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Sample records for hydroliquefaction solvent-induced scission

  1. Viral Membrane Scission

    PubMed Central

    Rossman, Jeremy S.; Lamb, Robert A.

    2014-01-01

    Virus budding is a complex, multistep process in which viral proteins make specific alterations in membrane curvature. Many different viral proteins can deform the membrane and form a budding virion, but very few can mediate membrane scission to complete the budding process. As a result, enveloped viruses have developed numerous ways of facilitating membrane scission, including hijacking host cellular scission machinery and expressing their own scission proteins. These proteins mediate scission in very different ways, though the biophysical mechanics underlying their actions may be similar. In this review, we explore the mechanisms of membrane scission and the ways in which enveloped viruses use these systems to mediate the release of budding virions. PMID:24099087

  2. Catalytic hydroliquefaction of low-rank coals

    SciTech Connect

    Guruz, K.; Kranich, W.L.; La Violette, L.J.; Mendes, C.

    1983-01-01

    Hydroliquefaction behavior of ..cap alpha..-cellulose, leonardite, four lignites, and two subbituminous coals suspended in an anthracene oil carrier has been investigated in the presence of Co-Mo/Al/sub 2/O/sub 3/ catalyst at 425/sup 0/C and at an average pressure of 1,300 psig in a batch reactor for 30-min reaction time. Both total conversion of moisture-ash free solids and total yield of liquid products were greater for all but one of the lignites than for the subbituminous coals. Partial demineralization by HCl washing decreased both the total conversion of and pentane-soluble oil yield from lignites. It had relatively little effect on subbituminous coals. Although cellulose was almost completely converted to liquids and gases, no pentane-soluble oils were produced.

  3. Catalytic hydroliquefaction of low-rank coals

    SciTech Connect

    Gueruez, K.; Kranich, W.L.; La Violette, L.J.; Mendes, C.

    1983-01-01

    Hydroliquefaction behaviour of a-cellulose, leonardite, four lignites, and two subbituminous coals suspended in an anthracene oil carrier has been investigated in the presence of Co-Mo/Al/sub 2/O/sub 3/ catalyst at 425/sup 0/C and at an average pressure of 1,300 psig in a batch reactor for 30-min reaction time. Both total conversion of moisture-ash free solids and total yield of liquid products were greater for all but one of the lignites than for the subbituminous coals. Partial demineralization by HCl washing decreased both the total conversion of and pentane-soluble oil yield from lignites. It had relatively little effect on subbituminous coals. Although cellulose was almost completely converted to liquids and gases, no pentane-soluble oils were produced.

  4. Nuclear scission and quantum localization.

    PubMed

    Younes, W; Gogny, D

    2011-09-23

    We examine nuclear scission within a fully quantum-mechanical microscopic framework, focusing on the nonlocal aspects of the theory. Using (240)Pu hot fission as an example, we discuss the identification of the fragments and the calculation of their kinetic, excitation, and interaction energies, through the localization of the orbital wave functions. We show that the disentanglement of the fragment wave functions is essential to the quantum-mechanical definition of scission and the calculation of physical observables. Finally, we discuss the fragments' prescission excitation mechanisms and give a nonadiabatic description of their evolution beyond scission. PMID:22026846

  5. Investigation of the heating up period of hydroliquefaction

    SciTech Connect

    Konig, M.; Fehl, C. ); Engelke, F. ); Mittelmeijer-Hazeleger, M. )

    1990-01-01

    Earthy soft brown coals from deposits of GDR (Leipzig area) were found to be a highly reactive feedstock for slurry phase hydroliquefaction (1). The question arose as to whether short-contact-time hydrogenation may be an efficient process for hydroconversion of reactive coals (2). Rapid heating up of the slurry to the final reaction temperature may have a beneficial effect on product yields. Moreover, a more detailed study of the heating up period in hydrogenation is of importance for the explanation of the phenomenon of coke formation in the preheater sections of hydrogenation units.

  6. Flow-induced scission of macromolecules

    NASA Astrophysics Data System (ADS)

    Sim, H.

    2005-11-01

    Mechanical scission of long chain synthetic and bio- polymers in strong flows is pertinent to applications ranging from genomics to polymer-induced turbulent drag reduction. Experiments generally differentiate between two types of fracture mechanisms in extensional flows depending on whether the polymer experiences a steady (e.g. cross slot flow) or transient (e.g. contraction flow) field. Theories based on ``mid-point scission hypothesis'' as well as computer simulations using bead-spring models that use ad hoc energy-based criteria have been used to explain experimental observations. We present the results of a study that for the first time couples Brownian Dynamics Simulation (BDS) using bead-rod (Kramers) chains with a novel algorithm for the determination of scission events which themselves are stochastic processes. Flexible lambda-phage DNA is selected as a model molecule. We will discuss effect of molecular weight (MW), flow type and hydrodynamic interactions on chain scission and the MW distribution.

  7. Evaluation of humic fractions potential to produce bio-oil through catalytic hydroliquefaction.

    PubMed

    Lemée, L; Pinard, L; Beauchet, R; Kpogbemabou, D

    2013-12-01

    Humic substances were extracted from biodegraded lignocellulosic biomass (LCBb) and submitted to catalytic hydroliquefaction. The resulting bio-oils were compared with those of the initial biomass. Compared to fulvic and humic acids, humin presented a high conversion rate (74 wt.%) and the highest amount of liquid fraction (66 wt.%). Moreover it represented 78% of LCBb. Humin produced 43 wt.% of crude oil and 33 wt.% of hexane soluble fraction containing hydrocarbons which is a higher yield than those from other humic substances as well as from the initial biomass. Hydrocarbons were mainly aromatics, but humin produces the highest amount of aliphatics. Considering the quantity, the quality and the molecular composition of the humic fractions, a classification of the potential of the latter to produce fuel using hydroliquefaction process can be assess: Hu>AF>AH. The higher heating value (HHV) and oxygen content of HSF from humin were fully compatible with biofuel characteristics. PMID:24140851

  8. Kinetics and mechanisms of catalytic hydroliquefaction and hydrogasification of lignite. Quarterly report, April-June 1981

    SciTech Connect

    Kranich, W.L.; Gueruez, K.; Weiss, A.H.

    1981-08-10

    The work reported in the Final Report for DOE Contract DE-AC22-77ET10618 has been continued under the current contract to expand the range of conditions previously studied. This has permitted a more detailed analysis of the variables involved in the hydroliquefaction and hydrogasification of lignite than was possible in the previous report. The principal progress has been a study of the catalytic batch hydroliquefaction of a range of low rank coals including two sub-bituminous coals, four lignites, and leonardite, as well as cellulose. These were studied both as received and after partial demineralization by washing with hydrochloric acid. The study is fully reported in the attached article which has been submitted for publication in a technical journal.

  9. Curvature Sensing by a Viral Scission Protein.

    PubMed

    Martyna, Agnieszka; Gómez-Llobregat, Jordi; Lindén, Martin; Rossman, Jeremy S

    2016-06-28

    Membrane scission is the final step in all budding processes wherein a membrane neck is sufficiently constricted so as to allow for fission and the release of the budded particle. For influenza viruses, membrane scission is mediated by an amphipathic helix (AH) domain in the viral M2 protein. While it is known that the M2AH alters membrane curvature, it is not known how the protein is localized to the center neck of budding virions where it would be able to cause membrane scission. Here, we use molecular dynamics simulations on buckled lipid bilayers to show that the M2AH senses membrane curvature and preferentially localizes to regions of high membrane curvature, comparable to that seen at the center neck of budding influenza viruses. These results were then validated using in vitro binding assays to show that the M2AH senses membrane curvature by detecting lipid packing defects in the membrane. Our results show that the M2AH senses membrane curvature and suggest that the AH domain may localize the protein at the viral neck where it can then mediate membrane scission and the release of budding viruses. PMID:27299375

  10. The scission point configuration of fissioning nuclei

    NASA Astrophysics Data System (ADS)

    Ivanyuk, Fedir

    2016-06-01

    We define the optimal shape which fissioning nuclei attain just before the scission and calculate the deformation energy as function of the mass asymmetry at the scission point. The calculated deformation energy is used in quasi-static approximation for the estimation of mass distribution, total kinetic and excitation energy of fission fragments, and the total number of prompt neutrons. The calculated results reproduce rather well the experimental data on the position of the peaks in the mass distribution of fission fragments, the total kinetic and excitation energy of fission fragments. The calculated value of neutron multiplicity is somewhat larger than experimental results. The saw-tooth structure of neutron multiplicity is qualitatively reproduced.

  11. Solvent-induced crystallization of poly(ether ether ketone)

    NASA Astrophysics Data System (ADS)

    McPeak, Jennifer Lynne

    The purpose of this study was learn how the diffusion, swelling, and crystallization processes are coupled during solvent-induced crystallization of poly(ether ether ketone) (PEEK). Unoriented amorphous PEEK films were immersed in aprotic organic liquids at ambient temperature and bulk properties or characteristics were monitored as a function of immersion time. The sorption behavior, T g and Tm° suppression, crystallinity, and dynamic mechanical response were correlated as a function of solvent chemistry and immersion time. The saturation time of methylene chloride, 1,3-dichloropropane, tetrahydrofuran, cyclopentanone, chlorobenzene, toluene, diethyl ketone, and ethylbenzene in amorphous PEEK films were found to range from hours to days depending on the level of polymer-solvent interactions. In-situ isochronal DMA spectra show that the Tg of PEEK was suppressed from 150°C to below ambient temperature such that crystallization was kinetically feasible during ambient immersion. In addition, an increase in viscoelastic dispersion was attributed to the presence of crystallinity. From dynamic mass uptake and wide-angle x-ray diffraction (WAXD) results, it was found that the bulk sorption rate was equal to the bulk crystallization rate for all solvent systems that promoted SINC and PEEK exhibited diffusion-limited crystallization, irrespective of the nature of the transport mechanism. In addition, the solvent-induced crystals exhibit preferred orientation as supported by photographic WAXD. A distinct sorption front, observed with scanning electron microscopy, further supports the scenario of diffusion-controlled crystallization and one-dimensional diffusion. Isothermal DMA spectra for THF, cyclopentanone, and chlorobenzene, indicate that, as the solvent diffuses into the films, the stiffness of the polymer decreases at short times, begins to increase, and then reaches a relatively time-independent value. It was determined that the initial decrease in the storage

  12. Effects of lignite properties on the hydroliquefaction behavior of representative Turkish lignites

    SciTech Connect

    Oener, M.; Bolat, E.; Dincer, S. )

    1992-01-01

    This paper reports on the conversion and yield data obtained for hydroliquefaction of 11 different Turkish lignites in tetralin, anthracene, and creosote oils with or without catalyst at 440{degrees}C and 80 bar that were correlated with the lignite properties obtained from proximate, ultimate, and petrographic analyses. The intercorrelation of experimental results and analytical data was evaluated by both simple linear regression and stepwise multiple linear regression analyses. Simple linear correlations between conversion and yield data with individual lignite parameters are unsatisfactory. An approach utilizing a stepwise multiple linear regression analysis lead to a number of linear equations relating oil yields to ash, sulfur, volatile matter, elemental carbon, maceral, and xylene extract contents of the lignites.

  13. Hydro-liquefaction of microcrystalline cellulose, xylan and industrial lignin in different supercritical solvents.

    PubMed

    Li, Qingyin; Liu, Dong; Hou, Xulian; Wu, Pingping; Song, Linhua; Yan, Zifeng

    2016-11-01

    The influences of solvent on hydro-liquefaction of cellulose, xylan, and lignin were investigated using micro-autoclave. The maximum conversion and bio-oil yield obtained from cellulose and xylan liquefaction were achieved in methanol, whereas similar liquefaction characteristics of lignin were observed in methanol and ethanol. The molecular simulation of interactions between solvents and subcomponents indicated that methanol and ethanol were highly miscible with raw materials. GC-MS and FT-ICR MS characterization revealed that the chemical compositions of liquid products highly depended on the utilized feedstocks. Esters, ketones, and aldehydes were mainly produced from cellulose and xylan conversion, whereas aromatic compounds were primarily derived from lignin conversion. EA results showed that methanol favored the hydrogenation and deoxygenation, resulting in the heating value increased. It could be concluded that the oil quality was highly improved in supercritical methanol. PMID:27497089

  14. A search for the radical hydrogen transfer pathway in coal hydroliquefaction

    SciTech Connect

    Autrey, T.; Franz, J.

    1990-04-01

    It is generally accepted that the formation of petroleum liquids produced in the thermal liquefaction of coal can not be completely explained by simple homolytic cleavage of strong linkages in coal structures. Model compound studies have been employed to elucidate the mechanisms of scission of strong bonds in coal structures and have provided useful information for increasing the efficiency of the coal liquefaction processes. Radical Hydrogen Transfer (RHT), the transfer of a hydrogen atom from a solvent-derived cyclohexadienyl substituted radical to the ipso position of an aryl-alkyl linkage, has been proposed as an important pathway for the cleavage of strong bonds in coal structures during coal liquefaction. Elegant numerical modeling studies of the scission of diarylmethane model compounds in the presence of a variety of solvent molecules demonstrated that an alternative mechanism for the scission of the strong bonds in these model compounds may be operative that involves cyclohexadienyl-derived solvent molecules rather than free hydrogen atoms.

  15. Solvent-induced desorption of alkanethiol ligands from Au nanoparticles.

    PubMed

    Huang, Yuanyuan; Liu, Wei; Cheng, Hao; Yao, Tao; Yang, Lina; Bao, Jie; Huang, Ting; Sun, Zhihu; Jiang, Yong; Wei, Shiqiang

    2016-06-21

    Removing surfactants from a colloidal metal nanoparticle surface is necessary for their realistic applications, and how they could be stripped is a subject of active investigation. Here, we report a solvent-induced desorption of dodecanethiol ligands from the gold nanoparticle surface, and traced this desorption process using a combination of in situ X-ray absorption fine structure (XAFS) and Raman spectroscopic techniques. In situ analysis results reveal that the solvent exchange of ethanol with tetrahydrofuran (THF) can effectively remove dodecanethiol ligands while keeping the particle morphology unchanged. Upon increasing the THF/ethanol ratio from 0 : 1 to 5 : 1, the surface coverage of thiol on the Au surface is reduced from 0.47 to 0.07, suggesting the depletion of ligands first from the nanoparticle facet sites, then from the edge sites, while the ligands at the corner sites are intact. This work enriches our knowledge on surfactant removal and may pave the way towards preparing surface-clean nanoparticles for practical applications. PMID:27241025

  16. Solvent-Induced Crystallization in Poly(Ethylene Terephthalate)

    NASA Astrophysics Data System (ADS)

    Ouyang, Hao

    2000-03-01

    The solvent transport in poly(ethylene terephthalate) (PET) and related phase transformation were investigated. Based on Harmon's model for Case I (Fickian), Case II (swelling) and anomalous transport, the data of mass uptake were analyzed. Pure Case I or Case II behavior did not appear in the PET-acetone system. The mass transport in PET is accompanied by a large-scale structural rearrangement, which leads to the induced crystallization of the original amorphous state. Solvent-induced crystallization was studied by wide angle X-ray scattering (WAXS), small angle x-ray scattering (SAXS), Differential Scanning Calorimeter (DSC), and Fourier Transform Infra-Red (FTIR), which is different from the thermal crystallization. During this process, the matrix is under compressive stress which causes different kinetic path of crystallization in comparison with that by thermal annealing. The crystallization process was proposed in terms of the long period L, the crystal thickness lc and the thickness of amorphous layer la, calculated from the linear correlation function and interface distribution function. The variation of trans conformation is used to monitor this process.

  17. Silk fibroin gelation via non-solvent induced phase separation.

    PubMed

    Kasoju, Naresh; Hawkins, Nicholas; Pop-Georgievski, Ognen; Kubies, Dana; Vollrath, Fritz

    2016-03-01

    Tissue engineering benefits from novel materials with precisely tunable physical, chemical and mechanical properties over a broad range. Here we report a practical approach to prepare Bombyx mori silk fibroin hydrogels using the principle of non-solvent induced phase separation (NIPS). A combination of reconstituted silk fibroin (RSF) and methanol (non-solvent), with a final concentration of 2.5% w/v and 12.5% v/v respectively, maintained at 22 °C temperature turned into a hydrogel within 10 hours. Freeze-drying of this gel gave a foam with a porosity of 88%, a water uptake capacity of 89% and a swelling index of 8.6. The gelation kinetics and the loss tangent of the gels were investigated by rheometry. The changes in the morphology of the porous foams were visualized by SEM. The changes in RSF chemical composition and the relative fraction of its secondary structural elements were analyzed by ATR-FTIR along with Fourier self-deconvolution. And, the changes in the glass transition temperature, specific heat capacity and the relative fraction of crystallinity of RSF were determined by TM-DSC. Data suggested that RSF-water-methanol behaved as a polymer-solvent-non-solvent ternary phase system, wherein the demixing of the water-methanol phases altered the thermodynamic equilibrium of RSF-water phases and resulted in the desolvation and eventual separation of the RSF phase. Systematic analysis revealed that both gelation time and the properties of hydrogels and porous foams could be controlled by the ratios of RSF and non-solvent concentration as well as by the type of non-solvent and incubation temperature. Due to the unique properties we envisage that the herein prepared NIPS induced RSF hydrogels and porous foams can possibly be used for the encapsulation of cells and/or for the controlled release of both hydrophilic and hydrophobic drugs. PMID:26730413

  18. Evaluation of the Rockwell International flash-hydroliquefaction process. Final summary report

    SciTech Connect

    Sirohi, V.P.

    1980-09-01

    At the request of the Department of Energy, UOP/SDC has evaluated the Rockwell Hydroliquefaction Process to determine the adequacy of the existing PDU data base and to assess the practicability and operability of the process. UOP/SDC conducted nine studies. Their findings follow: (1) A complete designed set of experiments must be run on the present PDU to make possible satisfactory analysis of the effects of variables especially the effect of diluents in the H/sub 2/ feed and the possibility of carbon deposition problems. (2) Basic improvements in the equipment and operation of the PDU should first be made (Ten specific recommendations are made). (3) A reactor design concept must be developed that looks feasible for design, fabrication, and operation. (4) A conceptual commercial design and economics should be prepared based on a realistic set of design bases and criteria. (5) If the above are accomplished successfully with attractive results, then and only then: (a) A study should be made of the refining requirements of the product, which are expected to be expensive based on the H/C ratio. (b) The PDU should be modified for continuous runs of up to one month to: Confirm the data correlations, estimate the reliability of the reactor and process, adhere to the requirements stated above, test cryogenic gas separation, study fouling and erosion, study lockhopper feeding, establish initial reliability of the coal injector and precombustion assembly head, collect scale-up and design data, and conduct a materials study and confirm materials choices. (c) Determine particle size of the char and of the solids in the oil product, the degree to which they may be separated, and how the ash should be removed from the product oil.

  19. Combination of pyrolysis and hydroliquefaction of CCB-treated wood for energy recovery: optimization and products characterization.

    PubMed

    Kinata, Silao Espérance; Loubar, Khaled; Paraschiv, Maria; Belloncle, Christophe; Tazerout, Mohand

    2012-08-01

    In this paper, pyrolysis and hydroliquefaction processes were successively used to convert CCB-treated wood into bio-oil with respect to environment. Pyrolysis temperature has been optimized to produce maximum yield of charcoal with a high metal content (Cu, Cr, and B). The results obtained indicate that the pyrolysis at 300 °C and 30 min are the optimal conditions giving high yield of charcoal about 45% which contains up to 94% of Cu, 100% of Cr and 88% of B. After pyrolysis process, the charcoal has been converted into bio-oil using hydroliquefaction process. The optimization approach for the yield of bio-oil using a complete factorial design with three parameters: charcoal/solvent, temperature and hydrogen pressure was discussed. It is observed that the temperature is the most significant parameter and the optimum yield of bio-oil is around 82%. The metal analysis shows that the metals present in the bio-oil is very negligible. PMID:22705538

  20. Characterization of the scission point from fission-fragment velocities

    NASA Astrophysics Data System (ADS)

    Caamaño, M.; Farget, F.; Delaune, O.; Schmidt, K.-H.; Schmitt, C.; Audouin, L.; Bacri, C.-O.; Benlliure, J.; Casarejos, E.; Derkx, X.; Fernández-Domínguez, B.; Gaudefroy, L.; Golabek, C.; Jurado, B.; Lemasson, A.; Ramos, D.; Rodríguez-Tajes, C.; Roger, T.; Shrivastava, A.

    2015-09-01

    The isotopic yield distributions and kinematic properties of fragments produced in the transfer-induced fission of 240Pu and fusion-induced fission of 250Cf, with 9 MeV and 45 MeV excitation energy, respectively, were measured in inverse kinematics with the spectrometer VAMOS. The kinematics of identified fission fragments allow to derive properties of the scission configuration such as the distance between fragments, the total kinetic energy, the neutron multiplicity, the total excitation energy, and, for the first time, the proton- and neutron-number sharing during the emergence of the fragments. These properties of the scission point are studied as functions of the fragment atomic number. The correlation between these observables, gathered in one single experiment and for two different fissioning systems at different excitation energies, give valuable information for the understanding and modeling of the fission process.

  1. Controlling the bond scission sequence of oxygenates for energy applications

    NASA Astrophysics Data System (ADS)

    Stottlemyer, Alan L.

    The so called "Holy Grail" of heterogeneous catalysis is a fundamental understanding of catalyzed chemical transformations which span multidimensional scales of both length and time, enabling rational catalyst design. Such an undertaking is realizable only with an atomic level understanding of bond formation and destruction with respect to intrinsic properties of the metal catalyst. In this study, we investigate the bond scission sequence of small oxygenates (methanol, ethanol, ethylene glycol) on bimetallic transition metal catalysts and transition metal carbide catalysts. Oxygenates are of interest both as hydrogen carriers for reforming to H2 and CO and as fuels in direct alcohol fuel cells (DAFC). To address the so-called "materials gap" and "pressure gap" this work adopted three parallel research approaches: (1) ultra high vacuum (UHV) studies including temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) on polycrystalline surfaces; (2) DFT studies including thermodynamic and kinetic calculations; (3) electrochemical studies including cyclic voltammetry (CV) and chronoamperometry (CA). Recent studies have suggested that tungsten monocarbide (WC) may behave similarly to Pt for the electrooxidation of oxygenates. TPD was used to quantify the activity and selectivity of oxygenate decomposition for WC and Pt-modifiedWC (Pt/WC) as compared to Pt. While decomposition activity was generally higher on WC than on Pt, scission of the C-O bond resulted in alkane/alkene formation on WC, an undesired product for DAFC. When Pt was added to WC by physical vapor deposition C-O bond scission was limited, suggesting that Pt synergistically modifies WC to improve the selectivity toward C-H bond scission to produce H2 and CO. Additionally, TPD confirmed WC and Pt/WC to be more CO tolerant than Pt. HREELS results verified that surface intermediates were different on Pt/WC as compared to Pt or WC and evidence of aldehyde

  2. Endocytic vesicle scission by lipid phase boundary forces

    PubMed Central

    Liu, Jian; Kaksonen, Marko; Drubin, David G.; Oster, George

    2006-01-01

    Endocytosis in budding yeast is thought to occur in several phases. First, the membrane invaginates and then elongates into a tube. A vesicle forms at the end of the tube, eventually pinching off to form a “free” vesicle. Experiments show that actin polymerization is an active participant in the endocytic process, along with a number of membrane-associated proteins. Here we investigate the possible roles of these components in driving vesiculation by constructing a quantitative model of the process beginning at the stage where the membrane invagination has elongated into a tube encased in a sheath of membrane-associated protein. This protein sheath brings about the scission step where the vesicle separates from the tube. When the protein sheath is dynamin, it is commonly assumed that scission is brought about by the constriction of the sheath. Here, we show that an alternative scenario can work as well: The protein sheath acts as a “filter” to effect a phase separation of lipid species. The resulting line tension tends to minimize the interface between the tube region and the vesicle region. Interestingly, large vesicle size can further facilitate the reduction of the interfacial diameter down to a few nanometers, small enough so that thermal fluctuations can fuse the membrane and pinch off the vesicle. To deform the membrane into the tubular vesicle shape, the membrane elastic resistance forces must be balanced by some additional forces that we show can be generated by actin polymerization and/or myosin I. These active forces are shown to be important in successful scission processes as well. PMID:16801551

  3. Constitutive models for rubber networks undergoing simultaneous crosslinking and scission.

    SciTech Connect

    Thompson, Aidan Patrick; Curro, John G.; Rottach, Dana R.; Grest, Gary Stephen; Budzien, Joanne L.; Lo, David Chi S.

    2006-01-01

    Constitutive models for chemically reacting networks are formulated based on a generalization of the independent network hypothesis. These models account for the coupling between chemical reaction and strain histories, and have been tested by comparison with microscopic molecular dynamics simulations. An essential feature of these models is the introduction of stress transfer functions that describe the interdependence between crosslinks formed and broken at various strains. Efforts are underway to implement these constitutive models into the finite element code Adagio. Preliminary results are shown that illustrate the effects of changing crosslinking and scission rates and history.

  4. Oxidative scission of plant cell wall polysaccharides by ascorbate-induced hydroxyl radicals.

    PubMed

    Fry, S C

    1998-06-01

    Scission of plant cell wall polysaccharides in vivo has generally been assumed to be enzymic. However, in the presence of l-ascorbate, such polysaccharides are shown to undergo non-enzymic scission under physiologically relevant conditions. Scission of xyloglucan by 1 mM ascorbate had a pH optimum of 4.5, and the maximum scission rate was reached after a 10-25-min delay. Catalase prevented the scission, whereas added H2O2 (0.1-10 mM) increased the scission rate and shortened the delay. Ascorbate caused detectable xyloglucan scission above approx. 5 microM. Dehydroascorbate was much less effective. Added Cu2+ (>0.3 microM) also increased the rate of ascorbate-induced scission; EDTA was inhibitory. The rate of scission in the absence of added metals appeared to be attributable to the traces of Cu (2.8 mg.kg-1) present in the xyloglucan. Ascorbate-induced scission of xyloglucan was inhibited by radical scavengers; their effectiveness was proportional to their rate constants for reaction with hydroxyl radicals (.OH). It is proposed that ascorbate non-enzymically reduces O2 to H2O2, and Cu2+ to Cu+, and that H2O2 and Cu+ react to form .OH, which causes oxidative scission of polysaccharide chains. Evidence is reviewed to suggest that, in the wall of a living plant cell, Cu+ and H2O2 are formed by reactions involving ascorbate and its products, dehydroascorbate and oxalate. Systems may thus be in place to produce apoplastic .OH radicals in vivo. Although .OH radicals are often regarded as detrimental, they are so short-lived that they could act as site-specific oxidants targeted to play a useful role in loosening the cell wall, e.g. during cell expansion, fruit ripening and organ abscission. PMID:9601081

  5. Probing postsaddle nuclear dissipation with excitation energy at scission

    NASA Astrophysics Data System (ADS)

    Ye, W.; Tian, J.

    2016-04-01

    Using the stochastic Langevin model coupled with a statistical decay model, we study postsaddle dissipation properties in fission by analyzing the excitation energy at scission (Esc*) measured in fissioning nuclei 179Re and Fm,256254. The postsaddle dissipation strength (β ) required to fit Esc* data is found to be larger for Fm,256254 than light 179Re which has a smaller postsaddle deformation compared to heavy Fm,256254, showing a rise of nuclear dissipation strength at a greater deformation. Furthermore, we explore the influence of initial excitation energy of a fissioning system 246Cf on the sensitivity of its Esc* to β , and find that the sensitivity is significantly enhanced with increasing the initial excitation energy. Our finding suggests that, on the experimental side, to more accurately probe the postsaddle dissipation strength through the measurement of Esc*, it is best to yield those fissioning systems with high energy.

  6. Non-linear scission/recombination kinetics of living polymerization

    NASA Astrophysics Data System (ADS)

    Nyrkova, I. A.; Semenov, A. N.

    2007-10-01

    Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization (one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution. Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M* (M* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find that: 1) for M* ≪ M ≪ M*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t1, t2, t3 and t*; 2) there are transient regimes (t1 ≲ t ≲ t3) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter than t2. The chain growth is auto-accelerated for t1 ≲ t ≲ t2 : the cut-off chain length (= polymerization degree w N1 ∝ t2 in this regime. 4) For t2 < t < t3 the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N1 is decreasing with time in this regime, while the length scale N2 of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t*, shows a sharp maximum in the vicinity of M*; the effective exponent {frac{{partialln1/t*}}{{partialln M}}} is as high as ˜ σ-1/3 just above M*.

  7. Can solvent induced surface modifications applied to screen-printed platforms enhance their electroanalytical performance?

    PubMed

    Blanco, Elias; Foster, Christopher W; Cumba, Loanda R; do Carmo, Devaney R; Banks, Craig E

    2016-04-25

    In this paper the effect of solvent induced chemical surface enhancements upon graphitic screen-printed electrodes (SPEs) is explored. Previous literature has indicated that treating the working electrode of a SPE with the solvent N,N-dimethylformamide (DMF) offers improvements within the electroanalytical response, resulting in a 57-fold increment in the electrode surface area compared to their unmodified counterparts. The protocol involves two steps: (i) the SPE is placed into DMF for a selected time, and (ii) it is cured in an oven at a selected time and temperature. Beneficial electroanalytical outputs are reported to be due to the increased surface area attributed to the binder within the bulk surface of the SPEs dissolving out during the immersion step (step i). We revisit this exciting concept and explore these solvent induced chemical surface enhancements using edge- and basal-plane like SPEs and a new bespoke SPE, utilising the solvent DMF and explore, in detail, the parameters utilised in steps (i) and (ii). The electrochemical performance following steps (i) and (ii) is evaluated using the outer-sphere redox probe hexaammineruthenium(iii) chloride/0.1 M KCl, where it is found that the largest improvement is obtained using DMF with an immersion time of 10 minutes and a curing time of 30 minutes at 100 °C. Solvent induced chemical surface enhancement upon the electrochemical performance of SPEs is also benchmarked in terms of their electroanalytical sensing of NADH (dihydronicotinamide adenine dinucleotide reduced form) and capsaicin both of which are compared to their unmodified SPE counterparts. In both cases, it is apparent that a marginal improvement in the electroanalytical sensitivity (i.e. gradient of calibration plots) of 1.08-fold and 1.38-fold are found respectively. Returning to the original exciting concept, interestingly it was found that when a poor experimental technique was employed, only then significant increases within the working

  8. Adsorption-induced scission of carbon carbon bonds

    NASA Astrophysics Data System (ADS)

    Sheiko, Sergei S.; Sun, Frank C.; Randall, Adrian; Shirvanyants, David; Rubinstein, Michael; Lee, Hyung-Il; Matyjaszewski, Krzysztof

    2006-03-01

    Covalent carbon-carbon bonds are hard to break. Their strength is evident in the hardness of diamonds and tensile strength of polymeric fibres; on the single-molecule level, it manifests itself in the need for forces of several nanonewtons to extend and mechanically rupture one bond. Such forces have been generated using extensional flow, ultrasonic irradiation, receding meniscus and by directly stretching a single molecule with nanoprobes. Here we show that simple adsorption of brush-like macromolecules with long side chains on a substrate can induce not only conformational deformations, but also spontaneous rupture of covalent bonds in the macromolecular backbone. We attribute this behaviour to the fact that the attractive interaction between the side chains and the substrate is maximized by the spreading of the side chains, which in turn induces tension along the polymer backbone. Provided the side-chain densities and substrate interaction are sufficiently high, the tension generated will be strong enough to rupture covalent carbon-carbon bonds. We expect similar adsorption-induced backbone scission to occur for all macromolecules with highly branched architectures, such as brushes and dendrimers. This behaviour needs to be considered when designing surface-targeted macromolecules of this type-either to avoid undesired degradation, or to ensure rupture at predetermined macromolecular sites.

  9. Interchangeable adaptors regulate mitochondrial dynamin assembly for membrane scission

    PubMed Central

    Koirala, Sajjan; Guo, Qian; Kalia, Raghav; Bui, Huyen T.; Eckert, Debra M.; Frost, Adam; Shaw, Janet M.

    2013-01-01

    Mitochondrial fission is mediated by the dynamin-related GTPases Dnm1/Drp1 (yeast/mammals), which form spirals around constricted sites on mitochondria. Additional membrane-associated adaptor proteins (Fis1, Mdv1, Mff, and MiDs) are required to recruit these GTPases from the cytoplasm to the mitochondrial surface. Whether these adaptors participate in both GTPase recruitment and membrane scission is not known. Here we use a yeast strain lacking all fission proteins to identify the minimal combinations of GTPases and adaptors sufficient for mitochondrial fission. Although Fis1 is dispensable for fission, membrane-anchored Mdv1, Mff, or MiDs paired individually with their respective GTPases are sufficient to divide mitochondria. In addition to their role in Drp1 membrane recruitment, MiDs coassemble with Drp1 in vitro. The resulting heteropolymer adopts a dramatically different structure with a narrower diameter than Drp1 homopolymers assembled in isolation. This result demonstrates that an adaptor protein alters the architecture of a mitochondrial dynamin GTPase polymer in a manner that could facilitate membrane constriction and severing activity. PMID:23530241

  10. Solvent-induced chirality control in the enantioseparation of 1-phenylethylamine via diastereomeric salt formation.

    PubMed

    Kodama, Koichi; Kimura, Yuria; Shitara, Hiroaki; Yasutake, Mikio; Sakurai, Rumiko; Hirose, Takuji

    2011-04-01

    Solvent-induced chirality control in the enantioseparation of 1-phenylethylamine 1 by N-(p-toluenesulfonyl)-(S)-phenylalanine 2 via diastereomeric salt formation was studied. (S)-1·(S)-2 was preferentially crystallized as a less-soluble salt from aqueous alcohol, while (R)-1·(S)-2 salt was mainly obtained by addition of solvents with a six-membered ring such as dioxane, cyclohexane, tetrahydropyran, and cyclohexene to 2-propanol. Further investigations were carried out from the viewpoints of molecular structures, optical rotation measurement, and X-ray crystallographic analyses. Crystallographic analyses have revealed that incorporation of the six-membered ring solvent molecule in (R)-1·(S)-2 without hydrogen bonds changed the molecular conformation of (S)-2 to stabilize the salt, which changed the selectivity of 1 in the enantioseparation. PMID:21384437

  11. Desalination membranes from functional block copolymer via non-solvent induced phase inversion

    NASA Astrophysics Data System (ADS)

    Sung, Hyemin; Poelma, Justin; Leibfarth, Frank; Hawker, Craig; Bang, Joona

    2012-02-01

    Commercially available reverse osmosis (RO) and forward osmosis (FO) membranes are most commonly derived from materials such as polysulfone, polyimide, and cellulose acetate. While these membranes have improved the efficiency of the desalination process, they suffer from mechanical and chemical stability, fouling issues, and low fluxes. In this study, we combine a well-established membrane formation method, non-solvent-induced phase separation, with the self-assembly of a functional amphiphilic block copolymersAn amine and acid functional polystyrene-block-poly(ethylene oxide-co-allyl glycidyl ether) were chosen for the membranes. Membranes were formed by casting a concentrated polymer solution (12 to 25 wt% polymer) on PET fabric followed by immersion in a non-solvent bath. Scanning electron microscopy revealed an asymmetric porous structure consisting of a dense skin layer on top of a highly porous layer. Membrane performance was investigating using an FO test cell under the seawater condition.

