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  • 1990-1994  (12,087)
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  • 1990  (12,087)
  • Chemistry  (9,691)
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  • 1990-1994  (12,087)
  • 1975-1979
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  • 101
    Electronic Resource
    Electronic Resource
    Inactivation of the catalytic subunit of bovine cAMP-dependent protein kinase by a peptide-based affinity inactivator (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 131-138 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A peptide affinity inactivator, Ac-Leu-Arg-Arg-Ala-(BrAc)Orn-Leu-Gly, was used as a tool to probe for active site residues in the catalytic subunit of bovine cAMP-dependent protein kinase. The peptide inactivated the catalytic subunit in an active site-directed and monophasic manner with a first-order rate constant of 0.03 min-1 and a dissociation constant of 675 μM. Studies with radioactive peptide indicated that approximately one equivalent of peptide was incorporated into each protein molecule. Protein sequencing identified the modified residue as Cys-199. A possible location for Cys-199 within the active site is suggested.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290118
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  • 102
    Electronic Resource
    Electronic Resource
    A comparative analysis of single- and multiple-residue substitutions in the alkaline phosphatase signal peptide (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 139-147 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alkaline phosphatase signal peptide participates in transport of the enzyme to the periplasmic space of Escherichia coli. The signal sequence, like that of other signal peptides, is composed of a polar amino-terminal segment, a central region rich in hydrophobic residues and a carboxy-terminal region recognized by signal peptidase. We have previously shown that an alkaline phosphatase signal peptide mutant containing a polyeucine core region functions efficiently in transport of the enzyme [D. A. Kendall, S. C. Bock, and E. T. Kaiser (1986) Nature 321, 706-708]. In this study, some of the amino acid changes involved in the polyleucine sequence are examined individually. A Phe to Leu substitution as the sole change results in impaired transport properties in contrast to when it is combined with three other amino acid changes in the polyleucine-containing sequence. A mutant with a Pro to Leu substitution in the hydrophobic core region is comparable to wild type while the same type of substitution (Pro to Leu) in the carboxy-terminal segment results in substantial accumulation of the mutant precursor. Finally, introduction of a basic residue into the hydrophobic segment (Leu to Arg substitution) results in a complete export block. These results exemplify the spectrum of properties produced by individual residue changes and suggest there is some interplay between hydrophobicity and conformation for signal peptide function.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290119
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  • 103
    Electronic Resource
    Electronic Resource
    The most highly amphiphilic α-helices include two amino acid segments in human immunodeficiency virus glycoprotein 41 (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 171-177 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A search for highly amphiphilic α-helices has been made in a data base of protein sequences, using the helical hydrophobic moment as a criterion of amphiphilicity. The protein segments of largest hydrophobic moment have been analyzed. For the segments whose structures are known, they are in fact α-helices. Two of the segments having very large hydrophobic moments are from the smaller C-terminal portion of the human immunodeficiency virus (HIV) envelope glycoprotein gp41. Also, among segments having large hydrophobic moments, but not among the most extreme, are lytic peptides such as melittin. Melittin seeks surfaces between polar and apolar phases, including the membrane-water interface. It is conceivable that the gp41 segments of extreme hydrophobic moment may participate in one of the membrane-related functions of the HIV virus.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290122
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  • 104
    Electronic Resource
    Electronic Resource
    Enkephalin analogues containing β-naphthylalanine at the fourth position (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 179-196 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To examine the importance of the aromatic side chains of enkephalin on opiate activity, we report the synthesis and conformational analysis of a series of analogues related to enkephalin with β-naphthylalanine in place of phenylalanine at the fourth position. Three linear analogues (Tyr-D-Ala-Gly-(L and D)-β Nal(1)-Leu-NH2 and Tyr-D-Ala-Gly-β Nal(2)-Leu-NH2) were initially synthesized to examine the effect of the substitution on biological activity. The increased activity of these peptides at the μ-opiate receptor, compared to native Leu-enkephalin, prompted us to examine the more conformational constrained analogues, Tr-c[D-A2bu-Gly-(L and D)-β Nal(1)-Leu], incorporating a α,γ-diaminobutyric acid at the second position and cyclization to the carboxylic end of the leucine. These two cyclic analogues provide insight into the necessity for the L chirality of the aromatic residue at position 4. The Tyr-c[D-A2bu-Gly-L-β Nal(1)-Leu] analogue is highly potent and displays a slight preference for the μ receptor. The conformational analysis indicates that despite the high flexibility of the tyrosine side chain, the aromatic rings of the tyrosine and naphthylalanine are relatively distant from each other. The presence of two intramolecular hydrogen bonds help maintain the conformation of the 14-membered backbone ring that keeps the side chains directed away from each other. These findings are in agreement with our model of an extended structure required for μ selectivity and a folded form with close aromatic ring placement for δ selectivity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290123
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  • 105
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290301
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  • 106
    Electronic Resource
    Electronic Resource
    Assessment of protien reorientational diffusion in solution by 13C off-resonance rotating frame spin-lattice relaxation: Effect of anisotropic tumbling (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 469-480 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C off-resonance rotating frame spin-lattice relaxation technique is applicable to the study of protien rotational diffusion behaviour in a variety of experimental situations. The original formalism of James and co-workers (1978) (J. Amer. Chem. Soc. 100, 3590-3594) was constrained by the assumption of random isotropic reorientational motion. Here we include in the formalism anisotropic tumbling, and present the results of computer simulations illustrating the differences between anisotropic and isotropic reorientational motion for the off-resonance rotating frame spin-lattice relaxation experiment. In addition, We have included chemical shift anisotropy of the peptide carbonyl carbon as an additional relaxation mechanism contribution, to permit high field nmr protein rotational diffusion measurements.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290302
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  • 107
    Electronic Resource
    Electronic Resource
    A unique binding cavity for divalent cations in the DNA-metal-chromomycin A3 complex (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 481-489 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of chromomycin A3 (CRA) to calf thymas DNA was investigated in the presence of divalent cations using visible absorption and 1H-nmr spectroscopies. An apparent equilibrium binding constant (∼ 1011M-1) was obtained from metal competition experiments using EDTA to remove the metal cation from the DNA-M-CRA (M: metal) complex. The large binding constant of the drug to DNA enabled us to obtain essentially complete complexation of CRA to the short homogeneous d(ATGCAT)2 duplex using stoichiometric amounts of the metal cation. Large induced chemical shifts were observed in the 1H-nmr spectrum of the above complex using the paramagnetic Co2+ cation indicating that the metal occupies a unique binding site. Since no induced 1H-nmr chemical shifts were observed for the drug-Co2+ mixture, it was concluded that no metal-drug complex is formed. In addition, it was found that bound CRA is negatively charged at physiological pH and binding to the DNA could be affected only by using metal cations whose ionic radius size (〈 0.85 Å) and charge (2+) were simultaneously satisfied. Stringent metal cation selectivity for the DNA-M-CRA complex may be intimately connected with the antitumor selectivity of CRA, since different types of cells generally possess widely differing molar concentrations of metal cations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290303
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  • 108
    Electronic Resource
    Electronic Resource
    Assesment of protein reorientational diffusion in solution by 13C off-resonance rotating frame spin-lattice relaxation: Effect of polydispersity (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 501-507 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C off-resonance rotating frame spin-lattice relaxation technique is applicable to the study of protein rotational diffusion behavior in both model in vitro and in vivo systems. The original formalism of James and co-workers [(1978) J. Am. Chem. Soc. 100, 3590-3594] was constrained by the assumption of random isotropic reorientational motion of a monodisperse protein population. Here we extend the formalism to include polydispersity. Application is made to the alkaline pH induced association of lysozyme, lysozyme-bovine serum albumin mixtures, and to the phase separation of lysozyme salt-water mixtures induced by low temperature.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290305
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  • 109
    Electronic Resource
    Electronic Resource
    Simulations of the B-DNA molecular dynamics of d(CGCGAATTCGCG)2 and d(GCGCGCGCGC)2: An analysis of the role of initial geometry and a comparison of united and all-atom models (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 517-532 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations on the sequence d(CGCGAATTCGCG)2 have been carried out using both united atom and all-atom representations, and starting the simulations both from a regular repeating B-DNA structure and from the x-ray single crystal B-DNA structure. An all-atom B-DNA simulation on the sequence d(GCGCGCGCGC)2 has also been carried out, in order to compare it with a previous united atom simulation. The helix repeats, H-bonding, sugar pucker profiles, and average torsional angles are all in the range observed in crystallographic and nmr studies for B-DNA helices. In some of the sequences, there is a significant bend in the DNA helices. The individual helix repeats, with focus on 3′CpG5′ and 3′GpC5′ units, show the opposite helix repeat to that suggested by Calladine's rules.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290307
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  • 110
    Electronic Resource
    Electronic Resource
    Synthesis, crystal structure, and molecular conformation of peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 509-515 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH was synthesized by the usual workup procedure and finally coupling the N-Boc-L-Pro-dehydro-Phe to glycine. The peptide crystallizes in monoclinic space group P21 with a = 8.951(4) Å, b = 5.677 (6) Å, c = 21.192(11) Å, β = 96.97(4)°, V = 1069(1) Å3, Z = 2, dm = 1.295(5) Mgm-3, and dc = 1.297(4) Mgm-3. The structure was determined by direct methods using SHELXS86. The structure was refined by the block-diagonal least-squares procedure to an R value of 0.074 for 1002 observed reflections. The C2α-C2β distance of 1.33(2) Å is an appropriate double bond length. The angle C2α-C2β-C2γ is 133(1)°. The peptide backbone torsion angles are θ1 = -167(1)°, ω0 = 179(1)°, φ1 = -48(1)°, ψ1 = 137(1)°, ω1 = 175(1)°, φ2 = 65(2)°, ψ2 = 15(2)°, ω2 = -179(1)°, and φ3 = -166(1)°. These values show that the Boc group has a trans-trans conformation while the peptide backbone adopts a β-turn II conformation, which is stablized by an intramolecular hydrogen bond of length of 3.05(1) Å. The structures of dehydro-Phe containing peptides suggest that the dehydro-Phe promotes the β-turn II conformation. The five-membered pyrrolidine ring of the Pro residue adopts an ideal Cγ-exo conformation with torsion angles χ11 = -24(1)°, χ12 = 34(1)°, χ13 = -30(1)°, χ14 = 15(1)°, and θ10 = 6(1)°. The side chain torsion angles in dehydro-Phe are χ21 = -1(2)°, χ22, 1 = -176(1)°, and χ22, 2 = 8(2)°. The Plane of C2α-C2β-C2γ is rotated with respect to the plane of the phenyl ring at 7(1)°, which indicates that the atoms of the side chain of dehydro-Phe are essentially coplanar. The molecules form a 21 screw axis related hydrogen-bonded rows along the b axis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290306
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  • 111
    Electronic Resource
    Electronic Resource
    Kinetics of cooperative ligand-lattice binding: Fast Monte Carlo integration (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 543-547 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fast Monte Carlo integration algorithm with varying time step is described for cooperative binding of ligands of arbitrary length to a one-dimensional lattice. This algorithm is particularly suitable for strongly cooperative or anticooperative systems, i.e., when the time scales for different kinetic events are very different. As an application, the kinetics of a bimodal two-ligand system are briefly discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290309
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  • 112
    Electronic Resource
    Electronic Resource
    Biodegradation of copoly(L-aspartic acid/L-glutamic acid) in vitro (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 549-557 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of copolypeptides consisting of L-aspartic acid and L-glutamic acid was performed to determine the effects of copolymer composition and sequential distributions on the rate of degradation by papain in a PECF (pseudoextracellular fluid) at pH 4.75 and 7.40, at 37.0°C, to simulate in vivo polymer degradation. Random copolymers consisting of β-benzyl L-aspartate and γ-benzyl L-glutamate were synthesized by the N-carboxyanhydride method. Water-soluble copolymers were obtained by successive reactions of side chains by anhydrous HBr treatment. All the samples were found to be degraded by random chain scission with papain. Further, the degradation data for the samples followed the Michaelis-Menten rate law, being the first order in papain concentration. The nature of side chains are important to the rate of degradation by papain and it was controlled by the comonomer composition as well as the sequential distribution of comonomers in the copolymer chains.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290310
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  • 113
    Electronic Resource
    Electronic Resource
    Electrophoresis and movements of fluorescence pattern after photobleaching of large DNA fragments in agarose gels (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 491-500 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By combining electrophoresis with movements of fluorescence pattern after photobleaching (MOFPAP), which is abbreviated as EMOFPAP, we are able to measure electrophoretic mobilities of large DNA fragments in an agarose gel within a fairly short time scale (about 10 min or even down to 1 min). The new method represents a significant improvement in experiment time when compared with the time (typically on the order of hours) required to determine the average electrophoretic mobility of large DNA fragments in agarose gels by means of either conventional gel electrophoresis or pulsed-field gel electrophoresis. In this article, we present the EMOFPAP experimental setup and consider optical conditions, including beam profile geometry and fluorescence pattern formation. A realistic formula that can explain the parameters governing the EMOFPAP method using our present optical setup has been derived. A comparison of results between experimental and computer simulation data is made, and an optimization of the EMOFPAP method is proposed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290304
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  • 114
    Electronic Resource
    Electronic Resource
    The elastic modulus of fibrin clots and fibrinogen gels: The effect of fibronectin and dithiothreitol (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 559-565 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The elastic modulus (G′) of factor XIIIa induced fibrinogen gels was found to be substantially lower than the G′ of fibrin gels that were formed by clotting fibrinogen with thrombin. The addition of fibronectin and/or the reducing reagent dithiothreitol (DTT) to the factor XIIIa coagulation mixture led to the formation of a weaker gel structure, while the rigidity of thrombin induced clots was not appreciably affected by the inclusion of the DTT but increased somewhat in the presence of fibronectin. The reasons for the differing clot rigidities are discussed in terms of biochemical mechanisms.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290311
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  • 115
    Electronic Resource
    Electronic Resource
    Solvent effects on protein association and protein folding (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 567-596 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent effects on the thermodynamics of two processes - folding of proteins and association between proteins - are examined in detail. A complete inventory of the multitude of solvent effects may be obtained by employing the concept of conditional solvation free energy. This theoretical tool allows for the isolation of specific side-chain effects from the entire protein and for the study of its contribution to the overall free energy change in small model compounds. Some numerical examples are presented, and ways of estimating other cases, for which no relevant experimental data are available, are suggested. Our findings lead to the conclusion that the currently used hydrophobicity scales, based on partition coefficients between water and an organic solvent, are inadequate measures of the contribution of side chains being transferred from water to the interior of the protein. We have also tentatively concluded that correlation between hydrophilic functional groups might be more important than correlations between hydrophobic side chains.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290312
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  • 116
    Electronic Resource
    Electronic Resource
    Melanin-concentrating hormone: A structural and conformational study based on synthesis, biological activity, high-field nmr, and molecular modeling techniques (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 609-622 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Melanin-concentrating hormone (MCH) fragments have been synthesized and their biological activities compared with the parent peptide. The substructural units, 5-14 linear and 5-14 cyclic, have been used as models for MCH -  in 1H-nmr conformational studies. Conformational features predicted by molecular dynamics analyses find support in the nmr experiments.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290314
