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  • Chemistry  (21,859)
  • Biochemistry and Biotechnology  (2,295)
  • 1995-1999  (15,137)
  • 1980-1984  (6,722)
  • 1975-1979
  • 1998  (5,528)
  • 1997  (9,609)
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  • 1995-1999  (15,137)
  • 1980-1984  (6,722)
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  • 101
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    Electronic Resource
    Conformational study of asialo-GM1 (GA1) ganglioside (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 19-35 
    Details
    ISSN: 0006-3525
    Keywords: conformation ; ganglioside GA1 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to investigate the significance of preferred conformations of the saccharide for the steric orientation and recognition of glycosphingolipids at the membrane surface, the conformational free energy calculations were carried out on the asialo-GM1 [GA1; β-D-Gal(1 → 3) β-D-GalNAc(1 → 4) β-D-Gal(1 → 4) β-D-Glc-O-ceramide] using a new program CONCARB (CONformational study program for CARBohydrate) in the unhydrated and hydrated states. The overall backbone conformation of GA1 appears nearly to be extended with a little bent at the glycosidic II-III linkage, in which two pyranose rings of Gal(IV)-GalNAc-(III) moiety orient approximately perpendicular to those of Gal(II)-Glc(I) moiety. This is consistent with the structures deduced from high-sensitivity differential scanning calorimetry experiments and the nmr study on GA1. The calculated glycosidic torsion angles of the lowest free energy conformation of GA1 in the hydrated state are in accord with the structures of relevant oligosaccharides deduced from nmr experiments and hard sphere exoanomeric calculations. A comparison of the values of glycosidic torsion angles φ and π of GA1 and its constituent oligosaccharides indicates that the overall backbone conformation of each oligosaccharide is retained when the oligosaccharide chain becomes longer. This implies that the short-range interactions between the nearest-neighbored saccharides are of significant importance in stabilizing the overall backbone conformation of GA1 in both the unhydrated and hydrated states. The different orientation and hydrogen bonds of hydroxymethyl and hydroxyl groups from one oligosaccharide to another suggest that the medium- and long-range interactions are also of consequence. Hydration seems to affect significantly the conformation of these groups, but not to perturb remarkably the overall backbone conformation of GA1. © 1997 John Wiley & Sons, Inc. Biopoly 42: 19-35, 1997
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  • 102
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    Energetics of drug-DNA interactions (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 201-215 
    Details
    ISSN: 0006-3525
    Keywords: DNA ; thermodynamics ; calorimetry ; drugs ; intercalators ; groove binders ; free energy ; solvent-accessible surface area ; polyelectrolyte effect ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Understanding the thermodynamics of drug binding to DNA is of both practical and fundamental interest. The practical interest lies in the contribution that thermodynamics can make to the rational design process for the development of new DNA targeted drugs. Thermodynamics offer key insights into the molecular forces that drive complex formation that cannot be obtained by structural or computational studies alone. The fundamental interest in these interactions lies in what they can reveal about the general problems of parsing and predicting ligand binding free energies. For these problems, drug-DNA interactions offer several distinct advantages, among them being that the structures of many drug-DNA complexes are known at high resolution and that such structures reveal that in many cases the drug acts as a rigid body, with little conformational change upon binding. Complete thermodynamic profiles (ΔG, ΔH, ΔS, ΔCp) for numerous drug-DNA interactions have been obtained, with the help of high-sensitivity microcalorimetry. The purpose of this article is to offer a perspective on the interpretation of these thermodynamics parameters, and in particular how they might be correlated with known structural features. Obligatory conformational changes in the DNA to accommodate intercalators and the loss of translational and rotational freedom upon complex formation both present unfavorable free energy barriers for binding. Such barriers must be overcome by favorable free energy contributions from the hydrophobic transfer of ligand from solution into the binding site, polyelectrolyte contributions from coupled ion release, and molecular interactions (hydrogen and ionic bonds, van der Waals interactions) that form within the binding site. Theoretical and semiempirical tools that allow estimates of these contributions to be made will be discussed, and their use in dissecting experimental data illustrated. This process, even at the current level of approximation, can shed considerable light on the drug-DNA binding process. © 1998 John Wiley & Sons, Inc. Biopoly 44: 201-215, 1997
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  • 103
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    Editorial (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 321-321 
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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: No abstract.
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  • 104
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    Conformation and interactions of bioactive peptides from insect venoms: The bombolitins (1997)
    New York : Wiley-Blackwell
    Biopolymers 43 (1997), S. 419-431 
    Details
    ISSN: 0006-3525
    Keywords: bombolitins ; conformation ; amphipathic helices ; lytic peptides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bombolitins are five structurally related heptadecapeptides originally isolated from the venom of a bumblebee, acting at membrane level and able to enhance the activity of Phospholipase A2. The biological activity of this class of natural peptides seems to be related to the their ability to form amphiphilic helical structures in the presence of phospholipid aggregates or related membrane model systems. We have carried out systematic investigations on a series of bombolitins and their synthetic analogs in order to establish the conditions in which amphipathic helices are formed and to elucidate the details of the interaction with phospholipids and related model systems. We have shown that bombolitins and their analogs interact with phospholipid aggregates and detergent micelles forming amphiphilic helices. By means of the Langmuir film balance technique, coupled with fluorescence microscopy, we have shown that bombolitins perturbe the structure of phospholipid monolayers, forming phase separated peptide domains. In aqueous solution, in the absence of detergent or phospholipids, bombolitins form oligomeric aggregates with consequent conformational transition from a random coil to an α-helical structure. In the aggregate structure, evidence was obtained that helices are oriented in an antiparallel fashion. In this article we summarize the most recent results of conformational studies by CD, NMR and computer simulations on a series of bombolitins and retro-, all-D- and all-D-retro-analogs. © 1998 John Wiley & Sons, Inc. Biopoly 43: 419-431, 1997
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  • 105
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    Crystallographic insights into DNA minor groove recognition by drugs (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 105-121 
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    ISSN: 0006-3525
    Keywords: crystal structures ; minor groove drugs ; oligonucleotides ; sequence recognition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review surveys the crystal structures between minor groove drugs and oligonucleotides, of which over thirty have now been determined. The various factors that are involved in the observed A/T sequence selectivity of these drugs are examined in structural terms. The roles of, in particular, hydrogen-bond recognition and sequence-dependent groove width, are assessed, and as a consequence the minor groove drugs have been classified into two categories, dependent on the relative roles played by these two factors in sequence recognition. Implications for the recognition of non-A/T sequences are discussed. © 1997 John Wiley & Sons, Inc. Biopoly 44: 105-121, 1997
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  • 106
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    DNA recognition and nucleosome organization (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 423-433 
    Details
    ISSN: 0006-3525
    Keywords: DNA recognition ; nucleosome recognition ; deformation ; DNA-binding protein ; conformational fluctuations ; protein-DNA complexes ; histone octamer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The affinity of a DNA sequence for the histone octamer in a core nucleosome depends on the intrinsic flexibility of the DNA. This parameter can be affected both by the sequence-dependent conformational preferences of individual base steps and by the nature and location of the exocyclic groups of the DNA bases. By adopting highly preferred conformations particular types of base step can influence the rotational positioning of the DNA on the surface of the histone octamer. The asymmetry of the next higher order of chromatin structure is determined in part by the asymmetric binding of the globular domain of histone H5 to the core nucleosome. © 1998 John Wiley & Sons, Inc. Biopoly 44: 423-433 1997
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    Helix bending as a factor in protein/DNA recognition (1997)
    New York : Wiley-Blackwell
    Biopolymers 44 (1997), S. 361-403 
    Details
    ISSN: 0006-3525
    Keywords: helix bending ; protein/DNA recognition ; B-DNA ; FREEHELIX ; roll ; tilt ; kink ; curvature ; writhe ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Normal vectors perpendicular to individual base pairs are a powerful tool for studying the bending behavior of B-DNA, both in the form of normal vector plots and in matrices that list angles between vectors for all possible base pair combinations. A new analysis program, FREEHELIX, has been written for this purpose, and applied to 86 examples of sequence-specific protein/DNA complexes whose coordinates are on deposit in the Nucleic Acid Data Base. Bends in this sample of 86 structures almost invariably follow from roll angles between adjacent base pairs; tilt makes no net contribution. Roll in a direction compressing the broad major groove is much more common than that which compresses the minor groove. Three distinct types of B-DNA bending are observed, each with a different molecular origin: (1) Localized kinking is produced by large roll at single steps or at two steps separated by one turn of helix. (2) Smooth, planar curvature is produced by positive and negative roll angles spaced a half-turn apart, with random side-to-side zigzag roll at intermediate points, rather than a tilt contribution that might have been expected theoretically. (3) Three-dimensional writhe results from significant roll angles at a continuous series of steps. Writhe need not change the overall direction of helix axis, if it is continued indefinitely or for an integral number of helical turns. A-DNA itself can be formally considered as possessing uniform, continuous writhe that yields no net helix bending. Smooth curvature is the most intricate deformation of the three, and is least common. Writhe is the simplest deformation and is most common; indeed, a low level of continuous writhe is the normal condition of an otherwise unbent B-DNA helix of general sequence. With one exception, every example of major kinking in this sample of 86 structures involves a pyrimidine-purine step: C-A/T-G, T-A, or C-G. Purine-purine steps, especially A-A, show the least tendency toward roll deformations. © 1998 John Wiley & Sons, Inc. Biopoly 44: 361-403, 1997
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    Folding type-specific secondary structure propensities of amino acids, derived from α-helical, β-sheet, α/β, and α+β proteins of known structures (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 35-49 
    Details
    ISSN: 0006-3525
    Keywords: folding type-specific secondary structure propensities ; amino acids ; α-helical proteins ; β sheet proteins ; α/β proteins ; α+β proteins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Folding type-specific secondary structure propensities of 20 naturally occurring amino acids have been derived from α-helical, β-sheet, α/β, and α+β proteins of known structures. These data show that each residue type of amino acids has intrinsic propensities in different regions of secondary structures for different folding types of proteins. Each of the folding types shows markedly different rank ordering, indicating folding type-specific effects on the secondary structure propensities of amino acids. Rigorous statistical tests have been made to validate the folding type-specific effects. It should be noted that α and β proteins have relatively small α-helices and β-strands forming propensities respectively compared with those of α+β and α/β proteins. This may suggest that, with more complex architectures than α and β proteins, α+β and α/β proteins require larger propensities to distinguish from interacting α-helices and β-strands. Our finding of folding type-specific secondary structure propensities suggests that sequence space accessible to each folding type may have differing features. Differing sequence space features might be constrained by topological requirement for each of the folding types. Almost all strong β-sheet forming residues are hydrophobic in character regardless of folding types, thus suggesting the hydrophobicities of side chains as a key determinant of β-sheet structures. In contrast, conformational entropy of side chains is a major determinant of the helical propensities of amino acids, although other interactions such as hydrophobicities and charged interactions cannot be neglected. These results will be helpful to protein design, class-based secondary structure prediction, and protein folding. © 1998 John Wiley & Sons, Inc. Biopoly 45: 35-49, 1998
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    Torsional control of double-stranded DNA branch migration (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 69-83 
    Details
    ISSN: 0006-3525
    Keywords: DNA branched junctions ; branch migration ; superhelical torque ; control of DNA structure ; endonuclease VII ; nanomechanical device ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA branched junctions are analogues of Holliday junction recombination intermediates. Partially mobile junctions contain a limited amount of homology flanking the branch point. A partially mobile DNA branched junction has been incorporated into a synthetic double-stranded circular DNA molecule. The junction is flanked by four homologous nucleotide pairs, so that there are five possible locations for the branch point. Two opposite arms of the branched junction are joined to form the circular molecule, which contains 262 nucleotides to the base of the junction. This molecule represents a system whereby torque applied to the circular molecule can have an impact on the junction, by relocating its branch point. Ligation of the molecule produces two topoisomers; about 87% of the product is a relaxed molecule, and the rest is a molecule with one positive supercoil. The position of the branch point is assayed by cleaving the molecule with endonuclease VII. We find that the major site of the branch point in the relaxed topoisomer is at the maximally extruded position in the relaxed molecule. Upon the addition of ethidium, the major site of the branch point migrates to the minimally extruded position. © 1998 John Wiley & Sons, Inc. Biopoly 45: 69-83, 1998
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  • 110
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    Conformational change and aggregation of κ-carrageenan studied by flow field-flow fractionation and multiangle light scattering (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 85-96 
    Details
    ISSN: 0006-3525
    Keywords: conformation ; aggregation ; κ-carrageenan ; flow field-flow fractionation ; multiangle light scattering ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relatively novel combination of flow field-flow fractionation (FFF) and multiangle light scattering (MALS) was employed to study a nondegraded κ-carrageenan in different 0.1M salt solutions. The applicability of the technique was tested, and the effects of salt type and salt composition on the molar mass and radius of gyration were studied. A conformational ordering was induced at room temperature by switching the solvent from 0.1M NaCl (coil form) to 0.1M NaI (helix form). An approximate doubling of the average molar mass and an increase in radius of gyration was then observed, in agreement with results obtained previously using size exclusion chromatography-MALS. This increase in size was attributed to conformational ordering and to the formation of double helices. Severe aggregation was observed above 40% CsI in the 0.1M mixed salt solution of CsI and NaI. This was ascribed to the association of helices into large aggregates. For these large associates, having molar masses of several millions, a reversal of the elution order in flow FFF was detected. © 1998 John Wiley & Sons, Inc. Biopoly 45: 85-96 1998
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  • 111
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    Calculations on the low energy conformers of N-acetyl-D-alanyl-D-alanine (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 119-133 
    Details
    ISSN: 0006-3525
