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Sample records for atom tranfer radical

  1. Electron affinities of atoms, molecules and radicals

    NASA Astrophysics Data System (ADS)

    Christodoulides, A. A.; McCorkle, D. L.; Christophorou, L. G.

    The theoretical, semiempirical and experimental methods employed to determine electron affinities (EAs) of atoms, molecules and radicals, and summarize the EA data obtained by these methods were reviewed. The detailed processes underlying the principles of the experimental methods are discussed very briefly. It is, nonetheless, instructive to recapitulate the definition of EA and those of the related quantities, namely, the vertical detachment energy, VDE, and the vertical attachment energy, VAE. The EA of an atom is defined as the difference in total energy between the ground state of the neutral atom (plus the electron at rest at infinity) and its negative ion. The EA of a molecule is defined as the difference in energy between the neutral molecule plus an electron at rest at infinity and the molecular negative ion when both, the neutral molecules and the negative ion, are in their ground electronic, vibrational and rotational states.

  2. The reaction of formyl radical with chlorine atom

    NASA Astrophysics Data System (ADS)

    Qu, Zhang-Wang; Dong, Feng; Zhang, Qiyuan; Kong, Fanao

    2004-03-01

    The radical-radical reaction of formyl radical with chlorine atom has been investigated by the time-resolved infrared emission spectroscopy and by the theoretical calculations at the UB3LYP/6-31++G(d,p) and single-point UCCSD(T)/6-311++G(d,p) levels. The products have been verified as the vibrationally excited CO ( v⩽4) and HCl. The reaction is initiated by radical-radical recombination forming an intermediate of formaldehyde chloride, which further dissociates into the products of HCl and CO.

  3. TRANSITION METAL CATALYSIS IN CONTROLLED RADICAL POLYMERIZATION: ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    EPA Science Inventory

    Novel and diversified macromolecular structures, which include polymers with designed topologies (top), compostions (middle), and functionalities (bottom), can be prepared by atom transfer radical polymerization processes. These polymers can be synthesized from a large variety of...

  4. How solvent modulates hydroxyl radical reactivity in hydrogen atom abstractions.

    PubMed

    Mitroka, Susan; Zimmeck, Stephanie; Troya, Diego; Tanko, James M

    2010-03-10

    The hydroxyl radical (HO*) is a highly reactive oxygen-centered radical whose bimolecular rate constants for reaction with organic compounds (hydrogen atom abstraction) approach the diffusion-controlled limit in aqueous solution. The results reported herein show that hydroxyl radical is considerably less reactive in dipolar, aprotic solvents such as acetonitrile. This diminished reactivity is explained on the basis of a polarized transition state for hydrogen abstraction, in which the oxygen of the hydroxyl radical becomes highly negative and can serve as a hydrogen bond acceptor. Because acetonitrile cannot participate as a hydrogen bond donor, the transition state cannot be stabilized by hydrogen bonding, and the reaction rate is lower; the opposite is true when water is the solvent. This hypothesis explains hydroxyl radical reactivity both in solution and in the gas phase and may be the basis for a "containment strategy" used by Nature when hydroxyl radical is produced endogenously.

  5. Development of atomic radical monitoring probe and its application to spatial distribution measurements of H and O atomic radical densities in radical-based plasma processing

    SciTech Connect

    Takahashi, Shunji; Takashima, Seigo; Yamakawa, Koji; Den, Shoji; Kano, Hiroyuki; Takeda, Keigo; Hori, Masaru

    2009-09-01

    Atomic radicals such as hydrogen (H) and oxygen (O) play important roles in process plasmas. In a previous study, we developed a system for measuring the absolute density of H, O, nitrogen, and carbon atoms in plasmas using vacuum ultraviolet absorption spectroscopy (VUVAS) with a compact light source using an atmospheric pressure microplasma [microdischarge hollow cathode lamp (MHCL)]. In this study, we developed a monitoring probe for atomic radicals employing the VUVAS with the MHCL. The probe size was 2.7 mm in diameter. Using this probe, only a single port needs to be accessed for radical density measurements. We successfully measured the spatial distribution of the absolute densities of H and O atomic radicals in a radical-based plasma processing system by moving the probe along the radial direction of the chamber. This probe allows convenient analysis of atomic radical densities to be carried out for any type of process plasma at any time. We refer to this probe as a ubiquitous monitoring probe for atomic radicals.

  6. Strong Exchange Anisotropy in Heavy Atom Radical Ferromagnets

    NASA Astrophysics Data System (ADS)

    Winter, Stephen

    2012-02-01

    The discovery twenty years ago of ferromagnetic ordering in ``light atom'' p-block (N, O based) radicals appeared to provide a major conceptual advance, suggesting the possibility of a new era in non-metal molecular magnetism. However, the weak through-space magnetic exchange interactions present in these early radical-based ferromagnets afforded very low Curie temperatures TC (< 2 K), and the localization of spin density on light atoms ensured low coercive fields Hc (< 100 Oe). In this context, the observation of ferromagnetic ordering in ``heavy atom'' (Se) radicals, with TC as high as 17 K and coercive fields Hc up to 1370 Oe (at 2 K), represents a significant improvement in properties. This presentation will provide a theoretical and experimental examination of the source of the large coercive fields reported for these ``heavy atom'' radical ferromagnets. High-field ferromagnetic resonance (FMR) measurements, interpreted in the context of the anisotropic exchange interactions between the radicals in the solid state, leads to the conclusion that spin-orbit effects are responsible for the large observed magnetic anisotropy. This conclusion is supported by detailed analysis of the symmetry and magnitude of the spin-orbit interactions. An interesting discussion is the extent to which these anisotropic exchange terms also contribute to the enhancement of TC. That is, in the field of organic magnetism, where low dimensional magnetic structures are commonly found, long range ordering may depend crucially on such anisotropy. [4pt] See JACS 130, 8414-8425 (2008), JACS 133, 8126-8129 (2011).

  7. Atomic scale behavior of oxygen-based radicals in water

    NASA Astrophysics Data System (ADS)

    Verlackt, C. C. W.; Neyts, E. C.; Bogaerts, A.

    2017-03-01

    Cold atmospheric pressure plasmas in and in contact with liquids represent a growing field of research for various applications. Understanding the interactions between the plasma generated species and the liquid is crucial. In this work we perform molecular dynamics (MD) simulations based on a quantum mechanical method, i.e. density-functional based tight-binding (DFTB), to examine the interactions of OH radicals and O atoms in bulk water. Our calculations reveal that the transport of OH radicals through water is not only governed by diffusion, but also by an equilibrium reaction of H-abstraction with water molecules. Furthermore, when two OH radicals encounter each other, they either form a stable cluster, or react, resulting in the formation of a new water molecule and an O atom. In addition, the O atoms form either oxywater (when in singlet configuration) or they remain stable in solution (when in triplet configuration), stressing the important role that O atoms can play in aqueous solution, and in contact with biomolecules. Our observations are in line with both experimental and ab initio results from the literature.

  8. Free radical scavenging by natural polyphenols: atom versus electron transfer.

    PubMed

    Di Meo, Florent; Lemaur, Vincent; Cornil, Jérôme; Lazzaroni, Roberto; Duroux, Jean-Luc; Olivier, Yoann; Trouillas, Patrick

    2013-03-14

    Polyphenols (synthetically modified or directly provided by human diet) scavenge free radicals by H-atom transfer and may thus decrease noxious effects due to oxidative stress. Free radical scavenging by polyphenols has been widely theoretically studied from the thermodynamic point of view whereas the kinetic point of view has been much less addressed. The present study describes kinetic-based structure-activity relationship for quercetin. This compound is very characteristic of the wide flavonoid subclass of polyphenols. H-atom transfer is a mechanism based on either atom or electron transfer. This is analyzed here by quantum chemical calculations, which support the knowledge acquired from experimental studies. The competition between the different processes is discussed in terms of the nature of the prereaction complexes, the pH, the formation of activated-deprotonated forms, and the atom- and electron-transfer efficiency. The role of the catechol moiety and the 3-OH group of quercetin as scavengers of different types of free radicals (CH3OO(•), CH3O(•), (•)OH, and (•)CH2OH) is rationalized. Identifying the exact mechanism and accurately evaluating kinetics is of fundamental importance to understand antioxidant behavior in physiological environments.

  9. Magnetic ordering and anisotropy in heavy atom radicals.

    PubMed

    Winter, Stephen M; Hill, Stephen; Oakley, Richard T

    2015-03-25

    Recent developments in stable radical chemistry have afforded "heavy atom" radicals, neutral open-shell (S = 1/2) molecular species containing heavy p-block elements (S, Se), which display solid-state magnetic properties once considered exclusive to conventional metal-based magnets. These highly spin-delocalized radicals do not associate in the solid state and yet display extensive networks of close intermolecular interactions. Spin density on the heavy atoms allows for increased isotropic and spin-orbit mediated anisotropic exchange effects. Structural variations induced by chemical modification and physical pressure, coupled with ab-initio methods to estimate exchange energies, have facilitated the development of predictive structure/property relationships. These results, coupled with detailed theoretical analyses and magnetic resonance spectroscopic measurements, have provided insight into the magnetic structure of ferromagnetic and spin-canted antiferromagnetic ordered materials as well as an understanding of the importance of spin-orbit coupling contributions to magnetic hysteresis and anisotropy. Isotropic and anisotropic ferromagnetic exchange can also be enhanced indirectly by the incorporation of heavy atoms into nonspin-bearing sites, where they can contribute to multi-orbital spin-orbit coupling.

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Pickering emulsion templated interfacial atom transfer radical polymerization for microencapsulation.

    PubMed

    Li, Jian; Hitchcock, Adam P; Stöver, Harald D H

    2010-12-07

    This Article describes a new microencapsulation method based on a Pickering emulsion templated interfacial atom transfer radical polymerization (PETI-ATRP). Cationic LUDOX CL nanoparticles were coated electrostatically with an anionic polymeric ATRP initiator, poly(sodium styrene sulfonate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate) (PSB), prepared by radical copolymerization of sodium styrene sulfonate and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). The resulting PSB-modified CL particles were surface active and could be used to stabilize oil-in-water Pickering emulsions. ATRP of water-soluble cross-linking monomers, confined to the oil-water interface by the surface-bound PSB, then led to nanoparticle/polymer composite shells. This method allowed encapsulation of core solvents (xylene, hexadecane, perfluoroheptane) with different solubility parameters. The microcapsule (MC) wall chemistry could accommodate different monomers, demonstrating the versatility of this method. Double-walled MCs were formed by sequentially carrying out PETI-ATRP and in situ polymerization of encapsulated monomers. The double-walled structure was verified by both transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).

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

    PubMed

    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.

  13. Nanostructured hybrid hydrogels prepared by a combination of atom transfer radical polymerization and free radical polymerization

    PubMed Central

    Bencherif, Sidi A.; Siegwart, Daniel J.; Srinivasan, Abiraman; Horkay, Ferenc; Hollinger, Jeffrey O.; Washburn, Newell R.; Matyjaszewski, Krzysztof

    2012-01-01

    A new method to prepare nanostructured hybrid hydrogels by incorporating well-defined poly(oligo (ethylene oxide) monomethyl ether methacrylate) (POEO300MA) nanogels of sizes 110–120 nm into a larger three-dimensional (3D) matrix was developed for drug delivery scaffolds for tissue engineering applications. Rhodamine B isothiocyanate-labeled dextran (RITC-Dx) or fluorescein isothiocyanate-labeled dextran (FITC-Dx)-loaded POEO300MA nanogels with pendant hydroxyl groups were prepared by activators generated electron transfer atom transfer radical polymerization (AGET ATRP) in cyclohexane inverse miniemulsion. Hydroxyl-containing nanogels were functionalized with methacrylated groups to generate photoreactive nanospheres. 1H NMR spectroscopy confirmed that polymerizable nanogels were successfully incorporated covalently into 3D hyaluronic acid-glycidyl methacrylate (HAGM) hydrogels after free radical photo-polymerization (FRP). The introduction of disulfide moieties into the polymerizable groups resulted in a controlled release of nanogels from cross-linked HAGM hydrogels under a reducing environment. The effect of gel hybridization on the macroscopic properties (swelling and mechanics) was studied. It is shown that swelling and nanogel content are independent of scaffold mechanics. In-vitro assays showed the nanostructured hybrid hydrogels were cytocompatible and the GRGDS (Gly–Arg–Gly–Asp–Ser) contained in the nanogel structure promoted cell–substrate interactions within 4 days of incubation. These nanostructured hydrogels have potential as an artificial extracellular matrix (ECM) impermeable to low molecular weight biomolecules and with controlled pharmaceutical release capability. Moreover, the nanogels can control drug or biomolecule delivery, while hyaluronic acid based-hydrogels can act as a macroscopic scaffold for tissue regeneration and regulator for nanogel release. PMID:19592087

  14. Development of materials from copolyacrylates via atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Jones, Melody Mersadez

    Homopolymerization of 2-(trimethylsilyl)ethyl acrylate, 3,3-dimethylbutyl acrylate, methyl acrylate, and methyl methacrylate using atom transfer radical polymerization (ATRP) is reported. In addition, polymethyl acrylate and polymethyl methacrylate were used as macroinitiators for diblock copolymerizations (via ATRP) with various monomers to yield pMA-b-TMSEA, pMMA-b-TMSEA, and pMMA-b-GMA copolymers; these results are also reported. Controlled polymerizations were performed using the CuBr/hexamethyltriethylenetetramine catalyst system in combination with methyl bromopropionate as the initiator. The protected acid block copolymers pMA-b-TMSEA and pMMA-b-TMSEA were deprotected to afford acrylic and meth acrylic acid block copolymers pMA-b-AA and pMMA-b-AA. Methylene chloride was used to micellize the amphiphilic copolymers in order to obtain the critical micelle concentration of the polymers (CMCpMA-b-AA = 10 mg/mL, CMCpMMA-b-AA = 0.4 mg/mL). The majority of polymerization were done in bulk; however, since poly(trimethylsilyl)ethyl acrylate displayed polydispersity (Mn = 11459, PDI = 1.437) on the high end of the acceptable range, various solvents were utilized to decrease the polymerization rate and afford low polydispersity materials. This differs from the ATRP of polymethyl acrylate or polymethyl methacrylate using this catalytic system, which do not require the addition of a solvent to obtain well-defined polymers. Also, for this polymerization system three different temperatures (60°C, 90°C, and 120°C) were used, in order to reduce the concentration of radicals and the contribution of termination. The homopolymers and protected acid block copolymers were characterized by gel permeation chromatography to determine the relative molecular weights. Differential scanning calorimetry was used to obtain the glass transition temperature of all polymers. Characterization using NMR (1H and 13C) and FTIR confirmed homopolymerization of 3,3-dimethylbutyl acrylate, 2

  15. Interaction of Si atoms and Si-based radicals with carbon nanotubes and graphene monolayers

    NASA Astrophysics Data System (ADS)

    Chang, Kiseok; Berber, Savas; Tománek, David

    2008-03-01

    We use ab initio density functional calculations to study the interaction of Si atoms and Si-based radicals, such as SiH3, with single-wall carbon nanotubes and graphene monolayers. We find that both Si atoms and radicals form a strong chemisorption bond, accompanied by a small relaxation and a locally increased sp^3 bond character of the graphitic nanostructure. We identify the optimum adsorption geometries at different adsorbate coverages and adsorbate-related changes in the electronic structure and vibration spectra of the systems. We propose that successful functionalization of carbon nanotubes or graphene by Si atoms or Si-based radicals can be verified by studying changes in the radial breathing mode of nanotubes and the G-band of graphitic nanocarbons using Raman spectroscopy.

  16. Role of plasma enhanced atomic layer deposition reactor wall conditions on radical and ion substrate fluxes

    SciTech Connect

    Sowa, Mark J.

    2014-01-15

    Chamber wall conditions, such as wall temperature and film deposits, have long been known to influence plasma source performance on thin film processing equipment. Plasma physical characteristics depend on conductive/insulating properties of chamber walls. Radical fluxes depend on plasma characteristics as well as wall recombination rates, which can be wall material and temperature dependent. Variations in substrate delivery of plasma generated species (radicals, ions, etc.) impact the resulting etch or deposition process resulting in process drift. Plasma enhanced atomic layer deposition is known to depend strongly on substrate radical flux, but film properties can be influenced by other plasma generated phenomena, such as ion bombardment. In this paper, the chamber wall conditions on a plasma enhanced atomic layer deposition process are investigated. The downstream oxygen radical and ion fluxes from an inductively coupled plasma source are indirectly monitored in temperature controlled (25–190 °C) stainless steel and quartz reactors over a range of oxygen flow rates. Etch rates of a photoresist coated quartz crystal microbalance are used to study the oxygen radical flux dependence on reactor characteristics. Plasma density estimates from Langmuir probe ion saturation current measurements are used to study the ion flux dependence on reactor characteristics. Reactor temperature was not found to impact radical and ion fluxes substantially. Radical and ion fluxes were higher for quartz walls compared to stainless steel walls over all oxygen flow rates considered. The radical flux to ion flux ratio is likely to be a critical parameter for the deposition of consistent film properties. Reactor wall material, gas flow rate/pressure, and distance from the plasma source all impact the radical to ion flux ratio. These results indicate maintaining chamber wall conditions will be important for delivering consistent results from plasma enhanced atomic layer deposition

  17. Laser-induced fluorescence of radicals produced in reactions of halogenated ethylenes with atomic oxygen

    NASA Astrophysics Data System (ADS)

    Washida, Nobuaki; Furubayashi, Masashi; Imamura, Takashi; Bridier, Isabelle; Miyoshi, Akira

    1997-11-01

    Three new laser-induced fluorescence spectra have been observed when reacting oxygen atoms with halogenated ethylenes such as CHFCF2, CF2CHCl, CH2CCl2, CH2CHCl, and CHClCHCl. These new spectra are similar to those reported previously for the vinoxy CH2CHO and CH2CFO radicals, which suggests that they can be assigned to other halogenated vinoxy-type radicals. Recently Williams and Fleming assigned one of these LIF spectra to the FCO radical; additional experiments have been done to address this conflicting assignment.

  18. H-atom elimination of n-propyl and iso-propyl radicals: a photodissociation study

    NASA Astrophysics Data System (ADS)

    Zhang, Jingsong; Zhou, Weidong; Yuan, Yan

    2006-03-01

    The H-atom elimination channels in the UV photodissociation of jet-cooled n-propyl and iso-propyl radicals are studied in the region of 237 nm using the high-n Rydberg-atom time-of-flight technique. Upon excitation to the 3p state by the UV photolysis radiation, n-propyl radical and iso-propyl radical dissociate into the H atom and propene products. The product center-of-mass translational energy release of both n-propyl and iso-propyl radicals have bimodal distributions. The H-atom product angular distribution in n-propyl is anisotropic (with β ˜ 0.5), and that in iso-propyl is isotropic. The overall average translational energy release is ˜ 0.27Eavail for n-propyl and ˜ 0.21Eavail for iso-propyl. The bimodal translational energy distributions indicate two dissociation pathways: (i) a unimolecular dissociation pathway from the ground-state propyl after internal conversion from the 3p state, and (ii) a repulsive pathway directly connected with the excited state of the propyl radical. Isotope labeling has also been carried out. The possible photodissociation mechanisms will be discussed.

  19. Atmospheric concentrations of the Cl atom, ClO radical, and HO radical in the coastal marine boundary layer.

    PubMed

    Chang, Chang-Tang; Liu, Tsun-Hsien; Jeng, Fu-Tien

    2004-01-01

    Atmospheric concentrations of chlorine atom (Cl*), chlorine monoxide radical (ClO*), and hydroxyl radical (HO*) in the coastal marine boundary layer are estimated in this study. A steady-state approach to their concentrations in equilibrium with other atmospheric chemical species is used. Measurements of atmospheric trace species, HCl, Cl2, HCHO, H2O2, CH3OOH, CH4, CO, SO2, NO, NO2, and O3, were performed at four sites in Taiwan during the spring of 1999. The results indicate that the concentrations of the Cl* atom and the ClO* and HO* radicals decrease significantly with cloud cover. The calculated average daytime concentrations of Cl*, ClO*, and HO* are 3 x 10(5), 1 x 10(7), and 6 x 10(5) molecules/cm3, respectively. Due to the high reactivity of Cl* with hydrocarbons and its concentration level competitive to that of HO*, Cl* should be a significant sink for hydrocarbons in these cases.

  20. Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen Atom Donors

    PubMed Central

    Jing, Linhong; Nash, John J.

    2009-01-01

    The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer (FT – ICR). Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropanol, were measured for twenty-three structurally different, positively-charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) vertical electron affinities (EA) of the aryl radicals. Transition state energies calculated for three of the aryl radicals with isopropanol were found to correlate linearly with their (calculated) EAs. No correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) enthalpy changes for the reactions. Measurement of the reaction efficiencies for the reactions of several different hydrogen-atom donors with a few selected aryl radicals revealed a logarithmic correlation between the hydrogen-atom abstraction reaction efficiencies and the vertical ionization energies (IE) of the hydrogen-atom donors, but not the lowest homolytic X – H (X = heavy atom) bond dissociation energies of the hydrogen-atom donors. Examination of the hydrogen-atom abstraction reactions of twenty-nine different aryl radicals and eighteen different hydrogen-atom donors showed that the reaction efficiency increases (logarithmically) as the difference between the IE of the hydrogen-atom donor and the EA of the aryl radical decreases. This dependence is likely to result from the increasing polarization, and concomitant stabilization, of the transition state as the energy difference between the neutral and ionic reactants decreases. Thus, the hydrogen-atom abstraction reaction efficiency for an aryl radical can be “tuned” by structural changes that influence either

  1. Correlation of hydrogen-atom abstraction reaction efficiencies for aryl radicals with their vertical electron affinities and the vertical ionization energies of the hydrogen-atom donors.

    PubMed

    Jing, Linhong; Nash, John J; Kenttämaa, Hilkka I

    2008-12-31

    The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropyl alcohol, were measured for 23 structurally different, positively charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) vertical electron affinities (EA) of the aryl radicals. Transition state energies calculated for the reaction of three of the aryl radicals with isopropyl alcohol were found to correlate linearly with their (calculated) EAs. No correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) enthalpy changes for the reactions. Measurement of the reaction efficiencies for the reactions of 15 different hydrogen-atom donors with two selected aryl radicals revealed a logarithmic correlation between the hydrogen-atom abstraction reaction efficiencies and the vertical ionization energies (IE) of the hydrogen-atom donors, but not the lowest homolytic X-H (X = heavy atom) bond dissociation energies of the hydrogen-atom donors. Examination of the hydrogen-atom abstraction reactions of 29 different aryl radicals and 18 different hydrogen-atom donors showed that the reaction efficiency increases (logarithmically) as the difference between the IE of the hydrogen-atom donor and the EA of the aryl radical decreases. This dependence is likely to result from the increasing polarization, and concomitant stabilization, of the transition state. Thus, the hydrogen-atom abstraction reaction efficiency for an aryl radical can be "tuned" by structural changes that influence either the vertical EA of the aryl radical or the vertical IE of the hydrogen atom donor.

  2. New horizons in chemical propulsion. [processes using free radicals, atomic hydrogen, excited species, etc

    NASA Technical Reports Server (NTRS)

    Cohen, W.

    1973-01-01

    After a review of the work of the late-Fifties on free radicals for propulsion, it is concluded that atomic hydrogen would provide a potentially large increase in specific impulse. Work conducted to find an approach for isolating atomic hydrogen is considered. Other possibilities for obtaining propellants of greatly increased capability might be connected with the technology for the generation of activated states of gases, metallic hydrogen, fuels obtained from other planets, and laser transfer of energy.

  3. Relative rate constants for the reactions of atomic oxygen with HO2 anad OH radicals

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1983-01-01

    Relative rate constants for the reactions O + HO2 - OH + O2 (1) and O + OH - H + O2 (2) were obtained by using the discharge-flow resonance fluorescence technique at 2 torr total pressure and 299 K. HO2 radicals were generated by reacting atomic hydrogen with an excess of O2. Quasi-steady-state concentrations of OH and HO2 were established in the presence of excess atomic oxygen. Observed concentration ratios, namely the ratio of the OH concentration to the HO2 concentration, resulted in a value of 1.7 + or 0.2 for k1/k2. The error limits are twice the standard deviation obtained from the data analysis. Overall experimental error is estimated to be + or - 25 percent. This result confirms earlier direct measurements of k1 and k2 which required knowledge of absolute radical or atomic oxygen concentrations.

  4. Relative rate constants for the reactions of atomic oxygen with HO2 anad OH radicals

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1983-01-01

    Relative rate constants for the reactions O + HO2 - OH + O2 (1) and O + OH - H + O2 (2) were obtained by using the discharge-flow resonance fluorescence technique at 2 torr total pressure and 299 K. HO2 radicals were generated by reacting atomic hydrogen with an excess of O2. Quasi-steady-state concentrations of OH and HO2 were established in the presence of excess atomic oxygen. Observed concentration ratios, namely the ratio of the OH concentration to the HO2 concentration, resulted in a value of 1.7 + or 0.2 for k1/k2. The error limits are twice the standard deviation obtained from the data analysis. Overall experimental error is estimated to be + or - 25 percent. This result confirms earlier direct measurements of k1 and k2 which required knowledge of absolute radical or atomic oxygen concentrations.

  5. Quantum mechanical study of atomic hydrogen interaction with a fluorinated boron-substituted coronene radical.

    PubMed

    Zhang, Hong; Smith, Sean C; Nanbu, Shinkoh; Nakamura, Hiroki

    2009-04-08

    In this work we study the transmission of atomic hydrogen across a fluorinated boron-substituted coronene radical (C(19)H(12)BF(6)) as a model for partially fluorinated and boron-doped nanotubes or fullerenes. Complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) methods are employed to calculate the potential energy surfaces for both ground and excited electronic states, and one-dimensional R-matrix propagation is utilized to investigate the transmission/reflection dynamics of atomic hydrogen, through the central six-member ring of the fluorinated boron-substituted coronene radical. The quantum scattering includes resonance effects as well as non-adiabatic transitions between the ground and excited electronic states. Within the sudden approximation, both centre and off-centre approach trajectories have been investigated. Implications for atomic hydrogen encapsulation by carbon nanotube and fullerene are discussed.

  6. Cytocompatible Polymer Grafting from Individual Living Cells by Atom-Transfer Radical Polymerization.

    PubMed

    Kim, Ji Yup; Lee, Bong Soo; Choi, Jinsu; Kim, Beom Jin; Choi, Ji Yu; Kang, Sung Min; Yang, Sung Ho; Choi, Insung S

    2016-12-05

    A cytocompatible method of surface-initiated, activator regenerated by electron transfer, atom transfer radical polymerization (SI-ARGET ATRP) is developed for engineering cell surfaces with synthetic polymers. Dopamine-based ATRP initiators are used for both introducing the ATRP initiator onto chemically complex cell surfaces uniformly (by the material-independent coating property of polydopamine) and protecting the cells from radical attack during polymerization (by the radical-scavenging property of polydopamine). Synthetic polymers are grafted onto the surface of individual yeast cells without significant loss of cell viability, and the uniform and dense grafting is confirmed by various characterization methods including agglutination assay and cell-division studies. This work will provide a strategic approach to the generation of living cell-polymer hybrid structures and open the door to their application in multitude of areas, such as sensor technology, catalysis, theranostics, and cell therapy. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Reversible H Atom Abstraction Catalyzed by the Radical S-Adenosylmethionine Enzyme HydG

    PubMed Central

    2015-01-01

    The organometallic H-cluster at the active site of [FeFe]-hydrogenases is synthesized by three accessory proteins, two of which are radical S-adenosylmethionine enzymes (HydE, HydG) and one of which is a GTPase (HydF). In this work we probed the specific role of H atom abstraction in HydG-catalyzed carbon monoxide and cyanide production from tyrosine. The isotope distributions of 5′-deoxyadenosine and p-cresol were evaluated using deuterium-labeled tyrosine substrates in H2O and D2O. The observation of multiply deuterated 5′-deoxyadenosine and deuterated S-adenosylmethionine when the reaction is carried out in D2O provides evidence for a 5′-deoxyadenosyl radical-mediated abstraction of a hydrogen atom from a solvent-exchangeable position as a reversible event. PMID:25099480

  8. Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst.

    PubMed

    Theriot, Jordan C; Ryan, Matthew D; French, Tracy A; Pearson, Ryan M; Miyake, Garret M

    2016-04-22

    A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

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

    PubMed

    Mao, Liang-Liang; Cong, Huan

    2017-09-09

    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.

  10. Role of the sulfur atom on the reactivity of methionine toward OH radicals: comparison with norleucine.

    PubMed

    Francisco-Marquez, Misaela; Galano, Annia

    2009-04-09

    Density functional theory has been used to model the OH reaction with Gly-Met-Gly and Gly-Nle-Gly tripeptides. The first one is predicted to be about 100 times faster than the second one. Therefore, if a methionine fragment is replaced by norleucine, the overall reactivity of the peptide toward free radicals is expected to be significantly reduced, which is in agreement with previous experimental findings. Since the most reactive sites were found to be located in the central backbone for Nle and in the terminal fragment of the side chain for Met, this decrease is expected to be even more critical for large-sized free radicals. The S atom seems to activate not only those alkyl sites next to it but also those located an odd number of bonds apart. In addition the viability of different paths explaining the formation of methionine sulfoxide has been tested, and it is proposed that this process involves the formation of R-SO radical and formaldehyde. The results from the present work offer an explanation to the role of sulfur atom on the reactivity of methionine toward free radicals. They also support the preponderant role of Met35 on the development of the Alzheimer disease.

  11. ATOM TRANSFER RADICAL POLYMERIZATION OF N-BUTYL METHACRYLATE IN AQUEOUS DISPERSED SYSTEMS: A MINIEMULSION APPROACH. (R826735)

    EPA Science Inventory

    Ultrasonication was applied in combination with a hydrophobe for the copper-mediated atom transfer radical polymerization of n-butyl methacrylate in an aqueous dispersed system. A controlled polymerization was successfully achieved, as demonstrated by a linear correlation between...

  12. Photo-Induced Atom-Transfer Radical Reactions Using Charge-Transfer Complex between Iodine and Tertiary Amine.

    PubMed

    Yoshioka, Eito; Kohtani, Shigeru; Hashimoto, Takurou; Takebe, Tomoko; Miyabe, Hideto

    2017-01-01

    In the presence of charge-transfer complexes between iodine and tertiary amines, the aqueous-medium atom-transfer radical reactions proceeded under visible light irradiation without the typical photocatalysts.

  13. ATOM TRANSFER RADICAL POLYMERIZATION OF N-BUTYL METHACRYLATE IN AQUEOUS DISPERSED SYSTEMS: A MINIEMULSION APPROACH. (R826735)

    EPA Science Inventory

    Ultrasonication was applied in combination with a hydrophobe for the copper-mediated atom transfer radical polymerization of n-butyl methacrylate in an aqueous dispersed system. A controlled polymerization was successfully achieved, as demonstrated by a linear correlation between...

  14. Tin-free generation of alkyl radicals from alkyl 4-pentynyl sulfides via homolytic substitution at the sulfur atom.

    PubMed

    Bencivenni, Giorgio; Lanza, Tommaso; Leardini, Rino; Minozzi, Matteo; Nanni, Daniele; Spagnolo, Piero; Zanardi, Giuseppe

    2008-03-20

    Homolytic substitution at the sulfur atom of beta-(phenylsulfanyl)vinyl radicals, obtained by radical reaction of benzenethiol with easily accessible alkyl 4-pentynyl sulfides, is a mild, effective, tin-free route for the generation of all types of alkyl radicals. This protocol can be employed in reductive defunctionalizations as well as cyclizations onto both electron-rich and electron-poor C-C double bonds.

  15. Ab initio Kinetics of Methylamine Radical Thermal Decomposition and H-abstraction from Monomethylhydrazine by H Atom

    DTIC Science & Technology

    2014-08-01

    of Mechanical and Aerospace Engineering , Princeton University, Princeton, New Jersey 08544 Abstract Methylamine radicals (CH3NH) and amino...kcal/mol, forming CH2=NH (R4). The N―H bond fission reaction in the CH3NH radical that leads to the triplet 3CH3N radical and H atom is endothermic by...elimination from the CH3NH radical is endothermic by 13.24 kcal mol-1 (R6), but its energy barrier is quite high, 99.62 kcal mol-1, and is not kinetically

  16. Synthesis and characterization of carbon fibers functionalized with poly (glycidyl methacrylate) via atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Wu, Yongwei; Xiong, Lei; Qin, Xiaokang; Wang, Zhengyue; Ding, Bei; Ren, Huan; Pi, Xiaolong

    2015-07-01

    In this work, polyacrylonitrile (PAN)-based carbon fibers (CF) were chemically modified with poly (glycidyl methacrylate) (PGMA) via atom transfer radical polymerization (ATRP) to improve the interaction between the CF and polymer matrix. The FT-IR, TGA, and XPS were used to determine the chemical structure of the resulting products and the quantities of PGMA chains grafted from the CF surface. The experimental results confirm that the CF surface was functionalized and glycidyl methacrylate was graft-polymerized onto the CF, and the grafting content of polymer could reach 10.2%.

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

    PubMed

    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.

  18. Lewis acid-water/alcohol complexes as hydrogen atom donors in radical reactions.

    PubMed

    Povie, Guillaume; Renaud, Philippe

    2013-01-01

    Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative.

  19. Quantitative aspects of ESR and spin trapping of hydroxyl radicals and hydrogen atoms in gamma-irradiated aqueous solutions.

    PubMed

    Carmichael, A J; Makino, K; Riesz, P

    1984-11-01

    The efficiency of 5,5-dimethylpyrroline-1-N-oxide (DMPO) and alpha-(4-pyridyl-1-oxide)-N-tert.-butylnitrone (POBN) to spin trap hydroxyl radicals and hydrogen atoms, respectively, was studied in gamma-irradiated solutions where the radical yields are accurately known. The effects of dose, spin trap concentration, and pH and of the stability of the spin adducts on the spin-trapping efficiency were investigated. In degassed or N2-saturated solutions the spin-trapping efficiencies were 35% for DMPO and hydroxyl radicals and 14% for POBN and hydrogen atoms. The low spin-trapping efficiencies were shown not to be due to the instability of the DMPO-OH and POBN-H spin adducts or to the effects of H2O2 or O2. The low spin-trapping efficiency of DMPO may be explained by the reaction of hydroxyl radicals to abstract hydrogen from the DMPO molecule to produce carbon radicals as well as addition to the N = C double bond to form nitroxide radicals. For POBN the low spin-trapping efficiency for hydrogen atoms is explained in terms of addition reactions of hydrogen atoms to the aromatic ring and the pyridinium and nitrone oxygens.

  20. Preparation and characterization of optical-functional diblock copolymer brushes on hollow sphere surface via atom transfer radical polymerization

    SciTech Connect

    Wang, Li-Ping; Li, Wen-Zhi; Zhao, Li-Min; Zhang, Chun-Juan; Wang, Yan-Dong; Kong, Li-Li; Li, Ling-Ling

    2010-09-15

    The optical-functional poly(methyl methacrylate)-block-Tb complex diblock copolymer brushes grafted from hollow sphere surface via atom transfer radical polymerization were investigated in this work. A sufficient amount of azo initiator was introduced onto hollow sphere surface firstly. Then the monomer methyl methacrylate was polymerized via surface-initiated reverse atom transfer radical polymerization using azo group modified hollow sphere as initiator. Following, the poly(methyl methacrylate) modified hollow sphere was used as maroinitiator for surface-initiated atom transfer radical polymerization of Tb complex. The samples were characterized by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, gel permeation chromatographer and transmission electron microscopy, respectively. The results indicated that the poly(methyl methacrylate) had grafted from hollow sphere surface and the average diameter of hollow core was about 1 {mu}m. The optical properties of the poly(methyl methacrylate)-block-Tb copolymer modified hollow sphere were also reported.

  1. Rate constants and isotope effects for the reaction of H-atom abstraction from RH substrates by PINO radicals

    NASA Astrophysics Data System (ADS)

    Opeida, I. A.; Litvinov, Yu. E.; Kushch, O. V.; Kompanets, M. A.; Shendrik, A. N.; Matvienko, A. G.; Novokhatko, A. A.

    2016-11-01

    The kinetics of the reactions of hydrogen atom abstraction from the C-H bonds of substrates of different structures by phthalimide- N-oxyl radicals is studied. The rate constants of this reaction are measured and the kinetic isotope effects are determined. It is shown that in addition to the thermodynamic factor, Coulomb forces and donor-acceptor interactions affect the reaction between phthalimide- N-oxyl radicals and substrate molecules, altering the shape of the transition state. This favors the tunneling of hydrogen atoms and leads to a substantial reduction in the activation energy of the process.

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

    PubMed

    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.

  3. Beta-sheet side chain polymers synthesized by atom-transfer radical polymerization.

    PubMed

    Ayres, Lee; Adams, P Hans H M; Löwik, Dennis W P M; van Hest, Jan C M

    2005-01-01

    Silks are a widely studied class of naturally occurring structural proteins. Dragline spider silk, in particular, is considered to be nature's high-performance material due to its remarkable combination of strength and toughness. These mechanical properties stem from the protein secondary structure, a combination of well-defined beta-sheets in a less well-defined glycine-rich matrix. The translation of this structure into a synthetic polymer was the aim of this investigation. To achieve this, a peptide-based monomer containing the sequence alanine-glycine-alanine-glycine, a well-known beta-sheet-forming sequence found in silk, was synthesized. Using atom-transfer radical polymerization and a bifunctional initiator, a well-defined peptide-based polymer was prepared. This was then used as the macroinitiator for the polymerization of methyl methacrylate. The resulting well-defined triblock copolymer was analyzed using IR spectroscopy, which clearly showed beta-sheet secondary structure had been introduced.

  4. Modification of jute fibers with polystyrene via atom transfer radical polymerization.

    PubMed

    Plackett, David; Jankova, Katja; Egsgaard, Helge; Hvilsted, Søren

    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 specimens were tensile tested and fracture surfaces examined using SEM. Although SEM examination suggested different fracture modes between unmodified fiber and ATRP-modified samples, the tensile strength of modified samples was slightly lower on average than that of unmodified samples. For fiber 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.

  5. Recent developments in atom transfer radical polymerization (ATRP): methods to reduce metal catalyst concentrations.

    PubMed

    Lou, Qin; Shipp, Devon A

    2012-10-08

    Atom transfer radical polymerization (ATRP) was initially developed in the mid-1990s, and with continued refinement and use has led to significant discoveries in new materials. However, metal contamination of the polymer product is an issue that has proven detrimental to widespread industrial application of ATRP. The laboratories of K. Matyjaszewski have made significant progress towards removing this impediment, leading the development of "activators regenerated by electron transfer" ATRP (ARGET ATRP) and electrochemically mediated ATRP (eATRP) technologies. These variants of ATRP allow polymers to be produced with great molecular weight and functionality control but at significantly reduced catalyst concentrations, typically at parts per million levels. This Concept examines these polymerizations in terms of their mechanism and outcomes, and is aimed at giving the reader an overview of recent developments in the field of ATRP. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Biocompatible Polymeric Analogues of DMSO Prepared by Atom Transfer Radical Polymerization.

    PubMed

    Li, Sipei; Chung, Hee Sung; Simakova, Antonina; Wang, Zongyu; Park, Sangwoo; Fu, Liye; Cohen-Karni, Devora; Averick, Saadyah; Matyjaszewski, Krzysztof

    2017-02-13

    The synthesis of a sulfoxide-based water-soluble polymer, poly(2-(methylsulfinyl)ethyl acrylate) (polyMSEA), a polymeric analogue of DMSO, by atom transfer radical polymerization (ATRP) is reported. Well-defined linear polymers were synthesized using relatively low amounts of copper catalyst (1000 or 100 ppm). Two types of star polymers were synthesized by either an "arm-first" approach or a "core-first" approach using a biodegradable β-cyclodextrin core. The glass transition temperatures of both the linear polymer (16 °C) and star polymer (32 °C) were determined by differential scanning calorimetry (DSC). The lower critical solution temperature (LCST) of poly(MSEA) was estimated to be ca. 140 °C by extrapolating the LCST of a series of copolymers with NIPAM. Cytotoxicity tests revealed that both the linear and star polymers have low toxicity, even at concentrations up to 3 mg/mL.

  7. Encapsidated atom-transfer radical polymerization in Qβ virus-like nanoparticles.

    PubMed

    Hovlid, Marisa L; Lau, Jolene L; Breitenkamp, Kurt; Higginson, Cody J; Laufer, Burkhardt; Manchester, Marianne; Finn, M G

    2014-08-26

    Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA.

  8. Surface-initiated atom transfer radical polymerization from chitin nanofiber macroinitiator film.

    PubMed

    Yamamoto, Kazuya; Yoshida, Sho; Kadokawa, Jun-Ichi

    2014-11-04

    This paper reports the preparation of chitin nanofiber-graft-poly(2-hydroxyethyl acrylate) (CNF-g-polyHEA) films by surface-initiated atom transfer radical polymerization (ATRP) of HEA monomer from a CNF macroinitiator film. First, a CNF film was prepared by regeneration from a chitin ion gel with an ionic liquid. Then, acylation of the CNF surface with α-bromoisobutyryl bromide was carried out to obtain the CNF macroinitiator film having the initiating moieties (α-bromoisobutyrate group). The surface-initiated graft polymerization of HEA from the CNF macroinitiator film by ATRP was performed to produce the CNF-g-polyHEA film. The IR, XRD, and SEM measurements of the resulting film indicated the progress of the graft polymerization of HEA on surface of CNFs. The molecular weights of the grafted polyHEAs increased with prolonged polymerization times, which affected the mechanical properties of the films under tensile mode.

  9. Encapsidated Atom-Transfer Radical Polymerization in Qβ Virus-like Nanoparticles

    PubMed Central

    2015-01-01

    Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA. PMID:25073013

  10. Rate constant calculations of H-atom abstraction reactions from ethers by HȮ2 radicals.

    PubMed

    Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

    2014-02-27

    In this work, we detail hydrogen atom abstraction reactions from six ethers by the hydroperoxyl radical, including dimethyl ether, ethyl methyl ether, propyl methyl ether, isopropyl methyl ether, butyl methyl ether, and isobutyl methyl ether, in order to test the effect of the functional group on the rate constant calculations. The Møller-Plesset (MP2) method with the 6-311G(d,p) basis set has been employed in the geometry optimizations and frequency calculations of all of the species involved in the above reaction systems. The connections between each transition state and the corresponding local minima have been determined by intrinsic reaction coordinate calculations. Energies are reported at the CCSD(T)/cc-pVTZ level of theory and include the zero-point energy corrections. As a benchmark in the electronic energy calculations, the CCSD(T)/CBS extrapolation was used for the reactions of dimethyl ether + HȮ2 radicals. A systematic calculation of the high-pressure limit rate constants has been performed using conventional transition-state theory, including asymmetric Eckart tunneling corrections, in the temperature range of 500-2000 K. The one dimensional hindrance potentials obtained at MP2/6-311G(d,p) for the reactants and transition states have been used to describe the low frequency torsional modes. Herein, we report the calculated individual, average, and total rate constants. A branching ratio analysis for every reaction site has also been performed.

  11. Chemical probing of RNA with the hydroxyl radical at single-atom resolution

    PubMed Central

    Ingle, Shakti; Azad, Robert N.; Jain, Swapan S.; Tullius, Thomas D.

    2014-01-01

    While hydroxyl radical cleavage is widely used to map RNA tertiary structure, lack of mechanistic understanding of strand break formation limits the degree of structural insight that can be obtained from this experiment. Here, we determine how individual ribose hydrogens of sarcin/ricin loop RNA participate in strand cleavage. We find that substituting deuterium for hydrogen at a ribose 5′-carbon produces a kinetic isotope effect on cleavage; the major cleavage product is an RNA strand terminated by a 5′-aldehyde. We conclude that hydroxyl radical abstracts a 5′-hydrogen atom, leading to RNA strand cleavage. We used this approach to obtain structural information for a GUA base triple, a common tertiary structural feature of RNA. Cleavage at U exhibits a large 5′ deuterium kinetic isotope effect, a potential signature of a base triple. Others had noted a ribose-phosphate hydrogen bond involving the G 2′-OH and the U phosphate of the GUA triple, and suggested that this hydrogen bond contributes to backbone rigidity. Substituting deoxyguanosine for G, to eliminate this hydrogen bond, results in a substantial decrease in cleavage at G and U of the triple. We conclude that this hydrogen bond is a linchpin of backbone structure around the triple. PMID:25313156

  12. Chemical probing of RNA with the hydroxyl radical at single-atom resolution.

    PubMed

    Ingle, Shakti; Azad, Robert N; Jain, Swapan S; Tullius, Thomas D

    2014-11-10

    While hydroxyl radical cleavage is widely used to map RNA tertiary structure, lack of mechanistic understanding of strand break formation limits the degree of structural insight that can be obtained from this experiment. Here, we determine how individual ribose hydrogens of sarcin/ricin loop RNA participate in strand cleavage. We find that substituting deuterium for hydrogen at a ribose 5'-carbon produces a kinetic isotope effect on cleavage; the major cleavage product is an RNA strand terminated by a 5'-aldehyde. We conclude that hydroxyl radical abstracts a 5'-hydrogen atom, leading to RNA strand cleavage. We used this approach to obtain structural information for a GUA base triple, a common tertiary structural feature of RNA. Cleavage at U exhibits a large 5' deuterium kinetic isotope effect, a potential signature of a base triple. Others had noted a ribose-phosphate hydrogen bond involving the G 2'-OH and the U phosphate of the GUA triple, and suggested that this hydrogen bond contributes to backbone rigidity. Substituting deoxyguanosine for G, to eliminate this hydrogen bond, results in a substantial decrease in cleavage at G and U of the triple. We conclude that this hydrogen bond is a linchpin of backbone structure around the triple. © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

  13. Nitroxyl Radical plus Hydroxylamine Pseudo Self-Exchange Reactions: Tunneling in Hydrogen Atom Transfer

    PubMed Central

    Wu, Adam; Mader, Elizabeth A.; Datta, Ayan; Hrovat, David A.; Borden, Weston Thatcher; Mayer, James M.

    2009-01-01

    Bimolecular rate constants have been measured for reactions that involve hydrogen atom transfer (HAT) from hydroxylamines to nitroxyl radicals, using the stable radicals TEMPO• (2,2,6,6-tetramethylpiperidine-1-oxyl radical), 4-oxo-TEMPO• (2,2,6,6-tetramethyl-4-oxo-piperidine-1-oxyl radical), di-tert-butylnitroxyl (tBu2NO•), and the hydroxylamines TEMPO-H, 4-oxo-TEMPO-H, 4-MeO-TEMPO-H (2,2,6,6-tetramethyl-N-hydroxy-4-methoxy-piperidine), and tBu2NOH. The reactions have been monitored by UV-vis stopped-flow methods, using the different optical spectra of nitroxyl radicals. The HAT reactions all have |ΔGo| ≤ 1.4 kcal mol−1 and therefore are close to self-exchange reactions. The reaction of 4-oxo-TEMPO• + TEMPO-H → 4-oxo-TEMPO-H + TEMPO• occurs with k2H,MeCN = 10 ± 1 M−1 s−1 in MeCN at 298 K (K2H,MeCN = 4.5 ± 1.8). Surprisingly, the rate constant for the analogous deuterium atom transfer reaction is much slower: k2D,MeCN = 0.44 ± 0.05 M−1 s−1 with k2H,MeCN/k2D,MeCN = 23 ± 3 at 298 K. The same large kinetic isotope effect (KIE) is found in CH2Cl2, 23 ± 4, suggesting that the large KIE is not caused by solvent dynamics or hydrogen bonding to solvent. The related reaction of 4-oxo-TEMPO• with 4-MeO-TEMPO-H(D) also has a large KIE, k3H/k3D = 21 ± 3 in MeCN. For these three reactions, the EaD – EaH values, between 0.3 ± 0.6 and 1.3 ± 0.6 kcal mol−1, and the log(AH/AD) values, between 0.5 ± 0.7 and 1.1 ± 0.6, indicate that hydrogen tunneling plays an important role. The related reaction of tBu2NO• + TEMPO-H(D) in MeCN has a large KIE, 16 ± 3 in MeCN, and very unusual isotopic activation parameters, EaD – EaH = −2.6 ± 0.4 and log(AH/AD) = 3.1 ± 0.6. Computational studies, using POLYRATE, also indicate substantial tunneling in the (CH3)2NO• + (CH3)2NOH model reaction for the experimental self-exchange processes. Additional calculations on TEMPO(•/H), tBu2NO(•/H), and Ph2NO(•/H) self-exchange reactions reveal why the

  14. Imaging quantum stereodynamics through Fraunhofer scattering of NO radicals with rare-gas atoms

    NASA Astrophysics Data System (ADS)

    Onvlee, Jolijn; Gordon, Sean D. S.; Vogels, Sjoerd N.; Auth, Thomas; Karman, Tijs; Nichols, Bethan; van der Avoird, Ad; Groenenboom, Gerrit C.; Brouard, Mark; van de Meerakker, Sebastiaan Y. T.

    2016-10-01

    Stereodynamics describes how the vector properties of molecules, such as the directions in which they move and the axes about which they rotate, affect the probabilities (or cross-sections) of specific processes or transitions that occur on collision. The main aspects of stereodynamics in inelastic atom-molecule collisions can often be understood from classical considerations, in which the particles are represented by billiard-ball-like hard objects. In a quantum picture, however, the collision is described in terms of matter waves, which can also scatter into the region of the geometrical shadow of the object and reveal detailed information on the pure quantum-mechanical contribution to the stereodynamics. Here we present measurements of irregular diffraction patterns for NO radicals colliding with rare-gas atoms that can be explained by the analytical Fraunhofer model. They reveal a hitherto overlooked dependence on (or 'propensity rule' for) the magnetic quantum number m of the molecules, and a previously unrecognized type of quantum stereodynamics that has no classical analogue or interpretation.

  15. Reactivity of hydrohaloethers with OH radicals and chlorine atoms: Correlation with molecular properties

    NASA Astrophysics Data System (ADS)

    Dalmasso, Pablo R.; Taccone, Raúl A.; Nieto, Jorge D.; Cometto, Pablo M.; Cobos, Carlos J.; Lane, Silvia I.

    2014-07-01

    The reactivity of halogenated ethers, especially hydrochloroethers, with hydroxyl radicals and chlorine atoms was studied by correlating the room-temperature rate coefficients with both the C-H bond dissociation energies and the vertical ionization potentials of the parent molecules. These molecular properties were estimated at the composite G3B3 level of theory. The results suggest that Cl-substituted ethyl-methyl-ethers and ethyl-ethyl-ethers at the β-position tend to raise the activating effect of the ether linkage -O- and to enhance the possibility of the abstraction of H atoms bonded to α-carbon. Derived relationships between the rate coefficients (in cm3 molecule-1 s-1) and ionization potentials (in eV): log kOH = -(1.248 ± 0.065) IP + (1.06 ± 0.73) and log kCl = -(1.46 ± 0.12) IP + (4.5 ± 1.3) allows, in average, to estimate rate coefficients within a factor of 2-3. The atmospheric implications of halogenated and hydrogenated ethers are briefly discussed on the basis of their estimated global lifetimes.

