Question

Which antibiotic undergoes light catalysed autoxidation:

• A. Polyene antibiotics
• B. Beta lactum antibiotics
• C. Sugar derived antibiotics
• D. Macrolide antibiotics

Hint:

Polyene antibiotics, like amphotericin B, are sensitive to light and oxygen, which can cause autoxidation. Always store them in dark conditions to preserve their efficacy.

Answer 1

The Correct Option is A

Autoxidation triggered by light happens when a molecule has a system of atoms that can absorb light energy and pass it on to start a reaction with oxygen. In antibiotics, the polyene chromophore is exactly this kind of system.

1. Polyene antibiotics: A polyene has several carbon-carbon double bonds in a row, all conjugated with each other. This arrangement absorbs light readily, and the absorbed energy generates reactive oxygen species that attack the double bonds one after another. The chain breaks up step by step, which is the classic picture of light catalysed autoxidation. Amphotericin B solutions, for example, are always protected from light for this reason.
2. Beta lactum antibiotics: The four membered beta lactam ring is under a lot of ring strain, and this strain, not light, is what makes the ring open. Water attacking the carbonyl carbon is the main cause of breakdown, so light exposure is not the deciding factor here.
3. Sugar derived antibiotics: These molecules do not have a conjugated chromophore, so there is nothing in their structure to absorb light strongly. Their glycosidic linkages are broken by hydrolysis instead, usually helped along by acidic conditions.
4. Macrolide antibiotics: The lactone ring in macrolides opens up through hydrolysis, particularly in acidic environments like the stomach. There is no light sensitive chromophore driving their degradation.

Since only the polyene structure has the conjugated system needed to absorb light and start an oxygen chain reaction, the correct answer is Polyene antibiotics.