Aminated Single-walled Carbon Nanotubes as Carrier for Covalent Immobilization of Phenylalanine Ammonia-lyase

A new and efficient immobilized form of phenylalanine ammonia-lyase (PAL) was obtained by covalent linkage onto amino functionalized single-walled carbon nanotubes (SwCNTNH2) as carrier. The catalytic properties of the resulted nanostructured biocatalyst (SwCNTNH2-PAL) were tested in the kinetic resolution of racemic 2-amino-3-(thiophen-2-yl)propanoic acid 1 by ammonia elimination and in the enantiotope selective addition of ammonia onto (E)-3-(thiophen-2-yl)acrylic acid 2. SwCNTNH2-PAL was a durable biocatalyst in batch mode for ammonia elimination from 1 (>85% of original activity after 7 cycles) and in ammonia addition to 2 (>70% of original activity after 3 cycles in 6 M NH3 , pH 10.0). The ammonia addition onto 2 was also studied in a continuous-flow microreactor packed with SwCNTNH2-PAL (2 M NH3, pH 10.0, 15 bar) in the 30-80 °C temperature range. No significant loss of PAL activity was observed over 72 h in the microreactor up to 60 °C. Productivity of SwCNTNH2-PAL at 30 °C was significantly higher in the enantiotope selective ammonia addition performed in a packed-bed reactor operated in continuous-flow mode (rflow =2.41 mmol min-1 g-1) than in the reaction performed in batch system (rbatch = 1.38 mmol min-1 g-1).