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

Carboxylated single‐walled carbon nanotubes (SwCNT(COOH)) were used as a support for the covalent immobilization of phenylalanine ammonia‐lyase (PAL) from parsley by two different methods. The nanostructured biocatalysts (SwCNT(COOH)‐PAL(I) and SwCNT(COOH)‐PAL(II)) 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. SwCNT(COOH)‐PAL(II) was a stable biocatalyst (>90 % of the original activity remained after six cycles with 1 and after three cycles in 6 m NH(3) with 2). The study of ammonia addition to 2 in a continuous‐flow microreactor filled with SwCNT(COOH)‐PAL(II) (2 m NH(3), pH 10.0, 15 bar) between 30–80 °C indicated no significant loss of activity over 72 h up to 60 °C. SwCNT(COOH)‐PAL(II) in the continuous‐flow system at 30 °C was more productive (specific reaction rate, r (flow)=2.39 μmol min(−1) g(−1)) than in the batch reaction (r (batch)=1.34 μmol min(−1) g(−1)).