(48a) Tandem Metal Nanoparticle-Oxidase Catalysis for Selective Oxidation Reactions

There is great potential in combining heterogeneous metallic nanoparticle catalytic active sites and enzymatic active sites for sequential chemical transformations. This work combines enzymes, namely oxidases, and metallic nanoparticles in one material for tandem catalytic activity, analogous to substrate channeling. We investigate the cooperativity between the metallic and oxidase catalytic active sites in two selective oxidation reaction systems.

Gold nanoparticles and gold alloy nanoparticles are very selective oxidation catalysts using mild oxidants such as hydrogen peroxide. Oxidases convert sugars to carboxylic acids and hydrogen peroxide. This work demonstrates tandem oxidative activity using glucose oxidase and gold and gold alloy nanoparticles. The glucose oxidase will oxidize glucose to gluconic acid and hydrogen peroxide, and the gold/gold alloy nanoparticle will perform a second oxidation reaction.

In the first reaction sequence, glucose is oxidized to gluconic acid and hydrogen peroxide using glucose oxidase, and the gluconic acid is further oxidized to saccharic acid using hydrogen peroxide as the oxidant on the gold nanoparticle surface. We demonstrate that glucose oxidase is bound to the gold nanoparticle surface and that the hybrid system produces saccharic acid, while the glucose oxidase on its own does not produce saccharic acid, only gluconic acid. The selectivity of the hybrid system can be adjusted by changing the pH. Higher pH values promote oxidation to saccharic acid.

The second reaction sequence uses the same glucose oxidase hybrid gold/gold alloy nanoparticle system for the oxidation of glucose by glucose oxidase, and the hydrogen peroxide product is used to partially oxidize benzyl alcohol to benzaldehyde. Cooperativity is demonstrated between the glucose oxidase and the gold nanoparticles through increased production of benzaldehyde in the hybrid system versus the gold nanoparticles on their own. The effect of the alkalinity of the solution on the catalytic performance is also demonstrated in this system.