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

Abstract

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 CβH2 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