Application of lipase encapsulated in silica aerogels to a transesterification reaction in hydrophobic and hydrophilic solvents: Bi-Bi Ping-Pong kinetics

Biocatalysts were prepared by encapsulation of the Burkholderia cepacia lipase in hydrophilic or hydrophobic silica aerogels dried under supercritical CO2. The hydrophobicity of the aerogels was modified by changing the ratio of two silicon precursors, the tetramethoxysilane and the methyltrimethoxysilane. The catalytic activities of the industrial lipase powder and entrapped lipase were compared in the transesterification reaction of I-octanol with vinyl laurate in various hydrophilic and hydrophobic solvents containing a low water ratio. This made it possible to study the influence of the entrapment, of the composition of the catalytic support and of the solvent mixture on the catalytic activity of the enzyme. This study showed that the aerogel network and the nature of liquid solvent had two significant and independent effects. That of the solvent is known but still not understood. As for the aerogel, it primarily offers a medium of immobilization allowing to dry the enzyme by supercritical CO2, therefore without compressing it. Also, it maintains the enzyme dispersed at the quasi-molecular level as if it were in solution even when using it in a liquid organic solvent where it would not be soluble. Moreover, the aerogel does not modify the nature of the kinetic mechanism proposed which is of the Bi-Bi Ping-Pong type with inhibition by the I-octanol. Nevertheless, it increases considerably the maximum transesterification rate since it multiplies it of a factor approximately 80 compared to the industrial lipase powder, because of a better enzyme dispersion. (C) 2004 Elsevier B.V.. All rights reserved.