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Hemerythrin is a respiratory protein found in nature among a
few marine phyla, arthropods, molluscs, vertebrates and invertebrates. This protein
functions as a reversible oxygen carrier. Hemerythrin is found in an octameric
form displayed in the left frame.
2 ligand to form a hydroperoxy ligand (HOO-). The HOO group then forms a hydrogen bond with the newly-formed bridging oxo (μ-O) group. (This hydrogen atom is not located in the X-ray structure. Do you know why?) These changes are reversed when O2 is released.
In order to better understand the conversion of deoxy- to
oxy- hemerythrin (the binding of dioxygen and its conversion to a hydroperoxy
group via proton transfer), several simple model systems have been prepared
The synthesis of a complex that contains an Fe-(μ-OH)-Fe
moiety in which one iron is five-coordinate while the other is six-coordinate
presents a challenge that has not yet been met.
The complex has two iron(II) ions bridged by a hydroxyl group (the hydrogen atom
is not located in the X-ray study). A dicarboxylic acid acts as a tetradentate
ligand. (If you would like to see the structure of this diacid click
usually abbreviated as OTf-). The second iron atom remains
pentacoordinate. This complex reacts with dioxygen in the presence of N-methyl
imidazole at –78 degrees to give an oxo-bridged diiron complex with a
hydroperoxy ligand on one iron and an N-methyl imidazole on the other. The structure of the
reaction product is supported by spectroscopic measurements but no crystal
structure is available yet.
In this case both of the irons are six-coordinate hence are not able to react
with dioxygen. However, it contains a rather interesting ligand:
usually abbreviated Tp) .
This ligand is often used in bioinorganic model complexes. Its structure is shown
If you would like to learn more about the hemerythrin model
compounds and their chemistry see:
and references therein.