Consider the following sequence for aspartic acid:

The pH (Isoelectric point) of aspartic acid is:

The isoelectric point ($$pI$$) is the pH at which an amino acid molecule carries no net electrical charge, existing primarily as a zwitterion. For acidic amino acids that possess an additional carboxyl group in their side chain, the $$pI$$ is calculated as the arithmetic mean of the two lowest $$pK_a$$ values, which are the ones that surround the neutral (zwitterionic) species.

$$\alpha$$-carboxyl group: $$pK_1 = 1.88$$

Side chain $$\beta$$-carboxyl group: $$pK_2 = 3.65$$

$$\alpha$$-amino group: $$pK_3 = 9.60$$

$$pI = \frac{pK_1 + pK_2}{2}$$

$$pI = \frac{1.88 + 3.65}{2}$$

$$pI = 2.765$$

Rounding to two decimal places yields approximately $$2.77$$