Re: Help: What material has ESR signal?
From: Jim (jmgong74_at_tom.com)
Date: 10/08/04
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Date: 8 Oct 2004 16:54:12 -0700
sbharris@ix.netcom.com (Steve Harris sbharris@ROMAN9.netcom.com) wrote in message news:<79cf0a8.0410071654.9a63639@posting.google.com>...
> Indeed, hemoglobin does not undergo oxidation with O2 binding (though
> free heme does!). The Fe(II) in hemoglobin has only 6 d electrons, no
> s electrons. In any octahedral field (like that in heme) these 6 can
> all go paired into the 3 lower d orbitals (so-called t2g orbitals),
> with none above in the two eg orbitals (so called low spin).
> Oxygenated hemoglobin is this type of low-spin ferrous complex, and
> thus should have no EPR/ESR signal.
>
> The problem is that deoxyhemoglobin contains Fe(II) which has the same
> 6 d electrons, is known to be in a *high spin* state, with at least 2
> and possibly 4 unpaired electrons (i.e., either one or two electrons
> get promoted from the 3 t2g ground state d orbitals to the 2 eg
> orbitals, I don't know which-- probably the latter.) The switch in
> spin-state with O2 binding by hemoglobin is one of the classical
> differences between deoxy and oxyhemoglobin, and no doubt has been
> studied by EPR/ESR. The deoxy version thus should indeed have an EPR
> signal, albeit possibly a weak one. I think the abstract you quote is
> simply wrong. EPR spectroscopy of deoxyhemoglobin I'm sure has been
> done.
>
> In any case, I don't know why the abstract (possibly erronously)
> reports such an unexpected result for deoxyhemoglobin, either. But
> I'll admit it.
>
> SBH
you and uncle Al freed my doubt axactly.
My background is electronics and physics. I just used Hund's rule--for
degenerate orbitals, the lowest energy is attained when the number of
electrons with the same spin is maximized-- to calculte the unpaired
electron. I came to know that it is too simple.
According to your description, sometimes it is almost impossible to
predict whether there is unpair electron or not. however, if any
organic compound trends to lose electron, usually there is unpaired
electron inside and thus can produce ESR signal. Otherwise, there will
be no or little ESR signal. Is it right?
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