(560gu) High Performance Enzymatic-Transesterification in an Anhydrous Gas Flux Using Lipase Encapsulated in Graphene Oxide Aerogel

Gaseous enzymatic catalysis that holds great promise to chemical engineering and related fields is hindered mainly by the extremely low activity of enzyme in a dry form. The adding of moisture, however, leads to a poor stability of the enzyme. Here we propose and demonstrate a method to prepare an enzyme encapsulated in graphene oxide (GO) for gaseous enzymatic reactions. A lipase-GO aerogel (LGA) was prepared by mixing Candida Antarctica lipase B (CALB) with the oppositely charged GO at pH 3.3 followed by lyophilization, and examined with gaseous transesterification of geraniol and vinyl acetate. While exhibiting a 5 to 10-fold apparent activity over lyophilized CALB powder independent of the water activity, the LGA maintains its initial activity in an anhydrous gas flux, being 67 % of the peak value obtained in the optimal water content, over the temperature range from 20 to 80°C. The solid-state circular dichroism (ssCD) measurement confirms that the lipase encapsulated in LGA keeps its native conformation, and the thermogravimetric analysis (TGA) shows that the GO sheets replace a significant amount of water molecules essential for the lipase activity in the bulk, possibly. These results indicate that GO stabilizes the lipase activity by forming a water-like microenvironment through multiple hydrogen bonding and eliminating the random attacks by free water molecules. The LGA is able to display its initial activity over 500 hours of in anhydrous gas-phase reactions, highlighting its great potential for industrial synthesis of chemicals by gas-phase enzymatic reactions.