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  • Enzyme catalysis  (1)
  • Heterogeneous  (1)
  • Long-Chain Thiols  (1)
  • 1
    ISSN: 1572-879X
    Schlagwort(e): Heterogeneous ; hydrogenation ; surface alkyls ; platinum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract This paper reports a comparison of the ethyl moieties generated on the surface of platinum black during the heterogeneous, platinum-catalyzed hydrogenations of (1,5-cyclooctadiene)diethylplatinum(II) ((COD)PtEt2), of (homohypostrophene)diethylplatinum(II) ((HOP)PtEt2), and of ethylene using D2 in ethyl alcohol-d. In reductions of the platinum complexes, the π-olefin and σ-alkyl organic ligands are converted to alkanes by reaction of the intermediate surface alkyls with surface hydrides, and the platinum(II) becomes part of the platinum(0) surface. These reductions are characterized by two kinetic regimes: one in which the rate of reaction is limited by the mass transport of hydrogen to the surface of the catalyst (the mass transport limited regime, MTL), and one in which the rate is limited by a reaction on the surface of the catalyst (the reaction rate limited regime, RRL). In the RRL regime, the isotopic compositions of the ethanes-d n produced from the reductions of the platinum complexes and of ethylene suggest that the surface ethyls (Et *) generated from each precursor have similar relative rates of isotopic exchange (and thus of C-H bond activation) and of reductive elimination as ethane. In the MTL regime, the Et * derived from each precursor have different reactivities: the Et* generated from (HOP)PtEt2 have reactivities that are more similar to the Et * generated from ethylene than do the Et * generated from (COD)PtEt2.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 0935-9648
    Schlagwort(e): Interfacial Structure ; Wettability ; Long-Chain Thiols ; on Gold ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The interfacial properties of organic materials are of critical importance in many applications, especially the control of wettability, adhesion, tribology, and corrosion. The relationships between the microscopic structure of an organic surface and its macroscopic physical properties are, however, only poorly understood. This short review presents a model system that has the ease of preparation and the structural definition required to provide a firm understanding of interfacial phenomena. Long-chain thiols, HS(CH2)nX, adsorb from solution onto gold and form densely packed, oriented monolayers. By varying the terminal functional group, X, of the thiol, organic surfaces can be created having a wide range of structures and properties. More, complex systems can be constructed by coadsorbing two or more thiols with different terminal functional groups or with different chain lengths onto a common gold substrate. By these techniques, controlled degrees of disorder can be introduced into model surfaces. We have used these systems to explore the relationships between the microscopic structure of the monolayers on a molecular and supramolecular scale and their macroscopic properties. Wettability is a macroscopic interfacial property that has proven of particular interest.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 617-638 
    ISSN: 0570-0833
    Schlagwort(e): Enzyme catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Enzymes have great potential as catalysts for use in synthetic organic chemistry. Applications of enzymes in synthesis have so far been limited to a relatively small number of largescale hydrolytic processes used in industry, and to a large number of small-scale syntheses of materials used in analytical procedures and in research. Changes in the technology for production of enzymes (in part attributable to improved methods from classical microbiology, and in part to the promise of genetic engineering) and for their stabilization and manipulation now make these catalysts practical for wider use in large-scale synthetic organic chemistry. This paper reviews the status of the rapidly developing field of enzyme-catalyzed organic synthesis, and outlines both present opportunities and probable future developments in this field.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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