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  • 117
    Electronic Resource
    Electronic Resource
    X-Ray studies on crystalline complexes involving amino acids and peptides. XVII. Chirality and molecular aggregation: The crystal structures of DL-arginine DL-glutamate monohydrate and DL-arginine DL-aspartate (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 533-542 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DL-Arginine DL-glutamate monohydrate and DL-arginine DL-aspartate, the first DL-DL amino acid-amino acid complexes to be prepared and x-ray analyzed, crystallize in the space group P1 with a = 5.139(2), b = 10.620(1), c = 14.473(2) Å, α = 101.34(1)°, β = 94.08(2)°, γ = 91.38(2)° and a = 5.402(3), b = 9.933(3), c = 13.881(2) Å, α = 99.24(2)°, β = 99.73(3)°, γ = 97.28(3)°, respectively. The structures were solved using counter data and refined to R values of 0.050 and 0.077 for 1827 and 1739 observed reflections, respectively. The basic element of aggregation in both structures is an infinite chain made up of pairs of molecules. Each pair, consisting of a L- and a D-isomer, is stabilized by two centrosymmetrically or nearly centrosymmetrically related hydrogen bonds involving the α-amino and the α-carboxylate groups. Adjacent pairs in the chain are then connected by specific guanidyl-carboxylate interactions. The infinite chains are interconnected through hydrogen bonds to form molecular sheets. The sheets are then stacked along the shortest cell translation. The interactions between sheets involve two head-to-tail sequences in the glutamate complex and one such sequence in the aspartate complex. However, unlike in the corresponding LL and DL complexes, head-to-tail sequences are not the central feature of molecular aggregation in the DL-DL complexes. Indeed, fundamental differences exist among the aggregation patterns in the LL, the LD, and the DL-DL complexes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290308
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  • 118
    Electronic Resource
    Electronic Resource
    Accessible conformations of melanin-concentrating hormone: A molecular dynamics approach (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 623-637 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations have been used to search for the accessible conformations of the melanin-concentrationg hormone (MCH). The studies have been performed on native MCH and two of its peptide fragments, a cyclic MCH(5-14) fragment and a linear MCH(5-14) fragment. An analysis of the molecular dynamics trajectories of the three peptides indicates that two regions of the peptide have characteristic conformational properties that may be important for the biological activity. One is a region around Gly8, which is conformationally mobile, and the other is around Pro13, which shows unusual rigidity. The molecular dynamics simulation results are discussed in terms of backbone structural features like β turns, side-chain interactions, and orientations of the disulfide bridge. The results of this analysis are used to suggest new analogues that will modify the conformational features of the peptide and further define the conformational requirements for activity. Finally, the results are related to nmr studies of the peptide and reveal agreements between the experimental nuclear Overhauser effect constraints and some of the accessible conformations obtained from the simulation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290315
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  • 119
    Electronic Resource
    Electronic Resource
    Thermal behavior of the 760-nm absorption band in photodissociated sperm whale carbonmonoxymyoglobin at cryogenic temperature: Dependence on external medium (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 639-643 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290316
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  • 120
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291401
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  • 121
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    Electronic Resource
    Distinct gelation mechanism between linear and branched (1 → 3)-β-D-glucans as revealed by high-resolution solid-state 13C NMR (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1689-1698 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have recorded high-resolution 13C-NMR spectra of linear (curdlan) and branched (lentinan, HA-β-glucan and its polyol and aldehyde derivatives) (1 → 3)-β-D-glucans in hydrate and gel states, in order to gain insight into their gelation mechanism. Network structure of curdlan turned out to be highly heterogeneous from its motional state, from liquid-like, through intermediate, to solid-like domains. They are studied by a variety of experiments, conventional high-resolution NMR by broad-band decoupling, high-power decoupling with magic angle spinning (MAS), and cross-polarization-magic-angle-spinning (CP-MAS). Nevertheless, we found that conformations of these distinct liquid-like and solid-like do- mains exhibit an identical single helix conformation with a small proportion of a triple helix form, supporting our previous view as to the gelation mechanism. In contrast, the network structure of branched (1 → 3)-β-D-glucans in the gel state arises mainly from the triple helix conformation. This means that gelation of branched (1 → 3)-β-D-glucan proceeds from partial association of the triple helical chains, previously proposed for gelation of a linear glucan. Furthermore, we found that conversion from the single chain to the single helix was not achieved readily by hydration of over 8h at 96% R. H. for branched glucan but the triple helix form is obtained when these samples are hydrated fully as in gel state.
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    Differential scanning calorimetry studies of the inverse temperature transition of the polypentapeptide of elastin and its analogues (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1699-1706 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential scanning calorimetry studies have been carried out on the sequential polypeptide of elastin, (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n, abrreviated as PPP, and its more hydrophobic analogues (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Leu1-PPP, and (L-Ile1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Ile1-PPP. Consistent with inverse temperature transitions, the temperatures of the transitions for which maximum heat absorption occurs are inversely proportional to the hydrophobicities of the polypentapeptides (31°C for PPP, 16°C for Leu1-PPP, and 12°C for Ile1-PPP), and the endothermic heats of the transitions are small and increase with increasing hydrophobicity, i.e., 1.2, 2.9, and 3.0 kcal/mol pentamer for PPP, Leu1-PPP, and Ile1-PPP, respectively. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order, as the temperature is raised above that of the transition, has been repeatedly observed using different physical characterizations. Furthermore, the studies demonstrated indentical conformations for PPP and Ile1-PPP above and below the transition. Both heats and temperature of the transitions vary with hydrophobicity, but not in simple proportionality.
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    URL: http://dx.doi.org/10.1002/bip.360291403
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    Viscoelastic properties of alginate aqueous solutions in the presence of salts (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1707-1713 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of added salts on the dynamic viscoelastic properties are investigated for aqueous solutions of alginates that have various molecular weights and mannuronate/guluronate (M/G) ratios. The dynamic moduli of the systems increase with increasing concentration of the added salt in the low-frequency region. The effect is notable in the order of KCl 〈 NaCl 〈 MgCl2 ≪ CaCl2. The values of the dynamic moduli in the rubbery plateau are independent of the addition of the salts, irrespective of the M/G ratio of the alginate. These facts strongly suggest that the structure that is formed by the interaction between the alginates and the metal ions does not work as cross-linking points but as heterogeneous relaxation units having a relatively long relaxation time from a rheological viewpoint.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360291404
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    Computational analysis of the effects of site-specific phosphate alkylation in the DNA oligomer {d-[GGAATTCC]}2 (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 597-607 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkylation of the sugar-phosphate backbone of DNA can result upon exposure to several potent carcinogens, inducing DNA misfunction. In order to assess the structural and energetic changes in DNA helices induced by such alkylation, we have performed AMBER-based analyses on phosphotriester containing analogues of {d-[GGAATTCC]}2. Fourteen analogues of the nonalkylated oligomer were examined, each bearing a single alkylation of known stereochemistry. Results indicate that although there is minimal effect on the aromatic bases, the presence of a phosphotriester disturbs the sugar-phosphate backbone in complex ways. For most analogues, total minimum energies are lower for the Sp-alkylations than for the Rp-alkylations which point directly into the major groove of the helix; however, different energetic contributions follow different, or no, trends in dependence on alkylation site and/or stereochemistry. Where data is available, experimental nmr results agree with the calculations reported here.
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    Statistical descriptors for the size and shape of globular proteins (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1745-1754 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The atomic structures of proteins epitomize the ideas of complexity and irregularity in three-dimensional objects. For such objects, size and shape are difficult to quantify, and therefore the development of unbiased parameters for these properties could facilitate their description. Statistical analysis of the frequency distribution of interatomic distances in protein structures of different classes has revealed two numerical descriptors that correlate with physicochemical properties of these macromolecules. The median (μ) of the distribution correlates (r 〉 .98, n = 45) with variables indicative of size (e.g., molecular weight and radius of gyration). The exponent of the Box-Cox transformation λ, used for converting this distribution into a symmetrical one, correlated (r = .75, n = 43) with a general dimensionless shape parameter defined as the combination of the shape-related accessible surface (As0), molecular volume (V), and radius of gyration (Rg) in the form s = (As0Rg/V). It is suggested that for globular proteins λ is a function of both the shape parameter s and the fractal dimension D of the protein surface. These objective descriptors of size and shape could be useful to describe other complex objects.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360291407
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    Determination of eigenvectors in DNA polymer spectroscopy by isotopic substitution (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 87-91 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple relationship between frequency shifts to be expected in molecular vibrational spectra upon isotopic substitution and component values of eigenvectors is displayed. Application of this expression to the problem of force constant refinement is discussed in terms of a refinement algorithm developed some years ago to overcome particular problems associated with large molecular systems. Calculations of expected isotopic shifts have been calculated and are tabulated here for experimental reference.
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    URL: http://dx.doi.org/10.1002/bip.360300110
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    Phase transitions of concentrated DNA solutions in low concentrations of 1 : 1 supporting electrolyte (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 57-71 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transitions between isotropic and liquid crystalline phases of concentrated solutions of DNA with an average contour length (500 Å) near the persistence length were examined in 0.01 M supporting 1 : 1 electrolyte (predominantly NaCl). A quantitative phase diagram describing the transitions occurring over a DNA concentration range from 100 to 290 mg/mL and temperatures from 20 to 60°C was constructed from solid-state31P-nmr data and examination of the morphologies of the mesophases by polarized light microscopy. Three anisotropic phases were observed in solutions with DNA concentrations of 160-290 mg/mL: an unidentified, weakly birefringent phase termed “precholesteric” a true cholesteric phase with pitch ≈ 2 μm, and a third, presumably more highly ordered phase. Comparison with previous studies showed that the critical concentration for anisotropic phase formation and the nature of the phases formed by these DNA molecules are not strongly affected by decreasing the supporting electrolyte concentration from ∼ 0.2 M to 10 mM. There are, however, profound effects of decreasing the supporting electrolyte concentration on the width of the transition from isotropic to totally anisotropic solutions, and the nature of the transitions between phases. Decreasing the supporting electrolyte concentration significantly increases the concentration range of persistence of the isotrophic phase, and results in the formation of triphasic solutions (isotropic and two liquid crystalline phases).Values of the critical DNA concentrations for anisotropic phase formation calculated from the theory of A. Stroobants et al. [(1986) Macromolecules 19, 2232 to 2238] were found to be significantly lower than the observed values for any reasonable estimate of the effective radius, probably because of the relatively short lengths of DNA fragments examined in the present study. Comparison of the experimentally determined DNA concentrations required for anisotropic phase formation with the values predicted from Flory's lattice statistics theory, which explicitly considers the rod length, permitted estimation of the effective DNA radius. The estimated radius was inconsistent with effective radii calculated from Poisson-Boltzmann (P-B) theory based on a supporting electrolyte concentration of 10 mM, but was in fair agreement with P-B theory assuming that Na+ DNA contributes approximately 0.24 Na+ counterions/nucleotide to the effective free sodium ion concentration.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300108
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    Helix-coil stability constants for the naturally occurring amino acids in water. XXIV. Half-cystine parameters from random poly(hydroxybutylglutamine-CO-S-methylthio-L-cysteine) (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 121-134 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Water-soluble, random copolymers containing N5-(4-hydroxybutyl)-L-glutamine (host) and S-methylthio-L-cysteine (guest) have been prepared, fractionated, and characterized, with S-methylthio-L-cysteine serving as a model for cystine residues in proteins. From the thermally induced helix-coil transition curves of these copolymers in water at neutral pH, the Zimm-Bragg parameters σ and s for the helix-coil transition of “poly(L-cystine)” were deduced. The results show that the cystine model acts as a weak helix-breaker over the entire temperature range from 0 to 60°C. The implications of this finding are evaluated in the context of a general discussion of the Zimm-Bragg parameters for all the 20 naturally occurring amino acids.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300113
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    A simple statistical field theory of heteropolymer collapse with application to protein folding (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 177-188 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple statistical extension of the Flory theory of excluded volume is developed, and applied to random heteropolymer collapse and a simple model of protein folding. Sequence heterogeneity is found to lead to new effects. The nucleation of protein folding is also briefly considered.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300117
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    Cyclic β-alanyl-β-alanine containing peptides: A new molecular tool for β-turned peptides (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 189-196 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present paper we describe the synthesis, purification, and single-crystal x-ray analysis of the cyclic tetrapeptide cyclo-(L-Pro-L-Phe-β-Ala-β-Ala). This compound contains the β-alanyl-β-alanine dipeptide as putative cyclization arm to force the remaining dipeptide-L-Pro-L-Phe- in a β-turned conformation. Thepeptide was synthesized by classical methods and cyclization of the free linear tetrapeptide was accomplished in reasonable yields in diluted methylene chloride solution. The compound crystallizes in space group P21 from hot water with two independent tetrapeptide molecules and seven solvent molecules in the unit cell. This compound shows in the solid state an intramolecular hydrogen bond between the CO group of the β-Ala4 and the NH group of the β-Ala3 residues stabilizing a type I β-turn conformation in which Pro1 and Phe2 occupy the relative position 2 and 3 of the turn, respectively. A rather complex network of 18 hydrogen bonds involving all the remaining CO and NH groups and the water molecules is present in the crystal.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300118
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    A new chiral feature in α-helical domains of proteins (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 211-214 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300121
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    Size and shape parameter of the actin-binding protein profilin in solution: A depolarized and polarized dynamic light scattering study (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 219-222 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300123
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    Drug-DNA binding specificity: Binding of netropsin and distamycin to poly(d2NH2A-dT) (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 223-227 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300124
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    Studies on the conformation of and metal ion binding by teichoic acid of Staphylococcus aureus (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 273-277 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Teichoic acid (TA) isolated from the gram-positive bacteria S. aureus binds cationic dyes like pinacyanol (PCYN), 1,9-dimethyl methylene blue, acridine orange, etc., depicting blue-shifted metachromasia, and they bind the cationic dye carbocyanine depicting the red-shifted J band. TAs do not show any uv absorption band, and exhibition of tailing CD in the short uv region hints at its chiral conformation. Chiral conformation of TA has been confirmed from the induction of strong biphasic CD in the TA-carbocyanine system.Relative affinities for Ca2+, Mg2+, and Na+ have been probed from the disruption of metachromasia of the TA-dye system by these ions. Results show Ca2+ and Mg2+ to be almost equally effective in destroying the metachromasia of the TA-PCYN system, thus not supporting the hypothesis of special affinity for Mg2+ ion.
