Use the following structures of amino acids to answer the questions below. Note that the difference in the structures (the side chains) is highlighted by gray shading.

a) A student performed chromatography of the four amino acids and the results were shown in the chromatogram below. If an anion exchange column (column is positively charged) was used in a neutral buffer, assign each amino acid to the corresponding peak in the chromatogram. (4 points)

b) Write 2 ? 3 sentences to describe the interactions that will occur for each amino acid with the anion exchange column and its effect on column retention.

c) Write 2 ? 3 sentences to describe how the results would differ if a cation exchange column (negatively charged column) were used.

Leucine COO- HN+-C-H CH CH CH CH Aspartate COO HN+- C-H CH COO Lysine COO HN+-C-H CH2 1 CH2 I CH T CH 1 +NH Threonine COO- HN+-C-H I H-C-OH | CH Conductance / S 60- 50- 40 30- 20 10- 0 0 A B LO 5 Time / min D 10 15