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  • Articles  (31)
  • Springer  (31)
  • Chemistry and Pharmacology  (31)
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  • Articles  (31)
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  • 1
    Electronic Resource
    Electronic Resource
    The first measurement of an absolute surface concentration of reaction intermediates in ethylene hydrogenation (1996)
    Springer
    Catalysis letters 40 (1996), S. 143-145 
    Details
    ISSN: 1572-879X
    Keywords: absolute surface intermediate concentration ; ethylene hydrogenation ; reaction intermediates in catalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The first measurement of a turnover rate with respect to surface intermediate concentration in a high pressure heterogeneous catalytic reaction is reported. By using infrared-visible sum frequency generation to study the hydrogenation of ethylene on Pt(111), it was found that the surface concentration of π-bonded ethylene, the key reaction intermediate, represented approximately 4% of a monolayer. Thus the absolute turnover rate per surface adsorbed ethylene molecule is 25 times faster than the rate measured per platinum atom. To explain these results, we propose a model of weakly adsorbed ethylene intermediates reacting on atop sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00815274
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  • 2
    Electronic Resource
    Electronic Resource
    Monitoring surfaces on the molecular level during catalytic reactions at high pressure by sum frequency generation vibrational spectroscopy and scanning tunneling microscopy (1995)
    Springer
    Catalysis letters 34 (1995), S. 11-18 
    Details
    ISSN: 1572-879X
    Keywords: in situ catalysis ; propylene hydrogenation ; STM ; SFG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sum frequency generation (SFG), using non-linear laser optics, detects vibrational spectra of submonolayer amounts of adsorbates with excellent energy and time resolution. Scanning tunneling spectroscopy (STM) is sensitive to the atomic surface structure; readily imaging defects, steps and kinks as well as stationary adsorbed species. Both of these techniques can be used during reactions at high pressures and temperatures to obtain molecular information in situ. We report studies of propylene hydrogenation over Pt(111) crystal surfaces at atmospheric pressures and 300 K using SFG and STM. Four surface species (2-propyl, π-bonded propylene, di σ-bonded propylene, and propylidyne) were identified; the first two being implicated as reaction intermediates. The platinum surface structure remains unchanged during the reaction, consistent with the structure insensitive nature of olefin hydrogénation. Propylene decomposition induced substantial surface reconstruction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808316
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  • 3
    Electronic Resource
    Electronic Resource
    The sequential release of three extrinsic polypeptides in the PSII particles by high concentrations of trichloroacetate (1995)
    Springer
    Naturwissenschaften 82 (1995), S. 477-478 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01131601
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  • 4
    Electronic Resource
    Electronic Resource
    The Sequential Release of Three Extrinsic Polypeptides in the PSII Particles by High Concentrations of Trichloroacetate (1995)
    Springer
    Naturwissenschaften 82 (1995), S. 477-478 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01131601
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  • 5
    Electronic Resource
    Electronic Resource
    Computer simulation and analysis of fountain flow in filling process of injection molding (1994)
    Springer
    Journal of polymer research 1 (1994), S. 163-173 
    Details
    ISSN: 1572-8935
    Keywords: Fourtain flow ; Injection mold filling ; Finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The viscous flow in the filling stage of injection molding can be described in terms of an one-dimensional fully developed main flow and a complex two-dimensional flow near the advancing front, which is often termed the ”fountain flow“. The transport characteristics in the front region of the mold flow are of increasing importance in injection process of composite materials such as resin injection molding (RIM). By using of finite element method, the simulation of non-isothermal viscous flow between two isothermal parallel plates with the generalized newtonian fluid is presented in detail. The ”un-folding” of the fluid particles towards the mold wall directly affects transport characteristics such as the distribution of temperature, the orientation and the concentration of molecule near the front in filling stage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01374091
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  • 6
    Electronic Resource
    Electronic Resource
    Packed capillary column supercritical fluid chromatography of fat-soluble vitamins using liquid crystal polysiloxane coated particles (1996)
    Springer
    Chromatographia 43 (1996), S. 53-58 
    Details
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Packed capillary columns ; Liquid crystalline polysiloxane ; Polymer encapsulated particles ; Vitamins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Liquid crystal polysiloxane stationary phases were prepared by coating two different polymers on deactivated porous silica particles (10 μm diameter, 80 Å pores). Deactivation of the silica particles before coating was necessary to prepare highly efficient and inert stationary phases for supercritical fluid chromatography (SFC). Fat-soluble vitamins E, A, K1, K2, D2, and D3 were separated on these columns using neat supercritical CO2 as mobile phase. The analyses were completed within 40 min at 70 °C. The results were compared to those obtained using a capillary column packed with less ordered liquid crystalm,m-cyanobiphenyl-substituted polysiloxane coated particles. Reduced shape selectivity was observed with this cyanobiphenyl phase. The response factors of vitamins A, E, K1, K2, D2, and D3 when using the flame ionization detector (FID) were determined to be very similar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02272821
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  • 7
    Electronic Resource
    Electronic Resource
    Peak capacity in packed capillary column solvating gas chromatography (1999)
    Springer
    Chromatographia 49 (1999), S. 333-337 
    Details
