SusChEM: C-H Bond Electroactivation of Nonpolar Organic Substrates in Water: Enzyme-Mediated Reaction Pathways in Microemulsions

University Of Connecticut, Storrs CT

Investigators

Abstract

Running organic reactions in water rather than organic solvents increases sustainability by reducing the use of harmful solvents and lowering overall cost. Unfortunately, most nonpolar organic molecules do not dissolve in water. Most synthetic catalysts also work poorly in water, especially those aimed at producing specialty products such as pharmaceuticals. Alternatively, enzymes are excellent biocatalysts, even for reactions taking place in water. This project aims to combine synthetic copper polymer catalysts with inexpensive peroxidase enzymes to speed reactions of nonpolar organic molecules in water. Electrosynthesis will take place in microemulsions, which are mixtures of oil, water and low-toxicity, low-cost detergents, that feature nanoscale interfaces of oil and water. These emulsions improve the solubility and diffusion rate of nonpolar reactants by delivering reactants to water-rich enzyme sites for catalysis. The findings from this project will provide practical guidelines to next-generation sustainable synthesis of pharmaceutical and specialty chemicals. In addition to advanced training of graduate students, the project will offer training opportunities to undergraduate and high school students though summer research activities. Workshops on electrochemical enzyme catalysis for chemical synthesis will be organized through outreach activities for K-12 teachers and students. This proposal targets the development of high-temperature, sustainable bioelectrocatalytic materials and their applications to electrooxidation of C-H bonds by oxygen in water. New catalytic films will be fabricated via layer-by-layer self-assembly of synthetic Cu polymer catalysts and peroxidase-like enzymes. Such electrocatalytic systems will be capable of carrying out cooperative, cascade electrocatalysis of oxygen activation by Cu catalysts through 2e- reduction to produce hydrogen peroxide which further activates peroxidases to drive the oxidization of nonpolar organic substrates. The hybrid film of Cu catalysts and peroxidases will also be stabilized by chemical crosslinking to carry out high-temperature electrosynthesis (> 90 degrees C). Detailed kinetic studies will be analyzed in the hybrid films and the film composition will be fine-tuned to optimize the production rate of hydrogen peroxide on the Cu catalysts and its consumption rate by the peroxidases. The activity and selectivity of hybrid films will be investigated and optimized for two types of C-H activations in naphthyls (sp2 C-H) and alkylbenzenes (sp3 C-H) in various nanostructured microemulsions. True green chemistry systems in microemulsions that not only resolve the solubility issue of non-polar substrates but also provide well-defined conditions for enzymatic catalysts similar to aqueous solutions at neutral pH will be developed. Electrochemical kinetic and spectroscopic studies will be used to understand diffusion kinetics and reaction pathways, as well as the thermodynamic activation barriers for nonpolar reactants. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.