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Re: Iron oxidation states

On Sun, 7 May 2000, Paul Sears wrote:
> I think you will find that plants can use Fe(III) just fine.  The usual
> problem is solubility, not oxidation state.

Solubility is the principle problem, and of course solubility varies
with oxidation state.

> Plants convert NO3- to
> C-NH2 species, so I don't think a single electron transfer is likely
> to be a big deal in the Fe conversion.

Plants regularly change the oxidation state of iron, at least once they
have it internalized.  From my reading it appears that most plants must
reduce it to ferrous iron before they can import it, but once it's
imported it's oxidation state switches back and forth rather easily.

> I seem to remember Dave Huebert
> confirming that Fe(III) was no big problem, and I'm pretty sure that
> Na Fe(III)EDTA is used as a plant iron source.  Also, "pulling off
> the chelating agent" is not such a big deal either, because the iron is well
> chelated in the plant environment as well.

Well, it looks like the plants think it is a problem, otherwise there
wouldn't be any need to supply it at rates that are orders of magnitude
above the plants' actual useage.

> I would also point out that formal oxidation states are not always well
> defined in complexed metal species.  Electrons can't always be "placed"
> that unequivocally.  The models can be too simple at times.

I'll keep that in mind.

Roger Miller