    Keywords: conformations of D-alanyl-D-alanine ; β-lactam ; structural overlay ; AMBER force field ; AM1 ; ab initio ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article a conformational analysis of the D-alanyl-D-alanine dipeptide, both charged and neutral, has been carried out. The preferred conformations were determined by means of ab initio and semiempirical quantum, together with empirical force field calculations. The AMBER* force field and the 6-31 + G** and 6-31G** ab initio levels give rise to a coincident minimum energy structure, which, on the other hand, differs from that determined by AM1, 3-21 + G, and 3-21G. The solvent effect on the different charged and neutral conformations have been considered through the AMSOL semiempirical method. A quantification regarding the structural similarities between the different dipeptide conformations and the ampicillin has been performed. The results show that the best overlay is attained by the minimum structure energy obtained by using the 6-31 + G** methodology, which presents a planar amidic nitrogen. © 1998 John Wiley & Sons, Inc. Biopoly 45: 119-133, 1998
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    C6-oxidized cellulose: Ion interactions with mono- and divalent cations (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 157-163 
    Details
    ISSN: 0006-3525
    Keywords: chemical oxidation ; cellulose ; conformational transition ; capillary viscosity ; microcalorimetry ; calcium ions ; gels ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational behavior of different molecular weight fractions of a synthetic C6-oxidized derivative of cellulose were investigated by means of capillary viscometry, CD, and microcalorimetric measurements. Experiments were carried out in the presence of either monovalent or divalent counterions.The experimental data indicated that C6-oxidized cellulose can assume an ordered extended conformation at low ionic strength, induced by the intrachain repulsions of negative charges. This conformation was suggested to be very similar to the fully extended structure of cellulose. In addition to this, upon increasing the ionic strength, a conformational transition of the order-to-disorder type occurred. In fact, the screening of the electrostatic repulsions introduced a number of conformational kinks into the cellulosic backbone, which enabled the polymer to assume a more coiled conformation hence producing less viscous aqueous solutions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 157-163, 1998
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    Conformational stability of biological polyelectrolytes: Evaluation of enthalpy and entropy changes of conformational transitions (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 203-216 
    Details
    ISSN: 0006-3525
    Keywords: conformational stability ; biological polyelectrolytes ; enthalpy ; entropy ; conformational transitions ; carrageenan ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method is proposed for the determination of the enthalpy and entropy changes of nonionic origin upon conformational transition of linear biopolyelectrolytes in solution. For all transition midpoints, defined by given temperature and ionic strength, the total free energy change of the system is zero, which means that the nonionic contribution to the free energy change is equal in value and opposite in sign to the polyelectrolytic one. The counterion condensation theory of linear polyelectrolytes provides for the appropriate analytical expression to be used in such calculations. Linear plots of the proper functions of the calculated free energy changes vs the proper functions of temperature allows for the determination of the enthalpic and entropic terms of the nonionic free energy change of transition.The method has been applied to the extensive available data of the ion-induced conformational change of κ-carrageenan, a linear sulfated galactan extracted from seaweeds. The method has proved very successful, with the results showing a remarkable convergency of the enthalpy values for different monovalent counterions. On the other hand, the above approach has made it possible to explain the known effect of counterion specificity on the transition by a small difference in the nonionic entropic contributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 203-216, 1998
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    UV resonance Raman spectroscopy of DNA and protein constituents of viruses: Assignments and cross sections for excitations at 257, 244, 238, and 229 nm (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 247-256 
    Details
    ISSN: 0006-3525
    Keywords: uv resonance Raman spectroscopy ; Raman cross section ; hypochromism ; DNA ; deoxynucleoside ; protein ; aromatic amino acid ; virus assembly ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ultraviolet resonance Raman (UVRR) spectra of H2O and D2O solutions of the nucleoside (dA, dG, dC, dT) and aromatic amino acid (Phe, Trp, Tyr) constituents of DNA viruses have been obtained with laser excitation wavelengths of 257, 244, 238, and 229 nm. Using the 981 cm-1 marker of Na2SO4 as an internal standard, Raman frequencies and scattering cross sections were evaluated for all prominent UVRR bands at each excitation wavelength. The results show that UVRR cross sections of both the nucleosides and amino acids are strongly dependent on excitation wavelength and constitute sensitive and selective probes of the residues. The results provide a library of UVRR marker bands for structural analysis of DNA viruses and other nucleoprotein assemblies. © 1998 John Wiley & Sons, Inc. Biopoly 45: 247-256, 1998
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    Lumbricus terrestris hemoglobin: A comparison of small-angle X-ray scattering and cryoelectron microscopy data (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 289-298 
    Details
    ISSN: 0006-3525
    Keywords: hemoglobin ; hexagonal bilayer ; Lumbricus ; electron microscopy ; three-dimensional reconstruction ; small-angle x-ray scattering ; three-dimensional models ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quaternary structure of Lumbricus terrestris hemoglobin was investigated by small-angle x-ray scattering (SAXS). Based on the SAXS data from several independent experiments, a three-dimensional (3D) consensus model was established to simulate the solution structure of this complex protein at low resolution (about 3 nm) and to yield the particle dimensions. The model is built up from a large number of small spheres of different weights, a result of the two-step procedure used to calculate the SAXS model. It accounts for the arrangement of 12 subunits in a hexagonal bilayer structure and for an additional central unit of cylinder-like shape. This model provides an excellent fit of the experimental scattering curve of the protein up to h = 1 nm-1 and a nearly perfect fit of the experimental distance distribution function p(r) in the whole range. Scattering curves and p(r) functions were also calculated for low-resolution models based on 3D reconstructions obtained by cryoelectron microscopy (EM). The calculated functions of these models also provide a very good fit of the experimental scattering curve (even at h 〉 1 nm-1) and p(r) function, if hydration is taken into account and the original model coordinates are slightly rescaled. The comparison of models reveals that both the SAXS-based and the EM-based model lead to a similar simulation of the protein structure and to similar particle dimensions. The essential differences between the models concern the hexagonal bilayer arrangement (eclipsed in the SAXS model, one layer slightly rotated in the EM model), and the mass distribution, mainly on the surface and in the central part of the protein complex. © John Wiley & Sons, Inc. Biopoly 45: 289-298, 1998
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    Conformational changes due to vicinal glycosylation: The branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide compared with its parent disaccharides* (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 417-432 
    Details
    ISSN: 0006-3525
    Keywords: conformational changes ; vicinal glycosylation ; branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide ; parent disaccharides ; hydrogen bond ; isotope effect ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformations of the α-l-Rhap(1-2)-β-d-Glc1-OMe and β-d-Galp(1-3)-β-d-Glc1-OMe disaccharides and the branched title trisaccharide were examined in DMSO-d6 solution by 1H-nmr. The distance mapping procedure was based on rotating frame nuclear Overhauser effect (NOE) constraints involving C- and O-linked protons, and hydrogen-bond constraints manifested by the splitting of the OH nmr signals for partially deuteriated samples. An “isotopomer-selected NOE” method for the unequivocal identification of mutually hydrogen-bonded hydroxyl groups was suggested. The length of hydrogen bonds thus detected is considered the only one motionally nonaveraged nmr-derived constraint. Molecular mechanics and molecular dynamics methods were used to model the conformational properties of the studied oligosaccharides. Complex conformational search, relying on a regular Φ,Ψ-grid based scanning of the conformational space of the selected glycosidic linkage, combined with simultaneous modeling of different allowed orientations of the pendant groups and the third, neighboring sugar residue, has been carried out. Energy minimizations were performed for each member of the Φ,Ψ grid generated set of conformations. Conformational clustering has been done to group the minimized conformations into families with similar values of glycosidic torsion angles. Several stable syn and anti conformations were found for the 1→2 and 1→3 bonds in the studied disaccharides. Vicinal glycosylation affected strongly the occupancy of conformational states in both branches of the title trisaccharide. The preferred conformational family of the trisaccharide (with average Φ,Ψ values of 38°, 17° for the 1→2 and 48°, 1° for the 1→3 bond, respectively) was shown by nmr to be stabilized by intramolecular hydrogen bonding between the nonbonded Rha and Gal residues. © 1998 John Wiley & Sons, Inc. Biopoly 46: 417-432, 1998
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    Buffer dependence of refractive index increments of protein solutions (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 489-492 
    Details
    ISSN: 0006-3525
    Keywords: refractive index increment ; proteins ; solvent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The refractive index increment of a protein solution is a property not only of the protein, but also of the solvent. This is demonstrated theoretically and confirmed experimentally using analytical interferometry. © 1998 John Wiley & Sons, Inc. Biopoly 46: 489-492, 1998
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    Editor's comments (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 1-1 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Conformational behavior of the HAV-VP3(110-121) peptidic sequence and synthetic analogs in membrane environments studied by CD and computational methods (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 479-492 
    Details
    ISSN: 0006-3525
    Keywords: hepatitis A ; synthetic peptides ; CD ; liposomes ; computational study ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present study was undertaken to examine the structural features that may be important to explain the immunogenicity of the (110-121) peptide sequence (FWRGDLVFDFQV) of VP3 capsid protein of hepatitis A virus. A conformational analysis of the preferred conformations by CD and molecular mechanics was carried out. Present results suggest that the interaction with liposomes as biomembrane model induces and stabilizes the amphipathic β-structure of the peptide.To study the contribution of amino acid replacements at the RGD tripeptide as well as the influence of the peptide chain length on peptide conformation, solid-phase peptide synthesis of several peptide analogs was carried out and the peptide conformation was studied using CD spectroscopy. The results show that the RGD sequence is necessary to induce the β-structure in the presence of liposomes. © 1998 John Wiley & Sons, Inc. Biopoly 45: 479-492, 1998
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    Liquid crystal formation in DNA fragment solutions (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 31-37 
    Details
    ISSN: 0006-3525
    Keywords: DNA liquid crystals ; DNA fragments ; screened Coulomb interactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The critical volume fractions pertaining to the formation of DNA liquid crystals were obtained from polarization microscopy, 31P-nmr, and phase separation experiments. The DNA length (approximately one to two times the persistence length 50 nm), ionic strength, and counterion variety dependencies are reported. The cholesteric-isotropic transition is interpreted in terms of the coexistence equations, which are derived from the solution free energy including orientational entropy and excluded volume effects. With the wormlike chain as reference system, the electrostatic contribution to the free energy is evaluated as a thermodynamic perturbation in the second virial approximation with a Debye-Hückel potential of mean force. The hard core contribution has been evaluated with scaled particle theory and/or a simple generalization of the Carnahan-Starling equation of state for hard spheres. For sufficiently high ionic strengths, the agreement is almost quantitative. At lower amounts of added salt deviations are observed, which are tentatively attributed to counterion screening effects. The contour length dependence agrees with a DNA persistence length 50 nm. © 1998 John Wiley & Sons, Inc. Biopoly 46: 31-37, 1998
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    Association of cyclic peptides in aqueous solution measured by fluorescence quenching (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 1-4 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
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    Characterization of lipid membrane dynamics by simulation: I. Torsion angle motions of the linear chains (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 37-50 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The torsion angle motions, generated from molecular dynamics (MD) simulations, of the two aliphatic chains of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in its lipid monolayer were evaluated by comparing these motions to those of an equivalent isolated (free) n-alkane chain, and the same n-alkane chain in its crystal lattice. The time-dependent autocorrelation and (1,2)-, (1,3)-, (1,4)-, and (1,5)-cross-correlation functions were constructed to analyze the torsion angle motions. It was found that the torsion angle motions of the DMPC lipid monolayer aliphatic chains are intermediate to those of the free n-alkane chain and the same n-alkane chain in its crystal lattice, particularly for short correlation times. The torsion angle motions of the aliphatic chains of DMPC are also found to be essentially independent of the charge state on the head group. The linear aliphatic chains of a DMPC lipid monolayer behave most like the isolated n-alkane chains with respect to torsion angle flexibility, even though the pairs of aliphatic chains of each DMPC are part of an ordered monolayer assembly. The aliphatic chains of the DMPC molecules in their monolayer exhibit at least two types of wave motions. One of the wave motions is the same in form, though somewhat more diffuse, as a traveling wave found in n-alkane crystals. The other wave motion involves major torsion angle transitions, and has some characteristics of the soliton properties observed in n-alkane crystals near their respective melt transition temperatures. © 1997 John Wiley & Sons, Inc.
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    A fast and efficient program for modeling protein loops (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 61-72 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We developed an efficient Monte Carlo Simulated Annealing (MCSA) program for modeling protein loops with high speed. The total conformational energy in each step of MCSA simulation consists of two parts: the nonbonded atomic interaction represented by a simple soft-sphere potential and the harmonic distance constraint to ensure the smooth connection of the loop segment to the rest of the protein structure. The soft-sphere potential was a simplified potential that has been successfully used by the authors in modeling the carbohydrate part of glycoprotein systems [H. Zhang, Y. Yang, L. Lai, and Y. Tang (1996), Carbohydrate Research, Vol. 284, pp. 25-34]. It only considers the purely repulsive steric interactions to avoid artificial attractive forces between atoms in the absence of solvent molecules. The N-terminal of the loop segment was connected to the bulk protein part, and two dummy main-chain atoms N and Cα immediately following the C-terminal of the loop segment were constrained to their real positions in the protein structure, which not only assures the correct geometry of loop-protein connection but also is more rigorous than the previous work. To improve the speed, two strategies, the local region method and grid-mapping method, were devised to accelerate the computation of environmental interaction that is responsible for the major part of the computing consumption. The grid-mapping method can reduce computational time dramatically. Conformations with rational steric packing and smooth connection to the rest of the protein structure were generated by the MCSA program, and then were refined by the empirical force field CHARMm [B. R. Brook, R. E. Braccoleri, B. D. Olafson, D. J. States, S. Swaminathan, and M. Karplus (1983), Journal of Computational Chemistry, Vol. 4, pp. 187-217]. Bovine pancreatic trypsin inhibitor (BPTI) was used as an example to test the ability of loop modeling of the method, and five loops in BPTI were calculated. Conformations close to the crystal structure were generated for all of them. With the criteria of CHARMm energy, near-native conformations can be selected, for example, the backbone rms deviation 0.93 A from the crystal structure was gotten for the longest 9-residue loop. © 1997 John Wiley & Sons, Inc.