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Gas chromatography ; Solvating gas chromatography ; Peak capacity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this paper, a general peak capacity expression was evaluated using columns containing various packing materials under solvating gas chromatography (SGC) conditions. Differing from column efficiency, peak capacity can describe both separation capability and speed when introducing the dead time into the peak capacity expression. Various factors that influence peak capacity in SGC are described, including particle pore size, chemical surface modification, particle size, column length, temperature, and pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467566
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  • 8
    Electronic Resource
    Electronic Resource
    Column wall modifications using polyethylene oxide for capillary electrophoresis of ribonucleotides (1999)
    Springer
    Chromatographia 49 (1999), S. 299-305 
    Details
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Column technology ; Deactivation ; Polyethyleneoxides ; Ribonucleotides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this study, a variety of fused silica capillaries with different combinations and sequences of treatments with HMDS and polyethylene oxide were prepared in order to develop an optimized column modification method for analysis of ribonucleotides. The 12 most common ribonucleotides (UTP, CTP, ATP, GTP, UDP, CDP, ADP, GDP, UMP, CMP, AMP, and GMP) in human cells were used as test solutes. Column performance measurements, including electroosmotic flow (EOF), solute migration speed and retention, column efficiency, peak shape, and resolution were investigated. By analyzing solute migration speed and retention of various hydrophilic/hydrophobic solutes, the column wall effects (EOF and adsorption) can be distinguished. This analysis method can give guidance in optimizing polymer coating properties (hydrophilicity/hydrophobicity) for CE columns. By studying the performance of these columns after various surface treatments, we were able to improve the separation of ribonucleotides from real samples to within 16 minutes with high efficiency and stability (over 300 analyses) using columns first deactivated with hexamethyldisilazane, and then coated with polyethylene oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467560
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  • 9
    Electronic Resource
    Electronic Resource
    Polymethylhydrosiloxane surface deactivation of silica particles for packed capillary column supercritical fluid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 665-670 
    Details
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Surface modification ; Deactivation ; Silica particles ; Stationary phases ; Packing materials ; Packed capillary columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Spherical porous silica particles (10 μm diameter, 300 Å and 80 Å pores), spherical nonporous silica particles (10 μm diameter), and irregular porous silica particles (≈10 μm diameter, 80 Å pores) were deactivated with polymethylhydrosiloxane (PS). The surface activities of the deactivated silica particles were investigated using various polar compounds under supercritical fluid chromatography (SFC) conditions (neat CO2), and compared with a commercial C18-bonded phase. The small pore (80 Å) silica particles could be more completely deactivated than larger pore (300 Å) and nonporous silica particles. The success of the PS deactivation method is ascribed to the excellent match between the reactive groups on the polymer backbone and the silica surface, and the formation of a highly crosslinked polymeric layer over the surface. Physical processes, such as adsorption and desorption of the deactivation reagent on the surface and diffusion from the surface, were found to have important effects on the deactivation. Using capillary columns packed with PS deactivated silica particles, typical polar organic compounds, including hydroxyl-containing compounds, carbonyl-containing compounds, free amines, and free carboxylic acids, were separated by SFC and compared with results from a commercial C18-bonded phase. While the results clearly show that the PS deactivated particles were more inert than the C18-bonded phase, better deactivation methods are still needed for separation of free acids and alkylamines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267802
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  • 10
    Electronic Resource
    Electronic Resource
    End-functionalized polyethylene oxide coated silica particles for packed capillary column supercritical fluid chromatography (1996)
    Springer
    Chromatographia 43 (1996), S. 373-379 
    Details
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Packed capillary columns ; Polyethylene oxide coated phases ; Polymer encapsulated particles ; Amines and acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polyethylene oxide (PEO)-based polymers with hydroxy, methoxy, and aminopropoxy terminal groups were coated on diol functionalized and hexamethyldisilazane end-capped silica particles. Proton-donor and proton-acceptor test solutes, including carboxylic acids, hydroxy-containing compounds, arylamines, and alkylamines were used to evaluate the chromatographic performances of these polymer coated particles under SFC conditions with neat CO2 as mobile phase. It was found that the particles coated with hydroxy-terminated PEO were suitable for the separation of proton-donor compounds such as hydroxy-containing compounds and carboxylic acids, and the particles coated with aminopropoxy-terminated PEO could be used for the separation of amines. That is, the proton-accepting stationary phase is suitable for the separation of proton accepting solutes, including strong basic alkylamines (pKb≈4), using neat CO2 as mobile phase, while the protondonating stationary phase is suitable for the separation of proton-donating compounds such as carboxylic acids (pKa≈4). Hydrogen bond basicity was found to be a critical factor for the chromatography of basic amines. Low volatility acidic and basic drugs were chromatographed using the new stationary phases. The stability of the PEO coated particles was determined by measuring the loss of organic carbon under SFC conditions. It was found that approximately 18 % of the coating (average molecular weight of 15,000) was washed out of the particles by supercritical CO2 after 7 h at 350 atm and 50°C
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02271014
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