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  • Polymer and Materials Science  (3)
  • I2·I 3 − ·I2  (1)
  • 1
    Electronic Resource
    Electronic Resource
    (β-Cyclodextrin)2·KI7·9 H2O. Spatial fitting of a polyiodide chain to a given matrix (1983)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 1 (1983), S. 181-191 
    Details
    ISSN: 1573-1111
    Keywords: (β-cyclodextrin)2·KI7·9H2O ; zigzag and linear polyiodide ; I2·I 3 − ·I2 ; starch-iodine model ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract α-Cyclodextrin, a torus shaped molecule with a 5 Å wide central cavity, forms a number of deep green, blue and black crystals when complexed with iodine/metal iodide. In contrast, β-cyclodextrin, having a 6 Å cavity produces only one type of reddish-brown crystal, no matter what metal iodide is used. The complex (β-cyclodextrin)2 ·KI7·9H2O displays space groupP21 (pseudo-C2) with cell constantsa=19.609(5),b=24.513(7),c=15.795(6)Å, β=109.50(2)°,Z=4. The crystal structure was solved inC2 on the basis of 3022 absorption corrected CuKα (Ni-filter) X-ray intensities and refined by full matrix least squares toR=17%. This relatively highR-factor is due to many weak reflections (pseudo-C2) and considerable disorder exhibited by water and iodine. In the complex, β-cyclodextrin adopts a ‘round’ shape with O(2)...O(3) interglucose hydrogen bonds formed and all O(6) hydroxyls pointing away from the cavity. Two molecules are arranged head-to-head to produce a dimer, and dimers are stacked such that a slightly zigzagged cylinder with a 6 Å-wide cavity is formed. In the cavity described by each dimer, an I 7 − ion composed of I2·I 3 − ·I2 units is located, with I2 and I 3 − perpendicular to each other. K+ ions and 9 H2O molecules are found in interstices between the β-cyclodextrin cylinders. This zigzag polyiodide contrasts with the linear form observed in the 5 Å wide α-cyclodextrin channels. It explains differences in color of the crystals and suggests that β-cyclodextrin polyiodide is not a good model for blue starch-iodine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656821
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  • 2
    Electronic Resource
    Electronic Resource
    Self-association of bovine pancreatic trypsin inhibitor: Specific or nonspecific? (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1347-1349 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311112
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  • 3
    Electronic Resource
    Electronic Resource
    The structure of the left-handed antiparallel amylose double helix: Theoretical studies (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 363-375 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The atomic coordinates from the crystal structure of a hexasaccharide complex accommodating a zigzag polyiodide [ W. Hinrichs, G. Büttner, M. Steifa, Ch. Betzel, V. Zabel, B. Pfannemüller, and W. Saenger (1987) Science Vol. 238, pp. 205-208; W. Hinrichs and W. Saenger (1990) Journal of the American Chemical Society, Vol. 112, pp. 2789-2796 ] served to construct an antiparallel-stranded amylose double helix with a 5 Å wide central cavity. Using our methodology for the energetic optimization of polymer structures in the internal/ helical variable space [ H. Sklenar, R. Lavery, and B. Pullman (1986) Journal of Biomolecular Structure Dynamics, Vol. 3, pp. 967-987, 989-1014; 1015-1031], we have calculated a theoretical counterpart of this idealized double helix by constraining the helical twist and rise to their experimental values (-45° and 2.33 Å, respectively). Applying the same constraints to the parallel-stranded duplex, this also leads to a low-energy structure with wide central cavity. It is considered as an alternative model to accommodate iodine as observed in the starch-iodine complex.Release of the helical constraints leads to left-handed antiparallel- and parallel-stranded double helices, respectively, with narrow central cavities. Both structures have very similar helix parameters and correspond, in their main characteristics, to the experimentally derived parallel-stranded structure of amylose in starch (6 residues per turn and a pitch height of about 21 Å). The intramolecular energy calculated for the optimized antiparallel-stranded amylose double helix is comparable to that of the parallel-stranded structure. This result raises the question why parallel-stranded amylose seems to be favored in nature. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330305
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical drug design: 6-Azauridine-5′-phosphate - its X-ray crystal structure, potential energy maps, and mechanism of inhibition of orotidine-5′-phosphate decarboxylase (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 2015-2036 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cytostatic drug 6-azauridine is converted in vivo to 6-azauridine-5′-phosphate (z6Urd-5′-P), which blocks the enzyme orotidine-5′-phosphate decarboxylase (Ord-5′-Pdecase) and therefore inhibits the de novo production of uridine-5′-phosphate (Urd-5′-P). In order to relate the structure and function of z6Urd-5′-P, it was crystallized as trihydrate, space group P212121 with a = 20.615 Å, b = 6.265 Å, c = 11.881 Å, and the structure established by Patterson methods. Atomic parameters were refined by full-matrix least-squares methods to R = 0.066 using 1638 counter measured x-ray data. The ribose of z6Urd-5′-P is in a twisted C(2′)-exo, C(3′)endo conformation, the heterocycle is in extreme anti position with angle N(6)-N(1)-C(1′)-O(4′) at 86.3°, and the orientation about the C(4′)-C(5′) bond is gauche, trans in contrast to gauche, gauche found for all the other 5′-ribonucleotides. Conformational energy calculations show that z6Urd-5′-P may adopt an extreme anti conformation not allowed to Urd-5′-P, and they also predict the same unusual trans, gauche conformation about the C(4′)-C(5′) bond in orotidine-5′-phosphate (Ord-5′-P) and in z6Urd-5′-P, which renders the distances O(2)…O(5′) in z6Urd-5′-P and O(7)…O(5′) in Ord-5′-P comparable. On this basis the function of z6Urd-5′-P as an Ord-5′-Pdecase inhibitor can be explained as being due to its structural similarity with the substrate Ord-5′-P and further clarifies the inhibitory action of 5′-nucleotides bearing the heterocycles oxipurinol, xanthine, or allopurinol [J. A. Fyfe, R. L. Miller, and T. A. Krenitsky, J. Biol. Chem. 248, 3801 (1973)]. With this in mind, new inhibitors for Ord-5′-Pdecase may be designed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1979.360180814
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