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Sample records for imide oligomers endcapped

  1. Imide Oligomers Endcapped with Phenylethynl Phthalic Anhydrides and Polymers Therefrom

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Smith, Joseph G., Jr. (Inventor)

    1998-01-01

    Controlled molecular weight phenylethynyl terminated imide oligomers (PETIs) have been prepared by the cyclodehydration of precursor phenylethynyl terminated amic acid oligomers. Amino terminated amic acid oligomers are prepared from the reaction of dianhydride(s) with an excess of diamine(s) and subsequently endcapped with phenylethynyl phthalic anhydride(s) (PEPA). The polymerizations are carried out in polar aprotic solvents such as N-methyl-2-pyrrolidinone or N.N-dimethylacetamide under nitrogen at room temperature. The amic acid oligomers are subsequently cyclodehydrated either thermally or cheznicauy to the corresponding imide oligomers. Direct preparation of PETIs from the reaction of dianhydxide(s) with an excess of diamine(s) and endcapped with phenylethynyl phthalic anhydride(s) has been performed in m-cresol. Phenylethynyl phthalic anhydrides are synthesized by the palladium catalyzed reaction of phenylacetylene with bromo substituted phthalic anhydrides in triethylamine. These new materials exhibit excellent properties and are potentially useful as adhesives, coatings, films, moldings and composite matrices.

  2. Imide oligomers endcapped with phenylethynyl phthalic anhydrides and polymers therefrom

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Smith, Jr., Joseph G. (Inventor)

    1996-01-01

    Controlled molecular weight phenylethynyl terminated imide oligomers (PETIs) have been prepared by the cyclodehydration of precursor phenylethynyl terminated amic acid oligomers. Amino terminated amic acid oligomers are prepared from the reaction of dianhydride(s) with an excess of diamine(s) and subsequently endcapped with phenylethynyl phthalic anhydride(s) (PEPA). The polymerizations are carried out in polar aprotic solvents such as N-methyl-2-pyrrolidinone or N,N-dimethylacetamide under nitrogen at room temperature. The amic acid oligomers are subsequently cyclodehydrated either thermally or chemically to the corresponding imide oligomers. Direct preparation of PETIs from the reaction of dianhydride(s) with an excess of diamine(s) and endcapped with phenylethynyl phthalic anhydride(s) has been performed in m-cresol. Phenylethynyl phthalic anhydrides are synthesized by the palladium catalyzed reaction of phenylacetylene with bromo substituted phthalic anhydrides in triethylamine. These new materials exhibit excellent properties and are potentially useful as adhesives, coatings, films, moldings and composite matrices.

  3. Phenylethynyl terminated imide oligomers

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Bryant, Robert G. (Inventor); Jensen, Brian J. (Inventor); Havens, Stephen J. (Inventor)

    1995-01-01

    Four phenylethynyl amine compounds - 3 and 4-aminophenoxy-4'-phenylethynylbenzophenone, and 3 and 4-amino-4'-phenylethynylbenzophenone - were readily prepared and were used to endcap imide oligomers. Phenylethynyl-terminated amide acid oligomers and phenylethynyl-terminated imide oligomers with various molecular weights and compositions were prepared and characterized. These oligomers were cured at 300 to 400 C to provide crosslinked polyimides with excellent solvent resistance, high strength and modulus, and good high temperature properties. Adhesive panels, composites, films, and moldings from these phenylethynyl terminated imide oligomers gave excellent mechanical performance.

  4. Characterization of geometric isomers of Norbornene end-capped imides

    NASA Technical Reports Server (NTRS)

    Young, P. R.; Chang, A. C.

    1983-01-01

    Three geometric isomers from the thermal isomerization of methylene-4,4' bis(endo-N-phenylbicyclo/2.2.1/hept-2-ene-5,6-di carboximide) (I) were chromatographically separated and isolated in order to investigate the thermal cure of norbornene end-capped imide oligomers, which display considerable promise for use in various aerospace adhesive and composite applications. Endo-endo (I), endo-exo (II), and exo-exo (III) configurations were assigned to each compound based on the results of NMR spectroscopy. Several chromatographic, spectroscopic, and thermal techniques were then used to characterize these three isomers which serve as model compounds for norbornene end-capped polyimides. It was found that each compound thermally isomerized to an equilibrium mixture of all three compounds prior to cure. It is proposed that these compounds react by different mechanisms in air and nitrogen.

  5. Liquid crystalline thermosets from ester, ester-imide, and ester-amide oligomers

    NASA Technical Reports Server (NTRS)

    Dingemans, Theodorous J. (Inventor); Weiser, Erik S. (Inventor); St. Clair, Terry L. (Inventor)

    2005-01-01

    Main chain thermotropic liquid crystal esters, ester-imides, and ester-amides were prepared from AA, BB, and AB type monomeric materials and were end-capped with phenylacetylene, phenylmaleimide, or nadimide reactive end-groups. The resulting reactive end-capped liquid crystal oligomers exhibit a variety of improved and preferred physical properties. The end-capped liquid crystal oligomers are thermotropic and have, preferably, molecular weights in the range of approximately 1000-15,000 grams per mole. The end-capped liquid crystal oligomers have broad liquid crystalline melting ranges and exhibit high melt stability and very low melt viscosities at accessible temperatures. The end-capped liquid crystal oligomers are stable for up to an hour in the melt phase. These properties make the end-capped liquid crystal oligomers highly processable by a variety of melt process shape forming and blending techniques including film extrusion, fiber spinning, reactive injection molding (RIM), resin transfer molding (RTM), resin film injection (RFI), powder molding, pultrusion, injection molding, blow molding, plasma spraying and thermo-forming. Once processed and shaped, the end-capped liquid crystal oligomers were heated to further polymerize and form liquid crystalline thermosets (LCT). The fully cured products are rubbers above their glass transition temperatures. The resulting thermosets display many properties that are superior to their non-end-capped high molecular weight analogs.

  6. Solvent free low-melt viscosity imide oligomers and thermosetting polymide composites

    NASA Technical Reports Server (NTRS)

    Chuang, Chun-Hua (Inventor)

    2012-01-01

    .[.This invention relates to the composition and a solvent-free process for preparing novel imide oligomers and polymers specifically formulated with effective amounts of a dianhydride such as 2,3,3',4-biphenyltetra carboxylic dianydride (a-BPDA), at least one aromatic diamine and an endcapped of 4-phenylethynylphthalic anhydride (PEPA) or nadic anhydride to produce imide oligomers that possess a low-melt viscosity of 1-60 poise at 260-280.degree. C. When the imide oligomer melt is cured at about 371.degree. C. in a press or autoclave under 100-500 psi, the melt resulted in a thermoset polyimide having a glass transition temperature (T.sub.g) equal to and above 310.degree. C. A novel feature of this process is that the monomers; namely the dianhydrides, diamines and the endcaps, are melt processable to form imide oligomers at temperatures ranging between 232-280.degree. C. (450-535.degree. F.) without any solvent. These low-melt imide oligomers can be easily processed by resin transfer molding (RTM), vacuum-assisted resin transfer molding (VARTM) or the resin infusion process with fiber preforms e.g. carbon, glass or quartz preforms to produce polyimide matrix composites with 288-343.degree. C. (550-650.degree. F.) high temperature performance capability..]. .Iadd.This invention relates to compositions and a solvent-free reaction process for preparing imide oligomers and polymers specifically derived from effective amounts of dianhydrides such as 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), at least one aromatic polyamine and an end-cap such as 4-phenylethynyphthalic anhydride (PEPA) or nadic anhydride to produce imide oligomers that possess a low-melt viscosity of 1-60 poise at 260.degree. C.-280.degree. C..Iaddend.

  7. Liquid Crystalline Thermosets from Ester, Ester-imide, and Ester-amide Oligomers

    NASA Technical Reports Server (NTRS)

    Dingemans, Theodorus J. (Inventor); Weiser, Erik S. (Inventor); St. Clair, Terry L. (Inventor)

    2009-01-01

    Main chain thermotropic liquid crystal esters, ester-imides, and ester-amides were prepared from AA, BB, and AB type monomeric materials and end-capped with phenylacetylene, phenylmaleimide, or nadimide reactive end-groups. The end-capped liquid crystal oligomers are thermotropic and have, preferably, molecular weights in the range of approximately 1000-15,000 grams per mole. The end-capped liquid crystaloligomers have broad liquid crystalline melting ranges and exhibit high melt stability and very low melt viscosities at accessible temperatures. The end-capped liquid crystal oli-gomers are stable forup to an hour in the melt phase. They are highly processable by a variety of melt process shape forming and blending techniques. Once processed and shaped, the end-capped liquid crystal oigomers were heated to further polymerize and form liquid crystalline thermosets (LCT). The fully cured products are rubbers above their glass transition temperatures.

  8. Liquid Crystalline Thermosets from Ester, Ester-Imide, and Ester-Amide Oligomers

    NASA Technical Reports Server (NTRS)

    Dingemans, Theodornus J. (Inventor); Weiser, Erik S. (Inventor); SaintClair, Terry L. (Inventor)

    2005-01-01

    Main chain thermotropic liquid crystal esters, ester-imides, and ester-amides were prepared from AA, BB, and AB type monomeric materials and were end-capped with phenylacetylene, phenylmaleimide, or nadimide reactive end-groups. The resulting reactive end-capped liquid crystal oligomers exhibit a variety of improved and preferred physical properties. The end-capped liquid crystal oligomers are thermotropic and have, preferably, molecular weights in the range of approximately 1000-15,OOO grams per mole. The end-capped liquid crystal oligomers have broad liquid crystalline melting ranges and exhibit high melt stability and very low melt viscosities at accessible temperatures. The end-capped liquid crystal oligomers are stable for up to an hour in the melt phase. These properties make the end-capped liquid crystal oligomers highly processable by a variety of melt process shape forming and blending techniques including film extrusion, fiber spinning, reactive injection molding (RIM), resin transfer molding (RTM), resin film injection (RFI), powder molding, pultrusion, injection molding, blow molding, plasma spraying and thermo-forming. Once processed and shaped, the end- capped liquid crystal oligomers were heated to further polymerize and form liquid crystalline thermosets (LCT). The fully cured products are rubbers above their glass transition temperatures. The resulting thermosets display many properties that are superior to their non-end-capped high molecular weight analogs.

  9. Solvent Free Low-Melt Viscosity Imide Oligomers And Thermosetting Polyimide Composites

    NASA Technical Reports Server (NTRS)

    Chuang, CHun-Hua (Inventor)

    2006-01-01

    This invention relates to the composition and a solvent-free process for preparing novel imide oligomers and polymers specifically formulated with effective amounts of a dianhydride such as 2,3,3',4-biphenyltetra carboxylic dianydride (a-BPDA), at least one aromatic diamine' and an endcapped of 4-phenylethynylphthalic anhydride (PEPA) or nadic anhydride to produce imide oligomers that possess a low-melt viscosity of 1-60 poise at 260-280" C. When the imide oligomer melt is cured at about 371 C. in a press or autoclave under 100-500 psi, the melt resulted in a thermoset polyimide having a glass transition temperature (T(sub g)) equal to and above 310 C. A novel feature of this process is that the monomers; namely the dianhydrides, diamines and the endcaps, are melt processable to form imide oligomers at temperatures ranging between 232-280 C. (450-535 F) without any solvent. These low-melt imide oligomers can be easily processed by resin transfer molding (RTM), vacuum-assisted resin transfer molding (VARTM) or the resin infusion process with fiber preforms e.g. carbon, glass or quartz preforms to produce polyimide matrix composites with 288-343C (550-650 F) high temperature performance capability.

  10. Curing chemistry of phenylethynyl-terminated imide oligomers: Model compounds, carbon-13 labeling and cure analysis

    NASA Astrophysics Data System (ADS)

    Roberts, Christopher Chad

    1998-11-01

    Phenylethynyl-terminated imide oligomers (PETI) are currently considered the state-of-the-art high performance resins for aerospace applications. The processing of these resins is more facile because of their low molecular weight, but PETI's cure to form a tough, solvent-resistant material. However, the final cure structure was a complete mystery. Hence, the present study was set forth with three essential goals. The determination of the final structure of the crosslinked polymer is of obvious importance. Second, the crosslinking mechanism and controlling factors is also of interest. Lastly, the final structure of the crosslinked polymers was correlated with mechanical and thermal properties, thereby helping to establish the structure-processing-properties relationships for PETI resins. These goals were accomplished by using a combination of synthesis of model compounds synthesis and proposed cure products, sp{13}C labeling of the ethynyl endgroup in PETI's, monitoring of the thermal cure using solid state sp{13}C NMR and ESR and molecular modeling techniques. Phenylethynyl endcapping agents, 4-(phenylethynyl)phthalic anhydride (PEPA) and 3-(phenylethynyl)aniline (3PEA), were synthesized via the palladium-catalyzed coupling of phenylacetylene with 4-bromophthalic anhydride or 3-iodonitrobenzene followed by reduction to 3PEA, respectively. Isolated yields of 41 and 86% for 3PEA and PEPA were obtained, respectively. Model compounds were synthesized from 3PEA and PEPA by reacting with them the appropriate aniline or phthalic anhydride derivative. Model compounds included N-pentafluorophenyl-4-(phenylethynyl)phthalimide (PEPA/F5An), N-(4-trifluoromethyl-phenyl)4-(phenylethynyl)phthalimide (PEPA/F3CAn), N-lbrack 3-(phenylethynyl)phenylrbrack\\ phthalimide (3PEA/PA), N-phenyl-4-(phenylethynyl)phthalimide (PEPA/An), N-(4-phenoxyphenyl)4-(phenylethynyl)phthalimide (PEPA/POAn), and N-(1-naphthyl)-4-(phenylethynyl)phthalimide (PEPA/Anaph). Proposed cure products such as

  11. Synthesis of imide/arylene ether copolymers for adhesives and composite matrices

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Hergenrother, P. M.; Bass, R. G.

    1991-01-01

    A series of imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was endcapped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesion and composite properties.

  12. Curing chemistry of phenylethynyl-terminated imide oligomers: Model compounds, carbon-13 labeling and cure analysis

    NASA Astrophysics Data System (ADS)

    Roberts, Christopher Chad

    1998-11-01

    Phenylethynyl-terminated imide oligomers (PETI) are currently considered the state-of-the-art high performance resins for aerospace applications. The processing of these resins is more facile because of their low molecular weight, but PETI's cure to form a tough, solvent-resistant material. However, the final cure structure was a complete mystery. Hence, the present study was set forth with three essential goals. The determination of the final structure of the crosslinked polymer is of obvious importance. Second, the crosslinking mechanism and controlling factors is also of interest. Lastly, the final structure of the crosslinked polymers was correlated with mechanical and thermal properties, thereby helping to establish the structure-processing-properties relationships for PETI resins. These goals were accomplished by using a combination of synthesis of model compounds synthesis and proposed cure products, sp{13}C labeling of the ethynyl endgroup in PETI's, monitoring of the thermal cure using solid state sp{13}C NMR and ESR and molecular modeling techniques. Phenylethynyl endcapping agents, 4-(phenylethynyl)phthalic anhydride (PEPA) and 3-(phenylethynyl)aniline (3PEA), were synthesized via the palladium-catalyzed coupling of phenylacetylene with 4-bromophthalic anhydride or 3-iodonitrobenzene followed by reduction to 3PEA, respectively. Isolated yields of 41 and 86% for 3PEA and PEPA were obtained, respectively. Model compounds were synthesized from 3PEA and PEPA by reacting with them the appropriate aniline or phthalic anhydride derivative. Model compounds included N-pentafluorophenyl-4-(phenylethynyl)phthalimide (PEPA/F5An), N-(4-trifluoromethyl-phenyl)4-(phenylethynyl)phthalimide (PEPA/F3CAn), N-lbrack 3-(phenylethynyl)phenylrbrack\\ phthalimide (3PEA/PA), N-phenyl-4-(phenylethynyl)phthalimide (PEPA/An), N-(4-phenoxyphenyl)4-(phenylethynyl)phthalimide (PEPA/POAn), and N-(1-naphthyl)-4-(phenylethynyl)phthalimide (PEPA/Anaph). Proposed cure products such as

  13. Chemistry and properties of imide oligomers containing pendant and terminal phenylethynyl groups

    SciTech Connect

    Smith, J.G. Jr.

    1996-12-31

    As part of a continuing effort to develop high performance/high temperature structural resins for aeronautical applications, oligomers containing latent reactive groups have been under investigation. Material requirements include ease of processability, retention of mechanical properties at elevated temperature, and no loss of mechanical properties after exposure to aircraft fluids such as hydraulic fluid, jet fuel, and cleaning fluids. The phenylethynyl group is an ideal latent reactive group. It has a relatively high cure temperature ({approximately}350{degrees}C) and a large processing window can be obtained with materials possessing the proper glass transition temperature. The thermally cured materials exhibit good retention of mechanical properties at elevated temperatures with no significant loss of properties after exposure to various solvents. To date, the phenylethynyl group has been incorporated either terminal or pendant to a variety of imide oligomers. Upon thermal cure, the phenylethynyl group undergoes chain extension, branching and/or crosslinking; however, the final cured product has not been well defined. As an extension of this work, a series of imide oligomers containing both pendant and terminal phenylethynyl groups (PTPEIs) were prepared as a means to improve retention of mechanical properties at elevated temperature while maintaining processability. The PTPEI oligomers were characterized, thermally cured and the cured polymers evaluated as unoriented thin films and adhesives. The chemistry, physical, and mechanical properties of these materials will be discussed.

  14. The Effect of Molecular Weight on the Composite Properties of Cured Phenylethynyl Terminated Imide Oligomers

    NASA Technical Reports Server (NTRS)

    Smith, J. G., Jr.; Connell, J. W.; Hergenrother, P. M.

    1997-01-01

    As part of a program to develop high temperature/high performance structural resins for aeronautical applications, imide oligomers containing terminal phenylethynyl groups with calculated number average molecular weights of 1250, 2500 and 5000 g/mol were prepared, characterized, and evaluated as adhesives and composite matrix resins. The goal of this work was to develop resin systems that are processable using conventional processing equipment into void free composites that exhibit high mechanical properties with long term high temperature durability, and are not affected by exposure to common aircraft fluids. The imide oligomers containing terminal phenylethynyl groups were fabricated into titanium adhesive specimens and IM-7 carbon fiber laminates under 0.1 - 1.4 MPa for 1 hr at 350-371 C. The lower molecular weight oligomers exhibited higher cured Tg, better processability, and better retention of mechanical properties at elevated temperature without significantly sacrificing toughness or damage tolerance than the higher molecular weight oligomer. The neat resin, adhesive and composite properties of the cured polymers will be presented.

  15. Copoly(imide siloxane) Abhesive Materials with Varied Siloxane Oligomer Length

    NASA Technical Reports Server (NTRS)

    Wohl, Christoper J.; Atkins, Brad M.; Lin, Yi; Belcher, Marcus A.; Connell, John W.

    2010-01-01

    In this work, low surface energy copoly(imide siloxane)s were synthesized with various siloxane segment lengths. Characterization of these materials revealed that domain formation of the low surface energy component within the matrix was more prevalent for longer siloxane segments as indicated by increased opacity, decreased mechanical properties, and variation of the Tg. Incorporation of siloxanes lowered the polymer s surface energy as indicated by water contact angle values. Topographical modification of these materials by laser ablation patterning further reduced the surface energy, even generating superhydrophobic surfaces. Combined, the contact angle data and particle adhesion testing indicated that copoly(imide siloxane) materials may provide greater mitigation to particulate adhesion than polyimide materials alone. These enhanced surface properties for abhesive applications did result in a reduction of the tensile moduli of the copolymers. It is possible that lower siloxane loading levels would result in retention of the mechanical properties of the polyimide while still affording abhesive surface properties. This hypothesis is currently being investigated. Laser ablation patterning offers further reduction in particle retention as the available surface area for particle adhesion is reduced. Pattern variation and size dependencies are currently being evaluated. For the purposes of lunar dust adhesion mitigation, it is likely that this approach, termed passive due to the lack of input from an external energy source, would not be sufficient to mitigate surface contamination or clean contaminated surfaces for some lunar applications. It is feasible to combine these materials with active mitigation strategies - methods that utilize input from external energy sources - would broaden the applicability of such materials for abhesive purposes. Collaborative efforts along these lines have been initiated with researchers at NASA Kennedy Space Center where experiments

  16. Copoly(Imide Siloxane) Abhesive Materials with Varied Siloxane Oligomer Length

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Atkins, Brad M.; Belcher, Marcus A.; Connell, John W.

    2010-01-01

    Incorporation of PDMS moieties into a polyimide matrix lowered the surface energy resulting in enhanced adhesive interactions. Polyimide siloxane materials were generated using amine-terminated PDMS oligomers of different lengths to study changes in surface migration behavior, phase segregation, mechanical, thermal, and optical properties. These materials were characterized using contact angle goniometry, tensile testing, and differential scanning calorimetry. The surface migration behavior of the PDMS component depended upon the siloxane molecular weight as indicated by distinct relationships between PDMS chain length and advancing water contact angles. Similar correlations were observed for percent elongation values obtained from tensile testing, while the addition of PDMS reduced the modulus. High fidelity topographical modification via laser ablation patterning further reduced the polyimide siloxane surface energy. Initial particulate adhesion testing experiments demonstrated that polyimide siloxane materials exhibited greater abhesive interactions relative to their respective homopolyimides.

  17. The synthesis, characterization and thermal chemistry of modified norbornenyl PMR endcaps

    NASA Technical Reports Server (NTRS)

    Sukenik, C. N.; Ritchey, W. M.; Malhotra, V.; Varde, U.

    1985-01-01

    As part of a program to further the understanding of the polymerization of Nadic-Endcapped PMR systems, a series of model Norbornenyl-Imides has been synthesized and their thermal behavior explored. Their syntheses and characterizations as well as their rearrangement and polymerization chemistry are described. Monomer isomerization at temperatures as low as 125 C and oligomer formation at somewhat higher temperatures are observed. Approximate relative rates for competing isomerization pathways are established and some information is obtained about the details of oligomer formation. The relationship of this data to current PMR systems is briefly discussed.

  18. Preparation and Surface Property of Fluoroalkyl End-Capped Vinyltrimethoxysilane Oligomer/Talc Composite-Encapsulated Organic Compounds: Application for the Separation of Oil and Water.

    PubMed

    Oikawa, Yuri; Saito, Tomoya; Yamada, Satoshi; Sugiya, Masashi; Sawada, Hideo

    2015-07-01

    Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [R(F)-(CH2-CHSi(OMe)3)n-R(F); n = 2, 3; R(F) = CF(CF3)OC3F7 (R(F)-VM oligomer)] can undergo the sol-gel reaction in the presence of talc particles under alkaline conditions at room temperature to provide the corresponding fluorinated oligomeric silica/talc nanocomposites (RF-VM-SiO2/Talc). A variety of guest molecules such as 2-hydroxy-4-methoxybenzophenone (HMB), bisphenol A (BPA), bisphenol AF, 3-(hydroxysilyl)-1-propanesulfonic acid (THSP), and perfluoro-2-methyl-3-oxahexanoic acid (R(F)-COOH) are effectively encapsulated into the R(F)-VM-SiO2/Talc composite cores to afford the corresponding fluorinated nanocomposites-encapsulated these guest molecules. The R(F)-VM-SiO2/Talc composites encapsulated low molecular weight aromatic compounds such as HMB and BPA can exhibit a superoleophilic-superhydrophobic characteristic on the surfaces; however, the R(F)-VM-SiO2/Talc composite-encapsulated THSP and R(F)-COOH exhibit a superoleophobic-superhydrophilic characteristic on the modified surfaces. In these nanocomposites, the R(F)-VM-SiO2/Talc/THSP composites are applicable to the surface modification of polyester fabric, and the modified polyester fabric possessing a superoleophobic-superhydrophilic characteristic on the surface can be used for the membrane for oil (dodecane)/water separation. In addition, the R(F)-VM-SiO2/Talc composites-encapsulated micrometer-size controlled cross-linked polystyrene particles can be also prepared under similar conditions, and the obtained composite white-colored particle powders are applied to the packing material for the column chromatography to separate water-in-oil (W/O) emulsion. PMID:26042807

  19. Low Viscosity Imides Based on Asymmetric Oxydiphthalic Anhydride

    NASA Technical Reports Server (NTRS)

    Chuang, Kathy C.; Criss, Jim M., Jr.; Mintz, Eric A.; Scheiman, Daniel A.; Nguyen, Baochau N.; McCorkle, Linda S.

    2008-01-01

    A series of low-melt viscosity imide resins were prepared from asymmetric oxydiphthalic dianhydride (a-ODPA) and 4-phenylethynylphthalic anhydride as the endcap, along with 3,4' - oxydianiline (3,4' -ODA), 3,4' -methylenedianiline (3,4' -MDA), 3,3' -methylenedianiline (3,3' - MDA) and 3,3'-diaminobenzophenone (3,3'-DABP), using a solvent-free melt process. These imide oligomers displays low-melt viscosities (2-15 poise) at 260-280 C, which made them amenable to low-cost resin transfer molding (RTM) process. The a-ODPA based RTM resins exhibits glass transition temperatures (Tg's) in the range of 265-330 C after postcure at 343 C. The mechanical properties of these polyimide/carbon fiber composites fabricated by RTM will be discussed.

  20. Adhesive and Composite Properties of a New Phenylethynyl Terminated Imide

    NASA Technical Reports Server (NTRS)

    Thompson, C. M.; Connell, J. W.; Hergenrother, P. M.

    2002-01-01

    A relatively new phenylethynyl terminated imide oligomer (PETI) from the reaction of 2,3,',4'- biphenyltetracarboxylic dianhydride, 4,4'-oxydianiline and endcapped with 4- phenylethynylphthalic anhydride at a calculated number average molecular weight of 5000 g/mole was evaluated as an adhesive and composite matrix. The asymmetric dianhydride imparts a low melt viscosity to the oligomer and a high glass transition temperature to the cured resin. Preliminary adhesive work with titanium (6Al-4V) adherend gave good room temperature (RT) tensile shear strengths and excellent retention of RT strength at 260 C. Preliminary composite work using unsized IM7 carbon fiber provided moderate to high mechanical properties. The chemistry, mechanical, and physical properties of the new PETI in neat resin, adhesive and composite form are presented.

  1. NMR Guided Design of Endcaps With Improved Oxidation Resistance

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Frimer, Aryeh A.

    2002-01-01

    A polyimide is a polymer composed of alternating units of diamine and dianhydride, linked to each other via an imide bond. PMR polyimides, commonly used in the aerospace industry, are generally capped at each end by a norbornene endcap which serves a double function: (1) It limits the number of repeating units and, hence, the average molecular weight of the various polymer chains (oligomers), thereby improving processibility; (2) Upon further treatment (curing), the endcap crosslinks the various oligomer strands into a tough heat-resistant piece. Norbornenyl-end capped PMR polyimide resins' are widely used as polymer matrix composite materials for aircraft engine applications,2 since they combine ease of processing with good oxidative stability up to 300 C. PMR resins are prepared by a twestep approach involving the initial formation of oligomeric pre-polymers capped at both ends by a latent reactive end cap. The end cap undergoes cross-linking during higher temperature processing, producing the desired low density, high specific strength materials, as shown for PMR-15.

  2. Imide/arylene ether copolymers. I

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Hergenrother, P. M.; Bass, R. G.

    1991-01-01

    The preparation of a series of novel imide/arylene ether copolymers is described together with the results of viscosity and DSC Tg(Tm) measurements. The copolymers were synthesized from an arylene ether block and either an amorphous or semicrystalline imide block. One block copolymer was end-capped, and the molecular weight was controlled to improve compression moldability. The paper also presents results of mechanical properties tests on copolymer samples.

  3. Phosphorus-containing imide resins

    NASA Technical Reports Server (NTRS)

    Varma, I. K.; Fohlen, G. M.; Parker, J. A. (Inventor)

    1983-01-01

    Bis- and tris-imides derived from tris (m-aminophenyl) phosphine oxides by reaction with maleic anhydride or its derivatives, and addition polymers of such imides, including a variant in which a mono-imide is condensed with a dianhydride and the product is treated with a further quantity of maleic anhydride. Such monomers or their oligomes may be used to impregnate fibers and fabrics which when cured, are flame resistant. Also an improved method of producing tris (m-aminophenyl) phosphine oxides from the nitro analogues by reduction with hydrazine hydrate using palladized charcoal or Raney nickel as the catalyst is described.

  4. Phenylethynyl endcapping reagents and reactive diluents

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Bryant, Robert G. (Inventor); Hergenrother, Paul M. (Inventor)

    1994-01-01

    A phenylethynyl composition which can be used to endcap nucleophilic species is employed in the production of phenylethynyl terminated reactive oligomers exclusively. These phenylethynyl terminated reactive oligomers display unique thermal characteristics, as exemplified by the model compound, 4-phenoxy 4'-phenylethynylbenzophenone, which is relatively stable at 200 C, but reacts at 350 C. In addition, a reactive diluent was prepared which decreases the melt viscosity of the phenylethynyl terminated oligomers and subsequently reacts therewith to increase density of the resulting thermoset. The novelty of this invention resides in the phenylethynyl composition used to terminate a nucleophilic reagent, resulting in the exclusive production of phenylethynyl terminated reactive oligomers which display unique thermal characteristics. A reactive diluent was also employed to decrease the melt viscosity of a phenylethynyl terminated reactive oligomer and to subsequently react therewith to increase the crosslink density of the resulting thermoset. These materials have features which make them attractive candidates for use as composite matrices and adhesives.

  5. Synthesis and Characterization of Modified Phenylethynyl Imides

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Chang, A. C.

    1998-01-01

    As an ongoing effort to develop structural adhesives for high-performance aerospace applications, recent work has focused on phenylethynyl terminated imide (PETI) oligomers. The work reported herein involves the synthesis and characterization of a series of phenylethynyl containing oligomers designated LARC(TM) MPEI (modified phenylethynyl imide). These oligomers presumably contain mixtures of linear, branched and star-shaped molecules. The fully imidized polymers exhibited minimum melt viscosities as low as 600 poise at 335 C, significantly lower than equivalent molecular weight linear materials. Ti/Ti lap shear specimens processed at 288 C under 15 psi showed tensile shear strengths as high as approx. 6000 psi and 5200 psi at ambient temperature and 177 C respectively. The chemistry and properties of these new MPEIs are presented and compared with an optimized linear PETI, LARC(TM)PETI-5.

  6. Adhesive Properties of Cured Phenylethynyl Containing Imides

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Chang, Alice C.

    1997-01-01

    Considerable attention has been directed towards acetylene terminated oligomers over the last 20 years' and recent work has focused on phenylethynyl terminated imide (PETI) oligomers. These reactive oligomers possess several features which make them attractive candidates for use as composite matrices and adhesives. The phenylethynyl group can be readily incorporated into many different functionalized oligomers. The reactive oligomers possess relatively low melt viscosities and thermally cure without the evolution of volatile by-products. Once cured, they typically display high glass transition temperatures (Tgs), excellent solvent resistance and high mechanical properties. new modified phenylethynyl-terminated imide (LaRC MPEI) oligomers were synthesized at various molecular weights utilizing a small amount of trifunctional amine. As long as the amount of triamine is relatively small, this approach produces a mixture of linear, star-shaped and branched polymer chains that has lower melt and solution viscosity than an equivalent molecular weight linear phenylethynyl terminated imide oligomers. The work reported herein involves the synthesis and characterization of a copolymer using this approach and the preparation of blends utilizing a phenylethynyl containing reactive plasticizer of lower molecular weight called LaRC LV-121. The chemistry and properties of this new MPEI as well as some blends of MPEI with LV-121, are presented and compared to the linear version, LARC-PETI-5.

  7. Phenylethynyl Terminated Imide (PETI) Composites Made by High Temperature Vartm

    NASA Technical Reports Server (NTRS)

    Ghose, Sayata; Watson, Kent A.; Cano, Roberto J.; Britton, Sean M.; Jensen, Brian J.; Connell, John W.; Herring, Helen M.; Lineberry, Quentin J.

    2010-01-01

    The use of composites as primary structures on aerospace vehicles has increased dramatically over the past decade. As these advanced structures increase in size and complexity, their production costs have grown significantly. A major contributor to these manufacturing costs is the requirement of elevated pressures, during high temperature processing, to create fully consolidated composite parts. Recently, NASA Langley has licensed a series of low viscosity Phenyl Ethynyl Terminated Imide, PETI, oligomers that possess a wide processing window to allow for Resin Transfer Molding, RTM, processing. These resins, PETI-8 and PETI-330, demonstrate void fractions of approx.1% under elevated pressure consolidation. However, when used with a standardized thermal curing cycle in a High Temperature Vacuum Assisted RTM (HT-VARTM) process, they display undesirable void contents in excess of 7%. It was determined previously that under the thermal cycles used for laminate fabrication, the phenylethynyl endcap underwent degradation leading to volatile evolution. Modifications to the processing cycle used in the laminate fabrication have reduced the void content significantly (typically less than 3%) for carbon fiber biaxially woven fabric. For carbon fiber uniaxial fabric, void contents of less than 2% have been obtained using both PETI-8 and PETI-330. The resins were infused into carbon fiber preforms at 260 C and cured between 316 C and 371 C. Photomicrographs of the panels were taken and void contents were determined by acid digestion. Mechanical properties of the panels were determined at both room and elevated temperatures. These include short beam shear and flexure tests. The results of this work are presented herein.

  8. Cooled turbine vane with endcaps

    DOEpatents

    Cunha, Frank J.; Schiavo, Jr., Anthony L.; Nordlund, Raymond Scott; Malow, Thomas; McKinley, Barry L.

    2002-01-01

    A turbine vane assembly which includes an outer endcap having a plurality of generally straight passages and passage segments therethrough, an inner endcap having a plurality of passages and passage segments therethrough, and a vane assembly having an outer shroud, an airfoil body, and an inner shroud. The outer shroud, airfoil body and inner shroud each have a plurality of generally straight passages and passage segments therethrough as well. The outer endcap is coupled to the outer shroud so that outer endcap passages and said outer shroud passages form a fluid circuit. The inner endcap is coupled to the inner shroud so that the inner end cap passages and the inner shroud passages from a fluid circuit. Passages in the vane casting are in fluid communication with both the outer shroud passages and the inner shroud passages. Passages in the outer endcap may be coupled to a cooling system that supplies a coolant and takes away the heated exhaust.

  9. Phosphorescent perylene imides.

    PubMed

    Ventura, Barbara; Langhals, Heinz; Böck, Bernd; Flamigni, Lucia

    2012-05-01

    Asymmetrically substituted perylene imide derivatives PIa and PIx display phosphorescence in glassy matrices at 77 K. The lifetime is 49.0 ms for PIa and 13.5 ms for PIx. The triplet energy is 1.79 eV for PIa and 1.68 eV for PIx as confirmed by sensitization experiments of the C(60) triplet. PMID:22436977

  10. Adhesive Properties of Cured Phenylethynyl containing Imides

    NASA Technical Reports Server (NTRS)

    Chang, Alice C.

    1997-01-01

    As part of a program to develop structural adhesives for high performance aerospace applications, several phenylethynyl containing oligomer blends of Larc(TM) MPEI and a reactive plasticizer designated LaRC LV-1 21 were prepared and evaluated. The fully imidized blends exhibited minimum melt viscosity as low as 1000 poise at 371 C. Ti/Ti lap shear specimens fabricated at 316 C under 15 psi gave RT strength of approx. 4300 psi and no change in strength was observed at 177 C. The chemistry and properties of this new MPEI as well as some blends of MPEI with LV-121 are presented and compared to the linear version, LARC(TM)-PETI-5.

  11. Phosphorus-containing imide resins

    NASA Technical Reports Server (NTRS)

    Varma, I. K.; Fohlen, G. M.; Parker, J. A. (Inventor)

    1984-01-01

    Flame-resistant reinforced bodies are disclosed which are composed of reinforcing fibers, filaments or fabrics in a cured body of bis- and tris-imide resins derived from tris(m-aminophenyl) phosphine oxides by reaction with maleic anhydride or its derivatives, or of addition polymers of such imides, including a variant in which a mono-imide is condensed with a dianhydride and the product is treated with a further quantity of maleic anhydride.

  12. Acceptor End-Capped Oligomeric Conjugated Molecules with Broadened Absorption and Enhanced Extinction Coefficients for High-Efficiency Organic Solar Cells.

    PubMed

    Yuan, Liu; Lu, Kun; Xia, Benzheng; Zhang, Jianqi; Wang, Zhen; Wang, Zaiyu; Deng, Dan; Fang, Jin; Zhu, Lingyun; Wei, Zhixiang

    2016-07-01

    Acceptor end-capping of oligomeric conjugated molecules is found to be an effective strategy for simultaneous spectral broadening, extinction coefficient enhancement, and energy level optimization, resulting in profoundly enhanced power conversion efficiencies (of 9.25% and 8.91%) compared to the original oligomers. This strategy is effective in overcoming the absorption disadvantage of oligomers and small molecules due to conjugation limitation. PMID:27172541

  13. Trezimides and tennimides: new imide-based macrocycles.

    PubMed

    Mocilac, Pavle; Gallagher, John F

    2013-03-15

    The reaction of isophthaloyl dichloride with 2-aminopyridine or 2-aminopyrimidine provides a facile entry into a new class of imide-based "3 + 3" macrocyclic trimer (trezimide), together with the known tetramer scaffold (tennimide). The trezimides can adopt two distinct asymmetric conformations in the solid state, isolated as (P) in (IO)3 (from 2-aminopyridine) and (R) in (26IO)3 (from 2-aminopyrimidine). The tennimide crystal structure (26IO)4 (from 2-aminopyrimidine) exhibits three discrete conformational states, highlighting subtle geometric changes with the tennimide channel (pore) open (o) and/or closed (c), as noted by three macrocycle conformations with their channel pores observed as cc/oc/oo. Macrocycle formation (though in competition with oligomer/polymer formation) relies on the o-pyr(im)idine N functionality and preorganized imide hinge (the "CO···CO" twist) together with the inherent flexibility of the isophthaloyl groups. PMID:23373531

  14. Organic-Inorganic Hybrids Using Novel Phenylethynyl Imide Silanes

    NASA Technical Reports Server (NTRS)

    Park, C.; Lowther, S. E.; Smith, J. G., Jr.

    2001-01-01

    In this presentation, polyimide-silica hybrids using novel phenylethynyl imide silanes are reported. The phenylethynyl group is present in the organic precursor as either a pendent or an end group to bond chemically with the polyimide adhesive containing phenylethynyl groups during processing, while the silane group of the organic precursor would chemically react with the inorganic precursor through oxane bond formation. The chemical compositions of these novel hybrids were examined using X-ray mapping modes of scanning electron microscopy (SEM), which revealed a silicon gradient interphase between the high surface energy substrate and the polyimide adhesive. Novel aromatic phenylethynyl imide silanes (APEISs) and pendent phenylethynyl imide oligomeric disilanes (PPEIDSs) have been synthesized, and sol-gel solutions containing the new silanes, a phenylethynyl terminated imide oligomer (PETI-5), and an inorganic precursor were formulated to develop a gradient hybrid interphase between a titanium alloy and the adhesive. Two different sol-gel systems were investigated to develop organic-inorganic hybrids. Hybrid I was composed of an organic precursor containing both phenylethynyl and silane groups (PPEIDS) and an inorganic precursor. Functional group concentrations were controlled by the variation of the molecular weight of the imide backbone of PPEIDS. Hybrid II was composed of organic and inorganic precursors and a coupling agent containing both phenylethynyl and silane groups. Morphology and chemical composition of the hybrid interphase between the inorganic substrate and the adhesive were investigated, and the bond strength and durability were evaluated using lap shear tests at various conditions. The assessment of how the bonding at an interface is affected by various sol-gel solution compositions and environments is reported.

  15. Cure Chemistry of Phenylethynyl Terminated Oligomers

    NASA Technical Reports Server (NTRS)

    Wood, Karen H.; Orwoll, Robert A.; Young, Philip R.; Jensen, Brian J.; McNair, Harold M.

    1997-01-01

    The ability to process high performance polymers into quality, void-free composites has been significantly advanced using oligomers terminated with reactive groups which cure or crosslink at elevated temperature without the evolution of volatile byproducts. Several matrix resin systems of considerable interest to the aerospace community utilize phenylethynyl-terminated imide (PETI) technology to achieve this advantage. The present paper addresses the cure chemistry of PETI oligomers. The thermal cure of a low molecular weight model compound was studied using a variety of analytical techniques including differential scanning calorimetry, Fourier transform infrared spectroscopy, and liquid chromatography-mass spectroscopy. The studies indicate an extremely complex cure process. Many stable products were isolated and this paper reports current work on identification of those products. The intent of this research is to provide fundamental insight into the molecular structure of the cured PETI engineering materials so that performance and durability can be more fully assessed.

  16. High Temperature VARTM of Phenylethynyl Terminated Imides

    NASA Technical Reports Server (NTRS)

    Ghose, Sayata; Cano, Roberto J.; Watson, Kent A.; Britton, Sean M.; Jensen, Brian J.; Connell, John W.; Herring, Helen M.; Linberry, Quentin J.

    2009-01-01

    Depending on the part type and quantity, fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) can be more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, the desired void fraction of less than 2% has not yet been achieved. In the current study, two PETI resins, LaRC PETI-330 and LaRC PETI-8 have been used to make test specimens using HT-VARTM. The resins were infused into ten layers of IM7-6K carbon fiber 5-harness satin fabric at 260 C or 280 C and cured at temperature up to 371 C. Initial runs yielded composites with high void content, typically greater than 7% by weight. A thermogravimetric-mass spectroscopic study was conducted to determine the source of volatiles leading to high porosity. It was determined that under the thermal cycle used for laminate fabrication, the phenylethynyl endcap was undergoing degradation leading to volatile evolution. This finding was unexpected as high quality composite laminates have been fabricated under higher pressures using these resin systems. The amount of weight loss experienced during the thermal cycle was only about 1% by weight, but this leads to a significant amount of volatiles in a closed system. By modifying the thermal cycle used in laminate fabrication, the void content was significantly reduced (typically 3% or less). The results of this work are presented herein.

  17. High Temperature VARTM of Phenylethynyl Terminated Imides

    NASA Technical Reports Server (NTRS)

    Cano, Roberto J.; Britton, Sean M.; Jensen, Brian J.; Connell, John W.; Herring, Helen M.; Linberry, Quentin J.; Ghose, Sayata; Watson, Kent A.

    2009-01-01

    Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, the desired void fraction of less than 2% has not yet been achieved. In the current study, two PETI resins, LaRC PETI-330 and LaRC PETI-8 have been used to make test specimens using HT-VARTM. The resins were infused into ten layers of IM7-6K carbon fiber 5-harness satin fabric at 260 C or 280 C and cured at 371 C. Initial runs yielded composites with high void content, typically greater than 7% by weight. A thermogravimetric-mass spectroscopic study was conducted to determine the source of volatiles leading to high porosity. It was determined that under the thermal cycle used for laminate fabrication, the phenylethynyl endcap was undergoing degradation leading to volatile evolution. By modifying the thermal cycle used in laminate fabrication, the void content was reduced significantly (typically approximately 3%). Densities of the composites were determined using a density gradient column and the glass transition temperatures of the cured composites were measured by dynamic mechanical analysis. Photomicrographs of the panels were taken and void contents were determined by acid digestion. The results of this work are presented herein.

  18. Synthesis, Characterization, Topographical Modification, and Surface Properties of Copoly(Imide Siloxane)s

    NASA Technical Reports Server (NTRS)

    Wohl, Christopher J.; Atkins, Brad M.; Belcher, Marcus A.; Connell, John W.

    2012-01-01

    Novel copoly(imide siloxane)s were synthesized from commercially available aminopropyl terminated siloxane oligomers, aromatic dianhydrides, and diamines. This synthetic approach produced copolymers with well-defined siloxane blocks linked with imide units in a random fashion. The copoly(amide acid)s were characterized by solution viscosity and subsequently used to cast thin films followed by thermal imidization in an inert atmosphere. Thin films were characterized using contact angle goniometry, attenuated total reflection Fourier transform infrared spectroscopy, confocal and optical microscopy, and tensile testing. Adhesion of micronsized particles was determined quantitatively using a sonication device. The polydimethylsiloxane (PDMS) moieties lowered the copolymer surface energy due to migration of siloxane moieties to the film s surface, resulting in a notable reduction in particle adhesion. A further reduction in particle adhesion was achieved by introducing topographical features on a scale of several to tens of microns by a laser ablation technique.

  19. Phosphorus-containing imide resins

    NASA Technical Reports Server (NTRS)

    Varma, I. K.; Fohlen, G. M.; Parker, J. A. (Inventor)

    1985-01-01

    Cured polymers of bis and tris-imides derived from tris(m-aminophenyl) phosphine oxides by reaction with maleic anhydride or its derivatives, and addition polymers of such imides, including a variant in which a monoimide is condensed with a dianhydride and the product is treated with a further quantity of maleic anhydride prior to curing are disclosed and claimed. Such polymers are flame resistant. Also disclosed are an improved method of producing tris(m-aminophenyl) phosphine oxides from the nitro analogues by reduction with hydrazine hydrate using palladized charcoal or Raney nickel as the catalyst and fiber reinforced cured resin composites.

  20. Ceramic pressure housing with metal endcaps

    DOEpatents

    Downing, Jr., John P.; DeRoos, Bradley G.; Hackman, Donald J.

    1995-01-01

    A housing for the containment of instrumentation in a high pressure fluid environment that consists of a metallic endcap and ceramic cylinder bonded together. The improvement comprises a structure which results in the improved sealing of said housing as the fluid pressure increases. The cylindrical ceramic tube and endcap are dimensioned such that mechanical failure does not occur when exposed to the desired external operating pressures which includes up to 36,000 feet of water. The housing is designed to withstand the external operating pressures without being subject to mechanical failure or excessive deformation which results in the loss of pressure housing integrity via cracking or deformation of the ceramic tube, deformation of the endcap, or from failure of the bonding agent.

  1. Ceramic pressure housing with metal endcaps

    DOEpatents

    Downing, J.P. Jr.; DeRoos, B.G.; Hackman, D.J.

    1995-06-27

    A housing is disclosed for the containment of instrumentation in a high pressure fluid environment that consists of a metallic endcap and ceramic cylinder bonded together. The improvement comprises a structure which results in the improved sealing of said housing as the fluid pressure increases. The cylindrical ceramic tube and endcap are dimensioned such that mechanical failure does not occur when exposed to the desired external operating pressures which includes up to 36,000 feet of water. The housing is designed to withstand the external operating pressures without being subject to mechanical failure or excessive deformation which results in the loss of pressure housing integrity via cracking or deformation of the ceramic tube, deformation of the endcap, or from failure of the bonding agent. 9 figs.

  2. Status of high-temperature laminating resins and adhesives

    NASA Technical Reports Server (NTRS)

    Hergenrother, P. M.; Johnston, N. J.

    1980-01-01

    High-temperature polymers now being developed as adhesives and composite matrices are reviewed, including aromatic polyimides, polybenzimidazoles, polyphenylquinoxalines, nadic end-capped imide oligomers, maleimide end-capped oligomers, and acetylene-terminated imide oligomers. The mechanical properties of laminates based on these resins are reported together with preliminary test results on the adhesive properties for titanium-to-titanium and composite-to-composite lap shear specimens.

  3. The endcap Cherenkov ring imaging detector at SLD

    SciTech Connect

    Abe, K.; Hasegawa, K.; Hawegawa, Y.; Iwasaki, Y.; Suekane, F.; Yuta, H.; Antilogus, P.; Aston, D.; Bienz, T.; Bird, F.; Dolinsky, S.

    1995-05-01

    The authors present the Cherenkov Ring Imaging Detector in the endcap regions of the SLD detector and report initial performance. The endcap CRID was completed and commissioned in 1993 and is fully operational for the 1994 run. First Cherenkov rings have been observed. The endcap CRID detectors and fluid systems are described and initial operational experience is discussed.

  4. Commissioning of CMS Endcap Muon System

    NASA Astrophysics Data System (ADS)

    Brownell, Elizabeth

    2009-05-01

    This talk is as an overview of the evolution and current state of commissioning work on the CMS endcap muon system. I intend to highlight the progress in operating the detector, some problems encountered and solutions developed, lessons learned in the process, points which still require action to be taken, and data taking results.

  5. Imide/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor); Bass, Robert G. (Inventor)

    1992-01-01

    Imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly(arylene ethers) in polar aprotic solvents and by chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The resulting block copolymers have one glass transition temperature or two, depending upon the particular structure and/or the compatibility of the block units. Most of these block copolymers form tough, solvent resistant films with high tensile properties.

  6. Synthesis and solution imidization studies of soluble poly(imide siloxane) segmented copolymers

    NASA Technical Reports Server (NTRS)

    Summers, J. D.; Arnold, C. A.; Bott, R. H.; Taylor, L. T.; Ward, T. C.

    1987-01-01

    Soluble metalinked poly(imide siloxane) segmented copolymers were synthesized utilizing a THF/NMP cosolvent system. The presence of dual solvent makes it possibled to reach high molecular weight in the amid acid stage. Incorporation of siloxanes at about 10 weight percent or higher enables the materials to be fully soluble in a range of polar solvents even after imidization. Imidization may be achieved either by conventional thermal methods on cast amic acid films or in appropriate solvent/azeotroping-agent systems employing moderate temperatures. The imidization procedure has been followed by FT-IR and NMR studies. FT-IR studies show the solution imidization follows first order kinetics and proceeds to about 96 percent completion. NMR studies of the isolated products show residual amic acid may be present after solution imidization, but only at very low levels. Properties of the solution imidized materials compared well with those obtained from samples imidized as thin films.

  7. Crystalline Imide/Arylene Ether Copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Hergenrother, Paul M.; Bass, Robert G.

    1991-01-01

    Series of imide/arylene ether block copolymers prepared by using arylene ether blocks to impart low melt viscosity, and imide blocks to provide high strength and other desirable mechanical properties. Work represents extension of LAR-14159 on imide/arylene ether copolymers in form of films, moldings, adhesives, and composite matrices. Copolymers potentially useful in variety of high-temperature aerospace and microelectronic applications.

  8. An Investigation of Solid-State Amidization and Imidization Reactions in Vapor Deposited Poly (amic acid)

    SciTech Connect

    Anthamatten, M; Letts, S A; Day, K; Cook, R C; Gies, A P; Hamilton, T P; Nonidez, W K

    2004-06-28

    The condensation polymerization reaction of 4,4'-oxydianiline (ODA) with pyromellitic dianhydride (PMDA) to form poly(amic acid) and the subsequent imidization reaction to form polyimide were investigated for films prepared using vapor deposition polymerization techniques. Fourier-transform infrared spectroscopy (FT-IR), thermal analysis, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of films at different temperatures indicate that additional solid-state polymerization occurs prior to imidization reactions. Experiments reveal that, upon vapor deposition, poly(amic acid) oligomers form that have a number-average molecular weight of about 1500 Daltons. Between 100 - 130 C these chains undergo additional condensation reaction to form slightly higher molecular weight oligomers. Calorimetry measurements show that this reaction is exothermic ({Delta}H {approx} -30 J/g) with an activation energy of about 120 kJ/mol. Experimental reaction enthalpies are compared to results from ab initio molecular modeling calculations to estimate the number of amide groups formed. At higher temperatures (150 - 300 C) imidization of amide linkages occurs as an endothermic reaction ({Delta}H {approx} +120 J/g) with an activation energy of about 130 kJ/mol. Solid-state kinetics were found to depend on reaction conversion as well as the processing conditions used to deposit films.

  9. Imide/Arylene Ether Copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Hergenrother, Paul M.; Bass, Robert G.

    1991-01-01

    New imide/arylene ether copolymers prepared by reacting anhydride-terminated poly(amic acids) with amine-terminated poly(arylene ethers) in polar aprotic solvents. Each resulting copolymer may have one glass-transition temperature or two, depending on chemical structure and/or compatibility of block units. Most of copolymers form tough, solvent-resistant films with high tensile properties. Films cast from solution tough and flexible, and exhibit useful thermal and mechanical properties. Potentially useful as moldings, adhesives, or composite matrices. Because of flexible arylene ether blocks, these copolymers easier to process than polyimides.

  10. Imide/arylene ether block copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Hergenrother, P. M.; Bass, R. G.

    1991-01-01

    Two series of imide/arylene either block copolymers were prepared using an arylene ether block and either an amorphous or semi-crystalline imide block. The resulting copolymers were characterized and selected physical and mechanical properties were determined. These results, as well as comparisons to the homopolymer properties, are discussed.

  11. Crystalline imide/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor); Bass, Robert G. (Inventor)

    1995-01-01

    Crystalline imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly)arylene ethers) in polar aprotic solvents and chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The block copolymers of the invention have one glass transition temperature or two, depending on the particular structure and/or the compatibility of the block units. Most of these crystalline block copolymers for tough, solvent resistant films with high tensile properties. While all of the copolymers produced by the present invention are crystalline, testing reveals that copolymers with longer imide blocks or higher imide content have increased crystallinity.

  12. Computational design of organometallic oligomers featuring 1,3-metal-carbon bonding and planar tetracoordinate carbon atoms.

    PubMed

    Zhao, Xue-Feng; Yuan, Cai-Xia; Wang, Xiang; Li, Jia-Jia; Wu, Yan-Bo; Wang, Xiaotai

    2016-01-15

    Density functional theory computations (B3LYP) have been used to explore the chemistry of titanium-aromatic carbon "edge complexes" with 1,3-metal-carbon (1,3-MC) bonding between Ti and planar tetracoordinate Cβ . The titanium-coordinated, end-capping chlorides are replaced with OH or SH groups to afford two series of difunctional monomers that can undergo condensation to form oxide- and sulfide-bridged oligomers. The sulfide-linked oligomers have less molecular strain and are more exergonic than the corresponding oxide-linked oligomers. The HOMO-LUMO gap of the oligomers varies with their composition and decreases with growing oligomer chain. This theoretical study is intended to enrich 1,3-MC bonding and planar tetracoordinate carbon chemistry and provide interesting ideas to experimentalists. Organometallic complexes with the TiE2 (E = OH and SH) decoration on the edge of aromatic hydrocarbons have been computationally designed, which feature 1,3-metal-carbon (1,3-MC) bonding between titanium and planar tetracoordinate β-carbon. Condensation of these difunctional monomers by eliminating small molecules (H2O and H2S) produce chain-like oligomers. The HOMO-LUMO gaps of the oligomers decreases with growing oligomer chain, a trend that suggests possible semiconductor properties for oligomers with longer chains. PMID:26399226

  13. Better End-Cap Processing for Oxidation-Resistant Polyimides

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Frimer, Aryeh A.

    2004-01-01

    A class of end-cap compounds that increase the thermo-oxidative stab ility of polyimides of the polymerization of monomeric reactants (PM R) type has been extended. In addition, an improved processing proto col for this class of end-cap compounds has been invented.

  14. Syntheses, phase behavior, supramolecular chirality, and field-effect carrier mobility of asymmetrically end-capped mesogenic oligothiophenes.

    PubMed

    Meng, Qingwei; Sun, Xiao-Hua; Lu, Zhengyu; Xia, Ping-Fang; Shi, Zehua; Chen, Dongzhong; Wong, Man Shing; Wakim, Salem; Lu, Jianping; Baribeau, Jean-Marc; Tao, Ye

    2009-01-01

    A novel series of asymmetrically end-capped mesogenic oligothiophenes, with various oligothiophene core lengths, alkoxy tail lengths, and molecular polarities through introducing alkylsulfanyl or alkylsulfonyl functionalities as the terminal group, have been synthesized by palladium-catalyzed Suzuki cross-coupling and Kumada cross-coupling reactions as key steps. For the single end-capped oligothiophenes, C(m)O-Ar-OT(4)-H in which m=10, 12, 14, 16, and 18, all of these oligomers exhibited a broad temperature range of highly ordered smectic E and enantiotropic nematic phases, apart from the one with the longest octadecyloxy tail. For the double end-capped series C(10)O-Ar-OT(n)-R, R=Ph-SC(6) or Ph-SO(2)C(6) in which n=1, 2, 3, and 4, oligomers with more than one thiophene ring exhibited smectic A and smectic C phases, various crystal polymorphs and/or unusual low-temperature condensed phases. In the nonpolar, alkylsulfanylphenyl-substituted oligothiophene series, both the crystal/solid melting point and mesogenic clear point increased significantly with an increasing oligothiophene conjugation length. In the polar, alkylsulfonylphenyl-substituted oligothiophene series, all the oligomers showed increased melting points, but decreased mesogenic temperature intervals than those of their corresponding alkylsulfanyl counterparts. Remarkably, two different helical structures showing distinct striated textures or striped patterns were observed with a pitch of several to tens of micrometers under a polarized optical microscope upon cooling from their preceding fluidic smectic phases. The unusual twisted smectic layer structures in the thin solid films exhibiting distinct supramolecular chirality of both handednesses, revealed by circular dichroism measurements, were further confirmed by XRD analyses characterized by a sharp layer reflection together with its higher orders and diffuse wide-angle scatterings. In addition, initial studies showed that the highly ordered smectic

  15. Corpectomy cage subsidence with rectangular versus round endcaps.

    PubMed

    Deukmedjian, Armen R; Manwaring, Jotham; Le, Tien V; Turner, Alexander W L; Uribe, Juan S

    2014-09-01

    Corpectomy cages with rectangular endcaps utilize the stronger peripheral part of the endplate, potentially decreasing subsidence risk. The authors evaluated cage subsidence during cyclic biomechanical testing, comparing rectangular versus round endcaps. Fourteen cadaveric spinal segments (T12-L2) were dissected and potted at T12 and L2, then assigned to a rectangular (n=7) or round (n=7) endcap group. An L1 corpectomy was performed and under uniform conditions a cage/plate construct was cyclically tested in a servo-hydraulic frame with increasing load magnitude. Testing was terminated if the test machine actuator displacement exceeded 6mm, or the specimen completed cyclic loading at 2400 N. Number of cycles, compressive force and force-cycles product at test completion were all greater in the rectangular endcap group compared with the round endcap group (cycles: 3027 versus 2092 cycles; force: 1943 N versus 1533 N; force-cycles product: 6162kN·cycles versus 3973 kN·cycles), however these differences were not statistically significant (p ⩾ 0.076). After normalizing for individual specimen bone mineral density, the same measures increased to a greater extent with the rectangular endcaps (cycles: 3014 versus 1855 cycles; force: 1944 N versus 1444 N; force-cycles product: 6040 kN·cycles versus 2980 kN·cycles), and all differences were significant (p⩽0.030). The rectangular endcap expandable corpectomy cage displayed increased resistance to subsidence over the round endcap cage under cyclic loading as demonstrated by the larger number of cycles, maximum load and force-cycles product at test completion. This suggests rectangular endcaps will be less susceptible to subsidence than the round endcap design. PMID:24831343

  16. Investigation of intermolecular interactions between single walled nanotubes and conjugated oligomers using the dispersion-corrected DFT methods

    NASA Astrophysics Data System (ADS)

    Lagowski, Jolanta B.; Aljohani, Suad; Khan, M. Zahidul H.; Zhao, Yuming

    The area of carbon nanotubes (CNT)-polymer composites has been progressing rapidly in recent years. Pure CNT and CNT-polymer composites have many useful (industry related) properties: ranging from electronic electrical conductivity to superior strength. However the full potential of using CNTs as reinforcements (in say a polymer matrix) has been severely limited because of complications associated with the dispersion of CNTs. CNTs tend to entangle with each other forming materials that have properties that fall short of the expectations. The goal of this work is to identify the type of conjugated oligomers that are best suited for the dispersion of single walled CNT (SWCNT). For this purpose, various methods of dispersion corrected density functional theory (DFT-D/B97D, /WB97XD, /CAM-B3LYP) have been used to investigate the interaction between the SWCNT and the organic conjugated oligomers with different end groups (aldehyde (ALD) and dithiafulvenyl (DTF)). We investigate the effect of intermolecular interactions on the structure, polarity and energetics of the oligomers and SWCNT combinations. The comparison of results obtained using different DFT approximations is made. Our results show that DFT-endcapped oligomer interact more strongly with CNT than ALD-endcapped oligomer. The financial support from NSERC, SACBC and Memorial University and the computational resources from Compute Canada were received.

  17. Imide modified epoxy matrix resins

    NASA Technical Reports Server (NTRS)

    Scola, D. A.; Pater, R. H.

    1981-01-01

    High char yield epoxy using novel bisimide amines (BIA's) as curing agents with a state of the art epoxy resin was developed. Stoichiometric quantities of the epoxy resin and the BIA's were studied to determine the cure cycle required for preparation of resin specimens. The bisimide cured epoxies were designated IME's (imide modified epoxy). The physical, thermal and mechanical properties of these novel resins were determined. The levels of moisture absorption exhibited by the bisimide amine cured expoxies (IME's) were considerably lower than the state of the art epoxies. The strain-to-failure of the control resin system was improved 25% by replacement of DDS with 6F-DDS. Each BIA containing resin exhibited twice the char yield of the control resin MY 720/DDS. Graphite fiber reinforced control (C) and IME resins were fabricated and characterized. Two of the composite systems showed superior properties compared to the other Celion 6000/IME composite systems and state of the art graphite epoxy systems. The two systems exhibited excellent wet shear and flexural strengths and moduli at 300 and 350 F.

  18. Imide modified epoxy matrix resins

    NASA Technical Reports Server (NTRS)

    Scola, D. A.

    1984-01-01

    The results of a program designed to develop tough imide modified epoxy resins cured by bisimide amine (BIA) hardeners are described. State-of-the-art epoxides MY720 and DER383 were used, and four bismide amines were evaluated. These were the BIA's derived from the 6F anhydride (4,4'-(hexafluoroisopropylidene) bis(phthalic anhydride) and the diamines 3,3'-diaminodiphynyl sulfone, 4,4'-oxygianiline, 4,4'-methylene dianiline, and 1,12-dodecane diamine. A key intermediate, designated 6F anhydride, is required for the synthesis of the bisimide amines. Reaction parameters to synthesize a precursor to the 6F anhydride (6FHC) in high yields were investigated. The catalyst trifluoromethane sulfonic acid was studied. Although small scale runs yielded the 6FHC in 50 percent yield, efforts to ranslate these results to a larger scale synthesis gave the 6FHC in only 9 percent yield. Results show that the concept of using bisimide amine as curing agents to improve the toughness properties of epoxies is valid.

  19. Imide modified epoxy matrix resins

    NASA Technical Reports Server (NTRS)

    Scola, D. A.

    1982-01-01

    Results of a program designed to develop tough imide modified epoxy (IME) resins cured by bisimide amine (BIA) hardeners are presented. State of the art epoxy resin, MY720, was used. Three aromatic bisimide amines and one aromatic aliphatic BIA were evaluated. BIA's derived from 6F anhydride (3,3 prime 4,4 prime-(hexafluoro isopropyl idene) bis (phthalic anhydride) and diamines, 3,3 prime-diam nodiphenyl sulfone (3,3 prime-DDS), 4,4 prime-diamino diphenyl sulfone (4,4 prime-DDS), 1.12-dodecane diamine (1,12-DDA) were used. BIA's were abbreviated 6F-3,3 prime-DDS, 6F-4,4 prime-DDS, 6F-3,3 prime-DDS-4,4 prime DDS, and 6F-3,3 prime-DDS-1,12-DDA corresponding to 6F anhydride and diamines mentioned. Epoxy resin and BIA's (MY720/6F-3,3 prime-DDS, MY720/6F-3,3 prime-DDS-4,4 prime-DDS, MY720/6F-3,3 prime-DDS-1,12-DDA and a 50:50 mixture of a BIA and parent diamine, MY720/6F-3,3 prime-DDS/3,3 prime-DDS, MY720/6F-3,3 prime-DDS-4,4 prime-DDS/3,3 prime-DDS, MY720/6F-3,3 prime-DDS-1,12-DDA/3,3 prime-DDS were studied to determine effect of structure and composition. Effect of the addition of two commercial epoxies, glyamine 200 and glyamine 100 on the properties of several formulations was evaluated. Bisimide amine cured epoxies were designated IME's (imide modified epoxy). Physical, thermal and mechanical properties of these resins were determined. Moisture absorption in boiling water exhibited by several of the IME's was considerably lower than the state of the art epoxies (from 3.2% for the control and state of the art to 2.0 wt% moisture absorption). Char yields are increased from 20% for control and state of the art epoxies to 40% for IME resins. Relative toughness characteristics of IME resins were measured by 10 deg off axis tensile tests of Celion 6000/IME composites. Results show that IME's containing 6F-3,3 prime-DDS or 6F-3,3 prime-DDS-1,12-DDA improved the "toughness" characteristics of composites by about 35% (tensile strength), about 35% (intralaminar shear

  20. Phenylethynyl amine

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Bryant, Robert G. (Inventor); Jensen, Brian J. (Inventor); Havens, Stephen J. (Inventor)

    1997-01-01

    Four phenylethynyl amine compounds--3 and 4-aminophenoxy-4'-phenylethynylbenzophenone, and 3 and 4-amino-4'-phenylethynylbenzophenone--were readily prepared and were used to endcap imide oligomers. Phenylethynyl-terminated amide acid oligomers and phenylethynyl-terminated imide oligomers with various molecular weights and compositions were prepared and characterized. These oligomers were cured at 300.degree. C. to 400.degree. C. to provide crosslinked polyimides with excellent solvent resistance, high strength and modulus and good high temperature properties. Adhesive panels, composites, films and moldings from these phenylethynyl terminated imide oligomers gave excellent mechanical performance.

  1. Process of end-capping a polyimide system

    NASA Technical Reports Server (NTRS)

    Stclair, T. L.; Burks, H. D. (Inventor)

    1985-01-01

    A process of endcapping a polyimide system with an endcapping agent in order to achieve a controlled decrease in molecular weight and melt viscosity along with predictable fracture resistance of the molded products is disclosed. The uncapped system is formed by combining an equimolar ratio of 4,4'-bis (3,4-dicarboxyphenoxy) diphenylsulfide dianhydride (BDSDA) and 1,-bis (aminophenoxy) benzene (APB) dissolved in bis (2-methoxyethyl)ether. The endcapped system is formed by dissolving APB in bis-(2-methoxyethyl)ether, adding the BDSDA. By varying the amount of endcapping from 0 to 4%, molecular weight is decreased from 13,900 to 8660. At a processing temperature of 250 C, there is a linear relationship between molecular weight and viscosity, with the viscosity decreasing by two orders of magnitude as the molecular weight decreased from 13,900 to 8660.

  2. Finite element analysis of the SDC barrel and endcap calorimeters

    SciTech Connect

    Guarino, V.; Hill, N.; Nasiakta, J.

    1992-03-11

    In designing the SCD barrel and endcap calorimeters, the inter-module connecting forces must be known in order to determine the required size and number of connecting links between modules, and in order to understand how individual modules will be affected by these forces when assembled to form a full barrel and endcap. The connecting forces were found by analyzing three-dimensional Finite Element Models of both the barrel and endcap. This paper is divided into two parts, the first part will describe in detail the results of the barrel analysis and the second part will describe the results obtained from the endcap analysis. A similar approach was used in constructing the models for both analysis.

  3. Ammonia decomposition catalysis using lithium-calcium imide.

    PubMed

    Makepeace, Joshua W; Hunter, Hazel M A; Wood, Thomas J; Smith, Ronald I; Murray, Claire A; David, William I F

    2016-07-01

    Lithium-calcium imide is explored as a catalyst for the decomposition of ammonia. It shows the highest ammonia decomposition activity yet reported for a pure light metal amide or imide, comparable to lithium imide-amide at high temperature, with superior conversion observed at lower temperatures. Importantly, the post-reaction mass recovery of lithium-calcium imide is almost complete, indicating that it may be easier to contain than the other amide-imide catalysts reported to date. The basis of this improved recovery is that the catalyst is, at least partially, solid across the temperature range studied under ammonia flow. However, lithium-calcium imide itself is only stable at low and high temperatures under ammonia, with in situ powder diffraction showing the decomposition of the catalyst to lithium amide-imide and calcium imide at intermediate temperatures of 200-460 °C. PMID:27092374

  4. Molecular-Weight-Controlled, End-Capped Polybenzimidazoles

    NASA Technical Reports Server (NTRS)

    Connell, John W.; Hergenrother, Paul M.; Smith, Joseph G., Jr.

    1993-01-01

    Novel molecular-weight-controlled end-capped poly(arylene ether benzimidazole)s (PAEBI's) prepared by nucleophilic displacement reaction of di(hydroxyl)benzimidazole monomers with activated aromatic dihalides. Polymers prepared at various molecular weights by upsetting stoichiometry of monomers and end-capped with monohydroxybenzimidazole. Exhibit favorable physical and mechanical properties, improved solubility in polar aprotic solvents and better compression moldability. Potential applications as adhesives, coatings, films, fibers, membranes, moldings, and composite matrix resins.

  5. The ATLAS SCT endcap: From module production to commissioning

    NASA Astrophysics Data System (ADS)

    Ferrère, D.

    2007-01-01

    The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is aiming for new physics at TeV scale energy and will be operational in 2007. The Semiconductor Tracker (SCT) is a part of the ATLAS Inner Detector (ID) and consists of 4088 silicon detector modules displayed on four concentric barrels and two endcaps on each side. Almost 2400 endcap modules have been produced in seven assembly sites including a 20% contingency. All the qualified modules have been shipped to the two macro-assembly sites where the modules are now mounted to the discs. A major organizational effort around the components and the logistics has been made to ensure that the project is running with a high yield and within the schedule. Well defined and strict quality assurance rules allowed the endcap community to achieve an average production yield of 92.9%. In order to complete the two endcaps, a major effort is made for finalizing the assembly of modules and services onto the discs and carbon fiber cylinder, respectively. After describing the organization of the endcap module assembly and the production results, a description and status of the endcap macro-assembly and services will be reported.

  6. 40 CFR 721.10578 - Unsaturated polyester imide (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Unsaturated polyester imide (generic... Specific Chemical Substances § 721.10578 Unsaturated polyester imide (generic). (a) Chemical substance and... polyester imide (PMN P-10-231) is subject to reporting under this section for the significant new...

  7. 40 CFR 721.10578 - Unsaturated polyester imide (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Unsaturated polyester imide (generic... Specific Chemical Substances § 721.10578 Unsaturated polyester imide (generic). (a) Chemical substance and... polyester imide (PMN P-10-231) is subject to reporting under this section for the significant new...

  8. Poly(imide-siloxane) segmented copolymer structural adhesives prepared by bulk and solution thermal imidization

    NASA Technical Reports Server (NTRS)

    Bott, R. H.; Summers, J. D.; Arnold, C. A.; Blankenship, C. P., Jr.; Taylor, L. T.

    1988-01-01

    The improved properties that have been demonstrated through thermal solution imidization in the case of polyimides and poly(imide-siloxane) segmented copolymers suggests significant potential for application of these new materials. Specifically, the enhancement in solubility, moisture reduction, and processability observed through this solution technique is quite dramatic. Previous work has shown that the presence of low amounts of siloxane does not detract significantly from the lap shear strength of these materials to titanium in the case of bulk thermal imidization synthesis. In addition, the siloxane incorporation results in the added advantage of resistance to hot, wet environments. This added durability is presumably due to the hydrophobic siloxane segments preventing the uptake of water at the critical interphase between the adhesive and the adherend. This paper discusses the extension of this work to the solution imidization synthesis technique recently developed in our laboratory. Results dealing with the absolute bond strengths as well as durability and failure surface analysis will be presented.

  9. Phenylethynyl terminated reactive oligomer

    NASA Technical Reports Server (NTRS)

    Bryant, Robert G. (Inventor); Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor)

    1995-01-01

    A composition of matter having the general structure: ##STR1## (wherein X is F, Cl, or NO.sub.2, and Y is CO, SO.sub.2 or C(CF.sub.3).sub.2) is employed to terminate a nucleophilic reagent, resulting in the exclusive production of phenylethynyl terminated reactive oligomers which display unique thermal characteristics. A reactive diluent having the general structure: ##STR2## (wherein R is any aliphatic or aromatic moiety) is employed to decrease the melt viscosity of a phenylethynyl terminated reactive oligomer and to subsequently react therewith to provide a thermosetting material of enhanced density. These materials have features which make them attractive candidates for use as composite matrices and adhesives.

  10. High Temperature VARTM of Phenylethynyl Terminated Imides

    NASA Technical Reports Server (NTRS)

    Ghose, Sayata; Watson, Kent A.; Cano, Roberto J.; Britton, Sean M.; Jensen, Brian J.; Connell, John W.; Herring, Helen M.; Linberry, Quentin J.

    2009-01-01

    LaRC phenylethynyl terminated imide (PETI) resins were processed into composites using high temperature vacuum assisted resin transfer molding (VARTM). Although initial runs yielded composites with high void content, process modifications reduced voids to <3%. Photomicrographs were taken and void contents and T(sub g)s of the panels were determined.

  11. Functional end-capped conducting poly (3,4-ethylenedioxythiophene)

    NASA Astrophysics Data System (ADS)

    Sabatini, V.; Farina, H.; Ortenzi, Marco A.

    2016-05-01

    Methacrylate-terminated Poly(3,4-Ethylenedioxythiophene) (PEDOT) polymers with controlled degree of polymerization were successfully prepared by direct oxidative polycondensation between Ethylenedioxythiophene (EDOT) and a cross-linkable methacrylate end-capper monomer, obtained via Friedel Crafts acylation starting from EDOT and Methacryloyl chloride. The new polymer was synthesized in order to overcome the well-known technical problems of PEDOT, i.e. difficult processability and patterning, due to its poor solubility in common organic and inorganic solvents. The chemical structure and the degree of polymerization of the end-capped polymers were determined by 1H NMR spectra. A new synthesis of Methacrylate end-capped PEDOT with controlled degree of polymerization, soluble in common organic and chlorinated solvents and with improved conductivity, 210 S/cm, was performed. This method includes: direct oxidative polycondensation of 3,4-Ethylenedioxythiophene (EDOT) in the presence of a cross-linkable end-capper, i.e. Methacrylate end-capped EDOT prepared via Friedel Crafts acylation with Methacryloyl chloride and oxidant species, i.e. ferric sulfate. Furthermore, the oxidative polycondensation of EDOT monomer and Methacrylate end-capped EDOT in the presence of Sulfonated Polyethersulfone (SPES)- characterized by different degree of Sulfonation (DS)- as dopant agent was performed, leading to functional end-capped conducting PEDOT, easy to process and pattern, with conductivity of 210 S/cm, 50 S/cm higher than the one of commercial PEDOT.

