Universal Free Energy Landscape Produces Efficient and Reversible Electron Bifurcation.

For decades, it was unknown how electron bifurcating systems in Nature prevented energy-wasting short-circuiting reactions that have large driving forces, so synthetic electron bifurcating molecular machines could not be designed and built. The underpinning free energy landscapes for electron bifurcation were also enigmatic. We predict that a simple and universal free energy landscape enables electron bifurcation, and we show that it enables high-efficiency bifurcation with limited short-circuiting (the EB-scheme). The landscape relies on steep free energy slopes in the two redox branches to insulate against short-circuiting without relying on nuanced changes in the microscopic rate constants for the short-circuiting reactions. The EB-scheme thus provides a blueprint for future campaigns to establish synthetic electron bifurcating machines.