Enhanced Activity of Immobilized Lipase by Phosphonium-Based Ionic Liquids Used in the Support Preparation and Immobilization Process

Abstract

Biocatalysis has significant advantages over chemocatalysis in the context of sustainability since environmentally compatible catalysts (enzymes) and mild reaction conditions are used. However, enzymes are labile macromolecules, and strategies such as the addition of cosolvents or additives or their immobilization in solid supports are the target of intensive investigation to improve the catalytic performance and recyclability potential. In this work, we investigated the use of phosphonium-based ionic liquids (ILs) on the activity of immobilized Burkholderia cepacia lipase (BCL) by two approaches: (i) use of ILs to prepare silica used as support and (ii) use of ILs during the enzyme immobilization process. Several phosphonium-based ILs were investigated, allowing us to address the cation alkyl side chain and anion nature effects. The enzymatic performance depends on the IL employed to prepare silica, with a positive effect observed when employing ILs comprising cations with longer alkyl side chains and more hydrophobic anions. The best identified IL, namely, [P666(14)][NTf2], allows for a relative activity of 209.8% and immobilization yield of 77.3% and is capable of being recycled eight times (keeping more than 50% of the enzyme initial activity). When ILs are added during the BCL immobilization process, similar negative and beneficial effects are observed. With IL [P666(14)][NTf2], the immobilized biocatalyst has a relative activity of 322.7%, a total activity recovery yield of 91.1%, and can be recycled 17 times (down to 50% of the enzyme initial activity). Finally, both approaches were combined; i.e., IL [P666(14)][NTf2] was used both in the material preparation and immobilization process of the enzyme. This strategy allows for an increase in the relative activity up to 231%, an immobilization yield of 98%, and an increase of 9% in the enzyme relative activity. Although BCL activity is not significantly enhanced by this strategy, the combined use of the IL in silica preparation and during the enzyme immobilization process increased the recyclability potential of the immobilized biocatalyst material, capable of being recycled 26 times, while keeping more than 50% of the enzyme initial activity (equivalent to a half-life of 13 h). The results obtained in this work open the path to the efficient use of ILs, and particularly of the less explored phosphonium-based ILs, in the biocatalysis field.