Problem 26 - A Complete Resource Book in Chemistry for JEE Main

Question

Haemoglobin, a complex containing iron is a const-ituent of blood. The oxidation state of iron in the complex is (a) \(+1\) (b) \(+2\) (c) \(+3\) (d) \(+4\)

Step-by-Step Solution

Answer

The oxidation state of iron in hemoglobin is +2.

Step 1: Understanding Hemoglobin

Hemoglobin is a protein complex in red blood cells that carries oxygen from the lungs to the rest of the body. The key component in hemoglobin responsible for binding oxygen is the heme group.

Step 2: Identifying Iron's Role in Hemoglobin

The heme group within hemoglobin contains iron as a central metal. This iron ion is vital for the binding of oxygen, and its oxidation state determines the binding characteristics.

Step 3: Oxidation of Iron in Hemoglobin

In the heme group, iron typically exists in the ferrous state, which is oxidation state +2, denoted as Fe(II). This state allows for the reversible binding of oxygen, which is essential for hemoglobin's function in oxygen transport.

Key Concepts

Hemoglobin Structure

Hemoglobin is a fascinating and essential protein found in red blood cells responsible for transporting oxygen throughout the body. It gains its function through a complex structure made up of four subunits. Each subunit consists of a polypeptide chain and a heme group.

• Two alpha (α) chains
• Two beta (β) chains

This quaternary structure allows hemoglobin to efficiently pick up oxygen in the lungs and release it where it's needed in the tissues.
The configuration of these chains plays a crucial role in hemoglobin's functionality, allowing it to adjust its shape and affinity for oxygen. This ability is vital for maintaining life-supporting activities in various physiological conditions.

Heme Group Function

The heme group, a small yet powerful feature of hemoglobin, is responsible for the actual binding of oxygen. It is an iron-containing compound that gives blood its distinctive red color. Each heme group can bind to one molecule of oxygen due to its iron center, which acts as the active site.

• Composed mainly of a porphyrin ring
• Contains an iron atom at its core
• Crucial for oxygen binding and release

The porphyrin ring structure stabilizes the iron atom, allowing it to alter between different states. Upon oxygen binding, the iron transitions to a higher oxidation state but temporarily returns to its normal state once the oxygen is released. This reversible binding and release of oxygen is what makes hemoglobin so efficient in oxygen transport.

Iron Oxidation States in Biology

Iron plays a pivotal role in biological systems, particularly within the heme group of hemoglobin. In this context, iron fluctuates between multiple oxidation states, which are crucial for its biological functions.
In hemoglobin, the iron typically exists in the ferrous state, denoted as Fe(II) or +2. This state allows iron to bind oxygen in a reversible manner, forming a temporary complex with the oxygen molecule.

• Fe(II): Iron in ferrous state
• Fe(III): Iron in ferric state, more oxidized

While in the ferrous state, iron's slightly positive charge enables it to form an optimal bond with oxygen, facilitating oxygen uptake and transport. The ability of iron to change oxidation states is essential, as it aids in the dynamic binding and release of oxygen, which is critical for cellular respiration in living organisms.