  12. Cyclic Imide Dioxime: Formation and Hydrolytic Stability

    SciTech Connect

    Kang, S.O.; Vukovic, Sinisa; Custelcean, Radu; Hay, Benjamin

    2012-01-01

    Poly(acrylamidoximes) play an important role in the uranium extraction from seawater. The present work reports solution studies of simple analogs to address the formation and stability of two binding sites present in these polymers, open-chain amidoximes and cyclic imide dioximes, including: 1) conditions that maximize the formation of the cyclic form, 2) existence of a base-induced conversion from open-chain to cyclic form, and 3) degradation under acid and base conditions.

  13. Contribution of Round vs. Rectangular Expandable Cage Endcaps to Spinal Stability in a Cadaveric Corpectomy Model

    PubMed Central

    Mundis, Gregory M.; Moazzaz, Payam; Turner, Alexander W. L.; Cornwall, G. Bryan

    2015-01-01

    Background Expandable cages are gaining popularity in anterior reconstruction of the thoracolumbar spine following corpectomy as they can provide adjustable distraction and deformity correction. Rectangular, rather than circular, endcaps provide increased resistance to subsidence by spanning the apophyseal ring; however their impact on construct stability is not known. The objective of this study was to investigate the contribution of expandable corpectomy cage endcap shape (round vs. rectangular) and fixation method (anterior plate vs. posterior pedicle screws) to the stability of an L1 sub-total corpectomy construct. Methods Eight fresh-frozen cadaveric specimens (T11-L3) were subjected to multi-directional flexibility testing to 6 N·m with a custom spine simulator. Test conditions were: intact, L1 sub-total corpectomy defect, expandable cage (round endcap) alone, expandable cage (round endcap) with anterior plate, expandable cage (round endcap) with bilateral pedicle screws, expandable cage (rectangular endcap) alone, expandable cage (rectangular endcap) with anterior plate, expandable cage (rectangular endcap) with bilateral pedicle screws. Range-of-motion across T12-L2 was measured with an optoelectronic system. Results The expandable cage alone with either endcap provided significant stability to the corpectomy defect, reducing motion to intact levels in flexion-extension with both endcap types, and in lateral bending with rectangular endcaps. Round endcaps allowed greater motion than intact in lateral bending, and axial rotation ROM was greater than intact for both endcaps. Supplemental fixation provided the most rigid constructs, although there were no significant differences between instrumentation or endcap types. Conclusions These results suggest anterior-only fixation may be adequate when using an expandable cage in a sub-total corpectomy application and choice of endcap type may be driven by other factors such as subsidence resistance. PMID:26609508

  14. Development of Polyamide-imide / Silica Nanocomposite Enameled Wire

    NASA Astrophysics Data System (ADS)

    Kikuchi, Hideyuki; Hanawa, Hidehito; Honda, Yuki

    The nanocomposite material based on polyamide-imide was not able to prevent nano-particles from aggregating up to now, therefore the development of this material was extremely difficult. However we prevented aggregation of nano-particles by developing the hygroscopicity solvent and copolyamide-imide, and commercialized the new partial discharge resistant enameled wire with nanocomposite polyamide-imide insulating material in 2010. The lifetime of newly developed partial discharge resistant nanocomposite polyamide-imide enameled wire has 1000 or more times compared to general organic enameled wire. Moreover lifetime of new wire is also extremely excellent in the high temperature atmosphere.

  15. Structural differences between amyloid beta oligomers.

    PubMed

    Breydo, Leonid; Kurouski, Dmitry; Rasool, Suhail; Milton, Saskia; Wu, Jessica W; Uversky, Vladimir N; Lednev, Igor K; Glabe, Charles G

    2016-09-01

    In Alzheimer's disease, soluble Aβ oligomers are believed to play important roles in the disease pathogenesis, and their levels correlate with cognitive impairment. We have previously shown that Aβ oligomers can be categorized into multiple structural classes based on their reactivity with conformation-dependent antibodies. In this study, we analyzed the structures of Aβ40 oligomers belonging to two of these classes: fibrillar and prefibrillar oligomers. We found that fibrillar oligomers were similar in structure to fibrils but were less stable towards denaturation while prefibrillar oligomers were found to be partially disordered. These results are consistent with previously proposed structures for both oligomer classes while providing additional structural information. PMID:27363332

  16. Imide/arylene ether copolymers with pendent trifluoromethyl groups

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Havens, Stephen J.

    1992-01-01

    A series of imide/arylene ether block copolymers were prepared using an arylene ether block containing a hexafluoroisopropylidene group and an imide block containing a hexafluoroisopropylidene and a trifluoromethyl group in the polymer backbone. The copolymers were characterized and mechanical properties were determined and compared to the homopolymers.

  17. Targeting Cancer with Antisense Oligomers

    SciTech Connect

    Hnatowich, DJ

    2008-10-28

    With financial assistance from the Department of Energy, we have shown definitively that radiolabeled antisense DNAs and other oligomers will accumulate in target cancer cells in vitro and in vivo by an antisense mechanism. We have also shown that the number of mRNA targets for our antisense oligomers in the cancer cell types that we have investigated so far is sufficient to provide and antisense image and/or radiotherapy of cancer in mice. These studies have been reported in about 10 publications. However our observation over the past several years has shown that radiolabeled antisense oligomers administered intravenously in their native and naked form will accumulate and be retained in target xenografts by an antisense mechanism but will also accumulate at high levels in normal organs such as liver, spleen and kidneys. We have investigated unsuccessfully several commercially available vectors. Thus the use of radiolabeled antisense oligomers for the imaging of cancer must await novel approaches to delivery. This laboratory has therefore pursued two new paths, optical imaging of tumor and Auger radiotherapy. We are developing a novel method of optical imaging tumor using antisense oligomers with a fluorophore is administered while hybridized with a shorter complementary oligomer with an inhibitor. In culture and in tumored mice that the duplex remains intact and thus nonfluorescent until it encounters its target mRNA at which time it dissociates and the antisense oligomer binds along with its fluorophore to the target. Simultaneous with the above, we have also observed, as have others, that antisense oligomers migrate rapidly and quantitatively to the nucleus upon crossing cell membranes. The Auger electron radiotherapy path results from this observation since the nuclear migration properties could be used effectively to bring and to retain in the nucleus an Auger emitting radionuclide such as 111In or 125I bound to the antisense oligomer. Since the object becomes

  18. Tests and developments of the PANDA Endcap Disc DIRC

    NASA Astrophysics Data System (ADS)

    Etzelmüller, E.; Belias, A.; Dzhygadlo, R.; Gerhardt, A.; Götzen, K.; Kalicy, G.; Krebs, M.; Lehmann, D.; Nerling, F.; Patsyuk, M.; Peters, K.; Schepers, G.; Schmitt, L.; Schwarz, C.; Schwiening, J.; Traxler, M.; Zühlsdorf, M.; Britting, A.; Eyrich, W.; Lehmann, A.; Pfaffinger, M.; Uhlig, F.; Düren, M.; Föhl, K.; Hayrapetyan, A.; Kröck, B.; Merle, O.; Rieke, J.; Schmidt, M.; Cowie, E.; Keri, T.; Achenbach, P.; Cardinali, M.; Hoek, M.; Lauth, W.; Schlimme, S.; Sfienti, C.; Thiel, M.

    2016-04-01

    The PANDA experiment at the future Facility for Antiproton and Ion Research (FAIR) requires excellent particle identification. Two different DIRC detectors will utilize internally reflected Cherenkov light of charged particles to enable the separation of pions and kaons up to momenta of 4 GeV/c. The Endcap Disc DIRC will be placed in the forward endcap of PANDA's central spectrometer covering polar angles between 5° and 22°. Its final design is based on MCP-PMTs for the photon detection and an optical system made of fused silica. A new prototype has been investigated during a test beam at CERN in May 2015 and first results will be presented. In addition a new synthetic fused silica material by Nikon has been tested and was found to be radiation hard.

  19. Some studies of data using the STAR endcap electromagnetic calorimeter.

    SciTech Connect

    Krueger, K.; Spinka, H. M.; Underwood, D. G.; High Energy Physics

    2009-02-24

    A series of studies was performed using data from the STAR detector at the Brookhaven National Laboratory's RHIC accelerator from collisions of protons at {radical}s = 200 GeV. Many of these involved the shower maximum detector (SMD) of the STAR endcap electromagnetic calorimeter (EEMC). Detailed studies of photon candidates from {eta} {yields} {gamma}{gamma} decay, and of {gamma} + Jet inclusive data and simulated events were performed.

  20. Thin gap gas chambers for the DELPHI endcaps

    SciTech Connect

    Adam, W.; Hrubec, J.

    1996-12-31

    Thin Gap Gas Chambers have been proposed for an upgrade of the endcaps of the DELPHI detector at LEP. Two full size chambers have been built and a study of the optimal operating conditions has been carried out. In this paper the main construction parameters are discussed and test results will be given. Tests of the electronic readout were performed and the general feasibility of the detector is demonstrated.

  1. Laser rods with undoped, flanged end-caps for end-pumped laser applications

    DOEpatents

    Meissner, Helmuth E.; Beach, Raymond J.; Bibeau, Camille; Sutton, Steven B.; Mitchell, Scott; Bass, Isaac; Honea, Eric

    1999-01-01

    A method and apparatus for achieving improved performance in a solid state laser is provided. A flanged, at least partially undoped end-cap is attached to at least one end of a laserable medium. Preferably flanged, undoped end-caps are attached to both ends of the laserable medium. Due to the low scatter requirements for the interface between the end-caps and the laser rod, a non-adhesive method of bonding is utilized such as optical contacting combined with a subsequent heat treatment of the optically contacted composite. The non-bonded end surfaces of the flanged end-caps are coated with laser cavity coatings appropriate for the lasing wavelength of the laser rod. A cooling jacket, sealably coupled to the flanged end-caps, surrounds the entire length of the laserable medium. Radiation from a pump source is focussed by a lens duct and passed through at least one flanged end-cap into the laser rod.

  2. Synthesis and Properties of Phenylethynyl-Terminated, Star-Branched, Phenylquinoxaline Oligomers

    NASA Technical Reports Server (NTRS)

    Ooi, I. H.; Hergenrother, P. M.; Harris, F. W.

    2000-01-01

    The primary objective of this work was to prepare readily melt and solution processable phenylquinoxaline (PQ) oligomers that could be thermally crosslinked to solvent-resistant resins. Thus, a mixture of 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline (HPFQ) was used to prepare star-branched PQ oligomers end-capped with 4-fluoro-4-phenylethynylbenzophenone (FPEB). 1,1,1-Tris(4-hydroxyphenyl)ethane (THPE) was used as the branching unit. The oligomer number-average molecular weights (M (bar) (sub n) S) as determined by size exclusion chromatography (SEC) were close to the calculated values of 2922, 4698, 6474, and 13,578 g/mol, and their intrinsic viscosities ranged from 0.16 to 0.57 dl/g (m-cresol at 30 C). The oligomers, which were quite soluble in common organic solvents, had glass transition temperatures (T (sub g) S) that ranged from 181 to 233 C (DSC, DELTA T = 20 C/min). They also underwent an exothermic cure with maxima from 377 to 443 C. The T (sub g) S of the cured oligomers ranged from 259 to 284 C depending on the oligomer M (bar) (sub n) and the curing conditions. The oligomers had low melt viscosities, e.g. an oligomer (SPQ-46) with an M (bar) (sub n) of 4816 g/mol (SEC) had a melt viscosity of 150 Pa s at 348 C. A cured thin film of SPQ-46, which was insoluble in common organic solvents, had a room temperature (RT) tensile strength of 100 MPa, a RT modulus of 2358 MPa, and a RT elongation of 5.9%. A cured sample of SPQ-46 displayed a RT titanium-titanium lap shear tensile strength of 35.2 MPa. SPQ-46/carbon fiber(IM-7) composites, were prepared that displayed a RT flexural strength of 1902 MPa, a RT modulus of 1.38 GPa and a RT open hole compressive strength of 433 MPa.

  3. Diamines Containing Pendent Phenylethynyl Groups

    NASA Technical Reports Server (NTRS)

    Connell, John W. (Inventor); Smith, Joseph G., Jr. (Inventor); Hergenrother, Paul M. (Inventor)

    1997-01-01

    Controlled molecular weight imide oligomers and co-oligomers containing pendent phenylethynyl groups (PEPIs) and endcapped with nonreactive or phenylethynyl groups have been prepared by the cyclodehydration of the precursor amide acid oligomers or co-oligomers containing pendent phenylethynyl groups and endcapped with nonreactive or phenylethynyl groups. The amine terminated amide acid oligomers or co-oligomers are prepared from the reaction of dianhydride(s) with an excess of diamine(s) and diamine containing pendent phenylethynyl groups and subsequently endcapped with a phenylethynyl phthalic anhydride or monofunctional anhydride. The anhydride terminated amide acid oligomers and co-oligomers are prepared from the reaction of diamine(s) and diamine containing pendent phenylethynyl group(s) with an excess of dianhydride(s) and subsequently endcapped with a phenylethynyl amine or monofunctional amine. The polymerizations are carried out in polar aprotic solvents such as and N,N-dimethylacetamide under nitrogen at room temperature. The amide acid oligomers or co-oligomers are subsequently cyclodehydrated either thermally or chemically to the corresponding imide oligomers. The polymers and copolymers prepared from these materials exhibit a unique and unexpected combination of properties that includes higher glass transition temperatures after curing and higher retention of neat resin, adhesive and carbon fiber reinforced mechanical properties at temperatures up to 204 C under wet conditions without sacrificing melt flow behavior and processability as compared to similar materials. These materials are useful as adhesives, coatings, films, moldings, and composite matrices.

  4. Process for preparing phthalocyanine polymer from imide containing bisphthalonitrile

    NASA Technical Reports Server (NTRS)

    Achar, Bappalige N. (Inventor); Fohlen, George M. (Inventor); Parker, John A. (Inventor)

    1987-01-01

    Imide-linked bisphthalonitrile compounds are prepared by combining a dicyano aromatic diamine and an organic dianhydride to produce an amic acid linked bisphthalonitrile compound. The amic acid linked bisphthalonitrile compound is dehydrocyclized to produce the imide-linked bisphthalonitrile compounds. The imide-linked bisphthalonitrile compounds may be polymerized to produce a phythalocyanine polymer by heating the imide-linked bisphthalonitrile compound, either alone or in the presence of a metal powder or a metal salt. These compounds are useful in the coating, laminating and molding arts. The polymers are useful in composite matrix resins where increased fire resistance, toughness and resistance to moisture are required, particularly as secondary structures in aircraft and spacecraft.

  5. Preparation and properties of silane-endcapped polyimide adhesives

    NASA Technical Reports Server (NTRS)

    Maudgal, S.; St. Clair, T. L.

    1984-01-01

    Silane-endcapped polyimide high temperature adhesive formulations were prepared by reacting anhydride-terminated poly(amic acid), obtained from benzophenonetetracarboxylic dianhydride and a diamine (3,3'-, 3,4'- or 4,4'-diaminodiphenylmethane and 3,3', 3,4'- or 4,4'-diaminobenzophenone) with varying amounts of gama-aminopropyltriethoxysilane in dimethylacetamide. Resin properties were evaluated by torsional braid analysis and thermogravimetric analysis. Lap shear strengths of some of the adhesive bonds were determined at room temperature and at 177 C before and after ageing at 200 C for 2500 h and after boiling in water for 72 h.

  6. Substituted Cyclohexene Endcaps for Polymers with Thermal-Oxidative Stability

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This invention relates to polyimides having improved thermal-oxidative stability, to the process of preparing said polyimides, and the use of polyimide prepolymers in the preparation of prepregs and composites. The polyimides are particularly usefull in the preparation of fiber-reinforced, high-temperature composites for use in various engine parts including inlets, fan ducts, exit flaps and other parts of high speed aircraft. The polyimides are derived from the polymerization of effective amounts of at least one tetracarboxylic dianhydride, at least one polyamine and a novel dicarboxylic endcap having the formula presented.

  7. 78 FR 57285 - 2,5-Furandione, Polymer With Ethenylbenzene, Hydrolyzed, 3-(Dimethylamino)propyl Imide, Imide...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-18

    ...This regulation establishes an exemption from the requirement of a tolerance for residues of 2,5-furandione, polymer with ethenylbenzene, hydrolyzed, 3-(dimethylamino)propyl imide, imide with polyethylene-polypropylene glycol 2-aminopropyl me ether, 2,2'-(1,2- diazenediyl)bis[2-methylbutanenitrile]-initiated (CAS Reg. No. 1062609- 13-5) when used as an inert ingredient in a pesticide......

  8. Overlap Technique for End-Cap Seals on Cylindrical Magnetic Shields

    NASA Astrophysics Data System (ADS)

    Malkowski, S.; Adhikari, R. Y.; Boissevain, J.; Daurer, C.; Filippone, B. W.; Hona, B.; Plaster, B.; Woods, D.; Yan, H.

    2013-01-01

    We present results from studies of the effectiveness of an overlap technique for forming a magnetic seal across a gap at the boundary between a cylindrical magnetic shield and an end-cap. In this technique a thin foil of magnetic material overlaps the two surfaces, thereby spanning the gap across the cylinder and the end-cap, with the magnetic seal then formed by clamping the thin magnetic foil to the surfaces of the cylindrical shield and the end-cap on both sides of the gap. In studies with a prototype 31-cm diameter, 91-cm long, 0.16-cm thick cylindrical magnetic shield and flared end-cap, the magnetic shielding performance of our overlap technique is comparable to that obtained with the conventional method in which the end-cap is placed in direct lapped contact with the cylindrical shield via through bolts or screws.

  9. The backward end-cap for the PANDA electromagnetic calorimeter

    NASA Astrophysics Data System (ADS)

    Capozza, L.; Maas, F. E.; Noll, O.; Rodriguez Pineiro, D.; Valente, R.

    2015-02-01

    The PANDA experiment at the new FAIR facility will cover a broad experimental programme in hadron structure and spectroscopy. As a multipurpose detector, the PANDA spectrometer needs to ensure almost 4π coverage of the scattering solid angle, full and accurate multiple-particle event reconstruction and very good particle identification capabilities. The electromagnetic calorimeter (EMC) will be a key item for many of these aspects. Particle energies ranging from some MeVs to several GeVs have to be measured with a relative resolution of 1% ⊕ 2%/√E/GeV . It will be a homogeneous calorimeter made of PbWO4 crystals and will be operated at -25°C, in order to improve the scintillation light yield. With the exception of the very forward section, the light will be detected by large area avalanche photodiodes (APDs). The current pulses from the APDs will be integrated, amplified and shaped by ASIC chips which were developed for this purpose. The whole calorimeter has been designed in three sections: a forward end-cap, a central barrel and a backward end-cap (BWEC). In this contribution, a status report on the development of the BWEC is presented.

  10. High-photosensitivity p-channel organic phototransistors based on a biphenyl end-capped fused bithiophene oligomer

    SciTech Connect

    Noh, Yong-Young; Kim, Dong-Yu; Yoshida, Yuji; Yase, Kiyoshi; Jung, Byung-Jun; Lim, Eunhee; Shim, Hong-Ku

    2005-01-24

    We report highly photosensitive organic phototransistors (OPTs) based on a 2,5-bis-biphenyl-4-yl-thieno[3,2-b]thiophene (BPTT). The measured maximum sensitivity and the ratio of photocurrent to dark current (I{sub ph}/I{sub dark}) in BPTT OPTs were 82 A/W and 2.0x10{sup 5} under 380 nm UV light with 1.55 mW/cm{sup 2}, respectively. The prepared OPTs show a photocurrent response similar to the absorption spectrum of BPTT. The major mechanisms for photocurrent amplification in this device were verified from experimental results as photovoltaic (turn-on) and photocurrent effect (turn-off) by a fitting to theoretic equations.

  11. Recent Results From The ATLAS Endcap Combined Test Beam

    SciTech Connect

    Schacht, Peter

    2006-10-27

    The ATLAS detector at the LHC at CERN is entering the last phase of construction, with the ATLAS calorimeter passing already the first steps of commissioning. The endcap region in the range of pseudorapidity 2.4 < |{eta}| < 4.0 is a particular complex one, with the electromagnetic, hadronic and forward calorimeters. In a dedicated beam run this region has been studied using the individual calorimeter modules. The set-up was as close as possible to the real ATLAS calorimeter, including all details like inactive support material structures. The goal is to validate the MC simulation for the different regions and to cross check the intercalibration of the various calorimeters. Electron and pion data have been taken in an energy range 6 < E < 200 GeV with special emphasis on lateral and vertical scans to study the transition regions in detail.

  12. Decomposition of lithium amide and imide films on nickel

    NASA Astrophysics Data System (ADS)

    Engbæk, Jakob; Nielsen, Gunver; Nielsen, Jane H.; Chorkendorff, Ib

    2007-02-01

    Thin films of lithium hydride, lithium amide and lithium imide were grown from lithium and ammonia under controlled conditions in an ultra high vacuum chamber. By making thin films instead of bulk or powder samples, it was possible to study the stability and the release of hydrogen without influence of transport phenomena. Surprisingly, lithium amide and lithium imide were seen to decompose at higher temperatures than lithium hydride. Furthermore, it was seen that hydrogen reversibly could be removed by heat treatment and subsequently refilled.

  13. Photophysics and redox properties of rylene imide and diimide dyes alkylated ortho to the imide groups.

    PubMed

    Bullock, Joseph E; Vagnini, Michael T; Ramanan, Charusheela; Co, Dick T; Wilson, Thea M; Dicke, Jay W; Marks, Tobin J; Wasielewski, Michael R

    2010-02-11

    Ruthenium-catalyzed C-H bond activation was used to directly attach phenethyl groups derived from styrene to positions ortho to the imide groups in a variety of rylene imides and diimides including naphthalene-1,8-dicarboximide (NMI), naphthalene-1,4:5,8-bis(dicarboximide) (NI), perylene-3,4-dicarboximide (PMI), perylene-3,4:9,10-bis(dicarboximide) (PDI), and terrylene-3,4:11,12-bis(dicarboximide) (TDI). The monoimides were dialkylated, while the diimides were tetraalkylated, with the exception of NI, which could only be dialkylated due to steric hindrance. The absorption, fluorescence, transient absorption spectra, and lowest excited singlet state lifetimes of these chromophores, with the exception of NI, are nearly identical to those of their unsubstituted parent chromophores. The reduction potentials of the dialkylated chromophores are approximately 100 mV more negative and oxidation potentials are approximately 40 mV less positive than those of the parent compounds, while the corresponding potentials of the tetraalkylated compounds are approximately 200 mV more negative and approximately 100 mV less positive than those of their parent compounds, respectively. Continuous wave electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) data on the radical anion of PDI reveals spin density on the perylene-core protons as well as on the beta-protons of the phenethyl groups. The phenethyl groups enhance the otherwise poor solubility of the bis(dicarboximide) chromophores and only weakly perturb the photophysical and redox properties of the parent molecules, rendering these derivatives and related molecules of significant interest to solar energy conversion. PMID:20073517

  14. Laser rods with undoped, flanged end-caps for end-pumped laser applications

    DOEpatents

    Meissner, H.E.; Beach, R.J.; Bibeau, C.; Sutton, S.B.; Mitchell, S.; Bass, I.; Honea, E.

    1999-08-10

    A method and apparatus for achieving improved performance in a solid state laser is provided. A flanged, at least partially undoped end-cap is attached to at least one end of a laserable medium. Preferably flanged, undoped end-caps are attached to both ends of the laserable medium. Due to the low scatter requirements for the interface between the end-caps and the laser rod, a non-adhesive method of bonding is utilized such as optical contacting combined with a subsequent heat treatment of the optically contacted composite. The non-bonded end surfaces of the flanged end-caps are coated with laser cavity coatings appropriate for the lasing wavelength of the laser rod. A cooling jacket, sealably coupled to the flanged end-caps, surrounds the entire length of the laserable medium. Radiation from a pump source is focused by a lens duct and passed through at least one flanged end-cap into the laser rod. 14 figs.

  15. Bipolar Charge Transport Properties of Poly(imide-thienyl(thienylenevinylene))

    NASA Astrophysics Data System (ADS)

    Lafalce, Evan; Jiang, Xiaomei; Zhang, Cheng

    2014-03-01

    The charge transport properties of π-conjugated polymers are of interest from a fundamental perspective and also because they are a limiting factor for many optoelectronic device applications. In this work, we study the charge carrier mobility and recombination in Poly(imide-thienyl(thienylenevinylene)) (imide-PTV), a novel PTV derivative with imide side group. The electron and hole mobility are determined separately through the Space Charge Limited Current (SCLC) analysis of single carrier diodes. These devices are fabricated using interfacial layers that provide carrier selective contacts. A mobility asymmetry factor of approximately 20 that favors hole transport is observed, with the hole mobility of the order of 10-5 [cm2/V*s]. Similar results are obtained from the analysis of the intensity dependence of photoconductivity. Complimentary analysis of the ambipolar carrier mobility through carrier extraction under linearly increasing voltage (CELIV) and double injection transient techniques are also presented. The effects of carrier recombination and trapping are discussed. We conclude that the hole transport is not the limiting factor for power conversion efficiency of photovoltaic device based on imide-PTV and PCBM.

  16. 21 CFR 177.2450 - Polyamide-imide resins.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...)(1) of this section shall have a solution viscosity of not less than 1.200. Polyamide-imide resins identified in paragraph (a)(2) of this section shall have a solution viscosity of not less than 1.190. Solution viscosity shall be determined by a method titled “Solution Viscosity” which is incorporated...

  17. 21 CFR 177.2450 - Polyamide-imide resins.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... paragraph (a)(1) of this section shall have a solution viscosity of not less than 1.200. Polyamide-imide resins identified in paragraph (a)(2) of this section shall have a solution viscosity of not less than 1.190. Solution viscosity shall be determined by a method titled “Solution Viscosity” which...

  18. 21 CFR 177.2450 - Polyamide-imide resins.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... paragraph (a)(1) of this section shall have a solution viscosity of not less than 1.200. Polyamide-imide resins identified in paragraph (a)(2) of this section shall have a solution viscosity of not less than 1.190. Solution viscosity shall be determined by a method titled “Solution Viscosity” which...

  19. 21 CFR 177.2450 - Polyamide-imide resins.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... paragraph (a)(1) of this section shall have a solution viscosity of not less than 1.200. Polyamide-imide resins identified in paragraph (a)(2) of this section shall have a solution viscosity of not less than 1.190. Solution viscosity shall be determined by a method titled “Solution Viscosity” which...

  20. 21 CFR 177.2450 - Polyamide-imide resins.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... paragraph (a)(1) of this section shall have a solution viscosity of not less than 1.200. Polyamide-imide resins identified in paragraph (a)(2) of this section shall have a solution viscosity of not less than 1.190. Solution viscosity shall be determined by a method titled “Solution Viscosity” which...

  1. Synthesis of Aryl Ketoamides via Aryne Insertion into Imides.

    PubMed

    Wright, Austin C; Haley, Christopher K; Lapointe, Guillaume; Stoltz, Brian M

    2016-06-17

    An insertion of arenes into both imides and anhydrides via reactive aryne intermediates is presented. The reaction is performed under exceptionally mild conditions, and the corresponding ketoamide products are amenable to derivatization to deliver a variety of synthetically useful motifs such as quinolones, indoles, and ketoanilines. PMID:27266278

  2. Solvent-Resistant, Thermally Stable Poly(Carbonate-Imides)

    NASA Technical Reports Server (NTRS)

    St. Clair, T. L.; Wakelyn, N. T.; Maudgal, S.; Pratt, J. R.

    1986-01-01

    New polymers and copolymers based on polyimide backbone with carbonate moieties exhibit high temperature capability. Because of carbonate unit, many of these materials also exhibit high order or crystallinity. All of new imidecontaining polymers insensitive to acetone. New poly (carbonate-imide) exhibits significantly increased temperature resistance and shows less sensitivity to solvents than commercial polycarbonates.

  3. Polyimide and polyamide-imide in a tritium atmosphere

    SciTech Connect

    Wylie, K.F.; Hockett, J.E.; Buxton, T.L.

    1981-01-01

    Five different commercial polyamide-imide and polyimide specimens were kept in a tritium atmosphere (96.9 mol %, 101 kPa, initial fill conditions) for three months. Selected physical and mechanical properties of the five plastics were examined. Mass spectrometric data showed the growth of protium and HT impurity in the tritium gas.

  4. Ballistic Energy Transport in Oligomers.

    PubMed

    Rubtsova, Natalia I; Qasim, Layla N; Kurnosov, Arkady A; Burin, Alexander L; Rubtsov, Igor V

    2015-09-15

    The development of nanocomposite materials with desired heat management properties, including nanowires, layered semiconductor structures, and self-assembled monolayer (SAM) junctions, attracts broad interest. Such materials often involve polymeric/oligomeric components and can feature high or low thermal conductivity, depending on their design. For example, in SAM junctions made of alkane chains sandwiched between metal layers, the thermal conductivity can be very low, whereas the fibers of ordered polyethylene chains feature high thermal conductivity, exceeding that of many pure metals. The thermal conductivity of nanostructured materials is determined by the energy transport between and within each component of the material, which all need to be understood for optimizing the properties. For example, in the SAM junctions, the energy transport across the metal-chain interface as well as the transport through the chains both determine the overall heat conductivity, however, to separate these contributions is difficult. Recently developed relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy is capable of studying energy transport in individual molecules in the time domain. The transport in a molecule is initiated by exciting an IR-active group (a tag); the method records the influence of the excess energy on another mode in the molecule (a reporter). The energy transport time can be measured for different reporters, and the transport speed through the molecule is evaluated. Various molecules were interrogated by RA 2DIR: in molecules without repeating units (disordered), the transport mechanism was expected and found to be diffusive. The transport via an oligomer backbone can potentially be ballistic, as the chain offers delocalized vibrational states. Indeed, the transport regime via three tested types of oligomers, alkanes, polyethyleneglycols, and perfluoroalkanes was found to be ballistic, whereas the transport within the end groups was diffusive

  5. Super radiation hard vacuum phototriodes for the CMS endcap ECAL

    NASA Astrophysics Data System (ADS)

    Gusev, Yu. I.; Kovalev, A. I.; Levchenko, L. A.; Lukianov, V. N.; Moroz, F. V.; Mamaeva, G. A.; Seliverstov, D. M.; Trautman, V. Yu.; Yakorev, D. O.

    2004-12-01

    The energy resolution σ/E of the electromagnetic calorimeter (ECAL) in the energy range of 50-500 GeV is defined mainly by two terms: stochastic α/√E and constant C. The photoreadout of the CMS Endcap ECAL consists of vacuum phototriodes (VPT), which are broadening a signal from np photoelectrons characterized by the excess noise factor F=np(σ/E)2. The technical specification of the CMS ECAL requires the value of F to be smaller than 4 in the CMS LHC environment during 10 years of detector operation. In this paper we present results of the VPT performance study in a magnetic field up to 4 T, in a gamma radiation field of 0-50 kGy and in a neutron fluence of 7×1015 n/cm2. The standard phototriodes FEU-188 with faceplates from UV glass used in CMS ECAL as well as VPTs with super radiation hard cerium-doped glasses were investigated at the 60Co gamma facility, a neutron generator and a nuclear reactor in the Petersburg Nuclear Physics Institute (PNPI). The dependence of the VPT gain and the excess noise factor in magnetic fields on the fine-mesh plane orientation has also been studied.

  6. Radiation testing of electronics for the CMS endcap muon system

    NASA Astrophysics Data System (ADS)

    Bylsma, B.; Cady, D.; Celik, A.; Durkin, L. S.; Gilmore, J.; Haley, J.; Khotilovich, V.; Lakdawala, S.; Liu, J.; Matveev, M.; Padley, B. P.; Roberts, J.; Roe, J.; Safonov, A.; Suarez, I.; Wood, D.; Zawisza, I.

    2013-01-01

    The electronics used in the data readout and triggering system for the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) particle accelerator at CERN are exposed to high radiation levels. This radiation can cause permanent damage to the electronic circuitry, as well as temporary effects such as data corruption induced by Single Event Upsets. Once the High Luminosity LHC (HL-LHC) accelerator upgrades are completed it will have five times higher instantaneous luminosity than LHC, allowing for detection of rare physics processes, new particles and interactions. Tests have been performed to determine the effects of radiation on the electronic components to be used for the Endcap Muon electronics project currently being designed for installation in the CMS experiment in 2013. During these tests the digital components on the test boards were operating with active data readout while being irradiated with 55 MeV protons. In reactor tests, components were exposed to 30 years equivalent levels of neutron radiation expected at the HL-LHC. The highest total ionizing dose (TID) for the muon system is expected at the innermost portion of the CMS detector, with 8900 rad over 10 years. Our results show that Commercial Off-The-Shelf (COTS) components selected for the new electronics will operate reliably in the CMS radiation environment.

  7. Combined Forward Calorimetry Option for Phase II CMS Endcap Upgrade

    NASA Astrophysics Data System (ADS)

    Akchurin, Nural

    2015-02-01

    Traditionally, EM and HAD compartments are thought to be separate and are often optimized individually. However, it is possible to optimize a robust and economical combined calorimeter system for myriad physics objectives. By employing event-by-event compensation afforded by the dual-readout technique, we have shown that excellent jet performance can be attained with a longitudinally un-segmented calorimeter that is calibrated only with electrons. In addition, the linear hadronic energy scale renders complex off-line correction schemes unnecessary. The proposed replacement of the CMS EE and HE calorimeters with a single Combined Forward Calorimeter (CFC) shows excellent jet performance complemented by good EM object detection. In this paper, we give brief snapshots on basic design criteria, timing characteristics of Cherenkov and scintillation pulses, trigger generation criteria and performance under high radiation fields. Although CMS has recently chosen different technologies for its endcap calorimetry in Phase II, the concepts developed here are likely to remain valuable for some time to come.

  8. Oxygen plasma resistant phosphine oxide containing imide/arylene copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.

    1993-01-01

    A series of oxygen plasma resistant imide/arylene ether copolymers were prepared by reacting anhydride-terminated poly(amide acids) and amine-terminated polyarylene ethers containing phosphine oxide units. Inherent viscosities for these copolymers ranged from 0.42 to 0.80 dL/g. After curing, the resulting copolymers had glass transition temperatures ranging from 224 C to 228 C. Solution cast films of the block copolymers were tough and flexible with tensile strength, tensile moduli, and elongation at break up to 16.1 ksi, 439 ksi, and 23 percent, respectively at 25 C and 9.1 ksi, 308 ksi and 97 percent, respectively at 150 C. The copolymers show a significant improvement in resistance to oxygen plasma when compared to the commercial polyimide Kapton. The imide/arylene ether copolymers containing phosphine oxide units are suitable as coatings, films, adhesives, and composite matrices.

  9. Pyrazine-imide complexes: reversible redox and MOF building blocks.

    PubMed

    Cowan, Matthew G; Miller, Reece G; Brooker, Sally

    2015-02-14

    The synthesis of the symmetric pyrazine imide ligand, N-(2-pyrazylcarbonyl)-2-pyrazinecarboxamide, (Hdpzca) and five new first row transition metal complexes of it are reported: [M(II)(dpzca)(2)], M(II) = Fe, Cu, Zn; [Cu(II)(dpzca)(H(2)O)(2)]BF(4), [Cu(II)(dpzca)(H(2)O)(3)](2)SiF(6). The crystal structures of Hdpzca, [Co(II)(dpzca)(2)], [Cu(II)(dpzca)(2)], {[Co(III)(dpzca)(2)](BF(4))}(2)·5CH(3)CN and [Cu(II)(dpzca)(H(2)O)(3))](2)SiF(6)·2H(2)O were determined and reveal an orthogonal positioning of the 'spare' pyrazine nitrogen atoms and 'spare' pairs of imide oxygen atoms. The [M(II)(dpzca)(2)] complexes are therefore useful six-coordinate building blocks for producing larger supramolecular assemblies. Two examples of secondary assembly of [M(II)(dpzca)(2)] complexes, with M = Co and Ni, with silver nitrate gave single crystals; {[Co(III)(dpzca)(2)Ag](NO(3))(2)·2H(2)O}n and {([Ni(II)(dpzca)(2)Ag(I)(1/2)](1/2NO(3))(xH(2)O}n were structurally characterised. The redox processes of [M(II)(dpzca)(2)], with M(II) = Fe, Ni, Cu and Zn, are reported and, as seen for M(II) = Co, reversible metal- and ligand-based redox processes are observed, with E(m)(M(II)/M(III)) values 0.15-0.24 V higher than for the analogous complexes of Hpypzca (non-symmetric pyridine/pyrazine imide ligand), and 0.35-0.36 V higher than for the complexes of Hbpca (symmetric pyridine imide ligand). PMID:25563508

  10. Discovery of the target for immunomodulatory drugs (IMiDs).

    PubMed

    Ito, Takumi; Ando, Hideki; Handa, Hiroshi

    2016-05-01

    Half a century ago, the sedative thalidomide caused a serious drug disaster because of its teratogenicity and was withdrawn from the market. However, thalidomide, which has returned to the market, is now used for the treatment of leprosy and multiple myeloma (MM) under strict control. The mechanism of thalidomide action had been a long-standing question. We developed a new affinity bead technology and identified cereblon (CRBN) as a thalidomide-binding protein. We found that CRBN functions as a substrate receptor of an E3 cullin-Ring ligase complex 4 (CRL4) and is a primary target of thalidomide teratogenicity. Recently, new thalidomide derivatives, called immunomodulatory drugs (IMiDs), have been developed by Celgene. Among them, lenalidomide (Len) and pomalidomide (Pom) were shown to exert strong therapeutic effects against MM. It was found that Len and Pom both bind CRBN-CRL4 and recruit neomorphic substrates (Ikaros and Aiolos). More recently it was reported that casein kinase 1a (Ck1a) was identified as a substrate for CRBN-CRL4 in the presence of Len, but not Pom. Ck1a breakdown explains why Len is specifically effective for myelodysplastic syndrome with 5q deletion. It is now proposed that binding of IMiDs to CRBN appears to alter the substrate specificity of CRBN-CRL4. In this review, we introduce recent findings on IMiDs. PMID:27263779

  11. In Situ Poling and Imidization of Amorphous Piezoelectric Polyimides

    NASA Technical Reports Server (NTRS)

    Park, Cheol; Ounaies, Zoubeida; Wise, Kristopher E.; Harrison, Joycelyn S.; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    An amorphous piezoelectric polyimide containing polar functional groups has been developed using a combination of experimental and molecular modeling for potential use in high temperature applications. This amorphous polyimide, (Beta-CN)APB/ODPA, has exhibited good thermal stability and piezoelectric response at temperatures up to 150C. Density functional calculations predicted that a partially cured amic acid (open imide ring) possesses a dipole moment four times larger than the fully imidized closed ring. In situ poling and imidization of the partially cured (Beta-CN)APB/ODPA, was studied in an attempt to maximize the degree of dipolar orientation and the resultant piezoelectric response. A positive corona poling was used to minimize localized arcing during poling and to allow use of higher poling fields without dielectric breakdown. The dielectric relaxation strength, remanent polarization, and piezoelectric response were evaluated as a function of the poling profile. The partially cured, corona poled polymers exhibited higher dielectric relaxation strength (delta varepsilon), remanent polarization (Pr) and piezoelectric strain coefficient (d33) than the fully cured, conventionally poled ones.

  12. Approaches to New Endcaps for Improved Oxidation Resistance

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Frimer, Aryeh A.

    1999-01-01

    Norbornenyl-end capped PMR polyimide resins are widely used as polymer matrix composite materials for aircraft engine applications, since they combine ease of processing with good oxidative stability up to 300 C. PMR resins are prepared by a two-step approach involving the initial formation of oligomeric pre-polymers capped at both ends by a latent reactive end cap. The end cap undergoes cross-linking during higher temperature processing, producing the desired low density, high specific strength materials, for PMR- 15. The end cap facilitates processing by controlling the molecular weight of the oligomer and allowing flow before it cross-links. However, after cross-linking, this very end cap accounts for much of the weight loss in the polymer on aging in air at elevated temperatures. Understanding this degradation provides clues for designing new end caps to slow down degradation, and prolong the lifetime of the material.

  13. High char imide-modified epoxy matrix resins. [for graphite-epoxy composites

    NASA Technical Reports Server (NTRS)

    Serafini, T. T.; Delvigs, P.; Vannucci, R. D.

    1979-01-01

    The synthesis of a class of bis(imide-amine) curing agents for epoxy matrix resins is discussed. Glass transition temperatures and char yield data of an epoxy cured with various bis(imide-amines) are presented. The room temperature and 350 F mechanical properties, and char yields of unidirectional graphite fiber laminates prepared with conventional epoxy and imide-modified epoxy resins are presented.

  14. Structural Insight into Proteorhodopsin Oligomers

    PubMed Central

    Stone, Katherine M.; Voska, Jeda; Kinnebrew, Maia; Pavlova, Anna; Junk, Matthias J.N.; Han, Songi

    2013-01-01

    Oligomerization has important functional implications for many membrane proteins. However, obtaining structural insight into oligomeric assemblies is challenging, as they are large and resist crystallization. We focus on proteorhodopsin (PR), a protein with seven transmembrane α-helices that was found to assemble to hexamers in densely packed lipid membrane, or detergent-solubilized environments. Yet, the structural organization and the subunit interface of these PR oligomers were unknown. We used site-directed spin-labeling together with electron spin-resonance lineshape and Overhauser dynamic nuclear polarization analysis to construct a model for the specific orientation of PR subunits within the hexameric complex. We found intersubunit distances to average 16 Å between neighboring 55 residues and that residues 177 are >20 Å apart from each other. These distance constraints show that PR has a defined and radial orientation within a hexamer, with the 55-site of the A-B loop facing the hexamer core and the 177-site of the E-F loop facing the hexamer exterior. Dynamic nuclear polarization measurements of the local solvent dynamics complement the electron spin-resonance-based distance analysis, by resolving whether protein surfaces at positions 55, 58, and 177 are exposed to solvent, or covered by protein-protein or protein-detergent contacts. PMID:23442869

  15. Mixture of cholesterol end-capped polyethylene glycol with DSPC liposomal

    NASA Astrophysics Data System (ADS)

    Sharifi, Soheil

    2015-07-01

    The dynamic of network of self-assembled liposome by end-capped polymer was investigated using dynamic light scattering. The liposome network, physically cross-linked by mixed liposome solutions with three different length scale of cholesterol end-capped polyethylene glycol. The network of liposome is dependent on both the polymer concentration and length scale. In the pure liposome, one motion at low time scale is observed by DLS. In the higher concentration of polymer in liposome, several motion is observed that the fast motion is alpha relaxation and other two slow motion are beta and gamma relaxations. The distance between diffusion coefficient of fast and slow relaxation is increased with increase of length scale of endcapped polymers. The SAXS data is fitted with a Percus-Yevick hard sphere model and it shows that the size of liposome increasing with increase of polymer length scale in the mixture system.

  16. Lorentz angle studies for the SLD endcap Cerenkov Ring Imaging Detector

    SciTech Connect

    Coyle, P.; Cavalli-Sforza, M.; Coyne, D.; Schneider, M.; Spencer, E.; Williams, D.; Ashford, V.; Bienz, T.; Bird, F.; Gaillard, M.

    1987-11-01

    The design of the endcap Cerenkov Ring Imaging Detectors for SLD requires a detailed understanding of how electrons drift in gases under the influence of crossed electric and magnetic fields. In this report, we present recent measurements of Lorentz angles and drift velocities in gases suitable for the endcap CRID photon detectors. We compare these measurements to predictions from a theoretical model; good agreement is observed. Based on our results we present a design for detectors operating in a 0.6 Tesla transverse magnetic field. 14 refs., 10 figs., 4 tabs.

  17. Cementitious building material incorporating end-capped polyethylene glycol as a phase change material

    DOEpatents

    Salyer, Ival O.; Griffen, Charles W.

    1986-01-01

    A cementitious composition comprising a cementitious material and polyethylene glycol or end-capped polyethylene glycol as a phase change material, said polyethylene glycol and said end-capped polyethylene glycol having a molecular weight greater than about 400 and a heat of fusion greater than about 30 cal/g; the compositions are useful in making pre-formed building materials such as concrete blocks, brick, dry wall and the like or in making poured structures such as walls or floor pads; the glycols can be encapsulated to reduce their tendency to retard set.

  18. Performance of the prototype readout system for the CMS endcap hadron calorimeter upgrade

    NASA Astrophysics Data System (ADS)

    Pastika, N. J.

    2016-03-01

    The CMS experiment at the CERN Large Hadron Collider (LHC) will upgrade the photon detection and readout systems of its barrel and endcap hadron calorimeters (HCAL) through the second long shutdown of the LHC in 2018. The upgrade includes new silicon photomultipliers (SiPMs), SiPM control electronics, signal digitization via the Fermilab QIE11 ASIC, data formatting and serialization via a Microsemi FPGA, and data transmission via CERN Versatile Link technology. The first prototype system for the endcap HCAL has been assembled and characterized on the bench and in a test beam. The design of this new system and prototype performance are described.

  19. Design and performance of the alignment system for the CMS muon endcaps

    SciTech Connect

    Hohlmann, Marcus; Baksay, Gyongyi; Browngold, Max; Dehmelt, Klaus; Guragain, Samir; Andreev, Valery; Yang, Xiaofeng; Bellinger, James; Carlsmith, Duncan; Feyzi, Farshid; Loveless, Richard J.; /Florida Inst. Tech. /UCLA /Wisconsin U., Madison /UC, Davis /Fermilab /St. Petersburg, INP /UC, Riverside

    2006-12-01

    The alignment system for the CMS Muon Endcap detector employs several hundred sensors such as optical 1-D CCD sensors illuminated by lasers and analog distance- and tilt-sensors to monitor the positions of one sixth of 468 large Cathode Strip Chambers. The chambers mounted on the endcap yoke disks undergo substantial deformation on the order of centimeters when the 4T field is switched on and off. The Muon Endcap alignment system is required to monitor chamber positions with 75-200 {micro}m accuracy in the R? plane, {approx}400 {micro}m in the radial direction, and {approx}1 mm in the z-direction along the beam axis. The complete alignment hardware for one of the two endcaps has been installed at CERN. A major system test was performed when the 4T solenoid magnet was ramped up to full field for the first time in August 2006. We present the overall system design and first results on disk deformations, which indicate that the measurements agree with expectations.

  20. Functionalized Metallated Cavitands via Imidation and Late-Stage Elaboration

    PubMed Central

    Zhao, Yanchuan

    2015-01-01

    Efficient methods for the preparation of functionalized metallated cavitands are described. Functional groups can be either introduced by an imidation of metal-oxo complexes or by a late-stage elaboration of the imido ligands. By using diversified iminophosphorane (PPh3=NR) reagents, π-conjugated pyrene, redox active ferrocene and polymerizable norbornene moieties were successfully introduced. Furthermore, the iodo and alkynyl groups on the imido ligands are capable of undergoing efficient Sonogashira cross-coupling and copper-catalyzed azide alkyne cycloaddition reactions, thereby providing facile access to complex architectures containing metallated cavitands. PMID:26962300

  1. The application and biology of immunomodulatory drugs (IMiDs) in cancer.

    PubMed

    Pan, Beiqing; Lentzsch, Suzanne

    2012-10-01

    Immunomodulatory drugs (IMiDs) have been used in hematologic malignancies for the last decade. However, the mechanism of action of IMiDs is largely unknown. Here we provide a comprehensive overview of pivotal studies, recent advances in the application of IMiDs in cancer as well as their effects on hematopoietic stem cells including the risk of secondary malignancies. IMiDs have a well-established role as first-line therapy for patients with newly diagnosed and relapsed/refractory multiple myeloma (MM). Variant combinations of IMiDs with other chemotherapy reagents show promising outcomes in MM. Recent concerns on increased rate of secondary cancer in MM patients treated with maintenance lenalidomide were raised. But analysis of maintenance studies showed that the benefit of maintenance outweighs the risk of secondary cancers in MM. IMiDs also show efficacy in myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), Non-Hodgkin's lymphoma (NHL) and myelofibrosis (MF), but not in solid tumors. The major adverse effects are venous thromboembolism, neuropathy and cytopenias. IMiDs induce expansion and self-renewal of CD34+ hematopoietic progenitors and inhibit lineage maturation/differentiation by affecting critical transcription factors which might contribute to myelosuppression effect of IMiDs. PMID:22796518

  2. Efficient end-capping synthesis of neutral donor-acceptor [2]rotaxanes under additive-free and mild conditions.

    PubMed

    Domoto, Yuya; Sase, Shohei; Goto, Kei

    2014-11-24

    Efficient end-capping synthesis of neutral donor-acceptor (D-A) [2]rotaxanes without loading any catalysts or activating agents was achieved by utilizing high reactivity of a pentacoordinated hydrosilane toward salicylic acid derivatives. As components of [2]rotaxanes, an electron-deficient naphthalenediimide-containing axle with a salicylic acid terminus and several electron-rich bis(naphthocrown) ether macrocycles were employed. End-capping reactions with the pentacoordinated hydrosilane underwent smoothly even at low temperature to afford the corresponding [2]rotaxanes in good yields. A [2]rotaxane containing bis-1,5-(dinaphtho)-38-crown-10 ether as a wheel molecule was synthesized and isolated in 84% yield by the end-capping at -10 °C, presenting the highest yield ever reported for the end-capping synthesis of a neutral D-A [2]rotaxane. It was found that the yields of the [2]rotaxanes in the end-capping reactions were almost parallel to the formation ratios of the corresponding pseudo[2]rotaxanes estimated by utilizing model systems. These results indicate that the end-capping reaction using the pentacoordinated hydrosilane proceeded without perturbing the threading process, and most of the pseudo[2]rotaxanes underwent efficient end-capping reaction even at low temperature. PMID:25284148

  3. Phosphorus-containing imide resins - Modification by elastomers

    NASA Technical Reports Server (NTRS)

    Varma, I. K.; Fohlen, G. M.; Parker, J. A.; Varma, D. S.

    1984-01-01

    The syntheses and general features of addition-type maleimide resins based on bis(m-aminophenyl)phosphine oxide and tris(m-aminophenyl)phosphine oxide have been reported previously. These resins have been used to fabricate graphite cloth laminates having excellent flame resistance. These composites did not burn even in pure oxygen. However, these resins were somewhat brittle. This paper reports the modification of these phosphorus-containing resins by an amine-terminated butadiene-acrylonitrile copolymer (ATBN) and a perfluoroalkylene diaromatic amine elastomer (3F). An approximately two-fold increase in short beam shear strength and flexural strength was observed at 7 percent ATBN concentration. The tensile, flexural, and shear strengths were reduced when 18 percent ATBN was used. Anaerobic char yields of the resins at 800 C and the limiting oxygen indexes of the laminates decreased with increasing ATBN concentration. The perfluorodiamine (3F) was used with both imide resins at 6.4 percent concentration. The shear strength was doubled in the case of the bisimide with no loss of flammability characteristics. The modified trisimide laminate also had improved properties over the unmodified one. The dynamic mechanical analysis of a four-ply laminate indicated a glass transition temperature above 300 C. Scanning electron micrographs of the ATBN modified imide resins were also recorded.

  4. Incomplete pneumolysin oligomers form membrane pores.

    PubMed

    Sonnen, Andreas F-P; Plitzko, Jürgen M; Gilbert, Robert J C

    2014-01-01

    Pneumolysin is a member of the cholesterol-dependent cytolysin (CDC) family of pore-forming proteins that are produced as water-soluble monomers or dimers, bind to target membranes and oligomerize into large ring-shaped assemblies comprising approximately 40 subunits and approximately 30 nm across. This pre-pore assembly then refolds to punch a large hole in the lipid bilayer. However, in addition to forming large pores, pneumolysin and other CDCs form smaller lesions characterized by low electrical conductance. Owing to the observation of arc-like (rather than full-ring) oligomers by electron microscopy, it has been hypothesized that smaller oligomers explain smaller functional pores. To investigate whether this is the case, we performed cryo-electron tomography of pneumolysin oligomers on model lipid membranes. We then used sub-tomogram classification and averaging to determine representative membrane-bound low-resolution structures and identified pre-pores versus pores by the presence of membrane within the oligomeric curve. We found pre-pore and pore forms of both complete (ring) and incomplete (arc) oligomers and conclude that arc-shaped oligomeric assemblies of pneumolysin can form pores. As the CDCs are evolutionarily related to the membrane attack complex/perforin family of proteins, which also form variably sized pores, our findings are of relevance to that class of proteins as well. PMID:24759615

  5. Wholly Aromatic Ether-Imides as n-Type Semiconductors

    NASA Technical Reports Server (NTRS)

    Weiser, Erik; St. Clair, Terry L.; Dingemans, Theo J.; Samulski, Edward T.; Irene, Gene

    2006-01-01

    Some wholly aromatic ether-imides consisting of rod-shaped, relatively-low-mass molecules that can form liquid crystals have been investigated for potential utility as electron-donor-type (ntype) organic semiconductors. It is envisioned that after further research to improve understanding of their physical and chemical properties, compounds of this type would be used to make thin film semiconductor devices (e.g., photovoltaic cells and field-effect transistors) on flexible electronic-circuit substrates. This investigation was inspired by several prior developments: Poly(ether-imides) [PEIs] are a class of engineering plastics that have been used extensively in the form of films in a variety of electronic applications, including insulating layers, circuit boards, and low-permittivity coatings. Wholly aromatic PEIs containing naphthalene and perylene moieties have been shown to be useful as electrochromic polymers. More recently, low-molecular-weight imides comprising naphthalene-based molecules with terminal fluorinated tails were shown to be useful as n-type organic semiconductors in such devices as field-effect transistors and Schottky diodes. Poly(etherimide)s as structural resins have been extensively investigated at NASA Langley Research Center for over 30 years. More recently, the need for multi-functional materials has become increasingly important. This n-type semiconductor illustrates the scope of current work towards new families of PEIs that not only can be used as structural resins for carbon-fiber reinforced composites, but also can function as sensors. Such a multi-functional material would permit so-called in-situ health monitoring of composite structures during service. The work presented here demonstrates that parts of the PEI backbone can be used as an n-type semiconductor with such materials being sensitive to damage, temperature, stress, and pressure. In the near future, multi-functional or "smart" composite structures are envisioned to be able

  6. Rodent repellents: Preparation and properties of thiouronium compounds and cyclic imides

    USGS Publications Warehouse

    Bellack, E.; DeWitt, J.B.

    1954-01-01

    Syntheses and bioassays of cyclic imides and thiouronium compounds were carried out as part of a search for materials capable of preventing rodent damage to packaged commodities. Previous studies had shown that repellent activity was associated with functional groups containing nitrogen and sulfur, and was enhanced by the presence of ionic linkages. Twenty-seven thiouronium compounds and 40 imides, including 1 0 compounds not described previously, were prepared for these tests. Ten imides and 26 thiouronium compounds were repellent under the conditions of test. Information obtained in these studies will be utilized in the development and selection of more effective materials for prevention of rodent damage to foods and other commodities.

  7. Effect of the endcapping of reversed-phase high-performance liquid chromatography adsorbents on the adsorption isotherm

    SciTech Connect

    Gritti, Fabrice; Guiochon, Georges A

    2005-09-01

    The retention mechanisms of n-propylbenzoate, 4-t ert-butylphenol, and caffeine on the endcapped Symmetry-C{sub 18} and the non-endcapped Resolve-C{sub 18} are compared. The adsorption isotherms were measured by frontal analysis (FA), using as the mobile phase mixtures of methanol or acetonitrile and water of various compositions. The isotherm data were modeled and the adsorption energy distributions calculated. The surface heterogeneity increases faster with decreasing methanol concentration on the non-endcapped than on the endcapped adsorbent. For instance, for methanol concentrations exceeding 30% (v/v), the adsorption of caffeine is accounted for by assuming three and two different types of adsorption sites on Resolve-C{sub 18} and Symmetry-C{sub 18}, respectively. This is explained by the effect of the mobile phase composition on the structure of the C{sub 18}-bonded layer. The bare surface of bonded silica appears more accessible to solute molecules at high water contents in the mobile phase. On the other hand, replacing methanol by a stronger organic modifier like acetonitrile dampens the differences between non-endcapped and endcapped stationary phase and decreases the degree of surface heterogeneity of the adsorbent. For instance, at acetonitrile concentrations exceeding 20%, the surface appears nearly homogeneous for the adsorption of caffeine.

  8. Synthesis and evaluation of new spacers for use as dsDNA endcaps

    PubMed Central

    Ng, Pei-Sze; Laing, Brian M.; Balasundarum, Ganesan; Pingle, Maneesh; Friedman, Alan; Bergstrom, Donald E.

    2010-01-01

    A series of aliphatic and aromatic spacer molecules designed to cap the ends of DNA duplexes have been synthesized. The spacers were converted into dimethoxytrityl protected phosphoramidites as synthons for oligonucleotides synthesis. The effect of the spacers on the stability of short DNA duplexes was assessed by melting temperature studies. Endcaps containing amide groups were found to be less stabilizing than the hexaethylene glycol spacer. Endcaps containing either a terthiophene or a naphthalene tetracarboxylic acid dimide were found to be significantly more stabilizing. The former showed a preference for stacking above an A•T base pair. Spacers containing only methylene (-CH2-) and amide (-CONH-) groups interact weakly with DNA and consequently may be optimal for applications that require minimal influence on DNA structure but require a way to hold the ends of double-stranded DNA together. PMID:20715857

  9. Thin scintillating tiles (with fiber readout and high light-yield) for the OPAL endcaps

    SciTech Connect

    Ball, Austin H.

    1998-11-09

    Scintillating tiles with embedded wavelength-shifting fiber readout have recently been installed in the OPAL endcaps to improve trigger performance, time resolution and hermeticity for experiments at LEP II. The design is constrained to provide hermetic coverage of the available area with high single particle efficiency, uniform response and good time resolution, notwithstanding the limited space for the detector and its long readout cables, and despite the strong endcap magnetic field. A high light yield per embedded fiber is required. This paper motivates and describes the design, and demonstrates that the performance meets the required targets. A light yield of 14 photoelectrons/MIP and a time resolution of 3ns have been obtained during 1997 LEP operation.

  10. Thin scintillating tiles (with fiber readout and high light-yield) for the OPAL endcaps

    SciTech Connect

    Ball, A.H.

    1998-11-01

    Scintillating tiles with embedded wavelength-shifting fiber readout have recently been installed in the OPAL endcaps to improve trigger performance, time resolution and hermeticity for experiments at LEP II. The design is constrained to provide hermetic coverage of the available area with high single particle efficiency, uniform response and good time resolution, notwithstanding the limited space for the detector and its long readout cables, and despite the strong endcap magnetic field. A high light yield per embedded fiber is required. This paper motivates and describes the design, and demonstrates that the performance meets the required targets. A light yield of 14 photoelectrons/MIP and a time resolution of 3ns have been obtained during 1997 LEP operation. {copyright} {ital 1998 American Institute of Physics.}

  11. Implementation of on-line data reduction algorithms in the CMS Endcap Preshower Data Concentrator Cards

    NASA Astrophysics Data System (ADS)

    Barney, D.; Bialas, W.; Kokkas, P.; Manthos, N.; Reynaud, S.; Sidiropoulos, G.; Vichoudis, P.

    2007-03-01

    The CMS Endcap Preshower (ES) sub-detector comprises 4288 silicon sensors, each containing 32 strips. The data are transferred from the detector to the counting room via 1208 optical fibres running at 800Mbps. Each fibre carries data from two, three or four sensors. For the readout of the Preshower, a VME-based system, the Endcap Preshower Data Concentrator Card (ES-DCC), is currently under development. The main objective of each readout board is to acquire on-detector data from up to 36 optical links, perform on-line data reduction via zero suppression and pass the concentrated data to the CMS event builder. This document presents the conceptual design of the Reduction Algorithms as well as their implementation in the ES-DCC FPGAs. These algorithms, as implemented in the ES-DCC, result in a data-reduction factor of 20.

  12. Hadronic Shower Validation Experience for the ATLAS End-Cap Calorimeter

    SciTech Connect

    Kiryunin, A. E.; Salihagic, D.

    2007-03-19

    Validation of GEANT4 hadronic physics models is carried out by comparing experimental data from beam tests of modules of the ATLAS end-cap calorimeters with GEANT4 based simulations. Two physics lists (LHEP and QGSP) for the simulation of hadronic showers are evaluated. Calorimeter performance parameters like the energy resolution and response for charged pions and shapes of showers are studied. Comparison with GEANT3 predictions is done as well.

  13. Interaction of arginine oligomer with model membrane

    SciTech Connect

    Yi, Dandan . E-mail: yi_dandan@yahoo.com.cn; Guoming, Li; Gao, Li; Wei, Liang

    2007-08-10

    Short oligomers of arginine (R8) have been shown to cross readily a variety of biological barriers. A hypothesis was put forward that inverted micelles form in biological membranes in the presence of arginine oligomer peptides, facilitating their transfer through the membranes. In order to define the role of peptide-lipid interaction in this mechanism, we prepared liposomes as the model membrane to study the ability of R8 inducing calcein release from liposomes, the fusion of liposomes, R8 binding to liposomes and membrane disturbing activity of the bound R8. The results show that R8 binding to liposome membrane depends on lipid compositions, negative surface charge density and interior water phase pH values of liposomes. R8 has no activity to induce the leakage of calcein from liposomes or improve liposome fusion. R8 does not permeabilize through the membrane spontaneously. These peptides delivering drugs through membranes may depend on receptors and energy.

  14. Oligomer functionalized nanotubes and composites formed therewith

    DOEpatents

    Zettl, Alexander K; Sainsbury, Toby; Frechet, Jean M.J.

    2014-03-18

    Disclosed herein is a sequential functionalization methodology for the covalent modification of nanotubes with between one and four repeat units of a polymer. Covalent attachment of oligomer units to the surface of nanotubes results in oligomer units forming an organic sheath around the nanotubes, polymer-functionalized-nanotubes (P-NTs). P-NTs possess chemical functionality identical to that of the functionalizing polymer, and thus provide nanoscale scaffolds which may be readily dispersed within a monomer solution and participate in the polymerization reaction to form a polymer-nanotube/polymer composite. Formation of polymer in the presence of P-NTs leads to a uniform dispersion of nanotubes within the polymer matrix, in contrast to aggregated masses of nanotubes in the case of pristine-NTs. The covalent attachment of oligomeric units to the surface of nanotubes represents the formation of a functional nanoscale building block which can be readily dispersed and integrated within the polymer to form a novel composite material.

  15. Ethynyl terminated ester oligomers and polymers therefrom

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); hesives and composite matrices. (Inventor)

    1987-01-01

    A new class of ethynyl-terminated oligomers and the process for preparing same are disclosed. Upon the application of heat, with or without a catalyst, the ethynyl groups react to provide crosslinking and chain extension to increase the polymer use temperature and improve the polymer solvent resistance. These improved polyesters are potentially useful in packaging, magnetic tapes, capacitors, industrial belting, protective coatings, structural adhesives and composite matrices.

  16. Formation of domain-swapped oligomer of cytochrome C from its molten globule state oligomer.

    PubMed

    Deshpande, Megha Subhash; Parui, Partha Pratim; Kamikubo, Hironari; Yamanaka, Masaru; Nagao, Satoshi; Komori, Hirofumi; Kataoka, Mikio; Higuchi, Yoshiki; Hirota, Shun

    2014-07-22

    Many proteins, including cytochrome c (cyt c), have been shown to form domain-swapped oligomers, but the factors governing the oligomerization process remain unrevealed. We obtained oligomers of cyt c by refolding cyt c from its acid molten globule state to neutral pH state under high protein and ion concentrations. The amount of oligomeric cyt c obtained depended on the nature of the anion (chaotropic or kosmotropic) in the solution: ClO4(-) (oligomers, 11% ± 2% (heme unit)), SCN(-) (10% ± 2%), I(-) (6% ± 2%), NO3(-) (3% ± 1%), Br(-) (2% ± 1%), Cl(-) (2% ± 1%), and SO4(2-) (3% ± 1%) for refolding of 2 mM cyt c (anion concentration 125 mM). Dimeric cyt c obtained by refolding from the molten globule state exhibited a domain-swapped structure, in which the C-terminal α-helices were exchanged between protomers. According to small-angle X-ray scattering measurements, approximately 25% of the cyt c molecules were dimerized in the molten globule state containing 125 mM ClO4(-). These results indicate that a certain amount of molten globule state oligomers of cyt c convert to domain-swapped oligomers during refolding and that the intermolecular interactions necessary for domain swapping are present in the molten globule state. PMID:24981551

  17. Kinetics of ligation of fibrin oligomers.

    PubMed

    Nelb, G W; Kamykowski, G W; Ferry, J D

    1980-07-10

    Human fibrinogen was treated with thrombin in the presence of fibrinoligase and calcium ion at pH 8.5, ionic strength 0.45, and the ensuring polymerization was interrupted at various time intervals (t) both before and after the clotting time (tc) by solubilization with a solution of sodium dodecyl sulfate and urea. Aliquots of the solubilized protein were subjected to gel electrophoresis on polyacrylamide gels after disulfide reduction by dithiothreitol and on agarose gels without reduction. The degree of gamma-gamma ligation was determined from the former and the size distribution of ligated oligomers, for degree of polymerization x from 1 to 10, from the latter. The degree of gamma-gamma ligation was calculated independently from the size distribution with the assumption that every junction between two fibrin monomers remaining intact after solubilization is ligated, and this agreed well with the direct determination. The size distribution at t/tc = 1.3 to 1.6 differed somewhat from that calculated by the classical theory of linear polycondensation on the assumption that all reactive sites react with equal probability and rate. Analysis of the difference suggests that ligation of a fibrin digomer is not a random process; the probability of ligation of a given junction between two monomers increases with the oligomer length. The number-average degree of polymerization, xn, of ligated oligomers increases approximately linearly with time up to a value of 1.6. PMID:7391026

  18. Synthesis of Imidates: TFA-Mediated Regioselective Amide Alkylation Using Meerwein's Reagent.

    PubMed

    Popov, Kirill; Somfai, Peter

    2016-04-15

    Regioselective O-alkylation of an amide to form the corresponding imidate is a common synthetic problem, often resulting in varying amounts of N-alkylation. Screening existing methods for converting amides to imidates gave inconsistent or irreproducible results, sometimes affording N-alkylamide as the major product. A simple and reliable protocol for amide O-alkylation with complete regioselectivity has been designed, and its scope and efficiency demonstrated on a number of substrates. PMID:27019206

  19. Structure of amyloid oligomers and their mechanisms of toxicities: Targeting amyloid oligomers using novel therapeutic approaches.

    PubMed

    Salahuddin, Parveen; Fatima, Munazza Tamkeen; Abdelhameed, Ali Saber; Nusrat, Saima; Khan, Rizwan Hasan

    2016-05-23

    Protein misfolding is one of the leading causes of amyloidoses. Protein misfolding occurs from changes in environmental conditions and host of other factors, including errors in post-translational modifications, increase in the rate of degradation, error in trafficking, loss of binding partners and oxidative damage. Misfolding gives rise to the formation of partially unfolded or misfolded intermediates, which have exposed hydrophobic residues and interact with complementary intermediates to form oligomers and consequently protofibrils and fibrils. The amyloid fibrils accumulate as amyloid deposits in the brain and central nervous system in Alzheimer's disease (AD), Prion disease and Parkinson's disease (PD). Initial studies have shown that amyloid fibrils were the main culprit behind toxicity that cause neurodegenerative diseases. However, attention shifted to the cytotoxicity of amyloid fibril precursors, notably amyloid oligomers, which are the major cause of toxicity. The mechanism of toxicity triggered by amyloid oligomers remains elusive. In this review, we have focused on the current knowledge of the structures of different aggregated states, including amyloid fibril, protofibrils, annular aggregates and oligomers. Based on the studies on the mechanism of toxicities, we hypothesize two major possible mechanisms of toxicities instigated by oligomers of Aβ (amyloid beta), PrP (prion protein) (106-126), and α-Syn (alpha-synuclein) including direct formation of ion channels and neuron membrane disruption by the increase in membrane conductance or leakage in the presence of small globulomers to large prefibrillar assemblies. Finally, we have discussed various novel innovative approaches that target amyloid oligomers in Alzheimer's diseases, Prion disease and Parkinson's disease. PMID:26974374

  20. Structural studies on HCN oligomers. [catalysts for prebiotic processes

    NASA Technical Reports Server (NTRS)

    Ferris, J. P.; Edelson, E. H.; Auyeung, J. M.; Joshi, P. C.

    1981-01-01

    NMR spectral studies on the HCN oligomers suggest the presence of carboxamide and urea groupings. The release of CO2, H2O, HCN, CH3CN, HCONH2 and pyridine on pyrolysis is consistent with the presence of these groupings as well as carboxylic acid groups. No basic primary amine groupings could be detected with fluorescamine. Hydrazinolysis of the HCN oligomers releases 10% of the amino acids normally released by acid hydrolysis. The oligomers give a positive biuret test but this is not due to the presence of peptide bonds. There is no conclusive evidence for the presence of peptide bonds in the HCN oligomers. No diglycine was detected on partial hydrolysis of the HCN oligomers at pH 8.5 suggesting that HCN oligomers were not a source of prebiotic peptides.

  1. DNA sequence similarity recognition by hybridization to short oligomers

    DOEpatents

    Milosavljevic, Aleksandar

    1999-01-01

    Methods are disclosed for the comparison of nucleic acid sequences. Data is generated by hybridizing sets of oligomers with target nucleic acids. The data thus generated is manipulated simultaneously with respect to both (i) matching between oligomers and (ii) matching between oligomers and putative reference sequences available in databases. Using data compression methods to manipulate this mutual information, sequences for the target can be constructed.

  2. Copper-Catalyzed Intermolecular Amidation and Imidation of Unactivated Alkanes

    PubMed Central

    2015-01-01

    We report a set of rare copper-catalyzed reactions of alkanes with simple amides, sulfonamides, and imides (i.e., benzamides, tosylamides, carbamates, and phthalimide) to form the corresponding N-alkyl products. The reactions lead to functionalization at secondary C–H bonds over tertiary C–H bonds and even occur at primary C–H bonds. [(phen)Cu(phth)] (1-phth) and [(phen)Cu(phth)2] (1-phth2), which are potential intermediates in the reaction, have been isolated and fully characterized. The stoichiometric reactions of 1-phth and 1-phth2 with alkanes, alkyl radicals, and radical probes were investigated to elucidate the mechanism of the amidation. The catalytic and stoichiometric reactions require both copper and tBuOOtBu for the generation of N-alkyl product. Neither 1-phth nor 1-phth2 reacted with excess cyclohexane at 100 °C without tBuOOtBu. However, the reactions of 1-phth and 1-phth2 with tBuOOtBu afforded N-cyclohexylphthalimide (Cy-phth), N-methylphthalimide, and tert-butoxycyclohexane (Cy-OtBu) in approximate ratios of 70:20:30, respectively. Reactions with radical traps support the intermediacy of a tert-butoxy radical, which forms an alkyl radical intermediate. The intermediacy of an alkyl radical was evidenced by the catalytic reaction of cyclohexane with benzamide in the presence of CBr4, which formed exclusively bromocyclohexane. Furthermore, stoichiometric reactions of [(phen)Cu(phth)2] with tBuOOtBu and (Ph(Me)2CO)2 at 100 °C without cyclohexane afforded N-methylphthalimide (Me-phth) from β-Me scission of the alkoxy radicals to form a methyl radical. Separate reactions of cyclohexane and d12-cyclohexane with benzamide showed that the turnover-limiting step in the catalytic reaction is the C–H cleavage of cyclohexane by a tert-butoxy radical. These mechanistic data imply that the tert-butoxy radical reacts with the C–H bonds of alkanes, and the subsequent alkyl radical combines with 1-phth2 to form the corresponding N-alkyl imide product

  3. Polyetherurethane oligomers with aldehyde groups as additives for lubricating oils

    SciTech Connect

    Nikolaev, V.N.; Abramov, E.G.; Tenyushev, A.I.

    1995-01-01

    Polyetherurethane oligomers with aldehyde groups, which we synthesized from polyoxypropylene diols (molecular weight 500, 1000, 1500, 2000, or 3000) with toluene diisocyanate and salicylaldehyde, are of interest as additives for lubricating oils. The effects of these oligomers on the service properties and physicochemical characteristics of lubricating oils were investigated by methods prreviously described. As the lube base stocks we used castor oil, a polyoxypropylene diol and a polyethoxysiloxane. The oligomers are readily soluble in organic solvents and in the lube base stocks, and their solutions are stable during storage and use. We found that the optimal concentration of oligomers is 5%, providing the best lubricating properties, in particular the best antiwear properties.

  4. Langley Research Center - Soluble Imide (LaRC-SI)

    NASA Technical Reports Server (NTRS)

    Stang, David

    1995-01-01

    This report is about experimenting and developing uses for the new thermal plastic developed by Dr. Robert Bryant called the 'Langley Research Center - Soluble Imide' (LaRC-SI). The three developments are: the use of the LaRC-SI as a dielectric for thin film sensors, as an adhesive to place diamonds on surfaces to increase thermal conductivity, and as an intermediate layer to allow the placement of metal on aluminum nitride. The LaRC-SI was developed by Dr. Robert G. Bryant, a chemical engineer at NASA Langley Research Center. The unique properties of this material is that it is an amorphous thermoplastic. This means that it can be reformed at elevated temperature and pressures. It can be applied in the form of a spray, spin, dip coating, paint, or spread with a doctors blade. The LaRC-SI has excellent adhesive and dielectric properties. It can also be recycled. Potential applications for this material are resin for mechanical parts such as gears, bearings and valves, advanced composites like carbon fiber, high strength adhesives, thin film circuits, and as a dielectric film for placing electrical components on conductive materials.

