Question

Which of the following is an example of an inclusion complex?

• A. Cyclodextrin–drug complex
• B. Iodine–potassium iodide
• C. EDTA–calcium
• D. Caffeine–benzoic acid

Hint:

An inclusion complex (also called a host–guest complex) forms when one molecule, the host, has a cavity in its structure that physically traps another molecule, the guest, inside it.

Answer 1

The Correct Option is A

Step 1: What is a complex?
Drug complexes form when a drug molecule associates with another molecule through non-covalent interactions. The type of association defines the complex class.

Step 2: Define inclusion complexes.
An inclusion complex forms when one molecule (guest) is physically enclosed inside the cavity of another molecule (host) without forming a true chemical bond.

Step 3: Cyclodextrins as hosts.
Cyclodextrins are cyclic oligosaccharides with a hydrophobic internal cavity. They trap hydrophobic drug molecules inside this cavity. This is the textbook example of an inclusion complex.

Step 4: Analyse the distractors.
Iodine-KI forms a charge-transfer complex, not an inclusion complex. EDTA-calcium is a chelate (coordination complex). Caffeine-benzoic acid is a molecular complex via stacking interactions.

Step 5: Confirm.
Only cyclodextrin-drug fits the inclusion complex definition because the drug sits inside the cyclodextrin cavity.


Answer: Option (1) — Cyclodextrin–drug complex