  16. Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates

    PubMed Central

    Foster, Rami N.; Keefe, Andrew J.; Jiang, Shaoyi; Castner, David G.

    2013-01-01

    This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone. PMID:24482558

  17. Imaging quantum stereodynamics through Fraunhofer scattering of NO radicals with rare-gas atoms.

    PubMed

    Onvlee, Jolijn; Gordon, Sean D S; Vogels, Sjoerd N; Auth, Thomas; Karman, Tijs; Nichols, Bethan; van der Avoird, Ad; Groenenboom, Gerrit C; Brouard, Mark; van de Meerakker, Sebastiaan Y T

    2017-03-01

    Stereodynamics describes how the vector properties of molecules, such as the directions in which they move and the axes about which they rotate, affect the probabilities (or cross-sections) of specific processes or transitions that occur on collision. The main aspects of stereodynamics in inelastic atom-molecule collisions can often be understood from classical considerations, in which the particles are represented by billiard-ball-like hard objects. In a quantum picture, however, the collision is described in terms of matter waves, which can also scatter into the region of the geometrical shadow of the object and reveal detailed information on the pure quantum-mechanical contribution to the stereodynamics. Here we present measurements of irregular diffraction patterns for NO radicals colliding with rare-gas atoms that can be explained by the analytical Fraunhofer model. They reveal a hitherto overlooked dependence on (or 'propensity rule' for) the magnetic quantum number m of the molecules, and a previously unrecognized type of quantum stereodynamics that has no classical analogue or interpretation.

  18. Effects of delocalization on intrinsic barriers for H-atom transfer: Implications for the radical hydrogen transfer reaction

    SciTech Connect

    Camaioni, D.M.; Autrey, S.T.; Ferris, K.F.; Franz, J.A.

    1992-08-01

    PM3 calculations of transition states (TS) for both normal H-atom transfer and radical hydrogen transfer (RHT) reactions of a a wide-variety of hydrocarbon structures have enabled development of quantitative structure-reactivity relationships. Results indicate that activation barriers for RHT reactions are large enough that thermoneutral and endothermic reactions should not compete with alternative multistep pathways.

  19. Distribution of Phosphorus Atoms and Carrier Concentrations in Single-Crystal Silicon Doped by Catalytically Generated Phosphorous Radicals

    NASA Astrophysics Data System (ADS)

    Hayakawa, Taro; Nakashima, Yuki; Koyama, Koichi; Ohdaira, Keisuke; Matsumura, Hideki

    2012-06-01

    A phosphorus (P)-doped ultrathin n+ layer is formed on crystalline silicon (c-Si) using radicals generated by the catalytic cracking reaction of phosphine (PH3) gas with a heated catalyzer. The carrier concentration and the depth distributions of P atoms are investigated by Hall effect and secondary ion mass spectrometry (SIMS), respectively. The surface of the p-type c-Si substrate is converted to n-type c-Si by this doping even at a substrate temperature of 20 °C, when the tungsten (W) catalyzer is heated at 1300 °C. SIMS measurements demonstrate that P atoms exist on the c-Si surface. However, the distributions of P atoms obtained by SIMS do not change, even for the increase in substrate temperature from 80 to 350 °C or the increase in radical exposure time from 60 to 3600 s. Although the sheet carrier concentration increased with the substrate temperature, the sheet carrier concentration increased only slightly with the radical exposure time. It is revealed that the doping mechanism does not appear to be the same as that of the thermal diffusion, but that the reaction of the P-related species with Si atoms on the surface plays a key role for this radical doping.

  20. Synthesis of selenium nano-composite (t-Se@PS) by surface initiated atom transfer radical polymerization.

    PubMed

    Wang, Michael C P; Gates, Byron D

    2012-09-04

    Selenium nanostructures, which are otherwise susceptible to oxidative damage, were encapsulated with a thin layer of polystyrene. The thin layer of polystyrene was grafted onto the surfaces of selenium by a surface initiated atom transfer radical polymerization reaction. These encapsulated nanostructures demonstrate an enhanced resistance towards corrosion.

  1. Role of spin-orbit coupling in the kinetics of geminal recombination of triplet radical pairs in micelles. Effect of an internal heavy atom

    SciTech Connect

    Levin, P.P.; Kuz'min, V.A.

    1987-07-01

    The authors use radicals from the laser photolysis of benzophenone, bromobenzophenone, 4-phenylphenol, and 4-phenylaniline to study the effect of a heavy atom introduced as a substituent on the recombination kinetics of triplet radical pairs in micelles as a function of the external magnetic field strength. They found that intercombination conversion, which takes place due to the spin-orbit coupling between radicals, makes a significant contribution to the process of singlet-triplet transitions in radical pairs together with the hyperfine interaction. The role of spin-orbit coupling increases significantly when heavy atoms are present in the radicals.

  2. PREFACE: Light element atom, molecule and radical behaviour in the divertor and edge plasma regions

    NASA Astrophysics Data System (ADS)

    Braams, Bastiaan J.; Chung, Hyun-Kung

    2015-01-01

    This volume of Journal of Physics: Conference Series contains contributions by participants in an International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on "Light element atom, molecule and radical behaviour in the divertor and edge plasma regions" (in magnetic fusion devices). Light elements are the dominant impurity species in fusion experiments and in the near-wall plasma they occur as atoms or ions and also as hydrides and other molecules and molecular ions. Hydrogen (H or D, and T in a reactor) is the dominant species in fusion experiments, but all light elements He - O and Ne are of interest for various reasons. Helium is a product of the D+T fusion reaction and is introduced in experiments for transport studies. Lithium is used for wall coating and also as a beam diagnostic material. Beryllium is foreseen as a wall material for the ITER experiment and is used on the Joint European Torus (JET) experiment. Boron may be used as a coating material for the vessel walls. Carbon (graphite or carbon-fiber composite) is often used as the target material for wall regions subject to high heat load. Nitrogen may be used as a buffer gas for edge plasma cooling. Oxygen is a common impurity in experiments due to residual water vapor. Finally, neon is another choice as a buffer gas. Data for collisional and radiative processes involving these species are important for plasma modelling and for diagnostics. The participants in the CRP met 3 times over the years 2009-2013 for a research coordination meeting. Reports and presentation materials for these meetings are available through the web page on coordinated research projects of the (IAEA) Atomic and Molecular Data Unit [1]. Some of the numerical data generated in the course of the CRP is available through the ALADDIN database [2]. The IAEA takes the opportunity to thank the participants in the CRP for their dedicated efforts in the course of the CRP and for their contributions to this volume. The IAEA

  3. Novel atmospheric pressure plasma device releasing atomic hydrogen: reduction of microbial-contaminants and OH radicals in the air

    NASA Astrophysics Data System (ADS)

    Nojima, Hideo; Park, Rae-Eun; Kwon, Jun-Hyoun; Suh, Inseon; Jeon, Junsang; Ha, Eunju; On, Hyeon-Ki; Kim, Hye-Ryung; Choi, Kyoung Hui; Lee, Kwang-Hee; Seong, Baik-Lin; Jung, Hoon; Kang, Shin Jung; Namba, Shinichi; Takiyama, Ken

    2007-01-01

    A novel atmospheric pressure plasma device releasing atomic hydrogen has been developed. This device has specific properties such as (1) deactivation of airborne microbial-contaminants, (2) neutralization of indoor OH radicals and (3) being harmless to the human body. It consists of a ceramic plate as a positive ion generation electrode and a needle-shaped electrode as an electron emission electrode. Release of atomic hydrogen from the device has been investigated by the spectroscopic method. Optical emission of atomic hydrogen probably due to recombination of positive ions, H+(H2O)n, generated from the ceramic plate electrode and electrons emitted from the needle-shaped electrode have been clearly observed in the He gas (including water vapour) environment. The efficacy of the device to reduce airborne concentrations of influenza virus, bacteria, mould fungi and allergens has been evaluated. 99.6% of airborne influenza virus has been deactivated with the operation of the device compared with the control test in a 1 m3 chamber after 60 min. The neutralization of the OH radical has been investigated by spectroscopic and biological methods. A remarkable reduction of the OH radical in the air by operation of the device has been observed by laser-induced fluorescence spectroscopy. The cell protection effects of the device against OH radicals in the air have been observed. Furthermore, the side effects have been checked by animal experiments. The harmlessness of the device has been confirmed.

  4. Velocity distributions of hydrogen atoms and hydroxyl radicals produced through solar photodissociation of water

    NASA Technical Reports Server (NTRS)

    Wu, C. Y. R.; Chen, F. Z.

    1993-01-01

    The velocity distributions of H and OH fragments produced through solar photodissociation of gaseous H2O molecules under collisionless conditions are presented. The calculations are carried out using: the most recently available absolute partial cross sections for the production of H and OH through photodissociation of H2O from its absorption onset at 1860 A down to 500 A; the newly available vibrational and rotational energy distributions of both the excited and ground state OH photofragments; the calculated cross sections for the total dissociation processes; and the integrated solar flux in 10 A increments from 500 to 1860 A in the continuum regions and the specific wavelength and flux at the bright solar lines. The calculated results show that the H atoms and the OH radicals produced exhibit multiple velocity groups. Since most current cometary modeling uses a single velocity of 20 km/sec associated with the photodissociation of H2O, the present results may be useful in interpreting the many peaks observed in the velocity distributions of the H Lyman alpha and H alpha of comets.

  5. Metal-Free Atom Transfer Radical Polymerization of Methyl Methacrylate with ppm Level of Organic Photocatalyst.

    PubMed

    Huang, Zhicheng; Gu, Yu; Liu, Xiaodong; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2016-10-28

    It is well known that the recently developed photoinduced metal-free atom transfer radical polymerization (ATRP) has been considered as a promising methodology to completely eliminate transition metal residue in polymers. However, a serious problem needs to be improved, namely, large amount of organic photocatalysts should be used to keep the controllability over molecular weights and molecular weight distributions. In this work, a novel photocatalyst 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) with strong excited state reduction potential is successfully used to mediate a metal-free ATRP of methyl methacrylate just with parts per million (ppm) level usage under irradiation of blue light emitting diode at room temperature, using ethyl α-bromophenyl-acetate as a typical initiator with high initiator efficiency. The polymerization kinetic study, multiple controlled "on-off" light switching cycle regulation, and chain extension experiment confirm the "living"/controlled features of this promising photoinduced metal-free ATRP system with good molecular weight control in the presence of ppm level photocatalyst 4CzIPN.

  6. Functionalization of nylon membranes via surface-initiated atom-transfer radical polymerization.

    PubMed

    Xu, F J; Zhao, J P; Kang, E T; Neoh, K G; Li, J

    2007-07-31

    The ability to manipulate and control the surface properties of nylons is of crucial importance to their widespread applications. In this work, surface-initiated atom-transfer radical polymerization (ATRP) is employed to tailor the functionality of the nylon membrane and pore surfaces in a well-controlled manner. A simple two-step method, involving the activation of surface amide groups with formaldehyde and the reaction of the resulting N-methylol polyamide with 2-bromoisobutyryl bromide, was first developed for the covalent immobilization of ATRP initiators on the nylon membrane and its pore surfaces. Functional polymer brushes of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)monomethacrylate (PEGMA) were prepared via surface-initiated ATRP from the nylon membranes. A kinetics study revealed that the chain growth from the membranes was consistent with a "controlled" process. The dormant chain ends of the grafted HEMA polymer (P(HEMA)) and PEGMA polymer (P(PEGMA)) on the nylon membranes could be reactivated for the consecutive surface-initiated ATRP to produce the corresponding nylon membranes functionalized by P(HEMA)-b-P(PEGMA) and P(PEGMA)-b-P(HEMA) diblock copolymer brushes. In addition, membranes with grafted P(HEMA) and P(PEGMA) brushes exhibited good resistance to protein adsorption and fouling under continuous-flow conditions.

  7. Velocity distributions of hydrogen atoms and hydroxyl radicals produced through solar photodissociation of water

    NASA Technical Reports Server (NTRS)

    Wu, C. Y. R.; Chen, F. Z.

    1993-01-01

    The velocity distributions of H and OH fragments produced through solar photodissociation of gaseous H2O molecules under collisionless conditions are presented. The calculations are carried out using: the most recently available absolute partial cross sections for the production of H and OH through photodissociation of H2O from its absorption onset at 1860 A down to 500 A; the newly available vibrational and rotational energy distributions of both the excited and ground state OH photofragments; the calculated cross sections for the total dissociation processes; and the integrated solar flux in 10 A increments from 500 to 1860 A in the continuum regions and the specific wavelength and flux at the bright solar lines. The calculated results show that the H atoms and the OH radicals produced exhibit multiple velocity groups. Since most current cometary modeling uses a single velocity of 20 km/sec associated with the photodissociation of H2O, the present results may be useful in interpreting the many peaks observed in the velocity distributions of the H Lyman alpha and H alpha of comets.

  8. Uranium recovery from seawater: development of fiber adsorbents prepared via atom-transfer radical polymerization

    SciTech Connect

    Saito, Tomonori; Brown, Suree; Chatterjee, Sabornie; Kim, Jungseung; Tsouris, Costas; Mayes, Richard T.; Kuo, Li-Jung; Gill, Gary; Oyola, Yatsandra; Janke, Christopher J.; Dai, Sheng

    2014-08-04

    We developed a novel adsorbent preparation method using atom-transfer radical polymerization (ATRP) combined with radiation-induced graft polymerization (RIGP) in order to synthesize an adsorbent for uranium recovery from seawater. Furthermore, the ATRP method allowed a much higher degree of grafting on the adsorbent fibers (595 2818%) than that allowed by RIGP alone. The adsorbents were prepared with varied composition of amidoxime groups and hydrophilic acrylate groups. The successful preparation revealed that both ligand density and hydrophilicity were critical for optimal performance of the adsorbents. Adsorbents synthesized in this study showed a relatively high performance (141 179 mg/g at 49 62 % adsorption) in laboratory screening tests using a uranium concentration of ~6 ppm. This performance is much higher than that of known commercial adsorbents. However, actual seawater experiment showed impeded performance compared to the recently reported high-surface-area-fiber adsorbents, due to slow adsorption kinetics. The impeded performance motivated an investigation of the effect of hydrophilic block addition on the graft chain terminus. The addition of hydrophilic block on the graft chain terminus nearly doubled the uranium adsorption capacity in seawater, from 1.56 mg/g to 3.02 mg/g. Our investigation revealed the importance of polymer chain conformation, in addition to ligand and hydrophilic group ratio, for advanced adsorbent synthesis for uranium recovery from seawater.

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

    NASA Astrophysics Data System (ADS)

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2016-12-01

    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 1H 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.

  10. Controlled synthesis of photochromic polymer brushes by atom transfer radical polymerization.

    SciTech Connect

    Piech, Marcin; Bell, Nelson Simmons; Long, Timothy Michael

    2005-06-01

    This work reports on the grafting of methyl methacrylate polymer brushes containing spirobenzopyran pendant groups from flat silica surfaces and colloidal particles utilizing atom transfer radical polymerization (ATRP). The reaction conditions were optimized with respect to the kind of surface bound initiator, the type of halide and ligand used in the catalytic complex, the presence/absence of untethered initiator, and solvent type. This enabled synthesis of coatings up to 80 {+-} 3 nm thick with controlled spirobenzopyran content. While polymerization kinetics indicate the presence of chain termination reactions, the 'living' character of the process is confirmed by controlled formation of block copolymer brushes. UV/vis spectroscopy was used to characterize the UV-induced isomerization of spirobenzopyran to zwitterionic merocyanine and the thermal back-reaction. Spectral and kinetic analyses of this latter bleaching process points to the existence of free and associated merocyanines in the polymeric brush in both tetrahydrofuran and toluene. However, stabilization of merocyanine species by the polymer matrix is considerably greater in toluene with thermal back-reaction rates approaching those determined for solid dry films.

  11. Understanding atom transfer radical polymerization: effect of ligand and initiator structures on the equilibrium constants.

    PubMed

    Tang, Wei; Kwak, Yungwan; Braunecker, Wade; Tsarevsky, Nicolay V; Coote, Michelle L; Matyjaszewski, Krzysztof

    2008-08-13

    Equilibrium constants in Cu-based atom transfer radical polymerization (ATRP) were determined for a wide range of ligands and initiators in acetonitrile at 22 degrees C. The ATRP equilibrium constants obtained vary over 7 orders of magnitude and strongly depend on the ligand and initiator structures. The activities of the Cu(I)/ligand complexes are highest for tetradentate ligands, lower for tridentate ligands, and lowest for bidentate ligands. Complexes with tripodal and bridged ligands (Me6TREN and bridged cyclam) tend to be more active than those with the corresponding linear ligands. The equilibrium constants are largest for tertiary alkyl halides and smallest for primary alkyl halides. The activities of alkyl bromides are several times larger than those of the analogous alkyl chlorides. The equilibrium constants are largest for the nitrile derivatives, followed by those for the benzyl derivatives and the corresponding esters. Other equilibrium constants that are not readily measurable were extrapolated from the values for the reference ligands and initiators. Excellent correlations of the equilibrium constants with the Cu(II/I) redox potentials and the carbon-halogen bond dissociation energies were observed.

  12. Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization.

    PubMed

    Xu, Jianxiong; Gao, Yong; Li, Huaming

    2011-02-01

    Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.

  13. Adsorption of perfluorinated compounds on aminated rice husk prepared by atom transfer radical polymerization.

    PubMed

    Deng, Shubo; Niu, Li; Bei, Yue; Wang, Bin; Huang, Jun; Yu, Gang

    2013-04-01

    Adsorption is considered as an effective method to remove perfluorinated compounds (PFCs) from aqueous solution. In this study, an aminated rice husk (RH) adsorbent was successfully prepared through surface-initiated atom transfer radical polymerization (ATRP) and subsequent amination reaction, and it was used to remove perfluorooctanoate (PFOA), perfluorobutanoic acid (PFBA) and perfluorooctane sulfonate (PFOS) from aqueous solution. Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) analysis verified the presence of grafted polymer brushes and amine groups on the RH surface. The zero point of zeta potential of aminated RH was 8.5, which facilitated the sorption of anionic PFCs on the positively charged adsorbent at pH below 8.5. The sorption equilibria of PFOA, PFBA and PFOS were achieved within 5 h, 3 h and 9 h, respectively, faster than the reported porous adsorbents. Sorption isotherms showed that the adsorption capacities of PFOA, PFBA and PFOS on the aminated RH at pH 5.0 were 2.49, 1.70 and 2.65 mmol g(-1), respectively. Sorption behavior and X-ray photoelectron spectroscopy (XPS) analysis confirmed that the electrostatic and hydrophobic interactions were involved in the sorption process, and the micelles and hemi-micelles of PFOA and PFOS may form on the adsorbent surface.

  14. Removal of cefalexin using yeast surface-imprinted polymer prepared by atom transfer radical polymerization.

    PubMed

    Li, Xiuxiu; Pan, Jianming; Dai, Jiangdong; Dai, Xiaohui; Ou, Hongxiang; Xu, Longcheng; Li, Chunxiang; Zhang, Rongxian

    2012-10-01

    The first use of yeast as a support in the molecular imprinting field combined with atom transfer radical polymerization was described. Then, the as-prepared molecularly imprinted polymers were characterized by Fourier transmission infrared spectrometry, scanning electron microscope, thermogravimetric analysis, and elemental analysis. The obtained imprinted polymers demonstrated elliptical-shaped particles with the thickness of imprinting layer of 0.63 μm. The batch mode experiments were adopted to investigate the adsorption equilibrium, kinetics, and selectivity. The kinetic properties of imprinted polymers were well described by the pseudo-second-order kinetic equation, indicating the chemical process was the rate-limiting step for the adsorption of cefalexin (CFX). The equilibrium data were well fitted by the Freundlich isotherm, and the multimolecular layers adsorption capacity of imprinted polymers was 34.07 mg g(-1) at 298 K. The selectivity analysis suggested that the imprinted polymers exhibited excellent selective recognition for CFX in the presence of other compounds with related structure. Finally, the analytical method based on the imprinted polymers extraction coupled with high-performance liquid chromatograph was successfully used for CFX analysis in spiked pork and water samples.

  15. Synthesis and characterization of grafting polystyrene from guar gum using atom transfer radical addition.

    PubMed

    Yang, Yang; Chen, Fu; Chen, Qi; He, Jie; Bu, Tao; He, Xuemei

    2017-11-15

    To broaden the application fields for guar gum, this natural polymer is often grafted to/from the surface to modify its properties. Polystyrene-guar gum (PS-guar gum) is successfully synthesized using atom transfer radical addition based n-BuBr(C4H9Br), Cu(I)Cl and N,N,N',N″,N‴-penthamethyldiethylenetriamine (C9H23N3,PMDETA) as initiator, electronating agent and ligand respectively in an inert atmosphere. The graft copolymer is characterized by FT-IR, (1)H NMR, XRD and scanning electron microscope (SEM). The results show that styrene is successfully introduced onto guar gum and particles of PS-guar gum adopt a disordered morphology with diameters of 100nm, and PS-guar gum are largely amorphous with poor crystallinity. Besides, add on shows an increasing trend on increasing the concentration of PS. Swelling behavior, hydrophobicity and thermal stability of PS-guar gum indicate that PS-guar gum has great thickening capacity and thermal stability. Nevertheless, modification of guar gum via ATRA truly is convenient to industrial production since facilitating the manufacturing process. Copyright © 2017 Elsevier Ltd. All rights reserved.

  16. Kinetic of the gas-phase reactions of OH radicals and Cl atoms with diethyl ethylphosphonate and triethyl phosphate

    NASA Astrophysics Data System (ADS)

    Laversin, H.; El Masri, A.; Al Rashidi, M.; Roth, E.; Chakir, A.

    2016-02-01

    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 cm3 molecule-1 s-1) were obtained for the reactions of OH and CL with DEEP and TEP: kOH+DEEP = (7.84 ± 0.65) × 10-14exp((1866 ± 824)/T), kOH+TEP = (6.54 ± 0.42) × 10-14exp((1897 ± 626)/T), kCl+DEEP = (5.27 ± 0.80) × 10-11exp(765 ± 140/T) and kCl+TEP = (5.23 ± 0.80) × 10-11exp(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.

  17. Rate constant and reaction channels for the reaction of atomic nitrogen with the ethyl radical

    SciTech Connect

    Stief, L.J.; Nesbitt, F.L.; Payne, W.A. ); Kuo, S.C.; Tao, W.; Klemm, R.B. )

    1995-04-01

    The absolute rate constant and primary reaction products have been determined at [ital T]=298 K for the atom--radical reaction N([sup 4][ital S])+C[sub 2]H[sub 5] in a discharge flow system with collision-free sampling to a mass spectrometer. The rate constant measurements employed low energy electron impact ionization while the product study used dispersed synchrotron radiation as the photoionization source. The rate constant was determined under pseudo-first-order conditions by monitoring the decay of C[sub 2]H[sub 5] or C[sub 2]D[sub 5] as a function of time in the presence of excess N atoms. The result is [ital k]=(1.1[plus minus]0.3)[times]10[sup [minus]10] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1]. For the reaction product experiments using photoionization mass spectrometry, products observed at 114 nm (10.9 eV) were CD[sub 3], D[sub 2]CN and C[sub 2]D[sub 4] for the N+C[sub 2]D[sub 5] reaction. The product identification is based on the unambiguous combination of product [ital m]/[ital z] values, the shift of the [ital m]/[ital z] peaks observed for the N+C[sub 2]D[sub 5] reaction products with respect to the N+C[sub 2]H[sub 5] reaction products and the photoionization threshold measured for the major products. The observed products are consistent with the occurrence of the reaction channels D[sub 2]CN+CD[sub 3](2a) and C[sub 2]D[sub 4]+ND(2c). Formation of C[sub 2]D[sub 4] product via channel (2c) accounts for approximately 65% of the C[sub 2]D[sub 5] reacted. Most, if not all, of the remaining 35% is probably accounted for by channel (2a). These rate constant and product results are compared with those for the N+CH[sub 3] reaction as well as other atom+C[sub 2]H[sub 5] reactions. The role of the N+C[sub 2]H[sub 5] reaction in the formation of HCN in the atmospheres of Titan and Neptune is briefly considered. (Abstract Truncated)

  18. Heavy atom nitroxyl radicals. VI. The electronic spectrum of jet-cooled H2PO, the prototypical phosphoryl free radical

    NASA Astrophysics Data System (ADS)

    Gharaibeh, Mohammed A.; Clouthier, Dennis J.; Tarroni, Riccardo

    2011-12-01

    The previously unknown electronic spectrum of the H2PO free radical has been identified in the 407-337 nm region using a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio predictions of the properties of the ground and first two excited doublet states were used to identify the spectral region in which to search for the electronic transition and were used to aid in the analysis of the data. The band system is assigned as the {tilde B}2A'-{tilde X}2A' electronic transition which involves promotion of an electron from the π to the π* molecular orbital. The excited state r0 molecular structure was determined by rotational analysis of high resolution LIF spectra to be r(PO) = 1.6710(2) Å, r(PH) = 1.4280(6) Å, θ(HPO) = 105.68(7)°, θ(HPH) = 93.3(2)°, and the out-of-plane angle = 66.8(2)°. The structural changes on electronic excitation, which include substantial increases in the PO bond length and out-of-plane angle, are as expected based on molecular orbital theory and our previous studies of the isoelectronic H2AsO, Cl2PS, and F2PS free radicals.

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

    PubMed

    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.

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

    PubMed

    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.

  1. Reactions of OOH radical with beta-carotene, lycopene, and torulene: hydrogen atom transfer and adduct formation mechanisms.

    PubMed

    Galano, Annia; Francisco-Marquez, Misaela

    2009-08-13

    The relative free radical scavenging activity of beta-carotene, lycopene, and torulene toward OOH radicals has been studied using density functional theory. Hydrogen atom transfer (HAT) and radical adduct formation (RAF) mechanisms have been considered. All the possible reaction sites have been included in the modeling, and detailed branching ratios are reported for the first time. The reactions of hydrocarbon carotenoids (Car) with peroxyl radicals, in both polar and nonpolar environments, are predicted to proceed via RAF mechanism, with contributions higher than 98% to the overall OOH + Car reactions. Lycopene and torulene were found to be more reactive than beta-carotene. In nonpolar environments the reactivity of the studied carotenoids toward peroxyl radical follows the trend LYC > TOR > BC, whereas in aqueous solutions it is TOR > LYC > BC. OOH adducts are predicted to be formed mainly at the terminal sites of the conjugated polyene chains. The main addition sites were found to be C5 for beta-carotene and lycopene and C30 for torulene. The general agreement between the calculated magnitudes and the available experimental data supports the predictions from this work.

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

    PubMed

    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

  3. The direct observation of secondary radical chain chemistry in the heterogeneous reaction of chlorine atoms with submicron squalane droplets.

    PubMed

    Liu, Chen-Lin; Smith, Jared D; Che, Dung L; Ahmed, Musahid; Leone, Stephen R; Wilson, Kevin R

    2011-05-21

    The reaction of Cl atoms, in the presence of Cl(2) and O(2), with sub-micron squalane particles is used as a model system to explore how surface hydrogen abstraction reactions initiate chain reactions that rapidly transform the chemical composition of an organic particle. The heterogeneous reaction is measured in a photochemical flow tube reactor in which chlorine atoms are produced by the photolysis of Cl(2) at 365 nm. By monitoring the heterogeneous reaction, using a vacuum ultraviolet photoionization aerosol mass spectrometer, the effective reactive uptake coefficient and the distributions of both oxygenated and chlorinated reaction products are measured and found to depend sensitively upon O(2), Cl(2), and Cl concentrations in the flow reactor. In the absence of O(2), the effective reactive uptake coefficient monotonically increases with Cl(2) concentration to a value of ∼3, clearly indicating the presence of secondary chain chemistry occurring in the condensed phase. The effective uptake coefficient decreases with increasing O(2) approaching a diffusion corrected value of 0.65 ± 0.07, when 20% of the total nitrogen flow rate in the reactor is replaced with O(2). Using a kinetic model it is found that the amount of secondary chemistry and the product distributions in the aerosol phase are controlled by the competitive reaction rates of O(2) and Cl(2) with alkyl radicals. The role that a heterogeneous pathway might play in the reaction of alkyl radicals with O(2) and Cl(2) is investigated within a reasonable range of reaction parameters. These results show, more generally, that for heterogeneous reactions involving secondary chain chemistry, time and radical concentration are not interchangeable kinetic quantities, but rather the observed reaction rate and product formation chemistry depends sensitively upon the concentrations and time evolution of radical initiators and those species that propagate or terminate free radical chain reactions. © The Owner

  4. Atmospheric reactions between E,E-2,4-hexadienal and OH, NO3 radicals and Cl atoms

    NASA Astrophysics Data System (ADS)

    Colmenar, I.; Martín, P.; Cabañas, B.; Salgado, S.; Martínez, E.

    2014-12-01

    E,E-2,4-Hexadienal is an α,β-unsaturated aldehyde whose presence in the atmosphere can arise from different sources. The rate coefficients for the reaction of this compound with Cl atoms, OH and NO3 radicals and for the photolysis process have been determined at atmospheric pressure and room temperature. A relative method has been developed with a Fourier Transform Infrared spectrometer (FTIR) or Solid Phase Micro Extraction fiber/chromatography-mass spectrometer (SPME/GC-MS) used as sampling/detection techniques. The absolute rate coefficients k (in units of cm3 molecule-1 s-1) obtained for Cl, OH and NO3 were (3.98 ± 0.44) × 10-10, (6.78 ± 0.47) × 10-11 and (1.34 ± 0.56) × 10-12, respectively. An estimation of the rate coefficient for the reaction of E,E-2,4-hexadienal with OH and NO3 radicals and Cl atoms has been carried out using correlations and SAR methods. The SAR substituent factor for the -C(O)H group, [G-(C(O)H)] = 3.58 × 10-3, has been obtained. This group reactivity factor allows the rate coefficients to be estimated for the reaction of unsaturated aldehydes with NO3 radicals. The results of this study confirm that the reaction of unsaturated aldehydes with Cl atoms is very fast and that the structure of the compound has little influence, with the influence of the structure being more marked in the case of the OH radical reaction and relatively large for the NO3 reaction. The results are consistent with a mechanism in which the first stage is addition of an atom or radical to the double bond of E,E-2,4-hexadienal as the main reaction channel and, to a minor extent, the abstraction of aldehydic hydrogen. These are the first data reported for the atmospheric reactions of this compound and this study therefore contributes to the database of rate coefficients for atmospheric reactions.

  5. Theoretical studies of the reactions of CF3CHCLOCHF2/CF3CHFOCHF2 with OH radical and Cl atom and their product radicals with OH.

    PubMed

    Yang, Lei; Liu, Jing-Yao; Wan, Su-Qin; Li, Ze-Sheng

    2009-03-01

    The mechanisms and dynamics studies of the OH radical and Cl atom with CF(3)CHClOCHF(2) and CF(3)CHFOCHF(2) have been carried out theoretically. The geometries and frequencies of all the stationary points are optimized at the B3LYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the G3(MP2) level of theory. For each reaction, two H-abstraction channels are found and four products (CF(3)CHFOCF(2), CF(3)CFOCHF(2), and CF(3)CHClOCF(2), CF(3)CClOCHF(2)) are produced during the above processes. The rate constants for the CF(3)CHClOCHF(2)/CF(3)CHFOCHF(2) + OH/Cl reactions are calculated by canonical variational transition-state theory (CVT) within 200-2000 K, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained. Our calculation shows that the substitution of Cl by F decreases the reactivity of CF(3)CHClOCHF(2) toward OH and Cl. In addition, the mechanisms of subsequent reactions of product radicals and OH radical are further investigated at the G3(MP2)//B3LYP/6-311G(d,p) level, and the main products are predicted in the this article.

  6. Extension of structure-reactivity correlations for the hydrogen abstraction reaction to methyl radical and comparison to chlorine atom, bromine atom, and hydroxyl radical

    SciTech Connect

    Poutsma, Marvin L.

    2016-06-07

    In this study, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp3-hybridized carbon by three electrophilic radicals (X + HCR3 → XH + CR3; X = Cl, HO, and Br); the reaction enthalpy effect was represented by the independent variable ΔrH and the polar effect by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH3. In spite of a limited and scattered data base, the resulting least-squares fit [log k437(CH3) = 0.0251(ΔrH) + 0.96(ΣF) 0.56(ΣR) – 19.15] was modestly successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the philicity of CH3, may depend on the nature of the substituents.

  7. Extension of structure-reactivity correlations for the hydrogen abstraction reaction to methyl radical and comparison to chlorine atom, bromine atom, and hydroxyl radical

    SciTech Connect

    Poutsma, Marvin L.

    2016-06-07

    In this study, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp3-hybridized carbon by three electrophilic radicals (X + HCR3 → XH + CR3; X = Cl, HO, and Br); the reaction enthalpy effect was represented by the independent variable ΔrH and the polar effect by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH3. In spite of a limited and scattered data base, the resulting least-squares fit [log k437(CH3) = 0.0251(ΔrH) + 0.96(ΣF) 0.56(ΣR) – 19.15] was modestly successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the philicity of CH3, may depend on the nature of the substituents.

  8. Extension of structure-reactivity correlations for the hydrogen abstraction reaction to methyl radical and comparison to chlorine atom, bromine atom, and hydroxyl radical

    DOE PAGES

    Poutsma, Marvin L.

    2016-06-07

    In this study, we presented structure-reactivity correlations for the gas-phase rate constants for hydrogen abstraction from sp3-hybridized carbon by three electrophilic radicals (X• + HCR3 → XH + •CR3; X = Cl•, HO•, and Br); the reaction enthalpy effect was represented by the independent variable ΔrH and the polar effect by the independent variables F and R, the Hammett-Taft constants for field/inductive and resonance effects. Here we present a parallel treatment for the less electronegative CH3•. In spite of a limited and scattered data base, the resulting least-squares fit [log k437(CH3•) = 0.0251(ΔrH) + 0.96(ΣF) 0.56(ΣR) – 19.15] was modestlymore » successful and useful for initial predictions. As expected, the polar effect appears to be minor and its directionality, i.e., the philicity of CH3, may depend on the nature of the substituents.« less

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

    PubMed

    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.

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

    PubMed Central

    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 (Tg) than those of pristine PMMA. PMID:25114639

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  12. The effect of spin-orbit splitting on the association kinetics of barrierless halogen atom-hydrocarbon radical reactions.

    SciTech Connect

    Jasper, A. W.; Klippenstein, S. J.; Harding, L. B.

    2010-01-01

    The effect of the geometry dependence of spin-orbit splitting on transition state theory (TST) predictions for radical-radical recombination rate coefficients is examined. The effects are illustrated with direct ab initio variable-reaction-coordinate (VRC)-TST calculations for the reactions of two types of hydrocarbon radicals (R = CH{sub 3} and CH{sub 2}CHCH{sub 2}) with three halogen atoms (X = F, Cl, and Br). These halogen atoms exhibit a range of spin-orbit interaction strengths, while their interactions with the two hydrocarbon radicals exhibit a range of attractiveness. The transition state dividing surfaces for these barrierless reactions occur over a range of R-X fragment separations ({approx}3-7 {angstrom}) where the magnitude of the spin-orbit splitting is strongly geometry dependent. Perturbative models for incorporating the energetic effect of spin-orbit splitting into barrierless kinetics are presented and tested. Simply neglecting the variation in the spin-orbit splitting is demonstrated to contribute an error of less than 15% to the predicted rate coefficients for all but the CH{sub 2}CHCH{sub 2} + Br reaction, where its neglect increases the rate by up to a factor of 2. For the CH{sub 2}CHCH{sub 2} + Br reaction, the effect of spin-orbit splitting is not perturbative and instead qualitatively changes the long-range interaction potential and association dynamics. The present theoretical predictions are compared with available experimental measurements and previous theoretical work. For the CH{sub 3} + F association reaction, the errors associated with limitations in the basis set and in the active space are studied, and a detailed comparison is made between VRC-TST and rigid rotor-harmonic oscillator variational TST.

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

    PubMed

    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.

  14. Kinetics of Hydrogen Atom Abstraction from Substrate by an Active Site Thiyl Radical in Ribonucleotide Reductase

    PubMed Central

    2015-01-01

    Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides in all organisms. Active E. coli class Ia RNR is an α2β2 complex that undergoes reversible, long-range proton-coupled electron transfer (PCET) over a pathway of redox active amino acids (β-Y122 → [β-W48] → β-Y356 → α-Y731 → α-Y730 → α-C439) that spans ∼35 Å. To unmask PCET kinetics from rate-limiting conformational changes, we prepared a photochemical RNR containing a [ReI] photooxidant site-specifically incorporated at position 355 ([Re]-β2), adjacent to PCET pathway residue Y356 in β. [Re]-β2 was further modified by replacing Y356 with 2,3,5-trifluorotyrosine to enable photochemical generation and spectroscopic observation of chemically competent tyrosyl radical(s). Using transient absorption spectroscopy, we compare the kinetics of Y· decay in the presence of substrate and wt-α2, Y731F-α2 ,or C439S-α2, as well as with 3′-[2H]-substrate and wt-α2. We find that only in the presence of wt-α2 and the unlabeled substrate do we observe an enhanced rate of radical decay indicative of forward radical propagation. This observation reveals that cleavage of the 3′-C–H bond of substrate by the transiently formed C439· thiyl radical is rate-limiting in forward PCET through α and has allowed calculation of a lower bound for the rate constant associated with this step of (1.4 ± 0.4) × 104 s–1. Prompting radical propagation with light has enabled observation of PCET events heretofore inaccessible, revealing active site chemistry at the heart of RNR catalysis. PMID:25353063

  15. Importance of π-stacking interactions in the hydrogen atom transfer reactions from activated phenols to short-lived N-oxyl radicals.

    PubMed

    Mazzonna, Marco; Bietti, Massimo; DiLabio, Gino A; Lanzalunga, Osvaldo; Salamone, Michela

    2014-06-06

    A kinetic study of the hydrogen atom transfer from activated phenols (2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols, 2,2,5,7,8-pentamethylchroman-6-ol, caffeic acid, and (+)-cathechin) to a series of N-oxyl radical (4-substituted phthalimide-N-oxyl radicals (4-X-PINO), 6-substituted benzotriazole-N-oxyl radicals (6-Y-BTNO), 3-quinazolin-4-one-N-oxyl radical (QONO), and 3-benzotriazin-4-one-N-oxyl radical (BONO)), was carried out by laser flash photolysis in CH3CN. A significant effect of the N-oxyl radical structure on the hydrogen transfer rate constants (kH) was observed with kH values that monotonically increase with increasing NO-H bond dissociation energy (BDENO-H) of the N-hydroxylamines. The analysis of the kinetic data coupled to the results of theoretical calculations indicates that these reactions proceed by a hydrogen atom transfer (HAT) mechanism where the N-oxyl radical and the phenolic aromatic rings adopt a π-stacked arrangement. Theoretical calculations also showed pronounced structural effects of the N-oxyl radicals on the charge transfer occurring in the π-stacked conformation. Comparison of the kH values measured in this study with those previously reported for hydrogen atom transfer to the cumylperoxyl radical indicates that 6-CH3-BTNO is the best N-oxyl radical to be used as a model for evaluating the radical scavenging ability of phenolic antioxidants.

  16. Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Laufer, A. H.

    1981-01-01

    Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

  17. Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Laufer, A. H.

    1981-01-01

    Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

  18. Surface-initiated reverse atom transfer radical polymerization (SI-RATRP) for blood-compatible polyurethane substrates

    NASA Astrophysics Data System (ADS)

    Lu, Chunyan; Zhou, Ninglin; Xu, Dong; Tang, Yida; Jin, Suxing; Wu, Yue; Shen, Jian

    2011-10-01

    A well-defined polymer brushes (2-(methacryloyloxy) ethyl phosphorylcholine, MPC) grafted from the polyurethane (PU) substrate by surface-initiated reverse atom transfer radical polymerization (SI-RATRP) was studied. In this work, a kind of silane coupling agent (3-chloropropyltrimethoxysilane, CPTM) was adopted to serve as a coupling agent as well as a ligand for the first time. Surface structure, wettability, morphology of the PU substrates before and after modification were characterized by Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy measurement (XPS), Atomic force microscope (AFM), Water contact angle measurement, respectively. The results showed that zwitterionic brushes were successfully fabricated on the PU surfaces, and the content of the grafted layer increased gradually with the polymerization time. The blood compatibility of the PU substrates was evaluated by protein adsorption tests and platelet adhesion tests in vitro. It was found that all the PU functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion.

  19. Laboratory studies of the kinetics of tropospheric and stratospheric atom and radical reactions

    NASA Technical Reports Server (NTRS)

    Golde, Michael F.

    1987-01-01

    Direct measurements of reaction rate constants and branching fractions for elementary reactions necessary in the modeling of the troposphere or stratosphere are provided. Details of reaction mechanisms are elucidated by studying pressure and temperature dependences of reactions, as well as by use of isotopic labels. Measurement techniques are improved for radical species in the laboratory. Progress and results in each area are given.

  20. Direct ab initio dynamics studies of the hydrogen abstraction reactions of hydrogen atom with n-propyl radical and isopropyl radical.

    PubMed

    Li, Qian Shu; Zhang, Yue; Zhang, Shaowen

    2005-02-01

    The kinetics of the hydrogen abstraction reactions of hydrogen atom with n-propyl radical and isopropyl radical were studied using the direct ab initio dynamics approach. BHandHLYP/cc-pVDZ method was employed to optimize the geometries of stationary points as well as the points on the minimum energy path (MEP). The energies of all the points for the two reactions were further refined at the QCISD(T)/cc-pVTZ level of theory. No barrier was found at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory for both reactions. The forward and reverse rate constants were evaluated with both canonical variational transition state theory (CVT) and microcanonical variational transition state theory (mu VT) in the temperature range of 300-2,500 K. The fitted three-parameter Arrhenius expression of the calculated CVT rate constants at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory are k(CVT) (n-C3H7) = 1.68 x 10(-14) T(0.84) e((319.5/T)) cm3 molecule(-1) s(-1) and k(CVT) (iso-C3H7)=4.99 x 10(-14) T(0.90) e((159.5/T)) cm3 molecule(-1) s(-1) for reactions of n-C3H7 + H and iso-C3H7 + H, respectively, which are in good agreement with available literature data. The variational effects were analysed.

  1. Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid.

    PubMed

    Cai, Yang; Koshino, Nobuyoshi; Saha, Basudeb; Espenson, James H

    2005-01-07

    Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively.

  2. The radical trap in atom transfer radical polymerization need not be thermodynamically stable. A study of the MoX(3)(PMe(3))(3) catalysts.

    PubMed

    Maria, Sébastien; Stoffelbach, François; Mata, José; Daran, Jean-Claude; Richard, Philippe; Poli, Rinaldo

    2005-04-27

    The molybdenum(III) coordination complexes MoX(3)(PMe(3))(3) (X = Cl, Br, and I) are capable of controlling styrene polymerization under typical atom transfer radical polymerization (ATRP) conditions, in conjunction with 2-bromoethylbenzene (BEB) as an initiator. The process is accelerated by the presence of Al(OPr(i))(3) as a cocatalyst. Electrochemical and synthetic studies aimed at identifying the nature of the spin trap have been carried out. The cyclic voltammogram of MoX(3)(PMe(3))(3) (X = Cl, Br, I) shows partial reversibility (increasing in the order Cl < Br < I) for the one-electron oxidation wave. Addition of X(-) changes the voltammogram, indicating the formation of MoX(4)(PMe(3))(3) for X = Cl and Br. On the other hand, I(-) is more easily oxidized than the MoI(3)(PMe(3))(3) complex; thus, the putative MoI(4)(PMe(3))(3) complex is redox unstable. Electrochemical studies of MoI(3)(PMe(3))(3) in the presence of X(-) (X = Cl or Br) reveal the occurrence of facile halide-exchange processes, leading to the conclusion that the MoI(3)X(PMe(3))(3) products are also redox unstable. The oxidation of MoX(3)(PMe(3))(3) with (1)/(2)Br(2) yields MoX(3)Br(PMe(3))(3) (X = Cl, Br), whose molecular nature is confirmed by single-crystal X-ray analyses. On the other hand, the oxidation of MoI(3)(PMe(3))(3) by I(2) slowly yields a tetraiodomolybdate(III) salt of iodotrimethylphosphonium, [Me(3)PI][MoI(4)(PMe(3))(3)], as confirmed by an X-ray study. This product has no controlling ability in radical polymerization. The redox instability of MoI(3)X(PMe(3))(3) can be reconciled with its involvement as a radical trapping species in the MoI(3)(PMe(3))(3)-catalyzed ATRP, given the second-order nature of its decomposition rate.

  3. Hydrogen atom abstraction selectivity in the reactions of alkylamines with the benzyloxyl and cumyloxyl radicals. The importance of structure and of substrate radical hydrogen bonding.

    PubMed

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

    2011-10-19

    A time-resolved kinetic study on the hydrogen abstraction reactions from a series of primary and secondary amines by the cumyloxyl (CumO(•)) and benzyloxyl (BnO(•)) radicals was carried out. The results were compared with those obtained previously for the corresponding reactions with tertiary amines. Very different hydrogen abstraction rate constants (k(H)) and intermolecular selectivities were observed for the reactions of the two radicals. With CumO(•), k(H) was observed to decrease on going from the tertiary to the secondary and primary amines. The lowest k(H) values were measured for the reactions with 2,2,6,6-tetramethylpiperidine (TMP) and tert-octylamine (TOA), substrates that can only undergo N-H abstraction. The opposite behavior was observed for the reactions of BnO(•), where the k(H) values increased in the order tertiary < secondary < primary. The k(H) values for the reactions of BnO(•) were in all cases significantly higher than those measured for the corresponding reactions of CumO(•), and no significant difference in reactivity was observed between structurally related substrates that could undergo exclusive α-C-H and N-H abstraction. This different behavior is evidenced by the k(H)(BnO(•))/k(H)(CumO(•)) ratios that range from 55-85 and 267-673 for secondary and primary alkylamines up to 1182 and 3388 for TMP and TOA. The reactions of CumO(•) were described in all cases as direct hydrogen atom abstractions. With BnO(•) the results were interpreted in terms of the rate-determining formation of a hydrogen-bonded prereaction complex between the radical α-C-H and the amine lone pair wherein hydrogen abstraction occurs. Steric effects and amine HBA ability play a major role, whereas the strength of the substrate α-C-H and N-H bonds involved appears to be relatively unimportant. The implications of these different mechanistic pictures are discussed.

  4. Role of low-energy ion irradiation in the formation of an aluminum germanate layer on a germanium substrate by radical-enhanced atomic layer deposition

    SciTech Connect

    Fukuda, Yukio Yamada, Daichi; Yokohira, Tomoya; Yanachi, Kosei; Yamamoto, Chiaya; Yoo, Byeonghak; Sato, Tetsuya; Yamanaka, Junji; Takamatsu, Toshiyuki; Okamoto, Hiroshi

    2016-03-15

    Radical-enhanced atomic layer deposition uses oxygen radicals generated by a remote microwave-induced plasma as an oxidant to change the surface reactions of the alternately supplied trimethylaluminum precursor and oxygen radicals on a Ge substrate, which leads to the spontaneous formation of an aluminum germanate layer. In this paper, the effects that low-energy ions, supplied from a remote microwave plasma to the substrate along with the oxygen radicals, have on the surface reactions were studied. From a comparative study of aluminum oxide deposition under controlled ion flux irradiation on the deposition surface, it was found that the ions enhance the formation of the aluminum germanate layer. The plasma potential measured at the substrate position by the Langmuir probe method was 5.4 V. Assuming that the kinetic energy of ions arriving at the substrate surface is comparable to that gained by this plasma potential, such ions have sufficient energy to induce exchange reactions of surface-adsorbed Al atoms with the underlying Ge atoms without causing significant damage to the substrate. This ion-induced exchange reaction between Al and Ge atoms is inferred to be the background kinetics of the aluminum germanate formation by radical-enhanced atomic layer deposition.

  5. Vibrationally quantum-state-specific reaction dynamics of H atom abstraction by CN radical in solution.

    PubMed

    Greaves, Stuart J; Rose, Rebecca A; Oliver, Thomas A A; Glowacki, David R; Ashfold, Michael N R; Harvey, Jeremy N; Clark, Ian P; Greetham, Gregory M; Parker, Anthony W; Towrie, Michael; Orr-Ewing, Andrew J

    2011-03-18

    Solvent collisions can often mask initial disposition of energy to the products of solution-phase chemical reactions. Here, we show with transient infrared absorption spectra obtained with picosecond time resolution that the nascent HCN products of reaction of CN radicals with cyclohexane in chlorinated organic solvents exhibit preferential excitation of one quantum of the C-H stretching mode and up to two quanta of the bending mode. On time scales of approximately 100 to 300 picoseconds, the HCN products undergo relaxation to the vibrational ground state by coupling to the solvent bath. Comparison with reactions of CN radicals with alkanes in the gas phase, known to produce HCN with greater C-H stretch and bending mode excitation (up to two and approximately six quanta, respectively), indicates partial damping of the nascent product vibrational motion by the solvent. The transient infrared spectra therefore probe solvent-induced modifications to the reaction free energy surface and chemical dynamics.

  6. Pushing TC to 27.5 K in a heavy atom radical ferromagnet.

    PubMed

    Lekin, Kristina; Ogata, Kazuma; Maclean, Adrian; Mailman, Aaron; Winter, Stephen M; Assoud, Abdeljalil; Mito, Masaki; Tse, John S; Desgreniers, Serge; Hirao, Naohisa; Dube, Paul A; Oakley, Richard T

    2016-11-24

    In the solid state the iodo-substituted bisdiselenazolyl radical 1c orders as a ferromagnet with TC = 10.5 K. With the application of pressure TC rises rapidly, reaching a value of 27.5 K at 2.4 GPa. The accompanying structural and magnetic changes have been examined by high resolution powder X-ray diffraction and by DFT calculations of magnetic exchange interactions.

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

    NASA Astrophysics Data System (ADS)

    Nikiforov, A.; Li, L.; Britun, N.; Snyders, R.; Vanraes, P.; Leys, C.

    2014-02-01

    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 controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of ˜1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to ˜4 mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H2O and O2 caused by the increasing electrical field, when the discharge is operated in ambient air.

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

    PubMed

    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.

