Evidence for intramolecular NH---S hydrogen bonds from deuterium-NMR spectroscopy of reduced-rubredoxin model iron(II) complexes with bidentate peptide ligands

The 1 H-NMR signals of Cys C β H 2 of reduced rubredoxin models, (NEt 4 ) 2 [Fe(Z-cys-Pro-Val-cys-OMe) 2 ] , (NEt 4 ) 2 [Fe(Z-cys-Pro-Leu-cys-OMe) 2 ] , and (NEt 4 ) 2 [Fe(-cys-Pro-Leu-cys-Gly-Val-OMe) 2 ] , were isotropically shifted to lower field and widely separated in the range 150-250 ppm in acetonitrile-d 3