  12. Solvent induced modifications to fiber nanostructure and morphology for 12HSA molecular gels

    NASA Astrophysics Data System (ADS)

    Gao, Jie

    Molecular organogels are thermo reversible quasi-solid materials, which are formed by low molecular weight organogelators (LMOGs) undergoing supramolecular aggregation via non-covalent interactions, forming a three-dimensional fibrillar network. Numerous applications of molecular organogels are been investigated as edible oils, drug release matrices and personal care products. The chemistry of the organic phase (i.e., solvent) influences every level of structure in organogels. Different solvents induce LMOG to assemble into "crystal like" fibers, which have more than one crystal form, lamellar arrangement and domain size. Differences in these solid states are known to affect the macroscopic properties of the gel, including critical gelator concentration (CGC), melting point, melting enthalpy and opacity.12-hydroxystearic acid (12HSA) was examined in several classes of organic solvents with different function groups. These gels, sols or precipitates were analyzed using a series of techniques including: powder x-ray diffraction (XRD), differential scanning calorimetry (DSC), fourier-transform infrared spectroscopy (FT-IR), pulsed nuclear magnetic resonance spectroscopy (pNMR) and microscopy. Specifically, certain solvents caused 12HSA to self-assemble into a triclinic parallel polymorphic form with subcell spacing of ~4.6, 3.9, and 3.8 A and an interdigitated unit cell with a lamellar arrangement (38~44 A). This polymorphic form corresponded to a less effective sphereultic supramolecular crystalline network, which immobilizes solvents at CGC greater than 1.5 wt %. The other group of solvents induce a hexagonal subcell spacing (i.e., unit sub cell spacing ~4.1 A) and are arranged in a multi lamellar fashion with a unit cell greater than the bimolecular length of 12HSA (~54 A).This polymorphic form corresponds to fibrillar aggregates with a CGC less than 1 wt %.

  13. Microscopic Calculation of 240Pu Scission with a Finite-Range Effective Force

    SciTech Connect

    Younes, W; Gogny, D

    2009-05-04

    Hartree-Fock-Bogoliubov calculations of hot fission in {sup 240}Pu have been performed with a newly-implemented code that uses the D1S finite-range effective interaction. The hot-scission line is identified in the quadrupole-octupole-moment coordinate space. Fission-fragment shapes are extracted from the calculations. A benchmark calculation for {sup 226}Th is obtained and compared to results in the literature. In addition, technical aspects of the use of HFB calculations for fission studies are examined in detail. In particular, the identification of scission configurations, the sensitivity of near-scission calculations to the choice of collective coordinates in the HFB iterations, and the formalism for the adjustment of collective-variable constraints are discussed. The power of the constraint-adjustment algorithm is illustrated with calculations near the critical scission configurations with up to seven simultaneous constraints.

  14. Solvent-Induced Crystallization in Poly(Ethylene Terephthalate) during Mass Transport

    NASA Astrophysics Data System (ADS)

    Ouyang, Hao

    2001-03-01

    The solvent transport in poly(ethylene terephthalate) (PET) and related phase transformation were investigated. The data of mass sorption were analyzed according to Harmon¡¦s model for Case I (Fickian), Case II (swelling) and anomalous transport. This transport process in PET is accompanied by the induced crystallization of the original amorphous state. The transformation was studied by wide angle x-ray scattering (WAXS), small angle x-ray scattering (SAXS), Differential Scanning Calorimeter (DSC), density gradient column, and Fourier Transform Infra-Red (FTIR). During this process, the matrix is under a compressive strain that causes different kinetic path of crystallization as compared to that by thermal annealing. This state of strain will assist the development of the solvent-induced crystallization. It also can be explained in terms of the principle of Le Chatelier if the local equilibrium is assumed. The model regarding the crystallization was proposed in terms of the study of long period L, the crystal thickness lc and the thickness of amorphous layer la, obtained from the linear correlation function and interface distribution function.

  15. Enhanced hydrophobicity of polyurethane via non-solvent induced surface aggregation of silica nanoparticles.

    PubMed

    Seyfi, Javad; Hejazi, Iman; Jafari, Seyed Hassan; Khonakdar, Hossein Ali; Simon, Frank

    2016-09-15

    Fabrication of superhydrophobic surfaces from hydrophilic polymers has always been regarded as a challenge. In this study, to achieve superhydrophobic polyurethane (PU) surfaces, silica nanoparticles and ethanol as non-solvent were simultaneously utilized during a solution casting-based process. Such modified version of phase separation process was found to be highly efficient, and also it required much lower concentration of nanoparticles to achieve superhydrophobicity as compared to the previously reported methods in the literature. According to the proposed mechanism, non-solvent induces a more profound aggregation of silica nanoparticles at the surface's top layer causing the surface energy to be highly diminished, and thus, the water repellency is improved. Morphology and topography results showed that a unique "triple-sized" structure was formed on the surface of superhydrophobic samples. X-ray photoelectron spectroscopy results proved that both PU macromolecules and silica nanoparticles were concurrently present at the surface layer of the superhydrophobic sample. It was concluded that surface composition and roughness could be regarded as competing factors in achieving superhydrophobicity. Based on the obtained results, the proposed method exhibits a promising potential in large-scale fabrication of surface layers with superhydrophobic property. Moreover, a mechanism was also presented to further explicate the physics behind the suggested method. PMID:27288577

  16. Control of charge transport in a semiconducting copolymer by solvent-induced long-range order

    PubMed Central

    Luzio, Alessandro; Criante, Luigino; D'Innocenzo, Valerio; Caironi, Mario

    2013-01-01

    Recent reports on high-mobility organic field-effect transistors (FETs) based on donor-acceptor semiconducting co-polymers have indicated an apparently strong deviation from the paradigm, valid for a series of semi-crystalline polymers, which has been strictly correlating charges mobility to crystalline order. This poses a severe limit on the control of mobility and a fundamental question on the critical length scale which is dominating charge transport. Here we focus on a well-known model material for electron transport, a naphthalene-diimide based copolymer, and we demonstrate that mobility can be controlled over two orders of magnitude, with maximum saturation mobility exceeding 1 cm2/Vs at high gate voltages, by controlling the extent of orientational domains through a deposition process as simple as spin-coating. High mobility values can be achieved by adopting solvents inducing a higher amount of pre-aggregates in the solution, which through the interaction with the substrate, provide the polymer with liquid-crystalline like ordering properties. PMID:24305756

  17. New statistical scission-point model to predict fission fragment observables

    NASA Astrophysics Data System (ADS)

    Lemaître, Jean-François; Panebianco, Stefano; Sida, Jean-Luc; Hilaire, Stéphane; Heinrich, Sophie

    2015-09-01

    The development of high performance computing facilities makes possible a massive production of nuclear data in a full microscopic framework. Taking advantage of the individual potential calculations of more than 7000 nuclei, a new statistical scission-point model, called SPY, has been developed. It gives access to the absolute available energy at the scission point, which allows the use of a parameter-free microcanonical statistical description to calculate the distributions and the mean values of all fission observables. SPY uses the richness of microscopy in a rather simple theoretical framework, without any parameter except the scission-point definition, to draw clear answers based on perfect knowledge of the ingredients involved in the model, with very limited computing cost.

  18. SPY: A new scission point model based on microscopic ingredients to predict fission fragments properties

    NASA Astrophysics Data System (ADS)

    Lemaître, J.-F.; Dubray, N.; Hilaire, S.; Panebianco, S.; Sida, J.-L.

    2013-12-01

    Our purpose is to determine fission fragments characteristics in a framework of a scission point model named SPY for Scission Point Yields. This approach can be considered as a theoretical laboratory to study fission mechanism since it gives access to the correlation between the fragments properties and their nuclear structure, such as shell correction, pairing, collective degrees of freedom, odd-even effects. Which ones are dominant in final state? What is the impact of compound nucleus structure? The SPY model consists in a statistical description of the fission process at the scission point where fragments are completely formed and well separated with fixed properties. The most important property of the model relies on the nuclear structure of the fragments which is derived from full quantum microscopic calculations. This approach allows computing the fission final state of extremely exotic nuclei which are inaccessible by most of the fission model available on the market.

  19. Membrane deformation and scission by the HSV-1 nuclear egress complex

    PubMed Central

    Bigalke, Janna M.; Heuser, Thomas; Nicastro, Daniela; Heldwein, Ekaterina E.

    2014-01-01

    The nuclear egress complex (NEC) of herpesviruses such as HSV-1 is essential for the exit of nascent capsids from the cell nucleus. The NEC drives nuclear envelope vesiculation in cells, but the precise budding mechanism and the potential involvement of cellular proteins are unclear. Here we report that HSV-1 NEC alone is sufficient for membrane budding in vitro and thus represents a complete membrane deformation and scission machinery. It forms ordered coats on the inner surface of budded vesicles, suggesting that it mediates scission by scaffolding the membrane bud and constricting the neck to the point of scission. The inward topology of NEC-mediated budding in vitro resembles capsid budding into the inner nuclear membrane during HSV-1 infection and nuclear envelope vesiculation in NEC-transfected cells. We propose that the NEC functions as minimal virus-encoded membrane-budding machinery during nuclear egress and does not require additional cellular factors. PMID:24916797

  20. Rapid RNA Strand Scission Following C2′-Hydrogen Atom Abstraction

    PubMed Central

    Paul, Rakesh; Greenberg, Marc M.

    2015-01-01

    C2′-Nucleotide radicals have been proposed as key intermediates in direct strand break formation in RNA exposed to ionizing radiation. Uridin-2′-yl radical (1) was independently generated in single- and double-stranded RNA via photolysis of a ketone precursor. Direct stand breaks result from heterolytic cleavage of the adjacent C3′-carbon–oxygen bond. Trapping of 1 by O2 or β-mercaptoethanol (1 M) does not compete with strand scission, indicating that phosphate elimination is >106 s−1. Uracil loss also does not compete with strand scission. When considered in conjunction with reports that nucleobase radicals produce 1, this chemistry explains why RNA is significantly more susceptible to strand scission by ionizing radiation (hydroxyl radical) than is DNA. PMID:25580810

  1. Prediction of enhanced solvent-induced enantioselectivity for a ring opening with a bifurcating reaction path

    DOE PAGESBeta

    Carpenter, Barry K.; Harvey, Jeremy N.; Glowacki, David R.

    2014-12-11

    Classical molecular dynamics simulations are reported for the deazetisation and ring opening of meso-2,3-difluoro-2,3-dimethyldiazocyclopropane in three solvents: CHCl3, CHFClBr and CH3CH(OH)CF3 (TFIPA). In this study, the achiral reactant leads to enantiomeric allene products, and the question addressed in the study is whether either of the chiral, enantiomerically pure solvents can induce significant enantiomeric excess in the products. The direct dynamics calculations use an empirical valence bond potential for the solute, with empirical parameters optimised against M06-2X/cc-pVTZ density functional results. The results reveal that the exothermic N2 loss and ring opening promote transient strong solvent–solute interactions within the first ~100 fsmore » of the reaction. Because of the bifurcating reaction path, these interactions occur at time when the “decision” about which enantiomer of the product to form has yet to be made (at least for many of the trajectories). Hence, it is possible in principle that the solvent could exert a larger-than-normal influence on the course of the reaction. In fact, the results reveal no such effect for CHFClBr but do predict that TFIPA should induce 15.2 ± 2.1% enantiomeric excess. This is roughly an order of magnitude larger than solvent-induced enantiomeric excesses found experimentally in reactions where the conversion of reactant(s) to enantiomeric products occur over separate transition states.« less

  2. Prediction of enhanced solvent-induced enantioselectivity for a ring opening with a bifurcating reaction path

    SciTech Connect

    Carpenter, Barry K.; Harvey, Jeremy N.; Glowacki, David R.

    2014-12-11

    Classical molecular dynamics simulations are reported for the deazetisation and ring opening of meso-2,3-difluoro-2,3-dimethyldiazocyclopropane in three solvents: CHCl3, CHFClBr and CH3CH(OH)CF3 (TFIPA). In this study, the achiral reactant leads to enantiomeric allene products, and the question addressed in the study is whether either of the chiral, enantiomerically pure solvents can induce significant enantiomeric excess in the products. The direct dynamics calculations use an empirical valence bond potential for the solute, with empirical parameters optimised against M06-2X/cc-pVTZ density functional results. The results reveal that the exothermic N2 loss and ring opening promote transient strong solvent–solute interactions within the first ~100 fs of the reaction. Because of the bifurcating reaction path, these interactions occur at time when the “decision” about which enantiomer of the product to form has yet to be made (at least for many of the trajectories). Hence, it is possible in principle that the solvent could exert a larger-than-normal influence on the course of the reaction. In fact, the results reveal no such effect for CHFClBr but do predict that TFIPA should induce 15.2 ± 2.1% enantiomeric excess. This is roughly an order of magnitude larger than solvent-induced enantiomeric excesses found experimentally in reactions where the conversion of reactant(s) to enantiomeric products occur over separate transition states.

  3. Controlling Palladium Nanocrystals by Solvent-Induced Strategy for Efficient Multiple Liquid Fuels Electrooxidation.

    PubMed

    Zhang, Ying; Zhu, Xing; Guo, Jun; Huang, Xiaoqing

    2016-08-17

    Pd has been considered as the possible economical substitute of rare Pt for catalyzing the liquid fuels electrooxidation reaction. However, the biggest problem of Pd nanocatalysts for alcohol oxidations is that they show the limited stability and activity, greatly impacting the development of liquid fuels-based fuel cell technology. We report herein a new solvent-induced procedure for making distinct Pd NCs with geometry tuning from Pd nanosheets, Pd tetrapods, to Pd concave tetrahedra by switching the solvent from 1-methyl-2-pyrrolidone, formamide, to acetylacetonate. The key features for the preparation of dimension-controlled Pd NCs herein are that the use of molybdenum carbonyl (Mo(CO)6) determines the exposed {111} facet in the final Pd NCs, while different solvents control the reduction kinetics to induce the growth of Pd NCs with distinct morphologies. The as-prepared distinct Pd NCs show the interesting shape-dependent electrocatalytic activities toward multiple liquid fuels electrooxidation reactions including ethylene glycol oxidation reaction, glycerol oxidation reaction, ethanol oxidation reaction, and also methanol oxidation reaction with Pd nanosheets exhibiting higher activity than all the other Pd catalysts and higher activity than the commercial Pd/C and also Pd black due to the thin character of Pd nanosheets. Most importantly, the Pd nanosheets exhibit much higher stability for multiple liquid fuels electrooxidation than all the other Pd catalysts tested. The present work gives the first example in exploring the effect of solvent in tuning the dimensions of Pd NCs, and thus optimizing the electrocatalytic performance for liquid fuels electrooxidation. PMID:27442912

  4. Solvent-induced helical assembly and reversible chiroptical switching of chiral cyclic-dipeptide-functionalized naphthalenediimides.

    PubMed

    Manchineella, Shivaprasad; Prathyusha, V; Priyakumar, U Deva; Govindaraju, T

    2013-12-01

    Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self-assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary-functionalized naphthalenediimides (NCDPs 1-6) have been prepared and their chiral self-assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1-3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M- to P-type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid-state thin-film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4-6), with an achiral or D-isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π-π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P-) and left (M-) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent-induced helical assembly and reversible chiroptical switching of naphthalenediimides. PMID:24281809

  5. Hydroliquefaction of coal

    DOEpatents

    Sze, Morgan C.; Schindler, Harvey D.

    1982-01-01

    Coal is catalytically hydroliquefied by passing coal dispersed in a liquefaction solvent and hydrogen upwardly through a plurality of parallel expanded catalyst beds, in a single reactor, in separate streams, each having a cross-sectional flow area of no greater than 255 inches square, with each of the streams through each of the catalyst beds having a length and a liquid and gas superficial velocity to maintain an expanded catalyst bed and provide a Peclet Number of at least 3. If recycle is employed, the ratio of recycle to total feed (coal and liquefaction solvent) is no greater than 2:1, based on volume. Such conditions provide for improved selectivity to liquid product to thereby reduce hydrogen consumption. The plurality of beds are formed by partitions in the reactor.

  6. Catalytic coal hydroliquefaction process

    DOEpatents

    Garg, Diwakar

    1984-01-01

    A process is described for the liquefaction of coal in a hydrogen donor solvent in the presence of hydrogen and a co-catalyst combination of iron and a Group VI or Group VIII non-ferrous metal or compounds of the catalysts.

  7. Comparison of Bond Scission Sequence of Methanol on Tungsten Monocarbide and Pt-Modified Tungsten Monocarbide

    SciTech Connect

    Liu, P.; Stottlemyer, A.L.; Chen, J.G.

    2010-09-14

    The ability to control the bond scission sequence of O-H, C-H, and C-O bonds is of critical importance in the effective utilization of oxygenate molecules, such as in reforming reactions and in alcohol fuel cells. In the current study, we use methanol as a probe molecule to demonstrate the possibility to control the decomposition pathways by supporting monolayer coverage of Pt on a tungsten monocarbide (WC) surface. Density functional theory (DFT) results reveal that on the WC and Pt/WC surfaces CH{sub 3}OH decomposes via O-H bond scission to form the methoxy (*CH{sub 3} O) intermediate. The subsequent decomposition of methoxy on the WC surface occurs through the C-O bond scission to form *CH{sub 3}, which reacts with surface *H to produce CH{sub 4}. In contrast, the decomposition of methoxy on the Pt/WC surface favors the C-H bond scission to produce *CH{sub 2} O, which prevents the formation of the *CH{sub 3} species and leads to the formation of a *CO intermediate through subsequent deprotonation steps. The DFT predictions are validated using temperature programmed desorption to quantify the gas-phase product yields and high resolution electron energy loss spectroscopy to determine the surface intermediates from methanol decomposition on Pt, WC, and Pt/WC surfaces.

  8. Comparison of bond scission sequence of methanol on tungsten monocarbide and Pt-modified tungsten monocarbide

    NASA Astrophysics Data System (ADS)

    Stottlemyer, Alan Lee; Liu, Ping; Chen, Jingguang G.

    2010-09-01

    The ability to control the bond scission sequence of OH, CH, and CO bonds is of critical importance in the effective utilization of oxygenate molecules, such as in reforming reactions and in alcohol fuel cells. In the current study, we use methanol as a probe molecule to demonstrate the possibility to control the decomposition pathways by supporting monolayer coverage of Pt on a tungsten monocarbide (WC) surface. Density functional theory (DFT) results reveal that on the WC and Pt/WC surfaces CH3OH decomposes via OH bond scission to form the methoxy (C∗H3 O) intermediate. The subsequent decomposition of methoxy on the WC surface occurs through the CO bond scission to form C∗H3, which reacts with surface H∗ to produce CH4. In contrast, the decomposition of methoxy on the Pt/WC surface favors the CH bond scission to produce C∗H2 O, which prevents the formation of the C∗H3 species and leads to the formation of a C∗O intermediate through subsequent deprotonation steps. The DFT predictions are validated using temperature programmed desorption to quantify the gas-phase product yields and high resolution electron energy loss spectroscopy to determine the surface intermediates from methanol decomposition on Pt, WC, and Pt/WC surfaces.

  9. The rotation of scissioning nucleus considered trajectory calculations for ternary fission induced by cold polarized neutrons

    NASA Astrophysics Data System (ADS)

    Guseva, I.; Gusev, Yu.

    2009-10-01

    On the base of modified trajectory calculations the shift of angular distribution of α-particles accompanied the reaction 235U(n,f) induced by cold polarized neutrons is evaluated. It was supposed that angular distribution shift is caused by the rotation of nuclear system before scission. The orientation of a rotation motion is determined by the neutron spin polarization along and opposite to the beam direction. For the first time the estimation was done in the frame of trajectory calculations assuming the rotation motion of scissioning nucleus [1]. The result of the calculation is in a good agreement with experimental data of paper [2], where this new phenomenon was named as ROT-effect.

  10. A Dynamin-Actin Interaction Is Required for Vesicle Scission during Endocytosis in Yeast

    PubMed Central

    Palmer, Sarah E.; Smaczynska-de Rooij, Iwona I.; Marklew, Christopher J.; Allwood, Ellen G.; Mishra, Ritu; Johnson, Simeon; Goldberg, Martin W.; Ayscough, Kathryn R.

    2015-01-01

    Summary Actin is critical for endocytosis in yeast cells, and also in mammalian cells under tension. However, questions remain as to how force generated through actin polymerization is transmitted to the plasma membrane to drive invagination and scission. Here, we reveal that the yeast dynamin Vps1 binds and bundles filamentous actin. Mutational analysis of Vps1 in a helix of the stalk domain identifies a mutant RR457-458EE that binds actin more weakly. In vivo analysis of Vps1 function demonstrates that the mutation disrupts endocytosis but not other functions of Vps1 such as vacuolar trafficking or peroxisome fission. The mutant Vps1 is stably expressed in cells and co-localizes with the endocytic reporters Abp1 and the amphiphysin Rvs167. Detailed analysis of individual endocytic patch behavior indicates that the mutation causes aberrant movements in later stages of endocytosis, consistent with a scission defect. Ultrastructural analysis of yeast cells using electron microscopy reveals a significant increase in invagination depth, further supporting a role for the Vps1-actin interaction during scission. In vitro analysis of the mutant protein demonstrates that—like wild-type Vps1—it is able to form oligomeric rings, but, critically, it has lost its ability to bundle actin filaments into higher-order structures. A model is proposed in which actin filaments bind Vps1 during invagination, and this interaction is important to transduce the force of actin polymerization to the membrane to drive successful scission. PMID:25772449

  11. The comparison of binary- and ternary-fission configurations close to the instant of scission

    NASA Astrophysics Data System (ADS)

    Guseva, I. S.; Gagarski, A. M.; Gusev, Yu. I.; Petrov, G. A.; Valski, G. V.

    2013-07-01

    A new way to bring into comparison the binary- and ternary-fission configurations is proposed. The method is founded on recently discovered ROT effect. The angle of fission axis deflection from its initial orientation at the moment of scission comes into existence as a result of dividing system rotation and carries information about fissioning nucleus deformation. The comparison of proper angles for binary and ternary fission can be used to estimate the difference in the rupture configurations.

  12. A QSPR study on the solvent-induced frequency shifts of acetone and dimethyl sulfoxide in organic solvents.

    PubMed

    Ou, Yu Heng; Chang, Chia Ming; Chen, Ying Shao

    2016-06-01

    In this study, solvent-induced frequency shifts (SIFS) in the infrared spectrum of acetone and dimethyl sulfoxide in organic solvents were investigated by using four types of quantum-chemical reactivity descriptors. The results showed that the SIFS of acetone is mainly affected by the electron-acceptance chemical potential and the maximum nucleophilic condensed local softness of organic solvents, which represent the electron flow and the polarization between acetone and solvent molecules. On the other hand, the SIFS of dimethyl sulfoxide changes with the maximum positive charge of hydrogen atom and the inverse of apolar surface area of solvent molecules, showing that the electrostatic and hydrophilic interactions are main mechanisms between dimethyl sulfoxide and solvent molecules. The introduction of the four-element theory model-based quantitative structure-property relationship approach improved the assessing quality and provided a basis for interpreting the solute-solvent interactions. PMID:26994584

  13. Durable, superoleophobic polymer-nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation.

    PubMed

    Brown, Philip S; Bhushan, Bharat

    2016-01-01

    Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices. PMID:26876479

  14. A QSPR study on the solvent-induced frequency shifts of acetone and dimethyl sulfoxide in organic solvents

    NASA Astrophysics Data System (ADS)

    Ou, Yu Heng; Chang, Chia Ming; Chen, Ying Shao

    2016-06-01

    In this study, solvent-induced frequency shifts (SIFS) in the infrared spectrum of acetone and dimethyl sulfoxide in organic solvents were investigated by using four types of quantum-chemical reactivity descriptors. The results showed that the SIFS of acetone is mainly affected by the electron-acceptance chemical potential and the maximum nucleophilic condensed local softness of organic solvents, which represent the electron flow and the polarization between acetone and solvent molecules. On the other hand, the SIFS of dimethyl sulfoxide changes with the maximum positive charge of hydrogen atom and the inverse of apolar surface area of solvent molecules, showing that the electrostatic and hydrophilic interactions are main mechanisms between dimethyl sulfoxide and solvent molecules. The introduction of the four-element theory model-based quantitative structure-property relationship approach improved the assessing quality and provided a basis for interpreting the solute-solvent interactions.

  15. Durable, superoleophobic polymer–nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation

    PubMed Central

    Brown, Philip S.; Bhushan, Bharat

    2016-01-01

    Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices. PMID:26876479

  16. Durable, superoleophobic polymer-nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation

    NASA Astrophysics Data System (ADS)

    Brown, Philip S.; Bhushan, Bharat

    2016-02-01

    Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices.

  17. SPY: a new scission-point model based on microscopic inputs to predict fission fragment properties

    NASA Astrophysics Data System (ADS)

    Panebianco, Stefano; Dubray, Nöel; Goriely, Stéphane; Hilaire, Stéphane; Lemaître, Jean-François; Sida, Jean-Luc

    2014-04-01

    Despite the difficulty in describing the whole fission dynamics, the main fragment characteristics can be determined in a static approach based on a so-called scission-point model. Within this framework, a new Scission-Point model for the calculations of fission fragment Yields (SPY) has been developed. This model, initially based on the approach developed by Wilkins in the late seventies, consists in performing a static energy balance at scission, where the two fragments are supposed to be completely separated so that their macroscopic properties (mass and charge) can be considered as fixed. Given the knowledge of the system state density, averaged quantities such as mass and charge yields, mean kinetic and excitation energy can then be extracted in the framework of a microcanonical statistical description. The main advantage of the SPY model is the introduction of one of the most up-to-date microscopic descriptions of the nucleus for the individual energy of each fragment and, in the future, for their state density. These quantities are obtained in the framework of HFB calculations using the Gogny nucleon-nucleon interaction, ensuring an overall coherence of the model. Starting from a description of the SPY model and its main features, a comparison between the SPY predictions and experimental data will be discussed for some specific cases, from light nuclei around mercury to major actinides. Moreover, extensive predictions over the whole chart of nuclides will be discussed, with particular attention to their implication in stellar nucleosynthesis. Finally, future developments, mainly concerning the introduction of microscopic state densities, will be briefly discussed.

  18. Stereospecific Metabolism of Itraconazole by CYP3A4: Dioxolane Ring Scission of Azole Antifungals

    PubMed Central

    Peng, Chi-Chi; Shi, Wei; Lutz, Justin D.; Kunze, Kent L.; Liu, Jun O.; Nelson, Wendel L.

    2012-01-01

    Itraconazole (ITZ) is a mixture of four cis-stereoisomers that inhibit CYP3A4 potently and coordinate CYP3A4 heme via the triazole nitrogen. However, (2R,4S,2′R)-ITZ and (2R,4S,2′S)-ITZ also undergo stereoselective sequential metabolism by CYP3A4 at a site distant from the triazole ring to 3′-OH-ITZ, keto-ITZ, and N-desalkyl-ITZ. This stereoselective metabolism demonstrates specific interactions of ITZ within the CYP3A4 active site. To further investigate this process, the binding and metabolism of the four trans-ITZ stereoisomers by CYP3A4 were characterized. All four trans-ITZ stereoisomers were tight binding inhibitors of CYP3A4-mediated midazolam hydroxylation (IC50 16–26 nM), and each gave a type II spectrum upon binding to CYP3A4. However, instead of formation of 3′-OH-ITZ, they were oxidized at the dioxolane ring, leading to ring scission and formation of two new metabolites of ITZ. These two metabolites were also formed from the four cis-ITZ stereoisomers, although not as efficiently. The catalytic rates of dioxolane ring scission were similar to the dissociation rates of ITZ stereoisomers from CYP3A4, suggesting that the heme iron is reduced while the triazole moiety coordinates to it and no dissociation of ITZ is necessary before catalysis. The triazole containing metabolite [1-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl)ethanone] also inhibited CYP3A4 (IC50 >15 μM) and showed type II binding with CYP3A4. The dioxolane ring scission appears to be clinically relevant because this metabolite was detected in urine samples from subjects that had been administered the mixture of cis-ITZ isomers. These data suggest that the dioxolane ring scission is a metabolic pathway for drugs that contain this moiety. PMID:22106171

  19. Radiolytic crosslinking and chain scission in aliphatic and alkyl-aromatic polyamides—II

    NASA Astrophysics Data System (ADS)

    Lyons, Bernard J.; Glover, Leon C.

    Regression analysis of the radiation parameters of nine aliphatic polyamides exposed to ionizing radiation leads to the conclusion that the decline in the ratio of chain scission to crosslinking in higher aliphatic polyamides is best related to the linear increase in the methylene content of, or the number of methylene groups in, the polyamide repeat unit. G(crosslink) [ G(X)] and G(chain scission) [ G(CS)] values, however, do not correlate well with either of these parameters. Rather it is found that the major determinant of yields [about 80-85% of the variation for G(X), 70% for G(CS)] is the number of hydrogen atoms or methylene groups in the amine residue. A minor determinant [15% of the variation for G(X) and 30% for G(CS)] is the number of hydrogen atoms or methylene groups in the acid residue of the repeat unit. Significantly, although there was little sign of a decrease in G(CS) in the higher aliphatic homologues (up to 11 methylene residues per amide group), G(CS) is found to be positively related to the number of methylene groups in the amine residue but negatively related to the number of methylene groups in the acid residue. Thus although the amine residue dominates the radiolytic response, the acid residue plays a critical if lesser role in determining chain scission yields in polyamides. Thus a polyamide with the repeat unit —(CH 2) 3 nCONH(CH 2) nNHCO— would be predicted to have a very low or zero G(CS) and, if n is 10 or more, a G(X) comparable to that of polyethylene. Although, logically, the yields of crosslinks and chain scissions in polyamides would be expected to tend to that of polyethylene as the number of methylene groups in the repeat unit increases, use of two models assuming an exponential trend to the G(X) value characteristic of polyethylene in the analysis did not provide better fits to the data than the simple linear model referred to above. Indeed, the assumption of a significant exponential trend factor led to a marked drop in

  20. Analysis of pre- and post-scission neutrons emitted in the reaction sup 169 Tm( sup 36 Ar, f ) at E sub lab =205 MeV

    SciTech Connect

    Rossner, H.; Hilscher, D.; Hinde, D.J.; Gebauer, B.; Lehmann, M.; Wilpert, M. ); Mordhorst, E. )

    1989-12-01

    Pre- and post-scission neutron multiplicities for the reaction {sup 169}Tm({sup 36}Ar,{ital f}) at {ital E}{sub lab}=205 MeV were measured in coincidence with fission fragments of different masses and total kinetic energies. The mass and total kinetic energy dependence of the total neutron multiplicity as well as the width of the out-of-plane fission fragment correlation angle are well described by evaporation calculations. An average time before scission of several 10{sup {minus}20} s is deduced from the average pre-scission neutron multiplicity. The mass dependence of the post-scission neutron multiplicity is consistent with an energy division at scission proportional to the mass of the fragments. For the first time clear evidence for an increase in pre-scission neutrons with increasing total kinetic energy values has been observed. Possible interpretations of this unexpected behavior are discussed.

  1. Comparing different energy partitions at scission used in prompt emission model codes GEF and Point-by-Point

    NASA Astrophysics Data System (ADS)

    Tudora, A.; Hambsch, F.-J.; Visan, I.; Giubega, G.

    2015-08-01

    Different methods to partition the total excitation energy (TXE) of fully accelerated fragments, presently used in prompt emission calculations include different assumptions about what is happening at scission. In fact the energy partition takes place at scission or even before scission, depending on the physical assumptions supporting the models used in different methods of TXE partition. The paper discusses two TXE partition methods in which the amount of energy to be shared (at scission and before scission, respectively) is very different. These methods (based on different principles and physical considerations) are: A. The method used in the Point-by-Point (PbP) treatment of prompt emission in which the available excitation energy at scission is shared between complementary nascent fragments. The amount of energy to be shared is sufficiently high to consider the nascent fragments in the Fermi-gas regime of the level density. B. The method used in the GEF code, in which the intrinsic energy before scission is shared between pre-nascent fragments according to the "energy sorting mechanism". This sorting mechanism is based on the assumption of level densities in the constant temperature regime, only. This is supported by the low amount of the shared intrinsic energy in the case of thermal and low energy neutron induced fission. Taking into account that the principles and physical considerations of any TXE partition method are independent on the way to treat the prompt emission (i.e. deterministically as in the PbP model or probabilistically by Monte-Carlo as in the code GEF) the methods A and B are applied to the same fission fragment range (built as in the PbP treatment). Extreme hypotheses are made for the fragment level densities on which the partitions are based (only in the Fermi-gas regime or only in the constant temperature regime). The results are compared with the energy partition obtained with fragment level densities described by the composite Gilbert

  2. Scission neutrons for U, Pu, Cm, and Cf isotopes: Relative multiplicities calculated in the sudden limit

    NASA Astrophysics Data System (ADS)

    Capote, R.; Carjan, N.; Chiba, S.

    2016-02-01

    The multiplicities of scission neutrons νs c are calculated for series of U, Pu, Cm, and Cf isotopes assuming a sudden transition between two different nuclear configurations (αi→αf ): one just before the neck rupture and one immediately after the disappearance of the neck. This calculation requires only the knowledge of the corresponding two sets of neutron eigenstates. The nuclear shapes around the scission point are described in terms of Cassinian ovals with only two parameters: α (that positions the shape with respect to the zero-neck shape) and α1 (that defines the mass asymmetry). Based on these shapes, a neutron mean field of the Woods-Saxon type is constructed using two prescriptions to calculate the distance to the nuclear surface. The accent in the present work is put on the dependence of νs c on the neutron number Nf of the fissioning nucleus and on the mass asymmetry AL/AH of the primary fission fragments. The relative dependence of these multiplicities, averaged over the mass yields, <νs c> , are finally compared with existing experimental data on prompt fission neutrons <νp> .

