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Sample records for gas-phase release characteristics

  1. Modeling gas phase nitric oxide release in lung epithelial cells

    PubMed Central

    Jiang, Jingjing; George, Steven C.

    2012-01-01

    Nitric oxide (NO) is present in exhaled breath and is generally considered to be a noninvasive marker of airway inflammation, and is thus of particular relevance to monitoring asthma. NO is produced when l-arginine is converted to l-citrulline by NO synthase (NOS); however, l-arginine is also the substrate for arginase and both enzymes are upregulated in asthma. Recent reports have speculated that enhanced expression of one or both enzymes could lead to a limitation in substrate availability, and hence impact downstream targets or markers such as exhaled NO. The non-linear nature and vastly different kinetics of the enzymes make predictions difficult, particularly over the wide range of enzyme activity between baseline and inflammation. In this study, we developed a steady state model of l-arginine transmembrane transport, NO production, diffusion, and gas phase NO release from lung epithelial cells. We validated our model with experimental results of gas phase NO release and intracellular l-arginine concentration in A549 cells, and then performed a sensitivity analysis to determine relative impact of each enzyme on NO production. Our model predicts intracellular l-arginine and gas phase NO release over a wide range of initial extracellular l-arginine concentrations following stimulation with cytomix (10 ng/ml TNF-α, IL-1β, and INF-γ). Relative sensitivity analysis demonstrates that enhanced arginase activity has little impact on l-arginine bioavailability for NOS. In addition, NOS activity is the dominant parameter which impacts gas phase NO release. PMID:21550413

  2. Dissociation energy for O2 release from gas-phase iron oxide clusters measured by temperature-programmed desorption experiments

    NASA Astrophysics Data System (ADS)

    Koyama, Kohei; Kudoh, Satoshi; Miyajima, Ken; Mafuné, Fumitaka

    2015-04-01

    Thermal dissociation of gas phase iron oxide cluster ions, FenOm+ (n = 2-6), was observed by mass spectrometry. The dissociation processes were investigated by temperature-programmed desorption (TPD) measurements for different sized clusters. Oxygen molecules were found to be released from the cluster ions. The threshold energy required for dissociation, determined by analyzing TPD, was compared with the energies obtained by experiments of collision-induced dissociation and by calculations of density functional theory. The agreement of the energies indicates that the oxygen atoms bonded to the terminal site of clusters are more readily released into the gas phase than those in the bridge site.

  3. Statistical parameter characteristics of gas-phase fluctuations for gas-liquid intermittent flow

    SciTech Connect

    Matsui, G.; Monji, H.; Takaguchi, M.

    1995-09-01

    This study deals with theoretical analysis on the general behaviour of statistical parameters of gas-phase fluctuations and comparison of statistical parameter characteristics for the real void fraction fluctuations measured with those for the wave form modified the real fluctuations. In order to investigate the details of the relation between the behavior of the statistical parameters in real intermittent flow and analytical results obtained from information on the real flow, the distributions of statistical parameters for general fundamental wave form of gas-phase fluctuations are discussed in detail. By modifying the real gas-phase fluctuations to a trapezoidaly wave, the experimental results can be directly compared with the analytical results. The analytical results for intermittent flow show that the wave form parameter, and the total amplitude of void fraction fluctuations, affects strongly on the statistical parameter characteristics. The comparison with experiment using nitrogen gas-water intermittent flow suggests that the parameters of skewness and excess may be better as indicators of flow pattern. That is, the macroscopic nature of intermittent flow can be grasped by the skewness and the excess, and the detailed flow structure may be described by the mean and the standard deviation.

  4. Detergent release prolongs the lifetime of native-like membrane protein conformations in the gas-phase.

    PubMed

    Borysik, Antoni J; Hewitt, Dominic J; Robinson, Carol V

    2013-04-24

    Recent studies have suggested that detergents can protect the structure of membrane proteins during their transition from solution to the gas-phase. Here we provide mechanistic insights into this process by interrogating the structures of membrane protein-detergent assemblies in the gas-phase using ion mobility mass spectrometry. We show a clear correlation between the population of native-like protein conformations and the degree of detergent attachment to the protein in the gas-phase. Interrogation of these protein-detergent assemblies, by tandem mass spectrometry, enables us to define the mechanism by which detergents preserve native-like protein conformations in a solvent free environment. We show that the release of detergent is more central to the survival of these conformations than the physical presence of detergent bound to the protein. We propose that detergent release competes with structural collapse for the internal energy of the ion and permits the observation of transient native-like membrane protein conformations that are otherwise lost to structural rearrangement in the gas-phase.

  5. Quantitation of gas-phase perfluoroalkyl surfactants and fluorotelomer alcohols released from nonstick cookware and microwave popcorn bags.

    PubMed

    Sinclair, Ewan; Kim, Seung Kyu; Akinleye, Henry B; Kannan, Kurunthachalam

    2007-02-15

    Fluoropolymer dispersions are used for coating certain cookware products and food-contact packaging to impart oil and water repellency. Since salts of perfluorooctanoic acid (PFOA) are used as a processing aid in the manufacture of many fluoropolymers, it is necessary to determine if these compounds are still present as residuals after the process used to coat nonstick cookware or packaging, and could be released during typical cooking conditions. In this study, we identified and measured perfluoroalkyl carboxylates (PFCAs), particularly PFOA, and fluorotelomer alcohols (FTOHs; 6:2 FTOH and 8:2 FTOH), released from nonstick cookware into the gas phase under normal cooking temperatures (179 to 233 degrees C surface temperature). PFOA was released into the gas phase at 7-337 ng (11-503 pg/cm2) per pan from four brands of nonstick frying pans. 6:2 FTOH and 8:2 FTOH were found in the gas phase of four brands of frying pans, and the sources of FTOHs released from nonstick cookware are under investigation. We observed a significant decrease in gas-phase PFOA following repeated use of one brand of pan, whereas the other brand did not show a significant reduction in PFOA release following multiple uses. PFOA was found at >5 ng during the fourth use of both brands of pans. FTOHs were not found after the second use of either brand of pans. PFOA was found at 5-34 ng in the vapors produced from a prepacked microwave popcorn bag. PFOA was not found in the vapors produced from plain white corn kernels popped in a polypropylene container. 6:2 FTOH and 8:2 FTOH were measured in the vapors produced from one brand of prepacked microwave popcorn at 223 + 37 ng and 258 +/- 36 ng per bag, respectively, but not measured at >20 ng (LOQ) in the other two brands. On the packaging surface of one brand of microwave popcorn several PFCAs, including C5-C12, 6:2 FTOH, and 8:2 FTOH, were found at concentrations in the order of 0.5-6.0 ng/cm2. This study suggests that residual PFOA is not

  6. Comparison of electrical and optical characteristics in gas-phase and gas-liquid phase discharges

    SciTech Connect

    Qazi, H. I. A.; Li, He-Ping Zhang, Xiao-Fei; Bao, Cheng-Yu; Nie, Qiu-Yue

    2015-12-15

    This paper presents an AC-excited argon discharge generated using a gas-liquid (two-phase) hybrid plasma reactor, which mainly consists of a powered needle electrode enclosed in a conical quartz tube and grounded deionized water electrode. The discharges in the gas-phase, as well as in the two-phase, exhibit two discharge modes, i.e., the low current glow-like diffuse mode and the high current streamer-like constrict mode, with a mode transition, which exhibits a negative resistance of the discharges. The optical emission spectral analysis shows that the stronger diffusion of the water vapor into the discharge region in the two-phase discharges boosts up the generation of OH (A–X) radicals, and consequently, leads to a higher rotational temperature in the water-phase plasma plume than that of the gas-phase discharges. Both the increase of the power input and the decrease of the argon flow rate result in the increase of the rotational temperature in the plasma plume of the water-phase discharge. The stable two-phase discharges with a long plasma plume in the water-phase under a low power input and gas flow rate may show a promising prospect for the degradation of organic pollutants, e.g., printing and dyeing wastewater, in the field of environmental protection.

  7. Comparison of electrical and optical characteristics in gas-phase and gas-liquid phase discharges

    NASA Astrophysics Data System (ADS)

    Qazi, H. I. A.; Nie, Qiu-Yue; Li, He-Ping; Zhang, Xiao-Fei; Bao, Cheng-Yu

    2015-12-01

    This paper presents an AC-excited argon discharge generated using a gas-liquid (two-phase) hybrid plasma reactor, which mainly consists of a powered needle electrode enclosed in a conical quartz tube and grounded deionized water electrode. The discharges in the gas-phase, as well as in the two-phase, exhibit two discharge modes, i.e., the low current glow-like diffuse mode and the high current streamer-like constrict mode, with a mode transition, which exhibits a negative resistance of the discharges. The optical emission spectral analysis shows that the stronger diffusion of the water vapor into the discharge region in the two-phase discharges boosts up the generation of OH (A-X) radicals, and consequently, leads to a higher rotational temperature in the water-phase plasma plume than that of the gas-phase discharges. Both the increase of the power input and the decrease of the argon flow rate result in the increase of the rotational temperature in the plasma plume of the water-phase discharge. The stable two-phase discharges with a long plasma plume in the water-phase under a low power input and gas flow rate may show a promising prospect for the degradation of organic pollutants, e.g., printing and dyeing wastewater, in the field of environmental protection.

  8. Seasonal characteristics of gas-phase air pollutants: implications for public health in northeastern New Jersey

    NASA Astrophysics Data System (ADS)

    Roberts-Semple, D. A.; Gao, Y.

    2011-12-01

    To characterize the impact of urban air pollution and local weather conditions on human health, the ambient air concentrations of nitrogen oxide (NOx) and ground-level ozone (O3) were measured at the Meadowlands in Lyndhurst, NJ (41N, 74W) from June 1, 2007 to May 31, 2008. Meteorological data, mainly temperature, wind speed, relative humidity and barometric pressure, were supplemented with data from Weather Underground. Public health data were obtained from the New Jersey Department of Health and Senior Services (NJDHSS). The relationship between gas-phase pollutants and hospital admissions were examined through path analytic models by using multiple regressions and bivariate correlations. The meteorological conditions and air pollutants that may be associated with human respiratory health effects are analyzed. Preliminary results demonstrate that the ambient levels of NOx and O3 are influenced by certain meteorological conditions in the Meadowlands, and that there is a strong relationship between hospital admission and personal exposure to NO2 over the short-term. There is no direct relationship between O3 and hospital admission (r=-0.092), whereas hospital admission and NOx correlate (r=0.317) but more significantly with NO2 (r=.359) at a significance level of 0.01. Hospital admission rates are indirectly affected by humidity (r=-0.077). The seasonal dependence of pollutants is caused mainly by low wind speed and differences in chemical processing, making them interdependent. The monthly average O3 ranged from 11.1ppb to 36.2ppb with the highest values in summer; NOx ranged from 17.0ppb to 29.0ppb with no marked seasonal variations and were lower on weekends than on week days. There were dissimilar diurnal patterns and an inverse relationship between the hourly average of NOx and O3 concentrations, suggesting that O3 formation was not limited by the availability of NOx but is likely influenced by a VOC-sensitive chemical regime. This study provides a basis for

  9. Release of gas-phase halogens by photolytic generation of OH in frozen halide-nitrate solutions: an active halogen formation mechanism?

    PubMed

    Abbatt, J; Oldridge, N; Symington, A; Chukalovskiy, V; McWhinney, R D; Sjostedt, S; Cox, R A

    2010-06-17

    To better define the mechanisms by which condensed-phase halides may be oxidized to form gas-phase halogens under polar conditions, experiments have been conducted whereby frozen solutions containing chloride (1 M), bromide (1.6 x 10(-3) to 5 x 10(-2) M), iodide (<1 x 10(-5) M), and nitrate (0.01 to 1 M) have been illuminated by ultraviolet light in a continually flushed cell. Gas-phase products are quantified using chemical ionization mass spectrometry, and experiments were conducted at both 248 and 263 K. Br(2) was the dominant product, along with smaller yields of IBr and trace BrCl and I(2). The Br(2) yields were largely independent of the Br(-)/Cl(-) ratio of the frozen solution, down to seawater composition. However, the yields of halogens were strongly dependent on the levels of NO(3)(-) and acidity in solution, consistent with a mechanism whereby NO(3)(-) photolysis yields OH that oxidizes the condensed-phase halides. In support, we observed the formation of gas-phase NO(2), formed simultaneously with OH. Gas-phase HONO was also observed, suggesting that halide oxidation by HONO in the condensed phase may also occur to some degree. By measuring the production rate of condensed-phase OH, using benzoic acid as a radical trap, we determine that the molar yield of Br(2) formation relative to OH generation is 0.6, consistent with each OH being involved in halide oxidation. These studies suggest that gas-phase halogen formation should occur simultaneously with NO(x) release from frozen sea ice and snow surfaces that contain sufficient halides and deposited nitrate.

  10. Transport characteristics of gas phase ozone in unsaturated porous media for in-situ chemical oxidation.

    SciTech Connect

    Choi, H.; Lim, H-N; Kang, J-W; Hwang, T-M; Kim, J.; Environmental Research; Kwangju Inst. of Science and Technology; Yonsei Univ.

    2002-07-01

    Laboratory column experiments were conducted by employing various porous media to delineate the characteristics of gaseous ozone transport in the unsaturated zone under various conditions. Water content, soil organic matter (SOM), and metal oxides (MOs) were found to be the factors most influential in the fate and transport of gaseous ozone in unsaturated porous media. The migration velocity of the gaseous ozone front was inversely proportional to the MO content of the porous media. Increased water content at fixed gas flux decreased the ozone breakthrough time proportionally as a result of reduced gas pore volume (PV) in the column, and increased pore water interfered with reactions of gaseous ozone with SOM and MOs on the surface of porous media. The feasibility of in-situ ozone injection for the remediation of unsaturated soils contaminated with either phenanthrene or diesel-range organics (DROs) was investigated under various conditions. The maximum removal after 1 h of ozone injection was achieved in columns packed with baked sand, followed, in descending order, by glass beads and by sand, indicating that catalytic ozone decomposition with MOs in columns packed with baked sand enhanced hydroxyl radical formation and resulted in increased contaminant removal. Overall removal efficiency of multicomponent C{sub 10}-C{sub 24} DROs after 14 h of ozonation was 78.7%. Ozone transport was retarded considerably because of the high ozone demand of DROs, requiring more than 6 h for the gaseous ozone to initially break through the soil column under the experimental conditions tested in this study. Overall, gaseous ozone was readily delivered and transported to remediate unsaturated soils contaminated with phenanthrene and DROs.

  11. Oxygen Release from Cationic Niobium-Vanadium Oxide Clusters, NbnVmOk(+), Revealed by Gas Phase Thermal Desorption Spectrometry and Density Functional Theory Calculations.

    PubMed

    Masuzaki, Daigo; Nagata, Toshiaki; Mafuné, Fumitaka

    2017-05-25

    Thermal dissociation of the cationic niobium-vanadium oxide clusters, NbnVmOk(+) (n + m = 2-8), was investigated by gas phase thermal desorption spectrometry. The oxygen-rich NbnVmOk(+) released O and O2 for odd and even values of n + m, respectively. Substitution of more than one Nb atom in NbnOk(+) by V drastically lowered the desorption temperature of O2 for even values of n + m, whereas the substitution of more than two Nb atoms opened a new desorption path involving the release of O2 for odd values of n + m. The substitution effects can be explained by the fact that Nb atoms display the +5 state, whereas V atoms can exist in either the +4 or +5 states. The geometrical structures of selected NbnVmOk(+) clusters were optimized and the energetics of the release of O/O2 from the clusters was discussed on the basis of the results of DFT calculations.

  12. Gas phase kinetics during normal combustion

    NASA Technical Reports Server (NTRS)

    Price, C. F.; Boggs, T. L.; Eisel, J. L.; Atwood, A. I.; Zurn, D. E.

    1980-01-01

    The role of gas phase kinetics during combustion was explored in the steady state modeling efforts and in the analysis of ignition phenomena. In both cases it was shown that the combustion characteristics of some high energy ingredients and propellants are strongly affected, if not dictated, by the gas phase reactions which take place.

  13. Volatile out gassing characteristics of highly filled ethylene vinyl acetate binder materials: Gas phase infra-red spectroscopy

    DOE PAGES

    Patel, Mogon; Bowditch, Martin; Jones, Ben; ...

    2012-12-08

    Gas phase Infra-red (IR) spectroscopy has been used to investigate volatile out gassing properties of highly filled poly (ethylene-co-vinyl acetate) materials. In these studies, a Scout-ENTM heated gas cell was interfaced to a vacuum FTIR spectrometer, and the quantification of evolved species was achieved through calibration of the gas cell with certified gas standards. The volatile out gassing properties were monitored as a function of time during storage at 75°C under vacuum conditions (< 1mbar). Acetic acid, carbon dioxide and water were identified as the major out gassing products through IR absorption peaks at 1797, 2354 and 3853 cm-1, respectively.more » We present a comparison of three highly filled poly (ethyleneco- vinyl acetate) resins.« less

  14. Volatile out gassing characteristics of highly filled ethylene vinyl acetate binder materials: Gas phase infra-red spectroscopy

    SciTech Connect

    Patel, Mogon; Bowditch, Martin; Jones, Ben; Netherton, David; Khan, Niaz; Letant, Sonia; Maxwell, Robert S.; Birdsell, Stephen A.

    2012-12-08

    Gas phase Infra-red (IR) spectroscopy has been used to investigate volatile out gassing properties of highly filled poly (ethylene-co-vinyl acetate) materials. In these studies, a Scout-ENTM heated gas cell was interfaced to a vacuum FTIR spectrometer, and the quantification of evolved species was achieved through calibration of the gas cell with certified gas standards. The volatile out gassing properties were monitored as a function of time during storage at 75°C under vacuum conditions (< 1mbar). Acetic acid, carbon dioxide and water were identified as the major out gassing products through IR absorption peaks at 1797, 2354 and 3853 cm-1, respectively. We present a comparison of three highly filled poly (ethyleneco- vinyl acetate) resins.

  15. Gas Phase Nanoparticle Synthesis

    NASA Astrophysics Data System (ADS)

    Granqvist, Claes; Kish, Laszlo; Marlow, William

    This book deals with gas-phase nanoparticle synthesis and is intended for researchers and research students in nanomaterials science and engineering, condensed matter physics and chemistry, and aerosol science. Gas-phase nanoparticle synthesis is instrumental to nanotechnology - a field in current focus that raises hopes for environmentally benign, resource-lean manufacturing. Nanoparticles can be produced by many physical, chemical, and even biological routes. Gas-phase synthesis is particularly interesting since one can achieve accurate manufacturing control and hence industrial viability.

  16. On-line analysis of gas-phase composition in the combustion chamber and particle emission characteristics during combustion of wood and waste in a small batch reactor.

    PubMed

    Ferge, T; Maguhn, J; Hafner, K; Mühlberger, F; Davidovic, M; Warnecke, R; Zimmermann, R

    2005-03-15

    The emission of particulate matter and gaseous compounds during combustion of wood and refuse-derived fuel in a small batch reactor is investigated by laser mass-spectrometric on-line measurement techniques for gas-phase analysis and simultaneous registration of physical aerosol properties (number size distribution). The gas-phase composition is addressed by a laser-based mass spectrometric method, namely, vacuum-UV single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Particle-size distributions are measured with a scanning mobility particle sizer. Furthermore, a photoelectric aerosol sensor is applied for detection of particle-bound polycyclic aromatic hydrocarbons. The different phases of wood combustion are distinguishable by both the chemical profiles of gas-phase components (e.g., polycyclic aromatic hydrocarbons, PAH) and the particle-size distribution. Furthermore, short disturbances of the combustion process due to air supply shortages are investigated regarding their effect on particle-size distribution and gas-phase composition, respectively. It is shown that the combustion conditions strongly influence the particle-size distribution as well as on the emission of particle-bound polycyclic aromatic hydrocarbons.

  17. Gas-phase chemical dynamics

    SciTech Connect

    Weston, R.E. Jr.; Sears, T.J.; Preses, J.M.

    1993-12-01

    Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

  18. 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.

  19. Gas phase chemistry in comets

    NASA Technical Reports Server (NTRS)

    Oppenheimer, M.

    1976-01-01

    The significance of gas phase reactions in determining the nuclear structure of comets is discussed. The sublimation of parent molecules such as H2O, CH4, CO2, and NH3 from the surface of the nucleus and their subsequent photodissociation and ionization in forming observed cometary molecular species are elaborated.

  20. Characteristics of retention and enthalpies of sorption from the gas phase of esters of trimethylolpropane and C2-C5 acids on DB-1 stationary phase

    NASA Astrophysics Data System (ADS)

    Krasnykh, E. L.; Aleksandrov, A. Yu.; Sokolova, A. A.; Levanova, S. V.

    2017-02-01

    Characteristics of retention and their temperature dependences, along with the thermodynamic characteristics of sorption on DB-1 nonpolar phase, are determined in the temperature range of 220-280°C for 21 mono-, di-, and trisubstituted esters of trimethylolpropane and monobasic acids with a variety of structures containing from 2 to 6 carbon atoms.

  1. [Preparation and in vitro release characteristics of pulsed-release tablets of Apocynum venetum].

    PubMed

    Yang, Huasheng; Xie, Fugui; Yang, Yuewen; Luo, Yongming

    2011-06-01

    Using Apocynum venetum as a model drug to prepare pulsed-release tablets based on diffusion, swelling, osmotic pressure mechanism and to evaluate the release characteristics. The pulsatile release tablets were prepared by film coating methods using HPMC E5 and Eudragit The effect of formulation on pulsatile release of A. venetum was investigated. The pulsed-release tablet was prepared by a swelling layer coating which contains HPMC E5 and a controlled-release membrane containning Eudragit. The delayed release time of the tablets was (5.0 +/- 0.5) h. The pulsatile release characteristics of A. venetum pulsatile release tablets were confirmed in vitro.

  2. Rate processes in gas phase

    NASA Technical Reports Server (NTRS)

    Hansen, C. F.

    1983-01-01

    Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

  3. CREKID: A computer code for transient, gas-phase combustion of kinetics

    NASA Technical Reports Server (NTRS)

    Pratt, D. T.; Radhakrishnan, K.

    1984-01-01

    A new algorithm was developed for fast, automatic integration of chemical kinetic rate equations describing homogeneous, gas-phase combustion at constant pressure. Particular attention is paid to the distinguishing physical and computational characteristics of the induction, heat-release and equilibration regimes. The two-part predictor-corrector algorithm, based on an exponentially-fitted trapezoidal rule, includes filtering of ill-posed initial conditions, automatic selection of Newton-Jacobi or Newton iteration for convergence to achieve maximum computational efficiency while observing a prescribed error tolerance. The new algorithm was found to compare favorably with LSODE on two representative test problems drawn from combustion kinetics.

  4. Estimation of gas phase mixing in packed beds

    SciTech Connect

    Frigerio, S.; Thunman, H.; Leckner, B.; Hermansson, S.

    2008-04-15

    An improved model is presented for estimation of the mixing of gaseous species in a packed bed for fuel conversion. In particular, this work clarifies the main characteristics of mixing of volatiles and oxidizers in a burning bed of high-volatile solid fuel. Expressions are introduced to represent the active role of degradation of the solid particles in the mixing within the gas phase. During drying and devolatilization the solids modify the behavior of the gas flow: the volatiles released from the surface of the particles increase the turbulence in the system, and hence the rates of the homogeneous reactions under mixing-limited conditions. Numerical experiments are carried out to test the validity of this conclusion regarding mixing in different geometries. The flow of volatiles leaving the fuel particles is shown to contribute significantly to mixing, especially at low air flows through a bed. However, the fraction of the particle surface where volatiles are released and its orientation in the bed should be better determined in order to increase the accuracy of the estimates of turbulent mixing. (author)

  5. Oscillatory burning of solid propellants including gas phase time lag.

    NASA Technical Reports Server (NTRS)

    T'Ien, J. S.

    1972-01-01

    An analysis has been performed for oscillatory burning of solid propellants including gas phase time lag. The gaseous flame is assumed to be premixed and laminar with a one-step overall chemical reaction. The propellant is assumed to decompose according to the Arrenhius Law, with no condensed phase reaction. With this model, strong gas phase resonance has been found in certain cases at the characteristic gas-phase frequencies, but the peaking of the acoustic admittance is in the direction favoring the damping of pressure waves. At still higher frequencies, moderate wave-amplifying ability was found. The limit of low frequency response obtained previously by Denison and Baum was recovered, and the limitations of the quasi-steady theory were investigated.

  6. Oscillatory burning of solid propellants including gas phase time lag.

    NASA Technical Reports Server (NTRS)

    T'Ien, J. S.

    1972-01-01

    An analysis has been performed for oscillatory burning of solid propellants including gas phase time lag. The gaseous flame is assumed to be premixed and laminar with a one-step overall chemical reaction. The propellant is assumed to decompose according to the Arrenhius Law, with no condensed phase reaction. With this model, strong gas phase resonance has been found in certain cases at the characteristic gas-phase frequencies, but the peaking of the acoustic admittance is in the direction favoring the damping of pressure waves. At still higher frequencies, moderate wave-amplifying ability was found. The limit of low frequency response obtained previously by Denison and Baum was recovered, and the limitations of the quasi-steady theory were investigated.

  7. Hydrated metal ions in the gas phase.

    PubMed

    Beyer, Martin K

    2007-01-01

    Studying metal ion solvation, especially hydration, in the gas phase has developed into a field that is dominated by a tight interaction between experiment and theory. Since the studied species carry charge, mass spectrometry is an indispensable tool in all experiments. Whereas gas-phase coordination chemistry and reactions of bare metal ions are reasonably well understood, systems containing a larger number of solvent molecules are still difficult to understand. This review focuses on the rich chemistry of hydrated metal ions in the gas phase, covering coordination chemistry, charge separation in multiply charged systems, as well as intracluster and ion-molecule reactions. Key ideas of metal ion solvation in the gas phase are illustrated with rare-gas solvated metal ions.

  8. [Nutrient release characteristics and use efficiency of slow- and controlled release fertilizers].

    PubMed

    Duan, Lu-Lu; Zhang, Min; Liu, Gang; Shang, Zhao-Cong; Yang, Yi

    2009-05-01

    Water extraction method and soil incubation method were used to study the nutrient release characteristics of four slow- and controlled release fertilizers (CRF1, CRF2, SCU, and IBDU), and pot experiment was conducted to assess the effects of the release characteristics on the nutrient requirements of canola (Brassica napus L.). The nutrient release curves of test fertilizers in water were S pattern for CRF1 and CRF2, burst pattern for SCU, and reverse L pattern for IBDU. The nutrient release characteristics of the four fertilizers in water and in soil all fitted binomial equations, suggesting that there existed some similarities in the nutrient release in the two media. The nutrient uptake and biomass of canola plants treated with CRF1 and CRF2 were significantly higher than those treated with SCU and IBDU, and CRF2 had the greatest effect. The nutrient release curves of CRF1 and CRF2 accorded more closely with the nutrient requirements of canola.

  9. An approximate calculation of advective gas-phase transport of 14C at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Knapp, R. B.

    1990-01-01

    A quasilinear partial differential equation, which describes gas-phase transport of a 14C kinematic wave through a porous medium, is derived, its sensitivity to system variables is analyzed and it is applied to one possible release scenarion at the porposed Yucca Mountain, Nevada high-level radioactive waste repository. Advection, isotope exchange between CO 2 in a flowing gas phase and HCO 3- in a static aqueous phase, and radioactive decay are incorporated. The governing equation is solved analytically by the method of characteristics. The mass fraction of 14C in the gas phase,X 14g, is controlled by radioactive decay. The relatively long half-line of 14C, about 5720 years, and the relatively shallow proposed burial depth of the radioactive waste, about 350m, requires significant retardation of the 14C wave velocity for significant reduction in X 14g. 14C wave velocity is most sensitive to temperature and pH which control the distribution of total carbon between gas and liquid phase; the greater the partitioning of carbon into the liquid phase, the greater the retardation of the 14C wave velocity and the greater the ultimate reduction in X 14g from initial conditions. Partitioning of total carbon into the liquid phase is greatest at low temperatures, < 100° C, and high pH values, > 8. Increasing water saturation also tends to retard 14C wave velocity but to a lesser extent. The governing equation has been applied using conditions that may possibly occur at the proposed Yucca Mountain repository. Calculations indicate that the 14C wave takes about 5900 years to reach the surface with a X 14g equal to 25 ppm. Diffusion and dispersion are not of major importance for these conditions. These calculations are approximate due to the number of assumptions involved. Discharge of 14C into the gas before the selected time would accelerate wave arrival and increase the amount of 14C reaching the surface.

  10. Gas-Phase Infrared; JCAMP Format

    National Institute of Standards and Technology Data Gateway

    SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

  11. Continuous-Flow Gas-Phase Bioreactors

    NASA Technical Reports Server (NTRS)

    Wise, Donald L.; Trantolo, Debra J.

    1994-01-01

    Continuous-flow gas-phase bioreactors proposed for biochemical, food-processing, and related industries. Reactor contains one or more selected enzymes dehydrated or otherwise immobilized on solid carrier. Selected reactant gases fed into reactor, wherein chemical reactions catalyzed by enzyme(s) yield product biochemicals. Concept based on discovery that enzymes not necessarily placed in traditional aqueous environments to function as biocatalysts.

  12. Continuous-Flow Gas-Phase Bioreactors

    NASA Technical Reports Server (NTRS)

    Wise, Donald L.; Trantolo, Debra J.

    1994-01-01

    Continuous-flow gas-phase bioreactors proposed for biochemical, food-processing, and related industries. Reactor contains one or more selected enzymes dehydrated or otherwise immobilized on solid carrier. Selected reactant gases fed into reactor, wherein chemical reactions catalyzed by enzyme(s) yield product biochemicals. Concept based on discovery that enzymes not necessarily placed in traditional aqueous environments to function as biocatalysts.

  13. EPA GAS PHASE CHEMISTRY CHAMBER STUDIES

    EPA Science Inventory

    Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

  14. EPA GAS PHASE CHEMISTRY CHAMBER STUDIES

    EPA Science Inventory

    Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

  15. Experimental Thermochemistry of Gas Phase Cytosine Tautomers

    NASA Astrophysics Data System (ADS)

    Morrison, A. M.; Douberly, G. E.

    2011-06-01

    Enthalpies of interconversion are measured for the three lowest energy tautomers of isolated cytosine. The equilibrium distribution of tautomers near 600 K is frozen upon the capture of the gas phase species by low temperature helium nanodroplets. The temperature dependence of the gas phase cytosine tautomer populations is determined with infrared laser spectroscopy of the helium solvated species. The interconverison enthalpies obtained from the van't Hoff relation are 1.14 ± 0.21 and 1.63 ± 0.12 for the C31 rightleftharpoons C32 and C31 rightleftharpoons C1 equilibria, respectively. C31 and C32 are rotamers of an enol tautomer, and C1 is a keto tautomer. The interconversion enthalpies are compared to recent CCSD(T) thermochemistry calculations of cytosine tautomers.

  16. Enzyme-catalyzed, gas-phase reactions.

    PubMed

    Barzana, E; Klibanov, A M; Karel, M

    1987-06-01

    Dehydrated preparations of alcohol oxidase adsorbed on DEAE-cellulose vigorously catalyze a gas-phase oxidation of ethanol vapors with molecular oxygen. The gas-phase reaction is strongly dependent on the water activity of the system. The enzymatic activity is severely inhibited by the product hydrogen peroxide. This inhibition can be alleviated, however, by an addition of catalase or peroxidase to the dry preparation. Such dehydrated, bienzymic catalysts afford a complete and selective conversion of the substrate to acetaldehyde. Dry alcohol oxidase is much more thermostable than in aqueous solution. The results of this work suggest that dehydrated enzymes have potential applications in the analysis of gaseous compounds and in the development of novel gas-solid bioreactors.

  17. Novel Method for Gas Phase Calibrations

    DTIC Science & Technology

    2010-11-01

    Connections 9 4. Control Chart of Repetitive Data Generated by the Ballast Calibrator 11 5. Phosgene Calibration from a GC -TCD/ECD 12 NOVEL METHOD...as phosgene , hydrogen cyanide, cyanogen chloride, and ethylene oxide. In addition, it has been used to successfully calibrate Miran® infrared...spectrometers and Fourier transfer infrared spectrometers with similar gas phase chemicals. For example. Figure 4 shows phosgene data collected over a 3

  18. Laser Studies of Gas Phase Radical Reactions.

    DTIC Science & Technology

    1989-01-01

    Acremonium chrysogenum , was prepared according to the published procedure [6]. This fungal enzyme had a specific activity of 0.023 IUmg1, and was estimated to...Dist-lbitionj Avdielbiity Codes jAvail atidjor Dist 6a A-I . p -1- Laser Studies of Gas Phase Radical Reactions G. Hancock Physical Chemistry...some additional experiments concerning the formation of carbene radicals in liquid phase enzyme cleavage studies are described. Keywords Laser

  19. Gas-Phase Photoionization Of A Protein

    NASA Astrophysics Data System (ADS)

    Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

    2010-07-01

    We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; ˜12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

  20. Characteristics of microbial aerosols released from chicken and swine feces.

    PubMed

    Chien, Yeh-Chung; Chen, Chiou-Jong; Lin, Tzu-Hsien; Chen, Shih-Hsun; Chien, Yu-Ching

    2011-08-01

    Bioaerosols generated during livestock and poultry production are significant occupational hazards. This study investigates the characteristics of bioaerosols released from animal feces. Fresh feces from pigs and chickens were obtained and tested in a controlled-environment facility. Airborne viable (culturable) bacteria and fungi were sampled hourly for 48 hr. The predominant species were identified via polymerase chain reaction analysis. The number of bacterial colonies released from chicken feces increased gradually, peaked at approximately 20 hr, and remained relatively constant to test end; however, the bacterial colonies released from swine feces did not increase significantly. The chicken feces released significantly (P < 0.05) more bacterial aerosols than swine feces over 40 hr, by approximately 1 order of magnitude. However, the difference in total fungal aerosols released from the two feces types was relatively small (30-40%) and insignificant (P > 0.05). Aerosols sized between approximately 0.65 and 1.1 microm were predominant for bacteria, whereas aerosols sized between approximately 2.1 and 3.3 microm prevailed for fungi. Genera Stenotrophomonas were the predominant bacterial aerosols, whereas Cladosporium and Acremonium accounted for the greatest amounts of fungi from chicken and swine feces, respectively. More than 1000 culturable bacterial colonies can be released from 1 g of chicken feces per hour, and approximately 80% of these bioaerosols are respirable. Most bacterial aerosols released from swine and chicken feces were opportunistic human pathogens; thus, the significance of their presence warrants further investigations.

  1. Gas-phase Dissociation of homo-DNA Oligonucleotides

    NASA Astrophysics Data System (ADS)

    Stucki, Silvan R.; Désiron, Camille; Nyakas, Adrien; Marti, Simon; Leumann, Christian J.; Schürch, Stefan

    2013-12-01

    Synthetic modified oligonucleotides are of interest for diagnostic and therapeutic applications, as their biological stability, pairing selectivity, and binding strength can be considerably increased by the incorporation of unnatural structural elements. Homo-DNA is an oligonucleotide homologue based on dideoxy-hexopyranosyl sugar moieties, which follows the Watson-Crick A-T and G-C base pairing system, but does not hybridize with complementary natural DNA and RNA. Homo-DNA has found application as a bioorthogonal element in templated chemistry applications. The gas-phase dissociation of homo-DNA has been investigated by ESI-MS/MS and MALDI-MS/MS, and mechanistic aspects of its gas-phase dissociation are discussed. Experiments revealed a charge state dependent preference for the loss of nucleobases, which are released either as neutrals or as anions. In contrast to DNA, nucleobase loss from homo-DNA was found to be decoupled from backbone cleavage, thus resulting in stable products. This renders an additional stage of ion activation necessary in order to generate sequence-defining fragment ions. Upon MS3 of the primary base-loss ion, homo-DNA was found to exhibit unspecific backbone dissociation resulting in a balanced distribution of all fragment ion series.

  2. Gas phase thermochemistry of organogermanium compounds

    SciTech Connect

    Engel, J.P.

    1993-12-07

    A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

  3. Gas-phase photolysis of tungsten hexachloride

    NASA Astrophysics Data System (ADS)

    Kullmer, R.

    1994-07-01

    The laser-induced decomposition of WCl6 in the gas-phase is investigated by means of absorption, Raman and laser-induced fluorescence spectroscopy. With visible Ar+-laser radiation dissociation of WCl6 into WCl4 and Cl2 has been observed. Further decomposition can be achieved in the presence of H2 employing ultraviolet Ar+-laser radiation at 360 nm. A complete reduction to W requires even shorter wavelengths. The experimental results are analyzed on the basis of model calculations. Implications on the Laser-induced Chemical Vapor Deposition (LCVD) of W are discussed.

  4. Receptors useful for gas phase chemical sensing

    DOEpatents

    Jaworski, Justyn W; Lee, Seung-Wuk; Majumdar, Arunava; Raorane, Digvijay A

    2015-02-17

    The invention provides for a receptor, capable of binding to a target molecule, linked to a hygroscopic polymer or hydrogel; and the use of this receptor in a device for detecting the target molecule in a gaseous and/or liquid phase. The invention also provides for a method for detecting the presence of a target molecule in the gas phase using the device. In particular, the receptor can be a peptide capable of binding a 2,4,6-trinitrotoluene (TNT) or 2,4,-dinitrotoluene (DNT).

  5. Release characteristics of encapsulated formulations incorporating plant growth factors.

    PubMed

    Wybraniec, Slawomir; Schwartz, Liliana; Wiesman, Zeev; Markus, Arie; Wolf, David

    2002-05-01

    The release characteristics of encapsulated formulations containing a combination of plant growth factors (PGF)--plant hormones (IBA, paclobutrazol), nutrients (fertilizers, microelements), and fungicide (prochloraz)--were studied. The formulations were prepared by encapsulating the active ingredients in a polyethylene matrix and, in some cases, subsequently coating the product with polyurethane. Dissolution experiments were carried out with both coated and non-coated formulations to determine the sustained release patterns of the active ingredients. The PGF controlled-release systems obtained have been shown to promote development of root systems, vegetative growth, and reproductive development in cuttings, potted plants, or garden plants of various plant species. These beneficial effects are attributable to the lasting and balanced PGF availability provided by these systems.

  6. Gas Phase Model of Surface Reactions for N{2} Afterglows

    NASA Astrophysics Data System (ADS)

    Marković, V. Lj.; Petrović, Z. Lj.; Pejović, M. M.

    1996-07-01

    The adequacy of the homogeneous gas phase model as a representation of the surface losses of diffusing active particles in gas phase is studied. As an example the recent data obtained for the surface recombination coefficients are reanalyzed. The data were obtained by the application of the breakdown delay times which consists of the measurements of the breakdown delay times t_d as a function of the afterglow period tau. It was found that for the conditions of our experiment, the diffusion should not be neglected as the final results are significantly different when obtained by approximate gas phase representation and by exact numerical solution to the diffusion equation. While application of the gas phase effective coefficients to represent surface losses gives an error in the value of the recombination coefficient, it reproduces correctly other characteristics such as order of the process which can be obtained from simple fits to the experimental data. Dans cet article, nous étudions la validité du modèle approximatif représentant les pertes superficielles des particules actives qui diffusent de la phase gazeuse comme pertes dans la phase homogène du gaz. Les données actuelles du coefficient de recombination en surface sont utilisées par cette vérification . Les données experimentales sont obtenues en utilisant la technique qui consiste en la mesure du temps de retard du début de la décharge en fonction de la période de relaxation. Nous avons trouvé que, pour nos conditions expérimentales, la diffusion ne peut être négligée. Aussi, les résultats finals sont considérablement différents quand ils sont obtenus en utilisant le modèle approximatif par comparaison aves les résultats obtenus par la solution numérique exacte de l'équation de la diffusion. L'application des coefficients effectifs dans la phase gaseuse pour la présentation des pertes superficielles donne, pour les coefficients de la recombinaison, des valeurs qui diffèrent en

  7. Stabilized enzymes in continuous gas phase reactions

    SciTech Connect

    Yang, Fangxiao; LeJeune, K.; Yang, Zhen

    1995-12-01

    We are assessing the utility of enzymes to catalyze reactions in a continuous gas phase reactor. First, alcohol dehydrogenase has been used to oxidize an unsaturated alcohol, 3-methyl-2-buten-1-ol (UOL), to the corresponding unsaturated aldehyde, 3-methyl-2-butenal (UAL). Cofactor NAD{sup +} was regenerated by concomitant acetone reduction to isopropyl alcohol. Second, organophosphorus hydrolase (OPH) has been used to hydrolyze pesticide vapors. In order to control enzyme hydration level, enzyme water adsorption isotherms at different temperature have been studied. Huttig`s isotherm model has been found suitable to describe adsorption behavior. The influence of enzyme hydration level, enzyme loading on glass beads, reaction temperature and flow rate on enzymatic reaction rate and biocatalyst stability were investigated. Reaction kinetics were studied and a kinetic model was proposed. We will also report our attempts to further stabilize enzymes for use in gas reactions by incorporating them into polymer matrices.

  8. The gas-phase metallicity of central and satellite galaxies in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Pasquali, Anna; Gallazzi, Anna; van den Bosch, Frank C.

    2012-09-01

    We exploit the galaxy groups catalogue of Yang et al. and the galaxy properties measured in the Sloan Digital Sky Survey Data Releases 4 and 7 to study how the gas-phase metallicities of star-forming galaxies depend on environment. We find that satellite and central galaxies follow a qualitatively similar stellar mass (M★)-gas-phase metallicity relation, whereby their gas-phase metallicity increases with M★. Satellites, though, have higher gas-phase metallicities than equally massive centrals, and this difference increases with decreasing stellar mass. We find a maximum offset of 0.06 dex at log(M★/h-2 M⊙) ≃ 8.25. At fixed halo mass, centrals are more metal rich than satellites by ˜0.5 dex on average. This is simply due to the fact that, by definition, centrals are the most massive galaxies in their groups, and the fact that gas-phase metallicity increases with stellar mass. More interestingly, we also find that the gas-phase metallicity of satellites increases with halo mass (Mh) at fixed stellar mass. This increment is more pronounced for less massive galaxies, and, at M★ ≃ 109 h-2 M⊙, corresponds to ˜0.15 dex across the range 11 < log (Mh/h-1 M⊙) < 14. We also show that low-mass satellite galaxies have higher gas-phase metallicities than central galaxies of the same stellar metallicity. This difference becomes negligible for more massive galaxies of roughly solar metallicity. We demonstrate that the observed differences in gas-phase metallicity between centrals and satellites at fixed M★ are not a consequence of stellar mass stripping (advocated by Pasquali et al. in order to explain similar differences but in stellar metallicity), nor to the past star formation history of these galaxies as quantified by their surface mass density or gas mass fraction. Rather, we argue that these trends probably originate from a combination of three environmental effects: (i) strangulation, which prevents satellite galaxies from accreting new, low

  9. Ignition and flame characteristics of cryogenic hydrogen releases

    DOE PAGES

    Panda, Pratikash P.; Hecht, Ethan S.

    2017-01-01

    In this work, under-expanded cryogenic hydrogen jets were investigated experimentally for their ignition and flame characteristics. The test facility described herein, was designed and constructed to release hydrogen at a constant temperature and pressure, to study the dispersion and thermo-physical properties of cryogenic hydrogen releases and flames. In this study, a non-intrusive laser spark focused on the jet axis was used to measure the maximum ignition distance. The radiative power emitted by the corresponding jet flames was also measured for a range of release scenarios from 37 K to 295 K, 2–6 barabs through nozzles with diameters from 0.75 tomore » 1.25 mm. The maximum ignition distance scales linearly with the effective jet diameter (which scales as the square root of the stagnant fluid density). A 1-dimensional (stream-wise) cryogenic hydrogen release model developed previously at Sandia National Laboratories (although this model is not yet validated for cryogenic hydrogen) was exercised to predict that the mean mole fraction at the maximum ignition distance is approximately 0.14, and is not dependent on the release conditions. The flame length and width were extracted from visible and infra-red flame images for several test cases. The flame length and width both scale as the square root of jet exit Reynolds number, as reported in the literature for flames from atmospheric temperature hydrogen. As shown in previous studies for ignited atmospheric temperature hydrogen, the radiative power from the jet flames of cold hydrogen scales as a logarithmic function of the global flame residence time. The radiative heat flux from jet flames of cold hydrogen is higher than the jet flames of atmospheric temperature hydrogen, for a given mass flow rate, due to the lower choked flow velocity of low-temperature hydrogen. Lastly, this study provides critical information with regard to the development of models to inform the safety codes and standards of hydrogen

  10. Ignition and flame characteristics of cryogenic hydrogen releases

    SciTech Connect

    Panda, Pratikash P.; Hecht, Ethan S.

    2017-01-01

    In this work, under-expanded cryogenic hydrogen jets were investigated experimentally for their ignition and flame characteristics. The test facility described herein, was designed and constructed to release hydrogen at a constant temperature and pressure, to study the dispersion and thermo-physical properties of cryogenic hydrogen releases and flames. In this study, a non-intrusive laser spark focused on the jet axis was used to measure the maximum ignition distance. The radiative power emitted by the corresponding jet flames was also measured for a range of release scenarios from 37 K to 295 K, 2–6 barabs through nozzles with diameters from 0.75 to 1.25 mm. The maximum ignition distance scales linearly with the effective jet diameter (which scales as the square root of the stagnant fluid density). A 1-dimensional (stream-wise) cryogenic hydrogen release model developed previously at Sandia National Laboratories (although this model is not yet validated for cryogenic hydrogen) was exercised to predict that the mean mole fraction at the maximum ignition distance is approximately 0.14, and is not dependent on the release conditions. The flame length and width were extracted from visible and infra-red flame images for several test cases. The flame length and width both scale as the square root of jet exit Reynolds number, as reported in the literature for flames from atmospheric temperature hydrogen. As shown in previous studies for ignited atmospheric temperature hydrogen, the radiative power from the jet flames of cold hydrogen scales as a logarithmic function of the global flame residence time. The radiative heat flux from jet flames of cold hydrogen is higher than the jet flames of atmospheric temperature hydrogen, for a given mass flow rate, due to the lower choked flow velocity of low-temperature hydrogen. Lastly, this study provides critical information with regard to the development of models to inform the safety codes and standards of hydrogen

  11. Fundamentals of gas phase plasmas for treatment of human tissue.

    PubMed

    Kushner, Mark J; Babaeva, Natalia Yu

    2011-01-01

    The use of gas phase plasmas for treating human tissue is at the intersection of two disciplines - plasma physics and engineering, and medicine. In this paper, a primer will be provided for the medical practitioner on the fundamentals of generating gas phase plasmas at atmospheric pressure in air for the treatment of human tissue. The mechanisms for gas phase plasmas interacting with tissue and biological fluids will also be discussed using results from computer modeling.

  12. Laser-induced chemical deposition from the gas phase

    NASA Astrophysics Data System (ADS)

    Teslenko, V. V.

    1990-02-01

    The results of the study of the chemical reactions involved in the deposition of various substances from the gas phase using the pulsed, quasi-continuous, and continuous laser radiation in the wavelength range 0.193-10.6 μm have been summarised. Particular attention has been paid to the deposition of inorganic substances, including non-metals (C, Si, Ge, etc.), metals (Cu, Au, Zn, Cd, Al, Cr, Mo, W, Ni), and a number of simple compounds. Detailed experimental data are given on the influence of the radiation parameters (wavelength, duration and spacing of the pulses, intensity of radiation, shape and position of the laser beam) and the nature of the reagents (hydrides, halides, carbonyls, alkyl organometallic compounds, etc.) on the rate of deposition and the composition of the deposit. The characteristics of photolytic deposition reactions and their possible applications have been examined. The bibliography contains 202 references.

  13. Why do disk galaxies present a common gas-phase metallicity gradient?

    NASA Astrophysics Data System (ADS)

    Chang, R.; Zhang, Shuhui; Shen, Shiyin; Yin, Jun; Hou, Jinliang

    2017-03-01

    CALIFA data show that isolated disk galaxies present a common gas-phase metallicity gradient, with a characteristic slope of -0.1dex/re between 0.3 and 2 disk effective radius re (Sanchez et al. 2014). Here we construct a simple model to investigate which processes regulate the formation and evolution.

  14. Intramolecular photoelectron diffraction in the gas phase

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Miron, C.; Plésiat, E.; Argenti, L.; Patanen, M.; Kooser, K.; Ayuso, D.; Mondal, S.; Kimura, M.; Sakai, K.; Travnikova, O.; Palacios, A.; Decleva, P.; Kukk, E.; Martín, F.

    2013-09-01

    We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.

  15. Intramolecular photoelectron diffraction in the gas phase.

    PubMed

    Ueda, K; Miron, C; Plésiat, E; Argenti, L; Patanen, M; Kooser, K; Ayuso, D; Mondal, S; Kimura, M; Sakai, K; Travnikova, O; Palacios, A; Decleva, P; Kukk, E; Martín, F

    2013-09-28

    We report unambiguous experimental and theoretical evidence of intramolecular photoelectron diffraction in the collective vibrational excitation that accompanies high-energy photoionization of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the surrounding atomic centers. This interpretation is supported by the excellent agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as by qualitative agreement at high energies with a model in which atomic displacements are treated to first order of perturbation theory. The latter model allows us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains information on the structure of the above three molecules and the corresponding molecular cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the method could be used to obtain structural information of both neutral and ionic molecular species.

  16. Instabilities in Lean Gas-Phase Combustion

    NASA Astrophysics Data System (ADS)

    Schneider, K.; Bockhorn, H.; Eigenbrod, Ch.; Emerson, D.; Haldenwang, P.; Hoffmann, F.; Roekaerts, D.; Ronney, P.; Triebel, W.; Tummers, M.

    2005-06-01

    Lean burning is the burning of fuel-air mixtures with less than the chemically- balanced (stoichiometric) mixture. It produces a significant increase in fuel efficiency and reduction in pollution. However, the limits and control of lean burning are still not well understood.This is the motivation behind the study of instabilities in lean gas-phase combustion under microgravity conditions via direct numerical simulations and comparison of the results with experimental data.The goal is to gain fundamental insights in order to identify and understand the intrinsic chemical and fluid dynamical mechanisms responsible for these instabilities.The potential of this microgravity combustion research includes the development of technology that would reduce pollution and fire and explosion hazards, improve hazardous waste incineration and increase efficiency of the conversion of chemical energy to electric power or motive force.The results from this fundamental research will thus benefit chemical engineering and power generation. Its wide range of applications in industry includes lean-burning car engines.

  17. Transferring pharmaceuticals into the gas phase

    NASA Astrophysics Data System (ADS)

    Christen, Wolfgang; Krause, Tim; Rademann, Klaus

    2008-11-01

    The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative l-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)3[dot operator]HCl), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent densityE The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility.

  18. Resolving Gas-Phase Metallicity In Galaxies

    NASA Astrophysics Data System (ADS)

    Carton, David

    2017-06-01

    Chapter 2: As part of the Bluedisk survey we analyse the radial gas-phase metallicity profiles of 50 late-type galaxies. We compare the metallicity profiles of a sample of HI-rich galaxies against a control sample of HI-'normal' galaxies. We find the metallicity gradient of a galaxy to be strongly correlated with its HI mass fraction {M}{HI}) / {M}_{\\ast}). We note that some galaxies exhibit a steeper metallicity profile in the outer disc than in the inner disc. These galaxies are found in both the HI-rich and control samples. This contradicts a previous indication that these outer drops are exclusive to HI-rich galaxies. These effects are not driven by bars, although we do find some indication that barred galaxies have flatter metallicity profiles. By applying a simple analytical model we are able to account for the variety of metallicity profiles that the two samples present. The success of this model implies that the metallicity in these isolated galaxies may be in a local equilibrium, regulated by star formation. This insight could provide an explanation of the observed local mass-metallicity relation. Chapter 3 We present a method to recover the gas-phase metallicity gradients from integral field spectroscopic (IFS) observations of barely resolved galaxies. We take a forward modelling approach and compare our models to the observed spatial distribution of emission line fluxes, accounting for the degrading effects of seeing and spatial binning. The method is flexible and is not limited to particular emission lines or instruments. We test the model through comparison to synthetic observations and use downgraded observations of nearby galaxies to validate this work. As a proof of concept we also apply the model to real IFS observations of high-redshift galaxies. From our testing we show that the inferred metallicity gradients and central metallicities are fairly insensitive to the assumptions made in the model and that they are reliably recovered for galaxies

  19. Gas phase hydration of organic ions.

    PubMed

    Momoh, Paul O; El-Shall, M Samy

    2008-08-28

    In this work, we study the hydration phenomenon on a molecular level in the gas phase where a selected number of water molecules can interact with the organic ion of interest. The stepwise binding energies (DeltaH degrees (n-1,n)) of 1-7 water molecules to the phenyl acetylene cation are determined by equilibrium measurements using an ion mobility drift cell. The stepwise hydration energies DeltaH degrees (n-1,n) are nearly constant at 39.7 +/- 6.3 kJ mol(-1) from n = 1 to 7. The entropy change is larger in the n = 7 step, suggesting cyclic or cage-like water structures. No water addition is observed on the ionized phenyl acetylene trimer consistent with cyclization of the trimer ion to form triphenyl benzene cations C(24)H(18) (+) which are expected to interact weakly with the water molecules due to steric interactions and the delocalization of the charge on the large organic ion. The work demonstrates that hydration studies of organic ions can provide structural information on the organic ions.

  20. Scopine Isolated in the Gas Phase.

    PubMed

    Écija, Patricia; Vallejo-López, Montserrat; Uriarte, Iciar; Basterretxea, Francisco J; Lesarri, Alberto; Fernández, José A; Cocinero, Emilio J

    2016-10-05

    The rotational spectrum of the tropane alkaloid scopine is detected by Fourier transform microwave spectroscopy in a pulsed supersonic jet. A nonconventional method for bringing the molecules intact into the gas phase is used in which scopine syrup is mixed with glycine powder and the solid mixture is vaporized with an ultrafast UV laser beam. Laser vaporization prevents the easy isomerization to scopoline previously observed with conventional heating methods. A single conformer is unambiguously observed in the supersonic jet and corresponds to the energetically most stable species according to quantum chemical calculations. Rotational and centrifugal distortion constants are accurately determined. The spectrum shows fine and hyperfine structure due to the hindered rotation of the methyl group and the presence of a quadrupolar nucleus ((14) N), respectively. This additional information allows the angle of N-methyl inversion between the N-CH3 bond and the bicyclic C-N-C plane to be determined (131.8-137.8°), as well as the internal rotation barrier of the methyl group (6.235(1) kJ mol(-1) ). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

    De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

    2004-01-01

    It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

  2. Hydrocarbon radical thermochemistry: Gas-phase ion chemistry techniques

    SciTech Connect

    Ervin, Kent M.

    2014-03-21

    Final Scientific/Technical Report for the project "Hydrocarbon Radical Thermochemistry: Gas-Phase Ion Chemistry Techniques." The objective of this project is to exploit gas-phase ion chemistry techniques for determination of thermochemical values for neutral hydrocarbon radicals of importance in combustion kinetics.

  3. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

    De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

    2004-01-01

    It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

  4. Gas-phase nitronium ion affinities.

    PubMed Central

    Cacace, F; de Petris, G; Pepi, F; Angelelli, F

    1995-01-01

    Evaluation of nitronium ion-transfer equilibria, L1NO2+ + L2 = L2NO2+ + L1 (where L1 and L2 are ligands 1 and 2, respectively) by Fourier-transform ion cyclotron resonance mass spectrometry and application of the kinetic method, based on the metastable fragmentation of L1(NO2+)L2 nitronium ion-bound dimers led to a scale of relative gas-phase nitronium ion affinities. This scale, calibrated to a recent literature value for the NO2+ affinity of water, led for 18 ligands, including methanol, ammonia, representative ketones, nitriles, and nitroalkanes, to absolute NO2+ affinities, that fit a reasonably linear general correlation when plotted vs. the corresponding proton affinities (PAs). The slope of the plot depends to a certain extent on the specific nature of the ligands and, hence, the correlations between the NO2+ affinities, and the PAs of a given class of compounds display a better linearity than the general correlation and may afford a useful tool for predicting the NO2+ affinity of a molecule based on its PA. The NO2+ binding energies are considerably lower than the corresponding PAs and well below the binding energies of related polyatomic cations, such as NO+, a trend consistent with the available theoretical results on the structure and the stability of simple NO2+ complexes. The present study reports an example of extension of the kinetic method to dimers, such as L1(NO2+)L2, bound by polyatomic ions, which may considerably widen its scope. Finally, measurement of the NO2+ affinity of ammonia allowed evaluation of the otherwise inaccessible PA of the amino group of nitramide and, hence, direct experimental verification of previous theoretical estimates. PMID:11607578

  5. The 'sticky business' of cleaning gas-phase membrane proteins: a detergent oriented perspective.

    PubMed

    Borysik, Antoni J; Robinson, Carol V

    2012-11-14

    In recent years the properties of gas-phase detergent clusters have come under close scrutiny due in part to their participation in the analysis of intact membrane protein complexes by mass spectrometry. The detergent molecules that cover the protein complex are removed in the gas-phase by thermally agitating the ions by collision-induced dissociation. This process however, is not readily controlled and can frequently result in the disruption of protein structure. Improved methods of releasing proteins from detergent clusters are clearly required. To facilitate this the structural properties of detergent clusters along with the mechanistic details of their dissociation need to be understood. Pivotal to understanding the properties of gas-phase detergent clusters is the technique of ion mobility mass spectrometry. This technique can be used to assign polydisperse detergent clusters and provide information about their geometries and packing densities. In this article we consider the shapes of detergent clusters and show that these clusters possess geometries that are inconsistent with those in solution. We analyse the distributions of clusters in detail using tandem mass spectrometry and suggest that the mean charge of clusters formed from certain detergents is governed by electrostatic repulsion. We discuss the dissociation of detergent clusters and propose that detergent evaporation it a key process in the protection of protein complexes during high energy collisions in the gas-phase.

  6. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.

    PubMed

    Zhu, Hongying; Huang, Guangming

    2015-03-31

    In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m(-3), ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages.

  7. The nature of ionic liquids in the gas phase.

    PubMed

    Leal, João P; Esperança, José M S S; da Piedade, Manuel E Minas; Lopes, José N Canongia; Rebelo, Luís P N; Seddon, Kenneth R

    2007-07-19

    Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experiments showed that when aprotic ionic liquids vaporize under pressure and temperature conditions similar to those of a reduced-pressure distillation, the gas phase is composed of discrete anion-cation pairs. The evolution of the mass spectrometric signals recorded during fractional distillations of binary ionic liquid mixtures allowed us to monitor the changes of the gas-phase composition and the relative volatility of the components. In addition, we have studied a protic ionic liquid, and demonstrated that it exists as separated neutral molecules in the gas phase.

  8. Time Dependent Studies of Reactive Shocks in the Gas Phase

    DTIC Science & Technology

    1978-11-16

    1 LEVEL NRL Memorandum Report 3W tO Time Dependent Studies of Reactive Shocks in the Gas Phase E.S. ORAN, ’T.R. YOUNG and J.P. BORIS Laboratory for...34-• TIME DEPENDENT STUDIES OF REACTIVE SHOCKS IN THE GAS PHASE I. Introduction This paper presents results obtained from a detailed numerical...chemical kinetics, reaction products, and intermediates produced in reactive gas mixtures ignited by the propagation of a shock front. The model is based

  9. Thermodynamic analysis of fuels in gas phase: ethanol, gasoline and ethanol - gasoline predicted by DFT method.

    PubMed

    Neto, A F G; Lopes, F S; Carvalho, E V; Huda, M N; Neto, A M J C; Machado, N T

    2015-10-01

    This paper presents a theoretical study using density functional theory to calculate thermodynamics properties of major molecules compounds at gas phase of fuels like gasoline, ethanol, and gasoline-ethanol mixture in thermal equilibrium on temperature range up to 1500 K. We simulated a composition of gasoline mixture with ethanol for a thorough study of thermal energy, enthalpy, Gibbs free energy, entropy, heat capacity at constant pressure with respect to temperature in order to study the influence caused by ethanol as an additive to gasoline. We used semi-empirical computational methods as well in order to know the efficiency of other methods to simulate fuels through this methodology. In addition, the ethanol influence through the changes in percentage fractions of chemical energy released in combustion reaction and the variations on thermal properties for autoignition temperatures of fuels was analyzed. We verified how ethanol reduces the chemical energy released by gasoline combustion and how at low temperatures the gas phase fuels in thermal equilibrium have similar thermodynamic behavior. Theoretical results were compared with experimental data, when available, and showed agreement. Graphical Abstract Thermodynamic analysis of fuels in gas phase.

  10. Mass Spectrometry of Protein-Ligand Complexes: Enhanced Gas Phase Stability of Ribonuclease-Nucleotide Complexes

    PubMed Central

    Yin, Sheng; Xie, Yongming; Loo, Joseph A.

    2008-01-01

    Noncovalent protein-ligand complexes are readily detected by electrospray ionization mass spectrometry (ESI-MS). Ligand binding stoichiometry can be determined easily by the ESI-MS method. The ability to detect noncovalent protein-ligand complexes depends, however, on the stability of the complexes in the gas phase environment. Solution binding affinities may or may not be accurate predictors of their stability in vacuo. Complexes composed of cytidine nucleotides bound to ribonuclease A (RNase A) and ribonuclease S (RNase S) were detected by ESI-MS and were further analyzed by MS/MS. RNase A and RNase S share similar structures and biological activity. Subtilisin-cleavage of RNase A yields an S-peptide and an S-protein; the S-peptide and S-protein interact through hydrophobic interactions with a solution binding constant in the nanomolar range to generate an active RNase S. Cytidine nucleotides bind to the ribonucleases through electrostatic interactions with a solution binding constant in the micromolar range. Collisionally activated dissociation (CAD) of the 1:1 RNase A-CDP and CTP complexes yields cleavage of the covalent phosphate bonds of the nucleotide ligands, releasing CMP from the complex. CAD of the RNase S-CDP and CTP complexes dissociates the S-peptide from the remaining S-protein/nucleotide complex; further dissociation of the S-protein/nucleotide complex fragments a covalent phosphate bond of the nucleotide with subsequent release of CMP. Despite a solution binding constant favoring the S-protein/S-peptide complex, CDP/CTP remains electrostatically bound to the S-protein in the gas phase dissociation experiment. This study highlights the intrinsic stability of electrostatic interactions in the gas phase and the significant differences in solution and gas phase stabilities of noncovalent complexes that can result. PMID:18565758

  11. Release characteristics of dibucaine dispersed in konjac gels.

    PubMed

    Nakano, M; Takikawa, K; Arita, T

    1979-09-01

    A possible use of konjac gel for sustained release of drugs was examined in a monolithic system containing dibucaine. Dibucaine was dispersed in the gel which was prepared by gelation of the konjac flour in a borax solution at 60 degrees. The cumulative amount of the drug released plotted against the square root of time was linear in the monolithic system. This relationship was in agreement with that expected from the theoretical equation for planar configuration. The mechanism of the release of the drug from the gel may be considered to be leaching of the drug by the permeating fluid. The release profile from dried konjac gel was similar to that from undried gel, but that from unwarmed gel showed a deviation from linearity although sustained release was similarly obtained.

  12. Surface induced dissociation: dissecting noncovalent protein complexes in the gas phase.

    PubMed

    Zhou, Mowei; Wysocki, Vicki H

    2014-04-15

    The quaternary structures of proteins are both important and of interest to chemists, because many proteins exist as complexes in vivo, and probing these structures allows us to better understand their biological functions. Conventional structural biology methods such as X-ray crystallography and nuclear magnetic resonance provide high-resolution information on the structures of protein complexes and are the gold standards in the field. However, other emerging biophysical methods that only provide low-resolution data (e.g. stoichiometry and subunit connectivity) on the structures of the protein complexes are also becoming more important to scientists. Mass spectrometry is one of these approaches that provide lower than atomic structural resolution, but the approach is higher throughput and provides not only better mass information than other techniques but also stoichiometry and topology. Fragile noncovalent interactions within the protein complexes can be preserved in the gas phase of MS under gentle ionization and transfer conditions. Scientists can measure the masses of the complexes with high confidence to reveal the stoichiometry and composition of the proteins. What makes mass spectrometry an even more powerful method is that researchers can further isolate the protein complexes and activate them in the gas phase to release subunits for more structural information. The caveat is that, upon gas-phase activation, the released subunits need to faithfully reflect the native topology so that useful information on the proteins can be extracted from mass spectrometry experiments. Unfortunately, many proteins tend to favor unfolding upon collision with neutral gas (the most common activation method in mass spectrometers). Therefore, this typically results in limited insights on the quaternary structure of the precursor without further manipulation of other experimental factors. Scientists have observed, however, that valuable structural information can be obtained

  13. Atomic and Molecular Gas Phase Spectrometry.

    DTIC Science & Technology

    1983-09-30

    Puil dstrlbutbl1o P e a s e 173~ V evaluation of the spatial and spectral characteristics of the EIKAC (CERMAX) xenon point arc source ; study of the...of the EIMAC (CERMAX) xenon point arc source ; study of the reaction sequences and quantitative changes of alkaline earth phosphates in the presence of

  14. Release characteristics of selected carbon nanotube polymer composites

    EPA Science Inventory

    Multi-walled carbon nanotubes (MWCNTs) are commonly used in polymer formulations to improve strength, conductivity, and other attributes. A developing concern is the potential for carbon nanotube polymer nanocomposites to release nanoparticles into the environment as the polymer ...