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    Gelation of gelatin observation in the bulk and at the air-water interface (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 245-252 
    Details
    ISSN: 0006-3525
    Keywords: gelatin ; gelation ; atomic force microscopy ; interfacial rheology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gelation of gelatin under various conditions has been followed by atomic force microscopy (AFM) with the objective of understanding more fully the structure formed during the gelation process. AFM images were obtained of the structures formed from both the bulk sol and in surface films during the onset of gelation. While gelation occurred in the bulk sol, the extent of helix formation was monitored by measurements of optical rotation, and the molecular aggregation was imaged by AFM. Interfacial gelatin films formed at the air-water interface were also studied. Measurements of surface tension and surface rheology were made periodically and Langmuir-Blodgett films were drawn from the interface to allow AFM imaging of the structure of the interfacial layer as a function of time. Structural studies reveal that at low levels of helical content the gelatin molecules assemble into aggregates containing short segments of dimensions comparable to those expected for gelatin triple helices. With time larger fibrous structures appear whose dimensions suggest that they are bundles of triple helices. As gelation proceeds, the number density of fibers increases at the expense of the smaller aggregates, eventually assembling into a fibrous network. The gel structure appears to be sensitive to the thermal history, and this is particularly important in determining the structure and properties of the interfacial films. © 1998 John Wiley & Sons, Inc. Biopoly 46: 245-252, 1998
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    Ribozyme chemogenetics (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 65-81 
    Details
    ISSN: 0006-3525
    Keywords: nucleotide analogue interference mapping ; phosphorothioate ; group I intron ; interference suppression ; RNA ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this review I will outline several chemogenetic approaches used to determine the chemical basis of large ribozyme function and structure. The term chemogenetics was first used to describe site-specific functional group modification experiments in the analysis of DNA-protein interactions. Within the past few years equivalent experiments have been performed on large catalytic RNAs using both single-site substitution and interference mapping techniques with nucleotide analogues. While functional group mutagenesis is an important aspect of a chemogenetic approach, chemical correlates to genetic revertants and suppressors must also be realized for the genetic analogy to be intellectually valid and experimentally useful. Several examples of functional group revertants and suppressors have now been obtained within the Tetrahymena group I ribozyme. These experiments define an ensemble of tertiary hydrogen bonds that have made it possible to construct a detailed model of the ribozyme catalytic core. The model includes a functionally important monovalent metal ion binding site, a wobble-wobble receptor motif for helix-helix packing interactions, and a minor groove triple helix. © 1998 John Wiley & Sons, Inc. Biopoly 48: 65-81, 1998
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    Design, synthesis, and analysis of conformationally constrained nucleic acids (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 83-96 
    Details
    ISSN: 0006-3525
    Keywords: nucleic acid ; disulfide cross-link ; structure ; dynamics ; stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this review I discuss straightforward and general methods to modify nucleic acid structure with disulfide cross-links. A motivating factor in developing this chemistry was the notion that disulfide bonds would be excellent tools to probe the structure, dynamics, thermodynamics, folding, and function of DNA and RNA, much in the way that cystine cross-links have been used to study proteins. The chemistry described has been used to synthesize disulfide cross-linked hairpins and duplexes, higher order structures like triplexes, nonground-state conformations, and tRNAs. Since the cross-links form quantitatively by mild air oxidation and do not perturb either secondary or tertiary structure, this modification should prove quite useful for the study of nucleic acids. © 1998 John Wiley & Sons, Inc. Biopoly 48: 83-96, 1998
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    On the role of magnesium ions in RNA stability (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 113-135 
    Details
    ISSN: 0006-3525
    Keywords: divalent cations ; magnesium ; RNA ; ion binding ; RNA folding ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Divalent cations, like magnesium, are crucial for the structural integrity and biological activity of RNA. In this article, we present a picture of how magnesium stabilizes a particular folded form of RNA. The overall stabilization of RNA by Mg2+ is given by the free energy of transferring RNA from a reference univalent salt solution to a mixed salt solution. This term has favorable energetic contributions from two distinct modes of binding: diffuse binding and site binding. In diffuse binding, fully hydrated Mg ions interact with the RNA via nonspecific long-range electrostatic interactions. In site binding, dehydrated Mg2+ interacts with anionic ligands specifically arranged by the RNA fold to act as coordinating ligands for the metal ion. Each of these modes has a strong coulombic contribution to binding; however, site binding is also characterized by substantial changes in ion solvation and other nonelectrostatic contributions. We will show how these energetic differences can be exploited to experimentally distinguish between these two classes of ions using analyses of binding polynomials. We survey a number of specific systems in which Mg2+-RNA interactions have been studied. In well-characterized systems such as certain tRNAs and some rRNA fragments these studies show that site-bound ions can play an important role in RNA stability. However, the crucial role of diffusely bound ions is also evident. We emphasize that diffuse binding can only be described rigorously by a model that accounts for long-range electrostatic forces. To fully understand the role of magnesium ions in RNA stability, theoretical models describing electrostatic forces in systems with complicated structures must be developed. © 1999 John Wiley & Sons, Inc. Biopoly 48: 113-135, 1998
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    Die ganz normale Wissenschaft. Hrsg. von R. H. Simen. Verlag Deutscher Forschungsdienst, Bonn-Bad Godesberg 1982. 128 S., DM 16,80 (1983)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 67-67 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19830170213
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    Der Widerspruch im eigenen Kopf. Hrsg. von H. Schöne. Verlag Deutscher Forschungsdienst, Bonn-Bad Godesberg 1982. 160 S., DM 18,80 (1983)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 67-67 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19830170214
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    Naturstoffe aus pflanzlichen Zellkulturen (1983)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 77-84 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/ciuz.19830170303
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    Masthead (1983)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983) 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19830170601
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    Chronik (1983)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 202-202 
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    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19830170608
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    Theoriewandel in der Wissenschaftsgeschichte - Chemie im 18. Jahrhundert. Von Elisabeth Ströker. Vittorio Klostermann Verlag, Frankfurt a. M. 1982. VIII, 324 S., DM 68, - (1983)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 17 (1983), S. 200-200 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19830170605
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    Chemical stability of some poly(amide imide) type polymers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 105-112 
    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 Saure- und Alkalibestandigkeit einiger heterozyklischer Poly(amidimid)e wurde mit der von strukturahnlichen Polyimiden und Poly(amidimid)en ohne heterozyklische Gruppen verglichen. Alle untersuchten Polymeren erwiesen sich in saurem Medium als sehr stabil. Der Einbau zusatzlicher Heterozyklen wie 1,3,4- Oxadiazol oder Phenylchinoxalin in die Polymerkette eines Poly(amidimid)s fiihrte zu einer erheblichen Verbesserung der Alkalistabilitat. Polyamide mit Imid-Ringen in der Seitenkette sind bestandiger gegen Hydrolyse als Polyamide mit Imid-Grup-pen in der Hauptkette.
    Notes: The stability of some heterocyclic poly(amide imide)s in acidic and alkaline medium was compared to the structurally related polyimide and poly(amide imide)s without other heterocyclic groups. All the polymers have high stability in acidic medium. The introduction of additional heterocycles such as 1,3,4-0xadiazole or phenylquinoxaline into the macromolecular chain of a poly(amide imide) increases substantially the resistance to alkaline medium. Polyamides containing imide rings only in the side chain are more stable to hydrolysis than related polyamide having imide units in the main chain.
    Additional Material: 4 Ill.
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    Synthesis and modification of a trifunctional epoxy resin with amino-terminated poly(dimethylsiloxane)s for semiconductor encapsulation (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 125-137 
    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: Ein trifunktionelles Hochleistungs-Epoxidharz auf Basis des Triglycidylethers von Tris(4-hydroxyphenyl)methane (TETM) wurde durch Kondensation von 4-Hydroxybenzaldehyd mit Phenol and anschließender Epoxidierung mit Epichlorhydrin hergestellt. Zur Strukturaufklärung wurde das Produkt mittels IR- und NMR-Spektroskopie sowie Masenspektrometrie untersucht. Durch Modifizierung mit einem aminoterminierten Poly(dimethylsiloxan) wurde die Eigenspannung des mit einem Phenolnovolak vernetzten TETM für die Anwendung als Verkapselung elektronischer Bauteile herabgesetzt. Durch das in der TETM-Matrix frei verteilte Silikonelastomere konnte die Spannung des vernetzten Epoxidharzes deutlich reduziert werden, indem der thermische Ausdehnungskoeffizient und der Elastizitätsmodul des Materials verringert wurden, während die Glasübergangstemperatur kaum abnahm.
    Notes: A high-performance trifunctional epoxy resin based on the triglycidyl ether of tris (4-hydroxyphenyl)-methane (TETM) was synthesized by the condensation of 4-hydroxybenzaldehyde with phenol followed by epoxidation with epichlorohydrin. The structure of TETM was confirmed by mass spectra, infrared and nuclear magnetic resonance spectroscopy. Amino-terminated poly(dimethylsiloxane)s were used to reduce the stress of the trifunctional epoxy resin cured with phenolic novolac resin for electronic encapsulation application. The dispersed silicone rubbers effectively reduce the stress of cured epoxy resins by reducing the coefficient of thermal expansion and flexural modulus while the glass transition temperature was hardly depressed.
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    Cationic polymerization using allyl sulfonium salt. 3. Allyl sulfonium salt/ascorbate redox coupleFor parts 1 and 2 cf.8 and 9, respectively. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 149-154 
    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 kationische Polymerisation von Cyclohexenoxid wurde durch Reduktion eines Allylsulfoniumsalzes in Gegenwart von Ascorbyl-6-hexadecanoat und Kupfer(II)-benzoat ausgelöst. Für die Initiation wird eine Redoxreaktion diskutiert, in der die Kupferverbindung als Elektronenüberträger dient.
    Notes: The cationic polymerization of cyclohexene oxide was initiated by reduction of allyl sulfonium salt in the presence of ascorbyl-6 hexadecanoate and copper (II) benzoate. A redox reaction in which the copper compound serving as an electron carrier for the initiation step was proposed.
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    Specialty polymeric membranes, 7. Pervaporation separation of benzene/cyclohexane mixtures with nylon 6-graft-poly(oxyethylene) membranes (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 193-202 
    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: Neuartige Membranmaterialien für die Auftrennung von Benzol/Cyclohexan-Gemischen wurden durch die Pfropfung von Nylon 6 mit Oligooxyethylenen wie Diethylenglykol, Poly(ethylenglykol) 200 (PEG200) und Polyethylenglykol 400 (PEG400) synthetisiert. Membranen aus derartig modifiziertem Nylon 6 zeigten eine Permselektivität gegenüber Benzol, wobei einige der Membranen ausschließlich für Benzol permeabel waren.
    Notes: Novel membrane materials for pervaporation separation of benzene/cyclohexane mixtures were prepared by the introduction of oligo(oxyethylene)s, such as diethylene glycol, poly(ethylene glycol) 200 (PEG200) and poly(ethylene glycol) 400 (PEG400) onto Nylon 6. The polymeric membranes from modified Nylon 6 thus prepared showed permselectivity toward benzene. Some membranes exclusively permeated benzene from benzene/cyclohexane mixture.
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    Mitteilungen/Announcements (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 211-212 
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    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.1997.052450119
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    Allylic polymers from resin acids (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 11-22 
    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 Diels-Alder Reaktion von aus Kolophonium gewonnenen Säuren mit Diallylmaleat wurde ein ungesättigtes Produkt erhalten, welches sowohl als Monomeres als auch als Vernetzer für Allylpolymere verwendet werden kann. Das Monomere und daraus hergestellte Polymere wurden mit üblichen chemischen und physikalischen Methoden charakterisiert. Die Polymeren haben eine lineare Struktur, möglicherweise einhergehend mit intramolekularer Zyklisierung bei niedrigen Molekulargewichten, oder eine dreidimensionale Struktur bei hohen Umsätzen. Sie sind einigermaßen thermostabil.
    Notes: An unsaturated adduct has been synthesized by the Diels-Alder reaction between resin acids and diallyl maleate. The obtained polymerizable product can be used both as monomer in the formation of allyl polymers and crosslinking agent. The monomer and its polymers were investigated by usual physical and chemical methods. The synthesized polymers present a linear structure, possibly associated with intramolecular cyclization at low molecular weights, or a three-dimensional structure at high conversions. They are fairly thermostable substances with carboxylic groups in the polymer chain.
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    Application of molecularly imprinted polymer as a drug retaining matrix (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 65-69 
    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: 2-Hydroxyethylmethacrylat wurde mit Ethylenglycol-dimethacrylate in Gegenwart von Hydrocortison als Modellsubstanz mit Gamma-Strahlen copolymerisiert, wobei ein “molecular imprinted polymer” (MIP) erhalten wurde. Das Hydrocortison wurde mit Chloroform extrahiert und anschließend aus Methanol wieder absorbiert. Nach 30 Tagen Lagerung in einer Methanol/Wasser-Mischung (3:1 v/v) waren noch 96% des Hydrocortisons in der Matrix eingelagert. Im Vergleich zu Hydrocortison wird Testosteron nur in geringer Menge absorbiert.
    Notes: Copolymerization by gamma irradiation of 2-hydroxyethyl methacrylate with ethylene glycol dimethacrylate in the presence of hydrocortisone as model drug gave a molecular imprinted polymer (MIP). The hydrocortisone was removed from the matrix with chloroform and incorporated again from methanol solution. Release data show that 96% of the incorporated drug is retained after 30 days storage in a methanol/water (3 : 1 v/v) mixture. In comparison with hydrocortisone, only a small quantity of testosterone is absorbed by the matrix.
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    Surface modification and bonding of poly(p-phenylene sulfide) (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 97-107 
    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: Es wird gezeigt, daß es sowohl durch Oxidation, z.B. mittels Essigsäure/Wasserstoffperoxid oder Chromschwefelsäure, als auch durch Plasmabehandlung möglich ist, auf Poly(p-phenylensulfid) (PPS)-Oberflächen polare Gruppen einzuführen. Die änderungen and den PPS-Oberflächen wurden mit FTIR-Spektroskopie, Röntgen-Photoelektronenspektroskopie und Kontaktwinkelmessungen verifiziert. Die verbesserte Adhäsion der behandelten Oberflächen wurde mit Hilfe von Zug-Scher-Messungen nach dem Verkleben mit Acrylatklebstoffen quantitativ erfaßt. Die Untersuchung der Oberflächen mittels AFM (Atomic Force Microscopy) zeigt, daß die verbesserte Adhäsion auch durch eine größere Oberflächenrauhigkeit als Folge der Oberflächenbehandlung erreicht wird. Dieser Effekt ist besonders deutlich bei Proben, die mit Chromschwefelsäure behandelt wurden.
    Notes: It is demonstrated that both chemical oxidation, e.g. by using acetic acid/hydrogen peroxide or chromosulfuric acid, and plasma treatment of poly(p-phenylene sulfide) (PPS) surfaces introduce polar groups. The changes of the surface chemistry are detected by FTIR spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements. The increased polarity is partially responsible for better adhesion as verified by lap shear measurements using acrylic adhesive. Another important contribution to the improved adhesion originates from increased surface roughness after surface modification as measured by atomic force microscopy. This effect is very pronounced for PPS surfaces treated with chromosulfuric acid.
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    Die chemische Beständigkeit eines Steinschutzstoffes auf Polyurethanbasis in der künstlichen Bewitterung (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 169-181 
    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: The durability of a polyurethane-based coating material, used as protecting agent on Sander Sandstone, is investigated after different periods of artificial weathering in an environment simulation chamber (VENUS) by means of surface-sensitive methods (ESCA, infrared spectroscopy) and gel permeation chromatography. Only the outermost 4 millimeters showed decay on the polyurethane-chemistry level.
    Notes: Die Dauerhaftigkeit eines Steinschutzstoffes auf Polyurethanbasis im Sander Schilfsandstein gegenüber chemischen Angriffen wurde nach verschieden langen Bewitterungszeiten in einer Versuchsanlage zur naturnahen Umweltsimulation untersucht. Dabei wurden sowohl die Gelpermeationschromatographie (GPC) als auch oberflächensensible Analysenmethoden (XPS und PAS-FTIR) zur Untersuchung der Polyurethan-Mikroschicht im Stein eingesetzt. Nur im Bereich der ersten vier Millimeter Gesteinstiefe konnten bewitterungsbedingte chemische Veränderungen des Polymeren festgestellt werden.
    Additional Material: 8 Ill.
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    Charakterisierung von vernetzten Polymeren, 9a. Verfolgung der Nachvernetzung von Poly(styrol-co-divinylbenzol) zu feinporigen Adsorberpolymeren (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 137-168 
    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: The post-crosslinking of chloromethylated poly(styrene-co-divinylbenzene) to highly crosslinked, porous adsorbent polymers has been studied over a wide range of reaction temperature (50-80°C) and reaction time (up to 24.5 h). The crosslinked materials were characterized by nitrogen adsorption/desorption, mercury porosimetry, determination of the chlorine content, swelling measurements, pyrolysis gas chromatography, and Fourier transform infrared spectroscopy.Surface area, pore size distribution, pore volume, chlorine content, swelling degree, selected peak ratios in the pyrograms and in the FTIR spectrograms are shown to be clear functions of the post-crosslinking time. Therefore the post-crosslinking process can be monitored by physical as well as by chemical characterization methods.Moreover, information on the chemical homogeneity or inhomogeneity of the chloromethylated copolymers and the porous adsorbent polymers can be derived from the swelling and pyrolysis gas chromatographic results. Application of different solvents in the swelling experiments enables the construction of swelling diagrams. Based on these swelling diagrams, the anomalous swelling behaviour of adsorbent polymers during the post-crosslinking can be explained.The surface area and pore volume strongly increase with progressing post-crosslinking, and well-defined correlations between sample texture, pyrolysis and FTIR data are found. In general, changes of physical properties can be attributed to the chemical modification of the material due to the post-crosslinking.
