Stabilization of hydrolytically labile iron(II)–cysteine peptide thiolate complexes in aqueous triton X-100 micelle solution: Spectroscopic properties mimicking of reduced rubredoxin

The absorption, CD, and ¹H- and ¹⁹F-nmr spectroscopic features of Fe(II) complexes with a series of cysteine-containing oligopeptides were investigated in aqueous (H₂O or D₂O) 10% Triton X-100 micelle solution. The complexes with distal aromatic rings, Fe(Z-cys-Pro-Leu-cys-Gly-X)₂]²⁻ (Z = benzyloxycarbonyl; X = NH-C₆H₄-p-F, NH-CH₂-CH₂-C₆H₄-p-F, and Phe-OMe), were found to be quite stable in such aqueous micelle solution. The coordination of cysteine–peptide ligands to the Fe(II) ion is revealed by isotropically shifted ¹H-nmr signals due to the Cys C_βH₂ protons occurring at 120 ∼ 250 ppm in a D₂O Triton X-100 micelle solution (10%) at 60°C that are very similar to those reported for native reduced rubredoxin. The high stability of these cysteine peptide–Fe(II) complexes in aqueous micellar system was explained by the combined contributions from NH—S hydrogen bonds and the effect of the proximity of aromatic groups. The existence of such NH—S hydrogen bonds and interactions between aromatic ring and sulfur atom was confirmed by ¹⁹F-nmr spectral and ¹⁹F spin–lattice relaxation times (T₁) measurements. © 1998 John Wiley & Sons, Inc. Biopoly 46: 1–10, 1998