Cyclam Second Sphere Reactions for Enhanced CO2 Reduction: A Chemical and Enzymatic Approach

• Applicants: Professor Dr. Ulf-Peter Apfel; Johannes Rebelein, Ph.D.
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569255924

This project aims to develop more efficient and selective catalysts for converting carbon dioxide (CO2) into hydrocarbons serving as bulk chemicals and fuels. CO2 levels have risen due to human activities, causing the current climate crisis. To mitigate this, CO2 capture and utilization (CCU) technologies are being developed, which convert CO2 into bulk chemicals. However, current CO2 reduction (CO2R) processes are unselective and require substantial energy. To achieve our long-term goal to develop more efficient and selective CO2R catalysts, we propose to further investigate the role and function of the second coordination sphere in CO2 activating transition metal complexes and artificial metalloenzymes. Although nature has evolved and optimized natural enzymes for CO2 conversion (i.e. carbon monoxide dehydrogenase, formate dehydrogenase, etc.) these enzymes are too complex to directly engineer and optimize their product spectrum. Thus, we propose to use cyclam, a macrocyclic ligand, to develop more efficient and selective CO2R catalysts. Cyclam has already shown promise in CO2R, but its performance can be further improved by modifying its second sphere. We will synthesize artificial second-sphere-modified cyclam frameworks and their metal complexes. By incorporating the cyclams into various protein scaffolds we will construct cyclam-based artificial metalloenzymes. These approaches allow us to investigate how different artificial second-sphere modifications influence the catalytic performance of cyclam systems and compare them to enzyme second spheres. We will use a combination of synthetic chemistry and biochemical approaches to achieve the following four objectives: (1) to synthesize artificial second-sphere-modified cyclams and their metal complexes, (2) to construct cyclam-based artificial metalloenzymes, (3) to characterize the cyclam-based metal catalysts and the artificial metalloenzymes for electro- and photochemical CO2R, and (4) to apply protein engineering on the best-performing artificial metalloenzymes to enhance their catalytic activity. To comprehensively characterize the cyclam-based complexes and artificial metalloenzymes we will use a range of techniques, including cyclic voltammetry, linear sweep voltammetry, and controlled potential coulometry, to analyze the electrocatalytic behavior as well as X-ray crystallography to obtain an atomic understanding of the complexes and the artificial metalloenzymes. The project will provide insights into the reaction mechanisms and assess whether artificial second spheres can match biological ones in selectivity, activity, and stability, providing new insights into the design of efficient and selective chemical and biological CO2R catalysts. We aim to develop more efficient and selective CO2R catalysts, which can be used to convert CO2 into value-added chemicals and fuels, contributing to the development of sustainable and circular technologies for CO2 conversion.

• DFG Programme: Research Grants