Aspirin and penicillin

Nature of science:

Serendipity and scientific discovery—the discovery of penicillin by Sir Alexander Fleming. (1.4)

Making observations and replication of data—many drugs need to be isolated, identified and modified from natural sources. For example, salicylic acid from bark of willow tree for relief of pain and fever. (1.8)

Understandings:

Aspirin:

• Mild analgesics function by intercepting the pain stimulus at the source, often by interfering with the production of substances that cause pain, swelling or fever.
• Aspirin is prepared from salicylic acid.
• Aspirin can be used as an anticoagulant, in prevention of the recurrence of heart attacks and strokes and as a prophylactic.

Penicillin:

• Penicillins are antibiotics produced by fungi.
• A beta-lactam ring is a part of the core structure of penicillins.
• Some antibiotics work by preventing cross-linking of the bacterial cell walls.
• Modifying the side-chain results in penicillins that are more resistant to the penicillinase enzyme.

• Aspirin is used in many different ways across the globe.
• The first antibacterial changed the way that disease was treated across the globe.

Theory of knowledge:

• Different painkillers act in different ways. How do we perceive pain, and how are our perceptions influenced by the other ways of knowing?
• “Chance favours only the prepared mind.” (Louis Pasteur). Fleming’s discovery of penicillin is often described as serendipitous but the significance of his observations would have been missed by non-experts. What influence does an open-minded attitude have on our perceptions?

Utilization:

• Syllabus and cross-curricular links:
• Topic 1.3—yield of reaction
• Topic 10.2—functional groups
• Biology topic 6.3—defence against infectious disease

Applications and skills:

Aspirin

• Description of the use of salicylic acid and its derivatives as mild analgesics.
• Explanation of the synthesis of aspirin from salicylic acid, including yield, purity by recrystallization and characterization using IR and melting point.
• Discussion of the synergistic effects of aspirin with alcohol.
• Discussion of how the aspirin can be chemically modified into a salt to increase its aqueous solubility and how this facilitates its bioavailability.

Penicillin

• Discussion of the effects of chemically modifying the side-chain of penicillins.
• Discussion of the importance of patient compliance and the effects of the over- prescription of penicillin.
• Explanation of the importance of the beta-lactam ring on the action of penicillin.

Guidance:

• Students should be aware of the ability of acidic (carboxylic) and basic (amino) groups to form ionic salts, for example soluble aspirin.
• Structures of aspirin and penicillin are available in the data booklet in section 37.

• Aim 6: Experiments could include the synthesis of aspirin.
• Aim 8: Discuss the use/overuse of antibiotics for animals.