Immobilization of Phenylalanine Ammonia‐Lyase on Single‐Walled Carbon Nanotubes for Stereoselective Biotransformations in Batch and Continuous‐Flow Modes

Carboxylated single-walled carbon nanotubes (SwCNTCOOH) were used as a support for the covalent immobilization of phenylalanine ammonia-lyase (PAL) from parsley by two different methods. The nanostructured biocatalysts (SwCNTCOOH-PALI and SwCNTCOOH-PALII) with low diffusional limitation were tested in the batch-mode kinetic resolution of racemic 2-amino-3-(thiophen-2-yl)propanoic acid (1) to yield a mixture of (R)-1 and (E)-3-(thiophen-2-yl)acrylic acid (2) and in ammonia addition to 2 to yield enantiopure (S)-1. SwCNTCOOH-PALII was a stable biocatalyst (>90 % of the original activity remained after six cycles with 1 and after three cycles in 6 m NH3 with 2). The study of ammonia addition to 2 in a continuous-flow microreactor filled with SwCNTCOOH-PALII (2 m NH3, pH 10.0, 15 bar) between 30-80 °C indicated no significant loss of activity over 72 h up to 60 °C. SwCNTCOOH-PALII in the continuous-flow system at 30 °C was more productive (specific reaction rate, rflow=2.39 μmol min-1 g-1) than in the batch reaction (rbatch=1.34 μmol min-1 g-1).