Synthesis of Sponge Mesoporous Silicas from lecithin/dodecylamine mixed-micelles in ethanol/water media : A route towards efficient biocatalysts
Résumé
Mixed-micelles of long-chain phosphatidylcholine and surfactants are of considerable scientific and biomedical interest. Lecithins are natural phospholipids from egg or soybean. Lecithin / dodecylamine mixed-micelles in an alcoholic/aqueous media have successfully lead to the formation of Sponge Mesoporous Silica (SMS) materials through a self-assembly process between mixed-micelles and tetraethoxysilane (TEOS). This “gentle” SMS synthesis (room temperature, neutral pH, natural surfactant) was previously used to encapsulate lipases directly during the synthesis to give remarkable activities in esters hydrolysis. SMS synthesis thanks to mixed micelles as templating agent, add the porosity control to the classical sol-gel synthesis used for enzymes encapsulation. We are reporting here the key parameters of this new synthesis (amount of amine, TEOS, ethanol, water, lecithin nature, salt addition,...), as well as a fine description of this new structure thanks to platinum replica. SMS present an isotropic 3-dimentional pore structure similarly to SBA-16, but less ordered, with cavities and connecting channels, which length is controlled by synthesis condition. Cavities diameters can reach 5 nm in accordance to lecithin maximum chain length. Surface areas are comprised between 300 and 800 m2/g and pore volume between 0.30 and 0.85 mL/g depending on the synthesis conditions. The use of lactose as enzyme stabilizing agent in SMS synthesis does not change the pore structure of SMS. A very fragile enzyme, alcohol deshydrogenase, has also been successfully encapsulated by this way, which represents the first successfull entrapment of this enzyme in an inorganic matrix. This new encapsulation process respecting biomolecules opens large perspectives for biomolecules processing such as biocatalysis, biosensors or biofuel cell applications.