| 1 | Author
| Ulrich Nagel, Christoph Roller | Requires 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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| default:Reihe_B/53/ZNB-1998-53b-0267.pdf | | | Identifier
| ZNB-1998-53b-0267 | | | Volume
| 53 | |
2 | Author
| FranciscoJ G M Urianaa, Marí, C. Alvarez-Ossorio3, Marí, M. Sánchez-Garcés3, FranciscoF. De, LaR. Osab, AngelM. Relimpio3 | Requires 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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| default:Reihe_C/47/ZNC-1992-47c-0375.pdf | | | Identifier
| ZNC-1992-47c-0375 | | | Volume
| 47 | |
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