  3. Clathrin modulates vesicle scission, but not invagination shape, in yeast endocytosis

    PubMed Central

    Kukulski, Wanda; Picco, Andrea; Specht, Tanja

    2016-01-01

    In a previous paper (Picco et al., 2015), the dynamic architecture of the protein machinery during clathrin-mediated endocytosis was visualized using a new live imaging and particle tracking method. Here, by combining this approach with correlative light and electron microscopy, we address the role of clathrin in this process. During endocytosis, clathrin forms a cage-like coat around the membrane and associated protein components. There is growing evidence that clathrin does not determine the membrane morphology of the invagination but rather modulates the progression of endocytosis. We investigate how the deletion of clathrin heavy chain impairs the dynamics and the morphology of the endocytic membrane in budding yeast. Our results show that clathrin is not required for elongating or shaping the endocytic membrane invagination. Instead, we find that clathrin contributes to the regularity of vesicle scission and thereby to controlling vesicle size. DOI: http://dx.doi.org/10.7554/eLife.16036.001 PMID:27341079

  4. Compound nucleus decay: Comparison between saddle point and scission point barriers

    SciTech Connect

    Santos, T. J.; Carlson, B. V.

    2014-11-11

    One of the principal characteristics of nuclear multifragmentation is the emission of complex fragments of intermediate mass. An extension of the statistical multifragmentation model has been developed, in which the process can be interpreted as the near simultaneous limit of a series of sequential binary decays. In this extension, intermediate mass fragment emissions are described by expressions almost identical to those of light particle emission. At lower temperatures, similar expressions have been shown to furnish a good description of very light intermediate mass fragment emission but not of the emission of heavier fragments, which seems to be determined by the transition density at the saddle-point rather than at the scission point. Here, we wish to compare these different formulations of intermediate fragmment emission and analyze the extent to which they remain distinguishable at high excitation energy.

  5. Signatures of bond formation and bond scission dynamics in dissociative electron attachment to methane.

    PubMed

    Douguet, N; Slaughter, D S; Adaniya, H; Belkacem, A; Orel, A E; Rescigno, T N

    2015-10-14

    We present a combined experimental and theoretical investigation of the dynamics and angular dependence of dissociative electron attachment to methane. We show that a triply degenerate (T2) Feshbach resonance is responsible for the broad 10 eV dissociation peak in methane. This resonance alone is shown to correlate asymptotically to the various dissociation channels observed experimentally. The molecular-frame entrance amplitude for electron attachment is calculated for each component of the threefold degenerate resonance. By investigating the topology of the anion potential energy surfaces, we deduce the main pathways to two- and three-body breakup channels involving both bond scission and bond formation. The computed fragment angular distributions reproduce the main trends of the experimental measurements. PMID:26371546

  6. Fission fragment mass yield deduced from density distribution in the pre-scission configuration

    NASA Astrophysics Data System (ADS)

    Warda, M.; Zdeb, A.

    2015-11-01

    Static self-consistent methods usually allow one to determine the most probable fission fragments mass asymmetry. We have applied random neck rupture mechanism to the nuclei in the configuration at the end of fission paths. Fission fragment mass distributions have been deduced from the pre-scission nuclear density distribution obtained from the self-consistent calculations. Potential energy surfaces as well as nuclear shapes have been calculated in the fully microscopic theory, namely the constrained Hartree-Fock-Bogoliubov model with the effective Gogny D1S density-dependent interaction. The method has been applied for analysis of fission of {}{256,258}Fm, 252Cf and 180Hg and compared with the experimental data.

  7. Niche nanoparticle-based FRET assay for bleomycin detection via DNA scission.

    PubMed

    Pei, Haimeng; Zheng, Yiqun; Kong, Rongmei; Xia, Lian; Qu, Fengli

    2016-11-15

    We describe a highly sensitive nanoparticle-based fluorescence resonance energy transfer (FRET) probe developed without using molecular fluorophores as donors and acceptors. The success of this work relies on the strategy that DNA scission was designed to occur to the probe when target presented, which enabled the fluorescence signal "turn-on" of graphene quantum dots (GQDs) and thus quantitative analysis. In particular, amino-modified SiO2 NPs were initially coated by GQDs to form highly emitting SiO2/GQDs, followed by conjunction with DNA functionalized gold nanoparticles (Au NPs-DNA) to form SiO2/GQDs-DNA-Au NPs composite. Owing to the FRET interactions between the GQDs and Au NPs, the fluorescence of GQDs was effectively quenched by Au NPs. When bleomycin (BLM), a model analyte, was mixed with the probe, the fluorescence signal of GQDs would be restored due to the removal of Au NPs from the SiO2/GQDs surface by DNA scission treatment with BLM in the presence of Fe (II). The current FRET probe shows a good linear relationship between the fluorescence intensity and the concentration of BLM in the range from 0.5nM to 1μM with a detection limit of 0.2nM. The probe also shows satisfactory results for the analysis of clinical serum samples. This method provides versatility to the application of GQDs in FRET biosensing and could be potentially extended to other similar systems by replacing the linker between the GQDs and Au NPs. PMID:27155119

  8. Robust self-replication of combinatorial information via crystal growth and scission

    PubMed Central

    Schulman, Rebecca; Yurke, Bernard; Winfree, Erik

    2012-01-01

    Understanding how a simple chemical system can accurately replicate combinatorial information, such as a sequence, is an important question for both the study of life in the universe and for the development of evolutionary molecular design techniques. During biological sequence replication, a nucleic acid polymer serves as a template for the enzyme-catalyzed assembly of a complementary sequence. Enzymes then separate the template and complement before the next round of replication. Attempts to understand how replication could occur more simply, such as without enzymes, have largely focused on developing minimal versions of this replication process. Here we describe how a different mechanism, crystal growth and scission, can accurately replicate chemical sequences without enzymes. Crystal growth propagates a sequence of bits while mechanically-induced scission creates new growth fronts. Together, these processes exponentially increase the number of crystal sequences. In the system we describe, sequences are arrangements of DNA tile monomers within ribbon-shaped crystals. 99.98% of bits are copied correctly and 78% of 4-bit sequences are correct after two generations; roughly 40 sequence copies are made per growth front per generation. In principle, this process is accurate enough for 1,000-fold replication of 4-bit sequences with 50% yield, replication of longer sequences, and Darwinian evolution. We thus demonstrate that neither enzymes nor covalent bond formation are required for robust chemical sequence replication. The form of the replicated information is also compatible with the replication and evolution of a wide class of materials with precise nanoscale geometry such as plasmonic nanostructures or heterogeneous protein assemblies. PMID:22493232

  9. Vibrational spectra from atomic fluctuations in dynamics simulations. II. Solvent-induced frequency fluctuations at femtosecond time resolution

    NASA Astrophysics Data System (ADS)

    Schmitz, Matthias; Tavan, Paul

    2004-12-01

    The midinfrared (MIR) spectra of molecules in polar solvents exhibit inhomogeneously broadened bands whose spectral positions are shifted as compared to the gas phase. The shifts are caused by interactions with structured solvation shells and the broadenings by fluctuations of these interactions. The MIR spectra can be calculated from hybrid molecular dynamics (MD) simulations, which treat the solute molecule by density functional theory and the solvent by molecular mechanics by the so-called instantaneous normal mode analysis (INMA) or by Fourier transforming the time correlation function (FTTCF) of the molecular dipole moment. In Paper I of this work [M. Schmitz and P. Tavan, J. Chem. Phys. 121, 12233 (2004)] we explored an alternative method based on generalized virial (GV) frequencies noting, however, that GV systematically underestimates frequencies. As shown by us these artifacts are caused by solvent-induced fluctuations of the (i) equilibrium geometry, (ii) force constants, and (iii) normal mode directions as well as by (iv) diagonal and (v) off-diagonal anharmonicities. Here we now show, by analyzing the time scales of fluctuations and sample MD trajectories of formaldehyde in the gas phase and in water, that all these sources of computational artifacts can be made visible by a Fourier analysis of the normal coordinates. Correspondingly, the error sources (i) and (iii)-(v) can be removed by bandpass filtering, as long as the spectral signatures of the respective effects are well separated from the fundamental band. Furthermore, the artifacts arising from effect (ii) can be strongly diminished by a time-resolved version of the GV approach (TF-GV). The TF-GV method then yields for each mode j a trajectory of the vibrational frequency ωj(t|τ) at a time resolution τ>τj, which is only limited by the corresponding oscillation time τj=2π/ωj and, thus, is in the femtosecond range. A correlation analysis of these trajectories clearly separates the

  10. Amide Link Scission in the Polyamide Active Layers of Thin-Film Composite Membranes upon Exposure to Free Chlorine: Kinetics and Mechanisms.

    PubMed

    Powell, Joshua; Luh, Jeanne; Coronell, Orlando

    2015-10-20

    The volume-averaged amide link scission in the aromatic polyamide active layer of a reverse osmosis membrane upon exposure to free chlorine was quantified at a variety of free chlorine exposure times, concentrations, and pH and rinsing conditions. The results showed that (i) hydroxyl ions are needed for scission to occur, (ii) hydroxide-induced amide link scission is a strong function of exposure to hypochlorous acid, (iii) the ratio between amide links broken and chlorine atoms taken up increased with the chlorination pH and reached a maximum of ∼25%, (iv) polyamide disintegration occurs when high free chlorine concentrations, alkaline conditions, and high exposure times are combined, (v) amide link scission promotes further chlorine uptake, and (vi) scission at the membrane surface is unrepresentative of volume-averaged scission in the active layer. Our observations are consistent with previously proposed mechanisms describing amide link scission as a result of the hydrolysis of the N-chlorinated amidic N-C bond due to nucleophilic attack by hydroxyl ions. This study increases the understanding of the physicochemical changes that could occur for membranes in treatment plants using chlorine as an upstream disinfectant and the extent and rate at which those changes would occur. PMID:26394532

  11. Chain scission and anti fungal effect of electron beam on cellulose membrane

    NASA Astrophysics Data System (ADS)

    Wanichapichart, Pikul; Taweepreeda, Wirach; Nawae, Safitree; Choomgan, Pastraporn; Yasenchak, Dan

    2012-08-01

    Two types of bacterial cellulose (BC) membranes were produced under a modified H&S medium using sucrose as a carbon source, with (CCB) and without (SHB) coconut juice supplement. Both membranes showed similar crystallinity of 69.24 and 71.55%. After being irradiated with E-beams under oxygen limited and ambient condition, the results from water contact angle showed that only the irradiated membrane CCB was increased from 30 to 40 degrees, and irradiation under oxygen ambient condition provided the greatest value. Comparing with the control membranes, smaller water flux was the cases after electron beam irradiation which indicated a reduction of membrane pore area. However, the results from molecular weight cut off (MWCO) revealed that chain scission was greater for membrane SHB and its cut off was increased from 28,000 Da to more than 35,000 Da. FTIR analysis revealed some changes in membrane functional groups, corresponding with the above results. These changes initiated new property of cellulose membranes, an anti-fungal food wrap.

  12. Cell Division by Longitudinal Scission in the Insect Endosymbiont Spiroplasma poulsonii

    PubMed Central

    Maclachlan, Catherine; Clerc-Rosset, Stéphanie; Knott, Graham W.

    2016-01-01

    ABSTRACT Spiroplasma bacteria are highly motile bacteria with no cell wall and a helical morphology. This clade includes many vertically transmitted insect endosymbionts, including Spiroplasma poulsonii, a natural endosymbiont of Drosophila melanogaster. S. poulsonii bacteria are mainly found in the hemolymph of infected female flies and exhibit efficient vertical transmission from mother to offspring. As is the case for many facultative endosymbionts, S. poulsonii can manipulate the reproduction of its host; in particular, S. poulsonii induces male killing in Drosophila melanogaster. Here, we analyze the morphology of S. poulsonii obtained from the hemolymph of infected Drosophila. This endosymbiont was not only found as long helical filaments, as previously described, but was also found in a Y-shaped form. The use of electron microscopy, immunogold staining of the FtsZ protein, and antibiotic treatment unambiguously linked the Y shape of S. poulsonii to cell division. Observation of the Y shape in another Spiroplasma, S. citri, and anecdotic observations from the literature suggest that cell division by longitudinal scission might be prevalent in the Spiroplasma clade. Our study is the first to report the Y-shape mode of cell division in an endosymbiotic bacterium and adds Spiroplasma to the so far limited group of bacteria known to utilize this cell division mode. PMID:27460796

  13. Catalytic strategy for carbon-carbon bond scission by the cytochrome P450 OleT.

    PubMed

    Grant, Job L; Mitchell, Megan E; Makris, Thomas Michael

    2016-09-01

    OleT is a cytochrome P450 that catalyzes the hydrogen peroxide-dependent metabolism of Cn chain-length fatty acids to synthesize Cn-1 1-alkenes. The decarboxylation reaction provides a route for the production of drop-in hydrocarbon fuels from a renewable and abundant natural resource. This transformation is highly unusual for a P450, which typically uses an Fe(4+)-oxo intermediate known as compound I for the insertion of oxygen into organic substrates. OleT, previously shown to form compound I, catalyzes a different reaction. A large substrate kinetic isotope effect (≥8) for OleT compound I decay confirms that, like monooxygenation, alkene formation is initiated by substrate C-H bond abstraction. Rather than finalizing the reaction through rapid oxygen rebound, alkene synthesis proceeds through the formation of a reaction cycle intermediate with kinetics, optical properties, and reactivity indicative of an Fe(4+)-OH species, compound II. The direct observation of this intermediate, normally fleeting in hydroxylases, provides a rationale for the carbon-carbon scission reaction catalyzed by OleT. PMID:27555591

  14. Molecular dynamics simulation of C-C bond scission in polyethylene and linear alkanes: effects of the condensed phase.

    PubMed

    Popov, Konstantin V; Knyazev, Vadim D

    2014-03-27

    The reaction of C-C bond scission in polyethylene chains of various lengths was studied using molecular dynamics under the conditions of vacuum and condensed phase (polymer melt). A method of assigning meaningful rate constant values to condensed-phase bond scission reactions based on a kinetic mechanism accounting for dissociation, reverse recombination, and diffusional separation of fragments was developed. The developed method accounts for such condensed-phase phenomena as cage effects and diffusion of the decay products away from the reaction site. The results of C-C scission simulations indicate that per-bond rate constants decrease by an order of magnitude as the density of the system increases from vacuum to the normal density of a polyethylene melt. Additional calculations were performed to study the dependence of the rate constant on the length of the polymer chain under the conditions of the condensed phase. The calculations demonstrate that the rate constant is independent of the degree of polymerization if polyethylene samples of different lengths are kept at the same pressure. However, if instead molecular systems of different polyethylene chain lengths decompose under the conditions of the same density, shorter chains result in higher pressures and lower rate constants. The observed effect is attributed to a higher degree of molecular crowding (lower fraction of free intermolecular space available for molecular motion) in the case of shorter molecules. PMID:24571517

  15. Detecting onset of chain scission and crosslinking of γ-ray irradiated elastomer surfaces using frictional force microscopy

    NASA Astrophysics Data System (ADS)

    Banerjee, S.; Sinha, N. K.; Gayathri, N.; Ponraju, D.; Dash, S.; Tyagi, A. K.; Raj, Baldev

    2007-02-01

    We report here that atomic force microscopy (AFM) in frictional force mode can be used to detect the onset of chain scission and crosslinking in polymeric and macromolecular samples upon irradiation. A systematic investigation to detect chain scission and crosslinking of two elastomers, (1) ethylene-propylene-diene monomer rubber and (2) fluorocarbon rubber, upon γ-ray irradiation has been carried out using frictional force microscopy (FFM). From the AFM results we observed that both the elastomers show a systematic smoothening of its surfaces, as the γ-ray dose rate increases. However, the frictional property studied using FFM of the sample surfaces show an initial increase and then a decrease as a function of dose rate. This behaviour of increase in its frictional property has been attributed to the onset of chain scission, and the subsequent decrease in friction has been attributed to the onset of crosslinking of the polymer chains. The evaluated qualitative and semi-quantitative changes observed in the overall frictional property as a function of the γ-ray dose rate for the two elastomers are presented in this paper.

  16. Decomposition Pathways of Glycerol via C–H, O–H, and C–C Bond Scission on Pt(111): A Density Functional Theory Study

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey P.

    2011-10-13

    Glycerol decomposition on Pt(111) via dehydrogenation or C–C bond scission is examined with periodic density functional theory (DFT) calculations. The thermochemistry of dehydrogenation intermediates is first estimated using an empirical correlation scheme with parameters fit to selected DFT calculations; the resulting estimates for the more stable intermediates are refined with full DFT calculations. Brønsted–Evans–Polanyi (BEP) relationships for dehydrogenation and C–C bond scission reactions are developed and used to estimate the kinetics of elementary dehydrogenation and C–C bond scission steps in the reaction network. The combined thermochemical and kinetic analysis implies that glycerol dehydrogenation products at intermediate levels of dehydrogenation are the most thermochemically stable. Additionally, although C–C bond scission transition state energies are high for glycerol and for intermediates at early stages of dehydrogenation, these energies decrease as the intermediates are successively dehydrogenated, reaching a minimum after the removal of several hydrogen atoms from glycerol. At these levels of dehydrogenation, the C–C scission transition state energies become comparable to those of O–H or C–H scission. These results suggest that C–C bonds are only broken after glycerol has been significantly dehydrogenated and demonstrate that DFT-based analyses, combined with simple correlation schemes, can be effective for elucidating general features of complex biomassic reaction networks.

  17. Decomposition Pathways of Glycerol via C–H, O–H, and C–C Bond Scission on Pt(111): A Density Functional Theory Study

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey

    2011-09-01

    Glycerol decomposition on Pt(111) via dehydrogenation or C–C bond scission is examined with periodic density functional theory (DFT) calculations. The thermochemistry of dehydrogenation intermediates is first estimated using an empirical correlation scheme with parameters fit to selected DFT calculations; the resulting estimates for the more stable intermediates are refined with full DFT calculations. Brønsted–Evans–Polanyi (BEP) relationships for dehydrogenation and C–C bond scission reactions are developed and used to estimate the kinetics of elementary dehydrogenation and C–C bond scission steps in the reaction network. The combined thermochemical and kinetic analysis implies that glycerol dehydrogenation products at intermediate levels of dehydrogenation are the most thermochemically stable. Additionally, although C–C bond scission transition state energies are high for glycerol and for intermediates at early stages of dehydrogenation, these energies decrease as the intermediates are successively dehydrogenated, reaching a minimum after the removal of several hydrogen atoms from glycerol. At these levels of dehydrogenation, the C–C scission transition state energies become comparable to those of O–H or C–H scission. These results suggest that C–C bonds are only broken after glycerol has been significantly dehydrogenated and demonstrate that DFT-based analyses, combined with simple correlation schemes, can be effective for elucidating general features of complex biomassic reaction networks.

  18. Electron Beam Lithographic Evaluation And Chain Scissioning Yields Of Itaconate Resists

    NASA Astrophysics Data System (ADS)

    Namaste, Y. M.; Obendorf, S. K.; Anderson, C. C.; Rodriguez, F.

    1984-05-01

    Previous work has demonstrated that copolymers of itaconic acid with methyl methacrylate, P(ItA-MMA), are promising positive working electron beam resists.1'2 However, synthesis of itaconic acid copolymers with molecular weights greater than 250,000 or itaconic acid contents higher than 50% is difficult, and these copolymers are quite sensitive to process conditions such as prebake temperature and aging times. To overcome these limitations and to develop resist materials with improved sensitivity, alkyl ester derivatives of itaconic acid have been synthesized, both as homopolymers and as copolymers with methyl methacrylate. In the present work, the electron-beam chain scissioning yields, G(s), of these derivatives have been determined, and the most promising of these copolymers and homopolymers have been evaluated as electron beam resists in terms of sensitivity, contrast, resolution, and thermal stability. The G(s) values of the alkyl itaconates depend greatly on the structure of the alkyl group. It was found that mono-alkyl itaconates yield polymers with G(s) values several times greater than the corresponding di-alkyl itaconates. The mono-methyl itaconate (MeI) copolymers with methyl methacrylate are very promising resist materials with high sensitivities. Methyl itaconate was polymerized with methyl methacrylate with compositions ranging from 20 to 85% MeI content and molecular weights well above one million. These copolymers are more sensitive than the itaconic acid copolymers and less dependent on prebake conditions and aging times. Sensitivities are presented for a series of MMA-MeI copolymers as well as for the we.er-soluble MeI homopolymer. Patterns exposed with P(MMA-73 mole % MeI) at 4 pC/cm4 (20 KV) were developed with less than 10% thinning of the unexposed resist and with a contrast (v) of 2. Vertical walls were observed for 1 pm wide lines using P(MMA - 73% MeI) at a dose of about 6 μC/cm2.

  19. Density Functional Theory Study of Selectivity Considerations for C–C Versus C–O Bond Scission in Glycerol Decomposition on Pt(111)

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey

    2012-05-01

    Glycerol decomposition via a combination of dehydrogenation, C–C bond scission, and C–O bond scission reactions is examined on Pt(111) with periodic Density Functional Theory (DFT) calculations. Building upon a previous study focused on C–C bond scission in glycerol, the current work presents a first analysis of the competition between C–O and C–C bond cleavage in this reaction network. The thermochemistry of various species produced from C–O bond breaking in glycerol dehydrogenation intermediates is estimated using an extension of a previously introduced empirical correlation scheme, with parameters fit to DFT calculations. Brønsted–Evans–Polanyi (BEP) relationships are then used to estimate the kinetics of C–O bond breaking. When combined with the previous results, the thermochemical and kinetic analyses imply that, while C–O bond scission may be competitive with C–C bond scission during the early stages of glycerol dehydrogenation, the overall rates are likely to be very low. Later in the dehydrogenation process, where rates will be much higher, transition states for C–C bond scission involving decarbonylation are much lower in energy than are the corresponding transition states for C–O bond breaking, implying that the selectivity for C–C scission will be high for glycerol decomposition on smooth platinum surfaces. Finally, it is anticipated that the correlation schemes described in this work will provide an efficient strategy for estimating thermochemical and kinetic energetics for a variety of elementary bond breaking processes on Pt(111) and may ultimately facilitate computational catalyst design for these and related catalytic processes.

  20. Electron cryotomography of ESCRT assemblies and dividing Sulfolobus cells suggests that spiraling filaments are involved in membrane scission

    PubMed Central

    Dobro, Megan J.; Samson, Rachel Y.; Yu, Zhiheng; McCullough, John; Ding, H. Jane; Chong, Parkson Lee-Gau; Bell, Stephen D.; Jensen, Grant J.

    2013-01-01

    The endosomal-sorting complex required for transport (ESCRT) is evolutionarily conserved from Archaea to eukaryotes. The complex drives membrane scission events in a range of processes, including cytokinesis in Metazoa and some Archaea. CdvA is the protein in Archaea that recruits ESCRT-III to the membrane. Using electron cryotomography (ECT), we find that CdvA polymerizes into helical filaments wrapped around liposomes. ESCRT-III proteins are responsible for the cinching of membranes and have been shown to assemble into helical tubes in vitro, but here we show that they also can form nested tubes and nested cones, which reveal surprisingly numerous and versatile contacts. To observe the ESCRT–CdvA complex in a physiological context, we used ECT to image the archaeon Sulfolobus acidocaldarius and observed a distinct protein belt at the leading edge of constriction furrows in dividing cells. The known dimensions of ESCRT-III proteins constrain their possible orientations within each of these structures and point to the involvement of spiraling filaments in membrane scission. PMID:23761076

  1. Cooperative Recruitment of Dynamin and BIN/Amphiphysin/Rvs (BAR) Domain-containing Proteins Leads to GTP-dependent Membrane Scission*♦

    PubMed Central

    Meinecke, Michael; Boucrot, Emmanuel; Camdere, Gamze; Hon, Wai-Ching; Mittal, Rohit; McMahon, Harvey T.

    2013-01-01

    Dynamin mediates various membrane fission events, including the scission of clathrin-coated vesicles. Here, we provide direct evidence for cooperative membrane recruitment of dynamin with the BIN/amphiphysin/Rvs (BAR) proteins, endophilin and amphiphysin. Surprisingly, endophilin and amphiphysin recruitment to membranes was also dependent on binding to dynamin due to auto-inhibition of BAR-membrane interactions. Consistent with reciprocal recruitment in vitro, dynamin recruitment to the plasma membrane in cells was strongly reduced by concomitant depletion of endophilin and amphiphysin, and conversely, depletion of dynamin dramatically reduced the recruitment of endophilin. In addition, amphiphysin depletion was observed to severely inhibit clathrin-mediated endocytosis. Furthermore, GTP-dependent membrane scission by dynamin was dramatically elevated by BAR domain proteins. Thus, BAR domain proteins and dynamin act in synergy in membrane recruitment and GTP-dependent vesicle scission. PMID:23297414

  2. Fabrication of DNA/RNA Hybrids Through Sequence-Specific Scission of Both Strands by pcPNA-S1 Nuclease Combination.

    PubMed

    Futai, Kazuki; Sumaoka, Jun; Komiyama, Makoto

    2016-05-01

    By combining two strands of pseudo-complementary peptide nucleic acid (pcPNA) with S1 nuclease, a tool for site-selective and dual-strand scission of DNA/RNA hybrids has been developed. Both of the DNA and the RNA strands in the hybrids are hydrolyzed at desired sites to provide unique sticky ends. The scission fragments are directly ligated with other DNA/RNA hybrids by using T4 DNA ligase, resulting in the formation of desired recombinant DNA/RNA hybrids. PMID:27057646

  3. Pre-scission configuration of the tri-nuclear system at spontaneous ternary fission of 252Cf

    NASA Astrophysics Data System (ADS)

    Nasirov, A. K.; Tashkhodjaev, R. B.; von Oertzen, W.

    2016-05-01

    The potential energy surface for the pre-scission configurations of tri-nuclear systems formed in the spontaneous ternary fission of 252Cf is calculated. The fission channel 70Ni + 50Ca + 132Sn is chosen as one of the more probable channels of true ternary fission of 252Cf . A study of the collinear arrangement of the reaction products for true ternary fission is the aim of this work. The results are presented as a function of the relative distance R12 between the centres of mass of 70Ni and 132Sn and the distance from the centre of mass of 50Ca , which is perpendicular to R12. The results show that only for a particular range of the R12 values the collinear tripartion of the fissioning nucleus occurs.

  4. Anisotropic pyrochemical microetching of poly(tetrafluoroethylene) initiated by synchrotron radiation-induced scission of molecule bonds

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Akinobu; Kido, Hideki; Ukita, Yoshiaki; Kishihara, Mitsuyoshi; Utsumi, Yuichi

    2016-02-01

    We developed a process for micromachining polytetrafluoroethylene (PTFE): anisotropic pyrochemical microetching induced by synchrotron X-ray irradiation. X-ray irradiation was performed at room temperature. Upon heating, the irradiated PTFE substrates exhibited high-precision features. Both the X-ray diffraction peak and Raman signal from the irradiated areas of the substrate decreased with increasing irradiation dose. The etching mechanism is speculated as follows: X-ray irradiation caused chain scission, which decreased the number-average degree of polymerization. The melting temperature of irradiated PTFE decreased as the polymer chain length decreased, enabling the treated regions to melt at a lower temperature. The anisotropic pyrochemical etching process enabled the fabrication of PTFE microstructures with higher precision than simultaneously heating and irradiating the sample.

  5. Elementary steps in Fischer-Tropsch synthesis: CO bond scission, CO oxidation and surface carbiding on Co(0001)

    NASA Astrophysics Data System (ADS)

    Weststrate, C. J.; van Helden, P.; van de Loosdrecht, J.; Niemantsverdriet, J. W.

    2016-06-01

    Dissociation of CO on a Co(0001) surface is explored in the context of Fischer-Tropsch synthesis on cobalt catalysts. Experiments show that CO dissociation can occur on defect sites around 330 K, with an estimated barrier between 90 and 104 kJ mol- 1. Despite the ease of CO dissociation on defect sites, extensive carbon deposition onto the cobalt surface up to 0.33 ML requires a combination of high surface temperature and a relatively high CO pressure. Experimental data on the CO oxidation reaction indicate a high reaction barrier for the CO + O reaction, and it is argued that, due to the rather strong Co-O bond, (i) oxygen removal is the rate-limiting step during surface carbidization and (ii) in the context of Fischer-Tropsch synthesis, removal of surface oxygen rather than CO bond scission might be limiting the overall reaction rate.

  6. Controlling Solution Self-assembly and Non-Solvent Induced Microphase Separation of Triblock Terpolymers to Generate Nanofiltration Membranes with Chemically-Tailored Pore Walls

    NASA Astrophysics Data System (ADS)

    Boudouris, Bryan; Mulvenna, Ryan; Weidman, Jacob; Phillip, William

    2014-03-01

    Block polymer-based templates have been utilized in a number of membrane applications; however, there has yet to be a demonstration of a nanoporous block polymer thin film that can achieve high flux and high selectivity simultaneously while also allowing for the facile tuning of the pore wall chemistry. Here, we demonstrate that by synthesizing and controlling the solution self-assembly of a triblock terpolymer, polyisoprene- b-polystyrene- b-poly(N, N-dimethylacrylamide) (PI-PS-PDMA), and precisely inducing non-solvent induced phase separation during the self-assembly process allows for the creation of an asymmetric nanoporous membrane with PDMA-lined pore walls. This PDMA functionality is then converted to any number of side chain functionalities through simple chemistry in the solid state. In this way, we are able to show a highly selectivity membrane that can separate analytes of interest based both on size and chemical composition at a high solution flux. In fact, this high fidelity structure has a very narrow distribution of pore sizes (<10% variation in diameter) over large areas (>500 cm2) . This has allowed for the separation of particles with hydrodynamic radii as low as 0.8 nm, which is the smallest separation achieved using a block polymer-based membrane to date.

  7. Solvent-induced conformational modifications of iturin A: an infrared and circular dichroic study of a L,D-lipopeptide of Bacillus subtilis

    NASA Astrophysics Data System (ADS)

    Besson, F.; Raimbault, C.; Hourdou, M. L.; Buchet, R.

    1996-07-01

    The structure of iturin A, an L,D-lipopeptide of Bacillus subtilis, has been investigated by measuring its infrared spectrum in different solvents. Because the amino acid side chain absorbances could overlap the component bands of the amide I region, the net contribution of peptide bonds are determined by curve fitting analysis of the IR spectra. Our results confirm the presence of β-turns, previously identified by NMR study of iturin in pyridine. The β-turns are identified in different states of iturin (dry or hydrated states) and in organic solvents (trifluoroethanol or chloroform-methanol). However, the number of β-turns cannot be estimated on the basis of FTIR spectra. The solvent-induced spectral changes are interpreted as interactions of carbonyl groups of peptide backbone and of side chains of Asn and Gln with the solvent molecules. These interactions indirectly modify the conformation of iturin, indicating that mobile side chains might have an important role in its conformational stability. The circular dichroism data on far- and near-UV spectra confirm the alteration of iturin conformation induced by trifluoroethanol and water.

  8. A solvent induced crystallisation method to imbue bioactive ingredients of neem oil into the compact structure of poly (ethylene terephthalate) polyester.

    PubMed

    Ali, Wazed; Sultana, Parveen; Joshi, Mangala; Rajendran, Subbiyan

    2016-07-01

    Neem oil, a natural antibacterial agent from neem tree (Azadarichtaindica) has been used to impart antibacterial activity to polyester fabrics. Solvent induced polymer modification method was used and that facilitated the easy entry of neem molecules into the compact structure of polyethylene terephthalate (PET) polyester. The polyester fabric was treated with trichloroacetic acid-methylene chloride (TCAMC) solvent system at room temperature prior to treatment with neem oil. The concentration of TCAMC and the treatment time were optimised. XRD and SEM results showed that the TCAMC treatment causes polymer modification and morphological changes in the PET polyester. Antibacterial activity of TCAMC pre-treated and neem-oil-treated polyester fabric was tested using AATCC qualitative and quantitative methods. Both Gram-positive and Gram-negative organisms were used to determine the antimicrobial activity. It was observed that the treated fabric registers substantial antimicrobial activity against both the Staphylococcus aureus (Gram-positive) and the Escherichia coli (Gram-negative) and the effect increases with the increase in concentration of TCAMC treatment. The antibacterial effect remains substantial even after 25 launderings. A kinetic growth study involving the effect of antibacterial activity at various incubation times was carried out. PMID:27127070

  9. Organic solvent-induced changes in membrane geometry in human SH-SY5Y neuroblastoma cells - a common narcotic effect?

    PubMed

    Meulenberg, Cécil J W; de Groot, Aart; Westerink, Remco H S; Vijverberg, Henk P M

    2016-07-01

    Exposure to organic solvents may cause narcotic effects. At the cellular level, these narcotic effects have been associated with a reduction in neuronal excitability caused by changes in membrane structure and function. In order to critically test whether changes in membrane geometry contribute to these narcotic effects, cultured human SH-SY5Y neuroblastoma cells have been exposed to selected organic solvents. The solvent-induced changes in cell membrane capacitance were investigated using the whole-cell patch clamp technique for real-time capacitance measurements. Exposure of SH-SY5Y cells to the cyclic hydrocarbons m-xylene, toluene, and cyclohexane caused a rapid and reversible increase of membrane capacitance. The aliphatic, nonpolar n-hexane did not cause a detectable change of whole-cell membrane capacitance, whereas the amphiphiles n-hexanol and n-hexylamine caused an increase of membrane capacitance and a concomitant reduction in membrane resistance. Despite a large difference in dielectric properties, the chlorinated hydrocarbons 1,1,2,2-tetrachoroethane and tetrachloroethylene caused a similar magnitude increase in membrane capacitance. The theory on membrane capacitance has been applied to deduce changes in membrane geometry caused by solvent partitioning. Although classical observations have shown that solvents increase the membrane capacitance per unit area of membrane, i.e., increase membrane thickness, the present results demonstrate that solvent partitioning predominantly leads to an increase in membrane surface area and to a lesser degree to an increase in membrane thickness. Moreover, the present results indicate that the physicochemical properties of each solvent are important determinants for its specific effects on membrane geometry. This implies that the hypothesis that solvent partitioning is associated with a common perturbation of membrane structure needs to be revisited and cannot account for the commonly observed narcotic effects of

  10. Self-assembly polymorphism of 2,7-bis-nonyloxy-9-fluorenone: solvent induced the diversity of intermolecular dipole-dipole interactions.

