Nanobiocatalyst with the advantages of high surface area, increased enzyme loading and reduced mass transfer resistance offers great opportunity for the green synthesis of fine chemicals and pharmaceuticals. A lot of enzymatic reactions are carried out in organic solvents because of the increased solubility of substrate and eliminiation of hydrolysis reactions and water-dependent side reactions. However, enzyme has low apparent activity in organic solvents. Here we report a new strategy of ‘imprinting’ enzyme-encapsulated polyacrylamide nanogels to achieve high enzymatic activities in organic media.
First, lipase from Thermomyces lanuginosus (Lipozyme TL 100L) was encapsulated in polyacrylamide nanogle by a two-step procedure including surface acryloylation and in-situ aqueous polymerization. Then the lipase nanogel was lyophilized in the presence of polyethyleneglycol (PEG) or a substrate, palmitic acid, which was then removed by solvent extraction after lyophilization.
The imprinted lipase nanogel showed a 4.6-fold activity compared to native lipase. Further investigation on the mechanism of the increased enzymatic activity suggested that PEG molecule activates lipase during the imprinting process. Substrate imprinting increases the affinity of polymer network to the substrate and favors the substrate uptake, thus gives a higher apparent activity. The imprinting treatment using PEG and substrate simultaneously gave the maximum increment in enzyme activity and enabled one-step synthesis of chloramphenicol palmitate, an antimicrobial, with an yield of ~99% and purity of ~99% within 6 h, indicating the imprinted lipase nanogel is an appealing catalyst for enzymatic catalysis in organic media.
Magnetic nanoparticle was covalently attached to lipase and then encapsulated in polyacrylamide nanogle thus combines the high stability of lipase nanogel and easy recovery of magnetic nanoparticle. The magnetic enzyme nanogel was then imprinted by PEG and the substrate to increase its catalytic activity in organic solvent. The increased activity, enhanced thermal stability and ease of reuse essentially ensure an expanded application of spectrum of enzymatic catalysis in organic solvents.
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3. Wang, R.; Zhang, Y.; Ge, J.*; Liu, Z.*. Activation of enzyme nanogel in organic solvents by PEG–substrate joint imprinting. RSC Advances, 2014, 4, 40301-40304.