Photodynamics of Asymmetric Di-Iron-Cyano Hydrogenases Examined by Time-Resolved Mid-Infrared Spectroscopy

Published

February 10, 2021

Author(s)

Edwin J. Heilweil, Amber Meyers, Christopher J. Stromberg

Abstract

Two anionic asymmetric Fe-Fe Hydrogenase model compounds containing a single CN and five CO ligands: [Fe2(μ-S2C3H6)(CO)5(CN)1]1− (1) and [Fe2(μ-S2C2H4)(CO)5(CN)1]1− (2) dissolved in room temperature acetonitrile are examined. The molecular asymmetry affects the redox potentials of the central iron atoms thus changing the catalytic properties of the compounds. Femtosecond ultraviolet excitation with mid-infrared probe spectroscopy was employed to better understand the ultrafast dynamics of the enzyme active site. Continuous ultraviolet lamp excitation with Fourier Transform infrared (FTIR) spectroscopy was also used to explore stable product formation on the second timescale. For both model compounds, two timescales are observed; a 20-30 ps decay and formation of a long-lived photoproduct. The picosecond decay is assigned to vibrational cooling and rotational dynamics while the residual spectra remains for up to 300 ps suggesting formation of new photoproducts. Static FTIR spectroscopy yielded a different stable photoproduct than observed on the ultrafast timescale. Density functional theory (DFT) calculations simulated photoproducts for CO-loss and CN-loss isomers and the resulting photoproduct spectra suggest the picosecond transients arise from a complex mixture of isomerization after CO-loss while dimerization and formation of a CN-containing Fe-CO-Fe bridged species are also considered.

Citation

The Journal of Physical Chemistry A

Volume

125

Issue

7

Pub Type

Journals

Download Paper

https://dx.doi.org/10.1021/acs.jpca.0c08921

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Keywords

Fe-Fe Hydrogenase models, ultrafast infrared, time-resolved infrared spectroscopy, static FTIR spectroscopy, Density Functional Theory

Citation

Heilweil, E. , Meyers, A. and Stromberg, C. (2021), Photodynamics of Asymmetric Di-Iron-Cyano Hydrogenases Examined by Time-Resolved Mid-Infrared Spectroscopy, The Journal of Physical Chemistry A, [online], https://dx.doi.org/10.1021/acs.jpca.0c08921 (Accessed October 9, 2025)