Continuous Production of N-(Benzyloxycarbonyl)-L-Glycyl-L-Phenylalanine Methyl Ester Utilizing Extractive Reaction in Aqueous/Organic Biphasic Medium
ABSTRACT N-(Benzyloxycarbonyl)-L-glycyl-L-phenylalanine methyl ester was continuously synthesized, enzymatically, utilizing an extractive reaction in an aqueous/organic biphasic system. The extremely high yield, ca.100%, was obtained continuously in a water/butyl acetate biphasic medium.
Protease-catalyzed synthesis of Leu-enkephalin in a solvent-free system.
The total enzymatic synthesis of a model peptide Leu-enkephalin on a preparative scale was accomplished in the so-called solvent-free system. The syntheses were carried out in a rotary glass homogenizer by admixing solid reactants with native proteases and Na2CO3.10H2O. The most feasible way leading to biologically active Leu-enkephalin, was based on the strategy of 2 + (1 + 2) condensation catalyzed by alpha-chymotrypsin, thermolysin and papain for the final segment coupling. Subtilisin was used for the ester hydrolysis of peptide intermediates. Alternative strategies as well as the influence of several reaction conditions on the yield of the protease-catalyzed synthesis of Leu-enkephalin or Leu-enkephalin amide were also investigated.
Phase characterisation of simulated high burn-up UO2 fuel
Abstract To determine the lattice constant variation with burn-up and the oxidation behaviour at high temperatures, simulated UO2-spent fuels with burn-ups up to 200 GWd tM−1 were prepared by cold pressing and sintering and characterised by X-ray diffraction analysis and thermogravimetry. The fcc-lattice parameter of the sintered samples determined at room temperature, showed a continuous decrease with the simulated burn-up. During oxidation the conversion of the simulated fuels to the (U,FP)4O9 and (U,FP)3O8-type phases was strongly delayed when the simulated burn-up exceeded 80 GWd tM−1. Also, at high burn-ups (>100 GWd tM−1), large fractions of the (U,FP)4O9-type phase remained untransformed to (U,FP)3O8 after prolonged exposure to air at 950–1000°C. This suggests a marked widening of the (U,FP)4O9-phase field when the amount of substituted uranium atoms exceeds values of about 8%.