Electrochemistry for applied biomaterials: designing biocatalysts for hydrogen-driven reduction of nitrogen-containing compounds

Thesis

The work encompassed within this thesis addresses the development of bio catalysts for more sustainable methods for the reduction of nitrogen containing compounds. Throughout this work hydrogenase enzymes are used to provide electrons from H2 splitting which are harnessed at a carbon surface for driving nitro reduction reactions, producing valuable amine products by a redox mechanism. Analogous industrial hydrogenations for amine synthesis generally operate using unsustainable platinum group metals, energy intensive conditions, and/or poor selectivity. Biocatalysis is a rapidly advancing tool for industrial processes, addressing requirements for sustainable, selective and low energy reactions.

The format of this thesis therefore considers the two site-separated redox half reactions of hydrogen oxidation and nitro reduction at carbon, where hydrogenase enzymes are used for the oxidation step and the nitro reduction occurs directly at the carbon surface. The thesis begins with electrochemical characterisation of several hydrogenase enzymes for H2 oxidation, followed by comprehensive electrochemical investigation of the of reduction of nitroaromatic compounds at the carbon interface in aqueous conditions. This enables comparative analysis of the potentials of reduction, and the influence of varied substituents as well as electrolytes on the reduction. The two redox components are then combined into a hydrogenase on carbon catalyst for mixed potential electrochemical analysis of the hybrid bio-electro catalyst. The insights provided by this work enable informed selection of the hydrogenase to extend the scope to nitroalkanes under mild, aqueous conditions. The catalyst is then shown in an industrially relevant continuous flow reactor for the synthesis of the precursor to the active pharmaceutical compound, paracetamol, demonstrating applicability to real world situations. Further study demonstrating the reductive cleavage of an azo dye using the hydrogenase on carbon catalyst is completed, culminating in a preliminary demonstration of this reaction in continuous flow.

Authors: Lurshay, TC

• Alternative title: Electrochemistry for applied biomaterials
• DOI: 10.5287/ora-8jmwazo2z
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: H₂ oxidation; hydrogenase; green chemistry; mixed potential; continuous flow; amine synthesis; sustainable manufacturing; bioelectrochemistry; biocatalysis; protein film electrochemistry; electrochemistry; pharmaceutical synthesis; heterogeneous catalysis
• Subjects: Biocatalysis; Electrodes, Enzyme; Hydrogenase; Pharmaceutical biotechnology; Flow chemistry; Electrochemistry; Heterogeneous catalysis; Bioelectrochemistry; Green chemistry