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  • 2000-2004
  • 1990-1994  (6)
  • 1950-1954
  • 1925-1929
  • 1992  (6)
  • Chemistry  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Structure of a rhombohedral R6 insulin/phenol complex (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 401-408 
    Details
    ISSN: 0887-3585
    Keywords: X-ray diffraction ; allosterism ; zinc/phenol interaction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Hexameric insulin has been crystallized from different conditions ina variety of crystalline modifications. In the presence of ∼1%phenol and at a pH of 8.5, a new rhom-bohedral form is produced, space group R3, a = 79.92 Åand c = 40.39 Å, in whichthe asymmetric unit consists of a dimer. The structur has been solved and refined, using data between 8.0 and 2.5 Å resolution, to a residual of0.157. The two monomers in the asymmetric unit have nearly identical R conformations, that is, residues Bl through B8 are α-helical, producing a continuous α-helix from Bl through B19. A phenol molecule is hydrogen bonded to the carbonyl oxygen of A6 Cys of each monomer. Small differences in conformation and the final (2Fo-Fc) and difference electron density maps suggest that an additional phenol molecule is coordinated to one of the two zinc ions.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340140309
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular structure, morphology, and antioxidant consumption in medium density polyethylene pipes in hot-water applications (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 649-657 
    Details
    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: Changes in polymer structure and antioxidant concentration have been systematically studied as functions of temperature, hoop stress, exposure time, and location in pipe wall on pressure tested pipes of medium density polyethylene. The pressure tests have been performed with water as the internal medium and air as the external medium at temperatures in the range 80 to 105°. Infrared spectroscopy shows that oxidation is initiated at the inner wall surface just prior to the onset of the so-called stage III fracture. X-ray diffraction and size exclusion chromatography show that oxidation involves only the amorphous phase and results in a significant molar mass reduction. The near-inner-wall material exhibits a 10% reduction in mass average molar mass before the onset of stage III fracture and thereafter a more dramatic decrease. Oxidation induction time measurements by differential scanning calorimetry show that the antioxidant concentration is almost twice as high in the center of the wall as in the near-inner-wall and outer-wall material of the unexposed pipe, that the loss of antioxidant is anomalously rapid at the beginning of the high temperature exposure, and that the antioxidant concentration profile gradually becomes more skewed towards the outer wall on prolonged exposure. The data presented in this paper are used in a parallel paper for modeling purposes.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321003
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling of antioxidant loss from polyolefins in hot-water applications. I: Model and application to medium density polyethylene pipes (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 658-667 
    Details
    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: This paper is the first in a series of related papers describing the application of a diffusion/reaction model to the loss of antioxidants from polyolefins in hot-water applications. The model, which is derived in detail, describes the time evolution of antioxidant concentration profiles in the exposed material in terms of adjustable parameters. The parameters describe the rates of diffusion, evaporation, extraction, and chemical reaction of antioxidant. Parameter values are determined by least-squares fitting of the calculated concentration profiles to experimental profiles. The model is applied to a commercial medium density polyethylene pipe material, where antioxidant concentration data from thermal analysis is available for water/air (internal/external) exposure at three temperatures. A comparison of parameter values with literature data is undertaken. The temperature dependence of the parameters is considered and activation energies are compared with literature values. The relative importances of the loss mechanisms are discussed. The effect of boundary conditions on parameter values is considered by application of the model to a limited amount of available data for air/air and water/water exposures. The results indicate that for water/air exposure, extraction by the water phase is the dominating loss mechanism.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321004
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular structure of cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)2-] revealed by X-ray analysis (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 757-764 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of a synthetic analogue of valinomycin, cyclo [-(D-Val-L-Hyi-L-Val-D-Hyi)2-] (octa-meso-valinomycin) (I) (C40H68N4O12 · 1.5 · C4H8O2, Mr = 937.01 + 88.10), has been determined. Crystals grown from dioxane are monoclinic, space group P21/a, with cell parameters a = 21.487(8), b = 16.836(5), c = 16.089(4) Å, β = 111.70(4), and Z = 4. The atomic coordinates for nonhydrogen atoms were refined in the anisotropic thermal motion approximation. H atom positions were included in the structure factor calculations at their geometrically expected positions. Values of the standard and weighted R factors after refinement are 0.11 and 0.13, respectively. The conformation of the depsipeptide crystallized from dioxane is different from that crystallized from chloroform (II). The molecule adopts a rectangular shape with two type IV β-turns containing a hydrogen bond and possesses pseudorotational symmetry. The side chains are located on the molecular periphery. The orientation of the carbonyl groups of the molecule is not conducive for efficient metal-ion coordination and in the observed conformation cannot behave as an ionophore.In the crystal the molecules form infinite chains parallel to the c axis, and are stabilized by two intermolecular hydrogen bonds that are shorter and have better geometry than the intramolecular hydrogen bonds.A φ/Ψ plot for dodecadepsipeptides with a (DLLD)3 sequence has well-defined areas for Val and Hyi residues only in cases when the crystals have been grown from nonpolar or medium-polar solvents. The Φ/Ψ plot for octadepsipeptides crystallized from chloroform (II) shows this behavior also. There also is a correlation between the polarity of the solvent from which crystals of octa-meso-valinomycin or valinomycin analogues with a (DLLD) sequence of configuration have been grown and the number of the intramolecular hydrogen bonds that are formed. The more polar the solvent the fewer the number of intramolecular hydrogen bonds.Empirical energy calculations on octa-meso-valinomycin indicate that for isolated molecules, the energy of the bracelet form (II) is 4.7 kcal/mole lower than that of the rectangular form (I).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320705
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    The structure of a rhombohedral R6 insulin hexamer that binds phenol (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 441-445 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different hexameric forms of insulin have been crystallized from a variety of conditions. In the presence of 1% phenol, 1.0 M sodium chloride, and at a pH of 8.5, a rhombohedral form is produced with two monomers in the asymmetric unit, space group R3, a = 79.92 Å and c = 40.39 Å. The structure has been solved and refined, using data between 8.0 and 2.5 Å resolution, to a residual of 0.157. Each of the monomers adopts an R conformation, that is residues B1-B8 are α-helical. As a result of the T to R transition, an elliptical cavity is created between symmetry-related monomers and is occupied by a phenol molecule. A region of density within bonding distance to one of the zinc ions has been interpreted as an additional phenol molecule.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320422
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Maximum entropy: A new approach to non-destructive deconvolution of depth profiles from angle-dependent XPS (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 19 (1992), S. 175-180 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The application of the maximum entropy method to non-destructive depth profiling by angle-dependent XPS is described. The algorithm gives the set of depth profiles that has maximum Skilling-Jaynes entropy, subject to the condition that the calculated data agree with the measured data within the experimental precision. The method does not require an inverse transform, is robust to experimental noise and is not restricted to small numbers of components. The programme can determine which of a set of prior estimates for the depth profiles is most probable; however, the reconstruction near the surface is virtually independent of this choice. Further, the method also estimates the accuracy of the reconstruction from a single data set. It is illustrated using model data and by a re-analysis of angle-resolved XPS data sets available in the literature.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740190134
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    Paper (German National Licenses)
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