What oxidation state is iron in hemoglobin?

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What oxidation state is iron in hemoglobin?

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Answer 1 · 2016-06-27T19:14:16

$Iron (II)$ $"Iron"("II")$ . It must be, in order for the iron in heme to get oxidized upon binding with $O_{2}$ $"O"_2$ .

Heme in hemoglobin starts out like this:

A histidine can bind at the fifth coordination site, while $O_{2}$ $"O"_2$ can bind to the sixth coordination site.

When $O_{2}$ $"O"_2$ binds to iron in this case, it temporarily and reversibly binds as the $O_{2}^{-}$ $"O"_2^(-)$ superoxide, so the reduction half-reaction is

$O_{2} + e^{-} \to O_{2}^{-},$ $"O"_2 + e^(-) -> "O"_2^(-),$

and the oxidation half-reaction is

${Fe}^{2 +} \to {Fe}^{3 +} + e^{-},$ $"Fe"^(2+) -> "Fe"^(3+) + e^(-),$

giving the overall reaction as:

$"O"_2 + cancel(e^(-)) -> "O"_2^(-)$
$"Fe"^(2+) -> "Fe"^(3+) + cancel(e^(-))$
$"-----------------------------------------"$
$color(blue)("O"_2 + "Fe"^(2+) -> "Fe"^(3+) + "O"_2^(-))$

On the other hand, $"Iron"("III")$ , in methemoglobin, cannot bind oxygen unless the iron center is reduced back to $"Iron"("II")$ .

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What oxidation state is iron in hemoglobin?

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