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  • Articles: DFG German National Licenses  (23)
  • Polymer and Materials Science  (23)
  • 1
    Electronic Resource
    Electronic Resource
    Electrostatic forces at helix-coil boundaries in DNA (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 393-405 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Tm of internal loop-forming (dA · dT)N domains in pBR322 DNA has been measured over a tenfold range of [Na+]. The slopes SN = dTm/d log[Na+] are linear and decrease in magnitude with decreasing loop size N, signaling a reduction in Na+ released during the transition of these domains to the coil state. Values of SN decrese linearly with increasing N-1 in accordance with the expectation of a simple model for the occurrence of a gradient of long-range electrostatic forces at helix-coil boundaries, and extrapolate almost precisely to the value of S∞ observed for (dA · dT)∞. These results indicate (1) less counterion is released per phosphate residue from the finite loop than from the infinitesized loop, and (2) the difference in binding is constant for each boundary formed and independent of the size of the loop within the range examined: ∼ 350 base pair (bp) 〉 N 〉 71 bp. The slope of the dependence of SN on N-1 indicates the region of higher charge density at the boundary extends at least 18 Å into the coil and probably 40-50 Å before dropping to a value characteristic of the unperturbed coil. The free energy for excess counterion binding at boundaries can be expressed by \documentclass{article}\pagestyle{empty}\begin{document}$$ {{ - \Delta G} \mathord{\left/ {\vphantom {{ - \Delta G} {RT}}} \right. \kern-\nulldelimiterspace} {RT}} = 10.47{\rm log}\left[{{\rm Na}^ + } \right] + 5.234 $$\end{document} When the loop entropy function in a statistical mechanical algorithm for the dissociation of DNA is weighted by this quantity, calculated Tm are seen to vary by only ±0.09°C from observed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290211
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  • 2
    Electronic Resource
    Electronic Resource
    Solution polymerization of selected polyphosphazenes (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 2293-2302 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Several alkoxy/aryloxy-substituted phosphazene polymers [P(OR)2 = N]n, where R = C6H5, CH2CF3, C8H10, were prepared by the reaction of polydichlorophosphazene with their corresponding sodium salts. The polydichlorophosphazene was obtained by the solution polymerization of hexachlorocyclotriphosphazene in 1,2,4-trichlorobenzene. Sulfamic acid and ammonium sulfamate were used as catalysts. Apparently, sulfamic acid functions as a catalyst through its acid group in some decomposed form. New catalysts, p-toluenesulfonic acid and sulfobenzoic aicd, have been developed for this solution polymerization. The polymerization favors a cationic mechanism. A promoter, CaSO4·2H2O, was found to speed up the polymerization reaction. Effect of several parameters such as dilution, catalyst concentration, and promoter concentration on the properties of the final polymer were investigated. The polymers were characterized by differential scanning calorimetry, gel permeation chromatography, and 31P solution NMR spectroscopy.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900930
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanisms of antioxidant action: Transformations involved in the antioxidant function of zinc dialkyl dithiocarbamates. I (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 789-797 
    Details
    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 antioxidant mechanism of zinc dialkyl dithiocarbamate is examined in detail in model compounds. The kinetics of the reaction of zinc dialkyl dithiocarbamate with hydroperoxides were studied in inert and oxidizable substrates. A typical electron donor antioxidant and a base (CaCO3) were found to inhibit the peroxide decomposition. The oxidation products of the Zinc II complex appear to be quite different from those of the nickel II and iron III complexes. Two processes are involved in the antioxidant function of the zinc complex: The first is a free radical decomposition of the peroxides, which predominates at molar cumene hydroperoxide (CHP)/zinc diethyl dithiocarbamate (ZnDEC) ratios of 10 or less. At higher molar ratios an ionic reaction predominates, although there is a radical contribution at all ratios. Thiocarbamoyl disulfide does not seem to be formed as an intermediate from ZnDEC during the ionic process.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1985.070300227
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanisms of antioxidant action: Transformations involved in the antioxidant function of metal dialkyl dithiocarbamates. III (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 1455-1471 
    Details
    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 behaviors of iron, nickel, and zinc dialkyl dithiocarbamates were compared with the corresponding thiuram disulphide in their reaction with cumene hydroperoxide (CHP) at 110°C. The metal complexes exhibit both homolytic and heterolytic processes and transformation products formed during the above reactions and not the initial metal complexes were found to be responsible for the heterolytic decomposition process. However, the nature of the initial transformation products in the case of the iron and nickel complexes differed from those of the corresponding zinc complex. In the former case the corresponding disulfide was shown to be the initial transformation product while there was no evidence for the formation of disulfide in the case of the zinc complex. This difference appears to be responsible for the observed different kinetic behavior of CHP decomposition in the presence of the nickel and iron complexes from that in the presence of zinc. This thiuram disulfide behaves quite differently from the metal complexes in that heterolytic decomposition of hydroperoxide predominates at all molar ratios of the disulphide to the CHP. The hydroperoxide decomposition curves in this case show only one step in contrast to the metal complexes which show a multistep behavior, and this was shown to correspond to the third catalytic stage in the reaction of the metal complexes. Comparison of the rate constant of this step with that of the final step of the metal complexes shows a close resemblance to the case of the iron and nickel and is quite different from that of the zinc complex, confirming the intermediacy of the disulfide in the former cases but not in the latter.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1987.070330502
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanisms of antioxidant action: Mechanochemical transformation products of 2,2,6,6-tetramethyl-4-hydroxypiperidinoxyl in polypropylene (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 703-713 
    Details
