Understanding the silica-based sol-gel encapsulation mechanism of Thermomyces lanuginosus lipase: The role of polyethylenimine

Silica-based sol-gel enzyme immobilization aided by polyamines has been used for generating active and stable heterogeneous biocatalysts. However, the encapsulation mechanism and its influence on the characteristics of the resulting biocatalysts have not been fully understood yet. This work aimed to shed light on how Thermomyces lanuginosus lipase, siliceous species and the additive polyethylenimine (PEI) interact during enzyme encapsulation, by establishing a correlation between addition of PEI, material formation and enzyme encapsulation. The addition of PEI appears to increase enzyme incorporation producing a biocatalyst with high encapsulation efficiency in terms of percentage of encapsulated protein (90%) and activity (47%). Furthermore, we observed that the addition of PEI resulted in a biocatalyst with high catalytic activity (600 U/g) and thermal stability (247-fold more stable than the soluble enzyme at 65 °C). The formation of silica particles was followed over time, showing a homogeneous incorporation of the enzyme in its active form. Intrinsic fluorescence spectroscopy suggested that the addition of PEI during the encapsulation process resulted in a conservation of the structural and functional features of the enzyme, suggesting a stabilizing role of the additive. The integration of the results of this work allowed proposing a polycondensation/enzyme encapsulation mechanism for silica-based sol-gel encapsulation mediated by PEI. These new evidences will contribute to the design of novel and more efficient silica-based biocatalysts achieved by sol gel encapsulation methodology.