Immobilization of Thermomyces lanuginosus lipase via ionic adsorption on superparamagnetic iron oxide nanoparticles: Facile synthesis and improved catalytic performance

The present work describes a simple, rational, and optimized methodology for the immobilization of lipase from Thermomyces lanuginosus (TLL) via ionic adsorption on non-commercial superparamagnetic iron oxide nanoparticles (SPIONs). First, the surface loads of both the enzyme and nanoparticles were evaluated by zeta potential measurements over a wide pH range. In addition, the loading surface of TLL was mapped computationally using the information obtained from the Protein Data Bank (PDB) under three different pH conditions. This information allowed to conduct the directional immobilization of the lipase on the surface of the SPIONs in order to maximize the lipase–SPION interaction and keep the enzyme’s active sites facing the solution. TLL was immobilized at a low ionic strength (5 mmol L–1) on the SPIONs under optimized conditions (sodium acetate buffer, pH 4, 25 °C using an initial enzyme loading of 30 mg per gram of support). Under such conditions, almost full immobilization (99.49% adsorption capacity) was observed. The prepared biocatalyst retained 62.3% of its hydrolytic activity relative to the initial activity of the free lipase. Maximum catalytic efficiency (or acid conversion percentage) of 80% in decyl oleate synthesis performed in a solvent-free system was observed after 12 consecutive cycles of reaction of 180 min each. In addition, the lipase–nanoparticle interaction was also evaluated by fluorescence spectroscopy and the thermodynamic parameter values ΔGo=-25.8kJmol-1, ΔHo=-10.44kJmol-1, and, ΔSo=0.122kJmol-1K-1 were found, which is consistent with the occurrence of predominantly ionic interactions. These results clearly show the promising use of the prepared biocatalyst to catalyze decyl oleate production, an ester with emollient properties, in an eco-friendly process (solvent-free system).