microfluidic stretchable electronics. By atomized spraying of a liquid alloy onto a soft surface with a tape transferred adhesive mask, a universal fabrication process is provided for high quality patterns of liquid conductors in a meter scale. With the developed multilayer fabrication technique, a microfluidic stretchable wireless power transfer device with an integrated LED was demonstrated, which could survive cycling between 0% and 25% strain over 1,000 times.

  19. Surprisingly Long-Lived Ascorbyl Radicals in Acetonitrile: Concerted Proton-Electron Transfer Reactions and Thermochemistry

    Science.gov (United States)

    Warren, Jeffrey J.; Mayer, James M.

    2008-01-01

    Proton-coupled electron transfer (PCET) reactions and thermochemistry of 5,6-isopropylidene ascorbate (iAscH−) have been examined in acetonitrile solvent.iAscH− is oxidized by 2,4,6-tBu3C6H2O• and by excess TEMPO• to give the corresponding 5,6-isopropylidene ascorbyl radical anion (iAsc•−), which persists for hours at 298 K in dry MeCN solution. The stability of iAsc•− is surprising in light of the transience of the ascorbyl radical in aqueous solutions, and is due to the lack of the protons needed for radical disproportionation. A concerted proton-electron transfer (CPET) mechanism is indicated for the reactions of iAscH−. Redox potential, pKa and equilibrium measurements define the thermochemical landscape for 5,6-isopropylidene ascorbic acid and its derivatives in MeCN. These measurements give an O–H bond dissociation free energy (BDFE) for iAscH−of 65.4 ± 1.5 kcal mol−1 in MeCN. Similar studies on underivatized ascorbate indicate a BDFE of 67.8 ± 1.2 kcal mol−1. These values are much lower than the aqueous BDFE for ascorbate of 74.0 ± 1.5 kcal mol−1 derived from reported data. PMID:18505256

  20. Scavenging of free-radical metabolites of aniline xenobiotics and drugs by amino acid derivatives: toxicological implications of radical-transfer reactions.

    Science.gov (United States)

    Michail, Karim; Baghdasarian, Argishti; Narwaley, Malyaj; Aljuhani, Naif; Siraki, Arno G

    2013-12-16

    We investigated a novel scavenging mechanism of arylamine free radicals by poly- and monoaminocarboxylates. Free radicals of arylamine xenobiotics and drugs did not react with oxygen in peroxidase-catalyzed reactions; however, they showed marked oxygen uptake in the presence of an aminocarboxylate. These free-radical intermediates were identified using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and electron paramagnetic resonance (EPR) spectrometry. Diethylenetriaminepentaacetic acid (DTPA), a polyaminocarboxylate, caused a concentration-dependent attenuation of N-centered radicals produced by the peroxidative metabolism of arylamines with the subsequent formation of secondary aliphatic carbon-centered radicals stemming from the cosubstrate molecule. Analogously, N,N-dimethylglycine (DMG) and N-methyliminodiacetate (MIDA), but not iminodiacetic acid (IDA), demonstrated a similar scavenging effect of arylamine-derived free radicals in a horseradish peroxidase/H2O2 system. Using human promyelocytic leukemia (HL-60) cell lysate as a model of human neutrophils, DTPA, MIDA, and DMG readily reduced anilinium cation radicals derived from the arylamines and gave rise to the corresponding carbon radicals. The rate of peroxidase-triggered polymerization of aniline was studied as a measure of nitrogen-radical scavenging. Although, IDA had no effect on the rate of aniline polymerization, this was almost nullified in the presence of DTPA and MIDA at half of the molar concentration of the aniline substrate, whereas a 20 molar excess of DMPO caused only a partial inhibition. Furthermore, the yield of formaldehyde, a specific reaction endproduct of the oxidation of aminocarboxylates by aniline free-radical metabolites, was quantitatively determined. Azobenzene, a specific reaction product of peroxidase-catalyzed free-radical dimerization of aniline, was fully abrogated in the presence of DTPA, as confirmed by GC/MS. Under aerobic conditions, a radical-transfer reaction

  1. Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer-Living Radical Polymerization.

    Science.gov (United States)

    Lligadas, Gerard; Grama, Silvia; Percec, Virgil

    2017-04-10

    Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X2. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

  2. Negative electron transfer dissociation of deprotonated phosphopeptide anions: choice of radical cation reagent and competition between electron and proton transfer.

    Science.gov (United States)

    Huzarska, Malwina; Ugalde, Israel; Kaplan, Desmond A; Hartmer, Ralf; Easterling, Michael L; Polfer, Nick C

    2010-04-01

    Despite significant developments in mass spectrometry technology in recent years, no routine proteomics sequencing tool is currently available for peptide anions. The use of a molecular open-shell cation is presented here as a possible reaction partner to induce electron transfer dissociation with deprotonated peptide anions. In this negative electron transfer dissociation (NETD) scheme, an electron is abstracted from the peptide anion and transferred to the radical cation. This is demonstrated for the example of the fluoranthene cation, C(16)H(10)(+*), which is reacted with deprotonated phosphorylated peptides in a 3-D ion trap mass spectrometer. Selective backbone cleavage at the C(alpha)-C bond is observed to yield a and x fragments, similarly to electron detachment dissociation (EDD) of peptide anions. Crucially, the phosphorylation site is left intact in the dissociation process, allowing an identification and localization of the post-translational modification (PTM) site. In contrast, NETD using Xe(+*) as the reagent cation results in sequential neutral losses (CO(2) and H(3)PO(4)) from a/x fragments, which complicate the interpretation of the mass spectra. This difference in dissociation behavior can be understood in the framework of the reduced recombination energy of the electron transfer process for fluoranthene, which is estimated at 2.5-4.5 eV, compared to 6.7-8.7 eV for xenon. Similarly to ETD, proton transfer is found to compete with electron transfer processes in NETD. Isotope fitting of the charge-reduced species shows that in the case of fluoranthene-mediated NETD, proton transfer only accounts for anions.

  3. Characterization of Porphyrin-Co(III)-'Nitrene Radical' Species Relevant in Catalytic Nitrene Transfer Reactions.

    Science.gov (United States)

    Goswami, Monalisa; Lyaskovskyy, Volodymyr; Domingos, Sérgio R; Buma, Wybren Jan; Woutersen, Sander; Troeppner, Oliver; Ivanović-Burmazović, Ivana; Lu, Hongjian; Cui, Xin; Zhang, X Peter; Reijerse, Edward J; DeBeer, Serena; van Schooneveld, Matti M; Pfaff, Florian Felix; Ray, Kallol; de Bruin, Bas

    2015-04-29

    To fully characterize the Co(III)-'nitrene radical' species that are proposed as intermediates in nitrene transfer reactions mediated by cobalt(II) porphyrins, different combinations of cobalt(II) complexes of porphyrins and nitrene transfer reagents were combined, and the generated species were studied using EPR, UV-vis, IR, VCD, UHR-ESI-MS, and XANES/XAFS measurements. Reactions of cobalt(II) porphyrins 1(P1) (P1 = meso-tetraphenylporphyrin (TPP)) and 1(P2) (P2 = 3,5-Di(t)Bu-ChenPhyrin) with organic azides 2(Ns) (NsN3), 2(Ts) (TsN3), and 2(Troc) (TrocN3) led to the formation of mono-nitrene species 3(P1)(Ns), 3(P2)(Ts), and 3(P2)(Troc), respectively, which are best described as [Co(III)(por)(NR″(•-))] nitrene radicals (imidyl radicals) resulting from single electron transfer from the cobalt(II) porphyrin to the 'nitrene' moiety (Ns: R″ = -SO2-p-C6H5NO2; Ts: R″ = -SO2C6H6; Troc: R″ = -C(O)OCH2CCl3). Remarkably, the reaction of 1(P1) with N-nosyl iminoiodane (PhI═NNs) 4(Ns) led to the formation of a bis-nitrene species 5(P1)(Ns). This species is best described as a triple-radical complex [(por(•-))Co(III)(NR″(•-))2] containing three ligand-centered unpaired electrons: two nitrene radicals (NR″(•-)) and one oxidized porphyrin radical (por(•-)). Thus, the formation of the second nitrene radical involves another intramolecular one-electron transfer to the "nitrene" moiety, but now from the porphyrin ring instead of the metal center. Interestingly, this bis-nitrene species is observed only on reacting 4(Ns) with 1(P1). Reaction of the more bulky 1(P2) with 4(Ns) results again in formation of mainly mono-nitrene species 3(P2)(Ns) according to EPR and ESI-MS spectroscopic studies. The mono- and bis-nitrene species were initially expected to be five- and six-coordinate species, respectively, but XANES data revealed that both mono- and bis-nitrene species are six-coordinate O(h) species. The nature of the sixth ligand bound to cobalt(III) in the

  4. Orientation dependence in the four-atom reaction of OH + HBr using the single-state oriented OH radical beam.

    Science.gov (United States)

    Tsai, Po-Yu; Che, Dock-Chil; Nakamura, Masaaki; Lin, King-Chuen; Kasai, Toshio

    2010-03-20

    The orientation dependence for the Br atom formation in the reaction of the oriented OH radicals with HBr molecules at 0.26 eV collision energy has been observed for the first time using the hexapole electric field, and we found that the reaction cross-section for O-end attack is more favorable than that for H-end attack by a factor of 3.4 +/- 2.3.

  5. Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

    OpenAIRE

    Nikiforov, Anton; Li, L.; Britun, N; Snyders, R.; Vanraes, Patrick; Leys, Christophe

    2014-01-01

    Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a...

  6. Kinetic of the gas-phase reactions of OH radicals and Cl atoms with Diethyl Ethylphosphonate and Triethyl Phosphate

    KAUST Repository

    Laversin, H.

    2015-11-30

    In this paper, the relative-rate technique has been used to obtain rate coefficients for the reaction of two organophosphorus compounds: Triethyl phosphate (TEP) and Diethyl ethylphosphonate (DEEP) with OH radicals and Cl atoms at atmospheric pressure and at different temperatures. The calculated rate constants were fitted to the Arrhenius expression over the temperature range 298 – 352 K. The following expressions (in cm3molecule-1s-1) were obtained for the reactions of OH and CL with DEEP and TEP: kOH+DEEP= (7.84±0.65)x10-14exp((1866±824)/T), kOH+TEP = (6.54±0.42)x10-14exp((1897±626)/T), kCl+DEEP = (5.27± 0.80)x10−11exp(765±140/T) and kCl+TEP = (5.23± 0.80)x10−11exp(736± 110/T). These results show that the reaction of the studied compounds with Cl atoms proceeds more rapidly than that with OH radicals. The related tropospheric lifetimes suggest that once emitted into the atmosphere, TEP and DEEP can be removed within a few hours in areas close to their emission sources. TEP and DEEP are principally removed by OH radicals. However, in coastal areas where the Cl atoms’ concentration is higher, TEP and DEEP removal by reaction with Cl atoms could be a competitive process.

  7. Atmospheric reactions of methylcyclohexanes with Cl atoms and OH radicals: determination of rate coefficients and degradation products.

    Science.gov (United States)

    Ballesteros, Bernabé; Ceacero-Vega, Antonio A; Jiménez, Elena; Albaladejo, José

    2015-04-01

    As the result of biogenic and anthropogenic activities, large quantities of chemical compounds are emitted into the troposphere. Alkanes, in general, and cycloalkanes are an important chemical class of hydrocarbons found in diesel, jet and gasoline, vehicle exhaust emissions, and ambient air in urban areas. In general, the primary atmospheric fate of organic compounds in the gas phase is the reaction with hydroxyl radicals (OH). The oxidation by Cl atoms has gained importance in the study of atmospheric reactions because they may exert some influence in the boundary layer, particularly in marine and coastal environments, and in the Arctic troposphere. The aim of this paper is to study of the atmospheric reactivity of methylcylohexanes with Cl atoms and OH radicals under atmospheric conditions (in air at room temperature and pressure). Relative kinetic techniques have been used to determine the rate coefficients for the reaction of Cl atoms and OH radicals with methylcyclohexane, cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane, and 1,3,5-trimethylcyclohexane at 298 ± 2 K and 720 ± 5 Torr of air by Fourier transform infrared) spectroscopy and gas chromatography-mass spectrometry (GC-MS) in two atmospheric simulation chambers. The products formed in the reaction under atmospheric conditions were investigated using a 200-L Teflon bag and employing the technique of solid-phase microextraction coupled to a GC-MS. The rate coefficients obtained for the reaction of Cl atoms with the studied compounds are the following ones (in units of 10(-10) cm(3) molecule(-1) s(-1)): (3.11 ± 0.16), (2.89 ± 0.16), (2.89 ± 0.26), and (2.61 ± 0.42), respectively. For the reactions with OH radicals the determined rate coefficients are (in units of 10(-11) cm(3) molecule(-1) s(-1)): (1.18 ± 0.12), (1.49 ± 0.16), (1.41 ± 0.15), and (1.77 ± 0.23), respectively. The reported error is twice the standard deviation. A detailed

  8. Kinetics and mechanism of the gas-phase reaction of Cl atoms and OH radicals with fluorobenzene at 296 K

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Nielsen, Ole John; Hurley, MD

    2002-01-01

    with Cl atoms via a mechanism which, at least in part, leads neither to production of C6H5Cl nor to reformation of C6H5F. As the steady-state Cl atom concentration is increased, the fraction of the C6H5F-Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate...... radical and adduct formation to give the C6H5F-Cl adduct. At 296 K the rate constant for the abstraction channel is k(5a)(Cl+C6H5F) = (1.1 +/- 0.1) x 10(-17) cm(3) molecule(-1) s(-1). The C6H5F-Cl adduct undergoes rapid (k similar to 10(8) s(-1)) decomposition to reform C6H5F and Cl atoms and reaction......) molecule(-1) s(-1) was, established for the reaction of the C6H5F-Cl adduct with O-2. The reaction of OH radicals with C6H5F was studied and a rate constant of k(OH + C6H5F) = (7.9 +/- 2.2) x 10(-13) cm(3) molecule(-1) s(-1) was determined. The results are discussed with respect to the available literature...

  9. Zwitterion radicals and anion radicals from electron transfer and solvent condensation with the fingerprint developing agent ninhydrin.

    Science.gov (United States)

    Schertz, T D; Reiter, R C; Stevenson, C D

    2001-11-16

    Ninhydrin (the fingerprint developing agent) spontaneously dehydrates in liquid ammonia and in hexamethylphosphoramide (HMPA) to form indantrione, which has a sufficiently large solution electron affinity to extract an electron from the solvent (HMPA) to produce the indantrione anion radical. In liquid NH(3), the presence of trace amounts of amide ion causes the spontaneous formation of an anion radical condensation product, wherein the no. 2 carbon (originally a carbonyl carbon) becomes substituted with -NH(2) and -OH groups. In HMPA, the indantrione anion radical spontaneously forms condensation products with the HMPA to produce a variety of zwitterionic radicals, wherein the no. 2 carbon becomes directly attached to a nitrogen of the HMPA. The mechanisms for the formation of the zwitterionic paramagnetic condensation products are analogous to that observed in the reaction of ninhydrin with amino acids to yield Ruhemann's Purple, the contrast product in fingerprint development. The formation of anion and zwitterionic radical condensation products from ninhydrin and nitrogen-containing solvents may represent an example of a host of analogous polyketone-solvent reactions.

  10. Reaction of benzene with atomic carbon: pathways to fulvenallene and the fulvenallenyl radical in extraterrestrial atmospheres and the interstellar medium.

    Science.gov (United States)

    da Silva, Gabriel

    2014-06-05

    The reaction of benzene with ground-state atomic carbon, C((3)P), has been investigated using the G3X-K composite quantum chemical method. A suite of novel energetically favorable pathways that lead to previously unconsidered products are identified. Reaction is initiated by barrierless C atom cycloaddition to benzene on the triplet surface, producing a vibrationally excited [C7H6]* adduct that can dissociate to the cycloheptatrienyl radical (+ H) via a relatively loose transition state 4.4 kcal mol(-1) below the reactant energies. This study also identifies that this reaction adduct can isomerize to generate five-membered ring intermediates that can further dissociate to the global C7H5 minima, the fulvenallenyl radical (+ H), or to c-C5H4 and acetylene, with limiting barriers around 20 and 10 kcal mol(-1) below the reactants, respectively. If intersystem crossing to the singlet surface occurs, isomerization pathways that are lower-yet in energy are available leading to the C7H6 minima fulvenallene, with all barriers over 40 kcal mol(-1) below the reactants. From here further barrierless fragmentation to fulvenallenyl + H can proceed at ca. 25 kcal mol(-1) below the reactants. In the reducing atmospheres of planets like Jupiter and satellites like Titan, where benzene and C((3)P) are both expected, it is proposed that fulvenallene and the fulvenallenyl radical would be the dominant products of the C6H6 + C((3)P) reaction. Fulvenallenyl may also be a significant reaction product under collision-free conditions representative of the interstellar medium, although further work is required here to confirm the identity of the C7H5 radical product.

  11. Theoretical and kinetic study of the hydrogen atom abstraction reactions of unsaturated C6 methyl esters with hydroxyl radical

    Science.gov (United States)

    Wang, Quan-De; Ni, Zhong-Hai

    2016-04-01

    This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydroxyl radical (OH) on typical isomers of unsaturated C6 methyl esters at the CBS/QB3 level of theory. The high-pressure limit rate constants at different reaction sites for all the methyl esters in the temperature range from 500 to 2000 K are calculated via transition-state theory with the Wigner method for quantum tunneling effect and fitted to the modified three parameters Arrhenius expression using least-squares regression. Further, a branching ratio analysis for each reaction site has been performed.

  12. Leveraging Electron Transfer Dissociation for Site Selective Radical Generation: Applications for Peptide Epimer Analysis

    Science.gov (United States)

    Lyon, Yana A.; Beran, Gregory; Julian, Ryan R.

    2017-07-01

    Traditional electron-transfer dissociation (ETD) experiments operate through a complex combination of hydrogen abundant and hydrogen deficient fragmentation pathways, yielding c and z ions, side-chain losses, and disulfide bond scission. Herein, a novel dissociation pathway is reported, yielding homolytic cleavage of carbon-iodine bonds via electronic excitation. This observation is very similar to photodissociation experiments where homolytic cleavage of carbon-iodine bonds has been utilized previously, but ETD activation can be performed without addition of a laser to the mass spectrometer. Both loss of iodine and loss of hydrogen iodide are observed, with the abundance of the latter product being greatly enhanced for some peptides after additional collisional activation. These observations suggest a novel ETD fragmentation pathway involving temporary storage of the electron in a charge-reduced arginine side chain. Subsequent collisional activation of the peptide radical produced by loss of HI yields spectra dominated by radical-directed dissociation, which can be usefully employed for identification of peptide isomers, including epimers.

  13. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    radicals containing two aromatic end groups connected by a flexible polymethylene chain or a rigid cyclohexane frame is thus trapped on either aromatic end group, and ET between these groups can be detected by ESR techniques. Intramolecular ET also occurs in binuclear transition metal complexes in which......, and for intramolecular and inner sphere ET for transition metal complexes. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....... the coupling between the metal centers [(Ru(II)/Ru(III) and Ru(II)/Co(III) couples] is sufficiently weak (class I or II mixed valence compounds). The ET mechanism can involve either direct transfer between the donor and acceptor groups or a higher order mechanism in which ET proceeds through intermediate...

  14. Transferable Atomic Multipole Machine Learning Models for Small Organic Molecules.

    Science.gov (United States)

    Bereau, Tristan; Andrienko, Denis; von Lilienfeld, O Anatole

    2015-07-14

    Accurate representation of the molecular electrostatic potential, which is often expanded in distributed multipole moments, is crucial for an efficient evaluation of intermolecular interactions. Here we introduce a machine learning model for multipole coefficients of atom types H, C, O, N, S, F, and Cl in any molecular conformation. The model is trained on quantum-chemical results for atoms in varying chemical environments drawn from thousands of organic molecules. Multipoles in systems with neutral, cationic, and anionic molecular charge states are treated with individual models. The models' predictive accuracy and applicability are illustrated by evaluating intermolecular interaction energies of nearly 1,000 dimers and the cohesive energy of the benzene crystal.

  15. Creation, destruction, and transfer of atomic multipole moments by electron scattering: Quantum-mechanical treatment

    Science.gov (United States)

    Csanak, G.; Kilcrease, D. P.; Fursa, D. V.; Bray, I.

    2008-12-01

    Using the wave-packet propagation method of Rodberg and Thaler and the density matrix method of Fano and Blum, we have defined by completely quantum-mechanical methods the cross sections for the creation, destruction, and transfer of atomic multipole moments by both elastic and inelastic scattering of electrons by atomic targets. All cross sections obtained quantum mechanically, except for the coherence transfer cross sections, agree in form with those obtained semiclassically by Fujimoto and co-workers. We also used the converged close-coupling (CCC) method to calculate numerically some of the above cross sections for selected transitions in electron scattering from hydrogen and barium atoms.

  16. Insights into the Hydrogen-Atom Transfer of the Blue Aroxyl.

    Science.gov (United States)

    Bächle, Josua; Marković, Marijana; Kelterer, Anne-Marie; Grampp, Günter

    2017-10-19

    An experimental and theoretical study on hydrogen-atom transfer dynamics in the hydrogen-bonded substituted phenol/phenoxyl complex of the blue aroxyl (2,4,6-tri-tert-butylphenoxyl) is presented. The experimental exchange dynamics is determined in different organic solvents from the temperature-dependent alternating line-width effect in the continuous-wave ESR spectrum. From bent Arrhenius plots, effective tunnelling contributions with parallel heavy-atom motion are concluded. To clarify the transfer mechanism, reaction paths for different conformers of the substituted phenol/phenoxyl complex are modelled theoretically. Various DFT and post-Hartree-Fock methods including multireference methods are applied. From the comparison of experimental and theoretical data it is concluded that the system favours concerted hydrogen-atom transfer along a parabolic reaction path caused by heavy-atom motion. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Transferable Pseudo-Classical Electrons for Aufbau of Atomic Ions

    Science.gov (United States)

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-01-01

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. PMID:24752384

  18. Transferable pseudoclassical electrons for aufbau of atomic ions.

    Science.gov (United States)

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-06-05

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. Copyright © 2014 Wiley Periodicals, Inc.

  19. Nitrogen Atom Transfer From High Valent Iron Nitrides

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Michael D. [New Mexico State Univ., Las Cruces, NM (United States); Smith, Jeremy M. [Indiana Univ., Bloomington, IN (United States)

    2015-10-14

    This report describes the synthesis and reactions of high valent iron nitrides. Organonitrogen compounds such as aziridines are useful species for organic synthesis, but there are few efficient methods for their synthesis. Using iron nitrides to catalytically access these species may allow for their synthesis in an energy-and atom-efficient manner. We have developed a new ligand framework to achieve these goals as well as providing a method for inducing previously unknown reactivity.

  20. Atomic recombination rate determination through heat-transfer measurement.

    Science.gov (United States)

    Park, C.; Anderson, L. A.; Sheldahl, R. E.

    1973-01-01

    A theoretical and experimental demonstration is presented which shows that under suitable conditions the volume recombination coefficient can be determined by measuring the heat transfer rate into the wall of a cylinder through which a dissociated stream is passing. The experimental results obtained are in agreement with those of other investigators.

  1. Clinical Physiology and Mechanism of Dizocilpine (MK-801: Electron Transfer, Radicals, Redox Metabolites and Bioactivity

    Directory of Open Access Journals (Sweden)

    Peter Kovacic

    2010-01-01

    Full Text Available Dizocilpine (MK-801, an extensively investigated drug possessing secondary amine and benzenoid functions, displays a wide array of biological properties, including anticonvulsant and anesthetic. There is scant discussion of biomechanism. A relevant, important finding is formation of oxidative metabolites in the hydroxylamine and phenolic categories. Analogy to cocaine metabolites suggests participation of redox entities, such as, hydroxylamine, nitroxide and nitrosonium, which can lead to electron transfer and radical formation. There is also similarity to metabolism by 3,3′-iminodipropionitrile and phencyclidine. Alternatively, the phenolic metabolites are well-known precursors of ET quinones. The review documents various physiological effects, mainly involving the central nervous system. Also of interest are the pro- and anti-oxidant properties. Considerable attention has been paid to MK-801 as an antagonist of the N-methyl-D-aspartate receptor in the glutamate category. This aspect is often associated with effects on the central nervous system. The review also provides recent literature dealing with MK-801/NMDA receptor in various areas of bioactivity. Studies were made of MK-801 involvement in working memory processing. Deficits in behavior were noted after administration of the drug. Treatment of mice with dizocilpine induced learning impairment. The influence of MK-801 on fear has been investigated. The substance is known to exert an analgesic effect in pain control. A number of reports deal with anesthetic properties.

  2. Fast adiabatic quantum state transfer and entanglement generation between two atoms via dressed states.

    Science.gov (United States)

    Wu, Jin-Lei; Ji, Xin; Zhang, Shou

    2017-04-11

    We propose a dressed-state scheme to achieve shortcuts to adiabaticity in atom-cavity quantum electrodynamics for speeding up adiabatic two-atom quantum state transfer and maximum entanglement generation. Compared with stimulated Raman adiabatic passage, the dressed-state scheme greatly shortens the operation time in a non-adiabatic way. By means of some numerical simulations, we determine the parameters which can guarantee the feasibility and efficiency both in theory and experiment. Besides, numerical simulations also show the scheme is robust against the variations in the parameters, atomic spontaneous emissions and the photon leakages from the cavity.

  3. Fast adiabatic quantum state transfer and entanglement generation between two atoms via dressed states

    Science.gov (United States)

    Wu, Jin-Lei; Ji, Xin; Zhang, Shou

    2017-04-01

    We propose a dressed-state scheme to achieve shortcuts to adiabaticity in atom-cavity quantum electrodynamics for speeding up adiabatic two-atom quantum state transfer and maximum entanglement generation. Compared with stimulated Raman adiabatic passage, the dressed-state scheme greatly shortens the operation time in a non-adiabatic way. By means of some numerical simulations, we determine the parameters which can guarantee the feasibility and efficiency both in theory and experiment. Besides, numerical simulations also show the scheme is robust against the variations in the parameters, atomic spontaneous emissions and the photon leakages from the cavity.

  4. Calculated Entropies for n-Heptane, 2-Methylhexane, 2,3-Dimethylpentane, and Radicals from the Loss of H Atoms

    Directory of Open Access Journals (Sweden)

    Jason M. Hudzik

    2013-01-01

    Full Text Available Entropy data are reported using different calculation methods for internal rotors on n-heptane, 2-methylhexane, and 2,3-dimethylpentane and on the different radical sites of each species corresponding to the loss of a hydrogen atom for temperatures between 298 and 1500 K. Structures, moments of inertia, vibration frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p level of theory. Comparisons with experimental literature data suggest limitations inuse of the rigid-rotor harmonic-oscillator (HO approximation and advantages to the use of internal rotation contributions for entropy relative to torsion frequencies. The comparisons suggest the need to include contributions from all internal rotors where the barriers are at or below those of the above molecules. Calculation of entropy from the use of internal rotor contributions provides acceptable approximations to available literature values. Entropy values for radicals corresponding to carbon sites on these hydrocarbons are presented.

  5. Hydrogen atom abstraction from C-H bonds of benzylamides by the aminoxyl radical BTNO: a kinetic study.

    Science.gov (United States)

    Coniglio, Alessandra; Galli, Carlo; Gentili, Patrizia; Vadalà, Raffaella

    2009-01-07

    The aminoxyl radical BTNO (benzotriazole-N-oxyl; >N-O*) is generated from HBT (1-hydroxybenzotriazole; >N-OH) by oxidation with a Ce(IV) salt. BTNO presents a broad absorption band with lambda(max) 474 nm that lends itself to investigate the kinetics of H-abstraction from H-donor substrates by spectrophotometry. Thus, rate constants (k(H)) of H-abstraction by BTNO from CH(2)-groups alpha to the nitrogen atom in X-substituted-(N-acetyl)benzylamines (X-C(6)H(4)CH(2)NHCOCH(3)) have been determined in MeCN solution at 25 degrees C. Correlation of the k(H)(X) data with the Hammett sigma(+) parameters gives a small value for rho (-0.65) that is compatible with a radical H-abstraction step. The sizeable value (k(H)/k(D)=8.8) of the kinetic isotope effect from a suitably deuteriated amide substrate further confirms H-abstraction as rate-determining. Evidence is acquired for the relevance of stereoelectronic effects that speed up the H-abstraction whenever the scissile C-H bond is co-linear with either the nitrogen lone-pair of the amide moiety or an adjacent aromatic group. An assessment of the dissociation energy value of the benzylic C-H bond in ArCH(2)NHCOMe is accordingly reported.

  6. Effect of energy transfer from atomic electron shell to an α particle emitted by decaying nucleus

    Energy Technology Data Exchange (ETDEWEB)

    Igashov, S. Yu., E-mail: igashov@theor.mephi.ru [All-Russian Research Institute of Automatics (Russian Federation); Tchuvil’sky, Yu. M. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation)

    2016-12-15

    The process of energy transfer from the electron shell of an atom to an α particle propagating through the shell is formulated mathematically. Using the decay of the {sup 226}Ra nucleus as an example, it is demonstrated that this phenomenon increases the α-decay intensity in contrast with other known effects of similar type. Moreover, the α decay of the nucleus is more strongly affected by the energy transfer than by all other effects taken together.

  7. Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

    Science.gov (United States)

    Havener, C. C.; Vane, C. R.; Krause, H. F.; Stancil, P. C.; Mroczkowski, T.; Savin, D. W.

    2002-01-01

    We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

  8. Optimization of transfer of laser-cooled atom cloud to a quadrupole ...

    Indian Academy of Sciences (India)

    2014-02-08

    Feb 8, 2014 ... We present here our experimental results on transfer of laser-cooled atom cloud to a quadrupole magnetic trap. We show that by choosing appropriately the ratio of potential energy in magnetic trap to kinetic energy of cloud in molasses, we can obtain the maximum phase-space density in the magnetic trap.

  9. Toward the Development of a Fundamentally Based Chemical Model for Cyclopentanone: High-Pressure-Limit Rate Constants for H Atom Abstraction and Fuel Radical Decomposition.

    Science.gov (United States)

    Zhou, Chong-Wen; Simmie, John M; Pitz, William J; Curran, Henry J

    2016-09-15

    Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. Calculated thermodynamic and kinetic data are presented for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. These radicals can be formed via H atom abstraction reactions by Ḣ and Ö atoms and ȮH, HȮ2, and ĊH3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when ȮH is involved, but the reverse holds true for HȮ2 radicals. The subsequent β-scission of the radicals formed is also determined, and it is shown that recent tunable VUV photoionization mass spectrometry experiments can be interpreted in this light. The bulk of the calculations used the composite model chemistry G4, which was benchmarked in the simplest case with a coupled cluster treatment, CCSD(T), in the complete basis set limit.

  10. Surface modification of carbon nanotubes via combination of mussel inspired chemistry and chain transfer free radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Qing; Tian, Jianwen; Liu, Meiying; Zeng, Guangjian; Huang, Qiang [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031 (China); Wang, Ke; Zhang, Qingsong [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084 (China); Deng, Fengjie, E-mail: fengjiedeng@aliyun.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang, 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084 (China)

    2015-08-15

    Graphical abstract: A novel strategy combination of mussel inspired chemistry and chain transfer free radical polymerization has been developed for surface modification of carbon nanotubes with polymers for the first time. - Highlights: • Surface modification of CNTs via mussel inspired chemistry. • Preparation of aminated polymers through free radical polymerization. • Functionalized CNTs with aminated polymers via Michael addition reaction. • Highly dispersed CNTs in organic and aqueous solution. - Abstract: In this work, a novel strategy for surface modification of carbon nanotubes (CNTs) was developed via combination of mussel inspired chemistry and chain transfer free radical polymerization. First, pristine CNTs were functionalized with polydopamine (PDA), which is formed via self-polymerization of dopamine in alkaline conditions. These PDA functionalized CNTs can be further reacted with amino-terminated polymers (named as PDMC), which was synthesized through chain transfer free radical polymerization using cysteamine hydrochloride as chain transfer agent and methacryloxyethyltrimethyl ammonium chloride as the monomer. PDMC perfectly conjugated with CNT-PDA was ascertained by a series of characterization techniques including transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The dispersibility of obtained CNT nanocomposites (named as CNT-PDA-PDMC) was further examined. Results showed that the dispersibility of CNT-PDA-PDMC in aqueous and organic solutions was obviously enhanced. Apart from PDMC, many other amino-terminated polymers can also be used to functionalization of CNTs via similar strategy. Therefore, the method described in this work should be a general strategy for fabrication various polymer nanocomposites.

  11. Kinetics of the reaction of F atoms with O2 and UV spectrum of FO2 radicals in the gas phase at 295 K

    DEFF Research Database (Denmark)

    Ellermann, T.; Sehested, J.; Nielsen, O.J.

    1994-01-01

    The ultraviolet absorption spectrum of FO2 radicals and the kinetics of the reaction of F atoms with O2 have been studied in the gas phase at 295 K using pulse radiolysis combined with kinetic UV spectroscopy. At 230 nm, sigma(FO2) = (5.08 +/- 0.70) X 10(-18) cm2 molecule-1. The kinetics...

  12. Porphyrin Cobalt(III “Nitrene Radical” Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH

    Directory of Open Access Journals (Sweden)

    Monalisa Goswami

    2016-02-01

    Full Text Available In the field of cobalt(II porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH aryl azides in Co(II porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT from the OH or NH2 group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O and phenylene diimine (Y = NH species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH2 moiety to the nitrene radical moiety has a low energy barrier.

  13. Muon transfer from muonic hydrogen to heavier atoms; Transfert de charge muonique

    Energy Technology Data Exchange (ETDEWEB)

    Dupays, A

    2004-06-01

    This work concerns muon transfer from muonic hydrogen to heavier atoms. Recently, a method of measurement of the hyperfine structure of ground-state muonic hydrogen based on the collision energy dependence of the muon transfer rate to oxygen has been proposed. This proposal is based on measurements which where performed at the Paul Scherrer Institute in the early nineties which indicate that the muon transfer from muonic hydrogen to oxygen increases by a factor of 4 going from thermal to 0.12 eV energies. The motivation of our calculations was to confirm this behaviour. To study the collision energy dependence of the muon transfer rate, we have used a time-independent close-coupling method. We have set up an hyperspherical elliptic formalism valid for nonzero total angular momentum which allows accurate computations of state-to-state reactive and charge exchange processes. We have applied this formalism to muon-transfer process to oxygen and neon. The comparison with experimental results is in both cases excellent. Finally, the neon transfer rate dependence with energy suggests to use neon instead of oxygen to perform a measurement of the hyperfine structure of muonic hydrogen. The results of accurate calculations of the muon transfer rates from muonic protium and deuterium atoms to nitrogen, oxygen and neon are also reported. Very good agreement with measured rates is obtained and for the three systems, the isotopic effect is perfectly reproduced. (author)

  14. Influence of ultrasonic condition on phase transfer catalyzed radical polymerization of methyl methacrylate in two phase system - A kinetic study.

    Science.gov (United States)

    Marimuthu, Elumalai; Murugesan, Vajjiravel

    2017-09-01

    An ultrasonic condition assisted phase transfer catalyzed radical polymerization of methyl methacrylate was investigated in an ethyl acetate/water two phase system at 60±1°C and 25kHz, 300W under inert atmosphere. The influence of monomer, initiator, catalyst and temperature, volume fraction of aqueous phase on the rate of polymerization was examined in detail. The reaction order was found to be unity for monomer, initiator and catalyst. Generally, the reaction rate was relatively fast in two phase system, when a catalytic amount of phase transfer catalyst was used. The combined approach, use of ultrasonic and PTC condition was significantly enhances the rate of polymerization. An ultrasonic and phase transfer catalyzed radical polymerization of methyl methacrylate has shown about three fold enhancements in the rate compared with silent polymerization of MMA using cetyltrimethylammonium bromide as PTC. The resultant kinetics was evaluated with silent polymerization and an important feature was discussed. The activation energy and other thermodynamic parameters were computed. Based on the obtained results an appropriate radical mechanism has been derived. TGA showed the polymer was stable up to 150°C. The FT-IR and DSC analysis validates the atactic nature of the obtained polymer. The XRD pattern reveals the amorphous nature of polymer was dominated. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Probing resonant energy transfer in collisions of ammonia with Rydberg helium atoms by microwave spectroscopy

    Science.gov (United States)

    Zhelyazkova, V.; Hogan, S. D.

    2017-12-01

    We present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH3 in the X1A1 ground electronic state to helium atoms in 1sns 3S1 Rydberg levels, where n = 37 and n = 40. For these values of n, the 1sns 3S1 → 1snp 3PJ transitions in helium lie close to resonance with the ground-state inversion transitions in NH3 and can be tuned through resonance using electric fields of less than 10 V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionization of the 3S1 and 3PJ Rydberg levels and by monitoring the population of the 3DJ levels following pulsed microwave transfer from the 3PJ levels. Detection by microwave spectroscopic methods represents a highly state selective, low-background approach to probing the collisional energy transfer process and the environment in which the atom-molecule interactions occur. The experimentally observed electric-field dependence of the resonant energy transfer process, probed both by direct electric field ionization and by microwave transfer, agrees well with the results of calculations performed using a simple theoretical model of the energy transfer process. For measurements performed in zero electric field with atoms prepared in the 1s40s 3S1 level, the transition from a regime in which a single energy transfer channel can be isolated for detection to one in which multiple collision channels begin to play a role has been identified as the NH3 density was increased.

  16. THERMOCHEMISTRY OF HYDROCARBON RADICALS

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. Electron transfer processes of atomic and molecular doubly charged ions: information from beam experiments

    Science.gov (United States)

    Herman, Zdenek

    2013-07-01

    Single-electron transfer reactions in collisions of atomic and molecular doubly charged ions, with atoms and molecules, were investigated in a series of crossed-beam scattering, translational spectroscopy and product luminescence experiments. Investigation of a series of atomic dication-atom electron transfer at collision energies of 0.1-10 eV provided data on differential and relative total cross sections of state-to-state processes. Populations of electronic and vibrational states and rotational temperatures of molecular product ions were obtained from studies of non-dissociative electron transfer in systems containing simple molecular dications and/or molecular targets. The product electronic states populated with highest probability were those for which the translational energy release was 3-5 eV, indicating that the 'reaction window' concept, based on the Landau-Zener formalism, is applicable also to molecular systems. Population of the vibrational states of the molecular products could be described by Franck-Condon factors of the vertical transitions between the reactant and product states, especially at higher (keV) collision energies. Rotational temperature of the product molecular cations was found to be surprisingly low, mostly 400-500 K, practically the temperature of the ion source.

  18. Novel Polymers Based on Atom Transfer Radical Polymerization of 2-Methoxyethyl Acrylate

    DEFF Research Database (Denmark)

    Bednarek, Melania; Jankova Atanasova, Katja; Hvilsted, Søren

    2007-01-01

    macroinitiators, however, for the latter the controlled conditions were somehow difficult to maintain. The amphiphilic behavior of the diblock copolymers lead to phase separation resulting in two glass transition temperatures as detected by DSC. Contact angle (Y) investigations with water on PMEA, PMMA...

  19. RATIONAL DESIGN OF THE CATALYST FOR ATOM TRANSFER RADICAL POLYMERIZATION IN AQUEOUS MEDIA. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  20. ATOM TRANSFER RADICAL POLYMERIZATION OF STYRENE IN TOLUENE-WATER MIXTURES. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  1. NMR MONITORING OF CHAIN-END FUNCTIONALITY IN ATOM TRANSFER RADICAL POLYMERIZATION OF STYRENE. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  2. Proton-Conducting Sulfonated Ionomers by Chemical Modification and Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Nielsen, Mads Møller

    (PSU), Udel, is chosen as backbone due to its mechanical and thermal properties. Sulfonic acid functionalized, dendronised side chains are attached by click chemistry in the study of hydrocarbon structures with highly flexible spacers. Various degrees of sulfonation (DS) are used in the perspectivation...... to a partially fluorinated system that is based on a poly(vinylidene fluoride) (PVDF)-containing backbone with fully sulfonated PS grafts. To counteract the dimensional change upon water contact that is a result of the increased IEC, the ionomer is blended with a high molecular weight PVDF, which contributes....... The blends are highly humidity sensitive, yet, despite lower absolute conductivities than Nafion, they display a reduced dependence on both humidity and temperature. Under fully humidified conditions the blends perform superior to fully sulfonated graft copolymer analogues. The combination of a high degree...

  3. Protein repellent hydrophilic grafts prepared by surface-initiated atom transfer radical polymerization from polypropylene

    DEFF Research Database (Denmark)

    Fristrup, Charlotte Juel; Jankova Atanasova, Katja; Eskimergen, Rüya

    2012-01-01

    with Attenuated Total Reflectance (ATR) Fourier Transform Infrared (FTIR) spectroscopy and Water Contact Angle (WCA) measurements. Confocal fluorescence microscopy of modified and unmodified substrates immersed in labelled insulin aspart showed superior repulsion of this protein for the poly(PEGMA) grafts, due...

  4. Hydrolysis of 4-Acetoxystyrene Polymers Prepared by Atom Transfer Radical Polymerization

    DEFF Research Database (Denmark)

    Chen, Xianyi; Jankova, Katja; Kops, Jørgen

    1999-01-01

    , by NaOH catalyzed deprotection, the 4-acetoxystyrene polymers including triblock copolymer poly(4-acetoxystyrene-b-isobutylene-b-4-toxystyrene) suffered from some degrees of coupling or even gelation, except for poly(styrene-b-4-acetoxystyrene-b-styrene) which also by this method could be conveniently...

  5. Direct time-resolved spectroscopic investigation of intramolecular hydrogen atom transfer of deoxyblebbistatin

    Science.gov (United States)

    Li, Ming-De; Zhu, Ruixue; Lee Phillips, David

    2017-09-01

    The photophysics and photochemistry of deoxyblebbistatin was investigated using femtosecond time-resolved transient absorption spectroscopy. An ultrafast intramolecular hydrogen atom transfer (IHAT) appears to take place via the first singlet excited state of deoxyblebbistatin within 8 ps. Absorption and fluorescence photochemical results indicate the IHAT process leads to mainly conversion of deoxyblebbistatin into an enol form final product which was observed and characterized by resonance Raman spectroscopy.

  6. Bibliography on electron transfer processes in ion-ion/atom/molecule collisions. Updated 1997

    Energy Technology Data Exchange (ETDEWEB)

    Tawara, H.

    1997-04-01

    Following our previous compilations (IPPJ-AM-45 (1986), NIFS-DATA-7 (1990), NIFS-DATA-20 (1993)), bibliographic information on experimental and theoretical studies on electron transfer processes in ion-ion/atom/molecule collisions is up-dated. The references published through 1954-1996 are listed in the order of the publication year. For easy finding of the references for a combination of collision partners, a simple list is provided. (author)

  7. Reducing power of simple polyphenols by electron-transfer reactions using a new stable radical of the PTM series, tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl radical.

    Science.gov (United States)

    Torres, Josep Lluís; Carreras, Anna; Jiménez, Aurora; Brillas, Enric; Torrelles, Xavier; Rius, Jordi; Juliá, Luis

    2007-05-11

    The synthesis and characterization of a new radical and its use for testing the antioxidant activity of polyphenols by electron transfer are reported. This new and stable species of magnetic nature, tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl (TNPTM) radical, has been characterized by electron paramagnetic resonance and its molecular structure determined by X-ray analysis. This new radical of the PTM (perchlorotriphenylmethyl) series, unlike 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, is stable in conditions of hydrogen abstraction reactions. TNPTM radical is able to discriminate between the antioxidant activities of catechol and pyrogallol in hydroxylated solvent mixtures such as chloroform/methanol (2:1). These features determine the antioxidant/pro-oxidant character and the biological activities of natural and synthetic flavonoids.

  8. Concerted hydrogen atom and electron transfer mechanism for catalysis by lysine-specific demethylase.

    Science.gov (United States)

    Yu, Tao; Higashi, Masahiro; Cembran, Alessandro; Gao, Jiali; Truhlar, Donald G

    2013-07-18

    We calculate the free energy profile for the postulated hydride transfer reaction mechanism for the catalysis of lysine demethylation by lysine-specific demethylase LSD1. The potential energy surface is obtained by using combined electrostatically embedded multiconfiguration molecular mechanics (EE-MCMM) and single-configuration molecular mechanics (MM). We employ a constant valence bond coupling term to obtain analytical energies and gradients of the EE-MCMM subsystem, which contains 45 quantum mechanics (QM) atoms and which is parametrized with density functional calculations employing specific reaction parameters obtained by matching high-level wave function calculations. In the MM region, we employ the Amber ff03 and TIP3P force fields. The free energy of activation at 300 K is calculated by molecular dynamics (MD) umbrella sampling on a system with 102,090 atoms as the maximum of the free energy profile along the reaction coordinate as obtained by the weighted histogram analysis method with 17 umbrella sampling windows. This yields a free energy of activation of only 10 kcal/mol, showing that the previously postulated direct hydride transfer reaction mechanism is plausible, although we find that it is better interpreted as a concerted transfer of a hydrogen atom and an electron.

  9. DFT and time-resolved IR investigation of electron transfer between photogenerated 17- and 19-electron organometallic radicals

    Energy Technology Data Exchange (ETDEWEB)

    Cahoon, James B.; Kling, Matthias F.; Sawyer, Karma R.; Andersen, Lars K.; Harris, Charles B.

    2008-04-30

    The photochemical disproportionation mechanism of [CpW(CO){sub 3}]{sub 2} in the presence of Lewis bases PR{sub 3} was investigated on the nano- and microsecond time-scales with Step-Scan FTIR time-resolved infrared spectroscopy. 532 nm laser excitation was used to homolytically cleave the W-W bond, forming the 17-electron radicals CpW(CO){sub 3} and initiating the reaction. With the Lewis base PPh{sub 3}, disproportionation to form the ionic products CpW(CO){sub 3}PPh{sub 3}{sup +} and CpW(CO){sub 3}{sup -} was directly monitored on the microsecond time-scale. Detailed examination of the kinetics and concentration dependence of this reaction indicates that disproportionation proceeds by electron transfer from the 19-electron species CpW(CO){sub 3}PPh{sub 3} to the 17-electron species CpW(CO){sub 3}. This result is contrary to the currently accepted disproportionation mechanism which predicts electron transfer from the 19-electron species to the dimer [CpW(CO){sub 3}]{sub 2}. With the Lewis base P(OMe){sub 3} on the other hand, ligand substitution to form the product [CpW(CO){sub 2}P(OMe){sub 3}]{sub 2} is the primary reaction on the microsecond time-scale. Density Functional Theory (DFT) calculations support the experimental results and suggest that the differences in the reactivity between P(OMe){sub 3} and PPh{sub 3} are due to steric effects. The results indicate that radical-to-radical electron transfer is a previously unknown but important process for the formation of ionic products with the organometallic dimer [CpW(CO){sub 3}]{sub 2} and may also be applicable to the entire class of organometallic dimers containing a single metal-metal bond.

  10. Method of making a membrane having hydrophilic and hydrophobic surfaces for adhering cells or antibodies by using atomic oxygen or hydroxyl radicals

    Science.gov (United States)

    Koontz, Steven L. (Inventor); Spaulding, Glenn F. (Inventor)

    1994-01-01

    A portion of an organic polymer article such as a membrane is made hydrophilic by exposing a hydrophobic surface of the article to a depth of about 50 to about 5000 angstroms to atomic oxygen or hydroxyl radicals at a temperature below 100C., preferably below 40 C, to form a hydrophilic uniform surface layer of hydrophilic hydroxyl groups. The atomic oxygen and hydroxyl radicals are generated by a flowing afterglow microwave discharge, and the surface is outside of a plasma produced by the discharge. A membrane having both hydrophilic and hydrophobic surfaces can be used in an immunoassay by adhering antibodies to the hydrophobic surface. In another embodiment, the membrane is used in cell culturing where cells adhere to the hydrophilic surface. Prior to adhering cells, the hydrophilic surface may be grafted with a compatibilizing compound. A plurality of hydrophilic regions bounded by adjacent hydrophobic regions can be produced such that a maximum of one cell per each hydrophilic region adheres.

  11. Reaction rate coefficients of OH radicals and Cl atoms with ethyl propanoate, n-propyl propanoate, methyl 2-methylpropanoate, and ethyl n-butanoate.

    Science.gov (United States)

    Cometto, Pablo M; Daële, Véronique; Idir, Mahmoud; Lane, Silvia I; Mellouki, Abdelwahid

    2009-10-08

    Kinetics of the reactions of OH radicals and Cl atoms with four saturated esters have been investigated. Rate coefficients for the gas-phase reactions of OH radicals with ethyl propanoate (k(1)), n-propyl propanoate (k(2)), methyl 2-methylpropanoate (k(3)), and ethyl n-butanoate (k(4)) were measured using a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. At (296 +/- 2) K, the rate coefficients obtained by the two methods were in good agreement. Significant curvatures in the Arrhenius plots have been observed in the temperature range 243-372 K for k(1), k(3), and k(4). The rate coefficients for the reactions of the four esters with Cl atoms were determined using the relative rate method at (296 +/- 2) K and atmospheric pressure. The values obtained are presented, compared with the literature values when they exist, and discussed. Reactivity trends and atmospheric implications for these esters are also presented.

