Question

Siderophores are small polydentate ligands and have a high affinity for:

• A. Fe
• B. Fe (II)
• C. Fe (III)
• D. Free Fe

Hint:

Remember the biological context of iron: in an oxygen-rich environment, iron is stable as insoluble Fe(III). Life needs a way to capture this form. Siderophores are the microbial solution, acting as high-affinity chelators specifically for Fe(III).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Siderophores are low-molecular-weight organic molecules produced by microorganisms (like bacteria and fungi) and plants to chelate, solubilize, and transport iron. This question asks about the specific form of iron for which they have a high affinity.
Step 2: Detailed Explanation:
Under aerobic conditions at neutral pH, iron predominantly exists in the ferric state, Fe(III) or Fe\(^{3+}\). In this state, it is highly insoluble, typically forming ferric hydroxide precipitates [Fe(OH)\(_3\)], making it biologically unavailable. Siderophores have evolved to overcome this problem. They are polydentate ligands (often containing catecholate or hydroxamate functional groups) that bind extremely tightly to Fe(III) ions. This chelation process forms a soluble Fe(III)-siderophore complex that can then be transported into the cell via specific membrane receptors. While they can also bind other metal ions, their affinity for Fe(III) is exceptionally high. Fe(II) is the ferrous state, which is more soluble but less common in aerobic environments.
Step 3: Final Answer:
Siderophores have an exceptionally high affinity for the ferric iron ion, Fe (III).