  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.
