Design and Construct Cyclic Carbonate Functionalized Chitosan-Based Hydrogel Enabling Photodecarboxylase Immobilization with Enhanced Stability and Reusability

Fatty acid photodecarboxylase (FAP) plays a crucial role in the green production of biofuel and other valuable biochemicals. However, the reusability of immobilized FAP has been limited due to inadequate durability. Here, a porous, translucent chitosan hydrogel sphere carrier functionalized with cyclic carbonate group to enhance the reusability of immobilized FAP is presented. Based on the arrangement of basic amino acid residues on the surface of FAP, bis(cyclic carbonate) containing a flexible chain from CO₂ is designed and synthesized. This compound is used to modify porous hydrogels obtained via a template-etching process. FAP is then covalently immobilized within the hydrogel framework through a reaction with the remaining cyclic carbonate groups, as evidenced by quartz crystal microbalance analysis. The modified porous hydrogel carrier, PH3-BC-II, significantly improves the activity of FAP, achieving a maximum conversion of 70.0%, with the enzyme loading of 125.3 mg g⁻¹ (dry carrier). Furthermore, PH3-BC-II retains >50% of its initial activity after eight consecutive reaction cycles (total runtime of 24 h) at high fatty acid substrate concentrations. This study provides an effective strategy for constructing stable immobilized (photo)enzymes from sustainable materials.