    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 effect of the processing operation on the nature and quantity of transformation products of 2,2,6,6-tetramethyl-4-hydroxypiperidinoxyl (〉NO.) and its corresponding hydroxylamine (〉NOH) was investigated in polypropylene. It was found that both 〉NO. and 〉NOH are actively involved in a regenerative cycle and that this redox couple is responsible for the stability of the polymer whether the initial additive is 〉NO. or 〉NOH. The alkyl hydroxylamine (〉NOR), on the other hand, does not appear to play a significant role in the melt stabilization of the polymer. Quantitative measurements of 〉NOH and 〉NO. concentrations show that, under conditions of both restricted oxygen (CM) and oxygen excess (OM), the concentrations of both species change reciprocally throughout the processing operation. In a closed mixer (CM), the total overall concentration of 〉NO. and 〉NOH remains at a high constant level, whereas in an open mixer (OM), their total concentration decreases continuously to a low level, indicating the irreversible destruction of the redox couple (〉NO. and 〉NOH). The photo-oxidative stability of the polymer was found to depend on the total concentration of the redox couple left in the system after processing in either CM or OM.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1987.070330302
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogels by atom transfer radical polymerization. I. Poly(N-vinylpyrrolidinone-g-styrene) via the macromonomer method (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 823-830 
    Details
    ISSN: 0887-624X
    Keywords: atom transfer radical polymerization ; poly(N-vinylpyrrolidinone-g-styrene) ; macromonomer method ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Atom transfer radical polymerization has been used to prepare well-defined vinyl macromonomers of polystyrene using vinyl chloroacetate as an initiator. Because styrene and vinyl chloroacetate do not copolymerize, no branching or incorporation of the initiator into the backbone was observed. Macromonomers of several molecular weights were prepared and copolymerized free radically with N-vinylpyrrolidinone in varying feed ratios in order to produce poly(NVP-g-Sty) graft copolymers. The macromonomers used were of sufficiently high molecular weight to form physical crosslinks in solvents which favor the hydrophilic NVP, such as water, which prevent the copolymer from dissolving and cause it to swell. These materials, therefore, formed hydrogels of swellabilities in water exceeding 95%, depending on the amount of styrene that was incorporated into the copolymer. Limitations of and alternatives to this method are also discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 823-830, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 7
    Electronic Resource
    Electronic Resource
    Loop energy in DNA (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 2009-2026 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The loop function ƒ(N), representing the statistical weight of N complementary residues in a closed ring, has been determined by analysis of high-resolution melting curves of a series of recombinant homopoly(A · T)N inserts in pBR322 DNA, where 150 〉 N 〉 50 base pairs (bp). Loops are found more stable and therefore presumably less elastic than expected for an ideal, freely jointed chain. A value of 97 ± 2 bp is obtained for the empirical orientation-stiffness parameter D in the expression for nonideal chains, ƒ(N) = (N + D)-1.7. The 10% increase in apparent stiffness over that of an ideal chain closely coincides with the extent of residual stacking in the loop. It is thus concluded that the more favorable loop energy, such as expected of smaller loops, is due to the incipient helical orientation of some residues, predisposing the loop to reclosure. A quantitative loop function is essential for the prediction and assignment of domains in DNA.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360261204
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of well-defined azido and amino end-functionalized polystyrene by atom transfer radical polymerization (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 18 (1997), S. 1057-1066 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mono and difunctional polystyrenes containing active halogenated end groups were prepared by atom transfer radical polymerization (ATRP). Substitution reactions were explored to convert the halogen termini to azido groups, followed by readuction to form the amino functional polymer. Quantitative conversion of the end groups was observed in each transformation reaction. 1H NMR demonstrated the formation of the azide from the bromide functionality without elimination. The difunctional α,ω-diaminopolystyrene was reacted with terephthaloyl chloride in a condensation process to produce chain-extended polystyrene containing amide bonds along the polymer backbone.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1997.030181209
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  • 9
    Electronic Resource
    Electronic Resource
    Preparation of hyperbranched polyacrylates by atom transfer radical polymerization, 4Part 3: ref.8. The use of zero-valent copper (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 19 (1998), S. 665-670 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The addition of zero-valent copper to the self-condensing vinyl polymerization (SCVP) of novel AB* (meth)acrylic monomers using atom transfer radical polymerization (ATRP) catalyst systems has allowed for their successful polymerization. Polymerization under homogeneous and heterogeneous catalyst conditions without additional Cu(0) were unsuccessful. The catalyst system that was designed comprised of Cu(I) bromide, 4,4′-bis(5-nonyl)-2,2′-bipyridine, and Cu(0) metal (powder or turning). From 1H NMR spectroscopy, the degree of branching was estimated for the acrylic polymers, DB = 0.48. The degree of branching could not be determined for methacrylates by this method due to overlapping signals in the 1H NMR spectra.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 10
    Electronic Resource
    Electronic Resource
    Mechanisms of antioxidant action: Nature of transformation products of dithiophosphates. II. Antioxidant action of thiophosphoryl disulphides (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 44 (1992), S. 1297-1305 
    Details
    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 nature of transformation products of high-temperature reactions of thiophosphoryl disulphides with hydroperoxides in the absence and presence of oxidisable substrates and the role of the disulphide in the overall antioxidant mechanism was investigated using a range of techniques such as oxygen absorption, 31P nuclear magnetic resonance (NMR), gas-liquid chromatography (GLC), and peroxide determination. The major transformation products of the above oxidation reactions were found to be the thio and thiono-phosphoric acids, in addition to mono and polysulphides. At high molar ratios of peroxide to disulphide (〉10), these oxidation products are the main catalysts for peroxide decomposition, while at lower ratios the disulphide itself was found to play a major role in the antioxidant mechanism.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070440720
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