Advanced Chemistry: PART
uv and visible light absorption spectroscopy - hemoglobin
Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB
KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry
of analysis and molecular structure determination
SPECTROSCOPY INDEXES *
All Advanced Organic
Chemistry Notes *
The origin of colour, the wavelengths of
visible light, our perception!
theory, spectrometer, examples of absorption & reflectance spectra
spectra - index of examples: uses, applications, more on the
chemistry of colour
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mobile phone/ipad etc. in 'landscape' mode *
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The oxygen carrier haemoglobin (hemoglobin, Hb), when oxygenated
forms oxyhaemoglobin (oxyhemoglobin, HbO2),
Hb + O2
However, there are four heme groups to which an
oxygen molecule can be attached (see diagram below), so at any given
time the oxygenated hemoglobin molecule may be carrying between one
and four O2 molecules.
This explains why iron is an essential mineral nutrient in
Oxyhemoglobin gives strong absorption in
many regions of the visible light spectrum except in the visible red region, so it
appears as red molecule - it is effectively a transition metal complex of
iron(II), though ligand system is a bit more complicated than usual.
Iron must be in the iron(II) state as square planar
bonding arrangement in the complex involving the Fe2+ ion.
Hb-FeII + O2
Deoxyhaemoglobin (deoxyhemoglobin) is a slightly pale
crimson colour with a greater absorbance in the red visible light region,
BUT NOT blue as indicated for convenience in many biology textbooks and my
website biology pages too!
The crucial part of the haemoglobin molecule and where it fits into the
In haemoglobin, the two hydrogen atoms of a porphyrin ring
(shown in the left) are replaced by the Fe2+ ion.
The porphyrin ring as 26 pi electrons and
forms a large conjugated system with the Fe2+
ion, a complex in which the energies
required for electron excitation include the energies of
visible light photons e.g. in the blue to yellow regions.
The co-ordination number of the iron complex is 6 with an
octahedral arrangement of 6 covalent bonds.
There are four covalent bonds from the four nitrogen
atoms of the porphyrin ring in a square planar arrangement.
Below the plane, a protein molecule is coordinated with
the Fe2+ ion and below the plane either a water molecule or
an oxygen molecule is coordinated to the Fe2+ ion to complete
the octahedral arrangement.
The haemoglobin molecule is effectively acting as a
polydentate ligand in forming the iron(II) complex.
See transition metals Appendix 2.
for an Introduction to complexes
The porphyrin ring - iron(II) association amounts a typical
transition metal complex and the oxygen molecule is effectively a fifth
Apart from the four heme groups capable of carrying an oxygen
rest of the molecular structure, for each heme group, includes polypeptide
sequences of 141 alpha amino acids and 146 beta amino acids. Its a big
The whole molecule is an association of two alpha and two
beta subunits, shown in red and blue on the above diagram.
The four heme groups are shown in green on the same diagram
The haemoglobin molecule image was adapted from
Hemoglobin and medical conditions
(i) Unfortunately, the iron(II) ion can bind with other
molecules including deadly carbon monoxide.
carbon monoxide's several mechanisms of toxicity is binding with
circulating hemoglobin to form carboxyhemoglobin, resulting in a
Hb-FeII + CO
Unfortunately, carbon monoxide binds to haemoglobin
240 x more strongly than oxygen, so the more CO you breathe in,
the less oxygen you have for respiration, hence its toxic nature.
So it can actually displace oxygen from
Hb-FeII -O2 + CO
Hb-FeII-CO + O2
Carbon monoxide poisoning can be reversed by
treating the patient with oxygen to move the equilibrium to the left
- the concentration rule of Le Chatelier's equilibrium principles.
(ii) Sickle cell anaemia
Hemoglobin (HbS) has existed in humans for thousands
HbS arise from a mutation in the gene controlling
the building of the beta-globin chain in the haemoglobin molecule.
It causes the formation of insoluble polymers that
severe damage to the red blood cell membrane causing a considerable
deficiency in transportation of oxygen around the body.
Damage to the red blood cell membrane gives rise to
reduced cell survival and chronic hemolytic anemia (haemolytic
Key words & phrases: interpreting the uv-visible absorption spectra of
identifying the maximum absorption peaks in the uv-visible absorption spectra of
hemoglobin haemoglobin, explaining the uv-visible absorption spectra of
hemoglobin haemoglobin, how to use the visible
absorption spectra of hemoglobin haemoglobin to explain the different colours of
hemoglobin haemoglobin, applications of the uv-visible absorption spectra of
hemoglobin haemoglobin aspects of the molecular of haemoglobin hemoglobin
oxyhaemoglobin oxyhemoglobin deoxyhemoglobin deoxyhaemoglobin spectra
UV and visible spectroscopy index
All Advanced Organic
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