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  • 11
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    Phosphorus partitioning between olivine and melt: An experimental study in the system Mg2SiO4-Ca2Al2Si2O9-NaAlSi3O8-Mg3(PO4)2 (2013)
    In:  American Mineralogist
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 12
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    An experimental and theoretical investigation of Mg isotope fractionation in the Earth´s mantle (2009)
    In:  GV 99th Annual Meeting (Göttingen 2009)
    Details
    Publication Date: 2020-02-12
    Description: Mg isotope analyses of mantle rocks and minerals revealed large variations. Systematic differences in δ26Mg found between minerals from mantle xenoliths offer the potential for this isotopic system as an isotope geothermometer. However, results from other studies reveal a more complicated picture, where isotopic variability was found in similar samples (San Carlos olivines). To date, the cause for the observed variability remains uncertain. We explore the role of inter-mineral Mg isotope fractionation at upper mantle conditions. Experiments were done at 2 GPa and 00°C for 167 to 185 hours to investigate isotope partitioning between forsterite (Fo) and enstatite (En). Mg isotopes of coexisting En and Fo were analysed by MC-ICP-MS. The experiments were complemented by analyses of olivine and orthopyroxene from a SC xenolith and by theoretical estimations of equilibrium inter-mineral Mg isotope fractionation, based on vibrational frequency calculations and minimization of the total free energy of the solids. First experimental results revealed no Mg isotope fractionation between En and Fo beyond analytical precision at 00°C, 2 GPa (∆26MGEn-Fo = -0.02‰±0.12 (2SD); -0.03‰±0.).This result is consistent with our measurement on the SC xenolith (∆26Mgopx-ol = -0.08‰±0.11) and is close to the theoretical estimate (0.21‰). The absence of equilibrium inter-mineral Mg isotope fractionation suggests that the variability observed in various mantle-derived rocks is caused by other processes, such as diffusion-induced kinetic isotope fractionation as previously observed for Li isotopes. This is supported by a co-variation between Li and Mg isotopes found by others in a global peridotite dataset, implying both Li and Mg isotopes are affected by the same process. Hence, a combined Mg and Li isotope approach has the potential to better understand processes leading to the observed isotopic variability.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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  • 13
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    The origin of S4+ detected in silicate glasses by XANES (2008)
    In:  American Mineralogist
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 14
    Electronic Resource
    Electronic Resource
    Tyrosine-derived polycarbonates: Backbone-modified “pseudo”-poly(amino acids) designed for biomedical applications (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 411-417 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from L-tyrosine (Tyr) and its metabolites desaminotyrosine (Dat) and tyramine (Tym), four structurally related model dipeptides were prepared: Dat-Tym (neither N- or C-terminus present), Z-Tyr-Tym (N-terminus protected by benzyloxycarbonyl), Dat-Tyr-Hex (C-terminus protected by a hexyl ester group), and Z-Tyr-Tyr-Hex (both N- and C-termini present, protected by benzyloxycarbonyl and hexyl ester, respectively). The model dipeptides were used as monomers in the synthesis of polycarbonates. The polymerization reaction in the presence of either phosgene or triphosgene proceeded via the phenolic hydroxyl groups. Polymers with molecular weights of 105,000-400,000 da (by gel permeation chromatography, relative to polystyrene standards) were obtained. The physicomechanical properties (solubility, mechanical strength, glass transition and decomposition temperature, processibility) of the polymers were determined, and an attempt was made to correlate the polymer properties with the nature of the N- and C-terminus protecting groups. The presence of the urethane bond at the N-terminus protecting group was found to reduce solubility, ductility, and processibility, probably due to interchain hydrogen bonding. The presence of a C-terminus alkyl ester group increased solubility and processibility. Thus, the most promising candidate polymer for biomedical applications was obtained from Dat-Tyr-Hex, the monomer carrying a C-terminus protecting group only. Since very similar results had recently been obtained for a series of structurally related polyiminocarbonates, the structure property correlations seem to be generally valid.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320418
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  • 15
