|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1996 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1995 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Entrapment of lipase in organically modified silicates, which are derved from a mixture of tetramethoxysilane (TMOS) and alkyl group-containing organic silanes by the sol-gel method, leads to enhancement in esterification activity and thermal stability of immobilized preparation. In this study, we tried to form the lipase-entrapping gels either (1) in W/O microemulsion or (2) on the surface of support materials, and investigated some enzymatic properties of resultant immobilized lipase. In ester synthesis from butyric acid either isoamyl alcohol or ((]SY.+-。[))-menthol as a test reaction, the following results were obtained.
(1) Microemulsion-based entrapment : Among various surfactants tested, the silicate-entrapped lipase prepared by using Brij 97 displayd a highest catalytic activity at room temperature. The organic-inorganic hybrid silicate derived from a mixture of TMOS and methyltrimethoxysilane resulted in a more enhanced activity of the immobilized lipase.
(2) Dispersed entrapmen
t on support surface : Among various organic silanes mixed with TMOS,alkyltrimethoxysilanes bearing longer chain length than propyl group, and methoxysilanes with multiple methyl groups brought about enhanced activity and thermostability of the immobilized lipase preparations. When kieselguhr such as commercially available Celite 545 was used as a support material, the entrapped lipase gave a mzximum esterification activity. There existed an optimum amount of gel and an optimum molar ratio of organic silane to TMOS.As the result of optimization of various preparation conditions, the thermostability of entrapped lipase was enhanced by 20-30ﾟC as compared with that of deposited counterpart.
These results and findings might be ascribed to 1) stabilization of tertiary structure of protein globules by reasonably tight entrapment in close proximity of the hybrid gel surface, 2) preferential partitioning of substrates to the hydrophobic gel, and 3) hydrophobic interaction between lipase molecules and alkyl groups of the organic silica gel. Less