Edexcel A Level Chemistry:复习笔记6.2.8 Haemoglobin



  • Haemoglobin is one of nature's complexes using a transition metal ion
  • The haem molecule is a complex with iron(II) at its centre
  • The haemoglobin complex contains a multidentate ligand made up of four haem groups
    • These consist of mostly carbon and hydrogen atoms
    • Each haem group has a nitrogen atom forming a dative covalent bond to the Fe2+ ion in a square planar complex
  • There is a fifth dative bond from the protein (globin) to the Fe2+ ion
  • Oxygen atoms form a dative covalent bond with the iron(II) which enables oxygen molecules to be transported around the body in the blood


The haem molecule with iron(II) at its centre

  • Oxygen molecules are not very good ligands and bond weakly to the iron(II)
  • The weak bonds allows them to break off easily and be transported into cells



Exam Tip

You do not need to be familiar with the structure of the haem group

Ligand Exchange in Haemoglobin

  • Carbon monoxide is toxic because it is a better ligand than oxygen and binds strongly and irreversibly to the iron(II) preventing oxygen from being carried to the cells
  • If oxygen attached to the haemoglobin (oxyhaemoglobin) is replaced by carbon monoxide (carboxyhaemoglobin), a darker red colour is produced in the haem complex
    • A sign of carbon monoxide poisoning
  • The condition anaemia occurs when a person does not have enough haemoglobin in their blood due to a loss of blood or deficiency in iron
    • Deficiency in iron can be restored by taking iron sulfate tables in the diet