Diiron complexes structures

Fatty acyl-CoA desaturases are terminal oxidases of a membrane-bound enzyme complex that also includes cytochrome b5 and cytochrome b5 reductase (Bloomfield and Bloch, 1960). They remove substrate hydrogen atoms at a position determined by the specificity of the enzyme. They play essential roles in regulating membrane fluidity and are also involved in insect lipid and pheromone metabolism. They share the presence of three highly conserved histidine-rich sequences (H-boxes) that coordinate the diiron-oxo structure at the active sites (Shanklin and Cahoon, 1998) and four hydrophobic a helices that appear to anchor the protein into the lipid bilayer and situate the H-boxes in their correct position in the active site. 

The molecular structures of some B-type silylene- and silylyne-bridged diiron complexes are shown in Fig. 1. All of (a), (b), and (c) have a bridging... 

An unusual diiron complex (49) resulted from the reaction of compound (16) with (CO)3Fe(CgH14)2 (Equation (4)). The structure of this complex (49) was unambiguously established as a result of... 

The longest known MMOs are soluble proteins contcdning a binuclecir iron active site. The MMO from Methylococcus capsulatus (Bath) consists of three proteins, a hydroxylcise (protein A), a reductaise (protein C), and a regulatory protein, (protein B). The C component uses NADH cis primary reductant that provides electrons necessary to reduce O2, the B component allows C to feed these electrons to A, and the A component intercicts with O2 and carries out the substrate oxidation step. The X-ray structure of the diiron complex from Methylococcus capsulatus (Bath) in am Fe2(III,III)... 

Mononuclear iron(II) complexes supported by aminopyridine ligands (TPA and its derivatives) self-assemble into bis-hydroxo-bridged diamond core-like structures under basic conditions. The donor atom sets in these diiron complexes are similar to the coordination environment created by dinucleating ligands such as HPTB. The differences in observed oxygenation rates, detailed below, can be attributed to significant steric hindrance about coordinatively saturated iron centers.73... 

Figure 5. Representative crystal structures of synthetic diiron complexes, (a) [Fe20(0Ac)2(HBpz3)2], (f.) [Fe30 02P(0Ph) 2(Me3TACN)3], (c) [Fe20(0Bz)(TPA)2l(C104) (d) (Me4N)[Fe2(5-Me-HXTA(OAc)2]. Reprinted with permission from Refs. 59, 62, 77, 81, American Chemical Society.

Structural and Magnetic Properties of Oxo-Bridged Diiron Complexes... 

Fig. 11 Structures of selected diiron complexes capable of proton reduction to generate hydrogen.

Biomimetic studies are currently focused on generating diiron complexes that can serve as structural and/or electronic models for oxidation states higher than Fe " that are proposed to partake in the catalytic cycles of diiron proteins such as methane monooxygenase and ribonucleotide reductase. Mossbauer spectroscopy has played a leading role in the eharacterization... 

Dioxygen diiron complexes have been synthesized by mimicking the probable intermediate structures in methane monooxygenase oxygenations. Examples are summarized in the recent review. One is the Fc2(i7-0)2 diamond core type and the other is the Fe2(tJ-02) peroxo type. Recently, an unusual Fe"-X-Fe (tl -02) species has been suggested in the reaction of O2 with carboxylate-bridged diiron(II,II) paddlewheel complexes, but its role in the oxygenation has not been clarified. ... 

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