    PubMed

    Cui, Lihua; Miao, Xinrui; Xu, Li; Hu, Yi; Deng, Wenli

    2015-02-01

    dipole-dipole and van der Waals (vdWs) forces at l/s interface. It is believed that the results are of significance to the fields of solvent induced polymorphism assembly and surface science. PMID:25554245

  11. Coal liquefaction model studies: free radical chain decomposition of diphenylpropane, dibenzyl ether, and phenyl ether via. beta. -scission reactions

    SciTech Connect

    Gilbert, K.E.; Gajewski, J.J.

    1982-01-01

    The thermal decompositions of 1,3-diphenylpropane (1), dibenzyl ether (2), and phenethyl phenyl ether (3) have been found to proceed by free radical chain processes. 1 gave toluene and styrene with a reaction order of 1.55, E/sub A/ = 51.4 kcal/mol, and log A = 12.5. The reaction could be initiated by benzyl phenyl ether but not by 1,2-diphenylethane. 2 gave toluene and benzaldehyde with a reaction order of 1.43, E/sub A/ = 48 kcal/mol, and log A = 12.6. The reaction could be initiated with benzyl phenyl ether. 3 gave phenol and styrene with a reaction order of 1.21, E/sub A/ = 50.3 kcal/mol, and log A = 12.3. The reaction could be initiated by benzyl phenyl ether. All of the data are consistent with free radical chain processes with the reaction order determined by the termination reaction. No evidence for concerted reactions has been found. The thermal chemistry of three-atom links is best described by free radical chain processes. The products are consistent with a free radical chain process involving a ..beta..-scission reaction, and the reaction orders range between first and three-halves order depending upon the nature of the chain termination reaction. Activation parameters are readily estimated from thermochemical kinetic data on the individual reactions with log A approx. = 12 and E/sub A/approx. = 50 kcal/mol. Unlike the one- and two-atom linkages, reactions of the three-atom linkages are promoted by free radical initiators. The potential for inhibition of free radical chains also exists and is currently being studied. 4 tables.

  12. Synthesis, Characterization, and Stoichiometric U-O Bond Scission in Uranyl Species Supported by Pyridine(diimine) Ligand Radicals.

    PubMed

    Kiernicki, John J; Cladis, Dennis P; Fanwick, Phillip E; Zeller, Matthias; Bart, Suzanne C

    2015-09-01

    Two uranium(VI) uranyl compounds, Cp*UO2((Mes)PDI(Me)) (3) and Cp*UO2((t)Bu-(Mes)PDI(Me)) (3-(t)Bu) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienide; (Mes)PDI(Me) = 2,6-((Mes)N=CMe)2C5H3N; (t)Bu-(Mes)PDI(Me) = 2,6-((Mes)N=CMe)2-p-C(CH3)3C5H2N; Mes = 2,4,6-trimethylphenyl), have been synthesized by addition of N-methylmorpholine N-oxide to trianionic pyridine(diimine) uranium(IV) precursors, Cp*U((Mes)PDI(Me))(THF) (1), Cp*U((Mes)PDI(Me))(HMPA) (1-HMPA), and Cp*U((t)Bu-(Mes)PDI(Me))(THF) (1-(t)Bu). These uranyl complexes contain singly reduced pyridine(diimine) ligands suggesting formation occurs via cooperative ligand/metal oxidation. Treating 3 or 3-(t)Bu with stoichiometric equivalents of Me3SiI results in stepwise oxo silylation to form (Me3SiO)2UI2((Mes)PDI(Me)) (5) or (Me3SiO)UI2((t)Bu-(Mes)PDI(Me)) (5-(t)Bu), respectively. Additional equivalents result in full uranium-oxo bond scission and formation of UI4(1,4-dioxane)2 with extrusion of hexamethyldisiloxane. The uranium complexes have been characterized via multinuclear NMR, vibrational, and electronic absorption spectroscopies and, in some cases, X-ray crystallography. PMID:26299269

  13. A toxicological study of inhalable particulates in an industrial region of Lanzhou City, northwestern China: Results from plasmid scission assay

    NASA Astrophysics Data System (ADS)

    Xiao, Zhenghui; Shao, Longyi; Zhang, Ning; Wang, Jing; Chuang, Hsiao-Chi; Deng, Zhenzhen; Wang, Zhen; BéruBé, Kelly

    2014-09-01

    The city of Lanzhou in northwestern China experiences serious air pollution episodes in the form of PM10 that is characterized by having high levels of heavy metals. The Xigu District represents the industrial core area of Lanzhou City and is denoted by having the largest petrochemical bases in western China. This study investigates heavy metal compositions and oxidative potential of airborne PM10 (particulate matter with aerodynamic diameter of 10 μm or less) collected in Xigu District in the summer and winter of 2010. An in vitro plasmid scission assay (PSA) was employed to study the oxidative potential of airborne PM10 and inductively coupled plasma-mass spectrometry (ICP-MS) was used to examine heavy metal compositions. Transmission electron microscopy coupled with energy-dispersive X-ray spectrometry (TEM/EDX) was used to investigate elemental compositions and mixing states of PM10. The average mass concentrations of PM10 collected in Xigu District were generally higher than the national standard for daily PM10 (150 μg/m3). Cr, Zn, Pb and Mn were the most abundant metals in the intact whole particles of PM10. Zn, Mn and As was the most abundant metal in the water-soluble fraction, while Cr, Pb, and V existed primarily in insoluble forms. TD20 values (i.e. toxic dosage of PM10 causing 20% of plasmid DNA damage) varied considerably in both winter and summer (from 19 μg/mL to >1000 μg/mL) but were typically higher in summer, suggesting that the winter PM10 exhibited greater bioreactivity. In addition, the PM10 collected during a dust storm episode had a highest TD20 value and thus the least oxidative damage to supercoiled plasmid DNA, while the particles collected on a hazy day had a lowest TD20 value and thus the highest oxidative damage to supercoiled plasmid DNA. The particles collected on the first day after snow fall and on a day of cold air intrusion exhibited minor oxidative potential (i.e. caused limited DNA damage). The water-soluble Zn, Mn, As, and

  14. Partition between the fission fragments of the excitation energy and of the neutron multiplicity at scission in low-energy fission

    NASA Astrophysics Data System (ADS)

    Carjan, N.; Hambsch, F.-J.; Rizea, M.; Serot, O.

    2012-04-01

    The partition between the light (L) and the heavy (H) fission fragments of the excitation energy available at scission is studied in the framework of the sudden approximation, i.e., under the assumption that the neck rupture and the absorption of the neck pieces by the fragments happen infinitely fast. We are dealing with a sudden transition between two different nuclear configurations (αi→αf) and we only need to know the two sets of neutron eigenstates involved. The accent in the present work is put on the dependence of this share of energy on the mass asymmetry AL/AH of the primary fission fragments during the low-energy fission of 236U. In particular, for every fragment mass A we estimate the scission neutron multiplicity νsc, the average energy cost for their release , the primary fragments' excitation energy Esc*, and the corresponding temperature Tsc. The results are analyzed separately for each value of Ω (the projection of the angular momentum on the symmetry axis). As general trends, a decrease of Esc* (Tsc) and an increase of νsc () with increasing A were observed.

  15. Effect of the energy spectrum and angular momentum of pre-scission neutrons on the prediction of fission fragment angular anisotropy by the models

    NASA Astrophysics Data System (ADS)

    Soheyli, Saeed; Khanlari, Marzieh Varasteh

    2016-04-01

    Effects of the various neutron emission energy spectra, as well as the influence of the angular momentum of pre-scission neutrons on theoretical predictions of fission fragment angular anisotropies for several heavy-ion induced fission systems are considered. Although theoretical calculations of angular anisotropy are very sensitive to neutron emission correction, the effects of the different values of kinetic energy of emitted neutrons derived from the various neutron emission energy spectra before reaching to the saddle point on the prediction of fission fragment angular distribution by the model are not significant and can be neglected, since these effects on angular anisotropies of fission fragments for a wide range of fissility parameters and excitation energies of compound nuclei are not more than 10%. Furthermore, the theoretical prediction of fission fragment angular anisotropy is not sensitive to the angular momentum of emitted neutrons.

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

    PubMed

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

    2016-07-15

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

  17. Solvent-induced syntheses, crystal structures, magnetic properties, and single-crystal-to-single-crystal transformation of azido-Cu(II) coordination polymers with 2-naphthoic acid as co-ligand.

    PubMed

    Liu, Xiangyu; Cen, Peipei; Li, Hui; Ke, Hongshan; Zhang, Sheng; Wei, Qing; Xie, Gang; Chen, Sanping; Gao, Shengli

    2014-08-01

    Based on the solvent-induced effect, three new azido-copper coordination polymers--[Cu(2-na)(N3)] (1), [Cu(2-na)(N3)] (2), and [Cu(2-na)(N3)(C2H5OH)] (3) (where 2-na = 2-naphthoic acid)--have been successfully prepared. Structure analysis shows that the Cu(II) cations in compounds 1-3 present tetra-, penta-, and hexa-coordination geometries, respectively. Compound 1 is a well-isolated one-dimensional (1D) chain with the EO-azido group, while 2 is an isomer of 1 and exhibits a two-dimensional (2D) layer involving the EE-azido group. Thermodynamically, density functional theory (DFT) calculation reveals that 2 occupies the stable state and 1 locates in the metastable state. Compound 3 consists of a 1D chain with triple bridging mode, which is derived from 1, and undergoes a single-crystal-to-single-crystal transformation by soaking in ethanol solvent; the powdery product of 1, namely 1b, could be yielded after the dealcoholization of compound 3. Magnetic measurements indicate that compounds 1-3 perform strong intrachain ferromagnetic interactions, experiencing long-range magnetic ordering and slow magnetic relaxation. Compound 1 features the metamagnetic behavior with a transition temperature of 15 K, while 2 and 3 display spin glass behavior with the phase transition temperatures of 15 and 12 K, respectively. Magneto-structure relationships are investigated as well. PMID:25014208

  18. Differentiation of O-H and C-H Bond Scission Mechanisms of Ethylene Glycol on Pt and Ni/Pt Using Theory and Isotopic Labeling Experiments

    SciTech Connect

    Salciccioli, Michael; Yu, Weiting; Barteau, Mark A.; Chen, Jingguang G.; Vlachos, Dionisios G.

    2011-05-25

    Understanding and controlling bond-breaking sequences of oxygenates on transition metal catalysts can greatly impact the utilization of biomass feedstocks for fuels and chemicals. The decomposition of ethylene glycol, as the simplest representative of biomass-derived polyols, was studied via density functional theory (DFT) calculations to identify the differences in reaction pathways between Pt and the more active Ni/Pt bimetallic catalyst. Comparison of the computed transition states indicated three potentially feasible paths from ethylene glycol to C1 oxygenated adsorbates on Pt. While not important on Pt, the pathway to 1,2-dioxyethylene (OCH₂CH₂O) is favored energetically on the Ni/Pt catalyst. Temperature-programmed desorption (TPD) experiments were conducted with deuterated ethylene glycols for comparison with DFT results. These experiments confirmed that decomposition of ethylene glycol on Pt proceeds via initial O–H bond cleavage, followed by C–H and the second O–H bond cleavages, whereas on the Ni/Pt surface, both O–H bonds are cleaved initially. The results are consistent with vibrational spectra and indicate that tuning of the catalyst surface can selectively control bond breaking. Finally, the significant mechanistic differences in decomposition of polyols compared to that of monoalcohols and hydrocarbons serve to identify general trends in bond scission sequences.

  19. Solvent induced track sensitization. Extraction of oligomers

    NASA Astrophysics Data System (ADS)

    Apel, P.; Angert, N.; Brüchle, W.; Hermann, H.; Kampschulte, U.; Klein, P.; Kravets, L. I.; Oganessian, Yu. Ts.; Remmert, G.; Spohr, R.; Steckenreiter, T.; Trautmann, C.; Vetter, J.

    1994-04-01

    Oligomer extraction from polyethylene terephthalate (PET) irradiated by xenon ions of 11.4 MeV/u is investigated using UV spectrophotometry and gel permeation chromatography (GPC). The cyclic trimer is identified as the predominant diffusing species removed during extraction by dimethyl formamide (DMF). Extraction dynamics is modeled by a rapid (time constant ≈ 2 min) and a slow (time constant ≈ 100 min) diffusion process attributed to the latent ion tracks and to the virgin material, respectively. Thereby latent tracks act simultaneously as irrigation and drainage pipes for the transfer of the solvent into and the extraction of oligomers from the polymer matrix. Thus tracks help to release osmotic pressure differences and to avoid blistering of the unirradiated polymer during solvent exchange. The total extracted mass per track shows a characteristic decrease with increasing ion fluence interpreted as oxygen effect, due to the decreasing supply of oxygen in the sample during irradiation. The extractable mass corresponds to an equivalent track diameter of initially around 10 nm contracting with increasing ion fluence to an asymptotic value around 3 nm.

  20. Solvent-induced autolysis of cells

    SciTech Connect

    Hopkins, T.R.

    1989-01-03

    A process is described for the recovery of alcohol oxidase from whole cells of Pichia pastoris grown on methanol which comprises (a) forming an aqueous mixture of the whole cells, wherein the cells are present in an amount of from 85 to 150 grams per liter of aqueous mixture and from 0.8 to 6 volume percent of a treating agent selected from the group consisting of chloroform, 1,1,1-trichloroethane and methylene chloride or mixtures thereof, and wherein, the aqueous mixture has a pH of about 6.5 to about 8.5; (b) incubating the aqueous mixture at a temperature of about 20/sup 0/ to 35/sup 0/C for a time of about 16 to 90 hours whereby at least a portion of the alcohol oxidase is released from the cells thereby forming a alcohol oxidase-containing aqueous liquor; and (c) separating alcohol oxidase-containing liquor liquid from solid cell material.

  1. Solvent induced conformer specific photochemistry of guaiacol.

    PubMed

    Greenough, Simon E; Horbury, Michael D; Thompson, James O F; Roberts, Gareth M; Karsili, Tolga N V; Marchetti, Barbara; Townsend, Dave; Stavros, Vasilios G

    2014-08-14

    Using a combination of ultrafast solution- and gas-phase spectroscopies, together with high-level theory calculations, we demonstrate that we are able to track conformer-specific photodissociation dynamics in solution through solvent choice. We reveal this phenomenon in guaiacol (2-methoxyphenol), a key subunit of the natural biopolymer lignin. In cyclohexane, the first electronically excited (1)ππ* (S1) state in guaiacol relaxes with a time-constant of τ = 4.5 ± 0.2 ns, mediated through intersystem crossing to lower lying triplet (Tn) states and internal conversion and fluorescence back to the ground state (S0). In contrast, in methanol, a further relaxation channel is also present; the S1 state relaxes with a time-constant of τ = 2.9 ± 0.1 ns, which is now additionally mediated through coupling onto a dissociative (1)πσ* (S2) state and subsequent O-H bond fission, evidenced through the appearance of a spectral signature for the guaiacoxyl radical after ∼250 ps. With the aid of complementary calculations, we attribute this to the now absent intramolecular H-bond between OH and OMe moieties, which now favours intermolecular H-bonding to methanol, lowering the barrier to O-H dissociation and facilitating H-atom loss via tunnelling. PMID:24967653

  2. A Green Solvent Induced DNA Package

    NASA Astrophysics Data System (ADS)

    Satpathi, Sagar; Sengupta, Abhigyan; Hridya, V. M.; Gavvala, Krishna; Koninti, Raj Kumar; Roy, Bibhisan; Hazra, Partha

    2015-03-01

    Mechanistic details of DNA compaction is essential blue print for gene regulation in living organisms. Many in vitro studies have been implemented using several compaction agents. However, these compacting agents may have some kinds of cytotoxic effects to the cells. To minimize this aspect, several research works had been performed, but people have never focused green solvent, i.e. room temperature ionic liquid as DNA compaction agent. To the best of our knowledge, this is the first ever report where we have shown that guanidinium tris(pentafluoroethyl)trifluorophosphate (Gua-IL) acts as a DNA compacting agent. The compaction ability of Gua-IL has been verified by different spectroscopic techniques, like steady state emission, circular dichroism, dynamic light scattering and UV melting. Notably, we have extensively probed this compaction by Gua-IL through field emission scanning electron microscopy (FE-SEM) and fluorescence microscopy images. We also have discussed the plausible compaction mechanism process of DNA by Gua-IL. Our results suggest that Gua-IL forms a micellar kind of self aggregation above a certain concentration (>=1 mM), which instigates this compaction process. This study divulges the specific details of DNA compaction mechanism by a new class of compaction agent, which is highly biodegradable and eco friendly in nature.

  3. Nonuniform character of the population of spin projections K for a fissile nucleus at the scission point and anisotropies in the angular distributions of fragments originating from the induced fission of nuclei

    SciTech Connect

    Kadmensky, S. G.; Bunakov, V. E.; Kadmensky, S. S.

    2012-11-15

    It is shown that the emergence of anisotropies in the angular distributions of fragments originating from the spontaneous and induced fission of oriented actinide nuclei is possible only if nonuniformities in the population of the projectionsM (K) of the fissile-nucleus spin onto the z axis of the laboratory frame (fissile-nucleus symmetry axis) appear simultaneously in the vicinity of the scission point but not in the vicinity of the outer saddle point of the deformation potential. The possibilities for creating the orientation of fissile nuclei for spontaneous and induced fission and the effect of these orientations on the anisotropies under analysis are considered. The role of Coriolis interaction as a unique source of the mixing of different-K fissile-nucleus states at all stages of the fission process is studied with allowance for the dynamical enhancement of this interaction for excited thermalized states of the nucleus involved that is characterized by a high energy density. It is shown that the absence of thermalization of excited states of the fissile nucleus that appear because of the effect of nonadiabaticity of its collective deformation motion in the vicinity of the scission point is a condition of conservation of the influence that transition fission states formed at the inner and outer fission barriers exerts on the distribution of the spin projections K for lowenergy spontaneous nuclear fission. It is confirmed that anisotropies observed in the angular distributions of fragments originating from the fission of nuclei that is induced by fast light particles (multiply charged ions) are due to the appearance of strongly excited equilibrium(nonequilibrium) states of the fissile nucleus in the vicinity of its scission point that have a Gibbs (non-Gibbs) distribution of projections K.

  4. Simultaneous quantification of ten constituents of Xanthoceras sorbifolia Bunge using UHPLC-MS methods and evaluation of their radical scavenging, DNA scission protective, and α-glucosidase inhibitory activities.

    PubMed

    Zhang, Yu; Ma, Jian-Nan; Ma, Chun-Li; Qi, Zhi; Ma, Chao-Mei

    2015-11-01

    The present study was designed to investigate the bioactive constituents of Xanthoceras sorbifolia in terms of amounts and their antioxidant, DNA scission protection, and α-glucosidase inhibitory activities. Simultaneous quantification of 10 X. sorbifolia constituents was carried out by a newly established ultra-high performance liquid chromatography-quadrupole mass spectrometry method (UHPLC-MS). The antioxidant activities were evaluated by measuring DPPH radical scavenging and DNA scission protective activities. The α-glucosidase inhibitory activities were investigated by using an assay with α-glucosidase from Bacillus Stearothermophilus and disaccharidases from mouse intestine. We found that the wood of X. sorbifolia was rich in phenolic compounds with the contents of catechin, epicatechin, myricetin, and dihydromyricetin being 0.12-0.19, 1.94-2.16, 0.77-0.91, and 6.76-7.89 mg·g(-1), respectively. The four constituents strongly scavenged DPPH radicals (with EC50 being 4.2, 3.8 and 5.7 μg·mL(-1), respectively) and remarkably protected peroxyl radical-induced DNA strand scission (92.10%, 94.66%, 75.44% and 89.95% of protection, respectively, at a concentration of 10 μmol·L(-1)). A dimeric flavan 3-ol, epigallocatechin-(4β→8, 2β→O-7)-epicatechin potently inhibited α-glucosidase with an IC50 value being as low as 1.2 μg·mL(-1). The established UHPLC-MS method could serve as a quality control tool for X. sorbifolia. In conclusion, the high contents of antioxidant and α-glucosidase inhibitory constituents in X. sorbifolia support its use as complementation of other therapeutic agents for metabolic disorders, such as diabetes and hypertension. PMID:26614463

  5. Hydroliquefaction of coal with supported catalysts: 1980 status review

    SciTech Connect

    Polinski, Leon M.; Stiegel, Gary J.; Tischer, Richard E.

    1981-06-01

    The objectives of the program have been to determine catalyst deactivation kinetic models and catalyst deactivation modes for supported Co-Mo and Ni-Mo catalysts used primarily in coal liquefaction via the H-COAL process. Emphasis has been on developing methods to increase catalyst usage by determining how to decrease catalyst replacement rates in the process and how to decrease catalyst poisoning. An important conclusion reached via model analysis and verified by experiment is that larger diameter (1/16 in.) catalysts resist poisoning deactivation much more than smaller (1/32 in.) catalysts over extended periods (60 to 110 hours) of time. If this trend can be verified, it gives a powerful tool for reducing catalyst replacement rate in the H-COAL ebullated bed system by factors of 2 or more. A second conclusion is that poisoning of catalysts occurs by several possible mechanisms or modes. Indirect or direct evidence of all these modes can be presented, though the relative importance of each mechanism has not been established. The modes include (a) poisoning by coking - with gradual increase in C/H ratio (more refractory coke) with time, (b) poisoning by metallization (selective/non-selective adsorption of inorganics such as Ti and Fe on the catalyst), (c) sintering - increase in larger pores/decrease in surface area, and (d) parallel poisoning by irreversible nitrogen compound adsorption.

  6. CONVERSION OF SEWAGE SLUDGE TO OIL BY HYDROLIQUEFACTION

    EPA Science Inventory

    A study was undertaken to determine the feasibility of converting municipal wastewater sludges into oil under hydrogen pressure. In a laboratory autoclave, raw and digested sludges were subjected to 14 MPa total pressure for 20 to 90 minutes. Aqueous suspensions were treated at a...

  7. Background Noise Contributes to Organic Solvent Induced Brain Dysfunction.

    PubMed

    Guthrie, O'neil W; Wong, Brian A; McInturf, Shawn M; Reboulet, James E; Ortiz, Pedro A; Mattie, David R

    2016-01-01

    Occupational exposure to complex blends of organic solvents is believed to alter brain functions among workers. However, work environments that contain organic solvents are also polluted with background noise which raises the issue of whether or not the noise contributed to brain alterations. The purpose of the current study was to determine whether or not repeated exposure to low intensity noise with and without exposure to a complex blend of organic solvents would alter brain activity. Female Fischer344 rats served as subjects in these experiments. Asynchronous volume conductance between the midbrain and cortex was evaluated with a slow vertex recording technique. Subtoxic solvent exposure, by itself, had no statistically significant effects. However, background noise significantly suppressed brain activity and this suppression was exacerbated with solvent exposure. Furthermore, combined exposure produced significantly slow neurotransmission. These abnormal neurophysiologic findings occurred in the absence of hearing loss and detectable damage to sensory cells. The observations from the current experiment raise concern for all occupations where workers are repeatedly exposed to background noise or noise combined with organic solvents. Noise levels and solvent concentrations that are currently considered safe may not actually be safe and existing safety regulations have failed to recognize the neurotoxic potential of combined exposures. PMID:26885406

  8. Background Noise Contributes to Organic Solvent Induced Brain Dysfunction

    PubMed Central

    Guthrie, O'neil W.; Wong, Brian A.; McInturf, Shawn M.; Reboulet, James E.; Ortiz, Pedro A.; Mattie, David R.

    2016-01-01

    Occupational exposure to complex blends of organic solvents is believed to alter brain functions among workers. However, work environments that contain organic solvents are also polluted with background noise which raises the issue of whether or not the noise contributed to brain alterations. The purpose of the current study was to determine whether or not repeated exposure to low intensity noise with and without exposure to a complex blend of organic solvents would alter brain activity. Female Fischer344 rats served as subjects in these experiments. Asynchronous volume conductance between the midbrain and cortex was evaluated with a slow vertex recording technique. Subtoxic solvent exposure, by itself, had no statistically significant effects. However, background noise significantly suppressed brain activity and this suppression was exacerbated with solvent exposure. Furthermore, combined exposure produced significantly slow neurotransmission. These abnormal neurophysiologic findings occurred in the absence of hearing loss and detectable damage to sensory cells. The observations from the current experiment raise concern for all occupations where workers are repeatedly exposed to background noise or noise combined with organic solvents. Noise levels and solvent concentrations that are currently considered safe may not actually be safe and existing safety regulations have failed to recognize the neurotoxic potential of combined exposures. PMID:26885406

  9. Effect of catalysts and solvents on the direct hydroliquefaction of Turkish lignites

    SciTech Connect

    Oner, M.; Bolat, E.; Dincer, S. )

    1990-01-01

    This paper reports the effectiveness of solvents on the liquefaction of 11 different Turkish lignites investigated by using tetralin, creosote, and anthracene oils. The highest total conversions were obtained with tetralin. The catalytic effects of CoMo and red mud were compared by using creosote oil as the solvent. It was found that red mud catalyzed mainly the asphaltene formation reaction for the given experimental conditions. The additional of CoMo significantly catalyzed the liquefaction reaction, thus increasing the lignite conversion and oil formation.

  10. Direct hydro-liquefaction of sawdust in petroleum ether and comprehensive bio-oil products analysis.

    PubMed

    Liu, Dong; Song, Linhua; Wu, Pingping; Liu, Yan; Li, Qingyin; Yan, Zifeng

    2014-03-01

    The effect of temperature, time, hydrogen pressure and amount of catalyst on production distribution and the bio-oil yield obtained from the direct liquefaction of sawdust in the petroleum ether (60-90°C) are investigated. The highest sawdust conversion obtained was 72.32% with a bio-oil yield of 47.69% were obtained at 370°C, 40min and 5wt.% catalyst content with the initial H2 pressure of 3.0MPa. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) approach was utilized to analyze the non-volatile fraction. In this study, the composition of bio-oil could be analyzed in an unprecedented detail through a combination of GC-MS and FT-ICR MS techniques. PMID:24445192

  11. Effects of the components of coal hydro-liquefaction residue on its rheological characteristics

    SciTech Connect

    Ren, Y.; Jin, S.; Xu, Y.; Wei, A.; Zhang, D.; Gao, J.

    2009-07-01

    Four kinds of typical coal liquefaction residue samples, coming from Shenhua coal liquefaction pilot plant, were used to investigate the effects of components of residue, separation time, and temperature on its rheological characteristics. Coal liquefaction residue is a non-Newtonian pseudoplastic fluid whose apparent viscosity decreases with increasing shear rate. Moreover, the residue has high viscosity at the initial softening temperature, and its viscosity drops greatly with increasing temperature. The oil content in residue has a great effect on the decline of the apparent viscosity of residue. The asphaltene can increase the apparent viscosity at lower temperatures but decrease it at higher temperatures. However, the solid only increases the apparent viscosity as it can be neither softened nor dissolved to become fluid. After simulating the separation condition, it is found that prolonging the separation time and enhancing the separation temperature will increase the apparent viscosity of residue, which is bad for preventing pipes from being blocked. So choosing the right separation time and separation temperature is necessary to actual industrial production.

  12. Mechanochemical Reactions Reporting and Repairing Bond Scission in Polymers.

    PubMed

    Clough, Jess M; Balan, Abidin; Sijbesma, Rint P

    2015-01-01

    The past 10 years have seen a resurgence of interest in the field of polymer mechanochemistry. Whilst the destructive effects of mechanical force on polymer chains have been known for decades, it was only recently that researchers tapped into these forces to realize more useful chemical transformations. The current review discusses the strategic incorporation of weak covalent bonds in polymers to create materials with stress-sensing and damage-repairing properties. Firstly, the development of mechanochromism and mechanoluminescence as stress reporters is considered. The second half focuses on the net formation of covalent bonds as a response to mechanical force, via mechanocatalysis and mechanically unmasked chemical reactivity, and concludes with perspectives for the field. PMID:26104999

  13. Entropy-Driven Selectivity for Chain Scission: Where Macromolecules Cleave.

    PubMed

    Pahnke, Kai; Brandt, Josef; Gryn'ova, Ganna; Lin, Ching Y; Altintas, Ozcan; Schmidt, Friedrich G; Lederer, Albena; Coote, Michelle L; Barner-Kowollik, Christopher

    2016-01-22

    We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high-temperature (HT) NMR spectroscopy of self-assembled supramolecular diblock systems as well as temperature-dependent size-exclusion chromatography (TD SEC) of covalently bonded Diels-Alder step-growth polymers. PMID:26663567

  14. New resist materials based on polyacetal main chain scission

    NASA Astrophysics Data System (ADS)

    Manouras, Theodoros; Olziersky, Antonis; Argitis, Panagiotis

    2016-03-01

    The main target of the current work was to develop new polymeric materials for lithographic applications, the main chain of which is cleaved under the influence of photogenerated acid. Acetals have been chosen as functional groups in the main polymer chain since they can be cleaved in the presence of an acid while they remain untouched in alkaline ambient. The synthesized polymers were designed to bear in addition suitable functional groups for the achievement of desirable lithographic characteristics (thermal stability, acceptable glass transition temperature, etch resistance, proper dissolution behaviour). The synthesis was carried out via polyaddition of a vinyloxyl compound and a diol compound to produce novel polymers with acetal repeating units in their backbone. We chose polyaromatic hydrocarbons as diol units to achieve increased etch resistance. In addition, the polyaromatic units allow exposure at 193 nm as well, where the absorption of simple aromatics is prohibitively high. Good solubility and increased surface adhesion were achieved by choosing cycloaliphatic vinyloxyl ethers as the second component for the polyaddition. In addition, the same route can be followed to incorporate chromophores that can tune the resist absorbance in different spectral regions. Furthermore, single component systems can be designed following this approach by the incorporation of suitable PAGs in the main chain.

  15. DNA strand scission by the novel antitumor antibiotic leinamycin

    SciTech Connect

    Hara, Mitsunobu; Saitoh, Yutaka; Nakano, Hirofumi )

    1990-06-19

    Leinamycin is a recently discovered antitumor antibiotic with an unusual 1,3-dioxo-1,2-dithiolane structure. It preferentially inhibits the incorporation of ({sup 3}H)thymidine into the acid-insoluble fraction of Bacillus subtilis. In vitro, leinamycin causes single-strand cleavage of supercoiled double-helical pBR322 DNA in the presence of thiol cofactors. Scavengers of oxygen radical did not suppress the DNA-cleaving activity. Thiol-activated leinamycin binds calf thymus DNA at 4{degree}C and thermal treatment of the leinamycin-DNA adduct released a chemically modified leinamycin from the complex. The lack of cytotoxicity and DNA-cleaving activity for S-deoxyleinamycin indicates that the 1,3-dioxo-1,2-dithiolane moiety is essential for the activity of leinamycin. Thus, the primary cellular target of leinamycin appears to be DNA. It binds DNA and causes single-strand break at low concentrations, which may account for the potent antitumor activity.

  16. A Sixth-order Image Approximation to the Ionic Solvent Induced Reaction Field.

    PubMed

    Xiang, Ming; Deng, Shaozhong; Cai, Wei

    2009-12-01

    A recent article by Deng and Cai introduced fourth-order image approximations to the reaction field for a charge inside a dielectric sphere immersed in a solvent of low ionic strength. To represent such a reaction field, the image approximations employ a point charge at the classical Kelvin image point and two line charges that extend from the Kelvin image point along the radial direction to infinity. In this paper, a sixth-order image approximation is developed, using the same point charge with three different line charges. Procedures on how to discretize the line charges by point image charges and how to implement the resulting point image approximation in O(N) complexity for potential and force field calculations are included. Numerical results demonstrate the sixth-order convergence rate of the image approximation and the O(N) complexity of the fast implementation of the point image approximation. PMID:21152236

  17. Solvent-induced conformational changes in cyclic peptides: a vibrational circular dichroism study.

    PubMed

    Merten, Christian; Li, Fee; Bravo-Rodriguez, Kenny; Sanchez-Garcia, Elsa; Xu, Yunjie; Sander, Wolfram

    2014-03-28

    The three-dimensional structure of a peptide is strongly influenced by its solvent environment. In the present study, we study three cyclic tetrapeptides which serve as model peptides for β-turns. They are of the general structure cyclo(Boc-Cys-Pro-X-Cys-OMe) with the amino acid X being either glycine (1), or L- or D-leucine (L- or D-2). Using vibrational circular dichroism (VCD) spectroscopy, we confirm previous NMR results which showed that D-2 adopts predominantly a βII turn structure in apolar and polar solvents. Our results for L-2 indicate a preference for a βI structure over βII. With increasing solvent polarity, the preference for 1 is shifted from βII towards βI. This conformational change goes along with the breaking of an intramolecular hydrogen bond which stabilizes the βII conformation. Instead, a hydrogen bond with a solvent molecule can stabilize the βI turn conformation. PMID:24513908

  18. Solvent induced helical aggregation in the self-assembly of cholesterol tailed platinum complexes.

    PubMed

    Mao, Yueyuan; Liu, Keyin; Meng, Luyan; Chen, Liang; Chen, Liming; Yi, Tao

    2014-10-14

    Three alkynylplatinum(ii) bipyridyl complexes in which two cholesterol groups are combined with a bipyridyl group via alkyl chains and amido bonds were designed and synthesized. The complexes have different lengths of ethylene glycol chains at the para-position of 1-phenylethyne. All three complexes can self-assemble to gel networks in DMSO, while only the morphology of 1a without an ether chain shows a well-defined right-handed helical structure in layer packing mode. However, 1c with long ethylene glycol chains forms perfect regular left-handed helical structures in aqueous ethanol solution while the volume percentage of water is less than 5% (v/v). As the ratio of water increases, the chirality changes from a left-handed helix to a right-handed helix and the packing mode alters from a monolayer structure to a hexagonal structure. As the ratio of water further increases to greater than 50% (v/v), the structure of the assembly finally transforms into bilayer vesicles. The process of the morphology transition is traced by circular dichroism spectra, powder X-ray diffraction, SEM and TEM images. The result indicates that a polar solvent (water) acts as a trigger to change the self-assembly of the chiral structures of the complex due to the strong hydrophobic interaction between cholesterol groups and the balance of the hydrophobicity and hydrophilicity of the solvent environment. PMID:25131259

  19. Computing solvent-induced forces in the solvation approach called Semi Explicit Assembly

    NASA Astrophysics Data System (ADS)

    Brini, Emiliano; Hummel, Michelle H.; Coutsias, Evangelos A.; Fennell, Christopher J.; Dill, Ken A.

