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  • 1
    Electronic Resource
    Electronic Resource
    Mobility-resolved 13C-NMR spectroscopy of primary plant cell walls (1996)
    New York : Wiley-Blackwell
    Biopolymers 39 (1996), S. 51-66 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Primary plant cell walls contain highly hydrated biopolymer networks, whose major chemistry is known but whose relationship to architectural and mechanical properties is poorly understood. Nuclear magnetic resonance spectroscopy has been used to characterize segmental mobilities via relaxation and anisotropy effects in order to add a dynamic element to emerging models for cell wall architecture.For hydrated onion cell wall material, single pulse excitation revealed galactan (pectin side chains), provided that dipolar decoupling was used, and some of the pectin backbone in the additional presence of magic angle spinning. Cross-polarization excitation revealed the remaining pectin backbones, which exhibited greater mobility (contact time dependence, dipolar dephasing) than the cellulose component, whose noncrystalline and crystalline fractions showed no mobility discrimination. 1HT2 behavior could be quantitatively interpreted in terms of high resolution observabilities. Mobility-resolved spectroscopy of cell walls from tomato fruit, pea stem, and tobacco leaf showed similar general effects.Nuclear magnetic resonance study of the sequential chemical extraction of onion cell wall material suggests that galactans fill many of the network pores, that extractability of pectins is not dependent on segmental mobility, and that some pectic backbone (and not side chain) is strongly associated with cellulose.Analysis of the state of cellulose in four hydrated cell walls suggests a noncrystalline content of 60-80% and comparable amounts of Iα and Iβ polymorphs in the crystalline fraction. Comparison with micrographs for onion cell walls shows that noncrystalline cellulose does not equate to chains on fibril surfaces, and chemical shifts show that fully solvated cellulose is not a significant component in cell walls. © 1996 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxidation behavior and stabilization of metallocene and other polyolefins (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 11-32 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: EXXPOL® metallocene catalyst technology featuring very high-productivity catalyst systems is expected to provide ethylene polymer compositions that show excellent oxidative stability based on their minimal unsaturation content and low innocuous metal residue of a non-acidic nature. Metallocene ethylene polymers such as mLLDPE should be comparable to the most stable, commercial polyethylenes such as linear low-density polyethylenes (LLDPE) from the UNIPOL® gas phase PE process.As background, the oxidation behavior and stabilization case of “total residue” polyolefins based on Ziegler-Natta or Cr catalysis systems are reviewed. The interacting effects of polymer structure (i.e., tertiary hydrogen and unsaturation) and catalyst residue are discussed in terms of competing degradation reactions - e.g., chain breakage, chain enlargement (or cross-linking) and chain branching. The metal (Ti, V and Al) and chlorine residues from Ziegler-Natta catalyst systems and the Cr residue for Cr catalyst systems can play a role in adversely affecting polymer oxidative stability. The residue levels and their nature govern whether there is an appreciable effect on oxidative stability, and therefore the stabilization requirements.Discussed are thermo-oxidative studies under melt processing conditions which compare selected EXXPOL®/UNIPOL® mLLDPEs with several state-of-the-art Ti/Mg and Cr catalyzed LLDPE from the UNIPOL® gas phase PE process and a high-pressure, low-density polyethylene (HP-LDPE). Standard melt flow and discoloration tests are combined with specialized experiments using dynamic oscillatory shear rheometry and size exclusion chromatographyviscometry to illustrate performance shifts due to polymer composition differences under melt processing conditions. The advantages of dynamic melt rheometry are illustrated in terms of sensitivity to subtle degradation changes in molecular structure. EXXPOL®/UNIPOL® mLLDPE having low unsaturation and metal residue which are non-catalytic to auto-oxidation show excellent intrinsic oxidative stability. The discoloration resistance of EXXPOL®/UNIPOL® mLLDPE is high, comparable with HP-LDPE and the high-activity Cr catalyzed LLDPE. Stabilization ease for EXXPOL®/UNIPOL® mLLDPE is equivalent to product counterparts (similar MI and density) made using high-activity, state-of-the-art Cr or Ti/Mg catalyst systems designed for use in the UNIPOL® gas phase PE process.
