4. Aspartame is a sweetener used in diet beverages. It is the methyl ester (below) of the dipeptide aspartyl-phenylalanine. Its stability in solution is highly dependent on pH. It breaks down readily at physiological pH (7.5) but is most stable at pH 5.0. O = C-d-CH3 | The C-terminal methylated carboxyl group prevents its ionizability. What are the percentages of principle (relevant) ionizable forms present at pH 5.0. Use the chart above. Note: Amino and carboxyl groups internal to the structure can also not ionize. At wh pH does the molecule carry the overall charge on the chart bel Hint: below or above +/- 1 pH units, a group is fully protonated or fully unprotonated. + 1: +0.5: 0 -0.5: - 1: (principle relative forms, charge w/pH changes, isoelectric point of a peptide)