Temperature-responsive nanobiocatalysts with an upper critical solution temperature for high performance biotransformation and easy catalyst recycling: efficient hydrolysis of cellulose to glucose†
The development of an immobilized enzyme for efficient biocatalysis and catalyst recycling is of great importance in cost-effective and green chemical synthesis, with the hydrolysis of cellulose to glucose for the utilization of lignocellulosic biomass as a prominent and challenging example. We developed a novel concept of engineering temperature-responsive nanobiocatalysts with an upper critical solution temperature (UCST) for efficient catalysis as a soluble catalyst at a temperature >UCST and for easy catalyst separation as an insoluble catalyst at a temperature <UCST. The first polymeric nanoparticles showing an UCST were fabricated in high yield, and the immobilization of cellulase and cellobiase onto the particles afforded the first UCST-biocatalysts, with high specific enzyme loading and enzyme loading efficiency, an UCST of 13–14 °C, and high retention of the initial hydrolysis activity of the free enzyme at 50 °C (>UCST). The hydrolysis of insoluble cellulose, such as filter paper and pre-treated oil palm Empty Fruit Bunch (EFB, a waste biomass), with a mixture of the UCST-nanobiocatalysts containing cellulase and cellobiase at 50 °C reached the same catalytic performance as the free enzymes and gave 97% and 93% glucose yield at 2 wt% of cellulase loading, respectively. These catalytic performances are much better than any other known immobilized cellulases, due to the use of soluble catalysts. The catalysts were easily recovered at 4 °C and recycled to retain 71% and 73% productivity in the 8th and 6th reaction cycles for hydrolyzing filter paper and pre-treated EFB, respectively. The engineered UCST-nanobiocatalysts are potentially useful for the practical green hydrolysis of cellulose to glucose.