  9. H-Atom Elimination Channel in UV Photodissociation of N-Propyl and Iso-Propyl Radicals: the Role of Conical Intersections

    NASA Astrophysics Data System (ADS)

    Zheng, Xianfeng; Zhou, Weidong; Song, Yu; Zhang, Jingsong

    2009-06-01

    The H-atom elimination channels in the UV photodissociation of jet-cooled n-propyl and iso-propyl radicals are studied in the region of 237 nm using the high-n Rydberg-atom time-of-flight technique. Upon excitation to the 3p state by the UV photolysis radiation, n-propyl radical and iso-propyl radical dissociate into the H atom and propene products. The product center-of-mass translational energy release of both n-propyl and iso-propyl radicals have bimodal distributions. The H-atom product angular distribution in n-propyl is anisotropic (with beta ˜0.5), and that in iso-propyl is isotropic. The overall average translational energy release is E_{trans} ˜0.27E_{avail} for n-propyl and E_{trans} ˜0.21E_{avail} for iso-propyl. The bimodal translational energy distributions indicate two dissociation pathways: (i) a unimolecular dissociation pathway from the ground-state propyl after internal conversion from the 3p state, and (ii) a repulsive pathway directly connected with the excited state of the propyl radical. Isotope labeling experiments have also been carried out. The possible photodissociation mechanisms and the role of conical intersections will be discussed.

  10. High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system

    NASA Astrophysics Data System (ADS)

    Whitney, Erin Sue

    chlorination. These two projects are followed by an investigation utilizing a well-characterized radical source, F, in a reaction with ethane to form HF and ethyl radical. The non-radical HF product is detected directly through similar high-resolution infrared absorption methods as described above, and its analysis is used to make inferences about the internal energy redistribution of the other radical fragment, ethyl. State-to-state reaction dynamics under single collision conditions are interpreted in the context of a simple impulsive model based on conservation of linear/angular momentum yields predictions in good agreement with experiment. Deviations from the model indicate only minor excitation of the ethyl vibrations, in contrast with a picture of extensive intramolecular vibrational energy flow but consistent with Franck-Condon excitation of the methylene CH2 bending mode. The results suggest a relatively simple dynamical picture for exothermic atom + polyatomic scattering, i.e., that of early barrier dynamics in atom + diatom systems but modified by impulsive recoil coupling at the transition state between translational/rotational degrees of freedom.

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

    PubMed

    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.

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

    PubMed

    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.

  13. Crystalline TiO 2 grafted with poly(2-methacryloyloxyethyl phosphorylcholine) via surface-initiated atom-transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Zhao, Yuancong; Tu, Qiufen; Wang, Jin; Huang, Qiongjian; Huang, Nan

    2010-12-01

    Crystalline TiO 2 films were prepared by unbalanced magnetron sputtering and the structure was confirmed by XRD. An organic layer of 11-hydroxyundecylphosphonic acid (HUPA) was prepared on the TiO 2 films by self-assembling, and the HUPA on TiO 2 films was confirmed by FTIR analysis. Simultaneously, hydroxyl groups were introduced in the phosphonic acid molecules to provide a functionality for further chemical modification. 2-Methacryloyloxyethyl phosphorylcholine (MPC), a biomimetic monomer, was chemically grafted on the HUPA surfaces at room temperature by surface-initiated atom-transfer radical polymerization. The surface characters of TiO 2 films modified by poly-MPC were confirmed by FTIR, XPS and SEM analysis. Platelet adhesion experiment revealed that poly-MPC modified surface was effective to inhibit platelet adhesion in vitro.

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

    PubMed

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

    2016-12-23

    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.

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

    PubMed

    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.

  16. Nanoengineered analytical immobilized metal affinity chromatography stationary phase by atom transfer radical polymerization: Separation of synthetic prion peptides

    PubMed Central

    McCarthy, P.; Chattopadhyay, M.; Millhauser, G.L.; Tsarevsky, N.V.; Bombalski, L.; Matyjaszewski, K.; Shimmin, D.; Avdalovic, N.; Pohl, C.

    2010-01-01

    Atom transfer radical polymerization (ATRP) was employed to create isolated, metal-containing nanoparticles on the surface of non-porous polymeric beads with the goal of developing a new immobilized metal affnity chromatography (IMAC) stationary phase for separating prion peptides and proteins. Transmission electron microscopy was used to visualize nanoparticles on the substrate surface. Individual ferritin molecules were also visualized as ferritin–nanoparticle complexes. The column's resolving power was tested by synthesizing peptide analogs to the copper binding region of prion protein and injecting mixtures of these analogs onto the column. As expected, the column was capable of separating prion-related peptides differing in number of octapeptide repeat units (PHGGGWGQ), (PHGGGWGQ)2, and (PHGGGWGQ)4. Unexpectedly, the column could also resolve peptides containing the same number of repeats but differing only in the presence of a hydrophilic tail, Q → A substitution, or amide nitrogen methylation. PMID:17481564

  17. Highly selective capture of nucleosides with boronic acid functionalized polymer brushes prepared by atom transfer radical polymerization.

    PubMed

    Cheng, Ting; Zhu, Shuqiang; Zhu, Bin; Liu, Xiaoyan; Zhang, Haixia

    2016-04-01

    The nucleoside or modified nucleoside level in biological fluids reflects the pathological or physiological state of the body. Boronate affinity absorbents are widely used to selectively extract nucleosides from complex samples. In this work, a novel functionalized absorbent was synthesized by attaching 4-mercaptophenylboronic acid to gold nanoparticles on modified attapulgite. The surface of the attapulgite was modified by poly(acryloyloxyethyltrimethyl ammonium chloride) by atom transfer radical polymerization, creating many polymer brushes on the surface. The resultant material exhibited superior binding capacity (30.83 mg/g) for adenosine and was able to capture cis-diol nucleosides from 1000-fold interferences. Finally, to demonstrate its potential for biomolecule extraction, this boronate affinity material was used to preconcentrate nucleosides from human urine and plasma. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Formation and decay of fluorobenzene radical anions affected by their isomeric structures and the number of fluorine atoms.

    PubMed

    Higashino, Saki; Saeki, Akinori; Okamoto, Kazumasa; Tagawa, Seiichi; Kozawa, Takahiro

    2010-08-12

    Aryl fluoride has attracted much attention as a resist component for extreme ultraviolet (EUV) lithography, because of the high absorption cross section of fluorine for EUV photons; however, less is known about electron attachment to fluorobenzene (FBz) and the stability of the reduced state. Picosecond and nanosecond pulse radiolysis of tetrahydrofuran solutions of FBz from mono-, di-, tri-, tetra-, penta-, and hexafluorobenzene was performed, and the effects of isomeric structure and number of fluorine atoms were examined. Scavenging of solvated electrons was found to correlate with the electron affinity obtained by density functional theory in the gas phase, whereas the decay of FBz radical anions was dominated by the activation energy of fluorine anion dissociation calculated using a polarized continuum model (PCM). A sharp contrast in the lifetimes of ortho-, meta-, and para-position difluorobenzene was observed, which could provide information on the molecular design of functional materials.

  19. Competitive Hydrogen Atom Migrations Accompanying Cascade Dissociations of Peptide Cation-Radicals of the z(+•) Type.

    PubMed

    Ledvina, Aaron R; Coon, Joshua J; Tureček, František

    2015-02-01

    We report a combined experimental and computational study of energy-resolved collision-induced dissociation (ER-CID) and time-resolved infrared multiphoton dissociation (TR-IRMPD) of z4 ions prepared by electron transfer dissociation of peptide (Ala-Ala-Asn-Ala-Arg + 2H)(2+) ions. The z4 cation-radicals, (•)ANAR(+), undergo competitive dissociations by backbone cleavage and loss of a CONH2 radical from the Asn side chain. The backbone cleavage proceeds by radical-assisted dissociation of the Asn Cα-CO bond, forming an x2 ion intermediate which rapidly dissociates by HNCO elimination to yield a stable z2 fragment ion, (•)AR(+). The ER-CID and TR-IRMPD data were consistent with the consecutive nature of the backbone dissociation but showed different branching ratios for the two major fragmentations. The ER-CID data showed branching ratios 0.6-1.0 for the side-chain and backbone cleavages whereas the TR-IRMPD data showed an earlier onset for the latter dissociation. Computational analysis of the potential energy surface with density functional theory and ab initio calculations was carried out to provide structures and energies for the reactant ions as well as several intermediates, products, and transition states. Dissociation pathways for cis and trans amide conformers were distinguished and their energies were evaluated. The threshold dissociation energies for the backbone and side-chain dissociations were similar in accordance with the experimental ER-CID branching ratio. The TR-IRMPD data were interpreted by different absorbances of intermediates produced by hydrogen atom migrations along the dissociation pathways.

  20. Competitive Hydrogen Atom Migrations Accompanying Cascade Dissociations of Peptide Cation-Radicals of the z+• Type

    PubMed Central

    Ledvina, Aaron R.; Coon, Joshua J.

    2014-01-01

    We report a combined experimental and computational study of energy-resolved collision-induced dissociation (ER-CID) and time-resolved infrared multiphoton dissociation (TR-IRMPD) of z4 ions prepared by electron transfer dissociation of peptide (Ala-Ala-Asn-Ala-Arg + 2H)2+ ions. The z4 cation-radicals, •ANAR+, undergo competitive dissociations by backbone cleavage and loss of a CONH2 radical from the Asn side chain. The backbone cleavage proceeds by radical-assisted dissociation of the Asn Cα—CO bond, forming an x2 ion intermediate which rapidly dissociates by HNCO elimination to yield a stable z2 fragment ion, •AR+. The ER-CID and TR-IRMPD data were consistent with the consecutive nature of the backbone dissociation but showed different branching ratios for the two major fragmentations. The ER-CID data showed branching ratios 0.6-1.0 for the side-chain and backbone cleavages whereas the TR-IRMPD data showed an earlier onset for the latter dissociation. Computational analysis of the potential energy surface with density functional theory and ab initio calculations was carried out to provide structures and energies for the reactant ions as well as several intermediates, products, and transition states. Dissociation pathways for cis and trans amide conformers were distinguished and their energies were evaluated. The threshold dissociation energies for the backbone and side-chain dissociations were similar in accordance with the experimental ER-CID branching ratio. The TR-IRMPD data were interpreted by different absorbances of intermediates produced by hydrogen atom migrations along the dissociation pathways. PMID:25844055

  1. Kinetic and Mechanistic Studies of Carbon-to-Metal Hydrogen Atom Transfer Involving Os-Centered Radicals: Evidence for Tunneling

    SciTech Connect

    Lewandowska-Androlojc, Anna; Grills, David C.; Zhang, Jie; Bullock, R. Morris; Miyazawa, Akira; Kawanishi, Yuji; Fujita, Etsuko

    2014-03-05

    We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Studies by means of time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene and 1,4-cyclohexadiene to Cp(CO)2Os• and (n5-iPr4C5H)(CO)2Os• radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons were found to be in the range 1.54 × 105 M 1 s 1 -1.73 × 107 M 1 s-1 at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary kinetic isotope effects of 13.4 ± 1.0 and 16.6 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (n5-iPr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 -C temperature range were carried out to obtain the difference in activation energies and the pre-exponential factor ratio. For hydrogen atom transfer from xanthene to (n5-iPr4C5H)(CO)2Os•, the (ED - EH) = 3.25 ± 0.20 kcal/mol and AH/AD = 0.056 ± 0.018 values are greater than the semi-classical limits and thus suggest a quantum mechanical tunneling mechanism. The work at BNL was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Geosciences & Biosciences, Office of Basic Energy Sciences. RMB also thanks the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for support. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

  2. Activators generated by electron transfer for atom transfer radical polymerization of styrene in the presence of mesoporous silica nanoparticles

    SciTech Connect

    Khezri, Khezrollah; Roghani-Mamaqani, Hossein

    2014-11-15

    Graphical abstract: Effect of mesoporous silica nanoparticles (MCM-41) on the activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is investigated. Decrement of conversion and number average molecular weight and also increment of polydispersity index (PDI) values are three main results of addition of MCM-41 nanoparticles. Incorporation of MCM-41 nanoparticles in the polystyrene matrix can clearly increase thermal stability and decrease glass transition temperature of the nanocomposites. - Highlights: • Spherical morphology, hexagonal structure, and high surface area with regular pore diameters of the synthesized MCM-41 nanoparticles are examined. • AGET ATRP of styrene in the presence of MCM-41 nanoparticles is performed. • Effect of MCM-41 nanoparticles addition on the polymerization rate, conversion and molecular weights of the products are discussed. • Improvement in thermal stability of the nanocomposites and decreasing T{sub g} values was also observed by incorporation of MCM-41 nanoparticles. - Abstract: Activator generated by electron transfer for atom transfer radical polymerization was employed to synthesize well-defined mesoporous silica nanoparticles/polystyrene composites. Inherent features of spherical mesoporous silica nanoparticles were evaluated by nitrogen adsorption/desorption isotherm, X-ray diffraction and scanning electron microscopy analysis techniques. Conversion and molecular weight evaluations were carried out using gas and size exclusion chromatography respectively. By the addition of only 3 wt% mesoporous silica nanoparticles, conversion decreases from 81 to 58%. Similarly, number average molecular weight decreases from 17,116 to 12,798 g mol{sup −1}. However, polydispersity index (PDI) values increases from 1.24 to 1.58. A peak around 4.1–4.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric

  3. Unimolecular decomposition of methylsubstituted benzenes into benzyl radicals and hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Park, Jeunghee; Bersohn, Richard; Oref, Izhack

    1990-10-01

    A homologous series of methylsubstituted benzenes and pyrazines are excited with an energy E by a short laser pulse following which, typically on a time scale of several hundred nanoseconds, hydrogen atoms are released from the methyl groups. The rate constants k(E) for the formation of the H or D atoms were determined from the time dependence of the laser-induced fluorescence (LIF) signals, and their velocity distributions were measured from the shapes of their LIF excitation curves. The velocity distributions were Maxwellian with translational temperatures remarkably close to the vibrational temperatures, typically 2000-3000 K, of the excited molecules assuming internal equilibration of the large energy E among the large number of internal modes. The logarithm of the rate constants obtained with 193 nm excitation plotted against 1/TV yields a straight line with an activation energy of 97 kcal/mol. A Rice-Ramsberger-Kassel-Marcus model invoking a transition state with several soft modes accounts very well for the rates of dissociation and for most but not all of the average kinetic energy of the released atoms.

  4. 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.

    PubMed

    Vaghjiani, Ghanshyam L

    2005-03-17

    The 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 CHBr(3) vapor in an excess of O atoms. O atoms were produced by dissociation of N(2)O (or O(2)) in a cw-microwave discharge cavity in 2.0 Torr of He at 298 K. The CO emission intensity in these bands showed a quadratic dependence on the laser fluence employed. Temporal profiles of the CO(A) and other excited-state products that formed in the photoproduced precursor + O-atom reactions were measured by recording their time-resolved chemiluminescence in discrete vibronic bands. The CO 4th positive transition (A(1)Pi, v' = 0 --> X(1)Sigma(+), v' ' = 2) near 165.7 nm was monitored in this work to deduce the pseudo-first-order decay kinetics of the CO(A) chemiluminescence in the presence of various added substrates (CH(4), NO, N(2)O, H(2), and O(2)). From this, the second-order rate coefficient values were determined for reactions of these substrates with the photoproduced precursors. The measured reactivity trends suggest that the prominent precursors responsible for the CO(A) chemiluminescence are the methylidyne radicals, CH(X(2)Pi) and CH(a(4)Sigma(-)), whose production requires the absorption of at least 2 laser photons by the photolysis mixture. The O-atom reactions with brominated precursors (CBr, CHBr, and CBr(2)), which also form in the photolysis, are shown to play a minor role in the production of the CO(A or a) chemiluminescence. However, the CBr(2) + O-atom reaction was identified as a significant source for the 289.9-nm Br(2) chemiluminescence that was also observed in this work. The 282.2-nm OH and the 336.2-nm NH chemiluminescences were also monitored to deduce the kinetics of CH(X(2)Pi) and CH(a(4)Sigma(-)) reactions when excess O(2) and NO were present.

  5. FTIR gas-phase kinetic study on the reactions of some acrylate esters with OH radicals and Cl atoms.

    PubMed

    Moreno, A; Gallego-Iniesta, M P; Taccone, R; Martín, M P; Cabañas, B; Salgado, M S

    2014-10-01

    Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298 ± 2 K) and atmospheric pressure (708 ± 8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm(3) molecule(-1) s(-1)): (3.27 ± 0.33) × 10(-11) and (4.43 ± 0.42) × 10(-11), for CH3CH═CHC(O)OCH3 and (CH3)2CH═CHC(O)OCH3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N2 and air were used as the bath gases. The following rate coefficients were obtained (in cm(3) molecule(-1) s(-1)): k3 (CH2═CHC(O)O(CH2)5CH3 + Cl) = (3.31 ± 0.31) × 10(-10), k4(CH2═CHC(O)OCH2CH(CH2CH3)(CH2)3CH3 + Cl) = (3.46 ± 0.31) × 10(-10), k5(CH2═CHC(O)O(CH2)5CH3 + OH) = (2.28 ± 0.23) × 10(-11), and k6(CH2═CHC(O)OCH2CH(CH2CH3)(CH2)3CH3 + OH) = (2.74 ± 0.26) × 10(-11). The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in -C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do

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

    DOE PAGES

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

    2016-08-25

    Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. We present calculated thermodynamic and kinetic data for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. Furthermore, these radicals can be formed via H atom abstraction reactions by H and Ö atoms and OH, HO2, and CH3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when OH is involved, but the reverse holds true for HO2more » radicals. We also determined the subsequent β-scission of the radicals formed, 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.« less

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

    SciTech Connect

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

    2016-08-25

    Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. We present calculated thermodynamic and kinetic data for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. Furthermore, these radicals can be formed via H atom abstraction reactions by H and Ö atoms and OH, HO2, and CH3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when OH is involved, but the reverse holds true for HO2 radicals. We also determined the subsequent β-scission of the radicals formed, 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.

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

    PubMed

    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.

  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

    SciTech Connect

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

    2016-08-25

    Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. We present calculated thermodynamic and kinetic data for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. Furthermore, these radicals can be formed via H atom abstraction reactions by H and Ö atoms and OH, HO2, and CH3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when OH is involved, but the reverse holds true for HO2 radicals. We also determined the subsequent β-scission of the radicals formed, 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. Hydrogel brushes grafted from stainless steel via surface-initiated atom transfer radical polymerization for marine antifouling

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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.

  12. Protein-resistant polyurethane via surface-initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate.

    PubMed

    Jin, Zhilin; Feng, Wei; Zhu, Shiping; Sheardown, Heather; Brash, John L

    2009-12-15

    Protein-resistant polyurethane (PU) surfaces were prepared by surface-initiated simultaneous normal and reverse atom transfer radical polymerization (s-ATRP) of poly(oligo(ethylene glycol) methacrylate) (poly (OEGMA)). Oxygen plasma treatment was employed for initial activation of the PU surface. The grafted polymer chain length was adjusted by varying the molar ratio of monomer to sacrificial initiator in solution from 5:1 to 200:1. The modified PU surfaces were characterized by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Protein adsorption experiments from tris-buffered saline (TBS) and plasma were carried out to evaluate the protein-resistance of the surfaces. Adsorption from single and binary protein solutions as well as from plasma was significantly reduced after modification. Adsorption decreased with increasing poly(OEGMA) chain length. Fibrinogen (Fg) adsorption on the 200:1 monomer/initiator surface was in the range of 3-33 ng/cm(2) representing 96-99% reduction compared with the unmodified PU. Fg adsorption from 0.01-10% plasma was as low as 1-5 ng/cm(2). Moreover, binary protein adsorption experiments using Fg and lysozyme (Lys) showed that protein size is a factor in the protein resistance of these surfaces.

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

    EPA Science Inventory

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

    EPA Science Inventory

    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 abstraction reactions from tertiary amines by benzyloxyl and cumyloxyl radicals: influence of structure on the rate-determining formation of a hydrogen-bonded prereaction complex.

    PubMed

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

    2011-08-05

    A time-resolved kinetic study on the hydrogen atom abstraction reactions from a series of tertiary amines by the cumyloxyl (CumO(•)) and benzyloxyl (BnO(•)) radicals was carried out. With the sterically hindered triisobutylamine, comparable hydrogen atom abstraction rate constants (k(H)) were measured for the two radicals (k(H)(BnO(•))/k(H)(CumO(•)) = 2.8), and the reactions were described as direct hydrogen atom abstractions. With the other amines, increases in k(H)(BnO(•))/k(H)(CumO(•)) ratios of 13 to 2027 times were observed. k(H) approaches the diffusion limit in the reactions between BnO(•) and unhindered cyclic and bicyiclic amines, whereas a decrease in reactivity is observed with acyclic amines and with the hindered cyclic amine 1,2,2,6,6-pentamethylpiperidine. These results provide additional support to our hypothesis that the reaction proceeds through the rate-determining formation of a C-H/N hydrogen-bonded prereaction complex between the benzyloxyl α-C-H and the nitrogen lone pair wherein hydrogen atom abstraction occurs, and demonstrate the important role of amine structure on the overall reaction mechanism. Additional mechanistic information in support of this picture is obtained from the study of the reactions of the amines with a deuterated benzyloxyl radical (PhCD(2)O(•), BnO(•)-d(2)) and the 3,5-di-tert-butylbenzyloxyl radical.

  14. Atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP) of styrene mediated by diaminobis(phenolato)iron(II) complexes: a DFT study.

    PubMed

    Poli, Rinaldo; Shaver, Michael P

    2014-07-21

    This study has addressed the radical polymerization of styrene mediated by the diaminobis(phenolate) complexes [Fe(O-2,4-Y2C6H2-5-CH2)2NCH2CH2NMe2], abbreviated as [Fe(II)]. The system is known to be well controlled when Y = Cl but not when Y = alkyl. The control was proposed to occur by a dual ATRP+OMRP mechanism. We have used DFT calculations to address the Y = Cl and Y = CH3 systems. The growing radical chain, ATRP dormant chain, and OMRP dormant chain were simplified to PhCH(CH3)(•), PhCH(CH3)-Cl, and [PhCH(CH3)-Fe(III)]. The idealized ATRP activation/deactivation equilibrium involves [Fe(III)-Cl] (I(Y)) and PhCH(CH3)(•) on the active side and [Fe(II)] (II(Y)) and PhCH(CH3)-Cl on the dormant side, whereas the OMRP activation/deactivation relates [Fe(II)] and PhCH(CH3)(•) with [PhCH(CH3)-Fe(III)] (III(Y)). A benchmarking of various functionals against the known spin properties of alkylporphyriniron(III) shows B3PW91* to be a suitable functional. For the purpose of bond dissociation energy calculations, a dispersion correction was made (B3PW91*-D3). For both Y systems, the ground state is a spin sextet for I, a spin quintet for II, and a spin quartet for III. The calculations show a greater energy cost for the ATRP activation process involving Cl atom addition to II(Cl) to yield I(Cl) (7.2 kcal/mol) relative to the process transforming II(Me) to I(Me) (2.1 kcal/mol). On the other hand, the alkyl addition transforming II to III provides slightly greater stabilization for II(Cl) (27.1 kcal/mol) than for II(Me) (26.1 kcal/mol). As a result, both ATRP and OMRP trapping processes provide greater stabilization for the Y = Cl system, in agreement with the observed better control. The charge analysis attributes these minor but determining energy differences to the inductive electron withdrawing effect of the phenolato Cl substituents. The ATRP and OMRP activation/deactivation pathways have been analyzed in relation to the spin state change; they show in each case

  15. Hydrogen-atom abstraction from a model amino acid: dependence on the attacking radical.

    PubMed

    Amos, Ruth I J; Chan, Bun; Easton, Christopher J; Radom, Leo

    2015-01-22

    We have used computational chemistry to examine the reactivity of a model amino acid toward hydrogen abstraction by HO•, HOO•, and Br•. The trends in the calculated condensed-phase (acetic acid) free energy barriers are in accord with experimental relative reactivities. Our calculations suggest that HO• is likely to be the abstracting species for reactions with hydrogen peroxide. For HO• abstractions, the barriers decrease as the site of reaction becomes more remote from the electron-withdrawing α-substituents, in accord with a diminishing polar deactivating effect. We find that the transition structures for α- and β-abstractions have additional hydrogen-bonding interactions, which lead to lower gas-phase vibrationless electronic barriers at these positions. Such favorable interactions become less important in a polar solvent such as acetic acid, and this leads to larger calculated barriers when the effect of solvation is taken into account. For Br• abstractions, the α-barrier is the smallest while the β-barrier is the largest, with the barrier gradually becoming smaller further along the side chain. We attribute the low barrier for the α-abstraction in this case to the partial reflection of the thermodynamic effect of the captodatively stabilized α-radical product in the more product-like transition structure, while the trend of decreasing barriers in the order β > γ > δ ∼ ε is explained by the diminishing polar deactivating effect. More generally, the favorable influence of thermodynamic effects on the α-abstraction barrier is found to be smaller when the transition structure for hydrogen abstraction is earlier.

  16. Theoretical investigation of the reactions of CF(3)CHFOCF(3) with the OH radical and Cl atom.

    PubMed

    Jia, Xiujuan; Liu, Youjun; Sun, Jingyu; Sun, Hao; Su, Zhongmin; Pan, Xiumei; Wang, Rongshun

    2010-01-14

    A dual-level direct dynamic method is employed to study the reaction mechanisms of CF(3)CHFOCF(3) (HFE-227 mc) with the OH radical and Cl atom. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the BH&H-LYP/6-311G(d,p) level, and the energetic information along the MEPs is further refined by MC-QCISD theory. The classical energy profile is corrected by the interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunneling effect (SCT) calculated by the variational transition state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k(1) = 2.87 x 10(-21)T(2.80) exp(-1328.60/T) and k(2) = 3.26 x 10(-16)T(1.65) exp(-4642.76/T) cm(3) molecule(-1) s(-1) over the temperature range 220-2000 K. The standard enthalpies of formation for the reactant CF(3)CHFOCF(3) and product radical CF(3)CFOCF(3) are evaluated via group-balanced isodesmic reactions, and the corresponding values are -454.06 +/- 0.2 and -402.74 +/- 0.2 kcal/mol, respectively, evaluated by MC-QCISD theory based on the BH&H-LYP/6-311G(d, p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of formation of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFE-227 mc.

  17. Shining Light on Copper: Unique Opportunities for Visible-Light-Catalyzed Atom Transfer Radical Addition Reactions and Related Processes.

    PubMed

    Reiser, Oliver

    2016-09-20

    Visible-light photoredox catalysis offers exciting opportunities to achieve challenging carbon-carbon bond formations under mild and ecologically benign conditions. Desired features of photoredox catalysts are photostability, long excited-state lifetimes, strong absorption in the visible region, and high reduction or oxidation potentials to achieve electron transfer to substrates, thus generating radicals that can undergo synthetic organic transformations. These requirements are met in a convincing way by Ru(II)(phenanthroline)3- and Ir(III)(phenylpyridine)3-type complexes and, as a low-cost alternative, by organic dyes that offer a metal-free catalyst but suffer in general from lower photostability. Cu(I)(phenanthroline)2 complexes have been recognized for more than 30 years as photoresponsive compounds with highly negative Cu(I)* → Cu(II) oxidation potentials, but nevertheless, they have not been widely considered as suitable photoredox catalysts, mainly because their excited lifetimes are shorter by a factor of 5 to 10 compared with Ru(II) and Ir(III) complexes, their absorption in the visible region is weak, and their low Cu(II) → Cu(I) reduction potentials might impede the closure of a catalytic cycle for a given process. Contrasting again with Ru(II)L3 and Ir(III)L3 complexes, Cu(I)L2 assemblies undergo more rapid ligand exchange in solution, thus potentially reducing the concentration of the photoactive species. Focusing on atom transfer radical addition (ATRA) reactions and related processes, we highlight recent developments that show the utility of Cu(I)(phenanthroline)2 complexes as photoredox catalysts, demonstrating that despite their short excited-state lifetimes and weak absorption such complexes are efficient at low catalyst loadings. Moreover, some of the inherent disadvantages stated above can even be turned to advantages: (1) the low Cu(II) → Cu(I) reduction potential might efficiently promote reactions via a radical chain pathway, and (2

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

    NASA Astrophysics Data System (ADS)

    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

  1. Product polarization distribution: Stereodynamics of the reaction of atom H and radical NH

    NASA Astrophysics Data System (ADS)

    Liu, Yu-Fang; Zhai, Hong-Sheng; Gao, Ya-Li

    2008-06-01

    The product angular momentum polarization of the reaction of H+NH is calculated via the quasiclassical trajectory method (QCT) based on the extended London-Eyring-Polanyi-Sato (LEPS) potential energy surface (PES) at a collision energy of 5.1 kcal/mol. The calculated results of the vector correlations are denoted by using the angular distribution functions. The polarization-dependent differential cross sections (PDDCSs) demonstrate that the rotational angular momentum of the product H2 is aligned and oriented along the direction perpendicular to the scattering plane. Vector correlation shows that the angular momentum of the product H2 is aligned in the plane perpendicular to the velocity vector. It suggests that the reaction proceeds preferentially when the reactant velocity vector lies in a plane containing all three atoms. The orientation and alignment of the product angular momentum affects the scattering direction of the product molecules. The polarization-dependent differential cross sections (PDDCSs) reveal that scattering is predominantly in the backward hemisphere.

  2. Isotope effect in the reaction of hydrogen atom transfer from molecules of the matrix to a carboxymethyl radical in crystalline potassium hydrogen malonate

    SciTech Connect

    Syutkin, V.M.; Tolkachev, V.A.

    1987-02-01

    Using the EPR method, the authors have studied the kinetics of abstraction of hydrogen and deuterium atoms by carboxymethyl radicals from molecules of the matrix in potassium hydrogen malonate and its deuterium-substituted analog exposed to ..gamma.. irradiation at 77 K. The authors have shown: (1) the kinetics is not described by an exponential law; (2) the activation energy for abstraction of a hydrogen atom is approx. 45 kJ/mole; (3) when the transfer H atom is replaced by a D atom, the reaction rate at 225 K drops by a factor of approx. 2. The authors discuss the hypothesis that the transfer of an atom is not the limiting step.

  3. A Coupled Cluster Investigation of SNO Radical Isomers and Their Reactions with Hydrogen Atom: Insight into Structures, Conformers, Barriers, and Energetics.

    PubMed

    Kumar, Manoj; Francisco, Joseph S

    2017-09-07

    High-level coupled cluster theory with single and double excitation, and including a perturbative triples correction (CCSD(T)) method and a series of Dunning's augmented correlation consistent basis sets, aug-cc-pVXZ (X = D, T, Q, and 5) was applied to examine the conformational landscape of SNO radical system. The basis set has an important effect on the relative stability of SNO radical isomers; that is, at the CCSD(T)/aug-cc-pV5Z level of theory, the NSO radical is the most stable member of SNO radical family. This is in contrast to previous density functional theory prediction suggesting SNO radical is the most stable isomer. The CCSD(T)/aug-cc-pV5Z//CCSD(T)/aug-cc-pVTZ results suggest that the reaction between SNO radical isomers and hydrogen atom result in the formation of their [H,N,S,O] hydrides with HNSO hydrides being the most stable ones. Subsequently, these hydrides could decompose either into SH and NO radicals or into SN and OH radicals. The former pathway is preferred due to relatively lower barriers and favorable reaction energies. The results from our calculations support the role of S-nitrosothiols as NO shuttling agent in signaling-pathways and as a new source of HS and NO radicals in the lower atmosphere of Venus. Overall, these high-level calculations will play an important role in improving our understanding about the chemistry of S-nitrosothiols that has recently become a topic of interest because of their involvement in biochemical pathways and planetary processes.

  4. Absolute density of precursor SiH3 radicals and H atoms in H2-diluted SiH4 gas plasma for deposition of microcrystalline silicon films

    NASA Astrophysics Data System (ADS)

    Abe, Yusuke; Ishikawa, Kenji; Takeda, Keigo; Tsutsumi, Takayoshi; Fukushima, Atsushi; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru

    2017-01-01

    Microcrystalline hydrogenated silicon films were produced at a high deposition rate of about 2 nm/s by using a capacitively coupled plasma under a practical pressure of around 1 kPa. The SiH4 source gas was almost fully dissociated when highly diluted with H2 gas, and the dominant species in the gas phase were found to be SiH3 radicals, which are film-growth precursors, and H atoms. The absolute density of these species was measured as the partial pressure of SiH4 gas was varied. With the increasing SiH4 gas flow rate, the SiH3 radical density, which was on the order of 1012 cm-3, increased linearly, while the H-atom density remained constant at about 1012 cm-3. The film growth mechanism was described in terms of precursors, based on the measured flux of SiH3 radicals and H atoms, and the relative fraction of higher-order radicals.

  5. Magnetic Properties of CoFe2O4 Thin Films Synthesized by Radical Enhanced Atomic Layer Deposition.

    PubMed

    Pham, Calvin D; Chang, Jeffrey; Zurbuchen, Mark A; Chang, Jane P

    2017-09-19

    A radical enhanced atomic layer deposition (RE-ALD) process was developed for growing ferrimagnetic CoFe2O4 thin films. By utilizing bis(2,2,6,6-tetramethyl-3,5-heptanedionato) cobalt (II) (Co(TMHD)2), Fe(TMHD)3, and atomic oxygen as the metal and oxidation sources respectively, amorphous and stoichiometric CoFe2O4 films were deposited onto SrTiO3 (001) substrates at 200 °C. The RE-ALD growth rate obtained for CoFe2O4 is ~2.4 Å/supercycle, significantly higher than the values reported for thermally activated ALD processes. Microstructural characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the CoFe2O4 films annealed between 450 °C and 750 °C were textured polycrystalline with an epitaxial interfacial layer, which allows strain-mediated tuning of the magnetic properties given its highly magnetostrictive nature. The magnetic behavior was studied as a function of film thickness and annealing temperature - saturation magnetization (Ms) ranged from 260 to 550 emu/cm(3) and magnetic coercivity (Hc) ranged from 0.2 to 2.2 kOe. Enhanced magnetic anisotropy achieved in the thinner samples while the overall magnetic strength improved after annealing at higher temperatures. The RE-ALD CoFe2O4 films exhibit magnetic properties that are comparable to both bulk crystal and films grown by other deposition methods - with thickness as low as ~7 nm - demonstrating the potential of RE-ALD for the synthesis of high-quality magnetic oxides with large scale processing compatibility.

  6. Combination of electrografting and atom-transfer radical polymerization for making the stainless steel surface antibacterial and protein antiadhesive.

    PubMed

    Ignatova, Milena; Voccia, Samuel; Gilbert, Bernard; Markova, Nadya; Cossement, Damien; Gouttebaron, Rachel; Jérôme, Robert; Jérôme, Christine

    2006-01-03

    A two-step "grafting from" method has been successfully carried out, which is based on the electrografting of polyacrylate chains containing an initiator for the atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) or copolymerization of TBAEMA with either monomethyl ether of poly(ethylene oxide) methacrylate (PEOMA) or acrylic acid (AA) or styrene. The chemisorption of this type of polymer brushes onto stainless steel surfaces has potential in orthopaedic surgery. These films have been characterized by ATR-FTIR, Raman spectroscopy, atomic force microscopy (AFM), and measurement of contact angles of water. The polymer formed in solution by ATRP and that one detached on purpose from the surface have been analyzed by size exclusion chromathography (SEC) and (1)H NMR spectroscopy. The strong adherence of the films onto stainless steel has been assessed by peeling tests. AFM analysis has shown that addition of hydrophilic comonomers to the grafted chains decreases the surface roughness. According to dynamic quartz crystal microbalance experiments, proteins (e.g., fibrinogen) are more effectively repelled whenever copolymer brushes contain neutral hydrophilic (PEOMA) co-units rather than negatively charged groups (PAA salt). Moreover, a 2- to 3-fold decrease in the fibrinogen adsorption is observed when TBAEMA is copolymerized with either PEOMA or AA rather than homopolymerized or copolymerized with styrene. Compared to the bare stainless steel surface, brushes of polyTBAEMA, poly(TBAEMA-co-PEOMA) and poly(TBAEMA-co-AA) decrease the bacteria adhesion by 3 to 4 orders of magnitude as revealed by Gram-positive bacteria S. aureus adhesion tests.

  7. The fabrication of superlow protein absorption zwitterionic coating by electrochemically mediated atom transfer radical polymerization and its application.

    PubMed

    Hu, Yichuan; Yang, Guang; Liang, Bo; Fang, Lu; Ma, Guanglong; Zhu, Qin; Chen, Shengfu; Ye, Xuesong

    2015-02-01

    A well-controllable electrochemically mediated surface-initiated atom transfer radical polymerization (e-siATRP) method for the fabrication of superlow protein absorption zwitterionic hydrogel coatings based on poly(sulbetaine methacrylate) (pSBMA) was developed in this work. The effects of the electric condition on polymerization as well as its antifouling performances both in vitro and in vivo were also investigated. Different potentials (-0.08 V, -0.15 V and -0.22 V) and polymerization times (from 8 to 48 h) were chosen to study the polymerization procedure. X-ray photoelectron spectroscopy, atomic force microscopy and ellipsometry measurements were used to characterize the properties of the polymer layers. Ellipsometry measurements showed that a higher potential provided faster polymerization and thicker polymer layers; however, the protein absorption experiments showed that the best polymerization condition was under a constant potential of -0.15 V and 32 h, under which the protein absorption was 0.8% in an enzyme-linked immunosorbent assay (compared to a bare gold electrode). The electrodes with a pSBMA coating effectively deduced the current sensitivity decay both in undiluted serum and in vivo. The usage of the commercially available polymerization monomer of SBMA, the simple convenient synthesis process regardless of the presence of oxygen and the excellent controllability of e-siATRP make it a very promising and universal technique in the preparation of zwitterionic polymer coatings, especially in the development of biocompatible material for implantable devices such as neural and biosensor electrodes.

  8. Efficient Cu-catalyzed atom transfer radical addition reactions of fluoroalkylsulfonyl chlorides with electron-deficient alkenes induced by visible light.

    PubMed

    Tang, Xiao-Jun; Dolbier, William R

    2015-03-27

    Fluoroalkylsulfonyl chlorides, R(f)SO2Cl, in which R(f)=CF3, C4F9, CF2H, CH2F, and CH2CF3, are used as a source of fluorinated radicals to add fluoroalkyl groups to electron-deficient, unsaturated carbonyl compounds. Photochemical conditions, using Cu mediation, are used to produce the respective α-chloro-β-fluoroalkylcarbonyl products in excellent yields through an atom transfer radical addition (ATRA) process. Facile nucleophilic replacement of the α-chloro substituent is shown to lead to further diverse functionalization of the products.

  9. Three-dimensionally ordered macroporous nitroxide polymer brush electrodes prepared by surface-initiated atom transfer polymerization for organic radical batteries.

    PubMed

    Lin, Chun-Hao; Chou, Wei-Jen; Lee, Jyh-Tsung

    2012-01-01

    The synthesis and electrochemical performance of three-dimensionally ordered macroporous (3DOM) nitroxide polymer brush electrodes for organic radical batteries are reported. The 3DOM electrodes are synthesized via polystyrene colloidal crystal templating with electropolymerization of polypyrrole, modification of surface initiator, and surface-initiated atom transfer radical polymerization. The discharge capacity of the 3DOM electrodes is proportional to the thickness of the inverse opal. The discharge capacity of the 3DOM electrode at a discharge rate of 5 C is 40 times higher than that of the planar electrode; its cycle-life performance exhibits 96.1% retention after 250 cycles.

  10. Diffusion controlled hydrogen atom abstraction from tertiary amines by the benzyloxyl radical. The importance of C-H/N hydrogen bonding.

    PubMed

    Salamone, Michela; Anastasi, Gloria; Bietti, Massimo; DiLabio, Gino A

    2011-01-21

    The rate constants for H-atom abstraction (k(H)) from 1,4-cyclohexadiene (CHD), triethylamine (TEA), triisobutylamine (TIBA), and DABCO by the cumyloxyl (CumO(•)) and benzyloxyl (BnO(•)) radicals were measured. Comparable k(H) values for the two radicals were obtained in their reactions with CHD and TIBA whereas large increases in k(H) for TEA and DABCO were found on going from CumO(•) to BnO(•). These differences are attributed to the rate-determining formation of BnO(•) C-H/amine N lone-pair H-bonded complexes.

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

    NASA Astrophysics Data System (ADS)

    Yuan, Huihui; Qian, Bin; Zhang, Wei; Lan, Minbo

    2016-02-01

    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/cm2, 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.

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

    PubMed

    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.

  13. Absolute rate constants for hydrogen atom transfer from tertiary amides to the cumyloxyl radical: evaluating the role of stereoelectronic effects.

    PubMed

    Salamone, Michela; Milan, Michela; DiLabio, Gino A; Bietti, Massimo

    2014-08-01

    A time-resolved kinetic study of the hydrogen atom transfer (HAT) reactions from a series of alkanamides to the cumyloxyl radical (CumO(•)) was carried out. With N,N-dialkylformamides HAT preferentially occurs from the formyl C-H bond, while in N-formylpyrrolidine HAT mostly occurs from the ring α-C-H bonds. With the acetamides and the alkanamides almost exclusive HAT from the C-H bonds that are α to nitrogen was observed. The results obtained show that alignment between the C-H bond being broken and the amide π-system can lead to significant increases in the HAT rate constant (kH). This finding points toward the important role of stereoelectronic effects on the HAT reactivity and selectivity. The highest kH values were measured for the reactions of CumO(•) with N-acylpyrrolidines. These substrates have ring α-C-H bonds that are held in a conformation that is optimally aligned with the amide π-system, thus allowing for the relatively facile HAT reaction. The lowest kH value was measured for the reaction of N,N-diisobutylacetamide, wherein the steric bulk associated with the N-isobutyl groups increases the energy barrier required to reach the most suitable conformation for HAT. The experimental results are well supported by the computed BDEs for the C-H bonds of the most representative substrates.

  14. Superparamagnetic lysozyme surface-imprinted polymer prepared by atom transfer radical polymerization and its application for protein separation.

    PubMed

    Gai, Qing-Qing; Qu, Feng; Liu, Zong-Jian; Dai, Rong-Ji; Zhang, Yu-Kui

    2010-07-30

    Molecular imprinting as a promising and facile separation technique has received much attention because of their high selectivity for target molecules. In this study, the superparamagnetic lysozyme surface-imprinted polymer was prepared by a novel fabricating protocol, the grafting of the imprinted polymer on magnetic particles in aqueous media was done by atom transfer radical polymerization (ATRP), and the properties of the imprinted polymer were characterized in detail. Its high selective adsorption and recognition to lysozyme demonstrated the separation ability of the magnetic imprinted material to template molecule, and it has been used for quick and direct separation of lysozyme from the mixture of standard proteins and real egg white samples under an external magnetic field. Furthermore, the elution of lysozyme from the imprinted material was achieved by PEG/sulphate aqueous two-phase system, which caused lysozyme not only desorption from the imprinted materials but also redistribution in the top and bottom phase of aqueous two-phase system. The aqueous two-phase system exhibited some of the extraction and enrichment effect to desorbed lysozyme. Our results showed that ATRP is a promising method for the protein molecularly imprinted polymer preparation.

  15. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization from Chlorinated Polypropylene and Polyethylene Trunk Fibers

    DOE PAGES

    Brown, Suree; Chatterjee, Sabornie; Li, Meijun; ...

    2015-12-10

    Seawater contains a large amount of uranium (~4.5 billion tons) which can serve as a limitless supply of an energy source. However, in order to make the recovery of uranium from seawater economically feasible, lower manufacturing and deployment costs are required, and thus, solid adsorbents must have high uranium uptake, reusability, and high selectivity toward uranium. In this study, atom-transfer radical polymerization (ATRP), without the radiation-induced graft polymerization (RIGP), was used for grafting acrylonitrile (AN) and tert-butyl acrylate (tBA) from a new class of trunk fibers, forming adsorbents in a readily deployable form. The new class of trunk fibers wasmore » prepared by the chlorination of PP round fiber, hollow-gear-shaped PP fiber, and hollow-gear-shaped PE fiber. During ATRP, degrees of grafting (d.g.) varied according to the structure of active chlorine sites on trunk fibers and ATRP conditions, and the d.g. as high as 2570% was obtained. Resulting adsorbent fibers were evaluated in U-spiked simulated seawater and the maximum adsorption capacity of 146.6 g U/kg, much higher than that of a standard adsorbent JAEA fiber (75.1 g/kg), was obtained. This new type of trunk fibers can be used for grafting a variety of uranium-interacting ligands, including designed ligands that are highly selective toward uranium.« less

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

    PubMed

    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.

  17. Synthesis of zwitterionic polymer-based amphiphilic triblock copolymers by atom transfer radical polymerization for production of extremely stable nanoemlusions

    NASA Astrophysics Data System (ADS)

    Lee, Jin Yong; Kim, Ji Eun; Kim, Jin Woong

    2015-03-01

    In fields of soft matter, there have been growing interests in utilizing amphiphilic block copolymers due to their intriguing properties, such as surface activity as well as self-assembly. In this work, we synthesize a series of poly (2-(methacryloyloxy) ethyl phosphorylcholine)- b-poly (ɛ-caprolactone)- b-poly (2-(methacryloyloxy) ethyl phosphorylcholine) (PMPC- b-PCL- b-PMPC) triblock copolymers by using atom transfer radical polymerization (ATRP). We have a particular interest in using poly (2-(methacryloyloxy) ethyl phosphorylcholine) (PMPC) as a hydrophilic block, since it can have both electrostatic repulsion and steric repulsion in complex fluid systems. Assembling them at the oil-water interface by using the phase inversion method enables production of highly stable nanoemulsions. From the analyses of the crystallography and self-assembly behavior, we have found that the triblock copolymers assemble to form a flexible but tough molecular thin film at the interface, which is essential for the remarkable improvement in the emulsion stability.

  18. Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization from Chlorinated Polypropylene and Polyethylene Trunk Fibers

    SciTech Connect

    Brown, Suree; Chatterjee, Sabornie; Li, Meijun; Yue, Yanfeng; Tsouris, Costas; Janke, Christopher J.; Saito, Tomonori; Dai, Sheng

    2015-12-10

    Seawater contains a large amount of uranium (~4.5 billion tons) which can serve as a limitless supply of an energy source. However, in order to make the recovery of uranium from seawater economically feasible, lower manufacturing and deployment costs are required, and thus, solid adsorbents must have high uranium uptake, reusability, and high selectivity toward uranium. In this study, atom-transfer radical polymerization (ATRP), without the radiation-induced graft polymerization (RIGP), was used for grafting acrylonitrile (AN) and tert-butyl acrylate (tBA) from a new class of trunk fibers, forming adsorbents in a readily deployable form. The new class of trunk fibers was prepared by the chlorination of PP round fiber, hollow-gear-shaped PP fiber, and hollow-gear-shaped PE fiber. During ATRP, degrees of grafting (d.g.) varied according to the structure of active chlorine sites on trunk fibers and ATRP conditions, and the d.g. as high as 2570% was obtained. Resulting adsorbent fibers were evaluated in U-spiked simulated seawater and the maximum adsorption capacity of 146.6 g U/kg, much higher than that of a standard adsorbent JAEA fiber (75.1 g/kg), was obtained. This new type of trunk fibers can be used for grafting a variety of uranium-interacting ligands, including designed ligands that are highly selective toward uranium.

  19. Facile synthesis of thermally stable poly(N-vinylpyrrolidone)-modified gold surfaces by surface-initiated atom transfer radical polymerization.

    PubMed

    Liu, Xiaoli; Sun, Kai; Wu, Zhaoqiang; Lu, Jianhong; Song, Bo; Tong, Weifang; Shi, Xiujuan; Chen, Hong

    2012-06-26

    Well-controlled polymerization of N-vinylpyrrolidone (NVP) on Au surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) was carried out at room temperature by a silanization method. Initial attempts to graft poly(N-vinylpyrrolidone) (PVP) layers from initiators attached to alkanethiol monolayers yielded PVP films with thicknesses less than 5 nm. The combined factors of the difficulty in the controllable polymerization of NVP and the instability of alkanethiol monolayers led to the difficulty in the controlled polymerization of NVP on Au surfaces. Therefore, the silanization method was employed to form an adhesion layer for initiator attachment. This method allowed well-defined ATRP polymerization to occur on Au surfaces. Water contact angle, X-ray photoelectron spectroscopy (XPS), and reflectance Fourier transform infrared (reflectance FTIR) spectroscopy were used to characterize the modified surfaces. The PVP-modified gold surface remained stable at 130 °C for 3 h, showing excellent thermal stability. Thus, postfunctionalization of polymer brushes at elevated temperatures is made possible. The silanization method was also applied to modify SPR chips and showed potential applications in biosensors and biochips.

  20. Thermoresponsive Melamine Sponges with Switchable Wettability by Interface-Initiated Atom Transfer Radical Polymerization for Oil/Water Separation.

    PubMed

    Lei, Zhiwen; Zhang, Guangzhao; Deng, Yonghong; Wang, Chaoyang

    2017-03-15

    Here we have obtained a temperature responsive melamine sponge with a controllable wettability between superhydrophilicity and superhydrophobicity by grafting the octadecyltrichlorosilane and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) onto the surface of melamine sponge skeletons. The whole process included the silanization in which step the rough surface with low surface energy and the NH2 were provided, and the atom transfer radical polymerization which ensured the successful grafting of PNIPAAm onto the skeleton's surface. The product exhibits a good reversible switch between superhydrophilicity and superhydrophobicity by changing the temperature below or above the lower critical solution temperature (LCST, about 32 °C) of PNIPAAm, and the modified sponge still retains a good responsiveness after undergoing two temperature switches for 20 cycles. Simultaneously, the functionalized sponges could be used to absorb the oil under water at 37 °C, and they released the absorbed oil in various ways under water at 20 °C, showing wide potential applications including oil/water separation.

  1. Reverse atom transfer radical polymerization (RATRP) for anti-clotting PU-LaCl3-g-P(MPC) films

    NASA Astrophysics Data System (ADS)

    Lu, Chunyan; Zhou, Ninglin; Xiao, Yinghong; Tang, Yida; Jin, Suxing; Wu, Yue; Shen, Jian

    2013-01-01

    Low grafting density is a disadvantage both in reverse atom transfer radical polymerization (RATRP) and ATRP. In this work, the surfaces of polyurethane (PU) were treated by LaCl3·6H2O to obtain modified surfaces with hydrated layers. The reaction of surface-initiated RATRP was carried out easily, which may be attributed to the enriched hydroxyl groups on the hydrated layers. An innovation found in this work is that some free lanthanum ions (La3+) reacted with the silane coupling agent (CPTM) and the product served as mixed ligand complex. The mixed ligand complex instead of conventional 2,2‧-bipyridine was adopted to serve as a ligand in the process of RATRP. As a result, PU surfaces grafted with well-defined polymer brushes (MPC) were obtained. PU substrates before and after modification were characterized by FTIR, XPS, AFM, SEM, SCA, respectively. The results showed that zwitterionic brushes were successfully fabricated on the PU surfaces (P(MPC)), and the content of the grafted layer increased gradually with polymerization time with the grafting density as high as 97.9%. The blood compatibility of the PU substrates was evaluated by plasma recalcification profiles test and platelet adhesion tests in vitro. It was found that all PU functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion.

  2. Effect of Surface Charge on Surface-Initiated Atom Transfer Radical Polymerization from Cellulose Nanocrystals in Aqueous Media.

