Abstract
In this study, two types of nanoparticles have been used as additives for the encapsulation of Candida rugosa lipase via the sol-gel method. In one case, the nanoparticles were covalently linked with a new synthesized calix[8]arene octa valeric acid derivative (C[8]-C4-COOH) to produce new calix[8]arene-adorned magnetite nanoparticles (NP-C[8]-C4-COOH), and then NP-C[8]-C4-COOH was used as an additive in the sol-gel encapsulation process. In the other case, iron oxide nanoparticles were directly added into the sol-gel encapsulation process in order to interact electrostatically with both C[8]-C4-COOH and Candida rugosa lipase. The catalytic activities and enantioselectivities of two novel encapsulated lipases (Enc-NP-C[8]-C4-COOH and Enc-C[8]-C4-COOH@Fe3O4) in the hydrolysis reaction of racemic naproxen methyl ester were evaluated. The results showed that the activity and enantioselectivity of the lipase were improved when the lipase was encapsulated in the presence of calixarene-based additives. Indeed, the encapsulated lipases have an excellent rate of enantioselectivity, with E = 371 and 265, respectively, as compared to the free enzyme (E = 137). The lipases encapsulated with C[8]-C4-COOH and iron oxide nanoparticles (Enc-C[8]-C4-COOH@Fe3O4) retained more than 86% of their initial activities after 5 repeated uses and 92% with NP-C[8]-C4-COOH.
Highlights
In order to improve the activity and enantioselectivity of lipases in the hydrolysis reaction of racemic naproxen methyl ester, some calixarene-grafted magnetite nanoparticles have successfully immobilized the lipase via the sol–gel method, which opens up a wide range of opportunities for future research
The C. rugosa lipase was encapsulated within a sol–gel system8,9,12,14,17,18 formed through polycondensation with tetraethoxysilane (TEOS) and octyltriethoxysilane (OTES) in the presence or absence of octa valeric acid functionalized calix[8]arene (C[8]-C4-COOH) with magnetite nanoparticles to afford Enc-C[8]-C4-COOH@Fe3O4
The treatment resulted in enantioselectivities toward naproxen methyl ester (E value) of 371 for Enc-C[8]-C4-COOH@Fe3O4 and 265 for Enc-NP-C[8]-C4-COOH, as compared to an E value of 137 for the encapsulated lipase without additives (Enc-lipase). These results show strong evidence that the immobilization of lipases with calixarene derivatives led to high stereoselectivity, high conversion, and fast recovery of the catalyst owing to the magnetite properties of the encapsulated lipases (Enc-C[8]-C4-COOH@Fe3O4 and/or Enc-NP-C[8]-C4-COOH)
Summary
Researchers have developed various methods involving enzymatic and non-enzymatic catalysts to enrich a derivative for one of the enantiomers from the reaction product.1–9 Biocatalysis has been applied as a viable and preferred technique in organic synthesis for the production of enantiopure compounds, for pharmaceutical compounds.10,11 Candida rugosa lipase has a wide range of natural substrates and is commonly chosen as a biocatalyst.12 lipases are usually used as aqueous solutions, which makes their recovery and reuse problematic and can result in contamination of the product.13 In an attempt to enhance the activity and enantioselectivity of C. rugosa, researchers have tried immobilizing C. rugosa using various types of carriers such as celite, kaolin, cyclodextrin, amberlite XAD 7, sporopollenin, chitosan, and calixarene.14–16Recently, immobilizing the lipase using calixarenes has become a common way of increasing the lipase activity and enantioselectivity.12,17,18 Calixarenes are used to this end. In order to improve the activity and enantioselectivity of lipases in the hydrolysis reaction of racemic naproxen methyl ester, some calixarene-grafted magnetite nanoparticles have successfully immobilized the lipase via the sol–gel method, which opens up a wide range of opportunities for future research.14,25
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