Effective immobilization of enzyme in glycidoxypropyl-functionalized periodic mesoporous organosilicas (PMOs)

Bifunctional periodic mesoporous organosilicas (PMOs) with ethane bridging groups within the framework and various amounts of terminally bonded groups in the pore channels was synthesized by the co-condensation of 1,2-bis(triethoxysilyl)ethane (BTESE) and 3-glycidoxypropyltrimethoxylsilane (GPTMS) in the presence of triblock copolymer poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (P123) surfactants under acidic conditions and utilized as supports for enzyme immobilization. It is revealed that glycidoxypropyl groups have been successfully covalently attached to the pore wall of PMOs and a fraction of them have experienced epoxy ring opening reaction to form diol groups. The functional materials still preserve a mesoscopic ordering at a concentration of GPTMS as high as 10% in the reaction mixtures. The BET surface area, pore volume and pore size of the functionalized materials decrease with increasing amount of GPTMS, but a desirable pore structure remains when the GPTMS amount increases to 10%. The coexistence of the epoxy groups and the diol groups provides an efficient two-step covalent enzyme immobilization mechanism. The bifunctional PMOs materials exhibit higher papain immobilization efficiency and stability than pure PMOs because of the covalent interaction between the amino groups of papain and the epoxy groups of functionalized PMOs.