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  • 1990-1994  (29)
  • 1960-1964  (6)
  • Polymer and Materials Science  (28)
  • Genetics  (4)
  • Rhenium  (3)
  • 1
    Electronic Resource
    Electronic Resource
    The quadruply bondedbis-carboxylatescis-Re2(μ-O2CCH3)2X4L2 (X = halide;L = neutral donor) as synthons in dirhenium chemistry (1994)
    Springer
    Journal of cluster science 5 (1994), S. 173-184 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dimetal comptexes ; phosphine ligands ; carboxylatebridged complexes ; redox chemistry ; preparation ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reactions of the quadruply bonded dirhenium(III) carboxylatescis-Re2(μ-O2CR)2X4L2 (X=CI or Br; L=a monodentate donor) with monodentate, bidentate, and tridentate phosphine donors result in several types of redox behavior, usually involving partial or complete reductive decarboxylation of the dirhenium unit. Examples of dirhenium(VI, II), dirhenium(IV, II), dirhenium(III, II), and dirhenium(II, II) complexes, in which Re-Re bond orders of 4, 3.5, 3, l, or zero are encountered, have been isolated and repre-sentative examples structurally characterized. The course of these reactions is dependent upon the nature of the phosphine. The scope of this remarkably rich chemistry is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165498
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  • 2
    Electronic Resource
    Electronic Resource
    The oxidative addition of hydrogen sulfide to the electron-rich triple bond: The isolation and characterization of compounds that contain the Re2(μ-H)(μ-SH) cluster unit (1991)
    Springer
    Journal of cluster science 2 (1991), S. 259-270 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; clusters ; hydrido-bridged ; hydrosulfido-bridged ; preparation ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reactions of Re2X4(μ-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) with H2S in THF afford the dirhenium (III) complexes Re2(μ-H)(μ-SH)X4(μ-dppm)2, the first examples of the oxidative addition of an S-H unit across an electron-rich metal-metal triple bond. The bromide complex Re2(μ-H)(μ-SH)Br4(μ-dppm)2 (C2H5)2O crystallizes in the space group P21/n witha=16.631(2) Å,b=15.967(3) Å,c=19.904(2) Å, β=92.698(7)°,V=5279(2) Å3, andZ=4. The structure which was refined toR=0.053 (R w=0.070) for 4903 data withI〉3.0σ(I), shows the presence of an edge-shared bioctahedral geometry with a very short Re-Re distance of 2.4566(7) Å. While the hydrogen atoms of the μ-H and μ-SH ligands were not located in the X-ray structure determination, their presence is confirmed by IR and1H NMR spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00702956
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  • 3
    Electronic Resource
    Electronic Resource
    The oxidative addition of diphenylphosphine and monophenylphosphine to the electron-rich rhenium-rhenium triple bond. The isolation and characterization of compounds that contain the four-center Re(μ-X)(μ-PR2)Re cluster (X=halide) (1992)
    Springer
    Journal of cluster science 3 (1992), S. 83-102 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dimetal clusters ; hydrido-complexes ; phosphidobridged ; preparation ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Diphenylphosphine oxidatively adds to the Re≡Re bonds of Re2 X 4(μ-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) and Re2Cl4(μ-dpam)2 (dpam=Ph2AsCH2AsPh2) to afford the dirhenium(III) complexes Re2(μ-X)(μ-PPh2)HX 3(μ-LL)2. The dppm complexes have also been prepared from the reactions of Re2(μ-O2CCH3)X 4(μ-dppm)2 with Ph2PH, and a similar strategy has been used to prepare Re2(μ-Cl)(μ-PPh2)HCl3(μ-dmpm)2 (dmpm=Me2PCH2PMe2) from Re2(μ-O2CCH3)Cl4(dmpm)2. Phenylphosphine likewise reacts with Re2 X 4(μ-dppm)2 to give Re2(μ-X)(μ-PHPh)HX 3(μ-dppm)2. An X-ray crystal structure determination on Re2(μ-Cl)(μ-PPh2)HCl3(μ-dppm)2 confirms its edge-shared bioctahedral structure. This complex crystallizes in the space group $$R\bar 3$$ (No. 148) witha=21.699(3) Å, α=84.50(4)°,V=10084(5) Å3, andZ=6. The structure was refined toR=0.049 (R w 0.069) for 5770 data withI〉3.0σ(I). The Re-Re distance is 2.5918(7) Å. Oxidation of the bromide complex Re2(μ-Br)(μ-PPh2)HBr3(μ-dppm)2 with NOPF6 produces the unusual dirhenium(III, II) cation [Re2(μ-H)(μ-Br)[P(O)Ph2]Br2(NO)(μ-dppm)2]+ which has been structurally characterized as its perrhenate salt, [Re2(μ-H)(μ-Br)[P(O)Ph2]Br2(NO)(μ-dppm)2]ReO4 · 2CH2Cl2. This complex crystallizes in the space group $$P\bar 1$$ (No. 2) witha=14.187(7) Å,b=16.419(5) Å,c=16.729(5) Å, α=98.76(2)°, β=110.11(3)°, γ=104.66(3)°,V=3414(6) Å3,Z=2. The structure was refined toR=0.040 (R w =0.051) for 5736 data withI〉3.0σ(I). The presence of a phosphorus-bound [P(O)Ph2]− ligand, a linear nitrosyl and a bridging hydrido ligand has been confirmed. The Re-Re distance is 2.6273(8) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814613
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  • 4
