Synthesis of sponge mesoporous silicas from lecithin/dodecylamine mixed-micelles in ethanol/water media: A route towards efficient biocatalysts

Abstract

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 allow to template the formation of sponge mesoporous silica (SMS) materials through a self-assembly process between mixed-micelles and tetraethoxysilane (TEOS). SMS synthesis adds a porosity control to the classical sol-gel synthesis used for enzymes encapsulation. We are reporting here the key parameters of SMS synthesis procedure (amount of amine, TEOS, ethanol, water, lecithin nature, salt addition, etc.), as well as a fine description of SMS structure by TEM. SMS features an isotropic 3-dimensional (3-D) pore structure similarly to SBA- 16, but with a lower degree of mesoscopic structural order. Its porosity results from cavities and connecting channels, whose length is controlled by the synthesis conditions. Cavity diameters can reach 4.7 nm in accordance to the lecithin maximum alkyl chain length. Surface areas range from 300 to 800 m(2)/g, and pore volumes from 0.30 to 0.85 mL/g. The use of lactose as an enzyme stabilizing agent does not change the pore structure of SMS. A very fragile enzyme, alcohol dehydrogenase, has been successfully encapsulated by this way, providing the first example of successful entrapment of this enzyme in an inorganic matrix. SMS encapsulation procedure is biomolecules friendly and opens a bright perspective for biomolecules processing for biocatalysis, biosensors or biofuel cell applications. (c) 2007 Elsevier Inc. All rights reserved.