Abstract: Polyethyleneimine(PEI) was coupled chemically to the surface of silica gel particles through the intermedium effect of γ\|chloropropyltrimethoxysilane, novel complex carrier PEI/SiO₂ for immobilizing penicillin acylase was prepared, and finally an immobilized penicillin acylase with a higher activity and stability was obtained. The influences of various factors on the preparation of the carrier were examined via measuring coupling amount of PEI on the compisite carrier. The chemical composition and structure of the surface of the composite carrier were characterized via IR and conductimetric titration. In order to explore the immobilization mechanism of the complex carrier for the penicillin acylase, the ζ potential of the support was determined before the enzyme was immobilized. The results show that the polyamine PEI can fully be coupled chemically to the surface of silica gel particles by the agency of γ-chloropropyltrimethoxysilane, and the linkage amount can reach 15%. The favorable reaction conditions are the reaction temperature is 90-94℃, the reaction time 5 h and the mass concentration 45-50 g/100 mL for PEI. Owing to a large quantity of amido contained on the macromolecular chains of PEI, there is not only chemical linkage, but also a great deal of physical adsorption during enzyme immobilization on the surface of PEI/SiO₂. The combination of a spot of chemical covalent linkage and a great deal of physical adsorption results in fast and stable immobilization, and excellent maintenance of constellation for penicillin acylase, so that the activity and activity recovery ratio of the immobilized enzyme are all higher. Moreover, the immobilized enzyme has a better continuous operating stability and its activity can keep at a level of 87.5% of fresh one all along after having been used for fifteen time repeatedly.

Key words: Polyethyleneimine, Silica gel, Composite carrier, Penicillin acylase,
Immobilization