Immobilization of carbonic anhydrase in a hydrophobic poly(ionic liquid): A new functional solid for CO2 capture

Abstract

Poly(ionic liquid)s are interesting materials for CO2 separation due to their affinity towards CO2. Carbonic anhydrase, as an enzyme that catalyzes the hydration reaction of CO2, represents tremendous opportunities for enhanced CO2 capture in aqueous solutions. Yet, when used as a free enzyme solubilized in the liquid medium, it has limited practicality. Here, we report the study on carbonic anhydrase immobilization in poly(ionic liquid)s by entrapment. Due to limited enzyme solubility in the hydrophobic ionic liquid monomer solution, carbonic anhydrase was suspended instead of solubilized prior to bulk polymerization. The immobilization protocol was optimized to maximize the catalytic efficiency of the resulting solid by evaluating the effect of lyophilized suspension hydration and particle size. Immobilized carbonic anhydrase properties were investigated by measurement of kinetic parameters, reusability, thermal and storage stability. Using p-NPA hydrolysis as a model reaction, kinetic parameters were 0.22 s−1 mM−1 (kcat/Km) for free enzyme and 0.06 s−1 mM−1 for the immobilized biocatalyst, indicating a decrease of activity upon immobilization. Immobilized enzyme, however, presented better storage stability than free enzyme as after one month the activity did not change. In the case of dissolved carbonic anhydrase, it decreased by about 30%. The entrapped enzyme could be utilized in 5 consecutive cycles of CO2 hydration while keeping a relative activity superior to 60%.