Question

1. Separation of amino acids by ion-exchange Chromatography. Mixtures of amino acids can be analyzed by first separating the mixture into its components through ion-exchange chromatography. Amino acids placed on a cation-exchange resin containing sulfate (-SO3-) groups flow down the column at different rates because of two factors that influence their movement (1) ionic attraction between the sulfonate residues on the column and positively charged functional groups on the amino acids, and (2) hydrophobic interactions between amino acid side chains and the strongly hydrophobic backbone of the polystyrene resin. For each pair of amino acids listed, determine which will be eluted first from the cation-exchange column by a ph 7.0 buffer.
a.) Asp and Lys

b.) Arg and Met

c.) Glu and Val

d.) Gly and Val

e.) Ser and Ala

Answer 1

a.) Asp and Lys

Asp will elute first from the column because it has less positively charged functional groups than Lys.

 

b.) Arg and Met

Met will elute first from the column because it has less positively charged functional groups than Lys.

c.) Glu and Val

Glu will elute first from the column because it has more negativity functional groups than Lys and will be not be much retained by the -SO₃⁻ groups from the ion-exchange coloumn.

d.) Gly and Val

 Gly will elute first from the column because Lys have a longer alkyl chain which will be attracted by the strongly hydrophobic backbone for the resin.

e.) Ser and Ala

Ser will be eluted first from the column because Ala alkyl chain will be more attracted by the strongly hydrophobic backbone for the resin. Ser have an -OH group which will decrease the hydrophobicity of the alkyl chain and will not be so much retained on the column.