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    URL: http://dx.doi.org/10.1002/bip.360300305
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    Conformational sampling using high-temperature molecular dynamics (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1847-1862 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-temperature molecular dynamics as a method for conformational search was explored on the antigen combining site of McPC 603, a phosphorylcholine binding immunoglobulin. Simulations at temperatures of 500, 800, and 1500 K were run for 111.5, 101.7, and 76.3 ps, respectively. The effectiveness of the search was assessed using a variety of methods. For the shorter hypervariable loops, molecular dynamics explored an appreciable fraction of the conformational space as evidenced by a comparison to a simple theoretical model of the size of the conformational space. However, for the longer loops and the antigen combining site as a whole, the simulation times were too short for a complete search. The simulations at 500 and 800 K both generated conformations that minimized to energies 200 kcal/mole lower than the crystal structure. However, the 1500 K simulation produced higher energy structures, even after minimization; in addition, this highest temperature run had many cis-trans peptide isomerizations. This suggests that 1500 K is too high a temperature for unconstrained conformational sampling. Comparison of the results of high temperature molecular dynamics with a direct conformational search method, [R. E. Bruccoleri & M. Karplus (1987) Biopolymers 26, 137-168]. showed that the two methods did not overlap much in conformational space. Simple geometric measures of the conformational space indicated that the direct method covered more space than molecular dynamics at the lower temperature, but not at 1500 K. The results suggest that high-temperature molecular dynamics can aid in conformational searches.
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    URL: http://dx.doi.org/10.1002/bip.360291415
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    Gel electrophoresis of micron-sized particles: A problem and a solution (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1863-1866 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gel electrophoresis of spherical particles with a radius above 0.2 μm has not been reported yet. In the present study, video phase-contrast light microscopy is used to observe the motion of individual latex spheres, 0.52 μm in radius, during electrophoresis in 0.1% agarose gels. At 2V/cm, the spheres initially migrate in the direction of the electrical field. However, each sphere eventually undergoes a cessation of all motion. Brownian motion is restored when the electrical potential gradient is reduced to zero. Arrest can be prevented by periodically inverting the direction of the electrical field. These observations are explained by electrical field- induced steric trapping of the spheres by gel fibers. Inversion of the electrical field should assist the application of agarose gel electrophoresis to micron sized cellular organelles and cells.
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    URL: http://dx.doi.org/10.1002/bip.360291416
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    Fluctuation of the solvent-accessible surface area of tuna ferrocytochrome c (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1877-1883 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291418
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    Solvent effects on the cooperative order-disorder transition of aqueous solutions of schizophyllan, a triple-helical polysaccharideContribution No. 23 from the Microcalorimetry Research Center, Faculty of Science, Osaka University. (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1867-1876 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A triple-helical polysaccharide schizophyllan in aqueous solution exhibited a highly cooperative transition between ordered and disordered states associated with the conformation of its side chains and nearby water molecules. The transition was followed by optical rotation and containing additives such as NaOH and DMSO as solvents. The ordered state was stabilized or destabilized or depending on the kind and amount of the additive employed; in particular, the addition of DMSO had a remarkable stabilizing effect. This effect was analyzed by means of a statistical mechanical theory of linear cooperative transitions, where DMSO was assumed to interact favorably with the ordered side chains. A small amount of NaOH in a solvent mixture stabilized the ordered state and made the transition curve very gradual. No molecular mechanism was elucidated to account for the role of NaOH.
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    URL: http://dx.doi.org/10.1002/bip.360291417
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    Masthead (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290401
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    Motions of an α-helical polypeptide: Comparison of molecular and harmonic dynamics (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 645-677 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular and harmonic dynamics simulations have been performed for a decaglycine α-helix. The extent of anharmonicity for various observables is studied by a direct comparison of the two types of simulations, at temperatures ranging from 5 to 300 K. The fluctuations of the cartesian, internal and normal mode coordinates, and their time dependence, are analyzed. The heat capacity of the α-helix is evaluated both from the temperature response of the system to an energy perturbation and from the fluctuations in the temperature of the system. It is shown that the anharmonicity depends on the kind of observable. The root mean square atomic fluctuations have significant anharmonic components at temperatures above 100 K. In contrast, the dihedral angle fluctuations are much closer to being harmonic at all the temperatures considered. The analysis of potentials of mean force experienced by individual atoms shows that atomic displacements have approximately Gaussian distributions from 50 to 300 K, with different force constants at each temperature (quasi-harmonic model). At 300 K, the force constants obtained by molecular dynamics are significantly lower than in the harmonic case. The time dependence of the projection of the molecular dynamics displacements on the normal mode coordinates shows that mode mixing is important above 100 K. The motions of the helix associated with the low-frequency normal modes are described and illustrated.
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    The program FANTOM for energy refinement of polypeptides and proteins using a Newton - Raphson minimizer in torsion angle space (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 679-694 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The program FANTOM (fast Newton-Raphson torsion angle energy minimizer) performs minimizations of the ECEPP/2 energy function for proteins with the Newton-Raphson method. It is implemented for use with conventional computer hardware. The torsion angles are chosen as independent variables. The first and second derivatives are calculated with a previously described rapid algorithm. For the matrix inversion a modified Cholesky factorization is used. A line search adjusts the step length and nonbonded interactions can be calculated with a cutoff. The following tests of the program are described: All local minima of the ECEPP/2 energy function for the amino acids glycine and alanine were determined. An exhaustive search by more than 16,000 independent energy minimizations was used to identify low-energy structures of Met-enkephalin, which were then compared with previously published structures of this pentapeptide. To investigate the use of FANTOM with disulfide bonds, it was applied with conotoxin. As an illustration of the intended primary use of the program, an energy refinement of the structure of the basic pancreatic trypsin inhibitor determined by nmr spectroscopy in solution is described.
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    URL: http://dx.doi.org/10.1002/bip.360290403
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    Uv resonance Raman spectroscopy of nucleic acid duplexes containing A-U and A-T base pairs (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 707-715 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Resonance Raman spectra have been obtained at several uv wavelengths (200-266 nm) for poly(rA)-poly(rU), poly(dA-dU), poly(dA)-poly(dT), and poly(dA-dT), representing nucleic acid duplexes containing A-U and A-T base pairs with different stacking interactions and different backbone conformations. Frequency shifts are seen in the exocyclic modes corresponding to coupled C4=O and C5=C6 stretching of U and T, although the NH2 scissors frequency of A is unshifted relative to that of the mononucleotide. These frequency patterns are interpreted as the superposition of H bonding and dipole-dipole coupling effects. Strong hypochromism is seen for most of the ring modes, resulting from the absorption hypochromism and from shifts in the electronic transitions due to stacking. The effects are larger for A bands in the homopolymers than in the heteropolymer duplexes, reflecting the larger influence of A/A than A/U(T) stacking. Poly(rA)-poly(rU) stands out among these polymers in showing 10 cm-1 downshifts in one U and several A modes. These shifts may be related to the A form structural parameters of this duplex, but the physical mechanism is not obvious.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360290405
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    Restrained energy refinement with two different algorithms and force fields of the structure of the α-amylase inhibitor tendamistat determined by nmr in solution (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 695-706 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution structure of an α-amylase inhibitor, tendamistat, calculated from nmr data with the distance geometry program DISMAN is subjected to restrained energy minimization. To study the influence of force field parametrizations and the convergence behavior of refinement algorithms, two different programs were used. AMBER is an established software package including a steepest descent and/or conjugent gradient optimizer in the Euclidian space; the name AMBER also represents a force field. The program FANTOM (fast Newton-Raphson torsion angle energy minimizer) is a new restrained energy refinement implementation of the Newton-Raphson algorithm, which uses second derivatives of the conformational energy in dihedral angle space with the ECEPP/2 force field. For both programs the normal energy force field was supplemented with an additional potential of the form ΣA(di - ui)6 (if di 〉 ui), which enforces upper limits ui to selected distances di as measured by nmr. Improvements of the intramolecular interactions with a decrease of the internal energies of about 1000 kcal/mol could be achieved without increasing the distance constraint violations. The restrained energy refinements caused only small changes of the molecular geometries: The root mean square distance values for the backbone atoms between the initial DISMAN structure and the refined structures are about 0.5 Å for AMBER and about 0.7 Å for FANTOM. Local conformational changes during the restrained energy minimizations are analyzed with respect to hydrogen-bond formation, and with respect to comparisons of the solution structure and the crystal structure.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360290404
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    Experimental evidence for predicted transmembrane peptide topography: Incorporation of hydrophobic peptide α-helical rods with an N-terminal positive charge having a length comparable to the thickness of lipid bilayers into the membranes (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 815-819 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liposomes consisting of egg yolk phosphatidylcholine and hydrophobic peptides Nps- and Cl-·+H2-(Met-Met-Leu)n-OEt (n = 6-10) with various polypeptide chain lengths were prepared by the sonication method. The conformation of the peptides incorporated into the liposomes was examined by CD spectroscopy. All the peptides incorporated assumed α-helical conformation. Quantitative analyses of the peptides and lipids in the membranes showed that the concentration of the peptides with a positive charge at the N-terminus in the liposomes decreased markedly as the peptide chain length increased, reaching zero for the peptides over n = 8. The peptides without a positive charge were hardly incorporated into the liposomes. Infrared attenuated reflection spectroscopy of multilayered membranes containing the peptides suggests that the axis of the α-helical peptide rods is oriented in parallel with the molecular axis of lipids in the membranes. These results suggest that the hydrophobic peptides can be incorporated into the lipid bilayers of the liposomes in the α-helical conformation, the rods of which have a length comparable to the thickness of the lipid bilayers, and the N-terminal positive charge of the peptides is essential for the stable peptide incorporated into the membranes.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300716
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  • 145
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    Thermodynamic stability of the 5′ dangling-ended DNA hairpins formed from sequences 5′-(XY)2GGATAC(T)4GTATCC-3′, where X, Y = A,T,G,C (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 829-845 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Expressions for the partition function Q(T) of DNA hairpins are presented. Calculations of Q(T), in conjunction with our previously reported numerically exact algorithm [T. M. Paner, M. Amaratunga, M. J. Doktycz, and A. S. Benight (1990) Biopolymers, 29, 1715-1734], yield a numerical method to evaluate the temperature dependence of the transition enthalpy, entropy, and free energy of a DNA hairpin directly from its optical melting curve. No prior assumptions that the short hairpins melt in a two-state manner are required. This method is then applied in a systematic manner to investigate the stability of the six base-pair duplex stem 5′-GGATAC-3′ having four-base dangling single-strand ends with the sequences (XY)2, where X, Y = A, T, G, C, on the 5′ end and a T4 loop on the 3′ end.Results show that all dangling ends of the sample set stabilize the hairpin against melting. Increases in transition temperatures as great as 4.0°C above the blunt-ended control hairpin were observed. The hierarchy of the hairpin transition temperatures is dictated by the identity of the first base of the dangling end adjoining the duplex in the order: purine 〉 T 〉 C. Calculated melting curves of every hairpin were fit to experimental curves by adjustment of a single parameter in the numerically exact theoretical algorithm. Exact fits were obtained in all cases. Experimental melting curves were also calculated assuming a two-state melting process. Equally accurate fits of all dangling-ended hairpin melting curves were obtained with the two-state model calculation. This was not the case for the melting curve of the blunt-ended hairpin, indicating the presence of a four-base dangling-end drives hairpin melting to a two-state process. Q(T) was calculated as a function of temperature for each hairpin using the theoretical parameters that provided calculated curves in exact agreement with the experimentally obtained optical melting curves. From Q(T), the temperature dependence of the transition enthply ΔH, enytropy ΔS, and free energy ΔG were calculated for every hairpin providing a quantitative assessment of the effects of dangling ends on hairpin thermodynamics. Comparisons of our results are made with those of the Breslauer group [M. Senior, R. A. Jones, and K. J. Breslauer (1988) Biochemistry 27, 3879-3885] on the T25′ dangling-ended d (GC)3 duplexes.To estimate the average contribution to stability of each single-stand nearest neighbor stack to the duplex stem, the relative values ΔΔH and ΔΔS of the transition enthalpy and entropy for each dangling-ended hairpin compared to the blunt-ended control hairpin were cast in a system of 16 equation in the 16 unkowns, The nonsingular system of equations was solved for the unknowns by matrix diagonalization, which yielded the relative average contribution of each of the 16 possible nearest neighbor dinucleotide 5′3′ stacks in single strand DNA to the stability of a 5′-GGATAC-3′ duplex stem.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300718
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    Counterion effects on the physical properties and the A to B transition of calf-thymus DNA films (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 877-887 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report measurements of the water content and swelling of wet-spun films of Na-, K-, Rb-, and Cs-DNA as a function of relative humidity (rh). The water contents (number of water molecules per base pair of DNA) of these films are found to be quite similar, indicating that the identity of the counterion species is unimportant for the water content. Since the A to B transition for these DNAs occurs at different rhs, the corresponding water contents of the A to B transition are found to be quite different. These films swell as a function of rh in a very similar manner, implying that the changes in the intermolecular bonds in the different DNAs are similar. Dramatic changes are observed in the dimensions of the films above 84% rh for all types of DNA. Combining the water content and swelling measurements yields the dependence of the volume per base pair on water content. The volume per base pair is observed to be a nonlinear function of water content, indicating nonideal mixing of the water with the DNA.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300903
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  • 147
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    The effect of the L-azetidine-2-carboxylic acid residue on protein conformation. III. Collagen-like poly(tripeptide)s (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 967-974 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical and biological properties of collagen are altered by the biosynthetic substitution of the L-azetidine-2-carboxylic acid (Aze) residue in the place of proline. The reasons for this alteration have been studied by means of conformational energy computations on single- and triple-stranded structures formed by poly (GIy-X-Y) poly(tripeptide)s, where X and Y can be Pro or Aze. The most stable triple helix formed by Poly (Gly-Pro-Aze) is collagen-like, but all low-energy triple helices that can be formed by poly (Gly-Aze-Pro) and poly (Gly-Aze-Aze) are very different from collagen. Thus, the regular substitution of Aze for Pro in position X is not compatible with the collagen structure. In the absence of solvent effects, all of these triple helices are stable, relative to the statistical coil, but the substitutions reduce the stability of the collagen-like triple helix, as compared with poly (Gly-Pro-Pro).