  12. A model for energy transfer in collisions of atoms with highly excited molecules.

    Science.gov (United States)

    Houston, Paul L; Conte, Riccardo; Bowman, Joel M

    2015-05-21

    A model for energy transfer in the collision between an atom and a highly excited target molecule has been developed on the basis of classical mechanics and turning point analysis. The predictions of the model have been tested against the results of trajectory calculations for collisions of five different target molecules with argon or helium under a variety of temperatures, collision energies, and initial rotational levels. The model predicts selected moments of the joint probability distribution, P(Jf,ΔE) with an R(2) ≈ 0.90. The calculation is efficient, in most cases taking less than one CPU-hour. The model provides several insights into the energy transfer process. The joint probability distribution is strongly dependent on rotational energy transfer and conservation laws and less dependent on vibrational energy transfer. There are two mechanisms for rotational excitation, one due to motion normal to the intermolecular potential and one due to motion tangential to it and perpendicular to the line of centers. Energy transfer is found to depend strongly on the intermolecular potential and only weakly on the intramolecular potential. Highly efficient collisions are a natural consequence of the energy transfer and arise due to collisions at "sweet spots" in the space of impact parameter and molecular orientation.

  13. Atmospheric chemistry of trans-CF3CH = CHCl: Kinetics of the gas-phase reactions with Cl atoms, OH radicals, and O-3

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Nilsson, E. J. K.; Nielsen, O. J.

    2008-01-01

    Long path length Fourier transform infrared (FTIR)-smog chamber techniques were used to study the kinetics of the gas-phase reactions of Cl atoms. OH radicals and O-3 with trans-3,3,3-trifluoro-1-chloropropene, t-CF3CH = CHCl, in 700Torr total pressure at 295 +/- 2 K. Values of k(Cl + t-CF3CH...

  14. Atmospheric chemistry of trans-CF3CH=CHCl: Kinetics of the gas-phase reactions with Cl atoms, OH radicals, and O3

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbaek; Nilsson, Elna Johanna Kristina; Nielsen, Ole John

    2008-01-01

    Long path length Fourier transform infrared (FTIR)–smog chamber techniques were used to study the kinetics of the gas-phase reactions of Cl atoms, OH radicals and O3 with trans-3,3,3-trifluoro-1-chloropropene, t-CF3CH CHCl, in 700 Torr total pressure at 295±2K. Values of k(Cl + t-CF3CH CHCl) = (5...

  15. Kinetics of the Hydrogen Atom Abstraction Reactions from 1-Butanol by Hydroxyl Radical: Theory Matches Experiment and More

    Energy Technology Data Exchange (ETDEWEB)

    Seal, Prasenjit; Oyedepo, Gbenga; Truhlar, Donald G.

    2013-01-17

    In the present work, we study the H atom abstraction reactions by hydroxyl radical at all five sites of 1-butanol. Multistructural variational transition state theory (MS-VTST) was employed to estimate the five thermal rate constants. MS-VTST utilizes a multifaceted dividing surface that accounts for the multiple conformational structures of the transition state, and we also include all the structures of the reactant molecule. The vibrational frequencies and minimum energy paths (MEPs) were computed using the M08-HX/MG3S electronic structure method. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) using a variational reaction path algorithm. The M08-HX/MG3S electronic model chemistry was then used to calculate multistructural torsional anharmonicity factors to complete the MS-VTST rate constant calculations. The results indicate that torsional anharmonicity is very important at higher temperatures, and neglecting it would lead to errors of 26 and 32 at 1000 and 1500 K, respectively. Our results for the sums of the site-specific rate constants agree very well with the experimental values of Hanson and co-workers at 896–1269 K and with the experimental results of Campbell et al. at 292 K, but slightly less well with the experiments of Wallington et al., Nelson et al., and Yujing and Mellouki at 253–372 K; nevertheless, the calculated rates are within a factor of 1.61 of all experimental values at all temperatures. Finally, this gives us confidence in the site-specific values, which are currently inaccessible to experiment.

  16. Kinetics of the hydrogen atom abstraction reactions from 1-butanol by hydroxyl radical: theory matches experiment and more.

    Science.gov (United States)

    Seal, Prasenjit; Oyedepo, Gbenga; Truhlar, Donald G

    2013-01-17

    In the present work, we study the H atom abstraction reactions by hydroxyl radical at all five sites of 1-butanol. Multistructural variational transition state theory (MS-VTST) was employed to estimate the five thermal rate constants. MS-VTST utilizes a multifaceted dividing surface that accounts for the multiple conformational structures of the transition state, and we also include all the structures of the reactant molecule. The vibrational frequencies and minimum energy paths (MEPs) were computed using the M08-HX/MG3S electronic structure method. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) using a variational reaction path algorithm. The M08-HX/MG3S electronic model chemistry was then used to calculate multistructural torsional anharmonicity factors to complete the MS-VTST rate constant calculations. The results indicate that torsional anharmonicity is very important at higher temperatures, and neglecting it would lead to errors of 26 and 32 at 1000 and 1500 K, respectively. Our results for the sums of the site-specific rate constants agree very well with the experimental values of Hanson and co-workers at 896-1269 K and with the experimental results of Campbell et al. at 292 K, but slightly less well with the experiments of Wallington et al., Nelson et al., and Yujing and Mellouki at 253-372 K; nevertheless, the calculated rates are within a factor of 1.61 of all experimental values at all temperatures. This gives us confidence in the site-specific values, which are currently inaccessible to experiment.

  17. An absolute- and relative-rate study of the gas-phase reaction of OH radicals and Cl atoms with n-alkyl nitrates

    DEFF Research Database (Denmark)

    Nielsen, O.J.; Sidebottom, H.W.; Donlon, M.

    1991-01-01

    Rate constants for the reactions of OH radicals and Cl atoms with CH3ONO2, C2H5ONO2, n-C3H7ONO2, n-C4H9ONO2, and n-C5H11ONO2 have been determined at 298 +/- 2 K and a total pressure of approximately 1 atm. The OH rate data were obtained using both the absolute-rate technique of pulse radiolysis...... combined with kinetic spectroscopy and a conventional photolytic relative-rate method. The Cl rate constants were measured using only the relative-rate method. Evidence is presented from the kinetic studies that reaction of OH radicals with alkyl nitrates may involve both addition and abstraction pathways....... The data show that the -ONO2 group substantially decreases the rate constant for H-atom abstraction by OH radicals from groups bonded to the -ONO2 group and also decreases that for groups in the beta-position. Similar results were found for the reaction of Cl atoms with these compounds. The results...

  18. Dual electron transfer pathways from the excited C60 radical anion: enhanced reactivities due to the photoexcitation of reaction intermediates.

    Science.gov (United States)

    Fujitsuka, Mamoru; Ohsaka, Tatsuya; Majima, Tetsuro

    2015-12-14

    In the present study, electron transfer (ET) processes from excited radical anions have been investigated using dyad molecules including C60. The deactivation process of excited C60˙(-), including the internal conversion from the D1 to the D0 state and the cooling process of the vibrationally hot ground state (D), was observed spectroscopically for the first time. These processes could be unambiguously distinguished by the observation of the stimulated emission from the D1 state. The intramolecular ET processes from the excited C60˙(-) were confirmed by the transient absorption spectra. Clearly, both D1 and D states acted as precursors for the ET, i.e., dual ET pathways were confirmed. The driving force dependence of the ET rates was well characterized by the Marcus theory, which revealed that the forward ET processes are located at the top region of the Marcus parabola. In addition, the ET from the excited imide radical anion to C60 and that from the ground state C60˙(-) to imide were examined. The ET rate from the excited imide radical anion and that from ground state C60˙(-) did not follow the Marcus parabola estimated for the ET from the excited C60˙(-). The observed difference can be attributed to the difference in the energy required to form the reduced spacer (Δ) in the superexchange mechanism. Because the Δ value tends to become smaller for ET processes from excited radical ions, fast and efficient ET processes are expected from these states as demonstrated in the present study.

  19. Handshake electron transfer from hydrogen Rydberg atoms incident at a series of metallic thin films.

    Science.gov (United States)

    Gibbard, J A; Softley, T P

    2016-06-21

    Thin metallic films have a 1D quantum well along the surface normal direction, which yields particle-in-a-box style electronic quantum states. However the quantum well is not infinitely deep and the wavefunctions of these states penetrate outside the surface where the electron is bound by its own image-charge attraction. Therefore a series of discrete, vacant states reach out from the thin film into the vacuum increasing the probability of electron transfer from an external atom or molecule to the thin film, especially for the resonant case where the quantum well energy matches that of the atom. We show that "handshake" electron transfer from a highly excited Rydberg atom to these thin-film states is experimentally measurable. Thicker films have a wider 1D box, changing the energetic distribution and image-state contribution to the thin film wavefunctions, resulting in more resonances. Calculations successfully predict the number of resonances and the nature of the thin-film wavefunctions for a given film thickness.

  20. Photonic quantum state transfer between a cold atomic gas and a crystal.

    Science.gov (United States)

    Maring, Nicolas; Farrera, Pau; Kutluer, Kutlu; Mazzera, Margherita; Heinze, Georg; de Riedmatten, Hugues

    2017-11-22

    Interfacing fundamentally different quantum systems is key to building future hybrid quantum networks. Such heterogeneous networks offer capabilities superior to those of their homogeneous counterparts, as they merge the individual advantages of disparate quantum nodes in a single network architecture. However, few investigations of optical hybrid interconnections have been carried out, owing to fundamental and technological challenges such as wavelength and bandwidth matching of the interfacing photons. Here we report optical quantum interconnection of two disparate matter quantum systems with photon storage capabilities. We show that a quantum state can be transferred faithfully between a cold atomic ensemble and a rare-earth-doped crystal by means of a single photon at 1,552  nanometre telecommunication wavelength, using cascaded quantum frequency conversion. We demonstrate that quantum correlations between a photon and a single collective spin excitation in the cold atomic ensemble can be transferred to the solid-state system. We also show that single-photon time-bin qubits generated in the cold atomic ensemble can be converted, stored and retrieved from the crystal with a conditional qubit fidelity of more than 85 per cent. Our results open up the prospect of optically connecting quantum nodes with different capabilities and represent an important step towards the realization of large-scale hybrid quantum networks.

  1. Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer

    Science.gov (United States)

    Cabrero-Vilatela, A.; Alexander-Webber, J. A.; Sagade, A. A.; Aria, A. I.; Braeuninger-Weimer, P.; Martin, M.-B.; Weatherup, R. S.; Hofmann, S.

    2017-12-01

    The transfer of chemical vapour deposited graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to remove completely and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100 nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.

  2. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Science.gov (United States)

    Froehlicher, Guillaume; Lorchat, Etienne; Berciaud, Stéphane

    2018-01-01

    Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe2 )] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene /MoSe2 is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps) room-temperature MoSe2 exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe2 Raman modes, which reveals net photoinduced electron transfer from MoSe2 to graphene and hole accumulation in MoSe2 . Remarkably, the steady-state Fermi energy of graphene saturates at 290 ±15 meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets) and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene /MoSe2 . This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron exchange or dipole-dipole interaction) is the

  3. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Directory of Open Access Journals (Sweden)

    Guillaume Froehlicher

    2018-01-01

    Full Text Available Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe_{2}] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene/MoSe_{2} is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps room-temperature MoSe_{2} exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe_{2} Raman modes, which reveals net photoinduced electron transfer from MoSe_{2} to graphene and hole accumulation in MoSe_{2}. Remarkably, the steady-state Fermi energy of graphene saturates at 290±15  meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene/MoSe_{2}. This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron

  4. One-electron reduction of N-chlorinated and N-brominated species is a source of radicals and bromine atom formation.

    Science.gov (United States)

    Pattison, David I; O'Reilly, Robert J; Skaff, Ojia; Radom, Leo; Anderson, Robert F; Davies, Michael J

    2011-03-21

    Hypochlorous (HOCl) and hypobromous (HOBr) acids are strong bactericidal oxidants that are generated by the human immune system but are implicated in the development of many human inflammatory diseases (e.g., atherosclerosis, asthma). These oxidants react readily with sulfur- and nitrogen-containing nucleophiles, with the latter generating N-halogenated species (e.g., chloramines/bromamines (RR'NX; X = Cl, Br)) as initial products. Redox-active metal ions and superoxide radicals (O(2)(•-)) can reduce N-halogenated species to nitrogen- and carbon-centered radicals. N-Halogenated species and O(2)(•-) are generated simultaneously at sites of inflammation, but the significance of their interactions remains unclear. In the present study, rate constants for the reduction of N-halogenated amines, amides, and imides to model potential biological substrates have been determined. Hydrated electrons reduce these species with k(2) > 10(9) M(-1) s(-1), whereas O(2)(•-) reduced only N-halogenated imides with complex kinetics indicative of chain reactions. For N-bromoimides, heterolytic cleavage of the N-Br bond yielded bromine atoms (Br(•)), whereas for other substrates, N-centered radicals and Cl(-)/Br(-) were produced. High-level quantum chemical procedures have been used to calculate gas-phase electron affinities and aqueous solution reduction potentials. The effects of substituents on the electron affinities of aminyl, amidyl, and imidyl radicals are rationalized on the basis of differential effects on the stabilities of the radicals and anions. The calculated reduction potentials are consistent with the experimental observations, with Br(•) production predicted for N-bromosuccinimide, while halide ion formation is predicted in all other cases. These data suggest that interaction of N-halogenated species with O(2)(•-) may produce deleterious N-centered radicals and Br(•).

  5. Charge transfer and association of Na+ with 87Rb atoms from extremely low to intermediate energies

    Science.gov (United States)

    Yan, L. L.; Liu, L.; Wu, Y.; Qu, Y. Z.; Wang, J. G.; Buenker, R. J.

    2013-07-01

    The nonradiative charge-transfer processes in Na++87Rb(5s) collisions have been investigated by using the quantum-mechanical molecular-orbital close-coupling method and the two-center atomic-orbital close-coupling method for the energy range of 10-4-5 and 0.3-100 keV/u, respectively. The radiative charge-transfer, radiative-decay, and radiative-association processes have been investigated by using the fully quantum, optical-potential, and semiclassical methods for the energy range of 10-18-0.2 eV/u. The nonradiative charge-transfer processes dominate the collisions for energies above 0.2 eV/u and radiative-decay processes dominate in the lower-energy region. At the very low collision energies of 10-18-10-3 eV/u, the radiative-association process is more important than the radiative charge-transfer process. Most importantly, it is found that the radiative cross sections exhibit Langevin behavior as E-1/2 for energies less than 10-2 eV/u.

  6. Manganese-Oxygen Intermediates in O-O Bond Activation and Hydrogen-Atom Transfer Reactions.

    Science.gov (United States)

    Rice, Derek B; Massie, Allyssa A; Jackson, Timothy A

    2017-11-21

    Biological systems capitalize on the redox versatility of manganese to perform reactions involving dioxygen and its derivatives superoxide, hydrogen peroxide, and water. The reactions of manganese enzymes influence both human health and the global energy cycle. Important examples include the detoxification of reactive oxygen species by manganese superoxide dismutase, biosynthesis by manganese ribonucleotide reductase and manganese lipoxygenase, and water splitting by the oxygen-evolving complex of photosystem II. Although these enzymes perform very different reactions and employ structurally distinct active sites, manganese intermediates with peroxo, hydroxo, and oxo ligation are commonly proposed in catalytic mechanisms. These intermediates are also postulated in mechanisms of synthetic manganese oxidation catalysts, which are of interest due to the earth abundance of manganese. In this Account, we describe our recent efforts toward understanding O-O bond activation pathways of Mn III -peroxo adducts and hydrogen-atom transfer reactivity of Mn IV -oxo and Mn III -hydroxo complexes. In biological and synthetic catalysts, peroxomanganese intermediates are commonly proposed to decay by either Mn-O or O-O cleavage pathways, although it is often unclear how the local coordination environment influences the decay mechanism. To address this matter, we generated a variety of Mn III -peroxo adducts with varied ligand environments. Using parallel-mode EPR and Mn K-edge X-ray absorption techniques, the decay pathway of one Mn III -peroxo complex bearing a bulky macrocylic ligand was investigated. Unlike many Mn III -peroxo model complexes that decay to oxo-bridged-Mn III Mn IV dimers, decay of this Mn III -peroxo adduct yielded mononuclear Mn III -hydroxo and Mn IV -oxo products, potentially resulting from O-O bond activation of the Mn III -peroxo unit. These results highlight the role of ligand sterics in promoting the formation of mononuclear products and mark an important

  7. Thermo-Responsive and Biocompatible Diblock Copolymers Prepared via Reversible Addition-Fragmentation Chain Transfer (RAFT Radical Polymerization

    Directory of Open Access Journals (Sweden)

    Kenichi Fukuda

    2014-03-01

    Full Text Available Poly(2-(methacryloyloxyethyl phosphorylcholine-b-poly(N,N-diethyl acrylamide (PMPCm-PDEAn was synthesized via reversible addition-fragmentation chain transfer (RAFT controlled radical polymerization. Below, the critical aggregation temperature (CAT the diblock copolymer dissolved in water as a unimer with a hydrodynamic radius (Rh of ca. 5 nm. Above the CAT the diblock copolymers formed polymer micelles composed of a PDEA core and biocompatible PMPC shells, due to hydrophobic self-aggregation of the thermo-responsive PDEA block. A fluorescence probe study showed that small hydrophobic small guest molecules could be incorporated into the core of the polymer micelle above the CAT. The incorporated guest molecules were released from the core into the bulk aqueous phase when the temperature decreased to values below the CAT because of micelle dissociation.

  8. Matrix-isolation studies on the radiation-induced chemistry in H₂O/CO₂ systems: reactions of oxygen atoms and formation of HOCO radical.

    Science.gov (United States)

    Ryazantsev, Sergey V; Feldman, Vladimir I

    2015-03-19

    The radiation-induced transformations occurring upon X-ray irradiation of solid CO2/H2O/Ng systems (Ng = Ar, Kr, Xe) at 8-10 K and subsequent annealing up to 45 K were studied by Fourier transform infrared spectroscopy. The infrared (IR) spectra of deposited matrices revealed the presence of isolated monomers, dimers, and intermolecular H2O···CO2 complexes. Irradiation resulted in effective decomposition of matrix-isolated carbon dioxide and water yielding CO molecules and OH radicals, respectively. Annealing of the irradiated samples led to formation of O3, HO2, and a number of xenon hydrides of HXeY type (in the case of xenon matrices). The formation of these species was used for monitoring of the postirradiation thermally induced chemical reactions involving O and H atoms generated by radiolysis. It was shown that the radiolysis of CO2 in noble-gas matrices produced high yields of stabilized oxygen atoms. In all cases, the temperatures at which O atoms become mobile and react are lower than those of H atoms. Dynamics and reactivity of oxygen atoms was found to be independent of the precursor nature. In addition, the formation of HOCO radicals was observed in all the noble-gas matrices at remarkably low temperatures. The IR spectra of HOCO and DOCO were first characterized in krypton and xenon matrices. It was concluded that the formation of HOCO was mainly due to the radiation-induced evolution of the weakly bound H2O···CO2 complexes. This result indicates the significance of weak intermolecular interactions in the radiation-induced chemical processes in inert low-temperature media.

  9. Theoretical studies on kinetics, mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom.

    Science.gov (United States)

    Deka, Ramesh Chandra; Mishra, Bhupesh Kumar

    2014-09-01

    A theoretical study on the mechanism and kinetics of the gas phase reactions of CF3CHFCF2OCH2CF3 (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF3CHFCF2OCH2CF3 and the most stable one is considered for detailed study. Reaction profiles for OH-initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH2 group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for CH bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250-450K. The calculated rate constant values are found to be 9.10×10(-15) and 4.77×10(-17)cm(3)molecule(-1)s(-1) for reactions with OH radicals and Cl atom, respectively. At 298K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years. Copyright © 2014 Elsevier Inc. All rights reserved.

  10. Alpha- and beta-thujone radical rearrangements and isomerizations. A new radical clock.

    Science.gov (United States)

    He, Xiang; Ortiz de Montellano, Paul R

    2004-08-20

    Radical clocks have been extensively used in chemical and biochemical mechanistic studies. The C4 radicals of alpha- and beta-thujone can undergo two distinct rearrangement reactions that could, in principle, serve as simultaneous but independent radical clocks. We have therefore generated these C4 radicals by photolysis of the corresponding N-hydroxypyridine-2-thione ester precursors and have investigated their fates and lifetimes. Photolysis of either alpha- or beta-thujone generates the same 6:100 mixture of alpha- and beta-thujone when the radicals are quenched by thiophenol. Hydrogen atom transfer from thiophenol to the radical thus occurs preferentially from the less sterically hindered alpha-face to give beta-thujone. The third product formed in the photolysis via opening of the cyclopropyl ring is 2-methyl-5-isopropylcyclopent-2-enone. The ratio of ring opened to unopened products gives very similar values of kralpha = 4.4 x 10(7) s(-1) and krbeta = 1.0 x 10(8) s(-1) for ring opening of the radicals generated from alpha- and beta-thujone, respectively. If the C4 cation rather than radical is generated, it is converted to carvacrol, a phenol that is not obtained in the radical reactions. Thujone therefore differentiates between radical and cation pathways and provides a measure of the radical lifetime. Copyright 2004 American Chemical Society

  11. The role of coherent excitation and collisional energy transfer in atomic vapor filters and photon detectors

    Science.gov (United States)

    Correll, Tiffany Lee

    Many optical techniques, including laser Doppler velocimetry, free space optical communications, and chemical imaging, require-or can be enhanced by-high spectral resolution photon detection. Such detection is characterized by spectral discrimination on the order of GHz or MHz i.e., approximately 10-4 nm in the near-infrared region. This spectral resolution has recently been achieved by exploiting the narrow absorption features of gas phase atoms. Absorption of light by alkali vapors is intrinsically selective and can be monitored by detecting the fluorescence resulting from laser excitation coupled to selectively excited atomic states. Imaging can be accomplished by spatially expanding the excitation lasers into two dimensions. Fluorescence photons are only created and detected when the interrogated object is forced to scatter radiation of an energy precisely matching one of the transitions of a pre-determined optimal excitation/fluorescence scheme. Devices based on resonance fluorescence photon detection have recently been described using cesium atoms. In this work, the sensitivity and spectral resolution of cesium-based photon detectors were evaluated and improved. To this end, initial experiments focused on laser induced fluorescence in room temperature cesium vapor. The fluorescence response of the detector was augmented by the use of cesium-induced collisional excitation energy transfer between states involved in the chosen excitation scheme. Additional studies focused on helium and argon-induced collisions in the vapor to increase the signal output while maintaining adequate spatial resolution in imaging mode. The probability or cross section of helium-cesium collisions at the operating temperature of the detector was determined by use of a simplified rate equation model. The spectral response of the detector was improved by the use of coherent optical effects resulting from the interaction of a multi-level atomic system with narrowband radiation. Superior

  12. 248-NM Laser Photolysis of CHBr3/O-Atom Mixtures: Kinetic Evidence for UV CO(A)-Chemiluminescence in the Reaction of Methylidyne Radicals With Atomic Oxygen

    National Research Council Canada - National Science Library

    Vaghjiani, Ghanshyam L

    2005-01-01

    4TH Positive and Cameron band emissions from electronically excited CO have been observed for the first time in 248-nm pulsed laser photolysis of a trace amount of CHBr3 vapor in an excess of O-atoms...

  13. Correlation among Singlet-Oxygen Quenching, Free-Radical Scavenging, and Excited-State Intramolecular-Proton-Transfer Activities in Hydroxyflavones, Anthocyanidins, and 1-Hydroxyanthraquinones.

    Science.gov (United States)

    Nagaoka, Shin-Ichi; Bandoh, Yuki; Nagashima, Umpei; Ohara, Keishi

    2017-10-26

    Singlet-oxygen (1O2) quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) activities of hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones were studied by means of laser, stopped-flow, and steady-state spectroscopies. In hydroxyflavones and anthocyanidins, the 1O2 quenching activity positively correlates to the free-radical scavenging activity. The reason for this correlation can be understood by considering that an early step of each reaction involves electron transfer from the unfused phenyl ring (B-ring), which is singly bonded to the bicyclic chromen or chromenylium moiety (A- and C-rings). Substitution of an electron-donating OH group at B-ring enhances the electron transfer leading to activation of the 1O2 quenching and free-radical scavenging. In 3-hydroxyflavones, the OH substitution at B-ring reduces the activity of ESIPT within C-ring, which can be explained in terms of the nodal-plane model. As a result, the 1O2 quenching and free-radical scavenging activities negatively correlate to the ESIPT activity. A catechol structure at B-ring is another factor that enhances the free-radical scavenging in hydroxyflavones. In contrast to these hydroxyflavones, 1-hydroxyanthraquinones having an electron-donating OH substituent adjacent to the O-H---O═C moiety susceptible to ESIPT do not show a simple correlation between their 1O2 quenching and ESIPT activities, because the OH substitution modulates these reactions.

  14. Synergistic Formation of Radicals by Irradiation with Both Vacuum Ultraviolet and Atomic Hydrogen: A Real-Time In Situ Electron Spin Resonance Study

    CERN Document Server

    Ishikawa, Kenji; Kono, Akihiko; Horibe, Hideo; Takeda, Keigo; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru; 10.1021/jz2002937

    2012-01-01

    We report on the surface modification of polytetrafluoroethylene (PTFE) as an example of soft- and bio-materials that occur under plasma discharge by kinetics analysis of radical formation using in situ real-time electron spin resonance (ESR) measurements. During irradiation with hydrogen plasma, simultaneous measurements of the gas-phase ESR signals of atomic hydrogen and the carbon dangling bond (C-DB) on PTFE were performed. Dynamic changes of the C-DB density were observed in real time, where the rate of density change was accelerated during initial irradiation and then became constant over time. It is noteworthy that C-DBs were formed synergistically by irradiation with both vacuum ultraviolet (VUV) and atomic hydrogen. The in situ real-time ESR technique is useful to elucidate synergistic roles during plasma surface modification.

  15. Simple preparation of thiol-ene particles in glycerol and surface functionalization by thiol-ene chemistry (TEC) and surface chain transfer free radical polymerization (SCT-FRP)

    DEFF Research Database (Denmark)

    Hoffmann, Christian; Chiaula, Valeria; Pinelo, Manuel

    2017-01-01

    functionalization of excess thiol groups via photochemical thiol-ene chemistry (TEC) resulting in a functional monolayer. In addition, surface chain transfer free radical polymerization (SCT-FRP) was used for the first time to introduce a thicker polymer layer on the particle surface. The application potential...

  16. Wideband laser locking to an atomic reference with modulation transfer spectroscopy.

    Science.gov (United States)

    Negnevitsky, V; Turner, L D

    2013-02-11

    We demonstrate that conventional modulated spectroscopy apparatus, used for laser frequency stabilization in many atomic physics laboratories, can be enhanced to provide a wideband lock delivering deep suppression of frequency noise across the acoustic range. Using an acousto-optic modulator driven with an agile oscillator, we show that wideband frequency modulation of the pump laser in modulation transfer spectroscopy produces the unique single lock-point spectrum previously demonstrated with electro-optic phase modulation. We achieve a laser lock with 100 kHz feedback bandwidth, limited by our laser control electronics. This bandwidth is sufficient to reduce frequency noise by 30 dB across the acoustic range and narrows the imputed linewidth by a factor of five.

  17. Effect of current and atomized grain size distribution on the solidification of Plasma Transferred Arc coatings

    Directory of Open Access Journals (Sweden)

    Danielle Bond

    2012-10-01

    Full Text Available Plasma Transferred Arc (PTA is the only thermal spray process that results in a metallurgical bond, being frequently described as a hardfacing process. The superior properties of coatings have been related to the fine microstructures obtained, which are finer than those processed under similar heat input with welding techniques using wire feedstock. This observation suggests that the atomized feedstock plays a role on the solidification of coatings. In this study a model for the role of the powders grains in the solidification of PTA coatings is put forward and discussed. An experiment was setup to discuss the model which involved the deposition of an atomized Co-based alloy with different grain size distributions and deposition currents. X ray diffraction showed that there were no phase changes due to the processing parameters. Microstructure analysis by Laser Confocal Microscopy, dilution with the substrate steel and Vickers microhardness were used the characterized coatings and enriched the discussion confirming the role of the powdered feedstock on the solidification of coatings.

  18. Time-resolved FTIR emission studies of laser photofragmentation and radical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Leone, S.R. [Univ. of Colorado, Boulder (United States)

    1993-12-01

    Recent studies have focused specifically on collision processes, such as single collision energy transfer, reaction dynamics, and radical reactions. The authors employ novel FTIR techniques in the study of single collision energy transfer processes using translationally fast H atom, as well as radical-radical reactions, e.g. CH{sub 3} + O, CF{sub 3} + H(D), and Cl + C{sub 2}H{sub 5}. The fast atoms permit unique high energy regions of certain transition states of combustion species to be probed for the first time.

  19. Atomic charge transfer-counter polarization effects determine infrared CH intensities of hydrocarbons: a quantum theory of atoms in molecules model.

    Science.gov (United States)

    Silva, Arnaldo F; Richter, Wagner E; Meneses, Helen G C; Bruns, Roy E

    2014-11-14

    Atomic charge transfer-counter polarization effects determine most of the infrared fundamental CH intensities of simple hydrocarbons, methane, ethylene, ethane, propyne, cyclopropane and allene. The quantum theory of atoms in molecules/charge-charge flux-dipole flux model predicted the values of 30 CH intensities ranging from 0 to 123 km mol(-1) with a root mean square (rms) error of only 4.2 km mol(-1) without including a specific equilibrium atomic charge term. Sums of the contributions from terms involving charge flux and/or dipole flux averaged 20.3 km mol(-1), about ten times larger than the average charge contribution of 2.0 km mol(-1). The only notable exceptions are the CH stretching and bending intensities of acetylene and two of the propyne vibrations for hydrogens bound to sp hybridized carbon atoms. Calculations were carried out at four quantum levels, MP2/6-311++G(3d,3p), MP2/cc-pVTZ, QCISD/6-311++G(3d,3p) and QCISD/cc-pVTZ. The results calculated at the QCISD level are the most accurate among the four with root mean square errors of 4.7 and 5.0 km mol(-1) for the 6-311++G(3d,3p) and cc-pVTZ basis sets. These values are close to the estimated aggregate experimental error of the hydrocarbon intensities, 4.0 km mol(-1). The atomic charge transfer-counter polarization effect is much larger than the charge effect for the results of all four quantum levels. Charge transfer-counter polarization effects are expected to also be important in vibrations of more polar molecules for which equilibrium charge contributions can be large.

  20. Tunable self-assembled spin chains of strongly interacting cold atoms for demonstration of reliable quantum state transfer

    DEFF Research Database (Denmark)

    Loft, N. J. S.; Marchukov, O. V.; Petrosyan, D.

    2016-01-01

    We have developed an efficient computational method to treat long, one-dimensional systems of strongly-interacting atoms forming self-assembled spin chains. Such systems can be used to realize many spin chain model Hamiltonians tunable by the external confining potential. As a concrete demonstrat...... demonstration, we consider quantum state transfer in a Heisenberg spin chain and we show how to determine the confining potential in order to obtain nearly-perfect state transfer....

  1. Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: an ab initio study of He + CH2(X) collisions.

    Science.gov (United States)

    Tscherbul, T V; Grinev, T A; Yu, H-G; Dalgarno, A; Kłos, Jacek; Ma, Lifang; Alexander, Millard H

    2012-09-14

    We develop a rigorous quantum mechanical theory for collisions of polyatomic molecular radicals with S-state atoms in the presence of an external magnetic field. The theory is based on a fully uncoupled space-fixed basis set representation of the multichannel scattering wave function. Explicit expressions are presented for the matrix elements of the scattering Hamiltonian for spin-1/2 and spin-1 polyatomic molecular radicals interacting with structureless targets. The theory is applied to calculate the cross sections and thermal rate constants for spin relaxation in low-temperature collisions of the prototypical organic molecule methylene [CH(2)(X(3)B(1))] with He atoms. To this end, two accurate three-dimensional potential energy surfaces (PESs) of the He-CH(2)(X(3)B(1)) complex are developed using the state-of-the-art coupled-cluster method including single and double excitations along with a perturbative correction for triple excitations and large basis sets. Both PESs exhibit shallow minima and are weakly anisotropic. Our calculations show that spin relaxation in collisions of CH(2), CHD, and CD(2) molecules with He atoms occurs at a much slower rate than elastic scattering over a large range of temperatures (1 μK-1 K) and magnetic fields (0.01-1 T), suggesting excellent prospects for cryogenic helium buffer-gas cooling of ground-state ortho-CH(2)(X(3)B(1)) molecules in a magnetic trap. Furthermore, we find that ortho-CH(2) undergoes collision-induced spin relaxation much more slowly than para-CH(2), which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.

  2. Mechanism of Action of Sulforaphane as a Superoxide Radical Anion and Hydrogen Peroxide Scavenger by Double Hydrogen Transfer: A Model for Iron Superoxide Dismutase.

    Science.gov (United States)

    Prasad, Ajit Kumar; Mishra, P C

    2015-06-25

    The mechanism of action of sulforaphane as a scavenger of superoxide radical anion (O2(•-)) and hydrogen peroxide (H2O2) was investigated using density functional theory (DFT) in both gas phase and aqueous media. Iron superoxide dismutase (Fe-SOD) involved in scavenging superoxide radical anion from biological media was modeled by a complex consisting of the ferric ion (Fe(3+)) attached to three histidine rings. Reactions related to scavenging of superoxide radical anion by sulforaphane were studied using DFT in the presence and absence of Fe-SOD represented by this model in both gas phase and aqueous media. The scavenging action of sulforaphane toward both superoxide radical anion and hydrogen peroxide was found to involve the unusual mechanism of double hydrogen transfer. It was found that sulforaphane alone, without Fe-SOD, cannot scavenge superoxide radical anion in gas phase or aqueous media efficiently as the corresponding reaction barriers are very high. However, in the presence of Fe-SOD represented by the above-mentioned model, the scavenging reactions become barrierless, and so sulforaphane scavenges superoxide radical anion by converting it to hydrogen peroxide efficiently. Further, sulforaphane was found to scavenge hydrogen peroxide also very efficiently by converting it into water. Thus, the mechanism of action of sulforaphane as an excellent antioxidant has been unravelled.

  3. Hydride, hydrogen atom, proton, and electron transfer driving forces of various five-membered heterocyclic organic hydrides and their reaction intermediates in acetonitrile.

    Science.gov (United States)

    Zhu, Xiao-Qing; Zhang, Ming-Tian; Yu, Ao; Wang, Chun-Hua; Cheng, Jin-Pei

    2008-02-27

    weak one-electron oxidation agents. The energies of the intramolecular hydrogen bond in 3H, 3H+*, and 3* with a hydroxyl group at ortho-position on the 2-phenyl ring were estimated by using experimental method, the results disclose that the hydrogen bond energy is 3.2, 2.8-3.0, and 3.9-4.0 kcal/mol for 3H, 3H+*, and 3* in acetonitrile, respectively, which is favorable for hydrogen atom transfer but unfavorable for hydride transfer from 3H. The relative effective charges on the active center in ZH, ZH+*, Z*, and Z+, which is an efficient measurement of electrophilicity or nucleophilicity as well as dimerizing ability of a chemical species, were estimated by using experimental method; the results indicate that 1*-5* belong to electron-sufficient carbon-radicals, 6*-7* belong to electron-deficient carbon radicals, they are all difficult to dimerize, and that 1+-5+ belong to weak electrophilic agents, 6+-7+ belong to strong electrophilic agents. All these information disclosed in this work could not only supply a gap of the chemical thermodynamics of the five-membered heterocyclic compounds as organic hydride donors, but also strongly promote the fast development of the chemistry and applications of the five-membered heterocyclic organic hydrides.

  4. Origins and Development of Initiation of Free Radical Polymerization Processes

    Directory of Open Access Journals (Sweden)

    Dietrich Braun

    2009-01-01

    Full Text Available At present worldwide about 45% of the manufactured plastic materials and 40% of synthetic rubber are obtained by free radical polymerization processes. The first free radically synthesized polymers were produced between 1910 and 1930 by initiation with peroxy compounds. In the 1940s the polymerization by redox processes was found independently and simultaneously at IG Farben in Germany and ICI in Great Britain. In the 1950s the systematic investigation of azo compounds as free radical initiators followed. Compounds with labile C–C-bonds were investigated as initiators only in the period from the end of the 1960s until the early 1980s. At about the same time, iniferters with cleavable S–S-bonds were studied in detail. Both these initiator classes can be designated as predecessors for “living” or controlled free radical polymerizations with nitroxyl-mediated polymerizations, reversible addition fragmentation chain transfer processes (RAFT, and atom transfer radical polymerizations (ATRP.

  5. ANISOTROPY EFFECTS IN SINGLE-ELECTRON TRANSFER BETWEEN LASER-EXCITED ATOMS AND HIGHLY-CHARGED IONS

    NARCIS (Netherlands)

    Recent collision experiments are reviewed in which one-electron transfer between laser excited target atoms and (highly charged) keV-ions has been studied. Especially results showing a dependence of the charge exchange on the initial target orbital alignment are discussed. The question to what

  6. Single crystal to single crystal transformation and hydrogen-atom transfer upon oxidation of a cerium coordination compound.

    Science.gov (United States)

    Williams, Ursula J; Mahoney, Brian D; Lewis, Andrew J; DeGregorio, Patrick T; Carroll, Patrick J; Schelter, Eric J

    2013-04-15

    Trivalent and tetravalent cerium compounds of the octamethyltetraazaannulene (H2omtaa) ligand have been synthesized. Electrochemical analysis shows a strong thermodynamic preference for the formal cerium(IV) oxidation state. Oxidation of the cerium(III) congener Ce(Homtaa)(omtaa) occurs by hydrogen-atom transfer that includes a single crystal to single crystal transformation upon exposure to an ambient atmosphere.

  7. Toward deformation densities for intramolecular interactions without radical reference states using the fragment, atom, localized, delocalized, and interatomic (FALDI) charge density decomposition scheme.

    Science.gov (United States)

    de Lange, Jurgens Hendrik; Cukrowski, Ignacy

    2017-05-15

    A novel approach for calculating deformation densities is presented, which enables to calculate the deformation density resulting from a change between two chemical states, typically conformers, without the need for radical fragments. The Fragment, Atom, Localized, Delocalized, and Interatomic (FALDI) charge density decomposition scheme is introduced, which is applicable to static electron densities (FALDI-ED), conformational deformation densities (FALDI-DD) as well as orthodox fragment-based deformation densities. The formation of an intramolecular NH⋅⋅⋅N interaction in protonated ethylene diamine is used as a case study where the FALDI-based conformational deformation densities (with atomic or fragment resolution) are compared with an orthodox EDA-based approach. Atomic and fragment deformation densities revealed in real-space details that (i) pointed at the origin of density changes associated with the intramolecular H-bond formation and (ii) fully support the IUPAC H-bond representation. The FALDI scheme is equally applicable to intra- and intermolecular interactions. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  8. Transferable aspherical atom model refinement of protein and DNA structures against ultrahigh-resolution X-ray data.

    Science.gov (United States)

    Malinska, Maura; Dauter, Zbigniew

    2016-06-01

    In contrast to the independent-atom model (IAM), in which all atoms are assumed to be spherical and neutral, the transferable aspherical atom model (TAAM) takes into account the deformed valence charge density resulting from chemical bond formation and the presence of lone electron pairs. Both models can be used to refine small and large molecules, e.g. proteins and nucleic acids, against ultrahigh-resolution X-ray diffraction data. The University at Buffalo theoretical databank of aspherical pseudo-atoms has been used in the refinement of an oligopeptide, of Z-DNA hexamer and dodecamer duplexes, and of bovine trypsin. The application of the TAAM to these data improves the quality of the electron-density maps and the visibility of H atoms. It also lowers the conventional R factors and improves the atomic displacement parameters and the results of the Hirshfeld rigid-bond test. An additional advantage is that the transferred charge density allows the estimation of Coulombic interaction energy and electrostatic potential.

  9. Relative roles of H-atom transfer and electron transfer in the debromination of polybrominated diphenyl ethers by palladized nanoscale zerovalent iron.

    Science.gov (United States)

    Wang, Rui; Lu, Guining; Lin, Haozhong; Huang, Kaibo; Tang, Ting; Xue, Xiuling; Yang, Xingjian; Yin, Hua; Dang, Zhi

    2017-03-01

    The relative significance of H-atom transfer versus electron transfer in the dehalogenation of halogenated organic compounds (HOCs) in bimetallic systems has long been debated. In this study, we have investigated this question through the case study of the debromination of 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47). The debromination rates of isomer products of BDE-47 by palladized nano zero-valent iron (n-ZVI/Pd) in the same reactor were compared. The results confirmed a shift in the debromination pathway of BDE-47 when treated with unpalladized nano zero-valent iron (n-ZVI) vs. treatment with n-ZVI/Pd. Study showed that BDEs could be rapidly debrominated in a palladium-H2 system, and the debromination pathway in this system is the same as that in the n-ZVI/Pd system. These results suggest that the H-atom species adsorbed on the surface of palladium are responsible for the enhanced reaction rates and the shift of the debromination pathway in the n-ZVI/Pd system. The Mulliken charges, calculated with density functional theory, on bromine atoms of PBDEs were directly correlated with the susceptibility to the e-transfer pathway in the n-ZVI system and inversely correlated with the susceptibility to the H-transfer pathway in n-ZVI/Pd system. These experimentally verified correlations in BDE-47 permit the prediction of the dominant debromination pathway in other BDEs. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. Effect of metal ions on the reactions of the cumyloxyl radical with hydrogen atom donors. Fine control on hydrogen abstraction reactivity determined by Lewis acid-base interactions.

    Science.gov (United States)

    Salamone, Michela; Mangiacapra, Livia; DiLabio, Gino A; Bietti, Massimo

    2013-01-09

    A time-resolved kinetic study on the effect of metal ions (M(n+)) on hydrogen abstraction reactions from C-H donor substrates by the cumyloxyl radical (CumO(•)) was carried out in acetonitrile. Metal salt addition was observed to increase the CumO(•) β-scission rate constant in the order Li(+) > Mg(2+) > Na(+). These effects were explained in terms of the stabilization of the β-scission transition state determined by Lewis acid-base interactions between M(n+) and the radical. When hydrogen abstraction from 1,4-cyclohexadiene was studied in the presence of LiClO(4) and Mg(ClO(4))(2), a slight increase in rate constant (k(H)) was observed indicating that interaction between M(n+) and CumO(•) can also influence, although to a limited extent, the hydrogen abstraction reactivity of alkoxyl radicals. With Lewis basic C-H donors such as THF and tertiary amines, a decrease in k(H) with increasing Lewis acidity of M(n+) was observed (k(H)(MeCN) > k(H)(Li(+)) > k(H)(Mg(2+))). This behavior was explained in terms of the stronger Lewis acid-base interaction of M(n+) with the substrate as compared to the radical. This interaction reduces the degree of overlap between the α-C-H σ* orbital and a heteroatom lone-pair, increasing the C-H BDE and destabilizing the carbon centered radical formed after abstraction. With tertiary amines, a >2-order of magnitude decrease in k(H) was measured after Mg(ClO(4))(2) addition up to a 1.5:1 amine/Mg(ClO(4))(2) ratio. At higher amine concentrations, very similar k(H) values were measured with and without Mg(ClO(4))(2). These results clearly show that with strong Lewis basic substrates variations in the nature and concentration of M(n+) can dramatically influence k(H), allowing for a fine control of the substrate hydrogen atom donor ability, thus providing a convenient method for C-H deactivation. The implications and generality of these findings are discussed.

  11. Intramolecular Halogen Atom Coordinated H Transfer via Ion-Neutral Complex in the Gas Phase Dissociation of Protonated Dichlorvos Derivatives

    Science.gov (United States)

    Zhang, Xiaoping; Cheng, Shuai

    2017-10-01

    Intramolecular halogen atom coordinated H transfer reaction in the gas phase dissociation of protonated dichlorvos derivatives has been explored by electrospray ionization tandem mass spectrometry. Upon collisional activation, protonated dichlorvos underwent dissociation reaction via cleavage of the P-O bond to give reactive ion-neutral complex (INC) intermediate, [dimethoxylphosphinoylium + dichloroacetaldehyde]. Besides direct dissociation of the complex, intramolecular chlorine atom coordinated H transfer reaction within the complex takes place, leading to the formation of protonated dimethyl chlorophosphate. To investigate the fragmentation mechanism, deuterium-labeled experiments and several other halogen-substituted (Br and F) analogs of dichlorvos were prepared and evaluated, which display a similar intramolecular halogen transfer. Density functional theory (DFT)-based calculations were performed and the computational results also support the mechanism. [Figure not available: see fulltext.

  12. Reactions of carbon radicals generated by 1,5-transposition of reactive centers

    Directory of Open Access Journals (Sweden)

    ZIVORAD CEKOVIC

    2005-03-01

    Full Text Available Radical intermediates can undergo specific reactions, such as intramolecular rearrangements, i.e., the transpositions of radical centers, which are not known in classical ionic organic reactions. 1,5-Transposition of a radical center to a non-activated carbon atom are of great synthetic importance. It can be successfully applied for the introduction of different functional groups (oxygen, nitrogen, sulfur, halogens onto a carbon atom remote from the present functional group. In addition to functionalization of a remote non-activated carbon atom, the formation of new C-C bonds on the d-carbon atom have also been achieved. 1,5-Transposition of the radical centers takes place from alkoxyl, aminyl and carbon radicals to a remote carbon atom. Relocation of the radical centers preferentially involves 1,5-transfer of a hydrogen atom, although migrations of some other groups are known. The reactions of the carbon radical generated by 1,5-relocation of the radical center are presented and their synthetic applications are reviewed.

  13. Customized atomic force microscopy probe by focused-ion-beam-assisted tip transfer

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Andrew; Butte, Manish J., E-mail: manish.butte@stanford.edu [Department of Pediatrics, Division of Immunology, Allergy and Rheumatology, Stanford University, Stanford, California 94305 (United States)

    2014-08-04

    We present a technique for transferring separately fabricated tips onto tipless atomic force microscopy (AFM) cantilevers, performed using focused ion beam-assisted nanomanipulation. This method addresses the need in scanning probe microscopy for certain tip geometries that cannot be achieved by conventional lithography. For example, in probing complex layered materials or tall biological cells using AFM, a tall tip with a high-aspect-ratio is required to avoid artifacts caused by collisions of the tip's sides with the material being probed. We show experimentally that tall (18 μm) cantilever tips fabricated by this approach reduce squeeze-film damping, which fits predictions from hydrodynamic theory, and results in an increased quality factor (Q) of the fundamental flexural mode. We demonstrate that a customized tip's well-defined geometry, tall tip height, and aspect ratio enable improved measurement of elastic moduli by allowing access to low-laying portions of tall cells (T lymphocytes). This technique can be generally used to attach tips to any micromechanical device when conventional lithography of tips cannot be accomplished.

  14. Free radical hydrogen atom abstraction from saturated hydrocarbons: A crossed-molecular-beams study of the reaction Cl + C{sub 3}H{sub 8} {yields} HCl + C{sub 3}H{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Blank, D.A.; Hemmi, N.; Suits, A.G.; Lee, Y.T. [Lawrence Berkeley National Lab., CA (United States)

    1997-04-01

    The abstraction of hydrogen atoms from saturated hydrocarbons are reactions of fundamental importance in combustion as well as often being the rate limiting step in free radical substitution reactions. The authors have begun studying these reactions under single collision conditions using the crossed molecular beam technique on beamline 9.0.2.1, utilizing VUV undulator radiation to selectively ionize the scattered hydrocarbon free radical products (C{sub x}H{sub 2x+1}). The crossed molecular beam technique involves two reactant molecular beams fixed at 90{degrees}. The molecular beam sources are rotatable in the plane defined by the two beams. The scattered neutral products travel 12.0 cm where they are photoionized using the VUV undulator radiation, mass selected, and counted as a function of time. In the authors initial investigations they are using halogen atoms as protypical free radicals to abstract hydrogen atoms from small alkanes. Their first study has been looking at the reaction of Cl + propane {r_arrow} HCl + propyl radical. In their preliminary efforts the authors have measured the laboratory scattering angular distribution and time of flight spectra for the propyl radical products at collision energies of 9.6 kcal/mol and 14.9 kcal/mol.

