The role of CN and CO ligands in the vibrational relaxation dynamics of model compounds of the [FeFe]-hydrogenase enzyme

Abstract

The vibrational dynamics of (μ-propanedithiolate)Fe(2)(CO)(4)(CN)(2)(2-), a model compound of the active site of the [FeFe]-hydrogenase enzyme, have been examined via ultrafast 2D-IR spectroscopy. The results indicate that the vibrational coupling between the stretching modes of the CO and CN ligands is small and restricted to certain modes but the slow growth of off-diagonal peaks is assigned to population transfer processes occurring between these modes on timescales of 30-40 ps. Analysis of the dynamics in concert with anharmonic density functional theory simulations shows that the presence of CN ligands alters the vibrational relaxation dynamics of the CO modes in comparison to all-carbonyl model systems and suggests that the presence of these ligands in the enzyme may be an important feature in terms of directing the vibrational relaxation mechanism.

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

“…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. 5) under acidic conditions that is not observed when L = CO. 8,15 Additionally, ground state investigations of the L = CN derivative by 2D-IR spectroscopy have revealed weak vibrational coupling between CO and CN − ligands 14,18 alongside evidence for CN-induced acceleration of the vibrational relaxation of the molecule in comparison to the L = CO derivative further showing that the nature of L plays a key role in the vibrational dynamics of these species.…”

“…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.…”

Photochemical dynamics of a trimethyl-phosphine derivatized [FeFe]-hydrogenase model compound

“…Furthermore, the native active site of [FeFe]-hydrogenase enzymes have been shown to react upon exposure to UV-visible light [35, 36]. Multidimensional IR spectroscopy (2D-IR) has been performed on 1a and [Fe 2 (μ- S2C3H6)(CO)4(CN)2] 2- in order to determine the vibrational mode energy and coupling dynamics and relaxation mechanisms [37, 38], which appear be solvent-dependent and changes when cyanide ligands are present in the models. 2D-IR has also been coupled with 350 nm excitation for studies of 1a [39].…”

Transient 2D-IR spectroscopy of inorganic excited states

“…Good examples of this effect are reported in Refs. 21,22 In this event however, it must be remembered that the effect is caused by the accidental overlap of peaks of different origin.…”

“…2D-IR is now employed extensively in the study of ground state systems. [11][12][13][14][15] Exemplars of this include the analysis of offdiagonal peak patterns to determine molecular geometries, 18,19 deconvolute complex spectra 20 or reveal vibrational 21,22 or chemical dynamics, 23,24 while 2D-IR lineshapes report on the fluctuations in a system introduced by interaction with its surroundings, typically nearby solvent molecules. [25][26][27] Crucially, much of this information is either impossible or technologically challenging to extract from 1D experiments.…”