Xem 1-20 trên 77 kết quả Chemical catalytic
  • Catalytic oxidation of organic compounds is an extremely important field of chemistry, spanning the range from biological oxidations to large scale industrial production of commodity chemicals. However, many of these transformations can hardly be classified as organometallic reactions, since the catalysts (often simple metal salts) and the intermediates can be rather regarded as coordination complexes than organometallic compounds.

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  • Chemical reaction engineering (reaction engineering or reactor engineering) is a specialty in chemical engineering or industrial chemistry dealing with chemical reactors. Frequently the term relates specifically to catalytic reaction systems where either a homogeneous or heterogeneous catalyst is present in the reactor.

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  • Chemical reaction engineering is concerned with the exploitation of chemical reactions on a commercial scale. It's goal is the successful design and operation of chemical reactors. This text emphasizes qualitative arguments, simple design methods, graphical procedures, and frequent comparison of capabilities of the major reactor types. Simple ideas are treated first, and are then extended to the more complex.

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  • The study of catalytic membranes and membrane reactor processes is a multidisciplinary activity, which in recent years has attracted the attention of scientists and engineers in a number of disciplines, including materials science, chemistry and biology, and chemical and biochemical engineering.

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  • Most glucoamylases (a-1,4-d-glucan glucohydrolase, EC have structures consisting of both a catalytic and a starch binding domain. The structure of a glucoamylase from Saccharomycopsis fibuligeraHUT 7212 (Glu), determined a few years ago, consists of a single catalytic domain. The structure of this enzyme with the resolution extended to 1.1 A˚ and that of the enzyme–acarbose complex at 1.6 A˚ resolution are presented here.

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  • The hyperthermostable chitinase from the hyperthermophilic archaeon Pyrococcus furiosushas a unique multidomain structure containing two chi-tin-binding domains and two catalytic domains, and exhibits strong crystal-line chitin hydrolyzing activity at high temperature.

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  • The cold-active protein tyrosine phosphatase found in psychrophilicShewa-nellaspecies exhibits high catalytic efficiency at low temperatures as well as low thermostability, both of which are characteristics shared by many cold-active enzymes.

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  • The catalytic mechanism underlying the aminopeptidase fromStreptomyces griseus (SGAP) was investigated. pH-dependent activity profiles revealed the enthalpy of ionization for the hydrolysis of leucine-para-nitroanilide by SGAP. The value obtained (30 ± 5 kJÆmol )1 ) is typical of a zinc-bound water molecule, suggesting that the zinc-bound water⁄hydroxide molecule acts as the reaction nucleophile.

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  • Catalytic antibodies capable of digesting crucial proteins of pathogenic bac-teria have long been sought for potential therapeutic use. Helicobacter pyloriurease plays a crucial role for the survival of this bacterium in the highly acidic conditions of human stomach. The HpU-9 monoclonal anti-body (mAb) raised againstH. pyloriurease recognized thea-subunit of the urease, but only slightly recognized theb-subunit. However, when isolated both the light and the heavy chains of this antibody were mostly bound to the b-subunit....

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  • UDP-galactose 4-epimerase fromKluyveromyces fragilisis a homodimer containing one catalytic site and one NAD + as cofactor per subunit. One 5¢-UMP, a competitive inhibitor, binds per dimer of epimerase as isolated and causes inactivation. Addition of 0.2 mminhibitor to the enzyme in vitro leads to three sequential steps: first, the inhibitor binds to the unoccupied site; second, the inhibitor bound ex vivo is displaced allosterically; and finally, both sites are occupied by the inhibitor.

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  • Thermobifida fuscaexocellulase Cel6B acts by an inverting hydrolysis mech-anism; however, the catalytic acid and base residues for this enzyme have not been confirmed. Site-directed mutagenesis and kinetic studies were used to show that Asp274 is the catalytic acid, which is consistent with what is found for other members of family-6 glycoside hydrolases; however, a sin-gle catalytic base was not identified.

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  • Thioesters are more reactive than oxoesters, and thioester chemistry is important for the reaction mechanisms of many enzymes, including the members of the thiolase superfamily, which play roles in both degradative and biosynthetic pathways. In the reaction mechanism of the biosynthetic thiolase, the thioester moieties of acetyl-CoA and the acetylated catalytic cysteine react with each other, forming the product acetoacetyl-CoA.

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  • Some starch-degrading enzymes accommodate carbohydrates at sites situ-ated at a certain distance from the active site. In the crystal structure of barleya-amylase 1, oligosaccharide is thus bound to the ‘sugar tongs’ site. This site on the non-catalytic domain C in the C-terminal part of the mole-cule contains a key residue, Tyr380, which has numerous contacts with the oligosaccharide.

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  • Although alkaline phosphatase (APase) fromEscherichia colicrystallizes as a symmetric dimer, it displays deviations from Michaelis–Menten kinetics, supported by a model describing a dimeric enzyme with unequal subunits [Orha-novic´ S., Pavela-Vrancˇicˇ M. and Flogel-Mrsˇic´ M. (1994) Acta. Pharm.44, 87–95]. The possibility, that the observed asymmetry could be attributed to negative cooperativity in Mg2+ binding, has been examined. The influence of the metal ion content on the catalytic properties of APase from E. colihas been examined by kinetic analyses. ...

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  • We live in the age of biology—the human and many other organisms’ genomes have been sequenced and we are starting to understand the function of the metabolic machinery responsible for life on our planet. Thousands of new genes have been discovered, many of these coding for enzymes of yet unknown function. Understanding the kinetic behavior of an enzyme provides clues to its possible physiological role. From a biotechnological point of view, knowledge of the catalytic properties of an enzyme is required for the design of immobilized enzyme-based industrial processes.

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  • If the 20th century could be characterized by the rapid increase in the production and consumption of materials that helped improving the standards of living, then the 21st certainly has many elements to qualify as the century of recycling. Since the duration of life of a number of wastes is very small (roughly 40% have duration of life smaller than one month), there is a vast waste stream that reaches each year to the final recipients creating a serious environmental problem.

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  • “There’s Plenty of Room at the Bottom” ⎯ this was the title of the lecture Prof. Richard Feynman delivered at California Institute of Technology on December 29, 1959 at the American Physical Society meeting. He considered the possibility to manipulate matter on an atomic scale. Indeed, the design and controllable synthesis of nanomaterials have attracted much attention because of their distinctive geometries and novel physical and chemical properties.

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  • This book is an introduction to the quantitative treatment of chemical reaction engineering. The level of the presentation is what we consider appropriate for a one-semester course. The text provides a balanced approach to the understanding of: (1) both homogeneous and heterogeneous reacting systems and (2) both chemical reaction engineering and chemical reactor engineering. We have emulated the teachings of Prof. Michel Boudart in numerous sections of this text.

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  • Just as the chemical and physical properties of petroleum have offered challenges in selecting and designing optimal upgrading schemes, they also introduce challenges when determining the effects of petroleum and its product on the environment. In particular, predicting the fate of the polynuclear aromatic systems, the heteroatom systems (principally, compounds containing nitrogen and sulfur), and the metal-containing systems (principally, compounds of vanadium, nickel, and iron) in the feedstocks is the subject of many studies and migration models....

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  • Characterization and elucidation of the size-dependent evolution of the physical and chemical properties of finite materials aggregates, having discrete quantized energy level spectra, specific structural and morphological motifs and exhibiting unique dynamical characteristics, are among the outstanding challenges of modern materials science.

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