  15. Mechanisms of electron transfer from structrual Fe(II) in reduced nontronite to oxygen for production of hydroxyl radicals

    Science.gov (United States)

    Yuan, Songhu; Liu, Xixiang; Liao, Wenjuan; Zhang, Peng; Wang, Xiaoming; Tong, Man

    2018-02-01

    Production of hydroxyl radicals (radOH) has been recently revealed upon oxygenation of sediments in redox-dynamic subsurface environments. In particular, Fe(II)-bearing clay minerals are the major sediment components contributing to radOH production upon oxygenation, and the produced radOH can oxidize contaminants and inactivate bacteria. Whereas, the mechanisms of radOH production from oxygenation of Fe(II)-bearing clay minerals remain elusive. The objectives of this study were to identify the structural variation of Fe(II) entities during the oxidation of Fe(II)-bearing clay minerals by O2, and to unravel the mechanisms of electron transfer within the mineral structure and from mineral to O2 for radOH production. Nontronite (NAu-2, 23% Fe) which was chemically reduced to 54.5% Fe(II) in total Fe was used as a model Fe(II)-bearing clay mineral. Production of radOH and oxidation of Fe(II) were measured during the oxidation of reduced NAu-2 by O2. A wide spectrum of spectroscopic techniques, including Fourier transform infrared spectroscopy (FTIR), Fe K-edge X-ray absorption spectroscopy (XAS), Mössbauer spectra, and X-ray photoelectron spectroscopy (XPS), were employed to explore the structural variation of Fe(II) entities in NAu-2 and the electron transfer within NAu-2 and from NAu-2 to O2. For 180 min oxidation of 1 g/L reduced NAu-2, a biphasic radOH production was observed, being quick within the initial 15 min and slow afterwards. Production of radOH correlates well with oxidation of Fe(II) in the reduced NAu-2. Within the initial 15 min, trioctahedral Fe(II)-Fe(II)-Fe(II) entities and edge Fe(II) in the reduced NAu-2 were preferentially and quickly oxidized, and electrons from the interior Fe(II)-Fe(II)-Fe(II) entities were most likely ejected from the basal siloxane plane to O2. Meanwhile, trioctahedral Fe(II)-Fe(II)-Fe(II) entities were mainly transformed to dioctahedral Fe(II)-Fe(II) entities. When the time of oxygenation was longer than 15 min

  16. Control of the transfer of oxidizing equivalents between heme iron and free radical site in yeast cytochrome c peroxidase.

    Science.gov (United States)

    Ho, P S; Hoffman, B M; Kang, C H; Margoliash, E

    1983-04-10

    A procedure has been developed for obtaining yeast cytochrome c peroxidase with the heme iron in the Fe(IV) state, without the concomitant formation of the protein free radical that occurs in the ES compound resulting from the oxidation of ferric peroxidase with hydrogen peroxide. In this procedure, ferrous peroxidase, prepared either by photochemical reduction or by trapping the dithionite-reduced enzyme with carbon monoxide, is oxidized with a stoichiometric amount of hydrogen peroxide. The resulting Fe(IV) enzyme oxidizes ferrocyanide monophasically, with a rate constant of 4 x 10(3) M-1 S-1. The optical spectrum of the free radical was obtained as the difference between the spectra of the ES and Fe(IV) compounds. EPR spectra of ES compound prepared with [16O]-and [17O]hydrogen peroxide are identical, demonstrating that no fragment of the oxidant is associated with the free radical. The heme in the Fe(IV) enzyme is stable and does not oxidize the free radical site either intra- or intermolecularly. On the other hand, previous results from the presteady state kinetics of reduction and reductive titrations of the ES compound with ferrocyanide imply that the heme and free radical sites exchange oxidizing equivalents, in particular that the radical site once reduced can be reoxidized, either intra- or intermolecularly, by the ferryl heme. To resolve these contradictions, we propose a catalytic mechanism for cytochrome c peroxidase in which the radical site can exist in two conformations having very different reduction potentials and in which a significant flow of oxidizing equivalents between heme and free radical sites occurs only (i) during the hydrogen peroxide oxidation of the resting Fe(III) enzyme to form compound ES and (ii) within the initial transient intermediate formed upon the one-electron reduction of this oxidized product.

  17. A charge transfer ionic-embedded atom method potential for the O-Al-Ni-Co-Fe system

    Energy Technology Data Exchange (ETDEWEB)

    Zhou Xiaowang; Wadley, Haydn N G [Department of Materials Science and Engineering, 116 Engineer' s Way, University of Virginia, Charlottesville, VA 22904-4745 (United States)

    2005-06-15

    Magnetic tunnel junctions (MTJs) require the growth of a thin ({approx}20 A) dielectric metal oxide layer, such as Al{sub 2}O{sub 3}, on a ferromagnetic metal layer, such as Co, CoFe, or CoNiFe. The atomic assembly mechanisms that combine to form a uniformly thin metal oxide layer on these metal surfaces are not well understood. The application of molecular dynamics simulations to the growth of metal and metal oxide multilayers that involve more than one metal element has not been possible using the conventional interatomic potentials. A recently proposed modified charge transfer ionic-embedded atom method potential appears to correctly enable the charge transfer between oxygen and numerous metal elements to be modelled in a format amenable for molecular dynamics studies. Here we parametrize this charge transfer ionic-embedded atom method potential for the quinternary O-Al-Ni-Co-Fe system so that a direct molecular dynamics simulation of the growth of the tunnelling magnetoresistive multilayers can be realized.

  18. Theoretical investigation of the coupling between hydrogen-atom transfer and stacking interaction in adenine-thymine dimers.

    Science.gov (United States)

    Villani, Giovanni

    2013-04-15

    Three different dimers of the adenine-thymine (A-T) base pair are studied to point out the changes of important properties (structure, atomic charge, energy and so on) induced by coupling between the movement of the atoms in the hydrogen bonds and the stacking interaction. The comparison of these results with those for the A-T monomer system explains the role of the stacking interaction in the hydrogen-atom transfer in this biologically important base pair. The results support the idea that this coupling depends on the exact dimer considered and is different for the N-N and N-O hydrogen bonds. In particular, the correlation between the hydrogen transfer and the stacking interaction is more relevant for the N-N bridge than for the N-O one. Also, the two different mechanisms of two-hydrogen transfer (step by step and concerted) can be modified by the stacking interaction between the base pairs. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Punicalagin and catechins contain polyphenolic substructures that influence cell viability and can be monitored by radical chemosensors sensitive to electron transfer.

    Science.gov (United States)

    Carreras, Anna; Mateos-Martín, María Luisa; Velázquez-Palenzuela, Amado; Brillas, Enric; Sánchez-Tena, Susana; Cascante, Marta; Juliá, Luis; Torres, Josep Lluís

    2012-02-22

    Plant polyphenols may be free radical scavengers or generators, depending on their nature and concentration. This dual effect, mediated by electron transfer reactions, may contribute to their influence on cell viability. This study used two stable radicals (tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl (TNPTM) and tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl (HNTTM)) sensitive only to electron transfer reduction reactions to monitor the redox properties of polyphenols (punicalagin and catechins) that contain phenolic hydroxyls with different reducing capacities. The use of the two radicals reveals that punicalagin's substructures consisting of gallate esters linked together by carbon-carbon (C-C) bonds are more reactive than simple gallates and less reactive than the pyrogallol moiety of green tea catechins. The most reactive hydroxyls, detected by TNPTM, are present in the compounds that affect HT-29 cell viability the most. TNPTM reacts with C-C-linked gallates and pyrogallol and provides a convenient way to detect potentially beneficial polyphenols from natural sources.

  20. Room temperature deintercalation of alkali metal atoms from epitaxial graphene by formation of charge-transfer complexes

    Energy Technology Data Exchange (ETDEWEB)

    Shin, H.-C.; Ahn, S. J.; Kim, H. W.; Moon, Y.; Rai, K. B. [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Woo, S. H. [College of Pharmacy, Chungnam National University, Daejeon 305–764 (Korea, Republic of); Ahn, J. R., E-mail: jrahn@skku.edu [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); SAINT, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2016-08-22

    Atom (or molecule) intercalations and deintercalations have been used to control the electronic properties of graphene. In general, finite energies above room temperature (RT) thermal energy are required for the intercalations and deintercalations. Here, we demonstrate that alkali metal atoms can be deintercalated from epitaxial graphene on a SiC substrate at RT, resulting in the reduction in density of states at the Fermi level. The change in density of states at the Fermi level at RT can be applied to a highly sensitive graphene sensor operating at RT. Na atoms, which were intercalated at a temperature of 80 °C, were deintercalated at a high temperature above 1000 °C when only a thermal treatment was used. In contrast to the thermal treatment, the intercalated Na atoms were deintercalated at RT when tetrafluorotetracyanoquinodimethane (F4-TCNQ) molecules were adsorbed on the surface. The RT deintercalation occurred via the formation of charge-transfer complexes between Na atoms and F4-TCNQ molecules.

  1. Radical-mediated 5-exo-trig cyclizations of 3-silylhepta-1,6-dienes.

    Science.gov (United States)

    James, Philippe; Schenk, Kurt; Landais, Yannick

    2006-04-28

    Regioselectivity of the sulfonyl radical mediated 5-exo-trig cyclization of 3-silylheptadienyl systems 3a-d has been studied. At low temperature, the reaction of the sulfonyl radical occurs regioselectively at the allylsilane terminus, while a reversal of regioselectivity is observed at 80 degrees C. This general trend has been rationalized on the basis of polar effects and radical stabilization. Thiyl-mediated radical cyclization of dienes 3a, 3c-d, 7 with subsequent sulfur atom transfer was also studied, providing thiabicyclo[3.3.0] skeleton in one step with excellent stereocontrol.

  2. Theory of laser-induced ultrafast magneto-optic spin flip and transfer in charged two-magnetic-center molecular ions: Role of bridging atoms

    Science.gov (United States)

    Li, Chun; Jin, Wei; Xiang, Hongping; Lefkidis, Georgios; Hübner, Wolfgang

    2011-08-01

    Laser-induced ultrafast spin manipulations in positively charged two-magnetic-center molecular ions with a small number of bridging atoms are investigated to explore the role of bridging atoms in the spin switching process and spin transferability between the magnetic centers via the Λ process. Taking O and Mg as examples for bridging atoms, fully ab initio calculations demonstrate that spin flip can be readily achieved on subpicosecond time scales at both magnetic centers of the linear structures composed of two nonidentical magnetic atoms with a single bridging atom in between. Although these two nonmagnetic elements possess completely different chemical and electronic natures, both types of bridging atoms contribute to spin density redistribution at the magnetic atoms, especially for the low-lying triplet states that are suitable to act as initial and final states in the Λ-type process of spin flip or transfer. This also provides a rule of thumb that spins in the linear structures can be flipped more easily since symmetric structures exhibit weaker magnetocrystalline anisotropy. The spin transfer process achieved in the structure [Fe-O(Mg)-Co]+ demonstrates that if both bridging atoms are involved to further lower the symmetry of the linear structures, spin transferability between the Fe and Co atoms can be improved.

  3. Visible-Light Organic Photocatalysis for Latent Radical-Initiated Polymerization via 2e–/1H+ Transfers: Initiation with Parallels to Photosynthesis

    Science.gov (United States)

    2015-01-01

    We report the latent production of free radicals from energy stored in a redox potential through a 2e–/1H+ transfer process, analogous to energy harvesting in photosynthesis, using visible-light organic photoredox catalysis (photocatalysis) of methylene blue chromophore with a sacrificial sterically hindered amine reductant and an onium salt oxidant. This enables light-initiated free-radical polymerization to continue over extended time intervals (hours) in the dark after brief (seconds) low-intensity illumination and beyond the spatial reach of light by diffusion of the metastable leuco-methylene blue photoproduct. The present organic photoredox catalysis system functions via a 2e–/1H+ shuttle mechanism, as opposed to the 1e– transfer process typical of organometallic-based and conventional organic multicomponent photoinitiator formulations. This prevents immediate formation of open-shell (radical) intermediates from the amine upon light absorption and enables the “storage” of light-energy without spontaneous initiation of the polymerization. Latent energy release and radical production are then controlled by the subsequent light-independent reaction (analogous to the Calvin cycle) between leuco-methylene blue and the onium salt oxidant that is responsible for regeneration of the organic methylene blue photocatalyst. This robust approach for photocatalysis-based energy harvesting and extended release in the dark enables temporally controlled redox initiation of polymer syntheses under low-intensity short exposure conditions and permits visible-light-mediated synthesis of polymers at least 1 order of magnitude thicker than achievable with conventional photoinitiated formulations and irradiation regimes. PMID:24786755

  4. Ion conducting solid polymer electrolytes based on polypentafluorostyrene-b-polyether-b-polypentafluorostyrene prepared by atom transfer radical polymerization

    DEFF Research Database (Denmark)

    Jankova, Katja; Jannasch, P.; Hvilsted, Søren

    2004-01-01

    blocks (T-g -65 degreesC) were immiscible and resulted in phase separation providing an elastomeric material in form of a physically cross-linked polyether network, even when the PFS block consisted of only about four monomer units. The salted triblock copolymers of PEGPG demonstrated conductivities...... lithium bis( trifluoromethylsulfonyl) imide salt with the block copolymers and the liquid PEGPG precursor. The crystallinity and the melting points of the salted MPEG-b-PFS and triblock copolymers were found by DSC to be substantially suppressed. Short PFS blocks (T-g 33 degreesC) and the salted PEGPG...... of 10(-5.1) to 10(-4.9) S cm(-1) at 20 degreesC....

  5. SYNTHESIS OF HYDROXY-TELECHELIC POLY(METHYL ACRYLATE) AND POLYSTYRENE BY ATOM TRANSFER RADICAL COUPLING. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  6. REMOVAL OF COPPER-BASED CATALYST IN ATOM TRANSFER RADICAL POLYMERIZATION USING ION EXCHANGE RESINS. (R826735)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  7. Surface-Initiated Atom Transfer Radical Polymerization and Electrografting Technique as a Means For Attaining Tailor-Made Polymer Coatings

    DEFF Research Database (Denmark)

    Chernyy, Sergey

    2012-01-01

    of the solution ATRP conditions and extending those conditions to the SI-ATRP. As a result, the new acetone/methyl methacrylate medium was found to be optimal for MMA polymerization both in the solution and on the surface. The reaction mixture was studied thoroughly; in addition to ex-situ techniques...

  8. Experimental verification of orbital engineering at the atomic scale: Charge transfer and symmetry breaking in nickelate heterostructures

    Science.gov (United States)

    Phillips, Patrick J.; Rui, Xue; Georgescu, Alexandru B.; Disa, Ankit S.; Longo, Paolo; Okunishi, Eiji; Walker, Fred; Ahn, Charles H.; Ismail-Beigi, Sohrab; Klie, Robert F.

    2017-05-01

    Epitaxial strain, layer confinement, and inversion symmetry breaking have emerged as powerful new approaches to control the electronic and atomic-scale structural properties of complex metal oxides. Trivalent rare-earth (RE) nickelate R E NiO3 heterostructures have been shown to be exemplars since the orbital occupancy, degeneracy, and, consequently, electronic/magnetic properties can be altered as a function of epitaxial strain, layer thickness, and superlattice structure. One recent example is the tricomponent LaTiO3-LaNiO3-LaAlO3 superlattice which exhibits charge transfer and orbital polarization as the result of its interfacial dipole electric field. A crucial step towards control of these parameters for future electronic and magnetic device applications is to develop an understanding of both the magnitude and range of the octahedral network's response towards interfacial strain and electric fields. An approach that provides atomic-scale resolution and sensitivity towards the local octahedral distortions and orbital occupancy is therefore required. Here, we employ atomic-resolution imaging coupled with electron spectroscopies and first-principles theory to examine the role of interfacial charge transfer and symmetry breaking in a tricomponent nickelate superlattice system. We find that nearly complete charge transfer occurs between the LaTiO3 and LaNiO3 layers, resulting in a mixed Ni2 +/Ni3 + valence state. We further demonstrate that this charge transfer is highly localized with a range of about 1 unit cell within the LaNiO3 layers. We also show how Wannier-function-based electron counting provides a simple physical picture of the electron distribution that connects directly with formal valence charges. The results presented here provide important feedback to synthesis efforts aimed at stabilizing new electronic phases that are not accessible by conventional bulk or epitaxial film approaches.

  9. Matter, energy, and heat transfer in a classical ballistic atom pump.

    Science.gov (United States)

    Byrd, Tommy A; Das, Kunal K; Mitchell, Kevin A; Aubin, Seth; Delos, John B

    2014-11-01

    A ballistic atom pump is a system containing two reservoirs of neutral atoms or molecules and a junction connecting them containing a localized time-varying potential. Atoms move through the pump as independent particles. Under certain conditions, these pumps can create net transport of atoms from one reservoir to the other. While such systems are sometimes called "quantum pumps," they are also models of classical chaotic transport, and their quantum behavior cannot be understood without study of the corresponding classical behavior. Here we examine classically such a pump's effect on energy and temperature in the reservoirs, in addition to net particle transport. We show that the changes in particle number, of energy in each reservoir, and of temperature in each reservoir vary in unexpected ways as the incident particle energy is varied.

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

    Science.gov (United States)

    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.

  11. Transferable Potentials for Phase Equilibria. 4. United-Atom Description of Linear and Branched Alkenes and Alkylbenzenes

    Energy Technology Data Exchange (ETDEWEB)

    WICK,COLLIN D.; MARTIN,MARCUS G.; SIEPMANN,J. ILJA

    2000-07-12

    The Transferable Potentials for Phase Equilibria-United Atom (TraPPE-UA) force field for hydrocarbons is extended to alkenes and alkylbenzenes by introducing the following pseudo-atoms: CH{sub 2}(sp{sup 2}), CH(sp{sup 2}), CH(aro), R-C(aro) for the link to aliphatic side chains, and C(aro) for the link of two benzene rings. In this united-atom force field, the nonbonded interactions of the hydrocarbon pseudo-atoms are solely governed by Lennard-Jones 12-6 potentials, and the Lennard-Jones well depth and size parameters for the new pseudo-atoms were determined by fitting to the single-component vapor-liquid phase equilibria of a few selected model compounds. Configurational-bias Monte Carlo simulations in the NVT version of the Gibbs ensemble were carried out to calculate the single-component vapor-liquid coexistence curves for ethene, propene, 1-butene, trans- and cis-2-butene. 2-methylpropene, 1,5-hexadiene, 1-octene, benzene, toluene, ethylbenzene, propylbenzene, isopropylbenzene, o-, m-, and p-xylene, and naphthalene. The phase diagrams for the binary mixtures of (supercritical) ethene/n-heptane and benzene/n-pentane were determined from simulations in the NpT Gibbs ensemble. Although the TraPPE-UA force field is rather simple and makes use of relatively few different pseudo-atoms, its performance, as judged by comparisons to other popular force fields and available experimental data, is very satisfactory.

  12. Enhancing the quantum state transfer between two atoms in separate cavities via weak measurement and its reversal

    Science.gov (United States)

    Li, Yan-Ling; Huang, Jinsong; Xu, Zhonghui; Xiao, Xing

    2017-10-01

    Taking the advantage of weak measurement and quantum measurement reversal, we propose a scheme to enhance the fidelity of transferring quantum state from one atom trapped in cavity to another distant one trapped in another cavity which is coupled by an optical fiber. It is turned out that the fidelity can be greatly improved even when the system is under serious dissipation. Moreover, the scheme works in both the strong-coupling and weak-coupling regimes. It is also robust to the ratio of the coupling constant between the atoms and the cavity modes to the coupling constant between the fiber and cavity modes. The underlying mechanism can be attributed to the probabilistic nature of weak measurements.

  13. Fluorinated Dodecaphenylporphyrins: Synthetic and Electrochemical Studies Including the First Evidence of Intramolecular Electron Transfer Between an Fe(II) Porphyrin -Anion Radical and an Fe(I) Porphyrin

    Energy Technology Data Exchange (ETDEWEB)

    D' Souza, F.; Forsyth, T.P.; Fukuzumi, S.; Kadish, K.M.; Krattinger, B.; Lin, M.; Medforth, C.J.; Nakanishi, I.; Nurco, D.J.; Shelnutt, J.A.; Smith, K.M.; Van Caemelbecke, E.

    1998-10-19

    Dodecaphenylporphyrins with varying degrees of fluorination of the peripheral phenyl rings (FXDPPS) were synthesized as model compounds for studying electronic effects in nonplan~ porphyrins, and detailed electrochemical studies of the chloroiron(HI) complexes of these compounds were undertaken. The series of porphyrins, represented as FeDPPCl and as FeFXDPPCl where x = 4, 8 (two isomers), 12, 20,28 or 36, could be reversibly oxidized by two electrons in dichloromethane to give n-cation radicals and n-dications. All of the compounds investigated could also be reduced by three electrons in benzonitrile or pyridine. In benzonitrile, three reversible reductions were observed for the unfluorinated compound FeDPPC1, whereas the FeFXDPPCl complexes generally exhibited irreversible first and second reductions which were coupled to chemical reactions. The chemical reaction associated with the first reduction involved a loss of the chloride ion after generation of Fe FXDPPC1. The second chemical reaction involved a novel intramolecular electron transfer between the initially generated Fe(H) porphyrin n-anion radical and the final Fe(I) porphyrin reduction product. In pyridine, three reversible one electron reductions were observed with the second reduction affording stable Fe(II) porphyrin o - anion radicals for ail of the complexes investigated.

  14. Comparative study of the molecularly imprinted polymers prepared by reversible addition-fragmentation chain transfer "bulk" polymerization and traditional radical "bulk" polymerization.

    Science.gov (United States)

    Ma, Yue; Pan, Guoqing; Zhang, Ying; Guo, Xianzhi; Zhang, Huiqi

    2013-05-01

    Bisphenol A (BPA) and propranolol-imprinted polymers have been prepared via both reversible addition-fragmentation chain transfer "bulk" polymerization (RAFTBP) and traditional radical "bulk" polymerization (TRBP) under similar reaction conditions, and their equilibrium binding properties were compared in detail for the first time. The chemical compositions, specific surface areas, equilibrium bindings, and selectivity of the obtained molecularly imprinted polymers (MIPs) were systematically characterized. The experimental results showed that the MIPs with molecular imprinting effects and quite fast binding kinetics could be readily prepared via RAFTBP, but they did not show improved template binding properties in comparison with those prepared via TRBP, which is in sharp contrast to many previous reports. This could be attributed to the heavily interrupted equilibrium between the dormant species and active radicals in the RAFT mechanism because of the occurrence of fast gelation during RAFTBP. The findings presented here strongly demonstrates that the application of controlled radical polymerizations (CRPs) in molecular imprinting does not always benefit the binding properties of the resultant MIPs, which is of significant importance for the rational use of CRPs in generating MIPs with improved properties. Copyright © 2013 John Wiley & Sons, Ltd.

  15. Hydrogen atom vs electron transfer in catecholase-mimetic oxidations by superoxometal complexes. Deuterium kinetic isotope effects.

    Science.gov (United States)

    Simándi, Tatiana M; May, Zoltán; Szigyártó, Imola Cs; Simándi, László I

    2005-01-21

    Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases.

  16. Localization and Targeted Transfer of Atomic-Scale Nonlinear Excitations: Perspectives for Applications

    Science.gov (United States)

    Kopidakis, G.; Aubry, S.

    We review nonlinearity-induced localization in discrete systems with emphasis on theory and numerical calculations on models used in materials physics to describe interatomic interactions. We discuss how the concept of discrete breather or intrinsic localized mode could become an important tool for understanding nanoscale phenomena in molecules and solids. A particularly attractive field of application for nonlinear localized excitations is the controlled and directed transport of energy. We discuss the recently proposed targeted transfer of localized excitations based on the concept of nonlinear resonance and its potential applications. As an area for such applications, we present directional ultrafast electron transfer at low temperatures using this selective transfer mechanism and we give examples from biological electron transfer. We finally discuss possible applications in nanotechnology and biomolecules.

  17. Intensification of volatile organic compounds mass transfer in a compact scrubber using the O3/H2O2 advanced oxidation process: kinetic study and hydroxyl radical tracking.

    Science.gov (United States)

    Biard, Pierre-François; Couvert, Annabelle; Renner, Christophe; Levasseur, Jean-Pierre

    2011-11-01

    This study assesses the potential of ozonation and advanced oxidation process O(3)/H(2)O(2) to enhance the dimethyldisulfide (DMDS) mass transfer in a compact chemical scrubber developed for air treatment applications. Theoretical calculations, through Hatta number and enhancement factor evaluations for two parallel irreversible reactions, were compared to experimental data and enabled the description of the mass transfer mechanisms. These calculations required the determination of the kinetic constant of the DMDS oxidation by molecular ozone ( [Formula: see text] ) and the measurement of the hydroxyl radical concentration within the scrubber. The competitive kinetic method using the 1,2-dihydroxybenzene (resorcinol) enabled to determine a value of the kinetic constant [Formula: see text] of 1.1×10(6)M(-1)s(-1) at 293K. Then, experiments using para-chlorobenzoic acid in solution allowed measuring the average hydroxyl concentration in the scrubber between the inlet and the outlet depending on the chemical conditions (pH and inlet O(3) and H(2)O(2) concentrations). High hydroxyl radical concentrations (10(-8)M) and ratio of the HO°-to-O(3) exposure (R(ct)≈10(-4)) were put in evidence. Copyright © 2011 Elsevier Ltd. All rights reserved.

  18. Nitrene Radical Intermediates in Catalytic Synthesis.

    Science.gov (United States)

    Kuijpers, Petrus F; van der Vlugt, Jarl Ivar; Schneider, Sven; de Bruin, Bas

    2017-10-09

    Nitrene radical complexes are reactive intermediates with discrete spin density at the nitrogen-atom of the nitrene moiety. These species have become important intermediates for organic synthesis, being invoked in a broad range of C-H functionalization and aziridination reactions. Nitrene radical complexes have intriguing electronic structures, and are best described as one-electron reduced Fischer type nitrenes. They can be generated by intramolecular single electron transfer to the "redox non-innocent" nitrene moiety at the metal. Nitrene radicals generated at open-shell cobalt(II) have thus far received most attention in terms of spectroscopic characterization, reactivity screening, catalytic nitrene-transfer reactions and (computational and experimental) mechanistic studies, but some interesting iron and precious metal catalysts have also been employed in related reactions involving nitrene radicals. In some cases, redox-active ligands are used to facilitate intramolecular single electron transfer from the complex to the nitrene moiety. Organic azides are among the most attractive nitrene precursors in this field, typically requiring pre-activated organic azides (e.g. RSO2 N3 , (RO)2 P(=O)N3 , ROC(=O)N3 and alike) to achieve efficient and selective catalysis. Challenging, non-activated aliphatic organic azides were recently added to the palette of reagents useful in synthetically relevant reactions proceeding via nitrene radical intermediates. This concept article describes the electronic structure of nitrene radical complexes, emphasizes on their usefulness in the catalytic synthesis of various organic products, and highlights the important developments in the field. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  19. PhnJ – A novel radical SAM enzyme from the C–P lyase complex

    Directory of Open Access Journals (Sweden)

    Siddhesh S. Kamat

    2015-03-01

    Full Text Available PhnJ from the C–P lyase complex catalyzes the cleavage of the carbon–phosphorus bond in ribose-1-phosphonate-5-phosphate (PRPn to produce methane and ribose-1,2-cyclic-phosphate-5-phosphate (PRcP. This protein is a novel radical SAM enzyme that uses glycyl and thiyl radicals as reactive intermediates in the proposed reaction mechanism. The overall reaction is initiated with the reductive cleavage of S-adenosylmethionine (SAM by a reduced [4Fe–4S]1+-cluster to form an Ado-CH2∙ radical intermediate. This intermediate abstracts the proR hydrogen from Gly-32 of PhnJ to form Ado-CH3 and a glycyl radical. In the next step, there is hydrogen atom transfer from Cys-272 to the Gly-32 radical to generate a thiyl radical. The thiyl radical attacks the phosphorus center of the substrate, PRPn, to form a transient thiophosphonate radical intermediate. This intermediate collapses via homolytic C–P bond cleavage and hydrogen atom transfer from the proS hydrogen of Gly-32 to produce a thiophosphate intermediate, methane, and a radical intermediate at Gly-32. The final product, PRcP, is formed by nucleophilic attack of the C2-hydroxyl on the transient thiophosphate intermediate. This reaction regenerates the free thiol group of Cys-272. After hydrogen atom transfer from Cys-272 to the Gly-32 radical, the entire process is repeated with another substrate molecule without the use of another molecule of SAM or involvement from the [4Fe–4S]-cluster again.

  20. effect of some free radicals on superoxide dismutase and ...

    African Journals Online (AJOL)

    dambayero

    ABSTRACT. Free radicals are species with unpaired electron in their outermost shell. Most free radicals come from oxygen or nitrogen atoms. Radical species such as superoxide radical, hydroxyl radicals and hydrated electron are called the primary radicals of water radiolysis and can be produced by irradiating water.

  1. Effect of some free radicals on superoxide dismutase and ...

    African Journals Online (AJOL)

    Free radicals are species with unpaired electron in their outermost shell. Most free radicals come from oxygen or nitrogen atoms. Radical species such as superoxide radical, hydroxyl radicals and hydrated electron are called the primary radicals of water radiolysis and can be produced by irradiating water molecule.

  2. Physiology of free radicals

    Directory of Open Access Journals (Sweden)

    Stevanović Jelka

    2011-01-01

    Full Text Available Free radicals imply that every atom, molecule, ion, group of atoms, or molecules with one or several non-paired electrons in outer orbital. Among these are: nitrogenoxide (NO•, superoxide-anion-radical (O2•-, hydroxyl radical (OH•, peroxyl radical (ROO•, alcoxyl radical (RO• and hydroperoxyl radical (HO2•. However, reactive oxygen species also include components without non-paired electrons in outer orbital (so-called reactive non-radical agents, such as: singlet oxygen (1O2, peroxynitrite (ONOO-, hydrogen-peroxide (H2O2, hypochloric acid (eg. HOCl and ozone (O3. High concentrations of free radicals lead to the development of oxidative stress which is a precondition for numerous pathological effects. However, low and moderate concentrations of these matter, which occur quite normally during cell metabolic activity, play multiple significant roles in many reactions. Some of these are: regulation of signal pathways within the cell and between cells, the role of chemoattractors and leukocyte activators, the role in phagocytosis, participation in maintaining, changes in the position and shape of the cell, assisting the cell during adaption and recovery from damage (e.g.caused by physical effort, the role in normal cell growth, programmed cell death (apoptosis and cell ageing, in the synthesis of essential biological compounds and energy production, as well as the contribution to the regulation of the vascular tone, actually, tissue vascularization.

  3. Oxygen-atom transfer chemistry and thermolytic properties of a di-tert-butylphosphate-ligated Mn4O4 cubane.

    Science.gov (United States)

    Van Allsburg, Kurt M; Anzenberg, Eitan; Drisdell, Walter S; Yano, Junko; Tilley, T Don

    2015-03-16

    [Mn4O4{O2P(OtBu)2}6] (1), an Mn4O4 cubane complex combining the structural inspiration of the photosystem II oxygen-evolving complex with thermolytic precursor ligands, was synthesized and fully characterized. Core oxygen atoms within complex 1 are transferred upon reaction with an oxygen-atom acceptor (PEt3), to give the butterfly complex [Mn4O2{O2P(OtBu)2}6(OPEt3)2]. The cubane structure is restored by reaction of the latter complex with the O-atom donor PhIO. Complex 1 was investigated as a precursor to inorganic Mn metaphosphate/pyrophosphate materials, which were studied by X-ray absorption spectroscopy to determine the fate of the Mn4O4 unit. Under the conditions employed, thermolyses of 1 result in reduction of the manganese to Mn(II) species. Finally, the related butterfly complex [Mn4O2{O2P(pin)}6(bpy)2] (pin = pinacolate) is described. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Threshold Particle Diameters in Miniemulsion Reversible-Deactivation Radical Polymerization

    Directory of Open Access Journals (Sweden)

    Hidetaka Tobita

    2011-11-01

    Full Text Available Various types of controlled/living radical polymerizations, or using the IUPAC recommended term, reversible-deactivation radical polymerization (RDRP, conducted inside nano-sized reaction loci are considered in a unified manner, based on the polymerization rate expression, Rp = kp[M]K[Interm]/[Trap]. Unique miniemulsion polymerization kinetics of RDRP are elucidated on the basis of the following two factors: (1 A high single molecule concentration in a nano-sized particle; and (2 a significant statistical concentration variation among particles. The characteristic particle diameters below which the polymerization rate start to deviate significantly (1 from the corresponding bulk polymerization, and (2 from the estimate using the average concentrations, can be estimated by using simple equations. For stable-radical-mediated polymerization (SRMP and atom-transfer radical polymerization (ATRP, an acceleration window is predicted for the particle diameter range, . For reversible-addition-fragmentation chain-transfer polymerization (RAFT, degenerative-transfer radical polymerization (DTRP and also for the conventional nonliving radical polymerization, a significant rate increase occurs for . On the other hand, for  the polymerization rate is suppressed because of a large statistical variation of monomer concentration among particles.

  5. Modelling of the heat transfer during oxygen atoms recombination on metallic surfaces in a plasma reactor

    NARCIS (Netherlands)

    Cavadias, S; Cauquot, P; Amouroux, J

    1997-01-01

    Space shuttle overheating during the re-entry phase, due to catalytic oxygen recombination on the thermal protection system, is a problem of practical and theoretical interest. The energy transfer is characterised by the product of the accommodation and the recombination coefficients. Previous

  6. Back-Influence of Molecular Motion on Energy Transfer in the Landau-Teller Model of Atom Molecule Scattering.

    Science.gov (United States)

    Pollak, Eli

    2016-07-21

    This year we celebrate the 80th anniversary of the Landau-Teller model for energy exchange in a collinear collision of an atom with a harmonic diatomic molecule. Even after 80 years though, the analytic theory to date has not included in it the back-influence of the oscillator's motion on the energy transfer between the approaching particle and the molecule. This is the topic of the present paper. The back-influence can be obtained by employing classical second-order perturbation theory. The second-order theory is used in both a classical and semiclassical context. Classically, analytic expressions are derived for the final phase and action of the diatom, after the collision. The energy loss of the atom is shown to decrease linearly with the increasing energy of the oscillator. The magnitude of this decrease is a direct consequence of the back-reaction of the oscillator on the translational motion. The qualitative result is universal, in the sense that it is not dependent on the details of the interaction of the atom with the oscillator. A numerical application to a model collision of an Ar atom with a Br2 diatom demonstrates the importance and accuracy of the second-order perturbation theory. The same results are then used to derive a second-order perturbation theory semiclassical expression for the quantum transition probability from initial vibrational state ni to final vibrational state nf of the oscillator. A comparison of the theory with exact quantum data is presented for a model collision of Br2 with a hydrogen molecule, where the hydrogen molecule is considered as a single approaching particle.

  7. All-Atom Multiscale Molecular Dynamics Theory and Simulation of Self-Assembly, Energy Transfer and Structural Transition in Nanosystems

    Science.gov (United States)

    Espinosa Duran, John Michael

    The study of nanosystems and their emergent properties requires the development of multiscale computational models, theories and methods that preserve atomic and femtosecond resolution, to reveal details that cannot be resolved experimentally today. Considering this, three long time scale phenomena were studied using molecular dynamics and multiscale methods: self-assembly of organic molecules on graphite, energy transfer in nanosystems, and structural transition in vault nanoparticles. Molecular dynamics simulations of the self-assembly of alkoxybenzonitriles with different tail lengths on graphite were performed to learn about intermolecular interactions and phases exhibited by self-organized materials. This is important for the design of ordered self-assembled organic photovoltaic materials with greater efficiency than the disordered blends. Simulations revealed surface dynamical behaviors that cannot be resolved experimentally today due to the lack of spatiotemporal resolution. Atom-resolved structures predicted by simulations agreed with scanning tunneling microscopy images and unit cell measurements. Then, a multiscale theory based on the energy density as a field variable is developed to study energy transfer in nanoscale systems. For applications like photothermal microscopy or cancer phototherapy is required to understand how the energy is transferred to/from nanosystems. This multiscale theory could be applied in this context and here is tested for cubic nanoparticles immersed in water for energy being transferred to/from the nanoparticle. The theory predicts the energy transfer dynamics and reveals phenomena that cannot be described by current phenomenological theories. Finally, temperature-triggered structural transitions were revealed for vault nanoparticles using molecular dynamics and multiscale simulations. Vault is a football-shaped supramolecular assembly very distinct from the commonly observed icosahedral viruses. It has very promising

  8. Atomic force microscopy study of the adsorption of protein molecules on transferred Langmuir monolayer

    Energy Technology Data Exchange (ETDEWEB)

    Gainutdinov, R. V., E-mail: radmir@ns.crys.ras.ru; Tolstikhina, A. L.; Stepina, N. D. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Novikova, N. N. [Russian Research Center Kurchatov Institute (Russian Federation); Yur' eva, E. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Khripunov, A. K. [Russian Academy of Sciences, Institute of Macromolecular Compounds (Russian Federation)

    2010-09-15

    Ordered protein films have been obtained by the adsorption of protein molecules on a Langmuir monolayer, which had previously formed on a silicon substrate, using the Langmuir-Blodgett and molecular self-organization methods. A mixture of cholesterol with dipalmitoylphosphatidylcholine (DPPC) and a polymer-cellulose acetopivalinate-were used as immobilization materials. Protein molecules (catalase and alkaline phosphatase) immobilized on solid substrates have been investigated by atomic force micros-copy. It was shown that the developed combined technique provides a deposition of homogeneous ultrathin protein films with a high degree of filling.

  9. The Unimolecular Reactions of CF3CHF2Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules.

    Science.gov (United States)

    Smith, Caleb A; Gillespie, Blanton R; Heard, George L; Setser, D W; Holmes, Bert E

    2017-11-22

    The recombination of CF 3 and CHF 2 radicals in a room-temperature bath gas was used to prepare vibrationally excited CF 3 CHF 2 * molecules with 101 kcal mol -1 of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF 3 , CF 3 (F)C: and C 2 F 4 product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF 3 (F)C: concentration was measured by trapping the carbene with trans-2-butene. The experimental rate constants are 3.6 × 10 4 , 4.7 × 10 4 , and 1.1 × 10 4 s -1 for the 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions, respectively. These experimental rate constants were matched to statistical RRKM calculated rate constants to assign threshold energies (E 0 ) of 88 ± 2, 88 ± 2, and 87 ± 2 kcal mol -1 to the three reactions. Pentafluoroethane is the only fluoroethane that has a competitive H atom transfer decomposition reaction, and it is the only example with 1,1-HF elimination being more important than 1,2-HF elimination. The trend of increasing threshold energies for both 1,1-HF and 1,2-HF processes with the number of F atoms in the fluoroethane molecule is summarized and investigated with electronic-structure calculations. Examination of the intrinsic reaction coordinate associated with the 1,1-HF elimination reaction found an adduct between CF 3 (F)C: and HF in the exit channel with a dissociation energy of ∼5 kcal mol -1 . Hydrogen-bonded complexes between HF and the H atom migration transition state of CH 3 (F)C: and the F atom migration transition state of CF 3 (F)C: also were found by the calculations. The role that these carbene-HF complexes could play in 1,1-HF elimination reactions is discussed.

  10. Dual electron transfer pathways from 4,4'-dimethoxybenzophenone ketyl radical in the excited state to parent molecule in the ground state.

    Science.gov (United States)

    Sakamoto, Masanori; Cai, Xichen; Fujitsuka, Mamoru; Majima, Tetsuro

    2005-08-11

    Dual intermolecular electron transfer (ELT) pathways from 4,4'-dimethoxybenzophenone (1) ketyl radical (1H*) in the excited state [1H*(D1)] to the ground-state 4,4'-dimethoxybenzophenone [1(S0)] were found in 2-methyltetrahydrofuran (MTHF) by observing bis(4-methoxyphenyl)methanol cation (1H+) and 4,4'-dimethoxybenzophenone radical anion (1*-) during nanosecond-picosecond two-color two-laser flash photolysis. ELT pathway I involved the two-photon ionization of 1H* following the injection of electron to the solvent. The solvated electron was quickly trapped by 1(S0) to produce 1*-. ELT pathway II was a self-quenching-like ELT from 1H*(D1) to 1(S0) to give 1H+ and 1*-. From the fluorescence quenching of 1H*(D1), the ELT rate constant was determined to be 1.0 x 10(10) M(-1) s(-1), which is close to the diffusion-controlled rate constant of MTHF. The self-quenching-like ELT mechanism was discussed on the basis of Marcus' ELT theory.

  11. A kinetic and mechanistic study of the reactions of OH radicals and Cl atoms with 3,3,3-trifluoropropanol under atmospheric conditions.

    Science.gov (United States)

    Kelly, Tanya; Bossoutrot, Valérie; Magneron, Isabelle; Wirtz, Klaus; Treacy, Jack; Mellouki, Abdelwahid; Sidebottom, Howard; Le Bras, Georges

    2005-01-20

    Product distribution studies of the OH radical and Cl atom initiated oxidation of CF3CH2CH2OH in air at 1 atm and 298 +/- 5 K have been carried out in laboratory and outdoor atmospheric simulation chambers in the presence and absence of NOx. The results show that CF3CH2CHO is the only primary product and that the aldehyde is fairly rapidly removed from the system. In the absence of NOx the major degradation product of CF3CH2CHO is CF3CHO, and the combined yields of the two aldehydes formed from CF3CH2CH2OH are close to unity (0.95 +/- 0.05). In the presence of NOx small amounts of CF3CH2C(O)O2NO2 were also observed (<15%). At longer reaction times CF3CHO is removed from the system to give mainly CF2O. The laser photolysis-laser induced fluorescence technique was used to determine values of k(OH + CF3CH2CH2OH) = (0.89 +/- 0.03) x 10(-12) and k(OH + CF3CH2CHO) = (2.96 +/- 0.04) x 10(-12) cm3 molecule(-1) s(-1). A relative rate method has been employed to measure the rate coefficients k(OH + CF3CH2CH2OH) = (1.08 +/- 0.05) x 10(-12), k(OH + C6F13CH2CH2OH) = (0.79 +/- 0.08) x 10(-12), k(Cl + CF3CH2CH2OH) = (22.4 +/- 0.4) x 10(-12), and k(Cl + CF3CH2CHO) = (25.7 +/- 0.4) x 10(-12) cm3 molecule(-1) s(-1). The results from this investigation are discussed in terms of the possible importance of emissions of fluorinated alcohols as a source of fluorinated carboxylic acids in the environment.

  12. Atmospheric chemistry of (CF3)2C=CH2: OH radicals, Cl atoms and O3 rate coefficients, oxidation end-products and IR spectra.

    Science.gov (United States)

    Papadimitriou, Vassileios C; Spitieri, Christina S; Papagiannakopoulos, Panos; Cazaunau, Mathieu; Lendar, Maria; Daële, Véronique; Mellouki, Abdelwahid

    2015-10-14

    The rate coefficients for the gas phase reactions of OH radicals, k1, Cl atoms, k2, and O3, k3, with 3,3,3-trifluoro-2(trifluoromethyl)-1-propene ((CF3)2C=CH2, hexafluoroisobutylene, HFIB) were determined at room temperature and atmospheric pressure employing the relative rate method and using two atmospheric simulation chambers and a static photochemical reactor. OH and Cl rate coefficients obtained by both techniques were indistinguishable, within experimental precision, and the average values were k1 = (7.82 ± 0.55) × 10(-13) cm(3) molecule(-1) s(-1) and k2 = (3.45 ± 0.24) × 10(-11) cm(3) molecule(-1) s(-1), respectively. The quoted uncertainties are at 95% level of confidence and include the estimated systematic uncertainties. An upper limit for the O3 rate coefficient was determined to be k3 < 9.0 × 10(-22) cm(3) molecule(-1) s(-1). In global warming potential (GWP) calculations, radiative efficiency (RE) was determined from the measured IR absorption cross-sections and treating HFIB both as long (LLC) and short (SLC) lived compounds, including estimated lifetime dependent factors in the SLC case. The HFIB lifetime was estimated from kinetic measurements considering merely the OH reaction, τOH = 14.8 days and including both OH and Cl chemistry, τeff = 10.3 days. Therefore, GWP(HFIB,OH) and GWP(HFIB,eff) were estimated to be 4.1 (LLC) and 0.6 (SLC), as well as 2.8 (LLC) and 0.3 (SLC) for a hundred year time horizon. Moreover, the estimated photochemical ozone creation potential (ε(POCP)) of HFIB was calculated to be 4.60. Finally, HCHO and (CF3)2C(O) were identified as final oxidation products in both OH- and Cl-initiated oxidation, while HC(O)Cl was additionally observed in the Cl-initiated oxidation.

  13. Improving the drug delivery characteristics of graphene oxide based polymer nanocomposites through the “one-pot” synthetic approach of single-electron-transfer living radical polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Peng; Liu, Meiying; Tian, Jianwen; Deng, Fengjie [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wang, Ke [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing 100084 (China); Xu, Dazhuang [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Liu, Liangji [Affiliated Hospital of Jiangxi University of Traditional Chinese Medicine, Nanchang 330006 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing 100084 (China)

    2016-08-15

    Graphical abstract: The PEGylated graphene oxides with high water dispersibility, good biocompatibility as well as high drug loading capability were fabricated via “one-pot” SET-LRP. - Highlights: • Surface modification of graphene oxide with polymers. • One-pot single-electron-transfer living radical polymerization. • Improving drug delivery characteristics. • The synthetic approach is rather simple, universal and effective. - Abstract: Graphene oxide (GO) based polymer nanocomposites have attracted extensive research interest recently for their outstanding physicochemical properties and potential applications. However, surface modification of GO with synthetic polymers has demonstrated to be trouble for most polymerization procedures are occurred under non-aqueous solution, which will in turn lead to the restacking of GO. In this work, a facile and efficient “one-pot” strategy has been developed for surface modification of GO with synthetic polymers through single-electron-transfer living radical polymerization (SET-LRP). The GO based polymer nanocomposites were obtained via SET-LRP in aqueous solution using poly(ethylene glycol) methyl ether methacrylate (PEGMA) as the monomer and 11-bromoundecanoic acid as the initiator, which could be effectively adsorbed on GO through hydrophobic interaction. The successful preparation of GO based polymer nanocomposites was confirmed by a series of characterization techniques such as {sup 1}H nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The resultant products exhibit high water disperisibility, excellent biocompatibility and high efficient drug loading capability, making these PEGylated GO nanocomposites promising candidates for biomedical applications.

  14. Accelerated Oxygen Atom Transfer and C-H Bond Oxygenation by Remote Redox Changes in Fe3Mn-Iodosobenzene Adducts.

    Science.gov (United States)

    de Ruiter, Graham; Carsch, Kurtis M; Gul, Sheraz; Chatterjee, Ruchira; Thompson, Niklas B; Takase, Michael K; Yano, Junko; Agapie, Theodor

    2017-04-18

    We report the synthesis, characterization, and reactivity of [LFe 3 (PhPz) 3 OMn( s PhIO)][OTf] x (3: x=2; 4: x=3), where 4 is one of very few examples of iodosobenzene-metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57 Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (Fe III 2 Fe II Mn II vs. Fe III 3 Mn II ) influence oxygen atom transfer in tetranuclear Fe 3 Mn clusters. In particular, a one-electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Atomic scattering in the diffraction limit: electron transfer in keV Li+-Na(3s, 3p) collisions

    DEFF Research Database (Denmark)

    Poel, Mike van der; Nielsen, C.V.; Rybaltover, M.

    2002-01-01

    We measure angle differential cross sections (DCS) in Li+ + Na --> Li + Na+ electron transfer collisions in the 2.7-24 keV energy range. We do this with a newly constructed apparatus which combines the experimental technique of cold target recoil ion momentum spectroscopy with a laser-cooled target...... of the de Broglie wavelength lambda(dB) = 150 fm at a velocity v = 0.20 au and the effective atomic diameter for electron capture 2R = 20 au. Parallel AO and MO semiclassical coupled-channel calculations of the Na(3s, 3p) --> Li(2s, 2p) state-to-state collision amplitudes have been performed, and quantum...

  16. Toxicity of imine-iminium dyes and pigments: electron transfer, radicals, oxidative stress and other physiological effects.

    Science.gov (United States)

    Kovacic, Peter; Somanathan, Ratnasamy

    2014-08-01

    Although conjugation is well known as an important contributor to color, there is scant recognition concerning involvement of imine and iminium functions in the physiological effects of this class of dyes and pigments. The group includes the dyes methylene blue, rhodamine, malachite green, fuchsin, crystal violet, auramine and cyanins, in addition to the pigments consisting of pyocyanine, phthalocyanine and pheophytin. The physiological effects consist of both toxicity and beneficial aspects. The unifying theme of electron transfer-reactive oxygen species-oxidative stress is used as the rationale in both cases. Toxicity is frequently prevented or alleviated by antioxidants. The apparent dichotomy of methylene blue action as both oxidant and antioxidant is rationalized based on similar previous cases. This mechanistic approach may have practical benefit. This review is important in conveying, for the first time, a unifying mechanism for toxicity based on electron transfer-reactive oxygen species-oxidative stress arising from imine-iminium. Copyright © 2014 John Wiley & Sons, Ltd.

  17. Three-dimensional effects in resonant charge transfer between atomic particles and nanosystems

    Science.gov (United States)

    Gainullin, I. K.; Sonkin, M. A.

    2015-08-01

    Resonant charge transfer (RCT) between negative ions and a metallic nanosystem was investigated by means of a high-performance ab initio three-dimensional (3D) numerical solver. During RCT, an electron was shown to occupy succesively nanosystem eigenstates along the z , ρ , and φ coordinates. Electron tunneling into a nanosystem is a reversible process, because after some time the electron propagates back to the ion. RCT efficiency in a nanosystem was found to exhibit quantum-size effects as well as lateral ion position dependence. This means that during ion-surface interaction, the nanosystem's size and the ion trajectory strongly influence the final charge state of the ion. In the case of real 3D systems (without cylindrical symmetry), the electron density currents form quantum vortices; this result is rather nontrivial for static systems. In addition, the limits of the adiabatic approximation (rate equation) for the RCT calculation with nanosystems are defined.