  5. High Temperature VARTM of Phenylethynyl Terminated Imides (PETI) Resins

    NASA Technical Reports Server (NTRS)

    Ghose, Sayata; Cano, Roberto J.; Britton, Sean M.; Watson, Kent A.; Jensen, Brian J.; Connell, John W.

    2010-01-01

    Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications a void fraction of less than 2% is desired. In the current study, two PETI resins, LARCTM PETI-330 and LARCTM PETI-8 have been used to fabricate test specimens using HT-VARTM. The resins were infused into carbon fiber preforms at 260 C and cured between 316 C and 371 C. Modifications to the thermal cycle used in the laminate fabrication have reduced the void content significantly (typically < 3%) for carbon fiber biaxially woven fabric. Photomicrographs of the panels were taken and void contents were determined by acid digestion. For carbon fiber uniaxial fabric, void contents of less than 2% have been obtained using both PETI-8 and PETI-330. Mechanical properties of the panels were determined at both room and elevated temperatures. These include short beam shear and flexure tests. The results of this work are presented herein.

  6. Phenylethynyl Terminated Imide (PETI) Composites Made by High Temperature VARTM

    NASA Technical Reports Server (NTRS)

    Chose, Sayata; Cano, Roberto J.; Britton, Sean M.; Watson, Kent A.; Jensen, Brian J.; Connell, John W.

    2010-01-01

    Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, a void fraction of <2% is desired. In the current study, two PETI resins, LARC. PETI-330 and LARC. PETI-8 have been used to fabricate test specimens using HT-VARTM. The resins were infused into carbon fiber preforms at 260 C and cured between 316 and 371 C. Photomicrographs of the panels were taken and void contents were determined by acid digestion. Modifications to the thermal cycle used in the laminate fabrication have reduced the void content significantly; typically .3% for carbon fiber biaxially woven fabric and less than 2% for carbon fiber uniaxial fabric. Mechanical properties (short beam shear and flexure) of the panels were determined at both room and elevated temperatures. The results of this work are presented herein. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

  7. Characterization of NH overtone and combination bands in the near-infrared absorption spectra of simple cyclic imides

    NASA Astrophysics Data System (ADS)

    McNeilly, Patrick J.; Andrea, Tariq A.; Krikorian, S. Edward

    1992-10-01

    Bands due to overtone and combination vibrational modes attributable to the imide grouping have been elucidated in the near-IR absorption spectra of small-ring cyclic imides, in which the grouping is in a cis, cis conformation. The spectra closely parallel the spectra of cis lactams except that two combination modes involving the carbonyl stretching fundamental, [ν(NH) + ν(CO)] and [2ν(C=O) + imide III], occur at higher wavenumbers in the imide spectra, reflecting the higher frequency at which this fundamental absorbs. This same factor results in a reversal in the wavenumber positions of the [2ν(CO) + imide III] and [ν(NH) + imide III] combination bands in the imide spectra relative to those in the lactam spectra. In addition, in-phase and out-of-phase vibrational coupling between the two carbonyl groups in the imides may compound the band due to the [ν(NH) + ν(CO)] combination mode. These three spectral characteristics serve to distinguish the imides from the lactams in the near-IR.

  8. Mx oligomer: a novel capsid pattern sensor?

    PubMed

    Kong, Jia; Ma, Min; He, Shuangyi; Qin, Xiaohong

    2016-08-01

    Myxovirus resistance proteins represent a family of interferon-induced restriction factors of the innate and adaptive immune system. Human MxB acts as a novel restriction factor with antiviral activity against a range of HIV-1 and other retroviruses mainly by inhibiting the uncoating process after reverse transcription but prior to integration. Based on published data and conservation analysis, we propose a novel hypothesis, in which MxB dimers form higher order oligomers that restrict retroviral replication by binding to the viral capsid. Insights into the mechanistic basis of structural and functional characteristics of MxB will greatly advance our understanding of MxB. PMID:27492442

  9. Anharmonic Vibrational Dynamics of DNA Oligomers

    NASA Astrophysics Data System (ADS)

    Kühn, O.; Došlić, N.; Krishnan, G. M.; Fidder, H.; Heyne, K.

    Combining two-color infared pump-probe spectroscopy and anharmonic force field calculations we characterize the anharmonic coupling patterns between fingerprint modes and the hydrogen-bonded symmetric vNH2 stretching vibration in adenine-thymine dA20-dT20 DNA oligomers. Specifically, it is shown that the anharmonic coupling between the δNH2 bending and the vC4=O4 stretching vibration, both absorbing around 1665 cm-1, can be used to assign the vNH2 fundamental transition at 3215 cm-1 despite the broad background absorption of water.

  10. Cooperative Switching in Nanofibers of Azobenzene Oligomers.

    PubMed

    Weber, Christopher; Liebig, Tobias; Gensler, Manuel; Zykov, Anton; Pithan, Linus; Rabe, Jürgen P; Hecht, Stefan; Bléger, David; Kowarik, Stefan

    2016-01-01

    Next-generation molecular devices and machines demand the integration of molecular switches into hierarchical assemblies to amplify the response of the system from the molecular level to the meso- or macro-scale. Here, we demonstrate that multi-azobenzene oligomers can assemble to form robust supramolecular nanofibers in which they can be switched repeatedly between the E- and Z-configuration. While in isolated oligomers the azobenzene units undergo reversible photoisomerization independently, in the nanofibers they are coupled via intermolecular interactions and switch cooperatively as evidenced by unusual thermal and kinetic behavior. We find that the photoisomerization rate from the Z-isomer to the E-isomer depends on the fraction of Z-azobenzene in the nanofibers, and is increased by more than a factor of 4 in Z-rich fibers when compared to E-rich fibers. This demonstrates the great potential of coupling individual photochromic units for increasing their quantum efficiency in the solid state with potential relevance for actuation and sensing. PMID:27161608

  11. Liquid Crystal Ordering of Random DNA Oligomers

    NASA Astrophysics Data System (ADS)

    Bellini, Tommaso; Zanchetta, Giuliano; Fraccia, Tommaso; Cerbino, Roberto; Tsai, Ethan; Moran, Mark; Smith, Gregory; Walba, David; Clark, Noel

    2012-02-01

    Concentrated solutions of DNA oligomers (6 to 20 base pairs) organize into chiral nematic (NEM) and columnar (COL) liquid crystal (LC) phases. When the oligomer duplexes are mixed with single strands, LC phase formation proceeds through macroscopic phase separation, as a consequence of the combination of various self-assembly processes including strand pairing, reversible linear aggregation, demixing and LC ordering. We extended our investigation to the case of LC ordering in oligonucleotides whose sequences are partially or entirely randomly chosen, and we observed LC phases even in entirely random 20mers, corresponding to a family of 4^20 10^12 different sequences. We have tracked the origin of this behaviour: random sequences pair into generally defected duplexes, a large fraction of them terminating with stretches of unpaired bases (overhangs); overhangs promote linear aggregation of duplexes, with a mean strength depending on the overhang length; LC formation is accompanied by a phase separation where the duplexes with longer overhangs aggregate to form COL LC domains that coexist with an isotropic fluid rich in duplexes whose structure cannot aggregate.

  12. Cooperative Switching in Nanofibers of Azobenzene Oligomers

    NASA Astrophysics Data System (ADS)

    Weber, Christopher; Liebig, Tobias; Gensler, Manuel; Zykov, Anton; Pithan, Linus; Rabe, Jürgen P.; Hecht, Stefan; Bléger, David; Kowarik, Stefan

    2016-05-01

    Next-generation molecular devices and machines demand the integration of molecular switches into hierarchical assemblies to amplify the response of the system from the molecular level to the meso- or macro-scale. Here, we demonstrate that multi-azobenzene oligomers can assemble to form robust supramolecular nanofibers in which they can be switched repeatedly between the E- and Z-configuration. While in isolated oligomers the azobenzene units undergo reversible photoisomerization independently, in the nanofibers they are coupled via intermolecular interactions and switch cooperatively as evidenced by unusual thermal and kinetic behavior. We find that the photoisomerization rate from the Z-isomer to the E-isomer depends on the fraction of Z-azobenzene in the nanofibers, and is increased by more than a factor of 4 in Z-rich fibers when compared to E-rich fibers. This demonstrates the great potential of coupling individual photochromic units for increasing their quantum efficiency in the solid state with potential relevance for actuation and sensing.

  13. SAXS fingerprints of aldehyde dehydrogenase oligomers.

    PubMed

    Tanner, John J

    2015-12-01

    Enzymes of the aldehyde dehydrogenase (ALDH) superfamily catalyze the nicotinamide adenine dinucleotide-dependent oxidation of aldehydes to carboxylic acids. ALDHs are important in detoxification of aldehydes, amino acid metabolism, embryogenesis and development, neurotransmission, oxidative stress, and cancer. Mutations in genes encoding ALDHs cause metabolic disorders, including alcohol flush reaction (ALDH2), Sjögren-Larsson syndrome (ALDH3A2), hyperprolinemia type II (ALDH4A1), γ-hydroxybutyric aciduria (ALDH5A1), methylmalonic aciduria (ALDH6A1), pyridoxine dependent epilepsy (ALDH7A1), and hyperammonemia (ALDH18A1). We previously reported crystal structures and small-angle X-ray scattering (SAXS) analyses of ALDHs exhibiting dimeric, tetrameric, and hexameric oligomeric states (Luo et al., Biochemistry 54 (2015) 5513-5522; Luo et al., J. Mol. Biol. 425 (2013) 3106-3120). Herein I provide the SAXS curves, radii of gyration, and distance distribution functions for the three types of ALDH oligomer. The SAXS curves and associated analysis provide diagnostic fingerprints that allow rapid identification of the type of ALDH oligomer that is present in solution. The data sets provided here serve as a benchmark for characterizing oligomerization of ALDHs. PMID:26693506

  14. 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.

  15. Cooperative Switching in Nanofibers of Azobenzene Oligomers

    PubMed Central

    Weber, Christopher; Liebig, Tobias; Gensler, Manuel; Zykov, Anton; Pithan, Linus; Rabe, Jürgen P.; Hecht, Stefan; Bléger, David; Kowarik, Stefan

    2016-01-01

    Next-generation molecular devices and machines demand the integration of molecular switches into hierarchical assemblies to amplify the response of the system from the molecular level to the meso- or macro-scale. Here, we demonstrate that multi-azobenzene oligomers can assemble to form robust supramolecular nanofibers in which they can be switched repeatedly between the E- and Z-configuration. While in isolated oligomers the azobenzene units undergo reversible photoisomerization independently, in the nanofibers they are coupled via intermolecular interactions and switch cooperatively as evidenced by unusual thermal and kinetic behavior. We find that the photoisomerization rate from the Z-isomer to the E-isomer depends on the fraction of Z-azobenzene in the nanofibers, and is increased by more than a factor of 4 in Z-rich fibers when compared to E-rich fibers. This demonstrates the great potential of coupling individual photochromic units for increasing their quantum efficiency in the solid state with potential relevance for actuation and sensing. PMID:27161608

  16. Amyloid β peptide oligomers directly activate NMDA receptors.

    PubMed

    Texidó, Laura; Martín-Satué, Mireia; Alberdi, Elena; Solsona, Carles; Matute, Carlos

    2011-03-01

    Amyloid beta (Aβ) oligomers accumulate in the brain tissue of Alzheimer disease patients and are related to disease pathogenesis. The precise mechanisms by which Aβ oligomers cause neurotoxicity remain unknown. We recently reported that Aβ oligomers cause intracellular Ca(2+) overload and neuronal death that can be prevented by NMDA receptor antagonists. This study investigated whether Aβ oligomers directly activated NMDA receptors (NMDARs) using NR1/NR2A and NR1/NR2B receptors that were heterologously expressed in Xenopus laevis oocytes. Indeed, Aβ oligomers induced inward non-desensitizing currents that were blocked in the presence of the NMDA receptor antagonists memantine, APV, and MK-801. Intriguingly, the amplitude of the responses to Aβ oligomers was greater for NR1/NR2A heteromers than for NR1/NR2B heteromers expressed in oocytes. Consistent with these findings, we observed that the increase in the cytosolic concentration of Ca(2+) induced by Aβ oligomers in cortical neurons is prevented by AP5, a broad spectrum NMDA receptor antagonist, but slightly attenuated by ifenprodil which blocks receptors with the NR2B subunit. Together, these results indicate that Aβ oligomers directly activate NMDA receptors, particularly those with the NR2A subunit, and further suggest that drugs that attenuate the activity of such receptors may prevent Aβ damage to neurons in Alzheimeŕs disease. PMID:21349580

  17. Atomic View of a Toxic Amyloid Small Oligomer

    SciTech Connect

    Laganowsky, Arthur; Liu, Cong; Sawaya, Michael R.; Whitelegge, Julian P.; Park, Jiyong; Zhao, Minglei; Pensalfini, Anna; Soriaga, Angela B.; Landau, Meytal; Teng, Poh K.; Cascio, Duilio; Glabe, Charles; Eisenberg, David

    2012-04-30

    Amyloid diseases, including Alzheimer's, Parkinson's, and the prion conditions, are each associated with a particular protein in fibrillar form. These amyloid fibrils were long suspected to be the disease agents, but evidence suggests that smaller, often transient and polymorphic oligomers are the toxic entities. Here, we identify a segment of the amyloid-forming protein {alpha}{beta} crystallin, which forms an oligomeric complex exhibiting properties of other amyloid oligomers: {beta}-sheet-rich structure, cytotoxicity, and recognition by an oligomer-specific antibody. The x-ray-derived atomic structure of the oligomer reveals a cylindrical barrel, formed from six antiparallel protein strands, that we term a cylindrin. The cylindrin structure is compatible with a sequence segment from the {beta}-amyloid protein of Alzheimer's disease. Cylindrins offer models for the hitherto elusive structures of amyloid oligomers.

  18. Atomic View of a Toxic Amyloid Small Oligomer

    PubMed Central

    Laganowsky, Arthur; Liu, Cong; Sawaya, Michael R.; Whitelegge, Julian P.; Park, Jiyong; Zhao, Minglei; Pensalfini, Anna; Soriaga, Angela; Landau, Meytal; Teng, Poh K.; Cascio, Duilio; Glabe, Charles; Eisenberg, David

    2014-01-01

    Amyloid diseases, including Alzheimer's, Parkinson's, and the prion conditions, are each associated with a particular protein in fibrillar form. These amyloid fibrils were long suspected to be the disease agents, but evidence suggests that smaller, often transient and polymorphic oligomers are the toxic entities. Here we identify a segment of the amyloid-forming protein, alphaB crystallin, which forms an oligomeric complex exhibiting properties of other amyloid oligomers: beta-sheet-rich structure, cytotoxicity, and recognition by an anti-oligomer antibody. The X-ray-derived atomic structure of the oligomer reveals a cylindrical barrel, formed from six anti-parallel, protein strands, which we term a cylindrin. The cylindrin structure is compatible with a sequence segment from the Abeta protein of Alzheimer's disease. Cylindrins offer models for the hitherto elusive structures of amyloid oligomers. PMID:22403391

  19. Vibronic line shapes of PTCDA oligomers in helium nanodroplets.

    PubMed

    Roden, Jan; Eisfeld, Alexander; Dvořák, Matthieu; Bünermann, Oliver; Stienkemeier, Frank

    2011-02-01

    Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C(24)H(8)O(6) (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitude larger than the width of the monomer lines. Using a simple theoretical model for the oligomer, in which a Frenkel exciton couples to internal vibrational modes of the monomers, these experimental findings are nicely reproduced. The three peaks present in the oligomer spectrum can already be obtained taking only one effective vibrational mode of the PTCDA molecule into account. The inclusion of more vibrational modes leads to quasicontinuous spectra, resembling the broad oligomer spectra. PMID:21303160

  20. In vivo demonstration that α-synuclein oligomers are toxic

    PubMed Central

    Winner, Beate; Jappelli, Roberto; Maji, Samir K.; Desplats, Paula A.; Boyer, Leah; Aigner, Stefan; Hetzer, Claudia; Loher, Thomas; Vilar, Marçal; Campioni, Silvia; Tzitzilonis, Christos; Soragni, Alice; Jessberger, Sebastian; Mira, Helena; Consiglio, Antonella; Pham, Emiley; Masliah, Eliezer; Gage, Fred H.; Riek, Roland

    2011-01-01

    The aggregation of proteins into oligomers and amyloid fibrils is characteristic of several neurodegenerative diseases, including Parkinson disease (PD). In PD, the process of aggregation of α-synuclein (α-syn) from monomers, via oligomeric intermediates, into amyloid fibrils is considered the disease-causative toxic mechanism. We developed α-syn mutants that promote oligomer or fibril formation and tested the toxicity of these mutants by using a rat lentivirus system to investigate loss of dopaminergic neurons in the substantia nigra. The most severe dopaminergic loss in the substantia nigra is observed in animals with the α-syn variants that form oligomers (i.e., E57K and E35K), whereas the α-syn variants that form fibrils very quickly are less toxic. We show that α-syn oligomers are toxic in vivo and that α-syn oligomers might interact with and potentially disrupt membranes. PMID:21325059

  1. The Common Cryogenic Test Facility for the ATLAS Barrel and End-Cap Toroid Magnets

    NASA Astrophysics Data System (ADS)

    Delruelle, N.; Haug, F.; Junker, S.; Passardi, G.; Pengo, R.; Pirotte, O.

    2004-06-01

    The large ATLAS toroidal superconducting magnet made of the Barrel and two End-Caps needs extensive testing at the surface of the individual components prior to their final assembly into the underground cavern of LHC. A cryogenic test facility specifically designed for cooling sequentially the eight coils making the Barrel Toroid (BT) has been fully commissioned and is now ready for final acceptance of these magnets. This facility, originally designed for testing individually the 46 tons BT coils, will be upgraded to allow the acceptance tests of the two End-Caps, each of them having a 160 tons cold mass. The integrated system mainly comprises a 1.2 kW@4.5 K refrigerator, a 10 kW liquid-nitrogen precooler, two cryostats housing liquid helium centrifugal pumps of respectively 80 g/s and 600 g/s nominal flow and specific instrumentation to measure the thermal performances of the magnets. This paper describes the overall facility with particular emphasis to the cryogenic features adopted to match the specific requirements of the magnets in the various operating scenarios.

  2. The Common Cryogenic Test Facility for the ATLAS Barrel and End-Cap Toroid Magnets

    SciTech Connect

    Delruelle, N.; Haug, F.; Junker, S.; Passardi, G.; Pengo, R.; Pirotte, O.

    2004-06-23

    The large ATLAS toroidal superconducting magnet made of the Barrel and two End-Caps needs extensive testing at the surface of the individual components prior to their final assembly into the underground cavern of LHC. A cryogenic test facility specifically designed for cooling sequentially the eight coils making the Barrel Toroid (BT) has been fully commissioned and is now ready for final acceptance of these magnets. This facility, originally designed for testing individually the 46 tons BT coils, will be upgraded to allow the acceptance tests of the two End-Caps, each of them having a 160 tons cold mass. The integrated system mainly comprises a 1.2 kW at 4.5 K refrigerator, a 10 kW liquid-nitrogen precooler, two cryostats housing liquid helium centrifugal pumps of respectively 80 g/s and 600 g/s nominal flow and specific instrumentation to measure the thermal performances of the magnets. This paper describes the overall facility with particular emphasis to the cryogenic features adopted to match the specific requirements of the magnets in the various operating scenarios.

  3. Synthesis and biological evaluation of some novel cyclic-imides as hypoglycaemic, anti-hyperlipidemic agents.

    PubMed

    Abdel-Aziz, Alaa A-M; El-Azab, Adel S; Attia, Sabry M; Al-Obaid, Abdulrahman M; Al-Omar, Mohamed A; El-Subbagh, Hussein I

    2011-09-01

    Certain new halogenated cyclic-imides related to N-substituted phthalimide moiety were synthesized. Spacers of one or two carbon atom distances were inserted to connect the N-terminus of the cyclic-imide nuclei to the used heteroaryl groups to evaluate the effect of such alteration on biological activity. The synthesized compounds were subjected to hypoglycaemic and anti-hyperlipidemic evaluation. Some of the tested compounds proved to be more potent than the reference drugs glibenclamide and clofibrate. Compound 5e remarkably reduced serum glucose level by 55%; while 5c, 5e, 7d and 8e reduced total serum cholesterol by 58, 56, 54 and 53%, respectively. Those new cyclic-imides could be considered as useful template for future development to obtain more potent hypoglycaemic and anti-hyperlipidemic agents. PMID:21783284

  4. Addition polyimide adhesives containing various end groups

    NASA Technical Reports Server (NTRS)

    Saint Clair, A. K.; Saint Clair, T. L.

    1982-01-01

    Addition polyimode oligomers have been synthesized from 3,3 prime, 4,4 prime-benzophenone tetracarboxylic acid dianhydride and 3,3 prime-methylenedianiline using a variety of latent crosslinking groups as end-caps. The nominal 1300 molecular weight imide prepolymers were isolated and characterized for solubility in amide, chlorinated and ether solvents, melt-flow and cure properties, glass transition temperature, and thermal stability on heating in an air atmosphere. Adhesive strengths of the polyimides were obtained both at ambient and elevated temperatures before and after aging at 232 C. Properties of the novel addition polyimides were compared to a known nadic end-capped adhesive, LARC-13.

  5. Rectification mechanism in diblock oligomer molecular diodes.

    PubMed

    Oleynik, I I; Kozhushner, M A; Posvyanskii, V S; Yu, L

    2006-03-10

    We investigated a mechanism of rectification in diblock oligomer diode molecules that have recently been synthesized and showed a pronounced asymmetry in the measured I-V spectrum. The observed rectification effect is due to the resonant nature of electron transfer in the system and the localization properties of bound state wave functions of resonant states of the tunneling electron interacting with an asymmetric molecule in an electric field. The asymmetry of the tunneling wave function is enhanced or weakened depending on the polarity of the applied bias. The conceptually new theoretical approach, the Green's function theory of sub-barrier scattering, is able to provide a physically transparent explanation of this rectification effect based on the concept of the bound state spectrum of a tunneling electron. The theory predicts the characteristic features of the I-V spectrum in qualitative agreement with experiment. PMID:16606295

  6. Enzymatic hydrolysis of PTT polymers and oligomers.

    PubMed

    Eberl, A; Heumann, S; Kotek, R; Kaufmann, F; Mitsche, S; Cavaco-Paulo, A; Gübitz, G M

    2008-05-20

    Oligomers and polymers (film, fabrics) of the linear aromatic polyester poly(trimethylene terephthalate) (PTT) were treated with polyesterases from Thermomyces lanuginosus, Penicillium citrinum, Thermobifida fusca and Fusarium solani pisi. The cutinase from T. fusca was found to release the highest amounts of hydrolysis products from PTT materials and was able to open and hydrolyse a cyclic PTT dimer according to RP-HPLC-UV detection. In contrast, the lipase from T. lanuginosus also showed activity on the PTT fibres and on bis(3-hydroxypropyl) terephthalate (BHPT) but was not able to hydrolyse the polymer film, mono(3-hydroxypropyl) terephthalate (MHPT) nor the cyclic dimer of PTT. As control enzymes inhibited with mercury chloride were used. Surface hydrophilicity changes were investigated with contact angle measurements and the degree of crystallinity changes were determined with DSC. PMID:18405994

  7. First-principles simulations of thiophene oligomers

    NASA Astrophysics Data System (ADS)

    Scherlis, Damian; Marzari, Nicola

    2003-03-01

    Conducting polymers, extensively investigated for their use in electronic and nanotechnology applications, have recently gained prominence for their possible use as molecular actuators in mechanical and bioengineering devices. We have focused our efforts on thiophene-based compounds, a class of materials that can be designed for high stress generation and large linear displacement (actuation strain), ideally outperforming mammalian muscle. Key features for the development of these materials are the microscopic binding properties of thiophene and thiophene oligomers stacks, where applied electric fields lead to oxidation and enhanced pi-pi bonding. We have completed the structural studies of neutral and charged oligothiophene dimers, in the search for efficient dimerization mechanisms. A comparison between different density-functional and quantum-chemistry approaches is critically presented, as are solvation effects, described in this work with a combination of first-principles molecular dynamics and a QM/MM approach for the solvating medium.

  8. Effect of Oligomer Length on Photophysical Properties of Platinum Acetylide Donor-Acceptor-Donor Oligomers.

    PubMed

    Cekli, Seda; Winkel, Russell W; Schanze, Kirk S

    2016-07-21

    We report a systematic study that explores how the triplet excited state is influenced by conjugation length in a series of benzothiadiazole units containing donor-acceptor-donor (DAD)-type platinum acetylide oligomers and polymer. The singlet and triplet excited states for the series were characterized by an array of photophysical methods including steady-state luminescence spectroscopy and femtosecond-nanosecond transient absorption spectroscopy. In addition to the experimental work, a computational study using density functional theory was conducted to gain more information about the structure, composition, and energies of the frontier molecular orbitals. It is observed that both the singlet and triplet excited states are mainly localized on a single donor-acceptor-donor unit in the oligomers. Interestingly, it is discovered that the intersystem crossing efficiency increases dramatically in the longer oligomers. The effect is attributed to an enhanced contribution of the heavy metal platinum in the frontier orbitals (HOMO and LUMO), an effect that leads to enhanced spin-orbit coupling. PMID:27291712

  9. Elucidating molecular mass and shape of a neurotoxic Aβ oligomer.

    PubMed

    Sebollela, Adriano; Mustata, Gina-Mirela; Luo, Kevin; Velasco, Pauline T; Viola, Kirsten L; Cline, Erika N; Shekhawat, Gajendra S; Wilcox, Kyle C; Dravid, Vinayak P; Klein, William L

    2014-12-17

    Alzheimer's disease (AD), the most prevalent type of dementia, has been associated with the accumulation of amyloid β oligomers (AβOs) in the central nervous system. AβOs vary widely in size, ranging from dimers to larger than 100 kDa. Evidence indicates that not all oligomers are toxic, and there is yet no consensus on the size of the actual toxic oligomer. Here we used NU4, a conformation-dependent anti-AβO monoclonal antibody, to investigate size and shape of a toxic AβO assembly. By using size-exclusion chromatography and immuno-based detection, we isolated an AβO-NU4 complex amenable for biochemical and morphological studies. The apparent molecular mass of the NU4-targeted oligomer was 80 kDa. Atomic force microscopy imaging of the AβO-NU4 complex showed a size distribution centered at 5.37 nm, an increment of 1.5 nm compared to the size of AβOs (3.85 nm). This increment was compatible with the size of NU4 (1.3 nm), suggesting a 1:1 oligomer to NU4 ratio. NU4-reactive oligomers extracted from AD human brain concentrated in a molecular mass range similar to that found for in vitro prepared oligomers, supporting the relevance of the species herein studied. These results represent an important step toward understanding the connection between AβO size and toxicity. PMID:25343357

  10. Elucidating Molecular Mass and Shape of a Neurotoxic Aβ Oligomer

    PubMed Central

    2015-01-01

    Alzheimer's disease (AD), the most prevalent type of dementia, has been associated with the accumulation of amyloid β oligomers (AβOs) in the central nervous system. AβOs vary widely in size, ranging from dimers to larger than 100 kDa. Evidence indicates that not all oligomers are toxic, and there is yet no consensus on the size of the actual toxic oligomer. Here we used NU4, a conformation-dependent anti-AβO monoclonal antibody, to investigate size and shape of a toxic AβO assembly. By using size-exclusion chromatography and immuno-based detection, we isolated an AβO-NU4 complex amenable for biochemical and morphological studies. The apparent molecular mass of the NU4-targeted oligomer was 80 kDa. Atomic force microscopy imaging of the AβO-NU4 complex showed a size distribution centered at 5.37 nm, an increment of 1.5 nm compared to the size of AβOs (3.85 nm). This increment was compatible with the size of NU4 (1.3 nm), suggesting a 1:1 oligomer to NU4 ratio. NU4-reactive oligomers extracted from AD human brain concentrated in a molecular mass range similar to that found for in vitro prepared oligomers, supporting the relevance of the species herein studied. These results represent an important step toward understanding the connection between AβO size and toxicity. PMID:25343357

  11. Structural and functional properties of prefibrillar α-synuclein oligomers

    PubMed Central

    Pieri, Laura; Madiona, Karine; Melki, Ronald

    2016-01-01

    The deposition of fibrillar alpha-synuclein (α-syn) within inclusions (Lewy bodies and Lewy neurites) in neurons and glial cells is a hallmark of synucleinopathies. α-syn populates a variety of assemblies ranging from prefibrillar oligomeric species to fibrils whose specific contribution to neurodegeneration is still unclear. Here, we compare the specific structural and biological properties of distinct soluble prefibrillar α-syn oligomers formed either spontaneously or in the presence of dopamine and glutaraldehyde. We show that both on-fibrillar assembly pathway and distinct dopamine-mediated and glutaraldehyde-cross-linked α-syn oligomers are only slightly effective in perturbing cell membrane integrity and inducing cytotoxicity, while mature fibrils exhibit the highest toxicity. In contrast to low-molecular weight and unstable oligomers, large stable α-syn oligomers seed the aggregation of soluble α-syn within reporter cells although to a lesser extent than mature α-syn fibrils. These oligomers appear elongated in shape. Our findings suggest that α-syn oligomers represent a continuum of species ranging from unstable low molecular weight particles to mature fibrils via stable elongated oligomers composed of more than 15 α-syn monomers that possess seeding capacity. PMID:27075649

  12. Antiparallel Triple-strand Architecture for Prefibrillar Aβ42 Oligomers*

    PubMed Central

    Gu, Lei; Liu, Cong; Stroud, James C.; Ngo, Sam; Jiang, Lin; Guo, Zhefeng

    2014-01-01

    Aβ42 oligomers play key roles in the pathogenesis of Alzheimer disease, but their structures remain elusive partly due to their transient nature. Here, we show that Aβ42 in a fusion construct can be trapped in a stable oligomer state, which recapitulates characteristics of prefibrillar Aβ42 oligomers and enables us to establish their detailed structures. Site-directed spin labeling and electron paramagnetic resonance studies provide structural restraints in terms of side chain mobility and intermolecular distances at all 42 residue positions. Using these restraints and other biophysical data, we present a novel atomic-level oligomer model. In our model, each Aβ42 protein forms a single β-sheet with three β-strands in an antiparallel arrangement. Each β-sheet consists of four Aβ42 molecules in a head-to-tail arrangement. Four β-sheets are packed together in a face-to-back fashion. The stacking of identical segments between different β-sheets within an oligomer suggests that prefibrillar oligomers may interconvert with fibrils via strand rotation, wherein β-strands undergo an ∼90° rotation along the strand direction. This work provides insights into rational design of therapeutics targeting the process of interconversion between toxic oligomers and non-toxic fibrils. PMID:25118290

  13. Toxic species in amyloid disorders: Oligomers or mature fibrils

    PubMed Central

    Verma, Meenakshi; Vats, Abhishek; Taneja, Vibha

    2015-01-01

    Protein aggregation is the hallmark of several neurodegenerative disorders. These protein aggregation (fibrillization) disorders are also known as amyloid disorders. The mechanism of protein aggregation involves conformation switch of the native protein, oligomer formation leading to protofibrils and finally mature fibrils. Mature fibrils have long been considered as the cause of disease pathogenesis; however, recent evidences suggest oligomeric intermediates formed during fibrillization to be toxic. In this review, we have tried to address the ongoing debate for these toxic amyloid species. We did an extensive literature search and collated information from Pubmed (http://www.ncbi.nlm.nih.gov) and Google search using various permutations and combinations of the following keywords: Neurodegeneration, amyloid disorders, protein aggregation, fibrils, oligomers, toxicity, Alzheimer's Disease, Parkinson's Disease. We describe different instances showing the toxicity of mature fibrils as well as oligomers in Alzheimer's Disease and Parkinson's Disease. Distinct structural framework and morphology of amyloid oligomers suggests difference in toxic effect between oligomers and fibrils. We highlight the difference in structure and proposed toxicity pathways for fibrils and oligomers. We also highlight the evidences indicating that intermediary oligomeric species can act as potential diagnostic biomarker. Since the formation of these toxic species follow a common structural switch among various amyloid disorders, the protein aggregation events can be targeted for developing broad-range therapeutics. The therapeutic trials based on the understanding of different protein conformers (monomers, oligomers, protofibrils and fibrils) in amyloid cascade are also described. PMID:26019408

  14. Direct Electrodeposition of UO2 from Uranyl Bis(trifluoromethanesulfonyl)imide Dissolved in 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide Room Temperature Ionic Liquid System

    DOE PAGESBeta

    Freiderich, John W.; Wanigasekara, Eranda P.; Sun, Xiao-Guang; Meisner, Roberta Ann; Meyer, III, Harry M.; Luo, Huimin; Delmau, Laetitia Helene; Dai, Sheng; Moyer, Bruce A

    2013-11-11

    Our study demonstrates a direct electrodeposition of UO2 at a Pt cathode from a solution of uranyl bis(trifluoromethanesulfonyl)imide [UO2(NTf2)2)] in a bulk room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM+NTf2–). Cyclic voltammetry (CV) studies revealed two reduction waves corresponding to the conversion of uranium(VI) to uranium(IV), and a mechanism for the overall electroreduction is proposed. A controlled-potential experiment was performed, holding the reduction potential at–1.0 V for 24 h to obtain a brown-black deposit of UO2 on the Pt cathode. The Faradaic efficiency of the reduction process was determined to be >80%. The UO2deposit was characterized by powder X-ray diffraction (XRD)more » and X-ray photoelectron spectroscopy (XPS).« less

  15. A Versatile and Scalable Strategy to Discrete Oligomers.

    PubMed

    Lawrence, Jimmy; Lee, Sang-Ho; Abdilla, Allison; Nothling, Mitchell D; Ren, Jing M; Knight, Abigail S; Fleischmann, Carolin; Li, Youli; Abrams, Austin S; Schmidt, Bernhard V K J; Hawker, Michael C; Connal, Luke A; McGrath, Alaina J; Clark, Paul G; Gutekunst, Will R; Hawker, Craig J

    2016-05-18

    A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (Đ = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications. PMID:27152711

  16. One-bead-one-compound library of end-capped dipeptides and deconvolution by microflow NMR.

    PubMed

    Simon, Rozalyn A; Schuresko, Laura; Dendukuri, Nagamani; Goers, Emily; Murphy, Brent; Lokey, R Scott

    2005-01-01

    As part of our program to identify novel small molecules with interesting biological activity, we have designed and synthesized a library of end-capped dipeptides with an emphasis on compound diversity, complexity, and membrane permeability. An approximately 1500-member library was synthesized manually on large polystyrene beads using the mix-and-split method. The final compounds were cleaved into 384-well plates to generate individual stock solutions for input into high-throughput biological screens. Individual compounds were decoded using a combination of mass spectrometry and microflow NMR spectroscopy. In principle, this approach to deconvolution obviates the need for complicated binary encoding-decoding strategies for one-bead-one-compound libraries. PMID:16153064

  17. Performance of the Prototype Readout System for the CMS Endcap Hadron Calorimeter Upgrade

    NASA Astrophysics Data System (ADS)

    Chaverin, Nate; Dittmann, Jay; Hatakeyama, Kenichi; Pastika, Nathaniel; CMS Collaboration

    2016-03-01

    The Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC) will upgrade the photodetectors and readout systems of the endcap hadron calorimeter during the technical stop scheduled for late 2016 and early 2017. A major milestone for this project was a highly successful testbeam run at CERN in August 2015. The testbeam run served as a full integration test of the electronics, allowing a study of the response of the preproduction electronics to the true detector light profile, as well as a test of the light yield of various new plastic scintillator materials. We present implications for the performance of the hadron calorimeter front-end electronics based on testbeam data, and we report on the production status of various components of the system in preparation for the upgrade.

  18. Synthesis of 1H-Indazoles from Imidates and Nitrosobenzenes via Synergistic Rhodium/Copper Catalysis.

    PubMed

    Wang, Qiang; Li, Xingwei

    2016-05-01

    Nitrosobenzenes have been used as a convenient aminating reagent for the efficient synthesis of 1H-indazoles via rhodium and copper catalyzed C-H activation and C-N/N-N coupling. The reaction occurred under redox-neutral conditions with high efficiency and functional group tolerance. Moreover, a rhodacyclic imidate complex has been identified as a key intermediate. PMID:27082502

  19. Biomimetic peptoid oligomers as dual-action antifreeze agents.

    PubMed

    Huang, Mia L; Ehre, David; Jiang, Qi; Hu, Chunhua; Kirshenbaum, Kent; Ward, Michael D

    2012-12-01

    The ability of natural peptides and proteins to influence the formation of inorganic crystalline materials has prompted the design of synthetic compounds for the regulation of crystal growth, including the freezing of water and growth of ice crystals. Despite their versatility and ease of structural modification, peptidomimetic oligomers have not yet been explored extensively as crystallization modulators. This report describes a library of synthetic N-substituted glycine peptoid oligomers that possess "dual-action" antifreeze activity as exemplified by ice crystal growth inhibition concomitant with melting temperature reduction. We investigated the structural features responsible for these phenomena and observed that peptoid antifreeze activities depend both on oligomer backbone structure and side chain chemical composition. These studies reveal the capability of peptoids to act as ice crystallization regulators, enabling the discovery of a unique and diverse family of synthetic oligomers with potential as antifreeze agents in food production and biomedicine. PMID:23169638

  20. Chemical Fluorescent Probe for Detection of Aβ Oligomers.

    PubMed

    Teoh, Chai Lean; Su, Dongdong; Sahu, Srikanta; Yun, Seong-Wook; Drummond, Eleanor; Prelli, Frances; Lim, Sulgi; Cho, Sunhee; Ham, Sihyun; Wisniewski, Thomas; Chang, Young-Tae

    2015-10-28

    Aggregation of amyloid β-peptide (Aβ) is implicated in the pathology of Alzheimer's disease (AD), with the soluble, Aβ oligomeric species thought to be the critical pathological species. Identification and characterization of intermediate species formed during the aggregation process is crucial to the understanding of the mechanisms by which oligomeric species mediate neuronal toxicity and following disease progression. Probing these species proved to be extremely challenging, as evident by the lack of reliable sensors, due to their heterogeneous and transient nature. We describe here an oligomer-specific fluorescent chemical probe, BoDipy-Oligomer (BD-Oligo), developed through the use of the diversity-oriented fluorescent library approach (DOFLA) and high-content, imaging-based screening. This probe enables dynamic oligomer monitoring during fibrillogenesis in vitro and shows in vivo Aβ oligomers staining possibility in the AD mice model. PMID:26218347

  1. Exosomal cell-to-cell transmission of alpha synuclein oligomers

    PubMed Central

    2012-01-01

    Background Aggregation of alpha-synuclein (αsyn) and resulting cytotoxicity is a hallmark of sporadic and familial Parkinson’s disease (PD) as well as dementia with Lewy bodies, with recent evidence implicating oligomeric and pre-fibrillar forms of αsyn as the pathogenic species. Recent in vitro studies support the idea of transcellular spread of extracellular, secreted αsyn across membranes. The aim of this study is to characterize the transcellular spread of αsyn oligomers and determine their extracellular location. Results Using a novel protein fragment complementation assay where αsyn is fused to non-bioluminescent amino-or carboxy-terminus fragments of humanized Gaussia Luciferase we demonstrate here that αsyn oligomers can be found in at least two extracellular fractions: either associated with exosomes or free. Exosome-associated αsyn oligomers are more likely to be taken up by recipient cells and can induce more toxicity compared to free αsyn oligomers. Specifically, we determine that αsyn oligomers are present on both the outside as well as inside of exosomes. Notably, the pathway of secretion of αsyn oligomers is strongly influenced by autophagic activity. Conclusions Our data suggest that αsyn may be secreted via different secretory pathways. We hypothesize that exosome-mediated release of αsyn oligomers is a mechanism whereby cells clear toxic αsyn oligomers when autophagic mechanisms fail to be sufficient. Preventing the early events in αsyn exosomal release and uptake by inducing autophagy may be a novel approach to halt disease spreading in PD and other synucleinopathies. PMID:22920859

  2. Wholly Aromatic Ether-imides. Potential Materials for n-Type Semiconductors

    NASA Astrophysics Data System (ADS)

    Dingemans, Theo J.; St.Clair, Terry L.; Samulski, Edward T.

    2002-12-01

    We report on the synthesis and characterization of a novel series low-molar-mass ether-imide rod-shaped model compounds. All ether-imides were obtained by terminating the appropriate rigid core dianhydride, i.e. pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3,4,4'-oxydiphthalic dianhydride (ODPA) with three flexible aryl-ether tails of different chain length. The mono-functional aryl-ether amines, i.e. 4-(3-phenoxy-phenoxy)-phenylamine (2) and 4-(3-phenoxy-3-phenoxy-phenoxy)-phenylamine (4), were synthesized using standard fluoro-displacement and Ullmann condensation techniques. The corresponding ether-imide model compounds were obtained in high yields using a one-step solution imidization procedure. Increasing the number of meta-substituted aryl-ether units reduces the melt transition temperatures and at the same time it increases the solubility of the model compounds. Most model compounds are crystalline solids and form isotropic melts upon heating. 2,7-Bis-(-4-phenoxy-phenyl)-benzoImn][3,8phenanthroline1,3,6,8-tetraone (NDA-n0), however, displays a smectic A (SA) when cooled from the isotropic phase, followed by what appears to be either a highly ordered smectic phase or a, columnar phase. This is the first example, known to date, in which a mesophase is detected in a wholly aromatic ether-imide compound. For all compounds we present spectroscopic data and X-ray diffraction data. Cyclic voltammetry was used to determine the redox behavior and pertinent energy levels of the model compounds.

  3. Wholly Aromatic Ether-imides. Potential Materials for n-Type Semiconductors

    NASA Technical Reports Server (NTRS)

    Dingemans, Theo J.; St.Clair, Terry L.; Samulski, Edward T.; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    We report on the synthesis and characterization of a novel series low-molar-mass ether-imide rod-shaped model compounds. All ether-imides were obtained by terminating the appropriate rigid core dianhydride, i.e. pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3,4,4'-oxydiphthalic dianhydride (ODPA) with three flexible aryl-ether tails of different chain length. The mono-functional aryl-ether amines, i.e. 4-(3-phenoxy-phenoxy)-phenylamine (2) and 4-(3-phenoxy-3-phenoxy-phenoxy)-phenylamine (4), were synthesized using standard fluoro-displacement and Ullmann condensation techniques. The corresponding ether-imide model compounds were obtained in high yields using a one-step solution imidization procedure. Increasing the number of meta-substituted aryl-ether units reduces the melt transition temperatures and at the same time it increases the solubility of the model compounds. Most model compounds are crystalline solids and form isotropic melts upon heating. 2,7-Bis-(-4-phenoxy-phenyl)-benzo[Imn][3,8]phenanthroline1,3,6,8-tetraone (NDA-n0), however, displays a smectic A (SA) when cooled from the isotropic phase, followed by what appears to be either a highly ordered smectic phase or a, columnar phase. This is the first example, known to date, in which a mesophase is detected in a wholly aromatic ether-imide compound. For all compounds we present spectroscopic data and X-ray diffraction data. Cyclic voltammetry was used to determine the redox behavior and pertinent energy levels of the model compounds.

  4. Siloxane containing polyimides with improved processability

    NASA Technical Reports Server (NTRS)

    Maudgal, Shubha; St. Clair, T. L.

    1985-01-01

    Siloxane containing polyimides were prepared in an effort to improve processability of linear aromatic polyimides and toughness of addition curing imide oligomers. Linear aromatic polyimides were endcapped with varying proportions of a silane; a diaminosiloxane was copolymerized with an aromatic diamine; polyimide oligomers were endcapped with reactive groups; and acetylene terminated siloxane-containing oligomers were blended with linear siloxane-containing polyimides. The resins were used to prepare moldings, titanium to titanium adhesive bonds, and graphite reinforced composites. In each case, physical properties and other characteristics were compared to those of chemically similar polyimides with no siloxane incorporation. The resins, in most cases, performed better at room temperature than the corresponding polyimide. At elevated temperatures, for high siloxane content, the performance deteriorated.

  5. Optimizing antisense oligonucleotides using phosphorodiamidate morpholino oligomers.

    PubMed

    Popplewell, Linda J; Malerba, Alberto; Dickson, George

    2012-01-01

    Duchenne muscular dystrophy (DMD) is caused by mutations that disrupt the reading frame of the human DMD gene. Selective removal of exons flanking an out-of-frame DMD mutation can result in an in-frame mRNA transcript that may be translated into an internally deleted Becker muscular dystrophy-like functionally active dystrophin protein with therapeutic activity. Antisense oligonucleotides (AOs) can be designed to bind to complementary sequences in the targeted mRNA and modify pre-mRNA splicing to correct the reading frame of a mutated transcript. AO-induced exon skipping resulting in functional truncated dystrophin has been demonstrated in animal models of DMD both in vitro and in vivo, in DMD patient cells in vitro in culture, and in DMD muscle explants. The recent advances made in this field suggest that it is likely that AO-induced exon skipping will be the first gene therapy for DMD to reach the clinic. However, it should be noted that personalized molecular medicine may be necessary, since the various reading frame-disrupting mutations are spread across the DMD gene. The different deletions that cause DMD would require skipping of different exons, which would require the optimization and clinical trial workup of many specific AOs. This chapter describes the methodologies available for the optimization of AOs, in particular phosphorodiamidate morpholino oligomers, for the targeted skipping of specific exons on the DMD gene. PMID:22454060

  6. I2/Aqueous TBHP-Catalyzed Coupling of Amides with Methylarenes/Aldehydes/Alcohols: Metal-Free Synthesis of Imides.

    PubMed

    Aruri, Hariprasad; Singh, Umed; Kumar, Sanjay; Kushwaha, Manoj; Gupta, Ajai Prakash; Vishwakarma, Ram A; Singh, Parvinder Pal

    2016-08-01

    We present a metal-free method for the synthesis of imides by the direct coupling of NH-amides with methylarenes under iodine/aqueous TBHP conditions. The optimized conditions worked very well with benzaldehydes and benzyl alcohol and furnished the corresponding imides in good to excellent yields. A series of control and radical scavenger experiments were also performed, which suggested the involvement of radical pathways. The labeling experiment in the presence of (18)O-labeled H2O suggested water as a source of oxygen in the imides. PMID:27434140

  7. Density functional theory study of neutral and oxidized thiophene oligomers

    NASA Astrophysics Data System (ADS)

    Dai, Yafei; Wei, Chengwei; Blaisten-Barojas, Estela

    2013-11-01

    The effect of oxidation on the energetics and structure of thiophene (Th) oligomers is studied with density functional theory at the B3PW91/6-311++G(d,p) level. Neutral n-Th oligomers (2 < n < 13) are gently curved planar chains. Ionization potential and electron affinity results show that n-Th oligomers are easier to be oxidized as their chain length increases. Oxidation states +2, +4, +6, and +8 are energetically stable in 12-Th. Upon oxidation the conjugated backbone of 12-Th switches from extended benzenoid phase to quinoid phase localized on groups of monomers regularly spaced along the chain. Oxidized states +2, +4, +6, and +8 of 12-Th display two +1e localized at the ends of their chains only because of the finite size of the chains. In 12-Th this end-effect extends over the two terminal monomers forming a positive-negative charge duet. This peculiar charge localization makes n-Th oligomers different from other conducting polymers with similar structure, such as polypyrrole. The spectrum of single-electron molecular states of oxidized 12-Th displays two localized single-electron states in the HOMO-LUMO energy gap per +2 oxidation state. Oligothiophene 12-Th doped with F atoms at 1:2 concentration presents a charge transfer of 3.4 e from oligomer to dopants that increases to 4.8 e in the presence of solvent. The charge distribution in these F-doped oligomers is similar to the +4 oxidation state of 12-Th. It is predicted that dopants produce an enhanced charge transfer localized in the proximity of their locations enhancing the formation of bipolarons in the central part of the oligomer chain.

  8. Key Role of End-Capping Groups in Optoelectronic Properties of Poly-p-phenylene Cation Radicals

    PubMed Central

    2015-01-01

    Poly-p-phenylenes (PPs) are prototype systems for understanding the charge transport in π-conjugated polymers. In a combined computational and experimental study, we demonstrate that the smooth evolution of redox and optoelectronic properties of PP cation radicals toward the polymeric limit can be significantly altered by electron-donating iso-alkyl and iso-alkoxy end-capping groups. A multiparabolic model (MPM) developed and validated here rationalizes this unexpected effect by interplay of the two modes of hole stabilization: due to the framework of equivalent p-phenylene units and due to the electron-donating end-capping groups. A symmetric, bell-shaped hole in unsubstituted PPs becomes either slightly skewed and shifted toward an end of the molecule in iso-alkyl-capped PPs or highly deformed and concentrated on a terminal unit in PPs with strongly electron-donating iso-alkoxy capping groups. The MPM shows that the observed linear 1/n evolution of the PP cation radical properties toward the polymer limit originates from the hole stabilization due to the growing chain of p-phenylene units, while shifting of the hole toward electron-donating end-capping groups leads to early breakdown of these 1/n dependencies. These insights, along with the readily applicable and flexible multistate parabolic model, can guide studies of complex donor–spacer–acceptor systems and doped molecular wires to aid the design of the next generation materials for long-range charge transport and photovoltaic applications. PMID:25264475

  9. Degradation of a Sodium Acrylate Oligomer by an Arthrobacter sp

    PubMed Central

    Hayashi, Takaya; Mukouyama, Masaharu; Sakano, Kouichi; Tani, Yoshiki

    1993-01-01

    Arthrobacter sp. strain NO-18 was first isolated from soil as a bacterium which could degrade the sodium acrylate oligomer and utilize it as the sole source of carbon. When 0.2% (wt/wt) oligomer was added to the culture medium, the acrylate oligomer was found to be degraded by 70 to 80% in 2 weeks, using gel permeation chromatography. To determine the maximum molecular weight for biodegradation, the degradation test was done with the hexamer, heptamer, and octamer, which were separated from the oligomer mixture by fractional gel permeation chromatography. The hexamer and heptamer were consumed to the extents of 58 and 36%, respectively, in 2 weeks, but the octamer was not degraded. Oligomers with three different terminal groups were synthesized to examine the effect of the different terminal groups on biodegradation, but few differences were found. Arthrobacter sp. NO-18 assimilated acrylic acid, propionic acid, glutaric acid, 2-methylglutaric acid, and 1,3,5-pentanetricarboxylic acid. Degradation of the acrylic unit structure by this strain is discussed. PMID:8517751

  10. Observation of Fano resonances in all-dielectric nanoparticle oligomers.

    PubMed

    Chong, Katie E; Hopkins, Ben; Staude, Isabelle; Miroshnichenko, Andrey E; Dominguez, Jason; Decker, Manuel; Neshev, Dragomir N; Brener, Igal; Kivshar, Yuri S

    2014-05-28

    It is well-known that oligomers made of metallic nanoparticles are able to support sharp Fano resonances originating from the interference of two plasmonic resonant modes with different spectral width. While such plasmonic oligomers suffer from high dissipative losses, a new route for achieving Fano resonances in nanoparticle oligomers has opened up after the recent experimental observations of electric and magnetic resonances in low-loss dielectric nanoparticles. Here, light scattering by all-dielectric oligomers composed of silicon nanoparticles is studied experimentally for the first time. Pronounced Fano resonances are observed for a variety of lithographically-fabricated heptamer nanostructures consisting of a central particle of varying size, encircled by six nanoparticles of constant size. Based on a full collective mode analysis, the origin of the observed Fano resonances is revealed as a result of interference of the optically-induced magnetic dipole mode of the central particle with the collective mode of the nanoparticle structure. This allows for effective tuning of the Fano resonance to a desired spectral position by a controlled size variation of the central particle. Such optically-induced magnetic Fano resonances in all-dielectric oligomers offer new opportunities for sensing and nonlinear applications. PMID:24616191

  11. Role of the Imide Axial Ligand in the Spin and Oxidation State of Manganese Corrole and Corrolazine Complexes.

    PubMed

    Alcover-Fortuny, Gerard; Caballol, Rosa; Pierloot, Kristine; de Graaf, Coen

    2016-06-01

    Electronic structure calculations have been performed on four different Mn corrole and corrolazine complexes to clarify the role of the imide axial ligand on the relative stability of the different spin states and the stabilization of the high-valent Mn ion in these complexes. Multiconfigurational perturbation theory energy calculations on the DFT-optimized geometries show that all complexes have a singlet ground state except the complex with the strongest electron-withdrawing substituent on the imide axial ligand, which is found to have a triplet ground state. The analysis of the σ and π interaction between the metal and imide ligand shows that this spin crossover is caused by a subtle interplay of geometrical factors (Mn-N distance and coordination angle) and the electron-withdrawing character of the substituent on the imide, which reduces the electron donation to the metal center. The analysis of the multiconfigurational wave functions reveals that the formally Mn(V) ion is stabilized by an important electron transfer from both the equatorial corrole/corrolazine ligand and the axial imide. The macrocycle donates roughly half an electron, being somewhere between the closed-shell trianionic and the dianionic radical form. The imide ligand transfers 2.5 electrons to the metal center, resulting in an effective d-electron count close to five in all complexes. PMID:27163862

  12. Corrosion of stainless steel battery components by bis(fluorosulfonyl)imide based ionic liquid electrolytes

    NASA Astrophysics Data System (ADS)

    Evans, Tyler; Olson, Jarred; Bhat, Vinay; Lee, Se-Hee

    2014-12-01

    While the anodic behavior of aluminum foil current collectors in imide-based room temperature ionic liquids (RTILs) is relatively well understood, interactions between such RTILs and other passive battery components have not been studied extensively. This study presents the solvent and potential dependent oxidation of SS316 coin-cell components in the N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) RTIL. While this phenomenon prohibits high-voltage cycling of Li(Ni1/3Mn1/3Co1/3)O2 cathodes in SS316 coin-type cells, Al-clad cell components or alternative cell configurations can be utilized to avoid SS316 oxidation-induced cell failure.

  13. N-15 NMR Spectroscopy as a Method for Comparing the Rates of Imidization of Several Diamines

    NASA Technical Reports Server (NTRS)

    Johnson, J. Christopher; Kuczmarski, Maria A.

    2006-01-01

    The relative rates of the conversion of amide-acid to imide was measured for a series or aromatic diamines that have been identified as potential replacements for 4,4'-methylene dianiline (MDA) in high-temperature polyimides and polymer composites. These rates were compared with the N-15 NMR resonances of the unreacted amines. The initial rates of imidization track with the difference in chemical shift between the amine nitrogens in MDA and those in the subject diamines. This comparison demonstrated that N-15 NMR spectroscopy is appropriate for the rapid screening of candidate diamines to determine their reactivity relative to MDA, and can serve to provide guidance to the process of creating the time-temperature profiles used in processing these materials into polymer matrix composites.

  14. Preparation and Characterization of Silica/Polyamide-imide Nanocomposite Thin Films

    NASA Astrophysics Data System (ADS)

    Ma, Xiaokun; Lee, Nam-Hee; Oh, Hyo-Jin; Hwang, Jong-Sun; Kim, Sun-Jae

    2010-11-01

    The functional silica/polyamide-imide composite films were prepared via simple ultrasonic blending, after the silica nanoparticles were modified by cationic surfactant—cetyltrimethyl ammonium bromide (CTAB). The composite films were characterized by scanning electron microscope (SEM), thermo gravimetric analysis (TGA) and thermomechanical analysis (TMA). CTAB-modified silica nanoparticles were well dispersed in the polyamide-imide matrix, and the amount of silica nanoparticles to PAI was investigated to be from 2 to 10 wt%. Especially, the coefficients of thermal expansion (CET) continuously decreased with the amount of silica particles increasing. The high thermal stability and low coefficient of thermal expansion showed that the nanocomposite films can be widely used in the enamel wire industry.

  15. Preparation and Characterization of Silica/Polyamide-imide Nanocomposite Thin Films

    PubMed Central

    2010-01-01

    The functional silica/polyamide-imide composite films were prepared via simple ultrasonic blending, after the silica nanoparticles were modified by cationic surfactant—cetyltrimethyl ammonium bromide (CTAB). The composite films were characterized by scanning electron microscope (SEM), thermo gravimetric analysis (TGA) and thermomechanical analysis (TMA). CTAB-modified silica nanoparticles were well dispersed in the polyamide-imide matrix, and the amount of silica nanoparticles to PAI was investigated to be from 2 to 10 wt%. Especially, the coefficients of thermal expansion (CET) continuously decreased with the amount of silica particles increasing. The high thermal stability and low coefficient of thermal expansion showed that the nanocomposite films can be widely used in the enamel wire industry. PMID:21124625

  16. Probing the stability of insulin oligomers using electrospray ionization ion mobility mass spectrometry.

    PubMed

    Boga Raja, Uday Kumar; Injeti, Srilakshmi; Culver, Tiffany; McCabe, Jacob W; Angel, Laurence A

    2015-01-01

    The peptide hormone insulin is central to regulating carbohydrate and fat metabolism in the body by controlling blood sugar levels. Insulin's most active form is the monomer and the extent of insulin oligomerization is related to insulin's activity of controlling blood sugar levels. Electrospray ionization (ESI) of human insulin produced a series of oligomers from the monomer to the undecamer identified using quadrupole ion mobility time-of-flight mass spectrometry. Previous research suggested that only the monomer, dimer and hexamer are native forms of insulin in solution and the range of oligomers observed in the gas-phase are ESI artifacts. Here the properties of three distinct oligomer bands I, II and III, where both the charge state and number of insulin units of the oligomer increase incrementally, were investigated. When Zn(ii) was added to the insulin sample the same oligomers were observed but with 0-6 Zn(ii) ions bound to each of the oligomers. The oligomers of bands I, II and III were characterized by comparing their drift times, collision cross- sections, relative intensities, collision-induced dissociation (CID) patterns and relative breakdown energies. Insulin oligomers of band I dissociated primarily by releasing either the 2+ or 3+ monomer accompanied by an oligomer that conserved the mass, charge and Zn(ii) of the precursor. Insulin oligomers of bands II and III dissociated primarily by releasing the 2+ monomer accompanied by an oligomer which conserved the mass, charge and Zn(ii) of the precursor. Comparison of CID patterns and breakdown energies showed all the oligomers in band II required higher collision energies to dissociate than the oligomers in band I, and the oligomers of band III required higher energies to dissociate than oligomers of band II. These results show that the amount of excess charge on the oligomer in respect to the number of insulin monomers in the oligomer affects their stability. PMID:26764306

  17. Imides: forgotten players in the Ugi reaction. One-pot multicomponent synthesis of quinazolinones.

    PubMed

    Mossetti, Riccardo; Pirali, Tracey; Saggiorato, Dèsirèe; Tron, Gian Cesare

    2011-06-28

    Up to now, the synthesis of quinazolinones has required lengthy synthetic procedures. Here, we describe an innovative one-pot multicomponent reaction leading to highly substituted quinazolinones. We believe that this novel transformation may open the door for the generation of new and pharmacologically active quinazolinones, but, most important of all, the resurrection of the imide-Ugi scaffold paves the way for the synthesis of novel molecular architectures. PMID:21589958

  18. Iodine(III)-Mediated para-Selective Direct Imidation of Anilides.

    PubMed

    Pialat, Amélie; Bergès, Julien; Sabourin, Axel; Vinck, Robin; Liégault, Benoît; Taillefer, Marc

    2015-07-01

    The direct, nucleophilic imidation of acetanilide derivatives has been performed under mild, iodine(III)-mediated or -catalyzed conditions, employing lithium triflimide as the nitrogen source. The reaction exhibits exclusive regioselectivity for the para position and shows a good tolerance for varied functional groups at both the ortho or meta positions. Preliminary mechanistic data suggest that the LiNTf2 reagent plays a key role in the reactivity. PMID:26095155

  19. Direct Electrodeposition of UO2 from Uranyl Bis(trifluoromethanesulfonyl)imide Dissolved in 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide Room Temperature Ionic Liquid System

    SciTech Connect

    Freiderich, John W.; Wanigasekara, Eranda P.; Sun, Xiao-Guang; Meisner, Roberta Ann; Meyer, III, Harry M.; Luo, Huimin; Delmau, Laetitia Helene; Dai, Sheng; Moyer, Bruce A

    2013-11-11

    Our study demonstrates a direct electrodeposition of UO2 at a Pt cathode from a solution of uranyl bis(trifluoromethanesulfonyl)imide [UO2(NTf2)2)] in a bulk room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM+NTf2). Cyclic voltammetry (CV) studies revealed two reduction waves corresponding to the conversion of uranium(VI) to uranium(IV), and a mechanism for the overall electroreduction is proposed. A controlled-potential experiment was performed, holding the reduction potential at–1.0 V for 24 h to obtain a brown-black deposit of UO2 on the Pt cathode. The Faradaic efficiency of the reduction process was determined to be >80%. The UO2deposit was characterized by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

  20. Photon-veto counters at the outer edge of the endcap calorimeter for the KOTO experiment

    NASA Astrophysics Data System (ADS)

    Matsumura, T.; Shinkawa, T.; Yokota, H.; Iwai, E.; Komatsubara, T. K.; Lee, J. W.; Lim, G. Y.; Ma, J.; Masuda, T.; Nanjo, H.; Nomura, T.; Odani, Y.; Ri, Y. D.; Shiomi, K.; Sugiyama, Y.; Suzuki, S.; Togawa, M.; Wah, Y.; Watanabe, H.; Yamanaka, T.

    2015-09-01

    The Outer-Edge Veto (OEV) counter subsystem for extra-photon detection from the backgrounds for the KL0 →π0 ν ν bar decay is located at the outer edge of the endcap CsI calorimeter of the KOTO experiment at J-PARC. The subsystem is composed of 44 counters with different cross-sectional shapes. All counters are made of lead and scintillator plates and read out through wavelength-shifting fibers. In this paper, we discuss the design and performances of the OEV counters under heavy load (~ 8 tons /m2) in vacuum. For 1-MeV energy deposit, the average light yield and time resolution are 20.9 photo-electrons and 1.5 ns, respectively. Although no pronounced peak by minimum-ionizing particles is observed in the energy distributions, an energy calibration method with cosmic rays works well in monitoring the gain stability with an accuracy of a few percent.

  1. Surface reconstruction and hemocompatibility improvement of a phosphorylcholine end-capped poly(butylene succinate) coating.

    PubMed

    Hao, Ni; Wang, Yan-Bing; Zhang, Shi-Ping; Shi, Su-Qing; Nakashima, Kenichi; Gong, Yong-Kuan

    2014-09-01

    Control over cell-material surface interactions is the key to many new and improved biomedical devices. In this study, we present a simple yet effective surface modification method that allows for the surface reconstruction and formation of cell outer membrane mimetic structure on coatings that have significantly increased hemocompatibility. To achieve this, a phosphorylcholine end-capped poly(butylene succinate) (PBS-PC) was synthesized and dip-coated on coverslips. The surface structure of the amphiphilic PBS-PC film was reconstructed by heating in a vacuum oven to obtain the less hydrophilic surface and by immersing in hot water to obtain the more hydrophilic surface. Significant changes in the surface element concentration were observed by X-ray photoelectron spectroscopy analysis and changes in surface wettability were measured by sensitive dynamic contact angle technique. Scanning electron microscope images showed different morphologies of the reconstructed surfaces. Interestingly, the reconstruction between the less hydrophilic and more hydrophilic surfaces is reversible. More importantly, both the reconstructed surfaces are stable in room condition for more than 6 months, and both the surfaces show significant improvement in hemocompatibility as revealed by protein adsorption and platelet adhesion measurements. This reversible surface reconstruction strategy and the interesting results may be significant for fabricating stable and hemocompatible surfaces on differently shaped biomedical devices. PMID:24115737

  2. The Forward Endcap of the Electromagnetic Calorimeter for the PANDA Detector at FAIR

    NASA Astrophysics Data System (ADS)

    Albrecht, Malte; PANDA Collaboration

    2015-02-01

    The versatile 4π-detector PANDA will be built at the Facility for Antiproton and Ion Research (FAIR), an accelerator complex, currently under construction near Darmstadt, Germany. A cooled antiproton beam in a momentum range of 1.5 - 15GeV/c will be provided by the High Energy Storage Ring (HESR). All measurements at PANDA rely on an excellent performance of the detector with respect to tracking, particle identification and energy measurement. The electromagnetic calorimeter (EMC) of the PANDA detector will be equipped with 15744 PbWO4 crystals (PWO-II), which will be operated at a temperature of - 25° C in order to increase the light output. The design of the forward endcap of the EMC has been finalized. The crystals will be read out with Large Area Avalanche Photo Diodes (LAAPDs) in the outer regions and with Vacuum Photo Tetrodes (VPTTs) in the innermost part. Production of photosensor units utilizing charge integrating preamplifiers has begun. A prototype comprised of 216 PbWO4 crystals has been built and tested at various accelerators (CERN SPS, ELSA/Bonn, MAMI/Mainz), where the crystals have been exposed to electron and photon beams of 25MeV up to 15GeV. The results of these test measurements regarding the energy and position resolution are presented.

  3. Characterization of the selenotrisulfide formed by reaction of selenite with end-capped phytochelatin-2.

    PubMed

    Spain, Stephen M; Rabenstein, Dallas L

    2004-03-01

    The phytochelatins are a family of peptides synthesized by plants in response to exposure to heavy metals and metalloids, including selenium in the form of selenite. The amino acid sequence of the phytochelatin (PC) peptides is (gamma-Glu-Cys)n-Gly, where n typically ranges from 2 to 5. In this paper, the products of the reaction of selenite with an end-capped analogue of PC2, Ac-(gamma-Glu-Cys)2-Gly-NH2, are characterized. Selenite reacts with Ac-(gamma-Glu-Cys)2-Gly-NH2 (Ac-PC2-NH2) to form a compound that contains an intramolecular selenotrisulfide (-SSeS-)-linkage (Se[Ac-PC2-NH2]) and oxidized Ac-PC2-NH2. Both Se[Ac-PC2-NH2] and oxidized Ac-PC2-NH2 were isolated by HPLC and were characterized by MALDI-TOF mass spectrometry, by two-dimensional 1H and 13C NMR and, in the case of Se[Ac-PC2-NH2], by 77Se NMR. Using dihedral angles determined from vicinal 1H-1H coupling constants as constraints for the conformations around the Cys(CalphaH)-Cys(CbetaH) bonds, structures were predicted for the most abundant form of both compounds by Monte Carlo molecular mechanics simulations. PMID:15214417

  4. CO2 - and O2 -sensitive fluorophenyl end-capped poly(ethylene glycol).

    PubMed

    Choi, Jung Yoon; Kim, Jin Young; Moon, Hyo Jung; Park, Min Hee; Jeong, Byeongmoon

    2014-01-01

    Pentafluorophenyl end-capped poly(ethylene glycol) (PF-PEG-PF) aqueous solution shows a lower critical solution temperature (LCST), which is sensitive to the type of gases dissolved in the solution. LCST increases from 24.5 to 26 °C when dissolved carbon dioxide is replaced by oxygen. The transparent-to-turbid transition is reversibly observed when the dissolved carbon dioxide in the PF-PEG-PF aqueous solution is exchanged with oxygen, and vice versa, at 24.5 °C. (19) F NMR and (1) H NMR spectra of the PF-PEG-PF in D2 O suggest that 1) dehydration of PEG is the main reason of developing LCST of the PF-PEG-PF aqueous solution, 2) minute differences in the intermolecular interactions, as demonstrated by changes in the chemical shift of the PF-PEG-PF peaks, induce such a difference in LCST. This paper provides a new insight in designing a stimuli-responsive polymer in that fine tuning of a phase transition can be controlled by the type of dissolved gas. PMID:24272990

  5. α-Synuclein Oligomers Impair Neuronal Microtubule-Kinesin Interplay*

    PubMed Central

    Prots, Iryna; Veber, Vanesa; Brey, Stefanie; Campioni, Silvia; Buder, Katrin; Riek, Roland; Böhm, Konrad J.; Winner, Beate

    2013-01-01

    Early α-synuclein (α-Syn)-induced alterations are neurite pathologies resulting in Lewy neurites. α-Syn oligomers are a toxic species in synucleinopathies and are suspected to cause neuritic pathology. To investigate how α-Syn oligomers may be linked to aberrant neurite pathology, we modeled different stages of α-Syn aggregation in vitro and investigated the interplay of α-Syn aggregates with proteins involved in axonal transport. The interaction of wild type α-Syn (WTS) and α-Syn variants (E57K, A30P, and aSyn(30–110)) with kinesin, tubulin, and the microtubule (MT)-associated proteins, MAP2 and Tau, is stronger for multimers than for monomers. WTS seeds but not α-Syn oligomers significantly and dose-dependently reduced Tau-promoted MT assembly in vitro. In contrast, MT gliding velocity across kinesin-coated surfaces was significantly decreased in the presence of α-Syn oligomers but not WTS seeds or fibrils (aSyn(30–110) multimers). In a human dopaminergic neuronal cell line, mild overexpression of the oligomerizing E57K α-Syn variant significantly impaired neurite network morphology without causing profound cell death. In accordance with these findings, MT stability, neuritic kinesin, and neuritic kinesin-dependent cargoes were significantly reduced by the presence of α-Syn oligomers. In summary, different α-Syn species act divergently on the axonal transport machinery. These findings provide new insights into α-Syn oligomer-driven neuritic pathology as one of the earliest events in synucleinopathies. PMID:23744071

  6. Tau oligomers as potential targets for early diagnosis of tauopathy.

    PubMed

    Sahara, Naruhiko; Ren, Yan; Ward, Sarah; Binder, Lester I; Suhara, Tetsuya; Higuchi, Makoto

    2014-01-01

    The discovery of tau mutations in frontotemporal dementia has been a key event in neurodegenerative disease research. The rTg4510 mouse line expressing human tau with P301L FTDP-17-tau mutation has been established to understand the role of tau in neurodegeneration. Our histological analyses with tau antibodies and fluorescent tau ligands on rTg4510 mice revealed that tau oligomer formation was distinct from tangle formation. While in vivo imaging of mature tangles is now available, imaging biomarkers for tau oligomers would be useful for clarifying their roles in neurotoxicity and for diagnosing early-stage tau pathology. PMID:24595194

  7. Oligomer-assisted synthesis of chiral polyaniline nanofibers.

    PubMed

    Li, Wenguang; Wang, Hsing-Lin

    2004-03-01

    We report here a novel approach to synthesize chiral PANI nanofibers in an aqueous solution. This new approach requires the following conditions: (1) Polymerization was carried out in concentrated camphor sulfonic acid solutions. (2) Aniline oligomers were used to accelerate the polymerization reaction. (3) Ammonium persulfate (oxidant) was added incrementally to the aniline solution. The high anisotropy factor of these PANI nanofibers is likely due to the "autocatalytic effect" resulting from lower oxidation potentials of aniline oligomers. Our chemical synthesis of the chiral PANI nanofibers is enantioselective and, under the optimized conditions, has an anisotropy factor (g = Deltaepsilon/epsilon) of 2.3 x 10-2. PMID:14982411

  8. Femtosecond spectroscopy of a thiophene oligomer with a photoswitch

    NASA Astrophysics Data System (ADS)

    Tamai, N.; Saika, T.

    1996-04-01

    Femtosecond transient absorption spectroscopy was applied to analyze the mechanism of optical switch of an endo-capped thiophene oligomer with a diarylethene structure as a new class of multimode chemical transducers. The rate of the optical switch of the proconductivity was estimated to be 1.1 ps, corresponding to the formation time of the closed-ring form of thiophene oligomer. From the direct observation of the precursor of closed-ring form, the mechanism of photochromic ring-closure reaction was discussed.

  9. Phenylethynyl Phthalic Anhydride

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Smith, Joseph G., Jr. (Inventor)

    1997-01-01

    Controlled molecular weight PhenylEthynyl Terminated Imide oligomers (PETIs) have been prepared by the cyclodehydration of precursor phenylethynyl terminated amic acid oligomers. Amino terminated amic acid oligomers are prepared from the reaction of dianhydride(s) with an excess of diamine(s) and subsequently endcapped with PhenylEthynyl Phthalic Anhydride(s) (PEPA). The polymerizations are carried out in polar aprotic solvents such as N-methyl-2pyrrolidinone or N N-dimethylacetamide under nitrogen at room temperature. The amic acid oligomers are subsequently cyclodehydrated either thermally or chemically to the corresponding imide oligomers. Direct preparation of PETIs from the reaction of dianhydride(s) with an excess of diamine(s) and endcapped with phenylethynyl phthalic anhydride(s) has been performed in m-cresol. Phenylethynyl phthalic anhydrides are synthesized by the palladium catalyzed reaction of phenylacetylene with bromo substituted phthalic anhydrides in triethylamine. These new materials exhibit excellent properties and are potentially useful as adhesives, coatings, films, moldings and composite matrices.

  10. Biophysical characterization data on Aβ soluble oligomers produced through a method enabling prolonged oligomer stability and biological buffer conditions

    PubMed Central

    Crisostomo, Amanda C.; Dang, Loan; Digambaranath, Jyothi L.; Klaver, Andrea C.; Loeffler, David A.; Payne, Jeremiah J.; Smith, Lynnae M.; Yokom, Adam L.; Finke, John M.