    PubMed

    Zoppe, Justin O; Xu, Xingyu; Känel, Cindy; Orsolini, Paola; Siqueira, Gilberto; Tingaut, Philippe; Zimmermann, Tanja; Klok, Harm-Anton

    2016-04-11

    Cellulose nanocrystals (CNCs) with different charge densities were utilized to examine the role of electrostatic interactions on surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media. To this end, growth of hydrophilic uncharged poly(N,N-dimethylacrylamide) (PDMAM) brushes was monitored by electrophoresis, (1)H NMR spectroscopy, and dynamic light scattering (DLS). Molecular weight and polydispersity of PDMAM brushes was determined by GPC analysis of hydrolytically cleaved polymers. Initiator and polymer brush grafting densities, and thus, initiator efficiencies were derived from elemental analysis. Higher initiator efficiency of polymer brush growth was observed for CNCs with higher anionic surface sulfate half-ester group density, but at the expense of high polydispersity caused by inefficient deactivation. PDMAM grafts with number-average molecular weights up to 530 kDa and polydispersity indices <1.5 were obtained under highly diluted monomer concentrations. The role of surface chemistry on the growth of neutral polymer brushes from CNCs in water is emphasized and a model of the interfacial region at the onset of polymerization is proposed. The results presented here could have implications for other substrates that present surface charges and for the assumption that the kinetics of Cu-mediated SI-CRP are analogous to those conducted in solution.

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

    PubMed

    Chen, Daqun; Hu, Weihua

    2017-03-28

    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 homogeneous polymerization and heterogeneous system (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 electrochemical technique with real-time surface plasmon resonance (SPR). In the experiment, the potential of a SPR gold chip modified by self-assembled monolayer of 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 on eSI-ATRP, and offers a powerful platform for in situ investigation of such complicated processes.

  4. Preparation of hydrophilic polymer-grafted polystyrene beads for hydrophilic interaction chromatography via surface-initiated atom transfer radical polymerization.

    PubMed

    Dai, Xiaojun; He, Yuan; Wei, Yinmao; Gong, Bolin

    2011-11-01

    A one-step procedure based on surface-initiated atom transfer radical polymerization (SI-ATRP) to hydrophilize monodisperse poly(chloromethylstyrene-co-divinylbenzene) beads has been presented in this work, using 2-hydroxyl-3-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]propyl 2-methylacrylate (HTMA) as a monomer. The chain length of the grafted poly(HTMA) was controlled via varying the ratio of HTMA to initiator on the surface of the beads. When using the grafted beads as a stationary phase in hydrophilic interaction chromatography (HILIC), good resolution for nucleobases/nucleosides was obtained with acetonitrile aqueous solution as an eluent; while for phenolic acids and glycosides, they could be eluted and separated in the presence of TFA. The retention time of the solutes increased with the amount of the grafted HTMA. The retention mechanisms of solutes were investigated by the effects of mobile phase composition and buffer pH on the retention of solutes. The results illustrated that the retention behaviors of the tested solutes were dominated by hydrogen bonding interaction and electrostatic interaction. From the chemical structure of the ligands, the modified beads could not only be used as a stationary phase in HILIC, but also act as a useful building block to develop new stationary phases for other chromatographic modes such as affinity media. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    NASA Astrophysics Data System (ADS)

    Yang, Wenming; Liu, Lukuan; Zhou, Zhiping; Liu, Hong; Xie, Binze; Xu, Wanzhen

    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.

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

    PubMed

    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-Cα 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

  7. Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions of mono-, di-, and tri-aryl-substituted donors, models for hydrogen atom transfers in polyunsaturated fatty acid radicals.

    PubMed

    DeZutter, Christopher B; Horner, John H; Newcomb, Martin

    2008-03-06

    Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions in models of polyunsaturated fatty acid radicals were measured via laser flash photolysis methods. Photolyses of PTOC (pyridine-2-thioneoxycarbonyl) ester derivatives of carboxylic acids gave primary alkyl radicals that reacted by 1,5-hydrogen transfer from mono-, di-, and tri-aryl-substituted positions or 1,6-hydrogen transfer from di- and tri-aryl-substituted positions to give UV-detectable products. Rate constants for reactions in acetonitrile at room temperature ranged from 1 x 10(4) to 4 x 10(6) s(-1). The activation energies for a matched pair of 1,5- and 1,6-hydrogen atom transfers giving tri-aryl-substituted radicals were approximately equal, as were the primary kinetic isotope effects, but the 1,5-hydrogen atom transfer reaction was 1 order of magnitude faster at room temperature than the 1,6-hydrogen atom transfer reaction due to a less favorable entropy of activation for the 1,6-transfer reaction. Solvent effects on the rate constants for the 1,5-hydrogen atom transfer reaction of the 2-[2-(diphenylmethyl)phenyl]ethyl radical at ambient temperature were as large as a factor of 2 with the reaction increasing in rate in lower polarity solvents. Hybrid density functional theory computations for the 1,5- and 1,6-hydrogen atom transfers of the tri-aryl-substituted donors were in qualitative agreement with the experimental results.

  8. Extension of structure-reactivity correlations for the hydrogen abstraction reaction by bromine atom and comparison to chlorine atom and hydroxyl radical

    DOE PAGES

    Poutsma, Marvin L.

    2015-12-14

    Recently we presented structure-reactivity correlations for the gas-phase ambient-temperature rate constants for hydrogen abstraction from sp3-hybridized carbon by chlorine atom and hydroxyl radical (Cl•/HO• + HCR3 → HCl/HOH + •CR3); the reaction enthalpy effect was represented by the independent variable ΔrH and the polar effect by the independent variables F and R, the Hammett constants for field/inductive and resonance effects. Both these reactions are predominantly exothermic and have early transition states. Here we present a parallel treatment for Br• whose reaction is significantly endothermic with a correspondingly late transition state. In spite of lower expectations because the available data basemore » is less extensive and much more scattered and because long temperature extrapolations are often required, the resulting least-squares fit (log k298,Br = –0.147 ΔrH –4.32 ΣF –4.28 ΣR –12.38 with r2 = 0.92) was modestly successful and useful for initial predictions. The coefficient of ΔrH was ~4-fold greater, indicative of the change from an early to a late transition state; meanwhile the sizable coefficients of ΣF and ΣR indicate the persistence of the polar effect. Although the mean unsigned deviation of 0.79 log k298 units is rather large, it must be considered in the context of a total span of over 15 log units in the data set. Lastly, the major outliers are briefly discussed.« less

  9. Extension of structure-reactivity correlations for the hydrogen abstraction reaction by bromine atom and comparison to chlorine atom and hydroxyl radical

    SciTech Connect

    Poutsma, Marvin L.

    2015-12-14

    Recently we presented structure-reactivity correlations for the gas-phase ambient-temperature rate constants for hydrogen abstraction from sp3-hybridized carbon by chlorine atom and hydroxyl radical (Cl•/HO• + HCR3 → HCl/HOH + •CR3); the reaction enthalpy effect was represented by the independent variable ΔrH and the polar effect by the independent variables F and R, the Hammett constants for field/inductive and resonance effects. Both these reactions are predominantly exothermic and have early transition states. Here we present a parallel treatment for Br• whose reaction is significantly endothermic with a correspondingly late transition state. In spite of lower expectations because the available data base is less extensive and much more scattered and because long temperature extrapolations are often required, the resulting least-squares fit (log k298,Br = –0.147 ΔrH –4.32 ΣF –4.28 ΣR –12.38 with r2 = 0.92) was modestly successful and useful for initial predictions. The coefficient of ΔrH was ~4-fold greater, indicative of the change from an early to a late transition state; meanwhile the sizable coefficients of ΣF and ΣR indicate the persistence of the polar effect. Although the mean unsigned deviation of 0.79 log k298 units is rather large, it must be considered in the context of a total span of over 15 log units in the data set. Lastly, the major outliers are briefly discussed.

  10. Atmospheric chemistry of t-CF3CH=CHCl: products and mechanisms of the gas-phase reactions with chlorine atoms and hydroxyl radicals.

    PubMed

    Andersen, M P Sulbaek; Nielsen, O J; Hurley, M D; Wallington, T J

    2012-02-07

    FTIR-smog chamber techniques were used to study the products and mechanisms of the Cl atom and OH radical initiated oxidation of trans-3,3,3-trifluoro-1-chloro-propene, t-CF(3)CH=CHCl, in 700 Torr of air or N(2)/O(2) diluent at 296 ± 2 K. The reactions of Cl atoms and OH radicals with t-CF(3)CH=CHCl occur via addition to the >C=C< double bond; chlorine atoms add 15 ± 5% at the terminal carbon and 85 ± 5% at the central carbon, OH radicals add approximately 40% at the terminal carbon and 60% at the central carbon. The major products in the Cl atom initiated oxidation of t-CF(3)CH=CHCl were CF(3)CHClCHO and CF(3)C(O)CHCl(2), minor products were CF(3)CHO, HCOCl and CF(3)COCl. The yields of CF(3)C(O)CHCl(2), CF(3)CHClCOCl and CF(3)COCl increased at the expense of CF(3)CHO, HCOCl and CF(3)CHClCHO as the O(2) partial pressure was increased over the range 10-700 Torr. Chemical activation plays a significant role in the fate of CF(3)CH(O)CHCl(2) and CF(3)CClHCHClO radicals. In addition to reaction with O(2) to yield CF(3)COCl and HO(2) the major competing fate of CF(3)CHClO is Cl elimination to give CF(3)CHO (not C-C bond scission as previously thought). As part of this study k(Cl + CF(3)C(O)CHCl(2)) = (2.3 ± 0.3) × 10(-14) and k(Cl + CF(3)CHClCHO) = (7.5 ± 2.0) × 10(-12) cm(3) molecule(-1) s(-1) were determined using relative rate techniques. Reaction with OH radicals is the major atmospheric sink for t-CF(3)CH=CHCl. Chlorine atom elimination giving the enol CF(3)CH=CHOH appears to be the sole atmospheric fate of the CF(3)CHCHClOH radicals. The yield of CF(3)COOH in the atmospheric oxidation of t-CF(3)CH=CHCl will be negligible (<2%). The results are discussed with respect to the atmospheric chemistry and environmental impact of t-CF(3)CH=CHCl.

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

    NASA Technical Reports Server (NTRS)

    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.

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

    PubMed

    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.

  13. Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

    DOE PAGES

    Welz, Oliver; Savee, John D.; Osborn, David L.; ...

    2014-07-04

    The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH3)2CCHCH2OH) and isoprenol (3-methyl-3-buten-1-ol, CH2C(CH3)CH2CH2OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant products arising from QOOH chemistry are observed. Thesemore » results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O2. These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O2. Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO2-forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce low-temperature reactivity during autoignition.« less

  14. First-principles molecular-dynamics calculations on chemical reactions and atomic structures induced by H radical impinging onto Si(001)2 x 1:H surface.

    PubMed

    Inagaki, Kouji; Kanai, Ryota; Hirose, Kikuji; Yasutake, Kiyoshi

    2011-04-01

    Chemical reactions between hydrogen terminated Si(001)2 x 1 surface and impinging H radical are investigated by means of first-principles molecular-dynamics simulations. Reaction probabilities of abstraction of surface terminating H atom with H2 formation, adsorption onto Si surface and reflection of impinging H atom are analyzed with respect to the kinetic energy of incident H radical. The probabilities of abstraction and adsorption turn out to be ranging from 0.81 to 0.58 and from 0.19 to 0.42, respectively, while that of reflection almost zero. As initial kinetic energy of the impinging atom increases, the reaction probability of abstraction decreases and that of absorption increases. Metastable H-absorbed atomic configurations are also derived by optimizing the structures obtained in the impinging dynamics calculations. They are candidates of the so-called reservoir site which is a key to understand the unity hydrogen coverage observed after an exposure to gaseous H atom ambient despite existing residual vacant sites due to abstraction.

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

    PubMed

    de Bruin, Bas; Dzik, Wojciech I; Li, Shan; Wayland, Bradford B

    2009-01-01

    The mechanisms for hydrogen-atom transfer from the cyanoisopropyl radical (*)C(CH(3))(2)CN to [Co(II)(por)](*) (yielding [Co(III)(H)(por)] and CH(2)=C(CH(3))(CN); por = porphyrinato) and the insertion of vinyl acetate (CH(2)=CHOAc) into the Co-H bond of [Co(H)(por)] (giving [Co(III){CH(OAc)CH(3)}(por)]) were investigated by DFT calculations. The results are compared with experimental data. These reactions are relevant to catalytic chain transfer (CCT) in radical polymerization of olefins mediated by [Co(II)(por)](*), the formation and homolysis of organo-cobalt complexes that mediate living radical polymerization of vinyl acetate, and cobalt-mediated hydrogenation of olefins. Hydrogen transfer from (*)C(CH(3))(2)CN to [Co(II)(por)](*) proceeds via a single transition state that has structural features resembling the products [Co(H)(por)] and CH(2)=C(CH(3))CN. The separated radicals approach to form a close-contact radical pair and then pass through the transition state for hydrogen-atom transfer to form [Co(III)(H)(por)] and CH(2)=C(CH(3))CN. This process provides a very low overall barrier for the hydrogen-atom transfer reaction (DeltaG(double dagger) = +3.8 kcal mol(-1)). The reverse reaction corresponding to the addition of [Co(H)(por)] to CH(2)=C(CH(3))CN has a low barrier (DeltaG(double dagger) = +8.9 kcal mol(-1)) as well. Insertion of vinyl acetate into the Co-H bond of [Co(III)(H)(por)] also proceeds over a low barrier (DeltaG(double dagger) = +11.4 kcal mol(-1)) hydrogen-transfer step from [Co(III)(H)(por)] to a carbon atom of the alkene to produce a close-contact radical pair. Dissociation of the radical pair, reorientation, and radical-radical coupling to form an organo-cobalt complex are the culminating steps in the net insertion of an olefin into the Co-H bond. The computed energies obtained for the hydrogen-atom transfer reactions from (*)C(CH(3))(2)CN to [Co(II)(por)](*) and from [Co(H)(por)] to olefins, as well as the organo-cobalt bond homolysis

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

    SciTech Connect

    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.

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

    PubMed

    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.

  18. Atomic-scale insight into the interactions between hydroxyl radicals and DNA in solution using the ReaxFF reactive force field

    NASA Astrophysics Data System (ADS)

    Verlackt, C. C. W.; Neyts, E. C.; Jacob, T.; Fantauzzi, D.; Golkaram, M.; Shin, Y.-K.; van Duin, A. C. T.; Bogaerts, A.

    2015-10-01

    Cold atmospheric pressure plasmas have proven to provide an alternative treatment of cancer by targeting tumorous cells while leaving their healthy counterparts unharmed. However, the underlying mechanisms of the plasma-cell interactions are not yet fully understood. Reactive oxygen species, and in particular hydroxyl radicals (OH), are known to play a crucial role in plasma driven apoptosis of malignant cells. In this paper we investigate the interaction of OH radicals, as well as H2O2 molecules and HO2 radicals, with DNA by means of reactive molecular dynamics simulations using the ReaxFF force field. Our results provide atomic-scale insight into the dynamics of oxidative stress on DNA caused by the OH radicals, while H2O2 molecules appear not reactive within the considered time-scale. Among the observed processes are the formation of 8-OH-adduct radicals, forming the first stages towards the formation of 8-oxoGua and 8-oxoAde, H-abstraction reactions of the amines, and the partial opening of loose DNA ends in aqueous solution.

  19. Photolysis of CH₃CHO at 248 nm: evidence of triple fragmentation from primary quantum yield of CH₃ and HCO radicals and H atoms.

    PubMed

    Morajkar, Pranay; Bossolasco, Adriana; Schoemaecker, Coralie; Fittschen, Christa

    2014-06-07

    Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH3CHO. 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 HO2 radicals by reaction with O2. The CH3 radical yield has been determined using the same technique following their conversion into CH3O2. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO2 profiles, obtained under various O2 concentrations, to a complex model, while the CH3 yield has been determined relative to the CH3 yield from 248 nm photolysis of CH3I. Time resolved HO2 profiles under very low O2 concentrations suggest that another unknown HO2 forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O2. HO2 profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH3CHO + hν(248nm) → CH3CHO*, CH3CHO* → CH3 + HCO ϕ(1a) = 0.125 ± 0.03, CH3CHO* → CH3 + H + CO ϕ(1e) = 0.205 ± 0.04, CH3CHO*[Formula: see text]CH3CO + HO2 ϕ(1f) = 0.07 ± 0.01. The CH3O2 quantum yield has been determined in separate experiments as ϕ(CH₃) = 0.33 ± 0.03 and is in excellent agreement with the CH3 yields derived from the HO2 measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH3CHO. From arithmetic considerations taking into account the HO2 and CH3 measurements we deduce a remaining quantum yield for the molecular pathway: CH3CHO* → CH4 + CO ϕ(1b) = 0.6. All experiments can be consistently explained with absence of the formerly considered pathway: CH3CHO* → CH3CO + H ϕ(1c) = 0.

  20. Reactions of excited I*(/sup 2/P /SUB 1/2/ ) and unexcited I(/sup 2/P /SUB 3/2/ ) iodine atoms in perfluoroalkyl radicals

    SciTech Connect

    Andreeva, T.L.; Kuznetsova, S.V.; Maslov, A.I.; Sobel'man, I.I.

    1983-01-01

    A method of investigating reactions of excited and unexcited atoms is discussed. It is based on pulsed photolysis of molecules with simultaneous passage of laser radiation through the working medium. The method proposed is used to investigate the reactions that accompany the photolysis of the molecules RI(CF/sub 3/I, n-C/sub 3/F/sub 7/I, i-C/sub 3/F/sub 7/I). The rate constants of the recombination of iodine atoms into I/sub 2/ in the presence of RI molecules are calculated for the atoms I(/sup 2/P /SUB 3/2/ ) and I*(/sup 2/P /SUB 1/2/ ), as are the recombination constants of the radicals R into R/sub 2/ and with the atoms I*(/sup 2/P /SUB 1/2/ ) and I(/sup 2/P /SUB 3/2/ ) into the RI molecule. It is shown that the I(/sup 2/P /SUB 3/2/ ) atoms are much more active in the recombination into I/sub 2/ and RI than the I*(/sup 2/P /SUB 1/2/ ) atoms. The role of the investigated reactions in the kinetics of a photodissociation iodine laser (PDIL) is discussed. The results are compared with the published data.

  1. Giant Molecular Clouds with High Abundance of Atomic Carbon and Cyano Radical in the Milky Way's Central Molecular Zone

    NASA Astrophysics Data System (ADS)

    Tanaka, Kunihiko; Oka, Tomoharu; Nagai, Makoto; Kamegai, Kazuhisa

    2015-08-01

    The central 400 pc region of the Milky Way Galaxy is the closest galactic central region to us, providing a unique opportunity to detailedly investigate gas dynamics, star formation activity, and chemistry under the extreme environment of galactic centers, where the presence of bar, intense UV/cosmic-ray fluxes, high degree of turbulence may significantly affect those processes. We report the results of molecular line surveys toward the Milky Way's central molecular zone (CMZ) performed with the ASTE 10m telescope, the Mopra 22m telescope, and the Nobeyama 45 m telescope. With the observations of the 500 GHz [CI] fine structure line of atomic carbon (C0), we have found a molecular cloud structure with remarkably bright [CI] emission in the Sgr A comlex in the innermost 20 pc region. The [CI] cloud is more extended than the GMCs in the region, and appears to connect the northern part of the 50 kms-1 (M-0.02-0.07) and the circumnuclear disk (CND), though no corresponding structures are visible in other molecular lines. The [C0]/[CO] abundance ratio is measured to be 0.5-2, which is 2-10 times those measured to the clouds at larger Galactic radii. This high ratio is close to the values measured toward centers of galaxies with starburst and AGN, suggesting that the chemical state of the cloud is similar to that in those active galaxies. We have also found a large scale gradient of the cyano radical (CN) abundance toward the Galactic center in the innermost 100 pc radius, showing near the Sgr A complex. We suggest that the cloud with high C0 and CN abundance is a feature formed as a result of inward transfer of diffuse molecular gas by the bar potential in the inner Galaxy, in which PDR-like chemical composition remains preserved, and that thus the [CI] cloud could be deeply related to formation of the GMCs and star formation in the CMZ. We also discuss other possible mechanisms to enhance C0 and CN abundances, including the enhanced cosmic-ray dissociation ratio.

  2. Inactivation of Penicillium digitatum Spores by a High-Density Ground-State Atomic Oxygen-Radical Source Employing an Atmospheric-Pressure Plasma

    NASA Astrophysics Data System (ADS)

    Iseki, Sachiko; Hashizume, Hiroshi; Jia, Fengdong; Takeda, Keigo; Ishikawa, Kenji; Ohta, Takayuki; Ito, Masafumi; Hori, Masaru

    2011-11-01

    Penicillium digitatum spores were inactivated using an oxygen-radical source that supplies only neutral oxygen radicals. Vacuum ultraviolet absorption spectroscopy was used to measure the ground-state atomic oxygen [O (3Pj)] densities and they were estimated to be in the range of 1014-1015 cm-3. The inactivation rate of P. digitatum spores was correlated with the O (3Pj) density. The result indicates that O (3Pj) is the dominant species in the inactivation. The inactivation rate constant of P. digitatum spores by O (3Pj) was estimated to be on the order of 10-17 cm3 s-1 from the measured O (3Pj) densities and inactivation rates.

  3. Assignment of high-lying bending mode levels in the threshold photoelectron spectrum of NH2: a comparison between pyrolysis and fluorine-atom abstraction radical sources.

    PubMed

    Holzmeier, F; Lang, M; Fischer, I; Hemberger, P; Garcia, G A; Tang, X; Loison, J-C

    2015-07-15

    In this manuscript we present threshold photoelectron spectra (TPES) of the amidogen radical, NH2, recorded at two vacuum ultraviolet synchrotron radiation beamlines, the DESIRS beamline of Synchrotron SOLEIL and the VUV beamline of the Swiss Light Source (SLS). Amidogen radicals were generated by two different methods, (a) H-atom abstraction of ammonia in a fluorine microwave discharge flow tube and (b) flash pyrolysis of methylhydrazine and diphenylmethylamine. Due to the large geometry change upon photoionization from the bent neutral molecule NH2 (X[combining tilde] (2)B1) to the quasi-linear cation NH2(+) (X[combining tilde] (3)B1), significant activity in the bending vibration υ2(+) of NH2(+) (X[combining tilde] (3)B1) is observed in the TPES. Transitions into a large number of υ2(+), Ka(+) levels of the cation are resolved.

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

    PubMed

    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.

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

    PubMed

    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.

  6. Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

    SciTech Connect

    Welz, Oliver; Savee, John D.; Osborn, David L.; Taatjes, Craig A.

    2014-07-04

    The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH3)2CCHCH2OH) and isoprenol (3-methyl-3-buten-1-ol, CH2C(CH3)CH2CH2OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant products arising from QOOH chemistry are observed. These results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O2. These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O2. Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO2-forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce

  7. Kinetic Study of the Reaction of the Phthalimide-N-oxyl Radical with Amides: Structural and Medium Effects on the Hydrogen Atom Transfer Reactivity and Selectivity.

    PubMed

    Bietti, Massimo; Forcina, Veronica; Lanzalunga, Osvaldo; Lapi, Andrea; Martin, Teo; Mazzonna, Marco; Salamone, Michela

    2016-12-02

    A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of secondary N-(4-X-benzyl)acetamides and tertiary amides to the phthalimide-N-oxyl radical (PINO) has been carried out. The results indicate that HAT is strongly influenced by structural and medium effects; in particular, the addition of Brønsted and Lewis acids determines a significant deactivation of C-H bonds α to the amide nitrogen of these substrates. Thus, by changing the reaction medium, it is possible to carefully control the regioselectivity of the aerobic oxidation of amides catalyzed by N-hydroxyphthalimide, widening the synthetic versatility of this process.

  8. Reactions of the cumyloxyl radical with secondary amides. The influence of steric and stereoelectronic effects on the hydrogen atom transfer reactivity and selectivity.

    PubMed

    Salamone, Michela; Basili, Federica; Mele, Riccardo; Cianfanelli, Marco; Bietti, Massimo

    2014-12-19

    A time-resolved kinetic study of the hydrogen atom transfer (HAT) reactions from secondary alkanamides to the cumyloxyl radical was carried out in acetonitrile. HAT predominantly occurs from the N-alkyl α-C-H bonds, and a >60-fold decrease in kH was observed by increasing the steric hindrance of the acyl and N-alkyl groups. The role of steric and stereoelectronic effects on the reactivity and selectivity is discussed in the framework of HAT reactions from peptides.

  9. Facile synthesis of brush poly(phosphoamidate)s via one-pot tandem ring-opening metathesis polymerization and atom transfer radical polymerization.

    PubMed

    Ding, Liang; Qiu, Jun; Wei, Jun; Zhu, Zhenshu

    2014-09-01

    Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA)-based brush poly(phosphoamidate)s are successfully synthesized by a combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) following either a commutative two-step procedure or a straightforward one-pot process using Grubbs ruthenium-based catalysts for tandem catalysis. Compared with the traditional polymerization method, combining ROMP and ATRP in a one-pot process allows the preparation of brush copolymers characterized by a relatively moderate molecular weight distribution and quantitative conversion of monomer. Moreover, the surface morphologies and aggregation behaviors of these polymers are studied by AFM and TEM measurements.

  10. Transport and Distribution of Hydroxyl Radicals and Oxygen Atoms from H2O Photodissociation in the Inner Coma of Comet 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Lai, Ian-Lin; Su, Cheng-Chin; Ip, Wing-Huen; Wei, Chen-En; Wu, Jong-Shinn; Lo, Ming-Chung; Liao, Ying; Thomas, Nicolas

    2016-03-01

    With a combination of the Direct Simulation Monte Carlo (DSMC) calculation and test particle computation, the ballistic transport process of the hydroxyl radicals and oxygen atoms produced by photodissociation of water molecules in the coma of comet 67P/Churyumov-Gerasimenko is modelled. We discuss the key elements and essential features of such simulations which results can be compared with the remote-sensing and in situ measurements of cometary gas coma from the Rosetta mission at different orbital phases of this comet.

  11. Tropospheric degradation of 2,2,2 trifluoroethyl butyrate: Kinetic study of their reactions with OH radicals and Cl atoms at 298 K

    NASA Astrophysics Data System (ADS)

    Blanco, María B.; Rivela, Cynthia; Teruel, Mariano A.

    2013-07-01

    Rate coefficients of the reactions of OH radicals and Cl atoms with 2,2,2 trifluoroethyl butyrate have been determined at 298 K and atmospheric pressure. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC-FID) and the rate coefficients were determined using the relative rate method. This is the first kinetic study for these reactions under atmospheric pressure. The kinetic data are used to update the correlation kOHvs. kCl for different fluoroesters, to develop reactivity trends in terms of halogen substitution and to estimate the tropospheric lifetime of 2,2,2 trifluoroethyl butyrate.

  12. Low-energy inelastic collisions of OH radicals with He atoms and D{sub 2} molecules

    SciTech Connect

    Kirste, Moritz; Scharfenberg, Ludwig; Meijer, Gerard; Meerakker, Sebastiaan Y. T. van de; Klos, Jacek; Lique, Francois; Alexander, Millard H.

    2010-10-15

    We present an experimental study on the rotational inelastic scattering of OH (X {sup 2}{Pi}{sub 3/2},J=3/2,f) radicals with He and D{sub 2} at collision energies between 100 and 500 cm{sup -1} in a crossed beam experiment. The OH radicals are state selected and velocity tuned using a Stark decelerator. Relative parity-resolved state-to-state inelastic scattering cross sections are accurately determined. These experiments complement recent low-energy collision studies between trapped OH radicals and beams of He and D{sub 2} that are sensitive to the total (elastic and inelastic) cross sections [Sawyer et al., Phys. Rev. Lett. 101, 203203 (2008)], but for which the measured cross sections could not be reproduced by theoretical calculations [Pavlovic et al., J. Phys. Chem. A 113, 14670 (2009)]. For the OH-He system, our experiments validate the inelastic cross sections determined from rigorous quantum calculations.

  13. Atmospheric Chemistry of Tetrahydrofuran, 2-Methyltetrahydrofuran, and 2,5-Dimethyltetrahydrofuran: Kinetics of Reactions with Chlorine Atoms, OD Radicals, and Ozone.

    PubMed

    Andersen, Christina; Nielsen, Ole John; Østerstrøm, Freja F; Ausmeel, Stina; Nilsson, Elna J K; Sulbaek Andersen, Mads P

    2016-09-22

    FTIR smog chamber techniques were used to study the kinetics of the gas-phase reactions of Cl atoms, OD radicals, and O3 with the five-membered ring-structured compounds tetrahydrofuran (C4H8O, THF), 2-methyltetrahydrofuran (CH3C4H7O, 2-MTHF), 2,5-dimethyltetrahydrofuran ((CH3)2C4H5O, 2,5-DMTHF), and furan (C4H4O). The rate coefficients determined using relative rate methods were kTHF+Cl = (1.96 ± 0.24) × 10(-10), kTHF+OD = (1.81 ± 0.27) × 10(-11), kTHF+O3 = (6.41 ± 2.90) × 10(-21), k2-MTHF+Cl = (2.65 ± 0.43) × 10(-10), k2-MTHF+OD = (2.41 ± 0.51) × 10(-11), k2-MTHF+O3 = (1.87 ± 0.82) × 10(-20), k2,5-DMTHF+OD = (4.56 ± 0.68) × 10(-11), k2,5-DMTHF+Cl = (2.84 ± 0.34) × 10(-10), k2,5-DMTHF+O3 = (4.58 ± 2.18), kfuran+Cl = (2.39 ± 0.27) × 10(-10), and kfuran+O3 = (2.60 ± 0.31) × 10(-18) molecules cm(-3) s(-1). Rate coefficients of the reactions with ozone were also determined using the absolute rate method under pseudo-first-order conditions. OD radicals, in place of OH radicals, were produced from CD3ONO to avoid spectral overlap of isopropyl and methyl nitrite with the reactants. The kinetics of OD radical reactions are expected to resemble the kinetics of OH radical reactions, and the rate coefficients of the reactions with OD radicals were used to calculate the atmospheric lifetimes with respect to reactions with OH radicals. The lifetimes of THF, 2-MTHF, and 2,5-DMTHF are approximately 15, 12, and 6 h, respectively.

  14. Reaction Rate Coefficients of OH Radicals and Cl Atoms with Ethyl Propanoate, n-Propyl Propanoate, Methyl 2-Methylpropanoate, and Ethyl n-Butanoate

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

    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 (k1), n-propyl propanoate (k2), methyl 2-methylpropanoate (k3), and ethyl n-butanoate (k4) 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 k1, k3, and k4. 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.

  15. Surface initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine on poly(ethylene terephthalate).

    PubMed

    Maaz, Mohamad; Elzein, Tamara; Bejjani, Alice; Barroca-Aubry, Nadine; Lepoittevin, Bénédicte; Dragoe, Diana; Mazerat, Sandra; Nsouli, Bilal; Roger, Philippe

    2017-08-15

    Poly(ethylene terephthalate) (PET) substrates were modified by means of surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine (4VP). Substrates were pretreated in order to graft chloromethylbenzene (CMB) units capable of initiating the radical polymerization reaction of 4VP units. Surface characterization techniques, including Water Contact Angle (WCA), Attenuated Total Reflection (ATR), X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) showed a successful grafting of a stable, smooth and homogenous layer of p4VP. This process offers the advantages of a rapid, simplified and low cost strategy to chemically modify polymer substrates with covalently bonded layer of the pH responsive p4VP for different applications. Moreover, by using TOF-SIMS profiling, we were able to track a density gradient along the z-axis generated by the interpenetrating phases of the different layers of the final modified surface. Fact that we correlated to the various positions of initiation sites within the polyethylenimine (PEI) used for PET aminolysis prior to CMB grafting. Our strategy will be used in future work to graft other polymers for different applications where industrial scale viable options are needed. Copyright © 2017 Elsevier Inc. All rights reserved.

  16. Atmospheric chemistry of sulfuryl fluoride: reaction with OH radicals, Cl atoms and O3, atmospheric lifetime, IR spectrum, and global warming potential.

    PubMed

    Andersen, M P Sulbaek; Blake, D R; Rowland, F S; Hurley, M D; Wallington, T J

    2009-02-15

    Sulfuryl fluoride (SO2F2) is a radiatively active industrial chemical released into the atmosphere in significant (ktonne/ year) quantities. The potential for SO2F2 to contribute to radiative forcing of climate change needs to be assessed. Long path length FTIR/smog chamber techniques were used to investigate the kinetics of the gas-phase reactions of Cl atoms, OH radicals, and O3 with SO2F2, in 700 Torr total pressure of air or N2 at 296 +/- 1 K. Upper limits of k(Cl + SO2F2) < 9 x 10(-19), k(OH + SO2F2) < 1.7 x 10(-14) and k(O3 + SO2F2) < 5.5 x 10(-24) cm3 molecule(-1) s(-1) were determined. Reaction with Cl atoms, OH radicals, or O3 does not provide an efficient removal mechanism for SO2F2. The infrared spectrum of SO2F2 is reported and a radiative efficiency of 0.196 W m(-2) ppbv(-1) was calculated. Historic production data estimates are presented which provide an upper limit for expected atmospheric concentrations. The radiative forcing of climate change associated with emissions of SO2F2 depends critically on the atmospheric lifetime of SO2F2. Further research is urgently needed to define the magnitude of potential nonatmospheric sinks.

  17. Kinetic study of the OH, NO3 radicals and Cl atom initiated atmospheric photo-oxidation of iso-propenyl methyl ether

    NASA Astrophysics Data System (ADS)

    Taccone, Raúl Alberto; Moreno, Alberto; Colmenar, Inmaculada; Salgado, Sagrario; Martín, María Pilar; Cabañas, Beatriz

    2016-02-01

    Rate coefficients at room temperature and atmospheric pressure for the reaction of isopropenyl methyl ether (i-PME) (CH2dbnd C(CH3)OCH3), with OH and NO3 radicals and with Cl atoms have been determined in a 50 L Pyrex glass reaction chamber in conjunction with Fourier Transform Infrared absorption spectroscopy (FTIR) as a detection technique. The chamber is equipped with a White-type multiple-reflection mirror system with a total optical path length of ≈200 m. Additional experiments were carried out using evacuable Teflon-coated bags (volume 150 L) and a gas chromatography/mass spectrometry-time of flight (GC-TOF MS) detection system. This is the first kinetic study carried out to date for these reactions. The rate coefficients k (in units of cm3 molecule-1 s-1) obtained are: (1.14 ± 0.10) × 10-10 for the OH reaction, (2.41 ± 0.50) × 10-11, for the NO3 reaction and (7.03 ± 0.67) × 10-10 for the Cl reaction. A mechanism is proposed from the observed reaction products. The atmospheric lifetimes of the studied ether is estimated considering the rate coefficients of the reactions with OH and NO3 radicals and Cl atom. Calculated atmospheric lifetimes reveal that the dominant loss process for i-PME is clearly the night-time reaction with the NO3 radical. The radiative efficiency (RE) is obtained from the infrared spectra of the ether and the global warming potential (GWP) is then estimated. Atmospheric implications of the ether emission are discussed.

  18. Theoretical chemical kinetic study of the H-atom abstraction reactions from aldehydes and acids by Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals.

    PubMed

    Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

    2014-12-26

    We have performed a systematic, theoretical chemical kinetic investigation of H atom abstraction by Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals from aldehydes (methanal, ethanal, propanal, and isobutanal) and acids (methanoic acid, ethanoic acid, propanoic acid, and isobutanoic acid). The geometry optimizations and frequencies of all of the species in the reaction mechanisms of the title reactions were calculated using the MP2 method and the 6-311G(d,p) basis set. The one-dimensional hindered rotor treatment for reactants and transition states and the intrinsic reaction coordinate calculations were also determined at the MP2/6-311G(d,p) level of theory. For the reactions of methanal and methanoic acid with Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals, the calculated relative electronic energies were obtained with the CCSD(T)/cc-pVXZ (where X = D, T, and Q) method and were extrapolated to the complete basis set limit. The electronic energies obtained with the CCSD(T)/cc-pVTZ method were benchmarked against the CCSD(T)/CBS energies and were found to be within 1 kcal mol(-1) of one another. Thus, the energies calculated using the less expensive CCSD(T)/cc-pVTZ method were used in all of the reaction mechanisms and in calculating our high-pressure limit rate constants for the title reactions. Rate constants were calculated using conventional transition state theory with an asymmetric Eckart tunneling correction, as implemented in Variflex. Herein, we report the individual and average rate constants, on a per H atom basis, and total rate constants in the temperature range 500-2000 K. We have compared some of our rate constant results to available experimental and theoretical data, and our results are generally in good agreement.

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    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(tilde{X}^3B_1)] with He atoms. To this end, two accurate three-dimensional potential energy surfaces (PESs) of the He-CH_2(tilde{X}^3B_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 CH2, CHD, and CD2 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(tilde{X}^3B_1) molecules in a magnetic trap. Furthermore, we find that ortho-CH2 undergoes collision-induced spin relaxation much more slowly than para-CH2, which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.

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

    PubMed

    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.

  1. Atmospheric chemistry of isoflurane, desflurane, and sevoflurane: kinetics and mechanisms of reactions with chlorine atoms and OH radicals and global warming potentials.

    PubMed

    Sulbaek Andersen, Mads P; Nielsen, Ole J; Karpichev, Boris; Wallington, Timothy J; Sander, Stanley P

    2012-06-21

    The smog chamber/Fourier-transform infrared spectroscopy (FTIR) technique was used to measure the rate coefficients k(Cl + CF(3)CHClOCHF(2), isoflurane) = (4.5 ± 0.8) × 10(-15), k(Cl + CF(3)CHFOCHF(2), desflurane) = (1.0 ± 0.3) × 10(-15), k(Cl + (CF(3))(2)CHOCH(2)F, sevoflurane) = (1.1 ± 0.1) × 10(-13), and k(OH + (CF(3))(2)CHOCH(2)F) = (3.5 ± 0.7) × 10(-14) cm(3) molecule(-1) in 700 Torr of N(2)/air diluent at 295 ± 2 K. An upper limit of 6 × 10(-17) cm(3) molecule(-1) was established for k(Cl + (CF(3))(2)CHOC(O)F). The laser photolysis/laser-induced fluorescence (LP/LIF) technique was employed to determine hydroxyl radical rate coefficients as a function of temperature (241-298 K): k(OH + CF(3)CHFOCHF(2)) = (7.05 ± 1.80) × 10(-13) exp[-(1551 ± 72)/T] cm(3) molecule(-1); k(296 ± 1 K) = (3.73 ± 0.08) × 10(-15) cm(3) molecule(-1), and k(OH + (CF(3))(2)CHOCH(2)F) = (9.98 ± 3.24) × 10(-13) exp[-(969 ± 82)/T] cm(3) molecule(-1); k(298 ± 1 K) = (3.94 ± 0.30) × 10(-14) cm(3) molecule(-1). The rate coefficient of k(OH + CF(3)CHClOCHF(2), 296 ± 1 K) = (1.45 ± 0.16) × 10(-14) cm(3) molecule(-1) was also determined. Chlorine atoms react with CF(3)CHFOCHF(2) via H-abstraction to give CF(3)CFOCHF(2) and CF(3)CHFOCF(2) radicals in yields of approximately 83% and 17%. The major atmospheric fate of the CF(3)C(O)FOCHF(2) alkoxy radical is decomposition via elimination of CF(3) to give FC(O)OCHF(2) and is unaffected by the method used to generate the CF(3)C(O)FOCHF(2) radicals. CF(3)CHFOCF(2) radicals add O(2) and are converted by subsequent reactions into CF(3)CHFOCF(2)O alkoxy radicals, which decompose to give COF(2) and CF(3)CHFO radicals. In 700 Torr of air 82% of CF(3)CHFO radicals undergo C-C scission to yield HC(O)F and CF(3) radicals with the remaining 18% reacting with O(2) to give CF(3)C(O)F. Atmospheric oxidation of (CF(3))(2)CHOCH(2)F gives (CF(3))(2)CHOC(O)F in a molar yield of 93 ± 6% with CF(3)C(O)CF(3) and HCOF as minor products. The IR

  2. Growth and characterization of hydrogenated amorphous silicon thin films from SiH2 radical precursor: Atomic-scale analysis

    NASA Astrophysics Data System (ADS)

    Sriraman, Saravanapriyan; Aydil, Eray S.; Maroudas, Dimitrios

    2004-02-01

    Molecular-dynamics (MD) simulations of hydrogenated amorphous silicon (a-Si:H) film growth on an initially H-terminated Si(001)-(2×1) substrate at T=500 K was studied through repeated impingement of SiH2 radicals to elucidate the effects of this species on the structural quality of the deposited films. A detailed analysis of the radical-surface interaction trajectories revealed the important reactions contributing to film growth. These reactions include (i) adsorption of SiH2 onto the deposition surface, (ii) insertion of SiH2 into surface Si-Si bonds, (iii) surface dimerization of adsorbed SiH2 groups, (iv) formation of polysilane chains and islands, (SiH2)n, n⩾2, on the surface, (v) formation of higher surface hydrides through the exchange of hydrogen, and (vi) dangling-bond-mediated dissociation of surface hydrides. The MD simulations of a-Si:H film growth predict an overall surface reaction probability of 39% for the SiH2 radical. Structural and chemical characterization of the deposited films was carried out through a detailed analysis of the evolution of the structure of the film, surface morphology, and roughness, surface reactivity, and surface composition. The analysis revealed that the deposited films exhibit a high concentration of H and columnar surface morphologies. In particular, islands or polysilane chains form on the growth surface and are believed to be responsible for the columnar structural features in the deposited film. Such polysilane chain formation may have significant effects on the structural, morphological, and optical properties of the a-Si:H films.

  3. 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.

    PubMed

    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.

  4. High-temperature shock tube and modeling studies on the reactions of methanol with D-atoms and CH3-radicals.

    PubMed

    Peukert, S L; Michael, J V

    2013-10-10

    The shock tube technique has been used to study the hydrogen abstraction reactions D + CH3OH → CH2O + H + HD (A) and CH3 + CH3OH → CH2O + H + CH4 (B). For reaction A, the experiments span a T-range of 1016 K ≤ T ≤ 1325 K, at pressures 0.25 bar ≤ P ≤ 0.46 bar. The experiments on reaction B, CH3 + CH3OH, cover a T-range of 1138 K ≤ T ≤ 1270 K, at pressures around 0.40 bar. Reflected shock tube experiments, monitoring the depletion of D-atoms by applying D-atom atomic resonance absorption spectrometry (ARAS), were performed on reaction A using gas mixtures of C2D5I and CH3OH in Kr bath gas. C2D5I was used as precursor for D-atoms. For reaction B, reflected shock tube experiments monitoring H-atom formation with H-ARAS, were carried out using gas mixtures of diacetyl ((CH3CO)2) and CH3OH in Kr bath gas. (CH3CO)2 was used as the source of CH3-radicals. Detailed reaction models were assembled to fit the D-atom and H-atom time profiles in order to obtain experimental rate constants for reactions A and B. Total rate constants from the present experiments on D + CH3OH and CH3 + CH3OH can be represented by the Arrhenius equations kA(T) = 1.51 × 10(-10) exp(-3843 K/T) cm(3) molecules(-1) s(-1) (1016 K ≤ T ≤ 1325 K) and kB(T) = 9.62 × 10(-12) exp(-7477 K/T) cm(3) molecules(-1) s(-1) (1138 K ≤ T ≤ 1270 K). The experimentally obtained rate constants were compared with available rate data from the literature. The results from quantum chemical studies on reaction A were found to be in good agreement with the present results. The present work represents the first direct experimental study on these bimolecular reactions at combustion temperatures and is important to the high-temperature oxidation of CH3OH.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  6. Fabrication of an ionic liquid-based macroporous polymer monolithic column via atom transfer radical polymerization for the separation of small molecules.

    PubMed

    Zhang, Hang; Bai, Ligai; Wei, Zhen; Liu, Sha; Liu, Haiyan; Yan, Hongyuan

    2016-01-01

    A polymer monolithic column was prepared in a stainless steel column (50×4.6mm i.d.) via atom transfer radical polymerization technique using triallyl isocyanurate and ionic liquid (1-allyl-3-methylimidazolium chloride) as co-monomers, ethylene dimethacrylate as cross linking agent, polyethylene glycol 200, 1,4-butanediol, and N, N- dimethylformamide as porogen system, CCl4 as initiator, and FeCl2 as catalyst. The optimized polymer columns were characterized by scanning electron microscope, nitrogen adsorption-desorption instrument, mercury intrusion porosimetry, infrared spectrometer, and thermogravimetric analysis technique. Respectively, all of these factors above could illustrate that the optimized columns had relative uniform macroporous structure and high thermal stability. A series of basic and acidic small molecules, isomers, and homologues were used to evaluate the performance of these monoliths and enhanced column efficiency was obtained. Copyright © 2015 Elsevier B.V. All rights reserved.

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

    PubMed

    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.

  8. Spatial control over brush growth through sunlight-induced atom transfer radical polymerization using dye-sensitized TiO2 as a photocatalyst.

    PubMed

    Li, Bin; Yu, Bo; Zhou, Feng

    2014-07-01

    Simulated-sunlight induced atom transfer radical polymerization is used for spatial control over polymer brush growth by in situ photo-generation of the Cu(I) /L activator complex from its higher oxidation state Cu(II) /L deactivator complex using dye sensitized titanium dioxide nano-particles. The polymerization is well controlled under sunlight irradiation. Another attractive feature of this method is the possibility of creating various patterned surfaces of brushes using photomasks. When a nanoporous alumina oxide membrane is used as the template for confinement diffusion of photogenerated Cu(I) /L catalyst, patterns with sub-50 nm resolution are obtained. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Development of new atom transfer radical polymerization system by iron (III)-metal salts without using any external initiator and reducing agent.

    PubMed

    Khan, Mohd Yusuf; Chen, Xiangxiong; Lee, Seung Woo; Noh, Seok Kyun

    2013-08-01

    Atom transfer radical polymerization (ATRP) catalyzed by high oxidation state metal salts of FeX3 is developed for the first time in the absence of both external initiator and reducing agent. Methyl methacrylate (MMA) and styrene are polymerized successfully using FeX3 /Phosphorous ligands with well-controlled molecular weight distributions (=1.5). The molecular weight of the polymers increases with monomer consumption with the progress of time and the polymerization behaviors show a decent ATRP trend. Activators and initiators are suggested to generate in situ by the addition reaction of MMA and one equivalent of FeX3 . The PMMA synthesized from without-initiator system is characterized by (1) H, (13) C and DEPT (distortionless enhancement by polarization transfer nuclear magnetic resonance) nuclear magnetic resonance spectroscopy. Chain extension and copolymerization experiments prove the livingness of the obtained polymer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Electrochemically mediated atom transfer radical polymerization from a substrate surface manipulated by bipolar electrolysis: fabrication of gradient and patterned polymer brushes.

    PubMed

    Shida, Naoki; Koizumi, Yuki; Nishiyama, Hiroki; Tomita, Ikuyoshi; Inagi, Shinsuke

    2015-03-23

    We report the first ever use of electrochemically mediated atom transfer radical polymerization (eATRP) employing a bipolar electrochemical method for the fabrication of both gradient and patterned polymer brushes. A potential gradient generated on a bipolar electrode allowed the formation of a concentration gradient of a Cu(I) polymerization catalyst through the one-electron reduction of Cu(II) , resulting in the gradient growth of poly(NIPAM) brushes from an initiator-modified substrate surface set close to a bipolar electrode. These polymer brushes could be fabricated in three-dimensional gradient shapes with control over thickness, steepness, and modified area by varying the electrolytic conditions. Moreover, by site-selective application of potential during bipolar electrolysis, a polymer brush with a circular pattern was successfully formed. Polymerization was achieved using both a polar monomer (NIPAM) and a nonpolar monomer (MMA) with the eATRP system.

  11. Kinetic solvent effects on the reactions of the cumyloxyl radical with tertiary amides. Control over the hydrogen atom transfer reactivity and selectivity through solvent polarity and hydrogen bonding.

    PubMed

    Salamone, Michela; Mangiacapra, Livia; Bietti, Massimo

    2015-01-16

    A laser flash photolysis study on the role of solvent effects on hydrogen atom transfer (HAT) from the C-H bonds of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-formylpyrrolidine (FPRD), and N-acetylpyrrolidine (APRD) to the cumyloxyl radical (CumO(•)) was carried out. From large to very large increases in the HAT rate constant (kH) were measured on going from MeOH and TFE to isooctane (kH(isooctane)/kH(MeOH) = 5-12; kH(isooctane)/kH(TFE) > 80). This behavior was explained in terms of the increase in the extent of charge separation in the amides determined by polar solvents through solvent-amide dipole-dipole interactions and hydrogen bonding, where the latter interactions appear to play a major role with strong HBD solvents such as TFE. These interactions increase the electron deficiency of the amide C-H bonds, deactivating these bonds toward HAT to an electrophilic radical such as CumO(•), indicating that changes in solvent polarity and hydrogen bonding can provide a convenient method for deactivation of the C-H bond of amides toward HAT. With DMF, a solvent-induced change in HAT selectivity was observed, suggesting that solvent effects can be successfully employed to control the reaction selectivity in HAT-based procedures for the functionalization of C-H bonds.

  12. Reactions of the phthalimide N-oxyl radical (PINO) with activated phenols: the contribution of π-stacking interactions to hydrogen atom transfer rates.

    PubMed

    D'Alfonso, Claudio; Bietti, Massimo; DiLabio, Gino A; Lanzalunga, Osvaldo; Salamone, Michela

    2013-02-01

    The kinetics of reactions of the phthalimide N-oxyl radical (PINO) with a series of activated phenols (2,2,5,7,8-pentamethylchroman-6-ol (PMC), 2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols) were investigated by laser flash photolysis in CH(3)CN and PhCl in order to establish if the reactions with PINO can provide a useful tool for evaluating the radical scavenging ability of phenolic antioxidants. On the basis of the small values of deuterium kinetic isotope effects, the relatively high and negative ρ values in the Hammett correlations and the results of theoretical calculations, we suggest that these reactions proceed by a hydrogen atom transfer (HAT) mechanism having a significant degree of charge transfer resulting from a π-stacked conformation between PINO and the aromatic ring of the phenols. Kinetic solvent effects were analyzed in detail for the hydrogen transfer from 2,4,6-trimethylphenol to PINO and the data obtained are in accordance with the Snelgrove-Ingold equation for HAT. Experimental rate constants for the reactions of PINO with activated phenols are in accordance with those predicted by applying the Marcus cross relation.

  13. Counter-intuitive experimental evidence on the initiation of radical crack in ceramic thin films at the atomic scale

    NASA Astrophysics Data System (ADS)

    Zhuang, Chunqiang; Li, Zhipeng; Lin, Songsheng

    2015-10-01

    The basic issue related to radial crack in ceramic thin films has received considerable attention due to the fact that the radial crack plays an important role in evaluating the toughness properties of ceramic materials. In this work, an atomic-scale new experimental evidence is clearly presented to reveal the counter-intuitive initiation, the nucleation and the propagation mechanism of the radial crack in Al-Cr-N ceramic thin films.