  18. Atomic layer deposition to prevent metal transfer from implants: An X-ray fluorescence study

    Energy Technology Data Exchange (ETDEWEB)

    Bilo, Fabjola [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy); Borgese, Laura, E-mail: laura.borgese@unibs.itl [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy); Prost, Josef; Rauwolf, Mirjam; Turyanskaya, Anna; Wobrauschek, Peter; Kregsamer, Peter; Streli, Christina [Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna (Austria); Pazzaglia, Ugo [Dipartimento Specialità Medico Chirurgiche Sc. Radiol. e Sanità Pubblica, University of Brescia, v.le Europa, 11, 25121 Brescia (Italy); Depero, Laura E. [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy)

    2015-12-30

    Highlights: • Co and Cr migrate from bare alloy implant to the surrounding tissue showing a cluster distribution. • Co and Cr migrate from the TiO{sub 2} coated implant to the surrounding tissue showing a decreasing gradient distribution from the alloy surface. • TiO{sub 2} coating layers obtained by ALD on Co–Cr alloy show a barrier effect for the migration of metals. • The thicker the TiO{sub 2} layer deposited by ALD, the lower the metal migration. • The migration of metals from bare alloy toward the surrounding tissue increases with time. This effect is not detected in the coated samples. - Abstract: We show that Atomic Layer Deposition is a suitable coating technique to prevent metal diffusion from medical implants. The metal distribution in animal bone tissue with inserted bare and coated Co–Cr alloys was evaluated by means of micro X-ray fluorescence mapping. In the uncoated implant, the migration of Co and Cr particles from the bare alloy in the biological tissues is observed just after one month and the number of particles significantly increases after two months. In contrast, no metal diffusion was detected in the implant coated with TiO{sub 2}. Instead, a gradient distribution of the metals was found, from the alloy surface going into the tissue. No significant change was detected after two months of aging. As expected, the thicker is the TiO{sub 2} layer, the lower is the metal migration.

  19. Evidences of Electron Transfer of a Fullerene Anion Radical (C60(•-)) Prepared under Visible-Light Illumination at a Nitrobenzene/Water Interface.

    Science.gov (United States)

    Watariguchi, Shigeru; Fujimori, Masaaki; Atsumi, Kosuke; Hinoue, Teruo

    2016-01-01

    Fullerene (C60) changes to its anion radical (C60(•-)) in the presence of tetraphenylborate (TPB(-)) under visible-light illumination. Using voltammetry at a liquid/liquid interface, we investigated the electron transfer (ET) between C60(•-), previously prepared based on this photochemical reaction, in a nitrobenzene (NB) solution and hexacyanoferrate(III) ([Fe(CN)6](3-)) or proton in an aqueous solution. We suggest that positive currents appearing in voltammograms are due to the ion transfer of decomposition products of TPB(-) and ET from C60(•-) in the NB phase to [Fe(CN)6](3-), or proton in the W phase. (11)B NMR revealed that TPB(-) decomposed to some borate anions during the photochemical reaction of fullerene. Furthermore, when the NB solution containing C60(•-) was mixed with an aqueous solution containing [Fe(CN)6](3-) or proton, absorption bands of C60(•-) in a visible/near infrared absorption spectrum disappeared. This disappearance supports the ET across the NB/W interface. This finding is significant as both an example of ET at a liquid/liquid interface including photochemical reactions and the photochemistry of C60.

  20. Dissociative Electron Transfer to Diphenyl-Substituted Bicyclic Endoperoxides: The Effect of Molecular Structure on the Reactivity of Distonic Radical Anions and Determination of Thermochemical Parameters

    Directory of Open Access Journals (Sweden)

    David C. Magri

    2014-08-01

    Full Text Available The heterogeneous electron transfer reduction of the bicyclic endoperoxide 1,4-diphenyl-2,3-dioxabicyclo[2.2.1]hept-5-ene (4 was investigated in N,N-dimethylformamide  at a glassy carbon electrode. The endoperoxide reacts by a concerted dissociative ET mechanism resulting in reduction of the O-O bond with an observed peak potential of −1.4 V at 0.2 V s−1. The major product (90% yield resulting from the heterogeneous bulk electrolysis of 4 at −1.4 V with a rotating disk glassy carbon electrode is 1,4-diphenyl-cyclopent-2-ene-cis-1,3-diol with a consumption of 1.73 electrons per mole. In contrast, 1,4-diphenyl-2,3-dioxabicyclo[2.2.2]oct-5-ene (1, undergoes a two-electron reduction mechanism in quantitative yield. This difference in product yield between 1 and 4 is suggestive of a radical-anion mechanism, as observed with 1,4-diphenyl-2,3-dioxabicyclo-[2.2.2] octane (2 and 1,4-diphenyl-2,3-dioxabicyclo[2.2.1]heptane (3. Convolution potential sweep voltammetry is used to determine unknown thermochemical parameters of 4, including the O-O bond dissociation energy and the standard reduction potential and a comparison is made to the previously studied bicyclic endoperoxides 1–3 with respect to the effect of molecular structure on the reactivity of distonic radical anions.

  1. Atmospheric Chemistry of Six Methyl-perfluoroheptene-ethers Used as Heat Transfer Fluid Replacement Compounds: Measured OH Radical Reaction Rate Coefficients, Atmospheric Lifetimes, and Global Warming Potentials

    Science.gov (United States)

    Jubb, A. M.; Gierczak, T.; Baasandorj, M.; Waterland, R. L.; Burkholder, J. B.

    2013-12-01

    Mixtures of methyl-perfluoroheptene-ethers (C7F13OCH3, MPHEs) are currently in use as a replacement for perfluorinated alkane (PFC) and polyether mixtures (both persistent greenhouse gases with atmospheric lifetimes >1000 years) used as heat transfer fluids. Currently, the atmospheric fate of the MPHE isomers are not well characterized, however, reaction with the OH radical is expected to be a dominant tropospheric loss process for these compounds. In order to assess the atmospheric lifetimes and environmental implications of MPHE use, rate coefficients for MPHE isomers' reaction with OH radicals are desired. In the work presented here, rate coefficients, k, for the gas-phase reaction of the OH radical with six MPHEs commonly used in commercial mixtures (isomers and stereoisomers) and their deuterated analogs (d3-MPHE) were determined at 296 K using a relative rate method with combined gas-chromatography/IR spectroscopy detection. A range of OH rate coefficient values was observed, up to a factor of 20× different, between the MPHE isomers with the (E)-stereoisomers exhibiting the greatest reactivity. The measured OH reaction rate coefficients for the d3-MPHE isomers were lower than the observed MPHE values although a large range of k values between isomers was still observed. The reduction in reactivity with deuteration signifies that the MPHE + OH reaction proceeds via both addition to the olefinic C=C bond and H-abstraction from the methyl ester group. OH addition to the C=C bond was determined to be the primary reaction channel. Atmospheric lifetimes with respect to the OH reaction for the six MPHE isomers were found to be in the range of days to months. The short lifetimes indicate that MPHE use will primarily impact tropospheric local and regional air quality. A MPHE atmospheric degradation mechanism will be presented. As part of this work, radiative efficiencies and global warming potentials (GWPs) for the MPHE isomers were estimated based on measured

  2. Theoretical investigation of hydrogen atom transfer in the cytosine-guanine base pair and its coupling with electronic rearrangement. Concerted vs stepwise mechanism.

    Science.gov (United States)

    Villani, Giovanni

    2010-07-29

    The transformation of the DNA base pairs from the Watson-Crick (WC) structures to its tautomers having imino-enol form can be achieved via two types of hydrogen atom transfer processes: (i) concerted, and/or (ii) stepwise (step by step). Here, we have studied and compared these two mechanisms in the cytosine-guanine (C-G) system. In the first mechanism there is the concerted movement of two hydrogen atoms along two of the three H-bridges that bond the bases, one from the cytosine to guanine and the other in the opposite direction. This movement must be coupled to an electronic reorganization, with some bond orders that pass from single to double and vice versa, in order to preserve the neutrality of these new structures. In the stepwise mechanism the movement of the hydrogen atoms and the electronic reorganization are not concerted, and it implicates the movement of a hydrogen atom at a time with the identification of two or more steps in this reaction. There are two possible neutral imino-enol structures in the C-G system, and both have been considered here. The principal result from this paper is that a different behavior is observed if the hydrogen transfer begins with a H of the guanine or of the cytosine and that a concerted (synchronic in the N-N and asynchronic in the N-O) double-hydrogen transfer can be activated only when the first H atom to move is that of the guanine, in particular. This is different from the A-T system(1) studied previously where the movement in a N-N bridge produces a zwitterionic structure and that in the N-O the concerted double-hydrogen transfer. In both cases a general conclusion can be given: the concerted double-hydrogen process begins with a hydrogen atom of a purinic base.

  3. Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

    Energy Technology Data Exchange (ETDEWEB)

    Chu, P.M.Y.

    1991-10-01

    The vibrational to translational (V{yields}T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V{yields}T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH{sub 3} production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam.

  4. Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

    Energy Technology Data Exchange (ETDEWEB)

    Chu, Pamela Mei-Ying [Univ. of California, Berkeley, CA (United States)

    1991-10-01

    The vibrational to translational (V→T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V→T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH3 production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam.

  5. Regeneration of β-Carotene from Radical Cation by Eugenol, Isoeugenol, and Clove Oil in the Marcus Theory Inverted Region for Electron Transfer.

    Science.gov (United States)

    Chang, Hui-Ting; Cheng, Hong; Han, Rui-Min; Wang, Peng; Zhang, Jian-Ping; Skibsted, Leif H

    2017-02-01

    The rate of regeneration of β-carotene by eugenol from the β-carotene radical cation, an initial bleaching product of β-carotene, was found by laser flash photolysis and transient absorption spectroscopy to be close to the diffusion limit in chloroform/methanol (9:1, v/v), with a second-order rate constant (k2) of 4.3 × 109 L mol-1 s-1 at 23 °C. Isoeugenol, more reducing with a standard reduction potential of 100 mV lower than eugenol, was slower, with k2 = 7.2 × 108 L mol-1 s-1. Regeneration of β-carotene following photobleaching was found 50% more efficient by eugenol, indicating that, for the more reducing isoeugenol, the driving force exceeds the reorganization energy for electron transfer significantly in the Marcus theory inverted region. For eugenol/isoeugenol mixtures and clove oil, kinetic control by the faster eugenol determines the regeneration, with a thermodynamic backup of reduction equivalent through eugenol regeneration by the more reducing isoeugenol for the mixture. Clove oil, accordingly, is a potential protector of provitamin A for use in red palm oils.

  6. Photolysis of CH{sub 3}CHO at 248 nm: Evidence of triple fragmentation from primary quantum yield of CH{sub 3} and HCO radicals and H atoms

    Energy Technology Data Exchange (ETDEWEB)

    Morajkar, Pranay; Schoemaecker, Coralie; Fittschen, Christa, E-mail: christa.fittschen@univ-lille1.fr [Université Lille Nord de France, PhysicoChimie des Processus de Combustion et de l’Atmosphère – PC2A, UMR 8522, F-59650 Villeneuve d’Ascq (France); Bossolasco, Adriana [Université Lille Nord de France, PhysicoChimie des Processus de Combustion et de l’Atmosphère – PC2A, UMR 8522, F-59650 Villeneuve d’Ascq (France); INFIQC (CONICET), Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba (Argentina)

    2014-06-07

    Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH{sub 3}CHO. HCO radical and H atom yields have been quantified by time resolved continuous wave Cavity Ring Down Spectroscopy in the near infrared following their conversion to HO{sub 2} radicals by reaction with O{sub 2}. The CH{sub 3} radical yield has been determined using the same technique following their conversion into CH{sub 3}O{sub 2}. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO{sub 2} profiles, obtained under various O{sub 2} concentrations, to a complex model, while the CH{sub 3} yield has been determined relative to the CH{sub 3} yield from 248 nm photolysis of CH{sub 3}I. Time resolved HO{sub 2} profiles under very low O{sub 2} concentrations suggest that another unknown HO{sub 2} forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O{sub 2}. HO{sub 2} profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH{sub 3}CHO + hν{sub 248nm} → CH{sub 3}CHO{sup *}, CH{sub 3}CHO{sup *} → CH{sub 3} + HCO ϕ{sub 1a} = 0.125 ± 0.03, CH{sub 3}CHO{sup *} → CH{sub 3} + H + CO ϕ{sub 1e} = 0.205 ± 0.04, CH{sub 3}CHO{sup *}→{sup o{sub 2}}CH{sub 3}CO + HO{sub 2} ϕ{sub 1f} = 0.07 ± 0.01. The CH{sub 3}O{sub 2} quantum yield has been determined in separate experiments as ϕ{sub CH{sub 3}} = 0.33 ± 0.03 and is in excellent agreement with the CH{sub 3} yields derived from the HO{sub 2} measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH{sub 3}CHO. From arithmetic considerations taking into account the HO{sub 2} and CH{sub 3} measurements we deduce a remaining quantum yield for the molecular pathway: CH{sub 3}CHO{sup *} → CH{sub 4} + CO ϕ{sub 1b} = 0.6. All experiments can be

  7. Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer.

    Science.gov (United States)

    Choe, Cholho; Yang, Ling; Lv, Zhanao; Mo, Wanling; Chen, Zhuqi; Li, Guangxin; Yin, Guochuan

    2015-05-21

    Redox-inactive metal ions can modulate the reactivity of redox-active metal ions in a variety of biological and chemical oxidations. Many synthetic models have been developed to help address the elusive roles of these redox-inactive metal ions. Using a non-heme manganese(II) complex as the model, the influence of redox-inactive metal ions as a Lewis acid on its catalytic efficiency in oxygen atom transfer was investigated. In the absence of redox-inactive metal ions, the manganese(II) catalyst is very sluggish, for example, in cyclooctene epoxidation, providing only 9.9% conversion with 4.1% yield of epoxide. However, addition of 2 equiv. of Al(3+) to the manganese(II) catalyst sharply improves the epoxidation, providing up to 97.8% conversion with 91.4% yield of epoxide. EPR studies of the manganese(II) catalyst in the presence of an oxidant reveal a 16-line hyperfine structure centered at g = 2.0, clearly indicating the formation of a mixed valent di-μ-oxo-bridged diamond core, Mn(III)-(μ-O)2-Mn(IV). The presence of a Lewis acid like Al(3+) causes the dissociation of this diamond Mn(III)-(μ-O)2-Mn(IV) core to form monomeric manganese(iv) species which is responsible for improved epoxidation efficiency. This promotional effect has also been observed in other manganese complexes bearing various non-heme ligands. The findings presented here have provided a promising strategy to explore the catalytic reactivity of some di-μ-oxo-bridged complexes by adding non-redox metal ions to in situ dissociate those dimeric cores and may also provide clues to understand the mechanism of methane monooxygenase which has a similar diiron diamond core as the intermediate.

  8. TRANSFER

    African Journals Online (AJOL)

    Abstract. Quenching of curcumine fluorescence by thionine, both immobilised in cellulose acetate occurs in accordance with the Forster mechanism of energy transfer. The rate constant of energy transfer for this donor - acceptor pair is found to be 9.4 x 109 L ' mol S1 with R0 = 37±1 Б. When this donor - acceptor pair is ...

  9. An unexpected ethyl transfer reaction between Et2Zn anddo(t-butyl)glyoxaldiimine (t-BuDAB).Studies of thepersistent [EtZn(t-BuDAB)] radical which is in equilibrium with its C-C coupled dimer

    NARCIS (Netherlands)

    Koten, G. van; Jastrzebski, J.T.B.H.; Klerks, J.M.; Vrieze, K.

    1981-01-01

    Whereas p-Tol{2}Zn reacts with t-BuN@?CHCH@?N-t-Bu (t-BuDAB) to give a stable 11 complex [p-Tol{2}Zn(t-BuDAB)], Et{2}Zn gives EtZnN(Et)(t-Bu)CH@?CHN-(t-Bu) via intramolecular ethyl transfer in the unstable Et{2}Zn(t-BuDAB) complex. In solution the stable persistent organozinc radical EtZn(t-BuDAB),

  10. Stabilization of sulfide radical cations through complexation with the peptide bond: mechanisms relevant to oxidation of proteins containing multiple methionine residues.

    Science.gov (United States)

    Bobrowski, Krzysztof; Hug, Gordon L; Pogocki, Dariusz; Marciniak, Bronislaw; Schöneich, Christian

    2007-08-16

    The recent study on the *OH-induced oxidation of calmodulin, a regulatory "calcium sensor" protein containing nine methionine (Met) residues, has supported the first experimental evidence in a protein for the formation of S therefore N three-electron bonded radical complexes involving the sulfur atom of a methionine residue and the amide groups in adjacent peptide bonds. To characterize reactions of oxidized methionine residues in proteins containing multiple methionine residues in more detail, in the current study, a small model cyclic dipeptide, c-(L-Met-L-Met), was oxidized by *OH radicals generated via pulse radiolysis and the ensuing reactive intermediates were monitored by time-resolved UV-vis spectroscopic and conductometric techniques. The picture that emerges from this investigation shows there is an efficient formation of the Met (S therefore N) radicals, in spite of the close proximity of two sulfur atoms, located in the side chains of methionine residues, and in spite of the close proximity of sulfur atoms and oxygen atoms, located in the peptide bonds. Moreover, it is shown, for the first time, that the formation of Met(S therefore N) radicals can proceed directly, via H+-transfer, with the involvement of hydrogen from the peptide bond to an intermediary hydroxysulfuranyl radical. Ultimately, the Met(S therefore N) radicals decayed via two different pH-dependent reaction pathways, (i) conversion into sulfur-sulfur, intramolecular, three-electron-bonded radical cations and (ii) a proposed hydrolytic cleavage of the protonated form of the intramolecular, three-electron-bonded radicals [Met(S therefore N)/Met(S therefore NH)+] followed by electron transfer and decarboxylation. Surprisingly, also alpha-(alkylthio)alkyl radicals enter the latter mechanism in a pH-dependent manner. Density functional theory computations were performed on the model c-(L-Met-Gly) and its radicals in order to obtain optimizations and energies to aid in the interpretation of the

  11. The perchlorotriphenylmethyl (PTM) radical.

    Science.gov (United States)

    Guasch, Judith; Fontrodona, Xavier; Ratera, Imma; Rovira, Concepció; Veciana, Jaume

    2013-03-01

    In spite of the considerable understanding and development of perchlorotriphenylmethyl (PTM) radical derivatives, the preparation of crystals of the pure unsubstituted PTM radical, C19Cl15, suitable for single-crystal X-ray diffraction has remained a challenge since its discovery, and only two studies dealing with the crystal structure of the unsubstituted PTM radical have been published. In one study, the radical forms clathrates with aromatic solvents [Veciana, Carilla, Miravitlles & Molins (1987). J. Chem. Soc. Chem. Commun. pp. 812-814], and in the other the structure was determined ab initio from powder X-ray diffraction data [Rius, Miravitlles, Molins, Crespo & Veciana (1990). Mol. Cryst. Liq. Cryst. 187, 155-163]. We report here the preparation of PTM crystals for single-crystal X-ray diffraction and their resolution. The structure, which shows monoclinic symmetry (C2/c), revealed a nonsymmetric molecular propeller conformation (D3 symmetry) caused by the steric strain between the ortho-Cl atoms, which protect the central C atom (sp(2)-hybridization and major spin density) and give high chemical and thermal persistence to the PTM. The supramolecular structure of PTM shows short Cl...Cl intermolecular interactions and can be described in terms of layers formed by rows of molecules positioned in a head-to-tail manner along the c axis.

  12. Atmospheric chemistry of CH3O(CF2CF2O)(n)CH3 (n=1-3): Kinetics and mechanism of oxidation initiated by Cl atoms and OH radicals, IR spectra, and global warmin potentials

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Hurley, MD; Wallington, TJ

    2004-01-01

    Smog chambers equipped with FTIR spectrometers were used to study the Cl atom and OH radical initiated oxidation of CH3O(CF2CF2O)(n)CH3 (n = 1-3) in 720 +/- 20 Torr of air at 296 +/- 3 K. Relative rate techniques were used to measure k(Cl + CH3O(CF2CF2O)(n)CH3) (3.7 +/- 10.7) x 10(-13) and k(OH +...... of 0.051, 0.058, and 0.055 (100 year time horizon, relative to CFC-11) for CH3OCF2CF2OCH3, CH3O(CF2CF2O)(2)CH3, and CH3O(CF2CF2O)(3)CH3, respectively. Results are discussed with respect to the atmospheric chemistry of hydrofluoropolyethers (HFPEs)....

  13. Preparation, structural characterization, and thermochemistry of an isolable 4-arylphenoxyl radical.

    Science.gov (United States)

    Porter, Thomas R; Kaminsky, Werner; Mayer, James M

    2014-10-17

    The preparation and full characterization of the 4-(nitrophenyl)phenoxyl radical, 2,6-di-(t)butyl-4-(4'-nitrophenyl) phenoxyl radical ((t)Bu2NPArO(•)) is described. This is a rare example of an isolable and crystallographically characterized phenoxyl radical and is the only example in which the parent phenol is also crystallographically well-defined. Analysis of EPR spectra indicates some spin delocalization onto the secondary aromatic ring and nitro group. Equilibrium studies show that the corresponding phenol has an O-H bond dissociation free energy (BDFE) of 77.8 ± 0.5 kcal mol(-1) in MeCN (77.5 ± 0.5 kcal mol(-1) in toluene). This value is higher than related isolated phenoxyl radicals, making this a useful reagent for hydrogen atom transfer (HAT) studies. Additional thermochemical and spectroscopic parameters are also discussed.

  14. Addition of e-aq and H atoms to hypoxanthine and inosine and the reactions of alpha-hydroxyalkyl radicals with purines. A pulse radiolysis and product analysis study.

    Science.gov (United States)

    Aravindakumar, C T; Mohan, H; Mudaliar, M; Rao, B S; Mittal, J P; Schuchmann, M N; Von Sonntag, C

    1994-10-01

    The reactions of hydrated electrons e-aq with hypoxanthine and inosine were followed using pulse radiolysis methods. In a neutral solution the electron adduct of inosine is immediately protonated at the heteroatoms of the purine ring by water (k > 2.5 x 10(6)s-1) to give In(N,O-H).. These N,O-protonated intermediates have a single absorption maximum at 300 nm. In basic solution the protonation of the electron adduct of inosine by water leads to other intermediate products with an absorption maximum at 350 nm. These intermediates are believed to be the C-protonated electron adducts of inosine (In(N,O-H).). In (N,O-H). and In(C-H). differ strongly in their ability to reduce p-nitroacetophenone (PNAP). In(N,O-H). are strong reductants and reduce PNAP quantitatively to PNAP.-. Based on the pH dependence of PNAP.- yields, two types of tautomers of In(C-H). could be distinguished. One of the tautomers can reduce PNAP, albeit with slower rate than In(N,O-H)., the other tautomer has no reducing properties. The latter is the one with the higher pKa and therefore thermodynamically more stable. The absorption spectrum of the intermediates produced in the reaction of e-aq with hypoxanthine at neutral pH is very similar to that of In(N,O-H). with a maximum at 300 nm. However, no build-up at 350 nm was observed in basic solution as in the case of the electron adduct of inosine. The reaction of H atoms with inosine produces in basic solution intermediate radicals with the same absorption spectrum as the C-protonated electron adducts of inosine. It is suggested that both the reactions of e-aq and H. with inosine in basic solution produce the same radical, namely the H-adduct of inosine (In(C-H)) with the highest pKa. alpha-Hydroxyalkyl radicals were found to react very slowly with purine bases and nucleosides in neutral to basic solutions. In acidic solution their reactivity increases and a number of rate constants were determined by pulse radiolysis measurements at pH 0.4. The

  15. Concerning 1e- transfer in reduction by dihydronicotinamide: reaction of oxidized flavin and flavin radical with N-benzyl-1,5-dihydronicotinamide.

    OpenAIRE

    Powell, M F; Wong, W. H.; Bruice, T C

    1982-01-01

    The rates of reaction of 5-ethyl-3-methyllumiflavinium perchlorate and 5-ethyl-3-methyllumiflavinyl radical with a NADH analogue, N-benzyl-1,4-dihydronicotinamide, were measured anaerobically in tert-butanol and 5% acetonitrile/95% tert-butanol solutions at 30 degrees C. The biphasic kinetics observed for the reaction of flavin radical with dihydronicotinamide were interpreted in terms of both a 1e- and a 2e- mechanism; the former was found to be inadequate based on experimental requirements ...

  16. Reaction between protein radicals and other biomolecules

    DEFF Research Database (Denmark)

    Østdal, Henrik; Davies, Michael Jonathan; Andersen, Henrik J

    2002-01-01

    The present study investigates the reactivity of bovine serum albumin (BSA) radicals towards different biomolecules (urate, linoleic acid, and a polypeptide, poly(Glu-Ala-Tyr)). The BSA radical was formed at room temperature through a direct protein-to-protein radical transfer from H(2)O(2....... Subsequent analysis showed a decrease in the concentration of urate upon reaction with the BSA radical, while the BSA radical in the presence of poly(Glu-Ala-Tyr) resulted in increased formation of the characteristic protein oxidation product, dityrosine. Reaction between the BSA radical and a linoleic acid...

  17. Radical scavenging activity of lipophilized products from lipase-catalyzed transesterification of triolein with cinnamic and ferulic acids.

    Science.gov (United States)

    Choo, Wee-Sim; Birch, Edward John

    2009-02-01

    Lipase-catalyzed transesterification of triolein with cinnamic and ferulic acids using an immobilized lipase from Candida antarctica (E.C. 3.1.1.3) was conducted to evaluate the antioxidant activity of the lipophilized products as model systems for enhanced protection of unsaturated oil. The lipophilized products were identified using ESI-MS. Free radical scavenging activity was determined using the DPPH radical method. The polarity of the solvents proved important in determining the radical scavenging activity of the substrates. Ferulic acid showed much higher radical scavenging activity than cinnamic acid, which has limited activity. The esterification of cinnamic acid and ferulic acid with triolein resulted in significant increase and decrease in the radical scavenging activity, respectively. These opposite effects were due to the effect of addition of electron-donating alkyl groups on the predominant mechanism of reaction (hydrogen atom transfer or electron transfer) of a species with DPPH. The effect of esterification of cinnamic acid was confirmed using ethyl cinnamate which greatly enhances the radical scavenging activity. Although, compared to the lipophilized cinnamic acid product, the activity was lower. The radical scavenging activity of the main component isolated from lipophilized cinnamic acid product using solid phase extraction, monocinnamoyl dioleoyl glycerol, was as good as the unseparated mixture of lipophilized product. Based on the ratio of a substrate to DPPH concentration, lipophilized ferulic acid was a much more efficient radical scavenger than lipophilized cinnamic acid.

  18. Heterogeneous Single-Atom Catalyst for Visible-Light-Driven High-Turnover CO2Reduction: The Role of Electron Transfer.

    Science.gov (United States)

    Gao, Chao; Chen, Shuangming; Wang, Ying; Wang, Jiawen; Zheng, Xusheng; Zhu, Junfa; Song, Li; Zhang, Wenkai; Xiong, Yujie

    2018-02-14

    Visible-light-driven conversion of CO 2 into chemical fuels is an intriguing approach to address the energy and environmental challenges. In principle, light harvesting and catalytic reactions can be both optimized by combining the merits of homogeneous and heterogeneous photocatalysts; however, the efficiency of charge transfer between light absorbers and catalytic sites is often too low to limit the overall photocatalytic performance. In this communication, it is reported that the single-atom Co sites coordinated on the partially oxidized graphene nanosheets can serve as a highly active and durable heterogeneous catalyst for CO 2 conversion, wherein the graphene bridges homogeneous light absorbers with single-atom catalytic sites for the efficient transfer of photoexcited electrons. As a result, the turnover number for CO production reaches a high value of 678 with an unprecedented turnover frequency of 3.77 min -1 , superior to those obtained with the state-of-the-art heterogeneous photocatalysts. This work provides fresh insights into the design of catalytic sites toward photocatalytic CO 2 conversion from the angle of single-atom catalysis and highlights the role of charge kinetics in bridging the gap between heterogeneous and homogeneous photocatalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems

    Directory of Open Access Journals (Sweden)

    Kirk W. Shimkin

    2015-11-01

    Full Text Available Recently, a number of papers have emerged demonstrating copper-catalyzed alkylation reactions of electron-rich small molecules. The processes are generally thought to be related to long established atom-transfer radical reactions. However, unlike classical reactions, these new transformations lead to simple alkylation products. This short review will highlight recent advances in alkylations of nitronate anions, alkenes and alkynes, as well as discuss current mechanistic understanding of these novel reactions.

  20. Energy-decomposition analysis of ion-neutral complexes along reaction coordinates of unimolecular proton-transfer reaction in gas phase: Comparison between 2-butanol radical ion and protonated 2-ethoxypropane ion

    Science.gov (United States)

    Sugimura, Natsuhiko; Igarashi, Yoko; Aoyama, Reiko; Shibue, Toshimichi

    2017-10-01

    An energy-decomposition analysis clarified the physical origins that change in gas-phase unimolecular proton-transfer reactions via ion-neutral complexes of the 2-butanol radical ion and protonated 2-ethoxypropane ion. In the bond cleavage and new bond-formation parts of the reaction coordinates, exchange and polarization energies provide a major source of the attraction. In the ion-neutral complex-formation part of the reaction coordinate, different major attractive sources, dispersion, and electrostatic energies were observed. The physical origins of weak interaction in the ion-neutral complexes were affected by the local charges and distances between the ion moieties and the neutral moieties.

  1. Bis-semiquinone (bi-radical) formation by photoinduced proton coupled electron transfer in covalently linked catechol-quinone systems: Aviram's hemiquinones revisited

    NARCIS (Netherlands)

    Nguyen, V.A.; Williams, R.M.

    2012-01-01

    The structure and reactivity of a covalently linked catechol-ortho-benzoquinone (hemiquinone) is studied by UV-Vis and IR absorption spectroscopy. Nanosecond transient absorption spectroscopy of the hemiquinone reveals the formation of bi-radical state consisting of two semiquinone units. It is a

  2. Names for inorganic radicals (IUPAC Recommendations 2000)

    OpenAIRE

    W. H. Koppenol

    2017-01-01

    Introduction: Knowledge of the properties and reactivities of stable inorganic radicals was obtained decades ago through gas-phase studies of various oxides of halogens, sulfur, and nitrogen. More recently, pulse radiolysis and flash photolysis techniques developed in the 1960s made it possible to study short-lived radicals, such as hydrated electrons, hydrogen atoms, and hydroxyl radicals. Because of the high time-resolution of these techniques, absorption spectra and redox properties of the...

  3. Oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives by nitrous oxide via selective oxygen atom transfer reactions: insights from quantum chemistry calculations.

    Science.gov (United States)

    Xie, Hujun; Liu, Chengcheng; Yuan, Ying; Zhou, Tao; Fan, Ting; Lei, Qunfang; Fang, Wenjun

    2016-01-21

    The mechanisms for the oxidation of phenyl and hydride ligands of bis(pentamethylcyclopentadienyl)hafnium derivatives (Cp* = η(5)-C5Me5) by nitrous oxide via selective oxygen atom transfer reactions have been systematically studied by means of density functional theory (DFT) calculations. On the basis of the calculations, we investigated the original mechanism proposed by Hillhouse and co-workers for the activation of N2O. The calculations showed that the complex with an initial O-coordination of N2O to the coordinatively unsaturated Hf center is not a local minimum. Then we proposed a new reaction mechanism to investigate how N2O is activated and why N2O selectively oxidize phenyl and hydride ligands of . Frontier molecular orbital theory analysis indicates that N2O is activated by nucleophilic attack by the phenyl or hydride ligand. Present calculations provide new insights into the activation of N2O involving the direct oxygen atom transfer from nitrous oxide to metal-ligand bonds instead of the generally observed oxygen abstraction reaction to generate metal-oxo species.

  4. Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations

    Energy Technology Data Exchange (ETDEWEB)

    Scherer, Michelle [Univ. of Iowa, Iowa City, IA (United States)

    2016-08-31

    During this project, we investigated Fe electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clay minerals. We used selective chemical extractions, enriched Fe isotope tracer experiments, computational molecular modeling, and Mössbauer spectroscopy. Our findings indicate that structural Fe(III) in clay minerals is reduced by aqueous Fe(II) and that electron transfer occurs when Fe(II) is sorbed to either basal planes and edge OH-groups of clay mineral. Findings from highly enriched isotope experiments suggest that up to 30 % of the Fe atoms in the structure of some clay minerals exhanges with aqueous Fe(II). First principles calculations using a small polaron hopping approach suggest surprisingly fast electron mobility at room temperature in a nontronite clay mineral and are consistent with temperature dependent Mössbauer data Fast electron mobility suggests that electrons may be able to conduct through the mineral fast enough to enable exchange of Fe between the aqueous phase and clay mineral structure. over the time periods we observed. Our findings suggest that Fe in clay minerals is not as stable as previously thought.

  5. Mechanistic elucidation of the stepwise formation of a tetranuclear manganese pinned butterfly cluster via N-N bond cleavage, hydrogen atom transfer, and cluster rearrangement.

    Science.gov (United States)

    Hamilton, Clifton R; Gau, Michael R; Baglia, Regina A; McWilliams, Sean F; Zdilla, Michael J

    2014-12-31

    A mechanistic pathway for the formation of the structurally characterized manganese-amide-hydrazide pinned butterfly complex, Mn4(μ3-PhN-NPh-κ(3)N,N')2(μ-PhN-NPh-κ(2)-N,N')(μ-NHPh)2L4 (L = THF, py), is proposed and supported by the use of labeling studies, kinetic measurements, kinetic competition experiments, kinetic isotope effects, and hydrogen atom transfer reagent substitution, and via the isolation and characterization of intermediates using X-ray diffraction and electron paramagnetic resonance spectroscopy. The data support a formation mechanism whereby bis[bis(trimethylsilyl)amido]manganese(II) (Mn(NR2)2, where R = SiMe3) reacts with N,N'-diphenylhydrazine (PhNHNHPh) via initial proton transfer, followed by reductive N-N bond cleavage to form a long-lived Mn(IV) imido multinuclear complex. Coordinating solvents activate this cluster for abstraction of hydrogen atoms from an additional equivalent of PhNHNHPh resulting in a Mn(II)phenylamido dimer, Mn2(μ-NHPh)2(NR2)2L2. This dimeric complex further assembles in fast steps with two additional equivalents of PhNHNHPh replacing the terminal silylamido ligands with η(1)-hydrazine ligands to give a dimeric Mn2(μ-NHPh)2(PhN-NHPh)2L4 intermediate, and finally, the addition of two additional equivalents of Mn(NR2)2 and PhNHNHPh gives the pinned butterfly cluster.

  6. Experimental evidence of resonant energy collisional transfers between argon 1s and 2p states and ground state H atoms by laser collisional induced fluorescence

    Science.gov (United States)

    Carbone, Emile; van Dijk, Jan; Kroesen, Gerrit

    2015-04-01

    In this paper, laser collisional induced fluorescence (LCIF) is used to probe resonant excitation transfers in an argon/hydrogen plasma resulting from heavy particle collisions. Different radiative transitions between the 1s and 2p states (in Paschen's notation) of argon are optically pumped by a nanosecond laser pulse. The spontaneous fluorescence and collisional responses of the argon and hydrogen systems are monitored by optical emission spectroscopy. A surfatron plasma source is used to generate an argon plasma with a few per cent hydrogen addition at pressures between 0.65 and 20 mbar. The electron density is measured independently by means of Thomson scattering. The overall response of the plasma due to optical pumping of argon is briefly discussed and an overview of the known heteronuclear excitation transfers in an argon/hydrogen plasma is given. The propagation of the shortcut in the Ar(1s) to H(n = 2) excitation transfer due to the optical pumping of the Ar(1s) states is seen in the atomic hydrogen LCIF responses. For the first time, we give direct experimental evidence of the existence of an efficient excitation transfer: Additionally, measurements are performed in order to estimate the resonant energy transfer between the resonant argon 1s states and hydrogen atoms: for which no previously measured cross sections could be found in the literature. These are extra quenching channels of argon 1s and 2p states that should be included in collisional-radiative modeling of argon-hydrogen discharges. The high repetition rate of the dye laser allows us to obtain a high sensitivity in the measurements. LCIF is shown to be a powerful tool for unraveling electron and also heavy particle excitation channels in situ in the plasma phase. The technique was previously developed for measuring electron or species densities locally in the plasma, but we show that it can be advantageously used to probe collisional transfers between very short-lived species which exist

  7. Oxidative atom-transfer to a trimanganese complex to form Mn6(μ6-E) (E = O, N) clusters featuring interstitial oxide and nitride functionalities.

    Science.gov (United States)

    Fout, Alison R; Zhao, Qinliang; Xiao, Dianne J; Betley, Theodore A

    2011-10-26

    Utilizing a hexadentate ligand platform, a trinuclear manganese complex of the type ((H)L)Mn(3)(thf)(3) was synthesized and characterized ([(H)L](6-) = [MeC(CH(2)N(C(6)H(4)-o-NH))(3)](6-)). The pale-orange, formally divalent trimanganese complex rapidly reacts with O-atom transfer reagents to afford the μ(6)-oxo complex ((H)L)(2)Mn(6)(μ(6)-O)(NCMe)(4), where two trinuclear subunits bind the central O-atom and the ((H)L) ligands cooperatively bind both trinuclear subunits. The trimanganese complex ((H)L)Mn(3)(thf)(3) rapidly consumes inorganic azide ([N(3)]NBu(4)) to afford a dianionic hexanuclear nitride complex [((H)L)(2)Mn(6)(μ(6)-N)](NBu(4))(2), which subsequently can be oxidized with elemental iodine to ((H)L)(2)Mn(6)(μ(6)-N)(NCMe)(4). EPR and alkylation of the interstitial light atom substituent were used to distinguish the nitride from the oxo complex. The oxo and oxidized nitride complexes give rise to well-defined Mn(II) and Mn(III) sites, determined by bond valence summation, while the dianionic nitride shows a more symmetric complex, giving rise to indistinguishable ion oxidation states based on crystal structure bond metrics.

  8. WATER-BORNE BLOCK COPOLYMER SYNTHESIS AND A SIMPLE AND EFFECTIVE ONE-POT SYNTHESIS OF ACRYLATE-METHACRYLATE BLOCK COPOLYMERS BY ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  9. COMBINING ATOM TRANSFER RADICAL POLYMERIZATION AND DISULFIDE /THIOL REDOX CHEMISTRY: A ROUTE TO WELL-DEFINED (BIO)DEGRADABLE POLYMERIC MATERIALS. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  10. EFFECT OF (PSEUDO)HALIDE INITIATORS AND COPPER COMPLEXES WITH NON-HALOGEN ANIONS ON THE ATOM TRANSFER RADICAL POLYMERIZATION. (R829580)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  11. Transferable Anisotropic United-Atom Force Field Based on the Mie Potential for Phase Equilibrium Calculations: n-Alkanes and n-Olefins.

    Science.gov (United States)

    Hemmen, Andrea; Gross, Joachim

    2015-09-03

    A new transferable force field parametrization for n-alkanes and n-olefins is proposed in this work. A united-atom approach is taken, where hydrogen atoms are lumped with neighboring atoms to single interaction sites. A comprehensive study is conducted for alkanes, optimizing van der Waals force field parameters in 6 dimensions. A Mie n-6 potential is considered for the van der Waals interaction, where for n-alkanes we simultaneously optimize the energy parameters ϵCH3 and ϵCH2 as well as the size parameters σCH3 and σCH2 of the CH3(sp(3)) and CH2(sp(3)) groups. Further, the repulsive exponent n of the Mie n-6 potential is varied. Moreover, we investigate the bond length toward the terminal CH3 group as a degree of freedom. According to the AUA (anisotropic united-atom) force field, the bond length between the terminal CH3 group and the neighboring interaction site should be increased by Δl compared with the carbon-carbon distance in order to better account for the hydrogen atoms. The parameter Δl is considered as a degree of freedom. The intramolecular force field parametrization is taken from existing force fields. A single objective function for the optimization is defined as squared relative deviations in vapor pressure and in liquid density of propane, n-butane, n-hexane, and n-octane. A similar study is also done for olefins, where the objective function includes 1-butene, 1-hexene, 1-octene, cis-2-pentene, and trans-2-pentene. Molecular simulations are performed in the grand canonical ensemble with transition-matrix sampling where the phase equilibrium properties are obtained with the histogram reweighting technique. The 6-dimensional optimization of strongly correlated parameters is possible, because the analytic PC-SAFT equation of state is used to locally correlate simulation results. The procedure is iterative but leads to very efficient convergence. An implementation is proposed, where the converged result is not affected (disturbed) by the

  12. Toward living radical polymerization.

    Science.gov (United States)

    Moad, Graeme; Rizzardo, Ezio; Thang, San H

    2008-09-01

    Radical polymerization is one of the most widely used processes for the commercial production of high-molecular-weight polymers. The main factors responsible for the preeminent position of radical polymerization are the ability to polymerize a wide array of monomers, tolerance of unprotected functionality in monomer and solvent, and compatibility with a variety of reaction conditions. Radical polymerization is simple to implement and inexpensive in relation to competitive technologies. However, conventional radical polymerization severely limits the degree of control that researchers can assert over molecular-weight distribution, copolymer composition, and macromolecular architecture. This Account focuses on nitroxide-mediated polymerization (NMP) and polymerization with reversible addition-fragmentation chain transfer (RAFT), two of the more successful approaches for controlling radical polymerization. These processes illustrate two distinct mechanisms for conferring living characteristics on radical polymerization: reversible deactivation (in NMP) and reversible or degenerate chain transfer (in RAFT). We devised NMP in the early 1980s and have exploited this method extensively for the synthesis of styrenic and acrylic polymers. The technique has undergone significant evolution since that time. New nitroxides have led to faster polymerization rates at lower temperatures. However, NMP is only applicable to a restricted range of monomers. RAFT was also developed at CSIRO and has proven both more robust and more versatile. It is applicable to the majority of monomers subject to radical polymerization, but the success of the polymerization depends upon the selection of the RAFT agent for the monomers and reaction conditions. We and other groups have proposed guidelines for selection, and the polymerization of most monomers can be well-controlled to provide minimal retardation and a high fraction of living chains by using one of just two RAFT agents. For example, a

  13. Preparation of PEGylated polymeric nanoprobes with aggregation-induced emission feature through the combination of chain transfer free radical polymerization and multicomponent reaction: Self-assembly, characterization and biological imaging applications.

    Science.gov (United States)

    Wan, Qing; Liu, Meiying; Mao, Liucheng; Jiang, Ruming; Xu, Dazhuang; Huang, Hongye; Dai, Yanfeng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-01

    Self-assembly of amphiphilic luminescent copolymers is a general route to fabricate fluorescent polymeric microparticles (FPMs). In this work, the FPMs with aggregation-induced emission (AIE) feature were fabricated via the combination of the chain transfer free radical polymerization and "one-pot" multicomponent reaction, which conjugated the aldehyde-containing AIE active dye AIE (CHO-An-CHO) and amino-terminated hydrophilic polymer (ATPPEGMA) using mercaptoacetic acid (MTA) as the "lock" molecule. The structure, chemical compositions, optical properties as well as biological properties of the PPEGMA-An-PPEGMA FPMs were characterized and investigated by means of a series of techniques and experiments in detail. We demonstrated the final copolymers showed amphiphilic properties, strong yellow fluorescence and high water dispersibility. Biological evaluation suggested that PPEGMA-An-PPEGMA FPMs possess low cytotoxicity and can be used for cell imaging. More importantly, many other AIE active FPMs are expected to be fabricated using the similar strategy because of the good substrate and monomer applicability of the multicomponent reaction and chain transfer living radical polymerization. Therefore, we could conclude that the strategy described in this work should be of great interest for fabrication of multifunctional AIE active nanoprobes for biomedical applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  14. Radical versus Non-Radical Inventions

    OpenAIRE

    Schoenmakers, Wilfred; Duysters, Geert; Vanhaverbeke, Wim

    2008-01-01

    This paper looks at the special characteristics of radical inventions. It tries to identify those variables that differentiate radical inventions from non-radical inventions. Since radical inventions are very important for the economy as a whole and for the individual firm performances, understanding what makes radical inventions differ from non-radical inventions is very important. For our research we made use of the EPO (European Patent Office) database on patents. We used...

  15. Bithiophene radical cation: Resonance Raman spectroscopy and molecular orbital calculations

    DEFF Research Database (Denmark)

    Grage, M.M.-L.; Keszthelyi, T.; Offersgaard, J.F.

    1998-01-01

    The resonance Raman spectrum of the photogenerated radical cation of bithiophene is reported. The bithiophene radical cation was produced via a photoinduced electron transfer reaction between excited bithiophene and the electron acceptor fumaronitrile in a room temperature acetonitrile solution a...

  16. Hydrodynamic, Atomic Kinetic, and Monte Carlo Radiation Transfer Models of the X-ray Spectra of Compact Binaries

    Energy Technology Data Exchange (ETDEWEB)

    Mauche, C W; Liedahl, D A; Akiyama, S; Plewa, T

    2008-02-08

    We describe the results of an effort, funded by the Lawrence Livermore National Laboratory Directed Research and Development Program, to model, using FLASH time-dependent adaptive-mesh hydrodynamic simulations, XSTAR photoionization calculations, HULLAC atomic data, and Monte Carlo radiation transport, the radiatively-driven photoionized wind and accretion flow of high-mass X-ray binaries (HMXBs). In this final report, we describe the purpose, approach, and technical accomplishments of this effort, including maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of the X-ray emission lines of the well-studied HMXB Vela X-1.

  17. Dichotomous Hydrogen Atom Transfer vs. Proton Coupled Electron Transfer During Activation of X-H Bonds (X = C, N, O) by Nonheme Iron-Oxo Complexes of Variable Basicity

    Science.gov (United States)

    Usharani, Dandamudi; Lacy, David C.; Borovik, A. S.; Shaik, Sason

    2013-01-01

    We describe herein the hydrogen-atom transfer (HAT)/ proton-coupled electron-transfer (PCET) reactivity for FeIV-oxo and FeIII-oxo complexes (1–4) that activate C-H, N-H, and O-H bonds in 9,10 dihydroanthracene (S1), dimethylformamide (S2), 1,2 diphenylhydrazine (S3), p-methoxyphenol (S4), and 1,4-cyclohexadiene (S5). In 1–3, the iron is pentacoordinated by tris[N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) or its derivatives. These complexes are basic, in the order 3 >> 1 > 2. Oxidant 4, [FeIVN4Py(O)]2+ (N4Py: N,N-bis(2-pyridylmethyl)-bis(2-pyridyl) methylamine), is the least basic oxidant. The DFT results match experimental trends and exhibit a mechanistic spectrum ranging from concerted HAT and PCET reactions to concerted-asynchronous proton transfer (PT) / electron transfer (ET) mechanisms, all the way to PT. The singly occupied orbital along the O---H---X (X= C, N, O) moiety in the TS shows clearly that in the PCET cases, the electron is transferred separately from the proton. The Bell-Evans-Polanyi principle does not account for the observed reactivity pattern, as evidenced by the scatter in the plot of calculated barrier vs. reactions driving forces. However, a plot of the deformation energy in the TS vs. the respective barrier provides a clear signature of the HAT/PCET dichotomy. Thus, in all C-H bond activations, the barrier derives from the deformation energy required to create the TS, whereas in N-H/O-H bond activations, the deformation energy is much larger than the corresponding barrier, indicating the presence of stabilizing interaction between the TS fragments. A valence bond model is used to link the observed results with the basicity/acidity of the reactants. PMID:24124906

  18. Resonant line transfer in a fog: using Lyman-alpha to probe tiny structures in atomic gas

    Science.gov (United States)

    Gronke, Max; Dijkstra, Mark; McCourt, Michael; Peng Oh, S.