  15. Release characteristics of selected carbon nanotube polymer composites

    EPA Science Inventory

    Multi-walled carbon nanotubes (MWCNTs) are commonly used in polymer formulations to improve strength, conductivity, and other attributes. A developing concern is the potential for carbon nanotube polymer nanocomposites to release nanoparticles into the environment as the polymer ...

  16. Gas phase depletion and flow dynamics in horizontal MOCVD reactors

    NASA Astrophysics Data System (ADS)

    Van de Ven, J.; Rutten, G. M. J.; Raaijmakers, M. J.; Giling, L. J.

    1986-08-01

    Growth rates of GaAs in the MOCVD process have been studied as a function of both lateral and axial position in horizontal reactor cells with rectangular cross-sections. A model to describe growth rates in laminar flow systems on the basis of concentration profiles under diffusion controlled conditions has been developed. The derivation of the growth rate equations includes the definition of an entrance length for the concentration profile to developed. In this region, growth rates appear to decrease with the 1/3 power of the axial position. Beyond this region, an exponential decrease is found. For low Rayleigh number conditions, the present experimental results show a very satisfactory agreement with the model without parameter fitting for both rectangular and tapered cells, and with both H 2 and N 2 as carrier gases. Theory also predicts that uniform deposition can be obtained over large areas in the flow direction for tapered cells, which has indeed been achieved experimentally. The influence of top-cooling in the present MOCVD system has been considered in more detail. From the experimental results, conclusions could be drawn concerning the flow characteristics. For low Rayleigh numbers (present study ≲ 700) it follows that growth rate distributions correspond with forced laminar flow characteristics. For relatively high Rayleigh numbers (present work 1700-2800), free convective effects with vortex formation are important. These conclusions are not specific for the present system, but apply to horizontal cold-wall reactors in general. On the basis of the present observations, recommendations for a cell design to obtain large area homogeneous deposition have been formulated. In addition, this work supports the conclusion that the final decomposition of trimethylgallium in the MOCVD process mainly takes place at the hot substrate and susceptor and not in the gas phase.

  17. Gas-phase saturation and evaporative cooling effects during wet compression of a fuel aerosol under RCM conditions

    SciTech Connect

    Goldsborough, S.S.; Johnson, M.V.; Zhu, G.S.; Aggarwal, S.K.

    2011-01-15

    Wet compression of a fuel aerosol has been proposed as a means of creating gas-phase mixtures of involatile diesel-representative fuels and oxidizer + diluent gases for rapid compression machine (RCM) experiments. The use of high concentration aerosols (e.g., {proportional_to}0.1 mL{sub fuel}/L{sub gas}, {proportional_to}1 x 10{sup 9} droplets/L{sub gas} for stoichiometric fuel loading at ambient conditions) can result in droplet-droplet interactions which lead to significant gas-phase fuel saturation and evaporative cooling during the volumetric compression process. In addition, localized stratification (i.e., on the droplet scale) of the fuel vapor and of temperature can lead to non-homogeneous reaction and heat release processes - features which could prevent adequate segregation of the underlying chemical kinetic rates from rates of physical transport. These characteristics are dependent on many factors including physical parameters such as overall fuel loading and initial droplet size relative to the compression rate, as well as fuel and diluent properties such as the boiling curve, vaporization enthalpy, heat capacity, and mass and thermal diffusivities. This study investigates the physical issues, especially fuel saturation and evaporative cooling effects, using a spherically-symmetric, single-droplet wet compression model. n-Dodecane is used as the fuel with the gas containing 21% O{sub 2} and 79% N{sub 2}. An overall compression time and compression ratio of 15.3 ms and 13.4 are used, respectively. It is found that smaller droplets (d{sub 0}{proportional_to} 2-3 {mu}m) are more affected by 'far-field' saturation and cooling effects, while larger droplets (d{sub 0}{proportional_to} 14 {mu}m) result in greater localized stratification of the gas-phase due to the larger diffusion distances for heat and mass transport. Vaporization of larger droplets is more affected by the volumetric compression process since evaporation requires more time to be completed

  18. On the effects of gas-phase species Lewis number in turbulent nonpremixed sooting flames

    NASA Astrophysics Data System (ADS)

    Bisetti, Fabrizio; Attili, Antonio; Mueller, Michael; Pitsch, Heinz

    2014-11-01

    Two large DNS of n-heptane/air turbulent nonpremixed combustion are compared to asses the effects of gas-phase species Lewis number on the dynamics of soot formation and growth. A detailed chemical mechanism, which includes PAHs, and a high-order method of moments for soot modeling are employed for the first time in the three-dimensional simulation of turbulent sooting flames. The results obtained employing a complex model (mixture average) for the transport of heat and mass are compared with those calculated with Le = 1 for all gas-phase species, including large soot precursor molecules. It is found that the statistics of temperature and other species governing the heat releasing chemistry are very similar in the two cases as the flow field achieves a fully turbulent state. The dynamics of the soot precursors and soot display quantitative differences between the two cases. Employing the Le = 1 approximation, the total mass of soot precursors in the flame decreases by 10 to 20 % only, but its field is less inhomogeneous in space and time. Due to the non-linearity of soot growth with respect to the concentration of gas-phase precursors, the domain-averaged rate of soot mass production decreases by a factor of 2.

  19. Characteristics of releases from TREAT source term experiment STEP-3

    SciTech Connect

    Fink, J.K.; Schlenger, B.J.; Baker, L. Jr.; Ritzman, R.L.

    1987-01-01

    Four in-pile experiments designed to characterize the radiological source term associated with postulated severe light water reactor accidents were performed at the Transient Reactor Test Facility. STEP-3 simulated a high-pressure TMLB' pressurized water reactor accident sequence that includes the extended loss of all ac power and leads to the loss of long-term decay heat removal. In STEP-3, four fuel elements from the Belgonucleaire BR3 reactor were subjected to temperature and pressures approaching those of a TMLB' accident. A description of the experiment and thermal-hydraulic analysis is reported elsewhere. The aerosols released into the flow stream were collected on coupons, settling plates, and wire impactors. Examination of the collected aerosol deposits was performed using scanning electron microscopy, electron microprobe microanalysis, and secondary ion mass spectroscopy (SIMS), to provide information about the chemical composition and morphology of the release. This paper describes the aerosol deposits and elemental composition of the release.

  20. Effect of duty-cycles on the air plasma gas-phase of dielectric barrier discharges

    NASA Astrophysics Data System (ADS)

    Barni, R.; Biganzoli, I.; Dell'Orto, E. C.; Riccardi, C.

    2015-10-01

    An experimental investigation concerning the effects of a duty-cycle in the supply of a dielectric barrier discharge in atmospheric pressure air has been performed. Electrical characteristics of the discharge have been measured, focusing mainly on the statistical properties of the current filaments and on dielectric surface charging, both affected by the frequent repetition of breakdown imposed by the duty-cycle. Information on the gas-phase composition was gathered too. In particular, a strong enhancement in the ozone formation rate is observed when suitable long pauses separate the active discharge phases. A simulation of the chemical kinetics in the gas-phase, based on a simplified discharge modeling, is briefly described in order to shed light on the observed increase in ozone production. The effect of a duty-cycle on surface modification of polymeric films in order to increase their wettability has been investigated too.

  1. Gas-Phase Chemistry of Multiply Charged Bioions in Analytical Mass Spectrometry

    PubMed Central

    Huang, Teng-Yi; McLuckey, Scott A.

    2011-01-01

    Ion chemistry has long played an important role in molecular mass spectrometry (MS), as it is central to the use of MS as a structural characterization tool. With the advent of ionization methods capable of producing gaseous ions from large biomolecules, the chemistry of gaseous bioions has become a highly active area of research. Gas-phase biomolecule-ion reactions are usually driven by interactions with neutral molecules, photons, electrons, ions, or surfaces. Ion dissociation or transformation into different ion types can be achieved. The types of reaction products observed depend on the characteristics of the ions, the transformation methods, and the time frame of observation. This review focuses on the gas-phase chemistries of ions derived from the electrospray ionization of peptides, proteins, and oligonucleotides, with particular emphasis on their utility in bioanalysis. Various ion-transformation strategies, which further facilitate structural interrogation by converting ions from one type to another, are also summarized. PMID:20636047

  2. MOVPE GaN gas phase chemistry for reactor design and optimization

    SciTech Connect

    Safvi, S.A.; Thon, A.; Kuech, T.F.; Redwing, J.M.; Flynn, J.S.; Tischler, M.A.

    1997-12-31

    The results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligomerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.

  3. Gas phase metal cluster model systems for heterogeneous catalysis.

    PubMed

    Lang, Sandra M; Bernhardt, Thorsten M

    2012-07-14

    Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed.

  4. Negative ion gas-phase chemistry of arenes.

    PubMed

    Danikiewicz, Witold; Zimnicka, Magdalena

    2016-01-01

    Reactions of aromatic and heteroaromatic compounds involving anions are of great importance in organic synthesis. Some of these reactions have been studied in the gas phase and are occasionally mentioned in reviews devoted to gas-phase negative ion chemistry, but no reviews exist that collect all existing information about these reactions. This work is intended to fill this gap. In the first part of this review, methods for generating arene anions in the gas phase and studying their physicochemical properties and fragmentation reactions are presented. The main topics in this part are as follows: processes in which gas-phase arene anions are formed, measurements and calculations of the proton affinities of arene anions, proton exchange reactions, and fragmentation processes of substituted arene anions, especially phenide ions. The second part is devoted to gas-phase reactions of arene anions. The most important of these are reactions with electrophiles such as carbonyl compounds and α,β-unsaturated carbonyl and related compounds (Michael acceptors). Other reactions including oxidation of arene anions and halogenophilic reactions are also presented. In the last part of the review, reactions of electrophilic arenes with nucleophiles are discussed. The best known of these is the aromatic nucleophilic substitution (SN Ar) reaction; however, other processes that lead to the substitution of a hydrogen atom in the aromatic ring are also very important. Aromatic substrates in these reactions are usually but not always nitroarenes bearing other substituents in the ring. The first step in these reactions is the formation of an anionic σ-adduct, which, depending on the substituents in the aromatic ring and the structure of the attacking nucleophile, is either an intermediate or a transition state in the reaction path. In the present review, we attempted to collect the results of both experimental and computational studies of the aforementioned reactions conducted since the

  5. Gas Phase Hydration of Methyl Glyoxal to Form the Gemdiol

    NASA Astrophysics Data System (ADS)

    Kroll, Jay A.; Axson, Jessica L.; Vaida, Veronica

    2016-06-01

    Methylglyoxal is a known oxidation product of volatile organic compounds (VOCs) in Earth's atmosphere. While the gas phase chemistry of methylglyoxal is fairly well understood, its modeled concentration and role in the formation of secondary organic aerosol (SOA) continues to be controversial. The gas phase hydration of methylglyoxal to form a gemdiol has not been widely considered for water-restricted environments such as the atmosphere. However, this process may have important consequences for the atmospheric processing of VOCs. We will report on spectroscopic work done in the Vaida laboratory studying the hydration of methylglyoxal and discuss the implications for understanding the atmospheric processing and fate of methylglyoxal and similar molecules.

  6. Gas-phase interactions of organotin compounds with cysteine.

    PubMed

    Latrous, Latifa; Salpin, Jean-Yves; Haldys, Violette; Léon, Emmanuelle; Correia, Catarina; Lamsabhi, Al Mokhtar

    2016-11-01

    The gas-phase interactions of cysteine with di-organotin and tri-organotin compounds have been studied by mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with cysteine results in the formation of [(R)2 Sn(Cys-H)](+) and [(R)3 Sn(Cys)](+) ions, respectively. MS/MS spectra of [(R)2 Sn(Cys-H)](+) complexes are characterized by numerous fragmentation processes, notably associated with elimination of NH3 and (C,H2 ,O2 ). Several dissociation routes are characteristic of each given organic species. Upon collision, both the [(R)3 Sn(Gly)](+) and [(R)3 Sn(Cys)](+) complexes are associated with elimination of the intact amino acid, leading to the formation of [(R)3 Sn](+) cation. But for the latter complex, two additional fragmentation processes are observed, associated with the elimination of NH3 and C3 H4 O2 S. Calculations indicate that the interaction between organotins and cysteine is predominantly electrostatic but also exhibits a considerable covalent character, which is slightly more pronounced in tri-organotin complexes. A preferred bidentate interaction of the type -η(2) -S-NH2 , with sulfur and the amino group, is observed. As for the [(R)3 Sn(Cys)](+) complexes, their stability is due to the combination of the hydrogen bond taking place between the amino group and the sulfur lone pair and the interaction between the carboxylic oxygen atom and the metal. Copyright © 2016 John Wiley & Sons, Ltd.

  7. Lycopene/arabinoxylan gels: rheological and controlled release characteristics.

    PubMed

    Hernández-Espinoza, Ana B; Piñón-Muñiz, Marina I; Rascón-Chu, Agustín; Santana-Rodríguez, Víctor M; Carvajal-Millan, Elizabeth

    2012-02-28

    Arabinoxylan gels exhibiting different rheological and lycopene transport properties were obtained by modifying the polysaccharide concentration from 3 to 4% (w/v). The apparent lycopene diffusion coefficient decreased from 2.7 × 10⁻⁷ to 2.4 × 10⁻⁷ cm²/s as the arabinoxylan concentration in the gel changed from 3 to 4% (w/v). A low amount of lycopene is released by diffusion from arabinoxylan gels. These results indicate that arabinoxylan gels could be carriers for lycopene delivery in specific sites after network degradation. The possibility to modulate lycopene release from arabinoxylan gels makes these biomaterials potential candidates for the controlled delivery of biomolecules.

  8. The Dipeptide Ala-Gly in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Bermúdez, Celina; Varela, Marcelino; Cabezas, Carlos; Peña, Isabel; Alonso, José L.

    2014-06-01

    The dipeptide Ala-Gly has been examined in gas phase by laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy in the frequency region 3-12 GHz. Three rotamers have been detected in the supersonic expansion. The quadrupole hyperfine structure of two 14N (I=1) nuclei has been totally resolved allowing the conclusive identification of one conformer.

  9. Ion-Molecule Reactions in Gas Phase Radiation Chemistry.

    ERIC Educational Resources Information Center

    Willis, Clive

    1981-01-01

    Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

  10. Ion-Molecule Reactions in Gas Phase Radiation Chemistry.

    ERIC Educational Resources Information Center

    Willis, Clive

    1981-01-01

    Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

  11. CHEMKIN2. General Gas-Phase Chemical Kinetics

    SciTech Connect

    Rupley, F.M.

    1992-01-24

    CHEMKIN is a high-level tool for chemists to use to describe arbitrary gas-phase chemical reaction mechanisms and systems of governing equations. It remains, however, for the user to select and implement a solution method; this is not provided. It consists of two major components: the Interpreter and the Gas-phase Subroutine Library. The Interpreter reads a symbolic description of an arbitrary, user-specified chemical reaction mechanism. A data file is generated which forms a link to the Gas-phase Subroutine Library, a collection of about 200 modular subroutines which may be called to return thermodynamic properties, chemical production rates, derivatives of thermodynamic properties, derivatives of chemical production rates, or sensitivity parameters. Both single and double precision versions of CHEMKIN are included. Also provided is a set of FORTRAN subroutines for evaluating gas-phase transport properties such as thermal conductivities, viscosities, and diffusion coefficients. These properties are an important part of any computational simulation of a chemically reacting flow. The transport properties subroutines are designed to be used in conjunction with the CHEMKIN Subroutine Library. The transport properties depend on the state of the gas and on certain molecular parameters. The parameters considered are the Lennard-Jones potential well depth and collision diameter, the dipole moment, the polarizability, and the rotational relaxation collision number.

  12. INVESTIGATION OF GAS-PHASE OZONE AS A POTENTIAL BIOCIDE

    EPA Science Inventory

    The paper presents data on the effect of ozone on both vegetative and spore-forming fungi as well as on spore-forming bacteria. (NOTE: Despite the wide use of ozone generators in indoor air cleaning, there is little research data on ozone's biocidal activity in the gas phase.) Dr...

  13. INVESTIGATION OF GAS-PHASE OZONE AS A POTENTIAL BIOCIDE

    EPA Science Inventory

    The paper presents data on the effect of ozone on both vegetative and spore-forming fungi as well as on spore-forming bacteria. (NOTE: Despite the wide use of ozone generators in indoor air cleaning, there is little research data on ozone's biocidal activity in the gas phase.) Dr...

  14. Gas-Phase Reactivity of Carboxylic Acid Functional Groups with Carbodiimides

    PubMed Central

    Prentice, Boone M.; Gilbert, Joshua D.; Stutzman, John R.; Forrest, William P.; McLuckey, Scott A.

    2012-01-01

    Gas-phase modification of carboxylic acid functionalities is performed via ion/ion reactions with carbodiimide reagents [N-cyclohexyl-N′-(2-morpholinoethyl)carbodiimide (CMC) and [3-(3-Ethylcarbodiimide-1-yl)propyl]trimethylaminium (ECPT). Gas-phase ion/ion covalent chemistry requires the formation of a long-lived complex. In this instance, the complex is stabilized by an electrostatic interaction between the fixed charge quaternary ammonium group of the carbodiimide reagent cation and the analyte dianion. Subsequent activation results in characteristic loss of an isocyanate derivative from one side of the carbodiimide functionality, a signature for this covalent chemistry. The resulting amide bond is formed on the analyte at the site of the original carboxylic acid. Reactions involving analytes that do not contain available carboxylic acid groups (e.g., they have been converted to sodium salts) or reagents that do not have the carbodiimide functionality do not undergo a covalent reaction. This chemistry is demonstrated using PAMAM generation 0.5 dendrimer, ethylenediaminetetraacetic acid (EDTA), and the model peptide DGAILDGAILD. This work demonstrates the selective gas-phase covalent modification of carboxylic acid functionalities. PMID:23208744

  15. Gas-phase reactivity of carboxylic acid functional groups with carbodiimides.

    PubMed

    Prentice, Boone M; Gilbert, Joshua D; Stutzman, John R; Forrest, William P; McLuckey, Scott A

    2013-01-01

    Gas-phase modification of carboxylic acid functionalities is performed via ion/ion reactions with carbodiimide reagents [N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) and [3-(3-Ethylcarbodiimide-1-yl)propyl]trimethylaminium (ECPT)]. Gas-phase ion/ion covalent chemistry requires the formation of a long-lived complex. In this instance, the complex is stabilized by an electrostatic interaction between the fixed charge quaternary ammonium group of the carbodiimide reagent cation and the analyte dianion. Subsequent activation results in characteristic loss of an isocyanate derivative from one side of the carbodiimide functionality, a signature for this covalent chemistry. The resulting amide bond is formed on the analyte at the site of the original carboxylic acid. Reactions involving analytes that do not contain available carboxylic acid groups (e.g., they have been converted to sodium salts) or reagents that do not have the carbodiimide functionality do not undergo a covalent reaction. This chemistry is demonstrated using PAMAM generation 0.5 dendrimer, ethylenediaminetetraacetic acid (EDTA), and the model peptide DGAILDGAILD. This work demonstrates the selective gas-phase covalent modification of carboxylic acid functionalities.

  16. Gas-phase IR spectra of intact [alpha]-helical coiled coil protein complexes

    NASA Astrophysics Data System (ADS)

    Pagel, Kevin; Kupser, Peter; Bierau, Frauke; Polfer, Nicolas C.; Steill, Jeffrey D.; Oomens, Jos; Meijer, Gerard; Koksch, Beate; von Helden, Gert

    2009-06-01

    Electrospray ionization (ESI) is the softest ionization method that is currently available and it is widely accepted, that ESI generated ions of proteins and protein assemblies at certain conditions retain characteristic aspects of their solution-state conformation. ESI mass spectrometry (MS) therefore evolved as a useful tool to obtain information on composition, stoichiometry, and dynamics of non-covalently associated protein complexes. While tertiary structure information of proteins can be obtained from ion mobility spectrometry (IMS), only a few techniques yield direct information on the secondary structure of gas-phase peptides and proteins. We present here the mid-IR spectroscopic secondary structural analysis of three de novo designed [alpha]-helical coiled coil model peptides and their non-covalently associated complexes in the gas-phase. The conformational stability of such coiled coil peptides in solution is primarily driven by aggregation. Isolated monomers usually remain unfolded. Two of the investigated peptides were designed to assemble into stable [alpha]-helical complexes in acidic solution, while the third one remains monomeric and unfolded at these conditions. Monomer ions of all three peptides show comparable photodissociation IR spectra and therefore suggest an unfolded conformation in the gas phase. In contrast, considerable CO stretch (amide-I) and N-H bend (amide-II) band shifts have been observed for the dimers which is consistent with an elevated H-bond content. These findings provide evidence that at least a fraction of the condensed phase [alpha]-helical structure is retained in the gas-phase coiled coil complexes.

  17. Verapamil hydrochloride release characteristics from new copolymer zwitterionic matrix tablets.

    PubMed

    Kostova, Bistra; Kamenska, Elena; Ivanov, Ivo; Momekov, George; Rachev, Dimitar; Georgiev, George

    2008-01-01

    The aim of this study was to synthesize stable copolymer (vinyl acetate-co-3-dimethyl[methacryloyloxyethyl] ammonium propane sulfinate) zwitterionic latex with different compositions for the first time by emulsifier-free emulsion copolymerization. Throughout the course of the study, a proposal was made for the explanation of the relationship between the "overshooting" phenomenon (a swelling kinetics with a maximum) and the specific self-association of the zwitterionic copolymers. The zwitterionic monomer unit mole fraction, pH, and ionic strength effects on this relationship, on the swelling kinetics of the zwitterionic copolymers, and on the sustained verapamil hydrochloride release from the model tablets were established by the study's authors.

  18. Flavin Adenine Dinucleotide Structural Motifs: From Solution to Gas Phase

    PubMed Central

    2015-01-01

    Flavin adenine dinucleotide (FAD) is involved in important metabolic reactions where the biological function is intrinsically related to changes in conformation. In the present work, FAD conformational changes were studied in solution and in gas phase by measuring the fluorescence decay time and ion-neutral collision cross sections (CCS, in a trapped ion mobility spectrometer, TIMS) as a function of the solvent conditions (i.e., organic content) and gas-phase collisional partner (i.e., N2 doped with organic molecules). Changes in the fluorescence decay suggest that FAD can exist in four conformations in solution, where the abundance of the extended conformations increases with the organic content. TIMS-MS experiments showed that FAD can exist in the gas phase as deprotonated (M = C27H31N9O15P2) and protonated forms (M = C27H33N9O15P2) and that multiple conformations (up to 12) can be observed as a function of the starting solution for the [M + H]+ and [M + Na]+molecular ions. In addition, changes in the relative abundances of the gas-phase structures were observed from a “stack” to a “close” conformation when organic molecules were introduced in the TIMS cell as collision partners. Candidate structures optimized at the DFT/B3LYP/6-31G(d,p) were proposed for each IMS band, and results showed that the most abundant IMS band corresponds to the most stable candidate structure. Solution and gas-phase experiments suggest that the driving force that stabilizes the different conformations is based on the interaction of the adenine and isoalloxazine rings that can be tailored by the “solvation” effect created with the organic molecules. PMID:25222439

  19. Is it biologically relevant to measure the structures of small peptides in the gas-phase?

    NASA Astrophysics Data System (ADS)

    Barran, Perdita E.; Polfer, Nick C.; Campopiano, Dominic J.; Clarke, David J.; Langridge-Smith, Patrick R. R.; Langley, Ross J.; Govan, John R. W.; Maxwell, Alison; Dorin, Julia R.; Millar, Robert P.; Bowers, Michael T.

    2005-02-01

    Recent developments in sample introduction of biologically relevant molecules have heralded a new era for gas-phase methods of structural determination. One of the biggest challenges is to relate gas-phase structures, often measured in the absence of water and counter ions, with in vivo biologically active structures. An advantage of gas-phase based techniques is that a given peptide can be analysed in a variety of different forms, for example, as a function of charge state, or with additional water molecules. Molecular modelling can provide insight into experimental findings and help elucidate the differences between structural forms. Combining experiment and theory provides a thorough interrogation of candidate conformations. Here two important naturally occurring peptide systems have been examined in detail and results are assessed in terms of their biological significance. The first of these is gonadotropin-releasing hormone (GnRH), a decapeptide which is the central regulator of the reproductive system in vertebrates. We have examined several naturally occurring variants of this peptide using Ion Mobility Mass Spectrometry and Electron Capture Dissociation (ECD) in conjunction with Fourier Transform Ion Cyclotron Mass Spectrometry (FT-ICR-MS). Candidate conformations are modelled using the AMBER force field. Single amino acid changes, for example Gly6 --> Ala6, or Ala6 --> D-Ala6, have observable effects on the gas phase structure of GnRH. It has been shown that evolutionary primary sequence variations are key to the biological activity of GnRH, and it is thought that this is due to different binding affinities at target receptors. This work provides strong evidence that this activity is structurally based. The second system examined is the relationship between the quaternary structure and activity of two novel [beta]-defensins. FT-ICR mass spectrometry has been employed to characterize di-sulphide bridging and dissociation based experiments utilised to

  20. Characteristics of pollutant gas releases from swine, dairy, beef, and layer manure, and municipal wastewater.

    PubMed

    Dai, Xiao-Rong; Saha, Chayan Kumer; Ni, Ji-Qin; Heber, Albert J; Blanes-Vidal, Victoria; Dunn, James L

    2015-06-01

    Knowledge about characteristics of gas releases from various types of organic wastes can assist in developing gas pollution reduction technologies and establishing environmental regulations. Five different organic wastes, i.e., four types of animal manure (swine, beef, dairy, and layer hen) and municipal wastewater, were studied for their characteristics of ammonia (NH3), carbon dioxide (CO2), hydrogen sulfide (H2S), and sulfur dioxide (SO2) releases for 38 or 43 days in reactors under laboratory conditions. Weekly waste additions and continuous reactor headspace ventilation were supplied to simulate waste storage conditions. Results demonstrated that among the five waste types, layer hen manure and municipal wastewater had the highest and lowest NH3 release potentials, respectively. Layer manure had the highest and dairy manure had the lowest CO2 release potentials. Dairy manure and layer manure had the highest and lowest H2S release potentials, respectively. Beef manure and layer manure had the highest and lowest SO2 releases, respectively. The physicochemical characteristics of the different types of wastes, especially the total nitrogen, total ammoniacal nitrogen, dry matter, and pH, had strong influence on the releases of the four gases. Even for the same type of waste, the variation in physicochemical characteristics affected the gas releases remarkably.

  1. Macro- and micro-nutrient release characteristics of three polymer-coated fertilizers: Theory and measurements

    USDA-ARS?s Scientific Manuscript database

    In spite of several published studies we have an incomplete understanding of the ion release mechanisms and characteristics of primary polymer-coated fertilizer (PCF) technologies. Here we extend current conceptual models describing release mechanisms and describe the critical effects of substrate m...

  2. Measuring Uptake Coefficients and Henry's Law Constants of Gas-Phase Species with Models for Secondary Organic Aerosol

    NASA Astrophysics Data System (ADS)

    Fairhurst, M. C.; Waring-Kidd, C.; Ezell, M. J.; Finlayson-Pitts, B. J.

    2014-12-01

    Volatile organic compounds (VOC) are oxidized in the atmosphere and their products contribute to secondary organic aerosol (SOA) formation. These particles have been shown to have effects on visibility, climate, and human health. Current models typically under-predict SOA concentrations from field measurements. Underestimation of these concentrations could be a result of how models treat particle growth. It is often assumed that particles grow via instantaneous thermal equilibrium partitioning between liquid particles and gas-phase species. Recent work has shown that growth may be better represented by irreversible, kinetically limited uptake of gas-phase species onto more viscous, tar-like SOA. However, uptake coefficients for these processes are not known. The goal of this project is to measure uptake coefficients and solubilities for different gases onto models serving as proxies for SOA and determine how they vary based on the chemical composition of the gas and the condensed phase. Experiments were conducted using two approaches: attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and a flow system coupled to a mass spectrometer. The ATR crystal was coated with the SOA proxy and the gas-phase species introduced via a custom flow system. Uptake of the gas-phase species was characterized by measuring the intensity of characteristic IR bands as a function of time, from which a Henry's law constant and initial estimate of uptake coefficients could be obtained. Uptake coefficients were also measured in a flow system where the walls of the flow tube were coated with the SOA proxy and gas-phase species introduced via a moveable inlet. Uptake coefficients were derived from the decay in gas-phase species measured by mass spectrometry. The results of this work will establish a structure-interaction relationship for uptake of gases into SOA that can be implemented into regional and global models.

  3. Enantiomeric Excess Determination for Monosaccharides Using Chiral Transmission to Cold Gas-Phase Tryptophan in Ultraviolet Photodissociation

    NASA Astrophysics Data System (ADS)

    Fujihara, Akimasa; Maeda, Naoto; Doan, Thuc N.; Hayakawa, Shigeo

    2017-02-01

    Chiral transmission between monosaccharides and amino acids via photodissociation in the gas phase was examined using a tandem mass spectrometer fitted with an electrospray ionization source and a cold ion trap in order to investigate the origin of the homochirality of biomolecules in molecular clouds. Ultraviolet photodissociation mass spectra of cold gas-phase noncovalent complexes of the monosaccharide enantiomers glucose (Glc) and galactose (Gal) with protonated l-tryptophan H+( l-Trp) were obtained by photoexcitation of the indole ring of l-Trp. l-Trp dissociated via Cα-Cβ bond cleavage when noncovalently complexed with d-Glc; however, no dissociation of l-Trp occurred in the homochiral H+( l-Trp)( l-Glc) noncovalent complex, where the energy absorbed by l-Trp was released through the evaporation of l-Glc. This enantioselective photodissociation of Trp was due to the transmission of chirality from Glc to Trp via photodissociation in the gas-phase noncovalent complexes, and was applied to the quantitative chiral analysis of monosaccharides. The enantiomeric excess of monosaccharides in solution could be determined by measuring the relative abundance of the two product ions in a single photodissociation mass spectrum of the cold gas-phase noncovalent complex with H+( l-Trp), and by referring to the linear relationships derived in this work.

  4. Gas-phase interactions of organotin compounds with glycine.

    PubMed

    Latrous, Latifa; Tortajada, Jeanine; Haldys, Violette; Léon, Emmanuelle; Correia, Catarina; Salpin, Jean-Yves

    2013-07-01

    Gas-phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with glycine results in the formation of [(R)2Sn(Gly)-H](+) and [(R)3Sn(Gly)](+) ions, respectively. Di-organotin complexes appear much more reactive than those involving tri-organotins. (MS/MS) spectra of the [(R)3Sn(Gly)](+) ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn](+) carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)-H](+) complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O + CO and formation of [(R)2SnOH](+) (-57 u),[(R)2SnNH2](+) (-58 u) and [(R)2SnH](+) (-73 u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O + CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH](+) and [(R2)SnNH2](+) ions. Interestingly, formation [(R)2SnH](+) ions is characterized by a migration of one the α hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)-H](+) complexes, a preferable bidentate interaction of the type η(2)-O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn](+) ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes.

  5. A robust estimate of the number and characteristics of persons released from prison in Australia.

    PubMed

    Avery, Alex; Kinner, Stuart A

    2015-08-01

    To estimate the number and characteristics of adults released from prison in Australia. We calculated ratios, stratified by age, sex and Indigenous status, by comparing the number of persons released from prison in New South Wales (NSW), with the number in NSW prisons on 30 June of the corresponding year. These stratified ratios were applied to Australia-wide prison data to estimate the number and characteristics of persons released annually. We estimated that in 2013, 38,576 persons were released from prison in Australia - 25.3% more than the daily prison population. Young people, Indigenous people and women were over-represented among those released. We estimated that 3.69 Indigenous women aged 18-24 were released annually for each equivalent person in prison; and 2.75 non-Indigenous women aged 18-24 were released annually for each equivalent person in prison. The annual 'flow' through Australia's prisons is well in excess of the daily number, but information on those moving through prison systems is not yet publicly available. The characteristics of those released from prison differ meaningfully from those of people in prison. Routine, national reporting of prison separations is critical to informing upscaling and targeting of Throughcare services for this profoundly vulnerable population. © 2015 Public Health Association of Australia.

  6. Correlation between the FT-IR characteristics and metoprolol tartrate release of methylcellulose-based patches.

    PubMed

    Papp, József; Horgos, József; Szente, Virág; Zelkó, Romána

    2010-06-15

    The aim of the present study was to investigate how the drug release and FT-IR characteristics of metolose patches were influenced by the changes of Metolose SM 4000 (methylcellulose) and Metolose 90SH 100.000SR (hypromellose) proportions. FT-IR spectroscopy measurements were performed in parallel with the metoprolol tartrate release study to track the effect of the composition on the drug release. The metoprolol tartrate release profile of the patches was evaluated by Weibull distribution. Linear relationship was found with good correlation between the logarithm of time interval necessary to release 63.2% of metoprolol tartrate (tau(d) values) and the peak area measured within the characteristic FT-IR wavenumbers of patches. The application of FT-IR measurements can be recommended as a rapid, non-destructive screening method during the in-process control of patches.

  7. Release characteristics of alkali and alkaline earth metallic species during biomass pyrolysis and steam gasification process.

    PubMed

    Long, Jiang; Song, Hu; Jun, Xiang; Sheng, Su; Lun-Shi, Sun; Kai, Xu; Yao, Yao

    2012-07-01

    Investigating the release characteristics of alkali and alkaline earth metallic species (AAEMs) is of potential interest because of AAEM's possible useful service as catalysts in biomass thermal conversion. In this study, three kinds of typical Chinese biomass were selected to pyrolyse and their chars were subsequently steam gasified in a designed quartz fixed-bed reactor to investigate the release characteristics of alkali and alkaline earth metallic species (AAEMs). The results indicate that 53-76% of alkali metal and 27-40% of alkaline earth metal release in pyrolysis process, as well as 12-34% of alkali metal and 12-16% of alkaline earth metal evaporate in char gasification process, and temperature is not the only factor to impact AAEMs emission. The releasing characteristics of AAEMs during pyrolysis and char gasification process of three kinds of biomass were discussed in this paper. Copyright © 2012 Elsevier Ltd. All rights reserved.

  8. Effect of heat release on movement characteristics of shock train in an isolator

    NASA Astrophysics Data System (ADS)

    Zhang, Chenlin; Chang, Juntao; Liu, MengMeng; Feng, Shuo; Shi, Wen; Bao, Wen

    2017-04-01

    In this paper, the effect of heat release on movement characteristics of shock train is numerically investigated in an isolator. It is found that the combustion heat release has a distinct effect on the shock train movement characteristics in the isolator. With increasing heat release, a shock train gradually forms and then propagates toward isolator entrance. In process of shock train formation, separation bubbles before injection ports entrain the high temperature burning gas into the boundary layer, which causes the shock train to shrink and stretch, and changes in configuration and number of shock waves. At the same time, the system force fluctuates. In addition, the shock train movement is divided into three stages, which have different wall pressure distribution. It is believed that these findings have a help the better understanding of the effect of heat release on the movement characteristics of shock train in an isolator.

  9. Substituent effects on the gas-phase acidity of silane

    SciTech Connect

    Gordon, M.S.; Volk, D.E. ); Gano, D.R. )

    1989-12-20

    In a previous paper, the gas-phase acidities of XH{sub n} compounds (X = C, N, O, F, Si, P, S, Cl) were predicted with ab initio wave functions. At the MP4{sup 2} level of theory with extended basis sets acidities for these species were determined to be within 2 kcal/mol of experimental value. In the present work, with 6-31G(d) geometries and full MP4/MC-311++G{sup 6}(3df,2pd) energies, the effects of CH{sub 3}, NH{sub 2}, OH, F, SiH{sub 3}, PH{sub 2}, SH, and Cl on the gas-phase acidity of silane are examined. Only a few related calculations have been carried out. All calculations were performed with Gaussian86, and all structures were verified as minima by diagonalizing the analytically determined hessians. Only the valence electrons were correlated in the perturbation theory calculations.

  10. Structure and dynamics of oligonucleotides in the gas phase.

    PubMed

    Arcella, Annalisa; Dreyer, Jens; Ippoliti, Emiliano; Ivani, Ivan; Portella, Guillem; Gabelica, Valérie; Carloni, Paolo; Orozco, Modesto

    2015-01-07

    By combining ion-mobility mass spectrometry experiments with sub-millisecond classical and ab initio molecular dynamics we fully characterized, for the first time, the dynamic ensemble of a model nucleic acid in the gas phase under electrospray ionization conditions. The studied oligonucleotide unfolds upon vaporization, loses memory of the solution structure, and explores true gas-phase conformational space. Contrary to our original expectations, the oligonucleotide shows very rich dynamics in three different timescales (multi-picosecond, nanosecond, and sub-millisecond). The shorter timescale dynamics has a quantum mechanical nature and leads to changes in the covalent structure, whereas the other two are of classical origin. Overall, this study suggests that a re-evaluation on our view of the physics of nucleic acids upon vaporization is needed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Gas Phase Chiral Separations By Ion Mobility Spectrometry

    PubMed Central

    Dwivedi, Prabha; Wu, Ching; Hill, Herbert H.

    2013-01-01

    This manuscript introduces the concept of Chiral Ion Mobility Spectrometry (CIMS) and presents examples demonstrating the gas phase separation of enantiomers of a wide range of racemates including pharmaceuticals, amino acids and carbohydrates. CIMS is similar to traditional ion mobility spectrometry (IMS), where gas phase ions, when subjected to a potential gradient are separated at atmospheric pressure due to differences in their shapes and sizes. In addition to size and shape, CIMS separates ions based on their stereospecific interaction with a chiral gas. In order to achieve chiral discrimination by CIMS, an asymmetric environment was provided by doping the drift gas with a volatile chiral reagent. In this study S-(+)-2-butanol was used as a chiral modifier to demonstrate enantiomeric separations of atenolol, serine, methionine, threonine, methyl-α-glucopyranoside, glucose, penicillamine, valinol, phenylalanine, and tryptophan from their respective racemic mixtures. PMID:17165808

  12. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    NASA Astrophysics Data System (ADS)

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ɛ-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.

  13. Gas phase dynamics of triplet formation in benzophenone.

    PubMed

    Spighi, Gloria; Gaveau, Marc-André; Mestdagh, Jean-Michel; Poisson, Lionel; Soep, Benoît

    2014-05-28

    Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0. We have found that the triplet formation can be described almost as a direct process in preparing T1, the lowest reacting triplet state, from the S1 state after S2 → S1 internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution.

  14. Gas-phase diffusion in porous media: Comparison of models

    SciTech Connect

    Webb, S.W.

    1998-09-01

    Two models are commonly used to analyze gas-phase diffusion in porous media in the presence of advection, the Advective-Dispersive Model (ADM) and the Dusty-gas Model (DGM). The ADM, which is used in TOUGH2, is based on a simple linear addition of advection calculated by Darcy`s law and ordinary diffusion using Fick`s law with a porosity-tortuosity-gas saturation multiplier to account for the porous medium. Another approach for gas-phase transport in porous media is the Dusty-Gas Model. This model applies the kinetic theory of gases to the gaseous components and the porous media (or dust) to combine transport due to diffusion and advection that includes porous medium effects. The two approaches are compared in this paper.

  15. Observation of gas-phase anionic bismuth zintl ions

    SciTech Connect

    Farley, R.W.; Castleman, A.W. Jr. )

    1989-03-29

    The authors report in this communication the first observation of gas-phase anionic Zintl ions of bismuth. Laser-ionization time-of-flight mass spectra of mixed bismuth/alkali clusters produced by a gas aggregation source were investigated in their laboratory and found to exhibit maxima for clusters corresponding to reported Zintl ions. Bonding in homoatomic clusters is a topic of fundamental as well as practical importance. The electronic and geometric structure of metal clusters in particular is currently the subject of intense investigation among a great number of researchers. Magic numbers corresponding to particularly abundant gas-phase cluster ions are observed to depend on the identity of the metal or alloy and on the ionization conditions. Reasons for the exceptional stabilities of such magic numbers have been ascribed to preferred electronic and structural configurations for either the neutral or ionic species.

  16. Model of boron diffusion from gas phase in silicon carbide

    SciTech Connect

    Aleksandrov, O. V.; Mokhov, E. N.

    2011-06-15

    Boron diffusion from the gas phase in silicon carbide is described on the basis of a two-component model. 'Shallow' boron, i.e., boron at silicon sites, is a slow component with a high surface concentration. Its diffusivity is proportional to the concentration of positively charged intrinsic point defects, which are presumably interstitial silicon atoms. 'Deep' boron, i.e., impurity-defect pairs of boron-carbon vacancy, is a fast component with lower surface concentration. The ratio between the surface concentrations of the components depends on the pressure of silicon or carbon vapors in the gas phase. The diffusion and interaction of components are described by the set of diffusion-reaction equations. The diffusion retardation observed on the concentration-profile tail is related to the capture of impurity-defect pairs and excess vacancies by traps of background impurities and defects.

  17. Gas-Phase Studies of Formamidopyrimidine Glycosylase (Fpg) Substrates.

    PubMed

    Kiruba, G S M; Xu, Jiahui; Zelikson, Victoria; Lee, Jeehiun K

    2016-03-07

    Gas-phase thermochemical properties (tautomerism, acidity, and proton affinity) have been measured and calculated for a series of nucleobase derivatives that have not heretofore been examined under vacuum. The studied species are substrates for the enzyme formamidopyrimidine glycosylase (Fpg), which cleaves damaged nucleobases from DNA. The gas-phase results are compared and contrasted to solution-phase data, to afford insight into the Fpg mechanism. Calculations are also used to probe the energetics of various possible mechanisms and to predict isotope effects that could potentially allow for discrimination between different mechanisms. Specifically, (18) O substitution at the ribose O4' is predicted to result in a normal kinetic isotope effect (KIE) for a ring-opening "endocyclic" mechanism and an inverse KIE for a direct base excision "exocyclic" pathway.

  18. Spectroscopic studies of cold, gas-phase biomolecular ions

    NASA Astrophysics Data System (ADS)

    Rizzo, Thomas R.; Stearns, Jaime A.; Boyarkin, Oleg V.

    While the marriage of mass spectrometry and laser spectroscopy is not new, developments over the last few years in this relationship have opened up new horizons for the spectroscopic study of biological molecules. The combination of electrospray ionisation for producing large biological molecules in the gas phase together with cooled ion traps and multiple-resonance laser schemes are allowing spectroscopic investigation of individual conformations of peptides with more than a dozen amino acids. Highly resolved infrared spectra of single conformations of such species provide important benchmarks for testing the accuracy of theoretical calculations. This review presents a number of techniques employed in our laboratory and in others for measuring the spectroscopy of cold, gas-phase protonated peptides. We show examples that demonstrate the power of these techniques and evaluate their extension to still larger biological molecules.

  19. The physical chemistry of Criegee intermediates in the gas phase

    DOE PAGES

    Osborn, David L.; Taatjes, Craig A.

    2015-07-24

    Here, carbonyl oxides, also known as Criegee intermediates, are key intermediates in both gas phase ozonolysis of unsaturated hydrocarbons in the troposphere and solution phase organic synthesis via ozonolysis. Although the study of Criegee intermediates in both arenas has a long history, direct studies in the gas phase have only recently become possible through new methods of generating stabilised Criegee intermediates in sufficient quantities. This advance has catalysed a large number of new experimental and theoretical investigations of Criegee intermediate chemistry. In this article we review the physical chemistry of Criegee intermediates, focusing on their molecular structure, spectroscopy, unimolecular andmore » bimolecular reactions. These recent results have overturned conclusions from some previous studies, while confirming others, and have clarified areas of investigation that will be critical targets for future studies. In addition to expanding our fundamental understanding of Criegee intermediates, the rapidly expanding knowledge base will support increasingly predictive models of their impacts on society.« less

  20. Para-Hydrogen-Enhanced Gas-Phase Magnetic Resonance Imaging

    SciTech Connect

    Bouchard, Louis-S.; Kovtunov, Kirill V.; Burt, Scott R.; Anwar,M. Sabieh; Koptyug, Igor V.; Sagdeev, Renad Z.; Pines, Alexander

    2007-02-23

    Herein, we demonstrate magnetic resonance imaging (MRI) inthe gas phase using para-hydrogen (p-H2)-induced polarization. A reactantmixture of H2 enriched in the paraspin state and propylene gas is flowedthrough a reactor cell containing a heterogenized catalyst, Wilkinson'scatalyst immobilized on modified silica gel. The hydrogenation product,propane gas, is transferred to the NMR magnet and is spin-polarized as aresult of the ALTADENA (adiabatic longitudinal transport and dissociationengenders net alignment) effect. A polarization enhancement factor of 300relative to thermally polarized gas was observed in 1D1H NMR spectra.Enhancement was also evident in the magnetic resonance images. This isthe first demonstration of imaging a hyperpolarized gaseous productformed in a hydrogenation reaction catalyzed by a supported catalyst.This result may lead to several important applications, includingflow-through porous materials, gas-phase reaction kinetics and adsorptionstudies, and MRI in low fields, all using catalyst-free polarizedfluids.

  1. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    PubMed Central

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ε-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas-phase, where they are shown to be reactive, and the solution-phase, where they are not regarded as reactive with NHS esters. PMID:25338221

  2. The physical chemistry of Criegee intermediates in the gas phase

    SciTech Connect

    Osborn, David L.; Taatjes, Craig A.

    2015-07-24

    Here, carbonyl oxides, also known as Criegee intermediates, are key intermediates in both gas phase ozonolysis of unsaturated hydrocarbons in the troposphere and solution phase organic synthesis via ozonolysis. Although the study of Criegee intermediates in both arenas has a long history, direct studies in the gas phase have only recently become possible through new methods of generating stabilised Criegee intermediates in sufficient quantities. This advance has catalysed a large number of new experimental and theoretical investigations of Criegee intermediate chemistry. In this article we review the physical chemistry of Criegee intermediates, focusing on their molecular structure, spectroscopy, unimolecular and bimolecular reactions. These recent results have overturned conclusions from some previous studies, while confirming others, and have clarified areas of investigation that will be critical targets for future studies. In addition to expanding our fundamental understanding of Criegee intermediates, the rapidly expanding knowledge base will support increasingly predictive models of their impacts on society.

  3. Hydration of Gas-Phase Ions Formed by Electrospray Ionization

    PubMed Central

    Rodriguez-Cruz, Sandra E.; Klassen, John S.; Williams, Evan R.

    2005-01-01

    The hydration of gas-phase ions produced by electrospray ionization was investigated. Evidence that the hydrated ions are formed by two mechanisms is presented. First, solvent condensation during the expansion inside the electrospray source clearly occurs. Second, some solvent evaporation from more extensively solvated ions or droplets is apparent. To the extent that these highly solvated ions have solution-phase structures, then the final isolated gas-phase structure of the ion will be determined by the solvent evaporation process. This process was investigated for hydrated gramicidin S in a Fourier-transform mass spectrometer. Unimolecular dissociation rate constants of isolated gramicidin S ions with between 2 and 14 associated water molecules were measured. These rate constants increased from 16 to 230 s−1 with increasing hydration, with smaller values corresponding to magic numbers. PMID:10497808

  4. [Sociodemographic characteristics of users of the contraceptive implant releasing etonogestrel].

    PubMed

    Rosales Aujang, Enrique; González Roque, María Guadalupe

    2009-03-01

    The search for options for contraception has always led to the development of increasingly effective methods and safe and, above all, varied for those with any contraindication to always find a viable alternative. To know the sociodemography characteristics the users of implants liberating contraceptive of etonogestrel and the effects in the 24 following months to its application. A cross-sectional descriptive study was made in 207 users of implants liberating of etonogestrel during 24 months in the Aguascalientes Delegation of IMSS through a structured questionnaire. The Statistic Program v 7 for the capture, data processing and analysis of were used. The group of more frequent age was of 25-29 years; the majority had at least secondary, lived in the urban middle, were married and catholic; 48.6% were dedicated to the home; 1.2% of the pairs did not work; 82.6% had a weekly sex at least; 84.3% had 1 to 2 children; 66.3% wished more children; 95.9% of the pairs approved the method; 29:6% referred a not planned previous pregnancy ; 72.1% used some contraceptive method previously; 36.6% referred bad experience with the previous method; 41.9% requested implants by comfort; 90:1% received information of the method but only 73.8% knew the indirect effect; 86.6% would recommend it; 11.6% left the method by undesirable effects of which the main one was the irregular bled one, whereas 33.1% did not present/display any indirect effect and no patient became pregnant during the time of study. It subdermal implant is a contraceptive alternative adapted by its effectiveness, its tolerance and the high rate of continuity, finding like basic characteristics of the users: young woman, with acceptable educative and economic level, low parity and desires of future fertility.

  5. The nucleoside uridine isolated in the gas phase.

    PubMed

    Peña, Isabel; Cabezas, Carlos; Alonso, José L

    2015-03-02

    Herein we present the first experimental observation of the isolated nucleoside uridine, placed in the gas phase by laser ablation and characterized by Fourier transform (FT) microwave techniques. Free from the bulk effects of their native environments, anti/C2'-endo-g+ conformation has been revealed as the most stable form of uridine. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside.

  6. The Kinetics and Dynamics of Elementary Gas-Phase Reactions

    DTIC Science & Technology

    2002-09-01

    Hawthorne Jati Salh Paul Sharkey Rowland Spencer-Smith Lee Herbert Meez Islam Chris Moore David Stewart Gary Ward Michael Osborne Sarah Henton...energy. The Kinetics and Dynamics of Elementary Gas Phase Reactions, 2002 23 REMPI-LIF Studies of Ion-Molecule Reactions Michael J. Frost...for the Study of Collisional Energy Transfer Hilary Crichton School of Engineering and Physical Sciences, Heriot-Watt University. Previous

  7. Laboratory Studies of Solvated Gas-Phase Anions.

    DTIC Science & Technology

    1982-02-01

    The Journal of Chemical Physics . 2. John F. Paulson, Michael J. Henchman, and Peter M. Hierl, "Effect of Reactant Ion Solvation on Gas-Phase SN2 Reactions," manuscript in final stages of preparation for submission to The Journal of Chemical Physics . D. PROFESSIONAL PERSONNEL Calvin Cole, Ph.D. Candidate, Department of Chemistry, University of Kansas, Lawrence, KS 66045 E. INTERACTIONS i. Oral Presentations P.M. Hierl, M.J. Henchman, and J; I Paulson,

  8. Gas phase fractionation method using porous ceramic membrane

    DOEpatents

    Peterson, Reid A.; Hill, Jr., Charles G.; Anderson, Marc A.

    1996-01-01

    Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

  9. The Nucleoside Uridine Isolated in the Gas Phase**

    PubMed Central

    Peña, Isabel; Cabezas, Carlos; Alonso, José L.

    2016-01-01

    Herein we present the first experimental observation of the isolated nucleoside uridine, placed in the gas phase by laser ablation and characterized by Fourier transform microwave techniques. Free from the bulk effects of their native environments, anti/C2’-endo-g+ conformation has been revealed as the most stable form of uridine. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside. PMID:25683559

  10. A Uranyl Peroxide Dimer in the Gas Phase.

    PubMed

    Dau, Phuong D; Dau, Phuong V; Rao, Linfeng; Kovács, Attila; Gibson, John K

    2017-04-03

    The gas-phase uranyl peroxide dimer, [(UO2)2(O2)(L)2](2+) where L = 2,2'-trifluoroethylazanediyl)bis(N,N'-dimethylacetamide), was synthesized by electrospray ionization of a solution of UO2(2+) and L. Collision-induced dissociation of this dimer resulted in endothermic O atom elimination to give [(UO2)2(O)(L)2](2+), which was found to spontaneously react with water via exothermic hydrolytic chemisorption to yield [(UO2)2(OH)2(L)2](2+). Density functional theory computations of the energies for the gas-phase reactions are in accord with observations. The structures of the observed uranyl dimer were computed, with that of the peroxide of particular interest, as a basis to evaluate the formation of condensed phase uranyl peroxides with bent structures. The computed dihedral angle in [(UO2)2(O2)(L)2](2+) is 145°, indicating a substantial deviation from the planar structure with a dihedral angle of 180°. Energies needed to induce bending in the most elementary gas-phase uranyl peroxide complex, [(UO2)2(O2)](2+), were computed. It was found that bending from the lowest-energy planar structure to dihedral angles up to 140° required energies of <10 kJ/mol. The gas-phase results demonstrate the inherent stability of the uranyl peroxide moiety and support the notion that the uranyl-peroxide-uranyl structural unit is intrinsically planar, with only minor energy perturbations needed to form the bent structures found in studtite and uranyl peroxide nanostructures.

  11. Gas phase chemical detection with an integrated chemical analysis system

    SciTech Connect

    CASALNUOVO,STEPHEN A.; FRYE-MASON,GREGORY CHARLES; KOTTENSTETTE,RICHARD; HELLER,EDWIN J.; MATZKE,CAROLYN M.; LEWIS,PATRICK R.; MANGINELL,RONALD P.; BACA,ALBERT G.; HIETALA,VINCENT M.

    2000-04-12

    Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample preconcentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described.

  12. Optically-Based Diagnostics for Gas-Phase Laser Development

    DTIC Science & Technology

    2010-08-01

    Phase Laser Development Acknowledgement of Support and Disclaimer This material is based upon work supported by Air Force Office of Scientific...00-2010 4. TITLE AND SUBTITLE Optically-Based Diagnostics for Gas-Phase Laser Development 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM...Sciences Inc. Role of Optical Diagnostics in High Energy Gas Laser Development  Chemically rich, energetic, reacting flow with competing phenomena

  13. Gas Phase Synthesis of Nanostructured Films and Coatings

    DTIC Science & Technology

    2000-01-01

    observed and conditions for stable growth are given. In the plateau regime additional formation of nanoparticles occurs in the gas phase and...suppressed and most of the precursor is transformed into nanoparticles because fewer precursor molecules reach the substrate surface. While this regime...is not desirable in conventional film growth because of the incorporation of the nanoparticles into the films, this regime is used for the formation

  14. Understanding Gas-Phase Ammonia Chemistry in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Chambers, Lauren; Oberg, Karin I.; Cleeves, Lauren Ilsedore

    2017-01-01

    Protoplanetary disks are dynamic regions of gas and dust around young stars, the remnants of star formation, that evolve and coagulate over millions of years in order to ultimately form planets. The chemical composition of protoplanetary disks is affected by both the chemical and physical conditions in which they develop, including the initial molecular abundances in the birth cloud, the spectrum and intensity of radiation from the host star and nearby systems, and mixing and turbulence within the disk. A more complete understanding of the chemical evolution of disks enables a more complete understanding of the chemical composition of planets that may form within them, and of their capability to support life. One element known to be essential for life on Earth is nitrogen, which often is present in the form of ammonia (NH3). Recent observations by Salinas et al. (2016) reveal a theoretical discrepancy in the gas-phase and ice-phase ammonia abundances in protoplanetary disks; while observations of comets and protostars estimate the ice-phase NH3/H2O ratio in disks to be 5%, Salinas reports a gas-phase NH3/H2O ratio of ~7-84% in the disk surrounding TW Hydra, a young nearby star. Through computational chemical modeling of the TW Hydra disk using a reaction network of over 5000 chemical reactions, I am investigating the possible sources of excess gas-phase NH3 by determining the primary reaction pathways of NH3 production; the downstream chemical effects of ionization by ultraviolet photons, X-rays, and cosmic rays; and the effects of altering the initial abundances of key molecules such as N and N2. Beyond providing a theoretical explanation for the NH3 ice/gas discrepancy, this new model may lead to fuller understanding of the gas-phase formation processes of all nitrogen hydrides (NHx), and thus fuller understanding of the nitrogen-bearing molecules that are fundamental for life as we know it.

  15. Effect of carboxymethylation on rheological and drug release characteristics of locust bean gum matrix tablets.

    PubMed

    Chakravorty, Amrita; Barman, Gouranga; Mukherjee, Sudipta; Sa, Biswanath

    2016-06-25

    This study was undertaken to investigate correlation between the carboxymethylation-induced rheological changes and drug release characteristics of locust bean gum (LBG) matrix tablets. LBG was derivatized to carboxymethyl LBG (CMLBG) and characterized by (13)C NMR, FTIR and elemental analyses. Rheological studies revealed that LBG, in contact with water, produced a strong elastic gel which swelled less due to lower penetration of water resulting in slower drug release. On the other hand, CMLBG formed a viscous polymer solution through which higher influx of water resulted in rapid swelling of the matrix and faster drug release. Although the release from a particular matrix was dependent on drugs' solubilities, CMLBG matrix tablet produced faster release of all the drugs than LBG matrix tablets. In conclusion, rheological study appeared to be an useful tool to predict release of drugs from polysaccharide matrix tablets.

  16. Going clean: structure and dynamics of peptides in the gas phase and paths to solvation

    NASA Astrophysics Data System (ADS)

    Baldauf, Carsten; Rossi, Mariana

    2015-12-01

    The gas phase is an artificial environment for biomolecules that has gained much attention both experimentally and theoretically due to its unique characteristic of providing a clean room environment for the comparison between theory and experiment. In this review we give an overview mainly on first-principles simulations of isolated peptides and the initial steps of their interactions with ions and solvent molecules: a bottom up approach to the complexity of biological environments. We focus on the accuracy of different methods to explore the conformational space, the connections between theory and experiment regarding collision cross section evaluations and (anharmonic) vibrational spectra, and the challenges faced in this field.

  17. Gas phase adduct reactions in MOCVD growth of GaN

    SciTech Connect

    Thon, A.; Kuech, T.F.

    1996-11-01

    Gas phase reactions between trimethylgallium (TMG) and ammonia were studied at high temperatures, characteristic to MOCVD of GaN reactors, by means of in situ mass spectroscopy in a flow tube reactor. It is shown, that a very fast adduct formation followed by elimination of methane occurs. The decomposition of TMG and the adduct-derived compounds are both first order and have similar apparent activation energy. The pre-exponential factor of the adduct decomposition is smaller, and hence is responsible for the higher full decomposition temperature of the adduct relative to that of TMG.

  18. [Release characteristics in vitro and pharmacokinetics of da chuanxiong fang multiunit drug delivery system in rats].

    PubMed

    Wei, Yuan-feng; Zhang, Ning; Lin, Xiao; Feng, Yi

    2011-09-01

    The drug release characteristics ofDa Chuanxiong Fang multiunit drug delivery system (DCXFMDDS) in vivo and in vitro were evaluated. Ferulic acid (FA) and senkyunolide I (SI) were used as marker components, which were two of the effective components of Da Chuanxiong Fang. And their contents were determined by HPLC. Drug release characteristics in vitro of DCXFMDDS and Da Chuanxiong pills and pharmacokinetics characteristics of DCXFMDDS and Da Chuanxiong Fang active fraction (DCXFAF) in rats were compared. It was obvious that FA released from the DCXFMDDS in a sustained fashion but SI in a fast fashion both in vitro and in vivo. The releasing process and the releasing mechanism of FA and SI from DCXFMDDS were different, but the AUC value indicated that compared with DCXFAF the extent of absorption of FA and SI from DCXFMDDS was increased. Though from the same multiunit drug delivery system, FA an SI had different drug release characteristics both in vitro and in vivo, and that may be one of the reason why DCXFMDDS has the good properties such as rapid and long-lasting effect and high efficiency.

  19. Impact of release characteristics of sinomenine hydrochloride dosage forms on its pharmacokinetics in beagle dogs

    PubMed Central

    Sun, Jin; Shi, Jie-Ming; Zhang, Tian-Hong; Gao, Kun; Mao, Jing-Jing; Li, Bing; Sun, Ying-Hua; He, Zhong-Gui

    2005-01-01

    AIM: To investigate the effect of release behavior of sustained-release dosage forms of sinomenine hydrochloride (SM•HCl) on its pharmacokinetics in beagle dogs. METHODS: The in vitro release behavior of two SM•HCl dosage forms, including commercial 12-h sustained-release tablets and 24-h sustained-release pellets prepared in our laboratory, was examined. The two dosage forms were orally administrated to beagle dogs, and then the in vivo SM•HCl pharmacokinetics was investigated and compared. RESULTS: The optimal SM•HCl sustained-release formulation was achieved by mixing slow- and rapid-release pellets (9:1, w/w). The SM•HCl release profiles of the sustained-release pellets were scarcely influenced by the pH of the dissolution medium. Release from the 12-h sustained-release tablets was markedly quicker than that from the 24-h sustained-release pellets, the cumulative release up to 12-h was 99.9% vs 68.7%. From a pharmacokinetic standpoint, the 24-h SM•HCl sustained-release pellets had longer tmax and lower Cmax compared to the 12-h sustained-release tablets, the tmax being 2.67×0.52 h vs 9.83×0.98 h and the Cmax being 1 334.45±368.76 ng/mL vs 893.12±292.55 ng/mL, respectively. However, the AUC0-tn of two SM•HCl dosage forms was comparable and both preparations were statistically bioequivalent. Furthermore, the two preparations had good correlations between SM•HCl percentage absorption in vivo and the cumulative percentage release in vitro. CONCLUSION: The in vitro release properties of the dosage forms strongly affect their pharmacokinetic behavior in vivo. Therefore, managing the in vitro release behavior of dosage forms is a promising strategy for obtaining the optimal in vivo pharmacokinetic characteristics and safe therapeutic drug concentration-time curves. PMID:16052686

  20. A study of critical functionality-related characteristics of HPMC for sustained-release tablets.

    PubMed

    Košir, Darjan; Ojsteršek, Tadej; Baumgartner, Saša; Vrečer, Franc

    2016-12-23

    The drug release profile from hydrophilic matrix tablets can be crucially affected by the variability of physicochemical properties of the controlled release agent. This study investigates and seeks to understand the functionality-related characteristics (FRCs) of hydroxypropyl methylcellulose (HPMC) type 2208, K4M grade, that influence the release rate of the model drug carvedilol from hydrophilic matrix tablets during the entire dissolution profile. The following FRCs were examined: particle size distribution, degree of substitution, and viscosity. Eight different HPMC samples were used to create a suitable design space. Multiple linear regression (MLR) and partial least squares regression (PLSR) analyses were used to create models for each time point. The PLSR results show that the first part of the drug release profiles is mainly regulated by the HPMC particle size. Apparent viscosity and hydroxypropoxy content (%HP) become important in later stages of the drug release profile, when the influence of particle size distribution decreases. These findings make it possible to better understand the importance of FRCs. Larger HPMC particles increase drug release in the first part of the drug release profile, whereas decreased apparent viscosity and a higher degree of %HP increase the drug release rate in the later part of the drug release profile.

  1. Estimate of radionuclide release characteristics into containment under severe accident conditions. Final report

    SciTech Connect

    Nourbakhsh, H.P.

    1993-11-01

    A detailed review of the available light water reactor source term information is presented as a technical basis for development of updated source terms into the containment under severe accident conditions. Simplified estimates of radionuclide release and transport characteristics are specified for each unique combination of the reactor coolant and containment system combinations. A quantitative uncertainty analysis in the release to the containment using NUREG-1150 methodology is also presented.

  2. Gas phase laser synthesis and processing of calcium phosphate nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Bapat, Parimal V.

    Biochemical processes make pervasive use of calcium and phosphate ions. Calcium phosphate salts that are naturally nontoxic and bioactive have been used for several medical applications in form of coatings and micropowders. Nanoparticle-based calcium phosphates have been shown to be internalized by living cells and be effective in DNA transfection, drug delivery, and transport of fluorophores for imaging of intracellular processes. They are also expected to interact strongly with cell adhesive proteins and are therefore promising elements in approaches to mimic the complex environment of the extra cellular matrix of bone. Harnessing this biomedical potential requires the ability to control the numerous characteristics of nanophase calcium phosphates that affect biological response, including nanoparticle chemical composition, crystal phase, crystallinity, crystallographic orientation of exposed faces, size, shape, surface area, number concentration, and degree of aggregation. This dissertation focuses on the use of laser-induced gas-phase synthesis for creation of calcium phosphate nanoparticles, and corresponding nanoparticle-based substrates that could offer new opportunities for guiding biological responses through well-controlled biochemical and topological cues. Gas-phase synthesis of nanoparticles has several characteristics that could enhance control over particle morphology, crystallinity, and surface area, compared to liquid-phase techniques. Synthesis from gas-phase precursors can be carried out at high temperatures and in high-purity inert or reactive gas backgrounds, enabling good control of chemistry, crystal structure, and purity. Moreover, the particle mean free path and number concentration can be controlled independently. This allows regulation of interparticle collision rates, which can be adjusted to limit aggregation. High-temperature synthesis of well-separated particles is therefore possible. In this work high power lasers are employed to

  3. Fluorescence Spectroscopy of Gas-phase Polycyclic Aromatic Hydrocarbons

    NASA Technical Reports Server (NTRS)

    Thomas, J. D.; Witt, A. N.

