1. Chapter 5
Bioinorganic Chemistry

2. Complexes of iron(II)
Complexes:
• in solution: [Fe(H2O)6]2+ (octahedral, pale green)
• easy oxidation to iron(III) (in basic solution)
• redoxpotential of Fe(III)/Fe(II) is changed by formation of
complexes
Fe3+/Fe2+: CN– +0,36 V
H2O +0,77 V
Phen +1,12 V

3. Complexes:
• intermediate (hard/soft) acid: binding to O-, N- and S-donoratoms
• most important ligands: aromatic nitrogen donors in
chelatable position
• bipiridine, fenantroline, porphyrins
• usually octahedral complexes (some tetrahedral complexes)

4. Complexes of iron(III)
• in solution: [Fe(H2O)6]3+ (pale violet)
• stable complexes in acid and basic pH range
• characteristic reaction: hydrolysis
pH > 1:
[Fe(H2O)6]3+ + H2O [Fe(H2O)5(OH)]2+ + H3O+
Ks = 1,8⋅10–3
• Dimerization → structure with oxo bridges (yellow)
[(H2O)5Fe–O–Fe(H2O)5]4+
Complexes

5. Complexes:
pH > 2: polynuclear structures, mixed hydroxo complexes →
Fe(OH)3 precipitation
• usually octahedral complexes
• hard acid:
• binding to F– and O-donors containing ligands
• [Fe(SCN)4]– + 6 F– [FeF6]3– + 4 SCN–
intensive red colorless

6. Biological role of iron
• Human body: cca. 4 g iron (~3 g in hemoglobin)
• uptaking of iron: 1 mg/day
Iron proteins
Hem proteins Non-hem proteins
~ 70 % ~ 30 %
iron-sulphur proteins
and others

7. Biological role of iron
Iron proteins
Hem proteins Non-hem proteins
hemerythrin
oxygen transport, storage
Hemoglobin
myoglobin
electron transfer
Cytochromes iron-sulphur proteins
oxidases, oxygenases
cytochrome c oxidase
iron transport transferrin
iron storage ferritin

8. Myoglobin (oxygen storage)
Globin: contains153 amino acids
Hem: Fe-porphyrin
Hem is bound to globin
protein via iron ion
(without covalent bound)
5. coordination side:
imidazole N

9. Hemoglobin (oxygen transport)
It contains 4
globin units
Fe(II) + O2: iron
ion passes to
porphyrin ring

10. Hemoglobin (oxygen transport)
uptaking of oxygen: high partial pressure of oxygen
giving down of oxygen: low partial pressure of oxygen

11. Iron-sulphur proteins
Tetrahedral geometry of iron
• Iron binding to inorganic and organic sulphur donors (Cys) S
• one e–-pass
• reduced ferredoxin – e– oxidized ferredoxin
+ e–
• unusually low redox potenctial: –0,05 - –0,49 V → they
behave as a reduction agents
Iron-sulphur proteins
• rubredoxin: [1Fe]3+(RS–)4 (–0,06 V)
• ferredoxins: [2Fe-2S]2+(RS–)4 (–0,3 - –0,4 V)
[4Fe-4S]2+(RS–)4 (–0,4 V)
HIPIP: [4Fe-4S]2+(RS–)4 (0,35 V)