    Notes: Die Nachvernetzung von chlormethyliertem Poly(styrol-co-divinylbenzol) zu hochvernetzten porösen Adsorberpolymeren wurde über einen weiten Temperatur-(50-80°C) und Reaktionszeitbereich (bis zu 24,5 h) untersucht. Die vernetzten Materialien wurden durch Stickstoffadsorption/Desorption, Quecksilberporosimetrie, Bestimmung des Chlorgehalts, Quellungsmessungen, Pyrolyse-Gaschromatographie und Fourier-Transform-Infrarotspektroskopie charakterisiert.Die Oberfläche, die Porengrößenverteilung, das Porenvolumen, der Chlorgehalt, ausgewählte Peakverhältnisse in den Pyrogrammen und den FTIR-Spektrogrammen sind eindeutige Funktionen der Nachvernetzungszeit. Der Nachvernetzungsprozeß kann somit sowohl mit physikalischen als auch mit chemischen Charakterisierungsmethoden verfolgt werden. Darüber hinaus ermöglichen Quellungsmessungen und pyrolysegaschromatographische Untersuchungen Aussagen zur Homogenität und Inhomogenität der chlormethylierten Copolymeren und porösen Adsorberpolymeren.Der Einsatz verschiedener Lösungsmittel bei der Quellung erlaubt die Konstruktion von Quellungsdiagrammen, anhand derer das anomale Quellungsverhalten der Adsorberpolymeren während der Nachvernetzung erklärt werden kann.Im Verlauf der Nachvernetzung werden die Oberfläche und das Porenvolumen stark vergrößert und eindeutige Korrelationen zwischen der Probentextur und den Pyrolyse- und FTIR-Daten gefunden. Die Veränderung der physikalischen Eigenschaften im Verlauf der Vernetzung kann generell auf die chemische Modifikation des Materials zurückgeführt werden.
    Additional Material: 14 Ill.
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    The influence of flame retardant structure on UV stabilization approaches in polypropylene (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 61-72 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: UV stabilization of polymer systems containing brominated flame retardants has proven to be a difficult technical challenge. Generation of acidic products during processing or exposure can cause a catastrophic deactivation of the Hindered Amine Light Stabilizer (HALS). An understanding of the mechanism for bromine generation from aliphatic and aromatic based flame retardants has lead to formulation approaches based on flame retardant structure. In formulations containing aromatic brominated flame retardants, combinations of UV absorbèrs and a new class of siloxane HALS provide the highest level of UV stabilization to date. Alternatively, bicomponent fiber spinning technology can also provide outstanding UV resistance at significantly lower levels of stabilizers than that used in the monocomponent formulation approach.
    Additional Material: 11 Ill.
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    Oxidation kinetics of poly(4-methylpentene) (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 73-89 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal oxidation (in air between 70 and 150°C) of unstabilised camples of poly(4-methylpentene) (PMP) were studied by infrared spectrometry and by gravimetry. The behaviour was compared to PP exposed in the same conditions.The thermal oxidation was found to exhibit two well differentiated kinetic regimes both for PP as for PMP. The first regime predominates at temperature higher than 90°C. It is characterized by an activation energy of the pseudo induction period of about 100 kJ mol-1. The induction period of mass gain is about 1,8 time shorter than the induction period of carbonyl gain. These characteristics, and the fact that induction periods are of the same order for both polymers, are consistent with a «close loop mechanistic» scheme with unimolecular POOH decomposition. The advantages of this hypothesis compared to other proposed hypothesis (bimolecular POOH decomposition, heterogeneous oxidation...) are discussed. The main theoretical difficulty is that of explaining why the unimolecular process predominates, whereas POOH are obviously hydrogen bonded, even at very low conversions of the oxidation process. This point remains to be explained.The second kinetic regime predominates at temperature lower than 90°C. It is characterized by a considerably lower activation energy. We have examined many hypothesis to explain the existence of a transition at that temperature (where neither PMP nor PP display a physical transition). A first hypothesis is that unimolecular POOH decomposition is replaced by a bimolecular one, which can explain a decrease of the apparent activation energy of about 50%. The bimolecular initiation creates pairs of radicals (POO·+ PO·). It can be imagined that a part of them desactivate mutually by termination after rearrangement of PO· by β scission. In this case, the transition at 90°C could be also a result of the temperature induced change in molecular mobility. Above 90°C, the radicals would diffuse almost freely out of the cage. In contrast, below 90°C, termination would become competitive with diffusion. A supplementary research is needed to fully elucidate the cause of this transition at 90°C.The eventuality of the existence of spatial heterogeneity of the oxidation process has been discussed. It is well known that oxidation is heterogeneous at the morphological scale, but there is no evidence of heterogeneity at smaller scale, where the chemical kinetic would not be applicable.
    Additional Material: 9 Ill.
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    Thermal degradation of polystyrene in different environments (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 179-195 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Several aspects of the thermal degradation of polystyrene are highlighted in this communication. The factors involved in determining the ratio of volatile to tar fraction products in the degradation of the pure polymer are examined, leading to the conclusion that the initial melt viscosity plays an important role in determining the balance between intra- and intermolecular transfer. The effect on the degradation of polystyrene of the presence of a second polymer is discussed. For polystyrene-polybutadiene and polystyrene-polyisoprene blends, stabilisation is observed, which is attributed to radical scavenging. The thermal degradation behaviour of polystyrene in the presence of oxygen has been investigated, with and without an antioxidant additive. Products have been characterised for oxidative conditions and the kinetics of degradation have been studied.
    Additional Material: 12 Ill.
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    Controlled degradation in tailor-made macromolecules elaboration. Controlled chain-cleavages of polydienes by oxidation and by metathesis (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 197-211 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A chain cleavage reaction allowing the transformation of high molecular weight polymers in well-defined oligomers can be considered as a step in a synthetic scheme. The control of oligomers with respect to their average molecular weights, their molecular weights distributions and their chain-end microstructures implies the control of the cleavage reaction with respect to its yield, its regiospecificity and its chemiospecificity. Among several examples of efficient uses of this principle for the preparation of liquid oligomers from unsaturated polymers, attention is focused (I) on controlled oxidative degradation of rubber and (II) on metathetical controlled degradation of 1,4-polydienes and polyakenamers. (I.a) The mechanism of the phenylhydrazine accelerated oxidation of rubber in the latex phase is described according to accurate structural studies on molecular model molecules. (I.b) The epoxidation of rubber and periodic acid cleavages of epoxides in the latex phase are interpretated referring to the influence of the biphasic medium. The results are in agreement with interfacial blocky epoxidation by the water-soluble reagent and interfacial arrangement of the epoxidized block to be cleaved. Finally the metathetical degradations resulting from back-bitting cyclisation and cross metathesis with acyclic alkenes are presented as preparative methods to get (II.a) well-defined cyclic oligomers and (II.b) telechclic oligomers (i.e. terminally functionalized oligomers).
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    Chemiluminescence in thermal oxidation of ABS (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 255-268 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two concepts in the chemiluminescence research-the heterogeneous model and the kinetic approach-are discussed. The analysis of published data obtained by a highly sensitive photon-counting system reveals the contradictory nature of the heterogeneous model and proves its inconsistency. On the other hand, the kinetic approach has been successfully applied to evaluation of thermal oxidation in a variety of systems, ABS compositions in particular. Emulsion grade ABS were found to be essentially less stable than ionic mass polymerization products. Among the antioxidants studied, Santonox R is clearly more efficient than Irganox 1076. In emulsion grades the superiority of Santonox R to Irganox 1076 is reflected primarily in larger induction period, while in ionic resin it is mostly due to smaller oxidation rate constant values. The introduction of UV stabilizers by themselves has no influence on durability in either ionic or emulsion resins. Similarly to systems without UV stabilizers, Santonox R is more efficient than Irganox 1076 in mixtures with UV stabilizers as well. The comparative study of various ABS-coloring agent compositions by chemiluminescence and DSC reveals much greater sensitivity of the former. While DSC lets one make only a trivial conclusion that the introduction of an antioxidant improves stability, chemiluminescence shows the differences in durability as large as 3 to 4 times for the samples DSC fails to distinguish. In addition, chemiluminescence furnishes a significant insight on the factors affecting stability. The DSC thermal oxidative stability data can be related to resistance to oxidation during processing, whereas the chemiluminescence results are expected to be useful in predicting materials' lifetime at service temperatures.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052470117
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    Mechanical properties of poly(propylene) filled with calcium carbonate of various shape (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 73-83 
    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: Mit Alkyldihydrogenphosphaten behandeltes Calciumcarbonat unterschiedlicher Teilchenform (sphärisch, kubisch, Nadeln) wurde als Füllstoff für Polypropylen (PP) verwendet. Der Einfluß der Kettenlänge der Alkylgruppe auf mechanische Eigenschaften (Zugdehnung, Zugfestigkeit, Schlagzugfestigkeit, Streckspannung) und die Adhäsion zwischen der PP-Matrix und den verschiedenen CaCO3-Teilchen wurde untersucht, ebenso der Einfluß der Teilchenform auf den Speichermodul des mit unbehandeltem CaCO3 gefüllten und verstreckten PP.Zugdehnung, Schlagzugfestigkeit und Adhäsion des mit kubischem bzw. nadelförmigem CaCO3 gefüllten PP nehmen mit steigender Kettenlänge der Phosphat-Alkylgruppe zu, während das mit sphärischem CaCO3 gefüllte PP keine einheitliche Tendenz zeigt.Die relativen Moduli Edc/Edr (Edc - Speichermodul der verstreckten Komposite; Edr - Speichermodul der ungefüllten verstreckten PP-Matrix) der verstreckten PP/CaCO3-Komposite lassen sich mit einer modifizierten Halpin-Tsai-Gleichung beschreiben, in der die Faktoren (i) Orientierung der Polymermatrix, (ii) Einfluß des Füllstoffes (Gehalt, Modul, Kantenverhältnis) und (iii) Hohlraumvolumen an der Grenzfläche Polymer-Füllstoff enthalten sind.
    Notes: Calcium carbonate of various particle shape (CaCO3, sphere, cube, needle) treated with alkyl dihydrogen phosphate ester (APEN, CnH2n+1OPO(OH)2, n = 1, 4, 8, 10, 12) and poly(propylene) (PP) were mixed on a two roll mill. The effect of carbon number of APEN on the mechanical properties (tensile elongation, tensile strength, impact strength, yield stress) and adhesion between PP matrix and various CaCO3 particles and the effect of CaCO3 shape on the storage modulus of elongated PP/CaCO3 has been investigated.The tensile elongation, impact strength and adhesion of PP-CaCO3 interface increased with carbon number of APEN (n ≦ 10) for needle and cube type, but the dependence of tensile properties on APEN carbon number is not clearly recognized for the sphere type.The relative storage moduli of elongated PP/CaCO3, Edc/Edr Edc - modulus of elongated PP/CaCO3 (untreated); Edr - modulus of elongated PP matrix could sufficiently be described with a modified Halpin-Tsai equation, which contains the factors of (i) polymer matrix orientation, (ii) particle effect (content, modulus, aspect ratio), and (iii) void volume at polymer-filler particle interface.
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    Permeability of CO2 through chitosan membrane swollen by water vapor in feed gas (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 85-94 
    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: In der vorliegenden Studie wurde die Permeation und Separation von Kohlendioxid durch eine wassergequollene Chitosanmembran untersucht. Die Chitosanmembran wurde durch in einem Trägergas enthaltenen Wasserdampf gequollen und zeigte nach dieser Behandlung eine hohe Gaspermeabilität. Bei Raumtemperatur durchdrang vorzugsweise Kohlendioxid die gequollene Chitosanmembran mit einer Permeabilität von 2,5·10-8 cm3 (STP) cm(s cm2 cmHg)-1 und einem CO2/N2 Trennfaktor von 70.Diese Trennleistung für Kohlendioxid wird durch die basischen Eigenschaften der Aminogruppen den Chitosanmolekülen hervorgerufen.Die Membranherstellungsbedingungen, wie zum Beispiel die Essigsäurekonzentration der Gießlösung, beeinflußten die Permeationsgeschwindigkeit. Der Einfluß der Arbeitstemperatur wurde ebenfalls untersucht. Um die Trennleistung der Membran zu erhöhen, wurden verschiedene Methoden der Membranbehandlung und Arbeitsbedingungen untersucht.
    Notes: The permeation and separation of carbon dioxide through a water-swollen chitosan membrane was studied. A chitosan membrane was swollen by water vapor contained in a feed gas and, thus treated, exhibited a large gas permeability. Carbon dioxide preferentially permeated through the swollen chitosan membrane with a permeability of 2.5·10-8 cm3 (STP) cm(s cm2 cmHg)-1 and a CO2/N2 separation factor of 70 at room temperature. This separation performance for CO2 resulted from the basic properties of the chitosan amino groups. The membrane preparation conditions, such as acetic acid concentration of the casting solution, affected the membrane permeation rate. The effect of the operation temperature was also measured. To increase the separation performance of the membrane, several methods of membrane treatment and operation were evaluated.
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    Modifizierung von Faseroberflächen durch die permanente Fixierung supramolekularer Komponenten, Teil 1: GrundlagenAuszug aus der eingereichten Dissertation von U. Denter, Universität Duisburg 1997. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 153-163 
    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: A new conception for modification of textile surfaces by permanent fixation of supramolecular components is explained. The principle of selective complexation is illustrated. Cyclodextrins, aza crown ethers, calixarenes, cyclotriveratrylenes and fullerenes are mainly suggested as suitable ligands for that procedure. The chemical structure and the complexation behaviour of the substances are described. Some surface properties which may be obtained with the ligands are especially emphasized.
    Notes: Ein neues Konzept zur Modifizierung von Faseroberflächen durch permanente Fixierung supramolekularer Verbindungen wird vorgestellt, und das Prinzip der selektiven Komplexierung wird erklärt. Als für die Behandlung grundsätzlich geeignete Liganden werden insbesondere Cyclodextrine, Azakronenether, Calixarene, Cyclotriveratrylene und Fullerene hinsichtlich ihrer chemischen Struktur sowie ihrer komplexierenden Eigenschaften beschrieben. Einige erreichbare Oberflächeneffekte werden hervorgehoben.
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    New preparation method of poly(amide-imide)s using direct polycondensation with thionyl chloride and their characterization (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 105-122 
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    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: Ein neues, wirtschftliches Verfahren zur Herstellung hochmolekularer Poly(amidimid)e (PAIs) basiert auf der direkten Polykondensation von Trimellitsäureanhydrid(TMA) oder Diimid-Disäuren (DIDAs) mit aromatischen Diaminen in Gegenwart von äquimolaren Mengen an Thionylchlorid in N-Methylpyrrolidon bei relativ niedrigen Temperaturen. Die Polyamidierung von Diimid-Disäuren und Diaminen zu Kopf-Kopf-Polymeren (H-PAIs) ist temperaturempfindlich und verläuft rasch; die Reaktionsdauer von 1 h war für die vollständige Umsetzung ausreichend. Der höchste Wert für die inhärente Viskosität ηinh wurde mit 72 mL g-1 bei Polymerisation bei Raumtemperatur erzielt. Durch die Polykondensation von TMA mit Diaminen und anschließende Imidisierung nach verschiedenen Methoden, wie die azeotrope Dehydrierung bzw. die Festphasenimidisierung von Polyamsäuren oder der Einsatz von Triphenylphosphit als Cokondensationsagens, wurden ebenfalls einige statistisch aufgebaute Polymere (R-PAJs) hergestellt. Von den Imidisierungsmethoden ergab die Festphasenimidisierung von Polyamsäuren mit inhärenten Viskositäten ηinh von 58-85 mL g-1 zufriedenstellende Ergebnisse. Imidisierungsgrade und Molekulargewichte wurden im wesentlichen von der Lösungsmittelmenge sowie der Imidisierungstemperatur und -zeit bestimmt. Sowohl H-PAI als auch R-PAI zeigten gute mechanische Eigenschaften, je nach Ausgangsmonomeren lagen die Zugfestigkeiten im Bereich 118-131 MPa und die Glasübergangstemperaturen im Bereich von 263-299°C. Die Schmelzviskositäten der PAIs bewegten sich zwischen 7,4·103 und 4,5·103 Pa s für H-PAI bzw. R-PAI und sind mit dem Wert fur konventionelles PAI, Torlon® 4000T, von 5,6·103 Pa s vergleichbar.
