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  • Polymer and Materials Science  (234)
  • 2005-2009
  • 1985-1989  (234)
  • 1970-1974
  • 1989  (234)
  • 1
    Electronic Resource
    Electronic Resource
    The effect of local controlled release of sodium fluoride on the stimulation of bone growth (1989)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 23 (1989), S. 571-589 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: This study was performed to test the feasibility of using a biodegradable delivery system for the local controlled release of sodium fluoride as a mechanism for the stimulation of local bone growth. Sodium fluoride grains were mixed with poly-DL-lactic acid (PLA), and the mixture was then dissolved in acetone. After driving off the solvent, sheets of this material were rolled into rods 3.2 mm in diameter and 28.6 mm long. These were inserted into the intramedullary canals of the right femora of adult New Zealand White rabbits. A sham implant, made the same way but containing no fluoride, was inserted into the contralateral left leg. The effects of three different concentrations of sodium fluoride, 0.125 g NaF/g PLA, 0.250 g NaF/g PLA, and 0.500 g NaF/g PLA, were determined after a 4-week implantation period. In a second set of experiments, the concentration was fixed at 0.500 g NaF/g PLA with implantation durations of 4, 8, and 16 weeks. Expressed in terms of property ratios (experimental/control), bending strengths of the femora were significantly raised in most groups with the notable exception of Group 3 (0.500 g NaF/g PLA, 4 weeks). Cross-sectional area ratios in the distal femora were increased in all groups compared to right/left values for a normal unoperated group (p 〈 0.05), with the highest ratio being 1.50 (SD = 0.44) for Group 4 (0.500 g NaF/g PLA, 8 weeks). Only Group 4 animals showed significant (p 〈 0.05) increases in midshaft area ratio and none had responses proximally. Growth rates, measured by sequential fluorochrome labeling of bone followed the area ratio data and were only significant for the distal femora.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820230604
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  • 2
    Electronic Resource
    Electronic Resource
    Solvated helical backbones: X-ray diffraction study of Boc-Ala-Leu-Aib-Ala-Leu-Aib-OMe · H2O (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 773-781 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A second example of insertion of a water molecule into the helical backbone of an apolar peptide is presented here and compared to a similar occurrence in a longer peptide with the same type of sequence of residues, i.e., Boc-Aib-(Ala-Leu-Aib)3-OMe. The backbone of the title compound assumes an approximate 310-helical form with three 4 → 1 hydrogen bonds. In the place of a fourth 4 → 1 hydrogen bond, a water molecule is inserted between O(1) and N(4), and acts as a bridge by forming hydrogen bonds N(4) … W(1) (2.95 Å) and W(1) … O(1) (2.81 Å). The water molecule participates in a third hydrogen bond with a neighboring peptide molecule, W(1) … O(4) (2.91 Å). The insertion of the water molecule causes the apolar peptide to mimic an amphiphilic helix. Crystals grown from ethyl acetate/petroleum ether (reported here) or from methanol/water solution are in space group P212121 with a = 12.024(4) Å, b = 15.714(6) Å, c = 21.411(7) Å, Z = 4 and dcalc = 1.124 g/cm3 for C32H58N6O9 · H2O. The overall agreement factor R is 6.3% for 2707 reflections observed with intensities 〉 3σ(F) and the resolution is 0.90 Å.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280307
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  • 3
    Electronic Resource
    Electronic Resource
    Site-specific laser modification (cleavage) of oligodeoxynucleotides (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1129-1147 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sequence-specific photomodification of oligodeoxynucleotide pAGAGTATTGACTTA (“a target”) has been carried out with the aid of complementary fluorescent probes. Such a probe consisted of oligodeoxynucleotide pAATACTCT and a chromophore group attached to its 5′ end. Three different derivatives of ethidium bromide were used as a chromophore. The photomodification was induced by nitrogen laser radiation (337 nm, 15 MW /cm2). The irradiation induces the following photodamages: target cleavage at the specific binding site with a cutting off of the 8-mer from its 5′ end (yield up to 12%), formation of specific covalent adduct target-probe with a yield of 20-70%, and piperidine-sensitive target modifications with a 7-27% yield (for different chromophores). The total yield of specific photodamages of all kinds is 50-80%. The target cleavage and generation of piperidine-sensitive modifications are optically nonlinear processes. Piperidine treatment of the irradiated samples led to specific cleavage of the target with the yield up to 40%. All kinds of observed modifications are not influenced by high concentrations of free radical scavengers: 1.3M tBuOH and 10 mM cystamine. The pattern of cleavage indicates that the most probable position of the chromophore is between T8 and G9 of the target, i.e., the chromophore stacks on top of the last A · T base pair of the duplex. The aggregate of evidence is in agreement with the mechanism of nonlinear photomodification (the cleavage and generation of piperidine-sensitive modifications) based on the transfer of two-photon excitation energy from the chromophore to the target.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280607
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  • 4
    Electronic Resource
    Electronic Resource
    Phonon interpretation of inelastic neutron scattering in DNA crystals (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1189-1193 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The calculated spectrum of longitudinal compressional waves on DNA polymer chains is shown to be in excellent agreement with recently performed inelastic neutron scattering measurements in hydrated, oriented DNA crystals. This opens up a previously unexplored frequency regime of DNA science and establishes the validity of the phonon extended wave description of DNA elementary excitations in this region.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280702
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational properties of 2,3-methanopyroglutamic acid in peptides: Nmr and X-ray diffraction studies (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 123-128 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of replacing L-pyroglutamic acid with the cyclopropane analogue 2,3-methanopyroglutamic acid (2,3-MeGlp) on conformation and enzymatic stability have been investigated in 2,3-MeGlp-NHMe and the novel thyrotropin releasing hormone (TRH) analogue [2,3-MeGlp1]-TRH by x-ray diffraction and nmr. While 2,3-MeGlp-NHMe adopts a folded conformation (small ψ angle) in the solid state, several conformations are available to the molecule in solution. 1H-nmr of the diastereomeric mixture [(±)-2,3-MeGlp1]-TRH indicates a close orientation of the pyrrolidone and imidazole rings. The 2,3-MeGlp-His amide bond is considerably more stable to pyroglutamate aminopeptidase than the Glp-His bond in TRH.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280114