    Electronic Resource
    Electronic Resource
    Excited states of CF4 plasma for polymerization of TMPTA monomer (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 323-328 
    Details
    ISSN: 0887-624X
    Keywords: CF4 plasma ; trimethylolpropane triacrylate ; excited states ; plasma induced polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The F and CF2-CF2+ excited states have been detected by emission spectroscopy in CF4RF plasmas used for TMPTA polymerization. These excited states are related through electron collision to F and CF2 ground states. The temporal variation of the F and CF2-CF2+ radiative states near the substrate reveals that the F atoms disappear first by incorporation in the monomer during the polymerization phase and, then, by a third body recombination process enhanced by the polymer surface. The CF2-CF2+ radiative states are varying as the inverse of the F states indicating a strong destruction mechanism of CF2 radicals by F atoms.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300217
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  • 5
    Electronic Resource
    Electronic Resource
    Polymer drying. VII. 1H-NMR studies of evaporation from liquid saturated poly(styrene-co-divinylbenzene) (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1155-1161 
    Details
    ISSN: 0887-624X
    Keywords: adsorption ; desorption ; association ; polystyrene ; NMR ; polymer transitions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Composition-studies were carried out in which samples of films composed of poly(styrene-co-divinylbenzene) particles enmeshed by poly(tetrafluoroethylene) fibers were saturated with dichloromethane and then allowed to evaporate at 23°C to virtual dryness as the 1H-NMR signals and residual weight of sorbed liquid were monitored. The correlations, of 1H-NMR line-widths with the corresponding log of the number, αt of residual sorbed molecules per monomer unit show that sharp changes occur as αt passes through αG the composition that exists when all the liquid not sorbed (i.e., not present within the liquid-saturated particles), has been eliminated, and again as αt passes through αg the composition that exists when the particles attain the rigidity characteristic of the glassy state. Correlation of the corresponding T1 relaxation times with log αt show that sharp changes occur when αt becomes equal first to α′s and then to α′g the compositions that exist respectively when, firstly, all the sorbed liquid not immobilized by adsorption to the polymer chains within the particles has been eliminated, and then when the desorption of immobilized liquid from the chains causes the composition to begin to undergo transition from its rubbery state to its glassy state.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300622
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2049-2056 
    Details
    ISSN: 0887-624X
    Keywords: metallocenes ; olefin polymerizations ; Ziegler-Natta catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propylene was polymerized with rac-ethylene-bis (1-η5-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; 13C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321106
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  • 7
    Electronic Resource
    Electronic Resource
    Bifunctional reagents and protein structure determination. The reaction of phenolic disulfonyl chlorides with lysozymeThis work was supported in part by grants from the National Science Foundation (GA-9794 and G-16161) and from the American Academy of Arts and Sciences. (1964)
    New York : Wiley-Blackwell
    Biopolymers 2 (1964), S. 349-360 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It was established that phenol-2,4-disulfonyl chloride and α-naphthol-2, 4-disulfonyl chloride introduce new intramolecular or tertiary bonds into lysozyme. The phenolic hydroxyl group seems to make the cross linking reagents soluble in aqueous media; it was established that a sulfonylating; species does dissolve prior to hydrolysis but that the chlorosulfonyl groups are hydrolyzed within seconds of dissolution. New covalently linked residues were shown to be introduced by different, spectra. Peptide maps of the lysozyme treated with phenol-2,4-disulfonyl chloride. peroxidized, and digested with trypsin showed definite deletions and additions when compared with the control. Partial analysis of the peptides showed that cross linking between ε-amino groups of lysine residues had occurred. A certain degree of stabilization of lysozyme to inactivation by certain inactivating conditions was noted after treatment with the two reagents. Ultra-centrifugal analysis of the lysozyme treated with phenol-2,4-disulfonyl chloride showed that there was no detectable fraction having a higher molecular weight than native lysozyme. Tentative assignments of positions of cross linking were made.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1964.360020406
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  • 8