    2014-03-01

    Many biologically relevant processes (e.g. protein folding) are often too big and slow to be simulated by computer methods that model atomically detailed water. Faster physical models of water are needed. We have developed an approach called Semi Explicit Assembly (SEA) [C.J. Fennell, C.W. Kehoe, K.A. Dill, PNAS, 108, 3234 (2011)]. It is physical because it uses pre-simulations of explicit-solvent models, and it is fast because at runtime, we just combine the pre-simulated results in rapid computations. SEA has also now been proven physically accurate in two blind tests called SAMPL. Here, we describe the computation of solvation forces in SEA, so that this solvation procedure can be incorporated into standard molecular dynamics codes. We describe experimental tests.

  20. Solvent-induced size reduction of self-assembled siRNA/copolymer nanoparticles

    NASA Astrophysics Data System (ADS)

    Qu, Wei; Wu, Juan; Mao, Hai-Quan; Luijten, Erik

    2013-03-01

    Small interfering RNA (siRNA) therapeutics has a demonstrated potential for treating numerous liver diseases. However, traditional polycation vectors used for siRNA delivery typically produce siRNA-containing particles of large size (> 100 nm), along with high cytotoxicity and low colloidal stability. Inspired by earlier work on nanoparticles for plasmid DNA delivery, we graft hydrophilic and biocompatible polyethylene glycol (PEG) blocks to the polycation vector to overcome these limitations. We find that the PEG-grafted polycations result in slightly larger particle size, even though the hydrophilic PEG blocks are expected to hinder the formation of larger aggregates. To explain this observation, we investigate siRNA/copolymer self-assembly via computer simulations of coarse-grained polymer and siRNA models. Our calculations suggest that hydrogen bonding between PEG and the polycation leads to the increased particle size, and that smaller particles can be obtained by inhibiting hydrogen bonding in such system. Subsequent experiments employing solvents of lower polarity indeed lead to particles with smaller size.

  1. SOLVENT-INDUCED OTOTOXICITY IN RATS: AN ATYPICAL SELECTIVE MID-FREQUENCY HEARING DEFICIT

    EPA Science Inventory

    Most previous reports of ototoxicity following exposure to a variety of volatile organic solvents have restricted testing to the low- and mid-frequencies of the hearing range in the rat (2-20 kHz). e report here that inhalation exposure to styrene, xylene, toluene and 1,1,2-trich...

  2. Solvent-induced structural transition of self-assembled dipeptide: from organogels to microcrystals.

    PubMed

    Zhu, Pengli; Yan, Xuehai; Su, Ying; Yang, Yang; Li, Junbai

    2010-03-01

    Organogels that are self-assembled from simple peptide molecules are an interesting class of nano- and mesoscale soft matter with simplicity and functionality. Investigating the precise roles of the organic solvents and their effects on stabilization of the formed organogel is an important topic for the development of low-molecular-weight gelators. We report the structural transition of an organogel self-assembled from a single dipeptide building block, diphenylalanine (L-Phe-L-Phe, FF), in toluene into a flower-like microcrystal merely by introducing ethanol as a co-solvent; this provides deeper insights into the phase transition between mesostable gels and thermodynamically stable microcrystals. Multiple characterization techniques were used to reveal the transitions. The results indicate that there are different molecular-packing modes formed in the gels and in the microcrystals. Further studies show that the co-solvent, ethanol, which has a higher polarity than toluene, might be involved in the formation of hydrogen bonds during molecular self-assembly of the dipeptide in mixed solvents, thus leading to the transition of organogels into microcrystals. The structural transformation modulated by the co-solvent might have a potential implication in controllable molecular self-assembly. PMID:20119986

  3. Solvent-Induced Reversal of Activities between Two Closely Related Heterogeneous Catalysts in the Aldol Reaction

    SciTech Connect

    Kandel, Kapil; Althaus, Stacey M; Peeraphatdit, Chorthip; Kobayashi, Takeshi; Trewyn, Brian G; Pruski, Marek; Slowing, Igor I

    2013-01-11

    The relative rates of the aldol reaction catalyzed by supported primary and secondary amines can be inverted by 2 orders of magnitude, depending on the use of hexane or water as a solvent. Our analyses suggest that this dramatic shift in the catalytic behavior of the supported amines does not involve differences in reaction mechanism, but is caused by activation of imine to enamine equilibria and stabilization of iminium species. The effects of solvent polarity and acidity were found to be important to the performance of the catalytic reaction. This study highlights the critical role of solvent in multicomponent heterogeneous catalytic processes.

  4. Metallogrid Single-Molecule Magnet: Solvent-Induced Nuclearity Transformation and Magnetic Hysteresis at 16 K.

    PubMed

    Huang, Wei; Shen, Fu-Xing; Wu, Shu-Qi; Liu, Li; Wu, Dayu; Zheng, Zhe; Xu, Jun; Zhang, Ming; Huang, Xing-Cai; Jiang, Jun; Pan, Feifei; Li, Yao; Zhu, Kun; Sato, Osamu

    2016-06-01

    Structural assembly and reversible transformation between a metallogrid Dy4 SMM (2) and its fragment Dy2 (1) were established in the different solvent media. The zero-field magnetization relaxation was slowed for dysprosium metallogrid (2) with relaxation barrier of Ueff = 61.3 K when compared to Dy2 (1). Both magnetic dilution and application of a moderate magnetic field suppress ground-state quantum tunneling of magnetization and result in an enhanced Ueff of 119.9 and 96.7 K for 2, respectively. Interestingly, the lanthanide metallogrid complex (2) exhibits magnetic hysteresis loop even up to 16 K at a given field sweep rate of 500 Oe/s. PMID:27164298

  5. Prediction of solvent-induced morphological changes of polyelectrolyte diblock copolymer micelles.

    PubMed

    Li, Nan K; Fuss, William H; Tang, Lei; Gu, Renpeng; Chilkoti, Ashutosh; Zauscher, Stefan; Yingling, Yaroslava G

    2015-11-14

    Self-assembly processes of polyelectrolyte block copolymers are ubiquitous in industrial and biological processes; understanding their physical properties can also provide insights into the design of polyelectrolyte materials with novel and tailored properties. Here, we report systematic analysis on how the ionic strength of the solvent and the length of the polyelectrolyte block affect the self-assembly and morphology of the polyelectrolyte block copolymer materials by constructing a salt-dependent morphological phase diagram using an implicit solvent ionic strength (ISIS) method for dissipative particle dynamics (DPD) simulations. This diagram permits the determination of the conditions for the morphological transition into a specific shape, namely vesicles or lamellar aggregates, wormlike/cylindrical micelles, and spherical micelles. The scaling behavior for the size of spherical micelles is predicted, in terms of radius of gyration (R(g,m)) and thickness of corona (Hcorona), as a function of solvent ionic strength (c(s)) and polyelectrolyte length (NA), which are R(g,m) ∼ c(s)(-0.06)N(A)(0.54) and Hcorona ∼ c(s)(-0.11)N(A)(0.75). The simulation results were corroborated through AFM and static light scattering measurements on the example of the self-assembly of monodisperse, single-stranded DNA block-copolynucleotides (polyT50-b-F-dUTP). Overall, we were able to predict the salt-responsive morphology of polyelectrolyte materials in aqueous solution and show that a spherical-cylindrical-lamellar change in morphology can be obtained through an increase in solvent ionic strength or a decrease of polyelectrolyte length. PMID:26315065

  6. Organic solvents induce the formation of oil-in-ionic liquid microemulsion aggregations.

    PubMed

    Gao, Yanan; Li, Na; Zhang, Shaohua; Zheng, Liqiang; Li, Xinwei; Dong, Bin; Yu, Li

    2009-02-01

    The role of four organic solvents in the formation process of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) based ionic liquid (IL) microemulsions is investigated. The results showed that the addition of Triton X-100 remarkably decreased the conductivity of bmimBF4. The added organic solvents provided a strong apolar environment for the hydrophobic tails of Triton X-100 and caused the surfactant molecules to aggregate into the interfacial film of oil-in-bmimBF4 (O/IL) microemulsions. As a result, the conductivities of the solutions were initially increased because the insulative Triton X-100 molecules were assembled, which corresponded to increasing the concentration of continuous bmimBF4 solutions. The hydrophobic interaction between the dispersed organic solvents and the hydrophobic tails of Triton X-100 may be the driving force for the formation of O/IL microemulsions. The droplets of O/IL microemulsions were successively swollen by organic solvents, and a bicontinuous IL-containing microemulsion was observed by freeze-fracture transmission electron microscopy for the first time. The current study can help in further understanding the ILs-containing microemulsions and thereby improve microemulsion theory. PMID:19138136

  7. Solvent-induced reversible solid-state colour change of an intramolecular charge-transfer complex.

    PubMed

    Li, Ping; Maier, Josef M; Hwang, Jungwun; Smith, Mark D; Krause, Jeanette A; Mullis, Brian T; Strickland, Sharon M S; Shimizu, Ken D

    2015-10-11

    A dynamic intramolecular charge-transfer (CT) complex was designed that displayed reversible colour changes in the solid-state when treated with different organic solvents. The origins of the dichromatism were shown to be due to solvent-inclusion, which induced changes in the relative orientations of the donor pyrene and acceptor naphthalenediimide units. PMID:26299357

  8. Solvent-Induced Proton Hopping at a Water–Oxide Interface

    PubMed Central

    2014-01-01

    Despite widespread interest, a detailed understanding of the dynamics of proton transfer at interfaces is lacking. Here, we use ab initio molecular dynamics to unravel the connection between interfacial water structure and proton transfer for the widely studied and experimentally well-characterized water–ZnO(101̅0) interface. We find that upon going from a single layer of adsorbed water to a liquid multilayer, changes in the structure are accompanied by a dramatic increase in the proton-transfer rate at the surface. We show how hydrogen bonding and rather specific hydrogen-bond fluctuations at the interface are responsible for the change in the structure and proton-transfer dynamics. The implications of this for the chemical reactivity and for the modeling of complex wet oxide interfaces in general are also discussed. PMID:24920998

  9. Retinoic acid reduces solvent-induced neuropathy and promotes neural regeneration in mice.

    PubMed

    Palencia, Guadalupe; Hernández-Pedro, Norma; Saavedra-Perez, David; Peña-Curiel, Omar; Ortiz-Plata, Alma; Ordoñez, Graciela; Flores-Estrada, Diana; Sotelo, Julio; Arrieta, Oscar

    2014-08-01

    In humans, exposure to organic solvents (OS) is frequent in work activities or as a recreational inhalant, inducing severe neuropathy (secondary to demyelization of peripheral nerves). We have previously shown that all-trans retinoic acid (ATRA) increases local content of neural growth factor (NGF), improving peripheral neuropathy of diverse origins. In this study, we evaluated the effect of ATRA on OS-induced peripheral neuropathy in experimental mice. Two simultaneous experiments were performed. The first one aimed to evaluate ATRA for the prevention of damage induced by OS, the second to test ATRA as an OS-induced neuropathy treatment. Nociceptive threshold latency and NGF concentration in serum and in peripheral nerves were determined. Morphological changes and evidence of sciatic nerve regeneration were evaluated. Mice exposed to OS developed neuropathy and axonal degeneration. ATRA diminished the effects of OS inhalation on sensorial changes and nerve morphology. Treatment with ATRA reversed sensorial and nerve morphological changes of OS-induced neuropathy, and this was associated with increased contents of NGF. Similar to previous experiences on diabetic and toxic neuropathy, ATRA reduced and partially reversed the peripheral neuropathy caused by OS exposure. These favorable effects apparently are due to local production of NGF induced by neural regeneration in response to the administration of retinoic acid. PMID:24647975

  10. Solvent-induced changes in PEDOT:PSS films for organic electrochemical transistors

    SciTech Connect

    Zhang, Shiming; Kumar, Prajwal; Nouas, Amel Sarah; Fontaine, Laurie; Tang, Hao; Cicoira, Fabio

    2015-01-01

    Organic electrochemical transistors based on the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) are of interest for several bioelectronic applications. In this letter, we investigate the changes induced by immersion of PEDOT:PSS films, processed by spin coating from different mixtures, in water and other solvents of different polarities. We found that the film thickness decreases upon immersion in polar solvents, while the electrical conductivity remains unchanged. The decrease in film thickness is minimized via the addition of a cross-linking agent to the mixture used for the spin coating of the films.

  11. SOP-GPU: influence of solvent-induced hydrodynamic interactions on dynamic structural transitions in protein assemblies.

    PubMed

    Alekseenko, Andrey; Kononova, Olga; Kholodov, Yaroslav; Marx, Kenneth A; Barsegov, Valeri

    2016-06-30

    Hydrodynamic interactions (HI) are incorporated into Langevin dynamics of the Cα -based protein model using the Truncated Expansion approximation (TEA) to the Rotne-Prager-Yamakawa diffusion tensor. Computational performance of the obtained GPU realization demonstrates the model's capability for describing protein systems of varying complexity (10(2) -10(5) residues), including biological particles (filaments, virus shells). Comparison of numerical accuracy of the TEA versus exact description of HI reveals similar results for the kinetics and thermodynamics of protein unfolding. The HI speed up and couple biomolecular transitions through cross-communication among protein domains, which result in more collective displacements of structure elements governed by more deterministic (less variable) dynamics. The force-extension/deformation spectra from nanomanipulations in silico exhibit sharper force signals that match well the experimental profiles. Hence, biomolecular simulations without HI overestimate the role of tension/stress fluctuations. Our findings establish the importance of incorporating implicit water-mediated many-body effects into theoretical modeling of dynamic processes involving biomolecules. © 2016 Wiley Periodicals, Inc. PMID:27015749

  12. Single-stranded DNA detection by solvent-induced assemblies of a metallo-peptide-based complex

    NASA Astrophysics Data System (ADS)

    Das, Priyadip; Reches, Meital

    2016-05-01

    DNA detection is highly important for the sensitive sensing of different pathogenic bacteria and viruses. The major challenge is to create a sensor that can selectively detect very small concentrations of DNA without the need for amplification or complicated equipment. Different technologies such as optical, electrochemical and microgravimetric approaches can detect DNA fragments. Here we show, for the first time, the use of self-assembled nanostructures generated by a metallo-peptide as an optical sensing platform for DNA detection. The system can selectively detect single stranded DNA fragments by fluorescence measurements as it can discriminate even one base mismatch and can perform in the presence of other interfering proteins. This system may be useful in lab-on-a-chip applications.DNA detection is highly important for the sensitive sensing of different pathogenic bacteria and viruses. The major challenge is to create a sensor that can selectively detect very small concentrations of DNA without the need for amplification or complicated equipment. Different technologies such as optical, electrochemical and microgravimetric approaches can detect DNA fragments. Here we show, for the first time, the use of self-assembled nanostructures generated by a metallo-peptide as an optical sensing platform for DNA detection. The system can selectively detect single stranded DNA fragments by fluorescence measurements as it can discriminate even one base mismatch and can perform in the presence of other interfering proteins. This system may be useful in lab-on-a-chip applications. Electronic supplementary information (ESI) available: Peptide and receptor synthesis, characterization of the final and intermediate products, experimental details and additional figures including SEM, TEM, DLS, XRD, UV analysis and AFM topographic analysis. See DOI: 10.1039/c5nr07714a

  13. Solvent induced rapid modulation of micro/nano structures of metal carboxylates coordination polymers: mechanism and morphology dependent magnetism

    PubMed Central

    Liu, Kun; Shen, Zhu-Rui; Li, Yue; Han, Song-De; Hu, Tong-Liang; Zhang, Da-Shuai; Bu, Xian-He; Ruan, Wen-Juan

    2014-01-01

    Rational modulation of morphology is very important for functional coordination polymers (CPs) micro/nanostructures, and new strategies are still desired to achieve this challenging target. Herein, organic solvents have been established as the capping agents for rapid modulating the growth of metal-carboxylates CPs in organic solvent/water mixtures at ambient conditions. Co-3,5-pyridinedicarboxylate (pydc) CPs was studied here as the example. During the reaction, the organic solvents exhibited three types of modulation effect: anisotropic growth, anisotropic growth/formation of new crystalline phase and the formation of new crystalline phase solely, which was due to the variation of their binding ability with metal cations. The following study revealed that the binding ability was critically affected by their functional groups and molecular size. Moreover, their modulation effect could be finely tuned by changing volume ratios of solvent mixtures. Furthermore, they could be applied for modulating other metal-carboxylates CPs: Co-1,3,5-benzenetricarboxylic (BTC), Zn-pydc and Eu-pydc etc. Additionally, the as-prepared Co-pydc CPs showed a fascinating morphology-dependent antiferromagnetic behavior. PMID:25113225

  14. Hydroxylic solvent-induced ring opening of the dehydropyrrolizidine alkaloids riddelliine and seneciphylline: implications for toxicity and analytical studies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    etabolites that can also cause various cancers in animal models. Riddelliine and seneciphylline are closely-related, macrocyclic diester dehydropyrrolizidine alkaloids produced by various species in the Asteraceae. Despite the evidence of carcinogenicity in animal models, and the increasing concerns...

  15. Solvent-induced multicolour fluorescence of amino-substituted 2,3-naphthalimides studied by fluorescence and transient absorption measurements.

    PubMed

    Fujii, Mayu; Namba, Misa; Yamaji, Minoru; Okamoto, Hideki

    2016-07-01

    A series of amino-2,3-naphthalimide derivatives having the amino functionality at 1-, 5- and 6-positions (, and , respectively) were prepared, and their photophysical properties were systematically investigated based on the measurements of steady-state absorption and fluorescence spectra, fluorescence lifetimes as well as transient absorption spectra. The s efficiently fluoresced in solution, and the emission spectra appreciably shifted depending on the solvent polarity. displayed only a slight fluorescence red-shift upon increasing the solvent polarity. In contrast, and showed marked positive solvatofluorochromism with large Stokes shifts displaying multicolour fluorescence; the fluorescence colours of and varied from violet-blue in hexane to orange-red in methanol. and , thus, serve as micro-environment responding fluorophores. In methanol, the intensity of the fluorescence emission band of and significantly reduced. Based on the fluorescence quantum yields and lifetimes, and transient absorption measurements, it has been revealed that internal conversion from the S1 state of s to the ground state was accelerated by the protic medium, resulting in a reduction in their fluorescence efficiency, while intersystem crossing from the S1 state to a triplet state was not responsible for the decrease of fluorescence intensity. PMID:27251860

  16. Gas/solvent-induced transformation and expansion of a nonporous solid to 1:1 host guest form

    SciTech Connect

    Thallapally, Praveen K.; McGrail, B. Peter; Dalgarno, Scott J.; Atwood, Jerry L.

    2008-07-01

    Herein we report the gas (CO2, N2O and propane) and solvent (CS2 and acetone) induced transformation and expansion of guest free thermodynamic form of a p-tert-butylcalix [4]arene to 1:1 host guest form.

  17. Influence of Isotope on Shell Effects of Pre-scission Particle Evaporation

    NASA Astrophysics Data System (ADS)

    Ye, Wei; Chen, Na

    2005-08-01

    The shell effects on the particle evaporation prior to fission for three Pb isotopes, 204Pb, 208Pb, and 212Pb, as well as three Sn isotopes, 128Sn, 132Sn, and 136Sn, are explored by a diffusion model. Calculations show that the magnitude of shell effects in the emission of particles changes with the neutron-to-proton ratio N/Z of these fissioning nuclei, and this change is affected significantly by the spin and excitation energy of the system. It is shown that high angular momentum enhances the dependence of shell effects on the N/Z while high excitation energy weakens such a dependence. The project supported by National Natural Science Foundation of China under Grand Nos. 10405007 and 90412014 and the Teaching and Researching Foundation for the Excellent Teachers of Southeast University

  18. A generalization of the Boltzmann superposition principle to polymer networks undergoing scission

    NASA Technical Reports Server (NTRS)

    Moacanin, J.; Landel, R. F.; Aklonis, J. J.

    1976-01-01

    Methods reported by Moacanin et al. (1975) and Moacanin and Aklonis (1971) are generalized with the objective to include strains (or stress) applied in an arbitrary manner to linearly viscoelastic materials. An imposition of changes in both the strain and the density of elastically effective chains in discrete increments is considered. In accordance with the Boltzmann superposition principle, each strain increment may be treated as a new independent experiment which adds linearly to the total response of the system.

  19. Facile scission of isonitrile carbon–nitrogen triple bond using a diborane(4) reagent

    PubMed Central

    Asakawa, Hiroki; Lee, Ka-Ho; Lin, Zhenyang; Yamashita, Makoto

    2014-01-01

    Transition metal reagents and catalysts are generally effective to cleave all three bonds (one σ and two π) in a triple bond despite its high bonding energy. Recently, chemistry of single-bond cleavage by using main-group element compounds is rapidly being developed in the absence of transition metals. However, the cleavage of a triple bond using non-transition-metal compounds is less explored. Here we report that an unsymmetrical diborane(4) compound could react with carbon monoxide and tert-butyl isonitrile at room temperature. In the latter case, the carbon–nitrogen triple bond was completely cleaved in the absence of transition metal as confirmed by X-ray crystallographic analysis, 13C NMR spectroscopy with 13C labelling and DFT calculations. The DFT calculations also revealed the detailed reaction mechanism and indicated that the key for the carbon–nitrogen triple-bond cleavage could be attributed to the presence of nucleophilic nitrogen atom in one of the intermediates. PMID:24967910

  20. Competing mechanisms and scaling laws for carbon nanotube scission by ultrasonication

    PubMed Central

    Pagani, Guido; Green, Micah J.; Poulin, Philippe; Pasquali, Matteo

    2012-01-01

    Dispersion of carbon nanotubes (CNTs) into liquids typically requires ultrasonication to exfoliate individuals CNTs from bundles. Experiments show that CNT length drops with sonication time (or energy) as a power law t-m. Yet the breakage mechanism is not well understood, and the experimentally reported power law exponent m ranges from approximately 0.2 to 0.5. Here we simulate the motion of CNTs around cavitating bubbles by coupling Brownian dynamics with the Rayleigh–Plesset equation. We observe that, during bubble growth, CNTs align tangentially to the bubble surface. Surprisingly, we find two dynamical regimes during the collapse: shorter CNTs align radially, longer ones buckle. We compute the phase diagram for CNT collapse dynamics as a function of CNT length, stiffness, and initial distance from the bubble nuclei and determine the transition from aligning to buckling. We conclude that, depending on their length, CNTs can break due to either buckling or stretching. These two mechanisms yield different power laws for the length decay (0.25 and 0.5, respectively), reconciling the apparent discrepancy in the experimental data. PMID:22752305

  1. Coal structure cleavage mechanisms: scission of methylene and ether linkages to hydroxylated rings

    SciTech Connect

    McMillen, D.F.; Ogier, W.C.; Ross, D.S.

    1981-07-31

    The kinetics of the thermolysis of the coal-model compounds (hydroxyphenyl)phenylmethanes and p-hydroxyphenyl phenyl ether in tetralin at 400/sup 0/C are described. The observed rates for (hydroxyphenyl)phenylmethanes are shown to be quantitatively consistent with thermochemical data and an enol-keto tautomerization followed by rate-determining homolysis of the cyclohexadienone intermediate. For p-hydroxyphenyl phenyl ether the breakdown of this quantitative agreement and the effects of various additives indicate that the tautomerization is rate determining and most probably involves electrophilic attack on the enolate ion. Implications for coal liquefaction and catalysis are briefly discussed.

  2. Solvent induced synthesis, structure and properties of coordination polymers based on 5-hydroxyisophthalic acid as linker and 1,10-phenanthroline as auxiliary ligand

    NASA Astrophysics Data System (ADS)

    Kariem, Mukaddus; Yawer, Mohd; Sheikh, Haq Nawaz

    2015-11-01

    Three new coordination polymers [Mn(hip)(phen) (H2O)]n (1), [Co(hip)(phen) (H2O)]n (2), and [Cd(hip) (phen) (H2O)]n (3) (H2hip=5-hydroxyisophthalic acid; phen=1,10-phenanthroline) have been synthesized by solvo-hydrothermal method using diethyl formamide-water (DEF-H2O) as solvent system. Single-crystal X-ray diffraction analysis reveals that all three coordination polymers 1, 2 and 3 crystallize in monoclinic space group P2/n. Metal ions are inter-connected by hydroxyisophthalate anions forming zig-zag 1D chain. 1D chains are further inter-connected by hydrogen bonding and π-π stacking interactions leading to 3D supramolecular architecture. Hydrogen-bonding and π-π stacking provide thermal stability to polymers. Compounds 1 and 2 are paramagnetic at room temperature and variable temperature magnetic moment measurements revealed weak ferromagnetic interactions between metal ions at low temperature. Compound 3 exhibits excellent photoluminescence with large Stokes shift.

  3. Solvent-induced O-H vibration red-shifts of oxygen-acids in hydrogen-bonded O-H···base complexes.

    PubMed

    Keinan, Sharon; Pines, Dina; Kiefer, Philip M; Hynes, James T; Pines, Ehud

    2015-01-22

    Infrared spectroscopy has been used to characterize the solvent effect on the OH stretching vibrations νOH of phenol, 1-naphthol, 2-naphthol, 1-hydroxypyrene, and ethanol. We distinguish the dielectric (nonspecific) effect of the solvent on ΔνOH, the observed red-shifts in νOH, from the much larger red-shift caused by direct hydrogen (H)-bonding interactions with the solvents. To isolate the solvent dielectric constant ε effect on νOH, the OH oscillator was also studied when it is already H-bonded with an invariant oxygen base, dimethyl sulfoxide. We find that ΔνOH depends importantly on ΔPA, the difference between the proton affinities of the conjugate base of the proton donor and the proton acceptor. For a given H-bonded complex, νOH tends to vary inversely with ε, exhibiting different slopes for polar and nonpolar solvents, i.e., solvents comprising molecules with and without a permanent dipole moment, respectively. We use a two-state valence-bond-based theory to analyze our experimental data. This demonstrates that the OH oscillator acquires a more ionic-like character in the vibrational excited state, i.e., charge transfer; this results in a stronger H-bond in a more anharmonic potential for the OH vibration. The theory distinguishes between nonpolar and polar solvents and successfully accounts for the observed 1/ε and ΔPA variations. PMID:24975617

  4. Evidence of entropy-driven bistability through (15)N NMR analysis of a temperature- and solvent-induced, chiroptical switching polycarbodiimide.

    PubMed

    Reuther, James F; Novak, Bruce M

    2013-12-26

    The thermo- and solvo-driven chiroptical switching process observed in specific polycarbodiimides occurs in a concerted fashion with large deviations in specific optical rotation (OR) and CD Cotton effect as a consequence of varying populations of two distinct polymer conformations. These two conformations are clearly visible in the (15)N NMR and IR spectra of the (15)N-labeled poly((15)N-(1-naphthyl)-N'-octadecylcarbodiimide) (Poly-3) and poly((15)N-(1-naphthyl)-(15)N'-octadecylcarbodiimide) (Poly-5). Using van't Hoff analysis, the enthalpies and entropies of switching (ΔHswitching; ΔSswitching) were calculated for both Poly-3 and Poly-5 using the relative integrations of both peaks in the (15)N NMR spectra at different temperatures to measure the populations of each state. The chiroptical switching (i.e., transitioning from state A to state B) was found to be an endothermic process (positive ΔHswitching) for both Poly-3 and Poly-5 in all solvents studied, meaning the conformation correlating with the downfield chemical shift (ca. 148 ppm, state B) is the higher enthalpy state. The compensating factor behind this phenomenon has been determined to be the large increase in entropy in CHCl3 as a result of the switching. Herein, we propose that the increased entropy in the system is a direct consequence of increased disorder in the solvent as the switching occurs. Specifically, the chloroform solvent molecules are very ordered around the polymer chains due to favorable solvent-polymer interactions, but as the switching occurs, these interactions become less favorable and disorder results. The same level of solvent disorder is not achieved in toluene, causing the chiroptical switching process to occur at higher temperatures. PMID:24313274

  5. Solvent induced channel interference in the two-photon absorption process--a theoretical study with a generalized few-state-model in three dimensions.

    PubMed

    Alam, Md Mehboob; Chattopadhyaya, Mausumi; Chakrabarti, Swapan

    2012-01-21

    For the first time, we report the effect of interference between different optical channels on the two-photon absorption (TPA) process in three dimensions. We have employed response theory as well as a sum-over-states (SOS) approach involving few intermediate states to calculate the TPA parameters like transition probabilities (δ(TP)) and TPA tensor elements. In order to use the limited SOS approach, we have derived a new formula for a generalized few-state-model (GFSM) in three dimensions. Due to the presence of additional terms related to the angle between different transition moment vectors, the channel interference associated with the TPA process in 3D is significantly different and much more complicated than that in 1D and 2D cases. The entire study has been carried out on the two simplest Reichardt's dyes, namely 2- and 4-(pyridinium-1-yl)-phenolate (ortho- and para-betain) in gas phase, THF, CH(3)CN and water solvents. We have meticulously inspected the effect of the additional angle related terms on the overall TPA transition probabilities of the two 3D isomeric molecules studied and found that the interfering terms involved in the δ(TP) expression contribute both constructively and destructively as well to the overall δ(TP) value. Moreover, the interfering term has a more conspicuous role in determining the net δ(TP) associated with charge transfer transition in comparison to that of π-π* transition of the studied systems. Interestingly, our model calculations suggest that, for o- and p-betain, the quenching of destructive interference associated with a particular two-photon process can be done with high polarity solvents while the enhancement of constructive interference will be achieved in solvents having relatively small polarity. All the one- and two-photon parameters are evaluated using a range separated CAMB3LYP functional. PMID:22127437

  6. Solvent-induced secondary building unit (SBU) variations in a series of Cu(II) metal-organic frameworks derived from a bifunctional ligand.

    PubMed

    Chen, Di-Ming; Ma, Jian-Gong; Cheng, Peng

    2015-05-21

    The role of auxiliary solvents in the formation of metal-organic frameworks (MOFs) has been studied for a series of copper-based framework systems. Herein we show the formation of three different 3D ordered frameworks with the formulae {[Cu4(cpt)4Cl4]·2DMF·dioxane·3H2O}n (1), {[Cu8(cpt)4(Hcpt)2Cl7(μ3-OH)2(H2O)4]Cl3·4CH3CN}n (2), and {[Cu8(cpt)4Cl4(μ3-OH)2(μ4-O)2]Cl2·4H2O·2CH3CN·3MeOH}n (3) [Hcpt = 4-(4-carboxyphenyl)-1,2,4-triazole], respectively, from the same reaction mixture through varying auxiliary solvents of the medium. These MOFs were fully characterized by single-crystal X-ray diffraction, showing interesting secondary building unit (SBU) variations. The varied SBUs not only bring different framework architectures to these MOFs, but also affect their framework stability. Gas sorption studies of MOF 3 reveal high CO2-N2 selectivity at 298 K and 0.16 bar (a typical partial pressure of CO2 in an industrial flue gas). A high isosteric heat of adsorption (Qst) at zero loading (53 kJ mol(-1)) was also observed in MOF 3. PMID:25873315

  7. Coal liquefaction model studies: free radical chain decomposition of diphenylpropane, dibenzyl ether, and phenyl ether via. beta. -scission reactions

    SciTech Connect

    Gillert, K.E.; Gojewski, J.J.

    1982-12-03

    The thermal decompositions to 1,3-diphenylpropane (1), dibenzyl ether (2), and phenethyl phenyl ether (3) have been found to proceed by free radical chain processes. 1 gave toluene and styrene with a reaction order of 1.55, E/sub A/ = 51.4 kcal/mol, and log A = 12.5. The reaction could be initiated by benzyl phenyl ether but not by 1,2-diphenylethane. 2 gave toluene and benzaldehyde with a reaction order of 1.43,E/sub A/ = 48 kcal/mol, and log A = 12.6. The reaction could be initiated with benzyl phenyl ether. 3 gave phenol and styrene with a reaction order of 1.21, E/sub A/ = 50.3 kcal/mol, and log A =12.3. The reaction could be initiated by benzyl phenyl ether. All of the data are consistent with free radical processes with the reaction order determined by the termination reaction. No evidence for concerted reactions has been found.

  8. Bond Formation and Bond Scission Dynamics in Polyatomic Molecules Revealed by Momentum Imaging Experiments and Electron Scattering Calculations

    NASA Astrophysics Data System (ADS)

    Slaughter, Daniel; Trevisan, Cynthia; Weyland, Marvin; Dorn, Alexander; Douguet, Nicolas; Orel, Ann; Adaniya, Hidehito; McCurdy, Bill; Belkacem, Ali; Rescigno, Tom

    2016-05-01

    We present combined experimental and theoretical studies of dissociative electron attachment (DEA) dynamics in methane and ammonia. DEA in each of these systems proceeds through electronic Feshbach resonances, where a valence electron is excited and captured with the incident electron in the lowest unoccupied orbital. In methane, one triply-degenerate resonance undergoes Jahn-Teller splitting through molecular distortions, leading to four observed final states, each having a 2-body and a 3-body dissociation with anionic products H- and CH2-and neutrals CH3, CH2, H2 or H. In ammonia, one resonance leads to H- + NH2 and NH2-+ H, the latter resulting from non-adiabatic charge transfer. A higher energy resonance leads directly to H- + NH2* and indirectly to NH2-+ H. We examine the dynamics of the transient anion in each of these processes. work supported by Chemical Sciences, Geosciences and Biosciences division of BES/DOE.

  9. The ultrasound-assisted oxidative scission of monoenic fatty acids by ruthenium tetroxide catalysis: influence of the mixture of solvents.

    PubMed

    Rup, Sandrine; Zimmermann, François; Meux, Eric; Schneider, Michel; Sindt, Michele; Oget, Nicolas

    2009-02-01

    Carboxylic acids and diacids were synthesized from monoenic fatty acids by using RuO4 catalysis, under ultrasonic irradiation, in various mixtures of solvents. Ultrasound associated with Aliquat 336 have promoted in water, the quantitative oxidative cleavage of the CH=CH bond of oleic acid. A design of experiment (DOE) shows that the optimal mixture of solvents (H2O/MeCN, ratio 1/1, 2.2% RuCl3/4.1 eq. NaIO4) gives 81% azelaic acid and 97% pelargonic acid. With the binary heterogeneous mixture H2O/AcOEt, the oxidation of the oleic acid leads to a third product, the alpha-dione 9,10-dioxostearic acid. PMID:18799341

  10. Coal liquefaction process using pretreatment with a binary solvent mixture

    DOEpatents

    Miller, Robert N.

    1986-01-01

    An improved process for thermal solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a hydrogen donor solvent comprises pretreating the coal with a binary mixture of an aromatic hydrocarbon and an aliphatic alcohol at a temperature below 300.degree. C. before the hydroliquefaction step. This treatment generally increases both conversion of coal and yields of oil.

