EPR, UV−Vis, IR, and X-ray Demonstration of the Anionic Dimeric Dinitrosyl Iron Complex [(NO)₂Fe(μ-S^tBu)₂Fe(NO)₂]^-: Relevance to the Products of Nitrosylation of Cytosolic and Mitochondrial Aconitases, and High-Potential Iron Proteins

Abstract

Complexes [(NO)2Fe(S-tBu)2]- (3-Na) and [Fe2(μ-StBu)2(NO)4] (1) are in dynamic equilibrium in the protic solvent MeOH. The subsequent addition of the equivalent of cobaltocene into the MeOH solution mixture of complexes 3-Na and 1 led to the formation of the fully delocalized mixed-valence [Fe(μ-S-tBu)(NO)2]2- (2) characterized by IR, UV−vis, EPR, SQUID, and single-crystal X-ray diffraction. The EPR spectrum of complex 2 displaying an axial signal at g⊥ = 2.009, g∥ = 1.965 (77 K) and an isotropic signal at g = 1.998 (298 K), identical to the EPR spectra of reduction of dinitrosyl iron complex (DNIC)/aconitase obtained from nitrosylation of aconitase and reduction of HiPIP-containing protein-bound DNIC, suggests that the [4Fe−4S]2+ clusters of aconitase/HiPIP were nitrosylated to produce a mixture of the monomeric and dimeric DNICs.