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/bip.360300911
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  • 148
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    Phase separation and hydrogen bonding in cells of the ocular lens (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 995-999 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300914
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  • 149
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    Partial molar volumes of polypeptides and their constituent groups in aqueous solution over a broad temperature range (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1001-1010 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The partial molar volumes of various compounds that model protein constituent groups, such as tripeptides (Gly-X-Gly, where X = Gly, Ala, Val, Leu, Ile, Pro, Met, His, Ser), homopeptides (Glyn, n = 3, 4, 5), and simple organic analogues of amino acid side chains (methanol, acetamide, propanamide, acetic acid, propanoic acid, n-butanamine, n-butanamine nitrate, n-propylguanidine nitrate, 4-methylphenol), have been determined in aqueous solution with a vibrational densimeter in the temperature range of 5-85°C. The partial molar volumes of amino acid side chains and the peptide unit were estimated from the data obtained. Assuming additivity of component groups, the partial molar volumes of polypeptide chains of several proteins over a broad temperature range were calculated. The partial molar volume functions of four proteins (myoglobin, cytochrome C, ribonuclease A, lysozyme) were compared with those determined experimentally for the unfolded and native forms of these proteins. It has been shown that the average deviation of the calculated functions from the experimental ones does not exceed 3% over the temperature range studied.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360301102
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  • 150
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    Synthesis and peptide bond orientation in tetrapeptides containing L-azetidine-2-carboxylic acid and L-proline (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1039-1049 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of the amino acid proline in influencing the secondary and tertiary structure of proteins and polypeptides has been an area of active study for many years. We have investigated this problem by incorporating the four-membered ring amino acid, azetidine-2-carboxylic acid, into some proline polypeptides. An adjunct to the synthesis of the peptides was the synthesis of azetidine-2-carboxylic acid and its resolution. We developed an improved synthesis of N-benzhydryl-2-carbobenzyloxy azetidine, an essential intermediate required for the synthesis of Lazetidine-2-carboxylic acid. This amino acid was subsequently obtained via the partial hydrogenation of the N-benzhydryl compound, under mild conditions. Our ability to isolate the intermediate N-benzhydryl-2-carboxylic acid demonstrated that the rate of cleavage of the O-benzyl ester group in this molecule is faster than the cleavage of the N-benzhydryl group.The tetrapeptides, Boc-(LPro)3-LAze-Opcp, and Boc-(LAze-LPro)2-Opcp (Boc: t-butoxycarbonyl; Pro: praline; Aze: azetidine-2-carboxyl acid; Opcp: pentachlorophenyl), were prepared using traditional solution peptide synthesis. They were characterized by direct chemical ionization-mass spectrometry, CD spectra, and 13C- and 1H-nmr spectroscopy. The assessment of the secondary structure assessment of the two peptides using the methods noted above has led us to conclude that the compound Boc-(L-Aze-LPro)2-Opcp, in trifluoroethanol, has an all-cis peptide bond conformation with φ and ψ torsion angles compatible with a left-handed helix. The secondary structure assessment of the peptide Boc-(LPro)3-LAze-Opcp, in chloroform or trifluoroethanol, leads to an assignment of both cis and trans peptide bonds as being present in the peptide. We have interpreted this latter finding as indicating that the introduction of the azetidine group into a peptide containing three consecutive praline residues in a linear sequence perturbs the normal proline peptide secondary structure in this tetrapeptide.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360301105
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    Quantitative IR spectrophotometry of peptide compounds in water (H2O) solutions. I. Spectral parameters of amino acid residue absorption bands (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1243-1257 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Infrared spectra of the amino acid residues in H2O solution have been obtained in the 1800-1400-cm-1 region. It has been established that amino acid residues of arginine, asparagine, glutamine, aspartic and glutamic acids, lysine, tyrosine, histidine, and phenylalanine have intensive absorption in this spectral region. Infrared spectra for a set of model compounds have been measured. On the basis of these data, spectral parameters of amino acid residue absorption bands have been determined.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360301309
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  • 152
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    Theoretical studies of cis-Pt(II)-diammine binding to duplex DNA (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 823-836 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of cis-Pt(II) diammine (cis-DP) to double-stranded DNA was studied with several kinked conformations that can accommodate the formation of a square planar complex. Molecular mechanics (MM) calculations were performed to optimize the molecular fit. These results were combined with quantum mechanical (QM) calculations to ascertain the relative energetics of ligand binding through water vs direct binding of the phosphate to the ammine and platinum, and to guide the selection of DNA conformations to model complex formation. Based on QM and MM calculations, models are proposed that may be characterized by several general features. A structure involving hydrogen bonding between each ammine and distinct adjacent phosphate groups, referred to as closed conformation (CC), has already been reported. This is also found in the crystal structure of small dimers. We report alternative conformations that may be important in platination of duplex DNA. They are characterized by an intermediate conformation (IC), involving hydrogen bonding between one ammine and phosphate group, and an open conformation (OC), without ammine phosphate hydrogen bonding. The IC and OC can be stabilized by water bridges in the space between the ammine and the phosphate groups. Sugar puckers alternate from the type C(2′)-endo or C(1′)-exo (S), to the type C(3′)-endo or C(2′)-exo (N), with intermediate types near O(1′)-endo (O). In general, the sugar puckers alternate from S to N to S through the platinated region (3′-TpG*pG*p-5′), with the complexed strand exhibiting, (3′)-S*-N*-S-(5′) alternation, while the complementary strand shows either (3′)-S*-N*-S(5′) or (3′)-S*-N*-O-(5′) alternation. In both the OC and IC, a hydrogen bond is found between the ammine and O4(T) on thymine (T) at the (3′) end, adjacent to the complex site. There is a continuous range of backbone conformations through the platinated region which relate the OC to the IC. The models presented suggest that the dynamics of the binding of the cis-Pt(II)-diammines to adjacent N7(G) in double-stranded DNA may encompass several conformational possibilities, and that water bridges may play a roll in supporting open and intermediate conformations. Proton-proton distances are reported to assist in the experimental determination of conformations.
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    URL: http://dx.doi.org/10.1002/bip.360290416
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    Ir and Raman spectroscopic studies on coulombic interaction between water-soluble porphyrins and nucleic acids (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 999-1004 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have shown previously that the N-methylpridyl group vibrations of water-soluble porphyrins, M(TMpy-P4), are shifted to lower frequencies (0.5-2.6 cm-1) as a result of coulombic interaction between the N+-CH3 group of M(TMpy-P4) and the PO2 group of a nucleic acid. We have now turned over our attention to the effect of this coulombic interaction on the PO2 group vibrations of nucleic acids. Using Fourier transform ir and Raman spectroscopy, we found that the νa(PO2) at 1221 cm-1 is shifted 12 ∼ 17 cm-1 to higher frequencies, whereas the νs(PO2) at 1087 cm-1 is shifted 18 ∼ 26 cm-1 to lower frequencies, when DNA is mixed with M(TMpy-P4). These results indicate that the N+-CH3 group of M(TMpy-P4) interacts preferentially with one of the two oxygen atoms of the PO2 group of the DNA duplex.
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    URL: http://dx.doi.org/10.1002/bip.360290611
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    The interaction of cyclosporin and calmodulin (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1005-1014 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of cyclosporin A and dansyl cyclosporin A with bovine and wheat germ calmodulin has been monitored by measurements of induced changes in dansyl and bound toluidinyl naphthalene sulfonate fluorescence. The interaction is Ca2+-dependent and 1 : 1 Measurements of the efficiency of radiationless energy transfer from bound dansyl cyclosporin A to an acceptor group located on Cys-27 of wheat germ calmodulin suggest that the primary binding site is not located on the N-terminal lobe (residues 1-65). However, studies with proteolytic fragments of calmodulin indicate that elements of the N-terminal half-molecule (residues 1-77) may be involved in the stabilization of the binding site. The binding of cyclosporin alters the physical properties of calmodulin and, in particular, reduces the localized rotational mobility of a fluorescent probe.
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    URL: http://dx.doi.org/10.1002/bip.360290612
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    The relative contribution of electrostatic interactions to stabilization of collagen fibrils (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1015-1026 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrostatic energies of interaction between type I collagen molecules were calculated, using models developed by Timasheff and Hill. These energies, along with a contribution from hydrophobic forces, were then incorporated into an equation due to Flory that described phase equilibria of rod-like polymers. The Flory formalism in turn permitted a calculation of the overall free energy of fibril formation (ΔFf), and an assessment of the relative contribution of electrostatic and hydrophobic forces to ΔFf. Lastly, ΔFf Lastly, ΔFf was used in a nucleation-growth model relating halftimes of fibril formation (t1/2) to ionic strength (I) and temperature. Because the theory provided no basis for setting absolute levels of the energetic contributions, five parameters in the model had to be derived from experimental data. Based on the fit of theory to experimental results both for intact and pepsinized collagen, it was found that very low electrostatic energies (about -1 kcal/mole per collagen molecule) were sufficient to explain experimental t1/2 vs I relationships. This energy is equivalent to 1 close charge-pair interaction per molecule and appears to be lower than the energy assignable to hydrophobic interactions.
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    URL: http://dx.doi.org/10.1002/bip.360290613
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    Binding of cationic dyes to potassium alginate: A spectrophotometric and dichroic probe (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1541-1548 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acridine orange (AO) binds to potassium alginate (KAlg) stoichiometrically as is evidenced from conductometric and spectrofluorometric titrations. However, AO as well as methylene blue (MB) exhibits weak metachromasia and no induced dichroism at any sensible polymer to dye ratio (P / D). KAlg induces large blue shifts (by as much as 125 nm) of the λmax of the strongly aggregating dyes 1, 9-dimethylmethyleneblue (DMMB) and pinacyanol at reasonable P / D values; KAlg also induces strong dichroism in these dyes. The signs of the induced CD spectra indicate KAlg to have a left-handed helical conformation. This polymer also induces red-shifted J band and dichroism in the dye N-N′-diethylpseudoisocyanine (PIC) at high P / D under which condition the signs of CD spectra in DMMB reverse with drastic reduction in [θ] values. This reversal of sign of CD or induction of J band in PIC at only high KAlg concentrations does not involve any conformational change in the polymer as indicated by the insensitivity of the UV-CD spectrum of KAlg as a function of concentration.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360291205
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    Cooperativity of carbohydrate moiety orientation and β- turn stability is determined by intramolecular hydrogen bonds in protected glycopeptide modelsThis is publication No. 1708 from the Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts, 02254-9110 (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1549-1564 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2, 3, 4, 6-Tetra-O-acetyl-β-D-gluco-, and β-D-galactopyranosides, as well as approximately 4 : 1 anomeric mixtures of α- and β-mannopyranosides of Boc-X-Y-NHCH3 dipeptides (X-Y = Pro-Ser, Pro-D-Ser, Val-Ser, Val-D-Ser, and Gly-Ser) have been synthesized. CD and ir spectroscopic studies were performed to characterize the conformation of the glycosylated peptide backbone and examine the possible formation of intrapeptide and glycopeptide intramolecular H-bonds. It was found that O-glycosylated peptides containing a D-serine residue are likely to adopt a type II β-turn while those with the Pro-Ser or Val-Ser sequence feature a type I(III) β-turn in solution. Glycosylation also increases the magnitude of the CD bands, characteristic of the given type of β-turns, which can be interpreted as an indication of the stablization of the folded backbone conformation. Infrared data showed that in nonpolar solutions the peracetyl glycopeptides adopt both single- and double H-bonded conformations whose ratio, in some cases, depends on the position at C-2′ of the H-bond acceptor acetoxy group. These data suggest that five-, seven-, or ten-membered glyco-turns may play an important role in fixing the steric orientation of the carbohydrate antennae systems in glycoproteins.
