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

Abstract

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 (<b>1</b>) to yield a mixture of (<i>R</i>)-<b>1</b> and (<i>E</i>)-3-(thiophen-2-yl)acrylic acid (<b>2</b>) and in ammonia addition to <b>2</b> to yield enantiopure (<i>S</i>)-<b>1</b>. SwCNT_COOH-PAL^II was a stable biocatalyst (>90 % of the original activity remained after six cycles with <b>1</b> and after three cycles in 6 m NH₃ with <b>2</b>). The study of ammonia addition to <b>2</b> in a continuous-flow microreactor filled with SwCNT_COOH-PAL^II (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. SwCNT_COOH-PAL^II in the continuous-flow system at 30 °C was more productive (specific reaction rate, <i>r</i>_flow=2.39 μmol min^-1 g^-1) than in the batch reaction (<i>r</i>_batch=1.34 μmol min^-1 g^-1).