    Notes: A study for the development of a new, economical manufacturing process for high-molecular-weight poly(amide-imide) (PAI) was performed via direct polycondensation of trimellitic acid anhydride (TMA) or diimide diacids (DIDAs) with aromatic diamines using an equimolar amount of thionyl chloride in NMP at relatively low temperatures. The polyamidation of DIDAs and diamines for head-to-head polymers (H-PAIs) was sensitive to the reaction temperature and proceeded very quickly, 1 h was sufficient to complete the reaction. The highest value of inherent viscosity, ηinh, of 72 mL g-1 was obtained by polymerization at room temperature. Also several randomly sequenced polymers (R-PAIs) were prepared by polycondensation from TMA and diamines, followed by imidization with various methods, such as using TPP as a co-condensing agent, azeotropic dehydration of polyamic acid (PAA) and solid-state imidization from PAA. Solid state imidization from polyamic acids at 235°C gave satisfactory results with an inherent viscosity 58-85 mL g-1. Solvent content, imidization temperature and time were major controlling factors for the degree of imidization as well as for the molecular weight. Both H-PAI and R-PAI showed good mechanical properties with tensile strength of 118-131 MPa and Tg ranged between 263-299°C depending on the nature of monomers. The melt viscosity of the PAIs ranged between 7.4 · 103 and 4.5 · 103 Pa s for H-PAI and R-PAI respectively. These values are comparable to that of conventional PAI, Torlon® 4000T of 5.6 · 103 Pa s.
    Additional Material: 3 Ill.
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    MITTEILUNGEN/ANNOUNCEMENTS (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 217-217 
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    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.1997.052480114
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    Carbon fibre oxidation, textural and surface changes (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 201-215 
    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: In dieser Arbeit werden die durch Oxidation mit Salpetersäure hervorgerufenen Veränderungen der spezifischen Oberfläche, Porosität, Oberflächenfunktionalität und der Faserdimensionen handelsüblicher Kohlenstoffasern untersucht. SEM-Untersuchungen ergaben keine Veränderungen, jedoch konnten durch Kryptonadsorptionsmessungen erhöhte spezifische Oberflächen-und Mikroporositätswerte nachgewiesen werden.Die oxidative Behandlung beeinträchtigt die Faserlänge und verringert, wenn auch nur geringfügig, den Faserdurchmesser und die Festigkeit, wie aus Messungen des Elastizitätsmoduls hervorgeht.Die durch volumetrische Messungen und XPS durchgeführte Funktionalitätsanalyse zeigt eine erhöhte Gesamtoberflächenazidität aufgrund einer Zunahme der Carboxygruppen. Längere Behandlung der Fasern vermindert den Gehalt an Hydroxygruppen an der Faseroberfläche.
    Notes: This work reports on the variations in specific surface, porosity, surface functionality and dimension of commercial carbon fibre subjected to oxidative treatment with nitric acid. Scanning electron microscopy (SEM) observation did not reveal any topographic changes on the fibres, although crypton adsorption evidences increases in specific surface and microporosity.Oxidative treatment has an effect on fibre length, although it also slightly reduces the fibre diameter and the fibre strength, as measured in terms of the elastic modulus.Functional analysis by means of volumetric measurements and X-ray photoelectron spectroscopy (XPS) reveals an increase in the overall fibre surface acidity through carboxy group increase. Prolonged treatment gradually removes hydroxy groups from the fibre surface.
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    Influence of emulsifier and initiator concentration on the copolymerization of 1,4-divinylbenzene with comonomers of different solubility in water (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 183-201 
    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 Konzentration von Natriumdodecylsulfat und von 2,2′-Azoisobutyronitril auf die vernetzende Emulsionscopolymerisation von 1,4-Divinylbenzol mit hydrophobem Cyclohexylmethacrylat und mit hydrophilem Methylacrylat wurde untersucht. Um festzustellen, welche Rolle die Diffusion von Monomeren bei der Copolymerisation spielt, wurden die Emulsionen durch gemeinsame und getrennte Solubilisierung hergestellt. Der Monomerumsatz wurde bestimmt. Die erhaltenen Microgele wurden bezüglich Molmasse, Teilchendurchmesser und Grenzviskositätszahl charakterisiert. Beim übergang von einer normalen zu einer mizellaren Emulsion war der Umsatz maximal. Mit dem hydrophoben Comonomeren bildete sich bei Verringerung der Emulgatormenge zunehmend unlösliches Koagulat aus polymerisierten Monomertröpfchen. Mit höherer Emulgatorkonzentrationen entstand zunehmend unlösliches Agglomerat durch Reaktion von Mikrogelteilchen miteinander.
    Notes: The influence of the concentration of sodium dodecylsulfate and 2,2′-azoisobutyronitrile on the crosslinking emulsion copolymerization of 1,4-divinylbenzene with hydrophobic cyclohexyl methacrylate and with hydrophilic methyl acrylate was studied. The emulsions were prepared by joint and by separate solubilization to study diffusion effects. Monomer conversion was measured and the microgels were characterized by molar mass, particle size diameter and intrinsic viscosity. The monomer conversion was maximal in the transition from a normal to a micellar emulsion. With the hydrophobic comonomer increasingly insoluble coagulates from polymerized monomer droplets were formed on decreasing the emulsifier concentration. Toward higher emulsifier concentration increasingly insoluble agglomerates were formed by reactions between microgels.
    Additional Material: 14 Ill.
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    Effect of accelerated exposure conditions on the photodegradation of BPA polycarbonate/ABS blends (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 1-18 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A BPA polycarbonate/ABS blend containing 2% TiO2 was exposed to xenon are irradiation under SAE J 1885 conditions (quartz/borosilicate filters). “CRD” conditions (borosilicate/borosilicate filters), and ASTM D4459-86 conditions (borosilicate/soda lime filters). The results are consistent with the conclusion that polycarbonate dominates the photochemistry of polycarbonate/ABS blends under SAE J1885 and CRD xenon are exposure conditions. Exposure under ASTM D4459-86 conditions produced results similar to CRD conditions with some additional contribution attributable to the ABS component. The “activation spectrum” of PC/ABS blends under CRD conditions closely resembled the sum of the activation spectra of ABS and PC determined under similar conditions. The well-known change in mechanism that occurs when polycarbonate is exposed to light with wavelengths 〈 300 nm was manifested by increased rates of yellowing, surface erosion. and loss of gloss under SAE J 1885 conditions. Because of the mechanism change, testing under quartz/borosilicate filtered xenon are exposure cannot be considered to be appropriate for polycarbonate-containing formulations.
    Additional Material: 15 Ill.
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    Degradation of ultra high molecular weight polyethylene in vivo (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 31-43 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mechanical and thermal oxidation of UHMWPE used in the preparation of prosthetic implants is studied and the mechanisms of degradation are reported. Oxidation of new and retrieved prosthetic implants are studied by IR microscopy and clear evidence of oxidation in vivo is shown.
    Additional Material: 9 Ill.
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    Mechanical and morphological properties of stabilized and non-stabilized HDPE films versus exposure time (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 91-110 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Non UV-stabilized and UV-stabilized (a UV-absorber) HDPE films were photo-oxidized in a Xenotest. The concentration of carbonyl and the UV-stabilizer, the molecular weight, the crystallinity and the density were studied versus exposure time. Furthermore, the mechanical behaviour was studied at different strain rates by tensile testing.The number of chain scissions was found equal to the number of carbonyl groups. The density of the film increased from 950 to 970 kg/m3 and the crystallinity from 70 to 82%. The increase in density is explained by the increase in crystallinity and by oxygen uptake.The rate at which carbonyl groups are formed, was found to accelerate with exposure time. This acceleration finally resulted in profiles, which could be measured by FT-IR and verified by computer simulations.After 14 days of exposure the specimen failed in a brittle manner. An activation volume was calculated and found to decrease. It is thought that a change in molecular mobility is responsible for the lower strain at yield values. The change in molecular mobility can also explain the increase in Young's modulus with the strain rate and exposure time. The Takayanagi and the Halpin/Tsai models were used to describe the increase of modulus of elasticity.
    Additional Material: 23 Ill.
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    Applicability and limitations of current lifetime prediction models for thermoplastics pipes under internal pressure (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 131-145 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Engineering thermoplastics, in particular polyolefins such as special grades of poly(ethylene), are gaining importance in pipe applications such as gas and water supply systems. To ensure proper performance of such pipes over the required lifetime, polymer physics and mechanics concepts are needed to adequately account for the effects of time, temperature, and environmental conditions as well as the occurrence of pipe defects and imperfections on relevant polymer properties and pipe performance. This article provides a critical overview of the scientific background of current methodologies to describe the long-term behavior of thermoplastic pressure pipes. In particular, the merits and limitations of two different approaches-namely, the standard extrapolation method (SEM) described in ISO/TR 9080 and the linear elastic fracture mechanics (LEFM) approach-are compared. Special attention is given to effects associated with material ageing and degradation.
    Additional Material: 10 Ill.
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    Polymers degradable under environmental conditions through end-modification of poly(α-methylstyrene) derivatives (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 163-178 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: To induce degradabilities in polymers in response to environmental conditions, the end-modification reactions of poly(α-methylstyrene) derivatives were carried out. When diphenylphosphine chloride was used as a modifier for the living end of para-substituted PMS, the coupling efficiency was ca. 50%. 2-Phenylallyl halide derivatives such as 2-phenylallyl bromide, 2-(4-tolyl)allyl bromide, and α-trifluoromethylstyrene were found to be suitable end-modification agents. For example, ω-2-phenylallyl PMS was prepared with almost quantitative functionality by the reaction of the living PMS with 2-phenylallyl bromide. In a similar way, ω-3,3-difluoro-2-phenylallyl and ω-2-(4-tolyl)allyl PMS derivatives were synthesized. Based on thermogravimetric analysis, onset of the degradation temperature of the end-modified PMS derivatives decreased in the following order: ω-hydrogen- 〉 ω-3,3-difluoro-2-phenylallyl- 〉 ω-2-phenylallyl- 〉 ω-2-(4-tolyl)allyl-PMS. Actually, the onset temperature of ω-2-(4-tolyl)allyl-PMS derivatives was 50°C lower than that of ω-H-PMS derivatives. These results indicate that the active species is produced effectively at the end unsaturated bond, which initiates the depolymerization of the polymer at rather low temperatures. Ionic degradation of these polymers was also investigated using butyllithium as an anionic initiator and methanesulfonic acid as a cationic initiator. Tendencies similar to the thermal degradation were observed. Therefore, it is concluded that a 2-phenylallyl substituent at the end of the PMS chain induces effective degradation through several mechanisms such as radical, anionic and cationic depolymerization reactions.
    Additional Material: 8 Ill.
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    Complexity of the hydrolytic degradation of aliphatic polyesters (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 239-253 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aliphatic polyesters are more or less hydrolytically degradable, depending on their chemical, configurational and morphological structures. Hydrolysis can be either homogeneous or heterogeneous, depending on many structural and environmental factors. The present understanding of this hydrolytic degradation is recalled. The importance of diffusion-reaction phenomena is discussed on the basis of the behaviors of polyesters derived from α-hydroxy acids, namely lactic and glycolic acids and attempts are made to extend the understanding to other members of the aliphatic polyester family. The main results of some recent investigations of the effects on poly(lactic acid) polymers of basic additives and of initiators such as stannous octoate and zinc metal, which are now industrially used, are presented.
    Additional Material: 3 Ill.
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    Reactions and kinetic modelling of silicone-carbon resins (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 1-21 
    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 Berechnung der mittleren Molekulargewichte einer idealen, nichtlinearen, stufenweise ablaufenden Polymerisation von Comonomeren mit mehreen reaktiven Zentren im B-Zustand vor der Gelierung wird beschrieben. Ein kinetisches Modell wird angewendet, um den Verlauf der Polymerisation unter Berücksichtigung der Massenverhältnisse der möglichen, unterschiedlich substituierten Verbindungen zu simulieren. Die Molekulargewichte werden entweder durch Anwenden der Miller-Macosko-Methode oder durch Lösen der Diffentialgelicheungen für die Polymerisation von Verbindungen mit niedrigem Molekulargewicht erhalten. Die Näherung wird angewendet auf die mit Platin katalysierte Hydrosilylierung von methylsubstituiertem Cyclosiloxan mit Dicyclopentadien zu einem Hochleistungs-Silikon-Kohlenstoff-Harz. Die Näherung ergibt die Konzentrationen und Molekulargewichte der verschiedenen, zu jedem beliebigen Zeitpunkt der Reaktion vorhandenen Verbindungen. Unterschiedliche Arten der Monomeraddition können ebenfalls simuliert werden.
    Notes: This paper aims to calculate the average properties of ideal non-linear stepwise polymerization of comonomers containing multiple reacting sites at the B-stage prior to gelation. A kinetic model is used to simulate the polymerization process taking into account the mass balances of differently substituted species possible. The molecular weights are obtained either by the use of the Miller-Macosko method or by solving the differential equations for the polymerization of low-molecular-weight species. The approach is applied to the Pt-catalyzed hydrosilation reaction between methyl-substituted cyclosiloxane and dicyclopentadiene which produces a high-performance silicone-carbon. resin. The approach gives the concentrations of various species present at any given time and the molecular weights. Different modes of monomer addition can also be simulated.
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    Preparation and characterization of copolymers from methyl methacrylate and cardanyl methacrylate (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 95-104 
    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: Copolymere aus Methylmethacrylat (MMA) und Cardanylmethacrylat (CMA) wurden synthetisiert, charakterisiert und hinsichtlich ihre physikomechanischen Eigenschaften untersucht. Die mit Benzoylperoxid initiierte Copolymerisation wurde mit unterschiedlichen Anteilen von CMA(0,02-0,01 mol/mol) im Reaktionsansatz bei 80°C durchgeführt. Die Strukturen der Copolymeren wurden mit FTIR- und 1H-NMR-Spektroskopie charakterisiert. Die thermische Stabilität der Copolymeren wurde mit dynamischer Thermogravimetrie bestimmt. Es zeigte sich, daß die thermische Stabilität der Polymeren durch den Einbau von CMA in die MMA-Hauptketten verbessert wird.
    Notes: Copolymers of methyl methacrylate (MMA) and cardanyl methacrylate (CMA) were synthesized, characterized and their physico-mechanical properties were investigated. The benzoyl peroxide-initiated copolymerization was carried out by using different mole fractions of CMA (0.02-0.10) in the initial feed at 80°C. Structural characterization of copolymers was done using FTIR and 1H NMR spectroscopic techniques. The thermal stability of the copolymers was evaluated using dynamic thermogravimetry. Incorporation of CMA in the MMA backbone leads to an improvement in thermal stability.