    2017-11-01

    Motivated by observational and theoretical work that suggest very small-scale (≲ 1 pc) structure in the circumgalactic medium of galaxies and in other environments, we study Lyman-α (Lyα) radiative transfer in an extremely clumpy medium with many clouds of neutral gas along the line of sight. While previous studies have typically considered radiative transfer through sightlines intercepting ≲ 10 clumps, we explored the limit of a very large number of clumps per sightline (up to fc 1000). Our main finding is that, for covering factors greater than some critical threshold, a multiphase medium behaves similarly to a homogeneous medium in terms of the emergent Lyα spectrum. The value of this threshold depends on both the clump column density and the movement of the clumps. We estimated this threshold analytically and compare our findings to radiative transfer simulations with a range of covering factors, clump column densities, radii, and motions. Our results suggest that (I) the success in fitting observed Lyα spectra using homogeneous "shell models" (and the corresponding failure of multiphase models) hints at the presence of very small-scale structure in neutral gas, which is in agreement within a number of other observations; and (II) the recurrent problems of reproducing realistic line profiles from hydrodynamical simulations may be due to their inability to resolve small-scale structure, which causes simulations to underestimate the effective covering factor of neutral gas clouds. The movie associated to Fig. B.2 is available at http://www.aanda.org

  19. Simulating Controlled Radical Polymerizations with mcPolymer—A Monte Carlo Approach

    Directory of Open Access Journals (Sweden)

    Georg Drache

    2012-07-01

    Full Text Available Utilizing model calculations may lead to a better understanding of the complex kinetics of the controlled radical polymerization. We developed a universal simulation tool (mcPolymer, which is based on the widely used Monte Carlo simulation technique. This article focuses on the software architecture of the program, including its data management and optimization approaches. We were able to simulate polymer chains as individual objects, allowing us to gain more detailed microstructural information of the polymeric products. For all given examples of controlled radical polymerization (nitroxide mediated radical polymerization (NMRP homo- and copolymerization, atom transfer radical polymerization (ATRP, reversible addition fragmentation chain transfer polymerization (RAFT, we present detailed performance analyses demonstrating the influence of the system size, concentrations of reactants, and the peculiarities of data. Different possibilities were exemplarily illustrated for finding an adequate balance between precision, memory consumption, and computation time of the simulation. Due to its flexible software architecture, the application of mcPolymer is not limited to the controlled radical polymerization, but can be adjusted in a straightforward manner to further polymerization models.

  20. Mechanism elucidation of the radical SAM enzyme spore photoproduct lyase (SPL)

    Science.gov (United States)

    Li, Lei

    2011-01-01

    Spore photoproduct lyase (SPL) repairs a special thymine dimer 5-thyminyl-5,6-dihydrothymine, which is commonly called spore photoproduct or SP at the bacterial early germination phase. SP is the exclusive DNA photo-damage product in bacterial endospores; its generation and swift repair by SPL are responsible for the spores’ extremely high UV resistance. The early in vivo studies suggested that SPL utilizes a direct reversal strategy to repair the SP in the absence of light. The research in the past decade further established SPL as a radical SAM enzyme, which utilizes a tri-cysteine CXXXCXXC motif to harbor a [4Fe-4S] cluster. At the 1+ oxidation state, the cluster provides an electron to the S-adenosylmethionine (SAM), which binds to the cluster in a bidentate manner as the fourth and fifth ligands, to reductively cleave the C-S bond associated with the sulfonium ion in SAM, generating a reactive 5′-deoxyadenosyl (5′-dA) radical. This 5′-dA radical abstracts the proR hydrogen atom from the C6 carbon of SP to initiate the repair process; the resulting SP radical subsequently fragments to generate a putative thymine methyl radical, which accepts a back-donated H atom to yield the repaired TpT. SAM is suggested to be regenerated at the end of each catalytic cycle; and only a catalytic amount of SAM is needed in the SPL reaction. The H atom source for the back donation step is suggested to be a cysteine residue (C141 in B. subtilis SPL), and the H-atom transfer reaction leaves a thiyl radical behind on the protein. This thiyl radical thus must participate in the SAM regeneration process; however how the thiyl radical abstracts an H atom from the 5′-dA to regenerate SAM is unknown. This paper reviews and discusses the history and the latest progress in the mechanistic elucidation of SPL. Despite some recent breakthroughs, more questions are raised in the mechanistic understanding of this intriguing DNA repair enzyme. PMID:22197590

  1. Kinetics and product identification of the reactions of (E)-2-hexenyl acetate and 4-methyl-3-penten-2-one with OH radicals and Cl atoms at 298 K and atmospheric pressure

    Science.gov (United States)

    Gaona-Colmán, Elizabeth; Blanco, María B.; Teruel, Mariano A.

    2017-07-01

    Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with two biogenic volatile organic compounds as (E)-2-hexenyl acetate and 4-methyl-3-penten-2-one have been determined at 298 K and atmospheric pressure. The decay of the organics was followed using a chromatograph with a flame ionization detector (GC-FID) and the rate constants were determined using a relative rate method. Rate coefficients are found to be (in cm3 molecule-1 s-1): k1(OH + (E)-2-hexenyl acetate) = (6.88 ± 1.41) × 10-11, k2(Cl + (E)-2-hexenyl acetate) = (3.10 ± 1.13) × 10-10, k3(OH + 4-methyl-3-penten-2-one) = (1.02 ± 0.20) × 10-10 and k4(Cl + 4-methyl-3-penten-2-one) = (2.66 ± 0.90) × 10-10 at 298 K. This is the first kinetic experimental study for these reactions studied under atmospheric pressure. The rate coefficients are compared with previous determinations for other unsaturated and oxygenated compounds and reactivity trends are presented. Products identification studies were performed using solid-phase microextraction (SPME) method employing on-fiber products derivatization with o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride using gas chromatograph with a mass spectrometer detector (GC-MS) for the reactions studied. In addition, atmospheric lifetimes of the unsaturated compounds studied are estimated and compared with other tropospheric sinks for these compounds.

  2. Selective deuteration illuminates the importance of tunneling in the unimolecular decay of Criegee intermediates to hydroxyl radical products

    Energy Technology Data Exchange (ETDEWEB)

    Green, Amy M.; Barber, Victoria P.; Fang, Yi; Klippenstein, Stephen J.; Lester, Marsha I.

    2017-11-21

    Ozonolysis of alkenes, an important nonphotolytic source of hydroxyl (OH) radicals in the atmosphere, proceeds through unimolecular decay of Criegee intermediates. Here, we report a large kinetic isotope effect associated with the rate-limiting hydrogen-transfer step that releases OH radicals for a prototypical Criegee intermediate, CH3CHOO. IR excitation of selectively deuterated syn-CD3CHOO is shown to result in deuterium atom transfer and release OD radical products. Vibrational activation of syn-CD3CHOO is coupled with direct time-resolved detection of OD products to measure a 10-fold slower rate of unimolecular decay upon deuteration in the vicinity of the transition state barrier, which is confirmed by microcanonical statistical theory that incorporates quantum mechanical tunneling. The corresponding kinetic isotope effect of similar to 10 is attributed primarily to the decreased probability of D-atom vs. H-atom transfer arising from tunneling. Master equation modeling is utilized to compute the thermal unimolecular decay rates for selectively and fully deuterated syn methyl-substituted Criegee intermediates under atmospheric conditions. At 298 K (1 atm), tunneling is predicted to enhance the thermal decay rate of syn-CH3CHOO compared with the deuterated species, giving rise to a significant kinetic isotope effect of similar to 50.

  3. Altered transfer of momentary mental states (ATOMS as the basic unit of psychosis liability in interaction with environment and emotions.

    Directory of Open Access Journals (Sweden)

    Johanna T W Wigman

    Full Text Available Psychotic disorders are thought to represent altered neural function. However, research has failed to map diagnostic categories to alterations in neural networks. It is proposed that the basic unit of psychotic psychopathology is the moment-to-moment expression of subtle anomalous experiences of subclinical psychosis, and particularly its tendency to persist from moment-to-moment in daily life, under the influence of familial, environmental, emotional and cognitive factors.In a general population twin sample (n = 579 and in a study of patients with psychotic disorder (n = 57, their non-psychotic siblings (n = 59 and unrelated controls (n = 75, the experience sampling paradigm (ESM; repetitive, random sampling of momentary mental states and context was applied. We analysed, in a within-person prospective design, (i transfer of momentary anomalous experience at time point (t-1 to time point (t in daily life, and (ii moderating effects of negative affect, positive affect, daily stressors, IQ and childhood trauma. Additionally, (iii familial associations between persistence of momentary anomalous experience and psychotic symptomatology were investigated. Higher level of schizotypy in the twins (but not higher level of psychotic symptoms in patients predicted more persistence of momentary anomalous experience in daily life, both within subjects and across relatives. Persistence of momentary anomalous experience was highest in patients, intermediate in their siblings and lowest in controls. In both studies, persistence of momentary anomalous experience was moderated by higher levels of negative affect, daily stressors and childhood trauma (only in twins, and by lower levels of positive affect. The study of alterations in the moment-to-moment transfer of subtle anomalous experience of psychosis, resulting in their persistence, helps to explain why psychotic and emotional dysregulation tend to cluster in a single phenotype such as

  4. Antioxidant activity of wine pigments derived from anthocyanins: hydrogen transfer reactions to the dpph radical and inhibition of the heme-induced peroxidation of linoleic acid.

    Science.gov (United States)

    Goupy, Pascale; Bautista-Ortin, Ana-Belen; Fulcrand, Helene; Dangles, Olivier

    2009-07-08

    The consumption of red wine can provide substantial concentrations of antioxidant polyphenols, in particular grape anthocyanins (e.g., malvidin-3-O-beta-d-glucoside (1)) and specific red wine pigments formed by reaction between anthocyanins and other wine components such as catechin (3), ethanol, and hydroxycinnamic acids. In this work, the antioxidant properties of red wine pigments (RWPs) are evaluated by the DPPH assay and by inhibition of the heme-induced peroxidation of linoleic acid in acidic conditions (a model of antioxidant action in the gastric compartment). RWPs having a 1 and 3 moieties linked via a CH(3)-CH bridge appear more potent than the pigment with a direct 1-3 linkage. Pyranoanthocyanins derived from 1 reduce more DPPH radicals than 1 irrespective of the substitution of their additional aromatic ring. Pyranoanthocyanins are also efficient inhibitors of the heme-induced lipid peroxidation, although the highly hydrophilic pigment derived from pyruvic acid appears less active.

  5. Photoinduced Electron-Transfer Mechanisms for Radical-Enhanced Photodynamic Therapy Mediated by Water-Soluble Decacationic C70 and C84O2 Fullerene Derivatives

    Science.gov (United States)

    Sperandio, Felipe F.; Sharma, Sulbha K.; Wang, Min; Jeon, Seaho; Huang, Ying-Ying; Dai, Tianhong; Nayka, Suhasini; de Sousa, Suzana C.O.M.; Chiang, Long Y.; Hamblin, Michael R.

    2012-01-01

    Fullerenes are promising candidates for photodynamic therapy (PDT). Thus, C70 and novel C84O2 fullerenes were functionalized with and without an additional deca-tertiary ethyleneamino-chain as an electron source, giving rise to two distinct pairs of photosensitizers, the monoadducts LC-17, LC-19 and the bisadducts LC18 and LC-20 to perform PDT in HeLa cells with UVA, blue, green, white and red light. Shorter wavelengths gave more phototoxicity with LC-20 while LC-19 was better at longer wavelengths; the ratio between killing obtained with LC-19 and LC-20 showed an almost perfect linear correlation (R = 0.975) with wavelength. The incorporation of a deca-tertiary amine chain in the C84O2 fullerene gave more PDT killing when excited with shorter wavelengths or in presence of low ascorbate concentration through higher generation of hydroxyl radicals. Photoactivated C84O2 fullerenes induced apoptosis of HeLa cancer cells, together with mitochondrial and lysosomal damage demonstrated by acridine orange and rhodamine 123 fluorescent probes. PMID:23117043

  6. Gas-Phase Intercluster Thiyl-Radical Induced C-H Bond Homolysis Selectively Forms Sugar C2-Radical Cations of Methyl D-Glucopyranoside: Isotopic Labeling Studies and Cleavage Reactions

    Science.gov (United States)

    Osburn, Sandra; Speciale, Gaetano; Williams, Spencer J.; O'Hair, Richard A. J.

    2017-07-01

    A suite of isotopologues of methyl D-glucopyranosides is used in conjunction with multistage mass spectrometry experiments to determine the radical site and cleavage reactions of sugar radical cations formed via a recently developed `bio-inspired' method. In the first stage of CID (MS2), collision-induced dissociation (CID) of a protonated noncovalent complex between the sugar and S-nitrosocysteamine, [H3NCH2CH2SNO + M]+, unleashes a thiyl radical via bond homolysis to give the noncovalent radical cation, [H3NCH2CH2S• + M]+. CID (MS3) of this radical cation complex results in dissociation of the noncovalent complex to generate the sugar radical cation. Replacement of all exchangeable OH and NH protons with deuterons reveals that the sugar radical cation is formed in a process involving abstraction of a hydrogen atom from a C-H bond of the sugar coupled with proton transfer to the sugar, to form [M - H• + D+]. Investigation of this process using individual C-D labeled sugars reveals that the main site of H/D abstraction is the C2 position, since only the C2-deuterium labeled sugar yields a dominant [M - D• + H+] product ion. The fragmentation reactions of the distonic sugar radical cation, [M - H•+ H+], were studied by another stage of CID (MS4). 13C-labeling studies revealed that a series of three related fragment ions each contain the C1-C3 atoms; these arise from cross-ring cleavage reactions of the sugar.

  7. Thermochemistry and Kinetic Analysis of the Unimolecular Oxiranyl Radical Dissociation Reaction: A Theoretical Study.

    Science.gov (United States)

    Wang, Heng; Bozzelli, Joseph W

    2016-07-04

    Oxirane structures are important in organic synthesis, and they are important initial products in the oxidation reactions of alkyl radicals. The thermochemical properties (enthalpy of formation, entropy, and heat capacity) for the reaction steps of the unimolecular oxiranyl radical dissociation reaction are determined and compared with the available literature. The overall ring opening and subsequent steps involve four types of reactions: β-scission ring opening, intramolecular hydrogen transfer, β-scission hydrogen elimination, and β-scission methyl radical elimination. The enthalpies of formation of the transition states are determined and evaluated using six popular Density Functional Theory (DFT) calculation methods (B3LYP, B2PLYP, M06, M06-2X, ωB97X, ωB97XD), each combined with three different basis sets. The DFT enthalpy values are compared with five composite calculation methods (G3, G4, CBS-QB3, CBS-APNO, W1U), and by CCSD(T)/aug-cc-pVTZ. Kinetic parameters are determined versus pressure and temperature for the unimolecular dissociation pathways of an oxiranyl radical, which include the chemical activation reactions of the ring-opened oxiranyl radical relative to the ring-opening barrier. Multifrequency quantum Rice Ramsperger Kassel (QRRK) analysis is used to determine k(E) with master equation analysis for falloff. The major overall reaction pathway at lower combustion temperatures is oxiranyl radical dissociation to a methyl radical and carbon monoxide. Oxiranyl radical dissociation to a ketene and hydrogen atom is the key reaction path above 700 K. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Cooperative Effects on Radical Recombination in CYP3A4-Catalyzed Oxidation of the Radical Clock β-Thujone**

    Science.gov (United States)

    Jiang, Yongying

    2009-01-01

    The oxidation of hydrocarbons by cytochrome P450 enzymes is commonly thought to involve hydrogen atom abstraction by a ferryl species comparable to that of peroxidase Compound I, followed by radical recombination of the resulting carbon radical with the equivalent of an iron-bound hydroxyl radical.1,2 This radical rebound mechanism, first proposed in 1978, is supported by a variety of experimental results, including (a) rearrangement and inversion reactions prior to the radical recombination step, (b) the large magnitude (up to kH/kD ~ 13) of the intrinsic isotope effect for hydrogen abstraction, and (c) computational modeling of the reaction pathway. However, radical clock substrates, in which the radical undergoes a rearrangement at a known rate prior to radical recombination, have provided conflicting evidence on the radical lifetime. Although several radical clocks support a radical recombination mechanism, so-called ultrafast radical clocks yield radical lifetime estimates more consistent with a transition state than an actual intermediate.3 This discrepancy has led to postulates that hydroxylation may involve concerted insertion into the C-H bond or the involvement of multiple oxidizing species. An alternative explanation is provided by computational studies that invoke a reaction manifold with a radical intermediate that exists in two different spin states.4 A further possible explanation is provided by the observation that ultrafast radical clocks generally involve primary radical rearrangements, whereas slower radical clocks generally involve secondary radical rearrangements. The recombination rates of primary and secondary radicals may be differentially susceptible to modulation by interactions with the active site and the iron-oxo species. However, there is little direct evidence that the radical complex exists in two different spin states, or that the radical recombination rates can be influenced by the active site environment. PMID:19189363

  9. Fabrication of an SPR Sensor Surface with Antifouling Properties for Highly Sensitive Detection of 2,4,6-Trinitrotoluene Using Surface-Initiated Atom Transfer Polymerization

    Directory of Open Access Journals (Sweden)

    Kiyoshi Toko

    2013-07-01

    Full Text Available In this study, we modified a surface plasmon resonance immunosensor chip with a polymer using surface-initiated atom transfer polymerization (SI-ATRP for the highly sensitive detection of 2,4,6-trinitrotoluene (TNT. To immobilize a TNT analogue on the polymer, mono-2-(methacryloyloxyethylsuccinate (MES, which has a carboxyl group, was used in this study. However, the anti-TNT antibody may adsorb non-specifically on the polymer surface by an electrostatic interaction because MES is negatively charged. Therefore, a mixed monomer with MES and diethylaminoethylmethacrylate (DEAEM, which has a tertiary amino group and is positively charged, was prepared to obtain electroneutrality for suppressing the nonspecific adsorption. The detection of TNT was performed by inhibition assay using the polymer surface. To ensure high sensitivity to TNT, the affinity between the surface and the antibody was optimized by controlling the density of the initiator for ATRP by mixing two types of self-assembled monolayer reagents. As a result, a limit of detection of 5.7 pg/mL (ppt for TNT was achieved using the optimized surface.

  10. Development of atom-economical catalytic asymmetric reactions under proton transfer conditions: construction of tetrasubstituted stereogenic centers and their application to therapeutics.

    Science.gov (United States)

    Kumagai, Naoya

    2011-01-01

    The development of atom-economical catalytic asymmetric reactions based on two distinct sets of catalyst, a rare earth metal/amide-based ligand catalyst and a soft Lewis acid/hard Brønsted base catalyst, is reviewed. These catalytic systems exhibit high catalytic activity and stereoselectivity by harnessing a cooperative catalysis through hydrogen bond/metal coordination and soft-soft interactions/hard-hard interactions, respectively. The effectiveness of these cooperative catalysts is clearly delineated by the high stereoselectivity in reactions with highly coordinative substrates, and the specific activation of otherwise low-reactive pronucleophiles under proton transfer conditions. The rare earth metal/amide-based ligand catalyst was successfully applied to catalytic asymmetric aminations, nitroaldol (Henry) reactions, Mannich-type reactions, and conjugate addition reactions, generating stereogenic tetrasubstituted centers. Catalytic asymmetric amination and anti-selective catalytic asymmetric nitroaldol reactions were successfully applied to the efficient enantioselective synthesis of therapeutic candidates, such as AS-3201 and the β(3)-adrenoreceptor agonist, showcasing the practical utility of the present protocols. The soft Lewis acid/hard Brønsted base cooperative catalyst was specifically developed for the chemoselective activation of soft Lewis basic allylic cyanides and thioamides, which are otherwise low-reactive pronucleophiles. The cooperative action of the catalyst allowed for efficient catalytic generation of active carbon nucleophiles in situ, which were integrated into subsequent enantioselective additions to carbonyl-type electrophiles.

  11. The Molybdenum Active Site of Formate Dehydrogenase Is Capable of Catalyzing C-H Bond Cleavage and Oxygen Atom Transfer Reactions.

    Science.gov (United States)

    Hartmann, Tobias; Schrapers, Peer; Utesch, Tillmann; Nimtz, Manfred; Rippers, Yvonne; Dau, Holger; Mroginski, Maria Andrea; Haumann, Michael; Leimkühler, Silke

    2016-04-26

    Formate dehydrogenases (FDHs) are capable of performing the reversible oxidation of formate and are enzymes of great interest for fuel cell applications and for the production of reduced carbon compounds as energy sources from CO2. Metal-containing FDHs in general contain a highly conserved active site, comprising a molybdenum (or tungsten) center coordinated by two molybdopterin guanine dinucleotide molecules, a sulfido and a (seleno-)cysteine ligand, in addition to a histidine and arginine residue in the second coordination sphere. So far, the role of these amino acids in catalysis has not been studied in detail, because of the lack of suitable expression systems and the lability or oxygen sensitivity of the enzymes. Here, the roles of these active site residues is revealed using the Mo-containing FDH from Rhodobacter capsulatus. Our results show that the cysteine ligand at the Mo ion is displaced by the formate substrate during the reaction, the arginine has a direct role in substrate binding and stabilization, and the histidine elevates the pKa of the active site cysteine. We further found that in addition to reversible formate oxidation, the enzyme is further capable of reducing nitrate to nitrite. We propose a mechanistic scheme that combines both functionalities and provides important insights into the distinct mechanisms of C-H bond cleavage and oxygen atom transfer catalyzed by formate dehydrogenase.

  12. Synthesis, Characterization, and Evaluation of Radical Scavenging Ability of Ellagic Acid-Loaded Nanogels

    Directory of Open Access Journals (Sweden)

    Gautam Behl

    2011-01-01

    Full Text Available Ellagic acid (EA, a potential antioxidant phytochemical has low aqueous solubility and bioavailability. In this paper, encapsulation of ellagic acid has been carried out into the biodegradable disulfide crosslinked poly (ethylene glycol PEO-based nanogels synthesized via AGET (activator generated electron transfer ATRP (atom transfer radical polymerization, and their radical scavenging ability was evaluated. The encapsulation of the EA was carried out at two drug loading percentages, that is, 10 and 20 wt.% of the nanogels. 1,1-Diphenyl-2-picryldrazyl (DPPH assay was utilized in order to assess the radical scavenging ability of the ellagic acid-loaded nanogels. A drug-loading level of about 2.5 wt.% was achieved with encapsulation efficiency of about 25% at 10 wt.% of the EA w.r.t nanogels, which was found to increase to about 4.7 wt.% with decreased encapsulation efficiency of 23.5% as EA content was increased to 20wt.% of the nanogels. Ellagic acid loading was found to be accompanied with increase in the size of the nanogels from 144.6±39.52 nm for neat nanogels to 217.8±105.5 and 633±160.1 nm at 2.5 and 4.7 wt.% drug loading level. The nanogels were found to be capable of scavenging radicals and biocompatible on human cervical cancer cell lines (HeLa cells at appropriate concentrations.

  13. Free radical scavenging potency of quercetin catecholic colonic metabolites: Thermodynamics of 2H(+)/2e(-) processes.

    Science.gov (United States)

    Amić, Ana; Lučić, Bono; Stepanić, Višnja; Marković, Zoran; Marković, Svetlana; Dimitrić Marković, Jasmina M; Amić, Dragan

    2017-03-01

    Reaction energetics of the double (2H(+)/2e(-)), i.e., the first 1H(+)/1e(-) (catechol→ phenoxyl radical) and the second 1H(+)/1e(-) (phenoxyl radical→ quinone) free radical scavenging mechanisms of quercetin and its six colonic catecholic metabolites (caffeic acid, hydrocaffeic acid, homoprotocatechuic acid, protocatechuic acid, 4-methylcatechol, and catechol) were computationally studied using density functional theory, with the aim to estimate the antiradical potency of these molecules. We found that second hydrogen atom transfer (HAT) and second sequential proton loss electron transfer (SPLET) mechanisms are less energy demanding than the first ones indicating 2H(+)/2e(-) processes as inherent to catechol moiety. The Gibbs free energy change for reactions of inactivation of selected free radicals indicate that catecholic colonic metabolites constitute an efficient group of more potent scavengers than quercetin itself, able to deactivate various free radicals, under different biological conditions. They could be responsible for the health benefits associated with regular intake of flavonoid-rich diet. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Mechanisms of radical removal by SO2

    DEFF Research Database (Denmark)

    Rasmussen, Christian Lund; Glarborg, Peter; Marshall, Paul

    2007-01-01

    It is well established from experiments in premixed, laminar flames, jet-stirred reactors, flow reactors, and batch reactors that SO2 acts to catalyze hydrogen atom removal at stoichiometric and reducing conditions. However, the commonly accepted mechanism for radical removal, SO2 + H(+M) reversi......It is well established from experiments in premixed, laminar flames, jet-stirred reactors, flow reactors, and batch reactors that SO2 acts to catalyze hydrogen atom removal at stoichiometric and reducing conditions. However, the commonly accepted mechanism for radical removal, SO2 + H...

  15. Photochemical generation, isomerization, and oxygenation of stilbene cation radicals

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, F.D.; Bedell, A.M.; Dykstra, R.E.; Elbert, J.E. (Northwestern Univ., Evanston, IL (USA)); Gould, I.R.; Farid, S. (Eastman Kodak Co., Rochester, NY (USA))

    1990-10-24

    The cation radicals of cis- and trans-stilbene and several of their ring-substituted derivatives have been generated in solution directly by means of pulsed-laser-induced electron transfer to singlet cyanoanthracenes or indirectly via electron transfer from biphenyl to the singlet cyanoanthracene followed by secondary electron transfer from the stilbenes to the biphenyl cation radical. Transient absorption spectra of the cis- and trans-stilbene cation radicals generated by secondary electron transfer are similar to those previously obtained in 77 K matrices. Quantum yields for radical ion-pair cage escape have been measured for direct electron transfer from the stilbenes to three neutral and one charged singlet acceptor. These values increase as the ion-pair energy increases due to decreased rate constants for radical ion-pair return electron transfer, in accord with the predictions of Marcus theory for highly exergonic electron transfer. Cage-escape efficiencies are larger for trans- vs cis-stilbene cation radicals, possibly due to the greater extent of charge delocalization in the planar trans vs nonpolar cis cation radicals. Cage-escape stilbene cation radicals can initiate a concentration-dependent one way cis- {yields} trans-stilbene isomerization reaction.

  16. A single transition state serves two mechanisms: an ab initio classical trajectory study of the electron transfer and substitution mechanisms in reactions of ketyl radical anions with alkyl halides.

    Science.gov (United States)

    Bakken, V; Danovich, D; Shaik, S; Schlegel, H B

    2001-01-10

    Molecular dynamics has been used to investigate the reaction of a series of ketyl anion radicals and alkyl halides, CH2O(*)(-) + CH3X (X = F, Cl, Br) and NCCHO(*)(-) + CH3Cl. In addition to a floppy outer-sphere transition state which leads directly to ET products, there is a strongly bound transition state that yields both electron transfer (ET) and C-alkylated (SUB(C)) products. This common transition state has significant C-- C bonding and gives ET and SUB(C) products via a bifurcation on a single potential energy surface. Branching ratios have been estimated from ab initio classical trajectory calculations. The SUB(C) products are favored for transition states with short C--C bonds and ET for long C--C bonds. ET reactivity can be observed even at short distances of r(C)(-)(C) = ca. 2.4 A as in the transition state for the reaction NCCHO(*)(-) + CH3Cl. Therefore, the ET/SUB(C) reactivity is entangled over a significant range of the C--C distance. The mechanistic significance of the molecular dynamics study is discussed.

  17. Oxygen atom transfer from {mu}-Oxo-bis[1,4,8,11,15,18,22,25-octakis(trifluoromethyl)ph-thalocya ninato]diiron(III) : evidence for an Fe(IV)=O intermediate.

    Energy Technology Data Exchange (ETDEWEB)

    Chen, M. J.; Rathke, J. W.; Chemical Engineering

    1998-01-01

    The dimeric [(FPc)Fe]2({mu}-O) (1) (FPc is the dianion of 1,4,8,11,15,18,22,25-octakis(trifluoromethyl)phthalocyanine) has been shown to transfer its -oxo atom quantitatively to trimethylphosphine and triphenylphosphine. In the case of triphenylphosphine a base such as 1-methylimidazole (MeIm) or pyridine (py) is needed to induce the oxygen atom transfer. The reaction of 1 with MeIm at -40 C and below gives [(MeIm)(FPc)Fe]2({mu}-O) (4), which disproportionates to give (MeIm)2(FPc)Fe (5) and (FPc)Fe=O (6) at higher temperatures. The oxo atom of 6 has been shown to transfer to triphenylphosphine. Similarly, 6 is generated by the disproportionation of 1 with py. It has also been generated by the oxidation of 1 with t-butyl hydroperoxide. [(FPc)Fe]2({mu}-O) catalyzes the oxidation of hydrocarbons by iodosylbenzene. With stilbenes, styrenes, cyclohexenes and butenes as substrates, both epoxidations and alkyl C-H bond oxidations have been observed. The epoxidation of cis-stilbene leads to a mixture of cis- and trans-stilbene oxides, indicating that epoxidation of cis-stilbene, and possibly other olefins as well, proceeds through a non-concerted mechanism.

  18. Structure and reactivity of the N-acetyl-cysteine radical cation and anion: does radical migration occur?

    Science.gov (United States)

    Osburn, Sandra; Berden, Giel; Oomens, Jos; O'Hair, Richard A J; Ryzhov, Victor

    2011-10-01

    The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S-NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol(-1) lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011, 17, 873-879) and the study by Sinha et al. for cysteine radical cation (Phys. Chem. Chem. Phys. 2010, 12, 9794-9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M - 2H)( •- ). IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol(-1)) position, and does not rearrange. © American Society for Mass Spectrometry, 2011

  19. A radical approach to radical innovation

    NARCIS (Netherlands)

    D. Deichmann (Dirk); J.C.M. van den Ende (Jan)

    2014-01-01

    textabstractInnovation pays. Amazon, Apple, Facebook, Google – nearly every one of today’s most successful companies has a talent for developing radical new ideas. But how best to encourage radical initiative taking from employees, and does their previous success or failure at it play a role?

  20. Role of atoms in atomic gravitational-wave detectors

    Science.gov (United States)

    Norcia, Matthew A.; Cline, Julia R. K.; Thompson, James K.

    2017-10-01

    Recently, it has been proposed that space-based atomic sensors may be used to detect gravitational waves. These proposals describe the sensors either as clocks or as atom interferometers. Here, we seek to explore the fundamental similarities and differences between the two types of proposals. We present a framework in which the fundamental mechanism for sensitivity is identical for clock and atom interferometer proposals, with the key difference being whether or not the atoms are tightly confined by an external potential. With this interpretation in mind, we propose two major enhancements to detectors using confined atoms, which allow for an enhanced sensitivity analogous to large momentum transfer used in atom interferometry (though with no transfer of momentum to the atoms), and a way to extend the useful coherence time of the sensor beyond the atom's excited-state lifetime.

  1. An approach to quantum chemical consideration of "hydride" transfer reactions

    Directory of Open Access Journals (Sweden)

    BORIS I. DREVKO

    2004-06-01

    Full Text Available An approach to the quantum chemical study of "hydride ion" transfer has been proposed, according to which the sequences of changes in ionization potentials, enthalpies and free energies of the affinities to the hydride ion, to the hydrogen atom and to the proton of substrates molecules and their derivatives (cations, radicals, anions, are compared with the experimentally substantiated series of "hydride" mobility. It has been established that the experimental series of "hydride" mobility for six chalcogenopyrans based on "semicyclic" 1,5-diketones is in conformity with the computed ionization potentials of the molecules, and with the affinity of the corresponding radicals to the hydrogen atom involved in the transfer. The direct splitting-out of the hydride ion and the primary deprotonation of the substrates followed by the withdrawal of two electrons was elucidated to be unlikely. Feasible are the mechanisms of "hydride" mobility, the first step of which consists of electron or hydrogen atom transfer from the chalcogenopyrans molecules.

  2. Involvement of free radicals in breast cancer.

    Science.gov (United States)

    Ríos-Arrabal, Sandra; Artacho-Cordón, Francisco; León, Josefa; Román-Marinetto, Elisa; Del Mar Salinas-Asensio, María; Calvente, Irene; Núñez, Maria Isabel

    2013-08-27

    Researchers have recently shown an increased interest in free radicals and their role in the tumor microenvironment. Free radicals are molecules with high instability and reactivity due to the presence of an odd number of electrons in the outermost orbit of their atoms. Free radicals include reactive oxygen and nitrogen species, which are key players in the initiation and progression of tumor cells and enhance their metastatic potential. In fact, they are now considered a hallmark of cancer. However, both reactive species may contribute to improve the outcomes of radiotherapy in cancer patients. Besides, high levels of reactive oxygen species may be indicators of genotoxic damage in non-irradiated normal tissues. The purpose of this article is to review recent research on free radicals and carcinogenesis in order to understand the pathways that contribute to tumor malignancy. This review outlines the involvement of free radicals in relevant cellular events, including their effects on genetic instability through (growth factors and tumor suppressor genes, their enhancement of mitogenic signals, and their participation in cell remodeling, proliferation, senescence, apoptosis, and autophagy processes; the possible relationship between free radicals and inflammation is also explored. This knowledge is crucial for evaluating the relevance of free radicals as therapeutic targets in cancer.

  3. Study of elementary transfer mechanisms during a collision between a swift multi-charged heavy ion and a neutral atom; Etude des mecanismes elementaires de transfert d`energie au cours d`une collision entre un ion lourd rapide multi-charge et un atome neutre

    Energy Technology Data Exchange (ETDEWEB)

    Jardin, P. [Caen Univ., 14 (France)

    1995-12-31

    This work is dedicated to the study of the energy transfer mechanisms which occur during a collision between a swift multicharged heavy ion and a neutral atom. The elementary energy energy transfer mechanisms (scattering, excitation, ionization, capture) and their consequences on the target velocity after the collision (recoil velocity) are recalled in the first chapter. In the case of small projectile diffusion angles, we show that the recoil velocity component, transverse to the incident projectile direction, results principally from the diffusion mechanism, while the longitudinal component is due essentially to the mass transfer and the inelastic energy transfer mechanisms. Since the target recoil velocities are very small, we have built an experimental set-up which reduces the impreciseness on their measurement due to the target thermal spread using, as targets, cooled atoms of a supersonic jet (temperature < 1 K). The association of time of flight and localisation techniques allows us, for each ionised target atom, to determine the three recoil velocity components with a very good accuracy (a few tens of meters per second). In chapter three, we describe the data analysis method. And then we present in the last chapter the results we have obtained for the collision systems Xe{sup 44+}(6.7 MeV/A) + Ar => Xe{sup 44} + Ar{sup q+}+qe{sup -} (q ranging from 1 to 7); Xe{sup 44+} (6.7 MeV/A) + He => Xe{sup 44+} He{sup 1+,2+}+1e{sup -},2e{sup -}. We show that it is possible to interpret the recoil velocity in terms of kinetic energy transferred to the target and to the electrons ejected from the target. (author) 44 refs.

  4. Theoretical Investigation of Kinetic Processes in Small Radicals of Importance in Combustion

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, Millard [Univ. of Maryland, College Park, MD (United States). Dept. of Chemistry and Biochemistry; Dagdigian, Paul J. [Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Chemistry

    2017-12-12

    Our group studies inelastic and reactive collisions of small molecules, focusing on radicals important in combustion environments. The goal is the better understanding of kinetic processes that may be difficult to access experimentally. An essential component is the accurate determination and fitting of potential energy surfaces (PESs). After fitting the ab initio points to obtain global PESs, we treat the dynamics using time-independent (close-coupling) methods. Cross sections and rate constants for collisions of are determined with our Hibridon program suite . We have studied energy transfer (rotationally, vibrationally, and/or electronically inelastic) in small hydrocarbon radicals (CH2 and CH3) and the CN radical. We have made a comparison with experimental measurements of relevant rate constants for collisions of these radicals. Also, we have calculated accurate transport properties using state-of-the-art PESs and to investigate the sensitivity to these parameters in 1-dimensional flame simulations. Of particular interest are collision pairs involving the light H atom.

  5. Synthesis, Radical Reactivity, and Thermochemistry of Monomeric Cu(II) Alkoxide Complexes Relevant to Cu/Radical Alcohol Oxidation Catalysis.

    Science.gov (United States)

    Porter, Thomas R; Capitao, Dany; Kaminsky, Werner; Qian, Zhaoshen; Mayer, James M

    2016-06-06

    Two new monomeric Cu(II) alkoxide complexes were prepared and fully characterized as models for intermediates in copper/radical mediated alcohol oxidation catalysis: Tp(tBuR)Cu(II)OCH2CF3 with Tp(tBu) = hydro-tris(3-tert-butyl-pyrazol-1-yl)borate 1 or Tp(tBuMe) = hydro-tris(3-tert-butyl-5-methyl-pyrazol-1-yl)borate 2. These complexes were made as models for potential intermediates in enzymatic and synthetic catalytic cycles for alcohol oxidation. However, the alkoxide ligands are not readily oxidized by loss of H; instead, these complexes were found to be hydrogen atom acceptors. They oxidize the hydroxylamine TEMPOH, 2,4,6-tri-t-butylphenol, and 1,4-cyclohexadiene to the nitroxyl radical, phenoxyl radical, and benzene, with formation of HOCH2CF3 (TFE) and the Cu(I) complexes Tp(tBuR)Cu(I)-MeCN in dichloromethane/1% MeCN or 1/2 [Tp(tBuR)Cu(I)]2 in toluene. On the basis of thermodynamics and kinetics arguments, these reactions likely proceed through concerted proton-electron transfer mechanisms. Thermochemical analyses give lower limits for the "effective bond dissociation free energies (BDFE)" of the O-H bonds in 1/2[Tp(tBuR)Cu(I)]2 + TFE and upper limits for the free energies associated with alkoxide oxidations via hydrogen atom transfer (effective alkoxide α-C-H BDFEs). These values are summations of the free energies of multiple chemical steps, which include the energetically favorable formation of 1/2[Tp(tBuR)Cu(I)]2. The effective alkoxide α-C-H bonds are very weak, BDFE ≤ 38 ± 4 kcal mol(-1) for 1 and ≤44 ± 5 kcal mol(-1) for 2 (gas-phase estimates), because C-H homolysis is thermodynamically coupled to one electron transfer to Cu(II) as well as the favorable formation of the 1/2[Tp(tBuR)Cu(I)]2 dimer. Treating 1 with the H atom acceptor (t)Bu3ArO(•) did not result in the expected alkoxide oxidation to an aldehyde, but rather net 2,2,2-trifluoroethoxyl radical transfer occurred to generate an unusual 2-substituted dienone-ether product. Treating 2

  6. Radical theory of rings

    CERN Document Server

    Gardner, JW

    2003-01-01

    Radical Theory of Rings distills the most noteworthy present-day theoretical topics, gives a unified account of the classical structure theorems for rings, and deepens understanding of key aspects of ring theory via ring and radical constructions. Assimilating radical theory's evolution in the decades since the last major work on rings and radicals was published, the authors deal with some distinctive features of the radical theory of nonassociative rings, associative rings with involution, and near-rings. Written in clear algebraic terms by globally acknowledged authorities, the presentation

  7. Radical Change by Entrepreneurial Design

    OpenAIRE

    Roberts, Nancy C.

    1998-01-01

    This article offers a conceptual framework to understand radical change. It opens with a typology that defines change in terms of its pace and scope, and defines radical change as the swift transformation of an entire system. How radical change in public policy has occurred in the past is then documented. We find examples of radical change by chance, radical change by consensus, radical change by learning, and radical change by entrepreneurial design. Radical chang...

  8. Lewis Structure Representation of Free Radicals Similar to ClO

    Science.gov (United States)

    Hirsch, Warren; Kobrak, Mark

    2007-01-01

    The study describes the Lewis structure representation of various free radicals, which are quite similar to the ClO radical and its isoelectronic analogues. The analysis of the periodic trends of these radicals shows that oxygen is the most electronegative atom among them.

  9. Exploring the electron transfer pathways in photosystem I by high-time-resolution electron paramagnetic resonance: observation of the B-side radical pair P700(+)A1B(-) in whole cells of the deuterated green alga Chlamydomonas reinhardtii at cryogenic temperatures.

    Science.gov (United States)

    Berthold, Thomas; von Gromoff, Erika Donner; Santabarbara, Stefano; Stehle, Patricia; Link, Gerhard; Poluektov, Oleg G; Heathcote, Peter; Beck, Christoph F; Thurnauer, Marion C; Kothe, Gerd

    2012-03-28

    Crystallographic models of photosystem I (PS I) highlight a symmetrical arrangement of the electron transfer cofactors which are organized in two parallel branches (A, B) relative to a pseudo-C2 symmetry axis that is perpendicular to the membrane plane. Here, we explore the electron transfer pathways of PS I in whole cells of the deuterated green alga Chlamydomonas reinhardtii using high-time-resolution electron paramagnetic resonance (EPR) at cryogenic temperatures. Particular emphasis is given to quantum oscillations detectable in the tertiary radical pairs P700(+)A1A(-) and P700(+)A1B(-) of the electron transfer chain. Results are presented first for the deuterated site-directed mutant PsaA-M684H in which electron transfer beyond the primary electron acceptor A0A on the PsaA branch of electron transfer is impaired. Analysis of the quantum oscillations, observed in a two-dimensional Q-band (34 GHz) EPR experiment, provides the geometry of the B-side radical pair. The orientation of the g tensor of P700(+) in an external reference system is adapted from a time-resolved multifrequency EPR study of deuterated and 15N-substituted cyanobacteria (Link, G.; Berthold, T.; Bechtold, M.; Weidner, J.-U.; Ohmes, E.; Tang, J.; Poluektov, O.; Utschig, L.; Schlesselman, S. L.; Thurnauer, M. C.; Kothe, G. J. Am. Chem. Soc. 2001, 123, 4211-4222). Thus, we obtain the three-dimensional structure of the B-side radical pair following photoexcitation of PS I in its native membrane. The new structure describes the position and orientation of the reduced B-side quinone A1B(-) on a nanosecond time scale after light-induced charge separation. Furthermore, we present results for deuterated wild-type cells of C. reinhardtii demonstrating that both radical pairs P700(+)A1A(-) and P700(+)A1B(-) participate in the electron transfer process according to a mole ratio of 0.71/0.29 in favor of P700(+)A1A(-). A detailed comparison reveals different orientations of A1A(-) and A1B(-) in their

  10. Explaining unexpected data via competitive equilibria and processes in radical reactions with reversible deactivation.

    Science.gov (United States)

    Konkolewicz, Dominik; Krys, Pawel; Matyjaszewski, Krzysztof

    2014-10-21

    lead to an acceleration of the reaction during the initial period. Similarly, in Cu mediated atom transfer radical polymerization (ATRP) with initiators for continuous radical regeneration (ICAR) initiated by a conventional radical initiator, the rate of polymerization should not depend on either the alkyl halide concentration or the Cu concentration. However, experiments show that the rate could be 10 times faster with alkyl halide than without alkyl halide. Finally, in aqueous media, the presence of active alkyl halides can appear to stop the disproportionation of Cu(I) complexes. These unusual data point to a more complex mechanism than originally envisioned, and in fact all these counterintuitive observations can be explained by the concept of competing equilibria and processes. In these cases, the presence of two or more reactions competing for the same reagent typically causes one pathway to dominate, while the rate of the other pathways are diminished. Alternatively, the competing pathways and processes can cause one or more reversible or pseudoreversible reactions to be imbalanced and lead to products distinct from the case where rates of forward and reverse reactions are balanced. In this Account, the concept of competitive processes and equilibria is developed and used to explain each of the unusual observations highlighted above.

  11. Improved Mechanical Performance Fracture Properties and Reliability of Radical-Cured Thermosets

    Energy Technology Data Exchange (ETDEWEB)

    Redline, Erica Marie [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bolintineanu, Dan S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lane, J. Matthew [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Stevens, Mark J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Alam, Todd M. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Celina, Mathias C. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2016-10-01

    The aim of this study was to alter polymerization chemistry to improve network homogeneity in free-radical crosslinked systems. It was hypothesized that a reduction in heterogeneity of the network would lead to improved mechanical performance. Experiments and simulations were carried out to investigate the connection between polymerization chemistry, network structure and mechanical properties. Experiments were conducted on two different monomer systems - the first is a single monomer system, urethane dimethacrylate (UDMA), and the second is a two-monomer system consisting of bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) in a ratio of 70/30 BisGMA/TEGDMA by weight. The methacrylate systems were crosslinked using traditional radical polymeriza- tion (TRP) with azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as an initiator; TRP systems were used as the control. The monomers were also cross-linked using activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) as a type of controlled radical polymerization (CRP). FTIR and DSC were used to monitor reac- tion kinetics of the systems. The networks were analyzed using NMR, DSC, X-ray diffraction (XRD), atomic force microscopy (AFM), and small angle X-ray scattering (SAXS). These techniques were employed in an attempt to quantify differences between the traditional and controlled radical polymerizations. While a quantitative methodology for characterizing net- work morphology was not established, SAXS and AFM have shown some promising initial results. Additionally, differences in mechanical behavior were observed between traditional and controlled radical polymerized thermosets in the BisGMA/TEGDMA system but not in the UDMA materials; this finding may be the result of network ductility variations between the two materials. Coarse-grained molecular dynamics simulations employing a novel model of the CRP reaction were carried out for

  12. Studies of transition states and radicals by negative ion photodetachment

    Energy Technology Data Exchange (ETDEWEB)

    Metz, Ricardo Baer [Univ. of California, Berkeley, CA (United States)

    1991-12-01

    Negative ion photodetachment is a versatile tool for the production and study of transient neutral species such as reaction intermediates and free radicals. Photodetachment of the stable XHY- anion provides a direct spectroscopic probe of the transition state region of the potential energy surface for the neutral hydrogen transfer reaction X + HY → XH + Y, where X and Y are halogen atoms. The technique is especially sensitive to resonances, which occur at a specific energy, but the spectra also show features due to direct scattering. We have used collinear adiabatic simulations of the photoelectron spectra to evaluate trail potential energy surfaces for the biomolecular reactions and have extended the adiabatic approach to three dimensions and used it to evaluate empirical potential energy surfaces for the I + Hl and Br + HI reactions. In addition, we have derived an empirical, collinear potential energy surface for the Br + HBr reaction that reproduces our experimental results and have extended this surface to three dimensions. Photodetachment of a negative ion can be also used to study neutral free radicals. We have studied the vibrational and electronic spectroscopy of CH2NO2 by photoelectron spectroscopy of CH2NO2-, determining the electron affinity of CH2NO2, gaining insight on the bonding of the 2B1 ground state and observing the 2A2 excited state for the first time. Negative ion photodetachment also provides a novel and versatile source of mass-selected, jet-cooled free radicals. We have studied the photodissociation of CH2NO2 at 270, 235, and 208 nm, obtaining information on the dissociation products by measuring the kinetic energy release in the photodissociation.

  13. Studies of transition states and radicals by negative ion photodetachment

    Energy Technology Data Exchange (ETDEWEB)

    Metz, R.B.

    1991-12-01

    Negative ion photodetachment is a versatile tool for the production and study of transient neutral species such as reaction intermediates and free radicals. Photodetachment of the stable XHY{sup {minus}} anion provides a direct spectroscopic probe of the transition state region of the potential energy surface for the neutral hydrogen transfer reaction X + HY {yields} XH + Y, where X and Y are halogen atoms. The technique is especially sensitive to resonances, which occur at a specific energy, but the spectra also show features due to direct scattering. We have used collinear adiabatic simulations of the photoelectron spectra to evaluate trail potential energy surfaces for the biomolecular reactions and have extended the adiabatic approach to three dimensions and used it to evaluate empirical potential energy surfaces for the I + Hl and Br + HI reactions. In addition, we have derived an empirical, collinear potential energy surface for the Br + HBr reaction that reproduces our experimental results and have extended this surface to three dimensions. Photodetachment of a negative ion can be also used to study neutral free radicals. We have studied the vibrational and electronic spectroscopy of CH{sub 2}NO{sub 2} by photoelectron spectroscopy of CH{sub 2}NO{sub 2}{sup {minus}}, determining the electron affinity of CH{sub 2}NO{sub 2}, gaining insight on the bonding of the {sup 2}B{sub 1} ground state and observing the {sup 2}A{sub 2} excited state for the first time. Negative ion photodetachment also provides a novel and versatile source of mass-selected, jet-cooled free radicals. We have studied the photodissociation of CH{sub 2}NO{sub 2} at 270, 235, and 208 nm, obtaining information on the dissociation products by measuring the kinetic energy release in the photodissociation.

  14. Generation and propagation of radical reactions on proteins

    DEFF Research Database (Denmark)

    Hawkins, C L; Davies, Michael Jonathan

    2001-01-01

    be propagated and transferred within protein structures. The emphasis of this article is primarily on the deleterious actions of radicals generated on proteins, and their mechanisms of action, rather than on enzymatic systems where radicals are deliberately formed as transient intermediates. The final section...

  15. Effective atomic number of some sugars and amino acids for scattering of (241)Am and (137)Cs gamma rays at low momentum transfer.

    Science.gov (United States)

    Vinaykumar, L; Umesh, T K

    2015-09-01

    In this paper, we report the effective atomic number of some H, C, N and O based sugars and amino acids. These have been determined by using a handy expression which is based on the theoretical angle integrated small angle (coherent+incoherent) scattering cross sections of seven elements of Z≤13 in four angular ranges of (0-4°), (0-6°), (0-8°) and (0-10°)for (241)Am (59.54 keV) and (137)Cs (661.6 keV) gamma rays. The theoretical scattering cross sections were computed by a suitable numerical integration of the atomic form factor and incoherent scattering function compilations of Hubbell et al. (1975) which make use of the non-relativistic Hartree-Fock (NRHF) model for the atomic charge distribution of the elements in the angular ranges of interest. The angle integrated small angle scattering cross sections of the H, C, N and O based sugars and amino acids measured by a new method reported recently by the authors were used in the handy expression to derive their effective atomic number. The results are compared with the other available data and discussed. Possible conclusions are drawn based on the present study. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Intracellular ROS protection efficiency and free radical-scavenging activity of curcumin.