    Additional Material: 32 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052520102
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  • 3
    Electronic Resource
    Electronic Resource
    CHO DUKX cell lineages preadapted to growth in serum-free suspension culture enable rapid development of cell culture processes for the manufacture of recombinant proteins (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 52 (1996), S. 518-528 
    Details
    ISSN: 0006-3592
    Keywords: CHO cells ; serum-free medium ; adaptation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Using an adaptive strategy, Chinese hamster ovary (CHO) cell lines were developed that are capable of robust growth in serum-free suspension culture. These preadapted derivatives of the commonly used strain of CHO cells (CHO DUKX), termed PA-DUKX, were used for the introduction and stable expression of several heterologous human genes. A significant advantage of recombinant PA-DUKX cells was their ability to readily resume growth in serum-free suspension culture after transfection and amplification of heterologous genes. Expression of recombinant human proteins in PA-DUKX cells was quantitatively similar to that of lineages generated using conventional CHO DUKX cells. In addition, recombinant human proteins expressed by transfected PA-DUKX lineages were shown to be biochemically and structurally similar to those expressed in CHO DUKX cells, PA-DUKX host cell technology provides an opportunity for reducing the time and resources required to develop large-scale, suspension culture-based manufacturing processes employing serum-free medium. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Metal-organic vapor phase epitaxial growth of cubic Gallium selenide, Ga2Se3We thank the Engineering and Physical Sciences Research Council for supporting our program on III-VI compound semiconductors and also the Higher Education Funding Council for Wales (HEFCW) for capital equipment. The authors also thank the EPSRC for supporting research into novel organo-selenium precursors. (1996)
    Weinheim : Wiley-Blackwell
    Chemical Vapor Deposition 2 (1996), S. 185-189 
    Details
    ISSN: 0948-1907
    Keywords: Ga2Se3 ; MOVPE ; TEM ; Wide-gap semiconductor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We present results of a study using metal-organic vapor phase epitaxy (MOVPE) to synthesize thin films of cubic Ga2Se3 on both nearly lattice matched GaP and mismatched GaAs substrates. We find that trimethylgallium (TMGa) pre-reacts with the hydride H2Se in the gas phase to yield films which are only partially epitaxial and that the combination of TMGa with ditertiarybutylselenide produces films of the best crystal quality under steady state flow conditions. We also show that GaAs is an unsuitable substrate for MOVPE growth of gallium selenide due to exchange reactions at the interface leading to poorly bonded films.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cvde.19960020507
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  • 5
    Electronic Resource
    Electronic Resource
    Simple technique for the preparation of silicone gel particles: The effect of silicone gel particles on oxidative responses of macrophages (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 101-105 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A simple technique was developed to prepare phagocytosable-size particles from the silicone gel used in breast implants. Sonication of silicone gel (1 g) in 5 ml of 20 mM sodium phosphate buffer (pH 7.2) containing 1% (wt/vol) polyoxypropylene-polyethylene block surfactant (F-68 or F-108) produced silicone gel particles ranging from 1-50 μm in diameter. Passage of the suspension through a series of filters yielded phagocytosable particles (1-5 μm in diameter) at a concentration of ca. 2 × 109 particles/ml. The particles remained as individual particles, did not coalesce to form large clumps, and were not pelleted by centrifugation (2000 × g, 20 min). They were not toxic for rabbit alveolar macrophages (AM) during 24 h of incubation at 37°C, did not elicit an oxidative burst from AM in vitro in a luminolenhanced chemiluminescent assay, and did not significantly increase the phorbol myristate acetate (PMA)-elicited oxidative burst by AM. AM isolated from rabbits 2 days after the intravenous injection of silicone particles were not primed or activated (i.e., the AM did not show an enhanced oxidative burst when elicited with PMA in vitro). However, AM isolated from rabbits 2 days after intratracheal injection of the particles were primed but only exhibited a 4-6-fold increase in the oxidative burst elicited with PMA. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820290114
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  • 6
    Electronic Resource
    Electronic Resource
    Rate constant for the gas-phase reaction of hydroxyl radical with the natural hydrocarbon bornyl acetate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 497-502 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase reaction of bornyl acetate (bicyclo[2,2,1]-heptan-2-ol-1,7,7-trimethyl-acetate) with hydroxyl radical has been studied. A relative method was used to determine the rate constant for this reaction, with n-octane as reference compound.Methyl nitrite photolysis experiments were carried out in an environmental smog chamber at atmospheric pressure and (294±2) K. The rate constant determined for bornyl acetate is k=(13.9±2.2)×10-12 cm3 molecule-1 s-1.The experimental rate constant has been compared with the rate constants calculated with the structure-activity relationship (SAR) and with the evolution trend of the acetate rate constants. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 497-502, 1998
