Figure 12.

Schematic of EB: In Step 1, a high-potential acceptor oxidizes the doubly reduced bifurcating site by one electron, generating the unstable singly reduced bifurcating site, which is a potent reductant. In Step 2, this reductant can transfer an electron to a low-potential acceptor, provided that the more exergonic electron transfer to a second high-potential acceptor is prevented (gated). Here the redox steps are shown as pure electron transfers, as is common in the field, but one or both of these steps is (in our view) likely to be PCET (see below).