Question

For an amino acid such as aspartic acid, what impact would you expect a neighboring carboxylic acid to have on the apparent pKa value of the side chain? The apparent pKa value for aspartic acid increases. The aspartic acid and the neighboring carboxylic acid would form a salt bridge, therefore the apparent pKa value is not affected. The neighboring carboxylic acid would have no impact on the pKa value for aspartic acid. The apparent pKa value for aspartic acid decreases.

Answer 1

The apparent
`\( pK_a \)` value for aspartic acid increases.

Step-by-step explanation:

The
`\( pK_a \)` value of an ionizable group is influenced by its surrounding environment. When two similar charges are close to each other, they tend to repel, and when opposite charges are close, they tend to attract.

If a neighbouring carboxylic acid is close to the side chain of aspartic acid (which also has a carboxylic acid), there would be repulsion between the negatively charged carboxylate ions when deprotonated. This repulsion would make it less favourable for both groups to be deprotonated simultaneously.

Therefore, the presence of a neighbouring carboxylic acid would make the aspartic acid side chain less likely to lose its proton, effectively increasing its
`\( pK_a \)` value.

Thus, the correct statement is:

The apparent
`\( pK_a \)` value for aspartic acid increases.