    Electronic Resource
    Electronic Resource
    Crystal structure and nmr conformation of a cyclic pseudotetrapeptide containing urethane backbone linkages (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 403-414 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Urethane bonds, derived from the hydroxyl group of the tyrosine side chain, have been investigated as a new type of amide bond mimetic in the design of pseudopeptides. The structure of a representative cyclic pseudotetrapeptide that consists of an  -  Ala  -  Tyr(urethane) Ala  -  Tyr (urethane) sequence fused into a rigid ring has been studied in the solid state by x-ray crystallography and in solution by two-dimensional nmr techniques. The cyclic pseudotetrapeptide has an oblong shape. The backbone urethane bonds assume a trans-trans conformation. The carbonyl groups in the ring have an alternating pattern of down, up, down, up with respect to the average ring plane. Solution nmr studies give observed nuclear Overhauser effects and coupling constants largely in agreement with the crystal structure. However, in solution the observed structure is likely to be conformationally averaged, and in the averaged structure, the urethane bond is perpendicular to the plane of the aromatic ring of the tyrosine, while in the crystal it is close to this plane. These differences may be explained by intermolecular hydrogen-bonding interactions. Four aspects of the conformation of the cyclic pseudotetrapeptide were investigated in detail: the tyrosine residue with the attached side-chain urethane bond (the tyrosine-urethane unit), the conformation of the two urethane backbone linkages, the conformation of the two conventional peptide bonds within this unusual ring structure, and the tight turns within the cyclic pseudotetrapeptide. The conformation of the tight turns present in the cyclic pseudotetrapeptide is very similar to that of a β-bend of type II. Intermolecular hydrogen bonding, joining adjacent layers of the cyclic pseudotetrapeptide in the solid state, resemble a parallel β-pleated sheet. The presence of these structural motifs in the cyclic pseudotetrapeptide indicates that the tyrosine urethane unit may find applications in peptide and protein engineering. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340312
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  • 16
    Electronic Resource
    Electronic Resource
    1,4,7,10,13,16,19,22-Octaazacyclotetracosane-1,4,7,10,13,16,19,22-octaacetic Acid (H8OTEC) and 1,4,7,10,14,17,20,23-Octaazacyclohexacosane- 1,4,7,10,14,17,20,23-octaacetic Acid (H8OHEC): Synthesis and Characterization of Two Large Macrocyclic Polyamine Polycarboxylic Ligands and Some of Their Copper(II) and Lanthanide(III) Complexes (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 267-277 
    Details
    ISSN: 0009-2940
    Keywords: Macrocyclic ligands ; Lanthanides ; Copper ; Polyamines ; Polycarboxylic acids ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optimized synthesis of two new macrocyclic polyamine polycarboxylic ligands, 1,4,7,10,14,17,20,23-octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetic acid (H8OHEC) (10) and 1,4,7, 10,13,16,19,22-octaazacyclotetracosane-1,4,7,10, 13,16,19,22-octaacetic acid (H8OTEC) (12), is presented. The key step in the synthesis of both is the high yield carboxymethylation of the corresponding macrocyclic amines using tert-butyl bromoacetate followed by acidic hydrolysis of the acetate protecting groups. The molecular structures of the intermediates 1,4,7,10,14,17,20,23-octaazacyclohexacosane (OHEC-amine) (8), and octa-tert-butyl 1,4,7,10,13,16,19,22- octaazacyclotetracosane-1,4,7,10,13,16,19,22-octaacetate (OTEC-ester) (11) are determined by X-ray crystal structure analysis. OHEC-amine 8 reacts with 2 equiv. of CuSO4 yielding the dinuclear complex [Cu2(OHEC-amine)](SO4)2 (13). Complex 13 crystallizes with 16 molecules of water. 13 · 16 H2O contains two copper atoms, which are coordinated in a strongly distorted octahedral fashion by four nitrogen atoms, one oxygen atom from the sulfate dianion and one oxygen atom from a water molecule. The new ligands 10 and 12 are fully characterized by 1D- and 2D-NMR spectroscopy. Both ligands form dinuclear lanthanide(III) chelates (Ln=Y, Sm, Eu, Gd, Yb, Lu), which are stable and highly water soluble. With lanthanum(III) only mononuclear complexes are formed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19971300221
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  • 17
    Electronic Resource
    Electronic Resource
    Dielectric loss features of some epoxy resins (1963)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 7 (1963), S. 2003-2023 
    Details
    ISSN: 0021-8995
