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1998 (1)
1992 (1)
1Author    Ulrich Nagel, Christoph RollerRequires cookie*
 Title    Enantioselective Catalysis, XVII [1], Enantioselective Catalytic Hydrogenation of Unfunctionalized Ketones  
 Abstract    Three diastereomeric rhodium bisphosphane complexes have been applied to asymmetric hydrogenation of unfunctionalized, non-chelating aliphatic and aromatic ketones. The ee values o f the catalysis products differ considerably for the diastereomerical catalysts. 70% ee were obtained in hydrogenating butyrophenone, and 83.7% ee for pinacoline. The results depend strongly on the solvent used. 
  Reference    Z. Naturforsch. 53b, 267—270 (1998); received January 15 1998 
  Published    1998 
  Keywords    Enantioselective Hydrogenation, Unfunctionalized Ketones, Rhodium, Salt Effect, Solvent Effect 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-0267.pdf 
 Identifier    ZNB-1998-53b-0267 
 Volume    53 
2Author    FranciscoJ G M Urianaa, Marí, C. Alvarez-Ossorio3, Marí, M. Sánchez-Garcés3, FranciscoF. De, LaR. Osab, AngelM. Relimpio3Requires cookie*
 Title    Effect of Salt on the Activity and Stability of Aspartate Aminotransferase from the Halophilic Archaebacterium Haloferax mediterranei  
 Abstract    The aspartate aminotransferase from Haloferax mediterranei, which is in the cell mainly as apoenzym e, requires high concentrations o f salt for both activity and stability. The maximum activity is reached with 3.5 m KC1 in the assay. The effect o f different cations and anions has been studied using several types o f salts. M onovalent cations show a significant difference in effectiveness o f promoting the activity with the follow ing order: K + > R b + > N a + > N H 4+. M g++ and polyvalent cations with organic character cause partial activity with maximum ef­ fectiveness at 0.1 m , an inhibition at higher concentration is observed. A nions, added as p otas­ sium salts, promote enzyme activity with the following order: Cl" > N 0 3~ > I " > SCN~. Like activity, the enzyme stability depends on salt concentrations. Incubation o f the enzyme with a low salt concentration leads to inactivation following pseudofirst order kinetics. The inactivat­ ed enzyme is partially reactivated by high concentrations o f KC1 follow ing second order kinet­ ics. Taking into account the dimeric structure o f this enzyme, high concentrations o f salt could stabilize the dimer, which is the active form. The salt effects on halophile aspartate am ino­ transferase are discussed considering hydrophobic and electrostatic interactions. 
  Reference    Z. Naturforsch. 47c, 375 (1992); received December 17 1991 /February 21 1992 
  Published    1992 
  Keywords    Halophilic Bacteria, Aspartate Aminotransferase, Salt Effects, Activity and Stability, H aloferax mediterranei 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0375.pdf 
 Identifier    ZNC-1992-47c-0375 
 Volume    47