Coating Novozyme435 with an ionic liquid: more than just a coating for the efficient ring-opening polymerization of δ-valerolactone

Abstract

Novozyme435, which is a successfully commercialized biocatalyst, can efficiently catalyze the ring-opening polymerization (ROP) of lactones. However, for six-membered unsubstituted lactones (δ-valerolactone), enzymatic ROP is difficult to perform and the catalyst is scarcely reused. In this study, an ionic liquid (IL) with different alkyl chain lengths was used to coat Novozyme435 in order to prevent the enzyme inside (Candida antarctica lipase B, CALB) from leaking out quickly. More interestingly, this simple coating can not only preserve CALB but also obviously increase its α-helix content. This change in CALB conformation was favorable for a stronger lid function as well as entry of the substrate towards the active site. The monomer conversion and molecular weight of the resultant poly (δ-valerolactone) were higher when the coated Novozyme435 was used as the catalyst, which presents superior catalytic activity compared to the control. In addition, catalytic activity increased with the IL alkyl chain length and the optimal weight ratio of IL/Novozyme435 was 3 : 1. In particular, the catalytic activity of the coated Novozyme435 in the second and third reaction runs was better than the fresh untreated catalyst, which indicates that the coating strategy is a powerful technique for use in enzyme technology.