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  • Chemistry  (146)
  • Biochemistry and Biotechnology  (11)
  • Cell & Developmental Biology  (9)
  • PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR  (8)
  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The secondary structure transformation of β-lactoglobulin from a predominantly β-structure into a predominantly α-helical one, under the influence of solvent polarity changes is reversible. Independent of the alcohol used  -  methanol, ethanol, or 2-propanol  -  the midpoints of the observed structural transformation occur around dielectric constant ε ≈ 60. The structural change destroying the hydrophobic core formed by the β-barrel structure leads, at room temperature, to the dissociation of the retinol/β-lactoglobulin complex in the neighborhood of dielectric constant ε ≈ 50. However, when the dielectric constant of the medium is raised back to ε ≈ 70 by the decrease of the temperature, both the refolding of BLG into a β-structure and the reassociation of the retinol/β-lactoglobulin complex are observed. The esterification of β-lactoglobulin carboxyl groups has two effects: on the one hand it accelerates the β-strand → α-helix transition induced by alcohols. On the other hand, the esterification of β-lactoglobulin strengthens its interaction with retinol as it may be deduced from the smaller apparent dissociation constant of retinol/methylated β-lactoglobulin complex. The binding of retinol to modified or unmodified β-lactoglobulin has no influence (stabilizing or destabilizing) on the folding changes induced by alcohol. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that the demosponge Corallistes sp. (Tetractinomorpha, Lithistida, Corallistidae) collected in the Coral Sea, contains corallistin A (1), the second example, of a free porphyrin from a living organism. The compound proved to be active against the Kb cell line. In contrast with the geoporphyrins which do not bear any O-atom corallistin A (1) carries two carboxylic groups.
    Additional Material: 1 Tab.
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variable-temperature and -pressure 13C-NMR studies of the 1,3,5-trithiane-capped triruthenium clusters [Ru3(CO)9{μ3-(η3-1,3,5-trithiane)}] (1) and [Ru3(t-BuNC)(CO)8{μ3-(η3-1,3,5-trithiane)}] (2) revealed that CO site exchanges occur via an intramolecular merry-go-round process, involving a transition state mostly dissociative in character.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [Ir2Rh2(CO)12] with 1 mol-equiv. of PPh3 yields [Ir2Rh2(CO)11PPh3] (1) as a mixture of two isomers with the phosphine ligand axially bound either to one basal Rh-atom in the kinetically preferred isomer 1 R or to one basal Ir-atom in the thermodynamically preferred isomer 11. Both isomers are fluxional on the 13C-NMR time scale at low temperature due to CO scrambling. Around room temperature, a new type of fluxional process starts to operate which is responsible for the isomerisation 1R⇄11, i.e. the intramolecular migration of the reputedly inert PPh3 ligand from one metal centre to another. The activation volumes of conversions 1R → 11 and 11 → 1R are both positive, indicating that the migration of PPh3 is dissociative in character. This article reports the first application of variable pressure 31P-NMR to mechanistic studies.
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 1213-1217 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Photoelektronenspektren, elektronische Struktur und Gasphasenthermolyse von substituierten TetrazolinenDie elektronische Struktur und die Gasphasenthermolyse der Tetrazoline 1-5 wurden durch Photoelektronenspektroskopie untersucht. Die Verbindungen 1-4 zerfallen durch Cycloreversion in Methylazid und die entsprechenden Imine. Demgegenüber wird aus 5 unter Ringkontraktion ein Diaziridin gebildet. Zur Zuordnung der PE-Spektren wurden an den Verbindungen 1, 2, 4 und 5 MNDO-Rechnungen, zur Konformationsanalyse von 5 auch AM1-Rechnungen durchgeführt.