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    URL: http://dx.doi.org/10.1002/bip.360291206
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  • 158
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    Solvent effect on the stability of isomaltose conformers (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 369-379 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational equilibria of the low-energy conformers of isomaltose have been studied in different solvents. The structure of each individual conformer was refined from the 18 distinct low-energy regions determined from potential energy function. Molecular geometry optimization was carried out using the quantum chemical method of perturbative configuration interaction with localized orbitals or PCILO and yielded to 15 distinct minima. Carbon-proton vicinal coupling constants 3JC-H have been calculated based on the finite perturbation theory formulation with the intermediate neglect of differential overlap for these minima. For evaluation of the influence of the environment on the conformational structure of isomaltose, the population of the low-energy conformers was estimated in four solvents by a method in which the total energy is divided into the energy of the isolated molecule and the solvation energy. The calculated abundances of conformers depend strongly on the solvents. Based on the determined abundance of conformers, thermodynamically averaged torsion angles and coupling constants 3JC-H describing the “average” conformation about glycosidic linkage have been calculated. Results obtained are compared with available experimental data from solution and solid state.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300314
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    Hydration effects on dynamics of polyglycine and sodium poly(L-glutamate) (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 691-701 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solid state nmr methods were applied to the study of the motions and structural heterogeneity in polyglycine, sodium poly (L-glutamate), and poly(L-alanine). The response of both the main-chain and side-chain resonances to the addition of water was studied using static and magic-angle sample-spinning line shapes as well as the carbon spin-lattice relaxation times, the proton spin-lattice relaxation time in the rotating frame, and the proton-carbon cross-polarization time. The polyglycine motions are not drastically affected by the addition of water when the polymer is in the 31-helix or the β-sheet structure. The sodium poly(L-glutamate), however, responds to increased hydration with little motion in the main-chain carbon atoms, but considerable flexibility of the side-chain atoms. The greatest motions are reported for the C5 carbon with rotational amplitudes about the C47-C5 bond of about of 50°. In addition, motions somewhat less than half this size are required closer to the main chain.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300705
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  • 160
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    Conditions for the stability of the alternative structures of duplex poly(dA-dT) (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 753-761 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alternative structures of the lithium, sodium, potassium, and rubidium salts of poly(dA-dT) were studied using ir spectra of hydrated, nonoriented gels. Poly (dA-dT) · Na existed as the B structure at high hydration and as the A structure at moderate hydration. A disordered state occurred at low hydration. No hint of the C, D, or other structures was observed at any hydration for nonoriented gels containing NaCl up to 0.56 moles NaCl/mole of nucleotide residue. Poly (dA-dT) · Li existed as the B structure at high hydration, made a gradual transition to the C structure at moderate hydration, and became disordered at low hydration. Poly (dA-dT) · K and poly (dA-dT) · Rb existed as the B structure at high hydration and as the presumptive D structure at lower hydration. The addition of Zn(II) to poly (dA-dT) · Na produced a gradual transition from the B to the C structure upon dehydration. The addition of NaNO3 to poly (dA-dT) · Na gave only the A and B structures, and not the C or Z structures that are promoted by NO3 in other base sequences. The DNA secondary structure stabilized by a given ion is determined by a specific base sequence and not simply by the properties of the ion.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300710
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  • 161
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    Thermodynamic cycle-perturbation study of the binding of trifluoroacetyl dipeptide anilide inhibitors with porcine pancreatic elastase (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 773-780 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The variety of results of crystallographic studies of the serine proteases complexed with isocoumnrin inhibitors presents a challenging problem to modeling methods and molecular energetics. Therefore, the thermodynamic cycle-perturbation technique has been used to study a model system of elastase and two peptidic inhibitors. Using the program AMBER, the technique correctly predicts changes of the binding constants for the trifluoroacetyl dipeptide inhibitors in comparison with available experimental (kinetic and crystallographic) data. However, the absolute values obtained are shown to be sensitive to the specific electrostatic interaction potential parameters used in the simulations. The reader and user are cautioned that thermodynamic cyle-perturbation results may be too optimistic by underestimating the accuracy of free energy values. This is especially a matter of concern for those cases where a direct comparison with experimental values is not possible, viz., (1) the simulation of binding of novel compounds, (2) structurally uncertain binding sites, or (3) structurally different binding modes. With our best 4-31G* ESP (electrostatic potential) charges we were able to reproduce experimentally determined free energy differences (ΔΔA) with an accuracy of about 1.5 kcal/mol. Dynamically induced structural changes in the binding site of elastase, and particularly changes in hydrogen-bond patterns of the binding site, are also reported.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300712
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  • 162
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    Synthesis and 1H-nmr studies of α-deuterated analogues of des-Trp1, Nle12-human minigastrin (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 847-854 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three analogues of the tridecapeptide amide H-Leu-(Glu)5-Ala-Tyr-Gly-Nle-Asp-Phe-NH2 were synthetized with α-deuterated glutamate residues in specific positions in order to assign unambiguously the 1H nmr spectrum of the parent peptide in water and in water-trifluoroethanol mixtures. The synthetic route is described and the assignment illustrated. A previous, tentative assignment based solely on indirect evidence [Mammi, S., Mammi, N. J. & Peggioa, E. (1988) Biochemistry 27, 1374-1379] was partially modified.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300719
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  • 163
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    Correlation between dinucleotide periodicities and nucleosome positioning on mouse satellite DNA (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 861-876 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous studies demonstrated 16 well-defined nucleosome locations (A-P) on a tandemly repeated prototype 234 base pair (bp) mouse satellite repeat unit. We have aligned the A-P fragments to search for DNA sequence elements that might contribute to nucleosome placement at these positions. Our results demonstrate a strikingly regular, uninterrupted, periodic pattern for the AA dinucleotide occurrences along the entire length of the aligned fragments. The periodicity of the AA occurrences is about 9.7 bp. The pattern exhibits a local minimum at position 74, near the nucleosome dyad axis of symmetry. Other dinucleotides - including AC : GT, CA : TG, and CC : GG - are also placed periodically, but their patterns of occurrence are less regular and less frequent than AA. The calculated spacings between consecutive preferred nucleosome locations on mouse satellite DNA are nearly identical, corresponding to multiples of 9.7 bp. The correlation between the periodicity of dinucleotide occurrences and the average spacing of nucleosome positions suggests that the preferred nucleosome locations recur at intervals that may correspond to the DNA helical repeat in the mouse satellite nucleosomes, and that the histone octamers sample (or slip along) the duplex in steps of 9.7 bp during nucleosome formation on mouse satellite DNA.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300902
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  • 164
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    Crystal and molecular structure of Boc-D-Ala-ΔPhe-Gly-ΔPhe-D-Ala-OMe: A 310-helical dehydropeptide (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 911-920 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal and molecular structure of the pentapeptide Boc-D-Ala-ΔPhe-Gly-ΔPhe-D-Ala-OMe, containing two dehydrophenylalanine residues, was determined by x-ray diffraction. The molecule crystallizes in the orthorombic P212121 space group, with a = 10.439(3), b = 15.319(3) and c = 21.099(4) Å.In the solid state, the conformation of the pentapeptide is characterized by the presence of two type III′ β-turns. Thus the peptide assumes a left-handed 310-helical conformation, the left sense being due to the D configuration of the alanine residues. The two unsaturated residues are located in the (i + 1) position of the first β-turn and in the (i + 2) position of the second β-turn, respectively.In the crystal, the helical molecules are linked head to tail by hydrogen bonds. Lateral hydrogen bonds are also formed between molecules related by a twofold screw symmetry. This gives rise to a typical mode of packing characterized by infinite helical “chains,” smiliar to the packing found in other oligopeptides that adopt a 310-helical structure.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300906
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  • 165
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    The effect of the L-azetidine-2-carboxylic acid residue on protein conformation. II. Homopolymers and copolymers (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 961-966 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alteration of polymer conformational properties caused by the replacement of L-proline by L-azetidine-2-carboxylic acid (Aze) has been studied by means of conformational energy computations. In addition to poly (Aze), two sequential copolymers, poly (Pro-Aze) and poly(Aze3-Pro3), have been investigated. All polymers containing Aze are more flexible than poly(Pro). This is a consequence of an increased number of permitted conformational states for the Aze residue, as compared to Pro, when they are incorporated into a polypeptide, as well as of a lessened cooperativity of the trans-cis transition. The results of the computation can be used to interpret the observed physical properties of poly (Aze) and of its copolymers.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300910
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  • 166
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    Internal dynamics of tRNAPhe studied by depolarized dynamic light scattering (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 975-983 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The collective internal dynamics of transfer RNAphe from brewer's yeast in solution was studied by depolarized dynamic light scattering (DDLS). Within the melting region of tRNA the depolarized spectra consist of two Lorentzian, where the narrow (slow) component describes the overall rotation of the macromolecule. The broad component is attributed to the collective reorientation of the bases within the biopolymer. At high temperature only this relaxation process is observed in the spectrum. The viscosity dependence of the collective internal relaxation process is described by the Stokes-Einstein-Debye equation for rotational diffusion. Estimates of the internal orientational pair correlation factor from the integral depolarized intensities of tRNAPhe solutions indicates that the observed dynamics correspond to the collective reorientation of approximately 5 bases. A comparison of the results presented with DDLS studies on the aggregation of the mononucleotide guanosine-5′-monophosphate confirms this result. For a further characterization of the relaxation process we studied the effect of hydrostatic pressure (1-1000 bar) on the depolarized spectra of tRNA. While other spectroscopic methods like nmr, fluorescence polarization anisotropy decay, or ESR give information about the very local motion of a single base within the DNA or RNA, this study shows that by DDLS one can characterize collective internal motions of macromolecules.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360300912
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  • 167
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    Conformational search in enkephalin analogues containing a disulfide bond (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1011-1025 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic Conformational search has been performed for the 14-membered ring in model compounds for disulfide-containing enkephalin analogues. The model compounds examined are , and the corresponding compounds with L-amino acids at the C-terminus. About 100 starting conformations were generated for each compound with the RNGCFM program and energy minimized with the AMBER program. Between 21 and 38 conformers within 3 kcal/mole of the apparent global minimum were found for each compound. There appeared to be fewer possible conformations of the disulfide-containing side chain than of the main chain. , whose parent compound is selective for opioid δ receptors, was found to prefer conformers with a positive dihedral angle of the disulfide bond, which is consistent with the previous proposal that δ-receptor selectivity may be associated with this conformational preference. Additional calculations were performed on the complete structure of (DPDPE) with various possible conformations of the tyrosine and phenylalanine side chains. Conformational free energies and entropies were computed for these conformers from the molecular vibrations obtained from a normal mode analysis. As was found previously, conformers with low energies tended to have lower entropies, which resulted in a narrowing of the free energy differences between conformers. A conformer is identified that has the lowest energy hitherto found for DPDPE. It is suggested that DPDPE may be a useful compound for evaluating conformational search strategies because of its relatively small size and the number of conformers that have already been identified. Conformational energy calculations are also reported for naltrindole using the MM2(87) program. Naltrindole, which incorporates two aromatic 6-membered rings in a rigid structure, is a highly selective and potent opioid δ-receptor antagonist and may be an important clue regarding the biologically active conformer of DPDPE. Various conformers of DPDPE have been superimposed quantitatively onto the structure of naltrindole using the SUPER program and those conformers of DPDPE that are the best fit to naltrindole are reported.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360301103
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  • 168
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    Eine neue methode zur herstellung von hydroxyterminierten polydienen (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 174 (1990), S. 69-80 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: It is shown, that hydroxyterminated polydienes of good microstructure and functionality and a narrow molecular weight distribution can be prepared using di-hydroxyethyl-azo-bis-isobutyramide as an initiator. The activation energy of the initiator decay has been determined by volumetric measurement of the nitrogen evolved in this reaction.
    Notes: Es wird gezeigt, daß hydroxyterminierte Polydiene mit guter Mikrostruktur und Funktionalität sowie enger Molekulargewichtsverteilung unter Verwendung von Azobis-isobuttersäure-di-hydroxyethylamid hergestellt werden können. Die Aktivierungsenergie des Initiatorzerfalls wurde durch volumetrische Messung des bei dieser Reaktion freiwerdenden Strickstoffs bestimmt.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051740106
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  • 169
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    Elution behaviour of diolmodified epoxides in size exclusion chromatography (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 174 (1990), S. 81-88 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Reaktion von Bisphenol A-diglycidether (BADGE) mit Butan-1,4-diol (BD) in Gegenwart von Mg(ClO4)2 führt in Abhängigkeit von der Reaktionstemperatur zu linearen und verzweigten Oligomeren. Bei 100°C Reaktionstemperatur läßt sich die Produktbildung bis ca. 70% Epoxid-Umsatz durch HPLC feststellen. In diesem Umsatzbereich sind alle Produkte gut in THF löslich, woudurch die Verfolgung des Molmassenanstieges mittels SEC möglich ist. Es wird eine charakteristische Molmasse-Umsatz-Beziehung erhalten sowie die SEC-Daten eines verzweigten Produktes diskutiert.
