title: Time-resolved vibrational spectroscopy of [FeFe]-hydrogenase model compounds.
abstract: Model compounds have been found to structurally mimic the catalytic hydrogen-producing active site of Fe-Fe hydrogenases and are being explored as functional models. The time-dependent behavior of Fe(2)(μ-S(2)C(3)H(6))(CO)(6) and Fe(2)(μ-S(2)C(2)H(4))(CO)(6) is reviewed and new ultrafast UV- and visible-excitation/IR-probe measurements of the carbonyl stretching region are presented. Ground-state and excited-state electronic and vibrational properties of Fe(2)(μ-S(2)C(3)H(6))(CO)(6) were studied with density functional theory (DFT) calculations. For Fe(2)(μ-S(2)C(3)H(6))(CO)(6) excited with 266 nm, long-lived signals (τ = 3.7 ± 0.26 μs) are assigned to loss of a CO ligand. For 355 and 532 nm excitation, short-lived (τ = 150 ± 17 ps) bands are observed in addition to CO-loss product. Short-lived transient absorption intensities are smaller for 355 nm and much larger for 532 nm excitation and are assigned to a short-lived photoproduct resulting from excited electronic state structural reorganization of the Fe-Fe bond. Because these molecules are tethered by bridging disulfur ligands, this extended di-iron bond relaxes during the excited state decay. Interestingly, and perhaps fortuitously, the time-dependent DFT-optimized exited-state geometry of Fe(2)(μ-S(2)C(3)H(6))(CO)(6) with a semibridging CO is reminiscent of the geometry of the Fe(2)S(2) subcluster of the active site observed in Fe-Fe hydrogenase X-ray crystal structures. We suggest these wavelength-dependent excitation dynamics could significantly alter potential mechanisms for light-driven catalysis.
authors.affiliation: Department of Chemistry and Physics, Hood College, 401 Rosemont Avenue, Frederick, Maryland 21701-8524, United States.
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Bingaman
authors.forename: Casey L
authors.initials: CL
authors.lastname: Kohnhorst
authors.forename: Glenn A
authors.initials: GA
authors.lastname: Van Meter
authors.forename: Brent A
authors.initials: BA
authors.lastname: McElroy
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Rakowski
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Caplins
authors.forename: Tiffany A
authors.initials: TA
authors.lastname: Gutowski
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Stromberg
authors.forename: Charles Edwin
authors.initials: CE
authors.lastname: Webster
authors.forename: Edwin J
authors.initials: EJ
authors.lastname: Heilweil
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002384:Catalysis; D020134:Catalytic Domain; D056831:Coordination Complexes / Q000138:chemical synthesis*; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D006864:Hydrogenase / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D011789:Quantum Theory; D013057:Spectrum Analysis; D013997:Time Factors; D014732:Vibration
chemical_list: D001426:Bacterial Proteins; D056831:Coordination Complexes; D004220:Disulfides; D007506:Iron-Sulfur Proteins; D008024:Ligands; D006859:Hydrogen; D007501:Iron; C118830:iron hydrogenase; D006864:Hydrogenase