  14. Counter-intuitive experimental evidence on the initiation of radical crack in ceramic thin films at the atomic scale

    SciTech Connect

    Zhuang, Chunqiang Li, Zhipeng; Lin, Songsheng

    2015-10-15

    The basic issue related to radial crack in ceramic thin films has received considerable attention due to the fact that the radial crack plays an important role in evaluating the toughness properties of ceramic materials. In this work, an atomic-scale new experimental evidence is clearly presented to reveal the counter-intuitive initiation, the nucleation and the propagation mechanism of the radial crack in Al-Cr-N ceramic thin films.

  15. 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}

    SciTech Connect

    Blank, D.A.; Hemmi, N.; Suits, A.G.; Lee, Y.T.

    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.

  16. Inorganic-organic hybrid coatings on stainless steel by layer-by-layer deposition and surface-initiated atom-transfer-radical polymerization for combating biocorrosion.

    PubMed

    Yuan, S J; Pehkonen, S O; Ting, Y P; Neoh, K G; Kang, E T

    2009-03-01

    To improve the biocorrosion resistance of stainless steel (SS) and to confer the bactericidal function on its surface for inhibiting bacterial adhesion and biofilm formation, well-defined inorganic-organic hybrid coatings, consisting of the inner compact titanium oxide multilayers and outer dense poly(vinyl-N-hexylpyridinium) brushes, were successfully developed. Nanostructured titanium oxide multilayer coatings were first built up on the SS substrates via the layer-by-layer sol-gel deposition process. The trichlorosilane coupling agent, containing the alkyl halide atom-transfer-radical polymerization (ATRP) initiator, was subsequently immobilized on the titanium oxide coatings for surface-initiated ATRP of 4-vinylpyridine (4VP). The pyridium nitrogen moieties of the covalently immobilized 4VP polymer, or P(4VP), brushes were quaternized with hexyl bromide to produce a high concentration of quaternary ammonium salt on the SS surfaces. The excellent antibacterial efficiency of the grafted polycations, poly(vinyl-N-pyridinium bromide), was revealed by viable cell counts and atomic force microscopy images of the surface. The effectiveness of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements.

  17. Experimental design and analysis of activators regenerated by electron transfer-atom transfer radical polymerization experimental conditions for grafting sodium styrene sulfonate from titanium substrates

    PubMed Central

    Foster, Rami N.; Johansson, Patrik K.; Tom, Nicole R.; Koelsch, Patrick; Castner, David G.

    2015-01-01

    A 24 factorial design was used to optimize the activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) grafting of sodium styrene sulfonate (NaSS) films from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate (ester ClSi) functionalized titanium substrates. The process variables explored were: (1) ATRP initiator surface functionalization reaction time; (2) grafting reaction time; (3) CuBr2 concentration; and (4) reducing agent (vitamin C) concentration. All samples were characterized using x-ray photoelectron spectroscopy (XPS). Two statistical methods were used to analyze the results: (1) analysis of variance with α=0.05, using average Ti XPS atomic percent as the response; and (2) principal component analysis using a peak list compiled from all the XPS composition results. Through this analysis combined with follow-up studies, the following conclusions are reached: (1) ATRP-initiator surface functionalization reaction times have no discernable effect on NaSS film quality; (2) minimum (≤24 h for this system) grafting reaction times should be used on titanium substrates since NaSS film quality decreased and variability increased with increasing reaction times; (3) minimum (≤0.5 mg cm−2 for this system) CuBr2 concentrations should be used to graft thicker NaSS films; and (4) no deleterious effects were detected with increasing vitamin C concentration. PMID:26396463

  18. Fuzzy ternary particle systems by surface-initiated atom transfer radical polymerization from layer-by-layer colloidal core-shell macroinitiator particles.

    PubMed

    Fulghum, Timothy M; Patton, Derek L; Advincula, Rigoberto C

    2006-09-26

    We report the synthesis of ternary polymer particle material systems composed of (a) a spherical colloidal particle core, coated with (b) a polyelectrolyte intermediate shell, and followed by (c) a grafted polymer brush prepared by surface-initiated polymerization as the outer shell. The layer-by-layer (LbL) deposition process was utilized to create a functional intermediate shell of poly(diallyl-dimethylammonium chloride)/poly(acrylic acid) multilayers on the colloid template with the final layer containing an atom transfer radical polymerization (ATRP) macroinitiator polyelectrolyte. The intermediate core-shell architecture was analyzed with FT-IR, electrophoretic mobililty (zeta-potential) measurements, atomic force microscopy, and transmission electron microscopy (TEM) techniques. The particles were then utilized as macroinitiators for the surface-initiated ATRP grafting process for poly(methyl methacrylate) polymer brush. The polymer grafting was confirmed with thermo gravimetric analysis, FT-IR, and TEM. The polymer brush formed the outermost shell for a ternary colloidal particle system. By combining the LbL and surface-initiated ATRP methods to produce controllable multidomain core-shell architectures, interesting functional properties should be obtainable based on independent polyelectrolyte and polymer brush behavior.

  19. Experimental design and analysis of activators regenerated by electron transfer-atom transfer radical polymerization experimental conditions for grafting sodium styrene sulfonate from titanium substrates.

    PubMed

    Foster, Rami N; Johansson, Patrik K; Tom, Nicole R; Koelsch, Patrick; Castner, David G

    2015-09-01

    A 2(4) factorial design was used to optimize the activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) grafting of sodium styrene sulfonate (NaSS) films from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate (ester ClSi) functionalized titanium substrates. The process variables explored were: (1) ATRP initiator surface functionalization reaction time; (2) grafting reaction time; (3) CuBr2 concentration; and (4) reducing agent (vitamin C) concentration. All samples were characterized using x-ray photoelectron spectroscopy (XPS). Two statistical methods were used to analyze the results: (1) analysis of variance with [Formula: see text], using average [Formula: see text] XPS atomic percent as the response; and (2) principal component analysis using a peak list compiled from all the XPS composition results. Through this analysis combined with follow-up studies, the following conclusions are reached: (1) ATRP-initiator surface functionalization reaction times have no discernable effect on NaSS film quality; (2) minimum (≤24 h for this system) grafting reaction times should be used on titanium substrates since NaSS film quality decreased and variability increased with increasing reaction times; (3) minimum (≤0.5 mg cm(-2) for this system) CuBr2 concentrations should be used to graft thicker NaSS films; and (4) no deleterious effects were detected with increasing vitamin C concentration.

  20. Dual-level direct dynamics studies for the reactions of dimethyl ether with hydrogen atom and methyl radical.

    PubMed

    Wu, Jia-Yan; Liu, Jing-Yao; Li, Ze-Sheng; Huang, Xu-Ri; Sun, Chia-Chung

    2003-04-15

    The dual-level direct dynamics approach is employed to study the dynamics of the CH(3)OCH(3) + H (R1) and CH(3)OCH(3) + CH(3) (R2) reactions. Low-level calculations of the potential energy surface are carried out at the MP2/6-311+G(d,p) level of theory. High-level energetic information is obtained at the QCISD(T) level of theory with the 6-311+G(3df,3pd) basis set. The dynamics calculations are performed using variational transition state theory (VTST) with the interpolated single-point energies (ISPE) method, and small-curvature tunneling (SCT) is included. It is shown that the reaction of CH(3)OCH(3) with H (R1) may proceed much easier and with a lower barrier height than the reaction with CH(3) radical (R2). The calculated rate constants and activation energies are in good agreement with the experimental values. The calculated rate constants are fitted to k(R1) = 1.16 x 10(-19) T(3) exp(-1922/T) and k(R2) = 1.66 x 10(-28) T(5) exp(-3086/T) cm(3) mol(-1) s(-1) over a temperature range 207-2100 K. Furthermore, a small variational effect and large tunneling effect in the lower temperature range are found for the two reactions.

  1. Gas-phase oxidation of methyl crotonate and ethyl crotonate. kinetic study of their reactions toward OH radicals and Cl atoms.

    PubMed

    Teruel, Mariano A; Benitez-Villalba, Julio; Caballero, Norma; Blanco, María B

    2012-06-21

    Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with methyl crotonate and ethyl crotonate have been determined at 298 K and atmospheric pressure. The decay of the organics was monitored using gas chromatography with flame ionization detection (GC-FID), and the rate constants were determined using the relative rate method with different reference compounds. Room temperature rate coeficcients were found to be (in cm(3) molecule(-1) s(-1)): k(1)(OH + CH(3)CH═CHC(O)OCH(3)) = (4.65 ± 0.65) × 10(-11), k(2)(Cl + CH(3)CH═CHC(O)OCH(3)) = (2.20 ± 0.55) × 10(-10), k(3)(OH + CH(3)CH═CHC(O)OCH(2)CH(3)) = (4.96 ± 0.61) × 10(-11), and k(4)(Cl + CH(3)CH═CHC(O)OCH(2)CH(3)) = (2.52 ± 0.62) × 10(-10) with uncertainties representing ±2σ. This is the first determination of k(1), k(3), and k(4) under atmospheric pressure. The rate coefficients are compared with previous determinations for other unsaturated and oxygenated VOCs and reactivity trends are presented. In addition, a comparison between the experimentally determined k(OH) with k(OH) predicted from k vs E(HOMO) relationships is presented. On the other hand, product identification under atmospheric conditions has been performed for the first time for these unsaturated esters by the GC-MS technique in NO(x)-free conditions. 2-Hydroxypropanal, acetaldehyde, formaldehyde, and formic acid were positively observed as degradation products in agreement with the addition of OH to C2 and C3 of the double bond, followed by decomposition of the 2,3- or 3,2-hydroxyalkoxy radicals formed. Atmospheric lifetimes, based on of the homogeneous sinks of the unsaturated esters studied, are estimated from the kinetic data obtained in the present work.

  2. Localized surface plasmon resonance nanosensing of C-reactive protein with poly(2-methacryloyloxyethyl phosphorylcholine)-grafted gold nanoparticles prepared by surface-initiated atom transfer radical polymerization.

    PubMed

    Kitayama, Yukiya; Takeuchi, Toshifumi

    2014-06-03

    Highly sensitive and selective protein nanosensing based on localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) on which polymerized specific ligands were grafted as an artificial protein recognition layer for the target protein were demonstrated. As a model, optical nanosensing for C-reactive protein (CRP), a known biomarker for chronic inflammation that predicts the risk of arteriosclerosis or heart attacks, was achieved by measuring the shift of LSPR spectra derived from the change of permittivity of poly(2-methacryloyloxyethyl phosphorylcholine)-grafted AuNPs (PMPC-g-AuNPs) upon interacting with CRP, in which the PMPC-g-AuNPs layer were grafted on AuNPs by surface-initiated atom transfer radical polymerization (ATRP). This nanosensing system was effective even for detecting CRP concentrations in a human serum solution diluted to 1% (w/w), at which point a limit of detection was ~50 ng/mL and nonspecific adsorption of other proteins was negligible. The nanosensing system using specific ligand-grafted AuNPs has several strengths, such as low preparation cost, avoiding the need for expensive instruments, no necessary complex pretreatments, and high stability, because it does not contain biobased molecules. We believe this novel synthetic route for protein nanosensors, composed of AuNPs and a polymerized specific ligand utilizing surface-initiated controlled/living radical polymerization, will provide a foundation for the design and synthesis of nanosensors targeting various other biomarker proteins, paving the way for future advances in the field of biosensing.

  3. Rate constants and H atom branching ratios of the gas-phase reactions of methylidyne CH(X2Pi) radical with a series of alkanes.

    PubMed

    Loison, Jean-Christophe; Bergeat, Astrid; Caralp, Françoise; Hannachi, Yacine

    2006-12-21

    The reactions of the CH radical with several alkanes were studied, at room temperature, in a low-pressure fast-flow reactor. CH(X2Pi, v = 0) radicals were obtained from the reaction of CHBr(3) with potassium atoms. The overall rate constants at 300 K are (0.76 +/- 0.20) x 10(-10) [Fleurat-Lessard, P.; Rayez, J. C.; Bergeat, A.; Loison, J. C. Chem. Phys. 2002, 279, 87],1 (1.60 +/- 0.60) x 10(-10)[Galland, N.; Caralp, F.; Hannachi, Y.; Bergeat, A.; Loison, J.-C. J. Phys. Chem. A 2003, 107, 5419],2 (2.20 +/- 0.80) x 10(-10), (2.80 +/- 0.80) x 10(-10), (3.20 +/- 0.80) x 10(-10), (3.30 +/- 0.60) x 10(-10), and (3.60 +/- 0.80) x 10(-10) cm3 molecule(-1) s(-1), (errors refer to +/-2sigma) for methane, ethane, propane, n-butane, n-pentane, neo-pentane, and n-hexane respectively. The experimental overall rate constants correspond to those obtained using a simple classical capture theory. Absolute atomic hydrogen production was determined by V.U.V. resonance fluorescence, with H production from the CH + CH4 reaction being used as a reference. Observed H branching ratios were for CH4, 1.00[Fleurat-Lessard, P.; Rayez, J. C.; Bergeat, A.; Loison, J. C. Chem. Phys. 2002, 279, 87];1 C(2)H(6), 0.22 +/- 0.08 [Galland, N.; Caralp, F.; Hannachi, Y.; Bergeat, A.; Loison, J.-C. J. Phys. Chem. A 2003, 107, 5419];2 C(3)H(8), 0.19 +/- 0.07; C(4)H(10) (n-butane), 0.14 +/- 0.06; C(5)H(12) (n-pentane), 0.52 +/- 0.08; C(5)H(12) (neo-pentane), 0.51 +/- 0.08; C(5)H(12) (iso-pentane), 0.12 +/- 0.06; C(6)H(14) (n-hexane), 0.06 +/- 0.04.

  4. Probing the kinetic energy-release dynamics of H-atom products from the gas-phase reaction of O(3P) with vinyl radical C2H3.

    PubMed

    Jang, Su-Chan; Choi, Jong-Ho

    2014-11-21

    The gas-phase radical-radical reaction dynamics of ground-state atomic oxygen O((3)P) with vinyl radicals C2H3 has been studied by combining the results of vacuum-ultraviolet laser-induced fluorescence spectroscopy in a crossed beam configuration with ab initio calculations. The two radical reactants O((3)P) and C2H3 were produced by photolysis of NO2 and supersonic flash pyrolysis of C2H3I, respectively. Doppler profile analysis of the kinetic energy release of the nascent H-atom products from the title reaction O((3)P) + C2H3→ H((2)S) + CH2CO (ketene) revealed that the average translational energy of the products and the average fraction of the total available energy were 7.03 ± 0.30 kcal mol(-1) and 7.2%. The empirical data combined with CBS-QB3 level ab initio theory and statistical calculations demonstrated that the title oxygen-hydrogen exchange reaction is a major reaction channel, through an addition-elimination mechanism involving the formation of a short-lived, dynamical complex on the doublet potential energy surface. On the basis of systematic comparison with several exchange reactions of hydrocarbon radicals, the observed kinetic energy release can be explained in terms of the weak impulse at the moment of decomposition in the loose transition state with a product-like geometry and a small reverse barrier along the exit channel.

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

    DOE PAGES

    Brown, Suree; Yue, Yanfeng; Kuo, Li-Jung; ...

    2016-03-11

    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 ligandsmore » (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). Lastly, 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.« less

  6. Theoretical study of the reactions of CF3OCHF2 with the hydroxyl radical and the chlorine atom.

    PubMed

    Wu, Jia-yan; Liu, Jing-yao; Li, Ze-sheng; Sun, Chia-chung

    2004-09-20

    Theoretical investigations are carried out on the reaction mechanism of the reactions of CF3OCHF2 (HFOC-125) with the OH radials and Cl atoms, as well as the heats of formation of CF3OCHF2 and CF3OCF2. The electronic structure information on the potential energy surface for each reaction is obtained at the B3LYP/6-311G(d,p) level, and energetic information is further refined by G3(MP2) theory. The direct dynamics calculation of the hydrogen abstraction reactions are also performed at the G3(MP2)//B3LYP/ 6-311G(d,p) level. The classical energy profile is corrected by interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunnelling effect (SCT) calculated by the variational transition-state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k1 = 4.95 x 10(-30)T(5.40)exp(-347/T) and k2 = 1.86 x 10(-23)T(3.43)exp(-1579/T) cm3 molecule(-1)s(-1) over the temperature range 200-2000 K. The rate constants at 298 K for these two reactions are 3.38 x 10(-16) and 2.80 x 10(-17) cm3 molecule(-1)s(-1), respectively. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF3OCHF2 and CF3OCF2 are -312.3 +/- 1.0 and -257.3 +/- 1.0 kcalmol(-1), respectively, evaluated by G3(MP2) theory based on the B3LYP/6-311G(d,p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFOC-125.

  7. Diffusion-regulated phase-transfer catalysis for atom transfer radical polymerization of methyl methacrylate in an aqueous/organic biphasic system.

    PubMed

    Ding, Mingqiang; Jiang, Xiaowu; Peng, Jinying; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2015-03-01

    A concept based on diffusion-regulated phase-transfer catalysis (DRPTC) in an aqueous-organic biphasic system with copper-mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC-based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α-bromophenylacetate (EBrPA) as an initiator, and tris(2-pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well-defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. pH-responsive controlled-release fertilizer with water retention via atom transfer radical polymerization of acrylic acid on mussel-inspired initiator.

    PubMed

    Ma, Zhi-yuan; Jia, Xin; Zhang, Guo-xiang; Hu, Jia-mei; Zhang, Xiu-lan; Liu, Zhi-yong; Wang, He-yun; Zhou, Feng

    2013-06-12

    This work reports a polydopamine-graft-poly(acrylic acid) (Pdop-g-PAA)-coated controlled-release multi-element compound fertilizer with water-retention function by a combination of mussel-inspired chemistry and surface-initiated atom transfer radical polymerization (SI-ATRP) techniques for the first time. The morphology and composition of the products were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and inductively coupled plasma (ICP) emission spectrometry. The results revealed that the stimuli-responsive layer formed by a Pdop inner layer and a PAA outer corona exhibit outstanding selective permeability to charged nutrients and the release rate of encapsulated elements can be tailored by the pH values. At low pH, the Pdop-g-PAA layer can reduce nutrient loss, and at high pH, the coating restrains transportation of negative nutrients but favors the release of cations. Moreover, PAA brushes provide good water-retention property. This Pdop-graft-polymer brushes coating will be effective and promising in the research and development of multi-functional controlled-release fertilizer.

  9. Grafting of antibacterial polymers on stainless steel via surface-initiated atom transfer radical polymerization for inhibiting biocorrosion by Desulfovibrio desulfuricans.

    PubMed

    Yuan, S J; Xu, F J; Pehkonen, S O; Ting, Y P; Neoh, K G; Kang, E T

    2009-06-01

    To enhance the biocorrosion resistance of stainless steel (SS) and to impart its surface with bactericidal function for inhibiting bacterial adhesion and biofilm formation, well-defined functional polymer brushes were grafted via surface-initiated atom transfer radical polymerization (ATRP) from SS substrates. The trichlorosilane coupling agent, containing the alkyl halide ATRP initiator, was first immobilized on the hydroxylated SS (SS-OH) substrates for surface-initiated ATRP of (2-dimethylamino)ethyl methacrylate (DMAEMA). The tertiary amino groups of covalently immobilized DMAEMA polymer or P(DMAEMA), brushes on the SS substrates were quaternized with benzyl halide to produce the biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes on the SS surface resulted in an increase in surface concentration of quaternary ammonium groups, accompanied by substantially enhanced antibacterial and anticorrosion capabilities against Desulfovibrio desulfuricans in anaerobic seawater, as revealed by antibacterial assay and electrochemical studies. With the inherent advantages of high corrosion resistance of SS, and the good antibacterial and anticorrosion capabilities of the viologen-quaternized P(DMAEMA) brushes, the functionalized SS is potentially useful in harsh seawater environments and for desalination plants. Copyright 2009 Wiley Periodicals, Inc.

  10. Antibacterial inorganic-organic hybrid coatings on stainless steel via consecutive surface-initiated atom transfer radical polymerization for biocorrosion prevention.

    PubMed

    Yuan, S J; Pehkonen, S O; Ting, Y P; Neoh, K G; Kang, E T

    2010-05-04

    To enhance the corrosion resistance of stainless steel (SS) and to impart its surface with antibacterial functionality for inhibiting biofilm formation and biocorrosion, well-defined inorganic-organic hybrid coatings, consisting of a polysilsesquioxane inner layer and quaternized poly(2-(dimethyamino)ethyl methacrylate) (P(DMAEMA)) outer blocks, were prepared via successive surface-initiated atom transfer radical polymerization (ATRP) of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The cross-linked P(TMASPMA), or polysilsesquioxane, inner layer provided a durable and resistant coating to electrolytes. The pendant tertiary amino groups of the P(DMAEMA) outer block were quaternized with alkyl halide to produce a high concentration of quaternary ammonium groups with biocidal functionality. The so-synthesized inorganic-organic hybrid coatings on the SS substrates exhibited good anticorrosion and antibacterial effects and inhibited biocorrosion induced by sulfate-reducing bacteria (SRB) in seawater media, as revealed by antibacterial assay and electrochemical analyses, and they are potentially useful to steel-based equipment under harsh industrial and marine environments.

  11. Functionalized cotton via surface-initiated atom transfer radical polymerization for enhanced sorption of Cu(II) and Pb(II).

    PubMed

    Zheng, Y Q; Deng, Shubo; Niu, Li; Xu, F J; Chai, M Y; Yu, Gang

    2011-09-15

    The surface-initiated atom transfer radical polymerization (ATRP) was used to successfully prepare the aminated cotton and polyacrylic acid sodium (P(AA-Na))-grafted cotton for the efficient removal of Cu(II) and Pb(II) from aqueous solution in this study. The modified cotton surfaces were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The grafted long polymers with high density of amine and carboxyl groups on the cotton surfaces were responsible for the enhanced adsorption of heavy metals. The sorption behaviors including sorption kinetics, isotherms and pH effect were investigated. The sorption equilibrium of Cu(II) and Pb(II) was achieved within 1h on the P(AA-Na)-grafted cotton, much faster than 8h on the aminated cotton. According to the Langmuir fitting, the maximum sorption capacities of Cu(II) and Pb(II) on the P(AA-Na)-grafted cotton were 2.45 and 2.44 mmol/g, respectively, higher than many adsorbents reported in the literature. The P(AA-Na)-grafted cotton had better adsorption behaviors for Cu(II) and Pb(II) than the aminated cotton.

  12. A poly(acrylonitrile)-functionalized porous aromatic framework synthesized by atom-transfer radical polymerization for the extraction of uranium from seawater

    SciTech Connect

    Yue, Yanfeng; Zhang, Chenxi; Tang, Qing; Mayes, Richard T.; Liao, Wei -Po; Liao, Chen; Tsouris, Costas; Stankovich, Joseph J.; Chen, Jihua; Hensley, Dale K.; Abney, Carter W.; Jiang, De-en; Brown, Suree; Dai, Sheng

    2015-10-30

    In order to ensure a sustainable reserve of fuel for nuclear power generation, tremendous research efforts have been devoted to developing advanced sorbent materials for extracting uranium from seawater. In this work, a porous aromatic framework (PAF) was surface-functionalized with poly(acrylonitrile) through atom-transfer radical polymerization (ATRP). Batches of this adsorbent were conditioned with potassium hydroxide (KOH) at room temperature or 80 °C prior to contact with a uranium-spiked seawater simulant, with minimal differences in uptake observed as a function of conditioning temperature. A maximum capacity of 4.81 g-U/kg-ads was obtained following 42 days contact with uranium-spiked filtered environmental seawater, which demonstrates a comparable adsorption rate. A kinetic investigation revealed extremely rapid uranyl uptake, with more than 80% saturation reached within 14 days. Furthermore, relying on the semiordered structure of the PAF adsorbent, density functional theory (DFT) calculations reveal cooperative interactions between multiple adsorbent groups yield a strong driving force for uranium binding.

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

    PubMed Central

    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

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

    PubMed Central

    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

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

    NASA Technical Reports Server (NTRS)

    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.

  16. Grafting N-Isopropyl Acrylamide) from Poly(vinylidene Fluoride) Mirofiltration, Membranes via Direct Surface-Initiated Atom Transfer Radical Polymerization, and Temperature Sensitivity

    NASA Astrophysics Data System (ADS)

    Chen, Yiwang; Xiao, Jichun; Zhou, Weihua; Deng, Qilan; Nie, Huarong; Wan, Meixiang; Bai, Fenglian

    Well-defined poly(N-isopropyl acrylamide) (PNIPAAm) brushes on commercial hydrophobic poly(vinylidene fluoride) (PVDF) microfiltration membrane surfaces were prepared, via direct atom transfer radical polymerization (ATRP) with the secondary fluorinated site of PVDF as initiator and water as solvent at 80°C. The effect of solvents on the ATRP was studied in detail. The water as reaction solvent was in favor of surface-initiated ATRP of N-isopropyl acrylamide (NIPAAm) from secondary fluoride of PVDF membranes. The chemical composition and structure of the modified PVDF membrane surfaces were determined by attenuated total reflectance (ATR) Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF membrane and the PNIPAAm-grafted PVDF membranes were measured using micro-image analysis and process software. The introduction of the well-defined PNIPAAm on the PVDF membrane gave rise to hydrophilicity. Water contact angles of PVDF membranes reduced after the surface grafting of PNIPAAm. Water fluxes and protein solution permeation experiments revealed that the PNIPAAm-grafted PVDF membranes exhibited temperature-responsive permeability. The unique microstructure of PNIPAAm brushes facilitated hydrophilicity below the lower critical solution temperature.

  17. Preparation of high-capacity, weak anion-exchange membranes by surface-initiated atom transfer radical polymerization of poly(glycidyl methacrylate) and subsequent derivatization with diethylamine

    NASA Astrophysics Data System (ADS)

    Qian, Xiaolei; Fan, Hua; Wang, Chaozhan; Wei, Yinmao

    2013-04-01

    Ion-exchange membrane is of importance for the development of membrane chromatography. In this work, a high-capacity anion-exchange membrane was prepared by grafting of glycidyl methacrylate (GMA) onto the surface of regenerated cellulose (RC) membranes via surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequent derivatization with diethylamine. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize changes in the chemical functionality, surface topography and pore morphology of the modified membranes. The static capacity of the prepared anion-exchange membrane was evaluated with bovine serum albumin (BSA) as a model protein. The results indicated that the anion-exchange membrane which could reach a maximum capacity of 96 mg/mL for static adsorption possesses a higher adsorption capacity, and the adsorption capacity increases with the polymerization time. The effect of pH and salt concentration confirmed that the adsorption of BSA followed ion-exchange mechanism. The established method would have potential application in the preparation of anion-exchange membrane.

  18. Using the Interior Cavity of the P22 Capsid for Site Specific Initiation of Atom Transfer Radical Polymerization with Tremendously Increased Cargo Loading

    PubMed Central

    Lucon, Janice; Qazi, Shefah; Uchida, Masaki; Bedwel, Gregory J.; LaFrance, Ben; Prevelige, Peter E.; Douglas, Trevor

    2013-01-01

    Virus-like particles (VLPs) have emerged as important and versatile architectures for chemical manipulation in the development of functional hybrid nanostructures. Here we have successfully demonstrated the site selective initiation of atom transfer radical polymerization (ATRP) reactions to form an addressable polymer constrained within the interior cavity of a VLP. This protein-polymer hybrid, of P22 and crosslinked poly(2-aminoethyl methacrylate), is potentially useful as a new high-density delivery vehicle for encapsulation and delivery of small molecule cargos. In particular, the encapsulated polymer can act as a scaffold for the attachment of primary amine reactive molecules of interest, such as a fluorescein dye or a Gd-DTPA MRI contrast agent. Using this approach, a significant increase in labeling density of the VLP, compared to previous modifications of VLPs, can be achieved. These results highlight the use of multimeric protein-polymer conjugates for their potential utility in the development of VLP-based MRI contrast agents with the possibility of loading other cargos. PMID:23000990

  19. Atom transfer radical polymerization to fabricate monodisperse poly[glycidyl methacrylate-co-poly (ethylene glycol) methacrylate] microspheres and its application for protein affinity purification.

    PubMed

    Yu, Ling; Shi, Zhuan Zhuan; Li, Chang Ming

    2015-09-01

    Poly[glycidyl methacrylate-co-poly (ethylene glycol) methacrylate] microspheres for the first time were successfully synthesized by atom transfer radical polymerization (ATRP) method at room temperature. The co-polymerization approach was investigated to delicately control the microsphere morphology and size-distribution by reaction conditions including solvent percentage, monomer loading and rotation speed. The results show that the average size of the microspheres is ∼5.7 μm with coexistence of epoxy, hydroxyl and ether groups, which provide plentiful functional sites for protein anchoring. The mechanism of the microsphere formation is proposed. The microsphere successfully demonstrates its unique application for affinity purification of proteins, in which the functional epoxy group facilitates a simple and efficient protein covalent immobilization to purify immunoglobulin G on the microspheres, while the hydrophilic poly (ethylene glycol) motif can repulse nonspecific protein adsorption for good specificity. This microspheres can be used in broad protein biosensors due to their abundant functional groups and high surface to volume ratio.

  20. A poly(acrylonitrile)-functionalized porous aromatic framework synthesized by atom-transfer radical polymerization for the extraction of uranium from seawater

    DOE PAGES

    Yue, Yanfeng; Zhang, Chenxi; Tang, Qing; ...

    2015-10-30

    In order to ensure a sustainable reserve of fuel for nuclear power generation, tremendous research efforts have been devoted to developing advanced sorbent materials for extracting uranium from seawater. In this work, a porous aromatic framework (PAF) was surface-functionalized with poly(acrylonitrile) through atom-transfer radical polymerization (ATRP). Batches of this adsorbent were conditioned with potassium hydroxide (KOH) at room temperature or 80 °C prior to contact with a uranium-spiked seawater simulant, with minimal differences in uptake observed as a function of conditioning temperature. A maximum capacity of 4.81 g-U/kg-ads was obtained following 42 days contact with uranium-spiked filtered environmental seawater, whichmore » demonstrates a comparable adsorption rate. A kinetic investigation revealed extremely rapid uranyl uptake, with more than 80% saturation reached within 14 days. Furthermore, relying on the semiordered structure of the PAF adsorbent, density functional theory (DFT) calculations reveal cooperative interactions between multiple adsorbent groups yield a strong driving force for uranium binding.« less

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

    NASA Technical Reports Server (NTRS)

    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.

  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.

    PubMed

    Lin, Jing; Kong, Tao; Ye, Lin; Zhang, Ai-Ying; Feng, Zeng-Guo

    2015-01-01

    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 (1)H NMR, GPC, (13)C CP/MAS NMR, 2D (1)H NOESY NMR, FTIR, WXRD, TGA and DSC analyses.

  3. Adsorption of fibrinogen and lysozyme on silicon grafted with poly(2-methacryloyloxyethyl phosphorylcholine) via surface-initiated atom transfer radical polymerization.

    PubMed

    Feng, Wei; Zhu, Shiping; Ishihara, Kazuhiko; Brash, John L

    2005-06-21

    Surfaces based on grafted poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) "brushes" with a constant graft density of 0.39 chain/nm2 and chain length from 5 to 200 monomer units were prepared by surface-initiated atom transfer radical polymerization (ATRP) on silicon wafers. The chain length and layer thickness of the poly(MPC) grafts were varied via the ratio of MPC to sacrificial initiator. The surfaces were characterized by water contact angle, XPS, and AFM. The effect of poly(MPC) chain length on fibrinogen and lysozyme adsorption was studied in TBS buffer at pH 7.4. The adsorption of both proteins on the poly(MPC)-grafted surfaces was greatly reduced compared to the unmodified silicon. Adsorption decreased with increasing chain length of the poly(MPC) grafts. Grafts of chain length 200 (MW 59 000) gave adsorption levels of 7 and 2 ng/cm2, respectively, for fibrinogen and lysozyme at 1 mg/mL protein concentration, corresponding to reductions of greater than 98% compared to the unmodified silicon. Adsorption experiments using mixtures of the two proteins showed that the suppression of protein adsorption on the poly(MPC)-grafted surfaces was not strongly dependent on protein size or charge.

  4. Surface grafting of Eu(3+) doped luminescent hydroxyapatite nanomaterials through metal free light initiated atom transfer radical polymerization for theranostic applications.

    PubMed

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

    2017-08-01

    We reported a simple and efficient method to prepare the hydrophilic luminescent HAp polymer nanocomposites through the combination of ligand exchange and metal free light initiated surface-initiated atom transfer radical polymerization (SI-ATRP) using 10-phenylphenothiazine (PTH) as organic catalyst and 2-methacryloyloxyethyl phosphorylcholine (MPC) and itaconic acid (IA) as monomers. The biological imaging and drug delivery performance of HAp-poly(MPC-IA) nanorods were examined to evaluate their potential for biomedical applications. Results suggested that hydrophilic HAp-poly(MPC-IA) nanorods can be successfully prepared. More importantly, the HAp-poly(MPC-IA) exhibited excellent water dispersibility, desirable biocompatibility and good performance for biological imaging and controlled drug delivery applications. As compared with other controlled living polymerization reactions, the metal free light initiated SI-ATRP displayed many advantages such as easy for handle, mild reaction conditions, toxicity and fluorescence quenching from metal catalysts. Therefore, we believe that this strategy should be a useful and effective strategy for preparation of HAp nanomaterials for biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Synthesis of poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABA block copolymers by the combination of quasiliving carbocationic and atom transfer radical polymerizations.

    PubMed

    Szabó, Ákos; Szarka, Györgyi; Iván, Béla

    2015-01-01

    Systematic investigations are carried out on the synthesis of a series of new, unique ABA-type triblock copolymers consisting of the hydrophobic and chemically inert polyisobutylene (PIB) inner and the hydrophilic comb-shaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer as an outer block. Telechelic PIB macroinitiators with narrow molecular weight distributions (MWD) are synthesized by quasiliving carbocationic polymerization of isobutylene with a bifunctional initiator followed by quantitative chain end derivatizations. Atom transfer radical polymerization (ATRP) of PEGMAs with various molecular weights is investigated by using these macroinitiators. It is found that CuBr is an inefficient ATRP catalyst, while CuCl leads to high, nearly complete conversions of the PEGMA macromonomers. Gel permeation chromatography (GPC) analyses reveal slow initiation of PEGMA at relatively high PIB/PEGMA ratios or with PEGMAs of higher molecular weights due to steric hindrance between the macroinitiator and macromonomer. The occurrence of slow initiation, and not permanent termination, is proven by highly efficient ATRP of a low-molecular-weight monomer, methyl methacrylate, with the block copolymers as macroinitiators. Successful synthesis of PPEGMA-PIB-PPEGMA ABA block copolymers is obtained by using either low-molecular-weight PEGMA or relatively low macroinitiator/macromonomer ratios. Differential scanning calorimetry (DSC) indicates phase separation and significant suppression of the crystallinity of the pendant poly(ethylene glycol) (PEG) chains in these new block copolymers. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    NASA Astrophysics Data System (ADS)

    Park, Jung Tae; Koh, Joo Hwan; Seo, Jin Ah; Cho, Yong Soo; Kim, Jong Hak

    2011-08-01

    We report on the novel ternary hybrid materials consisting of semiconductor (TiO 2), metal (Ag) and polymer (poly(oxyethylene methacrylate) (POEM)). First, a hydrophilic polymer, i.e. POEM, was grafted from TiO 2 nanoparticles via the surface-initiated atom transfer radical polymerization (ATRP) technique. These TiO 2-POEM brush nanoparticles were used to template the formation of Ag nanoparticles by introduction of a AgCF 3SO 3 precursor and a NaBH 4 aqueous solution for reduction process. Successful grafting of polymeric chains from the surface of TiO 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 dbnd 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.

  7. "Near perfect" amphiphilic conetwork based on end-group cross-linking of polydimethylsiloxane triblock copolymer via atom transfer radical polymerization.

    PubMed

    Xu, Jianfeng; Qiu, Ming; Ma, Bomou; He, Chunju

    2014-09-10

    Novel amphiphilic conetworks (APCNs) with uniform channel size were synthesized through end-cross-linking of well-defined amphiphilic triblock copolymers via atom transfer radical polymerization (ATRP). A new ditelechelic polydimethylsiloxane macroinitiator was synthesized to initiate the polymerization of N,N-dimethylacrylamide. The resulting triblock copolymers show well-defined molecular weight with narrow polydisperisty, which are telechelic modified by allylamine and fully cross-linked with polyhydrosiloxanes through hydrosilylation. Transmission electron microscopy shows that the APCN has the behavior of microphase separation with small channel size and uniform phase domain. The resulting APCNs with idealized microstructure exhibit a combination of excellent properties, i.e., superhigh mechanical strength (4 ± 1 MPa) and elongation ratio (175 ± 25%), outstanding oxygen permeability (350 ± 150 barrers), a high water uptake property, and excellent biocompatibility, indicating that in this way, "near perfect" networks are obtained. These results are better than those reported in the literature, suggesting a promising semipermeable barrier for islet encapsulation in relative biomaterial fields.

  8. 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).

    PubMed

    Goswami, Monalisa; Rebreyend, Christophe; de Bruin, Bas

    2016-02-20

    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.

  9. A crossed beams study of the reaction of carbon atoms, C(3Pj), with vinyl cyanide, C2H3CN(X 1A')--investigating the formation of cyano propargyl radicals.

    PubMed

    Guo, Y; Gu, X; Zhang, F; Tang, M S; Sun, B J; H Chang, A H; Kaiser, R I

    2006-12-14

    The chemical dynamics of the reaction of ground state carbon atoms, C(3Pj), with vinyl cyanide, C2H3CN(X 1A'), were examined under single collision conditions at collision energies of 29.9 and 43.9 kJ mol(-1) using the crossed molecular beams approach. The experimental studies were combined with electronic structure calculations on the triplet C4H3N potential energy surface (H. F. Su, R. I. Kaiser, A. H. H. Chang, J. Chem. Phys., 2005, 122, 074320). Our investigations suggest that the reaction follows indirect scattering dynamics via addition of the carbon atom to the carbon-carbon double bond of the vinyl cyanide molecule yielding a cyano cyclopropylidene collision complex. The latter undergoes ring opening to form cis/trans triplet cyano allene which fragments predominantly to the 1-cyano propargyl radical via tight exit transition states; the 3-cyano propargyl isomer was inferred to be formed at least a factor of two less; also, no molecular hydrogen elimination channel was observed experimentally. These results are in agreement with the computational studies predicting solely the existence of a carbon versus hydrogen atom exchange pathway and the dominance of the 1-cyano propargyl radical product. The discovery of the cyano propargyl radical in the reaction of atomic carbon with vinyl cyanide under single collision conditions implies that this molecule can be an important reaction intermediate in combustion flames and also in extraterrestrial environments (cold molecular clouds, circumstellar envelopes of carbon stars) which could lead to the formation of cyano benzene (C6H5CN) upon reaction with a propargyl radical.

  10. RATE CONSTANTS FOR THE REACTIONS OF OH RADICALS AND CL ATOMS WITH DI-N-PROPYL ETHER AND DI-N-BUTYL ETHER AND THEIR DEUTERATED ANALOGS. (R825252)

    EPA Science Inventory

    Using relative rate methods, rate constants for the gas-phase reactions of OH radicals and Cl atoms with di-n-propyl ether, di-n-propyl ether-d14, di-n-butyl ether and di-n-butyl ether-d18 have been measured at 296 ? 2 K and atmos...

  11. Tuning reactivity and selectivity in hydrogen atom transfer from aliphatic C-H bonds to alkoxyl radicals: role of structural and medium effects.

    PubMed

    Salamone, Michela; Bietti, Massimo

    2015-11-17

    Hydrogen atom transfer (HAT) is a fundamental reaction that takes part in a wide variety of chemical and biological processes, with relevant examples that include the action of antioxidants, damage to biomolecules and polymers, and enzymatic and biomimetic reactions. Moreover, great attention is currently devoted to the selective functionalization of unactivated aliphatic C-H bonds, where HAT based procedures have been shown to play an important role. In this Account, we describe the results of our recent studies on the role of structural and medium effects on HAT from aliphatic C-H bonds to the cumyloxyl radical (CumO(•)). Quantitative information on the reactivity and selectivity patterns observed in these reactions has been obtained by time-resolved kinetic studies, providing a deeper understanding of the factors that govern HAT from carbon and leading to the definition of useful guidelines for the activation or deactivation of aliphatic C-H bonds toward HAT. In keeping with the electrophilic character of alkoxyl radicals, polar effects can play an important role in the reactions of CumO(•). Electron-rich C-H bonds are activated whereas those that are α to electron withdrawing groups are deactivated toward HAT, with these effects being able to override the thermodynamic preference for HAT from the weakest C-H bond. Stereoelectronic effects can also influence the reactivity of the C-H bonds of ethers, amines, and amides. HAT is most rapid when these bonds can be eclipsed with a lone pair on an adjacent heteroatom or with the π-system of an amide functionality, thus allowing for optimal orbital overlap. In HAT from cyclohexane derivatives, tertiary axial C-H bond deactivation and tertiary equatorial C-H bond activation have been observed. These effects have been explained on the basis of an increase in torsional strain or a release in 1,3-diaxial strain in the HAT transition states, with kH(eq)/kH(ax) ratios that have been shown to exceed one order of

  12. Strong Inhibition of O-Atom Transfer Reactivity for Mn(IV)(O)(π-Radical-Cation)(Lewis Acid) versus Mn(V)(O) Porphyrinoid Complexes.

    PubMed

    Zaragoza, Jan Paulo T; Baglia, Regina A; Siegler, Maxime A; Goldberg, David P

    2015-05-27

    The oxygen atom transfer (OAT) reactivity of two valence tautomers of a Mn(V)(O) porphyrinoid complex was compared. The OAT kinetics of Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV-vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 10(4) M(-1) s(-1). Characterization of the OAT transition state analogues Mn(III)(OPPh3)(TBP8Cz) and Mn(III)(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A valence tautomer of the closed-shell Mn(V)(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell Mn(IV)(O)(TBP8Cz(•+)):LA (LA = Zn(II), B(C6F5)3, H(+)) complexes. These Mn(IV)(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10(-3) - 8.7 M(-1) s(-1)), contrasting the previously observed rate increase of H-atom transfer (HAT) for Mn(IV)(O)(TBP8Cz(•+)):LA with phenols. A Hammett analysis showed that the OAT reactivity for Mn(IV)(O)(TBP8Cz(•+)):LA is influenced by the Lewis acid strength. Spectral redox titration of Mn(IV)(O)(TBP8Cz(•+)):Zn(II) gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its valence tautomer Mn(V)(O)(TBP8Cz) (Ered = -0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) valence tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of valence tautomers such as M(V)(O)(porph) versus M(IV)(O)(porph(•+)) (M = Mn or Fe) found in heme enzymes.

  13. Hydrogen atom transfer from 1,n-alkanediamines to the cumyloxyl radical. Modulating C-H deactivation through acid-base interactions and solvent effects.

    PubMed

    Milan, Michela; Salamone, Michela; Bietti, Massimo

    2014-06-20

    A time-resolved kinetic study on the effect of trifluoroacetic acid (TFA) on the hydrogen atom transfer (HAT) reactions from 1,n-alkanediamines (R2N(CH2)nNR2, R = H, CH3; n = 1-4), piperazine, and 1,4-dimethylpiperazine to the cumyloxyl radical (CumO(•)), has been carried out in MeCN and DMSO. Very strong deactivation of the α-C-H bonds has been observed following nitrogen protonation and the results obtained have been explained in terms of substrate basicity, of the distance between the two basic centers and of the solvent hydrogen bond acceptor ability. At [substrate] ≤ 1/2 [TFA] the substrates exist in the doubly protonated form HR2N(+)(CH2)nN(+)R2H, and no reaction with CumO(•) is observed. At 1/2 [TFA] < [substrate] ≤ [TFA], HAT occurs from the C-H bonds that are α to the nonprotonated nitrogen in R2N(CH2)nN(+)R2H. At [substrate] > [TFA], HAT occurs from the α-C-H bonds of R2N(CH2)nNR2, and the mesured kH values are very close to those obtained in the absence of TFA. Comparison between MeCN and DMSO clearly shows that in the monoprotonated diamines R2N(CH2)nN(+)R2H remote C-H deactivation can be modulated through solvent hydrogen bonding.

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

    PubMed

    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 < 6, in contrast to the chitosan beads, which did not show clear selectivity for either of the two metal species. Mechanism study suggested that the enhanced mercury adsorption was due to the many amide groups grafted onto the surfaces of the beads, and the selectivity in mercury adsorption can be attributed to the ability of mercury ions to form covalent bonds with the amide. It was found that adsorbed mercury ions on the chitosan-g-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.

  15. Surface-active and stimuli-responsive polymer--Si(100) hybrids from surface-initiated atom transfer radical polymerization for control of cell adhesion.

    PubMed

    Xu, F J; Zhong, S P; Yung, L Y L; Kang, E T; Neoh, K G

    2004-01-01

    A simple two-step method was developed for the covalent immobilization of atom-transfer radical polymerization (ATRP) initiators on the hydrogen-terminated Si(100) (Si-H) surface. Well-defined functional polymer-Si hybrids, consisting of covalently tethered brushes of poly(ethylene glycol) monomethacrylate (PEGMA) polymer, N-isopropylacrylamide (NIPAAm) polymer, and NIPAAm-PEGMA copolymers and block copolymers on Si-H surfaces, were prepared via surface-initiated ATRP. Kinetics study revealed that the chain growth from the silicon surface was consistent with a "controlled" process. Surface cultures of the cell line 3T3-Swiss albino on the hybrids were evaluated. The PEGMA graft-polymerized silicon [Si-g-P(PEGMA)] surface is very effective in preventing cell attachment and growth. At 37 degrees C [above the lower critical solution temperature (LCST, approximately 32 degrees C) of NIPAAm], the seeded cells adhered, spread, and proliferated on the NIPAAm graft polymerized silicon [Si-g-P(NIPAAm)] surface. Below the LCST, the cells detached from the Si-g-P(NIPAAm) surface spontaneously. Incorporation of PEGMA units into the NIPAAm chains of the Si-g-P(NIPAAm) surface via copolymerization resulted in more rapid cell detachment during the temperature transition. The "active" chain ends on the Si-g-P(PEGMA) and Si-g-P(NIPAAm) hybrids were also used as the macroinitiators for the synthesis of diblock copolymer brushes. Thus, not only are the hybrids potentially useful as stimuli-responsive adhesion modifiers for cells in silicon-based biomedical microdevices but also the active chain ends on the hybrid surfaces offer opportunities for further surface functionalization and molecular design.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Preparation of a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine) by surface-initiated atom transfer radical polymerization and analysis of protein adsorption resistance.

    PubMed

    Inoue, Yuuki; Onodera, Yuya; Ishihara, Kazuhiko

    2016-05-01

    The purpose of this study was to prepare a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine (MPC)) and assess its resistance to protein adsorption from the dissolved state of poly(MPC) chains in an aqueous condition. The thick poly(MPC) brush layer was prepared through the surface-initiated atom transfer radical polymerization (SI-ATRP) of MPC with a free initiator from an initiator-immobilized substrate at given [Monomer]/[Free initiator] ratios. The ellipsometric thickness of the poly(MPC) brush layers could be controlled by the polymerization degree of the poly(MPC) chains. The thickness of the poly(MPC) brush layer in an aqueous medium was larger than that in air, and this tendency became clearer when the polymerization degree of the poly(MPC) increased. The maximum thickness of the poly(MPC) brush layer in an aqueous medium was around 110 nm. The static air contact angle of the poly(MPC) brush layer in water indicated a reasonably hydrophilic nature, which was independent of the thickness of the poly(MPC) brush layer at the surface. This result occurred because the hydrated state of the poly(MPC) chains is not influenced by the environment surrounding them. Finally, as measured with a quartz crystal microbalance, the amount of protein adsorbed from a fetal bovine serum solution (10% in phosphate-buffered saline) on the original substrate was 420 ng/cm(2). However, the poly(MPC) brush layer reduced this value dramatically to less than 50 ng/cm(2). This effect was independent of the thickness of the poly(MPC) brush layer for thicknesses between 20 nm and about 110 nm. These results indicated that the surface covered with a poly(MPC) brush layer is a promising platform to avoid biofouling and could also be applied to analyze the reactions of biological molecules with a high signal/noise ratio.

  18. Temperature-controlled flow switching in nanocapillary array membranes mediated by poly(N-isopropylacrylamide) polymer brushes grafted by atom transfer radical polymerization.

    PubMed

    Lokuge, Ishika; Wang, Xuejun; Bohn, Paul W

    2007-01-02

    We report actively controlled transport that is thermally switchable and size-selective in a nanocapillary array membrane (NCAM) prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) brushes onto the exterior surface of a Au-coated polycarbonate track-etched membrane. A smooth Au layer on the membrane surface, which is key to obtaining a uniform polymer film, was prepared by thermal evaporation of approximately 50 nm Au on both exterior surfaces. After evaporation, the inner diameter of the pore is reduced slightly, but the NCAM retains a narrow pore size distribution. PNIPPAm brushes with 10-30 nm (dry film) thickness were grafted onto the Au surface through surface-initiated atom transfer radical polymerization (ATRP) using a disulfide initiator, (BrC(CH3)2COO(CH2)11S)2. Molecular transport through the PNIPAAm polymer brush-modified NCAMs was investigated by real-time fluorescence measurements using fluorescein isothiocyanate (FITC)-labeled dextrans ranging from 4.4 to 282 kDa in membranes with variable initial pore diameters (80, 100, and 200 nm) and different PNIPAAm thicknesses. Manipulating the temperature of the NCAM through the PNIPAAm lower critical solution temperature (LCST) causes large, size-dependent changes in the transport rates. Over specific ranges of probe size, transport is completely blocked below the LCST but strongly allowed above the LCST. The combination of the highly uniform PNIPAAm brush and the monodisperse pore size distribution is critical in producing highly reproducible switching behavior. Furthermore, the reversible nature of the switching raises the possibility of using them as actively controlled filtration devices.

  19. Keto-ether and glycol-ethers in the troposphere: reactivity toward OH radicals and Cl atoms, global lifetimes, and atmospheric implications.

    PubMed

    Barrera, Javier A; Dalmasso, Pablo R; Taccone, Raúl A; Lane, Silvia I

    2017-09-23

    Rate coefficients for the gas-phase reactions of OH radicals and Cl atoms with 1-methoxy-2-propanone (1-M-2-PONE), 1-methoxy-2-propanol (1-M-2-POL), and 1-methoxy-2-butanol (1-M-2-BOL) were determined at room temperature and atmospheric pressure using a conventional relative-rate technique. The following absolute rate coefficients were derived: k 1(OH + 1-M-2-PONE) = (0.64 ± 0.13) × 10(-11), k 2(OH + 1-M-2-BOL) = (2.19 ± 0.23) × 10(-11), k 3(Cl + 1-M-2-PONE = (1.07 ± 0.24) × 10(-10), k 4(Cl + 1-M-2-POL) = (2.28 ± 0.21) × 10(-10), and k 5 (Cl + 1-M-2-BOL) = (2.79 ± 0.23) × 10(-10), in units of cm(3) molecule(-1) s(-1). This is the first experimental determination of k 2-k 5. These rate coefficients were used to discuss the influence of the structure on the reactivity of the studied polyfunctional organic compounds. The atmospheric implications for 1-M-2-PONE, 1-M-2-POL, and 1-M-2-BOL and their reactions were investigated estimating atmospheric parameters such as lifetimes, global warming potentials, and average photochemical ozone production. The approximate nature of these values was stressed considering that the studied oxygenated volatile organic compounds are short-lived compounds for which the calculated parameters may vary depending on chemical composition, location, and season at the emission points.

