eBioCO2n – Electricity-driven CO2 conversion through synthetic enzyme cascades

The "eBioCO2n" project, which is being carried out jointly by Fraunhofer and Max Planck scientists, pursues an ambitious approach to converting CO2 into chemicals with electricity from renewable sources: Similar to photosynthesis, CO2 is to be fixed with electron-transmitting biocatalysts and then linked to further enzymatic conversion steps.

Challenges

Not only chemical-catalytic processes can be considered for the current-driven synthesis of chemicals. It is also conceivable to combine CO2-fixing electron-transmitting biocatalysts with further enzymatic conversion steps in the form of an enzyme cascade for the production of fine chemicals.

Project plan

The "eBioCO2n" project, which is being carried out jointly by Fraunhofer and Max Planck researchers, meets this challenge. The aim of this ambitious project is to demonstrate the feasibility of such bioelectrocatalytic syntheses with a demonstrator on a 10 – 100 mL scale. To this end, suitable C02-fixing enzymes are to be assembled on electrodes (cathodes) using new molecular architectures and – depending on the target product – combined with other specific enzymes to form continuous and coupled reaction cascades. Recently discovered redox enzymes, enoyl-CoA carboxylases/reductases (ECRs), are used as CO2-fixing biocatalysts. They are among the most efficient CO2-converting biocatalysts described so far.

Impact

Chemical synthesis on the basis of biocatalytic CO2 fixation thus enables a new form of circular economy by using electricity from renewable resources for the enzymatic production of value-adding fine chemicals and decoupling chemical synthesis processes from fossil raw materials.

Publication

In novel bioelectrocatalytic approaches, the functional integration of CO2-fixing enzymes onto electrode materials for the electrosynthesis of stereochemically complex molecules remains to be demonstrated. In this publication, we show the electricity-driven regio- and stereoselective incorporation of CO2 into crotonyl-CoA by an NADPH-dependent enzymatic reductive carboxylation. Co-immobilization of a ferredoxin NADP+ reductase and crotonyl-CoA carboxylase/reductase within a 2,2′-viologen-modified hydrogel enabled iterative NADPH recycling and stereoselective formation of (2S)-ethylmalonyl-CoA, a prospective intermediate towards multi-carbon products from CO2. This approach paves the way for realizing even more complex bioelectrocatalyic cascades in the future.

Leonardo Castañeda-Losada, David Adam, Nicole Paczia, Darren Buesen, Fabian Steffler, Volker Sieber, Tobias J. Erb, Michael Richter, Nicolas Plumeré (2021) Bioelectrocatalytic Cofactor Regeneration Coupled to CO2 Fixation in a Redox-Active Hydrogel for Stereoselective C−C Bond Formation; Angewandte Chemie International Edition 2021, 60, 2–8; https://onlinelibrary.wiley.com/doi/10.1002/anie.202103634