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 (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 m -1 g -1) than in the batch reaction (r batch = 1.34 μmolmin -1 g -1).