A look into the “H-Cluster” of FeFe-Hydrogenase through spectroscopic and synthetic methods

Since iron-sulfur clusters exist in our oxidizing environment, it can be concluded that at one time in our evolutionary history that the environment was instead a reducing environment. Iron-sulfur clusters which contain high spin Fe(II) and Fe(III) tetracoordinated metals can help facilitate electron-transfer processes, nitrogen fixation, catalytic sites in hydrogenases, and oxidation of NADH to [NAD] in mitochondria. In this review, one very unique iron-sulfur cluster will be analyzed, the “H-Cluster” of the protein FeFe-Hydrogenase. This exceptional cluster has a 4Fe4S cubane sub-cluster covalently bridged by a cysteinate thiol to a 2Fe sub-cluster. After an initial review of the “H-Cluster,” some of the spectroscopic methods that are used to determine cluster properties will be discussed. Finally, some of the synthetic models will be analyzed to determine ways to build synthetically the active cluster of the protein FeFeHydrogenase.