  20. Covalent immobilization of glucose oxidase on well-defined poly(glycidyl methacrylate)-Si(111) hybrids from surface-initiated atom-transfer radical polymerization.

    PubMed

    Xu, F J; Cai, Q J; Li, Y L; Kang, E T; Neoh, K G

    2005-01-01

    A simple one-step procedure was employed for the covalent immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si-C bond, on the hydrogen-terminated Si(111) surface (Si-H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a "controlled" process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational freedom and a more hydrophilic environment. An equivalent enzyme activity above 1.6 units/cm2 [micromoles of beta-D-(+)-glucose oxidized to d-gluconolactone per minute per square centimeter] and a corresponding relative activity of about 60% could be readily achieved. The immobilized GOD also exhibited an improved stability during storage over that of the free enzyme. The GOD-functionalized silicon substrates are potentially useful to the development of silicon-based glucose biosensors.

  1. Radical aminomethylation of imines.

    PubMed

    Fujii, Shintaro; Konishi, Takehito; Matsumoto, Yusuke; Yamaoka, Yousuke; Takasu, Kiyosei; Yamada, Ken-Ichi

    2014-09-05

    Taking advantage of the high level of performance of N-alkoxycarbonyl-imines, we achieved the first example of addition of the aminomethyl radical to imine. The reaction efficiency depended on the structure of the radical precursor, whether it is an iodide or a xanthate, and an electron-withdrawing group on the nitrogen atom of the radical. This reaction allows direct introduction of an N-substituted aminomethyl group onto imine to provide 1,2-diamine as well as the short-step synthesis of ICI-199,441.

  2. Electrospun regenerated cellulose nanofibrous membranes surface-grafted with polymer chains/brushes via the atom transfer radical polymerization method for catalase immobilization.

    PubMed

    Feng, Quan; Hou, Dayin; Zhao, Yong; Xu, Tao; Menkhaus, Todd J; Fong, Hao

    2014-12-10

    In this study, an electrospun regenerated cellulose (RC) nanofibrous membrane with fiber diameters of ∼200-400 nm was prepared first; subsequently, 2-hydroxyethyl methacrylate (HEMA), 2-dimethylaminoethyl methacrylate (DMAEMA), and acrylic acid (AA) were selected as the monomers for surface grafting of polymer chains/brushes via the atom transfer radical polymerization (ATRP) method. Thereafter, four nanofibrous membranes (i.e., RC, RC-poly(HEMA), RC-poly(DMAEMA), and RC-poly(AA)) were explored as innovative supports for immobilization of an enzyme of bovine liver catalase (CAT). The amount/capacity, activity, stability, and reusability of immobilized catalase were evaluated, and the kinetic parameters (Vmax and Km) for immobilized and free catalase were determined. The results indicated that the respective amounts/capacities of immobilized catalase on RC-poly(HEMA) and RC-poly(DMAEMA) nanofibrous membranes reached 78 ± 3.5 and 67 ± 2.7 mg g(-1), which were considerably higher than the previously reported values. Meanwhile, compared to that of free CAT (i.e., 18 days), the half-life periods of RC-CAT, RC-poly(HEMA)-CAT, RC-poly(DMAEMA)-CAT, and RC-poly(AA)-CAT were 49, 58, 56, and 60 days, respectively, indicating that the storage stability of immobilized catalase was also significantly improved. Furthermore, the immobilized catalase exhibited substantially higher resistance to temperature variation (tested from 5 to 70 °C) and lower degree of sensitivity to pH value (tested from 4.0 and 10.0) than the free catalase. In particular, according to the kinetic parameters of Vmax and Km, the nanofibrous membranes of RC-poly(HEMA) (i.e., 5102 μmol mg(-1) min(-1) and 44.89 mM) and RC-poly(DMAEMA) (i.e., 4651 μmol mg(-1) min(-1) and 46.98 mM) had the most satisfactory biocompatibility with immobilized catalase. It was therefore concluded that the electrospun RC nanofibrous membranes surface-grafted with 3-dimensional nanolayers of polymer chains/brushes would be

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

    PubMed

    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.

  4. Rearrangement of sulfonamidyl radicals with hydrogen migration

    SciTech Connect

    Troyanskii, E.I.; Lazareva, M.I.; Nikishin, G.I.

    1987-01-20

    One-step outlying oxidative chlorination of alkanesulfonamides by the action of the Na/sub 2/S/sub 2/O/sub 8/-CuCl/sub 2/ system via intermediate sulfonamidyl radicals gives 3- and 4-chloroalkanesulfonamides. Rearrangements of sulfonamidyl radicals with H atom migration from the sulfonyl segment predominates over rearrangement with H atom migration from the amide segment.

  5. Reactivity and selectivity patterns in hydrogen atom transfer from amino acid C-H bonds to the cumyloxyl radical: polar effects as a rationale for the preferential reaction at proline residues.

    PubMed

    Salamone, Michela; Basili, Federica; Bietti, Massimo

    2015-04-03

    Absolute rate constants for hydrogen atom transfer (HAT) from the C-H bonds of N-Boc-protected amino acids to the cumyloxyl radical (CumO(•)) were measured by laser flash photolysis. With glycine, alanine, valine, norvaline, and tert-leucine, HAT occurs from the α-C-H bonds, and the stability of the α-carbon radical product plays a negligible role. With leucine, HAT from the α- and γ-C-H bonds was observed. The higher kH value measured for proline was explained in terms of polar effects, with HAT that predominantly occurs from the δ-C-H bonds, providing a rationale for the previous observation that proline residues represent favored HAT sites in the reactions of peptides and proteins with (•)OH. Preferential HAT from proline was also observed in the reactions of CumO(•) with the dipeptides N-BocProGlyOH and N-BocGlyGlyOH. The rate constants measured for CumO(•) were compared with the relative rates obtained previously for the corresponding reactions of different hydrogen-abstracting species. The behavior of CumO(•) falls between those observed for the highly reactive radicals Cl(•) and (•)OH and the significantly more stable Br(•). Taken together, these results provide a general framework for the description of the factors that govern reactivity and selectivity patterns in HAT reactions from amino acid C-H bonds.

  6. Binding to Redox-Inactive Alkali and Alkaline Earth Metal Ions Strongly Deactivates the C-H Bonds of Tertiary Amides toward Hydrogen Atom Transfer to Reactive Oxygen Centered Radicals.

    PubMed

    Salamone, Michela; Carboni, Giulia; Mangiacapra, Livia; Bietti, Massimo

    2015-09-18

    The effect of alkali and alkaline earth metal ions on the reactions of the cumyloxyl radical (CumO(•)) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) was studied by laser flash photolysis. In acetonitrile, a >2 order of magnitude decrease in the rate constant for hydrogen atom transfer (HAT) from the C-H bonds of these substrates (kH) was measured after addition of Li(+). This behavior was explained in terms of a strong interaction between Li(+) and the oxygen atom of both DMF and DMA that increases the extent of positive charge on the amide, leading to C-H bond deactivation toward HAT to the electrophilic radical CumO(•). Similar effects were observed after addition of Ca(2+), which was shown to strongly bind up to four equivalents of the amide substrates. With Mg(2+), weak C-H deactivation was observed for the first two substrate equivalents followed by stronger deactivation for two additional equivalents. No C-H deactivation was observed in DMSO after addition of Li(+) and Mg(2+). These results point toward the important role played by metal ion Lewis acidity and solvent Lewis basicity, indicating that C-H deactivation can be modulated by varying the nature of the metal cation and solvent and allowing for careful control over the HAT reactivity of amide substrates.

  7. Reactions between atomic chlorine and pyridine in solid para-hydrogen: Infrared spectrum of the 1-chloropyridinyl (C{sub 5}H{sub 5}N-Cl) radical

    SciTech Connect

    Das, Prasanta; Bahou, Mohammed; Lee, Yuan-Pern

    2013-02-07

    With infrared absorption spectra we investigated the reaction between Cl atom and pyridine (C{sub 5}H{sub 5}N) in a para-hydrogen (p-H{sub 2}) matrix. Pyridine and Cl{sub 2} were co-deposited with p-H{sub 2} at 3.2 K; a planar C{sub 5}H{sub 5}N-Cl{sub 2} complex was identified from the observed infrared spectrum of the Cl{sub 2}/C{sub 5}H{sub 5}N/p-H{sub 2} matrix. Upon irradiation at 365 nm to generate Cl atom in situ and annealing at 5.1 K for 3 min to induce secondary reaction, the 1-chloropyridinyl radical (C{sub 5}H{sub 5}N-Cl) was identified as the major product of the reaction Cl + C{sub 5}H{sub 5}N in solid p-H{sub 2}; absorption lines at 3075.9, 1449.7, 1200.6, 1148.8, 1069.3, 1017.4, 742.9, and 688.7 cm{sup -1} were observed. The assignments are based on comparison of observed vibrational wavenumbers and relative IR intensities with those predicted using the B3PW91/6-311++G(2d, 2p) method. The observation of the preferential addition of Cl to the N-site of pyridine to form C{sub 5}H{sub 5}N-Cl radical but not 2-, 3-, or 4-chloropyridine (ClC{sub 5}H{sub 5}N) radicals is consistent with the reported theoretical prediction that formation of the former proceeds via a barrierless path.

  8. 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

    SciTech Connect

    Morajkar, Pranay; Schoemaecker, Coralie; Fittschen, Christa; Bossolasco, Adriana

    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

  9. Osteoclast radicals.

    PubMed

    Silverton, S

    1994-11-01

    In biological research, new ideas arise and quickly spread to encompass the entire field. Thus, the evolution of molecular biology has significantly changed our methods of approaching our research. A similar far-reaching finding has been the advent of radical reactions into biology. Although radical chemistry has been utilized for many technological advances that affect our daily lives, the appreciation of this same process within our cells has opened an unexplored arena for research enquiry. As cellular messengers, radical molecules seem whimsically designed: they are evanescent, rapidly and apparently indiscriminately reactive, and barely detectable by most biological methods. Yet, our initial probing of these reactive agents in cells and organisms has led us to postulate a virtually undescribed system of communication within and among cells which may have significant effects in multiple organs. In bone, radical reactants have been attributed with an important role in the control of bone resorption.

  10. 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.

    PubMed

    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.

  11. THERMOCHEMISTRY OF HYDROCARBON RADICALS

    SciTech Connect

    Kent M. Ervin, Principal Investigator

    2004-08-17

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

  12. The collisional depolarization of (2S+1)Sigma radicals by closed shell atoms: Theory and application to OH(A (2)Sigma(+))+Ar.

    PubMed

    Aoiz, F J; Brouard, M; Eyles, C J; Kłos, J; de Miranda, M P

    2009-01-28

    Classical and quantum mechanical expressions for the j-j(') vector correlation (also referred to as the rotational tilt) are presented for the situation in which the initial and final relative velocity directions are unresolved. The quantum mechanical expressions are compared with previous descriptions in the literature. It is shown that in the case of (2S+1)Sigma radicals in collision with closed shell species, a tensor opacity formalism can be employed in quasiclassical trajectory calculations to provide classical estimates of both open shell spin-rotation state and nuclear hyperfine state changing (or conserving) cross sections. Polarization parameters are also obtained from the same formalism. The method is applied to calculations on the OH(A (2)Sigma(+))-Ar system using a recently developed potential energy surface. The results of both the closed and open shell quasiclassical trajectory calculations are found to compare favorably with those from close-coupled closed and open shell quantum mechanical scattering calculations. The accompanying paper provides an experimental test of these calculations and of the potential energy surface they employ.

  13. Abstraction kinetics of H-atom by OH radical from pinonaldehyde (C10H16O2): ab initio and transition-state theory calculations.

    PubMed

    Dash, Manas Ranjan; Rajakumar, B

    2012-06-21

    The kinetics and abstraction rate coefficients of hydroxyl radical (OH) reaction with pinonaldehyde were computed using G3(MP2) theory and transition-state theory (TST) between 200 and 400 K. Structures of the reactants, reaction complexes (RCs), product complexes (PCs), transition states (TSs), and products were optimized at the MP2(FULL)/6-31G* level of theory. Fifteen transition states were identified for the title reaction and confirmed by intrinsic reaction coordinate (IRC) calculations. The contributions of all the individual hydrogens in the substrate molecule to the total reaction are computed. The quantum mechanical tunneling effect was computed using Wigner's and Eckart's methods (both symmetrical and unsymmetrical methods). The reaction exhibits a negative temperature dependent rate coefficient, k(T) = (1.97 ± 0.34) × 10(-13) exp[(1587 ± 48)/T] cm(3) molecule(-1) s(-1), k(T) = (3.02 ± 0.56) × 10(-13) exp[(1534 ± 52/T] cm(3) molecule(-1) s(-1), and k(T) = (4.71 ± 1.85) × 10(-14) exp[(2042 ± 110)/T] cm(3) molecule(-1) s(-1) with Wigner's, Eckart's symmetrical, and Eckart's unsymmetrical tunneling corrections, respectively. Theoretically calculated rate coefficients are found to be in good agreement with the experimentally measured ones and other theoretical results. It is shown that hydrogen abstraction from -CHO position is the major channel, whereas H-abstraction from -COCH(3) is negligible. The atmospheric lifetime of pinonaldehyde is computed to be few hours and found to be in excellent agreement with the experimentally estimated ones.

  14. Catalytic Radical Domino Reactions in Organic Synthesis.

    PubMed

    Sebren, Leanne J; Devery, James J; Stephenson, Corey R J

    2014-02-07

    Catalytic radical-based domino reactions represent important advances in synthetic organic chemistry. Their development benefits synthesis by providing atom- and step-economical methods to complex molecules. Intricate combinations of radical, cationic, anionic, oxidative/reductive, and transition metal mechanistic steps result in cyclizations, additions, fragmentations, ring-expansions, and rearrangements. This Perspective summarizes recent developments in the field of catalytic domino processes.

  15. Free radical inactivation of pepsin

    NASA Astrophysics Data System (ADS)

    Josimović, Lj; Ruvarac, I.; Janković, I.; Jovanović, S. V.

    1994-06-01

    Alkylperoxy radicals containing one, two or three chlorine atoms, CO -2, O 2 - were reacted with pepsin in aqueous solutions. It was found that only Cl 3COO and CO -2 inactive pepsin, attacking preferentially the disulfide bridge. Transient spectra obtained upon completion of the Cl 3COO + pepsin reaction at pH 5 indicate that 20% of initially produced Cl 3COO radicals oxidizes tryptophan residues, and 40% disulfide bridges. The inactivation induced by the Cl 3COO radical increases at lower pH, and the maximal inactivation, Gin = 5.8, was observed at pH 1.5. The inactivation of pepsin by CO -2 radicals depends on the absorbed dose. The maximal inactivation, Gin = 4.5, was determined in the dose range from 38 to 53 Gy.

  16. OH-Radical Specific Addition to Glutathione S-Atom at the Air-Water Interface: Relevance to the Redox Balance of the Lung Epithelial Lining Fluid.

    PubMed

    Enami, Shinichi; Hoffmann, Michael R; Colussi, Agustín J

    2015-10-01

    Antioxidants in epithelial lining fluids (ELF) prevent inhaled air pollutants from reaching lung tissue. This process, however, may upset ELF's redox balance, which is deemed to be expressed by the ratio of the major antioxidant glutathione (GSH) to its putative oxidation product GSSG. Previously, we found that at physiological pH O3(g) rapidly oxidizes GS(2-)(aq) (but not GSH(-)) to GSO3(-) rather than GSSG. Here, we report that in moderately acidic pH ≤ 5 media ·OH(g) oxidizes GSH(-)(aq) to sulfenic GSOH(-), sulfinic GSO2(-), and sulfonic GSO3(-) acids via ·OH specific additions to reduced S-atoms. The remarkable specificity of ·OH on water versus its lack of selectivity in bulk water implicates an unprecedented steering process during [OH···GSH] interfacial encounters. Thus, both O3 and ·OH oxidize GSH to GSOH(-) under most conditions, and since GSOH(-) is reduced back to GSH in vivo by NADPH, redox balance may be in fact signaled by GSH/GSOH ratios.

  17. Rate constants of the reaction of C2-C4 peroxy radicals with OH radicals

    NASA Astrophysics Data System (ADS)

    Assaf, Emmanuel; Tanaka, Shisei; Kajii, Yoshizumi; Schoemaecker, Coralie; Fittschen, Christa

    2017-09-01

    The rate constants for the reaction of three peroxy radicals with OH have been measured using different precursors. Peroxy radicals have been prepared by either the reaction of Cl-atoms with C2H6, C3H8 and n-C4H10 or through photolysis of the corresponding alkyliodide. Using Cl-atoms, the following rate constants have been measured: Experiments using 248 nm photolysis of the corresponding alkyliodides as precursor enhances the rate constants by a factor of two, bringing up the suspicion of a fast reaction between I-atoms and OH radicals.

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

    SciTech Connect

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

    2016-03-11

    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). Lastly, 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.

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

    SciTech Connect

    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.

  20. DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals (·)HO2 and (·)O2(-) by caffeic acid phenethyl ester and some of its derivatives.

    PubMed

    Holtomo, Olivier; Nsangou, Mama; Fifen, Jean Jules; Motapon, Ousmanou

    2014-11-01

    H-atom transfer from caffeic acid phenethyl ester (CAPE), MBC (3-methyl-2-butenyl caffeate), BC (benzoic caffeate), P3HC (phenethyl-3-hydroxycinnamate), and P4HC (phenethyl-4-hydroxycinnamate) to the selected free radicals (·)HO2 and (·)O2(-) was studied. Such a transfer can proceed in three different ways: concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), and proton transfer followed by electron transfer (PT-ET). The latter pathway is sometimes competitive with SPLET (sequential proton loss electron transfer) in polar media. Analyzing the thermodynamic descriptors of the reactions of CAPE and its derivatives with co-reactive species-in particular, the free energies of reactions, the activation barrier to the CPCET mechanism, and their rate constants-appears to be the most realistic method of investigating the H-atom transfers of interest. These analyses were performed via DFT calculations, which agree well with the data acquired from experimental studies (IC50) and from CBS calculations. The CPCM solvation model was used throughout the work, while the SMD model-employed as a reference-was used only for CAPE. The main conclusion drawn from the analysis was that SPLET is the mechanism that governs the reaction of phenolic acids with (·)HO2, while PT-ET governs the reaction of phenols with (·)O2(-). In kinetic investigations of the CPCET process, the rate constant decreases as the solvent polarity increases, so the reaction velocity slows down.

  1. 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.

    PubMed

    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.

  2. OH-radical specific addition to the antioxidant glutathione S-atom at the air-water interface - Relevance to the redox balance of the lung epithelial lining fluid and the causality of adverse health effects induced by air pollution

    NASA Astrophysics Data System (ADS)

    Colussi, A. J.; Enami, S.; Hoffmann, M. R.

    2015-12-01

    Inhalation of oxidant pollutants upsets the redox balance (RB) of the lung epithelial lining fluid (ELF) by triggering the formation of reactive OH-radicals therein. RB is deemed to be controlled by the equilibrium between the most abundant ELF protective antioxidant glutathione (GSH) and its putative disulfide GSSG oxidation product. The actual species produced from the oxidation of GSH initiated by ·OH in ELF interfacial layers exposed to air, i.e., under realistic ELF conditions, however, were never identified. Here we report the online electrospray mass spectrometric detection of sulfenate (GSO-), sulfinate (GSO2-) and sulfonate (GSO3-) on the surface of aqueous GSH solutions collided with ·OH(g). We show that these products arise from ·OH specific additions to S-atoms, rather than via H-abstraction from GS-H. The remarkable specificity of ·OH in interfacial water vis-a-vis its lack of selectivity in bulk water implicates an unprecedented steering process during ·OH-GSH encounters at water interfaces. A non-specific systemic immune response to inhaled oxidants should be expected if they were initially converted into a common ·OH intermediate on the ELF (e.g., via fast Fenton chemistry) and oxidative stress signaled by the [GSH]/[GSOH] ratio.

  3. 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.

    PubMed

    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.

  4. 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.

    PubMed

    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.

  5. Surface functionalized SiO2 nanoparticles with cationic polymers via the combination of mussel inspired chemistry and surface initiated atom transfer radical polymerization: Characterization and enhanced removal of organic dye.

    PubMed

    Huang, Qiang; Liu, Meiying; Mao, Liucheng; Xu, Dazhuang; Zeng, Guangjian; Huang, Hongye; Jiang, Ruming; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2017-03-28

    Monodispersed SiO2 particles functionalized with cationic polymers poly-((3-acrylamidopropyl)trimethylammonium chloride) (PAPTCl) were prepared using mussel inspired surface modification strategy and surface initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, X-ray photoelectron spectroscopy, and zeta potential were employed to characterize these SiO2 samples. The adsorption performance of the functionalized SiO2 (donated as SiO2-PDA-PAPTCl) towards anionic organic dye Congo red (CR) was investigated to evaluate their potential environmental applications. We demonstrated that the surface of SiO2 particles can be successfully functionalized with cationic PAPTCl. The adsorption capability of as-prepared SiO2 was found to increases from 28.70 and 106.65mg/g after surface grafted with cationic polymers. The significant enhancement in the adsorption capability of SiO2-PDA-PAPTCl is mainly attributed to the introduction of cationic polymers. More importantly, this strategy is expected to be promising for fabrication of many other functional polymer nanocomposites for environmental applications due to the universality of mussel inspired chemistry and well designability and good monomer adaptability of SI-ATRP.

  6. Induction heating vs conventional heating for the hydrothermal treatment of nitinol and its subsequent 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate coating by surface-initiated atom transfer radical polymerization.

    PubMed

    Devillers, S; Barthélémy, B; Delhalle, J; Mekhalif, Z

    2011-10-01

    Nitinol is an alloy of great interest in general and especially in the biomedical field where many researches are aimed to improve both its corrosion resistance and its biocompatibility. In this work, we report on the advantage of an induction heating treatment in pure water compared to a conventional hydrothermal procedure. Both treatments lead to a hydroxylation of the surface, a decrease of the nickel amount in the outer part of the oxide layer, and a drastically decreased corrosion current density. However, the amount of surface hydroxyl groups is higher in the case of the induction heating treatment, which in turn leads to a denser grafting of atom transfer radical polymerization initiators and ultimately to a thicker 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate (MPC) polymer layer than in the case of conventional heating treatments. X-ray photoelectron spectroscopy (XPS), static contact angle, and polarization curves measurements as well as scanning electron microscopy (SEM) have been used to characterize the obtained modified surfaces. © 2011 American Chemical Society

  7. Determination of melamine and cyromazine in milk by high performance liquid chromatography coupled with online solid-phase extraction using a novel cation-exchange restricted access material synthesized by surface initiated atom transfer radical polymerization.

    PubMed

    Zhang, Yingying; Lin, Shen; Jiang, Ping; Zhu, Xudong; Ling, Jing; Zhang, Wen; Dong, Xiangchao

    2014-04-11

    A novel strong-cation-exchange restricted access material has been synthesized by atom transfer radical polymerization (ATRP). In the synthesis, poly(3-sulfopropyl methacrylate-co-ethylene dimethacrylate), [p(SPM/EDMA)] was grafted on the silica by surface-initiated ATRP first. The poly(glycerol mono-methacrylate) [pGMMA] was then immobilized on the external surface, which created a chemical diffusion barrier for protein exclusion. The resulting Sil-g-p(SPM/EDMA)-g-pGMMA has both functions of protein exclusion and cation exchange, exhibiting the property of cation-exchange restricted access material. The application of Sil-g-p(SPM/EDMA)-g-pGMMA has been studied by the determination of melamine and cyromazine in bovine milk using the online solid-phase extraction/HPLC method. In the process, the Sil-g-p(SPM/EDMA)-g-pGMMA was used for the sample pre-treatment and a HILIC column was employed as the analytical column. The method has shown good accuracy, precision and low limits of detections. The result demonstrated that the Sil-g-p(SPM/EDMA)-g-pGMMA can be used for the cation extraction from biological samples by direct HPLC injection.

  8. Atmospheric chemistry of cis-CF3CHdbnd CHCl (HCFO-1233zd(Z)): Kinetics of the gas-phase reactions with Cl atoms, OH radicals, and O3

    NASA Astrophysics Data System (ADS)

    Andersen, Lene Løffler; Østerstrøm, Freja From; Sulbaek Andersen, Mads P.; Nielsen, Ole John; Wallington, Timothy J.

    2015-10-01

    FTIR smog chamber techniques were used to measure the rate coefficients k(Cl + cis-CF3CHdbnd CHCl) = (6.26 ± 0.84) × 10-11, k(OH + cis-CF3CHdbnd CHCl) = (8.45 ± 1.52) × 10-13, and k(O3 + cis-CF3CHdbnd CHCl) = (1.53 ± 0.12) × 10-21 cm3 molecule-1 s-1. The atmospheric lifetime of cis-CF3CHdbnd CHCl is determined by reaction with OH radicals and is estimated to be 14 days. The infrared spectrum of cis-CF3CHdbnd CHCl was recorded and the integrated absorption over the range 600-2000 cm-1 was measured to be (1.48 ± 0.07) × 10-16 cm molecule-1. Accounting for non-uniform horizontal and vertical mixing leads to a GWP100 value of essentially zero. Correction to account for unwanted Cl atom chemistry in our previous relative rate study of the kinetics of the reaction of OH with trans-CF3CHdbnd CHCl gives k(OH + trans-CF3CHdbnd CHCl) = (3.61 ± 0.37) × 10-13 cm3 molecule-1 s-1.

  9. Primary radical yields in pulse irradiated alkaline aqueous solution

    NASA Technical Reports Server (NTRS)

    Fielden, E. M.; Hart, E. J.

    1969-01-01

    Primary radical yields of hydrated electrons, H atoms, and OH radicals are determined by measuring hydrated electron formation following a 4 microsecond pulse of X rays. The pH dependence of free radical yields beyond pH 12 is determined by observation of the hydrated electrons.

  10. Hydrogen-atom transfer in open-shell organometallic chemistry: the reactivity of Rh(II)(cod) and Ir(II)(cod) radicals.

    PubMed

    Hetterscheid, Dennis G H; Klop, Martijn; Kicken, Reinout J N A M; Smits, Jan M M; Reijerse, Eduard J; de Bruin, Bas

    2007-01-01

    coordination results in formation of more open, reactive species. Protonation of the noncoordinating pyridyl group increases the concentration of this species, and thus [H(+)] appears in the kinetic rate expression. The kinetic data are in agreement with bimolecular hydrogen-atom transfer from M(II)(cod) to another M(II) species (DeltaH( not equal)=11.5+/-2 kcal mol(-1), DeltaS( not equal)=-27+/-10 cal K(-1) mol(-1), and DeltaG( not equal)(298 K)=19.5+/-5 kcal mol(-1)).

  11. FTIR gas-phase kinetic study on the reactions of OH radicals and Cl atoms with unsaturated esters: Methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate

    NASA Astrophysics Data System (ADS)

    Colomer, Juan P.; Blanco, María B.; Peñéñory, Alicia B.; Barnes, Ian; Wiesen, Peter; Teruel, Mariano A.

    2013-11-01

    The relative-rate technique has been used to obtain rates coefficients for the reactions of the unsaturated esters methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate with OH radicals and chlorine atoms at (298 ± 2) K in synthetic air at a total pressure of (760 ± 10) Torr. The experiments were performed in an environmental chamber using in situ FTIR detection to monitor the decay of the esters relative to different reference compounds. The following room temperature rate coefficients (in units of cm3 molecule-1 s-1) were obtained: k1(OH + (CH3)2Cdbnd CHC(O)OCH3) = (4.46 ± 1.05) × 10-11, k2(Cl + (CH3)2Cdbnd CHC(O)OCH3) = (2.78 ± 0.46) × 10-10, k3(OH + CH3CHdbnd C(CH3)C(O)OCH2CH3) = (8.32 ± 1.93) × 10-11, k4(Cl + CH3CHdbnd C(CH3)C(O)OCH2CH3) = (2.53 ± 0.35) × 10-10, k5(OH + CH2dbnd CHCH2C(O)OCH3) = (3.16 ± 0.57) × 10-11, k4(Cl + CH2dbnd CHCH2C(O)OCH3) = (2.10 ± 0.35) × 10-10. With the exception of the reaction of Cl with methyl-3,3-dimethyl acrylate (k2), for which one determination exists in the literature, this study is the first kinetic study for these reactions under atmospheric pressure. Reactivity trends are discussed in terms of the effect of the alkyl and ester groups attached to the double bond on the overall rate coefficients towards OH radicals. The atmospheric implications of the reactions were assessed by the estimation of the tropospheric lifetimes of the title reactions.

  12. Radical-Mediated Enzymatic Polymerizations

    PubMed Central

    Zavada, Scott R.; Battsengel, Tsatsral; Scott, Timothy F.

    2016-01-01

    Polymerization reactions are commonly effected by exposing monomer formulations to some initiation stimulus such as elevated temperature, light, or a chemical reactant. Increasingly, these polymerization reactions are mediated by enzymes―catalytic proteins―owing to their reaction efficiency under mild conditions as well as their environmental friendliness. The utilization of enzymes, particularly oxidases and peroxidases, for generating radicals via reduction-oxidation mechanisms is especially common for initiating radical-mediated polymerization reactions, including vinyl chain-growth polymerization, atom transfer radical polymerization, thiol–ene step-growth polymerization, and polymerization via oxidative coupling. While enzyme-mediated polymerization is useful for the production of materials intended for subsequent use, it is especially well-suited for in situ polymerizations, where the polymer is formed in the place where it will be utilized. Such polymerizations are especially useful for biomedical adhesives and for sensing applications. PMID:26848652

  13. 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.

    PubMed

    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).

  14. Preparations and properties of a tunable void with shell thickness SiO2@SiO2 core-shell structures via activators generated by electron transfer for atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Ren, Yi-xian; Zhou, Guo-wei; Cao, Pei

    2016-02-01

    Core-shell structure nanoparticles are attracting considerable attention because of their applications in drug delivery, catalysis carrier, and nanomedicine. In this study, SiO2@SiO2 core-shell structure with tunable void and shell thickness was successfully prepared for the first time using SiO2-poly(buty acrylate) (PBA)-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) (SiO2-PBA-b-PDMAEMA) as the template and tetraethoxysilane (TEOS) as the silica source. An amphiphilic copolymer PBA-b-PDMAEMA was first grafted onto the SiO2 nanosphere surface through activators regenerated by electron transfer for atom transfer radical polymerization. TEOS was hydrolyzed along with the PDMAEMA chain through hydrogen bonding, and the core-shell structure of SiO2@SiO2 was obtained through calcination to remove the copolymer. The gradient hydrophilicity of the PBA-b-PDMAEMA copolymer template facilitated the hydrolysis of TEOS molecules along the PDMAEMA to PBA segments, thereby tuning the voids between the SiO2 core and SiO2 shell, as well as the SiO2 shell thickness. The voids were about 10-15 nm and the shell thicknesses were about 4-11 nm when adding different amounts of DMAEMA monomer. SiO2@SiO2 core-shell structures with tunable void and shell thickness were employed as supports for the loading and release of doxorubicin hydrochloride (DOX) in PBS (pH 4.0). The samples demonstrated good loading capacity and controlled release rate of DOX.

  15. Near-monodisperse poly(2-(methacryloyloxy)ethyl phosphorylcholine)-based macromonomers prepared by atom transfer radical polymerization and thiol-ene click chemistry: novel reactive steric stabilizers for aqueous emulsion polymerization.

    PubMed

    Warren, Nicholas J; Muise, Carl; Stephens, Alex; Armes, Steven P; Lewis, Andrew L

    2012-02-07

    Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepared by the atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diameter. As a comparison, the disulfide-containing PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw experiments and the addition of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addition of an electrolyte, as expected.

  16. 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

    NASA Astrophysics Data System (ADS)

    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.

  17. Fundamentals of Atom Transfer Radical Polymerization

    ERIC Educational Resources Information Center

    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…

  18. Fundamentals of Atom Transfer Radical Polymerization

    ERIC Educational Resources Information Center

    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…

  19. Dynamics of Radical-Mediated Enzyme Catalyses

    NASA Astrophysics Data System (ADS)

    Warncke, Kurt

    1997-11-01

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

  20. Emergence of oxyl radicals as selective oxidants.

    PubMed

    Ramasarma, T

    2012-10-01

    Hydroxyl radicals (HO*) are derived in Fenton reaction with ferrous salt and H2O2 in acid medium, and at neutral pH, metal-oxyl radicals (M-O*) predominate. Evidence is accumulating that M-O* radicals are also active in oxidation reactions, in addition to metal-oxo (M=O) now shown in many publications. Reactivity of these radicals gives selective oxidized products useful in cellular activities, in contrast to purported indiscriminate cell damage by hydroxyl radicals. Reactions with vanadium compounds, such as diperoxovanadate, peroxo-bridged mixed valency divanadate, vanadium-oxyl radical, tetravalent vanadyl and decavanadate illustrates selective gain in oxidative capacity of oxo- and oxyl- species. Occurrence of ESR signals typical of hydroxyl radicals is demonstrated in cell homogenates and tissue perfusates treated with spin trap agents. It is known for a long time lipid peroxides are formed in tissue microsomal systems exclusively in presence of salts of iron, among many metals tested. Oxygen and a reducing agent, ascorbate (non-enzymic) or NADPH (enzymic) are required to produce 'ferryl', the chelated Fe=O active form (possibly Fe-O* and Fe-O-O-Fe ?) for the crucial step of H-atom abstraction. Yet literature is replete with unsupported affirmations that hydroxyl radicals initiate lipid peroxidation, an unexplained fixation of mindset. The best-known *OH generator, a mixture of ferrous salt and H2O2, does not promote lipid peroxidation, nor do the many hydroxyl radical quenching agents stop it. The availability of oxo and oxyl-radical forms with transition metals, and also with non metals, P, S, N and V, calls for expansion of vision beyond superoxide and hydroxyl radicals and explore functions of multiple oxygen radicals for their biological relevance.

  1. Pyrimidine nucleobase radical reactivity in DNA and RNA

    NASA Astrophysics Data System (ADS)

    Greenberg, Marc M.

    2016-11-01

    Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

  2. Pyrimidine Nucleobase Radical Reactivity in DNA and RNA.

    PubMed

    Greenberg, Marc M

    2016-11-01

    Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

  3. Expanding Radical SAM Chemistry by Using Radical Addition Reactions and SAM Analogues.

    PubMed

    Ji, Xinjian; Li, Yongzhen; Xie, Liqi; Lu, Haojie; Ding, Wei; Zhang, Qi

    2016-09-19

    Radical S-adenosyl-l-methionine (SAM) enzymes utilize a [4Fe-4S] cluster to bind SAM and reductively cleave its carbon-sulfur bond to produce a highly reactive 5'-deoxyadenosyl (dAdo) radical. In almost all cases, the dAdo radical abstracts a hydrogen atom from the substrates or from enzymes, thereby initiating a highly diverse array of reactions. Herein, we report a change of the dAdo radical-based chemistry from hydrogen abstraction to radical addition in the reaction of the radical SAM enzyme NosL. This change was achieved by using a substrate analogue containing an olefin moiety. We also showed that two SAM analogues containing different nucleoside functionalities initiate the radical-based reactions with high efficiencies. The radical adduct with the olefin produced in the reaction was found to undergo two divergent reactions, and the mechanistic insights into this process were investigated in detail. Our study demonstrates a promising strategy in expanding radical SAM chemistry, providing an effective way to access nucleoside-containing compounds by using radical SAM-dependent reactions.

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

    PubMed

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

    2013-04-24

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

  5. Photoprocesses in diphenylpolyenes. 2. Excited-state interactions with stable free radicals

    SciTech Connect

    Chattopadhyay, S.K.; Das, P.K.; Hug, G.L.

    1983-01-01

    Singlet and triplet quenching by two stable free radicals, viz., di-tert-butylnitroxy (DTBN) and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HTMP), have been studied with three all-trans ..cap alpha..,..cap omega..-diphenylpolyenes, Ph(t-C=C)/sub n/Ph, n = 2-4, as excited-state substrates in different solvents. Data are presented for fluorescence quenching rate constants (0.8-2.1 x 10/sup 10/ M/sup -1/ s/sup -1/ in cyclohexane/methanol), the fraction of singlet quenching events that result in triplet generation (0.06-0.60), and rate constants for triplet quenching (0.18-4.8 x 10/sup 8/ M/sup -1/ s/sup -1/ in solvents ranging from dimethyl sulfoxide to cyclohexane). As with aromatic hydrcarbons, the dependence of triplet quenching rate constants for polyenes on triplet energy (E/sub T) is found to be parabolic; that is, they first decrease systematically on going from trans-stilbene (n = 1) to trans-1,6-diphenyl-1,3,5-hexatriene (n=3) and then increase on going from the latter to trans-1,8-diphenyl-1,3,5,7-octatetraene (n = 4). Possible interactions in terms of charge transfer, energy tranfer, and electron exchange as well as roles of torsional motions and twisted configurations of polyenes in the quenching processes are discussed. 29 references, 5 figures, 4 tables.

  6. On the mechanism of reaction of radicals with tirapazamine.

    PubMed

    Shi, Xiaofeng; Mandel, Sarah M; Platz, Matthew S

    2007-04-18

    Ketyl radicals produced by photolysis of ketones or di-tert-butyl peroxide (DTBP) in alcohol solvents react rapidly with tirapazamine (TPZ). The acetone ketyl radical (ACOH) reacts with TPZ with an absolute second-order rate constant of (9.7 +/- 0.4) x 108 M-1 s-1. The reaction kinetics can be followed by monitoring the bleaching of TPZ absorption at 475 nm or the formation of a reaction product which absorbs at 320 and 410 nm. The ACOD radical reacts with TPZ in 2-propanol-OD with an absolute rate constant of (6.7 +/- 0.5) x 108 M-1 s-1, corresponding to a kinetic isotope effect (KIE) of 1.4. Deuteration of the radical on carbon (ACOH-d6) retards the reaction of the radical with TPZ even further (absolute rate constant = (4.8 +/- 0.04) x 108 M-1 s-1). This result corresponds to a KIE of 2.0. Radicals derived from dioxane and diisopropyl ether by flash photolysis of DTBP in ethereal solvent react with TPZ more slowly than do ketyl radicals. It is concluded that ketyl radicals react, in part, with TPZ in organic solvents by transfer of a hydrogen atom from the OH and CH3 groups of the ketyl radical to the oxygen atom at the N4 position of TPZ to form acetone or acetone enol and a radical derivative of TPZ (TPZH). The latter species absorbs at 320 and 405 nm, has a lifetime of hundreds of microseconds in alcohol solvents, and decays by disproportionation to form TPZ and a reduced heterocycle. The reduced heterocycle eventually forms a desoxytirapazamine by a polar mechanism. The results are supported by density functional theory calculations. It is proposed that dioxanyl radical will also react, in part, with TPZ by transfer of a hydrogen atom from the carbon adjacent to the radical center to the oxygen atom at the N4 position of TPZ. This produces the enol ether and the previously mentioned TPZH radical. It is further posited that ether radicals react a bit more slowly than ketyl radicals because they lack the second mode of hydrogen transfer (from the OH group

  7. Structure and Reactivity of the N-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

    NASA Astrophysics Data System (ADS)

    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.

  8. Organic free radicals in clathrate hydrates investigated by muon spin spectroscopy.

    PubMed

    Percival, Paul W; Mozafari, Mina; Brodovitch, Jean-Claude; Chandrasena, Lalangi

    2014-02-20

    Very little is known about the behavior of free H atoms and small organic radicals inside clathrate hydrate structures despite the relevance of such species to combustion of hydrocarbon hydrates. Muonium is an H atom analog, essentially a light isotope of hydrogen, and can be used to probe the chemistry of H atoms and transient free radicals. We demonstrate the first application of muon spin spectroscopy to characterize radicals in clathrate hydrates. Atomic muonium was detected in hydrates of cyclopentane and tetrahydrofuran, and muoniated free radicals were detected in the hydrates of cyclopentene and 2,5-dihydrofuran, indicating rapid addition of muonium to the organic guest. Muon avoided level-crossing spectra of the radicals in hydrates are markedly different to those of the same radicals in pure organic liquids at the same temperature, and this can be explained by limited mobility of the enclathrated radicals, leading to anisotropy in the hyperfine interactions.

  9. Hydroxyl radical reaction with trans-resveratrol: initial carbon radical adduct formation followed by rearrangement to phenoxyl radical.

    PubMed

    Li, Dan-Dan; Han, Rui-Min; Liang, Ran; Chen, Chang-Hui; Lai, Wenzhen; Zhang, Jian-Ping; Skibsted, Leif H

    2012-06-21

    In the reaction between trans-resveratrol (resveratrol) and the hydroxyl radical, kinetic product control leads to a short-lived hydroxyl radical adduct with an absorption maximum at 420 nm and a lifetime of 0.21 ± 0.01 μs (anaerobic acetonitrile at 25 °C) as shown by laser flash photolysis using N-hydroxypyridine-2(1H)-thione (N-HPT) as a "photo-Fenton" reagent. The transient spectra of the radical adduct are in agreement with density functional theory (DFT) calculations showing an absorption maximum at 442 or 422 nm for C2 and C6 hydroxyl adducts, respectively, and showing the lowest energy for the transition state leading to the C2 adduct compared to other radical products. From this initial product, the relative long-lived 4'-phenoxyl radical of resveratrol (τ = 9.9 ± 0.9 μs) with an absorption maximum at 390 nm is formed in a process with a time constant (τ = 0.21 ± 0.01 μs) similar to the decay constant for the C2 hydroxyl adduct (or a C2/C6 hydroxyl adduct mixture) and in agreement with thermodynamics identifying this product as the most stable resveratrol radical. The hydroxyl radical adduct to phenoxyl radical conversion with concomitant water dissociation has a rate constant of 5 × 10(6) s(-1) and may occur by intramolecular hydrogen atom transfer or by stepwise proton-assisted electron transfer. Photolysis of N-HPT also leads to a thiyl radical which adds to resveratrol in a parallel reaction forming a sulfur radical adduct with a lifetime of 0.28 ± 0.04 μs and an absorption maximum at 483 nm.

  10. Pathways of arachidonic acid peroxyl radical reactions and product formation with guanine radicals.

    PubMed

    Crean, Conor; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-02-01

    Peroxyl radicals were derived from the one-electron oxidation of polyunsaturated fatty acids by sulfate radicals that were generated by the photodissociation of peroxodisulfate anions in air-equilibrated aqueous solutions. Reactions of these peroxyl and neutral guanine radicals, also generated by oxidation with sulfate radicals, were investigated by laser kinetic spectroscopy, and the guanine oxidation products were identified by HPLC and mass spectrometry methods. Sulfate radicals rapidly oxidize arachidonic (ArAc), linoleic (LnAc), and palmitoleic (PmAc) acids with similar rate constants, (2-4) x 10 (9) M (-1) s (-1). The C-centered radicals derived from the oxidation of ArAc and LnAc include nonconjugated Rn(.) ( approximately 80%) and conjugated bis-allylic Rba(.) ( approximately 20%) radicals. The latter were detectable in the absence of oxygen by their prominent, narrow absorption band at 280 nm. The Rn(.) radicals of ArAc (containing three bis-allylic sites) transform to the Rba(.) radicals via an intramolecular H-atom abstraction [rate constant (7.5 +/- 0.7) x 10 (4) s (-1)]. In contrast, the Rn(.) radicals of LnAc that contain only one bis-allylic site do not transform intramolecularly to the Rba(.) radicals. In the case of PmAc, which contains only one double bond, the Rba(.) radicals are not observed. The Rn(.) radicals of PmAc rapidly combine with oxygen with a rate constant of (3.8 +/- 0.4) x 10(9) M(-1) s(-1). The Rba(.) radicals of ArAc are less reactive and react with oxygen with a rate constant of (2.2 +/- 0.2) x 10 (8) M (-1) s (-1). The ArAc peroxyl radicals formed spontaneously eliminate superoxide radical anions [rate constant = (3.4 +/- 0.3) x 10 (4) M (-1) s (-1)]. The stable oxidative lesions derived from the 2',3',5'-tri- O-acetylguanosine or 2',3',5'-tri- O-acetyl-8-oxo-7,8-dihydroguanosine radicals and their subsequent reactions with ArAc peroxyl radicals were also investigated. The major products found were the 2,5-diamino-4 H

  11. Contemporary Radical Economics.

    ERIC Educational Resources Information Center

    Sherman, Howard J.

    1984-01-01

    The origins of contemporary radical economics are examined. Applications of radical economics to price and value theory, labor segmentation theory, business cycles, industrial organization, government and business, imperialism and development, and comparative systems are reviewed. (Author/RM)

  12. Contemporary Radical Economics.

    ERIC Educational Resources Information Center

    Sherman, Howard J.

    1984-01-01

    The origins of contemporary radical economics are examined. Applications of radical economics to price and value theory, labor segmentation theory, business cycles, industrial organization, government and business, imperialism and development, and comparative systems are reviewed. (Author/RM)

  13. Magnetic Trapping of Cold Methyl Radicals

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Vashishta, Manish; Djuricanin, Pavle; Zhou, Sida; Zhong, Wei; Mittertreiner, Tony; Carty, David; Momose, Takamasa

    2017-03-01

    We have demonstrated that a supersonic beam of methyl radicals (CH3 ) in the ground rotational state of both para and ortho species has been slowed down to standstill with a magnetic molecular decelerator, and successfully captured spatially in an anti-Helmholtz magnetic trap for >1 s . The trapped CH3 radicals have a mean translational temperature of about 200 mK with an estimated density of >5.0 ×1 07 cm-3 . The methyl radical is an ideal system for the study of cold molecules not only because of its high reactivities at low temperatures, but also because further cooling below 1 mK is plausible via sympathetic cooling with ultracold atoms. The demonstrated trapping capability of methyl radicals opens up various possibilities for realizing ultracold ensembles of molecules towards Bose-Einstein condensation of polyatomic molecules and investigations of reactions governed by quantum statistics.

  14. Radical prostatectomy - discharge

    MedlinePlus

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

  15. Energy storage possibilities of atomic hydrogen

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Dugan, J. V., Jr.; Palmer, R.

    1976-01-01

    The possibility of storing large amounts of energy in a free radical system such as atomic hydrogen is analyzed. Attention is focused on theoretical calculations of the ground state properties of spin-aligned atomic triplet hydrogen, deuterium, and tritium. The solid-liquid phase transition in atomic hydrogen is also examined.

  16. The radical amplifier

    NASA Technical Reports Server (NTRS)

    Hastie, D. R.

    1994-01-01

    The radical amplifier as a method for measuring radical concentrations in the atmosphere has received renewed attention lately. In principle, it can measure the total concentration of HO(x) and RO(x) radicals by reacting ambient air with high concentrations of CO (3-10 percent) and NO (2-6 ppmv), and measuring the NO2 produced.

  17. Involvement of free radicals in breast cancer.

    PubMed

    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.

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

    EPA Science Inventory

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

    EPA Science Inventory

    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. [Lavoisier and radicals].

    PubMed

    Lafont, Olivier

    2007-01-01

    Lavoisier and his co-workers (Guyton de Morveau, Bertholet, Fourcroy) considered that acids were constituted of oxygen and of something else that they called radicals. These radicals were known in some cases, i.e. nitrogen for nitrous acid, carbon for carbonic acid, phosphorus for phosphoric acid. In the case of sulfur, the sulfuric radical could be associated with different quantities of oxigen leading to sulfuric or sulfurous acids. In other cases radicals remained unknown at the time i.e. muriatic radical for muriatic acid, or benzoyl radical for benzoic acid. It is interesting to notice that Lavoisier evoked the case of compound radicals constituted of different substances such as carbon and hydrogen.

  1. Chemistry of The Oio Radical

    NASA Astrophysics Data System (ADS)

    Joseph, M.; Ashworth, S. H.; Plane, J. M. C.

    This paper will describe a laboratory study of the chemistry that the OIO radical under- goes in the marine boundary layer. The radical was produced by the pulsed photolysis at 193 nm of a N2O/CF3I mixture. The resulting OIO radicals, formed by the self- reaction of IO, were then observed by time-resolved cavity ringdown spectroscopy, using the vibrational bands between 540 and 620 nm. A high resoluting spectral scan found no rotational structure in these bands, indicating that the upper state of this electronic transition is predissociative (lifetime = 150 fs). Ab initio quantum calcula- tions indicate that I + O2 is formed, and this was confirmed by adding a third laser to photolyse OIO as a function of wavelength, with detection of atomic I by resonance fluorescence at 178 nm. This system was also used to measure the absolute absorption cross-section of OIO (1.6 x 10(-17) cm2 at 568 nm). The photodissociation lifetime of OIO is about 0.5 s at midday. Although of minor atmospheric importance, the reac- tions of OIO with NO and OH will also be discussed.

  2. Lewis Structure Representation of Free Radicals Similar to ClO

    ERIC Educational Resources Information Center

    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.

  3. Lewis Structure Representation of Free Radicals Similar to ClO

    ERIC Educational Resources Information Center

    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.

  4. Evidence of radicals created by plasma in bacteria in water

    NASA Astrophysics Data System (ADS)

    Lee, Chae Bok; Na, Young Ho; Hong, Tae-Eun; Choi, Eun Ha; Uhm, Han S.; Baik, Ku Youn; Kwon, Gichung

    2014-08-01

    Heavy water (D2O) was introduced into a non-thermal plasma-jet (NTPJ) device to generate deuterium monoxide (OD) radicals at room temperature. Owing to the similar reactivity and low prevalence of deuterium in nature, OD radicals can be utilized to visualize the OH radical interactions with water and living cells. Escherichia coli in water were treated with OD radicals, and D atom incorporation into cells was visualized using time-of-flight SIMS and Nano-SIMS. The results show that D atoms from NTPJ reach the cytoplasm of E. coli in H2O, indicating the usefulness of this OD-tracking method for the study of radical interactions with living cells.

  5. Evidence of radicals created by plasma in bacteria in water

    SciTech Connect

    Lee, Chae Bok; Na, Young Ho; Hong, Tae-Eun; Choi, Eun Ha; Uhm, Han S.; Baik, Ku Youn E-mail: gckwon@kw.ac.kr; Kwon, Gichung E-mail: gckwon@kw.ac.kr

    2014-08-18

    Heavy water (D{sub 2}O) was introduced into a non-thermal plasma-jet (NTPJ) device to generate deuterium monoxide (OD) radicals at room temperature. Owing to the similar reactivity and low prevalence of deuterium in nature, OD radicals can be utilized to visualize the OH radical interactions with water and living cells. Escherichia coli in water were treated with OD radicals, and D atom incorporation into cells was visualized using time-of-flight SIMS and Nano-SIMS. The results show that D atoms from NTPJ reach the cytoplasm of E. coli in H{sub 2}O, indicating the usefulness of this OD-tracking method for the study of radical interactions with living cells.