    Notes: The reaction of bisphenol A-diglycidyl ether (BADGE) with butane-1,4-diol (BD) in the presence of Mg(ClO4)2 leads to linear and branched oligomers. The formation ratio of these products depends on the reaction temperature. In experiments at 100°C, an epoxide consumption of up to 70% can be observed using HPLC. In this range all products show good solubility in THF, so that it is possible to follow the increasing molar mass by using SEC. A characteristic relation of the molar mass against the conversion rate is derived and SEC data of a branched product are discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051740107
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  • 170
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    Structural and mechanical changes of polyacrylate systems in correlation with their composition in degradative conditionsPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers”, in Prague (Czechoslovakia), July 24-29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 113-123 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermal and photodegradation of copolymer system based on styrene, butyl acrylate, acrylic acid and N-methylolacrylamide (S/BA/AA/MAA) shows mechanical, but no structural changes in examined temperature range and after 320 h of UV irradiation (simultaneously with 256 and 366 nm lamps). Content of acrylic acid is a very important factor for the mechanical stability of these systems which can be very successfully used as the coatings in the practice. Found correlations indicate mechanism and factors having influence on the excellent stability of copolymer films.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760110
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  • 171
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    Kinetic characteristics of the light ageing of rubbers based on polydieneurethanes and polyetherurethanesPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 147-160 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of light wavelength and intensity, as well as the temperature, on photooxidation has been studied for rubbers based on polydieneurethane (PDU) or polyetherurethane (PEU). Photooxidation is shown to proceed by the chain free-radical mechanism with bimolecular (for PDU) or linear (for PEU) kinetic chain termination. The PDU oxidation kinetic parameter is equal to 0.02 [mole/(kg·s)]1/2 and does not depend on temperature. In PEU photooxidation the kinetic chain length is constant in a wide range of light intensities and is equal to 7, while the activation energy is ca 18 kJ/mole. In distinction to PEU, PDU is sensitive not only to UV but also to visible light, with this sensitivity being preserved up to high oxidation levels. The dependences of photooxidation quantum yieldes on wavelength and irradiation time have been determined.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051760113
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  • 172
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    Influence of small amount dispersive additives on the weather ability of PVC-filmsPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Ageing and Stabilization of Polymers” in Prague (Czechoslovakia), July 24-29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 197-206 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three types of transparent PVC-films before and after exposition in the weather conditions are studied. The first film (the control) is plasticized and stabilized; the second is similar to the first but 1 part of cuprous oxide (CuzO) is incorporated in it, while in the third 1 part of aluminium (A1) powder is added. It is found that the light transparency decreases by 2-7% upon adding Cu2O and by 17-36% upon adding Al-powder. UV-visible measurements, colourimetric measurements and microscopic investigations are used for examining PVC-samples properties during weathering. The surface layer chemical changes are studied by means of MIR-IR-spectroscopy. The total colour variation (ΔE*ab) in the case of 12 months aged PVC-film, containing Cu2O, shows 11 relative units in comparison with 37 relative units for the other two materials. A retarding action of Cu2O and an accelerated effect of Al-powder on the weather degradation of clear soft PVC-films are established. The influence of the chemical properties and different size distribution of the dispersive additives on photooxidative behaviour of PVC-compositions are discussed.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051760117
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  • 173
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    Processing stabilization of polyolefinsPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 215-230 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The response of a HDPE, a L-LDPE and a PP homopolymer to processing conditions and processing stabilizer formulations in the 220°C to 280°C temperature range was investigated. The technique of multiple extrusion was used. Melt flow and melt flow ratio were measured after the first, third and fifth extrusion pass. In the case of the HDPE and the L-LDPE, degradation by cross-linking was the predominant reaction and the molecular weight distribution showed a significant broadening compared to the virgin samples. The PP homopolymer degraded by chain scission. By adding a multifunctional hindered phenol and a hydrolysis resistant phosphite, all polymers could be efficiently protected against degradation on processing. For the HDPE and the L-LDPE, increased amounts of phosphite provided increased processing stability at constant phenol concentration. A 4:1 ratio of phosphite to phenol exhibited the best performance. The most efficient ratio for protecting melt flow of the PP homopolymer was found when a two to one ratio of phosphite to phenol was added.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051760119
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  • 174
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    Mechanisms and kinetics of photostabilization of polyolefins with halsPaper presented at the 19th Colloquium of Danubian Countries on “Ageing and Stabilization of Polymers”, Prague, Czechoslovakia, July 24-27, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 241-289 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The HALS stabilization mechanisms usually envisaged do not explain the experimental facts. New mechanisms are proposed instead. They include quenching of excited charge-transfer complexes (CTC) polymer-oxygen by CTC HALS-oxygen. In addition, the formation of CTC between peroxy radicals and NH-HALS is of prime importance. These CTC HALS-peroxy radicals can either react photolytically after absorption of UV radiation or with a second peroxy radical, thus promoting termination between two peroxy radicals.Initiation of photooxidation in HALS stabilized polyethylene involves usually CTC HALS-oxygen throughout the useful lifetime of the polymer. In contrast to that, initiation of photooxidation in HALS stabilized polypropylene is classical and due to photolysis of tertiary hydroperoxides.The formal kinetics based on the mechanisms envisaged explain the experimental results observed with HALS stabilized polyethylene and polypropylene. On the one hand, they concern, the performance of HALS: in polyethylene it is a linear function of the square root of HALS concentration whereas in polypropylene it increases linearly with HALS concentration as long as the last does not become too high. On the other hand, the experimental facts explained, concern the decrease of the HALS concentration during W exposure of HALS-stabilized polyethylene and polypropylene. The decrease is first order in both polymers but is independent of the initial HALS concentration in polyethylene, whereas it decreases with increasing initial HALS concentration in polypropylene. This is in agreement with the corresponding initiation mechanisms envisaged for polyethylene and polypropylene.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760121
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  • 175
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    Stabilization of linear polyethylene crosslinked by irradiationPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24-29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 303-310 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Our experiments have shown that after a complex degradative effect, such as processing, irradiation and ageing, the effects of antioxidants and their mixtures are very different.The results of our investigation support the opinion, expressed by many researchers of stabilization, that there does not exist any universally practicable antioxidative system. The optimal effect has to be determined, for each system, in the knowledge of the quality and quantity of the given oxidative load.For polyethylene crosslinked by irradiation a satisfactory stability can be attained with the aid of the usual stabilizers; however, they must be used in relatively larger quantities owing to the additional degradative action of the irradiation. There are noticeable differences between the stabilizers not only in their stabilizing action, but also in influencing the degree of discoloration and in the dose number required to produce the same degree of crosslinking.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760123
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    Stabilization of polyacetalsPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 323-332 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A brief introduction describes the main differences between homo, and copolymer polyacetals and their main degradation mechanisms. A short overview describes the importance of stabilization and the necessity of using antioxidants and costabilizers during manufacturing, processing and end use of polyoxymethylene(polyacetals). Various stabilizer systems are presented and studies on the interaction of antioxidants with costabilizers added. The criteria for testing the performance of these additives are discussed and demonstrated by many examples.In a second part the increasing importance of light stabilized polyacetal is mentioned and investigations on the performance of light stabilizer systems are highlighted.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051760125
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  • 177
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    Properties and role of benzoquinone imines in polymer stabilizationPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 347-355 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Quinone imines are formed from aromatic amine antidegradants as a consequence of chemical transformations of the latter during the stabilization of hydrocarbon polymers. Quinone imines are deep coloured compounds and contribute to the antidegradant activity of the parent amines. The main interest is devoted to benzoquinone diimines (BQDI), generated from N,N '-disubstituted 1,4-phenylenediamines (PD). BQDI are antioxidants in unsaturated hydrocarbons, undergo hydrolytic deamination, addition and cyclization reactions, react with 2,6-dialkylphenols, thiols and C-centered radicals. PD are regenerated from BQDI in redox reactions. The active role of BQDI in antifatigue processes in rubbers has been explained using product analysis. BQDI account for staining and discoloring properties of PD but are not harmful to the polymer stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760127
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  • 178
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    Partikelgrößenanalyse von dispersen farbstoffsystemen, IITeil I cf. Lit.2.. Photonen-korrelations-spektroskopie an latexsuspensionen und ‚modellblindfärbungen‘ von polyethylenterephthalat-fasernHerrn Dr. Gerhard Heidemann zum 60. Geburtstag gewidmet. (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 17-32 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: As a first step to analyse the particle size distribution of dyebaths, photoncorrelation-spectroscopy is used to determine the particle sizes of latex suspensions. To simulate the procedure of dyeing polyester fibres with disperse dyes, latex suspensions are used as model for dyes. The ‘dyeing’ is carried out at various temperatures and the resulting particle size distribution of the ‘dyebath’ is measured using photon-correlation-spectroscopy.
    Notes: Als Vorstufe zur Teilchengrößenanalyse von Farbstoffbädern mittels Photonen-Korrelations-Spektroskopie werden Latexsuspensionen untersucht. Eine Simulation einer Färbung von Polyestermaterial mit Dispersionsfarbstoffen wird durch eine ‘Modellblindfärbung’ unter Benutzung von Latexsuspensionen bei unterschiedlichen Farbbadtemperaturen nachgestellt. Die sich innerhalb des ‘Färbebades’ ergebenden Partikelgrößenverteilungen werden mit Hilfe der Photonen-Korrelations-Spektroskopie analysiert.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051780102
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  • 179
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    Depolarization current of a novolac p-fluorophenol-formaldehyde resin (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 33-46 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Kondensation von p-Fluorphenol mit Formaldehyd wurde ein p-Fluorphenol-Formaldehyd-Novolak (NFF) hergestellt. Die Differential-Scanning-Calorimetrie zeigte je nach Vorgeschichte der Proben den normalen Glasübergang oder damit zusammenfallende endotherme Peaks. Es wird vermutet, daß die endothermen Peaks durch Spaltung intramolekularer Bindungen während des Glasübergangs verursacht werden. Diese Bindungen entstehen bei der Lagerung der Harze bei Raumtemperatur. Messungen des thermisch induzierten Polarisationsstroms (TSDC) wurden in einem Temperaturbereich von 290 bis 350 K an Proben mit Molekulargewichten von M̄n=375 bzw. 434 g/mol durchgeführt. Die TSDC-Kurven zeigten hauptsächlich die α-Peaks der dielektrischen Relaxation. Es wurde der Einfluß der Temperatur, der Einfluß von M̄n die Aktivierungsenergie Ea und die physikalische Alterung der Proben untersucht. Die physikalische Alterung wurde durch die reziproke Polarisierbarkeit R, als Funktion des Alters charakterisiert. Die Probe mit großerem M̄n wies eine höhere Glasübergangstemperatur, eine niedrigere Aktivierungsenergie und einen stärkeren Anstieg von Rp, auf als die Probe mit niedrigerem M̄n. Der Anstieg des Molekulargewichts verstärkte sich mit zunehmender Steifigkeit der NFF-Proben. Diese Effekte werden der starken Ausbildung von Wasserstoffbindungen zugeschrieben. Die Resultate werden mit analogen Ergebnissen von fluorfreien Phenol-Formaldehyd-Novolaken verglichen.
    Notes: A Novolac p-fluorophenol-formaldehyde (NFF) resin was prepared by condensation of p-fluorophenol with formaldehyde. DSC showed the glass transition effect or coinciding endothermal peak depending upon the thermal history of samples. It is supposed that the peaks are caused by breaking of the intermolecular bondings in the resin during the glass transition. The bondings are formed in the resin during the storage at room temperature. Thermally stimulated depolarization current (TSDC) measurements were carried out in the temperature range of 290 to 350 K, with the samples having an average number molecular weight M̄n of 375 and 434. TSDC curves mainly showed the dipolar relaxation α peaks. The influence of poling temperatures, the influence of M̄n, the activation energy Ea, and the physical ageing of the samples were investigated. Physical ageing was determined as the reciprocal polarizability Rp vs. time of ageing. Samples. with higher M̄n showed a higher glass transition temperature, a lower Ea, and a higher increase in Rp than the sample with lower M̄n. The increase in M̄n increased the rigidness of NFF samples. The effects are attributed to the strong hydrogen bonding. The comparison with analogous results in novolac phenol-formaldehyde resin without fluorine is given.
    Additional Material: 8 Ill.
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  • 180
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    Modification of polyamide 6 with hycar ATBN (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 85-93 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde die Synthese von Blockcopolymeren aus 6-Caprolactam und einem flüssigen aminotelechelischen Copolymeren aus 1,3-Butadien und Acrylnitril (Hycar ATBN 1300X21) studiert, die eine höhere Kerbschlagzähigkeit als das geläufige Poly(6-caprolactam) aufweisen. Bei der durch das Addukt aus Phosphorsäure und 6-Caprolactam initiierten Polymerisation von 6-Caprolactam wurde der Einfluß der Konzentration des Initiators (0-5 mol-%) und der Konzentration von Hycar ATBN 1300X21 (0-50 Gew.-%) im Polymerisationsgemisch, der Zeit (4-72 h) und der Temperatur (200-280°C) auf den Umsatz von 6-Caprolactam sowie auf die Eigenschaften des entstandenen Copolymeren untersucht. Die unter optimierten Bedingungen dargestellten Blockcopolymeren wiesen eine Kerbschlagzähigkeit von 13,5 kJ·m-2 auf.
    Notes: The preparation of block copolymers from 6-caprolactam and a liquid amine terminated butadiene-acrylonitrile copolymer Hycar ATBN 1300X21 having higher notched impact strength than ordinary poly(6-caprolactam) was studied. In the polymerization of 6-caprolactam initiated by an adduct of phosphoric acid with 6-caprolactam the influence of initiator concentration (0- 50 mol-%) and Hycar ATBN 1300X21 concentration (0-5 wt.-%) in the polymerization charge, of polymerization time (4 - 72 h) and of temperature (200-280°C) on the 6-caprolactam conversion and on the properties of the copolymers formed were followed. Notched impact strength of the block copolymers prepared under optimized conditions was as high as 13.5 kJ·m-2.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051780106
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  • 181
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    Graft polymerization of 4-vinylpyridine onto cellulosic fibres by the ceric ion method, I. The reaction time effect (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 109-118 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß der Reaktionsdauer auf die mit Cer(IV)-Ionen initiierte Pfropfung von 4-Vinylpyridin (4-VP) auf partiell carboxymethylierte Cellulose (PCMC) mit verschiedenen Substitutionsgraden (D.S.) wurde untersucht. Zum Vergleich wurde dasselbe Monomere auf Baumwolle und mercerisierte Baumwolle gepfropft. Die Pfropfparamater dieser Polymerisationsreaktionen wurden bestimmt. Der Pfropfungsgrad (G) war bei PCMC signifikant höher als bei Baumwolle und mercerisierter Baumwolle. Der durch Röntgenbeugung ermittelte Kristallisationsgrad der Pfropfcopolymeren war niedriger als der von unmodifizierter Baumwolle. Der Einfluß der Reaktionszeit auf die Pfropfung von Baumwolle mit 2-Vinylpyridin wurde ebenfalls untersucht.
