Lipase and Laccase Encapsulated on Zeolite Imidazolate Framework: Enzyme Activity and Stability from Voltammetric Measurements

Abstract: Lipase (Pseudomonas fluorescens) and laccase (Trametates versicolor) were encapsulated on two zeolite imidazolate framework, ZIF-8 and ZIF-zni, materials using a one-pot synthesis-immobilization method in aqueous solution at room temperature. The synthesized immobilized biocatalysts (Lip@ZIF-8, Lip@ZIF-zni, Lac@ZIF-8, and Lac@ZIF-zni) were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The enzymatic activities of the four immobilized biocatalysts were characterized via the electrochemical detection of the substrates, p-nitrophenyl butyrate and 2,2-azinobis-3-ethylbenzthiazoline-6-sulfonic acid. For Lip@ZIF-8 the specific activity was 91.9 U mg⁻¹ and 123.1 U mg⁻¹ for Lip@ZIF-zni, while for Lac@ZIF-8 and Lac@ZIF-zni, the activity was 51 U mg⁻¹ and 163 U mg⁻¹, respectively, confirming that laccase retains a higher level of activity when immobilized onto ZIF-zni than on ZIF-8. Lac@ZIF-8 was the most stable system on storage (15 days at 5 °C), retaining 94 % of initial activity, while Lip@ZIF-zni biocatalyst had the optimal level of reusability, retaining 40 % of initial activity after five reaction cycles.