  11. Density functional theory study of O-H and C-H bond scission of methanol catalyzed by a chemisorbed oxygen layer on Cu(111)

    NASA Astrophysics Data System (ADS)

    Li, Jonathan; Zhou, Guangwen

    2016-04-01

    Using the density-functional theory within the generalized gradient approximation, we have studied the partial oxidation of methanol on a Cu(111) surface covered with a chemisorbed oxygen layer that resembles a Cu2O layer. Adsorption energies and geometries were computed for methanol, methoxy, hydroxymethyl and formaldehyde on both clean Cu(111) and Cu2O/Cu(111) and electronic structures were computed for the reaction intermediates on Cu2O/Cu(111). We also calculated the energy barrier for partial oxidation of methanol to formaldehyde on Cu2O/Cu(111). These results show that the Cu2O monolayer slightly lowers the stability of each of the surface adsorbates and the oxygen strongly promotes hydrogen dissociation by lowering the energy barrier of methanol decomposition and causing the spontaneous dissociation of methanol into methoxy.

  12. Detection of Ligand- and Solvent-Induced Shape Alterations of Cell-Growth-Regulatory Human Lectin Galectin-1 in Solution by Small Angle Neutron and X-Ray Scattering

    PubMed Central

    He, Lizhong; André, Sabine; Siebert, Hans-Christian; Helmholz, Heike; Niemeyer, Bernd; Gabius, Hans-Joachim

    2003-01-01

    The bioactivity of galectin-1 in cell growth regulation and adhesion prompted us to answer the questions whether ligand presence and a shift to an aprotic solvent typical for bioaffinity chromatography might alter the shape of the homodimeric human lectin in solution. We used small angle neutron and synchrotron x-ray scattering studies for this purpose. Upon ligand accommodation, the radius of gyration of human galectin-1 decreased from 19.1 ± 0.1 Å in the absence of ligand to 18.2 ± 0.1 Å. In the aprotic solvent dimethyl sulfoxide, which did not impair binding capacity, galectin-1 formed dimers of a dimer, yielding tetramers with a cylindrical shape. Intriguingly, no dissociation into subunits occurred. In parallel, NMR monitoring was performed. The spectral resolution was in accord with these data. In contrast to the properties of the human protein, a nonhomologous agglutinin from mistletoe sharing galactose specificity was subject to a reduction in the radius of gyration from ∼62 Å in water to 48.7 Å in dimethyl sulfoxide. Evidently, the solvent caused opposite responses in the two tested galactoside-binding lectins with different folding patterns. We have hereby proven that ligand presence and an aprotic solvent significantly affect the shape of galectin-1 in solution. PMID:12829506

  13. Color tunable and near white-light emission of two solvent-induced 2D lead(II) coordination networks based on a rigid ligand 1-tetrazole-4-imidazole-benzene.

    PubMed

    Chen, Jun; Zhang, Qing; Liu, Zhi-Fa; Wang, Shuai-Hua; Xiao, Yu; Li, Rong; Xu, Jian-Gang; Zhao, Ya-Ping; Zheng, Fa-Kun; Guo, Guo-Cong

    2015-06-01

    Two new lead(II) coordination polymers, [Pb(NO3)(tzib)]n (1) and [Pb(tzib)2]n (2), were successfully synthesized from the reaction of a rigid ligand 1-tetrazole-4-imidazole-benzene (Htzib) and lead(II) nitrate in different solvents. The obtained polymers have been characterized by single-crystal X-ray diffraction analyses, which show that both polymers feature 2D layer structures. The inorganic anion nitrate in 1 shows a μ2-κO3:κO3 bridging mode to connect adjacent lead ions into a zigzag chain, and then the organic ligands tzib(-) join the neighboring chains into a 2D layer by a μ3-κN1:κN2:κN6 connection mode. In 2, there are two different bridging modes of the tzib(-) ligand: μ3-κN1:κN2:κN6 and μ3-κN1:κN6 to coordinate the lead ions into a 2D layer structure. Interestingly, both polymers displayed broadband emissions covering the entire visible spectra, which could be tunable to near white-light emission by varying excitation wavelengths. PMID:25952460

  14. Solvent-induced Mn(II)/Zn(II)/Co(II) organopolymolybdate compounds constructed by bis-pyridyl-bis-amide ligands through the Mo-N bond: synthesis, structures and properties.

    PubMed

    Xu, Na; Zhang, Ju-Wen; Wang, Xiu-Li; Liu, Guo-Cheng; Li, Tian-Jiao

    2016-01-14

    Three transition metal organopolymolybdate hybrid compounds, namely, H2[Mn(H2O)4L3(γ-Mo8O26)] 8H2O (), H[M2(CH3O)(H2O)6L3(γ-Mo8O26)] [M = Zn () and Co ()] [L = 1,4-bis(3-pyridinecarboxamido)benzene] have been synthesized under solvothermal conditions and characterized by IR spectroscopy, TG analysis, powder XRD and single-crystal X-ray diffraction. Compounds were obtained by the one-pot method, and the mixture of methanol and water with different ratios was used as the solvent. In compound , the γ-Mo8 anions were connected with pyridine groups of ligand L by the Mo-N bond, forming an uncommon 1D γ-Mo8-L chain. The adjacent chains were connected by [MnL2(H2O)4](2+) moieties through hydrogen bonding interaction to construct a 2D supramolecular network. Compounds and are isostructural, which show a 3D 2,4,6-connected {4(4)·6(2)}{4(4)·6(6)·8(4)·10}{6} framework. The γ-Mo8 anions were connected by [M(H2O)2(CH3O)](+) [M = Zn () and Co ()] subunits forming 1D M-Mo8 chains, which were connected by [ML2(H2O)4](2+) moieties to construct a 2D layer. In compounds and , there also exist the same 1D γ-Mo8-L chains as in , which extended the 2D networks to 3D frameworks. The Mo-N bond with pyridyl groups was formed under the solvothermal conditions, which is scarcely reported to our knowledge. The effect of the solvent on the assembly of the title compounds and the formation of the Mo-N bond, as well as the role of metal-organic moieties on the construction of diverse organopolymolybdate compounds have been discussed in detail. Furthermore, the electrochemical and photocatalytic properties of have been investigated. PMID:26631431

  15. 1,1,1,3,3,3-Hexafluoro-2-propanol and 2,2,2-trifluoroethanol solvents induce self-assembly with different surface morphology in an aromatic dipeptide.

    PubMed

    Reddy, Samala Murali Mohan; Shanmugam, Ganesh; Mandal, Asit Baran

    2014-08-28

    Peptide based self-assembled structures, especially those from smaller peptides, have attracted much research interest due to their potential applications as biomaterials. These structures have been produced using different solvents (one of the methods), including alcohols, except fluorinated alcohols, which are believed to support non-aggregated structures. Herein, we have studied the ability of 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solvents to induce self-assembly of an aromatic dipeptide, namely Tyr-Phe (YF). SEM images showed that HFIP and TFE can induce self-assembly with completely different morphologies, namely microribbons and microspheres, respectively, when YF is dried on a glass surface. Optical microscopic images showed that the microribbons possess birefringence under polarized light, whereas the microspheres do not, indicating that the self-assembled structures derived from HFIP solution are more highly ordered and crystalline in nature than those derived from TFE. Spectroscopic results indicated that the YF peptide adopts completely different conformations in these solvents. Time-dependent experiments suggested that the conformation of YF in HFIP is kinetically unstable and undergoes conformational change, whereas it is more stable in TFE, demonstrating that the modes of interaction of the TFE and HFIP solvents with the peptide are dissimilar. Different self-assembled structures were observed at different time intervals when YF was incubated in neat HFIP and 10% HFIP-90% TFE, establishing that the monomeric conformation plays a dominant role in deciding the final self-assembled structure (morphology) of YF. The current results demonstrate that TFE and HFIP solvents can produce self-assembled structures with different morphologies during solvent evaporation, despite their similar properties, such as secondary structural (α-helix) induction and preserving the peptide in its monomeric conformation in solution. PMID:24999600

  16. Time phased alternate blending of feed coals for liquefaction

    DOEpatents

    Schweigharett, Frank; Hoover, David S.; Garg, Diwaker

    1985-01-01

    The present invention is directed to a method for reducing process performance excursions during feed coal or process solvent changeover in a coal hydroliquefaction process by blending of feedstocks or solvents over time. ,

  17. Coal liquefaction process using pretreatment with a binary solvent mixture

    DOEpatents

    Miller, R.N.

    1986-10-14

    An improved process for thermal solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a hydrogen donor solvent comprises pretreating the coal with a binary mixture of an aromatic hydrocarbon and an aliphatic alcohol at a temperature below 300 C before the hydroliquefaction step. This treatment generally increases both conversion of coal and yields of oil. 1 fig.

  18. The mechanism of stimulation of NADPH oxidation during the mechanism-based inactivation of cytochrome P450 2B1 by N-methylcarbazole: redox cycling and DNA scission.

    PubMed

    Shen, T; Hollenberg, P F

    1994-01-01

    The oxidation rate of NADPH is markedly stimulated during the mechanism-based inactivation of cytochrome P450 2B1 by N-methylcarbazole (NMC) in a reconstituted system consisting of NADPH-cytochrome P450 reductase, cytochrome P450 and phospholipid. The stimulation of NADPH oxidation in this system is due to 1-hydroxy-N-methylcarbazole (1-OH-NMC), one of the major metabolites of NMC. The 1-OH-NMC is further metabolized in an NADPH-dependent manner by the reconstituted system or by purified NADPH-cytochrome P450 reductase to give a more polar metabolite which has been isolated by HPLC. The conversion of 1-OH-NMC to this product was inhibited by superoxide dismutase (SOD), and incubation of the 1-OH-NMC with hypoxanthine-xanthine oxidase resulted in the formation of the same product, suggesting that the superoxide anion was involved in the metabolism of 1-OH-NMC by the reductase. Redox cycling activity during the metabolism of 1-OH-NMC by reductase has been demonstrated. The oxidation of NADPH by the reductase in the presence of 35 microM 1-OH-NMC was enhanced approximately 23-fold [240 nmol of NADPH oxidized/(min.nmol of reductase)] relative to control levels in the presence of 500 microM NMC [10.5 nmol/(min.nmol of reductase)]. 1-OH-NMC (35 microM) caused a 40-fold increase in the rate of formation of superoxide during its metabolism by reductase. The rapid rates of NADPH oxidation and superoxide formation were inhibited by the addition of reduced glutathione (GSH) to the reaction mixture. Neither SOD nor GSH inhibited the reductase activity directly.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8199313

  19. Ambient pressure XPS and IRRAS investigation of ethanol steam reforming on Ni-CeO2(111) catalysts: an in situ study of C-C and O-H bond scission.

    PubMed

    Liu, Zongyuan; Duchoň, Tomáš; Wang, Huanru; Grinter, David C; Waluyo, Iradwikanari; Zhou, Jing; Liu, Qiang; Jeong, Beomgyun; Crumlin, Ethan J; Matolín, Vladimír; Stacchiola, Dario J; Rodriguez, José A; Senanayake, Sanjaya D

    2016-06-22

    Ambient-Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Infrared Reflection Absorption Spectroscopy (AP-IRRAS) have been used to elucidate the active sites and mechanistic steps associated with the ethanol steam reforming reaction (ESR) over Ni-CeO2(111) model catalysts. Our results reveal that surface layers of the ceria substrate are both highly reduced and hydroxylated under reaction conditions while the small supported Ni nanoparticles are present as Ni(0)/NixC. A multifunctional, synergistic role is highlighted in which Ni, CeOx and the interface provide an ensemble effect in the active chemistry that leads to H2. Ni(0) is the active phase leading to both C-C and C-H bond cleavage in ethanol and it is also responsible for carbon accumulation. On the other hand, CeOx is important for the deprotonation of ethanol/water to ethoxy and OH intermediates. The active state of CeOx is a Ce(3+)(OH)x compound that results from extensive reduction by ethanol and the efficient dissociation of water. Additionally, we gain an important insight into the stability and selectivity of the catalyst by its effective water dissociation, where the accumulation of surface carbon can be mitigated by the increased presence of surface OH groups. The co-existence and cooperative interplay of Ni(0) and Ce(3+)(OH)x through a metal-support interaction facilitate oxygen transfer, activation of ethanol/water as well as the removal of coke. PMID:27095305

  20. Solvent-induced and polyether-ligand-induced redox isomerization within an asymmetrically coordinated mixed-valence ion: trans-(py)(NH[sub 3])[sub 4]Ru(4-NCpy)Ru(2,2[prime]-bpy)[sub 2]Cl[sup 4+

    SciTech Connect

    Curtis, J.C.; Massum, M. ); Roberts, J.A.; Blackbourn, R.L.; Dong, Yuhua; Johnson, C.S.; Hupp, J.T. )

    1991-10-02

    Advantage is taken of oxidation-state-dependent ligand (ammine)/solvent interactions to shift redox potentials and effect redox isomerization in the title complex. In poorly basic solvents, the stable isomeric form is trans-(py)(NH[sub 3])[sub 4]Ru[sup II](NCpy)Ru[sup III](bpy)[sub 2]Cl[sup 4+] (py is pyridine; NCpy is 4-cyanopyridine; bpy is 2,2[prime]-bipyridine). In contrast, in stronger Lewis bases or in a mixture of strong and weak bases (dimethyl sulfoxide + nitromethane), the preferred isomer is trans-(py)(NH[sub 3])[sub 4]Ru[sup III](NCpy)Ru[sup II](bpy)Cl[sup 4+]. Evidence for redox isomerization was obtained, in part, from plots of formal potentials versus solvent Lewis basicity. Confirmatory evidence was obtained from a combination of electrochemical reaction entropy and resonance Raman spectroscopic experiments. UV-vis-near-IR absorption experiments, however, were not found to be useful in demonstrating isomerization. In a released series of experiments, redox isomerization was also demonstrated based on ammine binding by either a low molecular weight poly(ethylene glycol) species or by a macrocyclic ligand, dibenzo-36-crown-12. Much smaller molar amounts of either the polymer (substoichiometric) or crown (approximately stoichiometic) are required, in comparison to basic solvent (several-fold excess), in order to induce isomerization in nitromethane as the initial solvent. The possible general utility of the redox isomerization concept in time-resolved intramolecular charge-transfer studies and in optical studies of competitive hole- and electron hole- and electron-transfer pathways is mentioned.

  1. Catalytic coal liquefaction process

    DOEpatents

    Garg, Diwakar; Sunder, Swaminathan

    1986-01-01

    An improved process for catalytic solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a solvent comprises using as catalyst a mixture of a 1,2- or 1,4-quinone and an alkaline compound, selected from ammonium, alkali metal, and alkaline earth metal oxides, hydroxides or salts of weak acids.

  2. Catalytic coal liquefaction process

    DOEpatents

    Garg, D.; Sunder, S.

    1986-12-02

    An improved process for catalytic solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a solvent comprises using as catalyst a mixture of a 1,2- or 1,4-quinone and an alkaline compound, selected from ammonium, alkali metal, and alkaline earth metal oxides, hydroxides or salts of weak acids. 1 fig.

  3. Catalysts for coal liquefaction processes

    DOEpatents

    Garg, D.

    1986-10-14

    Improved catalysts for catalytic solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a hydrogen donor solvent comprise a combination of zinc or copper, or a compound thereof, and a Group VI or non-ferrous Group VIII metal, or a compound thereof.

  4. Catalysts for coal liquefaction processes

    DOEpatents

    Garg, Diwakar

    1986-01-01

    Improved catalysts for catalytic solvent refining or hydroliquefaction of non-anthracitic coal at elevated temperatures under hydrogen pressure in a hydrogen donor solvent comprise a combination of zinc or copper, or a compound thereof, and a Group VI or non-ferrous Group VIII metal, or a compound thereof.

  5. Angular correlations in emission of prescission neutrons from {sup 235}U fission induced by slow polarized neutrons

    SciTech Connect

    Danilyan, G. V.; Wilpert, T.; Granz, P.; Krakhotin, V. A.; Mezei, F.; Novitsky, V. V.; Pavlov, V. S.; Russina, M. V.; Shatalov, P. B.

    2008-12-15

    A new approach to searching for and studying scission neutrons, which is based on the analysis of specific angular correlations in nuclear fission induced by polarized neutrons, is described and used to evaluate the fraction of scission neutrons in the total number of prompt neutrons of {sup 235}U fission emitted perpendicularly to the fission axis.

  6. A Feedback Loop between Dynamin and Actin Recruitment during Clathrin-Mediated Endocytosis

    PubMed Central

    Taylor, Marcus J.; Lampe, Marko; Merrifield, Christien J.

    2012-01-01

    Clathrin-mediated endocytosis proceeds by a sequential series of reactions catalyzed by discrete sets of protein machinery. The final reaction in clathrin-mediated endocytosis is membrane scission, which is mediated by the large guanosine triophosphate hydrolase (GTPase) dynamin and which may involve the actin-dependent recruitment of N-terminal containing BIN/Amphiphysin/RVS domain containing (N-BAR) proteins. Optical microscopy has revealed a detailed picture of when and where particular protein types are recruited in the ∼20–30 s preceding scission. Nevertheless, the regulatory mechanisms and functions that underpin protein recruitment are not well understood. Here we used an optical assay to investigate the coordination and interdependencies between the recruitment of dynamin, the actin cytoskeleton, and N-BAR proteins to individual clathrin-mediated endocytic scission events. These measurements revealed that a feedback loop exists between dynamin and actin at sites of membrane scission. The kinetics of dynamin, actin, and N-BAR protein recruitment were modulated by dynamin GTPase activity. Conversely, acute ablation of actin dynamics using latrunculin-B led to a ∼50% decrease in the incidence of scission, an ∼50% decrease in the amplitude of dynamin recruitment, and abolished actin and N-BAR recruitment to scission events. Collectively these data suggest that dynamin, actin, and N-BAR proteins work cooperatively to efficiently catalyze membrane scission. Dynamin controls its own recruitment to scission events by modulating the kinetics of actin and N-BAR recruitment to sites of scission. Conversely actin serves as a dynamic scaffold that concentrates dynamin and N-BAR proteins at sites of scission. PMID:22505844

  7. Experimental laboratory measurement of thermophysical properties of selected coal types

    NASA Technical Reports Server (NTRS)

    Lloyd, W. G.

    1979-01-01

    A number of bituminous coals of moderate to high plasticity were examined, along with portions of their extrudates from the JPL 1.5-inch 850 F screw extruder. Portions of the condensed pyrolysis liquids released during extrusion, and of the gaseous products formed during extrusion were also analyzed. In addition to the traditional determinations, the coals and extrudates were examined in terms of microstructure (especially extractable fractions), thermal analysis (especially that associated with the plastic state), and reactivity towards thermal and catalyzed hydroliquefaction. The process of extrusion increases the fixed carbon content of coals by about 5% and tends to increase the surface area. Coals contaning 25% or more DMF-extractable material show an increase in extractables as a result of extrusion; those initially containing less than 20% extractables show a decrease as a result of extrusion. Both the raw and extruded samples of Kentucky #9 coal are highly reactive towards hydroliquefaction, undergoing conversions of 75 to 80% in 15 min and 85-94% in 60 min in a stirred clave.

  8. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, April--June 1993

    SciTech Connect

    Song, Chunshan; Parfitt, D.P.; Schobert, H.H.

    1993-08-01

    The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular precursors, that can be used in low concentrations (hydroliquefaction of coals under temperature-programmed conditions. Several heterometallic complexes consisting of two transition metals, Mo and Co, and sulfur in a single molecule were synthesized and tested as precursors of bimetallic dispersed catalysts for liquefaction of a Montana subbituminous coal (DECS-9) at the loading level of 0.5 wt% Mo on dmmf coal. It was found that the structure of the precursors, in particular the ligands to the metal species, affect the activity of the resulting catalyst significantly. Among the M-M` type precursors tested, Mo-Co thiocubane, Mo{sub 2}Co{sub 2}S{sub 4}(Cp){sub 2}(CO){sub 2} [Cp = cyclopentadiene], designated as MoCo-TC2, produced in-situ the best catalyst The performance of the Mo-Co bimetallic catalyst was further enhanced by using temperature programmed (TPL) conditions consisting of a low temperature soaking at 200{degrees}C, programmed heat-up to 400 or 425{degrees}C followed by a 30 minutes hold. The pro ed heat-up serves as an in-situ activation of catalyst and coal pretreatment, which contributes to more effective hydrogenation of reactive fragments at high temperature.

  9. Viscoelastic behavior of polymers undergoing crosslinking reactions.

    NASA Technical Reports Server (NTRS)

    Moacanin, J.; Aklonis, J. J.

    1971-01-01

    Previously a method was developed for predicting the viscoelastic response of polymers undergoing scission reactions. These results are now extended to include crosslinking reactions. As for scission, at any given time the character of the network chains is determined by the instantaneous crosslink density. For scission all chains were assumed to carry the same stress; for crosslinking, however, the stress is distributed between the 'new' and 'old' chains. Equations for calculating the creep response of a system which experiences a step increase in crosslink density are derived.

  10. Dynamical simulation of energy dissipation in asymmetric heavy-ion induced fission of {sup 200}Pb, {sup 213}Fr, and {sup 251}Es

    SciTech Connect

    Mirfathi, S. M.; Pahlavani, M. R.

    2008-12-15

    The dynamical model based on the asymmetric mass division has been applied to calculate pre-scission neutron multiplicity from heavy-ion induced fusion-fission reactions. Links between the pre-scission neutron multiplicity, excitation energy, and asymmetric mass distribution are clarified based on the Monte Carlo simulation and Langevin dynamics. The pre-scission neutron multiplicity is calculated and compared with the respective experimental data over a wide range of excitation energy and nonconstant viscosity. The analysis indicates a different effect for the application of asymmetric mass division in different energy regions of such processes.

  11. Microscopic Calculations of 240Pu Fission

    SciTech Connect

    Younes, W; Gogny, D

    2007-09-11

    Hartree-Fock-Bogoliubov calculations have been performed with the Gogny finite-range effective interaction for {sup 240}Pu out to scission, using a new code developed at LLNL. A first set of calculations was performed with constrained quadrupole moment along the path of most probable fission, assuming axial symmetry but allowing for the spontaneous breaking of reflection symmetry of the nucleus. At a quadrupole moment of 345 b, the nucleus was found to spontaneously scission into two fragments. A second set of calculations, with all nuclear moments up to hexadecapole constrained, was performed to approach the scission configuration in a controlled manner. Calculated energies, moments, and representative plots of the total nuclear density are shown. The present calculations serve as a proof-of-principle, a blueprint, and starting-point solutions for a planned series of more comprehensive calculations to map out a large set of scission configurations, and the associated fission-fragment properties.

  12. Catalytic conversion of polycyclic aromatic hydrocarbons: Mechanistic investigations of hydrogen transfer from an iron-based catalyst to alkylarenes

    SciTech Connect

    Autrey, T.; Linehan, J.C.; Camaioni, D.M.; Powers, T.R.; McMillan, E.F.; Franz, J.A.

    1995-08-01

    Results of our model compound studies suggest that free radical hydrogen transfer pathways from the catalyst to the alkylarene are responsible for the scission of strong carbon-carbon bonds. There are two requisites for the observed selective bond scission. First is the stability of the ipso adduct precursor leading to displacement, the more stable the adduct the more probable bond scission. This explains why benzyl radical displacement > phenoxy radical displacement in benzyldiphenyl ether and explains why PhCH{sub 2}CH{sub 2}PhCH{sub 2} radical > naphthylmethyl radical from NMBB. Second, given equal ipso adduct precursor stabilities, e.g. methyldiphenylmethane, the stability of the departing radical determines the selectivity. this explains benzyl radical > methyl radical in the methylated diphenylmethanes and explains why {alpha}-hydroxyphenethyl radical > methyl radical in 1,2-ditolylethanol. We have assumed little physical interaction between the molecules and the catalytic surface and have been able to satisfactorily explain most of the observed selectivity. However, for NMBB we expect a higher selectivity for -A- bond scission relative to -B- bond scission, given the ca. 6 kcal/mol difference between the radical adduct formed by the hydrogen atom addition to 1-methylnaphthalene and p-xylene. It is possible that physical properties play a role in lowering the selectivity in -B- bond scission. Also, catalysts prepared by other methods may contain different activity sites and operate by different mechanisms.

  13. Ruthenium ion-catalyzed oxidation of Shenfu coal and its residues

    SciTech Connect

    Yao-Guo Huang; Zhi-Min Zong; Zi-Shuo Yao; Yu-Xuan Zheng; Jie Mou; Guang-Feng Liu; Jin-Pei Cao; Ming-Jie Ding; Ke-Ying Cai; Feng Wang; Wei Zhao; Zhi-Lin Xia; Lin Wu; Xian-Yong Wei

    2008-05-15

    Shenfu coal (SFC), its liquefaction residue (RL), and carbon disulfide (CS{sub 2})/tetrahydrofuran (THF)-inextractable matter (RE) were subject to ruthenium ion-catalyzed oxidation to understand the differences in structural features among the above three samples. The results suggest that SFC is rich in long-chain arylalkanes and {alpha}. {omega}-diarylalkanes (DAAs) with carbon number of methylene linkage from 2 to 4 and that long-chain arylalkanes and DAAs are reactive toward hydroliquefaction and soluble in a CS{sub 2}/THF mixed solvent, whereas highly condensed aromatic species in SFC show poor solubility in the CS{sub 2}/THF mixed solvent. 29 refs., 6 figs., 4 tabs.

  14. Activity and selectivity of Fe catalysts from organometallic and inorganic precursors for hydrocracking of 4-(1-naphthylmethyl) bibenzyl

    SciTech Connect

    Song, C.; Schmidt, E.; Schobert, H.H.

    1995-12-31

    Various iron containing catalysts have been investigated for their use in hydroliquefaction of coal ever since Bergius demonstrated the feasibility of the process. Conventional iron catalysts have been widely used either unsupported or as catalysts dispersed directly onto coal. Iron catalysts have generally a lower cost and lower environmental detriment than Mo, Ni and Co catalyst precursors. The search for active high surface area iron particles has become recently an important pan in the development of a cost effective direct coal liquefaction process. To examine what determines the activity and selectivity of Fe catalysts for hydrogenation and hydrocracking, various molecular precursors with Fe in different chemical environments have been tested in this work to help understand the influence of precursor structure and the effect of sulfur addition on the activity and selectivity of resulting Fe catalysts in model reactions of 4-(naphthylmethyl)bibenzyl (NMBB).

  15. New apparatus for simultaneous determination of phase equilibria and rheological properties of fluids at high pressures: Its application to coal pastes studies up to 773 K and 30 MPa

    NASA Astrophysics Data System (ADS)

    Cohen, Albert; Richon, Dominique

    1986-06-01

    In this article, we present a new apparatus based on a static method to simultaneously measure rheological properties of a dense (liquid or liquid+solid) medium and sample phases (dense and gaseous) for analysis purposes. It was especially designed to study coal pastes in the working conditions of hydroliquefaction processes. It can also be used to study other mediums such as asphalts and polymers. The rheometer part of the apparatus was already tested and results published in a previous paper. The ability of the new apparatus to get reliable vapor-liquid equilibrium data in the range of thermal stability of chemical materials is shown as a result of measurements on the nitrogen-n-heptane system at 497.1 K and the methane-n-hexadecane system at 623.1 K and comparison to literature's data. Reproducibility tests have displayed very small data dispersion.

  16. The chemistry and technology of synthetic fuels

    NASA Astrophysics Data System (ADS)

    Schriesheim, A.; Kirshenbaum, I.

    1981-10-01

    The variety of methods by which crude oil residua, coal and oil shale may be converted to synthetic fuels are considered, with attention to the chemical conversion processes that must be implemented on a large industrial scale. Among the technologies highlighted are (1) Flexicoking, in which residuum, preheated to 300 C, is sprayed into a reactor containing a fluidized solids bed of hot coke; the resulting thermal cracking of the residuum at 525 C forming gaseous and liquid products for conventional processing; (2) coal pyrolysis, a carbon rejection process that produces liquids, tars and coke; (3) hydroliquefaction, in which coal is liquefied directly by treatment with hydrogen at 450 C and pressures in the 70-200 atmospheres range; and (4) oil shale retorting, which is seen as requiring considerable further development before commercial feasibility is reached.

  17. Process and analytical studies of enhanced low severity co-processing using selective coal pretreatment

    SciTech Connect

    Baldwin, R.M.; Miller, R.L.

    1991-12-01

    The findings in the first phase were as follows: 1. Both reductive (non-selective) alkylation and selective oxygen alkylation brought about an increase in liquefaction reactivity for both coals. 2. Selective oxygen alkylation is more effective in enhancing the reactivity of low rank coals. In the second phase of studies, the major findings were as follows: 1. Liquefaction reactivity increases with increasing level of alkylation for both hydroliquefaction and co-processing reaction conditions. 2. the increase in reactivity found for O-alkylated Wyodak subbituminous coal is caused by chemical changes at phenolic and carboxylic functional sites. 3. O-methylation of Wyodak subbituminous coal reduced the apparent activation energy for liquefaction of this coal.

  18. Process and analytical studies of enhanced low severity co-processing using selective coal pretreatment. Final technical report

    SciTech Connect

    Baldwin, R.M.; Miller, R.L.

    1991-12-01

    The findings in the first phase were as follows: 1. Both reductive (non-selective) alkylation and selective oxygen alkylation brought about an increase in liquefaction reactivity for both coals. 2. Selective oxygen alkylation is more effective in enhancing the reactivity of low rank coals. In the second phase of studies, the major findings were as follows: 1. Liquefaction reactivity increases with increasing level of alkylation for both hydroliquefaction and co-processing reaction conditions. 2. the increase in reactivity found for O-alkylated Wyodak subbituminous coal is caused by chemical changes at phenolic and carboxylic functional sites. 3. O-methylation of Wyodak subbituminous coal reduced the apparent activation energy for liquefaction of this coal.

  19. Fabrication of nanochannels on polystyrene surface

    PubMed Central

    Li, Dongqing

    2015-01-01

    Solvent-induced nanocrack formation on polystyrene surface is investigated experimentally. Solubility parameter and diffusion coefficient of alcohols are employed to elucidate the swelling and cracking processes as well as the crack size. Experimental results show that the crack size increases with the heating temperature, heating time, and the concentration and volume of the alcohols. A guideline on fabricating single smaller nanocracks on polymers by solvent-induced method is provided. Nanocracks of approximately 64 nm in width and 17.4 nm in depth were created and replicated onto PDMS (polydimethylsiloxane) slabs to form nanochannels. PMID:25945143

  20. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, October--December 1992

    SciTech Connect

    Song, Chunshan; Schobert, H.H.

    1993-02-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

  1. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction

    SciTech Connect

    Song, Chunshan; Schobert, H.H.

    1993-02-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

  2. STYRENE IMPAIRS SERIAL SPATIAL REVERSAL LEARNING IN RATS

    EPA Science Inventory

    Occupational exposure to styrene monomer has been implicated in the etiology of solvent-induced cognitive dysfunction. o evaluate the effects of styrene exposure on learning, rats were trained on a series of reversals of a spatial discrimination, permitting repeated evaluation of...

  3. A DFT study on the initial stage of thermal degradation of Poly(methyl methacrylate)/carbon nanotube system.

    PubMed

    Minisini, Benoit; Vathonne, Emerson; Chivas-Joly, Carine; Lopez-Cuesta, José-Marie

    2013-02-01

    DFT calculations, with VWN exchange correlation functional and double numeric basis set, were used to evaluate the energies required for the scission reactions taking place in the initial stage of the thermal degradation of Poly(methyl methacrylate) (PMMA) in the presence of a carbon nanotube (CNT). Side group and main chain scissions were investigated. The results averaged from five configurations of pure PMMA (DP=5) were used as references and compared to the results obtained for the five same configurations of PMMA grafted on three carbon nanotubes of similar diameter (1.49 nm). The bond dissociation energies (BDE) of main chain scission evaluated for grafted PMMA was 4 % less endothermic than for pure PMMA. These results seemed independent of the tested chirality (11,11); (12,10) and (16,5) of the carbon nanotubes. Comparisons with the BDE of the weakest bonds due to intrinsic defaults (head to head and unsaturated end chain) were performed. PMID:22983652

  4. Electron beam irradiation of maltodextrin and cinnamyl alcohol mixtures: influence of glycerol on cross-linking.

    PubMed

    Khandal, Dhriti; Aggarwal, Manjeet; Suri, Gunjan; Coqueret, Xavier

    2015-03-01

    The influence of glycerol on the electron beam-induced changes in maltodextrins-cinnamyl alcohol (CA) blends is examined with respect to its influence on the degree of chain scission, grafting, and cross-linking. The study is relevant to radiation-induced polysaccharide modification, specifically in the perspective of using blended starch as a thermoplastic material, where glycerol is commonly used as a plasticizer. In the absence of CA, glycerol protects maltodextrin from chromophore formation onto the main chain, but also induces more chain scission. The presence of CA provides efficient radiation-protection against scission. Glycerol is shown to affect the interaction between maltodextrin and CA, most likely in the form of an inclusion complex when glycerol is absent. The global behavior under radiation is therefore governed by the physical interactions between the blend constituents rather than on the role of glycerol role as a plasticizer, or as an OH˙ radical scavenger. PMID:25498620

  5. The Effects of Electron Radiation on the Glass Transition Temperature of a Polyetherimide.

    NASA Astrophysics Data System (ADS)

    Kern, Kristen Tulloch

    The effects of electron radiation on a polyetherimide (PEI), Ultem^{cdot}, were investigated. In particular, the changes in the glass transition temperature (T_{g} ) with absorbed radiation dose were studied. The polymer was exposed to mono-energetic beams of 100-keV electrons and 1.0-MeV electrons for doses up to 100 megagray (MGy). Dosimetry for the exposures was based on Monte -Carlo simulations of the transfer of energy from an energetic electron to the polymer and on comparison to Nylon standards. Dynamic mechanical analysis was used to determine the T _{g} for non-exposed PEI and the changes in T_{g} resulting from irradiation. The T_{g} did not change significantly for doses up to and including 75 MGy, while a significant increase in T_ {g} occurred for a dose of 100 MGy. The cross-link and chain scission densities in the irradiated PEI were determined using infrared spectroscopy. The cross -link density increased with dose for all doses investigated. The chain scission density increased with dose for doses up to 75 MGy, but was lower for a dose of 100 MGy than for a dose of 75 MGy. Radical population kinetics, based in part on data from an electron paramagnetic resonance study, were correlated with the cross-link density and chain scission density to investigate the mechanism for the observed density variations with dose. The radical population simulations suggest that chain scissioning occurs less readily when the average radical separation during the exposure is less than three molecular radii. Finally, a model for the combined effects of cross-linking and chain scissioning is proposed which combines a statistical-mechanical model for the change in T_{g} with cross-link density and a free-volume model for the change in T _{g} with chain scission density.

