Scheme 1. Proposed catalytic cycles of both Ru–Fd–Co and Ru–ApoFld–Co biohybrids as observed by EPR and transient optical kinetic studies. A Co(iii)–H species is shown as a catalytic intermediate as discussed in the text. (A) Ru–ApoFld–Co pathway is unidirectional using a reductive quenching pathway that produces H2. (B) Ru–Fd–Co pathway is bidirectional with an oxidative quenching pathway (top) as the primary pathway to H2 production as observed by EPR. There is evidence for a small component of the reductive quenching pathway (bottom), which can continue on to perform H2 through the above scheme.
