Preparation Of Mesoporous Materials Templated By Gelatin And Its Study In The Immobilization Of Lipase

Amorphous mesoporous silicas (MPS-3, MPS-4, MPS-5 and MPS-6) with different pore diameter were synthesized in hydrothermal solution with different pH at 100℃for 24 h, using biodegradable natural polymer gelatin as structure directing agents and sodium silicate as silica source. The prepared mesoporous silicas were characterized by N2 adsorption-desorption, small angle X-ray diffraction (SAXRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results showed that the mesoporous silica had nonrigid and wormhole-like pore structure. Distribution of pore size increased (3.6, 5.1, 6.3, 13.7 nm, respectively), specific surface area decreased (512.8, 437.5, 315.3, 247.8 m2 g?1, respectively) and pore volume reduced (1.344, 0.901, 0.775, 0.768 cm3 g?1, respectively) with the pH value of the hydrothermal solution increased. The synthesized MPS was then utilized as supports for immobilization of Porcine pancreatic lipase (PPL) by physical adsorption. The measurements of N2 adsorption-desorption, FT-IR and EDS demonstrated that PPL had been adsorbed into the channels of the MPS. Hydrolysis reaction of triacetin catalyzed by immobilized and free enzyme had been studied. The optimal reaction conditions of free PPL is pH = 7.0, 35℃, whereas the immobilized PPL was pH = 8.0, 45℃. The results indicated that immobilized PPL had the excellent adaptability in wide pH and temperature ranges of reaction medium. Compared to free PPL, the immobilized PPL samples possess better thermal stability, which still retain about 40% of the initial activity after being reused six times.The mesoporous materials with different distributions of pore size named M-SDS-1.2, M-SDS-6, M-SDS-12 and M-SDS-60 were prepared using gelatin and anionic surfactant sodium dodecylsulphate (SDS) as a dual-template and sodium silicate as silica source. By adding different concentrations of SDS, the distribution of the charge in gelatin could be changed, electrostatic interaction and intermolecular hydrogen bond were effected and the volume of gelatin chain was further adjusted. In this way the distribution of pore size of silica was controlled. The materials were characterized by N2 adsorption-desorption, EDS and TEM. The results suggested that mesoporous silica still had amorphous and wormhole-like pore structure, moreover, the morphology and structure of four materials were similar. PPL was immobilized on M-SDS-1.2, M-SDS-6, M-SDS-12 and M-SDS-60 with physical adsorption at optimal immobilized conditions (25℃, 6 h, phosphate buffer pH = 7.0). The immobilized PPL samples were characterized by N2 adsorption-desorption and FT-IR, these results indicated that PPL had been successfully immobilized in the pore of support. The influencing factors of catalytic activity of immobilized enzyme had been investigated. The pH resistance and thermal stability of PPL improved observably after immobilization. Leaching of immobilized PPL was unavoidable because PPL molecules were only immobilized on the mesoporous channel with physical adsorption by relatively weak hydrogen bond interaction. However, the immobilized PPL still retain about 40% of the initial activity after being reused six times.