    Electronic Resource
    Electronic Resource
    Peptide libraries: Determination of relative reaction rates of protected amino acids in competitive couplings (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1681-1689 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the solid phase preparation of synthetic peptide libraries, equimolarity of the resultant peptides in the mixture simplifies the identification of active compounds. Two primary methods for the preparation of combinatorial peptide mixtures are currently used. In the first method, the starting resin is divided into equal aliquots, individual amino acids are coupled to each aliquot, and the resin is then recombined. This process is repeated for each position. However, due to the physical process, each resin bead contains only one peptide sequence. Statistically, for mixtures of longer sequences, an ever-increasing amount of resin is necessary to ensure complete representation of each peptide in the library. Thus, each peptide will be represented in the library if a sufficient number of resin beads are used. In addition, the concentration of each peptide in the library depends on both the number of mixture positions in the library and the amount of resin used. In the second method, mixtures of amino acids are coupled simultaneously at each addition step. The proportion of each amino acid in the reaction mixture is varied inversely to its reaction rate such that, ideally, an equimolar mixture of each peptide is synthesized. An advantage of this method over the previous method is that each peptide is ensured to be represented in the library, although not necessarily in equimolar amounts. It is known that not only do the coupling rates of each amino acid vary, but the coupling rates of individual amino acids also change when coupled to different amino acid resins. Consequently, in order to obtain equimolar peptide mixtures through the use of mixtures of protected amino acids, the ratio of reaction rates of one amino acid over another must be constant irrespective of the resin-bound amino acid. If this premise is true, this method of synthesis offers a significant advantage over the previous method since, theoretically, equimolar peptide libraries could be synthesized. The influence of the resin-bound amino acid on the relative reaction rates of incoming amino acids was investigated in the current study. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360341212
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  • 9
    Electronic Resource
    Electronic Resource
    The electrostatic contribution to DNA base-stacking interactions (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 145-159 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Base-stacking and phosphate-phosphate interactions in B-DNA are studied using the finite difference Poisson-Boltzmann equation. Interaction energies and dielectric constants are calculated and compared to the predictions of simple dielectric models. No extant simple dielectric model adequately describes phosphate-phosphate interactions. Electrostatic effects contribute negligibly to the sequence and conformational dependence of base-stacking interactions. Electrostatic base-stacking interactions can be adequately modeled using the Hingerty screening function. The repulsive and dispersive Lennard-Jones interactions dominate the dependence of the stacking interactions on roll, tilt, twist, and propeller. The Lennard-Jones stacking energy in ideal B-DNA is found to be essentially independent of sequence.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320205
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  • 10
    Electronic Resource
    Electronic Resource
    A synopsis of empirical gel fraction analytical methods: Application of the Wanxi equation to polyethylenes irradiated in vacuo and in the presence of acetylene (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2049-2053 
    Details
    ISSN: 0887-6266
    Keywords: empirical gel fraction analysis ; application of Wanxi equation to polyethylenes irradiated in the presence of acetylene and in-vacuo ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gel fraction data from linear low-density polyethylene (LLDPE) films and high-modulus polyethylene (HMPE) fibers, which had previously failed to give reasonable results when treated with Charlesby-Pinner and Saito-Kang-Dole theory, have been fitted to a modified form of the Wanxi equation. The fitting yields parameters that compare very well with literature values derived by the Wanxi equation, confirming that fracture and cross-linking densities are proportional to a power function (β) of the radiation dose. Extrapolated G(S) values have been obtained from LLDPE using the fit parameters and UV-Vis spectroscopy data. A brief synopsis of the empirical analytical methods available for gel fraction analysis is given. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321211
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