    2006-01-01

    The purpose of this investigation was to produce fluorescence spectra of polycyclic aromatic hydrocarbon (PAH) molecules in the gas-phase for comparison with blue luminescence (BL) emission observed in astrophysical sources Vijh et al. (2004, 2005a,b). The BL occurs roughly from 350 to 450 nm, with a sharp peak near 380 nm. PAHs with three to four rings, e.g. anthracene and pyrene, were found to produce luminescence in the appropriate spectral region, based on existing studies. Relatively few studies of the gas-phase fluorescence of PAHs exist; those that do exist have dealt primarily with the same samples commonly available for purchase such as pyrene and anthracene. In an attempt to understand the chemistry of the nebular environment we also obtained several nitrogen substituted PAHs from our colleagues at NASA Ames. In order to simulate the astrophysical environment we also took spectra by heating the PAHs in a flame. The flame environment counteracts the formation of eximers and permits the spectroscopy of free-flying neutral molecules. Experiments with coal tar demonstrate that fluorescence spectroscopy reveals primarily the presence of the smallest molecules, which are most abundant and which possess the highest fluorescence efficiencies. One gas-phase PAH that seems to fit the BL spectrum most closely is phenanthridine. In view of the results from the spectroscopy of coal tar, a compound containing a mixture of PAHs ranging from small to very large PAH molecules, we can not preclude the presence of larger PAHs in interstellar sources exhibiting BL.

  4. Gas-phase chemistry of ruthenium and rhodium carbonyl complexes.

    PubMed

    Cao, Shiwei; Wang, Yang; Qin, Zhi; Fan, Fangli; Haba, Hiromitsu; Komori, Yukiko; Wu, Xiaolei; Tan, Cunmin; Zhang, Xin

    2016-01-07

    Short-lived ruthenium and rhodium isotopes were produced from a (252)Cf spontaneous fission (SF) source. Their volatile carbonyl complexes were formed in gas-phase reactions in situ with the carbon-monoxide containing gas. A gas-jet system was employed to transport the volatile carbonyls from the recoil chamber to the chemical separation apparatus. The gas-phase chemical behaviors of these carbonyl complexes were studied using an online low temperature isothermal chromatography (IC) technique. Long IC columns made up of FEP Teflon were used to obtain the chemical information of the high-volatile Ru and Rh carbonyls. By excluding the influence of precursor effects, short-lived isotopes of (109-110)Ru and (111-112)Rh were used to represent the chemical behaviours of Ru and Rh carbonyls. Relative chemical yields of about 75% and 20% were measured for Ru(CO)5 and Rh(CO)4, respectively, relative to the yields of KCl aerosols transported in Ar gas. The adsorption enthalpies of ruthenium and rhodium carbonyl complexes on a Teflon surface were determined to be around ΔHads = -33(+1)(-2) kJ mol(-1) and -36(+2)(-1) kJ mol(-1), respectively, by fitting the breakthrough curves of the corresponding carbonyl complexes with a Monte Carlo simulation program. Different from Mo and Tc carbonyls, a small amount of oxygen gas was found to be not effective for the chemical yields of ruthenium and rhodium carbonyl complexes. The general chemical behaviors of short-lived carbonyl complexes of group VI-IX elements were discussed, which can be used in the future study on the gas-phase chemistry of superheavy elements - Bh, Hs, and Mt carbonyls.

  5. Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis

    PubMed Central

    Buesser, B.; Gröhn, A.J.

    2013-01-01

    Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

  6. Femtosecond analysis of free molecular rotation in the gas phase

    NASA Astrophysics Data System (ADS)

    Borisevich, N. A.; Khoroshilov, E. V.; Kryukov, I. V.; Kryukov, P. G.; Sharkov, A. V.; Blokhin, A. P.; Tolstorozhev, G. B.

    1992-04-01

    The time-resolved S 1→S *n absorption anisotropy decay resulting from rotation of free gas phase POPOP molecules at 593 K and PPO molecules at 483 K was studied after S 0→S *1 excitation by femtosecond linearly polarized pulses at 308 nm. The time evolution of the anisotropy measured through a few picoseconds after excitation is in agreement with the results of calculations made for POPOP and PPO using orientational correlation functions developed for rigid asymmetric top molecules.

  7. Theoretical calculations of EPR parameters of gas phase hydracrylonitrile radical

    NASA Astrophysics Data System (ADS)

    Sarikaya, Ebru Karakaş; Dereli, Ömer

    2017-02-01

    As a result of detailed conformational search of the hydracrylonitrile, four different conformers of molecule have been obtained. For these conformations, eleven possible radicals were modelled by using density functional theory (DFT) computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were calculated by B3LYP method using 6-311++G(d,p) basis sets in gas phase.

  8. Neurotransmitters in the Gas Phase: La-Mb Studies

    NASA Astrophysics Data System (ADS)

    Cabezas, C.; Mata, S.; López, J. C.; Alonso, J. L.

    2011-06-01

    LA-MB-FTMW spectroscopy combines laser ablation with Fourier transform microwave spectroscopy in supersonic jets overcoming the problems of thermal decomposition associated with conventional heating methods. We present here the results on LA-MB-FTMW studies of some neurotransmitters. Six conformers of dopamine, four of adrenaline, five of noradrenaline and three conformers of serotonin have been characterized in the gas phase. The rotational and nuclear quadrupole coupling constants extracted from the analysis of the rotational spectrum are directly compared with those predicted by ab initio methods to achieve the conclusive identification of different conformers and the experimental characterization of the intramolecular forces at play which control conformational preferences.

  9. Hydration of monomeric metaphosphate anion in the gas phase

    SciTech Connect

    Keesee, R.G.; Castleman, A.W. Jr. )

    1989-12-06

    Thermochemical data for the clustering of water molecules onto the monomeric metaphosphate anion PO{sub 3}{sup {minus}} in the gas phase are derived from a study by high-pressure mass spectrometry. Experimental details are described, and the enthalpy and entropy changes for the successive addition of the first four water (D{sub 2}O) molecules are reported. The results indicate that PO{sub 3}{sup {minus}} undergoes simple adduct formation up to the second hydration step, but the third hydration step involves an isomerization of the ion-water cluster into the dihydrate of the dihydrogen orthophosphate anion.

  10. Gas Phase Chemical Detection with an Integrated Chemical Analysis System

    SciTech Connect

    Baca, Albert G.; Casalnuovo, Stephen A.; Frye-Mason, Gregory C.; Heller, Edwin J.; Hietala, Susan L.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carloyn M.; Reno, John L.; Sasaki, Darryl Y.; Schubert, W. Kent

    1999-07-08

    Microfabrication technology has been applied to the development of a miniature, multi-channel gas phase chemical laboratory that provides fast response, small size, and enhanced versatility and chemical discrimination. Each analysis channel includes a sample concentrator followed by a gas chromatographic separator and a chemically selective surface acoustic wave detector array to achieve high sensitivity and selectivity. The performance of the components, individually and collectively, is described. The design and performance of novel micromachined acoustic wave devices, with the potential for improved chemical sensitivity, are also described.

  11. The solar system/interstellar medium connection - Gas phase abundances

    NASA Technical Reports Server (NTRS)

    Lutz, Barry L.

    1987-01-01

    Gas-phase abundances in the outer solar system are presented as diagnostics of the interstellar medium at the time of the solar system formation, some 4.55 billion years ago. Possible influences of the thermal and chemical histories of the primitive solar nebula and of the processes which led to the formation and evolution of the outer planets and comets on the elemental and molecular composition of the primordial matter are outlined. The major components of the atmospheres of the outer planets and of the comae of comets are identified, and the cosmogonical and cosmological implications are discussed.

  12. Gas-phase energetics of thorium fluorides and their ions.

    PubMed

    Irikura, Karl K

    2013-02-14

    Gas-phase thermochemistry for neutral ThF(n) and cations ThF(n)(+) (n = 1-4) is obtained from large-basis CCSD(T) calculations, with a small-core pseudopotential on thorium. Electronic partition functions are computed with the help of relativistic MRCI calculations. Geometries, vibrational spectra, electronic fine structure, and ion appearance energies are tabulated. These results support the experimental results by Lau, Brittain, and Hildenbrand for the neutral species, except for ThF. The ion thermochemistry is presented here for the first time.

  13. Nanosized sustained-release pyridostigmine bromide microcapsules: process optimization and evaluation of characteristics

    PubMed Central

    Tan, Qunyou; Jiang, Rong; Xu, Meiling; Liu, Guodong; Li, Songlin; Zhang, Jingqing

    2013-01-01

    Background Pyridostigmine bromide (3-[[(dimethylamino)-carbonyl]oxy]-1-methylpyridinium bromide), a reversible inhibitor of cholinesterase, is given orally in tablet form, and a treatment schedule of multiple daily doses is recommended for adult patients. Nanotechnology was used in this study to develop an alternative sustained-release delivery system for pyridostigmine, a synthetic drug with high solubility and poor oral bioavailability, hence a Class III drug according to the Biopharmaceutics Classification System. Novel nanosized pyridostigmine-poly(lactic acid) microcapsules (PPNMCs) were expected to have a longer duration of action than free pyridostigmine and previously reported sustained-release formulations of pyridostigmine. Methods The PPNMCs were prepared using a double emulsion-solvent evaporation method to achieve sustained-release characteristics for pyridostigmine. The preparation process for the PPNMCs was optimized by single-factor experiments. The size distribution, zeta potential, and sustained-release behavior were evaluated in different types of release medium. Results The optimal volume ratio of inner phase to external phase, poly(lactic acid) concentration, polyvinyl alcohol concentration, and amount of pyridostigmine were 1:10, 6%, 3% and 40 mg, respectively. The negatively charged PPNMCs had an average particle size of 937.9 nm. Compared with free pyridostigmine, PPNMCs showed an initial burst release and a subsequent very slow release in vitro. The release profiles for the PPNMCs in four different types of dissolution medium were fitted to the Ritger-Peppas and Weibull models. The similarity between pairs of dissolution profiles for the PPNMCs in different types of medium was statistically significant, and the difference between the release curves for PPNMCs and free pyridostigmine was also statistically significant. Conclusion PPNMCs prepared by the optimized protocol described here were in the nanometer range and had good uniformity

  14. Nanosized sustained-release pyridostigmine bromide microcapsules: process optimization and evaluation of characteristics.

    PubMed

    Tan, Qunyou; Jiang, Rong; Xu, Meiling; Liu, Guodong; Li, Songlin; Zhang, Jingqing

    2013-01-01

    Pyridostigmine bromide (3-[[(dimethylamino)-carbonyl]oxy]-1-methylpyridinium bromide), a reversible inhibitor of cholinesterase, is given orally in tablet form, and a treatment schedule of multiple daily doses is recommended for adult patients. Nanotechnology was used in this study to develop an alternative sustained-release delivery system for pyridostigmine, a synthetic drug with high solubility and poor oral bioavailability, hence a Class III drug according to the Biopharmaceutics Classification System. Novel nanosized pyridostigmine-poly(lactic acid) microcapsules (PPNMCs) were expected to have a longer duration of action than free pyridostigmine and previously reported sustained-release formulations of pyridostigmine. The PPNMCs were prepared using a double emulsion-solvent evaporation method to achieve sustained-release characteristics for pyridostigmine. The preparation process for the PPNMCs was optimized by single-factor experiments. The size distribution, zeta potential, and sustained-release behavior were evaluated in different types of release medium. The optimal volume ratio of inner phase to external phase, poly(lactic acid) concentration, polyvinyl alcohol concentration, and amount of pyridostigmine were 1:10, 6%, 3% and 40 mg, respectively. The negatively charged PPNMCs had an average particle size of 937.9 nm. Compared with free pyridostigmine, PPNMCs showed an initial burst release and a subsequent very slow release in vitro. The release profiles for the PPNMCs in four different types of dissolution medium were fitted to the Ritger-Peppas and Weibull models. The similarity between pairs of dissolution profiles for the PPNMCs in different types of medium was statistically significant, and the difference between the release curves for PPNMCs and free pyridostigmine was also statistically significant. PPNMCs prepared by the optimized protocol described here were in the nanometer range and had good uniformity, with significantly slower pyridostigmine

  15. Gender differences in treatment and clinical characteristics among patients receiving extended release naltrexone.

    PubMed

    Herbeck, Diane M; Jeter, Kira E; Cousins, Sarah J; Abdelmaksoud, Reham; Crèvecoeur-MacPhail, Desirée

    2016-01-01

    Further research is needed to investigate real-world acceptability of extended-release naltrexone for alcohol and opioid use disorders, and potential gender differences. This study examines treatment and clinical characteristics among men and women receiving extended-release naltrexone in a large, publicly funded substance use disorder treatment system (N = 465; 52% female). Patient demographics, treatment characteristics, and the number of extended-release naltrexone doses received were collected from administrative data and treatment program staff. Additionally, patients provided information on experiences with extended-release naltrexone in an open-ended format at 1, 2, and 3 weeks following their first injection. For a subsample of patients (N = 220), alcohol/opioid cravings and specific adverse effects were also assessed. Compared to men, women reported experiencing a higher rate and mean number of adverse effects. Overall, craving scores showed substantial reductions over time. However, among patients taking extended-release naltrexone for alcohol use, women showed a significantly greater reduction in craving scores compared to men. No gender differences were observed in the number of extended-release naltrexone doses received. Although women may have a greater need for additional support in managing early adverse effects, extended-release naltrexone as an adjunct to psychosocial treatment may be an acceptable and promising treatment approach for both men and women, and particularly for women prescribed extended-release naltrexone for alcohol use. This study contributes further information on patients' experiences during the early course of extended-release naltrexone treatment in real-world settings. Understanding these experiences may assist policy makers and treatment providers in addressing challenges of implementing this treatment into wider practice.

  16. Cool Mist Scavenging of Gas-Phase Molecules.

    PubMed

    Wu, Pei-Chi; Dutkiewicz, Ewelina P; Urban, Pawel L

    2017-01-01

    The purpose of analytical extractions is to simplify sample matrix without losing analyte molecules. Here we present a technique of extracting volatile compounds by scavenging gas-phase molecules with tiny liquid droplets (<10 μm). A cool mist of the extracting solvent is generated by an ultrasonic transducer, transferred to the headspace of the sample chamber under atmospheric conditions, and pushed by a small pressure difference toward a condenser. By slowly passing over the sample, the microdroplets extract volatile species present in the sample headspace, and they coalesce in a cooled zone. The condensed liquid is collected for analysis by direct infusion mass spectrometry or chromatography coupled with mass spectrometry. Due to the high surface-to-volume ratio of the microdroplets, the mist depletes a great share of the volatile organics present in the headspace. Other advantages of cool mist scavenging include: selective extraction of gas-phase molecules, the extracting solvent can be miscible with the sample solvent, simplicity, high speed, and no requirement for heating that could potentially decompose the sample. In this study, cool mist scavenging was first tested on artificial samples containing esters. The relationship between the sample concentration and the extract concentration was verified theoretically and experimentally. Some of the possible confounding effects were tested and discussed. The technique was subsequently applied to qualitative analysis of selected complex samples in liquid and solid phase as well as an esterification reaction.

  17. Gas-phase reactions of cyclopropenylidene with protonated alkyl amines.

    PubMed

    Lin, Ziqing; Tan, Lei; Yang, Yang; Dai, Mingji; Tureček, František; Ouyang, Zheng; Xia, Yu

    2016-04-21

    Vinylidene carbenes (C3H2) are of high interest to interstellar, combustion, and organic chemistry. Due to their high instability, the direct experimental investigation of their chemical reactivity has rarely been achieved. Herein, we report a first study on the reactions of cyclopropenylidene (c-C3H2) with protonated alkyl amines in the gas phase using a home-built ion trap mass spectrometer. The high gas-phase basicity (GB) of ((1)A1) c-C3H2 (calculated as 920 kJ mol(-1)) facilitates the formation of a proton-bound dimer with protonated amines as the first step in the reaction. The dimer can stay as it is or rearrange to a covalent product. The formation of the covalent complex is highly exothermic and its yield is affected by the GB of alkyl amines. The highest yield (82%) was achieved when the GB of the amine was slightly lower but comparable to that of c-C3H2. Our results demonstrate a new reaction pathway of c-C3H2, which has long been considered as a "dead end" in interstellar carbon chemistry.

  18. Gas phase oxidation downstream of a catalytic combustor

    NASA Technical Reports Server (NTRS)

    Tien, J. S.; Anderson, D. N.

    1979-01-01

    Effect of the length available for gas-phase reactions downstream of the catalytic reactor on the emission of CO and unburned hydrocarbons was investigated. A premixed, prevaporized propane/air feed to a 12/cm/diameter catalytic/reactor test section was used. The catalytic reactor was made of four 2.5 cm long monolithic catalyst elements. Four water cooled gas sampling probes were located at positions between 0 and 22 cm downstream of the catalytic reactor. Measurements of unburned hydrocarbon, CO, and CO2 were made. Tests were performed with an inlet air temperature of 800 K, a reference velocity of 10 m/s, pressures of 3 and 600,000 Pa, and fuel air equivalence ratios of 0.14 to 0.24. For very lean mixtures, hydrocarbon emissions were high and CO continued to be formed downstream of the catalytic reactor. At the highest equivalence ratios tested, hydrocarbon levels were much lower and CO was oxidized to CO2 in the gas phase downstream. To achieve acceptable emissions, a downstream region several times longer than the catalytic reactor could be required.

  19. Gas-Phase Fragmentation Analysis of Nitro-Fatty Acids

    PubMed Central

    Bonacci, Gustavo; Asciutto, Eliana K.; Woodcock, Steven R.; Salvatore, Sonia R.; Freeman, Bruce A.; Schopfer, Francisco J.

    2012-01-01

    Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO2− anion or neutral loss of HNO2. The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional γ or δ unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond π electrons during NO2− rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of 13C and 15N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples. PMID:21953257

  20. Gas phase reaction of sulfur trioxide with water vapor

    SciTech Connect

    Kolb, C.E.; Molina, M.J.; Jayne, J.T.; Meads, R.F.; Worsnop, D.R.

    1994-12-31

    Sulfur trioxide (SO3) has long been known to react with water to produce sulfuric acid (H2S04). It has been commonly assumed that the gas phase reaction in the Earth`s atmosphere between SO3 and water vapor to produce sulfuric acid vapor is an important step in the production of sulfuric acid aerosol particles. The kinetics of the gas phase reaction of SO3 with water vapor have previously been studied by Castleman and co-workers, Wang et al and Reiner and Arnold. Each of these studies was carried out in a flow reactor, with the first two studies performed at low pressure (1-10 Torr) and the latter from approx. 30 to 260 Torr. Each of these studies measured SO3 decays over a range of H2O vapor levels, obtaining data consistent with interpreting the reaction of gaseous SO3 and H2O as a bimolecular process. It is not clear why previous experimental studies failed to observe a nonlinear dependence of SO3 consumption on water vapor concentration. It is probable that sufficient water dimer exists in much of the Earth`s atmosphere to allow dimer reactions to participate in sulfuric acid vapor formation.

  1. Star formation and gas phase history of the cosmic web

    NASA Astrophysics Data System (ADS)

    Snedden, Ali; Coughlin, Jared; Phillips, Lara Arielle; Mathews, Grant; Suh, In-Saeng

    2016-01-01

    We present a new method of tracking and characterizing the environment in which galaxies and their associated circumgalactic medium evolve. We have developed a structure finding algorithm that uses the rate of change of the density gradient to self-consistently parse and follow the evolution of groups/clusters, filaments and voids in large-scale structure simulations. We use this to trace the complete evolution of the baryons in the gas phase and the star formation history within each structure in our simulated volume. We vary the structure measure threshold to probe the complex inner structure of star-forming regions in poor clusters, filaments and voids. We find that the majority of star formation occurs in cold, condensed gas in filaments at intermediate redshifts (z ˜ 3). We also show that much of the star formation above a redshift z = 3 occurs in low-contrast regions of filaments, but as the density contrast increases at lower redshift, star formation switches to the high-contrast regions, or inner parts, of filaments. Since filaments bridge the void and cluster regions, it suggests that the majority of star formation occurs in galaxies in intermediate density regions prior to the accretion on to groups/clusters. We find that both filaments and poor clusters are multiphase environments distinguishing themselves by different distributions of gas phases.

  2. Preconceptual design of the gas-phase decontamination demonstration cart

    SciTech Connect

    Munday, E.B.

    1993-12-01

    Removal of uranium deposits from the interior surfaces of gaseous diffusion equipment will be a major portion of the overall multibillion dollar effort to decontaminate and decommission the gaseous diffusion plants. Long-term low-temperature (LTLT) gas-phase decontamination is being developed at the K-25 Site as an in situ decontamination process that is expected to significantly lower the decontamination costs, reduce worker exposure to radioactive materials, and reduce safeguard concerns. This report documents the preconceptual design of the process equipment that is necessary to conduct a full-scale demonstration of the LTLT method in accordance with the process steps listed above. The process equipment and method proposed in this report are not intended to represent a full-scale production campaign design and operation, since the gas evacuation, gas charging, and off-gas handling systems that would be cost effective in a production campaign are not cost effective for a first-time demonstration. However, the design presented here is expected to be applicable to special decontamination projects beyond the demonstration, which could include the Deposit Recovery Program. The equipment will therefore be sized to a 200 ft size 1 converter (plus a substantial conservative design margin), which is the largest item of interest for gas phase decontamination in the Deposit Recovery Program. The decontamination equipment will allow recovery of the UF{sub 6}, which is generated from the reaction of ClF{sub 3} with the uranium deposits, by use of NaF traps.

  3. High resolution dissociative electron attachment to gas phase adenine

    SciTech Connect

    Huber, D.; Beikircher, M.; Denifl, S.; Zappa, F.; Matejcik, S.; Bacher, A.; Grill, V.; Maerk, T. D.; Scheier, P.

    2006-08-28

    The dissociative electron attachment to the gas phase nucleobase adenine is studied using two different experiments. A double focusing sector field mass spectrometer is utilized for measurements requiring high mass resolution, high sensitivity, and relative ion yields for all the fragment anions and a hemispherical electron monochromator instrument for high electron energy resolution. The negative ion mass spectra are discussed at two different electron energies of 2 and 6 eV. In contrast to previous gas phase studies a number of new negative ions are discovered in the mass spectra. The ion efficiency curves for the negative ions of adenine are measured for the electron energy range from about 0 to 15 eV with an electron energy resolution of about 100 meV. The total anion yield derived via the summation of all measured fragment anions is compared with the total cross section for negative ion formation measured recently without mass spectrometry. For adenine the shape of the two cross section curves agrees well, taking into account the different electron energy resolutions; however, for thymine some peculiar differences are observed.

  4. Thermochemical aspects of proton transfer in the gas phase.

    PubMed

    Gal, J F; Maria, P C; Raczyńska, E D

    2001-07-01

    The beginning of the twentieth century saw the development of new theories of acidity and basicity, which are currently well accepted. The thermochemistry of proton transfer in the absence of solvent attracted much interest during this period, because of the fundamental importance of the process. Nevertheless, before the 1950s, few data were available, either from lattice energy evaluations or from calculations using the emerging molecular orbital theory. Advances in mass spectrometry during the last 40 years allowed studies of numerous systems with better accuracy. Thousands of accurate gas-phase acidities or basicities are now available, for simple atomic and molecular systems and for large biomolecules. The intrinsic effect of structure on the Brønsted basic or acidic properties of molecules and the influence of solvents have been unravelled. In this tutorial, the basics of the thermodynamic principles involved are given, and the mass spectrometric techniques are briefly reviewed. Advances in the design and measurements of gas-phase superacids and superbases are described. Recent studies concerning biomolecules are also evoked. Copyright 2001 John Wiley & Sons, Ltd.

  5. Analysis of gas-phase condensation of nickel nanoparticles

    NASA Astrophysics Data System (ADS)

    Gafner, S. L.; Gafner, Yu. Ya.

    2008-10-01

    Gas-phase condensation of 8000 nickel atoms is examined by molecular dynamics simulation with a tight-binding potential. A detailed study of the evolution of the system cooled at a constant rate from 1000 K to 77 K is presented. The results are used to identify four distinct stages of the evolution from a hot atomic gas to a few synthesized particles. An analysis of possible nanoparticle formation mechanisms suggests that cluster-cluster aggregation is the dominant one. The simulation shows that there two stages of cluster formation are of primary importance with regard to aggregation. At the first stage, spherical liquid clusters nucleate with uniform size distribution. The second stage is characterized by a distinct transition from uniform to bimodal size distribution due to aggregation of relatively large clusters. The particles obtained by gas-phase synthesis are analyzed by the CNA method [25]. It is found that most nanoparticles produced in the simulation have either icosahedral or mixed FCC/HCP structure.

  6. Nahoon: Time-dependent gas-phase chemical model

    NASA Astrophysics Data System (ADS)

    Wakelam, V.

    2014-09-01

    Nahoon is a gas-phase chemical model that computes the chemical evolution in a 1D temperature and density structure. It uses chemical networks downloaded from the KInetic Database for Astrochemistry (KIDA) but the model can be adapted to any network. The program is written in Fortran 90 and uses the DLSODES (double precision) solver from the ODEPACK package to solve the coupled stiff differential equations. The solver computes the chemical evolution of gas-phase species at a fixed temperature and density and can be used in one dimension (1D) if a grid of temperature, density, and visual extinction is provided. Grains, both neutral and negatively charged, and electrons are considered as chemical species and their concentrations are computed at the same time as those of the other species. Nahoon contains a test to check the temperature range of the validity of the rate coefficients and avoid extrapolations outside this range. A test is also included to check for duplication of chemical reactions, defined over complementary ranges of temperature.

  7. Chemical reactivity on gas-phase metal clusters driven by blackbody infrared radiation.

    PubMed

    Parry, Imogen S; Kartouzian, Aras; Hamilton, Suzanne M; Balaj, O Petru; Beyer, Martin K; Mackenzie, Stuart R

    2015-01-19

    We report the observation of chemical reactions in gas-phase Rh(n)(N2O)m(+) complexes driven by absorption of blackbody radiation. The experiments are performed under collision-free conditions in a Fourier transform ion cyclotron resonance mass spectrometer. Mid-infrared absorption by the molecularly adsorbed N2O moieties promotes a small fraction of the cluster distribution sufficiently to drive the N2O decomposition reaction, leading to the production of cluster oxides and the release of molecular nitrogen. N2O decomposition competes with molecular desorption and the branching ratios for the two processes show marked size effects, reflecting variations in the relative barriers. The rate of decay is shown to scale approximately linearly with the number of infrared chromophores. The experimental findings are interpreted in terms of calculated infrared absorption rates assuming a sudden-death limit.

  8. Electrons Mediate the Gas-Phase Oxidation of Formic Acid with Ozone.

    PubMed

    van der Linde, Christian; Tang, Wai-Kit; Siu, Chi-Kit; Beyer, Martin K

    2016-08-26

    Gas-phase reactions of CO3 (.-) with formic acid are studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Signal loss indicates the release of a free electron, with the formation of neutral reaction products. This is corroborated by adding traces of SF6 to the reaction gas, which scavenges 38 % of the electrons. Quantum chemical calculations of the reaction potential energy surface provide a reaction path for the formation of neutral carbon dioxide and water as the thermochemically favored products. From the literature, it is known that free electrons in the troposphere attach to O2 , which in turn transfer the electron to O3 . O3 (.-) reacts with CO2 to form CO3 (.-) . The reaction reported here formally closes the catalytic cycle for the oxidation of formic acid with ozone, catalyzed by free electrons. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. 3D Printing of Medicines: Engineering Novel Oral Devices with Unique Design and Drug Release Characteristics.

    PubMed

    Goyanes, Alvaro; Wang, Jie; Buanz, Asma; Martínez-Pacheco, Ramón; Telford, Richard; Gaisford, Simon; Basit, Abdul W

    2015-11-02

    Three dimensional printing (3D printing) was used to fabricate novel oral drug delivery devices with specialized design configurations. Each device was loaded with multiple actives, with the intent of applying this process to the production of personalized medicines tailored at the point of dispensing or use. A filament extruder was used to obtain drug-loaded--paracetamol (acetaminophen) or caffeine--filaments of poly(vinyl alcohol) with characteristics suitable for use in fused-deposition modeling 3D printing. A multinozzle 3D printer enabled fabrication of capsule-shaped solid devices containing the drug with different internal structures. The design configurations included a multilayer device, with each layer containing drug, whose identity was different to the drug in the adjacent layers, and a two-compartment device comprising a caplet embedded within a larger caplet (DuoCaplet), with each compartment containing a different drug. Raman spectroscopy was used to collect 2-dimensional hyper spectral arrays across the entire surface of the devices. Processing of the arrays using direct classical least-squares component matching to produce false color representations of distribution of the drugs was used. This clearly showed a definitive separation between the drug layers of paracetamol and caffeine. Drug release tests in biorelevant bicarbonate media showed unique drug release profiles dependent on the macrostructure of the devices. In the case of the multilayer devices, release of both paracetamol and caffeine was simultaneous and independent of drug solubility. With the DuoCaplet design, it was possible to engineer either rapid drug release or delayed release by selecting the site of incorporation of the drug in the device; the lag-time for release from the internal compartment was dependent on the characteristics of the external layer. The study confirms the potential of 3D printing to fabricate multiple-drug containing devices with specialized design

  10. Diesel-related hydrocarbons can dominate gas phase reactive carbon in megacities

    NASA Astrophysics Data System (ADS)

    Dunmore, R. E.; Hopkins, J. R.; Lidster, R. T.; Lee, J. D.; Evans, M. J.; Rickard, A. R.; Lewis, A. C.; Hamilton, J. F.

    2015-03-01

    Hydrocarbons are key precursors to two priority air pollutants, ozone and particulate matter. Those with two to seven carbons have historically been straightforward to observe and have been successfully reduced in many developed cities through air quality policy interventions. Longer chain hydrocarbons released from diesel vehicles are not considered explicitly as part of air quality strategies and there are few direct measurements of their gaseous abundance in the atmosphere. This study describes the chemically comprehensive and continuous measurements of organic compounds in a developed megacity (London), which demonstrate that on a seasonal median basis, diesel-related hydrocarbons represent only 20-30% of the total hydrocarbon mixing ratio but comprise more than 50% of the atmospheric hydrocarbon mass and are a dominant local source of secondary organic aerosols. This study shows for the first time that, 60% of the winter primary hydrocarbon hydroxyl radical reactivity is from diesel-related hydrocarbons and using the maximum incremental reactivity scale, we predict that they contribute up to 50% of the ozone production potential in London. Comparing real-world urban composition with regulatory emissions inventories in the UK and US highlights a previously unaccounted for but, very significant under-reporting of diesel related hydrocarbons; an underestimation of a factor ~ 4 for C9 species rising to a factor of over 70 for C12 during winter. These observations show that hydrocarbons from diesel vehicles can dominate gas phase reactive carbon in cities with high diesel fleet fractions. Future control of urban particulate matter and ozone in such locations requires a shift in policy focus onto gas phase hydrocarbons released from diesels as this vehicle type continues to displace gasoline world-wide.

  11. Diesel-related hydrocarbons can dominate gas phase reactive carbon in megacities

    NASA Astrophysics Data System (ADS)

    Dunmore, R. E.; Hopkins, J. R.; Lidster, R. T.; Lee, J. D.; Evans, M. J.; Rickard, A. R.; Lewis, A. C.; Hamilton, J. F.

    2015-09-01

    Hydrocarbons are key precursors to two priority air pollutants, ozone and particulate matter. Those with two to seven carbons have historically been straightforward to observe and have been successfully reduced in many developed cities through air quality policy interventions. Longer chain hydrocarbons released from diesel vehicles are not considered explicitly as part of air quality strategies and there are few direct measurements of their gaseous abundance in the atmosphere. This study describes the chemically comprehensive and continuous measurements of organic compounds in a developed megacity (London), which demonstrate that on a seasonal median basis, diesel-related hydrocarbons represent only 20-30 % of the total hydrocarbon mixing ratio but comprise more than 50 % of the atmospheric hydrocarbon mass and are a dominant local source of secondary organic aerosols. This study shows for the first time that 60 % of the winter primary hydrocarbon hydroxyl radical reactivity is from diesel-related hydrocarbons and using the maximum incremental reactivity scale, we predict that they contribute up to 50 % of the ozone production potential in London. Comparing real-world urban composition with regulatory emissions inventories in the UK and US highlights a previously unaccounted for, but very significant, under-reporting of diesel-related hydrocarbons; an underestimation of a factor ~4 for C9 species rising to a factor of over 70 for C12 during winter. These observations show that hydrocarbons from diesel vehicles can dominate gas phase reactive carbon in cities with high diesel fleet fractions. Future control of urban particulate matter and ozone in such locations requires a shift in policy focus onto gas phase hydrocarbons released from diesels as this vehicle type continues to displace gasoline world-wide.

  12. Low energy conformations and gas-phase acidity and basicity of pyrrolysine.

    PubMed

    Meng, Lingbiao; Wang, Zhuo; Zhang, Jicheng; Zhou, Minjie; Wu, Weidong

    2014-08-28

    The gas-phase conformational potential energy surfaces (PES) of the last, 22nd amino acid pyrrolysine and related derivatives (neutral, deprotonated, and protonated) were extensively searched for the first time. By considering all possible combinations of the single-bond rotational degrees of freedom with a semiempirical and ab initio combined computational approach, a large set of unique low-energy conformers was identified for each pyrrolysine species, and essential properties such as vibrational frequencies, dipole moments, rotational constants, and intramolecular hydrogen bonding configurations were presented and characterized. The conformational electronic energies and thermochemical properties of proton affinity/dissociation energy (PA/PDE) and gas-phase acidity/basicity (GA/GB) were determined by the density functional BHandHLYP, B3LYP, and M062X, and Møller-Plesset MP2 methods. The MP2 and DFT methods are found to predict disparate PES for neutral and protonated conformations and sufficiently different thermochemical data. The measurements of dipole moments and characteristic IR modes at low temperature as well as GA/GB are demonstrated to be feasible approaches to verify the theoretical predictions.

  13. A simple and rapid method for standard preparation of gas phase extract of cigarette smoke.

    PubMed

    Higashi, Tsunehito; Mai, Yosuke; Noya, Yoichi; Horinouchi, Takahiro; Terada, Koji; Hoshi, Akimasa; Nepal, Prabha; Harada, Takuya; Horiguchi, Mika; Hatate, Chizuru; Kuge, Yuji; Miwa, Soichi

    2014-01-01

    Cigarette smoke consists of tar and gas phase: the latter is toxicologically important because it can pass through lung alveolar epithelium to enter the circulation. Here we attempt to establish a standard method for preparation of gas phase extract of cigarette smoke (CSE). CSE was prepared by continuously sucking cigarette smoke through a Cambridge filter to remove tar, followed by bubbling it into phosphate-buffered saline (PBS). An increase in dry weight of the filter was defined as tar weight. Characteristically, concentrations of CSEs were represented as virtual tar concentrations, assuming that tar on the filter was dissolved in PBS. CSEs prepared from smaller numbers of cigarettes (original tar concentrations ≤ 15 mg/ml) showed similar concentration-response curves for cytotoxicity versus virtual tar concentrations, but with CSEs from larger numbers (tar ≥ 20 mg/ml), the curves were shifted rightward. Accordingly, the cytotoxic activity was detected in PBS of the second reservoir downstream of the first one with larger numbers of cigarettes. CSEs prepared from various cigarette brands showed comparable concentration-response curves for cytotoxicity. Two types of CSEs prepared by continuous and puff smoking protocols were similar regarding concentration-response curves for cytotoxicity, pharmacology of their cytotoxicity, and concentrations of cytotoxic compounds. These data show that concentrations of CSEs expressed by virtual tar concentrations can be a reference value to normalize their cytotoxicity, irrespective of numbers of combusted cigarettes, cigarette brands and smoking protocols, if original tar concentrations are ≤15 mg/ml.

  14. A Simple and Rapid Method for Standard Preparation of Gas Phase Extract of Cigarette Smoke

    PubMed Central

    Higashi, Tsunehito; Mai, Yosuke; Noya, Yoichi; Horinouchi, Takahiro; Terada, Koji; Hoshi, Akimasa; Nepal, Prabha; Harada, Takuya; Horiguchi, Mika; Hatate, Chizuru; Kuge, Yuji; Miwa, Soichi

    2014-01-01

    Cigarette smoke consists of tar and gas phase: the latter is toxicologically important because it can pass through lung alveolar epithelium to enter the circulation. Here we attempt to establish a standard method for preparation of gas phase extract of cigarette smoke (CSE). CSE was prepared by continuously sucking cigarette smoke through a Cambridge filter to remove tar, followed by bubbling it into phosphate-buffered saline (PBS). An increase in dry weight of the filter was defined as tar weight. Characteristically, concentrations of CSEs were represented as virtual tar concentrations, assuming that tar on the filter was dissolved in PBS. CSEs prepared from smaller numbers of cigarettes (original tar concentrations ≤15 mg/ml) showed similar concentration-response curves for cytotoxicity versus virtual tar concentrations, but with CSEs from larger numbers (tar ≥20 mg/ml), the curves were shifted rightward. Accordingly, the cytotoxic activity was detected in PBS of the second reservoir downstream of the first one with larger numbers of cigarettes. CSEs prepared from various cigarette brands showed comparable concentration-response curves for cytotoxicity. Two types of CSEs prepared by continuous and puff smoking protocols were similar regarding concentration-response curves for cytotoxicity, pharmacology of their cytotoxicity, and concentrations of cytotoxic compounds. These data show that concentrations of CSEs expressed by virtual tar concentrations can be a reference value to normalize their cytotoxicity, irrespective of numbers of combusted cigarettes, cigarette brands and smoking protocols, if original tar concentrations are ≤15 mg/ml. PMID:25229830

  15. Evaluation of a detailed gas-phase atmospheric reaction mechanism using environmental chamber data

    NASA Astrophysics Data System (ADS)

    Carter, William P. L.; Lurmann, Fredrick W.

    This paper describes an evaluation of the performance of a detailed gas-phase reaction mechanism in simulating the results of 561 experiments carried out in four different environmental chambers. The experiments included background air, NO x-air, CONO x-air and aldehyde-air irradiations used for chamber characterization, NO x-air irradiations of single organics as well as simple and complex organic mixtures, and irradiations of auto exhaust. The methods used to represent the major chamber effects and the lighting characteristics in the model simulations of the experiments are described and their associated uncertainties are discussed. Statistical measures of the performance of the mechanism in simulating results of the various types of experiments are summarized and discussed. The mechanism was able to predict maximum ozone yields and rates of NO oxidation to within ±30% for 63% of the experiments modeled, and to within ±50% for 85% of the runs. There is a slight bias (˜15%) towards overprediction of ozone in mixture runs. Although there are cases where the simulations suggest possible problems with the gas-phase mechanism, much of the variability in the goodness of the fits could be attributed to uncertainties in chamber effects. It is concluded that better characterization of chamber conditions are needed if more comprehensive tests of atmospheric photochemical mechanisms are desired.

  16. Formulation, release characteristics and bioavailability of novel monolithic hydroxypropylmethylcellulose matrix tablets containing acetaminophen.

    PubMed

    Cao, Qing-Ri; Choi, Yun-Woong; Cui, Jing-Hao; Lee, Beom-Jin

    2005-11-28

    Effect of incorporating pharmaceutical excipients on the in vitro release profiles and the release mechanism of monolithic hydroxypropylmethylcellulose (4000 cps) matrix tablets (m-HPMC tablets) in terms of mimicking the dual drug release character of bi-layered Tylenol ER tablets was studied. We also compared the in vitro release profiles of optimized m-HPMC matrix tablet and Tylenol ER tablet in water, pH 1.2 gastric fluid, and pH 6.8 intestinal fluid, and in vivo drug bioavailabilities in healthy human volunteers. Acetaminophen was used as the model drug. The m-HPMC tablets were prepared using a wet granulation method followed by direct compression. Release profiles and swelling rates of m-HPMC tablets were found to be highly influenced by the types and amounts of pharmaceutical excipients incorporated. Starch 1500 (Prejel) and sodium lauryl sulfate (SLS) played a key role in determining the dissolution rate of m-HPMC tablets. Additional excipients, i.e., microcrystalline cellulose (Avicel PH101) and NaH2PO4 were used to tune the release profiles of m-HPMC tablets. The effect of pharmaceutical excipients on drug release from HPMC-based matrix tablets was found to be mainly due to a change in hydrophilic gel expansion and on physical interactions between the drug and HPMC. The optimized m-HPMC tablet with a balanced ratio of Prejel, SLS, Avicel PH101, and NaH2PO4 in the formulation showed dual release profiles in water, pH 1.2 gastric fluid, and pH 6.8 intestinal fluid in vitro. Dual release was defined as immediate drug release within few minutes followed by extended release over 8 h. The similarity factors of m-HPMC tablets and bi-layered Tylenol ER tablets were 79.8, 66.1, and 82.7 in water, gastric fluid and intestinal fluid, respectively, indicating the equivalence of the two release profiles. No significant in vivo bioavailability differences were observed in healthy human volunteers. The developed m-HPMC tablet with dual release characteristics can be

  17. Gas-phase reactions of halogen species of atmospheric importance

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen-containing molecules and between NO3 radicals and the iodine species I2 and I. These experiments have shown that: (1) the reaction of methyl iodide with OH accounts for approximately 2 percent of the removal of CH3I from the troposphere as compared with photolysis; (2) abstraction of I-atoms from a C-I bond by OH is probable in the gas-phase; (3) the halogen-containing anaesthetic substances halothane CF3CClBrH, enflurane CF2HOCF2CFClH, isoflurane CF2HOCClHCF3 and sevoflurane (CF3)2CHOCFH2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross-sections of the compounds in the spectral region 800-1200 cm(exp -1) were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl3 for each compound. The study of the reactions between OH and CF3CFBrH and CF2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) x 10(exp -12)/cu cm

  18. Tramadol loading, release and iontophoretic characteristics of ion-exchange fiber.

    PubMed

    Gao, Yanan; Yuan, Jing; Liu, Hongzhuo; Yang, Yang; Hou, Yanlong; Li, Sanming

    2014-04-25

    The objective of this study was to investigate the drug loading, release and iontophoretic characteristics of strong acidic ion-exchange fiber, using tramadol hydrochloride as a model drug. The complex of charged model drug and ion-exchange fiber was studied as a new approach to achieve controlled drug delivery. Structural characterization of the fiber was elucidated through different approaches including differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), scanning electron microscope (SEM) and infrared spectroscopy (IR). And the mechanism of drug binding into ion-exchange fibers was validated to be ion-exchange. The drug loading into and release from ion-exchange fiber were affected by the concentration, volume and valence of the counter-ions in the external solution. Iontophoresis could significantly increase the delivery rate and amount of transdermal drug, and the iontophoretic dose could be easily controlled by adjusting the current intensity and the amount of release medium. The tramadol could be steadily released both from the drug-loaded fiber and drug solution when applied the iontophoretic method, which was in disagreement with the previous publications. As a drug reservoir, ion-exchange fiber has good regularity of drug loading, release and iontophoretic characteristics. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Drug Release Characteristics and Tissue Distribution of Rifapentine Polylactic Acid Sustained-Release Microspheres in Rabbits after Paravertebral Implantation

    PubMed Central

    Zhang, Zheng; Wu, Linbo; Li, Haijian; Long, Zhicheng; Song, Xinghua

    2016-01-01

    Background Rates of drug-resistant tuberculosis (TB) and TB associated with human immunodeficiency virus (HIV) infection have increased dramatically, intensifying challenges in TB control. New formulations of TB treatment drugs that control drug release and increase local drug concentrations will have a significant impact on mitigating the toxic side effects and increasing the clinical efficacy of anti-TB drugs. Objectives The aim was to observe the sustained release characteristics of rifapentine polylactic acid sustained-release microspheres in vivo and the accumulation of rifapentine in other tissues following paravertebral implantation. Methods This study is a basic animal experimental study that began on July 17, 2014 in the Fifth Affiliated hospital of Xinjiang Medical University. One hundred and eight New Zealand white rabbits (weighing 2.8 - 3.0 kg, male and female, China) were randomly divided into three groups of 36 rabbits each. Blood and tissue samples from the liver, lungs, kidneys, vertebrae, and paravertebral muscle were collected at different time points post-surgery. High performance liquid chromatography (HPLC) analysis with a biological internal standard was used to determine the drug concentrations in samples. Results In group A, no significant differences in rifapentine concentrations in the liver were detected between any two time points (P > 0.05). However, the differences in rifapentine concentrations between day 10 and day 21 were statistically significant (P < 0.05); for days 21, 35, 46, and 60, the differences in rifapentine concentrations between two sequential time points were not statistically significant (P > 0.05). In group B, the differences in rifapentine concentration between days 3 and 10 in vertebral bone and in paravertebral muscles were statistically significant (P < 0.05). Rifapentine was detected in the vertebral bone tissue in the group C animals. The rifapentine concentrations between two sequential time points were

  20. Silicon Nanowire-Based Devices for Gas-Phase Sensing

    PubMed Central

    Cao, Anping; Sudhölter, Ernst J.R.; de Smet, Louis C.P.M.

    2014-01-01

    Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

  1. Conformational Study of Taurine in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Cortijo, Vanessa; Sanz, M. Eugenia; López, Juan C.; Alonso, José L.

    2009-08-01

    The conformational preferences of the amino sulfonic acid taurine (NH2-CH2-CH2-SO3H) have been investigated in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) in the 6-14 GHz frequency range. One conformer has been observed, and its rotational, centrifugal distortion, and hyperfine quadrupole coupling constants have been determined from the analysis of its rotational spectrum. Comparison of the experimental constants with those calculated theoretically identifies the detected conformer unambiguously. The observed conformer of taurine is stabilized by an intramolecular hydrogen bond O-H···N between the hydrogen of the sulfonic acid group and the nitrogen atom of the amino group.

  2. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)

    2000-01-01

    Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.

  3. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)

    2000-01-01

    A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.

  4. Gas-phase synthesis of magnetic metal/polymer nanocomposites.

    PubMed

    Starsich, Fabian H L; Hirt, Ann M; Stark, Wendelin J; Grass, Robert N

    2014-12-19

    Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

  5. Gas-phase synthesis of magnetic metal/polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Starsich, Fabian H. L.; Hirt, Ann M.; Stark, Wendelin J.; Grass, Robert N.

    2014-12-01

    Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

  6. Dissociative attachment reactions of electrons with gas phase superacids

    SciTech Connect

    Liu, X.

    1992-01-01

    Using the flowing afterglow Langmuir probe (FALP) technique, dissociative attachment coefficients [beta] for reactions of electrons with gas phase superacids HCo(PF[sub 3])[sub 4], HRh(PF[sub 3])[sub 4] and carbonyl hydride complexes HMn(CO)[sub 5], HRe(CO)[sub 5] have been determined under thermal conditions over the approximate temperature range 300[approximately]550 K. The superacids react relatively slowly (<1/20 of [beta][sub max]) with free electrons in a thermal plasma, and the values of [beta] obtained this far do not show a correlation between acidity and [beta]. The pioneer researchers in this field had speculated that any superacid would be a rapid attacher of electrons; it was found that this speculation is not true in general. The product distribution of electron attachment reaction to HCo(PF[sub 3])[sub 4] was found to be independent of temperature even though the [beta][HCo(PF[sub 3])[sub 4

  7. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)

    2000-01-01

    Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.

  8. Enhancement of gas phase heat transfer by acoustic field application.

    PubMed

    Komarov, Sergey; Hirasawa, Masahiro

    2003-06-01

    This study discusses a possibility for enhancement of heat transfer between solids and ambient gas by application of powerful acoustic fields. Experiments are carried out by using preheated Pt wires (length 0.1-0.15 m, diameter 50 and 100 micro m) positioned at the velocity antinode of a standing wave (frequency range 216-1031 Hz) or in the path of a travelling wave (frequency range 6.9-17.2 kHz). A number of experiments were conducted under conditions of gas flowing across the wire surface. Effects of sound frequency, sound strength, gas flow velocity and wire preheating temperature on the Nusselt number are examined with and without sound application. The gas phase heat transfer rate is enhanced with acoustic field strength. Higher temperatures result in a vigorous radiation from the wire surface and attenuate the effect of sound. The larger the gas flow velocity, the smaller is the effect of sound wave on heat transfer enhancement.

  9. Stabilities and structures of gas phase MgO clusters

    SciTech Connect

    Ziemann, P.J.; Castleman, A.W. Jr. )

    1991-01-01

    Gas phase (MgO){sup +}{sub {ital n}} and (MgO){sub {ital n}}Mg{sup +} clusters ({ital n}{le}90) were produced in a gas aggregation source and studied by using laser-ionization time-of-flight mass spectrometry. The abundance maxima observed in the mass spectra indicate that the clusters form compact cubic structures similar to pieces of the MgO crystal lattice. The abundance maxima of the metal-rich clusters show an interesting dependence on the ionization wavelength that appears to be due to different fragmentation pathways for the cluster ions and neutrals, and may be indicative of excess electron behavior analogous to that observed in solid state color centers. Calculations of cluster structures and stabilities made with an ionic model were useful in obtaining qualitative information about the primary fragmentation channels and cluster electronic properties, but also indicate that covalent bonding interactions must be included to obtain quantitatively accurate results.

  10. Gas-phase folding and unfolding of cytochrome c cations.

    PubMed Central

    Wood, T D; Chorush, R A; Wampler, F M; Little, D P; O'Connor, P B; McLafferty, F W

    1995-01-01

    Water is thought to play a dominant role in protein folding, yet gaseous multiply protonated proteins from which the water has been completely removed show hydrogen/deuterium (H/D) exchange behavior similar to that used to identify conformations in solution. Indicative of the gas-phase accessibility to D2O, multiply-charged (6+ to 17+) cytochrome c cations exchange at six (or more) distinct levels of 64 to 173 out of 198 exchangeable H atoms, with the 132 H level found at charge values 8+ to 17+. Infrared laser heating and fast collisions can apparently induce ions to unfold to exchange at a higher distinct level, while charge-stripping ions to lower charge values yields apparent folding as well as unfolding. PMID:7708663

  11. Regenerable Air Purification System for Gas-Phase Contaminant Control

    NASA Technical Reports Server (NTRS)

    Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)

    2000-01-01

    A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.

  12. Visible and ultraviolet spectroscopy of gas phase protein ions.

    PubMed

    Antoine, Rodolphe; Dugourd, Philippe

    2011-10-06

    Optical spectroscopy has contributed enormously to our knowledge of the structure and dynamics of atoms and molecules and is now emerging as a cornerstone of the gas phase methods available for investigating biomolecular ions. This article focuses on the UV and visible spectroscopy of peptide and protein ions stored in ion traps, with emphasis placed on recent results obtained on protein polyanions, by electron photodetachment experiments. We show that among a large number of possible de-excitation pathways, the relaxation of biomolecular polyanions is mainly achieved by electron emission following photo-excitation in electronically excited states. Electron photodetachment is a fast process that occurs prior to relaxation on vibrational degrees of freedom. Electron photodetachment yield can then be used to record gas phase action spectra for systems as large as entire proteins, without the limitation of system size that would arise from energy redistribution on numerous modes and prevent fragmentation after the absorption of a photon. The optical activity of proteins in the near UV is directly related to the electronic structure and optical absorption of aromatic amino acids (Trp, Phe and Tyr). UV spectra for peptides and proteins containing neutral, deprotonated and radical aromatic amino acids were recorded. They displayed strong bathochromic shifts. In particular, the results outline the privileged role played by open shell ions in molecular spectroscopy which, in the case of biomolecules, is directly related to their reactivity and biological functions. The optical shifts observed are sufficient to provide unambiguous fingerprints of the electronic structure of chromophores without the requirement of theoretical calculations. They constitute benchmarks for calculating the absorption spectra of chromophores embedded in entire proteins and could be used in the future to study biochemical processes in the gas phase involving charge transfer in aromatic amino acids

  13. The intrinsic (gas-phase) acidities of bridgehead alcohols

    NASA Astrophysics Data System (ADS)

    Herrero, Rebeca; Dávalos, Juan Z.; Abboud, José-Luis M.; Alkorta, I.; Koppel, I.; Koppel, I. A.; Sonoda, T.; Mishima, M.

    2007-11-01

    The gas-phase acidities of 1-adamantanol and perfluoro1-adamantanol were determined by means of Fourier transform ion cyclotron resonance spectrometry (FT-ICR). The acidity of perfluoro1-adamantanol seems to be the highest ever reported for an alcohol. A computational study of these species and their anions at both the MP2/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) levels was performed. Also studied were the tertiary alcohols (including their perfluorinated forms) derived from norbornane, bicyclo[2.2E2]octane and cubane. It was found that: (i) the intrinsic acidity of non-fluorinated bridgehead alcohols increases with the strain of the hydrocarbon framework and, (ii) perfluorination of these compounds strongly increases their acidity and, likely, significantly modifies their internal strain.

  14. Four Structures of Tartaric Acid Revealed in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Cortijo, Vanessa; Díez, Verónica; Alonso, Elena R.; Mata, Santiago; Alonso, José L.

    2017-06-01

    The tartaric acid, one of the most important organic compounds, has been transferred into the gas phase by laser ablation of its natural crystalline form (m.p.174°C) and probed in a supersonic expansion by chirped-pulse Fourier transform microwave spectroscopy (CP-FTMW). Four stable structures, two with an extended (trans) disposition of the carbon chain and two with a bent (gauche) disposition, have been unequivocally identified on the basis of the experimental rotational constants in conjunction with ab initio predictions. The intramolecular interactions that govern the conformational preferences are dominated by cooperative O-H...O=C type and O-H?O hydrogen bonds extended along the entire molecule. The observation of only μc- type spectra for one "trans" and one "gauche" conformers, support the existence of a C2 symmetry for each structure.

  15. Ceramic microreactors for heterogeneously catalysed gas-phase reactions.

    PubMed

    Knitter, Regina; Liauw, Marcel A

    2004-08-01

    The high surface to volume ratio of microchannel components offers many advantages in micro chemical engineering. It is obvious, however, that the reactor material and corrosion phenomena play an important role when applying these components. For chemical reactions at very high temperatures or/and with corrosive reactants involved, microchannel components made of metals or polymers are not suited. Hence, a modular microreactor system made of alumina was developed and fabricated using a rapid prototyping process chain. With exchangeable inserts the system can be adapted to the requirements of various reactions. Two heterogeneously catalysed gas-phase reactions (oxidative coupling of methane, isoprene selective oxidation to citraconic anhydride) were investigated to check the suitability of the system at temperatures of up to 1000 degrees C. Apart from the high thermal and chemical resistance, the lack of any blind activity was found to be another advantage of ceramic components.

  16. Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds

    SciTech Connect

    Classen, Nathan Robert

    2002-01-01

    The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular β C-H insertion mechanism.

  17. Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase

    NASA Astrophysics Data System (ADS)

    MacLeod, N. A.; Simons, J. P.

    2007-03-01

    Protonated neurotransmitters have been produced in the gas phase via a novel photochemical scheme: complexes of the species of interest, 1-phenylethylamine, 2-amino-1-phenylethanol and the diastereo-isomers, ephedrine and pseudoephedrine, with a suitable proton donor, phenol (or indole), are produced in a supersonic expansion and ionized by resonant two photon ionization of the donor. Efficient proton transfer generates the protonated neurotransmitters, complexed to a phenoxy radical. Absorption of infrared radiation, and subsequent evaporation of the phenoxy tag, coupled with time of flight mass spectrometry, provides vibrational spectra of the protonated (and also hydrated) complexes for comparison with the results of quantum chemical computation. Comparison with the conformational structures of the neutral neurotransmitters (established previously) reveals the effect of protonation on their structure. The photochemical proton transfer strategy allows spectra to be recorded from individual laser shots and their quality compares favourably with that obtained using electro-spray or matrix assisted laser desorption ion sources.

  18. Photodissociation and spectroscopy of gas phase bimetallic clusters

    SciTech Connect

    Duncan, M.A.

    1992-05-01

    Focus of the research program is the study of gas phase metal clusters for modeling fundamental interactions on metal surfaces. We characterize the chemical bonding between component atoms in clusters as well as the bonding in adsorption on cluster surfaces. Electronic spectra, vibrational frequencies and bond dissociation energies are measured for both neutral and ionized clusters with laser/mass spectrometry techniques. Small bimetallic cluster cations containing Bi/Cr, Bi/Fe, Sn/Bi, and Pb/Sb were photodissociated at various uv wavelengths. Silver dimer van der Waals complexes were produced with a series of rare gas atoms (Ar, Kr, Xe), and their vibrational frequencies and dissociation energies were obtained. (DLC)

  19. Femtosecond gas phase electron diffraction with MeV electrons.

    PubMed

    Yang, Jie; Guehr, Markus; Vecchione, Theodore; Robinson, Matthew S; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Coffee, Ryan; Corbett, Jeff; Fry, Alan; Gaffney, Kelly; Gorkhover, Tais; Hast, Carsten; Jobe, Keith; Makasyuk, Igor; Reid, Alexander; Robinson, Joseph; Vetter, Sharon; Wang, Fenglin; Weathersby, Stephen; Yoneda, Charles; Wang, Xijie; Centurion, Martin

    2016-12-16

    We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.

  20. Surfactants from the gas phase may promote cloud droplet formation

    PubMed Central

    Sareen, Neha; Schwier, Allison N.; Lathem, Terry L.; Nenes, Athanasios; McNeill, V. Faye

    2013-01-01

    Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8–10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas–aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

  1. Feasibility of gas-phase decontamination of gaseous diffusion equipment

    SciTech Connect

    Munday, E.B.; Simmons, D.W.

    1993-02-01

    The five buildings at the K-25 Site formerly involved in the gaseous diffusion process contain 5000 gaseous diffusion stages as well as support facilities that are internally contaminated with uranium deposits. The gaseous diffusion facilities located at the Portsmouth Gaseous Diffusion Plant and the Paducah Gaseous Diffusion Plant also contain similar equipment and will eventually close. The decontamination of these facilities will require the most cost-effective technology consistent with the criticality, health physics, industrial hygiene, and environmental concerns; the technology must keep exposures to hazardous substances to levels as low as reasonably achievable (ALARA). This report documents recent laboratory experiments that were conducted to determine the feasibility of gas-phase decontamination of the internal surfaces of the gaseous diffusion equipment that is contaminated with uranium deposits. A gaseous fluorinating agent is used to fluorinate the solid uranium deposits to gaseous uranium hexafluoride (UF{sub 6}), which can be recovered by chemical trapping or freezing. The lab results regarding the feasibility of the gas-phase process are encouraging. These results especially showed promise for a novel decontamination approach called the long-term, low-temperature (LTLT) process. In the LTLT process: The equipment is rendered leak tight, evacuated, leak tested, and pretreated, charged with chlorine trifluoride (ClF{sub 3}) to subatmospheric pressure, left for an extended period, possibly > 4 months, while processing other items. Then the UF{sub 6} and other gases are evacuated. The UF{sub 6} is recovered by chemical trapping. The lab results demonstrated that ClF{sub 3} gas at subatmospheric pressure and at {approx} 75{degree}F is capable of volatilizing heavy deposits of uranyl fluoride from copper metal surfaces sufficiently that the remaining radioactive emissions are below limits.

  2. Surfactants from the gas phase may promote cloud droplet formation.

    PubMed

    Sareen, Neha; Schwier, Allison N; Lathem, Terry L; Nenes, Athanasios; McNeill, V Faye

    2013-02-19

    Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8-10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas-aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere.

  3. Seeds of Life in Space (SOLIS). II. Formamide in protostellar shocks: Evidence for gas-phase formation

    NASA Astrophysics Data System (ADS)

    Codella, C.; Ceccarelli, C.; Caselli, P.; Balucani, N.; Barone, V.; Fontani, F.; Lefloch, B.; Podio, L.; Viti, S.; Feng, S.; Bachiller, R.; Bianchi, E.; Dulieu, F.; Jiménez-Serra, I.; Holdship, J.; Neri, R.; Pineda, J. E.; Pon, A.; Sims, I.; Spezzano, S.; Vasyunin, A. I.; Alves, F.; Bizzocchi, L.; Bottinelli, S.; Caux, E.; Chacón-Tanarro, A.; Choudhury, R.; Coutens, A.; Favre, C.; Hily-Blant, P.; Kahane, C.; Jaber Al-Edhari, A.; Laas, J.; López-Sepulcre, A.; Ospina, J.; Oya, Y.; Punanova, A.; Puzzarini, C.; Quenard, D.; Rimola, A.; Sakai, N.; Skouteris, D.; Taquet, V.; Testi, L.; Theulé, P.; Ugliengo, P.; Vastel, C.; Vazart, F.; Wiesenfeld, L.; Yamamoto, S.

    2017-09-01

    Context. Modern versions of the Miller-Urey experiment claim that formamide (NH2CHO) could be the starting point for the formation of metabolic and genetic macromolecules. Intriguingly, formamide is indeed observed in regions forming solar-type stars and in external galaxies. Aims: How NH2CHO is formed has been a puzzle for decades: our goal is to contribute to the hotly debated question of whether formamide is mostly formed via gas-phase or grain surface chemistry. Methods: We used the NOrthern Extended Millimeter Array (NOEMA) interferometer to image NH2CHO towards the L1157-B1 blue-shifted shock, a well-known interstellar laboratory, to study how the components of dust mantles and cores released into the gas phase triggers the formation of formamide. Results: We report the first spatially resolved image (size 9″, 2300 AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM ≃ 5 km s-1. A column density of NNH2CHO = 8 × 1012 cm-1 and an abundance, with respect to H-nuclei, of 4 × 10-9 are derived. We show a spatial segregation of formamide with respect to other organic species. Our observations, coupled with a chemical modelling analysis, indicate that the formamide observed in L1157-B1 is formed by a gas-phase chemical process and not on grain surfaces as previously suggested. Conclusions: The Seeds of Life in Space (SOLIS) interferometric observations of formamide provide direct evidence that this potentially crucial brick of life is efficiently formed in the gas phase around Sun-like protostars. The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/L3

  4. Gas-phase products and secondary organic aerosol formation from the ozonolysis and photooxidation of myrcene

    NASA Astrophysics Data System (ADS)

    Böge, Olaf; Mutzel, Anke; Iinuma, Yoshiteru; Yli-Pirilä, Pasi; Kahnt, Ariane; Joutsensaari, Jorma; Herrmann, Hartmut

    2013-04-01

    Terrestrial vegetation releases a great variety of volatile organic compounds (VOC) into the atmosphere. Monoterpenes, like myrcene, contribute significantly to this global biogenic VOC emission. In the atmosphere, monoterpenes rapidly undergo oxidation reactions by OH radicals (mainly during the daytime), NO3 radicals (mainly during the nighttime) and O3 to form multifunctional oxidation products. The products of these reactions are likely to be of low volatility and hence might lead to secondary organic aerosol (SOA) formation. In the present study, we report results from a series of chamber experiments performed in the LEAK chamber at TROPOS in which the gas-phase products and SOA yields obtained from myrcene O3 reactions with and without an OH radical scavenger as well as from the myrcene OH radical reaction in the presence of NOx have been measured. During the experiments the consumption of myrcene as well as the formation of gas-phase products was monitored using a proton transfer reaction mass spectrometer (PTR-MS). Ozone concentration was measured by an O3 monitor and the mixing ratios of nitrogen oxides were measured by a NOx monitor. Particle size distributions between 3-900 nm were monitored every 11 min using a differential mobility particle sizer (DMPS) system. In addition to the products observed by means of the PTR-MS by their m/z values, an identification of carbonylic compounds by their DNPH derivatives was performed. Beside low molecular mass products the formation of 4-vinyl-4-pentenal with a yield of 55 % in myrcene ozonolysis has been observed. The further oxidation of this major first generation product lead to the formation of two dicarbonylic products with m/z 113 and to SOA formation. The influence of the continuing oxidation of 4-vinyl-4-pentenal on SOA formation will be discussed in detail. The emergence of the gas-phase product hydroxyacetone as direct result of the myrcene ozone reaction will be mooted, because hydroxyacetone seems to

  5. Ion Yields for Some Salts in MALDI: Mechanism for the Gas-Phase Ion Formation from Preformed Ions

    NASA Astrophysics Data System (ADS)

    Moon, Jeong Hee; Shin, Young Sik; Bae, Yong Jin; Kim, Myung Soo

    2012-01-01

    Preformed ion emission is the main assumption in one of the prevailing theories for peptide and protein ion formation in matrix-assisted laser desorption ionization (MALDI). Since salts are in preformed ion forms in the matrix-analyte mixture, they are ideal systems to study the characteristics of preformed ion emission. In this work, a reliable method to measure the ion yield (IY) in MALDI was developed and used for a solid salt benzyltriphenylphosphonium chloride and two room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate. IY for the matrix (α-cyano-4-hydroxycinnamic acid, CHCA) was also measured. Taking 1 pmol salts in 25 nmol CHCA as examples, IYs for three salts were similar, (4-8) × 10-4, and those for CHCA were (0.8-1.2) × 10-7. Even though IYs for the salts and CHCA remained virtually constant at low analyte concentration, they decreased as the salt concentrations increased. Two models, Model 1 and Model 2, were proposed to explain low IYs for the salts and the concentration dependences. Both models are based on the fact that the ion-pair formation equilibrium is highly shifted toward the neutral ion pair. In Model 1, the gas-phase analyte cations were proposed to originate from the same cations in the solid that were dielectrically screened from counter anions by matrix neutrals. In Model 2, preformed ions were assumed to be released from the solid sample in the form of neutral ion pairs and the anions in the ion pairs were assumed to be eliminated via reactions with matrix-derived cations.

