All amino adds have two ionizable functional groups: an a-amino group (average p

Question

All amino adds have two ionizable functional groups: an a-amino group (average pKa of 9.4) and an alpha-carboxylic acid group (average pK, of 2.2). Aspartic acid has an ionizable side chain (R group) with a pKm of -3.8. One of the possible ionization slates of aspartic acid is shown below At what pH would the above structure be the predominant ionization state? The protonated form of the R group of aspartic acid is shown in the structure above. The ratio of the protonated form to the charged (deprotonated) form depends on the pKa of the R group and the pH of the solution. Select all the pH values at which the charged form of the R group would predominate.

Explanation / Answer

Aspartic acid has three ionizable functional groups (two carboxylic acid and one amino group) with pka of 2.2, 3.8 and 9.4.

When pH of amino acid is less than pKa of functional group, functional group is predominantly in protonated form.

Given structure of aspartic acid contains all the three functional groups in protonated forms.

Therefore, pH of the amino acid solution must be lower than the lowest pKa value, i.e. 2.2

Thus, given ionization state will be predominant at pH less than 2.2

------------------------------------------------------------------------------------------------------------

The charged form of the R group (deprotonated form) predominates at pH values more than the pKa value of R group.

pKa of R group is 3.8. Therefore, at pH values above 3.8, the charged form will predominate. Such pH values are 7.0 and 10.4

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.