    2015-01-01

    The data here consists of time-dependent experimental parameters from chemical and biophysical methods used to characterize Aβ monomeric reactants as well as soluble oligomer and amyloid fibril products from a slow (3–4 week) assembly reaction under biologically-relevant solvent conditions. The data of this reaction are both of a qualitative and quantitative nature, including gel images from chemical cross-linking and Western blots, fractional solubility, thioflavin T binding, size exclusion chromatograms, transmission electron microscopy images, circular dichroism spectra, and fluorescence resonance energy transfer efficiencies of donor–acceptor pair labels in the Aβ chain. This data enables future efforts to produce the initial monomer and eventual soluble oligomer and amyloid fibril states by providing reference benchmarks of these states pertaining to physical properties (solubility), ligand-binding (thioflavin T binding), mesoscopic structure (electron microscopy, size exclusion chromatography, cross-linking products, SDS and native gels) and molecular structure (circular dichroism, FRET donor-acceptor distance). Aβ1-40 soluble oligomers are produced that are suitable for biophysical studies requiring sufficient transient stability to exist in their “native” conformation in biological phosphate-saline buffers for extended periods of time. The production involves an initial preparation of highly monomeric Aβ in a phosphate saline buffer that transitions to fibrils and oligomers through time incubation alone, without added detergents or non-aqueous chemicals. This criteria ensures that the only difference between initial monomeric Aβ reactant and subsequent Aβ oligomer products is their degree of peptide assembly. A number of chemical and biophysical methods were used to characterize the monomeric reactants and soluble oligomer and amyloid fibril products, including chemical cross-linking, Western blots, fraction solubility, thioflvain T binding

  11. Oligomer Molecules for Efficient Organic Photovoltaics.

    PubMed

    Lin, Yuze; Zhan, Xiaowei

    2016-02-16

    Solar cells, a renewable, clean energy technology that efficiently converts sunlight into electricity, are a promising long-term solution for energy and environmental problems caused by a mass of production and the use of fossil fuels. Solution-processed organic solar cells (OSCs) have attracted much attention in the past few years because of several advantages, including easy fabrication, low cost, lightweight, and flexibility. Now, OSCs exhibit power conversion efficiencies (PCEs) of over 10%. In the early stage of OSCs, vapor-deposited organic dye materials were first used in bilayer heterojunction devices in the 1980s, and then, solution-processed polymers were introduced in bulk heterojunction (BHJ) devices. Relative to polymers, vapor-deposited small molecules offer potential advantages, such as a defined molecular structure, definite molecular weight, easy purification, mass-scale production, and good batch-to-batch reproducibility. However, the limited solubility and high crystallinity of vapor-deposited small molecules are unfavorable for use in solution-processed BHJ OSCs. Conversely, polymers have good solution-processing and film-forming properties and are easily processed into flexible devices, whereas their polydispersity of molecular weights and difficulty in purification results in batch to batch variation, which may hamper performance reproducibility and commercialization. Oligomer molecules (OMs) are monodisperse big molecules with intermediate molecular weights (generally in the thousands), and their sizes are between those of small molecules (generally with molecular weights <1000) and polymers (generally with molecular weights >10000). OMs not only overcome shortcomings of both vapor-deposited small molecules and solution-processed polymers, but also combine their advantages, such as defined molecular structure, definite molecular weight, easy purification, mass-scale production, good batch-to-batch reproducibility, good solution processability

  12. Structure and topochemistry of azodioxide oligomers in solid state

    NASA Astrophysics Data System (ADS)

    Bibulić, Petar; Rončević, Igor; Varga, Katarina; Mihalić, Zlatko; Vančik, Hrvoj

    2016-01-01

    The structure of oligomers constructed from 1,4-dinitrosobenzene was studied computationally by DFT methods for shorter oligomers, and by the FMO approach for longer ones. It was demonstrated that the oligomers have helical structure. Formation of 1,4-dinitrosobenzene azodioxides from the corresponding nitroso monomers in solid state was examined by studying the kinetics of their oligomerization under cryogenic conditions. Dissociation of azodioxide bonds to nitroso groups was induced either by UV irradiation at cryogenic temperatures or by sublimation followed by cryogenic deposition. While warming the monomers prepared by UV photodissociation to 150 K gave E-polymers, oligomerization or polymerization of monomers prepared by cryogenic vapor deposition was less pronounced, giving Z-forms. Above 150 K, Z-dimers or short oligomers isomerized, probably by the dissociation-dimerization mechanism, to more stable E-forms. Fast formation of azodioxide bonds and the high stability of corresponding polymers can be ascribed to the strong topochemical effect in the solid state.

  13. Small Glycosylated Lignin Oligomers Are Stored in Arabidopsis Leaf Vacuoles

    PubMed Central

    Dima, Oana; Morreel, Kris; Vanholme, Bartel; Kim, Hoon; Ralph, John; Boerjan, Wout

    2015-01-01

    Lignin is an aromatic polymer derived from the combinatorial coupling of monolignol radicals in the cell wall. Recently, various glycosylated lignin oligomers have been revealed in Arabidopsis thaliana. Given that monolignol oxidation and monolignol radical coupling are known to occur in the apoplast, and glycosylation in the cytoplasm, it raises questions about the subcellular localization of glycosylated lignin oligomer biosynthesis and their storage. By metabolite profiling of Arabidopsis leaf vacuoles, we show that the leaf vacuole stores a large number of these small glycosylated lignin oligomers. Their structural variety and the incorporation of alternative monomers, as observed in Arabidopsis mutants with altered monolignol biosynthesis, indicate that they are all formed by combinatorial radical coupling. In contrast to the common believe that combinatorial coupling is restricted to the apoplast, we hypothesized that the aglycones of these compounds are made within the cell. To investigate this, leaf protoplast cultures were cofed with 13C6-labeled coniferyl alcohol and a 13C4-labeled dimer of coniferyl alcohol. Metabolite profiling of the cofed protoplasts provided strong support for the occurrence of intracellular monolignol coupling. We therefore propose a metabolic pathway involving intracellular combinatorial coupling of monolignol radicals, followed by oligomer glycosylation and vacuolar import, which shares characteristics with both lignin and lignan biosynthesis. PMID:25700483

  14. Ferroelectric and dielectric properties of electroactive oligomers and nanocomposites

    NASA Astrophysics Data System (ADS)

    Kraemer, Kristin L.

    Polyvinylidene fluoride (PVDF) and its copolymers have been well established as ferroelectric polymers. The dielectric and ferroelectric properties for vinylidene fluoride (VDF) oligomer thin films were investigated. By synthesizing oligomers instead of long polymer chains, films with higher crystalinity can be formed and the locations of oligomers can be controlled for applications such as molecular electronics. Evidence of ferroelectricity was observed in oligomer thin films evaporated onto room temperature substrates and by Langmuir-Blodgett (LB) deposition. Voltage and frequency dependence of the capacitance was measured. Oligomers functionalized with phosphonic acid formed self-assembled monolayers (SAM) on aluminum and mica substrates. Film thickness was measured by ellipsometry and atomic force microscopy (AFM). The time dependence on film growth was measured for SAMs on mica substrates by AFM. The islands had already formed by 1 minute, and by 1 hour film was continuous. Additionally, studies were performed on composite dielectric systems with the goal of fabricating high energy density dielectrics containing nanoparticles with an organic shell. The first two types of samples had barium titante nanoparticles coated with functionalized alkanes or VDF oligomers. The first sample type consisted of coated nanoparticles embedded in a PVDF copolymer or terpolymer spin-coated film. At low particle concentrations, the matrix properties dominated the electrical measurements while at high concentrations, the samples were electrically fragile. The second sample type consisted of alternating layers of LB terpolymer and LB nanoparticles. These samples allowed for high particle concentrations while maintaining the high breakdown strength of the polymer layers. The final type of sample was titanium dioxide nanoparticles formed by cluster deposition and coated with an evaporated paraffin or VDF oligomer. These samples tended to have low breakdown strengths and poor

  15. Montmorillonite Clay-Catalyzed Synthesis of RNA Oligomers

    NASA Astrophysics Data System (ADS)

    Ferris, J. P.; Miyakawa, S.; Huang, W.; Joshi, P.

    2005-12-01

    It is proposed that catalysis had a central role in the origins of life. This will be illustrated using the montmorillonite clay-catalyzed synthesis of oligomers of RNA from activated monomers, (Ferris and Ertem, 1993) a possible step in the origin of the RNA world (Ferris, 2005). Structural analysis of oligomers formed in the reaction of the activated monomer of 5'-AMP with that of 5'-CMP demonstrated that the oligomers formed were not produced by random synthesis but rather the sequences observed were directed by the montmorillonite catalyst (Miyakawa and Ferris, 2003). RNA oligomers containing up to 40 mers have been synthesized in reactions performed in water at 25 oC in the presence of montmorillonite (Huang and Ferris, 2003). Analysis of the structure elements in these oligomers from the 7 to 39 mers showed that they did not vary. Reaction of D, L-mixtures of the activated monomers of A and U resulted in the formation of greater amounts of the homochiral amounts of dimers and trimers of A than would be expected if there was no selectivity in the reaction. A limited number of the dimers and trimers of U were also formed but here the selectivity was for the formation of an excess of heterochiral products (Joshi et al., 2000). A postulate that explains why homochiral trimers of U are not formed and the significance of catalysis in prebiotic synthesis will be discussed. Ferris, J.P. (2005) Origins of life, molecular basis of. In R.A. Meyers, Ed. Encyclopedia of Molecular Cell Biology and Molecular Medicine, 10. Wiley-VCH Verlag, Weinheim, Germany. Ferris, J.P., and Ertem, G. (1993) Montmorillonite catalysis of RNA oligomer formation in aqueous solution. A model for the prebiotic formation of RNA. J. Am. Chem. Soc., 115, 12270-12275. Huang, W., and Ferris, J.P. (2003) Synthesis of 35-40 mers of RNA oligomers from unblocked monomers. A simple approach to the RNA world. Chem. Commun., 1458-1459. Joshi, P.C., Pitsch, S., and Ferris, J.P. (2000) Homochiral selection

  16. Unique Properties of the Rabbit Prion Protein Oligomer.

    PubMed

    Yu, Ziyao; Huang, Pei; Yu, Yuanhui; Zheng, Zhen; Huang, Zicheng; Guo, Chenyun; Lin, Donghai

    2016-01-01

    Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), are a group of fatal neurodegenerative disorders infecting both humans and animals. Recent works have demonstrated that the soluble prion protein oligomer (PrPO), the intermediate of the conformational transformation from the host-derived cellular form (PrPC) to the disease-associated Scrapie form (PrPSc), exerts the major neurotoxicity in vitro and in vivo. Rabbits show strong resistance to TSEs, the underlying mechanism is unclear to date. It is expected that the relative TSEs-resistance of rabbits is closely associated with the unique properties of rabbit prion protein oligomer which remain to be addressed in detail. In the present work, we prepared rabbit prion protein oligomer (recRaPrPO) and human prion protein oligomer (recHuPrPO) under varied conditions, analyzed the effects of pH, NaCl concentration and incubation temperature on the oligomerization, and compared the properties of recRaPrPO and recHuPrPO. We found that several factors facilitated the formation of prion protein oligomers, including low pH, high NaCl concentration, high incubation temperature and low conformational stability of monomeric prion protein. RecRaPrPO was formed more slowly than recHuPrPO at physiological-like conditions (< 57°C, < 150 mM NaCl). Furthermore, recRaPrPO possessed higher susceptibility to proteinase K and lower cytotoxicity in vitro than recHuPrPO. These unique properties of recRaPrPO might substantially contribute to the TSEs-resistance of rabbits. Our work sheds light on the oligomerization of prion proteins and is of benefit to mechanistic understanding of TSEs-resistance of rabbits. PMID:27529173

  17. Tetracycline prevents Aβ oligomer toxicity through an atypical supramolecular interaction.

    PubMed

    Airoldi, Cristina; Colombo, Laura; Manzoni, Claudia; Sironi, Erika; Natalello, Antonino; Doglia, Silvia Maria; Forloni, Gianluigi; Tagliavini, Fabrizio; Del Favero, Elena; Cantù, Laura; Nicotra, Francesco; Salmona, Mario

    2011-01-21

    The antibiotic tetracycline was reported to possess an anti-amyloidogenic activity on a variety of amyloidogenic proteins both in in vitro and in vivo models. To unveil the mechanism of action of tetracycline on Aβ1-40 and Aβ1-42 at both molecular and supramolecular levels, we carried out a series of experiments using NMR spectroscopy, FTIR spectroscopy, dynamic laser light-scattering (DLS) and atomic force microscopy (AFM). Firstly we showed that the co-incubation of Aβ1-42 oligomers with tetracycline hinders the toxicity towards N2a cell lines in a dose-dependent manner. Therefore, the nature of the interaction between the drug and Aβ oligomers was investigated. To carry out NMR and FTIR studies we have prepared Aβ peptide solutions containing assemblies ranging from monomers to large oligomers. Saturation transfer difference (STD) NMR experiments have shown that tetracycline did not interact with monomers at variance with oligomers. Noteworthy, in this latter case we observed that this interaction was very peculiar since the transfer of magnetization from Aβ oligomers to tetracycline involved all drug protons. In addition, intermolecular cross-peaks between tetracycline and Aβ were not observed in NOESY spectra, indicating the absence of a specific binding site and suggesting the occurrence of a supramolecular interaction. DLS and AFM studies supported this hypothesis since the co-dissolution of Aβ peptides and tetracycline triggered the immediate formation of new aggregates that improved the solubility of Aβ peptides, preventing in this way the progression of the amyloid cascade. Moreover, competitive NMR binding experiments showed for the first time that tetracycline competes with thioflavin T (ThT) in the binding to Aβ peptides. Our data shed light on a novel mechanism of anti-amyloidogenic activity displayed by tetracycline, governed by hydrophobic and charge multiparticle interactions. PMID:21063627

  18. Unique Properties of the Rabbit Prion Protein Oligomer

    PubMed Central

    Yu, Ziyao; Huang, Pei; Yu, Yuanhui; Zheng, Zhen; Huang, Zicheng; Guo, Chenyun; Lin, Donghai

    2016-01-01

    Prion diseases, also known as transmissible spongiform encephalopathies (TSEs), are a group of fatal neurodegenerative disorders infecting both humans and animals. Recent works have demonstrated that the soluble prion protein oligomer (PrPO), the intermediate of the conformational transformation from the host-derived cellular form (PrPC) to the disease-associated Scrapie form (PrPSc), exerts the major neurotoxicity in vitro and in vivo. Rabbits show strong resistance to TSEs, the underlying mechanism is unclear to date. It is expected that the relative TSEs-resistance of rabbits is closely associated with the unique properties of rabbit prion protein oligomer which remain to be addressed in detail. In the present work, we prepared rabbit prion protein oligomer (recRaPrPO) and human prion protein oligomer (recHuPrPO) under varied conditions, analyzed the effects of pH, NaCl concentration and incubation temperature on the oligomerization, and compared the properties of recRaPrPO and recHuPrPO. We found that several factors facilitated the formation of prion protein oligomers, including low pH, high NaCl concentration, high incubation temperature and low conformational stability of monomeric prion protein. RecRaPrPO was formed more slowly than recHuPrPO at physiological-like conditions (< 57°C, < 150 mM NaCl). Furthermore, recRaPrPO possessed higher susceptibility to proteinase K and lower cytotoxicity in vitro than recHuPrPO. These unique properties of recRaPrPO might substantially contribute to the TSEs-resistance of rabbits. Our work sheds light on the oligomerization of prion proteins and is of benefit to mechanistic understanding of TSEs-resistance of rabbits. PMID:27529173

  19. Self-assembly of 33-mer gliadin peptide oligomers.

    PubMed

    Herrera, M G; Benedini, L A; Lonez, C; Schilardi, P L; Hellweg, T; Ruysschaert, J-M; Dodero, V I

    2015-11-28

    The 33-mer gliadin peptide, LQLQPF(PQPQLPY)3PQPQPF, is a highly immunogenic peptide involved in celiac disease and probably in other immunopathologies associated with gliadin. Herein, dynamic light scattering measurements showed that 33-mer, in the micromolar concentration range, forms polydisperse nano- and micrometer range particles in aqueous media. This behaviour is reminiscent of classical association of colloids and we hypothesized that the 33-mer peptide self-assembles into micelles that could be the precursors of 33-mer oligomers in water. Deposition of 33-mer peptide aqueous solution on bare mica generated nano- and microstructures with different morphologies as revealed by atomic force microscopy. At 6 μM, the 33-mer is organised in isolated and clusters of spherical nanostructures. In the 60 to 250 μM concentration range, the spherical oligomers associated mainly in linear and annular arrangements and structures adopting a "sheet" type morphology appeared. At higher concentrations (610 μM), mainly filaments and plaques immersed in a background of nanospherical structures were detected. The occurrence of different morphologies of oligomers and finally the filaments suggests that the unique specific geometry of the 33-mer oligomers has a crucial role in the subsequent condensation and organization of their fractal structures into the final filaments. The self-assembly process on mica is described qualitatively and quantitatively by a fractal diffusion limited aggregation (DLA) behaviour with the fractal dimension in the range of 1.62 ± 0.02 to 1.73 ± 0.03. Secondary structure evaluation of the oligomers by Attenuated Total Reflection FTIR spectroscopy (ATR-FTIR) revealed the existence of a conformational equilibrium of self-assembled structures, from an extended conformation to a more folded parallel beta elongated structures. Altogether, these findings provide structural and morphological information about supramolecular organization of the 33-mer

  20. Sulphonated imidized graphene oxide (SIGO) based polymer electrolyte membrane for improved water retention, stability and proton conductivity

    NASA Astrophysics Data System (ADS)

    Pandey, Ravi P.; Shahi, Vinod K.

    2015-12-01

    Sulphonated imidized graphene oxide (SIGO) (graphene oxide (GO) tethered sulphonated polyimide) has been successfully synthesized by polycondensation reaction using dianhydride and sulphonated diamine. Polymer electrolyte membranes (PEMs) are prepared by using SIGO (different wt%) and sulphonated poly(imide) (SPI). Resultant SPI/SIGO composite PEMs exhibit improved stabilities (thermal, mechanical and oxidative) and good water-retention properties (high bound water content responsible for proton conduction at high temperature by internal self-humidification). Incorporation of covalent bonded SIGO into SPI matrix results hydrophobic-hydrophilic phase separation and facile architecture of proton conducting path. Well optimized sulphonated poly(imide)/sulphonated imidized graphene oxide (15 wt%) (SPI/SIGO-15) composite membrane shows 2.24 meq g-1 ion-exchange capacity (IEC); 11.38 × 10-2 S cm-1 proton conductivity; 5.12% bound water content; and 10.52 × 10-7 cm2 s-1 methanol permeability. Maximum power density for pristine SPI membrane (57.12 mW cm-2) improves to 78.53 mW cm-2 for SPI/SIGO-15 membrane, in single-cell direct methanol fuel cell (DMFC) test at 70 °C using 2 M methanol fuel. Under similar experimental conditions, Nafion 117 membrane exhibits 62.40 mW cm-2 maximum power density. Reported strategy for the preparation of PEMs, offers a useful protocol for grafting of functionalized inorganic materials with in organic polymer chain by imidization.

  1. Aryne [3 + 2] cycloaddition with N-sulfonylpyridinium imides and in situ generated N-sulfonylisoquinolinium imides: a potential route to pyrido[1,2-b]indazoles and indazolo[3,2-a]isoquinolines.

    PubMed

    Zhao, Jingjing; Li, Pan; Wu, Chunrui; Chen, Hongli; Ai, Wenying; Sun, Renhong; Ren, Hailong; Larock, Richard C; Shi, Feng

    2012-03-01

    The aryne [3 + 2] cycloaddition process with pyridinium imides breaks the aromaticity of the pyridine ring. By equipping the imide nitrogen with a sulfonyl group, the intermediate readily eliminates a sulfinate anion to restore the aromaticity, leading to the formation of pyrido[1,2-b]indazoles. The scope and limitation of this reaction are discussed. As an extension of this chemistry, N-tosylisoquinolinium imides, generated in situ from N'-(2-alkynylbenzylidene)-tosylhydrazides via an AgOTf-catalyzed 6-endo-dig electrophilic cyclization, readily undergo aryne [3 + 2] cycloaddition to afford indazolo[3,2-a]-isoquinolines in the same pot, offering a highly efficient route to these potential anticancer agents. PMID:22278679

  2. Quaternary structure defines a large class of amyloid-β oligomers neutralized by sequestration

    PubMed Central

    Liu, Peng; Reed, Miranda N.; Kotilinek, Linda A.; Grant, Marianne K.O.; Forster, Colleen L.; Qiang, Wei; Shapiro, Samantha L.; Reichl, John H.; Chiang, Angie C.A.; Jankowsky, Joanna L.; Wilmot, Carrie M.; Cleary, James P.; Zahs, Kathleen R.; Ashe, Karen H.

    2015-01-01

    Summary The accumulation of amyloid-β (Aβ) as amyloid fibrils and toxic oligomers is an important step in the development of Alzheimer's disease (AD). However, there are numerous potentially toxic oligomers and little is known about their neurological effects when generated in the living brain. Here, we show that Aβ oligomers can be assigned to one of at least two classes (Type 1 and Type 2) based on their temporal, spatial and structural relationships to amyloid fibrils. The Type 2 oligomers are related to amyloid fibrils and represent the majority of oligomers generated in vivo, but remain confined to the vicinity of amyloid plaques and do not impair cognition at levels relevant to AD. Type 1 oligomers are unrelated to amyloid fibrils and may have greater potential to cause global neural dysfunction in AD because they are dispersed. These results refine our understanding of the pathogenicity of Aβ oligomers in vivo. PMID:26051935

  3. Self-complementary quadruply hydrogen-bonded duplexes based on imide and urea units.

    PubMed

    Li, Xianghui; Fang, Yuyu; Deng, Pengchi; Hu, Jinchuan; Li, Tian; Feng, Wen; Yuan, Lihua

    2011-09-01

    The quadruply hydrogen-bonded duplexes based on an imide-urea structure preorganized by three-center hydrogen bonds were found to associate via bifurcated hydrogen bonds. (1)H NMR dilution experiments revealed the high stability of the homodimer in apolar solvent (K(dim) > 10(5) M(-1) in CDCl(3)) and enhancement of association ability due to electron-withdrawing substituent effects. The ready synthetic availability and adjustable association affinity via electronic effects may render these association units potentially applicable in constructing supramolecular architectures. PMID:21819056

  4. Poly(imide)/Organically-Modified Montmorillonite Nanocomposite as a Potential Membrane for Alkaline Fuel Cells

    PubMed Central

    Battirola, Liliane C.; Gasparotto, Luiz H. S.; Rodrigues-Filho, Ubirajara P.; Tremiliosi-Filho, Germano

    2012-01-01

    In this work we evaluated the potentiality of a poly(imide) (PI)/organically-modified montmorillonite (O-MMT) nanocomposite membrane for the use in alkaline fuel cells. Both X-ray diffraction and scanning electron microscopy revealed a good dispersion of O-MMT into the PI matrix and preservation of the O-MMT layered structure. When compared to the pure PI, the addition of O-MMT improved thermal stability and markedly increased the capability of absorbing electrolyte and ionic conductivity of the composite. The results show that the PI/O-MMT nanocomposite is a promising candidate for alkaline fuel cell applications. PMID:24958290

  5. Stabilization of different conformers of bis(trifluoromethanesulfonyl)imide anion in ammonium-based ionic liquids at low temperatures.

    PubMed

    Vitucci, F M; Trequattrini, F; Palumbo, O; Brubach, J-B; Roy, P; Navarra, M A; Panero, S; Paolone, A

    2014-09-25

    The infrared absorption spectra of two ionic liquids with bis(trifluoromethanesulfonyl)imide (TFSI) as an anion and ammonium with different alkyl chains as cations are reported as a function of temperature. Using the comparison with ab initio calculations of the infrared-active intramolecular vibrations, the experimental lines were ascribed to the various ions composing the ionic liquids. In the liquid state of the samples, both conformers of the TFSI ion are present. In the solid state, however, the two conformers survive in N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), while only cis-TFSI is retained in N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI). We suggest that the longer alkyl chains of the former compound stabilize the less stable conformer of TFSI by means of stronger interactions between anions and cations. PMID:25188394

  6. An electric nose based on arylenevinylene polymers and oligomers

    NASA Astrophysics Data System (ADS)

    de Wit, Michael

    An electronic nose is an instrument, which comprises an array of electronic chemical sensors with partial specificity and an appropriate pattern-recognition system, capable of recognising simple or complex odours. Our efforts are centred around the sensors part of the nose. In fact, we applied a number of polymeric and oligomeric members of the arylenevinylene group of molecules as the active layer for conductimetric sensors (chemiresistors). The electric resistance of the active layer changes when it is exposed to vapors. The response of the sensor on a vapour is defined as the fractional, percentual change of the resistance compared to that in clean air. We made the sensors by depositing the organic layers on a substrate containing pre-printed gold contacts. At first we tested poly(2,5-thienylene vinylene) (PTV). A synthetic method was employed in which a soluble methoxy-precursor polymer of PTV was isolated, which was then spin-coated onto the substrate, and after being converted thermally to PTV, subsequently doped by iodine. The values of the responses of the PTV sensors are comparable to those sensors based on other conducting polymers, but the (partial) selectivity for the vapors is different. The responses of the PTV sensor are linearly related to the concentration. Incomplete conversion of the precursor polymer to the final PTV leads to copolymers of methoxy-PTV and PTV itself varying inter alia in the degree of conjugation. Chemiresistors based on these new materials show an affinity to vapors differing from that of PTV. We discovered that the arylenevinylenes need not to be of polymeric nature for this application. In fact, the arylenevinylene oligomers perform better. The oligomers are easier to modify and to process than polymers. We tested 2,5-dimethoxy-1,4-bis(3,4,5-trimethoxystyrylbenzene) (OMT) in its pure form and in blends with polycarbonate. The responses of these oligomeric sensors are on the average five times higher than those of the

  7. Low Melt Viscosity Resins for Resin Transfer Molding

    NASA Technical Reports Server (NTRS)

    Harris, Frank W.

    2002-01-01

    In recent years, resin transfer molding (RTM) has become one of the methods of choice for high performance composites. Its cost effectiveness and ease of fabrication are major advantages of RTM. RTM process usually requires resins with very low melt viscosity (less than 10 Poise). The optimum RTM resins also need to display high thennal-oxidative stability, high glass transition temperature (T(sub g)), and good toughness. The traditional PMR-type polyimides (e.g. PMR-15) do not fit this requirement, because the viscosities are too high and the nadic endcap cures too fast. High T(sub g), low-melt viscosity resins are highly desirable for aerospace applications and NASA s Reusable Launch Vehicle (RLV) program. The objective of this work is to prepare low-melt viscosity polyimide resins for RTM or resin film infusion (RFI) processes. The approach involves the synthesis of phenylethynyl-terminated imide oligomers. These materials have been designed to minimize their melt viscosity so that they can be readily processed. During the cure, the oligomers undergo both chain extension and crosslinking via the thermal polymerization of the phenylethynyl groups. The Phenylethynyl endcap is preferred over the nadic group due to its high curing temperature, which provides broader processing windows. This work involved the synthesis and polymerization of oligomers containing zig-zag backbones and twisted biphenyl structures. Some A-B type precursors which possessed both nitro and anhydride functionality, or both nitro and amine functionality, were also synthesized in order to obtain the well defined oligomers. The resulting zig-zag structured oligomers were then end-capped with 4-phenylethynylphthalic anhydride (PEPA) for further cure. The properties of these novel imide oligomers are evaluated.

  8. A Comparative Ab Initio Study of the Primary Hydration and Proton Dissociation of Various Imide and Sulfonic Acid Ionomers

    SciTech Connect

    Clark II, Jeffrey K.; Paddison, Stephen J.; Eikerling, Michael; Dupuis, Michel; Zawodzinski, Jr., Thomas A.

    2012-03-29

    We compare the role of neighboring group substitutions on proton dissociation of hydrated acidic moieties suitable for proton exchange membranes through electronic structure calculations. Three pairs of ionomers containing similar electron withdrawing groups within the pair were chosen for the study: two fully fluorinated sulfonyl imides (CF3SO2NHSO2CF3 and CF3CF2SO2NHSO2CF3), two partially fluorinated sulfonyl imides (CH3SO2NHSO2CF3 and C6H5SO2NHSO2CF2CF3), and two aromatic sulfonic acid based material s (CH3C6H4SO3H and CH3 OC6 - H3OCH3C6H4SO3H). Fully optimized counterpoise (CP) corrected geometries were obtained for each ionomer fragment with the inclusion of water molecules at the B3LYP/6-311G** level of density functional theory. Spontaneous proton dissociation was observed upon addition of three water molecules in each system, and the transition to a solvent-separated ion pair occurred when four water molecules were introduced. No considerable quantitative or qualitative differences in proton dissociation, hydrogen bond networks formed, or water binding energies were found between systems containing similar electron withdrawing groups. Each of the sulfonyl imide ionomers exhibited qualitatively similar results regarding proton dissociation and separation. The fully fluorinated sulfonyl imides, however, showed a greater propensity to exist in dissociated and ion-pair separated states at low degrees of hydration than the partially fluorinated sulfonyl imides. This effect is due to the additional electron withdrawing groups providing charge stabilization as the dissociated proton migrates away from the imide anion.

  9. Integrated real time studies to track all physical and chemical changes in polyimide film processing from casting to imidization

    NASA Astrophysics Data System (ADS)

    Unsal, Emre

    Physical and chemical changes during the complex multi-step thermal imidization reaction were investigated including all processing steps (solution casting, drying and imidization), using newly developed highly instrumented measurement systems. These instruments allowed us to observe the dynamic relationship between the bound solvent evaporation that causes relaxation and chain orientation during the imidization. Drying and imidization of PMDA-ODA solutions in NMP were investigated by a novel custom designed measurement system that tracks real time weight, thickness, surface temperature, in-plane and out-of-plane birefringence. At low temperature drying stage (T < 120°C), the weight and thickness reductions occurred rapidly as a result of solvent evaporation. All the parameters started leveling off while the out of plane birefringence steadily increased and reached a plateau at longer drying times. When the temperature was increased for imidization reaction (T=200°C), additional weight loss accompanied by temporary reduction of birefringence was observed due to evaporation of bound solvent as solvent molecules decomplexed from the polymer chains and plasticized the film. During the latter stage, out-of-plane birefringence rose rapidly as the polymer chains increasingly became oriented with their chain axes were preferentially oriented in the film plane. Throughout the whole process the in-plane birefringence remained zero. For the first time, these real time measurements allowed us to quantitatively show the dynamics between chain relaxation due to evaporation of the decomplexed solvent molecules, and orientation development due to decreased chain mobility caused by imidization reaction and increasing Tg for the PMDA-ODA/NMP solutions. In addition, the dynamics of this interplay was investigated by varying the processing conditions: initial casting thickness and drying temperature. Chemical conversion, bound solvent and chain orientation that take place during

  10. Synthesis of long Prebiotic Oligomers on Mineral Surfaces

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; Hill, Aubrey R., Jr.; Liu, Rihe; Orgel, Leslie E.

    1996-01-01

    Most theories of the origin of biological organization assume that polymers with lengths in the range of 30-60 monomers are needed to make a genetic system viable. But it has not proved possible to synthesize plausibly prebiotic polymers this long by condensation in aqueous solution, because hydrolysis competes with polymerization. The potential of mineral surfaces to facilitate prebiotic polymerization was pointed out long ago. Here we describe a system that models prebiotic polymerization by the oligomerization of activated monomers -both nucleotides and amino acids. We find that whereas the reactions in solution produce only short oligomers (the longest typically being a 10-mer), the presence of mineral surfaces (montmorillonite for nucleotides, illite and hydroxylapatite for amino adds) induces the formation of oligomers up to 55 monomers long. These are formed by successive "feedings" with the monomers; polymerization takes place on the mineral surfaces in a manner akin to solid-phase synthesis of biopolymers.

  11. Phase transition in conjugated oligomers suspended in chloroform

    NASA Astrophysics Data System (ADS)

    Dwivedi, Shikha; Kumar, Anupam; Yadav, S. N. S.; Mishra, Pankaj

    2015-08-01

    Density functional theory (DFT) has been used to investigate the isotropic-nematic (I-N) phase transition in a system of high aspect ratio conjugated oligomers suspended in chloroform. The interaction between the oligomers is modeled using Gay-Berne potential in which effect of solvent is implicit. Percus-Yevick integral equation theory has been used to evaluate the pair correlation functions of the fluid phase at several temperatures and densities. These pair correlation function has been used in the DFT to evaluate the I-N freezing parameters. Highly oriented nematic is found to stabilize at low density. The results obtained are in qualitative agreement with the simulation and are verifiable.

  12. Pigment oligomers as natural and artificial photosynthetic antennas

    SciTech Connect

    Blankenship, R.E.

    1996-12-31

    Green photosynthetic bacteria contain antenna complexes known as chlorosomes. These complexes are appressed to the cytoplasmic side of the inner cell membrane and function to absorb light and transfer the energy to the photochemical reaction center, where photochemical energy storage takes place. Chlorosomes differ from all other known photosynthetic antenna complexes in that the geometrical arrangement of pigments is determined primarily by pigment-pigment interactions instead of pigment-protein interactions. The bacteriochlorophyll c, d or e pigments found in chlorosomes form large oligomers with characteristic spectral properties significantly perturbed from those exhibited by monomeric pigments. Because of their close spatial interaction, the pigments are thought to be strongly coupled electronically, and many of the optical properties result from exciton interactions. This presentation will summarize existing knowledge on the chemical composition and properties of chlorosomes, the evidence for the oligomeric nature of chlorosome pigment organization and proposed structures for the oligomers, and the kinetics and mechanisms of energy transfer in chlorosomes.

  13. Ethynyl-terminated ester oligomers and polymers therefrom

    NASA Technical Reports Server (NTRS)

    Hergenrother, Paul M. (Inventor); Havens, Stephen J. (Inventor)

    1986-01-01

    A class of ethynyl terminated oligomers and the process for preparing the same are disclosed. Upon the application of heat, with or without a catalyst, the ethynyl groups react to provide crosslinking and chain extension to increase the polymer use temperature and improve the polymer solvent resistance. These polyesters are potentially useful in packaging, magnetic tapes, capacitors, industrial belting, protective coatings, structural adhesives and composite matrices.

  14. Circular dichroism from Fano resonances in planar chiral oligomers

    NASA Astrophysics Data System (ADS)

    Hopkins, Ben; Poddubny, Alexander N.; Miroshnichenko, Andrey E.; Kivshar, Yuri S.

    2015-05-01

    Here we present a general approach for describing the physics of Fano resonances in nanoparticle oligomers. It is shown that the interference of nonorthogonal collective eigenmodes is a sufficient condition to produce Fano resonances. We then show that such nonorthogonality between eigenmodes also permits the existence of a new form circular dichroism in the absorption and scattering cross-sections, even when circular dichroism is forbidden in the extinction cross-section.

  15. Porous Cross-Linked Polyimide Networks

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B. (Inventor); Guo, Haiquan (Inventor)

    2015-01-01

    Porous cross-linked polyimide networks are provided. The networks comprise an anhydride end-capped polyamic acid oligomer. The oligomer (i) comprises a repeating unit of a dianhydride and a diamine and terminal anhydride groups, (ii) has an average degree of polymerization of 10 to 50, (iii) has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups, and (iv) has been chemically imidized to yield the porous cross-linked polyimide network. Also provided are porous cross-linked polyimide aerogels comprising a cross-linked and imidized anhydride end-capped polyamic acid oligomer, wherein the oligomer comprises a repeating unit of a dianhydride and a diamine, and the aerogel has a density of 0.10 to 0.333 g/cm.sup.3 and a Young's modulus of 1.7 to 102 MPa. Also provided are thin films comprising aerogels, and methods of making porous cross-linked polyimide networks.

  16. Proton vibrational dynamics in lithium imide investigated through incoherent inelastic and Compton neutron scattering.

    PubMed

    Pietropaolo, A; Colognesi, D; Catti, M; Nale, A-C; Adams, M A; Ramirez-Cuesta, A J; Mayers, J

    2012-11-28

    In the present study we report neutron spectroscopic measurements on polycrystalline lithium imide, namely, incoherent inelastic neutron scattering at 20 K, and neutron Compton scattering from 10 K up to room temperature. From the former technique the H-projected density of phonon states up to 100 meV is derived, while the latter works out the spherically averaged single-particle (i.e., H, Li, and N) momentum distributions and, from this, the mean kinetic energies. Only for H at the lowest investigated temperature, non-gaussian components of its momentum distribution are detected. However, these components do not seem directly connected to the system anharmonicity, being fully compatible with the simple N-H bond anisotropy. Neutron data are also complemented by ab initio lattice dynamics simulations, both harmonic and, at room temperature, carried out in the framework of the so-called "quantum colored noise thermostat" method. The single-particle mean kinetic energies in lithium imide as a function of temperature show a quite peculiar behavior at the moment not reproduced by ab initio lattice dynamics methods, at least as far as H and Li are concerned. As matter of fact, neither their low temperature values nor their temperature trends can be precisely explained in terms of standard phonon calculations. PMID:23206005

  17. Role of native defects in the Li amide/Li imide hydrogen storage reaction

    NASA Astrophysics Data System (ADS)

    Hoang, Khang; van de Walle, Chris G.

    2010-03-01

    Reversible reaction involving Li amide/Li imide (LiNH2 + LiH <-> Li2NH + H2) has been shown to be a potential mechanism for hydrogen storage [1]. Recent synchrotron x-ray diffraction refinement suggests that the transformation between LiNH2 and Li2NH is a bulk reaction that occurs through non-stoichiometric processes [2]. To build a deeper understanding of these processes, we have carried out first-principles studies based on density functional theory of native point defects and defect complexes in LiNH2 and Li2NH. Among the native defects, we find that positively and negatively charged Li and H interstitials and vacancies have the lowest formation energies. Some of the Li-related defects are found to be very mobile, and should be the dominant migratory species in the systems. Our first-principles results suggest specific mechanisms for the role of native defects in the Li amide/Li imide reaction. [1] P. Chen et al., Nature 420, 302 (2002). [2] W. I. F. David et al., J. Am. Chem. Soc. 129, 1594 (2007).

  18. Ab-initio Investigations of Li and Mg Amide-Imide Systems for Hydrogen Storage

    NASA Astrophysics Data System (ADS)

    Tsumuraya, Takao; Shishidou, Tatsuya; Oguchi, Tamio

    2007-03-01

    Reversible hydrogen storage in light-element materials has been recognized as one of the most practical approaches for on-board application. Lithium nitride Li3N can reversibly store large amount of hydrogen in the two-step reversible reaction composed of lithium amide LiNH2 and imide Li2NH[1]. Quite recently, in an effort to reach further performance, several types of magnesium substitutions in Li-N-H system have been investigated. For instance, Leng et al. have examined a composite material made by ball milling of 3:8 molar mixture of magnesium amide Mg(NH2)2 and lithium hydride LiH[2]. The hydrogenating and dehydrogenating reaction mechanism and fundamental properties of these hydrides still remain as a matter to be investigated. In particular, crystal structures of some metel imides such as Li2NH, MgNH and Li2Mg(NH)2 are not fully determined yet. In this paper, we discuss structural stability and heats of formation of these hydrides from first-principles calculations based on the all-electron FLAPW method. [1] P. Chen Z. Xiong, J. Luo, J. Lin and K.L. Tan, Nature 420, 302 (2002). [2] H. Y. Leng, T. Ichikawa, S. Hino, N. Hanada, S. Isobe and H. Fujii, J. Phys. Chem. B 108, 8763 (2004).

  19. Chlorins with six-membered imide ring as prospective sensitizers for cancer PDT

    NASA Astrophysics Data System (ADS)

    Mironov, Andrei F.; Lebedeva, Victoria S.; Yakubovskaya, Raisa I.; Kazachkina, Natalia I.; Fomina, Galina I.

    1999-02-01

    A series of promising PDT sensitizers having intensive absorption maximum at 710 - 750 nm has been synthesized from the readily available purpurin 18. Modification of an anhydride ring is purpurin 18 afforded two series of cyclic imides. The first group comprises the N-substituted derivatives containing residues of aliphatic alcohols (C2- C4) and carboxylic acids (C1, C5). The second series is represented by the cyclic N-hydroxyimides containing the -N-OR group, where R is either alkyl or acyl residue. Cyclic imides possess increased resistance to alkali treatment, which enhances their water solubility. They absorb in the region of 706 - 718 nm. Further development of the spectral characteristics was achieved by the oxidation of a 3- vinyl group into the formyl one. The obtained compounds have the absorption maximum in the region of 750 nm, which makes them comparable to those of bacteriochlorophyll derivatives. The presence of a spacer group in the molecule of compounds synthesized affords their attachment to the carriers for the directed transport of a sensitizer into tumor.

  20. Combinations of fluorinated solvents with imide salts or methide salts for electrolytes

    SciTech Connect

    Tikhonov, Konstantin; Yip, Ka Ki; Lin, Tzu-Yuan; Lei, Norman; Guerrero-Zavala, Guillermo; Kwong, Kristie W

    2015-11-10

    Provided are electrochemical cells and electrolytes used to build such cells. The electrolytes include imide salts and/or methide salts as well as fluorinated solvents capable of maintaining single phase solutions at between about -30.degree. C. to about 80.degree. C. The fluorinated solvents, such as fluorinated carbonates, fluorinated esters, and fluorinated esters, are less flammable than their non-fluorinated counterparts and improve safety characteristics of cells containing these solvents. The amount of fluorinated solvents in electrolytes may be between about 30% and 80% by weight not accounting weight of the salts. Linear and cyclic imide salts, such as LiN(SO.sub.2CF.sub.2CF.sub.3).sub.2, and LiN(SO.sub.2CF.sub.3).sub.2, as well as methide salts, such as LiC(SO.sub.2CF.sub.3).sub.3 and LiC(SO.sub.2CF.sub.2CF.sub.3).sub.3, may be used in these electrolytes. Fluorinated alkyl groups enhance solubility of these salts in the fluorinated solvents. In some embodiments, the electrolyte may also include a flame retardant, such as a phosphazene, and/or one or more ionic liquids.

  1. Aβ42 oligomers selectively disrupt neuronal calcium release.

    PubMed

    Lazzari, Cristian; Kipanyula, Maulilio J; Agostini, Mario; Pozzan, Tullio; Fasolato, Cristina

    2015-02-01

    Accumulation of amyloid-β (Aβ) peptides correlates with aging and progression of Alzheimer's disease (AD). Aβ peptides, which cause early synaptic dysfunctions, spine loss, and memory deficits, also disturb intracellular Ca(2+) homeostasis. By cytosolic and endoplasmic reticulum Ca(2+) measurements, we here define the short-term effects of synthetic Aβ42 on neuronal Ca(2+) dynamics. When applied acutely at submicromolar concentration, as either oligomers or monomers, Aβ42 did not cause Ca(2+) release or Ca(2+) influx. Similarly, 1-hour treatment with Aβ42 modified neither the resting cytosolic Ca(2+) level nor the long-lasting Ca(2+) influx caused by KCl-induced depolarization. In contrast, Aβ42 oligomers, but not monomers, significantly altered Ca(2+) release from stores with opposite effects on inositol 1,4,5-trisphosphate (IP3)- and caffeine-induced Ca(2+) mobilization without alteration of the total store Ca(2+) content. Ca(2+) dysregulation by Aβ42 oligomers involves metabotropic glutamate receptor 5 and requires network activity and the intact exo-endocytotic machinery, being prevented by tetrodotoxin and tetanus toxin. These findings support the idea that Ca(2+) store dysfunction is directly involved in Aβ42 neurotoxicity and represents a potential therapeutic target in AD-like dementia. PMID:25453559

  2. In Vitro and In Vivo Neurotoxicity of Prion Protein Oligomers

    PubMed Central

    Simoneau, Steve; Rezaei, Human; Salès, Nicole; Kaiser-Schulz, Gunnar; Lefebvre-Roque, Maxime; Vidal, Catherine; Fournier, Jean-Guy; Comte, Julien; Wopfner, Franziska; Grosclaude, Jeanne; Schätzl, Hermann; Lasmézas, Corinne Ida

    2007-01-01

    The mechanisms underlying prion-linked neurodegeneration remain to be elucidated, despite several recent advances in this field. Herein, we show that soluble, low molecular weight oligomers of the full-length prion protein (PrP), which possess characteristics of PrP to PrPsc conversion intermediates such as partial protease resistance, are neurotoxic in vitro on primary cultures of neurons and in vivo after subcortical stereotaxic injection. Monomeric PrP was not toxic. Insoluble, fibrillar forms of PrP exhibited no toxicity in vitro and were less toxic than their oligomeric counterparts in vivo. The toxicity was independent of PrP expression in the neurons both in vitro and in vivo for the PrP oligomers and in vivo for the PrP fibrils. Rescue experiments with antibodies showed that the exposure of the hydrophobic stretch of PrP at the oligomeric surface was necessary for toxicity. This study identifies toxic PrP species in vivo. It shows that PrP-induced neurodegeneration shares common mechanisms with other brain amyloidoses like Alzheimer disease and opens new avenues for neuroprotective intervention strategies of prion diseases targeting PrP oligomers. PMID:17784787

  3. The Viscoelastic Behavior of Polymer/Oligomer Blends

    NASA Astrophysics Data System (ADS)

    Zheng, Wei; McKenna, Gregory; Simon, Sindee

    2009-03-01

    The dynamics in athermal blends of poly(α-methyl styrene) (PaMS) and its short chain oligomer are investigated using rheometry and differential scanning calorimetry (DSC). Master curves for the dynamic shear responses, G' and G", are successfully constructed for both the pure materials and the blends, indicating the validity of the time-temperature superposition principle. The temperature dependence of the shift factor follows the WLF (Williams-Landel-Ferry) behavior over the temperature range studied, and for the blends, the dependence is dominated by the high mobility oligomer. The discrete relaxation spectra of the materials are calculated and are found to be broader for the blends than for the pure materials. A similar domination of the dynamics by the oligomer is observed in DSC enthalpy recovery studies and in the broadened glass transition from DSC. The ability to predict the dynamic responses of the blends from the responses of the neat materials is examined, and whether this prediction needs to incorporate the self-concentration idea as described in Colmenero's model will be discussed.

  4. Oligomers, organosulfates, and nitroxy organosulfates identified in rainwater

    NASA Astrophysics Data System (ADS)

    Altieri, K. E.; Turpin, B. J.; Seitzinger, S. P.

    2008-12-01

    Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50 percent of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We document the presence of 552 unique compounds in the rainwater over a mass range of 50-500 Da, in four compound classes (i.e., CHO, CHOS, CHON, and CHONS). The presence of oligomers, organosulfates, nitroxy organosulfates, organic acids, and linear alkylbenzene sulfonates is reported. Some compounds detected have distinct primary sources; however, the composition of the bulk of this material suggests it is formed in the atmosphere and composed of known contributors to secondary organic aerosol. For example, eight oligomer series known to form through aqueous photooxidation of methylglyoxal and organosulfate compounds known to form from 4 precursors in smog chamber experiments were identified in the rainwater samples. The oligomers, organosulfates, and nitroxy organosulfates detected in the rainwater could all contribute to the HULIS fraction of atmospheric organic matter.

  5. Synthesis of novel polyfluorinated acrylic monomers and oligomers

    SciTech Connect

    Antonucci, J.M.; Stansbury, J.W.

    1993-12-31

    An unhindered tertiary amine catalyzed reaction of monofunctional and difunctional hydrocarbon acrylates with paraformaldehyde under neat conditions yields unique difunctional acrylic monomers and oligomers, respectively. These multifunctional vinyl products have a predominantly 1,6-diene structure which favors cyclopolymerization. This reaction has been extended to the synthesis of similar polyfluorinated aliphatic monomers arrangements are determined by the nature of their fluoroester groups, e.g.-CF{sub 2}CH{sub 2}O{sub 2}C- favors a 1,4-diene rather than a 1,6-diene structure. In the present study the scope of this novel formaldehyde/acrylate insertion condensation reaction was further extended to include the synthesis of polyfluorinated aryl difunctional monomers and oligomers, e.g. from 2,3,4,5,6-pentafluorobenzyl acrylate and hexafluorobisphenol A diacrylate. The former did not require DMSO and yielded 1,6-, 1,8- and 1,10-dienes whereas the latter required DMSO and yielded oligomers mainly with 1,4-diene linkages.

  6. Size-dependent neurotoxicity of β-amyloid oligomers

    PubMed Central

    Cizas, Paulius; Budvytyte, Rima; Morkuniene, Ramune; Moldovan, Radu; Broccio, Matteo; Lösche, Mathias; Niaura, Gediminas; Valincius, Gintaras; Borutaite, Vilmante

    2010-01-01

    The link between the size of soluble amyloid β (Aβ) oligomers and their toxicity to rat cerebellar granule cells (CGC) was investigated. Variation in conditions during in vitro oligomerization of Aβ1-42 resulted in peptide assemblies with different particle size as measured by atomic force microscopy and confirmed by the dynamic light scattering and fluorescence correlation spectroscopy. Small oligomers of Aβ1-42 with a mean particle z-height of 1-2 nm exhibited propensity to bind to the phospholipid vesicles and they were the most toxic species that induced rapid neuronal necrosis at submicromolar concentrations whereas the bigger aggregates (z-height above 4-5 nm) did not bind vesicles and did not cause detectable neuronal death. Similar neurotoxic pattern was also observed in primary cultures of cortex neurons whereas Aβ1–42 oligomers, monomers and fibrils were non-toxic to glial cells in CGC cultures or macrophage J774 cells. However, both oligomeric forms of Aβ1-42 induced reduction of neuronal cell densities in the CGC cultures. PMID:20153288

  7. Radiative decay of excitons in model aggregates of {pi}-conjugated oligomers

    SciTech Connect

    Manas, E.S.; Spano, F.C.

    1998-07-01

    Spontaneous emission from exciton states in an aggregate of {pi}-conjugated oligomers is studied theoretically. Each oligomer is taken as a ring of N carbon atoms and is treated using a PPP Hamiltonian. Coulombic interactions between rings are treated to first order. The radiative decay rate {gamma} from an exciton state in an aggregate of M aligned oligomers is superradiant, being M times faster than the decay rate of an isolated oligomer exciton. Inter-oligomer interactions have little effect on the exciton size and energy when the oligomer size N is large compared to the interoligomer spacing. However, when N is small, both the exciton size and energy are strongly affected by these interactions, leading to a markedly different N dependence for {gamma}.

  8. Soluble state high resolution atomic force microscopy study of Alzheimer’s β-amyloid oligomers

    PubMed Central

    Shekhawat, Gajendra S.; Lambert, Mary P.; Sharma, Saurabh; Velasco, Pauline T.; Viola, Kirsten L.; Klein, William L.; Dravid, Vinayak P.

    2009-01-01

    We report here the direct observation of high resolution structures of assemblies of Alzheimer β-amyloid oligomers and monomers using liquid atomic force microscopy (AFM). Visualization of nanoscale features of Aβ oligomers (also known as ADDLs) was carried out in tapping mode AFM in F12 solution. Our results indicate that ADDL preparations exist in solution primarily as a mixture of monomeric peptides and higher molecular mass oligomers. Our study clearly reveals that the size and shape of these oligomer aggregates exhibit a pronounced dependence on concentration. These studies show that wet AFM enables direct assessment of oligomers in physiological fluids and suggests that this method may be developed to visualize Aβ oligomers from human fluids. PMID:19997583

  9. Soluble state high resolution atomic force microscopy study of Alzheimer's β-amyloid oligomers

    NASA Astrophysics Data System (ADS)

    Shekhawat, Gajendra S.; Lambert, Mary P.; Sharma, Saurabh; Velasco, Pauline T.; Viola, Kirsten L.; Klein, William L.; Dravid, Vinayak P.

    2009-11-01

    We report here the direct observation of high resolution structures of assemblies of Alzheimer β-amyloid oligomers and monomers using liquid atomic force microscopy (AFM). Visualization of nanoscale features of Aβ oligomers (also known as ADDLs) was carried out in tapping mode AFM in F12 solution. Our results indicate that ADDL preparations exist in solution primarily as a mixture of monomeric peptides and higher molecular mass oligomers. Our study clearly reveals that the size and shape of these oligomer aggregates exhibit a pronounced dependence on concentration. These studies show that wet AFM enables direct assessment of oligomers in physiological fluids and suggests that this method may be developed to visualize Aβ oligomers from human fluids.

  10. Intrinsic versus imposed curvature in cyclical oligomers: the portal protein of bacteriophage SPP1.

    PubMed Central

    van Heel, M; Orlova, E V; Dube, P; Tavares, P

    1996-01-01

    Large cyclical oligomers may be formed by (curvi-) linear polymerization of monomers until the n(th) monomer locks in with the first member of the chain. The subunits in incomplete structures exhibit a natural curvature with respect to each other which can be perturbed when the oligomer closes cyclically. Using cryo-electron microscopy and multivariate statistical image processing we report herein a direct structural observation of this effect. A sub-population (approximately 15%) of incomplete oligomers was found within a sample of SPP1 bacteriophage portal proteins embedded in vitreous ice. Whereas the curvature between adjacent subunits of the closed circular 13-fold symmetric oligomer is 27.7 degrees, in these incomplete oligomers the angle is only 25.8 degrees, a value which almost allows for a 14-subunit cyclical arrangement. A simple model for the association of large cyclical oligomers is suggested by our data. Images PMID:8890151

  11. Apoptosis induced by islet amyloid polypeptide soluble oligomers is neutralized by diabetes-associated specific antibodies

    PubMed Central

    Bram, Yaron; Frydman-Marom, Anat; Yanai, Inbal; Gilead, Sharon; Shaltiel-Karyo, Ronit; Amdursky, Nadav; Gazit, Ehud

    2014-01-01

    Soluble oligomeric assemblies of amyloidal proteins appear to act as major pathological agents in several degenerative disorders. Isolation and characterization of these oligomers is a pivotal step towards determination of their pathological relevance. Here we describe the isolation of Type 2 diabetes-associated islet amyloid polypeptide soluble cytotoxic oligomers; these oligomers induced apoptosis in cultured pancreatic cells, permeated model lipid vesicles and interacted with cell membranes following complete internalization. Moreover, antibodies which specifically recognized these assemblies, but not monomers or amyloid fibrils, were exclusively identified in diabetic patients and were shown to neutralize the apoptotic effect induced by these oligomers. Our findings support the notion that human IAPP peptide can form highly toxic oligomers. The presence of antibodies identified in the serum of diabetic patients confirms the pathological relevance of the oligomers. In addition, the newly identified structural epitopes may also provide new mechanistic insights and a molecular target for future therapy. PMID:24589570

  12. Pyridine-containing m-phenylene ethynylene oligomers having tunable basicities.

    PubMed

    Heemstra, Jennifer M; Moore, Jeffrey S

    2004-03-01

    Incorporation of a pyridine monomer into the backbone of a m-phenylene ethynylene oligomer allows functionalization of the interior binding cavity of the folded oligomer. The basicity of the inwardly directed pyridine moiety was modulated by changing the substituents on the pyridine ring and through oligomer folding, granting access to a pK(a) range of 5-14 in acetonitrile. [reaction: see text] PMID:14986943

  13. Case study on the evolution of hetero-oligomer interfaces based on the differences in paralogous proteins

    PubMed Central

    Aoto, Saki; Yura, Kei

    2015-01-01

    We addressed the evolutionary trace of hetero-oligomer interfaces by comparing the structures of paralogous proteins; one of them is a monomer or homo-oligomer and the other is a hetero-oligomer. We found different trends in amino acid conservation pattern and hydrophobicity between homo-oligomer and hetero-oligomer. The degree of amino acid conservation in the interface of homo-oligomer has no obvious difference from that in the surface, whereas the degree of conservation is much higher in the interface of hetero-oligomer. The interface of homo-oligomer has a few very conserved residue positions, whereas the residue conservation in the interface of hetero-oligomer tends to be higher. In addition, the interface of hetero-oligomer has a tendency of being more hydrophobic compared with the one in homo-oligomer. We conjecture that these differences are related to the inherent symmetry in homo-oligomers that cannot exist in hetero-oligomers. Paucity of the structural data precludes statistical tests of these tendencies, yet the trend can be applied to the prediction of the interface of hetero-oligomer. We obtained putative interfaces of the subunits in CPSF (cleavage and polyadenylation specificity factor), one of the human pre-mRNA 3′-processing complexes. The locations of predicted interface residues were consistent with the known experimental data. PMID:27493859

  14. Solvation of sodium chloride in the 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid: a molecular dynamics study.

    PubMed

    Sieffert, Nicolas; Wipff, Georges

    2007-06-28

    We report molecular dynamics studies on the solvation of sodium chloride in the 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid ([BMI][Tf2N] IL). We first consider the potential of mean force for dissociating a single Na+Cl- ion pair, showing that the latter prefers to be undissociated rather than dissociated (by ca. 9 kcal/mol), with a free energy barrier of ca. 5 kcal/mol (at d approximately 5.2 A) for the association process. The preference for Na+Cl- association is also observed from a 100 ns molecular dynamics simulation of a concentrated solution, where the Na+Cl- ions tend to form oligomers and microcrystals in the IL. Conversely, the simulation of Na13Cl14- and Na14Cl13+ cubic microcrystals (with, respectively, Cl- and Na+ at the vertices) does not lead to dissolution in the IL. Among these, Na14Cl13+ is found to be better solvated than Na13Cl14-, mainly due to the stronger Na+...Tf2N- interactions as compared to the Cl-...BMI+ interactions at the vertices of the cube. We finally consider the solid/liquid interface between the 100 face of NaCl and the IL, revealing that, in spite of its polar nature, the crystal surface is solvated by the less polar IL components (CF3(Tf2N) and butyl(BMI) groups) rather than by the polar ones (O(Tf2N) and imidazolium(BMI) ring). Specific ordering at the interface is described for both Tf2N- anions and BMI+ cations. In the first IL layer, the ions are rather parallel to the surface, whereas in the second "layer" they are more perpendicular. A similar IL structure is found at the surface of the all-neutral Na0Cl0 solid analogue, confirming that the solvation of the crystal is rather "apolar", due to the mismatch between the IL and the crystal ions. Several comparisons with water, methanol, or different BMI+-based ILs as solvents are presented, allowing us to better understand the specificity of the ionic liquid-NaCl interactions. PMID:17550283

  15. A chromatographic estimate of the degree of surface heterogeneity of reversed-phase liquid chromatography packing materials II-Endcapped monomeric C18-bonded stationary phase

    SciTech Connect

    Gritti, Fabrice; Guiochon, Georges A

    2006-01-01

    In a previous report, the heterogeneity of a non-endcapped C{sub 30}-bonded stationary phase was investigated, based on the results of the measurements of the adsorption isotherms of two neutral compounds (phenol and caffeine) and two ionizable compounds (sodium naphthalene sulfonate and propranololium chloride) by frontal analysis (FA). The same method is applied here for the characterization of the surface heterogeneity of two new brands of endcapped C{sub 18}-bonded stationary phases (Gemini and Sunfire). The adsorption isotherms of the same four chemicals were measured by FA and the results confirmed by the independent calculation of the adsorption energy distribution (AED), using the expectation-maximization (EM) method. The effect of the length of the bonded alkyl chain was investigated. Shorter alkyl-bonded-chains (C{sub 18} versus C{sub 30}) and the end-capping of the silica surface contribute to decrease the surface heterogeneity under the same experimental conditions (30% methanol, 25 mM NaCl). The AEDs of phenol and caffeine are bimodal with the C{sub 18}-bonded columns while they are trimodal and quadrimodal, respectively, with a non-endcapped C{sub 30}-bonded column. The 'supersites' (adsorption energy >20 kJ/mol) found on the C{sub 30}-Prontosil column and attributed to a cation exchange mechanism completely disappear on the C{sub 18}-Gemini and C{sub 18}-Sunfire, probably because the end-capping of the silica surface eliminates most if not all the ionic interactions.

  16. Quantitative analysis of co-oligomer formation by amyloid-beta peptide isoforms

    NASA Astrophysics Data System (ADS)

    Iljina, Marija; Garcia, Gonzalo A.; Dear, Alexander J.; Flint, Jennie; Narayan, Priyanka; Michaels, Thomas C. T.; Dobson, Christopher M.; Frenkel, Daan; Knowles, Tuomas P. J.; Klenerman, David

    2016-06-01

    Multiple isoforms of aggregation-prone proteins are present under physiological conditions and have the propensity to assemble into co-oligomers with different properties from self-oligomers, but this process has not been quantitatively studied to date. We have investigated the amyloid-β (Aβ) peptide, associated with Alzheimer’s disease, and the aggregation of its two major isoforms, Aβ40 and Aβ42, using a statistical mechanical modelling approach in combination with in vitro single-molecule fluorescence measurements. We find that at low concentrations of Aβ, corresponding to its physiological abundance, there is little free energy penalty in forming co-oligomers, suggesting that the formation of both self-oligomers and co-oligomers is possible under these conditions. Our model is used to predict the oligomer concentration and size at physiological concentrations of Aβ and suggests the mechanisms by which the ratio of Aβ42 to Aβ40 can affect cell toxicity. An increased ratio of Aβ42 to Aβ40 raises the fraction of oligomers containing Aβ42, which can increase the hydrophobicity of the oligomers and thus promote deleterious binding to the cell membrane and increase neuronal damage. Our results suggest that co-oligomers are a common form of aggregate when Aβ isoforms are present in solution and may potentially play a significant role in Alzheimer’s disease.

  17. Quantitative analysis of co-oligomer formation by amyloid-beta peptide isoforms

    PubMed Central

    Iljina, Marija; Garcia, Gonzalo A.; Dear, Alexander J.; Flint, Jennie; Narayan, Priyanka; Michaels, Thomas C. T.; Dobson, Christopher M.; Frenkel, Daan; Knowles, Tuomas P. J.; Klenerman, David

    2016-01-01

    Multiple isoforms of aggregation-prone proteins are present under physiological conditions and have the propensity to assemble into co-oligomers with different properties from self-oligomers, but this process has not been quantitatively studied to date. We have investigated the amyloid-β (Aβ) peptide, associated with Alzheimer’s disease, and the aggregation of its two major isoforms, Aβ40 and Aβ42, using a statistical mechanical modelling approach in combination with in vitro single-molecule fluorescence measurements. We find that at low concentrations of Aβ, corresponding to its physiological abundance, there is little free energy penalty in forming co-oligomers, suggesting that the formation of both self-oligomers and co-oligomers is possible under these conditions. Our model is used to predict the oligomer concentration and size at physiological concentrations of Aβ and suggests the mechanisms by which the ratio of Aβ42 to Aβ40 can affect cell toxicity. An increased ratio of Aβ42 to Aβ40 raises the fraction of oligomers containing Aβ42, which can increase the hydrophobicity of the oligomers and thus promote deleterious binding to the cell membrane and increase neuronal damage. Our results suggest that co-oligomers are a common form of aggregate when Aβ isoforms are present in solution and may potentially play a significant role in Alzheimer’s disease. PMID:27346247

  18. Quantitative analysis of co-oligomer formation by amyloid-beta peptide isoforms.

    PubMed

    Iljina, Marija; Garcia, Gonzalo A; Dear, Alexander J; Flint, Jennie; Narayan, Priyanka; Michaels, Thomas C T; Dobson, Christopher M; Frenkel, Daan; Knowles, Tuomas P J; Klenerman, David

    2016-01-01

    Multiple isoforms of aggregation-prone proteins are present under physiological conditions and have the propensity to assemble into co-oligomers with different properties from self-oligomers, but this process has not been quantitatively studied to date. We have investigated the amyloid-β (Aβ) peptide, associated with Alzheimer's disease, and the aggregation of its two major isoforms, Aβ40 and Aβ42, using a statistical mechanical modelling approach in combination with in vitro single-molecule fluorescence measurements. We find that at low concentrations of Aβ, corresponding to its physiological abundance, there is little free energy penalty in forming co-oligomers, suggesting that the formation of both self-oligomers and co-oligomers is possible under these conditions. Our model is used to predict the oligomer concentration and size at physiological concentrations of Aβ and suggests the mechanisms by which the ratio of Aβ42 to Aβ40 can affect cell toxicity. An increased ratio of Aβ42 to Aβ40 raises the fraction of oligomers containing Aβ42, which can increase the hydrophobicity of the oligomers and thus promote deleterious binding to the cell membrane and increase neuronal damage. Our results suggest that co-oligomers are a common form of aggregate when Aβ isoforms are present in solution and may potentially play a significant role in Alzheimer's disease. PMID:27346247

  19. Algorithm and implementation of muon trigger and data transmission system for barrel-endcap overlap region of the CMS detector

    NASA Astrophysics Data System (ADS)

    Zabolotny, W. M.; Byszuk, A.

    2016-03-01

    The CMS experiment Level-1 trigger system is undergoing an upgrade. In the barrel-endcap transition region, it is necessary to merge data from 3 types of muon detectors—RPC, DT and CSC. The Overlap Muon Track Finder (OMTF) uses the novel approach to concentrate and process those data in a uniform manner to identify muons and their transversal momentum. The paper presents the algorithm and FPGA firmware implementation of the OMTF and its data transmission system in CMS. It is foreseen that the OMTF will be subject to significant changes resulting from optimization which will be done with the aid of physics simulations. Therefore, a special, high-level, parameterized HDL implementation is necessary.

  20. Modified Phenylethynyl Containing Imides for Secondary Bonding: Non-Autoclave, Low Temperature Processable Adhesives

    NASA Technical Reports Server (NTRS)

    Dezern, James F. (Technical Monitor); Chang, Alice C.

    1999-01-01

    As part of a program to develop structural adhesives for high performance aerospace applications, research continued on the development of modified phenylethynyl containing imides, LaRC(trademark)MPEIs. In previous reports, the polymer properties were controlled by varying the molecular weight, the amount of branching, and the phenylethynyl content and by blending with low molecular weight materials. This research involves changing the flexibility in the copolyimide backbone of the branched, phenylethynyl terminated adhesives. These adhesives exhibit excellent processability at pressures as low as 15 psi and temperatures as low as 288 C. The Ti/Ti lap shear specimens are processable in an autoclave or a temperature programmable oven under a vacuum bag at 288-300 C without external pressure. The cured polymers exhibit high mechanical properties and excellent solvent resistance. The chemistry and properties of these adhesives are presented.

  1. Self-Assembly of Telechelic Tyrosine End-Capped PEO and Poly(alanine) Polymers in Aqueous Solution.

    PubMed

    Kirkham, Steven; Castelletto, Valeria; Hamley, Ian William; Reza, Mehedi; Ruokolainen, Janne; Hermida-Merino, Daniel; Bilalis, Panayiotis; Iatrou, Hermis

    2016-03-14

    The self-assembly in aqueous solution of three novel telechelic conjugates comprising a central hydrophilic polymer and short (trimeric or pentameric) tyrosine end-caps has been investigated. Two of the conjugates have a central poly(oxyethylene) (polyethylene oxide, PEO) central block with different molar masses. The other conjugate has a central poly(L-alanine) (PAla) sequence in a purely amino-acid based conjugate. All three conjugates self-assemble into β-sheet based fibrillar structures, although the fibrillar morphology revealed by cryogenic-TEM is distinct for the three polymers--in particular the Tyr5-PEO6k-Tyr5 forms a population of short straight fibrils in contrast to the more diffuse fibril aggregates observed for Tyr5-PEO2k-Tyr5 and Tyr3-PAla-Tyr3. Hydrogel formation was not observed for these samples (in contrast to prior work on related systems) up to quite high concentrations, showing that it is possible to prepare solutions of peptide-polymer-peptide conjugates with hydrophobic end-caps without conformational constraints associated with hydrogelation. The Tyr5-PEO6k-Tyr5 shows significant PEO crystallization upon drying in contrast to the Tyr5-PEO2k-Tyr5 conjugate. Our findings point to the remarkable ability of short hydrophobic peptide end groups to modulate the self-assembly properties of polymers in solution in model peptide-capped "associative polymers". Retention of fluidity at high conjugate concentration may be valuable in potential future applications of these conjugates as bioresponsive or biocompatible materials, for example exploiting the enzyme-responsiveness of the tyrosine end-groups. PMID:26867986

  2. A chromatographic estimate of the degree of surface heterogeneity of RPLC packing materials. III. Endcapped amido-embedded reversed phase

    SciTech Connect

    Gritti, Fabrice; Guiochon, Georges A

    2006-01-01

    The difference in adsorption behavior between a conventional monomeric endcapped C{sub 18} stationary phase (3.43 {micro}mol/m{sup 2}) and an endcapped polymeric RP-Amide phase (3.31 {micro}mol/m{sup 2}) was investigated. The adsorption isotherms of four compounds (phenol, caffeine, sodium 2-naphthalene sulfonate, and propranololium chloride) were measured by frontal analysis (FA) and the degree of heterogeneity of each phase for each solute was characterized by their adsorption energy distributions (AED), derived using the Expectation-Maximization method. The results show that only certain analytes (phenol and 2-naphthalene sulfonate) are sensitive to the presence of the polar embedded amide groups within the RP phase. Their binding constants on the amide-bonded phase are significantly higher than on conventional RPLC phases. Furthermore, an additional type of adsorption sites was observed for these two compounds. However, these sites having a low density, their presence does not affect much the retention factors of the two analytes. On the other hand, the adsorption behavior of the other two analytes (caffeine and propranololium chloride) is almost unaffected by the presence of the amide group in the bonded layer. Strong selective interactions may explain these observations. For example, hydrogen-bond interactions between an analyte (e.g., phenol or naphthalene sulfonate) and the carbonyl group (acceptor) or the nitrogen (donor) of the amido-embedded group may take place. No such interactions may take place with either caffeine or the cation propranololium chloride. This study confirms the hypothesis that analytes have ready access to locations deep inside the bonded layer, where the amide groups are present.

  3. (Photo)physical Properties of New Molecular Glasses End-Capped with Thiophene Rings Composed of Diimide and Imine Units

    PubMed Central

    2014-01-01

    New symmetrical arylene bisimide derivatives formed by using electron-donating–electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N′-bis(5-aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5-thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69–0.90%. PMID:24966893

  4. (Photo)physical Properties of New Molecular Glasses End-Capped with Thiophene Rings Composed of Diimide and Imine Units.

    PubMed

    Grucela-Zajac, Marzena; Bijak, Katarzyna; Kula, Slawomir; Filapek, Michal; Wiacek, Malgorzata; Janeczek, Henryk; Skorka, Lukasz; Gasiorowski, Jacek; Hingerl, Kurt; Sariciftci, Niyazi Serdar; Nosidlak, Natalia; Lewinska, Gabriela; Sanetra, Jerzy; Schab-Balcerzak, Ewa

    2014-06-19

    New symmetrical arylene bisimide derivatives formed by using electron-donating-electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N'-bis(5-aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5-thiophenedicarboxaldehyde or 2,2'-bithiophene-5,5'-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (E g) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and E g were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm(2) were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of V oc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69-0.90%. PMID:24966893

  5. Mechanisms for the decomposition and dehydrogenation of Li amide/imide

    NASA Astrophysics Data System (ADS)

    Hoang, Khang; Janotti, Anderson; van de Walle, Chris G.

    2012-02-01

    Reversible reaction involving Li amide (LiNH2) and Li imide (Li2NH) is a potential mechanism for hydrogen storage. Recent synchrotron x-ray diffraction experiments [W. I. David , J. Am. Chem. Soc.JACSAT0002-786310.1021/ja066016s 129, 1594 (2007)] suggest that the transformation between LiNH2 and Li2NH is a bulk reaction that occurs through nonstoichiometric processes and involves the migration of Li+ and H+ ions. In order to understand the atomistic mechanisms behind these processes, we carry out comprehensive first-principles studies of native point defects and defect complexes in the two compounds. We find that both LiNH2 and Li2NH are prone to Frenkel disorder on the Li sublattice. Lithium interstitials and vacancies have low formation energies and are highly mobile, and therefore play an important role in mass transport and ionic conduction. Hydrogen interstitials and vacancies, on the other hand, are responsible for forming and breaking N-H bonds, which is essential in the Li amide/imide reaction. Based on the structure, energetics, and migration of hydrogen-, lithium-, and nitrogen-related defects, we propose that LiNH2 decomposes into Li2NH and NH3 according to two competing mechanisms with different activation energies: one mechanism involves the formation of native defects in the interior of the material, the other at the surface. As a result, the prevailing mechanism and hence the effective activation energy for decomposition depend on the surface-to-volume ratio or the specific surface area, which changes with particle size during ball milling. These mechanisms also provide an explanation for the dehydrogenation of LiNH2 + LiH mixtures.

