Explain how penicillins work and why it is necessary to continually modify the side-chain.

Explain the importance of the beta-lactam ring in the action of penicillin.

penicillins interfere with (enzymes involved with) development of cell wall/(cross-link) structure of bacteria;

(due to damage) cells absorb water (by osmosis) and burst / OWTTE;

modifying side-chain overcomes resistance (by bacteria) / OWTTE;

beta lactam ring has strained structure/(four-membered ring with) 90° bond angles on the carbon and nitrogen atoms;

atoms should have larger bond angles based on VSEPR theory / OWTTE;

ring stress increases chemical reactivity and opens;

open ring reacts/bonds with enzyme/penicillinase to prevent formation of bacteria cell walls (prevents cross-linking of peptides);

The role of Florey and Chain did not seem to be too well known with many incorrectly listing large-scale production. In (b), the side-chain modification was better known than the working of penicillins. Whilst many had the correct general idea of the importance of the beta-lactam ring in (c), a precise explanation was needed.

The role of Florey and Chain did not seem to be too well known with many incorrectly listing large-scale production. In (b), the side-chain modification was better known than the working of penicillins. Whilst many had the correct general idea of the importance of the beta-lactam ring in (c), a precise explanation was needed.