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  • Chemistry  (17)
  • Organic Chemistry  (4)
  • Atomic, Molecular and Optical Physics  (2)
  • Inorganic Chemistry
  • Magnetism
  • Wiley-Blackwell  (19)
  • 1990-1994  (19)
  • 1991  (19)
Collection
Publisher
  • Wiley-Blackwell  (19)
Years
  • 1990-1994  (19)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 25 (1991), S. viii 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 813-825 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photon correlation spectroscopy has been used to study the translational (D0)and internal dynamics of monodisperse linear and polydisperse superhelical plasmid-DNAs. Scattering vector dependent correlation functions were measured and analyzed with the inverse Laplace transform CONTIN written by S. Provencher. For scattering vectors (q) lower than 1.3 × 105cm-1, D0 can be separated from internal dynamics. Using the measured D0value, the q dependence of internal modes was determined. Extrapolation of the internal relaxation times for q → 0 yields the longest internal relaxation time t1. This time can be connected to the persistence length in terms of the Berg-Soda model, which describes the molecule as a semiflexible circular polymer with hydrodynamic interactions. The calculated length of 76 nm for DNA, I = 0.15 mol/L, is a little higher than the one obtained from static light scattering data without excluded volume corrections. A comparison of experimental and simulated correlation functions for the Berg-Soda model shows that the model gives a fairly good description of the dynamics of the linear molecule, whereas large discrepancies between model and experimental functions are observed for the superhelical DNA. Small differences between model and experimental functions are mainly attributed to the neglect of the torsional modes that may be coupled to bending and flexing modes. For the superhelical DNA the agreement is improved if the calculation is carried out with a linear molecule, with shorter contour length and increased diameter. Both quantities can be derived from the known superhelix tilt angle.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 25 (1991), S. VIII 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 49-59 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of the solvent on the stability of the zwitterion in the active site of papain is investigated with numerical methods. The solvent is represented by a homogeneous dielectric continuum surrounding a cavity, defined by a fragment of the protein enclosed by a surface obtained following Connolly's method. The discretisized boundary surface is used to solve the Poisson equation in its integral form by means of a numerical approximation based on the boundary element method (BEM), resulting in a set of surface polarization charges. The solvent effect on the proton transfer in papain is studied on the basis of MO-SCF-direct reaction field (DRF) calculations of the energy and charge distribution of the fragment in the field of the surface charges. The role of Asp-158 in the proton transfer in the active site of papain is reevaluated in the presence of the solvent. It is concluded that the effect of the negative charge of Asp-158 is nearly completely screened by the solvent.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 687-702 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the computation of the tunnel current in a scanning tunneling microscope (STM). The calculation accounts for the three-dimensional scattering taking place simultaneously in the first atomic layers of the sample and in the apex of the probing tip. The model is built with the following ingredients: (a) the tip is represented by a cluster of atoms attached to an otherwise planar, free-electron metal surface, and (b) the analyzed sample is a planar free-electron metal with a local potential corrugation induced by an isolated molecule or adatom. The potential barrier includes the strong bending effect due to the image-charge formation occurring as the tunneling electron crosses the gap between the tip and the sample. The specific theoretical approach designed to solve this scattering problem exploits the fast Fourier transform algorithm to construct a transfer matrix in a mixed real- and momentum-spaces representation. The total current is obtained by summing the contributions of all scattered waves traveling in the barrier between the tip and the sample, and it is studied in this article for various positions of the tip relative to the adsorbed atomic cluster. The theory is used here to simulate the scan of a model-aluminum atom on a free-electron metal substrate using electrons focused by a single-atom tungsten tip.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 0935-6304
    Keywords: Micropacked liquid chromatography ; Enantiomer separation ; HPLC-TID ; Organophosphorus pesticides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Microcolumn liquid chromatography (micro-LC) of some chiral organophosphorus pesticides has been studied using Chiralcel OD columns and simultaneous ultraviolet (UV) and phosphorus selective detection, the latter by means of a micro-UV cell coupled on-line to a thermionic detector (TID). Micro-LC showed a ca. 5-fold improved separation impedance, a ca. 1.8-fold increased column permeability, and greater inertness compared with conventional LC.By using the TID, organophosphorus pesticides could be satisfactorily determined at trace levels, the detection limit being 4 pg/s of phosphorus. The response of the micro-LC-TID system is linear in the range of 0.05-20 ng (r = 0.9994).
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 912-915 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Planar polymer lightguides of poly(methyl methacrylate)(PMMA) doped with the azo dye, N,N-dihexyl-4-amino-4′-nitro-azobenzene (DHANA) were fabricated on a suitable glass substrate or on one surface of a regular prism. The absorption of this azo dye is strong in the green spectral region. With the red light of a HeNe laser (633 nm) these polymer films may be used as lightguides. However, in this spectral region, the guided light influences the waveguiding properties of the polymer film, making this combination a possible candidate for an all optical device material. The observed refractive index changes are intensity dependent and the response time is of the order of 100ms.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 1171-1180 
    ISSN: 0021-8995
    Keywords: 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 , Physics
    Notes: The relationship of 10 basic physico-mechanical properties and the concentration of the filler is investigated through narrow filling intervals of seven different composite series containing various types of HD polyethylene and different grades of kaolin. A variety of mixing techniques for the preparation of the composites is used, and testing is carried out by applying different techniques and conditions. The investigations show that, in all cases when an identical mixing technique is applied for a given series of composite formulations, the relationship linking the physico-mechanical and dynamic-mechanical G′, G″, and tan δ properties with the concentration of the filler is not a monotonous curve, and displays a multiextermal character. We propose as one possible explanation that a periodic change in the free volume and the content of crystal polyethylene phase exists, as a function of the filling. The nonmonotonous character of the changes of properties is related to the proposed mechanism for the change of the physical structure of composites, which are composed of filler particles coated with n monolayers of polyethylene crystallites, when, as filling continues, periodically new types of filler particles are formed. The nonmonotonous character of the relationship between the properties and the concentration of the filler should be taken into consideration when these relationships are approximated or expressed in a mathematical-analytical form, especially when high amounts of fillers (more than 20 vol %) are used.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 63 (1991), S. 960-968 
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 10
    ISSN: 0935-6304
    Keywords: HR-GC ; Organochlorine pesticides ; Pyrethroids ; Water analysis ; Sample clean-up ; Solid-phase extraction cartridges ; LC-GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ASPEC (Automatic Sample Preparation with Extraction Columns) system has been coupled on-line to capillary GC-ECD by means of a loop-type interface equipped with a solvent vapour exit. Both ASPEC and GC conditions have been optimized leading to an effective clean-up of the extracts analyzed.By means of solid-phase extraction cartridges filled with silica, it has been possible to analyze concentrated surface water extracts for a group of 18 electron-capturing compounds present in the water at ppt levels. ASPEC-GC has also been applied to the determination of synthetic pyrethroids at ppt levels in surface water.The complete analytical procedure is greatly facilitated by automation and miniaturization. Miniaturization results in a considerable decrease in the sample volume required. The potential of the method for the analysis of other pesticides is estimated.
    Additional Material: 6 Ill.
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