  6. Towards vast libraries of scaffold-diverse, conformationally constrained oligomers.

    PubMed

    Kodadek, Thomas; McEnaney, Patrick J

    2016-05-01

    There is great interest in the development of probe molecules and drug leads that would bind tightly and selectively to protein surfaces that are difficult to target with traditional molecules, such as those involved in protein-protein interactions. The currently available evidence suggests that this will require molecules that are larger and have quite different chemical properties than typical Lipinski-compliant molecules that target enzyme active sites. We describe here efforts to develop vast libraries of conformationally constrained oligomers as a potentially rich source of these molecules. PMID:26996593

  7. Rare Individual Amyloid-β Oligomers Act on Astrocytes to Initiate Neuronal Damage

    PubMed Central

    2014-01-01

    Oligomers of the amyloid-β (Aβ) peptide have been implicated in the neurotoxicity associated with Alzheimer’s disease. We have used single-molecule techniques to examine quantitatively the cellular effects of adding well characterized Aβ oligomers to primary hippocampal cells and hence determine the initial pathway of damage. We found that even picomolar concentrations of Aβ (1–40) and Aβ (1–42) oligomers can, within minutes of addition, increase the levels of intracellular calcium in astrocytes but not in neurons, and this effect is saturated at a concentration of about 10 nM of oligomers. Both Aβ (1–40) and Aβ (1–42) oligomers have comparable effects. The rise in intracellular calcium is followed by an increase in the rate of ROS production by NADPH oxidase in both neurons and astrocytes. The increase in ROS production then triggers caspase-3 activation resulting in the inhibition of long-term potentiation. Our quantitative approach also reveals that only a small fraction of the oligomers are damaging and that an individual rare oligomer binding to an astrocyte can initiate the aforementioned cascade of responses, making it unlikely to be due to any specific interaction. Preincubating the Aβ oligomers with an extracellular chaperone, clusterin, sequesters the oligomers in long-lived complexes and inhibits all of the physiological damage, even at a ratio of 100:1, total Aβ to clusterin. To explain how Aβ oligomers are so damaging but that it takes decades to develop Alzheimer’s disease, we suggest a model for disease progression where small amounts of neuronal damage from individual unsequestered oligomers can accumulate over time leading to widespread tissue-level dysfunction. PMID:24717093

  8. A Mechanism of Subunit Recruitment in Human Small Heat Shock Protein Oligomers

    PubMed Central

    2016-01-01

    Small heat shock proteins (sHSPs) make up a class of molecular chaperones broadly observed across organisms. Many sHSPs form large oligomers that undergo dynamic subunit exchange that is thought to play a role in chaperone function. Though remarkably heterogeneous, sHSP oligomers share three types of intermolecular interactions that involve all three defined regions of a sHSP: the N-terminal region (NTR), the conserved α-crystallin domain (ACD), and a C-terminal region (CTR). Here we define the structural interactions involved in incorporation of a subunit into a sHSP oligomer. We demonstrate that a minimal ACD dimer of the human sHSP, HSPB5, interacts with an HSPB5 oligomer through two types of interactions: (1) interactions with CTRs in the oligomer and (2) via exchange into and out of the dimer interface composed of two ACDs. Unexpectedly, although dimers are thought to be the fundamental building block for sHSP oligomers, our results clearly indicate that subunit exchange into and out of oligomers occurs via monomers. Using structure-based mutants, we show that incorporation of a subunit into an oligomer is predicated on recruitment of the subunit via its interaction with CTRs on an oligomer. Both the rate and extent of subunit incorporation depend on the accessibility of CTRs within an HSPB5 oligomer. We show that this mechanism also applies to formation of heterooligomeric sHSP species composed of HSPB5 and HSPB6 and is likely general among sHSPs. Finally, our observations highlight the importance of NTRs in the thermodynamic stability of sHSP oligomers. PMID:26098708

  9. Polycaprolactone/oligomer compound scaffolds for cardiac tissue engineering.

    PubMed

    Reddy, Chaganti Srinivasa; Venugopal, Jayarama Reddy; Ramakrishna, Seeram; Zussman, Eyal

    2014-10-01

    Polycaprolactone (PCL), a synthetic biocompatible and biodegradable polymer generally used as a scaffold material for tissue engineering applications. The high stiffness and hydrophobicity of the PCL fiber mesh does not provide significant cell attachment and proliferation in cardiac tissue engineering. Towards this goal, the study focused on a compound of PCL and oligomer hydrogel [Bisphenol A ethoxylated dimethacrylate (BPAEDMA)] processed into electrospun nanofibrous scaffolds. The composition, morphology and mechanical properties of the compound scaffolds, composed of varying ratios of PCL and hydrogel were characterized by scanning electron microscopy, infrared spectroscopy and dynamic mechanical analyzer. The elastic modulus of PCL/BPAEDMA nanofibrous scaffolds was shown to be varying the BPAEDMA weight fraction and was decreased by increasing the BPAEDMA weight fraction. Compound fiber meshes containing 75 wt % BPAEDMA oligomer hydrogel exhibited lower modulus (3.55 MPa) and contact angle of 25(o) . Rabbit cardiac cells cultured for 10 days on these PCL/BPAEDMA compound nanofibrous scaffolds remained viable and expressed cardiac troponin and alpha-actinin proteins for the normal functioning of myocardium. Cell adhesion and proliferations were significantly increased on compound fiber meshes containing 75 wt % BPAEDMA, when compared with other nanofibrous scaffolds. The results observed that the produced PCL/BPAEDMA compound nanofibrous scaffolds promote cell adhesion, proliferation and normal functioning of cardiac cells to clinically beneficial levels, relevant for cardiac tissue engineering. PMID:24288184

  10. Amyloid oligomer structure characterization from simulations: A general method

    SciTech Connect

    Nguyen, Phuong H.; Li, Mai Suan

    2014-03-07

    Amyloid oligomers and plaques are composed of multiple chemically identical proteins. Therefore, one of the first fundamental problems in the characterization of structures from simulations is the treatment of the degeneracy, i.e., the permutation of the molecules. Second, the intramolecular and intermolecular degrees of freedom of the various molecules must be taken into account. Currently, the well-known dihedral principal component analysis method only considers the intramolecular degrees of freedom, and other methods employing collective variables can only describe intermolecular degrees of freedom at the global level. With this in mind, we propose a general method that identifies all the structures accurately. The basis idea is that the intramolecular and intermolecular states are described in terms of combinations of single-molecule and double-molecule states, respectively, and the overall structures of oligomers are the product basis of the intramolecular and intermolecular states. This way, the degeneracy is automatically avoided. The method is illustrated on the conformational ensemble of the tetramer of the Alzheimer's peptide Aβ{sub 9−40}, resulting from two atomistic molecular dynamics simulations in explicit solvent, each of 200 ns, starting from two distinct structures.

  11. A covalent homodimer probing early oligomers along amyloid aggregation.

    PubMed

    Halabelian, Levon; Relini, Annalisa; Barbiroli, Alberto; Penco, Amanda; Bolognesi, Martino; Ricagno, Stefano

    2015-01-01

    Early oligomers are crucial in amyloid aggregation; however, due to their transient nature they are among the least structurally characterized species. We focused on the amyloidogenic protein beta2-microglobulin (β2m) whose early oligomers are still a matter of debate. An intermolecular interaction between D strands of facing β2m molecules was repeatedly observed, suggesting that such interface may be relevant for β2m dimerization. In this study, by mutating Ser33 to Cys, and assembling the disulphide-stabilized β2m homodimer (DimC33), such DD strand interface was locked. Although the isolated DimC33 display a stability similar to wt β2m under native conditions, it shows enhanced amyloid aggregation propensity. Three distinct crystal structures of DimC33 suggest that dimerization through the DD interface is instrumental for enhancing DimC33 aggregation propensity. Furthermore, the crystal structure of DimC33 in complex with the amyloid-specific dye Thioflavin-T pinpoints a second interface, which likely participates in the first steps of β2m aggregation. The present data provide new insight into β2m early steps of amyloid aggregation. PMID:26420657

  12. CHIP targets toxic alpha-Synuclein oligomers for degradation.

    PubMed

    Tetzlaff, Julie E; Putcha, Preeti; Outeiro, Tiago F; Ivanov, Alexander; Berezovska, Oksana; Hyman, Bradley T; McLean, Pamela J

    2008-06-27

    alpha-Synuclein (alphaSyn) can self-associate, forming oligomers, fibrils, and Lewy bodies, the pathological hallmark of Parkinson disease. Current dogma suggests that oligomeric alphaSyn intermediates may represent the most toxic alphaSyn species. Here, we studied the effect of a potent molecular chaperone, CHIP (carboxyl terminus of Hsp70-interacting protein), on alphaSyn oligomerization using a novel bimolecular fluorescence complementation assay. CHIP is a multidomain chaperone, utilizing both a tetratricopeptide/Hsp70 binding domain and a U-box/ubiquitin ligase domain to differentially impact the fate of misfolded proteins. In the current study, we found that co-expression of CHIP selectively reduced alphaSyn oligomerization and toxicity in a tetratricopeptide domain-dependent, U-box-independent manner by specifically degrading toxic alphaSyn oligomers. We conclude that CHIP preferentially recognizes and mediates degradation of toxic, oligomeric forms of alphaSyn. Further elucidation of the mechanisms of CHIP-induced degradation of oligomeric alphaSyn may contribute to the successful development of drug therapies that target oligomeric alphaSyn by mimicking or enhancing the powerful effects of CHIP. PMID:18436529

  13. EGFP oligomers as natural fluorescence and hydrodynamic standards.

    PubMed

    Vámosi, György; Mücke, Norbert; Müller, Gabriele; Krieger, Jan Wolfgang; Curth, Ute; Langowski, Jörg; Tóth, Katalin

    2016-01-01

    EGFP oligomers are convenient standards for experiments on fluorescent protein-tagged biomolecules. In this study, we characterized their hydrodynamic and fluorescence properties. Diffusion coefficients D of EGFP1-4 were determined by analytical ultracentrifugation with fluorescence detection and by fluorescence correlation spectroscopy (FCS), yielding 83.4…48.2 μm(2)/s and 97.3…54.8 μm(2)/s from monomer to tetramer. A "barrels standing in a row" model agreed best with the sedimentation data. Oligomerization red-shifted EGFP emission spectra without any shift in absorption. Fluorescence anisotropy decreased, indicating homoFRET between the subunits. Fluorescence lifetime decreased only slightly (4%) indicating insignificant quenching by FRET to subunits in non-emitting states. FCS-measured D, particle number and molecular brightness depended on dark states and light-induced processes in distinct subunits, resulting in a dependence on illumination power different for monomers and oligomers. Since subunits may be in "on" (bright) or "off" (dark) states, FCS-determined apparent brightness is not proportional to that of the monomer. From its dependence on the number of subunits, the probability of the "on" state for a subunit was determined to be 96% at pH 8 and 77% at pH 6.38, i.e., protonation increases the dark state. These fluorescence properties of EGFP oligomeric standards can assist interpreting results from oligomerized EGFP fusion proteins of biological interest. PMID:27622431

  14. Charge transfer interactions in oligomer coated gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Newmai, M. Boazbou; Kumar, Pandian Senthil

    2016-05-01

    Gold nanoclusters were synthesized by a bottom-up synergistic approach of in-situ oligomerization of the monomer, N-vinyl pyrrolidone (NVP) and simultaneous weak reduction of Au-NVP complexes in the absence of any other external energy sources, thereby making these tiny gold clusters as the most elemental building blocks to construct further novel nano/microstructures with application potentials. It is well-known that metal clusters with less than 2 nm size do not show the usual surface plasmon band, because of the presence of a band-gap at the fermi level. Nevertheless, our present oligomer coated gold clusters show a discrete intense band at around 630 nm, which could very well be attributed to the charge transfer between the oligomer chain and the surface Au atoms. Such kind of sacrificial plasmon induced charge transfer interaction, observed for the very first time to the best of our knowledge, were also strongly corroborated through the enhancement / shifting of specific vibrational / rotational peaks as observed from the FTIR and Raman measurements as a function of the metal oxidation states, thus representing a new prototype for an efficient solar energy conversion probe.

  15. In vivo resolution of oligomers with fluorescence photobleaching recovery histograms

    PubMed Central

    Youn, B.S.; Lepock, J.R.; Borrelli, M.J.; Jervis, E.J.

    2006-01-01

    Simple independent enzyme-catalyzed reactions distributed homogeneously throughout an aqueous environment cannot adequately explain the regulation of metabolic and other cellular processes in vivo. Such an unstructured system results in unacceptably slow substrate turnover rates and consumes inordinate amounts of cellular energy. Current approaches to resolving compartmentalization in living cells requires the partitioning of the molecular species in question such that its localization can be resolved with fluorescence microscopy. Standard imaging approaches will not resolve localization of protein activity for proteins that are ubiquitously distributed, but whose function requires a change in state of the protein. The small heat shock protein sHSP27 exists as both dimers and large multimers and is distributed homogeneously throughout the cytoplasm. A fusion of the green fluorescent protein variant S65T and sHSP27 is used to assess the ability of diffusion rate histograms to resolve compartmentalization of the 2 dominant oligomeric species of sHSP27. Diffusion rates were measured by multiphoton fluorescence photobleaching recovery. Under physiologic conditions, diffusion rate histograms resolved at least 2 diffusive transport rates within a living cell potentially corresponding to the large and small oligomers of sHSP27. Given that oligomerization is often a means of regulation, compartmentalization of different oligomer species could provide a means for efficient regulation and localization of sHsp27 activity. PMID:16817323

  16. A covalent homodimer probing early oligomers along amyloid aggregation

    PubMed Central

    Halabelian, Levon; Relini, Annalisa; Barbiroli, Alberto; Penco, Amanda; Bolognesi, Martino; Ricagno, Stefano

    2015-01-01

    Early oligomers are crucial in amyloid aggregation; however, due to their transient nature they are among the least structurally characterized species. We focused on the amyloidogenic protein beta2-microglobulin (β2m) whose early oligomers are still a matter of debate. An intermolecular interaction between D strands of facing β2m molecules was repeatedly observed, suggesting that such interface may be relevant for β2m dimerization. In this study, by mutating Ser33 to Cys, and assembling the disulphide-stabilized β2m homodimer (DimC33), such DD strand interface was locked. Although the isolated DimC33 display a stability similar to wt β2m under native conditions, it shows enhanced amyloid aggregation propensity. Three distinct crystal structures of DimC33 suggest that dimerization through the DD interface is instrumental for enhancing DimC33 aggregation propensity. Furthermore, the crystal structure of DimC33 in complex with the amyloid-specific dye Thioflavin-T pinpoints a second interface, which likely participates in the first steps of β2m aggregation. The present data provide new insight into β2m early steps of amyloid aggregation. PMID:26420657

  17. How Epigallocatechin Gallate Can Inhibit α-Synuclein Oligomer Toxicity in Vitro♦

    PubMed Central

    Lorenzen, Nikolai; Nielsen, Søren B.; Yoshimura, Yuichi; Vad, Brian S.; Andersen, Camilla Bertel; Betzer, Cristine; Kaspersen, Jørn D.; Christiansen, Gunna; Pedersen, Jan S.; Jensen, Poul Henning; Mulder, Frans A. A.; Otzen, Daniel E.

    2014-01-01

    Oligomeric species of various proteins are linked to the pathogenesis of different neurodegenerative disorders. Consequently, there is intense focus on the discovery of novel inhibitors, e.g. small molecules and antibodies, to inhibit the formation and block the toxicity of oligomers. In Parkinson disease, the protein α-synuclein (αSN) forms cytotoxic oligomers. The flavonoid epigallocatechin gallate (EGCG) has previously been shown to redirect the aggregation of αSN monomers and remodel αSN amyloid fibrils into disordered oligomers. Here, we dissect EGCG's mechanism of action. EGCG inhibits the ability of preformed oligomers to permeabilize vesicles and induce cytotoxicity in a rat brain cell line. However, EGCG does not affect oligomer size distribution or secondary structure. Rather, EGCG immobilizes the C-terminal region and moderately reduces the degree of binding of oligomers to membranes. We interpret our data to mean that the oligomer acts by destabilizing the membrane rather than by direct pore formation. This suggests that reduction (but not complete abolition) of the membrane affinity of the oligomer is sufficient to prevent cytotoxicity. PMID:24907278

  18. Heat Resistant Characteristics of Major Royal Jelly Protein 1 (MRJP1) Oligomer

    PubMed Central

    Moriyama, Takanori; Ito, Aimi; Omote, Sumire; Miura, Yuri; Tsumoto, Hiroki

    2015-01-01

    Soluble royal jelly protein is a candidate factor responsible for mammiferous cell proliferation. Major royal jelly protein 1 (MRJP1), which consists of oligomeric and monomeric forms, is an abundant proliferative protein in royal jelly. We previously reported that MRJP1 oligomer has biochemical heat resistance. Therefore, in the present study, we investigated the effects of several heat treatments (56, 65 and 96°C) on the proliferative activity of MRJP1 oligomer. Heat resistance studies showed that the oligomer molecular forms were slightly maintained until 56℃, but the molecular forms were converted to macromolecular heat-aggregated MRJP1 oligomer at 65℃ and 96℃. But, the growth activity of MRJP1 oligomer treated with 96°C was slightly attenuated when compared to unheated MRJP1 oligomer. On the other hand, the cell proliferation activity was preserved until 96℃ by the cell culture analysis of Jurkat cells. In contrast, those of IEC-6 cells were not preserved even at 56°C. The present observations suggest that the bioactive heat-resistance properties were different by the origin of the cells. The cell proliferation analysis showed that MRJP1 oligomer, but not MRJP2 and MRJP3, significantly increased cell numbers, suggesting that MRJP1 oligomer is the predominant proliferation factor for mammiferous cells. PMID:26020775

  19. β-to-β 2,5-Pyrrolylene-Linked Cyclic Porphyrin Oligomers.

    PubMed

    Rao, Yutao; Kim, Jun Oh; Kim, Woojae; Zhong, Guangming; Yin, Bangshao; Zhou, Mingbo; Shinokubo, Hiroshi; Aratani, Naoki; Tanaka, Takayuki; Liu, Shubin; Osuka, Atsuhiro; Kim, Dongho; Song, Jianxin

    2016-06-20

    β-to-β 2,5-Pyrrolylene linked cyclic porphyrin oligomers have been synthesized by Suzuki-Miyaura coupling of 2,5-diborylpyrrole and 3,7-dibromoporphyrin. The cyclic porphyrin oligomers exhibit roughly coplanar structures, strong excitonic coupling, small electrochemical HOMO-LUMO gaps, and ultrafast excitation energy transfer between the neighboring porphyrins via the pyrrolylene bridge. PMID:27124728

  20. Fibrillogenic oligomers of human cystatin C are formed by propagated domain swapping.

    PubMed

    Wahlbom, Maria; Wang, Xin; Lindström, Veronica; Carlemalm, Eric; Jaskolski, Mariusz; Grubb, Anders

    2007-06-22

    Cystatin C and the prion protein have been shown to form dimers via three-dimensional domain swapping, and this process has also been hypothesized to be involved in amyloidogenesis. Production of oligomers of other amyloidogenic proteins has been reported to precede fibril formation, suggesting oligomers as intermediates in fibrillogenesis. A variant of cystatin C, with a Leu68-->Gln substitution, is highly amyloidogenic, and carriers of this mutation suffer from massive cerebral amyloidosis leading to brain hemorrhage and death in early adulthood. This work describes doughnut-shaped oligomers formed by wild type and L68Q cystatin C upon incubation of the monomeric proteins. Purified oligomers of cystatin C are shown to fibrillize faster and at a lower concentration than the monomeric protein, indicating a role of the oligomers as fibril-assembly intermediates. Moreover, the present work demonstrates that three-dimensional domain swapping is involved in the formation of the oligomers, because variants of monomeric cystatin C, stabilized against three-dimensional domain swapping by engineered disulfide bonds, do not produce oligomers upon incubation under non-reducing conditions. Redox experiments using wild type and stabilized cystatin C strongly suggest that the oligomers, and thus probably the fibrils as well, are formed by propagated domain swapping rather than by assembly of domain-swapped cystatin C dimers. PMID:17470433

  1. Radical-mediated dehydrative preparation of cyclic imides using (NH4)2S2O8–DMSO: application to the synthesis of vernakalant

    PubMed Central

    Garad, Dnyaneshwar N; Tanpure, Subhash D

    2015-01-01

    Summary Ammonium persulfate–dimethyl sulfoxide (APS–DMSO) has been developed as an efficient and new dehydrating reagent for a convenient one-pot process for the synthesis of miscellaneous cyclic imides in high yields starting from readily available primary amines and cyclic anhydrides. A plausible radical mechanism involving DMSO has been proposed. The application of this facile one-pot imide forming process has been demonstrated for a practical synthesis of vernakalant. PMID:26199655

  2. Radical-mediated dehydrative preparation of cyclic imides using (NH4)2S2O8-DMSO: application to the synthesis of vernakalant.

    PubMed

    Garad, Dnyaneshwar N; Tanpure, Subhash D; Mhaske, Santosh B

    2015-01-01

    Ammonium persulfate-dimethyl sulfoxide (APS-DMSO) has been developed as an efficient and new dehydrating reagent for a convenient one-pot process for the synthesis of miscellaneous cyclic imides in high yields starting from readily available primary amines and cyclic anhydrides. A plausible radical mechanism involving DMSO has been proposed. The application of this facile one-pot imide forming process has been demonstrated for a practical synthesis of vernakalant. PMID:26199655

  3. Supramolecular aggregates with distinct optical properties from PDI oligomers of similar structures.

    PubMed

    Yan, Qifan; Cai, Kang; Zhao, Dahui

    2016-01-21

    The self-assembly behaviors of two series of monodispersed oligomers consisting of perylenediimide (PDI) linked by ethynylene and butadiynylene spacers are investigated in solutions. In spite of the very similar chemical structures, the two sets of oligomers manifest completely different optical properties upon self-aggregation, implying differed aggregate structures. While the oligomers containing butadiynylene spacers form H-aggregates, those featuring ethynylene linkers display J-aggregation characteristics. Thermodynamic analysis revealed that the self-association constants of both series of oligomers increase with the number of PDI units in the backbones. Oligomers containing the same number of PDI units but different spacers display nearly identical enthalpy changes. According to the molecular exciton theory, the observed H- and J-aggregates are suggested to comprise similar packing motifs with slightly varied slipping angles, giving rise to greatly disparate optical properties. PMID:26686554

  4. Preparation of Chito-Oligomers by Hydrolysis of Chitosan in the Presence of Zeolite as Adsorbent

    PubMed Central

    Ibrahim, Khalid A.; El-Eswed, Bassam I.; Abu-Sbeih, Khaleel A.; Arafat, Tawfeeq A.; Al Omari, Mahmoud M. H.; Darras, Fouad H.; Badwan, Adnan A.

    2016-01-01

    An increasing interest has recently been shown to use chitin/chitosan oligomers (chito-oligomers) in medicine and food fields because they are not only water-soluble, nontoxic, and biocompatible materials, but they also exhibit numerous biological properties, including antibacterial, antifungal, and antitumor activities, as well as immuno-enhancing effects on animals. Conventional depolymerization methods of chitosan to chito-oligomers are either chemical by acid-hydrolysis under harsh conditions or by enzymatic degradation. In this work, hydrolysis of chitosan to chito-oligomers has been achieved by applying adsorption-separation technique using diluted HCl in the presence of different types of zeolite as adsorbents. The chito-oligomers were retrieved from adsorbents and characterized by differential scanning calorimetry (DSC), liquid chromatography/mass spectroscopy (LC/MS), and ninhydrin test. PMID:27455287

  5. Amplified spontaneous emission from a new 4-triarylamine substituted 1,8-naphthalimide semiconductor oligomer

    NASA Astrophysics Data System (ADS)

    Lu, Wu; Tu, Guoli; Zhong, Bo; Ma, Dongge; Wang, Lixiang; Jing, Xiabin; Wang, Fosong

    2005-06-01

    Amplified spontaneous emission has been observed in a new semiconductor oligomer of 2-decyl-6-{[4'-(naphthalene-1-yl-phenyl-amino)-biphenyl-4-yl]-[4-(naphthalene-1-yl-phenyl-amino)-phenyl]-amino}-benzo[ de]isoquinoline-1,3-dione (4-triarylamine substituted 1,8-naphthalimide TAANPI) doped polymer films pumped by the second harmonic of a Nd:YAG laser. The dependence of the threshold and gain on the oligomer concentration in polymer was studied in detail. It was found that the semiconductor oligomer shows low threshold, high gain and low loss even though the doped oligomer concentration is up to 60%, indicating a low concentration quenching effect. This demonstrates that the oligomer could be a promising candidate as gain medium for organic diode lasers.

  6. Star-shaped tetrathiafulvalene oligomers towards the construction of conducting supramolecular assembly

    PubMed Central

    Hasegawa, Masashi

    2015-01-01

    Summary The construction of redox-active supramolecular assemblies based on star-shaped and radially expanded tetrathiafulvalene (TTF) oligomers with divergent and extended conjugation is summarized. Star-shaped TTF oligomers easily self-aggregate with a nanophase separation to produce supramolecular structures, and their TTF units stack face-to-face to form columnar structures using the fastener effect. Based on redox-active self-organizing supramolecular structures, conducting nanoobjects are constructed by doping of TTF oligomers with oxidants after the formation of such nanostructures. Although radical cations derived from TTF oligomers strongly interact in solution to produce a mixed-valence dimer and π-dimer, it seems to be difficult to produce nanoobjects of radical cations different from those of neutral TTF oligomers. In some cases, however, radical cations form nanostructured fibers and rods by controlling the supramolecular assembly, oxidation states, and counter anions employed. PMID:26664579

  7. The Role of Amyloid-β Oligomers in Toxicity, Propagation, and Immunotherapy

    PubMed Central

    Sengupta, Urmi; Nilson, Ashley N.; Kayed, Rakez

    2016-01-01

    The incidence of Alzheimer's disease (AD) is growing every day and finding an effective treatment is becoming more vital. Amyloid-β (Aβ) has been the focus of research for several decades. The recent shift in the Aβ cascade hypothesis from all Aβ to small soluble oligomeric intermediates is directing the search for therapeutics towards the toxic mediators of the disease. Targeting the most toxic oligomers may prove to be an effective treatment by preventing their spread. Specific targeting of oligomers has been shown to protect cognition in rodent models. Additionally, the heterogeneity of research on Aβ oligomers may seem contradictory until size and conformation are taken into account. In this review, we will discuss Aβ oligomers and their toxicity in relation to size and conformation as well as their influence on inflammation and the potential of Aβ oligomer immunotherapy. PMID:27211547

  8. Preparation of Chito-Oligomers by Hydrolysis of Chitosan in the Presence of Zeolite as Adsorbent.

    PubMed

    Ibrahim, Khalid A; El-Eswed, Bassam I; Abu-Sbeih, Khaleel A; Arafat, Tawfeeq A; Al Omari, Mahmoud M H; Darras, Fouad H; Badwan, Adnan A

    2016-01-01

    An increasing interest has recently been shown to use chitin/chitosan oligomers (chito-oligomers) in medicine and food fields because they are not only water-soluble, nontoxic, and biocompatible materials, but they also exhibit numerous biological properties, including antibacterial, antifungal, and antitumor activities, as well as immuno-enhancing effects on animals. Conventional depolymerization methods of chitosan to chito-oligomers are either chemical by acid-hydrolysis under harsh conditions or by enzymatic degradation. In this work, hydrolysis of chitosan to chito-oligomers has been achieved by applying adsorption-separation technique using diluted HCl in the presence of different types of zeolite as adsorbents. The chito-oligomers were retrieved from adsorbents and characterized by differential scanning calorimetry (DSC), liquid chromatography/mass spectroscopy (LC/MS), and ninhydrin test. PMID:27455287

  9. Structural Characteristics of the Alpha-Synuclein Oligomers Stabilized By the Flavonoid Baicalein

    SciTech Connect

    Hong, D.-P.; Fink, A.L.; Uversky, V.N.

    2009-05-18

    The flavonoid baicalein inhibits fibrillation of alpha-synuclein, which is a major component of Lewy bodies in Parkinson's disease. It has been known that baicalein induces the formation of alpha-synuclein oligomers and consequently prevents their fibrillation. In order to evaluate the structural properties of baicalein-stabilized oligomers, we purified oligomer species by HPLC and examined their stability and structure by CD, Fourier transform infrared spectroscopy, size exclusion chromatography HPLC, small-angle X-ray scattering, and atomic force microscopy. Baicalein-stabilized oligomers are beta-sheet-enriched according to CD and Fourier transform infrared spectroscopy analyses. They did not form fibrils even after very prolonged incubation. From small-angle X-ray scattering data and atomic force microscopy images, the oligomers were characterized as quite compact globular species. Oligomers were extremely stable, with a GdmCl C(m)=3.3 M. This high stability explains the previously observed inhibition properties of baicalein against alpha-synuclein fibrillation. These baicalein-stabilized oligomers, added to the solution of aggregating alpha-synuclein, were able to noticeably inhibit its fibrillation. After prolonged coincubation, short fibrils were formed, suggesting an effective interaction of oligomers with monomeric alpha-synuclein. Membrane permeability tests suggested that the baicalein-stabilized oligomers had a mild effect on the integrity of the membrane surface. This effect was rather similar to that of the monomeric protein, suggesting that targeted stabilization of certain alpha-synuclein oligomers might offer a potential strategy for the development of novel Parkinson's disease therapies.

  10. New Poly(amide-imide)/Nanocomposites Reinforced Silicate Nanoparticles Based on N-pyromellitimido-L-phenyl Alanine Containing Ether Moieties

    NASA Astrophysics Data System (ADS)

    Faghihi, Khalil; Shabanian, Meisam; Dadfar, Ehsan

    2012-02-01

    A series of Poly(amide-imide)/montmorillonite nanocomposites containing N-pyromellitimido-L-phenyl alanine moiety in the main chain were synthesized by a convenient solution intercalation technique. Poly(amide-imide) (PAI) 5 as a source of polymer matrix was synthesized by the direct polycondensation reaction of N-pyromellitimido-L-phenyl alanine 3 with 4,4'-diamino diphenyl ether 4 in the presence of triphenyl phosphite (TPP), CaCl2, pyridine and N-methyl-2-pyrrolidone (NMP). The resulting nanocomposite films were characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results showed that organo-modified clay was dispersed homogeneously in PAI matrix. TGA indicated an enhancement of thermal stability of new nanocomposites compared with the pure polymer.

  11. Characterization of high performance randomly segmented poly(urethane siloxane) and poly(imide siloxane) block copolymers

    NASA Astrophysics Data System (ADS)

    Doǧan, Türkan; Baydoǧan, Nilgün; Köken, Nesrin

    2016-03-01

    Poly(imide siloxane) block copolymers with the same polydimethlysiloxane(APPS) were prepared by using 4,4'-oxydianiline (ODA) and Benzofenon-3,3,4,4-tetrakarboksilik dianhydride(BTDA) to compose the polyimide hard block. APPS and BTDA composed the polysiloxane soft block. The length of polysiloxane soft blocks increased with increasing the length of polyimide hard block. Copolymerization of soft and hard segments were determined by using this method. Copolymer structures could be obtained by holding constant hard block segments and by adjusting and increasing soft block segments. Thus, more flexible randomly segmented poly(imide siloxane) block copolymers can be obtained. These composed structure as flexible and high performance copolymers were characterized by FT-IR and evaluated. The structures were tested mechanically to detect their elastic recovery property as flexible material. The characterization of the samples enabled to examine flexible substrates in order to use in solar cell, aerospace applications and microelectronic devices.

  12. Are ionic liquids based on pyrrolidinium imide able to wet separators and electrodes used for Li-ion batteries?

    NASA Astrophysics Data System (ADS)

    Stefan, Claudia Simona; Lemordant, Daniel; Claude-Montigny, Bénédicte; Violleau, David

    Surface free energy and contact angle measurements were conducted with a series of room temperature ionic liquids (RTILs) based on N,N‧-alkyl-pyrrolidinium imide. Wetting characteristics of various separators (Celgard ® and Separion ®) and electrodes (LiCoO 2, Li 4Ti 5O 12 and graphite), commonly used in Li-ion batteries, were performed. Initially, the free surface energies were determined for both smooth polymeric materials, constituent of the separators, and pyrrolidinium RTILs. Experimental results and calculations show that (i) N-methyl-N-pentyl pyrrolidinium imide is the most wetting RTIL whatever the separator used, and that (ii) the separator wettability is one of the most important factor to take into account in electrochemical devices.

  13. Thermal and Optical Properties of New Poly(amide-imide)/Nanocomposite Reinforced by Layer Silicate Containing Diphenyl Ether Moieties

    NASA Astrophysics Data System (ADS)

    Faghihi, Khalil; Faramarzi, Ellahe; Shabanian, Meisam

    2011-04-01

    New poly(amide-imide)-montmorillonite reinforced nanocomposites containing Bis(4-N-trimellitylimido) diphenyl ether moiety in the main chain were synthesized by a convenient solution intercalation technique. Poly(amide-imide) (PAI) 4 was synthesized by the direct polycondensation reaction of Bis(4-N-trimellitylimido) diphenyl ether 3 with 4,4'-diamino diphenyl ether 2 in the presence of triphenyl phosphite (TPP), CaCl2, pyridine and N-methyl-2-pyrrolidone (NMP). Morphology and structure of the resulting PAI-nanocomposite films 4a and 4b with 10 and 20 mass% silicate particles respectively, were characterized by FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The properties of nanocomposites films were investigated by using Uv-vis spectroscopy, thermogravimetric analysis (TGA) and water uptake measurements.

  14. Redox-responsive nanocarrier based on heparin end-capped mesoporous silica nanoparticles for targeted tumor therapy in vitro and in vivo.

    PubMed

    Dai, Liangliang; Li, Jinghua; Zhang, Beilu; Liu, Junjie; Luo, Zhong; Cai, Kaiyong

    2014-07-01

    This study reports a smart controlled drug release system based on mesoporous silica nanoparticles (MSNs) for targeted drug delivery. The system was fabricated by employing heparin as an end-capping agent to seal the mesopores of MSNs via disulfide bonds as intermediate linkers for intracellular glutathione triggered drug release. Lactobionic acid molecules were then coupled to heparin end-capped MSNs that serve as targeting motifs for facilitating the uptake of doxorubicin (DOX) loaded MSNs by HepG2 cells and tumors, respectively. Detailed investigations demonstrated that the fabricated drug delivery systems could deliver DOX to cancer cells to induce cell apoptosis in vitro and tumor tissue for the inhibition of tumor growth in vivo with minimal side effects. The study affords a promising nanocarrier for redox-responsive cargo delivery with high curative efficiency for cancer therapy. PMID:24933090

  15. Synthesis of imides via palladium-catalyzed decarboxylative amidation of α-oxocarboxylic acids with secondary amides.

    PubMed

    Xu, Ning; Liu, Jie; Li, Dengke; Wang, Lei

    2016-05-18

    An efficient synthesis of imides has been developed through a Pd-catalyzed decarboxylative amidation of α-oxocarboxylic acids with secondary amides. The reactions of N-substituted N-heteroarene-2-carboxamides with 2-oxo-2-arylacetic acids proceeded smoothly to generate the corresponding products in good yields in the presence of Pd(OAc)2 and K2S2O8. PMID:27143171

  16. Polyimide-Silica Hybrids Containing Novel Phenylethynyl Imide Silanes as Coupling Agents for Surface-Treated Titanium Alloy

    NASA Technical Reports Server (NTRS)

    Park, C.; Lowther, S. E.; Smith, J. G., Jr.; Connell, J. W.; Hergenrother, P. M.; SaintClair, T. L.

    2000-01-01

    Polyimide-silica hybrids composed of an organic precursor containing a novel phenylethynyl imide silane and an inorganic precursor were evaluated as an adhesion-promoting interphase between surface-treated titanium alloy and a phenylethynyl-containing imide adhesive. The phenylethynyl groups present in the organic precursor, either as a pendent or end group, can bond chemically with a phenylethynyl-containing imide adhesive during processing, while the silane groups of the organic precursor would react chemically with the inorganic precursor. In addition, the inorganic precursor is able to react with the titanium alloy to form a stable bond with the metal oxide. Bond strength and durability were evaluated by single lap shear tests at various conditions. Lap shear specimens exhibited predominantly cohesive failure after a 3-d water boil with 92% retention of the initial room temperature strength. Morphology and chemical composition of the hybrid interphase were investigated with scanning electron microscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy, which revealed development of a silicon-gradient, hybrid structure between the metal substrate and the adhesive.

  17. Mitigation of copper toxicity by DNA oligomers in green paramecia

    PubMed Central

    Takaichi, Hiroshi; Comparini, Diego; Iwase, Junichiro; Bouteau, François; Mancuso, Stefano; Kawano, Tomonori

    2015-01-01

    Impact of transition metals which catalyze the generation of reactive oxygen species (ROS), on activation of cell death signaling in plant cells have been documented to date. Similarly in green paramecia (Paramecium bursaria), an aquatic protozoan species harboring symbiotic green algae in the cytoplasm, toxicities of various metallic ions have been documented. We have recently examined the effects of double-stranded GC-rich DNA fragments with copper-binding nature and ROS removal catalytic activity as novel plant cell-protecting agents, using the suspension-cultured tobacco cells. Here, we show that above DNA oligomers protect the cells of green paramecia from copper-induced cell death, suggesting that the phenomenon firstly observed in tobacco cells is not limited only within higher plants but it could be universally observable in wider range of organisms. PMID:26418558

  18. Opposite translocation of long and short oligomers through a nanopore

    NASA Astrophysics Data System (ADS)

    Getfert, Sebastian; Töws, Thomas; Reimann, Peter

    2013-06-01

    We consider elongated cylindrical particles, modeling, e.g., DNA fragments or nanorods, while they translocate under the action of an externally applied voltage through a solid state nanopore. Particular emphasis is put on the concomitant potential energy landscape encountered by the particle on its passage through the pore due to the complex interplay of various electrohydrodynamic effects beyond the realm of small Debye lengths. We find that the net potential energy difference across the membrane may be of opposite sign for short and long particles of equal diameters and charge densities (e.g., oligomers). Thermal noise thus leads to biased diffusion through the pore in opposite directions. By means of an additional membrane gate electrode it is even possible to control the specific particle length at which this transport inversion occurs.

  19. Formation of RNA oligomers on montmorillonite: site of catalysis

    NASA Technical Reports Server (NTRS)

    Ertem, G.; Ferris, J. P.

    1998-01-01

    Certain montmorillonites catalyze the self condensation of the 5'-phosphorimidazolide of nucleosides in pH 8 aqueous electrolyte solutions at ambient temperatures leading to formation of RNA oligomers. In order to establish the nature of the sites on montmorillonite responsible for this catalytic activity, oligomerization reactions were run with montmorillonites which had been selectively modified (I) at the edges by (a) fluoride treatment, (b) silylation, (c) metaphosphate treatment of the anion exchange sites (II) in the interlayer by (a) saturation with quaternary alkylammonium ions of increasing size, (b) aluminum polyoxo cations. High pressure liquid chromatography, HPLC, analysis of condensation products for their chain lengths and yields indicated that modification at the edges did not affect the catalytic activity to a significant extent, while blocking the interlayer strongly inhibited product formation.

  20. Electronic properties of acenes: Oligomer to polymer structure

    NASA Astrophysics Data System (ADS)

    Dos Santos, M. C.

    2006-07-01

    The conformations and electronic structures of long oligoacenes [ C2H2(C4H2)n , 20⩽n⩽23 ] and polyacene [(C8H4)x] were theoretically investigated through density functional theory adopting the hybrid B3LYP/6-31G(d) functional. The long oligoacenes present a cis conformation and solitonlike distortions along the chain. The defective regions having uniform bond lengths produce localized states on the top of the oligomer valence band. The spontaneous creation of bond alternation defects leads to high-spin magnetic ground states. The nonmagnetic state of polyacene presents a Peierls-distorted trans conformation which is lower in energy by a few meV per unit cell from the symmetric (nonalternating) state. The lowest-energy structure is predicted to present a cis pattern of bonds with alternation defects and a triplet state per unit cell.

  1. Mitigation of copper toxicity by DNA oligomers in green paramecia.

    PubMed

    Takaichi, Hiroshi; Comparini, Diego; Iwase, Junichiro; Bouteau, François; Mancuso, Stefano; Kawano, Tomonori

    2015-01-01

    Impact of transition metals which catalyze the generation of reactive oxygen species (ROS), on activation of cell death signaling in plant cells have been documented to date. Similarly in green paramecia (Paramecium bursaria), an aquatic protozoan species harboring symbiotic green algae in the cytoplasm, toxicities of various metallic ions have been documented. We have recently examined the effects of double-stranded GC-rich DNA fragments with copper-binding nature and ROS removal catalytic activity as novel plant cell-protecting agents, using the suspension-cultured tobacco cells. Here, we show that above DNA oligomers protect the cells of green paramecia from copper-induced cell death, suggesting that the phenomenon firstly observed in tobacco cells is not limited only within higher plants but it could be universally observable in wider range of organisms. PMID:26418558

  2. Transthyretin as both Sensor and Scavenger of Aβ Oligomers

    PubMed Central

    Yang, Dennis T.; Joshi, Gururaj; Cho, Patricia Y.; Johnson, Jeffrey A.; Murphy, Regina M.

    2013-01-01

    Transthyretin (TTR) is a homotetrameric transport protein, assembled from monomers that each contains two four-stranded β-sheets and a short α-helix and loop. In the tetramer, the ‘inner’ β-sheet forms a hydrophobic pocket while the helix and loop are solvent-exposed. Beta-amyloid (Aβ) aggregates bind to TTR, and the binding is significantly reduced in mutants L82A (on the loop) and L110A (on the inner β-sheet). Protection against Aβ toxicity was demonstrated for wild-type TTR but not L82A or L110A, providing a direct link between TTR-Aβ binding, and TTR-mediated cytoprotection. Protection is afforded at substoichiometric (1:100) TTR:Aβ molar ratios, and binding of Aβ to TTR is highest for partially aggregated materials and decreased for freshly-prepared or heavily aggregated Aβ, suggesting that TTR binds selectively to soluble toxic Aβ aggregates. A novel technique, nanoparticle tracking, is used to show that TTR arrests Aβ aggregation by both preventing formation of new aggregates and inhibiting growth of existing aggregates. TTR tetramers are normally quite stable; tetrameric structure is necessary for the protein’s transport functions, and mutations that decrease tetramer stability have been linked to TTR amyloid diseases. However, TTR monomers bind more Aβ than do tetramers, presumably because the hydrophobic ‘inner’ sheet is solvent-exposed upon tetramer disassembly. Wild-type and L110A tetramers, but not L82A, were destabilized when co-incubated with Aβ, suggesting that Aβ binding to L82 triggers tetramer dissociation. Taken together, these results suggest a novel mechanism of action for TTR: the EF helix/loop ‘senses’ the presence of soluble toxic Aβ oligomers, triggering destabilization of TTR tetramers and exposure of the hydrophobic inner sheet, which then ‘scavenges’ these toxic oligomers and prevents them from causing cell death PMID:23570378

  3. Characteristics of Amyloid-Related Oligomers Revealed by Crystal Structures of Macrocyclic [beta]-Sheet Mimics

    SciTech Connect

    Liu, Cong; Sawaya, Michael R.; Cheng, Pin-Nan; Zheng, Jing; Nowick, James S.; Eisenberg, David

    2011-09-20

    Protein amyloid oligomers have been strongly linked to amyloid diseases and can be intermediates to amyloid fibers. {beta}-Sheets have been identified in amyloid oligomers. However, because of their transient and highly polymorphic properties, the details of their self-association remain elusive. Here we explore oligomer structure using a model system: macrocyclic peptides. Key amyloidogenic sequences from A{beta} and tau were incorporated into macrocycles, thereby restraining them to {beta}-strands, but limiting the growth of the oligomers so they may crystallize and cannot fibrillate. We determined the atomic structures for four such oligomers, and all four reveal tetrameric interfaces in which {beta}-sheet dimers pair together by highly complementary, dry interfaces, analogous to steric zippers found in fibers, suggesting a common structure for amyloid oligomers and fibers. In amyloid fibers, the axes of the paired sheets are either parallel or antiparallel, whereas the oligomeric interfaces display a variety of sheet-to-sheet pairing angles, offering a structural explanation for the heterogeneity of amyloid oligomers.

  4. Fluorene- and benzofluorene-cored oligomers as low threshold and high gain amplifying media

    NASA Astrophysics Data System (ADS)

    Kazlauskas, Karolis; Kreiza, Gediminas; Bobrovas, Olegas; AdomÄ--nienÄ--, Ona; AdomÄ--nas, Povilas; Jankauskas, Vygintas; JuršÄ--nas, Saulius

    2015-07-01

    Deliberate control of intermolecular interactions in fluorene- and benzofluorene-cored oligomers was attempted via introduction of different-length alkyl moieties to attain high emission amplification and low amplified spontaneous emission (ASE) threshold at high oligomer concentrations. Containing fluorenyl peripheral groups decorated with different-length alkyl moieties, the oligomers were found to express weak concentration quenching of emission, yet excellent carrier drift mobilities (close to 10-2 cm2/V/s) in the amorphous films. Owing to the larger radiative decay rates (>1.0 × 109 s-1) and smaller concentration quenching, fluorene-cored oligomers exhibited down to one order of magnitude lower ASE thresholds at higher concentrations as compared to those of benzofluorene counterparts. The lowest threshold (300 W/cm2) obtained for the fluorene-cored oligomers at the concentration of 50 wt % in polymer matrix is among the lowest reported for solution-processed amorphous films in ambient conditions, what makes the oligomers promising for lasing application. Great potential in emission amplification was confirmed by high maximum net gain (77 cm-1) revealed for these compounds. Although the photostability of the oligomers was affected by photo-oxidation, it was found to be comparable to that of various organic lasing materials including some commercial laser dyes evaluated under similar excitation conditions.

  5. Fluorene- and benzofluorene-cored oligomers as low threshold and high gain amplifying media

    SciTech Connect

    Kazlauskas, Karolis Kreiza, Gediminas; Bobrovas, Olegas; Adomėnienė, Ona; Adomėnas, Povilas; Juršėnas, Saulius; Jankauskas, Vygintas

    2015-07-27

    Deliberate control of intermolecular interactions in fluorene- and benzofluorene-cored oligomers was attempted via introduction of different-length alkyl moieties to attain high emission amplification and low amplified spontaneous emission (ASE) threshold at high oligomer concentrations. Containing fluorenyl peripheral groups decorated with different-length alkyl moieties, the oligomers were found to express weak concentration quenching of emission, yet excellent carrier drift mobilities (close to 10{sup −2} cm{sup 2}/V/s) in the amorphous films. Owing to the larger radiative decay rates (>1.0 × 10{sup 9 }s{sup −1}) and smaller concentration quenching, fluorene-cored oligomers exhibited down to one order of magnitude lower ASE thresholds at higher concentrations as compared to those of benzofluorene counterparts. The lowest threshold (300 W/cm{sup 2}) obtained for the fluorene-cored oligomers at the concentration of 50 wt % in polymer matrix is among the lowest reported for solution-processed amorphous films in ambient conditions, what makes the oligomers promising for lasing application. Great potential in emission amplification was confirmed by high maximum net gain (77 cm{sup −1}) revealed for these compounds. Although the photostability of the oligomers was affected by photo-oxidation, it was found to be comparable to that of various organic lasing materials including some commercial laser dyes evaluated under similar excitation conditions.

  6. Rescue from tau-induced neuronal dysfunction produces insoluble tau oligomers

    PubMed Central

    Cowan, Catherine M.; Quraishe, Shmma; Hands, Sarah; Sealey, Megan; Mahajan, Sumeet; Allan, Douglas W.; Mudher, Amritpal

    2015-01-01

    Aggregation of highly phosphorylated tau is a hallmark of Alzheimer’s disease and other tauopathies. Nevertheless, animal models demonstrate that tau-mediated dysfunction/toxicity may not require large tau aggregates but instead may be caused by soluble hyper-phosphorylated tau or by small tau oligomers. Challenging this widely held view, we use multiple techniques to show that insoluble tau oligomers form in conditions where tau-mediated dysfunction is rescued in vivo. This shows that tau oligomers are not necessarily always toxic. Furthermore, their formation correlates with increased tau levels, caused intriguingly, by either pharmacological or genetic inhibition of tau kinase glycogen-synthase-kinase-3beta (GSK-3β). Moreover, contrary to common belief, these tau oligomers were neither highly phosphorylated, and nor did they contain beta-pleated sheet structure. This may explain their lack of toxicity. Our study makes the novel observation that tau also forms non-toxic insoluble oligomers in vivo in addition to toxic oligomers, which have been reported by others. Whether these are inert or actively protective remains to be established. Nevertheless, this has wide implications for emerging therapeutic strategies such as those that target dissolution of tau oligomers as they may be ineffective or even counterproductive unless they act on the relevant toxic oligomeric tau species. PMID:26608845

  7. The case for soluble Aβ oligomers as a drug target in Alzheimer's disease.

    PubMed

    Hefti, Franz; Goure, William F; Jerecic, Jasna; Iverson, Kent S; Walicke, Patricia A; Krafft, Grant A

    2013-05-01

    Soluble Aβ oligomers are now widely recognized as key pathogenic structures in Alzheimer's disease. They inhibit synaptic function, leading to early memory deficits and synaptic degeneration, and they trigger the downstream neuronal signaling responsible for phospho-tau Alzheimer's pathology. The marginal effects observed in recent clinical studies of solanezumab, targeting monomeric Aβ, and bapineuzumab, targeting amyloid plaques, prompted expert comments that drug discovery efforts in Alzheimer's disease should focus on soluble forms of Aβ rather than fibrillar Aβ deposits found in amyloid plaques. Accumulating scientific data suggest that soluble Aβ oligomers represent the optimal intervention target within the amyloid manifold. Active drug discovery approaches include antibodies that selectively capture soluble Aβ oligomers, selective modifiers of oligomer assembly, and receptor antagonists. The onset of symptomatic clinical benefit is expected to be rapid for such agents, because neuronal memory signaling should normalize on blockage of soluble Aβ oligomers. This key feature is not shared by amyloid-lowering therapeutics, and it should translate into streamlined clinical development for oligomer-targeting drugs. Oligomer-targeting drugs should also confer long-term disease modification and slowing of disease progression, because they prevent the downstream signaling responsible for phospho-tau mediated cytoskeletal degeneration. PMID:23582316

  8. Synthesis and Optoelectronic Properties of Thiophene Donor and Thiazole Acceptor Based Blue Fluorescent Conjugated Oligomers.

    PubMed

    Mahesh, K; Karpagam, S

    2016-07-01

    We report on the synthesis and characterization of low band gap, blue light emitting and thermal stable conjugated oligomer by Wittig condensation. Thiophene and thiazole type of donor-acceptor based series of conjugated oligomers, Oligo-4,5-bis-[2-[5-[2-thiophene-2-yl-vinyl]thiophene-2-yl]-vinyl]-thiazole (OBTV-TZ) and Oligo-2,4,5-Tris-[2-[5-[2-thiophene-2-yl-vinyl]thiophene-2-yl]-vinyl]-thiazole (OTTV-TZ) were synthesized. These oligomers were confirmed by FT-IR and (1)H-NMR and LC/MS analysis. The effect of the number of thiophene rings on the optical, electrochemical, thermal and morphological properties of the oligomers were systematically investigated. Both oligomers were exhibited almost same absorption wavelength in methanol solution (λmax = 365 nm and 369 nm) which indicates both oligomers illustrate similar intra molecular charge transfer (ICT). In solid state, the oligomers were exhibited broadening peaks with higher onset absorptions (λmax = 600 nm and 580 nm). The photoluminescence absorption spectrum of the oligomers was observed at 433 nm and 434 nm respectively in methanol solution with blue emission. The electrochemical band gap ([Formula: see text]) of the OBTV-TZ was 1.55 eV (low band gap) and OTTV-TZ was exhibited greater highest occupied molecular orbital (HOMO) value (E HOMO = -6.6 eV). Moreover morphological parameters of both oligomer film of 2D and 3D diagrams were observed by using AFM studies. PMID:27256285

  9. Modelling Ser129 Phosphorylation Inhibits Membrane Binding of Pore-Forming Alpha-Synuclein Oligomers

    PubMed Central

    Nübling, Georg Sebastian; Levin, Johannes; Bader, Benedikt; Lorenzl, Stefan; Hillmer, Andreas; Högen, Tobias; Kamp, Frits; Giese, Armin

    2014-01-01

    Background In several neurodegenerative diseases, hyperphosphorylation at position Ser129 is found in fibrillar deposits of alpha-synuclein (asyn), implying a pathophysiological role of asyn phosphorylation in neurodegeneration. However, recent animal models applying asyn phosphorylation mimics demonstrated a protective effect of phosphorylation. Since metal-ion induced asyn oligomers were identified as a potential neurotoxic aggregate species with membrane pore-forming abilities, the current study was undertaken to determine effects of asyn phosphorylation on oligomer membrane binding. Methods We investigated the influence of S129 phosphorylation on interactions of metal-ion induced asyn oligomers with small unilamellar lipid vesicles (SUV) composed of POPC and DPPC applying the phosphorylation mimic asyn129E. Confocal single-particle fluorescence techniques were used to monitor membrane binding at the single-particle level. Results Binding of asyn129E monomers to gel-state membranes (DPPC-SUV) is slightly reduced compared to wild-type asyn, while no interactions with membranes in the liquid-crystalline state (POPC-SUV) are seen for both asyn and asyn129E. Conversely, metal-ion induced oligomer formation is markedly increased in asyn129E. Surprisingly, membrane binding to POPC-SUV is nearly absent in Fe3+ induced asyn129E oligomers and markedly reduced in Al3+ induced oligomers. Conclusion The protective effect of pseudophosphorylation seen in animal models may be due to impeded oligomer membrane binding. Phosphorylation at Ser129 may thus have a protective effect against neurotoxic asyn oligomers by preventing oligomer membrane binding and disruption of the cellular electrophysiological equilibrium. Importantly, these findings put a new complexion on experimental pharmaceutical interventions against POLO-2 kinase. PMID:24911099

  10. Alzheimer's amyloid-β oligomers rescue cellular prion protein induced tau reduction via the Fyn pathway.

    PubMed

    Chen, Rong-Jie; Chang, Wei-Wei; Lin, Yu-Chun; Cheng, Pei-Lin; Chen, Yun-Ru

    2013-09-18

    Amyloid-β (Aβ) and tau are the pathogenic hallmarks in Alzheimer's disease (AD). Aβ oligomers are considered the actual toxic entities, and the toxicity relies on the presence of tau. Recently, Aβ oligomers have been shown to specifically interact with cellular prion protein (PrP(C)) where the role of PrP(C) in AD is still not fully understood. To investigate the downstream mechanism of PrP(C) and Aβ oligomer interaction and their possible relationships to tau, we examined tau expression in human neuroblastoma BE(2)-C cells transfected with murine PrP(C) and studied the effect under Aβ oligomer treatment. By Western blotting, we found that PrP(C) overexpression down-regulated tau protein and Aβ oligomer binding alleviated the tau reduction induced by wild type but not M128V PrP(C), the high AD risk polymorphic allele in human prion gene. PrP(C) lacking the Aβ oligomer binding site was incapable of rescuing the level of tau reduction. Quantitative RT-PCR showed the PrP(C) effect was attributed to tau reduction at the transcription level. Treatment with Fyn pathway inhibitors, Fyn kinase inhibitor PP2 and MEK inhibitor U0126, reversed the PrP(C)-induced tau reduction and Aβ oligomer treatment modulated Fyn kinase activity. The results suggested Fyn pathway regulated Aβ-PrP(C)-tau signaling. Overall, our results demonstrated that PrP(C) down-regulated tau via the Fyn pathway and the effect can be regulated by Aβ oligomers. Our study facilitated the understanding of molecular mechanisms among PrP(C), tau, and Aβ oligomers. PMID:23805846

  11. The Structure-Property Relationship of Poly(amide-imide)/Organoclay Nanocomposites

    NASA Astrophysics Data System (ADS)

    Faghihi, Khalil; Soleimani, Masoumeh; Shabanian, Meisam; Abootalebi, Ashraf Sadateh

    2011-06-01

    Surface treated montmorillonite (MMT) was used to prepare nanocomposites with poly(amide-imide) (PAI) 5 by solution intercalation technique with various percent of organoclay (5-15 mass %). Surface modification of the MMT was performed with Cloisite 20A for ample compatibilization with the PAI matrix. The PAI 5 chains were produced through polycondensation of 4,4-diamino diphenyl sulfone 4 with N-trimellitylimido-L-alanine 3 in a medium consisting of triphenyl phosphite, N-methyl-2-pyrolidone (NMP), pyridine and calcium chloride. The PAI-Nanocomposites morphology and clay dispersion were investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The effect of clay dispersion and the interaction between clay and PAI chains on the properties of PAI-Nanocomposites films were investigated by using UV-Vis spectroscopy, thermogravimetric analysis (TGA) and water uptake measurements. Thermal stability of nanocomposites increased relative to the neat polyamide with increasing organoclay content but water uptake of these materials decreased as compared to the neat polyamide indicating reduced permeability.

  12. Tribological behavior of blends of polyether ether ketone and polyether imide

    NASA Astrophysics Data System (ADS)

    Yoo, Jong H.; Eiss, Norman S., Jr.

    1993-04-01

    The friction and wear properties of injection-molded disks of PEEK/polyether imide (PEI) blends in dry sliding by a stainless steel ball were determined at room temperature at two normal loads and two sliding velocities for as-molded and annealed samples. The wear rates increased as the amount of PEI in the blends increased. The decrease in elongation to rupture caused by the increase in PEI content seemed to cause the wear mechanism to change from plastic grooving to fatigue wear. The wear rate increased as the normal load increased, although the relationship was nonlinear and related to the sliding speed and composition. The wear rate increased as the crystallinity of the PEEK component decreased. PEEK did not wear for the given test conditions. A steel ball plastically grooved the PEEK and there was no net loss of material. The wear rate was insensitive to change in velocity, except at the higher loads, for 50/50 and 0/100 blends. The friction coefficient was 0.1-0.16 when plastic grooving was occurring and 0.23-0.34 when wear particles were being formed.

  13. Self-assembly of organogels via new luminol imide derivatives: diverse nanostructures and substituent chain effect

    PubMed Central

    2013-01-01

    Luminol is considered as an efficient sycpstem in electrochemiluminescence (ECL) measurements for the detection of hydrogen peroxide. In this paper, new luminol imide derivatives with different alkyl substituent chains were designed and synthesized. Their gelation behaviors in 26 solvents were tested as novel low molecular mass organic gelators. It was shown that the length and number of alkyl substituent chains linked to a benzene ring in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. Longer alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscope and atomic force microscope observations revealed that the gelator molecules self-assemble into different micro/nanoscale aggregates from a dot, flower, belt, rod, and lamella to wrinkle with change of solvents. Spectral studies indicated that there existed different H-bond formations and hydrophobic forces, depending on the alkyl substituent chains in molecular skeletons. The present work may give some insight to the design and characteristic of new versatile soft materials and potential ECL biosensors with special molecular structures. PMID:23758979

  14. Ammonia Decomposition with Manganese Nitride-Calcium Imide Composites as Efficient Catalysts.

    PubMed

    Yu, Pei; Guo, Jianping; Liu, Lin; Wang, Peikun; Wu, Guotao; Chang, Fei; Chen, Ping

    2016-02-19

    Ammonia has high gravimetric and volumetric hydrogen densities and is, therefore, considered a promising carrier for the production of COx -free molecular H2 for forthcoming energy systems. Alkaline earth metals are generally regarded as structural promoters of catalysts and employed in numerous catalytic processes. Here, we report that calcium imide (CaNH) has a strong synergistic effect on Mn6 N5 in catalyzing the decomposition of NH3 , leading to a ca. 40 % drop in apparent activation energy. At 773 K, the H2 formation rate over a Mn6 N5 -11CaNH composite catalyst is about an order of magnitude higher than that of Mn6 N5 and comparable to the highly active Ni/SBA-15 and Ru/Al2 O3 catalysts. Analysis by means of temperature-programmed decomposition (TPD), X-ray diffraction (XRD), and X-ray absorption near edge spectroscopy (XANES) reveal that CaNH participates in the catalysis via forming a [Ca6 MnN5 ]-like intermediate, thus altering the reaction pathway and energetics. A two-step catalytic cycle, accounting for the synergy between CaNH and Mn6 N5 , is proposed. PMID:26914173

  15. Synthesis and characterization of cross-linkable polyurethane-imide electro-optic waveguide polymer

    NASA Astrophysics Data System (ADS)

    Wang, Long-De; Tang, Jie; Li, Ruo-Zhou; Zhang, Tong; Tong, Ling; Tang, Jing

    2016-01-01

    The novel electro-optic (EO) polymers of fluorinated cross-linkable polyurethane-imides (CLPUI) were designed and synthesized by polycondensation of azo chromophore C1 and C2, diisocyanate MDI, and aromatic dianhydride 6FDA. Molecular structural characterization for the resulting polymers was achieved by 1HNMR, FT-IR, elemental analysis, and gel permeation chromatography. The polymers exhibit good film-forming properties, high glass transition temperature ( T g) in the range of 193-200 °C, and thermal stability up to 290 °C. The polymers that possess a high EO coefficient (γ_{33} = 48 and 56 pm/V) at 1550 nm for poled polymer thin films were measured by the simple reflection technique. Excellent temporal stability and low optical losses in the range of 1.1-1.7 dB/cm at 1550 nm were observed for these polymers. Using the synthesized side-chain electro-optic CLPUI as the active core material and of a fluorinated polyimide as cladding material, we have designed and successfully fabricated the high-performance polymer waveguide Mach-Zehnder EO modulators.

  16. Processing and Properties of Vacuum Assisted Resin Transfer Molded Phenylethynyl Terminated Imide Composites

    NASA Technical Reports Server (NTRS)

    Cano, Roberto J.; Ghose, Sayata; Watson, Kent A.; Chunchu, Prasad B.; Jensen, Brian J.; Connell, John W.

    2012-01-01

    Polyimide composites are very attractive for applications that require a high strength to weight ratio and thermal stability. Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide resin systems that can be processed without the use of an autoclave for advanced aerospace applications. Due to their low melt viscosities and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature vacuum assisted resin transfer molding (HT-VARTM). VARTM has shown the potential to reduce the manufacturing cost of composite structures. In the current study, two PETI resins, LARC(Trademark) PETI-330 and LARC(Trademark) PETI-9, were infused into carbon fiber preforms at 260 C and cured at temperatures up to 371 C. Photomicrographs of polished cross sections were taken and void contents, determined by acid digestion, were below 4.5%. Mechanical properties including short block compression (SBC), compression after impact (CAI), and open hole compression (OHC) were determined at room temperature, 177 C, and 288 C. Both PETI-9 and PETI-330 composites demonstrated very good retention of mechanical properties at elevated temperatures. SBC and OHC properties after aging for 1000 hours at temperatures up to 288 C were also determined.

  17. Synthesis and Characterization of Group 4 Amide Chloride and Amide Imide Complexes

    SciTech Connect

    Yu, Xianghua; Cheng, Shu-Jian; Wang, Xiaoping; Chen, Xue-Tai; Xue, Zi-Ling

    2009-01-01

    Group 4 amide chloride complexes (Me2N)(2)Ht[N(SiMe3)(2)]Cl (1b), [(Me3Si)(2)N](2)MCl2Li(THF)(3)Cl (M = Zr, 2a; Hf, 2b), and [(Me3Si)(2)MCl2MCl2(THF) (M = Zr, 3a; Hf, 3b) and their X-ray crystal structures are reported. An improved synthesis of {[(Me3Si)(2)N]Ti(mu-NSiMe3)Cl}(2) (4) and its use to prepare amide imide {[(Me3Si)(2)N]Ti(mu-NSiMe3)(NMe2}(2) (5) are also presented. X-ray crystal structures of 5 and previously reported complexes (Me2N)(2)Zr[N(SiMe3)(2)]Cl (1a), [(Me3Si)(2)N](2)TiCl2 (6), and [(Me3Si)(2)N]ZrCl3(THF)(2) (7) have been determined. Both 1a and 1b are dimers {[(Me3Si)(2)N](2)TiCl2 (M = Zr, Hf) in the solid state.

  18. P-V-T Properties of Polyimides and Model Imide Compounds

    NASA Technical Reports Server (NTRS)

    Orwoll, Robert A.

    1997-01-01

    Aromatic polyimides are used as matrix resins in advanced composites, as high strength films, and as high-temperature adhesives, owing in part to their unusual thermal and chemical stability. The polyimides' desirable qualities of very high softening temperatures and negligibly small solubilities in and low permeabilities by most solvents have limited the kinds of fundamental studies that can be performed on these systems. Consequently, relationships between the molecular structure of polyimides and their bulk properties are not as well understood as might be expected given their widespread applications. In particular, the intermolecular forces in polyimides that play a critical role determining their densities, solubilities, viscosities, moduli, glass transitions, etc. are less well characterized for polyimides than for other widely used polymeric materials. The purpose of the present study is to obtain experimental data for establishing parameters that characterize the intermolecular forces in polyimides. We report here our studies on tractable low molecular-weight imides that contain the same structural features that are present in polyimide materials. We have measured equation-of-state properties and dipole moments for a variety of such systems in the liquid state. Both pure compounds and binary mixtures have been studied.

  19. Positively charged and bipolar layered poly(ether imide) nanofiltration membranes for water softening applications

    NASA Astrophysics Data System (ADS)

    Gassara, S.; Abdelkafi, A.; Quémener, D.; Amar, R. Ben; Deratani, A.

    2015-07-01

    Poly(ether imide) (PEI) ultrafiltration membranes were chemically modified with branched poly(ethyleneimine) to obtain nanofiltration (NF) membrane Cat PEI with a positive charge in the pH range below 9. An oppositely charged polyelectrolyte layer was deposited on the resulting membrane surface by using sodium polystyrene sulfonate (PSSNa) and sodium polyvinyl sulfonate (PVSNa) to prepare a bipolar layered membrane NF Cat PEI_PSS and Cat PEI_PVS having a negatively charged surface and positively charged pores. Cat PEI exhibited good performance to remove multivalent cations (more than 90% of Ca2+) from single salt solutions except in presence of sulfate ions. Adding an anionic polyelectrolyte layer onto the positively charged surface resulted in a significant enhancement of rejection performance even in presence of sulfate anions. Application of the prepared membranes in water softening of natural complex mixtures was successful for the different studied membranes and a large decrease of hardness was obtained. Moreover, Cat PEI_PSS showed a good selectivity for nitrate removal. Fouling experiments were carried out with bovine serum albumin, as model protein foulant. Cat PEI_PSS showed much better fouling resistance than Cat PEI with a quantitative flux recovery ratio.

  20. Ionic conduction properties of PVDF-HFP type gel polymer electrolytes with lithium imide salts

    SciTech Connect

    Saito, Yuria; Kataoka, Hiroshi; Capiglia, C.; Yamamoto, Hitoshi

    2000-03-09

    Conduction properties of gel polymer electrolytes composed of lithium imide salts, LiN(CF{sub 3}SO{sub 2}){sub 2}, LiN(C{sub 2}F{sub 5}SO{sub 2}){sub 2}, and PVDF-HFP copolymer were investigated using the pulsed-field gradient NMR and complex impedance techniques. The diffusion coefficients of the gel decreased with an increase in the polymer fraction in the gel. Carrier concentration exhibited 3 orders of magnitude variation in the fraction change in polymer from 80% to 20%. These results suggest that the polymer interacts with the electrolyte to affect the carrier concentration and mobility of the gel electrolytes. The interactive effect of polymer would be detected in the measurements of spin-lattice relaxation time (T{sub 1}). The deviation of the symmetric curve of the temperature dependence of T{sub 1} could be divided into two components, one was consistent with the component of solution and independent of the polymer fraction and the other depended on the polymer fraction in the gel.

  1. Initial adhesive screening of novel polyamide-imides and their copolymers

    NASA Technical Reports Server (NTRS)

    Progar, Donald J.; Dezern, James F.

    1988-01-01

    Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

  2. Self-assembly of organogels via new luminol imide derivatives: diverse nanostructures and substituent chain effect

    NASA Astrophysics Data System (ADS)

    Jiao, Tifeng; Huang, Qinqin; Zhang, Qingrui; Xiao, Debao; Zhou, Jingxin; Gao, Faming

    2013-06-01

    Luminol is considered as an efficient sycpstem in electrochemiluminescence (ECL) measurements for the detection of hydrogen peroxide. In this paper, new luminol imide derivatives with different alkyl substituent chains were designed and synthesized. Their gelation behaviors in 26 solvents were tested as novel low molecular mass organic gelators. It was shown that the length and number of alkyl substituent chains linked to a benzene ring in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. Longer alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscope and atomic force microscope observations revealed that the gelator molecules self-assemble into different micro/nanoscale aggregates from a dot, flower, belt, rod, and lamella to wrinkle with change of solvents. Spectral studies indicated that there existed different H-bond formations and hydrophobic forces, depending on the alkyl substituent chains in molecular skeletons. The present work may give some insight to the design and characteristic of new versatile soft materials and potential ECL biosensors with special molecular structures.

  3. Synthesis and characterization of new optically active poly(azo-ester-imide)s via interfacial polycondensation

    PubMed Central

    Zahmatkesh, Saeed; Roosta, Parniyan; Ruoho, Arnold E.

    2015-01-01

    N,N′-Pyromelliticdiimido-di-L-amino acids (1a–1d) were prepared from the reaction of pyromellitic dianhydride with the corresponding L-amino acids in a solution of glacial acetic acid/pyridine (3:2) at refluxing temperature. 4,4′-sulfonyl bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol, 4,4′-oxy bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol and 4,4′-methylene bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol, were prepared from 4,4′-diamino diphenyl sulfone, 4,4′-diamino diphenyl ether, 4,4′-diamino diphenyl methane, sodium nitrite and phenol following the general procedure of diazo coupling. Interfacial polycondensation method was used to prepare the corresponding poly(azo-ester-imid)s (PAEI1–12) in biphasic solution of water/dichloromethane. The resulting polymers (PAEIs) have been obtained in high yields having good inherent viscosities (0.32–0.57 dl g−1), optical activities and thermal stabilities. PMID:18563518

  4. Electronic structures and second hyperpolarizabilities of alkaline earth metal complexes end-capped with NA2 (A = H, Li, Na).

    PubMed

    Banerjee, Paramita; Nandi, Prasanta K

    2016-05-14

    The ground state structures and NLO properties of a number of alkaline earth metal complexes end-capped with NA2 groups (A = H, Li, Na) are calculated by employing the CAM-B3LYP, wB97XD and B2PLYP functionals along with MP2 and CCSD(T) for 6-311++G(d,p), 6-311++G(3df,3pd), aug-cc-pVTZ, aug-pc-2 and Hypol basis sets. The complexes are found to be significantly stable. The magnitude of second hyperpolarizability enhances appreciably with increase in the number of magnesium and calcium atoms in the chain, which has been indicated by the power law dependence γ = a + bn(c) with c values ranging from 2.4-4.3 for Mg and 2.4-3.7 for Ca complexes, respectively. The largest second-hyperpolarizability (10(9) au) is obtained for the complex Ca7(NNa2)2 at the CAM-B3LYP level. The two state model has been used to explain the variation of hyperpolarizabilities. PMID:27088138

  5. The Design of an Upgrade to the Level-1 Trigger for the Endcap Muon System of the CMS Experiment

    NASA Astrophysics Data System (ADS)

    Carver, Matthew

    2014-03-01

    We present a description of a novel track finding algorithm and associated hardware to be implemented as an upgrade to the L1-Trigger of the endcap muon system of the CMS experiment at the LHC in Geneva, Switzerland. To handle the increased luminosity and pile-up expected from the LHC after the current shutdown, the algorithm uses predefined patterns to identify tracks left by muons in the detector at a rate of 40 MHz. If multiple tracks are found they are sorted on the quality of the muon, defined by the number of hit detectors and straightness of the pattern. The track finding logic is pipelined such that the trigger will operate with no deadtime and has an available latency on the order of 1 μs to make a decision. The electronics board housing this logic makes use of state-of-the-art field-programmable gate arrays and large memory lookup tables to accomplish its track finding purpose. Preliminary studies on simulated data show roughly 99.5% efficiency for both single and multiple muon tracks.

  6. Performance of the Level-1 Muon Trigger for the CMS Endcap Muon System with Cosmic Rays and First LHC Beams

    NASA Astrophysics Data System (ADS)

    Gartner, Joseph

    2008-10-01

    We report on the performance of the level-1 muon trigger for the cathode strip chambers (CSCs) comprising the endcaps of the Compact Muon Solenoid (CMS) experiment. CMS is a general-purpose experiment designed to capitalize on the rich physics program of the Large Hadron Collider (LHC), which begins operation this autumn and which opens a window onto physics at the TeV energy scale. After many years of preparation, the CMS detectors and electronics have undergone a series of commissioning exercises involving the triggering and data acquisition of signals induced from cosmic ray muons, and most recently, first LHC beams. Here we report on the successful synchronization of signals from the 468 CSCs in the level-1 trigger path, and the successful triggering of the experiment based on those signals. The triggers that are provided by a specially built set of ``Track-Finder'' processors include triggers based on single CSC segments, tracks based on a coincidence of segments along a predefined road emanating from the beam collision point, and tracks parallel to the beam line that accept accelerator-induced halo muons. Evidence of the proper functioning of these triggers will be reported.

  7. Red-emitting π-conjugated oligomers infused single-wall carbon nanotube sheets

    NASA Astrophysics Data System (ADS)

    Fujimori, Toshihiko; Urita, Koki

    2016-04-01

    We demonstrate the one-step thermal fusion and infusion of pyrene molecules inside single-wall carbon nanotubes (SWCNTs). Despite the presence of metallic-SWCNTs, which behave as a quencher due to gapless electronic states, the nanohybrids consisting of pyrene and/or azupyrene oligomers infused SWCNT sheets exhibit red fluorescence by the ultraviolet, blue, and green light excitations. The wavelength-independent light-emitting behavior is explained by (1) infused PAH oligomers inside semiconducting-SWCNTs and (2) the peculiar π-π interaction through mixed π-conjugated state between the π-conjugated oligomers and non-armchair metallic-SWCNTs.

  8. Phenylethynyl Terminated Arylene Ether Oxadiazole and Triazole Oligomers and Their Cured Polymers

    NASA Technical Reports Server (NTRS)

    Thompson, C. M.; Hergenrother, P. M.

    2001-01-01

    Several novel phenylethynyl terminated arylene ether oligomers containing oxadiazole and triazole rings were prepared as part of an effort to develop high performance polymers with an attractive combination of properties (e.g. processability and mechanical performance) for future NASA applications. The oligomers displayed low melt viscosities and good solubilities. Thin films cast from solutions of the oligomers and cured for one hour at 350 C in air gave good tensile properties. Titanium to titanium (6Al-4V) tensile shear specimens were readily fabricated and provided moderate strengths. The chemistry and properties of these new materials are discussed.

  9. ACD toxin-produced actin oligomers poison formin-controlled actin polymerization

    PubMed Central

    Heisler, David B.; Kudryashova, Elena; Grinevich, Dmitry O.; Suarez, Cristian; Winkelman, Jonathan D.; Birukov, Konstantin G.; Kotha, Sainath R.; Parinandi, Narasimham L.; Vavylonis, Dimitrios; Kovar, David R.; Kudryashov, Dmitri S.

