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  • 1990-1994  (9)
  • 1935-1939
  • Polymer and Materials Science  (5)
  • General Chemistry  (4)
  • 1
    Digitale Medien
    Digitale Medien
    The effect of polymer structure on the efficiency of acid generation from triarylsulfonium salts (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 309-316 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The irradiation of triarylsulfonium salts produces Brönsted acid along with diarylsulfide products. This photochemical conversion has been applied in several areas of polymer film technology including imaging and curing of films. This paper discusses the dependency of acid generation in polymer films on the structures of both polymer and sulfonium salt. The results suggest that the structures of both polymer and sulfonium salt. The results suggest that the efficiency of acid generation is dependent on the interaction between polymer structure and the charged sulfonium salt. Studies have been carried out for both deep-UV and electron beam irradiation of polymer films. The variation of acid generation with sulfonium salt loading has been determined. Finally the effect of accelerating voltage on the amount of acid generation following electron beam irradiation is discussed. ESR spectroscopy has been done on films after uv irradiation to determine the nature of the radicals which are formed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1991.080290303
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  • 2
    Digitale Medien
    Digitale Medien
    Customized neonatal incubator for measurement of platelet-artificial microvascular graft interactions under controlled flow, temperature, and transmural pressure (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 3 (1992), S. 1-7 
    Details
    ISSN: 1045-4861
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: A neonatal incubator has been custom modified to enable measurement of initial platelet retention on biomaterials in vitro under clinically relevant hemodynamic conditions. To calibrate this device, platelet retention on several materials having microconduit geometry (0.7-1.0 mm i.d.) has been measured after perfusion with citrated whole blood (containing 111 Indium-labelled platelets) at a shear rate of 312 s-1, 37°C, and 80 cm H2O transmural pressure. The relative reactivity of these materials toward platelets was: glass 〈 Fibrinogen(Fg)-coatedglass 〈 Fg-coated polyethylene 〈 polyethylene ∼ = Expanded polytetrafluoroethylene. Interindividual variation is relatively large (coefficient of variation = 35.5 ± 9.3%), but comparison to intraindividual controls reduces the variability to 14.8 ± 10.3%, a level which is suitable for economical testing of platelet retention to biomaterials in the presence or absence of drugs. This approach may have particular value in the study of the mechanism of platelet interactions with artificial microvascular grafts under perfusion conditions which are relevant to the first moments of flow, when initial platelet deposition occurs.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jab.770030102
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  • 3
    Digitale Medien
    Digitale Medien
    Spatial and temporal changes in compliance following implantation of bioresorbable vascular grafts (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 1449-1461 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Compliance matching between the host vessel and vascular grafts used for smalldiameter arterial replacements is thought to be important for longterm patency. However, currently available grafts elicit fibroplastic reactions, resulting in decreasing compliance with time after implantation. Bioresorbable prostheses elicit ingrowth of myofibroblasts containing abundant contractile elements. This led us to investigate whether compliance of implanted bioresorbable prostheses decreased as a function of time and if the kinetics of change correlated with the progession of tissue ingrowth. Woven polyglactin 910 prostheses (10 mm × 4 mm i.d.) were implanted into adult NZW rabbit infrarenal aortas and replicates were harvested serially through 8 months. Control grafts were implanted, and immediately resected. Dynamic compliance was measured a t 1-mm axial increments along each explant using a pulse duplicator apparatus which exposed the harvested samples to realistic pulsatile hemodynamics. Compliance was calculated for proximal, mid, and distal segments of each graft and averaged at each time point by grouping into control (zero time, n =3), early (1-4 weeks, n = 13), and late (6-36 weeks, n = 9) explant periods. At late explant periods both proximal and distal compliance were significantly greater than mid graft compliance (p ≤ .02 and p ≤ .03, respectively). There was a significant increase in proximal compliance between early and late explant times (p ≤ .01). Measured increases in mid and distal segment compliance over time did not reach statistical significance. Myofibroblast laden tissue ingrowth into the inner capsule followed macrophage phagocytosis and was nearly complete prior to the time that an increase in compliance was demonstrated. Thus since the major histologic episodes precede the change in compliance, these are not likely initiated by this biomechanical change. We hypothesize the graft resorption coupled with the ingrowth of more compliant tissue likely leads to the increased compliance of the graft material. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820261105
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  • 4
    Digitale Medien
