Active centers of ironsulfur proteins and rubredoxin are surrounded with cysteine thiolates and peptide bonds in a hydrophobic environment, where specific interactions, such as NH⋯S hydrogen bonds, exist between FeS cores and peptide bonds. The active site of rubredoxin consist of one iron and two specific sequences, Cys–X–Y–Cys, as shown in Fig. 1. Thus, Z–Cys–Thr–Val–Cys–OMe and ▪ Z–Cys–Pro–Leu–Cys–OMe were synthesized. Z–Cys–Ala–Ala–Cys–OMe was also examined as a chelating ligand for reference. A dipeptide, Z–Ala–Cys–OMe, was examined as non-chelating peptide. 1Fe and Fe 4S 4 complexes of t-Boc ▪GlyCysGly ▪ 4 NH 2 were reported by Rydon [1] and Holm [2], respectively. However, the -Gly–Gly- sequence between the two Cys residues is not preferable for turn conformation which is essential for chelation and for formation of the NH⋯S hydrogen bonds. We reported that Fe(III)/Z–Cys–Ala–Ala–Cys–OMe is a good spectral model of rubredoxin in Me 2SO [3]. The electrochemical properties of 1Fe and Fe 4S 4 complexes are important in aqueous solutions. The redox potentials of ferredoxins are influenced by the core as well as the surrounding environments. In native proteins, the core is non-polar and surrounded by polar aqueous environments. Therefore, we examined these model complexes spectrally and electrochemically in micelle by using 2–10% solutions of Triton X-100. The redox potential values obtainable by cyclic voltammogram in micelle are compared with the values of native rubredoxin or ironsulfur proteins in aqueous solution. Fe(II)/Z–Cys–Pro–Leu–Cys–OMe (1:2) complex in aqueous micelle exhibited CD extrema at 309 nm (Δϵ: −24.2) and 332 nm (Δϵ: 10.9), similar to those of reduced rubredoxin [4]. A redox couple of Fe(II)/Fe(III) was observed for Fe(II)/Z–Cy–Pro–Leu–Cys–OMe (1:2) at −0.37 V(SCE) in aqueous micelle, which is very close to −0.30 V(SCE) reported for rubredoxin. Such a positive shift was observed for the first time in synthetic model complexes of rubredoxin. No redox couple was found for Fe(II)/Z–Cys–Thr–Val–OMe (1:2) or Fe(II)/Z–Cys–Ala–Ala–Cys–OMe (1:2) in aqueous micelle, whereas Fe(II)/Z–Ala–Cys–OMe (1:4) decomposed gradually in micelle. Observation of the redox couple of [Fe(S 2- o-xyl) 2] 2− [5] at −0.64 V(SCE) in aqueous micelle reveals that the potentials of the Fe(II) complexes having two specific peptide ligands (Cys–X–Y–Cys) shift extraordinarily to the positive side. CD and visible spectra of Fe 4S 4-type complexes of Cys-containing peptides, Z–Cys–Gly–OMe, Z–Cys–Gly–Ala–OMe, and Z–Cys–Gly–Ala–Cys–OMe, in aqueous micelle were found to be very similar to native 4Fe4S proteins. These complexes provided redox couples (2 – /3 –) except for the Fe 4S 4 complex of Z–Cys–Gly–OMe.