    Notes: A study was made of the time affecting the ceric ion induced grafting of 4-vinylpyridine (4-VP) onto partially carboxymethylated cotton (PCMC) having different degrees of substitution (D.S.). For comparison the same monomer was grafted onto cotton and mercerized cotton. The grafting parameters of these copolymerization reactions were determined. The graft yields for PCMC were significantly higher than those for unmodified cotton and mercerized cotton. The degree of crystallinity of the graft copolymers and of the unmodified cotton and PCMC samples was determined by the X-ray method. The crystallinity index decreased with the presence of grafted polymer. The reaction time effect of the grafting of 2-VP on cotton was also studied.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780108
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  • 182
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    Light induced polymer and polymerization reactions, 35Part 34 cf. J. prakt. Chem. 330 (1988) 704.. Influence of monomer structure and binder composition on the photoinduced polymerization of multifunctional acrylic esters (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 131-142 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die photoinduzierte Polymerisation von Acrylaten in verschiedenen Bindemitteln wurde mit Hilfe der Photokalorimetrie, der DSC und der ESR-Spektroskopie untersucht. Um die Reaktivität vergleichend zu diskutieren, wurden zur Auswertung photokalorimetrischer Meßergebnisse folgende Parameter ausgewählt: Grenzumsatz, maximale Polymerisationsgeschwindigkeit, Inhibierungszeit und die Zeit, welche notwendig ist, um das Maximum der Polymerisationsgeschwindigkeit zu erreichen. Zwischen dem Grenzumsatz und der chemischen Struktur der Acrylate sowie dem Glaspunkt und der Sauerstoffpermeabilität des verwendeten Bindemittels bestehen eindeutige Korrelationen. Für die anderen Größen existieren keine deutlichen Zusammenhänge, da andere Faktoren wie z. B. ein verändertes Phasenverhalten order veränderte Diffusionsbedingungen diese Werte in komplexer Weise beeinflussen können.
    Notes: Photocalorimetry, differential scanning calorimetry and ESR-spectroscopy were used to analyse the photoinduced polymerization of multifunctional acrylic esters in various polymeric binders. Limiting conversion, maximal polymerization rate, inhibition time, and the time necessary to reach the maximum of the polymerization reaction rate were used to compare the reactivity of the photopolymer systems investigated in this work. Significant correlations exist between the limiting conversion and chemical structure of the acrylic esters used. A relation was also found between the glass transition temperature and oxygen permeability of the binder and the limiting conversion measured calorimetrically. A good correlation does not exist for the other reactivity parameters, because other factors such as phase change and changing diffusion conditions can have a complex influence on those values.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051780110
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  • 183
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    Visco-Elastic properties of blends of crystalline polymers possessing a weak phase coupling. Studies on blends of poly(ethylene) and poly(oxymethylene) (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 153-169 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Arbeit befaßt sich mit dem Einfluß einer schwachen Phasenkopplung auf die viskoelastischen Eigenschaften von heterogenen Polymermischungen im linearen und nichtlinearen Deformationsbereich. Als Modellmischungen wurden Polyethylen Polyoxymethylen-Mischungen ausgewählt. Die beiden Polymeren eignen sich als Komponenten einer Modellmischung besonders gut, da sie vollständig unverträglich miteinander sind, da die Grenzflächenenergie groß und die Ausdehnung der Grenzschicht folglich gering ist und da die mechanischen Eigenschaften der beiden Komponenten in erster Näherung ahnlich sind. Solche Mischungen sollten folglich den Beitrag der Phasenkopplung zu den viskoelastischen Eigenschaften besonders deutlich aufzeigen.Für die Modellmischung wurden die viskoelastischen Eigenschaften als Funktion der Konzentration der Komponenten durch die Erfassung des Spannungs-Dehnungsver-haltens, des komplexen Schubmodulus sowie der elastischen, anelastischen und plastischen Anteile der Deformationsenergie charakterisiert. Der experimentelle Befund ist, daß sich die meisten der genannten Eigenschaften linear mit der Mischungszusammensetzung ändern und daß folglich die schwache Phasenkopplung keinen Einfluß auf die Eigenschaften der Mischungen hat. Eine Ausnahme ist die Bruchdehnung, die bei etwa gleichen Anteilen der beiden Komponenten in der Mischung einen Minimalwert aufweist. Insgesamt gilt, daß die Gegenwart von mechanisch schwachen Phasengrenzen einen iiberraschend geringen Einfluß auf die viskoelastischen Eigenschaften der Mischungen hat.
    Notes: The investigations reported in this paper aimed at evaluating the impact of a weak interfacial strength on visco-elastic properties in multiphase polymer blends both in the linear and nonlinear deformation regime. Blends of poly(ethylene) and poly(oxymethylene) were used as model systems. The particular choice of the components of the blend was based on the fact that the two components are incompatible, possess strong interfacial energies and thus narrow and weak interfacial layers, and finally that their individual visco-elastic properties are within the same order of magnitude. This allows to evaluate the contributions of the phase boundaries to the visco-elastic properties in a transparent way.We investigated the visco-elastic properties of blends of various compositions by analyzing the stress-strain behavior, the dynamical torsional behavior as well as by determinating their cyclic stress-strain behavior. The experimental finding is that most of the properties studied vary linearly with the composition and are not influenced by the weakness of the interfacial strength-contrary to the expectation. An exception is the elongation at break which varies nonlinearly with the composition and which shows a minimum value at intermediate compositions. The impact of a weak phase coupling on visco-elastic properties is thus rather limited.
    Additional Material: 11 Ill.
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    Solution properties of polyacrylic esters. I. Light scattering and viscosity measurements in tetrahydrofuran (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 191-200 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Methyl-, Ethyl-, n-Propyl-, n-, i- und t-Butyl-, n-Hexyl-, 2-Ethylhexyl- und Laurylacrylat wurden in Benzol polymerisiert. Verdünnte Lösungen in THF einzelner Fraktionen dieser Polymeren wurden durch Lichtstreuungs- und Viskositätsmessungen untersucht. Polyacrylsäure wurde in Dioxan gemessen.Für die verschiedenen Polyacrylester und Polyacrylsäure wird die Molekulargewichtsabhängigkeit des Staudinger-Index [η] und des Trägheitsradius 〈r2w〉 angegeben.
    Notes: Dilute THF-solutions of different fractions of polymers of methyl, ethyl, n-propyl, n-, i- and t-butyl, n-hexyl, 2-ethylhexyl, and lauryl acrylate, prepared by solution polymerization in benzene, were studied by light scattering and viscosity methods. Poly(acrylic acid) was examined in dioxane. For the different polyacrylic esters the [η]-Mw-relations were established and the dependence of the radius of gyration 〈r2w〉 on the molecular weight was determined.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051780114
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    Mitteilungen (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 220-220 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780117
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    Analysis of the linear methods for determining copolymerization reactivity ratios, VIII. A critical reexamination of radical copolymerization of methylmethacrylate or styrenePart VII cf. lit.5. (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 209-219 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Anhand der erweiterten Kelen-Tüdős-Methode wurden Copolymerisationsparameter für Copolymerisationen mit Methylmethacrylat bzw. Styrol geprüft. Es wurden r-Werte einschließlich des 95% Vertrauensintervalls berechnet. Zur Klassifizierung des jeweiligen Systems wurden die Größen δ und Q angewendet. Bei der Copolymerisation mit Methylmethacrylat wurden 71 Systeme ausgewertet. Hiervon wurden 40 (56,3%) System der Klasse I und 20 (28,2%) Systeme der Klasse I(!) zugeordnet. Insgesamt ist also für 60 (84,5%) Monomerpaare die konventionelle Copolymerisationsglei- chung zutreffend. Für 3 (4,2%) Systeme, die der Klasse II zugeordnet werden, ist das Zwei-Parameter-Model1 ungültig. Zur Klasse 111 gehören 8 (I 1, Woo) Monomersysteme, für die die experimentellen Daten inkonsistent und die publizierten r-Werte unzutreffend sind. Im Falle der Copolymerisation mit Styrol wurden 32 Systeme ausgewertet, und es ergab sich folgende Einteilung in Klassen: 19 (59,4%) Systeme in Klasse I, 5 (15,6%) Systeme in Klasse I(!), 2 Systeme in Klasse I1 und 6 (18,8%) Systeme in Klasse 111.
    Notes: The reactivity ratios of selected methylmethacrylate or styrene copolymerisation systems have been reviewed in terms of the extended Kelen-Tüdős method. r-values, together with their 95% confidence limits have been calculated. Quantities δ and Q, suitable for classification of the systems, have been applied. Of the 71 reevaluated methylmethacrylate systems 40 (56.3%) were found to belong to class I and 20 (28.2%) to class I(!), i. e. 60 (84.5%) systems for which the conventional copolymerisation equation was found to be adequate. For 3 (4.2%) systems belonging to class II the two-parameter model does not hold and 8 (11.3%) systems were related to class III, i. e. systems for which the experimental data are inconsistent and the published r-values meaningless. 32 styrene copolymerisation systems were reevaluated with the following classification: 19 (59.4%) systems in class I, 5 (15.6%) systems in class I(!), 2 systems in class II and 6 (18.8%) in class III.
    Additional Material: 2 Tab.
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    Material wear and erosion at the surface of plastics caused by weatheringPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24-29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 43-53 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: When exposed to the weather (moderate climate, Darmstadt), polymethylmethacrylate (PMMA) experiences weight changes, depending on the seasonal humidity, but no material loss. Polycarbonate (PC) on the other hand, and to a lesser degree PC with a “weather skin”, shows marked weight changes when exposed to artificial weathering (Xenotest 1200), which set in with some delay.Surface profile measurements across the borderline between exposed and covered material provide no evidence of material wear in the case of PMMA. With PC, and to a lesser degree with PC protected by a “weather skin”, wear does occur in the region of several μm. The extent of this material wear, which normally sets in with considerable delay after first exposure, is in good agreement with our weight loss measurements. The correlation between outdoor weathering and Xenotest weathering period (shortest wavelength 300 nm) is linear for all degrees of wear (time acceleration factor 13).Contrary to PMMA, scanning electron micrographs of PC show degradation morphologies dependent on the type of weathering which first develop after a certain weathering period.The degradation of PC occurs in two steps. Immediately after first weathering an embrittlement of the surface sets in, caused by molecular weight reduction and the formation of short-chain degradation products. Moreover, as a result of weathering-related dry/wet cycles and temperature fluctuations, the reduced elongation at break is exceeded locally and eventually cracking at the surface occurs, surface roughness and material loss increase and the gloss reduces.
    Additional Material: 8 Ill.
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    Polyethylene recycling during processingPaper presented at the 19th Colloqium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymer” in Prague (Czechoslovakia), July 24-29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 65-78 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Low-density polyethylene was recycled in blown-film production using own factory scrap material. The amounts of the addition of recycled materials to the virgin polyethylene were established, having in mind the fullfilmet of the requirements for quality performances of the obtained films.In the second part of the paper several successive injection-mouldings were made on the same low-density polyethylene. Along with the mechanical characteristics of the obtained reprocessed polyethylene samples, the newly developed method for measuring thermally stimulated depolarization current (TSDC) was evaluated. It was found that the polyethylene samples reprocessed several times differ between themselves also by the fact that the current peaks appeared at some characteristic polymer temperatures, depending on the number of reprocessing cycles, and in lesser degree also, depending on the abcence or the presence of a heat stabilizer.
    Additional Material: 9 Ill.