    Directory of Open Access Journals (Sweden)

    Abolfazl Barzegar

    Full Text Available Curcumin has many pharmaceutical applications, many of which arise from its potent antioxidant properties. The present research examined the antioxidant activities of curcumin in polar solvents by a comparative study using ESR, reduction of ferric iron in aqueous medium and intracellular ROS/toxicity assays. ESR data indicated that the steric hindrance among adjacent big size groups within a galvinoxyl molecule limited the curcumin to scavenge galvinoxyl radicals effectively, while curcumin showed a powerful capacity for scavenging intracellular smaller oxidative molecules such as H₂O₂, HO•, ROO•. Cell viability and ROS assays demonstrated that curcumin was able to penetrate into the polar medium inside the cells and to protect them against the highly toxic and lethal effects of cumene hydroperoxide. Curcumin also showed good electron-transfer capability, with greater activity than trolox in aqueous solution. Curcumin can readily transfer electron or easily donate H-atom from two phenolic sites to scavenge free radicals. The excellent electron transfer capability of curcumin is because of its unique structure and different functional groups, including a β-diketone and several π electrons that have the capacity to conjugate between two phenyl rings. Therfore, since curcumin is inherently a lipophilic compound, because of its superb intracellular ROS scavenging activity, it can be used as an effective antioxidant for ROS protection within the polar cytoplasm.

  17. Glutathione--hydroxyl radical interaction: a theoretical study on radical recognition process.

    Directory of Open Access Journals (Sweden)

    Béla Fiser

    Full Text Available Non-reactive, comparative (2 × 1.2 μs molecular dynamics simulations were carried out to characterize the interactions between glutathione (GSH, host molecule and hydroxyl radical (OH(•, guest molecule. From this analysis, two distinct steps were identified in the recognition process of hydroxyl radical by glutathione: catching and steering, based on the interactions between the host-guest molecules. Over 78% of all interactions are related to the catching mechanism via complex formation between anionic carboxyl groups and the OH radical, hence both terminal residues of GSH serve as recognition sites. The glycine residue has an additional role in the recognition of OH radical, namely the steering. The flexibility of the Gly residue enables the formation of further interactions of other parts of glutathione (e.g. thiol, α- and β-carbons with the lone electron pair of the hydroxyl radical. Moreover, quantum chemical calculations were carried out on selected GSH/OH(• complexes and on appropriate GSH conformers to describe the energy profile of the recognition process. The relative enthalpy and the free energy changes of the radical recognition of the strongest complexes varied from -42.4 to -27.8 kJ/mol and from -21.3 to 9.8 kJ/mol, respectively. These complexes, containing two or more intermolecular interactions, would be the starting configurations for the hydrogen atom migration to quench the hydroxyl radical via different reaction channels.

  18. Iron-Mediated ICAR ATRP of Styrene and Methyl Methacrylate in the Absence of Thermal Radical Initiator.

    Science.gov (United States)

    Zhang, Lifen; Miao, Jie; Cheng, Zhenping; Zhu, Xiulin

    2010-02-02

    Initiators for continuous activator regeneration in atom transfer radical polymerization (ICAR ATRP) is a new technique for conducting ATRP. ICAR ATRP has many strong advantages over normal ATRP, such as forming the reductive transition metal species in situ using oxidatively stable transition metal species and a lower amount of metal catalyst in comparison with the normal ATRP system. In this work, the iron-mediated ICAR ATRP of styrene and methyl methacrylate are reported for the first time using oxidatively stable FeCl(3)  · 6H(2) O as the catalyst in the absence of any thermal radical initiator. The kinetics of the polymerizations and effect of different polymerization conditions are studied. It is found that the polymerization of styrene can be conducted well even if the amount of iron(III) is as low as 50 ppm. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Electron transfer reactions

    CERN Document Server

    Cannon, R D

    2013-01-01

    Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

  20. Comparison between Two Bromine Containing Free Radical Initiators in PRESAGE®

    Energy Technology Data Exchange (ETDEWEB)

    Park, Hyeonsuk; Ryu, Dongmin; Ye, Sung-Joon [Seoul National University, Seoul (Korea, Republic of)

    2016-10-15

    PRESAGE® is an optically clear 3-D polyurethane dosimeter which contains a halogenated carbon as a free radical initiator and leucomalachite dye. The change of the optical density is known to be linear with respect to the absorbed dose and the sensitivity is related to the carbon–halogen bond dissociation energy of the free radical initiator. Although there are some studies regarding free radical initiators and dye materials, there’s a lack of reports about the effect of other elements like LMG solvent which can be added when there’s a difficulty mixing materials. Also, there are some studies about comparison between free radicals with different kind of halogen atoms but there’s a lack of studies of comparison between initiators with the same halogen atom. In this experiments, two kinds of halocarbon free radical initiator with the same halogen atom (bromine) as well as the effect of the LMG solvent were studied to use the dosimeter as a therapeutic purpose. Effective atomic numbers were also calculated. The initiators with the same halogen atom, CBr{sub 4} and C{sub 2}H{sub 2}Br{sub 4}, reacted totally differently. CBr{sub 4} was more sensitive to the radiation and emitted maximum 4 times more free radicals upon irradiation with no additional effective atomic number but the absorbance after irradiation was highly variable with time. For stable measurement, C{sub 2}H{sub 2}Br{sub 4} would be more appropriate as a free radical initiator.

  1. Online Radicalization: Bangladesh Perspective

    Science.gov (United States)

    2017-06-09

    develop a sustainable counter radicalization mechanism without impinging citizens’ democratic rights. 15. SUBJECT TERMS Bangladesh, cyber, online, social... sustainable counter radicalization mechanism without impinging citizens’ democratic rights. v ACKNOWLEDGMENTS At first, I would like to convey my... restaurant in the Dhaka diplomatic zone that became a lead story in the world media. The Government of Bangladesh claims the militants to be home-grown

  2. Orgasm after radical prostatectomy

    NARCIS (Netherlands)

    Koeman, M; VanDriel, MF; Schultz, WCMW; Mensink, HJA

    Objective To evaluate the ability to obtain and the quality of orgasm after radical prostatectomy, Patients and methods The orgasms experienced after undergoing radical prostatectomy were evaluated in 20 men (median age 65 years, range 56-76) using a semi-structured interview and a self-administered

  3. Exploring possible reaction pathways for the o-atom transfer reactions to unsaturated substrates catalyzed by a [Ni-NO2] ↔ [Ni-NO] redox couple using DFT methods.

    Science.gov (United States)

    Tsipis, Athanassios C

    2017-07-15

    The (nitro)(N-methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] complex catalyses efficiently the O-atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] ↔ Ni(NO 2 )(S 2 CNHMe)(PMe 3 ) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five-member metallacycle intermediate, via a [3 + 2] cyclo-addition reaction of HC≡CH to the Ni-N = O moiety of the Ni(NO 2 )(S 2 CNHMe)(PMe 3 )] complex, followed by a β H-atom migration toward the C α carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( κN1-NO 2 )(S 2 CNHMe)(PMe 3 )] ⇌ [Ni( κO,O2-ONO)(S 2 CNHMe)(PMe 3 )] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  4. Carbonyl Activation by Borane Lewis Acid Complexation: Transition States of H2Splitting at the Activated Carbonyl Carbon Atom in a Lewis Basic Solvent and the Proton-Transfer Dynamics of the Boroalkoxide Intermediate.

    Science.gov (United States)

    Heshmat, Mojgan; Privalov, Timofei

    2017-07-06

    By using transition-state (TS) calculations, we examined how Lewis acid (LA) complexation activates carbonyl compounds in the context of hydrogenation of carbonyl compounds by H 2 in Lewis basic (ethereal) solvents containing borane LAs of the type (C 6 F 5 ) 3 B. According to our calculations, LA complexation does not activate a ketone sufficiently enough for the direct addition of H 2 to the O=C unsaturated bond; but, calculations indicate a possibly facile heterolytic cleavage of H 2 at the activated and thus sufficiently Lewis acidic carbonyl carbon atom with the assistance of the Lewis basic solvent (i.e., 1,4-dioxane or THF). For the solvent-assisted H 2 splitting at the carbonyl carbon atom of (C 6 F 5 ) 3 B adducts with different ketones, a number of TSs are computed and the obtained results are related to insights from experiment. By using the Born-Oppenheimer molecular dynamics with the DFT for electronic structure calculations, the evolution of the (C 6 F 5 ) 3 B-alkoxide ionic intermediate and the proton transfer to the alkoxide oxygen atom were investigated. The results indicate a plausible hydrogenation mechanism with a LA, that is, (C 6 F 5 ) 3 B, as a catalyst, namely, 1) the step of H 2 cleavage that involves a Lewis basic solvent molecule plus the carbonyl carbon atom of thermodynamically stable and experimentally identifiable (C 6 F 5 ) 3 B-ketone adducts in which (C 6 F 5 ) 3 B is the "Lewis acid promoter", 2) the transfer of the solvent-bound proton to the oxygen atom of the (C 6 F 5 ) 3 B-alkoxide intermediate giving the (C 6 F 5 ) 3 B-alcohol adduct, and 3) the S N 2-style displacement of the alcohol by a ketone or a Lewis basic solvent molecule. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. On the Radicalization Process.

    Science.gov (United States)

    Leistedt, Samuel J

    2016-11-01

    This study aimed to provide an in-depth description of the radicalization process, which is a very important step in terrorist activities. The author proposes a translational analysis that is first based on the author's experience in the psychological evaluation of terrorist behavior and second on an exhaustive review of the current literature. The search terms "terrorism," "radicalization," "social psychology," and "psychopathology" were used to identify relevant studies in the following databases: Scopus, Medline, PubCentral, and Science Direct. Because of its importance, understanding radicalization process should be one of the priorities of behavioral scientists. International studies should be performed with a focus on several aspects, such as radicalization risk factors, brainwashing, the role of the media, and finally, in de-radicalization programs. © 2016 American Academy of Forensic Sciences.

  6. Beer thiol-containing compounds and redox stability: kinetic study of 1-hydroxyethyl radical scavenging ability.

    Science.gov (United States)

    de Almeida, Natália E C; Lund, Marianne N; Andersen, Mogens L; Cardoso, Daniel R

    2013-10-02

    The 1-hydroxyethyl radical is a central intermediate in oxidative reactions occurring in beer. The reactivity of thiol-containing compounds toward 1-hydroxyethyl radical was evaluated in beer model solutions using a competitive kinetic approach, employing the spin-trap 4-POBN as a probe and by using electron paramagnetic resonance to detect the generated 1-hydroxyethyl/4-POBN spin adduct. Thiol-containing compounds were highly reactive toward the 1-hydroxyethyl radical with apparent second-order rate constants close to the diffusion limit in water and ranging from 0.5 × 10⁹ L mol⁻¹ s⁻¹ for the His-Cys-Lys-Phe-Trp-Trp peptide to 6.1 × 10⁹ L mol⁻¹ s⁻¹ for the reduced lipid transfer protein 1 (LTP1) isolated from beer. The reactions gave rise to a moderate kinetic isotope effect (k(H)/k(D) = 2.3) suggesting that reduction of the 1-hydroxyethyl radical by thiol-containing compounds takes place by hydrogen atom abstraction from the RSH group rather than electron transfer. The content of reduced thiols in different beers was determined using a previously established method based on ThioGlo-1 as the thiol derivatization reagent and detection of the derivatized thiols by reverse-phase liquid chromatography coupled to a fluorescence detector. The total level of thiol in beer (oxidized and reduced) was determined after a reduction step employing 3,3',3″-phosphanetriyltripropanoic acid (TCEP) as the disulfide reductant. A good correlation among total protein and total thiol content in different beers was observed. The results suggest a similar ratio between reduced thiols and disulfides in all of the tested beers, which indicates a similar redox state.

  7. Linear Atom Guides: Guiding Rydberg Atoms and Progress Toward an Atom Laser

    Science.gov (United States)

    Traxler, Mallory A.

    In this thesis, I explore a variety of experiments within linear, two-wire, magnetic atom guides. Experiments include guiding of Rydberg atoms; transferring between states while keeping the atoms contained within the guide; and designing, constructing, and testing a new experimental apparatus. The ultimate goal of the atom guiding experiments is to develop a continuous atom laser. The guiding of 87Rb 59D5/2 Rydberg atoms is demonstrated. The evolution of the atoms is driven by the combined effects of dipole forces acting on the center-of-mass degree of freedom as well as internal-state transitions. Time delayed microwave and state-selective field ionization, along with ion detection, are used to investigate the evolution of the internal-state distribution as well as the Rydberg atom motion while traversing the guide. The observed decay time of the guided-atom signal is about five times that of the initial state. A population transfer between Rydberg states contributes to this lengthened lifetime, and also broadens the observed field ionization spectrum. The population transfer is attributed to thermal transitions and, to a lesser extent, initial state-mixing due to Rydberg-Rydberg collisions. Characteristic signatures in ion time-of-flight signals and spatially resolved images of ion distributions, which result from the coupled internal-state and center-of-mass dynamics, are discussed. Some groups have used a scheme to make BECs where atoms are optically pumped from one reservoir trap to a final state trap, irreversibly transferring those atoms from one trap to the other. In this context, transfer from one guided ground state to another is studied. In our setup, before the atoms enter the guide, they are pumped into the | F = 1, mF = --1> state. Using two repumpers, one tuned to the F = 1 → F' = 0 transition (R10) and the other tuned to the F = 1 → F' = 2 transition (R12), the atoms are pumped between these guided states. Magnetic reflections within the guide

  8. Atomic polarizabilities

    Energy Technology Data Exchange (ETDEWEB)

    Safronova, M. S. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Mitroy, J. [School of Engineering, Charles Darwin University, Darwin NT 0909 (Australia); Clark, Charles W. [Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, Gaithersburg, Maryland 20899-8410 (United States); Kozlov, M. G. [Petersburg Nuclear Physics Institute, Gatchina 188300 (Russian Federation)

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  9. Atomic Physics

    CERN Document Server

    Foot, Christopher J

    2007-01-01

    This text will thoroughly update the existing literature on atomic physics. Intended to accompany an advanced undergraduate course in atomic physics, the book will lead the students up to the latest advances and the applications to Bose-Einstein Condensation of atoms, matter-wave inter-ferometry and quantum computing with trapped ions. The elementary atomic physics covered in the early chapters should be accessible to undergraduates when they are first introduced to the subject. To complement. the usual quantum mechanical treatment of atomic structure the book strongly emphasizes the experimen

  10. The Origins of Radical Inventions

    OpenAIRE

    SCHOENMAKERS, Wilfred; DUYSTERS, Geert; VANHAVERBEKE, Wim

    2008-01-01

    This paper looks at the special characteristics of radical inventions. It tries to identify those variables that differentiate radical inventions from non-radical inventions. Since radical inventions are very important for the economy as a whole and for the individual firm performances, understanding what makes radical inventions differ from non-radical inventions is very important. For our research we made use of the EPO (European Patent Office) database on patents. We used the number of for...

  11. The Nature of Radical Inventions

    OpenAIRE

    SCHOENMAKERS, Wilfred

    2007-01-01

    Inventions come in many different forms ranging from incremental technical change to radical inventions. Radical inventions are very important for industry competition as well as for individual firm survival. In spite of many theoretical discussions on the effect of radical inventions the specific nature of radical inventions has so far remained relatively unclear. We try to shed some light on the nature of these radical inventions by investigating a group of radical, as well as a group of no...

  12. Ultracold atoms on atom chips

    DEFF Research Database (Denmark)

    Krüger, Peter; Hofferberth, S.; Haller, E.

    2005-01-01

    Miniaturized potentials near the surface of atom chips can be used as flexible and versatile tools for the manipulation of ultracold atoms on a microscale. The full scope of possibilities is only accessible if atom-surface distances can be reduced to microns. We discuss experiments in this regime...

  13. Radical chemistry of artemisinin

    Energy Technology Data Exchange (ETDEWEB)

    Denisov, Evgenii T; Solodova, S L; Denisova, Taisa G [Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region (Russian Federation)

    2010-12-29

    The review summarizes physicochemical characteristics of the natural sesquiterpene peroxide artemisinin. The kinetic schemes of transformations of artemisinin radicals under anaerobic conditions are presented and analyzed. The sequence of radical reactions of artemisinin in the presence of oxygen is considered in detail. Special emphasis is given to the intramolecular chain oxidation resulting in the transformation of artemisinin into polyatomic hydroperoxide. The kinetic characteristics of elementary reaction steps involving alkyl, alkoxyl, and peroxyl radicals generated from artemisinin are discussed. The results of testing of artemisinin and its derivatives for the antimalarial activity and the scheme of the biochemical synthesis of artemisinin in nature are considered.

  14. Gnosticism and Radical Feminism

    DEFF Research Database (Denmark)

    Cahana, Jonathan

    2016-01-01

    and radical feminism would easily fall under this definition. There is, however, one major difference: since radical feminism is a relatively recent phenomenon which also benefited from modern modes of text production and preservation, almost all of the sources are still with us. This, in turn, may allow us...... to use radical feminism to make certain aspects of ancient Gnosticism re-emerge from their long submersion, provided that enough similarities can be independently drawn between the two phenomena to merit such a comparison. This paper therefore presents a comparison between concepts and positions...

  15. Homegrown religious radicalization

    DEFF Research Database (Denmark)

    Khawaja, Iram

    It has been reported that a growing number of youngsters from Western Europe are engaging in conflicts motivated by religious and political conflicts in the Middle East. This paper explores the reasons behind this seemingly religious radicalization from the point of view of the youngsters...... youngsters and parents of youngsters who have chosen a radicalized path in life. The paper will shed light on how the sense of and yearning for belonging and recognition have to be taken into account in our understanding of homegrown religious radicalization...

  16. Aminoxyl (nitroxyl) radicals in the early decomposition of the nitramine RDX.

    Science.gov (United States)

    Irikura, Karl K

    2013-03-14

    The explosive nitramine RDX (1,3,5-trinitrohexahydro-s-triazine) is thought to decompose largely by homolytic N-N bond cleavage, among other possible initiation reactions. Density-functional theory (DFT) calculations indicate that the resulting secondary aminyl (R2N·) radical can abstract an oxygen atom from NO2 or from a neighboring nitramine molecule, producing an aminoxyl (R2NO·) radical. Persistent aminoxyl radicals have been detected in electron-spin resonance (ESR) experiments and are consistent with autocatalytic "red oils" reported in the experimental literature. When the O-atom donor is a nitramine, a nitrosamine is formed along with the aminoxyl radical. Reactions of aminoxyl radicals can lead readily to the "oxy-s-triazine" product (as the s-triazine N-oxide) observed mass-spectrometrically by Behrens and co-workers. In addition to forming aminoxyl radicals, the initial aminyl radical can catalyze loss of HONO from RDX.

  17. Structure of the biliverdin radical intermediate in phycocyanobilin:ferredoxin oxidoreductase identified by high-field EPR and DFT.

    Science.gov (United States)

    Stoll, Stefan; Gunn, Alexander; Brynda, Marcin; Sughrue, Wesley; Kohler, Amanda C; Ozarowski, Andrew; Fisher, Andrew J; Lagarias, J Clark; Britt, R David

    2009-02-11

    The cyanobacterial enzyme phycocyanobilin:ferredoxin oxidoreductase (PcyA) catalyzes the two-step four-electron reduction of biliverdin IXalpha to phycocyanobilin, the precursor of biliprotein chromophores found in phycobilisomes. It is known that catalysis proceeds via paramagnetic radical intermediates, but the structure of these intermediates and the transfer pathways for the four protons involved are not known. In this study, high-field electron paramagnetic resonance (EPR) spectroscopy of frozen solutions and single crystals of the one-electron reduced protein-substrate complex of two PcyA mutants D105N from the cyanobacteria Synechocystis sp. PCC6803 and Nostoc sp. PCC7120 are examined. Detailed analysis of Synechocystis D105N mutant spectra at 130 and 406 GHz reveals a biliverdin radical with a very narrow g tensor with principal values 2.00359(5), 2.00341(5), and 2.00218(5). Using density-functional theory (DFT) computations to explore the possible protonation states of the biliverdin radical, it is shown that this g tensor is consistent with a biliverdin radical where the carbonyl oxygen atoms on both the A and the D pyrrole rings are protonated. This experimentally confirms the reaction mechanism recently proposed (Tu, et al. Biochemistry 2007, 46, 1484).

  18. The structure of the biliverdin radical intermediate in phycocyanobilin:ferredoxin oxidoreductase identified by high-field EPR and DFT

    Science.gov (United States)

    Stoll, Stefan; Gunn, Alexander; Brynda, Marcin; Sughrue, Wesley; Kohler, Amanda C.; Ozarowski, Andrew; Fisher, Andrew J.; Lagarias, J. Clark; Britt, R. David

    2009-01-01

    The cyanobacterial enzyme phycocyanobilin:ferredoxin oxidoreductase (PcyA) catalyzes the two-step four-electron reduction of biliverdin IXα to phycocyanobilin, the precursor of biliprotein chromophores found in phycobilisomes. It is known that catalysis proceeds via paramagnetic radical intermediates, but the structure of these intermediates and the transfer pathways for the four protons involved are not known. In this study, high-field electron paramagnetic resonance (EPR) spectroscopy of frozen solutions and single crystals of the one-electron reduced protein-substrate complex of two PcyA mutants D105N from the cyanobacteria Synechocystis sp. PCC6803 and Nostoc sp. PCC7120 are examined. Detailed analysis of Synechocystis D105N mutant spectra at 130 GHz and 406 GHz reveals a biliverdin radical with a very narrow g tensor with principal values 2.00359(5), 2.00341(5) and 2.00218(5). Using density-functional theory (DFT) computations to explore the possible protonation states of the biliverdin radical, it is shown that this g tensor is consistent with a biliverdin radical where the carbonyl oxygen atoms on both the A and the D pyrrole rings are protonated. This experimentally confirms the reaction mechanism recently proposed (Tu et al, Biochemistry 2007, 46, 1484). PMID:19159240

  19. Spectroscopic Evidence for Through-Space Arene-Sulfur-Arene Bonding Interaction in m-Terphenyl Thioether Radical Cations.

    Science.gov (United States)

    Monney, Nicolas P-A; Bally, Thomas; Yamamoto, Takuhei; Glass, Richard S

    2015-12-31

    Electronic absorption spectra and quantum chemical calculations of the radical cations of m-terphenyl tert-butyl thioethers, where the S-t-Bu bond is forced to be perpendicular to the central phenyl ring, show the occurrence of through-space [π···S···π](+) bonding interactions which lead to a stabilization of the thioether radical cations. In the corresponding methyl derivatives there is a competition between delocalization of the hole that is centered on a p-AO of the S atom into the π-system of the central phenyl ring or through space into the flanking phenyl groups, which leads to a mixture of planar and perpendicular conformations in the radical cation. Adding a second m-terphenyl tert-butyl thioether moiety does not lead to further delocalization; the spin and charge remain in one of the two halves of the radical cation. These findings have interesting implications with regard to the role of methionines as hopping stations in electron transfer through proteins.

  20. Atom transfer as a preparative tool in coordination chemistry. Synthesis and characterization of Cr(V) nitrido complexes of bidentate ligands

    DEFF Research Database (Denmark)

    Birk, Torben; Bendix, Jesper

    2003-01-01

    The transfer of a terminal nitrido ligand from MnV(N)(salen) to Cr(III) complexes is explored as a new preparative route to CrV nitrido complexes. Reaction of MnV(N)(salen) with labile CrCl3(THF)3 in acetonitrile solution precipitate [Mn(Cl)(salen)]·(CH3CN) and yields a solution containing a mixt...

  1. UV-Induced Hydrogen-Atom-Transfer Processes in 3-Thio-1,2,4-triazole Isolated in Ar and H2 Low-Temperature Matrixes.

    Science.gov (United States)

    Rostkowska, Hanna; Lapinski, Leszek; Nowak, Maciej J

    2017-09-21

    The UV-induced thione → thiol phototautomeric reaction has been studied for monomeric 3-thio-1,2,4-triazole (3-ST) isolated in low-temperature Ar and n-H2 (normal hydrogen) matrixes. Prior to any UV irradiation, monomers of 3-ST isolated in solid Ar or solid n-H2 adopted mainly the most stable thione tautomeric form, as revealed by the IR spectra. Upon UV (λ > 275 nm) irradiation of 3-ST isolated in Ar matrixes, the IR bands due to this thione form decreased, while a set of initially weak bands increased in intensity. Growing bands indicated generation of a photoproduct, which was identified as the thiol tautomer with labile hydrogen atoms attached to sulfur and N(2) atoms. The UV-induced spectral changes allowed also identification of another minor thiol tautomer of 3-ST, which was present in the matrix prior to any irradiation and did not change its population upon exposure to UV light. The identification of the observed isomeric forms was supported by comparison of their separated experimental IR spectra with the spectra theoretically predicted for the various structures of 3-ST. The thione → thiol phototautomerization that was the main UV-induced process observed for 3-ST in Ar matrixes did not occur for monomers of the compound trapped in solid n-H2.

  2. Study of atomic and condensed atomic indices for reactive sites of ...

    Indian Academy of Sciences (India)

    In this paper, we have introduced the atomic descriptors () to determine the local reactive sites of the molecular systems during electrophilic, nucleophilic and radical attacks. The condensed Fukui function and the newly introduced condensed atomic descriptor have been calculated for six different systems, namely ...

  3. Formation and stabilization of persistent free radicals

    Science.gov (United States)

    Dellinger, Barry; Lomnicki, Slawomir; Khachatryan, Lavrent; Maskos, Zofia; Hall, Randall W.; Adounkpe, Julien; McFerrin, Cheri; Truong, Hieu

    2014-01-01

    We demonstrate that stable and relatively unreactive “environmentally persistent free radicals (PFRs)” can be readily formed in the post-flame and cool-zone regions of combustion systems and other thermal processes. These resonance-stabilized radicals, including semiquinones, phenoxyls, and cyclopentadienyls, can be formed by the thermal decomposition of molecular precursors including catechols, hydroquinones and phenols. Association with the surfaces of fine particles imparts additional stabilization to these radicals such that they can persist almost indefinitely in the environment. A mechanism of chemisorption and electron transfer from the molecular adsorbate to a redox-active transition metal or other receptor is shown through experiment, and supported by molecular orbital calculations, to result in PFR formation. Both oxygen-centered and carbon-centered PFRs are possible that can significantly affect their environmental and biological reactivity. PMID:25598747

  4. Radical prostatectomy - discharge

    Science.gov (United States)

    ... to 6 months. You will learn exercises (called Kegel exercises) that strengthen the muscles in your pelvis. ... Radical prostatectomy Retrograde ejaculation Urinary incontinence Patient Instructions Kegel exercises - self-care Suprapubic catheter care Urinary catheters - ...

  5. Structural features, kinetics and SAR study of radical scavenging and antioxidant activities of phenolic and anilinic compounds.

    Science.gov (United States)

    Ali, Hussein M; Abo-Shady, Ahmed; Sharaf Eldeen, Hany A; Soror, Hany A; Shousha, Wafaa G; Abdel-Barry, Osama A; Saleh, Ahmed M

    2013-03-16

    Phenolic compounds are widely distributed in plant kingdom and constitute one of the most important classes of natural and synthetic antioxidants. In the present study fifty one natural and synthetic structurally variant phenolic, enolic and anilinic compounds were examined as antioxidants and radical scavengers against DPPH, hydroxyl and peroxyl radicals. The structural diversity of the used phenolic compounds includes monophenols with substituents frequently present in natural phenols e.g. alkyl, alkoxy, ester and carboxyl groups, besides many other electron donating and withdrawing groups, in addition to polyphenols with 1-3 hydroxyl groups and aminophenols. Some common groups e.g. alkyl, carboxyl, amino and second OH groups were incorporated in ortho, meta and para positions. SAR study indicates that the most important structural feature of phenolic compounds required to possess good antiradical and antioxidant activities is the presence of a second hydroxyl or an amino group in o- or p-position because of their strong electron donating effect in these positions and the formation of a stable quinone-like products upon two hydrogen-atom transfer process; otherwise, the presence of a number of alkoxy (in o or p-position) and /or alkyl groups (in o, m or p-position) should be present to stabilize the resulted phenoxyl radical and reach good activity. Anilines showed also similar structural feature requirements as phenols to achieve good activities, except o-diamines which gave low activity because of the high energy of the resulted 1,2-dimine product upon the 2H-transfer process. Enols with ene-1,2-diol structure undergo the same process and give good activity. Good correlations were obtained between DPPH inhibition and inhibition of both OH and peroxyl radicals. In addition, good correlations were obtained between DPPH inhibition and antioxidant activities in sunflower oil and liver homogenate systems. In conclusion, the structures of good anti radical and

  6. Violent Radicalization in Europe

    DEFF Research Database (Denmark)

    Dalgaard-Nielsen, Anja

    2010-01-01

    and foiled plots inspired by militant Islamism have grabbed European and American headlines. This article identifies and discusses empirical studies of radicalization and points to the strengths as well as the weaknesses characterizing these studies. The aim is to take stock of the current state of research...... within this field and to answer the question: From an empirical point of view, what is known and what is not known about radicalization connected to militant Islamism in Europe?...

  7. Photo-induced free radicals on a simulated Martian surface

    Science.gov (United States)

    Tseng, S.-S.; Chang, S.

    1974-01-01

    Results of an electron spin resonance study of free radicals in the ultraviolet irradiation of a simulated Martian surface suggest that the ultraviolet photolysis of CO or CO2, or a mixture of both, adsorbed on silica gel at minus 170 C involves the formation of OH radicals and possibly of H atoms as the primary process, followed by the formation of CO2H radicals. It is concluded that the photochemical synthesis of organic compounds could occur on Mars if the siliceous surface dust contains enough silanol groups and/or adsorbed H2O in the form of bound water.

  8. Transverse flow reactor studies of the dynamics of radical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Macdonald, R.G. [Argonne National Laboratory, IL (United States)

    1993-12-01

    Radical reactions are in important in combustion chemistry; however, little state-specific information is available for these reactions. A new apparatus has been constructed to measure the dynamics of radical reactions. The unique feature of this apparatus is a transverse flow reactor in which an atom or radical of known concentration will be produced by pulsed laser photolysis of an appropriate precursor molecule. The time dependence of individual quantum states or products and/or reactants will be followed by rapid infrared laser absorption spectroscopy. The reaction H + O{sub 2} {yields} OH + O will be studied.

  9. A direct investigation of photocharge transfer across monomolecular layer between C60 and CdS quantum dots by photoassisted conductive atomic force microscopy

    Directory of Open Access Journals (Sweden)

    Xiaohong Jiang

    2016-04-01

    Full Text Available The composite assembly of C60 and CdS Quantum Dots (QDs on ITO substrate was prepared by Langmuir-Blodgett (LB technique using arachic acid (AA, stearic acid (SA and octadecanyl amine (OA as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V measurements on both the CdS QDs and the composite assembly of C60/CdS. The result make it clear that the CdS, C60/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

  10. A direct investigation of photocharge transfer across monomolecular layer between C{sub 60} and CdS quantum dots by photoassisted conductive atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xiaohong; Liu, He; Zhang, Xingtang; Cheng, Gang; Wang, Shujie; Du, Zuliang, E-mail: zld@henu.edu.cn [Key Laboratory for Special Functional Materials, Collaborative Innovation Center of Nano Functional Materials and Applications, Henan University, Kaifeng, 475004, PR. China (China)

    2016-04-15

    The composite assembly of C{sub 60} and CdS Quantum Dots (QDs) on ITO substrate was prepared by Langmuir-Blodgett (LB) technique using arachic acid (AA), stearic acid (SA) and octadecanyl amine (OA) as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V) measurements on both the CdS QDs and the composite assembly of C{sub 60}/CdS. The result make it clear that the CdS, C{sub 60}/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

  11. Redox-neutral rhodium-catalyzed C-H functionalization of arylamine N-oxides with diazo compounds: primary C(sp(3))-H/C(sp(2))-H activation and oxygen-atom transfer.

    Science.gov (United States)

    Zhou, Bing; Chen, Zhaoqiang; Yang, Yaxi; Ai, Wen; Tang, Huanyu; Wu, Yunxiang; Zhu, Weiliang; Li, Yuanchao

    2015-10-05

    An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by-products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp(3) )H bond and C(sp(2) )H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)-catalyzed coupling of readily available tertiary aniline N-oxides with α-diazomalonates was also developed under external oxidant-free conditions to access various aminomandelic acid derivatives by an O-atom-transfer reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Functional Interfaces Constructed by Controlled/Living Radical Polymerization for Analytical Chemistry.

    Science.gov (United States)

    Wang, Huai-Song; Song, Min; Hang, Tai-Jun

    2016-02-10

    The high-value applications of functional polymers in analytical science generally require well-defined interfaces, including precisely synthesized molecular architectures and compositions. Controlled/living radical polymerization (CRP) has been developed as a versatile and powerful tool for the preparation of polymers with narrow molecular weight distributions and predetermined molecular weights. Among the CRP system, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) are well-used to develop new materials for analytical science, such as surface-modified core-shell particles, monoliths, MIP micro- or nanospheres, fluorescent nanoparticles, and multifunctional materials. In this review, we summarize the emerging functional interfaces constructed by RAFT and ATRP for applications in analytical science. Various polymers with precisely controlled architectures including homopolymers, block copolymers, molecular imprinted copolymers, and grafted copolymers were synthesized by CRP methods for molecular separation, retention, or sensing. We expect that the CRP methods will become the most popular technique for preparing functional polymers that can be broadly applied in analytical chemistry.

  13. D/sup -/ production by multiple charge-transfer collisions of low-energy D ions and atoms in cesium vapor

    Energy Technology Data Exchange (ETDEWEB)

    Hooper, E.B. Jr.; Willmann, P.A.; Schlachter, A.S.

    1978-01-22

    The production of D/sup -/ by multiple charge-transfer collisions of a D/sup +/ beam in a cesium-vapor target is considered for D/sup +/ energies above 300 eV. The cross sections relevant to D/sup -/ formation are obtained by a least-squares fit of three-charge-state differential equations to experimental yield curves. Implications for production of intense negative-ion beams are discussed, and speculations are made about extrapolation to lower engeries.

  14. Free Radical Reactions in Food.

    Science.gov (United States)

    Taub, Irwin A.

    1984-01-01

    Discusses reactions of free radicals that determine the chemistry of many fresh, processed, and stored foods. Focuses on reactions involving ascorbic acid, myoglobin, and palmitate radicals as representative radicals derived from a vitamin, metallo-protein, and saturated lipid. Basic concepts related to free radical structure, formation, and…

  15. Atomic physics

    CERN Document Server

    Born, Max

    1969-01-01

    The Nobel Laureate's brilliant exposition of the kinetic theory of gases, elementary particles, the nuclear atom, wave-corpuscles, atomic structure and spectral lines, electron spin and Pauli's principle, quantum statistics, molecular structure and nuclear physics. Over 40 appendices, a bibliography, numerous figures and graphs.

  16. Early Atomism

    Indian Academy of Sciences (India)

    http://www.ias.ac.in/article/fulltext/reso/015/10/0905-0925. Keywords. Atomic theory; Avogadro's hypothesis; atomic weights; periodic table; valence; molecular weights; molecular formula; isomerism. Author Affiliations. S Ramasesha1. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, ...

  17. Electron transfer in systems of well-defined geometry

    Energy Technology Data Exchange (ETDEWEB)

    Overfield, R.E.; Kaufmann, K.J.; Wasielewski, M.R.

    1980-01-01

    Two mesopyropheophorbide macrocycles can be joined via two covalent linkages to produce a cyclophane. It is possible to insert one or two Mg atoms into the cyclophane. The Qy transitions of the macrocycles are nearly orthogonal. The visible absorption spectrum of the monometal cyclophane is nearly a superposition of the spectra of the monomers. Emission from the monometal cyclophane arises primarily from the red most absorbing chromophore. The excited state difference spectrum shows that both macrocycles are excited. Fluorescence lifetimes of the monometal cyclophane decrease with increasing dielectric strength. Changes in the fluorescence and the triplet yield parallel the shortening of the singlet lifetime. Thus the radiative rate is solvent independent. This is in contrast to what one would expect if the emitting state had charge transfer character. Since the fluorescence lifetime is dependent on dielectric, the nonradiative relaxation from the singlet state is due to formation of a radical pair. The decay rate of the postulated radical pair was monitored by observing the kinetics of ground state repopulation. For the geometry of this cyclophane, electron transfer proceeds relatively slowly (k = 3 x 10/sup 9/ sec/sup -1/) in the forward direction. Modeling calculations indicate that the rate of annihilation of the radical pair may decrease as the solvent dielectric decreases.

  18. Laparoscopic radical trachelectomy.

    Science.gov (United States)

    Rendón, Gabriel J; Ramirez, Pedro T; Frumovitz, Michael; Schmeler, Kathleen M; Pareja, Rene

    2012-01-01

    The standard treatment for patients with early-stage cervical cancer has been radical hysterectomy. However, for women interested in future fertility, radical trachelectomy is now considered a safe and feasible option. The use of minimally invasive surgical techniques to perform this procedure has recently been reported. We report the first case of a laparoscopic radical trachelectomy performed in a developing country. The patient is a nulligravid, 30-y-old female with stage IB1 adenocarcinoma of the cervix who desired future fertility. She underwent a laparoscopic radical trachelectomy and bilateral pelvic lymph node dissection. The operative time was 340 min, and the estimated blood loss was 100mL. There were no intraoperative or postoperative complications. The final pathology showed no evidence of residual disease, and all pelvic lymph nodes were negative. At 20 mo of follow-up, the patient is having regular menses but has not yet attempted to become pregnant. There is no evidence of recurrence. Laparoscopic radical trachelectomy with pelvic lymphadenectomy in a young woman who desires future fertility may also be an alternative technique in the treatment of early cervical cancer in developing countries.

  19. Thematic planning: the role of the International Atomic Energy Agency in promoting education, medical research, and technology transfer among nuclear medicine communities of developing countries.

    Science.gov (United States)

    Padhy, Ajit Kumar; Dondi, Maurizio

    2008-03-01

    One of the major mechanisms of implementing the International Atomic Energy Agency's (IAEA) programs in nuclear medicine has been through coordinated research projects (CRPs). In recent years, the IAEA has initiated a new type of CRP, called Doctoral CRP, in an attempt to further improve the effectiveness of its programs. The structure of the Doctoral CRP has been built on the structure of the existing CRP concept, but with a broader "thematic" approach. The word "thematic" indicates that these CRPs should both have a fairly broad scope and be designed so that their outcome, in terms of practical applications, might readily fit into the selected nuclear applications that are offered to Member States under the IAEA's mechanism for thematic planning. The Nuclear Medicine Section of IAEA's Division of Human Health initiated the first Doctoral CRP of IAEA in the year 2000, entitled, "Management of Liver Cancer Using Radionuclide Methods with Special Emphasis on Trans-Arterial Radio-conjugate Therapy and Internal Dosimetry." Since then, the CRP has accomplished several milestones, including development of a new therapeutic radiopharmaceutical ((188)Re lipiodol) and successfully carrying out Phase I and Phase II clinical trials on patients using the new therapeutic radiopharmaceutical.

  20. Sexuality Following Radical Prostatectomy

    DEFF Research Database (Denmark)

    Fode, Mikkel; Serefoglu, Ege C; Albersen, Maarten

    2017-01-01

    INTRODUCTION: Radical prostatectomies can result in urinary incontinence and sexual dysfunction. Traditionally, these issues have been studied separately, and the sexual problem that has received the most focus has been erectile dysfunction. AIM: To summarize the literature on sexually related side...... effects and their consequences after radical prostatectomy and focus on the occurrence and management of problems beyond erectile dysfunction. METHODS: The literature on sexuality after radical prostatectomy was reviewed through a Medline search. Original research using quantitative and qualitative...... methodologies was considered. Priority was given to studies exploring aspects of sexuality other than erectile function. MAIN OUTCOME MEASURES: The prevalence, predictive factors, and management of post-prostatectomy sexual problems beyond erectile dysfunction. RESULTS: Most patients will develop urinary...

  1. Laparoscopic radical prostatectomy

    Directory of Open Access Journals (Sweden)

    Lipke Michael

    2005-01-01

    Full Text Available Millions of men are diagnosed annually with prostate cancer worldwide. With the advent of PSA screening, there has been a shift in the detection of early prostate cancer, and there are increased numbers of men with asymptomatic, organ confined disease. Laparoscopic radical prostatectomy is the latest, well accepted treatment that patients can select. We review the surgical technique, and oncologic and functional outcomes of the most current, large series of laparoscopic radical prostatectomy published in English. Positive margin rates range from 2.1-6.9% for pT2a, 9.9-20.6% for pT2b, 24.5-42.3% for pT3a, and 22.6-54.5% for pT3b. Potency rates after bilateral nerve sparing laparoscopic radical prostatectomy range from 47.1 to 67%. Continence rates at 12 months range from 83.6 to 92%.

  2. Gangs, Terrorism, and Radicalization

    Directory of Open Access Journals (Sweden)

    Scott Decker

    2011-01-01

    Full Text Available What can street gangs tell us about radicalization and extremist groups? At first glance, these two groups seem to push the boundaries of comparison. In this article, we examine the important similarities and differences across criminal, deviant, and extremist groups. Drawing from research on street gangs, this article explores issues such as levels of explanation,organizational structure, group process, and the increasingly important role of technology and the Internet in the context of radicalization. There are points of convergence across these groups, but it is important to understand the differences between these groups. This review finds little evidence to support the contention that American street gangs are becoming increasingly radicalized. This conclusion is based largely on organizational differences between gangs and terror groups.

  3. On-demand degrafting of polymer brushes prepared by controlled radical polymerization on flat silica substrates

    Science.gov (United States)

    Patil, Rohan; Srogl, Jiri; Kiserow, Douglas; Genzer, Jan

    2014-03-01

    Polymer brush degrafting refers to the removal of grafted polymer chains from the substrate without harming the polymer chemical structure. We grow poly(methyl methacrylate) (PMMA) brushes on flat silicon substrates using atom transfer radical polymerization (ATRP) and remove them from the surface by exposing the samples to tetrabutyl ammonium fluoride. We then analyze the polymer molecular weight of degrafted PMMA chains by size exclusion chromatography. The kinetics of PMMA brush degrafting exhibits double exponential behavior suggesting a transition from `brush' to `mushroom' regime. The dry brush thickness increases initially with increasing polymerization time. At longer reaction times, the thickness starts to plateau due to loss in the living nature of ATRP. We examine the relationship between the brush dry thickness and molecular weight and show that grafting density of the PMMA brush does not remain constant over the course of polymerization but reduces with time.

  4. Rate Constant of the Reaction between CH3O2Radicals and OH Radicals Revisited.

    Science.gov (United States)

    Assaf, Emmanuel; Song, Bo; Tomas, Alexandre; Schoemaecker, Coralie; Fittschen, Christa

    2016-11-17

    The reaction between CH 3 O 2 and OH radicals has been studied in a laser photolysis cell using the reaction of F atoms with CH 4 and H 2 O for the simultaneous generation of both radicals, with F atoms generated through 248 nm photolysis of XeF 2 . An experimental setup combining cw-Cavity Ring Down Spectroscopy (cw-CRDS) and high repetition rate laser-induced fluorescence (LIF) to a laser photolysis cell has been used. The absolute concentration of CH 3 O 2 was measured by cw-CRDS, while the relative concentration of OH(v = 0) radicals was determined by LIF. To remove dubiety from the quantification of CH 3 O 2 by cw-CRDS in the near-infrared, its absorption cross section has been determined at 7489.16 cm -1 using two different methods. A rate constant of k 1 = (1.60 ± 0.4) × 10 -10 cm 3 s -1 has been determined at 295 K, nearly a factor of 2 lower than an earlier determination from our group ((2.8 ± 1.4) × 10 -10 cm 3 s -1 ) using CH 3 I photolysis as a precursor. Quenching of electronically excited I atoms (from CH 3 I photolysis) in collision with OH(v = 0) is suspected to be responsible for a bias in the earlier, fast rate constant.

  5. Thermochemistry, reaction paths, and kinetics on the tert-isooctane radical reaction with O2.

    Science.gov (United States)

    Snitsiriwat, Suarwee; Bozzelli, Joseph W

    2014-07-03

    Thermochemical properties of tert-isooctane hydroperoxide and its radicals are determined by computational chemistry. Enthalpies are determined using isodesmic reactions with B3LYP density function and CBS QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the tert-isooctane hydroperoxide and its radicals in order to identify isomer energies. Recommended values derived from the most stable conformers of tert-isooctane hydroperoxide of are -77.85 ± 0.44 kcal mol(-1). Isooctane is a highly branched molecule, and its structure has a significant effect on its thermochemistry and reaction barriers. Intramolecular interactions are shown to have a significant effect on the enthalpy of the isooctane parent and its radicals on peroxy/peroxide systems, the R• + O2 well depths and unimolecular reaction barriers. Bond dissociation energies and well depths, for tert-isooctane hydroperoxide → R• + O2 are 33.5 kcal mol(-1) compared to values of ∼38 to 40 kcal mol(-1) for the smaller tert-butyl-O2 → R• + O2. Transition states and kinetic parameters for intramolecular hydrogen atom transfer and molecular elimination channels are characterized to evaluate reaction paths and kinetics. Kinetic parameters are determined versus pressure and temperature for the chemically activated formation and unimolecular dissociation of the peroxide adducts. Multifrequency quantum RRK (QRRK) analysis is used for k(E) with master equation analysis for falloff. The major reaction paths at 1000 K are formation of isooctane plus HO2 followed by cyclic ether plus OH. Stabilization of the tert-isooctane hydroperoxy radical becomes important at lower temperatures.

  6. Radical dematerialization and degrowth

    Science.gov (United States)

    Kallis, Giorgos

    2017-05-01

    The emission targets agreed in Paris require a radical reduction of material extraction, use and disposal. The core claim of this article is that a radical dematerialization can only be part and parcel of degrowth. Given that capitalist economies are designed to grow, this raises the question of whether, and under what circumstances, the inevitable `degrowth' can become socially sustainable. Three economic policies are discussed in this direction: work-sharing, green taxes and public money. This article is part of the themed issue 'Material demand reduction'.

  7. Kinetic study of the aroxyl radical-scavenging reaction of alpha-tocopherol in methanol solution: notable effect of the alkali and alkaline earth metal salts on the reaction rates.

    Science.gov (United States)

    Ouchi, Aya; Nagaoka, Shin-ichi; Abe, Kouichi; Mukai, Kazuo

    2009-10-08

    A kinetic study of the aroxyl (ArO*) radical-scavenging reaction of alpha-tocopherol (alpha-TocH) has been performed in the presence of six kinds of alkali and alkaline earth metal salts (LiI, LiClO(4), NaI, NaClO(4), KI, and Mg(ClO(4))(2)) in methanol solution, using stopped-flow spectrophotometry. The decay rate of the ArO* for the reaction of alpha-TocH with ArO* increased linearly with increasing concentration of metal salts. The second-order rate constants (k(s)) for the reaction of alpha-TocH with ArO* increased in the order of no metal salt concentration of metal salts. For example, the k(s) values in methanol solution including 4.00 x 10(-1) M of LiI and Mg(ClO(4))(2) were 3.04 and 1.30 times larger than that in the absence of metal salts, respectively. The alkali and alkaline earth metal salts having smaller ionic radius of cation and anion and larger charge of cation gave larger rate constants (k(s)). Effects of metal cations on the UV-vis absorption spectra of the alpha-Toc* (and ArO*) radical were negligible in methanol solution, suggesting that the complex formation between the alpha-Toc* (and ArO*) radical molecule and metal cations is hindered by the hydrogen bond between radical and methanol molecules. The results indicate that the hydrogen transfer reaction of alpha-TocH proceeds via an electron transfer intermediate from alpha-TocH to ArO* radicals followed by proton transfer. Both the coordinations of metal cations to the one-electron reduced anions of ArO* (ArO: (-)) and of counteranions to the one-electron oxidized cations of alpha-TocH (alpha-TocH(+)*) may stabilize the intermediate, resulting in the acceleration of electron transfer. On the other hand, the effect of metal salts on the rate of bimolecular self-reaction (2k(d)) of the alpha-Toc* radical was not observed. The result suggests that the hydrogen transfer reaction between two alpha-Toc* radical molecules proceeds via a one-step hydrogen atom transfer mechanism rather than via an

  8. Insights into Proton-Coupled Electron Transfer from Computation

    Science.gov (United States)

    Provorse, Makenzie R.

    Proton-coupled electron transfer (PCET) is utilized throughout Nature to facilitate essential biological processes, such as photosynthesis, cellular respiration, and DNA replication and repair. The general approach to studying PCET processes is based on a two-dimensional More O'Ferrall-Jencks diagram in which electron transfer (ET) and proton transfer (PT) occur in a sequential or concerted fashion. Experimentally, it is difficult to discern the contributing factors of concerted PCET mechanisms. Several theoretical approaches have arisen to qualitatively and quantitatively investigate these reactions. Here, we present a multistate density functional theory (MSDFT) method to efficiently and accurately model PCET mechanisms. The MSDFT method is validated against experimental and computational data previously reported on an isoelectronic series of small molecule self-exchange hydrogen atom transfer reactions and a model complex specifically designed to study long-range ET through a hydrogen-bonded salt-bridge interface. Further application of this method to the hydrogen atom abstraction of ascorbate by a nitroxyl radical demonstrates the sensitivity of the thermodynamic and kinetic properties to solvent effects. In particular, the origin of the unusual kinetic isotope effect is investigated. Lastly, the MSDFT is employed in a combined quantum mechanical/molecular mechanical (QM/MM) approach to explicitly model PCET in condensed phases.