    Notes: The electronic structures and the gas-phase thermolyses of tetrazolines 1 -5 have been studied by photoelectron spectroscopy. For compounds 1-4 cycloreversion to imine and methyl azide is observed, whereas compound 5 is contracted to give the respective diaziridine. To assign the PE spectra, MNDO calculations were performed for compounds 1, 2, 4, and 5; some conformational properties of 5 have also been studied by AM 1 calculations.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1739-1746 
    ISSN: 0009-2940
    Keywords: Nitrilimines ; Phosphorus heterocycles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions involving the λ3-phosphorus atom of N-[bis(diisopropylamino)phosphanyl)]-C-[(bis(diisopropylamino) -thio-phosphoranyl)nitrilimine (1) are reported. Addition of elemental sulfur or selenium to 1 leads, by a formal [1 + 4] cycloaddition, to 1,3,4,2λ5-thiadiazaphosphole 3a or 1,3,4,2λ5-selenodiazaphosphole 3b in 85 and 84% yield, respectively. Reactions of 1 with dimethyl acetylenedicarboxylate and tetracyanoethylene afford the corresponding [2 + 4] adducts 1,2,3λ5-diazaphosphinine 6 (80% yield) and 1,2,4,3λ5-triazaphosphinine 10 (80% yield). Phenyl azide reacts with 1 with loss of nitrogen to give 1,2,4,3λ5-triazaphosphole 15 (74% yield), while the reaction of 1 with α-diazo ketone 17 leads with conservation of the N2 grouping to the formation of 1,2,4,3λ5-triazaphosphole 20 (85% yield). Addition of methyl trifluoromethanesulfonate to 1 affords N-[bis(diisopropylamino)methylphosphonioyl]-C-[bis(diisopropylamino)thiophosphoranyl]nitrilimine 22. In contrast to 1, the new stable nitrilimine 22 is strongly electrophilic. [2 + 3] cycloadditions are observed with ethyl vinyl ether, styrene, methyl acrylate and phenylacetylene to furnish the corresponding pyrazolines 23 - 25 and pyrazole 26 in good yields. Water adds to 22 by a 1,3-addition process to give hydrazine 27 (88% yield). The lithium salt 30 of [bis(diisopropyl-amino)thiophosphoranyl](diazo)methane reacts with [bis(pentafluorophenyl)](chloro)phosphane to afford the corresponding diazo compound 32 (50% yield) while the reaction with (chloro)(phenyl)[2,4,6-tris(trifluoromethyl)phenyl]phosphane furnishes nitrilimine 33 in 82% yield. Only 1,3-addition reactions with water or diisopropylamine leading to hydrazine 34 (65% yield) and hydrazone 35 (54% yield) are observed on treatment with this new poorly reactive nitrilimine.
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 581-589 
    ISSN: 0009-2940
    Keywords: Silene, dichloroneopentyl- ; Imines ; Cycloaddition reactions ; 2-Silaazetidines ; Thermolysis reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Silaheterocycles, XXIII[1]. - Synthesis and Thermolysis Reactions of Si-Functionalized 2-SilaazetidinesDichloroneopentylsilene (1) is formed in situ by the reaction of trichlorovinylsilane with LitBu. The [2 + 2] cycloaddition to imines yields Si, Si1-dichloro-functionalized 2-silaazetidines in a preparative scale. With aldimines as trapping agents for 1, the resulting SiN four-membered ring compounds are isolated as syn/anti1-isomers (e.g. syn/anti-15 and -16; syn/anti ≍ 2:1). Silene 1 is not liberated from the silaazetidines on heating, but the Si, Si1-dichloro-substituted silanimine Cl2Si=NtBu (24) is formed. This can be trapped by Me3SiOMe or Ph2C=NtBu to give the addition products 25 and 26, respectively. The pathways are discussed which lead to stereoisomeric SiN ring compounds by a multiple-step mechanism including zwitterionic intermediates (1,4-dipoles). In addition there is strong evidence for the formation of 1, depending on the trapping reagent used. This fact may be explained by donor→silene interactions. The thermolysis products of silaazetidines support the formulation of a stepwise decomposition to an alkene and Cl2Si=NR derivatives.