  6. Irradiation of linear polyethylene - Partitioning between sol and gel.

    NASA Technical Reports Server (NTRS)

    Rijke, A. M.; Mandelkern, L.

    1971-01-01

    Investigation of the importance of chain-scission processes and of the applicability of the general theory of network formation to polyethylene with respect to critical conditions for gelation, using molecular weight fractions of linear polyethylene irradiated at 133 C. The partitioning between sol and gel was found to adhere to the theory just beyond the gel point. Deviations from theory occurred as the irradiation dosage was increased. It was concluded that main-chain scission at the temperatures concerned is not a significant process.

  7. Radiolytic stabilization of poly(hydroxybutyrate)

    NASA Astrophysics Data System (ADS)

    Santos, Renata F. S.; Araujo, Elmo S.; Ferreira, Carlas R. C.; Ribeiro, Abene S.

    2009-02-01

    Stabilization against gamma irradiation effects on Brazilian poly(hydroxybutyrate) (PHB) films was investigated by using commercial additives. With the most effective additive the G value of main chain scissions decreased from 8.6 to 1.5 scissions/100 eV in the absorbed dose range up to 35 kGy. Irradiation increased the biodegradability of the samples, whereas the additives-induced reduction in biodegradability. Irradiation treatment did not influence the degree of crystallinity. Protonic nuclear magnetic resonance (NMR- 1H) analysis revealed formation of hydroxyl-terminal groups upon irradiation.

  8. Thermochemistry of C-O, (CO)-O, and (CO)-C bond breaking in fatty acid methyl esters

    SciTech Connect

    Osmont, Antoine; Yahyaoui, Mohammed; Catoire, Laurent; Goekalp, Iskender; Swihart, Mark T.

    2008-10-15

    Density functional theory quantum chemical calculations corrected with empirical atomic increments have been used to examine C-O, (CO)-O, and (CO)-C bond scission enthalpies in gas-phase fatty acid methyl esters (FAMEs) present in biodiesel derived from rapeseed oil methyl ester and soybean oil methyl ester. Mechanistic information, currently not available elsewhere for these large species, is obtained based on thermochemical considerations and compared to thermochemical considerations reported for methyl butanoate, a small methyl ester sometimes used as a model for FAMEs. These results are compared to previously reported C-C and C-H bond scissions in these FAMEs, derived using this same protocol. (author)

  9. Stress-induced colouration and crosslinking of polymeric materials by mechanochemical formation of triphenylimidazolyl radicals.

    PubMed

    Verstraeten, F; Göstl, R; Sijbesma, R P

    2016-06-30

    Under mechanical stress, the hexaarylbiimidazole (HABI) motif can cleave to triphenylimidazolyl radicals when incorporated into a polymer matrix. The mechanically produced coloured radicals can initiate secondary radical reactions yielding polymer networks. Thus, the HABI mechanophore combines optical reporting of bond scission and reinforcement of polymers in a single molecular moiety. PMID:27326922

  10. Searching for New Long-Lived Shape Isomers

    NASA Astrophysics Data System (ADS)

    Kamanin, D. V.; Alexandrov, A. A.; Alexandrova, I. A.; Kondtatyev, N. A.; Kuznetsova, E. A.; Shvetsov, V. N.; Strekalovsky, A. O.; Strekalovsky, O. V.; Zhuchko, V. E.; Pyatkov, Yu. V.; Jacobs, N.; Malaza, V.

    2015-06-01

    According to theoretical predictions there is a possibility of an existence of shapeisomeric states in heavy nuclei based on ternary pre-scission configurations. Expected life time ranges up to some milliseconds. Preliminary result of the experiment dedicated to searching for such ling-lived shape-isomeric states in the compound system from the 235U(nth, f) reaction is presented.

  11. Methanol Oxidation on Pt3Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition.

    PubMed

    Lu, Xiaoqing; Deng, Zhigang; Guo, Chen; Wang, Weili; Wei, Shuxian; Ng, Siu-Pang; Chen, Xiangfeng; Ding, Ning; Guo, Wenyue; Wu, Chi-Man Lawrence

    2016-05-18

    PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt3Sn(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CHxOHy, x = 1-3, y = 0-1) were strongly adsorbed and preferred decomposition rather than desorption on Pt3Sn(111). The competitive methanol decomposition started with the initial O-H bond scission followed by successive C-H bond scissions, (i.e., CH3OH → CH3O → CH2O → CHO → CO). The Brønsted-Evans-Polanyi relations and energy barrier decomposition analyses identified the C-H and O-H bond scissions as being more competitive than the C-O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt3Sn(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure. PMID:27119198

  12. Repeatable mechanochemical activation of dynamic covalent bonds in thermoplastic elastomers.

    PubMed

    Imato, Keiichi; Kanehara, Takeshi; Nojima, Shiki; Ohishi, Tomoyuki; Higaki, Yuji; Takahara, Atsushi; Otsuka, Hideyuki

    2016-08-18

    Repeated mechanical scission and recombination of dynamic covalent bonds incorporated in segmented polyurethane elastomers are demonstrated by utilizing a diarylbibenzofuranone-based mechanophore and by the design of the segmented polymer structures. The repeated mechanochemical reactions can accompany clear colouration and simultaneous fading. PMID:27424868

  13. THE EFFECT OF MOLECULAR SIZE ON HUMIC ACID ASSOCIATIONS (R822832)

    EPA Science Inventory

    Abstract

    Aqueous solutions of two humic acids were subjected to UV photolysis, resulting in chain scission of the solute. The molecular fragments were found to have diminished detergent properties, indicated by a reduced tendency to associate with small hydrophobic spe...

  14. ENDONUCLEASE II OF E. coli, I. ISOLATION AND PURIFICATION*

    PubMed Central

    Friedberg, Errol C.; Goldthwait, David A.

    1969-01-01

    The isolation and purification of a new endonuclease of E. coli is described. This enzyme degrades alkylated DNA as assayed by a technique that requires double-strand scission. The enzyme also makes a limited number of single-strand breaks in native nonalkylated DNA. PMID:4895219

  15. Molecular weight distributions of irradiated siloxane-based elastomers: A complementary study by statistical modeling and multiple quantum nuclear magnetic resonance

    SciTech Connect

    Dinh, L. N.; Mayer, B. P.; Maiti, A.; Chinn, S. C.; Maxwell, R. S.

    2011-05-01

    The statistical methodology of population balance (PB) has been applied in order to predict the effects of cross-linking and chain-scissioning induced by ionizing radiation on the distribution of molecular weight between cross-links (MWBC) of a siloxane-based elastomer. Effective molecular weight distributions were extracted from the quantification of residual dipolar couplings via multiple quantum nuclear magnetic resonance (MQ-NMR) measurements and are taken to reflect actual MWBC distributions. The PB methodology is then applied to the unirradiated MWBC distribution and considers both chain-scissioning and the possibility of the formation of three types of cross-links: random recombination of scissioned-chain ends (end-linking), random covalent bonds of free radicals on scissioned-chain ends (Y-cross-linking), and the formation of random cross-links from free radicals on side groups (H-cross-linking). The qualitative agreement between the statistical modeling approach and the NMR data confirms that it is possible to predict trends for the evolution of the distribution of MWBC of polymers under irradiation. The approach described herein can also discern heterogeneities in radiation effects in different structural motifs in the polymer network.

  16. Multi angle laser light scattering evaluation of field exposed thermoplastic photovoltaic encapsulant materials

    DOE PAGESBeta

    Kempe, Michael D.; Miller, David C.; Wohlgemuth, John H.; Kurtz, Sarah R.; Moseley, John M.; Nobles, Dylan L.; Stika, Katherine M.; Brun, Yefim; Samuels, Sam L.; Shah, Qurat Annie; et al

    2016-01-08

    As creep of polymeric materials is potentially a safety concern for photovoltaic modules, the potential for module creep has become a significant topic of discussion in the development of IEC 61730 and IEC 61215. To investigate the possibility of creep, modules were constructed, using several thermoplastic encapsulant materials, into thin-film mock modules and deployed in Mesa, Arizona. The materials examined included poly(ethylene)-co-vinyl acetate (EVA, including formulations both cross-linked and with no curing agent), polyethylene/polyoctene copolymer (PO), poly(dimethylsiloxane) (PDMS), polyvinyl butyral (PVB), and thermoplastic polyurethane (TPU). The absence of creep in this experiment is attributable to several factors of which themore » most notable one was the unexpected cross-linking of an EVA formulation without a cross-linking agent. It was also found that some materials experienced both chain scission and cross-linking reactions, sometimes with a significant dependence on location within a module. The TPU and EVA samples were found to degrade with cross-linking reactions dominating over chain scission. In contrast, the PO materials degraded with chain scission dominating over cross-linking reactions. Furthermore, we found no significant indications that viscous creep is likely to occur in fielded modules capable of passing the qualification tests, we note that one should consider how a polymer degrades, chain scission or cross-linking, in assessing the suitability of a thermoplastic polymer in terrestrial photovoltaic applications.« less

  17. On the degelation of networks - Case of the radiochemical degradation of methyl methacrylate - ethylene glycol dimethacrylate copolymers

    NASA Astrophysics Data System (ADS)

    Richaud, Emmanuel; Gilormini, Pierre; Verdu, Jacques

    2016-05-01

    Methyl methacrylate networks were synthetized and submitted to radiochemical degradation. Ageing was monitored by means of sol-gel analysis and glass transition temperature measurements. Networks were shown to undergo exclusively chain scission process leading to the degelation of network. The critical conversion degree corresponding to degelation (loss of all elastically active chains) is discussed regarding a statistical theory.

  18. Site specific cleavage of thetaX-174 replicative form DNA after modification by N-acetoxy-N-2-acetylaminofluorene

    SciTech Connect

    Bases, R.; Mendez, F.; Mendez, L.

    1983-01-01

    Three kinds of structural disturbances were found in an 88 base pair (bp) fragment of thetaX-174 DNA after exposure to N-acetoxy-N-2-acetylaminofluorene (N-Aco-AAF). Frequent strand scissions at two specific guanine sites on the 5' /sup 32/P-end-labeled fragment were identified by base sequence analysis. Scissions at these two sites were induced at neutral pH and they were not increased by treatment with apurinic endonuclease. They are an immediate consequence of N-Aco-AAF action and are not primarily apurinic sites. Alkali treatment with 1 M piperidine at 90/sup 0/C induced strand scissions at every guanine, demonstrating adduct slices, depurination and strand scissions. Adducted DNA was sensitive to single-strand specific nuclease digestion, suggesting unwound DNA. These studies indicate the prediliction of N-Aco-AAF for certain DNA sites and they suggest three kinds of DNA modifications which can be expected after adduction by this carcinogen. Some of the sites may be premutational carcinogen-induced DNA structural modifications.

  19. Thermal stability and degradation of chitosan modified by benzophenone

    NASA Astrophysics Data System (ADS)

    Diab, M. A.; El-Sonbati, A. Z.; Bader, D. M. D.

    2011-09-01

    N-(biphenylmethylidenyl) chitosan polymer was prepared, characterized and thermal stability was compared with chitosan. Thermal degradation products of the modified polymer were identified by GC-MS technique. It seems that the mechanism of degradation of the prepared polymer is characterized by formation of low molecular weight radicals, followed by random scission mechanism along the backbond chain.

  20. Investigation of the reaction {sup 208}Pb({sup 18}O, f): Fragment spins and phenomenological analysis of the angular anisotropy of fission fragments

    SciTech Connect

    Rusanov, A. Ya. Adeev, G. D.; Itkis, M. G.; Karpov, A. V.; Nadtochy, P. N.; Pashkevich, V. V.; Pokrovsky, I. V.; Salamatin, V. S.; Chubarian, G. G.

    2007-10-15

    The average multiplicity of gamma rays emitted by fragments originating from the fission of {sup 226}Th nuclei formed via a complete fusion of {sup 18}O and {sup 208}Pb nuclei at laboratory energies of {sup 18}O projectile ions in the range E{sub lab} = 78-198.5 MeV is measured and analyzed. The total spins of fission fragments are found and used in an empirical analysis of the energy dependence of the anisotropy of these fragments under the assumption that their angular distributions are formed in the vicinity of the scission point. The average temperature of compound nuclei at the scission point and their average angular momenta in the entrance channel are found for this analysis. Also, the moments of inertia are calculated for this purpose for the chain of fissile thorium nuclei at the scission point. All of these parameters are determined at the scission point by means of three-dimensional dynamical calculations based on Langevin equations. A strong alignment of fragment spins is assumed in analyzing the anisotropy in question. In that case, the energy dependence of the anisotropy of fission fragments is faithfully reproduced at energies in excess of the Coulomb barrier (E{sub c.m.} - E{sub B} {>=} 30 MeV). It is assumed that, as the excitation energy and the angular momentum of a fissile nucleus are increased, the region where the angular distributions of fragments are formed is gradually shifted from the region of nuclear deformations in the vicinity of the saddle point to the region of nuclear deformations in the vicinity of the scission point, the total angular momentum of the nucleus undergoing fission being split into the orbital component, which is responsible for the anisotropy of fragments, and the spin component. This conclusion can be qualitatively explained on the basis of linear-response theory.

  1. A comparative theoretical study for the methanol dehydrogenation to CO over Pt3 and PtAu2 clusters.

    PubMed

    Zhong, Wenhui; Liu, Yuxia; Zhang, Dongju

    2012-07-01

    The density functional theory (DFT) calculations are carried out to study the mechanism details and the ensemble effect of methanol dehydrogenation over Pt(3) and PtAu(2) clusters, which present the smallest models of pure Pt clusters and bimetallic PtAu clusters. The energy diagrams are drawn out along both the initial O-H and C-H bond scission pathways via the four sequential dehydrogenation processes, respectively, i.e., CH(3)OH → CH(2)OH → CH(2)O → CHO → CO and CH(3)OH → CH(3)O → CH(2)O → CHO → CO, respectively. It is revealed that the reaction kinetics over PtAu(2) is significantly different from that over Pt(3). For the Pt(3)-mediated reaction, the C-H bond scission pathway, where an ensemble composed of two Pt atoms is required to complete methanol dehydrogenation, is energetically more favorable than the O-H bond scission pathway, and the maximum barrier along this pathway is calculated to be 12.99 kcal mol(-1). In contrast, PtAu(2) cluster facilitates the reaction starting from the O-H bond scission, where the Pt atom acts as the active center throughout each elementary step of methanol dehydrogenation, and the initial O-H bond scission with a barrier of 21.42 kcal mol(-1) is the bottom-neck step of methanol decomposition. Importantly, it is shown that the complete dehydrogenation product of methanol, CO, can more easily dissociate from PtAu(2) cluster than from Pt(3) cluster. The calculated results over the model clusters provide assistance to some extent for understanding the improved catalytic activity of bimetal PtAu catalysts toward methanol oxidation in comparison with pure Pt catalysts. PMID:22160734

  2. Ethanol decomposition on a Pd(110) surface: a density functional theory investigation.

    PubMed

    Guo, Wenyue; Li, Ming; Lu, Xiaoqing; Zhu, Houyu; Li, Yang; Li, Shaoren; Zhao, Lianming

    2013-02-14

    Ethanol decomposition on Pd(110) is comprehensively investigated using self-consistent periodic density functional theory. Geometries and energies for all the intermediates involved are analyzed, and the decomposition network is mapped out to illustrate the reaction mechanism. On Pd(110), the most stable adsorption of the involved species tends to follow the gas-phase bond order rules, wherein C is tetravalent and O is divalent with the missing H atoms replaced by metal atoms. The most likely decomposition pathway of ethanol on Pd(110) is CH(3)CH(2)OH → CH(3)CH(2)O → CH(3)CHO → CH(3)CO → CH(3) + CO → CO + H + CH(4) + C, in which the initial dehydrogenation is the rate-limited step. No C-O scission pathway is identified. Comparing with ethanol decomposition on Pd(111) [Langmuir, 2010, 26, 1879-1888], Pd(110) characterizes relatively high activity and different selectivity. Two crucial factors controlling the variations of reactivity and selectivity from Pd(111) to Pd(110), i.e., the local electronic effect of the metals and the geometrical effect of the relevant transition states, are identified. Four distinct Brønsted-Evans-Polanyi (BEP) relations are identified for the three types of bond scission (C-H, C-O, and C-C) if we consider Pd(111) and Pd(110) as a whole, one for C-H bond scission, one for C-O bond scission, and two for C-C bond scission. PMID:23169574

  3. Mechanical Stiffening of Porphyrin Nanorings through Supramolecular Columnar Stacking

    PubMed Central

    2013-01-01

    Solvent-induced aggregates of nanoring cyclic polymers may be transferred by electrospray deposition to a surface where they adsorb as three-dimensional columnar stacks. The observed stack height varies from single rings to four stacked rings with a layer spacing of 0.32 ± 0.04 nm as measured using scanning tunneling microscopy. The flexibility of the nanorings results in distortions from a circular shape, and we show, through a comparison with Monte Carlo simulations, that the bending stiffness increases linearly with the stack height. Our results show that noncovalent interactions may be used to control the shape and mechanical properties of artificial macromolecular aggregates offering a new route to solvent-induced control of two-dimensional supramolecular organization. PMID:23789845

  4. Effects of angiotensin, vasopressin and atrial natriuretic peptide on intraocular pressure in anesthetized rats

    NASA Technical Reports Server (NTRS)

    Palm, D. E.; Shue, S. G.; Keil, L. C.; Balaban, C. D.; Severs, W. B.

    1995-01-01

    The effects of atrial natriuretic peptide (ANP), vasopressin (AVP) and angiotensin (ANG) on blood and intraocular pressures of pentobarbital anesthetized rats were evaluated following intravenous, intracerebroventricular or anterior chamber routes of administration. Central injections did not affect intraocular pressure. Equipressor intravenous infusions of ANG raised, whereas AVP decreased, intraocular pressure. Direct infusions of a balanced salt solution (0.175 microliter/min) raised intraocular pressure between 30 and 60 min. Adding ANG or ANP slightly reduced this solvent effect but AVP was markedly inhibitory. An AVP-V1 receptor antagonist reversed the blunting of the solvent-induced rise by the peptide, indicating receptor specificity. Acetazolamide pretreatment lowered intraocular pressure, but the solvent-induced rise in intraocular pressure and inhibition by AVP still occurred without altering the temporal pattern. Thus, these effects appear unrelated to aqueous humor synthesis rate. The data support the possibility of intraocular pressure regulation by peptides acting from the blood and aqueous humor.

  5. Three-dimensional molecular theory of solvation coupled with molecular dynamics in Amber

    PubMed Central

    Luchko, Tyler; Gusarov, Sergey; Roe, Daniel R.; Simmerling, Carlos; Case, David A.; Tuszynski, Jack; Kovalenko, Andriy

    2010-01-01

    We present the three-dimensional molecular theory of solvation (also known as 3D-RISM) coupled with molecular dynamics (MD) simulation by contracting solvent degrees of freedom, accelerated by extrapolating solvent-induced forces and applying them in large multi-time steps (up to 20 fs) to enable simulation of large biomolecules. The method has been implemented in the Amber molecular modeling package, and is illustrated here on alanine dipeptide and protein G. PMID:20440377

  6. Simple, benign, aqueous-based amination of polycarbonate surfaces

    DOE PAGESBeta

    VanDelinder, Virginia; Wheeler, David R.; Small, Leo J.; Brumbach, Michael T.; Spoerke, Erik D.; Henderson, Ian; Bachand, George D.

    2015-03-18

    Here we report a simple, safe, environmentally-friendly aqueous method that uses diamines to functionalize a polycarbonate surface with amino groups. We demonstrate the ability of this facile method to serve as a foundation upon which other functionalities may be attached, including anti-fouling coatings and oriented membrane proteins. The use of water as the solvent for the functionalization ensures that solvent induced swelling does not affect the optical or mechanical properties of the polycarbonate.

  7. Comparative Investigation of Benzene Steam Reforming over Spinel Supported Rh and Ir Catalysts

    SciTech Connect

    Mei, Donghai; Lebarbier, Vanessa M.; Rousseau, Roger; Glezakou, Vassiliki-Alexandra; Albrecht, Karl O.; Kovarik, Libor; Flake, Matt; Dagle, Robert A.

    2013-06-07

    In a combined experimental and first-principles density functional theory (DFT) study, benzene steam reforming (BSR) over MgAl2O4 supported Rh and Ir catalysts was investigated. Experimentally, it has been found that both highly dispersed Rh and Ir clusters (1-2 nm) on the MgAl2O4 spinel support are stable during the BSR in the temperature range of 700-850°C. Compared to the Ir/MgAl2O4 catalyst, the Rh/MgAl2O4 catalyst is more active with higher benzene turnover frequency and conversion. At typical steam conditions with the steam-to-carbon ratio > 12, the benzene conversion is only a weak function of the H2O concentration in the feed. This suggests that the initial benzene decomposition step rather than the benzene adsorption is most likely the rate-determined step in BSR over supported Rh and Ir catalysts. In order to understand the differences between the two catalysts, we followed with a comparative DFT study of initial benzene decomposition pathways over two representative model systems for each supported metal (Rh and Ir) catalysts. A periodic terrace (111) surface and an amorphous 50-atom metal cluster with a diameter of 1.0 nm were used to represent the two supported model catalysts under low and high dispersion conditions. Our DFT results show that the decreasing catalyst particle size enhances the benzene decomposition on supported Rh catalysts by lowering both C-C and C-H bond scission. The activation barriers of the C-C and the C-H bond scission decrease from 1.60 and 1.61 eV on the Rh(111) surface to 1.34 and 1.26 eV on the Rh50 cluster. For supported Ir catalysts, the decreasing particle size only affects the C-C scission. The activation barrier of the C-C scission of benzene decreases from 1.60 eV on the Ir(111) surface to 1.35 eV on the Ir50 cluster while the barriers of the C-H scission are practically the same. The experimentally measured higher BSR

  8. Progress of fossil fuel science

    SciTech Connect

    Demirbas, M.F.

    2007-07-01

    Coal is the most abundant and widely distributed fossil fuel. More than 45% of the world's electricity is generated from coal, and it is the major fuel for generating electricity worldwide. The known coal reserves in the world are enough for more than 215 years of consumption, while the known oil reserves are only about 39 times of the world's consumption and the known natural gas reserves are about 63 times of the world's consumption level in 1998. In recent years, there have been effective scientific investigations on Turkish fossil fuels, which are considerable focused on coal resources. Coal is a major fossil fuel source for Turkey. Turkish coal consumption has been stable over the past decade and currently accounts for about 24% of the country's total energy consumption. Lignite coal has had the biggest share in total fossil fuel production, at 43%, in Turkey. Turkish researchers may investigate ten broad pathways of coal species upgrading, such as desulfurization and oxydesulfurization, pyrolysis and hydropyrolysis, liquefaction and hydroliquefaction, extraction and supercritical fluid extraction, gasification, oxidation, briquetting, flotation, and structure identification.

  9. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Final report

    SciTech Connect

    Chunshan Song; Schobert, H.H.; Parfitt, D.P.

    1997-11-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that dispersed catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on exploring novel bimetallic dispersed catalysts for coal liquefaction and the effectiveness of temperature-programmed liquefaction using dispersed catalysts. The primary objective of this research was to explore novel bimetallic dispersed catalysts from organometallic molecular precursors, that could be used in low concentrations but exhibit relatively high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. We have synthesized and tested various catalyst precursors in liquefaction of subbituminous and bituminous coals and in model compound studies to examine how do the composition and structure of the catalytic precursors affect their effectiveness for coal liquefaction under different reaction conditions, and how do these factors affect their catalytic functions for hydrogenation of polyaromatic hydrocarbons, for cleavage of C-C bonds in polycyclic systems such as 4-(1-naphthylmethyl)bibenzyl, for hydrogenolysis of C-O bond such as that in dinaphthylether, for hydrodeoxygenation of phenolic compounds and other oxygen-containing compounds such as xanthene, and for hydrodesulfurization of polycyclic sulfur compounds such as dibenzothiophene. The novel bimetallic and monometallic precursors synthesized and tested in this project include various Mo- and Fe-based compounds.

  10. Effect of pretreating of host oil on coprocessing

    SciTech Connect

    Hajdu, P.E.; Tierney, J.W.; Wender, I.

    1995-12-31

    The principal objective of this research was to determine if coprocessing performance (i.e., coal conversion and oil yield) could be significantly improved by pretreating the heavy resid prior to reacting it with coal. For this purpose, two petroleum vacuum resids (1000{degrees}F+), one from the Amoco Co. and another from the Citgo Co., were used as such and after they had been pretreated by catalytic hydrogenation and hydrocracking reactions. The pretreatments were aimed at improving the host oil by; (1) converting any aromatic structures in the petroleum to hydroaromatic compounds capable of donating hydrogen, (2) cracking the heavy oil to lower molecular weight material that might serve as a better solvent, (3) reducing the coking propensity of the heavy oil through the hydrogenation of polynuclear aromatic compounds, and (4) removing metals and heteroatoms that might poison a coprocessing catalyst. Highly dispersed catalysts, including fine particle Fe- and Mo-based, and dicobalt octacarbonyl, Co{sub 2}(CO){sub 8}, were used in this study. The untreated and pretreated resids were extensively characterized in order to determine chemical changes brought about by the pretreatments. The modified heavy oils were then coprocessed with an Illinois No. 6 coal as well as with a Wyodak coal, and compared to coprocessing with untreated resids under the same hydroliquefaction conditions. The amount of oil derived from coal was estimated by measuring the level of phenolic oxygen (derived mainly from coal) present in the oil products. Results are presented and discussed.

  11. Tryptophan Lyase (NosL): Mechanistic Insights from Substrate Analogues and Mutagenesis.

    PubMed

    Bhandari, Dhananjay M; Xu, Hui; Nicolet, Yvain; Fontecilla-Camps, Juan C; Begley, Tadhg P

    2015-08-11

    NosL is a member of a family of radical S-adenosylmethionine enzymes that catalyze the cleavage of the Cα-Cβ bond of aromatic amino acids. In this paper, we describe a set of experiments with substrate analogues and mutants for probing the early steps of the NosL mechanism. We provide biochemical evidence in support of the structural studies showing that the 5'-deoxyadenosyl radical abstracts a hydrogen atom from the amino group of tryptophan. We demonstrate that d-tryptophan is a substrate for NosL but shows relaxed regio control of the first β-scission reaction. Mutagenesis studies confirm that Arg323 is important for controlling the regiochemistry of the β-scission reaction and that Ser340 binds the substrate by hydrogen bonding to the indolic N1 atom. PMID:26204056

  12. Stability of a salicylate-based poly(anhydride-ester) to electron beam and gamma radiation

    PubMed Central

    Rosario-Meléndez, Roselin; Lavelle, Linda; Bodnar, Stanko; Halperin, Frederick; Harper, Ike; Griffin, Jeremy; Uhrich, Kathryn E.

    2011-01-01

    The effect of electron beam and gamma radiation on the physicochemical properties of a salicylate-based poly(anhydride-ester) was studied by exposing polymers to 0 (control), 25 and 50 kGy. After radiation exposure, salicylic acid release in vitro was monitored to assess any changes in drug release profiles. Molecular weight, glass transition temperature and decomposition temperature were evaluated for polymer chain scission and/or crosslinking as well as changes in thermal properties. Proton nuclear magnetic resonance and infrared spectroscopies were also used to determine polymer degradation and/or chain scission. In vitro cell studies were performed to identify cytocompatibility following radiation exposure. These studies demonstrate that the physicochemical properties of the polymer are not substantially affected by exposure to electron beam and gamma radiation. PMID:21909173

  13. A Density Functional Theory Analysis of Trends in Glycerol Decomposition on Close-Packed Transition Metal Surfaces

    SciTech Connect

    Liu, Bin; Greeley, Jeffrey P.

    2013-05-07

    We describe an accelerated density functional theory (DFT)-based computational strategy to determine trends in the decomposition of glycerol via elementary dehydrogenation, C–C, and C–O bond scission reactions on close-packed transition metal surfaces. Beginning with periodic DFT calculations on Pt(111), the thermochemistry of glycerol dehydrogenation on Pd(111), Rh(111), Cu(111) and Ni(111) is determined using a parameter-free, bond order-based scaling relationship. By combining the results with Brønsted–Evans–Polanyi (BEP) relationships to estimate elementary reaction barriers, free energy diagrams are developed on the respective metal surfaces, and trends concerning the relative selectivity and activity for C–C and C–O bond scission in glycerol on the various metals are obtained. The results are consistent with available theoretical and experimental literature and demonstrate that scaling relationships are capable of providing powerful insights into the catalytic chemistry of complex biomolecules.

  14. Irradiation of linear polyethylene - Partitioning between sol and gel.

    NASA Technical Reports Server (NTRS)

    Rijke, A. M.; Mandelkern, L.

    1971-01-01

    Molecular weight fractions of linear polyethylene were irradiated at 133 C, in the completely molten and highly crystalline states, for the purpose of assessing the importance of chain-scission processes and establishing the critical conditions for gelation. The partitioning between sol and gel in either state was found to adhere to the theory for the intermolecular cross-linking of monodisperse species for dosages just beyond the gel point. Deviations from theory occurred as the dosage was increased further. It was concluded that main-chain scission, at these temperatures, is not a significant process. High molecular weight samples in the completely molten state obeyed the Flory-Stockmayer condition for critical gelation.

  15. New experimental approaches to investigate the fission dynamics

    NASA Astrophysics Data System (ADS)

    Benlliure, J.; Rodríguez-Sánchez, J. L.; Alvarez-Pol, H.; Audouin, L.; Ayyad, Y.; Bélier, G.; Boutoux, G.; Casarejos, E.; Chatillon, A.; Cortina-Gil, D.; Gorbinet, T.; Heinz, A.; Kelić-Heil, A.; Laurent, B.; Martin, J.-F.; Paradela, C.; Pellereau, E.; Pietras, B.; Ramos, D.; Rodríguez-Tajes, C.; Rossi, D. M.; Simon, H.; Taïeb, J.; Vargas, J.; Voss, B.

    2016-07-01

    The first ever achieved full identification of both fission fragments, in atomic and mass number, made it possible to define new observables sensitive to the fission dynamics along the fission path up to the scission point. Moreover, proton-induced fission of 208Pb at high energies offers optimal conditions for the investigation of dissipative, and transient effects, because of the high-excitation energy of the fissioning nuclei, its low angular momentum, and limited shape distortion by the reaction. In this work we show that the charge distribution of the final fission fragments can constrain the ground-to-saddle dynamics while the mass distribution is sensitive to the dynamics until the scission point.

  16. Effects of nuclear deformation in dinuclear systems: Application to the fission process

    SciTech Connect

    Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.; Ivanova, S. P. Scheid, W.

    2006-02-15

    The relative yields of fission fragments, the mean values of their total kinetic energy, and the variances of their distributions with respect to the total kinetic energy are described within the improved scission-point model. It is shown that, for fixed charge and mass numbers of fragments, the potential energy of the precision configuration as a function of the deformation parameters of the fragments has several minima. The scission at these minima leads to a relative enhancement of the yields of the fragments that have the corresponding values of the total kinetic energy and to the appearance of a fine structure in the mass-energy distribution, this structure being different from that induced by the even-odd effect.

  17. Evaporation residue cross sections for the {sup 64}Ni + {sup 144,154}Sm reaction -- Energy dissipation in hot nuclei

    SciTech Connect

    Back, B.B.; Blumenthal, D.J.; Davids, C.N.

    1995-08-01

    The fission hindrance of hot nuclei was deduced recently from an enhanced emission of GDR {gamma} rays, neutrons and charged particles prior to scission of heavy nuclei. In the most recent experiments addressing this topic, namely new measurements of the pre-scission {gamma} rays and evaporation residues from the {sup 32}S + {sup 184}W reaction, a rather sharp transition from negligible to full one-body dissipation occurs over the excitation energy region E{sub exc} = 60-100 MeV. However, the cross section does not appear to level out or start to decline again at the upper end of the energy range as expected in this interpretation. It is therefore clearly desirable to extend the excitation energy range to look for such an effect in order to either corroborate or refute this interpretation.

  18. Membrane Fission Is Promoted by Insertion of Amphipathic Helices and Is Restricted by Crescent BAR Domains

    PubMed Central

    Boucrot, Emmanuel; Pick, Adi; Çamdere, Gamze; Liska, Nicole; Evergren, Emma; McMahon, Harvey T.; Kozlov, Michael M.

    2012-01-01

    Summary Shallow hydrophobic insertions and crescent-shaped BAR scaffolds promote membrane curvature. Here, we investigate membrane fission by shallow hydrophobic insertions quantitatively and mechanistically. We provide evidence that membrane insertion of the ENTH domain of epsin leads to liposome vesiculation, and that epsin is required for clathrin-coated vesicle budding in cells. We also show that BAR-domain scaffolds from endophilin, amphiphysin, GRAF, and β2-centaurin limit membrane fission driven by hydrophobic insertions. A quantitative assay for vesiculation reveals an antagonistic relationship between amphipathic helices and scaffolds of N-BAR domains in fission. The extent of vesiculation by these proteins and vesicle size depend on the number and length of amphipathic helices per BAR domain, in accord with theoretical considerations. This fission mechanism gives a new framework for understanding membrane scission in the absence of mechanoenzymes such as dynamin and suggests how Arf and Sar proteins work in vesicle scission. PMID:22464325

  19. Modeling Initial Stage of Ablation Material Pyrolysis: Graphitic Precursor Formation and Interfacial Effects

    NASA Technical Reports Server (NTRS)

    Desai, Tapan G.; Lawson, John W.; Keblinski, Pawel

    2010-01-01

    Reactive molecular dynamics simulations are used to study initial stage of pyrolysis of ablation materials and their composites with carbon nanotubes and carbon fibers. The products formed during pyrolysis are characterized and water is found as the primary product in all cases. The water formation mechanisms are analyzed and the value of the activation energy for water formation is estimated. A detailed study on graphitic precursor formation reveals the presence of two temperature zones. In the lower temperature zone (less than 2000 K) polymerization occurs resulting in formation of large, stable graphitic precursors, and in the high temperature zone (greater than 2000 K) polymer scission results in formation of short polymer chains/molecules. Simulations performed in the high temperature zone on the phenolic resin composites (with carbon nanotubes and carbon fibers) shows that the presence of interfaces had no substantial effect on the chain scission rate or the activation energy value for water formation.

