(397bm) Substrate-Imprinted Lipase Nanogel for Enzymatic Catalysis in Organic Solvents

In recent years, the employment of enzymes in industrial catalysis has become an increasingly promising alternative to conventional chemical catalysis due to their high specifity, selectivity and activity. Enzymatic catalysis in organic solvents has a lot of advantages, such as the increased solubility of non-polar substrates, enantioselectivity, and prohibition of water-dependent side reactions. However, enzymes quite often display very low activity and low stability in organic solvents, restricting wide applications of enzymes in organic solvents. We introduced a new method of preparing a ‘substrate-imprinted’ lipase nanogel that displays high activity and selectivity in organic solvents [1].

The enzyme nanogel was synthesized using lipase from Thermomyces lanuginosus (Lipozyme TL 100L) as the model enzyme. A two-step procedure including surface acryloylation and in-situ aqueous polymerization was applied to encapsulate lipase into a nanogel. The lipase nanogel was then lyophilized in the presence of a substrate of lipase, palmitic acid. Then palmitic acid was removed from the lyophilized lipase nanogel by solvent extraction.

The imprinting treatment brought about 2-fold and 1.4-fold increase in the catalytic activity of transesterification reaction between para-nitrophenyl palmitate and ethanol, ascorbic acid and vinyl palmitate, respectively. The effects of temperature, solvent and molar ratio of reactants on the yield and selectivity of the enzymatic synthesis of chloramphenicol palmitate were examined. One-step synthesis of chloramphenicol palmitate catalyzed by the imprinted lipase nanogel gave a yield of ∼99% and a purity of ∼99% within 12 hours at 20 °C, whereas the imprinted free lipase gave a yield below 60% in 20 hours. The increased catalytic activity could be attributed to the imprinted molecular ‘cavities’ in polymer shells which enhanced substrate transport and recognition. The hydrophilic micro-environment of the polyacrylamide network also facilitated the conformational transition of the encapsulated lipase.

To further elaborate the mechanism underlying the increased activity of the imprinted lipase nanogel, lipase nanogel imprinted with polyethylene glycol of different molecular weights were prepared to compare their catalytic activities with palmitic acid-imprinted lipase nanogel. By this study, it will be revealed that whether the porous structures or the increased affinity of molecular cavities in polymer shells after imprinting resulted in the increased enzymatic activity. Candida antarctica lipase type B (CAL-B) was chosen as the model enzyme in the study, which also demonstrated the effectiveness of the imprinting treatment for different enzymes.

1.      Wang, R., Zhang, Y. F., Huang, J. H., Lu, D. N., Ge, J., Liu, Z. Substrate imprinted lipase nanogel for one-step synthesis of chloramphenicol palmitate. Green Chemistry, 2013. 15: p.1155-1158