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  • 1
    Electronic Resource
    Electronic Resource
    Pseudohalogenverbindungen, XXI. Darstellung und Eigenschaften von Trifluormethyldisulfanderivaten (1975)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 1365-1368 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Pseudohalogeno Compounds, XXI. Preparation and Properties of Trifluoromethyldisulfane DerivativesReactions of R2NSCl with Hg(SCF3)2 result in R2NSSCF3 (R = CH3, C2H5), which can be cleaved with HX to give CF3SSX and [R2NH2]X (X = Cl, Br). CF3SSCl reacts with C2H5OC(S)SK or AgOCN to yield C2H5OC(S)SSSCF3 or CF3SSNCO, respectively. This latter hydrolysis to CF3SSNHC(O)NHSSCF3 and CO2. Infra-red, n.m.r. and mass-spectroscopic data are given.
    Notes: Umsetzungen von R2NSCl mit Hg(SCF3)2 führen zu R2NSSCF3 (R = CH3, C2H5), die mit HX zu CF3SSX und [R2NH2]X (X = Cl, Br) gespalten werden können. Mit C2H5OC(S)SK bzw. AgOCN reagiert CF3SSCl zu C2H5OC(S)SSSCF3 bzw. CF3SSNCO. Letzteres hydrolysiert zu CF3SSNHC(O)NHSSCF3 und CO2. IR-, NMR und massenspektroskopische Daten werden angegeben.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19751080502
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  • 2
    Electronic Resource
    Electronic Resource
    Metabolic products of microorganisms. Part 262Part 261: [1].. The absolute configuration of sphydrofuran, a widespread metabolite from streptomycetes (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1281-1286 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sphydrofuran (1) was isolated from the culture filtrate of Streptomyces sp. (strain Gö 28 and Tü 3616) by chemical screening methods. Metabolite 1 is an anomeric and ring-chain tautomeric mixture and could easily be transformed into the stable furan derivative 2 under acidic conditions. The constitution and relative configuration of 1 was established by X-ray crystallography of its 8-O-methyl derivative 3a. The absolute configuration at C(4) of 1 and thus of the whole molecule (3R,4S,5S) could be determined starting from 2 using the Helmchen method.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740617
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  • 3
    Electronic Resource
    Electronic Resource
    L-Phenylalanine Cyclohexylamide: A simple and convenient auxiliary for the synthesis of optically pure α,α-disubstituted (R)- and (S)-amino acids (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 563-580 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes L-phenylalanine cyclohexylamide (5c) as a simple, cheap, and powerful chiral auxiliary for the synthesis of a series of optically pure α,α-disubstituted (R)- and (S)-amino acids of type 1, such as (R)- and (S)-2-methyl-phenylalanine (1a), (R)- and (S)-2-methyl-2-phenylglycine (1b), and (R)- and (S)-2-methylvaline (1c; Scheme 3). These amino acids were efficiently transformed into the suitably protected and activated amino acid building blocks (R)- and (S)-12b and (R)- and (S)-12c (Scheme 4) which are ready for incorporation into peptides by solution or solid-phase techniques. Based on the crystal structures of 6b, 6c, and 7a belonging to the diastereoisomeric peptides series 6 and 7, the absolute configurations of each member of the series were determined. β-Turn geometries of type II′ and I were observed for 6b and 7a, respectively, whereas 6c crystallized in an extended conformation. The impacts of side-chain variation on conformation and crystal packing of these triamides are discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780305
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  • 4
    Electronic Resource
    Electronic Resource
    Imidazole-Analogues of 6-Epicastanospermine and of 3,7a-Diepialexine (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 934-940 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral bicyclic imidazol derivatives 7 and 8 were obtained from D-glucose derivative 9 by a sequence of selective protection/deprotection and intramolecular SN2 reactions. Triols 7 and 8 are analogues of 6-epica-stanospermine (4) and of 3,7a-diepialexine (6), respectively, and are potential glycosidase inhibitors. However, their anti-HIV activity proved to be only marginal.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740503
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational Analysis of 1,2:3,4-Diepoxides: Ab Initio and semiempirical molecular-orbital calculations (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1651-1658 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using semiempirical and ab initio procedures, the most stable conformations of meso- and rac-bioxirane and of some substituted 1,2:3,4-diepoxides were calculated. For threo-diepoxides (having the same relative configurations as rac-bioxirane, 3), two stable conformations with CCCC dihedral angles of ca. 90 and ca. 270° were found. For erythro-diepoxides (derivatives of meso-bioxirane, 4) the calculations suggest three preferred conformations with corresponding dihedral CCCC angles of ca. 90°, ca. 180°, and ca. 270°. The calculations are in fair agreement with the experimental data available for the unsubstituted compounds 3 and 4.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750520
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  • 6
    Electronic Resource
    Electronic Resource
