Lipase Encapsulation onto ZIF-8: A Comparison between Biocatalysts Obtained at Low and High Zinc/2-Methylimidazole Molar Ratio in Aqueous Medium

Lipase AK from Pseudomonas fluorescens and Lipase RM from Rhizomucor miehei were encapsulated into a zeolite imidazolate framework (ZIF-8) by a “one-pot” synthesis to obtain AK@ZIF-8 and RM@ZIF-8 biocatalysts. The effect of a high (1:40) and low (1:4) Zn/2-methylimidazole molar ratio on the biocatalysts synthesis was investigated. The different Zn/ligand (L) ratios affected both the surface area, the loading, and the specific activity of the biocatalysts. Samples synthesized by using a high Zn/L ratio had high values of surface area whereas those obtained by using a low Zn/L ratio had higher loadings and specific activities. The decrease of pH (from 11.6 to 9.4) during the synthesis at high Zn/L ratio produced ZIF-8 samples with features similar to those observed for low Zn/L ratio samples. The low Zn/L (1:4) ratio AK@ZIF-8 biocatalyst retained 99 % activity after storage for 15 days at 5 °C and 40 % activity after five reaction cycles.