    Digitale Medien
    Verbindungen mit Si—Si-, Ge—Ge- und Sn—Sn-Doppelbindungen sowie gespannte Ringsysteme mit Si-, Ge- und Sn-GerüstenProfessor Emanuel Vogel gewidmet (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 103 (1991), S. 916-944 
    Details
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Als Höhepunkte auf dem Gebiet der Organoelementchemie der schwereren Elemente der vierten Hauptgruppe (Gruppe 14 des Periodensystems) in den 80er Jahren gelten die Darstellung und vollständige Charakterisierung dreier Verbindungsklassen, deren Existenz bis dahin aufgrund ihrer Reaktivität für nicht möglich gehalten wurde. Hierbei handelt es sich um 1) die dreigliedrigen Ringsysteme Cyclotrisilan, -trigerman und -tristannan, 2) Moleküle mit Element-Element-Doppelbindungen einschließlich Disilen, Digermen und Distannen sowie 3) gespannte Polycyclen mit einem Gerüst aus den schwereren Elementen der 4. Hauptgruppe, z. B. Bicyclo[1.1.0]tetrasilan, Hexagermaprisman und Octasilacuban. Die meisten dieser Verbindungen sind durch sperrige Substituenten stabilisiert. Die Verbindungen ermöglichten Untersuchungen über die Veränderungen physikalischer und chemischer Eigenschaften in Abhängigkeit vom Element und den Substituenten sowie über die thermische und photochemische Reaktivität dieser Systeme, wobei zweiwertige Carben-Analoga nachgewiesen wurden. Parallel zu den experimentellen Arbeiten wurden an nahezu allen im Beitrag diskutierten Stammverbindungen Rechnungen durchgeführt. Einige Polycyclen weisen den Weg zu Verbindungen mit einer Element-Element-Dreifachbindung.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/ange.19911030805
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  • 5
    Digitale Medien
    Digitale Medien
    Wie die Natur Vitamin B12 synthetisiert - ein Überblick über die letzten vier Milliarden JahreNach einem Vortrag bei der 27. Euchem-Konferenz über Stereochemie, Bürgenstock (Schweiz). 26. April - 4. Mai 1992. Eine ausführlichere Übersicht zu diesem Forschungsgebiet findet sich in dem Beitrag “Genetically Engineered Synthesis of Complex Natural Products” (A. I. Scott. Tetrahedron 1992, 48, 2559). (1993)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 105 (1993), S. 1281-1302 
    Details
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Diese Übersicht stellt neuere experimentelle Ergebnisse der Erforschung der unendlichen Geschichte der Vitamin-B12-Biosynthese vor, wobei hauptsächlich auf Arbeiten aus der Arbeitsgruppe des Autors zurückgegriffen wird. Darüber hinaus gibt sie einen persönlichen Ausblick auf die Zukunft der Naturstoff-Biosyntheseforschung. Von zentraler Bedeutung ist mittlerweile die leistungsfähige Kombination von molekularbiologischen und modernsten spektroskopischen Techniken. Jene dienen der Suche nach und der Expression von Genen, die für die Enzyme der Biosynthese codieren, diese machen die biochemischen Vorgänge im NMR-Röhrchen direkt beobachtbar. Als logische Weiterentwicklung dieser Ansätze wird die Durchführbarkeit der Eintopf-Multienzymsynthese von Naturstoffen vorgestellt. Dank der Entwicklung und Nutzung von Klonierungstechniken und der daraus resultierenden Verfügbarkeit von Enzymen für die C-C-Verknüpfung hat sich ein grundlegender Wandel im “Handwerkszeug“ des Bioorganikers vollzogen. Gleichzeitig seien aber auch die Organiker angesprochen, die sich diesen technischen Fortschritt zunutze machen wollen. Ihnen wird sich eine neue Welt natürlicher Katalysatoren erschließen, die Synthesen mit hohen Ausbeuten bei einem oftmals überraschenden, aber durchaus willkommenen Mangel an Substratspezifität versprechen. Und schließlich hoffen wir, unsere Begeisterung für diese modernen Methoden weiterzugeben, mit denen heutige wie auch künftige Generationen von Chemikern die Synthesewege der Natur zu komplexen Naturstoffen erforschen können.
    Zusätzliches Material: 24 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/ange.19931050904
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  • 6
    Digitale Medien
    Digitale Medien
    Strained-Ring and Double-Bond Systems Consisting of the Group 14 Elements Si, Ge, and SnAbbreviations used in the text: Solvents and reagents: m-CPBA = metachloroperbenzoic acid; DCA = 9,10-dicyanoanthracene; DME = dimethoxyethane; TCNE = tetracyanoethylene. Substituent groups: 1-Ad = 1-adamantyl; Cy = cyclohexyl; Dep = 2,6-diethylphenyl; Dip = 2,6-diisopropylphenyl; Dis = bis(trimethylsilyl)methyl; Dit = 4-tert-butyl-2,6-diisopropylphenyl; Dmp = 2,6-dimethylphenyl; Dmt = 4-tert-butyl-2,6-dimethylphenyl; mes = mesityl(2,4,6-trimethylphenyl); Nep = neopentyl; Np = naphthalenide; Phen = 9-phenanthryl; Tip = 2,4,6-triisopropylphenyl; TMS = trimethylsilyl; p-Tol = p-tolyl; Tsi = tris(trimethylsilyl)methyl.Dedicated to Professor Dr. Emanuel Vogel. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 30 (1991), S. 902-930 
    Details
    ISSN: 0570-0833
    Schlagwort(e): Bond theory ; Tin ; Germanium ; Silicon ; Strained molecules ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The organometallic chemistry of the Group 14 elements E = Si, Ge, Sn in the 1980's is highlighted by the successful construction and characterization of three systems previously thought to be too reactive to exists: (1) three-membered ring compounds including cyclotrisilane, cyclotrigermane, and cyclotristannane, (2) molecules containing E—E double bonds including disilene, digermene, and distannene, and (3) strained polycycles containing a skeleton of Group 14 elements, such as bicyclo[1.1.0]tetrasilane, hexagemaprismane, and octasilacubane. The majority of these numerous compounds now available are fully substituted with bulky ligands to suppress the reactivity intrinsic to the systems. These compounds permit examinations of (1) the variation of physical and chemical properties of a system with these elements and also with the ligands and (2) how two systems are interrelated thermally and photochemically with the intermediacy of the divalent (carbene-like) species. Theoretical calculations on virtually all of the parent compounds discussed in this review are evaluated alongside the experimental results. Some polycycles may constitute a stepping-stone on the way to compounds with a triple bond.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/anie.199109021