  20. On-line and post irradiation analysis of swift heavy ion induced modification of PMMA (polymethyl-methacrylate)

    NASA Astrophysics Data System (ADS)

    Hossain, U. H.; Lima, V.; Baake, O.; Severin, D.; Bender, M.; Ensinger, W.

    2014-05-01

    The present work is part of a research program studying the swift heavy ion induced modification of aliphatic polymers with some comparable side groups, here polymethyl-methacrylate (PMMA). This paper presents a study on Fourier-transform-infrared spectroscopy (FTIR), residual gas analysis (RGA), and Ultraviolet-Visible (UV-Vis) spectroscopy of the transformations of a PMMA film under gold (Au) and uranium (U) ion irradiation in the MeV/u range in vacuum to fluences up to 3 × 1011 ions per cm2. The results show a general ion induced degradation of the polymer, with release of volatile fragments, scission of side chains and polymeric backbone, formation of conjugated double bonds, and the resulting increased absorption of the UV part in the UV-Vis spectral region. A molecular scission mechanism which explains the main degradation products is proposed.

  1. Solubilisation of tomato fruit pectins by ascorbate: a possible non-enzymic mechanism of fruit softening.

    PubMed

    Dumville, Jo C; Fry, Stephen C

    2003-10-01

    The aim of this work was to test the hypothesis that endogenous ascorbate, released into the apoplast by membrane permeabilisation early in fruit ripening, could promote the solubilisation and depolymerisation of polysaccharides, and thus contribute to fruit softening. In vitro, ascorbate (1 mM), especially in the presence of traces of either Cu2+ or H2O2, solubilised up to 40% of the total pectin from the alcohol-insoluble residue of mature-green tomato (Lycopersicon esculentum Mill.) fruit. Solubilisation was due to the action of ascorbate-generated hydroxyl radicals (*OH), which can cause non-enzymic scission of polysaccharides. The pectins solubilised by ascorbate in vitro were polydisperse (4-1,000 kDa), partially esterified and galactose-rich. Excised pieces of living tomato fruit released ascorbate into the medium (apoplast); the ability of different tissues to do this increased in the order pericarp < placenta < locule. In all three tissues, but especially in the locule, the ability to release ascorbate increased during ripening. The Cu content of each tissue also increased during ripening, whereas neither Fe nor Mn showed a similar trend. We suggest that progressively increasing levels of Cu and ascorbate in the fruit apoplast would lead to elevated *OH production there and thus to non-enzymic scission of pectins during ripening. Such scission could contribute to the natural softening of the fruit. De-esterified citrus pectin was more susceptible to ascorbate-induced scission in vitro than methylesterified pectin, suggesting a possible new significance for pectin methylesterase activity in fruit ripening. In conclusion, non-enzymic mechanisms of fruit softening should be considered alongside the probable roles of hydrolases, xyloglucan endotransglucosylases and expansins. PMID:12838420

  2. The role of the cytoskeleton and molecular motors in endosomal dynamics.

    PubMed

    Granger, Elizabeth; McNee, Gavin; Allan, Victoria; Woodman, Philip

    2014-07-01

    The endocytic pathway is essential for processes that define how cells interact with their environment, including receptor signalling, cell adhesion and migration, pathogen entry, membrane protein turnover and nutrient uptake. The spatial organisation of endocytic trafficking requires motor proteins that tether membranes or transport them along the actin and microtubule cytoskeletons. Microtubules, actin filaments and motor proteins also provide force to deform and assist in the scission of membranes, thereby facilitating endosomal sorting and the generation of transport intermediates. PMID:24727350

  3. The study of ionizing radiation effects on polypropylene and rice husk ash composite

    NASA Astrophysics Data System (ADS)

    Alfaro, E. F.; Dias, D. B.; Silva, L. G. A.

    2013-03-01

    The aim of this work was to study the ionizing radiation effects on polypropylene/20% of rice husk ash composites. The composites were irradiated by electron beam at different doses and the mechanical and thermal properties were evaluated using tensile strength, Izod impact, hardness, softening temperature, differential scanning calorimetry (DSC) and thermogravimetry (TG). The results showed that the properties decreased by increasing irradiation dose due to chain scission.

  4. N-Methylmorpholine-N-oxide ring cleavage registration by ESR under heating conditions of the Lyocell process.

    PubMed

    Konkin, A; Wendler, F; Meister, F; Roth, H-K; Aganov, A; Ambacher, O

    2008-03-01

    Thermal cleavage processes of N-methylmorpholine-N-oxide monohydrate (NMMO) were observed in pure NMMO as well as in cellulose/NMMO solutions by ESR at temperatures of the industrial Lyocell process ( approximately 370K). Generated radicals were attributed to the alkylnitroxyl type radicals -CH(2)-NO-CH(3) in NMMO and additional (and dominated) -CH(2)-NO-CH(2)- in cellulose/NMMO solutions. Formation of both radical types formed due to NMMO ring scission is suggested. PMID:17686653

  5. The role of the cytoskeleton and molecular motors in endosomal dynamics

    PubMed Central

    Granger, Elizabeth; McNee, Gavin; Allan, Victoria; Woodman, Philip

    2014-01-01

    The endocytic pathway is essential for processes that define how cells interact with their environment, including receptor signalling, cell adhesion and migration, pathogen entry, membrane protein turnover and nutrient uptake. The spatial organisation of endocytic trafficking requires motor proteins that tether membranes or transport them along the actin and microtubule cytoskeletons. Microtubules, actin filaments and motor proteins also provide force to deform and assist in the scission of membranes, thereby facilitating endosomal sorting and the generation of transport intermediates. PMID:24727350

  6. Protection in radiolysis of n-hexadecane—I. Radiolysis of pure liquid n-hexadecane

    NASA Astrophysics Data System (ADS)

    Soebianto, Yanti S.; Yamaguchi, Tetsuro; Katsumura, Yosuke; Ishigure, Kenkichi; Kubo, Junichi; Koizumi, Takeo

    Radiolysis of pure liquid n-hexadecane under vacuum has been studied to obtain greater understanding about the effect of radiation on open chain polymers such as polyethylene. Gas chromatography, gel permeation chromatography and mass spectrometry have been used to analyze the radiolysis products and their yields have been determined. The gas products mainly contain H 2, the condensed products contain saturated and unsaturated scission products, hexadecene and crosslink products. Mass analysis of the condensed products shows unsaturations in the crosslink products.

  7. Economic efficiency and effectiveness of ways of separating materials electro diamond processing

    NASA Astrophysics Data System (ADS)

    Khafizov, I. I.

    2016-06-01

    Purveying operations on the division of all types of materials include a hand and machine scission on the equipment of the different setting. In an engineer there is reliable information about the mastered methods, their maximum possibilities and defects. With the increase of stake of expenses there was a problem of research of new types of division of materials on materials, especially it touched scarce and expensive alloys.

  8. Conjugation-Driven "Reverse Mars-van Krevelen"-Type Radical Mechanism for Low-Temperature C-O Bond Activation.

    PubMed

    Mironenko, Alexander V; Vlachos, Dionisios G

    2016-07-01

    C-O bond activation on monofunctional catalysts (metals, carbides, and oxides) is challenging due to activity constraints imposed by energy scaling relationships. Yet, contrary to predictions, recently discovered multifunctional metal/metal oxide catalysts (e.g., Rh/ReOx, Rh/MoOx, Ir/VOx) demonstrate unusually high C-O scission activity at moderate temperatures. Herein, we use extensive density functional theory calculations, first-principles microkinetic modeling, and electronic structure analysis to elucidate the metal/metal oxide synergy in the Ru/RuO2 catalyst, which enables up to 76% yield of the C-O scission product (2-methyl furan) in catalytic transfer hydrogenolysis of furfural at low temperatures. Our key mechanistic finding is a facile radical-mediated C-O bond activation on RuO2 oxygen vacancies, which directly leads to a weakly bound final product. This is the first time the radical reduction mechanism is reported in heterogeneous catalysis at temperatures <200 °C. We attribute the unique catalytic properties to the formation of a conjugation-stabilized furfuryl radical upon C-O bond scission, the strong hydroxyl affinity of oxygen vacancies due to the metallic character of RuO2, and the acid-base heterogeneity of the oxide surface. The conjugation-driven radical-assisted C-O bond scission applies to any catalytic surface that preserves the π-electron system of the reactant and leads to C-O selectivity enhancement, with notable examples including Cu, H-covered Pd, self-assembled monolayers on Pd, and oxygen-covered Mo2C. Furthermore, we reveal the cooperativity of active sites in multifunctional catalysts. The mechanism is fully consistent with kinetic studies and isotopic labeling experiments, and the insights gained might prove useful more broadly in overcoming activity constraints induced by energy scaling relationships. PMID:27281043

  9. Unexpected Photo-instability of 2,6-Sulfonamide-Substituted BODIPYs and Its Application to Caged GABA.

    PubMed

    Takeda, Aoi; Komatsu, Toru; Nomura, Hiroshi; Naka, Masamitsu; Matsuki, Norio; Ikegaya, Yuji; Terai, Takuya; Ueno, Tasuku; Hanaoka, Kenjiro; Nagano, Tetsuo; Urano, Yasuteru

    2016-07-01

    Investigation of the unexpected photo-instability of 2,6-sulfonamide-substituted derivatives of the boron dipyrromethene (BODIPY) fluorophore led to the discovery of a photoreaction accompanied by multiple bond scissions. We characterized the photoproducts and utilized the photoreaction to design a caged γ-aminobutyric acid (GABA) derivative that can release GABA upon irradiation in the visible range (>450 nm). This allowed us to stimulate neural cells in mouse brain slices. PMID:27038199

  10. 1,2,5-Oxadiazole analogues of leflunomide and related compounds.

    PubMed

    Giorgis, Marta; Lolli, Marco Lucio; Rolando, Barbara; Rao, Angela; Tosco, Paolo; Chaurasia, Shilpi; Marabello, Domenica; Fruttero, Roberta; Gasco, Alberto

    2011-01-01

    A new series of compounds, structurally related to leflunomide, based on the 1,2,5-oxadiazole ring system (furazan) has been synthesised, and their ability to undergo ring scission at physiological pH to afford the corresponding cyano-oximes has been analyzed. The latter, together with the respective nitro derivatives obtained by oxidation, have been characterised as weak inhibitors of rat dihydroorotate dehydrogenase (DHODH). PMID:21109332

  11. O2 Plasma Etch Rate Reduction on Synchrotron Radiation Exposed PMMA Film

    NASA Astrophysics Data System (ADS)

    Saito, Kunio; Yoshikawa, Akira

    1987-09-01

    The etch rate of PMMA film in O2 plasma is found to be reduced by synchrotron radiation (SR) exposure. This phenomenon is accompanied by a reduction in film thickness. IR and XPS analyses reveal that this thickness reduction is caused by scission and removal of the ester side chain. Etch rate of the SR-exposed film decreases to about 1/3 of the unexposed film. This characteristic makes dry-development possible.

  12. Lithographic Evaluation Of Copolymers With Enhanced Dry Etch Resistance

    NASA Astrophysics Data System (ADS)

    Namaste, Y. M.; Obendorf, S. K.; Rosenblum, J. M.; Gifford, G. G.; Dems, B. C.; Rodriguez, F.

    1987-08-01

    Alternating copolymers of alphamethylstyrene (AMS) with maleic anhydride (MA) and methyl maleate (MeM) are evaluated as positive electron resists. The chain scission efficiency (Gs) of P(AMS-MA), determined by exposure to 50 keV electrons, is 0.90 scissions/100 eV. When the maleic anhydride in the copolymer is reacted with sodium methoxide to form its methyl ester, P(AMS-MeM), the Gs increases to 2.9 for electrons and to 3.5 for gamma radiation. Based on these G-scission values, this copolymer is expected to exhibit enhanced sensitivity, while having good dry etch resistance due to the aromatic nature of alphamethylstyrene. Lithographically, P(AMS-MeM) is more sensitive than P(AMS-MA), as expected from G-scission data. Film properties such as adhesion are also superior for P(AMS-MeM). Using a one hour prebake at 140°C, 10% thinning of unexposed P(AMS-MeM) occurs upon development of pads exposed to an incident electron dose of 8 jC/cm2 (accelerating voltage = 20 kV). The contrast (1) is 2.0 for development of 12 iiC/cm exposur2es. In comparison, P(AMS-MA) exhibited 10% thinning for an incident dose of 40 pC/cm, which is similar to observations with PMMA. The copolymers are developed with mixtures of ethyl 3-ethoxypropionate and 1-methoxy-2-propanol acetate. The dry etch rate of P(AMS-MA) in CFI.' plasma with 8% 02 varies from 45 to 53% of the etch rate of a PMMA standard. The etch rate of P(AMS-MeM) after a 140°C prebake is about 65% that of PMMA. Thus, much of the etch resistance of alphamethylstyrene is maintained in copolymers with maleic anhydride or methyl maleate, while the copolymer with methyl maleate also exhibits significantly enhanced sensitivity.

  13. Energy dependence of fission observables

    NASA Astrophysics Data System (ADS)

    Paşca, Horia

    2016-01-01

    The mass, charge and isotopic distributions of fission fragments are studied within an improved scission-point statistical model in the reaction 235U+n at different energies of the incident neutron. The available experimental data are well reproduced and the energy-dependencies of the observable characteristics of fission are predicted for future experiments. The calculated mass distribution of 238U+n is also compared with experimental data.

  14. Superfluid fission dynamics with microscopic approaches

    NASA Astrophysics Data System (ADS)

    Simenel, C.; Scamps, G.; Lacroix, D.; Umar, A. S.

    2016-01-01

    Recent progresses in the description of the latter stage of nuclear fission are reported. Dynamical effects during the descent of the potential towards scission and in the formation of the fission fragments are studied with the time-dependent Hartree-Fock approach with dynamical pairing correlations at the BCS level. In particular, this approach is used to compute the final kinetic energy of the fission fragments. Comparison with experimental data on the fission of 258Fm are made.

  15. A theoretical and experimental study of unimolecular and biomolecular radical hydrogen transfer reactions

    SciTech Connect

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

    1991-04-01

    We have examined the intramolecular radical hydrogen transfer (RHT) reaction of the 2-(2-phenylethyl)cyclohexadienyl radical. Intramolecular hydrogen shift from the cyclohexadienyl ring to the ipso position of the phenyl ring, followed by {beta}-scission would have given benzene and ethylbenzene as products. Competing with this reaction is {beta}-scission to give benzyl radical and isotoluene, or hydrogen loss to give bibenzyl. Studies to date suggest a barrier for thermoneutral hydrogen transfer in the RHT reaction between aromatic systems of ca. 18 kcal/mole. None of the studies of RHT or equivalent mechanisms have attempted to directly observe H{sub 2}, and direct determination of Arrhenius parameters and a detailed examination of the pathway of the hydrogen transfer process remains to be carried out. To better understand the structural and energetic aspects of RHT, we have carried out a semiempirical molecular orbital study of bimolecular and intramolecular RHT reactions for a variety of aromatic systems. We also examined in detail the energetics of hydrogen transfer between ethyl radical and ethylene via RHT, an addition/metathesis/scission pathway, and a hybrid concerted'' pathway. 11 refs., 1 fig., 4 tabs.

  16. Irradiation effects on polymer-model compounds

    NASA Astrophysics Data System (ADS)

    Seguchi, Tadao; Katsumura, Yosuke; Hayashi, Nariyuki; Hayakawa, Naohiro; Tamura, Naoyuki; Tabata, Yoneho

    Irradiation effects on n-paraffins and squalane, used as models of polymers, were investigated by product analysis. Four n-paraffins, C 20H 42, C 21H 44, C 23H 48 and C 24H 50, and squalane (C 30H 62) were γ-irradiated under vacuum in liquid, crystalline and glassy states. The evolved gases were analyzed by gas chromatography and changes in molecular weight were analyzed by liquid chromatography and mass spectroscopy. G-values for crosslinking of n-paraffins were 1.2 for crystalline states (at 25°C) and 1.7 for liquid states (at 55°C), and showed no difference between odd and even carbon numbers. The G-value of liquid squalane was 1.7; it was 1.3 for the glassy state at low temperature (-77°C). Double bonds were common in the crosslinked products, especially after liquid-phase irradiation. The probability of chain scission was estimated as being negligible, though a small number of chain-scission products (which were products of scission at chain-ends or side chains) were observed by gas analysis.

  17. Phosphorylation Regulates the Endocytic Function of the Yeast Dynamin-Related Protein Vps1.

    PubMed

    Smaczynska-de Rooij, Iwona I; Marklew, Christopher J; Allwood, Ellen G; Palmer, Sarah E; Booth, Wesley I; Mishra, Ritu; Goldberg, Martin W; Ayscough, Kathryn R

    2016-03-01

    The family of dynamin proteins is known to function in many eukaryotic membrane fusion and fission events. The yeast dynamin-related protein Vps1 functions at several stages of membrane trafficking, including Golgi apparatus to endosome and vacuole, peroxisomal fission, and endocytic scission. We have previously shown that in its endocytic role, Vps1 functions with the amphiphysin heterodimer Rvs161/Rvs167 to facilitate scission and release of vesicles. Phosphoproteome studies of Saccharomyces cerevisiae have identified a phosphorylation site in Vps1 at serine 599. In this study, we confirmed this phosphorylation event, and we reveal that, like Rvs167, Vps1 can be phosphorylated by the yeast cyclin-associated kinase Pho85 in vivo and in vitro. The importance of this posttranslational modification was revealed when mutagenesis of S599 to a phosphomimetic or nonphosphorylatable form caused defects in endocytosis but not in other functions associated with Vps1. Mutation to nonphosphorylatable valine inhibited the Rvs167 interaction, while both S599V and S599D caused defects in vesicle scission, as shown by both live-cell imaging and electron microscopy of endocytic invaginations. Our data support a model in which phosphorylation and dephosphorylation of Vps1 promote distinct interactions and highlight the importance of such regulatory events in facilitating sequential progression of the endocytic process. PMID:26711254

  18. Interactions between lac repressor protein and site-specific bromodeoxyuridine-substituted operator DNA. Ultraviolet footprinting and protein-DNA cross-link formation

    SciTech Connect

    Wick, K.L.; Matthews, K.S. )

    1991-04-05

    Specific contacts between the lac repressor and operator have been explored using 5-bromodeoxyuridine-substituted DNA. Substitution of BrdU for single thymidine positions in a synthetic 40-base pair operator provides substrate for ultraviolet irradiation; upon irradiation, strand scission occurs at the BrdU residues. When bound, lac repressor protein provides protection against UV-induced breakage depending on the nature of the sites and type of interaction. We have confirmed 13 unique sites of inducer-sensitive protection along the operator sequence using this method compared to complete substitution with BrdU; differences were observed at two positions for singly substituted versus completely substituted DNAs. The ability of these photosensitive DNAs to form short range cross-links to bound protein has been used to determine the efficiency with which cross-linked protein-DNA complexes are generated at each individual site of BrdU substitution. Five sites of high efficiency cross-linking to the repressor protein have been identified. At one site, cross-linking without protection from strand scission was observed; this result suggests an unusual mechanism of strand scission and/or cross-linking at this site. Comparison of the UV protection results and the cross-linking data show that these processes provide complementary tools for identifying and analyzing individual protein-DNA contacts.

  19. Role of carbon-carbon phenyl migration in the pyrolysis mechanism of β-O-4 lignin model compounds: phenethyl phenyl ether and α-hydroxy phenethyl phenyl ether.

    PubMed

    Beste, Ariana; Buchanan, A C

    2012-12-20

    We investigate phenyl shift and subsequent β-scission reactions for PhCHXCH·OPh [X = H, OH], which are part of the pyrolysis mechanism of phenethyl phenyl ether (PPE) and α-hydroxy PPE. PPE and its derivatives are model compounds for the most common linkage in lignin, the β-O-4 linkage. We use density functional theory to locate transition states and equilibrium structures and kinetic Monte Carlo in combination with transition-state theory for kinetic simulations. Oxygen-carbon and carbon-carbon phenyl shift reactions proceed through cyclic intermediates with similar barriers. However, while subsequent β-scission of the oxygen-carbon shift products proceeds with virtually no barrier, the activation energy for β-scission of the carbon-carbon shift products exceeds 15 kcal/mol. We found that about 15% of β-radical conversion can be attributed to carbon-carbon shift for PPE and α-hydroxy PPE at 618 K. Whereas the oxygen-carbon shift reaction has been established as an integral part of the pyrolysis mechanism of PPE and its derivatives, participation of the carbon-carbon shift reaction has not been shown previously. PMID:23194314

  20. The role of carbon-carbon phenyl migration in the pyrolysis mechanism of beta-O-4 lignin model compounds: phenethyl phenyl ether and alpha-hydroxy phenethyl phenyl ether

    SciTech Connect

    Beste, Ariana; Buchanan III, A C

    2012-01-01

    We investigate phenyl shift and subsequent beta-scission reactions for PhCHXCHOPh [X = H, OH], which are part of the pyrolysis mechanism of phenethyl phenyl ether (PPE) and alpha-hydroxy PPE. PPE and its derivatives are model compounds for the most common linkage in lignin, the beta-O-4 linkage. We use density functional theory to locate transition states and equilibrium structures, and kinetic Monte Carlo in combination with transition state theory for kinetic simulations. Oxygen-carbon and carbon-carbon phenyl shift reactions proceed through cyclic intermediates with similar barriers. But, while subsequent beta-scission of the oxygen-carbon shift products proceeds with virtually no barrier, the activation energy for beta-scission of the carbon-carbon shift products exceeds 15 kcal/mol. We found that about 15 % of beta-radical conversion can be attributed to carbon-carbon shift for PPE and alpha-hydroxy PPE at 618 K. Whereas the oxygen-carbon shift reaction has been established as an integral part of the pyrolysis mechanism of PPE and its derivatives, participation of the carbon-carbon shift reaction has not been shown previously.

  1. Aging studies of Kevlar 49 fibers

    SciTech Connect

    Morgan, R.J.; Pruneda, C.O.; Kong, F.M.

    1983-11-01

    The aging mechanisms in service environment of Kevlar 49 fibers, E.I. duPont, (poly(p-phenylene)terephthalamide) are reviewed. The principal aging mechanisms considered are (i) u.v.-, (ii) hydrolytic- and (iii) stress-induced macromolecular chain scission and microvoid growth. U.V.-induced strength degradation can be significant as a result of photo-oxidative and photodegradative radical formation but in Kevlar 49-epoxy composites only the exterior yarn layer is deteriorated. Hydrolytic chain scission of the amide linkage and corresponding fiber strength deterioration is considered in terms of R.H., time, temperature and stress level. The rates of hydrolytic degradation at 100% R.H. in the 100 to 200/sup 0/C range are reported. The estimated rates of fiber degradation in various service environment conditions are also reported and shown not to be serious. The stress-induced aging of Kevlar 49 fibers is considered in terms of the growth and coalescence of inherent microvoids along the fiber axis together with the generation of new microvoids. (These growth processes involve no detectable macromolecular chain scission or deterioration in fiber strength.) At a critical microvoid volume fraction catastrophic failure occurs by interconnection of such voids.

  2. Phosphorylation Regulates the Endocytic Function of the Yeast Dynamin-Related Protein Vps1

    PubMed Central

    Smaczynska-de Rooij, Iwona I.; Marklew, Christopher J.; Allwood, Ellen G.; Palmer, Sarah E.; Booth, Wesley I.; Mishra, Ritu; Goldberg, Martin W.

    2015-01-01

    The family of dynamin proteins is known to function in many eukaryotic membrane fusion and fission events. The yeast dynamin-related protein Vps1 functions at several stages of membrane trafficking, including Golgi apparatus to endosome and vacuole, peroxisomal fission, and endocytic scission. We have previously shown that in its endocytic role, Vps1 functions with the amphiphysin heterodimer Rvs161/Rvs167 to facilitate scission and release of vesicles. Phosphoproteome studies of Saccharomyces cerevisiae have identified a phosphorylation site in Vps1 at serine 599. In this study, we confirmed this phosphorylation event, and we reveal that, like Rvs167, Vps1 can be phosphorylated by the yeast cyclin-associated kinase Pho85 in vivo and in vitro. The importance of this posttranslational modification was revealed when mutagenesis of S599 to a phosphomimetic or nonphosphorylatable form caused defects in endocytosis but not in other functions associated with Vps1. Mutation to nonphosphorylatable valine inhibited the Rvs167 interaction, while both S599V and S599D caused defects in vesicle scission, as shown by both live-cell imaging and electron microscopy of endocytic invaginations. Our data support a model in which phosphorylation and dephosphorylation of Vps1 promote distinct interactions and highlight the importance of such regulatory events in facilitating sequential progression of the endocytic process. PMID:26711254

  3. Dynamin-Actin Cross Talk Contributes to Phagosome Formation and Closure.

    PubMed

    Marie-Anaïs, Florence; Mazzolini, Julie; Herit, Floriane; Niedergang, Florence

    2016-05-01

    Phagocytosis is a mechanism used by macrophages to internalize and eliminate microorganisms or cellular debris. It relies on profound rearrangements of the actin cytoskeleton that is the driving force allowing plasma membrane extension around the particle. The closure step of phagocytosis, however, remains poorly defined. We used a dedicated experimental setup with Total Internal Reflection Fluorescence Microscopy (TIRFM) to monitor phagosome formation and closure in three dimensions in living cells. We show that dynamin-2, which mediates the scission of endocytic vesicles, was recruited early and concomitantly with actin during phagosome formation. Dynamin-2 accumulated at the site of phagosome closure in living macrophages. Inhibition of its activity with dominant negative mutants or drugs demonstrated that dynamin-2 is implicated in actin dynamics and pseudopod extension. Depolymerization of actin led to impaired dynamin-2 recruitment or activity. Finally, we show that dynamin-2 plays a critical role in the effective scission of the phagosome from the plasma membrane. Thus, we establish that a cross talk between actin and dynamin takes place for phagosome formation and closure before dynamin functions for scission. PMID:26847957

  4. Surface chemistry of palladium

    SciTech Connect

    Gentle, T.M.

    1984-05-01

    Several classes of catalytically important molecules on Pd single crystals were studied. Influence of surface structure and composition on reactions involving formation and scission of carbon-carbon and carbon-hydrogen bonds was investigated under uhv conditions on single crystals and higher pressures on polycrystalline films. Reactions of acetylene on Pd(111), Pd(100), and Pd(110) were studied using thermal desorption spectroscopy, chemical displacement reactions, and isotopic labeling techniques. Pd single crystals catalyzes trimerization to benzene, hydrogenation to ethylene, and hydrosilation with trimethylsilane. Several atoms such as Si, P, S, and Cl have a profound influence on the catalysis. Single-crystal Pd surfaces catalyzes the dehydrogenation of organosilanes; silacyclohexane chemisorbed on Pd(110) underwent dehydrogenation upon thermal desorption to form silabenzene. Desulfurization products were observed in the thermal desorption spectra chemisorbed thiophene, 3-methylthiophene, and 2,5-dimethylthiophene. Mechanisms of carbon-hydrogen bond scission were investigated for a variety of methyl-substituted benzenes, revealing some degree of regiospecificity in C-H bond scission. Several reactions of unsaturated hydrocarbons were also investigated at higher pressures (10/sup -2/ torr) on polycrystalline Pd films.

  5. The influence of gamma radiation on the molecular weight and glass transition of PLLA and HAp/PLLA nanocomposite

    NASA Astrophysics Data System (ADS)

    Milicevic, D.; Trifunovic, S.; Dojcilovic, J.; Ignjatovic, N.; Suljovrujic, E.

    2010-09-01

    The influence of gamma radiation on the molecular weight and glass transition behaviour of poly- L-lactide (PLLA) and hydroxyapatite/poly- L-lactide (HAp/PLLA) nanocomposite has been studied. Since PLLA exposed to high-energy radiation in the presence of air is prone to chain scission reactions and large degradation, changes in molecular weight were obtained by gel permeation chromatography (GPC). Alterations in the glass transition behaviour were investigated by differential scanning calorimetry (DSC). The apparent activation energy (Δ H∗) for glass transition was determined on the basis of the heating rate dependence of the glass transition temperature ( T g). Our findings support the fact that chain scission is the main reason for the decrease of T g and Δ H∗ with the absorbed dose. Furthermore, more intensive chain scission degradation of PLLA was observed in HAp/PLLA and can only be ascribed to the presence of HAp nanoparticles. Consequently, initial differences in the glass transition temperature and/or apparent activation energy of PLLA and HAp/PLLA became more pronounced with absorbed dose. This study reveals that radiation-induced changes in molecular weight and glass transition temperature occur in a predictable and fairly accurate manner. Therefore, gamma radiation can be used not only for sterilization but also for tailoring desirable end-use properties of these biomaterials.

  6. Solid state photochemistry of polycarbonates

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Rembaum, A.; Moacanin, J.

    1978-01-01

    The quantum yield of photoFries rearrangement in a polycarbonate film has been analyzed as a function of temperature and humidity on the basis of previously reported (Koyler and Mann, 1977) experimental data. Results indicate that in the homogeneous amorphous phase, photoFries rearrangement is a concerted process proceeding either from the pi star reversed arrow n singlet, in which case it must be subject to considerable self quenching, or from a triplet, presumably the first triplet since the lifetime of higher triplets is expected to be very short in the solid phase. If the parent excited state is the first triplet, chain scission is possibly an independent process, probably occurring from the pi star reversed arrow n singlet. Evidence of chain scission on photodegradation in the solid state includes loss of C-O and C-C bond intensities revealed in the Fourier transform infrared spectra, gel permeation chromotography elution profiles of degraded film samples dissolved in CHCl3, and a decrease in tensile strength and T sub g as photodegradation proceeds. Chain scission is apparently inhibited as photoFries products accumulate.

  7. Inertial solvent dynamics and the analysis of spectral line shapes: Temperature-dependent absorption spectrum of beta-carotene in nonpolar solvent.

    PubMed

    Burt, Jim A; Zhao, Xihua; McHale, Jeanne L

    2004-03-01

    The influence of solvent dynamics on optical spectra is often described by a stochastic model which assumes exponential relaxation of the time-correlation function for solvent-induced frequency fluctuations. In contrast, theory and experiment suggest that the initial (subpicosecond) phase of solvent relaxation, resulting from inertial motion of the solvent, is a Gaussian function of time. In this work, we employ numerical and analytical calculations to compare the predicted absorption line shapes and the derived solvent reorganization energies obtained from exponential (Brownian oscillator) versus Gaussian (inertial) solvent dynamics. Both models predict motional narrowing as the ratio kappa = Lambda/Delta is increased, where Lambda and Delta are the frequency and variance, respectively, of the solvent-induced frequency fluctuations. However, the motional narrowing limit is achieved at lower values of kappa for the Brownian oscillator model compared to the inertial model. For a given line shape, the derived value of the solvent reorganization energy lambdasolv is only weakly dependent on the solvent relaxation model employed, though different solvent parameters Lambda and Delta are obtained. The two models are applied to the analysis of the temperature-dependent absorption spectrum of beta-carotene in isopentane and CS2. The derived values of lambdasolv using the Gaussian model are found to be in better agreement with the high temperature limit of Delta2/2kBT than are the values obtained using the Brownian oscillator model. In either approach, the solvent reorganization energy is found to increase slightly with temperature as a result of an increase in the variance Delta of the solvent-induced frequency fluctuations. PMID:15268604

  8. Inertial solvent dynamics and the analysis of spectral line shapes: Temperature-dependent absorption spectrum of β-carotene in nonpolar solvent

    NASA Astrophysics Data System (ADS)

    Burt, Jim A.; Zhao, Xihua; McHale, Jeanne L.

    2004-03-01

    The influence of solvent dynamics on optical spectra is often described by a stochastic model which assumes exponential relaxation of the time-correlation function for solvent-induced frequency fluctuations. In contrast, theory and experiment suggest that the initial (subpicosecond) phase of solvent relaxation, resulting from inertial motion of the solvent, is a Gaussian function of time. In this work, we employ numerical and analytical calculations to compare the predicted absorption line shapes and the derived solvent reorganization energies obtained from exponential (Brownian oscillator) versus Gaussian (inertial) solvent dynamics. Both models predict motional narrowing as the ratio κ=Λ/Δ is increased, where Λ and Δ are the frequency and variance, respectively, of the solvent-induced frequency fluctuations. However, the motional narrowing limit is achieved at lower values of κ for the Brownian oscillator model compared to the inertial model. For a given line shape, the derived value of the solvent reorganization energy λsolv is only weakly dependent on the solvent relaxation model employed, though different solvent parameters Λ and Δ are obtained. The two models are applied to the analysis of the temperature-dependent absorption spectrum of β-carotene in isopentane and CS2. The derived values of λsolv using the Gaussian model are found to be in better agreement with the high temperature limit of Δ2/2kBT than are the values obtained using the Brownian oscillator model. In either approach, the solvent reorganization energy is found to increase slightly with temperature as a result of an increase in the variance Δ of the solvent-induced frequency fluctuations.

  9. Regio- and stereochemically controlled formation of hydroxamic acids from indium triflate-mediated nucleophilic ring-opening reactions with acylnitroso-Diels–Alder adducts

    PubMed Central

    Yang, Baiyuan; Miller, Marvin J.

    2010-01-01

    Treatment of acylnitroso-Diels–Alder [2.2.1] bicyclic adducts 2a–b with indium triflate in an alcohol solvent induces ring opening reactions to afford monocyclic anti-1,2-, anti-1,4- and syn-1,4-hydroxamic acids with good to excellent regio- and stereoselectivity (up to 7:86:7). Treatment of [2.2.2] bicyclic nitroso adducts 2c–d under similar reaction conditions generates only anti-1,2- and anti-1,4-hydroxamic acids with anti-1,4-product predominant (up to 17:83). PMID:20209116

  10. CH 2 Cl 2 + OH - Reaction in Aqueous Solution: A Combined Quantum Mechanical and Molecular Mechanics Study

    SciTech Connect

    Wang, Dunyou; Valiev, Marat; Garrett, Bruce C.

    2011-03-03

    The CH2Cl2 + OH- reaction in aqueous solution was investigated using combined quantum mechanical and molecular mechanics approach. We present analysis of the reactant, transition, and product state structures, and calculate the free energy reaction profile through the CCSD(T) level of the theory for the reactive region. Our results show that the aqueous environment has a significant impact on the reaction process raising the reaction barrier by ~17 kcal/mol and the reaction energy by ~20 kcal/mol. While solvation effects play a predominant role, we also find sizable contributions from solvent-induced polarization effects.