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    Competition between degradation and orientation in semicrystalline polymersPaper presented at the 19th Colloquim of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague, July 25-27, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 93-104 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This lecture summarizes some recent results and ideas about interrelations between degradation and mechanical behaviour of polyolefins. Aspects of the heterogeneous nature of oxidative degradation in the solid state, the feedback mechanism in degradation, effects of morphology, particularly orientation, on the degradation process, and the influence of degradation on plasticity and on the ultimate mechanical behaviour are discussed.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051760108
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  • 190
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    Properties of adhesive polymer compositions in ageing conditionsPaper Presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Prague (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 125-134 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In our work the degradative changes in properties of polyurethane adhesives based on aliphatic isocyanates were defined and compared with similar changes occurring when using aromatic isocyanates. The readily observed PUR adhesive discolouration in situations of its contact with leather does imply the necessity for the establishing the real proportions of the polyurethane constituents responsible for this ever-present problem. The structure-property relationship of hydroxylterminated polyester-based segmented aliphatic polyurethanes, as a component in adhesive composition were studied using wide angle X-ray diffraction spectroscopy (WAXD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) as well as attenuated total reflectance infrared spectroscopy (ATR-IR) and nuclear magnetic resonance spectroscopy (NMR). The results show that crystalline phase in segmented PUR component influence on morphological and structural properties in degradative conditions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760111
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  • 191
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    The effect of degradation degree of the dispersed phase on the ozone aging of rubbers filled with crushed rubber powderPaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Aging and Stabilization of Polymers” in Praque (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 173-183 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of crushed rubber powder as a filler of rubber compounds on the ozone aging of vulcanizates has been investigated. It has been shown that the ozone resistance depends significantly both on the concentration and the degradation degree of the dispersed phase. Results of laboratory and atmospheric aging tests are summarized.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760115
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  • 192
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    Alterung und degradation des ledersVortrag anlässlich des 19. Donauländergesprächs über “Atmosphärische Alterung und Stabilisierung von Polymeren” in Prag (Tschechoslovakei), vom 24. - 29. Juli 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 207-213 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Leather has been an important natural polymer undergoing aging when exposed to physical (temperature, radiation) and chemical (oxygen, water, metal ions) deteriogens. Degradation of collagen and changes of mechanical properties of leather are the consequences. The aging has been influenced by tan process, by changes of pH due to chemical degradation and by losses of fat due to extraction or blooming. The understanding of degradation process taking place in leather is necessary for the restoration of aged products from leather having a historical value.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760118
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  • 193
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    Antioxidative efficiency of N-(arylamine) imides in thermal oxidation of polypropylenePaper presented at the 19th Colloquium of Danubian Countries on “Atmospheric Ageing and Stabilization of Polymers” in Prague (Czechoslovakia), July 24 - 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 176 (1990), S. 231-240 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electron-donating substituents of N-(arylamine) phthalimides and succinimides promote antioxidative efficiency of these compounds in thermooxidation of polypropylene (190°C, oxygen), while electron-withdrawing substituents contribute to a reduced volatilization of the polymer. 2,6-Ditert.butyl-4-methylphenol (ionol) raises the antioxidative efficiency of 4-methoxy and 4-methyl substituted derivatives displaying a distinct synergism.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051760120
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  • 194
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    New oligomers with isatin. Condensation reactions of thiophene and 2,2′-bithiophene with isatin (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 1-16 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die seit langem in der Literatur als “Indophenin-Reaktion” bekannte Umsetzung von Isatin mit Thiophen wurde systematisch untersucht und auf die Umsetzung mit Bithiophen erweitert. Die Reaktionsprodukte wurden isoliert und durch FT-IR, UV, 1H-NMR, 13C-NMR sowie GPC charakterisiert.Im Gegensatz zu den Literaturdaten wurden Reaktionsprodukte mit höheren Molgewichten und anderer Molmassenverteilung gefunden. Die Reaktionsbedingungen - Lösungsmittel, Temperatur und Konzentration - sind für den Reaktionsablauf und die entstehenden Produkte von entscheidender Bedeutung.Füur die oligomeren Reaktionsprodukte werden neue Strukturen vorgeschlagen, die in Übereinstimmung mit allen analytischen Daten sind. Anhand eines Formelschemas werden die Reaktionen des Isatins mit Thiophen (Bithiophen) erläutert.
    Notes: A systematic study of the well-known indophenin reaction between isatin and thiophene was extended to embrace bithiophene. The products of the reactions were isolated and characterized by FT-IR, UV, 1H-NMR, 13C-NMR, and GPC. The values of the thus determined molar masses and molar mass distributions differed from the data given in the literature. The reaction conditions - solvent, temperature, and concentration - are of crucial importance for the course of the reaction and the products obtained.New structures suggested for the oligomeric reaction products agree with all the analytical data. The reactions between isatin and thiophene (bithiophene) are explained schematically.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780101
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  • 195
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    Unvernetzte epoxid-amin-additionspolymere, 2524. Mitteilung cf1.. Oligoether-diamine als elastifizierende comonomere für lineare epoxid-amin-additionspolymere (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 63-83 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: N,N'-Dibenzyl-3,6-dioxaoctane-diamine-1,8 and three analogous secondary diamines (EDA) all of which have long chain aliphatic ether groups were prepared and reacted with diglycidylether of bisphenol-A (DGEBA) to give well defined linear epoxide-amine addition polymers. Due to the flexible spacer in the amine component, the glass transition temperatures (Tg) of DGEBA/EDA copolymers decrease to 9-23°C. Likewise Tg's of DGEBA/polyamine networks are significantly lowered by copolymerization with EDA (Tg = 25 -100°C). Such flexible copolymers may be used as strain free optical adhesives or as the soft component in polymer blends and interpenetrating networks.Thermodynamic and kinetic polyreaction parameters were measured by DSC. In excellent correspondence with experiments, data have been calculated using a refined reaction model. This includes both noncatalyzed and catalyzed parallel reactions. The latter ones are activated by NH···HO complexation resulting from growing amounts of HO groups in the addition product.
    Notes: N,N'-Dibenzyl-3,6-dioxaoctandiamin-1,8 und drei analoge sekundäre Diamine mit langen aliphatischen Ethergruppierungen (EDA) sind hergestellt und mit Bisphenol-A-diglycidylether DGEBA polymerisiert worden. Der lineare Charakter der Additions-polymerisation wurde durch die Molmassenverteilung, Mw/Mn = 2, sowie elementaranalytische und spektroskopische Untersuchungen der Additionspolymeren und ihrer Hydroxylderivate (Acetate, Dicarbonsäurehalbester, Urethane) belegt.Durch ein verbessertes Reaktionsmodell wurde die Epoxid-Amin-Reaktion in ausgezeichneter Übereinstimmung mit dem Experiment (Zeit-Umsatz-Kurve und dynamische Wärmekapazitätsmessung) bis zum höchsmöglichen Umsatz beschrieben. Das Reaktionsmodell berücksichtigt die nichtkatalysierte Reaktion und eine durch Addukt-OH-Gruppen katalysierte Parallelreaktion.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1990.051780105
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  • 196
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    Influence de l'epaisseur de l'adhésif et du vieillissement sur les propriétés mécaniques dynamiques d'un assemblage: Adhésif structural/acier inoxydable (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 47-62 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Les propriétés mécaniques dynamiques d'un assemblage collé type «sandwich» - acier inoxydable/adhésif en film - sont étudiées en fonction de I'épaisseur du film d'adhésif et du temps de vieillissement en atmosphere chaude et humide.A partir d'analyses thermomécaniques dynamiques, il est montré que les températures de transition vitreuse (Tg) de l'adhésif seul et de ce même adhésif dans un assemblage métal/adhésif sont différentes.Avant collage, la surface du métal subit divers traitements chimiques ou électrochimiques qui provoquent un déplacement de la température de transition vitreuse du polymère. L'évolution de cette même température avec l'épaisseur de l'adhésif montre que le taux de réticulation est plus élevé dans les couches superficielles de l'adhésif en contact avec le métal qu'au sein du polymkre.Lors du vieillissement, l'absorption d'eau entraîne des phénomknès de plastification de l'adhésif et une baisse importante de la température de transition vitreuse est observée. L'anodisation sulfochromique du métal confère une meilleure stabilitté à l'lassemblage.
    Notes: Dynamic mechanical properties of bounded joints - stainless steel/epoxy adhesive - are investigated as a function of the thickness of the adhesive and aging conditions. The viscoelastic properties of the bounded joints have been investigated by Dynamic Thermo Mechanical Analysis (DTMA).The glass transition temperature (Tg) showed a dependence on both the chemical/electrochemical pretreatments of the substrate and the thickness of the adhesive in the bounded joint. The crosslinking density in the adhesive thus seemed more important in the interfacial region than in adhesion bulk.The water uptake induces a plasticization of the adhesive and a decrease in Tg. The most stable bounded joints were obtained by carrying out sulfochromic acid anodization as a pretreatment step. The most important stability of the bounded joints was obtained with the sulfochromic anodization of the substrate.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780104
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  • 197
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    Sphärische ionotrope gele carboxygruppenhaltiger cellulosederivate als trägermaterialien für biologische wirkstoffe, IVTeil III cf.4.. Synthese von carboxycellulose und ionotrope gelbildung mit calciumionen (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 95-107 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Sodium carboxy cellulose with a degree of substitution up to 0.8 can be prepared by oxidation of cellulose with NaNO2/H3PO4 and subsequent treatment with NaBH4. The extent of oxidation increases with raising molecular weight ranging from 170 to 1500 of the starting material. IR and NMR studies show that only the C-6 atom of the anhydroglucose unit is oxidized. The sodium carboxy celluloses show a high tendency to form ionotropic gels even in spherical shape with calcium ions. The mechanically stable gels are characterized by investigation of the swelling behaviour and SEM.
    Notes: Natriumcarboxycellulose mit einem Substitutionsgrad bis 0,8 kann durch Oxidation von Cellulose mit einem Polymerisationsgrad im Bereich von 170 bis 1500 mit NaNO2/H3PO4 und anschließender Behandlung mit NaBH4 hergestellt werden. Das Ausmaß der Oxidation steigt mit wachsender Molmasse des Ausgangsmaterials. IR-und NMR-Untersuchungen zeigen, daß nur das C-6-Atom der Anhydroglucoseeinheit oxidiert ist. Die Natriumcarboxycellulosen weisen eine hohe Tendenz zur ionotropen Gelbildung auch in sphärischer Form mit Calciumionen auf. Die mechanisch stabilen Gele werden durch Quellungsuntersuchungen und REM charakterisiert.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780107
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  • 198
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    Graft polymerization of 4-vinylpyridine onto cellulosic fibres by the ceric ion method, IIPart I cf.14.. The ph effect (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 119-129 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß des pH-Wertes auf die mit Cer(IV)-ammoniumnitrat initiierte Pfropfpolymerisation von 4-Vinylpyridin (4-VP) auf Cellulose und partiell carboxymethylierte Cellulose (PCMC) in verdünnter Salpetersäure wurde untersucht. Die Abhängigkeiten von Pfropfausbeute (GE), Pfropfungsgrad (G), Pfropfhäufigkeit (GF) und Cerionenverbrauch (Ce(IV)c) von der Salpetersäurekonzentration wurden ermittelt. Bei pH = 1 sind Gesamtumsatz und Pfropfumsatz am größten; wird die Nitratkonzentration konstant gehalten (0,86 mol/1), läßt sich der Pfropfumsatz noch erhöhen. Zum Vergleich wurden einige Experimente mit Cersulfat als Initiator durchgeführt.
    Notes: The effect of pH on the graft polymerization of 4-vinylpyridine (4-VP) onto cellulose and on partially carboxymethylated cotton (PCMC) initiated by ceric ammonium nitrate (CAN) in dilute nitric acid was examined. The grafting parameters grafting efficiency (GE), graft yield (G), graft frequency (GF), and ceric ion consumption (Ce(IV)c) were studied as a function of nitric acid concentration. Also the effect of pH on the graft polymerization was examined and the total nitrate ion concentration was maintained high and constant at 0.86 mol/1 by addition of sodium nitrate. Maximum grafting and total conversion occurred at pH 1, but these values were smaller than the ones obtained in the previous case. For comparison some experiments were carried out using ceric sulfate as initiator.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780109
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  • 199
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    Oberflächenstrukturierung polymerer fasern durch UV-laserbestrahlung. 6. Zur vermeidung von vergilbungen bei der laserbehandlung von polymerenTeil 5 cf. Lit1. (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 178 (1990), S. 143-151 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: It is shown in this paper, that during laser treatment of polymeric materials the occurrence of discolouring layers of laser crack deposits onto the substrate can be avoided without preventing the formation of a laser-induced microstructuring of the surface. Using water, alcohols, ethers or aqueous surfactant solutions as impregnating media during laser treatment a high degree of whiteness of fabrics can be maintained.
    Notes: Es wird gezeigt, daß die Ausbildung einer Schicht von verfärbenden Lasercrackprodukten - wie sie bei der Laserbehandlung von trockenen Polymeren gebildet wird - durch Imprägnierung mit verschiedenen Lösungsmitteln während der Laserbearbeitung verhindert werden kann. Die Ausbildung einer laserinduzierten Mikrostrukturierung der Polymeroberfläche wird davon nicht beeinflußt. Es läßt sich damit auch bei stärkeren Energiedichten der Laserbehandlung ein hoher Weißgrad aufrechterhalten.Zur Verhinderung der Vergilbung sind Wasser, Alkohole, Ether und wäßrige Tensidlösungen als Imprägniermedien während der Laserbestrahlung vorteilhaft einsetzbar.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051780111
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  • 200
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    Durability of radiation-sterilized polymers, XIIIPart XI cf. lit.6.. The effects of nucleating agent on the oxidative degradation of poly(propylene-co-ethylene) (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 174 (1990), S. 131-140 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Bestrahlungsstabilität von statistischen und Blockcopolymeren aus Propen und Ethen (CP, Copolymeres mit 6% Etheneinheiten) mit und ohne Keimbildner (NA) wurde in bezug auf die Bestrahlungssterilisation von medizinischen Gütern verglichen. In beiden Fällen war die Bestrahlungsstabilität von CP in Gegenwart von NA geringer als ohne.Die Zugabe von NA zu CP verbesserte zwar nicht die Transparenz, die Kristallisation erfolgte aber bei höherer Temperatur. Sie hat deshalb den Vorteil kürzerer Formzeiten bei der Produktion von medizinischen Gütern.Die Bestrahlungsinstabilität von CP mit NA rührt von einer unterschiedlichen Kristallstruktur her, weil sich die Form der Spharolite von der des CP ohne NA unterscheidet. Weiterhin wurde durch Chemiluminiszenz-Analyse ein stärkerer oxidativer Abbau in der Probe mit NA beobachtet.
    Notes: The radiation stability of the random and block poly(propylene-co-ethylene) (CP, copolymer with 6% ethylene units) with and without nucleating agent (NA) was compared in relation to radiation sterilization of medical supplies. In both cases, it was found that the radiation stability of CP in the presence of NA was lower than that of CP without NA.Addition of NA to CP did not improve the transparency but the crystallization occurred at higher temperature. Thus, adding NA to CP has the advantage of shorter moulding time in the production of medical supplies.The radiation instability of the CP with NA was due to a different crystal structure, because the spherulite shape differs from that of CP without NA. Furthermore, by the chemiluminescence analysis, a higher oxidative degradation was observed in the sample with NA.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051740111
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