    2015-01-01

    The actin crosslinking domain (ACD) is an actin-specific toxin produced by several pathogens, including life-threatening spp. of Vibrio cholerae, Vibrio vulnificus, and Aeromonas hydrophila. Actin crosslinking by ACD is thought to lead to slow cytoskeleton failure owing to a gradual sequestration of actin in the form of nonfunctional oligomers. Here we found that ACD converted cytoplasmic actin into highly toxic oligomers that potently “poisoned” the ability of major actin assembly proteins, formins, to sustain actin polymerization. Thus, ACD can target the most abundant cellular protein by employing actin oligomers as secondary toxins to efficiently subvert cellular functions of actin while functioning at very low doses. PMID:26228148

  10. Migration into food of polyethylene terephthalate (PET) cyclic oligomers from PET microwave susceptor packaging.

    PubMed

    Begley, T H; Dennison, J L; Hollifield, H C

    1990-01-01

    A quantitative method has been developed to measure the migration of polyethylene terephthalate (PET) cyclic oligomers from aluminized PET susceptor film-type food packaging into several food types. Microwaveable French fries, popcorn, fish sticks, waffles and pizza sold in susceptor-type packaging were purchased in local markets, cooked according to package instructions and analysed for PET oligomers. Appropriate food blanks were cooked in glass containers. Quantities of PET oligomers found in the foods ranged from less than 0.012 micrograms/g to approximately 7 micrograms/g. PMID:2150379

  11. Dependence of tunneling current through a single molecule of phenylene oligomers on the molecular length.

    PubMed

    Wakamatsu, Satoshi; Fujii, Shintaro; Akiba, Uichi; Fujihira, Masamichi

    2003-01-01

    The electrical properties of single phenylene oligomers were studied in terms of the dependence of the tunneling current on the length of the oligomers using self-assembling techniques and scanning tunneling microscopy (STM). It is important to isolate single molecules in an insulating matrix for the measurement of the conductivity of the single molecule. We demonstrate here a novel self-assembled monolayer (SAM) matrix appropriate for isolation of the single molecules. A bicyclo[2.2.2]octane derivative was used for a SAM matrix, in which the single molecules were inserted at molecular lattice defects. The isolated single molecules of phenylene oligomers inserted in the SAM matrix were observed as protrusions in STM topography using a constant current mode. We measured the topographic heights of the molecular protrusions using STM and estimated the decay constant, beta, of the tunneling current through the single phenylene oligomers using a bilayer tunnel junction model. PMID:12801653

  12. The Anti-Prion Antibody 15B3 Detects Toxic Amyloid-β Oligomers.

    PubMed

    Stravalaci, Matteo; Tapella, Laura; Beeg, Marten; Rossi, Alessandro; Joshi, Pooja; Pizzi, Erika; Mazzanti, Michele; Balducci, Claudia; Forloni, Gianluigi; Biasini, Emiliano; Salmona, Mario; Diomede, Luisa; Chiesa, Roberto; Gobbi, Marco

    2016-07-01

    15B3 is a monoclonal IgM antibody that selectively detects pathological aggregates of the prion protein (PrP). We report the unexpected finding that 15B3 also recognizes oligomeric but not monomeric forms of amyloid-β (Aβ)42, an aggregating peptide implicated in the pathogenesis of Alzheimer's disease (AD). The 15B3 antibody: i) inhibits the binding of synthetic Aβ42 oligomers to recombinant PrP and neuronal membranes; ii) prevents oligomer-induced membrane depolarization; iii) antagonizes the inhibitory effects of oligomers on the physiological pharyngeal contractions of the nematode Caenorhabditis elegans; and iv) counteracts the memory deficits induced by intracerebroventricular injection of Aβ42 oligomers in mice. Thus this antibody binds to pathologically relevant forms of Aβ, and offers a potential research, diagnostic, and therapeutic tool for AD. PMID:27392850

  13. Beta-Amyloid Oligomers Activate Apoptotic BAK Pore for Cytochrome c Release

    PubMed Central

    Kim, Jaewook; Yang, Yoosoo; Song, Seung Soo; Na, Jung-Hyun; Oh, Kyoung Joon; Jeong, Cherlhyun; Yu, Yeon Gyu; Shin, Yeon-Kyun

    2014-01-01

    In Alzheimer’s disease, cytochrome c-dependent apoptosis is a crucial pathway in neuronal cell death. Although beta-amyloid (Aβ) oligomers are known to be the neurotoxins responsible for neuronal cell death, the underlying mechanisms remain largely elusive. Here, we report that the oligomeric form of synthetic Aβ of 42 amino acids elicits death of HT-22 cells. But, when expression of a bcl-2 family protein BAK is suppressed by siRNA, Aβ oligomer-induced cell death was reduced. Furthermore, significant reduction of cytochrome c release was observed with mitochondria isolated from BAK siRNA-treated HT-22 cells. Our in vitro experiments demonstrate that Aβ oligomers bind to BAK on the membrane and induce apoptotic BAK pores and cytochrome c release. Thus, the results suggest that Aβ oligomers function as apoptotic ligands and hijack the intrinsic apoptotic pathway to cause unintended neuronal cell death. PMID:25296312

  14. Preparative production of colominic acid oligomers via a facile microwave hydrolysis

    PubMed Central

    Patane, Jonathan; Trapani, Vincent; Villavert, Janice; McReynolds, Katherine Dawn

    2009-01-01

    The hydrolysis of colominic acid via microwave irradiation was studied for the production of short chain oligomers with a degree of polymerization (DP) of 1–6. This method was compared to the traditional acid hydrolytic method for the production of preparative quantities of short colominic acid oligomers. The oligomers were purified by size exclusion chromatography and characterized by 1H NMR. Optimal conditions for producing the dimer were found to be 12 minutes at 10% power in a 1000 Watt domestic microwave. This method is advantageous over the traditional technique in that the hydrolysis can be completed in just a few minutes, rather than hours, it is reproducible, and yields large quantities of the desirable short chain oligomers of colominic acid. PMID:19281967

  15. A semiempirical study of heterocycle oligomers and polymers in different dielectric media

    SciTech Connect

    Juerimaee, T.; Strandberg, M.; Karelson, M.

    1995-06-15

    Four common five-membered heterocycles-pyrrole, phosphole, thiophene, and furan- and their oligomers with the chain length of 2, 4, 6, and 10 units have been studied quantum chemically using the semiempirical PM3 parameterization. The oligomers of pyrrole and phosphole with the homolytically dissociated N-H bond and P-H bond, respectively, and oligomers of thiophene and furan with one electron removed per monomer unit (4n + 2 {pi}-electron bipolaron systems) have also been studied. The electronic properties of the respective polymers were extrapolated from the oligomer data. Bulk polymer effects on the electronic structure were modeled using the self-consistent reaction field theory in the multicavity approximation (MCa SCRF). 48 refs., 3 figs., 6 tabs.

  16. Cofilin Oligomer Formation Occurs In Vivo and Is Regulated by Cofilin Phosphorylation

    PubMed Central

    Goyal, Pankaj; Pandey, Dharmendra; Brünnert, Daniela; Hammer, Elke; Zygmunt, Marek; Siess, Wolfgang

    2013-01-01

    Background ADF/cofilin proteins are key regulators of actin dynamics. Their function is inhibited by LIMK-mediated phosphorylation at Ser-3. Previous in vitro studies have shown that dependent on its concentration, cofilin either depolymerizes F-actin (at low cofilin concentrations) or promotes actin polymerization (at high cofilin concentrations). Methodology/Principal Findings We found that after in vivo cross-linking with different probes, a cofilin oligomer (65 kDa) could be detected in platelets and endothelial cells. The cofilin oligomer did not contain actin. Notably, ADF that only depolymerizes F-actin was present mainly in monomeric form. Furthermore, we found that formation of the cofilin oligomer is regulated by Ser-3 cofilin phosphorylation. Cofilin but not phosphorylated cofilin was present in the endogenous cofilin oligomer. In vitro, formation of cofilin oligomers was drastically reduced after phosphorylation by LIMK2. In endothelial cells, LIMK-mediated cofilin phosphorylation after thrombin-stimulation of EGFP- or DsRed2-tagged cofilin transfected cells reduced cofilin aggregate formation, whereas inhibition of cofilin phosphorylation after Rho-kinase inhibitor (Y27632) treatment of endothelial cells promoted formation of cofilin aggregates. In platelets, cofilin dephosphorylation after thrombin-stimulation and Y27632 treatment led to an increased formation of the cofilin oligomer. Conclusion/Significance Based on our results, we propose that an equilibrium exists between the monomeric and oligomeric forms of cofilin in intact cells that is regulated by cofilin phosphorylation. Cofilin phosphorylation at Ser-3 may induce conformational changes on the protein-protein interacting surface of the cofilin oligomer, thereby preventing and/or disrupting cofilin oligomer formation. Cofilin oligomerization might explain the dual action of cofilin on actin dynamics in vivo. PMID:23951242

  17. Structure and properties of binary polystyrene-epoxy acrylate oligomer mixtures irradiated by electron beams

    SciTech Connect

    Lomonosova, N.V.

    1995-03-01

    The change in the structure of oriented polymer-oligomer systems based on polystyrene (PS) with M > 10{sup 6} and epoxy acrylate oligomers (aliphatic and aromatic) under irradiation by accelerated electrons was studied using birefringence, isometric heating, IR dichroism, and thermooptical analysis. Mechanical properties of these systems were investigated. It was found that, by adding aliphatic epoxy acrylate to PS and further irradiating this mixture, one can obtain both isotropic and oriented composites with higher strengths, elasticity moduli, and glass transition temperatures.

  18. Redox effects on the excited-state lifetime in chlorosomes and bacteriochlorophyll c oligomers.

    PubMed Central

    van Noort, P I; Zhu, Y; LoBrutto, R; Blankenship, R E

    1997-01-01

    Oligomers of [E,E] BChl CF (8, 12-diethyl bacteriochlorophyll c esterified with farnesol (F)) and [Pr,E] BChl CF (analogously, M methyl, Pr propyl) in hexane and aqueous detergent or lipid micelles were studied by means of steady-state absorption, time-resolved fluorescence, and electron spin resonance spectroscopy. The maximum absorption wavelength, excited-state dynamics, and electron spin resonance (EPR) linewidths are similar to those of native and reconstituted chlorosomes of Chlorobium tepidum. The maximum absorption wavelength of oligomers of [E,E] BChl CF was consistently blue-shifted as compared to that of [Pr,E] BChl CF oligomers, which is ascribed to the formation of smaller oligomers with [E,E] BChl CF than [Pr,E] BChl CF. Time-resolved fluorescence measurements show an excited-state lifetime of 10 ps or less in nonreduced samples of native and reconstituted chlorosomes of Chlorobium tepidum. Under reduced conditions the excited-state lifetime increased to tens of picoseconds, and energy transfer to BChl a or long-wavelength absorbing BChl c was observed. Oligomers of [E,E] BChl CF and [Pr,E] BChl CF in aqueous detergent or lipid micelles show a similar short excited-state lifetime under nonreduced conditions and an increase up to several tens of picoseconds upon reduction. These results indicate rapid quenching of excitation energy in nonreduced samples of chlorosomes and aqueous BChl c oligomers. EPR spectroscopy shows that traces of oxidized BChl c radicals are present in nonreduced and absent in reduced samples of chlorosomes and BChl c oligomers. This suggests that the observed short excited-state lifetimes in nonreduced samples of chlorosomes and BChl c oligomers may be ascribed to excited-state quenching by BChl c radicals. The narrow EPR linewidth suggests that the BChl c are arranged in clusters of 16 and 6 molecules in chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, respectively. PMID:8994616

  19. Computer simulations and theoretical aspects of the depletion interaction in protein-oligomer mixtures

    NASA Astrophysics Data System (ADS)

    Bončina, M.; Reščič, J.; Kalyuzhnyi, Yu. V.; Vlachy, V.

    2007-07-01

    The depletion interaction between proteins caused by addition of either uncharged or partially charged oligomers was studied using the canonical Monte Carlo simulation technique and the integral equation theory. A protein molecule was modeled in two different ways: either as (i) a hard sphere of diameter 30.0Å with net charge 0, or +5, or (ii) as a hard sphere with discrete charges (depending on the pH of solution) of diameter 45.4Å. The oligomers were pictured as tangentially jointed, uncharged, or partially charged, hard spheres. The ions of a simple electrolyte present in solution were represented by charged hard spheres distributed in the dielectric continuum. In this study we were particularly interested in changes of the protein-protein pair-distribution function, caused by addition of the oligomer component. In agreement with previous studies we found that addition of a nonadsorbing oligomer reduces the phase stability of solution, which is reflected in the shape of the protein-protein pair-distribution function. The value of this function in protein-protein contact increases with increasing oligomer concentration, and is larger for charged oligomers. The range of the depletion interaction and its strength also depend on the length (number of monomer units) of the oligomer chain. The integral equation theory, based on the Wertheim Ornstein-Zernike approach applied in this study, was found to be in fair agreement with Monte Carlo results only for very short oligomers. The computer simulations for a model mimicking the lysozyme molecule (ii) are in qualitative agreement with small-angle neutron experiments for lysozyme-dextran mixtures.

  20. Styrene-terminated polysulfone oligomers as matrix material for graphite reinforced composites: An initial study

    NASA Technical Reports Server (NTRS)

    Garcia, Dana; Bowles, Kenneth J.; Vannucci, Raymond D.

    1987-01-01

    Styrene terminated polysulfone oligomers are part of an oligomeric class of compounds with end groups capable of thermal polymerization. These materials can be used as matrices for graphite reinforced composites. The initial evaluation of styrene terminated polysulfone oligomer based composites are summarized in terms of fabrication methods, and mechanical and environmental properties. In addition, a description and evaluation is provided of the NASA/Industry Fellowship Program for Technology Transfer.

  1. Sub-cellular temporal and spatial distribution of electrotransferred LNA/DNA oligomer.

    PubMed

    Orio, Julie; Bellard, Elisabeth; Baaziz, Houda; Pichon, Chantal; Mouritzen, Peter; Rols, Marie-Pierre; Teissié, Justin; Golzio, Muriel; Chabot, Sophie

    2013-01-01

    Low biological activity and inefficient targeted delivery in vivo have hindered RNA interference (RNAi)-based therapy from realising its full clinical potential. To overcome these hurdles, progresses have been made to develop new technologies optimizing oligonucleotides chemistry on one hand and achieving its effective delivery on the other hand. In this report, we achieved, by using the electropulsation technique (EP), efficient cellular delivery of chemically-modified oligonucleotide: The locked nucleic acid (LNA)/DNA oligomer. We used single cell level confocal fluorescence microscopy to follow the spatial and temporal distribution of electrotransferred cyanine 5 (Cy5)-labeled LNA/DNA oligomer. We observed that EP allowed LNA/DNA oligomer cellular uptake providing the oligomer a rapid access to the cytoplasm of HeLa cells. Within a few minutes after electrotransfer, Cy5-LNA/DNA oligomers shuttle from cytoplasm to nucleus whereas in absence of pulses application, Cy5-LNA/DNA oligomers were not detected. We then observed a redistribution of the Cy5 fluorescence that accumulated over time into cytoplasmic organelles. To go further and to identify these compartments, we used the HeLa GFP-Rab7 cell line to visualise late endosomes, and lysosomal or mitochondrial specific markers. Our results showed that the EP technique allowed direct entry into the cytoplasm of the Cy5-LNA/DNA oligomer bypassing the endocytosic pathway. However, in absence of pulses application, Cy5-LNA/DNA oligomer were able to enter cells through the endocytosic pathway. We demonstrated that EP is an efficient technique for LNA-based oligonucleotides delivery offering strong advantages by avoiding the endolysosomal compartmentalization, giving a rapid and free access to the cytoplasm and the nucleus where they can find their targets. PMID:23946765

  2. Transthyretin suppresses the toxicity of oligomers formed by misfolded proteins in vitro.

    PubMed

    Cascella, Roberta; Conti, Simona; Mannini, Benedetta; Li, Xinyi; Buxbaum, Joel N; Tiribilli, Bruno; Chiti, Fabrizio; Cecchi, Cristina

    2013-12-01

    Although human transthyretin (TTR) is associated with systemic amyloidoses, an anti-amyloidogenic effect that prevents Aβ fibril formation in vitro and in animal models has been observed. Here we studied the ability of three different types of TTR, namely human tetramers (hTTR), mouse tetramers (muTTR) and an engineered monomer of the human protein (M-TTR), to suppress the toxicity of oligomers formed by two different amyloidogenic peptides/proteins (HypF-N and Aβ42). muTTR is the most stable homotetramer, hTTR can dissociate into partially unfolded monomers, whereas M-TTR maintains a monomeric state. Preformed toxic HypF-N and Aβ42 oligomers were incubated in the presence of each TTR then added to cell culture media. hTTR, and to a greater extent M-TTR, were found to protect human neuroblastoma cells and rat primary neurons against oligomer-induced toxicity, whereas muTTR had no protective effect. The thioflavin T assay and site-directed labeling experiments using pyrene ruled out disaggregation and structural reorganization within the discrete oligomers following incubation with TTRs, while confocal microscopy, SDS-PAGE, and intrinsic fluorescence measurements indicated tight binding between oligomers and hTTR, particularly M-TTR. Moreover, atomic force microscopy (AFM), light scattering and turbidimetry analyses indicated that larger assemblies of oligomers are formed in the presence of M-TTR and, to a lesser extent, with hTTR. Overall, the data suggest a generic capacity of TTR to efficiently neutralize the toxicity of oligomers formed by misfolded proteins and reveal that such neutralization occurs through a mechanism of TTR-mediated assembly of protein oligomers into larger species, with an efficiency that correlates inversely with TTR tetramer stability. PMID:24075940

  3. Causative factors for formation of toxic islet amyloid polypeptide oligomer in type 2 diabetes mellitus

    PubMed Central

    Jeong, Hye Rin; An, Seong Soo A

    2015-01-01

    Human islet amyloid polypeptide (h-IAPP) is a peptide hormone that is synthesized and cosecreted with insulin from insulin-secreting pancreatic β-cells. Recently, h-IAPP was proposed to be the main component responsible for the cytotoxic pancreatic amyloid deposits in patients with type 2 diabetes mellitus (T2DM). Since the causative factors of IAPP (or amylin) oligomer aggregation are not fully understood, this review will discuss the various forms of h-IAPP aggregation. Not all forms of IAPP aggregates trigger the destruction of β-cell function and loss of β-cell mass; however, toxic oligomers do trigger these events. Once these toxic oligomers form under abnormal metabolic conditions in T2DM, they can lead to cell disruption by inducing cell membrane destabilization. In this review, the various factors that have been shown to induce toxic IAPP oligomer formation will be presented, as well as the potential mechanism of oligomer and fibril formation from pro-IAPPs. Initially, pro-IAPPs undergo enzymatic reactions to produce the IAPP monomers, which can then develop into oligomers and fibrils. By this mechanism, toxic oligomers could be generated by diverse pathway components. Thus, the interconnections between factors that influence amyloid aggregation (eg, absence of PC2 enzyme, deamidation, reduction of disulfide bonds, environmental factors in the cell, genetic mutations, copper metal ions, and heparin) will be presented. Hence, this review will aid in understanding the fundamental causative factors contributing to IAPP oligomer formation and support studies for investigating novel T2DM therapeutic approaches, such as the development of inhibitory agents for preventing oligomerization at the early stages of diabetic pathology. PMID:26604727

  4. Causative factors for formation of toxic islet amyloid polypeptide oligomer in type 2 diabetes mellitus.

    PubMed

    Jeong, Hye Rin; An, Seong Soo A

    2015-01-01

    Human islet amyloid polypeptide (h-IAPP) is a peptide hormone that is synthesized and cosecreted with insulin from insulin-secreting pancreatic β-cells. Recently, h-IAPP was proposed to be the main component responsible for the cytotoxic pancreatic amyloid deposits in patients with type 2 diabetes mellitus (T2DM). Since the causative factors of IAPP (or amylin) oligomer aggregation are not fully understood, this review will discuss the various forms of h-IAPP aggregation. Not all forms of IAPP aggregates trigger the destruction of β-cell function and loss of β-cell mass; however, toxic oligomers do trigger these events. Once these toxic oligomers form under abnormal metabolic conditions in T2DM, they can lead to cell disruption by inducing cell membrane destabilization. In this review, the various factors that have been shown to induce toxic IAPP oligomer formation will be presented, as well as the potential mechanism of oligomer and fibril formation from pro-IAPPs. Initially, pro-IAPPs undergo enzymatic reactions to produce the IAPP monomers, which can then develop into oligomers and fibrils. By this mechanism, toxic oligomers could be generated by diverse pathway components. Thus, the interconnections between factors that influence amyloid aggregation (eg, absence of PC2 enzyme, deamidation, reduction of disulfide bonds, environmental factors in the cell, genetic mutations, copper metal ions, and heparin) will be presented. Hence, this review will aid in understanding the fundamental causative factors contributing to IAPP oligomer formation and support studies for investigating novel T2DM therapeutic approaches, such as the development of inhibitory agents for preventing oligomerization at the early stages of diabetic pathology. PMID:26604727

  5. Ultrarobust Thin-Film Devices from Self-Assembled Metal-Terpyridine Oligomers.

    PubMed

    Karipidou, Zoi; Branchi, Barbara; Sarpasan, Mustafa; Knorr, Nikolaus; Rodin, Vadim; Friederich, Pascal; Neumann, Tobias; Meded, Velimir; Rosselli, Silvia; Nelles, Gabriele; Wenzel, Wolfgang; Rampi, Maria Anita; von Wrochem, Florian

    2016-05-01

    Ultrathin molecular layers of Fe(II) -terpyridine oligomers allow the fabrication of large-area crossbar junctions by conventional electrode vapor deposition. The junctions are electrically stable for over 2.5 years and operate over a wide range of temperatures (150-360 K) and voltages (±3 V) due to the high cohesive energy and packing density of the oligomer layer. Electrical measurements reveal ideal Richardson-Shottky emission in surprising agreement with electrochemical, optical, and photoemission data. PMID:26970207

  6. A HRMS study of oligomer formation through aqueous phase photooxidation of methylvinyl-ketone and methacrolein

    NASA Astrophysics Data System (ADS)

    Salque-moreton, G.; Liu, Y.; Voisin, D.; Siekmann, F.; Renard, P.; Monod, A.; Thissen, R.

    2012-04-01

    Global estimates of secondary organic aerosol (SOA) formation flux show that the current descriptions miss a large fraction of the sources. Aqueous phase photochemistry in cloud droplets and deliquescent aerosol may provide some of this missing flux. Organic reactions in those media, particularly leading to higher molecular weight products thus need better understanding. Here, we investigated the aqueous phase photooxidation of methacrolein (MACR) and methylvinyl-ketone (MVK), which are the two main oxidation products of isoprene, the volatile organic compound (VOC) that is mostly emitted on the global scale. In our experiments, photolysis of H2O2 provided OH radicals whose reaction with MACR or MVK produced oligomers. Firstly, oligomers were analyzed using electrospray ionization coupled with high-resolution linear ion trap Orbitrap™ (Thermo Corp.) mass spectrometer (HRMS). This technique enabled to propose the unambiguous elemental composition of the produced compounds as data were collected for a mass range of m/z 50-2000 amu. The mass of oligomers increased strongly in positive and negative ionization modes when initial concentrations of MACR and MVK were increased from 2 to 20 mM. Typical regular patterns of oligomer formation were observed for both precursors, and extended up to 1400 amu. These patterns were very different from each other for the two precursors although both showed regular mass differences of 70 amu. In addition, we used a Kendrick analysis and identified more than 20 distinct chemical oligomer series produced by photooxidation of both MACR and MVK, some of which reaching more than 1400 amu. The HRMS investigations allowed us to propose a mechanism of production of oligomers. Upon nebulization, both oligomer systems produce SOA with a mass yield of 2-12%. This mass yield increases with reaction time and precursor concentration. Moreover, time evolution of the oligomer systems observed with the Orbitrap will be compared to HR

  7. Spectroscopic Identification of Cyclic Imide b2-Ions from Peptides Containing Gln and Asn Residues

    NASA Astrophysics Data System (ADS)

    Grzetic, Josipa; Oomens, Jos

    2013-08-01

    In mass-spectrometry based peptide sequencing, formation of b- and y-type fragments by cleavage of the amide C-N bond constitutes the main dissociation pathway of protonated peptides under low-energy collision induced dissociation (CID). The structure of the b 2 fragment ion from peptides containing glutamine (Gln) and asparagine (Asn) residues is investigated here by infrared ion spectroscopy using the free electron laser FELIX. The spectra are compared with theoretical spectra calculated using density functional theory for different possible isomeric structures as well as to experimental spectra of synthesized model systems. The spectra unambiguously show that the b2-ions do not possess the common oxazolone structure, nor do they possess the alternative diketopiperazine structure. Instead, cyclic imide structures are formed through nucleophilic attack by the amide nitrogen atom of the Gln and Asn side chains. The alternative pathway involving nucleophilic attack from the side-chain amide oxygen atom leading to cyclic isoimide structures, which had been suggested by several authors, can clearly be excluded based on the present IR spectra. This mechanism is perhaps surprising as the amide oxygen atom is considered to be the better nucleophile; however, computations show that the products formed via attack by the amide nitrogen are considerably lower in energy. Hence, b2-ions with Asn or Gln in the second position form structures with a five-membered succinimide or a six-membered glutarimide ring, respectively. b2-Ions formed from peptides with Asn in the first position are spectroscopically shown to possess the classical oxazolone structure.

  8. Effects of imidization and rubbing of polyimides on their surface free energy

    NASA Astrophysics Data System (ADS)

    Borycki, Jerzy; Okulska-Bozek, Malgorzata

    2002-06-01

    According to classical method polyimides were obtained in two-step polycondensation process via 10% solutions of poly(amic acid)s in dimethylformamide (DMF). Poly(amic acid)s were synthesized from chosen tetracarboxylic acids dianhydrides: pyromellitic (PMDA), 4,4'- (hexafluoroisopropylidene)diphthalic (6FDA), 4,4'- oxydiphthalic (ODPA) and aromatic diamines: 4,4'- oxydianiline (ODA), 1,4-phenylenediamine (PPD), 4,4'- ethylenedianiline (DAB), 4,4'-diaminodiphenylmethane (MDA), 4-methyl-1,3-phenylenediamine (MMPD) and 2,3,5,6- tetramethyl-1,4-phenylenediamine (DAD) in the first step of this reaction. The indium tin oxide (ITO)-glass plates or glass plates were spin-coated with the poly(amic acid)s solutions and dried. The polyimide layers were prepared by gradual heating in various temperatures (100 degree(s)C, 150 degree(s)C, 180 degree(s)C, 200 degree(s)C, 220 degree(s)C and 250 degree(s)C). The degree of imidization was estimated by means of IR spectroscopy. Obtained PI layers were mechanically modified by rubbing. Three various rubbing materials were used: cotton, silk and chamois leather. Surface free energy and its components of polymer layers were evaluated on the basis of their wet ability by standard liquids (diiodomethane, 1- bromonaphthalene, formamide, ethylene glycol, water). It was found that decrease of intensity of rubbing process yields to increase of contact angle for each of rubbing materials. Polyimide layers rubbed with chamois leather were characterized by the best wet ability. The rubbing process increase surface free energy of tested polyimide films.

  9. Rare-earth-metal methyl, amide, and imide complexes supported by a superbulky scorpionate ligand.

    PubMed

    Schädle, Dorothea; Maichle-Mössmer, Cäcilia; Schädle, Christoph; Anwander, Reiner

    2015-01-01

    The reaction of monomeric [(Tp(tBu,Me) )LuMe2 ] (Tp(tBu,Me) =tris(3-Me-5-tBu-pyrazolyl)borate) with primary aliphatic amines H2 NR (R=tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(Tp(tBu,Me) )LuMe(NHR)], the solid-state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(Tp(tBu,Me) )LnMe({μ2 -Me}AlMe3 )] (Ln=Y, Ho) reacted selectively and in high yield with H2 NR, according to methane elimination, to afford heterobimetallic complexes: [(Tp(tBu,Me) )Ln({μ2 -Me}AlMe2 )(μ2 -NR)] (Ln=Y, Ho). X-ray structure analyses revealed that the monomeric alkylaluminum-supported imide complexes were isostructural, featuring bridging methyl and imido ligands. Deeper insight into the fluxional behavior in solution was gained by (1) H and (13) C NMR spectroscopic studies at variable temperatures and (1) H-(89) Y HSQC NMR spectroscopy. Treatment of [(Tp(tBu,Me) )LnMe(AlMe4 )] with H2 NtBu gave dimethyl compounds [(Tp(tBu,Me) )LnMe2 ] as minor side products for the mid-sized metals yttrium and holmium and in high yield for the smaller lutetium. Preparative-scale amounts of complexes [(Tp(tBu,Me) )LnMe2 ] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(Tp(tBu,Me) )LnMe(AlMe4 )] with N,N,N',N'-tetramethylethylenediamine (tmeda). The solid-state structures of [(Tp(tBu,Me) )HoMe(AlMe4 )] and [(Tp(tBu,Me) )HoMe2 ] were analyzed by XRD. PMID:25392940

  10. Infusion Processing of Phenylethynyl Terminated Imides by High Temperature RTM and VARTM

    NASA Technical Reports Server (NTRS)

    Ghose, Sayata; Lewis, Todd M.; Cano, Roberto J.; Watson, Kent A.; Isayev, Avraam I.

    2011-01-01

    Fabrication of composite structures using infusion processes such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting both technologies for the fabrication of high temperature (HT) resistant composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using these high temperature out-of-autoclave processes. In the current study, two PETI resins, LARC(TradeMark) PETI-330 and LARC(TradeMark) PETI-8 have been used to make test specimens using both RTM and VARTM. For aerospace applications, a void fraction of less than 2% is desired. Traditionally, RTM has had the advantage over VARTM for generating composites with low void content. However, the process is limited in terms of size. Work at NASA LaRC has incorporated modifications to the thermal cycle used in laminate fabrication that have reduced the void content significantly (typically 1-3%) using the current HT-VARTM process. For composite fabrication by both RTM and VARTM, the resins were infused into three carbon fiber preforms (T650-35-3k 5HS, IM7-6k 5HS, and IM7-6k Uniweave) at 316 C and 260 C respectively and cured up to 371 C. The details of the RTM processing carried out at the University of Akron are discussed in this work along with a brief description of the HT-VARTM processing carried out at NASA-LaRC. Photomicrographs of the panels were taken and void contents were determined by acid digestion. Mechanical properties (short beam shear, SBS) of the panels fabricated by both infusion processes were determined at room temperature as well as at various elevated temperatures. The results of this work are presented herein.

  11. The role of imidoselenium(ii) chlorides in the formation of cyclic selenium imides via cyclocondensation.

    PubMed

    Karhu, Aino J; Pakkanen, Olli J; Rautiainen, J Mikko; Oilunkaniemi, Raija; Chivers, Tristram; Laitinen, Risto S

    2016-03-30

    The third member of the series of imidoselenium(ii) chlorides ClSe[N((t)Bu)Se]nCl (n = 3) () has been isolated from the cyclocondensation reaction of (t)BuNH2 and SeCl2 in THF in a molar ratio of ca. 3 : 1 and characterized in the form of two polymorphs and by single crystal X-ray analysis. The unusual structural features of this nine-atom chain are explained satisfactorily in terms of a bonding model that invokes intra-molecular secondary bonding interactions and hyperconjugation. The reaction of the bifunctional reagent ClSe[N((t)Bu)Se]2Cl () with (t)BuNH2 in THF occurs via concurrent pathways to give 1,3,5-Se3(N(t)Bu)3 () and 1,3-Se3(N(t)Bu)2 (). The energetics of the reactions of (t)BuNH2 and SeCl2 in THF have been calculated at the PBE0/def2-TZVPP level of theory in order to assess the feasibility of ClSe[N((t)Bu)Se]nCl (, n = 1-3) as intermediates in the formation of known cyclic selenium imides. DFT calculations were also employed to explore the energy profile of the pathway of the formation of the first member of the series ClSeN((t)Bu)SeCl () from (t)BuNH2 and SeCl2 in THF at 298 K. The neutral ligand ClSeN((t)Bu)SeCl () is Se,Se'-coordinated to the metal centre in the unusual adduct [PdCl2{Se,Se'-(SeCl)2N((t)Bu)}]·[PdCl2{Se,Se'-Se4(N(t)Bu)3}]·MeCN (·MeCN), which is the first metal complex of an imidoselenium(ii) chloride. PMID:26629863

  12. Effect of Zn(2+) ions on the assembly of amylin oligomers: insight into the molecular mechanisms.

    PubMed

    Wineman-Fisher, Vered; Miller, Yifat

    2016-08-01

    Amylin is an endocrine hormone and is a member of the family of amyloid peptides and proteins that emerge as potential scaffolds by self-assembly processes. Zn(2+) ions can bind to amylin peptides to form self-assembled Zn(2+)-amylin oligomers. In the current work the binding sites of Zn(2+) ions in the self-assembled amylin oligomers at various concentrations of zinc have been investigated. Our results yield two conclusions. First, in the absence of Zn(2+) ions polymorphic states (i.e. various classes of amylin oligomers) are obtained, but when Zn(2+) ions bind to amylin peptides to form Zn(2+)-amylin oligomers, the polymorphism is decreased, i.e. Zn(2+) ions bind only to specific classes of amylin. At low concentrations of Zn(2+) ions the polymorphism is smaller than at high concentrations. Second, the structural features of the self-assembled amylin oligomers are not affected by the presence of Zn(2+) ions. This study proposes new molecular mechanisms of the self-assembly of Zn(2+)-amylin oligomers. PMID:27425207

  13. Cellulose oligomers production and separation for the synthesis of new fully bio-based amphiphilic compounds.

    PubMed

    Billès, Elise; Onwukamike, Kelechukwu N; Coma, Véronique; Grelier, Stéphane; Peruch, Frédéric

    2016-12-10

    Cellulose oligomers are water-soluble, on the contrary to cellulose, which greatly increase their application range. In this study, cellulose oligomers were obtained from the acidic hydrolysis of cellulose with phosphoric acid. The global yield in water-soluble oligomers was around 23% with polymerization degree (DP) ranging from 1 to 12. The cellulose oligomers DP distribution was successfully reduced by differential solubilisation in methanol as one of the goals of this work was to avoid the use of a time-consuming full chromatographic separation. The methanol-soluble oligomers were mainly low DP (≤3). The oligomers of higher molar mass, composed of 42% of cellotetraose and 36% of cellopentaose, were then functionalized and coupled with stearic acid through azide-alkyne click chemistry to obtain amphiphilic compounds. The self-assembly of these new bio-based compounds was finally investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM) and their critical micellar concentration (CMC) was found to be in the same range as alkylmaltosides and alkylglucosides. PMID:27577903

  14. Low Molecular Weight Oligomers with Aromatic Backbone as Efficient Nonviral Gene Vectors.

    PubMed

    Luan, Chao-Ran; Liu, Yan-Hong; Zhang, Ji; Yu, Qing-Ying; Huang, Zheng; Wang, Bing; Yu, Xiao-Qi

    2016-05-01

    A series of oligomers were synthesized via ring-opening polymerization. Although the molecular weights of these oligomers are only ∼2.5 kDa, they could efficiently bind and condense DNA into nanoparticles. These oligomers gave comparable transfection efficiency (TE) to PEI 25 kDa, while their TE could even increase with the presence of serum, and up to 65 times higher TE than PEI was obtained. The excellent serum tolerance was also confirmed by TEM, flow cytometry, and BSA adsorption assay. Moreover, structure-activity relationship studies revealed some interesting factors. First, oligomers containing aromatic rings in the backbone showed better DNA binding ability. These materials could bring more DNA cargo into the cells, leading to much better TE. Second, the isomerism of the disubstituted phenyl group on the oligomer backbone has large effect on the transfection. The ortho-disubstituted ones gave at least 1 order of magnitude higher TE than meta- or para-disubstituted oligomers. Gel electrophoresis involving DNase and heparin indicated that the difficulty to release DNA might contribute to the lower TE of the latter. Such clues may help us to design novel nonviral gene vectors with high efficiency and biocompatibility. PMID:27077449

  15. Application of an Amyloid Beta Oligomer Standard in the sFIDA Assay.

    PubMed

    Kühbach, Katja; Hülsemann, Maren; Herrmann, Yvonne; Kravchenko, Kateryna; Kulawik, Andreas; Linnartz, Christina; Peters, Luriano; Wang, Kun; Willbold, Johannes; Willbold, Dieter; Bannach, Oliver

    2016-01-01

    Still, there is need for significant improvements in reliable and accurate diagnosis for Alzheimer's disease (AD) at early stages. It is widely accepted that changes in the concentration and conformation of amyloid-β (Aβ) appear several years before the onset of first symptoms of cognitive impairment in AD patients. Because Aβ oligomers are possibly the major toxic species in AD, they are a promising biomarker candidate for the early diagnosis of the disease. To date, a variety of oligomer-specific assays have been developed, many of them ELISAs. Here, we demonstrate the sFIDA assay, a technology highly specific for Aβ oligomers developed toward single particle sensitivity. By spiking stabilized Aβ oligomers to buffer and to body fluids from control donors, we show that the sFIDA readout correlates with the applied concentration of stabilized oligomers diluted in buffer, cerebrospinal fluid (CSF), and blood plasma over several orders of magnitude. The lower limit of detection was calculated to be 22 fM of stabilized oligomers diluted in PBS, 18 fM in CSF, and 14 fM in blood plasma. PMID:26858588

  16. Fluorinated arene, imide and unsaturated pyrrolidinone based donor acceptor conjugated polymers: Synthesis, structure-property and device studies

    NASA Astrophysics Data System (ADS)

    Liyanage, Arawwawala Don Thilanga

    the structure-property study of imide functionalized D-A polymers. Here we used thiophene-imide (TPD) as the acceptor moiety and prepare several D-A polymers by varying the donor units. When selecting the donor units, more priority goes to the fused ring systems. One main reason to use imide functionality is due to the, open position of the imide nitrogen, which provides an attaching position to alkyl substituent. Through this we can easily manipulate solubility and solid state packing arrangement. Also these imide acceptors have low-lying LUMOs due to their electron deficient nature and this will allow tuning the optical energy gap by careful choice of donor materials with different electron donating ability. The fourth chapter mainly contribute to the synthesis and structure property study of a completely novel electron acceptor moiety consist of a unsaturated pyrrolidinone unit known as Pechmann dye (PD) core. Pechmann dyes are closely related to the Indigo family. This can refer as 3-butenolide dimer connected via an alkene bridge, containing a benzene ring at the 5 and 5' positions of the lactone rings. We have prepared several D-A polymers using this PD system with benzodithiophene (BDT) as the donor unit. Different to common D-A polymers the HOMO and LUMO of the PD acceptor moiety are energetically located within the gap of the BDT, so that the electronic and optical properties (HOMO-LUMO transition) are dictated by the PD properties. The promising electronic properties, band gaps, high absorption coefficients and broad absorption suggest this new D-A polymers as an interesting donor material for organic solar cell (OSC) applications. KEY WORDS: Organic semiconductor materials, Self assembly, (opto)-electronic properties, Donor-Acceptor conjugated polymers, Fluorinated arene, 3,3'-bithiophene donors, Thiophene-imide (TPD), Pechmann dye, benzodithiophene, organic solar cell.

  17. GeneGenie: optimized oligomer design for directed evolution

    PubMed Central

    Swainston, Neil; Currin, Andrew; Day, Philip J.; Kell, Douglas B.

    2014-01-01

    GeneGenie, a new online tool available at http://www.gene-genie.org, is introduced to support the design and self-assembly of synthetic genes and constructs. GeneGenie allows for the design of oligonucleotide cohorts encoding the gene sequence optimized for expression in any suitable host through an intuitive, easy-to-use web interface. The tool ensures consistent oligomer overlapping melting temperatures, minimizes the likelihood of misannealing, optimizes codon usage for expression in a selected host, allows for specification of forward and reverse cloning sequences (for downstream ligation) and also provides support for mutagenesis or directed evolution studies. Directed evolution studies are enabled through the construction of variant libraries via the optional specification of ‘variant codons’, containing mixtures of bases, at any position. For example, specifying the variant codon TNT (where N is any nucleotide) will generate an equimolar mixture of the codons TAT, TCT, TGT and TTT at that position, encoding a mixture of the amino acids Tyr, Ser, Cys and Phe. This facility is demonstrated through the use of GeneGenie to develop and synthesize a library of enhanced green fluorescent protein variants. PMID:24782527

  18. Oligomer Formation of Tau Protein Hyperphosphorylated in Cells*

    PubMed Central

    Tepper, Katharina; Biernat, Jacek; Kumar, Satish; Wegmann, Susanne; Timm, Thomas; Hübschmann, Sabrina; Redecke, Lars; Mandelkow, Eva-Maria; Müller, Daniel J.; Mandelkow, Eckhard

    2014-01-01

    Abnormal phosphorylation (“hyperphosphorylation”) and aggregation of Tau protein are hallmarks of Alzheimer disease and other tauopathies, but their causative connection is still a matter of debate. Tau with Alzheimer-like phosphorylation is also present in hibernating animals, mitosis, or during embryonic development, without leading to pathophysiology or neurodegeneration. Thus, the role of phosphorylation and the distinction between physiological and pathological phosphorylation needs to be further refined. So far, the systematic investigation of highly phosphorylated Tau was difficult because a reliable method of preparing reproducible quantities was not available. Here, we generated full-length Tau (2N4R) in Sf9 cells in a well defined phosphorylation state containing up to ∼20 phosphates as judged by mass spectrometry and Western blotting with phospho-specific antibodies. Despite the high concentration in living Sf9 cells (estimated ∼230 μm) and high phosphorylation, the protein was not aggregated. However, after purification, the highly phosphorylated protein readily formed oligomers, whereas fibrils were observed only rarely. Exposure of mature primary neuronal cultures to oligomeric phospho-Tau caused reduction of spine density on dendrites but did not change the overall cell viability. PMID:25339173

  19. Deciphering aggregates, prefibrillar oligomers and protofibrils of cytochrome c.

    PubMed

    Amani, Samreen; Naeem, Aabgeena

    2014-08-01

    Aggregation of protein into insoluble intracellular complexes and inclusion bodies underlies the pathogenesis of human neurodegenerative diseases. Importance of cytochrome c (cyt c) arises from its involvement in apoptosis, sequence homology and for studying molecular evolution. A systemic investigation of polyethylene glycol (PEG) and trifluoroethanol (TFE) on the conformational stability of cyt c as a model hemeprotein was made using multi-methodological approach. Cyt c exists as molten globule (MG) at 60% PEG-400 and 40% TFE as confirmed by far-UV CD, attenuated total reflection Fourier transform infrared spectroscopy, Trp environment, 8-anilino-1-naphthalene-sulfonic acid (ANS) binding and blue shift in the soret band. Q-band splitting in MG states specifies conformational changes in the hydrophobic heme-binding pocket. Aggregates were detected at 90% PEG-400 and 50% TFE as confirmed by increase thioflavin T and ANS fluorescence and shift in Congo red absorbance. Detection of prefibrils and protofibrils at 90% PEG-400 and 50% TFE was possible after 72-h incubation. Single cell gel electrophoresis of prefibrils and protofibrils showed DNA damage confirming their toxicity and potential health hazards. Scanning electron microscopy and XRD analysis confirmed prefibrillar oligomers and protofibrils of cyt c. PMID:24729012

  20. Mapping eGFP Oligomer Mobility in Living Cell Nuclei

    PubMed Central

    Zwerger, Monika; Müller, Gabriele; Waldeck, Waldemar; Langowski, Jörg

    2009-01-01

    Movement of particles in cell nuclei can be affected by viscosity, directed flows, active transport, or the presence of obstacles such as the chromatin network. Here we investigate whether the mobility of small fluorescent proteins is affected by the chromatin density. Diffusion of inert fluorescent proteins was studied in living cell nuclei using fluorescence correlation spectroscopy (FCS) with a two-color confocal scanning detection system. We first present experiments exposing FCS-specific artifacts encountered in live cell studies as well as strategies to prevent them, in particular those arising from the choice of the fluorophore used for calibration of the focal volume, as well as temperature and acquisition conditions used for fluorescence fluctuation measurements. After defining the best acquisition conditions, we show for various human cell lines that the mobility of GFP varies significantly within the cell nucleus, but does not correlate with chromatin density. The intranuclear diffusional mobility strongly depends on protein size: in a series of GFP-oligomers, used as free inert fluorescent tracers, the diffusion coefficient decreased from the monomer to the tetramer much more than expected for molecules free in aqueous solution. Still, the entire intranuclear chromatin network is freely accessible for small proteins up to the size of eGFP-tetramers, regardless of the chromatin density or cell line. Even the densest chromatin regions do not exclude free eGFP-monomers or multimers. PMID:19347038

  1. Synthesis and Characterization of Poly (Arylene Ether Benzimidazole) Oligomers

    NASA Technical Reports Server (NTRS)

    Leonard, Michael J.

    1995-01-01

    Several poly(arylene ether benzimidazole) oligomers were prepared by the nucleophilic aromatic substitution reaction of a bisphenol benzimidazole and various alkyl-substituted aromatic bisphenols with an activated aromatic dihalide in N, N-dimethylacetarnide. Moderate to high molecular weight terpolymers were obtained in all cases, as shown by their inherent viscosities, which ranged from 0.50 to 0.87 dL g(sup -1). Glass transition temperatures (T(sub g)s) of polymer powders ranged from 267-280 C. Air-dried unoriented thin film T(sub g)s were markedly lower than those of the powders, whereas T(sub g)s of films dried in a nitrogen atmosphere were identical to those of the corresponding powders. In addition, air-dried films were dark amber and brittle, whereas nitrogen-dried films were yellow and creasable. Nitrogen-dried films showed slightly higher thin-film tensile properties than the air-dried films, as well.

  2. High performance hyperbranched polymers for improved processing and mechanical properties in thermoset composites

    NASA Astrophysics Data System (ADS)

    Marsh, Timothy

    Hyperbranched polymers, specifically hyperbranched poly(arylene ether ketone imide)s (HBPAEKI), are here studied as blend additives in thermoset composites to improve processing and ultimate performance properties of the composite. Monomer synthesis for HBPAEKI was further advanced in this work leading to higher yields, fewer reactions, and shorter production times. A five step synthetic method with an overall yield of 12% was reduced to a three step process with an overall yield of 38%. Polymer was synthesized under varying conditions and end group chemistry for use in thermoset blends. NMR characterization allowed for the assignment of chemical shifts in monomer and cataloguing of shifts in polymer for use in future work to characterize degree of branching. Cure kinetics of blends of HBPAEKI are explored through the use of differential scanning calorimetry (DSC) and chemorheology using small angle oscillatory shear. In a phenylethynyl terminated imide oligomer (PETI) thermoset resin, reactive phenylethynyl endcapped PAEKI (PEPAEKI) was found to retard cure while non reactive alkyl endcapped PAEKI was found to accelerate cure in DGEBA/DAH epoxy systems. Minimal effect was seen on early stage blend viscosity. Composite properties tested focused on the effect on bulk fracture and interfacial shear strength. No significant effect was seen in fracture toughness by SENB. XPS was used to verify that PEPAEKI was surface active to DGEBA/DDS epoxy/air interfaces to the complete exclusion of the epoxy at the surface. Evidence was also seen consistent with surface activity in alkyl endcapped PAEKI in DGEBA/DAH systems, although the contrast is much lower. Effect of alkyl endcapped HBPAEKI on interfacial shear strength was examined through the use of t-peel and single fiber fracture (SFF) techniques. In some systems, t-peel indicates a clear improvement in peel force, proportional to the blend concentration. In SFF, interfacial shear strength was found to be equal or slightly

  3. Improvement of hydrophilic properties of electrospun polyamide-imide fibrous mats by atmospheric-pressure plasma treatment

    NASA Astrophysics Data System (ADS)

    Park, Soo-Jin; Yop Rhee, Kyong; Jin, Fan-Long

    2015-03-01

    Polyamide-imide (PAI) fibrous mats were fabricated through electrospinning and further treated with atmospheric-pressure plasma. The surface characteristics of the PAI fibrous mats were examined to determine the effect of plasma treatment on the hydrophilic properties. FT-IR, X-ray photoelectron spectroscopy, and contact-angle analysis indicated that the hydrophilicity of the PAI fibrous mats increased upon the introduction of hydrophilic groups by plasma treatment. The concentration of functional groups, including oxygen, and the surface roughness of the PAI fibrous mats increased with increasing treatment time. The optimum plasma treatment time for surface modification of the PAI fibrous mats under atmospheric pressure was 120 s.

  4. Electrolyte Solvation and Ionic Association. V. Acetonitrile-Lithium Bis(fluorosulfonyl)imide (LiFSI) Mixtures

    SciTech Connect

    Han, Sang D.; Borodin, Oleg; Seo, D. M.; Zhou, Zhi B.; Henderson, Wesley A.

    2014-09-30

    Electrolytes with the salt lithium bis(fluorosulfonyl)imide (LiFSI) have been evaluated relative to comparable electrolytes with other lithium salts. Acetonitrile (AN) has been used as a model electrolyte solvent. The information obtained from the thermal phase behavior, solvation/ionic association interactions, quantum chemical (QC) calculations and molecular dynamics (MD) simulations (with an APPLE&P many-body polarizable force field for the LiFSI salt) of the (AN)n-LiFSI mixtures provides detailed insight into the coordination interactions of the FSI- anions and the wide variability noted in the electrolyte transport property (i.e., viscosity and ionic conductivity).

  5. Surface-enhanced spectroscopy on plasmonic oligomers assembled by AFM nanoxerography

    NASA Astrophysics Data System (ADS)

    Moutet, Pierre; Sangeetha, Neralagatta M.; Ressier, Laurence; Vilar-Vidal, Noelia; Comesaña-Hermo, Miguel; Ravaine, Serge; Vallée, Renaud A. L.; Gabudean, Ana Maria; Astilean, Simion; Farcau, Cosmin

    2015-01-01

    Surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) from individual plasmonic oligomers are investigated by confocal Raman micro-spectroscopy and time-resolved fluorescence microscopy coupled to steady state micro-spectroscopy. The nanoparticle (NP) oligomers are made of either ligand protected Au or Au@SiO2 core-shell colloidal NPs, which were assembled into ordered arrays by atomic force microscopy (AFM) nanoxerography. A strong dependence of the SERS emission on the polarization of incident light relative to the specific geometry of the plasmonic oligomer was observed. The SEF studies, performed on a large collection of NP oligomers of various known configurations showed interesting fluorophore decay rate modification and red-shift of the emission spectra. The experimental results are analyzed theoretically by employing finite-difference time-domain (FDTD) simulations on equivalent realistic structures, within the local density of optical states (LDOS) framework. The presented results, together with the proven potential of the LDOS approach as a useful common tool for analyzing both SERS and SEF effects further the general understanding of plasmon-related phenomena in nanoparticle oligomers.Surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) from individual plasmonic oligomers are investigated by confocal Raman micro-spectroscopy and time-resolved fluorescence microscopy coupled to steady state micro-spectroscopy. The nanoparticle (NP) oligomers are made of either ligand protected Au or Au@SiO2 core-shell colloidal NPs, which were assembled into ordered arrays by atomic force microscopy (AFM) nanoxerography. A strong dependence of the SERS emission on the polarization of incident light relative to the specific geometry of the plasmonic oligomer was observed. The SEF studies, performed on a large collection of NP oligomers of various known configurations showed interesting fluorophore decay rate

  6. Synthesis and self-assembly of terpyridine end-capped poly(N-isopropylacrylamide)-block-poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers.

    PubMed

    Brassinne, Jérémy; Poggi, Elio; Fustin, Charles-André; Gohy, Jean-François

    2015-04-01

    At the basis of smart self-assembled materials are lying small building blocks that can hierarchically assemble in response to stimuli, e.g., temperature or chemical species. In this context, the synthesis of terpyridine end-capped poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N-isopropylacrylamide) diblock copolymers via controlled radical copolymerization is reported here. The self-assembly of those copolymers is investigated in dilute aqueous solutions while varying temperature or adding transition metal ions, respectively, leading to the formation of micellar nanostructures or metallosupramolecular triblock copolymers. PMID:25491079

  7. Effects of magnesium ions on the stabilization of RNA oligomers of defined structures.

    PubMed Central

    Serra, Martin J; Baird, John D; Dale, Taraka; Fey, Bridget L; Retatagos, Kimberly; Westhof, Eric

    2002-01-01

    Optical melting was used to determine the stabilities of 11 small RNA oligomers of defined secondary structure as a function of magnesium ion concentration. The oligomers included helices composed of Watson-Crick base pairs, GA tandem base pairs, GU tandem base pairs, and loop E motifs (both eubacterial and eukaryotic). The effect of magnesium ion concentration on stability was interpreted in terms of two simple models. The first assumes an uptake of metal ion upon duplex formation. The second assumes nonspecific electrostatic attraction of metal ions to the RNA oligomer. For all oligomers, except the eubacterial loop E, the data could best be interpreted as nonspecific binding of metal ions to the RNAs. The effect of magnesium ions on the stability of the eubacterial loop E was distinct from that seen with the other oligomers in two ways. First, the extent of stabilization by magnesium ions (as measured by either change in melting temperature or free energy) was three times greater than that observed for the other helical oligomers. Second, the presence of magnesium ions produces a doubling of the enthalpy for the melting transition. These results indicate that magnesium ion stabilizes the eubacterial loop E sequence by chelating the RNA specifically. Further, these results on a rather small system shed light on the large enthalpy changes observed upon thermal unfolding of large RNAs like group I introns. It is suggested that parts of those large enthalpy changes observed in the folding of RNAs may be assigned to variations in the hydration states and types of coordinating atoms in some specifically bound magnesium ions and to an increase in the observed cooperativity of the folding transition due to the binding of those magnesium ions coupling the two stems together. Brownian dynamic simulations, carried out to visualize the metal ion binding sites, reveal rather delocalized ionic densities in all oligomers, except for the eubacterial loop E, in which precisely

  8. One-step, regioselective synthesis of up to 50-mers of RNA oligomers by montmorillonite catalysis.

    PubMed

    Huang, Wenhua; Ferris, James P

    2006-07-12

    5'-Nucleotides of A and U with the phosphate activated with 1-methyladenine generate RNA oligomers containing 40-50 monomers in 1 day in reactions catalyzed by montmorillonite. The corresponding monomers of C give oligomers that are 20-25-mers in length after a 9-day reaction. It was not possible to determine the chain lengths of the oligomers of G since they did not give well-defined bands on gel electrophoresis. Co-oligomers of A and U as well as A, U, G, and C were also prepared. The oligo(A)s formed were separated by gel electrophoresis, and the bands of the 7-39-mers were isolated, the 3',5'-phosphodiester bonds were cleaved by RNase T(2), and the terminal phosphate groups were cleaved with alkaline phosphatase. HPLC analysis revealed that the proportions of A(5)'pp(5)'A, A, A(2)'pA, and A(2)'pA(2)'pA formed were almost the same for the long and shorter oligomers. A similar structure analysis performed on the oligo(U)s established that the proportions of U(5)'pp(5)'U, U, U(2)'pU, U(2)'pU(2)'pU, U(2)'pU(2)'pU(2)'pU, and U(2)'pU(2)'pU(2)'pU(2)'pU did not vary with chain length. The structural analysis of the oligomers of A revealed that 74% of the phosphodiester bonds were 3',5'-linked a value slightly greater than 67% observed when imidazole was the activating group. 61% of the bonds in the U oligomers were 3',5'-linked, which is almost 3 times greater than the 20% measured when imidazole was the activating group. The potential significance of these data to the origin and early evolution of life is discussed. PMID:16819887

  9. Prestin forms oligomer with four mechanically independent subunits

    PubMed Central

    Wang, Xiang; Yang, Shiming; Jia, Shuping; He, David Z.Z.

    2010-01-01

    Prestin is the motor protein of cochlear outer hair cells (OHCs) with the unique capability of performing direct, rapid and reciprocal electromechanical conversion. Prestin consists of 744 amino acids with a molecular mass of ~81.4 kDa. The predicted membrane topology and molecular mass of a single prestin molecule appear inadequate to account for the size of intramembrane particles (IMPs) expressed in the OHC membrane. Although recent biochemical evidence suggests that prestin forms homo-oligomers, most likely as a tetramer, the oligomeric structure of prestin in OHCs remains unclear. We obtained the charge density of prestin in the gerbil OHCs by measuring their nonlinear capacitance (NLC). The average charge density (22,608 μm−2) measured was four times the average IMP density (5,686 μm−2) reported in the freeze-fracture study. This suggests that each IMP contains four prestin molecules, based on the general notion that each prestin transfers a single elementary charge. We subsequently compared the voltage dependency and the values of slope factor of NLC and somatic motility simultaneously measured from the same OHCs to determine whether NLC and motility are fully coupled and how prestin subunits function within the tetramer. We showed that the voltage dependency and slope factors of NLC and motility were not statistically different, suggesting that NLC and motility are fully coupled. The fact that the slope factor is the same between NLC and motility suggests that each prestin monomer in the tetramer is in parallel, each interacting independently with cytoplasmic or other partners to facilitate the mechanical response. PMID:20347723

  10. Phosphorodiamidate morpholino oligomers suppress mutant huntingtin expression and attenuate neurotoxicity.

    PubMed

    Sun, Xin; Marque, Leonard O; Cordner, Zachary; Pruitt, Jennifer L; Bhat, Manik; Li, Pan P; Kannan, Geetha; Ladenheim, Ellen E; Moran, Timothy H; Margolis, Russell L; Rudnicki, Dobrila D

    2014-12-01

    Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the huntingtin (HTT) gene. Disease pathogenesis derives, at least in part, from the long polyglutamine tract encoded by mutant HTT. Therefore, considerable effort has been dedicated to the development of therapeutic strategies that significantly reduce the expression of the mutant HTT protein. Antisense oligonucleotides (ASOs) targeted to the CAG repeat region of HTT transcripts have been of particular interest due to their potential capacity to discriminate between normal and mutant HTT transcripts. Here, we focus on phosphorodiamidate morpholino oligomers (PMOs), ASOs that are especially stable, highly soluble and non-toxic. We designed three PMOs to selectively target expanded CAG repeat tracts (CTG22, CTG25 and CTG28), and two PMOs to selectively target sequences flanking the HTT CAG repeat (HTTex1a and HTTex1b). In HD patient-derived fibroblasts with expanded alleles containing 44, 77 or 109 CAG repeats, HTTex1a and HTTex1b were effective in suppressing the expression of mutant and non-mutant transcripts. CTGn PMOs also suppressed HTT expression, with the extent of suppression and the specificity for mutant transcripts dependent on the length of the targeted CAG repeat and on the CTG repeat length and concentration of the PMO. PMO CTG25 reduced HTT-induced cytotoxicity in vitro and suppressed mutant HTT expression in vivo in the N171-82Q transgenic mouse model. Finally, CTG28 reduced mutant HTT expression and improved the phenotype of Hdh(Q7/Q150) knock-in HD mice. These data demonstrate the potential of PMOs as an approach to suppressing the expression of mutant HTT. PMID:25035419

  11. Spacer effect on nanostructures and self-assembly in organogels via some bolaform cholesteryl imide derivatives with different spacers

    PubMed Central

    2013-01-01

    In this paper, new bolaform cholesteryl imide derivatives with different spacers were designed and synthesized. Their gelation behaviors in 23 solvents were investigated, and some of them were found to be low molecular mass organic gelators. The experimental results indicated that these as-formed organogels can be regulated by changing the flexible/rigid segments in spacers and organic solvents. Suitable combination of flexible/rigid segments in molecular spacers in the present cholesteryl gelators is favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle and belt to fiber with the change of spacers and solvents. Spectral studies indicated that there existed different H-bond formations between imide groups and assembly modes, depending on the substituent spacers in molecular skeletons. The present work may give some insight into the design and character of new organogelators and soft materials with special molecular structures. PMID:24083361

  12. Homogeneous liquid-liquid extraction of rare earths with the betaine-betainium bis(trifluoromethylsulfonyl)imide ionic liquid system.

    PubMed

    Vander Hoogerstraete, Tom; Onghena, Bieke; Binnemans, Koen

    2013-01-01

    Several fundamental extraction parameters such as the kinetics and loading were studied for a new type of metal solvent extraction system with ionic liquids. The binary mixture of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water shows thermomorphic behavior with an upper critical solution temperature (UCST), which can be used to avoid the slower mass transfer due to the generally higher viscosity of ionic liquids. A less viscous homogeneous phase and mixing on a molecular scale are obtained when the mixture is heated up above 55 °C. The influence of the temperature, the heating and cooling times, were studied for the extraction of neodymium(III) with betaine. A plausible and equal extraction mechanism is proposed in bis(trifluoromethylsulfonyl)imide, nitrate, and chloride media. After stripping of the metals from the ionic liquid phase, a higher recovery of the ionic liquid was obtained by salting-out of the ionic liquid fraction lost by dissolution in the aqueous phase. The change of the upper critical solution temperature by the addition of HCl or betaine was investigated. In addition, the viscosity was measured below and above the UCST as a function of the temperature. PMID:24169434

  13. Homogeneous Liquid–Liquid Extraction of Rare Earths with the Betaine—Betainium Bis(trifluoromethylsulfonyl)imide Ionic Liquid System

    PubMed Central

    Hoogerstraete, Tom Vander; Onghena, Bieke; Binnemans, Koen

    2013-01-01

    Several fundamental extraction parameters such as the kinetics and loading were studied for a new type of metal solvent extraction system with ionic liquids. The binary mixture of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water shows thermomorphic behavior with an upper critical solution temperature (UCST), which can be used to avoid the slower mass transfer due to the generally higher viscosity of ionic liquids. A less viscous homogeneous phase and mixing on a molecular scale are obtained when the mixture is heated up above 55 °C. The influence of the temperature, the heating and cooling times, were studied for the extraction of neodymium(III) with betaine. A plausible and equal extraction mechanism is proposed in bis(trifluoromethylsulfonyl)imide, nitrate, and chloride media. After stripping of the metals from the ionic liquid phase, a higher recovery of the ionic liquid was obtained by salting-out of the ionic liquid fraction lost by dissolution in the aqueous phase. The change of the upper critical solution temperature by the addition of HCl or betaine was investigated. In addition, the viscosity was measured below and above the UCST as a function of the temperature. PMID:24169434

  14. Synthetic amyloid-beta oligomers impair long-term memory independently of cellular prion protein.

    PubMed

    Balducci, Claudia; Beeg, Marten; Stravalaci, Matteo; Bastone, Antonio; Sclip, Alessandra; Biasini, Emiliano; Tapella, Laura; Colombo, Laura; Manzoni, Claudia; Borsello, Tiziana; Chiesa, Roberto; Gobbi, Marco; Salmona, Mario; Forloni, Gianluigi

    2010-02-01

    Inability to form new memories is an early clinical sign of Alzheimer's disease (AD). There is ample evidence that the amyloid-beta (Abeta) peptide plays a key role in the pathogenesis of this disorder. Soluble, bio-derived oligomers of Abeta are proposed as the key mediators of synaptic and cognitive dysfunction, but more tractable models of Abeta-mediated cognitive impairment are needed. Here we report that, in mice, acute intracerebroventricular injections of synthetic Abeta(1-42) oligomers impaired consolidation of the long-term recognition memory, whereas mature Abeta(1-42) fibrils and freshly dissolved peptide did not. The deficit induced by oligomers was reversible and was prevented by an anti-Abeta antibody. It has been suggested that the cellular prion protein (PrP(C)) mediates the impairment of synaptic plasticity induced by Abeta. We confirmed that Abeta(1-42) oligomers interact with PrP(C), with nanomolar affinity. However, PrP-expressing and PrP knock-out mice were equally susceptible to this impairment. These data suggest that Abeta(1-42) oligomers are responsible for cognitive impairment in AD and that PrP(C) is not required. PMID:20133875

  15. Synthetic amyloid-β oligomers impair long-term memory independently of cellular prion protein

    PubMed Central

    Balducci, Claudia; Beeg, Marten; Stravalaci, Matteo; Bastone, Antonio; Sclip, Alessandra; Biasini, Emiliano; Tapella, Laura; Colombo, Laura; Manzoni, Claudia; Borsello, Tiziana; Chiesa, Roberto; Gobbi, Marco; Salmona, Mario; Forloni, Gianluigi

    2010-01-01

    Inability to form new memories is an early clinical sign of Alzheimer’s disease (AD). There is ample evidence that the amyloid-β (Aβ) peptide plays a key role in the pathogenesis of this disorder. Soluble, bio-derived oligomers of Aβ are proposed as the key mediators of synaptic and cognitive dysfunction, but more tractable models of Aβ−mediated cognitive impairment are needed. Here we report that, in mice, acute intracerebroventricular injections of synthetic Aβ1–42 oligomers impaired consolidation of the long-term recognition memory, whereas mature Aβ1–42 fibrils and freshly dissolved peptide did not. The deficit induced by oligomers was reversible and was prevented by an anti-Aβ antibody. It has been suggested that the cellular prion protein (PrPC) mediates the impairment of synaptic plasticity induced by Aβ. We confirmed that Aβ1–42 oligomers interact with PrPC, with nanomolar affinity. However, PrP-expressing and PrP knock-out mice were equally susceptible to this impairment. These data suggest that Aβ1–42 oligomers are responsible for cognitive impairment in AD and that PrPC is not required. PMID:20133875

  16. Indirect detection of ethylene glycol oligomers using a contactless conductivity detector in capillary liquid chromatography.

    PubMed

    Takeuchi, Toyohide; Sedyohutomo, Anang; Lim, Lee Wah

    2009-07-01

    Ethylene glycol oligomers were visualized by indirect conductimetric detection based on dilution of the mobile phase due to the analytes. A high electrical conductivity background was maintained by the addition of 5 mM sodium nitrate in the mobile phase, and the analytes were visualized by decreases in the background when they eluted. A capacitively coupled contactless conductivity detector was convenient to monitor effluents from the microcolumn with minimum extra-column band broadening. The signals as negative peaks were linear to the concentration of the analytes, and a concentration detection limit of 0.025% was achieved for tetraethylene glycol at S/N=3, corresponding to the mass detection limit of 38 ng for 0.15 microl injection. The logarithm of the retention factor of ethylene glycol oligomers was linear to the degree of polymerization (DP) as well as to the acetonitrile composition in the mobile phase. These situations allowed us to estimate the DP of eluted ethylene glycol oligomers by using a few oligomers with known DP. The dynamic reserve, defined as the ratio of the background to its noise level achieved under the present conditions, was 2.3 x 10(5) which was much larger than that achieved by UV absorption detection. The present method was applied to profile ethylene glycol oligomers contained in commercially available PEG reagents. PMID:19609021

  17. Nitrogen Containing Organic Compounds and Oligomers in Secondary Organic Aerosol Formed by Photooxidation of Isoprene

    SciTech Connect

    Nguyen, Tran B.; Laskin, Julia; Laskin, Alexander; Nizkorodov, Serguei

    2011-07-06

    Electrospray ionization high-resolution mass spectrometry (ESI HR-MS) was used to probe molecular structures of oligomers in secondary organic aerosol (SOA) generated in laboratory experiments on isoprene photooxidation at low- and high-NOx conditions. Up to 80-90% of the observed products are oligomers and up to 33% are nitrogen-containing organic compounds (NOC). We observe oligomers with up to 8 monomer units in length. Tandem mass spectrometry (MSn) confirms NOC compounds are organic nitrates and elucidates plausible chemical building blocks contributing to oligomer formation. Most organic nitrates are comprised of methylglyceric acid units. Other important multifunctional C2-C5 monomer units are identified including methylglyoxal, hydroxyacetone, hydroxyacetic acid, glycolaldehyde, and 2-methyltetrols. The majority of the NOC oligomers contain only one nitrate moiety resulting in a low average N:C ratio of 0.019. Average O:C ratios of the detected SOA compounds are 0.54 under the low-NOx conditions and 0.83 under the high-NOx conditions. Our results underscore the importance of isoprene photooxidation as a source of NOC in organic particulate matter.

  18. Mitochondrial Ca2+ Overload Underlies Aβ Oligomers Neurotoxicity Providing an Unexpected Mechanism of Neuroprotection by NSAIDs

    PubMed Central

    Sanz-Blasco, Sara; Valero, Ruth A.; Rodríguez-Crespo, Ignacio; Villalobos, Carlos; Núñez, Lucía

    2008-01-01

    Dysregulation of intracellular Ca2+ homeostasis may underlie amyloid β peptide (Aβ) toxicity in Alzheimer's Disease (AD) but the mechanism is unknown. In search for this mechanism we found that Aβ1–42 oligomers, the assembly state correlating best with cognitive decline in AD, but not Aβ fibrils, induce a massive entry of Ca2+ in neurons and promote mitochondrial Ca2+ overload as shown by bioluminescence imaging of targeted aequorin in individual neurons. Aβ oligomers induce also mitochondrial permeability transition, cytochrome c release, apoptosis and cell death. Mitochondrial depolarization prevents mitochondrial Ca2+ overload, cytochrome c release and cell death. In addition, we found that a series of non-steroidal anti-inflammatory drugs (NSAIDs) including salicylate, sulindac sulfide, indomethacin, ibuprofen and R-flurbiprofen depolarize mitochondria and inhibit mitochondrial Ca2+ overload, cytochrome c release and cell death induced by Aβ oligomers. Our results indicate that i) mitochondrial Ca2+ overload underlies the neurotoxicity induced by Aβ oligomers and ii) inhibition of mitochondrial Ca2+ overload provides a novel mechanism of neuroprotection by NSAIDs against Aβ oligomers and AD. PMID:18648507

  19. Methods for the Specific Detection and Quantitation of Amyloid-β Oligomers in Cerebrospinal Fluid.

    PubMed

    Schuster, Judith; Funke, Susanne Aileen

    2016-05-01

    Protein misfolding and aggregation are fundamental features of the majority of neurodegenerative diseases, like Alzheimer's disease (AD), Parkinson's disease, frontotemporal dementia, and prion diseases. Proteinaceous deposits in the brain of the patient, e.g., amyloid plaques consisting of the amyloid-β (Aβ) peptide and tangles composed of tau protein, are the hallmarks of AD. Soluble oligomers of Aβ and tau play a fundamental role in disease progression, and specific detection and quantification of the respective oligomeric proteins in cerebrospinal fluid may provide presymptomatically detectable biomarkers, paving the way for early diagnosis or even prognosis. Several studies on the development of techniques for the specific detection of Aβ oligomers were published, but some of the existing tools do not yet seem to be satisfactory, and the study results are contradicting. The detection of oligomers is challenging due to their polymorphous and unstable nature, their low concentration, and the presence of competing proteins and Aβ monomers in body fluids. Here, we present an overview of the current state of the development of methods for Aβ oligomer specific detection and quantitation. The methods are divided in the three subgroups: (i) enzyme linked immunosorbent assays (ELISA), (ii) methods for single oligomer detection, and (iii) others, which are mainly biosensor based methods. PMID:27163804

  20. Surface-enhanced spectroscopy on plasmonic oligomers assembled by AFM nanoxerography.

    PubMed

    Moutet, Pierre; Sangeetha, Neralagatta M; Ressier, Laurence; Vilar-Vidal, Noelia; Comesaña-Hermo, Miguel; Ravaine, Serge; Vallée, Renaud A L; Gabudean, Ana Maria; Astilean, Simion; Farcau, Cosmin

    2015-02-01

    Surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) from individual plasmonic oligomers are investigated by confocal Raman micro-spectroscopy and time-resolved fluorescence microscopy coupled to steady state micro-spectroscopy. The nanoparticle (NP) oligomers are made of either ligand protected Au or Au@SiO2 core-shell colloidal NPs, which were assembled into ordered arrays by atomic force microscopy (AFM) nanoxerography. A strong dependence of the SERS emission on the polarization of incident light relative to the specific geometry of the plasmonic oligomer was observed. The SEF studies, performed on a large collection of NP oligomers of various known configurations showed interesting fluorophore decay rate modification and red-shift of the emission spectra. The experimental results are analyzed theoretically by employing finite-difference time-domain (FDTD) simulations on equivalent realistic structures, within the local density of optical states (LDOS) framework. The presented results, together with the proven potential of the LDOS approach as a useful common tool for analyzing both SERS and SEF effects further the general understanding of plasmon-related phenomena in nanoparticle oligomers. PMID:25553777

  1. Parametrization of the Gay-Berne potential for conjugated oligomer with a high aspect ratio

    NASA Astrophysics Data System (ADS)

    Lee, Cheng K.; Hua, Chi C.; Chen, Show A.

    2010-08-01

    The Gay-Berne (GB) potential has been a popular semiempirical model for describing the short-range intermolecular forces for a wide variety of aspherical molecules, including liquid crystals and anisotropic colloids, with generally small molecular dimensions and low aspect ratios (<5). This study evaluates the parametrization of the GB potential for a high-aspect-ratio (=10) oligomer belonging to a model conjugated polymer. We elaborate that the semiflexibility associated with a large oligomer species demands a variant umbrella-sampling scheme in establishing the potentials of mean force (PMFs) for four pair ellipsoid arrangements typically utilized to parametrize the GB potential. The model ellipsoid so constructed is shown to capture the PMFs of essential intermediate arrangements as well, and, according to the results of simplex optimizations, recommendations are given for the minimum set of parameters to be included in the optimization of a large oligomer or particulate species. To further attest the parametrized GB potential, the coarse-grained (CG) Monte Carlo simulations employing the GB potential and the back-mapped, full-atom atomistic molecular dynamics (AMD) simulations were performed for a dense oligomer system at two representative system temperatures. The results indicated that the CG simulations can capture, with exceptional computational efficiency, the AMD predictions with good thermal transferability. In future perspectives, we remark on potential applications to construct efficient, parameter-free CG models for capturing fundamental material properties of large oligomer/particulate species as well as long-chain conjugated polymers.

