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I moved the following sentence from the main article here:

In fact, both blood and the planet Mars get their reddish hue from oxidized iron (rust).

I am not sure this is correct. First of all, hemoglobin is red whether it contains oxygen or not. Second, if it contains oxygen, then it contains molecular oxygen (O2) and not oxydized iron. Could somebody with a firmer grasp on these things please confirm? --AxelBoldt


Yeah I think this is correct. Oxygen is bound to the Haem groups in haemoglobin chains to form oxyhaemoglobin (HbO8:

Hb + 4O2 -> HbO8

Although 'oxidized' may not be so chemically correct (I don't know about loss of electrons) they are loosely bound and not in the 02 form.


Do you think the original statement, claiming that blood is red because of oxidized iron, is correct, or that my statement above is correct? --AxelBoldt


original statemen -- sodium


Well, I don't understand your argument. What are you claiming actually causes the red colour of haemoglobin? As far as I know, haematite is red because of the Fe3+ ions. Haemoglobin (both oxy- and deoxy-) has Fe2+ ions - the iron is not oxidized by the binding of oxygen. Fe2+ ions cause a yellow-green colour, I think, so they can't be what makes haemoglobin red. Unless I've got something wrong here, the original statement is at best very misleading. --Zundark, 2001 Oct 8

The color of an ion depends on its environment. In aqueous solution ferric irons (Fe3+) are coordinated with six water molecules and have a yellow color rather than the reddish color of hematite, where they are coordinated with six oxide ions, while the anhydrous chloride is greenish. Fe2+ are green in aqueous solution but that doesn't say much, the presence of nitrogen and oxygen (only oxyhemoglobin is bright red) are going to affect the color significantly. The iron is definitely what is responsible, though, and most brightly colored compounds are made so by coordinated transition metals. Someday we should have an article on ligand field theory.


How about the following statement:

"Both the red color of Mars and the red color of blood are caused by an interaction of oxygen and iron."

That avoids the term "oxidization" which is not involved in hemoglobin if I understand it correctly. --AxelBoldt