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    Study on the kinetics of interfacial polycondensation for polyarylate (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 123-137 
    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 Kinetik der Polyarylastynthese durch Grenzflächenpolykondensation von Bisphenol A mit Tere-/Isophthalsäuredichlorid wurde durch UV-spektrometrische Verfolgung der Bisphenolatkonzentration in der wäßrigen Phase untersucht. Der Reaktionsmechanismus besteht aus drei Schritten, von denen der dritte Schritt geschwindigkeitsbestimmend ist: 1. Transport von Bisphenolat in der wäßrigen Phase; 2. Transfer von Bisphenolat durch die Grenzschicht und Transport in der organischen Phase; 3. Reaktion von Bisphenolat mit Säuredichlorid in der organischen Phase. Der Einfluß der Konzentration der Reaktanden in der wäßrigen bzw. organischen Phase und der Menge des Phasentransferkatalysators auf den Verlauf der Grenzflächenpolykondensation wurde untersucht.
    Notes: For the synthesis of polyarylate by interfacial polycondensation of bisphenol A with terephthaloyl/isophthaloyl dichloride, the kinetic mechanism was studied through the detection of the concentration of bisphenolate in the aqueous phase by UV spectrometry. The mechanism consists of three steps: 1. the transportation of bisphenolate in the aqueous phase, 2. the transfer of bisphenolate through the interface followed by its transportation in the organic phase, 3. the reaction of bisphenolate with the phthaloylic dichloride in the organic phase. The reaction of bisphenolate with the phthaloylic dichloride in the organic phase is the rate-determining step. The influence of the concentration in either the aqueous phase or the organic phase and of the quantity of the phase transfer agent on interfacial polycondensation were studied.
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    Preparation and properties of composites of kevlar-nomex copolymer and boehmite (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 139-151 
    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: Ein neuartiges organisch-anorganisches Hybridmaterial wurde durch den Einbau des Minerals Böhmit mittels eines Sol-Gel-Prozesses in ein Kevlar-Nomex-Copolymeres hergestellt. Durch Reaktion eines Gemisches aus m- und p-Phenylendiamin mit Terephthaloylchlorid und anschließender Umsetzung mit Aminophenyltrimethoxysilan wurden Poly(phenylenterephthalamid)-Ketten mit Aminophenyltri-methoxysilan-Endgruppen synthetisiert. In dieser Polymermatrix wurde die Hydrolyse der Alkoxygruppen einer Lösung von Aluminium-sec-butanolat in Butanol durchgeführt. Dadurch wurde ein chemisch an die Aramid-Ketten gebundenes anorganisches Netzwerk aufgebaut. Aus den hergestellten Hybridmaterialien mit unterschiedlichen Böhmit-Gehalten in der Aramidmatrix wurden Filme gegossen. Die Filme aus Hybridmaterial mit bis zu 15 Gew.-% Böhmit waren transparent gelb, während bei 20 und mehr Gew.-% Böhmit opake Filme erhalten wurden. Die mechanischen Eigenschaften dieser Filme wurden untersucht. Zugfestigkeit, Zugmodul, Härte und maximale Bruchdehnung nahmen mit steigendem Böhmitgehalt zunächst zu, vemngerten sich jedoch bei weiterer Erhöhung des Mineralanteils wieder. Der Zugmodul des Hybridmaterials bei 25°C lag zwischen 3,0 und 4,5 GPa. Die Materialien hielten einer maximalen Zugspannung von 252 MPa stand und zeigten Zersetzungstemperaturen von etwa 450°C. Die rnit DMTA ermittelten Werte für den Speichemodul lagen im Bereich 7,6-18,9 GPa. Das tan δ-Signal verbreiterte sich mit zunehmendem Böhmitanteil und ging bei hohen Böhmitgehalten in eine Schulter über. Die Signalpositionen des Verlustfaktors wurden infolge der zunehmenden sterischen Einschränkung der Segmentbewegungen rnit steigendem anorganischen Anteil zu höheren Temperaturen verschoben.
    Notes: A new organic-inorganic hybrid material was prepared by incorporating boehmite into a Kevlar-Nomex copolymer via a sol-gel process. Poly(phenylene-terephthalamide) chains having aminophenyltrimethoxysilane end groups were prepared by reacting a mixture of m-and p-phenylenediamine with terephthaloyl chloride, followed by end-capping with aminophenyltrimethoxysilane. The hydrolysis of the alkoxy groups of an aluminium sec-butoxide solution in butanol was carried out in the polymer matrix, thus creating an inorganic network structure combined chemically with the aramid chains. Hybrid materials containing different proportions of boehmite in aramid were thus produced and films were cast by solvent evaporation technique. These films with up to 15 wt.-% of boehmite were yellow and transparent, whereas the films with 20 wt.-% or more contents of boehmite were opaque. Mechanical properties of these films were analyzed. The values of tensile strength, initial modulus, toughness and maximum strain at rupture were initially found to increase and then decrease with further addition of boehmite. The tensile modulus of the hybrid material was found to be in the range of 3.0-4.5 GPa at 25°C. These ceramers were found to withstand maximum tensile stress of the order of 252 MPa, and the thermal decomposition temperature was around 450°C. The storage modulus as measured using DMTA was in the range of 7.6-18.9 GPa. The tan δ peak which in general became broader with increasing boehmite content showed a shoulder for composites containing large amounts of boehmite. The position of the peaks shifted towards high temperature with the increase in the inorganic contents showing hindrance in motion with increasing boehmite contents.
    Additional Material: 8 Ill.
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    Crystallization behavior of poly(propylene)/polyamide 1010 blends using poly(propylene)-graft-glycidyl methacrylate as compatibilizer (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 248 (1997), S. 189-200 
    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: Blends aus Polyamid 1010 (PA 1010) und Polypropylen(PP) wurden mit oder ohne Zusatz von Polypropylen-Glycidylmethacrylat-Pfropfcopolymeren (PP-g-GMA) untersucht. Der Einfluß dieses Verträglichkeitsvermittlers auf die thermischen Eigenschaften und das Kristallisationsverhalten der Blends wurde mit Differentialkalorimetrie und Weitwinkel-Röntgenbeugung ermittelt. Die Ergebnisse zeigen, daß die Kristallisation von PA 1010 durch PP-g-GMA merklich beeinflußt wird. PP/PA 1010 (75/25)-Blends mit höheren PP-g-GMA-Gehalten weisen eine konkurrierende Kristallisation der Phasen bei der Kristallisationstemperatur des Polypropylens auf. Die Kinetik der isothermen Kristallisation wurde untersucht, um den Einfluß der Verträglichkeitsvermittlung auf die Keimbildung und den Mechanismus des Keimwachstums zu beurteilen. In PP/PA 1010 (25/75)-Blends wurde trotz hoher PP-g-GMA-Gehalte keine konkurrierende Kristallisation beobachtet.
    Notes: Polyamide 1010/poly(propylene) (PA1010/PP) blends were investigated with and without the addition of poly(propylene)-graft-glycidyl methacrylate (PP-g-GMA). The effect of the compatibilizer on the thermal properties and crystallization behavior was determined by differential scanning calorimetry and wide-angle X-ray diffraction. From the results it is found that the crystallization of PA 1010 is significantly affected by the presence of PP-g-GMA. PP/PA 1010 (75/25) blends containing higher amounts of PP-g-GMA show concurrent crystallization at the crystallization temperature of PP. Isothermal crystallization kinetics also were performed in order to investigate the influence of the compatibilized process on the nucleation and growth mechanism. In the PP/PA 1010 (25/75) blends, concurrent crystallization behavior was not observed, even though the amount of PP-g-GMA was high.
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    Mechanical properties-structure relationships of crosslinked blends based on LDPE/HDPE waste (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 47-57 
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    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: Aus Abfällen von Polyethylen niedriger Dichte (LDPE) und Polyethylen hoher Dichte (HDPE) mit unterschiedlichen Abbaugraden wurden Blends hergestelt und deren strukturelle, mechanische und rheologische Eigenschaften untersucht. Durch die Zumischung von 2 Gew.-% Dicumylperoxid konnte sowohl die Zugfestigkeit als auch die Bruchdehnung der Proben verbessert werden, ohne daß sich die Schmelzelastizität der LDPE- bzw. HDPE-Abfälle und deren Blends gegenüber nichtmodifiziertem Material merkbar verringerte. Außerdem wurde durch DSC-Messungen eine verbesserte Kompatibilität zwischen LDPE und HDPE festgestellt.
    Notes: Low-density polyethylene (LDPE) waste was blended with high-density polyethylene (HDPE) waste of different degrees of degradation. Structural, mechanical and rheological properties of these blends were investigated. It was found that 2 wt.-% of dicumyl peroxide improves simultaneously the tensile strength and elongation at break without serious decrease of the melt elasticity of separate PE wastes and their binary blends in comparison with unmodified PE. It was shown by DSC analyses that modification of the blends leads to better compatibility between LDPE and HDPE.
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    Polymerization of butadiene and isoprene with the NdCl3 · 3TBP-TIBA catalyst system (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 59-77 
    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 Polymerisation von Isopren und Butadien mit dem NdCl3 · 3TBP-TIBA-Katalysatorsystem (TBP: Tributylphosphat, TIBA: Triisobutylaluminium) wurde mit einer sehr exakten experimentellen Technik detailliert untersucht. Die Einflüsse der Ausgangsmonomerenkonzentration, der Polymerisationstemperatur und der Katalysator- und Cokatalysatorkonzentrationen auf den Umsatz, die mittlere Molmasse, die Molmassenverteilung und die Mikrostruktur der Polymeren werden diskutiert und unter Berücksichtigung der durch Neodym-Atome mit endständigen Monomereinheiten der Polymerkette gebildeten Allyl-Komplexe erklärt. Die Untersuchungen ergaben für die Monomeren eine Reaktion erster Ordnung. Die berechnete Aktivierungsenergie (25.58 kJ mol-1) ist niedriger als für klassische Ziegler-Natta-Katalysatoren und zeigt die höhere katalytische Aktivität des eingesetzten NdCl3 · 3TBP-TIBA-Katalysatorsystems. Die Ergebnisse von GPC-Messungen weisen auf zwei mögliche aktive Zentren hin, von denen jenes mit Aluminium eine höhere Stabilität aufweist und die Umwandlung von “anti”-Allyl-Gruppen in “syn”-Allyl-Gruppen begünstigt. Der Gehalt der Polymeren an 1,4-cis-Einheiten wird hauptsächlich von der TIBA-Konzentration bestimmt. Der Katalysator geht jedoch keine übertragungsreaktionen ein, wie dies bei TIBA der Fall ist. Die Umsätze sind für Butadien aufgrund der ausgeprägteren Tendenz zur Bildung von Allyl-Komplexen mit Neodym-Atomen höher als für Isopren.
    Notes: The isoprene and butadiene polymerization processes with the NdCl3 · 3TBP-TIBA catalyst system (TBP: tributylphosphate, TIBA: triisobutylaluminium) are studied in detail using an original and very accurate experimental technique. The influences of the initial monomer concentration, the polymerization temperature and the catalyst and cocatalyst concentrations on the conversion, the average molar masses, the polydispersity and the microstructure of the polymers are discussed and explained considering the allylic complexes formed between the neodymium atom and the last monomer unit in the macromolecular chain. A first-order reaction with respect to the monomer was obtained. The calculated value of the activation energy (25.58 kJ mol-1) is lower than for classical Ziegler-Natta catalysts, thus demonstrating the higher catalytic activity of the NdCl3 · 3TBP-TIBA catalyst system used. Two types of active centers are possible, as confirmed by GPC data. One of them, which includes aluminium, is more stable and favors the transformation from “anti” allylic units to “syn” allylic units. Thus, the 1,4-cis unit content of the prepared polymers is mainly determined by the TIBA concentration. The catalyst does not react by transfer reactions as TIBA does. The obtained conversions are always higher for butadiene than for isoprene due to a higher tendency of the former to complexate with the neodymium atom and forming allylic complexes.
    Additional Material: 14 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052490105
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    Heat-shrinkable films based on polyolefin waste (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 151-162 
    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: Polyethylen-Abfälle (LDPE, HDPE sowie Blends aus beiden) wurden energiereicher Gammastrahlung aus einer 60Co-Quelle ausgesetzt. Durch die so induzierte Vernetzung des Polyethylens konnte das Material zu Schrumpffolien verarbeitet werden. Die Zugfestigkeit der Proben konnte durch Erhöhung der Strahlendosis bis auf 20 Mrad entscheidend verbessert werden, wobei gleichzeitig auch die Bruchdehnung des meist zersetzten PE-Abfalls erhöht wurde. Außerdem wurde die Kompatibilität zwischen LDPE- und HDPE-Abfall verbessert. Alle untersuchten PE-Proben zeigten einen Memoryeffekt, nachdem das Material bei 130°C zu Folien gezogen, unter Spannung gekühlt und anschließend spannungslos erwärmt wurde. Das Ausmaß der Schrumpfung war abhängig vom Abbaugrad des eingesetzten PE-Abfalls und von der Strahlendosis.
    Notes: Polyethylene wastes (low-density polyethylene, high-density polyethylene and their binary blends) were subjected to high-energy radiation, using a 60Co gamma radiation source. The crosslinked materials thus obtained were processed to heatshrinkable films. Tensile strength could be sharply improved by increasing the dose up to 20 Mrad, simultaneously increasing the elongation at break of the most degraded PE waste. An increase of the degree of compatibility of LDPE and HDPE waste was also observed. All samples examined exhibit a “memory effect” after drawing at 130°C and cooling under tension followed by further heating under relaxed conditions. The value of shrinkage depended on the degree of degradation of the PE waste and on the irradiation dose.
    Additional Material: 6 Ill.
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    Simulation of the hydrolytic polymerization of ∊-caprolactam with bifunctional regulatorsResearch supported by Laboratory of Polymer and Molecular Engineering. Fudan University, P.R. China (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 250 (1997), S. 1-14 
    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: Ein Modell zur Simulierung der Kinetik der hydrolytischen Polymerisation von ∊-Caprolactam mit bifunktionellen Molekulargewichtsreglern wird vorgeschlagen, um charakteristische Daten wie die Konzentrationen von Caprolactam, Endgruppen, ∊-Aminocapronsäre und cyclischem Dimeren sowie Umsatz, zahlen- und gewichtsmittlere Molekulargewichte und die Uneinheitlichkeit zu analysieren. Die anhand dieses Modells berechneten Werte stimmen gut mit den experimentellen Ergebnissen überein. Es wurde festgestellt, daß bei Verwendung bifunktioneller Säure als Regler mit zunehmender Reglerkonzentration die Uneinheitlichkeit abnimmt, während sich mit monofunktioneller Säure als Regler die Uneinheitlichkeit mit steigender Reglerkonzentration asymptotisch einem Wert von 2 nähert.
