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

Abstract

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.

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

“…XRD patterns of ZIF samples obtained using a Zn:2‐MIm molar ratio ranging from 20 to 100 demonstrated that high molar Zn:2‐MIm ratios (1 : 40, 1 : 60, 1 : 80, 1 : 100) had a crystalline ZIF‐8 SOD like structure, whereas mixed phases associated with the formation of Zn(OH) 2 , Zn(OH)NO 3 , and Zn 5 (OH) 8 (NO 3 ) 2 (H 2 O) 2 were obtained at lower ratios (Zn : 2‐MIm ratio 1 : 20) . We recently observed different XRD patterns for ZIFs samples obtained with 1 : 40 and 1 : 4 Zn 2+ :2‐MIM ratios . Although a pure ZIF‐8 phase resulted at Zn : 2‐MIm 1 : 40 molar ratio, the optimal catalytic performance of Lipase@ZIF‐8 biocatalyst was observed at a low Zn : 2‐MIm (=1 : 4) molar ratio.…”

“…The Lip@ZIF‐zni biocatalyst retained 40 % of its initial activity at the fifth reaction cycle (Figure B). We recently investigated the long‐term stability and recycling of Pseudomonas fluorescens lipase immobilized on ZIF‐8 . After 15 days storage, the immobilized lipase retained 99 % of its initial activity.…”

“…After 15 days storage, the immobilized lipase retained 99 % of its initial activity. Similarly to the present case, also Lip@ZIF‐8 could be recycled five times with about 40 % of activity retention at the fifth reaction cycle . Although Lip@ZIF‐zni was less stable to storage than Lip@ZIF‐8, both samples showed practically the same stability to recycling.…”

“…This is ascribed to the thermal decomposition of the encapsulated enzymes and other organic compounds (i. e. carbohydrates) present in the commercial enzymatic preparations. [43] Finally, the mass loss measured above 500 8C is likely due to the decomposition of the ZIF structures. [42] Additional characterization details, e. g. scanning electron microscopy (Figure S1 and S2) and Fourier transform infrared spectroscopy ( Figure S3), are reported in supporting information.…”

“…The loading of enzyme@ZIF biocatalysts was performed by measuring the enzyme concentrations of the initial, final and washing solutions. Although not always correct, [43] here we assume that the commercially available enzymatic (lipase and laccase) preparations contain only the selected enzyme and no other inactive enzymes. The concentrations of enzyme in the different solutions were obtained through UV-Vis spectrophotometry by the Bradford assay, [44] using BSA as the standard.…”