Sol–gel encapsulation: An efficient and versatile immobilization technique for cutinase in non-aqueous media

Cutinase from Fusarium solani pisi was encapsulated in sol–gel matrices prepared with a combination of alkyl-alkoxysilane precursors of different chain-lengths. The specific activity of cutinase in a model transesterification reaction at fixed water activity in n-hexane was highest for the precursor combination tetramethoxysilane/n-butyltrimetoxysilane (TMOS/BTMS) in a 1:5 ratio, lower and higher chain lengths of the mono-alkylated precursor or decreasing proportions of the latter relative to TMOS leading to lower enzyme activity. Results obtained using combinations of three precursors confirmed the beneficial effect of the presence of BTMS in the preparations. Scanning electron microscopy of the 1:5 TMOS/n-alkylTMS gels showed a direct correlation between the macropore dimensions and the alkyl chain length of the alkylated precursor and revealed that TMOS/n-octylTMS gels suffered extensive pore collapse during the drying process. The specific activity of TMOS/BTMS sol–gel entrapped cutinase was similar to that exhibited by the enzyme immobilized by adsorption on zeolite NaY. However, the incorporation of different additives (zeolites, silica, Biogel, grinded sol–gel, etc.) having in common the capability to react with residual silanol groups of the sol–gel matrix brought about remarkable enhancements of cutinase activity, despite the fact that the global porosity of the gels did not change. The behavior of the gels in supercritical CO2 (sc-CO2) paralleled that exhibited in n-hexane, although cutinase activity was ca. one order of magnitude lower (i.e. sol–gel encapsulation did not prevent the deleterious effect of CO2). The impact that functionalization of some of the additives had on cutinase activity indicates that the enzyme/matrix interactions must play an important role. Some of the best additives from the standpoint of enzyme activity were also the best from the standpoint of its operational stability (ca. 80% retention of enzyme activity at the tenth reutilization cycle). None of the additives that proved effective for cutinase could improve the catalytic activity of sol–gel encapsulated Pseudomonas cepacia lipase.