Functionalized poly(aspartic acid) hydrogel particles as carriers for covalent enzyme immobilization†

Abstract

Enzyme immobilization has been extensively studied to access higher enzyme stability and recyclability, enable continuous operations, and thus increase overall productivity in lab- and technical-scale processes. Among different immobilization methods, covalent immobilization on polymer surfaces can be the key to improved mass transport, reduced enzyme leaching, and faster conversions. Poly(aspartic acid) (PASP) hydrogels provide modifiable surface areas and the possibility of functionalization for introducing different linkers for covalent enzyme immobilization. PASP is an anionic polypeptide that is a highly versatile, biocompatible, and biodegradable polymer, hence a sustainable compound for its integration in enzyme immobilization design. Within this article, we present functionalized PASP hydrogel particles with glycidol (carrier I), ethylenediamine (carrier II), and glutaraldehyde (carrier III), and their in-depth characterization. These novel hydrogel-based enzyme carriers were applied to immobilize Candida antarctica lipase B (CalB). Despite the relatively low immobilization yield, the immobilized CalB on carrier II demonstrated a notable increase in stability with a 2.6-fold prolongation of its half-life from 454 ± 116 h to 1181 ± 350 h at 30 °C compared to the free enzyme. The proof-of-concept reaction of immobilized CalB on carrier II for the kinetic resolution of (R,S)-1-phenylethanolacetate demonstrated the potential for performing more than eight cycles without any significant reduction in the product yield. This corresponds to an operational time of over 200 hours, demonstrating the possible applicability of these hydrogel-based novel enzyme carriers.