    Additional Material: 1 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Kinetics of the reaction of OH radicals with a series of esters under simulated conditions at 295 K (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 28 (1996), S. 609-614 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constants of the isopropyl acetate, n-propyl acetate, isopropenyl acetate, n-propenyl acetate, n-butyl acetate, and ethyl butyrate reactions with OH radicals were determined in purified air under atmospheric conditions, at 750 torr and (295 ± 2) K. A relative rate experimental method was used; n-heptane, n-octane, and n-nonane were the reference compounds, with, respectively, rate constants for the reaction with OH of 7.12 × 10-12, 8.42 × 10-12, and 9.70 × 10-12 molecule-1 cm3s-1. The following rate constants were obtained in units of 10-12 molecule-1 cm3s-1; isopropyl acetate, (3.12 ± 0.29); n-propyl acetate, (1.97 ± 0.24); isopropenyl acetate, (62.53 ± 1.24); n-propenyl acetate, (24.57 ± 0.24); n-butyl acetate, (3.29 ± 0.35); and ethyl butyrate, (4.37 ± 0.42). Tertiary butyl acetate has a low reactivity with OH radicals (〈1 × 10-12 molecule-1 cm3s-1). © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.6
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  • 8
    Electronic Resource
    Electronic Resource
    Toward high-performance computational chemistry: II. A scalable self-consistent field program (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 124-132 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We discuss issues in developing scalable parallel algorithms and focus on the distribution, as opposed to the replication, of key data structures. Replication of large data structures limits the maximum calculation size by imposing a low ratio of processors to memory. Only applications which distribute both data and computation across processors are truly scalable. The use of shared data structures that may be independently accessed by each process even in a distributed memory environment greatly simplifies development and provides a significant performance enhancement. We describe tools we have developed to support this programming paradigm. These tools are used to develop a highly efficient and scalable algorithm to perform self-consistent field calculations on molecular systems. A simple and classical strip-mining algorithm suffices to achieve an efficient and scalable Fock matrix construction in which all matrices are fully distributed. By strip mining over atoms, we also exploit all available sparsity and pave the way to adopting more sophisticated methods for summation of the Coulomb and exchange interactions. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Toward high-performance computational chemistry: I. Scalable Fock matrix construction algorithms (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 109-123 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Several parallel algorithms for Fock matrix construction are described. The algorithms calculate only the unique integrals, distribute the Fock and density matrices over the processors of a massively parallel computer, use blocking techniques to construct the distributed data structures, and use clustering techniques on each processor to maximize data reuse. Algorithms based on both square and row-blocked distributions of the Fock and density matrices are described and evaluated. Variants of the algorithms are discussed that use either triple-sort or canonical ordering of integrals, and dynamic or static task clustering schemes. The algorithms are shown to adapt to screening, with communication volume scaling down with computation costs. Modeling techniques are used to characterize algorithm performance. Given the characteristics of existing massively parallel computers, all the algorithms are shown to be highly efficient for problems of moderate size. The algorithms using the row-blocked data distribution are the most efficient. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Gas-phase reaction of n-butyl acetate with the hydroxyl radical under simulated tropospheric conditions: Relative rate constant and product study (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 28 (1996), S. 235-243 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase reaction of n-butyl acetate with hydroxyl radicals has been studied in an environmental smog chamber at 298 K atmospheric pressure, and simulated tropospheric concentrations.The rate constant for this reaction has been determined by a relative method and the experimental result, relative to n-octane used as reference compound, is $$k=(5.2\pm 0.5)\times 10^{-12}{\rm cm}^3\ {\rm molecule}^{-1}\ s^{-1},$$This value appears to be about 25% higher than absolute rate constants found in the literature, but agrees very well with the other relative determination.Two reaction products have been identified and their production yield has been estimated, each accounting for about (15 ± 5)% of the overall OH reaction processes.The two observed products are \centerline{ 2--oxobutil acetate ($\rm CH_3$--C0--0--$\rm CH_2$--CO--$\rm CH_2$--$\rm CH_3$)}and \centerline{ 2--oxobutil acetate ($\rm CH_3$--C0--0--$\rm CH_2$--$\rm CH_2$--CO--$\rm CH_3$)}The accuracy of the relative rate constant obtained is examined considering the evolution of the reactivity of the alkoxy end of the esters. Formation mechanisms for the two observed products are proposed and the likely other degradation channels are discussed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.1
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