    Conformational Analysis of Open-Chain 1,2:3,4-Diepoxides: Comparison of crystal structures, NMR data, and molecular-orbital calculationsDedicated to Professor Dr. Christoph Tamm on the occasion of his 70th birthday (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1863-1875 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several pairs of diastereoisomeric open-chain 1,2:3,4-diepoxides with different substitution patterns were prepared (see 3-9). As far as possible, crystal structures were determined to corroborate the relative configurations and to give insight into the solid-state conformations of these compounds. The comparison with our earlier molecular-orbital calculations and with 1H-NMR measurements shows that the solid-state conformations of eight out of the nine open-chain 1,2:3,4-diepoxides, whose crystal structures had been determined, correspond to minima on the calculated energy profiles for these compounds or for closely related derivatives. In solution, highly substituted diepoxides of the erythro-series (e-6, e-7, e-9) seem to prefer the same conformation as in the crystal. The solution conformations of all other diepoxides differ from the arrangement in the solid state.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760506
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  • 7
    Electronic Resource
    Electronic Resource
    Optisch aktive Bipyridine in der asymmetrischen KatalyseDiese Arbeit wurde von der Volkswagen-Stiftung gefördert C. B. dankt dem Fonds der Chemischen Industrie für ein Liebig-Stipendium sowie Herrn Prof. Dr. B. Giese für seine Unterstützung. (1990)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 102 (1990), S. 206-208 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19901020218
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  • 8
    Electronic Resource
    Electronic Resource
    Monitoring the quality of mix of polymer melts with particulate fillers using fluorescence spectroscopy (1989)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1759-1765 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: Fluorescence spectroscopy has been employed to monitor the mixing of polymer melts with filler material. The polymer melts were low molecular weight polybutadiene and PBAN, a terpolymer consisting of 85% butadiene, 11% acrylonitrile, 4% acrylic acid, and the filler material was aluminum oxide. To carry out the fluorescence observations, a dopant chromophore was mixed into the polymer melt at very low concentrations, 10-4 to 10-6 molar or 11 to 0.11 ppm by weight. The mixing experiments were carried out using a small laboratory mixer which had glass walls for viewing the fluorescence spectra from the dopant chromophore. Fluctuations in fluorescence intensity were observed to decrease as a function of mixing time indicating that the spatial distribution of the fluorescent chromophores was becoming more uniform. Concerning the mixing of polymer melt and filler, we hypothesize that uniform mixing of ingredients is achieved when fluorescence intensity as a function of time is constant. In order to obtain quantitative support for this hypothesis, we used a fluorescence microscope to measure fluorescence intensity and optical transmittance from microscopic regions of well-mixed and poorly mixed specimens.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760292405
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  • 9
    Electronic Resource
    Electronic Resource
    Fluorescence monitoring of twin screw extrusion (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1365-1371 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: An optical fiber probe has been constructed in order to obtain real-time measurements of fluorescence radiation during twin screw mixing and extrusion of plasticized polybutadiene and calcium carbonate particulate. The probe consists of an optical fiber bundle which was inserted along the axis of a half-inch sensor bolt, and it was used to transmit optical excitation energy to the processed material and to detect the subsequent fluorescence. The source of fluorescence radiation was a fluorescent dye which was doped into the processed ingredients at very low concentrations. Although most of our measurements were taken with the probe positioned close to the exit die, the sensor bolt can be placed in any instrumentation port along the extruder line. Experiments were carried out to measure residence time distribution, quality-of-mix, and mix concentrations as a function of processing conditions. Product mix changes in response to variations in material feed rates and screw RPM were also observed. Values of residence time were obtained by measuring the transit times for the dye to travel from an upstream injection port to the measurement probe, a distance of 63 cm. Flow instabilities, such as mat formation of the solids, were observed by noting the abrupt changes and discontinuities in the fluorescence signal.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760311902
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  • 10
    Electronic Resource
    Electronic Resource
    In-line optical monitoring of polymer injection molding (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 671-679 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: An optical sensor, consisting of optical fibers to transmit light to and from the mold cavity, was constructed for the purpose of measuring the onset of polymer solidification during injection molding. The sensor was used to detect characteristic fluorescence radiation from a dye which had been doped into the resin at very low concentration. By measuring changes in fluorescence intensity it was possible to detect whether the state of the resin was liquid or solid. We observed that, as the resin cooled in the mold, the onset of solidification was indicated by highly characteristic and distinct changes in the fluorescence intensity/time profile. Application of the method involved the use of a calibration relationship between the fluorescence intensity and temperature of the doped polymer in order to determine the distict features which characterize the onset of solidification. Injection molding of a glass forming polymer (polystyrene) and a crystallizable polymer (polyethylene) was monitored by this technique.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340809
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