Experimental redox tuning of designed ferredoxins through sulfur to selenium substitutions

Iron–sulfur (Fe–S) clusters are essential for electron transfer in biology, and their redox potentials are finely tuned by both first-sphere ligation and the surrounding peptide environment. Here, we investigate both how minimal peptide scaffolds control cluster redox properties and how chalcogen substitution modulates these effects. Two designed peptides, corresponding to 28 residues of a bacterial ferredoxin-like sequence were assembled with both [4Fe–4S] and [4Fe–4Se] clusters, allowing a direct comparison of sulfur-to-selenium substitution within identical scaffolds. UV–visible and EPR spectroscopy were consistent with cluster incorporation and predominantly dimeric assemblies. Voltammetry measurements showed redox energetics were dependent on both chalcogen identity in a cubane cluster, and on the peptide environment. Minimal motifs capture sequence-dependent environmental effects on cluster redox chemistry and highlight the potential of chalcogen substitution combined with peptide design for bioinspired tuning of electron-transfer properties.