  2. Sequestration of toxic oligomers by HspB1 as a cytoprotective mechanism.

    PubMed

    Ojha, Juhi; Masilamoni, Gunasingh; Dunlap, David; Udoff, Ross A; Cashikar, Anil G

    2011-08-01

    Small heat shock proteins (sHsps) are molecular chaperones that protect cells from cytotoxic effects of protein misfolding and aggregation. HspB1, an sHsp commonly associated with senile plaques in Alzheimer's disease (AD), prevents the toxic effects of Aβ aggregates in vitro. However, the mechanism of this chaperone activity is poorly understood. Here, we observed that in two distinct transgenic mouse models of AD, mouse HspB1 (Hsp25) localized to the penumbral areas of plaques. We have demonstrated that substoichiometric amounts of human HspB1 (Hsp27) abolish the toxicity of Aβ oligomers on N2a (mouse neuroblastoma) cells. Using biochemical methods, spectroscopy, light scattering, and microscopy methods, we found that HspB1 sequesters toxic Aβ oligomers and converts them into large nontoxic aggregates. HspB1 was overexpressed in N2a cells in response to treatment with Aβ oligomers. Cultured neurons from HspB1-deficient mice were more sensitive to oligomer-mediated toxicity than were those from wild-type mice. Our results suggest that sequestration of oligomers by HspB1 constitutes a novel cytoprotective mechanism of proteostasis. Whether chaperone-mediated cytoprotective sequestration of toxic aggregates may bear clues to plaque deposition and may have potential therapeutic implications must be investigated in the future. PMID:21670152

  3. Prefibrillar transthyretin oligomers and cold stored native tetrameric transthyretin are cytotoxic in cell culture

    SciTech Connect

    Soergjerd, Karin; Klingstedt, Therese; Lindgren, Mikael; Kagedal, Katarina; Hammarstroem, Per

    2008-12-26

    Recent studies suggest that soluble, oligomeric species, which are intermediates in the fibril formation process in amyloid disease, might be the key species in amyloid pathogenesis. Soluble oligomers of human wild type transthyretin (TTR) were produced to elucidate oligomer properties. Employing ThT fluorescence, time-resolved fluorescence anisotropy of pyrene-labeled TTR, chemical cross-linking, and electron microscopy we demonstrated that early formed soluble oligomers (within minutes) from A-state TTR comprised on the average 20-30 TTR monomers. When administered to neuroblastoma cells these early oligomers proved highly cytotoxic and induced apoptosis after 48 h of incubation. More mature fibrils (>24 h of fibrillation) were non-toxic. Surprisingly, we also found that native tetrameric TTR, when purified and stored under cold conditions (4 deg. C) was highly cytotoxic. The effect could be partially restored by increasing the temperature of the protein. The cytotoxic effects of native tetrameric TTR likely stems from a hitherto unexplored low temperature induced rearrangement of the tetramer conformation that possibly is related to the conformation of misfolded TTR in amyloigogenic oligomers.

  4. Parametrization of the Gay-Berne potential for conjugated oligomer with a high aspect ratio.

    PubMed

    Lee, Cheng K; Hua, Chi C; Chen, Show A

    2010-08-14

    The Gay-Berne (GB) potential has been a popular semiempirical model for describing the short-range intermolecular forces for a wide variety of aspherical molecules, including liquid crystals and anisotropic colloids, with generally small molecular dimensions and low aspect ratios (<5). This study evaluates the parametrization of the GB potential for a high-aspect-ratio (=10) oligomer belonging to a model conjugated polymer. We elaborate that the semiflexibility associated with a large oligomer species demands a variant umbrella-sampling scheme in establishing the potentials of mean force (PMFs) for four pair ellipsoid arrangements typically utilized to parametrize the GB potential. The model ellipsoid so constructed is shown to capture the PMFs of essential intermediate arrangements as well, and, according to the results of simplex optimizations, recommendations are given for the minimum set of parameters to be included in the optimization of a large oligomer or particulate species. To further attest the parametrized GB potential, the coarse-grained (CG) Monte Carlo simulations employing the GB potential and the back-mapped, full-atom atomistic molecular dynamics (AMD) simulations were performed for a dense oligomer system at two representative system temperatures. The results indicated that the CG simulations can capture, with exceptional computational efficiency, the AMD predictions with good thermal transferability. In future perspectives, we remark on potential applications to construct efficient, parameter-free CG models for capturing fundamental material properties of large oligomer/particulate species as well as long-chain conjugated polymers. PMID:20707586

  5. Effects of end-capped acceptors subject to subtle structural changes on solution-processable small molecules for organic solar cells.

    PubMed

    Deng, Dan; Zhang, Yajie; Zhu, Lingyun; Zhang, Jianqi; Lu, Kun; Wei, Zhixiang

    2015-04-14

    Self-assembly is crucial for small molecular organic solar cells, which are extremely sensitive to the molecular structure. In this work, three subtle structural changed end-capped acceptors with increased electron withdrawing ability, named octyl 2-cyanoacetate (=CNCOOC8H17), 3-oxoundecanenitrile (=CNCOC8H17), and 2-(octylsulfonyl) acetonitrile (=CNSOOC8H17), were synthesized and introduced into a planar conjugated backbone using ethylhexyl-thiophene substituted benzodithiophene (TBDT) as a core and trithiophene as a π-bridge (labelled M1, M2 and M3, respectively). Their effects on absorption, thermal properties, and morphologies were studied and compared. In particular, the molecular packing of the three materials varied significantly, and the hole mobilities differed by orders of magnitude. As a result, the fill factors of devices varied from 52% to 72%. Combining the effects of electron-withdrawing capability and molecular packing, the power conversion efficiencies of the optimized devices increased from 3.0% for M3 to 6.4% for M1 and M2. The relationship between end-capped acceptors and photovoltaic properties would generate valuable insights into further producing more efficient solution-processable organic solar cells. PMID:25742902

  6. A simple method for the synthesis of a polar-embedded and polar-endcapped reversed-phase chromatographic packing with low activity of residue silanols.

    PubMed

    Liu, Hai-Yan; Li, Zhi-Yong; Liu, Dan; Xue, Ying-Wen; Shi, Zhi-Guo

    2016-04-22

    Octadecyl bonded silica (ODS) is the most popular packing for reversed-phase chromatography. However, it generally demonstrates bad resolution for polar analytes because of the residue silanols and its poor stability in aqueous mobile phase. To address the problem, a new reversed-phase packing containing both polar-embedded and polar-endcapped moieties was proposed. It was prepared by a very simple method, in which the epoxide addition reaction of 3-glycidoxypropyltrimethoxysilane with 1-octadecanethiol proceeded simultaneously with the reaction of silane coupling onto silica particles. By controlling the molecular ratio of 3-glycidoxypropyltrimethoxysilane to 1-octadecanethiol higher than 1.0 (1.56 for the present study), both polar-embedded and polar-endcapped moieties were achieved onto the packing. The performance of the packing was evaluated in detail. The results demonstrated that neutral, acidic and basic analytes were well separated on the packing. The column efficiency for phenanthrene was 34,200 theoretical plates per meter. In addition, four nucleotides can be separated in 100% phosphate buffered saline solution with good reproducibility, which indicates the packing has good stability in aqueous mobile phase. Amitriptyline, a typical basic analytes, was eluted out with relatively symmetric peak shape (asymmetry factor of 1.36), which implies that the packing has not suffered from the negative effect of residue silanols significantly. Good stability in buffer solution of pH ranging from 2.0 to 10.0 was also documented for the packing. PMID:27033982

  7. Construction of a lithium ion transport network in cathode with lithiated bis(benzene sulfonyl)imide based single ion polymer ionomers

    NASA Astrophysics Data System (ADS)

    Pan, Qiyun; Zhang, Wenchao; Pan, Meize; Zhang, Baodan; Zeng, Danli; Sun, Yubao; Cheng, Hansong

    2015-06-01

    We demonstrate a novel method to construct a lithium ion transport network in cathode materials by replacing PVDF with lithiated poly(bis(4-carbonyl benzene sulfonyl)imide-co-bis(4-amino benzene sulfonyl)imide) as the binder. The single ion conducting polymer was synthesized via polycondensation of bis(4-carbonyl benzene sulfonyl)imide and bis(4-amino benzene sulfonyl)imide followed by lithium ion exchange. By blending the ionomers with LiFePO4 and acetylene carbon, the ionic network was well constructed, resulting in a maximum use of active cathode material inside the cathode. The membrane of the polymer electrolyte exhibits an ionic conductivity of 0.14 mS cm-1 at room temperature, a high ion transference number of 0.92 and a wide electrochemical window of 4.5 V (vs. Li+/Li). A lithium ion battery assembled with the single ion conducting polymer electrolyte delivers excellent performance at room temperature with various C-rates.

  8. Rh(III)-Catalyzed C-C/C-N Coupling of Imidates with α-Diazo Imidamide: Synthesis of Isoquinoline-Fused Indoles.

    PubMed

    Wang, He; Li, Lei; Yu, Songjie; Li, Yunyun; Li, Xingwei

    2016-06-17

    Imidate esters and diazo compounds have been established as bifunctional substrates for the construction of biologically active fused heterocycles via rhodium-catalyzed C-H activation and C-C/C-N coupling. This reaction occurs under mild conditions with high efficiency, step economy, and low catalyst loading. PMID:27280947

  9. Cooperative Co(III)/Cu(II)-Catalyzed C-N/N-N Coupling of Imidates with Anthranils: Access to 1H-Indazoles via C-H Activation.

    PubMed

    Li, Lei; Wang, He; Yu, Songjie; Yang, Xifa; Li, Xingwei

    2016-08-01

    Cooperative cobalt- and copper-catalyzed C-H activation of imidate esters and oxidative coupling with anthranils allowed efficient synthesis of 1H-indazoles in the absence of metal oxidants. The anthranil acts as a convenient aminating reagent as well as an organic oxidant in this transformation. The copper catalyst likely functions at the stage of N-N formation. PMID:27415586

  10. Temperature sensitivity trends and multi-stimuli sensitive behavior in amphiphilic oligomers.

    PubMed

    Wang, Feng; Klaikherd, Akamol; Thayumanavan, S

    2011-08-31

    A series of oligomers, containing oligo(ethylene glycol) (OEG) moieties, with the same composition of amphiphilic functionalities has been designed, synthesized, and characterized on the basis of their temperature-sensitive behavior. The non-covalent amphiphilic aggregates, formed from these molecules, influence their temperature sensitivity. Covalent tethering of the amphiphilic units also has a significant influence on their temperature sensitivity. The lower critical solution temperatures of these oligomers show increasingly sharp transitions with increasing numbers of OEG functional groups, indicating enhanced cooperativity in dehydration of the OEG moieties when they are covalently tethered. These molecules were also engineered to be concurrently sensitive to enzymatic reaction and pH. This possibility was investigated using porcine liver esterase as the enzyme; we show that enzymatic action on the pentamer lowers its temperature sensitivity. The product moiety from the enzymatic reaction also gives the amphiphilic oligomer a pH-dependent temperature sensitivity. PMID:21739959

  11. Soluble androgen receptor oligomers underlie pathology in a mouse model of spinobulbar muscular atrophy.

    PubMed

    Li, Mei; Chevalier-Larsen, Erica S; Merry, Diane E; Diamond, Marc I

    2007-02-01

    In polyglutamine diseases such as X-linked spinobulbar muscular atrophy (SBMA), it is unknown whether the toxic form of the protein is an insoluble or soluble aggregate or a monomer. We have addressed this question by studying a full-length androgen receptor (AR) mouse model of SBMA. We used biochemistry and atomic force microscopy to immunopurify oligomers soluble after ultracentrifugation that are comprised of a single approximately 50-kDa N-terminal polyglutamine-containing AR fragment. AR oligomers appeared several weeks prior to symptom onset, were distinct and temporally dissociated from intranuclear inclusions, and disappeared rapidly after castration, which halts disease. This is the first demonstration of soluble AR oligomers in vivo and suggests that they underlie neurodegeneration in SBMA. PMID:17121819

  12. Mitochondrial oligomers boost glycolysis in cancer stem cells to facilitate blebbishield-mediated transformation after apoptosis

    PubMed Central

    Jinesh, GG; Molina, JR; Huang, L; Laing, NM; Mills, GB; Bar-Eli, M; Kamat, AM

    2016-01-01

    Apoptosis culminates in secondary necrosis due to lack of ATP. Cancer stem cells form spheres after apoptosis by evoking the blebbishield emergency program. Hence, determining how blebbishields avoid secondary necrosis is crucial. Here we demonstrate that N-Myc and VEGFR2 control transformation from blebbishields, during which oligomers of K-Ras, p27, BAD, Bax, and Bak boost glycolysis to avoid secondary necrosis. Non-apoptotic cancer cells also utilize oligomers to boost glycolysis, which differentiates the glycolytic function of oligomers from their apoptotic action. Smac mimetic in combination with TNF-α or TRAIL but not in combination with FasL abrogates transformation from blebbishields by inducing secondary necrosis. Thus blebbishield-mediated transformation is dependent on glycolysis, and Smac mimetics represent potential candidates to abrogate the blebbishield emergency program. PMID:27551498

  13. Mitochondrial oligomers boost glycolysis in cancer stem cells to facilitate blebbishield-mediated transformation after apoptosis.

    PubMed

    Jinesh, G G; Molina, J R; Huang, L; Laing, N M; Mills, G B; Bar-Eli, M; Kamat, A M

    2016-01-01

    Apoptosis culminates in secondary necrosis due to lack of ATP. Cancer stem cells form spheres after apoptosis by evoking the blebbishield emergency program. Hence, determining how blebbishields avoid secondary necrosis is crucial. Here we demonstrate that N-Myc and VEGFR2 control transformation from blebbishields, during which oligomers of K-Ras, p27, BAD, Bax, and Bak boost glycolysis to avoid secondary necrosis. Non-apoptotic cancer cells also utilize oligomers to boost glycolysis, which differentiates the glycolytic function of oligomers from their apoptotic action. Smac mimetic in combination with TNF-α or TRAIL but not in combination with FasL abrogates transformation from blebbishields by inducing secondary necrosis. Thus blebbishield-mediated transformation is dependent on glycolysis, and Smac mimetics represent potential candidates to abrogate the blebbishield emergency program. PMID:27551498

  14. Excitonic Coupling and Femtosecond Relaxation of Zinc Porphyrin Oligomers Linked with Triazole Bridge: Dynamics and Modeling.

    PubMed

    Bukreev, Alexey; Mikhailov, Konstantin; Shelaev, Ivan; Gostev, Fedor; Polevaya, Yuliya; Tyurin, Vladimir; Beletskaya, Irina; Umansky, Stanislav; Nadtochenko, Victor

    2016-03-31

    The synthesis of new zinc porphyrin oligomers linked by a triazole bridge was carried out via "click" reaction. A split in the porphyrin oligomer B-band was observed. It was considered as evidence of exciton-excitonic coupling. The relaxation of excited states in Q-band porphyrin oligomers was studied by the femtosecond laser spectroscopy technique with a 20 fs pump pulse. The transient oscillations of two B-band excitonic peaks have a π-radian shift. For explanation of the coherent oscillation, a theoretical model was developed. The model considered the combination of the exciton-excitonic coupling between porphyrin rings in dimer and weak exciton-vibronic coupling in one porphyrin ring. By varying the values of the structural parameters of porphyrins (the strength values of this couplings and measure of symmetry breaking), we obtained correspondence between the experimental data (phase shift and amplitudes of the spectrum oscillations) and the predictions of the model developed here. PMID:26935579

  15. Biodegradable polyester-based eco-composites containing hemp fibers modified with macrocyclic oligomers

    NASA Astrophysics Data System (ADS)

    Conzatti, Lucia; Utzeri, Roberto; Hodge, Philip; Stagnaro, Paola

    2016-05-01

    An original compatibilizing pathway for hemp fibers/poly(1,4-butylene adipate-co-terephtalate) (PBAT) eco-composites was explored exploiting the capability of macrocyclic oligomers (MCOs), obtained by cyclodepolymerization (CDP) of PBAT at high dilution, of being re-converted into linear chains by entropically-driven ring-opening polymerization (ED-ROP) that occurs simply heating the MCOS in the bulk. CDP reaction of PBAT was carried out varying solvent, catalyst and reaction time. Selected MCOs were used to adjust the conditions of the ED-ROP reaction. The best experimental conditions were then adopted to modify hemp fibers. Eco-composites based on PBAT and hemp fibers as obtained or modified with PBAT macrocyclics or oligomers were prepared by different process strategies. The best fiber-PBAT compatibility was observed when the fibers were modified with PBAT oligomers before incorporation in the polyester matrix.

  16. New insight into the dynamical system of αB-crystallin oligomers

    PubMed Central

    Inoue, Rintaro; Takata, Takumi; Fujii, Norihiko; Ishii, Kentaro; Uchiyama, Susumu; Sato, Nobuhiro; Oba, Yojiro; Wood, Kathleen; Kato, Koichi; Fujii, Noriko; Sugiyama, Masaaki

    2016-01-01

    α-Crystallin possesses a dynamic quaternary structure mediated by its subunit dynamics. Elucidation of a mechanism of subunit dynamics in homo-oligomers of αB-crystallin was tackled through deuteration-assisted small-angle neutron scattering (DA-SANS) and electrospray ionization (ESI) native mass spectrometry (nMS). The existence of subunit exchange was confirmed with DA-SANS, and monomers liberated from the oligomers were observed with nMS. With increasing temperature, an increase in both the exchange rate and monomer population was observed despite the absence of oligomer collapse. It is proposed that transiently liberated subunits, namely, “traveling subunits,” play a role in subunit exchange. Moreover, we propose that protein function is regulated by these traveling subunits. PMID:27381175

  17. Hydrolysis of GTP associated with the formation of tubulin oligomers is involved in microtubule nucleation.

    PubMed Central

    Carlier, M F; Didry, D; Pantaloni, D

    1997-01-01

    Hydrolysis of GTP is known to accompany microtubule assembly. Here we show that hydrolysis of GTP is also associated with the formation of linear oligomers of tubulin, which are precursors (prenuclei) in microtubule assembly. The hydrolysis of GTP on these linear oligomers inhibits the lateral association of GTP-tubulin that leads to the formation of a bidimensional lattice. Therefore GTP hydrolysis interferes with the nucleation of microtubules. Linear oligomers are also formed in mixtures of GTP-tubulin and GDP-tubulin. The hydrolysis of GTP associated with heterologous interactions between GTP-tubulin and GDP-tubulin in the cooligomer takes place at a threefold faster rate than upon homologous interactions between GTP-tubulins. The implication of these results in a model of vectorial GTP hydrolysis in microtubule assembly is discussed. Images FIGURE 7 PMID:9199805

  18. A mechanistic model of tau amyloid aggregation based on direct observation of oligomers

    NASA Astrophysics Data System (ADS)

    Shammas, Sarah L.; Garcia, Gonzalo A.; Kumar, Satish; Kjaergaard, Magnus; Horrocks, Mathew H.; Shivji, Nadia; Mandelkow, Eva; Knowles, Tuomas P. J.; Mandelkow, Eckhard; Klenerman, David

    2015-04-01

    Protein aggregation plays a key role in neurodegenerative disease, giving rise to small oligomers that may become cytotoxic to cells. The fundamental microscopic reactions taking place during aggregation, and their rate constants, have been difficult to determine due to lack of suitable methods to identify and follow the low concentration of oligomers over time. Here we use single-molecule fluorescence to study the aggregation of the repeat domain of tau (K18), and two mutant forms linked with familial frontotemporal dementia, the deletion mutant ΔK280 and the point mutant P301L. Our kinetic analysis reveals that aggregation proceeds via monomeric assembly into small oligomers, and a subsequent slow structural conversion step before fibril formation. Using this approach, we have been able to quantitatively determine how these mutations alter the aggregation energy landscape.

  19. Regeneration of cello-oligomers via selective depolymerization of cellulose fibers derived from printed paper wastes.

    PubMed

    Voon, Lee Ken; Pang, Suh Cem; Chin, Suk Fun

    2016-05-20

    Cellulose extracted from printed paper wastes were selectively depolymerized under controlled conditions into cello-oligomers of controllable chain lengths via dissolution in an ionic liquid, 1-allyl-3-methylimidazolium chloride (AMIMCl), and in the presence of an acid catalyst, Amberlyst 15DRY. The depolymerization process was optimized against reaction temperature, concentration of acid catalyst, and reaction time. Despite rapid initial depolymerization process, the rate of cellulose depolymerization slowed down gradually upon prolonged reaction time, with 75.0wt% yield of regenerated cello-oligomers (mean Viscosimetric Degree of Polymerization value of 81) obtained after 40min. The depolymerization of cellulose fibers at 80°C appeared to proceed via a second-order kinetic reaction with respect to the catalyst concentration of 0.23mmol H3O(+). As such, the cellulose depolymerization process could afford some degree of control on the degree of polymerization or chain lengths of cello-oligomers formed. PMID:26917370

  20. Solution State Structure Determination of Silicate Oligomers by 29Si NMR Spectroscopy and Molecular Modeling

    SciTech Connect

    Cho, Herman M.; Felmy, Andrew R.; Craciun, Raluca; Keenum, Johnathan P.; Shah, Neil K.; Dixon, David A.

    2006-02-22

    Evidence for nine new solution state silicate oligomers has been discovered by 29Si NMR homonuclear correlation experiments of 29Si-enriched samples. In addition to enhancing signal sensitivity, the isotopic enrichment increases the probability of the 29Si–29Si two-bond scalar couplings that are necessary for the observation of internuclear correlations in 2-D experiments. The proposed assignments are validated by comparisons of experimental and simulated crosspeaks obtained with high digital resolution. The internuclear connectivity indicated by the NMR data suggests that several of these oligomers can have multiple stereoisomers, including conformers and/or diastereomers. The stability of these oligomers and their possible stereoisomers have been investigated by electronic structure calculations.

  1. Solution state structure determination of silicate oligomers by 29SI NMR spectroscopy and molecular modeling.

    PubMed

    Cho, Herman; Felmy, Andrew R; Craciun, Raluca; Keenum, J Patrick; Shah, Neil; Dixon, David A

    2006-02-22

    Evidence for nine new solution state silicate oligomers has been discovered by (29)Si NMR homonuclear correlation experiments of (29)Si-enriched samples. In addition to enhancing signal sensitivity, the isotopic enrichment increases the probability of the (29)Si-(29)Si two-bond scalar couplings that are necessary for the observation of internuclear correlations in 2-D experiments. The proposed assignments are validated by comparisons of experimental and simulated cross-peaks obtained with high digital resolution. The internuclear connectivity indicated by the NMR data suggests that several of these oligomers can have multiple stereoisomers, including conformers and/or diastereomers. The stabilities of these oligomers and their possible stereoisomers have been investigated by electronic structure calculations. PMID:16478188

  2. Deleterious effects of soluble amyloid-β oligomers on multiple steps of synaptic vesicle trafficking.

    PubMed

    Park, Joohyun; Jang, Mirye; Chang, Sunghoe

    2013-07-01

    Growing evidence supports a role for soluble amyloid-β oligomer intermediates in the synaptic dysfunction associated with Alzheimer's disease (AD), but the molecular mechanisms underlying this effect remain unclear. We found that acute treatment of cultured rat hippocampal neurons with nanomolar concentrations of Aβ oligomers reduced the recycling pool and increased the resting pool of synaptic vesicles. Endocytosis of synaptic vesicles and the regeneration of fusion-competent vesicles were also severely impaired. Furthermore, the release probability of the readily-releasable pool (RRP) was increased, and recovery of the RRP was delayed. All these effects were prevented by antibody against Aβ. Moreover reduction of the pool size was prevented by inhibiting calpain or CDK5, while the defects in endocytosis were averted by overexpressing phosphatidylinositol-4-phosphate-5-kinase type I-γ, indicating that these two downstream pathways are involved in Aβ oligomers-induced presynaptic dysfunction. PMID:23523634

  3. Simple extrapolation method to predict the electronic structure of conjugated polymers from calculations on oligomers

    DOE PAGESBeta

    Larsen, Ross E.

    2016-04-12

    In this study, we introduce two simple tight-binding models, which we call fragment frontier orbital extrapolations (FFOE), to extrapolate important electronic properties to the polymer limit using electronic structure calculations on only a few small oligomers. In particular, we demonstrate by comparison to explicit density functional theory calculations that for long oligomers the energies of the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and of the first electronic excited state are accurately described as a function of number of repeat units by a simple effective Hamiltonian parameterized from electronic structure calculations on monomers, dimers and, optionally,more » tetramers. For the alternating copolymer materials that currently comprise some of the most efficient polymer organic photovoltaic devices one can use these simple but rigorous models to extrapolate computed properties to the polymer limit based on calculations on a small number of low-molecular-weight oligomers.« less

  4. Formation of nitrogen-containing oligomers by methylglyoxal and amines in simulated evaporating cloud droplets.

    PubMed

    De Haan, David O; Hawkins, Lelia N; Kononenko, Julia A; Turley, Jacob J; Corrigan, Ashley L; Tolbert, Margaret A; Jimenez, Jose L

    2011-02-01

    Reactions of methylglyoxal with amino acids, methylamine, and ammonium sulfate can take place in aqueous aerosol and evaporating cloud droplets. These processes are simulated by drying droplets and bulk solutions of these compounds (at low millimolar and 1 M concentrations, respectively) and analyzing the residuals by scanning mobility particle sizing, nuclear magnetic resonance, aerosol mass spectrometry (AMS), and electrospray ionization MS. The results are consistent with imine (but not diimine) formation on a time scale of seconds, followed by the formation of nitrogen-containing oligomers, methylimidazole, and dimethylimidazole products on a time scale of minutes to hours. Measured elemental ratios are consistent with imidazoles and oligomers being major reaction products, while effective aerosol densities suggest extensive reactions take place within minutes. These reactions may be a source of the light-absorbing, nitrogen-containing oligomers observed in urban and biomass-burning aerosol particles. PMID:21171623

  5. New insight into the dynamical system of αB-crystallin oligomers.

    PubMed

    Inoue, Rintaro; Takata, Takumi; Fujii, Norihiko; Ishii, Kentaro; Uchiyama, Susumu; Sato, Nobuhiro; Oba, Yojiro; Wood, Kathleen; Kato, Koichi; Fujii, Noriko; Sugiyama, Masaaki

    2016-01-01

    α-Crystallin possesses a dynamic quaternary structure mediated by its subunit dynamics. Elucidation of a mechanism of subunit dynamics in homo-oligomers of αB-crystallin was tackled through deuteration-assisted small-angle neutron scattering (DA-SANS) and electrospray ionization (ESI) native mass spectrometry (nMS). The existence of subunit exchange was confirmed with DA-SANS, and monomers liberated from the oligomers were observed with nMS. With increasing temperature, an increase in both the exchange rate and monomer population was observed despite the absence of oligomer collapse. It is proposed that transiently liberated subunits, namely, "traveling subunits," play a role in subunit exchange. Moreover, we propose that protein function is regulated by these traveling subunits. PMID:27381175

  6. The Aβ oligomer hypothesis for synapse failure and memory loss in Alzheimer's disease.

    PubMed

    Ferreira, Sergio T; Klein, William L

    2011-11-01

    Alzheimer's disease (AD) is the 3rd most costly disease and the leading cause of dementia. It can linger for many years, but ultimately is fatal, the 6th leading cause of death. Alzheimer's disease (AD) is fatal and affected individuals can sometimes linger many years. Current treatments are palliative and transient, not disease modifying. This article reviews progress in the search to identify the primary AD-causing toxins. We summarize the shift from an initial focus on amyloid plaques to the contemporary concept that AD memory failure is caused by small soluble oligomers of the Aβ peptide, toxins that target and disrupt particular synapses. Evidence is presented that links Aβ oligomers to pathogenesis in animal models and humans, with reference to seminal discoveries from cell biology and new ideas concerning pathogenic mechanisms, including relationships to diabetes and Fragile X. These findings have established the oligomer hypothesis as a new molecular basis for the cause, diagnosis, and treatment of AD. PMID:21914486

  7. Rad54 oligomers translocate and cross-bridge double-stranded DNA to stimulate synapsis

    PubMed Central

    Bianco, Piero R.; Bradfield, Justin J.; Castanza, Lauren R.; Donnelly, Andrea N.

    2007-01-01

    Rad54 is a key component of the eukaryotic recombination machinery. Its presence in DNA strand exchange reactions in vitro results in a significant stimulation in the overall reaction rate. Using untagged Rad54, we show that this stimulation can be attributed to enhancement of the formation of a key reaction intermediate known as DNA networks. Using a novel, single DNA molecule, dual-optical tweezers approach we show how Rad54 stimulates DNA network formation. We discovered that Rad54 oligomers possess a unique ability to cross-bridge or bind dsDNA molecules positioned in close proximity. Further, Rad54 oligomers rapidly translocate dsDNA while simultaneously inducing topological loops in the DNA at the locus of the oligomer. The combination of the cross-bridging and dsDNA translocation activities of Rad54 stimulates the formation of DNA networks, leading to rapid and efficient DNA strand exchange by Rad51. PMID:17949748

  8. Conformational Switching and Nanoscale Assembly of Human Prion Protein into Polymorphic Amyloids via Structurally Labile Oligomers.

    PubMed

    Dalal, Vijit; Arya, Shruti; Bhattacharya, Mily; Mukhopadhyay, Samrat

    2015-12-29

    Conformational switching of the prion protein (PrP) from an α-helical normal cellular form (PrP(C)) to an aggregation-prone and self-propagating β-rich scrapie form (PrP(Sc)) underlies the molecular basis of pathogenesis in prion diseases. Anionic lipids play a critical role in the misfolding and conformational conversion of the membrane-anchored PrP into the amyloidogenic pathological form. In this work, we have used a diverse array of techniques to interrogate the early intermediates during amyloid formation from recombinant human PrP in the presence of a membrane mimetic anionic detergent such as sodium dodecyl sulfate. We have been able to detect and characterize two distinct types of interconvertible oligomers. Our results demonstrate that highly ordered large β-oligomers represent benign off-pathway intermediates that lack the ability to mature into amyloid fibrils. On the contrary, structurally labile small oligomers are capable of switching to an ordered amyloid-state that exhibits profound toxicity to mammalian cells. Our fluorescence resonance energy transfer measurements revealed that the partially disordered PrP serves as precursors to small amyloid-competent oligomers. These on-pathway oligomers are eventually sequestered into higher order supramolecular assemblies that conformationally mature into polymorphic amyloids possessing varied nanoscale morphology as evident by the atomic force microscopy imaging. The nanoscale diversity of fibril architecture is attributed to the heterogeneous ensemble of early obligatory oligomers and offers a plausible explanation for the existence of multiple prion strains in vivo. PMID:26645611

  9. Thio-urethane oligomers improve the properties of light-cured resin cements

    PubMed Central

    Bacchi, Ataís; Consani, Rafael L.; Martim, Gedalias C.; Pfeifer, Carmem S.

    2015-01-01

    Thio-urethanes were synthesized by combining 1,6-Hexanediol-diissocyante (aliphatic) with pentaerythritol tetra-3-mercaptopropionate (PETMP) or 1,3-bis(1-isocyanato-1-methylethyl)benzene (aromatic) with trimethylol-tris-3-mercaptopropionate (TMP), at 1:2 isocyanate:thiol, leaving pendant thiols. Oligomers were added at 10–30 phr to BisGMA-UDMA-TEGDMA (5:3:2, BUT). 25wt% silanated inorganic fillers were added. Commercial cement (Relyx Veneer, 3M-ESPE) was also evaluated with 10–20 phr of aromatic oligomer. Near-IR was used to follow methacrylate conversion (DC) and rate of polymerization (Rpmax). Mechanical properties were evaluated in three-point bending (ISO 4049) for flexural strength/modulus (FS/FM, and toughness), and notched specimens (ASTM Standard E399-90) for fracture toughness (KIC). Polymerization stress (PS) was measured on the Bioman. Volumetric shrinkage (VS, %) was measured with the bonded disk technique. Results were analyzed with ANOVA/Tukey’s test (α=5%). In general terms, for BUT cements, conversion and mechanical properties in flexure increased for selected groups with the addition of thio-urethane oligomers. The aromatic versions resulted in greater FS/FM than aliphatic. Fracture toughness increased by twofold in the experimental groups (from 1.17±0.36 to around 3.23±0.22 MPa.m1/2). Rpmax decreased with the addition of thio-urethanes, though the vitrification point was not statistically different from the control. VS and PS decreased with both oligomers. For the commercial cement, 20 phr of oligomer increased DC, vitrification, reduced Rpmax and also significantly increased KIC, and reduced PS and FM. Thio-urethane oligomers were shown to favorably modify conventional dimethacrylate networks. Significant reductions in polymerization stress were achieved at the same time conversion and fracture toughness increased. PMID:25740124

  10. Nicotinamide mononucleotide protects against β-amyloid oligomer-induced cognitive impairment and neuronal death.

    PubMed

    Wang, Xiaonan; Hu, Xuejun; Yang, Yang; Takata, Toshihiro; Sakurai, Takashi

    2016-07-15

    Amyloid-β (Aβ) oligomers are recognized as the primary neurotoxic agents in Alzheimer's disease (AD). Impaired brain energy metabolism and oxidative stress are implicated in cognitive decline in AD. Nicotinamide adenine dinucleotide (NAD(+)), a coenzyme involved in redox activities in the mitochondrial electron transport chain, has been identified as a key regulator of the lifespan-extending effects, and the activation of NAD(+) expression has been linked with a decrease in Aβ toxicity in AD. One of the key precursors of NAD(+) is nicotinamide mononucleotide (NMN), a product of the nicotinamide phosphoribosyltransferase reaction. To determine whether improving brain energy metabolism will forestall disease progress in AD, the impact of the NAD(+) precursor NMN on Aβ oligomer-induced neuronal death and cognitive impairment were studied in organotypic hippocampal slice cultures (OHCs) and in a rat model of AD. Treatment of intracerebroventricular Aβ oligomer infusion AD model rats with NMN (500mg/kg, intraperitoneally) sustained improvement in cognitive function as assessed by the Morris water maze. In OHCs, Aβ oligomer-treated culture media with NMN attenuated neuronal cell death. NMN treatment also significantly prevented the Aβ oligomer-induced inhibition of LTP. Furthermore, NMN restored levels of NAD(+) and ATP, eliminated accumulation of reactive oxygen species (ROS) in the Aβ oligomer-treated hippocampal slices. All these protective effects were reversed by 3-acetylpyridine, which generates inactive NAD(+). The present study indicates that NMN could restore cognition in AD model rats. The beneficial effect of NMN is produced by ameliorating neuron survival, improving energy metabolism and reducing ROS accumulation. These results suggest that NMN may become a promising therapeutic drug for AD. PMID:27130898

  11. Detection of TDP-43 Oligomers in Frontotemporal Lobar Degeneration–TDP

    PubMed Central

    Kao, Patricia F.; Chen, Yun-Ru; Liu, Xiao-Bo; DeCarli, Charles; Seeley, William W.; Jin, Lee-Way

    2016-01-01

    Objective The proteinaceous inclusions in TDP-43 proteinopathies such as frontotemporal lobar degeneration (FTLD)-TDP are made of high–molecular-weight aggregates of TDP-43. These aggregates have not been classified as amyloids, as prior amyloid staining results were not conclusive. Here we used a specific TDP-43 amyloid oligomer antibody called TDP-O to determine the presence and abundance of TDP-43 oligomers among different subtypes of FTLD-TDP as well as in hippocampal sclerosis (HS), which represents a non-FTLD pathology with TDP-43 inclusions. Methods Postmortem tissue from the hippocampus and anterior orbital gyrus from 54 prospectively assessed and diagnosed subjects was used for immunostaining with TDP-O. Electron microscopy was used to assess the subcellular locations of TDP-O–decorated structures. Results TDP-43 inclusions staining with TDP-O were present in FTLD-TDP and were most conspicuous for FTLD-TDP type C, the subtype seen in most patients with semantic variant primary progressive aphasia. TDP-O immunoreactivity was absent in the hippocampus of HS patients despite abundant TDP-43 inclusions. Ultrastructurally, TDP-43 oligomers resided in granular or tubular structures, frequently in close proximity to, but not within, neuronal lysosomes. Interpretation TDP-43 forms amyloid oligomers in the human brain, which may cause neurotoxicity in a manner similar to other amyloid oligomers. Oligomer formation may contribute to the conformational heterogeneity of TDP-43 aggregates and mark the different properties of TDP-43 inclusions between FTLD-TDP and HS. PMID:25921485

  12. DT-Diaphorase Prevents Aminochrome-Induced Alpha-Synuclein Oligomer Formation and Neurotoxicity

    PubMed Central

    Muñoz, Patricia; Cardenas, Sergio; Huenchuguala, Sandro; Briceño, Andrea; Couve, Eduardo; Paris, Irmgard; Segura-Aguilar, Juan

    2015-01-01

    It was reported that aminochrome induces the formation of alpha synuclein (SNCA) oligomers during dopamine oxidation. We found that DT-diaphorase (NQO1) prevents the formation of SNCA oligomers in the presence of aminochrome determined by Western blot, transmission electron microscopy, circular dichroism, and thioflavin T fluorescence, suggesting a protective role of NQO1 by preventing the formation of SNCA oligomers in dopaminergic neurons. In order to test NQO1 protective role in SNCA neurotoxicity in cellular model, we overexpressed SNCA in both RCSN-3 cells (wild-type) and RCSN-3Nq7 cells, which have constitutive expression of a siRNA against NQO1. The expression of SNCA in RCSN-3SNCA and RCSN-3Nq7SNCA cells increased 4.2- and 4.4-fold, respectively. The overexpression of SNCA in RCSN-3Nq7SNCA cells induces a significant increase in cell death of 2.8- and 3.2-fold when they were incubated with 50 and 70 µM aminochrome, respectively. The cell death was found to be of apoptotic character determined by annexin/propidium iodide technique with flow cytometry and DNA laddering. A Western blot demonstrated that SNCA in RCSN-3SNCA is only found in monomer form both in the presence of 20 µM aminochrome or cell culture medium contrasting with RCSN-3Nq7SNCA cells where the majority SNCA is found as oligomer. The antioligomer compound scyllo-inositol induced a significant decrease in aminochrome-induced cell death in RCSN-3Nq7SNCA cells in comparison to cells incubated in the absence of scyllo-inositol. Our results suggest that NQO1 seems to play an important role in the prevention of aminochrome-induced SNCA oligomer formation and SNCA oligomers neurotoxicity in dopaminergic neurons. PMID:25634539

  13. Synthesis and incorporation of thienylene vinylene oligomers in main-chain copolymers

    SciTech Connect

    Madrigal, L.G.; Elandaloussi, E.H.; Spangler, C.W.

    1998-07-01

    Poly [2,5-thienylene vinylene] (PTV) has been studied extensively over the past decade for both its metallic conductivity behavior upon chemical doping, as well as its interesting third order nonlinear optical properties. PTV oligomers have been synthesized by the group, as well as others, and the formation of polaron-like radical-cations or bipolaron-like dications by oxidative doping has been demonstrated. In this paper the authors describe a general synthetic approach to PTV oligomers functionalized for copolymer formation by step-growth reaction.

  14. Endogenous Docosahexaenoic Acid (DHA) Prevents Aβ1-42 Oligomer-Induced Neuronal Injury.

    PubMed

    Tan, Yuan; Ren, Huixia; Shi, Zhe; Yao, Xiaoli; He, Chengwei; Kang, Jing-X; Wan, Jian-Bo; Li, Peng; Yuan, Ti-Fei; Su, Huanxing

    2016-07-01

    The intake of the polyunsaturated fatty acid docosahexaenoic acid (DHA) or n-3 fatty acid has been associated with reduced risk of Alzheimer's disease (AD) in epidemiological reports. However, the underlying mechanism remains to be elucidated. Here, we report that exogenous DHA administration could protect neurons against Aβ oligomer-induced injury both in vitro and in vivo, partly through reducing the endoplasmic reticulum (ER) stress, and preventing cell apoptosis. In transgenic fat-1 mice with enriched ω-3 fatty acids, Aβ oligomers induced fewer neuronal losses, when compared to wild-type (WT) mice. We conclude that endogenous DHA are neuroprotective in pathogenesis processes of AD. PMID:26021747

  15. Fibrillar Oligomers Nucleate the Oligomerization of Monomeric Amyloid β but Do Not Seed Fibril Formation*

    PubMed Central

    Wu, Jessica W.; Breydo, Leonid; Isas, J. Mario; Lee, Jerome; Kuznetsov, Yurii G.; Langen, Ralf; Glabe, Charles

    2010-01-01

    Soluble amyloid oligomers are potent neurotoxins that are involved in a wide range of human degenerative diseases, including Alzheimer disease. In Alzheimer disease, amyloid β (Aβ) oligomers bind to neuronal synapses, inhibit long term potentiation, and induce cell death. Recent evidence indicates that several immunologically distinct structural variants exist as follows: prefibrillar oligomers (PFOs), fibrillar oligomers (FOs), and annular protofibrils. Despite widespread interest, amyloid oligomers are poorly characterized in terms of structural differences and pathological significance. FOs are immunologically related to fibrils because they react with OC, a conformation-dependent, fibril-specific antibody and do not react with antibodies specific for other types of oligomers. However, fibrillar oligomers are much smaller than fibrils. FOs are soluble at 100,000 × g, rich in β-sheet structures, but yet bind weakly to thioflavin T. EPR spectroscopy indicates that FOs display significantly more spin-spin interaction at multiple labeled sites than PFOs and are more structurally similar to fibrils. Atomic force microscopy indicates that FOs are approximately one-half to one-third the height of mature fibrils. We found that Aβ FOs do not seed the formation of thioflavin T-positive fibrils from Aβ monomers but instead seed the formation of FOs from Aβ monomers that are positive for the OC anti-fibril antibody. These results indicate that the lattice of FOs is distinct from the fibril lattice even though the polypeptide chains are organized in an immunologically identical conformation. The FOs resulting from seeded reactions have the same dimensions and morphology as the initial seeds, suggesting that the seeds replicate by growing to a limiting size and then splitting, indicating that their lattice is less stable than fibrils. We suggest that FOs may represent small pieces of single fibril protofilament and that the addition of monomers to the ends of FOs is

  16. Synthesis and g-quadruplex-binding properties of defined acridine oligomers.

    PubMed

    Ferreira, Rubén; Aviñó, Anna; Pérez-Tomás, Ricardo; Gargallo, Raimundo; Eritja, Ramon

    2010-01-01

    The synthesis of oligomers containing two or three acridine units linked through 2-aminoethylglycine using solid-phase methodology is described. Subsequent studies on cell viability showed that these compounds are not cytotoxic. Binding to several DNA structures was studied by competitive dialysis, which showed a clear affinity for DNA sequences that form G-quadruplexes and parallel triplexes. The fluorescence spectra of acridine oligomers were affected strongly upon binding to DNA. These spectral changes were used to calculate the binding constants (K). Log K were found to be in the order of 4-6. PMID:20725626

  17. Enzymatic production of defined chitosan oligomers with a specific pattern of acetylation using a combination of chitin oligosaccharide deacetylases

    NASA Astrophysics Data System (ADS)

    Hamer, Stefanie Nicole; Cord-Landwehr, Stefan; Biarnés, Xevi; Planas, Antoni; Waegeman, Hendrik; Moerschbacher, Bruno Maria; Kolkenbrock, Stephan

    2015-03-01

    Chitin and chitosan oligomers have diverse biological activities with potentially valuable applications in fields like medicine, cosmetics, or agriculture. These properties may depend not only on the degrees of polymerization and acetylation, but also on a specific pattern of acetylation (PA) that cannot be controlled when the oligomers are produced by chemical hydrolysis. To determine the influence of the PA on the biological activities, defined chitosan oligomers in sufficient amounts are needed. Chitosan oligomers with specific PA can be produced by enzymatic deacetylation of chitin oligomers, but the diversity is limited by the low number of chitin deacetylases available. We have produced specific chitosan oligomers which are deacetylated at the first two units starting from the non-reducing end by the combined use of two different chitin deacetylases, namely NodB from Rhizobium sp. GRH2 that deacetylates the first unit and COD from Vibrio cholerae that deacetylates the second unit starting from the non-reducing end. Both chitin deacetylases accept the product of each other resulting in production of chitosan oligomers with a novel and defined PA. When extended to further chitin deacetylases, this approach has the potential to yield a large range of novel chitosan oligomers with a fully defined architecture.

  18. Permeability and partitioning of ferrocene ethylene oxide and propylene oxide oligomers into electropolymerized films from acetonitrile and polyether solutions

    SciTech Connect

    Pyati, R.; Murray, R.W. )

    1994-10-27

    We report the first electrochemically-based measurements of the rates of small polymer permeation into another polymer. The small polymer permeants are ferrocene ethylene oxide oligomers containing 2, 7, and 16 units and a propylene oxide oligomer containing 3 units. Their permeation into ultrathin microelectrode-supported films of the metal complex polymer poly[Ru(vbpy)[sub 3

  19. Efficient access to conjugated 4,4'-bipyridinium oligomers using the Zincke reaction: synthesis, spectroscopic and electrochemical properties.

    PubMed

    Chen, Long; Willcock, Helen; Wedge, Christopher J; Hartl, František; Colquhoun, Howard M; Greenland, Barnaby W

    2016-01-21

    The cyclocondensation reaction between rigid, electron-rich aromatic diamines and 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridinium (Zincke) salts has been harnessed to produce a series of conjugated oligomers containing up to twelve aromatic/heterocyclic residues. These oligomers exhibit discrete, multiple redox processes accompanied by dramatic changes in electronic absorption spectra. PMID:26626110

  20. An oligomer complementary to c-myc mRNA inhibits proliferation of HL-60 promyelocytic cells and induces differentiation.

    PubMed Central

    Holt, J T; Redner, R L; Nienhuis, A W

    1988-01-01

    To study the role of a nuclear proto-oncogene in the regulation of cell growth and differentiation, we inhibited HL-60 c-myc expression with a complementary antisense oligomer. This oligomer was stable in culture and entered cells, forming an intracellular duplex. Incubation of cells with the anti-myc oligomer decreased the steady-state levels of c-myc protein by 50 to 80%, whereas a control oligomer did not significantly affect the c-myc protein concentration. Direct inhibition of c-myc expression with the anti-myc oligomer was associated with a decreased cell growth rate and an induction of myeloid differentiation. Related antisense oligomers with 2- to 12-base-pair mismatches with c-myc mRNA did not influence HL-60 cells. Thus, the effects of the antisense oligomer exhibited sequence specificity, and furthermore, these effects could be reversed by hybridization competition with another complementary oligomer. Antisense inhibition of a nuclear proto-oncogene apparently bypasses cell surface events in affecting cell proliferation and differentiation. Images PMID:3280975

  1. Enzymatic production of defined chitosan oligomers with a specific pattern of acetylation using a combination of chitin oligosaccharide deacetylases

    PubMed Central

    Hamer, Stefanie Nicole; Cord-Landwehr, Stefan; Biarnés, Xevi; Planas, Antoni; Waegeman, Hendrik; Moerschbacher, Bruno Maria; Kolkenbrock, Stephan

    2015-01-01

    Chitin and chitosan oligomers have diverse biological activities with potentially valuable applications in fields like medicine, cosmetics, or agriculture. These properties may depend not only on the degrees of polymerization and acetylation, but also on a specific pattern of acetylation (PA) that cannot be controlled when the oligomers are produced by chemical hydrolysis. To determine the influence of the PA on the biological activities, defined chitosan oligomers in sufficient amounts are needed. Chitosan oligomers with specific PA can be produced by enzymatic deacetylation of chitin oligomers, but the diversity is limited by the low number of chitin deacetylases available. We have produced specific chitosan oligomers which are deacetylated at the first two units starting from the non-reducing end by the combined use of two different chitin deacetylases, namely NodB from Rhizobium sp. GRH2 that deacetylates the first unit and COD from Vibrio cholerae that deacetylates the second unit starting from the non-reducing end. Both chitin deacetylases accept the product of each other resulting in production of chitosan oligomers with a novel and defined PA. When extended to further chitin deacetylases, this approach has the potential to yield a large range of novel chitosan oligomers with a fully defined architecture. PMID:25732514

  2. A spiropyran-based fluorescent probe for the specific detection of β-amyloid peptide oligomers in Alzheimer's disease.

    PubMed

    Lv, Guanglei; Sun, Anyang; Wei, Peng; Zhang, Ning; Lan, Haichuang; Yi, Tao

    2016-07-01

    We report a new spiropyran-based fluorescent probe that exhibits high affinity and specificity towards Aβ oligomers both in vitro and in vivo. This probe can penetrate the blood brain barrier and specifically target Aβ oligomers in the brains of transgenic mice in models for Alzheimer's disease. PMID:27346489

  3. Construction of human Fab library and screening of a single-domain antibody of amyloid-beta 42 oligomers

    PubMed Central

    Yuan, Zuanning; Du, Minge; Chen, Yiwen; Dou, Fei

    2013-01-01

    Screening humanized antibodies from a human Fab phage display library is an effective and quick method to obtain beta-amyloid oligomers. Thus, the present study prepared amyloid-beta 42 oli-gomers and constructed a naïve human Fab phage display library based on blood samples from six healthy people. After three rounds of biopanning in vitro, a human single-domain antibody that specifically recognized amyloid-beta 42 oligomers was identified. Western blot and enzyme-linked immunosorbent assay demonstrated this antibody bound specifically to human amyloid-beta 42 tetramer and nonamer, but not the monomer or high molecular weight oligomers. This study successfully constructed a human phage display library and screened a single-domain antibody that specifically recognized amyloid-beta 42 oligomers. PMID:25206631

  4. Crystallization and preliminary crystallographic study of oligomers of the haemolytic lectin CEL-III from the sea cucumber Cucumaria echinata.

    PubMed

    Unno, Hideaki; Hisamatsu, Keigo; Nagao, Tomonao; Tateya, Yuki; Matsumoto, Naoki; Goda, Shuichiro; Hatakeyama, Tomomitsu

    2013-04-01

    CEL-III is a Ca(2+)-dependent haemolytic lectin isolated from the marine invertebrate Cucumaria echinata. This lectin binds to Gal/GalNAc-containing carbohydrate chains on the cell surface and, after conformational changes, oligomerizes to form ion-permeable pores in cell membranes. CEL-III also forms soluble oligomers similar to those formed in cell membranes upon binding of specific carbohydrates in high-pH and high-salt solutions. These soluble and membrane CEL-III oligomers were crystallized and X-ray diffraction data were collected. Crystals of soluble oligomers and membrane oligomers diffracted X-rays to 3.3 and 4.2 Å resolution, respectively, using synchrotron radiation and the former was found to belong to space group C2. Self-rotation functional analysis of the soluble oligomer crystal suggested that it might be composed of heptameric CEL-III. PMID:23545649

  5. Crystallization and preliminary crystallographic study of oligomers of the haemolytic lectin CEL-III from the sea cucumber Cucumaria echinata

    PubMed Central

    Unno, Hideaki; Hisamatsu, Keigo; Nagao, Tomonao; Tateya, Yuki; Matsumoto, Naoki; Goda, Shuichiro; Hatakeyama, Tomomitsu

    2013-01-01

    CEL-III is a Ca2+-dependent haemolytic lectin isolated from the marine invertebrate Cucumaria echinata. This lectin binds to Gal/GalNAc-containing carbohydrate chains on the cell surface and, after conformational changes, oligomerizes to form ion-permeable pores in cell membranes. CEL-III also forms soluble oligomers similar to those formed in cell membranes upon binding of specific carbohydrates in high-pH and high-salt solutions. These soluble and membrane CEL-III oligomers were crystallized and X-ray diffraction data were collected. Crystals of soluble oligomers and membrane oligomers diffracted X-rays to 3.3 and 4.2 Å resolution, respectively, using synchrotron radiation and the former was found to belong to space group C2. Self-rotation functional analysis of the soluble oligomer crystal suggested that it might be composed of heptameric CEL-III. PMID:23545649

  6. Cellulose acetate-lithium bis(trifluoromethanesulfonyl)imide solid polymer electrolyte: ATR-FTIR and ionic conductivity behavior

    NASA Astrophysics Data System (ADS)

    Mohd Razalli, Siti Masyitah; Sheikh Mohd Saaid, Siti Irma Yuana; Marwan Ali, Ab Malik; Hassan, Oskar Hasdinor; Yahya, Muhd Zu Azhan

    2015-05-01

    Solid polymer electrolytes (SPEs) based on cellulose acetate (CA) doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are prepared by solution cast technique. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy of the polymer salt complexes are recorded in the frequency range between 400 cm-1 and 4000 cm-1. The shifting of carbonyl band (C=O) at 1737 cm-1 to a lower wavenumber confirms the occurrence of complexation between the polymer and the salt. The electrochemical impedance spectroscopy (EIS) analysis discovered that the film with 25 wt.% of salt shows the highest ionic conductivity at room temperature. The change in real dielectric permittivity (ɛr) as a function of frequency at different salt concentrations which exhibits a dispersive behavior at low frequencies and decays at higher frequencies, shows the electrode polarization and space charge effect. The real modulus formalism (Mr) analysis shows that the polymer electrolytes in this work are ionic conductors.

  7. The electrochemical oxidation of toluene catalysed by Co(II) in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide.

    PubMed

    Balaji, S; Kannan, K; Moon, I S

    2015-12-14

    The electrochemical oxidation of toluene in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([bmpyr](+)[Ntf2](-)) was investigated by using cyclic voltammetry and galvanostatic electrolysis in the presence of Co(II) at a Pt disc working electrode. Cyclic voltammetry (CV) investigations revealed that Co(II)-Co(III) oxidation is a diffusion controlled electron transfer process. The diffusion coefficient values of Co(II) were found to increase from 0.38 × 10(-7) to 1.9 × 10(-7) cm(2) s(-1) as the temperature was increased from 25 °C to 80 °C. The CV peak current for toluene electro-oxidation increased by nearly 7 fold in the presence of Co(II) demonstrating a good catalytic effect. Co(II) catalysed galvanostatic electrolysis of toluene at room temperature has shown that benzaldehyde was formed along with a small quantity of 3-methyl-1-hexanol. PMID:26538114

  8. “Newton’s cradle” proton relay with amide–imidic acid tautomerization in inverting cellulase visualized by neutron crystallography

    PubMed Central

    Nakamura, Akihiko; Ishida, Takuya; Kusaka, Katsuhiro; Yamada, Taro; Fushinobu, Shinya; Tanaka, Ichiro; Kaneko, Satoshi; Ohta, Kazunori; Tanaka, Hiroaki; Inaka, Koji; Higuchi, Yoshiki; Niimura, Nobuo; Samejima, Masahiro; Igarashi, Kiyohiko

    2015-01-01

    Hydrolysis of carbohydrates is a major bioreaction in nature, catalyzed by glycoside hydrolases (GHs). We used neutron diffraction and high-resolution x-ray diffraction analyses to investigate the hydrogen bond network in inverting cellulase PcCel45A, which is an endoglucanase belonging to subfamily C of GH family 45, isolated from the basidiomycete Phanerochaete chrysosporium. Examination of the enzyme and enzyme-ligand structures indicates a key role of multiple tautomerizations of asparagine residues and peptide bonds, which are finally connected to the other catalytic residue via typical side-chain hydrogen bonds, in forming the “Newton’s cradle”–like proton relay pathway of the catalytic cycle. Amide–imidic acid tautomerization of asparagine has not been taken into account in recent molecular dynamics simulations of not only cellulases but also general enzyme catalysis, and it may be necessary to reconsider our interpretation of many enzymatic reactions. PMID:26601228

  9. Polymer electrolyte based on crosslinked poly(glycidyl methacrylate) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

    NASA Astrophysics Data System (ADS)

    Fei, Beatrice Wong Chui; Hanifah, Sharina Abu; Ahmad, Azizan; Hassan, Nur Hasyareeda

    2015-09-01

    Polymer electrolytes based on crosslinked poly(glycidyl methacrylate) as polymer host and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimTFSI) as incorporated salt were prepared by in-situ photopolymerization technique. The complexes with different mass ratio of glycidyl methacrylate (GMA) monomer to BmimTFSI were investigated. The ionic conductivity of the polymer electrolyte was increased and reach the highest value of 7.50 × 10-4 S cm-1 at the ratio of 3:7 (GMA: BmimTFSI). The interaction between the polymer host and ionic liquid was proved by Attenuated Total Reflectance-Fourier Transformation Infra-Red Spectroscopy (ATR-FTIR). Meanwhile, the X-ray diffraction analysis shows the amorphousity of the polymer electrolyte film increase with the ionic liquid ratio.

  10. Theoretical analysis of x-ray absorption spectra of Ti compounds used as catalysts in lithium amide/imide reactions

    NASA Astrophysics Data System (ADS)

    Tsumuraya, Takao; Shishidou, Tatsuya; Oguchi, Tamio

    2008-06-01

    We present a theoretical analysis and interpretation of the x-ray absorption near-edge structure of x-ray absorption spectroscopy (XAS) at the titanium K -edge of several Ti compounds for understanding catalysis mechanism in lithium amide LiNH2 and imide Li2NH systems for hydrogen storage. Our theoretical approach is based on first-principles calculations using all-electron full-potential linear augmented plane-wave method. Chemical bonding and local geometry of catalytically-active Ti states in the hydrogen desorption reaction LiNH2+LiH→Li2NH+H2 are investigated. It is found that XAS spectra of some compounds consisting of elements Li, N, H, and Ti are quite similar to measured ones of catalytically-active Ti compounds. We conclude that Ti ions may occupy the Li sites in LiNH2 during the reaction.

  11. Polymer electrolyte based on crosslinked poly(glycidyl methacrylate) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

    SciTech Connect

    Fei, Beatrice Wong Chui; Hanifah, Sharina Abu; Ahmad, Azizan; Hassan, Nur Hasyareeda

    2015-09-25

    Polymer electrolytes based on crosslinked poly(glycidyl methacrylate) as polymer host and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimTFSI) as incorporated salt were prepared by in-situ photopolymerization technique. The complexes with different mass ratio of glycidyl methacrylate (GMA) monomer to BmimTFSI were investigated. The ionic conductivity of the polymer electrolyte was increased and reach the highest value of 7.50 × 10{sup −4} S cm{sup −1} at the ratio of 3:7 (GMA: BmimTFSI). The interaction between the polymer host and ionic liquid was proved by Attenuated Total Reflectance-Fourier Transformation Infra-Red Spectroscopy (ATR-FTIR). Meanwhile, the X-ray diffraction analysis shows the amorphousity of the polymer electrolyte film increase with the ionic liquid ratio.

  12. Optically active poly(amide-imide)/TiO2 nanocomposites containing amino acid moieties: synthesis and properties.

    PubMed

    Rafiee, Zahra; Zare, Elham

    2015-11-01

    The novel optically active poly(amide-imide) (PAI)/TiO2 nanocomposites containing fluorene moieties have been successfully synthesized through ultrasonic irradiation. The surface of nanoparticles was chemically modified with γ-aminopropyltriethoxyl silane to enhance the compatibility with polymeric matrix and to avoid the aggregation of nanoparticles. The dispersion of surface-modified TiO2 in PAI film was confirmed by the transmission electron microscope (TEM) analysis showing the well-dispersed nanosized TiO2 nanoparticles. The thermal stabilities and optical properties of PAI/surface-modified TiO2 nanocomposite films were also investigated. The thermogravimetric analysis data showed an improvement of thermal stability of novel nanocomposite films as compared to the pure polymer. PMID:26002811

  13. Molecular Dynamics Study on the Particle Dispersion Mechanism of Polyamide-imide/Silica Nano-composite Materials

    NASA Astrophysics Data System (ADS)

    Kikuchi, Hideyuki; Iwasaki, Tomio; Hanawa, Hidehito; Honda, Yuki

    We studied the particle dispersion mechanism of polyamide-imide/silica nano-composite material by using molecular-dynamics simulation technique based on Newtonian dynamics and quantum mechanics. In simulations, adhesive fracture energies at the interfaces between silica and solvents were calculated, and Brownian motions of silica particles were simulated to clarify dispersion properties. The simulation results showed that the colloidal state of silica was maintained by covering the silica surface with a new low hygroscopicity solvent and that the chemical structure of polymer contributed to the dispersion of silica. It is found that the results obtained from molecular dynamics agree well with those obtained by experiments, and that molecular-dynamics simulation technique will become very useful for the development of nano-composite materials in the future.

  14. Synthesis and surface properties of aqueous dispersions of poly(ester-imide) prepared from anhydride terminated polyester prepolymer and diisocyanate.

    PubMed

    Banu, P; Sundar, S; Dhathathreyan, A; Radhakrishnan, G

    2004-09-15

    Aqueous dispersions of poly(ester-imide)s [P(E-I)s] have been prepared by dispersing the P(E-I)s in water without any external solubilizing agents. P(E-I)s were prepared from anhydride-terminated polyester prepolymer and diisocyanate. The -COOH groups in the polymer were then neutralized using triethylamine and the P(E-I)s were subsequently dispersed in water. The influence of the degree of ionization of polymers on the particle size and viscosity of the dispersion has been studied. The dispersions were crosslinked using polyaziridine. The crosslinked dispersion cast films were characterized for dynamic mechanical properties. As the ionic content increased the particle size decreased and the viscosity increased. When the amount of crosslinker added was varied, for a fixed percentage of ionization, the glass transition temperature Tg shifted to higher values. Critical surface tension (CST) measurements indicated reorganization of hydrophobic groups on the surface after crosslinking. PMID:15341840

  15. Carbon dioxide solubility in 1-hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide in a wide range of temperatures and pressures.

    PubMed

    Safarov, Javid; Hamidova, Rena; Stephan, Martin; Kul, Ismail; Shahverdiyev, Astan; Hassel, Egon

    2014-06-19

    Solubility measurement data of carbon dioxide (CO2) in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [HMIM][NTf2] at T = 273.15-413.15 K and pressures up to p = 4.5 MPa using an isochoric method in decrements of ΔT = 20 K are presented. The temperature dependency of the Henry's law constant was calculated, and the average deviation of the Henry's law constant is always better than ±1%. Thermodynamic properties of solution such as the free energy of solvation, the enthalpy of solvation, the entropy of solvation, and the heat capacity of solvation were calculated to evaluate the solute-solvent molecular interactions. PMID:24848716

  16. The Complex Dance of the Two Conformers of Bis(trifluoromethanesulfonyl)imide as a Function of Pressure and Temperature.

    PubMed

    Capitani, F; Gatto, S; Postorino, P; Palumbo, O; Trequattrini, F; Deutsch, M; Brubach, J-B; Roy, P; Paolone, A

    2016-02-25

    Absorbance spectra of two ionic liquids, the short alkyl chain N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) and the longer chain N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI) are reported as a function of pressure and temperature. The occurrence of various phase transitions is evidenced by the changes in the relative concentration of the cisoid and transoid conformers of their common TFSI anion. The infrared spectrum of TMPA-TFSI was measured at 300 K with an applied pressure varying over the 0-5 GPa range. Above 0.2 GPa only the trans conformer is detected, suggesting the occurrence of a pressure induced crystallization. When pressure is applied to TMHA-TFSI at T = 310 K, both TFSI conformers subsist up to ∼11 GPa. However, the clear change of their intensity ratio observed around 2 GPa, suggests the onset of a glass phase as supported by measurements carried out at 4.2 GPa along a cooling/heating cycle. A careful analysis of the spectra collected along different p-T thermodynamic paths shows the occurrence of a cold crystallization at 295 K on heating from 139 K along the p = 0.5 GPa isobar. The rich phase diagrams of the two ionic liquids is the result of the competition among the anion-cation intermolecular interactions, the lower energy of trans-TFSI with respect to cis-TFSI and the smaller volume of cis-TFSI with respect to trans-TFSI. PMID:26840077

  17. Sorption Behavior of Compressed CO2 and CH4 on Ultrathin Hybrid Poly(POSS-imide) Layers.

    PubMed

    Raaijmakers, Michiel J T; Ogieglo, Wojciech; Wiese, Martin; Wessling, Matthias; Nijmeijer, Arian; Benes, Nieck E

    2015-12-01

    Sorption of compressed gases into thin polymeric films is essential for applications including gas sensors and membrane based gas separation. For glassy polymers, the sorption behavior is dependent on the nonequilibrium status of the polymer. The uptake of molecules by a polymer is generally accompanied by dilation, or swelling, of the polymer material. In turn, this dilation can result in penetrant induced plasticization and physical aging that affect the nonequilibrium status of the polymer. Here, we investigate the dilation and sorption behavior of ultrathin membrane layers of a hybrid inorganic-organic network material that consists of alternating polyhedral oligomeric silsesquioxane and imide groups, upon exposure to compressed carbon dioxide and methane. The imide precursor contains fluoroalkene groups that provide affinity toward carbon dioxide, while the octa-functionalized silsesquioxane provides a high degree of cross-linking. This combination allows for extremely high sorption capacities, while structural rearrangements of the network are hindered. We study the simultaneous uptake of gases and dilation of the thin films at high pressures using spectroscopic ellipsometry measurements. Ellipsometry provides the changes in both the refractive index and the film thickness, and allows for accurate quantification of sorption and swelling. In contrast, gravimetric and volumetric measurements only provide a single parameter; this does not allow an accurate correction for, for instance, the changes in buoyancy because of the extensive geometrical changes of highly swelling films. The sorption behavior of the ultrathin hybrid layers depends on the fluoroalkene group content. At low pressure, the apparent molar volume of the gases is low compared to the liquid molar volume of carbon dioxide and methane, respectively. At high gas concentrations in the polymer film, the apparent molar volume of carbon dioxide and methane exceeds that of the liquid molar volume, and

  18. A New Class Of Bilevel And Mono-Level Positive Resist Systems Based On A Chemically Stable Imide Polymer

    NASA Astrophysics Data System (ADS)

    Legenza, M. W.; Vidusek, D. A.; de Grandpre, M.

    1985-04-01

    A new resin system, comprising a thermoplastic polymer backbone with chemically stable imide functionality, has been adapted for use in three different positive resist product types. These include an advanced bilayer system, a near, mid and deep UV monolevel resist; and an antireflective coating. The key features of the imide polymer system which are utilized for the new resist products are: 1. Novolac-like solubility in aqueous base. This property allows formulation of resists, including the planarizing layer of a bilevel system, with conventional types of positive resist photoactive compounds and aqueous base developers, unlike the situation with PMMA which is not base soluble. 2. Transparency to wavelengths above 260nm. This permits use of the polymer as the matrix for systems which utilize mid and deep UV exposure, including the planarizing layer for a bilevel system and mid and deep UV monolayer resists. This is in contrast to novolac resin wHch absorbs strongly in the deep UV region. 3. Insolubility in solvents used for conventional positive resists. This property is critical to use of the resin in planarizing layers of bilevel systems, including antirefiective coatings. It eliminates the intermixing problems which represent a major problem in conventional PMMA bilevel systems. 4. High Tg (185°C). This value is about 80°C higher than that of PMMA and allows higher temperature processing without pattern distortion. 5. Chemical stability and plasma resistance. Unlike conventional reactive polyimide resins the subject polymer is chemically unreactive and is stable to temperatures above 300°C. Further, the polymer has significantly greater resistance to plasma than does PMMA.

  19. Amylin-Aβ oligomers at atomic resolution using molecular dynamics simulations: a link between Type 2 diabetes and Alzheimer's disease

    PubMed Central

    Baram, Michal; Atsmon-Raz, Yoav; Ma, Buyong; Nussinov, Ruth; Miller, Yifat

    2015-01-01

    Clinical studies identified Type 2 diabetes (T2D) as a risk factor of Alzheimer's disease (AD). One of the potential mechanisms that link T2D and AD is the loss of cells associated with degenerative changes. Amylin1-37 aggregates (the pathological species in T2D) were found to be co-localized with those of Aβ1-42 (the pathological species in AD) to form the Amylin1-37-Aβ1-42 plaques, promoting aggregation and thus contributing to the etiology of AD. However, the mechanisms by which Amylin1-37 co-aggregate with Aβ1-42 are still elusive. This work presents the interactions between Amylin1-37 oligomers and Aβ1-42 oligomers at atomic resolution applying extensive molecular dynamics simulations for relatively large ensemble of cross-seeding Amylin1-37 -Aβ1-42 oligomers. The main conclusions of this study are first, Aβ1-42 oligomers prefer to interact with Amylin1-37 oligomers to form single layer conformations (in-register interactions) rather than double layer conformations; and second, in some double layer conformations of the cross-seeding Amylin1-37 -Aβ1-42 oligomers, the Amylin1-37 oligomers destabilize the Aβ1-42 oligomers and thus inhibit Aβ1-42 aggregation, while in other double layer conformations, the Amylin1-37 oligomers stabilize Aβ1-42 oligomers and thus promote Aβ1-42 aggregation. PMID:26349542

  20. Allosteric modulation in monomers and oligomers of a G protein-coupled receptor

    PubMed Central

    Shivnaraine, Rabindra V; Kelly, Brendan; Sankar, Krishana S; Redka, Dar'ya S; Han, Yi Rang; Huang, Fei; Elmslie, Gwendolynne; Pinto, Daniel; Li, Yuchong; Rocheleau, Jonathan V; Gradinaru, Claudiu C; Ellis, John; Wells, James W

    2016-01-01

    The M2 muscarinic receptor is the prototypic model of allostery in GPCRs, yet the molecular and the supramolecular determinants of such effects are unknown. Monomers and oligomers of the M2 muscarinic receptor therefore have been compared to identify those allosteric properties that are gained in oligomers. Allosteric interactions were monitored by means of a FRET-based sensor of conformation at the allosteric site and in pharmacological assays involving mutants engineered to preclude intramolecular effects. Electrostatic, steric, and conformational determinants of allostery at the atomic level were examined in molecular dynamics simulations. Allosteric effects in monomers were exclusively negative and derived primarily from intramolecular electrostatic repulsion between the allosteric and orthosteric ligands. Allosteric effects in oligomers could be positive or negative, depending upon the allosteric-orthosteric pair, and they arose from interactions within and between the constituent protomers. The complex behavior of oligomers is characteristic of muscarinic receptors in myocardial preparations. DOI: http://dx.doi.org/10.7554/eLife.11685.001 PMID:27151542

  1. High-resolution NMR characterization of low abundance oligomers of amyloid-β without purification

    PubMed Central

    Kotler, Samuel A.; Brender, Jeffrey R.; Vivekanandan, Subramanian; Suzuki, Yuta; Yamamoto, Kazutoshi; Monette, Martine; Krishnamoorthy, Janarthanan; Walsh, Patrick; Cauble, Meagan; Holl, Mark M. Banaszak; Marsh, E. Neil. G.; Ramamoorthy, Ayyalusamy

    2015-01-01

    Alzheimer’s disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-β (Aβ). The aggregation of Aβ leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into Aβ oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling 1H-1H NMR experiments to overcome many of these limitations. Using 1H-1H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the Aβ1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time 1H-1H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered Aβ1-40 oligomer 5–15 nm in diameter can form and coexist in parallel with the well-known cross-β-sheet fibrils. PMID:26138908

  2. Cognitive effects of cell-derived and synthetically-derived Aβ oligomers

    PubMed Central

    Reed, Miranda N.; Hofmeister, Jacki J.; Jungbauer, Lisa; Welzel, Alfred T.; Yu, Chunjiang; Sherman, Mathew A.; Lesné, Sylvain; LaDu, Mary Jo; Walsh, Dominic M.; Ashe, Karen H.; Cleary, James P.

    2010-01-01

    Soluble forms of amyloid-β peptide (Aβ) are a molecular focus in Alzheimer's disease research. Soluble Aβ dimers (≈ 8 kDa), timers (≈ 12 kDa), tetramers (≈ 16 kDa) and Aβ*56 (≈ 56 kDa) have shown biological activity. These Aβ molecules have been derived from diverse sources, including chemical synthesis, transfected cells, and mouse and human brain, leading to uncertainty about toxicity and potency. Herein, synthetic Aβ peptide-derived oligomers, cell- and brain-derived low-n oligomers, and Aβ*56, were injected intracerebroventricularly (icv) into rats assayed under the Alternating Lever Cyclic Ratio (ALCR) cognitive assay. Cognitive deficits were detected at 1.3μM of synthetic Aβ oligomers and at low nanomolar concentrations of cell-secreted Aβ oligomers. Trimers, from transgenic mouse brain (Tg2576), did not cause cognitive impairment at any dose tested, whereas Aβ*56 induced concentration-dependent cognitive impairment at 0.9μM and 1.3μM. Thus, while multiple forms of Aβ have cognition impairing activity, there are significant differences in effective concentration and potency. PMID:20031278

  3. Cytotoxic Helix-Rich Oligomer Formation by Melittin and Pancreatic Polypeptide

    PubMed Central

    Singh, Pradeep K.; Ghosh, Dhiman; Tewari, Debanjan; Mohite, Ganesh M.; Carvalho, Edmund; Jha, Narendra Nath; Jacob, Reeba S.; Sahay, Shruti; Banerjee, Rinti; Bera, Amal K.; Maji, Samir K.

    2015-01-01

    Conversion of amyloid fibrils by many peptides/proteins involves cytotoxic helix-rich oligomers. However, their toxicity and biophysical studies remain largely unknown due to their highly dynamic nature. To address this, we chose two helical peptides (melittin, Mel and pancreatic polypeptide, PP) and studied their aggregation and toxicity. Mel converted its random coil structure to oligomeric helical structure upon binding to heparin; however, PP remained as helix after oligomerization. Interestingly, similar to Parkinson’s associated α-synuclein (AS) oligomers, Mel and PP also showed tinctorial properties, higher hydrophobic surface exposure, cellular toxicity and membrane pore formation after oligomerization in the presence of heparin. We suggest that helix-rich oligomers with exposed hydrophobic surface are highly cytotoxic to cells irrespective of their disease association. Moreover as Mel and PP (in the presence of heparin) instantly self-assemble into stable helix-rich amyloidogenic oligomers; they could be represented as models for understanding the biophysical and cytotoxic properties of helix-rich intermediates in detail. PMID:25803428

  4. Aqueous-phase oligomerization of methyl vinyl ketone through photooxidation - Part 1: Aging processes of oligomers

    NASA Astrophysics Data System (ADS)

    Renard, P.; Siekmann, F.; Salque, G.; Demelas, C.; Coulomb, B.; Vassalo, L.; Ravier, S.; Temime-Roussel, B.; Voisin, D.; Monod, A.

