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  • 1995-1999  (6)
  • 1970-1974  (5)
  • Polymer and Materials Science  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Raman studies of nucleic acids. XII. Conformations of oligonucleotides and deuterated polynucleotides (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1821-1845 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Laser Raman spectra of the trinucleoside diphoshate ApApA and dinucleoside phosphates ApU, UpA, GpC, CpG, and GpU are reported and discussed. Assignments of conformationally sensitive frequencies are-facilitated by comparison with spectra reported here of poly(rA), poly(rC), and poly(rU) in deuterium oxide solutions. The significant spectral differences between ApU and UpA, and between GpC and CpG, reveal that the sequence isomers have nonidentical conformations in aqueous solution. In UpA at low temperature the bases are stacked and the backbone conformation is similar to that found in ordered polynucleotide structures and RNA. In ApU no base stacking can be detected and the backbone conformation differs from that found in UpA, both in the orientation of phosphodiester linkages and in the internal conformation of ribose. At the conditions employed neither ApU nor UpA exhibits base pairing in aqueous solutions. In both GpC and CpG the bases are stacked and the phosphodiester conformations are similar to those encountered for UpA and RNA. However, major differences between spectra of GpC and CpG indicate that the geometries of stacking and ribosyl conformations are different. In GpC the Raman data favor the formation of hydrogen bonded dimers containing GC pairs. Protonation of C in GpC is sufficient to eliminate the ordered conformation detected by Raman spectroscopy. Despite the ordered backbone conformation evident in GpU, this dinucleoside apparently contains neither stacked nor hydrogen bonded bases at the conditions employed here. The Raman data also confirm the stacking interactions in ApApA, poly(rA), and poly(rC) but suggest that the backbone conformation in poly(rC) differs qualitatively from that found in most ordered polynucleotide structures and is thermally more stable. The present results demonstrate the sensitivity of the Raman technique to sequence-related structural differences in oligonucleotides and provide additional spectra-structure correlations for future conformational studies of RNA by laser Raman spectroscopy.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130914
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  • 2
    Electronic Resource
    Electronic Resource
    General theory of stationary random sequences with applications to the tacticity of polymersPaper presented at the 142nd Meeting of the American Chemical Society, Atlantic City, New Jersey, September 1962. (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1635-1649 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When, in a poly-α-olefin, the probability that a given placement be isotactic depends upon the tacticity of only a finite number of immediate predecessors, the resulting diastereosequence distribution obeys the theory of Markoff chains. When this is not the case, one says that the resulting diastereosequence distribution is non-Markoffian. A special case of a Markoffian distribution is given by a simple Markof chain in which the tacticity of a given placement is assumed to be affected by only the tacticity of the immediately preceding placement. Another special case is, of course, the Bernoulli trial distribution in which the probability that a given placement be isotactic is independent of the tacticity of all other placements. A high resolution NMR spectrum can sometimes yield a quantitative determination of the concentrations of isotactic and syndiotactic placements and the concentrations of the three types of possible adjacent pairs of such placements (i.e., isotactic, syndiotactic, and heterotactic pairs). When this is the case, the spectrum can be used to determine whether or not a given diastereosequence distribution is Bernoullian. However, because the longest diastereosequences whose concentration can be measured by NMR spectroscopy involve only two placements, an NMR spectrum cannot check whether a given non-Bernoullian distribution be simple Markoffian or Markoffian in general. In fact, non-Markoffian distributions are compatible with existing NMR spectra on polymers prepared by anionic polymerizations. In this paper we work within the framework of Kac's theory of stationary statistical processes and point out some general results which are valid for both Markoffian and non-Markoffian processes. The results are applied to NMR spectroscopy and it is pointed out which calculations used to check the self-consistency of NMR data and to obtain the mean length of closed diastereosequences are valid for both Markoffian and non-Markoffian distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1996.838
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  • 3
    Electronic Resource
    Electronic Resource
    Erhöhung der Verschleißfestigkeit der TiAl6V4-Legierung durch Implantieren mit Stickstoff-Ionen (1996)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 27 (1996), S. 9-13 
    Details
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Increasing of wear resistance of Ti-6Al-4V alloy by nitrogen implantationNitrogen ion implantation is used to improve the wear resistance of Ti-6Al-4V alloy. Different implantation doses up to 1 · 1018N+/cm2 and E = 170 KeV were used. The unimplanted and the implanted specimens were tested in a wear model system with oscillation loading. The results show, that the wear performance was influenced by implantation dose and also by mean pressure. It was found, that surfaces, which are produced by a high implantation dose (1 · 1018N+/cm2), exhibited greater were resistance than untreated Ti-6Al-4V alloy. The best wear behaviour was achieved by a high implantation dose (1 · 1018N+/cm2) and a low mean pressure (p =0.22 MPa) at the wear test. The difference between the wear rate of the untreated and of the implantated specimen can obtain a factor about 10. The effective depth of the implantation action is greater than the penetration depth of the nitrogen ions.
