C.9.3

= = =Outline the importance of d-block elements copper ions in electron transport and iron ions in oxygen carriers. Use cytochromes and hemoglobin as examples.=

Electron Transport to Produce Energy from Food
To produce energy from food, the body oxidizes the food (e.g. glucose) using oxygen as the reducing agent (it is itself reduced) which results in the transfer / transport of electrons. The half equation for the reduction of oxygen is:

The reduction of oxygen take place in organelles called mitochondria inside the cells using an enzyme called **cytochrome oxidase**. Water is produced. A cytochrome is a molecule consisting of a copper or iron ion (**Fe2+ or Cu+**) surrounded by a porphyrin ligand. There are four nitrogen atoms on the porphyrin molecule that donate a pair of electrons to each of the four sites of the metal ion to form a **coordinate bond**. Since oxygen is reduced, the metal ion is oxidized.

HL students Remember form topic 13.2 a **ligand** is defined as a neutral molecule or negative ion which has a pair of //non-bonding / lone electron pairs// that it donates to form a coordinate covalent bond with a transition metal ion.

Figure 1. Figure 2: Cytochrome with an Fe2+ ion



Figure 3: Cytochrome with a Cu+ ion

Iron Ions as Oxygen Carriers
Iron ions are important in the process of carrying oxygen around the body. Like cytochrome oxidase it consists iron ion **Fe2+** at the center which binds to the oxygen molecule and is surrounded by a porphyrin ligand. There are four nitrogen atoms on the porphyrin molecule that donate a pair of electrons to each of the four sites of the metal ion to form a coordinate bond. When O binds to the iron ion, the hemoglobin molecule is oxygenated and appears bright red, giving blood its bright red color. Without the iron center, oxygen wouldn't bind to hemoglobin, and oxygen couldn't be carried through the blood stream and to the cells in the body.
 * Hemoglobin** in the molecule in the blood that carries the oxygen.

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