Iron–sulfur cluster

[[Image:OBINIX2.png|thumb|right|Structure of [Fe₄S₄(SMe)₄]²⁻, a synthetic analogue of 4Fe–4S cofactors.]]

Iron–sulfur clusters are molecular ensembles of iron and sulfide. They are most often discussed in the context of the biological role for iron–sulfur proteins, which are pervasive. Many Fe–S clusters are known in the area of organometallic chemistry and as precursors to synthetic analogues of the biological clusters. It is supposed that the last universal common ancestor had many iron-sulfur clusters.

In biology

Iron–sulfur clusters occur in many biological systems, often as components of electron transfer proteins. The ferredoxin proteins are the most common Fe–S proteins in nature. They feature either 2Fe–2S or 4Fe–4S centers. They occur in all branches of life.

Fe–S clusters can be classified according to their Fe:S stoichiometry [2Fe–2S], [4Fe–3S], [3Fe–4S], and [4Fe–4S]. The [4Fe–4S] clusters occur in two forms: normal ferredoxins and high potential iron proteins (HiPIP). Both adopt cuboidal structures, but they utilize different oxidation states. They are found in all forms of life.

The relevant redox couple in all Fe–S proteins is Fe(II)/Fe(III).

Synthetic Fe–S clusters

[[image:Roussins black salt from crystallographic coordinates.tif|thumb|right|Structure of the hydrated ammonium salt of [Fe₄S₃(NO)₇]⁻.]]

Synthetic Fe–S clusters are laboratory-prepared coordination compounds or chains, often designed to mimic the structural, electronic, or chemical properties of biological Fe–S clusters.

Roussin's black anion, [Fe₄S₃(NO)₇]⁻, described in 1858, is the first synthetic Fe-S cluster. It has the geometry of an incomplete cubane-type cluster with C_3v symmetry. The dark color of the complex is attributed to a number of charge-transfer interactions. Since the 1970s, many of these Fe-S clusters have been described. A key property of Fe–S clusters is their ability to undergo redox.

Organometallic clusters

Organometallic Fe–S clusters include the sulfido carbonyls with the formula Fe₂S₂(CO)₆, H₂Fe₃S(CO)₉, and Fe₃S₂(CO)₉. Compounds are also known that incorporate cyclopentadienyl ligands, such as (C₅H₅)₄Fe₄S₄.

[[Image:FeS.png|thumb|center|600px|Figure. Illustrative synthetic Fe–S clusters. From left to right: Fe₃S₂(CO)₉, [Fe₃S(CO)₉]²⁻, (C₅H₅)₄Fe₄S₄, and [Fe₄S₄Cl₄]²⁻.]]

Inorganic materials

thumb|center|Structure of [[potassium dithioferrate, which features infinite chains of Fe(III) centers.]]

In maquettes and artificial proteins

It is possible to incorporate Fe–S clusters into maquettes (smaller minimal functional proteins designed from biological proteins) and artificial proteins, often abbreviated to MAPs. The first examples of Fe–S MAPs emerged in the early 1970s, as a means to mimic naturally occurring iron-containing proteins like rubredoxins. These contained [Fe(S-Cys)₄] motifs.

See also

• Bioinorganic chemistry
• Ligand (biochemistry)
• Iron-binding proteins
• Biometal (biology)
• FeMoco

References

External links