Key to Exercise on Amino Acids and pH
Return to Chemistry 340 Home Page

1.

2.

3.

4.

5.

6.

Peptides and pH

1.

2.

3.

4.

dipeptide

L-W

A-N

K-T

C-D

relevant pKa's

2.38 and 9.60

2.17 and 9.69

8.95 and 10.53

1.88* and 3.65

pI

5.99

5.93

9.74

2.765 = 2.77

*Note that at pH 3.0 the α-carboxyl of aspartate has already donated H+, so that at pH 3.0 the dipeptide has a net charge = 0.
Also note that the presence of a positively charged residue results in a basic pI, while the presence of a negatively charged residue means that the pI is acidic.

 

top of page