    Notes: Durch Implantation von Stickstoff-Ionen wurde die Randschicht der Ti-Al6-V4-Legierung mit dem Ziel der Verbesserung des Verschleißverhaltens modifiziert. Es wurde dazu mit unterschiedlichen Stickstoffdosen bis 1 · 1018N+/cm2 bei E = 170 keV implantiert. Die Modellverschleißuntersuchungen bei oszillierender Beanspruchung wiesen nach, daß die Implantationsdosis in Abhängigkeit von der im Tribosystem wirkenden mittleren Pressung den Verschleiß deutlich beeinflußt. Wird mit einer hohen Dosis (1 ·1018N+/cm2) implantiert und werden die Beanspruchungsbedingungen so gewählt, daß nur eine relativ geringe Pressung von p ≤ 0.22 MPa auftritt, dann ist mit einer Erhöhung der Verschleißbeständigkeit mindestens um den Faktor 10 zu rechnen. Für größere Pressungen nimmt die Erhöhung des Verschleißwiderstandes ab. Die verschleißmindernde Wirktiefe der Implantation liegt weit über der Eindringtiefe der implantierten Stickstoffionen.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19960270106
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  • 4
    Electronic Resource
    Electronic Resource
    Raman studies of nucleic acids. VII. Poly A · poly U and poly G · Poly C (1972)
    New York : Wiley-Blackwell
    Biopolymers 11 (1972), S. 2423-2437 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Laser-excited Raman spectra of the double-helical complexes poly A·poly U and poly G·poly C are reported for 2H2O and H2O solutions. The spectra are discussed in relation to their use as quantitative reference spectra for determining the dependence of the Raman scattering of RNA on secondary structure. The Raman line at 815 cm-1, due to the phosphodiester group, exhibits the same intrinsic intensity in spectra of poly A·poly U and poly G·poly C and is thus dependent only upon the amount of ordering of the helix and not on the kinds of nucleotides involved. The hypochromic Raman lines in spectra of poly A·poly U are identified and their intensity changes are determined quantitatively over the temperature range 32-85°C. Comparison of the spectra in the 1500-1750 cm-1 region reveals that the Raman lines from carbonyl group vibrations of uracil are about sevenfold more intense than those of guanine and cytosine for both paired and unpaired states and will thus dominate the spectra of RNA. The Raman frequencies in this region are also compared with previously reported infrared frequencies and give evidence of being strongly perturbed by base-stacking interactions in the helices.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1972.360111205
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  • 5
    Electronic Resource
    Electronic Resource
    Raman spectral studies of nucleic acids. XI. Conformations of yeast tRNAPhe and E. coli ribosomal RNA in aqueous solution and in the solid statePaper X in this series is G. J. Thomas, Jr., M. C. Chen, and K. A. Hartman, Biochim. Biophys. Acta, 324, 37 (1973) (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 615-626 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Laser-excited Raman spectra of tRNAPhe from yeast and of fractionated 16S and 23S rRNA from E. coli are reported for samples in aqueous solution and in the solid state. The Raman scattering spectrum of each RNA is not significantly altered by the change from an aqueous to a solid environment and displays the same characteristic frequencies and intensities associated with ordered polyribonucleotide structures. Unlike DNA, the backbone conformation of RNA thus appears to be largely insensitive to gross changes in the degree of hydration.Raman scattering from the phosphate group vibrations of aqueous tRNAyeastPhe is qualitatively and quantitatively the same as obtained from previously studied tRNA's and is indicative of a highly ordered conformational structure in which some 85% of the nucleotide residues are in ordered configurations. The major differences observed between spectra of tRNA and rRNA are attributed to differences in base composition of these RNA's.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130313
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular configuration and thermodynamic parameters from intrinsic viscositiesThis investigation was carried out at Cornell University in connection with the Government Research Program on Synthetic Rubber under contract with the Office of Rubber Reserve, Reconstruction Finance Corporation (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 207-209 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1996.888
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  • 7
    Electronic Resource
    Electronic Resource
    Interaction of slightly crosslinked gels of poly(diallyldimethylammonium bromide) with sodium dodecyl sulfate and cetylpyridinium bromide (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 1855-1863 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interaction of slightly crosslinked gels of poly(diallyldimethylammonium bromide) (PDADMAB) with both the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetylpyridinium bromide (CPB; system. name: N-hexadecylpyridinium bromide) in aqueous medium has been investigated. The absorption of the anionic surfactant by the oppositely charged gel leads to contraction or collapse of the network. The absorption of the cationic surfactant by the gel-SDS complexes results in a reswelling of the network. By means of IR and UV spectroscopy it has been shown that in the presence of the anionic detergent the cationic network absorbs the cationic surfactant. It has been shown that both reversible and irreversible complex formation in the gel phase is possible depending on the initial ratio between the components. Small-angle-X-ray scattering experiments demonstrated that the complexes may have a regular microstructure.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021960605
