Organic-inorganic hybrid mesoporous silica materials and their application as host matrix for protein molecules

Hua Dong

doi:10.17918/etd-34

Transparent, organic-inorganic hybrid mesoporous silica materials have been prepared successfully via the acid-catalyzed hydrolysis and cocondensation of tetramethyl orthosilicate and various organosiloxanes via the nonsurfactant templated sol-gel process. The organic groups were attached to the silica matrix via the non-hydrolyzable Si-C covalent bond and functioned as network modifier. The synthetic conditions have been systematically studied and optimized. Nitrogen adsorption and transmission electronic microscopy characterizations show that the sol-gel matrices obtained after removing the templates possess a three-dimensional network of interconnected mesopores. The pore parameters are tunable to some extent by varying the template content. Several enzyme systems, such as horseradish peroxidase (HRP), glucose oxidase (GOx), lipase, alcohol dehydrogenase (ADH) etc. have been immobilized in situ in these hybrid mesostructured, or more generally, nanostructured silica matrix. The catalytic activity of immobilized enzymes has been assayed and correlated with the microstructures of the host silica materials under varied conditions. The enzymes encapsulated in the nonsurfactant-templated mesoporous sol-gel materials exhibit remarkably higher apparent catalytic activity, from a few-fold to three-orders of magnitude greater, than those in the non-templated conventional microporous hosts synthesized in the absence of the templates under otherwise identical conditions. Co-immobilization of more than one enzyme in the mesoporous host materials has been achieved, in which one enzyme's product is another's substrate. Protein unfolding and refolding in the nonporous host have been investigated. Thermal stability of enzymes were found to improve remarkably in the host materials. Nonionic poly(ethylene oxide) copolymer surfactants were also utilized as templates for in situ immobilization of multiple enzymes. To minimize the denaturation of the enzyme in methanol which is liberated during the hydrolysis, a low-shrinking sol-gel process is also adapted to the direct immobilization of organophosphorus acid anhydrolase (OPAA). The thus immobilized OPAA showed high resistance to organic solvent and is promising as the enzyme-based decontaminant. This study demonstrates that the novel sol-gel mesoporous materials have potential applications in biocatalyst, biosensor devices, etc.

Organic-inorganic hybrid mesoporous silica materials and their application as host matrix for protein molecules

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Organic-inorganic hybrid mesoporous silica materials and their application as host matrix for protein molecules

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