Iron complexes synthetic model

All but two of the known synthetic iron(IV)-oxo compounds are low-spin, 5=1 [202, 240]. The first example of an iron(IV)-oxo model compound with spin 5 = 2 was the quasioctahedral complex [(H20)5Fe =0] (5 = 0.38 mm s, A q = 0.33 mm s ) which was obtained by treating [Fe°(H20)6] with ozone in acidic aqueous solution [204]. The spin state of iron in this type of structure is determined by the energy gap between the d,2 y2 and the d y orbitals [241]. The weak water ligands induce a sufficiently small gap being less than the spin paring energy and stabilizing the HS state (Fig. 8.25, case a). 

More important than the demonstration (107) of nitrosylation of synthetic model clusters is the demonstration (108) of nitrosylation by nitrite of the [4Fe-4S] center in vegetative cells of Clostridium botulinum. Treatment of a reduced culture of C. botulinum with nitrite in the presence of ascorbate resulted in loss of the ESR signal at g = 1.94, characteristic of the reduced iron-sulfur protein, and its replacement by a signal at g — 2.035, characteristic of [Fe(NO)2X2] complexes, most likely of the [Fe(NO)2(SR)2] type. 

A wide variety of synthetic binuclear iron complexes (39) bridged by sulfide, disulfide and/or thiolate groups are known. They have proven to be good models for the two-iron ferredoxin proteins, as demonstrated by comparisons of structure and properties. Early attempts to isolate two-iron complexes by direct reaction of a monothiol with FeCl3, NaSH and NaOMe afforded only four-iron products suggesting that a particularly high stability is associated with the tetrameric... 

In vivo, the source of protons and electrons necessary to generate the active, formally oxoiron(V) oxidant from the iron(II) dioxygen complex is provided by the cofactor NADPH. Synthetic models have long been studied by chemists in... 

Synthetic iron complexes have provided models for two stages of ferritin iron storage and biomineralization (1) the early stages, when small num-... 

In many cases, synthetic iron porphyrins have been investigated primarily as models of hemes in various proteins, but also as potentially useful magnetic materials, or as metal coordination complexes, since the porphyrin Macrocycle often confers upon the metal unique electronic, magnetic, and redox properties see Redox Properties Processed and chemical reactivities that are interesting in their own right. The properties and chemical reactivities of iron porphyrins will be summarized in this article. Iron complexes of related macrocycles, including reduced hemes (chlorins, isobacteriochlorins, etc.)... 

Roussin s red salt, K2[Fe2S2(NO)4] is a historically important complex of a great interest for biochemists, being the first synthetic model of iron-sulfur cluster, analogical to those present widely in proteins (vide infra). Moreover, it is already a nitrosylated form of such a cluster, and the cluster nitrosylation just recently has been widely studied, since this process is associated with the regulatory action of many non-heme iron-sulfur enzymes. 

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