  9. Scattering of state-selected and oriented hydroxyl radicals by halogen hydrides and xenon

    NARCIS (Netherlands)

    Moise, Angelica Valentina

    2007-01-01

    The interaction of the OH radical with atoms and other molecules is relevant for many physical and chemical processes involved in atmospheric, combustion and interstellar chemistry. Various experimental and theoretical studies have revealed information concerning the interaction of the hydroxyl

  10. Quantitative Structure--Activity Relationship (QSAR) for the Oxidation of Trace Organic Contaminants by Sulfate Radical.

    Science.gov (United States)

    Xiao, Ruiyang; Ye, Tiantian; Wei, Zongsu; Luo, Shuang; Yang, Zhihui; Spinney, Richard

    2015-11-17

    The sulfate radical anion (SO4•–) based oxidation of trace organic contaminants (TrOCs) has recently received great attention due to its high reactivity and low selectivity. In this study, a meta-analysis was conducted to better understand the role of functional groups on the reactivity between SO4•– and TrOCs. The results indicate that compounds in which electron transfer and addition channels dominate tend to exhibit a faster second-order rate constants (kSO4•–) than that of H–atom abstraction, corroborating the SO4•– reactivity and mechanisms observed in the individual studies. Then, a quantitative structure activity relationship (QSAR) model was developed using a sequential approach with constitutional, geometrical, electrostatic, and quantum chemical descriptors. Two descriptors, ELUMO and EHOMO energy gap (ELUMO–EHOMO) and the ratio of oxygen atoms to carbon atoms (#O:C), were found to mechanistically and statistically affect kSO4•– to a great extent with the standardized QSAR model: ln kSO4•– = 26.8–3.97 × #O:C – 0.746 × (ELUMO–EHOMO). In addition, the correlation analysis indicates that there is no dominant reaction channel for SO4•– reactions with various structurally diverse compounds. Our QSAR model provides a robust predictive tool for estimating emerging micropollutants removal using SO4•– during wastewater treatment processes.

  11. Gravitational Wave Detection with Atom Interferometry

    Energy Technology Data Exchange (ETDEWEB)

    Dimopoulos, Savas; /Stanford U., Phys. Dept.; Graham, Peter W.; /SLAC /Stanford U., Phys. Dept.; Hogan, Jason M.; Kasevich, Mark A.; /Stanford U., Phys. Dept.; Rajendran, Surjeet; /SLAC /Stanford U., Phys. Dept.

    2008-01-23

    We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite-based, utilizing the core technology of the Stanford 10m atom interferometer presently under construction. The terrestrial experiment can operate with strain sensitivity {approx} 10{sup -19}/{radical}Hz in the 1 Hz-10 Hz band, inaccessible to LIGO, and can detect gravitational waves from solar mass binaries out to megaparsec distances. The satellite experiment probes the same frequency spectrum as LISA with better strain sensitivity {approx} 10{sup -20}/{radical}Hz. Each configuration compares two widely separated atom interferometers run using common lasers. The effect of the gravitational waves on the propagating laser field produces the main effect in this configuration and enables a large enhancement in the gravitational wave signal while significantly suppressing many backgrounds. The use of ballistic atoms (instead of mirrors) as inertial test masses improves systematics coming from vibrations and acceleration noise, and reduces spacecraft control requirements.

  12. Pulse radiolysis studies of intramolecular electron transfer in model peptides and proteins. 7. Trp -> TyrO radical transformation in hen egg-white lysozyme. Effects of pH, temperature, Trp62 oxidation and inhibitor binding

    DEFF Research Database (Denmark)

    Bobrowski, K.; Holcman, J.; Poznanski, J.

    1997-01-01

    by ozone had a pronounced effect on its temperature-dependence. Taken together these observations indicate that of the six tryptophans present in HEWL Trp62 contributes about 50% to the yield of the observed LRET. In the enzyme-inhibitor complex, HEWL(GlcNAc)(3), where Trp62 and Trp63 are completely...... oxidation of Trp with N-3(.) radicals under low concentration of the reactants but at a high HEWL/N-3(.) molar ratio, so that more than 99% of the oxidized protein molecules contained only a single tryptophyl radical. Synchronous decay of Trp(.) and build-up of TyrO(.) conformed satisfactorily to first......(.). Arrhenius plots of the temperature-dependence of k(5) showed that the activation energy of LRET varies both with temperature and the protonation state of the enzyme. The activation energies are in the range 7.6-56.0 kJ mol(-1) and are similar to those for activation of amide hydrogen exchange in native HEWL...

  13. Radical School Reform.

    Science.gov (United States)

    Gross, Beatrice, Ed.; Gross, Ronald, Ed.

    This book provides a comprehensive examination of the nature of the school crisis and the ways in which radical thinkers and educators are dealing with it. Excerpts from the writings of Jonathan Kozol, John Holt, Kenneth Clark, and others are concerned with the realities of education in ghettos and suburbs. Paul Goodman, Marshall McLuhan, Sylvia…

  14. Beyond Radical Educational Cynicism.

    Science.gov (United States)

    Wood, George H.

    1982-01-01

    An alternative is presented to counter current radical arguments that the schools cannot bring about social change because they are instruments of capitalism. The works of Samuel Bowles, Herbert Gintis, and Louis Althusser are discussed. Henry Giroux's "Ideology, Culture and the Process of Schooling" provides an alternative to cynicism.…

  15. Radical Financial Innovation

    OpenAIRE

    Robert J. Shiller

    2004-01-01

    Radical financial innovation is the development of new institutions and methods that permit risk management to be extended far beyond its former realm, covering important new classes of risks. This paper compares past such innovation with potential future innovation, looking at the process that produced past success and the possibilities for future financial innovation.

  16. Homegrown religious radicalization

    DEFF Research Database (Denmark)

    Khawaja, Iram

    and their families. Existing literature and ways of thinking about the social psychological process of radicalization will be reviewed, such as social identity theory and transformative learning theory, and a theoretical framework based on a focus on belonging, recognition and the sense of community will be proposed...

  17. Radically enhanced molecular recognition

    KAUST Repository

    Trabolsi, Ali

    2009-12-17

    The tendency for viologen radical cations to dimerize has been harnessed to establish a recognition motif based on their ability to form extremely strong inclusion complexes with cyclobis(paraquat-p-phenylene) in its diradical dicationic redox state. This previously unreported complex involving three bipyridinium cation radicals increases the versatility of host-guest chemistry, extending its practice beyond the traditional reliance on neutral and charged guests and hosts. In particular, transporting the concept of radical dimerization into the field of mechanically interlocked molecules introduces a higher level of control within molecular switches and machines. Herein, we report that bistable and tristable [2]rotaxanes can be switched by altering electrochemical potentials. In a tristable [2]rotaxane composed of a cyclobis(paraquat-p-phenylene) ring and a dumbbell with tetrathiafulvalene, dioxynaphthalene and bipyridinium recognition sites, the position of the ring can be switched. On oxidation, it moves from the tetrathiafulvalene to the dioxynaphthalene, and on reduction, to the bipyridinium radical cation, provided the ring is also reduced simultaneously to the diradical dication. © 2010 Macmillan Publishers Limited. All rights reserved.

  18. Current status of free radicals and electronically excited metastable species as high energy propellants

    Science.gov (United States)

    Rosen, G.

    1973-01-01

    A survey is presented of free radicals and electronically excited metastable species as high energy propellants for rocket engines. Nascent or atomic forms of diatomic gases are considered free radicals as well as the highly reactive diatomic triatomic molecules that posess unpaired electrons. Manufacturing and storage problems are described, and a review of current experimental work related to the manufacture of atomic hydrogen propellants is presented.

  19. α-Melanocyte stimulating hormone (MSH) and prostaglandin E2 (PGE2) drive melanosome transfer by promoting filopodia delivery and shedding spheroid granules: Evidences from atomic force microscopy observation.

    Science.gov (United States)

    Ma, Hui-Jun; Ma, Hui-Yong; Yang, Yang; Li, Peng-Cheng; Zi, Shao-Xia; Jia, Chi-Yu; Chen, Rong

    2014-12-01

    Skin pigmentation is accomplished by production of melanin in melanosome and by transfer of these organelles from melanocytes (MCs) to surrounding keratinocytes (KCs). However, the detailed mechanism is still unknown. We aimed to investigate the morphological structure changes on human epidermal MCs and KCs, which were either mono-cultured or co-cultured, with or without the treatment of both α-Melanocyte-stimulating hormone (α-MSH) and prostaglandin E2 (PGE2), by atomic force microscopy (AFM) and to provide more direct proofs for process of melanosome transfer. Human epidermal MCs and KCs were isolated and co-cultured with 1:10 ratio in a defined Keratinocyte-serum free medium (K-SFM). After exposure with 100 nM α-MSH or 20 μM PGE2 for 3 days, cells were fixed with 0.5% glutaraldehyde and AFM images of scanning observation were captured by contacting and tapping model under normal atmospheric pressure and temperature. It showed that human epidermal MCs in culture had secondary or tertiary branches. Except for globular granules structure on the surface of dendrites, some filopodia were protruded on the tips and lateral sides of the dendrites. The administration of α-MSH and PGE2 made not only the dendrites thinner and longer, but also the globular granules more intensive and denser. Many spheroid granules were shed from branches of dendrite and most of them adhered with dense filopodia. Compared with untreated group, the number of filopodia per cell, diameter of filopodia, and shedding spheroid granules per field all increased following α-MSH and PGE2 exposure (Pspheroid granules per field all increased after the administration of α-MSH and PGE2 (Pspheroid granules, filopodia delivery and KC phagocytosis are major mode of melanosome transfer between MCs and KCs. PGE2, as well as α-MSH, drives melanosome transfer by promoting filopodia delivery and numbers of shedding spheroid granules in MCs, but no direct morphological effects on KCs. These findings open a

  20. Hydrogen transfer in the formation and destruction of retrograde products in coal conversion

    Energy Technology Data Exchange (ETDEWEB)

    McMillen, D.F.; Malhotra, R. [SRI International, Menlo Park, CA (United States)

    2006-06-01

    The conversion of coals to volatiles or liquids during pyrolysis and liquefaction is notoriously limited by the formation of retrograde products. Analysis of literature data for coals with grafted structures and for polymeric coal models demonstrates that the formation of volatile products from these materials does not correlate primarily with the weakness of the original bonding but correlates with the facility for retrogressive reaction. This analysis suggests further that simple recombination of resonance-stabilized radicals does not tend to yield true retrograde products, except in the case of aryloxy radicals. For pure hydrocarbon structural elements, radical addition to aromatic systems appears to be a key class of retrograde reactions, where the key factor is the kinetics of radical or H-atom loss from a cyclohexadienyl intermediate. We have used a mechanistic numerical model with a detailed set of radical reactions and thermochemically based kinetic parameters operating on a limited set of hydrocarbon structures to delineate important factors in mitigating retrograde processes. This showed that, not only the cleavage of critical bonds in the original coal structures but also the net prevention of retrogression may be due to the H-transfer-induced cleavage of strong bonds.

  1. Water-Soluble Fe(II)−H2O Complex with a Weak O−H Bond Transfers a Hydrogen Atom via an Observable Monomeric Fe(III)−OH

    Science.gov (United States)

    Brines, Lisa M.; Coggins, Michael K.; Poon, Penny Chaau Yan; Toledo, Santiago; Kaminsky, Werner; Kirk, Martin L.

    2015-01-01

    Understanding the metal ion properties that favor O−H bond formation versus cleavage should facilitate the development of catalysts tailored to promote a specific reaction, e.g., C−H activation or H2O oxidation. The first step in H2O oxidation involves the endothermic cleavage of a strong O−H bond (BDFE = 122.7 kcal/mol), promoted by binding the H2O to a metal ion, and by coupling electron transfer to proton transfer (PCET). This study focuses on details regarding how a metal ion’s electronic structure and ligand environment can tune the energetics of M(HO−H) bond cleavage. The synthesis and characterization of an Fe(II)−H2O complex, 1, that undergoes PCET in H2O to afford a rare example of a monomeric Fe(III)−OH, 7, is described. High-spin 7 is also reproducibly generated via the addition of H2O to {[FeIII(OMe2N4(tren))]2-(µ-O)}2+ (8). The O−H bond BDFE of Fe(II)−H2O (1) (68.6 kcal/mol) is calculated using linear fits to its Pourbaix diagram and shown to be 54.1 kcal/mol less than that of H2O and 10.9 kcal/mol less than that of [Fe(II)(H2O)6]2+. The O−H bond of 1 is noticeably weaker than the majority of reported Mn+(HxO−H) (M = Mn, Fe; n+ = 2+, 3+; x = 0, 1) complexes. Consistent with their relative BDFEs, Fe(II)−H2O (1) is found to donate a H atom to TEMPO•, whereas the majority of previously reported Mn+−O(H) complexes, including [MnIII(SMe2N4(tren))(OH)]+ (2), have been shown to abstract H atoms from TEMPOH. Factors responsible for the weaker O−H bond of 1, such as differences in the electron-donating properties of the ligand, metal ion Lewis acidity, and electronic structure, are discussed. PMID:25611075

  2. Water-soluble Fe(II)-H2O complex with a weak O-H bond transfers a hydrogen atom via an observable monomeric Fe(III)-OH.

    Science.gov (United States)

    Brines, Lisa M; Coggins, Michael K; Poon, Penny Chaau Yan; Toledo, Santiago; Kaminsky, Werner; Kirk, Martin L; Kovacs, Julie A

    2015-02-18

    Understanding the metal ion properties that favor O-H bond formation versus cleavage should facilitate the development of catalysts tailored to promote a specific reaction, e.g., C-H activation or H2O oxidation. The first step in H2O oxidation involves the endothermic cleavage of a strong O-H bond (BDFE = 122.7 kcal/mol), promoted by binding the H2O to a metal ion, and by coupling electron transfer to proton transfer (PCET). This study focuses on details regarding how a metal ion's electronic structure and ligand environment can tune the energetics of M(HO-H) bond cleavage. The synthesis and characterization of an Fe(II)-H2O complex, 1, that undergoes PCET in H2O to afford a rare example of a monomeric Fe(III)-OH, 7, is described. High-spin 7 is also reproducibly generated via the addition of H2O to {[Fe(III)(O(Me2)N4(tren))]2-(μ-O)}(2+) (8). The O-H bond BDFE of Fe(II)-H2O (1) (68.6 kcal/mol) is calculated using linear fits to its Pourbaix diagram and shown to be 54.1 kcal/mol less than that of H2O and 10.9 kcal/mol less than that of [Fe(II)(H2O)6](2+). The O-H bond of 1 is noticeably weaker than the majority of reported M(n+)(HxO-H) (M = Mn, Fe; n+ = 2+, 3+; x = 0, 1) complexes. Consistent with their relative BDFEs, Fe(II)-H2O (1) is found to donate a H atom to TEMPO(•), whereas the majority of previously reported M(n+)-O(H) complexes, including [Mn(III)(S(Me2)N4(tren))(OH)](+) (2), have been shown to abstract H atoms from TEMPOH. Factors responsible for the weaker O-H bond of 1, such as differences in the electron-donating properties of the ligand, metal ion Lewis acidity, and electronic structure, are discussed.

  3. Direct determination of rate constants for coupling between aromatic radical anions and alkyl and benzyl radicals by laser-flash photolysis

    DEFF Research Database (Denmark)

    Lund, T.; Christensen, P.; Wilbrandt, Robert Walter

    2003-01-01

    Coupling rates between the radicals methyl, n-, sec-, tert-butyl and benzyl (R-.) and the aromatic radical anions of 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene and fluorenone (A(-.)) have been obtained using a new laser-flash photolysis method. The radicals R-. and the radical anions A(-.) we...... of the radicals and the structure and standard potentials of the aromatic radical anions.......Coupling rates between the radicals methyl, n-, sec-, tert-butyl and benzyl (R-.) and the aromatic radical anions of 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene and fluorenone (A(-.)) have been obtained using a new laser-flash photolysis method. The radicals R-. and the radical anions A(-.) were...... generated by a photoinduced electron transfer reaction between the aromatic compound A and the alkyl or benzyl triphenylborate anion RB(Ph)(3)(-). For the first time the rate constants of the coupling reaction between methyl and benzyl radicals with aromatic radical anions have been obtained. For all...

  4. Atomic Covalent Functionalization of Graphene

    Science.gov (United States)

    Johns, James E.; Hersam, Mark C.

    2012-01-01

    Conspectus Although graphene’s physical structure is a single atom thick, two-dimensional, hexagonal crystal of sp2 bonded carbon, this simple description belies the myriad interesting and complex physical properties attributed to this fascinating material. Because of its unusual electronic structure and superlative properties, graphene serves as a leading candidate for many next generation technologies including high frequency electronics, broadband photodetectors, biological and gas sensors, and transparent conductive coatings. Despite this promise, researchers could apply graphene more routinely in real-world technologies if they could chemically adjust graphene’s electronic properties. For example, the covalent modification of graphene to create a band gap comparable to silicon (~1 eV) would enable its use in digital electronics, and larger band gaps would provide new opportunities for graphene-based photonics. Towards this end, researchers have focused considerable effort on the chemical functionalization of graphene. Due to its high thermodynamic stability and chemical inertness, new methods and techniques are required to create covalent bonds without promoting undesirable side reactions or irreversible damage to the underlying carbon lattice. In this Account, we review and discuss recent theoretical and experimental work studying covalent modifications to graphene using gas phase atomic radicals. Atomic radicals have sufficient energy to overcome the kinetic and thermodynamic barriers associated with covalent reactions on the basal plane of graphene but lack the energy required to break the C-C sigma bonds that would destroy the carbon lattice. Furthermore, because they are atomic species, radicals substantially reduce the likelihood of unwanted side reactions that confound other covalent chemistries. Overall, these methods based on atomic radicals show promise for the homogeneous functionalization of graphene and the production of new classes of two

  5. Atomic spectroscopy and radiative processes

    CERN Document Server

    Landi Degl'Innocenti, Egidio

    2014-01-01

    This book describes the basic physical principles of atomic spectroscopy and the absorption and emission of radiation in astrophysical and laboratory plasmas. It summarizes the basics of electromagnetism and thermodynamics and then describes in detail the theory of atomic spectra for complex atoms, with emphasis on astrophysical applications. Both equilibrium and non-equilibrium phenomena in plasmas are considered. The interaction between radiation and matter is described, together with various types of radiation (e.g., cyclotron, synchrotron, bremsstrahlung, Compton). The basic theory of polarization is explained, as is the theory of radiative transfer for astrophysical applications. Atomic Spectroscopy and Radiative Processes bridges the gap between basic books on atomic spectroscopy and the very specialized publications for the advanced researcher: it will provide under- and postgraduates with a clear in-depth description of theoretical aspects, supported by practical examples of applications.

  6. Toward Radicalizing Community Service Learning

    Science.gov (United States)

    Sheffield, Eric C.

    2015-01-01

    This article advocates a radicalized theoretical construction of community service learning. To accomplish this radicalization, I initially take up a discussion of traditional understandings of CSL rooted in pragmatic/progressive thought. I then suggest that this traditional structural foundation can be radicalized by incorporating Deborah…

  7. Atomic and molecular adsorption on Rh(111)

    DEFF Research Database (Denmark)

    Mavrikakis, Manos; Rempel, J.; Greeley, Jeffrey Philip

    2002-01-01

    A systematic study of the chemisorption of both atomic (H, O, N, S, C), molecular (N-2, CO, NO), and radical (CH3, OH) species on Rh(111) has been performed. Self-consistent, periodic, density functional theory (DFT-GGA) calculations, using both PW91 and RPBE functionals, have been employed to de...

  8. Atomic theories

    CERN Document Server

    Loring, FH

    2014-01-01

    Summarising the most novel facts and theories which were coming into prominence at the time, particularly those which had not yet been incorporated into standard textbooks, this important work was first published in 1921. The subjects treated cover a wide range of research that was being conducted into the atom, and include Quantum Theory, the Bohr Theory, the Sommerfield extension of Bohr's work, the Octet Theory and Isotopes, as well as Ionisation Potentials and Solar Phenomena. Because much of the material of Atomic Theories lies on the boundary between experimentally verified fact and spec

  9. Facile Synthesis of Well-Defined MDMO-PPV Containing (TriBlock—Copolymers via Controlled Radical Polymerization and CuAAC Conjugation

    Directory of Open Access Journals (Sweden)

    Neomy Zaquen

    2015-02-01

    Full Text Available A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene (PPV materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC. PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3',7'-dimethyloctyloxy]-1,4-phenylenevinylene to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP. In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene-block-poly(tert-butyl acrylate-block-poly(ethylene glycol (PPV-b-PtBuA-b-PEG.

  10. Quantification of ion or atom transfer phenomena in materials implanted by nuclear methods; Quantification de phenomenes de transferts ioniques ou atomiques dans des materiaux implantes par la mise en oeuvre de methodes nucleaires

    Energy Technology Data Exchange (ETDEWEB)

    Oudadesse, Hassane [Clermont-Ferrand-2 Univ., 63 - Aubiere (France)

    1998-05-18

    Knowledge of transfer of the constituents of a system from regions of higher to lower concentration is of interest for implanted bio-materials. It allows determining the rate at which this material is integrated in a living material. To evaluate the ossification kinetics and to study the bio-functionality in corals of Ca and Sr, irradiations with a 10{sup 13} n.cm{sup -2}.s{sup -1} was performed, followed by the examination of changes in the localization of these elements. By using PIXE analysis method the distribution of Ca, P, Sr, Zn and Fe in the implant, bone and bone-implant interfaces were determined. Thus, it was shown that resorption of coral in sheep is achieved in 5 months after implantation and is identical to the cortical tissues 4 months after implantation in animals as for instance in hares. We have analyzed the tissues from around the prostheses extracted from patients. The samples were calcined and reduced to powder weighting some milligrams. We have adopted for this study the PIXE analysis method. The samples were irradiated by a proton beam of 3 MeV and about 400 {mu}m diameter. The results show the presence of the elements Ti, Fe, Cr, Ni or Zn according to the type of the implanted prosthesis. This dispersal of the metallic ions and atoms contaminate the tissues. The transfer factors translate the exchanges between bone and the implanted material. The solvatation phenomenon and the electric charge equilibrium explain the transfer order of cations Mg{sup 2+}, Ca{sup 2+} and Sr{sup 2+} and of the anion PO{sub 4}{sup 3-}. We have also determined these factors for the elements Ti, Cr and Ni. An original technique to study the bone bio-functionality was used. Use of phosphate derivatives labelled by {sup 99m}Tc allows obtaining information about the fixation of radioactive tracer. It was found that only after the eighth month at the implantation the neo-formed bone fixes the MDP (methyl diphosphate) labelled by {sup 99m}Tc in a similar way as in the

  11. Effects of Molecular Iodine and 4-tert-Butylcatechol Radical Inhibitor on the Radical Polymerization of Styrene

    Directory of Open Access Journals (Sweden)

    Mojtaba Bozorg

    2017-05-01

    Full Text Available The presence of molecular iodine was studied in relation the molecular weight and molecular weight distribution of polystyrene, produced by radical poly merization. Radical polymerization of styrene initiated by 2,2׳-azobisisobutyronitrile (AIBN was performed at 70°C in the presence of molecular iodine. The synthesized polymers were characterized by gel permeation chromatography (GPC and proton- nuclear magnetic resonance (1H NMR techniques. The results of these reactions including conversion data, number-average molecular weight and molecular weight distribution were compared with those obtained for styrene radical polymerization initiated by AIBN at the same temperature in the absence of molecular iodine. It was found that the presence of iodine had a profound effect on the molecular weight and its distribution in the produced polystyrene. This was attributed to the ability of iodine to control the polymerization of styrene initiated by AIBN via reverse iodine transfer polymerization (RITP mechanism. The polymer produced by this method had a molecular weight of 10600 g/mol with a molecular weight polydispersity index of 1.3. Due to the importance of induction period in reverse iodine transfer radical polymerization, increasing the temperature to 120°C during the induction period resulted in shorter induction periods and the produced species led to better control of the molecular weight. Also, due to the role of iodine molecules as a radical inhibitor, the presence of a secondary radical inhibitor, i.e. 4-tert-butylcatechol, along with the iodine was investigated in radical polymerization of polystyrene initiated by AIBN. It was observed that the secondary radical inhibitor prevented the consumption of the iodine molecules by the radicals produced from decomposition of the AIBN initiator; therefore, alkyl halides were not produced during the induction period.

  12. Atomic Power

    African Journals Online (AJOL)

    Atomic Power. By Denis Taylor: Dr. Taylor was formerly Chief UNESCO Advisor at the University. College, Nairobi, Kenya and is now Professor of Electrical Engineering in the Uni- versity of ... method of producing radioactive isotopes, which are materials .... the sealing and the pressure balancing, all can be carried out ...

  13. A ¹H NMR Investigation of the Interaction between Phenolic Acids Found in Mango (Manguifera indica cv Ataulfo) and Papaya (Carica papaya cv Maradol) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) Free Radicals.

    Science.gov (United States)

    López-Martínez, Luis M; Santacruz-Ortega, Hisila; Navarro, Rosa-Elena; Sotelo-Mundo, Rogerio R; González-Aguilar, Gustavo A

    2015-01-01

    The benefits of phenolic acids on human health are very often ascribed to their potential to counteract free radicals to provide antioxidant protection. This potential has been attributed to their acidic chemical structure, which possesses hydroxyl groups in different positions. Phenolic acids can interact between themselves and exhibit an additive, antagonistic or synergistic effect. In this paper, we used 1H NMR to analyze the interactions and mechanisms that are present in major phenolic acids found in mango (gallic, protocatechuic, chlorogenic and vanillic acids) and papaya (caffeic, ferulic and p-coumaric acids), and the DPPH radical was used to evaluate the effect of the antioxidant mixtures. The interactions were found to occur via hydrogen bonds between the -OH and -COOH groups. Moreover, the phenolic acids exhibit two types of mechanisms for the neutralization of the DPPH radical. According to the results, these two mechanisms are Hydrogen Atom Transfer (HAT) and Single Electron Transfer (SET). The ability of the phenolic acid to neutralize the DPPH radical decreases in the following order in mango: gallic > chlorogenic > protocatechuic > vanillic. Moreover, within the acids found in papaya, the order was as follows: caffeic > p-coumaric > ferulic.

  14. On rings generating supernilpotent and special atoms | France ...

    African Journals Online (AJOL)

    We show that the class of all **-rings strictly contains the class of all *-rings and that the smallest supernilpotent (respectively the smallest special) radical containing a nonzero **-ring is a supernilpotent (respectively special) atom. This generalizes H. France-Jackson¡s results concerning supernilpotent and special atoms.

  15. Accurate Theoretical Thermochemistry for Fluoroethyl Radicals.

    Science.gov (United States)

    Ganyecz, Ádám; Kállay, Mihály; Csontos, József

    2017-02-09

    An accurate coupled-cluster (CC) based model chemistry was applied to calculate reliable thermochemical quantities for hydrofluorocarbon derivatives including radicals 1-fluoroethyl (CH3-CHF), 1,1-difluoroethyl (CH3-CF2), 2-fluoroethyl (CH2F-CH2), 1,2-difluoroethyl (CH2F-CHF), 2,2-difluoroethyl (CHF2-CH2), 2,2,2-trifluoroethyl (CF3-CH2), 1,2,2,2-tetrafluoroethyl (CF3-CHF), and pentafluoroethyl (CF3-CF2). The model chemistry used contains iterative triple and perturbative quadruple excitations in CC theory, as well as scalar relativistic and diagonal Born-Oppenheimer corrections. To obtain heat of formation values with better than chemical accuracy perturbative quadruple excitations and scalar relativistic corrections were inevitable. Their contributions to the heats of formation steadily increase with the number of fluorine atoms in the radical reaching 10 kJ/mol for CF3-CF2. When discrepancies were found between the experimental and our values it was always possible to resolve the issue by recalculating the experimental result with currently recommended auxiliary data. For each radical studied here this study delivers the best heat of formation as well as entropy data.

  16. New free radicals to measure antiradical capacity: a theoretical study.

    Science.gov (United States)

    León-Carmona, Jorge Rafael; Martínez, Ana; Galano, Annia

    2014-08-28

    A new family of free radicals, that are soluble in water and stable at all pH values, were recently synthesized and used to assess the antiradical capacity of several polyphenols. In the present work, density functional calculations were used to investigate the single electron transfer reactions between these new free radicals and polyphenols in aqueous solution. The quantification of the antiradical capacity is a challenge, particularly for polyphenols, since they become unstable under experimental conditions. It was found that the electron transfer from polyphenols to the newly developed free radicals can be used to assess the efficiency of this kind of compound for preventing oxidative stress. Since one of the free radicals can be deprotonated under experimental conditions, this newly synthesized radical can help distinguish more clearly between different antiradical compounds with similar antioxidant capacity by modifying the pH in the experiments. The results reported here are in good agreement with the available experimental data and allowed making recommendations about possible experimental conditions in the design of antioxidant assays using the investigated radicals.

  17. Optical lattice on an atom chip

    DEFF Research Database (Denmark)

    Gallego, D.; Hofferberth, S.; Schumm, Thorsten

    2009-01-01

    Optical dipole traps and atom chips are two very powerful tools for the quantum manipulation of neutral atoms. We demonstrate that both methods can be combined by creating an optical lattice potential on an atom chip. A red-detuned laser beam is retroreflected using the atom chip surface as a high......-quality mirror, generating a vertical array of purely optical oblate traps. We transfer thermal atoms from the chip into the lattice and observe cooling into the two-dimensional regime. Using a chip-generated Bose-Einstein condensate, we demonstrate coherent Bloch oscillations in the lattice....

  18. Reaction mechanism and kinetics of the degradation of terbacil initiated by OH radical - A theoretical study

    Science.gov (United States)

    Ponnusamy, S.; Sandhiya, L.; Senthilkumar, K.

    2018-02-01

    The reaction of terbacil with OH radical is studied by using electronic structure calculations. The reaction of terbacil with OH radical is found to proceed by H-atom abstraction, Cl-atom abstraction and OH addition reactions. The initially formed alkyl radical will undergo atmospheric transformation in the presence of molecular oxygen leading to the formation of peroxy radical. The reaction of peroxy radical with other atmospheric oxidants, such as HO2 and NO radicals is studied. The rate constant is calculated for the H-atom abstraction reactions over the temperature range of 200-1000 K. The results obtained from electronic structure calculations and kinetic study show that the H-atom abstraction reaction is more favorable. The calculated lifetime of terbacil is 24 h in normal atmospheric OH concentration. The rate constant calculated for H-atom abstraction reactions is 6 × 10-12, 4.4 × 10-12 and 3.2 × 10-12 cm3molecule-1s-1, respectively which is in agreement with the previous literature value of 1.9 × 10-12 cm3molecule-1s-1.

  19. A nine-atom rhodium-aluminum oxide cluster oxidizes five carbon monoxide molecules

    National Research Council Canada - National Science Library

    Li, Xiao-Na; Zhang, Hua-Min; Yuan, Zhen; He, Sheng-Gui

    2016-01-01

    ... catalysis is elusive. Here we report that a single atom of rhodium, a powerful noble metal catalyst, can promote the transfer of five oxygen atoms to oxidize carbon monoxide from a nine-atom rhodium-aluminum oxide cluster...

  20. Relative stability of radicals derived from artemisinin: A semiempirical and DFT study

    Science.gov (United States)

    Arantes, C.; de Araujo, M. T.; Taranto, A. G.; de M. Carneiro, J. W.

    The semiempirical AM1 and PM3 methods, as well as the density functional (DFT/B3LYP) approach using the 6-31g(d) basis set, were employed to calculate the relative stability of intermediate radicals derived from artemisinin, a sesquiterpene lactone having an endoperoxide bridge that is essential for its antimalarial activity. The compounds studied have their nonperoxidic oxygen atom of the trioxane ring and/or the carbonyl group replaced by a CH2 unit. Relative stabilities were calculated by means of isodesmic equations using artemisinin as reference. It was found that replacement of oxygen atoms decreases the relative stability of the anionic radical intermediates. In contrast, for compounds with inverted stereochemistry the intermediate radicals were found to be more stable than those with the artemisinin-like stereochemistry. These relative stabilities may modulate the antimalarial potency. Radicals centered on carbon are always more stable than the corresponding radicals centered on oxygen.

  1. Radical distinction: Support for radical left and radical right parties in Europe.

    Science.gov (United States)

    Rooduijn, Matthijs; Burgoon, Brian; van Elsas, Erika J; van de Werfhorst, Herman G

    2017-12-01

    Support for radical parties on both the left and right is on the rise, fueling intuition that both radicalisms have similar underpinnings. Indeed, existing studies show that radical left and right voters have overlapping positions and preferences. In this article, however, we focus on the differences in the voting bases of such parties. We show that radical left and right voters have sharply diverging ideological profiles. When it comes to the historical traditions of the 'left' and 'right', these voters differ radically from each other. Both groups express the traditions associated with their mainstream counterparts-particularly with respect to (non-)egalitarian, (non-)altruistic, and (anti-)cosmopolitan values. Such differences also explain why radical left voters tend to be more, not less, educated than mainstream or radical right voters.

  2. Radical distinction: Support for radical left and radical right parties in Europe

    Science.gov (United States)

    Burgoon, Brian; van Elsas, Erika J; van de Werfhorst, Herman G

    2017-01-01

    Support for radical parties on both the left and right is on the rise, fueling intuition that both radicalisms have similar underpinnings. Indeed, existing studies show that radical left and right voters have overlapping positions and preferences. In this article, however, we focus on the differences in the voting bases of such parties. We show that radical left and right voters have sharply diverging ideological profiles. When it comes to the historical traditions of the ‘left’ and ‘right’, these voters differ radically from each other. Both groups express the traditions associated with their mainstream counterparts—particularly with respect to (non-)egalitarian, (non-)altruistic, and (anti-)cosmopolitan values. Such differences also explain why radical left voters tend to be more, not less, educated than mainstream or radical right voters. PMID:29187802

  3. Spectroscopic Studies of Atmospheric Radical-Radical Reactions

    Science.gov (United States)

    Okumura, Mitchio

    2004-03-01

    The reactions of trace free radicals largely determine the chemical composition of gas phase species in the atmosphere. Reactions between pairs of radicals are very important, but exhibit a high degree of complexity; fundamental studies have revealed the importance of multiple wells, adduct formation, chaperone effects, and nonadiabatic coupling among potential energy surfaces. We have investigated the spectra, kinetics, and dynamics of a number of radical-radical reactions using infrared cavity ringdown, FM diode laser, and action spectroscopic methods. New results will be presented on peroxynitrous acid, HOONO, a minor but significant channel in the OH + NO2 + M reaction, a major sink for HOx and NOx radicals in polluted tropospheric air. These experiments lead to a detailed understanding of HOONO formation and kinetics under thermal conditions. Additional work on peroxyl radical spectroscopy and chemistry, including the role of hydrogen-bonded adducts, will also be discussed.

  4. Catalysis of Radical Reactions: A Radical Chemistry Perspective.

    Science.gov (United States)

    Studer, Armido; Curran, Dennis P

    2016-01-04

    The area of catalysis of radical reactions has recently flourished. Various reaction conditions have been discovered and explained in terms of catalytic cycles. These cycles rarely stand alone as unique paths from substrates to products. Instead, most radical reactions have innate chains which form products without any catalyst. How do we know if a species added in "catalytic amounts" is a catalyst, an initiator, or something else? Herein we critically address both catalyst-free and catalytic radical reactions through the lens of radical chemistry. Basic principles of kinetics and thermodynamics are used to address problems of initiation, propagation, and inhibition of radical chains. The catalysis of radical reactions differs from other areas of catalysis. Whereas efficient innate chain reactions are difficult to catalyze because individual steps are fast, both inefficient chain processes and non-chain processes afford diverse opportunities for catalysis, as illustrated with selected examples. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Intramolecular Photogeneration of a Tyrosine Radical in a Designed Protein

    Science.gov (United States)

    Tebo, Alison G.; Quaranta, Annamaria; Herrero, Christian; Pecoraro, Vincent L.; Aukauloo, Ally

    2017-01-01

    Long-distance biological electron transfer occurs through a hopping mechanism and often involves tyrosine as a high potential intermediate, for example in the early charge separation steps during photosynthesis. Protein design allows for the development of minimal systems to study the underlying principles of complex systems. Herein, we report the development of the first ruthenium-linked designed protein for the photogeneration of a tyrosine radical by intramolecular electron transfer. PMID:29046892

  6. Atomic arias

    Science.gov (United States)

    Crease, Robert P.

    2009-01-01

    The American composer John Adams uses opera to dramatize controversial current events. His 1987 work Nixon in China was about the landmark meeting in 1972 between US President Richard Nixon and Chairman Mao Zedong of China; The Death of Klinghoffer (1991) was a musical re-enactment of an incident in 1985 when Palestinian terrorists kidnapped and murdered a wheelchair-bound Jewish tourist on a cruise ship. Adams's latest opera, Doctor Atomic, is also tied to a controversial event: the first atomic-bomb test in Alamogordo, New Mexico, on 16 June 1945. The opera premièred in San Francisco in 2005, had a highly publicized debut at the Metropolitan Opera in New York in 2008, and will have another debut on 25 February - with essentially the same cast - at the English National Opera in London.

  7. Atomic rivals

    Energy Technology Data Exchange (ETDEWEB)

    Goldschmidt, B.

    1990-01-01

    This book is a memoir of rivalries among the Allies over the bomb, by a participant and observer. Nuclear proliferation began in the uneasy wartime collaboration of the United States, England, Canada, and Free France to produce the atom bomb. Through the changes of history, a young French chemist had a role in almost every act of this international drama. This memoir is based on Goldschmidt's own recollections, interviews with other leading figures, and 3,000 pages of newly declassified documents in Allied archives. From his own start as Marie Curie's lab assistant, Goldschmidt's career was closely intertwined with Frances complicated rise to membership in the nuclear club. As a refugee from the Nazis, he became part of the wartime nuclear energy project in Canada and found himself the only French scientist to work (although briefly) on the American atom bomb project.

  8. The electronic structure of the primary electron donor of reaction centers of purple bacteria at atomic resolution as observed by photo-CIDNP 13C NMR.

    Science.gov (United States)

    Daviso, Eugenio; Prakash, Shipra; Alia, A; Gast, Peter; Neugebauer, Johannes; Jeschke, Gunnar; Matysik, Jörg

    2009-12-29

    Composed of the two bacteriochlorophyll cofactors, P(L) and P(M), the special pair functions as the primary electron donor in bacterial reaction centers of purple bacteria of Rhodobacter sphaeroides. Under light absorption, an electron is transferred to a bacteriopheophytin and a radical pair is produced. The occurrence of the radical pair is linked to the production of enhanced nuclear polarization called photochemically induced dynamic nuclear polarization (photo-CIDNP). This effect can be used to study the electronic structure of the special pair at atomic resolution by detection of the strongly enhanced nuclear polarization with laser-flash photo-CIDNP magic-angle spinning NMR on the carotenoid-less mutant R26. In the electronic ground state, P(L) is strongly disturbed, carrying a slightly negative charge. In the radical cation state, the ratio of total electron spin densities between P(L) and P(M) is 2:1, although it is 2.5:1 for the pyrrole carbons, 2.2:1 for all porphyrinic carbons, and 4:1 for the pyrrole nitrogen. It is shown that the symmetry break between the electronic structures in the electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of P(L). The significant difference in electron density distribution between the ground and radical cation states is explained by an electric polarization effect of the nearby histidine.

  9. Repair reactions of pyrimidine-derived radicals by aliphatic thiols.

    Science.gov (United States)

    Wójcik, Aleksandra; Naumov, Sergej; Marciniak, Bronislaw; Brede, Ortwin

    2006-06-29

    Pyrimidinyl radicals of various structures (Pyr*) were generated in aqueous and alcohol-containing solutions by means of pulse radiolysis to determine the rate constants of their repair reactions by different thiols (RSH = cysteamine, 2-mercaptoethanol, cysteine, and penicillamine): Pyr* + RSH --> PyrH + RS*. C5-OH and C6-OH adduct radicals of the pyrimidines react with thiols with k9 = (1.2-10.0) x 10(6) dm3 mol(-1) s(-1). Similar repair rate constants were found for uracil- and thymine-derived N1-centered radicals, k31 = (1.5-6.1) x 10(6) dm3 mol(-1) s(-1). However, pyrimidine radical anions protonated at their C6 position and C6-uracilyl radicals, with carbonyl groups at their C5 position, react with thiols faster, with k24 = (0.5-7.6) x 10(7) dm3 mol(-1) s(-1) and k14 = (1.4-4.8) x 10(7) dm3 mol(-1) s(-1), respectively. Quantum chemical calculations, at the B3LYP/6-31G(d,p) and self-consistent reaction field polarizable continuum model level point to the combined effects of the energy gap between interacting molecular orbitals, charge distribution within different pyrimidine-derived radicals, and the coefficients of the atomic orbitals as the possible reasons for the differences in the rate constants of repair.

  10. METHODS OF SAMPLE THERMAL MODIFICATION BY MEANS DOUBLE VAPORIZATION IN TWO STEP ATOMIZER FOR ATOMIC ABSORPTION ANALYSIS

    OpenAIRE

    Grinshtein, Ilia; Vilpan, Yuri; Saraev, Alexei; Vasilieva, Lubov

    2000-01-01

    After sample vaporization in two-step atomizer with a purged vaporizer sample vapors can be transferred into preheated or into non-heated atomizer. In the last case the atomizer walls trap the vapors and then the sample is second time vaporized and atomized by heating the atomizer. Thermal pre-treatment of a sample using this double vaporization makes possible the direct analysis of samples with strongly interfering matrices including solids. The technique was used for the direct determinatio...

  11. Manipulating radicals : Using cobalt to steer radical reactions

    NARCIS (Netherlands)

    Chirilă, A.

    2017-01-01

    This thesis describes research aimed at understanding and exploiting metallo-radical reactivity and explores reactions mediated by square planar, low-spin cobalt(II) complexes. A primary goal was to uncover novel reactivity of discrete cobalt(III)-bound carbene radicals generated upon reaction of

  12. Functionalized graphene quantum dots loaded with free radicals combined with liquid chromatography and tandem mass spectrometry to screen radical scavenging natural antioxidants from Licorice and Scutellariae.

    Science.gov (United States)

    Wang, Guoying; Niu, XiuLi; Shi, Gaofeng; Chen, Xuefu; Yao, Ruixing; Chen, Fuwen

    2014-12-01

    A novel screening method was developed for the detection and identification of radical scavenging natural antioxidants based on a free radical reaction combined with liquid chromatography with tandem mass spectrometry. Functionalized graphene quantum dots were prepared for loading free radicals in the complex screening system. The detection was performed with and without a preliminary exposure of the samples to specific free radicals on the functionalized graphene quantum dots, which can facilitate charge transfer between free radicals and antioxidants. The difference in chromatographic peak areas was used to identify potential antioxidants. This is a novel approach to simultaneously evaluate the antioxidant power of a component versus a free radical, and to identify it in a vegetal matrix. The structures of the antioxidants in the samples were identified using tandem mass spectrometry and comparison with standards. Fourteen compounds were found to possess potential antioxidant activity, and their free radical scavenging capacities were investigated. The order of scavenging capacity of 14 compounds was compared according to their free radical scavenging rate. 4',5,6,7-Tetrahydroxyflavone (radical scavenging rate: 0.05253 mL mg(-1) s(-1) ) showed the strongest capability for scavenging free radicals. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Dissociative Photoionization of the Elusive Vinoxy Radical.

    Science.gov (United States)

    Adams, Jonathan D; Scrape, Preston G; Lee, Shih-Huang; Butler, Laurie J

    2017-08-24

    These experiments report the dissociative photoionization of vinoxy radicals to m/z = 15 and 29. In a crossed laser-molecular beam scattering apparatus, we induce C-Cl bond fission in 2-chloroacetaldehyde by photoexcitation at 157 nm. Our velocity measurements, combined with conservation of angular momentum, show that 21% of the C-Cl photofission events form vinoxy radicals that are stable to subsequent dissociation to CH3 + CO or H + ketene. Photoionization of these stable vinoxy radicals, identified by their velocities, which are momentum-matched with the higher-kinetic-energy Cl atom photofragments, shows that the vinoxy radicals dissociatively photoionize to give signal at m/z = 15 and 29. We calibrated the partial photoionization cross section of vinoxy to CH3+ relative to the bandwidth-averaged photoionization cross section of the Cl atom at 13.68 eV to put the partial photoionization cross sections on an absolute scale. The resulting bandwidth-averaged partial cross sections are 0.63 and 1.3 Mb at 10.5 and 11.44 eV, respectively. These values are consistent with the upper limit to the cross section estimated from a study by Savee et al. on the O(3P) + propene bimolecular reaction. We note that the uncertainty in these values is primarily dependent on the signal attributed to C-Cl primary photofission in the m/z = 35 (Cl+) time-of-flight data. While the value is a rough estimate, the bandwidth-averaged partial photoionization cross section of vinoxy to HCO+ calculated from the signal at m/z = 29 at 11.53 eV is approximately half that of vinoxy to CH3+. We also present critical points on the potential energy surface of the vinoxy cation calculated at the G4//B3LYP/6-311++G(3df,2p) level of theory to support the observation of dissociative ionization of vinoxy to both CH3+ and HCO+.

  14. Etude de la fixation d'atomes de brome dans les traces latentes d'ions

    Science.gov (United States)

    Vareille, J. C.; Moliton, J. P.; Decossas, J. L.; Teyssier, J. L.; Delaunay, B.

    1981-09-01

    We show that the branching of bromide atoms is possible on chemically active sites produced by Kr 8+, Cl 6+ and He 2+ ion irradiation on cellulose triacetate. The number of fixed atoms increases with ion fluence and atomic number. These results are in good agreement with those concerning radical yield around the ions' path.

  15. Atom Skimmers and Atom Lasers Utilizing Them

    Science.gov (United States)

    Hulet, Randall; Tollett, Jeff; Franke, Kurt; Moss, Steve; Sackett, Charles; Gerton, Jordan; Ghaffari, Bita; McAlexander, W.; Strecker, K.; Homan, D.

    2005-01-01

    Atom skimmers are devices that act as low-pass velocity filters for atoms in thermal atomic beams. An atom skimmer operating in conjunction with a suitable thermal atomic-beam source (e.g., an oven in which cesium is heated) can serve as a source of slow atoms for a magneto-optical trap or other apparatus in an atomic-physics experiment. Phenomena that are studied in such apparatuses include Bose-Einstein condensation of atomic gases, spectra of trapped atoms, and collisions of slowly moving atoms. An atom skimmer includes a curved, low-thermal-conduction tube that leads from the outlet of a thermal atomic-beam source to the inlet of a magneto-optical trap or other device in which the selected low-velocity atoms are to be used. Permanent rare-earth magnets are placed around the tube in a yoke of high-magnetic-permeability material to establish a quadrupole or octupole magnetic field leading from the source to the trap. The atoms are attracted to the locus of minimum magnetic-field intensity in the middle of the tube, and the gradient of the magnetic field provides centripetal force that guides the atoms around the curve along the axis of the tube. The threshold velocity for guiding is dictated by the gradient of the magnetic field and the radius of curvature of the tube. Atoms moving at lesser velocities are successfully guided; faster atoms strike the tube wall and are lost from the beam.

  16. Construction of energy transfer systems within nanosized polymer micelles and their fluorescence modulation properties.

    Science.gov (United States)

    Chen, Jian; Zeng, Fang; Wu, Shuizhu

    2010-04-06

    The nanoparticle-based fluorescence resonance energy transfer (FRET) systems have recently attracted considerable attention due to some of their advantages; however, these systems are structurally more complicated than that of small molecule systems, and the energy transfer behavior for particle systems has been seldom investigated. In this study, we synthesized a series of ABC triblock copolymers that contain hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(styrene) (PS) and photochromic poly(2-(3-(3',3'-dimethyl-6-nitrospiro(indoline-2',2-[2H-1]benzopyran)-1'-yl)propanoylo-xy)ethyl methacrylate) (PSPMA) blocks by using the sequential two-step atom transfer radical polymerization (ATRP). The amphiphilic micelles made from these copolymers can incorporate a hydrophobic fluorescent dye, the nitrobenzoxadiazolyl derivative (NBD), thus forming a water dispersible energy transfer system with the fluorescent dye NBD as the donor and spiropyran moieties as the potential acceptor. The spectral properties of NBD/triblock copolymers with varied PS block lengths and PSPMA block lengths have been investigated; the results indicate that the length of PS block in triblock copolymers can affect the energy transfer efficiency of the micelle-based fluorescence modulation system, the micelles with moderate PS block length are preferable for forming FRET system with higher energy transfer efficiency, and short PSPMA blocks (less than 5 repetition units) are enough for efficient energy transfer.

