Intermediate States and Reaction Mechanisms

1 [NiFe] Hydrogenase In the aerobically as isolated form, the [NiFe] hydrogenases are inactive and require activation under H2 or other reductants 

4 Molecular Concepts of Water Splitting Nature s Approach 

2 [FeFe] Hydrogenase Less information on the electronic structure is available from EPR on [FeFe] hydrogenase as compared to [NiFe] hydrogenase since only the Hox state (and Hox-CO) is paramagnetic. In particular, the hydride-carrying species (Hred) cannot be characterized by EPR techniques. However, FTIR and Moss-bauer spectroscopy have revealed important information on the intermediate states of the H cluster [128, 129]. 

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