  6. Ion yields for some salts in MALDI: mechanism for the gas-phase ion formation from preformed ions.

    PubMed

    Moon, Jeong Hee; Shin, Young Sik; Bae, Yong Jin; Kim, Myung Soo

    2012-01-01

    Preformed ion emission is the main assumption in one of the prevailing theories for peptide and protein ion formation in matrix-assisted laser desorption ionization (MALDI). Since salts are in preformed ion forms in the matrix-analyte mixture, they are ideal systems to study the characteristics of preformed ion emission. In this work, a reliable method to measure the ion yield (IY) in MALDI was developed and used for a solid salt benzyltriphenylphosphonium chloride and two room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate. IY for the matrix (α-cyano-4-hydroxycinnamic acid, CHCA) was also measured. Taking 1 pmol salts in 25 nmol CHCA as examples, IYs for three salts were similar, (4-8) × 10(-4), and those for CHCA were (0.8-1.2) × 10(-7). Even though IYs for the salts and CHCA remained virtually constant at low analyte concentration, they decreased as the salt concentrations increased. Two models, Model 1 and Model 2, were proposed to explain low IYs for the salts and the concentration dependences. Both models are based on the fact that the ion-pair formation equilibrium is highly shifted toward the neutral ion pair. In Model 1, the gas-phase analyte cations were proposed to originate from the same cations in the solid that were dielectrically screened from counter anions by matrix neutrals. In Model 2, preformed ions were assumed to be released from the solid sample in the form of neutral ion pairs and the anions in the ion pairs were assumed to be eliminated via reactions with matrix-derived cations. © American Society for Mass Spectrometry, 2011

  7. High resolution ion mobility measurements for gas phase proteins: correlation between solution phase and gas phase conformations

    NASA Astrophysics Data System (ADS)

    Hudgins, Robert R.; Woenckhaus, Jürgen; Jarrold, Martin F.

    1997-11-01

    Our high resolution ion mobility apparatus has been modified by attaching an electrospray source to perform measurements for biological molecules. While the greater resolving power permits the resolution of more conformations for BPTI and cytochrome c, the resolved features are generally much broader than expected for a single rigid conformation. A major advantage of the new experimental configuration is the much gentler introduction of ions into the drift tube, so that the observed gas phase conformations appear to more closely reflect those present in solution. For example, it is possible to distinguish between the native state of cytochrome c and the methanol-denatured form on the basis of the ion mobility measurements; the mass spectra alone are not sensitive enough to detect this change. Thus this approach may provide a quick and sensitive tool for probing the solution phase conformations of biological molecules.

  8. Cold energy release characteristics of an ice/air direct contact heat exchanger

    SciTech Connect

    Ohira, Akiyoshi; Yanadori, Michio; Iwabuchi, Kunihiko; Kimura, Toshikatsu; Tsubota, Yuji

    1998-12-31

    This paper deals with the cold energy release characteristics of an ice/air direct contact heat exchanger in a refined cold energy conveyance system. Characteristics of the outlet temperature, the humidity, and time history of released heat are examined when the initial height of the ice-cube-packed bed in the heat exchanger is changed. The following are the results obtained in these experiments: (1) Inlet air of 30 C is lowered to about 0 C by passing the air through the heat exchanger, and absolute humidity of the outlet air is reduced to about a quarter of that of the inlet air. (2) There is an optimum height of the ice-cube-packed bed for maximizing the amount of cold energy released. (3) This heat exchange method can supply about twice the amount of cold energy released by an ordinary fin-tube-type heat exchanger even if the air velocity in the heat exchanger is reduced to about 0.38 times that of the fin-tube-type heat exchanger.

  9. Absolute bioavailability and absorption characteristics of divalproex sodium extended-release tablets in healthy volunteers.

    PubMed

    Dutta, Sandeep; Reed, Ronald C; Cavanaugh, John H

    2004-07-01

    Conventional delayed-release, enteric-coated divalproex sodium tablet has an absolute bioavailability of approximately 100%. Divalproex sodium extended-release (ER) tablet is a novel formulation of valproic acid (VPA) designed to release the drug slowly at a constant zero-order rate. The purpose of this study was to evaluate the absolute bioavailability and absorption characteristics of divalproex ER. Healthy adult volunteers (n = 16) received divalproex ER and intravenous VPA in crossover fashion. Absolute bioavailability was calculated as the divalproex ER/intravenous VPA ratio of area under the curve extrapolated to infinity. The duration and rate of absorption of VPA from divalproex ER tablets were determined by deconvolution analysis. The geometric mean absolute bioavailability of divalproex ER was 0.896. The mean (coefficient of variation) duration of drug absorption from divalproex ER was 21.8 (17%) hours, and the zero-order absorption rate was 21.6 (24%) mg/h for a 500-mg tablet. Divalproex ER has a lower absolute bioavailability than conventional divalproex tablets but exhibits good extended-release characteristics without any dose dumping.

  10. Novel Solid Encapsulation of Ethylene Gas Using Amorphous α-Cyclodextrin and the Release Characteristics.

    PubMed

    Ho, Binh T; Bhandari, Bhesh R

    2016-05-04

    This research investigated the encapsulation of ethylene gas into amorphous α-cyclodextrins (α-CDs) at low (LM) and high (HM) moisture contents at 1.0-1.5 MPa for 24-120 h and its controlled release characteristics at 11.2-52.9% relative humidity (RH) for 1-168 h. The inclusion complexes (ICs) were characterized using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP-MAS (13)C NMR), and scanning electron microscopy (SEM). Ethylene concentrations in the ICs were from 0.45 to 0.87 mol of ethylene/mol CD and from 0.42 to 0.54 mol of ethylene/mol CD for LM and HM α-CDs, respectively. Ethylene gas released from the encapsulated powder at higher rates with increasing RH. An analysis of release kinetics using Avrami's equation showed that the LM and HM amorphous α-CDs were not associated with significant differences in release constant k and parameter n for any given RH condition. NMR spectra showed the presence of the characteristic carbon-carbon double bond of ethylene gas in the encapsulated α-CD powder.

  11. GAS-PHASE FLAME SYNTHESIS AND PROPERTIES OF MAGNETIC IRON OXIDE NANOPARTICLES WITH REDUCED OXIDATION STATE

    PubMed Central

    Kumfer, Benjamin M; Shinoda, Kozo; Jeyadevan, Balachandran; Kennedy, Ian M

    2010-01-01

    Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane. PMID:20228941

  12. INFRARED MULTIPLE-PHOTON PHOTODISSOCIATION OF GAS-PHASE GROUP II METAL-NITRATE ANIONS

    SciTech Connect

    Jos Oomens; Linda Myers; Ryan Dain; Chris Leavitt; Vy Pham; Garold Gresham; Gary Groenewold; Mike Van Stipdonk

    2008-06-01

    Infrared spectra of gas-phase metal-nitrate anions M(NO3)3-, where M=Mg2+, Ca2+, Sr2+ and Ba2+, were recorded by infrared multiple photon dissociation (IRMPD) spectroscopy. Photodissociation of each of the precursors produces NO3- through the elimination of a neutral M(NO3)2 unit. An absorption pattern characteristic of metal nitrates is observed in the IRMPD spectra, including the symmetric and antisymmetric NO3 stretches. The latter is split into high and low frequency components as a result of perturbation of the nitrate symmetry by complexation to the metal ion, and the magnitude of the splitting decreases following the trend Mg2+ > Ca2+ > Sr2+ ? Ba2+. The experimental spectra are in good general agreement with those obtained from density functional theory calculations.

  13. Direct gas-phase synthesis of single-phase β-FeSi2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Bywalez, Robert; Orthner, Hans; Mehmedovic, Ervin; Imlau, Robert; Kovacs, Andras; Luysberg, Martina; Wiggers, Hartmut

    2013-09-01

    For the first time, phase-pure β-FeSi2 nanoparticles were successfully produced by gas-phase synthesis. We present a method to fabricate larger quantities of semiconducting β-FeSi2 nanoparticles, with crystallite sizes between 10 and 30 nm, for solar and thermoelectric applications utilizing a hot-wall reactor. A general outline for the production of those particles by thermal decomposition of silane and iron pentacarbonyl is provided based on kinetic data. The synthesized particles are investigated by X-ray diffraction and transmission electron microscopy, providing evidence that the as-prepared materials are indeed β-FeSi2, while revealing morphological characteristics inherent to the nanoparticles created.

  14. Dissociative Water Adsorption by Al3O4(+) in the Gas Phase.

    PubMed

    Fagiani, Matias R; Song, Xiaowei; Debnath, Sreekanta; Gewinner, Sandy; Schöllkopf, Wieland; Asmis, Knut R; Bischoff, Florian A; Müller, Fabian; Sauer, Joachim

    2017-03-06

    We use cryogenic ion trap vibrational spectroscopy in combination with density functional theory (DFT) to study the adsorption of up to four water molecules on Al3O4(+). The infrared photodissociation spectra of [Al3O4(D2O)1-4](+) are measured in the O-D stretching (3000-2000 cm(-1)) as well as the fingerprint spectral region (1300-400 cm(-1)) and are assigned based on a comparison with simulated harmonic infrared spectra for global minimum-energy structures obtained with DFT. We find that dissociative water adsorption is favored in all cases. The unambiguous assignment of the vibrational spectra of these gas phase model systems allows identifying characteristic spectral regions for O-D and O-H stretching modes of terminal (μ1) and bridging (μ2) hydroxyl groups in aluminum oxide/water systems, which sheds new light on controversial assignments for solid Al2O3 phases.

  15. Physicochemical and drug release characteristics of acetylated starches of five Lagenaria siceraria cultivars.

    PubMed

    Kulkarni, Sameer D; Sinha, Barij N; Kumar, K Jayaram

    2015-01-01

    Modified starches play a crucial role in the pharmaceutical industries in controlling the drug release at a pre-determined rate. The effect of acetylation on the physicochemical and drug release characteristics of the starches from five different Indian L. siceraria cultivars was investigated. Starches isolated from the seeds of L. siceraria were subjected to varying degrees of acetylation. Using a range of characterization methods including amylose content, elemental analysis, light transmittance, swelling power, scanning electron microscopy, FT-IR and X-ray diffraction, the effect of acetylation was determined. The swelling power of starch acetates improved significantly (P < 0.05) with the increase in degree of substitution. The increase in swelling shows that acetylation improved the accessibility of an amorphous area to the water. The formation of V-type of complex crystalline structures confirmed the acetylation of L. siceraria starch. Modification in the crystalline structure of starch acetate retarded the drug release, which is controlled by water uptake. The starch acetates from all the cultivars showed better sustained release properties with the increase in degree of substitution. Drug release through the swellable matrix was found to be controlled by fickian diffusion from the gel layer as indicated by Korsmeyer-Peppas models (R(2)) 0.9885-0.9984.

  16. Formation and emissions of carbonyls during and following gas-phase ozonation of indoor materials

    NASA Astrophysics Data System (ADS)

    Poppendieck, D. G.; Hubbard, H. F.; Weschler, C. J.; Corsi, R. L.

    Ozone concentrations that are several orders of magnitude greater than typical urban ambient concentrations are necessary for gas-phase ozonation of buildings, either for deodorization or for disinfection of biological agents. However, there is currently no published literature on the interaction of building materials and ozone under such extreme conditions. It would be useful to understand, for example in the case of building re-occupation planning, what types and amounts of reaction products may form and persist in a building after ozonation. In this study, 24 materials were exposed to ozone at concentrations of 1000 ppm in the inlet stream of experimental chambers. Fifteen target carbonyls were selected and measured as building ozonation by-products (BOBPs). During the 36 h that include the 16 h ozonation and 20 h persistence phase, the total BOBP mass released from flooring and wall coverings ranged from 1 to 20 mg m -2, with most of the carbonyls being of lower molecular weight (C 1-C 4). In contrast, total BOBP mass released from wood-based products ranged from 20 to 100 mg m -2, with a greater fraction of the BOBPs being heavier carbonyls (C 5-C 9). The total BOBP mass released during an ozonation event is a function of both the total surface area of the material and the BOBP emission rate per unit area of material. Ceiling tile, carpet, office partition, and gypsum wallboard with flat latex paint often have large surface areas in commercial buildings and these same materials exhibited relatively high BOBP releases. The greatest overall BOBP mass releases were observed for three materials that building occupants might have significant contact with: paper, office partition, and medium density fiberboard, e.g., often used in office furniture. These materials also exhibited extended BOBP persistence following ozonation; some BOBPs (e.g., nonanal) persist for months or more at emission rates large enough to result in indoor concentrations that exceed their odor

  17. Gas-phase synthesis of semiconductor nanocrystals and its applications

    NASA Astrophysics Data System (ADS)

    Mandal, Rajib

    Luminescent nanomaterials is a newly emerging field that provides challenges not only to fundamental research but also to innovative technology in several areas such as electronics, photonics, nanotechnology, display, lighting, biomedical engineering and environmental control. These nanomaterials come in various forms, shapes and comprises of semiconductors, metals, oxides, and inorganic and organic polymers. Most importantly, these luminescent nanomaterials can have different properties owing to their size as compared to their bulk counterparts. Here we describe the use of plasmas in synthesis, modification, and deposition of semiconductor nanomaterials for luminescence applications. Nanocrystalline silicon is widely known as an efficient and tunable optical emitter and is attracting great interest for applications in several areas. To date, however, luminescent silicon nanocrystals (NCs) have been used exclusively in traditional rigid devices. For the field to advance towards new and versatile applications for nanocrystal-based devices, there is a need to investigate whether these NCs can be used in flexible and stretchable devices. We show how the optical and structural/morphological properties of plasma-synthesized silicon nanocrystals (Si NCs) change when they are deposited on stretchable substrates made of polydimethylsiloxane (PDMS). Synthesis of these NCs was performed in a nonthermal, low-pressure gas phase plasma reactor. To our knowledge, this is the first demonstration of direct deposition of NCs onto stretchable substrates. Additionally, in order to prevent oxidation and enhance the luminescence properties, a silicon nitride shell was grown around Si NCs. We have demonstrated surface nitridation of Si NCs in a single step process using non?thermal plasma in several schemes including a novel dual-plasma synthesis/shell growth process. These coated NCs exhibit SiNx shells with composition depending on process parameters. While measurements including

  18. Gas-Phase Reactions of Halogen Species of Atmospheric Importance.

    NASA Astrophysics Data System (ADS)

    Heard, Anne C.

    Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of

  19. The gas-phase ozonolysis of α-humulene.

    PubMed

    Beck, M; Winterhalter, R; Herrmann, F; Moortgat, G K

    2011-06-21

    α-Humulene contains three double bonds (DB), and after ozonolysis of the first DB the first-generation products are still reactive towards O(3) and produce second- and third-generation products. The primary aim of this study consisted of identifying the products of the three generations, focusing on the carboxylic acids, which are known to have a high aerosol formation potential. The experiments were performed in a 570 litre spherical glass reactor at 295 K and 730 Torr. Initial mixing ratios were 260-2090 ppb for O(3) and 250-600 ppb for α-humulene in synthetic air. Reactants and gas-phase products were measured by in situ FTIR spectroscopy. Particulate products were sampled on Teflon filters, extracted with methanol and analyzed by LC-MS/MS-TOF. Using cyclohexane (10-100 ppm) as an OH-radical scavenger and by monitoring the yield of cyclohexanone by PTR-MS, an OH-yield of (10.5 ± 0.7)% was determined for the ozonolysis of the first DB, and (12.9 ± 0.7)% of the first-generation products. The rate constant of the reaction of O(3) with α-humulene is known as k(0) = 1.17 × 10(-14) cm(3) molecule(-1) s(-1) [Y. Shu and R. Atkinson, Int. J. Chem. Kinet., 1994, 26, 1193-1205]. The reaction rate constants of O(3) with the first-generation products and the second-generation products were, respectively, determined as k(1) = (3.6 ± 0.9) × 10(-16) and k(2) = (3.0 ± 0.7) × 10(-17) cm(3) molecule(-1) s(-1) by Facsimile-simulation of the observed ozone decay by FTIR. A total of 37 compounds in the aerosol phase and 5 products in the gas phase were tentatively identified: 25 compounds of the first-generation products contained C13-C15 species, 9 compounds of the second-generation products contained C8-C11 species, whereas 8 compounds of the third-generation products contained C4-C6 species. The products of all three generations consisted of a variety of dicarboxylic-, hydroxy-oxocarboxylic- and oxo-carboxylic acids. The formation mechanisms of some of the products are

  20. Gas-phase impregnation of porous media with pyrocarbon as a promising trend in the manufacturing technology of carbon-graphite materials and products for reactor engineering

    SciTech Connect

    Gurin, V.A.; Zelensky, V.F.; Konotop, Yu.F.

    1993-12-31

    This paper presents some special features of producing carbon-graphite materials by gas-phase methods. Main differences between these methods and the traditional one of graphite fabrication are discussed; basic characteristics of the equipment available at the KIPT are given. The HTGR type reactors need radiation resistant grades of graphite with a normal operation guaranteed for a specified time.

  1. Substrate-free gas-phase synthesis of graphene

    NASA Astrophysics Data System (ADS)

    Dato, Albert Manglallan

    Graphene is a single atomic layer of sp2-bonded carbon atoms tightly packed in a two-dimensional honeycomb lattice. The material possesses remarkable properties and has been envisioned for use in numerous applications. Contemporary graphene production techniques require substrates or graphite crystals to create graphene. Furthermore, these approaches involve multiple steps, and sometimes non-ambient conditions, to produce atomically-thin sheets. This dissertation presents the first substrate-free gas-phase graphene synthesis method. The technique can synthesize graphene in a single step at atmospheric pressure, without the use of graphite or substrates. The novel synthesis method was discovered through experiments that tested the hypothesis that graphene could be synthesized through the delivery of alcohols into argon plasmas. The experiments presented in this dissertation were conducted in an atmospheric-pressure microwave plasma reactor. Solid carbon materials were produced by delivering liquid ethanol droplets directly into argon plasmas. Numerous characterization techniques were used to unambiguously prove that the synthesized materials were clean and highly ordered graphene sheets. Additional studies investigated the effects of variable experimental parameters on the graphene synthesis process. The applied microwave power did not significantly affect the types of structures produced in the reactor. Lowering the volumetric flow rate of the plasma gas resulted in the synthesis of graphitic particles. The composition of the precursors delivered into the reactor also affected graphene synthesis. Graphene was not produced through the delivery of methanol or isopropyl alcohol droplets. However, graphene was obtained through dimethyl ether, which is an organic compound with the same atomic composition as ethanol. Thus, the flow rate and precursor composition significantly affected the nucleation, growth, and residence time of the materials created during experiments

  2. Gas-phase fragmentation of protonated piplartine and its fungal metabolites using tandem mass spectrometry and computational chemistry.

    PubMed

    da Silva-Junior, E A; Paludo, C R; Gouvea, D R; Kato, M J; Furtado, N A J C; Lopes, N P; Vessecchi, R; Pupo, M T

    2017-08-01

    Piplartine, an alkaloid produced by plants in the genus Piper, displays promising anticancer activity. Understanding the gas-phase fragmentation of piplartine by electrospray ionization tandem mass spectrometry can be a useful tool to characterize biotransformed compounds produced by in vitro and in vivo metabolism studies. As part of our efforts to understand natural product fragmentation in electrospray ionization tandem mass spectrometry, the gas-phase fragmentation of piplartine and its two metabolites 3,4-dihydropiplartine and 8,9-dihydropiplartine, produced by the endophytic fungus Penicillium crustosum VR4 biotransformation, were systematically investigated. Proposed fragmentation reactions were supported by ESI-MS/MS data and computational thermochemistry. Cleavage of the C-7 and N-amide bond, followed by the formation of an acylium ion, were characteristic fragmentation reactions of piplartine and its analogs. The production of the acylium ion was followed by three consecutive and competitive reactions that involved methyl and methoxyl radical eliminations and neutral CO elimination, followed by the formation of a four-member ring with a stabilized tertiary carbocation. The absence of a double bond between carbons C-8 and C-9 in 8,9-dihydropiplartine destabilized the acylium ion and resulted in a fragmentation pathway not observed for piplartine and 3,4-dihydropiplartine. These results contribute to the further understanding of alkaloid gas-phase fragmentation and the future identification of piplartine metabolites and analogs using tandem mass spectrometry techniques. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

  3. The structures of tellurium(IV) halides in the gas phase and as solvated molecules.

    PubMed

    Shlykov, Sergey A; Giricheva, Nina I; Titov, Anton V; Szwak, Małgorzata; Lentz, Dieter; Girichev, Georgiy V

    2010-04-07

    The structures of molecular tellurium tetrafluoride and tellurium tetrachloride were determined by a combination of gas-phase electron diffraction, mass spectrometry and quantum chemical calculations. The combined GED/MS experiments showed no evidence of decomposition of TeF(4) and TeCl(4). No ions of oligomeric (dimeric, trimeric, etc.) or any other composition were found in the mass spectra. The monomeric molecules possess a pseudo trigonal bipyramidal structure (C(2v) symmetry) with the equatorial Te-X distances being shorter than the axial ones. The fluorine atoms are bent away from the lone pair resulting in X(eq)-Te-X(eq) and X(eq)-Te-X(ax) bond angles smaller than 120 and 90 degrees, respectively. The structure of solvates TeF(4) (THF)(2), TeF(4) (dioxane) TeF(4) (DME)(2), TeF(4)(Et(2)O) TeF(4)(toluene), TeCl(4)(CH(3)CN)(2), TeCl(4)(DME)(2) and TeCl(4)(dioxane) were determined by X-ray diffraction. The structures of tellurium tetrafluoride solvates are strongly influenced by the choice of the solvent molecules. Monomeric TeF(4) units were obtained with THF, DME and dioxane whereas fluoride bridged coordination polymers were formed using diethyl ether or toluene. All tellurium tetrachloride solvates studied contain monomeric TeCl(4) units with coordinated solvent molecules. Coordination numbers range from four in the gas phase to eight in the TeF(4) dimethoxyethane solvate. Geometric parameters of the TeX(4) molecules in the crystal, solvates and gas phase were compared. DFT, MP2, CCSD, CCSD(T) methods were applied for calculation of geometric and vibrational characteristics of free TeX(4) molecules (X = F, Cl). The pseudorotation barriers were estimated and an NBO analysis was performed. It was shown that both, GED and theoretical, quantitative results are in agreement with the qualitative results of the VSEPR model.

  4. Surface plasmon sensing of gas phase contaminants using optical fiber.

    SciTech Connect

    Thornberg, Steven Michael; White, Michael I.; Rumpf, Arthur Norman; Pfeifer, Kent Bryant

    2009-10-01

    Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H{sub 2}, H{sub 2}S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 70mTorr partial pressures of H{sub 2} using this technique and <280 {micro}Torr partial pressures of H{sub 2}S. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H{sub 2}, H{sub 2}S, and H{sub 2}O without changing the fiber or the analytical system.

  5. Gas-phase Chemistry of the Cyanate Ion, OCN-

    NASA Astrophysics Data System (ADS)

    Cole, Callie A.; Wang, Zhe-Chen; Snow, Theodore P.; Bierbaum, Veronica M.

    2015-10-01

    Cyanate (OCN-) is the only ion to date whose presence has been confirmed in the icy mantles that coat interstellar dust grains. Understanding the chemical behavior of cyanate at a fundamental level is therefore integral to the advancement of astrochemistry. We seek to unravel the chemistry of this intriguing anion through a combination of gas-phase experiments and theoretical explorations. Our approach is twofold: first, employing a flowing afterglow-selected ion flow tube apparatus, the reactions between OCN- and three of the most abundant atomic species in the interstellar medium, hydrogen, nitrogen, and oxygen, are examined. Hydrogen atoms readily react by associative detachment, but the remarkable stability of OCN- does not give rise to an observable reaction with either nitrogen or oxygen atoms. To explain these results, the potential energy surfaces of several reactions are investigated at the B3LYP/6-311++G(d,p) level of theory. Second, collision induced dissociation experiments involving deprotonated uracil, thymine, and cytosine in an ion trap mass spectrometer reveal an interesting connection between these pyrimidine nucleobase anions and OCN-. Theoretical calculations at the B3LYP/6-311++G(d,p) level of theory are performed to delineate the mechanisms of dissociation and explore the possible role of OCN- as a biomolecule precursor.

  6. Full field gas phase velocity measurements in microgravity

    NASA Technical Reports Server (NTRS)

    Griffin, Devon W.; Yanis, William

    1995-01-01

    Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

  7. Gas phase structures of peroxides: experiments and computational problems.

    PubMed

    Oberhammer, Heinz

    2015-02-02

    Gas-phase structures of several organic and inorganic peroxides X-O-O-X and X-O-O-X', which have been determined experimentally by gas electron diffraction and/or microwave spectroscopy, are discussed. The OO bond length in these peroxides varies from 1.481(8) Å in Me3 SiOOSiMe3 to 1.214(2) Å in FOOF and the dihedral angle ϕ(XO-OX) between 0° in HC(O)O-OH and near 180° in Bu(t) O-OBu(t) . Some of the peroxides cause problems for quantum chemistry, since several computational methods fail to reproduce the experimental structures. Extreme examples are MeO-OMe and FO-OF. In the case of MeO-OMe only about half of the more than 100 computational methods reported in the literature reproduce the experimentally determined double-minimum shape of the torsional potential around the OO bond correctly. For FO-OF only a small number of close to 200 computational methods reproduce the OO and OF bond lengths better than ±0.02 Å.

  8. Experimental Determination of Gas Phase Thermodynamic Properties of Bimolecular Complexes

    NASA Astrophysics Data System (ADS)

    Hansen, Anne S.; Maroun, Zeina; Mackeprang, Kasper; Kjaergaard, Henrik G.

    2016-06-01

    Accurate determination of the atmospheric abundance of hydrogen bound bimolecular complexes is necessary, as hydrogen bonds are partly responsible for the formation and growth of aerosol particles. The abundance of a complex is related to the Gibbs free energy of complex formation (Δ G), which is often obtained from quantum chemical calculations that rely on calculated values of the enthalpy (Δ H) and entropy (Δ S) of complex formation. However, calculations of Δ H and in particular Δ S are associated with large uncertainties, and accurate experimental values are therefore crucial for theoretical benchmarking studies. Infrared measurements of gas phase hydrogen bound complexes were performed in the 300 to 373 K range, and lead to a purely experimental determination of Δ H using the van't Hoff equation. Equilibrium constants were determined by combining an experimental and calculated OH-stretching intensity, from which values of Δ G and hence Δ S could be determined. Thus we can determine Δ G, Δ H and Δ S for a bimolecular complex. We find that in the 300 to 373 K temperature range the determined Δ H and Δ S values are independent of temperature.

  9. Gas-phase clusterization of zinc during magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Abduev, A. Kh.; Akhmedov, A. K.; Asvarov, A. Sh.; Alikhanov, N. M.-R.; Emirov, R. M.; Muslimov, A. E.; Belyaev, V. V.

    2017-01-01

    The processes of gas-phase clusterization of zinc during dc magnetron sputtering of a zinc target in an argon atmosphere have been investigated. The influence of the working gas pressure and magnetron discharge current on the morphology and structure of the precipitates formed on substrates previously cooled to-50°C is studied. It is shown that dense textured (002)Zn layers with a columnar structure are formed at relatively low argon pressures in the chamber ( P = 0.5 Pa) and low discharge currents (100 mA). X-ray amorphous deposits with a fractal coral-like structure arise on substrates at an extremely high argon pressure in the chamber ( P = 5 Pa). An increase in the magnetron discharge current at an operating gas pressure of 5 Pa leads to the formation of polycrystalline layers on substrates; the intensity of the XRD peaks related to crystalline zinc increases with an increase in the discharge current. Possible mechanisms of the structural transformation of Zn deposits are considered.

  10. Project ARGO: Gas phase formation in simulated microgravity

    NASA Technical Reports Server (NTRS)

    Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

    1993-01-01

    The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

  11. Gas-phase Electronic Spectra of Coronene and Corannulene Cations

    NASA Astrophysics Data System (ADS)

    Hardy, F.-X.; Rice, Corey A.; Maier, John P.

    2017-02-01

    Gas-phase electronic spectra of the coronene ({{{C}}}24{{{{H}}}12}+) and corannulene ({{{C}}}20{{{{H}}}10}+) cations complexed with helium have been recorded in a quadrupole ion trap at 5 K by photodissociation. The electronic spectrum of {{{C}}}20{{{{H}}}10}+ with two helium atoms was also measured to estimate the perturbation. This method is sufficient for an astronomical comparison because the shift due to the weakly bound helium is on the order of 0.2 Å. {{{C}}}24{{{{H}}}12}+{--}{He} has the origin band of the {{{A}}}2{{{E}}}1g≤ftarrow X{}2{{{E}}}2u transition at 9438.3 Å and that to a much higher state {{{D}}}3≤ftarrow X{}2{{{E}}}2u at 4570 Å. The corannulene cation is subject to a Jahn–Teller distortion in the electronic ground state, leading to the {3}2{{A}}\\prime ≤ftarrow {{X}}{}2{{A}}\\prime \\prime and {3}2{{A}}\\prime \\prime ≤ftarrow {{X}}{}2{{A}}\\prime transitions with origin band maxima when complexed with helium at 5996.1 and 5882.6 Å. These absorptions lie in a region where there is a congestion of diffuse interstellar bands (DIBs). However, the recorded features have no match with astronomical observations, removing coronene and corannulene cations and probably other aromatic hydrocarbons of this size as possible carriers of the DIBs.

  12. Direct synthesis of multifunctional heterostructured magnetic nanoparticles in gas phase

    NASA Astrophysics Data System (ADS)

    Xu, Yunhao

    Most applications of the nanotechnology require the nanoscale objects to have a controllable size, narrow size distribution, and to be in an assembled form if possible. An approach to go beyond the current performance of these nanoscale objects is to combine and couple different properties into one single object, making them multifunctional. To achieve these goals, we developed a bottom-up approach engaging a sputtering-gas-condensation technique to deposit nanoparticles with controlled size, size distribution, crystallographic phase and heterostructures. This technique is compatible to micro/nanoelectronic materials and devices fabrication processes. Three-dimensional assembly of nanoparticle-crystals is demonstrated by using the technique. A model is developed to explain the detailed nucleation, growth, phase separation processes based on the classic nucleation as well as kinetic processes. To combine and couple different properties into a single nanoparticle, a new method is developed to generate different heterostructures at single-particle level directly in gas phase. Sharp and clean interfaces were formed between the different components in the single nanoparticle. The control of the diffusion in nanoscale objects opens a door for the synthesis of heterostructures with high quality interfaces and desirable phases. The model-material systems of ferromagnetic metals and alloys (Fe, Co, and FeCo), noble metals (Ag and Au) and semiconductor element (Si) were demonstrated in the work, which have great potential in biomedical, spintronics and photonics applications. Other fields such as renewable energy devices can also benefit by adopting this novel approach in different material systems.

  13. Gas phase production and loss of isoprene epoxydiols.

    PubMed

    Bates, Kelvin H; Crounse, John D; St Clair, Jason M; Bennett, Nathan B; Nguyen, Tran B; Seinfeld, John H; Stoltz, Brian M; Wennberg, Paul O

    2014-02-20

    Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-β- and trans-β-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-β- and trans-β, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10(-11), (1.52 ± 0.07) × 10(-11), and (0.98 ± 0.05) × 10(-11) cm(3) molecule(-1) s(-1) for the δ1, cis-β, and trans-β isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions.

  14. Microwave spectrum and the gas phase structure of phthalimide

    NASA Astrophysics Data System (ADS)

    Pejlovas, Aaron M.; Lin, Wei; Oncer, Onur; Kukolich, Stephen G.

    2015-11-01

    The microwave spectrum of phthalimide (PhI) was measured in the 4.8-9.5 GHz range using a Flygare-Balle type, pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent and all unique single 13C substituted isotopologues. The rotational (MHz), centrifugal distortion (kHz), and quadrupole coupling constants (MHz) were determined for the parent to be A = 1745.6655(10), B = 1199.3309(6), C = 711.0864(3), DJ = 0.012(7), DJK = -0.05(9), 1.5χaa = 2.719(11), and 0.25(χbb - χcc) = 1.236(3). Using the measured rotational constants of the isotopologues, a nonlinear least squares fit was performed to obtain the best fit gas phase structure. The inertial defect is Δ = -0.175 amu Å2, indicating a planar structure for PhI. Calculations using B3LYP/aug-cc-pVQZ provided rotational constants which are much closer to the experimental values compared to the MP2/6-311++G∗∗ calculated values.

  15. Microwave spectrum and gas phase structure of maleimide

    NASA Astrophysics Data System (ADS)

    Pejlovas, Aaron M.; Oncer, Onur; Kang, Lu; Kukolich, Stephen G.

    2016-01-01

    The rotational spectrum of maleimide was measured in the 5-12 GHz range using a Flygare-Balle type, pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent, all unique singly substituted 13C isotopologues, and an sbnd ND, deuterium substituted isotopologue. The parent (or normal isotopologue) rotational constants, centrifugal distortion constants, and quadrupole coupling constants are A = 6815.3251(12) MHz, B = 2361.85011(64) MHz, C = 1754.32750(64) MHz, DJ = 0.232(24) kHz, DJK = 0.546(54) kHz, 1.5χaa = 2.4227(53) MHz, and 0.25(χbb-χcc) = 1.3679(15) MHz. A best fit gas phase structure was determined using the experimental rotational constants of the isotopologues and some parameters from calculations. The inertial defect is Δ = -0.054 amu Å2, indicating a planar structure for maleimide, with no large amplitude motions observed on the sbnd NH hydrogen atom. Calculations using B3LYP/aug-cc-pVTZ provided rotational constants which are much closer (within 1-2%) to the experimental values compared to the MP2/aug-cc-pVTZ calculated values.

  16. Relating gas phase to solution conformations: Lessons from disordered proteins

    PubMed Central

    Beveridge, Rebecca; Phillips, Ashley S.; Denbigh, Laetitia; Saleem, Hassan M.; MacPhee, Cait E.

    2015-01-01

    In recent years both mass spectrometry (MS) and ion mobility mass spectrometry (IM‐MS) have been developed as techniques with which to study proteins that lack a fixed tertiary structure but may contain regions that form secondary structure elements transiently, namely intrinsically disordered proteins (IDPs). IM‐MS is a suitable method for the study of IDPs which provides an insight to conformations that are present in solution, potentially enabling the analysis of lowly populated structural forms. Here, we describe the IM‐MS data of two IDPs; α‐Synuclein (α‐Syn) which is implicated in Parkinson's disease, and Apolipoprotein C‐II (ApoC‐II) which is involved in cardiovascular diseases. We report an apparent discrepancy in the way that ApoC‐II behaves in the gas phase. While most IDPs, including α‐Syn, present in many charge states and a wide range of rotationally averaged collision cross sections (CCSs), ApoC‐II presents in just four charge states and a very narrow range of CCSs, independent of solution conditions. Here, we compare MS and IM‐MS data of both proteins, and rationalise the differences between the proteins in terms of different ionisation processes which they may adhere to. PMID:25920945

  17. Gas phase synthesis of two ensembles of silicon nanoparticles

    NASA Astrophysics Data System (ADS)

    Mohan, A.; de Jong, M. M.; Poulios, I.; Schropp, R. E. I.; Rath, J. K.

    2015-09-01

    Dusty plasmas provide a very favorable environment for the growth of silicon nanocrystals. For application of silicon nanocrystals in a solar cell, the fabrication of monodisperse silicon quantum dots has been challenging. We report a single step method to synthesize silicon (Si) nanoparticles in a custom designed dedicated plasma reactor. The nanoparticles produced in the gas phase belong to two different phases exhibiting different structural and optical properties. Particles made in the bulk of the plasma are aggregates of crystalline particles with a mean size of 100 nm. Particles made in locally enhanced plasma regions produced at holes present in the grounded electrode contain free-standing quantum sized particles with crystallites (with mean size of 2.95 nm) embedded within an amorphous matrix. We provide insight on different plasma processes leading to the formation of aggregates and free-standing particles. We hypothesize that the free standing particles are formed due to the excess energetic electrons present in locally enhanced discharges.

  18. Precursor-Less Coating of Nanoparticles in the Gas Phase

    PubMed Central

    Pfeiffer, Tobias V.; Kedia, Puneet; Messing, Maria E.; Valvo, Mario; Schmidt-Ott, Andreas

    2015-01-01

    This article introduces a continuous, gas-phase method for depositing thin metallic coatings onto (nano)particles using a type of physical vapor deposition (PVD) at ambient pressure and temperature. An aerosol of core particles is mixed with a metal vapor cloud formed by spark ablation by passing the aerosol through the spark zone using a hollow electrode configuration. The mixing process rapidly quenches the vapor, which condenses onto the core particles at a timescale of several tens of milliseconds in a manner that can be modeled as bimodal coagulation. Gold was deposited onto core nanoparticles consisting of silver or polystyrene latex, and silver was deposited onto gold nanoparticles. The coating morphology depends on the relative surface energies of the core and coating materials, similar to the growth mechanisms known for thin films: a coating made of a substance having a high surface energy typically results in a patchy coverage, while a coating material with a low surface energy will normally “wet” the surface of a core particle. The coated particles remain gas-borne, allowing further processing. PMID:28787986

  19. Gas phase plasma impact on phenolic compounds in pomegranate juice.

    PubMed

    Herceg, Zoran; Kovačević, Danijela Bursać; Kljusurić, Jasenka Gajdoš; Jambrak, Anet Režek; Zorić, Zoran; Dragović-Uzelac, Verica

    2016-01-01

    The aim of the study was to evaluate the effect of gas phase plasma on phenolic compounds in pomegranate juice. The potential of near infrared reflectance spectroscopy combined with partial least squares for monitoring the stability of phenolic compounds during plasma treatment was explored, too. Experiments are designed to investigate the effect of plasma operating conditions (treatment time 3, 5, 7 min; sample volume 3, 4, 5 cm(3); gas flow 0.75, 1, 1.25 dm(3) min(-1)) on phenolic compounds and compared to pasteurized and untreated pomegranate juice. Pasteurization and plasma treatment resulted in total phenolic content increasing by 29.55% and 33.03%, respectively. Principal component analysis and sensitivity analysis outputted the optimal treatment design with plasma that could match the pasteurized sample concerning the phenolic stability (5 min/4 cm(3)/0.75 dm(3) min(-1)). Obtained results demonstrate the potential of near infrared reflectance spectroscopy that can be successfully used to evaluate the quality of pomegranate juice upon plasma treatment considering the phenolic compounds.

  20. ENGINE EXHAUST PARTICULATE AND GAS PHASE CONTRIBUTIONS TO VASCULAR TOXICITY

    PubMed Central

    Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob

    2014-01-01

    Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicular emissions (MVE; combined gasoline and diesel exhausts) for 6 h/d × 50 days, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase 9 (MMP9) protein, 3-nitrotyrosine, and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681

  1. Visible and ultraviolet spectroscopy of gas phase rhodamine 575 cations.

    PubMed

    Daly, Steven; Kulesza, Alexander; Knight, Geoffrey; MacAleese, Luke; Antoine, Rodolphe; Dugourd, Philippe

    2015-06-04

    The visible and ultraviolet spectroscopy of gas phase rhodamine 575 cations has been studied experimentally by action-spectroscopy in a modified linear ion trap between 220 and 590 nm and by time-dependent density functional theory (TDDFT) calculations. Three bands are observed that can be assigned to the electronic transitions S0 → S1, S0 → S3, and S0 → (S8,S9) according to the theoretical prediction. While the agreement between theory and experiment is excellent for the S3 and S8/S9 transitions, a large shift in the value of the calculated S1 transition energy is observed. A theoretical analysis of thermochromism, potential vibronic effects, and-qualitatively-electron correlation revealed it is mainly the latter that is responsible for the failure of TDDFT to accurately reproduce the S1 transition energy, and that a significant thermochromic shift is also present. Finally, we investigated the nature of the excited states by analyzing the excitations and discussed their different fragmentation behavior. We hypothesize that different contributions of local versus charge transfer excitations are responsible for 1-photon versus 2-photon fragmentation observed experimentally.

  2. Gas phase chromatography of halides of elements 104 and 105

    SciTech Connect

    Tuerler, A.; Gregorich, K.E.; Czerwinski, K.R.; Hannink, N.J.; Henderson, R.A.; Hoffman, D.C.; Kacher, C.D.; Kadkhodayan, B.; Kreek, S.A.; Lee, D.M.; Leyba, J.D.; Nurmia, M.J. ); Gaeggeler, H.W.; Jost, D.T.; Kovacs, J.; Scherer, U.W.; Vermeulen, D.; Weber, A. , Villigen ); Barth, H.; Gober, M.K.; Kratz, J.V. (Philipps-Univ., Marburg

    1991-04-01

    On-line isothermal gas phase chromatography was used to study halides of {sup 261}104 (T{sub {1/2}} = 65 s) and {sup 262,263}105 (T{sub {1/2}} = 34 s and 27 s) produced an atom-at-a time via the reactions {sup 248}Cm({sup 18}O, 5n) and {sup 249}Bk({sup 18}O, 5n, 4n), respectively. Using HBr and HCl gas as halogenating agents, we were able to produce volatile bromides and chlorides of the above mentioned elements and study their behavior compared to their lighter homologs in Groups 4 or 5 of the periodic table. Element 104 formed more volatile bromides than its homolog Hf. In contrast, element 105 bromides were found to be less volatile than the bromides of the group 5 elements Nb and Ta. Both 104 and Hf chlorides were observed to be more volatile than their respective bromides. 31 refs., 8 figs.

  3. Release characteristics of single-wall carbon nanotubes during manufacturing and handling

    NASA Astrophysics Data System (ADS)

    Ogura, I.; Kotake, M.; Hashimoto, N.; Gotoh, K.; Kishimoto, A.

    2013-04-01

    We investigated the release characteristics of single-wall carbon nanotubes (CNTs) synthesized by a pilot-scale plant. In addition to on-site aerosol measurements at the pilot-scale plant where the CNTs were synthesized, harvested, and packed, we conducted dustiness tests by vortex shaking and by transferring CNTs from one bowl to another. In the results of the on-site aerosol measurements, slight increases in the concentration were observed by aerosol monitoring instruments in the enclosure where CNTs were harvested and packed. In filter samples collected in this enclosure, micron-sized CNT clusters were observed by electron microscopy analysis. For samples collected outside the enclosure or during other processes, no CNTs were observed. The concentrations of elemental carbon at all locations were lower than the proposed occupational exposure limits of CNTs. The results of the dustiness tests revealed that submicron-sized particles were dominant in the number concentration measured by aerosol monitoring instruments, whereas micron-sized CNT clusters were mainly observed by electron microscopy analysis. The results of dustiness tests indicate that these CNTs have a low release characteristic. The lower drop impact of CNT clusters due to their lower bulk density resulted in lower CNT release from falling CNTs.

  4. Modifying release characteristics from 3D printed drug-eluting products.

    PubMed

    Boetker, Johan; Water, Jorrit Jeroen; Aho, Johanna; Arnfast, Lærke; Bohr, Adam; Rantanen, Jukka

    2016-07-30

    This work describes an approach to modify the release of active compound from a 3D printed model drug product geometry intended for flexible dosing and precision medication. The production of novel polylactic acid and hydroxypropyl methylcellulose based feed materials containing nitrofurantoin for 3D printing purposes is demonstrated. Nitrofurantoin, Metolose® and polylactic acid were successfully co-extruded with up to 40% Metolose® content, and subsequently 3D printed into model disk geometries (ø10mm, h=2mm). Thermal analysis with differential scanning calorimetry and solid phase identification with Raman spectroscopy showed that nitrofurantoin remained in its original solid form during both hot-melt extrusion and subsequent 3D printing. Rheological measurements of the different compositions showed that the flow properties were sensitive to the amount of undissolved particles present in the formulation. Release of nitrofurantoin from the disks was dependent on Metolose® loading, with higher accumulated release observed for higher Metolose® loads. This work shows the potential of custom-made, drug loaded feed materials for 3D printing of precision drug products with tailored drug release characteristics. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. Influence of formulation composition and process on the characteristics and in vitro release from PLGA-based sustained release injectables.

    PubMed

    Meeus, Joke; Scurr, David J; Appeltans, Bernard; Amssoms, Katie; Annaert, Pieter; Davies, Martyn C; Roberts, Clive J; Van den Mooter, Guy

    2015-02-01

    Understanding and controlling the in vitro release behavior of a formulation is a first step toward rationalized selection of a solubility enhancing formulation strategy with a desired release profile in vivo. Therefore six model formulations, representing three different formulation strategies, were physicochemically analyzed and their in vitro release was determined. Solid dispersions based on a PLGA/PVP matrix were compared to solid dispersions in a pure PLGA matrix. Additionally these solid dispersion strategies were compared to the strategy of particle size reduction by means of an API microsuspension. Depending on composition and manufacturing method, formulations varied in particle size, porosity, phase behavior, surface coverage and physical state of the API. This resulted in observed differences in their in vitro release profile. For the various formulation strategies tested both a porous PLGA-based formulation and PLGA/PVP-based formulations, resulted in vitro in sustained release of the poorly soluble API with over 50% of drug released after 24h. For PLGA-based formulations the porosity was identified as a critical parameter influencing in vitro drug release. For the PLGA/PVP-based formulations the release rate can be tailored by the amount of PLGA present. Particle size reduction resulted in immediate total drug release.

  6. A Phosphohistidine Proteomics Strategy Based on Elucidation of a Unique Gas-Phase Phosphopeptide Fragmentation Mechanism

    PubMed Central

    2015-01-01

    Protein histidine phosphorylation is increasingly recognized as a critical posttranslational modification (PTM) in central metabolism and cell signaling. Still, the detection of phosphohistidine (pHis) in the proteome has remained difficult due to the scarcity of tools to enrich and identify this labile PTM. To address this, we report the first global proteomic analysis of pHis proteins, combining selective immunoenrichment of pHis peptides and a bioinformatic strategy based on mechanistic insight into pHis peptide gas-phase fragmentation during LC–MS/MS. We show that collision-induced dissociation (CID) of pHis peptides produces prominent characteristic neutral losses of 98, 80, and 116 Da. Using isotopic labeling studies, we also demonstrate that the 98 Da neutral loss occurs via gas-phase phosphoryl transfer from pHis to the peptide C-terminal α-carboxylate or to Glu/Asp side chain residues if present. To exploit this property, we developed a software tool that screens LC–MS/MS spectra for potential matches to pHis-containing peptides based on their neutral loss pattern. This tool was integrated into a proteomics workflow for the identification of endogenous pHis-containing proteins in cellular lysates. As an illustration of this strategy, we analyzed pHis peptides from glycerol-fed and mannitol-fed Escherichia coli cells. We identified known and a number of previously speculative pHis sites inferred by homology, predominantly in the phosphoenolpyruvate:sugar transferase system (PTS). Furthermore, we identified two new sites of histidine phosphorylation on aldehyde-alcohol dehydrogenase (AdhE) and pyruvate kinase (PykF) enzymes, previously not known to bear this modification. This study lays the groundwork for future pHis proteomics studies in bacteria and other organisms. PMID:25156620

  7. GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN

    EPA Science Inventory

    Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen

    Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

  8. GAS PHASE SELECTIVE PHOTOXIDATION OF ALCOHOLS USING LIGHT-ACTIVATED TITANIUM DIOXIDE AND MOLECULAR OXYGEN

    EPA Science Inventory

    Gas Phase Selective Oxidation of Alcohols Using Light-Activated Titanium Dioxide and Molecular Oxygen

    Gas phase selective oxidations of various primary and secondary alcohols are studied in an indigenously built stainless steel up-flow photochemical reactor using ultravi...

  9. Characteristics and kinetics simulation of controlled-release KMnO4 for phenol remediation.

    PubMed

    Xiong, Houfeng; Huo, Mingxin; Zhou, Dandan; Dong, Shuangshi; Zou, Donglei

    Controlled-release KMnO4 (CRP) technology has been recently developed as an improved, highly efficient technique in wastewater treatment. In this study, batch-style experiments were conducted to evaluate this technology. The release characteristics of CRP in distilled water and the reaction between CRP and phenol were studied and fitted using MATLAB software. Results indicated that in distilled water, temperature (T) and pH value had a larger effect than dissolved oxygen (DO) concentration on the release characteristics of KMnO4, and this relationship can be accurately described by the following kinetic equation: logQ = log[1.141T(0.152)(pH)(-1.0536)(DO)(0.4674)] + [0.0048T(0.3756)(pH)(1.8854)(DO)(-0.0509)]logt. KMnO4 released from CRP can effectively degrade phenol-contaminated water with different concentrations. A simulated equation (r = -dCA/dt = -15.1705 CA(0.6840)CP(-0.1406)) characterizing phenol degradation was developed using MATLAB software. Comparison between the theoretical phenol removal rates deduced by the above two equations and the initial phenol concentration as well as the CRP dosage with the experimental data indicates that the differences between them were less than 20%. The results indicate phenol can be effectively removed by CRP and smaller dosage of KMnO4 was required compared with literature values. The models can provide guidance for CRP application in real polluted sites, which can lower the cost for site remediation.

  10. Ignition and flame characteristics of [under-expanded] cryogenic hydrogen releases

    DOE PAGES

    Panda, Pratikash P.; Hecht, Ethan S.

    2016-09-04

    In this work, under-expanded cryogenic hydrogen jets were investigated experimentally for their ignition and flame characteristics. The test facility described herein, was designed and constructed to release hydrogen at a constant temperature and pressure, to study the dispersion and thermo-physical properties of cryogenic hydrogen releases and flames. In this study, a non-intrusive laser spark focused on the jet axis was used to measure the maximum ignition distance. The radiative power emitted by the corresponding jet flames was also measured for a range of release scenarios from 37 K to 295 K, 2–6 barabs through nozzles with diameters from 0.75 tomore » 1.25 mm. The maximum ignition distance scales linearly with the effective jet diameter (which scales as the square root of the stagnant fluid density). A 1-dimensional (stream-wise) cryogenic hydrogen release model developed previously at Sandia National Laboratories (although this model is not yet validated for cryogenic hydrogen) was exercised to predict that the mean mole fraction at the maximum ignition distance is approximately 0.14, and is not dependent on the release conditions. The flame length and width were extracted from visible and infra-red flame images for several test cases. The flame length and width both scale as the square root of jet exit Reynolds number, as reported in the literature for flames from atmospheric temperature hydrogen. As shown in previous studies for ignited atmospheric temperature hydrogen, the radiative power from the jet flames of cold hydrogen scales as a logarithmic function of the global flame residence time. The radiative heat flux from jet flames of cold hydrogen is higher than the jet flames of atmospheric temperature hydrogen, for a given mass flow rate, due to the lower choked flow velocity of low-temperature hydrogen. Lastly, this study provides critical information with regard to the development of models to inform the safety codes and standards of hydrogen

  11. Evaluating the Impact of Releasing an Item Pool on a Test's Empirical Characteristics.

    PubMed

    Buckendahl, Chad W; Gerrow, Jack D

    2016-10-01

    Protecting the security of examination questions is an important task for high-stakes examining boards/agencies and university programs. To maintain the security of questions, examining boards and university programs use a combination of prevention, detection, and enforcement strategies. A common prevention strategy is to establish a number of controls on access to questions; however, restricting access can motivate examinees to try harder to reconstruct questions that may appear on future versions of the test. Moreover, access to study materials by some groups and not others can present a challenge to the fairness of examinations. The aim of this study was to evaluate the empirical stability of test characteristics. Specifically, the primary research objective was to investigate the empirical stability of the items and test forms of a written examination before and after a specific policy decision was implemented. As a response to both of these concerns, this article describes a study that evaluated how psychometric (i.e., statistical) properties of test forms and individual questions might be affected by publicly releasing a larger number of questions from an item question pool. A series of analyses were conducted, including item drift to evaluate stability of the characteristics. The results suggest that empirical characteristics of the test forms and individual questions have remained relatively stable since the release policy was implemented. Specifically, statistical properties of the test forms have continued to perform similarly to test forms that were constructed prior to the release. Although the results of this study were promising, the context of this specific testing program may have offered additional protections such as a limited number of administrations that others may not. Therefore, testing/examining agencies and university programs may want to consider this strategy with appropriate caution.

  12. Modeling of the burst release from PLGA micro- and nanoparticles as function of physicochemical parameters and formulation characteristics.

    PubMed

    Rodrigues de Azevedo, Cristiana; von Stosch, Moritz; Costa, Mariana S; Ramos, A M; Cardoso, M Margarida; Danhier, Fabienne; Préat, Véronique; Oliveira, Rui

    2017-10-30

    A substantial drug release from poly(lactic-co-glycolic) acid (PLGA) micro- and nanoparticles can occur in the first hours of immersion, which is referred to as burst release. A strong burst release (when not intentional) is to be avoided as it decreases the efficacy of the treatment and could be dangerous to the host. In this work we analyze the total amount of drug released during burst and respective kinetics in relation to formulations characteristics, experimental conditions and drug molecular properties in 154 drug release experiments with 41 different drugs by partial least squares (PLS) and decision tree regression. The model created enables to quantify to which degree the physicochemical parameters control the burst release from PLGA particles. Our analysis shows that the amount of drug released during burst is mostly influenced by the formulation characteristics and the synthesis parameters, whereas the drug release kinetics is also influenced by the molecular properties of the drug. The variables that significantly influence the amount and kinetics of the burst release are discussed in detail and compared with findings from other researchers. The final regression models are shown to predict the release profile of a new drug, opening the possibility to be applied to systematically manipulate the burst release by means of designing an optimized drug delivery system. Copyright © 2017. Published by Elsevier B.V.

  13. IV-VI semiconductor lasers for gas phase biomarker detection

    NASA Astrophysics Data System (ADS)

    McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

    2007-09-01

    A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

  14. Measurement of Gas-phase Acids in Diesel Exhaust

    NASA Astrophysics Data System (ADS)

    Wentzell, J. J.; Liggio, J.; Li, S.; Vlasenko, A. L.; Staebler, R. M.; Brook, J.; Lu, G.; Poitras, M.; Chan, T.

    2012-12-01

    Gas-phase acids were measured using chemical ionization mass spectrometry (CIMS) as part of the Diesel Engine Emission Research Experiment (DEERE). The CIMS technique, utilizing acetate ion (CH3COO-) as a reagent ion, proved to be a rapid (measurements on the order of seconds) and sensitive (several counts/pptv) method of quantifying the acid emissions. Diluted diesel exhaust measurements were made from a Constant Volume Sampling dilution tunnel using a light duty (1.9L turbocharged Volkswagen Jetta TDI) diesel engine equipped with an OEM diesel oxidation catalyst and exhaust gas recirculation, mounted on an engine dynamometer. Acids measured included isocyanic, nitrous, nitric, propionic and sum of lactic and oxalic, as well as other unidentified compounds. Complimentary measurements of CO, CO2, Total Hydrocarbon (THC), and NOx, were also performed. Several engine modes (different engine rpm and torque outputs) at steady state were examined to determine their effect on acid emissions. Emission rates with respect to NOx and fuel based emission factors were determined. Measurements of HONO fuel emission factors agree well with real-world measurements within a traffic tunnel.1 The first estimate of isocyanic acid emission factors from a diesel engine is reported, and suggests that the emission of this highly toxic compound in diesel exhaust should not be ignored. 1. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J.,Lorzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A.,and Platt, U.: Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel, Atmos. Environ., 35, 3385-3394, doi:10.1016/S1352-2310(01)00138-8, 2001.

  15. Isomerization of the protonated acetone dimer in the gas phase.

    PubMed

    Norrman, K; Sølling, T I; McMahon, T B

    2005-08-01

    Mass spectrometry-based methods have been employed in order to study the reactions of non- (h(6)/h(6)), half (d(6)/h(6)), and fully (d(6)/d(6)) deuterium labeled protonated dimers of acetone in the gas phase. Neither kinetic nor thermodynamic isotope effects were found. From MIKES experiments (both spontaneous and collision-induced dissociations), it was found that the relative ion yield (m/z 65 vs m/z 59) from the dissociation reaction of half deuterium labeled (d(6)/h(6)) protonated dimer of acetone is dependent on the internal energy. A relative ion yield (m/z 65 vs m/z 59) close to unity is observed for cold, nonactivated, metastable ions, whereas the ion yield is observed to increase (favoring m/z 65) when the pressure of the collision gas is increased. This is in striking contrast to what would be expected if a kinetic isotope effect were present. A combined study of the kinetics and the thermodynamics of the association reaction between acetone and protonated acetone implicates the presence of at least two isomeric adducts. We have employed G3(MP2) theory to map the potential energy surface leading from the reactants, acetone and protonated acetone, to the various isomeric adducts. The proton-bound dimer of acetone was found to be the lowest-energy isomer, and protonated diacetone alcohol the next lowest-energy isomer. Protonated diacetone alcohol, even though it is an isomer hidden behind many barriers, can possibly account for the observed relative ion yield and its dependence on the mode of activation.

  16. CHAOS III: Gas-phase Abundances in NGC 5457

    NASA Astrophysics Data System (ADS)

    Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A.; Skillman, Evan D.; Moustakas, John

    2016-10-01

    We present Large Binocular Telescope observations of 109 H ii regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more temperature-sensitive auroral emission lines for 74 H ii regions, permitting the measurement of “direct” gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of T[N ii] with T[S iii] and T[O iii], consistent with little or no intrinsic scatter; (2) a correlation of T[S iii] with T[O iii], but with significant intrinsic dispersion; (3) overall agreement between T[N ii], T[S ii], and T[O ii], as expected, but with significant outliers; (4) the correlations of T[N ii] with T[S iii] and T[O iii] match the predictions of photoionization modeling while the correlation of T[S iii] with T[O iii] is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation H ii regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of H ii regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074 ± 0.009 in O/H and 0.095 ± 0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of H ii regions in NGC 5457.

  17. Gas-Phase Combustion Synthesis of Aluminum Nitride Powder

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Lottes, C. R.; Huertas, J. I.; Rosen, L. J.

    1996-01-01

    Due to its combined properties of high electrical resistivity and high thermal conductivity aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This novel approach involves reacting AlCl3, NH3, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H2. The NaCl by-product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl3 and NH3 were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powders show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775 C tinder dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl3 with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.

  18. Dissociative electron attachment to the gas-phase nucleobase hypoxanthine

    SciTech Connect

    Dawley, M. Michele; Tanzer, Katrin; Denifl, Stephan E-mail: Sylwia.Ptasinska.1@nd.edu; Carmichael, Ian; Ptasińska, Sylwia E-mail: Sylwia.Ptasinska.1@nd.edu

    2015-06-07

    We present high-resolution measurements of the dissociative electron attachment (DEA) to isolated gas-phase hypoxanthine (C{sub 5}H{sub 4}N{sub 4}O, Hyp), a tRNA purine base. The anion mass spectra and individual ion efficiency curves from Hyp were measured as a function of electron energy below 9 eV. The mass spectra at 1 and 6 eV exhibit the highest anion yields, indicating possible common precursor ions that decay into the detectable anionic fragments. The (Hyp − H) anion (C{sub 5}H{sub 3}N{sub 4}O{sup −}) exhibits a sharp resonant peak at 1 eV, which we tentatively assign to a dipole-bound state of the keto-N1H,N9H tautomer in which dehydrogenation occurs at either the N1 or N9 position based upon our quantum chemical computations (B3LYP/6-311+G(d,p) and U(MP2-aug-cc-pVDZ+)) and prior studies with adenine. This closed-shell dehydrogenated anion is the dominant fragment formed upon electron attachment, as with other nucleobases. Seven other anions were also observed including (Hyp − NH){sup −}, C{sub 4}H{sub 3}N{sub 4}{sup −}/C{sub 4}HN{sub 3}O{sup −}, C{sub 4}H{sub 2}N{sub 3}{sup −}, C{sub 3}NO{sup −}/HC(HCN)CN{sup −}, OCN{sup −}, CN{sup −}, and O{sup −}. Most of these anions exhibit broad but weak resonances between 4 and 8 eV similar to many analogous anions from adenine. The DEA to Hyp involves significant fragmentation, which is relevant to understanding radiation damage of biomolecules.

  19. Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Kumfer, B. M.; Sun, Z.; Chao, B. H.

    2001-01-01

    Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.

  20. Gas-phase chemistry of technetium carbonyl complexes.

    PubMed

    Wang, Yang; Qin, Zhi; Fan, Fang-Li; Haba, Hiromitsu; Komori, Yukiko; Cao, Shi-Wei; Wu, Xiao-Lei; Tan, Cun-Min

    2015-05-28

    Gas-phase chemical behaviors of short-lived technetium carbonyl complexes were studied using a low temperature isothermal chromatograph (IC) coupled with a (252)Cf spontaneous fission (SF) source. Fission products recoiled from the (252)Cf SF source were thermalized in a mixed gas containing CO, and then technetium carbonyl complexes were formed from reactions between CO gas and various technetium isotopes. A gas-jet system was employed to transport the volatile carbonyl complexes from a recoil chamber to the IC. Short IC columns made of Fluorinated Ethylene Propylene (FEP) Teflon and quartz were used to obtain chemical information about the technetium carbonyl complexes. The results for the (104)Tc-(106)Tc carbonyl complexes were found to be strongly influenced by the precursors, and showed the chemical behaviors of (104)Mo-(106)Mo carbonyl complexes, respectively. However, (107)Tc and (108)Tc could represent the chemical information of the element technetium due to their high independent yields and the very short half-lives of their precursors (107)Mo and (108)Mo. An adsorption enthalpy of about ΔHads = -43 kJ mol(-1) was determined for the Tc carbonyl complexes on both the Teflon and quartz surfaces by fitting the breakthrough curves of the (107)Tc and (108)Tc carbonyl complexes with a Monte Carlo simulation program. Chemical yields of around 25% were measured for the Tc carbonyl complexes relative to the transport yields obtained with the gas-jet transport of KCl aerosol particles with Ar carrier gas. Furthermore, the influence of a small amount of O2 gas on the yields of the Mo and Tc carbonyl complexes was studied.

  1. Gas-phase spin relaxation of Xe129

    NASA Astrophysics Data System (ADS)

    Anger, B. C.; Schrank, G.; Schoeck, A.; Butler, K. A.; Solum, M. S.; Pugmire, R. J.; Saam, B.

    2008-10-01

    We have completed an extensive study of Xe129 longitudinal spin relaxation in the gas phase, involving both intrinsic and extrinsic mechanisms. The dominant intrinsic relaxation is mediated by the formation of persistent Xe2 van der Waals dimers. The dependence of this relaxation on applied magnetic field yields the relative contributions of the spin-rotation and chemical-shift-anisotropy interactions; the former dominates at magnetic fields below a few tesla. This relaxation also shows an inverse quadratic dependence on temperature T ; the maximum low-field intrinsic relaxation for pure xenon at room temperature (measured here to be 4.6h , in agreement with previous work) increases by ≈60% for T=100°C . The dominant extrinsic relaxation is mediated by collisions with the walls of the glass container. Wall relaxation was studied in silicone-coated alkali-metal-free cells, which showed long (many hours or more) and robust relaxation times, even at the low magnetic fields typical for spin-exchange optical pumping (≈3mT) . The further suppression of wall relaxation for magnetic fields above a few tesla is consistent with the interaction of Xe129 with paramagnetic spins on or inside the surface coating. At 14.1T and sufficiently low xenon density, we measured a relaxation time T1=99h , with an inferred wall-relaxation time of 174h . A prototype large storage cell ( 12cm diameter) was constructed to take advantage of the apparent increase in wall-relaxation time for cells with a smaller surface-to-volume ratio. The measured relaxation time in this cell at 3mT and 100°C was 5.75h . Such a cell (or one even larger) could be used to store many liters of hyperpolarized Xe129 produced by a flow-through polarizer and accumulator for up to three times longer than currently implemented schemes involving freezing xenon in liquid nitrogen.

  2. Infrared spectroscopy of ionized corannulene in the gas phase

    NASA Astrophysics Data System (ADS)

    Galué, Héctor Alvaro; Rice, Corey A.; Steill, Jeffrey D.; Oomens, Jos

    2011-02-01

    The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H2, and C2Hx losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp3 hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C5v geometry induced by the Jahn-Teller effect as a consequence of the degenerate 2E1 ground electronic state. As indicated by the calculations, the five equivalent Cs minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm-1 region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

  3. The Gas-Phase Deuterium Fractionation of Formaldehyde

    NASA Astrophysics Data System (ADS)

    Osamura, Yoshihiro; Roberts, Helen; Herbst, Eric

    2005-03-01

    The dominant mechanism for the deuteration of formaldehyde in the gas phase of low-temperature interstellar cloud cores occurs via reaction with the deuterating ions H2D+, HD+2, and D+3. Until now, it has been assumed that deuteration leads to an ion that, on recombination with electrons, can produce a deuterated neutral species with a statistical branching fraction. Quantum chemical calculations reported here, however, show an entirely different picture, in which the deuteration of formaldehyde leads to the molecular ion H2COD+, where the deuterium binds only on the oxygen side of the molecule. The structure is quite stable, while an alternative structure, H2DCO+, cannot be produced in a straightforward manner. Dissociative recombination of H2COD+ to reproduce a formaldehyde structure then removes the deuteration if the dissociation is direct, i.e., it occurs without change of structure. There are several possible indirect mechanisms by which dissociative recombination can lead to HDCO, however. For example, if the direct products are HCOD+H, it is possible that subsequent isomerization to HDCO can occur, although this involved process is unlikely. Another possibility is isomerization during the actual dissociation of the H2COD intermediate. Models of deuterium fractionation in which dissociative recombination is predominantly direct are presented, and it is found that the deuterium fractionation of formaldehyde to form both HDCO and D2CO can still occur via other mechanisms, although with less efficiency than previously obtained. If the dissociative recombination is half indirect, however, then we can recover the previously calculated efficiency.