  17. Semiconductor Photocatalysis for Chemoselective Radical Coupling Reactions.

    Science.gov (United States)

    Kisch, Horst

    2017-04-18

    problem of quantitative comparisons of photocatalytic activities or apparent quantum yields and propose a basic three-step mechanistic model. Finally, we address the question whether or not the unique photoredox properties of simple inorganic semiconductor powders may lead to previously unknown visible light induced organic syntheses. For that, we summarize novel radical C-C- and C-N- couplings photocatalyzed by self-prepared cadmium sulfide powders. Electron acceptor and donor substrates like imines or 1,2-diazenes, and cyclic olefins or unsaturated ethers, respectively, undergo a linear addition reaction. The hitherto unknown products have all been isolated in good to moderate yields and may be of pharmaceutical interest. In the first reaction step photogenerated electron-hole pairs produce through proton-coupled electron transfer the corresponding radicals. Their subsequent chemoselective heterocoupling affords the products, correlating with an insertion of the imine or 1,2-diazene into an allylic C(sp 3 )-H bond of the donor substrate. In the absence of an imine or 1,2-diazene, cyclic allyl/enol ethers are dehydrodimerized under concomitant hydrogen evolution. Even a visible light photosulfoxidation of alkanes is catalyzed by titania. In these heterogeneous photoredox reactions the role of the semiconductor photocatalyst is multifunctional. It induces favorable substrate preorientations in the surface-solvent layer, it catalyzes proton-coupled interfacial electron transfer to and from substrates generating intermediate radicals, and it enables their subsequent chemoselective coupling in the surface-solvent interface. Different from molecular photosensitizers, which enable only one one-electron transfer with one single substrate, photoexcited semiconductors induce two concerted one-electron transfer reactions with two substrates. This is because the light generated electron-hole pairs are trapped at distinct surface sites and undergo proton-coupled interfacial electron

  18. Free radicals and polarized targets

    Science.gov (United States)

    Bunyatova, E. I.

    2004-06-01

    Many free radicals were added to organic compounds in search of high proton and deuteron polarizations. Few found practical application. A short review is presented, and special attention is given to some stable nitroxyl radicals which have lately been admixed to organic compounds solid at room temperature, in particular to scintillators.

  19. Free radicals and polarized targets

    Energy Technology Data Exchange (ETDEWEB)

    Bunyatova, E.I. E-mail: bunyatel@nusun.jinr.ru

    2004-06-21

    Many free radicals were added to organic compounds in search of high proton and deuteron polarizations. Few found practical application. A short review is presented, and special attention is given to some stable nitroxyl radicals which have lately been admixed to organic compounds solid at room temperature, in particular to scintillators.

  20. CHARACTERISTIC RADICALS OF STOCHASTIC MATRICES,

    Science.gov (United States)

    The paper investigates the distribution on a complex plane of characteristic radicals of stochastic matrices of the n-th order. The results obtained...can be interpreted as theorems on the relative distribution of characteristic radicals of an arbitrary matrix with non-negative elements. (Author)

  1. Radical polymerization of styrene controlled by half-sandwich Mo(III)/Mo(IV) couples: all basic mechanisms are possible.

    Science.gov (United States)

    Le Grognec, E; Claverie, J; Poli, R

    2001-10-03

    Density functional calculations of bond dissociation energies (BDEs) have been used as a guide to the choice of metal system suitable for controlling styrene polymerization by either the stable free radical polymerization (SFRP) or the atom transfer radical polymerization (ATRP) mechanism. In accord with the theoretical prediction, CpMo(eta(4)-C(4)H(6))(CH(2)SiMe(3))(2), 2, is not capable of yielding SFRP of styrene. Still in accord with theoretical prediction, CpMo(eta(4)-C(4)H(6))Cl(2), 1, CpMo(PMe(3))(2)Cl(2), 3, and CpMo(dppe)Cl(2) (dppe = 1,2-bis(diphenylphosphino)ethane), 4, yield controlled styrene polymerization by the SFRP mechanism in the presence of 2,2'-azobisisobutyronitrile (AIBN). This arises from the generation of a putative Mo(IV) alkyl species from the AIBN-generated radical addition to the Mo(III) compound. The controlled nature of the polymerizations is indicated by linear M(n) progression with the conversion in all cases and moderate polydispersity indices (PDIs). Controlled polymerization of styrene is also given by compounds 3 and 4 in combination with alkyl bromides. These complexes then operate by the ATRP mechanism, again in accord with the theoretical predictions. Controlled character is revealed by linear increase of M(n) versus conversion, low PDIs, a stop-and-go experiment, and (1)H NMR and MALDI-TOF analyses of the polymer end groups. The same controlled polymerization is given by a "reverse" ATRP experiment, starting from AIBN and CpMo(PMe(3))(2)Cl(2)Br, 5. On the other hand, when compound 1 or 2 is used in combination with an alkyl bromide (as for an ATRP experiment), the isolated polystyrene shows by M(n), (1)H NMR, and MALDI-TOF analyses that catalytic chain transfer (CCT) radical polymerization takes place in this case. Kinetics simulations underscore the conditions regulating the radical polymerization mechanism and the living character of the polymerization. The complexes herein described are ineffective at controlling the

  2. Pressure-Dependent Rate Rules for Intramolecular H-Migration Reactions of Hydroperoxyalkylperoxy Radicals in Low Temperature.

    Science.gov (United States)

    Yao, Qian; Sun, Xiao-Hui; Li, Ze-Rong; Chen, Fang-Fang; Li, Xiang-Yuan

    2017-04-27

    Intramolecular H-migration reaction of hydroperoxyalkylperoxy radicals (•O2QOOH) is one of the most important reaction families in the low-temperature oxidation of hydrocarbon fuels. This reaction family is first divided into classes depending upon H atom transfer from -OOH bonded carbon or non-OOH bonded carbon, and then the two classes are further divided depending upon the ring size of the transition states and the types of the carbons from which the H atom is transferred. High pressure limit rate rules and pressure-dependent rate rules for each class are derived from the rate constants of a representative set of reactions within each class using electronic structure calculations performed at the CBS-QB3 level of theory. For the intramolecular H-migration reactions of •O2QOOH radicals for abstraction from an -OOH substituted carbon atom (-OOH bonded case), the result shows that it is acceptable to derive the rate rules by taking the average of the rate constants from a representative set of reactions with different sizes of the substitutes. For the abstraction from a non-OOH substituted carbon atom (non-OOH bonded case), rate rules for each class are also derived and it is shown that the difference between the rate constants calculated by CBS-QB3 method and rate constants estimated from the rate rules may be large; therefore, to get more reliable results for the low-temperature combustion modeling of alkanes, it is better to assign each reaction its CBS-QB3 calculated rate constants, instead of assigning the same values for the same reaction class according to rate rules. The intramolecular H-migration reactions of •O2QOOH radicals (a thermally equilibrated system) are pressure-dependent, and the pressure-dependent rate constants of these reactions are calculated by using the Rice-Ramsberger-Kassel-Marcus/master-equation theory at pressures varying from 0.01 to 100 atm. The impact of molecular size on the pressure-dependent rate constants of the

  3. Decay and microwave power saturation features to determine the radiation-induced radicals of sorbic acid and potassium sorbate

    Science.gov (United States)

    Tuner, Hasan

    2017-12-01

    Gamma irradiated sorbic acid (SA) and its potassium salt (KSA) were present complex unresolved Electron Paramagnetic Resonance (EPR) spectra. Spectroscopic features and possible structures of the radiation-induced radicals were determined using spectrum simulation calculations according to the microwave power saturations, room and high-temperatures decay findings. It is found that while the radicals decayed in time some of the radicals transferred to another type of radical. The spectrum simulations of SA and KSA were carried out on different spectra recorded in different conditions. Although, most of the radiation-induced radicals of SA and KSA have the similar chemical structures different EPR spectroscopic features were observed. It has been determined that there are three and four different radical species best describe the experimental spectra of SA and KSA, respectively. If the decay rates of the radiation-induced radicals are different, using the information derived from the decay findings present significant information about the spectroscopic features of the existing radicals.

  4. Radical abundance how a revolution in nanotechnology will change civilization

    CERN Document Server

    Drexler, K Eric

    2013-01-01

    K. Eric Drexler is the founding father of nanotechnology--the science of engineering on a molecular level. In Radical Abundance, he shows how rapid scientific progress is about to change our world. Thanks to atomically precise manufacturing, we will soon have the power to produce radically more of what people want, and at a lower cost. The result will shake the very foundations of our economy and environment. Already, scientists have constructed prototypes for circuit boards built of millions of precisely arranged atoms. The advent of this kind of atomic precision promises to change the way we make things--cleanly, inexpensively, and on a global scale. It allows us to imagine a world where solar arrays cost no more than cardboard and aluminum foil, and laptops cost about the same. A provocative tour of cutting edge science and its implications by the field's founder and master, Radical Abundance offers a mind-expanding vision of a world hurtling toward an unexpected future.

  5. Teaching Semantic Radicals Facilitates Inferring New Character Meaning in Sentence Reading for Nonnative Chinese Speakers

    Directory of Open Access Journals (Sweden)

    Thi Phuong Nguyen

    2017-10-01

    Full Text Available This study investigates the effects of teaching semantic radicals in inferring the meanings of unfamiliar characters among nonnative Chinese speakers. A total of 54 undergraduates majoring in Chinese Language from a university in Hanoi, Vietnam, who had 1 year of learning experience in Chinese were assigned to two experimental groups that received instructional intervention, called “old-for-new” semantic radical teaching, through two counterbalanced sets of semantic radicals, with one control group. All of the students completed pre- and post-tests of a sentence cloze task where they were required to choose an appropriate character that fit the sentence context among four options. The four options shared the same phonetic radicals but had different semantic radicals. The results showed that the pre-test and post-test score increases were significant for the experimental groups, but not for the control group. Most importantly, the experimental groups successfully transferred the semantic radical strategy to figure out the meanings of unfamiliar characters containing semantic radicals that had not been taught. The results demonstrate the effectiveness of teaching semantic radicals for lexical inference in sentence reading for nonnative speakers, and highlight the ability of transfer learning to acquire semantic categories of sub-lexical units (semantic radicals in Chinese characters among foreign language learners.

  6. Teaching Semantic Radicals Facilitates Inferring New Character Meaning in Sentence Reading for Nonnative Chinese Speakers

    Science.gov (United States)

    Nguyen, Thi Phuong; Zhang, Jie; Li, Hong; Wu, Xinchun; Cheng, Yahua

    2017-01-01

    This study investigates the effects of teaching semantic radicals in inferring the meanings of unfamiliar characters among nonnative Chinese speakers. A total of 54 undergraduates majoring in Chinese Language from a university in Hanoi, Vietnam, who had 1 year of learning experience in Chinese were assigned to two experimental groups that received instructional intervention, called “old-for-new” semantic radical teaching, through two counterbalanced sets of semantic radicals, with one control group. All of the students completed pre- and post-tests of a sentence cloze task where they were required to choose an appropriate character that fit the sentence context among four options. The four options shared the same phonetic radicals but had different semantic radicals. The results showed that the pre-test and post-test score increases were significant for the experimental groups, but not for the control group. Most importantly, the experimental groups successfully transferred the semantic radical strategy to figure out the meanings of unfamiliar characters containing semantic radicals that had not been taught. The results demonstrate the effectiveness of teaching semantic radicals for lexical inference in sentence reading for nonnative speakers, and highlight the ability of transfer learning to acquire semantic categories of sub-lexical units (semantic radicals) in Chinese characters among foreign language learners. PMID:29109694

  7. High Atom Number in Microsized Atom Traps

    Science.gov (United States)

    2015-12-14

    Final Performance Report on ONR Grant N00014-12-1-0608 High atom number in microsized atom traps for the period 15 May 2012 through 14 September...TYPE Final Technical Report 3. DATES COVERED (From - To) 05/15/2012-09/14/2012 4. TITLE AND SUBTITLE High atom number in microsized atom traps...forces for implementing a small-footprint, large-number atom -chip instrument. Bichromatic forces rely on absorption and stimulated emission to produce

  8. Reversible Bergman cyclization by atomic manipulation

    Science.gov (United States)

    Schuler, Bruno; Fatayer, Shadi; Mohn, Fabian; Moll, Nikolaj; Pavliček, Niko; Meyer, Gerhard; Peña, Diego; Gross, Leo

    2016-03-01

    The Bergman cyclization is one of the most fascinating rearrangements in chemistry, with important implications in organic synthesis and pharmacology. Here we demonstrate a reversible Bergman cyclization for the first time. We induced the on-surface transformation of an individual aromatic diradical into a highly strained ten-membered diyne using atomic manipulation and verified the products by non-contact atomic force microscopy with atomic resolution. The diyne and diradical were stabilized by using an ultrathin NaCl film as the substrate, and the diyne could be transformed back into the diradical. Importantly, the diradical and the diyne exhibit different reactivity, electronic, magnetic and optical properties associated with the changes in the bond topology, and spin multiplicity. With this reversible, triggered Bergman cyclization we demonstrated switching on demand between the two reactive intermediates by means of selective C-C bond formation or cleavage, which opens up the field of radical chemistry for on-surface reactions by atomic manipulation.

  9. Anion photoelectron spectroscopy of radicals and clusters

    Energy Technology Data Exchange (ETDEWEB)

    Travis, Taylor R. [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    Anion photoelectron spectroscopy is used to study free radicals and clusters. The low-lying 2Σ and 2π states of C2nH (n = 1--4) have been studied. The anion photoelectron spectra yielded electron affinities, term values, and vibrational frequencies for these combustion and astrophysically relevant species. Photoelectron angular distributions allowed the author to correctly assign the electronic symmetry of the ground and first excited states and to assess the degree of vibronic coupling in C2H and C4H. Other radicals studied include NCN and I3. The author was able to observe the low-lying singlet and triplet states of NCN for the first time. Measurement of the electron affinity of I3 revealed that it has a bound ground state and attachment of an argon atom to this moiety enabled him to resolve the symmetric stretching progression.

  10. Free radicals and male reproduction.

    Science.gov (United States)

    Agarwal, Ashok; Allamaneni, Shyam S R

    2011-03-01

    Male factor accounts for almost 50% cases of infertility. The exact mechanism of sperm dysfunction is not known in many cases. Extensive research in the last decade has led to the identification of free radicals (reactive oxygen species) as mediators of sperm dysfunction in both specific diagnoses and idiopathic cases of male infertility. Elevated levels of reactive oxygen species are seen in up to 30-80% of men with male infertility. The role of free radicals has been studied extensively in the process of human reproduction. We know now that a certain level of free radicals is necessary for normal sperm function, whereas an excessive level of free radicals can cause detrimental effect on sperm function and subsequent fertilisation and offspring health. Oxidative stress develops when there is an imbalance between generation of free radicals and scavenging capacity of anti-oxidants in reproductive tract. Oxidative stress has been shown to affect both standard semen parameters and fertilising capacity. In addition, high levels of free radicals have been associated with lack of or poor fertility outcome after natural conception or assisted reproduction. Diagnostic techniques to quantify free radicals in infertile patients can assist physicians treating patients with infertility to plan for proper treatment strategies. In vivo anti-oxidants can be used against oxidative stress in male reproductive tract. Supplementation of in vitro anti-oxidants can help prevent the oxidative stress during sperm preparation techniques in assisted reproduction.

  11. An Atomic Gravitational Wave Interferometric Sensor (AGIS)

    Energy Technology Data Exchange (ETDEWEB)

    Dimopoulos, Savas; /Stanford U., Phys. Dept.; Graham, Peter W.; /SLAC; Hogan, Jason M.; Kasevich, Mark A.; /Stanford U., Phys. Dept.; Rajendran, Surjeet; /SLAC /Stanford U., Phys. Dept.

    2008-08-01

    We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite-based, utilizing the core technology of the Stanford 10m atom interferometer presently under construction. Each configuration compares two widely separated atom interferometers run using common lasers. The signal scales with the distance between the interferometers, which can be large since only the light travels over this distance, not the atoms. The terrestrial experiment with baseline {approx} 1 km can operate with strain sensitivity {approx} 10{sup -19}/{radical}Hz in the 1 Hz-10 Hz band, inaccessible to LIGO, and can detect gravitational waves from solar mass binaries out to megaparsec distances. The satellite experiment with baseline {approx} 1000 km can probe the same frequency spectrum as LISA with comparable strain sensitivity {approx} 10{sup -20}/{radical}Hz. The use of ballistic atoms (instead of mirrors) as inertial test masses improves systematics coming from vibrations, acceleration noise, and significantly reduces spacecraft control requirements. We analyze the backgrounds in this configuration and discuss methods for controlling them to the required levels.

  12. Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

    Science.gov (United States)

    Miller, David C.; Tarantino, Kyle T.; Knowles, Robert R.

    2016-01-01

    Proton-coupled electron transfers (PCETs) are unconventional redox processes in which both protons and electrons are exchanged, often in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic energy conversion technologies, its applications in organic synthesis are only beginning to be explored. In this chapter we aim to highlight the origins, development and evolution of PCET processes most relevant to applications in organic synthesis. Particular emphasis is given to the ability of PCET to serve as a non-classical mechanism for homolytic bond activation that is complimentary to more traditional hydrogen atom transfer processes, enabling the direct generation of valuable organic radical intermediates directly from their native functional group precursors under comparatively mild catalytic conditions. The synthetically advantageous features of PCET reactivity are described in detail, along with examples from the literature describing the PCET activation of common organic functional groups. PMID:27573270

  13. Comb-Type Grafted Hydrogels of PNIPAM and PDMAEMA with Reversed Network-Graft Architectures from Controlled Radical Polymerizations

    Directory of Open Access Journals (Sweden)

    Sheng-Qi Chen

    2016-02-01

    Full Text Available Dual thermo- and pH-responsive comb-type grafted hydrogels of poly(N,N-dimethylaminoethyl methacrylate (PDMAEMA and poly(N-isopropylacrylamide (PNIPAM with reversed network-graft architectures were synthesized by the combination of atom transfer radical polymerization (ATRP, reversible addition-fragmentation chain transfer (RAFT polymerization and click chemistry. Two kinds of macro-cross-linkers with two azido groups at one chain-end and different chain length [PNIPAM–(N32 and PDMAEMA–(N32] were prepared with N,N-di(β-azidoethyl 2-halocarboxylamide as the ATRP initiator. Through RAFT copolymerization of DMAEMA or NIPAM with propargyl acrylate (ProA using dibenzyltrithiocarbonate as a chain transfer agent, two network precursors with different content of alkynyl side-groups [P(DMAEMA-co-ProA and P(NIPAM-co-ProA] were obtained. The subsequent azido-alkynyl click reaction of macro-cross-linkers and network precursors led to the formation of the network-graft hydrogels. These dual stimulus-sensitive hydrogels exhibited rapid response, high swelling ratio and reproducible swelling/de-swelling cycles under different temperatures and pH values. The influences of cross-linkage density and network-graft architecture on the properties of the hydrogels were investigated. The release of ceftriaxone sodium from these hydrogels showed both thermal- and pH-dependence, suggesting the feasibility of these hydrogels as thermo- and pH-dependent drug release devices.

  14. CONTINENT RADICAL PROSTATECTOMY

    Directory of Open Access Journals (Sweden)

    Yu. P. Sernyak

    2014-07-01

    Full Text Available Objective: to evaluate the impact of dissection of the dorsal venous complex without pre-ligation, suturing, or coagulation during radical prostatectomy (RPE in patients with localized prostate cancer (PC on the quality of surgery and the function of urinary retention.Subjects and methods. The data of 42 patients who had undergone posterior and anterior anatomical repair and vesicourethral anastomosis using a V-lock suture after prostatectomy were analyzed. All the patients were divided into 2 groups. Group 1 consisted of 22 patients in whom the dorsal venous complex was closed using a 3-0 vicryl suture before urethral dissection. Group 2 included 20 patients in whom the urethra was dissected without suturing the venous complex.Results. In group 1, complete urinary retention after catheter removal was noted in 9 (40.9 % and 15 (68 % patients within 24 hours and after 3 months, respectively. Following 12 months, two (9 % patients were observed to have partial mild urinary incontinence (as many as 2 pads per day. Group 2 patients showed complete urinary retention in 17 (85 % cases on the first day after catheter removal; all the patients retained urine 3 months later.Conclusion. In patients with localized PC, dissection of the dorsal venous complex without presuturing during laparoscopic RPE exerts a considerable impact on the preservation of urinary retention, namely 45% more of the patients reported complete urinary retention in early periods and 10 % more did this in later periods. At the same time, there was no statistically significant increase in intraoperative blood loss (p > 0.05, the number of positive edges, or biochemical recurrences.

  15. CONTINENT RADICAL PROSTATECTOMY

    Directory of Open Access Journals (Sweden)

    Yu. P. Sernyak

    2013-01-01

    Full Text Available Objective: to evaluate the impact of dissection of the dorsal venous complex without pre-ligation, suturing, or coagulation during radical prostatectomy (RPE in patients with localized prostate cancer (PC on the quality of surgery and the function of urinary retention.Subjects and methods. The data of 42 patients who had undergone posterior and anterior anatomical repair and vesicourethral anastomosis using a V-lock suture after prostatectomy were analyzed. All the patients were divided into 2 groups. Group 1 consisted of 22 patients in whom the dorsal venous complex was closed using a 3-0 vicryl suture before urethral dissection. Group 2 included 20 patients in whom the urethra was dissected without suturing the venous complex.Results. In group 1, complete urinary retention after catheter removal was noted in 9 (40.9 % and 15 (68 % patients within 24 hours and after 3 months, respectively. Following 12 months, two (9 % patients were observed to have partial mild urinary incontinence (as many as 2 pads per day. Group 2 patients showed complete urinary retention in 17 (85 % cases on the first day after catheter removal; all the patients retained urine 3 months later.Conclusion. In patients with localized PC, dissection of the dorsal venous complex without presuturing during laparoscopic RPE exerts a considerable impact on the preservation of urinary retention, namely 45% more of the patients reported complete urinary retention in early periods and 10 % more did this in later periods. At the same time, there was no statistically significant increase in intraoperative blood loss (p > 0.05, the number of positive edges, or biochemical recurrences.

  16. The role of charge transfer in the oxidation state change of Ce atoms in the TM13-CeO2(111) systems (TM = Pd, Ag, Pt, Au): a DFT + U investigation.

    Science.gov (United States)

    Tereshchuk, Polina; Freire, Rafael L H; Ungureanu, Crina G; Seminovski, Yohanna; Kiejna, Adam; Da Silva, Juarez L F

    2015-05-28

    Despite extensive studies of transition metal (TM) clusters supported on ceria (CeO2), fundamental issues such as the role of the TM atoms in the change in the oxidation state of Ce atoms are still not well understood. In this work, we report a theoretical investigation based on static and ab initio molecular dynamics density functional theory calculations of the interaction of 13-atom TM clusters (TM = Pd, Ag, Pt, Au) with the unreduced CeO2(111) surface represented by a large surface unit cell and employing Hubbard corrections for the strong on-site Coulomb correlation in the Ce f-electrons. We found that the TM13 clusters form pyramidal-like structures on CeO2(111) in the lowest energy configurations with the following stacking sequence, TM/TM4/TM8/CeO2(111), while TM13 adopts two-dimensional structures at high energy structures. TM13 induces a change in the oxidation state of few Ce atoms (3 of 16) located in the topmost Ce layer from Ce(IV) (itinerant Ce f-states) to Ce(III) (localized Ce f-states). There is a charge flow from the TM atoms to the CeO2(111) surface, which can be explained by the electronegativity difference between the TM (Pd, Ag, Pt, Au) and O atoms, however, the charge is not uniformly distributed on the topmost O layer due to the pressure induced by the TM13 clusters on the underlying O ions, which yields a decrease in the ionic charge of the O ions located below the cluster and an increase in the remaining O ions. Due to the charge flow mainly from the TM8-layer to the topmost O-layer, the charge cannot flow from the Ce(IV) atoms to the O atoms with the same magnitude as in the clean CeO2(111) surface. Consequently, the effective cationic charge decreases mainly for the Ce atoms that have a bond with the O atoms not located below the cluster, and hence, those Ce atoms change their oxidation state from IV to III. This increases the size of the Ce(III) compared with the Ce(IV) cations, which builds-in a strain within the topmost Ce layer, and

  17. Atom-specific surface magnetometry

    Science.gov (United States)

    Sirotti, Fausto; Panaccione, Giancarlo; Rossi, Giorgio

    1995-12-01

    A powerful atom-specific surface magnetometry can be based on efficient measurements of magnetic dichroism in l>~0 core level photoemission. The temperature dependence M(T) of the Fe(100) surface magnetization was obtained from the photoemission magnetic asymmetry of 3p core levels, providing the measure of the surface exchange coupling via the spin-wave stiffness and of the surface critical exponent. Beyond the magnetic order the photoemission dichroism allows us to derive the energy splitting of the magnetic sublevels of the photoexcited core hole. Fe 3p photoemission dichroism probes directly the magnetic moment changes of iron atoms at Fe(100) surfaces as a function of structural disorder or sulfur segregation. The appearance of dichroism in the 2p photoemission of segregated sulfur atoms in the c(2×2)S/Fe(100) superstructure measures the magnetic-moment transfer and shows the possibility of investigating surface magnetochemistry in a very direct way.

  18. Dynamics of an all-optical atomic spin gyroscope.

    Science.gov (United States)

    Fang, Jiancheng; Wan, Shuangai; Yuan, Heng

    2013-10-20

    We present the transfer function of an all-optical atomic spin gyroscope through a series of differential equations and validate the transfer function by experimental test. A transfer function is the basis for further control system design. We build the differential equations based on a complete set of Bloch equations describing the all-optical atomic spin gyroscope, and obtain the transfer function through application of the Laplace transformation to these differential equations. Moreover, we experimentally validate the transfer function in an all-optical Cs-Xe129 atomic spin gyroscope through a series of step responses. This transfer function is convenient for analysis of the form of control system required. Furthermore, it is available for the design of the control system specifically to improve the performance of all-optical atomic spin gyroscopes.

  19. Magnetic trapping of cold bromine atoms.

    Science.gov (United States)

    Rennick, C J; Lam, J; Doherty, W G; Softley, T P

    2014-01-17

    Magnetic trapping of bromine atoms at temperatures in the millikelvin regime is demonstrated for the first time. The atoms are produced by photodissociation of Br2 molecules in a molecular beam. The lab-frame velocity of Br atoms is controlled by the wavelength and polarization of the photodissociation laser. Careful selection of the wavelength results in one of the pair of atoms having sufficient velocity to exactly cancel that of the parent molecule, and it remains stationary in the lab frame. A trap is formed at the null point between two opposing neodymium permanent magnets. Dissociation of molecules at the field minimum results in the slowest fraction of photofragments remaining trapped. After the ballistic escape of the fastest atoms, the trapped slow atoms are lost only by elastic collisions with the chamber background gas. The measured loss rate is consistent with estimates of the total cross section for only those collisions transferring sufficient kinetic energy to overcome the trapping potential.

  20. Toward the Oxidation of the Phenyl Radical and Prevention of PAH Formation in Combustion Systems.

    Science.gov (United States)

    Parker, Dorian S N; Kaiser, Ralf I; Troy, Tyler P; Kostko, Oleg; Ahmed, Musahid; Mebel, Alexander M

    2015-07-16

    The reaction of the phenyl radical (C6H5) with molecular oxygen (O2) plays a central role in the degradation of poly- and monocyclic aromatic radicals in combustion systems which would otherwise react with fuel components to form polycyclic aromatic hydrocarbons (PAHs) and eventually soot. Despite intense theoretical and experimental scrutiny over half a century, the overall reaction channels have not all been experimentally identified. Tunable vacuum ultraviolet photoionization in conjunction with a combustion simulating chemical reactor uniquely provides the complete isomer specific product spectrum and branching ratios of this prototype reaction. In the reaction of phenyl radicals and molecular oxygen at 873 K and 1003 K, ortho-benzoquinone (o-C6H4O2), the phenoxy radical (C6H5O), and cyclopentadienyl radical (C5H5) were identified as primary products formed through emission of atomic hydrogen, atomic oxygen and carbon dioxide. Furan (C4H4O), acrolein (C3H4O), and ketene (C2H2O) were also identified as primary products formed through ring opening and fragmentation of the 7-membered ring 2-oxepinoxy radical. Secondary reaction products para-benzoquinone (p-C6H4O2), phenol (C6H5OH), cyclopentadiene (C5H6), 2,4-cyclopentadienone (C5H4O), vinylacetylene (C4H4), and acetylene (C2H2) were also identified. The pyranyl radical (C5H5O) was not detected; however, electronic structure calculations show that it is formed and isomerizes to 2,4-cyclopentadienone through atomic hydrogen emission. In combustion systems, barrierless phenyl-type radical oxidation reactions could even degrade more complex aromatic radicals. An understanding of these elementary processes is expected to lead to a better understanding toward the elimination of carcinogenic, mutagenic, and environmentally hazardous byproducts of combustion systems such as PAHs.

  1. Evidence for transfer of radicals between oil-in-water emulsion droplets as detected by the probe (E,E)-3,5-Bis(4-phenyl-1,3-butadienyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY665/676

    DEFF Research Database (Denmark)

    Raudsepp, Piret; Brüggemann, Dagmar Adeline; Andersen, Mogens Larsen

    2014-01-01

    (E,E)-3,5-Bis(4-phenyl-1,3-butadienyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY(665/676), is a lipophilic radical-sensitive fluorescent probe that can be used to study radical-driven lipid autoxidation. The sensitivity of BODIPY(665/676) was studied in the presence of radical initiators...

  2. 8-METHOXYNEORAUTENOL AND RADICAL SCAVENGING ...

    African Journals Online (AJOL)

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    8-METHOXYNEORAUTENOL AND RADICAL SCAVENGING FLAVONOIDS FROM. ERYTHRINA ABYSSINICA. Abiy Yenesew1*, Hannington Twinomuhwezi1 ... shown that the plant elaborates alkaloids [1], flavanones, pterocarpans, chalcones and isoflavonoids [1, 3]; some of which have been shown to have antimicrobial ...

  3. Redox Properties of Free Radicals.

    Science.gov (United States)

    Neta, P.

    1981-01-01

    Describes pulse radiolysis as a useful means in studing one-electron redox potentials. This method allows the production of radicals and the determination of their concentration and rates of reaction. (CS)

  4. The thermal decomposition of the benzyl radical in a heated micro-reactor. I. Experimental findings

    Science.gov (United States)

    Buckingham, Grant T.; Ormond, Thomas K.; Porterfield, Jessica P.; Hemberger, Patrick; Kostko, Oleg; Ahmed, Musahid; Robichaud, David J.; Nimlos, Mark R.; Daily, John W.; Ellison, G. Barney

    2015-01-01

    The pyrolysis of the benzyl radical has been studied in a set of heated micro-reactors. A combination of photoionization mass spectrometry (PIMS) and matrix isolation infrared (IR) spectroscopy has been used to identify the decomposition products. Both benzyl bromide and ethyl benzene have been used as precursors of the parent species, C6H5CH2, as well as a set of isotopically labeled radicals: C6H5CD2, C6D5CH2, and C6H513CH2. The combination of PIMS and IR spectroscopy has been used to identify the earliest pyrolysis products from benzyl radical as: C5H4=C=CH2, H atom, C5H4—C ≡ CH, C5H5, HCCCH2, and HC ≡ CH. Pyrolysis of the C6H5CD2, C6D5CH2, and C6H513CH2 benzyl radicals produces a set of methyl radicals, cyclopentadienyl radicals, and benzynes that are not predicted by a fulvenallene pathway. Explicit PIMS searches for the cycloheptatrienyl radical were unsuccessful, there is no evidence for the isomerization of benzyl and cycloheptatrienyl radicals: C6H5CH2⇋C7H7. These labeling studies suggest that there must be other thermal decomposition routes for the C6H5CH2 radical that differ from the fulvenallene pathway.

  5. "Bohr's Atomic Model."

    Science.gov (United States)

    Willden, Jeff

    2001-01-01

    "Bohr's Atomic Model" is a small interactive multimedia program that introduces the viewer to a simplified model of the atom. This interactive simulation lets students build an atom using an atomic construction set. The underlying design methodology for "Bohr's Atomic Model" is model-centered instruction, which means the central model of the…

  6. Estimation of standard reduction potentials of halogen atoms and alkyl halides.

    Science.gov (United States)

    Isse, Abdirisak A; Lin, Ching Yeh; Coote, Michelle L; Gennaro, Armando

    2011-02-03

    Standard reduction potentials, SRPs, of the halogen atoms have been calculated in water on the basis of an appropriate thermochemical cycle. Using the best up-to-date thermodynamic data available in the literature, we have calculated E(o)(X•/X-) values of 3.66, 2.59, 2.04, and 1.37 V vs SHE for F•, Cl•, Br•, and I•, respectively. Additionally, we have computed the SRPs of Cl•, Br•, and I• in acetonitrile (CH3CN) and dimethylformamide (DMF) by correcting the values obtained in water for the free energies of transfer of X• and X- from water to the nonaqueous solvent S and the intersolvent potential between water and S. From the values of E(o)(X •/X-) in CH(3)CN and DMF, the SRPs of a series of alkyl halides of relevance to atom transfer radical polymerization and other important processes such as pollution abatement have been calculated in these two solvents. This has been done with the aid of a thermochemical cycle involving the gas-phase homolytic dissociation of the C-X bond, solvation of RX, R•, and X•, and reduction of X• to X- in solution.

  7. Possible Involvement of Hydrosulfide in B12-Dependent Methyl Group Transfer

    Directory of Open Access Journals (Sweden)

    John I. Toohey

    2017-04-01

    Full Text Available Evidence from several fields of investigation lead to the hypothesis that the sulfur atom is involved in vitamin B12-dependent methyl group transfer. To compile the evidence, it is necessary to briefly review the following fields: methylation, the new field of sulfane sulfur/hydrogen sulfide (S°/H2S, hydrosulfide derivatives of cobalamins, autoxidation of hydrosulfide radical, radical S-adenosylmethionine methyl transfer (RSMT, and methionine synthase (MS. Then, new reaction mechanisms for B12-dependent methyl group transfer are proposed; the mechanisms are facile and overcome difficulties that existed in previously-accepted mechanisms. Finally, the theory is applied to the effect of S°/H2S in nerve tissue involving the “hypomethylation theory” that was proposed 50 years ago to explain the neuropathology resulting from deficiency of vitamin B12 or folic acid. The conclusions are consistent with emerging evidence that sulfane sulfur/hydrogen sulfide may be beneficial in treating Alzheimer’s disease.

  8. Energy transfer processes in solar energy conversion

    Energy Technology Data Exchange (ETDEWEB)

    Fayer, M.D.

    1986-11-01

    By combining picosecond optical experiments and detailed statistical mechanics theory we continue to increase our understanding of the complex interplay of structure and dynamics in important energy transfer situations. A number of different types of problems will be focused on experimentally and theoretically. They are excitation transport among chromophores attached to finite size polymer coils; excitation transport among chromophores in monolayers, bilayers, and finite and infinite stacks of layers; excitation transport in large vesicle systems; and photoinduced electron transfer in glasses and liquids, focusing particularly on the back transfer of the electron from the photogenerated radical anion to the radical cation. 33 refs., 13 figs.

  9. Suprathermal oxygen atoms in the Martian upper atmosphere: Contribution of the proton and hydrogen atom precipitation

    Science.gov (United States)

    Shematovich, V. I.

    2017-07-01

    This is a study of the kinetics and transport of hot oxygen atoms in the transition region (from the thermosphere to the exosphere) of the Martian upper atmosphere. It is assumed that the source of the hot oxygen atoms is the transfer of momentum and energy in elastic collisions between thermal atmospheric oxygen atoms and the high-energy protons and hydrogen atoms precipitating onto the Martian upper atmosphere from the solar-wind plasma. The distribution functions of suprathermal oxygen atoms by the kinetic energy are calculated. It is shown that the exosphere is populated by a large number of suprathermal oxygen atoms with kinetic energies up to the escape energy 2 eV; i.e., a hot oxygen corona is formed around Mars. The transfer of energy from the precipitating solar-wind plasma protons and hydrogen atoms to the thermal oxygen atoms leads to the formation of an additional nonthermal escape flux of atomic oxygen from the Martian atmosphere. The precipitation-induced escape flux of hot oxygen atoms may become dominant under the conditions of extreme solar events, such as solar flares and coronal mass ejections, as shown by recent observations onboard NASA's MAVEN spacecraft (Jakosky et al., 2015).

  10. Stable Organic Radicals as Hole Injection Dopants for Efficient Optoelectronics.

    Science.gov (United States)

    Bin, Zhengyang; Guo, Haoqing; Liu, Ziyang; Li, Feng; Duan, Lian

    2018-02-07

    Precursors of reactive organic radicals have been widely used as n-dopants in electron-transporting materials to improve electron conductivity and enhance electron injection. However, the utilization of organic radicals in hole counterparts has been ignored. In this work, stable organic radicals have been proved for the first time to be efficient dopants to enhance hole injection. From the absorbance spectra and the ultraviolet photoelectron spectra, we could observe an efficient electron transfer between the organic radical, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz), and the widely used hole injection material, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN). When the unpaired electron of TTM-1Cz is transferred to HAT-CN, it would be oxidized to a TTM-1Cz cation with a newly formed lowest unoccupied molecular orbital which is quite close to the highest occupied molecular orbital (HOMO) of the hole-transporting material (HTM). In this way, the TTM-1Cz cation would promote the electron extraction from the HOMO of the HTM and improve hole injection. Using TTM-1Cz-doped HAT-CN as the hole injection layer, efficient organic light-emitting diodes with extremely low voltages can be attained.

  11. Transperitoneal laparoscopic radical prostatectomy: ascending technique.

    Science.gov (United States)

    Rassweiler, J; Marrero, R; Hammady, A; Erdogru, T; Teber, D; Frede, T

    2004-09-01

    To demonstrate the operative steps of transperitoneal laparoscopic radical prostatectomy with the ascending approach (Heilbronn technique). The technique is based on our experience with more than 1000 cases of clinically localized prostate cancer from March 1999 to April 2004. The technical steps, instrumental requirements, patient data, complications, and reintervention rate were reviewed. The principles of the technique include the routine use of a voice-controlled robot (AESOP) for the camera, exposure of the prostatic apex with 120 degree retracting forceps, free-hand suturing for Santorini plexus control, application of 5-mm clips during the nerve-sparing technique, control of the prostatic pedicles by 12-mm Hem-o-Lock clips, the bladder neck-sparing technique in patients with stage T1c and T2a tumors, and use of interrupted sutures for the urethrovesical anastomosis. A considerable improvement was observed when comparing the first 300 with the most recent 300 cases (mean operating time 280 v 208 minutes; conversion rate 2.7% v 0.3%; reintervention rate 3.7% v 1.0%). Through our experience with more than 1000 cases, transperitoneal access for laparoscopic radical prostatectomy has proven to be feasible and transferable with results comparable to those of the original open approach. Besides the well-known advantages of minimally invasive surgery, the video endoscopic approach may offer further benefits in permitting optimization of the technique by video assessment.

  12. Free radical facilitated damage of ungual keratin.

    Science.gov (United States)

    Khengar, Rajeshree H; Brown, Marc B; Turner, Rob B; Traynor, Matthew J; Holt, Katherine B; Jones, Stuart A

    2010-09-01

    Thioglycolic acid (TA) and urea hydrogen peroxide (urea H(2)O(2)) are thought to disrupt alpha-keratin disulfide links in the nail. However, optimal clinical use of these agents to improve the treatment of nail disorders is currently hindered by a lack of fundamental data to support their mechanism of action. The aim of this study was to investigate how the redox environment of ungual keratin, when manipulated by TA and urea H(2)O(2), influenced the properties of the nail barrier. Potentiometric and voltammetric measurements demonstrated that urea H(2)O(2) obeyed the Nernst equation for a proton coupled one-electron transfer redox process while TA underwent a series of redox reactions that was complicated by electrode adsorption and dimer formation. The functional studies demonstrated that nail permeability, measured through TBF penetration (38.51+/-10.94 microg/cm(2)/h) and nail swelling (244.10+/-14.99% weight increase), was greatest when relatively low concentrations of the thiolate ion were present in the applied solution. Limiting the thiolate ion to low levels in the solution retards thiolate dimerisation and generates thiyl free radicals. It appeared that this free radical generation was fundamental in facilitating the redox-mediated keratin disruption of the ungual membrane. Copyright 2010 Elsevier Inc. All rights reserved.

  13. Solvent driving force ensures fast formation of a persistent and well-separated radical pair in plant cryptochrome

    DEFF Research Database (Denmark)

    Lüdemann, Gesa; Solov'yov, Ilia; Kubar, Tomás

    2015-01-01

    upon the electron transfer. This approach allows us to follow the time evolution of the electron transfer in an unbiased fashion and to reveal the molecular driving force which ensures fast electron transfer in cryptochrome guaranteeing formation of a persistent radical pair suitable...

  14. Separation of photo-induced radical pair in cryptochrome to a functionally critical distance

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Domratcheva, Tatiana; Schulten, Klaus

    2014-01-01

    Cryptochrome is a blue light receptor that acts as a sensor for the geomagnetic field and assists many animals in long-range navigation. The magnetoreceptor function arises from light-induced formation of a radical pair through electron transfer between a flavin cofactor (FAD) and a triad...... of tryptophan residues. Here, this electron transfer is investigated by quantum chemical and classical molecular dynamics calculations. The results reveal how sequential electron transfer, assisted by rearrangement of polar side groups in the cryptochrome interior, can yield a FAD-Trp radical pair state...... with the FAD and Trp partners separated beyond a critical distance. The large radical pair separation reached establishes cryptochrome's sensitivity to the geomagnetic field through weakening of distance-dependent exchange and dipole-dipole interactions. It is estimated that the key secondary electron transfer...

  15. Teach us atom structure

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Suh Yeon

    2006-08-15

    This book is written to teach atom structure in very easy way. It is divided into nine chapters, which indicates what is the components of matter? when we divide matter continuously, it becomes atom, what did atom look like? particles comprised of matter is not only atom, discover of particles comprised of atom, symbol of element, various radiation, form alchemy to nuclear transmutation, shape of atom is evolving. It also has various pictures in each chapters to explain easily.

  16. Playing pinball with atoms.

    Science.gov (United States)

    Saedi, Amirmehdi; van Houselt, Arie; van Gastel, Raoul; Poelsema, Bene; Zandvliet, Harold J W

    2009-05-01

    We demonstrate the feasibility of controlling an atomic scale mechanical device by an external electrical signal. On a germanium substrate, a switching motion of pairs of atoms is induced by electrons that are directly injected into the atoms with a scanning tunneling microscope tip. By precisely controlling the tip current and distance we make two atom pairs behave like the flippers of an atomic-sized pinball machine. This atomic scale mechanical device exhibits six different configurations.

  17. Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

    CERN Document Server

    Swann, A R; Deller, A; Gribakin, G F

    2016-01-01

    Predicted twenty years ago, positron binding to neutral atoms has not yet been observed experimentally. A new scheme is proposed to detect positron-atom bound states by colliding Rydberg positronium (Ps) with neutral atoms. Estimates of the charge-transfer-reaction cross section are obtained using the first Born approximation for a selection of neutral atom targets and a wide range of incident Ps energies and principal quantum numbers. We also estimate the corresponding Ps ionization cross section. The accuracy of the calculations is tested by comparison with earlier predictions for Ps charge transfer in collisions with hydrogen and antihydrogen. We describe an existing Rydberg Ps beam suitable for producing positron-atom bound states and estimate signal rates based on the calculated cross sections and realistic experimental parameters. We conclude that the proposed methodology is capable of producing such states and of testing theoretical predictions of their binding energies.

  18. Structural and molecular basis of the peroxynitrite-mediated nitration and inactivation of Trypanosoma cruzi iron-superoxide dismutases (Fe-SODs) A and B: disparate susceptibilities due to the repair of Tyr35 radical by Cys83 in Fe-SODB through intramolecular electron transfer.

    Science.gov (United States)

    Martinez, Alejandra; Peluffo, Gonzalo; Petruk, Ariel A; Hugo, Martín; Piñeyro, Dolores; Demicheli, Verónica; Moreno, Diego M; Lima, Analía; Batthyány, Carlos; Durán, Rosario; Robello, Carlos; Martí, Marcelo A; Larrieux, Nicole; Buschiazzo, Alejandro; Trujillo, Madia; Radi, Rafael; Piacenza, Lucía

    2014-05-02

    Trypanosoma cruzi, the causative agent of Chagas disease, contains exclusively iron-dependent superoxide dismutases (Fe-SODs) located in different subcellular compartments. Peroxynitrite, a key cytotoxic and oxidizing effector biomolecule, reacted with T. cruzi mitochondrial (Fe-SODA) and cytosolic (Fe-SODB) SODs with second order rate constants of 4.6 ± 0.2 × 10(4) M(-1) s(-1) and 4.3 ± 0.4 × 10(4) M(-1) s(-1) at pH 7.4 and 37 °C, respectively. Both isoforms are dose-dependently nitrated and inactivated by peroxynitrite. Susceptibility of T. cruzi Fe-SODA toward peroxynitrite was similar to that reported previously for Escherichia coli Mn- and Fe-SODs and mammalian Mn-SOD, whereas Fe-SODB was exceptionally resistant to oxidant-mediated inactivation. We report mass spectrometry analysis indicating that peroxynitrite-mediated inactivation of T. cruzi Fe-SODs is due to the site-specific nitration of the critical and universally conserved Tyr(35). Searching for structural differences, the crystal structure of Fe-SODA was solved at 2.2 Å resolution. Structural analysis comparing both Fe-SOD isoforms reveals differences in key cysteines and tryptophan residues. Thiol alkylation of Fe-SODB cysteines made the enzyme more susceptible to peroxynitrite. In particular, Cys(83) mutation (C83S, absent in Fe-SODA) increased the Fe-SODB sensitivity toward peroxynitrite. Molecular dynamics, electron paramagnetic resonance, and immunospin trapping analysis revealed that Cys(83) present in Fe-SODB acts as an electron donor that repairs Tyr(35) radical via intramolecular electron transfer, preventing peroxynitrite-dependent nitration and consequent inactivation of Fe-SODB. Parasites exposed to exogenous or endogenous sources of peroxynitrite resulted in nitration and inactivation of Fe-SODA but not Fe-SODB, suggesting that these enzymes play distinctive biological roles during parasite infection of mammalian cells.

  19. Peroxy radical partitioning during the AMMA radical intercomparison exercise

    Directory of Open Access Journals (Sweden)

    M. D. Andrés-Hernández

    2010-11-01

    Full Text Available Peroxy radicals were measured onboard two scientific aircrafts during the AMMA (African Monsoon Multidisciplinary Analysis campaign in summer 2006. This paper reports results from the flight on 16 August 2006 during which measurements of HO2 by laser induced fluorescence spectroscopy at low pressure (LIF-FAGE and total peroxy radicals (RO2* = HO2+ΣRO2, R = organic chain by two similar instruments based on the peroxy radical chemical amplification (PeRCA technique were subject of a blind intercomparison. The German DLR-Falcon and the British FAAM-BAe-146 flew wing tip to wing tip for about 30 min making concurrent measurements on 2 horizontal level runs at 697 and 485 hPa over the same geographical area in Burkina Faso. A full set of supporting measurements comprising photolysis frequencies, and relevant trace gases like CO, NO, NO2, NOy, O3 and a wider range of VOCs were collected simultaneously.

    Results are discussed on the basis of the characteristics and limitations of the different instruments used. Generally, no data bias are identified and the RO2* data available agree quite reasonably within the instrumental errors. The [RO2*]/[HO2] ratios, which vary between 1:1 and 3:1, as well as the peroxy radical variability, concur with variations in photolysis rates and in other potential radical precursors. Model results provide additional information about dominant radical formation and loss processes.

  20. Radical recombination in interstellar ices, a not so simple mechanism.

    Science.gov (United States)

    Butscher, Teddy; Duvernay, Fabrice; Rimola, Albert; Segado-Centellas, Mireia; Chiavassa, Thierry

    2017-01-25

    Many complex organic molecules (hereafter COMs) have been detected in different regions of the interstellar medium (ISM). In each region, different energetic processes - UV irradiation, atom bombardments, etc. - that could be linked to the formation of detected COMs may occur depending on the environment. Several formation mechanisms were proposed but increasing attention is paid to radical recombination reactions. Previous studies showed that glycolaldehyde (HC(O)CH2OH) and ethylene glycol (HOCH2CH2OH) are formed by radical recombination between HC˙O and ˙CH2OH, and by ˙CH2OH dimerisation, respectively. Formyl (HC˙O), one of the most famous astrophysically-relevant radical species, has been detected as a gaseous component of the ISM. Its reactivity was already attributed to the formation of several COMs. This work aims to study the dimerisation of formyl radical HC˙O using a cryogenic matrix technique. The evolution of the chemical sample composition is monitored by infrared spectroscopy and by mass spectrometry during temperature programmed desorption (TPD) monitoring. Results indicate that the reaction of one HC˙O with another does not lead to the direct formation of glyoxal (HC(O)C(O)H) but yields H2CO and CO. Results are also compared with those for the reaction between two ˙CH2OH radicals and the recombination between HC˙O and ˙CH2OH. Also, glyceraldehyde was tentatively detected in our experiment using different spectroscopic techniques. A radical mechanism is proposed to explain its formation in our experiments. Complementary quantum chemical calculations provide an atomistic interpretation of the experimental findings.