Femtosecond to Microsecond Photochemistry of a [FeFe]hydrogenase Enzyme Model Compound

Abstract

The photochemistry and dynamics of a model compound of the active site of the [FeFe]hydrogenase enzyme system have been studied on a wide range of time scales using a unique combination of femtosecond time-resolved infrared spectroscopy, nanosecond time-resolved infrared spectroscopy, and steady-state UV-FTIR methods. Using three different solvents, heptane, acetonitrile, and cyanoheptane, we have observed the rapid formation of solvent adduct species from the first solvation shell of the solute following photolysis of a carbonyl ligand and global fitting techniques have been employed to provide new insights into the ultrafast dynamics of this process. In addition, the use of solvent mixtures has enabled the observation of competitive ligand substitution processes at the newly created coordination site on time scales of a few nanoseconds, shedding new light on the chemical behavior of these enzyme models.

PhotoCORMs: CO release moves into the visible

“…9) when irradiated using flash photolysis. In accord with related work by Hunt and co-workers, 54,55 The dicationic monocarbonyl 12 ( Fig. 10, R = H) is both air stable and water soluble, and was reported by Kodanko and coworkers as a rapid CO releaser when irradiated at 365 nm.…”

Solution-phase photochemistry of a [FeFe]hydrogenase model compound: Evidence of photoinduced isomerisation

“…These are consistent with earlier studies of hydrogenase model systems using TRIR and are assignable to a combination of the short-lived MLCT excited state, vibrationally hot species formed by irradiation, and tricarbonyl photoproducts created by the loss of a CO ligand, which has been shown to occur on sub-ps time scales. 13,16 At intermediate pump-probe time delays (80 ps, Fig. 2(a), red) the bleaches show some recovery while the transient absorptions decay via narrowing and blueshifting, a process consistent with vibrational cooling.…”

“…Time-resolved infrared spectroscopic methods are well suited to investigating these processes and have been used to observe the dynamics and photochemistry of (μ-S(CH 2 ) 3 S)Fe 2 (CO) 4 (L) 2 (L = CO, CN) systems in solution. 13,14,16,18 . In these experiments, time-resolved infrared (TRIR) and transient 2D-IR studies employed UVinduced carbonyl photolysis to create a vacant coordination site.…”

“…Further analysis revealed a subsequent competitive mechanism involving geminate recombination and solvent substitution for the L = CO variant in a range of solvents and solvent mixtures. 13,16,19 Studies of the chemistry of these model systems have shown, however, that the presence of non-carbonyl ligands, L, can significantly influence the chemical characteristics of the compound and, in particular, they can impact upon the propensity for protonation. 8,10,15 For example, (μ-S(CH 2 ) 3 S)Fe 2 (CO) 4 (PMe 3 ) 2 (1) has been shown to form a bridged protonation product (μ-H)Fe 2 (pdt)(CO) 4 (PMe 3 ) 2 (propane dithiolate) (Ref.…”

Investigation of the Ultrafast Dynamics Occurring during Unsensitized Photocatalytic H2 Evolution by an [FeFe]-Hydrogenase Subsite Analogue

“…16,17,19,[22][23][24][25]27 Indeed, all the CO ligand vibrational mode frequencies were predicted by DFT calculations to redshift by an average of 6 cm -1 relative to those of 1 when simulations were performed on a MeCN molecule coordinating via its nitrogen atom lone pair as a solvent adduct to the vacant site on the Fe after CO loss (see SI, Fig. S5).…”