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Time-Resolved Infrared Spectroscopy of an [FeFe]-Hydrogenase Model Compound



Edwin J. Heilweil


Naturally occurring hydrogenases catalyze the reaction of H+ to form H2 gas. To develop a hydrogen source that is not reliant on fossil fuels, synthetic [FeFe]-hydrogenase model species are being studied. These compounds have a wing-like structure with a Fe-Fe bond, three pendant ligands on each Fe, two sulfur atoms bridging the irons, and a short organic chain connecting the sulfurs. The turnover rates for these compounds are substantially lower than that of the natural enzyme, although varying the active site ligands affects the catalytic properties. One active area of research is to pair hydrogenase models with visible/UV absorbing chromophores, in a mechanism inspired by photosynthesis. To successfully create photo-driven hydrogenase catalysts, their behavior after light exposure must be better understood. Our research involves studying Fe2(mu-S2C2H4)(CO)4(PMe3)2 and related mimics for the enzyme chromophore using time-resolved ultraviolet/visible pump, infrared probe spectroscopy.[1] Fe2(mu-S2C2H4)(CO)4(PMe3)2 was dissolved in acetonitrile and n-heptane and excited with 532 nm, 355 nm, and 266 nm light. For 355 nm and 532 nm excitation in both solvents, the bleach signals from loss of the original molecule and new photoproduct absorptions both decay to roughly 50% of their original intensities with an average time constant of 360 ± 91 ps. The remaining signals persist out to the microsecond timescale. Observed absorption decay kinetics are similar to those for the analogous propyl-bridged phosphine model compound, Fe2(mu-S2C3H6)(CO)4(PMe3)2.[1] Short-lived signals likely correspond to excited electronic state, CO-loss photoproducts. These excited state photoproducts decay back to the ground electronic state with roughly half recombining with CO to generate the original isomer.
Proceedings Title
Time Resolved Vibrations Spectroscopy 2015
Conference Dates
June 21-26, 2015
Conference Location
Madison, WI


Iron-hydrogenase, enzymes, photo-physics, hydrogen fuel, ultrafast infrared spectroscopy


Heilweil, E. (2012), Time-Resolved Infrared Spectroscopy of an [FeFe]-Hydrogenase Model Compound, Time Resolved Vibrations Spectroscopy 2015, Madison, WI, [online], (Accessed April 20, 2024)
Created March 26, 2012, Updated November 10, 2018