  6. Silicon meets cyclotron: muon spin resonance of organosilicon radicals.

    PubMed

    West, Robert; Samedov, Kerim; Percival, Paul W

    2014-07-21

    Muons, generated at a high-powered cyclotron, can capture electrons to form muonium atoms. Muon spin resonance spectra can be recorded for organosilyl radicals obtained by addition of muonium atoms to silylenes and silenes. We present a brief summary of progress in this new area since the first such experiments were reported in 2008.

  7. Trisphenalenyl-based neutral radical molecular conductor.

    PubMed

    Pal, Sushanta K; Itkis, Mikhail E; Tham, Fook S; Reed, Robert W; Oakley, Richard T; Haddon, Robert C

    2008-03-26

    We report the preparation, crystallization, and solid-state characterization of the first member of a new family of tris(1,9-disubstituted phenalenyl)silicon neutral radicals. In the solid state, the radical packs as weak partial pi-dimers with intermolecular carbon...carbon contacts that fall at the van der Waals atomic separation. Magnetic susceptibility measurements indicate approximately 0.7 Curie spins per molecule from room temperature down to 50 K, below which antiferromagnetic coupling becomes apparent; the compound has a room-temperature single-crystal conductivity of sigmaRT = 2.4 x 10(-6) S cm(-1).

  8. Product detection of the CH radical reaction with acetaldehyde.

    PubMed

    Goulay, Fabien; Trevitt, Adam J; Savee, John D; Bouwman, Jordy; Osborn, David L; Taatjes, Craig A; Wilson, Kevin R; Leone, Stephen R

    2012-06-21

    The reaction of the methylidyne radical (CH) with acetaldehyde (CH(3)CHO) is studied at room temperature and at a pressure of 4 Torr (533.3 Pa) using a multiplexed photoionization mass spectrometer coupled to the tunable vacuum ultraviolet synchrotron radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory. The CH radicals are generated by 248 nm multiphoton photolysis of CHBr(3) and react with acetaldehyde in an excess of helium and nitrogen gas flow. Five reaction exit channels are observed corresponding to elimination of methylene (CH(2)), elimination of a formyl radical (HCO), elimination of carbon monoxide (CO), elimination of a methyl radical (CH(3)), and elimination of a hydrogen atom. Analysis of the photoionization yields versus photon energy for the reaction of CH and CD radicals with acetaldehyde and CH radical with partially deuterated acetaldehyde (CD(3)CHO) provides fine details about the reaction mechanism. The CH(2) elimination channel is found to preferentially form the acetyl radical by removal of the aldehydic hydrogen. The insertion of the CH radical into a C-H bond of the methyl group of acetaldehyde is likely to lead to a C(3)H(5)O reaction intermediate that can isomerize by β-hydrogen transfer of the aldehydic hydrogen atom and dissociate to form acrolein + H or ketene + CH(3), which are observed directly. Cycloaddition of the radical onto the carbonyl group is likely to lead to the formation of the observed products, methylketene, methyleneoxirane, and acrolein.

  9. Mobile protons versus mobile radicals: gas-phase unimolecular chemistry of radical cations of cysteine-containing peptides.

    PubMed

    Lam, Adrian K Y; Ryzhov, Victor; O'Hair, Richard A J

    2010-08-01

    A combination of electrospray ionization (ESI), multistage, and high-resolution mass spectrometry experiments are used to examine the gas-phase fragmentation reactions of radical cations of cysteine containing di- and tripeptides. Two different chemical methods were used to form initial populations of radical cations in which the radical sites were located at different positions: (1) sulfur-centered cysteinyl radicals via bond homolysis of protonated S-nitrosocysteine containing peptides; and (2) alpha-carbon backbone-centered radicals via Siu's sequence of reactions (J. Am. Chem. Soc.2008, 130, 7862). Comparison of the fragmentation reactions of these regiospecifically generated radicals suggests that hydrogen atom transfer (HAT) between the alpha C-H of adjacent residues and the cysteinyl radical can occur. In addition, using accurate mass measurements, deuterium labeling, and comparison with an authentic sample, a novel loss of part of the N-terminal cysteine residue was shown to give rise to the protonated, truncated N-formyl peptide (an even-electron x(n) ion). DFT calculations were performed on the radical cation [GCG]*(+) to examine: the relative stabilities of isomers with different radical and protonation sites; the barriers associated with radical migration between four possible radical sites, [G*CG](+), [GC*G](+), [GCG*](+), and [GC(S*)G](+); and for dissociation from these sites to yield b(2)-type ions. Copyright 2010 American Society for Mass Spectrometry. Published by Elsevier Inc. All rights reserved.

  10. Forgotten Radicals in Biology

    PubMed Central

    Luc, Rochette; Vergely, Catherine

    2008-01-01

    Redox reactions play key roles in intra- and inter-cellular signaling, and in adaptative processes of tissues towards stress. Among the major free radicals with essential functions in cells are reactive oxygen species (ROS) including superoxide anion (O2•-), hydroxyl radical (•OH) and reactive nitrogen species (RNS) such as nitric oxide (•NO). In this article, we review the forgotten and new radicals with potential relevance to cardiovascular pathophysiology. Approximately 0.3% of O2•- present in cytosol exists in its protonated form: hydroperoxyl radical (HO2•). Water (H2O) can be split into two free radicals: •OH and hydrogen radical (H•). Several free radicals, including thiyl radicals (RS•) and nitrogen dioxide (NO2•) are known to isomerize double bonds. In the omega-6 series of poly-unsaturated fatty acids (PUFAs), cis-trans isomerization of γ-linolenate and arachidonate catalyzed by RS• has been investigated. Evidence is emerging that hydrogen disulphide (H2S) is a signaling molecule in vivo which can be a source of free radicals. The Cu-Zn superoxide dismutase (SOD) enzyme can oxidize the ionized form of H2S to hydro-sulphide radical: HS•. Recent studies suggest that H2S plays an important function in cardiovascular functions. Carbonate radical, which can be formed when •OH reacts with carbonate or bicarbonate ions, is also involved in the activity of Cu-Zn-SOD. Recently, it has been reported that carbonate anion were potentially relevant oxidants of nucleic acids in physiological environments. In conclusion, there is solid evidence supporting the formation of many free radicals by cells leading which may play an important role in their homeostasis. PMID:23675099

  11. Glycyl radical activating enzymes: structure, mechanism, and substrate interactions.

    PubMed

    Shisler, Krista A; Broderick, Joan B

    2014-03-15

    The glycyl radical enzyme activating enzymes (GRE-AEs) are a group of enzymes that belong to the radical S-adenosylmethionine (SAM) superfamily and utilize a [4Fe-4S] cluster and SAM to catalyze H-atom abstraction from their substrate proteins. GRE-AEs activate homodimeric proteins known as glycyl radical enzymes (GREs) through the production of a glycyl radical. After activation, these GREs catalyze diverse reactions through the production of their own substrate radicals. The GRE-AE pyruvate formate lyase activating enzyme (PFL-AE) is extensively characterized and has provided insights into the active site structure of radical SAM enzymes including GRE-AEs, illustrating the nature of the interactions with their corresponding substrate GREs and external electron donors. This review will highlight research on PFL-AE and will also discuss a few GREs and their respective activating enzymes.

  12. Carbohydrates and their free radical scavenging capability: a theoretical study.

    PubMed

    Hernandez-Marin, Elizabeth; Martínez, Ana

    2012-08-16

    A density functional theory (DFT) study on the free radical (OH(•) and OOH(•)) scavenging properties of some mono- and polysaccharides is presented. Two mechanisms, single electron transfer (SET) and hydrogen atom transfer (HAT), are considered. The former mechanism is studied by making use of the vertical ionization energy and vertical electron affinity of the radicals and carbohydrates. It is confirmed that the SET mechanism is not plausible to occur. With respect to the HAT, not only does the OH(•) radical react preferably with one hydrogen atom bonded to one carbon atom, but also the reaction with a hydrogen atom bonded to an oxygen is possible. Finally, it is suggested that the carbohydrates are not able to directly scavenge OOH(•).

  13. Glutathione – Hydroxyl Radical Interaction: A Theoretical Study on Radical Recognition Process

    PubMed Central

    Fiser, Béla; Jójárt, Balázs; Csizmadia, Imre G.; Viskolcz, Béla

    2013-01-01

    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. PMID:24040010

  14. Glutathione--hydroxyl radical interaction: a theoretical study on radical recognition process.

    PubMed

    Fiser, Béla; Jójárt, Balázs; Csizmadia, Imre G; Viskolcz, Béla

    2013-01-01

    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.

  15. Mechanically controlled radical polymerization initiated by ultrasound

    NASA Astrophysics Data System (ADS)

    Mohapatra, Hemakesh; Kleiman, Maya; Esser-Kahn, Aaron Palmer

    2017-02-01

    In polymer chemistry, mechanical energy degrades polymeric chains. In contrast, in nature, mechanical energy is often used to create new polymers. This mechanically stimulated growth is a key component of the robustness of biological materials. A synthetic system in which mechanical force initiates polymerization will provide similar robustness in polymeric materials. Here we show a polymerization of acrylate monomers initiated and controlled by mechanical energy provided by ultrasonic agitation. The activator for an atom-transfer radical polymerization is generated using piezochemical reduction of a Cu(II) precursor complex, which thus converts a mechanical activation of piezoelectric particles to the synthesis of a new material. This polymerization reaction has some characteristics of controlled radical polymerization, such as narrow molecular-weight distribution and linear dependence of the polymeric chain length on the time of mechanical activation. This new method of controlled radical polymerization complements the existing methods to synthesize commercially useful well-defined polymers.

  16. Mechanically controlled radical polymerization initiated by ultrasound

    NASA Astrophysics Data System (ADS)

    Mohapatra, Hemakesh; Kleiman, Maya; Esser-Kahn, Aaron Palmer

    2016-10-01

    In polymer chemistry, mechanical energy degrades polymeric chains. In contrast, in nature, mechanical energy is often used to create new polymers. This mechanically stimulated growth is a key component of the robustness of biological materials. A synthetic system in which mechanical force initiates polymerization will provide similar robustness in polymeric materials. Here we show a polymerization of acrylate monomers initiated and controlled by mechanical energy provided by ultrasonic agitation. The activator for an atom-transfer radical polymerization is generated using piezochemical reduction of a Cu(II) precursor complex, which thus converts a mechanical activation of piezoelectric particles to the synthesis of a new material. This polymerization reaction has some characteristics of controlled radical polymerization, such as narrow molecular-weight distribution and linear dependence of the polymeric chain length on the time of mechanical activation. This new method of controlled radical polymerization complements the existing methods to synthesize commercially useful well-defined polymers.

  17. Iodine(III) Reagents in Radical Chemistry

    PubMed Central

    2017-01-01

    ) and iodonium salts. In the presence of alkenes as radical acceptors, vicinal trifluoromethyl-, azido-, and arylaminoxylation products result via a sequence comprising radical addition to the alkene and subsequent TEMPO trapping. Electron-rich arenes also react with I(III) reagents via single electron transfer (SET) to give arene radical cations, which can then engage in arylation reactions. We also recognized that the isonitrile functionality in aryl isonitriles is a highly efficient perfluoroalkyl radical acceptor, and reaction of Rf-benziodoxoles (Togni type reagents) in the presence of a radical initiator provides various perfluoroalkylated N-heterocycles (indoles, phenanthridines, quinolines, etc.). We further found that aryliodonium ylides, previously used as carbene precursors in metal-mediated cyclopropanation reactions, react via SET reduction with TEMPONa to the corresponding aryl radicals. As a drawback of all these transformations, we realized that only one ligand of the iodine(III) reagent gets transferred to the substrate. To further increase atom-economy of such conversions, we identified cyano or perfluoroalkyl iodonium triflate salts as valuable reagents for stereoselective vicinal alkyne difunctionalization, where two ligands from the I(III) reagent are sequentially transferred to an alkyne acceptor. Finally, we will discuss alkynyl-benziodoxoles as radical acceptors for alkynylation reactions. Similar reactivity was found for the Zhdankin reagent that has been successfully applied to azidation of C-radicals, and also cyanation is possible with a cyano I(III) reagent. To summarize, this Account focuses on the design, development, mechanistic understanding, and synthetic application of hypervalent iodine(III) reagents in radical chemistry. PMID:28636313

  18. The photodissociation dynamics of alkyl radicals

    SciTech Connect

    Giegerich, Jens; Fischer, Ingo

    2015-01-28

    The photodisscociation dynamics of the alkyl radicals i-propyl (CH(CH{sub 3}){sub 2}) and t-butyl (C(CH{sub 3}){sub 3}) are investigated by H-atom photofragment imaging. While i-propyl is excited at 250 nm, the photodynamics of t-butyl are explored over a large energy range using excitation wavelengths between 347 nm and 233 nm. The results are compared to those obtained previously for ethyl, CH{sub 3}CH{sub 2}, and to those reported for t-butyl using 248 nm excitation. The translational energy (E{sub T}) distribution of the H-atom photofragments is bimodal and appears rather similar for all three radicals. The low E{sub T} part of the distribution shows an isotropic photofragment angular distribution, while the high E{sub T} part is associated with a considerable anisotropy. Thus, for t-butyl, two H-atom loss channels of roughly equal importance have been identified in addition to the CH{sub 3}-loss channel reported previously. A mechanism for the photodissociation of alkyl radicals is suggested that is based on interactions between Rydberg- and valence states.

  19. Radical chemistry of artemisinin

    NASA Astrophysics Data System (ADS)

    Denisov, Evgenii T.; Solodova, S. L.; Denisova, Taisa G.

    2010-12-01

    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.

  20. Hydroaminations of alkenes: a radical, revised, and expanded version.

    PubMed

    Villa, Matteo; Jacobi von Wangelin, Axel

    2015-10-05

    Radical changes: The applicability of alkene hydroamination has recently been significantly expanded by the development of radical variants that are based on initial hydrogen atom transfer to the alkene. This Highlight assesses the current state of the art, focusing on an iron-catalyzed reaction that utilizes stable nitroarenes as the electrophilic N component and is based on the dual catalytic activation of both starting materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Formation and reactivity of vinylperoxyl radicals in aqueous solutions

    SciTech Connect

    Khaikin, G.I.; Neta, P.

    1995-03-30

    Vinyl, carboxyvinyl and dicarboxyvinyl radicals were produced in irradiated aqueous solutions from acetylene and acetylenecarboxylic and acetylenedicarboxylic acid by addition of H atom to the triple bond or by reaction with e{sub aq}{sup -}, followed by protonation. Vinyl and phenylvinyl radicals were produced by reductive dehalogenation of vinyl bromide and {beta}-bromostyrene with e{sub aq}{sup -}. All these vinyl radicals react rapidly with oxygen to produce the corresponding vinylperoxyl radicals. Vinylperoxyl radicals exhibit optical absorptions in the UV ({lambda}{sub max} 250-290 nm) and in the visible range. The peaks in the visible range were at 440 nm for unsubstituted vinylperoxyl radical, between 480 and 520 nm for carboxylated vinylperoxyl, depending on pH and number of carboxyl groups, and at 540 and 690 nm for (2-phenylvinyl)peroxyl. These vinylperoxyl radicals oxidize organic reductants such as 2,2`azinobis(3-ethylbenzothiazoline-6-sulfonate ion) (ABTS), chlorpromazine, ascorbate, and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox C) with rate constants between 4 x 10{sup 5} and 2 x 10{sup 9} L mol{sup -1} s{sup -1}, depending on the radical and the reductant. Vinylperoxyl radicals are more reactive than similarly substituted alkylperoxyl. 20 refs., 5 figs., 1 tab.

  2. Online Radicalization: Bangladesh Perspective

    DTIC Science & Technology

    2017-06-09

    will work on developing a sustainable social awareness against radicalization. It will be responsible for coordinating and integrating all government...PAGE Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response , including...coordination among the counter-terrorism agencies, and lack of positive initiatives to grow enduring social resilience against radicalization. Bangladesh

  3. Formation and reactivity of carboxyphenyl radicals in aqueous solution

    NASA Astrophysics Data System (ADS)

    Janković, Ivana A.; Josimović, Ljubica R.; Jovanović, Slobodan V.

    1998-03-01

    Carboxyphenyl radicals were generated in aqueous solutions by reacting the solvated electron with ortho-, meta- and para-chlorobenzoate. These radicals were found to add to chlorobenzoates and abstract hydrogen atoms from a H-atom donor. It was concluded that the rate constants for the addition of carboxyphenyl radicals to chlorobenzoate depend on steric hindrance, since ortho-carboxyphenyl radical adds to 2-chlorobenzoate [ kadd=(1.0±0.2)×10 6 dm 3 mol -1 s -1] an order of magnitude slower than para-carboxyphenyl radical to 4-chlorobenzoate [ kadd=(1.0±0.2)×10 7 dm 3 mol -1 s -1]. The products of these addition reactions were detected by GC-MS. All three carboxyphenyl radical isomers abstract a H-atom from 4-methoxybenzen thiol at the same rate [ kH-aps˜1×10 9 dm 3 mol -1 s -1], i.e. the position of the carboxylate group seems not to influence the rate of the H-abstraction reaction.

  4. Reactions of methyl and ethyl radicals with uranium hexafluoride

    NASA Astrophysics Data System (ADS)

    Lyman, John L.; Laguna, Glenn

    1985-01-01

    We have measured the rates of reaction of both methyl and ethyl radicals with uranium hexafluoride (UF6) in the gas phase. The method we used was to photolyze samples of UF6 in the presence of either methane or ethane. The radicals produced by reaction of fluorine atoms with these species then react with either themselves or with UF6. We inferred the rate constants from ratios of the reaction products and the published rate constants for radical recombination. The diagnostic technique was gas chromatography. The resulting rate constants for reaction with UF6 were (1.6±0.8)×10-14 cm3 molecule-1 s-1 for methyl radicals and (4±2)×10-11 cm3 molecule-1 s-1 for ethyl radicals.

  5. Atomic gravitational wave interferometric sensor

    SciTech Connect

    Dimopoulos, Savas; Hogan, Jason M.; Kasevich, Mark A.; Graham, Peter W.; Rajendran, Surjeet

    2008-12-15

    We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite based, utilizing the core technology of the Stanford 10 m 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 two {approx}10 m atom interferometers separated by a {approx}1 km baseline 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 two atom interferometers separated by a {approx}1000 km baseline 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 and 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.

  6. Transverse flow reactor studies of the dynamics of radical reactions

    SciTech Connect

    Macdonald, R.G.

    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.

  7. Radical-mediated adsorption: Ozone oxidation of passivated silicon

    NASA Astrophysics Data System (ADS)

    Fink, Christian K.; Jenkins, Stephen J.

    2008-07-01

    We report first-principles molecular dynamics calculations on the initial oxidation of hydrogen-passivated Si{0 0 1} by ozone (O 3). We observe an intriguing radical-mediated adsorption mechanism, archetypal of a class not reported in the literature so far. Singlet ozone abstracts one hydrogen atom to form a short-lived hydrotrioxy radical (HO3rad ), before dissociating into surface hydroxyl ( sbnd OH) and gas-phase O 2. Vibrational and electronic analysis of the hydrotrioxy species confirms the genuine radical nature of the reaction intermediate.

  8. Photo-induced free radicals on a simulated Martian surface

    NASA Technical Reports Server (NTRS)

    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.

  9. Ultraviolet Photodissociation Dynamics of the 3-CYCLOHEXENYL Radical

    NASA Astrophysics Data System (ADS)

    Lucas, Michael; Liu, Yanlin; Bryant, Raquel; Minor, Jasmine; Zhang, Jingsong

    2014-06-01

    The ultraviolet (UV) photodissociation dynamics of the cyclohexenyl radical (c-C_6H_9) was studied for the first time in the photolysis region of 232-262 nm using the high-n Rydberg atom time-of-flight (HRTOF) technique. The cyclohexenyl radical was produced by the 193 nm photodissociation of 3-chlorocyclohexene and 3-bromocyclohexene. The H-atom photofragment yield (PFY) spectrum contains a broad peak centering around 250 nm, in good agreement with the UV absorption spectra of the 2B1 ← 2A2 transition in cyclohexenyl. The translational energy distributions of the H-atom loss product channel, P(ET)'s, for cyclohexenyl show a modest translational energy release peak at ˜ 10 kcal/mol. The fraction of average translational energy in the total excess energy, , is ˜ 0.16 from 232-262 nm. The H-atom product angular distribution is isotropic with a β parameter ˜ 0. The dissociation mechanism is a statistical unimolecular dissociation of a hot radical following internal conversion from the excited electronic state to produce the lowest energy product, H + cyclohexadiene. The dissociation mechanisms of the cyclohexenyl radical and cyclohexyl radical will be compared.

  10. Ultraviolet photodissociation dynamics of the phenyl radical

    SciTech Connect

    Song Yu; Lucas, Michael; Alcaraz, Maria; Zhang Jingsong; Brazier, Christopher

    2012-01-28

    Ultraviolet (UV) photodissociation dynamics of jet-cooled phenyl radicals (C{sub 6}H{sub 5} and C{sub 6}D{sub 5}) are studied in the photolysis wavelength region of 215-268 nm using high-n Rydberg atom time-of-flight and resonance enhanced multiphoton ionization techniques. The phenyl radicals are produced from 193-nm photolysis of chlorobenzene and bromobenzene precursors. The H-atom photofragment yield spectra have a broad peak centered around 235 nm and are in good agreement with the UV absorption spectra of phenyl. The H + C{sub 6}H{sub 4} product translational energy distributions, P(E{sub T})'s, peak near {approx}7 kcal/mol, and the fraction of average translational energy in the total excess energy, , is in the range of 0.20-0.35 from 215 to 268 nm. The H-atom product angular distribution is isotropic. The dissociation rates are in the range of 10{sup 7}-10{sup 8} s{sup -1} with internal energy from 30 to 46 kcal/mol above the threshold of the lowest energy channel H +o-C{sub 6}H{sub 4} (ortho-benzyne), comparable with the rates from the Rice-Ramsperger-Kassel-Marcus theory. The results from the fully deuterated phenyl radical are identical. The dissociation mechanism is consistent with production of H +o-C{sub 6}H{sub 4}, as the main channel from unimolecular decomposition of the ground electronic state phenyl radical following internal conversion of the electronically excited state.

  11. Free Radical Reactions in Food.

    ERIC Educational Resources Information Center

    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…

  12. Free Radical Reactions in Food.

    ERIC Educational Resources Information Center

    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…

  13. Chemistry of ascorbic acid radicals

    SciTech Connect

    Bielski, B.H.J.

    1982-01-01

    The chemistry of ascorbic acid free radicals is reviewed. Particular emphasis is placed on identification and characterization of ascorbate radicals by spectrophotometric and electron paramagnetic resonance techniques, the kinetics of formation and disappearance of ascorbate free radicals in enzymatic and nonenzymatic reactions, the effect of pH upon the spectral and kinetic properties of ascorbate anion radical, and chemical reactivity of ascorbate free radicals.

  14. Nitrene Radical Intermediates in Catalytic Synthesis.

    PubMed

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

    2017-07-04

    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 application 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. RSO2N3, (RO)2P(=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 synthetically useful 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 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Laparoscopic radical trachelectomy.

    PubMed

    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.

  16. Laparoscopic Radical Trachelectomy

    PubMed Central

    Rendón, Gabriel J.; Ramirez, Pedro T.; Frumovitz, Michael; Schmeler, Kathleen M.

    2012-01-01

    Introduction: 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. Case Description: 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. Conclusion: 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. PMID:23318085

  17. Free Radical-Surface Interactions Using Multiphoton Ionization of Free Radicals

    DTIC Science & Technology

    1989-01-01

    Atoms, Rgf4PI 9 t Free Radl!cals)aj"i Atoms, Cross Section -’ r RE)*I of Free Radicals arid Atonn. 𔄃 43S’RACT (Conti n reverse if necessary Ind identi...Phy’s 71,2682f 19’q molecules,3 whereas the etch probability on a fluorinated ’M. T . Duignan, J. W. Hudgens, and J. R Wyatt, 1. Phys. Chem 86, 4156 (1982...80. (15) Kerr, J. A.; Wright. J. P. J Chem. Soc., Faraday Trans. 1 1915. 81. (17) Adams. T . E.; Morrtson. R J S.; Grant, E R Rev Sci Instrum 1471. 1980

  18. Mechanistic Enzymology of the Radical SAM Enzyme DesII.

    PubMed

    Ruszczycky, Mark W; Liu, Hung-Wen

    2015-04-01

    DesII is a member of the radical SAM family of enzymes that catalyzes radical-mediated transformations of TDP-4-amino-4,6-didexoy-D-glucose as well as other sugar nucleotide diphosphates. Like nearly all radical SAM enzymes, the reactions begin with the reductive homolysis of SAM to produce a 5'-deoxyadenosyl radical which is followed by regiospecific hydrogen atom abstraction from the substrate. What happens next, however, depends on the nature of the substrate radical so produced. In the case of the biosynthetically relevant substrate, a radical-mediated deamination ensues; however, when this amino group is replaced with a hydroxyl, one instead observes dehydrogenation. The factors that govern the fate of the initially generated substrate radical as well as the mechanistic details underlying these transformations have been a key focus of research into the chemistry of DesII. This review will discuss recent discoveries pertaining to the enzymology of DesII, how it may relate to understanding other radical-mediated lyases and dehydrogenases and the working hypotheses currently being investigated regarding the mechanism of DesII catalysis.

  19. A fluorine 1,2-migration via aryl cation/radical/radical anion/radical sequence.

    PubMed

    Pretali, Luca; Dondi, Daniele; D'Angelantonio, Mila; Manet, Ilse; Fasani, Elisa; Monti, Sandra; Bovio, Bruna; Albini, Angelo

    2013-08-02

    Irradiation of a 7-piperazino-8-fluoroquinolone causes formal 1,2-fluorine migration, piperazine loss and reduction, or nucleophile addition in 8. Product study, laser flash photolysis, and computational modeling support F(-) detachment to yield a triplet 8-quinolyl cation that either inserts intramolecularly or is trapped by Cl(-), Br(-). However, iodide and pyrrole reduce it to the radical that continues the 'redox tour' (aryl cation→ radical→ radical anion→ radical and then again radical or radical anion) leading to the rearranged products.

  20. Radical dematerialization and degrowth.

    PubMed

    Kallis, Giorgos

    2017-06-13

    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'. © 2017 The Author(s).

  1. Radical dematerialization and degrowth

    NASA Astrophysics Data System (ADS)

    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'.

  2. Structures and energies of the radicals and anions generated from chlorpyrifos.

    PubMed

    Zhang, Yi; Liu, Chang-Zhong; Li, Xiao-Jun; Wang, Zi-Liang; Zhang, Hai-Tang; Miao, Zhi-Guo

    2010-08-01

    The radicals and anions generated from chlorpyrifos by removing a hydrogen atom have been investigated using the hybrid density functional B3PW91 method. The results show that all the radicals have been classified as three groups and their stability order is methylene (radical 1, 3, 5, and 7) > methyl (radical 9, 11 and 13) > ring (15); the anions have the relative energetic order: methyl > methylene > ring. Moreover, some decomposition reactions are also reported. The large HOMO-LUMO gaps indicate that both radicals and anions are predicted to be high-kinetic stable molecules. We also find that radicals 9, 11 and 13 have the highest AEAs and anions 2, 4 and 6 have higher VDEs. Additionally, natural population analysis charges show that there is the lowest Deltaq (0.14) for the C7 and C9 atoms. We hope that our theoretical results may provide a reference for further experiment and practical application.

  3. The Reaction of Acetyl Peroxy Radical with Aldehyde: Impact on the OH Radical Model Simulation

    NASA Astrophysics Data System (ADS)

    Huang, D.; Chen, Z.

    2014-12-01

    Understanding the budget of OH (hydroxyl radical) is very important for investigating the atmospheric oxidation capacity, aerosol formation and climate change. Recent studies indicate that there may be a great gap between the modeled and measured OH concentrations in some rural forest areas. This gap may result from our incomplete knowledge about the oxidation mechanism of volatile organic compounds (VOCs). Here, we suggest that acetyl peroxy radical (CH3C(O)OO•), the OH-initiated oxidation intermediate of most VOCs, can take the H-atom from the aldehyde group to form corresponding peroxy carboxylic acids. This reaction has not been concerned in the atmosphere. The acetyl peroxy radical may share the "oxidation responsibility" of OH, and help saving OH from being consumed by aldehyde. Using a box model coupled with the isoprene-OH reaction mechanism selected from MCM v3.2, we get OH saving ratio (SROH) when we compare the modeled OH levels in the presence and absence of the reaction of acetyl peroxy radical with aldehyde. We find that SROH is not a constant but a function of OH production rate, reaction time, isoprene concentration and the ratio of aldehyde to isoprene. It is expected that CH3C(O)OO• radical, a non-OH oxidant, plays an important role in maintaining the oxidation capacity of the troposphere.

  4. Atomic polarizabilities

    SciTech Connect

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    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.

  5. Resonant cavity spectroscopy of radical species

    NASA Astrophysics Data System (ADS)

    Ritchie, Grant

    2015-04-01

    Photo-oxidation in the troposphere is highly complex, being initiated by short lived radical species, in the daytime dominated by the hydroxyl radical, OH, with contributions from Cl atoms, and at night by either NO3 radicals or ozone. Chemical oxidation cycles, which couple OH, HO2 and peroxy (RO2) radical species, remove primary emitted trace species which are harmful to humans or to the wider environment. However, many of the secondary products produced by atmospheric photo-oxidation are also directly harmful, for example O3, NO2, acidic and multifunctional species, many of which are of low volatility and are able to partition effectively to the condensed phase, creating secondary organic aerosol (SOA), which contributes a significant fraction of tropospheric aerosol, with associated impacts on climate and human health. The accuracy of atmospheric models to predict these impacts necessarily requires accurate knowledge of the chemical oxidative cycling. Two of the simplest intermediates are the hydroperoxy radical, HO2, and the smallest and dominant organic peroxy radical, CH3O2, formed directly by the reactions of OH with CO/O2 and CH4/O2, respectively, and indirectly following the oxidation of larger VOCs. OH, HO2 and RO2 (collectively known as ROx) are rapidly cycled, being at the centre of tropospheric oxidation, and hence are some of the best targets for models to compare with field data. The reaction of HO2 and RO2 with NO constitutes the only tropospheric in-situ source of O3. Despite their importance, neither HO2 nor CH3O2 is measured directly in the atmosphere. HO2 is only measured indirectly following its conversion to OH and CH3O2 is not measured at all. Typically only the sum of RO2 radicals is measured, making no distinction between different organic peroxy radicals. This contribution will detail recent studies using (i) optical feedback cavity enhanced absorption spectroscopy with both quantum and inter-band cascade lasers in the mid-IR, and (ii

  6. Beyond Radical Educational Cynicism.

    ERIC Educational Resources Information Center

    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.…

  7. Radical School Reform.

    ERIC Educational Resources Information Center

    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…

  8. Against Radical Multiculturalism.

    ERIC Educational Resources Information Center

    Zorn, Jeff

    This essay presents two strands of arguments against radical or critical emancipatory multiculturalism. In strand 1, "'Culture' is...whatever..." the looseness of the core concept of "culture," which can refer to anything at all concerning a social group that itself may exist only theoretically, is shown. In strand 2, "From ideology to leveling,…

  9. Beyond Radical Educational Cynicism.

    ERIC Educational Resources Information Center

    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.…

  10. Radically enhanced molecular recognition

    NASA Astrophysics Data System (ADS)

    Trabolsi, Ali; Khashab, Niveen; Fahrenbach, Albert C.; Friedman, Douglas C.; Colvin, Michael T.; Cotí, Karla K.; Benítez, Diego; Tkatchouk, Ekaterina; Olsen, John-Carl; Belowich, Matthew E.; Carmielli, Raanan; Khatib, Hussam A.; Goddard, William A.; Wasielewski, Michael R.; Stoddart, J. Fraser

    2010-01-01

    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.

  11. Radical Socioeducational Analysis.

    ERIC Educational Resources Information Center

    Sigmon, Scott B.

    This book describes an interactive-interdisciplinary way of looking at the social conditions which impinge upon schooling, and which impact upon the social facts of life. It examines current schooling problems from the perspective of radical social democratic thought. The book is organized into four major sections. Part 1 provides an overview and…

  12. The Oxonium Rydberg Radical

    NASA Astrophysics Data System (ADS)

    Lavín, C.; Martin, I.

    The Quantum Defect Orbital (QDO) method has been applied to the study of transition probabiUties in the oxonium Rydberg radical H3O. Absorption oscillator strengths and Einstein emission coefficients are reported and compared with the results of an earlier, simplified, molecular version of QDO method.

  13. Interrogating Hydrocarbon Radicals

    NASA Astrophysics Data System (ADS)

    Schmidt, Timothy W.

    2010-06-01

    Motivated by astrophysical problems (and a sense of fun) for some years my research group has been obtaining new spectra of hitherto unobserved hydrocarbon radicals. We employ the complementary techniques of resonant ionization and laser induced fluorescence to rigorously identify radicals by matching their ground state vibrational frequencies to those obtained using density functional theory (DFT). While some radicals were made to order in our pulsed electrical discharge source, others of particular chemical importance have been found lurking in the congested forest of dicarbon and tricarbon fluorescence. Using a 2-dimensional fluorescence (2df) map, we have extracted pure spectra, unpolluted by C_2 and C_3, from a benzene discharge. One spectrum was first presented at this symposium in 2006, but at that stage was not identified. Subsequent measurement of a matching resonant ionization spectrum revealed a mass of 115, much higher than the benzene precursor. With the aid of DFT calculations, the species was positively identified, giving clues to hydrocarbon-building chemistry of relevance to combustion; planetary atmospheres; and the interstellar and circumstellar space. Further experiments revealed other surprising additions to the radical zoo, also identified with the help of 2df. Along the way we have also identified two new band systems of C_2, the first involving the hidden c^3Σ_u^+ state, and have ventured into the world of larger molecules, such as hexabenzocoronene, C42H18.

  14. Effect of venlafaxine on scavenging free radicals in vitro.

    PubMed

    Plachá, Katerina; Valachová, Katarína; Rapta, Peter; Topol'ská, Dominika; Melichercíková, Kristína; Soltés, Ladislav

    2016-01-01

    O BJECTIVE: Venlafaxine (VLF) was examined as a potential donor of H atom(s) to scavenge hydroxyl and peroxy-type radicals generated under aerobic conditions by catalytic oxidation of ascorbate with Cu²⁺ ions. Kinetics of the electron-donor property of VLF was investigated by standard ABTS and DPPH assays. Electron paramagnetic resonance measurements were applied to prove/disprove the VLF ability to scavenge superoxide anion radical. Results indicated that the drug venlafaxine was slightly capable of donating ·H, this way VLF scavenged the in situ generated hydroxyl radicals. Under the experimental conditions VLF was not able to inhibit/retard the propagation of the peroxy-type radicals. Regarding to the drug electron donating property, VLF did not show any ABTS·⁺ or DPPH· radical quenching property. Venlafaxine was not effective in scavenging O2·⁻. Results of ABTS and DPPH assay showed a negligible redox activity of venlafaxine to both DPPH· and ABTS·⁺. Venlafaxine was not capable of scavenging the superoxide anion radical generated in KO₂/DMSO system, which indicates that VLF is not an efficient electron/proton donor molecule.

  15. Auxiliary iron-sulfur cofactors in radical SAM enzymes.

    PubMed

    Lanz, Nicholas D; Booker, Squire J

    2015-06-01

    A vast number of enzymes are now known to belong to a superfamily known as radical SAM, which all contain a [4Fe-4S] cluster ligated by three cysteine residues. The remaining, unligated, iron ion of the cluster binds in contact with the α-amino and α-carboxylate groups of S-adenosyl-l-methionine (SAM). This binding mode facilitates inner-sphere electron transfer from the reduced form of the cluster into the sulfur atom of SAM, resulting in a reductive cleavage of SAM to methionine and a 5'-deoxyadenosyl radical. The 5'-deoxyadenosyl radical then abstracts a target substrate hydrogen atom, initiating a wide variety of radical-based transformations. A subset of radical SAM enzymes contains one or more additional iron-sulfur clusters that are required for the reactions they catalyze. However, outside of a subset of sulfur insertion reactions, very little is known about the roles of these additional clusters. This review will highlight the most recent advances in the identification and characterization of radical SAM enzymes that harbor auxiliary iron-sulfur clusters. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases. Copyright © 2015 Elsevier B.V. All rights reserved.

  16. Tyrosyl Radicals in Dehaloperoxidase

    PubMed Central

    Dumarieh, Rania; D'Antonio, Jennifer; Deliz-Liang, Alexandria; Smirnova, Tatyana; Svistunenko, Dimitri A.; Ghiladi, Reza A.

    2013-01-01

    Dehaloperoxidase (DHP) from Amphitrite ornata, having been shown to catalyze the hydrogen peroxide-dependent oxidation of trihalophenols to dihaloquinones, is the first oxygen binding globin that possesses a biologically relevant peroxidase activity. The catalytically competent species in DHP appears to be Compound ES, a reactive intermediate that contains both a ferryl heme and a tyrosyl radical. By simulating the EPR spectra of DHP activated by H2O2, Thompson et al. (Thompson, M. K., Franzen, S., Ghiladi, R. A., Reeder, B. J., and Svistunenko, D. A. (2010) J. Am. Chem. Soc. 132, 17501–17510) proposed that two different radicals, depending on the pH, are formed, one located on either Tyr-34 or Tyr-28 and the other on Tyr-38. To provide additional support for these simulation-based assignments and to deduce the role(s) that tyrosyl radicals play in DHP, stopped-flow UV-visible and rapid-freeze-quench EPR spectroscopic methods were employed to study radical formation in DHP when three tyrosine residues, Tyr-28, Tyr-34, and Tyr-38, were replaced either individually or in combination with phenylalanines. The results indicate that radicals form on all three tyrosines in DHP. Evidence for the formation of DHP Compound I in several tyrosine mutants was obtained. Variants that formed Compound I showed an increase in the catalytic rate for substrate oxidation but also an increase in heme bleaching, suggesting that the tyrosines are necessary for protecting the enzyme from oxidizing itself. This protective role of tyrosines is likely an evolutionary adaptation allowing DHP to avoid self-inflicted damage in the oxidative environment. PMID:24100039

  17. Radicals in ionic liquids.

    PubMed

    Strehmel, Veronika

    2012-05-14

    Stable radicals and recombination of photogenerated lophyl radicals are investigated in ionic liquids. The 2,2,6,6-tetramethylpiperidine-1-yloxyl derivatives contain various substituents at the 4-position to the nitroxyl group, including hydrogen-bond-forming or ionic substituents that undergo additional interactions with the individual ions of the ionic liquids. Some of these spin probes contain similar ions to ionic liquids to avoid counter-ion exchange with the ionic liquid. Depending on the ionic liquid anion, the Stokes-Einstein theory or the Spernol-Gierer-Wirtz theory can be applied to describe the temperature dependence of the average rotational correlation time of the spin probe in the ionic liquids. Furthermore, the spin probes give information about the micropolarity of the ionic liquids. In this context the substituent at the 4-position to the nitroxyl group plays a significant role. Covalent bonding of a spin probe to the imidazolium ion results in bulky spin probes that are strongly immobilized in the ionic liquid. Furthermore, lophyl radical recombination in the dark, which is chosen to understand the dynamics of bimolecular reactions in ionic liquids, shows a slow process at longer timescale and a rise time at a shorter timescale. Although various reactions may contribute to the slower process during lophyl radical recombination, it follows a second-order kinetics that does not clearly show solvent viscosity dependence. However, the rise time, which may be attributed to radical pair formation, increases with increasing solvent viscosity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Biotin synthase: insights into radical-mediated carbon-sulfur bond formation.

    PubMed

    Fugate, Corey J; Jarrett, Joseph T

    2012-11-01

    The enzyme cofactor and essential vitamin biotin is biosynthesized in bacteria, fungi, and plants through a pathway that culminates with the addition of a sulfur atom to generate the five-membered thiophane ring. The immediate precursor, dethiobiotin, has methylene and methyl groups at the C6 and C9 positions, respectively, and formation of a thioether bridging these carbon atoms requires cleavage of unactivated CH bonds. Biotin synthase is an S-adenosyl-l-methionine (SAM or AdoMet) radical enzyme that catalyzes reduction of the AdoMet sulfonium to produce 5'-deoxyadenosyl radicals, high-energy carbon radicals that can directly abstract hydrogen atoms from dethiobiotin. The available experimental and structural data suggest that a [2Fe-2S](2+) cluster bound deep within biotin synthase provides a sulfur atom that is added to dethiobiotin in a stepwise reaction, first at the C9 position to generate 9-mercaptodethiobiotin, and then at the C6 position to close the thiophane ring. The formation of sulfur-containing biomolecules through a radical reaction involving an iron-sulfur cluster is an unprecedented reaction in biochemistry; however, recent enzyme discoveries suggest that radical sulfur insertion reactions may be a distinct subgroup within the burgeoning Radical SAM superfamily. This article is part of a Special Issue entitled: Radical SAM enzymes and Radical Enzymology.

  19. A Mechanism of Formation of Radicals in Crystal KDP (KH2PO4)

    NASA Astrophysics Data System (ADS)

    Koketai, Temirgaly; Tagayeva, Batima; Tussupbekova, Ainura; Mussenova, Elmira

    The mechanisms of formation of A-radicals in the crystal K2SO4. Calculations established that the excitation of oscillations on the O-H bond in the triplet excitons in the excited state leads to a situation vibronic instability leading to the disintegration of the exciton with the formation of hydrogen atoms and A- radical.

  20. Dissociation of the Ethyl Radical: An Exercise in Computational Chemistry

    ERIC Educational Resources Information Center

    Nassabeh, Nahal; Tran, Mark; Fleming, Patrick E.

    2014-01-01

    A set of exercises for use in a typical physical chemistry laboratory course are described, modeling the unimolecular dissociation of the ethyl radical to form ethylene and atomic hydrogen. Students analyze the computational results both qualitatively and quantitatively. Qualitative structural changes are compared to approximate predicted values…

  1. Dissociation of the Ethyl Radical: An Exercise in Computational Chemistry

    ERIC Educational Resources Information Center

    Nassabeh, Nahal; Tran, Mark; Fleming, Patrick E.

    2014-01-01

    A set of exercises for use in a typical physical chemistry laboratory course are described, modeling the unimolecular dissociation of the ethyl radical to form ethylene and atomic hydrogen. Students analyze the computational results both qualitatively and quantitatively. Qualitative structural changes are compared to approximate predicted values…

  2. Current status of free radicals and electronically excited metastable species as high energy propellants

    NASA Technical Reports Server (NTRS)

    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.

  3. A Radical Transfer Pathway in Spore Photoproduct Lyase

    PubMed Central

    Yang, Linlin; Nelson, Renae S.; Benjdia, Alhosna; Lin, Gengjie; Telser, Joshua; Stoll, Stefan; Schlichting, Ilme; Li, Lei

    2013-01-01

    Spore photoproduct lyase (SPL) repairs a covalent UV-induced thymine dimer, spore photoproduct (SP), in germinating endospores and is responsible for endospores’ strong UV resistance. SPL is a radical SAM enzyme, which uses a [4Fe-4S]1+ cluster to reduce the S-adenosyl-L-methionine (SAM), generating a catalytic 5′-deoxyadenosyl radical (5′-dA•). This in turn abstracts an H atom from SP, generating an SP radical that undergoes β scission to form a repaired 5′-thymine and a 3′-thymine allylic radical. Recent biochemical and structural data suggest that a conserved cysteine donates an H atom to the thymine radical, resulting in a putative thiyl radical. Here we present structural and biochemical data which suggest that two conserved tyrosines are also critical in enzyme catalysis. One (Y99(Bs) in Bacillus subtilis SPL) is downstream of the cysteine, suggesting that SPL uses a novel hydrogen atom transfer (HAT) pathway with a pair of cysteine-tyrosine residues to regenerate SAM. The other tyrosine (Y97(Bs)) has a structural role to facilitate SAM binding; it may also contribute to the SAM regeneration process by interacting with the putative •Y99(Bs) and/or 5′-dA• intermediates to lower the energy barrier for the second H-abstraction step. Our results indicate that SPL is the first member of the radical SAM superfamily (comprising more than 44,000 members) to bear a catalytically operating HAT chain. PMID:23607538

  4. Laser Studies of Gas Phase Radical Reaction.

    DTIC Science & Technology

    1985-11-30

    1nai Irvest-aator Or.G. Hancock gn; FILE CO, Contr3ctor : Oxford University . Physical Chemistry Laboratory. South Parks Road.AD-A 193 689 Oxfor o~d...HIF spectrum and study of reaction of this and the CCI radical with atoms vi) sea;rchtrr; f(r FC) ’ndlict of the 0 *CF, reaction. OXFORD UNIVERSITY -. - SOUTH...0 Awtilability Codes I Avail ’and/or Dis Spcal0 Spoo OXFORD UNIVERSITY Tt SOUTH PARKS ROAD OXFCRD OXFORD � X3Z U.S. Army Contract DAJA45-85-C-0034

  5. A new stable perfluoroalkyl radical

    SciTech Connect

    Allayarov, S.R.; Barkalov, I.M.; Mikhailov, A.I.

    1986-01-01

    This paper uses ESR spectroscopy to study the radical formed upon the gamma-irradiation of liquid perfluoro-methyl-2-pentene (PMP). The ESR spectrum of this radical shows a well resolved doublet of triplets with splitting 6.2 and 1.5 mT with additional splitting of each component by 0.25 mT. This ESR corresponds to a radical formed upon the addition of a radical r, in particlular, CF/sub 3/ to PMP.

  6. Stabilization of Two Radicals with One Metal: A Stepwise Coupling Model for Copper-Catalyzed Radical–Radical Cross-Coupling

    NASA Astrophysics Data System (ADS)

    Qi, Xiaotian; Zhu, Lei; Bai, Ruopeng; Lan, Yu

    2017-03-01

    Transition metal-catalyzed radical–radical cross-coupling reactions provide innovative methods for C–C and C–heteroatom bond construction. A theoretical study was performed to reveal the mechanism and selectivity of the copper-catalyzed C–N radical–radical cross-coupling reaction. The concerted coupling pathway, in which a C–N bond is formed through the direct nucleophilic addition of a carbon radical to the nitrogen atom of the Cu(II)–N species, is demonstrated to be kinetically unfavorable. The stepwise coupling pathway, which involves the combination of a carbon radical with a Cu(II)–N species before C–N bond formation, is shown to be probable. Both the Mulliken atomic spin density distribution and frontier molecular orbital analysis on the Cu(II)–N intermediate show that the Cu site is more reactive than that of N; thus, the carbon radical preferentially react with the metal center. The chemoselectivity of the cross-coupling is also explained by the differences in electron compatibility of the carbon radical, the nitrogen radical and the Cu(II)–N intermediate. The higher activation free energy for N–N radical–radical homo-coupling is attributed to the mismatch of Cu(II)–N species with the nitrogen radical because the electrophilicity for both is strong.

  7. Stabilization of Two Radicals with One Metal: A Stepwise Coupling Model for Copper-Catalyzed Radical–Radical Cross-Coupling

    PubMed Central

    Qi, Xiaotian; Zhu, Lei; Bai, Ruopeng; Lan, Yu

    2017-01-01

    Transition metal-catalyzed radical–radical cross-coupling reactions provide innovative methods for C–C and C–heteroatom bond construction. A theoretical study was performed to reveal the mechanism and selectivity of the copper-catalyzed C–N radical–radical cross-coupling reaction. The concerted coupling pathway, in which a C–N bond is formed through the direct nucleophilic addition of a carbon radical to the nitrogen atom of the Cu(II)–N species, is demonstrated to be kinetically unfavorable. The stepwise coupling pathway, which involves the combination of a carbon radical with a Cu(II)–N species before C–N bond formation, is shown to be probable. Both the Mulliken atomic spin density distribution and frontier molecular orbital analysis on the Cu(II)–N intermediate show that the Cu site is more reactive than that of N; thus, the carbon radical preferentially react with the metal center. The chemoselectivity of the cross-coupling is also explained by the differences in electron compatibility of the carbon radical, the nitrogen radical and the Cu(II)–N intermediate. The higher activation free energy for N–N radical–radical homo-coupling is attributed to the mismatch of Cu(II)–N species with the nitrogen radical because the electrophilicity for both is strong. PMID:28272407

  8. Toward Radicalizing Community Service Learning

    ERIC Educational Resources Information Center

    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…

  9. Toward Radicalizing Community Service Learning

    ERIC Educational Resources Information Center

    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…

  10. Spectroscopy of Benzyl-Type Radicals Generated by Electric Discharge : Jet-Cooled Dichlorobenzyl Radicals

    NASA Astrophysics Data System (ADS)

    Yoon, Young Wook; Lee, Sang Kuk

    2013-06-01

    The technique of corona excited supersonic expansion coupled with a pinhole-type glass nozzle has been proved a useful laser-free spectroscopic tool for observation of vibronic emission spectra of large aromatic molecules, especially for molecular radicals which are long believed to play an important role as a reaction intermediate in aromatic chemical reactions. The vibronic emission spectra recorded with a long-path monochromator exhibit the electronic transition energy in the D_1 → D_0 transition and vibrational mode frequencies at the D_0 state. In this laboratory, all six isomeric dichlorobenzyl radicals have been produced from the corona discharge of corresponding dichlorotoluenes seeded in a large amount of inert carrier gas He. The vibronic emission spectra show very weak intensity due to the existence of Cl atoms in the precursor molecules and possible breakdown of benzene ring by free Cl atoms. Nevertheless, we clearly identified the origin band and a few well-known vibrational modes for each isomer. From an analysis of the spectra observed, we determined the energy of electronic transition and several vibrational modes in the ground electronic state. Also, the red-shift of the origin band from the parental benzyl radical clearly shows the substituent effect of Cl atoms on electronic energy, for which we satisfactorily explain in terms of the shape of the molecular planes and position of the nodal points at a given electronic state, recently developed in this laboratory for identification of isomeric multi-substituted benzyl-type radicals. Y. W. Yoon, C. S. Huh, and S. K. Lee, Chem. Phys. Lett. {550}, 58 (2012). S. K. Lee and S. J. Kim, Chem. Phys. Lett. {412}, 88 (2005).

