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Theoretical Insights into the Unique Ligation of [Fe 4 S 4 ] Iron–Sulfur Clusters
Author(s) -
Kubas Adam,
Maszota Paweł
Publication year - 2018
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201800165
Subject(s) - chemistry , protonation , deprotonation , ligand (biochemistry) , molecule , cubane , crystallography , cluster (spacecraft) , stereochemistry , ion , computational chemistry , photochemistry , organic chemistry , biochemistry , receptor , computer science , programming language
[Fe 4 S 4 ] iron–sulfur clusters are typically anchored to the protein scaffold via four cysteine residues, but in a number of proteins one of the Cys is replaced with another ligand. The biological role of such a replacement is unknown although essential to maintain catalytic activity. Here, we explore the geometries and electronic structures of 3:1 site differentiated model compounds [Fe 4 S 4 ][S(CH 3 )] 3 (L) using quantum chemical methods. The unique ligands L were chosen to represent biologically relevant molecules: methanethiol (represents cysteine), acetic acid (asparagine), 4‐methylimidazole (histidine), and water/hydroxyl anion. Each ligand was considered as deprotonated anion or protonated neutral molecule. We found the replacements do not influence structure of the cluster significantly. On the contrary, the impact on the reduction potentials is visible and may reach up to 0.2 V depending on the charge of the ligand. We also studied previously unconsidered asymmetry in excess charge distribution in a reduced [Fe 4 S 4 ] + cubane caused by a unique ligation. Our findings show that protonation/deprotonation reactions may provide gating mechanisms in the electron flow carried by iron–sulfur clusters. Additionally, we calculated X‐ray absorption (XAS) and emission (XES) spectra of all compounds under investigation. Particularly, theoretical XES show clear features characteristic to each unique ligand. However, their intensity may be too small to be observed experimentally.