    2015-01-01

    It has recently been established that unsaturated water-soluble organic compounds (UWSOCs) might efficiently form oligomers in polluted fogs and wet aerosol particles, even for weakly soluble ones like methyl vinyl ketone (MVK). The atmospheric relevance of these processes is explored by means of multiphase process model studies in a companion paper. In the present study, we investigate the aging of these aqueous-phase MVK oligomers formed via •OH oxidation, as well as their ability to form secondary organic aerosol (SOA) upon water evaporation. The comparison between aqueous-phase composition and aerosol composition after nebulization of the corresponding solutions shows similar trends for oligomer formation and aging. The measurements reveal that oligomer aging leads to the formation of organic diacids. Quantification of the SOA mass formed after nebulization is performed, and the obtained SOA mass yields seem to depend on the spectral irradiance of the light used to initiate the photochemistry. Investigating a large range of initial MVK concentrations (0.2-20 mM), the results show that their •OH oxidation undergoes competition between functionalization and oligomerization that is dependent on the precursor concentration. At high initial MVK concentrations (≥ 2 mM), oligomerization prevails over functionalization, while at lower initial concentrations, oligomerization is not the major process, and functionalization dominates, resulting in small carbonyls, dicarbonyls and monoacids. The atmospheric implications of these processes are discussed.

  5. Diverse Metastable Structures Formed by Small Oligomers of α-Synuclein Probed by Force Spectroscopy

    PubMed Central

    Sosova, Iveta; Belov, Miro; Woodside, Michael T.

    2014-01-01

    Oligomeric aggregates are widely suspected as toxic agents in diseases caused by protein aggregation, yet they remain poorly characterized, partly because they are challenging to isolate from a heterogeneous mixture of species. We developed an assay for characterizing structure, stability, and kinetics of individual oligomers at high resolution and sensitivity using single-molecule force spectroscopy, and applied it to observe the formation of transient structured aggregates within single oligomers of α-synuclein, an intrinsically-disordered protein linked to Parkinson’s disease. Measurements of the molecular extension as the proteins unfolded under tension in optical tweezers revealed that even small oligomers could form numerous metastable structures, with a surprisingly broad range of sizes. Comparing the structures formed in monomers, dimers and tetramers, we found that the average mechanical stability increased with oligomer size. Most structures formed within a minute, with size-dependent rates. These results provide a new window onto the complex α-synuclein aggregation landscape, characterizing the microscopic structural heterogeneity and kinetics of different pathways. PMID:24475132

  6. Oligomers with pendant isocyanate groups as adhesives for dentin and other tissues.

    PubMed

    Lee, C H; Brauer, G M

    1989-03-01

    Oligomers containing pendant isocyanate groups were synthesized from various vinyl monomers, m-isopropenyldimethylbenzyl isocyanate (TMI), and 2-isocyanatoethyl methacrylate (IEM). The liquids were characterized by their refractive indices, infrared spectra, and percentage of isocynate groups in the molecule. Adhesive properties of these compounds were compared with those of oligomers prepared from methacrylate esters, IEM, and/or TMI which had been synthesized previously. Bond strengths of the sodium salt of ethylenediamine-tetraacetic acid (Na2EDTA adjusted to pH 7.4) and glutaraldehyde-treated dentin cemented to composite resin with dilute solutions of the oligomers and then stored in water were determined by the procedure of Kemper and Kilian (1975). These adhesive compositions, especially formulations synthesized from vinyl monomers, adhered at least as well to dentin as did other dentin bonding agents. Oligomers synthesized with methacrylate esters bonded more strongly to bone than did other hard-tissue adhesives. These oligomeric compositions are also excellent soft-tissue adhesives. For example, they provide a strong bond between a collagenous substrate (such as calfskin) and cured denture-base resin. Provided that their biological properties prove satisfactory, these compositions could find many applications as hard- and soft-tissue adhesives in clinical dentistry. PMID:2921392

  7. Development of new fusion proteins for visualizing amyloid-β oligomers in vivo

    PubMed Central

    Ochiishi, Tomoyo; Doi, Motomichi; Yamasaki, Kazuhiko; Hirose, Keiko; Kitamura, Akira; Urabe, Takao; Hattori, Nobutaka; Kinjo, Masataka; Ebihara, Tatsuhiko; Shimura, Hideki

    2016-01-01

    The intracellular accumulation of amyloid-β (Aβ) oligomers critically contributes to disease progression in Alzheimer’s disease (AD) and can be the potential target of AD therapy. Direct observation of molecular dynamics of Aβ oligomers in vivo is key for drug discovery research, however, it has been challenging because Aβ aggregation inhibits the fluorescence from fusion proteins. Here, we developed Aβ1-42-GFP fusion proteins that are oligomerized and visualize their dynamics inside cells even when aggregated. We examined the aggregation states of Aβ-GFP fusion proteins using several methods and confirmed that they did not assemble into fibrils, but instead formed oligomers in vitro and in live cells. By arranging the length of the liker between Aβ and GFP, we generated two fusion proteins with “a long-linker” and “a short-linker”, and revealed that the aggregation property of fusion proteins can be evaluated by measuring fluorescence intensities using rat primary culture neurons transfected with Aβ-GFP plasmids and Aβ-GFP transgenic C. elegans. We found that Aβ-GFP fusion proteins induced cell death in COS7 cells. These results suggested that novel Aβ-GFP fusion proteins could be utilized for studying the physiological functions of Aβ oligomers in living cells and animals, and for drug screening by analyzing Aβ toxicity. PMID:26982553

  8. UV curable lens production using molecular weight controlled PEEK based acrylic oligomer (Ac-PEEK).

    PubMed

    İnan, Tulay Y; Yıldız, Emel; Karaca, Birsen; Dogan, Hacer; Vatansever, Alican; Nalbant, Muhammed; Eken, Koray

    2014-08-01

    We produced UV curable lenses with properties blocking short wave UV light. In the UV-curable formulations, we used an oligomer (Ac-PEEK) with another urethan oligomer (Mw = 2000). Radically active, molecular weight controlled Ac-PEEK was obtained by reacting 2-hydroxyl ethyl methacrylate with molecular- weight- controlled and isocyanate terminated PEEK (Mn = 4500). We characterized all synthesized monomer, oligomer and optical materials with UV/Vis spectrophotometer with interferogram, elemental analyser, mass spectrophotometer, proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermal gravimetric analyzer, differential scanning calorimeter, scanning electron microscopy and gas chromatography. Results suggested that newly synthesized oligomer with the structure of PEEK absorbs short wave UV-light. Ageing tests [ISO 11979-5, Ophthalmic implants-intraocular lenses (IOL)-Part 5: Biocompatibility] performed on the IOL materials were successful. High contact angle of the obtained lenses suggests that all lenses were hydrophobic and SEM results revealed that lenses are morphologically homogeneous. Based on all positive properties just mentioned, we safely conclude that the lenses produced in this study are very promising for IOL production. PMID:24796625

  9. High-resolution NMR characterization of low abundance oligomers of amyloid-β without purification

    NASA Astrophysics Data System (ADS)

    Kotler, Samuel A.; Brender, Jeffrey R.; Vivekanandan, Subramanian; Suzuki, Yuta; Yamamoto, Kazutoshi; Monette, Martine; Krishnamoorthy, Janarthanan; Walsh, Patrick; Cauble, Meagan; Holl, Mark M. Banaszak; Marsh, E. Neil. G.; Ramamoorthy, Ayyalusamy

    2015-07-01

    Alzheimer’s disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-β (Aβ). The aggregation of Aβ leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into Aβ oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling 1H-1H NMR experiments to overcome many of these limitations. Using 1H-1H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the Aβ1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time 1H-1H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered Aβ1-40 oligomer 5-15 nm in diameter can form and coexist in parallel with the well-known cross-β-sheet fibrils.

  10. Structural characterization of toxic oligomers that are kinetically trapped during α-synuclein fibril formation

    PubMed Central

    Chen, Serene W.; Drakulic, Srdja; Deas, Emma; Ouberai, Myriam; Aprile, Francesco A.; Arranz, Rocío; Ness, Samuel; Roodveldt, Cintia; Guilliams, Tim; De-Genst, Erwin J.; Klenerman, David; Wood, Nicholas W.; Knowles, Tuomas P.J.; Alfonso, Carlos; Rivas, Germán; Abramov, Andrey Y.; Valpuesta, José María; Dobson, Christopher M.; Cremades, Nunilo

    2015-01-01

    We describe the isolation and detailed structural characterization of stable toxic oligomers of α-synuclein that have accumulated during the process of amyloid formation. Our approach has allowed us to identify distinct subgroups of oligomers and to probe their molecular architectures by using cryo-electron microscopy (cryoEM) image reconstruction techniques. Although the oligomers exist in a range of sizes, with different extents and nature of β-sheet content and exposed hydrophobicity, they all possess a hollow cylindrical architecture with similarities to certain types of amyloid fibril, suggesting that the accumulation of at least some forms of amyloid oligomers is likely to be a consequence of very slow rates of rearrangement of their β-sheet structures. Our findings reveal the inherent multiplicity of the process of protein misfolding and the key role the β-sheet geometry acquired in the early stages of the self-assembly process plays in dictating the kinetic stability and the pathological nature of individual oligomeric species. PMID:25855634

  11. DFT calculation of the electronic properties of fluorene-1,3,4-thiadiazole oligomers.

    PubMed

    Sánchez-Bojorge, Nora Aydeé; Rodríguez-Valdez, Luz María; Flores-Holguín, Norma

    2013-09-01

    Thiadiazole derivatives have been widely employed in the areas of pharmaceutical, agricultural, industrial, and polymer chemistry. The electronic and molecular structures of thiadiazoles are of interest because they have an equal number of valence electrons and similar molecular structures to thiophenes, which are currently used in the construction of organic solar cells due to their relatively high hole mobilities and good light-harvesting properties. For this reason, the electronic properties of fluorene-1,3,4-thiadiazole oligomers warrant investigation. In the present work, the structure of fluorene-1,3,4-thiadiazole with one thiadiazole unit in the structure was analyzed. This molecule was then expanded until there were 10 thiadiazole units in the structure. The band gap, HOMO and LUMO distributions, and absorption spectrum were analyzed for each molecule. All calculations were performed by applying the B3LYP/6-31G(d) chemical model in the Gaussian 03W and GaussView software packages. The electronic properties were observed to significantly enhance as the number of monomeric units increased, which also caused the gap energy to decrease from 3.51 eV in the oligomer with just one thiadiazole ring to 2.33 eV in the oligomer with 10 units. The HOMO and LUMO regions were well defined and separated for oligomers with at least 5 monomer units of thiadiazole. PMID:23722558

  12. Styrene-terminated polysulfone oligomers as matrix material for graphite reinforced composites - An initial study

    NASA Technical Reports Server (NTRS)

    Garcia, Dana; Bowles, Kenneth J.; Vannucci, Raymond D.

    1987-01-01

    Results pertaining to graphite reinforced composites containing styrene-terminated oligomers as the matrix material are summarized. The processing parameters are determined and the properties of the resulting composite are evaluated. In terms of solvent impregnation techniques, CH2Cl2 is the preferred solvent due to its easy removal during the prepreg drying and consolidation steps.

  13. Methyl-esterified 3-hydroxybutyrate oligomers protect bacteria from hydroxyl radicals.

    PubMed

    Koskimäki, Janne J; Kajula, Marena; Hokkanen, Juho; Ihantola, Emmi-Leena; Kim, Jong H; Hautajärvi, Heidi; Hankala, Elina; Suokas, Marko; Pohjanen, Johanna; Podolich, Olga; Kozyrovska, Natalia; Turpeinen, Ari; Pääkkönen, Mirva; Mattila, Sampo; Campbell, Bruce C; Pirttilä, Anna Maria

    2016-05-01

    Bacteria rely mainly on enzymes, glutathione and other low-molecular weight thiols to overcome oxidative stress. However, hydroxyl radicals are the most cytotoxic reactive oxygen species, and no known enzymatic system exists for their detoxification. We now show that methyl-esterified dimers and trimers of 3-hydroxybutyrate (ME-3HB), produced by bacteria capable of polyhydroxybutyrate biosynthesis, have 3-fold greater hydroxyl radical-scavenging activity than glutathione and 11-fold higher activity than vitamin C or the monomer 3-hydroxybutyric acid. We found that ME-3HB oligomers protect hypersensitive yeast deletion mutants lacking oxidative stress-response genes from hydroxyl radical stress. Our results show that phaC and phaZ, encoding polymerase and depolymerase, respectively, are activated and polyhydroxybutyrate reserves are degraded for production of ME-3HB oligomers in bacteria infecting plant cells and exposed to hydroxyl radical stress. We found that ME-3HB oligomer production is widespread, especially in bacteria adapted to stressful environments. We discuss how ME-3HB oligomers could provide opportunities for numerous applications in human health. PMID:26974813

  14. Development of new fusion proteins for visualizing amyloid-β oligomers in vivo.

    PubMed

    Ochiishi, Tomoyo; Doi, Motomichi; Yamasaki, Kazuhiko; Hirose, Keiko; Kitamura, Akira; Urabe, Takao; Hattori, Nobutaka; Kinjo, Masataka; Ebihara, Tatsuhiko; Shimura, Hideki

    2016-01-01

    The intracellular accumulation of amyloid-β (Aβ) oligomers critically contributes to disease progression in Alzheimer's disease (AD) and can be the potential target of AD therapy. Direct observation of molecular dynamics of Aβ oligomers in vivo is key for drug discovery research, however, it has been challenging because Aβ aggregation inhibits the fluorescence from fusion proteins. Here, we developed Aβ1-42-GFP fusion proteins that are oligomerized and visualize their dynamics inside cells even when aggregated. We examined the aggregation states of Aβ-GFP fusion proteins using several methods and confirmed that they did not assemble into fibrils, but instead formed oligomers in vitro and in live cells. By arranging the length of the liker between Aβ and GFP, we generated two fusion proteins with "a long-linker" and "a short-linker", and revealed that the aggregation property of fusion proteins can be evaluated by measuring fluorescence intensities using rat primary culture neurons transfected with Aβ-GFP plasmids and Aβ-GFP transgenic C. elegans. We found that Aβ-GFP fusion proteins induced cell death in COS7 cells. These results suggested that novel Aβ-GFP fusion proteins could be utilized for studying the physiological functions of Aβ oligomers in living cells and animals, and for drug screening by analyzing Aβ toxicity. PMID:26982553

  15. A simple procedure for preparing chitin oligomers through acetone precipitation after hydrolysis in concentrated hydrochloric acid.

    PubMed

    Kazami, Nao; Sakaguchi, Masayoshi; Mizutani, Daisuke; Masuda, Tatsuhiko; Wakita, Satoshi; Oyama, Fumitaka; Kawakita, Masao; Sugahara, Yasusato

    2015-11-01

    Chitin oligomers are of interest because of their numerous biologically relevant properties. To prepare chitin oligomers containing 4-6 GlcNAc units [(GlcNAc)4-6], α- and β-chitin were hydrolyzed with concentrated hydrochloric acid at 40 °C. The reactant was mixed with acetone to recover the acetone-insoluble material, and (GlcNAc)4-6 was efficiently recovered after subsequent water extraction. Composition analysis using gel permeation chromatography and MALDI-TOF mass spectrometry indicated that (GlcNAc)4-6 could be isolated from the acetone-insoluble material with recoveries of approximately 17% and 21% from the starting α-chitin and β-chitin, respectively. The acetone precipitation method is highly useful for recovering chitin oligomers from the acid hydrolysate of chitin. The changes in the molecular size and higher-order structure of chitin during the course of hydrolysis were also analyzed, and a model that explains the process of oligomer accumulation is proposed. PMID:26256353

  16. High-resolution NMR characterization of low abundance oligomers of amyloid-β without purification.

    PubMed

    Kotler, Samuel A; Brender, Jeffrey R; Vivekanandan, Subramanian; Suzuki, Yuta; Yamamoto, Kazutoshi; Monette, Martine; Krishnamoorthy, Janarthanan; Walsh, Patrick; Cauble, Meagan; Holl, Mark M Banaszak; Marsh, E Neil G; Ramamoorthy, Ayyalusamy

    2015-01-01

    Alzheimer's disease is characterized by the misfolding and self-assembly of the amyloidogenic protein amyloid-β (Aβ). The aggregation of Aβ leads to diverse oligomeric states, each of which may be potential targets for intervention. Obtaining insight into Aβ oligomers at the atomic level has been a major challenge to most techniques. Here, we use magic angle spinning recoupling (1)H-(1)H NMR experiments to overcome many of these limitations. Using (1)H-(1)H dipolar couplings as a NMR spectral filter to remove both high and low molecular weight species, we provide atomic-level characterization of a non-fibrillar aggregation product of the Aβ1-40 peptide using non-frozen samples without isotopic labeling. Importantly, this spectral filter allows the detection of the specific oligomer signal without a separate purification procedure. In comparison to other solid-state NMR techniques, the experiment is extraordinarily selective and sensitive. A resolved 2D spectra could be acquired of a small population of oligomers (6 micrograms, 7% of the total) amongst a much larger population of monomers and fibers (93% of the total). By coupling real-time (1)H-(1)H NMR experiments with other biophysical measurements, we show that a stable, primarily disordered Aβ1-40 oligomer 5-15 nm in diameter can form and coexist in parallel with the well-known cross-β-sheet fibrils. PMID:26138908

  17. Student-Driven Design of Peptide Mimetics: Microwave-Assisted Synthesis of Peptoid Oligomers

    ERIC Educational Resources Information Center

    Pohl, Nicola L. B.; Kirshenbaum, Kent; Yoo, Barney; Schulz, Nathan; Zea, Corbin J.; Streff, Jennifer M.; Schwarz, Kimberly L.

    2011-01-01

    An experiment for the undergraduate organic laboratory is described in which peptide mimetic oligomers called "peptoids" are built stepwise on a solid-phase resin. Students employ two modern strategies to facilitate rapid multistep syntheses: solid-phase techniques to obviate the need for intermediate purifications and microwave irradiation to…

  18. Optimization of the All-D Peptide D3 for Aβ Oligomer Elimination

    PubMed Central

    Klein, Antonia Nicole; Ziehm, Tamar; Tusche, Markus; Buitenhuis, Johan; Bartnik, Dirk; Boeddrich, Annett; Wiglenda, Thomas; Wanker, Erich; Funke, Susanne Aileen; Brener, Oleksandr; Gremer, Lothar; Kutzsche, Janine; Willbold, Dieter

    2016-01-01

    The aggregation of amyloid-β (Aβ) is postulated to be the crucial event in Alzheimer’s disease (AD). In particular, small neurotoxic Aβ oligomers are considered to be responsible for the development and progression of AD. Therefore, elimination of thesis oligomers represents a potential causal therapy of AD. Starting from the well-characterized d-enantiomeric peptide D3, we identified D3 derivatives that bind monomeric Aβ. The underlying hypothesis is that ligands bind monomeric Aβ and stabilize these species within the various equilibria with Aβ assemblies, leading ultimately to the elimination of Aβ oligomers. One of the hereby identified d-peptides, DB3, and a head-to-tail tandem of DB3, DB3DB3, were studied in detail. Both peptides were found to: (i) inhibit the formation of Thioflavin T-positive fibrils; (ii) bind to Aβ monomers with micromolar affinities; (iii) eliminate Aβ oligomers; (iv) reduce Aβ-induced cytotoxicity; and (v) disassemble preformed Aβ aggregates. The beneficial effects of DB3 were improved by DB3DB3, which showed highly enhanced efficacy. Our approach yielded Aβ monomer-stabilizing ligands that can be investigated as a suitable therapeutic strategy against AD. PMID:27105346

  19. Stabilizing Off-pathway Oligomers by Polyphenol Nanoassemblies for IAPP Aggregation Inhibition

    PubMed Central

    Nedumpully-Govindan, Praveen; Kakinen, Aleksandr; Pilkington, Emily H.; Davis, Thomas P.; Chun Ke, Pu; Ding, Feng

    2016-01-01

    Experimental studies have shown that many naturally occurring polyphenols have inhibitory effect on the aggregation of several proteins. Here, we use discrete molecular dynamics (DMD) simulations and high-throughput dynamic light scattering (DLS) experiments to study the anti-aggregation effects of two polyphenols, curcumin and resveratrol, on the aggregation of islet amyloid polypeptide (IAPP or amylin). Our DMD simulations suggest that the aggregation inhibition is caused by stabilization of small molecular weight IAPP off-pathway oligomers by the polyphenols. Our analysis indicates that IAPP-polyphenol hydrogen bonds and π-π stacking combined with hydrophobic interactions are responsible for the stabilization of oligomers. The presence of small oligomers is confirmed with DLS measurements in which nanometer-sized oligomers are found to be stable for up to 7.5 hours, the time frame within which IAPP aggregates in the absence of polyphenols. Our study offers a general anti-aggregation mechanism for polyphenols, and further provides a computational framework for the future design of anti-amyloid aggregation therapeutics. PMID:26763863

  20. A method for the 32P labeling of peptides or peptide nucleic acid oligomers

    NASA Technical Reports Server (NTRS)

    Kozlov, I. A.; Nielsen, P. E.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    1998-01-01

    A novel approach to the radioactive labeling of peptides and PNA oligomers is described. It is based on the conjugation of a deoxynucleoside 3'-phosphate with the terminal amine of the substrate, followed by phosphorylation of the 5'-hydroxyl group of the nucleotide using T4 polynucleotide kinase and [gamma-32P]ATP.

  1. Parkinson's Disease with Fatigue: Clinical Characteristics and Potential Mechanisms Relevant to α-Synuclein Oligomer

    PubMed Central

    Zuo, Li-Jun; Yu, Shu-Yang; Wang, Fang; Hu, Yang; Piao, Ying-Shan; Du, Yang; Lian, Teng-Hong; Wang, Rui-Dan; Yu, Qiu-Jin; Wang, Ya-Jie; Wang, Xiao-Min; Chan, Piu; Chen, Sheng-Di; Wang, Yongjun

    2016-01-01

    Background and Purpose The aim of this study was to identify the clinical characteristics and potential mechanisms relevant to pathological proteins in Parkinson's disease (PD) patients who experience fatigue. Methods PD patients (n=102) were evaluated using a fatigue severity scale and scales for motor and nonmotor symptoms. The levels of three pathological proteins—α-synuclein oligomer, β-amyloid (Aβ)1-42, and tau—were measured in 102 cerebrospinal fluid (CSF) samples from these PD patients. Linear regression analyses were performed between fatigue score and the CSF levels of the above-listed pathological proteins in PD patients. Results The frequency of fatigue in the PD patients was 62.75%. The fatigue group had worse motor symptoms and anxiety, depression, and autonomic dysfunction. The CSF level of α-synuclein oligomer was higher and that of Aβ1-42 was lower in the fatigue group than in the non-fatigue group. In multiple linear regression analyses, fatigue severity was significantly and positively correlated with the α-synuclein oligomer level in the CSF of PD patients, after adjusting for confounders. Conclusions PD patients experience a high frequency of fatigue. PD patients with fatigue have worse motor and part nonmotor symptoms. Fatigue in PD patients is associated with an increased α-synuclein oligomer level in the CSF. PMID:26869370

  2. Synthesis and characterization of an isoindigo-dithienocarbazole-isoindigo oligomer for organic solar cells

    NASA Astrophysics Data System (ADS)

    Lyu, Fuzhen; Park, Hanok; Lee, Soo-Hyoung; Lee, Sang Hee; Lee, Youn-Sik

    2014-08-01

    An isoindigo-dithienocarbazole-isoindigo oligomer (II-DTC-II) was synthesized by a Stille coupling reaction between N-hexadecyl-2,8-bis(trimethylstannyl)dithieno[3,2-b:6,7-b]carbazole and 6-bromo-N,N‧-dioctylisoindigo. The oligomer exhibited a broad absorption with an optical band gap of 1.75 eV and a highest occupied molecular orbital energy level of -5.46 eV. Photovoltaic devices were fabricated using the II-DTC-II oligomer and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM), to obtain the configuration ITO/PEDOT:PSS/II-DTC-II:PC71BM/LiF/Al. The best power conversion efficiency of the II-DTC-II-based devices was 1.13% when 0.8 wt% diiodooctane was mixed into the active layer of II-DTC-II/PC71BM (1:1). The low conversion efficiency was attributed to the oligomer's poor solubility and miscibility with PC71BM.

  3. Stabilizing Off-pathway Oligomers by Polyphenol Nanoassemblies for IAPP Aggregation Inhibition.

    PubMed

    Nedumpully-Govindan, Praveen; Kakinen, Aleksandr; Pilkington, Emily H; Davis, Thomas P; Chun Ke, Pu; Ding, Feng

    2016-01-01

    Experimental studies have shown that many naturally occurring polyphenols have inhibitory effect on the aggregation of several proteins. Here, we use discrete molecular dynamics (DMD) simulations and high-throughput dynamic light scattering (DLS) experiments to study the anti-aggregation effects of two polyphenols, curcumin and resveratrol, on the aggregation of islet amyloid polypeptide (IAPP or amylin). Our DMD simulations suggest that the aggregation inhibition is caused by stabilization of small molecular weight IAPP off-pathway oligomers by the polyphenols. Our analysis indicates that IAPP-polyphenol hydrogen bonds and π-π stacking combined with hydrophobic interactions are responsible for the stabilization of oligomers. The presence of small oligomers is confirmed with DLS measurements in which nanometer-sized oligomers are found to be stable for up to 7.5 hours, the time frame within which IAPP aggregates in the absence of polyphenols. Our study offers a general anti-aggregation mechanism for polyphenols, and further provides a computational framework for the future design of anti-amyloid aggregation therapeutics. PMID:26763863

  4. High-Capacity Conductive Nanocellulose Paper Sheets for Electrochemically Controlled Extraction of DNA Oligomers

    PubMed Central

    Razaq, Aamir; Nyström, Gustav; Strømme, Maria; Mihranyan, Albert; Nyholm, Leif

    2011-01-01

    Highly porous polypyrrole (PPy)-nanocellulose paper sheets have been evaluated as inexpensive and disposable electrochemically controlled three-dimensional solid phase extraction materials. The composites, which had a total anion exchange capacity of about 1.1 mol kg−1, were used for extraction and subsequent release of negatively charged fluorophore tagged DNA oligomers via galvanostatic oxidation and reduction of a 30–50 nm conformal PPy layer on the cellulose substrate. The ion exchange capacity, which was, at least, two orders of magnitude higher than those previously reached in electrochemically controlled extraction, originated from the high surface area (i.e. 80 m2 g−1) of the porous composites and the thin PPy layer which ensured excellent access to the ion exchange material. This enabled the extractions to be carried out faster and with better control of the PPy charge than with previously employed approaches. Experiments in equimolar mixtures of (dT)6, (dT)20, and (dT)40 DNA oligomers showed that all oligomers could be extracted, and that the smallest oligomer was preferentially released with an efficiency of up to 40% during the reduction of the PPy layer. These results indicate that the present material is very promising for the development of inexpensive and efficient electrochemically controlled ion-exchange membranes for batch-wise extraction of biomolecules. PMID:22195031

  5. Secondary Ion Mass Spectrometry of Zeolite Materials: Observation of Abundant Aluminosilicate Oligomers Using an Ion Trap

    SciTech Connect

    Groenewold, Gary Steven; Kessinger, Glen Frank; Scott, Jill Rennee; Gianotto, Anita Kay; Appelhans, Anthony David; Delmore, James Edward

    2000-12-01

    Oligomeric oxyanions were observed in the secondary ion mass spectra (SIMS) of zeolite materials. The oxyanions have the general composition AlmSinO2(m+n)H(m-1)- (m + n = 2 to 8) and are termed dehydrates. For a given mass, multiple elemental compositions are possible because (Al + H) is an isovalent and isobaric substitute for Si. Using 18 keV Ga+ as a projectile, oligomer abundances are low relative to the monomers. Oligomer abundance can be increased by using the polyatomic projectile ReO4- (~5 keV). Oligomer abundance can be further increased using an ion trap (IT-) SIMS; in this instrument, long ion lifetimes (tens of ms) and relatively high He pressure result in significant collisional stabilization and increased high-mass abundance. The dehydrates rapidly react with adventitious H2O present in the IT-SIMS to form mono-, di-, and trihydrates. The rapidity of the reaction and comparison to aluminum oxyanion hydration suggest that H2O adds to the aluminosilicate oxyanions in a dissociative fashion, forming covalently bound product ions. In addition to these findings, it was noted that production of abundant oligomeric aluminosilicates could be significantly increased by substituting the countercation (NH4+) with the larger alkali ions Rb+ and Cs+. This constitutes a useful tactic for generating large aluminosilicate oligomers for surface characterization and ion-molecule reactivity studies.

  6. The Volumetric Diversity of Misfolded Prion Protein Oligomers Revealed by Pressure Dissociation*

    PubMed Central

    Torrent, Joan; Lange, Reinhard; Rezaei, Human

    2015-01-01

    Protein oligomerization has been associated with a wide range of diseases. High pressure approaches offer a powerful tool for deciphering the underlying molecular mechanisms by revealing volume changes associated with the misfolding and assembly reactions. We applied high pressure to induce conformational changes in three distinct β-sheet-rich oligomers of the prion protein PrP, a protein characterized by a variety of infectious quaternary structures that can propagate stably and faithfully and cause diseases with specific phenotypic traits. We show that pressure induces dissociation of the oligomers and leads to a lower volume monomeric PrP state that refolds into the native conformation after pressure release. By measuring the different pressure and temperature sensitivity of the tested PrP oligomers, we demonstrate significantly different void volumes in their quaternary structure. In addition, by focusing on the kinetic and energetic behavior of the pressure-induced dissociation of one specific PrP oligomer, we reveal a large negative activation volume and an increase in both apparent activation enthalpy and entropy. This suggests a transition state ensemble that is less structured and significantly more hydrated than the oligomeric state. Finally, we found that site-specific fluorescent labeling allows monitoring of the transient population of a kinetic intermediate in the dissociation reaction. Our results indicate that defects in atomic packing may deserve consideration as a new factor that influences differences between PrP assemblies and that could be relevant also for explaining the origin of prion strains. PMID:26126829

  7. Conformational Flexibility of Soluble Cellulose Oligomers: Chain Length and Temperature Dependence

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Structures, dynamics, and stabilities of different sized cellulosic oligomers need to be considered when designing enzymatic cocktails for the conversion of biomass to biofuels since they can be both productive substrates and inhibitors of the overall process. In the present work, the conformational...

  8. Chemical evolution. XXII - The hydantoins released on hydrolysis of HCN oligomers

    NASA Technical Reports Server (NTRS)

    Ferris, J. P.; Wos, J. D.; Lobo, A. P.

    1974-01-01

    The isolation of three hydantoins from HCN oligomers is described. One of these hydantoins, 5-carboxymethylidine hydantoin (5-CMH), rearranges to pyrimidine orotic acid in basic solution. The isolation of 5-CMH suggests the possibility that pyrimidines were formed directly from HCN on the primitive earth.

  9. Rapid Multistep Synthesis of a Bioactive Peptidomimetic Oligomer for the Undergraduate Laboratory

    ERIC Educational Resources Information Center

    Utku, Yeliz; Rohatgi, Abhinav; Yoo, Barney; Kirshenbaum, Kent; Zuckermann, Ronald N.; Pohl, Nicola L.

    2010-01-01

    Peptidomimetic compounds are increasingly important in drug-discovery applications. We introduce the synthesis of an N-substituted glycine oligomer, a bioactive "peptoid" trimer. The six-step protocol is conducted on solid-phase resin, enabling the synthesis to be performed by undergraduate organic chemistry students. This synthesis lab was…

  10. Hybrid conjugated organic oligomers consisting of oligodiacetylene and thiophene units: synthesis and optical properties.

    PubMed

    Pilzak, Gregor S; van Gruijthuijsen, Kitty; van Doorn, Reindert H; van Lagen, Barend; Sudhölter, Ernst J R; Zuilhof, Han

    2009-09-14

    Novel and highly soluble hybrid conjugated organic oligomers consisting of oligodiacetylene and thiophene units have been synthesized in high purity through iterative and divergent approaches based on a sequence of Sonogashira reactions. The series of thiophene-containing oligodiacetylenes (ThODAs) and homocoupled ThODAs (HThODAs) show--both in solution and in the solid state--a strong optical absorption, which is progressively red shifted with increasing chain length. The linear correlation of the absorption maximum (lambda(A)(max)) with the inverse of conjugation length (CL = number of double and triple bonds) shows that the effective conjugation length of this system is extended up to at least CL = 20. Furthermore, absorption measurements of dropcast thin films display not only a bathochromic shift of the absorption maxima but also a higher wavelength absorption, which is attributed to increased pi-pi interactions. The wavelength of the maximum fluorescence emission (lambda(E)(max)) also increases with CL, and emission is maximal for oligomers with CL=7-12 (fluorescence quantum yield Phi(F) = approximately 0.2). Both longer and shorter oligomers display marginal emission. The calculated Stokes shifts of these planar materials are relatively large (0.4 eV) for all oligomers, and likely due to excitation to the S(2) state, thus suggesting that the presence of enyne moieties dominates the ordering of the lowest excited states. The fluorescence lifetimes (tau(F)) are short (tau(F,max) = <1 ns) and closely follow the tendency obtained for the fluorescence quantum yield. The anisotropy lifetimes show a near-linear increase with CL, in line with highly rigid oligomers. PMID:19637259

  11. Native metastable prefibrillar oligomers are the most neurotoxic species among amyloid aggregates.

    PubMed

    Diociaiuti, Marco; Macchia, Gianfranco; Paradisi, Silvia; Frank, Claudio; Camerini, Serena; Chistolini, Pietro; Gaudiano, Maria Cristina; Petrucci, Tamara Corinna; Malchiodi-Albedi, Fiorella

    2014-09-01

    Many proteins belonging to the amyloid family share the tendency to misfold and aggregate following common steps, and display similar neurotoxicity. In the aggregation pathway different kinds of species are formed, including several types of oligomers and eventually mature fibers. It is now suggested that the pathogenic aggregates are not the mature fibrils, but the intermediate, soluble oligomers. Many kinds of aggregates have been described to exist in a metastable state and in equilibrium with monomers. Up to now it is not clear whether a specific structure is at the basis of the neurotoxicity. Here we characterized, starting from the early aggregation stages, the oligomer populations formed by an amyloid protein, salmon calcitonin (sCT), chosen due to its very slow aggregation rate. To prepare different oligomer populations and characterize them by means of photoinduced cross-linking SDS-PAGE, Energy Filtered-Transmission Electron Microscopy (EF-TEM) and Circular Dichroism (CD) spectroscopy, we used Size Exclusion Chromatography (SEC), a technique that does not influence the aggregation process leaving the protein in the native state. Taking advantage of sCT low aggregation rate, we characterized the neurotoxic potential of the SEC-separated, non-crosslinked fractions in cultured primary hippocampal neurons, analyzing intracellular Ca(2+) influx and apoptotic trend. We provide evidence that native, globular, metastable, prefibrillar oligomers (dimers, trimers and tetramers) were the toxic species and that low concentrations of these aggregates in the population was sufficient to render the sample neurotoxic. Monomers and other kind of aggregates, such as annular or linear protofibers and mature fibers, were totally biologically inactive. PMID:24932517

  12. Protective spin-labeled fluorenes maintain amyloid beta peptide in small oligomers and limit transitions in secondary structure

    SciTech Connect

    Altman, Robin; Ly, Sonny; Hilt, Silvia; Petrlova, Jitka; Maezawa, Izumi; Kálai, Tamás; Hideg, Kálmán; Jin, Lee-Way; Laurence, Ted A.; Voss, John C.

    2015-12-01

    Alzheimer’s disease is characterized by the presence of extracellular plaques comprised of amyloid beta (Aβ) peptides. Soluble oligomers of the Aβ peptide underlie a cascade of neuronal loss and dysfunction associated with Alzheimer's disease. Single particle analyses of Aβ oligomers in solution by fluorescence correlation spectroscopy (FCS) were used to provide real-time descriptions of how spin-labeled fluorenes (SLFs; bi-functional small molecules that block the toxicity of Aβ) prevent and disrupt oligomeric assemblies of Aβ in solution. The FCS results, combined with electron paramagnetic resonance spectroscopy and circular dichroism spectroscopy, demonstrate SLFs can inhibit the growth of Aβ oligomers and disrupt existing oligomers while retaining Aβ in a largely disordered state. Furthermore, while the ability of SLF to block Aβ toxicity correlates with a reduction in oligomer size, our results suggest the conformation of Aβ within the oligomer determines the toxicity of the species. Attenuation of Aβ toxicity, which has been associated primarily with the soluble oligomeric form, can be achieved through redistribution of the peptides into smaller oligomers and arrest of the fractional increase in beta secondary structure.

  13. Protective spin-labeled fluorenes maintain amyloid beta peptide in small oligomers and limit transitions in secondary structure

    DOE PAGESBeta

    Altman, Robin; Ly, Sonny; Hilt, Silvia; Petrlova, Jitka; Maezawa, Izumi; Kálai, Tamás; Hideg, Kálmán; Jin, Lee-Way; Laurence, Ted A.; Voss, John C.

    2015-12-01

    Alzheimer’s disease is characterized by the presence of extracellular plaques comprised of amyloid beta (Aβ) peptides. Soluble oligomers of the Aβ peptide underlie a cascade of neuronal loss and dysfunction associated with Alzheimer's disease. Single particle analyses of Aβ oligomers in solution by fluorescence correlation spectroscopy (FCS) were used to provide real-time descriptions of how spin-labeled fluorenes (SLFs; bi-functional small molecules that block the toxicity of Aβ) prevent and disrupt oligomeric assemblies of Aβ in solution. The FCS results, combined with electron paramagnetic resonance spectroscopy and circular dichroism spectroscopy, demonstrate SLFs can inhibit the growth of Aβ oligomers and disruptmore » existing oligomers while retaining Aβ in a largely disordered state. Furthermore, while the ability of SLF to block Aβ toxicity correlates with a reduction in oligomer size, our results suggest the conformation of Aβ within the oligomer determines the toxicity of the species. Attenuation of Aβ toxicity, which has been associated primarily with the soluble oligomeric form, can be achieved through redistribution of the peptides into smaller oligomers and arrest of the fractional increase in beta secondary structure.« less

  14. Hypoglycemic activities of A- and B-type procyanidin oligomer-rich extracts from different Cinnamon barks.

    PubMed

    Lu, Zhaolian; Jia, Qi; Wang, Rui; Wu, Ximin; Wu, Yingchun; Huang, Caiguo; Li, Yiming

    2011-02-15

    Procyanidin oligomers in Cinnamon are thought to be responsible for the biological activity in the treatment of diabetes mellitus (DM). To clarify types of procyanidin oligomers in different Cinnamon species and investigate their different effects, the present study investigated procyanidin oligomers in polyphenolic oligomer-rich extracts of three Cinnamon samples by LC-MS methods, and their hypoglycemic activities were detected in vivo and in vitro. The results showed that two of the three samples from Cinnamomum cassia were rich in B-type procyanidin oligomers, and the other sample was rich in A-type procyanidin oligomers. The Cinnamon extracts were administered at doses of 200 and 300 mg/kg body wt. in high-fat diet-fed and low-dose streptozotocin (STZ)-induced diabetic mice for 14 days. The results showed that blood glucose concentrations were significantly decreased in all Cinnamon extract groups compared with the control group (p<0.05). Administration of the Cinnamon extracts significantly increased the consumption of extracellular glucose in insulin-resistant HepG2 cells and normal HepG2 cells compared with the control group. These results suggest that both A- and B-type procyanidin oligomers in different Cinnamon species have hypoglycemic activities and may improve insulin sensitivity in type 2 DM. PMID:20851586

  15. Amyloid β oligomers elicit mitochondrial transport defects and fragmentation in a time-dependent and pathway-specific manner.

    PubMed

    Rui, Yanfang; Zheng, James Q

    2016-01-01

    Small oligomeric forms of amyloid-β (Aβ) are believed to be the culprit for declined brain functions in AD in part through their impairment of neuronal trafficking and synaptic functions. However, the precise cellular actions of Aβ oligomers and underlying mechanisms in neurons remain to be fully defined. Previous studies have identified mitochondria as a major target of Aβ toxicity contributing to early cognitive decline and memory loss in neurodegenerative diseases including Alzheimer's disease (AD). In this study, we report that Aβ oligomers acutely elicit distinct effects on the transport and integrity of mitochondria. We found that acute exposure of hippocampal neurons to Aβ oligomers from either synthetic peptides or AD brain homogenates selectively impaired fast transport of mitochondria without affecting the movement of late endosomes and lysosomes. Extended exposure of hipoocampal neurons to Aβ oligomers was found to result in mitochondrial fragmentation. While both mitochondrial effects induced by Aβ oligomers can be abolished by the inhibition of GSK3β, they appear to be independent from each other. Aβ oligomers impaired mitochondrial transport through HDAC6 activation whereas the fragmentation involved the GTPase Drp-1. These results show that Aβ oligomers can acutely disrupt mitochondrial transport and integrity in a time-dependent and pathway-specific manner. These findings thus provide new insights into Aβ-induced mitochondrial defects that may contribute to neuronal dysfunction and AD pathogenesis. PMID:27535553

  16. Thiophene-based donor-acceptor co-oligomers by copper-catalyzed 1,3-dipolar cycloaddition.

    PubMed

    Potratz, Stefanie; Mishra, Amaresh; Bäuerle, Peter

    2012-01-01

    Herein we present a three-component one-pot procedure to synthesize co-oligomers of a donor-acceptor-donor type, in which thiophene moieties work as donor and 1,2,3-triazoles as acceptor units. In this respect, terminally ethynylated (oligo)thiophenes were coupled to halogenated (oligo)thiophenes in the presence of sodium azide and a copper catalyst. Optoelectronic properties of various thiophene-1,2,3-triazole co-oligomers were investigated by UV-vis spectroscopy and cyclic voltammetry. Several co-oligomers were electropolymerized to the corresponding conjugated polymers. PMID:23015814

  17. Thiophene-based donor–acceptor co-oligomers by copper-catalyzed 1,3-dipolar cycloaddition

    PubMed Central

    Potratz, Stefanie; Mishra, Amaresh

    2012-01-01

    Summary Herein we present a three-component one-pot procedure to synthesize co-oligomers of a donor–acceptor–donor type, in which thiophene moieties work as donor and 1,2,3-triazoles as acceptor units. In this respect, terminally ethynylated (oligo)thiophenes were coupled to halogenated (oligo)thiophenes in the presence of sodium azide and a copper catalyst. Optoelectronic properties of various thiophene-1,2,3-triazole co-oligomers were investigated by UV–vis spectroscopy and cyclic voltammetry. Several co-oligomers were electropolymerized to the corresponding conjugated polymers. PMID:23015814

  18. Nonenzymatic synthesis of RNA and DNA oligomers on hexitol nucleic acid templates: the importance of the A structure

    NASA Technical Reports Server (NTRS)

    Kozlov, I. A.; Politis, P. K.; Van Aerschot, A.; Busson, R.; Herdewijn, P.; Orgel, L. E.; Bada, J. L. (Principal Investigator); Dolan, M. (Principal Investigator)

    1999-01-01

    Hexitol nucleic acid (HNA) is an analogue of DNA containing the standard nucleoside bases, but with a phosphorylated 1,5-anhydrohexitol backbone. HNA oligomers form duplexes having the nucleic acid A structure with complementary DNA or RNA oligomers. The HNA decacytidylate oligomer is an efficient template for the oligomerization of the 5'-phosphoroimidazolides of guanosine or deoxyguanosine. Comparison of the oligomerization efficiencies on HNA, RNA, and DNA decacytidylate templates under various conditions suggests strongly that only nucleic acid double helices with the A structure support efficient template-directed synthesis when 5'-phosphoroimidazolides of nucleosides are used as substrates.

  19. Comparison of the anodic behavior of aluminum current collectors in imide-based ionic liquids and consequences on the stability of high voltage supercapacitors

    NASA Astrophysics Data System (ADS)

    Kühnel, Ruben-Simon; Balducci, Andrea

    2014-03-01

    In this work, the influence of two common ionic liquid (IL) anions on the anodic stability of Al current collectors was studied. Namely, the Al corrosion/passivation process in N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) is compared to the one in N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI). It is shown, that Al slowly corrodes in PYR14FSI, while it is much better passivated in PYR14TFSI, although the ionic liquids were prepared in the same way. Float tests were carried out to illustrate the consequences of these different anodic stabilities of Al on the cycling stability of supercapacitors. Interestingly, when the chloride content of PYR14FSI was <1 ppm, Al electrodes were also pretty stable in this IL, and a similar cycling stability during float tests than for PYR14TFSI could be obtained.

  20. Rifampicin is a candidate preventive medicine against amyloid-β and tau oligomers.

    PubMed

    Umeda, Tomohiro; Ono, Kenjiro; Sakai, Ayumi; Yamashita, Minato; Mizuguchi, Mineyuki; Klein, William L; Yamada, Masahito; Mori, Hiroshi; Tomiyama, Takami

    2016-05-01

    Amyloid-β, tau, and α-synuclein, or more specifically their soluble oligomers, are the aetiologic molecules in Alzheimer's disease, tauopathies, and α-synucleinopathies, respectively. These proteins have been shown to interact to accelerate each other's pathology. Clinical studies of amyloid-β-targeting therapies in Alzheimer's disease have revealed that the treatments after disease onset have little benefit on patient cognition. These findings prompted us to explore a preventive medicine which is orally available, has few adverse effects, and is effective at reducing neurotoxic oligomers with a broad spectrum. We initially tested five candidate compounds: rifampicin, curcumin, epigallocatechin-3-gallate, myricetin, and scyllo-inositol, in cells expressing amyloid precursor protein (APP) with the Osaka (E693Δ) mutation, which promotes amyloid-β oligomerization. Among these compounds, rifampicin, a well-known antibiotic, showed the strongest activities against the accumulation and toxicity (i.e. cytochrome c release from mitochondria) of intracellular amyloid-β oligomers. Under cell-free conditions, rifampicin inhibited oligomer formation of amyloid-β, tau, and α-synuclein, indicating its broad spectrum. The inhibitory effects of rifampicin against amyloid-β and tau oligomers were evaluated in APPOSK mice (amyloid-β oligomer model), Tg2576 mice (Alzheimer's disease model), and tau609 mice (tauopathy model). When orally administered to 17-month-old APPOSK mice at 0.5 and 1 mg/day for 1 month, rifampicin reduced the accumulation of amyloid-β oligomers as well as tau hyperphosphorylation, synapse loss, and microglial activation in a dose-dependent manner. In the Morris water maze, rifampicin at 1 mg/day improved memory of the mice to a level similar to that in non-transgenic littermates. Rifampicin also inhibited cytochrome c release from the mitochondria and caspase 3 activation in the hippocampus. In 13-month-old Tg2576 mice, oral rifampicin at 0.5 mg

  1. Accumulation of oligomer-prone α-synuclein exacerbates synaptic and neuronal degeneration in vivo

    PubMed Central

    Rockenstein, Edward; Nuber, Silke; Overk, Cassia R.; Ubhi, Kiren; Mante, Michael; Patrick, Christina; Adame, Anthony; Trejo-Morales, Margarita; Gerez, Juan; Picotti, Paola; Jensen, Poul H.; Campioni, Silvia; Riek, Roland; Winkler, Jürgen; Gage, Fred H.; Winner, Beate

    2014-01-01

    In Parkinson’s disease and dementia with Lewy bodies, α-synuclein aggregates to form oligomers and fibrils; however, the precise nature of the toxic α-synuclein species remains unclear. A number of synthetic α-synuclein mutations were recently created (E57K and E35K) that produce species of α-synuclein that preferentially form oligomers and increase α-synuclein-mediated toxicity. We have shown that acute lentiviral expression of α-synuclein E57K leads to the degeneration of dopaminergic neurons; however, the effects of chronic expression of oligomer-prone α-synuclein in synapses throughout the brain have not been investigated. Such a study could provide insight into the possible mechanism(s) through which accumulation of α-synuclein oligomers in the synapse leads to neurodegeneration. For this purpose, we compared the patterns of neurodegeneration and synaptic damage between a newly generated mThy-1 α-synuclein E57K transgenic mouse model that is prone to forming oligomers and the mThy-1 α-synuclein wild-type mouse model (Line 61), which accumulates various forms of α-synuclein. Three lines of α-synuclein E57K (Lines 9, 16 and 54) were generated and compared with the wild-type. The α-synuclein E57K Lines 9 and 16 were higher expressings of α-synuclein, similar to α-synuclein wild-type Line 61, and Line 54 was a low expressing of α-synuclein compared to Line 61. By immunoblot analysis, the higher-expressing α-synuclein E57K transgenic mice showed abundant oligomeric, but not fibrillar, α-synuclein whereas lower-expressing mice accumulated monomeric α-synuclein. Monomers, oligomers, and fibrils were present in α-synuclein wild-type Line 61. Immunohistochemical and ultrastructural analyses demonstrated that α-synuclein accumulated in the synapses but not in the neuronal cells bodies, which was different from the α-synuclein wild-type Line 61, which accumulates α-synuclein in the soma. Compared to non-transgenic and lower-expressing mice, the

  2. Accumulation of oligomer-prone α-synuclein exacerbates synaptic and neuronal degeneration in vivo.

    PubMed

    Rockenstein, Edward; Nuber, Silke; Overk, Cassia R; Ubhi, Kiren; Mante, Michael; Patrick, Christina; Adame, Anthony; Trejo-Morales, Margarita; Gerez, Juan; Picotti, Paola; Jensen, Poul H; Campioni, Silvia; Riek, Roland; Winkler, Jürgen; Gage, Fred H; Winner, Beate; Masliah, Eliezer

    2014-05-01

    In Parkinson's disease and dementia with Lewy bodies, α-synuclein aggregates to form oligomers and fibrils; however, the precise nature of the toxic α-synuclein species remains unclear. A number of synthetic α-synuclein mutations were recently created (E57K and E35K) that produce species of α-synuclein that preferentially form oligomers and increase α-synuclein-mediated toxicity. We have shown that acute lentiviral expression of α-synuclein E57K leads to the degeneration of dopaminergic neurons; however, the effects of chronic expression of oligomer-prone α-synuclein in synapses throughout the brain have not been investigated. Such a study could provide insight into the possible mechanism(s) through which accumulation of α-synuclein oligomers in the synapse leads to neurodegeneration. For this purpose, we compared the patterns of neurodegeneration and synaptic damage between a newly generated mThy-1 α-synuclein E57K transgenic mouse model that is prone to forming oligomers and the mThy-1 α-synuclein wild-type mouse model (Line 61), which accumulates various forms of α-synuclein. Three lines of α-synuclein E57K (Lines 9, 16 and 54) were generated and compared with the wild-type. The α-synuclein E57K Lines 9 and 16 were higher expressings of α-synuclein, similar to α-synuclein wild-type Line 61, and Line 54 was a low expressing of α-synuclein compared to Line 61. By immunoblot analysis, the higher-expressing α-synuclein E57K transgenic mice showed abundant oligomeric, but not fibrillar, α-synuclein whereas lower-expressing mice accumulated monomeric α-synuclein. Monomers, oligomers, and fibrils were present in α-synuclein wild-type Line 61. Immunohistochemical and ultrastructural analyses demonstrated that α-synuclein accumulated in the synapses but not in the neuronal cells bodies, which was different from the α-synuclein wild-type Line 61, which accumulates α-synuclein in the soma. Compared to non-transgenic and lower-expressing mice, the

  3. Ionogel fibres of bis(trifluoromethanesulfonyl)imide anion-based ionic liquids for the headspace solid-phase microextraction of chlorinated organic pollutants.

    PubMed

    Pena-Pereira, F; Marcinkowski, Ł; Kloskowski, A; Namieśnik, J

    2015-11-01

    Ionogels, a family of hybrid materials in which ionic liquids (ILs) are confined in a sol-gel network, are receiving much attention in a variety of scientific and technological fields. In this work, ionogels derived from three different ILs based on the anion bis(trifluoromethanesulfonyl)imide (TFSI), namely 1-butyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide ([C4C1Py][TFSI]), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([C4C1Pyrr][TFSI]), and 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide ([C4C1Pip][TFSI]) were obtained on the outer surface of optical fibres by sol-gel technology. The obtained hybrid materials were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX), and subsequently evaluated as sorbent coatings for the headspace solid-phase microextraction (HS-SPME) of volatile chlorinated organic compounds in combination with gas chromatography with barrier ionization discharge detection (GC-BID). The ionogel based on [C4C1Pyrr][TFSI] exhibited the highest extractability for target analytes. The experimental parameters that affect the extraction process were optimized by means of a central composite design. Under optimal conditions, the proposed method yielded excellent enrichment factors (EFs) in the range 3889-20 919 and limits of detection (LODs) between 11 and 151 ng L(-1) for the target compounds. The inter-day repeatability, intra-day reproducibility and fibre-to-fibre reproducibility, were less than 8.5, 9.6 and 16.9%, respectively. Finally, the developed method was applied to the analysis of water samples, showing recovery values in the range 95-106%. PMID:26364989

  4. Poly-phenylated diamines and their use as polycondensation monomers in the synthesis of polyamide, poly(amide-imide), and polyimide polymers

    NASA Technical Reports Server (NTRS)

    Harris, Frank W. (Inventor)

    1992-01-01

    New polyphenylated polynuclear aromatic diamines, such as 1,3-bis[4-aminophenyl]-2,3,5-triphenylbenzene, a process for their manufacture and their use as polycondensation components for the manufacture of polyamide, polyamide-imide and polyimide polymers are described. The polymers obtained with the aromatic diamines according to the invention are readily soluble, rigid-rod polymers and are distinguished by outstanding modulus, tensile compression strength, energy absorption, coefficient of expansion and electrical properties.

  5. Activity Coefficients at Infinite Dilution of Organic Compounds in Trihexyl(tetradecyl)phophonium Bis(trifluoromethylsulfonyl)imide Using Inverse Gas Chromatography

    SciTech Connect

    Revelli, Anne-Laure; Sprunger, Laura; Gibbs, Jennifer; Acree, William; Baker, Gary A; Mutelet, Fabrice

    2009-01-01

    Activity coefficients at infinite dilution of organic compounds in the ionic liquid (IL) trihexyl(tetradecyl) phosphonium bis(trifluoromethylsulfonyl)imide were determined using inverse gas chromatography at three temperatures, T ) (302.45, 322.35, and 342.45) K. Linear free energy relationship (LFER) correlations have been obtained for describing the gas-to-IL and water-to-IL partition coefficients.

  6. Amyloid β oligomers induce interleukin-1β production in primary microglia in a cathepsin B- and reactive oxygen species-dependent manner

    SciTech Connect

    Taneo, Jun; Adachi, Takumi; Yoshida, Aiko; Takayasu, Kunio; Takahara, Kazuhiko; Inaba, Kayo

    2015-03-13

    Amyloid β (Aβ) peptide, a causative agent of Alzheimer's disease, forms two types of aggregates: oligomers and fibrils. These aggregates induce inflammatory responses, such as interleukin-1β (IL-1β) production by microglia, which are macrophage-like cells located in the brain. In this study, we examined the effect of the two forms of Aβ aggregates on IL-1β production in mouse primary microglia. We prepared Aβ oligomer and fibril from Aβ (1–42) peptide in vitro. We analyzed the characteristics of these oligomers and fibrils by electrophoresis and atomic force microscopy. Interestingly, Aβ oligomers but not Aβ monomers or fibrils induced robust IL-1β production in the presence of lipopolysaccharide. Moreover, Aβ oligomers induced endo/phagolysosome rupture, which released cathepsin B into the cytoplasm. Aβ oligomer-induced IL-1β production was inhibited not only by the cathepsin B inhibitor CA-074-Me but also by the reactive oxygen species (ROS) inhibitor N-acetylcysteine. Random chemical crosslinking abolished the ability of the oligomers to induce IL-1β. Thus, multimerization and fibrillization causes Aβ oligomers to lose the ability to induce IL-1β. These results indicate that Aβ oligomers, but not fibrils, induce IL-1β production in primary microglia in a cathepsin B- and ROS-dependent manner. - Highlights: • We prepared amyloid β (Aβ) fibrils with minimum contamination of Aβ oligomers. • Primary microglia (MG) produced IL-1β in response to Aβ oligomers, but not fibrils. • Only Aβ oligomers induced leakage of cathepsin B from endo/phagolysosomes. • IL-1β production in response to Aβ oligomers depended on both cathepsin B and ROS. • Crosslinking reduced the ability of the Aβ oligomers to induce IL-1β from MG.

  7. Towards directional assembly of hierarchical structures: aniline oligomers as the model precursors

    NASA Astrophysics Data System (ADS)

    Zhao, Yanchai; Stejskal, Jaroslav; Wang, Jixiao

    2013-03-01

    Hierarchical architectures attract a large number of scientists and engineers because of their unique physicochemical properties compared with bulk materials and their precursors. It is believed that intermolecular interactions play a key role in the formation of these hierarchical architectures. However, the principle of coordination of various intermolecular interactions in the self-assembly process is not clear. Here, an aniline oligomer is used as a model brick to study the formation process of well-defined hierarchical architectures, and the directional growth mechanism is proposed. It is assumed that aniline oligomer molecules are asymmetric, and driven by intermolecular attractive forces to aggregate in various manners. Combined with the interactions between the aniline oligomer and molecules from the medium, three-dimensional assemblies, flower-like and urchin-like microspheres, can be formed. The variability and complexity of morphologies produced in the process was analyzed according to the intermolecular interactions, which includes hydrogen bonding, π-π stacking, hydrophobic interaction, etc. The applicability of these special hierarchical architectures, such as in the preparation of superhydrophobic surfaces, is also discussed.Hierarchical architectures attract a large number of scientists and engineers because of their unique physicochemical properties compared with bulk materials and their precursors. It is believed that intermolecular interactions play a key role in the formation of these hierarchical architectures. However, the principle of coordination of various intermolecular interactions in the self-assembly process is not clear. Here, an aniline oligomer is used as a model brick to study the formation process of well-defined hierarchical architectures, and the directional growth mechanism is proposed. It is assumed that aniline oligomer molecules are asymmetric, and driven by intermolecular attractive forces to aggregate in various manners

  8. Localization of a carboxylic residue possibly involved in the inhibition of vacuolar H+-pyrophosphatase by N, N'-dicyclohexylcarbodi-imide.

    PubMed Central

    Yang, S J; Jiang, S S; Kuo, S Y; Hung, S H; Tam, M F; Pan, R L

    1999-01-01

    A vacuolar H(+)-pyrophosphatase (EC 3.6.1.1) that catalyses PP(i) hydrolysis and the electrogenic translocation of protons from the cytosol to the vacuole lumen, was purified from etiolated hypocotyls of mung bean seedlings (Vigna radiata L.). Group-specific modification was used to identify a carboxylic residue involved in the inhibition of vacuolar H(+)-pyrophosphatase. Carbodi-imides, such as N,N'-dicyclohexylcarbodi-imide (DCCD) and 1-ethyl-3-(3-dimethylamino-propyl)carbodi-imide, and Woodward's reagent K caused a progressive decline in the enzymic activity of vacuolar H(+)-pyrophosphatase in a time- and concentration-dependent manner. The stoichiometry of labelling of the vacuolar H(+)-pyrophosphatase by [(14)C]DCCD determined that DCCD modifies one carboxylic residue per subunit of the enzyme. Protection studies suggest that the DCCD-reactive carboxylic residue resides at or near the substrate-binding site. Furthermore, peptide mapping analysis reveals that Asp(283), located in the putative loop V of a tentative topological model of vacuolar H(+)-pyrophosphatase on the cytosolic side, was labelled by radioactive [(14)C]DCCD. Cytosolic loop V contains both DCCD-sensitive Asp(283) and a conserved motif sequence, rendering it a candidate for the catalytic site of vacuolar H(+)-pyrophosphatase. A topological picture of the active domain of vacuolar H(+)-pyrophosphatase is tentatively proposed. PMID:10477275

  9. Well-Known Mediators of Selective Oxidation with Unknown Electronic Structure: Metal-Free Generation and EPR Study of Imide-N-oxyl Radicals.

    PubMed

    Krylov, Igor B; Kompanets, Mykhailo O; Novikova, Katerina V; Opeida, Iosip O; Kushch, Olga V; Shelimov, Boris N; Nikishin, Gennady I; Levitsky, Dmitri O; Terent'ev, Alexander O

    2016-01-14

    Nitroxyl radicals are widely used in chemistry, materials sciences, and biology. Imide-N-oxyl radicals are subclass of unique nitroxyl radicals that proved to be useful catalysts and mediators of selective oxidation and CH-functionalization. An efficient metal-free method was developed for the generation of imide-N-oxyl radicals from N-hydroxyimides at room temperature by the reaction with (diacetoxyiodo)benzene. The method allows for the production of high concentrations of free radicals and provides high resolution of their EPR spectra exhibiting the superhyperfine structure from benzene ring protons distant from the radical center. An analysis of the spectra shows that, regardless of the electronic effects of the substituents in the benzene ring, the superhyperfine coupling constant of an unpaired electron with the distant protons at positions 4 and 5 of the aromatic system is substantially greater than that with the protons at positions 3 and 6 that are closer to the N-oxyl radical center. This is indicative of an unusual character of the spin density distribution of the unpaired electron in substituted phthalimide-N-oxyl radicals. Understanding of the nature of the electron density distribution in imide-N-oxyl radicals may be useful for the development of commercial mediators of oxidation based on N-hydroxyimides. PMID:26674210

  10. Polyethyleneimine-functionalized polyamide imide (Torlon) hollow-fiber sorbents for post-combustion CO2 capture.

    PubMed

    Li, Fuyue Stephanie; Qiu, Wulin; Lively, Ryan P; Lee, Jong Suk; Rownaghi, Ali A; Koros, William J

    2013-07-01

    Carbon dioxide emitted from existing coal-fired power plants is a major environmental concern due to possible links to global climate change. In this study, we expand upon previous work focused on aminosilane-functionalized polymeric hollow-fiber sorbents by introducing a new class of polyethyleneimine (PEI)-functionalized polymeric hollow-fiber sorbents for post-combustion carbon dioxide capture. Different molecular weight PEIs (M(n) ≈600, 1800, 10,000, and 60,000) were studied as functional groups on polyamide imide (PAI, Torlon) hollow fibers. This imide ring-opening modification introduces two amide functional groups and was confirmed by FTIR attenuated total reflectance spectroscopy. The carbon dioxide equilibrium sorption capacities of PEI-functionalized Torlon materials were characterized by using both pressure decay and gravimetric sorption methods. For equivalent PEI concentrations, PAI functionalized with lower molecular weight PEI exhibited higher carbon dioxide capacities. The effect of water in the ring-opening reaction was also studied. Up to a critical value, water in the reaction mixture enhanced the degree of functionalization of PEI to Torlon and resulted in higher carbon dioxide uptake within the functionalized material. Above the critical value, roughly 15% w/w water, the fiber morphology was lost and the fiber was soluble in the solvent. PEI-functionalized (Mn ≈600) PAI under optimal reaction conditions was observed to have the highest CO2 uptake: 4.9 g CO2 per 100 g of polymer (1.1 mmol g(-1)) at 0.1 bar and 35 °C with dry 10% CO2/90% N2 feed for thermogravimetric analysis. By using water-saturated feeds (10% CO2 /90% N2 dry basis), CO2 sorption was observed to increase to 6.0 g CO2 per 100 g of sorbent (1.4 mmol g(-1)). This material also demonstrated stability in cyclic adsorption-desorption operations, even under wet conditions at which some highly effective sorbents tend to lose performance. Thus, PEI-functionalized PAI fibers can be

  11. The effect of terminal substituents on the electronic properties of rod-shaped [HGaNH]n oligomers.

    PubMed

    Pomogaeva, A V; Timoshkin, A Y

    2016-07-20

    The effect of electron-donating and electron-withdrawing terminal groups on the electronic structure of the rod-shaped X3[HGaNH]nY3 or needle-shaped XGa[HGaNH]nNY oligomers (X, Y = H, CH3, F, CF3; n = 9, 30 and 114) was computationally studied at the B3LYP/SVP level of density functional theory. While the needle-shaped oligomers exhibit moderate variability in the electronic structure upon changing the terminal substituents X and Y, the energy gap of long rod-shaped oligomers varies within 2 eV. For oligomers with n = 114, F3[HGaNH]n(CH3)3 exhibits the largest HOMO-LUMO gap of 2.91 eV, while (CH3)3[HGaNH]nF3 has the smallest gap of 0.94 eV. PMID:27389813

  12. Use of complementary DNA oligomers to probe trp leader transcript secondary structures involved in transcription pausing and termination.

    PubMed Central

    Fisher, R; Yanofsky, C

    1984-01-01

    DNA oligomers were synthesized that are perfectly complementary to different segments of the tryptophan (trp) operon leader transcript. These 15 nucleotide long oligomers were used as probes of the involvement of transcript secondary structures in two processes: transcription pausing at the pause site located near base pair 90 in the leader region, and transcription termination at the attenuator. The 15-mers were complementary to the four segments of the trp leader transcript which have been shown to form the alternative secondary structures that are believed to be responsible for pausing, termination, and antitermination. Oligomers complementary to RNA segments 1 and 3 relieved termination while the 15-mer complementary to RNA segment 1 relieved pausing. 15-mers complementary to segment 2 had no effect on pausing and the oligomer complementary to segment 4 had virtually no effect on termination. PMID:6201827

  13. Montmorillonite-catalysed formation of RNA oligomers: the possible role of catalysis in the origins of life

    PubMed Central

    Ferris, James P

    2006-01-01

    Large deposits of montmorillonite are present on the Earth today and it is believed to have been present at the time of the origin of life and has recently been detected on Mars. It is formed by aqueous weathering of volcanic ash. It catalyses the formation of oligomers of RNA that contain monomer units from 2 to 30–50. Oligomers of this length are formed because this catalyst controls the structure of the oligomers formed and does not generate all possible isomers. Evidence of sequence-, regio- and homochiral selectivity in these oligomers has been obtained. Postulates on the role of selective versus specific catalysts on the origins of life are discussed. An introduction to the origin of life is given with an emphasis on reaction conditions based on the recent data obtained from zircons 4.0–4.5 Ga. PMID:17008218

  14. Synthetic approaches to mixed ligand chelators on t-butylphenol-formaldehyde oligomer (PFO) platforms

    PubMed Central

    Young, Jennifer A.; Karmakar, Sukhen

    2012-01-01

    Synthetic approaches to mixed ligand chelators on readily available t-butylphenol-formaldehyde oligomer, PFO, scaffolds were examined. In a promising approach, tris and tetraphenol oligomers were selectively mono or di protected using t-butyldiphenyl silyl chloride. The utility of these protected intermediates to prepare representative mixed PFO chelators, carrying ligands such as hydroxamic acid, 3,2-hydroxypyridinones and others was then demonstrated. The introduction of the ligand tethers onto the phenolic scaffold can be done sequentially under relatively mild conditions that tolerate the presence of other sensitive ligand groups. The differential reactivity of the disilyl derivative 20b, allowed stepwise introduction of two different ligands on the internal phenolic positions. This enabled the introduction of three different ligand groups of choice onto the tetra phenol platform. PMID:23226883

  15. QIAD assay for quantitating a compound’s efficacy in elimination of toxic Aβ oligomers

    PubMed Central

    Brener, Oleksandr; Dunkelmann, Tina; Gremer, Lothar; van Groen, Thomas; Mirecka, Ewa A.; Kadish, Inga; Willuweit, Antje; Kutzsche, Janine; Jürgens, Dagmar; Rudolph, Stephan; Tusche, Markus; Bongen, Patrick; Pietruszka, Jörg; Oesterhelt, Filipp; Langen, Karl-Josef; Demuth, Hans-Ulrich; Janssen, Arnold; Hoyer, Wolfgang; Funke, Susanne A.; Nagel-Steger, Luitgard; Willbold, Dieter

    2015-01-01

    Strong evidence exists for a central role of amyloid β-protein (Aβ) oligomers in the pathogenesis of Alzheimer’s disease. We have developed a fast, reliable and robust in vitro assay, termed QIAD, to quantify the effect of any compound on the Aβ aggregate size distribution. Applying QIAD, we studied the effect of homotaurine, scyllo-inositol, EGCG, the benzofuran derivative KMS88009, ZAβ3W, the D-enantiomeric peptide D3 and its tandem version D3D3 on Aβ aggregation. The predictive power of the assay for in vivo efficacy is demonstrated by comparing the oligomer elimination efficiency of D3 and D3D3 with their treatment effects in animal models of Alzheimer´s disease. PMID:26394756

  16. Toxic tau oligomer formation blocked by capping of cysteine residues with 1,2-dihydroxybenzene groups

    PubMed Central

    Soeda, Yoshiyuki; Yoshikawa, Misato; Almeida, Osborne F. X.; Sumioka, Akio; Maeda, Sumihiro; Osada, Hiroyuki; Kondoh, Yasumitsu; Saito, Akiko; Miyasaka, Tomohiro; Kimura, Tetsuya; Suzuki, Masaaki; Koyama, Hiroko; Yoshiike, Yuji; Sugimoto, Hachiro; Ihara, Yasuo; Takashima, Akihiko

    2015-01-01

    Neurofibrillary tangles, composed of hyperphosphorylated tau fibrils, are a pathological hallmark of Alzheimer's disease; the neurofibrillary tangle load correlates strongly with clinical progression of the disease. A growing body of evidence indicates that tau oligomer formation precedes the appearance of neurofibrillary tangles and contributes to neuronal loss. Here we show that tau oligomer formation can be inhibited by compounds whose chemical backbone includes 1,2-dihydroxybenzene. Specifically, we demonstrate that 1,2-dihydroxybenzene-containing compounds bind to and cap cysteine residues of tau and prevent its aggregation by hindering interactions between tau molecules. Further, we show that orally administered DL-isoproterenol, an adrenergic receptor agonist whose skeleton includes 1,2-dihydroxybenzene and which penetrates the brain, reduces the levels of detergent-insoluble tau, neuronal loss and reverses neurofibrillary tangle-associated brain dysfunction. Thus, compounds that target the cysteine residues of tau may prove useful in halting the progression of Alzheimer's disease and other tauopathies. PMID:26671725

  17. Light-triggered reversible self-assembly of gold nanoparticle oligomers for tunable SERS.

    PubMed

    Zhang, Lei; Dai, Liwei; Rong, Yun; Liu, Zhenzhong; Tong, Dingyi; Huang, Youju; Chen, Tao

    2015-01-27

    A photoresponsive amphiphilic gold nanoparticle (AuNP) is achieved through the decoration of AuNP with hydrophilic poly(ethylene glycol) (PEG) and hydrophobic photoresponsive polymethacrylate containing spiropyran units (PSPMA). Owing to the photoresponsive property of spiropyran units, the amphiphilic AuNPs can easily achieve the controllable assembly/disassembly behaviors under the trigger by light. Under visible light, spiropyran units provide weak intermolecular interactions between neighbored AuNPs, leading to isolated AuNPs in the solution. While under UV light irradiation, spiropyran units in the polymer brushes transform into merocyanine isomer with conjugated structure and zwitterionic state, promoting the integration of adjacent AuNPs through π-π stacking and electrostatic attractions, further leading to the formation of Au oligomers. The smart reversible AuNP oligomers exhibited switchable plasmonic coupling for tuning surface-enhanced Raman scattering (SERS) activity, which is promising for the application of SERS based sensors and optical imaging. PMID:25540841

  18. Preparation and NMR characterization of glucosamine oligomers bearing an azide function using chitosan.

    PubMed

    Maria Marzaioli, Alberto; Bedini, Emiliano; Lanzetta, Rosa; Perino, Vincenzo; Parrilli, Michelangelo; De Castro, Cristina

    2012-10-01

    In this study, a procedure to produce glucosamine oligomers with the amino functions transformed into azido groups was optimized, and HPLC purification afforded to the isolation of nine different oligosaccharides derivatives, with the reducing end transformed in alditol. These oligomers differed for the degree of polymerization and for the type of alditol at the reducing end. The first group comprehended species from di- to hexasaccharide, with all the amino functions converted into an azido group. The second and the third groups were isolated in minor yields, and were both constituted from tri- and tetrasaccharides; the difference between the two groups regarded exclusively the type of alditol found at the reducing end, which was a glucosaminitol in the first case, or a N-acetylglucosaminitol in the other. Products were fully characterized by 2D NMR spectroscopy. The azido moieties installed on these oligosaccharides can be further exploited in Cu(I) catalyzed azido-alkyne cycloaddition reactions. PMID:22840011

  19. Rapamycin-induced oligomer formation system of FRB-FKBP fusion proteins.

    PubMed

    Inobe, Tomonao; Nukina, Nobuyuki

    2016-07-01

    Most proteins form larger protein complexes and perform multiple functions in the cell. Thus, artificial regulation of protein complex formation controls the cellular functions that involve protein complexes. Although several artificial dimerization systems have already been used for numerous applications in biomedical research, cellular protein complexes form not only simple dimers but also larger oligomers. In this study, we showed that fusion proteins comprising the induced heterodimer formation proteins FRB and FKBP formed various oligomers upon addition of rapamycin. By adjusting the configuration of fusion proteins, we succeeded in generating an inducible tetramer formation system. Proteins of interest also formed tetramers by fusing to the inducible tetramer formation system, which exhibits its utility in a broad range of biological applications. PMID:26777239

  20. Cholesterol facilitates interactions between α-synuclein oligomers and charge-neutral membranes.

    PubMed

    van Maarschalkerweerd, Andreas; Vetri, Valeria; Vestergaard, Bente

    2015-09-14

    Oligomeric species formed during α-synuclein fibrillation are suggested to be membrane-disrupting agents, and have been associated with cytotoxicity in Parkinson's disease. The majority of studies, however, have revealed that the effect of α-synuclein oligomers is only noticeable on systems composed of anionic lipids, while the more physiologically relevant zwitterionic lipids remain intact. We present experimental evidence for significant morphological changes in zwitterionic membranes containing cholesterol, induced by α-synuclein oligomers. Depending on the lipid composition, model membranes are either unperturbed, disrupt, or undergo dramatic morphological changes and segregate into structurally different components, which we visualize by 2-photon fluorescence microscopy and generalized polarization analysis using the fluorescent probe Laurdan. Our results highlight the crucial role of cholesterol for mediating interactions between physiologically relevant membranes and α-synuclein. PMID:26297828