  11. Radicals derived from acetaldehyde and vinyl alcohol.

    PubMed

    Estep, Marissa L; Morgan, W James; Winkles, Alexander T; Abbott, Adam S; Villegas-Escobar, Nery; Mullinax, J Wayne; Turner, Walter E; Wang, Xiao; Turney, Justin M; Schaefer, Henry F

    2017-09-04

    Vinyl alcohol and acetaldehyde are isoelectronic products of incomplete butanol combustion. Along with the radicals resulting from the removal of atomic hydrogen or the hydroxyl radical, these species are studied here using ab initio methods as complete as coupled cluster theory with single, double, triple, and perturbative quadruple excitations [CCSDT(Q)], with basis sets as large as cc-pV5Z. The relative energies provided herein are further refined by including corrections for relativistic effects, the frozen core approximation, and the Born-Oppenheimer approximation. The effects of anharmonic zero-point vibrational energies are also treated. The syn conformer of vinyl alcohol is predicted to be lower in energy than the anti conformer by 1.1 kcal mol(-1). The alcoholic hydrogen of syn-vinyl alcohol is found to be the easiest to remove, requiring 84.4 kcal mol(-1). Five other radicals are also carefully considered, with four conformers investigated for the 1-hydroxyvinyl radical. Beyond energetics, we have conducted an overhaul of the spectroscopic literature for these species. Our results also provide predictions for fundamental modes yet to be reported experimentally. To our knowledge, the ν3 (3076 cm(-1)) and ν4 (2999 cm(-1)) C-H stretches for syn-vinyl alcohol and all but one of the vibrational modes for anti-vinyl alcohol (ν1-ν14) are yet to be observed experimentally. For the acetyl radical, ν6 (1035 cm(-1)), ν11 (944 cm(-1)), ν12 (97 cm(-1)), and accounting for our changes to the assignment of the 1419.9 cm(-1) experimental mode, ν10 (1441 cm(-1)), are yet to be observed. We have predicted these unobserved fundamentals and reassigned the experimental 1419.9 cm(-1) frequency in the acetyl radical to ν4 rather than to ν10. Our work also strongly supports reassignment of the ν10 and ν11 fundamentals of the vinoxy radical. We suggest that the bands assigned to the overtones of these fundamentals were in fact combination bands. Our findings may be

  12. Free radical explosive composition

    DOEpatents

    Walker, Franklin E.; Wasley, Richard J.

    1979-01-01

    An improved explosive composition is disclosed and comprises a major portion of an explosive having a detonation velocity between about 1500 and 10,000 meters per second and a minor amount of a getter additive comprising a compound or mixture of compounds capable of capturing or deactivating free radicals or ions under mechanical or electrical shock conditions and which is not an explosive. Exemplary getter additives are isocyanates, olefins and iodine.

  13. Probability and radical behaviorism

    PubMed Central

    Espinosa, James M.

    1992-01-01

    The concept of probability appears to be very important in the radical behaviorism of Skinner. Yet, it seems that this probability has not been accurately defined and is still ambiguous. I give a strict, relative frequency interpretation of probability and its applicability to the data from the science of behavior as supplied by cumulative records. Two examples of stochastic processes are given that may model the data from cumulative records that result under conditions of continuous reinforcement and extinction, respectively. PMID:22478114

  14. Radicals in melanin biochemistry.

    PubMed

    Riley, P A

    1988-01-01

    Melanins are light-absorbant polymeric pigments found widely dispersed in nature. They possess many interesting physicochemical properties. One of these is the expression in the polymer of stable free radicals which appear to have a protective action in cells, probably by acting as a sink for diffusible free-radical species. Polymer formation is thought to occur by a free-radical process in which semiquinones are added to the chain. Semiquinones are formed by redox equilibration interactions between metabolic intermediates formed during the tyrosinase-catalyzed oxidation process. In the continued presence of substrate, steady-state concentrations of reactive species are predicted in the reaction system, and the melanogenic pathway may be considered as potentially hazardous for pigment-generating cells. This feature has been exploited by the use of analogue substrates to generate cytotoxic species as a possible rational approach to the treatment of malignant melanoma. One such substance is 4-hydroxyanisole, the oxidation of which gives rise to semiquinone radical species. The possibility that the anisyl semiquinone initiates a mechanism leading to cell damage has not been excluded. However, the current view is that the major cytotoxicity due to the oxidation products of this compound is the result of the action of the corresponding orthoquinone. A number of mechanisms exist for detoxifying quinones if they reach the cytosol such as O-methylation and the formation of thiol adducts with cysteine or glutathione, and these can be used as markers of melanogenesis. In general, however, only small amounts of reactive intermediates of melanogenesis escape from the confines of the melanosome, probably because of their limited lipid solubility. The selective toxic action of anisyl quinone in the treatment of melanoma may, in part, be due to membrane defects in the melanosomes of malignant melanocytes.

  15. A Successful Experiment for Tranferring Prior Learning Experience.

    ERIC Educational Resources Information Center

    Snow, Roslyn; Bruns, Phyllis A.

    1982-01-01

    Describes Orange Coast College's Assessment of Prior Learning (APL) program, which involves student preparation of a fully documented autobiographical essay and an assessment procedure used to award credit for demonstrated competencies. Highlights faculty and industry involvement. (DMM)

  16. Mechanics/heat-tranfer relation for particulate materials

    SciTech Connect

    Campbell, C.S.

    1990-01-01

    In this quarter, we have been working (1) on publishing our fluidized bed research, (2) development of the new particle-pressure transducer and (3) developing a computer control system for the heaters in the conductivity shear cell. Results are discussed. 3 figs.

  17. Observation of the widetilde{A} - widetilde{X} Electronic Transition of C_6-C_{10} Peroxy Radicals

    NASA Astrophysics Data System (ADS)

    Kline, Neal D.; Miller, Terry A.

    2013-06-01

    The widetilde{A} - widetilde{X} electronic transition of straight chain C_6-C_{10} peroxy radicals and of the isooctyl peroxy radical have been observed and analyzed. These larger hydrocarbons are significant constituents of gasoline with heptane (octane rating of 0) and isooctane (2,2,4 trimethylpentane; octane rating of 100) being the two standards on which the octane rating scale is based. Spectra were obtained by abstraction of hydrogen atoms from the hydrocarbons using chlorine atoms. The origin and -OO stretch regions of the straight chain peroxy radicals are easily identifiable. It is relatively easy to uniquely identify hexyl peroxy, but differentiation among the spectra of the larger straight chain peroxy radicals has proven difficult. However, isooctyl peroxy is easily distinguished and the observation of the tertiary peroxy radical along with the primary and/or secondary peroxy radical(s) is discussed.

  18. Oxygen radical functionalization of boron nitride nanosheets.

    PubMed

    Sainsbury, Toby; Satti, Amro; May, Peter; Wang, Zhiming; McGovern, Ignatius; Gun'ko, Yurii K; Coleman, Jonathan

    2012-11-14

    The covalent chemical functionalization of exfoliated hexagonal boron-nitride nanosheets (BNNSs) is achieved by the solution-phase oxygen radical functionalization of boron atoms in the h-BN lattice. This involves a two-step procedure to initially covalently graft alkoxy groups to boron atoms and the subsequent hydrolytic defunctionalization of the groups to yield hydroxyl-functionalized BNNSs (OH-BNNSs). Characterization of the functionalized-BNNSs using HR-TEM, Raman, UV-vis, FTIR, NMR, and TGA was performed to investigate both the structure of the BNNSs and the covalent functionalization methodology. OH-BNNSs were used to prepare polymer nanocomposites and their mechanical properties analyzed. The influence of the functional groups grafted to the surface of the BNNSs is investigated by demonstrating the impact on mechanical properties of both noncovalent and covalent bonding at the interface between the nanofiller and polymer matrixes.

  19. Low Temperature Phosphorus Doping in Silicon Using Catalytically Generated Radicals

    NASA Astrophysics Data System (ADS)

    Hayakawa, Taro; Nakashima, Yuki; Miyamoto, Motoharu; Koyama, Koichi; Ohdaira, Keisuke; Matsumura, Hideki

    2011-12-01

    In this paper, we report the possibility of forming a phosphorus (P)-doped layer on silicon (Si) at low temperatures. Using the radicals catalytically generated from phosphine (PH3), a thin n-type layer is formed on a crystalline Si (c-Si) wafer at 150 °C. The secondary ion mass spectrometry (SIMS) profile of doped P atoms indicates that P atoms exist in the vicinity of the c-Si surface, and the depth at which P atom concentration decreases to 1/10 of the surface concentration is less than 12 nm for 300 s of radical treatment. The sheet carrier density on radical-treated c-Si wafers measured using the Hall effect shows that P atoms act as donors without annealing. The sheet carrier concentration of the P-doped layer is increased by adding hydrogen (H2) to the PH3 source gas. The effect of adding H2 to PH3 suggests that the surface reaction of atomic H plays an important role in the doping process.

  20. Diaryldichalcogenide radical cations.

    PubMed

    Mallow, Ole; Khanfar, Monther A; Malischewski, Moritz; Finke, Pamela; Hesse, Malte; Lork, Enno; Augenstein, Timo; Breher, Frank; Harmer, Jeffrey R; Vasilieva, Nadezhda V; Zibarev, Andrey; Bogomyakov, Artem S; Seppelt, Konrad; Beckmann, Jens

    2015-01-01

    One-electron oxidation of two series of diaryldichalcogenides (C6F5E)2 (13a-c) and (2,6-Mes2C6H3E)2 (16a-c) was studied (E = S, Se, Te). The reaction of 13a and 13b with AsF5 and SbF5 gave rise to the formation of thermally unstable radical cations [(C6F5S)2]˙(+) (14a) and [(C6F5Se)2]˙(+) (14b) that were isolated as [Sb2F11](-) and [As2F11](-) salts, respectively. The reaction of 13c with AsF5 afforded only the product of a Te-C bond cleavage, namely the previously known dication [Te4](2+) that was isolated as [AsF6](-) salt. The reaction of (2,6-Mes2C6H3E)2 (16a-c) with [NO][SbF6] provided the corresponding radical cations [(2,6-Mes2C6H3E)2]˙(+) (17a-c; E = S, Se, Te) in the form of thermally stable [SbF6](-) salts in nearly quantitative yields. The electronic and structural properties of these radical cations were probed by X-ray diffraction analysis, EPR spectroscopy, and density functional theory calculations and other methods.

  1. Types of radical hysterectomies

    PubMed Central

    Marin, F; Plesca, M; Bordea, CI; Moga, MA; Blidaru, A

    2014-01-01

    Abstract The treatment for cervical cancer is a complex, multidisciplinary issue, which applies according to the stage of the disease. The surgical elective treatment of cervical cancer is represented by the radical abdominal hysterectomy. In time, many surgeons perfected this surgical technique; the ones who stood up for this idea were Thoma Ionescu and Ernst Wertheim. There are many varieties of radical hysterectomies performed by using the abdominal method and some of them through vaginal and mixed way. Each method employed has advantages and disadvantages. At present, there are three classifications of radical hysterectomies which are used for the simplification of the surgical protocols: Piver-Rutledge-Smith classification which is the oldest, GCG-EORTC classification and Querlow and Morrow classification. The last is the most evolved and recent classification; its techniques can be adapted for conservative operations and for different types of surgical approaches: abdominal, vaginal, laparoscopic or robotic. Abbreviations: GCG-EORTC = Gynecologic Cancer Group of the European Organization of Research and Treatment of Cancer; LEEP = loop electrosurgical excision procedure; I.O.B. = Institute of Oncology Bucharest; PRS = Piver-Rutledge-Smith PMID:25408722

  2. [Radical prostatectomy - pro robotic].

    PubMed

    Gillitzer, R

    2012-05-01

    Anatomical radical prostatectomy was introduced in the early 1980s by Walsh and Donker. Elucidation of key anatomical structures led to a significant reduction in the morbidity of this procedure. The strive to achieve similar oncological and functional results to this gold standard open procedure but with further reduction of morbidity through a minimally invasive access led to the establishment of laparoscopic prostatectomy. However, this procedure is complex and difficult and is associated with a long learning curve. The technical advantages of robotically assisted surgery coupled with the intuitive handling of the device led to increased precision and shortening of the learning curve. These main advantages, together with a massive internet presence and aggressive marketing, have resulted in a rapid dissemination of robotic radical prostatectomy and an increasing patient demand. However, superiority of robotic radical prostatectomy in comparison to the other surgical therapeutic options has not yet been proven on a scientific basis. Currently robotic-assisted surgery is an established technique and future technical improvements will certainly further define its role in urological surgery. In the end this technical innovation will have to be balanced against the very high purchase and running costs, which remain the main limitation of this technology.

  3. Free radical propulsion concept

    NASA Technical Reports Server (NTRS)

    Hawkins, C. E.; Nakanishi, S.

    1981-01-01

    The concept of a free radical propulsion system, utilizing the recombination energy of dissociated low molecular weight gases to produce thrust, is analyzed. The system, operating at a theoretical impulse with hydrogen, as high as 2200 seconds at high thrust to power ratio, is hypothesized to bridge the gap between chemical and electrostatic propulsion capabilities. A comparative methodology is outlined by which characteristics of chemical and electric propulsion for orbit raising mission can be investigated. It is noted that free radicals proposed in rockets previously met with difficulty and complexity in terms of storage requirements; the present study proposes to eliminate the storage requirements by using electric energy to achieve a continuous-flow product of free radicals which are recombined to produce a high velocity propellant. Microwave energy used to dissociate a continuously flowing gas is transferred to the propellant via three-body-recombination for conversion to propellant kinetic energy. Microwave plasma discharge was found in excess of 90 percent over a broad range of pressure in preliminary experiments, and microwave heating compared to electrothermal heating showed much higher temperatures in gasdynamic equations.

  4. 2.10 Titanium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  5. 1.35 Ruthenium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  6. 2.33 Mercury-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  7. 2.32 Gold-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  8. 2.8 Potassium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  9. 2.28 Tantalum-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  10. 1.42 Iodine-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  11. 4.6.3 Vinyl radicals

    NASA Astrophysics Data System (ADS)

    Beckwith, A. L. J.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  12. 1.48 Gold-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  13. 2.7 Phosphorus-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  14. 1.46 Iridium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  15. 2.16 Zinc-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  16. 1.38 Cadmium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  17. 2.15 Copper-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  18. 2.4 Sodium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  19. 2.17 Gallium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  20. 2.31 Iridium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  1. 2.21 Niobium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  2. 1.36 Palladium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  3. 2.3 Boron-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  4. 1.37 Silver-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  5. 2.24 Silver-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  6. 2.18 Rubidium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  7. 2.20 Zirconium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  8. 1.40 Tin-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  9. 1.41 Tellurium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  10. 2.2 Lithium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  11. 2.5 Aluminum-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  12. 2.22 Molybdenum-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  13. 2.12 Chromium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  14. 2.14 Cobalt-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  15. 2.9 Scandium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  16. 2.6 Silicon-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  17. 2.19 Yttrium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  18. 2.27 Lanthanum-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  19. 2.23 Rhodium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  20. 2.13 Manganese-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  1. 4.6.2 Aryl radicals

    NASA Astrophysics Data System (ADS)

    Beckwith, A. L. J.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  2. 1.34 Molybdenum-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  3. 1.43 Lanthanum-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  4. 2.30 Osmium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  5. 2.29 Tungsten-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  6. 1.47 Platinum-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  7. 2.26 Cesium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  8. 1.45 Osmium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  9. 1.44 Tantalum-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  10. 2.11 Vanadium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  11. 2.25 Cadmium-centered radicals

    NASA Astrophysics Data System (ADS)

    Howard, J. A.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  12. 1.49 Mercury-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  13. 1.39 Indium-centered radicals

    NASA Astrophysics Data System (ADS)

    Claridge, R. F. C.

    This document is part of Subvolume A1 `Inorganic Radicals, Metal Complexes and Nonconjugated Carbon Centered Radicals' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

  14. An electron spin resonance investigation of the structure and formation of sulfinyl radicals: Reaction of peroxyl radicals with thiols

    SciTech Connect

    Swarts, S.G.; Becker, D.; DeBolt, S.; Sevilla, M.D. )

    1989-01-12

    In this work we present an electron spin resonance investigation of the irradiation of the alkyl mercaptans methyl, n-butyl, and tert-butyl mercaptan and the radioprotective thiols cysteamine and dithiothreitol in a number of aqueous and organic matrices in the present of oxygen. Matrix peroxyl radicals (ROO*) are formed after the irradiation of organic matrices in the presence of oxygen at 77 K. Upon annealing, these react with added thiols to form sulfinyl radicals (RSO*). Evidence for a thiol peroxyl radical (RSOO*) intermediate is found. Hyperfine couplings and g values are reported for the sulfinyl radicals formed from the five thiols investigated. The incorporation of {sup 17}O-labeled oxygen into the RSO* radical confirms that molecular oxygen is the source of the oxygen atom in the radical. The isotropic and parallel anisotropic {sup 17}O couplings indicate slightly less than 0.5 spin density on the oxygen. The couplings and spin densities are compared to those predicted from ab inito molecular orbital calculations for CH{sub 3}SO*. Calculations for the sulfur-peroxyl intermediate, CH{sub 3}SOO*, predict that it will have similar ESR parameters as those predicted for the carbon-centered peroxyl radical, CH{sub 3}OO*.

  15. Roaming dynamics in radical addition-elimination reactions.

    PubMed

    Joalland, Baptiste; Shi, Yuanyuan; Kamasah, Alexander; Suits, Arthur G; Mebel, Alexander M

    2014-06-06

    Radical addition-elimination reactions are a major pathway for transformation of unsaturated hydrocarbons. In the gas phase, these reactions involve formation of a transient strongly bound intermediate. However, the detailed mechanism and dynamics for these reactions remain unclear. Here we show, for reaction of chlorine atoms with butenes, that the Cl addition-HCl elimination pathway occurs from an abstraction-like Cl-H-C geometry rather than a conventional three-centre or four-centre transition state. Furthermore, access to this geometry is attained by roaming excursions of the Cl atom from the initially formed adduct. In effect, the alkene π cloud serves to capture the Cl atom and hold it, allowing many subsequent opportunities for the energized intermediate to find a suitable approach to the abstraction geometry. These bimolecular roaming reactions are closely related to the roaming radical dynamics recently discovered to play an important role in unimolecular reactions.

  16. Atomic oxygen testing with thermal atom systems - A critical evaluation

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L.; Albyn, Keith; Leger, Lubert J.

    1991-01-01

    The use of thermal atom (kinetic energy near 0.04 eV) test methods as a materials selection and screening technique for LEO spacecraft is critically evaluated in this paper. The physics and chemistry of the thermal atom environments are shown to produce specific mass loss rates (mg/sq cm per min) and reaction efficiencies (Re) radically different from those produced in the LEO environment. A response surface study shows that specific mass loss rates change rapidly with plasma-asher parameters and seldom agree with flight data. FEP Teflon is shown to react by a different mechanism than Kapton, polyethylene, or graphite. The Re (Re = volume of material removed/oxygen atom) of Kapton, polyethylene, Mylar, Tedlar, FEP Teflon, and graphite measured in a flowing afterglow apparatus are 0.001 to 0.0001 those measured with high-energy atoms (kinetic energy 1.5 eV or greater) in beam systems or in LEO. The effect of sample temperature and atom impact energy on Re is discussed. A simple kinetic model describing the reaction of atomic oxygen with polymer surfaces is developed. Guidelines and recommendations for thermal atom testing and interpretation of test results are presented.

  17. Atomic oxygen testing with thermal atom systems - A critical evaluation

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L.; Albyn, Keith; Leger, Lubert J.

    1991-01-01

    The use of thermal atom (kinetic energy near 0.04 eV) test methods as a materials selection and screening technique for LEO spacecraft is critically evaluated in this paper. The physics and chemistry of the thermal atom environments are shown to produce specific mass loss rates (mg/sq cm per min) and reaction efficiencies (Re) radically different from those produced in the LEO environment. A response surface study shows that specific mass loss rates change rapidly with plasma-asher parameters and seldom agree with flight data. FEP Teflon is shown to react by a different mechanism than Kapton, polyethylene, or graphite. The Re (Re = volume of material removed/oxygen atom) of Kapton, polyethylene, Mylar, Tedlar, FEP Teflon, and graphite measured in a flowing afterglow apparatus are 0.001 to 0.0001 those measured with high-energy atoms (kinetic energy 1.5 eV or greater) in beam systems or in LEO. The effect of sample temperature and atom impact energy on Re is discussed. A simple kinetic model describing the reaction of atomic oxygen with polymer surfaces is developed. Guidelines and recommendations for thermal atom testing and interpretation of test results are presented.

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

    SciTech Connect

    Leone, S.R.

    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. Rapid Dihydrogen Cleavage by Persistent Nitroxide Radicals under Frustrated Lewis Pair Conditions.

    PubMed

    Tao, Xin; Kehr, Gerald; Wang, Xiaowu; Daniliuc, Constantin G; Grimme, Stefan; Erker, Gerhard

    2016-07-04

    Persistent radicals undergo hydrogen atom abstraction reactions with a great variety of substrates, but not with dihydrogen. It has now been found that the TEMPO radical splits dihydrogen under mild conditions in the presence of the strong bulky B(C6 F5 )3 boron Lewis acid. The reaction is thought to proceed by a typical frustrated Lewis pair mechanism with the TEMPO radical acting as the active Lewis base. The reaction was analyzed by DFT, which indicates that no significant spin density on the hydrogen atoms is accumulated along the H2 splitting reaction path.

  20. Atomic Calligraphy

    NASA Astrophysics Data System (ADS)

    Imboden, Matthias; Pardo, Flavio; Bolle, Cristian; Han, Han; Tareen, Ammar; Chang, Jackson; Christopher, Jason; Corman, Benjamin; Bishop, David

    2013-03-01

    Here we present a MEMS based method to fabricate devices with a small number of atoms. In standard semiconductor fabrication, a large amount of material is deposited, after which etching removes what is not wanted. This technique breaks down for structures that approach the single atom limit, as it is inconceivable to etch away all but one atom. What is needed is a bottom up method with single or near single atom precision. We demonstrate a MEMS device that enables nanometer position controlled deposition of gold atoms. A digitally driven plate is swept as a flux of gold atoms passes through an aperture. Appling voltages on four comb capacitors connected to the central plate by tethers enable nanometer lateral precision in the xy plane over 15x15 sq. microns. Typical MEMS structures have manufacturing resolutions on the order of a micron. Using a FIB it is possible to mill apertures as small as 10 nm in diameter. Assuming a low incident atomic flux, as well as an integrated MEMS based shutter with microsecond response time, it becomes possible to deposit single atoms. Due to their small size and low power consumption, such nano-printers can be mounted directly in a cryogenic system at ultrahigh vacuum to deposit clean quench condensed metallic structures.

  1. Atomic supersymmetry

    NASA Technical Reports Server (NTRS)

    Kostelecky, V. Alan

    1993-01-01

    Atomic supersymmetry is a quantum-mechanical supersymmetry connecting the properties of different atoms and ions. A short description of some established results in the subject are provided and a few recent developments are discussed including the extension to parabolic coordinates and the calculation of Stark maps using supersymmetry-based models.

  2. Gravitational Wave Detection with Atom Interferometry

    SciTech Connect

    Dimopoulos, Savas; Graham, Peter W.; Hogan, Jason M.; Kasevich, Mark A.; 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.

  3. The Spectroscopy of the Formyl Radical.

    NASA Astrophysics Data System (ADS)

    Adamson, George William

    Fluorescence-excitation and stimulated emission pumping (SEP) spectroscopies were used to study the properties of photolytically generated, gas phase, formyl radical (HCO). This work focused on the ground doublet electronic state, between 4000-11 200cm^{-1} of energy, and the second excited doublet electronic state, between 38 590-38 750cm^{-1 } of energy. From the fluorescence-excitation spectrum the rotational, centrifugal distortion, and spin -rotational constants were determined for the vibrationless level of the second excited doublet electronic state. From the stimulated emission pumping spectrum vibrational term values, rotational constants, spin-rotational constants, and rotational linewidths were determined for ground electronic state vibrational levels--both above and below the dissociation limit for formyl radical dissociating to hydrogen atom and carbon monoxide. The systematics of the dissociation lifetimes, inferred from the observed rotational linewidths, for rovibrational levels of the ground electronic state were studied. The dissociating lifetimes were found to be strongly correlated with bending vibrational excitation and the amount of angular momentum about the minimum inertial axis of formyl radical. The observed dissociation lifetimes indicates the need for an upward adjustment of the currently accepted dissociation limit and barrier height. (Copies available exclusively from MIT Libraries, Rm. 14-0951, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.).

  4. Accurate Theoretical Thermochemistry for Fluoroethyl Radicals.

    PubMed

    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.

  5. Computational study on the attack of ·OH radicals on aromatic amino acids.

    PubMed

    Mujika, J I; Uranga, J; Matxain, J M

    2013-05-17

    The attack of hydroxyl radicals on aromatic amino acid side chains, namely phenylalanine, tyrosine, and tryptophan, have been studied by using density functional theory. Two reaction mechanisms were considered: 1) Addition reactions onto the aromatic ring atoms and 2) hydrogen abstraction from all of the possible atoms on the side chains. The thermodynamics and kinetics of the attack of a maximum of two hydroxyl radicals were studied, considering the effect of different protein environments at two different dielectric values (4 and 80). The obtained theoretical results explain how the radical attacks take place and provide new insight into the reasons for the experimentally observed preferential mechanism. These results indicate that, even though the attack of the first (·)OH radical on an aliphatic C atom is energetically favored, the larger delocalization and concomitant stabilization that are obtained by attack on the aromatic side chain prevail. Thus, the obtained theoretical results are in agreement with the experimental evidence that the aromatic side chain is the main target for radical attack and show that the first (·)OH radical is added onto the aromatic ring, whereas a second radical abstracts a hydrogen atom from the same position to obtain the oxidized product. Moreover, the results indicate that the reaction can be favored in the buried region of the protein. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Structure and reactions of cation-radicals of esters in freon matrices

    SciTech Connect

    Belevskii, V.N.; Belopushkin, S.I.; Fel'dman, V.I.

    1987-11-01

    In CFCl/sub 3/ matrices the cation-radicals of methyl and ethyl formates, formed in ..gamma..-irradiated solutions, at 77 K efficiently undergo intramolecular H atom transfer to form the secondary cation-radicals HC(OH)OCH/sub 2/CH/sub 2/ and DC(OH)OCD/sub 2/CH/sub 2/. This process does not occur in the deuteroformate cation-radical DCOOCH/sub 2/CD/sub 3//sup +./, which is observed in the ESR spectra in different conformations, depending on the temperature. Ion-molecule reactions involving cation-radicals are indicated

  7. Contrasting reactions of hydrated electron and formate radical with 2-thio analogues of cytosine and uracil.

    PubMed

    Prasanthkumar, Kavanal P; Alvarez-Idaboy, Juan R; Kumar, Pavitra V; Singh, Beena G; Priyadarsini, K Indira

    2016-10-19

    2-Thiocytosine (TC) and 2-thiouracil (TU) were subjected to hydrated electron (eaq(-)), formate radical (CO2˙(-)) and 2-hydroxypropan-2-yl radical ((CH3)2˙COH) reactions in aqueous medium. Transients were characterized by absorption spectroscopy and the experimental findings were rationalized by DFT calculations at LC-ωPBE and M06-2X levels using a 6-311+G(d,p) basis set and SMD solvation. In eaq(-) reactions, a ring N-atom protonated radical of TC and an exocyclic O-atom protonated radical of TU were observed via addition of eaq(-) and subsequent protonation by solvent molecules. However, two competing but simultaneous mechanisms are operative in CO2˙(-) reactions with TC and TU. The first one corresponds to formations of N(O)-atom protonated radicals (similar to eaq(-) reactions); the second mechanism led to 2 center-3 electron, sulfur-sulfur bonded neutral dimer radicals, TCdim˙ and TUdim˙. DFT calculations demonstrated that H-abstraction by CO2˙(-) from TC(TU) results in S-centered radical which upon combination with TC(TU) provide the dimer radical. In some cases, DFT energy profiles were further validated by CBS-QB3//M06-2X calculations. This is the first time report for a contradictory behavior in the mechanisms of eaq(-) and CO2˙(-) reactions with any pyrimidines or their thio analogues.

  8. EPR study of the stable radical in a γ-irradiated single crystal of progesterone

    NASA Astrophysics Data System (ADS)

    Krzyminiewski, R.; Masiakowski, J.; Pietrzak, J.; Szyczewski, A.

    The molecular structure of free radicals formed in a γ-irradiated single crystal of progesterone was investigated by EPR spectroscopy. Two different types of radicals with different rates of recombination were observed. It is proposed that the stable radical is formed by the loss of a hydrogen atom in position 6 of the molecule, leaving an unpaired electron in the 2 pz orbital of the carbon atoms in positions 6 and 4. The hyperfine spectrum of this radical originates from the interaction of the unpaired electron with the two equivalent a protons in positions 4 and 6 and with the two non-equivalent β protons in position 7. The hyperfine tensors of the couplings are given together with the g tensor of this radical.

  9. Relative stability of radicals derived from artemisinin: A semiempirical and DFT study

    NASA Astrophysics Data System (ADS)

    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.

  10. Matrix Isolation of H Atoms at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Khmelenko, V. V.; Lee, D. M.; Vasiliev, S.

    2011-02-01

    The recent history of the matrix isolation of atomic free radicals at low temperatures started with a research program at the US National Bureau of Standards and continued with the important breakthrough at Chernogolovka in Russia where a jet containing atomic free radicals was directed onto the surface of superfluid 4He. The samples collected consisted of gel-like substances made up of molecular nanoclusters, allowing the atomic free radicals to be isolated from one another and studied at 1.3 K. More recently, techniques were developed at Turku University which have been made the region T<1 K accessible for studies of H atoms entrapped in H2 films. Very high concentrations of H atomic free radicals (˜1018-1019 cm-3) have been attained using both the Turku and Chernogolovka methods. A discussion of the most recent experiments at Cornell and Turku will be given. Microwave and mm wave electron paramagnetic resonance techniques have been employed in these experiments. These techniques permitted studies of the exchange tunneling chemical reaction D+HD→H+D2. Diffusion of H atoms through solid H2 proceeds via the reaction H+H2→H2+H, leading to recombination (H+H→H2). Quantum overlap of H atoms is thought to be responsible for exotic behavior of H atoms in solid H2 films below 1 K, including a significant departure from the Boltzmann distribution of the relative populations of the two lowest hyperfine levels of atomic H.

  11. Catalysis of Radical Reactions: A Radical Chemistry Perspective.

    PubMed

    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.

  12. Ab initio studies of hydrocarbon peroxyl radicals

    SciTech Connect

    Besler, B.H.; Sevilla, M.D.; MacNeille, P.

    1986-11-20

    Extensive ab initio molecular orbital calculations have been performed for the importance series of peroxyl radicals (O/sub 2//sup .-/), HO/sub 2//sup ./, CH/sub 3/O/sub 2//sup ./, (CH/sub 3/)/sub 2/CHO/sub 2//sup ./, and (CH/sub 3/CH/sub 2/)/sub 2/CHO/sub 2//sup ./. Parameters calculated include equilibrium geometries, harmonic vibrational frequencies, dipole moments, and isotropic and anisotropic hyperfine couplings. Equilibrium geometries were of primary interest. In the two large hydrocarbon peroxyl radicals the carbon atoms and appropriate hydrogen atoms were constrained to be coplanar and the O-O group was forced to be perpendicular to the carbon chain in order to stimulate the presence of a peroxyl radical site in a polyethylene chain. Calculations were performed with large Gaussian basis sets (up to 6-311 ++G(d,p)). Calculations for HO/sub 2//sup ./ including electron correlation utilizing Moeller-Plesset perturbation theory were performed at the following levels: MP2(6-31G(d)) and 6-311G(d,p), MP3(6-311G(d,p)) and MP4SDTQ(6-311(d,p)). Calculated values are compared against the highly accurate experimental data for HO/sub 2//sup ./ known from microwave, laser magnetic resonance, and diode laser studies in order to determine the level of calculation necessary for accurate predictions. Comparison of the various calculations shows that MP2(6-31G(d)) compares favorably with MP4SDTQ(6-311G(d,p)) at a considerable savings in computation time.

  13. Products of the reaction of chlorine atoms and ozone

    NASA Technical Reports Server (NTRS)

    Hall, J. H., Jr.; Merideth, C. W.; Bhatia, S.; Guillory, W. A.; Gayles, J. N.

    1976-01-01

    Preliminary matrix-isolation infrared spectroscopic studies of the gas-phase reaction of chlorine atoms and ozone are reported. It was shown that the major product of the reaction is the symmetric OClO radical, while very little of the asymmetric ClOO radical is produced. It was also shown that the presence of O2 enhances the OClO production and the ClOO is the primary product in the reaction of Cl atoms and pure O2. The radical ClO was observed for the first time in a gas-phase reaction of Cl and O3. A mechanism for these observations is proposed.

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

    EPA Science Inventory

    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...

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

    EPA Science Inventory

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

    EPA Science Inventory

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

    EPA Science Inventory

    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...

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

    EPA Science Inventory

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

    EPA Science Inventory

    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. Radical production from photosensitization of imidazoles

    NASA Astrophysics Data System (ADS)

    Corral Arroyo, P.; Gonzalez, L.; Steimer, S.; Aellig, R.; Volkamer, R. M.; George, C.; Bartels-Rausch, T.; Ammann, M.

    2015-12-01

    Reactions promoted by light are key in atmospheric chemistry. Some of them occur in the condensed phase of aerosols containing light absorbing organic compounds (George et al., 2015). This work explores the radical reactions initiated by near-UV light in mixtures of citric acid (CA) and imidazole-2-carboxaldehyde (IC) using NO as a probe molecule for HO2, by means of coated wall flow tube experiments. Citric acid may act as H atom or electron donor in condensed phase radical cycles. IC may act as a photosensitizer. The loss of NO was measured by a chemiluminescence detector. The dependence of the NO loss on the NO concentration, the IC/CA ratio in the film, relative humidity, light intensity, oxygen molar fraction were investigated as well as the HONO and NO2 yields. We also added halide salts to investigate the effect of a competing electron donor in the system and the output of halogens to the gas phase. We found a correlation between the loss of NO above the film and the molar ratio of IC/CA and the light intensity. The variation of the NO loss with oxygen corroborates a mechanism, in which the triplet excited state of IC is reduced by citric acid, to a reduced ketyl radical that transfers an electron to molecular oxygen, which in turn leads to production of HO2 radicals. Therefore, the NO loss in the gas phase is related to the production of HO2 radicals. Relative humidity had a strong impact on the HO2 output, which shows a maximum production rate at around 30%. The addition of halide ions (X- = Cl-, Br-, I-) increases the HO2 output at low concentration and decrease it at higher concentration when X2- radical ions likely scavenge HO2. We could preliminarily quantify for the first time the contribution of these processes to the oxidative capacity in the atmosphere and conclude that their role is significant for aerosol aging and potentially a significant source of halogen compounds to the gas phase.

  1. Electronic emission spectroscopy of the 4-methyl-3-azabenzyl radical

    NASA Astrophysics Data System (ADS)

    Lightcap, Johnny; Butler, Joseph T.; Goebbert, Daniel J.

    2015-12-01

    The 4-methyl-3-azabenzyl radical was generated from 2,5-lutidine in a corona excited supersonic expansion, and its fluorescence emission spectrum was recorded. Two possible radical isomers could form by loss of an H atom from either methyl group in 2,5-lutidine. Theoretical studies of both isomers confirmed the only species observed was 4-methyl-3-azabenzyl. The emission spectrum corresponded to the D1 → D0 transition, with a strong origin peak and several vibronic bands. The origin transition is located at 21 401 cm-1, in good agreement with a previous assignment, and calculated vibrational energies were in good agreement experimental vibrational energies.

  2. Gas-Phase Reactivity of Protonated 2-, 3- and 4-Dehydropyridine Radicals Toward Organic Reagents

    PubMed Central

    Adeuya, Anthony; Price, Jason M.; Jankiewicz, Bartłomiej J.; Nash, John J.; Kenttämaa, Hilkka I.

    2009-01-01

    In order to explore the effects of the electronic nature of charged phenyl radicals on their reactivity, reactions of the three distonic isomers of ndehydropyridinium cation (n = 2, 3 or 4) have been investigated in the gas phase by using Fourier-transform ion cyclotron resonance mass spectrometry. All three isomers react with cyclohexane, methanol, ethanol and 1-pentanol exclusively via hydrogen atom abstraction, and with allyl iodide mainly via iodine atom abstraction, with a reaction efficiency ordering: 2 > 3 > 4. The observed reactivity ordering correlates well with the calculated vertical electron affinities of the charged radicals (i.e., the higher the vertical electron affinity, the faster the reaction). Charged radicals 2 and 3 also react with tetrahydrofuran exclusively via hydrogen atom abstraction, but the reaction of 4 with tetrahydrofuran yields products arising from nonradical reactivity. The unusual reactivity of 4 is likely to result from the contribution of an ionized carbene-type resonance structure that facilitates nucleophilic addition to the most electrophilic carbon atom (C-4) in this charged radical. The influence of such a resonance structure on the reactivity of 2 is not obvious, and this may be due to stabilizing hydrogen-bonding interactions in the transition states for this molecule. Charged radicals 2 and 3 abstract a hydrogen atom from the substituent in both phenol and toluene, but 4 abstracts a hydrogen atom from the phenyl ring – a reaction that is unprecedented for phenyl radicals. Charged radical 4 reacts with tert-butyl isocyanide mainly by hydrogen cyanide (HCN) abstraction while CN abstraction is the principal reaction for 2 and 3. The different reactivity observed for 4 (compared to 2 and 3) is likely to result from different charge and spin distributions of the reaction intermediates for these charged radicals. PMID:19902945

  3. Atomic covalent functionalization of graphene.

    PubMed

    Johns, James E; Hersam, Mark C

    2013-01-15

    Although graphene's physical structure is a single atom thick, two-dimensional, hexagonal crystal of sp(2) 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. Toward 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

  4. Atomic Covalent Functionalization of Graphene

    PubMed Central

    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. Acting Atoms.

    ERIC Educational Resources Information Center

    Farin, Susan Archie

    1997-01-01

    Describes a fun game in which students act as electrons, protons, and neutrons. This activity is designed to help students develop a concrete understanding of the abstract concept of atomic structure. (DKM)

  6. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  7. Acting Atoms.

    ERIC Educational Resources Information Center

    Farin, Susan Archie

    1997-01-01

    Describes a fun game in which students act as electrons, protons, and neutrons. This activity is designed to help students develop a concrete understanding of the abstract concept of atomic structure. (DKM)

  8. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  9. Radically innovative steelmaking technologies

    NASA Astrophysics Data System (ADS)

    Szekely, Julian

    1980-09-01

    The steel industry is faced with serious problems caused by the increasing cost of energy, labor and capital and by tough overseas competition, employing new highly efficient process plants. The very high cost of capital and of capital equipment renders the construction of new green field site plants, exemplifying the best available technology economically unattractive. For this reason, over the long term the development radically innovative steelmaking technologies appears to be the only satisfactory resolution of this dilemma. The purpose of this article is to present a critical review of some of the radically innovative steelmaking technologies that have been proposed during the past few years and to develop the argument that these indeed do deserve serious consideration at the present time. It should be stressed, however, that these innovative technologies can be implemented only as part of a carefully conceived long range plan, which contains as a subset short term solutions, such as trigger prices improved investment credits, and so forth and intermediate term solutions, such as more extensive use of continuous casting, external desulfurization and selective modernization in general.

  10. Oligorotaxane Radicals under Orders.

    PubMed

    Wang, Yuping; Frasconi, Marco; Liu, Wei-Guang; Sun, Junling; Wu, Yilei; Nassar, Majed S; Botros, Youssry Y; Goddard, William A; Wasielewski, Michael R; Stoddart, J Fraser

    2016-02-24

    A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components-namely oligoviologens-in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT(4+)) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY(•+) radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne-azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers.

  11. Oligorotaxane Radicals under Orders

    PubMed Central

    2016-01-01

    A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components—namely oligoviologens—in which different numbers of 4,4′-bipyridinium (BIPY2+) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT4+) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY•+ radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne–azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers. PMID:27163033

  12. Adenosyl radical: reagent and catalyst in enzyme reactions.

    PubMed

    Marsh, E Neil G; Patterson, Dustin P; Li, Lei

    2010-03-22

    Adenosine is undoubtedly an ancient biological molecule that is a component of many enzyme cofactors: ATP, FADH, NAD(P)H, and coenzyme A, to name but a few, and, of course, of RNA. Here we present an overview of the role of adenosine in its most reactive form: as an organic radical formed either by homolytic cleavage of adenosylcobalamin (coenzyme B(12), AdoCbl) or by single-electron reduction of S-adenosylmethionine (AdoMet) complexed to an iron-sulfur cluster. Although many of the enzymes we discuss are newly discovered, adenosine's role as a radical cofactor most likely arose very early in evolution, before the advent of photosynthesis and the production of molecular oxygen, which rapidly inactivates many radical enzymes. AdoCbl-dependent enzymes appear to be confined to a rather narrow repertoire of rearrangement reactions involving 1,2-hydrogen atom migrations; nevertheless, mechanistic insights gained from studying these enzymes have proved extremely valuable in understanding how enzymes generate and control highly reactive free radical intermediates. In contrast, there has been a recent explosion in the number of radical-AdoMet enzymes discovered that catalyze a remarkably wide range of chemically challenging reactions; here there is much still to learn about their mechanisms. Although all the radical-AdoMet enzymes so far characterized come from anaerobically growing microbes and are very oxygen sensitive, there is tantalizing evidence that some of these enzymes might be active in aerobic organisms including humans.

  13. How are radicals (re)generated in photochemical ATRP?

    PubMed

    Ribelli, Thomas G; Konkolewicz, Dominik; Bernhard, Stefan; Matyjaszewski, Krzysztof

    2014-09-24

    The polymerization mechanism of photochemically mediated Cu-based atom-transfer radical polymerization (ATRP) was investigated using both experimental and kinetic modeling techniques. There are several distinct pathways that can lead to photochemical (re)generation of Cu(I) activator species or formation of radicals. These (re)generation pathways include direct photochemical reduction of the Cu(II) complexes by excess free amine moieties and unimolecular reduction of the Cu(II) complex, similar to activators regenerated by electron-transfer (ARGET) ATRP processes. Another pathway is photochemical radical generation either directly from the alkyl halide, ligand, or via interaction of ligand with either monomer or with alkyl halides. These photochemical radical generation processes are similar to initiators for continuous activator regeneration (ICAR) ATRP processes. A series of model experiments, ATRP reactions, and kinetic simulations were performed to evaluate the contribution of these reactions to the photochemical ATRP process. The results of these studies indicate that the dominant radical (re)generation reaction is the photochemical reduction of Cu(II) complexes by free amines moieties (from amine containing ligands). The unimolecular reduction of the Cu(II) deactivator complex is not significant, however, there is some contribution from ICAR ATRP reactions involving the interaction of alkyl halides and ligand, ligand with monomer, and the photochemical cleavage of the alkyl halide. Therefore, the mechanism of photochemically mediated ATRP is consistent with a photochemical ARGET ATRP reaction dominating the radical (re)generation.

  14. Photochemistry and photophysics of ketyl radicals containing the anthrone moiety

    SciTech Connect

    Netto-Ferreira, J.C.; Murphy, W.F.; Redmond, R.W.; Scaiano, J.C. )

    1990-05-23

    The photochemistry of several ketones containing an anthrone moiety has been employed to produce the corresponding ketyl radicals 1-4 by photoreduction in the presence of suitable hydrogen donors. The excited-state behavior of these radicals has been examined with use of two-laser, two-color techniques. The lifetimes for the excited ketyl radicals, ranging from 7.9 ns for 3 to 33 ns for 2, are longer than that observed for benzophenone ketyl, thus suggesting that conformational restrictions play a key role in controlling excited radical lifetimes. In the case of 3 the dominant mode of decay involves loss of a benzyl radical from the 10-position, while for 1 and 2 the process involves the loss of a hydrogen atom from the hydroxylic position; in the case of 2 this has been confirmed by Raman spectroscopy. The quantum yields of radical photobleaching are 0.20, 0.46, and 0.75 for 1, 2, and 3, respectively, while 4 is essentially photostable.

  15. 'Carbene radicals' in Co(II)(por)-catalyzed olefin cyclopropanation.

    PubMed

    Dzik, Wojciech I; Xu, Xue; Zhang, X Peter; Reek, Joost N H; de Bruin, Bas

    2010-08-11

    The mechanism of cobalt(II)-porphyrin-mediated cyclopropanation of olefins with diazoesters was studied. The first step--reaction of cobalt(II)-porphyrin with ethyl diazoacetate (EDA)--was examined using EPR and ESI-MS techniques. EDA reacts with cobalt(II)-porphyrin to form a 1:1 Co(por)(CHCOOEt) adduct that exists as two isomers: the 'bridging carbene' C' in which the 'carbene' is bound to the metal and the pyrrolic nitrogen of the porphyrin that has a d(7) configuration on the metal, and the 'terminal carbene' C in which the 'carbene' behaves as a redox noninnocent ligand having a d(6) cobalt center and the unpaired electron residing on the 'carbene' carbon atom. The subsequent reactivities of the thus formed 'cobalt carbene radical' with propene, styrene, and methyl acrylate were studied using DFT calculations. The calculations suggest that the formation of the carbene is the rate-limiting step for the unfunctionalized Co(II)(por) and that the cyclopropane ring formation proceeds via a stepwise radical process: Radical addition of the 'carbene radical' C to the C=C double bonds of the olefins results in formation of the gamma-alkyl radical intermediates D. Species D then easily collapse in almost barrierless ring-closure reactions (TS3) to form the cyclopropanes. This radical mechanism readily explains the high activity of Co(II)(por) species in the cyclopropanation of electron-deficient olefins such as methyl acrylate.

  16. Reactions of allylic radicals that impact molecular weight growth kinetics.

    PubMed

    Wang, Kun; Villano, Stephanie M; Dean, Anthony M

    2015-03-07

    The reactions of allylic radicals have the potential to play a critical role in molecular weight growth (MWG) kinetics during hydrocarbon oxidation and/or pyrolysis. Due to their stability (when compared to alkyl radicals), they can accumulate to relatively high concentrations. Thus, even though the rate coefficients for their various reactions are small, the rates of these reactions may be significant. In this work, we use electronic structure calculations to examine the recombination, addition, and abstraction reactions of allylic radicals. For the recombination reaction of allyl radicals, we assign a high pressure rate rule that is based on experimental data. Once formed, the recombination product can potentially undergo an H-atom abstraction reaction followed by unimolecular cyclization and β-scission reactions. Depending upon the conditions (e.g., higher pressures) these pathways can lead to the formation of stable MWG species. The addition of allylic radicals to olefins can also lead to MWG species formation. Once again, cyclization of the adduct followed by β-scission is an important energy accessible route. Since the recombination and addition reactions produce chemically-activated adducts, we have explored the pressure- and temperature-dependence of the overall rate constants as well as that for the multiple product channels. We describe a strategy for estimating these pressure-dependencies for systems where detailed electronic structure information is not available. We also derive generic rate rules for hydrogen abstraction reactions from olefins and diolefins by methyl and allyl radicals.

  17. Visualizing materials chemistry at atomic resolution.

    PubMed

    Sanchez, Sergio I; Small, Matthew W; Sivaramakrishnan, Shankar; Wen, Jian-guo; Zuo, Jian-Min; Nuzzo, Ralph G

    2010-04-01

    Analytical electron microscopy--empowered by advances in electron optics and detectors--is poised to radically transform our understanding of the complex phenomena arising from atomic and electronic structure in materials chemistry. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).

  18. Engaging unactivated alkyl, alkenyl and aryl iodides in visible-light-mediated free radical reactions.

    PubMed

    Nguyen, John D; D'Amato, Erica M; Narayanam, Jagan M R; Stephenson, Corey R J

    2012-10-01

    Radical reactions are a powerful class of chemical transformations. However, the formation of radical species to initiate these reactions has often required the use of stoichiometric amounts of toxic reagents, such as tributyltin hydride. Recently, the use of visible-light-mediated photoredox catalysis to generate radical species has become popular, but the scope of these radical precursors has been limited. Here, we describe the identification of reaction conditions under which photocatalysts such as fac-Ir(ppy)3 can be utilized to form radicals from unactivated alkyl, alkenyl and aryl iodides. The generated radicals undergo reduction via hydrogen atom abstraction or reductive cyclization. The reaction protocol utilizes only inexpensive reagents, occurs under mild reaction conditions, and shows exceptional functional group tolerance. Reaction efficiency is maintained upon scale-up and decreased catalyst loading, and the reaction time can be significantly shortened when the reaction is performed in a flow reactor.

  19. p-Nitrobenzenesulfenate esters as precursors for laser flash photolysis studies of alkyl radicals.

    PubMed

    Newcomb, Martin; Daublain, Pierre; Horner, John H

    2002-11-29

    A series of p-nitrobenzenesulfenate esters was used in laser flash photolysis (LFP) studies to generate alkoxyl radicals that fragmented to give the (2,2-diphenylcyclopropyl)methyl radical. Rate constants for the beta-scission reactions increased as a function of the carbonyl compound produced in the fragmentation reaction in the order CH2O < MeCHO < Me2CO < PhCHO < Ph2CO and increased with increasing solvent polarity. For alkoxyl radicals that fragment to produce benzaldehyde and benzophenone, the beta-scission reactions are faster than 1,5-hydrogen atom abstractions when the incipient carbon radical is as stable as a secondary alkyl radical, and this entry to carbon radicals can be used in LFP kinetic studies.

  20. Free radical scavenging injectable hydrogels for regenerative therapy.

    PubMed

    Komeri, Remya; Thankam, Finosh Gnanaprakasam; Muthu, Jayabalan

    2017-02-01

    Pathological free radicals generated from inflamed and infarcted cardiac tissues interferes natural tissue repair mechanisms. Hypoxic microenvironment at the injured zone of non-regenerating cardiac tissues hinders the therapeutic attempts including cell therapy. Here we report an injectable, cytocompatible, free radical scavenging synthetic hydrogel formulation for regenerative therapy. New hydrogel (PEAX-P) is prepared with D-xylitol-co-fumarate-co-poly ethylene adipate-co-PEG comaromer (PEAX) and PEGDiacrylate. PEAX-P hydrogel swells 4.9 times the initial weight and retains 100.07kPa Young modulus at equilibrium swelling, which is suitable for cardiac applications. PEAX-P hydrogel retains elastic nature even at 60% compressive strain, which is favorable to fit with the dynamic and elastic natural tissue counterparts. PEAX-P hydrogel scavenges 51% DPPH radical, 40% hydroxyl radicals 41% nitrate radicals with 31% reducing power. The presence of hydrogel protects 62% cardiomyoblast cells treated with stress inducing media at LD 50 concentration. The free hydroxyl groups in sugar alcohols of the comacromer influence the free radical scavenging. Comparatively, PEAX-P hydrogel based on xylitol evinces slightly lower scavenging characteristics than with previously reported PEAM-P hydrogel containing mannitol having more hydroxyl groups. The possible free radical scavenging mechanism of the present hydrogel relies on the free π electrons associated with uncrosslinked fumarate bonds, hydrogen atoms associated with sugar alcohols/PEG and radical dilution by free water in the matrix. Briefly, the present PEAX-P hydrogel is a potential injectable system for combined antioxidant and regenerative therapy. Copyright © 2016 Elsevier B.V. All rights reserved.