  4. Ozone Cross-Section Measurement by Gas Phase Titration.

    PubMed

    Viallon, Joële; Moussay, Philippe; Flores, Edgar; Wielgosz, Robert I

    2016-11-01

    Elevated values of ground-level ozone damage health, vegetation, and building materials and are the subject of air quality regulations. Levels are monitored by networks using mostly ultraviolet (UV) absorption instruments, with traceability to standard reference photometers, relying on the UV absorption of ozone at the 253.65 nm line of mercury. We have redetermined the ozone cross-section at this wavelength based on gas phase titration (GPT) measurements. This is a well-known chemical method using the reaction of ozone (O3) with nitrogen monoxide (NO) resulting in nitrogen dioxide (NO2) and oxygen (O2). The BIPM GPT facility uses state-of-the-art flow measurement, chemiluminescence for NO concentration measurements, a cavity phase shift analyzer (CAPS) for NO2 measurements, and a UV ozone analyzer. The titration experiment is performed over the concentration range 100-500 nmol/mol, with NO and NO2 reactants/calibrants diluted down from standards with nominal mole fractions of 50 μmol/mol. Accurate measurements of NO, NO2, and O3 mole fractions allow the calculation of ozone absorption cross section values at 253.65 nm, and we report a value of 11.24 × 10(-18) cm(2) molecule(-1) with a relative expanded uncertainty of 1.8% (coverage factor k = 2) based on nitrogen monoxide titration values and a value of 11.22 × 10(-18) cm(2) molecule(-1) with a relative expanded uncertainty of 1.4% (coverage factor k = 2) based on nitrogen dioxide titration values. The excellent agreement between these values and recently published absorption cross-section measurements directly on pure ozone provide strong evidence for revising the conventionally accepted value of ozone cross section at 253.65 nm.

  5. Proton irradiation of DNA nucleosides in the gas phase.

    PubMed

    Poully, Jean-Christophe; Miles, Jordan; De Camillis, Simone; Cassimi, Amine; Greenwood, Jason B

    2015-03-21

    The four DNA nucleosides guanosine, adenosine, cytidine and thymidine have been produced in the gas phase by a laser thermal desorption source, and irradiated by a beam of protons with 5 keV kinetic energy. The molecular ions as well as energetic neutrals formed have been analyzed by mass spectrometry in order to shed light on the ionization and fragmentation processes triggered by proton collision. A range of 8-20 eV has been estimated for the binding energy of the electron captured by the proton. Glycosidic bond cleavage between the base and sugar has been observed with a high probability for all nucleosides, resulting in predominantly intact base ions for guanosine, adenosine, and cytidine but not for thymidine where intact sugar ions are dominant. This behavior is influenced by the ionization energies of the nucleobases (G < A < C < T), which seems to determine the localization of the charge following the initial ionization. This charge transfer process can also be inferred from the production of protonated base ions, which have a similar dependence on the base ionization potential, although the base proton affinity might also play a role. Other dissociation pathways have also been identified, including further fragmentation of the base and sugar moieties for thymidine and guanosine, respectively, and partial breakup of the sugar ring without glycosidic bond cleavage mainly for adenosine and cytidine. These results show that charge localization following ionization by proton irradiation is important in determining dissociation channels of isolated nucleosides, which could in turn influence direct radiation damage in DNA.

  6. Uridine Nucleoside Thiation: Gas-Phase Structures and Energetics

    NASA Astrophysics Data System (ADS)

    Hamlow, Lucas; Lee, Justin; Rodgers, M. T.; Berden, Giel; Oomens, Jos

    2016-06-01

    The naturally occurring thiated uridine nucleosides, 4-thiouridine (s4Urd) and 2-thiouridine (s2Urd), play important roles in the function and analysis of a variety of RNAs. 2-Thiouridine and its C5 modified analogues are commonly found in tRNAs and are believed to play an important role in codon recognition possibly due to their different structure, which has been shown by NMR to be predominantly C3'-endo. 2-Thiouridine may also play an important role in facilitating nonenzymatic RNA replication and transcription. 4-Thiouridine is a commonly used photoactivatable crosslinker that is often used to study RNA-RNA and RNA-protein cross-linking behavior. Differences in the base pairing between uracil and 4-thiouracil with adenine and guanine are an important factor in their role as a cross linker. The photoactivity of s4Urd may also aid in preventing near-UV lethality in cells. An understanding of their intrinsic structure in the gas-phase may help further elucidate the roles these modified nucleosides play in the regulation of RNAs. In this work, infrared multiple photon dissociation (IRMPD) action spectra of the protonated forms of s2Urd and s4Urd were collected in the IR fingerprint region. Structural information is determined by comparison with theoretical linear IR spectra generated from density functional theory calculations using molecular modeling to generate low-energy candidate structures. Present results are compared with analogous results for the protonated forms of uridine and 2'-deoxyuridine as well as solution phase NMR data and crystal structures.

  7. Preparation, Characterization and in vivo Evaluation of Simple Monolithic Ethylcellulose-coated Pellets Containing Topiramate with Biphasic Release Characteristics.

    PubMed

    Gong, Wei; Wang, Yuli; Shao, Shuai; Xie, Si; Shan, Li; Yang, Meiyan; Gao, Chunsheng; Zhong, Wu

    2016-01-01

    In our previous study, polyvinylpyrrolidone (PVP) was used both as a binder and a pore-former to prepare ethylcellulose (EC)-coated pellets to deliver topiramate (TPM) for a controlled release profile. The objective of this work was to further optimize the formulation and evaluate the in vivo profiles of TPM sustained-release pellets. Similar to the previous formulation with no binder, the in vitro drug release of TPM sustained-release pellets with 50% PVP binder in drug layer was sensitive to pore-former PVP level ranged from 27.0% to 29.0%. The higher the level of PVP was, the quicker release rate in vitro was. Moreover, when the proportion of poreformer PVP decreased, the Cmax decreased, and the tmax and mean residence time of TPM coated pellets were both prolonged. The in vitro release profile of optimal formulation showed biphasic release characteristics similar to reference formulation Trokendi XR(®), i.e., involving immediate release of TPM in initial release stage followed by a sustained release up to 24 h. Moreover, the impact of the pH of release medium on the drug release rate of TPM sustained-release pellets was not significant. The release mechanism of TPM from the sustained-release pellets might be the interaction of diffusion (coating-film) and corrosion (drug layer). The in vivo pharmacokinetics results showed the TPM sustained-release pellets had the similar in vivo pattern compared with Trokendi XR(®). These studies provide valuable basis for further development of TPM sustained-release pellets.

  8. Effect of carboxymethylation on physicochemical and release characteristics of Indian Palo starch.

    PubMed

    Das, D; Jha, S; Kumar, K Jayaram

    2015-01-01

    Limited application of native starch has created the interest in the modification of starch to extend its asset for pharmaceutical application. An effort has been made to study the influence of carboxymethylation on morphological, physicochemical and drug release properties of wild Indian Palo (Curcuma angustifolia) starch. Carboxymethyl starches of different degree of substitution (0.046-0.256) were prepared using varying amount of monochloroacetic acid. The characteristic peaks at around 1600cm(-1) confirmed the carboxymethylation of starch. Morphological studies showed that porous structure formed on the surface of the starch granules and degree of deformity was found to be increased with the increment in the degree of substitution. Amylose content was decreased with the increase in degree of substitution. The TGA data showed that the carboxymethyl starches were thermally stable. Swelling and solubility power was found to be improved with the increase in the temperature. Micromeritic properties of carboxymethyl starches proved its usefulness as excipients in tablet manufacturing. Release profile of paracetamol was found to be decreased with the increase in the degree of substitution, and this proves the suitability of carboxymethyl Indian Palo starch in sustained-release tablets.

  9. Effect of carboxymethylation on physicochemical, micromeritics and release characteristics of Kyllinga nemoralis starch.

    PubMed

    Paramakrishnan, N; Jha, S; Kumar, K Jayaram

    2016-11-01

    Lesser usages of native starch has attracted attention in the modification of starch to incorporate its benefits for pharmaceutical application. A work has been carried out to study the influence of carboxymethylation on the morphological, physico-chemical, powder, spectroscopical and drug discharge characteristics of native starch. Various amount of monochloroacetic acid was used to study the influence of degree of substitution (DS) on the diverse characteristics of modified starch. Amylose content was found to be reduced with the increase in degree of substitution. An enhanced degree of structure deformation was observed with the increment in the DS by the help of scanning electron micrographs. The FT-IR spectra established the polysaccharide nature and the carboxymethylation of the chemically modified starch molecules through the new bands at 1602cm(-1), and 1418.69cm(-1). The stability of carboxymethyl starches pertaining to the temperature has been revealed by thermogravimetric analysis. Micromeritics of carboxymethylated starches shows their effectiveness as excipients in tablet formulation. The delayed % release of the drug, with the rise in degree of substitution from the tablets prepared marks that the carboxymethyl derivatives of Kyllinga nemoralis rhizomes starch may be used as a suitable source of excipient for sustained release formulations.

  10. Characteristic odor of Osmoderma eremita identified as a male-released pheromone.

    PubMed

    Larsson, Mattias C; Hedin, Jonas; Svensson, Glenn P; Tolasch, Till; Francke, Wittko

    2003-03-01

    Osmoderma eremita (Scopoli) is an endangered scarab beetle living in hollow trees. It has mainly been known for its characteristic odor, typically described as a fruity, peachlike or plumlike aroma. The odor emanating from a single beetle can sometimes be perceived from a distance of several meters. In this paper, we show that the characteristic odor from O. eremita is caused by the compound (R)-(+)-gamma-decalactone, released in large quantities mainly or exclusively by male beetles. Antennae from male and female beetles responded in a similar way to (R)-(+)-gamma-decalactone in electroantennographic recordings. Field trapping experiments showed that (R)-(+)-gamma-decalactone is a pheromone attracting female beetles. Lactones similar to (R)-(+)-gamma-decalactone are frequently used as female-released sex pheromones by phytophagous scarabs. This is, however, the first evidence of a lactone used as a male-produced pheromone in scarab beetles. We propose that the strong signal from males is a sexually selected trait used to compete for females and matings. The signal could work within trees but also act as a guide to tree hollows, which are an essential resource for O. eremita. Males may, thus, attract females dispersing from their natal tree by advertising a suitable habitat. This signal could also be exploited by other males searching for tree hollows or for females, which would explain the catch of several males in our traps.

  11. A new method for measurement of gas-phase ammonia and amines in air

    NASA Astrophysics Data System (ADS)

    Dawson, M. L.; Gomez, A.; Arquero, K. D.; Perraud, V. M.; Finlayson-Pitts, B. J.

    2013-12-01

    Accurately predicting particle formation and growth from gas phase precursors is an essential component of modeling the impact of particulate matter on human health, visibility and climate. While the reactions of ammonia with nitric and sulfuric acids to form particulate nitrate and sulfate particles is well known, it has been recently recognized that gas-phase amines, even at low ppb levels, significantly enhance particle formation from common atmospheric acids. As a result, accurate data on the sources, sinks and typical background concentrations of gas-phase amines, are crucial to predicting new particle formation in the atmosphere. However, gas-phase amines are notoriously difficult to measure, as they have a tendency to stick to surfaces, including sampling lines and inlets. In addition, background amine concentrations in the atmosphere are typically a few ppb or lower, requiring low detection limits for ambient sampling techniques. Here we report the development of a simple, reliable method for detection of gas-phase amines at atmospherically relevant concentrations using collection on a cation exchange sorbent followed by in-line extraction and ion chromatography. Gas-phase standards of several amines and ammonia are used to characterize the technique and results from ambient samples in an agricultural area are presented. The application of this technique to field measurements as well as to laboratory measurements of new particle formation from gas-phase ammonia and amines are discussed.

  12. Structural Dynamics of Native-Like Ions in the Gas Phase: Results from Tandem Ion Mobility of Cytochrome c.

    PubMed

    Allen, Samuel J; Eaton, Rachel M; Bush, Matthew F

    2017-07-18

    Ion mobility (IM) is a gas-phase separation technique that is used to determine the collision cross sections of native-like ions of proteins and protein complexes, which are in turn used as restraints for modeling the structures of those analytes in solution. Here, we evaluate the stability of native-like ions using tandem IM experiments implemented using structures for lossless ion manipulations (SLIM). In this implementation of tandem IM, ions undergo a first dimension of IM up to a switch that is used to selectively transmit ions of a desired mobility. Selected ions are accumulated in a trap and then released after a delay to initiate the second dimension of IM. For delays ranging from 16 to 33 231 ms, the collision cross sections of native-like, 7+ cytochrome c ions increase monotonically from 15.1 to 17.1 nm(2). The largest products formed in these experiments at near-ambient temperature are still far smaller than those formed in energy-dependent experiments (∼21 nm(2)). However, the collision cross section increases by ∼2% between delay times of 16 and 211 ms, which may have implications for other IM experiments on these time scales. Finally, two subpopulations from the full population were each mobility selected and analyzed as a function of delay time, showing that the three populations can be differentiated for at least 1 s. Together, these results suggest that elements of native-like structure can have long lifetimes at near-ambient temperature in the gas phase but that gas-phase dynamics should be considered when interpreting results from IM.

  13. Peptide bond formation via glycine condensation in the gas phase.

    PubMed

    Van Dornshuld, Eric; Vergenz, Robert A; Tschumper, Gregory S

    2014-07-24

    Four unique gas phase mechanisms for peptide bond formation between two glycine molecules have been mapped out with quantum mechanical electronic structure methods. Both concerted and stepwise mechanisms, each leading to a cis and trans glycylglycine product (four mechanisms total), were examined with the B3LYP and MP2 methods and Gaussian atomic orbital basis sets as large as aug-cc-pVTZ. Electronic energies of the stationary points along the reaction pathways were also computed with explicitly correlated MP2-F12 and CCSD(T)-F12 methods. The CCSD(T)-F12 computations indicate that the electronic barriers to peptide bond formation are similar for all four mechanisms (ca. 32-39 kcal mol(-1) relative to two isolated glycine fragments). The smallest barrier (32 kcal mol(-1)) is associated with the lone transition state for the concerted mechanism leading to the formation of a trans peptide bond, whereas the largest barrier (39 kcal mol(-1)) was encountered along the concerted pathway leading to the cis configuration of the glycylglycine dipeptide. Two significant barriers are encountered for the stepwise mechanisms. For both the cis and trans pathways, the early electronic barrier is 36 kcal mol(-1) and the subsequent barrier is approximately 1 kcal mol(-1) lower. A host of intermediates and transition states lie between these two barriers, but they all have very small relative electronic energies (ca. ± 4 kcal mol(-1)). The isolated cis products (glycylglycine + H2O) are virtually isoenergetic with the isolated reactants (within -1 kcal mol(-1)), whereas the trans products are about 5 kcal mol(-1) lower in energy. In both products, however, the water can hydrogen bond to the dipeptide and lower the energy by roughly 5-9 kcal mol(-1). This study indicates that the concerted process leading to a trans configuration about the peptide bond is marginally favored both thermodynamically (exothermic by ca. 5 kcal mol(-1)) and kinetically (barrier height ≈ 32 kcal mol(-1

  14. Detection of Gas-Phase Ammonia Using Photothermal Interferometry.

    NASA Astrophysics Data System (ADS)

    Owens, Melody Avery

    1995-01-01

    Ammonia in the atmosphere plays an important chemical role in diverse ecological and physical systems. It is challenging to measure because it adheres to many commonly used sampling materials, is soluble in water, and forms particles. A new instrument has been built to detect gas -phase ammonia in ambient air by photothermal interferometry. Ammonia molecules in sampled air are excited to upper vibrational rotational states of the nu_2 band of ammonia by absorption of 9.22 mu m light from the 9R30 line of a carbon dioxide laser. Excited ammonia molecules transfer this energy as heat to the air by collisions. The temperature and consequent refractive index change is measured as a phase shift in one arm of a sensitive homodyne interferometer. The CO_2 laser output is modulated at 1.2 kHz, and the AC signal from the interferometer is measured with a lock -in amplifier. The +/-2sigma detection limit of the interferometer at this frequency is 1.2 times 10^{ -7} radians, only a factor of four above the quantum noise limit. The ammonia detector is calibrated by dynamic dilution of two permeation tube outputs and by standard addition. Permeation rates are verified by NH _3 conversion to nitric oxide on hot platinum foil followed by chemiluminescent NO detection, and are monitored by mass loss history. The sample cell, inlet and calibration plumbing is glass to minimize NH _3 sample loss by wall adsorption. Sample flow is 2 l/min, with residence time less than one second. The detector is zeroed by sampling through tubing filled with H_3PO_4-coated Teflon. A Stark signal shift of 7.9 mV was measured for 507 ppb of NH_3 with 925 V/mm of applied field density as an alternative zeroing method. The linear dynamic range of the detector is broad, (greater than 5 orders of magnitude), and the detector is sensitive, with a 31 ppt 4sigma lower detection limit measured in 100 s. Signal gain is insensitive to water vapor and CO_2. The instrument response is fast, with a 1 s e

  15. Electron attachment to ? and ? in the gas phase

    NASA Astrophysics Data System (ADS)

    Smith, David; Spanel, Patrik

    1996-11-01

    The fullerene molecule 0953-4075/29/21/030/img3 is known to attach several electrons in the solid phase, but only recently has it been recognized that it can also attach electrons in the gas phase. The first electron - molecular beam results showed that 0953-4075/29/21/030/img3 and 0953-4075/29/21/030/img5 molecules non-dissociatively attached a single electron over the unusually wide electron energy range from near thermal to about 10 eV, but these studies were not able to provide either the magnitude of the cross sections or describe the low-energy attachment behaviour. But using our flowing afterglow - Langmuir probe (FALP) apparatus we have been able to determine the absolute attachment rate coefficients for both 0953-4075/29/21/030/img3 and 0953-4075/29/21/030/img5 over the electron temperature range 300 - 4500 K. These FALP experiments have shown that attachment to 0953-4075/29/21/030/img3 at low electron energies (<1 eV) proceeds predominantly by p-wave electron capture, and that a centrifugal barrier of 0.26 eV is evident which was corroborated by subsequent theory. A similar situation is observed for attachment to 0953-4075/29/21/030/img5 except that for this fullerene molecule there is evidence that at very low electron energies (< 0.05 eV) inefficient s-wave capture may also occur. These FALP data further indicate that at energies above about 0.3 eV extraordinarily efficient electron attachment occurs to both 0953-4075/29/21/030/img3 and 0953-4075/29/21/030/img5, and when the mean thermal cross sections derived from these FALP data are used to normalize the crossed electron - molecular beam data at the common low energies accessible in both experiments, it is clear that electron attachment to these fullerene molecules is very efficient over a wide electron energy range from about 0.3 - 10 eV above which electron thermionic emission occurs from the hot 0953-4075/29/21/030/img12 and 0953-4075/29/21/030/img13 nascent negative ions.

  16. Hydrophobic protein-ligand interactions preserved in the gas phase.

    PubMed

    Liu, Lan; Bagal, Dhanashri; Kitova, Elena N; Schnier, Paul D; Klassen, John S

    2009-11-11

    the cavity. The loss of ligand from the closed structure would require both the cleavage of the H-bonds and the nonpolar contacts. Taken together, these results suggest that the aliphatic chain of the FA remains bound within the hydrophobic cavity in the gas phase (Lg + FA)(7-) ions. Furthermore, the barrier to dissociation of the (Lg + FA)(f)(7-) ions reflects predominantly the cleavage of the nonpolar intermolecular interactions, while for the (Lg + FA)(s)(7-) ions the FA is stabilized by both nonpolar interactions and H-bonds.

  17. Calcium-containing diatomic dications in the gas phase.

    PubMed

    Alves, Tiago Vinicius; Hermoso, Willian; Franzreb, Klaus; Ornellas, Fernando R

    2011-11-07

    Sputtering (ion surface bombardment) of various calcium-containing powder samples with an energetic (17 keV), high-current (16)O(-) beam has produced the diatomic dications of CaSi(2+), CaP(2+), CaF(2+), CaH(2+), CaCl(2+), CaBr(2+) and CaI(2+). These molecular gas-phase species have been identified in positive ion mass spectra at half-integer m/z values; their ion flight times through a magnetic-sector mass spectrometer were roughly 10(-5) s. Most of them appear to be novel molecular ions; the stability of the latter four (CaH(2+), CaCl(2+), CaBr(2+) and CaI(2+)) had been demonstrated in previous theoretical studies, whereas only CaF(2+) and CaBr(2+) had been observed before. Here we combine the results of our experimental search with a detailed theoretical study of the remaining three systems CaSi(2+), CaP(2+) and CaF(2+). All electronic states correlating with the first dissociation channel are characterized using high level ab initio electronic structure calculations. In their ground states, we find CaSi(2+) to be a long-lived metastable molecule, whereas CaF(2+) and CaP(2+) are thermodynamically stable, with respective equilibrium internuclear distances of 6.253, 4.740, and 5.731 a(0). CaSi(2+) has a well depth of 7116 (0.88) cm(-1) (eV) and a dissociation asymptote 7956 (0.99) cm(-1) (eV) below the ground state minimum. The dissociation energy of CaF(2+) is estimated to be 3404 (0.42) cm(-1) (eV), whereas for CaP(2+) we found 2547 (0.32) cm(-1) (eV), and a barrier height of 8118 (1.01) cm(-1) (eV). Their adiabatic double ionisation energies are 22.87, 16.91, and 17.32 eV, respectively, for the F, Si, and P containing dications. This journal is © the Owner Societies 2011

  18. Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

    NASA Astrophysics Data System (ADS)

    Ali, A. N.; Son, S. F.; Asay, B. W.; Sander, R. K.

    2005-03-01

    Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6mm±0.4mm exists below which ignition by CO2 laser is not possible at the tested irradiances of 29W /cm2 and 38W/cm2 for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

  19. Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

    SciTech Connect

    Ali, A.N.; Son, S.F.; Asay, B.W.; Sander, R.K.

    2005-03-15

    Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6 mm{+-}0.4 mm exists below which ignition by CO{sub 2} laser is not possible at the tested irradiances of 29 W/cm{sup 2} and 38 W/cm{sup 2} for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

  20. Gas-Phase Synthesis and Characterization of CH4-Loaded Hydroquinone Clathrates

    SciTech Connect

    Lee, J.; Lee, Y; Takeya, S; Kawamura, T; Yamamoto, Y; Lee, Y; Yoon, J

    2010-01-01

    A CH{sub 4}-loaded hydroquinone (HQ) clathrate was synthesized via a gas-phase reaction using the {alpha}-form of crystalline HQ and CH{sub 4} gas at 12 MPa and room temperature. Solid-state {sup 13}C cross-polarization/magic angle spinning (CP/MAS) NMR and Raman spectroscopic measurements confirm the incorporation of CH{sub 4} molecules into the cages of the HQ clathrate framework. The chemical analysis indicates that about 69% of the cages are filled by CH{sub 4} molecules, that is, 0.69 CH{sub 4} per three HQ molecules. Rietveld refinement using synchrotron X-ray powder diffraction (XRD) data shows that the CH{sub 4}-loaded HQ clathrate adopts the {beta}-form of HQ clathrate in a hexagonal space group R3 with lattice parameters of a = 16.6191 {angstrom} and c = 5.5038 {angstrom}. Time-resolved synchrotron XRD and quadrupole mass spectroscopic measurements show that the CH{sub 4}-loaded HQ clathrate is stable up to 368 K and gradually transforms to the {alpha}-form by releasing the confined CH{sub 4} gases between 368-378 K. Using solid-state {sup 13}C CP/MAS NMR, the reaction kinetics between the {alpha}-form HQ and CH{sub 4} gas is qualitatively described in terms of the particle size of the crystalline HQ.

  1. Gas-phase synthesis and characterization of CH4-loaded hydroquinone clathrates.

    PubMed

    Lee, Jong-Won; Lee, Yongjae; Takeya, Satoshi; Kawamura, Taro; Yamamoto, Yoshitaka; Lee, Yun-Je; Yoon, Ji-Ho

    2010-03-11

    A CH(4)-loaded hydroquinone (HQ) clathrate was synthesized via a gas-phase reaction using the alpha-form of crystalline HQ and CH(4) gas at 12 MPa and room temperature. Solid-state (13)C cross-polarization/magic angle spinning (CP/MAS) NMR and Raman spectroscopic measurements confirm the incorporation of CH(4) molecules into the cages of the HQ clathrate framework. The chemical analysis indicates that about 69% of the cages are filled by CH(4) molecules, that is, 0.69 CH(4) per three HQ molecules. Rietveld refinement using synchrotron X-ray powder diffraction (XRD) data shows that the CH(4)-loaded HQ clathrate adopts the beta-form of HQ clathrate in a hexagonal space group R3 with lattice parameters of a = 16.6191 A and c = 5.5038 A. Time-resolved synchrotron XRD and quadrupole mass spectroscopic measurements show that the CH(4)-loaded HQ clathrate is stable up to 368 K and gradually transforms to the alpha-form by releasing the confined CH(4) gases between 368-378 K. Using solid-state (13)C CP/MAS NMR, the reaction kinetics between the alpha-form HQ and CH(4) gas is qualitatively described in terms of the particle size of the crystalline HQ.

  2. Removal of pyridine from liquid and gas phase by copper forms of natural and synthetic zeolites.

    PubMed

    Reháková, Mária; Fortunová, Lubica; Bastl, Zdeněk; Nagyová, Stanislava; Dolinská, Silvia; Jorík, Vladimír; Jóna, Eugen

    2011-02-15

    Zeoadsorbents on the basis of copper forms of synthetic zeolite ZSM5 and natural zeolite of the clinoptilolite type (CT) have been studied taking into account their environmental application in removing harmful pyridine (py) from liquid and gas phase. Sorption of pyridine by copper forms of zeolites (Cu-ZSM5 and Cu-CT) has been studied by CHN, X-ray photoelectron spectroscopy, X-ray powder diffractometry, FTIR spectroscopy, thermal analysis (TG, DTA and DTG) and analysis of the surface areas and the pore volumes by low-temperature adsorption of nitrogen. The results of thermal analyses of Cu-ZSM5, Cu-(py)(x)ZSM5, Cu-CT and Cu-(py)(x)CT zeolitic products with different composition (x depends on the experimental conditions of sorption of pyridine) clearly confirmed their different thermal properties as well as the sorption of pyridine. In the zeolitic pyridine containing samples the main part of the pyridine release process occurs at considerably higher temperatures than is the boiling point of pyridine, which proves strong bond and irreversibility of py-zeolite interaction. FTIR spectra of Cu-(py)(x)zeolite samples showed well resolved bands of pyridine. The results of thermal analysis and FTIR spectroscopy are in a good agreement with the results of other used methods.

  3. Interference-free coherence dynamics of gas-phase molecules using spectral focusing.

    PubMed

    Wrzesinski, Paul J; Roy, Sukesh; Gord, James R

    2012-10-08

    Spectral focusing using broadband femtosecond pulses to achieve highly selective measurements has been employed for numerous applications in spectroscopy and microspectroscopy. In this work we highlight the use of spectral focusing for selective excitation and detection of gas-phase species. Furthermore, we demonstrate that spectral focusing, coupled with time-resolved measurements based upon probe delay, allows the observation of interference-free coherence dynamics of multiple molecules and gas-phase temperature making this technique ideal for gas-phase measurements of reacting flows and combustion processes.

  4. Mm/submm Study of Gas-Phase Photoproducts from Methanol Interstellar Ice Analogues

    NASA Astrophysics Data System (ADS)

    Mesko, AJ; Smith, Houston Hartwell; Milam, Stefanie N.; Widicus Weaver, Susanna L.

    2016-06-01

    Icy grain reactions have gained quite the popularity in the astrochemistry community to explain the formation of complex organic molecules. Through temperature programmed desorption and photolysis experiments we use rotational spectroscopy to measure the gas-phase products of icy grain reactions. Previous results include testing detection limits of the system by temperature programmed desorption of methanol and water ices, photochemistry of gas-phase methanol, and detection of photodesorbed water from a pure water ice surface. Current work that will be discussed focuses on the detection of gas-phase CO and other photoproducts from an ice surface.

  5. Design of the strongest organic Brønsted acids in gas phase

    NASA Astrophysics Data System (ADS)

    Valadbeigi, Younes

    2017-08-01

    A new type of organic Brønsted acids is proposed exhibiting very high acidity in gas phase. The calculated gas phase enthalpies (ΔHacid) of deprotonation were 220-240 kcal/mol for the proposed acids with -CN substituents indicating that they can rival the inorganic carborane acid derivatives in gas phase. The hyperacidity of these compounds rises from the extra stability of the corresponding conjugate bases due to formation of a hydrogen bonding network and an aromatic five-membered ring.

  6. The gas-phase thermal chemistry of tetralin and related model systems

    SciTech Connect

    Malandra, James

    1993-05-01

    The thesis is divided into 5 papers: gas-phase thermal decomposition of tetralin; flash vacuum pyrolysis of 3-benzocycloheptenone and 1,3, 4,5-tetrahydro-2-benzothiepin-2,2-dioxide (model systems for gas-phase pyrolysis of tetralin); high-temperature gas-phase reactions of o-allylbenzyl radicals generated by flash vacuum pyrolysis of is(o-allylbenzyl) oxalate; flash vacuum pyrolysis of 1,4-diphenylbutane; and flash vacuum pyrolysis of o-allyltoluene, o-(3-butenyl)toluene and o-(pentenyl)toluene were also used.

  7. Thermal degradation events as health hazards: Particle vs gas phase effects, mechanistic studies with particles

    NASA Astrophysics Data System (ADS)

    Oberdörster, G.; Ferin, J.; Finkelstein, J.; Soderholm, S.

    Exposure to thermal degradation products arising from fire or smoke could be a major concern for manned space missions. Severe acute lung damage has been reported in people after accidental exposure to fumes from plastic materials, and animal studies revealed the extremely high toxicity of freshly generated fumes whereas a decrease in toxicity of aged fumes has been found. This and the fact that toxicity of the freshly generated fumes can be prevented with filters raises the question whether the toxicity may be due to the particulate rather than the gas phase components of the thermodegradation products. Indeed, results from recent studies implicate ultrafine particles (particle diameter in the nm range) as potential severe pulmonary toxicants. We have conducted a number of in vivo (inhalation and instillation studies in rats) and in vitro studies to test the hypothesis that ultrafine particles possess an increased potential to injure the lung compared to larger-sized particles. We used as surrogate particles ultrafine TiO 2 particles (12 and 20 nm diameter). Results in exposed rats showed that the ultrafine TiO 2 particles not only induce a greater acute inflammatory reaction in the lung than larger-sized TiO 2 particles, but can also lead to persistent chronic effects, as indicated by an adverse effect on alveolar macrophage mediated clearance function of particles. Release of mediators from alveolar macrophages during phagocytosis of the ultrafine particles and an increased access of the ultrafine particles to the pulmonary interstitium are likely factors contributing to their pulmonary toxicity. In vitro studies with lung cells (alveolar macrophages) showed, in addition, that ultrafine TiO 2 particles have a greater potential to induce cytokines than larger-sized particles. We conclude from our present studies that ultrafine particles have a significant potential to injure the lung and that their occurrence in thermal degradation events can play a major role in

  8. Secondary organic aerosol formation from low-NO(x) photooxidation of dodecane: evolution of multigeneration gas-phase chemistry and aerosol composition.

    PubMed

    Yee, Lindsay D; Craven, Jill S; Loza, Christine L; Schilling, Katherine A; Ng, Nga Lee; Canagaratna, Manjula R; Ziemann, Paul J; Flagan, Richard C; Seinfeld, John H

    2012-06-21

    The extended photooxidation of and secondary organic aerosol (SOA) formation from dodecane (C(12)H(26)) under low-NO(x) conditions, such that RO(2) + HO(2) chemistry dominates the fate of the peroxy radicals, is studied in the Caltech Environmental Chamber based on simultaneous gas and particle-phase measurements. A mechanism simulation indicates that greater than 67% of the initial carbon ends up as fourth and higher generation products after 10 h of reaction, and simulated trends for seven species are supported by gas-phase measurements. A characteristic set of hydroperoxide gas-phase products are formed under these low-NO(x) conditions. Production of semivolatile hydroperoxide species within three generations of chemistry is consistent with observed initial aerosol growth. Continued gas-phase oxidation of these semivolatile species produces multifunctional low volatility compounds. This study elucidates the complex evolution of the gas-phase photooxidation chemistry and subsequent SOA formation through a novel approach comparing molecular level information from a chemical ionization mass spectrometer (CIMS) and high m/z ion fragments from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Combination of these techniques reveals that particle-phase chemistry leading to peroxyhemiacetal formation is the likely mechanism by which these species are incorporated in the particle phase. The current findings are relevant toward understanding atmospheric SOA formation and aging from the "unresolved complex mixture," comprising, in part, long-chain alkanes.

  9. Photophysics of sunscreen molecules in the gas phase: a stepwise approach towards understanding and developing next-generation sunscreens

    NASA Astrophysics Data System (ADS)

    Rodrigues, Natércia D. N.; Staniforth, Michael; Stavros, Vasilios G.

    2016-11-01

    The relationship between exposure to ultraviolet (UV) radiation and skin cancer urges the need for extra photoprotection, which is presently provided by widespread commercially available sunscreen lotions. Apart from having a large absorption cross section in the UVA and UVB regions of the electromagnetic spectrum, the chemical absorbers in these photoprotective products should also be able to dissipate the excess energy in a safe way, i.e. without releasing photoproducts or inducing any further, harmful, photochemistry. While sunscreens are tested for both their photoprotective capability and dermatological compatibility, phenomena occurring at the molecular level upon absorption of UV radiation are largely overlooked. To date, there is only a limited amount of information regarding the photochemistry and photophysics of these sunscreen molecules. However, a thorough understanding of the intrinsic mechanisms by which popular sunscreen molecular constituents dissipate excess energy has the potential to aid in the design of more efficient, safer sunscreens. In this review, we explore the potential of using gas-phase frequency- and time-resolved spectroscopies in an effort to better understand the photoinduced excited-state dynamics, or photodynamics, of sunscreen molecules. Complementary computational studies are also briefly discussed. Finally, the future outlook of expanding these gas-phase studies into the solution phase is considered.

  10. Photophysics of sunscreen molecules in the gas phase: a stepwise approach towards understanding and developing next-generation sunscreens

    PubMed Central

    Rodrigues, Natércia D. N.; Staniforth, Michael

    2016-01-01

    The relationship between exposure to ultraviolet (UV) radiation and skin cancer urges the need for extra photoprotection, which is presently provided by widespread commercially available sunscreen lotions. Apart from having a large absorption cross section in the UVA and UVB regions of the electromagnetic spectrum, the chemical absorbers in these photoprotective products should also be able to dissipate the excess energy in a safe way, i.e. without releasing photoproducts or inducing any further, harmful, photochemistry. While sunscreens are tested for both their photoprotective capability and dermatological compatibility, phenomena occurring at the molecular level upon absorption of UV radiation are largely overlooked. To date, there is only a limited amount of information regarding the photochemistry and photophysics of these sunscreen molecules. However, a thorough understanding of the intrinsic mechanisms by which popular sunscreen molecular constituents dissipate excess energy has the potential to aid in the design of more efficient, safer sunscreens. In this review, we explore the potential of using gas-phase frequency- and time-resolved spectroscopies in an effort to better understand the photoinduced excited-state dynamics, or photodynamics, of sunscreen molecules. Complementary computational studies are also briefly discussed. Finally, the future outlook of expanding these gas-phase studies into the solution phase is considered. PMID:27956888

  11. Characteristics and release profiles of MPEG-PCL-MPEG microspheres containing immunoglobulin G.

    PubMed

    Erdemli, Özge; Usanmaz, Ali; Keskin, Dilek; Tezcaner, Ayşen

    2014-05-01

    Polyester-polyether type block copolymers have attracted attention in the area of drug delivery systems with their capability in providing a broad range of amphiphilic characteristics. The aim of the present work was to prepare and characterize immunoglobulin G (IgG) loaded methoxy poly(ethylene glycol)-poly(ɛ-caprolactone)-methoxy poly(ethylene glycol) (MPEG-PCL-MPEG) microspheres as potential carrier for therapeutic monoclonal antibodies used in clinics. MPEG-PCL-MPEG triblock copolymer was synthesized by ring-opening polymerization of ɛ-caprolactone initiated by MPEG and then characterized. Microspheres were prepared by double emulsion-solvent evaporation method and their properties were compared with those of PCL microspheres. Microspheres had spherical shape with a mean particle size around 6 μm. MPEG-PCL-MPEG microspheres had higher encapsulation efficiency than PCL microspheres. After 90 days of release, 30±2% and 57±3% of the bioactivity of IgG released from non-irradiated PCL and MPEG-PCL-MPEG microspheres were protected, respectively. Presence of MPEG in microspheres provided more controlled IgG release rate and protected IgG from denaturation during γ-irradiation (20±3% and 49±2% for PCL and MPEG-PCL-MPEG microspheres, respectively). In vitro cytotoxicity tests revealed that both MPEG-PCL-MPEG and PCL microspheres had no toxic effect on cells. This study showed that MPEG-PCL-MPEG microspheres are promising delivery systems for therapeutic monoclonal antibodies. Copyright © 2014 Elsevier B.V. All rights reserved.

  12. Spectroscopy of PAH species in the gas phase

    NASA Astrophysics Data System (ADS)

    Robinson, Michael S.; Beegle, Luther W.; Wdowiak, Thomas J.

    1995-02-01

    At elevated temperatures, the structured CH stretch absorption occurring at room temperature of polycyclic aromatic hydrocarbon (PAH) molecules encapsulated in KBr coalesces to a single peak whose wavelength is a very close match for that of the observed 3.3 μm unidentified infrared band (UIR) emission feature (Flickinger and Wdowiak. Astrophys. J.362, L71-L74. 1990). The temperature of approximately 800 K is significant because a PAH molecule in the interstellar radiation field, upon absorption of an ultraviolet photon, is expected to be excited to an energy equivalent to temperatures of this order (Sellgren, Astrophys. J.277, 623 1984). Our previous study of PAH molecules in the vapor phase at 600-800 K showed that the C-H stretch PAH feature near 3.3 μm is at a shorter wavelength than in the condensed state (Flickinger et al., Astrophys. J.380, L43-L46, 1991). Recent work by Joblin et al. ( 1st Symp. on the Infrared Cirrus and Diffuse Interstellar Clouds. 1994) in a short path length diamond cell indicates the gas phase wavelength of the 3.3 μm region C-H stretch feature of naphthalene is directly proportional to temperature over a large temperature range. Laser-excited IR fluorescence studies have also suggested that the wavelength is sensitive to laser photon energy in a direct relationship (Williams and Leone, The Diffuse Interstellar Bands Conf., 1994). Comprehensive studies of PAHs thermally excited up to the decomposition temperature are therefore important to carry out. We have utilized a long-path-length optical heat pipe to confirm that the wavelength of the peak of the C-H stretch band of naphthalene vapor obeys a direct relationship with temperature as reported by Joblin, and to demonstrate that this feature undergoes a strengthening with respect to the longer wavelength band due to an out-of-plane deformation (782 cm -1) as temperature increases. The shift from 3067.6 to 3063.7 cm -1 over the temperature range of 316-996 K seems to be linear

  13. Gas-phase water-mediated equilibrium between methylglyoxal and its geminal diol

    PubMed Central

    Axson, Jessica L.; Takahashi, Kaito; De Haan, David O.; Vaida, Veronica

    2010-01-01

    In aqueous solution, aldehydes, and to a lesser extent ketones, hydrate to form geminal diols. We investigate the hydration of methylglyoxal (MG) in the gas phase, a process not previously considered to occur in water-restricted environments. In this study, we spectroscopically identified methylglyoxal diol (MGD) and obtained the gas-phase partial pressures of MG and MGD. These results, in conjunction with the relative humidity, were used to obtain the equilibrium constant, KP, for the water-mediated hydration of MG in the gas phase. The Gibbs free energy for this process, ΔG°, obtained as a result, suggests a larger than expected gas-phase diol concentration. This may have significant implications for understanding the role of organics in atmospheric chemistry. PMID:20142510

  14. Gas-phase dynamics in graphene growth by chemical vapour deposition.

    PubMed

    Li, Gan; Huang, Sheng-Hong; Li, Zhenyu

    2015-09-21

    Chemical vapour deposition on a Cu substrate is becoming a very important approach to obtain high quality graphene samples. Previous studies of graphene growth on Cu mainly focus on surface processes. However, recent experiments suggest that gas-phase dynamics also plays an important role in graphene growth. In this article, gas-phase processes are systematically studied using computational fluid dynamics. Our simulations clearly show that graphene growth is limited by mass transport under ambient pressures while it is limited by surface reactions under low pressures. The carbon deposition rate at different positions in the tube furnace and the concentration of different gas phase species are calculated. Our results confirm that the previously realized graphene thickness control by changing the position of the Cu foil is a result of gas-phase methane decomposition reactions.

  15. Titanium defect structure change after gas-phase hydrogenation at different temperatures and cooling rates

    NASA Astrophysics Data System (ADS)

    Mikhaylov, Andrey A.; Laptev, Roman S.; Kudiiarov, Viktor N.; Volokitina, Tatiana L.

    2016-11-01

    Influence of gas-phase hydrogenation temperature and cooling rate on defect structure of commercially pure titanium alloy was experimentally studied by means of positron annihilation spectroscopy. The change of temperature in the process of gas-phase hydrogenation was in the range of 500-700°C, while the change of cooling rate was in the range of 0.4-10.4°C/min. With increasing of gas-phase hydrogenation temperature, significant increase of hydrogen sorption rate was found. High temperature gas-phase hydrogenation of commercially pure titanium alloy lead to the formation of vacancy and hydrogen-vacancy complexes. For the same concentration of hydrogen, temperature variation or variation of cooling rate had no effect on the type of defect. However, this variation provides significant changes in defect concentration.

  16. Identification of gas-phase dimethyl sulfate and monomethyl hydrogen sulfate in the Los Angeles atmosphere

    SciTech Connect

    Eatough, D.J.; White, V.F.; Hansen, L.D.; Eatough, N.L.; Cheney, J.L.

    1986-01-01

    Analytical techniques were developed for the collection and determination of gas-phase dimethyl sulfate and monomethyl sulfuric acid based on collection of the alkyl sulfate compounds with both denuder tubes and resin sorption beds and analysis of the collected material by ion chromatography. Gas-phase dimethyl sulfate and monomethyl sulfuric acid were identified in Los Angeles using these techniques. The data indicate that dimethyl sulfate is present in both particles and in the gas phase. The concentration of gas-phase methyl sulfates was found to be several micrograms/cu m. These species thus account for a significant fraction of the total sulfur budget in the Los Angeles Basin during the sample period.

  17. Identification of gas-phase dimethyl sulfate and monomethyl hydrogen sulfate in the Los Angeles atmosphere

    SciTech Connect

    Eatough, D.J.; White, V.F.; Hansen, L.D.; Eatough, N.L.; Cheney, J.L.

    1986-09-01

    Gas-phase dimethyl sulfate and monomethyl hydrogen sulfate have been identified in the atmosphere in Los Angeles. Gas-phase concentrations of these two alkyl sulfates were determined by using analytical methods based on the collection of the compounds before collection of particles using diffusion denuders and after collection of particles using resin beds or sorption filters, and specific analysis of the collected alkyl sulfates by ion chromatography. The data show the dimethyl sulfate is present in both particles and the gas phase. The concentration of total gas-phase methyl sulfates was found to vary from 34 to 178 nmol/m/sup 3/ during the smog episode studied. These species constituted a significant fraction of the total sulfur budget in the Los Angeles basin during the sampling period.

  18. Fluorescence resonance energy transfer of gas-phase ions under ultra high vacuum and ambient conditions.

    PubMed

    Frankevich, Vladimir; Chagovets, Vitaliy; Widjaja, Fanny; Barylyuk, Konstantin; Yang, Zhiyi; Zenobi, Renato

    2014-05-21

    We report evidence for fluorescence resonance energy transfer (FRET) of gas-phase ions under ultra high vacuum conditions (10(-9) mbar) inside a mass spectrometer as well as under ambient conditions inside an electrospray plume. Two different FRET pairs based on carboxyrhodamine 6G (donor) and ATTO590 or Bodipy TR (acceptor) dyes were examined and their gas-phase optical properties were studied. Our measurements indicate a different behavior for the two FRET pairs, which can be attributed to their different conformations in the gas phase. Upon desolvation via electrospray ionization, one of the FRET pairs undergoes a conformational change that leads to disappearance of FRET. This study shows the promise of FRET to obtain a direct correlation between solution and gas-phase structures.

  19. Magnetic PECA nanoparticles as drug carriers for targeted delivery: synthesis and release characteristics.

    PubMed

    Yang, J; Lee, H; Hyung, W; Park, S-B; Haam, S

    2006-03-01

    Magnetic poly(ethyl-2-cyanoacrylate) (PECA) nanoparticles containing anti-cancer drugs (Cisplatin and Gemcitabine) were prepared by inter-facial polymerization. The spherical nanoparticles (d = 250 +/- 15 nm) with smooth surfaces and moderately uniform size distributions were obtained. The amount of magnetite encapsulated inside the polymer matrix was increased up to 14.26% (w/w) by controlling the initial weight ratio of monomer/magnetite. It was found that the amount of Cisplatin encapsulated in the magnetic nanoparticle is much higher than that of Gemcitabine because Cisplatin (hydrophobic) is highly soluble in the oil phase and encapsulated easier inside nanoparticles compared to Gemcitabine (hydrophilic). The presence of magnetite and its super-paramagnetic characteristic were confirmed by FTIR spectra and VSM. In-vitro experiments of drug release and magnetic mobility under external magnetic field demonstrated that magnetic poly(ethyl-2-cyanoacrylate) (PECA) nanoparticles can be a highly versatile magnetic drug carrier with sustained release behaviour and sufficient magnetic susceptibility.

  20. Experimental study of PLLA/INH slow release implant fabricated by three dimensional printing technique and drug release characteristics in vitro

    PubMed Central

    2014-01-01

    Background Local slow release implant provided long term and stable drug release in the lesion. The objective of this study was to fabricate biodegradable slow release INH/PLLA tablet via 3 dimensional printing technique (3DP) and to compare the drug release characteristics of three different structured tablets in vitro. Methods Three different drug delivery systems (columnar-shaped tablet (CST), doughnut-shaped tablet (DST) and multilayer doughnut-shaped tablet (MDST)) were manufactured by the three dimensional printing machine and isoniazid was loaded into the implant. Dynamic soaking method was used to study the drug release characteristics of the three implants. MTT cytotoxicity test and direct contact test were utilized to study the biocompatibility of the implant. The microstructures of the implants’ surfaces were observed with electron microscope. Results The PLLA powder in the tablet could be excellently combined through 3DP without disintegration. Electron microscope observations showed that INH distributed evenly on the surface of the tablet in a “nest-shaped” way, while the surface of the barrier layer in the multilayer doughnut shaped tablet was compact and did not contain INH. The concentration of INH in all of the three tablets were still higher than the effective bacteriostasis concentration (Isoniazid: 0.025 ~ 0.05 μg/ml) after 30 day’s release in vitro. All of the tablets showed initial burst release of the INH in the early period. Drug concentration of MDST became stable and had little fluctuation starting from the 6th day of the release. Drug concentration of DST and CST decreased gradually and the rate of decrease in concentration was faster in DST than CST. MTT cytotoxicity test and direct contact test indicated that the INH-PLLA tablet had low cytotoxicity and favorable biocompatibility. Conclusions Three dimensional printing technique was a reliable technique to fabricate complicated implants. Drug release pattern in MDST was

  1. Optimization of caseinate-coated simvastatin-zein nanoparticles: improved bioavailability and modified release characteristics

    PubMed Central

    Ahmed, Osama AA; Hosny, Khaled M; Al-Sawahli, Majid M; Fahmy, Usama A

    2015-01-01

    The current study focuses on utilization of the natural biocompatible polymer zein to formulate simvastatin (SMV) nanoparticles coated with caseinate, to improve solubility and hence bioavailability, and in addition, to modify SMV-release characteristics. This formulation can be utilized for oral or possible depot parenteral applications. Fifteen formulations were prepared by liquid–liquid phase separation method, according to the Box–Behnken design, to optimize formulation variables. Sodium caseinate was used as an electrosteric stabilizer. The factors studied were: percentage of SMV in the SMV-zein mixture (X1), ethanol concentration (X2), and caseinate concentration (X3). The selected dependent variables were mean particle size (Y1), SMV encapsulation efficiency (Y2), and cumulative percentage of drug permeated after 1 hour (Y3). The diffusion of SMV from the prepared nanoparticles specified by the design was carried out using an automated Franz diffusion cell apparatus. The optimized SMV-zein formula was investigated for in vivo pharmacokinetic parameters compared with an oral SMV suspension. The optimized nanosized SMV-zein formula showed a 131 nm mean particle size and 89% encapsulation efficiency. In vitro permeation studies displayed delayed permeation characteristics, with about 42% and 85% of SMV cumulative amount released after 12 and 48 hours, respectively. Bioavailability estimation in rats revealed an augmentation in SMV bioavailability from the optimized SMV-zein formulation, by fourfold relative to SMV suspension. Formulation of caseinate-coated SMV-zein nanoparticles improves the pharmacokinetic profile and bioavailability of SMV. Accordingly, improved hypolipidemic activities for longer duration could be achieved. In addition, the reduced dosage rate of SMV-zein nanoparticles improves patient tolerability and compliance. PMID:25670883

  2. On the role of ethenol in equilibrium gas-phase ethanal

    NASA Astrophysics Data System (ADS)

    Slanina, Zdeněk

    1984-03-01

    The ethenol content in gas-phase ethanal has been evaluated under equilibrium conditions within a broad temperature interval, and it has been shown that the content thresholds of 1% and 1% can be crossed at about 650 and 1000 K, respectively. At moderate and higher temperatures the presence of ethenol is manifested by contributions to thermodynamic functions of the equilibrium gas-phase ethanal which can be even higher than the usual anharmonicity and non-rigidity corrections.

  3. Ultrafast electronic relaxation of excited state vitamin B 12 in the gas phase

    NASA Astrophysics Data System (ADS)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoıˆt

    2008-06-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  4. Theory and Computing of Gas Phase Chemical Reactions: From Exact Quantum to Approximates Dynamical Treatments

    DTIC Science & Technology

    2006-02-08

    Phys. 110, 5526 (1999); Chem. Phys. 242, 341(1999). [51] R. M. Dreizler and E. K. U. Gross, Density Functional Theory (Springer Verlag, Berlin, 1990...the right hand side member of expression 3 can be derived from the square modulus of the S matrix Theory and Computing of Gas Phase Chemical...deal at the same time with different terms of the electronic functions manifolds (15). In these approaches the Theory and Computing of Gas Phase

  5. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall, G.E.

    2011-05-31

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  6. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall G. E.; Goncharov, V.

    2012-05-29

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  7. Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase.

    PubMed

    Lin, Z P; Aue, W A

    2000-01-01

    Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones.

  8. An atmospheric pressure flow reactor: Gas phase kinetics and mechanism in tropospheric conditions without wall effects

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L.; Davis, Dennis D.; Hansen, Merrill

    1988-01-01

    A new type of gas phase flow reactor, designed to permit the study of gas phase reactions near 1 atm of pressure, is described. A general solution to the flow/diffusion/reaction equations describing reactor performance under pseudo-first-order kinetic conditions is presented along with a discussion of critical reactor parameters and reactor limitations. The results of numerical simulations of the reactions of ozone with monomethylhydrazine and hydrazine are discussed, and performance data from a prototype flow reactor are presented.

  9. Detection Of Gas-Phase Polymerization in SiH4 And GeH4

    NASA Technical Reports Server (NTRS)

    Shing, Yuh-Han; Perry, Joseph W.; Allevato, Camillo E.

    1990-01-01

    Inelastic scattering of laser light found to indicate onset of gas-phase polymerization in plasma-enhanced chemical-vapor deposition (PECVD) of photoconductive amorphous hydrogenated silicon/germanium alloy (a-SiGe:H) film. In PECVD process, film deposited from radio-frequency glow-discharge plasma of silane (SiH4) and germane (GeH4) diluted with hydrogen. Gas-phase polymerization undesirable because it causes formation of particulates and defective films.

  10. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    SciTech Connect

    Hall,G.E.; Sears, T.J.

    2009-04-03

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

  11. Excitation and dissociation of molecules by femtosecond IR laser radiation in the gas phase and on dielectric surfaces

    SciTech Connect

    Kompanets, V O; Laptev, Vladimir B; Makarov, Aleksandr A; Pigulskii, S V; Ryabov, Evgenii A; Chekalin, Sergei V

    2013-04-30

    This paper presents an overview of early studies and new experimental data on the effect of near-IR (0.8-1.8 {mu}m) and mid-IR (3.3-5.8 {mu}m) intense femtosecond (130-350 fs) laser pulses on polyatomic molecules in the gas phase and on the surface of substrates. We examine the vibrational dynamics of nine molecules containing a C=O chromophore group, which are initiated by resonance femtosecond IR laser radiation at a wavelength of {approx}5 {mu}m, and report measured characteristic times of intramolecular vibrational redistribution. The characteristic time of molecules containing a single C=O group lies in the range 2.4-20 ps and that of the Fe(CO){sub 5} and Cr(CO){sub 6} molecules lies in the nanosecond range ({approx}1.0 and {approx}1.5 ns, respectively). Carbon structures have been observed for the first time to result from the decomposition of (CF{sub 3}){sub 2}CCO molecules on the surface of metal fluorides under the effect of femtosecond IR laser radiation in the wavelength range 3.3-5.4 {mu}m with no gas-phase decomposition of the molecules. (extreme light fields and their applications)

  12. Electronic Effects of 11β Substituted 17β-Estradiol Derivatives and Instrumental Effects on the Relative Gas Phase Acidity

    NASA Astrophysics Data System (ADS)

    Bourgoin-Voillard, Sandrine; Fournier, Françoise; Afonso, Carlos; Zins, Emilie-Laure; Jacquot, Yves; Pèpe, Claude; Leclercq, Guy; Tabet, Jean-Claude

    2012-12-01

    Numerous studies have highlighted the role of the proton donor characteristics of the phenol group of 17β-estradiol (E2) in its association with the estrogen receptor alpha (ERα). Since the substitutions at position C(11) have been reported to modulate this association, we hypothesized that such substitutions may modify the phenol acidity. Hence, phenol gas-phase acidity of nine C(11)-substituted E2-derivatives were evaluated using the extended Cooks' kinetic method, which is a method widely used to determine thermochemical properties by mass spectrometry. To enhance accuracy in data collection we recorded data from several instruments, including quadrupole ion trap, triple quadrupole, and hybrid QqTOF. Indeed, we report for the first time the use of the QqTOF instrument to provide a novel means to improve data accuracy by giving access to an intermediate effective temperature range. All experimental gas-phase acidity values were supported by theoretical calculations. Our results confirmed the ability of distant substituents at C(11) to modulate the phenol acidity through electrostatic interactions, electron withdrawing inductive effects, and mesomeric effects. However, no relationship was found between the phenol gas-phase acidity of investigated steroids and their binding affinity for ERα assessed in solution. Thus, our results highlight that the intrinsic properties of the hormone do not influence sufficiently the stabilization of the hormone/ERα complex. It is more likely that such stabilization would be more related to factors depending on the environment within the binding pocket such as hydrophobic, steric as well as direct intermolecular electrostatic effects between ERα residues and the substituted steroidal estrogens.

  13. The enormous apparent gas-phase acidity of cubylamine

    NASA Astrophysics Data System (ADS)

    Abboud, José-Luis M.; Alkorta, Ibon; Burk, Peeter; Dávalos, Juan Z.; Quintanilla, Esther; Della, Ernest W.; Koppel, Ilmar A.; Koppel, Ivar

    2004-11-01

    The high acidity of cubylamine ( 1NH 2) seems to originate in the release of strain energy attending the breaking of some C-C bonds in 1NH -. This process is greatly facilitated by the strong stereoelectronic interactions in 1NH -. The anionic species thus formed are less strained, and their corresponding conjugate acids seem unable to 'borrow strength' from the residual strain, at least within the time-scale of the FT ICR experiments.

  14. Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles.

    PubMed

    Fang, Yigang; Bennett, Andrew; Liu, Jianbo

    2011-01-28

    We report a study on encapsulation of various amino acids into gas-phase sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) reverse micelles, using electrospray ionization guided-ion-beam tandem mass spectrometry. Collision-induced dissociation of mass-selected reverse micellar ions with Xe was performed to probe structures of gas-phase micellar assemblies, identify solute-surfactant interactions, and determine preferential incorporation sites of amino acids. Integration into gas-phase reverse micelles depends upon amino acid hydrophobicity and charge state. For examples, glycine and protonated amino acids (such as protonated tryptophan) are encapsulated within the micellar core via electrostatic interactions; while neutral tryptophan is adsorbed in the surfactant layer. As verified using model polar hydrophobic compounds, the hydrophobic effect and solute-interface hydrogen-bonding do not provide sufficient driving force needed for interfacial solubilization of neutral tryptophan. Neutral tryptophan, with a zwitterionic structure, is intercalated at the micellar interface between surfactant molecules through complementary effects of electrostatic interactions between tryptophan backbone and AOT polar heads, and hydrophobic interactions between tryptophan side chain and AOT alkyl tails. Protonation of tryptophan could significantly improve its incorporation capacity into gas-phase reverse micelles, and displace its incorporation site from the micellar interfacial zone to the core; protonation of glycine, on the other hand, has little effect on its encapsulation capacity. Another interesting observation is that amino acids of different isoelectric points could be selectively encapsulated into, and transported by, reverse micelles from solution to the gas phase, based upon their competition for protonation and subsequent encapsulation within the micellar core.

  15. Gas Phase Pressure Effects on the Apparent Thermal Conductivity of JSC-1A Lunar Regolith Simulant

    NASA Technical Reports Server (NTRS)

    Yuan, Zeng-Guang; Kleinhenz, Julie E.

    2011-01-01

    Gas phase pressure effects on the apparent thermal conductivity of a JSC-1A/air mixture have been experimentally investigated under steady state thermal conditions from 10 kPa to 100 kPa. The result showed that apparent thermal conductivity of the JSC-1A/air mixture decreased when pressure was lowered to 80 kPa. At 10 kPa, the conductivity decreased to 0.145 W/m/degree C, which is significantly lower than 0.196 W/m/degree C at 100 kPa. This finding is consistent with the results of previous researchers. The reduction of the apparent thermal conductivity at low pressures is ascribed to the Knudsen effect. Since the characteristic length of the void space in bulk JSC-1A varies over a wide range, both the Knudsen regime and continuum regime can coexist in the pore space. The volume ratio of the two regimes varies with pressure. Thus, as gas pressure decreases, the gas volume controlled by Knudsen regime increases. Under Knudsen regime the resistance to the heat flow is higher than that in the continuum regime, resulting in the observed pressure dependency of the apparent thermal conductivity.

  16. LIAD-fs scheme for studies of ultrafast laser interactions with gas phase biomolecules.

    PubMed

    Calvert, C R; Belshaw, L; Duffy, M J; Kelly, O; King, R B; Smyth, A G; Kelly, T J; Costello, J T; Timson, D J; Bryan, W A; Kierspel, T; Rice, P; Turcu, I C E; Cacho, C M; Springate, E; Williams, I D; Greenwood, J B

    2012-05-14

    Laser induced acoustic desorption (LIAD) has been used for the first time to study the parent ion production and fragmentation mechanisms of a biological molecule in an intense femtosecond (fs) laser field. The photoacoustic shock wave generated in the analyte substrate (thin Ta foil) has been simulated using the hydrodynamic HYADES code, and the full LIAD process has been experimentally characterised as a function of the desorption UV-laser pulse parameters. Observed neutral plumes of densities >10(9) cm(-3) which are free from solvent or matrix contamination demonstrate the suitability and potential of the source for studying ultrafast dynamics in the gas phase using fs laser pulses. Results obtained with phenylalanine show that through manipulation of fundamental femtosecond laser parameters (such as pulse length, intensity and wavelength), energy deposition within the molecule can be controlled to allow enhancement of parent ion production or generation of characteristic fragmentation patterns. In particular by reducing the pulse length to a timescale equivalent to the fastest vibrational periods in the molecule, we demonstrate how fragmentation of the molecule can be minimised whilst maintaining a high ionisation efficiency. This journal is © the Owner Societies 2012

  17. Interaction of Gas Phase Oxalic Acid with Ammonia and its Atmospheric Implications

    SciTech Connect

    Peng, Xiu-Qiu; Liu, Yi-Rong; Huang, Teng; Jiang, Shuai; Huang, Wei

    2015-04-14

    Oxalic acid is believed to play an important role in the formation and growth of atmospheric organic aerosols. However, as a common organic acid, the understanding of the larger clusters formed by gas phase oxalic acid with multiple ammonia molecules is incomplete. In this work, the structural characteristics and thermodynamics of oxalic acid clusters with up to six ammonia molecules have been investigated at the PW91PW91/6-311++G(3df,3pd) level of theory. We found that oxalic acid forms relatively stable clusters with ammonia molecules, and that ionization events play a key role. The analyses of the thermodynamics and atmospheric relevance indicate that the heterodimer (H2C2O4)(NH3) shows an obvious relative concentration in the atmosphere, and thus likely participates in new particle formation. However, with increasing number of ammonia molecules, the concentration of clusters decreases gradually. Additionally, clusters of oxalic acid with ammonia molecules are predicted to form favorably in low temperature conditions and show high Rayleigh scattering intensities.

  18. Characterization of ultrafast hard x-ray pulses for LCLS using gas phase techniques

    NASA Astrophysics Data System (ADS)

    Hertlein, Marcus P.; Kienberger, Reinhard; Adaniya, Hidehito

    2005-05-01

    The availability of ultrafast (sub-100 fs) hard x-ray pulses (E > 1000 eV) promises new experimental opportunities, but also requires new techniques for their use. The Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center (SLAC) is such a source that is expected to provide a high flux of 230 fs monochromatic x-ray photons with energy between 0.8 and 8 keV. Characterization methods for beams with such characteristics still need to be developed. We are presenting several techniques that show promise for the spatial and temporal characterization of ultrafast hard x-rays. They were developed and used at the Advanced Light Source (ALS), and will undergo further testing at the Sub-Picosecond Photon Source (SPPS) at SLAC. Our methods exploit effects such as ultrafast core-hole binding energy changes in atoms after laser excitation, and creation of energy sidebands on Auger electrons that are emitted in a laser field. We have demonstrated the usefulness of these effects on a picosecond time scale, but their use can be extended well into the femtosecond domain. We will also discuss time-of-flight techniques which offer the possibility of nondestructive x-ray spatial mode characterization. Our focus is on gas phase experiments, since they offer the possibility of nondestructive, transparent monitoring of the x-rays, leaving the main beam nearly undisturbed and available for experiments.

  19. Gas-Phase Oxidation via Ion/Ion Reactions: Pathways and Applications

    NASA Astrophysics Data System (ADS)

    Pilo, Alice L.; Zhao, Feifei; McLuckey, Scott A.

    2017-06-01

    Here, we provide an overview of pathways available upon the gas-phase oxidation of peptides and DNA via ion/ion reactions and explore potential applications of these chemistries. The oxidation of thioethers (i.e., methionine residues and S-alkyl cysteine residues), disulfide bonds, S-nitrosylated cysteine residues, and DNA to the [M+H+O]+ derivative via ion/ion reactions with periodate and peroxymono-sulfate anions is demonstrated. The oxidation of neutral basic sites to various oxidized structures, including the [M+H+O]+, [M-H]+, and [M-H-NH3]+ species, via ion/ion reactions is illustrated and the oxidation characteristics of two different oxidizing reagents, periodate and persulfate anions, are compared. Lastly, the highly efficient generation of molecular radical cations via ion/ion reactions with sulfate radical anion is summarized. Activation of the newly generated molecular radical peptide cations results in losses of various neutral side chains, several of which generate dehydroalanine residues that can be used to localize the amino acid from which the dehydroalanine was generated. The chemistries presented herein result in a diverse range of structures that can be used for a variety of applications, including the identification and localization of S-alkyl cysteine residues, the oxidative cleavage of disulfide bonds, and the generation of molecular radical cations from even-electron doubly protonated peptides. [Figure not available: see fulltext.

  20. Phosphorescence lifetime-based sensing of SO{sub 2} in the gas phase

    SciTech Connect

    Papkovsky, D.B.; Desyaterik, I.V.; Ponomarev, G.V.

    1995-08-01

    Two different types of solid-state coatings based on the phosphorescent metalloporphyrins - polymer film compositions or Langmuir-Blodgett films - were studied comparatively with respect to their application to sensing of SO{sub 2}. While the polymer films were only slightly sensitive to SO{sub 2}, LB-coatings appeared to be highly suitable for analyzing SO{sub 2} in the air in the range 0.01-2% (v/v). Performance characteristics of the new phosphorescence lifetime-based sensor for SO{sub 2} were studied. Interferences by a number important species on sensing of SO{sub 2} in gas phase were studied. The new SO{sub 2} sensor was shown to be rather inert to quenching with molecular oxygen and interference by such species, as CO{sub 2}, CO, NH{sub 3}, CH{sub 4} gases. On the other hand, NOx interfere with SO{sub 2} sensing and vapors of water (i.e. high relative air humidity); alcohols, acids at concentrations close to saturated also cause interference by enhancing quenching with environmental oxygen.

  1. Gas-Phase Oxidation via Ion/Ion Reactions: Pathways and Applications

    NASA Astrophysics Data System (ADS)

    Pilo, Alice L.; Zhao, Feifei; McLuckey, Scott A.

