Question

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?
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-.

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