Which of the following functional groups of an amino acid would be in the ionized (deprotonated) state at high pH?

• A. Amino group (\(-NH_2\))
• B. Side chain of glycine
• C. Hydrogen atom attached to the alpha carbon
• D. Carboxyl group (\(-COO^-\))

Answer: (D)

Verified step by step guidance

1. Understand the concept of pH and its effect on ionization: At high pH (basic conditions), the environment has a low concentration of hydrogen ions ( ext{H}^+), which promotes deprotonation of acidic functional groups.
2. Identify the functional groups in an amino acid: Amino acids typically have an amino group ( ext{-NH}_2), a carboxyl group ( ext{-COOH}), a hydrogen atom attached to the alpha carbon, and a side chain (R group).
3. Determine the behavior of the carboxyl group ( ext{-COOH}) at high pH: The carboxyl group is acidic and tends to lose a proton ( ext{H}^+) under basic conditions, becoming ionized as ext{-COO}^-.
4. Analyze the amino group ( ext{-NH}_2): The amino group is basic and tends to accept a proton ( ext{H}^+) under acidic conditions, but at high pH, it remains in its neutral state ( ext{-NH}_2) and does not ionize further.
5. Conclude that the carboxyl group ( ext{-COO}^-) is the functional group that would be in the ionized (deprotonated) state at high pH, as it loses a proton and becomes negatively charged.