    Additional Material: 4 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 3557-3566 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The structure and the orientation of cold stretched and hot stretched polyethylene films are investigated by transmission electron microscopy during an annealing treatment. In cold stretched films, the crystallite length (dimension perpendicular to chain direction) increases from 100 Å directly after drawing to 3000 Å after an annealing of 8 weeks at a temperature of 122°C. The orientation of the films changes during this treatment from a fiber texture to a b-texture and finally to a (110)-texture. In hot stretched films the crystallite length is about 500 Å after the deformation and increases with about the same velocity as in the cold stretched films. In contrast with the cold stretched films, the b-texture appears immediately after deformation and turns over to a (110)-texture. These observations are interpreted in terms of a recrystallization.
    Notes: Das Gefüge und die Orientierungen von kalt- und warmverstreckten Polyäthylenfilmen werden in Abhängigkeit von der Temperzeit mittels Transmissionselektronenmikroskopie untersucht. Die Kristallitlänge (Dimension senkrecht zur Molekülrichtung) wächst stetig von ca. 100 Å direkt nach der Kaltverformung auf 3000 Å nach einer Temperzeit von 8 Wochen bei 122°C an. Die Orientierung der Filme ändert sich während des Temperns von einer Fasertextur über eine b-Textur zu einer (110)-Textur. In warmverstreckten Filmen ist die Kristallitlänge nach der Verformung ca. 500 Å und wächst dann mit ähnlicher Geschwindigkeit wie bei kaltverstreckten Filmen. Im Unterschied zu den kaltverstreckten Filmen tritt die b-Textur direkt nach der Verformung auf und geht in eine (110)-Textur über. Diese Beobachtungen werden mit Hilfe der Rekristallisation gedeutet.
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  • 9
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It could be shown that the structure of poly(styrylpyridine)s (PSP), which are heat resistant thermosetting resins resulting from the polycondensation of 2,4,6-trimethylpyridine (1) with terephtalaldehyde (2), is much more complicated than that expected from this polycondensation. 2-Styrylpyridines were synthesized from benezaldehyde (5) and 2-methylpyridines and the stability of the respective intermediate alcohol was studied. The thermal behaviour of the styrylpyridines alone or in the presence of their precursors was studied by GPC, IR and NMR spectroscopy and by chemical analyses. It could be shown that the methyl group of 2-methylpyridine (4) adds reversibly to the double bond of 2-styrylpyridine (7) to form 2-phenyl-1,3-bis-(2-pyridyl)propane (8). This side reaction takes place also in the case of the condensation of 1 with 5. The structures and the reactivity of the condensation products of 1 with 1,2 or 3 molecules of 5 (compounds 14, 17 and 18) were studied. The condensation product 19, a component of PSP resins, was synthesized from 1 and 2 and its reactivity was studied at 200 and 250°C and compared with the non-methylated derivative 1,4-bis[2-(2-pyridyl)vinyl]benzene (25). The results of a preliminary analysis of the reactions taking place during the PSP thermosetting are reported.
    Additional Material: 7 Ill.
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  • 10
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of the compounds, resulting from the condensation of 2-methylpyridine, 2,6-dimethylpyridine and 2,4,6-trimethylpyridine with benzaldehyde and terephtalaldehyde, were confirmed by high field 1H and 13C NMR spectroscopy. Structural assignments were made based on the NMR spectra of the intermediate compounds, 4-[1-hydroxy-2-4,6-dimethyl-2-pyridyl-ethyl]benzaldehyde (5) and 4-[1-hydroxy-2-(6-methyl-2-pyridyl)ethyl]benzaldehyde (6), of the main reaction products 2-styrylpyridine (3) and 1,4-bis[2-(4,6-dimethyl-2-pyridyl)vinyl]-benzene (1), and of the side reaction product 2-phenyl-1,3-bis(2-pyridyl)propane (4) resulting from the addition of the methyl groups of 2-methylpyridine to the double bond of 3.
    Additional Material: 12 Ill.
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