Porous Texture Modification of Silica Aerogels in Liquid Media and Its Effect on the Activity of a Lipase

The effect of the porous texture of silica gels on the catalytic efficiency of enzymes was investigated by submitting similarly prepared aerogels to different postgelation treatments in liquid media. The samples investigated comprised wet gels aged either in water at different pH, in an organic solvent miscible with water (dioxane) containing different water concentrations, or in an organic solvent immiscible with water (isooctane). Aerogels were obtained after aging by supercritically drying the samples with carbon dioxide. Some gels were also partially dried by evaporation for increasing periods of time prior to a final drying step with supercritical CO2. The evolution of the pore texture of these-materials was analyzed from their nitrogen adsorption isotherms. The esterification activities of the lipase Pseudomonas cepacia immobilized in the various gels were compared. Results show that the evolution in the texture of the silica aerogel resulted in a change in the lipase activity. This suggests that the enzyme can be considered as a gel type material, whose behavior to transformations in liquid media is similar, to some extent, to that of silica aerogels.