Abstract
The enzymatic ring-opening polymerization of lactones is a method of increasing interest for the synthesis of biodegradable and biocompatible polymers. In the past it was shown that immobilization of Candida antarctica lipase B (CaLB) and the reaction medium play an important role in the polymerization ability especially of medium ring size lactones like ε-caprolactone (ε-CL). We investigated a route for the preparation of compartmentalized microgels based on poly(glycidol) in which CaLB was immobilized to increase its esterification ability. To find the ideal environment for CaLB, we investigated the acceptable water concentration and the accessibility for the monomer in model polymerizations in toluene and analyzed the obtained oligomers/polymers by NMR and SEC. We observed a sufficient accessibility for ε-CL to a toluene like hydrophobic phase imitating a hydrophobic microgel. Comparing free CaLB and Novozym® 435 we found that not the monomer concentration but rather the solubility of the enzyme, as well as the water concentration, strongly influences the equilibrium of esterification and hydrolysis. On the basis of these investigations, microgels of different polarity were prepared and successfully loaded with CaLB by physical entrapment. By comparison of immobilized and free CaLB, we demonstrated an effect of the hydrophobicity of the microenvironment of CaLB on its enzymatic activity.
Highlights
The demand for biocompatible and biodegradable materials like polyesters has been greatly increased during the last decades especially due to its versatile applications in the fields ofmedicine and tissue engineering [1,2]
Further we will analyze the dispersity of the polymeric products and discuss the activation of the lipase by immobilization as well as the possible coexistence of different active “forms” of Candida antarctica lipase B (CaLB) according to the classification described by Fernández-Lafuente et al [28]
Results and Discussion ε-Caprolactone is converted in aqueous media in the presence of free or immobilized CaLB as ε-Caprolactone is converted in aqueous media in the presence of free or immobilized CaLB as catalyst either by hydrolysis or or byby ring form6-hydroxy
Summary
The demand for biocompatible and biodegradable materials like polyesters has been greatly increased during the last decades especially due to its versatile applications in the fields of (bio)medicine and tissue engineering [1,2]. Due to the high water concentration in the close environment of both the active site of the lipase and the monomer, hydrolysis of the lactone ring yielding 6-hydroxycaproic acid is the preferably catalyzed reaction These results show that by changing the microenvironment of the enzyme and the substrate, the catalyzed synthesis can be directed to the desired product. The reason for the great performance of Novozym® 435 in organic solvents and the low degree of polymerization in water has never been discussed in literature so far and will be taken up in the publication in hand At this point it should be mentioned that by working with Novozym® 435 in water we detected traces of a nonionic poly(ethylene oxide/propylene oxide) copolymer surfactant in the reaction products (unpublished results). Further we will analyze the dispersity of the polymeric products and discuss the activation of the lipase by immobilization as well as the possible coexistence of different active “forms” of CaLB (aggregated, soluble, bound, protected, inhibited) according to the classification described by Fernández-Lafuente et al [28]
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