Understanding the Oxygen Sensitivity of [FeFe]-Hydrogenase: A Reactive Study of Active Site Mimics and Functional Enzyme

[FeFe]-hydrogenase is nature’s most efficient proton reducing and H2 oxidising enzyme. However, biotechnological applications of the enzyme are currently restricted due to its aerobic sensitivity which is poorly understood. Herein, we spectroscopically investigate four mimics of the active site cofactor, Fe2(adt)(CO)6-x(CN–)x and Fe2(pdt)(CO)6-x(CN–)x (X = 1,2) as well as two cofactor variants of the [FeFe]-hydrogenase from Chlamydomonas reinhardtii towards their reactivity with O2 and reactive oxygen species, ROS. The amine bearing adt mimic, which is the synthetic precursor molecule of the active site cofactor, was found to be most oxygen sensitive. This highlights the role of hydrogen bonding and proton transfer in aerobic deactivation. Moreover, we observed that the ligand environment around the iron ions has a significant influence on the overall reactivity with O2 and ROS, as the deactivation velocity increased with the exchange of CO to CN–. In order to mimic the catalytically relevant states, deactivation studies were conducted under acidic conditions. Here, the mimics formed a bridging hydride state, which resisted further oxidation. Thus, the results presented herein shed light on the chemistry of oxygen induced deactivation of [FeFe]-hydrogenase.