    2017-01-01

    Here, we provide an overview of pathways available upon the gas-phase oxidation of peptides and DNA via ion/ion reactions and explore potential applications of these chemistries. The oxidation of thioethers (i.e., methionine residues and S-alkyl cysteine residues), disulfide bonds, S-nitrosylated cysteine residues, and DNA to the [M+H+O]+ derivative via ion/ion reactions with periodate and peroxymono-sulfate anions is demonstrated. The oxidation of neutral basic sites to various oxidized structures, including the [M+H+O]+, [M-H]+, and [M-H-NH3]+ species, via ion/ion reactions is illustrated and the oxidation characteristics of two different oxidizing reagents, periodate and persulfate anions, are compared. Lastly, the highly efficient generation of molecular radical cations via ion/ion reactions with sulfate radical anion is summarized. Activation of the newly generated molecular radical peptide cations results in losses of various neutral side chains, several of which generate dehydroalanine residues that can be used to localize the amino acid from which the dehydroalanine was generated. The chemistries presented herein result in a diverse range of structures that can be used for a variety of applications, including the identification and localization of S-alkyl cysteine residues, the oxidative cleavage of disulfide bonds, and the generation of molecular radical cations from even-electron doubly protonated peptides.

  2. Interaction of gas phase oxalic acid with ammonia and its atmospheric implications.

    PubMed

    Peng, Xiu-Qiu; Liu, Yi-Rong; Huang, Teng; Jiang, Shuai; Huang, Wei

    2015-04-14

    Oxalic acid is believed to play an important role in the formation and growth of atmospheric organic aerosols. However, as a common organic acid, the understanding of the larger clusters formed by gas phase oxalic acid with multiple ammonia molecules is incomplete. In this work, the structural characteristics and thermodynamics of oxalic acid clusters with up to six ammonia molecules have been investigated at the PW91PW91/6-311++G(3df,3pd) level of theory. We found that oxalic acid forms relatively stable clusters with ammonia molecules, and that ionization events play a key role. The analyses of the thermodynamics and atmospheric relevance indicate that the heterodimer (H2C2O4)(NH3) shows an obvious relative concentration in the atmosphere, and thus likely participates in new particle formation. However, with increasing number of ammonia molecules, the concentration of clusters decreases gradually. Additionally, clusters of oxalic acid with ammonia molecules are predicted to form favorably in low temperature conditions and show high Rayleigh scattering intensities.

  3. Sociolegal characteristics and parole infractions among Israeli released prisoners during electronic monitoring.

    PubMed

    Shoham, Efrat; Yehosha-Stern, Shirley; Efodi, Rotem

    2013-07-01

    The objective of this study is to examine the part played by sociolegal characteristics such as ethnic background, family status, or criminal past in the rate of infractions among ex-prisoners in Electronic Monitoring (EM) Programs. In addition, it focuses on the nature of the formal decisions made by community supervision agents regarding such infractions and their correlation with the sociolegal characteristics of the participants. The research population included all prisoners on license (i.e., prisoners who have been granted conditional early release) who took part in the EM project from mid-2007 until mid-2009 (24 months), altogether 155 participants. The data show no significant correlation between the number of infractions and the participant's sociolegal background. In spite of the fact that the EM coordinators have extensive discretionary power, which is likely to lead to discrimination attributable to variables such as ethnicity, this research shows that the most efficacious variable for explaining formal responses is an objective one-the number of infractions.

  4. Development of hollow microspheres as floating controlled-release systems for cardiovascular drugs: preparation and release characteristics.

    PubMed

    Soppimath, K S; Kulkarni, A R; Aminabhavi, T M

    2001-07-01

    Hollow microspheres of cellulose acetate loaded with four cardiovascular drugs (nifedipine [NFD], nicardapine hydrochloride [NCD], verapamil hydrochloride [VRP], and dipyridamole [DIP]) were prepared by a novel solvent diffusion-evaporation method. The oil-in-water emulsion prepared in an aqueous solution of 0.05% poly(vinyl alcohol) medium with ethyl acetate, a water-soluble and less toxic solvent, was used as the dispersing solvent. The yield of the microspheres was up to 80%. The microspheres had smooth surfaces, with free-flowing and good-packing properties. Scanning electron microscopy (SEM) confirmed their hollow structures, with sizes in the range 489-350 microm. The microspheres tended to float over the gastric media for more than 12 h. The drug loaded in hollow microspheres was in an amorphous state, as confirmed by differential scanning microscopy (DSC). The release of the drugs was controlled for more than 8 h. The release kinetics followed different transport mechanisms depending on the nature of the drug molecules.

  5. Co-delivery nanoparticles with characteristics of intracellular precision release drugs for overcoming multidrug resistance.

    PubMed

    Zhang, DanDan; Kong, Yan Yan; Sun, Jia Hui; Huo, Shao Jie; Zhou, Min; Gui, Yi Ling; Mu, Xu; Chen, Huan; Yu, Shu Qin; Xu, Qian

    2017-01-01

    Combination chemotherapy in clinical practice has been generally accepted as a feasible strategy for overcoming multidrug resistance (MDR). Here, we designed and successfully prepared a co-delivery system named S-D1@L-D2 NPs, where denoted some smaller nanoparticles (NPs) carrying a drug doxorubicin (DOX) were loaded into a larger NP containing another drug (vincristine [VCR]) via water-in-oil-in-water double-emulsion solvent diffusion-evaporation method. Chitosan-alginate nanoparticles carrying DOX (CS-ALG-DOX NPs) with a smaller diameter of about 20 nm formed S-D1 NPs; vitamin E D-α-tocopheryl polyethylene glycol 1000 succinate-modified poly(lactic-co-glycolic acid) nanoparticles carrying VCR (TPGS-PLGA-VCR NPs) with a larger diameter of about 200 nm constituted L-D2 NPs. Some CS-ALG-DOX NPs loaded into TPGS-PLGA-VCR NPs formed CS-ALG-DOX@TPGS-PLGA-VCR NPs. Under the acidic environment of cytosol and endosome or lysosome in MDR cell, CS-ALG-DOX@TPGS-PLGA-VCR NPs released VCR and CS-ALG-DOX NPs. VCR could arrest cell cycles at metaphase by inhibiting microtubule polymerization in the cytoplasm. After CS-ALG-DOX NPs escaped from endosome, they entered the nucleus through the nuclear pore and released DOX in the intra-nuclear alkaline environment, which interacted with DNA to stop the replication of MDR cells. These results indicated that S-D1@L-D2 NPs was a co-delivery system of intracellular precision release loaded drugs with pH-sensitive characteristics. S-D1@L-D2 NPs could obviously enhance the in vitro cytotoxicity and the in vivo anticancer efficiency of co-delivery drugs, while reducing their adverse effects. Overall, S-D1@L-D2 NPs can be considered an innovative platform for the co-delivery drugs of clinical combination chemotherapy for the treatment of MDR tumor.

  6. Co-delivery nanoparticles with characteristics of intracellular precision release drugs for overcoming multidrug resistance

    PubMed Central

    Zhang, DanDan; Kong, Yan Yan; Sun, Jia Hui; Huo, Shao Jie; Zhou, Min; Gui, Yi Ling; Mu, Xu; Chen, Huan; Yu, Shu Qin; Xu, Qian

    2017-01-01

    Combination chemotherapy in clinical practice has been generally accepted as a feasible strategy for overcoming multidrug resistance (MDR). Here, we designed and successfully prepared a co-delivery system named S-D1@L-D2 NPs, where denoted some smaller nanoparticles (NPs) carrying a drug doxorubicin (DOX) were loaded into a larger NP containing another drug (vincristine [VCR]) via water-in-oil-in-water double-emulsion solvent diffusion-evaporation method. Chitosan-alginate nanoparticles carrying DOX (CS-ALG-DOX NPs) with a smaller diameter of about 20 nm formed S-D1 NPs; vitamin E D-α-tocopheryl polyethylene glycol 1000 succinate-modified poly(lactic-co-glycolic acid) nanoparticles carrying VCR (TPGS-PLGA-VCR NPs) with a larger diameter of about 200 nm constituted L-D2 NPs. Some CS-ALG-DOX NPs loaded into TPGS-PLGA-VCR NPs formed CS-ALG-DOX@TPGS-PLGA-VCR NPs. Under the acidic environment of cytosol and endosome or lysosome in MDR cell, CS-ALG-DOX@TPGS-PLGA-VCR NPs released VCR and CS-ALG-DOX NPs. VCR could arrest cell cycles at metaphase by inhibiting microtubule polymerization in the cytoplasm. After CS-ALG-DOX NPs escaped from endosome, they entered the nucleus through the nuclear pore and released DOX in the intra-nuclear alkaline environment, which interacted with DNA to stop the replication of MDR cells. These results indicated that S-D1@L-D2 NPs was a co-delivery system of intracellular precision release loaded drugs with pH-sensitive characteristics. S-D1@L-D2 NPs could obviously enhance the in vitro cytotoxicity and the in vivo anticancer efficiency of co-delivery drugs, while reducing their adverse effects. Overall, S-D1@L-D2 NPs can be considered an innovative platform for the co-delivery drugs of clinical combination chemotherapy for the treatment of MDR tumor. PMID:28356731

  7. Desorption of Oxygen from Cationic Niobium Oxide Clusters Revealed by Gas Phase Thermal Desorption Spectrometry and Density Functional Theory Calculations.

    PubMed

    Masuzaki, Daigo; Nagata, Toshiaki; Mafuné, Fumitaka

    2017-03-16

    Thermal dissociation of cationic niobium oxide clusters (NbnOm(+)) was investigated by gas phase thermal desorption spectrometry. The dominant species formed at 300 K were NbnO(5/2)n+p(+) (n = 2, 4, 6, ...; p = 0, 1, 2, ...) and NbnO((5/2)n-1/2)+q(+) (n = 3, 5, ...; q = 0, 1, 2, ...). At higher temperatures, the more oxygen-rich clusters were observed to release O2. However, the desorption of O2 from NbnOm(+) was found to be insignificant in comparison with VnOm(+) because Nb tends to have a +5 oxidation state exclusively, whereas V can have both +4 and +5 oxidation states. The propensity for the release of O atoms was manifested in the formation of NbnO(5/2)n-1/2(+) from NbnO((5/2)n-1/2)+1(+) for odd values of n, whereas VnO((5/2)n-1/2)+1(+) released O2 molecules instead. The energetics of the O and O2 release from the Nb and V oxide clusters, respectively, was consistent with the results of DFT calculations.

  8. Characteristics of CO2 release from forest soil in the mountains near Beijing.

    PubMed

    Sun, Xiang Yang; Gao, Cheng Da; Zhang, Lin; Li, Su Yan; Qiao, Yong

    2011-04-01

    CO2 release from forest soil is a key driver of carbon cycling between the soil and atmosphere ecosystem. The rate of CO2 released from soil was measured in three forest stands (in the mountainous region near Beijing, China) by the alkaline absorption method from 2004 to 2006. The rate of CO2 released did not differ among the three stands. The CO2 release rate ranged from - 341 to 1,193 mg m(-2) h(-1), and the mean value over all three forests and sampling times was 286 mg m(-2) h(-1). CO2 release was positively correlated with soil water content and the soil temperature. Diurnally, CO2 release was higher in the day than at night. Seasonally, CO2 release was highest in early autumn and lowest in winter; in winter, negative values of CO2 release suggested that CO2 was absorbed by soil.

  9. Absolute configuration assignment of a chiral molecule in the gas phase using foil-induced Coulomb explosion imaging

    NASA Astrophysics Data System (ADS)

    Herwig, Philipp; Zawatzky, Kerstin; Schwalm, Dirk; Grieser, Manfred; Heber, Oded; Jordon-Thaden, Brandon; Krantz, Claude; Novotný, Oldřich; Repnow, Roland; Schurig, Volker; Vager, Zeev; Wolf, Andreas; Trapp, Oliver; Kreckel, Holger

    2014-11-01

    Chiral molecules exist in two configurations that are nonsuperposable mirror images of one another. The underlying molecular structure is referred to as the absolute configuration. In chiral environments, the handedness of molecules influences their chemical characteristics dramatically, and therefore the determination of absolute configurations is of fundamental interest in organic chemistry and biology. Commonly applied techniques to assign absolute configuration are anomalous single-crystal x-ray diffraction and vibrational circular dichroism. However, these techniques become increasingly more challenging when applied to molecules that are made out of light atoms exclusively. Furthermore, there is no established method to determine the absolute handedness of gas-phase molecules that are not optically active. In this work, we apply the foil-induced Coulomb explosion imaging technique to determine directly the absolute configuration of the chiral molecule trans-2,3-dideuterooxirane (C2OD2H2) in the gas phase. The experiment leads to the definitive assignment of the (R ,R ) configuration to an enantio-selected dideuterooxirane sample with a statistical confidence of 5 σ . As the handedness of trans-2,3-dideuterooxirane is unambiguously linked by chemical synthesis to the stereochemical key reference glyceraldehyde, our results provide an independent verification of the absolute configuration of the stereochemical reference standard.

  10. Processes forming Gas, Tar, and Coke in Cellulose Gasification from Gas-Phase Reactions of Levoglucosan as Intermediate.

    PubMed

    Fukutome, Asuka; Kawamoto, Haruo; Saka, Shiro

    2015-07-08

    The gas-phase pyrolysis of levoglucosan (LG), the major intermediate species during cellulose gasification, was studied experimentally over the temperature range of 400-900 °C. Gaseous LG did not produce any dehydration products, which include coke, furans, and aromatic substances, although these are characteristic products of the pyrolysis of molten LG. Alternatively, at >500 °C, gaseous LG produced only fragmentation products, such as noncondensable gases and condensable C1 -C3 fragments, as intermediates during noncondensable gas formation. Therefore, it was determined that secondary reactions of gaseous LG can result in the clean (tar- and coke-free) gasification of cellulose. Cooling of the remaining LG in the gas phase caused coke formation by the transition of the LG to the molten state. The molecular mechanisms that govern the gas- and molten-phase reactions of LG are discussed in terms of the acid catalyst effect of intermolecular hydrogen bonding to promote the molten-phase dehydration reactions.

  11. Generation of gas-phase zirconium fluoroanions by electrospray of an ionic liquid

    SciTech Connect

    Gary S. Groenewold; James E. Delmore; Michael T. Benson; Tetsuya Tsuda; Rika Hagiwara

    2014-06-01

    RATIONALE: When measuring extremely wide isotope ratios (= 1 x 109) accelerator mass spectrometry (AMS) is the instrument of choice, however it requires an anion for injection into the tandem accelerator. Since many elements do not have positive electronegativities they do not form stable negative atomic ions, and hence are not compatible for isotope ratio measurement using AMS. Thus new approaches for forming anions are sought; fluoroanions are particularly attractive because fluorine is monoisotopic, and thus will not have overlapping isobars with the isotope of interest. METHODS: An approach is described for making zirconium fluoroanions using the fluorinating ionic liquid (IL) 1-ethyl-3-methylimidazolium fluorohydrogenate, which was used to generate abundant [ZrF5-] using electrospray ionization. The IL was dissolved in acetonitrile, combined with a dilute solution of either Zr4+ or ZrO2+, and then electrosprayed. Mass analysis and collision induced dissociation were conducted using a time-of-flight mass spectrometer. Cluster structures were predicted using density functional theory calculations. RESULTS: The fluorohydrogenate IL solutions generated abundant [ZrF5-] starting from solutions of both Zr4+ and ZrO2+. The mass spectra also contained IL-bearing cluster ions, whose compositions indicated the presence of [ZrF6]2- in solution, a conclusion supported by the structural calculations. Rinsing out the zirconium-IL solution with acetonitrile decreased the IL clusters, but enhanced [ZrF5]-, which was sorbed by the polymeric electrospray supply capillary, and then released upon rinsing. This reduced the ion background in the mass spectrum. CONCLUSIONS: The fluorohydrogenate-IL solutions are a facile way to form zirconium fluoroanions in the gas phase using electrospray. The approach has potential as a source of fluoroanions for injection into an AMS, which would enable high-sensitivity measurement of minor zirconium isotopes, and benefits from the absence of

  12. Drug release characteristics from chitosan-alginate matrix tablets based on the theory of self-assembled film.

    PubMed

    Li, Liang; Wang, Linlin; Shao, Yang; Ni, Rui; Zhang, Tingting; Mao, Shirui

    2013-06-25

    The aim of this study was to better understand the underlying drug release characteristics from chitosan-alginate matrix tablets containing different types of drugs. Theophylline, paracetamol, metformin hydrochloride and trimetazidine hydrochloride were used as model drugs exhibiting significantly different solubilities (12, 16, 346 and >1000 mg/ml at 37 °C in water). A novel concept raised was that drugs were released from chitosan-alginate matrix tablets based on the theory of a self-assembled film-controlled release system. The film was only formed on the surface of tablets in gastrointestinal environment and originated from chitosan-alginate polyelectrolyte complex, confirmed by differential scanning calorimetry characterization. The formed film could decrease the rate of polymer swelling to a degree, also greatly limit the erosion of tablets. Drugs were all released through diffusion in the hydrated matrix and polymer relaxation, irrespective of the drug solubility. The effects of polymer level and initial drug loading on release depended on drug properties. Drug release was influenced by the change of pH. In contrast, the impact of ionic strength of the release medium within the physiological range was negligible. Importantly, hydrodynamic conditions showed a key factor determining the superiority of the self-assembled film in controlling drug release compared with conventional matrix tablets. The new insight into chitosan-alginate matrix tablets can help to broaden the application of this type of dosage forms.

  13. Molecular characteristics of continuously released DOM during one year of root and leaf litter decomposition

    NASA Astrophysics Data System (ADS)

    Altmann, Jens; Jansen, Boris; Kalbitz, Karsten; Filley, Timothy

    2013-04-01

    Dissolved organic matter (DOM) is one of the most dynamic carbon pools linking the terrestrial with the aquatic carbon cycle. Besides the insecure contribution of terrestrial DOM to the greenhouse effect, DOM also plays an important role for the mobility and availability of heavy metals and organic pollutants in soils. These processes depend very much on the molecular characteristics of the DOM. Surprisingly the processes that determine the molecular composition of DOM are only poorly understood. DOM can originate from various sources, which influence its molecular composition. It has been recognized that DOM formation is not a static process and DOM characteristics vary not only between different carbon sources. However, molecular characteristics of DOM extracts have scarcely been studied continuously over a longer period of time. Due to constant molecular changes of the parent litter material or soil organic matter during microbial degradation, we assumed that also the molecular characteristics of litter derived DOM varies at different stages during root and needle decomposition. For this study we analyzed the chemical composition of root and leaf samples of 6 temperate tree species during one year of litter decomposition in a laboratory incubation. During this long-term experiment we measured continuously carbon and nitrogen contents of the water extracts and the remaining residues, C mineralization rates, and the chemical composition of water extracts and residues by Curie-point pyrolysis mass spectrometry with TMAH We focused on the following questions: (I) How mobile are molecules derived from plant polymers like tannin, lignin, suberin and cutin? (II) How does the composition of root and leaf derived DOM change over time in dependence on the stage of decomposition and species? Litter derived DOM was generally dominated by aromatic compounds. Substituded fatty acids as typically cutin or suberin derived were not detected in the water extracts. Fresh leaf and

  14. Migration of photoinitiators by gas phase into dry foods.

    PubMed

    Rodríguez-Bernaldo de Quirós, Ana; Paseiro-Cerrato, Rafael; Pastorelli, Sarah; Koivikko, Riitta; Simoneau, Catherine; Paseiro-Losada, Perfecto

    2009-11-11

    Photoinitiators are components widely used in UV-cured inks for printing food packaging. In the present study, the migration of seven photoinitiators through the vapor phase was investigated. To perform the migration test, an additive enriched polyethylene wax was used as a source to release photoinitiators. The method was applied to evaluate the migration of the photoinitiators into five selected dry foods (cake, bread, cereals, rice and pasta). The highest level of migration was found in the cake. Parameters affecting the migration process were evaluated, and high migration level was found to correlate with both the porosity and the fat content. In addition, the kinetics of migration of the photoinitiators from the additive enriched wax into the cake were studied under accelerated conditions.

  15. Imidazole and imidazolium porphyrins: gas-phase chemistry of multicharged ions.

    PubMed

    Ramos, Catarina I V; Pereira, Patrícia M R; Santana-Marques, M Graça; De Paula, Rodrigo; Simões, Mário M Q; Neves, M Graça P M S; Cavaleiro, José A S

    2014-05-01

    Electrospray ionization mass spectrometry/mass spectrometry in the positive ion mode was used to investigate the gas-phase chemistry of multicharged ions from solutions of porphyrins with 1,3-dimethylimidazolium-2-yl (DMIM) and 1-methylimidazol-2-yl (MIm) meso-substituents. The studied compounds include two free bases and 12 complexes with transition metals (Cu(II), Zn(II), Mn(III), and Fe(III)). The observed multicharged ions are either preformed or formed during the electrospraying process by reduction or protonation and comprise closed-shell and hypervalent mono-radical and bi-radical ions. The observed extensive and abundant fragmentation of the DMIM and MIm meso-substituents is a characteristic feature of these porphyrins. Fragments with the same mass values can be lost from the meso-substituents either as charged or neutral species and from closed-shell and hypervalent radical ions. Reduction processes are observed for both the free bases and the metallated DMIM porphyrins and occur predominantly by formation of hypervalent radicals that fragment, at low energy collisions, by loss of methyl radicals with formation of the corresponding MIm functionalities. These findings confirm that, when using electrospray ionization, reduction is an important characteristic of cationic meso-substituted tetrapyrrolic macrocycles, always occurring when delocalization of the formed hypervalent radicals is possible. For the Fe(III) and Mn(III) complexes, reduction of the metal centers is also observed as the predominant fragmentation of the corresponding reduced ions through losses of charged fragments testifies. The fragmentation of the closed-shell ions formed by protonation of the MIm porphyrins mirrors the fragmentation of the closed-shell ions of their DMIM counterparts.

  16. Intermolecular interactions of trifluorohalomethanes with Lewis bases in the gas phase: An ab initio study

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Siang; Yin, Chih-Chien; Chao, Sheng D.

    2014-10-01

    We perform an ab initio computational study of molecular complexes with the general formula CF3X—B that involve one trifluorohalomethane CF3X (X = Cl or Br) and one of a series of Lewis bases B in the gas phase. The Lewis bases are so chosen that they provide a range of electron-donating abilities for comparison. Based on the characteristics of their electron pairs, we consider the Lewis bases with a single n-pair (NH3 and PH3), two n-pairs (H2O and H2S), two n-pairs with an unsaturated bond (H2CO and H2CS), and a single π-pair (C2H4) and two π-pairs (C2H2). The aim is to systematically investigate the influence of the electron pair characteristics and the central atom substitution effects on the geometries and energetics of the formed complexes. The counterpoise-corrected supermolecule MP2 and coupled-cluster single double with perturbative triple [CCSD(T)] levels of theory have been employed, together with a series of basis sets up to aug-cc-pVTZ. The angular and radial configurations, the binding energies, and the electrostatic potentials of the stable complexes have been compared and discussed as the Lewis base varies. For those complexes where halogen bonding plays a significant role, the calculated geometries and energetics are consistent with the σ-hole model. Upon formation of stable complexes, the C-X bond lengths shorten, while the C-X vibrational frequencies increase, thus rendering blueshifting halogen bonds. The central atom substitution usually enlarges the intermolecular bond distances while it reduces the net charge transfers, thus weakening the bond strengths. The analysis based on the σ-hole model is grossly reliable but requires suitable modifications incorporating the central atom substitution effects, in particular, when interaction components other than electrostatic contributions are involved.

  17. Efficient and directed peptide bond formation in the gas phase via ion/ion reactions.

    PubMed

    McGee, William M; McLuckey, Scott A

    2014-01-28

    Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase-labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing "anchor" peptide to form an amide bond by protonating the anchor peptide's basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase.

  18. Effect of additives on gas-phase catalysis with immobilised Thermoanaerobacter species alcohol dehydrogenase (ADH T).

    PubMed

    Trivedi, A H; Spiess, A C; Daussmann, T; Büchs, J

    2006-07-01

    This paper presents a strategy for preparing an efficient immobilised alcohol dehydrogenase preparation for a gas-phase reaction. The effects of additives such as buffers and sucrose on the immobilisation efficiency (residual activity and protein loading) and on the gas-phase reaction efficiency (initial reaction rate and half-life) of Thermoanaerobacter sp. alcohol dehydrogenase were studied. The reduction of acetophenone to 1-phenylethanol under in situ cofactor regeneration using isopropanol as co-substrate was used as a model reaction at fixed reaction conditions (temperature and thermodynamic activities). A strongly enhanced thermostability of the enzyme in the gas-phase reaction was achieved when the enzyme was immobilised with 50 mM phosphate buffer (pH 7) containing sucrose five times the protein amount (on weight/weight basis). This resulted in a remarkable productivity of 200 g L(-1) day(-1) even at non-optimised reaction conditions. The interaction of additives with the enzyme and water affects the immobilisation and gas-phase efficiencies of the enzyme. However, it was not possible to predict the effect of additives on the gas-phase reaction efficiency even after knowing their effect on the immobilisation efficiency.

  19. Transferring Ions from Solution to the Gas Phase: The Two Basic Principles

    NASA Astrophysics Data System (ADS)

    Teunissen, Sebastiaan F.; Eberlin, Marcos N.

    2017-08-01

    The efficient formation of gaseous ions is the crucial step in all successful mass spectrometric experiments. The invention of electrospray ionization (ESI) has strongly facilitated this step by transferring preformed ions directly from solution to the gas phase - thereby circumventing the need to first convert analytes to the gas phase and then ionize them - and therefore ESI has become an extremely useful and widely applied MS technique. The invention of sonic spray ionization (SSI) has also allowed for the transfer of ions from solution into the gas phase, but without the assistance of a voltage or heating. Numerous ionization techniques, using similar principles to those applied in either ESI or SSI, have subsequently been developed. Although experimental conditions used in such techniques vary markedly, herein we argue that they are all based on either one of two basic principles by which ions can be transferred from solution to the gas phase, that is: via (1) neutralizing the counter ion, or (2) separating the ions. We have selected 35 such techniques and categorized them accordingly. This article thereby aims to establish the basic principles by which gaseous ions can be obtained from solvated ions. We further propose that any new ionization technique used to transfer solvated ions to the gas phase will similarly fall into one of these two mechanistic categories. [Figure not available: see fulltext.

  20. Formation of complex organic molecules in cold objects: the role of gas-phase reactions

    NASA Astrophysics Data System (ADS)

    Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

    2015-04-01

    While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ≳ 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

  1. Impact of pore characteristics of silica materials on loading capacity and release behavior of ibuprofen.

    PubMed

    Numpilai, Thanapha; Muenmee, Suthaporn; Witoon, Thongthai

    2016-02-01

    Impact of pore characteristics of porous silica supports on loading capacity and release behavior of ibuprofen was investigated. The porous silica materials and ibuprofen-loaded porous silica materials were thoroughly characterized by N2-sorption, thermal gravimetric and derivative weight analyses (TG-DTW), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) to determine the physical properties of materials, amount of ibuprofen adsorbed and position of ibuprofen. The detailed characterization reveals that the ibuprofen molecules adsorbed inside the mesopores. Increasing the mesopore size from 5nm to 10nm increased the ibuprofen loading from 0.74 to 0.85mmol/g, respectively. Incorporation of macropore into the structure of porous silica materials enhanced the ibuprofen loading capacity of 11.8-20.3%. The ibuprofen-loaded bimodal meso-macroporous silica materials exhibited the highest dissolution of 92wt.% within an hour. The ibuprofen particles deposited on the external surface of the porous silica materials showed a lower dissolution rate than the ibuprofen adsorbed inside the mesopores due to the formation of ibuprofen crystalline.

  2. Cumulative release characteristics of controlled-release nitrogen and potassium fertilizers and their effects on soil fertility, and cotton growth

    PubMed Central

    Yang, Xiuyi; Geng, Jibiao; Li, Chengliang; Zhang, Min; Tian, Xiaofei

    2016-01-01

    To investigate the interacting effects of polymer coated urea (PCU) and polymer coated potassium chloride (PCPC) on cotton growth, an experiment was conducted with containerized plants in 2014 and 2015. There were two kinds of nitrogen fertilizer, PCU and urea, which were combined with PCPC at three application rates (40, 80 and 120 kg ha−1). The kinds of nitrogen fertilizer formed the main plot, while individual rates of PCPC were the subplots. The results suggested N and K release patterns for PCU and PCPC in the soil were closely matched to the N and K requirements by cotton. Soil inorganic nitrogen contents significantly increased by using PCU instead of urea, and the same trend was observed with soil available potassium contents, which also had increased rates. Meanwhile, the number of bolls and lint yields of cotton in the PCU treatments were 4.9–35.3% and 2.9–40.7% higher than from urea treatments. Lint yields also increased by 9.1–12.7% with PCPC80 and PCPC120 treatments compared with PCPC40 treatment at the same nitrogen type. Hence, application of PCU combined with 80 kg ha−1 of PCPC fertilizer on cotton increased the yields and fertilizer use efficiencies in addition to improving fiber quality and delaying leaf senescence. PMID:27966638

  3. Cumulative release characteristics of controlled-release nitrogen and potassium fertilizers and their effects on soil fertility, and cotton growth.

    PubMed

    Yang, Xiuyi; Geng, Jibiao; Li, Chengliang; Zhang, Min; Tian, Xiaofei

    2016-12-14

    To investigate the interacting effects of polymer coated urea (PCU) and polymer coated potassium chloride (PCPC) on cotton growth, an experiment was conducted with containerized plants in 2014 and 2015. There were two kinds of nitrogen fertilizer, PCU and urea, which were combined with PCPC at three application rates (40, 80 and 120 kg ha(-1)). The kinds of nitrogen fertilizer formed the main plot, while individual rates of PCPC were the subplots. The results suggested N and K release patterns for PCU and PCPC in the soil were closely matched to the N and K requirements by cotton. Soil inorganic nitrogen contents significantly increased by using PCU instead of urea, and the same trend was observed with soil available potassium contents, which also had increased rates. Meanwhile, the number of bolls and lint yields of cotton in the PCU treatments were 4.9-35.3% and 2.9-40.7% higher than from urea treatments. Lint yields also increased by 9.1-12.7% with PCPC80 and PCPC120 treatments compared with PCPC40 treatment at the same nitrogen type. Hence, application of PCU combined with 80 kg ha(-1) of PCPC fertilizer on cotton increased the yields and fertilizer use efficiencies in addition to improving fiber quality and delaying leaf senescence.

  4. Discovery of the Methoxy Radical, CH3O, toward B1: Dust Grain and Gas-phase Chemistry in Cold Dark Clouds

    NASA Astrophysics Data System (ADS)

    Cernicharo, J.; Marcelino, N.; Roueff, E.; Gerin, M.; Jiménez-Escobar, A.; Muñoz Caro, G. M.

    2012-11-01

    We report on the discovery of the methoxy radical (CH3O) toward the cold and dense core B1-b based on the observation, with the IRAM 30 m radio telescope, of several lines at 3 and 2 mm wavelengths. Besides this new molecular species we also report on the detection of many lines arising from methyl mercaptan (CH3SH), formic acid (HCOOH), propynal (HCCCHO), acetaldehyde (CH3CHO), dimethyl ether (CH3OCH3), methyl formate (CH3OCOH), and the formyl radical (HCO). The column density of all these species is sime1012 cm-2, corresponding to abundances of sime10-11. The similarity in abundances for all these species strongly suggest that they are formed on the surface of dust grains and ejected to the gas phase through non-thermal desorption processes, most likely cosmic rays or secondary photons. Nevertheless, laboratory experiments indicate that the CH3O isomer released to the gas phase is CH2OH rather than the methoxy one. Possible gas-phase formation routes to CH3O from OH and methanol are discussed. This work was based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  5. Evaluation of in vitro release rate and in vivo absorption characteristics of four metoprolol tartrate immediate-release tablet formulations.

    PubMed

    Rekhi, G S; Eddington, N D; Fossler, M J; Schwartz, P; Lesko, L J; Augsburger, L L

    1997-02-01

    The purpose of this investigation was to examine the impact of formulation and process changes on dissolution and bioavailability/bioequivalency of metoprolol tartrate tablets manufactured using a high-shear granulation process. A half-factorial (2(4-1), Res IV) design was undertaken to study the selected formulation and processing variables during scale-up. Levels and ranges for excipients and processing changes studied represented level 2 or greater changes as indicated by the SUPAC-IR Guidance. Blend and tableting properties were evaluated. Changes in sodium starch glycolate and magnesium stearate levels, and the order of addition microcrystalline cellulose (intra- vs. extragranular) were significant only in affecting percent drug released (Q) in 5, 10, and 15 min. Statistical analysis of data showed no significant curvature. No interaction effects were found to be statistically significant. To examine the impact of formulation and processing variables on in vivo absorption, three batches were selected for a bioavailability study based on their dissolution profiles. Subjects received four metoprolol treatments (Lopressor, slow-, medium-, and fast-dissolving formulations) separated by 1 week according to a randomized crossover design. After an overnight fast, subjects were administered one tablet (100 mg), blood samples were collected over 24 hr and plasma samples were analyzed. The formulations were found to be bioequivalent with respect to the log Cmax and log AUC0-infinity. The results of this study suggest that: (i) bioavailability/bioequivalency studies may not be necessary for metoprolol tartrate and perhaps other class 1 drugs after level 2 type changes and (ii) in vitro dissolution tests may be used to show bioequivalence of metoprolol formulations with processing or formulation changes within the specified level 2 ranges for the equipment examined.

  6. Photooxygenation and gas-phase reactivity of multiply threaded pseudorotaxanes.

    PubMed

    Nowosinski, Karol; Warnke, Stephan; Pagel, Kevin; Komáromy, Dávid; Jiang, Wei; Schalley, Christoph A

    2016-04-01

    The solution-phase photooxygenation of multiply threaded crown/ammonium pseudorotaxanes containing anthracene spacers is monitored by electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometry. The oxygenated pseudorotaxanes are mass-selected and fragmented by infrared multiphoton dissociation (IRMPD) and/or collision-induced dissociation (CID) experiments and and their behavior compared to that of the non-oxygenated precursors. [4+2]Cycloreversion reactions lead to the loss of O2, when no other reaction channel with competitive energy demand is available. Thus, the release of molecular oxygen can serve as a reference reaction for the energy demand of other fragmentation reactions such as the dissociation of the crown/ammonium binding motifs. The photooxygenation induces curvature into the initially planar anthracene and thus significantly changes the geometry of the divalent, anthracene-spacered wheel. This is reflected in ion-mobility data. Coulomb repulsion in multiply charged pseudorotaxanes assists the oxygen loss as the re-planarization of the anthracene increases the distance between the two charges. Copyright © 2016 John Wiley & Sons, Ltd.

  7. Characteristics of nitrogen release from synthetic zeolite Na-P1 occluding NH4NO3.

    PubMed

    Park, Man; Kim, Jong Su; Choi, Choong Lyeal; Kim, Jang-Eok; Heo, Nam Ho; Komarneni, Sridhar; Choi, Jyung

    2005-08-18

    Zeolites can accommodate a considerable amount of occluded salt such as NH4NO3, which can serve as a good source of slow-release plant nutrient. This study evaluates the kinetics of ion release from NH4NO3-occluded Na-P1 (N-NaP) using a simulated soil solution and deionized water as leaching solutions. The patterns of ion releases were examined as a function of leaching time under both static and continuous-flow conditions for more than one month. Releases of both NH4+ and NO3- from N-NaP were found to be slow and steady under both the above conditions. The soil solution affected the release of NH4+ and NO3- differently, while deionized water released nearly the same equivalents of these ions. This clearly indicates that ion release from salt-occluded zeolite involves two different reactions, cation exchange and dissolution. The kinetics of ion release from occluded NH4NO3 under static condition was best described by the standard Elovich model while the power function model best expressed these under continuous-flow condition. The initial ion release patterns under both conditions exhibited considerable deviation from the simulated models, probably as a result of the presence of hydrated occluded NH4NO3. Flow condition and the presence of electrolytes in leaching solution affected the release kinetics significantly. Release of occluded NH4NO3 was delayed by the presence of the NH4NO3 coated on zeolite crystals. These results indicate that the ion release property of occluded salt could be predicted and controlled. This study clearly shows that NH4NO3-occluded zeolites could be developed as slow release fertilizers.

  8. Gas-phase and liquid-phase pre-irradiation grafting of AAc onto LDPE and HDPE films for pervaporation membranes

    NASA Astrophysics Data System (ADS)

    Zhigong, Rao; Guixiang, Li; Sugo, Takanobu; Okamoto, Jiro

    A study has been made on gas-phase and liquid-phase pre-irradiation grafting of acrylic acid onto LDPE and HDPE films for pervaporation membranes of ethanol-water mixtures. It was found that the degree of grafting, percent volume change of grafted membranes and length of grafting chains depend on the methods of grafting, crystal state of substrate films and diffusion rate of the monomer in the films. The pervaporation characteristics of grafted membranes is influenced directly by the surface hydrophilicity of grafted membranes, temperature of the feed, degree of grafting, crosslinking of grafted chains and alkaline metal ions in the functional groups. The potassium ion exchange membrane of HDPE synthesized by gas-phase grafting has better pervaporation efficiency. At 80 wt% ethanol in the feed, 25°C feed temperature and 70% degree of grafting a grafted membrane has a 0.65 kg/m 2h flux and a separation factor of 20.

  9. Structural effect of the in situ generated titania on its ability to oxidize and capture the gas-phase elemental mercury.

    PubMed

    Lee, Tai Gyu; Hyun, Jung Eun

    2006-01-01

    Structural effect of the in situ generated TiO(2) sorbent particle was examined for its ability to capture elemental mercury under UV irradiation in a simulated combustion flue gas. Titania particles were prepared by thermal gas-phase oxidation of Titanium (IV) isopropoxide (TTIP) using a high temperature electric furnace reactor. The structural characteristics of the in situ generated TiO(2) at various synthesis temperatures were investigated; size distribution and the geometric mean diameter were measured using a scanning mobility particle sizer, while fractal dimension and radius of gyration were evaluated from the transmission electron microscopy images. Results from the Hg(0) capture experiment show that with increasing titania synthesis temperature, the overall aggregate size increases and the morphology becomes more open-structured to gas-phase Hg(0) and UV light, resulting in the improved mercury removal capability.

  10. Device for two-dimensional gas-phase separation and characterization of ion mixtures

    DOEpatents

    Tang, Keqi; Shvartsburg, Alexandre A.; Smith, Richard D.

    2006-12-12

    The present invention relates to a device for separation and characterization of gas-phase ions. The device incorporates an ion source, a field asymmetric waveform ion mobility spectrometry (FAIMS) analyzer, an ion mobility spectrometry (IMS) drift tube, and an ion detector. In one aspect of the invention, FAIMS operating voltages are electrically floated on top of the IMS drift voltage. In the other aspect, the FAIMS/IMS interface is implemented employing an electrodynamic ion funnel, including in particular an hourglass ion funnel. The present invention improves the efficiency (peak capacity) and sensitivity of gas-phase separations; the online FAIMS/IMS coupling creates a fundamentally novel two-dimensional gas-phase separation technology with high peak capacity, specificity, and exceptional throughput.

  11. Gas phase diffusion coefficients of reactive trace gases in the atmosphere

    NASA Astrophysics Data System (ADS)

    Tang, Mingjin; Shiraiwa, Manabu; Cox, Tony; Pöschl, Ulrich; Kalberer, Markus

    2015-04-01

    Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions. However, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. We have compiled and evaluated, for the first time, the diffusivities (pressure independent diffusion coefficients) of atmospheric inorganic (Tang et al., 2014) and organic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed.

  12. Direct observation of the gas-phase Criegee intermediate (CH2OO).

    PubMed

    Taatjes, Craig A; Meloni, Giovanni; Selby, Talitha M; Trevitt, Adam J; Osborn, David L; Percival, Carl J; Shallcross, Dudley E

    2008-09-10

    Carbonyl oxide species play a key role in tropospheric oxidation of organic molecules and in low-temperature combustion processes. In the late 1940s, Criegee first postulated the participation of carbonyl oxides, now often called "Criegee intermediates," in ozonolysis of alkenes. However, despite decades of effort, no gas phase Criegee intermediate has before been observed. As a result, knowledge of gas phase carbonyl oxide reactions has heretofore been inferred by indirect means, with derived rate coefficients spanning orders of magnitude. We have directly detected the primary Criegee intermediate, formaldehyde oxide (CH2OO), in the chlorine-initiated gas-phase oxidation of dimethyl sulfoxide (DMSO). This work not only establishes that the Criegee intermediate is formed in DMSO oxidation also but opens the possibility for explicit kinetics studies on this critical atmospheric species.

  13. Oxidation of formic acid on the Pt(111) surface in the gas phase.

    PubMed

    Gao, Wang; Keith, John A; Anton, Josef; Jacob, Timo

    2010-09-28

    Formic acid (HCOOH) oxidation on Pt(111) under gas-phase conditions is a benchmark heterogeneous catalysis reaction used to probe electro-catalytic HCOOH conversion in fuel cells, itself an important reaction in energy conversion. We used density functional theory (DFT) calculations to elucidate the fundamental oxidation mechanisms of HCOOH in the gas phase, determining the relative strengths of chemical interactions between HCOOH oxidation intermediates and the Pt(111) surface. We focused on investigating how water and adsorption coverage affects reaction intermediate structures and transition states. Our results show that adsorbed HCOO is a reactive intermediate in gas phase, and co-adsorbed water plays a key role in HCOOH oxidation influencing the structure of reaction intermediates and reaction barriers on Pt(111). The simulations show the preferred catalytic pathway is qualitatively dependent on surface coverage. These results provide a conceptual basis to better interpret its complicated experimental reaction kinetics.

  14. Insights into diastereoisomeric characterization of tetrahydropyridazine amino acid derivatives: crystal structures and gas phase ion chemistry.

    PubMed

    Giorgi, Gianluca; Favi, Gianfranco; Attanasi, Orazio A

    2013-08-14

    Structural, conformational properties, and gas phase reactivity of two representative diastereoisomeric members of a series of α,α-tetrahydropyridazine amino acid derivatives have been investigated by using X-ray crystallography, tandem mass spectrometry and theoretical calculations. Both diastereoisomers show an unusual screw-boat conformation of the tetrahydropyridazine ring. While protonated molecules mainly decompose in the gas phase by loss of acetamide, the main reactivity of the [M + Na](+) species consists of loss of PhNCO followed by acetamide and it is strictly dependent upon the stereochemistry of the parent compound. The most stable energy minimized structures obtained by theoretical calculations are in full agreement with the experimental data and allowed us to rationalize the gas phase reaction pathways.

  15. Influence of gas phase equilibria on the chemical vapor deposition of graphene.

    PubMed

    Lewis, Amanda M; Derby, Brian; Kinloch, Ian A

    2013-04-23

    We have investigated the influence of gas phase chemistry on the chemical vapor deposition of graphene in a hot wall reactor. A new extended parameter space for graphene growth was defined through literature review and experimentation at low pressures (≥0.001 mbar). The deposited films were characterized by scanning electron microscopy, Raman spectroscopy, and dark field optical microscopy, with the latter showing promise as a rapid and nondestructive characterization technique for graphene films. The equilibrium gas compositions have been calculated across this parameter space. Correlations between the graphene films grown and prevalent species in the equilibrium gas phase revealed that deposition conditions associated with a high acetylene equilibrium concentration lead to good quality graphene deposition, and conditions that stabilize large hydrocarbon molecules in the gas phase result in films with multiple defects. The transition between lobed and hexagonal graphene islands was found to be linked to the concentration of the monatomic hydrogen radical, with low concentrations associated with hexagonal islands.

  16. Native biomolecules in the gas phase? The case of green fluorescent protein.

    PubMed

    Frankevich, Vladimir; Barylyuk, Konstantin; Chingin, Konstantin; Nieckarz, Robert; Zenobi, Renato

    2013-04-02

    Green fluorescent protein (GFP) was ionized by native electrospray ionization and trapped for many seconds in high vacuum, allowing fluorescence emission to be measured as a probe of its biological function, to answer the question whether GFP exists in the native form in the gas phase or not. Although a narrow charge-state distribution, a collision cross-section very close to that expected for correctly folded GFP, and a large stability against dissociation all support a near-native gas-phase structure, no fluorescence emission was observed. The loss of the native form is attributed to the absence of residual water in the gas phase, which normally stabilizes the para-hydroxybenzylidene imidazolone chromophore of GFP.

  17. OMVPE growth and gas-phase reactions of AlGaN for UV emitters

    SciTech Connect

    Han, J.; Figiel, J.J.; Crawford, M.H.; Banas, M.A.; Bartram, M.E.; Biefeld, R.M.; Song, Y.K.; Nurmikko, A.V.

    1998-06-01

    Gas-phase parasitic reactions among TMG, TMA, and NH3, are investigated by monitoring of the growth rate/incorporation efficiency of GaN and AlN using an in-situ optical reflectometer. It is suggested that gas phase adduct (TMA: NH{sub 3}) reactions not only reduce the incorporation efficiency of TMA but also affect the incorporation behavior of TMGa. The observed phenomena can be explained by either a synergistic gas-phase scavenging effect or a surface site-blocking effect. Relatively low reactor pressures (30--50 Torr) are employed to grow an AlGaN/GaN QW p-n diode structure. The UV emission at 354 nm (FWHM {approximately} 6 nm) represents the first report of LED operation from an indium-free GaN QW diode.

  18. Experimental study of Gas Phase Formation and Evolution in Low fO2 Planetary Basalts.

    NASA Astrophysics Data System (ADS)

    Rutherford, M. J.; Wetzel, D. T.; Saal, A. E.; Hauri, E. H.

    2012-12-01

    The existence of a gas phase in planetary basaltic magmas is demonstrated by the ubiquitous presence of vesicles in returned lunar samples and meteorites as well as basalts from Earth and Mars. Additionally, formation of the fine-grained glass bead deposits during eruption of lunar picritic glasses required a large gas-bubble volume (> 90%) at the time of eruption/fragmentation. Up to 100-200 ppm levels of H, S, Cl and F still remain as diffusion-loss profiles in individual lunar glass beads SIMS (1), and higher volatile concentrations occur in olivine melt inclusions (2). The composition and origin of such volcanic gases were investigated by experiments on a volatile (C-O-H-S-Cl-F)-bearing picritic glass composition as a function of fO2 near iron-wustite (IW). The C-O-H species dissolved in gas-saturated basaltic melt above IW-0.5 are carbonate, OH and H2O with 100 to 10,000 ppm H2O in the sample; below IW-0.5, the C-species present (Raman and FTIR) are Fe(CO)5 (iron pentacarbonyl) and lesser CH4 [3]. The change in melt speciation in part reflects a change in calculated speciation in the coexisting gas [4]. The carbon solubility in these experimental melts increases linearly with increasing pressure; the more oxidized glasses contain 32-620 ppm C for pressures of 98 to 980 MPa, the reduced glasses contain 8-240 ppm C for pressures between 36 and 900 MPa. Thus, the C solubility of the more reduced Fe-carbonyl and CH4 is about one-half that of carbonate at the same pressure, and indicates the carrying capacity for C in reduced (i.e., lunar) magmas is much lower than it is in present day terrestrial magmas. Varioles up to 200 um in diameter formed in some experiments with higher dissolved water contents (1%); they have radiating crystalline textures (olivine, glass and poorly crystallized graphite) initiated at a central nucleation site. A sharp peak in the variole Ramen spectra indicates methane as well as CO is released during variole formation and a reaction such

  19. Dynamics of gas-phase trichloramine (NCl3) in chlorinated, indoor swimming pool facilities.

    PubMed

    Weng, S-C; Weaver, W A; Afifi, M Zare; Blatchley, T N; Cramer, J S; Chen, J; Blatchley, E R

    2011-10-01

    Trichloramine (NCl(3)) is recognized as an irritant of the human respiratory system and other tissues. Processes that lead to volatilization from the liquid phase allow for human exposure to gas-phase NCl(3) in swimming pool settings. The dynamics of these processes are not well defined. A N,N-diethyl-p-phenylenediamine/potassium iodide (DPD/KI)-based wet-chemistry method for measuring gas-phase NCl(3) concentration was verified and applied in chlorinated, indoor swimming pool facilities. Other gas-phase oxidants in the air of indoor pools provided interference of 15% or less. The DPD/KI method was applied for the measurement of gas-phase NCl(3) in four chlorinated, indoor swimming pool facilities. All results showed a correlation between bather loading and gas-phase NCl(3) concentration. The nature of swimmer activities also influenced air quality, presumably because of the effects of these activities on mixing near the gas-liquid interface. The activities of swimmers promote transfer of volatile compounds from water to the surrounding air. For chlorinated, indoor pool facilities, this can lead to exposure to gas-phase chemicals that can cause irritation of the respiratory system and other tissues. The focus of this study was on NCl(3), a common disinfection by-product (DBP) in chlorinated pools. However, the conditions that promote NCl(3) transfer are likely to promote transfer of other volatile chemicals from water to air. As such, it is possible that other DBPs formed in pools may also contribute to diminished air quality. © 2011 John Wiley & Sons A/S.

  20. Strategies for the Gas Phase Modification of Cationized Arginine via Ion/ion Reactions.

    PubMed

    Prentice, Boone M; McGee, William M; Stutzman, John R; McLuckey, Scott A

    2013-11-15

    The gas phase acetylation of cationized arginine residues is demonstrated here using ion/ion reactions with sulfosuccinimidyl acetate (sulfo-NHS acetate) anions. Previous reports have demonstrated the gas phase modification of uncharged primary amine (the N-terminus and ε-amino side chain of lysine) and uncharged guanidine (the arginine side chain) functionalities via sulfo-NHS ester chemistry. Herein, charge-saturated arginine-containing peptides that contain sodium ions as the charge carriers, such as [ac-ARAAARA+2Na](2+), are shown to exhibit strong reactivity towards sulfo-NHS acetate whereas the protonated peptide analogues exhibit no such reactivity. This difference in reactivity is attributed to the lower sodium ion (as compared to proton) affinity of the arginine, which results in increased nucleophilicity of the cationized arginine guanidinium functionality. This increased nucleophilicity improves the arginine residue's reactivity towards sulfo-NHS esters and enhances the gas phase covalent modification pathway. No such dramatic increase in reactivity towards sulfo-NHS acetate has been observed upon sodium cationization of lysine amino acid residues, indicating that this behavior appears to be unique to arginine. The sodium cationization process is demonstrated in the condensed phase by simply spiking sodium chloride into the peptide sample solution and in the gas phase by a peptide-sodium cation exchange process with a sulfo-NHS acetate sodium-bound dimer cluster reagent. This methodology demonstrates several ways by which arginine can be covalently modified in the gas phase even when it is charged. Collisional activation of an acetylated arginine product can result in deguanidination of the residue, generating an ornithine. This gas phase ornithination exhibits similar site-specific fragmentation behavior to that observed with peptides ornithinated in solution and may represent a useful approach for inducing selective peptide cleavages.

  1. Amphipols Outperform Dodecylmaltoside Micelles in Stabilizing Membrane Protein Structure in the Gas Phase

    PubMed Central

    2014-01-01

    Noncovalent mass spectrometry (MS) is emerging as an invaluable technique to probe the structure, interactions, and dynamics of membrane proteins (MPs). However, maintaining native-like MP conformations in the gas phase using detergent solubilized proteins is often challenging and may limit structural analysis. Amphipols, such as the well characterized A8-35, are alternative reagents able to maintain the solubility of MPs in detergent-free solution. In this work, the ability of A8-35 to retain the structural integrity of MPs for interrogation by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is compared systematically with the commonly used detergent dodecylmaltoside. MPs from the two major structural classes were selected for analysis, including two β-barrel outer MPs, PagP and OmpT (20.2 and 33.5 kDa, respectively), and two α-helical proteins, Mhp1 and GalP (54.6 and 51.7 kDa, respectively). Evaluation of the rotationally averaged collision cross sections of the observed ions revealed that the native structures of detergent solubilized MPs were not always retained in the gas phase, with both collapsed and unfolded species being detected. In contrast, ESI-IMS-MS analysis of the amphipol solubilized MPs studied resulted in charge state distributions consistent with less gas phase induced unfolding, and the presence of lowly charged ions which exhibit collision cross sections comparable with those calculated from high resolution structural data. The data demonstrate that A8-35 can be more effective than dodecylmaltoside at maintaining native MP structure and interactions in the gas phase, permitting noncovalent ESI-IMS-MS analysis of MPs from the two major structural classes, while gas phase dissociation from dodecylmaltoside micelles leads to significant gas phase unfolding, especially for the α-helical MPs studied. PMID:25495802

  2. Probing the energetics of dissociation of carbonic anhydrase-ligand complexes in the gas phase.

    PubMed Central

    Gao, J; Wu, Q; Carbeck, J; Lei, Q P; Smith, R D; Whitesides, G M

    1999-01-01

    This paper describes the use of electrospray ionization-Fourier transform ion cyclotron mass spectrometry (ESI-FTICR-MS) to study the relative stabilities of noncovalent complexes of carbonic anhydrase II (CAII, EC 4.2.1.1) and benzenesulfonamide inhibitors in the gas phase. Sustained off-resonance irradiation collision-induced dissociation (SORI-CID) was used to determine the energetics of dissociation of these CAII-sulfonamide complexes in the gas phase. When two molecules of a benzenesulfonamide (1) were bound simultaneously to one molecule of CAII, one of them was found to exhibit significantly weaker binding (DeltaE50 = 0.4 V, where E50 is defined as the amplitude of sustained off-resonance irradiation when 50% of the protein-ligand complexes are dissociated). In solution, the benzenesulfonamide group coordinates as an anion to a Zn(II) ion bound at the active site of the enzyme. The gas phase stability of the complex with the weakly bound inhibitor was the same as that of the inhibitor complexed with apoCAII (i.e., CAII with the Zn(II) ion removed from the binding site). These results indicate that specific interactions between the sulfonamide group on the inhibitor and the Zn(II) ion on CAII were preserved in the gas phase. Experiments also showed a higher gas phase stability for the complex of para-NO2-benzenesulfonamide-CAII than that for ortho-NO2-benzenesulfonamide-CAII complex. This result further suggests that steric interactions of the inhibitors with the binding pocket of CAII parallel those in solution. Overall, these results are consistent with the hypothesis that CAII retains, at least partially, the structure of its binding pocket in the gas phase on the time scale (seconds to minutes) of the ESI-FTICR measurements. PMID:10354450

  3. Gas Phase Spectra and Structural Determination of Glucose 6 Phosphate Using Cryogenic Ion Vibrational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kregel, Steven J.; Voss, Jonathan; Marsh, Brett; Garand, Etienne

    2014-06-01

    Glucose-6-Phosphate (G6P) is one member of a class of simple phosphorylated sugars that are relevant in biological processes. We have acquired a gas phase infrared spectrum of G6P- using cryogenic ion vibrational spectroscopy (CIVS) in a home-built spectrometer. The experimental spectrum was compared with calculated vibrational spectra from a systematic conformer search. For both of the α and β anomers, results show that only the lowest energy conformers are present in the gas phase. If spectral signatures for similar sugars could be cataloged, it would allow for conformer-specific determination of mixture composition, for example, for glycolyzation processes.

  4. Gas-phase reactions in extraterrestrial environments: laboratory investigations by crossed molecular beams.

    PubMed

    Balucani, Nadia; Casavecchia, Piergiorgio

    2006-12-01

    We have investigated gas-phase reactions of N((2)D) with the most abundant hydrocarbons in the atmosphere of Titan by the crossed molecular beam technique. In all cases, molecular products containing a novel CN bond are formed, thus suggesting possible routes of formation of gas-phase nitriles in the atmosphere of Titan and primordial Earth. The same approach has been recently extended to the study of radical-radical reactions, such as the reaction of atomic oxygen with the CH(3) and C(3)H(5) radicals. Products other than those already considered in the modeling of planetary atmospheres and interstellar medium have been identified.

  5. Resonance Energy Transfer Relates the Gas-Phase Structure and Pharmacological Activity of Opioid Peptides.

    PubMed

    Kopysov, Vladimir; Boyarkin, Oleg V

    2016-01-11

    Enkephalins are efficient pain-relief drugs that bind to transmembrane opioid receptors. One key structural parameter that governs the pharmacological activity of these opioid peptides and is typically determined from condensed-phase structures is the distance between the aromatic rings of their Tyr and Phe residues. We use resonance energy transfer, detected by a combination of cold ion spectroscopy and mass spectrometry, to estimate the Tyr-Phe spacing for enkephalins in the gas phase. In contrast to the condensed-phase structures, these distances appear to differ substantially in enkephalins with different pharmacological efficiencies, suggesting that gas-phase structures might be a better pharmacophoric metric for ligand peptides.

  6. Gas phase infrared spectra and corresponding DFT calculations of α, ω-diphenylpolyenes

    NASA Astrophysics Data System (ADS)

    Biemann, Lars; Braun, Michaela; Kleinermanns, Karl

    2010-01-01

    We present gas phase Fourier Transform Infrared (FTIR) spectra of the homologue series of α, ω-diphenylpolyenes consisting of trans- and cis-stilbene, diphenylbutadiene (DPB) and diphenylhexatriene (DPH) obtained by a fast thermal heating technique that enables vaporization without decomposition. Infrared marker bands for the cis-isomers of the polyenes have been identified by density functional calculations at the B3LYP/TZVP level of theory. The all trans isomers of DPB and DPH do not interconvert to the cis-isomers in the gas phase at 200 °C.

  7. Fischer Indole Synthesis in the Gas Phase, the Solution Phase, and at the Electrospray Droplet Interface

    NASA Astrophysics Data System (ADS)

    Bain, Ryan M.; Ayrton, Stephen T.; Cooks, R. Graham

    2017-02-01

    Previous reports have shown that reactions occurring in the microdroplets formed during electrospray ionization can, under the right conditions, exhibit significantly greater rates than the corresponding bulk solution-phase reactions. The observed acceleration under electrospray ionization could result from a solution-phase, a gas-phase, or an interfacial reaction. This study shows that a gas-phase ion/molecule (or ion/ion) reaction is not responsible for the observed rate enhancement in the particular case of the Fischer indole synthesis. The results show that the accelerated reaction proceeds in the microdroplets, and evidence is provided that an interfacial process is involved.

  8. A New Paradigm to Identify Reaction Pathways in Gas-phase

    DTIC Science & Technology

    2015-04-27

    AFRL-OSR-VA-TR-2015-0167 A New Paradigm to Identify Reaction Pathways in Gas-phase Angela Violi UNIVERSITY OF MICHIGAN 04/29/2015 Final Report...DATES COVERED (From - To) 01 FEB 2013 - 30 JAN 2015 4. TITLE AND SUBTITLE A New Paradigm to Identify Reaction Pathways in Gas-phase 5a. CONTRACT NUMBER...makes the heuristic search of the most likely reactions an unfeasible task even with today’s computer power. As a consequence, the main advancements in

  9. Study of Hind Limb Tissue Gas Phase Formation in Response to Suspended Adynamia and Hypokinesia

    NASA Technical Reports Server (NTRS)

    Butler, Bruce D.

    1996-01-01

    The purpose of this study was to investigate the hypothesis that reduced joint/muscle activity (hypo kinesia) as well as reduced or null loading of limbs (adynamia) in gravity would result in reduced decompression-induced gas phase and symptoms of decompression sickness (DCS). Finding a correlation between the two phenomena would correspond to the proposed reduction in tissue gas phase formation in astronauts undergoing decompression during extravehicular activity (EVA) in microgravity. The observation may further explain the reported low incidence of DCS in space.

  10. Liquid-gas phase transitions in a multicomponent nuclear system with Coulomb and surface effects

    SciTech Connect

    Lee, S. J.; Mekjian, A. Z.

    2001-04-01

    The liquid-gas phase transition is studied in a multicomponent nuclear system using a local Skyrme interaction with Coulomb and surface effects. Some features are qualitatively the same as the results of Mu''ller and Serot where a relativistic mean field was used without Coulomb and surface effects. Surface tension brings the coexistence binodal surface to lower pressure. The Coulomb interaction makes the binodal surface smaller and causes another pair of binodal points at low pressure and large proton fraction with fewer protons in the liquid phase and more protons in the gas phase.

  11. Gas-phase formation of silicon carbides, oxides, and sulphides from atomic silicon ions

    NASA Technical Reports Server (NTRS)

    Bohme, Diethard K.; Wlodek, Stanislaw; Fox, Arnold

    1989-01-01

    A systematic experimental study of the kinetics and mechanisms of the chemical reactions in the gas phase between ground-state Si(+)2p and a variety of astrophysical molecules. The aim of this study is to identify the reactions which trigger the formation of chemical bonds between silicon and carbon, oxygen and sulphur, and the chemical pathways which lead to further molecular growth. Such knowledge is valuable in the identification of new extraterrestrial silicon-bearing molecules and for an assessment of the gas-phase transition from atomic silicon to silicon carbide and silicate grain particles in carbon-rich and oxygen-rich astrophysical environments.

  12. Order from the disorder: hierarchical nanostructures self-assembled from the gas phase (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Di Fonzo, Fabio

    2017-02-01

    The assembly of nanoscale building blocks in engineered mesostructures is one of the fundamental goals of nanotechnology. Among the various processes developed to date, self-assembly emerges as one of the most promising, since it relays solely on basic physico-chemical forces. Our research is focused on a new type of self-assembly strategy from the gas-phase: Scattered Ballistic Deposition (SBD). SBD arises from the interaction of a supersonic molecular beam with a static gas and enables the growth of quasi-1D hierarchical mesostructures. Overall, they resemble a forest composed of individual, high aspect-ratio, tree-like structures, assembled from amorphous or crystalline nanoparticles. SBD is a general occurring phenomenon and can be obtained with different vapour or cluster sources. In particular, SBD by Pulsed Laser Deposition is a convenient physical vapor technique that allows the generation of supersonic plasma jets from any inorganic material irrespective of melting temperature, preserving even the most complex stoichiometries. One of the advantages of PLD over other vapour deposition techniques is extremely wide operational pressure range, from UHV to ambient pressure. These characteristics allowed us to develop quasi-1D hierarchical nanostructures from different transition metal oxides, semiconductors and metals. The precise control offered by the SBD-PLD technique over material properties at the nanoscale allowed us to fabricate ultra-thin, high efficiency hierarchical porous photonic crystals with Bragg reflectivity up to 85%. In this communication we will discuss the application of these materials to solar energy harvesting and storage, stimuli responsive photonic crystals and smart surfaces with digital control of their wettability behaviour.

  13. Time-slice last millennium experiments with interactive gas-phase chemistry and aerosols

    NASA Astrophysics Data System (ADS)

    Tsigaridis, K.; Legrande, A. N.; Koch, D. M.

    2010-12-01

    Preliminary results from coupled atmosphere-ocean simulations with interactive gas-phase chemistry and aerosols are presented. These experiments are decadal scale time-slices within millennial-length simulations performed with the GISS GCM (ModelE), using two different ocean models. The boundary conditions for the transient simulations follow the last millennium coordinated PMIP3 experiment protocol. This experiment directly links in with other pre-Industrial experiments being completed as part of IPCC AR5, using the same model and resolution as in GISS IPCC AR5. Preliminary time-slice results from the early medieval and Maunder Minimum periods will be presented. The impact of the presence of short-lived gases and aerosols on the simulated climate is studied. An initial attempt to identify previously omitted additional forcing mechanisms will be performed during these contrasting climate periods, in short duration experiments driven by ocean conditions from the transient experiments. The results presented are the initial runs from a larger set of experiments that will assess the climate impact of changes to dust, sea-salt, and ocean-derived sulfate, biomass burning ozone-precursors and aerosols, organic carbon, wetland methane emissions, and a final set with all components. These species are standard components in the GISS model’s 20th century simulations, so that we may compare millennial variability characteristics with those better constrained from more recent climate periods. Dust and sea-salt are wind-driven aerosols from deserts and oceans, sulfate comes from oxidation of volcanic and oceanic precursors, while organic carbon comes from biomass burning, secondary plant sources and primary oceanic emissions. Comparison of model and proxy records will test model-simulated mechanisms while the model provides insight into factors contributing to proxy variability. The addition of potentially important forcing mechanisms will enable a more comprehensive

  14. Coupled Variations in HNO3 and Soluble Gas Phase Chloride in the Houston Region

    NASA Astrophysics Data System (ADS)

    Dibb, J. E.; Corr, C. A.; Lefer, B. L.; Flynn, J. H.

    2010-12-01

    The University of New Hampshire mist chamber/ion chromatography (MC/IC) system was operated on the north Moody Tower as part of the Study of Houston Atmospheric and Radical Precursors (SHARP) during April-May, 2009. The MC/IC system provided 5-minute resolution measurements of HONO, HNO3, and soluble gas phase chloride (soluble Cl-) throughout the intensive campaign. Several other papers in this session discuss the HONO results, here we focus on HNO3, and soluble Cl-. These gases were highly correlated on short (minutes to hours time scales) throughout the SHARP campaign but anticorrelated when binned by broad wind direction sectors. Peak mixing ratios of HNO3, occurred during transport from the north and east and minima were observed under southerly flow, with the opposite true for soluble Cl-, yet strong correlation from sample to sample and diurnally were observed regardless of wind direction. It should be noted that the mixing ratios of soluble Cl- are substantial in Houston. Even during intervals with sustained northerly flow (relatively low Cl-) daytime maxima routinely exceeded 1 ppbv. Similar observations made during TexAQS 2006 on the Moody Tower and the NOAA vessel Ronald H Brown indicate that abundant soluble Cl-, linked with HNO3, by processes not yet understood, is characteristic of the Houston-Galveston Bay region during both spring and summer. Limited data on bulk aerosol composition at Moody Tower suggest that displacement of HCl from sea salt is not sufficient to account for all of the soluble Cl- observed in Houston.