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  • 8
    Electronic Resource
    Electronic Resource
    Preparation of bis(chloroformate)s for use in cyclization reactionsPresented at ‘MacroAkron '94, 35th IUPAC Symposium on Macromolecules Akron’, Ohio, 11-15 July 1994. (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 37 (1995), S. 179-186 
    Details
    ISSN: 0959-8103
    Keywords: bis(chloroformate) ; cyclization ; interfacial condensation ; phosgene ; cyclic carbonate ; chloroformate ; bisphenol ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Cyclic oligomeric carbonates are prepared by a hydrolysis/condensation reaction from aromatic bis(chloroformate)s. Three methods for convenient preparation of bis(chloroformate)s have been developed: (1) use of diethylaniline to scavenge HCl, in a modification of an earlier procedure; (2) low pH, low temperature interfacial condensation of bisphenols with phosgene; and (3) use of Ca(OH)2 in interfacial condensation with phosgene. Reaction parameters which control formation of monomeric bis(chloroformate)s versus higher oligomerization include temperature, pH, and rate of phosgene addition. For water-soluble bisphenols such as hydroquinone, the phase ratio of water to CH2Cl2 can also be important.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1995.210370305
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  • 9
    Electronic Resource
    Electronic Resource
    Polymerization mechanisms and stereosequence distributions: A monomer-dimer model (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 9 (1971), S. 615-632 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A polymerization mechanism in which monomers and dimers add to a growing polymer chain with different rate constants and different stereospecificity is considered. A fraction of the dimers are in isotactic placement internally, and low conversion to polymer is assumed. The stereosequence distribution generated by this monomer-dimer model is calculated and found to be non-Markovian in general. A method of determining kinetic parameters of the mechanism from experimentally obtained placement sequence probabilities and related experimental tests for the applicability of the mechanism are also described. A few ramifications of the general monomer-dimer model are then discussed. A case of special interest is the one in which all the dimers have a single internal tacticity, a model recently proposed by Blumstein, et al., for a polymerization involving the surface of certain aluminosilicate minerals. For the case where all dimers are isotactic, it is found that although the propagation of consecutive syndiotactic placements alone is simple Markovian, the overall stereosequence distribution is non-Markovian. Another special case of interest is the limiting case with dimers only in the feed. This case turns out to correspond to a special case of the cyclopolymerization mechanism proposed previously by Reinmöller and Fox. Although the tacticity distribution of the placements created by the head (or tail) monomer units alone of the dimers is Bernoullian, the composite stereosequence distribution is again non-Markovian.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.160090405
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  • 10
    Electronic Resource
    Electronic Resource
    Photoreactive analog of peptide FN-C/H-V from the carboxy-terminal heparin-binding domains of fibronectin supports endothelial cell adhesion and spreading on biomaterial surfaces (1996)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 31 (1996), S. 555-567 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The extracellular matrix protein fibronectin (FN) plays an important role in cell adhesion, spreading, and motility. Several cell-adhesion promoting domains exist within fibronectin, and peptide sequences from these domains have been shown to play an important role in cell interactions with fibronectin. Recently, a peptide sequence (FN-C/H-V) from the 33/66 kD carboxy-terminal heparin-binding domains of fibronectin was shown to promote the adhesion and spreading of vascular endothelial cells in vitro. Endothelial cell spreading on this peptide was followed by cytoskeletal reorganization, focal contact formation, and, ultimately, cell migration. In the current study, a photoreactive analog of FN-C/H-V (ASD-V) was generated using a heterobifunctional photoreactive crosslinking agent, sulfosuccinimidyl 2-(p-azidosalicylamido) ethyl-1,3′-dithio-propionate. ASD-V was then covalently coupled to polystyrene (PS) and polyethylene terephthalate film (PET) in order to assess the utility of ASD-V for preparing biomaterial surfaces with endothelial cell-adhesion promoting properties. The effects of pre-adsorption time and initial coating concentration on the efficiency of ASD-V coupling to PS and to PET were examined. Contact angle measurements and atomic force microscopy were used to characterize ASD-V-modified surfaces. Finally, the adhesion and spreading of vascular endothelial cells on ASD-V-modified surfaces was assessed. Our results suggest that photoreactive peptides are an effective and convenient means of modifying biomaterial surfaces to impart adhesion-promoting properties and that ASD-V, when coupled to PS and PET, promotes endothelial cell adhesion and spreading and may therefore be useful as a biomaterial surface modification in applications where re-endothelialization is desired (e.g., autologous endothelial seeding of vascular grafts, or transplantation of genetically engineered endothelial cells via polymer-coated stents). © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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