Effect of surface modification of low cost mesoporous SiO₂ carriers on the properties of immobilized lipase

To investigate the surface effects of low cost mesoporous SiO₂ on the properties of lipase, a series of modified mesoporous SiO₂ was synthesized through various alkoxysilanes reacted with hydroxyl of SiO₂ (C₁-SiO₂, C₈-SiO₂, C₁₆-SiO₂, SH-SiO₂, Ph-SiO₂, NH₂-SiO₂). Particularly, ionic liquids as novel alkoxysilane were synthesized and subjected to modify the low cost mesoporous SiO₂ (CH₃IL-SiO₂ and COOHIL-SiO₂). The porcine pancreas lipase (PPL) was immobilized on the prepared materials. The activity assay indicated that the activation of enzymatic activity site was benefit from the longer alkyl chain of alkoxysilane because of the growing hydrophobic nature. Nevertheless, the loading of lipase decreased from 69% for PPL-C₁-SiO₂ to 59% for PPL-C₁₆-SiO₂, reflecting the growing hydrophobic property limited the immobilization yield. The characteristic of alkoxysilane group (SH-SiO₂, Ph-SiO₂, NH₂-SiO₂) was another important factor to influence immobilization efficiency and enzymatic performance besides the alkyl chain length. The immobilization efficiency of PPL-SH-SiO₂, PPL-Ph-SiO₂ and PPL-NH₂-SiO₂ maintained at least 93%. Compared with conventional alkoxysilane, the activity of PPL-CH₃IL-SiO₂ improved to 2.60 folds of PPL-SiO₂. The immobilization efficiency of PPL-COOHIL-SiO₂ was up to 97% and the relative activity was above 62% after five recycles.