Glutamic acid [side chain R = (CH2)2CO2H] has pKa values of 2.19, 4.25, and 9.67. What would be the predominant species in solution at pH 8?

1 answer

At pH 8, the protonated form of glutamic acid would be mostly deprotonated.

The carboxylic acid group (pKa = 2.19) would be fully ionized and exist as COO-, while the amino group (pKa = 9.67) would be fully protonated and exist as NH3+.

The side chain (pKa = 4.25) would be in a partially protonated state, with approximately equal amounts of the protonated (R-COOH) and deprotonated (R-COO-) forms present in solution.

Therefore, the predominant species in solution at pH 8 would be the fully deprotonated form of glutamic acid, with a negative charge on both the carboxylic acid and side chain groups: HOOC-CH2-CH2-COO-.