Immobilization of dextransucrase on functionalized TiO₂ supports

The TiO₂ based hybrid supports with different functional groups (amino, glutaraldehyde or epoxy) were prepared and their influence on immobilization of dextransucrase (DS) was studied. Novel synthetic route for surface modification of TiO₂ with amino and glutaraldehyde groups was developed taking advantage of charge transfer complex (CTC) formation between surface Ti atoms and salicylate-type of ligand (5‑aminosalicylic acid (5-ASA)). The proposed coordination of 5-ASA to the surface of TiO₂ powder and optical properties of CTC was presented. The pristine TiO₂ and amino functionalized TiO₂ have higher sorption capacity for DS (12.6 and 12.0mgg^-1, respectively) compared to glutaraldehyde and epoxy activated supports (9.6 and 9.8mgg^-1, respectively). However, immobilized enzyme to either glutaraldehyde or epoxy functionalized TiO₂ have almost two times higher expressed activities compared to pristine TiO₂ support (258, 235 and 142IUg^-1, respectively). Thermal stability of enzyme immobilized on glutaraldehyde and epoxy functionalized supports was studied at 40°C, as well as operational stability under long-run working conditions in repeated cycles. After five cycles, DS imobilized on glutaraldehyde activated support retained almost 70% of its initial expressed activity, while, after five cycles, performance of DS immobilized on epoxy activated support was significantly lower (15%).