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  • 7
    Digitale Medien
    Digitale Medien
    Deuterium Isotope Effects during RDX Combustion: Mechanistic burn rate-controlling step determination (1991)
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 16 (1991), S. 279-286 
    Details
    ISSN: 0721-3115
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: High pressure (500 psig/3.55 MPa and 1000 psigl6.99 MPa) burn rate comparisons from the combustion of solid RDX (hexahydro- 1.3,.5-trinitro-1,3,5-triazine) and perdeuterio-labeled RDX-dh cylindrical pressed pellets reveals a large kinetic deuterium isotope cffect (KDIE). This experimental KDIE confirms that chemical reaction kinetics are a significant mechanistic factor in controlling the inherent RDX burn rate and further shows the six-membered RDX hcterocycle's rate-controlling mechanistic step during com- bustion is the same as that previously reported for its larger eight-membered HMX (octahydro-l.3,5,7-tetranitro-l.3.5,7 tetrazocine) homologuc. As with HMX. This experimental KDTE approach also demonstrates a direct mechanistic relationship between RDX's higher order cornbustion regime and its ambient pressure thermochemical decomposition process.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/prep.19910160605
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  • 8
    Digitale Medien
    Digitale Medien
    How Nature Synthesizes Vitamin B12—A Survey of the Last Four Billion Years (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 32 (1993), S. 1223-1243 
    Details
    ISSN: 0570-0833
    Schlagwort(e): Vitamins ; Natural products ; Biosynthesis ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This review contains an account of recent experimental results in the continuing saga of vitamin B12 biosynthesis (largely from the author's laboratory) as well as a personal view of future directions of research in natural product biosynthesis. The emphasis is on the powerful combination of molecular biology in the search for, and the expression of, the genes encoding the biosynthetic enzymes and state-of-the-art spectroscopic techniques, in order to “view” the biochemical events as they take place in the NMR tube. As a logical development of these approaches, the feasibility of one-flask, multienzyme synthesis of natural products is addressed.[Based on a lecture given at the 27th Euchem Conference on Stereochemistry, 26th April to 4th May, 1992. Bürgenstock, Switzerland. A more explicit account of this new field has been given in “Genetically Engineered Synthesis of Complex Natural Products” (A. I. Scott Terruhedron, 1992, 48, 2559).] Implicit throughout is the profound change in the “tools of the trade” of the bioorganic chemist, thanks to the harnessing and exploitation of cloning techniques and the resultant availability of enzymes which can make carbon-carbon bonds. It is also our desire to alert organic chemists, who may wish to take advantage of these technical developments, to the fact that they will be rewarded by a new world of natural catalysts capable of high yielding, synthetic chemistry often with a surprising, but welcome, lack of substrate specificity. Finally we hope to convey our enthusiasm for the methods now at the disposal of present and future generations of chemists for studying Nature's synthetic routes to complex natural products.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/anie.199312233
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  • 9
    Digitale Medien
    Digitale Medien
    Kinetic Deuterium Isotope Effects in the combustion of formulated nitramine propellants (1994)
    Weinheim : Wiley-Blackwell
    Propellants, Explosives, Pyrotechnics 19 (1994), S. 42-58 
    Details
    ISSN: 0721-3115
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetic deuterium isotope effect was used to investigate the rate-limiting process in the combustion of formulated nitramine propellants. Model propellant formulations containing either octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), or their deuteriated analogues were pressed into pellets and burned under nitrogen pressure in a window bomb. The magnitudes of the observed deuterium isotope effects indicate that the HMX and RDX exert significant control over the combustion phenomenon of the propellants studied. Furthermore, assuming a consistent mechanism between decomposition and combustion, the observed isotope effects suggest that a carbon-hydrogen bond rupture in HMX or RDX is the rate-controlling step in the combustion of the model nitramine propellants. Observed isotope effect values for HMX-CW5 and RDX-CW5 formulated propellants at 1000 psig (6.99 MPa) pressure were 1.29 ± 0.09 and 1.24 ± 0.07, respectively, compared to a theoretical estimate of 1.29 for a primary effect due to C—H bond rupture at 673 K.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/prep.19940190108
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