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  • 6
    Electronic Resource
    Electronic Resource
    Conformation of bombesin in buffer and in the presence of lysolecithin micelles: Nmr, CD, and fluorescence studies (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 441-463 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of the tetradecapeptide hormone bombesin has been studied in buffer and in the presence of lysolecithin micelles, using static and dynamic fluorescence, CD, and one- and two-dimensional nmr. The results obtained show that in buffer bombesin is present in an extended flexible chain, with no evidence for any ordered secondary structure. A marked change in the CD spectrum is observed changing from buffer to the lipid suspension. Concomitantly, the 1H-nmr spectrum of bombesin, in a D2O lipid dispersion, shows the persistence of resonances due to exchangeable protons and in similar conditions the fluorescence intensity increases. We think therefore that these results strongly support the hypothesis that bombesin interacts with the lipid phase, assuming ordered secondary structure. Finally, the marked dependence of tryptophan fluorescence quantum efficiency and order parameter from the hormone concentration in the presence of lysolecithin but not in buffer leads to the conclusion that bombesin can associate into the lipid matrix.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280140
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  • 7
    Electronic Resource
    Electronic Resource
    Solvation thermodynamics of biopolymers. II. Correlations between functional groups (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1327-1337 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The extent of correlations between functional groups that can form hydrogen bonds with solvent molecules has been estimated. From the observed distance distribution of functional groups on the surfaces of several proteins, and from the extent of correlation between pairs of such functional grups, we conclude that the assumption of independence of functional groups made in part I is probably a good approximation. The reason is that even when correlations exist there is, on average, cancellation of the positive and negative correlations. The relevance of hydrogen bonding with the solvent to the relative stability of different conformers of biopolymers is also indicated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280712
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  • 8
    Electronic Resource
    Electronic Resource
    Emulsion polymerization of butadiene, 1. The effects of initiator and emulsifier concentration (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 777-788 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the emulsion polymerization of butadiene was investigated using Dresinate 214 as emulsifier and three dissociative initiators, viz. potassium peroxodisulfate, 4,4′-azobis-(4-cyanopentanoic acid) and 2,2′-azoisobutyronitrile. All experiments were conducted in the presence of a thiol as chain transfer agent, as usual in diene-polymerizations. The polymerization rate in interval II, Rpol, was found to be highly insensitive to changes in the initiator concentration (Rpol ∝ [I]0,08). Primary radicals are generated in large abundance in interval I as compared with the final particle number, indicating that the initiator efficiency with regard to particle nucleation is very low. The development of particle number as a function of conversion at several emulsifier concentrations shows that limited coagulation is occurring in the present system. Rpol depends on the emulsifier concentration with an exponent of 0,61, while the final particle number after cessation of coagulation depends on the emulsifier concentration to the 1,6th power. As a consequence the average number of radicals per particle must be a function of particle size, because the monomer concentration in the latex particles is approximately constant in interval II. A certain analogy in behaviour between the emulsion polymerization of various polar monomers, kinetically dominated by radical desorption, and the emulsion polymerization of butadiene, suggests that similar events determine the kinetic course in the present system.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900411
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  • 9
    Electronic Resource
    Electronic Resource
    Wavelength sensitivity of acrylonitrile-butadiene-styrene (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 1341-1357 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The wavelength sensitivity of unpigmented 100 mil thick ABS exposed to sunlight and filtered xenon are radiation was determined by the sharp cut filter technique based on three types of photochemical changes: bleaching, yellowing and loss in impact strength. Bleaching of the yellow-colored species formed in the processed material is caused by wavelengths between 380 and 525 nm with maximum color change by the 475-485 nm region. Photochemical yellowing is due to wavelengths between 300 and 380 nm with all wavelengths being almost equally effective. The spectral sensitivity based on change in impact strength shifts from the UV to the visible region as photochemical yellowing progresses. Addition of two stabilizers, a benzotriazole ultraviolet absorber and a hindered amine stabilizer, shifts the wavelength sensitivity based on yellowing to wavelengths shorter than 330 nm, but has no influence on the spectral effects based on impact strength. It is postulated that the rate of yellowing is reduced mainly by the ultraviolet absorber and stabilization against loss in impact strength is due largely to the hindered amine. Differences in rates and spectral response of the three types of photochemical changes indicate that they are due to different initiating mechanisms and thus require different types of stabilization. The significance to stability testing is discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1989.080270418
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  • 10
    Electronic Resource
    Electronic Resource
    Electroninitiated polymerization of bis(trichlorophenoxo)-tetramethylethylene diamine copper(II) (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 1599-1608 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electroninitiated polymerization of bis(trichlorophenoxo)-N,N,N′,N′-tetramethylethylene diamine copper(II) was achieved in acetonitrile at various peak potentials of the monomer. A constant potential approach was selected in polymerization reactions. Electrolyses were carried out under air, nitrogen, and oxygen atmospheres. Structural analyses of the polymers were done by 1H-NMR and 13C-NMR FT-IR spectroscopy. Molecular weights of the polymers were determined by vapor pressure (isopiestic) method.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1989.080270511
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