John said:
I read in sci.electronics.design that DarkMatter <DarkMatter@thebaratthe
endoftheuniverse.org> wrote (in <scek40d33f7b9cuq49mpmouejm9cic1ppn@4ax.
com>) about 'Safety warning?!!!
', on Sat, 6 Mar 2004:
In the middle of each haemoglobin molecule. I can't remember the
oxidation state (2?), but I doubt that it has an unpaired electron, so
presumably no magnetic moment.
Christ... nobody is keeping it a secret.
Hemoglobin is an AABB protein tetramer, MW=65,000. Each of the four
heme prosthetic groups chelates one high spin Fe(II).
http://www.crystal.uwa.edu.au/~ddb/bio3hhb.pdb
High spin is defined as having unpaired electrons in both the eg and
t2g orbitals, while low spin is unpaired electrons in only the t2g
orbitals. In deoxy-globins the iron atom is five-coordinate, high
spin, and sited below the plane of the porphyrin ring towards an axial
imidazole ligand. Upon oxygenation, the iron in Hb moves towards the
porphyrin plane (from 0.60 A to 0.13 A from the plane) and pulls this
histidine, thus commencing the cooperativity shown by Hb in binding
dioxygen. In Mb this change is not so pronounced (from 0.42 A to 0.18
A). It is still high spin.
Fe(0) has 2 s-electrons and 6 d-electrons. Fe(II) then has 6
d-electrons. If we model an octahedral ligand field,
eg _ _
t2g _ _ _
then four unpaired electrons. Each Fe(2+) is paramagnetic. Now, how
do things vary with tetramer spin coupling overall and with
oxygenation? Oxygenated hemoglobin is diamagnetic. Deoxygenated
hemoglobin is very weakly paramagnetic by measurement,
http://www.fmrib.ox.ac.uk/~peterj/lectures/fMRI_Exp_V/sld004.htm
faraday.ufbi.ufl.edu/~thmareci/bch6741/lecture10.pdf
middle
/_\chi=0.08 ppm.
The red color is from ligand to metal charge transfer. No high
gradient supercon magnet is about to pull the red goo from your veins.
OTOH, intense high divergence magnetic fields have a distinct affect
upon mental function. There is a old (magnet poorly shielded)
multi-nuclear 360 MHz NMR in the basement of the UVic chemistry
building. One must bloody crawl under the supercon magnet with one's
head pushing against the bottom of the armored dewar to get at the
probe switchbox for changing nuclei. That is the field divergence
sweet spot. Everybody who goes underneath comes up giggling - even
the flesh-eating NMR lady. Uncle Al was careful never to be checked
out on that machine.