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) 2 Fe(S- t Bu) 2 ] - ( 3-Na ) and [Fe 2 (μ-S t Bu) 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- t Bu)(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.