    Notes: A simulation model dealing with the kinetic behavior of the hydrolytic polymerization of ∊-caprolactam with bifunctional regulators has been proposed to analyse such characteristic data of the polymerization as the concentrations of caprolactam. endgroups, ∊-aminocaproic acid, cyclic dimer, and as well as conversion, number- and weight-average molecular weights, and polydispersity index. The calculated values based upon the model were found to be quite compatible with the observed values. It is found that the presence of more bifunctional acid leads to a lower equilibrium value of polydispersity index, unlike the case of monofunctional acid where the polydispersity index asymptotically reaches a value of 2, regardless of the amount of monofunctional acid initially added.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052500101
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    Makrogelierung von Polyacrylsäuredispersionen durch Vernetzung (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 250 (1997), S. 67-83 
    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: The reaction of poly(acrylic acid) dispersions with diglycidyl ether or dicarboxylic dichlorides as crosslinking agents leads to the formation of macrogels without shrinking of the original dispersions. The particles of the dispersion are stabilized by block copolymers and are about 100 nm in diameter. Micrographs of scanning electron microscopy of the freeze-dried gel show a three-dimensional network structure formed by the particles. The kinetics of the crosslinking reaction was studied by differential scanning calorimetry. A model is presented considering a partition equilibrium of the crosslinking agent between the disperse and the continuous phase and the influence of mass transport of the crosslinking molecules in the interior of the particle. By means of dynamic rheology it was shown that the macrogels obtained are the result of chemical crosslinking reactions between the particles. Frequency-dependent measurements of the dynamic modulus during the crosslinking reaction showed that the network formation is a reaction-controlled cluster-cluster aggregation process. Dynamic light scattering experiments indicate a dominating cluster fraction with sizes of about 1 to 2 l m just before the gel point. The evolution of clusters is described by a simple model based on a stochastic method. Catalytically active materials can be prepared by anchoring metal colloids within the polymer particle network.
    Notes: Mit Blockcopolymeren stabilisierte Polyacrylsäuredispersionen mit ca. 100 nm großen Partikeln führen bei Reaktion mit Diglycidylethern oder Disäuredichloriden als Vernetzer ohne Schrumpfung zur Bildung von Makrogelen. Rasterelektronenmikroskopische Aufnahmen zeigen das Vorliegen einer aus den Partikeln aufgebauten dreidimensionalen Netzwerkstruktur. Die Kinetik der Vernetzungsreaktion wurde mit Hilfe der Differential-Scanning-Kalorimetrie untersucht. Das aufgestellte Modell berücksichtigt ein Verteilungsgleichgewicht des Vernetzers zwischen disperser und kontinuierlicher Phase und geht von einem Stofftransportprozeß der Vernetzermoleküle in das Partikelinnere aus. Mit Hilfe dynamisch-rheologischer Messungen wurde gezeigt, daß das Gel ein kovalent vernetztes Gebilde darstellt. Frequenzabhängige Messungen der dynamischen Moduln während der Reaktion führten zu dem Schluß, daß sich das Partikelnetzwerk infolge einer reaktionskontrollierten Cluster-Cluster-Aggregation bildet. Mit Hilfe der dynamischen Lichtstreuung wurde festgestellt, daß kurz vor dem Gelpunkt eine Fraktion mit Clustergrößen um 1 bis 2 μm dominiert. Die zeitliche Entwicklung dieser Gebilde von Reaktionsbeginn an wurde mit Hilfe eines einfachen Modells auf Basis der stochastischen Methode beschrieben. Die Verankerung eines Palladium-Kolloids in dem Partikelnetzwerk führte zu einem katalytisch aktiven Material.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052500105
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    Two-component diacrylate networks from liquid-crystalline and non-liquid-crystalline monomers I. Synthesis of the monomers, phase behaviour of the binary monomer mixtures, network formation (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 250 (1997), S. 105-117 
    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: Aus Bisacrylaten wurden durch photoinduzierte Vernetzung in der isotropen Phase zweikomponentige Netzwerke synthetisiert. Bei allen Systemen wurde als eine Komponente ein Bisacrylat verwendet, das eine flüssigkristalline Phase bilden kann, und als zweite Komponente ein Bisacrylat, das dazu nicht in der Lage ist. Die isotrope Komponente wurde hinsichtlich ihrer Größe, Geometrie und Polarität variiert. Für alle Systeme wurden mittels einer Wärmeflußkalorimetrie (DSC) Phasendiagramme der Monomermischungen erstellt. Das Phasenverhalten der Systeme zeigt eine Abhängigkeit vom Schmelzpunkt und der chemischen Struktur der isotropen Zweitkomponente. Die Vernetzungstemperatur wurde so gewählt, dafß die Vernetzung in der isotropen Phase 10 °C über der Phasenllbergangstemperatur erfolgte. Die Reaktionskinetik wurde aus den Photopolymerisationsenthalpien mittels eines für photochemische Vernetzungen modifizierten DSC-Gerätes untersucht. Die Zeitabhängigkeit des Umsatzes und der Gesamtumsatz an Acrylatbindungen wurden aus den DSC-Kurven ermittelt. Der Gesamtumsatz hängt nicht von der Reaktionstemperatur und der Struktur der Monomeren ab und liegt je nach Zusammensetzung füralle Systeme zwischen 53 und 71%. Die Zeitabhängigkeit des Umsatzes hingegen wird von der Struktur des nicht flüssigkristallinen Comonomeren beeinflufßt.
    Notes: Two-component networks of diacrylate monomers were synthesized by photoinduced polymerization in the isotropic phase. In all systems one component was a liquid-crystalline diacrylate, whereas the second component was a non-liquid-crystalline diacrylate, which was varied in size, geometry and polarity. The phase behaviour of the monomer mixtures has been analysed by differential scanning calorimetry (DSC). It is influenced by the melting point and the structure of the non-liquid-crystalline component. All samples were cross-linked in the isotropic phase 10°C above the phase transition temperature and a modified differential scanning calorimeter was used to investigate the enthalpies of photopolymerization. The final value and the time dependence of the conversion of acrylate double bonds were calculated from the DSC curves. The final degree of conversion of the acrylate double bonds was between 53 and 71% for all samples, whereas no significant dependence of the degree of conversion on the chemical structure of the monomers or the reaction temperature has been found. In contrast, the time dependence of the conversion was influenced by the chemical structure of the non-liquid-crystalline component.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052500108
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    Synthèse d'une résine antistatique par introduction de sites ioniques dans le système Epikote 1001®-Euredur 423® (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 111-130 
    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: This work is an attempt to provide antistatic properties to a commercial epoxy resin made up with Epikote 1001® and Euredur 423®. In this aim, two compounds were selected which could be chemically bonded to the resin network: (2,3-epoxypropyl)-trimethylammonium chloride which contains an epoxy group and the ammonium chloride group for the antistatic properties and also tetrabutylammonium 2-aminoethanesulfonate which contains an amino group and the tetrabutylammonium sulfonate group. Different formulations of the resin were prepared with both compounds, their viscosity and their resistivity were measured. Antistatic properties were obtained with the highest contents of epoxy compound. On the contrary no antistatic properties could be observed with the amino compound. Hardness and adherence tests have given suitable results for the antistatic formulations.
    Notes: Le but de cette étude est d'apporter des propriétés antistatiques durables à la résine époxy obtenue à partir d'Epikote 1001® et d'Euredur 423®. Deux composés pouvant se lier chimiquement à la résine ont été choisis: le chlorure de (2,3-époxypropyl)triméthylammonium qui contient un groupe époxy comme l'Epikote 1001® et un groupement chlorure d'ammonium pour les propriétés antistatiques et le 2-aminoéthanesulfonate de tétrabutylammonium qui contient un groupement amine comme l'Euredur 423® et le groupement sulfonate. Différentes formulations de la résine ont été préparées avec ces deux composés. Leur viscosité et leur résistivité ont été mesurées. Des propriétés antistatiques ont été observées avec des échantillons à taux élevé de composé époxyde. Par contre, le composé à groupement amine n'a montré aucune propriété antistatique. Des tests de dureté et d'adhérence se sont révèlés intéressants pour les formulations présentant des propriétés antistatiques.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052530109
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    Compared properties of aromatic polyamides containing silicon in the main chain (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 169-182 
    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: Zwei Reihen aromatischer Polyamide mit Silicium und Phenylchinoxalin- oder Hexafluorisopropyliden-Gruppen wurden hergestellt und ihre Eigenschaften mit denen verwandter Polymerer verglichen. Die Polymeren sind leicht löslich in polaren amidischen Lösungsmitteln wie N-Methyl-2-pyrrolidinon und Dimethylformamid sowie in Tetrahydrofuran. Aus diesen Lösungen können dünne, transparente Filme gegossen werden. Die gewichts- und zahlenmittleren Molekulargewichte der Polyamide liegen im Bereich 10000-40000 bzw. 3000-6000, die Uneinheitlichkeiten im Bereich 3-10. Die Glasübergangstemperaturen liegen zwischen 236°C und 275°C, die Zersetzungstemperaturen oberhalb von 400°C. Die Dielektrizitätskonstanten der Polymerfilme sind niedrig (3.26-3.68), die mechanischen Eigenschaften gut (Zugfestigkeit 74-100 MPa, Zugmodul 180-386 MPa) und mit denen anderer „high performance“-Dielektrika vergleichbar.
    Notes: Two series of aromatic polyamides incorporating silicon together with phenylquinoxaline or with hexafluoroisopropylidene groups have been synthesized and their properties have been characterized and compared with those of related polymers. These polymers are easily soluble in polar amidic solvents such as N-methyl-2-pyrrolidinone and dimethylformamide, and in tetrahydrofuran, and can be cast into thin, transparent films from solution. The polyamides have weight- and number-average molecular weights in the range of 10 000-40 000 and 3 000-6 000, respectively, and polydispersities in the range of 3-10. They show glass transition temperatures in the range of 236°C-275°C and decomposition temperatures above 400°C. The polymer films have low dielectric constants in the range of 3.26-3.68, and good mechanical properties (tensile strength 74-100 MPa, tensile modulus 180-386 MPa), thus being comparable with other high performance dielectrics.
    Additional Material: 6 Ill.
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    Biological degradation of cellulose acetate films: Effect of plasticizer (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 193-200 
    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: Der Bioabbau von weichgemachtem Celluloseacetat (PCA) wurde durch Kompostierung mit einem standardisierten kommunalen Feststoffabfall (ED 73) untersucht. Der relative prozentuale Gewichtsverlust der Proben wurde gemessen und der aerobe Bioabbau in einem kontrollierten aeroben Kompostiersystem ermittelt, mit dem das durch den mikrobiologischen Metabolismus gebildete CO2 aufgefangen wurde. Infrarotspektren (FTIR), mechanische Eigenschaften und Molekulargewicht zersetzter PCA-Filme zeigen, daß die Fraktionen mit niedrigerem Molekulargewicht (wie z.B. Weichmacher und niedriger substituierte Fraktionen von PCA) bevorzugt abgebaut und aus dem PCA entfernt werden.
    Notes: Biodegradation of plasticized cellulose acetate (PCA) was established with a standard municipal solid waste (ED 73). The relative percent weight loss of the specimen was measured, and the aerobic biodegradation was evaluated in a controlled aerobic composting system that was designed to capture CO2 produced by microbiological metabolism. Infrared spectra (FTIR), mechanical properties and molecular weight of degraded PCA films indicate that the lower molecular weight fractions, such as plasticizer and lower substituted fractions of PCA, are biodegraded and removed preferentially from the PCA.
    Additional Material: 8 Ill.
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    Preface (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. xi 
    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.360220103
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    Interactions between poly(Gly-Pro-Pro) triple helices: A model for molecular packing in collagen (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 33-36 
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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: Potential-energy calculations are reported on the interaction between two collagenlike triple-stranded poly(Gly-L-Pro-L-Pro) helices. Short helices can pack in a variety of orientations, but there is a unique parallel packing arrangement of the two helices for longer polypeptide chains.
    Additional Material: 1 Tab.
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    Coupling between the helix-coil transition and nematic-isotropic transitions in polypeptide solutions (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 43-47 
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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 lattice model of Flory has been extended in order to consider equilibrium between isotropic and nematic phases containing helix-coil type chains. Nearly complete exclusion of coil sequences from the lyotropic nematic phase produces an enhanced cooperativity in the helix-coil transition. In poor solvents this enhancement begins to occur at concentrations typical of some experiments.
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    Strategy for trapping intermediates in the folding of ribonuclease and for using 1H-NMR to determine their structures (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 59-67 
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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 major unfolded form of ribonuclease A is known to show well-populated structural intermediates transiently during folding at 0°-10°C. We describe here how the exchange reaction between D2O and peptide NH protons can be used to trap folding intermediates. The protons protected from exchange during folding can be characterized by 1H-nmr after folding is complete. The feasibility of using 1H-nmr to resolve a set of protected peptide protons is demonstrated by using a specially prepared sample of ribonuclease S in D2O in which only the peptide protons of residues 7-14 are in the 1H-form. All eight of these protected peptide protons are H-bonded. Resonance assignments made on isolated peptides containing these residues have been used to identify the protected protons. Other sets of protected protons trapped in the 1H-form can also be isolated by differential exchange, using either ribonuclease A or S. Earlier model compound studies have indicated that H-bonded folding intermediates should be unstable in water unless stabilized by additional interactions. Nevertheless, peptides derived from ribonuclease A that contain residues 3-13 do show partial helix formation in water at low temperatures. We discuss the possibility that specific interactions between side chains can stabilize short α-helixes by nucleating the helix, and that specific interactions may also define the helix boundaries at early stages in folding.
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    Multiphasic conformation transition of globular proteins under denaturating perturbation (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 93-99 
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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: Denaturation profiles of 17 globular proteins were studied by the spectroscopic and chromatographic methods with high-data-point density. The denaturational transitions are broadly classified into three types according to their multiphasic characteristics. In general, more or less complex internal cooperative events seem to take place in the conformation transition of globular proteins.
    Additional Material: 3 Ill.
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    Conformational and functional properties of hemoglobin in water-organic cosolvent mixtures: Effect of ethylene glycol and glycerol on oxygen affinity (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 119-123 
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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: We report on the effects that the presence of ethylene glycol or glycerol has on the oxygen affinity of hemoglobin. We attribute these effects to an altered equilibrium between T and R quaternary conformations of hemoglobin and separate them into bulk-electrostatic and non-bulk-electrostatic contributions to the standard free-energy difference between the R and T states.
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    URL: http://dx.doi.org/10.1002/bip.360220119
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    NMR analysis of structure and function of snake neurotoxins (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 139-145 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 270-MHz proton-nmr spectra of short neurotoxins (erabutoxins from Laticauda semifasciata and cobrotoxin from Naja naja atra) and long neurotoxins (toxin B from Naja naja and α-bungarotoxin from Bungarus multicinctus) have been analyzed. The conformation of erabutoxin b in solution is largely consistent with the x-ray crystal analysis, although the environment of His-7 in solution is definitely different from that in the crystal. The pH-dependent transition has been found for toxin B, indicating that the conformation in neutral solution is different from that in the crystal as grown from acidic solution. The deuterium-exchange rates of the amide protons for the four neurotoxins have been measured. The order of structural rigidity is the same as the order of the irreversibility of neuromuscular block by neurotoxins.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360220122
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    1H-NMR studies on poly(oxyethylene)-bound oligopeptides (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 163-169 
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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: Conformational studies on poly(oxyethylene)-bound homo-, oligo-, guest-host, and sequential peptides synthesized according to the liquid-phase method were carried out by means of 1H-nmr spectroscopy. The solubilizing effect of the C-terminal polymeric support allowed a thorough investigation of the secondary structure in solution.
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    Vibrational analysis of conformation in peptides, polypeptides, and proteinsThis is paper number 16 in a series of which Ref. 20 is paper 15. (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 217-225 
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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 vibrational force field for the polypeptide chain has been developed for normal-mode analysis of such molecules. It can reproduce observed frequencies of known structures to within about 5 cm-1. We review the application of this technique to conformational problems in peptides (β-turns and their model compounds), polypeptides [the αII-helix and crystalline poly(glycine II)], and proteins (bacteriorhodopsin and glucagon).
