Synthesis of a new 4Fe4S cluster with a biomimetic bulky thiolate ligand as model for the [Fe 4S 4] [formula omitted] states of high potential iron-sulfur proteins

Abstract

The new clusters (X) 2[Fe 4S 4(SCH 2tib 4] (XEt 4N, Ph 4P) have been synthesized with a sterically encumbered and benzyl-type thiolate ligand, in order to study its influence on the formation and stability of the oxidized state [Fe 4S 4] 3+. Both clusters exhibit a stable redox couple in CH 2Cl 2, and the oxidized (Ph 4P) [Fe 4S 4(SCH 2tib) 4] can be generated in solution by chemical oxidation. EPR and 1H NMR studies show that this species is unstable in solution at room temperature and that it decomposes, possibly by way of a transient [3Fe4S] + state. The isotropic shift, longitudinal relaxation time and temperature dependence of the SCH 2 protons' resonance have been analyzed both in the [4Fe4S] 2+ and [4Fe4S] 3+ states, and compared to results available on the same oxidation state centers in [4Fe4S] proteins.