Exploring the use of AOx for organic synthesis and biofuel cells

Abstract

Chapter 1 shows a general presentation of catalysts. Chapter 2 presents a cascade system for alcohol oxidase with the enzyme benzaldehyde lyase. The project was successful in producing in one container only a two-step compound; first, alcohol was converted into aldehyde by alcohol oxidase and, sequentially, the aldehyde converted into the compounds of interest. Background crystals are formed in the final product, turning the removal of the material of interest simpler and more effective.
In Chapter 3, alcohol oxidase was converted into aldehyde in a flow system, but now using the enzyme aryl alcohol oxidase. As oxidase requires oxygen as an electron acceptor, this is a limiting factor due to the low solubility of O2 in the buffer solution. A flow system becomes more interesting as it can overcome this limitation by improving the oxygen mass transport in buffer solution due to the increased contact area between two fluids. Vigorous agitation is required to achieve similar results in a standard system, which normally compromises the enzymatic structure due to mechanical stress generated by aeration strength. The expected impairment of the structured tertiary enzyme was not observed for the aryl alcohol oxidase enzyme.
The findings in Chapter 3 about the mechanical resistance of aryl alcohol oxidase under vigorous motivated us to scale up the system from 50mL to 1L, presented in Chapter 4. It was possible to obtain high catalytic frequency values in this new configuration, but another challenge appeared: the low solubility of both substrate and product in an aqueous medium. This challenge was overcome by the biphasic liquid system composed the organic phase in the upper portion and the buffer in the lower part of the solution. In this system, the aqueous phase was fed with the substrate by the organic phase at all times, and the product removed. The encouraging results showed that aryl alcohol oxidase is a strong candidate for industrial applications.
In Chapter 5, we have evaluated carbon compounds deposited on electrodes to produce locally hydrogen peroxide for peroxidase; the idea is getting the halogenation of a model compound by combining catalytic and electrochemical techniques. Here, a fine tune of the voltage or current on a gas diffusion electrode covered with carbon nanotubes enabled the hydrogen peroxide formation. Since the CiVCPO (vanadium chloroperoxidase from Curvularia inaequalis) enzyme used in this project needs hydrogen peroxide, the system is interesting to make the enzymatic reaction always working at its maximum efficiency. Finally, Chapter 6 shows a synthesis of carbon-based materials to support the enzyme immobilization on electrodes, bringing a new possibility of using some of the enzymes studied here in biofuel cells and third-generation biosensors. The main idea is to work with enzymes without mediators using these carbon-based materials to sequester electrons from the enzymes to the electrodes. Higher currents were achieved with the newly synthesized carbon-based materials and glucose oxidase, paving the way to design devices having faster electrochemical responses.