(12c) Cooperative Catalysis for Selective Oxidation with Hybrid Gold Nanoparticle Enzyme Materials

Recent advances in heterogeneous catalysis in combination with enzymatic catalysis have created new possibilities and opportunities in nanomaterial sensing, medicine, and catalysis. Thus, it is important to understand the interactions of enzymes and nanoparticles. In this work, we studied these interactions using the combination of gold nanoparticles and oxidase enzymes in order to facilitate the synergistic effects of catalysis in substrate channeling.

Gold nanoparticles are known for their proficiency at oxidation catalysis, particularly selective oxidation catalysis. Oxidases convert sugars to carboxylic acids and hydrogen peroxide. Gold in the presence of hydrogen peroxide can catalyze further oxidation. The goal of this work is to demonstrate substrate channeling where the enzyme performs the first oxidation producing a carboxylic acid and hydrogen peroxide and then the hydrogen peroxide is used in a second oxidation catalyzed by the gold nanoparticles (Au NP).

Two different hybrid systems were studied: Au NP-glucose oxidase and Au NP-xanthine oxidase. In the Au NP-glucose oxidase system, glucose is oxidized by glucose oxidase to gluconic acid and hydrogen peroxide. The hydrogen peroxide and gluconic acid are further oxidized by the Au NP to form glucaric acid. Our results indicate that the glucose oxidase is bound to the Au NP surface and the hybrid system produces glucaric acid while the glucose oxidase on its own does not produce glucaric acid. Additionally, it was determined that the reaction exhibits a glucaric acid selectivity dependence on the solution pH.

In a second hybrid system, Au NP-xanthine oxidase, xanthine is converted to uric acid and hydrogen peroxide. The hydrogen peroxide is then used to oxidize benzyl alcohol on the surface of the gold nanoparticles. Results indicate that the presence of bound xanthine oxidase on the Au NP surface shifts the selectivity from the carboxylic acid product to the less oxidized aldehyde product. This work demonstrates the cooperativity between enzymes and gold nanoparticles and different enzyme-metallic nanoparticles can be investigated to produce new catalytic functionalities.