Integration of racemization and a resolution process is an attractive way to overcome yield limitations in the production of pure chiral molecules. Preferential crystallization and other crystallization-based techniques usually produce low enantiomeric excess in solution, which is a constraint for coupling with racemization. We developed an enzymatic fixed bed reactor that can potentially overcome these unfavorable conditions and improve the overall yield of preferential crystallization. Enzyme immobilization strategies were investigated on covalentbinding supports. The amino acid racemase immobilized in Purolite ECR 8309F with a load of 35 mg-enzyme/g-support showed highest specific activity (approx. 500 U/g-support) and no loss in activity in reusability tests. Effects of substrate inhibition observed for the free enzyme were overcome after immobilization. A packed bed reactor with the immobilized racemase showed good performance in steady state operation processing low enantiomeric excess inlet. Kinetic parameters from batch reactor experiments can be successfully used for prediction of packed bed reactor performance. Full conversions could be achieved for residence times above 1.1 min. The results suggest the potential of the prepared racemase reactor to be combined with preferential crystallization to improve resolution of asparagine enantiomers.

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We have fabricated and tested several single cell cavities using material from very large grain niobium ingots. In one case the central grain exceeded 7" in diameter and this was used to fabricate two 2.2 GHz cavities. This activity had a dual purpose: to investigate the influence of grain boundaries on the often observed Qdrop at gradients E acc > 20 MV/m in the absence of field emission, and to study the possibility of using ingot material for cavity fabrication without going through the expensive rolling process. The sheets for these cavities were cut from the ingot by wire electro-discharge machining (EDM) and subsequently formed into halfcells by deep drawing. The following fabrication steps were standard: machining of weld recesses, electron beam welding of beam pipes onto the half cells and final equator weld to join both half cell/beam pipe subunits. The cavities showed heavy Q-disease caused by the EDM. After hydrogen degassing at 800 °C for 3 hrs in UHV and about 200 µm total removals from the inner surface by BCP 1:1:1, the cavities showed promising results, however, the Q-drop was still present. In the two cavities made from large grain material accelerating gradients of 30 MV/m have been reached. After "in-situ" baking the Q-drop disappeared. The smaller cavities made from single crystal material showed very low residual resistances and accelerating gradients up to E acc = 45 MV/m were reached (one of the highest ever achieved), corresponding to a peak surface magnetic fields (B p ) of 160 mT. In one rf test at 2 K, a B p = 185 mT was reached for few hundred milliseconds, close to the theoretical critical field of this material.

Temperature cycling induced deracemization (TCID) is an attractive method to provide a pure enantiomer from a racemic solid phase. In this work, we performed deracemization of the nonessential amino acid asparagine using TCID of DL-asparagine monohydrate crystals (DL-ASN•H 2 O) and an immobilized amino acid racemase (imAAR) as a racemization agent. Experiments were performed with varying initial suspension densities and dosages of imAAR to better understand the process and included measurements of both solid-phase and solution-phase enantiomeric excesses. Furthermore, we demonstrate how to improve the productivity and yield of the TCID process by adding a temperature hold at the end of the process to ensure the maximum possible yield and compare these results to a process using only standard temperature cycles. Finally, we also discuss the effect of both temperature programs on the performances of the TCID process to be a strategy to further improve this process for industrial application.