Density functional theory calculations on Fe2S2 clusters: Effect of ligand environment on geometric/electronic structure and reduction potential

The Fe2S2 clusters in nature are generally coordinated to the peptide backbone using thiolate ligands (from cysteines). A known variation of these are the imidazole (from histidine) coordinated active sites of Riesky proteins. Recently, a few newer modifications have been observed, e.g., the arginine coordinated cluster in biotin synthases. Very recently, a cysteine persulfide coordinated cluster has been observed in the hydrogenase maturase enzyme, HydE. Herein, density functional theory calculations are used to investigate the effect of the unusual arginine and cysteine persulfide coordinations on the geometric and electronic properties of these clusters. Further, the effect of these ligands in tuning the thermodynamic reduction potentials of these clusters has also been investigated.