Glucose-6-phosphate dehydrogenase encapsulated in silica- based hydrogels for operation in a microcreactor

The future of hydrogen as fuel strongly depends on the possibility to produce it in an economic and clean way. Hydrogen can be produced from carbohydrates and water under mild conditions by means of a multistep synthetic pathway (13 enzymes) with very high yield. Crossover inhibitions and different optimal conditions of involved enzymes hinder the use of one-pot approach. Immobilization of enzymes in coupled individual reactors may avoid this problem. This work deals with the immobilization in silica-based hydrogels of one key enzyme of this pathway: glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides. The carriers were prepared with an ethylene glycol-modified silane, two polymers (polyethylene oxide and Pluronic (R)) and amino groups created by 3-aminopropyltriethoxysilane. These parameters influenced the enzymatic activity after immobilization. Gels prepared by addition of polyethylene oxide gave the best results and were used as monoliths in microreactors with two different geometries. The systems showed a high operational stability but a low effective enzyme activity. Enzyme leaching and a nonideal flow pattern may account for the low activity observed. This work is possibly the first one dealing with the immobilization of glucose 6-phosphate dehydrogenase in silica-based gels for its application in flow-through microreactors.