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    URL: http://dx.doi.org/10.1002/bip.360220130
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  • 185
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    1H-NMR studies on substance P hexapeptide analogs (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 247-253 
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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: 1H-nmr studies of [pGlu6]SP6-11, [gpGlu6,mPhe7]SP6-11, and [pGlu6,N-CH3Phe7]SP6-11 in DMSO-d6 reveal characteristic chemical shifts, 3JNH-αCH, temperature dependence, as well as deuterium exchange half-times. Marked similarities are revealed for the two first analogs, whereas the N-methylated analog is clearly different. Possible conformations are considered.
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  • 186
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    Conformational flexibility in a small globular hormone: X-ray analysis of avian pancreatic polypeptide at 0.98-Å resolution (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 293-304 
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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 36-amino acid avian pancreatic polypeptide has been studied by x-ray analysis at 0.98-Å resolution and refined using a restrained least-squares technique to an agreement factor of 15.6%. The polypeptide, which has a compact globular structure with a hydrophobic core, comprises a polyproline-like helix (residues 2-8) and an α-helix (residues 14-32). The molecule forms symmetrical dimers linked through zinc atoms in the crystal lattice. The high-resolution analysis defines sequence-dependent distortions in the α-helical parameters due to hydrogen bonding of water molecules and side chains. The thermal parameters indicate an increased flexibility of the main chain at the turn between the helices and in the C-terminal residues. For the first time, six-parameter anisotropic thermal ellipsoids have been refined for each atom; these define the directions of the molecular motions in the polypeptide, indicating concerted vibrations. The physiological roles of conformation, flexibility, and dynamics of this polypeptide hormone are discussed.
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    Solid-state geometry and conformation of linear, diastereoisomeric oligoprolinesAbbreviations, description of the atoms, and conventions for the conformation of the peptide chain follow the recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature [(1972) Biochem. J. 126, 773-780]. Further abbreviations used are: Ac, acetyl; n-Prp, n-propionyl; Mmp, 1-(3-mercapto-2-methylpropionyl); Piv, pivaloyl; t-Boc, tert-butyloxycarbonyl; t-Aoc, tert-amyloxycarbonyl; Z, benzyloxycarbonyl; Hyp, 4-hydroxyproline; Aze, azetidine-4-carboxylic acid; Thz, thiazolidine-4-carboxylic acid; Δβ-Pro, 3,4-dehydroproline; Aib, α-aminoisobutyric acid; Pip, pipecolic acid; pGlu, pyroglutamic acid; OMe, methoxy; OBzl, benzyloxy. (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 305-317 
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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: We have carried out a systematic analysis of the solid-state conformational preferences of a number of linear homo-oligoprolines (to the tetramer) by ir absorption and x-ray diffraction. The peptides present different chiral sequences (tacticities), various types (urethane and amide) of N-protecting groups, and free and blocked C-termini (which imply different capabilities of forming H-bonds). The following conclusions can be drawn: (i) values for the geometry of the prolyl residue and the peptide bond in the cis and in the trans conformations are proposed; (ii) in general the conformational angles ϕ and ψ in the linear homo-oligoprolines have values appropriate for the polyproline II structure (conformation F); (iii) the pyrrolidine ring shows various types of puckering with no apparent relation to the backbone conformation; (iv) Pro-Pro peptide bonds generally take the trans conformation, the few cases of cis conformation being formed by Pro residues of different chirality; (v) the single H-bond donor  -  OH, when present, is always bonded to H-acceptors, which can be either the urethane or the amide or the peptide carbonyl but never the carbonyl group of the  -  COOH moiety.
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    Microheterogeneity of bovine myelin basic protein studied by nuclear magnetic resonance spectroscopy (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 377-380 
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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: Myelin basic protein isolated from bovine white matter is known to consist of a mixture of three or more “charge isomers”, which can be separated by cation-exchange chromatography. We are using 360-MHz 1H-nmr spectroscopy to establish the chemical and structural differences among them. Preliminary studies by difference spectroscopy between two of the isomers suggest (a) all aromatic residues, and probably their nearest-neighbors, are unchanged; (b) the less cationic isomer lacks one (or two) of its C-terminal Arg residues; and (c) a significant fraction of the two Met residues in the less cationic isomer is present as methionine sulfoxide.
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    Spectroscopic studies of a hydrophobic peptide in membranelike environments (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 381-385 
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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 hydrophobic linear peptide has been synthesized and studied over a range of environments using several complementary spectroscopic approaches, including nmr, CD, and vibrational spectroscopies. The sequence of this model peptide, carbobenzoxy-L-Pro-D-Phe-D-Ala-L-Pro-NHCH3, was designed such that a small number of “folded” conformations, stabilized by intramolecular hydrogen bonding, would be accessible to it. Additionally, the extremely hydrophobic character of the peptide favors its interactions with hydrophobic regions of a membrane. The conformational impact of the membrane environment on the peptide, and the effect of the peptide on lipid organization have been explored both in micellar media and in vesicles. To facilitate nmr analysis, the peptide has been synthesized with one of the prolines perdeuterated. Results of these studies reveal that the peptide experiences a microenvironment of moderate polarity in micellar media and causes changes in lipid structure in a vesicle that are indicative of a hydrophobic peptide-lipid interaction.
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    How antigenic are antigenic peptides? (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 425-440 
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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: Most of a protein surface is potentially antigenic, consisting of numerous overlapping domains each complementary to antibody-combining sites. These domains may include peptide sequences that are demonstrably antigenic but only when antibodies from the appropriate host individuals and species are used. Methods for locating antigenic peptide sequences are described in which hydrophilic polyamide supports are used for peptide synthesis, then solid-phase radioimmunoassay with antisera and protein A. Most antigenic domains, however, comprise amino acid side chains contributed by two or more nearby polypeptide chains. Such domains can be identified by comparing the cross-reactivities of groups of very closely related proteins towards monoclonal antibodies raised to one of them. Such studies, using myoglobins, have identified a number of residues not previously shown to be antigenic and have provided a guide for the choice of synthetic peptides which are likely to carry several immunodominant side chains. One such peptide corresponding to residues (72-89) of beef myoglobin has been shown, using CD and antibodies to the parent protein, to have interesting conformational and antigenic properties. The peptide (25-55) is also antigenic.
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    Some novel approaches to the design and synthesis of peptide-catecholamine conjugates (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 531-545 
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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 series of novel, functionalized catecholamines (congeners) has been synthesized in which, formalistically, the N-isopropyl group of isoproterenol has been extended by a linear alkyl chain of varying length, terminated by a carboxyl group. Model amide derivatives have also been prepared in order to optimize the biological activity of these derivatives and also to aid in the design of appropriate peptides for the synthesis of conjugates. As a result of these studies, a series of amino acid and monodisperse peptide carriers, containing p-aminophenylalanine as the point of attachment for the drug, was prepared, together with the corresponding conjugates. In vitro and in vivo evaluation of the congeners, model amides, and conjugates has demonstrated that the biological activity of these derivatives is extremely sensitive to structural modifications at a point far-removed from the pharmacophore, in both the congener amide and conjugate series. A number of the model amides and conjugates have proven to be highly active when tested in both in vitro and in vivo test systems. The implications of these results in terms of a novel structure-activity approach to drug design are discussed.
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    Specific and nonspecific macromolecule-drug conjugates for the improvement of cancer chemotherapy (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 557-567 
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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: Antineoplastic drugs such as daunomycin, adriamycin, methotrexate, 5-fluorouridine, cytosine arabinoside, and platinate were bound to antibodies directly or via a polymeric bridge. The drug antibody conjugates retained most of their drug and antibody activities when tested in vitro. Daunomycin-antibody conjugates were shown to penetrate tumor cells in the conjugated form. In animals, daunomycin-antibody conjugates were at least as effective chemotherapeutically as the corresponding free drugs and considerably less toxic. In some tumor systems, the daunomycin-antibody conjugates represented an improvement over the free drug. This improvement was restricted in some tumors to a particular injection route of the tumor and the treatment.
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    Synthesis and spectroscopic characterization of insulin derivatives containing one or two poly(ethylene oxide) chains at specific positions (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 569-573 
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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: We describe a synthetic method aimed at specifically coupling poly(ethylene oxide) (PEO) to proteins without altering their spectroscopic properties. To do so, we have first modified the alcohol end group of PEO to an acid end group (PEO-COOH). Coupling of PEO-COOH to Gly A1 methylsulfonylethyloxycarbonyl (Msc) protected insulin yielded NαB1,N∊B29-(PEO)2-insulin. Conversely, coupling of PEO-COOH to insulin whose Gly A1 and Lys B29 amino groups were protected with Msc yielded NαB1-PEO-insulin. The products were obtained in a spectroscopically pure form and characterized by uv and CD spectroscopy. Conformational and biological studies are in progress.
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    Poly(2-aminodeoxyadenylic acid): Circular dichroism and thermal stability of its complexes and their relevance to phage DNA in which A is replaced by 2NH2A (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 597-600 
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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: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360220204
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    Crystal structure and conformation of a cyclic tetrapeptide cyclo(L-Pro-Sar)2 containing all-cis peptide units (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 633-641 
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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 crystal structure and conformation of the synthetic cyclic tetrapeptide, cyclo(L-Pro-Sar)2, was determined by x-ray analysis. The peptide crystallizes in the orthorhombic space group P212121 with cell parameters a = 9.277(1), b = 12.884(1), and c = 15.581(2) Å. The crystal structure was solved by the symbolic addition procedure for direct phase determination and least-squares refinement using 1796 reflections, which led to the final R value of 0.043. This structure provides the first example observed in a crystal of a cyclic tetrapeptide in which all four peptide units have been found in the cis conformation with ω angles deviating slightly by 2°-10° from the ideal value of 0°. It was also found that the two Pro Cα-CO single bonds assumed a trans′ (ψ = 159.6° and 158.4°) conformation. Adjoining average planes of the peptide groups fall at nearly right angles to each other. The pyrrolidine ring conformations of the two prolyl residues are in the envelope form, with Cγ carbon out of the least-squares planes for the remaining four atoms.
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    An analysis of the sequence dependence of the structure and energy of A- and B-DNA models using molecular mechannics (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 969-1002 
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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-mechanics calculations have been carried out on the base-paired hexanucleoside pentaphosphates d(TATATA)2, d(ATATAT)2, d(A6)·d(T6), d(CGCGCG)2, d(GCGCGC)2, and d(C6)·d(G6) in both A- and B-DNA geometries. The calculated relative energies of these polymers are consistent with the relative stabilities of the polymers found experimentally. In particular, the results of our calculations support the observation that the homopolymer d(A)n·d(T)n is more stable in a B-DNA conformation, while the homopolymer d(G)n·d(C)n is more stable in an A-DNA conformation. The molecular interactions responsible for these differential stabilities include both inter- and intrastrand base stacking, as well as base-phosphate interactions. While definitive experiments on the heteropolymer stabilities have not yet been carried out, the results of our calculations also suggest a greater stability of the purine-3′,5′-pyrimidine sequence over the pyrimidine-3′,5′-purine sequence in both the A- and B-conformations. The reason for this greater stability lies in the importance of the inherent directionality (5′ → 3′ vs 3′ → 5′) of phosphate-base and base-base interactions. The largest conformation change observed on energy refinement is sugar repuckering, which occurs mainly on pyrimidine-attched sugars and only in the B-DNA geometry. We suggest a molecular mechanism, specifically, differential base-sugar steric interactions involving neighboring sugars, to explain why this repuckering occurs more with d(A6)·d(T6) than with other isomers.
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    Salt- and sequence-dependence of the secondary structure of DNA in Solution by 31P-nmr spectroscopy (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 879-893 
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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: We examined three sonicated, specific-seqiemce polydeoxynucleotides in solution over a wide range of concentrations of several salts by 13P-nmr spectroscopy, and we found that the alternating copolymer poly(dAdT)·poly(dAdT) exhibits a dinucleotide repeat unit in all five salts and at all concentrations studied, as indicated by the presence of a doubled in its 31P-nmr spectra. The two components of the doublet show selective shift effects. The upfield component is assigned to dApdT in the gauche--gauche- conformation and shifts upfield in all four monovalent salts used, relative to a single-stranded oligonucleotide control. The downfield component is assigned to dTpdA in the trans-gauche- conformation and shifts downfield with increasing CsF concentration but remains essentially constant in LiCl, NaCl, and CsCl. These changes indicate a fast noncooperative transition for poly(dAdT)·poly-(dAdT) from a presumed right-handed dinucleotide-repeat B-form to another conformation with a dinucleotide-repeat structure, via a continuum of structures that may differ in the extent of the winding of the double helix. Ethanol causes the upfield component to collapse into the other component, indicating conversion to a structure with a mononucleotide repeat unit and a trans-gauche- conformation. Up to 1M Mg2+ appears to have no significant effect on the phosphodiester conformations of poly(dAdT)·poly(dAdT). By contrast, poly-(dGdC)·poly(dGdC) gives a slow cooperative transition from what is considered to be a right-handed regular B-form to a left-handed Z-form on increasing MgCl2 and NaCl concentrations, although we observed no changes in chemical shifts below the transition points. The homopolymer poly(dA)·poly(dT) exhibits no unusual shift effects or transitions upon the addition of salts when compared to the oligonucleotide control and is considered to be a regular B-form with a gauche--gauche- phosphodiester backbone conformation. These differences emphasize the distinct secondary structures of DNAs of different sequences and their selective responses to changes in solution conditions.
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    1H-nmr studies on the dinucleoside monophosphates containing 2′-halogeno-2′-deoxypurinenucleosides: Effects of 2′-substitutes on conformation (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 1189-1202 
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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: Seven dinucleoside monophosphates containing 2′-halogeno-2′-deoxypurine nucleoside residue, dAfl-U, dAcl-U, dAbr-U, dAio-U, dGfl-U, and dIfl-C, were chemically synthesized and investigated by 1H-nmr spectroscopy at 300 MHz. The sugar and backbone conformations of these compounds were analyzed by the spectral pattern of furanose proton resonances; and the extents of base-base interaction were estimated from chemical shifts and their temperature-dependent changes of base-proton resonances. It is found that the population of C3′-endo conformer and the extent of base-base interaction decrease as the electronegativity of 2′-substituent decreases in dAx-U (x = fl, cl, br, and io) series. The C3′-endo (3E) population and the base-base interaction in Nfl-U (N = A,G)-type dimers as well as dIfl-C are relatively higher than the corresponding natural ribo-dimers but can be recognized as grossly similar to the conformation of regular RNA dimers.
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    Masthead (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983) 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.360220501
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    Raman spectra and normal vibrations of dipeptides. I. Glycylglycine (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 1267-1283 
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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: We studied the Raman spectra of the zwitterionic glycylglycine crystal (GG) and its N-deuterated analog. A normal coordinate analysis on its α-crystalline form was performed and the effects of intra-and intermolecular couplings are discussed. A modified Urey-Bradley potential was used as a model of the intramolecular force field. Factor group splittings are described by the use of intermolecular potentials consisting of nonbonded atom-atom interactions and dipole-dipole interactions. Effects of hydrogen bonds on the vibrational frequencies of amino and carboxylate groups are also analyzed.
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    URL: http://dx.doi.org/10.1002/bip.360220503
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