    Keywords: 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: At temperatures far below the heat distortion point, the dissipation factor (and therefore power factor) of epoxy resins is comparably low - in the order of 0.001-0.01. Internally flexibilized, polyester-modified resins may have higher loss tangents, in the order of 0.01-0.10, even at room temperature. At temperatures far above the heat distortion point, anhydride curing agents give lower dissipation factors than do amines or acids. With anhydride cures, the higher molecular weight resins investigated cure faster than the lower molecular weight resins, give lower elevated temperature power factors and loss tangents, and are tougher. With any hardener-epoxy resin system, the optimum elevated temperature power factor, weight loss on aging and heat distortion point will probably depend on a close examination of the optimum hardener/resin ratio.With certain anhydride-cured low molecular weight epoxy resin systems, an increased rate of cure and lower elevated temperature power factor may be obtained by use of a small amount of higher molecular weight (polyhydroxy) epoxy resin. Attempts to compare the effect on power factor of changing the hydroxyl groups to less mobile dipoles by acetylation were unsuccessful, since the resulting acetoxy groups changed the cure mechanisms. However studies with resins of different molecular weights indicated that the effect of hydroxyl content on elevated temperature power factor is subordinate to other effects such as the rigidity of the cured resin system, rate of cure and ionic impurities. Acetylation of hydroxyl-containing epoxy resins may inhibit cure with some curing agents, due to side reactions of the resulting acetoxy group with specific hardeners.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1963.070070605
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  • 18
    Electronic Resource
    Electronic Resource
    Copolymerization of styrene. IV. Copolymerization with esters of benzylidenecyanoacetic acid (1970)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 14 (1970), S. 1491-1505 
    Details
    ISSN: 0021-8995
    Keywords: 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: Styrene was copolymerized in bulk with a number of esters of benzylidenecyanoacetic acid. The kinetic scheme of all pairs fitted the improved scheme of copolymerization, taking into account the effect of the penultimate unit. The Alfrey-Price Q and e values were calculated. Using the modified Taft equation, log (1/r1) = ρ*σ* + δEs, it was found that the relative reactivities of the ester monomers toward the polystyryl radical were correlated by the polar substituent constants σ* of the ester alkyl groups (ρ* = 0.14) and not by their steric substituent constants Es (δ = 0.008).
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1970.070140607
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  • 19
    Electronic Resource
    Electronic Resource
    Terpolymerization studies. I. Terpolymerization of acrylonitrile, styrene, and esters of α-cyanocinnamic acid (1975)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 19 (1975), S. 2359-2377 
    Details
    ISSN: 0021-8995
    Keywords: 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: The terpolymerizations of acrylonitrile, styrene, and seven esters of α-cyanocinamic acid were investigated up to low conversions. Polymerizations, carried out in bulk at 70°C, were initiated by free radicals. The relationships between monomer feed and terpolymer composition were determined on a triangular coordinate graph as proposed by Slocombe. In all cases, there exists an azeotropic line, connecting the binary azeotrope of the pair acrylonitrile-styrene and that of the various pairs of styrene with the esters of α-cyanocinnamic acid, yet no real ternary azeotrope was found.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1975.070190902
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  • 20
    Electronic Resource
    Electronic Resource
    Terpolymerization studies. II. Terpolymerization of acrylonitrile, styrene, and esters of α-cyanocinnamic acid. Polymerization methods and properties (1975)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 19 (1975), S. 2379-2389 
    Details
    ISSN: 0021-8995
    Keywords: 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: Terpolymers of acrylonitrile, styrene, and seven esters of α-cyanocinnamic acid were prepared by conventional polymerization methods up to high conversions. For emulsion polymerization systems, the rate dependence on the concentration of the emulsifier was determined. Terpolymers, made in suspension and in bulk, were used for the preparation of films and molded specimens in order to study their physical properties/chemical structure relationships.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1975.070190903
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