  15. Exposure characteristics of ferric oxide nanoparticles released during activities for manufacturing ferric oxide nanomaterials.

    PubMed

    Xing, Mingluan; Zhang, Yuanbao; Zou, Hua; Quan, Changjian; Chang, Bing; Tang, Shichuan; Zhang, Meibian

    2015-02-01

    The exposure characteristics of Fe2O3 nanoparticles (NPs) released in a factory were investigated, as exposure data on this type of NP is absent. The nature of the particles was identified in terms of their concentrations [i.e. number concentration (NC(20-1000 nm)), mass concentration (MC(100-1000 nm)), surface area concentration (SAC(10-1000 nm))], size distribution, morphology and elemental composition. The relationships between different exposure metrics were determined through analyses of exposure ranking (ER), concentration ratios (CR), correlation coefficients and shapes of the particle concentration curves. Work activities such as powder screening, material feeding and packaging generated higher levels of NPs as compared to those of background particles (p < 0.01). The airborne Fe2O3 NPs exhibited a unimodal size distribution and a spindle-like morphology and consisted predominantly of the elements O and Fe. Periodic and activity-related characteristics were noticed in the temporal variations in NC(20-1000 nm) and SAC(10-1000 nm). The modal size of the Fe2O3 NPs remained relatively constant (ranging from 10 to 15 nm) during the working periods. The ER, CR values and the shapes of NC(20-1000 nm) and SAC(10-1000 nm) curves were similar; however, these were significantly different from those for MC(100-1000 nm). There was a high correlation between NC(20-1000 nm) and SAC(10-1000 nm), and relatively lower correlations between the two and MC(100-1000 nm). These findings suggest that the work activities during the manufacturing processes generated high levels of primary Fe2O3 NPs. The particle concentrations exhibited periodicity and were activity dependent. The number and SACs were found to be much more relevant metrics for characterizing NPs than was the mass concentration.

  16. Theoretical studies on the deacylation step of serine protease catalysis in the gas phase, in solution, and in elastase.

    PubMed

    Topf, Maya; Richards, W Graham

    2004-11-10

    The deacylation step of serine protease catalysis is studied using DFT and ab initio QM/MM calculations combined with MD/umbrella sampling calculations. Free energies of the entire reaction are calculated in the gas phase, in a continuum solvent, and in the enzyme elastase. The calculations show that a concerted mechanism in the gas phase is replaced by a stepwise mechanism when solvent effects or an acetate ion are added to the reference system, with the tetrahedral intermediate being a shallow minimum on the free energy surface. In the enzyme, the tetrahedral intermediate is a relatively stable species ( approximately 7 kcal/mol lower in energy than the transition state), mainly due to the electrostatic effects of the oxyanion hole and Asp102. It is formed in the first step of the reaction, as a result of a proton transfer from the nucleophilic water to His57 and of an attack of the remaining hydroxyl on the ester carbonyl. This is the rate-determining step of the reaction, which requires approximately 22 kcal/mol for activation, approximately 5 kcal/mol less than the reference reaction in water. In the second stage of the reaction, only small energy barriers are detected to facilitate the proton transfer from His57 to Ser195 and the breakdown of the tetrahedral intermediate. Those are attributed mainly to a movement of Ser195 and to a rotation of the His57 side chain. During the rotation, the imidazolium ion is stabilized by a strong H-bond with Asp102, and the C(epsilon)(1)-H...O H-bond with Ser214 is replaced by one with Thr213, suggesting that a "ring-flip mechanism" is not necessary as a driving force for the reaction. The movements of His57 and Ser195 are highly correlated with rearrangements of the binding site, suggesting that product release may be implicated in the deacylation process.

  17. Qualitative characteristics of histamine release from human basophils by covalently cross-linked LgE

    SciTech Connect

    Kagey-Sobotka, A.; Dembo, M.; Goldstein, B.; Metzger, H.; Lichtenstein, L.M.

    1981-12-01

    The effects of permanent oligomers of human lgE produced was studied using the cross-linking reagent, dimethyl suberimidate, on histamine release from human basophils. lgE dimers were found to be sufficient stimuli for both release and desensitization of these cells; monomeric lgE had no effect. Histamine release was augmented by deuterium oxide (D/sub 2/O) in the media, but D/sub 2/O was not an absolute requirement to observe release. Desensitization by the dimeric lgE was specific in that the response to anti-lgE was not affected by preincubation of the leukocytes with the lgE dimer under suboptimal releasing conditions. lgE trimers and higher oligomers of lgE also caused both release and desensitization. lgE also trimers were 3- to 4-fold more effective than lgE dimers with regard to the amount required for 50% histamine release. Dilution studies with monomeric lgE suggested that the difference was due to the presence of more ''active'' dimers in the trimeric lgE fractions. We conclude that dimeric lgE, by juxtaposing 2 receptors on the basophil membrane, is the ''unit signal'' for both release and desensitization of these cells.

  18. Ion mobility-mass spectrometry and orthogonal gas-phase techniques to study amyloid formation and inhibition.

    PubMed

    Hoffmann, Waldemar; von Helden, Gert; Pagel, Kevin

    2017-03-23

    Amyloidogenic peptide oligomers are responsible for a variety of neurodegenerative disorders such as Alzheimer's and Parkinson's disease. Due to their dynamic, polydisperse, and polymorphic nature, these oligomers are very challenging to characterize using traditional condensed-phase methods. In the last decade, ion mobility-mass spectrometry (IM-MS) and related gas-phase techniques have emerged as a powerful alternative to disentangle the structure and assembly characteristics of amyloid forming systems. This review highlights recent advances in which IM-MS was used to characterize amyloid oligomers and their underlying assembly pathway. In addition, we summarize recent studies in which IM-MS was used to size- and mass-select species for a further spectroscopic investigation and outline the potential of IM-MS as a tool for the screening of amyloid inhibitors.

  19. Numerical Computation of Flame Spread over a Thin Solid in Forced Concurrent Flow with Gas-phase Radiation

    NASA Technical Reports Server (NTRS)

    Jiang, Ching-Biau; T'ien, James S.

    1994-01-01

    Excerpts from a paper describing the numerical examination of concurrent-flow flame spread over a thin solid in purely forced flow with gas-phase radiation are presented. The computational model solves the two-dimensional, elliptic, steady, and laminar conservation equations for mass, momentum, energy, and chemical species. Gas-phase combustion is modeled via a one-step, second order finite rate Arrhenius reaction. Gas-phase radiation considering gray non-scattering medium is solved by a S-N discrete ordinates method. A simplified solid phase treatment assumes a zeroth order pyrolysis relation and includes radiative interaction between the surface and the gas phase.

  20. The load and release characteristics on a strong cationic ion-exchange fiber: kinetics, thermodynamics, and influences.

    PubMed

    Yuan, Jing; Gao, Yanan; Wang, Xinyu; Liu, Hongzhuo; Che, Xin; Xu, Lu; Yang, Yang; Wang, Qifang; Wang, Yan; Li, Sanming

    2014-01-01

    Ion-exchange fibers were different from conventional ion-exchange resins in their non-cross-linked structure. The exchange was located on the surface of the framework, and the transport resistance reduced significantly, which might mean that the exchange is controlled by an ionic reaction instead of diffusion. Therefore, this work aimed to investigate the load and release characteristics of five model drugs with the strong cationic ion-exchange fiber ZB-1. Drugs were loaded using a batch process and released in United States Pharmacopoeia (USP) dissolution apparatus 2. Opposing exchange kinetics, suitable for the special structure of the fiber, were developed for describing the exchange process with the help of thermodynamics, which illustrated that the load was controlled by an ionic reaction. The molecular weight was the most important factor to influence the drug load and release rate. Strong alkalinity and rings in the molecular structures made the affinity between the drug and fiber strong, while logP did not cause any profound differences. The drug-fiber complexes exhibited sustained release. Different kinds and concentrations of counter ions or different amounts of drug-fiber complexes in the release medium affected the release behavior, while the pH value was independent of it. The groundwork for in-depth exploration and further application of ion-exchange fibers has been laid.

  1. Characteristics of histamine release from rat mast cells in relation to the valency of the stimulating ligand.

    PubMed Central

    Healicon, R M; Foreman, J C

    1986-01-01

    The relationship between the valency of a ligand and the subsequent characteristics of histamine release was investigated in rat peritoneal mast cells. The cells were passively sensitized to the DNP hapten and a series of DNP-human serum albumin conjugates of known valency were used to induce histamine release. The rate of release of histamine induced by these conjugates was independent of the DNP/HSA ratio when the ratio was between 71.3 and 7.2. Marked slowing of the release occurred as the ratio was reduced below 7.2. The rate of desensitization of the cells slowed as a continuous function as the DNP/HSA ratio was reduced. 45Calcium uptake measurements showed that the changes in histamine release were paralleled by changes in the membrane permeability to calcium. The rate of release of histamine from mast cells and the rate of desensitization of the cells are discussed in terms of the size of IgE receptor complexes on the cell membrane. PMID:2420710

  2. SPECIATION OF GAS-PHASE AND FINE PARTICLE EMISSIONS FROM BURNING OF FOLIAR FUELS

    EPA Science Inventory

    Particle size distributions (10-1000 nm aerodynamic diameter), physical and chemical properties of fine particle matter (PM2.5) with aerodynamic diameter <2.5 micrometers, and gas-phase emissions from controlled open burning of assorted taxa were measured. Chemical speciation of ...

  3. Methylation of 2-Naphthol Using Dimethyl Carbonate under Continuous-Flow Gas-Phase Conditions

    ERIC Educational Resources Information Center

    Tundo, Pietro; Rosamilia, Anthony E.; Arico, Fabio

    2010-01-01

    This experiment investigates the methylation of 2-naphthol with dimethyl carbonate. The volatility of the substrates, products, and co-products allows the reaction to be performed using a continuous-flow gas-phase setup at ambient pressure. The reaction uses catalytic quantities of base, achieves high conversion, produces little waste, and…

  4. SELECTIVE OXIDATION OF ALCOHOLS IN GAS PHASE USING LIGHT-ACTIVATED TITANIUM DIOXIDE

    EPA Science Inventory

    Selective oxidations of various primary and secondary alcohols were studied in a gas phase photochemical reactor using immobilized TiO2 catalyst. An annular photoreactor was used at 463K with an average contact time of 32sec. The system was found to be specifically suited for the...

  5. Analytical solutions for a soil vapor extraction model that incorporates gas phase dispersion and molecular diffusion

    NASA Astrophysics Data System (ADS)

    Huang, Junqi; Goltz, Mark N.

    2017-06-01

    To greatly simplify their solution, the equations describing radial advective/dispersive transport to an extraction well in a porous medium typically neglect molecular diffusion. While this simplification is appropriate to simulate transport in the saturated zone, it can result in significant errors when modeling gas phase transport in the vadose zone, as might be applied when simulating a soil vapor extraction (SVE) system to remediate vadose zone contamination. A new analytical solution for the equations describing radial gas phase transport of a sorbing contaminant to an extraction well is presented. The equations model advection, dispersion (including both mechanical dispersion and molecular diffusion), and rate-limited mass transfer of dissolved, separate phase, and sorbed contaminants into the gas phase. The model equations are analytically solved by using the Laplace transform with respect to time. The solutions are represented by confluent hypergeometric functions in the Laplace domain. The Laplace domain solutions are then evaluated using a numerical Laplace inversion algorithm. The solutions can be used to simulate the spatial distribution and the temporal evolution of contaminant concentrations during operation of a soil vapor extraction well. Results of model simulations show that the effect of gas phase molecular diffusion upon concentrations at the extraction well is relatively small, although the effect upon the distribution of concentrations in space is significant. This study provides a tool that can be useful in designing SVE remediation strategies, as well as verifying numerical models used to simulate SVE system performance.

  6. ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE THERMAL DESORPTION UNIT - APPLICATIONS ANALYSIS REPORT

    EPA Science Inventory

    ELI ECO Logic International, Inc.'s Thermal Desorption Unit (TDU) is specifically designed for use with Eco Logic's Gas Phase Chemical Reduction Process. The technology uses an externally heated bath of molten tin in a hydrogen atmosphere to desorb hazardous organic compounds fro...

  7. Chemical studies of elements with Z ⩾ 104 in gas phase

    NASA Astrophysics Data System (ADS)

    Türler, Andreas; Eichler, Robert; Yakushev, Alexander

    2015-12-01

    Chemical investigations of superheavy elements in the gas-phase, i.e. elements with Z ≥ 104, allow assessing the influence of relativistic effects on their chemical properties. Furthermore, for some superheavy elements and their compounds quite unique gas-phase chemical properties were predicted. The experimental verification of these properties yields supporting evidence for a firm assignment of the atomic number. Prominent examples are the high volatility observed for HsO4 or the very weak interaction of Cn with gold surfaces. The unique properties of HsO4 were exploited to discover the doubly-magic even-even nucleus 270Hs and the new isotope 271Hs. The combination of kinematic pre-separation and gas-phase chemistry allowed gaining access to a new class of relatively fragile compounds, the carbonyl complexes of elements Sg through Mt. A not yet resolved issue concerns the interaction of Fl with gold surfaces. While competing experiments agree on the fact that Fl is a volatile element, there are discrepancies concerning its adsorption on gold surfaces with respect to its daughter Cn. The elucidation of these and other questions amounts to the fascination that gas-phase chemical investigations exert on current research at the extreme limits of chemistry today.

  8. Multiple Multidentate Halogen Bonding in Solution, in the Solid State, and in the (Calculated) Gas Phase.

    PubMed

    Jungbauer, Stefan H; Schindler, Severin; Herdtweck, Eberhardt; Keller, Sandro; Huber, Stefan M

    2015-09-21

    The binding properties of neutral halogen-bond donors (XB donors) bearing two multidentate Lewis acidic motifs toward halides were investigated. Employing polyfluorinated and polyiodinated terphenyl and quaterphenyl derivatives as anion receptors, we obtained X-ray crystallographic data of the adducts of three structurally related XB donors with tetraalkylammonium chloride, bromide, and iodide. The stability of these XB complexes in solution was determined by isothermal titration calorimetry (ITC), and the results were compared to X-ray analyses as well as to calculated binding patterns in the gas phase. Density functional theory (DFT) calculations on the gas-phase complexes indicated that the experimentally observed distortion of the XB donors during multiple multidentate binding can be reproduced in 1:1 complexes with halides, whereas adducts with two halides show a symmetric binding pattern in the gas phase that is markedly different from the solid state structures. Overall, this study demonstrates the limitations in the transferability of binding data between solid state, solution, and gas phase in the study of complex multidentate XB donors.

  9. Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation.

    PubMed

    Hamuro, Yoshitomo

    2017-05-01

    Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation. Graphical Abstract ᅟ.

  10. SPECIATION OF GAS-PHASE AND FINE PARTICLE EMISSIONS FROM BURNING OF FOLIAR FUELS

    EPA Science Inventory

    Particle size distributions (10-1000 nm aerodynamic diameter), physical and chemical properties of fine particle matter (PM2.5) with aerodynamic diameter <2.5 micrometers, and gas-phase emissions from controlled open burning of assorted taxa were measured. Chemical speciation of ...

  11. DEMONSTRATION BULLETIN: GAS-PHASE CHEMICAL REDUCTION - ECO LOGIC INTERNATIONAL, INC.

    EPA Science Inventory

    The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...

  12. OH REACTION KINETICS OF GAS-PHASE A- AND G-HEXACHLOROCYCLOHEXANE AND HEXACHLOROBENZENE. (R825377)

    EPA Science Inventory

    Rate constants for the gas-phase reactions of the hydroxyl
    radical (OH) with - and -hexachlorocyclohexane (-
    and ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA

    EPA Science Inventory

    The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

  13. Gas-phase deposition of polychlorinated biphenyls (PCBs) to a water surface sampler.

    PubMed

    Tasdemir, Yücel; Holsen, Thomas M

    2006-01-01

    In this study a water surface sampler (WSS) was utilized to directly measure gas phase deposition of polychlorinated biphenyls (PCBs). The measured gas phase PCB fluxes averaged about 880 +/- 660 ngm(-2)d(-1), which was higher than the fluxes calculated using simultaneously measured air and water concentrations for natural surface waters. These large fluxes were due to fact that the measured fluxes were only in the absorption direction since deposited PCBs were continuously removed from the system using an XAD column resulting in the maximum possible flux rate from the air to the WSS water. Ambient air PCBs were also sampled simultaneously with a modified high volume sampler. The gas phase PCB concentrations changed between 0.90 and 4.46 ngm(-3) (2.18 +/- 1.16 ngm(-3)). The mass transfer coefficients (MTCs), calculated by dividing the fluxes by the gas phase concentrations was 0.40 +/- 0.36 cms(-1). The average MTC was comparable with those calculated using a similar configuration of a WSS.

  14. GAS-PHASE OXIDATION PRODUCTS OF BIPHENYL AND POLYCHLORINATED BIPHENYLS (R825377)

    EPA Science Inventory

    Our laboratory recently measured the gas-phase reaction rate constants of
    polychlorinated biphenyls (PCBs) with the hydroxyl radical (OH) and concluded
    that OH reactions are the primary removal pathway of PCBs from the atmosphere.
    With the reaction system previousl...

  15. SELECTIVE OXIDATION OF ALCOHOLS IN GAS PHASE USING LIGHT-ACTIVATED TITANIUM DIOXIDE

    EPA Science Inventory

    Selective oxidations of various primary and secondary alcohols were studied in a gas phase photochemical reactor using immobilized TiO2 catalyst. An annular photoreactor was used at 463K with an average contact time of 32sec. The system was found to be specifically suited for the...

  16. Generation of naphthoquinone radical anions by electrospray ionization: solution, gas-phase, and computational chemistry studies.

    PubMed

    Vessecchi, Ricardo; Naal, Zeki; Lopes, José N C; Galembeck, Sérgio E; Lopes, Norberto P

    2011-06-02

    Radical anions are present in several chemical processes, and understanding the reactivity of these species may be described by their thermodynamic properties. Over the last years, the formation of radical ions in the gas phase has been an important issue concerning electrospray ionization mass spectrometry studies. In this work, we report on the generation of radical anions of quinonoid compounds (Q) by electrospray ionization mass spectrometry. The balance between radical anion formation and the deprotonated molecule is also analyzed by influence of the experimental parameters (gas-phase acidity, electron affinity, and reduction potential) and solvent system employed. The gas-phase parameters for formation of radical species and deprotonated species were achieved on the basis of computational thermochemistry. The solution effects on the formation of radical anion (Q(•-)) and dianion (Q(2-)) were evaluated on the basis of cyclic voltammetry analysis and the reduction potentials compared with calculated electron affinities. The occurrence of unexpected ions [Q+15](-) was described as being a reaction between the solvent system and the radical anion, Q(•-). The gas-phase chemistry of the electrosprayed radical anions was obtained by collisional-induced dissociation and compared to the relative energy calculations. These results are important for understanding the formation and reactivity of radical anions and to establish their correlation with the reducing properties by electrospray ionization analyses.

  17. ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA

    EPA Science Inventory

    The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

  18. Supported Rh-phosphine complex catalysts for continuous gas-phase decarbonylation of aldehydes.

    PubMed

    Malcho, Phillip; Garcia-Suarez, Eduardo J; Mentzel, Uffe Vie; Engelbrekt, Christian; Riisager, Anders

    2014-12-14

    Heterogeneous silica supported rhodium-phosphine complex catalysts are employed for the first time in the catalytic decarbonylation of aldehydes in continuous gas-phase. The reaction protocol is exemplified for the decarbonylation of p-tolualdehyde to toluene and further extended to other aromatic and aliphatic aldehydes achieving excellent results in terms of both conversion and selectivity.

  19. Noncovalent Halogen Bonding as a Mechanism for Gas-Phase Clustering

    NASA Astrophysics Data System (ADS)

    Wegeberg, Christina; Donald, William A.; McKenzie, Christine J.

    2017-07-01

    Gas-phase clustering of nonionizable iodylbenzene (PhIO2) is attributed to supramolecular halogen bonding. Electrospray ionization results in the formation of ions of proton-charged and preferably sodium-charged clusters assignable to [H(PhIO2) n ]+, n = 1-7; [Na(PhIO2) n ]+, n = 1-6; [Na2(PhIO2) n ]2+, n = 7-20; [HNa(PhIO2) n ]2+, n = 6-19; [HNa2(PhIO2) n ]3+, n = 15-30; and [Na3(PhIO2) n ]3+, n = 14-30. The largest cluster detected has a supramolecular mass of 7147 Da. Electronic structure calculations using the M06-2X functional with the 6-311++G(d,p) basis set for C, H, and O, and LANL2DZ basis set for I and Na predict 298 K binding enthalpies for the protonated and sodiated iodylbenzene dimers and trimers are greater than 180 kJ/mol. This is exceptionally high in comparison with other protonated and sodiated clusters with well-established binding enthalpies. Strongly halogen-bonded motifs found in the crystalline phases of PhIO2 and its derivatives serve as models for the structures of larger gas-phase clusters, and calculations on simple model gas-phase dimer and trimer clusters result in similar motifs. This is the first account of halogen bonding playing an extensive role in gas-phase associations.

  1. Gas-phase reactions of methyl thiocyanate with aliphatic carbanions - A mass spectrometry and computational study.

    PubMed

    Repeć, Barbara; Błaziak, Kacper; Danikiewicz, Witold

    2016-02-15

    Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with carbanions differing by structure and proton affinity values. All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Mass spectra recorded for the gas-phase reactions of five aliphatic carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the carbanion. The pathways considered are: SN 2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  2. Specific and reproducible gas sensors utilizing gas-phase chemical reaction on organic transistors.

    PubMed

    Zang, Yaping; Zhang, Fengjiao; Huang, Dazhen; Di, Chong-an; Meng, Qing; Gao, Xike; Zhu, Daoben

    2014-05-01

    Utilizing a textbook reaction on the surface of an organic active channel, achieves sensitive detection of HCl, NH3 and NO2, with good selectivity, excellent reproducibility, and satisfactory stability. These results reveal gas-phase reaction assisted detection as a unique and promising approach to construct practical applicable gas sensors with typical organic transistors.

  3. DEMONSTRATION BULLETIN: GAS-PHASE CHEMICAL REDUCTION - ECO LOGIC INTERNATIONAL, INC.

    EPA Science Inventory

    The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...

  4. Methylation of 2-Naphthol Using Dimethyl Carbonate under Continuous-Flow Gas-Phase Conditions

    ERIC Educational Resources Information Center

    Tundo, Pietro; Rosamilia, Anthony E.; Arico, Fabio

    2010-01-01

    This experiment investigates the methylation of 2-naphthol with dimethyl carbonate. The volatility of the substrates, products, and co-products allows the reaction to be performed using a continuous-flow gas-phase setup at ambient pressure. The reaction uses catalytic quantities of base, achieves high conversion, produces little waste, and…

  5. Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation

    NASA Astrophysics Data System (ADS)

    Hamuro, Yoshitomo

    2017-05-01

    Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation.

  6. OH REACTION KINETICS OF GAS-PHASE A- AND G-HEXACHLOROCYCLOHEXANE AND HEXACHLOROBENZENE. (R825377)

    EPA Science Inventory

    Rate constants for the gas-phase reactions of the hydroxyl
    radical (OH) with - and -hexachlorocyclohexane (-
    and GAS-PHASE OXIDATION PRODUCTS OF BIPHENYL AND POLYCHLORINATED BIPHENYLS (R825377)

    EPA Science Inventory

    Our laboratory recently measured the gas-phase reaction rate constants of
    polychlorinated biphenyls (PCBs) with the hydroxyl radical (OH) and concluded
    that OH reactions are the primary removal pathway of PCBs from the atmosphere.
    With the reaction system previousl...

  7. ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE THERMAL DESORPTION UNIT - APPLICATIONS ANALYSIS REPORT

    EPA Science Inventory

    ELI ECO Logic International, Inc.'s Thermal Desorption Unit (TDU) is specifically designed for use with Eco Logic's Gas Phase Chemical Reduction Process. The technology uses an externally heated bath of molten tin in a hydrogen atmosphere to desorb hazardous organic compounds fro...

  8. Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation

    NASA Astrophysics Data System (ADS)

    Hamuro, Yoshitomo

    2017-02-01

    Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation.

  9. Dominant factors controlling concentrations of aldehydes in rain, fog, dew water, and in the gas phase

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kiyoshi; Kawai, Shunji; Igawa, Manabu

    Low-molecular weight aldehyde compounds in rain, fog, dew water, and in the gas phase were measured at urban and suburban mountain sites, to characterize the chemical composition of aldehydes in liquid droplets and in the gas phase in the ambient atmosphere, and discuss the factors controlling wet removal processes of aldehydes. Higher concentrations of total aldehydes were found in dew water than in rain and fog water due to the small amount of water volume. Both formaldehyde and acetaldehyde were detected as dominant aldehydes in the gas phase. Secondary formation processes are dominant sources for both aldehydes in the suburban site, whereas primary sources are relatively important for the urban atmosphere. In rainwater, by contrast, formaldehyde was the most abundant aldehyde, followed by glyoxal. Glyoxal was detected as the most dominant aldehyde in fog and dew water. Acetaldehyde was not detected as a main component in liquid droplets in spite of its abundance in the gas phase. Water solubility of each aldehyde compound and dilution effect by water are critical factors that control the compositions and concentrations of these aldehydes in ambient liquid droplets.

  10. Molecular recognition properties of tartrates and metal-tartrates in solution and gas phase.

    PubMed

    Wijeratne, Aruna B; Schug, Kevin A

    2009-05-01

    Solution phase and gas phase chiral molecular recognition properties of tartrates (salts or esters of tartaric acid) and metal tartrates (binuclear tartrato(4-)-metal-bridged complexes) are reviewed in conjunction with their applications in enantiomeric separation science and their mass spectrometric chiral discrimination properties.

  11. Development of a gas phase source for perfluoroalkyl acids to examine atmospheric sampling methods.

    PubMed

    MacInnis, John J; VandenBoer, Trevor C; Young, Cora J

    2016-06-21

    An inability to produce environmentally relevant gaseous mixing ratios of perfluoroalkyl acids (PFAAs), ubiquitous global contaminants, limits the analytical reliability of atmospheric chemists to make accurate gas and particulate measurements that are demonstrably free of interferences due to sampling artefacts. A gas phase source for PFAAs based on the acid displacement mechanism using perfluoropropionate (PFPrA), perfluorobutanoate (PFBA), perfluorohexanoate (PFHxA), and perfluorooctanoate (PFOA) has been constructed. The displacement efficiency of gas phase perfluorocarboxylic acids (PFCAs) is inversely related to chain length. Decreasing displacement efficiencies for PFPrA, PFBA, PFHxA, and PFOA were 90% ± 20%, 40% ± 10%, 40% ± 10%, 9% ± 4%, respectively. Generating detectable amounts of gas phase perfluorosulfonic acids (PFSAs) was not possible. It is likely that lower vapour pressure and much higher acidity play a role in this lack of emission. PFCA emission rates were not elevated by increasing relative humidity (25%-75%), nor flow rate of carrier gas from 33-111 sccm. Overall, reproducible gaseous production of PFCAs was within the error of the production of hydrochloric acid (HCl) as a displacing acid (±20%) and was accomplished using a dry nitrogen flow of 33 ± 2 sccm. A reproducible mass emission rate of 0.97 ± 0.10 ng min(-1) (n = 8) was observed for PFBA. This is equivalent to an atmospheric mixing ratio of 12 ppmv, which is easily diluted to environmentally relevant mixing ratios of PFBA. Conversely, generating gas phase perfluorononanoic acid (PFNA) by sublimating the solid acid under the same conditions produced a mass emission rate of 2800 ng min(-1), which is equivalent to a mixing ratio of 18 ppthv and over a million times higher than suspected atmospheric levels. Thus, for analytical certification of atmospheric sampling methods, generating gas phase standards for PFCAs is best accomplished using acid displacement under dry conditions

  12. Gonadotropin-releasing Hormone Agonist Overuse: Urologists’ Response to Reimbursement and Characteristics Associated with Persistent Overuse

    PubMed Central

    Ellis, Shellie D.; Nielsen, Matthew E.; Carpenter, William R.; Jackson, George L.; Wheeler, Stephanie B.; Liu, Huan; Weinberger, Morris

    2015-01-01

    BACKGROUND Medicare reimbursement cuts have been associated with declining Gonadotropin-releasing Hormone (GnRH) agonist overuse in localized prostate cancer. Medical school affiliation and foreign training have been associated with persistent overuse. However, physician-level prescribing changes and the practice type of persistent overusers have not been examined. We sought to describe physician-level changes in GnRH agonist overuse and test the association of time in practice and solo practice type with GnRH agonist overuse. METHODS We matched American Medical Association physician data for 2,138 urologists to SEER–Medicare data for 12,943 men diagnosed with early stage and lower grade adenocarcinoma of the prostate between 2000 and 2007. We conducted a population-based, retrospective study using multi-level modeling to control for patient and provider characteristics. RESULTS Three distinct patterns of GnRH agonist overuse were observed. Urologists’ time in practice was not associated with GnRH agonist overuse (OR 0.89; 95% CI 0.75–1.05).However, solo practice type (OR 1.65; 95% CI 1.34–2.02), medical school affiliation (OR 0.65; 95% CI 0.55–0.77), and patient race were. Compared to non-Hispanic whites, non-Hispanic blacks (OR 1.76; 95% CI 1.37–2.27), Hispanics (OR 1.41; 95% CI 1.12–1.79) and men of “other” race (OR 1.44; 95% CI 1.04–1.99) had greater odds of receiving unnecessary GnRH agonists. CONCLUSIONS GnRH agonist overuse remains high among some urologists who may be professionally isolated and difficult to reach. These urologists treat more vulnerable populations, which may contribute to health disparities in prostate cancer treatment quality. Nonetheless, these findings provide guidance to develop interventions to address overuse in prostate cancer. PMID:25849354

  13. Diffusion characteristics and controlled release of bacterial fertilizers from modified calcium alginate capsules.

    PubMed

    Liu, Chien-Hung; Wu, Jane-Yii; Chang, Jo-Shu

    2008-04-01

    An indigenous Cellulosimicrobium cellulans GS6 isolate able to solubilize insoluble phosphate complexes in soil is a potential bacterial fertilizer. Enclosure of the phosphate-solubilizing bacterium (PSB) in biodegradable capsules may protect the PSB cells inoculated into soil and, in the meantime, enable the control of cell release that confers long-term fertilizing effects. In this study, calcium alginate (CA) was used as the core matrix to encapsulate cells of C. cellulans GS6. The cell-liberating properties of the CA-based capsules were modified by blending with a variety of supplemental materials (SM), including chitin, cellulose, olive oil, and gelatin. The experimental results showed that the maximum cell-release percentage (MCR%) of the capsules decreased in the order of CA-cellulose>CA-olive oil>CA-chitin>CA-gelatin>CA. Furthermore, a mass transport model was developed to accurately describe the kinetics of cell release results for each capsule. The diffusion coefficient (D(e)) of each capsule was also determined from the model simulation. We found that the estimated D(e) values are positively correlated to the release rate with rare exceptions. Lastly, as our results underscored the crucial roles that the type of capsules plays in the rate and amount of cell release, controlled release of the bacterial fertilizer (C. cellulans GS6 cells) may be achieved via the design of capsule materials.

  14. Comparison of different gas-phase mechanisms and aerosol modules for simulating particulate matter formation.

    PubMed

    Kim, Youngseob; Couvidat, Florian; Sartelet, Karine; Seigneur, Christian

    2011-11-01

    The effects of two gas-phase chemical kinetic mechanisms, Regional Atmospheric Chemistry Mechanism version 2 (RACM2) and Carbon-Bond 05 (CB05), and two secondary organic aerosol (SOA) modules, the Secondary Organic Aerosoi Model (SORGAM) and AER/EPRI/Caltech model (AEC), on fine (aerodynamic diameter < or =2.5 microm) particulate matter (PM2.5) formation is studied. The major sources of uncertainty in the chemistry of SOA formation are investigated. The use of all major SOA precursors and the treatment of SOA oligomerization are found to be the most important factors for SOA formation, leading to 66% and 60% more SOA, respectively. The explicit representation of high-NO, and low-NOx gas-phase chemical regimes is also important with increases in SOA of 30-120% depending on the approach used to implement the distinct SOA yields within the gas-phase chemical kinetic mechanism; further work is needed to develop gas-phase mechanisms that are fully compatible with SOA formation algorithms. The treatment of isoprene SOA as hydrophobic or hydrophilic leads to a significant difference, with more SOA being formed in the latter case. The activity coefficients may also be a major source of uncertainty, as they may differ significantly between atmospheric particles, which contain a myriad of SOA, primary organic aerosol (POA), and inorganic aerosol species, and particles formed in a smog chamber from a single precursor under dry conditions. Significant interactions exist between the uncertainties of the gas-phase chemistry and those of the SOA module.

  15. Levels of maternal serum corticotropin-releasing hormone (CRH) at midpregnancy in relation to maternal characteristics

    PubMed Central

    Chen, Yumin; Holzman, Claudia; Chung, Hwan; Senagore, Patricia; Talge, Nicole M; Siler-Khodr, Theresa

    2009-01-01

    Summary BACKGROUND Corticotropin-releasing hormone (CRH) in maternal blood originates primarily from gestational tissues and elevated levels in midpregnancy have been linked to adverse pregnancy outcomes. Investigators have hypothesized that high levels of maternal stress might lead to elevated CRH levels in pregnancy. Yet a few studies have measured maternal CRH levels among subgroups of women who experience disproportionate socioeconomic disadvantage, such as African-American and Hispanic women, and found that these groups have lower CRH levels in pregnancy. Our goal was to identify maternal characteristics related to CRH levels in midpregnancy and examine which if any of these factors help to explain race differences in CRH levels. METHODS The Pregnancy Outcomes and Community Health (POUCH) Study prospectively enrolled women at 15–27 weeks’ gestation from 52 clinics in five Michigan communities (1998–2004). Data from the POUCH Study were used to examine maternal demographics, anthropometrics, health behaviors, and psychosocial factors (independent variables) in relation to midpregnancy blood CRH levels modeled as log CRH pg/ml (dependent variable). Analyses were conducted within a subcohort from the POUCH Study (671 non-Hispanic Whites, 545 African Americans) and repeated in the subcohort subset with uncomplicated pregnancies (n=746). Blood levels of CRH and independent variables were ascertained at the time of enrollment. All regression models included week of enrollment as a covariate. In addition, final multivariable regression models alternately incorporated different psychosocial measures along with maternal demographics and weight. Psychosocial variables included measures of current depressive symptoms, perceived stress, coping style, hostility, mastery, anomie, and a chronic stressor (history of abuse as a child and adult). RESULTS In subcohort models, the adjusted mean CRH level was significantly lower in African Americans vs. non-Hispanic whites

  16. Intermolecular interactions of trifluorohalomethanes with Lewis bases in the gas phase: An ab initio study

    SciTech Connect

    Wang, Yi-Siang; Yin, Chih-Chien; Chao, Sheng D.

    2014-10-07

    We perform an ab initio computational study of molecular complexes with the general formula CF{sub 3}X—B that involve one trifluorohalomethane CF{sub 3}X (X = Cl or Br) and one of a series of Lewis bases B in the gas phase. The Lewis bases are so chosen that they provide a range of electron-donating abilities for comparison. Based on the characteristics of their electron pairs, we consider the Lewis bases with a single n-pair (NH{sub 3} and PH{sub 3}), two n-pairs (H{sub 2}O and H{sub 2}S), two n-pairs with an unsaturated bond (H{sub 2}CO and H{sub 2}CS), and a single π-pair (C{sub 2}H{sub 4}) and two π-pairs (C{sub 2}H{sub 2}). The aim is to systematically investigate the influence of the electron pair characteristics and the central atom substitution effects on the geometries and energetics of the formed complexes. The counterpoise-corrected supermolecule MP2 and coupled-cluster single double with perturbative triple [CCSD(T)] levels of theory have been employed, together with a series of basis sets up to aug-cc-pVTZ. The angular and radial configurations, the binding energies, and the electrostatic potentials of the stable complexes have been compared and discussed as the Lewis base varies. For those complexes where halogen bonding plays a significant role, the calculated geometries and energetics are consistent with the σ-hole model. Upon formation of stable complexes, the C–X bond lengths shorten, while the C–X vibrational frequencies increase, thus rendering blueshifting halogen bonds. The central atom substitution usually enlarges the intermolecular bond distances while it reduces the net charge transfers, thus weakening the bond strengths. The analysis based on the σ-hole model is grossly reliable but requires suitable modifications incorporating the central atom substitution effects, in particular, when interaction components other than electrostatic contributions are involved.

  17. Preparation and characteristics of nanostructured lipid carriers for control-releasing progesterone by melt-emulsification.

    PubMed

    Yuan, Hong; Wang, Lei-Lei; Du, Yong-Zhong; You, Jian; Hu, Fu-Qiang; Zeng, Su

    2007-11-15

    Nanostructured lipid carriers (NLC) made from mixtures of solid and spatially incompatible liquid lipids were prepared by melt-emulsification. Their drug loading capacity and releasing properties of progesterone were compared with those of solid lipid nanoparticles (SLN), and the NLC prepared by solvent diffusion method. Monostearin (MS) and stearic acid (SA) were used as solid lipid, whilst the oleic acid (OA) was used as liquid lipid. Properties of carriers such as the particle size and its distribution, drug loading, drug encapsulation efficiency and drug release behavior were investigated. As a result, the drug encapsulation efficiencies were improved by adding the liquid lipid into the solid lipid of nanoparticles. The drug release behavior could be adjusted by the addition of liquid lipid, and the NLC with higher OA content showed the faster rate of drug releasing. NLC had higher efficiency of encapsulation and slower rate of drug release than those of NLC prepared by solvent diffusion method. On the other hand, the NLC with higher drug loading was obtained, though the drug encapsulation efficiency was decreased slightly due to the increase of the amount of drug. The NLC modified with polyethylene glycol (PEG) was also prepared by using polyethylene glycol monostearate (PEG-SA). It was observed that the incorporation of PEG-SA reduced the drug encapsulation efficiency, but increased the rate of drug release. A sample with almost complete drug release in 24h was obtained by modifying with 1.30mol% PEG-SA. It indicated that the modified NLC was a potential drug delivery system for oral administration.

  18. Effect of food characteristics, storage conditions, and electron beam irradiation on active agent release from polyamide-coated LDPE films.

    PubMed

    Han, J; Castell-Perez, M E; Moreira, R G

    2008-03-01

    We investigated the effect of electron beam irradiation, storage conditions, and model food pH on the release characteristics of trans-cinnamaldehyde incorporated into polyamide-coated low-density polyethylene (LDPE) films. Active agent release rate on irradiated films (up to 20.0 kGy) decreased by 69% compared with the nonirradiated controls, from 0.252 to 0.086 microg/mL/h. Storage temperature (4, 21, and 35 degrees C) and pH (4, 7, and 10) of the food simulant solutions (10% aqueous ethanol) affected the release rate of trans-cinnamaldehyde. As expected, antimicrobial release rate decreased to 0.013 microg/mL/h at the refrigerated temperature (4 degrees C) compared to the higher temperatures (0.029 and 0.035 microg/mL/h at 21 and 35 degrees C). The fastest release rate occurred when exposed to the acidic food simulant solution (pH 4). In aqueous solution, trans-cinnamaldehyde was highly unstable to ionizing radiation, with loss in concentration from 24.50 to 1.36 microg/mL after exposure to 2.0 kGy. Fourier transform infrared (FTIR) analysis revealed that exposure to ionizing radiation up to 10.0 kGy did not affect the structural conformation of LDPE/polyamide films and the trans-cinnamaldehyde in the films, though it induced changes in the functional group of trans-cinnamaldehyde when dose increased up to 20.0 kGy. Studies with a radiation-stable compound (naphthalene) showed that ionizing radiation induced the crosslinking in polymer networks of LDPE/polyamide film and caused slow and gradual release of the compound. This study demonstrated that irradiation serves as a controlling factor for release of active compounds, with potential applications in the development of antimicrobial packaging systems.

  19. Characteristics and kinetics of iron release from the ferritin under the EGCG reduction.

    PubMed

    Ji, Xuetao; Huang, Lin; Lin, Qing; Huang, Heqing

    2012-04-01

    The mechanism of iron release from ferritin in vivo is still unclear even though it represents a key step of the metabolism of iron in vivo. Here, both interaction intensity and binding stability between epigallocatechin gallate (EGCG) from tea and liver ferritin of Dasyatis akajei (DALF) were investigated using UV-visible, fluorescence and circular dichroism (CD) spectrometry, respectively. The results indicated that EGCG could reduce the iron within the ferritin shell directly in the absence of chemical reducers such as Na(2)S(2)O(4), but this process was strictly pH-dependent, and the rate of iron release is faster at low pH than at high pH. The kinetic study of iron release showed that this process fitted the law of zero order reaction, which differed from that of first order reaction by various chemical reducers such as Vitamin C. In addition, Both fluorescence and CD spectrometry were further used to study the reduction mechanism of iron release in vitro, showing that there was a slight conformation change of the ferritin shell during EGCG reduction because of a complex formation of DALF-EGCG. It appears that chemical reducers with large molecular sizes reduce the iron across the protein shell by the way of an electron transfer pathway (ETP). A novel pathway for iron release from DALF with EGCG reduction is suggested to explain for a reductive route of iron metabolism by biological reducers in vivo.

  1. Drug release characteristics of physically cross-linked thermosensitive poly(N-vinylcaprolactam) hydrogel particles.

    PubMed

    Vihola, Henna; Laukkanen, Antti; Tenhu, Heikki; Hirvonen, Jouni

    2008-11-01

    The effect of physical cross-linking was studied on the formation and properties of thermosensitive polymer particles of poly(N-vinylcaprolactam), PVCL, and PVCL grafted with poly(ethylene oxide) macromonomer, PVCL-graft-C(11)EO(42). Loading and release of model drugs into/from the hydrogel particles were evaluated. Thermosensitive particles were stabilized by cross-linkers, the most feasible of which was salicylic acid (SA). At 23 degrees C, below the lower critical solution temperature (LCST) of the thermosensitive polymers, stability of the hydrogels was poor, whereas at 37 degrees C stable hydrogel particles were formed. All the drugs and also the cross-linker (SA) were released more efficiently from the PVCL particles compared to the PVCL-graft-C(11)EO(42) particles. Drug concentration and pH affected clearly the rate and extent of drug release in physiological buffer. The higher drug release from the PVCL was based on the more open gel-like structure as opposed to PVCL-graft-C(11)EO(42) particles. Complex formation between the cross-linker and the polymers was due to the hydrogen bonding between the hydroxyl groups of SA and H-bond acceptors of the PVCL. In the case of PVCL-graft-C(11)EO(42), the ethylene oxide chain provided more opportunities for H-bonding in comparison to the pure PVCL, creating more stable complexes (more tightly packed particles) leading to sustained drug release.

  2. Coordinated coupling control of tethered space robot using releasing characteristics of space tether

    NASA Astrophysics Data System (ADS)

    Huang, Panfeng; Zhang, Fan; Xu, Xiudong; Meng, Zhongjie; Liu, Zhengxiong; Hu, Yongxin

    2016-04-01

    Tethered space robot (TSR) is a new concept of space robot, which is released from the platform satellite, and retrieved via connected tether after space debris capture. In this paper, we propose a new coordinate control scheme for optimal trajectory and attitude tracking, and use releasing motor torque to instead the tension force, since it is difficult to track in practical. Firstly, the 6-DOF dynamics model of TSR is derived, in which the dynamics of tether releasing system is taken into account. Then, we propose and design the coordinated coupled controller, which is composed of a 6-DOF sliding mode controller and a PD controller tether's releasing. Thrust is treated as control input of the 6-DOF sliding mode controller to control the in-plane and out-of-plane angle of the tether and attitude angles of the TSR. The torque of releasing motor is used as input of PD controller, which controls the length rate of space tether. After the verification of the control scheme, finally, the simulation experiment is presented in order to validate the effectiveness of this control method. The results show that TSR can track the optimal approaching trajectory accurately. Simultaneously, the attitude angles can be changed to the desired attitude angles in control period, and the terminal accuracy is ±0.3°.

  3. The role of gas phase reactions in the deflagration-to-detonation transition of high energy propellants

    NASA Technical Reports Server (NTRS)

    Boggs, T. L.; Price, C. F.; Atwood, A. I.; Zurn, D. E.; Eisel, J. L.; Derr, R. L.

    1980-01-01

    The inadequacies of the two commonly used assumptions are shown, along with the need for considering gas phase reactions. Kinetic parameters that describe the gas phase reactions for several ingredients are provided, and the first steps in convective combustion leading to deflagration to detonation transition are described.

  4. The role of gas phase reactions in the deflagration-to-detonation transition of high energy propellants

    NASA Technical Reports Server (NTRS)

    Boggs, T. L.; Price, C. F.; Atwood, A. I.; Zurn, D. E.; Eisel, J. L.; Derr, R. L.

    1980-01-01

    The inadequacies of the two commonly used assumptions are shown, along with the need for considering gas phase reactions. Kinetic parameters that describe the gas phase reactions for several ingredients are provided, and the first steps in convective combustion leading to deflagration to detonation transition are described.

  5. Preparation and Analysis of Type II Xerogel Films with Antifouling/Foul Release Characteristics

    NASA Astrophysics Data System (ADS)

    Sokolova, Anastasiya

    In order to combat biofouling, xerogel coatings comprised of aminopropyl, fluorocarbon, and hydrocarbon silanes were prepared and tested for their antifouling/foul release properties against Ulva, Navicula, barnacles, and tubeworms. Many of the coatings showed settlement and removal of Ulva to be as good as or better than the poly(dimethylsiloxane) (PDMSE) standard. Barnacle removal assays showed excellent results for some coatings while others did not fair so well. The best foul release coatings for barnacles were comprised of aminopropyl/hydrocarbon- and fluorocarbon/hydrocarbon-modified silanes. For the majority of coatings tested, water wettability and surface energy did not play a role in the antifouling/ foul release properties of the coatings.

  6. Gamma-oryzanol-loaded calcium pectinate microparticles reinforced with chitosan: optimization and release characteristics.

    PubMed

    Lee, Ji-Soo; Kim, Jong Soo; Lee, Hyeon Gyu

    2009-05-01

    Response surface methodology was used to optimize microparticle preparation conditions, including the ratio of pectin:gamma-oryzanol (OZ) (X(1)), agitation speed (X(2)), and the concentration of emulsifier (X(3)), for maximal entrapment efficiency (EE) of OZ-loaded Ca pectinate microparticles. The optimized values of X(1), X(2), and X(3) were found to be 2.72:5.28, 1143.5 rpm, and 2.61%, respectively. Experimental results obtained for the optimum formulation agreed favorably with the predicted results, indicating the usefulness of predicting models for EE. In order to evaluate the effect of chitosan-coating and blending on the release pattern of the entrapped OZ from microparticles, chitosan-coated and blended Ca pectinate microparticles were prepared. Release studies revealed that the chitosan treatments, especially the chitosan-coating, were effective in suppressing the release in both simulated gastric fluid (SGF) and intestinal fluid (SIF).

  7. Comprehensive Gas-Phase Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 2. Gas-Phase Hydrogen/Deuterium Exchange for Ion Population Estimation.

    PubMed

    Khakinejad, Mahdiar; Ghassabi Kondalaji, Samaneh; Tafreshian, Amirmahdi; Valentine, Stephen J

    2017-05-01

    Gas-phase hydrogen/deuterium exchange (HDX) using D2O reagent and collision cross-section (CCS) measurements are utilized to monitor the ion conformers of the model peptide acetyl-PAAAAKAAAAKAAAAKAAAAK. The measurements are carried out on a home-built ion mobility instrument coupled to a linear ion trap mass spectrometer containing electron transfer dissociation (ETD) capabilities. ETD is utilized to obtain per-residue deuterium uptake data for select ion conformers, and a new algorithm is presented for interpreting the HDX data. Using molecular dynamics (MD) production data and a hydrogen accessibility scoring (HAS)-number of effective collisions (NEC) model, hypothetical HDX behavior is attributed to various in-silico candidate (CCS match) structures. The HAS-NEC model is applied to all candidate structures, and non-negative linear regression is employed to determine structure contributions resulting in the best match to deuterium uptake. The accuracy of the HAS-NEC model is tested with the comparison of predicted and experimental isotopic envelopes for several of the observed c-ions. It is proposed that gas-phase HDX can be utilized effectively as a second criterion (after CCS matching) for filtering suitable MD candidate structures. In this study, the second step of structure elucidation, 13 nominal structures were selected (from a pool of 300 candidate structures) and each with a population contribution proposed for these ions. Graphical Abstract ᅟ.

  8. Gas phase RNA and DNA ions 2. Conformational dependence of the gas-phase H/D exchange of nucleotide-5'-monophosphates.

    PubMed

    Freitas, M A; Marshall, A G

    2001-07-01

    The conformational dependence of the gas-phase hydrogen/deuterium (H/D) exchange of nucleotide-5-monophosphate anions with the H/D exchange reagent D2S is reported here. The electrospray-generated [M-H]- anions of adenosine-5'-monophosphate, adenosine-5'-carboxylic acid, ribitol-5-phosphate, and 2-deoxy-ribitol-5-phosphate were reacted with D2S in the gas phase. Their reactivity (adenosine-5'-monophosphate exchanged 2 of 5 labile hydrogens, adenosine-5'-carboxylic acid exchanged 1 of 4, ribitol-5-phosphate exchanged 2 of 3, and 2-deoxy-ribitol-5-phosphate exchanged 1 of 2) suggests that the hydroxyl group in the 2 position of the ribose sugar and the amino hydrogen on the nucleobase do not exchange readily with D2S. Semiempirical molecular orbital calculations suggest that the labile hydrogens in these positions are thermodynamically facile to exchange but as a conformation inaccessible to the presumed phosphate anion, consistent with a mechanism in which the phosphate anion complexes with the exchange reagent and assists H/D exchange at a neighboring site.

  9. Ambient observations of dimers from terpene oxidation in the gas phase: Implications for new particle formation and growth: Ambient Observations of Gas-Phase Dimers

    DOE PAGES

    Mohr, Claudia; Lopez-Hilfiker, Felipe D.; Yli-Juuti, Taina; ...

    2017-03-28

    Here, we present ambient observations of dimeric monoterpene oxidation products (C16–20HyO6–9) in gas and particle phases in the boreal forest in Finland in spring 2013 and 2014, detected with a chemical ionization mass spectrometer with a filter inlet for gases and aerosols employing acetate and iodide as reagent ions. These are among the first online dual-phase observations of such dimers in the atmosphere. Estimated saturation concentrations of 10-15 to 10-6 µg m-3 (based on observed thermal desorptions and group-contribution methods) and measured gas-phase concentrations of 10-3 to 10-2 µg m-3 (~106–107 molecules cm-3) corroborate a gas-phase formation mechanism. Regular newmore » particle formation (NPF) events allowed insights into the potential role dimers may play for atmospheric NPF and growth. The observationally constrained Model for Acid-Base chemistry in NAnoparticle Growth indicates a contribution of ~5% to early stage particle growth from the ~60 gaseous dimer compounds.« less

  10. Comprehensive Gas-Phase Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 2. Gas-Phase Hydrogen/Deuterium Exchange for Ion Population Estimation

    NASA Astrophysics Data System (ADS)

    Khakinejad, Mahdiar; Ghassabi Kondalaji, Samaneh; Tafreshian, Amirmahdi; Valentine, Stephen J.

    2017-03-01

    Gas-phase hydrogen/deuterium exchange (HDX) using D2O reagent and collision cross-section (CCS) measurements are utilized to monitor the ion conformers of the model peptide acetyl-PAAAAKAAAAKAAAAKAAAAK. The measurements are carried out on a home-built ion mobility instrument coupled to a linear ion trap mass spectrometer containing electron transfer dissociation (ETD) capabilities. ETD is utilized to obtain per-residue deuterium uptake data for select ion conformers, and a new algorithm is presented for interpreting the HDX data. Using molecular dynamics (MD) production data and a hydrogen accessibility scoring (HAS)-number of effective collisions (NEC) model, hypothetical HDX behavior is attributed to various in-silico candidate (CCS match) structures. The HAS-NEC model is applied to all candidate structures, and non-negative linear regression is employed to determine structure contributions resulting in the best match to deuterium uptake. The accuracy of the HAS-NEC model is tested with the comparison of predicted and experimental isotopic envelopes for several of the observed c-ions. It is proposed that gas-phase HDX can be utilized effectively as a second criterion (after CCS matching) for filtering suitable MD candidate structures. In this study, the second step of structure elucidation, 13 nominal structures were selected (from a pool of 300 candidate structures) and each with a population contribution proposed for these ions.

  11. Comprehensive Gas-Phase Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 2. Gas-Phase Hydrogen/Deuterium Exchange for Ion Population Estimation

    NASA Astrophysics Data System (ADS)

    Khakinejad, Mahdiar; Ghassabi Kondalaji, Samaneh; Tafreshian, Amirmahdi; Valentine, Stephen J.

    2017-05-01

    Gas-phase hydrogen/deuterium exchange (HDX) using D2O reagent and collision cross-section (CCS) measurements are utilized to monitor the ion conformers of the model peptide acetyl-PAAAAKAAAAKAAAAKAAAAK. The measurements are carried out on a home-built ion mobility instrument coupled to a linear ion trap mass spectrometer containing electron transfer dissociation (ETD) capabilities. ETD is utilized to obtain per-residue deuterium uptake data for select ion conformers, and a new algorithm is presented for interpreting the HDX data. Using molecular dynamics (MD) production data and a hydrogen accessibility scoring (HAS)-number of effective collisions (NEC) model, hypothetical HDX behavior is attributed to various in-silico candidate (CCS match) structures. The HAS-NEC model is applied to all candidate structures, and non-negative linear regression is employed to determine structure contributions resulting in the best match to deuterium uptake. The accuracy of the HAS-NEC model is tested with the comparison of predicted and experimental isotopic envelopes for several of the observed c-ions. It is proposed that gas-phase HDX can be utilized effectively as a second criterion (after CCS matching) for filtering suitable MD candidate structures. In this study, the second step of structure elucidation, 13 nominal structures were selected (from a pool of 300 candidate structures) and each with a population contribution proposed for these ions.

  12. Swelling characteristics and drug release kinetics of Ag/PVA hydrogel nanocomposites

    NASA Astrophysics Data System (ADS)

    Swaroop, K.; Somashekarappa, H. M.

    2017-05-01

    Ag/PVA hydrogels nanocomposites (HNC's) of different Ag concentrations were synthesized using gamma irradiation technique. The prepared hydrogels were characterized using powder XRD, UV, SEM and TEM analysis. The equilibrium and dynamic swelling properties of different concentrations of Ag/PVA HNC's were studied. It has been observed that the swelling properties of the Ag/PVA HNC's increase with the Ag concentration. L-ascorbic acid was loaded to Ag/PVA HNC's and the release data was monitored by the absorption wavelength at 252 nm. The results indicate that both swelling and the ascorbic acid release process of Ag/PVA HNC's follows non-Fickian mechanism.

  13. Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption

    NASA Technical Reports Server (NTRS)

    Bergin, E. A.; Langer, W. D.; Goldsmith, P. F.

    1995-01-01

    We present time-dependent models of the chemical evolution of molecular clouds which include depletion of atoms and molecules onto grain surfaces and desorption, as well as gas-phase interactions. We have included three mechanisms to remove species from the grain mantles: thermal evaporation, cosmic-ray-induced heating, and photodesorption. A wide range of parameter space has been explored to examine the abundance of species present both on the grain mantles and in the gas phase as a function of both position in the cloud (visual extinction) and of evolutionary state (time). The dominant mechanism that removes molecules from the grain mantles is cosmic-ray desorption. At times greater than the depletion timescale, the abundances of some simple species agree with abundances observed in the cold dark cloud TMC-1. Even though cosmic-ray desorption preserves the gas-phase chemistry at late times, molecules do show significant depletions from the gas phase. Examination of the dependence of depletion as a function of density shows that when the density increases from 10(exp 3)/cc to 10(exp 5)/cc several species including HCO(+), HCN, and CN show gas-phase abundance reductions of over an order of magnitude. The CO: H2O ratio in the grain mantles for our standard model is on the order of 10:1, in reasonable agreement with observations of nonpolar CO ice features in rho Ophiuchus and Serpens. We have also examined the interdependence of CO depletion with the space density of molecular hydrogen and binding energy to the grain surface. We find that the observed depletion of CO in Taurus in inconsistent with CO bonding in an H2O rich mantle, in agreement with observations. We suggest that if interstellar grains consist of an outer layer of CO ice, then the binding energies for many species to the grain mantle may be lower than commonly used, and a significant portion of molecular material may be maintained in the gas phase.

  14. Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption

    NASA Technical Reports Server (NTRS)

    Bergin, E. A.; Langer, W. D.; Goldsmith, P. F.

    1995-01-01

    We present time-dependent models of the chemical evolution of molecular clouds which include depletion of atoms and molecules onto grain surfaces and desorption, as well as gas-phase interactions. We have included three mechanisms to remove species from the grain mantles: thermal evaporation, cosmic-ray-induced heating, and photodesorption. A wide range of parameter space has been explored to examine the abundance of species present both on the grain mantles and in the gas phase as a function of both position in the cloud (visual extinction) and of evolutionary state (time). The dominant mechanism that removes molecules from the grain mantles is cosmic-ray desorption. At times greater than the depletion timescale, the abundances of some simple species agree with abundances observed in the cold dark cloud TMC-1. Even though cosmic-ray desorption preserves the gas-phase chemistry at late times, molecules do show significant depletions from the gas phase. Examination of the dependence of depletion as a function of density shows that when the density increases from 10(exp 3)/cc to 10(exp 5)/cc several species including HCO(+), HCN, and CN show gas-phase abundance reductions of over an order of magnitude. The CO: H2O ratio in the grain mantles for our standard model is on the order of 10:1, in reasonable agreement with observations of nonpolar CO ice features in rho Ophiuchus and Serpens. We have also examined the interdependence of CO depletion with the space density of molecular hydrogen and binding energy to the grain surface. We find that the observed depletion of CO in Taurus in inconsistent with CO bonding in an H2O rich mantle, in agreement with observations. We suggest that if interstellar grains consist of an outer layer of CO ice, then the binding energies for many species to the grain mantle may be lower than commonly used, and a significant portion of molecular material may be maintained in the gas phase.

  15. Characteristics of a newly released runner-type peanut cultivar ‘AU-NPL 17’

    USDA-ARS?s Scientific Manuscript database

    Auburn University- National Peanut Laboratory (‘AU-NPL 17’) was developed from a pure line population intended for cultivar release. The original pure line, AU14-29, originated as an F6 single-plant selection from the cross of Tifguard (Holbrook, et al. 2008) x York (Gorbet, et al., 2011) and was c...

  16. Emission characteristics of elm bark beetle aggregation attractants from controlled-release dispensers

    Treesearch

    Roy A. Cuthbert; John W. Peacock; Susan L. Wright

    1983-01-01

    Release rates of the aggregation attractants of the smaller European elm bark beetle, Scolytus multistriatus (Marsham), from laboratory-aged and field-aged Conrel and Hercon dispensers were monitored for 85 days by GLC analysis of cold-trapped volatiles. Both dispensers had relatively low and constant rates of decay for all three attractant...

  17. New citrus rootstocks released by USDA 2001-2010: field performance and nursery characteristics

    USDA-ARS?s Scientific Manuscript database

    Four new citrus rootstocks developed by USDA, ARS and released between 2001 and 2010 have gained considerable commercial popularity in Florida and have been used for propagation of more than 2 million trees over the last two years. Trends in commercial use of these rootstocks are discussed. Results ...

  18. pH-dependent release characteristics of antimony and arsenic from typical antimony-bearing ores.

    PubMed

    Hu, Xingyun; Guo, Xuejun; He, Mengchang; Li, Sisi

    2016-06-01

    The pH-dependent leaching of antimony (Sb) and arsenic (As) from three typical Sb-bearing ores (Banxi, Muli and Tongkeng Antimony Mine) in China was assessed using a pH-static leaching experiment. The pH changes of the leached solutions and pH-dependent leaching of Sb and As occurred in different ways. For the Banxi and Muli Sb ores, alkaline conditions were more favorable for the release of Sb compared to neutral and acidic conditions, but the reverse was true for the pH-dependent release of As. For the Tongkeng Sb ore, unlike the previous two Sb-bearing ores, acidic conditions were more favorable for Sb release than neutral and alkaline conditions. The ores with lower Sb and As contents released higher percentages of their Sb and As after 16day leaching, suggesting that they are the largest potential sources of pollution. This work may provide key information on the geochemistry of Sb and As in the weathering zone. Copyright © 2016. Published by Elsevier B.V.

  19. Some Characteristics of the Outer Membrane Material Released by Growing Enterotoxigenic Escherichia coli

    PubMed Central

    Gankema, Henk; Wensink, Jan; Guinée, Pieter A. M.; Jansen, Wim H.; Witholt, Bernard

    1980-01-01

    The high-molecular-weight material released into the medium by Escherichia coli AP1, an enterotoxigenic strain of porcine origin, has been isolated and resolved into two clearly distinct fractions, based on sucrose density gradient and differential centrifugation, chemical analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and freeze-fracture electron microscopy. These two fractions, referred to as “medium vesicles” and “medium lipopolysaccharides”, were compared with the cellular outer and cytoplasmic membranes, the periplasmic fraction, and the cytoplasmic fraction. The medium vesicles closely resembled outer membrane and accounted for 3 to 5% of the total cellular outer membrane. They contained most of the heat-labile enterotoxin (LT) activity released into the medium by E. coli AP1. The medium lipopolysaccharide consisted mostly of lipopolysaccharide and a small amount of outer membrane and contained relatively little LT activity. Based on experiments with E. coli K-12 strains, in which about 5% of the newly synthesized outer membrane is lost from areas of outer membrane synthesis, it is proposed that enterotoxigenic E. coli strains release LT as part of such newly synthesized outer membrane fragments and that released outer membrane fragments may function as physiologically significant LT carriers. ImagesFig. 4Fig. 1Fig. 2Fig. 2Fig. 3 PMID:7011982

  20. Effect of alginate-pectin composition on drug release characteristics of microcapsules.

    PubMed

    Jaya, S; Durance, T D; Wang, R

    2009-03-01

    Microencapsulation of model drug, acetylsalicylic acid into bio-based polymer, alginate-pectin matrix has been undertaken in this work to characterize the microcapsules based on their composition. Different proportions of the alginate-pectin solutions prepared with drug were homogenized and atomized using nitrogen gas into 1.0 M calcium chloride solution to form sol-gel microcapsules. Drug loaded microcapsules were dried using microwave energy under vacuum at low temperature. Average particle size of the microcapsules was found to be 90 micron. Scanning electron microscopy graphs and Fourier Transform Infrared Spectroscopy analysis on the microcapsules confirm the presence of drug in the polymer matrix. X-ray diffraction pattern showed that the microstructure was more like an amorphous pattern. Drug release of the microcapsules was tested in three different pH levels of 1.2, 7.4 and 8.2. Slow and controlled release of drug was observed at all the pH levels. Increase in pectin increased the drug release and also the release was more in acidic pH (1.2) as 75.6% for alginate: pectin-20:80.

  1. Nanomaterial release characteristics in a single-walled carbon nanotube manufacturing workplace

    NASA Astrophysics Data System (ADS)

    Ji, Jun Ho; Kim, Jong Bum; Lee, Gwangjae; Bae, Gwi-Nam

    2015-02-01

    As carbon nanotubes (CNTs) are widely used in various applications, exposure assessment also increases in importance with other various toxicity tests for CNTs. We conducted 24-h continuous nanoaerosol measurements to identify possible nanomaterial release in a single-walled carbon nanotube (SWCNT) manufacturing workplace. Four real-time aerosol instruments were used to determine the nanosized and microsized particle numbers, particle surface area, and carbonaceous species. Task-based exposure assessment was carried out for SWCNT synthesis using the arc plasma and thermal decomposition processes to remove amorphous carbon components as impurities. During the SWCNT synthesis, the black carbon (BC) concentration was 2-12 μg/m3. The maximum BC mass concentrations occurred when the synthesis chamber was opened for harvesting the SWCNTs. The number concentrations of particles with sizes 10-420 nm were 10,000-40,000 particles/cm3 during the tasks. The maximum number concentration existed when a vacuum pump was operated to remove exhaust air from the SWCNT synthesis chamber due to the penetration of highly concentrated oil mists through the window opened. We analyzed the particle mass size distribution and particle number size distribution for each peak episode. Using real-time aerosol detectors, we distinguished the SWCNT releases from background nanoaerosols such as oil mist and atmospheric photochemical smog particles. SWCNT aggregates with sizes of 1-10 μm were mainly released from the arc plasma synthesis. The harvesting process was the main release route of SWCNTs in the workplace.

  2. Incorporation of low molecular weight biocides into polystyrene-divinyl benzene beads with controlled release characteristics.

