The [FeFe]-hydrogenases are extraordinarily efficient enzymes for producing H2 in living systems.  The [FeFe]-hydrogenases have been the subject of much interest, given the potential for these enzymes in producing hydrogen gas.  This has included studies of both the enzymes and related models compounds.  These models contain a diiron core linked by a dithiol bridging ligand.  Each iron also contains three small-molecule ligands (CO, CN, or PMe3 are the most common).One active area of research has been combining [FeFe]-hydrogenase model compounds with a chromophore, to allow light-driven catalysis.  Unfortunately, much of this work has been done without an understanding of how the model compounds react when exposed to visible or ultra-violet light.  In this work, we have been systematically studying small-molecule models of the [FeFe]-hydrogenases using ultrafast UV or visible pump, IR probe spectroscopy.  We have studied the effects of altering both the bridging and small-molecule ligands.In Fe2(�-S2C3H6)(CO)6 (1 ) and Fe2(�-S2C2H4)(CO)6 (2 ), two separate photoproducts were observed.  The first photoproduct involves an excited electronic state with an elongated Fe-Fe bond that decays in ~150 ps.  The second photoproduct involved the loss of a CO ligand, which only slowly recovers (~3 �s).  The relative amounts of these photoproducts depend strongly on the pump wavelength used.Studies on trimethylphosphine derivatives, Fe2(�-S2C3H6)(CO)4(PMe3)2 (3 ) and Fe2(�-S2C2H4)(CO)4(PMe3)2 (4 ), show different behavior.  In these models, a complicated mixture of short-lived, excited-state CO-loss photoproducts is observed.  These excited photoproducts decay in ~150 ps.  Roughly half recombine with CO and return to the starting isomer in the ground state.  The other half relax into a complicated mixture of ground-state 3-CO and 4-CO isomers.These studies show that changing the small-molecule ligands can strongly alter the electronic environment of the active site.  This in turn dramatically alters the dynamic behavior of the active site.

Ultraviolet/visible pump, time-resolved infrared probe spectroscopy of [FeFe]-hydrogenase model compounds

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.