Background/Objectives
Developing new catalysts is critical to enabling a future which reuses carbon instead of extracting new fossil fuels. Nature has developed catalysts (enzymes) that are efficient, fast, use ambient conditions, and non-precious metals. While the active site is important, there is extensive evidence that the protein scaffold in enzymes is also critical in their performance. In order to learn from nature and understand how enzymes operate so efficiently, we are adding enzyme-inspired outer coordination spheres to thermal catalysts for CO2 hydrogenation.
Approach/Activities
By covalently attaching a Rh-bis(diphosphine) complex within a structured protein scaffold which does not natively contain a metal, we see the complex activated for CO2 hydrogenation. To develop a mechanistic understanding of the scaffold, we are testing the hypothesis that charged groups will impact catalysis, with the expectation that positively charged groups will stabilize the transition state, enhancing catalysis, while negatively charged groups will slow catalysis. We modified single amino acids to (positive) arginine, lysine, or histidine, or (negative) aspartic acid or glutamic acid. We used kinetics, spectroscopy, and molecular dynamics, to explore the effects of the influence of the outer coordination sphere on this model system.
Results/Lessons Learned
By modifying single amino acids to positive or negative charges, we have demonstrated that a positive charge can enhance the catalytic rate, while negative charges can reduce catalysis. Interestingly, neither positive or negative charge has a consistent impact, an observation that we attribute to additional functionality in the scaffold which impacts the single feature upon which we were focused. In general, the theme of complexity is an important on in biology, and the cooperativity between single features not only needs to be considered but taken advantage of. More broadly, this system provides a platform to understand the role of a protein scaffold for both enzymatic and synthetic systems.