    PubMed

    Iconomopoulou, S M; Andreopoulou, A K; Soto, A; Kallitsis, J K; Voyiatzis, G A

    2005-01-20

    Triclosan and phosphonium salt biocides have been separately incorporated into polystyrene-divinylbenzene (PS-DVB) beads by suspension polymerization. Ultraviolet (UV) absorption measurements have been used to monitor the release of these low molecular weight biocides out of the PS-DVB beads immersed in water-ethanol mixtures and in physiological saline. The release of the biocide agents is strongly dependent on either the DVB or/and the antimicrobial composition ratio in the beads. An increase of biocide incorporation in the PS/DVB beads was accompanied by a corresponding enhancement of its concentration in liquid mixtures. On the contrary, higher cross-linking densities hindered the biocide migration out of the beads by diminishing its release rate into either the aqueous ethanol solutions or the natural serum. Moreover, Fourier transform Raman (FT-Raman) spectra and Attenuated Total Reflectance Infrared (ATR-FTIR) measurements of the PS-DVB-Triclosan and PS-DVB-phosphonium salt beads, before and after their immersion in water-ethanol solutions, gave a similar qualitative evidence of the biocide release.

  3. Physiological characteristics and related gene expression of after-ripening on seed dormancy release in rice.

    PubMed

    Du, W; Cheng, J; Cheng, Y; Wang, L; He, Y; Wang, Z; Zhang, H

    2015-11-01

    After-ripening is a common method used for dormancy release in rice. In this study, the rice variety Jiucaiqing (Oryza sativa L. subsp. japonica) was used to determine dormancy release following different after-ripening times (1, 2 and 3 months). Germination speed, germination percentage and seedling emergence increased with after-ripening; more than 95% germination and 85% seedling emergence were observed following 1 month of after-ripening within 10 days of imbibition, compared with <45% germination and 20% seedling emergence in freshly harvested seed. Hence, 3 months of after-ripening could be considered a suitable treatment period for rice dormancy release. Dormancy release by after-ripening is mainly correlated with a rapid decline in ABA content and increase in IAA content during imbibition. Subsequently, GA(1)/ABA, GA(7)/ABA, GA(12)/ABA, GA(20)/ABA and IAA/ABA ratios significantly increased, while GA(3)/ABA, GA(4)/ABA and GAs/IAA ratio significantly decreased in imbibed seeds following 3 months of after-ripening, thereby altering α-amylase activity during seed germination. Peak α-amylase activity occurred at an earlier germination stage in after-ripened seeds than in freshly harvested seeds. Expression of ABA, GA and IAA metabolism genes and dormancy-related genes was regulated by after-ripening time upon imbibition. Expression of OsCYP707A5, OsGA2ox1, OsGA2ox2, OsGA2ox3, OsILR1, OsGH3-2, qLTG3-1 and OsVP1 increased, while expression of Sdr4 decreased in imbibed seeds following 3 months of after-ripening. Dormancy release through after-ripening might be involved in weakening tissues covering the embryo via qLTG3-1 and decreased ABA signalling and sensitivity via Sdr4 and OsVP1.

  4. Chemical Ionization Mass Spectrometry Techniques for Measurements of Gas-Phase Ammonia

    NASA Astrophysics Data System (ADS)

    Nowak, J. B.; Neuman, J. A.; Yoshida, K.; Ryerson, T. B.; Huey, L. G.; Tanner, D. J.; Sjostedt, S. J.; Hubler, G.; Fortin, T. J.; Sueper, D. J.; Fehsenfeld, F. C.

    2005-12-01

    Chemical Ionization Mass Spectrometry (CIMS) can be a highly selective technique with fast time response for measuring many atmospheric trace gases (e.g., hydroxyl radical (OH), sulfuric acid (H2SO4), nitric acid (HNO3)). CIMS is highly versatile and has been used under a wide variety of conditions with many different ion-molecule detection schemes, even for detecting the same molecule. Because of its high proton affinity (853.6 kJ/mol), ammonia (NH3) is another ideal candidate for detection by CIMS. NH3, the dominant gas-phase base in the atmosphere, is a precursor of ammonium nitrate and ammonium sulfates, compounds that are important constituents of airborne fine particulate matter that affect air quality. The characterization of three NH3 CIMS instruments: an atmospheric pressure ionization instrument and a low-pressure flow tube reactor instrument, both utilizing protonated ethanol cluster ion chemistry, and a different low-pressure flow tube reactor instrument using protonated acetone dimer ion chemistry, is presented here. Instrument performance is assessed using ambient data from both ground-based and airborne field programs to examine detection sensitivity, background signal, and time response. Laboratory characterization of different inlet materials is also presented. All three instruments used PFA Teflon sampling inlets. Instrumental backgrounds were determined by scrubbing NH3 from ambient air using silicon phosphates that release phosphoric acid when exposed to ambient levels of humidity. Standard addition calibrations were performed using NH3 permeation devices whose output was determined via 185nm optical absorption. Regardless of CIMS technique or ion chemistry used, the observed detection sensitivities were all adequate for detecting changes in NH3 at the 10 pptv level on a 1s timescale. The time responses, defined by a 1/e2 decay in the calibration signal, ranged from 5s to 45s for the different sampling inlet configurations and are rapid enough

  5. Influence of magnesium aluminium silicate on rheological, release and permeation characteristics of diclofenac sodium aqueous gels in-vitro.

    PubMed

    Pongjanyakul, Thaned; Priprem, Aroonsri; Puttipipatkhachorn, Satit

    2005-04-01

    The effect of magnesium aluminium silicate (MAS) on rheological, release and permeation characteristics of diclofenac sodium (DS) aqueous gels was investigated. DS aqueous gels were prepared using various gelling agents, such as 15% w/w poloxamer 407 (PM407), 1% w/w hydroxypropylmethylcellulose (HPMC), and 1% w/w high and low viscosity grades of sodium alginate (HV-SA and LV-SA, respectively). Different amounts of MAS (0.5, 1.0 and 1.5% w/w) were incorporated into the DS gels. Incorporation of MAS into the DS gels prepared using SA or PM407 caused a statistical increase in viscosity (P<0.05) and a shift from Newtonian flow to pseudoplastic flow with thixotropic property. The DS release rates of these composite gels were significantly decreased (P<0.05) when compared with the control gels. This was due to an interaction between MAS and PM407 or SA, and adsorption of DS onto MAS particles. Moreover, a longer lag time and no change in DS permeation flux were found when MAS was added to the gels. The findings suggest that the rheological characteristics of gels prepared using PM407 or SA could be improved by incorporating MAS. However, the use of MAS could retard the DS release and extend the lag time of DS permeation.

  6. Influence of excipients on characteristics and release profiles of poly(ε-caprolactone) microspheres containing immunoglobulin G.

    PubMed

    Erdemli, Özge; Keskin, Dilek; Tezcaner, Ayşen

    2015-03-01

    Protein instability during microencapsulation has been one of the major drawbacks of protein delivery systems. In this study, the effects of various excipients (poly vinyl alcohol, glucose, starch, heparin) on the stability of encapsulated human immunoglobulin G (IgG) in poly(ε-caprolactone) (PCL) microspheres and on microsphere characteristics were investigated before and after γ-sterilization. Microspheres formulated without any excipients and with glucose had a mean particle size around 3-4μm whereas the mean particle sizes of other microspheres were around 5-6μm. Use of PVA significantly increased the IgG-loading and encapsulation efficiency of microspheres. After γ-irradiation, IgG stability was mostly maintained in the microspheres with excipients compared to microspheres without any excipients. According to the μBCA results, microspheres without any excipient showed a high initial burst release as well as a fast release profile among all groups. Presence of PVA decreased the loss in the activity of IgG released before (completely retained after 6h and 15.69% loss after 7days) and after γ-irradiation (26.04% loss and 52.39% loss after 6h and 7days, respectively). The stabilization effect of PVA on the retention of the activity of released IgG was found more efficient compared to other groups formulated with carbohydrates.

  7. Simplification of the CBS-QB3 method for predicting gas-phase deprotonation free energies

    NASA Astrophysics Data System (ADS)

    Casasnovas, Rodrigo; Frau, Juan; Ortega-Castro, Joaquín; Salvà, Antoni; Donoso, Josefa; Muñoz, Francisco

    Simplified versions of CBS-QB3 model chemistry were used to calculate the free energies of 36 deprotonation reactions in the gas phase. The best such version, S9, excluded coupled cluster calculation [CCSD(T)], and empirical (ΔEemp) and spin-orbit (ΔEint) correction terms. The mean absolute deviation and root mean square thus obtained (viz. 1.24 and 1.56 kcal/mol, respectively) were very-close to those provided by the original CBS-QB3 method (1.19 and 1.52 kcal/mol, respectively). The high-accuracy of the proposed simplification and its computational expeditiousness make it an excellent choice for energy calculations on gas-phase deprotonation reactions in complex systems.

  8. Distinct Fragmentation Pathways of Anticancer Drugs Induced by Charge-Carrying Cations in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Hong, Areum; Lee, Hong Hee; Heo, Chae Eun; Cho, Yunju; Kim, Sunghwan; Kang, Dukjin; Kim, Hugh I.

    2017-04-01

    With the growth of the pharmaceutical industry, structural elucidation of drugs and derivatives using tandem mass spectrometry (MS2) has become essential for drug development and pharmacokinetics studies because of its high sensitivity and low sample requirement. Thus, research seeking to understand fundamental relationships between fragmentation patterns and precursor ion structures in the gas phase has gained attention. In this study, we investigate the fragmentation of the widely used anticancer drugs, doxorubicin (DOX), vinblastine (VBL), and vinorelbine (VRL), complexed by a singly charged proton or alkali metal ion (Li+, Na+, K+) in the gas phase. The drug-cation complexes exhibit distinct fragmentation patterns in tandem mass spectra as a function of cation size. The trends in fragmentation patterns are explicable in terms of structures derived from ion mobility mass spectrometry (IM-MS) and theoretical calculations.

  9. Atmospheric Consequences of the Hydration in Gas Phase of Aldehydes and Ketones

    NASA Astrophysics Data System (ADS)

    Vaida, V.; Axson, J. L.; Maron, M. K.

    2010-12-01

    Aldehydes and ketones are known oxidation products of biogenic and anthropogenic VOCs and have been observed by field studies to be present in aerosol and cloud particles. While the gas-phase chemistry of these compounds is fairly well understood, their modeled concentration and role in SOA formation remains controversial. In aqueous solution aldehydes and ketones hydrate to form alcohols. We explore the hydration of these compounds in the gas phase and examine the water and photon mediated processes of these hydrates. The formation of hydrates can contribute to aerosol growth and formation by partitioning into clouds and aerosols because of their lower vapor pressure and tendency to form intermolecular hydrogen bonds. Hydration of aldehydes and ketones has important consequences to the atmospheric photochemistry of these organic compounds. The experimental approaches employ Fourier transform spectroscopy (FTS) and cavity ringdown spectroscopy (CRDS) to observe the formation of diols and hydrates by these molecules as a function of relative humidity.

  10. Gas-phase catalysis by atomic and cluster metal ions: the ultimate single-site catalysts.

    PubMed

    Böhme, Diethard K; Schwarz, Helmut

    2005-04-15

    Gas-phase experiments with state-of-the-art techniques of mass spectrometry provide detailed insights into numerous elementary processes. The focus of this Review is on elementary reactions of ions that achieve complete catalytic cycles under thermal conditions. The examples chosen cover aspects of catalysis pertinent to areas as diverse as atmospheric chemistry and surface chemistry. We describe how transfer of oxygen atoms, bond activation, and coupling of fragments can be mediated by atomic or cluster metal ions. In some cases truly unexpected analogies of the idealized gas-phase ion catalysis can be drawn with related chemical transformations in solution or the solid state, and so improve our understanding of the intrinsic operation of a practical catalyst at a strictly molecular level.

  11. Photoelectron Velocity Map Imaging of Vibrationally Excited, Gas-Phase Biomolecules and Their Anions

    NASA Astrophysics Data System (ADS)

    Bakker, Daniël; Bakels, Sjors; van der Made, Rutger; Peters, Atze; Rijs, Anouk

    2016-06-01

    A powerful method in spectroscopy to characterize the structure of large, gas phase molecules is to probe the ionization yield upon irradiating the molecules with infrared (IR) and/or ultraviolet (UV) radiation. When this spectroscopic technique is employed, the photodetached electrons are usually ignored, although they contain information on, for example, the ionization threshold of the molecule and the excited states of the formed ions. Here, the novel combination of a molecular beam mass spectrometer equipped with a laser desorption source, the free electron laser FELIX and the powerful velocity map imaging (VMI) technique is presented. With this extended set of tools we can bring large molecules intact into the gas phase and prepare them in specific vibrationally excited states. UV or VUV radiation can subsequently be used to ionize the molecules. The kinetic energy and the radial distribution of the photoelectrons can be measured using VMI combined with ion detection using a time-of-flight mass spectrometer.

  12. Accumulation of polycyclic aromatic hydrocarbons by lichen transplants: Comparison with gas-phase passive air samplers.

    PubMed

    Loppi, S; Pozo, K; Estellano, V H; Corsolini, S; Sardella, G; Paoli, L

    2015-09-01

    This study compared the accumulation of 16 polycyclic aromatic hydrocarbons (PAHs) in samples of the lichen Evernia prunastri exposed for 3 months in and around an industrial area of S Italy with that in co-located passive gas-phase air samplers. The results showed a strong linear correlations (R=0.96, P<0.05) between total PAHs in lichens and in passive samplers, clearly indicating that lichen transplants may provide direct quantitative information on the atmospheric load by total PAHs, allowing translation of lichen values into atmospheric concentrations. To the best of our knowledge this is the first study reporting such a correlation with gas-phase passive air samplers. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Gas-Phase Femtosecond Particle Spectroscopy: A Bottom-Up Approach to Nucleotide Dynamics.

    PubMed

    Stavros, Vasilios G; Verlet, Jan R R

    2016-05-27

    We summarize how gas-phase ultrafast charged-particle spectroscopy has been used to provide an understanding of the photophysics of DNA building blocks. We focus on adenine and discuss how, following UV excitation, specific interactions determine the fates of its excited states. The dynamics can be probed using a systematic bottom-up approach that provides control over these interactions and that allows ever-larger complexes to be studied. Starting from a chromophore in adenine, the excited state decay mechanisms of adenine and chemically substituted or clustered adenine are considered and then extended to adenosine mono-, di-, and trinucleotides. We show that the gas-phase approach can offer exquisite insight into the dynamics observed in aqueous solution, but we also highlight stark differences. An outlook is provided that discusses some of the most promising developments in this bottom-up approach.

  14. Gas-Phase Synthesis of 1-Silacyclopenta-2,4-diene.

    PubMed

    Yang, Tao; Dangi, Beni B; Thomas, Aaron M; Sun, Bing-Jian; Chou, Tzu-Jung; Chang, Agnes H H; Kaiser, Ralf I

    2016-07-04

    Silole (1-silacyclopenta-2,4-diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon-bearing radical, silylidyne (SiH), with 1,3-butadiene (C4 H6 ) in the gas phase under single-collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels-Alder dimerization, thus enabling the clean gas-phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single-collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods.

  15. Fundamental studies of gas phase ionic reactions by ion mobility spectrometry

    NASA Technical Reports Server (NTRS)

    Giles, K.; Knighton, W. B.; Sahlstrom, K. E.; Grimsrud, E. P.

    1995-01-01

    Ion mobility spectrometry (IMS) provides a promising approach to the study of gas phase ionic reactions in buffer gases at unusually high pressures. This point is illustrated here by studies of the Sn2 nucleophilic displacement reaction, Cl(-) + CH3Br yields Br + CH3Br, using IMS at atmospheric pressure. The equilibrium clustering reaction, Cl(-)(CHCI3)(n - 1) + CHCI3 yields Cl(-)(CHCI3)(n), where n = 1 and 2, and the effect of clustering on the Sn2 reaction with CH3Br have also been characterized by this IMS-based kinetic method. Present problems and anticipated improvements in the application of ion mobility spectrometry to studies of other gas phase ionic processes are discussed.

  16. Taming molecular beams; towards a gas-phase molecular laboratory on a chip

    NASA Astrophysics Data System (ADS)

    Meek, Samuel A.; Santambrogio, Gabriele; Conrad, Horst; Meijer, Gerard

    2009-11-01

    The manipulation of gas-phase molecules with electric and magnetic fields above a chip is an emerging field of research. Miniaturization of the electric and magnetic field structures allows for the creation of large field gradients and tight traps above the chip. Present-day microelectronics technology enables the integration of complicated tools and devices on a compact surface area. The molecules can be positioned extremely accurately and reproducibly above the chip where they can be held isolated from their environment and where there is excellent access to them. It is expected that several of the gas-phase molecular beam experiments that are currently being done in machines that are up to several meters in length can in the future be performed on a surface area of a few cm2 and that many new experiments will become possible.

  17. Gas-phase reactivity of [Ca(formamide)](2+) complex: an example of different dynamical behaviours.

    PubMed

    Martin-Somer, Ana; Spezia, Riccardo; Yáñez, Manuel

    2017-04-28

    In the present contribution, we have summarized our recent work on the comprehension of [Ca(formamide)](2+) complex gas-phase unimolecular dissociation. By using different theoretical approaches, we were able to revise the original (and typical for such kind of problems) understanding given in terms of stationary points on the potential energy surface, which did not provide a satisfactory explanation of the experimentally observed reactivity. In particular, we point out how non-statistical and non-intrinsic reaction coordinate mechanisms are of fundamental importance.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.

  18. Properties of clusters in the gas phase. V - Complexes of neutral molecules onto negative ions

    NASA Technical Reports Server (NTRS)

    Keesee, R. G.; Lee, N.; Castleman, A. W., Jr.

    1980-01-01

    Ion-molecules association reactions of the form A(-)(B)n-1 + B = A(-)(B)n were studied over a range of temperatures in the gas phase using high pressure mass spectrometry. Enthalpy and entropy changes were determined for the stepwise clustering reactions of (1) sulfur dioxide onto Cl(-), I(-), and NO2(-) with n ranging from one to three or four, and onto SO2(-) and SO3(-) with n equal to one; and (2) carbon dioxide onto Cl(-), I(-), NO2(-), CO3(-), and SO3(-) with n equal to one. From these data and earlier hydration results, the order of the magnitude of the enthalpy changes on the association of the first neutral for a series of negative ions was found to parallel the gas-phase basicity of those anions.

  19. Imaging molecular structure through femtosecond photoelectron diffraction on aligned and oriented gas-phase molecules.

    PubMed

    Boll, Rebecca; Rouzée, Arnaud; Adolph, Marcus; Anielski, Denis; Aquila, Andrew; Bari, Sadia; Bomme, Cédric; Bostedt, Christoph; Bozek, John D; Chapman, Henry N; Christensen, Lauge; Coffee, Ryan; Coppola, Niccola; De, Sankar; Decleva, Piero; Epp, Sascha W; Erk, Benjamin; Filsinger, Frank; Foucar, Lutz; Gorkhover, Tais; Gumprecht, Lars; Hömke, André; Holmegaard, Lotte; Johnsson, Per; Kienitz, Jens S; Kierspel, Thomas; Krasniqi, Faton; Kühnel, Kai-Uwe; Maurer, Jochen; Messerschmidt, Marc; Moshammer, Robert; Müller, Nele L M; Rudek, Benedikt; Savelyev, Evgeny; Schlichting, Ilme; Schmidt, Carlo; Scholz, Frank; Schorb, Sebastian; Schulz, Joachim; Seltmann, Jörn; Stener, Mauro; Stern, Stephan; Techert, Simone; Thøgersen, Jan; Trippel, Sebastian; Viefhaus, Jens; Vrakking, Marc; Stapelfeldt, Henrik; Küpper, Jochen; Ullrich, Joachim; Rudenko, Artem; Rolles, Daniel

    2014-01-01

    This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C(8)H(5)F) and dissociating, laser-aligned 1,4-dibromobenzene (C(6)H(4)Br(2)) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.

  20. Distinct Fragmentation Pathways of Anticancer Drugs Induced by Charge-Carrying Cations in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Hong, Areum; Lee, Hong Hee; Heo, Chae Eun; Cho, Yunju; Kim, Sunghwan; Kang, Dukjin; Kim, Hugh I.

    2016-12-01

    With the growth of the pharmaceutical industry, structural elucidation of drugs and derivatives using tandem mass spectrometry (MS2) has become essential for drug development and pharmacokinetics studies because of its high sensitivity and low sample requirement. Thus, research seeking to understand fundamental relationships between fragmentation patterns and precursor ion structures in the gas phase has gained attention. In this study, we investigate the fragmentation of the widely used anticancer drugs, doxorubicin (DOX), vinblastine (VBL), and vinorelbine (VRL), complexed by a singly charged proton or alkali metal ion (Li+, Na+, K+) in the gas phase. The drug-cation complexes exhibit distinct fragmentation patterns in tandem mass spectra as a function of cation size. The trends in fragmentation patterns are explicable in terms of structures derived from ion mobility mass spectrometry (IM-MS) and theoretical calculations.

  1. Hydration energies of deprotonated amino acids from gas phase equilibria measurements.

    PubMed

    Wincel, Henryk

    2008-08-01

    Singly hydrated clusters of deprotonated amino acids were studied using an electrospray high-pressure mass spectrometer equipped with a pulsed ion-beam reaction chamber. Thermochemical data, DeltaH(o), DeltaS(o), and DeltaG(o), for the hydration reaction [AA - H](-) + H(2)O = [AA - H](-).(H(2)O) were obtained from gas-phase equilibria determinations for AA = Gly, Ala, Val, Pro, Phe, Lys, Met, Trp, Gln, Arg, and Asp. The hydration free-energy changes are found to depend significantly on the side-chain substituents. The water binding energy in [AA - H](-).(H(2)O) increases with the gas-phase acidity of AA. The anionic hydrogen bond strengths in [AA - H](-).(H(2)O) are compared with those of the cationic bonds in the corresponding AAH(+).(H(2)O) systems.

  2. Unusual hydroxyl migration in the fragmentation of β-alanine dication in the gas phase.

    PubMed

    Piekarski, Dariusz Grzegorz; Delaunay, Rudy; Maclot, Sylvain; Adoui, Lamri; Martín, Fernando; Alcamí, Manuel; Huber, Bernd A; Rousseau, Patrick; Domaracka, Alicja; Díaz-Tendero, Sergio

    2015-07-14

    We present a combined experimental and theoretical study of the fragmentation of doubly positively charged β-alanine molecules in the gas phase. The dissociation of the produced dicationic molecules, induced by low-energy ion collisions, is analysed by coincidence mass spectrometric techniques; the coupling with ab initio molecular dynamics simulations allows rationalisation of the experimental observations. The present strategy gives deeper insights into the chemical mechanisms of multiply charged amino acids in the gas phase. In the case of the β-alanine dication, in addition to the expected Coulomb explosion and hydrogen migration processes, we have found evidence of hydroxyl-group migration, which leads to unusual fragmentation products, such as hydroxymethyl cation, and is necessary to explain some of the observed dominant channels.

  3. Selective covalent bond formation in polypeptide ions via gas-phase ion/ion reaction chemistry.

    PubMed

    Han, Hongling; McLuckey, Scott A

    2009-09-16

    Primary amines present in protonated polypeptides can be covalently modified via gas-phase ion/ion reactions using bifunctional reagent ions. The use of reagent anions with a charge-bearing site that leads to strong interactions with the polypeptide, such as sulfonic acid, gives rise to the formation of a long-lived adduct. A distinct reactive functional group, an aldehyde in the present case, can then undergo reaction with the peptide. Collisional activation of the adduct ion formed from a reagent with an aldehyde group and a peptide ion with a primary amine gives rise to water loss in conjunction with imine (Schiff base) formation. The covalently bound modification is retained upon subsequent collisional activation. This work demonstrates the ability to selectively modify polypeptide ions in the gas phase within the context of a multistage mass spectrometry experiment.

  4. Ultraviolet Study of the Gas Phase Hydration of Methylglyoxal to Form the Gemdiol

    NASA Astrophysics Data System (ADS)

    Kroll, Jay A.; Hansen, Anne S.; Møller, Kristian H.; Axson, Jessica L.; Kjaergaard, Henrik G.; Vaida, Veronica

    2017-06-01

    Methylglyoxal is a known oxidation product of volatile organic compounds (VOCs) in Earth's atmosphere. While the gas phase chemistry of methylglyoxal is fairly well understood, its modeled concentration and role in the formation of secondary organic aerosol (SOA) continues to be controversial. The gas phase hydration of methylglyoxal to form a gemdiol has been shown to occur in infrared studies but has not been widely considered for water-restricted environments such as the atmosphere. However, this process may have important consequences for the atmospheric processing or VOCs. We have recorded UV spectroscopic measurements following the hydration of methylglyoxal and have compared these measurements to calculated spectra of the electronic transitions of methylglyoxal and methylglyoxal diol. We will report on these measurements and discuss the implications for understanding the atmospheric processing and fate of methylglyoxal and similar molecules

  5. Gas-Phase Femtosecond Particle Spectroscopy: A Bottom-Up Approach to Nucleotide Dynamics

    NASA Astrophysics Data System (ADS)

    Stavros, Vasilios G.; Verlet, Jan R. R.

    2016-05-01

    We summarize how gas-phase ultrafast charged-particle spectroscopy has been used to provide an understanding of the photophysics of DNA building blocks. We focus on adenine and discuss how, following UV excitation, specific interactions determine the fates of its excited states. The dynamics can be probed using a systematic bottom-up approach that provides control over these interactions and that allows ever-larger complexes to be studied. Starting from a chromophore in adenine, the excited state decay mechanisms of adenine and chemically substituted or clustered adenine are considered and then extended to adenosine mono-, di-, and trinucleotides. We show that the gas-phase approach can offer exquisite insight into the dynamics observed in aqueous solution, but we also highlight stark differences. An outlook is provided that discusses some of the most promising developments in this bottom-up approach.

  6. Gas-phase composition of the HgTe-NH/sub 4/Cl system

    SciTech Connect

    Akhromenko, Yu.G.; Viblyi, I.F.; Il'chuk, G.A.; Pavlishin, S.P.; Petrenko, S.I.

    1987-04-01

    The authors have calculated the equilibrium partial pressures of the gas phase components of the closed HgTe-NH/sub 4/Cl system in the 563-883/sup 0/K temperature range and pressures of 0.01 x 10/sup 5/ to 1 x 10/sup 5/ Pa produced by the products of NH/sub 4/Cl reacting with HgTe at the homogeneity-region boundaries of HgTe with Hg and Te. The authors have demonstrated that in this system the transfer of HgTe is due mostly to the sublimation of mercury telluride in the source region followed by its condensation in the crystallization region, limited by the low tellurium content of the gas phase.

  7. Infrared Action Spectroscopy of Low-Temperature Neutral Gas-Phase Molecules of Arbitrary Structure

    NASA Astrophysics Data System (ADS)

    Yatsyna, Vasyl; Bakker, Daniël J.; Salén, Peter; Feifel, Raimund; Rijs, Anouk M.; Zhaunerchyk, Vitali

    2016-09-01

    We demonstrate a technique for IR action spectroscopy that enables measuring IR spectra in a background-free fashion for low-temperature neutral gas-phase molecules of arbitrary structure. The method is exemplified experimentally for N -methylacetamide molecules in the mid-IR spectral range of 1000 - 1800 cm-1 , utilizing the free electron laser FELIX. The technique involves the resonant absorption of multiple mid-IR photons, which induces molecular dissociation. The dissociation products are probed with 10.49 eV vacuum ultraviolet photons and analyzed with a mass spectrometer. We also demonstrate the capability of this method to record, with unprecedented ease, mid-IR spectra for the molecular associates, such as clusters and oligomers, present in a molecular beam. In this way the mass-selected spectra of low-temperature gas-phase dimers and trimers of N -methylacetamide are measured in the full amide I-III range.

  8. Counting basic sites in oligopeptides via gas-phase ion chemistry

    SciTech Connect

    Stephenson, J.L. Jr.; McLuckey, S.A.

    1997-02-01

    Cations derived from oligopeptides ranging from laminin fragment (5 residues) to {beta}-lactoglobulin (162 residues) have been subjected to gas-phase ion/molecule reactions with hydroiodic acid. The sum of the ion charge state and the maximum number of molecules of hydroiodic acid that attach to the ion is equal to the total number of lysines, arginines, histidines, and N-termini consisting of a primary amine for ions derived from all 21 oligopeptides studied. These results suggest that ion/molecule reactions can provide useful information regarding oligopeptide basic site number, which might be used as a criterion for searching protein data bases instead of, or in conjunction with, use of proteolytic digestion or gas-phase ion dissociation procedures. 31 refs., 3 figs., 1 tab.

  9. Anchoring the gas-phase acidity scale: From formic acid to methanethiol

    NASA Astrophysics Data System (ADS)

    Eyet, Nicole; Villano, Stephanie M.; Bierbaum, Veronica M.

    2009-06-01

    We have measured the gas-phase acidities of nine compounds: formic acid, acetic acid, 1,3-propanedithiol, 2-methyl-2-propanethiol, 3-methyl-1-butanethiol, 2-propanethiol, 1-propanethiol, ethanethiol, and methanethiol, with acidities ranging from 338.6 to 351.1 kcal mol-1 using proton transfer kinetics and the resulting equilibrium constants. These acids were anchored to the well-known acidity of hydrogen sulfide; the measured acidities are in good agreement with previous experimental values, but error bars are significantly reduced. The gas-phase acidity of 3-methyl-1-butanethiol was determined to be 347.1 (5) kcal mol-1; there were no previous measurements of this value. Entropies of deprotonation were calculated and enthalpies of deprotonation were determined.

  10. Gas-phase acidities of tetrahedral oxyacids from ab initio electronic structure theory

    SciTech Connect

    Rustad, J.R.; Dixon, D.A.; Kubicki, J.D.; Felmy, A.R.

    2000-05-04

    Density functional calculations have been performed on several protonation states of the oxyacids of Si, P, V, As, Cr, and S. Structures and vibrational frequencies are in good agreement with experimental values where these are available. A reasonably well-defined correlation between the calculated gas-phase acidities and the measured pK{sub a} in aqueous solution has been found. The pK{sub a}/gas-phase acidity slopes are consistent with those derived from previous molecular mechanics calculations on ferric hydrolysis and the first two acidity constants for orthosilicic acid. The successive deprotonation of other H{sub n}TO{sub 4} species, for a given tetrahedral anion T are roughly consistent with this slope, but not to the extent that there is a universal correlation among all species.

  11. Surface elastic modulus of barnacle adhesive and release characteristics from silicone surfaces.

    PubMed

    Sun, Yujie; Guo, Senli; Walker, Gilbert C; Kavanagh, Christopher J; Swain, Geoffrey W

    2004-12-01

    The properties of barnacle adhesive on silicone surfaces were studied by AFM indentation, imaging, and other tests and compared to the barnacle shear adhesion strength. A multilayered structure of barnacle adhesive plaque is proposed based on layered modulus regions measured by AFM indentation. The fracture of barnacles from PDMS surfaces was found to include both interfacial and cohesive failure of barnacle adhesive plaque, as determined by protein staining of the substratum after forced barnacle release from the substrate. Data for freshly released barnacles showed that there was a strong correlation between the mean Young's modulus of the outermost (softest) adhesive layer (E<0.3 MPa) and the shear strength of adhesion, but no correlation for other higher modulus regions. Linear, quadratic, and Griffith's failure criterion (based on rough estimate of crack length) regressions were used in the fit, and showed significance.

  12. Release characteristics of reattached barnacles to non-toxic silicone coatings.

    PubMed

    Kim, Jongsoo; Nyren-Erickson, Erin; Stafslien, Shane; Daniels, Justin; Bahr, James; Chisholm, Bret J

    2008-01-01

    Release mechanisms of barnacles (Amphibalanus amphitrite or Balanus amphitrite) reattached to platinum-cured silicone coatings were studied as a function of coating thickness (210-770 microm), elastic modulus (0.08-1.3 MPa), and shear rate (2-22 microm s(-1)). It was found that the shear stress of the reattached, live barnacles necessary to remove from the silicone coatings was controlled by the combined term (E/t)(0.5) of the elastic modulus (E) and thickness (t). As the ratio of the elastic modulus to coating thickness decreased, the barnacles were more readily removed from the silicone coatings, showing a similar release behavior to pseudobarnacles (epoxy glue). The barnacle mean shear stress ranged from 0.017 to 0.055 MPa whereas the pseudobarnacle mean shear stress ranged from 0.022 to 0.095 MPa.

  13. Antimicrobial and water-triggered release characteristics of a copper sulfate-polyvinyl acetate adhesive composite

    NASA Astrophysics Data System (ADS)

    De Jesus, A. P. O.; Roxas-Villanueva, R. M. L.; Herrera, M. U.

    2017-05-01

    Water-triggered release of antimicrobial solutions is advantageous in inhibiting the growth of bacteria and fungi in moist and wet environments. In this study, we fabricated a composite, by mixing polyvinyl acetate adhesive with copper sulfate solution, which exhibits antimicrobial activities against bacteria. Polyvinyl acetate adhesive serves as the binder and water soluble substance while copper sulfate serves as the antimicrobial agent. The composite was coated in an acetate film and air-dried. To monitor the rate of release of copper ions, the composite was submerged in water and the conductivity was measured. The conductivity saturation time was determined. The composite showed antimicrobial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive).

  14. GAS PHASE MOLECULAR DYNAMICS: HIGH-RESOLUTION SPECTROSCOPIC PROBES OF CHEMICAL DYNAMICS.

    SciTech Connect

    HALL, G.E.

    2006-05-30

    This research is carried out as part of the Gas Phase Molecular Dynamics group program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopic tools are developed and applied to problems in chemical dynamics. Recent topics have included the state-resolved studies of collision-induced electronic energy transfer, dynamics of barrierless unimolecular reactions, and the kinetics and spectroscopy of transient species.

  15. Conformational Study of DNA Sugars: from the Gas Phase to Solution

    NASA Astrophysics Data System (ADS)

    Uriarte, Iciar; Vallejo-López, Montserrat; Cocinero, Emilio J.; Corzana, Francisco; Davis, Benjamin G.

    2017-06-01

    Sugars are versatile molecules that play a variety of roles in the organism. For example, they are important in energy storage processes or as structural scaffolds. Here, we focus on the monosaccharide present in DNA by addressing the conformational and puckering properties in the gas phase of α- and β-methyl-2-deoxy-ribofuranoside and α- and β-methyl-2-deoxy-ribopiranoside. Other sugars have been previously studied in the gas phase The work presented here stems from a combination of chemical synthesis, ultrafast vaporization methods, supersonic expansions, microwave spectroscopy (both chirped-pulsed and Balle-Flygare cavity-based spectrometers) and NMR spectroscopy. Previous studies in the gas phase had been performed on 2-deoxyribose, but only piranose forms were detected. However, thanks to the combination of these techniques, we have isolated and characterized for the first time the conformational landscape of the sugar present in DNA in its biologically relevant furanose form. Our gas phase study serves as a probe of the conformational preferences of these biomolecules under isolation conditions. Thanks to the NMR experiments, we can characterize the favored conformations in solution and extract the role of the solvent in the structure and puckering of the monosaccharides. E. J. Cocinero, A. Lesarri, P. Écija, F. J. Basterretxea, J.-U. Grabow, J. A. Fernández, F. Castaño, Angew. Chem. Int. Edit. 2012, 51, 3119. P. Écija, I. Uriarte, L. Spada, B. G. Davis, W. Caminati, F. J. Basterretxea, A. Lesarri, E. J. Cocinero, Chem. Commun. 2016, 52, 6241. I. Peña, E. J. Cocinero, C. Cabezas, A. Lesarri, S. Mata, P. Écija, A. M. Daly, Á. Cimas, C. Bermúdez, F. J. Basterretxea, S. Blanco, J. A. Fernández, J. C. López, F. Castaño, J. L. Alonso, Angew. Chem. Int. Edit. 2013, 52, 11840.

  16. Method and apparatus for selective capture of gas phase analytes using metal .beta.-diketonate polymers

    DOEpatents

    Harvey, Scott D [Kennewick, WA

    2011-06-21

    A process and sensor device are disclosed that employ metal .beta.-diketonate polymers to selectively capture gas-phase explosives and weaponized chemical agents in a sampling area or volume. The metal .beta.-diketonate polymers can be applied to surfaces in various analytical formats for detection of: improvised explosive devices, unexploded ordinance, munitions hidden in cargo holds, explosives, and chemical weapons in public areas.

  17. Comparison of ozone determinations by ultraviolet photometry and gas-phase titration

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Patapoff, M.

    1976-01-01

    A comparison of ozone determinations based on ultraviolet absorption photometry and gas-phase titration (GPT) shows good agreement between the two methods. Together with other results, these findings indicate that three candidate reference methods for ozone, UV photometry, IR photometry, and GPT are in substantial agreement. However, the GPT method is not recommended for routine use by air pollution agencies for calibration of ozone monitors because of susceptibility to experimental error.

  18. Missing gas-phase source of HONO inferred from Zeppelin measurements in the troposphere

    NASA Astrophysics Data System (ADS)

    Li, Xin; Rohrer, Franz; Hofzumahaus, Andreas; Brauers, Theo; Häseler, Rolf; Bohn, Birger; Broch, Sebastian; Fuchs, Hendrik; Gomm, Sebastian; Holland, Frank; Jäger, Julia; Kaiser, Jennifer; Keutsch, Frank N.; Lohse, Insa; Tillmann, Ralf; Wegener, Robert; Wolfe, Glenn M.; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas

    2014-05-01

    Nitrous acid (HONO) is an important trace gas in the atmosphere due to its contribution to the cycles of nitrogen oxides (NOX) and hydrogen oxides (HOX). In the past decades, ground-based observations of HONO around the world showed much higher daytime concentrations than can be explained by the known gas-phase chemistry (i.e., HONO + hν → OH + NO, HONO + OH → NO2 + H2O, OH + NO + M → HONO + M). Different light-dependent reactions on ground surfaces have been proposed as additional daytime HONO sources. However, due to lack of measurements, little is known about the concentrations of HONO and its sources in the planetary boundary layer (PBL) at higher altitudes above the earth's surface. The airship Zeppelin NT is an ideal platform to investigate the chemistry and dynamics of the PBL. During the PEGASOS field campaigns in 2012 and 2013, HONO and its gas-phase sources and sinks were measured simultaneously on-board the airship Zeppelin NT, for the lowest 1 km of the PBL. In the upper part of the altitude range during morning hours, when the airmass is still isolated from processes at the earth's surface by the remaining nocturnal boundary layer, we find unexpectedly large concentrations of HONO which can neither be explained by heterogeneous reactions on aerosol and ground surfaces, nor by known gas-phase reactions. Our observations show evidence for an unknown gas-phase light-dependent HONO production which dominates the overall HONO formation in the lower troposphere. This new HONO source requires NOX and possibly OH or HO2 radicals. As a result, the general impact of HONO on the OH formation is likely overestimated.

  19. Method and apparatus for selective capture of gas phase analytes using metal .beta.-diketonate polymers

    DOEpatents

    Harvey, Scott D [Kennewick, WA

    2011-06-21

    A process and sensor device are disclosed that employ metal .beta.-diketonate polymers to selectively capture gas-phase explosives and weaponized chemical agents in a sampling area or volume. The metal .beta.-diketonate polymers can be applied to surfaces in various analytical formats for detection of: improvised explosive devices, unexploded ordinance, munitions hidden in cargo holds, explosives, and chemical weapons in public areas.

  20. Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

    DOEpatents

    Lin, Manhua; Wang, Xiang; Yeom, Younghoon

    2015-09-29

    A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase is dispersed.

  1. Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

    DOEpatents

    Lin, Manhua; Wang, Xiang; Yeom, Younghoon

    2015-03-17

    A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase id dispersed.

  2. Abundant gas-phase H2O in absorption toward massive protostars

    NASA Astrophysics Data System (ADS)

    Boonman, A. M. S.; van Dishoeck, E. F.

    2003-06-01

    We present infrared spectra of gas-phase H2O around 6 mu m toward 12 deeply embedded massive protostars obtained with the Short Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The nu2 ro-vibrational band has been detected toward 7 of the sources and the excitation temperatures indicate an origin in the warm gas at Tex>~ 250 K. Typical derived gas-phase H2O abundances are ~ 5*E-6-6*E-5, with the abundances increasing with the temperature of the warm gas. The inferred gas/solid ratios show a similar trend with temperature and suggest that grain-mantle evaporation is important. The increasing gas/solid ratio correlates with other indicators of increased temperatures. If the higher temperatures are due to a larger ratio of source luminosity to envelope mass, this makes gas-phase H2O a good evolutionary tracer. Comparison with chemical models shows that three different chemical processes, ice evaporation, high-T chemistry, and shocks, can reproduce the high inferred gas-phase H2O abundances. In a forthcoming paper each of these processes are investigated in more detail in comparison with data from the Long Wavelength Spectrometer on board ISO and the Submillimeter Wave Astronomy Satellite (SWAS). Comparison with existing SWAS data indicates that a jump in the H2O abundance is present and that the observed nu2 ro-vibrational band traces primarily the warm inner envelope. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

  3. Comparison of ozone determinations by ultraviolet photometry and gas-phase titration

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Patapoff, M.

    1976-01-01

    A comparison of ozone determinations based on ultraviolet absorption photometry and gas-phase titration (GPT) shows good agreement between the two methods. Together with other results, these findings indicate that three candidate reference methods for ozone, UV photometry, IR photometry, and GPT are in substantial agreement. However, the GPT method is not recommended for routine use by air pollution agencies for calibration of ozone monitors because of susceptibility to experimental error.

  4. Microsequence analysis of peptides and proteins. IX. Manual gas-phase microsequencing of multiple samples.

    PubMed

    Haniu, M; Shively, J E

    1988-09-01

    A novel apparatus for performing manual gas-phase Edman chemistry on protein and peptide samples is described. Edman chemistry is performed in 6 to 10 Teflon continuous flow reactors (CFR), previously described by J.E. Shively et al. (1987) Anal. Biochem. 163, 517-529). The CFRs are packed with 10-15 mg of Polybrene-coated spherical silica (Porasil B, Waters Associates). The gas-phase coupling reagent and cleavage reagent are 5% aqueous triethylamine and anhydrous trifluoroacetic acid, respectively, delivered by a stream of argon gas. The delivery of the gas-phase reagents is manually controlled with Hamilton 3-way valves and 2-way valves, and that of the solvents, ethyl acetate and butyl chloride, by syringe pipetting. The average cycle time is 15-20 min for 6 to 10 samples run simultaneously. Conversion of the anilinothiazolinone to phenylthiohydantoin (PTH) amino acid derivatives is accomplished manually with 25% aqueous trifluoroacetic acid. The PTH amino acids are analyzed by reversed-phase HPLC using an autosampler for handling multiple samples. Excellent results were obtained in the 100-200 pmol range. Protein samples can be sequenced from 15-20 cycles, and peptide samples usually to the COOH terminus. Initial yields ranged from 30 to 60% and repetitive yields ranged from 90 to 96%. The sample washout and size of background peaks are significantly reduced, compared to older methods of manual sequence analysis. The yields and background signal to noise are comparable to automated gas-phase Edman chemistry. The improved manual Edman described represents a low cost alternative to automated sequence analysis, and has the advantage being able to process multiple samples simultaneously.

  5. Test and Characterization of Some Zeolite Supported Gas Phase Desulfurization Sorbents

    DTIC Science & Technology

    2009-06-01

    of-the-art SOFC electrode material is improving, the gas phase desulfurization step at high temperature is still essential to SOFCs . Our report ...NOTICES Disclaimers The findings in this report are not to be construed as an official Department of the Army position unless so...the use thereof. Destroy this report when it is no longer needed. Do not return it to the originator. Army Research Laboratory Adelphi, MD

  6. Noncovalent Halogen Bonding as a Mechanism for Gas-Phase Clustering

    NASA Astrophysics Data System (ADS)

    Wegeberg, Christina; Donald, William A.; McKenzie, Christine J.

    2017-10-01

    Gas-phase clustering of nonionizable iodylbenzene (PhIO2) is attributed to supramolecular halogen bonding. Electrospray ionization results in the formation of ions of proton-charged and preferably sodium-charged clusters assignable to [H(PhIO2) n ]+, n = 1-7; [Na(PhIO2) n ]+, n = 1-6; [Na2(PhIO2) n ]2+, n = 7-20; [HNa(PhIO2) n ]2+, n = 6-19; [HNa2(PhIO2) n ]3+, n = 15-30; and [Na3(PhIO2) n ]3+, n = 14-30. The largest cluster detected has a supramolecular mass of 7147 Da. Electronic structure calculations using the M06-2X functional with the 6-311++G(d,p) basis set for C, H, and O, and LANL2DZ basis set for I and Na predict 298 K binding enthalpies for the protonated and sodiated iodylbenzene dimers and trimers are greater than 180 kJ/mol. This is exceptionally high in comparison with other protonated and sodiated clusters with well-established binding enthalpies. Strongly halogen-bonded motifs found in the crystalline phases of PhIO2 and its derivatives serve as models for the structures of larger gas-phase clusters, and calculations on simple model gas-phase dimer and trimer clusters result in similar motifs. This is the first account of halogen bonding playing an extensive role in gas-phase associations. [Figure not available: see fulltext.

  7. Mesoporous silica-based dosage forms improve release characteristics of poorly soluble drugs: case example fenofibrate.

    PubMed

    Dressman, Jennifer B; Herbert, Elisabeth; Wieber, Alena; Birk, Gudrun; Saal, Christoph; Lubda, Dieter

    2016-05-01

    Mesoporous silica-based dosage forms offer the potential for improving the absorption of poorly soluble drugs after oral administration. In this investigation, fenofibrate was used as a model drug to study the ability of monomodal ('PSP A') and bimodal ('PSP B') porous silica to improve release by a 'spring' effect in in vitro biorelevant dissolution tests. Also investigated was the addition of various polymers to provide a 'parachute' effect, that is, to keep the drug in solution after its release. Loading fenofibrate onto PSP A or PSP B porous silica substantially improved the dissolution profile of fenofibrate under fasted state conditions compared with both pure drug and the marketed product, TriCor® 145 mg. Adding a polymer such as hydroxypropyl methylcellulose acetate succinate, polyvinylpyrrolidone or copovidon (HPMCAS, PVP or PVPVA) sustains the higher release of fenofibrate from the PSP A silica, resulting in a combination 'spring and parachute' effect - loading the drug onto the silica causes a 'spring' effect while the polymer enhances the spring effect (HPMCAS, PVP) and adds a sustaining 'parachute'. Interestingly, a silica to polymer ratio of 4:1 w/w appears to have an optimal effect for fenofibrate (HPMCAS, PVP). Dissolution results under conditions simulating the fasted state in the small intestine with the PSP A or the PSP B silica with HPMCAS added in a 4:1 w/w ratio show very substantial improvement over the marketed, nanosized product (TriCor® 145 mg). Further experiments to determine whether the highly positive effects on fenofibrate release observed with the silica prototypes investigated to date can be translated to further poorly soluble drugs and to what extent they translate into improved in-vivo performance are warranted. © 2015 Royal Pharmaceutical Society.

  8. [Spectral characteristics of dissolved organic matter released during the metabolic process of small medusa].

    PubMed

    Guo, Dong-Hui; Yi, Yue-Yuan; Zhao, Lei; Guo, Wei-Dong

    2012-06-01

    The metabolic processes of jellyfish can produce dissolved organic matter (DOM) which will influence the functioning of the aquatic ecosystems, yet the optical properties of DOM released by jellyfish are unknown. Here we report the absorption and fluorescence properties of DOM released by a medusa species Black fordia virginica during a 24 h incubation experiment. Compared with the control group, an obvious increase in the concentrations of dissolved organic carbon (DOC), absorption coefficient (a280) and total dissolved nitrogen (TDN) was observed in incubation group. This clearly demonstrated the release of DOM, chromophoric DOM (CDOM) and dissolved nutrients by B. virginica which feed on enough of Artemia sp. before the experiment. The increase in spectral slope ratio (SR) and decrease in humification index (HIX) indicated that the released DOM was less-humified and had relatively lower molecular weight. Parallel factor analysis (PARAFAC) decomposed the fluorescence matrices of DOM into three humic-like components (C1-C3) and one protein-like component (C4). The Fmax of two components (C2: < 250, 295/386 nm; C4: 275/334 nm) with the emission wavelength < 400 nm increased significantly during the metabolic process of B. virginica. However, the Fmax of the other two components with the emission wavelength > 400 nm showed little changes. Thus, we suggested a zooplankton index (ZIX) to trace and characterize the DOM excreted by metabolic activity of zooplankton, which is calculated as the ratio of the sum of Fmax of all fluorescence components with the emission wavelength < 400 nm to the sum of Fmax of the other components with the emission wavelength > 400 nm.

  9. Phosphorus release rates from sediments and pollutant characteristics in Han River, Seoul, Korea.

    PubMed

    Kim, Lee-Hyung; Choi, Euiso; Gil, Kyung-Ik; Stenstrom, Michael K

    2004-04-05

    The Han River is 469.7-km long and drains a 26219-km(2) watershed. The sediments in the river are highly polluted due to inputs from upstream tributaries as well as partially treated municipal wastewaters that are discharged to the river. The water quality and strategy for control are important because the river is the primary drinking water supply for the City of Seoul, as well as being a major source for irrigation and industrial water. The Jamsil submerged dam partitions the river to isolate an upstream area for drinking water, but also captures sediments. Samples from four sites were studied to determine sediment pollutant concentrations and phosphorus release rates. Phosphorus tends to desorb from sediments when the concentration of overlying water is less than 1.4 mg/l. Water column P concentrations range from 0.04 to 0.1 mg/l, which suggests that sediments will act as a P source. In a series of batch experiments, P was released at approximately 15-20 mg/m(2)week in the winter (1-5 degrees C) and as much as 90 mg/m(2)week in the summer (20-24 degrees C), and is also a function of pH and dissolved oxygen concentration. The sediment total phosphorus concentration, which averages 833 mg/kg, is evenly distributed among non-apatite-P (33%), apatite-P (32%) and residual-P (34%). An equilibrium model is proposed to describe release rate.

  10. Quantitative measurements of vaporization, burst ionization, and emission characteristics of shaped charge barium releases

    NASA Technical Reports Server (NTRS)

    Hoch, Edward L.; Hallinan, Thomas J.; Stenbaek-Nielsen, Hans C.

    1994-01-01

    Intensity-calibrated color video recordings of three barium-shaped charge injections in the ionopshere were used to determine the initial ionization, the column density corresponding to unity optical depth, and the yield of vaporized barium in the fast jet. It was found that the initial ionization at the burst was less than 1% and that 0% burst ionization was consistent with the observations. Owing to the Doppler shift, the column density for optical thickness in the neutral barium varies somewhat according to the velocity distribution. For the cases examined here, the column density was 2-5 x 10(exp 10) atoms/sq cm. This value, which occurred 12 to 15 s after release, should be approximately valid for most shaped charge experiments. The yield was near 30% (15% in the fast jet) for two of the releases and was somewhat lower in the third, which also had a lower peak velocity. This study also demonstrated the applicability of the computer simulation code developed for chemical releases by Stenbaek-Nielsen and provided experimental verification of the Doppler-corrected emission rates calculated b Stenbaek-Nielsen (1989).

  11. Organic contaminant release from melting snow. 2. Influence of snow pack and melt characteristics.

    PubMed

    Meyer, Torsten; Lei, Ying Duan; Muradi, Ibrahim; Wania, Frank

    2009-02-01

    Large reservoirs of organic contaminants in seasonal snowpack can be released in short pulses during spring snowmelt, potentially impacting the receiving ecosystems. Laboratory experiments using artificial snow spiked with organic target substances were conducted to investigate the behavior of six organic contaminants with widely variable distribution properties in melting snow. Whereas the influence of a chemical's equilibrium phase partitioning on the elution behavior is explored in a companion paper, we discuss here the impact of snow properties and melt features, including the snowpack depth, the temperature at the interface between soil and snow, the meltwater content the internal ice surface area, and the existence of distinct snow layers. Water-soluble organic substances are released in high concentrations at the beginning of a melt period when a deep and aged snowpack undergoes intense melting. Warm ground can cause notable melting at the snow bottom leading to a delayed and dampened concentration peak. Hydraulic barriers in layered snow packs cause preferential meltwater flow which also mitigates the early contaminant flush. Hydrophobic organic pollutants that are associated with particles accumulate near the snow surface and are released at the end of melting. Dirt cones at the surface of a dense snowpack enhance this enrichment. The findings of this laboratory study will aid in the understanding of the behavior of organic pollutants during the melting of more complex, natural snow covers.

  12. Study of drug release and tablet characteristics of silicone adhesive matrix tablets.

    PubMed

    Tolia, Gaurav; Li, S Kevin

    2012-11-01

    Matrix tablets of a model drug acetaminophen (APAP) were prepared using a highly compressible low glass transition temperature (T(g)) polymer silicone pressure sensitive adhesive (PSA) at various binary mixtures of silicone PSA/APAP ratios. Matrix tablets of a rigid high T(g) matrix forming polymer ethyl cellulose (EC) were the reference for comparison. Drug release study was carried out using USP Apparatus 1 (basket), and the relationship between the release kinetic parameters of APAP and polymer/APAP ratio was determined to estimate the excipient percolation threshold. The critical points attributed to both silicone PSA and EC tablet percolation thresholds were found to be between 2.5% and 5% w/w. For silicone PSA tablets, satisfactory mechanical properties were obtained above the polymer percolation threshold; no cracking or chipping of the tablet was observed above this threshold. Rigid EC APAP tablets showed low tensile strength and high friability. These results suggest that silicone PSA could eliminate issues related to drug compressibility in the formulation of directly compressed oral controlled release tablets of poorly compressible drug powder such as APAP. No routinely used excipients such as binders, granulating agents, glidants, or lubricants were required for making an acceptable tablet matrix of APAP using silicone PSA. Copyright © 2012 Elsevier B.V. All rights reserved.

  13. Seleniranium Ions Undergo π-Ligand Exchange via an Associative Mechanism in the Gas Phase.

    PubMed

    Lim, S Fern; Harris, Benjamin L; Khairallah, George N; Bieske, E J; Maître, Philippe; da Silva, Gabriel; Adamson, Brian D; Scholz, Michael S; Coughlan, Neville J A; O'Hair, Richard A J; Rathjen, Michael; Stares, Daniel; White, Jonathan M

    2017-06-16

    Collision-induced dissociation mass spectrometry of the ammonium ions 4a and 4b results in the formation of the seleniranium ion 5, the structure and purity of which were verified using gas-phase infrared spectroscopy coupled to mass spectrometry and gas-phase ion-mobility measurements. Ion-molecule reactions between the ion 5 (m/z = 261) and cyclopentene, cyclohexene, cycloheptene, and cyclooctene resulted in the formation of the seleniranium ions 7 (m/z = 225), 6 (m/z = 239), 8 (m/z = 253), and 9 (m/z = 267), respectively. Further reaction of seleniranium 6 with cyclopentene resulted in further π-ligand exchange giving seleniranium ion 7, confirming that direct π-ligand exchange between seleniranium ion 5 and cycloalkenes occurs in the gas phase. Pseudo-first-order kinetics established relative reaction efficiencies for π-ligand exchange for cyclopentene, cyclohexene, cycloheptene. and cyclooctene as 0.20, 0.07, 0.43, and 4.32. respectively. DFT calculations at the M06/6-31+G(d) level of theory provide the following insights into the mechanism of the π-ligand exchange reactions; the cycloalkene forms a complex with the seleniranium ion 5 with binding energies of 57 and 62 kJ/mol for cyclopentene and cyclohexene, respectively, with transition states for π-ligand exchange having barriers of 17.8 and 19.3 kJ/mol for cyclopentene and cyclohexene, respectively.

  14. The Decomposition of Hydrazine in the Gas Phase and over an Iridium Catalyst

    SciTech Connect

    Schmidt, Michael W.; Gordon, Mark S.

    2013-09-30

    Hydrazine is an important rocket fuel, used as both a monopropellant and a bipropellant. This paper presents theoretical results to complement the extensive experimental studies of the gas phase and Ir catalyzed decompositions involved in the monopropellant applications of hydrazine. Gas phase electronic structure theory calculations that include electron correlation predict that numerous molecular and free radical reactions occur within the same energy range as the basic free radical pathways: NN bond breaking around 65 kcal/mol and NH bond breaking around 81 kcal/mol. The data suggest that a revision to existing kinetics modeling is desirable, based on the energetics and the new elementary steps reported herein. A supported Ir-6 octahedron model for the Shell 405 Iridium catalyst used in thrusters was developed. Self-Consistent Field and electron correlation calculations (with core potentials and associated basis sets) find a rich chemistry for hydrazine on this catalyst model. The model catalyst provides dramatically lower NN and NH bond cleavage energies and an even smaller barrier to breaking the NH bond by NH2 abstractions. Thus, the low temperature decomposition over the catalyst is interpreted in terms of consecutive NH2 abstractions to produce ammonia and nitrogen. The higher temperature channel, which has hydrogen and nitrogen products, may be due to a mixture of two mechanisms. These two mechanisms are successive NH cleavages with surface H + H recombinations, and the same type of assisted H-2 eliminations found to occur in the gas phase part of this study.

  15. New quantum chemical computations of formamide deuteration support gas-phase formation of this prebiotic molecule

    NASA Astrophysics Data System (ADS)

    Skouteris, D.; Vazart, F.; Ceccarelli, C.; Balucani, N.; Puzzarini, C.; Barone, V.

    2017-06-01

    Based on recent work, formamide might be a potentially very important molecule in the emergence of terrestrial life. Although detected in the interstellar medium for decades, its formation route is still debated, whether in the gas phase or on the dust grain surfaces. Molecular deuteration has proven to be, in other cases, an efficient way to identify how a molecule is synthesized. For formamide, new published observations towards the IRAS16293-2422 B hot corino show that its three deuterated forms have all the same deuteration ratio, 2-5 per cent and that this is a factor of 3-8 smaller than that measured for H2CO towards the IRAS16293-2422 protostar. Following a previous work on the gas-phase formamide formation via the reaction NH2 + H2CO → HCONH2 + H, we present here new calculations of the rate coefficients for the production of monodeuterated formamide through the same reaction, starting from monodeuterated NH2 or H2CO. Some misconceptions regarding our previous treatment of the reaction are also cleared up. The results of the new computations show that, at the 100 K temperature of the hot corino, the rate of deuteration of the three forms is the same, within 20 per cent. On the contrary, the reaction between non-deuterated species proceeds three times faster than that with deuterated ones. These results confirm that a gas-phase route for the formation of formamide is perfectly in agreement with the available observations.

  16. All-gas-phase synthesis of UiO-66 through modulated atomic layer deposition

    PubMed Central

    Lausund, Kristian Blindheim; Nilsen, Ola

    2016-01-01

    Thin films of stable metal-organic frameworks (MOFs) such as UiO-66 have enormous application potential, for instance in microelectronics. However, all-gas-phase deposition techniques are currently not available for such MOFs. We here report on thin-film deposition of the thermally and chemically stable UiO-66 in an all-gas-phase process by the aid of atomic layer deposition (ALD). Sequential reactions of ZrCl4 and 1,4-benzenedicarboxylic acid produce amorphous organic–inorganic hybrid films that are subsequently crystallized to the UiO-66 structure by treatment in acetic acid vapour. We also introduce a new approach to control the stoichiometry between metal clusters and organic linkers by modulation of the ALD growth with additional acetic acid pulses. An all-gas-phase synthesis technique for UiO-66 could enable implementations in microelectronics that are not compatible with solvothermal synthesis. Since this technique is ALD-based, it could also give enhanced thickness control and the possibility to coat irregular substrates with high aspect ratios. PMID:27876797

  17. Gas-phase Ion Isomer Analysis Reveals the Mechanism of Peptide Sequence Scrambling

    PubMed Central

    Jia, Chenxi; Wu, Zhe; Lietz, Christopher B.; Liang, Zhidan; Cui, Qiang; Li, Lingjun

    2014-01-01

    Peptide sequence scrambling during mass spectrometry-based gas-phase fragmentation analysis causes misidentification of peptides and proteins. Thus, there is a need to develop an efficient approach to probing the gas-phase fragment ion isomers related to sequence scrambling and the underlying fragmentation mechanism, which will facilitate the development of bioinformatics algorithm for proteomics research. Herein, we report on the first use of electron transfer dissociation (ETD)-produced diagnostic fragment ions to probe the components of gas-phase peptide fragment ion isomers. In combination with ion mobility spectrometry (IMS) and formaldehyde labeling, this novel strategy enables qualitative and quantitative analysis of b-type fragment ion isomers. ETD fragmentation produced diagnostic fragment ions indicative of the precursor ion isomer components, and subsequent IMS analysis of b ion isomers provided their quantitative and structural information. The isomer components of three representative b ions (b9, b10, and b33 from three different peptides) were accurately profiled by this method. IMS analysis of the b9 ion isomers exhibited dynamic conversion among these structures. Furthermore, molecular dynamics simulation predicted theoretical drift time values which were in good agreement with experimentally measured values. Our results strongly support the mechanism of peptide sequence scrambling via b ion cyclization, and provide the first experimental evidence to support that the conversion from molecular precursor ion to cyclic b ion (M→cb) pathway is less energetically (or kinetically) favored. PMID:24313304

  18. Solution Versus Gas-Phase Modification of Peptide Cations with NHS-Ester Reagents

    NASA Astrophysics Data System (ADS)

    Mentinova, Marija; Barefoot, Nathan Z.; McLuckey, Scott A.

    2012-02-01

    A comparison between solution and gas phase modification of primary amine sites in model peptide cations with N-hydroxysuccinimide (NHS) ester reagents is presented. In all peptides, the site of modification in solution was directed to the N-terminus by conducting reactions at pH = 5, whereas for the same peptides, a lysine residue was preferentially modified in the gas phase. The difference in pKa values of the N-terminus and ɛ-amino group of the lysine allows for a degree of control over sites of protonation of the peptides in aqueous solution. With removal of the dielectric and multiple charging of the peptide ions in the gas phase, the accommodation of excess charge can affect the preferred sites of reaction. Interaction of the lone pair of the primary nitrogen with a proton reduces its nucleophilicity and, as a result, its reactivity towards NHS-esters. While no evidence for reaction of the N-terminus with sulfo-NHS-acetate was noted in the model peptide cations, a charge inversion experiment using bis[sulfosuccinimidyl] suberate, a cross-linking reagent with two sulfo-NHS-ester functionalities, showed modification of the N-terminus. Hence, an unprotonated N-terminus can serve as a nucleophile to displace NHS, which suggests that its lack of reactivity with the peptide cations is likely due to the participation of the N-terminus in solvating excess charge.

  19. Rupture of the cell envelope by induced intracellular gas phase expansion in gas vacuolate bacteria.

    PubMed Central

    Hemmingsen, B B; Hemmingsen, E A

    1980-01-01

    Using a new approach, we estimated the physical strength of the cell envelopes of three species of gram-negative, gas vacuolate bacteria (Microcyclus aquaticus, Prosthecomicrobium pneumaticum, and Meniscus glaucopis). Populations of cells were slowly (0.5 to 2.9 h) saturated with argon, nitrogen, or helium to final pressures up to 100 atm (10, 132 kPa). The gas phases of the vesicles remained intact and, upon rapid (1 to 2 s) decompression to atmospheric pressure, expanded and ruptured the cells; loss of colony-forming units was used as an index of rupture. Because the cell envelope is the cellular component most likely to resist the expanding intracellular gas phase, its strength can be estimated from the minimum gas pressures that produce rupture. The viable counts indicated that these minimum pressures were between 25 and 50 atm; the majority of the cell envelopes were ruptured at pressures between 50 and 100 atm. Cells in which the gas vesicles were collapsed and the gas phases were effectively dissolved by rapid compression tolerated decompression from much higher gas saturations. Cells that do not normally possess gas vesicles (Escherichia coli) or that had been prevented from forming them by addition of L-lysine to the medium (M. aquaticus) were not harmed by decompression from gas saturation pressures up to 300 atm. PMID:7204336

  20. Gas-phase ion isomer analysis reveals the mechanism of peptide sequence scrambling.

    PubMed

    Jia, Chenxi; Wu, Zhe; Lietz, Christopher B; Liang, Zhidan; Cui, Qiang; Li, Lingjun

    2014-03-18

    Peptide sequence scrambling during mass spectrometry-based gas-phase fragmentation analysis causes misidentification of peptides and proteins. Thus, there is a need to develop an efficient approach to probing the gas-phase fragment ion isomers related to sequence scrambling and the underlying fragmentation mechanism, which will facilitate the development of bioinformatics algorithm for proteomics research. Herein, we report on the first use of electron transfer dissociation (ETD)-produced diagnostic fragment ions to probe the components of gas-phase peptide fragment ion isomers. In combination with ion mobility spectrometry (IMS) and formaldehyde labeling, this novel strategy enables qualitative and quantitative analysis of b-type fragment ion isomers. ETD fragmentation produced diagnostic fragment ions indicative of the precursor ion isomer components, and subsequent IMS analysis of b ion isomers provided their quantitative and structural information. The isomer components of three representative b ions (b9, b10, and b33 from three different peptides) were accurately profiled by this method. IMS analysis of the b9 ion isomers exhibited dynamic conversion among these structures. Furthermore, molecular dynamics simulation predicted theoretical drift time values, which were in good agreement with experimentally measured values. Our results strongly support the mechanism of peptide sequence scrambling via b ion cyclization, and provide the first experimental evidence to support that the conversion from molecular precursor ion to cyclic b ion (M → (c)b) pathway is less energetically (or kinetically) favored.