Question

Which of the following must be true if the penicillin-serine reaction 'locks' in the ester formation as described in the passage?

1) The thermodynamic cost of breaking the penicillin-serine ester is larger than the thermodynamic release of amide formation.
2) The thermodynamic release of forming an amide is equal to the thermodynamic cost of forming an ester.
3) The thermodynamic cost of breaking the penicillin-serine ester is smaller than the thermodynamic release of amide formation.
4) The thermodynamic release of forming the penicillin cyclic amide is larger than the thermodynamic release of breaking the penicillin-serine ester.

Answer 1

Based on the information provided, the correct statement that must be true if the penicillin-serine reaction 'locks' in the ester formation is:

3) The thermodynamic cost of breaking the penicillin-serine ester is smaller than the thermodynamic release of amide formation.

In order for the reaction to favor the formation of the penicillin-serine ester and 'lock' it in, the energy required to break the ester bond should be lower than the energy released during the formation of the amide bond. This means that the thermodynamic cost of breaking the penicillin-serine ester should be smaller than the thermodynamic release of amide formation.

Answer 2

The correct scenario for the penicillin-serine reaction being 'locked' is that the thermodynamic cost to break the penicillin-serine ester must be larger than the energy released from amide formation, making the reaction highly favorable and effectively irreversible.

Step-by-step explanation:

If the penicillin-serine reaction 'locks' in the ester formation, it suggests that this is a highly favorable process. Given the information about the reaction mechanism, the most likely scenario is that the thermodynamic cost of breaking the penicillin-serine ester must be larger than the thermodynamic release from amide formation. This would explain why the reaction is irreversible, as mentioned in the passage. The strain present in the β-lactam ring, exacerbated by the thiazolidine ring, and the protection from hydrolysis due to the anionic form of β-lactam make the reaction with serine very favorable. Consequently, the correct answer is option 1) The thermodynamic cost of breaking the penicillin-serine ester is larger than the thermodynamic release of amide formation.