Repetitive ultrafiltration

After a hydroformylation run, the reaction solution was subjected to ultrafiltration using an asymmetric polyethersulfone membrane (MWCO 50 kDa) supplied by Sartorius. A retention of 99.8% was found. When the catalyst solution was recycled, virtually the same catalytic activity was observed again (165 TO h 1). Repetitive recycling experiments resulted in 2-7% loss of rhodium, which was subscribed to partial oxidation of the phosphine ligand. 

Kaiser and colleagues (Fukushima et ai, 1980) showed that a 22-residue peptide can be synthesized entirely from Glu, Lys, and Leu arranged periodically in the typical class A distribution to form an am-phipathic a helix with equal polar and nonpolar faces. Indeed, as studied by quantitative ultrafiltration, gel-permeation chromatography, and circular dichroism, the peptide associated effectively with phospholipid and mimicked some of the physical and chemical properties of apoA-I (Fukushima a/., 1980 Kaiser and Kezdy, 1983, 1984 Nakagawa a/., 1985). Because of the presence of tandem repetitive amphipathic helical domains in apoA-I, a dimer of this 22-residue peptide was later synthesized and found to more closely mimic apoA-I than the monomer thus the study of peptide analogs supported the concept that 44-mers represent the minimal functional domain in apoA-I (Nakagawa et ai, 1985). 

For synthesis on a preparative scale, repetitive batch processing has proved to be an effective and easy-to-handle method1128. The repeated use of the enzyme is possible after concentration of the solution by means of commercially available ultrafiltration equipment and adding fresh substrate solution. Some of the advantages given for the Enzyme Membrane Reactor (see below) are also valid for the repetitive batch technique. 

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